publicationDate,title,abstract,id
2012-12-14,Saturation of magnetic films with spin-polarized current in presence of magnetic field,"Influence of perpendicular magnetic field on the process of transversal
saturation of ferromagnetic films with spin-polarized current is studied
theoretically. It is shown that the saturation current $J_s$ is decreased
(increased) in case of codirected (oppositely directed) magnetic field and
current. There exists a critical current $J_c>J_s$ which provides ""rigid""
saturation -- the saturated state is stable with respect to the transverse
magnetic field of any amplitude and direction. Influence of the magnetic field
on the vortex-antivortex crystals, which appear in pre-saturated regime, is
studied numerically. All analytical results are verified using micromagnetic
simulations.",1212.3578v1
2009-04-20,Saturation of Magnetorotational Instability through Magnetic Field Generation,"The saturation mechanism of Magneto-Rotational Instability (MRI) is examined
through analytical quasilinear theory and through nonlinear computation of a
single mode in a rotating disk. We find that large-scale magnetic field is
generated through the alpha effect (the correlated product of velocity and
magnetic field fluctuations) and causes the MRI mode to saturate. If the
large-scale plasma flow is allowed to evolve, the mode can also saturate
through its flow relaxation. In astrophysical plasmas, for which the flow
cannot relax because of gravitational constraints, the mode saturates through
field generation only.",0904.2941v1
2000-10-19,Magnetic Field Saturation in the Riga Dynamo Experiment,"After the dynamo experiment in November 1999 had shown magnetic field
self-excitation in a spiraling liquid metal flow, in a second series of
experiments emphasis was placed on the magnetic field saturation regime as the
next principal step in the dynamo process. The dependence of the strength of
the magnetic field on the rotation rate is studied. Various features of the
saturated magnetic field are outlined and possible saturation mechanisms are
discussed.",0010047v1
2013-12-03,Dependence of the cross polar cap potential saturation on the type of solar wind streams,"We compare of the cross polar cap potential (CPCP) saturation during magnetic
storms induced by various types of the solar wind drivers. By using the model
of Siscoe-Hill
\citep{Hilletal1976,Siscoeetal2002a,Siscoeetal2002b,Siscoeetal2004,Siscoe2011}
we evaluate criteria of the CPCP saturation during the main phases of 257
magnetic storms ($Dst_{min} \le -50$ nT) induced by the following types of the
solar wind streams: magnetic clouds (MC), Ejecta, the compress region Sheath
before MC ($Sh_{MC}$) and before Ejecta ($Sh_{E}$), corotating interaction
regions (CIR) and indeterminate type (IND). Our analysis shows that occurrence
rate of the CPCP saturation is higher for storms induced by ICME ($13.2%$) than
for storms driven by CIR ($3.5%$) or by IND ($3.5%$).The CPCP saturation was
obtained more often for storms initiated by MC ($25%$) than by Ejecta ($2.9%$);
it was obtained for $8.6%$ of magnetic storms induced by sum of MC and Ejecta,
and for $21.5%$ magnetic storms induced by Sheath before them (sum of $Sh_{MC}$
and $Sh_{E}$). These results allow us to conclude that occurrence rate of the
CPCP saturation at the main phase of magnetic storms depends on the type of the
solar wind stream.",1312.0778v1
2018-12-05,Quantum mechanics basis of quality control in hard metals,"Non-destructive and reliable quality control methods are a key aspect to
designing, developing and manufacturing new materials for industrial
applications and new technologies. The measurement of the magnetic saturation
is one of such methods and it is conventionally employed in the cemented
carbides industry. We present a general quantum mechanics based relation
between the magnetic saturation and the components of the binder phase of
cemented carbides, which can be directly employed as a quality control. To
illustrate our results, we calculate the magnetic saturation of a binder phase,
85Ni15Fe binary alloy, using ab-initio methods and compare the theoretical
predictions to the magnetic saturation measurements. We also analyse interface
and segregation effects on the magnetic saturation by studying the electronic
structure of the binder phase. The excellent agreement between calculations and
measurements demonstrates the applicability of our method to any binder phase.
Since the magnetic saturation is employed to ensure the quality of cemented
carbides, the present method allows us to explore new materials for alternative
binder phases efficiently",1812.01960v1
2005-01-20,Saturation mechanism of the Weibel instability in weakly magnetized plasmas,"The saturation mechanism of the Weibel instability is investigated
theoretically by considering the evolution of currents in numerous cylindrical
beams that are generated in the initial stage of the instability. Based on a
physical model of the beams, it is shown that the magnetic field strength
attains a maximum value when the currents in the beams evolve into the Alfven
current and that there exist two saturation regimes. The theoretical prediction
of the magnetic field strength at saturation is in good agreement with the
results of two-dimensional particle-in-cell simulations for a wide range of
initial anisotropy.",0501110v2
2023-05-21,An Alternative Derivation of the Landau-Lifshitz-Gilbert Equation for Saturated Ferromagnets,"The Landau-Lifshitz-Gilbert equation for rigid and saturated ferromagnets is
derived using a two-continuum model constructed by H.F. Tiersten for elastic
and saturated ferromagnets. The relevant basic laws of physics are applied
systematically to the two continua or their combination. The exchange
interaction is introduced into the model through surface distributed magnetic
couples. This leads to a continuum theory with magnetization gradients in the
stored energy density. The saturation condition of the magnetization functions
as constraints on the energy density and has implications in the constitutive
relations.",2305.18232v1
2012-07-24,Sensorless position estimation of Permanent-Magnet Synchronous Motors using a saturation model,"Sensorless control of Permanent-Magnet Synchronous Motors (PMSM) at low
velocity remains a challenging task. A now well-established method consists in
injecting a high-frequency signal and use the rotor saliency, both geometric
and magnetic-saturation induced. This paper proposes a clear and original
analysis based on second-order averaging of how to recover the position
information from signal injection; this analysis blends well with a general
model of magnetic saturation. It also proposes a simple parametric model of the
saturated PMSM, based on an energy function which simply encompasses saturation
and cross-saturation effects. Experimental results on a surface-mounted PMSM
and an interior magnet PMSM illustrate the relevance of the approach.",1207.5743v1
2020-09-08,Automatic Detection and Correction Algorithms for Magnetic Saturation in the SMFT/HSOS longitudinal Magnetograms,"longitudinal magnetic field often suffers the saturation effect in strong
magnetic field region when the measurement performs in a single-wavelength
point and linear calibration is adopted. In this study, we develop a method
that can judge the threshold of saturation in Stokes $V/I$ observed by the
Solar Magnetic Field Telescope (SMFT) and correct for it automatically. The
procedure is that first perform the second-order polynomial fit to the Stokes
$V/I$ \textit{vs} $I/I_{m}$ ($I_{m}$ is the maximum value of Stokes $I$) curve
to estimate the threshold of saturation, then reconstruct Stokes $V/I$ in
strong field region to correct for saturation. The algorithm is proved to be
effective by comparing with the magnetograms obtained by the Helioseismic and
Magnetic Imager (HMI). The accurate rate of detection and correction for
saturation is $\sim$99.4\% and $\sim$88\% respectively among 175 active
regions. The advantages and disadvantages of the algorithm are discussed.",2009.03597v1
2016-03-24,Saturation properties of nuclear matter in the presence of strong magnetic field,"Different saturation properties of cold symmetric nuclear matter in the
strong magnetic field have been considered. We have seen that for magnetic
fields about $B> 3 \times 10 ^ {17}\ G$, {for both cases with and without
nucleon anomalous magnetic moments}, the saturation density and saturation
energy grow by increasing the magnetic field. It is indicated that the magnetic
susceptibility of symmetric nuclear matter becomes negative showing the
diamagnetic response especially at $B< 3 \times 10 ^ {17}\ G$. We have found
that for the nuclear matter, the magnitude of orbital magnetization reaches the
higher values comparing to the spin magnetization. Our results for the
incompressibility show that at high enough magnetic fields, i.e. $B> 3 \times
10 ^ {17}\ G$, {the softening of equation of state caused by Landau
quantization is overwhelmed by stiffening due to the magnetization of nuclear
matter.} We have shown that the effects of strong magnetic field on nuclear
matter may affect the constraints on the equation of state of symmetric nuclear
matter obtained applying the experimental observable.",1603.07561v1
2013-04-30,Saturated symmetric nuclear matter in strong magnetic fields,"Strongly magnetized symmetric nuclear matter is investigated within the
context of effective baryon-meson exchange models. The magnetic field is
coupled to the charge as well as the dipole moment of the baryons by including
the appropriate terms in the Lagrangian density. The saturation density of
magnetized, symmetric nuclear matter was calculated for magnetic fields of the
order of 10^17 gauss. For the calculated range of saturation densities the
binding energy, symmetry energy coefficient and compressibility of nuclear
matter were also calculated. It is found that with an increasing magnetic field
the saturation density increases, while the system becomes less bound.
Furthermore, the depopulation of proton Landau levels leaves a distinct
fluctuating imprint on the symmetry energy coefficient and compressibility. The
calculations were also performed for increased values of the baryon magnetic
dipole moment. By increasing the dipole moment strength the saturation density
is found to decrease, but the system becomes more tightly bound while the
fluctuations in the symmetry energy coefficient and compressibility persist.",1304.7951v2
2008-09-10,How do dynamos saturate?,"In order better to understand how dynamo systems saturate, we study the
kinematic dynamo properties of velocity fields that arise from nonlinearly
saturated dynamos. The technique is implemented by solving concurrently, in
addition to the momentum equation, two induction equations, one for the actual
magnetic field, and one for an independent passive field. We apply this
technique to two illustrative examples: convectively driven turbulence, and
turbulence represented by a shell model. In all cases we find that the velocity
remains an efficient kinematic dynamo even after nonlinear saturation occurs.
We discuss the implications to the process of dynamo saturation.",0809.1801v2
2011-03-15,Estimation of Saturation of Permanent-Magnet Synchronous Motors Through an Energy-Based Model,"We propose a parametric model of the saturated Permanent-Magnet Synchronous
Motor (PMSM) together with an estimation method of the magnetic parameters. The
model is based on an energy function which simply encompasses the saturation
effects. Injection of fast-varying pulsating voltages and measurements of the
resulting current ripples then permit to identify the magnetic parameters by
linear least squares. Experimental results on a surface-mounted PMSM and an
interoir magnet PMSM illustrate the relevance of the approach.",1103.2923v1
2012-06-13,Saturation Magnetization of Inorganic/polymer Nanocomposites Higher than That of Their Inorganic Magnetic Component,"Herein, some magnetic nanoparticles (MNP)/clay/polymer nanocomposites have
been prepared, whose saturation magnetization is higher than that of pure oleic
acid coated MNP component. The existence of unique 'nano-network' structure and
tight three-phase nano-interface in the nanocomposites contribute to the
surprising saturation magnetization.",1206.2805v1
2007-02-13,Inverse cascades and alpha-effect at low magnetic Prandtl number,"Dynamo action in a fully helical Beltrami (ABC) flow is studied using both
direct numerical simulations and subgrid modeling. Sufficient scale separation
is given in order to allow for large-scale magnetic energy build-up. Growth of
magnetic energy obtains down to a magnetic Prandtl number PM=RM/RV close to
0.005, where RV and RM are the kinetic and magnetic Reynolds numbers. The
critical magnetic Reynolds number for dynamo action RMc seems to saturate at
values close to 20. Detailed studies of the dependence of the amplitude of the
saturated magnetic energy with PM are presented. In order to decrease PM,
numerical experiments are conducted with either RV or RM kept constant. In the
former case, the ratio of magnetic to kinetic energy saturates to a value
slightly below unity as PM decreases. Examination of energy spectra and
structures in real space both reveal that quenching of the velocity by the
large-scale magnetic field takes place, with an inverse cascade of magnetic
helicity and a force-free field at large scale in the saturated regime.",0702109v1
2015-04-23,The Tayler instability at low magnetic Prandtl numbers: between chiral symmetry breaking and helicity oscillations,"The Tayler instability is a kink-type, current driven instability that plays
an important role in plasma physics but might also be relevant in liquid metal
applications with high electrical currents. In the framework of the
Tayler-Spruit dynamo model of stellar magnetic field generation, the question
of spontaneous helical (chiral) symmetry breaking during the saturation of the
Tayler instability has received considerable interest. Focusing on fluids with
low magnetic Prandtl numbers, for which the quasistatic approximation can be
applied, we utilize an integro-differential equation approach in order to
investigate the saturation mechanism of the Tayler instability. Both the
exponential growth phase and the saturated phase are analyzed in terms of the
action of the alpha and beta effects of mean-field magnetohydrodynamics. In the
exponential growth phase we always find a spontaneous chiral symmetry breaking
which, however, disappears in the saturated phase. For higher degrees of
supercriticality, we observe helicity oscillations in the saturated regime. For
Lundquist numbers in the order of one we also obtain chiral symmetry breaking
of the saturated magnetic field.",1504.06120v1
2022-08-08,Study of Asymmetric Magnetization Reversal and Exchange Bias in FePt(L10)/FeCo/CoO/FeCo Magnetic Multilayer,"The effect of the saturation field on the magnetization reversal of
FePt(L10)/FeCo/CoO/FeCo multilayer (ML) has been investigated to understand the
origin of asymmetric magnetization reversal and its correlation with exchange
bias (EB). In the ML structure, the bottom FeCo layer is coupled to the hard
FePt(L10) layer, and the top FeCo layer is comparatively free due to the
relatively more distance from it. The ML has been deposited under UHV
conditions and characterized at each stage of growth using magneto-optical Kerr
effect and x-ray reflectivity techniques. Magnetization reversal is further
studied through domain imaging using the Kerr microscopy technique. The
experimental findings reveal that ML exhibits asymmetrical magnetization
reversal for a certain range of azimuthal angles for both 1.5kOe and 50kOe
saturation fields; however, this angular range of asymmetry decreases with the
increase in the saturation field. Furthermore, EB was absent at the low
saturation field, whereas, EB, in addition to asymmetry, is observed at the
large saturation field. The origin of asymmetry is attributed to
non-collinearity between magnetic anisotropy axes of both FeCo layers. It
results from the proximity effect through short-range Heisenberg exchange
interaction via the CoO barrier layer. On the other hand, EB arises due to
unidirectional anisotropy induced in the FePt layer due to the high saturation
field. It is further proposed that asymmetry would disappear when
unidirectional anisotropy is strong enough to align both the FeCo layers in the
saturation direction leading to loss of the non-collinearity between them.",2208.04038v1
2020-02-17,Enhancement of magnetization plateaus in low dimensional spin systems,"We study the low-energy properties and, in particular, the magnetization
process of a spin-1/2 Heisenberg $J_1-J_2$ sawtooth and frustrated chain (also
known as zig-zag ladder) with a spatially anisotropic $g$-factor. We treat the
problem both analytically and numerically while keeping the $J_2/J_1$ ratio
generic. Numerically, we use complete and Lanczos diagonalization as well as
the infinite time-evolving block decimation (iTEBD) method. Analytically we
employ (non-)Abelian bosonization. Additionally for the sawtooth chain, we
provide an analytical description in terms of flat bands and localized magnons.
By considering a specific pattern for the $g$-factor anisotropy for both
models, we show that a small anisotropy significantly enhances a magnetization
plateau at half saturation. For the magnetization of the frustrated chain, we
show the destruction of the $1/3$ of the full saturation plateau in favor of
the creation of a plateau at half-saturation. For large anisotropies, the
existence of an additional plateau at zero magnetization is possible. Here and
at higher magnetic fields, the system is locked in the half-saturation plateau,
never reaching full saturation.",2002.07190v1
2023-05-17,Role of magnetic pressure forces in fluctuation dynamo saturation,"Using magnetohydrodynamic simulations of fluctuation dynamos in turbulent
flows with rms Mach numbers $\mathcal{M}_{\rm rms} = 0.2, 1.1$ and $3$, we show
that magnetic pressure forces play a crucial role in dynamo saturation in
supersonic flows. First, as expected when pressure forces oppose compression,
an increase in anticorrelation between density and magnetic field strengths
obtains even in subsonic flows with the anti-correlation arising from the
intense but rarer magnetic structures. In supersonic flows, due to stronger
compressive motions density and magnetic field strength continue to maintain a
positive correlation. However, the degree of positive correlation decreases as
the dynamo saturates. Secondly, we find that the unit vectors of $\nabla\rho$
and $\nabla B^{2}$ are preferentially antiparallel to each other in subsonic
flows. This is indicative of magnetic pressure opposing compression. This
antiparallel alignment persists in transonic and supersonic flows at dynamo
saturation. However, compressive motions also lead to the emergence of a
parallel alignment in these flows. Finally, we consider the work done against
the components of the Lorentz force and the different sources of magnetic
energy growth and dissipation. We show that while in subsonic flows,
suppression of field line stretching is dominant in saturating the dynamo, the
picture is different in supersonic flows. Both field line stretching and
compression initially amplifies the field. However, growing magnetic pressure
opposes further compression of magnetic flux which tends to reduce the
compressive motions. Simultaneously, field line stretching also reduces. But,
suppression of compressive amplification dominates the saturation of the
dynamo.",2305.09969v2
2018-10-12,Gyrokinetic theory of the nonlinear saturation of toroidal Alfven eigenmode,"Nonlinear saturation of toroidal Alfven eigenmode (TAE) via ion induced
scatterings is investigated in the short-wavelength gyrokinetic regime. It is
found that the nonlinear evolution depends on the thermal ion \b{eta} value.
Here, \b{eta} is the plasma thermal to magnetic pressure ratio. Both the
saturation levels and associated energetic-particle transport coefficients are
derived and estimated correspondingly.",1810.05295v1
2001-01-06,Evidence for Adiabatic Magnetization of cold Dy_N Clusters,"Magnetic properties of Dy_N clusters in a molecular beam generated with a
liquid helium cooled nozzle are investigated by Stern-Gerlach experiments. The
cluster magnetizations \mu_z are measured as a function of magnetic field (B =
0 - 1.6T) and cluster size (16 < N < 56). The most important observation is the
saturation of the magnetization \mu_z(B) at large field strengths. The
magnetization approaches saturation following the power law |\mu_z-\mu_0|
proportional to 1/\sqrt{B}, where \mu_0 denotes the magnetic moment. This gives
evidence for adiabatic magnetization.",0101075v1
2014-01-28,Magnetic Field Amplification and Saturation in Turbulence Behind a Relativistic Shock,"We have investigated via two-dimensional relativistic MHD simulations the
long-term evolution of turbulence created by a relativistic shock propagating
through an inhomogeneous medium. In the postshock region, magnetic field is
strongly amplified by turbulent motions triggered by preshock density
inhomogeneities. Using a long-simulation box we have followed the
magnetic-field amplification until it is fully developed and saturated. The
turbulent velocity is sub-relativistic even for a strong shock. Magnetic-field
amplification is controled by the turbulent motion and saturation occurs when
the magnetic energy is comparable to the turbulent kinetic energy.
Magnetic-field amplification and saturation depend on the initial strength and
direction of the magnetic field in the preshock medium, and on the shock
strength. If the initial magnetic field is perpendicular to the shock normal,
the magnetic field is first compressed at the shock and then can be amplified
by turbulent motion in the postshock region. Saturation occurs when the
magnetic energy becomes comparable to the turbulent kinetic energy in the
postshock region. If the initial magnetic field in the preshock medium is
strong, the postshock region becomes turbulent but significant field
amplification does not occur. If the magnetic energy after shock compression is
larger than the turbulent kinetic energy in the postshock region, significant
field amplification does not occur. We discuss possible applications of our
results to gamma-ray bursts and active galactic nuclei.",1401.7080v1
2009-09-24,Discovery of localized states of Fe 3d electrons in Fe16N2 and Fe8N films: an evidence of the existence of giant saturation magnetization,"The mystery of giant saturation magnetization of Fe16N2 has remained for 37
years. In this letter, X-ray absorption spectroscopy (XAS) and magnetic
circular dichroism (XMCD) are used to study the electron states of Fe atoms in
Fe16N2 and Fe8N films. Localized Fe 3d electron states, which are not expected
from current theories (models), are observed. The XMCD spectra and elemental
hysteresis loops reveal the polarization of N atoms and the hybridization of N
and Fe atoms. This discovery points to the origin of giant saturation
magnetization in Fe16N2.",0909.4478v1
2012-03-26,Signal injection and averaging for position estimation of Permanent-Magnet Synchronous Motors,"Sensorless control of Permanent-Magnet Synchronous Motors at low velocity
remains a challenging task. A now well-established method consists in injecting
a high-frequency signal and use the rotor saliency, both geometric and
magnetic-saturation induced. This paper proposes a clear and original analysis
based on second-order averaging of how to recover the position information from
signal injection; this analysis blends well with a general model of magnetic
saturation. It also experimentally demonstrates the relevance for position
estimation of a simple parametric saturation model recently introduced by the
authors.",1203.5672v1
2020-03-18,On the saturation mechanism of the fluctuation dynamo at ${\text{Pr}_\mathrm{M}} \ge 1$,"The presence of magnetic fields in many astrophysical objects is due to
dynamo action, whereby a part of the kinetic energy is converted into magnetic
energy. A turbulent dynamo that produces magnetic field structures on the same
scale as the turbulent flow is known as the fluctuation dynamo. We use
numerical simulations to explore the nonlinear, statistically steady state of
the fluctuation dynamo in driven turbulence. We demonstrate that as the
magnetic field growth saturates, its amplification and diffusion are both
affected by the back-reaction of the Lorentz force upon the flow. The
amplification of the magnetic field is reduced due to stronger alignment
between the velocity field, magnetic field, and electric current density.
Furthermore, we confirm that the amplification decreases due to a weaker
stretching of the magnetic field lines. The enhancement in diffusion relative
to the field line stretching is quantified by a decrease in the computed local
value of the magnetic Reynolds number. Using the Minkowski functionals, we
quantify the shape of the magnetic structures produced by the dynamo as
magnetic filaments and ribbons in both kinematic and saturated dynamos and
derive the scalings of the typical length, width, and thickness of the magnetic
structures with the magnetic Reynolds number. We show that all three of these
magnetic length scales increase as the dynamo saturates. The magnetic
intermittency, strong in the kinematic dynamo (where the magnetic field
strength grows exponentially) persists in the statistically steady state, but
intense magnetic filaments and ribbons are more volume-filling.",2003.07997v1
2015-03-27,Dynamo Saturation in Rapidly Rotating Solar-Type Stars,"The magnetic activity of solar-type stars generally increases with stellar
rotation rate. The increase, however, saturates for fast rotation. The
Babcock-Leighton mechanism of stellar dynamos saturates as well when the mean
tilt-angle of active regions approaches ninety degrees. Saturation of magnetic
activity may be a consequence of this property of the Babcock-Leighton
mechanism. Stellar dynamo models with a tilt-angle proportional to the rotation
rate are constructed to probe this idea. Two versions of the model - treating
the tilt-angles globally and using Joy's law for its latitude dependence - are
considered. Both models show a saturation of dynamo-generated magnetic flux at
high rotation rates. The model with latitude-dependent tilt-angles also shows a
change in dynamo regime in the saturation region. The new regime combines a
cyclic dynamo at low latitudes with an (almost) steady polar dynamo.",1503.07956v3
2015-03-16,Dynamics of Current and Field Driven Domain Wall Motion under the Influence of Transverse Magnetic Field,"The dynamics of transverse Neel domain wall in a ferromagnetic nanostrip in
the presence of driving field, current and transverse magnetic field is
investigated by the Landau-Lifshitz-Gilbert(LLG) equation with the adiabatic
and non-adiabatic spin-transfer torques both analytically and numerically. The
analytical expressions for the velocity, width, excitation angle and
displacement for the domain wall are obtained by using small angle
approximation along with Walkers trial function. The results show that the
initial velocity of the domain wall can be controlled by the adiabatic
spin-transfer torque and the saturated velocity can be controlled by the
non-adiabatic spin-transfer torque and driving field. The large increase in the
saturated velocity of the domain wall driven by current and field due to the
transverse magnetic field is identified through the presence of driving field.
There is no impact in the saturated velocity of the domain wall driven by
current from the transverse magnetic field. For the domain wall driven by the
current in the presence of the transverse magnetic field, the saturated
velocity remains constant. The transverse magnetic field along with current and
driving field is more advantageous that the transverse magnetic field along
with current for increasing the saturated velocity of the domain wall. The
numerical results showed that the saturated velocity is increased by the
transverse magnetic field with the irrespective of the directions of the
driving field and current further it is higher and lower when the directions of
driving field and current are antiparallel and parallel respectively. The
obtained analytical solutions are closely coincided with the computed numerical
results.",1503.04560v2
2015-06-11,Dependence of the saturation level of magnetorotational instability on gas pressure and magnetic Prandtl number,"A large set of numerical simulations of magnetohydrodynamic (MHD) turbulence
induced by the magnetorotational instability (MRI) is presented. Revisiting the
previous survey conducted by Sano et al. (2004), we investigate the gas
pressure dependence of the saturation level. In ideal MHD simulations, the gas
pressure dependence is found to be very sensitive to the choice of a numerical
scheme. This is because the numerical magnetic Prandtl number varies according
to the scheme as well as the pressure, which considerably affects the results.
The saturation level is more sensitive to the numerical magnetic Prandtl number
than the pressure. In MHD simulations with explicit viscosity and resistivity,
the saturation level increases with the physical magnetic Prandtl number, and
it is almost independent of the gas pressure when the magnetic Prandtl number
is constant. This is indicative of the incompressible turbulence saturated by
the secondary tearing instability.",1506.03524v1
2016-12-12,Electron Weibel Instability in Relativistic Counter-Streaming Plasmas with Flow-Aligned External Magnetic Fields,"The Weibel instability driven by two symmetric counter-streaming relativistic
electron plasmas, also referred to as current-filamentation instability, is
studied in a constant and uniform external magnetic field aligned with the
plasma flows. Both the linear and non linear stages of the instability are
investigated using analytical modeling and Particle-In-Cell (PIC) simulations.
While previous studies have already described the stabilizing effect of the
magnetic field, we show here that the saturation stage is only weakly affected.
The different mechanisms responsible for the saturation are discussed in detail
in the relativistic cold fluid framework considering a single unstable mode.
The application of an external field leads to a slighlt increase of the
saturation level for large wavelengths, while it does not affect the small
wavelengths. Multi-mode and temperature effects are then investigated. While at
large temperature the saturation level is independent of the external magnetic
field, at small but finite temperature the competition between different modes
in the presence of an external magnetic field leads to a saturation level lower
with respect to the unmagnetized case.",1612.03934v1
1993-12-21,Magnetic Properties of the Spin-1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic Trimerized Heisenberg Chain:,"The magnetic properties of the ferromagnetic-ferromagnetic-antiferromagnetic
trimerized spin-1/2 Heisenberg chain are studied theoretically. The high
temperature susceptibilty and the ground state saturation magnetic field are
calculated and the exchange energies of the trimer compound 3CuCl${}_2\cdot$2dx
are determined. The magnetization curve is obtained by numerical
diagonalization of finite size systems. The result explains the low temperature
magnetization data for 3CuCl${}_2\cdot$2dx with the exchange energies obtained
as above. It is predicted that the magnetization curve has a plateau at 1/3 of
the saturation magnetization if the ferromagnetic exchange energy is comparable
to or smaller than the antiferromagnetic exchange energy.",9312084v1
2004-11-10,Magnetotransport in inhomogeneous magnetic fields,"Quantum transport in inhomogeneous magnetic fields is investigated
numerically in two-dimensional systems using the equation of motion method. In
particular, the diffusion of electrons in random magnetic fields in the
presence of additional weak uniform magnetic fields is examined. It is found
that the conductivity is strongly suppressed by the additional uniform magnetic
field and saturates when the uniform magnetic field becomes on the order of the
fluctuation of the random magnetic field. The value of the conductivity at this
saturation is found to be insensitive to the magnitude of the fluctuation of
the random field. The effect of random potential on the magnetoconductance is
also discussed.",0411248v1
2017-05-22,Nonlinear saturation of the Weibel instability,"The growth and saturation of magnetic fields due to the Weibel instability
(WI) have important implications for laboratory and astrophysical plasmas, and
this has drawn significant interest recently. Since the WI can generate a large
magnetic field from no initial field, the maximum magnitudes achieved can have
significant consequences for a number of applications. Hence, an understanding
of the detailed dynamics driving the nonlinear saturation of the WI is
important. This work considers the nonlinear saturation of the WI when
counter-streaming populations of initially unmagnetized electrons are perturbed
by a magnetic field oriented perpendicular to the direction of streaming.
Previous works have found magnetic trapping to be important and connected
electron skin depth spatial scales to the nonlinear saturation of the WI. 2
Results presented in this work are consistent with these findings for a
high-temperature case. However, using a high-order continuum kinetic simulation
tool, this work demonstrates that, when the electron populations are colder, a
significant electrostatic potential develops that works with the magnetic field
to create potential wells. The electrostatic field develops due to transverse
flows induced by the WI, and in some cases is strengthened by a secondary
instability. This field plays a key role in saturation of the WI for colder
populations. The role of the electrostatic potential in Weibel instability
saturation has not been studied in detail previously.",1705.07930v4
2013-02-15,A novel magnetic phase prior to a saturation moment in frustrated spinel oxides in ultra-high magnetic fields,"We have investigated the magnetic-field induced phases of a typical
three-dimensional frustrated magnet, CdCr$_2$O$_4$, in magnetic fields of up to
120 T that is generated by the single-turn coil techniques. We focused on
magnetic phase transitions in proximity of a saturated magnetization moment. We
utilized both the electromagnetic induction method using magnetic pick-up coils
and magneto-optical spectroscopies of the $d$-$d$ transitions and the
exciton-magnon-phonon transitions to study the magnetic properties subjected to
ultra-high magnetic fields. Anomalies were observed in magneto-optical
absorption intensity as well as differential magnetization prior to a fully
polarized magnetic phase (a vacuum state in the magnon picture), revealing a
novel magnetic phase associated with changes in both crystal and magnetic
structures accompanied by the first order phase transition. Magnetic superfluid
state such as an umbrella-like magnetic structure or a spin nematic state, is
proposed as a candidate for the novel magnetic phase, which is found universal
in the series of chromium spinel oxides, $A$Cr$_2$O$_4$ ($A$ = Zn, Cd, Hg).",1302.3664v1
2022-09-22,Growth or Decay -- I: universality of the turbulent dynamo saturation,"The turbulent small-scale dynamo (SSD) is likely to be responsible for the
magnetisation of the interstellar medium (ISM) that we observe in the Universe
today. The SSD efficiently converts kinetic energy $E_{\rm kin}$ into magnetic
energy $E_{\rm mag} $, and is often used to explain how an initially weak
magnetic field with $E_{\rm mag} \ll E_{\rm kin}$ is amplified, and then
maintained at a level $E_{\rm mag} \lesssim E_{\rm kin}$. Usually, this process
is studied by initialising a weak seed magnetic field and letting the
turbulence grow it to saturation. However, in this Part I of the Growth or
Decay series, using three-dimensional, visco-resistive magnetohydrodynamical
turbulence simulations up to magnetic Reynolds numbers of 2000, we show that
the same final state in the integral quantities, energy spectra, and
characteristic scales of the magnetic field can also be achieved if initially
$E_{\rm mag} \sim E_{\rm kin}$ or even if initially $E_{\rm mag} \gg E_{\rm
kin}$. This suggests that the final saturated state of the turbulent dynamo is
set by the turbulence and the material properties of the plasma, independent of
the initial structure or amplitude of the magnetic field. We discuss the
implications this has for the maintenance of magnetic fields in turbulent
plasmas and future studies exploring the dynamo saturation.",2209.10749v2
2015-06-06,Saturation of the Turbulent Dynamo,"The origin of strong magnetic fields in the Universe can be explained by
amplifying weak seed fields via turbulent motions on small spatial scales and
subsequently transporting the magnetic energy to larger scales. This process is
known as the turbulent dynamo and depends on the properties of turbulence, i.e.
on the hydrodynamical Reynolds number and the compressibility of the gas, and
on the magnetic diffusivity. While we know the growth rate the magnetic energy
in the linear regime, the saturation level, i.e. the ratio of magnetic energy
to turbulent kinetic energy that can be reached, is not known from analytical
calculations. In this paper we present the first scale-dependent saturation
model based on an effective turbulent resistivity which is determined by the
turnover timescale of turbulent eddies and the magnetic energy density. The
magnetic resistivity increases compared to the Spitzer value and the effective
scale on which the magnetic energy spectrum is at its maximum moves to larger
spatial scales. This process ends when the peak reaches a characteristic
wavenumber k* which is determined by the critical magnetic Reynolds number. The
saturation level of the dynamo also depends on the type of turbulence and
differs for the limits of large and small magnetic Prandtl numbers Pm. With our
model we find saturation levels between 43.8% and 1.3% for Pm>>1 and between
2.43% and 0.135% for Pm<<1, where the higher values refer to incompressible
turbulence and the lower ones to highly compressible turbulence.",1506.02182v2
2013-01-31,Asymptotic theory of magnetic island saturation in equilibria with a finite current gradient,"A novel asymptotic matching procedure is developed to revisit the problem of
magnetic island saturation in case of a finite current gradient at the rational
surface. Nonlinear dispersion relation is derived for saturated magnetic
island. It is shown that arbitrary normalization factors that were present in
previous theories are fully specified with the asymptotic matching.",1302.0024v2
2023-07-18,"Propagation of Coupled Acoustic, Electromagnetic and Spin Waves in Saturated Ferromagnetoelastic Solids","We study the propagation of plane waves in an unbounded body of a saturated
ferromagnetoelastic solid. The equations by Tiersten for small fields
superposed on finite initial fields in a saturated ferromagnetoelastic material
are employed, with their quasistatic magnetic field extended to dynamic
electric and magnetic fields for electromagnetic waves. Dispersion relations of
the plane waves are obtained. The cutoff frequencies and long wave
approximation of the dispersion curves are determined. Results show that
acoustic, electromagnetic and magnetic spin waves are coupled in such a
material. For YIG which is a cubic crystal without piezoelectric coupling, the
acoustic and electromagnetic waves are not directly coupled but they can still
interact indirectly through spin waves.",2307.09171v1
2014-05-14,Ferromagnetism and quantum anomalous Hall effect in one-side-saturated buckled honeycomb lattices,"The recently synthesized silicene as well as theoretically discussed
germanene are examples of buckled honeycomb structures. The buckled structures
allow one to manipulate asymmetry between two underlying sublattices of
honeycomb structures. Here by taking germanene as a prototype of buckled
honeycomb lattices, we explore magnetism induced by breaking sublattice
symmetry through saturating chemical bonds on one-side of the buckled honeycomb
lattice. It is shown that when fractions of chemical bonds on one-side are
saturated, two narrow bands always exist at half filling. Furthermore, the
narrow bands generally support flat band ferromagnetism in the presence of the
Hubbard $U$ interaction. The induced magnetization is directly related to the
saturation fraction and is thus controllable in magnitude through the
saturation fraction. Most importantly, we find that depending on the saturation
fraction, the ground state of an one-side saturated germanene may become a
quantum anomalous Hall (QAH) insulator characterized by a Chern number that
vanishes for larger magnetization. The non-vanishing Chern number for smaller
magnetization implies that the associated quantum Hall effect tends to survive
at high temperatures. Our findings provide a potential method to engineer
buckled honeycomb structures into high-temperature QAH insulators.",1405.3349v1
2022-09-28,Numerical Study of S=1/2 Heisenberg Antiferromagnet on the Floret Pentagonal Lattice,"The $S=1/2$ Heisenberg antiferromagnet on the floret-pentagonal lattice with
two kinds of interaction strength is studied by the numerical-diagonalization
method. It is known that, near the five-ninth of the saturation magnetization,
this system shows a magnetization jump that is not accompanied by magnetization
plateaux. We focus our attention on the behavior of this system around the
five-ninth of the saturation magnetization; the changes of the magnetization
jump and plateau at and around this magnetization are clarified from the
diagonalization data for finite-size systems up to 45 sites.",2209.13887v1
2017-12-11,Transition to turbulent dynamo saturation,"While the saturated magnetic energy is independent of viscosity in dynamo
experiments, it remains viscosity-dependent in state-of-the-art 3D direct
numerical simulations (DNS). Extrapolating such viscous scaling-laws to
realistic parameter values leads to an underestimation of the magnetic energy
by several orders of magnitude. The origin of this discrepancy is that fully 3D
DNS cannot reach low enough values of the magnetic Prandtl number $Pm$. To
bypass this limitation and investigate dynamo saturation at very low $Pm$, we
focus on the vicinity of the dynamo threshold in a rapidly rotating flow: the
velocity field then depends on two spatial coordinates only, while the magnetic
field consists of a single Fourier mode in the third direction. We perform
numerical simulations of the resulting set of reduced equations for $Pm$ down
to $2\cdot 10^{-5}$. This parameter regime is currently out of reach to fully
3D DNS. We show that the magnetic energy transitions from a high-$Pm$ viscous
scaling regime to a low-$Pm$ turbulent scaling regime, the latter being
independent of viscosity. The transition to the turbulent saturation regime
occurs at a low value of the magnetic Prandtl number, $Pm \simeq 10^{-3}$,
which explains why it has been overlooked by numerical studies so far.",1712.03787v1
2018-02-24,Non-saturating Quantum Magnetization in Weyl semimetal TaAs,"Detecting the spectroscopic signatures of Dirac-like quasiparticles in
emergent topological materials is crucial for searching their potential
applications. Magnetometry is a powerful tool for fathoming electrons in
solids, yet its ability for discerning Dirac-like quasiparticles has not been
recognized. Adopting the probes of magnetic torque and parallel magnetization
for the archetype Weyl semimetal TaAs in strong magnetic field, we observed a
quasi-linear field dependent effective transverse magnetization and a strongly
enhanced parallel magnetization when the system is in the quantum limit.
Distinct from the saturating magnetic responses for massive carriers, the
non-saturating signals of TaAs in strong field is consistent with our newly
developed magnetization calculation for a Weyl fermion system in an arbitrary
angle. Our results for the first time establish a thermodynamic criterion for
detecting the unique magnetic response of 3D massless Weyl fermions in the
quantum limit.",1802.08801v1
2021-09-24,Saturation mechanism of the fluctuation dynamo in supersonic turbulent plasmas,"Magnetic fields in several astrophysical objects are amplified and maintained
by a dynamo mechanism, which is the conversion of the turbulent kinetic energy
to magnetic energy. A dynamo that amplifies magnetic fields at scales $<$ the
driving scale of turbulence is known as the fluctuation dynamo. We study the
properties of the fluctuation dynamo in supersonic turbulent plasmas, which is
of relevance to the ISM, structure formation, and lab experiments of
laser-plasma turbulence. Using simulations, we explore the properties of the
exponentially growing and saturated state of the fluctuation dynamo for
subsonic and supersonic turbulence. We confirm that the fluctuation dynamo
efficiency decreases with compressibility. We show that the fluctuation dynamo
generated magnetic fields are spatially intermittent and the level of
intermittency decreases as the field saturates. We find a stronger back
reaction of the magnetic field on the velocity for the subsonic case as
compared to the supersonic case. Locally, we find that the level of alignment
between vorticity and velocity, velocity and magnetic field, and current
density and magnetic field in the saturated stage is enhanced in comparison to
the exponentially growing phase for the subsonic case, but only the current
density and magnetic field alignment is enhanced for the supersonic case. We
show that both the magnetic field amplification (due to weaker stretching of
field lines) and diffusion decreases when the field saturates, but the
diffusion is enhanced relative to amplification. This occurs throughout the
volume in the subsonic turbulence, but primarily in the strong-field regions
for the supersonic case. This leads to the saturation of the fluctuation
dynamo. Overall, both the amplification and diffusion of magnetic fields are
affected and thus a drastic change in either of them is not required for the
saturation. [Abstract abridged]",2109.11698v1
2011-03-16,Magnetization Plateaus in the Spin-1/2 Kagome Antiferromagnets: Volborthite and Vesignieite,"The magnetization of two spin-1/2 kagome antiferromagnets, volborthite and
vesignieite, has been measured in pulsed magnetic fields up to 68 T. A
magnetization plateau is observed for each compound near the highest magnetic
field. Magnetizations at saturation are approximately equal to 0.40Ms for both
compounds, where Ms is the fully saturated magnetization, irrespective of a
difference in the distortion of the kagome lattice between the two compounds.
It should be noted that these values of magnetizations are significantly larger
than Ms/3 predicted theoretically for the one-third magnetization plateau in
the spin-1/2 kagome antiferromagnet. The excess magnetization over Ms/3 is
nearly equal to the sum of the magnetizations gained at the second and third
magnetization steps in volborthite, suggesting that there is a common origin
for the excess magnetization and the magnetization steps.",1103.3116v1
2005-06-23,"Magnetic phase diagram copper metaborate CuB_2O_4 in magnetic field parallel c-axis: resonant, magnetic and magnetoelastic investigations","The magnetic phase diagram in a single crystal of copper metaborate CuB_2O_4
in a magnetic field parallel to a tetragonal axis $c$ has been investigated.
  From the resonant, magnetic and magnetostrictive data the phase diagram of
CuB_2O_4 on a plane ``temperature - magnetic field'' is constructed. The
magnetic incommensurate-commensurate phase transition is caused by the
saturation of weak subsystem of copper ions in the strong magnetic field
$H\|c$.",0506596v1
2014-06-08,Stability and magnetization curve of spin-nematic phase slightly below saturation field,"We discuss the magnetization process slightly below the saturation field in
frustrated magnets. A condensation of bound magnons on the spin-polarized state
induces either a spin nematic phase or a state with phase separation. The
(effective) interaction between the bound magnon pairs not only is crucial to
the stability of the nematic phase, but also determines the slope of the
magnetization curve near saturation. We generally derive the expression of this
interaction by using the perturbative scattering theory. By applying the method
to coupled zigzag chains LiCuVO4, we find the positive pair-pair interaction
implying the stability of the spin nematic phase. We also point out that the
magnetization curve of LiCuVO4 is almost vertical (i.e. very large dM/dH) near
the saturation exhibiting one-dimensional feature despite non-negligible
interchain couplings.",1406.1960v1
2011-08-10,A route towards finding large magnetic anisotropy in nano-composites: application to a W$_{1-x}$Re$_x$/Fe multilayer,"We suggest here a novel nano-laminate, 5[Fe]/2[W$_x$Re$_{1-x}$] (x=0.6-0.8),
with enhanced magnetic hardness in combination with a large saturation moment.
The calculated magnetic anisotropy of this material reaches values of 5.3-7.0
MJ/m$^3$, depending on alloying conditions. We also propose a recipe in how to
identify other novel magnetic materials, such as nano-laminates and
multilayers, with large magnetic anisotropy in combination with a high
saturation moment.",1108.2105v1
2012-02-15,Magnetic field amplification during gravitational collapse - Influence of initial conditions on dynamo evolution and saturation,"We study the influence of initial conditions on the magnetic field
amplification during the collapse of a magnetised gas cloud. We focus on the
dependence of the growth and saturation level of the dynamo generated field on
the turbulent properties of the collapsing cloud. In particular, we explore the
effect of varying the initial strength and injection scale of turbulence and
the initial uniform rotation of the collapsing magnetised cloud. In order to
follow the evolution of the magnetic field in both the kinematic and the
nonlinear regime, we choose an initial field strength of $\simeq 1\,\mkG$ with
the magnetic to kinetic energy ratio, $E_{\rm m}/E_{\rm k} \sim 10^{-4}$. Both
gravitational compression and the small-scale dynamo initially amplify the
magnetic field. Further into the evolution, the dynamo-generated magnetic field
saturates but the total magnetic field continues to grow because of
compression. The saturation of the small-scale dynamo is marked by a change in
the slope of $B/\rho^{2/3}$ and by a shift in the peak of the magnetic energy
spectrum from small scales to larger scales. For the range of initial Mach
numbers explored in this study, the dynamo growth rate increases as the Mach
number increases from $v_{\rm rms}/c_{\rm s}\sim 0.2$ to 0.4 and then starts
decreasing from $v_{\rm rms}/c_{\rm s}\sim 1.0$. We obtain saturation values of
$E_{\rm m}/E_{\rm k} = 0.2 - 0.3$ for these runs. Simulations with different
initial injection scales of turbulence also show saturation at similar levels.
For runs with different initial rotation of the cloud, the magnetic energy
saturates at $E_{\rm m}/E_{\rm k}\sim 0.2 - 0.4$ of the equipartition value.
(Abridged)",1202.3206v1
2015-10-14,Dynamo saturation in direct simulations of the multi-phase turbulent interstellar medium,"The ordered magnetic field observed via polarized synchrotron emission in
nearby disc galaxies can be explained by a mean-field dynamo operating in the
diffuse interstellar medium (ISM). Additionally, vertical-flux initial
conditions are potentially able to influence this dynamo via the occurrence of
the magneto-rotational instability (MRI). We aim to study the influence of
various initial field configurations on the saturated state of the mean-field
dynamo. This is motivated by the observation that different saturation behavior
was previously obtained for different supernova rates. We perform direct
numerical simulations (DNS) of three-dimensional local boxes of the vertically
stratified, turbulent interstellar medium, employing shearing-periodic boundary
conditions horizontally. Unlike in our previous work, we also impose a vertical
seed magnetic field. We run the simulations until the growth of the magnetic
energy becomes negligible. We furthermore perform simulations of equivalent 1D
dynamo models, with an algebraic quenching mechanism for the dynamo
coefficients. We compare the saturation of the magnetic field in the DNS with
the algebraic quenching of a mean-field dynamo. The final magnetic field
strength found in the direct simulation is in excellent agreement with a
quenched $\alpha\Omega$~dynamo. For supernova rates representative of the Milky
Way, field losses via a Galactic wind are likely responsible for saturation. We
conclude that the relative strength of the turbulent and regular magnetic
fields in spiral galaxies may depend on the galaxy's star formation rate. We
propose that a mean field approach with algebraic quenching may serve as a
simple sub-grid scale model for galaxy evolution simulations including a
prescribed feedback from magnetic fields.",1510.04178v1
2004-05-05,Radiation Chemistry of Organic Liquids: Saturated Hydrocarbons,"In this review (124 refs), several problems in radiolysis of saturated
hydrocarbons are examined. Special attention is paid to the chemistry of
radical cations, high-mobility holes, excited state and spur dynamics, magnetic
field and spin effects, and optically detected magnetic resonance spectroscopy.",0405014v1
2007-11-08,Phenomenology of turbulent dynamo growth and saturation,"With a non local shell model of magnetohydrodynamic turbulence we investigate
numerically the turbulent dynamo action for low and high magnetic Prandtl
numbers ($Pm$). The results obtained in the kinematic regime and along the way
to dynamo saturation are understood in terms of a phenomenological approach
based on the local ($Pm\ll 1$) or non local ($Pm\gg 1$) nature of the energy
transfers. In both cases the magnetic energy grows at small scale and saturates
as an inverse `` cascade ''.",0711.1237v1
2022-04-29,Saturation of turbulent helical dynamos,"The presence of large scale magnetic fields in nature is often attributed to
the inverse cascade of magnetic helicity driven by turbulent helical dynamos.
In this work we show that in turbulent helical dynamos, the inverse flux of
magnetic helicity towards the large scales $\Pi_{\mathcal{H}}$ is bounded by
$|\Pi_{\mathcal{H}}|\le c \epsilon k_\eta^{-1}$, where $\epsilon$ is the energy
injection rate, $k_\eta$ is the Kolmogorov magnetic dissipation wavenumber and
$c$ an order one constant. Assuming the classical isotropic turbulence scaling,
the inverse flux of magnetic helicity $\Pi_{\mathcal{H}}$ decreases at least as
a $-3/4$ power-law with the magnetic Reynolds number $Rm$ : $|\Pi_{\mathcal{H}}
| \le c \epsilon \ell_f Rm^{-3/4}\max[Pm,1]^{1/4}$, where $Pm$ the magnetic
Prandtl number and $\ell_f$ the forcing lengthscale. We demonstrate this
scaling with $Rm$ using direct numerical simulations of turbulent dynamos
forced at intermediate scales. The results further indicate that nonlinear
saturation is achieved by a balance between the inverse cascade and dissipation
at domain size scales $L$ for which the saturation value of the magnetic energy
is bounded by ${\mathcal{E}}_\text{m}\leq c L (\epsilon \ell_f)^{2/3}
Rm^{1/4}\max[1,Pm]^{1/4}$. Numerical simulations also demonstrate this bound.",2204.14091v2
2008-10-29,The saturation of the electron beam filamentation instability by the self-generated magnetic field and magnetic pressure gradient-driven electric field,"Two counter-propagating cool and equally dense electron beams are modelled
with particle-in-cell (PIC) simulations. The electron beam filamentation
instability is examined in one spatial dimension. The box length resolves one
pair of current filaments. A small, a medium-sized and a large filament are
considered and compared. The magnetic field amplitude at the saturation time of
the filamentation instability is proportional to the filament size. It is
demonstrated, that the force on the electrons imposed by the electrostatic
field, which develops during the nonlinear stage of the instability, oscillates
around a mean value that equals the magnetic pressure gradient force. The
forces acting on the electrons due to the electrostatic and the magnetic field
have a similar strength. The electrostatic field reduces the confining force
close to the stable equilibrium of each filament and increases it farther away.
The confining potential is not sinusoidal, as assumed by the magnetic trapping
model, and it permits an overlap of current filaments (plasmons) with an
opposite flow direction. The scaling of the saturation amplitude of the
magnetic field with the filament size observed here thus differs from that
expected from the magnetic trapping model. The latter nevertheless gives a good
estimate for the magnetic saturation amplitude. The increase of the peak
electrostatic and magnetic field amplitudes with the filament size implies,
that the electrons heat up more and that the spatial modulation of their mean
speed along the beam flow direction increases with the filament size.",0810.5267v1
2015-11-22,Passively Q-switched EDFL using Fe3O4-nanoparticle saturable absorber,"We experimentally demonstrate a passively Q-switched erbium-doped fiber laser
(EDFL) operation by using a saturable absorber based on Fe3O4 nanoparticles
(FONP) in magnetic fluid (MF). As a kind of transition metal oxide, the FONP
has a large nonlinear optical response with a fast response time for saturable
absorber. By depositing MF at the end of optical fiber ferrule, we fabricated a
FONP-based saturable absorber, which enables a strong light-matter interaction
owing to the confined transmitted optical field within the single mode fiber.
Because of large third-order optical nonlinearities of FONP-based saturable
absorber, large modulation depth of 8.2% and non saturable absorption of 56.6%
are demonstrated. As a result, stable passively Q-switched EDFL pulses with
maximum output pulse energy of 23.76 nJ, repetition rate of 33.3 kHz, and pulse
width of 3.2 {\mu}s are achieved when the input pump power is 110 mW at the
wavelength of 980 nm. The laser features a low threshold pump power of ~15 mW.",1511.07016v1
2021-05-10,Influence of grain morphology and orientation on saturation magnetostriction of polycrystalline Terfenol-D,"In this work we computationally study the effect of microstructure on
saturation magnetostriction of Terfenol-D (Tb$_{0.27}$Dy$_{0.73}$Fe$_{2}$) by
means of Finite Element Method. The model is based on the equilibrium
magnetoelastic strain tensor at magnetic saturation, and shows that the crystal
orientation might play a more significant role on saturation magnetostriction
than the morphology of the grains. We also calculate the dependence of
saturation magnetostriction on the dispersion angle of the distribution of
grains in the oriented growth crystal directions $<011>$ and $<111>$, finding
that not highly oriented grain distributions reduce saturation magnetostriction
significantly. This result evinces the importance of high-quality control of
grain orientation in the synthesis of grain-aligned polycrystalline Terfenol-D,
and provides a quantitative estimation for the range of acceptable values for
the dispersion angle of the distribution of the oriented grains.",2105.04315v4
2021-04-30,Correction of FLASH-based MT saturation in human brain for residual bias of B1-inhomogeneity at 3T,"Background: Magnetization transfer (MT) saturation reflects the additional
saturation of the MRI signal imposed by an MT pulse and is largely driven by
the saturation of the bound pool. This reduction of the bound polarization by
the MT pulse is less efficient than predicted by the differential B1-square law
of absorption. Thus, B1 inhomogeneities lead to a residual bias in the MT
saturation maps. We derive a heuristic correction to reduce this bias for a
widely used multi-parameter mapping protocol at 3T. Methods: The amplitude of
the MT pulse was varied via the nominal flip angle to mimic variations in B1.
The MT saturation's dependence on the actual flip angle features a linear
correction term, which was determined separately for gray and white matter.
Results: The deviation of MT saturation from differential B1-square law is well
described by a linear decrease with the actual flip angle of the MT pulse. This
decrease showed no significant differences between gray and white matter. Thus,
the post hoc correction does not need to take different tissue types into
account. Bias-corrected MT saturation maps appeared more symmetric and
highlighted highly myelinated tracts. Discussion: Our correction involves a
calibration that is specific for the MT pulse. While it can also be used to
rescale nominal flip angles, different MT pulses and/or protocols will require
individual calibration. Conclusion: The suggested B1 correction of the MT maps
can be applied post hoc using an independently acquired flip angle map.",2104.14878v1
2008-10-28,Evidence for Magnetic Flux Saturation in Rapidly Rotating M Stars,"We present magnetic flux measurements in seven rapidly rotating M dwarfs. Our
sample stars have X-ray and H-alpha emission indicative of saturated emission,
i.e., emission at a high level independent of rotation rate. Our measurements
are made using near-infrared FeH molecular spectra observed with HIRES at Keck.
Because of their large convective overturn times, the rotation velocity of M
stars with small Rossby numbers is relatively slow and does not hamper the
measurement of Zeeman splitting. The Rossby numbers of our sample stars are as
small as 0.01. All our sample stars exhibit magnetic flux of kilo-Gauss
strength. We find that the magnetic flux saturates in the same regime as
saturation of coronal and chromospheric emission, at a critical Rossby number
of around 0.1. The filling factors of both field and emission are near unity by
then. We conclude that the strength of surface magnetic fields remains
independent of rotation rate below that; making the Rossby number yet smaller
by a factor of ten has little effect. These saturated M-star dynamos generate
an integrated magnetic flux of roughly 3 kG, with a scatter of about 1 kG. The
relation between emission and flux also has substantial scatter.",0810.5139v1
2014-05-28,"Electron Heating, Magnetic Field Amplification, and Cosmic Ray Precursor Length at Supernova Remnant Shocks","We investigate the observability, by direct and indirect means, of a shock
precursor arising from magnetic field amplification by cosmic rays. We estimate
the depth of such a precursor under conditions of nonresonant amplification,
which can provide magnetic field strengths comparable to those inferred for
supernova remnants. Magnetic field generation occurs as the streaming cosmic
rays induce a plasma return current, and may be quenched either by nonresonant
or resonant channels. In the case of nonresonant saturation, the cosmic rays
become magnetized and amplification saturates at higher magnetic fields. The
precursor can extend out to $10^{17} - 10^{18}$ cm and is potentially
detectable. If resonant saturation occurs, the cosmic rays are scattered by
turbulence and the precursor length will likely be much smaller.
  The dependence of precursor length on shock velocity has implications for
electron heating. In the case of resonant saturation, this dependence is
similar to that in the more familiar resonantly generated shock precursor,
which when expressed in terms of the cosmic ray diffusion coefficient
$\varkappa $ and shock velocity $v_s$ is $\varkappa /v_s$. In the nonresonantly
saturated case, the precursor length declines less quickly with increasing
$v_s$. Where precursor length proportional to $1/v_s$ gives constant electron
heating, this increased precursor length could be expected to lead to higher
electron temperatures for nonresonant amplification. This should be expected at
faster supernova remnant shocks than studied by previous works. Existing
results and new data analysis of SN 1006 and Cas A suggest some observational
support for this idea.",1405.7332v1
2017-03-16,"3D magnetization currents, magnetization loop, and saturation field in superconducting rectangular prisms","Bulk superconductors are used in both many applications and material
characterization experiments, being the bulk shape of rectangular prism very
frequent. However the magnetization currents are still mostly unknown for this
kind of three dimensional (3D) shape, specially below the saturation magnetic
field. Knowledge of the magnetization currents in this kind of samples is
needed to interpret the measurements and the development of bulk materials for
applications. This article presents a systematic analysis of the magnetization
currents in prisms of square base and several thicknesses. We make this study
by numerical modeling using a variational principle that enables high number of
degrees of freedom. We also compute the magnetization loops and the saturation
magnetic field, using a definition that is more relevant for thin prisms than
previous ones. The article presents a practical analytical fit for any aspect
ratio. For applied fields below the saturation field, the current paths are not
rectangular, presenting 3D bending. The thickness-average results are
consistent with previous modeling and measurements for thin films. The 3D
bending of the current lines indicates that there could be flux cutting effects
in rectangular prisms. The component of the critical current density in the
applied field direction may play a role, being the magnetization currents in a
bulk and a stack of tapes not identical.",1703.05529v3
2009-04-07,Saturated magnetic field amplification at supernova shocks,"Cosmic-ray streaming instabilities at supernova shocks are discussed in the
quasilinear diffusion formalism which takes into account the feedback effect of
wave growth on the cosmic ray streaming motion. In particular, the nonresonant
instability that leads to magnetic field amplification in the short wavelength
regime is considered. The linear growth rate is calculated using kinetic theory
for a streaming distribution. We show that the nonresonant instability is
actually driven by a compensating current in the background plasma. The
nonresonant instability can develop into a nonlinear regime generating
turbulence. The saturation of the amplified magnetic fields due to particle
diffusion in the turbulence is derived analytically. It is shown that the
evolution of parallel and perpendicular cosmic-ray pressures is predominantly
determined by nonresonant diffusion. However, the saturation is determined by
resonant diffusion which tends to reduce the streaming motion through pitch
angle scattering. The saturated level can exceed the mean background magnetic
field.",0904.1038v1
2011-04-21,Edge Saturation effects on the magnetism and band gaps in multilayer graphene ribbons and flakes,"Using a density functional theory based electronic structure method and
semi-local density approximation, we study the interplay of geometric
confinement, magnetism and external electric fields on the electronic structure
and the resulting band gaps of multilayer graphene ribbons whose edges are
saturated with molecular hydrogen (H$_2$) or hydroxyl (OH) groups. We discuss
the similarities and differences of computed features in comparison with the
atomic hydrogen (or H-) saturated ribbons and flakes. For H$_2$
edge-saturation, we find \emph{shifted} labeling of three armchair ribbon
classes and magnetic to non-magnetic transition in narrow zigzag ribbons whose
critical width changes with the number of layers. Other computed
characteristics, such as the existence of a critical gap and external electric
field behavior, layer dependent electronic structure, stacking-dependent band
gap induction and the length confinement effects remain qualitatively same with
those of H-saturated ribbons.",1104.4354v1
2014-10-23,Magnetic phase diagram slightly below the saturation field in the stacked $J_1$-$J_2$ model in the square lattice with the $J_{\text{C}}$ interlayer coupling,"We study the effect of adding interlayer coupling to the square lattice,
$J_1$-$J_2$ Heisenberg model in high external magnetic field. In particular, we
consider a cubic lattice formed from stacked $J_1$-$J_2$ layers, with
interlayer exchange coupling $J_{\text{C}}$. For the 2-dimensional model
($J_{\text{C}}=0$) it has been shown that a spin-nematic phase appears close to
the saturation magnetic field for the parameter range $-0.4 \lesssim J_2/J_1$
and $J_2>0$. We determine the phase diagram for 3-dimensional model at high
magnetic field by representing spin flips out of the saturated state as bosons,
considering the dilute boson limit and using the Bethe-Salpeter equation to
determine the first instability of the saturated paramagnet. Close to the
highly frustrated point $J_2/J_1\sim0.5$, we find that the spin-nematic state
is stable even for $|J_{\text{C}}/J_1|\sim 1$. For larger values of $J_2/J_1$,
interlayer coupling favors a broad, phase-separated region. Further increase of
$|J_{\text{C}}|$ stabilizes a collinear antiferromagnet, which is selected via
the order-by-disorder mechanism.",1410.8094v3
2020-04-15,Noise-Induced Magnetic Field Saturation in Kinetic Simulations,"Monte Carlo methods are often employed to numerically integrate kinetic
equations, such as the particle-in-cell method for the plasma kinetic equation,
but these methods suffer from the introduction of counting noise to the
solution. We report on a cautionary tale of counting noise modifying the
nonlinear saturation of kinetic instabilities driven by unstable beams of
plasma. We find a saturated magnetic field in under-resolved particle-in-cell
simulations due to the sampling error in the current density. The noise-induced
magnetic field is anomalous, as the magnetic field damps away in continuum
kinetic and increased particle count particle-in-cell simulations. This
modification of the saturated state has implications for a broad array of
astrophysical phenomena beyond the simple plasma system considered here, and it
stresses the care that must be taken when using particle methods for kinetic
equations.",2004.07255v2
1994-09-12,New observational limits on dynamo saturation in young solar-type stars,"We present statistically robust observational evidence which imposes new
limits on dynamo saturation in young solar-type stars. These are inferred from
the increasing amplitude of the V-band optical flux with rotation, caused by
the filling of the disc with surface spots in a non-axisymmetric pattern.
Assuming spot coverage acts as a tracer of the total magnetic surface flux we
find that the magnetic activity saturates at a level at least 6 -- 10 times
greater than that inferred from chromospheric and transition line indicators.
We suggest that these new limits imply a minimum rotation for saturation of the
dynamo and that for high rotation rates starspot coverage acts as an
alternative diagnostic for the stellar dynamo to the chromospheric and
transition region line emission fluxes. The fact that the dynamo does not
appear to saturate at the low rotation rates indicated by chromospheric
indicators should assist evolutionary braking models that have to explain the
sudden spin-down of young fast rotating G-dwarfs. ( + 3 figures, available on
request) To appear in Astronomy and Astrophysics (A&A latex style file,
laa.sty, included at beginning of file)",9409023v1
2014-02-20,On the saturation of non-axisymmetric instabilites of magnetized spherical Couette flow,"We numerically investigate the saturation of the hydromagnetic instabilities
of a magnetized spherical Couette flow. Previous simulations [Hollerbach, 2009]
demonstrated region where the axisymmetric flow, calculated from a 2-D
simulation, was linearly unstable to nonaxisymmetric perturbations. Full,
nonlinear, 3d simulations [Hollerbach 2009, Travnikov 2011] showed that the
saturated state would consist only of harmonics of one azimuthal wave number,
though there were bifurcations and transitions as nondimensional parameters
(Re, Ha) were varied. Here, the energy transfer between different aziumthal
modes is formulated as a network. This demonstrates a mechanism or the
saturation of one mode and for the suppression of other unstable modes. A given
mode grows by extracting energy from the axisymmetric flow, and then saturates
as the energy transfer to its second harmonic equals this inflow. At the same
time, this mode suppresses other unstable modes by facilitating an energy
transfer to linearly stable modes.",1402.5064v2
2019-09-13,Modeling the Saturation of the Bell Instability Using Hybrid Simulations,"The nonresonant cosmic ray instability, predicted by Bell (2004), is thought
to play an important role in the acceleration and confinement of cosmic rays
(CRs) close to supernova remnants. Despite its importance, the exact mechanism
responsible for the saturation of the instability has not been determined, and
there is no first-principle prediction for the amplitude of the saturated
magnetic field. Using a survey of self-consistent kinetic hybrid simulations
(with kinetic ions and fluid electrons), we study the saturation of the
non-resonant streaming instability as a function of the parameters of both the
thermal background plasma and the CR population. The strength of the saturated
magnetic field has important implications for both CR acceleration in supernova
remnants and CR diffusion in the Galaxy.",1909.06481v1
2012-08-19,Magnetization curve of the kagome-strip-lattice antiferromagnet,"We study the magnetization curve of the Heisenberg model on the
quasi-one-dimensional kagome-strip lattice that shares the same lattice
structure in the inner part with the two-dimensional kagome lattice. Our
numerical calculations based on the density matrix renormalization group method
reveal that the system shows several magnetization plateaus between zero
magnetization and the saturated one; we find the presence of the magnetic
plateaus with the n=7 height of the saturation for n =1,2,3,4,5 and 6 in the S
=1/2 case, whereas we detect only the magnetic plateaus of n =1,3,5 and 6 in
the S =1 case. In the cases of n =2,4 and 6 for the S=1/2 system, the
Oshikawa-Yamanaka-Affleck condition suggests the occurrence of the
translational symmetry breaking (TSB). We numerically confirm this non-trivial
TSB in our results of local magnetizations. We have also found that the
macroscopic jump appears near the saturation field irrespective of the spin
amplitude as well as the two-dimensional kagome model.",1208.3825v1
2019-09-29,Effect of Ge-substitution on Magnetic Properties in the Itinerant Chiral Magnet MnSi,"We have investigated the effect of Ge-substitution to the magnetic ordering
in the B20 itinerant chiral magnet MnSi prepared by melting and annealing under
ambient pressure. From metallurgical survey, the solubility limit of Ge was
found to be $x=0.144(5)$ with annealing temperature $T_\mathrm{an} = 1073$ K.
Magnetization measurements on MnSi$_{1-x}$Ge$_x$ samples show that the helical
ordering temperature $T_{\mathrm{c}}$ increases rapidly in the low-$x$ range,
whereas it becomes saturated at higher concentration $x>~0.1$. The Ge
substitution also increases both the saturation magnetization $M_\mathrm{s}$
and the critical field to the fully polarized state $H_\mathrm{c2}$. In
contrast to the saturation behavior of $T_\mathrm{c}$, those parameters
increase linearly up to the highest Ge concentration investigated. In the
temperature-magnetic field phase diagram, we found enlargement of the skyrmion
phase region for large $x$ samples. We, furthermore, observed the non-linear
behavior of helical modulation vector $k$ as a function of Ge concentration,
which can be described qualitatively using the mean field approximation.",1909.13246v1
2023-03-26,The effect of the magnetically dead layer on the magnetization and the magnetic anisotropy of the dextran coated magnetite nanoparticles,"We present a study on the magnetic behavior of dextran-coated magnetite
nanoparticles (DM NPs) with sizes between 3 and 19 nm, synthesized by
hydrothermal-assisted co-precipitation method. The decrease of saturation
magnetization ($M_s$) with decreasing particle size has been modeled by
assuming the existence of a spin-disordered layer at the particle surface,
which is magnetically dead. Based on this core-shell model and taking into
account the weight contribution of the non-magnetic coating layer (dextran) to
the whole magnetization, the dead layer thickness ($t$) and saturation
magnetization $M_s$ of the magnetic cores in our samples were estimated to be
$t = 6.8~\mathrm{\AA}$ and $M_s = 98.8~\mathrm{emu/g}$, respectively. The data
of $M_s$ were analyzed using a law of approach to saturation, indicating an
increase in effective magnetic anisotropy ($K_{eff}$) with decreasing particle
size as expected from the increased surface/volume ratio in small MNPs. The
obtained $K_{eff}$ values were successfully modeled by including an extra
contribution of dipolar interactions due to the formation of chain-like
clusters of MNPs. The surface magnetic anisotropy ($K_s$) was estimated to be
about $K_s = 1.04\times10^5~\mathrm{J/m^3}$. Our method provides a simple and
accurate way to obtain the $M_s$ core values in surface-disordered MNPs, a
relevant parameter required for magnetic modeling in many applications.",2303.14654v1
1997-07-09,Magnetization Curves of Antiferromagnetic Heisenberg Spin-1/2 Ladders,"Magnetization processes of spin-1/2 Heisenberg ladders are studied using
strong-coupling expansions, numerical diagonalization of finite systems and a
bosonization approach. We find that the magnetization exhibits plateaux as a
function of the applied field at certain rational fractions of the saturation
value. Our main focus are ladders with 3 legs where plateaux with magnetization
one third of the saturation value are shown to exist.",9707090v2
1998-05-04,Ladders in a magnetic field: a strong coupling approach,"We show that non-frustrated and frustrated ladders in a magnetic field can be
systematically mapped onto an XXZ Heisenberg model in a longitudinal magnetic
field in the limit where the rung coupling is the dominant one. This mapping is
valid in the critical region where the magnetization goes from zero to
saturation. It allows one to relate the properties of the critical phase
($H_c^1$, $H_c^2$, the critical exponents) to the exchange integrals and
provide quantitative estimates of the frustration needed to create a plateau at
half the saturation value for different models of frustration.",9805029v2
2002-09-24,Dephasing by extremely dilute magnetic impurities revealed by Aharonov-Bohm oscillations,"We have probed the magnetic field dependence of the electron phase coherence
time $\tau_\phi$ by measuring the Aharonov-Bohm conductance oscillations of
mesoscopic Cu rings. Whereas $\tau_\phi$ determined from the low-field
magnetoresistance saturates below 1 K, the amplitude of Aharonov-Bohm $h/e$
oscillations increases strongly on a magnetic field scale proportional to the
temperature. This provides strong evidence that a likely explanation for the
frequently observed saturation of $\tau_\phi$ at low temperature in weakly
disordered metallic thin films is the presence of extremely dilute magnetic
impurities.",0209562v1
2007-10-02,Low temperature magnetization of the S=1/2 kagome antiferromagnet ZnCu_3(OH)_6Cl_2,"The dc-magnetization of the unique S=1/2 kagome antiferromagnet
Herbertsmithite has been measured down to 0.1K. No sign of spin freezing is
observed in agreement with former muSR and ac-susceptibility results. The low
temperature magnetic response is dominated by a defect contribution which
exhibits a new energy scale $\simeq 1$ K, likely reflecting the coupling of the
defects. The defect component is saturated at low temperature by H>8T applied
magnetic fields which enables us to estimate an upper bound for the non
saturated intrinsic kagome susceptibility at T=1.7K.",0710.0451v1
1999-11-23,Magnetization-plateau state of the S=3/2 spin chain with single ion anisotropy,"We reexamine the numerical study of the magnetized state of the S=3/2 spin
chain with single ion anisotropy D(> 0) for the magnetization M=M_{S}/3, where
M_{S} is the saturation magnetization. We find at this magnetization that for
D<D_{c1}=0.387 the system is critical and the magnetization plateau does not
appear. For D > D_{c1}, the parameter region is divided into two parts D_{c1} <
D < D_{c2}=0.943 and D_{c2} < D. In each region, the system is gapful and the
M=M_{S}/3 magnetization plateau appears in the magnetization process. From our
numerical calculation, the intermediate region D_{c1} < D < D_{c2} should be
characterized by a magnetized valence-bond-solid state.",9911364v1
2003-09-11,Giant Keplerate molecule Fe30 - the first octopole magnet,"The multipole expansion technique is applied to one of the largest magnetic
molecules, Fe30. The molecule's dipole, toroid and quadrupole magnetic moments
are equal to zero (in the absence of magnetic field) so the multipole expansion
starts from the octopole moment. Probably the Fe30 molecule is the most
symmetrical magnetic body synthesized so far. The magnetization process is
considered theoretically in different geometries. Some components of the
octopole moment experience a jump while the magnetization rises linearly up to
its saturation value. An elementary octopole moment consisting of four magnetic
dipoles is proposed as a hint for designing of an experiment for measurement of
octopole magnetic moment components.",0309282v1
2009-09-25,Probing punctual magnetic singularities during magnetization process in FePd films,"We report the use of Lorentz microscopy to observe the domain wall structure
during the magnetization process in FePd thin foils. We have focused on the
magnetic structure of domain walls of bubble-shaped magnetic domains near
saturation. Regions are found along the domain walls where the magnetization
abruptly reverses. Multiscale magnetic simulations shown that these regions are
vertical Bloch lines (VBL) and the different bubble shapes observed are then
related to the inner structure of the VBLs. We were thus able to probe the
presence of magnetic singularities as small as Bloch points in the inner
magnetization of the domain walls.",0909.4645v1
2010-04-20,Radiation stability of biocompatibile magnetic fluid,"The radiation stability of biocompatibile magnetic fluid used in nanomedicine
after electron irradiation was studied. Two types of the water-based magnetic
fluids were prepared. The first one was based on the magnetite nanoparticles
stabilized by one surfactant natrium oleate. The second one was biocompatibile
magnetic fluid stabilized with two surfactants, natrium oleate as a first
surfactant and Poly(ethylene glycol) (PEG) as a second surfactant. The
magnetization measurements showed that electron irradiation up to 1000Gy caused
50% reduction of saturation magnetization in the case of the first sample with
only one surfactant while in the case of the second biocompatibile magnetic
fluid, only 25% reduction of saturation magnetization was observed. In the
first magnetic fluid the radiation caused the higher sedimentation of the
magnetic particles than in the second case, when magnetic particles are covered
also with PEG. The obtained results show that PEG behave as a protective
element.",1004.3448v2
2019-12-02,Magnetic Inflation and Stellar Mass. V. Intensification and saturation of M dwarf absorption lines with Rossby number,"In young sun-like stars and field M dwarf stars, chromospheric and coronal
magnetic activity indicators such as H$\alpha$, X-ray and radio emission are
known to saturate with low Rossby number ($Ro \lesssim 0.1$), defined as the
ratio of rotation period to convective turnover time. The mechanism for the
saturation is unclear. In this paper, we use photospheric Ti I and Ca I
absorption lines in $Y$ band to investigate magnetic field strength in M dwarfs
for Rossby numbers between 0.01 and 1.0. The equivalent widths of the lines are
magnetically enhanced by photospheric spots, a global field or a combination of
the two. The equivalent widths behave qualitatively similar to the
chromospheric and coronal indicators: we see increasing equivalent widths
(increasing absorption) with decreasing $Ro$ and saturation of the equivalent
widths for $Ro \lesssim 0.1$. The majority of M dwarfs in this study are fully
convective. The results add to mounting evidence that the magnetic saturation
mechanism occurs at or beneath the stellar photosphere.",1912.01004v1
2022-01-16,Parallel transmit PUlse design for Saturation Homogeneity (PUSH) for Magnetization Transfer imaging at 7T,"Purpose: This work proposes a novel RF pulse design for parallel transmit
(pTx) systems to obtain uniform saturation of semisolid magnetization for
Magnetization Transfer (MT) contrast in the presence of transmit field
($B_1^+$) inhomogeneities. The semisolid magnetization is usually modeled as
being purely longitudinal, with the applied $B_1^+$ field saturating but not
rotating its magnetization, thus standard pTx pulse design methods do not
apply. Theory and Methods: Pulse design for Saturation Homogeneity (PUSH)
optimizes pTx RF pulses by considering uniformity of root-mean squared $B_1^+$,
$B_1^{rms}$, which relates to the rate of semisolid saturation. Here we
considered designs consisting of a small number of spatially non-selective
sub-pulses optimized over either a single 2D plane or 3D. Simulations and in
vivo experiments on a 7T Terra system with an 8-TX Nova head coil in 5 subjects
were carried out to study the homogenization of $B_1^{rms}$ and of the MT
contrast by acquiring MT ratio maps. Results: Simulations and in vivo
experiments showed up to 6 and 2 times more uniform $B_1^{rms}$ compared to
circular polarized (CP) mode for 2D and 3D optimizations, respectively. This
translated into 4 and 1.25 times more uniform MT contrast, consistently for all
subjects, where 2 sub-pulses were enough for the implementation and coil used.
Conclusion: The proposed PUSH method obtains more uniform and higher MT
contrast than CP mode within the same SAR budget.",2201.06091v1
2017-07-19,The Development of Magnetic Field Line Wander by Plasma Turbulence,"Plasma turbulence occurs ubiquitously in space and astrophysical plasmas,
mediating the nonlinear transfer of energy from large-scale electromagnetic
fields and plasma flows to small scales at which the energy may be ultimately
converted to plasma heat. But plasma turbulence also generically leads to a
tangling of the magnetic field that threads through the plasma. The resulting
wander of the magnetic field lines may significantly impact a number of
important physical processes, including the propagation of cosmic rays and
energetic particles, confinement in magnetic fusion devices, and the
fundamental processes of turbulence, magnetic reconnection, and particle
acceleration. The various potential impacts of magnetic field line wander are
reviewed in detail, and a number of important theoretical considerations are
identified that may influence the development and saturation of magnetic field
line wander in astrophysical plasma turbulence. The results of nonlinear
gyrokinetic simulations of kinetic Alfven wave turbulence of sub-ion length
scales are evaluated to understand the development and saturation of the
turbulent magnetic energy spectrum and of the magnetic field line wander. It is
found that turbulent space and astrophysical plasmas are generally expected to
contain a stochastic magnetic field due to the tangling of the field by strong
plasma turbulence. Future work will explore how the saturated magnetic field
line wander varies as a function of the amplitude of the plasma turbulence and
the ratio of the thermal to magnetic pressure, known as the plasma beta.",1707.06230v1
2013-09-27,Structures and Lagrangian statistics of the Taylor-Green Dynamo,"The evolution of a Taylor-Green forced magnetohydrodynamic (MHD) system
showing dynamo activity is analyzed via direct numerical simulations. The
statistical properties of the velocity and magnetic field in Eulerian
coordinates and along trajectories of fluid elements (Lagrangian coordinates)
are found to change between the kinematic, non-linear and saturated regime.
Fluid element (tracer) trajectories change from chaotic quasi-isotropic
(kinematic phase) to mean magnetic field aligned (saturated phase). The
probability density functions (PDFs) of the magnetic field change from strongly
non-Gaussian in the kinematic to quasi-Gaussian PDFs in the saturated regime so
that their flatness give a precise handle on the definition of the limiting
points of the three regimes. Also the statistics of the fluctuations of the
kinetic and magnetic energy along fluid trajectories change. All this goes
along with a dramatic increase of the correlation time of velocity and magnetic
field fluctuations experienced by tracers significantly exceeding one turbulent
large-eddy turn-over time. A remarkable consequence is an intermittent scaling
regime of the Lagrangian magnetic field structure functions at unusually long
time scales.",1309.7975v2
2022-06-17,Melting of magnetization plateaus for kagome and square-kagome lattice antiferromagnets,"Unconventional features of the magnetization curve at zero temperature such
as plateaus or jumps are a hallmark of frustrated spin systems. Very little is
known about their behavior at non-zero temperatures. Here we investigate the
temperature dependence of the magnetization curve of the kagome lattice
antiferromagnet in particular at 1/3 of the saturation magnetization for large
lattice sizes of up to N=48 spins. We discuss the phenomenon of asymmetric
melting and trace it back to a combined effect of unbalanced magnetization
steps on either side of the investigated plateau as well as on the behavior of
the density of states across the plateau. We compare our findings to the
square-kagome lattice that behaves similarly at low temperatures at zero field,
but as we will demonstrate differently at 1/3 of the saturation magnetization.
Both systems possess a flat one-magnon band and therefore share with the class
of flat-band systems the general property that the plateau that precedes the
jump to saturation melts asymmetrically but now with a minimal susceptibility
that bends towards lower fields with increasing temperature.",2206.08710v3
2016-03-30,Distributed chaos and solitons at the edges of magnetically confined plasmas,"It is shown, using results of measurements of ion saturation current in the
plasma edges of different magnetic fusion confinement devices (tokamaks and
stellarators), that the plasma dynamics in the edges is dominated by
distributed chaos with spontaneously broken translational symmetry at low
magnetic field, and with spontaneously broken reflexional symmetry (by helical
solitons) at high magnetic field.",1603.09186v2
2013-06-26,Periodic magnetic structures generated by spin-polarized currents in nanostripes,"The influence of a spin-polarized current on long ferromagnetic nanostripes
is studied numerically. The current flows perpendicularly to the stripe. The
study is based on the Landau-Lifshitz phenomenological equation with the
Slonczewski-Berger spin-torque term. The magnetization behavior is analyzed for
all range of the applied currents, up to the saturation. It is shown that the
saturation current is a nonmonotonic function of the stripe width. For a stripe
width increasing it approaches the saturation value for an infinite film. A
number of stable periodic magnetization structures are observed below the
saturation. Type of the periodical structure depends on the stripe width.
Besides the one-dimensional domain structure, typical for narrow wires, and the
two-dimensional vortex-antivortex lattice, typical for wide films, a number of
intermediate structures are observed, e.g. cross-tie and diamond state. For
narrow stripes an analytical analysis is provided.",1306.6296v1
2017-11-23,Physics of the saturation of particle acceleration in relativistic magnetic reconnection,"We investigate the saturation of particle acceleration in relativistic
reconnection using two-dimensional particle-in-cell simulations at various
magnetizations \sigma. We find that the particle energy spectrum produced in
reconnection quickly saturates as a hard power law that cuts off at
\gamma~4\sigma, confirming previous work. Using particle tracing, we find that
particle acceleration by the reconnection electric field in X-points determines
the shape of the particle energy spectrum. By analyzing the current sheet
structure, we show that physical cause of saturation is the spontaneous
formation of secondary magnetic islands that can disrupt particle acceleration.
By comparing the size of acceleration regions to the typical distance between
disruptive islands, we show that the maximum Lorentz factor produced in
reconnection is \gamma ~ 5 \sigma, which is very close to what we find in our
particle energy spectra. We also show that the dynamic range in Lorentz factor
of the power law spectrum in reconnection is < 40. The hardness of the power
law combined with its narrow dynamic range implies that relativistic
reconnection is capable of producing the hard narrowband flares observed in the
Crab Nebula but has difficulty producing the softer broadband prompt GRB
emission.",1711.08701v1
2009-08-13,Susceptibility at the edge points of magnetization plateau of 1D electron/spin systems,"We study the behavior of magnetization curve as a function of magnetic field
in the immediate vicinity of the magnetization plateaus of 1D electron systems
within the bosonization formalism. First we discuss the plateau that is formed
at the saturation magnetization of 1D electron system. Interactions between
electrons we treat in the lowest order of perturbation. We show that for
isolated systems, where total number of electrons is not allowed to vary,
magnetic susceptibility stays always finite away of half filling. Similar
statement holds for many other magnetization plateaus supporting nonmagnetic
gapless excitations encountered in 1D electron/spin systems in the absence of
special symmetries or features responsible for the mode decoupling. We
demonstrate it on example of the plateaus at irrational values of magnetization
in doped modulated Hubbard chains. Finally we discuss the connection between
the weak coupling description of saturation magnetization plateau and strong
coupling description of zero magnetization plateau of attractively interacting
electrons/ antiferromagnetically interacting spin 1 Bosons.",0908.1894v1
2020-07-09,Shaping nanoscale magnetic domain memory in exchange-coupled ferromagnets by field cooling,"The advance of magnetic nanotechnologies relies on detailed understanding of
nanoscale magnetic mechanisms in materials. Magnetic domain memory (MDM), i.e.,
the tendency for magnetic domains to repeat the same pattern during
field-cycling, is important to many technologies including magnetic recording
developments. We show coherent x-ray magnetic scattering studies unveiling MDM
in [Co/Pd]/IrMn films. When illuminated by coherent x-rays, the magnetic
domains in the [Co/Pd] multilayer produce a speckle pattern unique to their
specific nanoscale configuration. By cross-correlating such speckle patterns
throughout the magnetization loop, we measure the MDM. When cooled below its
blocking temperature, the film exhibits up to 100% MDM, induced by
exchange-couplings with the IrMn layer. Furthermore, the degree of MDM
drastically depends on cooling conditions. If the film is cooled under moderate
fields, MDM is high throughout the entire magnetization loop. If the film is
cooled under nearly saturating field, MDM vanishes, except at nucleation and
saturation",2007.04930v1
2023-05-17,Material Parameters for Faster Ballistic Switching of an In-plane Magnetized Nanomagnet,"High-speed magnetization switching of a nanomagnet is necessary for faster
information processing. The ballistic switching by a pulsed magnetic filed is a
promising candidate for the high-speed switching. It is known that the
switching speed of the ballistic switching can be increased by increasing the
magnitude of the pulsed magnetic field. However it is difficult to generate a
strong and short magnetic field pulse in a small device. Here we explore
another direction to achieve the high-speed ballistic switching by designing
material parameters such as anisotropy constant, saturation magnetization, and
the Gilbert damping constant. We perform the macrospin simulations for the
ballistic switching of in-plane magnetized nano magnets with varying material
parameters. The results are analyzed based on the switching dynamics on the
energy density contour. We show that the pulse width required for the ballistic
switching can be reduced by increasing the magnetic anisotropy constant or by
decreasing the saturation magnetization. We also show that there exists an
optimal value of the Gilbert damping constant that minimizes the pulse width
required for the ballistic switching.",2305.10111v1
2013-12-09,Magnetic fields in cosmological simulations of disk galaxies,"Observationally, magnetic fields reach equipartition with thermal energy and
cosmic rays in the interstellar medium of disk galaxies such as the Milky Way.
However, thus far cosmological simulations of the formation and evolution of
galaxies have usually neglected magnetic fields. We employ the moving-mesh code
\textsc{Arepo} to follow for the first time the formation and evolution of a
Milky Way-like disk galaxy in its full cosmological context while taking into
account magnetic fields. We find that a prescribed tiny magnetic seed field
grows exponentially by a small-scale dynamo until it saturates around $z=4$
with a magnetic energy of about $10\%$ of the kinetic energy in the center of
the galaxy's main progenitor halo. By $z=2$, a well-defined gaseous disk forms
in which the magnetic field is further amplified by differential rotation,
until it saturates at an average field strength of $\sim 6 \mug$ in the disk
plane. In this phase, the magnetic field is transformed from a chaotic
small-scale field to an ordered large-scale field coherent on scales comparable
to the disk radius. The final magnetic field strength, its radial profile and
the stellar structure of the disk compare well with observational data. A minor
merger temporarily increases the magnetic field strength by about a factor of
two, before it quickly decays back to its saturation value. Our results are
highly insensitive to the initial seed field strength and suggest that the
large-scale magnetic field in spiral galaxies can be explained as a result of
the cosmic structure formation process.",1312.2620v2
2022-07-25,Insight into ground-state spin arrangement and bipartite entanglement of the polymeric coordination compound [Dy$_2$Cu$_2$]$_n$ through the symmetric spin-1/2 Ising-Heisenberg orthogonal-dimer chain,"The ground-state spin arrangement and the bipartite entanglement within
Cu$^{2+}$-Cu$^{2+}$ dimers across the magnetization process of the 4f-3d
heterometallic coordination polymer
[{Dy(hfac)$_2$(CH$_3$OH)}$_2${Cu(dmg)(Hdmg)}$_2$]$_n$ (H$_2$dmg =
dimethylglyoxime, Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) are
theoretically examined using the symmetric isotropic spin-$1/2$
Ising-Heisenberg orthogonal-dimer chain. The numerical results point to five
possible ground states of the compound with three different degrees of the
quantum entanglement within Cu$^{2+}$-Cu$^{2+}$. Besides the standard
ferrimagnetic and saturated phases without quantum entanglement of Cu$^{2+}$
ions, which are manifested in low-temperature magnetization curve as wide
plateaus at the non-saturated magnetization $16.26\mu_{\rm B}$ and at the
saturation value $20.82\mu_{\rm B}$, respectively, one also finds an intriguing
singlet-like phase with just partial entanglement within Cu$^{2+}$-Cu$^{2+}$
and two singlet phases with fully entangled Cu$^{2+}$-Cu$^{2+}$ dimers. The
former quantum phase can be identified in the low-temperature magnetization
process as very narrow intermediate plateau at the magnetization $9.27\mu_{\rm
B}$ per unit cell, while the latter ones as zero magnetization plateau and
intermediate plateau at the magnetization $18.54\mu_{\rm B}$. Non-monotonous
temperature variations of the concurrence, through which the entanglement
within cooper dimers is quantified, point to the possible temporary thermal
activation of the entangled states of Cu$^{2+}$-Cu$^{2+}$ also above
non-entangled ferrimagnetic and saturated phases.",2207.11943v1
1995-10-06,Magnetic excitations and effects of magnetic fields on the spin-Peierls transition in CuGeO$_3$,"We analyze the magnetic excitations of a spin-1/2 antiferromagnetic
Heisenberg model with alternating nearest neighbor interactions and uniform
second neighbor interactions recently proposed to describe the spin-Peierls
transition in CuGeO$_3$. We show that there is good agreement between the
calculated excitation dispersion relation and the experimental one. We have
also shown that this model reproduces satisfactorily the experimental results
for the magnetization vs. magnetic field curve and its saturation value. The
model proposed also reproduces qualitatively some features of the magnetic
phase diagram of this compound and the overall behavior of the magnetic
specific heat in the presence of applied magnetic fields.",9509160v1
2010-04-15,Magnetization Process of Kagome-Lattice Heisenberg Antiferromagnet,"The magnetization process of the isotropic Heisenberg antiferromagnet on the
kagome lattice is studied. Data obtained from the numerical-diagonalization
method are reexamined from the viewpoint of the derivative of the magnetization
with respect to the magnetic field. We find that the behavior of the derivative
at approximately one-third of the height of the magnetization saturation is
markedly different from that for the cases of typical magnetization plateaux.
The magnetization process of the kagome-lattice antiferromagnet reveals a new
phenomenon, which we call the ""magnetization ramp"".",1004.2528v1
2013-10-23,Magnetization Characteristic of Ferromagnetic Thin Strip by Measuring Anisotropic Magnetoresistance and Ferromagnetic Resonance,"The magnetization characteristic in a permalloy thin strip is investigated by
electrically measuring the anisotropic magnetoresistance and ferromagnetic
resonance in in-plane and out-of-plane configurations. Our results indicate
that the magnetization vector can rotate in the film plane as well as out of
the film plane by changing the intensity of external magnetic field of certain
direction. The magnetization characteristic can be explained by considering
demagnetization and magnetic anisotropy. Our method can be used to obtain the
demagnetization factor, saturated magnetic moment and the magnetic anisotropy.",1310.6117v1
2014-07-01,Explaining Mercury's Density through Magnetic Erosion,"In protoplanetary disks, dust grains rich in metallic iron can attract each
other magnetically. If they are magnetized to values near saturation, the
magnetically induced collision speeds are high enough to knock off the
non-magnetized, loosely bound silicates. This process enriches the surviving
portions of the dust grains in metallic iron, which further enhances the
magnetically mediated collisions. The magnetic enhancement to the collisional
cross-section between the iron rich dust results in rapid grain growth leading
to planetesimal formation. While this process of knocking off silicates, which
we term ""magnetic erosion"", occurs only in a very limited portion of a
protoplanetary disk, it is a possible explanation for Mercury's
disproportionately large iron core.",1407.0274v1
2016-11-14,Magnetization process and magnetocaloric effect of the spin-1/2 XXZ Heisenberg cuboctahedron,"Magnetic properties of the spin-1/2 XXZ Heisenberg cuboctahedron are examined
using exact numerical diagonalization depending on a relative strength of the
exchange anisotropy. While the Ising cuboctahedron exhibits in a
low-temperature magnetization curve only one-third magnetization plateau, the
XXZ Heisenberg cuboctahedron displays another four intermediate plateaux at
zero, one-sixth, one-half and two-thirds of the saturation magnetization. The
novel magnetization plateaux generally extend over a wider range of magnetic
fields with increasing of a quantum ($xy$) part of the XXZ exchange
interaction. It is shown that the XXZ Heisenberg cuboctahedron exhibits in a
vicinity of all magnetization jumps anomalous thermodynamic behavior
accompanied with an enhanced magnetocaloric effect.",1611.04301v1
2005-06-15,Saturated Ferromagnetism from Statistical Transmutation in Two Dimensions,"The total spin of the ground state is calculated in the U -> infinity Hubbard
model with uniform magnetic flux perpendicular to a square lattice, in the
absence of Zeeman coupling. It is found that the saturated ferromagnetism
emerges in a rather wide region in the space of the flux density \phi and the
electron density n_e. In particular, the saturated ferromagnetism at \phi = n_e
is induced by the formation of a spin-1/2 boson, which is a composite of an
electron and the unit flux quantum.",0506352v3
2015-10-08,Nematic ordering in pyrochlore antiferromagnets: high-field phase of chromium spinel oxides,"Motivated by recent observation of a new high field phase near saturation in
chromium spinels $A$Cr$_2$O$_4$ ($A=$ Zn, Cd, Hg), we study the $S = 3/2$
pyrochlore Heisenberg antiferromagnet with biquadratic interactions. Magnon
instability analysis at the saturation field reveals that a very small
biquadratic interaction can induce magnon pairing in pyrochlore
antiferromagnets, which leads to the emergence of a ferro-quadrupolar phase, or
equivalently a spin nematic phase, below the saturation field. We present the
magnetic phase diagram in an applied field, studying both $S=3/2$ and $S=1$
spin systems. The relevance of our result to chromium spinels is discussed.",1510.02373v1
2010-09-13,Can conduction induce convection? The non-linear saturation of buoyancy instabilities in dilute plasmas,"We study the effects of anisotropic thermal conduction on low-collisionality,
astrophysical plasmas using two and three-dimensional magnetohydrodynamic
simulations. For weak magnetic fields, dilute plasmas are buoyantly unstable
for either sign of the temperature gradient: the heat-flux-driven buoyancy
instability (HBI) operates when the temperature increases with radius while the
magnetothermal instability (MTI) operates in the opposite limit. In contrast to
previous results, we show that, in the presence of a sustained temperature
gradient, the MTI drives strong turbulence and operates as an efficient
magnetic dynamo (akin to standard, adiabatic convection). Together, the
turbulent and magnetic energies contribute up to ~10% of the pressure support
in the plasma. In addition, the MTI drives a large convective heat flux, ~1.5%
of rho c_s^3. These findings are robust even in the presence of an external
source of strong turbulence. Our results on the nonlinear saturation of the HBI
are consistent with previous studies but we explain physically why the HBI
saturates quiescently by re-orienting the magnetic field (suppressing the
conductive heat flux through the plasma), while the MTI saturates by generating
sustained turbulence. We also systematically study how an external source of
turbulence affects the saturation of the HBI: such turbulence can disrupt the
HBI only on scales where the shearing rate of the turbulence is faster than the
growth rate of the HBI. In particular, our results provide a simple mapping
between the level of turbulence in a plasma and the effective isotropic thermal
conductivity. We discuss the astrophysical implications of these findings, with
a particular focus on the intracluster medium of galaxy clusters.",1009.2498v1
2004-09-08,Dynamo action in late-type giants,"Recent numerical MHD simulations suggest that magnetic activity may occur in
late-type giants. A entire red supergiant with stellar parameters equal to
Betelgeuse was modelled in 3d with the high-order ""Pencil Code"". Linear
kinematic and non-linear saturated dynamo action are found and the non-linear
magnetic field saturates at a super-equipartition value, while in the linear
regime two different modes of dynamo action are found. Magnetic activity of
late-type giants, if it exists, may influence dust and wind formation and
possibly lead to the heating of the outer atmospheres of these stars.",0409192v1
2004-06-07,Spin switch and spin amplifier: magnetic bipolar transistor in the saturation regime,"It is shown that magnetic bipolar transistors (MBT) can amplify currents even
in the saturation regime, in which both the emitter-base and collector-base
junctions are forward biased. The collector current and the current gain can
change sign as they depend on the relative orientation of the equilibrium spin
in the base and on the nonequilibrium spin in the emitter and collector. The
predicted phenomena should be useful for electrical detection of nonequilibrium
spins in semiconductors, as well as for magnetic control of current
amplification and for current switching.",0406170v1
2010-01-24,Stability problem in dynamo,"It is shown, that the saturated $\alpha$-effect taken from the nonlinear
dynamo equations for the thin disk can still produce exponentially growing
magnetic field in the case, when this field does not feed back on the $\alpha$.
For negative dynamo number (stationary regime) stability is defined by the
structure of the spectra of the linear problem for the positive dynamo numbers.
Stability condition for the oscillatory solution (positive dynamo number) is
also obtained and related to the phase shift of the original magnetic field,
which produced saturated $\alpha$ and magnetic field in the kinematic regime.
Results can be used for explanation of the similar effect observed in the shell
models simulations as well in the 3D dynamo models in the plane layer and
sphere.",1001.4234v1
2011-01-25,Onset and saturation of ion heating by odd-parity rotating-magnetic-fields in a field-reversed configuration,"Heating of figure-8 ions by odd-parity rotating magnetic fields ($RMF_o$)
applied to an elongated field-reversed configuration (FRC) is investigated. The
largest energy gain occurs at resonances ($s \equiv \omega_R/ \omega$) of the
$RMF_o$ frequency, $\omega_R$, with the figure-8 orbital frequency, $\omega$,
and is proportional to $s^2$ for $s-even$ resonances and to $s$ for $s-odd$
resonances. The threshold for the transition from regular to stochastic orbits
explains both the onset and saturation of heating. The FRC magnetic geometry
lowers the threshold for heating below that in the tokamak by an order of
magnitude.",1101.4774v1
2011-04-11,Hydrogen mediated ferromagnetism in ZnO single crystals,"We investigated the magnetic properties of hydrogen plasma treated ZnO single
crystals by SQUID magnetometry. In agreement with the expected hydrogen
penetration depth we found ferromagnetic behavior located at the first 20 nm of
the H-treated surface of ZnO with magnetization at saturation up to 6 emu/g at
300 K and Curie temperature T$_c$ $\gtrsim $ 400 K. In the ferromagnetic
samples a hydrogen concentration of a few atomic percent in the first 20 nm
surface layer was determined by nuclear reaction analysis. The saturation
magnetization of H-treated ZnO increases with the concentration of hydrogen.",1104.1899v1
2011-06-06,Rise and fall of defect induced ferromagnetism in SiC single crystals,"6H-SiC (silicon carbide) single crystals containing VSi-VC divacancies are
investigated with respect to magnetic and structural properties. We found that
an initial increase of structural disorder leads to pronounced ferromagnetic
properties at room temperature. Further introduction of disorder lowers the
saturation magnetization and is accompanied with the onset of lattice
amorphization. Close to the threshold of full amorphization, also divacancy
clusters are formed and the saturation magnetization nearly drops to zero.",1106.0966v1
2019-10-09,Scattering of exchange spin waves from regions of modulated magnetization,"We investigate the reflection coefficient of spin waves propagating in an
ultra-thin ferromagnetic film with regions where saturation magnetization is
modulated. We find analytically and using micromagnetic simulations that there
are transmission resonances that depend on the width of the regions and on the
energy of excitation. Our results resemble the quantum mechanical
Ramsauer-Townsend effect in which an electron with certain energies can
propagate above a potential field without scattering. Our findings are useful
for reconfigurable magnonic devices where the saturation magnetization can be
dynamically controlled via a thermal landscape.",1910.04303v1
2012-03-09,Exchange-dependent relaxation in the rotating frame for slow and intermediate exchange - modeling off-resonant spin-lock and chemical exchange saturation transfer,"Chemical exchange observed by NMR saturation transfer (CEST) and spin-lock
(SL) experiments provide an MRI contrast by indirect detection of exchanging
protons. The determination of the relative concentrations and exchange rates is
commonly achieved by numerical integration of the Bloch-McConnell equations. We
derive an analytical solution of the Bloch-McConnell equations that describes
the magnetization of coupled spin populations under radiofrequency
irradiation.As CEST and off-resonant SL are equivalent, their steady-state
magnetization and dynamics can be predicted by the same single eigenvalue: the
longitudinal relaxation rate in the rotating frame R1rho. For the case of
slowly exchanging systems, e.g. amide protons, the saturation of the small
proton pool is affected by transverse relaxation (R2b). It turns out, that R2b
is also significant for intermediate exchange, such as amine- or
hydroxyl-exchange or paramagnetic CEST agents, if pools are only partially
saturated. We propose a solution for R1rho that includes R2 of the exchanging
pool by extending existing approaches, and verify it by numerical simulations.
With the appropriate projection factors, we obtain an analytical solution for
CEST and SL for nonzero R2 of the exchanging pool, whilst considering the
dilution by direct water saturation across the entire Z-spectra. This allows
the optimization of irradiation parameters and the quantification of
pH-dependent exchange rates and metabolite concentrations. In addition, we
propose evaluation methods that correct for concomitant direct saturation
effects. It is shown that existing theoretical treatments for CEST are special
cases of this approach.",1203.2067v2
2003-12-01,Simulations of small-scale turbulent dynamo,"We report an extensive numerical study of the small-scale turbulent dynamo at
large magnetic Prandtl numbers Pm. A Pm scan is given for the model case of
low-Reynolds-number turbulence. We concentrate on three topics: magnetic-energy
spectra and saturation levels, the structure of the field lines, and the
field-strength distribution. The main results are (1) the folded structure
(direction reversals at the resistive scale, field lines curved at the scale of
the flow) persists from the kinematic to the nonlinear regime; (2) the field
distribution is self-similar and appears to be lognormal during the kinematic
regime and exponential in the saturated state; and (3) the bulk of the magnetic
energy is at the resistive scale in the kinematic regime and remains there
after saturation, although the spectrum becomes much shallower. We propose an
analytical model of saturation based on the idea of partial
two-dimensionalization of the velocity gradients with respect to the local
direction of the magnetic folds. The model-predicted spectra are in excellent
agreement with numerical results. Comparisons with large-Re, moderate-Pm runs
are carried out to confirm the relevance of these results. New features at
large Re are elongation of the folds in the nonlinear regime from the viscous
scale to the box scale and the presence of an intermediate nonlinear stage of
slower-than-exponential magnetic-energy growth accompanied by an increase of
the resistive scale and partial suppression of the kinetic-energy spectrum in
the inertial range. Numerical results for the saturated state do not support
scale-by-scale equipartition between magnetic and kinetic energies, with a
definite excess of magnetic energy at small scales. A physical picture of the
saturated state is proposed.",0312046v3
1995-08-14,BPS Saturated and Non-Extreme States in Abelian Kaluza-Klein Theory and Effective N=4 Supersymmetric String Vacua,"We summarize results for all four-dimensional Bogomol'nyi-Sommerfield-Prasat
(BPS) saturated and non-extreme solutions of the ($4+n$)-dimensional Abelian
Kaluza-Klein theory. Within effective N=4 supersymmetric string vacua,
parameterized in terms of fields of the heterotic string on a six-torus, we
then present a class of BPS saturated states and the corresponding non-extreme
solutions, specified by $O(6,22,Z)$ and $SL(2,Z)$ orbits of general dyonic
charge configurations with zero axion. The BPS saturated states with
non-negative $O(6,22,Z)$ norms for electric and magnetic charge vectors, along
with the corresponding set of non-extreme solutions, are regular with non-zero
masses. BPS saturated states with the negative charge norms are singular,
unaccompanied by non-extreme solutions and become massless at particular points
of the moduli space. The role that such massless states may play in the
enhancement of non-Abelian gauge symmetry as well as local supersymmetry is
addressed.",9508058v1
2019-11-09,Tangency property and prior-saturation points in minimal time problems in the plane,"In this paper, we consider minimal time problems governed by
control-affine-systems in the plane, and we focus on the synthesis problem in
presence of a singular locus that involves a saturation point for the singular
control. After giving sufficient conditions on the data ensuring occurence of a
prior-saturation point and a switching curve, we show that the bridge (i.e.,
the optimal bang arc issued from the singular locus at this point) is tangent
to the switching curve at the prior-saturation point. This property is proved
using the Pontryagin Maximum Principle that also provides a set of non-linear
equations that can be used to compute the prior-saturation point. These issues
are illustrated on a fed-batch model in bioprocesses and on a Magnetic
Resonance Imaging (MRI) model for which minimal time syntheses for the
point-to-point problem are discussed.",1911.03652v2
2023-08-17,Comparison of saturation rules used for gyrokinetic quasilinear transport modeling,"Theory-based transport modeling has been widely successful and is built on
the foundations of quasilinear theory. Specifically, the quasilinear expression
of the flux can be used in combination with a saturation rule for the toroidal
mode amplitude. Most transport models follow this approach. Saturation rules
are heuristic and difficult to rigorously derive. We compare three common
saturation rules using a fairly accurate quasilinear expression for the fluxes
computed using local linear gyrokinetic simulation. We take plasma parameters
from experimental H-mode profiles and magnetic equilibrium and include
electrons, Deuterium, and Carbon species. We find that the various saturation
rules give qualitatively similar behavior. This may help explain why the
different theory-based transport models can all predict core tokamak profiles
reasonably well. Comparisons with nonlinear local and global gyrokinetic
simulations are also discussed.",2308.09181v1
2001-10-05,Saturation and Thermalization of the Magnetorotational Instability: Recurrent Channel Flows and Reconnections,"The nonlinear evolution and the saturation mechanism of the magnetorotational
instability (MRI) are investigated using three-dimensional resistive MHD
simulations. A local shearing box is used for our numerical analysis and the
simulations begin with a purely vertical magnetic field. We find that the
magnetic stress in the nonlinear stage of the MRI is strongly fluctuating. The
time evolution shows the quasi-periodic recurrence of spike-shape variations
typically for a few orbits which correspond to the rapid amplification of the
magnetic field by the nonlinear growth of a two-channel solution followed by
the decay through magnetic reconnections. The increase rate of the total energy
in the shearing box system is analytically related to the volume-averaged
torque in the system. We find that at the saturated state this energy gain of
the system is balanced with the increase of the thermal energy mostly due to
the joule heating. The spike-shape time evolution is a general feature of the
nonlinear evolution of the MRI in the disks threaded by vertical fields and can
be seen if the effective magnetic Reynolds number is larger than about unity.",0110125v1
2007-09-28,Electron coherence at low temperatures: The role of magnetic impurities,"We review recent experimental progress on the saturation problem in metallic
quantum wires. In particular, we address the influence of magnetic impurities
on the electron phase coherence time. We also present new measurements of the
phase coherence time in ultra-clean gold and silver wires and analyse the
saturation of \tauphi in these samples, cognizant of the role of magnetic
scattering. For the cleanest samples, Kondo temperatures below 1 mK and
extremely-small magnetic-impurity concentration levels of less than 0.08 ppm
have to be assumed to attribute the observed saturation to the presence of
magnetic impurities.",0709.4663v1
2010-04-24,Domain structure of bulk ferromagnetic crystals in applied fields near saturation,"We investigate the ground state of a uniaxial ferromagnetic plate with
perpendicular easy axis and subject to an applied magnetic field normal to the
plate. Our interest is the asymptotic behavior of the energy in macroscopically
large samples near the saturation field. We establish the scaling of the
critical value of the applied field strength below saturation at which the
ground state changes from the uniform to a branched domain magnetization
pattern and the leading order scaling behavior of the minimal energy.
Furthermore, we derive a reduced sharp-interface energy giving the precise
asymptotic behavior of the minimal energy in macroscopically large plates under
a physically reasonable assumption of small deviations of the magnetization
from the easy axis away from domain walls. On the basis of the reduced energy,
and by a formal asymptotic analysis near the transition, we derive the precise
asymptotic values of the critical field strength at which non-trivial
minimizers (either local or global) emerge. The non-trivial minimal energy
scaling is achieved by magnetization patterns consisting of long slender
needle-like domains of magnetization opposing the applied field",1004.4292v1
2011-03-05,Transmission of Excitations in a Spin-1 Bose-Einstein Condensate through a Barrier,"We investigate tunneling of excitations across a potential barrier separating
two spin-1 Bose-Einstein condensates. Using the mean-field theory at the
absolute zero temperature, we determine transmission coefficients of
excitations in the saturated magnetization state and unsaturated magnetization
states. All excitations except the quadrupolar spin mode in the saturated
magnetization state show the anomalous tunneling phenomenon characterized as
perfect tunneling in the low momentum limit through a potential barrier. The
quadrupolar spin mode in the saturated magnetization state, whose spectrum is
massive, shows total reflection. We discuss properties common between
excitations showing the anomalous tunneling phenomenon. Excitations showing
perfect tunneling have gapless spectrum in the absence of the magnetic field,
and their wave functions in the low energy limit are the same as the condensate
wave function.",1103.1004v2
2014-08-20,Anomalous Behavior of the Magnetization Process of the S = 1/2 Kagome-Lattice Heisenberg Antiferromagnet at One-Third Height of the Saturation,"The magnetization process of the S=1/2 Heisenberg antiferromagnet on the
kagome lattice is studied by the numerical-diagonalization method. We
successfully obtain a new result of the magnetization process of a 42-site
cluster in the entire range. Our analysis clarifies that the critical behavior
around one-third of the height of the saturation is different from the typical
behavior of the well-known magnetization plateau in two-dimensional systems. We
also examine the effect of the $\sqrt{3}\times\sqrt{3}$-type distortion added
to the kagome lattice. We find at one-third of the height of the saturation in
the magnetization process that the undistorted kagome point is just the
boundary between two phases that show their own properties that are different
from each other. Our results suggest a relationship between the anomalous
critical behavior at the undistorted point and the fact that the undistorted
point is the boundary.",1408.4538v1
2019-01-04,How to accurately determine a saturation magnetization of the sample in a ferromagnetic resonance experiment?,"The phenomenon of ferromagnetic resonance (FMR) is still being exploited for
determining the magnetocrystalline anisotropy constants of magnetic materials.
We show that one can also determine accurately the saturation magnetization of
the sample using results of FMR experiments after taking into account the
relationship between resonance frequency and curvature of the spatial
distribution of free energy at resonance. Specifically, three examples are
given of calculating saturation magnetization from FMR data: we use historical
Bickford's measurements from 1950 for bulk magnetite, Liu's measurements from
2007 for a 500 mn thin film of a weak ferromagnet (Ga, Mn)As, and Wang's
measurements from 2014 for an ultrathin film of YIG. In all three cases, the
magnetization values we have determined are consistent with the results of
measurements.",1901.01207v1
2021-08-19,Saturation of large-scale dynamo in anisotropically forced turbulence,"Turbulent dynamo theories have faced difficulties in obtaining evolution of
large-scale magnetic fields on short dynamical time-scales due to the
constraint imposed by magnetic helicity balance. This has critical implications
for understanding the large-scale magnetic field evolution in astrophysical
systems like the Sun, stars and galaxies. Direct numerical simulations (DNS) in
the past with isotropically forced helical turbulence have shown that
large-scale dynamo saturation time-scales are dependent on the magnetic
Reynolds number (Rm). In this work, we have carried out periodic box DNS of
helically forced turbulence leading to a large-scale dynamo with two kinds of
forcing function, an isotropic one based on that used in PENCIL-CODE and an
anisotropic one based on Galloway-Proctor flows. We show that when the
turbulence is forced anisotropically, the nonlinear (saturation) behaviour of
the large-scale dynamo is only weakly dependent on Rm. In fact the magnetic
helicity evolution on small and large scales in the anisotropic case is
distinctly different from that in the isotropic case. This result possibly
holds promise for the alleviation of important issues like catastrophic
quenching.",2108.08740v2
2007-07-24,Magnetic braking in young late-type stars: the effect of polar spots,"The concentration of magnetic flux near the poles of rapidly rotating cool
stars has been recently proposed as an alternative mechanism to dynamo
saturation in order to explain the saturation of angular momentum loss. In this
work we study the effect of magnetic surface flux distribution on the coronal
field topology and angular momentum loss rate. We investigate if magnetic flux
concentration towards the pole is a reasonable alternative to dynamo
saturation. We construct a 1D wind model and also apply a 2-D self-similar
analytical model, to evaluate how the surface field distribution affects the
angular momentum loss of the rotating star. From the 1D model we find that, in
a magnetically dominated low corona, the concentrated polar surface field
rapidly expands to regions of low magnetic pressure resulting in a coronal
field with small latitudinal variation. We also find that the angular momentum
loss rate due to a uniform field or a concentrated field with equal total
magnetic flux is very similar. From the 2D wind model we show that there are
several relevant factors to take into account when studying the angular
momentum loss from a star. In particular, we show that the inclusion of force
balance across the field in a wind model is fundamental if realistic
conclusions are to be drawn from the effect of non-uniform surface field
distribution on magnetic braking. This model predicts that a magnetic field
concentrated at high latitudes leads to larger Alfven radii and larger braking
rates than a smoother field distribution. From the results obtained, we argue
that the magnetic surface field distribution towards the pole does not directly
limit the braking efficiency of the wind.",0707.3588v1
2010-05-28,Magnetic helicity fluxes in interface and flux transport dynamos,"Dynamos in the Sun and other bodies tend to produce magnetic fields that
possess magnetic helicity of opposite sign at large and small scales,
respectively. The build-up of magnetic helicity at small scales provides an
important saturation mechanism. In order to understand the nature of the solar
dynamo we need to understand the details of the saturation mechanism in
spherical geometry. In particular, we want to understand the effects of
magnetic helicity fluxes from turbulence and meridional circulation. We
consider a model with just radial shear confined to a thin layer (tachocline)
at the bottom of the convection zone. The kinetic alpha owing to helical
turbulence is assumed to be localized in a region above the convection zone.
The dynamical quenching formalism is used to describe the build-up of mean
magnetic helicity in the model, which results in a magnetic alpha effect that
feeds back on the kinetic alpha effect. In some cases we compare with results
obtained using a simple algebraic alpha quenching formula. In agreement with
earlier findings, the magnetic alpha effect in the dynamical alpha quenching
formalism has the opposite sign compared with the kinetic alpha effect and
leads to a catastrophic decrease of the saturation field strength with
increasing magnetic Reynolds numbers. However, at high latitudes this quenching
effect can lead to secondary dynamo waves that propagate poleward due to the
opposite sign of alpha. Magnetic helicity fluxes both from turbulent mixing and
from meridional circulation alleviate catastrophic quenching.",1005.5335v1
2017-09-27,Magnetic properties of optimized cobalt nanospheres grown by Focused Electron Beam Induced Deposition (FEBID) on cantilever tips,"In this work, we present a detailed investigation of the magnetic properties
of cobalt nanospheres grown on cantilever tips by Focused Electron Beam Induced
Deposition (FEBID). The cantilevers are extremely soft and the cobalt
nanospheres are optimized for Magnetic Resonance Force Microscopy (MRFM)
experiments, which implies that the cobalt nanospheres must be as small as
possible while bearing high saturation magnetization. It is found that the
cobalt content and the corresponding saturation magnetization of the
nanospheres decrease for nanosphere diameters below 300 nm. Electron holography
measurements show the formation of a magnetic vortex state in remanence, which
nicely agrees with magnetic hysteresis loops performed by local magnetometry
showing negligible remanent magnetization. As investigated by local
magnetometry, optimal behavior for high-resolution MRFM has been found for
cobalt nanospheres with diameter of $\approx$ 200 nm, which present atomic
cobalt content of $\approx$ 83 at% and saturation magnetization of 106 A/m,
around 70% of the bulk value. These results represent the first comprehensive
investigation of the magnetic properties of cobalt nanospheres grown by FEBID
for application in MRFM.",1709.09374v1
2010-11-01,Quantitative magnetic force microscopy on permalloy dots using an iron filled carbon nanotube probe,"We have characterized a new Magnetic Force Microscopy (MFM) probe based on an
iron filled carbon nanotube (FeCNT) using MFM imaging on permalloy (Py) disks
saturated in a high magnetic field perpendicular to the disk plane. The
experimental data are accurately modeled by describing the FeCNT probe as
having a single magnetic monopole at its tip whose effective magnetic charge is
determined by the diameter of the iron wire enclosed in the carbon nanotube and
its saturation magnetization 4 \pi M_s ~ 2.2 x 10^4 G. A magnetic monopole
probe enables quantitative measurements of the magnetic field gradient close to
the sample surface. The lateral resolution is defined by the diameter of the
iron wire ~15 nm and the probe-sample separation. As a demonstration, the
magnetic field gradients close to the surface of a Py dot in domain and vortex
states were imaged.",1011.0389v1
2015-12-02,Field-driven successive phase transitions in quasi-two-dimensional frustrated antiferromagnet Ba$_2$CoTeO$_6$ and highly degenerate classical ground states,"We report the results of magnetization and specific heat measurements of
Ba$_2$CoTeO$_6$ composed of two subsystems A and B, which are magnetically
described as an $S\,{=}\,1/2$ triangular-lattice Heisenberg-like
antiferromagnet and a $J_1-J_2$ honeycomb-lattice Ising-like antiferromagnet,
respectively. These two subsystems were found to be approximately decoupled.
Ba$_2$CoTeO$_6$ undergoes magnetic phase transitions at $T_{\rm N1}\,{=}\,12.0$
K and $T_{\rm N2}\,{=}\,3.0$ K, which can be interpreted as the orderings of
subsystems B and A, respectively. Subsystem A exhibits a magnetization plateau
at one-third of the saturation magnetization for the magnetic field $H$
perpendicular to the $c$ axis owing to the quantum order-by-disorder, whereas
for $H\,{\parallel}\,c$, subsystem B shows three-step metamagnetic transitions
with magnetization plateaus at zero, one-third and one-half of the saturation
magnetization. The analysis of the magnetization process for subsystem B shows
that the classical ground states at these plateaus are infinitely degenerate
within the Ising model.",1512.00693v1
2017-02-15,Hot magnetized nuclear matter: Thermodynamic and Saturation Properties,"We have used a realistic nuclear potential, AV18, and a many body technique,
the lowest order constraint variational (LOCV) approach, to calculate the
properties of hot magnetized nuclear matter. By investigating the free energy,
spin polarization parameter, and symmetry energy, we have studied the
temperature and magnetic field dependence of the saturation properties of
magnetized nuclear matter. In addition, we have calculated the equation of
state of magnetized nuclear matter at different temperatures and magnetic
fields. It was found that the flashing temperature of nuclear matter decreases
by increasing the magnetic field. In addition, we have studied the effect of
the magnetic field on liquid gas phase transition of nuclear matter. The liquid
gas coexistence curves, the order parameter of the liquid gas phase transition,
and the properties of critical point at different magnetic fields have been
calculated.",1702.04765v1
2019-09-28,Size-Dependent Structural and Magnetic Properties of Disordered Co2FeAl Heusler Alloy Nanoparticles,"Co2FeAl (CFA) nanoparticles (NPs) of different sizes were synthesized by
chemical route. The effect of the size of NPs upon the structure and
magnetization compared to its bulk counterpart was investigated. The structure
and composition were determined from X-ray diffraction (XRD) and electron
microscopy. XRD analysis shows that the samples are having single (A2-type)
disordered phase. Magnetization measurements suggest that the samples are soft
ferromagnetic in nature with very low coercivity. Enhanced magnetic properties
like saturation magnetization, coercive force, retentivity, and
Curie-temperature are observed with a decrease in particle size. The effect of
particle size on hysteresis losses is also discussed. The smallest particles of
size 16 nm exhibited the highest saturation magnetization and transition
temperature of 180.73 emu/g and 1261 K, respectively. The origin of enhancement
in the magnetization of Co2FeAl nano-alloy is attributed to the strong Co-Co
exchange interaction due to disorder present in the systems.",1909.13088v1
2010-02-08,The nonlinear saturation of the non-resonant kinetically driven streaming instability,"A non-resonant instability for the amplification of the interstellar magnetic
field in young Supernova Remnant (SNR) shocks was predicted by Bell (2004), and
is thought to be relevant for the acceleration of cosmic ray (CR) particles.
For this instability, the CRs streaming ahead of SNR shock fronts drive
electromagnetic waves with wavelengths much shorter than the typical CR Larmor
radius, by inducing a current parallel to the background magnetic field. We
explore the nonlinear regime of the non-resonant mode using Particle-in-Cell
(PIC) hybrid simulations, with kinetic ions and fluid electrons, and analyze
the saturation mechanism for realistic CR and background plasma parameters. In
the linear regime, the observed growth rates and wavelengths match the
theoretical predictions; the nonlinear stage of the instability shows a strong
reaction of both the background plasma and the CR particles, with the
saturation level of the magnetic field varying with the CR parameters. The
simulations with CR-to-background density ratios of n_CR/n_b=10^(-5) reveal the
highest magnetic field saturation levels, with energy also being transferred to
the background plasma and to the perpendicular velocity components of the CR
particles. The results show that amplification factors >10 for the magnetic
field can be achieved, and suggest that this instability is important for the
generation of magnetic field turbulence, and for the acceleration of CR
particles.",1002.1701v1
2018-10-22,Nonlinear Evolution of the Resonant Drag Instability in Magnetized Gas,"We investigate, for the first time, the nonlinear evolution of the magnetized
""resonant drag instabilities"" (RDIs). We explore magnetohydrodynamic (MHD)
simulations of gas mixed with (uniform) dust grains subject to Lorentz and drag
forces, using the GIZMO code. The magnetized RDIs exhibit fundamentally
different behaviour than the purely acoustic RDIs. The dust organizes into
coherent structures and the system exhibits strong dust-gas separation. In the
linear and early nonlinear regime, the growth rates agree with linear theory
and the dust self-organizes into two-dimensional planes or ""sheets."" Eventually
the gas develops fully nonlinear, saturated Alfv\'enic and compressible
fast-mode turbulence, which fills the under-dense regions with a small amount
of dust, and drives a dynamo which saturates at equipartition of kinetic and
magnetic energy. The dust density fluctuations exhibit significant
non-Gaussianity, and the power spectrum is strongly weighted towards the
largest (box-scale) modes. The saturation level can be understood via
quasi-linear theory, as the forcing and energy input via the instabilities
becomes comparable to saturated tension forces and dissipation in turbulence.
The magnetized simulation presented here is just one case; it is likely that
the magnetic RDIs can take many forms in different parts of parameter space.",1810.09491v1
2022-09-16,Unveiling new quantum phases in the Shastry-Sutherland compound SrCu2(BO3)2up to the saturation magnetic field,"Under magnetic fields, quantum magnets often undergo exotic phase transitions
with various kinds of order. The discovery of a sequence of fractional
magnetization plateaus in the Shastry-Sutherland compound SrCu2(BO3)2 has
played a central role in the high-field research on quantum materials, but so
far this system could only be probed up to half the saturation value of the
magnetization. Here, we report the first experimental and theoretical
investigation of this compound up to the saturation magnetic field of 140 T and
beyond. Using ultrasound and magnetostriction techniques combined with
extensive tensor-network calculations (iPEPS), several spin-supersolid phases
are revealed between the 1/2 plateau and saturation (1/1 plateau). Quite
remarkably, the sound velocity of the 1/2 plateau exhibits a drastic decrease
of -50%, related to the tetragonal-to-orthorhombic instability of the
checkerboard-type magnon crystal. The unveiled nature of this paradigmatic
quantum system is a new milestone for exploring exotic quantum states of matter
emerging in extreme conditions.",2209.07652v2
2011-08-19,Magnetic field amplification and X-ray emission in galaxy minor mergers,"We investigate the magnetic field evolution in a series of galaxy minor
mergers using the N-body/smoothed particle hydrodynamics (SPH) code
\textsc{Gadget}. The simulations include the effects of radiative cooling, star
formation and supernova feedback. Magnetohydrodynamics (MHD) is implemented
using the SPH method. We present 32 simulations of binary mergers of disc
galaxies with mass ratios of 2:1 up to 100:1, whereby we have additionally
varied the initial magnetic field strengths, disc orientations and resolutions.
We investigate the amplification of a given initial magnetic field within the
galaxies and an ambient intergalactic medium (IGM) during the interaction. We
find that the magnetic field strengths of merger remnants with mass ratios up
to 10:1 saturate at a common value of several $\mu$G. For higher mass ratios,
the field strength saturates at lower values. The saturation values correspond
to the equipartition value of magnetic and turbulent energy density. The
initial magnetization, disc orientation and numerical resolution show only
minor effects on the saturation value of the magnetic field. We demonstrate
that a higher impact energy of the progenitor galaxies leads to a more
efficient magnetic field amplification. The magnetic and turbulent energy
densities are higher for larger companion galaxies, consistent with the higher
impact energy supplied to the system. We present a detailed study of the
evolution of the temperature and the bolometric X-ray luminosity within the
merging systems. Thereby we find that magnetic fields cause a more efficient
increase of the IGM temperature and the corresponding IGM X-ray luminosity
after the first encounter. However, the presence of magnetic fields does not
enhance the total X-ray luminosity. Generally, the final value of the X-ray
luminosity is even clearly lower for higher initial magnetic fields.",1108.4006v1
2004-11-17,Magnetic helicity and cosmological magnetic field,"The magnetic helicity has paramount significance in nonlinear saturation of
galactic dynamo. We argue that the magnetic helicity conservation is violated
at the lepton stage in the evolution of early Universe. As a result, a
cosmological magnetic field which can be a seed for the galactic dynamo obtains
from the beginning a substantial magnetic helicity which has to be taken into
account in the magnetic helicity balance at the later stage of galactic dynamo.",0411496v3
1999-07-19,Doping Induced Magnetization Plateaus,"The low temperature magnetization process of antiferromagnetic spin-S chains
doped with mobile spin-(S-1/2) carriers is studied in an exactly solvable
model. For sufficiently high magnetic fields the system is in a metallic phase
with a finite gap for magnetic excitations. In this phase which exists for a
large range of carrier concentrations x the zero temperature magnetization is
determined by x alone. This leads to plateaus in the magnetization curve at a
tunable fraction of the saturation magnetization. The critical behaviour at the
edges of these plateaus is studied in detail.",9907258v1
2001-02-02,Singlet Ground State and Magnetization Plateaus in Ba$_3$Mn$_2$O$_8$,"Magnetic susceptibility and the magnetization process have been measured in
\green polycrystal. In this compound, the magnetic manganese ion exists as
Mn$^{5+}$ in a tetrahedral environment, and thus the magnetic interaction can
be described by an S=1 Heisenberg model. The ground state was found to be a
spin singlet with an excitation gap $\Delta/k_{\rm B}=11.2$ K. Magnetization
plateaus were observed at zero and at half of the saturation magnetization.
These results indicate that the present system can be represented by a coupled
antiferromagnetic dimer model.",0102026v2
2000-05-01,Magnetic Fractal Dimensionality of the Dielectric Breakdown Under Strong Magnetic Fields,"The formation of breakdown pattern on an insulating surface under the
influence of a transverse magnetic field is theoretically investigated. We have
generalized the Dielectric Breakdown Model (DBM) for the case of external
magnetic field. Concept of the Magnetic Fractal Dimensionality (MFD) is
introduced and its universality is demonstrated. It is shown that MFD saturates
with magnetic fields. The magnetic field dependence of the streamer curvature
is obtained. It is conjectured that nonlinear current interaction is
responsible for the experimentally observed 'spider-legs' like streamer
patterns.",0005002v1
2011-03-02,Magnetic structure of azurite above the 1/3 magnetization plateau,"The transition from the 1/3 magnetization plateau towards the saturation
magnetization in azurite has been studied by low-temperature,
high-magnetic-field, high-frequency proton nuclear magnetic resonance (NMR).
The observed symmetrical splitting of the NMR spectra is incompatible with the
longitudinal incommensurate order appearing when the longitudinal correlation
function becomes dominant over the transverse one, which is the expected
framework for the existence of the 2/3 magnetization plateau. The spectra are
rather interpreted in terms of a more standard transverse antiferromagnetic
(canted) order.",1103.0376v1
2018-12-26,Probing the Relationship between Anisotropic Magnetoresistance and Magnetization of ferromagnetic films,"The anisotropic magnetoresistance (AMR) in thin permalloy strips was
calculated at each steps during magnetization by the finite element method. The
magnetization at equilibrium under different external fields was obtained by
micromagnetic simulations, while the resistance with different magnetization
was obtained by solving the Poisson equations iteratively until
self-consistence. We find that the relation between magnetization and AMR
deviates from the Stoner-Wohlfarth prediction when the magnetization is reduced
from saturation. The reason is that the demagnetization is not necessarily from
coherent rotation of the magnetic moment. We conclude that it is necessary to
use numeric simulations to optimize the responses of AMR sensors.",1812.10294v1
2017-04-19,A small-scale dynamo in feedback-dominated galaxies - II. The saturation phase and the final magnetic configuration,"Magnetic fields in galaxies are believed to be the result of dynamo
amplification of initially weak seed fields, reaching equipartition strength
inside the interstellar medium. The small-scale dynamo appears to be a viable
mechanism to explain observations of strong magnetic fields in present-day and
high-redshift galaxies, considering the extreme weakness of seed fields
predicted by battery mechanisms or primordial fields. Performing
high-resolution adaptive mesh magneto-hydrodynamic simulations of a small mass,
isolated cooling halo with an initial magnetic seed field strength well below
equipartition, we follow the small-scale dynamo amplification from
supernova-induced turbulence up to saturation of the field. We find that
saturation occurs when the average magnetic pressure reaches only 3 % to 5 % of
the turbulent pressure. The magnetic energy growth transitions from exponential
to linear, and finally comes to halt. The saturation level increases slightly
with grid resolution. These results are in good agreement with theoretical
predictions for magnetic Prandtl numbers of order $\mathrm{Pr_M} \sim 1$ and
turbulent Mach numbers of order $\mathrm{M} \sim 10$. When we suppress
supernova feedback after our simulation has reached saturation, we find that
turbulence decays and that the gas falls back onto a thin disk with the
magnetic field in local equipartition.
  We propose a scenario in which galactic magnetic fields are amplified from
weak seed fields in the early stages of the Universe to sub-equipartition
fields, owing to the turbulent environment of feedback-dominated galaxies at
high redshift, and are evolved further in a later stage up to equipartition, as
galaxies transformed into more quiescent, large spiral disks.",1704.05845v1
2013-01-08,Magnetic energy cascade in spherical geometry: I. The stellar convective dynamo case,"We present a method to characterize the spectral transfers of magnetic energy
between scales in simulations of stellar convective dynamos. The full triadic
transfer functions are computed thanks to analytical coupling relations of
spherical harmonics based on the Clebsch-Gordan coefficients. The method is
applied to mean field $\alpha\Omega$ dynamo models as benchmark tests. From the
physical standpoint, the decomposition of the dynamo field into primary and
secondary dynamo families proves very instructive in the $\alpha\Omega$ case.
The same method is then applied to a fully turbulent dynamo in a solar
convection zone, modeled with the 3D MHD ASH code. The initial growth of the
magnetic energy spectrum is shown to be non-local. It mainly reproduces the
kinetic energy spectrum of convection at intermediate scales. During the
saturation phase, two kinds of direct magnetic energy cascades are observed in
regions encompassing the smallest scales involved in the simulation. The first
cascade is obtained through the shearing of magnetic field by the large scale
differential rotation that effectively cascades magnetic energy. The second is
a generalized cascade that involves a range of local magnetic and velocity
scales. Non-local transfers appear to be significant, such that the net
transfers cannot be reduced to the dynamics of a small set of modes. The
saturation of the large scale axisymmetric dipole and quadrupole are detailed.
In particular, the dipole is saturated by a non-local interaction involving the
most energetic scale of the magnetic energy spectrum, which points out the
importance of the magnetic Prandtl number for large-scale dynamos.",1301.1606v1
2018-01-25,Strong dipole magnetic fields in fast rotating fully convective stars,"M dwarfs are the most numerous stars in our Galaxy with masses between
approximately 0.5 and 0.1 solar mass. Many of them show surface activity
qualitatively similar to our Sun and generate flares, high X-ray fluxes, and
large-scale magnetic fields. Such activity is driven by a dynamo powered by the
convective motions in their interiors. Understanding properties of stellar
magnetic fields in these stars finds a broad application in astrophysics,
including, e.g., theory of stellar dynamos and environment conditions around
planets that may be orbiting these stars. Most stars with convective envelopes
follow a rotation-activity relationship where various activity indicators
saturate in stars with rotation periods shorter than a few days. The activity
gradually declines with rotation rate in stars rotating more slowly. It is
thought that due to a tight empirical correlation between X-ray and magnetic
flux, the stellar magnetic fields will also saturate, to values around ~4kG.
Here we report the detection of magnetic fields above the presumed saturation
limit in four fully convective M-dwarfs. By combining results from
spectroscopic and polarimetric studies we explain our findings in terms of
bistable dynamo models: stars with the strongest magnetic fields are those in a
dipole dynamo state, while stars in a multipole state cannot generate fields
stronger than about four kilogauss. Our study provides observational evidence
that dynamo in fully convective M dwarfs generates magnetic fields that can
differ not only in the geometry of their large scale component, but also in the
total magnetic energy.",1801.08571v1
2004-09-08,On the Saturation of Astrophysical Dynamos: Numerical Experiments with the No-cosines flow,"In the context of astrophysical dynamos we illustrate that the no-cosines
flow, with zero mean helicity, can drive fast dynamo action and study the
dynamo's mode of operation during both the linear and non-linear saturation
regime: It turns out that in addition to a high growth rate in the linear
regime, the dynamo saturates at a level significantly higher than normal
turbulent dynamos, namely at exact equipartition when the magnetic Prandtl
number is on the order of unity. Visualization of the magnetic and velocity
fields at saturation will help us to understand some of the aspects of the
non-linear dynamo problem.",0409193v1
2007-02-28,On the nonlinear saturation of the magnetorotational instability near threshold in a thin-gap Taylor-Couette setup,"We study the saturation near threshold of the axisymmetric magnetorotational
instability (MRI) of a viscous, resistive, incompressible fluid in a thin-gap
Taylor-Couette configuration. A vertical magnetic field, Keplerian shear and
no-slip, conducting radial boundary conditions are adopted. The weakly
non-linear theory leads to a real Ginzburg-Landau equation for the disturbance
amplitude, like in our previous idealized analysis. For small magnetic Prandtl
number (P \ll 1), the saturation amplitude scales as P^{2/3} while the
magnitude of angular momentum transport scales as P^{4/3}. The difference with
the previous scalings (~P^{1/2} and P respectively) is attributed to the
emergence of radial boundary layers. Away from those, steady-state non-linear
saturation is achieved through a modest reduction in the destabilizing shear.
These results will be useful to understand MRI laboratory experiments and
associated numerical simulations.",0702747v2
2006-10-28,Exact one- and two-particle excitation spectra of acute-angle helimagnets above their saturation magnetic field,"The two-magnon problem for the frustrated XXZ spin-1/2 Heisenberg Hamiltonian
and external magnetic fields exceeding the saturation field Bs is considered.
We show that the problem can be exactly mapped onto an effective tight-binding
impurity problem. It allows to obtain explicit exact expressions for the
two-magnon Green's functions for arbitrary dimension and number of
interactions. We apply this theory to a quasi-one dimensional helimagnet with
ferromagnetic nearest neighbor J1 < 0 and antiferromagnetic next-nearest
neighbor J2 > 0 interactions. An outstanding feature of the excitation spectrum
is the existence of two-magnon bound states. This leads to deviations of the
saturation field Bs from its classical value Bs(classical) which coincides with
the one-magnon instability. For the refined frustration ratio |J2/J1|> 0.374661
the minimum of the two-magnon spectrum occurs at the boundary of the Brillouin
zone. Based on the two-magnon approach, we propose general analytic expressions
for the saturation field Bs, confirming known previous results for
one-dimensional isotropic systems, but explore also the role of interchain and
long-ranged intrachain interactions as well as of the exchange anisotropy.",0610801v1
2022-03-23,A Kinetic Study of the Saturation of the Bell Instability,"The nonresonant cosmic ray instability, predicted by Bell (2004), is thought
to play an important role in the acceleration and confinement of cosmic rays
(CR) close to supernova remnants. Despite its importance, the exact mechanism
responsible for the saturation of the instability has not been determined, and
there is no first-principle prediction for the amplitude of the saturated
magnetic field. Using a survey of self-consistent hybrid simulations (with
kinetic ions and fluid electrons), we study the non-linear evolution of the
Bell instability as a function of the parameters of the CR population. We find
that saturation is achieved when the magnetic pressure in the amplified field
is comparable to the initial CR momentum flux.",2203.12568v1
2022-08-31,Modified Froelich's Equation for Modelling of a Three Phase Self-Excited Synchronous Generator,"With advancement in design and analysis of electro-mechanical and
electromagnetic devices, the modelling of magnetic saturation of a synchronous
generator has emerged to be a subject of interest in number of publications.
Most of the existing electrical machine modelling methods does ignore the
saturation effect for simplicity. On the other hand, who incorporate saturation
effect, are dealing with complex computation of coefficients which involves
tedious curve fitting techniques like non-linear regression, least-squares.
This paper presents the novel method of modelling of the self-excited
synchronous generator along with magnetizing characteristics with ease and good
accuracy which is inspired from Froelichs equation. The proposed mathematical
model is implemented in simulation environment and validated the results with a
practical three phase self-excited synchronous generator in which saturation
plays a vital role.",2208.14775v1
2004-10-22,Magnetostriction in an array of spin chains under magnetic field,"We consider an array of XX spin-1/2 chains coupled to acoustic phonons and
placed in a magnetic field. Treating the phonons in the mean field
approximation, we show that this system presents a first order transition as a
function of the magnetic field between a partially magnetized distorted state
and the fully polarized undistorted state at low temperature. This behavior
results from the magnetostriction of the coupled chain system. A dip in the
elastic constant of the material near the saturation field along with an
anomaly in the magnetic susceptibility is predicted. We also predict the
contraction of the material as the magnetic field is reduced (positive
magnetostriction) and the reciprocal effect i.e. a decrease of magnetization
under applied pressure. At higher temperature, the first order transition is
replaced by a crossover. However, the anomalies in the susceptibilities in the
system near the saturation field are still present. We discuss the relevance of
our analysis in relation to recent experiments on spin-1/2 chain and ladder
materials in strong magnetic fields.",0410571v2
2021-11-09,Oxygen Defect Engineered Magnetism of La2NiMnO6 Thin Films,"The double perovskite La2NiMnO6 (LNMO) exhibits complex magnetism due to the
competition of magnetic interactions that are strongly affected by structural
and magnetic inhomogeneities. In this work, we study the effect of oxygen
annealing on the structure and magnetism of epitaxial thin films grown by
pulsed laser deposition. The key observations are that a longer annealing time
leads to a reduction of saturation magnetization and an enhancement in the
ferromagnetic transition temperature. We explain these results based upon
epitaxial strain and oxygen defect engineering. The oxygen enrichment by
annealing caused a decrease in the volume of the perovskite lattice. This
increased the epitaxial strain of the films that are in-plane locked to the
SrTiO3 substrate. The enhanced strain caused a reduction in the saturation
magnetization due to randomly distributed anti-site defects. The reduced oxygen
defects concentration in the films due to the annealing in oxygen improved the
ferromagnetic long-range interaction and caused an increase in the magnetic
transition temperature.",2111.05037v1
2023-07-03,Magnetic lump motion in saturated ferromagnetic films,"In this paper, we study in detail the nonlinear propagation of magnetic
soliton in a ferromagnetic film. The sample is magnetized to saturation by an
external field perpendicular to film plane. A new generalized (2+1)-dimensional
short-wave asymptotic model is derived. The bilinear-like forms of this
equation are constructed, and exact magnetic line soliton solutions are
exhibited. It is observed that a series of stable lumps can be generated by an
unstable magnetic soliton under Gaussian disturbance. Such magnetic lumps are
highly stable and can maintain their shapes and velocities during evolution or
collision. The interaction between lump and magnetic soliton, as well as
interaction between two lumps, are numerically investigated. We further discuss
the nonlinear motion of lumps in ferrites with Gilbert-damping and
inhomogeneous exchange effects. The results show that the Gilbert-damping
effects make the amplitude and velocity of the magnetic lump decay
exponentially during propagation. And the shock waves are generated from a lump
when quenching the strength of inhomogeneous exchange.",2307.00903v1
2023-07-27,Generation of near-equipartition magnetic fields in turbulent collisionless plasmas,"The mechanisms that generate ""seed"" magnetic fields in our Universe and that
amplify them throughout cosmic time remain poorly understood. By means of
fully-kinetic particle-in-cell simulations of turbulent, initially unmagnetized
plasmas, we study the genesis of magnetic fields via the Weibel instability and
follow their dynamo growth up to near-equipartition levels. In the kinematic
stage of the dynamo, we find that the rms magnetic field strength grows
exponentially with rate $\gamma_B \simeq 0.4\,u_{\rm rms}/L$, where $L/2 \pi$
is the driving scale and $u_{\rm rms}$ is the rms turbulent velocity. In the
saturated stage, the magnetic field energy reaches about half of the turbulent
kinetic energy. Here, magnetic field growth is balanced by dissipation via
reconnection, as revealed by the appearance of plasmoid chains. At saturation,
the integral-scale wavenumber of the magnetic spectrum approaches $k_{\rm
int}\simeq 12\pi/L$. Our results show that turbulence -- induced by, e.g., the
gravitational build-up of galaxies and galaxy clusters -- can magnetize
collisionless plasmas with large-scale near-equipartition fields.",2307.15112v1
2006-10-08,Relaxation oscillations of Zeeman and dipole magnetizations of a paramagnet under conditions of deep low-frequency modulation,"The relaxation oscillations of Zeeman and dipole magnetizaions in spin system
of a solid paramagnet are theoretically analyzed under conditions of
intermediate saturation of magnetic resonance and strong low-frequency
modulation of the external magnetic field. Peculiarities of the relaxation
oscillations in the synchronous detection regime are considered.",0610211v1
2021-02-22,Robust skyrmion mediated reversal of ferromagnetic nanodots of 20 nm lateral dimension with high Ms and moderate DMI,"Implementation of skyrmion based energy efficient and high-density data
storage devices requires aggressive scaling of skyrmion size. Ferrimagnetic
materials are considered to be a suitable platform for this purpose due to
their low saturation magnetization (i.e. smaller stray field). However, we show
by performing rigorous micromagnetic simulation that such scaling of skyrmion
size by lowering saturation magnetization while applicable in infinite films or
where the skyrmion size is very small compared to the film's lateral dimension,
does not hold in confined geometries. We also found in confined geometries,
where skyrmion occupies the whole volume of a nanodot, high saturation
magnetization helps form stable skyrmions. Specifically, such skyrmions can be
formed in 20 nm lateral dimension nanodots with high saturation magnetization
(1.6-1.71 MA/m) and moderate DMI (3 mJ/m2). This result could stimulate
experiments on implementation of highly dense skyrmion devices. In particular,
we show that Voltage Controlled Magnetic Anisotropy (VCMA) based switching
mediated by an intermediate skyrmion state can be achieved in the soft layer of
a ferromagnetic p-MTJ of lateral dimensions 20 nm with sub 1fJ/bit energy in
the presence of room temperature thermal noise with reasonable DMI ~3 mJ/m2.",2102.10721v1
2006-08-01,Understanding the saturation of proton-driven Weibel instabilities and implications for astrophysics,"The linear growth rate and saturation level of magnetic fields for Weibel
instabilities driven by ion temperature anisotropy, defined as
$\alpha=(T_\perp/T_\parallel)-1$ where $T_\perp$ and $T_\parallel$ are ion
temperatures perpendicular and parallel to the wave vector, are derived in the
small $\alpha$-limit. It is shown that the ratio of the saturated magnetic
energy to the initial ion energy scales as the fourth power of the electron to
ion mass ratio, $m/M$, for an initially unmagnetized plasma with $\alpha\leq
M/m$. Particle-in-cell simulations confirm the mass scaling and also show that
the electron energy gain is of the same order of magnitude as the magnetic
field energy. This implies that the Weibel instabilities cannot provide a
faster-than-Coulomb collisionless mechanism to equilibrate ion-electron plasmas
with ions initially much hotter than electrons, a key component in
low-luminosity astrophysical accretion flows. The results here also show that
the large $\alpha$-limit formulae used in the study of magnetic field
generation in collisionless shocks are only valid if $\alpha\geq M/m$.",0608041v2
2012-11-02,Giant saturation magnetization effect in epitaxial Fe16N2 thin films grown on MgO (001) substrate,"Whether {\alpha}double prime-Fe16N2 possesses a giant saturation
magnetization (Ms) has been a daunting problem among magnetic researchers for
almost 40 years, mainly due to the unshakable faith of famous Slater-Pauling
(SP) curve and poor consistency on evaluating its Ms. Here we demonstrate that,
using epitaxy and mis-fit strain imposed by an underlying substrate, the
in-plane lattice constant of Fe16N2 thin films can be fine tuned to create
favorable conditions for exceptionally large saturation magnetization. Combined
study using polarized neutron reflectometry and X-ray diffraction shows that
with increasing strain at the interface the Ms of these film can be changed
over a broad range, from ~2.1T (non-high Ms) up to ~3.1T (high Ms). We suggest
that the equilibrium in-plane lattice constant of Fe16N2 sits in the vicinity
of the spin crossover point, in which a transition between low spin to high
spin configuration of Fe sites can be realized with sensitive adjustment of
crystal structure.",1211.0555v1
2014-12-11,High-field magnetic resonance of spinons and magnons in a triangular lattice S=1/2 antiferromagnet Cs2CuCl4,"The electron spin resonance doublet indicating the width of the two spinon
continuum in a spin-1/2 triangular-lattice Heisenberg antiferromagnet Cs2CuCl4
was studied in high magnetic field. The doublet was found to collapse in a
magnetic field of a half of the saturation field. The collapse of the doublet
occurs via vanishing of the high frequency component in a qualitative agreement
with the theoretical prediction for the S=1/2 chain. The field of the collapse
is, however, much lower than expected for the S=1/2 chain. This is proposed to
be due to the destruction of frustration of interchain exchange bonds in a
magnetic field, which restores the 2D character of this spin system. In the
saturated phase the mode with the Larmor frequency and a much weaker mode
downshifted for 119~GHz are observed. The weak mode is of exchange origin, it
demonstrates a positive frequency shift at heating corresponding to the
repulsion of magnons in the saturated phase.",1412.3776v1
2015-08-23,A study of the physical properties of single crystalline Fe5B2P,"Single crystals of Fe5B2P were grown by self-flux growth technique.
Structural and magnetic properties are studied. The Curie temperature of Fe5B2P
is determined to be 655$pm$2K. The saturation magnetization is determined to be
1.72 MuB/Fe at 2K. The temperature variation of the anisotropy constant K1 is
determined for the first time, reaching ~0.50 MJ/m3 at 2K, and it is comparable
to that of hard ferrites. The saturation magnetization is found to be larger
than the hard ferrites. The first principle calculations of saturation
magnetization and anisotropy constant are found to be consistent with the
experimental results.",1508.05629v1
2016-05-27,A comparison between grid and particle methods on the small-scale dynamo in magnetised supersonic turbulence,"We perform a comparison between the smoothed particle magnetohydrodynamics
(SPMHD) code, Phantom, and the Eulerian grid-based code, Flash, on the
small-scale turbulent dynamo in driven, Mach 10 turbulence. We show, for the
first time, that the exponential growth and saturation of an initially weak
magnetic field via the small-scale dynamo can be successfully reproduced with
SPMHD. The two codes agree on the behaviour of the magnetic energy spectra, the
saturation level of magnetic energy, and the distribution of magnetic field
strengths during the growth and saturation phases. The main difference is that
the dynamo growth rate, and its dependence on resolution, differs between the
codes, caused by differences in the numerical dissipation and shock capturing
schemes leading to differences in the effective Prandtl number in Phantom and
Flash.",1605.08662v1
2017-10-02,Magnetic phase transitions and unusual antiferromagnetic states in the Hubbard model,"Ground state magnetic phase diagrams of the square and simple cubic lattices
are investigated for the narrow band Hubbard model within the slave-boson
approach by Kotliar and Ruckenstein. The transitions between saturated
(half-metallic) and non-saturated ferromagnetic phases as well as similar
transition in antiferromagnetic (AFM) state are considered in the
three-dimensional case. Two types of saturated antiferromagnetic state with
different concentration dependences of sublattice magnetization are found in
the two-dimensional case in the vicinity of half-filling: the state with a gap
between AFM subbands and AFM state with large electron mass. The latter state
is hidden by the phase separation in the finite-U case.",1710.00712v1
2018-05-18,Magnetic Field Saturation of the Ion Weibel Instability in Interpenetrating Relativistic Plasmas,"The time evolution and saturation of the Weibel instability at the ion
Alfv\'en current are presented by ab initio particle-in-cell simulations. We
found that the ion Weibel current in 3D could evolve into the Alfv\'en current
where the magnetic field energy is sustained at 1.5\% of the initial beam
kinetic energy. The current filaments are no longer isolated at saturation, but
rather connected to each other to form a network structure. Electrons are
continuously heated during the coalescence of the filaments, which is crucial
for obtaining sustained magnetic fields with much stronger levels than with 2D
simulations. The results highlight again the importance of the Weibel
instability in generating magnetic fields in laboratory, astrophysical, and
cosmological situations.",1805.07188v1
2019-02-21,Understanding quality control of hard metals in industry -- A quantum mechanics approach,"For many decades, the magnetic saturation of, e.g. hard metals (HM) such as
WC-Co-based cemented carbides, has been used as process and quality control in
industry to ensure consistency of product properties. In an urge of replacing
cobalt as a binder phase, a demand on understanding the magnetic response as a
function of composition on the atomic scale is growing. In this paper, a
theoretical description of the measured weight specific magnetic saturation of
hard metals as a function of the tungsten weight fraction present in the cobalt
binder phase, based on first-principle calculations, has been established for
standard WC-Co. The predicted magnetic saturation agrees well with the
experimental one. Furthermore, it is proposed that the theoretical description
can be extended to alternative and more complex binder phases which allows to
transfer the production control to those hard metals.",1902.08193v1
2020-11-23,Asymmetric spin wave dispersion due to a saturation magnetization gradient,"We demonstrate using micromagnetic simulations and a theoretical model that a
gradient in the saturation magnetization ($M_s$) of a perpendicularly
magnetized ferromagnetic film induces a non-reciprocal spin wave propagation
and, consequently an asymmetric dispersion relation. The $M_s$ gradient adds a
linear potential to the spin wave equation of motion consistent with the
presence of a force. We consider a transformation from an inertial reference
frame in which the $M_s$ is constant to an accelerated reference frame where
the resulting inertial force corresponds to the force from the $M_s$ gradient.
As in the Doppler effect, the frequency shift leads to an asymmetric dispersion
relation. Additionally, we show that under certain circumstances,
unidirectional propagation of spin waves can be achieved which is essential for
the design of magnonic circuits. Our results become more relevant in light of
recent experimental works in which a suitable thermal landscape is used to
dynamically modulate the saturation magnetization.",2011.11148v2
2023-11-25,Imaging a Semi-Analytical Jet model Generated by 3D GRMHD Simulation,"Employing 3D GRMHD simulation, we study the images of a geometrically thin
jet, whose emissions concentrate on its surface, for accretion system
surrounding a central spinning BH. By introducing a strong magnetic field, we
observe three phases of BH accretion evolution: (a) initially, both the
accretion rate and the magnetic flux on the horizon gradually increase; (b) at
an intermediate stage, the magnetic flux approximately reaches saturation, and
a jet forms via the Blandford-Znajek (BZ) mechanism; (c) ultimately, the entire
system achieves a dynamic equilibrium, and a magnetically arrested disk (MAD)
forms. We carefully study the jet images during the saturation and MAD regimes
at various frequencies and from different observational angles. We reveal the
presence of U-shaped brighter lines near the jet surface boundaries, which can
be attributed to the photons whose trajectories skim over the jet surface. The
existence of these brighter lines is a unique feature of a geometrically thin
jet. Moreover, we notice that the jet images are relatively insensitive to the
observed frequencies of interest. Additionally, we observe that the
time-averaged images for the highly oscillating MAD regime show only slight
differences from those of the saturation regime.",2311.14954v1
2009-02-05,The Saturation Limit of the Magnetorotational Instability,"Simulations of the magnetorotational instability (MRI) in a homogeneous
shearing box have shown that the asymptotic strength of the magnetic field
declines steeply with increasing resolution. Here I model the MRI driven dynamo
as a large scale dynamo driven by the vertical magnetic helicity flux. This
growth is balanced by large scale mixing driven by a secondary instability. The
saturated magnetic energy density depends almost linearly on the vertical
height of the typical eddies. The MRI can drive eddies with arbitrarily large
vertical wavenumber, so the eddy thickness is either set by diffusive effects,
by the magnetic tension of a large scale vertical field component, or by
magnetic buoyancy effects. In homogeneous, zero magnetic flux, simulations only
the first effect applies and the saturated limit of the dynamo is determined by
explicit or numerical diffusion. The exact result depends on the numerical
details, but is consistent with previous work, including the claim that the
saturated field energy scales as the gas pressure to the one quarter power
(which we interpret as an artifact of numerical dissipation). The magnetic
energy density in a homogeneous shearing box will tend to zero as the
resolution of the simulation increases, but this has no consequences for the
dynamo or for angular momentum transport in real accretion disks. The claim
that the saturated state depends on the magnetic Prandtl number may also be an
artifact of simulations in which microphysical transport coefficients set the
MRI eddy thickness. Finally, the efficiency of the MRI dynamo is a function of
the ratio of the Alfv\'en velocity to the product of the pressure scale height
and the local shear. As this approaches unity from below the dynamo reaches
maximum efficiency.",0902.0942v1
2010-03-04,Small-scale dynamo action during the formation of the first stars and galaxies. I. The ideal MHD limit,"We explore the amplification of magnetic seed fields during the formation of
the first stars and galaxies. During gravitational collapse, turbulence is
created from accretion shocks, which may act to amplify weak magnetic fields in
the protostellar cloud. Numerical simulations showed that such turbulence is
sub-sonic in the first star-forming minihalos, and highly supersonic in the
first galaxies with virial temperatures larger than 10^4 K. We investigate the
magnetic field amplification during the collapse both for Kolmogorov and
Burgers-type turbulence with a semi-analytic model that incorporates the
effects of gravitational compression and small-scale dynamo amplification. We
find that the magnetic field may be substantially amplified before the
formation of a disk. On scales of 1/10 of the Jeans length, saturation occurs
after ~10^8 yr. Although the saturation behaviour of the small-scale dynamo is
still somewhat uncertain, we expect a saturation field strength of the order
~10^{-7} n^{0.5} G in the first star-forming halos, with n the number density
in cgs units. In the first galaxies with higher turbulent velocities, the
magnetic field strength may be increased by an order of magnitude, and
saturation may occur after 10^6 to 10^7 yr. In the Kolmogorov case, the
magnetic field strength on the integral scale (i.e. the scale with most
magnetic power) is higher due to the characteristic power-law indices, but the
difference is less than a factor of 2 in the saturated phase. Our results thus
indicate that the precise scaling of the turbulent velocity with length scale
is of minor importance. They further imply that magnetic fields will be
significantly enhanced before the formation of a protostellar disk, where they
may change the fragmentation properties of the gas and the accretion rate.",1003.1135v2
2013-05-29,Multiferroicity with coexisting isotropic and anisotropic spins in Ca$_{3}$Co$_{2-x}$Mn$_{x}$O$_{6}$,"We study magnetic and multiferroic behavior in Ca$_3$Co$_{2-x}$Mn$_{x}$O$_6$
($x \sim$0.97) by high-field measurements of magnetization ($M$),
magnetostriction ($L$($H$)/$L$), electric polarization ($P$), and
magnetocaloric effect. This study also gives insight into the zero and low
magnetic field magnetic structure and magnetoelectric coupling mechanisms. We
measured $M$ and $\Delta$$L$/$L$ up to pulsed magnetic fields of 92 T, and
determined the saturation moment and field. On the controversial topic of the
spin states of Co$^{2+}$ and Mn$^{4+}$ ions, we find evidence for $S$ = 3/2
spins for both ions with no magnetic field-induced spin-state crossovers. Our
data also indicate that Mn$^{4+}$ spins are quasi-isotropic and develop
components in the $ab$-plane in applied magnetic fields of 10 T. These spins
cant until saturation at 85 T whereas the Ising Co$^{2+}$ spins saturate by 25
T. Furthermore, our results imply that mechanism for suppression of electric
polarization with magnetic fields near 10 T is flopping of the Mn$^{4+}$ spins
into the $ab$-plane, indicating that appropriate models must include the
coexistence of Ising and quasi-isotropic spins.",1305.6892v3
2017-08-05,Modification of the Magnetic Properties of Co2Y Hexaferrites by Divalent and Trivalent Metal Substitutions,"The present study is concerned with the fabrication and characterization of
Me2Y substituted hexaferrites, Ba2Me2Fe12-xTxO22 (Me = Co2+, Mg2+, and Cr2+,
and T = Fe3+, and Ga3+). The samples were prepared by the conventional ball
milling technique and sintering at 1200{\deg} C. The effect of the choices of
Me and T ions on the structural and magnetic properties of the hexaferrites
were investigated. XRD patterns, magnetic parameters, and M\""ossbauer spectra
of the Co2Y were consistent with a single phase Y-type hexaferrite. However,
the CoCr-Y sample was found to be dominated by the Y-type hexaferrite, and
M-type and BaCrO4 minority phases were observed in the XRD pattern of the
sample. The small increase in saturation magnetization from about 34 emu/g up
to 37.5 emu/g was therefore attributed to the development of the M-type phase.
On the other hand, XRD pattern of the Cr2Y sample indicated the dominance of
the M-type phase in this sample. The high coercivity (1445 Oe) of this sample
is evidence of the transformation of the material from a typically soft
magnetic material (Y-type) to a hard magnet (M-type). The Ga-substitution for
Fe in Co2Y did not affect the saturation magnetization significantly, but the
coercivity was reduced. However, the sample Ba2CoMgFe11GaO22 exhibited a
significant reduction of the saturation magnetization down to a value 26.6
emu/g, which could be due to the attenuation of the super-exchange interactions
induced by the Mg2+ substitution.",1708.01768v1
2018-05-15,Non-linear Galactic Dynamos and the Magnetic Rädler Effect,"We show that the magnetic analogue of the R\""{a}dler effect of mean-field
dynamo theory leads to a non-linear backreaction that quenches a large-scale
galactic dynamo, and can result in saturation of the large-scale magnetic field
at near-equipartition with turbulent kinetic energy density. In a rotating
fluid containing small-scale magnetic fluctuations, anisotropic terms in the
mean electromotive force are induced via the Coriolis effect and these terms
lead to a reduction of the growth rate in a predominantly $\alpha\Omega$-type
galactic dynamo (Chamandy & Singh 2017). By including the generation of
small-scale magnetic fluctuations by turbulent tangling of the large-scale
magnetic field, one obtains a negative feedback effect that quenches the dynamo
and leads to the saturation of the large-scale field. This saturation mechanism
is found to be competitive with the dynamical $\alpha$-quenching mechanism for
realistic galactic parameter values. Furthermore, in the context of the
dynamical $\alpha$-quenching model, a separate non-linear term is obtained
which has the same form as the helicity flux term of Vishniac & Cho (2001), but
which depends on the strength of small-scale magnetic fluctuations. We briefly
discuss the observational implications of the magnetic R\""{a}dler effect for
galaxies.",1805.05548v2
2009-08-13,Angular Momentum Transport in Protoplanetary and Black-Hole Accretion Disks: The Role of Parasitic Modes in the Saturation of MHD Turbulence,"The magnetorotational instability (MRI) is considered a key process for
driving efficient angular momentum transport in astrophysical disks.
Understanding its non-linear saturation constitutes a fundamental problem in
modern accretion disk theory. The large dynamical range in physical conditions
in accretion disks makes it challenging to address this problem only with
numerical simulations. We analyze the concept that (secondary) parasitic
instabilities are responsible for the saturation of the MRI. Our approach
enables us to explore dissipative regimes that are relevant to astrophysical
and laboratory conditions that lie beyond the regime accessible to current
numerical simulations. We calculate the spectrum and physical structure of
parasitic modes that feed off the fastest, exact (primary) MRI mode when its
amplitude is such that the fastest parasitic mode grows as fast as the MRI. We
argue that this ""saturation"" amplitude provides an estimate of the magnetic
field that can be generated by the MRI before the secondary instabilities
suppress its growth significantly. Recent works suggest that the saturation
amplitude of the MRI depends mainly on the magnetic Prandtl number. Our results
suggest that, as long as viscous effects do not dominate the fluid dynamics,
the saturation level of the MRI depends only on the Elsasser number
$\Lambda_\eta$. We calculate the ratio between the stress and the magnetic
energy density, $\alpha_{\rm sat}\beta_{\rm sat}$, associated with the primary
MRI mode. We find that for $\Lambda_\eta >1$ Kelvin-Helmholtz modes are
responsible for saturation and $\alpha_{\rm sat}\beta_{\rm sat} = 0.4$, while
for $\Lambda_\eta < 1$ tearing modes prevail and $\alpha_{\rm sat}\beta_{\rm
sat} \simeq 0.5 \, \Lambda_\eta$. Several features of MRI simulations in
accretion disks surrounding young stars and compact objects can be interpreted
in terms of our findings.",0908.1791v2
2021-02-24,Phases saturation control on mixing driven reactions in 3D porous media,"Transported chemical reactions in unsaturated porous media are relevant
across a range of environmental and industrial applications. Continuum scale
dispersive models are often based on equivalent parameters derived from analogy
with saturated conditions, and cannot appropriately account for processes such
as incomplete mixing. It is also unclear how the third dimension controls
mixing and reactions in unsaturated conditions. We obtain 3$D$ experimental
images of the phases distribution and of transported chemical reaction by
Magnetic Resonance Imaging (MRI) using an immiscible non-wetting liquid as a
second phase and a fast irreversible bimolecular reaction. Keeping the P\'eclet
number (Pe) constant, we study the impact of phases saturation on the dynamics
of mixing and the reaction front. By measuring the local concentration of the
reaction product, we quantify temporally resolved effective reaction rate
($R$). We describe the temporal evolution of $R$ using the lamellar theory of
mixing, which explains faster than Fickian ($t^{0.5}$) rate of product
formation by accounting for the deformation of mixing interface between the two
reacting fluids. For a given Pe, although stretching and folding of the
reactive front are enhanced as saturation decreases, enhancing the product
formation, this is larger as saturation increases, i.e., volume controlled.
After breakthrough, the extinction of the reaction takes longer as saturation
decreases because of the larger non-mixed volume behind the front. These
results are the basis for a general model to better predict reactive transport
in unsaturated porous media not achievable by the current continuum paradigm.",2102.12113v1
2004-05-04,Oscillations of the Electric-Dipole Echo in Glasses in a Magnetic Field,"Using a simple diagram technique we derive the electric-dipole echo amplitude
from two-level systems with a quadrupole nuclear moment in glasses in an
external magnetic field. We show, that due to the quadrupole moment interaction
of a tunneling particle with a gradient of an internal electric field, the echo
amplitude experiences oscillations in rather weak magnetic fields. With an
increase of the magnetic field, when the Zeeman energy becomes larger than the
quadrupole energy splitting, the average echo amplitude increases and saturates
(for high magnetic fields) at some level which is above the average level of
echo oscillations for small magnetic fields.",0405058v1
1994-07-22,Thermal Versus Vacuum Magnetization in QED,"The magnetized relativistic Fermi and Bose gases are studied at finite
temperature and density.In the case of the Fermi gas, the contribution to the
magnetization from the vacuum becomes dominant for high magnetic fields, when
the thermal contribution saturates.
  In the case of the charged Bose gas, the (paramagnetic) vacuum--magnetization
becomes dominant when the gas changes from a diamagnetic to a paramagnetic
behaviour. We furthermore find that the scalar--QED effective coupling constant
for a weak non--zero external magnetic field is a decreasing function of the
temperature.",9407356v1
2010-01-11,Nonlocal effects on magnetism in the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As,"The magnetic properties of the diluted magnetic semiconductor
Ga_{1-x}Mn_{x}As are studied within the dynamical cluster approximation. We use
the k-dot-p Hamiltonian to describe the electronic structure of GaAs with
spin-orbit coupling and strain effects. We show that nonlocal effects are
essential for explaining the experimentally observed transition temperature and
saturation magnetization. We also demonstrate that the cluster anisotropy is
very strong and induces rotational frustration and a cube-edge direction
magnetic anisotropy at low temperature. With this, we explain the
temperature-driven spin reorientation in this system.",1001.1716v1
2011-02-17,Critical magnetization behaviors of the triangular and Kagome lattice quantum antiferromagnets,"We investigate the $S=1/2$ quantum spin antiferromagnets on the triangular
and Kagome lattices in magnetic field, using the numerical exact
diagonalization. Particularly we focus on an anomalous magnetization behavior
of each system at 1/3 of the saturation magnetization. The critical exponent
analyses suggest that it is a conventional magnetization plateau on the
triangular lattice, while an unconventional phenomenon, called the
magnetization ramp, on the Kagome lattice.",1102.3486v1
2013-12-02,Critical Field of Spin Torque Oscillator with Perpendicularly Magnetized Free Layer,"The oscillation properties of a spin torque oscillator consisting of a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer
are studied based on an analysis of the energy balance between spin torque and
damping. The critical value of an external magnetic field applied normal to the
film plane is found, below which the controllable range of the oscillation
frequency by the current is suppressed. The value of the critical field depends
on the magnetic anisotropy, the saturation magnetization, and the spin torque
parameter.",1312.0300v1
2020-10-12,Magnetization steps of $J_{1}$ quintets in the hcp lattice,"The magnetization steps of quintets, consisting of five identical magnetic
ions coupled by isotropic nearest neighbors antiferromagnetic exchange
interaction, in the hcp lattice, have been investigated. In that model there
are 17 types of quintets. The values of the magnetic field of the magnetization
steps of the quintets have been determined by numerical diagonalization of the
spin Hamiltonian, which is composed by the isotropic exchange and the Zeeman
interactions. The quintets are composed of individual spin $S$ = 1/2, 3/2 and
5/2. The contribution of the quintets for the effective concentration (or
technical saturation) as a function of the magnetic ions concentration was also
calculated.",2010.06051v1
2003-08-28,A Spontaneous Generation of the Magnetic Field and Suppression of the Heat Conduction in Cold Fronts,"We have determined the physical mechanism responsible for the plasma
instabilities, which was first found by Ramani and Laval (1978), associated
with anisotropic velocity distributions induced by the temperature gradient in
which there are growing low frequency transverse magnetic waves, even in the
absence of background magnetic fields. We have shown that the physical
mechanism responsible for the growth of one of the modes is identical to the
Weibel instability. The nonlinear saturation level of the instability is also
provided by considering the wave-particle interactions. The non-linear
evolutions of the magnetic fields after the saturation are speculated. The
results are applied to the cold fronts which is one of the newly discovered
structures in clusters of galaxies by the Chandra X-ray observatory. We predict
the existence of the magnetic field of $\sim 10\mu$G tangential to the surface
over the entire region of the cold front surface and that the heat conduction
is significantly suppressed by the trapping of the electrons by the generated
magnetic fields. The instability may provide a new possibility on the origin of
cosmic magnetic field.",0308503v2
2006-01-23,Magnetic helicity in primordial and dynamo scenarios of galaxies,"Some common properties of helical magnetic fields in decaying and driven
turbulence are discussed. These include mainly the inverse cascade that
produces fields on progressively larger scales. Magnetic helicity also
restricts the evolution of the large scale field: the field decays less rapidly
than a non-helical field, but it also saturates more slowly, i.e. on a
resistive time scale if there are no magnetic helicity fluxes. The former
effect is utilized in primordial field scenarios, while the latter is important
for successfully explaining astrophysical dynamos that saturate faster than
resistively. Dynamo action is argued to be important not only in the galactic
dynamo, but also in accretion discs in active galactic nuclei and around
protostars, both of which contribute to producing a strong enough seed magnetic
field. Although primordial magnetic fields may be too weak to compete with
these astrophysical mechanisms, such fields could perhaps still be important in
producing polarization effects in the cosmic background radiation.",0601496v1
2000-09-01,Lanczos Study of the S=1/2 Frustrated Square-Lattice Antiferromagnet in a Magnetic Field,"We study the zero-temperature phase diagram of the frustrated square-lattice
S=1/2 antiferromagnet in an external magnetic field numerically with the
Lanczos algorithm. For strong frustration, we find disordered phases at high
(and low) magnetic fields. Between these two disordered phases we find a
plateau in the magnetization curve at half of the saturation magnetization
which corresponds to a state with up-up-up-down (uuud) spin order. This and
other considerations [cond-mat/0003343] suggest an unusual ordering scenario:
There are an ordered phase with a spin gap (the plateau) and disordered
magnetically gapless phases above and below.
  The transition to saturation is studied in further detail and problematic
conclusions in earlier investigations of this region are pointed out.",0009006v1
2008-02-28,Magnetic studies of multi-walled carbon nanotube mats: Evidence for the paramagnetic Meissner effect,"We report magnetic measurements up to 1200 K on multi-walled carbon nanotube
mats using Quantum Design vibrating sample magnetometer. Extensive magnetic
data consistently show two ferrromagnetic-like transitions at about 1000 K and
1275 K, respectively. The lower transition at about 1000 K is associated with
an Fe impurity phase and its saturation magnetization is in quantitative
agreement with the Fe concentration measured by an inductively coupled plasma
mass spectrometer. On the other hand, the saturation magnetization for the
higher transition phase ($\geq$1.0 emu/g) is about four orders of magnitude
larger than that expected from the measured concentration of Co or CoFe, which
has a high enough Curie temperature to explain this high transition. We show
that this transition at about 1275 K is not consistent with a magnetic
proximity effect of Fe-carbon systems and ferromagnetism of any carbon-based
materials or magnetic impurities but with the paramagnetic Meissner effect due
to the existence of $\pi$ Josephson junctions in a granular superconductor.",0802.4108v2
2011-07-27,The effects of plasma beta and anisotropy instabilities on the dynamics of reconnecting magnetic fields in the heliosheath,"The plasma {\beta} (the ratio of the plasma pressure to the magnetic
pressure) of a system can have a large effect on its dynamics as high {\beta}
enhances the effects of pressure anisotropies. We investigate the effects of
{\beta} in a system of stacked current sheets that break up into magnetic
islands due to magnetic reconnection. We find significant differences between
{\beta} < 1 and {\beta} > 1. At low {\beta} growing magnetic islands are
modestly elongated and become round as contraction releases magnetic stress and
reduces magnetic energy. At high {\beta} the increase of the parallel pressure
in contracting islands causes saturation of modestly elongated islands as
island cores approach the marginal firehose condition. Only highly elongated
islands reach finite size. The kinking associated with the Weibel and firehose
instabilities prevents full contraction of these islands, leading to a final
state of highly elongated islands in which further reconnection is suppressed.
The results are directly relevant to reconnection in the sectored region of the
heliosheath and possibly to saturation mechanisms of the magnetorotational
instability in accretion flows.",1107.5558v2
2012-01-25,Universal Magnetic Properties of sp$^3$-type Defects in Covalently Functionalized Graphene,"Using density-functional calculations, we study the effect of sp$^3$-type
defects created by different covalent functionalizations on the electronic and
magnetic properties of graphene. We find that the induced magnetic properties
are {\it universal}, in the sense that they are largely independent on the
particular adsorbates considered. When a weakly-polar single covalent bond is
established with the layer, a local spin-moment of 1.0 $\mu_B$ always appears
in graphene. This effect is similar to that of H adsorption, which saturates
one $p_z$ orbital in the carbon layer. The magnetic couplings between the
adsorbates show a strong dependence on the graphene sublattice of
chemisorption. Molecules adsorbed at the same sublattice couple
ferromagnetically, with an exchange interaction that decays very slowly with
distance, while no magnetism is found for adsorbates at opposite sublattices.
Similar magnetic properties are obtained if several $p_z$ orbitals are
saturated simultaneously by the adsorption of a large molecule. These results
might open new routes to engineer the magnetic properties of graphene
derivatives by chemical means.",1201.5326v1
2013-03-04,"Ground-state phase diagram and magnetization process of the exactly solved mixed spin-(1,1/2) Ising diamond chain","The ground state and magnetization process of the mixed spin-(1,1/2) Ising
diamond chain is exactly solved by employing the generalized
decoration-iteration mapping transformation and the transfer-matrix method. The
decoration-iteration transformation is first used in order to establish a
rigorous mapping equivalence with the corresponding spin-1
Blume-Emery-Griffiths chain in a non-zero magnetic field, which is subsequently
exactly treated within the framework of the transfer-matrix technique. It is
shown that the ground-state phase diagram includes just four different ground
states and the low-temperature magnetization curve may exhibit an intermediate
plateau precisely at one half of the saturation magnetization. Our rigorous
results disprove recent Monte Carlo simulations of Zihua Xin et al. [Z. Xin, S.
Chen, C. Zhang, J. Magn. Magn. Mater. 324 (2012) 3704], which imply an
existence of the other magnetization plateaus at 0.283 and 0.426 of the
saturation magnetization.",1303.0636v1
2019-07-16,Enhanced Magnetization from Proton Irradiated Bulk van der Waals Magnet CrSiTe3,"Van der Waals (vdWs) crystals have attracted a great deal of scientific
attention due to their interesting physical properties and widespread practical
applications. Among all, CrSiTe3 (CST) is a ferromagnetic semiconductor with
the Curie temperature (TC) of ~32 K. In this letter, we study the magnetic
properties of bulk CST single-crystal upon proton irradiation with the fluence
of 1x1018 protons/cm2. Most significantly, we observed an enhancement (23%) in
the saturation magnetization from 3.9 {\mu}B to 4.8 {\mu}B and is accompanied
by an increase in the coercive field (465-542 Oe) upon proton irradiation.
Temperature-dependent X-band electron paramagnetic resonance measurements show
no additional magnetically active defects/vacancies that are generated upon
proton irradiation. The findings from X-ray photoelectron spectroscopy and
Raman measurements lead us to believe that modification in the spin-lattice
coupling and introduction of disorder could cause enhancement in saturation
magnetization. This work demonstrates that proton irradiation is a feasible
method in modifying the magnetic properties of vdWs crystals, which represents
a significant step forward in designing future spintronic and
magneto-electronic applications.",1907.07222v2
2005-02-06,Model for a Macroscopically Disordered Conductor with an Exactly Linear High-Field Magnetoresistance,"We calculate the effective resistivity of a macroscopically disordered two
dimensional conductor consisting of two components in a perpendicular magnetic
field. When two components have equal area fractions, we use a duality theorem
to show that the magnetoresistance is non-saturating and at high fields varies
exactly linearly with magnetic field. At other compositions, an effective
medium calculation leads to a saturating magnetoresistance. We briefly discuss
possible connections between these results and magnetoresistance measurements
on heavily disordered chalconide semiconductors.",0502162v2
2006-03-20,Influence of lattice distortions in classical spin systems,"We investigate a simple model of a frustrated classical spin chain coupled to
adiabatic phonons under an external magnetic field. A thorough study of the
magnetization properties is carried out both numerically and analytically. We
show that already a moderate coupling with the lattice can stabilize a plateau
at 1/3 of the saturation and discuss the deformation of the underlying lattice
in this phase. We also study the transition to saturation where either a first
or second order transition can occur, depending on the couplings strength.",0603514v2
2006-01-26,Further Results on Active Magnetic Bearing Control with Input Saturation,"We study the low-bias stabilization of active magnetic bearings (AMBs)
subject to voltage saturation based on a recently proposed model for the AMB
switching mode of operation. Using a forwarding-like approach, we construct a
stabilizing controller of arbitrarily small amplitude and a control-Lyapunov
function for the AMB dynamics. We illustrate our construction using a numerical
example.",0601650v1
1996-12-31,Resonance Broadening Induced Nonlinear Saturation of Kinetic Alfven Turbulence in the Interplanetary Plasma,"The saturation of ion cyclotron Alfven turbulence excited by beam particles
is investigated using resonance broadening theory. The stochastic scattering
which decorrelates particles, includes both random acceleration by electric
fields and a turbulent magnetic mirroring effect. Turbulent mirroring is shown
to yield non-Gaussian corrections to the orbits even if the random electric and
magnetic fields are Gaussian. The predicted steady-state turbulence level
exhibits a peaked anglular distribution, with a maximum near Theta ~ 60
degrees.",9612019v1
2008-01-10,The magneto-rotational instability near threshold: spatio-temporal amplitude equation and saturation,"We show, by means of a perturbative weakly nonlinear analysis, that the
axisymmetric magneto-rotational instability (MRI) in a magnetic Taylor-Couette
(mTC) flow in a thin-gap gives rise, for very small magnetic Prandtl numbers
(P_m), to a real Ginzburg-Landau equation for the disturbance amplitude. The
saturation amplitude A_s is found to scale in this regime as P^\delta, with
1/2<\delta<2/3 (depending on the boundary conditions adopted). The asymptotic
results are shown to comply with numerical calculations performed by using a
spectral code. They suggest that the transport due to the nonlinearly developed
MRI may be vanishingly small for P_m << 1.",0801.1637v1
2010-05-26,Ferromagnetism in the Highly-Correlated Hubbard Model,"The Hubbard model with strong correlations is treated in the many-electron
representation of Hubbard's operators. The regions of stability of saturated
and non-saturated ferromagnetism in the n-U plane for the square and simple
cubic lattices are calculated. The role of the bare density of states
singularities for the magnetic phase diagram is discussed. A comparison with
the results of previous works is performed.",1005.4795v1
2011-03-08,Saturation of a spin 1/2 particle by generalized Local control,"We show how to apply a generalization of Local control design to the problem
of saturation of a spin 1/2 particle by magnetic fields in Nuclear Magnetic
Resonance. The generalization of local or Lyapunov control arises from the fact
that the derivative of the Lyapunov function does not depend explicitly on the
control field. The second derivative is used to determine the local control
field. We compare the efficiency of this approach with respect to the
time-optimal solution which has been recently derived using geometric methods.",1103.1570v1
2013-12-16,Physical properties of CeGe2-x (x = 0.24) single crystals,"We present data on the anisotropic magnetic properties, heat capacity and
transport properties of CeGe2-x (x = 0.24) single crystals. The electronic
coefficient of the heat capacity, gamma ~ 110 mJ/mol K^2, is enhanced; three
magnetic transitions, with critical temperatures of ~ 7 K, ~ 5 K, and ~ 4 K are
observed in thermodynamic and transport measurements. The ground state has a
small ferromagnetic component along the c - axis. Small applied field, below 10
kOe, is enough to bring the material to an apparent saturated paramagnetic
state (with no further metamagnetic transitions up to 55 kOe) with a reduced,
below 1 mu_B, saturated moment.",1312.4580v1
2014-05-02,Dynamic nuclear polarization from current-induced electron spin polarization,"Current-induced electron spin polarization is shown to produce nuclear
hyperpolarization through dynamic nuclear polarization. Saturated fields of
several millitesla are generated upon the application of electric field over a
timescale of a hundred seconds in InGaAs epilayers and measured using optical
Larmor magnetometry. The dependence on temperature, external magnetic field,
and applied voltage is investigated. We find an asymmetry in which the
saturation nuclear field depends on the relative alignment of the electrically
generated spin polarization and the external magnetic field, which we attribute
to an interplay between various electron spin dynamical processes.",1405.0342v1
2017-03-09,Distinct turbulence saturation regimes in stellarators,"In the complex 3D magnetic fields of stellarators, ion-temperature-gradient
turbulence is shown to have two distinct saturation regimes, as revealed by
petascale numerical simulations, and explained by a simple turbulence theory.
The first regime is marked by strong zonal flows, and matches previous
observations in tokamaks. The newly observed second regime, in contrast,
exhibits small- scale quasi-two-dimensional turbulence, negligible zonal flows,
and, surprisingly, a weaker heat flux scaling. Our findings suggest that key
details of the magnetic geometry control turbulence in stellarators.",1703.03257v2
2019-09-16,Experimental Confirmation of Quantum Hall Ferromagnetic State in an Organic Dirac Fermion System,"We have experimentally confirmed the quantum Hall ferromagnetic state with
Chern number \nu=0, characterized by the helical edge state, in a layered
organic Dirac fermion system \alpha-(BEDT-TTF)_2I_3. The interlayer resistance
saturates at low temperatures and high magnetic fields. It does not scale with
the sample cross-sectional area in the saturating region, and resonantly
depends on the magnetic field direction. These results strongly suggest that
the helical edge state dominates transport. This is the first observation of
the topological phase in organic molecular crystals.",1909.07006v1
2008-08-07,Large-scale dynamos at low magnetic Prandtl numbers,"Using direct simulations of hydromagnetic turbulence driven by random
polarized waves it is shown that dynamo action is possible over a wide range of
magnetic Prandtl numbers from 10^-3 to 1. Triply periodic boundary conditions
are being used. In the final saturated state the resulting magnetic field has a
large-scale component of Beltrami type. For the kinematic phase, growth rates
have been determined for magnetic Prandtl numbers between 0.01 and 1, but only
the case with the smallest magnetic Prandtl number shows large-scale magnetic
fields. It is less organized than in the nonlinear stage. For small magnetic
Prandtl numbers the growth rates are comparable to those calculated from an
alpha squared mean-field dynamo. In the linear regime the magnetic helicity
spectrum has a short inertial range compatible with a -5/3 power law, while in
the nonlinear regime it is the current helicity whose spectrum may be
compatible with such a law. In the saturated case, the spectral magnetic energy
in the inertial range is in slight excess over the spectral kinetic energy,
although for small magnetic Prandtl numbers the magnetic energy spectrum
reaches its resistive cut off wavenumber more quickly. The viscous energy
dissipation declines with the square root of the magnetic Prandtl number, which
implies that most of the energy is dissipated via Joule heat.",0808.0961v2
2014-11-03,"Anisotropic putative ""up-up-down"" magnetic structure in EuTAl$_4$Si$_2$ (T = Rh and Ir)","We present detailed investigations in single crystals of two recently
reported quaternary intermetallic compounds EuRhAl$_4$Si$_2$ and
EuIrAl$_4$Si$_2$ employing magnetization, electrical resistivity in zero and
applied fields, heat capacity and $^{151}$Eu M\""{o}ssbauer spectroscopy
measurements. The two compounds order antiferromagnetically at $T_{\rm N1}$ =
11.7 and 14.7\,K, respectively, each undergoing two magnetic transitions: the
first from paramagnetic to incommensurate modulated antiferromagnetic, the
second at lower temperature to a commensurate antiferromagnetic phase as
confirmed by heat capacity and M\""{o}ssbauer spectra. The magnetic properties
in the ordered state present a large anisotropy despite Eu$^{2+}$ being an
$S$-state ion for which the single-ion anisotropy is expected to be weak. Two
features in the magnetization measured along the $c$-axis are prominent. At
1.8\,K, a ferromagnetic-like jump occurs at very low field to a value one third
of the saturation magnetization (1/3 M$_0$) followed by a wide plateau up to
2\,T for T = Rh and 4\,T for T = Ir. At this field value, a sharp hysteretic
spin-flop transition occurs to a fully saturated state (M$_0$). Surprisingly,
the magnetization does not return to origin when the field is reduced to zero
in the return cycle, as expected in an antiferromagnet. Instead, a remnant
magnetization 1/3 M$_0$ is observed and the magnetic loop around the origin
shows hysteresis. This suggests that the zero field magnetic structure has a
ferromagnetic component, and we present a model with up to third neighbor
exchange and dipolar interaction which reproduces the magnetization curves and
hints to an ""up-up-down"" magnetic structure in zero field.",1411.0379v1
2015-06-09,On the absence of actual plateaus in zero-temperature magnetization curves of quantum spin clusters and chains,"We examine the general features of the non-commutativity of the magnetization
operator and Hamiltonian for the small quantum spin clusters. The source of
this non-commutativity can be a difference in the Land\'{e} g-factors for
different spins in the cluster, XY-anisotropy in the exchange interaction and
the presence of the Dzyaloshinskii-Moriya term in the direction different for
the direction of the magnetic field. As a result, a zero-temperature
magnetization curve for the small spin clusters mimics that for the macroscopic
systems with the band(s) of magnetic excitations, i.e. for the given eigenstate
of the spin cluster the corresponding magnetic moment can be an explicit
function of the external magnetic field yielding the non-constant (non-plateau)
form of the magnetization curve within the given eigenstate. Also, the
XY-anisotropy makes the saturated magnetization (the eigenstate when all spins
in cluster are aligned along the magnetic field) inaccessible for finite
magnetic field magnitude (asymptotical saturation). We demonstrate all these
features on three examples: spin-1/2 dimer, mixed spin-(1/2,1) dimer, spin-1/2
ring trimer. We consider the simplest Ising-Heisenberg chain, the XYZ-Ising
diamond chain with four different g-factors as well. In the chain model the
magnetization curve has more complicated and non trivial structure with than
that for clusters.",1506.02933v2
2016-01-19,Collective magnetic response of CeO2 nanoparticles,"The magnetism of nanoparticles and thin films of wide-bandgap oxides that
include no magnetic cations is an unsolved puzzle. Progress has been hampered
both by the irreproducibility of much of the experimental data, and the lack of
any generally-accepted theoretical explanation. The characteristic signature is
a virtually anhysteretic, temperature-independent magnetization curve which
saturates in an applied field that is several orders of magnitude greater than
the magnetization. It appears as if a tiny volume fraction, < 0.1%, of the
samples is magnetic and that the energy scale of the problem is unusually high
for spin magnetism. Here we investigate the effect of dispersing 4 nm CeO2
nanoparticles with powders of gamma-Al2O3, sugar or latex microspheres. The
saturation magnetization, Ms ~ 60 A/m for compact samples, is maximized by 1
wt% lanthanum doping. Dispersing the CeO2 nanopowder reduces its magnetic
moment by up to an order of magnitude. There is a characteristic length scale
of order 100 nm for the magnetism to appear in CeO2 nanoparticle clusters. The
phenomenon is explained in terms of a giant orbital paramagnetism that appears
in coherent mesoscopic domains due to resonant interaction with zero-point
fluctuations of the vacuum electromagnetic field. The theory explains the
observed temperature-independent magnetization curve and its doping and
dispersion dependence, based on a length scale of 300 nm that corresponds to
the wavelength of a maximum in the UV absorption spectrum of the magnetic CeO2
nanoparticles. The coherent domains occupy roughly ten percent of the sample
volume.",1601.04933v1
1999-01-13,Growth and saturation of the Kelvin-Helmholtz instability with parallel and anti-parallel magnetic fields,"We investigate the Kelvin-Helmholtz instability occuring at the interface of
a shear flow configuration in 2D compressible magnetohydrodynamics (MHD). The
linear growth and the subsequent non-linear saturation of the instability are
studied numerically. We consider an initial magnetic field aligned with the
shear flow, and analyze the differences between cases where the initial field
is unidirectional everywhere (uniform case), and where the field changes sign
at the interface (reversed case). We recover and extend known results for pure
hydrodynamic and MHD cases with a discussion of the dependence of the
non-linear saturation on the wavenumber, the sound Mach number, and the
Alfvenic Mach number for the MHD case.
  A reversed field acts to destabilize the linear phase of the Kelvin-Helmholtz
instability compared to the pure hydrodynamic case, while a uniform field
suppresses its growth. In resistive MHD, reconnection events almost instantly
accelerate the buildup of a global plasma circulation. They play an important
role throughout the further non-linear evolution as well, since the initial
current sheet gets amplified by the vortex flow and can become unstable to
tearing instabilities forming magnetic islands. As a result, the saturation
behaviour and the overall evolution of the density and the magnetic field is
markedly different for the uniform versus the reversed field case.",9901166v1
2000-04-05,Ferromagnetism of quark liquid and magnetars,"Spontaneous magnetization of quark liquid is examined on the analogy with
that in electron gas. It is pointed out that quark liquid has potential to be
ferromagnetic at rather low densities, around nuclear saturation density. Somme
comments are given as for implications on magnetars.",0004062v1
2013-05-29,A Predictive Model of Geosynchronous Magnetopause Crossings,"We have developed a model predicting whether or not the magnetopause crosses
geosynchronous orbit at given location for given solar wind pressure Psw, Bz
component of interplanetary magnetic field (IMF) and geomagnetic conditions
characterized by 1-min SYM-H index. The model is based on more than 300
geosynchronous magnetopause crossings (GMCs) and about 6000 minutes when
geosynchronous satellites of GOES and LANL series are located in the
magnetosheath (so-called MSh intervals) in 1994 to 2001. Minimizing of the Psw
required for GMCs and MSh intervals at various locations, Bz and SYM-H allows
describing both an effect of magnetopause dawn-dusk asymmetry and saturation of
Bz influence for very large southward IMF. The asymmetry is strong for large
negative Bz and almost disappears when Bz is positive. We found that the larger
amplitude of negative SYM-H the lower solar wind pressure is required for GMCs.
We attribute this effect to a depletion of the dayside magnetic field by a
storm-time intensification of the cross-tail current. It is also found that the
magnitude of threshold for Bz saturation increases with SYM-H index such that
for small negative and positive SYM-H the effect of saturation diminishes. This
supports an idea that enhanced thermal pressure of the magnetospheric plasma
and ring current particles during magnetic storms results in the saturation of
magnetic effect of the IMF Bz at the dayside magnetopause. A noticeable
advantage of the model prediction capabilities in comparison with other
magnetopause models makes the model useful for space weather predictions.
Supplement : a program-code of the GMC-model",1305.6707v1
2023-11-07,Evidence for saturated and disrupted magnetic braking from samples of detached close binaries with M and K dwarfs,"Context. Recent observations of close detached eclipsing M and K dwarf
binaries have provided substantial support for magnetic saturation when stars
rotate sufficiently fast, leading to a magnetic braking (MB) torque
proportional to the spin of the star.
  Aims. We investigated here how strong MB torques need to be to reproduce the
observationally-inferred relative numbers of white dwarf plus M dwarf
post-common-envelope binaries under the assumption of magnetic saturation.
  Methods. We carried out binary population simulations with the BSE code
adopting empirically-derived inter-correlated main-sequence binary
distributions as initial binary populations and compared the simulation
outcomes with observations.
  Results. We found that the dearth of extreme mass ratio binaries in the
inter-correlated initial distributions is key to reproduce the large fraction
of post-common-envelope binaries hosting low-mass M dwarfs (${\sim0.1-0.2}$
M$_\odot$). In addition, orbital angular momentum loss rates due to MB should
be high for M dwarfs with radiative cores and orders of magnitude smaller for
fully convective stars to explain the observed dramatic change of the fraction
of short-period binaries at the fully convective boundary.
  Conclusions. We conclude that saturated but disrupted, that is, dropping
drastically at the fully convective boundary, MB can explain the observations
of both close main-sequence binaries containing M and K dwarfs and
post-common-envelope binaries. Whether a similar prescription can explain the
spin down rates of single stars and of binaries containing more massive stars
needs to be tested.",2311.04309v1
2003-12-18,Angular Momentum Transport by MHD Turbulence in Accretion Disks: Gas Pressure Dependence of the Saturation Level of the Magnetorotational Instability,"The saturation level of the magnetorotational instability (MRI) is
investigated using three-dimensional MHD simulations. The shearing box
approximation is adopted and the vertical component of gravity is ignored, so
that the evolution of the MRI is followed in a small local part of the disk. We
focus on the dependence of the saturation level of the stress on the gas
pressure, which is a key assumption in the standard alpha disk model. From our
numerical experiments it is found that there is a weak power-law relation
between the saturation level of the Maxwell stress and the gas pressure in the
nonlinear regime; the higher the gas pressure, the larger the stress. Although
the power-law index depends slightly on the initial field geometry, the
relationship between stress and gas pressure is independent of the initial
field strength, and is unaffected by Ohmic dissipation if the magnetic Reynolds
number is at least 10. The relationship is the same in adiabatic calculations,
where pressure increases over time, and nearly-isothermal calculations, where
pressure varies little with time. Our numerical results are qualitatively
consistent with an idea that the saturation level of the MRI is determined by a
balance between the growth of the MRI and the dissipation of the field through
reconnection. The quantitative interpretation of the pressure-stress relation,
however, may require advances in the theoretical understanding of non-steady
magnetic reconnection.",0312480v1
2004-03-16,Incommensurate state in a quasi-one-dimensional $S=1/2$ bond-alternating antiferromagnet with frustration in magnetic fields,"We investigate the critical properties of the $S=1/2$ bond-alternating spin
chain with a next-nearest-neighbor interaction in magnetic fields. By the
numerical calculation and the exact solution based on the effective
Hamiltonian, we show that there is a parameter region where the longitudinal
incommensurate spin correlation becomes dominant around the half-magnetization
of the saturation. Possible interpretations of our results are discussed. We
next investigate the effects of the interchain interaction ($J^{\prime}$). The
staggered susceptibility and the uniform magnetization are calculated by
combining the density-matrix renormalization group method with the interchain
mean-field theory. For the parameters where the dominant longitudinal
incommensurate spin correlation appears in the case $J^{\prime}=0$, the
staggered long-range order does not emerge up to a certain critical value of
$J^{\prime}$ around the half-magnetization of the saturation. We calculate the
static structure factor in such a parameter region. The size dependence of the
static structure factor at $k=2k_{\rm F}$ implies that the system has a
tendency to form an incommensurate long-range order around the
half-magnetization of the saturation. We discuss the recent experimental
results for the NMR relaxation rate in magnetic fields performed for
pentafluorophenyl nitronyl nitroxide.",0403404v3
2010-03-31,Local simulations of the magnetized Kelvin-Helmholtz instability in neutron-star mergers,"Context. Global MHD simulations show Kelvin-Helmholtz (KH) instabilities at
the contact surface of two merging neutron stars. That region has been
identified as the site of efficient amplification of magnetic fields. However,
these global simulations, due to numerical limitations, were unable to
determine the saturation level of the field strength, and thus the possible
back-reaction of the magnetic field onto the flow. Aims. We investigate the
amplification of initially weak fields in KH unstable shear flows, and the
back-reaction of the field onto the flow. Methods. We use a high-resolution
ideal MHD code to perform 2D and 3D local simulations of shear flows. Results.
In 2D, the magnetic field is amplified in less than 0.01ms until it reaches
locally equipartition with the kinetic energy. Subsequently, it saturates due
to resistive instabilities that disrupt the KH vortex and decelerate the shear
flow on a secular time scale. We determine scaling laws of the field
amplification with the initial field strength and the grid resolution. In 3D,
this hydromagnetic mechanism may be dominated by purely hydrodynamic
instabilities limiting the amplification. We find maximum magnetic fields of
10^16 G locally, and r.m.s. maxima within the box of 10^15 G. However, such
strong fields exist only for a short period. In the saturated state, the
magnetic field is mainly oriented parallel to the shear flow for strong initial
fields, while weaker initial fields tend to lead to a more balanced
distribution of the field energy. In all models the flow shows small-scale
features. The magnetic field is at most in equipartition with the decaying
shear flow. (abridged)",1003.6031v1
2020-12-18,Rare-earth-free ferrimagnetic Mn4N sub-20 nm thin films as high-temperature spintronic material,"Ferrimagnetic alloy thin films that exhibit perpendicular (out-of-plane)
magnetic anisotropy (PMA) with low saturation magnetization, such as GdCo and
Mn4N, were predicted to be favorable for hosting small Neel skyrmions for room
temperature applications. Due to the exponential decay of interfacial
Dzyaloshinskii-Moriya interaction (DMI) and the limited range of
spin-orbit-torques, which can be used to drive skyrmion motion, the thickness
of the ferrimagnetic layer has to be small, preferably under 20 nm. While there
are examples of sub-20 nm, rare earth-transition metal (RE-TM), ferrimagnetic
thin films fabricated by sputter deposition, to date rare-earth-free sub-20 nm
Mn4N films with PMA have only been reported to be achieved by molecular beam
epitaxy, which is not suitable for massive production. Here we report the
successful thermal growth of sub-20 nm Mn4N films with PMA at 400-450 {\deg}C
substrate temperatures on MgO substrates by reactive sputtering. The Mn4N films
were achieved by reducing the surface roughness of MgO substrate through a
high-temperature vacuum annealing process. The optimal films showed low
saturation magnetization (Ms = 43 emu/cc), low magnetic anisotropy energy (0.7
Merg/cc), and a remanent magnetization to saturation magnetization ratio
(Mr/Ms) near 1 at room temperature. Preliminary ab-initio density functional
theory (DFT) calculations have confirmed the ferrimagnetic ground state of Mn4N
grown on MgO. The magnetic properties, along with the high thermal stability of
Mn4N thin films in comparison with RE-TM thin films, provide the platform for
future studies of practical skyrmion-based spintronic materials.",2012.10493v1
2023-09-27,Magnetic flux plays an important role during a BHXRB outburst in radiative 2T GRMHD simulations,"Black hole (BH) X-ray binaries cycle through different spectral states of
accretion over the course of months to years. Although fluctuations in the BH
mass accretion rate are generally recognized as the most important component of
state transitions, it is becoming increasingly evident that magnetic fields
play a similarly important role. In this article, we present the first
radiative two-temperature (2T) general relativistic magnetohydrodynamics
(GRMHD) simulations in which an accretion disk transitions from a quiescent
state at an accretion rate of $\dot{M} \sim 10^{-10} \dot{M}_{\rm Edd}$ to a
hard-intermediate state at an accretion rate of $\dot{M} \sim 10^{-2}
\dot{M}_{\rm Edd}$. This huge parameter space in mass accretion rate is bridged
by artificially rescaling the gas density scale of the simulations. We present
two jetted BH models with varying degrees of magnetic flux saturation. We
demonstrate that in `Standard and Normal Evolution' models, which are
unsaturated with magnetic flux, the hot torus collapses into a thin and cold
accretion disk when $\dot{M} \gtrsim 5\times 10^{-3} \dot{M}_{\rm Edd}$. On the
other hand, in `Magnetically Arrested Disk' models, which are fully saturated
with vertical magnetic flux, the plasma remains mostly hot with substructures
that condense into cold clumps of gas when $\dot{M} \gtrsim 1 \times 10^{-2}
\dot{M}_{\rm Edd}$. This suggests that the spectral signatures observed during
state transitions are closely tied to the level of magnetic flux saturation.",2309.15926v2
2006-06-30,Finite-temperature order-disorder phase transition in a frustrated bilayer quantum Heisenberg antiferromagnet in strong magnetic fields,"We investigate the thermodynamic properties of the frustrated bilayer quantum
Heisenberg antiferromagnet at low temperatures in the vicinity of the
saturation magnetic field. The low-energy degrees of freedom of the spin model
are mapped onto a hard-square gas on a square lattice. We use exact
diagonalization data for finite spin systems to check the validity of such a
description. Using a classical Monte Carlo method we give a quantitative
description of the thermodynamics of the spin model at low temperatures around
the saturation field. The main peculiarity of the considered two-dimensional
Heisenberg antiferromagnet is related to a phase transition of the hard-square
model on the square lattice, which belongs to the two-dimensional Ising model
universality class. It manifests itself in a logarithmic (low-)temperature
singularity of the specific heat of the spin system observed for magnetic
fields just below the saturation field.",0606806v1
2007-11-02,Dynamical feedback of the curvature drift instability on its saturation process,"We investigate the reconstruction of pulsar magnetospheres close to the light
cylinder surface to study the curvature drift instability (CDI) responsible for
the twisting of magnetic field lines in the mentioned zone. The influence of
plasma dynamics on the saturation process of the CDI is studied. On the basis
of the Euler, continuity, and induction equations, we derive the increment of
the CDI and analyze parametrically excited drift modes. The dynamics of the
reconstruction of the pulsar magnetosphere is studied analytically. We show
that there is a possibility of a parametrically excited rotational-energy
pumping-process in the drift modes. It is indicated by the generation of a
toroidal component of the magnetic field that transforms the field lines into
such a configuration, in which plasma particles do not experience any forces.
At this stage, the instability process saturates and the further amplification
of the toroidal component to the magnetic field lines is suspended.",0711.0295v8
2009-10-01,The filamentation instability driven by warm electron beams: Statistics and electric field generation,"The filamentation instability of counterpropagating symmetric beams of
electrons is examined with 1D and 2D particle-in-cell (PIC) simulations, which
are oriented orthogonally to the beam velocity vector. The beams are uniform,
warm and their relative speed is mildly relativistic. The dynamics of the
filaments is examined in 2D and it is confirmed that their characteristic size
increases linearly in time. Currents orthogonal to the beam velocity vector are
driven through the magnetic and electric fields in the simulation plane. The
fields are tied to the filament boundaries and the scale size of the
flow-aligned and the perpendicular currents are thus equal. It is confirmed
that the electrostatic and the magnetic forces are equally important, when the
filamentation instability saturates in 1D. Their balance is apparently the
saturation mechanism of the filamentation instability for our initial
conditions. The electric force is relatively weaker but not negligible in the
2D simulation, where the electron temperature is set higher to reduce the
computational cost. The magnetic pressure gradient is the principal source of
the electrostatic field, when and after the instability saturates in the 1D
simulation and in the 2D simulation.",0910.0228v1
2010-02-02,Low magnetic-Prandtl number flow configurations for cold astrophysical disk models: speculation and analysis,"Simulations of astrophysical disks in the shearing box that are subject to
the magnetorotational instability (MRI) show that activity appears to be
reduced as the magnetic Prandtl number (Pm) is lowered. On the other hand,
calculations for laboratory experiments show that saturation is achieved
through modification of the background shear for Pm << 1. Guided by the results
of calculations appropriate for laboratory experiments when Pm is very low, the
axisymmetric stability of inviscid disturbances in a shearing box model
immersed in a constant vertical background magnetic field is considered under a
variety of shear profiles and boundary conditions in order to evaluate the
hypothesis that modifications of the shear bring about saturation of the
instability. It is found that the emergence and stability of the MRI is
sensitive to the boundary conditions adopted. Channel modes do not appear to be
stabilized through any modification of the background shear whose average
remains Keplerian. However, systems that have non-penetrative boundaries can
saturate the MRI through modification of the background shear. Conceptually
equating the qualitative results from laboratory experiments to the conditions
in a disk may therefore be misleading.",1002.0506v1
2011-12-24,Frustrated spin chains in strong magnetic field: dilute two-component Bose gas regime,"We study the ground state of frustrated spin-S chains in a strong magnetic
field in the immediate vicinity of saturation. In strongly frustrated chains,
the magnon dispersion has two degenerate minima at inequivalent momenta $\pm
Q$, and just below the saturation field the system can be effectively
represented as a dilute one-dimensional lattice gas of two species of bosons
that correspond to magnons with momenta around $\pm Q$. We present a theory of
effective interactions in such a dilute magnon gas that allows us to make
quantitative predictions for arbitrary values of the spin. With the help of
this method, we are able to establish the magnetic phase diagram of frustrated
chains close to saturation and study phase transitions between several
nontrivial states, including a two-component Luttinger liquid, a vector chiral
phase, and phases with bound magnons. We study those phase transitions
numerically and find a good agreement with our analytical predictions.",1112.5720v2
2013-03-26,Double zigzag spin chain in strong magnetic field close to saturation,"We study the ground state phase diagram of a frustrated spin tube in a strong
external magnetic field. This model can be viewed as two coupled zigzag spin
chains, or as a two-leg spin ladder with frustrating next-nearest-neighbor
couplings along the legs, and its study is motivated by the physics of such
materials as Sulfolane-Cu_{2}Cl_{4} and BiCu_{2}PO_{6}. In magnetic fields
right below the saturation, the system can be effectively represented as a
dilute gas of two species of bosonic quasiparticles that correspond to magnons
with inequivalent incommensurate momenta at two degenerate minima of the magnon
dispersion. Using the method previously proposed and tested for frustrated spin
chains, we calculate effective interactions in this two-component Bose gas. On
this basis, we establish the phase diagram of nearly-saturated frustrated spin
tube, which is shown to include the two-component Luttinger liquid, two types
of vector chiral phases, and phases whose physics is determined by the presence
of bound magnons. We study the phase diagram of the model numerically by means
of the density matrix renormalization group technique, and find a good
agreement with our analytical predictions.",1303.6662v1
2015-09-23,Four-level N-scheme crossover resonances in Rb saturation spectroscopy in magnetic fields,"We perform saturated absorption spectroscopy on the D$\_2$ line for room
temperature rubidium atoms immersed in magnetic fields within the 0.05-0.13 T
range. At those medium-high field values the hyperfine structure in the excited
state is broken by the Zeeman effect, while in the ground state hyperfine
structure and Zeeman shifts are comparable. The observed spectra are composed
by a large number of absorption lines. We identify them as saturated
absorptions on two-level systems, on three-level systems in a V configuration
and on four-level systems in a N or double-N configuration where two optical
transitions not sharing a common level are coupled by spontaneous emission
decays. We analyze the intensity of all those transitions within a unified
simple theoretical model. We concentrate our attention on the double-N
crossovers signals whose intensity is very large because of the symmetry in the
branching ratios of the four levels. We point out that these structures,
present in all alkali atoms at medium-high magnetic fields, have interesting
properties for electromagnetically induced transparency and slow light
applications.",1509.06978v1
2016-12-22,Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor CrAs,"In conventional metals, modification of electron trajectories under magnetic
field gives rise to a magnetoresistance that varies quadratically at low field,
followed by a saturation at high field for closed orbits on the Fermi surface.
Deviations from the conventional behaviour, e.g. the observation of a linear
magnetoresistance, or a non-saturating magnetoresistance, have been attributed
to exotic electron scattering mechanisms. Recently, linear magnetoresistance
has been observed in many Dirac materials, in which the electron-electron
correlation is relatively weak. The strongly correlated helimagnet CrAs
undergoes a quantum phase transition to a nonmagnetic superconductor under
pressure. Near the magnetic instability, we observe a large and non-saturating
quasilinear magnetoresistance from the upper critical field to 14 T at low
temperatures. We show that the quasilinear magnetoresistance arises from an
intricate interplay between a nontrivial band crossing protected by
nonsymmorphic crystal symmetry and strong magnetic fluctuations",1612.07480v1
2018-04-17,Metamagnetism and zero-scale-factor universality in the two-dimensional $J$-$Q$ model,"Using a combination of quantum Monte Carlo and exact methods, we study the
field-driven saturation transition of the two-dimensional $J$-$Q$ model, in
which the antiferromagnetic Heisenberg exchange $(J)$ coupling competes with an
additional four-spin interaction $(Q)$ that favors valence-bond solid order.
For small values of $Q$, the saturation transition is continuous, and is
expected to be governed by zero-scale-factor universality at its upper critical
dimension, with a specific form of logarithmic corrections to scaling (first
proposed by Sachdev \textit{et al.} [Phys. Rev. B \textbf{50}, 258 (1994)]).
Our results conform to this expectation, but the logarithmic corrections to
scaling do not match the form predicted by Sachdev \textit{et al.} We also show
that the saturation transition becomes first order above a critical coupling
ratio $(Q/J)_{\rm min}$ and is accompanied by magnetization
jumps---metamagnetism. We obtain an exact solution for $(Q/J)_{\rm min}$ using
a high magnetization expansion, and confirm the existence of the magnetization
jumps beyond this value of coupling using quantum Monte Carlo simulations.",1804.06045v2
2022-10-14,Modeling the Saturation of the Bell Instability using Hybrid Simulations,"The nonresonant streaming instability (Bell instability) plays a pivotal role
in the acceleration and confinement of cosmic rays (CRs); yet, the exact
mechanism responsible for its saturation and the magnitude of the final
amplified magnetic field have not been assessed from first-principles. Using a
survey of hybrid simulations (with kinetic ions and fluid electrons), we study
the evolution of the Bell instability as a function of the parameters of the CR
population. We find that, at saturation, the magnetic pressure in the amplified
field is comparable with the initial CR anisotropic pressure, rather than with
the CR energy flux as previously argued. These results provide a predictive
prescription for the total magnetic field amplification expected in the many
astrophysical environments where the Bell instability is important.",2210.08072v2
2023-09-06,Magnetized Baryonic layer and a novel BPS bound in the gauged-Non-Linear-Sigma-Model-Maxwell theory in (3+1)-dimensions through Hamilton-Jacobi equation,"It is show that one can derive a novel BPS bound for the gauged
Non-Linear-Sigma-Model (NLSM) Maxwell theory in (3+1) dimensions which can
actually be saturated. Such novel bound is constructed using Hamilton-Jacobi
equation from classical mechanics. The configurations saturating the bound
represent Hadronic layers possessing both Baryonic charge and magnetic flux.
However, unlike what happens in the more common situations, the topological
charge which appears naturally in the BPS bound is a non-linear function of the
Baryonic charge. This BPS bound can be saturated when the surface area of the
layer is quantized. The far-reaching implications of these results are
discussed. In particular, we determine the exact relation between the magnetic
flux and the Baryonic charge as well as the critical value of the Baryonic
chemical potential beyond which these configurations become thermodynamically
unstable.",2309.03153v3
2019-04-15,Improvements of the Longitudinal Magnetic Field Measurement from the Solar Magnetic Field Telescope at Huairou Solar Observing Station,"The weak-field approximation implying linear relationship between Stokes
$V/I$ and longitudinal magnetic field, $B_{\Vert}$, often suffers from
saturation observed in strong magnetic field regions such as sunspot umbra. In
this work, we intend to improve the magnetic field observations carried out by
the \textit{Solar Magnetic Field Telescope} (SMFT) at Huairou Solar Observing
Station, China. We propose using non-linear relationship between Stokes $V/I$
and $B_{\Vert}$ to derive the magnetic field. To determine the form of the
relationship, we perform a cross-calibration of the observed SMFT data and
magnetograms provided by the \textit{Helioseismic and Magnetic Imager} on board
the \textit{Solar Dynamics Observatory}. The algorithm of the magnetic field
derivation is described in details. We show that using non-linear relationship
between Stokes $V/I$ and $B_{\Vert}$ allows us to eliminate magnetic field
saturation inside sunspot umbra. The proposed technique enables one to enhance
the reliability of the SMFT magnetic field data obtained even long before the
space-based instrumentation era, since 1987.",1904.07081v7
2022-07-02,Jets from accretion disk dynamos: consistent quenching modes for dynamo and resistivity,"Astrophysical jets are launched from strongly magnetized systems that host an
accretion disk surrounding a central object. The origin of the magnetic field,
which is a key component of the launching process, is still an open question.
Here we address the question of how the magnetic field required for jet
launching is generated and maintained by a dynamo process. By carrying out
non-ideal MHD simulations (PLUTO code), we investigate how the feedback of the
generated magnetic field on the mean-field dynamo affects the disk and jet
properties. We find that a stronger quenching of the dynamo leads to a
saturation of the magnetic field at a lower disk magnetization. Nevertheless,
we find that, while applying different dynamo feedback models, the overall jet
properties remain unaffected. We then investigate a feedback model which
encompasses a quenching of the magnetic diffusivity. Our modeling considers a
more consistent approach for mean-field dynamo modeling simulations, as the
magnetic quenching of turbulence should be considered for both, a turbulent
dynamo and turbulent magnetic diffusivity. We find that, after the magnetic
field is saturated, the Blandford-Payne mechanism can work efficiently, leading
to more collimated jets, that move, however, with slower speed. We find strong
intermittent periods of flaring and knot ejection for low Coriolis numbers. In
particular, flux ropes are built up and advected towards the inner disk thereby
cutting off of the inner disk wind, leading to magnetic field reversals,
reconnection and the emergence of intermittent flares.",2207.00811v1
2014-10-30,Saturation of Zeldovich Stretch-Twist-Fold Map Dynamos,"Zeldovich's stretch-twist fold (STF) dynamo provided a breakthrough in
conceptual understanding of fast dynamos, including fluctuation or small scale
dynamos. We study the evolution and saturation behaviour of two types of
Baker's map dynamos, which have been used to model Zeldovich's STF dynamo
process. Using such maps allows one to analyze dynamos at much higher magnetic
Reynolds numbers $R_M$ as compared to direct numerical simulations. In the
2-strip map dynamo there is constant constructive folding while the 4-strip map
dynamo also allows the possibility of field reversal. Incorporating a diffusive
step parameterised by $R_M$, we find that the magnetic field $B(x)$ is
amplified only above a critical $R_M=R_{crit} \sim 4$ for both types of
dynamos. We explore the saturation of these dynamos in 3 ways; by a
renormalized decrease of the effective $R_M$ (Case I) or due to a decrease in
the efficiency of field amplification by stretching (Case II), or a combination
of both effects (Case III). For Case I, we show that $B(x)$ in the saturated
state, for both types of maps, goes back to the marginal eigenfunction, which
is obtained for the critical $R_M=R_{crit}$. This is independent of the initial
$R_M=R_{M0}$. On the other hand in Case II, for the 2-strip map, we show that
$B(x)$ now saturates preserving the structure of the kinematic eigenfunction.
Thus the energy is transferred to larger scales in Case I but remains at the
smallest resistive scales in Case II. For the 4-strip map, the $B(x)$
oscillates with time, although with a structure similar to the kinematic
eigenfunction. Interestingly, the saturated state for Case III shows an
intermediate behaviour, with $B(x)$ now similar to the kinematic eigenfunction
for an intermediate $R_M=R_{sat}$, with $R_{M0}>R_{sat}>R_{crit}$. These
saturation properties are akin to the ones discussed in the context of
fluctuation dynamos.",1410.8455v3
1999-02-11,A Comparative Study of the Magnetization Process of Two-Dimensional Antiferromagnets,"Plateaux in the magnetization curves of the square, triangular and hexagonal
lattice spin-1/2 XXZ antiferromagnet are investigated. One finds a zero
magnetization plateau (corresponding to a spin-gap) on the square and hexagonal
lattice with Ising-like anisotropies, and a plateau with one third of the
saturation magnetization on the triangular lattice which survives a small
amount of easy-plane anisotropy. Here we start with transfer matrix
computations for the Ising limit and continue with series in the XXZ-anisotropy
for plateau-boundaries using the groundstates of the Ising limit. The main
focus is then a numerical computation of the magnetization curves with
anisotropies in the vicinity of the isotropic situation. Finally, we discuss
the universality class associated to the asymptotic behaviour of the
magnetization curve close to saturation, as observed numerically in two and
higher dimensions.",9902163v1
2001-08-08,Magnetic anisotropy of the spin ice compound Dy2Ti2O7,"We report magnetization and ac susceptibility of single crystals of the spin
ice compound Dy2Ti2O7. Saturated moments at 1.8 K along the charasteristic axes
[100] and [110] agree with the expected values for an effective ferromagnetic
nearest-neighbor Ising pyrochlore with local <111> anisotropy, where each
magnetic moment is constrained to obey the `ice-rule'. At high enough magnetic
fields along the [111] axis, the saturated moment exhibits a beaking of the
ice-rule; it agrees with the value expected for a three-in one-out spin
configuration. Assuming the realistic magnetic interaction between Dy ions
given by the dipolar spin ice model, we completely reproduce the results at 2 K
by Monte Carlo calculations. However, down to at least 60 mK, we have not found
any experimental evidence of the long-range magnetic ordering predicted by this
model to occur at around 180 mK. Instead, we confirm the spin freezing of the
system below 0.5 K.",0108129v1
2002-09-04,Magnetization Plateaux in Random Frustrated S=1/2 Heisenberg Chains,"The $S=1/2$ frustrated Heisenberg chains with bond alternation is known to
exhibit a magnetization plateau at half of the saturation magnetization $\Ms$
accompanied by the spontanuous translational symmetry breakdown. The effect of
randomness on the magnetization process of this model is investigated. First we
consider the mixture of the two kinds of chains both of which possess the
$\Ms/2$-plateau in the common interval of the magnetization field. The plateau
at $\Ms/2$ is found to vanish immediately if the randomness is switched on in
agreement with Totsuka's prediction. The small plateau also appears near the
saturation field due to the localization of inverted spins around the minority
bond. On the other hand, if the stronger bond is replaced by the ferromagnetic
bonds randomly, the randomness induced fractional plateau appears as in the
nonfrustrated case. The plateau at $\Ms/2$ does not simply vanish but shifts
and splits into two smaller plateaux. The magnetization on this plateau varies
nonlinearly with $1-p$. The physical origin of this behavior is explained based
on the strong coupling picture.",0209074v2
2003-09-11,Quantum phase diagram of an exactly solved mixed spin ladder,"We investigate the quantum phase diagram of the exactly solved mixed
spin-(1/2,1) ladder via the thermodynamic Bethe ansatz (TBA). In the absence of
a magnetic field the model exhibits three quantum phases associated with su(2),
su(4) and su(6) symmetries. In the presence of a strong magnetic field, there
is a third and full saturation magnetization plateaux within the strong
antiferromagnetic rung coupling regime. Gapless and gapped phases appear in
turn as the magnetic field increases. For weak rung coupling, the fractional
magnetization plateau vanishs and exhibits new quantum phase transitions.
However, in the ferromagnetic coupling regime, the system does not have a third
saturation magnetization plat eau. The critical behaviour in the vicinity of
the critical points is also derived systematically using the TBA.",0309267v1
2003-09-18,Magnetization plateaus in frustrated antiferromagnetic quantum spin models,"Plateaus can be observed in the zero-temperature magnetization curve of
quantum spin systems at rational values of the magnetization. In one dimension,
the appearance of a plateau is controlled by a quantization condition for the
magnetization which involves the length of the local spin and the volume of a
translational unit cell of the ground state. We discuss examples of
geometrically frustrated quantum spin systems with large (in general unbounded)
periodicities of spontaneous breaking of translational symmetry in the ground
state.
  In two dimensions, we discuss the square, triangular and Kagome lattices
using exact diagonalization (ED) for up to N=40 sites. For the spin-1/2 XXZ
model on the triangular lattice we study the nature and stability region of a
plateau at one third of the saturation magnetization. The Kagome lattice gives
rise to particularly rich behaviour with several plateaus in the magnetization
curve and a jump due to local magnon excitations just below saturation.",0309425v2
2004-01-16,Observation of a Transient Magnetization Plateau in a Quantum Antiferromagnet on the Kagome Lattice,"The magnetization process of an S=1/2 antiferromagnet on the kagome lattice,
[Cu_3(titmb)_2(OCOCH_3)_6]H_2O {titmb= 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6
trimethylbenzene} has been measured at very low temperatures in both pulsed and
steady fields. We have found a new dynamical behavior in the magnetization
process: a plateau at one third of the saturation magnetization appears in the
pulsed field experiments for intermediate sweep rates of the magnetic field and
disappears in the steady field experiments. A theoretical analysis using exact
diagonalization yields J_1=-19K and J_2=6K, for the nearest neighbor and second
nearest neighbor interactions, respectively. This set of exchange parameters
explains the very low saturation field and the absence of the plateau in the
thermodynamic equilibrium as well as the two-peak feature in the magnetic heat
capacity. Supported by numerical results we argue that a dynamical order by
disorder phenomenon could explain the transient appearance of the 1/3 plateau
in pulsed field experiments.",0401288v2
2006-03-29,A new type of bound magnetic polaron state: the formation of long-range spin distortions,"The structure of bound magnetic polarons in an antiferromagnetic matrix is
studied in the framework of two-dimensional (2D) and three-dimensional (3D)
Kondo-lattice models in the double exchange limit (J_H >> t). The conduction
electron is bound by a nonmagnetic donor impurity and forms a ferromagnetic
core of the size about the electron localization length (bound magnetic
polaron). We find that the magnetic polaron produces rather long-range extended
spin distortions of the antiferromagnetic background around the core. In a wide
range of distances, these distortions decay as 1/r^2 and 1/r^4 in 2D and 3D
cases, respectively. In addition, the magnetization of the core is smaller than
its saturation value. Such a magnetic polaron state is favorable in energy in
comparison to usually considered one (saturated core without extended
distortions).",0603798v2
2007-01-12,Fully developed turbulent dynamo at low magnetic Prandtl numbers,"We investigate the dynamo problem in the limit of small magnetic Prandtl
number ($\Pm$) using a shell model of magnetohydrodynamic turbulence. The model
is designed to satisfy conservation laws of total energy, cross helicity and
magnetic helicity in the limit of inviscid fluid and null magnetic diffusivity.
The forcing is chosen to have a constant injection rate of energy and no
injection of kinetic helicity nor cross helicity. We find that the value of the
critical magnetic Reynolds number ($\Rm$) saturates in the limit of small
$\Pm$. Above the dynamo threshold we study the saturated regime versus $\Rm$
and $\Pm$. In the case of equipartition, we find Kolmogorov spectra for both
kinetic and magnetic energy except for wave numbers just below the resistive
scale. Finally the ratio of both dissipation scales (viscous to resistive)
evolves as $\Pm^{-3/4}$ for $\Pm < 1$",0701152v1
2012-07-24,Colossal non-saturating linear magnetoresistance in two-dimensional electron systems at a GaAs/AlGaAs heterointerface,"Engineering devices with a large electrical response to magnetic field is of
fundamental importance for a range of applications such as magnetic field
sensing and magnetic read-heads. We show that a colossal non-saturating linear
magnetoresistance (NLMR) arises in two-dimensional electron systems hosted in a
GaAs/AlGaAs heterostructure in the strongly insulating regime. When operated at
high source-drain bias, the magnetoresistance of our devices increases almost
linearly with magnetic field reaching nearly 10,000% at 8 Tesla, thus
surpassing many known non-magnetic materials that exhibit giant NLMR. The
temperature dependence and mobility analysis indicate that the NLMR has a
purely classical origin, driven by nanoscale inhomogeneities. A large NLMR
combined with small device dimensions makes these systems a new and attractive
candidate for on-chip magnetic field sensing.",1207.5709v2
2013-02-20,Periodic magnetization structures generated by transverse spin-current in magnetic nanowires,"Magnetization behavior of long nanowires with square cross-section under
influence of strong perpendicular spin-polarized current is studied
theoretically. The study is based on Landau-Lifshitz-Slonczewski phenomenology.
In the no current case the wire is magnetized uniformly along its axis. For
small currents the wire magnetization remains uniform but it inclines with
respect to the wire axis within the plane perpendicular to the current
direction. With the current increasing the inclination angle increases up to
the maximum value $\pi/4$. Further current increase leads either to saturation
or to stable periodic multidomain structure depending on the wire thickness.
For thick wires a hysteresis is observed in the saturation process under the
action of current. All critical parameters of the current induced magnetization
behavior are determined theoretically. The study is carried out both
analytically and using micromagnetic simulations.",1302.4899v1
2013-06-18,"Modification in structural, dielectric and magnetic properties of La and Nd co-substituted epitaxial BiFeO3 thin films","The influence of La and Nd co-substitution on the structural and magnetic
properties of BiFeO3 (BFO) thin films was examined. Epitaxial thin films of
pure and, La and Nd co-doped BFO on the SrRuO3 buffered single crystal SrTiO3
(001) substrate were deposited using pulsed laser deposition. The structural
change in co doped La and Nd BFO thin films which was caused by the changes of
force constant in the crystal lattice induced by ionic radii mismatch was
investigated. Raman spectroscopy studies manifest the structural change in
doped BFO films from rhombohedral to monoclinic distorted phase which is
induced by the co substitution of La and Nd. Room temperature magnetic
hysteresis curves indicated that saturation magnetization is enhanced in the
doped film with saturation magnetization of ~20 emu/cm3. The dielectric and
magnetic properties are effectively improved in BLNFO films compared to pure
BFO thin films.",1306.4214v1
2013-12-26,Where is magnetic anisotropy field pointing to?,"The desired result of magnetic anisotropy investigations is the determination
of value(s) of various anisotropy constant(s). This is sometimes difficult,
especially when the precise knowledge of saturation magnetization is required,
as it happens in ferromagnetic resonance (FMR) studies. In such cases we
usually resort to `trick' and fit our experimental data to the quantity called
\emph{anisotropy field}, which is strictly proportional to the ratio of the
searched anisotropy constant and saturation magnetization. Yet, this quantity
is scalar, simply a number, and is therefore of little value for modeling or
simulations of the magnetostatic or micromagnetic structures. Here we show how
to `translate' the values of magnetic anisotropy constants into the complete
vector of magnetic anisotropy field. Our derivation is rigorous and covers the
most often encountered cases, from uniaxial to cubic anisotropy.",1312.7130v1
2020-06-08,Pre-saturation phase in the frustrated ferro-antiferromagnet Pb$_2$VO(PO$_4$)$_2$,"Magnetization, magnetic torque, neutron diffraction and NMR experiments are
used to map out the $H$$-$$T$ phase diagram of the prototypical
quasi-two-dimensional ferro-antiferromagnet Pb$_2$VO(PO$_4$)$_2$ in magnetic
fields up to 27 T. When the field is applied perpendicular to the axis of
magnetic anisotropy, a new magnetic state emerges through a discontinuous
transition and persists in a narrow field range just below saturation. The
measured NMR spectra suggest a complex and possibly incommensurate magnetic
order in that regime.",2006.04592v1
2021-04-16,Magnetic field amplification by a nonlinear electron streaming instability,"Magnetic field amplification by relativistic streaming plasma instabilities
is central to a wide variety of high-energy astrophysical environments as well
as to laboratory scenarios associated with intense lasers and electron beams.
We report on a new secondary nonlinear instability which arises for
relativistic dilute electron beams after the saturation of the linear Weibel
instability. This instability grows due to the transverse magnetic pressure
associated with the beam current filaments, which cannot be quickly neutralized
due to the inertia of background ions. We show that it can amplify the magnetic
field strength and spatial scale by orders of magnitude, leading to large-scale
plasma cavities with strong magnetic field and to very efficient conversion of
the beam kinetic energy into magnetic energy. The instability growth rate,
saturation level, and scale length are derived analytically and shown to be in
good agreement with fully-kinetic simulations.",2104.08246v1
2022-01-27,Simultaneous measurement of the exchange parameter and saturation magnetization using propagating spin waves,"The exchange interaction in ferromagnetic ultra-thin films is a critical
parameter in magnetization-based storage and logic devices, yet the accurate
measurement of it remains a challenge. While a variety of approaches are
currently used to determine the exchange parameter, each has its limitations,
and good agreement among them has not been achieved. To date, neutron
scattering, magnetometry, Brillouin light scattering, spin-torque ferromagnetic
resonance spectroscopy, and Kerr microscopy have all been used to determine the
exchange parameter. Here we present a novel method that exploits the wavevector
selectivity of Brillouin light scattering to measure the spin wave dispersion
in both the backward volume and Damon-Eshbach orientations. The exchange,
saturation magnetization, and magnetic thickness are then determined by a
simultaneous fit of both dispersion branches with general spin wave theory
without any prior knowledge of the thickness of a magnetic ""dead layer"". In
this work, we demonstrate the strength of this technique for ultrathin metallic
films, typical of those commonly used in industrial applications for magnetic
random-access memory.",2201.11270v1
2022-05-03,Robustness of binary stochastic neurons implemented with low barrier nanomagnets made of dilute magnetic semiconductors,"Binary stochastic neurons (BSNs) are excellent hardware accelerators for
machine learning. A popular platform for implementing them are low- or
zero-energy barrier nanomagnets possessing in-plane magnetic anisotropy (e.g.
circular disks or quasi-elliptical disks with very small eccentricity).
Unfortunately, small geometric variations in the lateral shapes of such
nanomagnets can produce large changes in the BSN response times if the
nanomagnets are made of common metallic ferromagnets (Co, Ni, Fe) with large
saturation magnetization. Additionally, the response times are also very
sensitive to initial conditions. Here, we show that if the nanomagnets are made
of dilute magnetic semiconductors with much smaller saturation magnetization,
then the variability in their response times (due to shape variations and
variation in the initial condition) is drastically suppressed. This
significantly reduces the device-to-device variation, which is a serious
challenge for large scale neuromorphic systems.",2205.01793v1
2022-08-19,Modulation of magnetic property of double-perovskite La2MnCoO6 films by controlling B-antisite disorder,"The predicted physical properties of double perovskites have usually been
compromised by their intrinsic B-antisite (AS) disorder effect, but the
relationship between them is still unclear for the La2MnCoO6 (LMCO) system.
This study focuses on controlling the AS disorder and quantitatively reveals
correlations with magnetic and electronic states in epitaxial LMCO films grown
on (111) SrTiO3 substrates. The AS fraction was precisely controlled by tuning
the growth conditions as evaluated from saturation magnetization and x-ray
reflection profiles. The saturation magnetization at 5 K decreased linearly
from 6 uB per formula unit by 50% as the AS fraction increased from 0
(perfectly ordered) to 0.5 (fully disordered). The x-ray absorption
spectroscopy revealed that valence states of Mn and Co were 4+ (3d^3) and 2+
(3d^7), respectively, regardless of AS fraction. A local-spin-moment model is
proposed to explain the net magnetizations with and without AS disorder and
Mn/Co valence states, suggesting that only the rearrangement of local spin
moment of Co at the antisite plays a key role in tuning the magnetism in this
LMCO system.",2208.09166v1
2023-07-10,Increasing Flips per Second and Speed of p-Computers by Using Dilute Magnetic Semiconductors to Implement Binary Stochastic Neurons,"Probabilistic computing with binary stochastic neurons (BSN) implemented with
low- or zero-energy barrier nanoscale ferromagnets (LBMs) possessing in-plane
magnetic anisotropy has emerged as an efficient paradigm for solving
computationally hard problems. The fluctuating magnetization of an LBM at room
temperature encodes a p-bit which is the building block of a BSN. Its only
drawback is that the dynamics of common (transition metal) ferromagnets are
relatively slow and hence the number of uncorrelated p-bits that can be
generated per second - the so-called ""flips per second"" (fps) - is
insufficient, leading to slow computational speed in autonomous co-processing
with p-computers. Here, we show that a simple way to increase fps is to replace
commonly used ferromagnets (e.g. Co, Fe, Ni), which have large saturation
magnetization Ms, with a dilute magnetic semiconductor like GaMnAs with much
smaller saturation magnetization. The smaller Ms reduces the energy barrier
within the LBM and increases the fps significantly. It also offers other
benefits such as increased packing density for increased parallelization and
reduced device to device variation. This provides a way to realize the hardware
acceleration and energy efficiency promise of p-computers.",2307.04663v1
2023-08-15,"Reflective, polarizing, and magnetically soft amorphous Fe/Si multilayer neutron optics with isotope-enriched 11B4C inducing atomically flat interfaces","The utilization of polarized neutrons is of great importance in scientific
disciplines spanning materials science, physics, biology, and chemistry.
Polarization analysis offers insights into otherwise unattainable sample
information such as magnetic domains and structures, protein crystallography,
composition, orientation, ion-diffusion mechanisms, and relative location of
molecules in multicomponent biological systems. State-of-the-art multilayer
polarizing neutron optics have limitations, particularly low specular
reflectivity and polarization at higher scattering vectors/angles, and the
requirement of high external magnetic fields to saturate the polarizer
magnetization. Here, we show that by incorporating 11B4C into Fe/Si
multilayers, amorphization and smooth interfaces can be achieved, yielding
higher neutron reflectivity, less diffuse scattering and higher polarization.
Magnetic coercivity is eliminated, and magnetic saturation can be reached at
low external fields (>2 mT). This approach offers prospects for significant
improvement in polarizing neutron optics, enabling; nonintrusive positioning of
the polarizer, enhanced flux, increased data accuracy, and further
polarizing/analyzing methods at neutron scattering facilities.",2308.07630v1
2023-11-13,Translational symmetry broken magnetization plateau of the S=1 antiferromagnetic Heisenberg chain with competing anisotropies,"We investigate the S=1 antiferromagnetic quantum spin chain with the exchange
and single-ion anisotropies in a magnetic field, using the numerical exact
diagonalization of finite-size clusters, the level spectroscopy analysis, and
the density matrix renormalization group (DMRG) method. It is found that a
translational symmetry broken magnetization plateau possibly appears at the
half of the saturation magnetization, when the anisotropies compete with each
other. The level spectroscopy analysis gives the phase diagram at half the
saturation magnetization. The DMRG calculation presents the magnetization
curves for some typical parameters and clarifies the spin structure in the
plateau phase.",2311.07123v1
2023-12-15,Hyperbolic Bloch points in ferrimagnetic exchange spring,"Bloch points in magnetic materials are attractive entities in view of
magnetic information transport. Here, Bloch point configuration has been
investigated and experimentally determined in a magnetic trilayer
($Gd_{12}Co_{88}/Nd_{17}Co_{83}/Gd_{24}Co_{76}$) with carefully adjusted
composition within the ferrimagnetic $Gd_{x}Co_{1-x}$ alloys in order to
engineer saturation magnetization, exchange length, and interlayer couplings
(ferromagnetic vs antiferromagnetic). X-ray vector magnetic tomography has
allowed us to determine experimentally Bloch point polarity (related to
topological charge) and Bloch point helicity ${\gamma}$ (determined by
magnetostatic energy). At the bottom layer (close to the ferromagnetic
interface), Bloch points adopt a standard circulating configuration with
helicity ${\gamma}$ close to ${\pi}/2$. Within the top layer (with much lower
saturation magnetization), Bloch points nucleate within a Neel-like exchange
spring domain wall created by the antiferromagnetic coupling and adopt an
uncommon hyperbolic configuration, characterized by much larger helicity
angles. Our results indicate a path for Bloch point engineering in future
applications adjusting material parameters and domain wall characteristics.",2312.09836v1
2014-01-31,Understanding nonlinear saturation in zonal-flow-dominated ion temperature gradient turbulence,"We propose a quantitative model of ion temperature gradient driven turbulence
in toroidal magnetized plasmas. In this model, the turbulence is regulated by
zonal flows, i.e. mode saturation occurs by a zonal-flow-mediated energy
cascade (""shearing""), and zonal flow amplitude is controlled by nonlinear
decay. Our model is tested in detail against numerical simulations to confirm
that both its assumptions and predictions are satisfied. Key results include
(1) a sensitivity of the nonlinear zonal flow response to the energy content of
the linear instability, (2) a persistence of zonal-flow-regulated saturation at
high temperature gradients, (3) a physical explanation of the nonlinear
saturation process in terms of secondary and tertiary instabilities, and (4)
dependence of heat flux in terms of dimensionless parameters.",1401.8140v3
2016-12-09,Bulk Saturable absorption in Topological Insulator thin Films,"We present nonlinear optical absorption properties of pulsed laser deposited
thin films of topological insulator (TI), Bi2Se3 on quartz substrate, using
open aperture Z - scan technique. The saturable intensity of as-deposited thin
films has been found remarkably improved by an order of magnitude compared to
the values reported earlier in the literature. Past results from the literature
are inconclusive in establishing whether the saturable absorption is coming
from surface states or the bulk. Specifically designed experiments with
magnetically doped TI samples allow us to attribute the saturable absorption
characteristic of TI to the bulk states. Detailed experimental procedures and
possible explanation of observed results have been discussed.",1612.02977v1
2017-07-17,Finite-temperature correlations in a quantum spin chain near saturation,"Inelastic neutron-scattering and finite-temperature density matrix
renormalization group (DMRG) calculations are used to investigate the spin
excitation spectrum of the $S=1/2$ Heisenberg spin chain compound
K$_2$CuSO$_4$Cl$_2$ at several temperatures in a magnetic field near
saturation. Critical correlations characteristic of the predicted $z=2$, $d=1$
quantum phase transition occurring at saturation are shown to be consistent
with the observed neutron spectra. The data is well described with a scaling
function computed using a free fermion description of the spins, valid close to
saturation, and the corresponding scaling limits. One of the most prominent
non-universal spectral features of the data is a novel thermally activated
longitudinal mode that remains underdamped across most of the Brillouin zone.",1707.05243v2
2019-11-04,Effect of the electron redistribution on the nonlinear saturation of Alfvén eigenmodes and the excitation of zonal flows,"Numerical simulations of Alfv\'en modes (AM) driven by energetic particles
are performed with the GK global PIC code ORB5. A reversed shear equilibrium
magnetic field is adopted. A simplified configuration with circular flux
surfaces and large aspect ratio is considered. The nonlinear saturation of
beta-induced Alfv\'en eigenmodes (BAE) is investigated. The roles of the
wave-particle nonlinearity of the different species, i.e. thermal ions,
electrons, and energetic ions are described, in particular for their role in
the saturation of the BAE and the generation of zonal flows. The nonlinear
redistribution of the electron population is found to be important in
increasing the BAE saturation level and the zonal flow amplitude.",1911.01243v1
2022-12-13,Assessing the saturation of Krylov complexity as a measure of chaos,"Krylov complexity is a novel approach to study how an operator spreads over a
specific basis. Recently, it has been stated that this quantity has a long-time
saturation that depends on the amount of chaos in the system. Since this
quantity not only depends on the Hamiltonian but also on the chosen operator,
in this work we study the level of generality of this hypothesis by studying
how the saturation value varies in the integrability to chaos transition when
different operators are expanded. To do this, we work with an Ising chain with
a transverse-longitudinal magnetic field and compare the saturation of the
Krylov complexity with the standard spectral measure of quantum chaos. Our
numerical results show that the usefulness of this quantity as a predictor of
the chaoticity is strongly dependent on the chosen operator.",2212.06619v2
2024-01-14,Axion Detection with Quantum Hall Effect,"Plateau-plateau transition in integer quantum Hall effect is a phase
transition between metal and insulator. The behavior how the width $\Delta B$
of the transition changes with temperature and frequency of radiations imposed
has been explored extensively. It decreases with the decrease of temperature
and frequency, but saturates at critical temperature or frequency. We have
recently discussed the effect of axion dark matter on the saturation. The axion
generates radiations under strong magnetic field in the experiment of quantum
Hall effect. The radiations play a similar role to the one of radiations
imposed externally. In this paper we discuss in detail how the width behaves in
temperature and frequency under the effect of axion dark matter. We show that
the axion effect can be observable in low temperature roughly below $100$mK.
According to our detailed analysis of the saturation, we find that critical
frequency of saturation observed in previous experiment strongly suggests axion
mass $m_a=(0.95\sim 0.99)\times 10^{-5}$eV.",2401.07180v2
1999-11-03,Magnetic properties of submicron Co islands and their use as artificial pinning centers,"We report on the magnetic properties of elongated submicron magnetic islands
and their influence on a superconducting film. The magnetic properties were
studied by magnetization hysteresis loop measurements and scanning-force
microscopy. In the as-grown state, the islands have a magnetic structure
consisting of two antiparallel domains. This stable domain configuration has
been directly visualized as a 2x2-checkerboard pattern by magnetic-force
microscopy. In the remanent state, after magnetic saturation along the easy
axis, all islands have a single-domain structure with the magnetic moment
oriented along the magnetizing field direction. Periodic lattices of these Co
islands act as efficient artificial pinning arrays for the flux lines in a
superconducting Pb film deposited on top of the Co islands. The influence of
the magnetic state of the dots on their pinning efficiency is investigated in
these films, before and after the Co dots are magnetized.",9911034v1
2005-10-21,Magnetostrictive hysteresis of TbCo/CoFe multilayers and magnetic domains,"Magnetic and magnetostrictive hysteresis loops of TbCo/CoFe multilayers under
field applied along the hard magnetization axis are studied using vectorial
magnetization measurements, optical deflectometry and magneto optical Kerr
microscopy. Even a very small angle misalignment between hard axis and magnetic
field direction is shown to drastically change the shape of magnetization and
magnetostrictive torsion hysteresis loops. Two kinds of magnetic domains are
revealed during the magnetization: big regions with opposite rotation of
spontaneous magnetization vector and spontaneous magnetic domains which appear
in a narrow field interval and provide an inversion of this rotation.
  We show that the details of the hysteresis loops of our exchange-coupled
films can be described using the classical model of homogeneous magnetization
rotation of single uniaxial films and the configuration of observed domains.
The understanding of these features is crucial for applications (for MEMS or
microactuators) which benefit from the greatly enhanced sensitivity near the
point of magnetic saturation at the transverse applied field.",0510568v1
2019-04-12,The magnetic structure factor of correlated moments in small-angle neutron scattering,"The interplay between structural and magnetic properties of nanostructured
magnetic materials allows to realize unconventional magnetic effects, which
results in a demand for experimental techniques to determine the magnetization
profile with nanoscale resolution. Magnetic small-angle neutron scattering
(SANS) probes both the chemical and magnetic nanostructure and is thus a
powerful technique e.g. for the characterization of magnetic nanoparticles.
Here, we show that the conventionally used particle-matrix approach to describe
SANS of magnetic particle assemblies, however, leads to a flawed
interpretation. As remedy, we provide general expressions for the
field-dependent 2D magnetic SANS cross-section of correlated moments. It is
shown that for structurally disordered ensembles the magnetic structure factor
is in general, and contrary to common assumptions, (i) anisotropic also in zero
field, and (ii) that even in saturation the magnetic structure factor deviates
from the nuclear one. These theoretical predictions explain qualitatively the
intriguing experimental, polarized SANS data of an ensemble of dipolar-coupled
iron oxide nanoparticles.",1904.06243v3
2021-08-26,Magnetic design study of coil-dominated superconducting quadrupole magnets based on racetrack coils,"Several coil structures have been used in accelerator superconducting
quadrupole magnets, and cos2{\theta} quadrupole magnets are the most mature in
theoretical research and engineering applications. However, the cos2{\theta}
quadrupole magnet has a complicated coil structure, especially at the end of
the coil, which makes it difficult to apply strain-sensitive high-temperature
superconductors. Racetrack quadrupole magnets are friendly to high-temperature
superconductors. Field strength of iron-dominated racetrack magnets is limited
by the magnetic saturation of the iron poles. Therefore, coil-dominated
racetrack quadrupole magnets with simple geometry have become the focus of our
research. In this paper, analytical expressions of the magnetic field harmonics
related to racetrack quadrupole coil parameters are obtained. These expressions
are used to find the solution of coil geometry parameters with field harmonics
on the order of 10-4. Then, examples are given to build ideal quadrupole model
and verify the theoretical formulas. Next, the design and optimization of
example racetrack quadrupole magnets are completed in ROXIE. Finally, the
advantages and disadvantages of the racetrack coils and the cos2{\theta} coils
are compared and discussed.",2108.11643v1
2001-11-29,Magnetic helicity in stellar dynamos: new numerical experiments,"The theory of large scale dynamos is reviewed with particular emphasis on the
magnetic helicity constraint in the presence of closed and open boundaries. In
the presence of closed or periodic boundaries, helical dynamos respond to the
helicity constraint by developing small scale separation in the kinematic
regime, and by showing long time scales in the nonlinear regime where the scale
separation has grown to the maximum possible value. A resistively limited
evolution towards saturation is also found at intermediate scales before the
largest scale of the system is reached. Larger aspect ratios can give rise to
different structures of the mean field which are obtained at early times, but
the final saturation field strength is still decreasing with decreasing
resistivity. In the presence of shear, cyclic magnetic fields are found whose
period is increasing with decreasing resistivity, but the saturation energy of
the mean field is in strong super-equipartition with the turbulent energy. It
is shown that artificially induced losses of small scale field of opposite sign
of magnetic helicity as the large scale field can, at least in principle,
accelerate the production of large scale (poloidal) field. Based on mean field
models with an outer potential field boundary condition in spherical geometry,
we verify that the sign of the magnetic helicity flux from the large scale
field agrees with the sign of alpha. For solar parameters, typical magnetic
helicity fluxes lie around 10^{47} Mx^2 per cycle.",0111567v3
2003-01-22,Understanding Helical Magnetic Dynamo Spectra with a Nonlinear Four-Scale Theory,"Recent MHD dynamo simulations for magnetic Prandtl number $>1$ demonstrate
that when MHD turbulence is forced with sufficient kinetic helicity, the
saturated magnetic energy spectrum evolves from having a single peak below the
forcing scale to become doubly peaked with one peak at the system (=largest)
scale and one at the forcing scale. The system scale field growth is well
modeled by a recent nonlinear two-scale nonlinear helical dynamo theory in
which the system and forcing scales carry magnetic helicity of opposite sign.
But a two-scale theory cannot model the shift of the small-scale peak toward
the forcing scale. Here I develop a four-scale helical dynamo theory which
shows that the small-scale helical magnetic energy first saturates at very
small scales, but then successively saturates at larger values at larger
scales, eventually becoming dominated by the forcing scale. The transfer of the
small scale peak to the forcing scale is completed by the end of the kinematic
growth regime of the large scale field, and does not depend on magnetic
Reynolds number $R_M$ for large $R_M$. The four-scale and two-scale theories
subsequently evolve almost identically, and both show significant field growth
on the system and forcing scales that is independent of $R_M$. In the present
approach, the helical and nonhelical parts of the spectrum are largely
decoupled. Implications for fractionally helical turbulence are discussed.",0301432v2
2010-10-04,Defects induced ferromagnetism in Mn doped ZnO,"Single phase Mn doped (2 at %) ZnO samples have been synthesized by
solid-state reaction technique. Before the final sintering at 500 C, the mixed
powders have been milled for different milling periods (6, 24, 48 and 96
hours). The grain sizes of the samples are very close to each other (~ 32 \pm 4
nm). However, the defective state of the samples is different from each other
as manifested from the variation of magnetic properties and electrical
resistivity with milling time. All the samples have been found to be
ferromagnetic with clear hysteresis loops at room temperature. The maximum
value for saturation magnetization (0.11 {\mu}_B / Mn atom) was achieved for 96
hours milled sample. Electrical resistivity has been found to increase with
increasing milling time. The most resistive sample bears the largest saturation
magnetization. Variation of average positron lifetime with milling time bears a
close similarity with that of the saturation magnetization. This indicates the
key role played by open volume vacancy defects, presumably zinc vacancies near
grain surfaces, in inducing ferromagnetic order in Mn doped ZnO. To attain
optimum defect configuration favorable for ferromagnetism in this kind of
samples proper choice of milling period and annealing conditions is required.",1010.0547v1
2012-11-02,Direct Observation of Giant Saturation Magnetization in Fe16N2,"Magnetic materials with giant saturation magnetization have been a holy grail
for magnetic researchers and condensed matter physicists for decades because of
its great scientific and technological impacts. As described by the famous
Slater-Pauling curve the material with highest Ms is the Fe65Co35 alloy. This
was challenged in 1972 by a report on the compound Fe16N2 with Ms much higher
than that of Fe65Co35. Following this claim, there have been enormous efforts
to reproduce this result and to understand the magnetism of this compound.
However, the reported Ms by different groups cover a broad range, mainly due to
the unavailability of directly assessing Ms in Fe16N2. In this article, we
report a direct observation of the giant saturation magnetization up to 2500
emu/cm3 using polarized neutron reflectometry (PNR) in epitaxial constrained
Fe16N2 thin films prepared using a low-energy and surface-plasma-free
sputtering process. The observed giant Ms is corroborated by a previously
proposed Cluster + Atom model, the characteristic feature of which, namely, the
directional charge transfer is evidenced by polarization-dependent x-ray
absorption near edge spectroscopy (XANES).",1211.0553v1
2012-11-26,Nonlinear Evolution of the Radiation-Driven Magneto-Acoustic Instability (RMI),"We examine the nonlinear development of unstable magnetosonic waves driven by
a background radiative flux -- the Radiation-Driven Magneto-Acoustic
Instability (RMI, a.k.a. the ""photon bubble"" instability). The RMI may serve as
a persistent source of density, radiative flux, and magnetic field fluctuations
in stably-stratified, optically-thick media. The conditions for instability are
present in a variety of astrophysical environments, and do not require the
radiation pressure to dominate or the magnetic field to be strong. Here we
numerically study the saturation properties of the RMI, covering three orders
of magnitude in the relative strength of radiation, magnetic field, and gas
energies. Two-dimensional, time-dependent radiation-MHD simulations of local,
stably-stratified domains are conducted with Zeus-MP in the optically-thick,
highly-conducting limit. Our results confirm the theoretical expectations of
Blaes and Socrates (2003) in that the RMI operates even in gas
pressure-dominated environments that are weakly magnetized. The saturation
amplitude is a monotonically increasing function of the ratio of radiation to
gas pressure. Keeping this ratio constant, we find that the saturation
amplitude peaks when the magnetic pressure is comparable to the radiation
pressure. We discuss the implications of our results for the dynamics of
magnetized stellar envelopes, where the RMI should act as a source of
sub-photospheric perturbations.",1211.6107v2
2017-10-13,Possible quadrupolar nematic phase in the frustrated spin chain LiCuSbO$_4$: an NMR investigation,"The frustrated one-dimensional (1D) quantum magnet LiCuSbO$_4$ is one rare
realization of the $J_1-J_2$ spin chain model with an easily accessible
saturation field, formerly estimated to 12~T. Exotic multipolar nematic phases
were theoretically predicted in such compounds just below the saturation field,
but without unambiguous experimental observation so far. In this paper we
present extensive experimental research of the compound in the wide temperature
(30mK$-$300K) and field (0$-$13.3T) range by muon spin rotation ($\mu$SR),
$^7$Li nuclear magnetic resonance (NMR) and magnetic susceptibility (SQUID).
$\mu$SR experiments in zero magnetic field demonstrate the absence of long
range 3D ordering down to 30mK. Together with former heat capacity data [S.E.
Dutton \emph{et al}, Phys. Rev. Lett. 108, 187206 (2012)], magnetic
susceptibility measurements suggest short range correlated vector chiral phase
in the field range $0-4$T. In the intermediate field values (5$-$12T), the
system enters in a 3D ordered spin density wave phase with 0.75$\mu_B$ per
copper site at lowest temperatures (125mK), estimated by NMR. At still higher
field, the magnetization is found to be saturated above 13T where the spin
lattice $T_1^{-1}$ relaxation reveals a spin gap estimated to 3.2(2)K. We
narrow down the possibility of observing a multipolar nematic phase to the
range 12.5$-$13T.",1710.05004v1
2018-06-14,Selection of axial dipole from a seed magnetic field in rapidly rotating dynamo models,"In this study, we investigate preferences of dipolar magnetic structure from
a seed magnetic field in the rapidly rotating spherical shell dynamo models. In
this study, we set up a realistic model to show the effect of the Lorentz force
in the polarity selection. The important results that has come out from our
study is that the magnetic field acts on the flow much before the saturation.
Our study suggests that the growth of the magnetic field is not a kinematic
effect as one might think off, rather a dynamic effect. This dynamic effect
grows as the field generated with time and finally brings the saturation to the
dynamo action. Previous studies show that Lorentz force effect the flow when
Elsasser number more or less 1 and the studies were focused on the saturation
by looking at the time-averaged quantities. However, in this study, we show a
clear effect of the Lorentz force even at Elsasser number of $0.3-0.4$. To show
the effect of the Lorentz force, we did two different simulations, one is a
nonlinear model and another is kinematic model and shows that how a magnetic
field can change the flow structure and by doing that the generated field
changes, while this kind of behavior is not observed in kinematic dynamo
models. This study shows a scale dependent behaviour of the kinetic helicity at
two different spectral range.",1806.05368v1
2018-12-21,Dynamo saturation down to vanishing viscosity: strong-field and inertial scaling regimes,"We present analytical examples of fluid dynamos that saturate through the
action of the Coriolis and inertial terms of the Navier-Stokes equation. The
flow is driven by a body force and is subject to global rotation and uniform
sweeping velocity. The model can be studied down to arbitrarily low viscosity
and naturally leads to the strong-field scaling regime for the magnetic energy
produced above threshold: the magnetic energy is proportional to the global
rotation rate and independent of the viscosity. Depending on the relative
orientations of global rotation and large-scale sweeping, the dynamo
bifurcation is either supercritical or subcritical. In the supercritical case,
the magnetic energy follows the scaling-law for supercritical strong-field
dynamos predicted on dimensional grounds by Petrelis & Fauve (2001). In the
subcritical case, the system jumps to a finite-amplitude dynamo branch. The
magnetic energy obeys a magneto-geostrophic scaling-law (Roberts & Soward
1972), with a turbulent Elsasser number of the order of unity, where the
magnetic diffusivity of the standard Elsasser number appears to be replaced by
an eddy diffusivity. In the absence of global rotation, the dynamo bifurcation
is subcritical and the saturated magnetic energy obeys the equipartition
scaling regime. We consider both the vicinity of the dynamo threshold and the
limit of large distance from threshold to put these various scaling behaviors
on firm analytical ground.",1812.09166v1
2021-07-23,Wrinkling of soft magneto-active plates,"Coupled magneto-mechanical wrinkling has appeared in many scenarios of
engineering and biology. Hence, soft magneto-active (SMA) plates buckle when
subject to critical uniform magnetic field normal to their wide surface. Here,
we provide a systematic analysis of the wrinkling of SMA plates subject to an
in-plane mechanical load and a transverse magnetic field?. We consider two
loading modes: plane-strain loading and uni-axial loading, and two models of
magneto-sensitive plates: the neo-Hookean ideal magneto-elastic model and the
neo-Hookean magnetization saturation Langevin model. Our analysis relies on the
theory of nonlinear magneto-elasticity and the associated linearized theory for
superimposed perturbations. We derive the Stroh formulation of the governing
equations of wrinkling, and combine it with the surface impedance method to
obtain explicitly the bifurcation equations identifying the onset of symmetric
and antisymmetric wrinkles. We also obtain analytical expressions of
instability in the thin- and thick-plate limits. For thin plates, we make the
link with classical Euler buckling solutions. We also perform an exhaustive
numerical analysis to elucidate the effects of loading mode, load amplitude,
and saturation magnetization on the nonlinear static response and bifurcation
diagrams. We find that antisymmetric wrinkling modes always occur before
symmetric modes. Increasing the pre-compression or heightening the magnetic
field has a destabilizing effect for SMA plates, while the saturation
magnetization enhances their stability. We show that the Euler buckling
solutions are a good approximation to the exact bifurcation curves for thin
plates.",2107.11093v1
2021-10-28,On the Potential of Fourier-Encoded Saturation Transfers for Sensitizing Solid-State Magic-Angle Spinning NMR Experiments,"Chemical exchange saturation transfer (CEST) is widely used for enhancing the
solution NMR signatures of magnetically-dilute spin pools; in particular
species at low concentrations undergoing chemical exchanges with an abundant
spin pool. CEST's main feature involves encoding and then detecting the weak
NMR signals of the magnetically dilute spin pools on a magnetically abundant
spin pool of much easier detection - for instance the protons of H2O. Inspired
by this method, we propose and exemplify a methodology to enhance the
sensitivity of magic-angle spinning (MAS) solid-state NMR spectra. Our proposal
uses the abundant 1H reservoir arising in organic solids as the magnetically
abundant spin pool, and relies on proton spin diffusion in lieu of chemical
exchange to mediate polarization transfer between a magnetically dilute spin
pool and this magnetically abundant spin reporter. As an initial test of this
idea we target the spectroscopy of naturally-abundant 13C, and rely on a
Fourier-encoded version of the CEST experiment for achieving broadbandness in
coordination with both MAS and heteronuclear decoupling - features normally
absent in CEST. Arbitrary evolutions of multiple 13C sites can thus be
imprinted on the entire 1H reservoir, which is subsequently detected.
Theoretical predictions suggest that orders-of-magnitude signal enhancements
should be achievable in this manner - on the order of the ratio between the 13C
and the 1H reservoirs' abundances. Experiments carried out under magic-angle
spinning conditions evidenced ca. 5-10x enhancements. Further opportunities and
challenges arising in this Fourier-Encoded Saturation Transfer (FEST) MAS NMR
approach are briefly discussed.",2110.15451v1
2001-11-01,The Nonlinear Turbulent Dynamo,"We simulate the evolution of an initially weak magnetic field in forced
turbulence for a range of Prandtl numbers. The field grows exponentially with
the Kulsrud-Anderson $k^{3/2}$ spectrum until the magnetic energy approaches
the viscous-scale kinetic energy, where the magnetic forces then backreact on
the velocity. Further growth proceeds more slowly until a saturated state is
reached where the magnetic and kinetic energies are equal, and where the
magnetic energy exists primarily at the resistive scale. We discuss the
structure of this turbulence and the extrapolation of the results to
astrophysically-large Prandtl numbers.",0111008v1
2002-09-02,Pauli Paramagnetism of Neutron Star Matter and the Upper Limit for Neutron Star Magnetic Fields,"A relativistic version of Pauli paramagnetism for $n-p-e$ system inside a
strongly magnetized neutron star has been developed. An analytical expressions
for the saturation value of magnetic field strength for each of these
constituents at which they are completely polarized have been obtained. From
the fully polarized configuration of electronic component, an upper limit for
neutron star magnetic field is predicted. It has been concluded that indeed,
magnetars, as stronly magnetized young neutron stars can not exist if the
constituents are electron, proton and neutron in $\beta$-equilibrium. An
alternative model has been proposed.",0209015v1
1999-08-17,Fluctuation-driven insulator-to-metal transition in an external magnetic field,"We consider a model for a metal-insulator transition of correlated electrons
in an external magnetic field. We find a broad region in interaction and
magnetic field where metallic and insulating (fully magnetized) solutions
coexist and the system undergoes a first-order metal-insulator transition. A
global instability of the magnetically saturated solution precedes the local
ones and is caused by collective fluctuations due to poles in electron-hole
vertex functions.",9908241v1
2000-02-08,Magnetic properties of frustrated spin ladder,"The magnetic properties of the antiferromagnetic spin ladder with the
next-nearest neighbor interaction, particularly under external field, are
investigated by the exact diagonalization of the finite clusters and size
scaling techniques. It is found that there exist two phases, the rung-dimer and
rung-triplet phases, not only in the nonmagnetic ground state but also
magnetized one, where the phase boundary has a small magnetization dependence.
Only in the former phase, the magnetization curve is revealed to have a
possible plateau at half the saturation moment, with a sufficient frustration.",0002113v1
2001-05-07,Magnetoresistance of single-domain ferromagnetic particles,"We have performed magnetoresistance measurements on single-domain, submicron
elliptical Ni particles using nonmagnetic probes in a four probe geometry at
liquid helium temperatures. In the smallest particles, the magnetoresistance
shows sharp jumps which are associated with the switching of individual
domains. Using an anisotropic magnetoresistance model, we can reconstruct
hysteresis loops of the normalized magnetization. The remanent magnetization in
zero applied magnetic field is typically 15 percent less than the saturation
magnetization. This relaxation of the magnetization may be due to surface
effects or crystal grain structure in the particles.",0105144v1
2001-08-31,Magnetization Plateau in the S=1 Spin Ladder with Competing Interactions,"Very recently a non-trivial magnetization plateau at 1/4 of the saturation
magnetization was observed in the S=1 spin ladder BIP-TENO. In our previous
work we proposed a possible mechanism of the plateau based on the second- and
third-neighbor exchange couplings which lead to frustration. In order to
confirm the realization of the mechanism, we compare the temperature dependence
of the magnetic susceptibility and some critical magnetic fields obtained by
the numerical calculation for the proposed model with the experimental results.",0108527v1
2003-04-07,Magnetic excitations in the quantum spin system NH4CuCl3,"NH4CuCl3 has two magnetization plateaus at one-quarter and three-quarters of
the saturation magnetization, irrespective of the external field direction.
Magnetic excitations in NH4CuCl3 have been investigated by means of neutron
inelastic scattering experiments. The constant-Q energy scan profiles were
collected in a*-c* plane. Two well-defined magnetic excitations were observed.
The dispersion relations along four different directions were determined. Both
excitations are found weakly dispersive. The results were compared with those
obtained from the ESR measurements.",0304172v1
2003-04-24,Microscopic model for the magnetization plateaus in NH4CuCl3,"A simple model consisting of three distinct dimer sublattices is proposed to
describe the magnetism of NH4CuCl3. It explains the occurrence of magnetization
plateaus only at 1/4 and 3/4 of the saturation magnetization. The field
dependence of the excitation modes observed by ESR measurements is also
explained by the model. The model predicts that the magnetization plateaus
should disappear under high pressure.",0304547v2
2004-02-23,Dynamo mechanism: Effects of correlations and viscosities,"We analyze the effects of the background velocity and the initial magnetic
field correlations, and viscosities on the turbulent dynamo and the
\alpha-effect. We calculate the \alpha-coefficients for arbitrary magnetic and
fluid viscosities, background velocity and the initial magnetic field
correlations. We explicitly demonstrate that the general features of the
initial growth and late-time saturation of the magnetic fields due to the
non-linear feedback are qualitatively independent of these correlations. We
also examine the hydrodynamic limit of the magnetic field growth in a
renormalization group framework and discuss the possibilities of suppression of
the dynamo growth below a critical rotation. We demonstrate that for
Kolmogorov- (K41) type of spectra the Ekman number M >1/2 for dynamo growth to
occur.",0402567v1
2004-05-22,"Oxygen stoichiometry, crystal structure, and magnetism in La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$","We have prepared a series of polycrystalline samples
La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$} with $0 < \delta \le 0.21$ and
characterized their oxygen content, crystal structure, and magnetic properties.
While the fully oxygenated samples are good ferromagnets, samples with larger
$\delta$ values display increasingly broad magnetic transitions. The saturation
magnetization at 5 K falls rapidly as $\delta$ increases. First principles
electronic structure calculations provide insights into the magnetic behavior
of the fully oxygenated compound, and the manner in which ferromagnetic
ordering is affected by increasing oxygen non-stoichiometry.",0405535v2
2005-11-03,Step-like magnetization in a spin-chain system: Ca3Co2O6,"Due to a ferromagnetic in-chain coupling between Co$^{3+}$ ions at trigonal
sites, chains Co$_2$O$_6$ are considered as large rigid spin moments. The
antiferromagnetic Ising model on the triangular lattice is applied to describe
an interchain ordering. An evolution of metastable states in a sweeping
magnetic field is investigated by the single-flip technique. At the first
approximation two steps in the magnetization curve and a plateau at 1/3 of the
saturation magnetization are found. Four steps in magnetization are determined
in high-order approximations in agreement with experimental results.",0511087v1
2006-10-09,The Icosahedral Symmetry Antiferromagnetic Heisenberg Model,"The antiferromagnetic Heisenberg model on icosahedral symmetry $I_{h}$
fullerene clusters exhibits unconventional magnetic properties, despite the
lack of anisotropic interactions. At the classical level, and for number of
sites $n \leq 720$, the magnetization has two discontinuities in an external
magnetic field, except from the dodecahedron where it has three, emphasizing
the role of frustration introduced by the pentagons in the unusual magnetic
properties. For spin magnitudes $s_{i}={1/2}$ there is a discontinuity of
quantum character close to saturation for $n \leq 80$. This common magnetic
behavior indicates that it is a generic feature of $I_{h}$ fullerene clusters,
irrespectively of $n$.",0610218v1
2007-11-21,Anomalous Hall effect in a two dimensional electron gas with magnetic impurities,"Magnetic impurities play an important role in many spintronics-related
materials. Motivated by this fact, we study the anomalous Hall effect in the
presence of magnetic impurities, focusing on two-dimensional electron systems
with Rashba spin-orbit coupling. We find a highly nonlinear dependence on the
impurity polarization, including possible sign changes. At small impurity
magnetizations, this is a consequence of the remarkable result that the linear
term is independent of the spin-orbit coupling strength. Near saturation of the
impurity spins, the anomalous Hall conductivity can be resonantly enhanced, due
to interference between potential and magnetic scattering.",0711.3415v1
2008-06-24,Reduction of velocity fluctuations in a turbulent flow of gallium by an external magnetic field,"The magnetic field of planets or stars is generated by the motion of a
conducting fluid through a dynamo instability. The saturation of the magnetic
field occurs through the reaction of the Lorentz force on the flow. In relation
to this phenomenon, we study the effect of a magnetic field on a turbulent flow
of liquid Gallium. The measurement of electric potential differences provides a
signal related to the local velocity fluctuations. We observe a reduction of
velocity fluctuations at all frequencies in the spectrum when the magnetic
field is increased.",0806.3872v1
2008-08-28,Inhomogeneous ferrimagnetic-like behavior in Gd2/3Ca1/3MnO3 single crystals,"We present a study of the magnetic properties of Gd2/3Ca1/3MnO3 single
crystals at low temperatures. We show that this material behave as an
inhomogeneous ferrimagnet. In addition to small saturation magnetization at 5
K, we have found history dependent effects in the magnetization and the
presence of exchange bias. These features are compatible with microscopic phase
separation in the clean Gd2/3Ca1/3MnO3 system studied.",0808.3922v1
2009-04-20,Magnetization of the Shastry-Sutherland antiferromagnet near the Ising limit,"Motivated by recent experiments on TmB4 (arXiv:0712.1537), we examine the
phase diagram of the Shastry-Sutherland antiferromagnet in an applied magnetic
field in the limit of strong Ising anisotropy. In classical Ising limit, we
demonstrate that the only fractional magnetization plateau is at 1/3 of the
saturated magnetization. We study the perturbative influence of transverse
quantum spin fluctuations, and present evidence that they can stabilize a
narrow 1/2 magnetization plateau.",0904.3018v1
2009-10-19,Magnetic bubbles in FePd thin films near saturation,"The structure of domain walls delimiting magnetic bubbles in L10 FePd thin
layers is described on the basis of Lorentz transmission electron microscopy
(LTEM) and multiscale magnetic simulations. Images obtained by high resolution
LTEM show the existence of magnetization reversal areas inside domain walls,
called vertical Bloch lines (VBLs). Combining these observations and multiscale
simulations on various geometries, we can identify the structure of these VBLs,
notably the presence or not of magnetic singularities.",0910.3551v1
2011-05-20,Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet Ba$_3$NiSb$_2$O$_9$,"We report the results of magnetization and specific heat measurements on
Ba$_3$NiSb$_2$O$_9$, which is a quasi-two-dimensional spin-1 triangular-lattice
antiferromagnet. We observed a nonclassical magnetization plateau at one-third
of the saturation magnetization that is driven by spin frustration and quantum
fluctuation. Exact diagonalization for a 21-site rhombic cluster was performed
to analyze the magnetization process. Experimental and calculated results agree
well.",1105.4046v2
2011-06-10,Stress controlled magnetic properties of Cobalt nanowires,"We investigate the magnetic properties of a composite comprising of
ferromagnetic Cobalt nanowires embedded in nanoporous anodized alumina
template. We observe unusual increase in, the saturation magnetization and the
coercive field, of the nanowires below 100 K. We also report the appearance of
an unusual exchange bias effect in nanowires below 100 K. We argue our results
can be understood on the basis of a competition between different magnetic
energy scales induced by significant stresses acting on the nanowires at low
temperatures. The composite behaves as an effective medium in which the
magnetic anisotropy of nanowires can be conveniently controlled via stress on
the nanowires.",1106.1965v1
2011-10-10,Low-Temperature Magnetization Relaxation in Magnetic Molecular Solids,"The low temperature relaxation of the magnetization in magnetic molecular
solids such as Fe$_8$ is studied using Monte Carlo simulations. A set of rate
equations is developed to understand the simulations, and the results are
compared. The simulations show that the magnetization of an initially saturated
samples deviates as a square-root in time at short times, as observed
experimentally, and this law is derived from the rate equations analytically.",1110.1899v1
2012-12-17,Quantum Anomalous Hall Effect in Kagome Ice,"An anomalous Hall insulator without magnetic long-range ordering is
theoretically reported in the absence of the relativistic spin-orbit coupling.
It is realized in itinerant electrons coupled with the Ising spins on a <111>
kagome plane of pyrochlore spin ice in applied magnetic field. We find that the
kagome-ice type local spin correlation in the magnetization plateau state opens
a charge gap without magnetic ordering, which results in quantization of the
Hall conductivity. By Monte Carlo simulation, we identify the anomalous Hall
insulating region in the magnetic phase diagram, in addition to another
anomalous Hall insulator in a fully-saturated state.",1212.3855v1
2013-10-01,Magnetization plateaus in generalized Shastry-Sutherland models,"We study an anisotropic Heisenberg antiferromagnet with ferromagnetic
transverse spin exchange using exact quantum Monte Carlo methods. Such a model
is relevant to a class of rare earth tetraboride materials that display a range
of magnetization plateaus under applied magnetic field. The layered arrangement
of magnetic ions in these materials is topologically equivalent to the
Shastry-Sutherland lattice. In this frustrated geometry, we study the interplay
of next-nearest neighbor interactions in stabilizing a plateau at half the
saturation magnetization (or 1/2 plateau). We also show hysteresis-like
behavior at the onset of the 1/3 plateau.",1310.0135v1
2014-03-05,Magnetized strange quark matter in a mass-density-dependent model,"We investigate the properties of strange quark matter in a strong magnetic
field with quark confinement by the density dependence of quark mass
considering the total baryon number conservation, charge neutrality and
chemical equilibrium. The strength of the magnetic field considered in this
article is $10^{16} \sim 10^{20}$ G. It is found that an additional term should
appear in the pressure expression to maintain thermodynamic consistency. At
fixed density, the energy density of magnetized strange quark matter varies
with the magnetic field strength. The exists a minimum with increasing the
field strength, depending on the density. It is about $6\times10^{19}$ Gauss at
two times the normal nuclear saturation density.",1403.1143v1
2014-03-14,Magnetic Phases and Specific Heat of Ultra-Thin Holmium Films,"We report model calculations of the magnetic phases of very thin Ho films in
the temperature interval between 20K and 132K, and show that slab size, surface
effects and magnetic field due to spin ordering may impact significantly the
magnetic phase diagram. There is a relevant reduction of the external field
strength required to saturate the magnetization and for ultra-thin films the
helical state does not form. We explore the heat capacity and the
susceptibility as auxiliary tools to discuss the nature of the phase
transitions.",1403.3589v1
2014-06-04,Magnetization plateaus of an exactly solvable spin-1 Ising-Heisenberg diamond chain,"The spin-1 Ising-Heisenberg diamond chain in a magnetic field is exactly
solved by a rigorous treatment based on the transfer-matrix method. An exact
ground-state phase diagram includes in total three unconventional quantum
ground states with a quantum entanglement of the decorating spin-1 Heisenberg
dimers apart from two ground states with a classical spin arrangement. It is
evidenced that all three values of the magnetization allowed for the spin-1
diamond chain without translationally broken symmetry by the
Oshikawa-Yamanaka-Affleck criterion can become evident in an outstanding
stepwise magnetization curve with three intermediate plateaus at zero,
one-third, and two-thirds of the saturation magnetization.",1406.0999v1
2014-06-10,Spontaneous chiral symmetry breaking on a fully polarized frustrated magnet at finite temperature,"Frustration can introduce more-than-two minima in a spin dispersion relation
even in a fully polarized magnet under high magnetic field. We generally
discuss, on the fully polarized phase, the possibility of the chiral symmetry
breaking where the number of magnons pumped by finite temperature deviates to
one side of minima. We study this phase by constructing the Ginzburg-Landau
energy which is controlled by the external magnetic field and interactions
between magnons near the dispersion minima. This chirality breaking phase
accompanies, not a magnetization perpendicular to the external field, but the
vector chirality $S_m \times S_n$. We also discuss the possibility of the
chirality breaking phase on LiCuVO4 slightly above the saturation field.",1406.2617v1
2015-05-20,Dipolar spin-misalignment correlations in inhomogeneous magnets: comparison between neutron scattering and micromagnetic approaches,"In inhomogeneous bulk ferromagnets, the dominating sources of spin disorder
are related to spatial variations of (i) the magnitude of the local saturation
magnetization and of (ii) the magnitude and/or direction of the magnetic
anisotropy field. For the particular example of a porous ferromagnet, where the
magnetization inhomogeneity is at maximum, we demonstrate, by means of
experimental neutron scattering data and micromagnetic simulations, the
anisotropic character of magnetization fluctuations induced by the dipolar
interaction.",1505.05337v1
2016-02-26,Microscopic mechanism of the giant magnetocaloric effect in MnCoGe alloys probed by XMCD,"One important aspect of the magneto-structural transition in MnCoGe and
related materials is the reduction in saturation magnetization from the
orthorhombic to the hexagonal phase. Here, by combining an element specific
magnetization probe such as x-ray magnetic circular dichroism and band
structure calculations, we show that the magnetic moment instability between
orthorhombic and hexagonal structures originates from a reduction in the Mn
sub-lattice magnetization. The consequences of the moment instability for the
magnetocaloric effect are discussed.",1602.08263v1
2017-04-05,Magnetization process in a frustrated plaquette dimerized ladder,"The magnetic phase diagram of a plaquette dimerized antiferromagnetic system
is studied by using a combination of numerical and analytical techniques. For
the strongly frustrated regime, series expansions and bond operators techniques
are employed to analyze zero magnetization plateau, whereas low energy
effective models are used to study the complete magnetization process. The
interplay between frustration and dimerization gives rise to a rich plateaus
structure that is captured by effective models and corroborated by numerical
density matrix renormalization group simulations, in particular the emergence
of intermediate plateaus at M = 1/4 and 3/4 of saturation in the magnetization
curve.",1704.01588v1
2017-08-24,Magnetization Process of the Spin-1/2 Triangular-Lattice Heisenberg Antiferromagnet with Next-Nearest-Neighbor Interactions -- Plateau or Nonplateau,"An $S=1/2$ triangular-lattice Heisenberg antiferromagnet with
next-nearest-neighbor interactions is investigated under a magnetic field by
the numerical-diagonalization method. It is known that, in both cases of weak
and strong next-nearest-neighbor interactions, this system reveals a
magnetization plateau at one-third of the saturated magnetization. We examine
the stability of this magnetization plateau when the amplitude of
next-nearest-neighbor interactions is varied. We find that a nonplateau region
appears between the plateau phases in the cases of weak and strong
next-nearest-neighbor interactions.",1708.07248v1
2019-02-01,Accurate Taylor transfer maps for large aperture iron dominated magnets used in charged particle separators and spectrometers,"For high-resolution separators like the projected Super-FRS at FAIR, an
adapted and accurate ion-optical model considering realistic B-dependent magnet
parameters is crucial in achieving the desired parameters (e.g. resolution) and
to enable a fast optimization. Starting from the magnetic field measurements
and simulations, rigidity-dependent Taylor transfer maps are generated for the
Super-FRS preseparator dipole magnets. The effects of the magnetic saturation
in the steel yoke on the image aberrations are analyzed.",1902.00464v1
2020-01-31,Electric field control of interfacial Dzyaloshinskii-Moriya interaction in Pt/Co/AlO$_x$ thin films,"We studied electric field modification of magnetic properties in a
Pt/Co/AlO$_x$ trilayer via magneto-optical Kerr microscopy. We observed the
spontaneous formation of labyrinthine magnetic domain structure due to
thermally activated domain nucleation and propagation under zero applied
magnetic field. A variation of the period of the labyrinthine structure under
electric field is observed as well as saturation magnetization and magnetic
anisotropy variations. Using an analytical formula of the stripe equilibrium
width we estimate the variation of the interfacial Dzyaloshinskii-Moriya
interaction under electric field as function of the exchange stiffness
constant.",2001.11982v1
2020-12-13,Tunneling magnetoresistance in ensembles of ferromagnetic granules with exchange interaction and random easy axes of magnetic anisotropy,"We study the tunneling magnetoresistance in the ensembles of ferromagnetic
granules with random easy axes of magnetic anisotropy taking into account the
exchange interaction between granules. It is shown that due to the exchange
interaction magnetoresistance is effectively decoupled from magnetization, i.e.
the strongest negative magnetoresistance can be observed at the field where
magnetization is almost saturated. Under some conditions, the sign of
magnetoresistance can be reversed and tunneling magnetoresistance can become
positive at certain magnetic fields. Our theory agrees with measurements of
magnetoresistance in ensembles of Fe granules in SiCxNy matrix.",2012.07114v1
2009-04-18,Quantum transport through a graphene nanoribbon-superconductor junction,"We study the electron transport through a graphene nanoribbon-superconductor
junction. Both zigzag and armchair edge graphene nanoribbons are considered,
and the effects of the magnetic field and disorder on the transport property
are investigated. By using the tight-binding model and the non-equilibrium
Green's function method, the expressions of the current, conductance, normal
tunneling coefficient, and Andreev reflection coefficient are obtained. For a
clean system and at zero magnetic field, the linear conductance increases
approximatively in a linear fashion with the on-site energy. In the presence of
a magnetic field and a moderate disorder, the linear conductance exhibits
plateau structures for both armchair and zigzag edges. The plateau values
increase with the width of the graphene ribbon. With a wide sample width, a
saturated plateau value of $|\nu|e^2/h$ emerges at the filling factor $\nu$.
For a small filling factor, the conductance can reach the saturated value at a
small width, but for a high filling factor, it requires to have a quite wide
sample width to reach the saturated value. In particular, the Andreev
reflection coefficient is always at 0.5 after reaching the saturated value,
independent of any system parameters. In addition, we also consider the finite
bias case, in which the Andreev reflection coefficient and normal tunneling
coefficient are studied.",0904.2838v1
2018-05-22,Non-saturating large magnetoresistance in semimetals,"The rapidly expanding class of quantum materials known as {\emph{topological
semimetals}} (TSM) display unique transport properties, including a striking
dependence of resistivity on applied magnetic field, that are of great interest
for both scientific and technological reasons. However, experimental signatures
that can identify or discern the dominant mechanism and connect to available
theories are scarce. Here we present the magnetic susceptibility ($\chi$), the
tangent of the Hall angle ($\tan\theta_H$) along with magnetoresistance in four
different non-magnetic semimetals with high mobilities, NbP, TaP, NbSb$_2$ and
TaSb$_2$, all of which exhibit non-saturating large MR. We find that the
distinctly different temperature dependences, $\chi(T)$ and the values of
$\tan\theta_H$ in phosphides and antimonates serve as empirical criteria to
sort the MR from different origins: NbP and TaP being uncompensated semimetals
with linear dispersion, in which the non-saturating magnetoresistance arises
due to guiding center motion, while NbSb$_2$ and TaSb$_2$ being {\it
compensated} semimetals, with a magnetoresistance emerging from nearly perfect
charge compensation of two quadratic bands. Our results illustrate how a
combination of magnetotransport and susceptibility measurements may be used to
categorize the increasingly ubiquitous non-saturating large magnetoresistance
in TSMs.",1805.08797v2
2021-11-08,Saturation of the asymmetric current filamentation instability under conditions relevant to relativistic shock precursors,"The current filamentation instability, which generically arises in the
counterstreaming of supersonic plasma flows, is known for its ability to
convert the free energy associated with anisotropic momentum distributions into
kinetic-scale magnetic fields. The saturation of this instability has been
extensively studied in symmetric configurations where the interpenetrating
plasmas share the same properties (velocity, density, temperature). In many
physical settings, however, the most common configuration is that of asymmetric
plasma flows. For instance, the precursor of relativistic collisionless shock
waves involves a hot, dilute beam of accelerated particles reflected at the
shock front and a cold, dense inflowing background plasma. To determine the
appropriate criterion for saturation in this case, we have performed
large-scale 2D particle-in-cell simulations of counterstreaming
electron-positron pair and electron-ion plasmas. We show that, in
interpenetrating pair plasmas, the relevant criterion is that of magnetic
trapping as applied to the component (beam or plasma) that carries the larger
inertia of the two; namely, the instability growth suddenly slows down once the
quiver frequency of those particles equals or exceeds the instability growth
rate. We present theoretical approximations for the saturation level. These
findings remain valid for electron-ion plasmas provided that electrons and ions
are close to equipartition in the plasma flow of larger inertia. Our results
can be directly applied to the physics of relativistic, weakly magnetized shock
waves, but they can also be generalized to other cases of study.",2111.04651v1
2016-10-10,Spintronics via non-axisymmetric chiral skyrmions,"Micromagnetic calculations demonstrate a peculiar evolution of
non-axisymmetric skyrmions driven by an applied magnetic field in confined
helimagnets with longitudinal modulations. We argue that these specific
solitonic states can be employed in nanoelectronic devices as an effective
alternative to the common axisymmetric skyrmions which occur in magnetically
saturated states.",1610.02817v1
2022-03-22,High-field magnetoresistance of microcrystalline and nanocrystalline Ni metal at 3 K and 300 K,"The magnetoresistance (MR) and the magnetization isotherms were studied up to
high magnetic fields at T = 3 K and 300 K for a microcrystalline ($\mu$c) Ni
foil corresponding to bulk Ni and for a nanocrystalline (nc) Ni foil. At T = 3
K, for the $\mu$c-Ni sample with a residual resistivity ratio (RRR) of 331, the
field dependence of the resistivity was similar to what was reported previously
for high-purity ferromagnets whereas the MR(H) behavior for the nc-Ni sample
with RRR = 9 resembled that what was observed at low temperatures for Ni-based
alloys with low impurity concentration. In the magnetically saturated state,
the resistivity increased with magnetic field for both samples at T = 3 K and
the field dependence was dominated by the ordinary MR due to the Lorentz force
acting on the electron trajectories. However, the MR(H) curves were found to be
saturating for $\mu$c-Ni and non-saturating for nc-Ni, the difference arising
from their very different electron mean free paths. At T = 300 K, the MR(H)
curves of both Ni samples were very similar to those known for bulk Ni. After
magnetic saturation, the resistivity decreased nearly linearly with magnetic
field which behavior is due to the suppression of thermally-induced magnetic
disorder with increasing magnetic field. The MR(H) data were analyzed at both
temperatures with the help of Kohler plots from which the resistivity
anisotropy splitting ($\Delta\rho_{AMR}$) and the anisotropic magnetoresistance
(AMR) ratio were derived. It was demonstrated that at T = 300 K,
$\rho(H\rightarrow 0)=\rho(B\rightarrow 0)$ due to the negligible contribution
of the ordinary MR. The data for the two Ni samples at 3 K and 300 K were found
to indicate an approximately linear scaling of $\Delta\rho_{AMR}$ with the
zero-field resistivity. This implies that the AMR ratio does not vary
significantly with temperature in either microstructural state of Ni.",2203.11568v1
2006-04-07,New mechanism of generation of large-scale magnetic fields in merging protogalactic and protostellar clouds,"A new mechanism of generation of large-scale magnetic fields in colliding
protogalactic clouds and merging protostellar clouds is discussed. Interaction
of the colliding clouds produces large-scale shear motions which are
superimposed on small-scale turbulence. Generation of the large-scale magnetic
field is due to a ''shear-current"" effect (or ""vorticity-current"" effect), and
the mean vorticity is caused by the large-scale shear motions of colliding
clouds. This effect causes the generation of the mean magnetic field even in a
nonrotating and nonhelical homogeneous turbulence. There is no quenching of the
nonlinear shear-current effect contrary to the quenching of the nonlinear alpha
effect, the nonlinear turbulent magnetic diffusion, etc. During the nonlinear
growth of the mean magnetic field, the shear-current effect only changes its
sign at some value of the mean magnetic field which determines the level of the
saturated mean magnetic field. Numerical study shows that the saturated level
of the mean magnetic field is of the order of the equipartition field
determined by the turbulent kinetic energy. The estimated large-scale magnetic
field for merging protogalactic clouds is about several microgauss, and for
merging protostellar clouds is of the order of several tenth of microgauss.",0604170v1
1998-06-09,Magnetization Properties of Some Quantum Spin Ladders,"The experimental realization of various spin ladder systems has prompted
their detailed theoretical investigations. Here we study the evolution of
ground state magnetization with an external magnetic field for two different
antiferromagnetic systems: a three-legged spin-1/2 ladder, and a two-legged
spin-1/2 ladder with an additional diagonal interaction. The finite system
density-matrix renormalization group method is employed for numerical studies
of the three-chain system, and an effective low-energy Hamiltonian is used in
the limit of strong interchain coupling to study the two- and three-chain
systems. The three-chain system has a magnetization plateau at one-third of the
saturation magnetization. The two-chain system has a plateau at zero
magnetization due to a gap above the singlet ground state. It also has a
plateau at half of the saturation magnetization for a certain range of values
of the couplings. We study the regions of transitions between plateaus
numerically and analytically, and find that they are described, at first order
in a strong-coupling expansion, by an XXZ spin-1/2 chain in a magnetic field;
the second order terms give corrections to the XXZ model. We also study
numerically some low-temperature properties of the three-chain system, such as
the magnetization, magnetic susceptibility and specific heat.",9806111v2
2012-01-04,Simulations of a Magnetic Fluctuation Driven Large Scale Dynamo and Comparison with a Two-scale Model,"Models of large scale (magnetohydrodynamic) dynamos (LSD) which couple large
scale field growth to total magnetic helicity evolution best predict the
saturation of LSDs seen in simulations. For the simplest so called ""{\alpha}2""
LSDs in periodic boxes, the electromotive force driving LSD growth depends on
the difference between the time-integrated kinetic and current helicity
associated with fluctuations. When the system is helically kinetically forced
(KF), the growth of the large scale helical field is accompanied by growth of
small scale magnetic (and current) helicity which ultimately quench the LSD.
Here, using both simulations and theory, we study the complementary
magnetically forced(MF) case in which the system is forced with an electric
field that supplies magnetic helicity. For this MF case, the kinetic helicity
becomes the back-reactor that saturates the LSD. Simulations of both MF and KF
cases can be approximately modeled with the same equations of magnetic helicity
evolution, but with complementary initial conditions. A key difference between
KF and MF cases is that the helical large scale field in the MF case grows with
the same sign of injected magnetic helicity, whereas the large and small scale
magnetic helicities grow with opposite sign for the KF case. The MF case can
arise even when the thermal pressure is approximately smaller than the magnetic
pressure, and requires only that helical small scale magnetic fluctuations
dominate helical velocity fluctuations in LSD driving. We suggest that LSDs in
accretion discs and Babcock models of the solar dynamo are actually MF LSDs.",1201.0800v2
2013-09-27,Phonons correlation with magnetic excitations in weak ferromagnet YCrO3,"We report on the temperature dependent Raman spectroscopic studies of
orthorombic distorted perovskite YCrO3 in the temperature range of 20-300K.
Temperature dependence of DC-magnetization measurement under field cooled and
zero field cooled modes confirmed the transition temperature (TN ~142K) and
anomalous characteristic temperature (T* ~60K), above which magnetization tends
to saturate. Magnetization isotherm recorded below TN at 125K shows clear loop
opening without magnetization saturation up to 20kOe, indicating the
coexistence of antiferromagnetic (AFM) interaction with weak ferromagnetic
(WFM) phase. Mean field calculation for exchange constants further confirms the
complex magnetic phase below TN. Temperature evolution of lineshape parameters
of selected modes (associated with the octahedral rotation and A-shift in the
unit cell) revealed anomalous phonon shift near Cr3+ magnetic ordering
temperature (TN ~142K). Additional phonon anomaly was identified at T* ~60K in
agreement with the magnetization results and reflects the change in spin
dynamics, plausibly due to the change in Cr-spin configuration. Moreover, the
positive and negative shift in Raman frequency below TN revel the existence of
competing WFM and AFM exchanges. The phonon shift of B3g (3)-octahedral
rotation mode fairly scaled with the square of sublattice magnetization from TN
to T*, below which it start to depart from theconventional behaviour and need
further attention. This correlation between magnetic and Raman data elucidate
the spin-phonon coupling owing to the multiferroic phenomenon in YCrO3.",1309.7254v1
2021-07-27,Dynamo instabilities in plasmas with inhomogeneous chiral chemical potential,"We study the dynamics of magnetic fields in chiral magnetohydrodynamics,
which takes into account the effects of an additional electric current related
to the chiral magnetic effect in high energy plasmas. We perform direct
numerical simulations, considering weak seed magnetic fields and
inhomogeneities of the chiral chemical potential mu_5 with a zero mean. We
demonstrate that a small-scale chiral dynamo can occur in such plasmas if
fluctuations of mu_5 are correlated on length scales that are much larger than
the scale on which the dynamo growth rate reaches its maximum. Magnetic
fluctuations grow by many orders of magnitude due to the small-scale chiral
dynamo instability. Once the nonlinear backreaction of the generated magnetic
field on fluctuations of mu_5 sets in, the ratio of these scales decreases and
the dynamo saturates. When magnetic fluctuations grow sufficiently to drive
turbulence via the Lorentz force before reaching maximum field strength, an
additional mean-field dynamo phase is identified. The mean magnetic field grows
on a scale that is larger than the integral scale of turbulence after the
amplification of the fluctuating component saturates. The growth rate of the
mean magnetic field is caused by a magnetic alpha effect that is proportional
to the current helicity. With the onset of turbulence, the power spectrum of
mu_5 develops a universal k^(-1) scaling independently of its initial shape,
while the magnetic energy spectrum approaches a k^(-3) scaling.",2107.13028v3
2013-10-02,Magnetic Field Amplification in Young Galaxies,"The Universe at present is highly magnetized, with fields of the order of a
few 10^-5 G and coherence lengths larger than 10 kpc in typical galaxies like
the Milky Way. We propose that the magnetic field was amplified to this values
already during the formation and the early evolution of the galaxies.
Turbulence in young galaxies is driven by accretion as well as by supernova
(SN) explosions of the first generation of stars. The small-scale dynamo can
convert the turbulent kinetic energy into magnetic energy and amplify very weak
primordial magnetic seed fields on short timescales. The amplification takes
place in two phases: in the kinematic phase the magnetic field grows
exponentially, with the largest growth on the smallest non-resistive scale. In
the following non-linear phase the magnetic energy is shifted towards larger
scales until the dynamo saturates on the turbulent forcing scale. To describe
the amplification of the magnetic field quantitatively we model the
microphysics in the interstellar medium (ISM) of young galaxies and determine
the growth rate of the small-scale dynamo. We estimate the resulting saturation
field strengths and dynamo timescales for two turbulent forcing mechanisms:
accretion-driven turbulence and SN-driven turbulence. We compare them to the
field strength that is reached, when only stellar magnetic fields are
distributed by SN explosions. We find that the small-scale dynamo is much more
efficient in magnetizing the ISM of young galaxies. In the case of
accretion-driven turbulence a magnetic field strength of the order of 10^-6 G
is reached after a time of 24-270 Myr, while in SN-driven turbulence the dynamo
saturates at field strengths of typically 10^-5 G after only 4-15 Myr. This is
considerably shorter than the Hubble time. Our work can help to understand why
present-day galaxies are highly magnetized.",1310.0853v2
2023-11-30,Anomalous Hall effect with plateaus observed in a magnetic Weyl semimetal NdAlGe at low temperatures,"In the $R$Al(Si,Ge) ($R$: lanthanides) family, both spatial inversion and
time-reversal symmetries are broken. This may offer opportunities to study
Weyl-fermion physics in nontrivial spin structures emerging from a
noncentrosymmetric crystal structure. In this study, we investigated the
anomalous Hall effect (AHE) in NdAlGe via magnetotransport, magnetization, and
magnetic torque measurements down to 40 mK (0.4 K for magnetization). The
single crystals grown by a laser-heated floating-zone method exhibit a single
magnetic phase transition at $T_{\rm M}$ = 13.5 K, where the $T_{\rm M}$ is the
transition temperature. With the magnetic field parallel to the easy
$\lbrack$001$\rbrack$ axis, the AHE gradually evolves as the temperature
decreases below $T_{\rm M}$. The anomalous Hall conductivity (AHC) reaches
$\sim$320 $\Omega^{-1}$cm$^{-1}$ at 40 mK in the magnetically saturated state.
Except in low-temperature low-field plateau phases, the AHC and magnetization
are proportional, and their ratio agrees with the ratios for conventional
ferromagnets, suggesting that the intrinsic AHE occurs by the Karplus-Luttinger
mechanism. Below $\sim$0.6 K, the curves of Hall resistivity against the field
exhibit plateaus at low fields below $\sim$0.5 T, correlating with the plateaus
in the magnetization curve. For the first plateau, the magnetization is one
order of magnitude smaller than the magnetically saturated state, whereas the
AHE is more than half that in the saturated state. This finding under well
below $T_{\rm M}$ suggests that the AHE at the first plateau is not governed by
the magnetization and may be interpreted based on a multipole or spin
chirality.",2312.00222v2
2002-05-21,Field-Induced Magnetic Ordering in the Quantum Spin System KCuCl$_3$,"KCuCl$_3$ is a three-dimensional coupled spin-dimer system and has a singlet
ground state with an excitation gap ${\Delta}/k_{\rm B}=31$ K. High-field
magnetization measurements for KCuCl$_3$ have been performed in static magnetic
fields of up to 30 T and in pulsed magnetic fields of up to 60 T. The entire
magnetization curve including the saturation region was obtained at $T=1.3$ K.
  From the analysis of the magnetization curve, it was found that the exchange
parameters determined from the dispersion relations of the magnetic excitations
should be reduced, which suggests the importance of the renormalization effect
in the magnetic excitations. The field-induced magnetic ordering accompanied by
the cusplike minimum of the magnetization was observed as in the isomorphous
compound TlCuCl$_3$. The phase boundary was almost independent of the field
direction, and is represented by the power law. These results are consistent
with the magnon Bose-Einstein condensation picture for field-induced magnetic
ordering.",0205429v1
2002-11-21,Temperature-dependent magnetization in diluted magnetic semiconductors,"We calculate magnetization in magnetically doped semiconductors assuming a
local exchange model of carrier-mediated ferromagnetic mechanism and using a
number of complementary theoretical approaches. In general, we find that the
results of our mean-field calculations, particularly the dynamical mean field
theory results, give excellent qualitative agreement with the experimentally
observed magnetization in systems with itinerant charge carriers, such as
Ga_{1-x}Mn_xAs with 0.03 < x < 0.07, whereas our percolation-theory-based
calculations agree well with the existing data in strongly insulating
materials, such as Ge_{1-x}Mn_x. We comment on the issue of non-mean-field like
magnetization curves and on the observed incomplete saturation magnetization
values in diluted magnetic semiconductors from our theoretical perspective. In
agreement with experimental observations, we find the carrier density to be the
crucial parameter determining the magnetization behavior. Our calculated
dependence of magnetization on external magnetic field is also in excellent
agreement with the existing experimental data.",0211496v1
2004-03-09,Magnetization plateaux of S = 1/2 two-dimensional frustrated antiferromagnet Cs$_2$CuBr$_4$,"The field induced magnetic phase transitions of Cs$_2$CuBr$_4$ were
investigated by means of magnetization process and neutron scattering
experiments. This system undergoes magnetic phase transition at Ne\'{e}l
temperature $T_\mathrm{N}=1.4$ K at zero field, and exhibits the magnetization
plateau at approximately one third of the saturation magnetization for the
field directions $H\parallel b$ and $H\parallel c$. In the present study,
additional symptom of the two-third magnetization plateau was found in the
field derivative of the magnetization process. The magnetic structure was found
to be incommensurate with the ordering vector $\boldsymbol{Q}=(0, 0.575, 0)$ at
zero field. With increasing magnetic field parallel to the c-axis, the ordering
vector increases continuously and is locked at $\boldsymbol{Q}=(0, 0.662, 0)$
in the plateau field range $13.1 \mathrm{T} < H < 14.4 \mathrm{T}$. This
indicates that the collinear \textit{up-up-down} spin structure is stabilized
by quantum fluctuation at the magnetization plateau.",0403234v1
2008-09-09,Magnetic Properties of Ni-Fe Nanowire Arrays: Effect of Template Material and Deposition Conditions,"The objective of this work is to study the magnetic properties of arrays of
Ni-Fe nanowires electrodeposited in different template materials such as porous
silicon, polycarbonate and alumina. Magnetic properties were studied as a
function of template material, applied magnetic field (parallel and
perpendicular) during deposition, wire length, as well as magnetic field
orientation during measurement. The results show that application of magnetic
field during deposition strongly influences the c-axis preferred orientation
growth of Ni-Fe nanowires. The samples with magnetic field perpendicular to
template plane during deposition exhibits strong perpendicular anisotropy with
greatly enhanced coercivity and squareness ratio, particularly in Ni-Fe
nanowires deposited in polycarbonate templates. In case of polycarbonate
template, as magnetic field during deposition increases, both coercivity and
squareness ratio also increase. The wire length dependence was also measured
for polycarbonate templates. As wire length increases, coercivity and
squareness ratio decrease, but saturation field increases. Such magnetic
behavior (dependence on template material, magnetic field, wire length) can be
qualitatively explained by preferential growth phenomena, dipolar interactio",0809.1657v1
2018-11-01,High-field Magnetism of the Honeycomb-lattice Antiferromagnet Cu$_2$(pymca)$_3$(ClO$_4$),"We report on the experimental results of magnetic susceptibility, specific
heat, electron spin resonance (ESR), and high-field magnetization measurements
on a polycrystalline sample of the spin-$1/2$ distorted honeycomb-lattice
antiferromagnet Cu$_2$(pymca)$_3$(ClO$_4$). Magnetic susceptibility shows a
broad peak at about 25~K, which is typical of a low dimensional
antiferromagnet, and no long range magnetic order is observed down to 0.6~K in
the specific heat measurements. Magnetization curve up to 70~T at 1.4~K shows
triple stepwise jumps. Assuming three different exchange bonds $J_{\rm A}$,
$J_{\rm B}$ and $J_{\rm C}$ from the structure, the calculated magnetization
curve reproduces the observed one when $J_{\rm A}/k_{\rm B} = 43.7~{\rm K}$,
$J_{\rm B}/J_{\rm A} = 1$ and $J_{\rm C}/J_{\rm A} = 0.2$ except the
magnetization near 70~T, where the observed magnetization indicates another
step while the calculated magnetization becomes saturated. The relationship
between magnetization plateaus and exchange bonds is discussed based on the
numerical calculations.",1811.00278v1
2002-04-29,Dynamic nonlinearity in large scale dynamos with shear,"We supplement the mean field dynamo growth equation with the total magnetic
helicity evolution equation. This provides an explicitly time dependent model
for alpha quenching in dynamo theory. For dynamos without shear, this approach
accounts for the observed large scale field growth and saturation in numerical
simulations. After a significant kinematic phase, the dynamo is resistively
quenched, i.e. the saturation time depends on the microscopic resistivity. This
is independent of whether or not the turbulent diffusivity is resistively
quenched. We find that the approach is also successful for dynamos that include
shear and exhibit migratory waves (cycles). In this case however, whether or
not the cycle period remains of the order of the dynamical time scale at large
magnetic Reynolds numbers does depend how on how the turbulent magnetic
diffusivity quenches. Since this is unconstrained by magnetic helicity
conservation, the diffusivity is presently an input parameter. Comparison to
current numerical experiments suggests a turbulent diffusivity that depends
only weakly on the magnetic Reynolds number, but higher resolution simulations
are needed.",0204497v2
2004-12-02,Nonlinear behavior of a non-helical dynamo,"A three-dimensional numerical computation of magnetohydrodynamic dynamo
behavior is described. The dynamo is mechanically forced with a driving term of
the Taylor-Green type. The magnetic field development is followed from
negligibly small levels to saturated values that occur at magnetic energies
comparable to the kinetic energies. Though there is locally a helicity density,
there is no overall integrated helicity in the system. Persistent oscillations
are observed in the saturated state for not-too-large mechanical Reynolds
numbers, oscillations in which the kinetic and magnetic energies vary out of
phase but with no reversal of the magnetic field. The flow pattern exhibits
considerable geometrical structure in this regime. As the Reynolds number is
raised, the oscillations disappear and the energies become more nearly
stationary, but retain some unsystematically fluctuating turbulent time
dependence. The regular geometrical structure of the fields gives way to a more
spatially disordered distribution. The injection and dissipation scales are
identified and the different components of energy transfer in Fourier space are
analyzed, in particular in the context of clarifying the role played by
different flow scales in the amplification of the magnetic field.",0412071v1
2004-01-31,Magnetic properties of amorphous Co$_x$Nb$_{100-x}$ alloys produced by mechanical alloying,"Three amorphous Co$_x$Nb$_{100-x}$ alloys, Co$_{25}$Nb$_{75}$,
Co$_{57}$Nb$_{43}$ and Co$_{80}$Nb$_{20}$, were produced by Mechanical Alloying
starting from the elemental powders. Their magnetic properties were determined
using an alternating gradient force magnetometer (AGFM), and the remanent
magnetizations, saturation fields and coercive fields were obtained from the
hysteresis loop. The alloys have a relatively high saturation field, which
decreases as the composition becomes richer in Co. The coercivity and remanent
magnetization reach an optimal value around 57% at.Co, making {\em
a}-Co$_{57}$Nb$_{43}$ the hardest magnetic material among the three alloys.
Further addition of Co produces a soft alloy.",0402014v1
2004-06-08,Magnetism and electron spin resonance in single crystalline beta-AgNpO2(SeO3),"We report magnetization, susceptibility, electrical transport, and electron
spin resonance (ESR) studies of single crystals of beta-AgNpO2(SeO3). Here the
valence of the Np sites is expected to be Np(V). We observe a magnetic
transition below 8 K, where the transition temperature is dependent on the
effective magnetic moment. Although the transition appears to be ferromagnetic,
no hysteresis is seen in the magnetization, and the saturation moment above 0.1
T is found to be about 60% of the free NpO2 ion moment. The decrease in the Np
moments determined experimentally is thought to arise from crystal field and
spin-orbit effects. Although Np(V) is expected to be ESR silent, we observe
temperature dependent ESR spectra at ~44 GHz (for fields above the saturation
field) that show slight shifts in the g-factor and line width at low
temperatures. Our results provide evidence that both Np(V) and Np(IV) valences
are present, where the latter may be a minority population. The crystals,
although dark in appearance, are electrically insulating (rho > 10^10 Ohm-cm)
at room temperature.",0406194v1
2005-04-07,Observation of spin-wave characteristics in the two-dimensional ferromagnetic ordering of in-plane spins,"The role of dipolar interactions and anisotropy are important to obtain,
otherwise forbidden, ferromagnetic ordering at finite temperature for ions
arranged in two-dimensional (2D) arrays (monolayers). Here we demonstrate that
conventional low temperature magnetometry and polarized neutron scattering
measurements can be performed to study ferromagnetic ordering of in-plane spins
in 2D systems using a multilayer stack of non-interacting monolayers of
gadolinium ions. The spontaneous magnetization is absent in the heterogenous
magnetic phase observed here and the saturation value of the net magnetization
was found to depend on the applied magnetic field. The net magnetization rises
exponentially with lowering temperature and then reaches saturation following a
$T\ln(\beta T)$ dependence. These findings verify predictions of the spin-wave
theory of 2D in-plane spin system with ferromagnetic interaction and will
initiate further theoretical development.",0504155v1
2008-01-17,Bose-Einstein condensation in antiferromagnets close to the saturation field,"At zero temperature and strong applied magnetic fields the ground sate of an
anisotropic antiferromagnet is a saturated paramagnet with fully aligned spins.
We study the quantum phase transition as the field is reduced below an upper
critical $H_{c2}$ and the system enters a XY-antiferromagnetic phase. Using a
bond operator representation we consider a model spin-1 Heisenberg
antiferromagnetic with single-ion anisotropy in hyper-cubic lattices under
strong magnetic fields. We show that the transition at $H_{c2}$ can be
interpreted as a Bose-Einstein condensation (BEC) of magnons. The theoretical
results are used to analyze our magnetization versus field data in the organic
compound $NiCl_2$-$4SC(NH_2)_2$ (DTN) at very low temperatures. This is the
ideal BEC system to study this transition since $H_{c2}$ is sufficiently low to
be reached with static magnetic fields (as opposed to pulsed fields). The
scaling of the magnetization as a function of field and temperature close to
$H_{c2}$ shows excellent agreement with the theoretical predictions. It allows
to obtain the quantum critical exponents and confirm the BEC nature of the
transition at $H_{c2}$.",0801.2795v2
2009-08-09,Synthetic antiferromagnet with Heusler alloy Co2FeAl ferromagnetic layers,"Heusler alloy Co2FeAl was employed as ferromagnetic layers in
Co2FeAl/Ru/Co2FeAl synthetic antiferromagnet structures. The experimental
results show that the structure with a Ru thickness of 0.45 nm takes on
strongly antiferromagnetic coupling, which maintains up to 150 oC annealing for
1 hour. The structure has a very low saturation magnetization Ms of 425 emu/cc,
a low switching field Hsw of 4.3 Oe and a high saturation field Hs of 5257 Oe
at room temperature, which are favorable for application in ultrahigh density
magnetic read heads or other magnetic memory devices. XRD study testifies that
the as-deposited Co2FeAl film is in B2 phase. Therefore Heusler alloys can be
used to fabricate SyAF and it is possible to make ""all-Heusler"" spin-valves or
magnetic tunneling junctions with better magnetic switching properties and high
magnetoresistance.",0908.1215v1
2012-04-24,Interstitial Transition Metal Doping in Hydrogen Saturated Silicon Nanowires,"We report a first principles systematic study of atomic, electronic, and
magnetic properties of hydrogen saturated silicon nanowires (H-SiNW) which are
doped by transition metal (TM) atoms placed at various interstitial sites. Our
results obtained within the conventional GGA+U approach have been confirmed
using an hybrid functional. In order to reveal the surface effects we examined
three different possible facets of H-SiNW along [001] direction with a diameter
of ~2nm. The energetics of doping and resulting electronic and magnetic
properties are examined for all alternative configurations. We found that
except Ti, the resulting systems have magnetic ground state with a varying
magnetic moment. While H-SiNWs are initially non-magnetic semiconductor, they
generally become ferromagnetic metal upon TM doping. Even they posses
half-metallic behavior for specific cases. Our results suggest that H-SiNWs can
be functionalized by TM impurities which would lead to new electronic and
spintronic devices at nanoscale.",1204.5468v1
2012-05-23,Two-step transition in a magnetoelectric ferrimagnet Cu2OSeO3,"We report a detailed single crystal investigation of a magnetoelectric
ferrimagnet Cu2OSeO3 using dc magnetization and ac susceptibility along the
three principal directions [100], [110] and [111]. We have observed that in
small magnetic fields two magnetic transitions occur, one at Tc = 57 K and the
second one at TN = 58 K. At Tc the non-linear susceptibility reveals the
emergence of the ferromagnetic component and below Tc the magnetization
measurements show the splitting between field-cooled and zero-field-cooled
regimes. Above 1000 Oe the magnetization saturates and the system is in a
single domain state. The temperature dependence of the saturation below Tc can
be well described by m(T) = m(0)[1 - (T/Tc)^2]^{\beta}, with m(0) = 0.56
(mu)B/Cu, corresponding to the 3-up-1-down configuration. The dielectric
constant measured on a thin single crystal shows a systematic deviation below
the transition, indicating an intrinsic magnetoelectric effect.",1205.5100v1
2012-10-24,Coherent structures and the saturation of a nonlinear dynamo,"Eulerian and Lagrangian tools are used to detect coherent structures in the
velocity and magnetic fields of a mean--field dynamo, produced by direct
numerical simulations of the three--dimensional compressible
magnetohydrodynamic equations with an isotropic helical forcing and moderate
Reynolds number. Two distinct stages of the dynamo are studied, the kinematic
stage, where a seed magnetic field undergoes exponential growth, and the
saturated regime. It is shown that the Lagrangian analysis detects structures
with greater detail, besides providing information on the chaotic mixing
properties of the flow and the magnetic fields. The traditional way of
detecting Lagrangian coherent structures using finite--time Lyapunov exponents
is compared with a recently developed method called function M. The latter is
shown to produce clearer pictures which readily permit the identification of
hyperbolic regions in the magnetic field, where chaotic transport/dispersion of
magnetic field lines is highly enhanced.",1210.6637v1
2013-03-12,Global Simulations of Magnetorotational Instability in The Collapsed Core of A Massive Star,"We performed the first numerical simulations of magnetorotational instability
from a sub-magnetar-class seed magnetic field in core collapse supernovae. As a
result of axisymmetric ideal MHD simulations, we found that the magnetic field
is greatly amplified to magnetar-class strength. In saturation phase, a
substantial part of the core is dominated by turbulence, and the magnetic field
possesses dominant large scale components, comparable to the size of the
proto-neutron star. A pattern of coherent chanel flows, which generally appears
during exponential growth phase in previous local simulations, is not observed
in our global simulations. While the approximate convergence in the exponential
growth rate is attained by increasing spatial resolution, that of the
saturation magnetic field is not achieved due to still large numerical
diffusion. Although the effect of magnetic field on the dynamics is found to be
mild, a simulation with a high-enough resolution might result in a larger
impact.",1303.2856v1
2014-03-10,Effective anisotropy gradient in pressure graded [Co/Pd] multilayers,"A vertically graded anisotropy profile has been proposed as an optimized
balance of low coercivity and thermal stability for multilayers used in
magnetic media. Deposition pressure is known to have a profound effect on the
magnetic reversal properties of Co/Pd multilayers, making it an attractive
control parameter for achieving an anisotropy gradient. We have used polarized
neutron reflectometry to study the depth-dependent reversal behavior of
""pressure-graded"" Co/Pd, and observed pronounced gradients in the saturation
magnetization and in the rate at which magnetization changes with field (the
effective anisotropy). While the anisotropy gradient likely arises from a
combination of factors intrinsic to deposition pressure, micromagnetic
simulations indicate that the observed saturation magnetization gradient alone
has a major effect on the resulting coercivity.",1403.2126v2
2014-09-04,NaCuMoO_4(OH) as a Candidate Frustrated J_1-J_2 Chain Quantum Magnet,"In a frustrated J_1-J_2 chain with the nearest-neighbor ferromagnetic
interaction J_1 and the next-nearest-neighbor antiferromagnetic interaction
J_2, novel magnetic states such as a spin-nematic state are theoretically
expected. However, they have been rarely examined in experiments because of the
difficulty in obtaining suitable model compounds. We show here that the
quasi-one-dimensional antiferromagnet NaCuMoO_4(OH), which comprises
edge-sharing CuO_2 chains, is a good candidate J_1-J_2 chain antiferromagnet.
The exchange interactions are estimated as J_1 = - 51 K and J_2 = 36 K by
comparing the magnetic susceptibility, heat capacity, and magnetization data
with the data obtained using calculations by the exact diagonalization method.
High-field magnetization measurements at 1.3 K show a saturation above 26 T
with little evidence of a spin nematic state expected just below the saturation
field, which is probably due to smearing effects caused by thermal fluctuations
and the polycrystalline nature of the sample.",1409.1310v1
2015-07-17,First-order commensurate-incommensurate magnetic phase transition in the coupled FM spin-1/2 two-leg ladders,"We consider the spin-1/2 two-leg ladders with ferromagnetic (FM) interactions
along legs and rungs. Using the stochastic series expansion QMC method, we
study the low-temperature magnetic behavior of the system. An isolated spin-1/2
FM two-leg ladder is in the gapped saturated FM phase at zero temperature. As
soon as the spin-1/2 FM two-leg ladders are connected with antiferromagnetic
(AFM) inter-ladder interaction, a first-order commensurate-incommensurate
quantum phase transition occurs in the ground state magnetic phase diagram. In
fact a jump in the magnetization curve is observed. We found that, coupled
spin-1/2 FM two-leg ladders are in a nonmagnetic phase at zero temperature.
Applying a magnetic field, the ground state of coupled spin-1/2 FM two-leg
ladders remains in the nonmagnetic phase up to a quantum saturate critical
field.",1507.04954v1
2019-02-08,Magnetization beyond the Ising limit of Ho$_2$Ti$_2$O$_7$,"We report that the local Ising anisotropy in pyrochlore oxides - the crucial
requirement for realizing the spin-ice state - can be broken by means of high
magnetic fields. For the case of the well-established classical spin-ice
compound Ho$_2$Ti$_2$O$_7$ the magnetization exceeds the angle-dependent
saturation value of the Ising limit using ultra-high fields up to 120 T.
However, even under such extreme magnetic fields full saturation cannot be
achieved. Crystal-electric-field calculations reveal that a level crossing for
two of the four ion positions leads to magnetization steps at 55 and 100 T. In
addition, we show that by using a field sweep rate in the range of the
spin-relaxation time the dynamics of the spin system can be probed. Exclusively
at 25 ns/T a new peak of the susceptibility appears around 2 T. We argue, this
signals the cross-over between spin-ice and polarized correlations.",1902.02990v1
2020-10-16,Magnetoelastic study on the frustrated quasi-one-dimensional spin-1/2 magnet LiCuVO$_4$,"We investigated the magnetoelastic properties of the quasi-one-dimensional
spin-1/2 frustrated magnet LiCuVO$_4$. Longitudinal-magnetostriction
experiments were performed at 1.5 K in high magnetic fields of up to 60 T
applied along the $b$ axis, i.e., the spin-chain direction. The
magnetostriction data qualitatively resemble the magnetization results, and
saturate at $H_{\text{sat}} \approx 54$ T, with a relative change in sample
length of $\Delta L/L \approx 1.8\times10^{-4}$. Remarkably, both the
magnetostriction and the magnetization evolve gradually between $H_{\text{c3}}
\approx 48$ T and $H_{\text{sat}}$, indicating that the two quantities
consistently detect the spin-nematic phase just below the saturation. Numerical
analyses for a weakly coupled spin-chain model reveal that the observed
magnetostriction can overall be understood within an exchange-striction
mechanism. Small deviations found may indicate nontrivial changes in local
correlations associated with the field-induced phase transitions.",2010.08396v1
2020-12-09,Spin-lattice model for cubic crystals,"We present a methodology based on the N\'{e}el model to build a classical
spin-lattice Hamiltonian for cubic crystals capable of describing magnetic
properties induced by the spin-orbit coupling like magnetocrystalline
anisotropy and anisotropic magnetostriction, as well as exchange
magnetostriction. Taking advantage of the analytical solutions of the N\'{e}el
model, we derive theoretical expressions for the parameterization of the
exchange integrals and N\'{e}el dipole and quadrupole terms that link them to
the magnetic properties of the material. This approach allows to build accurate
spin-lattice models with the desire magnetoelastic properties. We also explore
a possible way to model the volume dependence of magnetic moment based on the
Landau energy. This new feature can allow to consider the effects of
hydrostatic pressure on the saturation magnetization. We apply this method to
develop a spin-lattice model for BCC Fe and FCC Ni, and we show that it
accurately reproduces the experimental elastic tensor, magnetocrystalline
anisotropy under pressure, anisotropic magnetostrictive coefficients, volume
magnetostriction and saturation magnetization under pressure at
zero-temperature. This work could constitute a step towards large-scale
modeling of magnetoelastic phenomena.",2012.05076v3
2021-10-04,Spontaneous magnetization of collisionless plasma through the action of a shear flow,"We study in a fully kinetic framework the generation of seed magnetic fields
through the Weibel instability driven in an initially unmagnetized plasma by a
large-scale shear force. We develop an analytical model that describes the
development of thermal pressure anisotropy via phase mixing, the ensuing
exponential growth of magnetic fields in the linear Weibel stage, and its
saturation when the seed magnetic fields become strong enough to instigate
gyromotion of particles and thereby inhibit their free-streaming. The predicted
scaling dependencies of the saturated seed fields on key parameters (e.g.,
ratio of system scale to electron skin depth, the forcing amplitude) are
confirmed by 3D and 2D particle-in-cell simulations using an electron-positron
plasma. This work demonstrates the spontaneous magnetization of a collisionless
plasma through large-scale motions as simple as a shear flow, and therefore has
important implications for magnetogenesis in dilute astrophysical systems.",2110.01134v1
2022-07-06,Saturated absorption technique used in Potassium microcell for magnetic field sensing,"It is demonstrated that the use of a Micrometric Thin $^{39}$K vapor Cell
(MTC) and Saturated Absorption spectroscopy (SA) allows to form narrow atomic
lines in transmission spectrum without unwanted Cross-Over (CO) resonances.
Another important feature is the small characteristic magnetic field value $B_0
= A_{hf}/\mu_B$ of $^{39}$K, significantly smaller than for Rb and Cs. As a
consequence, decoupling of $J$ and $I$ can be observed at relatively low
magnetic fields $\sim$300 G, which results in the formation of two groups of
four well-spectrally-resolved and equidistantly-positioned atomic transitions
having the same amplitude (each group corresponds to a given circular
polarization $\sigma^\pm$) which we record using a simple experimental setup
with a linearly polarized tunable diode-laser and a longitudinal magnetic field
obtained with two permanent magnets. Fabrication of a MTC is much easier than
the fabrication of the $^{39}$K nanocells used in our previous works. A simple
method to determine the magnitude of a wide range of B-fields with a spatial
resolution of 30 $\mu$m is presented, which is intrinsically calibrated and
does not require a frequency reference.",2207.02703v1
2023-08-28,Spin-wave spectral analysis in crescent-shaped ferromagnetic nanorods,"The research on the properties of spin waves (SWs) in three-dimensional
nanosystems is an innovative idea in the field of magnonics. Mastering and
understanding the nature of magnetization dynamics and binding of SWs at
surfaces, edges, and in-volume parts of three-dimensional magnetic systems
enables the discovery of new phenomena and suggests new possibilities for their
use in magnonic and spintronic devices. In this work, we use numerical methods
to study the effect of geometry and external magnetic field manipulations on
the localization and dynamics of SWs in crescent-shaped (CS) waveguides. It is
shown that changing the magnetic field direction in these waveguides breaks the
symmetry and affects the localization of eigenmodes with respect to the static
demagnetizing field. This in turn has a direct effect on their frequency.
Furthermore, CS structures were found to be characterized by significant
saturation at certain field orientations, resulting in a cylindrical
magnetization distribution. Thus, we present chirality-based nonreciprocal
dispersion relations for high-frequency SWs, which can be controlled by the
field direction (shape symmetry) and its amplitude (saturation).",2308.14678v1
2024-03-11,Effect of Ir growth pressure on the domain wall dynamics in Ta/Pt/Co/Ir/Ta stacks,"The dynamical response of magnetic domain walls to external magnetic fields
in ultra-thin multilayer magnetic films is determined not only by the
composition and thickness of the layers but also by the growth conditions.
Growth conditions can induce significant structural changes inside the layers
and at the interfaces between them, affecting in particular the dynamics of
domain walls, their mobility, elastic tension, and the pinning forces acting on
them. In this work, we focus specifically on the effect of Ir layer growth
pressure in Ta/Pt/Co/Ir/Ta ultra-thin multilayers films. Measurements of the DC
magnetic properties, domain wall velocity and domain morphology in the creep
regime for both constant and alternating field pulses, were performed for a
batch of samples where the Ir layer was grown at different pressures. We find
that the saturation magnetization, the effective anisotropy constant and the
domain wall surface tension grow with increasing pressure and saturate at a
threshold pressure, while the Dzyaloshinskii-Moriya field and the strength of
the disorder remain practically unaltered over the range of pressures
considered.",2403.07141v1
2018-09-25,Frictionless Zonal Flow Saturation by Vorticity Mixing,"Consideration of wave--flow resonance addresses the long-standing problem of
how zonal flows (ZF) saturate in the limit of weak or zero frictional drag, and
also determines the ZF scale. For relevant magnetic geometries, the frequently
quoted tertiary instability requires unphysical enhancement of ZF shear and
thus is irrelevant to the near-marginal, frictionless regime. We show that
resonant vorticity mixing, which conserves potential enstrophy, enables ZF
saturation in the absence of drag, and so is effective in the Dimits up-shift
regime. Vorticity mixing is incorporated as a nonlinear, self-regulation effect
in an extended 0D predator--prey model of drift--ZF turbulence. This analysis
determines the saturated ZF shear and shows that the mesoscopic ZF width scales
as $L_{ZF}\sim f^{3/16} (1-f)^{1/8} \rho_s^{5/8} l_0^{3/8}$ in the relevant
adiabatic limit (i.e., $\tau_{ck} k_\|^2 D_\| \gg 1$). $f$ is the fraction of
turbulence energy coupled to ZF and $l_0$ is the mixing length absent ZF
shears. We calculate and compare the stationary flow and turbulence level in
frictionless, weakly frictional, and strongly frictional regimes. In the
frictionless limit, the results differ significantly from conventionally quoted
scalings derived for frictional regimes. The flow is independent of turbulence
intensity. The turbulence level scales as $E \sim (\gamma_L/\varepsilon_c)^2$,
which defines the extent of the ""near-marginal"" regime to be $\gamma_L <
\varepsilon_c$, for the case of avalanche-induced profile variability. Here,
$\varepsilon_c$ is the rate of dissipation of potential enstrophy and
$\gamma_L$ is the characteristic linear growth rate of fluctuations. The
implications for dynamics near marginality of the strong scaling of saturated
$E$ with $\gamma_L$ are discussed.",1809.09589v1
2006-12-07,Saturation of the Magnetothermal Instability in Three Dimensions,"In dilute astrophysical plasmas, thermal conduction is primarily along
magnetic field lines, and therefore highly anisotropic. As a result, the usual
convective stability criterion is modified from a condition on entropy to a
condition on temperature. For small magnetic fields or small wavenumbers,
instability occurs in any atmosphere where the temperature and pressure
gradients point in the same direction. We refer to the resulting convective
instability as the magnetothermal instability (MTI). We present fully
three-dimensional simulations of the MTI and show that saturation results in an
atmosphere with different vertical structure, dependent upon the boundary
conditions. When the temperature at the boundary of the unstable layer is
allowed to vary, the temperature gradient relaxes until the unstable region is
almost isothermal. When the temperature at the boundary of the unstable region
is fixed, the magnetic field is reoriented to an almost vertical geometry as a
result of buoyant motions. This case exhibits more vigorous turbulence. In both
cases the resulting saturated heat flux is almost one-half of the value
expected if the conduction were purely isotropic. The action of the MTI results
in dynamical processes that lead to significant transport perpendicular to the
initial direction of the magnetic field. The resulting magnetoconvection in
both cases amplifies the magnetic field until it is almost in equipartition
with sustained subsonic turbulence. These results are relevant to understanding
measurements of the temperature profiles of the intracluster medium of clusters
of galaxies as well as the structure of radiatively inefficient accretion
flows.",0612195v1
2010-11-13,Fabrication and characterization of a Ni-Mn-Ga uniaxially textured freestanding film deposited by DC magnetron sputtering,"Homogeneous freestanding films have been obtained by the direct current (DC)
magnetron sputtering technique using a sacrificial layer. After annealing, the
films are crystallized with a strong out-of-plane texture along the (022)
direction. The stoichiometry of the annealed films is close to the target
composition and leads to a martensitic transformation around 255K. The annealed
films demonstrate ferromagnetic behavior with a Curie temperature of about
362K. The magnetization process has been studied on the both states and during
the martensitic transition. The saturation magnetizations have been determined
by fitting the experimental data with a saturation approach law in the range
1-5T. Results show the saturation magnetization of the martensite is around 10%
higher than that of the austenite. A model based on intrinsic magnetic
properties of each state allowing the description of the magnetization M=f (H,
T) of such polycrystalline films during the martensitic transformation is
presented. The mass fraction of martensite inside the austenite phase can be
determined using this model. The shape memory effect is analyzed both by
scanning electron microscopy and by optical microscopy with in-situ measurement
of the resistance temperature dependence.",1011.3109v1
2016-06-13,Stellar wind-magnetosphere interaction at exoplanets: computations of auroral radio powers,"We present calculations of the auroral radio powers expected from exoplanets
with magnetospheres driven by an Earth-like magnetospheric interaction with the
solar wind. Specifically, we compute the twin cell-vortical ionospheric flows,
currents, and resulting radio powers resulting from a Dungey cycle process
driven by dayside and nightside magnetic reconnection, as a function of
planetary orbital distance and magnetic field strength. We include saturation
of the magnetospheric convection, as observed at the terrestrial magnetosphere,
and we present power law approximations for the convection potentials, radio
powers and spectral flux densities. We specifically consider a solar-age system
and a young (1 Gyr) system. We show that the radio power increases with
magnetic field strength for magnetospheres with saturated convection potential,
and broadly decreases with increasing orbital distance. We show that the
magnetospheric convection at hot Jupiters will be saturated, and thus unable to
dissipate the full available incident Poynting flux, such that the magnetic
Radiometric Bode's Law (RBL) presents a substantial overestimation of the radio
powers for hot Jupiters. Our radio powers for hot Jupiters are $\sim$5-1300 TW
for hot Jupiters with field strengths of 0.1-10 $B_J$ orbiting a Sun-like star,
while we find that competing effects yield essentially identical powers for hot
Jupiters orbiting a young Sun-like star. However, in particular for planets
with weaker magnetic fields our powers are higher at larger orbital distances
than given by the RBL, and there are many configurations of planet that are
expected to be detectable using SKA.",1606.03997v1
2024-01-08,Magnetic field amplification in massive primordial halos: Influence of Lyman-Werner radiation,"The potential importance of magnetic fields during structure formation and
gravitational collapse in the early Universe has been shown in several studies.
In particular, magnetic field amplification by the small-scale dynamo plays an
important role in addition to the pure amplification expected from
gravitational collapse. In this paper, we study the small-scale dynamo for
halos of $\gtrsim10^7$ M$_\odot$ collapsing at $z\gtrsim12$, under different
ambient conditions due to the strength of the Lyman-Werner background.
Additionally, we estimate the approximate saturation level by varying the
initial magnetic field strength. We performed cosmological
magnetohydrodynamical simulations for three distinct halos of $\sim10^7$
M$_{\odot}$ at $z\geq13$ by varying the Jeans resolution from $32-256$ cells
and employed Lyman Werner background flux of strengths $10^2-10^5$ in units of
$J_{21}$, where $J_{21}=10^{-21}$ erg$/$cm$^2/$sr$/$s$/$Hz. To follow the
chemical and thermal evolution of the gas we made use of the KROME package. In
addition to the compression by collapse, we find magnetic field amplification
via the dynamo both in the regimes of atomic and molecular hydrogen cooling.
Moreover, we find a lower saturation level in the molecular hydrogen cooling
regime. This behaviour can be understood due to the generally reduced radial
infall velocities and vorticities in this regime, as well as the higher Mach
numbers of the gas, which give rise to a smaller saturation ratio. Our results
overall suggest that the dynamo operates over a large range of conditions in
the collapsing gas.",2401.04054v1
2023-09-22,Magnetic field amplification in cosmological zoom simulations from dwarf galaxies to galaxy groups,"Magnetic fields are ubiquitous in the Universe. Recently, cosmological
simulations of galaxies have successfully begun to incorporate magnetic fields
and their evolution in galaxies and their haloes. However, so far they have
mostly focused on Milky Way-like galaxies. Here we analyse a sample of high
resolution cosmological zoom simulations of disc galaxies in haloes with mass
$M_\mathrm{200c}$ from $10^{10}\,\mathrm{M}_\odot$ to
$10^{13}\,\mathrm{M}_\odot$, simulated with the Auriga galaxy formation model.
We show that with sufficient numerical resolution the magnetic field
amplification and saturation is converged. The magnetic field strength reaches
equipartition with turbulent energy density for galaxies in haloes with
$M_\mathrm{200c}\gtrsim 10^{11.5}\,\mathrm{M_\odot}$. For galaxies in less
massive haloes, the magnetic field strength saturates at a fraction of
equipartition that decreases with decreasing halo mass. For our lowest mass
haloes, the magnetic field saturates significantly below $10\%$ of
equipartition. We quantify the resolution we need to obtain converged magnetic
field strengths and discuss our resolution requirements also in the context of
the IllustrisTNG cosmological box simulations. We show that, at $z=0$,
rotation-dominated galaxies in our sample exhibit for the most part an ordered
large scale magnetic field, with fewer field reversals in more massive
galaxies. Finally, we compare the magnetic fields in our cosmological galaxies
at $z=0$ with simulations of isolated galaxies in a collapsing halo setup. Our
results pave the way for detailed studies of cosmic rays and other physical
processes in similar cosmological galaxy simulations that crucially depend on
the strength and structure of magnetic fields.",2309.13104v2
2007-02-01,Saturated nucleate pool boiling of oxygen under magnetically-enhanced effective gravity,"We investigate the effect of enhancing gravity on saturated nucleate pool
boiling of oxygen for effective gravities of 1g, 6.0g, and 16g (g=9.8 m/s^2) at
a saturation pressure of 760 torr and for heat fluxes of 10 ~ 3000 W/m^2. The
effective gravity on the oxygen is increased by applying a magnetic body force
generated by a superconducting solenoid. We measure the heater temperature
(expressed as a reduced superheat) as a function of heat flux and fit this data
to a piecewise power-law/linear boiling curve. At low heat flux (<400 W/m^2)
the superheat is proportional to the cube root of the heat flux. At higher heat
fluxes, the superheat is a linear function of the heat flux. To within
statistical uncertainties, which are limited by variations among experimental
runs, we find no variation of the boiling curve over our applied gravity range.",0702012v1
2011-11-14,Nematic phase and phase separation near saturation field in frustrated ferromagnets,"We study the effects of quantum fluctuations in magnetic properties of
quantum frustrated ferromagnets in a magnetic field. It is shown that a
non-classical phase or a phase separation appears due to quantum fluctuations
below the saturation field in a parameter range close to the classical
zero-field phase boundary between ferromagnetic and antiferromagnetic phases,
for the case that the classical antiferromagnetic state is not an eigenstate of
the quantum model. As an example to which this argument is applicable, we study
the S=1/2 J1-J2 Heisenberg model with ferromagnetic J1 (J1<0) on the bcc
lattice using a dilute Bose gas approach. For -1.50097 < J1/J2 < -1.389,
magnons form f-wave two-magnon bound states, leading to a spin nematic phase,
and for -1.389 < J1/J2 < -0.48 a canted coplanar antiferromagnetic phase
appears accompanied with a phase separation below the saturation field.",1111.3184v3
2012-06-25,Particle simulation study of electron heating by counterstreaming ion beams ahead of supernova remnant shocks,"The growth and saturation of Buneman-type instabilities is examined with a
particle-in-cell (PIC) simulation for parameters that are representative for
the foreshock region of fast supernova remnant (SNR) shocks. A dense ion beam
and the electrons correspond to the upstream plasma and a fast ion beam to the
shock-reflected ions. The purpose of the 2D simulation is to identify the
nonlinear saturation mechanisms, the electron heating and potential secondary
instabilities that arise from anisotropic electron heating and result in the
growth of magnetic fields. We confirm that the instabilities between both ion
beams and the electrons saturate by the formation of phase space holes by the
beam-aligned modes. The slower oblique modes accelerate some electrons, but
they can not heat up the electrons significantly before they are trapped by the
faster beam-aligned modes. Two circular electron velocity distributions
develop, which are centred around the velocity of each ion beam. They develop
due to the scattering of the electrons by the electrostatic wave potentials.
The growth of magnetic fields is observed, but their amplitude remains low.",1206.5713v1
2014-06-05,Numerical comparison between a Gyrofluid and Gyrokinetic model investigating collisionless magnetic reconnection,"The first detailed comparison between gyrokinetic and gyrofluid simulations
of collisionless magnetic reconnection has been carried out. Both the linear
and nonlinear evolution of the collisionless tearing mode have been analyzed.
In the linear regime, we have found a good agreement between the two approaches
over the whole spectrum of linearly unstable wave numbers, both in the drift
kinetic limit and for finite ion temperature. Nonlinearly, focusing on the
small-$\Delta '$ regime, with $\Delta '$ indicating the standard tearing
stability parameter, we have compared relevant observables such as the
evolution and saturation of the island width, as well as the island oscillation
frequency in the saturated phase.The results are basically the same, with small
discrepancies only in the value of the saturated island width for moderately
high values of $\Delta '$. Therefore, in the regimes investigated here, the
gyrofluid approach can describe the collisionless reconnection process as well
as the more complete gyrokinetic model.",1406.1334v1
2016-01-27,Coherent population oscillation produced by saturating probe and pump fields on the intercombination Line,"We present a theoretical study of the experiments on coherent population
oscillations and coher- ent population trapping on the intercombination line of
174Y b. The transition involves a change of the spin and thus can not be
interpreted in terms of an effective Lambda system. The reported experiments
are done in the regime where both pump and probe fields can saturate the
transition. We demonstrate by both numerical and analytical calculations the
appearance of the interference minimum as both pump and probe start saturating
the transition. We present an analytical result for the threshold probe power
when the interference minimum can appear. We also present de- tailed study of
the appearance of the interference minimum when magnetic fields are applied.
The magnetic fields not only create Zeeman splittings but in addition make the
system open because of the couplings to other levels. We show the possibility
of interference minimum at the position of subharmonic resonances.",1601.07786v1
2016-09-14,On the possibility of helicity oscillations in the saturation of the Tayler instability,"Recent numerical results of current-driven instabilities at low magnetic
Prandtl number and high Hartmann number support the possibility of a saturation
state characterized by helicity oscillations. We investigate the underlying
mechanism by analyzing this possibility using an higher-order Landau-Ginzburg
effective Lagrangian for the weakly non-linear amplitude dynamics, where the
magnetic and velocity perturbations are linearly dependent. We find that, if
the mirror symmetry between left- and right-handed modes is spontaneously
broken, it is impossible to achieve an oscillating helical state. We argue that
the result is likely to hold also adding higher-order terms and in the presence
of an explicit symmetry breaking. We conclude that an oscillating saturating
state for the Tayler instability is unlikely to depend on the interaction of
chiral modes.",1610.00616v2
2018-07-02,A-priori study of the subgrid energy transfers for small-scale dynamo in kinematic and saturation regimes,"The statistical properties of the subgrid energy transfers of homogeneous
small-scale dynamo are investigated during the kinematic, nonlinear and
statistically saturated stages. We carry out an a priori analysis of data
obtained from an ensemble of direct numerical simulations on $512^3$ grid
points and at unity magnetic Prandtl number. In order to provide guidance for
subgrid-scale (SGS) modelling of different types of energy transfer that occur
in magnetohydrodynamic dynamos, we consider the SGS stress tensors originating
from inertial dynamics, Lorentz force and the magnetic induction separately. We
find that all SGS energy transfers display some degree of intermittency as
quantified by the scale-dependence of their respective probability density
functions. Concerning the inertial dynamics, a depletion of intermittency
occurs in presence of a saturated dynamo.",1807.00759v2
2018-07-14,Thermally assisted skyrmions creation in Pt/Co/Ta multilayer films,"N\'eel-type magnetic skyrmions in multilayer films have attracted significant
amount of attention recently for their stability at room temperature and
capability of motion driven by a low-density electrical current, which can be
potentially applied to spintronic devices. However, the thermal effect on the
formation of the skyrmions and their behavior has rarely been studied. Here, we
report a study on the creation of skyrmions in [Pt/Co/Ta]10 multilayer samples
at different temperatures using an in-situ Lorentz transmission electron
microscopy. By imaging the magnetization reversal process from positive
(negative) saturation to negative (positive) saturation, we found that the
skyrmions can be created by nucleation from ferromagnetic saturation state and
by breaking the labyrinth domains under certain external fields. By tuning the
external fields, a maximum density of skyrmions was reached at different
temperatures. The key finding is that the creation of the skyrmions in the
multilayers depends critically on the temperature and thermal history.",1807.05335v1
2022-06-22,Accurate finite-difference micromagnetics of magnets including RKKY interaction -- analytical solution and comparison to standard micromagnetic codes,"Within this paper we show the importance of accurate implementations of the
RKKY interactions for antiferromagnetically coupled ferromagnetic layers with
thicknesses exceeding the exchange length. In order to evaluate the performance
of different implementations of RKKY interaction, we develop a benchmark
problem by deriving the analytical formula for the saturation field of two
infinitely thick magnetic layers that are antiparallelly coupled. This
benchmark problem shows that state-of-the-art implementations in commonly used
finite-difference codes lead to errors of the saturation field that amount to
more than 20% for mesh sizes of 2 nm which is well below the exchange length of
the material. In order to improve the accuracy, we develop higher order cell
based and nodal based finite-difference codes that significantly reduce the
error compared to state-of-the-art implementations. For the second order cell
based and first order nodal based finite element approach the error of the
saturation field is reduced by about a factor of 10 (2% error) for the same
mesh size of 2 nm.",2206.11063v1
2022-09-16,Magnetohydrodynamic Simulations of the Tayler Instability in Rotating Stellar Interiors,"The Tayler instability is an important but poorly studied magnetohydrodynamic
instability that likely operates in stellar interiors. The nonlinear saturation
of the Tayler instability is poorly understood and has crucial consequences for
dynamo action and angular momentum transport in radiative regions of stars. We
perform three-dimensional MHD simulations of the Tayler instability in a
cylindrical geometry, including strong buoyancy and Coriolis forces as
appropriate for its operation in realistic rotating stars. The linear growth of
the instability is characterized by a predominantly $m=1$ oscillation with
growth rates roughly following analytical expectations. The non-linear
saturation of the instability appears to be caused by secondary shear
instabilities and is also accompanied by a morphological change of the flow. We
argue, however, that non-linear saturation likely occurs via other mechanisms
in real stars where the separation of scales is larger than those reached by
our simulations. We also observe dynamo action via the amplification of the
axisymmetric poloidal magnetic field, suggesting that Tayler instability could
be important for magnetic field generation and angular momentum transport in
the radiative regions of evolving stars.",2209.08104v2
2024-01-10,Narrowly avoided spin-nematic phase in BaCdVO(PO$_4$)$_2$: NMR evidence,"We present a $^{31}$P nuclear magnetic resonance (NMR) investigation of
BaCdVO(PO$_4$)$_2$ focusing on the nearly saturated regime between
$\mu_0H_{c1}$ = 4.05 T and $\mu_0H_{c2}$ = 6.5 T, used to be considered as a
promising candidate for a spin-nematic phase. NMR spectra establish the absence
of any dipolar order there, whereas the weak field dependence of the
magnetization above $H_{c1}$ is accounted for by Dzyaloshinskii-Moriya
interaction terms. The low-energy spin dynamics (fluctuations), measured by
nuclear spin-lattice relaxation rate ($T_1^{-1}$), confirms the continuity of
this phase and the absence of any low-temperature phase transition.
Unexpectedly, the spin dynamics above $H_{c1}$ is largely dominated by
two-magnon processes, which is expected above the saturation field of a
spin-nematic phase, but not inside. This shows that BaCdVO(PO$_4$)$_2$ is
indeed close to a spin-nematic instability, however, this phase is not
stabilized. We thus confirm recent theoretical predictions that the
spin-nematic phase can be stabilized, at most, in an extremely narrow field
range close to saturation or is rather narrowly avoided [Jiang et al., Phys.
Rev. Lett. 130, 116701 (2023)].",2401.05269v1
2017-07-28,Limits on Magnetic Field Amplification from the r-Mode Instability,"At second order in perturbation theory, the unstable r-mode of a rotating
star includes growing differential rotation whose form and growth rate are
determined by gravitational-radiation reaction. With no magnetic field, the
angular velocity of a fluid element grows exponentially until the mode reaches
its nonlinear saturation amplitude and remains nonzero after saturation. With a
background magnetic field, the differential rotation winds up and amplifies the
field, and previous work where large mode amplitudes were considered suggests
that the amplification may damp out the instability. A background magnetic
field, however, turns the saturated time-independent perturbations
corresponding to adding differential rotation into perturbations whose
characteristic frequencies are of order the Alfv\'en frequency. As found in
previous studies, we argue that magnetic- field growth is sharply limited by
the saturation amplitude of an unstable mode. In contrast to previous work,
however, we show that if the amplitude is small, i.e., of order 10^(-4), then
the limit on the magnetic-field growth is stringent enough to prevent the loss
of energy to the magnetic field from damping or significantly altering an
unstable r-mode in nascent neutron stars with normal interiors and in cold
stars whose interiors are type II superconductors. We show this result first
for a toy model, and we then obtain an analogous upper limit on magnetic field
growth using a more realistic model of a rotating neutron star. Our analysis
depends on the assumption that there are no marginally unstable perturbations,
and this may not hold when differential rotation leads to a magnetorotational
instability.",1707.09419v2
2004-10-21,Novel magnetic behavior of single crystalline Er2PdSi3,"We report the results of ac and dc magnetic susceptibility (chi) and
electrical resistivity (rho) measurements on the single crystals of Er2PdSi3,
crystallizing in an AlB2-derived hexagonal structure, for two orientations
H//[0001] and H//[2 -1 -1 0]. For H//[0001], there are apparently two magnetic
transitions as revealed by the ac chi data, one close to 7 K attributable to
antiferromagnetic ordering and the other around 2 K. However, for H // [2 -1 -1
0], we observe additional features above 7 K (near 11 and 23 K) in the plot of
low-field chi(T); also, there is no corresponding anomaly in the rho(T) plot.
In this respect, the magnetic behavior of this compound is novel, particularly
while compared with other members of this series. The features in ac chi
respond differently to the application of a small dc magnetic field for the two
directions. As far as low temperature (T= 1.8 and 5 K) isothermal magnetization
(M) behaviour is concerned, it exhibits meta-magnetic-like features around 2
kOe saturating at high fields for the former orientation, whereas for the
latter, there is no saturation even at 120 kOe. The sign of paramagnetic Curie
temperature is different for these two directions. Thus, there is a strong
anisotropy in the magnetic behavior. However, interestingly, the rho(T) plots
are found to be essentially isotropic, with the data revealing possible
formation of magnetic superzone formation below 7 K.",0410532v1
2009-02-15,Magnetic phase diagram of the dimerized spin $S=1/2$ ladder,"The ground-state magnetic phase diagram of a spin $S=1/2$ two-leg ladder with
alternating rung exchange $J_{\perp}(n)=J_{\perp}[1 + (-1)^{n} \delta]$ is
studied using the analytical and numerical approaches. In the limit where the
rung exchange is dominant, we have mapped the model onto the effective quantum
sine-Gordon model with topological term and identified two quantum phase
transitions at magnetization equal to the half of saturation value from a
gapped to the gapless regime. These quantum transitions belong to the
universality class of the commensurate-incommensurate phase transition. We have
also shown that the magnetization curve of the system exhibits a plateau at
magnetization equal to the half of the saturation value. We also present a
detailed numerical analysis of the low energy excitation spectrum and the
ground state magnetic phase diagram of the ladder with rung-exchange
alternation using Lanczos method of numerical diagonalizations for ladders with
number of sites up to N=28. We have calculated numerically the magnetic field
dependence of the low-energy excitation spectrum, magnetization and the on-rung
spin-spin correlation function. We have also calculated the width of the
magnetization plateau and show that it scales as $\delta^{\nu}$, where critical
exponent varies from $\nu =0.87\pm0.01$ in the case of a ladder with isotropic
antiferromagnetic legs to $\nu =1.82\pm0.01 $ in the case of ladder with
ferromagnetic legs. Obtained numerical results are in an complete agreement
with estimations made within the continuum-limit approach.",0902.2530v2
2009-08-05,Characteristic Lengths of Magnetic Field in Magnetohydrodynamic Turbulence,"In the framework of turbulence dynamo, flow motions amplify a weak seed
magnetic field through the stretching of field lines. Although the
amplification process has been a topic of active research, less attention has
been paid to the length scales of magnetic field. In this paper, we described a
numerical study on characteristic lengths of magnetic field in
magnetohydrodynamic turbulence. We considered the case of very weak or zero
mean magnetic field, which is applicable to the turbulence in the intergalactic
space. Our findings are as follows. (1) At saturation, the peak of magnetic
field spectrum occurs at $\sim L_0/2$, where $L_0$ is the energy injection
scale, while the most energy containing scale is $\sim L_0/5$. The peak scale
of spectrum of projected, two-dimensional field is $\sim L_0$. (2) During the
stage of magnetic field amplification, the energy equipartition scale shows a
power-law increase of $\sim t^{1.5}$, while the integral and curvature scales
show a linear increase. The equipartition, integral, and curvature scales
saturate at $\sim L_0$, $\sim 0.3L_0$, and $\sim 0.15L_0$, respectively. (3)
The coherence length of magnetic field defined in the Faraday rotation measure
(RM) due to the intergalactic magnetic field (IGMF) is related to the integral
scale. We presented a formula that expresses the standard deviation of RM,
$\sigma_{RM}$, in terms of the integral scale and rms strength of the IGMF, and
estimated that $\sigma_{RM}$ would be $\sim 100$ and $\sim$ a few rad m$^{-2}$
for clusters and filaments, respectively.",0908.0610v2
2014-10-21,Neutron Reflectometry Studies on Magnetic Stripe Domains in Permalloy/Superconductor bilayers,"We explored changes in magnetic domain structures in a magnetic layer due to
the onset of the superconductivity of an adjacent superconductive layer using
neutron reflectometry. Magnetic domain structures in 1~$\mu$m thick permalloy
(Py) films were studied as functions of magnetic field, temperature and under
the influence of the onset of superconductivity in a neighboring layer. Bragg
peaks in the off-specular scattering were observed at low fields following
saturation with an in-plane field, which are attributed to the quasi-parallel
magnetic stripes along the field direction. During the magnetization reversal
from saturation, the stripe pattern shows increases in the period, the
transverse coherence length (\textit{i.e.}, perpendicular to the stripes) and
the amplitude of the out-of-plane magnetization component. The coherence length
of the magnetic stripes is anisotropic in the remnant state with the
longitudinal coherence length (\textit{i.e.}, along the stripes) being larger
than the transverse one. The stripe period shows a weak temperature dependence
between 300~K and 3~K, but no abrupt change in the period is observed when the
temperature crosses the superconducting critical temperature.",1410.5520v1
2020-03-31,Magnetic properties of Co/Ni-based multilayers with Pd and Pt insertion layers,"In this study, the influence of Pd and Pt insertion layers in Co/Ni
multilayers (MLs) on their magnetic properties, e.g. magnetic anisotropies,
saturation magnetization, coercivity, magnetic domain size, and Curie
temperature, is investigated. We compare three series of [Co/Ni/X]N ML systems
(X = Pd, Pt, no insertion layer), varying the individual Co layer thickness as
well as the repetition number N. All three systems behave very similarly for
the different Co layer thicknesses. For all systems, a maximum effective
magnetic anisotropy was achieved for MLs with a Co layer thickness between 0.15
nm and 0.25 nm. The transition from an out-of-plane to an in-plane system
occurs at about 0.4 nm of Co. While [Co(0.2 nm)/Ni(0.4 nm)]N MLs change their
preferred easy magnetization axis from out-of-plane to in-plane after 6 bilayer
repetitions, insertion of Pd and Pt results in an extension of this transition
beyond 15 repetitions. The maximum effective magnetic anisotropy was more than
doubled from 105 kJ/m3 for [Co/Ni]3 to 275 and 186 kJ/m3 for Pt and Pd,
respectively. Furthermore, the insertion layers strongly reduce the initial
saturation magnetization of 1100 kA/m of Co/Ni MLs and lower the Curie
temperature from 720 to around 500 K",2003.14306v1
2020-04-17,Reversible and magnetically unassisted voltage-driven switching of magnetization in FeRh/PMN-PT,"Reversible control of magnetization by electric fields without assistance
from a subsidiary magnetic field or electric current could help reduce the
power consumption in spintronic devices. When increasing temperature above room
temperature, FeRh displays an uncommon antiferromagnetic to ferromagnetic phase
transition linked to a unit cell volume expansion. Thus, using the strain
exerted by an adjacent piezoelectric layer, the relative amount of
antiferromagnetic and ferromagnetic regions can be tuned by an electric field
applied to the piezoelectric material. Indeed, large variations in the
saturation magnetization have been observed when straining FeRh films grown on
suitable piezoelectric substrates. In view of its applications, the variations
in the remanent magnetization rather than those of the saturation magnetization
are the most relevant. Here, we show that in the absence of any bias external
magnetic field, permanent and reversible magnetization changes as high as 34%
can be induced by an electric field, which remain after this has been zeroed.
Bulk and local magnetoelectric characterization reveals that the fundamental
reason for the large magnetoelectric response observed at remanence is the
expansion (rather than the nucleation) of ferromagnetic nanoregions.",2004.08087v1
2020-08-12,Solar dynamo cycle variations with a rotational period,"Using the non-linear mean-field dynamo models we calculate the magnetic cycle
parameters, like the dynamo cycle period, the amplitude of the total magnetic
energy, and the Poynting flux luminosity from the surface for the solar analogs
with rotation periods of range from 1 to 30 days. We do simulations both for
the kinematic and non-kinematic dynamo models. The kinematic dynamo models,
which take into account the non-linear $\alpha$-effect and the loss of the
magnetic flux due to magnetic buoyancy, show a decrease of the magnetic cycle
with the decrease of the stellar rotation period. The stars with a rotational
period of less than 10 days show the non-stationary long-term variations of the
magnetic activity. The non-kinematic dynamo models take into account the
magnetic field feedback on the large-scale flow and heat transport inside the
convection zone. They show the non-monotonic variation of the dynamo period
with the rotation rate. The models for the rotational periods fewer than 10
days show the non-stationary evolution with a slight increase in the primary
dynamo period with the increase of the rotation rate. The non-kinematic models
show the growth of the dynamo generated magnetic flux with the increase of the
rotation rate. There is a dynamo saturation for the star rotating with a period
of two days and less. The saturation of the magnetic activity parameters is
accompanied by depression of the differential rotation.",2008.05083v3
2022-10-19,Three-dimensional numerical simulations of ambipolar diffusion in NS cores in the one-fluid approximation: instability of poloidal magnetic field,"We numerically model evolution of magnetic fields inside a neutron star under
the influence of ambipolar diffusion in the weak-coupling mode in the one-fluid
MHD approximation. Our simulations are three-dimensional and performed in
spherical coordinates. Our model covers the neutron star core and includes
crust where the magnetic field decay is due to Ohmic decay. We discover an
instability of poloidal magnetic field under the influence of ambipolar
diffusion. This instability develops in the neutron star core and grows on a
timescale of 0.2 dimensionless times, reaching saturation by 2 dimensionless
times. The instability leads to formation of azimuthal magnetic field with
azimuthal wavenumber $m=14$ (at the moment of saturation) which keeps merging
and reaches $m=4$ by 16 dimensionless times. Over the course of our simulations
(16 dimensionless times) the surface dipolar magnetic field decays, reaching 20
percent of its original value and keeps decaying. The decay timescale for the
total magnetic energy is six dimensionless times. The ambipolar diffusion
induces electric currents in the crust where these currents dissipate
efficiently. Strong electric currents in the crust lead to heating, which could
correspond to luminosities of $\approx 10^{29}$ erg s$^{-1}$ during hundreds of
Myrs for an initial magnetic field of $10^{14}$ G. Ambipolar diffusion leads to
formation of small-scale magnetic fields at the neutron star surface.",2210.10869v1
2023-09-18,Computational Exploration of Magnetic Saturation and Anisotropy Energy for Nonstoichiometric Ferrite Compositions,"A grand challenge in materials research is identifying the relationship
between composition and performance. Herein, we explore this relationship for
magnetic properties, specifically magnetic saturation (M$_s$) and magnetic
anisotropy energy (MAE) of ferrites. Ferrites are materials derived from
magnetite (which has the chemical formulae Fe$_3$O$_4$) that comprise metallic
elements in some combination such as Fe, Mn, Ni, Co, Cu and Zn. They are used
in a variety of applications such as electromagnetism, magnetic hyperthermia,
and magnetic imaging. Experimentally, synthesis and characterization of
magnetic materials is time consuming. In order to create insight to help guide
synthesis, we compute the relationship between ferrite composition and magnetic
properties using density functional theory (DFT). Specifically, we compute
M$_s$ and MAE for 571 ferrite structures with the formulae
M1$_x$M2$_y$Fe$_{3-x-y}$O$_4$, where M1 and M2 can be Mn, Ni, Co, Cu and/or Zn
and 0 $\le$ x $\le$ 1 and y = 1 - x. By varying composition, we were able to
vary calculated values of M$_s$ and MAE by up to 9.6$\times$10$^5$ A m$^{-1}$
and 14.1$\times$10$^5$ J m$^{-3}$, respectively. Our results suggest that
composition can be used to optimize magnetic properties for applications in
heating, imaging, and recording. This is mainly achieved by varying M$_s$, as
these applications are more sensitive to variation in M$_s$ than MAE.",2309.09754v1
2024-01-18,Amplification and saturation of turbulent magnetic field in collapsing primordial gas clouds,"Recent numerical studies suggest that magnetic fields play an important role
in primordial star formation in the early universe. However, the detailed
evolution of the magnetic field in the collapse phase still has uncertainties
because of the complicated physics associated with turbulence in a collapsing
magnetized system. Here, we perform a suite of numerical MHD simulations that
follow the collapse of magnetized, turbulent primordial gas clouds to
investigate the evolution of the magnetic field associated with the turbulence,
assuming a polytropic equation of state with exponent $\gamma_{\rm eff}$ and
with various numerical resolutions. In addition, we generalize the analytic
theory of magnetic field growth/saturation so that it can deal with various
exponents $\gamma_{\rm eff}$ and turbulence energy spectra. We find that the
numerical results are well reproduced by the theory for various $\gamma_{\rm
eff}$ through the collapse phase during the formation of the first stars. The
magnetic field is eventually amplified by a factor of $10^{12}$ -- $10^{15}$
due to kinematic and non-linear turbulent dynamo effects and reaches 3% -- 100%
of the equipartition level, depending on $\gamma_{\rm eff}$. We also find that
the transition between the kinematic and non-linear stages can be analytically
estimated. These results indicate that the strong magnetic field accompanied by
supersonic turbulence is a general property and suggest that it can play a
crucial role in the formation of the first stars.",2401.09739v1
2020-07-26,Effect of the anomalous magnetic moment of quarks on magnetized QCD matter and meson spectra,"We systematically investigate the effect of the anomalous magnetic
moment(AMM) of quarks on the magnetized QCD matter, including the magnetic
susceptibility, the inverse magnetic catalysis around the critical temperature
and the neutral/charged pion and rho meson spectra under magnetic fields. The
dynamical AMM of quarks, its coupling with magnetic field causes Zeeman
splitting of the dispersion relation of quarks thus changes the magnetism
properties and meson mass spectra under magnetic fields. It is found that
including the AMM of quarks cannot fully understand lattice results of the
magnetized matter: The AMM of quarks reduces the dynamical quark mass thus
causes the inverse magnetic catalysis around $T_c$. The neutral pion mass is
very sensitive to the AMM, it decreases with magnetic field quickly, and the
charged pion mass shows a nonlinear behavior, i.e., firstly linearly increases
with the magnetic field and then saturates at strong magnetic field. For rho
meson, it is observed that AMM reduces the mass of neutral rho meson mass with
different $s_z$, and reduces the mass of $s_z=+1,0$ component charged rho meson
mass but enhances the $s_z=-1$ component charged rho meson mass. The magnetic
susceptibility at low temperature can be either positive or negative with
different AMM.",2007.13122v3
2024-03-23,Engineering the electronic and magnetic properties of monolayer TiS$_2$ through systematic transition-metal doping,"Layered materials that exhibit magnetic ordering in their pristine form are
very rare. Several standard approaches, such as adsorption of atoms,
introduction of point defects, and edge engineering, have been developed to
induce magnetism in two-dimensional materials. In this way, we investigate the
electronic and magnetic properties of monolayer TiS$_2$ doped with 3$d$
transition metals (TMs) atoms in both octahedral 1T and trigonal prismatic 1H
structures using first-principles calculations. In its pristine form, TiS$_2$
is a non-magnetic semiconductor. The bands near the Fermi energy primarily
exhibit $d$ orbital characters, and due to the presence of ideal octahedral and
trigonal arrangements, they are well separated from other bands with $p$
character. Upon substituting 3$d$-TM atoms in both structures, a variety of
electronic and magnetic phases emerge, including magnetic semiconductor,
magnetic half-metal, non-magnetic metal, and magnetic metal. Chromium exhibits
the largest magnetic moment in both the 1T and 1H structures. The 1T structure
shows a slightly higher magnetic moment of 3.419 $\mu_B$ compared to the 1H
structure 3.138 $\mu_B$, attributed to the distorted octahedral structure of
the 1T structure. Unlike pristine TiS$_2$, the deficiency in saturation of
neighboring S atoms in the presence of impurities leads to the proximity of
energy levels of $d$ and $p$ states, resulting in unexpectedly sizable magnetic
moments. Another interesting case is Cobalt, which leads to a magnetic moment
of approximately 0.805 $\mu_B$ in the 1H structure, while the Co exhibits a
non-magnetic state in the 1H structure. These materials demonstrate a high
degree of tunability and can be optimized for various magnetic applications.",2403.15850v1
2002-06-16,Nonlinear Turbulent Magnetic Diffusion and Mean-Field Dynamo,"The nonlinear coefficients defining the mean electromotive force (i.e., the
nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, the
nonlinear kappa-tensor, etc.) are calculated for an anisotropic turbulence. A
particular case of an anisotropic background turbulence (i.e., the turbulence
with zero mean magnetic field) with one preferential direction is considered.
It is shown that the toroidal and poloidal magnetic fields have different
nonlinear turbulent magnetic diffusion coefficients. It is demonstrated that
even for a homogeneous turbulence there is a nonlinear effective velocity which
exhibits diamagnetic or paramagnetic properties depending on anisotropy of
turbulence and level of magnetic fluctuations in the background turbulence.
Analysis shows that an anisotropy of turbulence strongly affects the nonlinear
mean electromotive force. Two types of nonlinearities (algebraic and dynamic)
are also discussed. The algebraic nonlinearity implies a nonlinear dependence
of the mean electromotive force on the mean magnetic field. The dynamic
nonlinearity is determined by a differential equation for the magnetic part of
the alpha-effect. It is shown that for the alpha-Omega axisymmetric dynamo the
algebraic nonlinearity alone cannot saturate the dynamo generated mean magnetic
field while the combined effect of the algebraic and dynamic nonlinearities
limits the mean magnetic field growth. Astrophysical applications of the
obtained results are discussed.",0206261v1
2006-11-04,Cotunneling and non-equilibrium magnetization in magnetic molecular monolayers,"Transport and non-equilibrium magnetization in monolayers of magnetic
molecules subject to a bias voltage are considered. We apply a master-equation
approach going beyond the sequential-tunneling approximation to study the
Coulomb-blockade regime. While the current is very small in this case, the
magnetization shows changes of the order of the saturation magnetization for
small variations of the bias voltage. Inelastic cotunneling processes manifest
themselves as differential-conductance steps, which are accompanied by much
larger changes in the magnetization. In addition, the magnetization in the
Coulomb-blockade regime exhibits strong signatures of sequential tunneling
processes de-exciting molecular states populated by inelastic cotunneling. We
also consider the case of a single molecule, finding that cotunneling processes
lead to the occurrence of magnetic sidebands below the Coulomb-blockade
threshold. In the context of molecular electronics, we study how additional
spin relaxation suppresses the fine structure in transport and magnetization.",0611108v2
2008-10-01,Lattice disorder and Ferromagnetism in La0.67Ca0.33MnO3 nanoparticle,"We study the ferromagnetism of La0.67Ca0.33MnO3 in bulk polycrystalline,
nanocrystalline and amorphous phase. The structural change from crystalline
phase to amorphous phase exhibited a systematic decrease of TC(paramagnetic to
ferromagnetic transition temperature) and spontaneous magnetization (MS). The
experimental results suggested few more features, e.g., appearance of large
magnetic irreversibility in the temperature dependence of magnetization, lack
of magnetic saturation at high magnetic field, blocking of magnetization below
TB, and enhancement of coercivity. In addition, the magnetic phase transition
near to TC has changed from first order character in bulk sample to second
order character in nanocrystalline and amorphous samples. We understand the
observed magnetic features as the effects of decreasing particle size and
increasing magnetic (spin- lattice) disorder. We noted that magnetic dynamics
of amorphous samples is distinctly different from the nanocrystalline samples.
The ferromagnetism of amorphous samples are comparable with the properties of
reported amorphous ferromagnetic nanoparticles. We also demonstrate the effect
of disorder shell in controlling the dynamics of ferromagnetic cores.",0810.0090v1
2012-08-08,Magnetic properties of charged spin-1 Bose gases with ferromagnetic coupling,"Magnetic properties of a charged spin-1 Bose gas with ferromagnetic
interactions is investigated within mean-field theory. It is shown that a
competition between paramagnetism, diamagnetism and ferromagnetism exists in
this system. It is shown that diamagnetism, being concerned with spontaneous
magnetization, cannot exceed ferromagnetism in very weak magnetic field. The
critical value of reduced ferromagnetic coupling of paramagnetic phase to
ferromagnetic phase transition $\bar I_{c}$ increases with increasing
temperature. The Lande-factor $g$ is introduced to describe the strength of
paramagnetic effect which comes from the spin degree of freedom. The
magnetization density $\bar M$ increases monotonically with $g$ for fixed
reduced ferromagnetic coupling $\bar I$ as $\bar I>\bar I_{c}$. In a weak
magnetic field, ferromagnetism makes immense contribution to the magnetization
density. While at a high magnetic field, the diamagnetism inclines to saturate.
Evidence for condensation can be seen in the magnetization density at weak
magnetic field.",1208.1580v1
2013-04-11,Theory of magnetic small-angle neutron scattering of two-phase ferromagnets,"Based on micromagnetic theory we have derived analytical expressions for the
magnetic small-angle neutron scattering (SANS) cross section of a two-phase
particle-matrix-type ferromagnet. The approach---valid close to magnetic
saturation---provides access to several features of the spin structure such as
perturbing magnetic anisotropy and magnetostatic fields. Depending on the
applied magnetic field and on the magnitude $H_p$ of the magnetic anisotropy
field relative to the magnitude $\Delta M$ of the jump in the longitudinal
magnetization at the particle-matrix interface, we observe a variety of angular
anisotropies in the magnetic SANS cross section. In particular, the model
explains the ""clover-leaf""-shaped angular anisotropy which was previously
observed for several nanostructured magnetic materials, and it provides access
to the magnetic interaction parameters such as the average exchange-stiffness
constant. It is also shown that the ratio $H_p / \Delta M$ decisively
determines the asymptotic power-law exponent and the range of spin-misalignment
correlations.",1304.3214v1
2013-04-23,Interfacial tuning of perpendicular magnetic anisotropy and spin magnetic moment in CoFe/Pd multilayers,"We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4nm/Pd t]6
(t = 1.0-2.0 nm) multilayers fabricated by DC sputtering in a ultrahigh vacuum
chamber. Saturation magnetization, $M_s$, and uniaxial anisotropy, $K_u$, of
the multilayers decrease with increasing the spacing thickness, with a $M_s$ of
155 emu/cc and a $K_u$ of 1.14$\times 10^5$ J/m$^3$ at a spacing thickness of t
= 2 nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism
measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe
film decrease as function of Pd thickness, indicating the major contribution of
surface/interfacial magnetism to the magnetic properties of the film.",1304.6156v2
2013-06-27,Amorphous GdFeCo Films Exhibiting Large and Tunable Perpendicular Magnetic Anisotropy,"We report the compositional and temperature dependence of magnetic
compensation in amorphous GdFeCo films. Magnetic compensation is attributed to
the competition between antiferromagnetic coupling of rare-earth with
transition-metal (TM) ions and ferromagnetic interaction between the TM ions.
The low-Gd region from 20 to 34 at. % was found to exhibit compensation
phenomena characterized by a low saturation magnetization and perpendicular
magnetic anisotropy (PMA) near the compensation temperature. Compensation
temperature was not observed in previously unreported high-Gd region from 52 to
59 at. %, in qualitative agreement with results from recent model calculations.
However, low magnetization was achieved at room temperature, accompanied by a
large PMA with coercivity reaching ~6.6 kOe. The observed perpendicular
magnetic anisotropy of amorphous GdFeCo films probably has a structural origin
consistent with certain aspects of the atomic-scale anisotropy. Our findings
have broadened the composition range of transition metal-rare earth alloys for
designing PMA films, making it attractive for tunable magnetic anisotropy in
nanoscale devices.",1306.6451v1
2014-05-22,Zero-Temperature Configurations of Short Odd-Numbered Classical Spin Chains with Bilinear and Biquadratic Exchange Interactions,"The lowest energy configurations of short odd open chains with classical
spins are determined for antiferromagnetic bilinear and biquadratic
nearest-neighbor exchange interactions. The zero field residual magnetization
generates differences with the magnetic behavior of even chains, as the odd
chain is like a small magnet for weak magnetic fields. The lowest energy
configuration is calculated as a function of the total magnetization M, even
for M less than the zero field residual magnetization. Analytic expressions and
their proofs are provided for the threshold magnetic field needed to drive the
system away from the antiferromagnetic configuration and the spin polar angles
in its vicinity, when the biquadratic interaction is relatively weak. They are
also given for the saturation magnetic field and the spin polar angles close to
it. Finally, an analytic expression along with its proof is given for the
maximum magnetization in zero magnetic field for stronger biquadratic
interaction, where the lowest energy configuration is highly degenerate.",1405.5931v2
2014-12-02,Third-order effect in magnetic small-angle neutron scattering by a spatially inhomogeneous medium,"Magnetic small-angle neutron scattering (SANS) is a powerful tool for
investigating nonuniform magnetization structures inside magnetic materials.
Here, considering a ferromagnetic medium with weakly inhomogeneous uniaxial
magnetic anisotropy, saturation magnetization, and exchange stiffness, we
derive the second-order (in the amplitude of the inhomogeneities) micromagnetic
solutions for the equilibrium magnetization textures and compute the
corresponding magnetic SANS cross sections up to the next, third order. We find
that in the case of perpendicular scattering (the incident neutron beam is
perpendicular to the applied magnetic field) if twice the cross section along
the direction orthogonal to both the field and the neutron beam is subtracted
from the cross section along the field direction, the result has only a
third-order contribution (the lower-order terms are canceled). This difference
does not depend on the amplitude of the exchange inhomogeneities and provides a
separate gateway for a deeper analysis of the sample's magnetic structure. We
derive and analyze analytical expressions for the dependence of this
combination on the scattering-vector magnitude for the case of spherical
Gaussian inhomogeneities.",1412.1059v1
2015-10-15,Magnetization process of spin-1/2 Heisenberg antiferromagnets on a layered triangular lattice,"We study the magnetization process of the spin-1/2 antiferromagnetic
Heisenberg model on a layered triangular lattice by means of a numerical
cluster mean-field method with a scaling scheme (CMF+S). It has been known that
antiferromagnetic spins on a two-dimensional (2D) triangular lattice with
quantum fluctuations exhibit a one-third magnetization plateau in the
magnetization curve under magnetic field. We demonstrate that the CMF+S
quantitatively reproduces the magnetization curve including the stabilization
of the plateau. {We also discuss the effects of a finite interlayer coupling,
which is unavoidable in real quasi-2D materials. It has been recently argued
for a model of the layered-triangular-lattice compound Ba3CoSb2O9 that such
interlayer coupling can induce an additional first-order transition at a strong
field. We present the detailed CMF+S results for the magnetization and
susceptibility curves of the fundamental Heisenberg Hamiltonian in the presence
of magnetic field and weak antiferromagnetic interlayer coupling. The extra
first-order transition appears as a quite small jump in the magnetization curve
and a divergence in the susceptibility at a strong magnetic field ~ 0.712 of
the saturation field.",1510.04402v1
2017-07-24,"Magnetic properties of monoclinic lanthanide metaborates, $Ln$(BO$_2$)$_3$, $Ln$ = Pr, Nd, Gd, Tb","The bulk magnetic properties of the lanthanide metaborates, $Ln$(BO$_2$)$_3$,
$Ln$ = Pr, Nd, Gd, Tb are studied using magnetic susceptibility, heat capacity
and isothermal magnetisation measurements. They crystallise in a monoclinic
structure containing chains of magnetic $Ln^{3+}$ and could therefore exhibit
features of low-dimensional magnetism and frustration. Pr(BO$_2$)$_3$ is found
to have a non-magnetic singlet ground state. No magnetic ordering is observed
down to 0.4 K for Nd(BO$_2$)$_3$. Gd(BO$_2$)$_3$ exhibits a sharp magnetic
transition at 1.1 K, corresponding to three-dimensional magnetic ordering.
Tb(BO$_2$)$_3$ shows two magnetic ordering features at 1.05 K and 1.95 K. A
magnetisation plateau at a third of the saturation magnetisation is seen at 2 K
for both Nd(BO$_2$)$_3$ and Tb(BO$_2$)$_3$ which persists in an applied field
of 14 T. This is proposed to be a signature of quasi one-dimensional behaviour
in Nd(BO$_2$)$_3$ and Tb(BO$_2$)$_3$.",1707.07485v1
2017-11-08,Magnetization measurements on as prepared and annealed Fe3-xMnxSi alloys,"The magnetic properties of the alloy system Fe3-xMnxSi have been studied by
measuring magnetization for samples with x = 0, 0.1, 0.25, 0.5, and by thermal
scanning techniques for samples with x = 0, 0.1. The results reveal that the
system is ferromagnetic in this composition range. Zero field cooling and field
cooling magnetization measurements indicate a similar magnetic ordering and
magnetic anisotropy in all samples. The saturation magnetization for the
annealed samples was higher than that for as prepared samples. This is
attributed to the reduction of magnetic domain boundaries rather than to
improving magnetic order as a result of annealing. Further, TC values
determined from thermal DSC measurements are in good agreement with previously
reported results based on magnetic measurements.",1711.03052v1
2018-01-10,Quantum Theory of Rare-Earth Magnets,"Strong permanent magnets mainly consist of rare earths ($R$) and transition
metals ($T$). The main phase of the neodymium magnet, which is the strongest
magnet, is Nd$_2$Fe$_{14}$B. Sm$_{2}$Fe$_{17}$N$_{3}$ is another magnet
compound having excellent magnetic properties comparable to those of
Nd$_{2}$Fe$_{14}$B. Their large saturation magnetization, strong
magnetocrystalline anisotropy, and high Curie temperature originate from the
interaction between the $T$-3d electrons and $R$-4f electrons. This article
discusses the magnetism of rare-earth magnet compounds. The basic theory and
first-principles calculation approaches for quantitative description of the
magnetic properties are presented, together with applications to typical
compounds such as Nd$_2$Fe$_{14}$B, Sm$_{2}$Fe$_{17}$N$_{3}$, and the recently
synthesized NdFe$_{12}$N.",1801.03455v1
2020-07-21,Nonlinear turbulent dynamo during gravitational collapse,"Via amplification by turbulent dynamo, magnetic fields can be potentially
important for the formation of the first stars. To examine the dynamo behavior
during the gravitational collapse of primordial gas, we extend the theory of
nonlinear turbulent dynamo to include the effect of gravitational compression.
The relative importance between dynamo and compression varies during
contraction, with the transition from dynamo- to compression-dominated
amplification of magnetic fields with the increase of density. In the nonlinear
stage of magnetic field amplification with the scale-by-scale energy
equipartition between turbulence and magnetic fields, reconnection diffusion of
magnetic fields in ideal magnetohydrodynamic (MHD) turbulence becomes
important. It causes the violation of flux-freezing condition and accounts for
(a) the small growth rate of nonlinear dynamo, (b) the weak dependence of
magnetic energy on density during contraction, (c) the saturated magnetic
energy, and (d) the large correlation length of magnetic fields. The resulting
magnetic field structure and the scaling of magnetic field strength with
density are radically different from the expectations of flux-freezing.",2007.11004v1
2021-11-23,Controlling magnetic configuration in soft-hard bilayers probed by polarized neutron reflectometry,"Hard/soft magnetic bilayer thin films have been widely used in data storage
technologies and permanent magnet applications. The magnetic configuration and
response to temperatures and magnetic fields in these heterostructures are
considered to be highly dependent on the interfacial coupling. However, the
intrinsic properties of each of the layers, such as the saturation
magnetization and layer thickness, also strongly influence the magnetic
configuration. Changing these parameters provides an effective method to tailor
magnetic properties in composite magnets. Here, we use polarized neutron
reflectometry (PNR) to experimentally probe the interfacial magnetic
configurations in hard/soft bilayer thin films: L10-FePt/A1-FePt, [Co/Pd]
/CoPd, [Co/Pt] /FeNi and L10-FePt/Fe, which all have a perpendicular magnetic
anisotropy in the hard layer. These films were designed with different soft and
hard layer thicknesses (t_soft and t_hard) and saturation magnetization
(M_s^soft and M_s^hard), respectively. The influences of an in-plane magnetic
field (H_ip) and temperature (T) are also studied using a L10 FePt/A1-FePt
bilayer sample. Comparing the PNR results to micromagnetic simulations reveals
that the interfacial magnetic configuration is highly dependent on t_soft,
M_s^soft and the external factors (H_ip and T), and has a relatively weak
dependence on t_hard and M_s^hard. Key among these results, for thin t_soft,
the hard and soft layers are rigidly coupled in the out-of-plane direction,
then undergo a transition to relax in-plane. This transition can be delayed to
larger t_soft by decreasing M_s^soft. Understanding the influence of these
parameters on the magnetic configuration is critical to designing functional
composite magnets for applications.",2111.12191v1
1995-05-31,On the Existence of States Saturating the Bogomol'nyi Bound in N=4 Supersymmetry,"We give an argument showing that in N=4 supersymmetric gauge theories there
exists at least one bound state saturating the Bogomol'nyi bound with electric
charge $p$ and magnetic charge $q$, for each $p$ and $q$ relatively prime, and
we comment on the uniqueness of such state. This result is a necessary
condition for the existence of an exact S-duality in N=4 supersymmetric
theories.",9505187v3
1998-03-16,3-String Junction and BPS Saturated Solutions in SU(3) Supersymmetric Yang-Mills Theory,"We construct BPS saturated regular configurations of N=4 SU(3) supersymmetric
Yang-Mills theory carrying non-parallel electric and magnetic charges. These
field theory BPS states correspond to the string theory BPS states of 3-string
junctions connecting three different D3-branes by regarding the N=4
supersymmetric Yang-Mills theory as an effective field theory on parallel
D3-branes.",9803127v2
2005-01-26,Perturbative approach to the nonlinear saturation of the tearing mode for any current gradient,"Within the traditional frame of reduced MHD, a new rigorous perturbation
expansion provides the equation ruling the nonlinear growth and saturation of
the tearing mode for any current gradient. The small parameter is the magnetic
island width w. For the first time, the final equation displays at once terms
of order w ln(1/w) and w which have the same magnitude for practical purposes;
two new O(w) terms involve the current gradient. The technique is applicable to
the case of an external forcing. The solution for a static forcing is computed
explicitly and it exhibits three physical regimes.",0501136v1
2013-02-06,p-wave superconductivity near a transverse saturation field,"We investigate reentrant superconductivity in an Ising ferromagnetic
superconductor URhGe under a transverse magnetic field h_x. The superconducting
transition temperature for p-wave order parameters T_{sc} is calculated and
shows two domes as a function of h_x. We find strong enhancement of T_{sc} in
the high-field dome near a saturation field h_s where the spins align in the
transverse direction. Soft magnons generate strong attractive interactions
there. Spin components of the pairing show a significant change between h_x<h_s
and h_x>h_s. We also discuss the appearance of superconductivity with zero-spin
pair due to cancellation between external and exchange fields.",1302.1364v1
2013-09-30,Free convection over a non-isothermal axisymmetric body immersed in a porous medium saturated with an electrically conducting non-Newtonian fluid,"The study investigates the problem of magnetohydrodynamic (MHD) free
convection over a non-isothermal axisymmetric body under the action of
transverse magnetic field. The body is embedded in a porous medium saturated
with electrically conducting non-Newtonian power law fluid. In order to obtain
similarity solution, it is assumed that the viscosity of the fluid decays
exponentially with temperature. The qualitative results are illustrated for a
vertical flat plate, horizontal cylinder and sphere.",1309.7864v1
2013-12-09,Pseudofermion ferromagnetism in the Kondo lattices: a mean-field approach,"Ground state ferromagnetism of the Kondo lattices is investigated within
slave fermion approach by Coleman and Andrei within a mean-field approximation
in the effective hybridization model. Conditions for formation of both
saturated (half-metallic) and non-saturated magnetic state are obtained for
various lattices. A description in terms of universal functions which depend
only on bare electron density of states (DOS) is presented. A crucial role of
the energy dependence of the bare DOS (especially, of DOS peaks) for the
small-moment ferromagnetism formation is demonstrated.",1312.2438v2
2013-12-20,Energy Efficient Control of an Induction Machine under Load Torque Step Change,"Optimal control of magnetizing current for minimizing induction motor power
losses during load torque step change was developed. Obtained strategy has
feedback form and is exactly optimal of ideal speed controller performance and
absence of saturation in motor. The impact of limited bandwidth of real speed
controller is analyzed. For case of main induction saturation the sub-optimal
optimal control is suggested. Relative accuracy of sub-optimality is studied.
Hardware implementation of optimal strategy and experimentation conducted with
induction motors under vector control.",1312.6094v2
2015-11-30,An analysis of the benefits of signal injection for low-speed sensorless control of induction motors,"We analyze why low-speed sensorless control of the IM is intrinsically
difficult, and what is gained by signal injection. The explanation relies on
the control-theoretic concept of observability applied to a general model of
the saturated IM. We show that the IM is not observable when the stator speed
is zero in the absence of signal injection, but that observability is restored
thanks to signal injection and magnetic saturation. The analysis also reveals
that existing sensorless algorithms based on signal injection may perform
poorly for some IMs under particular operating conditions. The approach is
illustrated by simulations and experimental data.",1511.09349v1
2022-08-08,Measurement of hyperfine constants and the isotope shift of rubidium 5P$_{1/2}$ excited-state using Saturated Absorption Spectroscopy,"The Saturated Absorption Spectroscopy (SAS) was performed to measure the
hyperfine energy splittings of rubidium 5P$_{1/2}$ excited state using a
homemade external-cavity diode laser (ECDL) operating at 795 nm. Any
nonlinearities associated with ECDL scans were removed by using a low-expansion
confocal Fabry-Perot cavity and hence created a linearized frequency axis for
the spectra collected in a fully automated fashion. We report our measurements
for the magnetic dipole coupling constants 120.79(29) and 407.75(50) for
$^{85}Rb$ and $^{87}Rb$ respectively.",2208.04244v1
2023-06-08,A Macroscopic Theory of Saturated Ferromagnetic Conductors,"A phenomenological theory of rigid and saturated ferromagnetic conductors is
constructed from a four-continuum model consisting of a rigid lattice
continuum, a bound charge continuum for polarization, a circulating current
continuum for magnetization, and a free charge continuum for electrical
conduction. The basic laws of physics are applied to the four continua. Thermal
couplings and the related dissipative effects are also included. The theory
includes the Landau-Lifshitz-Gilbert equation as one of a system of
simultaneous equations.",2306.11525v1
2023-07-31,A Continuum Theory of Elastic-Ferromagnetic Conductors,"In this paper, a phenomenological theory of saturated ferromagnetoelastic
conductors is established using a multi-continuum model and the classical laws
of mechanics, thermodynamics and electromagnetics. The theory is nonlinear and
is valid for large deformations and strong electromagnetic fields. The
constitutive relations in the theory satisfy the saturation condition of the
magnetization vector. The theory is with full electromagnetic couplings as
governed by the equations of electrodynamics. It can describe the interactions
of elastic, electromagnetic and spin waves. The theory can be reduced to
various quasistatic theories with appropriate approximations of the
electromagnetic fields. It is for anisotropic materials in general.",2307.16669v1
2023-10-10,The saturation of the Bell instability and its implications for cosmic ray acceleration and transport,"The non-resonant (Bell) streaming instability driven by energetic particles
is crucial for producing amplified magnetic fields that are key to the
acceleration of cosmic rays (CRs) in supernova remnants, around Galactic and
extra-galactic CR sources, and for the CR transport. We present a covariant
theory for the saturation of the Bell instability, substantiated by
self-consistent kinetic simulations, that can be applied to arbitrary CR
distributions and discuss its implications in several heliospheric and
astrophysical contexts.",2310.07038v1
2015-12-03,Saturation of the magnetorotational instability in the unstratified shearing box with zero net flux: convergence in taller boxes,"Previous studies of the nonlinear regime of the magnetorotational instability
in one particular type of shearing box model -- unstratified with no net
magnetic flux -- find that without explicit dissipation (viscosity and
resistivity) the saturation amplitude decreases with increasing numerical
resolution. We show that this result is strongly dependent on the vertical
aspect ratio of the computational domain $L_z/L_x$. When $L_z/L_x\lesssim 1$,
we recover previous results. However, when the vertical domain is extended
$L_z/L_x \gtrsim 2.5$, we find the saturation level of the stress is greatly
increased (giving a ratio of stress to pressure $\alpha \gtrsim 0.1$), and
moreover the results are independent of numerical resolution. Consistent with
previous results, we find that saturation of the MRI in this regime is
controlled by a cyclic dynamo which generates patches of strong toroidal field
that switches sign on scales of $L_x$ in the vertical direction. We speculate
that when $L_z/L_x\lesssim 1$, the dynamo is inhibited by the small size of the
vertical domain, leading to the puzzling dependence of saturation amplitude on
resolution. We show that previous toy models developed to explain the MRI
dynamo are consistent with our results, and that the cyclic pattern of toroidal
fields observed in stratified shearing box simulations (leading to the
so-called butterfly diagram) may also be related. In tall boxes the saturation
amplitude is insensitive to whether or not explicit dissipation is included in
the calculations, at least for large magnetic Reynolds and Prandtl number.
Finally, we show MRI turbulence in tall domains has a smaller critical
$\rm{Pm}_c$, and an extended lifetime compared to $L_z/L_x\lesssim 1$ boxes.",1512.01106v1
2000-09-21,Mean Field Dynamo Saturation: Toward Understanding Conflicting Results,"Mean field dynamos may explain the origin of large scale magnetic fields of
galaxies, but controversy arises over the extent of dynamo quenching by the
growing field. Here we explain how apparently conflicting results may be
mutually consistent, by showing the role of magnetic helicity conservation and
boundary terms usually neglected. We estimate the associated magnetic energy
flowing out of the Galaxy but emphasize that the mechanism of field escape
needs to be addressed.",0009355v1
2000-12-03,Synthesis of Small and Large scale Dynamos,"Using a closure model for the evolution of magnetic correlations, we uncover
an interesting plausible saturated state of the small-scale fluctuation dynamo
(SSD) and a novel anology between quantum mechanical tunneling and the
generation of large-scale fields. Large scale fields develop via the
$\alpha$-effect, but as magnetic helicity can only change on a resistive
timescale, the time it takes to organize the field into large scales increases
with magnetic Reynolds number. This is very similar to the results which obtain
from simulations using full MHD.",0012053v1
2005-12-23,Galactic dynamo and helicity losses through fountain flow,"Nonlinear behaviour of galactic dynamos is studied, allowing for magnetic
helicity removal by the galactic fountain flow. A suitable advection speed is
estimated, and a one-dimensional mean-field dynamo model with dynamic
alpha-effect is explored. It is shown that the galactic fountain flow is
efficient in removing magnetic helicity from galactic discs. This alleviates
the constraint on the galactic mean-field dynamo resulting from magnetic
helicity conservation and thereby allows the mean magnetic field to saturate at
a strength comparable to equipartition with the turbulent kinetic energy.",0512592v2
1997-12-05,Spin flip scattering in magnetic junctions,"Processes which flip the spin of an electron tunneling in a junction made up
of magnetic electrodes are studied. It is found that: i) Magnetic impurities
give a contribution which increases the resistance and lowers the
magnetoresistance, which saturates at low temperatures. The conductance
increases at high fields. ii) Magnon assisted tunneling reduces the
magnetoresistance as $T^{3/2}$, and leads to a non ohmic contribution to the
resistance which goes as $V^{3/2}$, iii) Surface antiferromagnetic magnons,
which may appear if the interface has different magnetic properties from the
bulk, gives rise to $T^2$ and $V^2$ contributions to the magnetoresistance and
resistance, respectively, and, iv) Coulomb blockade effects may enhance the
magnetoresistance, when transport is dominated by cotunneling processes.",9712075v1
1998-03-02,Field induced transition of the S=1 antiferromagnetic chain with anisotropy,"The ground state magnetization process of the S=1 antiferromagnetic chain
with the easy-axis single-ion anisotropy described by negative $D$ is
investigated. It is numerically found that a phase transition between two
different gapless phases occurs at an intermediate magnetic field between the
starting and saturation points of the magnetization for $-1.49<D<-0.35$. The
transition is similar to the spin flopping, but it is second-order and not
accompanied with any significant anomalous behaviors in the magnetization
curve. We also present the phase diagrams in the m-D and H-D planes which
reveal a possible re-entrant transition.",9803022v2
1998-04-15,Quantum Antiferromagnets in a Magnetic Field,"Motivated by recent experiments on low-dimensional quantum magnets in applied
magnetic fields, we present a theoretical analysis of their properties based on
the nonlinear sigma model. The spin stiffness and a 1/N expansion are used to
map the regimes of spin-gap behavior, predominantly linear magnetization, and
spin saturation. A two-parameter renormalization-group study gives the
characteristic properties over the entire parameter range. The model is
relevant to many systems exhibiting Haldane physics, and is applied here to the
two-chain spin ladder compound CuHpCl.",9804151v1
1999-05-15,Critical Behavior of Anisotropic Heisenberg Mixed-Spin Chains in a Field,"We numerically investigate the critical behavior of the spin-(1,1/2)
Heisenberg ferrimagnet with anisotropic exchange coupling in a magnetic field.
A quantized magnetization plateau as a function of the field, appearing at a
third of the saturated magnetization, is stable over whole the
antiferromagnetic coupling region. The plateau vanishes in the ferromagnetic
coupling region via the Kosterlitz-Thouless transition. Comparing the quantum
and classical magnetization curves, we elucidate what are essential quantum
effects.",9905224v1
1999-12-14,Magnetization Plateau in the Frustrated Spin Ladder,"The magnetization process of the S=1/2 antiferromagnetic spin ladder at T=0
is studied by the exact diagonalization of finite clusters and size scaling
analyses. It is found that a magnetization plateau appears at half the
saturation value (m=1/2) in the presence of a sufficiently large
next-nearest-neighbor exchange interaction to yield the frustration, when the
rung coupling is larger than the leg one. The phase diagram at m=1/2 is given
by the analysis based on the conformal invariance. The magnetization curves are
also presented in several cases.",9912234v2
2000-03-29,Enhanced Pinning of Vortices in Thin Film Superconductors by Magnetic Dot Arrays,"We study the pinning of vortices in thin film superconductors by magnetic
dots in the London approximation. A single dot is in general able to pin
multiple field-induced vortices, up to a saturation number n_s, which can be
much larger than one. However, the magnetic field of the dot also creates
intrinsic vortices and anti-vortices, which must be accounted for. In a
ferromagnetic dot array, the intrinsic anti-vortices are pinned only
interstitially. Much stronger pinning effect is expected of an
antiferromagnetic dot array. Possible realizations of various magnetic
configurations are discussed.",0003462v1
2003-07-01,Magnetic Properties of Fe75Cu4Ni4Mo2B15 Alloy,"The structural and magnetic properties of ball-milled Fe75Cu4Ni4Mo2B15 alloy
have been investigated through powder X-ray diffraction studies, magnetization
and magnetoimpedance measurements. The particle size decreased rapidly with
ball-milling up to 165 hours and then remained as a constant with further hours
of milling while, the lattice expanded with milling time up to 165 hours and
contracted back with further milling. Saturation magnetization is found to
decrease rapidly up to 165 hours of milling and then started decreasing slowly
with further milling time. Magnetoimpedance studies were carried out in pellets
and thin films of Fe75Cu4Ni4Mo2B15. Magnetoimpedance in pellet is observed to
be ~2.5% at 5Hz whereas, in thin films, it is observed to be ~1.5% at 3 MHz.",0307019v1
2003-12-04,Ground states of quantum kagome antiferromagnets in a magnetic field,"We study the ground state properties of a quantum antiferromagnet in the
kagome lattice in the presence of a magnetic field, paying particular attention
to the stability of the plateau at magnetization 1/3 of saturation. While the
plateau is reinforced by certain deformations of the lattice, like the
introduction of structural defect lines and against an Ising anisotropy, ground
state correlations are seen to be quite different and the undistorted SU(2)
case appears to be rather special.",0312119v1
2006-08-04,Effective Hamiltonians for some highly frustrated magnets,"In prior work, the authors developed a method of degenerate perturbation
theory about the Ising limit to derive an effective Hamiltonian describing
quantum fluctuations in a half-polarized magnetization plateau on the
pyrochlore lattice. Here, we extend this formulation to an arbitrary lattice of
corner sharing simplexes of $q$ sites, at a fraction $(q-2k)/q$ of the
saturation magnetization, with $0<k<q$. We present explicit effective
Hamiltonians for the examples of the checkerboard, kagome, and pyrochlore
lattices. The consequent ground states in these cases for $k=1$ are also
discussed.",0608131v1
2006-09-28,Derivation of effective parameters of magnetic metamaterials composed of passive resonant LC inclusions,"We determine rigorously the effective permeability of magnetic metamaterials
composed of passive particles exhibiting magnetic resonances. The effective
permeability is expressed in terms of circuit parameters characteristic to
these particles (L, C, and R) and particle geometry. The derivation takes into
account the magnetic coupling between particles. We show that a bigger
concentration of particles leads to an improvement in the metamaterial
performances (such as bandwidth or loss tangent), but this effect saturates as
the particles are packed more tightly. The theory is validated through
numerical simulations of physically realizable metamaterials.",0609745v1
2007-02-24,Quantum spin tunneling of magnetization in small ferromagnetic particles,"A new quantum approach is presented that can account for the description of
small ferromagnetic particles magnetization tunneling. An estimate of the
saturation value of an external applied magnetic field along the easy axis is
obtained. An analytic expression for the tunneling factor in the absence of an
external magnetic field is deduced from the present approach that also allows
to obtain the crossover temperature characterizing the regime where tunneling
is dominated by the quantum effects.",0702572v1
2004-12-03,Numerical solutions of the three-dimensional magnetohydrodynamic alpha-model,"We present direct numerical simulations and alpha-model simulations of four
familiar three-dimensional magnetohydrodynamic (MHD) turbulence effects:
selective decay, dynamic alignment, inverse cascade of magnetic helicity, and
the helical dynamo effect. The MHD alpha-model is shown to capture the
long-wavelength spectra in all these problems, allowing for a significant
reduction of computer time and memory at the same kinetic and magnetic Reynolds
numbers. In the helical dynamo, not only does the alpha-model correctly
reproduce the growth rate of magnetic energy during the kinematic regime, but
it also captures the nonlinear saturation level and the late generation of a
large scale magnetic field by the helical turbulence.",0412025v1
2005-05-26,Low magnetic Prandtl number dynamos with helical forcing,"We present direct numerical simulations of dynamo action in a forced Roberts
flow. The behavior of the dynamo is followed as the mechanical Reynolds number
is increased, starting from the laminar case until a turbulent regime is
reached. The critical magnetic Reynolds for dynamo action is found, and in the
turbulent flow it is observed to be nearly independent on the magnetic Prandtl
number in the range from 0.3 to 0.1. Also the dependence of this threshold with
the amount of mechanical helicity in the flow is studied. For the different
regimes found, the configuration of the magnetic and velocity fields in the
saturated steady state are discussed.",0505192v1
2007-04-27,Nonfrustrated magnetoelectric with incommensurate magnetic order in magnetic field,"We discuss a model nonfrustrated magnetoelectric in which strong enough
magnetoelectric coupling produces incommensurate magnetic order leading to
ferroelectricity. Properties of the magnetoelectric in magnetic field directed
perpendicular to wave vector describing the spin helix are considered in
detail. Analysis of classical energy shows that in contrast to naive
expectation the onset of ferroelectricity takes place at a field $H_{c1}$ that
is lower than the saturation field $H_{c2}$. One has $H_{c1}=H_{c2}$ at strong
enough magnetoelectric coupling. We show that at H=0 the ferroelectricity
appears at $T=T_{FE}<T_N$. Qualitative discussion of phase diagram in $H-T$
plane is presented within mean field approach.",0704.3660v1
2008-12-02,Magnetization Plateau of Classical Ising Model on Shastry-Sutherland Lattice,"We study the magnetization for the classical antiferromagnetic Ising model on
the Shastry-Sutherland lattice using the tensor renormalization group approach.
With this method, one can probe large spin systems with little finite-size
effect. For a range of temperature and coupling constant, a single
magnetization plateau at one third of the saturation value is found. We
investigate the dependence of the plateau width on temperature and on the
strength of magnetic frustration. Furthermore, the spin configuration of the
plateau state at zero temperature is determined.",0812.0402v1
2008-12-10,Effect of oxygen concentration on the structural and magnetic properties of LaRh1/2Mn1/2O3 thin films,"Epitaxial LaRh1/2Mn1/2O3 thin films have been grown on (001)-oriented LaAlO3
and SrTiO3 substrates using pulsed laser deposition. The optimized thin film
samples are semiconducting and ferromagnetic with a Curie temperature close to
100 K, a coercive field of 1200 Oe, and a saturation magnetization of 1.7muB
per formula unit. The surface texture, structural, electrical, and magnetic
properties of the LaRh1/2Mn1/2O3 films was examined as a function of the oxygen
concentration during deposition. While an elevated oxygen concentration yields
thin films with optimal magnetic properties, slightly lower oxygen
concentrations result in films with improved texture and crystallinity.",0812.1852v1
2009-01-14,Interface coupling properties and reflection of bulk spin waves from biaxial multilayer ferromagnetic media,"The reflection coefficient of bulk spin waves from multilayer ferromagnetic
structure with periodically modulated parameters of exchange interaction,
uniaxial and rhombic magnetic anisotropy and saturation magnetization is
calculated with a non-ideal coupling between layers. The strong dependence of
spin-wave reflection coefficient on frequency, magnetic field and parameter of
interfacial coupling is revealed. It allows changing the reflection intensity
from 0 to 1 by changing either only external magnetic field value or frequency.
The proposed model of boundary conditions gives the opportunity to take into
account the quality of interfaces when studying the reflection processes of
spin waves in multilayer structures.",0901.2012v1
2010-11-10,Repair of magnetism in oxidized graphene nanoribbons,"Novel route for the establishing of magnetism in realistic oxidized graphene
nanoribbons is proposed. Modelling of the migration of hydroxyl groups from
central part to the zig-zag edges of graphene nanoribbons passivated by oxygen
are performed with using density functional theory. The presence of hydroxyl
groups near the edges leads formation of dangling bonds there instead saturated
due to oxidation and repairs of magnetism diminished by edges oxidation. The
route of manufacturing and stability of new type of magnetic graphene
nanoribbons are also discussed.",1011.2342v1
2011-03-23,Nonlinear Dynamics of Magnetic Islands Imbedded in Small-Scale Turbulence,"The nonlinear dynamics of magnetic tearing islands imbedded in a pressure
gradient driven turbulence is investigated numerically in a reduced
magnetohydrodynamic model. The study reveals regimes where the linear and
nonlinear phases of the tearing instability are controlled by the properties of
the pressure gradient. In these regimes, the interplay between the pressure and
the magnetic flux determines the dynamics of the saturated state. A secondary
instability can occur and strongly modify the magnetic island dynamics by
triggering a poloidal rotation. It is shown that the complex nonlinear
interaction between the islands and turbulence is nonlocal and involves small
scales.",1103.4443v1
2013-01-14,A complete theory for the magnetism of an ideal gas of electrons,"We have explored Pauli paramagnetism, Landau diamagnetism and de Haas-van
Alphen effect in a single framework, and unified these three effects for all
temperatures as well as for all strengths of magnetic field. Our result goes
beyond Pauli-Landau result on the magnetism of the 3-D ideal gas of electrons,
and is able to describe crossover of the de Haas-van Alphen oscillation to the
saturation of magnetization. We also have obtained a novel asymptotic series
expansion for the low temperature properties of the system.",1301.3025v2
2013-05-13,Magnetic screening in high-energy heavy-ion collisions,"We show that classical chromomagnetic fields produced coherently in the
initial stage of a heavy-ion collision exhibit screening. From the two-point
field strength correlator we determine the magnetic mass for SU(2) to be m ~ 5
times the saturation scale. Magnetic screening leads to an intuitive
understanding of the area law scaling of spatial Wilson loops observed
previously. The presence of screening effects in the initial state provides a
basis for defining kinetic processes in the early stage of heavy-ion
collisions, with electric and magnetic masses of the same order.",1305.2780v1
2013-05-29,Magnetization Process and Adiabatic Demagnetization of the Antiferromagnetic Spin-1/2 Heisenberg Cubic Cluster,"A full energy spectrum of the spin-1/2 Heisenberg cubic cluster is used to
investigate a low-temperature magnetization process and adiabatic
demagnetization of this zero-dimensional 2x2x2 quantum spin system. It is shown
that the antiferromagnetic spin-1/2 Heisenberg cube exhibits at low enough
temperatures a stepwise magnetization curve with four intermediate plateaux at
zero, one quarter, one half, and three quarters of the saturation
magnetization. We have also found the enhanced magnetocaloric effect close to
level-crossing fields that determine transitions between the intermediate
plateaux.",1305.6704v1
2013-07-03,Numerical study of magnetization plateaux in the spin-1/2 kagome Heisenberg antiferromagnet,"We clarify the existence of several magnetization plateaux for the kagome
$S=1/2$ antiferromagnetic Heisenberg model in a magnetic field. Using
approximate or exact localized magnon eigenstates, we are able to describe in a
similar manner the plateau states that occur for magnetization per site
$m=1/3$, $5/9$, and $7/9$ of the saturation value. These results are confirmed
using large-scale Exact Diagonalization on lattices up to 63 sites.",1307.0975v2
2013-07-24,Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy,"We present a method to map the saturation magnetization of soft ultrathin
films with perpendicular anisotropy, and we illustrate it to assess the
compositional dependence of the magnetization of CoFeB(1 nm)/MgO films. The
method relies on the measurement of the dipolar repulsion of parallel domain
walls that define a linear domain. The film magnetization is linked to the
field compressibility of the domain. The method also yields the minimal
distance between two walls before their merging, which sets a practical limit
to the storage density in spintronic devices using domain walls as storage
entities.",1307.6479v1
2013-08-06,Broadband ferromagnetic resonance characterization of GaMnAs thin films,"The precessional magnetization dynamics of GaMnAs thin films are
characterized by broadband network analyzer ferromagnetic resonance (FMR) in a
coplanar geometry at cryogenic temperatures. The FMR frequencies are
characterized as function of in-plane field angle and field amplitude. Using an
extended Kittel model of the FMR dispersion the magnetic film parameters such
as saturation magnetization and anisotropies are derived. The modification of
the FMR behavior and of the magnetic parameters of the thin film upon annealing
is analyzed.",1308.1232v1
2014-01-14,Defects induced ferromagnetism in plasma-enabled graphene nanopetals,"Ferromagnetism in graphene is fascinating, but it is still a big challenge
for practical applications due to the weak magnetization. In order to enhance
the magnetization, here, we design plasma-enabled graphene nanopetals with
ultra-long defective edges of up to 105 m/g, ultra-dense lattice vacancies and
hydrogen chemisorptions. The designed graphene nanopetals display robust
ferromagnetism with large saturation magnetization of up to 2 emu/g at 5 K and
1.2 emu/g at room temperatures. This work identifies the plasma-enabled
graphene nanopetals as a promising candidate for graphene-based magnetic
devices.",1401.3060v1
2015-05-19,Magnetization Process of the Spin-S Kagome-Lattice Heisenberg Antiferromagnet,"The magnetization process of the spin-S Heisenberg antiferromagnet on the
kagome lattice is studied by the numerical-diagonalization method. Our
numerical-diagonalization data for small finite-size clusters with S=1, 3/2, 2,
and 5/2 suggest that a magnetization plateau appears at one-third of the height
of the saturation in the magnetization process irrespective of S. We discuss
the S dependences of the edge fields and the width of the plateau in comparison
with recent results obtained by real-space perturbation theory.",1505.04853v1
2016-02-06,Lieb-Mattis ferrimagnetism in diluted magnetic semiconductors,"We show the possibility of long-range ferrimagnetic ordering with a
saturation magnetisation of the order of 1 Bohr magneton per spin for
arbitrarily low concentration of magnetic impurities in semiconductors,
provided that the impurities form a superstructure satisfying the conditions of
the Lieb-Mattis theorem. Explicit examples of such superstructures are given
for the wurtzite lattice, and the temperature of ferrimagnetic transition is
estimated from a high-temperature expansion. Exact diagonalization studies show
that small fragments of the structure exhibit enhanced magnetic response and
isotropic superparamagnetism at low temperatures. A quantum transition in a
high magnetic field is considered and similar superstructures in cubic
semiconductors are discussed as well.",1602.02239v1
2017-06-30,Switching of Magnetic Moments of Nanoparticles by Surface Acoustic Waves,"We report evidence of the magnetization reversal in nanoparticles by surface
acoustic waves (SAWs). The experimental system consists of isolated magnetite
nanoparticles dispersed on a piezoelectric substrate. Magnetic relaxation from
a saturated state becomes significantly enhanced in the presence of the SAW at
a constant temperature of the substrate. The dependence of the relaxation on
SAW power and frequency has been investigated. The effect is explained by the
effective ac magnetic field generated by the SAW in the nanoparticles.",1707.00045v1
2017-07-11,Nature of Magnetoelectric coupling in corundum antiferromagnet Co4Ta2O9,"We study the magnetocapacitance (MC) effect and magnetoelectric (ME) coupling
in spin-flop driven antiferromagnet Co4Ta2O9. The magnetocapacitance data at
high magnetic fields are analyzed by phenomenological Ginzburg-landau theory of
ferroelectromagnets and it is found that change in dielectric constant is
proportional to the square of magnetization. The saturation polarization and
magnetoelectric coupling are estimated to be 52microC/m2 and $\gamma$ = 1.4
x10-3 (emu/g)-2 respectively at 6 Tesla. Electric polarization is achieved
below Neel temperature only when the sample is cooled in the presence of
magnetic field and it is established that the ground state is non-ferroelectric
implying that magnetic lattice does not lead to spontaneous symmetry breaking
in Co4Ta2O9.",1707.03127v1
2017-07-23,Tuning the Magnetic Properties of M-type Hexaferrites,"In this article, common experimental techniques and preparation conditions
adopted for the synthesis of M-type hexaferrites and their influence on the
magnetic properties are briefly reviewed. The effects of various strategies of
cationic substitutions on the properties of the hexaferrites are addressed.
Further, our synthesis and findings on Co-Ti substituted hexaferrites are
presented. It was found that Co-Ti substitution results in improving the
saturation magnetization, and reducing the coercivity down to values favorable
for high density magnetic recording. Also, evidence of inter-particle
interactions in the particulate samples was observed.",1707.07243v1
2018-06-21,"Magnetic Properties of Lithium-Containing Rare Earth Garnets Li3RE3Te2O12 (RE = Y, Pr, Nd, Sm-Lu)","The synthesis, structural description, temperature dependent magnetic
susceptibilities and field dependent magnetizations of a series of rare earth
garnets of the form Li3RE3Te2O12 (RE = Y, La, Pr, Nd, Sm-Lu) are reported. The
structure of Li3Dy3Te2O12 is refined from powder X-ray diffraction data. The
field dependent magnetizations saturate for some of the members by 9 Tesla at 2
K. Of particular interest for further study in this family is the behavior of
the Pr, Tb, Dy and Yb garnets.",1806.08399v1
2018-07-24,Pushing the limits of magnetic anisotropy in the Sm-Co system,"Materials based on the Sm-Co system exhibit remarkable magnetic performance
due to their high Curie temperature, large saturation magnetization, and strong
magnetic anisotropy, which are the result of the electronic structure in Co and
Sm and their arrangement in the hexagonal lattice. In this paper we show, using
first-principles calculations, mean-field theory, and atomistic Monte Carlo
simulations that slight modifications of the SmCo5 crystal structure, induced
by strain or partial substitution of Sm by Ce, change the exchange interaction
energy and increase the magnetocrystalline anisotropy energy drastically. This
finding shows how small changes in local-structure environments lead to
substantial changes in macroscopic properties and enables the optimization of
high-performance materials at the atomic level.",1807.09257v1
2020-01-18,Synthesis of Fe$_3$O$_4$ nanoparticles and their magnetic properties,"Fe$_3$O$_4$ magnetic nanoparticles (MNPs) were synthesized by a
co-precipitation method using sodium citrate and oleic acid as modifiers. Phase
composition and microstructure analysis indicate that the sodium citrate and
oleic acid have been successfully grafted onto the surface of Fe$_3$O$_4$ MNPs.
The magnetic behaviors reveal that the modification can decrease the saturation
magnetization of Fe$_3$O$_4$ MNPs due to the surface effect. Fe$_3$O$_4$ MNPs
modified by sodiumcitrate and oleic acid show excellent dispersion capability,
which should be ascribed to the great reduction of high surface energy and
dipolar attraction of the nanoparticles.",2001.06583v1
2020-03-28,Magnon binding in BaCdVO(PO$_4$)$_2$,"The bond-nematic state has both long-range ordering of magnetic quadrupoles
and the high entanglement typical of spin liquids, and as such can be thought
of as a spin liquid crystal. One of the most promising materials in which to
find such a state is BaCdVO(PO$_4$)$_2$, in which a magnetically silent phase
has been found between a magnetically ordered low-field phase and the
high-field polarised phase. Here I study the magnetic Hamiltonian of
BaCdVO(PO$_4$)$_2$, and, for the Hamiltonian-parameters determined by fits to
inelastic neutron scattering experiments, show that magnons condense out of the
polarised state as bound pairs. This is direct theoretical support for the
existence of a bond-nematic state just below the saturation field.",2003.12747v1
2023-07-25,Effect of resonance magnetic perturbation on edge-core turbulence spreading in a tokamak plasma,"Turbulence spreading from edge to core region with resonance magnetic
perturbation (RMP) is investigated using an electromagnetic Landau-fluid model
in toroidal geometry. When RMP field with appropriate amplitude are employed in
the simulation, long wavelength fluctuations around the resonance surface are
excited due to the forced magnetic reconnection. Strong shear flow at the
magnetic island separatrix are observed, and break the radial elongated vortex
structures of the turbulent fluctuation. The inward flux could be blocked by
this shear flow and the saturation level in the core region declines.",2307.13351v1
2023-11-28,Origin of the classical magnetization discontinuities of the dodecahedron,"The classical antiferromagnetic Heisenberg model on the dodecahedron has been
shown to have three magnetization discontinuities in an external field. Here it
is shown that the highest-field discontinuity can be directly traced back to
the strong magnetization jump leading to saturation at the Ising limit, which
originates from the frustrated connectivity of the molecule. This discontinuity
survives up to the $XY$ limit and disappears just before the ferromagnetic
Ising interaction fully polarizes the spins. The two lower-field jumps of the
model result from the competition of discontinuities that emerge from the
magnetization plateau surviving away from the Ising limit.",2311.17205v1
2024-01-31,Impurity effects in one dimensional spin nematic liquid,"We study impurity effects in the spin nematic phase of the $S=1/2$
$J_1$-$J_2$ frustrated spin chain under an external magnetic field by using the
infinite density matrix renormalization group and the bosonization. It is found
that local magnetization almost saturates around the impurity and the
entanglement entropy nearly vanishes at the corresponding bonds, not only when
the magnetic interactions near the impurity are weakened but also when they are
strengthened compared to those in the bulk. Then, we examine spin correlations
and Friedel oscillations induced by the impurity. The bosonization provides a
qualitative understanding of the characteristic behaviors of the magnetization.
We also discuss impacts of the impurity on experiments by focusing on NMR
spectra.",2401.17552v1
2022-06-02,A new scenario for magnetar formation: Tayler-Spruit dynamo in a proto-neutron star spun up by fallback,"Magnetars are isolated young neutron stars characterized by the most intense
magnetic fields known in the universe. The origin of their magnetic field is
still a challenging question. In situ magnetic field amplification by dynamo
action is a promising process to generate ultra-strong magnetic fields in
fast-rotating progenitors. However, it is unclear whether the fraction of
progenitors harboring fast core rotation is sufficient to explain the entire
magnetar population. To address this point, we propose a new scenario for
magnetar formation, in which a slow-rotating proto-neutron star is spun up by
the supernova fallback. We argue that this can trigger the development of the
Tayler-Spruit dynamo while other dynamo processes are disfavored. Using
previous works done on this dynamo and simulations to characterize the
fallback, we derive equations modelling the coupled evolution of the
proto-neutron star rotation and magnetic field. Their time integration for
different fallback masses is successfully compared with analytical estimates of
the amplification timescales and saturation value of the magnetic field. We
find that the magnetic field is amplified within $20$ to $40$s after the core
bounce, and that the radial magnetic field saturates at intensities
$10^{14}-10^{15}$G, therefore spanning the full range of magnetar's dipolar
magnetic fields. We also compare predictions of two proposed saturation
mechanisms showing that magnetar-like magnetic fields can be generated for
neutron star spun up to rotation periods $\lesssim8$ms and $\lesssim28$ms,
corresponding to fallback masses $\gtrsim4\times10^{-2}{\rm M}_{\odot}$ and
$\gtrsim10^{-2}{\rm M}_{\odot}$. Thus, our results suggest that magnetars can
be formed from slow-rotating progenitors for fallback masses compatible with
recent supernova simulations and leading to plausible initial rotation periods
of the proto-neutron star.",2206.01269v2
2009-09-11,Saturation and time dependence of geodynamo models,"In this study we address the question under which conditions a saturated
velocity field stemming from geodynamo simulations leads to an exponential
growth of the magnetic field in a corresponding kinematic calculation. We
perform global self-consistent geodynamo simulations and calculate the
evolution of a kinematically advanced tracer field. The self-consistent
velocity field enters the induction equation in each time step, but the tracer
field does not contribute to the Lorentz force. This experiment has been
performed by Cattaneo & Tobias (2009) and is closely related to the test field
method by Schrinner et al. (2005, 2007). We find two dynamo regimes in which
the tracer field either grows exponentially or approaches a state aligned with
the actual self-consistent magnetic field after an initial transition period.
Both regimes can be distinguished by the Rossby number and coincide with the
dipolar and multipolar dynamo regimes identified by Christensen & Aubert
(2006). Dipolar dynamos with low Rossby number are kinematically stable whereas
the tracer field grows exponentially in the multipolar dynamo regime. This
difference in the saturation process for dynamos in both regimes comes along
with differences in their time variability. Within our sample of 20 models,
solely kinematically unstable dynamos show dipole reversals and large
excursions. The complicated time behaviour of these dynamos presumably relates
to the alternating growth of several competing dynamo modes. On the other hand,
dynamos in the low Rossby number regime exhibit a rather simple time dependence
and their saturation merely results in a fluctuation of the fundamental dynamo
mode about its critical state.",0909.2181v1
2021-10-14,Superconductor-insulator transitions in three-dimensional indium-oxide at high pressures,"Experiments investigating magnetic-field-tuned superconductor-insulator
transition (HSIT) mostly focus on two-dimensional material systems where the
transition and its proximate ground-state phases, often exhibit features that
are seemingly at odds with the expected behavior. Here we present a
complementary study of a three-dimensional pressure-packed amorphous
indium-oxide (InOx) powder where granularity controls the HSIT. Above a low
threshold pressure of ~0.2 GPa, vestiges of superconductivity are detected,
although neither a true superconducting transition nor insulating behavior are
observed. Instead, a saturation at very high resistivity at low pressure is
followed by saturation at very low resistivity at higher pressure. We identify
both as different manifestations of anomalous metallic phases dominated by
superconducting fluctuations. By analogy with previous identification of the
low resistance saturation as a ""failed superconductor"", our data suggests that
the very high resistance saturation is a manifestation of a ""failed insulator"".
Above a threshold pressure of ~6 GPa, the sample becomes fully packed, and
superconductivity is robust, with TC tunable with pressure. A quantum critical
point at PC~25 GPa marks the complete suppression of superconductivity. For a
finite pressure below PC, a magnetic field is shown to induce a HSIT from a
true zero-resistance superconducting state to a weakly insulating behavior.
Determining the critical field, HC, we show that similar to the 2D behavior,
the insulating-like state maintains a superconducting character, which is
quenched at higher field, above which the magnetoresistance decreases to its
fermionic normal state value.",2110.07251v3
2022-06-28,Turbulent magnetic helicity fluxes in solar convective zone,"Combined action of helical motions of plasma (the $\alpha$ effect) and
non-uniform (differential) rotation is a key dynamo mechanism of solar and
galactic large-scale magnetic fields. Dynamics of magnetic helicity of
small-scale fields is a crucial mechanism in a nonlinear dynamo saturation
where turbulent magnetic helicity fluxes allow to avoid catastrophic quenching
of the $\alpha$ effect. The convective zone of the Sun and solar-like stars as
well as galactic discs are the source for production of turbulent magnetic
helicity fluxes. In the framework of the mean-field approach and the spectral
$\tau$ approximation, we derive turbulent magnetic helicity fluxes using the
Coulomb gauge in a density-stratified turbulence. The turbulent magnetic
helicity fluxes include non-gradient and gradient contributions. The
non-gradient magnetic helicity flux is proportional to a nonlinear effective
velocity (which vanishes in the absence of the density stratification)
multiplied by small-scale magnetic helicity, while the gradient contributions
describe turbulent magnetic diffusion of the small-scale magnetic helicity. In
addition, the turbulent magnetic helicity fluxes contain source terms
proportional to the kinetic $\alpha$ effect or its gradients, and also
contributions caused by the large-scale shear (solar differential rotation). We
have demonstrated that the turbulent magnetic helicity fluxes due to the
kinetic $\alpha$ effect and its radial derivative in combination with the
nonlinear magnetic diffusion of the small-scale magnetic helicity are dominant
in the solar convective zone.",2206.14152v2
2015-11-18,"Minimalist coupled evolution model for stellar x-ray activity, rotation, mass loss, and magnetic field","Late-type main sequence stars exhibit an x-ray to bolometric flux ratio that
depends on ${\tilde Ro}$, the ratio of rotation period to convective turnover
time, as ${\tilde Ro}^{-\zeta}$ with $2\le \zeta \le 3$ for ${\tilde Ro}
>0.13$, but saturates with $|\zeta| <0.2$ for ${\tilde Ro} < 0.13$. Saturated
stars are younger than unsaturated stars and show a broader spread of rotation
rates and x-ray activity. The unsaturated stars have magnetic fields and
rotation speeds that scale roughly with the square root of their age, though
possibly flattening for stars older than the sun. The connection between faster
rotators, stronger fields, and higher activity has been established
observationally, but a theory for the unified time-evolution of x-ray
luminosity, rotation, magnetic field and mass loss that captures the above
trends has been lacking. Here we derive a minimalist holistic framework for the
time evolution of these quantities built from combining a Parker wind with new
ingredients: (1) explicit sourcing of both the thermal energy launching the
wind and the x-ray luminosity via dynamo produced magnetic fields; (2) explicit
coupling of x-ray activity and mass loss saturation to dynamo saturation (via
magnetic helicity build-up and convection eddy shredding); (3) use of coronal
equilibrium to determine how magnetic energy is divided into wind and x-ray
contributions. For solar-type stars younger than the sun, we infer conduction
to be a subdominant power loss compared to x-rays and wind. For older stars,
conduction is more important, possibly quenching the wind and reducing angular
momentum loss. We focus on the time evolution for stars younger than the sun,
highlighting what is possible for further generalizations. Overall, the
approach shows promise toward a unified explanation of all of the
aforementioned observational trends.",1511.05658v4
1995-10-23,The MHD Kelvin-Helmholtz Instability: A Two-Dimensional Numerical Study,"Using a new numerical code we have carried out two-dimensional simulations of
the nonlinear evolution of unstable sheared magnetohydrodynamic flows. We
considered two cases: a strong magnetic field (Alfven Mach number, M_a = 2.5)
and a weak field (M_a =5). Each flow rapidly evolves until it reaches a nearly
steady condition, which is fundamentally different from the analogous
gasdynamic state. Both MHD flows relax to a stable, laminar flow on timescales
less than or of the order of 15 linear growth times, measured from saturation
of the instability. That timescale is several orders of magnitude less than the
nominal dissipation time for these simulated flows, so this condition
represents an quasi-steady relaxed state. The strong magnetic field case
reaches saturation as magnetic tension in the displaced flow boundary becomes
sufficient to stabilize it. That flow then relaxes in a straightforward way to
the steady, laminar flow condition. The weak magnetic field case, on the other
hand, begins development of the vortex expected for gasdynamics, but that
vortex is destroyed by magnetic stresses that locally become strong. Magnetic
topologies lead to reconnection and dynamical alignment between magnetic and
velocity fields. Together these processes produce a sequence of intermittent
vortices and subsequent relaxation to a nearly laminar flow condition in which
the magnetic cross helicity is nearly maximized. Remaining irregularities
consist of a pair of flux tubes straddling the shear layer. Fluctuations within
those features are closely aligned, representing Alfv\'en waves propagating
locally downstream.",9510115v1
2005-05-25,Magnetic turbulence in cool cores of galaxy clusters,"We argue that the recently reported Kolmogorov-like magnetic turbulence
spectrum in the cool core of the Hydra A galaxy cluster can be understood by
kinetic energy injection by active galaxies that drives a turbulent non-helical
magnetic dynamo into its saturated state. Although dramatic differences exist
between small-scale dynamo scenarios, their saturated state is expected to be
similar, as we show for three scenarios: the flux rope dynamo, the fluctuation
dynamo, and the explosive dynamo. Based on those scenarios, we develop an
analytical model of the hydrodynamic and magnetic turbulence in cool cores. The
model implies magnetic field strengths that fit well with Faraday rotation
measurements and minimum energy estimates for the sample of cool core clusters
having such data available. Predictions for magnetic fields in clusters for
which the appropriate observational information is still missing, and for yet
unobserved quantities like the hydrodynamical turbulence velocity and
characteristic length-scale are provided. The underlying dynamo models suggest
magnetic intermittency and possibly a large-scale hydrodynamic viscosity. We
conclude that the success of the model to explain the field strength in cool
core clusters indicates that in general cluster magnetic fields directly
reflect hydrodynamical turbulence, also in clusters without cool cores.",0505517v3
1999-10-21,A Spin-1/2 Model for CsCuCl_3 in an External Magnetic Field,"CsCuCl_3 is a ferromagnetically stacked triangular spin-1/2 antiferromagnet.
We discuss models for its zero-temperature magnetization process. The models
range from three antiferromagnetically coupled ferromagnetic chains to the full
three-dimensional situation. The situation with spin-1/2 is treated by
expansions around the Ising limit and exact diagonalization. Further,
weak-coupling perturbation theory is used mainly for three coupled chains which
are also investigated numerically using the density-matrix renormalization
group technique. We find that already the three-chain model gives rise to the
plateau-like feature at one third of the saturation magnetization which is
observed in magnetization experiments on CsCuCl_3 for a magnetic field
perpendicular to the crystal axis. For a magnetic field parallel to the crystal
axis, a jump is observed in the experimental magnetization curve in the region
of again about one third of the saturation magnetization. In contrast to
earlier spinwave computations, we do not find any evidence for such a jump with
the model in the appropriate parameter region.",9910318v2
2008-08-03,Metamagnetic transition in EuFe$_2$As$_2$ single crystals,"We report the measurements of anisotropic magnetization and magnetoresistance
on single crystals of EuFe$_2$As$_2$, a parent compound of ferro-arsenide
high-temperature superconductor. Apart from the antiferromagnetic (AFM)
spin-density-wave transition at 186 K associated with Fe moments, the compound
undergoes another magnetic phase transition at 19 K due to AFM ordering of
Eu$^{2+}$ spins ($J=S=7/2$). The latter AFM state exhibits metamagnetic
transition under magnetic fields. Upon applying magnetic field with $H\parallel
c$ at 2 K, the magnetization increases linearly to 7.0 $\mu_{B}$/f.u. at
$\mu_{0}H$=1.7 T, then keeps at this value of saturated Eu$^{2+}$ moments under
higher fields. In the case of $H\parallel ab$, the magnetization increases
step-like to 6.6 $\mu_{B}$/f.u. with small magnetic hysteresis. A metamagnetic
phase was identified with the saturated moments of 4.4 $\mu_{B}$/f.u. The
metamagnetic transition accompanies with negative in-plane magnetoresistance,
reflecting the influence of Eu$^{2+}$ moments ordering on the electrical
conduction of FeAs layers. The results were explained in terms of
spin-reorientation and spin-reversal based on an $A$-type AFM structure for
Eu$^{2+}$ spins. The magnetic phase diagram has been established.",0808.0325v2
2010-10-19,Numerical Simulations of Dynamos Generated in Spherical Couette Flows,"We numerically investigate the efficiency of a spherical Couette flow at
generating a self-sustained magnetic field. No dynamo action occurs for
axisymmetric flow while we always found a dynamo when non-axisymmetric
hydrodynamical instabilities are excited. Without rotation of the outer sphere,
typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few
thousands. They increase as the mechanical forcing imposed by the inner core on
the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the
magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\sim 1$.
Oscillating quadrupolar dynamos are present in the vicinity of the dynamo
onset. Saturated magnetic fields obtained in supercritical regimes (either
$Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and
kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3},
10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic
Prandtl number, but we find a peculiar regime where dynamo action may be
obtained for relatively low magnetic Reynolds numbers ($Rm_c\sim 300$). In this
dynamical regime (Rossby number $Ro\sim -1$, spheres in opposite direction) at
a moderate Ekman number ($E=10^{-3}$), a enhanced shear layer around the inner
core might explain the decrease of the dynamo threshold. For lower $E$
($E=10^{-4}$) this internal shear layer becomes unstable, leading to small
scales fluctuations, and the favorable dynamo regime is lost. We also model the
effect of ferromagnetic boundary conditions. Their presence have only a small
impact on the dynamo onset but clearly enhance the saturated magnetic field in
the ferromagnetic parts. Implications for experimental studies are discussed.",1010.3859v2
2012-02-15,Origin of strong magnetic fields in Milky-Way like galactic haloes,"An analytical model predicting the growth rates, the absolute growth times
and the saturation values of the magnetic field strength within galactic haloes
is presented. The analytical results are compared to cosmological MHD
simulations of Milky-Way like galactic halo formation performed with the N-body
/ \textsc{Spmhd} code \textsc{Gadget}. The halo has a mass of
$\approx{}3\cdot{}10^{12}$ $M_{\odot}$ and a virial radius of $\approx{}$270
kpc. The simulations in a $\Lambda$CDM cosmology also include radiative
cooling, star formation, supernova feedback and the description of non-ideal
MHD. A primordial magnetic seed field ranging from $10^{-10}$ to $10^{-34}$ G
in strength agglomerates together with the gas within filaments and
protohaloes. There, it is amplified within a couple of hundred million years up
to equipartition with the corresponding turbulent energy. The magnetic field
strength increases by turbulent small-scale dynamo action. The turbulence is
generated by the gravitational collapse and by supernova feedback.
Subsequently, a series of halo mergers leads to shock waves and amplification
processes magnetizing the surrounding gas within a few billion years. At first,
the magnetic energy grows on small scales and then self-organizes to larger
scales. Magnetic field strengths of $\approx{}10^{-6}$ G are reached in the
center of the halo and drop to $\approx{}10^{-9}$ G in the IGM. Analyzing the
saturation levels and growth rates, the model is able to describe the process
of magnetic amplification notably well and confirms the results of the
simulations.",1202.3349v1
2013-10-11,Trace element content and magnetic properties of commercial HOPG samples studied by ion beam microscopy and SQUID magnetometry,"In this study, the impurity concentration and magnetic response of nine
highly oriented pyrolytic graphite (HOPG) samples with different grades and
from different providers were determined using ion beam microscopy and SQUID
magnetometry. Apart from sideface contaminations in the as-received state, bulk
contamination of the samples in most cases consists of disk-shaped micron-sized
particles made of Ti and V with an additional Fe contamination around the grain
perimeter. The saturation magnetization typically increases with Fe
concentration, however, there is no simple correlation between Fe content and
magnetic moment. The saturation magnetization of one, respectively six, out of
nine samples clearly exceeds the maximum contribution from pure Fe or Fe3C. For
most samples the temperature dependence of the remanence decreases linearly
with T - a dependence found previously for defect-induced magnetism (DIM) in
HOPG. We conclude that apart from magnetic impurities, additional contribution
to the ferromagnetic magnetization exists in pristine HOPG in agreement with
previous studies. A comparative study between the results of ion beam
microscopy and the commonly used EDX analysis shows clearly that EDX is not a
reliable method for quantitative trace elemental analysis in graphite,
clarifying weaknesses and discrepancies in the element concentrations given in
the recent literature.",1310.3056v2
2014-02-05,Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers,"We present a comprehensive study of the current-induced spin-orbit torques in
perpendicularly magnetized Ta/CoFeB/MgO layers. The samples were annealed in
steps up to 300 degrees C and characterized using x-ray absorption
spectroscopy, transmission electron microscopy, resistivity, and Hall effect
measurements. By performing adiabatic harmonic Hall voltage measurements, we
show that the transverse (field-like) and longitudinal (antidamping-like)
spin-orbit torques are composed of constant and magnetization-dependent
contributions, both of which vary strongly with annealing. Such variations
correlate with changes of the saturation magnetization and magnetic anisotropy
and are assigned to chemical and structural modifications of the layers. The
relative variation of the constant and anisotropic torque terms as a function
of annealing temperature is opposite for the field-like and antidamping
torques. Measurements of the switching probability using sub-{\mu}s current
pulses show that the critical current increases with the magnetic anisotropy of
the layers, whereas the switching efficiency, measured as the ratio of magnetic
anisotropy energy and pulse energy, decreases. The optimal annealing
temperature to achieve maximum magnetic anisotropy, saturation magnetization,
and switching efficiency is determined to be between 240 degrees and 270
degrees C.",1402.0986v2
2015-11-11,A global galactic dynamo with a corona constrained by relative helicity,"We present a model for a global axisymmetric turbulent dynamo operating in a
galaxy with a corona which treats the supernovae (SNe) and magneto-rotational
instability (MRI) driven turbulence parameters under a common formalism. The
nonlinear quenching of the dynamo is alleviated by inclusion of small-scale
advective and diffusive magnetic helicity fluxes, which allow the gauge
invariant magnetic helicity to be transferred outside the disk and consequently
build up a corona during the course of dynamo action. The time-dependent dynamo
equations are expressed in a separable form and solved through an eigenvector
expansion constructed using the steady-state solutions of the dynamo equation.
The parametric evolution of the dynamo solution allows us to estimate the final
structure of the global magnetic field and the saturated value of the
turbulence parameter $\alpha_m$, even before solving the dynamical equations
for evolution of magnetic fields in the disk and the corona, along with
$\alpha$-quenching. We then solve these equations simultaneously to study the
saturation of large-scale magnetic field, its dependence on the small-scale
magnetic helicity fluxes and corresponding evolution of the force-free field in
the corona. The quadrupolar large-scale magnetic field in the disk is found to
reach equipartition strength within a timescale of 1 Gyr. The large-scale
magnetic field in the corona obtained is much weaker in strength compared to
the field inside the disk and has only a weak impact on the dynamo operation.",1511.03392v2
2017-12-17,"Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures","We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as
the function of pH at which the material was prepared by chemical route and
post annealing temperature. The material is a ferri or ferromagnet, but showed
magnetic blocking and random spin freezing process on lowering the measurement
temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C
showed a sharp magnetization peak at 105 K, the superparamagnetic blocking
temperature of the particles. The magnetization peak remained incomplete within
measurement temperature up to 350 K for rest of the samples, although peak
temperature was brought down by increasing applied dc field. The fitting of
temperature dependence of coercivity data according to Kneller law suggested
random orientation of ferromagnetic particles. The fitting of saturation
magnetization according to Bloch law provided the exponent that largely
deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt
increase of saturation magnetization below 50 K suggested the active role of
frozen surface spins in low temperature magnetic properties. AC susceptibility
data elucidated the low temperature spin freezing dynamics and exhibited the
characters of cluster spin glass in the samples depending on pH value and
annealing temperature.",1712.06114v1
2019-09-16,Magnetic ground state of the frustrated spin-1/2 chain compound $β$-TeVO$_4$ at high magnetic fields,"Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit
remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave
(SDW) and multipolar/spin-nematic phases as a function of the magnetic field.
Here we report a study of $\beta$-TeVO$_4$, an archetype of such compounds,
based on magnetization and neutron diffraction measurements up to 25 T. We find
the transition from the helical VC ground state to the SDW state at $\sim$3 T
for the magnetic field along the $a$ and $c$ crystal axes, and at $\sim$9 T for
the field along the $b$ axis. The high-field (HF) state, existing above
$\sim$18 T, i.e., above $\sim$1/2 of the saturated magnetization, is an
incommensurate magnetically ordered state and not the spin-nematic state, as
theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF
state is likely driven by sizable interchain interactions and symmetric
intrachain anisotropies uncovered in previous studies. Consequently, the
potential existence of the spin nematic phase in $\beta$-TeVO$_4$ is limited to
a narrow field range, i.e., a few tenths of a tesla bellow the saturation of
the magnetization, as also found in other frustrated spin-1/2 chain compounds.",1909.07085v1
2020-10-06,Insights into nature of magnetization plateaus of a nickel complex [Ni4(CO3)2(aetpy)8](ClO4)4 from a spin-1 Heisenberg diamond cluster,"Magnetic and magnetocaloric properties of a spin-1 Heisenberg diamond cluster
with two different coupling constants are investigated with the help of an
exact diagonalization based on the Kambe's method, which employs a local
conservation of composite spins formed by spin-1 entities located in opposite
corners of a diamond spin cluster. It is shown that the spin-1 Heisenberg
diamond cluster exhibits several intriguing quantum ground states, which are
manifested in low-temperature magnetization curves as intermediate plateaus at
1/4, 1/2 and 3/4 of the saturation magnetization. Besides, the spin-1
Heisenberg diamond cluster may also exhibit an enhanced magnetocaloric effect,
which may be relevant for a low-temperature refrigeration achieved through the
adiabatic demagnetization. It is evidenced that the spin-1 Heisenberg diamond
cluster with the antiferromagnetic coupling constants J1/kB = 41.4 K and J2/kB
= 9.2 K satisfactorily reproduces a low-temperature magnetization curve
recorded for the tetranuclear nickel complex [Ni4(CO3)2(aetpy)8](ClO4)4 (aetpy
= 2-aminoethyl-pyridine) including a size and position of intermediate plateaus
detected at 1/2 and 3/4 of the saturation magnetization. A microscopic nature
of fractional magnetization plateaus observed experimentally is clarified and
interpreted in terms of valence-bond crystal with either a single or double
valence bond. It is suggested that this frustrated magnetic molecule can
provide a prospective cryogenic coolant with the maximal isothermal entropy
change - Delta S = 10.6 J/(K.kg) in a temperature range below 2.3 K.",2010.02535v1
2020-08-10,"Rapid, $B_1$-insensitive, dual-band quasi-adiabatic saturation transfer with optimal control for complete quantification of myocardial ATP flux","Purpose: Phosphorus saturation-transfer experiments can quantify metabolic
fluxes non-invasively. Typically, the forward flux through the creatine-kinase
reaction is investigated by observing the decrease in phosphocreatine (PCr)
after saturation of $\gamma$-ATP. The quantification of total ATP utilisation
is currently under-explored, as it requires simultaneous saturation of
inorganic phosphate (Pi) and PCr. This is challenging, as currently available
saturation pulses reduce the already-low $\gamma$-ATP signal present.
  Methods: Using a hybrid optimal-control and Shinnar-Le-Roux method, a
quasi-adiabatic RF pulse was designed for the dual-saturation of PCr and Pi to
enable determination of total ATP utilisation. The pulses were evaluated in
Bloch equation simulations, compared with a conventional hard-cosine DANTE
saturation sequence, before application to perfused rat hearts at 11.7 Tesla.
  Results: The quasi-adiabatic pulse was insensitive to a $>2.5$-fold variation
in $B_1$, producing equivalent saturation with a 53% reduction in delivered
pulse power and a 33-fold reduction in spillover at the minimum effective
$B_1$. This enabled the complete quantification of the synthesis and
degradation fluxes for ATP in 30-45 minutes in the perfused rat heart. While
the net synthesis flux ($4.24\pm0.8$ mM/s, SEM) was not significantly different
from degradation flux ($6.88\pm2$ mM/s, $p=0.06$) and both measures are
consistent with prior work, nonlinear error analysis highlights uncertainties
in the Pi-to-ATP measurement that may explain a trend suggesting a possible
imbalance.
  Conclusion: This work demonstrates a novel quasi-adiabatic dual-saturation RF
pulse with significantly improved performance that can be used to measure ATP
turnover in the heart in vivo.",2008.04261v2
2001-07-31,The Relationship Between the Circular Polarization and the Magnetic Field for Astrophysical Masers with Weak Zeeman Splitting,"The relationship between the magnetic field and the circular polarization of
astrophysical maser radiation due to the Zeeman effect under idealized
conditions is investigated when the Zeeman splitting is much smaller than the
spectral linebreadth and when radiative saturation is significant. The
description of the circular polarization, as well as inferences about the
magnetic field from the observations, are clearest when the rate for stimulated
emission is much less than the Zeeman splitting. The calculations here are
performed in this regime, which is relevant for some (if not most) observations
of astrophysical masers. We demonstrate that Stokes-$V$ is proportional to the
Zeeman splitting and the fractional linear polarization is independent of the
Zeeman splitting when the ratio of the Zeeman splitting to the spectral line
breadth is small---less than about 0.1. In contrast to its behavior for
ordinary spectral lines, the circular polarization for masers that are at least
partially saturated does not decrease with increasing angle between the
magnetic field and the line-of-sight until they are nearly perpendicular.",0107599v1
2001-10-08,The effect of hyperdiffusivity on turbulent dynamos with helicity,"In numerical studies of turbulence, hyperviscosity is often used as a tool to
extend the inertial subrange and to reduce the dissipative subrange. By
analogy, hyperdiffusivity (or hyperresistivity) is sometimes used in
magnetohydrodynamics. The underlying assumption is that only the small scales
are affected by this manipulation. In the present paper, possible side effects
on the evolution of the large scale magnetic field are investigated. It is
found that for turbulent flows with helicity, hyperdiffusivity causes the
dynamo-generated magnetic field to saturate at a higher level than normal
diffusivity. This result is successfully interpreted in terms of magnetic
helicity conservation, which also predicts that full saturation is only reached
after a time comparable to the large scale magnetic (hyper)diffusion time.",0110171v1
2003-08-14,Saturated State of the Nonlinear Small-Scale Dynamo,"We consider the problem of incompressible, forced, nonhelical, homogeneous
and isotropic MHD turbulence with no mean magnetic field and large magnetic
Prandtl number. This type of MHD turbulence is the end state of the turbulent
dynamo, which generates folded fields with small-scale direction reversals. We
propose a model in which saturation is achieved as a result of the velocity
statistics becoming anisotropic with respect to the local direction of the
magnetic folds. The model combines the effects of weakened stretching and
quasi-two-dimensional mixing and produces magnetic-energy spectra in remarkable
agreement with numerical results at least in the case of a one-scale flow. We
conjecture that the statistics seen in numerical simulations could be explained
as a superposition of these folded fields and Alfv\'en-like waves that
propagate along the folds.",0308252v2
2004-03-13,Magnetic activity in late-type giant stars: Numerical MHD simulations of non-linear dynamo action in Betelgeuse,"Evidence is presented from numerical magneto-hydrodynamical simulations for
the existence of magnetic activity in late-type giant stars. A red supergiant
with stellar parameters similar to that of Betelgeuse (alpha Orionis) is
modeled as a ""star-in-a-box"" with the high-order ""Pencil Code"". Both linear
kinematic and non-linear saturated dynamo action are found: the non-linear
magnetic field saturates at a super-equipartition value (a factor two above
equipartition yielding surface fields with strengths on the order of 500
Gauss), while in the linear regime two different modes of dynamo action are
found. It is speculated that magnetic activity of late-type giants may
influence dust and wind formation and possibly lead to the heating of the outer
atmospheres of these stars.",0403321v1
2003-06-12,On Aharonov-Bohm oscillation in a ferromagnetic ring,"Aharonov-Bohm effect in a ferromagnetic thin ring in diffusive regime is
theoretically studied by calculating the Cooperon and Diffuson. In addition to
the spin-orbit interaction, we include the spin-wave excitation and the spin
splitting, which are expected to be dominant sources of dephasing in
ferromagnets at low temperatures. The spin splitting turns out to kill the
spin-flip channel of Cooperon but leaves the spin-conserving channel untouched.
For the experimental confirmation of interference effect (described by
Cooperons) such as weak localization and Aharonov-Bohm oscillation with period
$h/2e$, we need to suppress the dominant dephasing by orbital motion. To do
this we propose experiments on a thin film or thin ring with magnetization and
external field perpendicular to the film, in which case the effective field
inside the sample is equal to the external field (magnetization does not add
up). The field is first applied strong enough to saturate the magnetization and
then carrying out the measurement down to zero field keeping the magnetization
nearly saturated, in order to avoid domain formations (negative fields may also
be investigated if the coercive field is large enough).",0306309v1
2006-09-11,"$^{133}$Cs NMR investigation of 2D frustrated Heisenberg antiferromagnet, Cs$_2$CuCl$_4$","We report $^{133}$Cs nuclear magnetic resonance (NMR) measurements on the 2D
frustrated Heisenberg antiferromagnet Cs$_2$CuCl$_4$ down to 2 K and up to 15
T. We show that $^{133}$Cs NMR is a good probe of the magnetic degrees of
freedom in this material. Cu spin degrees of freedom are sensed through a
strong anisotropic hyperfine coupling. The spin excitation gap opens above the
critical saturation field. The gap value was determined from the activation
energy of the nuclear spin-lattice relaxation rate in a magnetic field applied
parallel to the Cu chains (b axis). The values of the g-factor and the
saturation field are consistent with the neutron-scattering and magnetization
results. The measurements of the spin-spin relaxation time are exploited to
show that no structural changes occur down to the lowest temperatures
investigated.",0609256v1
2008-02-22,Three-dimensional stability of magnetically confined mountains on accreting neutron stars,"We examine the hydromagnetic stability of magnetically confined mountains,
which arise when material accumulates at the magnetic poles of an accreting
neutron star. We extend a previous axisymmetric stability analysis by
performing three-dimensional simulations using the ideal-magnetohydrodynamic
(ideal-MHD) code \textsc{zeus-mp}, investigating the role played by boundary
conditions, accreted mass, stellar curvature, and (briefly) toroidal magnetic
field strength. We find that axisymmetric equilibria are susceptible to the
undular sub-mode of the Parker instability but are not disrupted. The
line-tying boundary condition at the stellar surface is crucial in stabilizing
the mountain. The nonlinear three-dimensional saturation state of the
instability is characterized by a small degree of nonaxisymmetry ($\la 0.1$ per
cent) and a mass ellipticity of $\epsilon \sim 10^{-5}$ for an accreted mass of
$M_a = 10^{-5} M_\odot$. Hence there is a good prospect of detecting
gravitational waves from accreting millisecond pulsars with long-baseline
interferometers such as Advanced LIGO. We also investigate the ideal-MHD
spectrum of the system, finding that long-wavelength poloidal modes are
suppressed in favour of toroidal modes in the nonaxisymmetric saturation state.",0802.3238v1
2008-03-07,Nonlinear Saturation of the Weibel Instability in a Dense Fermi Plasma,"We present an investigation for the generation of intense magnetic fields in
dense plasmas with an anisotropic electron Fermi-Dirac distribution. For this
purpose, we use a new linear dispersion relation for transverse waves in the
Wigner-Maxwell dense quantum plasma system. Numerical analysis of the
dispersion relation reveals the scaling of the growth rate as a function of the
Fermi energy and the temperature anisotropy. The nonlinear saturation level of
the magnetic fields is found through fully kinetic simulations, which indicates
that the final amplitudes of the magnetic fields are proportional to the linear
growth rate of the instability. The present results are important for
understanding the origin of intense magnetic fields in dense Fermionic plasmas,
such as those in the next generation intense laser-solid density plasma
experiments.",0803.1036v1
2009-05-21,Long-range Ni/Mn structural order in epitaxial double perovskite La2NiMnO6 thin films,"We report and compare the structural, magnetic, and optical properties of
ordered La2NiMnO6 thin films and its disordered LaNi0.5Mn0.5O3 counterpart. An
x-ray diffraction study reveals that the B-site Ni/Mn ordering induces
additional XRD reflections as the crystal symmetry is transformed from a
pseudocubic perovskite unit cell in the disordered phase to a monoclinic form
with larger lattice parameters for the ordered phase. Polarized Raman
spectroscopy studies reveal that the ordered samples are characterized by
additional phonon excitations that are absent in the disordered phase. The
appearance of these additional phonon excitations is interpreted as the
clearest signature of Brillouin zone folding as a result of the long-range
Ni/Mn ordering in La2NiMnO6. Both ordered and disordered materials display a
single ferromagnetic-to-paramagnetic transition. The ordered films display also
a saturation magnetization close to 4.8 mB/f.u. and a transition temperature
(FM-TC) around 270 K, while the disordered ones have only a 3.7 mB/f.u.
saturation magnetization and a FM-TC around 138 K. The differences in their
magnetic behaviours are understood based on the distinct local electronic
configurations of their Ni/Mn cations.",0905.3550v1
2009-08-24,The two-dimensional frustrated Heisenberg model on the orthorhombic lattice,"We discuss new high-field magnetization data recently obtained by Tsirlin et
al. for layered vanadium phosphates in the framework of the square-lattice
model. Our predictions for the saturation fields compare exceptionally well to
the experimental findings, and the strong bending of the curves below
saturation agrees very well with the experimental field dependence. Furthermore
we discuss the remarkably good agreement of the frustrated Heisenberg model on
the square lattice in spite of the fact that the compounds described with this
model actually have a lower crystallographic symmetry. We present results from
our calculations on the thermodynamics of the model on the orthorhombic (i.e.,
rectangular) lattice, in particular the temperature dependence of the magnetic
susceptibility. This analysis also sheds light on the discussion of magnetic
frustration and anisotropy of a class of iron pnictide parent compounds, where
several alternative suggestions for the magnetic exchange models were proposed.",0908.3442v1
2011-02-03,Strongly enhanced magnetic moments in ferromagnetic FeMnP$_{0.50}$Si$_{0.50}$,"The compound FeMnP$_{0.50}$Si$_{0.50}$ has been studied by magnetic
measurements, M\""ossbauer spectroscopy and electronic structure and total
energy calculations. An unexpected high magnetic hyperfine field for Fe atoms
located at the tetrahedral Me(1) site in the Fe$_2$P structure is found. The
saturation moment derived from magnetic measurements corresponds to 4.4
$\mu_B$/f.u. at low temperatures, a value substantially higher than previously
reported, but in accord with the results from our electron structure
calculations. This high saturation moment, a first order nature of the
ferromagnetic transition and a tunable transition temperature make the
Fe$_{2-x}$Mn$_{x}$P$_{1-y}$Si$y$ system promising for magnetocaloric
applications.",1102.0636v1
2011-07-02,Energy dissipation and switching delay in spin-transfer torque switching of nanomagnets with low-saturation magnetization in the presence of thermal fluctuations,"A common ploy to reduce the switching current and energy dissipation in
spin-transfer-torque driven magnetization switching of shape-anisotropic
single-domain nanomagnets is to employ magnets with low saturation
magnetization $M_s$ and high shape-anisotropy. The high shape-anisotropy
compensates for low $M_s$ to keep the static switching error rate constant.
However, this ploy increases the switching delay, its variance in the presence
of thermal noise, and the dynamic switching error rate. Using the stochastic
Landau-Lifshitz-Gilbert equation with a random torque emulating thermal noise,
we show that pumping some excess spin-polarized current into the nanomagnet
during switching will keep the mean switching delay and its variance constant
as we reduce $M_s$, while still reducing the energy dissipation significantly.",1107.0387v2
2011-09-03,Atmospheres of Hot Super-Earths,"Hot super-Earths likely possess minimal atmospheres established through vapor
saturation equilibrium with the ground. We solve the hydrodynamics of these
tenuous atmospheres at the surface of Corot-7b, Kepler 10b and 55 Cnc-e,
including idealized treatments of magnetic drag and ohmic dissipation. We find
that atmospheric pressures remain close to their local saturation values in all
cases. Despite the emergence of strongly supersonic winds which carry
sublimating mass away from the substellar point, the atmospheres do not extend
much beyond the day-night terminators. Ground temperatures, which determine the
planetary thermal (infrared) signature, are largely unaffected by exchanges
with the atmosphere and thus follow the effective irradiation pattern.
Atmospheric temperatures, however, which control cloud condensation and thus
albedo properties, can deviate substantially from the irradiation pattern.
Magnetic drag and ohmic dissipation can also strongly impact the atmospheric
behavior, depending on atmospheric composition and the planetary magnetic field
strength. We conclude that hot super-Earths could exhibit interesting
signatures in reflection (and possibly in emission) which would trace a
combination of their ground, atmospheric and magnetic properties.",1109.0659v2
2011-11-30,Radius Dependent Angular Momentum Evolution in Low-Mass Stars. I,"Angular momentum evolution in low-mass stars is determined by initial
conditions during star formation, stellar structure evolution, and the
behaviour of stellar magnetic fields. Here we show that the empirical picture
of angular momentum evolution arises naturally if rotation is related to
magnetic field strength instead of to magnetic flux, and formulate a corrected
braking law based on this. Angular momentum evolution then becomes a strong
function of stellar radius, explaining the main trends observed in open
clusters and field stars at a few Gyr: the steep transition in rotation at the
boundary to full convection arises primarily from the large change in radius
across this boundary, and does not require changes in dynamo mode or field
topology. Additionally, the data suggest transient core-envelope decoupling
among solar-type stars, and field saturation at longer periods in very low-mass
stars. For solar-type stars, our model is also in good agreement with the
empirical Skumanich law. Finally, in further support of the theory, we show
that the predicted age at which low-mass stars spin down from the saturated to
unsaturated field regimes in our model corresponds remarkably well to the
observed lifetime of magnetic activity in these stars.",1111.7071v1
2012-12-07,The small scale dynamo and the amplification of magnetic fields in massive primordial haloes,"While present standard model of cosmology yields no clear prediction for the
initial magnetic field strength, efficient dynamo action may compensate for
initially weak seed fields via rapid amplification. In particular, the
small-scale dynamo is expected to exponentially amplify any weak magnetic field
in the presence of turbulence. We explore whether this scenario is viable using
cosmological magneto-hydrodynamics simulations modeling the formation of the
first galaxies, which are expected to form in so-called atomic cooling halos
with virial temperatures $\rm T_{vir} \geq 10^{4}$ K. As previous calculations
have shown that a high Jeans resolution is needed to resolve turbulent
structures and dynamo effects, our calculations employ resolutions of up to 128
cells per Jeans length. The presence of the dynamo can be clearly confirmed for
resolutions of at least 64 cells per Jeans length, while saturation occurs at
approximate equipartition with turbulent energy. As a result of the large
Reynolds numbers in primordial galaxies, we expect saturation to occur at early
stages, implying magnetic field strengths of \sim0.1 $\mu$G at densities of
10^4 cm^{-3}.",1212.1619v2
2013-01-09,High coercivity induced by mechanical milling in cobalt ferrite powders,"In this work we report a study of the magnetic behavior of ferrimagnetic
oxide CoFe2O4 treated by mechanical milling with different grinding balls. The
cobalt ferrite nanoparticles were prepared using a simple hydrothermal method
and annealed at 500oC. The non-milled sample presented coercivity of about 1.9
kOe, saturation magnetization of 69.5 emu/g, and a remanence ratio of 0.42.
After milling, two samples attained coercivity of 4.2 and 4.1 kOe, and
saturation magnetization of 67.0 and 71.4 emu/g respectively. The remanence
ratio MR/MS for these samples increase to 0.49 and 0.51, respectively. To
investigate the influence of the microstructure on the magnetic behavior of
these samples, we used X-ray powder diffraction (XPD), transmission electron
microscopy (TEM), and vibrating sample magnetometry (VSM). The XPD analysis by
the Williamson-Hall plot was used to estimate the average crystallite size and
strain induced by mechanical milling in the samples.",1301.1945v1
2013-04-17,Turbulent amplification of magnetic field driven by dynamo effect at rippled shocks,"We derive analytically the vorticity generated downstream of a
two-dimensional rippled hydromagnetic shock neglecting fluid viscosity and
resistivity. The growth of the turbulent component of the downstream magnetic
field is driven by the vortical eddies motion. We determine an analytic
time-evolution of the magnetic field amplification at shocks, so far described
only numerically, until saturation occurs due to seed-field reaction to field
lines whirling. The explicit expression of the amplification growth rate and of
the non-linear field back-reaction in terms of the parameters of shock and
interstellar density fluctuations is derived from MHD jump conditions at
rippled shocks. A magnetic field saturation up to the order of milligauss and a
short-time variability in the $X$-ray observations of supernova remnants can be
obtained by using reasonable parameters for the interstellar turbulence.",1304.4956v1
2013-10-31,Exchange bias associated with phase separation in the Nd2/3Ca1/3MnO3 manganite,"The exchange bias (EB) phenomenon has been found in Nd2/3Ca1/3MnO3
perovskite. The phenomenon manifests itself as a negative horizontal shift of
magnetization hysteresis loops. The EB phenomenon is evident of an interface
exchange coupling between coexisting antiferromagnetic (AFM) and ferromagnetic
(FM) phases and confirms the phase separated state of the compound at low
temperatures. The EB effect is found to be strongly dependent on the cooling
magnetic field and the temperature, which is associated with the evolution of
spontaneous AFM - FM phase separated state of the compound. Analysis of
magnetic hysteresis loops has shown that ferromagnetic moment $M_{FM}$
originating from the FM clusters saturates in a relatively low magnetic field
about H ~ 0.4T. The obtained saturation value $M_{FM}$(1T) ~ 0.45$\mu_{B}$ is
in a good agreement with our previous neutron diffraction data.",1310.8590v1
2013-11-13,Fokker-Planck approach to the theory of magnon-driven spin Seebeck effect,"Following the theoretical approach by Xiao et al [Phys. Rev. B 81, 214418
(2010)] to the spin Seebeck effect, we calculate the mean value of the total
spin current flowing through a normalmetal/ ferromagnet interface. The spin
current emitted from the ferromagnet to the normal metal is evaluated in the
framework of the Fokker-Planck approach for the stochastic
Landau-Lifshitz-Gilbert equation. We show that the total spin current depends
not only on the temperature difference between the electron and the magnon
baths, but also on the external magnetic field and magnetic anisotropy. Apart
from this, the spin current is shown to saturate with increasing magnon
temperature, and the saturation temperature increases with increasing magnetic
field and/or magnetic anisotropy.",1311.3117v1
2014-01-31,Firehose and Mirror Instabilities in a Collisionless Shearing Plasma,"Hybrid-kinetic numerical simulations of firehose and mirror instabilities in
a collisionless plasma are performed in which pressure anisotropy is driven as
the magnetic field is changed by a persistent linear shear $S$. For a
decreasing field, it is found that mostly oblique firehose fluctuations grow at
ion Larmor scales and saturate with energies $\sim$$S^{1/2}$; the pressure
anisotropy is pinned at the stability threshold by particle scattering off
microscale fluctuations. In contrast, nonlinear mirror fluctuations are large
compared to the ion Larmor scale and grow secularly in time; marginality is
maintained by an increasing population of resonant particles trapped in
magnetic mirrors. After one shear time, saturated order-unity magnetic mirrors
are formed and particles scatter off their sharp edges. Both instabilities
drive sub-ion-Larmor--scale fluctuations, which appear to be
kinetic-Alfv\'{e}n-wave turbulence. Our results impact theories of momentum and
heat transport in astrophysical and space plasmas, in which the stretching of a
magnetic field by shear is a generic process.",1402.0010v2
2014-04-10,Thermal effect on magnetic parameters of high-coercivity cobalt ferrite,"We prepared very high-coercivity cobalt ferrite nanoparticles using
short-time high-energy mechanical milling. After the milling process, the
coercivity of the nanoparticles reached 3.75 kOe - a value almost five times
higher than that obtained for the non-milled sample. We performed a thermal
treatment on the milled sample at 300, 400, and 600 oC for 30 and 180 mins, and
studied the changes in the magnetic parameters due to the thermal treatment
using the hysteresis curves, Williamson-Hall analysis, and transmission
electron microscopy. The thermal treatment at 600 oC causes a decrease in the
microstructural strain and density of structural defects resulting in a
significant decrease in coercivity. Furthermore, this thermal treatment
increases the size of the nanoparticles and, as a consequence, there is a
substantial increase in the saturation magnetization. The coercivity and the
saturation magnetization are less affected by the thermal treatment at 300 and
400 oC.",1404.2965v1
2014-11-21,"Structural transitions, magnetic properties, and electronic structures of Co(Fe)-doped MnNiSi compounds","The structural transitions, magnetic properties, and electronic structures of
Co(Fe)-doped MnNiSi compounds are investigated by x-ray powder diffraction
(XRD), differential scanning calorimetry (DSC), magnetic measurements, and
first-principles calculations. Results indicate that all samples undergo a
martensitic transition from the Ni2In-type parent phase to TiNiSi-type
orthorhombic phase at high temperatures. The substitution of Co(Fe) for Mn in
Mn1-xCoxNiSi (x = 0.2, 0.3, 0.4) and Mn1-yFeyNiSi (y = 0.26, 0.30, 0.36, 0.46,
0.55) samples decreases the structural transition temperature (Tt) and Curie
temperature of martensite (TCM). The martensite phases show a typical
ferromagnetic behavior with saturation field (HS) being basically unchanged
with increasing Co(Fe) content, while the saturation magnetization (MS) shows a
decreasing tendency. The theoretically calculated moments are in good agreement
with the experimentally measured results. The orbital hybridizations between
different 3d elements are analyzed from the distribution of density of states.",1411.5766v1
2015-06-01,Evaluation of (BH)max and magnetic anisotropy of cobalt ferrite nanoparticles synthesized in gelatin,"CoFe2O4 nanoparticles were synthesized using gelatin as a polymerizing agent.
Structural, morphological and magnetic properties of samples treated at
different temperatures were investigated by X-ray diffraction, scanning
electron microscopy, Mossbauer spectroscopy and magnetization measurements. Our
results revealed that the samples annealed at 623 K and temperatures above 973
K have a cation distributions given by (Co0.19Fe0.81)[Co0.81Fe1.19]O4 and
(Co0.06Fe0.94)[Co0.94Fe1.06]O4, respectively. The particle sizes varied from 73
to 296 nm and the magnetocrystalline anisotropy, K1, has values ranging from
2.60x10^6 to 2.71x10^6 J/m3, as determined from the law of approach to
saturation applied to the MxH data at high field. At 5 K, the saturation
magnetization, coercive field and (BH)max varied from 76 to 95 Am2/kg, 479.9 to
278.5 kA/m and 9.7 to 20.9 kJ/m3, respectively. The reported values are in good
agreement with near-stoichiometric cobalt ferrite samples.",1506.00505v1
2018-04-29,"The mirror mode: A ""superconducting'' space plasma analogue","We examine the physics of the magnetic mirror mode in its final state of
saturation, the thermodynamic equilibrium, to demonstrate that the mirror mode
is the analogue of a superconducting effect in a classical anisotropic-pressure
space plasma. Two different spatial scales are identified which control the
behaviour of its evolution. These are the ion inertial scale
$\lambda_{im}(\tau)$ based on the excess density $N_m(\tau)$ generated in the
mirror mode, and a correlation length. This can be either the Debye length, the
ion gyro-radius, or a turbulent correlation length. The mirror mode equilibrium
structure under saturation is determined by the Landau-Ginzburg ratio of these
two length scales. Mirror modes then behave like type II superconductors,
naturally giving rise to chains of local depletions of the magnetic field of
the kind observed in the mirror mode, providing the plasma a short scale
magnetic bubble texture. This might be important in the study of magnetic
turbulence in plasmas.",1804.10900v2
2019-08-21,One- and three-dimensional quantum phase transitions and anisotropy in Rb$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$,"Single crystal samples of the frustrated quasi one-dimensional quantum magnet
Rb$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$ are investigated by magnetic, thermodynamic,
and electron spin resonance (ESR) measurements. Quantum phase transitions
between the gapped, magnetically ordered and fully saturated phases are
observed. Surprisingly, the former has a distinctive three-dimensional
character, while the latter is dominated by one-dimensional quantum spin
fluctuations. The entire $H$-$T$ phase diagram is mapped out and found to be
substantially anisotropic. In particular, the lower critical fields differ by
over 50\% depending on the direction of applied field, while the upper ones are
almost isotropic, as is the magnetization above saturation. The ESR spectra are
strongly dependent on field orientation and point to a helical structure with a
rigidly defined spin rotation plane.",1908.07739v3
2019-11-18,Large Scale Dynamo in a Primordial Accretion Flow -- An Interpretation from Hydrodynamic Simulation,"Without an existing large scale coherent magnetic field in the early
Universe, Population III (PopIII) stars would likely rotate at or near break-up
speed. In this work, focusing on the accretion phase of PopIII stars, we
investigate the possibility of generating a coherent magnetic field through
large scale dynamo processes, as well as the corresponding field saturation
level. Using results from hydrodynamic simulations, we demonstrate that
primordial accretion disks are turbulent with a Shakura-Sunyaev disk parameter
$\alpha_{ss} \gtrsim 10^{-3}$, and evidence helical turbulence with a dynamo
number $\vert D_{\alpha \Omega} \vert \gg 10$. The presence of helical
turbulence at these levels allows large scale dynamo modes to grow, and the
saturation level is determined by the amount of net helicity remaining in the
dynamo-active regions (a.k.a. the quenching problem). %We demonstrate that the
magnetic field can reach approximate equipartition, with $B/B_{\rm eq} \sim 3$,
indicating that the dynamo quenching problem could be alleviated through an
accretion flow. We demonstrate that, if the accretion could successfully
alleviate the quenching problem, the magnetic field can reach approximate
equipartition with $B/B_{\rm eq} \sim 3$.",1911.07898v1
2020-02-14,Two-channel anomalous Hall effect in SrRuO3,"The Hall effect in SrRuO$_3$ thin-films near the thickness limit for
ferromagnetism shows an extra peak in addition to the ordinary and anomalous
Hall effects. This extra peak has been attributed to a topological Hall effect
due to two-dimensional skyrmions in the film around the coercive field;
however, the sign of the anomalous Hall effect in SrRuO$_3$ can change as a
function of saturation magnetization. Here we report Hall peaks in SrRuO$_3$ in
which volumetric magnetometry measurements and magnetic force microscopy
indicate that the peaks result from the superposition of two anomalous Hall
channels with opposite sign. These channels likely form due to thickness
variations in SrRuO$_3$, creating two spatially separated magnetic regions with
different saturation magnetizations and coercive fields. The results are
central to the development of strongly correlated materials for spintronics.",2002.06062v2
2020-09-07,Magnetic Binary Supersaturated Solid Solutions Processed by Severe Plastic Deformation,"Samples consisting of one ferromagnetic and one diamagnetic component which
are immiscible at the thermodynamic equilibrium (Co-Cu, Fe-Cu, Fe-Ag) are
processed by high-pressure torsion at various compositions. The received
microstructures are investigated by electron microscopy and synchrotron X-ray
diffraction, showing a microstructural saturation. Results gained from
microstructural investigations are correlated to magnetometry data. The Co-Cu
samples show mainly ferromagnetic behavior and a decrease in coercivity with
increasing Co-content. The saturation microstructure of Fe-Cu samples is found
to be dual phase. Results of magnetic measurements also revealed the occurrence
of two different magnetic phases in this system. For Fe-Ag, the microstructural
and magnetic results indicate that no intermixing between the elemental phases
takes place.",2009.02939v1
2020-10-22,Pressure-tuned intralayer exchange in superlattice-like MnBi2Te4/(Bi2Te3)n topological insulators,"The magnetic structures of MnBi2Te4(Bi2Te3)n can be manipulated by tuning the
interlayer coupling via the number of Bi2Te3 spacer layers n, while the
intralayer ferromagnetic (FM) exchange coupling is considered too robust to
control. By applying hydrostatic pressure up to 3.5 GPa, we discover opposite
responses of magnetic properties for n = 1 and 2. MnBi4Te7 stays at A-type
antiferromagnetic (AFM) phase with a decreasing N\'eel temperature and an
increasing saturation field. In sharp contrast, MnBi6Te10 experiences a phase
transition from A-type AFM to a quasi-two-dimensional FM state with a
suppressed saturation field under pressure. First-principles calculations
reveal the essential role of intralayer exchange coupling from lattice
compression in determining these magnetic properties. Such magnetic phase
transition is also observed in 20% Sb-doped MnBi6Te10 due to the in-plane
lattice compression.",2010.11466v2
2020-12-20,Reconstructing phase-resolved hysteresis loops from first-order reversal curves,"The first order reversal curve (FORC) method is a magnetometry based
technique used to capture nanoscale magnetic phase separation and interactions
with macroscopic measurements using minor hysteresis loop analysis. This makes
the FORC technique a powerful tool in the analysis of complex systems which
cannot be effectively probed using localized techniques. However, recovering
quantitative details about the identified phases which can be compared to
traditionally measured metrics remains an enigmatic challenge. We demonstrate a
technique to reconstruct phase-resolved magnetic hysteresis loops by
selectively integrating the measured FORC distribution. From these minor loops,
the traditional metrics - including the coercivity and saturation field, and
the remanent and saturation magnetization - can be determined. In order to
perform this analysis, special consideration must be paid to the accurate
quantitative management of the so-called reversible features. This technique is
demonstrated on three representative materials systems, high anisotropy FeCuPt
thin-films, Fe nanodots, and SmCo/Fe exchange spring magnet films, and shows
excellent agreement with the direct measured major loop, as well as the phase
separated loops.",2012.11041v1
2023-07-10,Optical-power-dependent splitting of magnetic resonance in nitrogen-vacancy centers in diamond,"Nitrogen-vacancy (NV) centers in diamonds are a powerful tool for accurate
magnetic field measurements. The key is precisely estimating the
field-dependent splitting width of the optically detected magnetic resonance
(ODMR) spectra of the NV centers. In this study, we investigate the optical
power dependence of the ODMR spectra using NV ensemble in nanodiamonds (NDs)
and a single-crystal bulk diamond. We find that the splitting width
exponentially decays and is saturated as the optical power increases.
Comparison between NDs and a bulk sample shows that while the decay amplitude
is sample-dependent, the optical power at which the decay saturates is almost
sample-independent. We propose that this unexpected phenomenon is an intrinsic
property of the NV center due to non-axisymmetry deformation or impurities. Our
finding indicates that diamonds with less deformation are advantageous for
accurate magnetic field measurements.",2307.04414v1
2023-09-19,Multiple Magnetoelectric Plateaux in Polar Magnet Fe$_2$Mo$_3$O$_8$,"The magnetization and electric polarization of a polar antiferromagnet
Fe$_2$Mo$_3$O$_8$ are studied up to 66 T for spin-saturation magnetic fields
applied along the polar axis. The magnetization process at 1.4 K exhibited
multistep structures below the saturation field of 65 T. The electric
polarization along the polar axis exhibits a similar multistep behavior with a
total change of 1.2 $\rm{\mu}C/cm^{2}$. A combined triangular-lattice
antiferromagnetic model with strong Ising-type spin anisotropy reproduces this
multistep magnetoelectric (ME) effect. The exchange striction mechanism
explains the remarkable ME response in the two sub-lattice type-I multiferroic
materials. These results and interpretation demonstrate a method for realizing
multistage magnetoelectric effects in hybrid spin systems.",2309.10583v1
2004-10-20,Nonlinear saturation of magnetic curvature driven Rayleigh Taylor instability in three dimensions,"We present three dimensional fluid simulation results on the temporal
evolution and nonlinear saturation of the magnetic curvature driven
Rayleigh-Taylor (RT) instability. The model set of coupled nonlinear equations
evolve the scalar electric field potential $\phi$, plasma density $n$ and the
parallel component of the magnetic vector potential $\psi$. The simulations
have been carried out in two limits, (i) a low resistivity case in which RT is
the only linearly growing mode, and (ii) a high resistivity case where the
drift wave is unstable and for which the magnetic curvature parameter is set to
zero to ensure the absence of the RT growth. Our simulations show nonlinear
stabilization in both these limits. The stabilization mechanism is similar to
that observed in earlier two dimensional simulations, namely the generation of
zonal shear flows which decorrelate the radially extended unstable modes.
However the nature of the saturated nonlinear state in the 3d case differs from
that of 2d in some important ways such as by having significant levels of power
in short scales and by the presence of electromagnetic fluctuations. Though, in
the linear regime the electromagnetic effects reduce the growth rates, in the
nonlinear regime their presence hinders the process of stabilization by
inhibiting the process of zonal flow formation. Thus the parameter regime for
which nonlinear stabilization takes place is considerably reduced in three
dimensions.",0410178v1
2014-01-21,Exploring the magnetic field complexity in M dwarfs at the boundary to full convection,"Based on detailed spectral synthesis we carry out quantitative measurements
of the strength and complexity of surface magnetic fields in the four
well-known M-dwarfs GJ 388, GJ 729, GJ 285, and GJ 406 populating the mass
regime around the boundary between partially and fully convective stars. Very
high resolution R=100000, high signal-to-noise (up to 400) near-infrared Stokes
I spectra were obtained with CRIRES at ESO's Very Large Telescope covering
regions of the FeH Wing-Ford transitions at 1mum. The field distributions in
all four stars are characterized by three distinct groups of field components,
the data are neither consistent with a smooth distribution of different field
strengths, nor with one average field strength covering the full star. We find
evidence of a subtle difference in the field distribution of GJ 285 compared to
the other three targets. GJ 285 also has the highest average field of 3.5kG and
the strongest maximum field component of 7-7.5kG. The maximum local field
strengths in our sample seem to be correlated with rotation rate. While the
average field strength is saturated, the maximum local field strengths in our
sample show no evidence for saturation. We find no difference between the field
distributions of partially and fully convective stars. The one star with
evidence for a field distribution different to the other three is the most
active star (i.e. with largest x-ray luminosity and mean surface magnetic
field) rotating relatively fast. A possible explanation is that rotation
determines the distribution of surface magnetic fields, and that local field
strengths grow with rotation even in stars in which the average field is
already saturated.",1401.5250v1
2015-01-16,Direct measurement of the magnetic anisotropy field in Mn--Ga and Mn--Co--Ga Heusler films,"The static and dynamic magnetic properties of tetragonally distorted Mn--Ga
based alloys were investigated. Static properties are determined in magnetic
fields up to 6.5~T using SQUID magnetometry. For the pure Mn$_{1.6}$Ga film,
the saturation magnetisation is 0.36~MA/m and the coercivity is 0.29~T. Partial
substitution of Mn by Co results in Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$. The
saturation magnetisation of those films drops to 0.2~MA/m and the coercivity is
increased to 1~T.
  Time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the
high-frequency dynamics of Mn--Ga. The ferromagnetic resonance frequency
extrapolated to zero-field is found to be 125~GHz with a Gilbert damping,
$\alpha$, of 0.019. The anisotropy field is determined from both SQUID and
TR-MOKE to be 4.5~T, corresponding to an effective anisotropy density of
0.81~MJ/m$^3$.
  Given the large anisotropy field of the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film,
pulsed magnetic fields up to 60~T are used to determine the field strength
required to saturate the film in the plane. For this, the extraordinary Hall
effect was employed as a probe of the local magnetisation. By integrating the
reconstructed in--plane magnetisation curve, the effective anisotropy energy
density for Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ is determined to be 1.23~MJ/m$^3$.",1501.03973v1
2015-10-23,Quantum Critical Scaling for a Heisenberg Spin-$1/2$ Chain around Saturation,"We demonstrate quantum critical scaling for an $S=1/2$ Heisenberg
antiferromagnetic chain compound CuPzN in a magnetic field around saturation,
by analysing previously reported magnetization [Y. Kono {\it et al.}, Phys.
Rev. Lett. {\bf 114}, 037202 (2015)], thermal expansion [J. Rohrkamp {\it et
al.}, J. Phys.: Conf. Ser. {\bf 200}, 012169 (2010)] and NMR relaxation data
[H. K\""uhne {\it et al.}, Phys. Rev. B {\bf 80}, 045110 (2009)]. The scaling of
magnetization is demonstrated through collapsing the data for a range of both
temperature and field onto a single curve without making any assumption for a
theoretical form. The data collapse is subsequently shown to closely follow the
theoretically-predicted scaling function without any adjustable parameters.
Experimental boundaries for the quantum critical region could be drawn from the
variable range beyond which the scaled data deviate from the theoretical
function. Similarly to the magnetization, quantum critical scaling of the
thermal expansion is also demonstrated. Further, the spin dynamics probed via
NMR relaxation rate $1/T_1$ close to the saturation is shown to follow the
theoretically-predicted quantum critical behavior as $1/T_1\propto T^{-0.5}$
persisting up to temperatures as high as $k_\mathrm{B}T \simeq J$, where $J$ is
the exchange coupling constant.",1510.07056v1
2016-11-08,Kondo screening and beyond: an x-ray absorption and dichroism study of CePt$_5$/Pt(111),"We use x-ray absorption spectroscopy as well as its linear and circular
magnetic dichroisms to characterize relevant interactions and energy scales in
the surface intermetallic CePt$_5$/Pt(111). The experiments provide insight
into crystal field splitting, effective paramagnetic moments, their Kondo
screening and mutual interactions and thus into many aspects which typically
determine the low temperature behavior of correlated rare earth compounds.
Exploiting the tuneability of Ce valence through the thickness dependent
epitaxial strain at the CePt$_5$/Pt(111) interface, we are able to
systematically investigate the impact of hybridization strength on these
interactions. Considerable Kondo screening is indeed observed at all CePt$_5$
thicknesses, and found to be strongest in case of strongest hybridization.
While the magnetic response is commensurate with an impurity Kondo scale of
$T_K \gtrsim 10^2$ K for specimen temperatures $T \gtrsim 30$ K, this is no
longer the case at lower temperature. Its detailed study by XMCD at one
specific thickness of CePt$_5$ reveals an anomaly of the susceptibility at $T^*
\approx 25$ K instead, which we tentatively associate with the onset of lattice
coherence. At lowest temperature we observe paramagnetic saturation with a
small Ce $4f$ saturation magnetization. Within the framework of itinerant $4f$
electrons, saturation is due to a field induced Lifshitz transition involving a
very heavy band with correspondingly small degeneracy temperature of $T_F
\approx 7$ K. This small energy scale results in the persistence of Curie-Weiss
behavior across the entire range of experimentally accessible temperatures ($T
\gtrsim 2$ K). Our work highlights the potential of magnetic circular dichroism
studies in particular for Kondo and heavy fermion materials, which so far has
remained largely unexplored.",1611.02599v1
2017-11-30,"Self-inhibiting thermal conduction in high-beta, whistler-unstable plasma","A heat flux in a high-$\beta$ plasma with low collisionality triggers the
whistler instability. Quasilinear theory predicts saturation of the instability
in a marginal state characterized by a heat flux that is fully controlled by
electron scattering off magnetic perturbations. This marginal heat flux does
not depend on the temperature gradient and scales as $1/\beta$. We confirm this
theoretical prediction by performing numerical particle-in-cell simulations of
the instability. We further calculate the saturation level of magnetic
perturbations and the electron scattering rate as functions of $\beta$ and the
temperature gradient to identify the saturation mechanism as quasilinear.
Suppression of the heat flux is caused by oblique whistlers with
magnetic-energy density distributed over a wide range of propagation angles.
This result can be applied to high-$\beta$ astrophysical plasmas, such as the
intracluster medium, where thermal conduction at sharp temperature gradients
along magnetic-field lines can be significantly suppressed. We provide a
convenient expression for the amount of suppression of the heat flux relative
to the classical Spitzer value as a function of the temperature gradient and
$\beta$. For a turbulent plasma, the additional independent suppression by the
mirror instability is capable of producing large total suppression factors
(several tens in galaxy clusters) in regions with strong temperature gradients.",1711.11462v3
2019-02-26,Enhanced Gilbert Damping in Re doped FeCo Films: A Combined Experimental and Theoretical Study,"The effects of rhenium doping in the range 0 to 10 atomic percent on the
static and dynamic magnetic properties of Fe65Co35 thin films have been studied
experimentally as well as with first principles electronic structure
calculations focusing on the change of the saturation magnetization and the
Gilbert damping parameter. Both experimental and theoretical results show that
the saturation magnetization decreases with increasing Re doping level, while
at the same time Gilbert damping parameter increases. The experimental low
temperature saturation magnetic induction exhibits a 29 percent decrease, from
2.31 T to 1.64 T, in the investigated doping concentration range, which is more
than predicted by the theoretical calculations. The room temperature value of
the damping parameter obtained from ferromagnetic resonance measurements,
correcting for extrinsic contributions to the damping, is for the undoped
sample 0.0027, which is close to the theoretically calculated Gilbert damping
parameter. With 10 atomic percent Re doping, the damping parameter increases to
0.0090, which is in good agreement with the theoretical value of 0.0073. The
increase in damping parameter with Re doping is explained by the increase in
density of states at Fermi level, mostly contributed by the spin-up channel of
Re. Moreover, both experimental and theoretical values for the damping
parameter are observed to be weakly decreasing with decreasing temperature.",1902.09896v1
2019-11-05,General relativistic magnetohydrodynamic dynamo in thick accretion disks: fully nonlinear simulations,"The recent imaging of the M87 black hole at millimeter wavelengths by the
Event Horizon Telescope (EHT) collaboration has triggered a renewed interest in
numerical models for the accretion of magnetized plasma in the regime of
general relativistic magnetohydrodynamics (GRMHD). Here non-ideal simulations,
including both the resistive effects and, above all, the mean-field dynamo
action due to sub-scale, unresolved turbulence, are applied for the first time
to such systems in the fully nonlinear regime. Combined with the differential
rotation of the disk, the dynamo process is able to produce an exponential
growth of any initial seed magnetic field up to the values required to explain
the observations, when the instability tends to saturate even in the absence of
artificial quenching effects. Before reaching the final saturation stage we
observe a secondary regime of exponential growing, where the magnetic field
increases more slowly due to accretion, which is modifying the underlying
equilibrium. By varying the dynamo coefficient we obtain different growth
rates, though the field seems to saturate at approximately the same level, at
least for the limited range of parameters explored here, providing substantial
values for the MAD parameter for magnetized accretion. For reasonable values of
the central mass density and the commonly employed recipes for synchrotron
emission by relativistically hot electrons, our model is able to reproduce
naturally the observed flux of Sgr A*, the next target for EHT.",1911.01838v1
2023-07-13,Black Hole Accretion with Saturated Magnetic Pressure and Disk Wind,"We construct an analytical black hole accretion disk model that incorporates
both magnetic pressure and disk wind, which are found to be important from
numerical simulations. A saturated magnetic pressure that relates the Alfven
velocity with local Keplerian velocity and gas sound speed is assumed in
addition to radiation and gas pressures. The mass accretion rate is assumed to
have a power-law form in response to mass loss in the wind. We find three sets
of self-consistent solutions that are thermally stable and satisfy the model
assumptions. At high accretion rates, the disk is geometrically and optically
thick, resembling the slim disk solution. At relatively low accretion rates,
our model predicts an accretion flow consisting of a geometrically thin and
optically thick outer disk (similar to the standard disk), and a geometrically
thick and optically thin inner disk (similar to the advection-dominated
accretion flow or ADAF). Thus, this is a natural solution for a truncated disk
connected with an inner ADAF, which has been proposed to explain some
observations. The magnetic pressure plays a more important role than the
outflow in shaping the disk structure. The observed disk luminosity tends to
saturate around 8 times the Eddington limit, suggesting that supercritical
accretion onto black holes can be used for black hole mass estimate, or a
standard candle with known black hole masses.",2307.06585v1
2005-09-15,Polarization of Water Masers in the presence of Velocity and Magnetic Field Gradients,"Through polarization observations water masers are excellent probes of
magnetic fields in the maser region. Magnetic field strengths, such as those in
the water masers regions of the envelopes of late-type stars and star-forming
regions, are typically determined using a direct relation between the field
strength and the observed circular polarization. Here it is shown that velocity
and magnetic field gradients along the maser have a significant effect on the
field strengths obtained from circular polarization observations. Due to
velocity gradients the actual magnetic field strength could be up to 100%
higher than the field strength derived from the observations. Additionally,
when a magnetic field gradient is present, the resulting circular polarization
derived is caused predominantly by the average magnetic field in the
unsaturated maser core. Measurements of the fractional linear polarization are
not affected by velocity or magnetic field strength gradients, though changes
in the magnetic field angle along the maser do quench the linear polarization
intensity when the maser saturates.",0509435v1
2002-04-05,Magnetic Phase Transition and Magnetization Plateau in Cs$_2$CuBr$_4$,"The crystal structure of Cs$_2$CuBr$_4$ is the same as that of
Cs$_2$CuCl$_4$, which has been characterized as a spin-1/2
quasi-two-dimensional frustrated system. The magnetic properties of
Cs$_2$CuBr$_4$ were investigated by magnetization and specific heat
measurements. The phase transition at zero magnetic field was detected at
$T_{\rm N}=1.4$ K. It was observed that the magnetization curve has a plateau
at about one-third of the saturation magnetization for magnetic field $H$
parallel to the $b$- and $c$-axes, while no plateau was observed for
$H\parallel a$. The field-induced phase transition to the plateau state appears
to be of the first order. The mechanism leading to the magnetization plateau is
discussed.",0204125v1
2006-11-08,Anisotropic magnetic properties of CeAg$_2$Ge$_2$ single crystal,"In order to investigate the anisotropic magnetic properties of
CeAg$_2$Ge$_2$, we have successfully grown the single crystals, for the first
time, by high temperature solution growth (flux) method. We have performed a
detailed study of the grown single crystals by measuring their electrical
resistivity, magnetic susceptibility, magnetization, specific heat and
magnetoresistance. A clear anisotropy and an antiferromagnetic transition at
$T_{\rm N}$ = 4.6 K have been observed in the magnetic properties. The magnetic
entropy reaches $R$ ln 4 at 20 K indicating that the ground state and the first
excited state are very closely spaced (a quasi-quartet state). From the
specific heat measurements and crystalline electric field (CEF) analysis of the
magnetic susceptibility, we have found the level splitting energies as 5 K and
130 K. The magnetization measurements reveal that the a-axis is the easy axis
of magnetization and the saturation moment is $\mu_{\rm s}$ = 1.6 $\mu_{\rm
B}$/Ce, corroborating the previous neutron diffraction measurements on a
polycrystalline sample.",0611197v2
2010-04-02,Structure and magnetic properties of nanocrystalline PrCo3,"The structure and magnetic properties of nanocrystalline PrCo$_3$ prepared by
high-energy milling technique have been investigated by means of X-ray
diffraction using the Rietveld method coupled to Curie temperature and magnetic
measurements. The as-milled samples were subsequently annealed in temperature
range from 750 to 1050 {\deg}C for 30 min to optimize the extrinsic properties.
From x-ray studies of magnetic aligned samples, the magnetic anisotropy of this
compounds is found uniaxial. The Curie temperature is 349 {\deg}K and no
saturation reached at room temperature for applied field of 90 kOe. The
coercive field of 55 kOe and 12 kOe measured at 10 and 293 K respectively is
obtained after annealing at 750 {\deg}C for 30 min suggests that
nanocrystalline PrCo$_3$ are interesting candidates in the field of permanent
magnets. We have completed this experimental study by simulations in the
micromagnetic framework in order to get a qualitative picture of the
microstructure effect on the macroscopic magnetization curve. From this simple
model calculation, we can suggest that the after annealing the system behaves
as magnetically hard crystallites embedded in a weakly magnetized amorphous
matrix. PACS : 75.50.Bb, 75.50.Tt, 76.80.+y",1004.0307v2
2013-12-12,Influence of the structure defects on the magnetic properties of the FePt/Fe bilayer,"Thin magnetic multilayered films containing FePt have attracted a lot of
attention recently due to their possible usage in ultra-high density magnetic
storage. Although structure defects play a dramatic role in the magnetization
process and influence magnetic properties in general this dependence haven't
been studied thoroughly. The main aim of this work was to perform theoretical
investigation of the magnetic properties of FePt and Fe/FePt thin films with
high coercivity with respect to the structure defects such as anisotropy
constant, magnetization saturation, exchange constant fluctuations and easy
axis deviation. For selected defect patterns the coercive field dependence on
layer thicknesses was analysed. Numerical study of the bilayer with hard
magnetic layer having the planar anisotropy was carried on using micromagnetic
calculations. Values of layers thickness have been found optimal for
perspective applications, the dependence of the hysteresis loop shape upon the
magnetization process has been shown and analysed.",1312.3541v1
2014-03-25,Simulations of magnetic nanoparticle Brownian motion,"Magnetic nanoparticles are useful in many medical applications because they
interact with biology on a cellular level thus allowing microenvironmental
investigation. An enhanced understanding of the dynamics of magnetic particles
may lead to advances in imaging directly in magnetic particle imaging (MPI) or
through enhanced MRI contrast and is essential for nanoparticle sensing as in
magnetic spectroscopy of Brownian motion (MSB). Moreover, therapeutic
techniques like hyperthermia require information about particle dynamics for
effective, safe, and reliable use in the clinic. To that end, we have developed
and validated a stochastic dynamical model of rotating Brownian nanoparticles
from a Langevin equation approach. With no field, the relaxation time toward
equilibrium matches Einstein's model of Brownian motion. In a static field, the
equilibrium magnetization agrees with the Langevin function. For high frequency
or low amplitude driving fields, behavior characteristic of the linearized
Debye approximation is reproduced. In a higher field regime where magnetic
saturation occurs, the magnetization and its harmonics compare well with the
effective field model. On another level, the model has been benchmarked against
experimental results, successfully demonstrating that harmonics of the
magnetization carry enough information to infer environmental parameters like
viscosity and temperature.",1403.6427v1
2016-03-27,High resolution Kerr microscopy study of exchange bias phenomena in FePt/Fe exchange spring magnets,"Magnetization and magnetic microstructure of top soft magnetic layer (Fe),
which is exchange spring coupled to bottom hard magnetic layer ($L1_0$ FePt) is
studied using high resolution Kerr microscopy. When the sample (FePt/Fe) is at
remanent condition of hard magnetic layer, considerable shifting of Fe layer
hysteresis loop from centre i.e., exchange bias phenomena is observed. It is
observed that one can tune the magnitude of exchange bias shift by reaching the
remanent state from different saturating fields ($H_{SAT}$) and also by varying
the angle between measuring field and $H_{SAT}$. The M-H loops and domain
images of top soft Fe layer demonstrates unambiguously that soft magnetic layer
at remanent state in such exchange coupled system is having unidirectional
anisotropy. An analogy is drawn and the observations are explained in terms of
the mostly accepted models of exchange bias phenomena exhibited by bilayers
consisting of ferromagnetic(FM) and anti-ferromagnetic (AFM) layers, when the
AFM layer is field cooled across $N\acute{e}el$ transition temperature.",1603.08164v1
2017-03-22,Magnetization process and magnetocaloric effect in geometrically frustrated Ising antiferromagnet and spin ice models on a `Star of David' nanocluster,"Magnetic and magnetocaloric properties of geometrically frustrated
antiferromagnetic Ising (IA) and ferromagnetic spin ice (SI) models on a
nanocluster with a `Star of David' topology, including next-nearest-neighbor
(NNN) interactions, are studied by an exact enumeration. In an external field
applied in characteristic directions of the respective models, depending on the
NNN interaction sign and magnitude, the ground state magnetization of the IA
model is found to display up to three intermediate plateaus at fractional
values of the saturation magnetization, while the SI model shows only one
zero-magnetization plateau and only for the antiferromagnetic NNN coupling. A
giant magnetocaloric effect is revealed in the the IA model with the NNN
interaction either absent or equal to the nearest-neighbor coupling. The latter
is characterized by abrupt isothermal entropy changes at low temperatures and
infinitely fast adiabatic temperature variations for specific entropy values in
the processes when the magnetic field either vanishes or tends to the critical
values related to the magnetization jumps.",1703.07756v1
2017-10-20,Deterministic switching of perpendicularly magnetic layers by spin orbital torque through stray field engineering,"We proposed a novel multilayer structure to realize the deterministic
switching of perpendicularly magnetized layers by spin orbital torque from the
spin Hall effect through stray field engineering. In our design, a pinned
magnetic layer is introduced under the heave metal separated by an insulator,
generating an in-plane stray field in the perpendicularly magnetized layer. We
have confirmed the deterministic switching of perpendicularly magnetized layers
through micromagnetic simulation and theoretical analysis. The in-plane stray
field accounts for the deterministic switching exhibited in the structure and
the reversal ultimate state of the magnetic layer is predictable when the
applied spin current density is above the critical spin current density.
Moreover, the stray field is easily tunable in a wide range by adjusting the
saturation magnetization and dimensions of the pinned layer, and can
accommodate different perpendicularly magnetized materials without any external
magnetic field.",1710.08282v1
2018-04-02,Magnetism and high-magnetic field magnetization in alkali superoxide CsO2,"Alkali superoxide CsO2 is one of candidates for the spin-1/2 one-dimensional
(1D) antiferromagnet, which may be sequentially caused by an ordering of the
pi-orbital of O2- molecule below TS ~ 70 K. Here, we report on the magnetism in
powder CsO2 and high-magnetic field magnetization measurements in
pulsed-magnetic fields of up to 60 T. We obtained the low temperature phase
diagram around the antiferromagnetic ordering temperature TN = 9.6 K under the
magnetic field. At 1.3 K, remarkable up-turn curvature in the magnetization
around a saturation field of ~ 60 T is found, which corresponds to the
spin-1/2. We will compare it with the theoretical calculation.",1804.00377v1
2019-08-18,Anomalous magnetic behavior and complex magnetic structure of proximate LaCrO3 LaFeO3 system,"We investigated complex magnetic properties of multifunctional LaCrO3-LaFeO3
system. The magnetic measurements substantiate the presence of competing
complex magnetic ordering against temperature, showing paramagnetic to
ferrimagnetic transition at 300 K, followed by antiferromagnetic (AFM)
transition near 250 K superimposed on ferrimagnetic phase. The onset of weak
ferrimagnetic ordering is attributed to the competing complex interaction
between two AFM LaCrO3-LaFeO3 sublattices. The low-temperature AFM ordering is
also substantiated by temperature-dependent Raman measurements, where the
intensity ratio of 700 cm-1 Raman active mode showed the clear enhancement with
lowering the temperature. The non-saturating nature of magnetic moments in
LaCrO3-LaFeO6 suggests the predominating AFM ordering in conjunction with
ferrimagnetic ordering between 250 K to 300 K up to 5 T magnetic field. A
complex magnetic structure of LaCrO3-LaFeO3 is constructed, emphasizing the
metastable magnetic phase near room temperature and low temperature
antiferromagnetic state.",1908.06450v1
2019-08-22,Tunable Birefringence in Silica Mediated Magnetic Fluid,"The present study reports magnetic and optical properties of silica mediated
lauric acid stabilized magnetic fluids. The tunable birefringence ({\Delta}n)
and other properties are investigated as a function of (i) concentrations of
silica suspension, and (ii) saturation magnetization (MS) 0.5099 kA/m (FN30)
and 1.2855 kA/m (F30) of magnetite magnetic fluid (MF). The study reveals that
{\Delta}n suppresses on addition of silica in FN30, whereas enhances (up to
critical concentrations of silica) in F30. The magnetic field induced chain
observed in the FN30 based fluids are long, thick and scattered, while short,
thin and dense chains emerges in F30 based fluid. The magnetic field induced
assembly and the magnetic parameters correlates with the results of {\Delta}n.
The particle size analysis indicates increment of particle size on addition of
silica nanoparticles. The thermogravimetry analysis confirms the direct
interaction of silica nanoparticles and the lauric acid coated magnetite
particles. This is the first report of direct interaction of silica - magnetite
magnetic fluids, and its subsequent effect on tunable birefringence and other
properties.",1908.08366v2
2021-09-21,Effect of uniaxial single-ion anisotropy on a stability of intermediate magnetization plateaus of a spin-1 Heisenberg diamond cluster,"Ground-state phase diagrams and magnetization curves of a spin-1 Heisenberg
diamond cluster with two different coupling constants and uniaxial single-ion
anisotropy are investigated in a presence of the external magnetic field with
the help of exact diagonalization methods. It is shown that the spin-1
Heisenberg diamond cluster exhibits several remarkable quantum ground states,
which are manifested in zero- and low-temperature magnetization curves as
intermediate plateaus at one-quarter, one-half and three-quarters of the
saturation magnetization. It is found that the width of the fractional
magnetization plateaus depends basically on a relative strength of the coupling
constants as well as uniaxial single-ion anisotropy, which may substantially
shrink or even cause full breakdown of some intermediate magnetization
plateaus. It is evidenced that a relatively weak uniaxial single-ion anisotropy
of the easy-axis type considerably improves a theoretical fit of
low-temperature magnetization curves of the tetranuclear nickel complex
[Ni4(CO3)2(aetpy)8](ClO4)4 in a low-field region without spoiling the previous
fit based on the fully isotropic Heisenberg model in a high-field region.",2109.10030v1
2021-12-07,Magnetization process of the S=1/2 Heisenberg antiferromagnet on the floret pentagonal lattice,"We study the S=1/2 Heisenberg antiferromagnet on the floret pentagonal
lattice by numerical diagonalization method. This system shows various
behaviours that are different from that of the Cairo-pentagonal-lattice
antiferromagnet. The ground-state energy without magnetic field and the
magnetization process of this system are reported. Magnetization plateaux
appear at one-ninth height of the saturation magnetization, at one-third
height, and at seven-ninth height. The magnetization plateaux at one-third and
seven-ninth heights come from interactions linking the sixfold-coordinated spin
sites. A magnetization jump appears from the plateau at one-ninth height to the
plateau at one-third height. Another magnetization jump is observed between the
heights corresponding to the one-third and seven-ninth plateaux; however the
jump is away from the two plateaux, namely, the jump is not accompanied with
any magnetization plateaux. The jump is a peculiar phenomenon that has not been
reported.",2112.03516v1
2022-06-27,Field-Induced Magnetic States in the Metallic Rare-Earth Layered Triangular Antiferromagnet TbAuAl$_4$Ge$_2$,"Magnetic frustration in metallic rare earth lanthanides ($Ln$) with
$4f$-electrons is crucial for producing interesting magnetic phases with high
magnetic anisotropy where intertwined charge and spin degrees of freedom lead
to novel phenomena. Here we report on the magnetic, thermodynamic, and
electrical transport properties of TbAuAl$_4$Ge$_2$. Tb ions form 2-dimensional
triangular lattice layers which stack along the crystalline $c$-axis. The
magnetic phase diagram reveals multiple nearly degenerate ordered states upon
applying field along the magnetically easy $ab$-plane before saturation. The
magnetoresistance in this configuration exhibits intricate field dependence
that closely follows that of the magnetization while the specific heat reveals
a region of highly enhanced entropy, suggesting the possibility of a
non-trivial spin textured phase. For fields applied along the $c$-axis (hard
axis), we find linear magnetoresistance over a wide range of fields. We compare
the magnetic properties and magnetoresistance with an isostructral
GdAuAl$_4$Ge$_2$ single crystals. These results identify TbAuAl$_4$Ge$_2$ as an
environment for complex quantum spin states and pave the way for further
investigations of the broader $Ln$AuAl$_4$Ge$_2$ family of materials.",2206.13118v1
2019-05-01,"Evolution of structural, magnetic and transport properties in MnBi2-xSbxTe4","Here we report the evolution of structural, magnetic and transport properties
in MnBi$_{2-x}$Sb$_x$Te$_4$ (0$\leq x \leq$2) single crystals. MnSb$_2$Te$_4$,
isostructural to MnBi$_2$Te$_4$, has the lattice parameters of
\textit{a}=4.2445(3)$\AA$ and \textit{c}=40.869(5)$\AA$, respectively. With
increasing Sb content in MnBi$_{2-x}$Sb$_x$Te$_4$, the \textit{a}-lattice
decreases linearly following the Vegards law while the \textit{c}-lattice shows
little compositional dependence. The \textit{a}-lattice contraction occurs by
reducing Mn-Te-Mn bond angle while Mn-Te bond length remains nearly constant.
The anisotropic magnetic properties suggest an antiferromagnetic order below
T$_N$=19\,K for MnSb$_2$Te$_4$ with the magnetic moments aligned along the
crystallographic \textit{c}-axis. The antiferromagnetic ordering temperature
slightly decreases from 24\,K for MnBi$_2$Te$_4$ to 19\,K for MnSb$_2$Te$_4$.
More dramatic change was observed for the critical magnetic fields required for
the spin-flop transition and moment saturation. With increasing Sb content,
both critical fields decrease and in MnSb$_2$Te$_4$ a small field of 3\,kOe is
enough to saturate the moment. In high magnetic fields, the saturation moment
shows significant suppression from 3.56$\mu_B$/Mn for MnBi$_2$Te$_4$ to
1.57$\mu_B$/Mn for MnSb$_2$Te$_4$. Data analyses suggest that both the
interlayer magnetic interaction and single ion anisotropy decrease with
increasing Sb content. The partial substitution of Bi by Sb also dramatically
affects the transport properties. A crossover from n-type to p-type conducting
behavior is observed around x=0.63. Our results show close correlation between
structural, magnetic and transport properties in MnBi$_{2-x}$Sb$_x$Te$_4$ and
that partial substitution of Bi by Sb is an effective approach to fine tuning
both the magnetism and transport properties of MnBi$_{2-x}$Sb$_x$Te$_4$.",1905.00400v2
2022-11-19,Nonlinear evolution of magnetorotational instability in a magnetized Taylor-Couette flow: scaling properties and relation to upcoming DRESDYN-MRI experiment,"Magnetorotational instability (MRI) is the most likely mechanism driving
angular momentum transport in astrophysical disks. However, despite many
efforts, a conclusive experimental evidence of MRI is still missing. Recently,
performing 1D linear analysis of the standard MRI (SMRI) in a cylindrical
Taylor-Couette (TC) flow with an axial magnetic field, we showed that SMRI can
be detected in the upcoming DRESDYN-MRI experiment based on a magnetized TC
flow of liquid sodium. In this study, also related to DRESDYN-MRI experiments,
we focused on the nonlinear evolution and saturation properties of SMRI and
analyzed its scaling behavior with respect to the main parameters of the TC
flow. We did a detailed analysis over the extensive ranges of magnetic Reynolds
number $Rm\in [8.5, 37.1]$, Lundquist number $Lu\in[1.5, 15.5]$ and Reynolds
number, $Re\in[10^3, 10^5]$. We considered small magnetic Prandtl numbers, $Pm
\ll 1$, down to $Pm\sim 10^{-4}$, aiming at values typical of liquid sodium in
the experiments. In the saturated state, the magnetic energy of SMRI and torque
due to perturbations on the cylinders, which characterizes angular momentum
transport, both increase with $Rm$ for fixed $(Lu, Re)$, while for fixed $(Lu,
Rm)$, the magnetic energy decreases and torque increases with increasing $Re$.
We studied the scaling of the magnetic energy and torque in the saturated state
as a function of $Re$ and find a power law dependence $Re^{-0.6...-0.5}$ for
the magnetic energy and $Re^{0.4...0.5}$ for the torque at all $(Lu, Rm)$ and
high $Re\geq 4000$. We also explored the dependence on Lundquist number and
angular velocity of the cylinders. These scaling laws will be instrumental in
the subsequent analysis of more realistic finite-length TC flows and comparison
of numerical results with those obtained from the DRESDYN-MRI experiments to
unambiguously identify SMRI in laboratory.",2211.10811v3
2018-11-29,"Effect of YIG Nanoparticle Size and Clustering in Proximity-Induced Magnetism in Graphene/YIG Composite Probed with Magnetoimpedance Sensors: Towards Improved Functionality, Sensitivity and Proximity Detection","Proximity-induced magnetism (PIM) in graphene (Gr) adjacent to magnetic
specimen has raised great fundamental interests. The subject is under debate
and yet no application is proposed and granted. In this paper, toward
accomplishment of fundamental facts, we first explore the effect of particle
size and clustering in the PIM in Gr nanoplates (GNPs)/yttrium iron garnet
(YIG) magnetic nanoparticle (MNP) composite. Microscopic analyzes suggest that
fine MNPs distributed uniformly on the GNPs have higher saturation
magnetization due to the PIM in Gr. We propose that such magnetic plates can
thus be used to shield the stray field generated on the surface of magnetic
sensors and play a role as a magnetic lens to prevent the field emanating
outside the body of magnetic specimen. The GNPs/YIG composites are coated on a
magnetic ribbon and proposed for application in magneto-impedance (MI) sensors.
We show that such planar magnetic flakes enhance the MI response against the
external applied magnetic field significantly. The suggested application can be
furthermore developed toward bio-sensing and magnetic shielding in different
magnetic sensors and devices.",1811.12317v2
2020-01-19,Impact of the magnetic proximity effect in Pt on the total magnetic moment of Pt/Co/Ta trilayers studied by x-ray resonant magnetic reflectivity,"In this work, we study the influence of the magnetic proximity effect (MPE)
in Pt on the total magnetic moment of thin film trilayer systems consisting of
the ferromagnet (FM) Co adjacent to the heavy metals (HMs) Pt and Ta. We
investigate the trilayer systems HM1/FM/HM2 with different stacking order as
well as a reference bilayer without any MPE. X-ray resonant magnetic
reflectivity (XRMR) is a powerful tool to probe induced magnetism, especially
when buried at interfaces in a multilayer. By using XRMR, we are able to obtain
magnetic depth profiles of the structural, optical and magnetic parameters. By
fitting the experimental data with a Gaussian-like magnetooptic profile taking
the structural roughness at the interface into account, we can extract the
magnetic moment of the spin-polarized layer. Comparing the obtained moments to
the measured total moment of the sample, we can determine the impact of the MPE
on the total magnetic moment of the system. Such information can be critical
for analyzing spin transport experiments, including spin-orbit torque and spin
Hall angle measurements, where the saturation magnetization $M_s$ has to be
taken into account. Therefore, by combining magnetization measurements and XRMR
methods we were able to get a complete picture of the magnetic moment
distribution in these trilayer systems containing spin-polarized Pt.",2001.06857v1
2021-06-09,Unraveling the role of the magnetic anisotropy on thermoelectric response: a theoretical and experimental approach,"Magnetic anisotropies have key role to taylor magnetic behavior in
ferromagnetic systems. Further, they are also essential elements to manipulate
the thermoelectric response in Anomalous Nernst (ANE) and Longitudinal Spin
Seebeck systems (LSSE). We propose here a theoretical approach and explore the
role of magnetic anisotropies on the magnetization and thermoelectric response
of noninteracting multidomain ferromagnetic systems. The magnetic behavior and
the thermoelectric curves are calculated from a modified Stoner Wohlfarth model
for an isotropic system, a uniaxial magnetic one, as well as for a system
having a mixture of uniaxial and cubic magnetocrystalline magnetic
anisotropies. It is verified remarkable modifications of the magnetic behavior
with the anisotropy and it is shown that the thermoelectric response is
strongly affected by these changes. Further, the fingerprints of the energy
contributions to the thermoelectric response are disclosed. To test the
robustness of our theoretical approach, we engineer films having the specific
magnetic properties and compare directly experimental data with theoretical
results. Thus, experimental evidence is provided to confirm the validity of our
theoretical approach. The results go beyond the traditional reports focusing on
magnetically saturated films and show how the thermoelectric effect behaves
during the whole magnetization curve. Our findings reveal a promising way to
explore the ANE and LSSE effects as a powerful tool to study magnetic
anisotropies, as well as to employ systems with magnetic anisotropy as sensing
or elements in technological applications.",2106.05063v1
2024-01-24,Magnetic nanoparticles: from the nanostructure to the physical properties,"Some of the synthesis methods and physical properties of iron-oxide based
magnetic nanoparticles such as Fe3-xO4 and CoxFe3-xO4 are reviewed because of
their interest in health, environmental applications, and ultra-high-density
magnetic recording. Unlike high crystalline quality nanoparticles larger than a
few nanometers that show bulk-like magnetic and electronic properties,
nanostructures with increasing structural defects yield a progressive worsening
of their general performance due to frozen magnetic disorder and local breaking
of their crystalline symmetry. Thus, it is shown that single-crystal,
monophasic nanoparticles do not exhibit significant surface or finite-size
effects, such as spin canting, reduced saturation magnetization, high closure
magnetic fields, hysteresis-loop shift or dead magnetic layer features which
are mostly associated with crystallographic defective systems. Besides, the key
role of the nanoparticle coating, surface anisotropy, and inter-particle
interactions are discussed. Finally, the results of some single particle
techniques -- magnetic force microscopy, X-ray photoemission electron
microscopy, and electron magnetic chiral dichroism -- that allow studying
individual nanoparticles down to sub-nanometer resolution with element, valence
and magnetic selectivity, are presented. All in all, the intimate, fundamental
correlation of the nanostructure (crystalline, chemical, magnetic) to the
physical properties of the nanoparticles is ascertained.",2401.13422v1
2024-02-26,"Magnetic filaments: formation, stability, and feedback","As well known, magnetic fields in space are distributed very inhomogeneously.
Some-times field distributions have forms of filaments with high magnetic field
values. As many ob-servations show, such a filamentation takes place in
convective cells in the Sun and other astro-physical objects. This effect is
associated with the frozenness of the magnetic field into a medium with high
conductivity that leads to compression of magnetic field lines and forming
magnetic filaments. We show analytically, based on the general analysis, that
the magnetic field intensifies in the regions of downward flows in both
two-dimensional and three-dimensional convective cells. These regions of the
hyperbolic type for magnetic fields play a role of a specific attractor. This
analysis was confirmed by numerical simulations for 2D convective cells of the
roll-type. Without dissipation the magnetic field grows exponentially in time
and does not depend on the aspect ratio between horizontal and vertical scale
of the cell. An increase due to compression in the magnetic field in the high
conductive plasma is saturated due to the natural limitation associated with
dissipative effects when the maximum magnitude of the magnetic field is of the
order of the root of the magnetic Reynolds number Rem. For the solar convective
zone the mean kinetic energy density exceeds mean magnetic energy density at
least for two orders of magnitude that allows one to use the kinematic
approximation for the MHD induction equation. In this paper based on the
stability analysis we explain why downward flows influence magnetic filaments
from making them more flat with orientation along interfaces between convective
cells.",2402.16989v1
2002-07-23,A model of nonlinear evolution and saturation of the turbulent MHD dynamo,"The growth and saturation of magnetic field in conducting turbulent media
with large magnetic Prandtl numbers are investigated. This regime is very
common in low-density hot astrophysical plasmas. During the early (kinematic)
stage, weak magnetic fluctuations grow exponentially and concentrate at the
resistive scale, which lies far below the hydrodynamic viscous scale. The
evolution becomes nonlinear when the magnetic energy is comparable to the
kinetic energy of the viscous-scale eddies. A physical picture of the ensuing
nonlinear evolution of the MHD dynamo is proposed. Phenomenological
considerations are supplemented with a simple Fokker--Planck model of the
nonlinear evolution of the magnetic-energy spectrum. It is found that, while
the shift of the bulk of the magnetic energy from the subviscous scales to the
velocity scales may be possible, it occurs very slowly -- at the resistive,
rather than dynamical, time scale (for galaxies, this means that generation of
large-scale magnetic fields cannot be explained by this mechanism). The role of
Alfvenic motions and the implications for the fully developed isotropic MHD
turbulence are discussed.",0207503v2
2004-08-05,Angular dependent planar metamagnetism in the hexagonal compounds TbPtIn and TmAgGe,"Detailed magnetization measurements, M(T,H,theta), were performed on single
crystals of TbPtIn and TmAgGe (both members of the hexagonal Fe_2P/ZrNiAl
structure type), for the magnetic field H applied perpendicular to the
crystallographic c axis. These data allowed us to identify, for each compound,
the easy-axes for the magnetization, which coincided with high symmetry
directions ([120] for TbPtIn and [110] for TmAgGe). For fixed orientations of
the field along each of the two six-fold symmetry axes, a number of
magnetically ordered phases is being revealed by M(H,T) measurements below T_N.
Moreover, T ~ 2 K, M(H)|_theta measurements for both compounds (with H applied
parallel to the basal plane), as well as T = 20 K data for TbPtIn, reveal five
metamagnetic transitions with simple angular dependencies: H_{ci,j} ~
1/cos(theta +/- phi), where phi = 0^0 or 60^0. The high field magnetization
state varies with theta like 2/3*mu_{sat}(R^{3+})*cos(theta), and corresponds
to a crystal field limited saturated paramagnetic, CL-SPM, state. Analysis of
these data allowed us to model the angular dependence of the locally saturated
magnetizations M_{sat} and critical fields H_c with a three coplanar Ising-like
model, in which the magnetic moments are assumed to be parallel to three
adjacent easy axes. Furthermore, net distributions of moments were inferred
based on the measured data and the proposed model.",0408121v1
2006-05-18,Mechanisms of degeneracy breaking in pyrochlore antiferromagnets,"Motivated by the low temperature magnetization curves of several spinel
chromites, we theoretically study classical mechanisms of degeneracy lifting in
pyrochlore antiferromagnets. Our main focus is on the coupling of spin exchange
to lattice distortions. Prior work by Penc et al. (Phys. Rev. Lett. 93, 197203
(2004)) has demonstrated that such coupling leads to a robust magnetization
plateau at half the saturation moment per spin, in agreement with experiment.
We show that a simple Einstein model incorporating local site distortions
generates a ``universal'' magnetic order on the plateau, and highlight the
distinct predictions of this model from that in Penc et al. (Phys. Rev. Lett.
93, 197203 (2004)). We also consider the complementary degeneracy-lifting
effects of further neighbor exchange interactions. We discuss the implications
for transitions off the plateau at both the high field and low field end, as
well as at fields close to the saturation value. We predict that under certain
circumstances there is spontaneous {\sl uniform} XY magnetization (transverse
to the field) for field values just above the plateau. These features may be
tested in experiments. While selecting a unique magnetic order in the half
magnetization plateau, at zero magnetic field the Einstein model retains an
extensive degeneracy, though significantly reduced compared with the pure
Heisenberg antiferromagnet.",0605467v1
2007-05-30,Magnetic turbulence production by streaming cosmic rays upstream of SNR shocks,"We present preliminary results of Particle-In-Cell simulations of magnetic
turbulence production by isotropic cosmic-ray ions streaming upstream of
supernova remnant shocks. The studies aim at testing the MHD predictions by
Bell (2004, 2005) of a strong amplification of short-wavelength nonresonant
wave modes and at studying the subsequent evolution of the magnetic turbulence
and its backreaction on cosmic ray trajectories. The detailed knowledge of the
upstream turbulence properties is crucial to ascertain all aspects of the shock
acceleration process - the transport properties of cosmic rays, the shock
structure, thermal particle injection and heating processes. An amplification
of magnetic field would also facilitate the acceleration of particles beyond
the ""knee"" in the cosmic-ray spectrum. Our kinetic approach is particularly
suited to address the backreaction on the cosmic rays, and it allows us to test
Bell's prediction of the eventual formation of extended filamentary structure
in the cosmic-ray distribution and also to arrive at a reliable estimate of the
total saturation magnetic-field level. The parameters chosen for the
simulations are favorable for the rapid excitation of purely growing modes. We
confirm the generation of the turbulent magnetic field due to the drift of
cosmic-ray ions in the upstream plasma, but show that the growth rate of the
field perturbations is much slower than estimated using the MHD approach and
the amplitude of the turbulence saturates at about dB/B~1. The magnetic field
also remains below equipartition with the upstream plasma.",0705.4459v1
2007-10-16,A generalization of Snoek's law to ferromagnetic films and composites,"The present paper establishes characteristics of the relative magnetic
permeability spectrum $\mu$(f) of magnetic materials at microwave frequencies.
The integral of the imaginary part of $\mu$(f) multiplied with the frequency f
gives remarkable properties. A generalisation of Snoek's law consists in this
quantity being bounded by the square of the saturation magnetization multiplied
with a constant. While previous results have been obtained in the case of
non-conductive materials, this work is a generalization to ferromagnetic
materials and ferromagnetic-based composites with significant skin effect. The
influence of truncating the summation to finite upper frequencies is
investigated, and estimates associated to the finite summation are provided. It
is established that, in practice, the integral does not depend on the damping
model under consideration. Numerical experiments are performed in the exactly
solvable case of ferromagnetic thin films with uniform magnetization, and these
numerical experiments are found to confirm our theoretical results. Microwave
permeability measurements on soft amorphous films are reported. The relation
between the integral and the saturation magnetization is verified
experimentally, and some practical applications of the theoretical results are
introduced. The integral can be used to determine the average magnetization
orientation in materials with complex configurations of the magnetization, and
furthermore to demonstrate the accuracy of microwave measurement systems. For
certain applications, such as electromagnetic compatibility or radar absorbing
materials, the relations established herein provide useful indications for the
design of efficient materials, and simple figures of merit to compare the
properties measured on various materials.",0710.2980v2
2008-12-16,Turbulent dynamos in spherical shell segments of varying geometrical extent,"We use three-dimensional direct numerical simulations of the helically forced
magnetohydrodynamic equations in spherical shell segments in order to study the
effects of changes in the geometrical shape and size of the domain on the
growth and saturation of large-scale magnetic fields. We inject kinetic energy
along with kinetic helicity in spherical domains via helical forcing using
Chandrasekhar-Kendall functions. We take perfect conductor boundary conditions
for the magnetic field to ensure that no magnetic helicity escapes the domain
boundaries. We find dynamo action giving rise to magnetic fields at scales
larger than the characteristic scale of the forcing. The magnetic energy
exceeds the kinetic energy over dissipative time scales, similar to that seen
earlier in Cartesian simulations in periodic boxes. As we increase the size of
the domain in the azimuthal direction we find that the nonlinearly saturated
magnetic field organizes itself in long-lived cellular structures with aspect
ratios close to unity. These structures tile the domain along the azimuthal
direction, thus resulting in very small longitudinally averaged magnetic fields
for large domain sizes. The scales of these structures are determined by the
smallest scales of the domain, which in our simulations is usually the radial
scale. We also find that increasing the meridional extent of the domains
produces little qualitative change, except a marginal increase in the
large-scale field. We obtain qualitatively similar results in Cartesian domains
with similar aspect ratios.",0812.3106v2
2012-09-25,Strong magnetic field effect on above-barrier transport in Pb-p-HgCdTe Schottky barriers,"Due to large difference in effective masses of light and heavy holes it is
usually supposed that the above-barrier current in Schottky barriers on p-type
semiconductor is controlled only by the heavy holes. However, in real
structures, there is an additional potential barrier caused by a oxide layer at
interface. For typical values of thickness and height of a barrier its tunnel
transparency for light holes can be higher by three order of magnitude than
that for heavy holes. Due to such separative role of insulator layer one can
expect that the current is manly a contribution of light holes. To clear up
this problem the investigation of transport in a magnetic field is used as a
key experiment in this work. The pronounced magnetic field effect for heavy
holes in investigated Pb-p-HgCdTe Schottky barriers is expected only at
extremely strong magnetic fields B>10 T within the framework of both diode and
diffusion mechanism of transport. At the same time experimentally more than
twofold decrease in saturation current is observed even at B=0.5 T at any
orientation of magnetic field. The studies performed for HgCdTe with different
Kane's gap and at different temperatures show that the magnitude of magnetic
field effect is uniquely determined by the ratio of light hole cyclotron energy
to a thermal energy. However the magnitude of effect exceeds considerably the
prediction of the simple theory and the experimental magnetic field
dependencies of a saturation current do not follow the simple exponential
falling predicted for thermionic current. The reason of this discrepancy
remains a mystery.",1209.5528v1
2014-03-11,Non-linear galactic dynamos: A toolbox,"We compare various models and approximations for non-linear mean-field
dynamos in disc galaxies to assess their applicability and accuracy, and thus
to suggest a set of simple solutions suitable to model the large-scale galactic
magnetic fields in various contexts. The dynamo saturation mechanisms
considered are the magnetic helicity balance involving helicity fluxes (the
dynamical $\alpha$-quenching) and an algebraic $\alpha$-quenching. The
non-linear solutions are then compared with the marginal kinematic and
asymptotic solutions. We also discuss the accuracy of the no-$z$ approximation.
Although these tools are very different in the degree of approximation and
hence complexity, they all lead to remarkably similar solutions for the mean
magnetic field. In particular, we show that the algebraic $\alpha$-quenching
non-linearity can be obtained from a more physical dynamical $\alpha$-quenching
model in the limit of nearly azimuthal magnetic field. This suggests, for
instance, that earlier results on galactic disc dynamos based on the simple
algebraic non-linearity are likely to be reliable, and that estimates based on
simple, even linear models are often a good starting point. We suggest improved
no-$z$ and algebraic $\alpha$-quenching models, and also incorporate galactic
outflows into a simple analytical dynamo model to show that the outflow can
produce leading magnetic spirals near the disc surface. The simple dynamo
models developed are applied to estimate the magnetic pitch angle and the
arm-interarm contrast in the saturated magnetic field strength for realistic
parameter values.",1403.2562v2
2017-10-16,Stellar feedback strongly alters the amplification and morphology of galactic magnetic fields,"Using high-resolution magnetohydrodynamic simulations of idealized,
non-cosmological galaxies, we investigate how cooling, star formation, and
stellar feedback affect galactic magnetic fields. We find that the
amplification histories, saturation values, and morphologies of the magnetic
fields vary considerably depending on the baryonic physics employed, primarily
because of differences in the gas density distribution. In particular,
adiabatic runs and runs with a sub-grid (effective equation of state) stellar
feedback model yield lower saturation values and morphologies that exhibit
greater large-scale order compared with runs that adopt explicit stellar
feedback and runs with cooling and star formation but no feedback. The
discrepancies mostly lie in gas denser than the galactic average, which
requires cooling and explicit fragmentation to capture. Independent of the
baryonic physics included, the magnetic field strength scales with gas density
as $B\propto n^{2/3}$, suggesting isotropic flux freezing or equipartition
between the magnetic and gravitational energies during the field amplification.
We conclude that accurate treatments of cooling, star formation, and stellar
feedback are crucial for obtaining the correct magnetic field strength and
morphology in dense gas, which, in turn, is essential for properly modeling
other physical processes that depend on the magnetic field, such as cosmic ray
feedback.",1710.05932v1
2020-01-15,Generation of Solenoidal Modes and Magnetic Fields in Turbulence Driven by Compressive Driving,"We perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic
(MHD) turbulence driven by compressive driving to study generation of
solenoidal velocity component and small-scale magnetic field. We mainly focus
on the effects of mean magnetic field ($B_0$) and the sonic Mach number
($M_s$). We also consider two different driving schemes in terms of correlation
timescale of forcing vectors: a finite-correlated driving and a
delta-correlated driving. The former has a longer correlation timescale of
forcing vectors, which is comparable to large-eddy turnover time, than the
latter. Our findings are as follows. First, when we fix the value of $B_0$, the
level of solenoidal velocity component after saturation increases as $M_s$
increases. A similar trend is observed for generation of magnetic field when
$B_0$ is small. Second, when we fix the value of $M_s$, HD and MHD simulations
result in similar level of the solenoidal component when $B_0$ $\lesssim$ 0.2
(or Alfven Mach number of $\sim$ 5). However, the level increases when $B_0$
$\gtrsim$ 0.2. Roughly speaking, the magnetic energy density after saturation
is a linearly increasing function of $B_0$ irrespective of $M_s$. Third,
generation of solenoidal velocity component is not sensitive to numerical
resolution, but that of magnetic energy density is mildly sensitive. Lastly,
when initial conditions are same, the finite-correlated driving always produces
more solenoidal velocity and small-scale magnetic field components than the
delta-correlated driving. We additionally analyze the vorticity equation to
understand why higher $M_s$ and $B_0$ yield larger quantity of the solenoidal
velocity component.",2001.05154v1
2002-05-22,The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability: II. Saturation Level and Critical Magnetic Reynolds Number,"The nonlinear evolution of the magnetorotational instability (MRI) in weakly
ionized accretion disks, including the effect of the Hall term and ohmic
dissipation, is investigated using local three-dimensional MHD simulations and
various initial magnetic field geometries. When the magnetic Reynolds number,
Re_M \equiv v_A^2 / \eta \Omega (where v_A is the Alfven speed, \eta the
magnetic diffusivity, and \Omega the angular frequency), is initially larger
than a critical value Re_{M, crit}, the MRI evolves into MHD turbulence in
which angular momentum is transported efficiently by the Maxwell stress. If
Re_M < Re_{M, crit}, however, ohmic dissipation suppresses the MRI, and the
stress is reduced by several orders of magnitude. The critical value is in the
range of 1 - 30 depending on the initial field configuration. The Hall effect
does not modify the critical magnetic Reynolds number by much, but enhances the
saturation level of the Maxwell stress by a factor of a few. We show that the
saturation level of the MRI is characterized by v_{Az}^2 / \eta \Omega, where
v_{Az} is the Alfven speed in the nonlinear regime along the vertical component
of the field. The condition for turbulence and significant transport is given
by v_{Az}^2 / \eta \Omega \gtrsim 1, and this critical value is independent of
the strength and geometry of the magnetic field or the size of the Hall term.
If the magnetic field strength in an accretion disk can be estimated
observationally, and the magnetic Reynolds number v_A^2 / \eta \Omega is larger
than about 30, this would imply the MRI is operating in the disk.",0205383v1
2008-02-15,Production of Magnetic Turbulence by Cosmic Rays Drifting Upstream of Supernova Remnant Shocks,"We present results of 2D and 3D PIC simulations of magnetic turbulence
production by isotropic cosmic-ray ions drifting upstream of SNR shocks. The
studies aim at testing recent predictions of a strong amplification of short
wavelength magnetic field and at studying the evolution of the magnetic
turbulence and its backreaction on cosmic rays. We observe that an oblique
filamentary mode grows more rapidly than the non-resonant parallel modes found
in analytical theory, and the growth rate of the field perturbations is much
slower than is estimated for the parallel plane-wave mode, possibly because in
our simulations we cannot maintain omega << Omega_i, the ion gyrofrequency, to
the degree required for the plane-wave mode to emerge. The evolved oblique
filamentary mode was also observed in MHD simulations to dominate in the
nonlinear phase. We thus confirm the generation of the turbulent magnetic field
due to the drift of cosmic-ray ions in the upstream plasma, but as our main
result find that the amplitude of the turbulence saturates at about dB/B~1. The
backreaction of the turbulence on the particles leads to an alignment of the
bulk-flow velocities of the cosmic rays and the background medium, which is an
essential characteristic of cosmic-ray modified shocks. It accounts for the
saturation of the instability at moderate field amplitudes. Previously
published MHD simulations have assumed a constant cosmic-ray current and no
energy or momentum flux in the cosmic rays, which excludes a backreaction of
the generated magnetic field on cosmic rays, and thus the saturation of the
field amplitude is artificially suppressed. This may explain the continued
growth of the magnetic field in the MHD simulations. A strong magnetic field
amplification to amplitudes dB >> B0 has not been demonstrated yet.",0802.2185v2
2021-05-25,Simulating radio synchrotron emission in star-forming galaxies: small-scale magnetic dynamo and the origin of the far infrared-radio correlation,"In star-forming galaxies, the far-infrared (FIR) and radio-continuum
luminosities obey a tight empirical relation over a large range of
star-formation rates (SFR). We examine magneto-hydrodynamic galaxy simulations
with cosmic rays (CRs), accounting for their advective and anisotropic
diffusive transport. We show that gravitational collapse of the proto-galaxy
generates a corrugated accretion shock, which injects turbulence and drives a
small-scale magnetic dynamo. As the shock propagates outwards and the
associated turbulence decays, the large velocity shear between the
supersonically rotating cool disc with respect to the (partially)
pressure-supported hot circumgalactic medium excites Kelvin-Helmholtz surface
and body modes. Those inject turbulence and drive multiple small-scale dynamos,
which exponentially amplify magnetic fields. They grow in scale to reach
equipartition with thermal and CR energies in Milky Way-mass galaxies. In small
galaxies, the magnetic energy saturates at the turbulent energy while it fails
to reach equipartition with thermal and CR energies. We solve for steady-state
spectra of CR protons, secondary electrons/positrons from hadronic CR-proton
interactions with the interstellar medium, and primary shock-accelerated
electrons at supernovae. The radio-synchrotron emission is dominated by primary
electrons, irradiates the magnetised disc, bulge, and bubble-shaped
magnetically-loaded outflows of our simulated Milky Way-mass galaxy. Our
star-forming and star-bursting galaxies with saturated magnetic fields match
the global FIR-radio correlation (FRC) across four orders of magnitude. Its
intrinsic scatter arises due to (i) different magnetic saturation levels that
result from different seed magnetic fields, (ii) different radio synchrotron
luminosities for different specific SFRs at fixed SFR and (iii) a varying radio
intensity with galactic inclination. (abridged)",2105.12132v3
2016-01-27,Dynamic nuclear polarization in a magnetic resonance force microscope experiment,"We report achieving enhanced nuclear magnetization in a magnetic resonance
force microscope experiment at 0.6 tesla and 4.2 kelvin using the dynamic
nuclear polarization (DNP) effect. In our experiments a microwire coplanar
waveguide delivered radiowaves to excite nuclear spins and microwaves to excite
electron spins in a 250 nm thick nitroxide-doped polystyrene sample. Both
electron and proton spin resonance were observed as a change in the mechanical
resonance frequency of a nearby cantilever having a micron-scale nickel tip.
NMR signal, not observable from Curie-law magnetization at 0.6 tesla, became
observable when microwave irradiation was applied to saturate the electron
spins. The resulting NMR signal's size, buildup time, dependence on microwave
power, and dependence on irradiation frequency was consistent with a transfer
of magnetization from electron spins to nuclear spins. Due to the presence of
an inhomogenous magnetic field introduced by the cantilever's magnetic tip, the
electron spins in the sample were saturated in a microwave-resonant slice 10's
of nm thick. The spatial distribution of the nuclear polarization enhancement
factor $\epsilon$ was mapped by varying the frequency of the applied
radiowaves. The observed enhancement factor was zero for spins in the center of
the resonant slice, was $\epsilon = +10$ to $+20$ for spins proximal to the
magnet, and was $\epsilon = -10$ to $-20$ for spins distal to the magnet. We
show that this bipolar nuclear magnetization profile is consistent with
cross-effect DNP in a $\sim \! 10^{5} \: \mathrm{T} \: \mathrm{m}^{-1}$
magnetic field gradient. Potential challenges associated with generating and
using DNP-enhanced nuclear magnetization in a nanometer-resolution magnetic
resonance imaging experiment are elucidated and discussed.",1601.07253v2
2017-11-23,The evolution of surface magnetic fields in young solar-type stars II: The early main sequence (250-650 Myr),"There is a large change in surface rotation rates of sun-like stars on the
pre-main sequence and early main sequence. Since these stars have dynamo driven
magnetic fields, this implies a strong evolution of their magnetic properties
over this time period. The spin-down of these stars is controlled by
interactions between stellar winds and magnetic fields, thus magnetic evolution
in turn plays an important role in rotational evolution. We present here the
second part of a study investigating the evolution of large-scale surface
magnetic fields in this critical time period. We observed stars in open
clusters and stellar associations with known ages between 120 and 650 Myr, and
used spectropolarimetry and Zeeman Doppler Imaging to characterize their
large-scale magnetic field strength and geometry. We report 15 stars with
magnetic detections here. These stars have masses from 0.8 to 0.95 Msun,
rotation periods from 0.326 to 10.6 days, and we find large-scale magnetic
field strengths from 8.5 to 195 G with a wide range of geometries. We find a
clear trend towards decreasing magnetic field strength with age, and a
power-law decrease in magnetic field strength with Rossby number. There is some
tentative evidence for saturation of the large-scale magnetic field strength at
Rossby numbers below 0.1, although the saturation point is not yet well
defined. Comparing to younger classical T Tauri stars, we support the
hypothesis that differences in internal structure produce large differences in
observed magnetic fields, however for weak lined T Tauri stars this is less
clear.",1711.08636v1
2020-12-14,A nonlinear solar magnetic field calibration method for the filter-based magnetograph by the residual network,"The method of solar magnetic field calibration for the filter-based
magnetograph is normally the linear calibration method under weak-field
approximation that cannot generate the strong magnetic field region well due to
the magnetic saturation effect. We try to provide a new method to carry out the
nonlinear magnetic calibration with the help of neural networks to obtain more
accurate magnetic fields. We employed the data from Hinode/SP to construct a
training, validation and test dataset. The narrow-band Stokes I, Q, U, and V
maps at one wavelength point were selected from all the 112 wavelength points
observed by SP so as to simulate the single-wavelength observations of the
filter-based magnetograph. We used the residual network to model the nonlinear
relationship between the Stokes maps and the vector magnetic fields. After an
extensive performance analysis, it is found that the trained models could infer
the longitudinal magnetic flux density, the transverse magnetic flux density,
and the azimuth angle from the narrow-band Stokes maps with a precision
comparable to the inversion results using 112 wavelength points. Moreover, the
maps that were produced are much cleaner than the inversion results. The method
can effectively overcome the magnetic saturation effect and infer the strong
magnetic region much better than the linear calibration method. The residual
errors of test samples to standard data are mostly about 50 G for both the
longitudinal and transverse magnetic flux density. The values are about 100 G
with our previous method of multilayer perceptron, indicating that the new
method is more accurate in magnetic calibration.",2012.07286v1
2011-07-26,Magnetic Behaviour of Disordered Ising Ferrimagnet in High Magnetic Field,"The magnetic behaviour of a disordered ferrimagnetic system Ap B1-p where
both A and B represent the magnetic atoms with respective spin SA = 1/2 and SB
= 1 in presence of high magnetic field is treated theoretically.Assuming the
magnetic interaction can be described through Ising Hamiltonian the approximate
free energy is obtained using the cluster-variational method. The field
dependence of the magnetization is then obtained for different concentration p
and exchange parameters (JAA, JBB and JAB). For p = 0.5,the magnetization M in
ferrimagnetic state and in absence of compensation temperature Tcm vanishes at
TC.Field induced reversal of M is found at switching temperature TS (<TC) which
is decreasing function of field H.A maximum in M is found above TS and the
maximum value of M increases with field.In ferrimagnetic state M increases
almost linearly at high H region. For system with large ferromagnetic JAA,the
compensation temperature Tcm is increasing function of JBB and JAB .The
decrease in compensation temperature is linear at small field and tends to
saturate at higher field.The sharpness of the magnetization reversal is
increased with H.For fully compensated state of the system with p = 2/3,the
magnetization in presence of H also exhibits switching behaviour at TS .For p =
0.2 the field induced reversal of magnetization occurs more sharply.The
orientational switching of the sublattice magnetization MA and MB with field
increases the Zeeman energy and is the origin of magnetization reversal at Ts",1107.5225v1
2013-11-23,Universal Scaling Law to Predict the Efficiency of Magnetic Nanoparticles as MRI T2-Contrast Agents,"Magnetic particles are very efficient Magnetic Resonance Imaging (MRI)
contrast agents. In the recent years, chemists have unleashed their imagination
to design multi-functional nanoprobes for biomedical applications including MRI
contrast enhancement. This study is focused on the direct relationship between
the size and magnetization of the particles and their nuclear magnetic
resonance relaxation properties, which condition their efficiency. Experimental
relaxation results with maghemite particles exhibiting a wide range of sizes
and magnetizations are compared to previously published data and to
well-established relaxation theories with a good agreement. This allows
deriving the experimental master curve of the transverse relaxivity versus
particle size and to predict the MRI contrast efficiency of any type of
magnetic nanoparticles. This prediction only requires the knowledge of the size
of the particles impermeable to water protons and the saturation magnetization
of the corresponding volume. To predict the T2 relaxation efficiency of
magnetic single crystals, the crystal size and magnetization obtained through a
single Langevin fit of a magnetization curve is the only information needed.
For contrast agents made of several magnetic cores assembled into various
geometries (dilute fractal aggregates, dense spherical clusters, core-shell
micelles, hollow vesicles), one needs to know a third parameter, namely the
intra-aggregate volume fraction occupied by the magnetic materials relatively
to the whole (hydrodynamic) sphere. Finally a calculation of the maximum
achievable relaxation effect and the size needed to reach this maximum is
performed for different cases: maghemite single crystals and dense clusters,
core-shell particles (oxide layer around a metallic core) and zinc manganese
ferrite crystals.",1311.6022v1
2013-12-09,High magnetic field evolution of ferroelectricity in CuCrO2,"CuCrO2 offers insights into the different types of spiral magnetic orderings
that can form spontaneously due to frustration in triangular-lattice
antiferromagnets. We explore the magnetic phase diagram up to 65 T along all
the principle axes, and also use electric polarization to probe changes in the
spiral order at high magnetic fields. It is known that at zero magnetic field a
proper-screw spiral of the Cr S = 3/2 spins forms that in turn induces electric
polarization with six possible orientations ab-plane. Applied magnetic fields
in the (hard) ab-plane have been shown to induce a transition to cycloidal
spiral magnetic order above 5.3 T in those domains that have spins
perpendicular to the applied magnetic field. We show that the cycloidal order
remains unchanged all the way up to 65 T, which is one quarter of the
extrapolated saturation magnetization. On the other hand for magnetic fields
along the (easy) c-axis, we observe a transition in the electric polarization
near 45 T, and it is followed by a series of steps and/or oscillations in the
electric polarization. The data is consistent with the a
proper-screw-to-cycloidal transition that is pushed from 5.3 to 45 T by
easy-axis anisotropy, and is in turn followed by stretching of the magnetic
spiral through commensurate and incommensurate wave vectors. This work also
highlights the ability of the magnetically-induced electric polarization to
probe complex magnetic orders in regimes of phase space that are difficult to
reach with neutron diffraction.",1312.2548v1
2020-09-28,Magnetic domains and domain wall pinning in two-dimensional ferromagnets revealed by nanoscale imaging,"Magnetic-domain structure and dynamics play an important role in
understanding and controlling the magnetic properties of two-dimensional
magnets, which are of interest to both fundamental studies and
applications[1-5]. However, the probe methods based on the spin-dependent
optical permeability[1,2,6] and electrical conductivity[7-10] can neither
provide quantitative information of the magnetization nor achieve nanoscale
spatial resolution. These capabilities are essential to image and understand
the rich properties of magnetic domains. Here, we employ cryogenic scanning
magnetometry using a single-electron spin of a nitrogen-vacancy center in a
diamond probe to unambiguously prove the existence of magnetic domains and
study their dynamics in atomically thin CrBr$_3$. The high spatial resolution
of this technique enables imaging of magnetic domains and allows to resolve
domain walls pinned by defects. By controlling the magnetic domain evolution as
a function of magnetic field, we find that the pinning effect is a dominant
coercivity mechanism with a saturation magnetization of about 26~$\mu_B$/nm$^2$
for bilayer CrBr$_3$. The magnetic-domain structure and pinning-effect
dominated domain reversal process are verified by micromagnetic simulation. Our
work highlights scanning nitrogen-vacancy center magnetometry as a quantitative
probe to explore two-dimensional magnetism at the nanoscale.",2009.13440v1
2022-05-02,Computational Study of Magnetic Switching Mechanism and Magnetoresistive Behaviour of Nanoscale Spin Valve Elements,"Investigation of the magnetic switching and magnetoresistive behaviour of
nanoscale spin valve elements of different sizes, shapes and arrays is of vital
importance for their application in future magnetic memory and storage devices.
To this end, we have inspected the magnetic switching mechanism and
magnetoresistive behaviour of nanoscale spin valve (Co/Cu/Ni80Fe20) elements of
two different shapes with varying lateral aspect ratios (ARs) by computational
micromagnetic simulation. Further, we have inspected the same for 2x2 and 3x3
arrays of the elliptical elements with AR = 1.25 of varying interelement
spacing. We have analysed how the shape of the hysteresis loop and its various
parameters such as the coercive field, remanence, saturation field were altered
by the variation in magnetic field. The magnetization reversal states were
simulated to explore the spatial coherence of magnetization switching. We
observe that the elements with higher AR show the Ni80Fe20 and Co layers
forming antiparallel states in the plateau similar to synthetic
antiferromagnets. As we reduce the AR, more complex quasi-uniform magnetic
states are observed which are even more complicated for elliptical elements.
The elliptical elements with the aspect ratio of 1.25 shows coherent and
predictable switching behaviour, showing its suitability for the application in
magnetic memory elements. We observe a gradual increase in magnetoresistance
(MR%) with the increase in AR of the spin valve elements, and the decrease in
interelement spacing between the spin valve elements in their arrays. The
magnetic flux density decreases, as we increase the cell spacing between the
elements. The magnetic hysteresis loops, magnetoresistance and spatial
coherence of magnetic switching give a guiding principle for selection of
geometric parameters of nanoscale spin valve arrays towards their application
in magnetic memory devices.",2205.00739v1
2023-03-01,Proton-fluence dependent magnetic properties of exfoliable quasi-2D van der Waals Cr2Si2Te6 magnet,"The discovery of long-range magnetic ordering in atomically thin materials
catapulted the van der Waals (vdW) family of compounds into an unprecedented
popularity. In particular, with a current push in space exploration, it is
beneficial to study how the properties of such materials evolve under proton
irradiation. Owing to their robust intra-layer stability and sensitivity to
external perturbations, these materials provide excellent opportunities for
studying proton irradiation as a non-destructive tool for controlling their
magnetic properties. Specifically, the exfoliable Cr2Si2Te6 (CST) is a
ferromagnetic semiconductor with the Curie temperature (TC) of ~32 K. Here, we
have investigated the magnetic properties of CST upon proton irradiation as a
function of fluence (1 x 1015, 5 x 1015, 1 x 1016, 5 x 1016, and 1 x 1018
H+/cm2) by employing variable-temperature, variable-field magnetization
measurements coupled with electron paramagnetic resonance (EPR) spectroscopy
and detail how the magnetization, magnetic anisotropy and EPR spectral
parameters vary as a function of proton fluence across the magnetic phase
transition. While the TC remains constant as a function of proton fluence, we
observed that the saturation magnetization and magnetic anisotropy diverge at
the proton fluence of 5 x 1016 H+/cm2, which is prominent in the ferromagnetic
phase, in particular. This work demonstrates that proton irradiation is a
feasible method for modifying the magnetic properties and local magnetic
interactions of vdWs crystals, which represents a significant step forward in
the design of future spintronic and magneto-electronic applications.",2303.00824v1
2023-12-14,Nanoscale magnetism and magnetic phase transitions in atomically thin CrSBr,"Since their first observation in 2017, atomically thin van der Waals (vdW)
magnets have attracted significant fundamental, and application-driven
attention. However, their low ordering temperatures, $T_c$, sensitivity to
atmospheric conditions and difficulties in preparing clean large-area samples
still present major limitations to further progress. The remarkably stable
high-$T_c$ vdW magnet CrSBr has the potential to overcome these key
shortcomings, but its nanoscale properties and rich magnetic phase diagram
remain poorly understood. Here we use single spin magnetometry to
quantitatively characterise saturation magnetization, magnetic anisotropy
constants, and magnetic phase transitions in few-layer CrSBr by direct magnetic
imaging. We show pristine magnetic phases, devoid of defects on micron
length-scales, and demonstrate remarkable air-stability down the monolayer
limit. We address the spin-flip transition in bilayer CrSBr by direct imaging
of the emerging antiferromagnetic (AFM) to ferromagnetic (FM) phase wall and
elucidate the magnetic properties of CrSBr around its ordering temperature. Our
work will enable the engineering of exotic electronic and magnetic phases in
CrSBr and the realisation of novel nanomagnetic devices based on this highly
promising vdW magnet.",2312.09279v1
2001-05-28,Nonlinear States of the Screw Dynamo,"The self-excitation of magnetic field by a spiral Couette flow between two
coaxial cylinders is considered. We solve numerically the fully nonlinear,
three-dimensional MHD equations for magnetic Prandtl numbers Pm (ratio of
kinematic viscosity to magnetic diffusivity) between 0.14 and 10 and kinematic
and magnetic Reynolds numbers up to about 2000. In the initial stage of
exponential field growth (kinematic dynamo regime), we find that the dynamo
switches from one distinct regime to another as the radial width \delta r_B$ of
the magnetic field distribution becomes smaller than the separation of the
field maximum from the flow boundary. The saturation of magnetic field growth
is due to a reduction in the velocity shear resulting mainly from the
azimuthally and axially averaged part of the Lorentz force, which agrees with
an asymptotic result for the limit of Pm<<1. In the parameter regime
considered, the magnetic energy decreases with kinematic Reynolds number as
Re^{-0.84}, which is approximately as predicted by the nonlinear asymptotic
theory (\sim Re^{-1}). However, when the velocity field is maintained by a
volume force (rather than by viscous stress) the dependence of magnetic energy
on the kinematic Reynolds number is much weaker.",0105484v2
2002-02-01,Dipole coupling induced magnetic ordering in an ensemble of nanostructured islands,"The magnetic ordering due to the long range dipole coupling in an ensemble of
magnetic islands is investigated. If the islands are large enough and closely
separated, the average dipole energy per island can explain the magnitude of
the observed ordering temperature of such an ensemble. The energetical
degeneracy with respect to a continuous in-plane rotation of the magnetic
moments in a periodic ensemble of islands is lifted in presence of an island
size dispersion and an irregular island array. Many different (metastable)
magnetic states are obtained, reminiscent of a spin-glass behavior. We obtain
that the average magnetic binding energy per island due to the dipole coupling
increases with increasing positional disorder. The island ensembles exhibit
non-collinear magnetic structures, resulting in non-saturated ensemble
magnetizations. The calculations are performed with a classical spin model for
ensembles of islands in unit cells with periodic boundary conditions. The point
dipole sums are augmented by an island areal correction.",0202013v1
2002-10-11,Quasi two-dimensional antiferromagnet on a triangular lattice RbFe(MoO4)2,"RbFe(MoO4)2 is a rare example of a nearly two-dimensional Heisenberg
antiferromagnet on a triangular lattice. Magnetic resonance spectra and
magnetization curves reveal that the system has a layered spin structure with
six magnetic sublattices. The sublattices within a layer are arranged in a
triangular manner with the magnetization vectors 120 degree apart. The H-T
phase diagram, containing at least five different magnetic phases is
constructed. In zero field, RbFe(MoO4)2 undergoes a phase transition at T_N=3.8
K into a non-collinear triangular spin structure with all the spins confined in
the basal plane. The application of an in-plane magnetic field induces a
collinear spin state between the fields H_c1=47 kOe and H_c2=71 kOe and
produces a magnetization plateau at one-third of the saturation moment. Both
the ESR and the magnetization measurements also clearly indicate an additional
first-order phase transition in a field of 35 kOe. The exact nature of this
phase transition is uncertain.",0210262v1
2002-12-18,Coexistence of ferro- and antiferromagnetic order in Mn-doped Ni$_2$MnGa,"Ni-Mn-Ga is interesting as a prototype of a magnetic shape-memory alloy
showing large magnetic field induced strains. We present here results for the
magnetic ordering of Mn-rich Ni-Mn-Ga alloys based on both experiments and
theory. Experimental trends for the composition dependence of the magnetization
are measured by a vibrating sample magnetometer (VSM) in magnetic fields of up
to several tesla and at low temperatures. The saturation magnetization has a
maximum near the stoichiometric composition and it decreases with increasing Mn
content. This unexpected behaviour is interpreted via first-principles
calculations within the density-functional theory. We show that extra Mn atoms
are antiferromagnetically aligned to the other moments, which explains the
dependence of the magnetization on composition. In addition, the effect of Mn
doping on the stabilization of the structural phases and on the magnetic
anisotropy energy is demonstrated.",0212442v1
2003-04-09,Field-induced magnetic anisotropy in La0.7Sr0.3CoO3,"Magnetic anisotropy has been measured for the ferromagnetic La0.7Sr0.3CoO3
perovskite from an analysis of the high-field part of the magnetization vs.
field curves, i.e., the magnetic saturation regime. These measurements give a
magnetic anistropy one order of magnitude higher than that of reference
manganites. Surprisingly, the values of the magnetic anisotropy calculated in
this way do not coincide with those estimated from measurements of coercive
fields which are one order of magnitude smaller. It is proposed that the reason
of this anomalous behaviour is a transition of the trivalent Co ions under the
external magnetic field from a low-spin to an intermediate-spin state. Such a
transition converts the Co3+ ions into Jahn-Teller ions having an only
partially quenched orbital angular momentum, which enhances the intra-atomic
spin-orbit coupling and magnetic anisotropy.",0304211v1
2006-03-22,"Out-of-plane magnetization reversal processes of (Ga,Mn)As with two different hole concentrations","We study magnetization reversal processes of in-plane magnetized (Ga,Mn)As
epilayers with different hole concentrations in out-of-plane magnetic fields
using magnetotransport measurements. A clear difference in the magnetization
process is found in two separate samples with hole concentrations of 10^20
cm^-3 and 10^21 cm^-3 as the magnetization rotates from the out-of-plane
saturation to the in-plane remanence. Magnetization switching process from the
in-plane remanence to the out-of-plane direction, on the other hand, shows no
hole concentration dependence, where the switching process occurs via domain
wall propagation. We show that the balance of <100> cubic magnetocrystalline
anisotropy and uniaxial [110] anisotropy gives an understanding of the
difference in the out-of-plane magnetization processes of (Ga,Mn)As epilayers.",0603568v1
2009-12-17,How Gold nanoparticle acquires magnetism? - Formation of large orbital moment at the interface,"In this paper, we have tried to find out the origin of magnetism in Gold
nanoparticles (Au- NPs). We observe that upon incorporating Gold nanoparticles
(Au-NPs) in Fe3O4 nanoparticle medium the net magnetisation increases compared
to the pure Fe3O4 nanoparticle medium. This increase of magnetization can be
attributed to the large orbital magnetic moment formation at the Au/magnetic
particle interface indicating that magnetism observed in Au-NPs is an
interfacial effect. This interfacial effect has been supported by the
observation of sudden transition from positive saturated magnetisation to a
negative diamagnetic contribution as a function of magnetic field on citrate
coated gold Au-NPs.",0912.3319v2
2011-01-30,Titanium pyrochlore magnets: how much can be learned from magnetization measurements?,"We report magnetization data for several titanium pyrochlore systems measured
down to 0.5 K. The measurements, performed on single crystal samples in fields
of up to 7 T, have captured the essential elements of the previously reported
phase transitions in these compounds and have also revealed additional
important features overlooked previously either because of the insufficiently
low temperatures used, or due to limitations imposed by polycrystalline
samples. For the spin-ice pyrochlores Dy2Ti2O7 and Ho2Ti2O7, an unusually slow
relaxation of the magnetization has been observed in lower fields, while the
magnetization process in higher fields is essentially hysteresis-free and does
not depend on sample history. For the XY pyrochlore Er2Ti2O7, the magnetic
susceptibility shows nearly diverging behaviour on approach to a critical
field, HC = 13.5 kOe, above which the magnetization does not saturate but
continues to grow at a significant rate. For the Heisenberg pyrochlore
Gd2Ti2O7, the magnetic susceptibility shows a pronounced change of slope at
both transition temperatures, TN1 = 1.02 K and TN2 = 0.74 K, contrary to the
earlier reports.",1101.5812v1
2011-07-01,"Magnetic model for A2CuP2O7 (A = Na, Li) revisited: 1D versus 2D behavior","We report magnetization measurements, full-potential band structure
calculations, and microscopic modeling for the spin-1/2 Heisenberg magnets
A2CuP2O7 (A = Na, Li). Based on a quantitative evaluation of the leading
exchange integrals and the subsequent quantum Monte-Carlo simulations, we
propose a quasi-one-dimensional magnetic model for both compounds, in contrast
to earlier studies that conjectured on the two-dimensional scenario. The
one-dimensional nature of A2CuP2O7 is unambiguously verified by magnetization
isotherms measured in fields up to 50 T. The saturation fields of about 40 T
for both Li and Na compounds are in excellent agreement with the intrachain
exchange J1 ~ 27 K extracted from the magnetic susceptibility data. The
proposed magnetic structure entails spin chains with the dominating
antiferromagnetic nearest-neighbor interaction J1 and two inequivalent,
nonfrustrated antiferromagnetic interchain couplings of about 0.01*J1 each. A
possible long-range magnetic ordering is discussed in comparison with the
available experimental information.",1107.0250v3
2012-06-25,Modification of structural and magnetic properties of Zn0.96 Mn0.04O samples by Li3+ ion irradiation,"Zn0.96Mn0.04O samples were synthesized by solid state reaction technique to
explore their magnetic behavior. Structural, morphological and magnetic
properties of the samples have been found to be modified by 50 MeV Li+3 ion
beam irradiation. The samples exhibit impurity phase and upon irradiation it
disappears. Rietveld refinement analysis indicates that substitutional
incorporation of Mn in the host lattice increases with irradiation. Grain size
decreases with irradiation. Field dependent magnetization (M-H) measurement
explicitly indicates ferromagnetic (FM) nature. It has been established from
temperature dependent magnetization (M-T) measurement (500 Oe) and ac
susceptibility (\chi-T) measurement that ferromagnetism in the system seems to
be mainly intrinsic; though superparamagnetic Mn nanoparticles also has a minor
role. The analysis of M-T data at comparatively high field (5000-Oe) provides
an estimation of antiferromagnetic (AFM) exchange, which acts as a reducing
agent for observed magnetic moment. The value of saturation magnetization has
been increased upon irradiation and is highly correlated with dissolution of
impurity phase. Actually structural property has been modified with ion
irradiation and this modification may cause some definite positive change in
magnetic property.",1206.5619v1
2012-07-12,Ground States of the Ising Model on the Shastry-Sutherland Lattice and the Origin of the Fractional Magnetization Plateaus in Rare-Earth Tetraborides,"A complete and exact solution of the ground-state problem for the Ising model
on the Shastry-Sutherland lattice in the applied magnetic field is found. The
magnetization plateau at the one third of the saturation value is shown to be
the only possible fractional plateau in this model. However, stripe magnetic
structures with magnetization 1/2 and $1/n$ ($n > 3$), observed in the
rare-earth tetraborides RB$_4$, occur at the boundaries of the
three-dimensional regions of the ground-state phase diagram. These structures
give rise to new magnetization plateaus if interactions of longer ranges are
taken into account. For instance, an additional third-neighbor interaction is
shown to produce a 1/2 plateau. The results obtained significantly refine the
understanding of the magnetization process in RB$_4$ compounds, especially in
TmB$_4$ and ErB$_4$ which are strong Ising magnets.",1207.3030v1
2013-03-21,Magnetization Process and Collective Excitations in the S=1/2 Triangular-Lattice Heisenberg Antiferromagnet Ba3CoSb2O9,"We have performed high-field magnetization and ESR measurements on
Ba$_3$CoSb$_2$O$_9$ single crystals, as a representative two-dimensional
spin-1/2 Heisenberg antiferromagnet on a uniform triangular lattice, and have
determined all the magnetic parameters. For an applied magnetic field $H$
parallel to the $ab$-plane, the entire magnetization curve including the
plateau at one-third of the saturation magnetization ($M_\mathrm{s}$) is in
excellent agreement with the results of theoretical calculations except an
anomaly near $(3/5)M_\mathrm{s}$, indicative of an additional field-induced
transition. However, for $H\,{\parallel}\,c$, the magnetization curve exhibits
a cusp near $M_\mathrm{s}/3$. Paramagnetic resonance signals above the N\'eel
temperature indicate the nearly isotropic $g$-factor. A detailed analysis of
the collective ESR modes observed in the ordered state, combined with the
magnetization process, provides evidence of the weak easy-plane anisotropy.",1303.5271v3
2013-04-14,Influence of initial conditions on the large-scale dynamo growth rate,"To investigate the effect of energy and helicity on the growth of magnetic
field, helical kinetic forcing was applied to the magnetohydrodynamic(MHD)
system that had a specific distribution of energy and helicity as initial
conditions. Simulation results show the saturation of a system is not
influenced by the initial conditions, but the growth rate of large scale
magnetic field is proportionally dependent on the initial large scale magnetic
energy and helicity. It is already known that the helical component of small
scale magnetic field(i.e., current helicity $<{\bf j}\cdot {\bf b}>$) quenches
the growth of large scale magnetic field. However, $<{\bf j}\cdot {\bf b}>$ can
also boost the growth of large scale magnetic field by changing its sign and
magnitude. In addition, simulation shows the nonhelical magnetic field can
suppress the velocity field through Lorentz force. Comparison of the profiles
of evolving magnetic and kinetic energy indicates that kinetic energy migrates
backward when the external energy flows into the three dimensional MHD system,
which means the velocity field may play a preceding role in the very early MHD
dynamo stage.",1304.3870v3
2013-07-14,In-plane and out of plane magnetic properties in Ni46Co4Mn38Sb12 Heusler alloys ribbons,"Magnetic, magnetocaloric and exchange bias properties have been
systematically investigated in Ni46Co4Mn38Sb12 ribbon by applying magnetic
field along (IP) and perpendicular (OP) to the ribbon plane. From the
thermo-magnetization curves, the sharpness of the martensitic transition is
observed to be nearly the same for both IP and OP ribbons. The thermomagnetic
irreversibility region is found to be larger in the OP ribbon at 500 Oe,
indicating that the magnetic anisotropy is larger in this case. The OP ribbon
shows the Hopkinson maximum at 500 Oe, both for the FCC and ZFC modes. The
magnetization curve for IP ribbon shows a faster approach to saturation,
compared to the OP ribbon. Isothermal magnetic entropy change at 50 kOe has
been found to be nearly same for both the ribbons. At 5 K the coercivity and
exchange bias values are larger for the OP ribbon. Crystallographic texturing
of the ribbons and its effect in the easy magnetization direction are found to
be the reason behind the differences between the two ribbons.",1307.3778v1
2013-11-21,Magnetization Enhancement in Magnetite Nanoparticles Capped with Alginic Acid,"We report on the effect of organic acid capping on the behavior of magnetite
nanoparticles. The nanoparticles of magnetite were obtained using microwave
activated process, and the magnetic properties as well as the electron magnetic
resonance behavior were studied for the Fe3O4 nanoparticles capped with alginic
acid. The capped nanoparticles exhibit improved crystalline structure of the
surface which leads to an enhanced magnetization. The saturation magnetization
Ms increases to ~75% of the bulk magnetization. The improved structure also
facilitates quantization of spin-wave spectrum in the finite size nanoparticles
and this in turn is responsible for unconventional behavior at low
temperatures. In magnetic resonance these anomalies are manifested as an
unusual increase in the resonant field Hr(T) and also as a maximum of the
spectroscopic splitting geff parameter at low temperatures. The unconventional
behavior of the nanoparticles also leads to pronounced upturn of magnetization
at low temperatures and a deviation from the Bloch law M(T) T^3/2.",1311.5379v1
2014-02-27,Universal logarithmic temperature dependence of magnetic susceptibility of one-dimensional electrons at critical values of magnetic field,"We study the leading low temperature dependence of magnetic susceptibility of
one-dimensional electrons with fixed total number of particles at the magnetic
fields equal to zero temperature critical values where magnetic field induces
commensurate-incommensurate quantum phase transitions. For free and repulsively
interacting electrons there is only one such critical field corresponding to
the transition to the fully polarized state. For attractively interacting
electrons besides saturation field there is another critical field equal to the
spin gap where zero temperature magnetization sets in. For all cases, except of
the lattice models at half filling, the magnetic susceptibility at critical
values of magnetic field has a universal logarithmic temperature
dependence,x(T)=x(0)(1+2/Log(T)+...) for T -> 0.",1402.6801v1
2014-04-29,Nanowire Spin Torque Oscillator Driven by Spin Orbit Torques,"Spin torque from spin current applied to a nanoscale region of a ferromagnet
can act as negative magnetic damping and thereby excite self-oscillations of
its magnetization. In contrast, spin torque uniformly applied to the
magnetization of an extended ferromagnetic film does not generate
self-oscillatory magnetic dynamics but leads to reduction of the saturation
magnetization. Here we report studies of the effect of spin torque on a system
of intermediate dimensionality - a ferromagnetic nanowire. We observe coherent
self-oscillations of magnetization in a ferromagnetic nanowire serving as the
active region of a spin torque oscillator driven by spin orbit torques. Our
work demonstrates that magnetization self-oscillations can be excited in a
one-dimensional magnetic system and that dimensions of the active region of
spin torque oscillators can be extended beyond the nanometer length scale.",1404.7262v2
2014-06-08,Perpendicular magnetic anisotropy and magnetization process in CoFeB/Pd multilayer films,"Perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal
process in [CoFeB $t$ nm/Pd 1.0 nm]$_n$ ($t$ = 0.4, 0.6, 0.8, 1.0, and 1.2 nm;
$n$ = 2 - 20) multilayer films have been studied by means of magnetic
hysteresis and Kerr effect measurements. Strong and controllable PMA with an
effective uniaxial anisotropy up to 7.7$\times$ 10$^6$ J.m$^{-3}$ and a
saturation magnetization as low as 200 emu/cc are achieved. Surface/interfacial
anisotropy of CoFeB/Pd interfaces, the main contribution to the PMA, is
separated from the effective uniaxial anisotropy of the films, and appears to
increase with the number of the CoFeB/Pd bilayers. Observation of the magnetic
domains during a magnetization reversal process using polar magneto-optical
Kerr microscopy shows the detailed behavior of nucleation and displacement of
the domain walls.",1406.2028v1
2016-01-06,Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy,"Multifunctional materials composed of ultrathin magnetic films with
perpendicular magnetic anisotropy combined with ferroelectric substrates
represent a new approach toward low power, fast, high density spintronics. Here
we demonstrate Co/Ni multilayered films with tunable saturation magnetization
and perpendicular anisotropy grown directly on ferroelectric PZT
[Pb(Zr_xTi_1-x)O_3] substrate plates. Electric fields up to +/- 2 MV/m expand
the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni
multilayered film. Modifying the strain with a voltage can reduce the coercive
field by over 30%. We also demonstrate that alternating in-plane tensile and
compressive strains (less than 0.01%) can be used to propagate magnetic domain
walls. This ability to manipulate high anisotropy magnetic thin films could
prove useful for lowering the switching energy for magnetic elements in future
voltage-controlled spintronic devices.",1601.01349v1
2018-01-31,The Heisenberg spin-1/2 XXZ chain in the presence of electric and magnetic fields,"We study the interplay of electric and magnetic order in the one dimensional
Heisenberg spin-1/2 XXZ chain with large Ising anisotropy in the presence of
the Dzyaloshinskii-Moriya (D-M) interaction and with longitudinal and
transverse magnetic fields, interpreting the D-M interaction as a coupling
between the local electric polarization and an external electric field. We
obtain the ground state phase diagram using the density matrix renormalization
group method and compute various ground state quantities like the
magnetization, staggered magnetization, electric polarization and spin
correlation functions, etc. In the presence of both longitudinal and transverse
magnetic fields, there are three different phases corresponding to a gapped
N\'{e}el phase with antiferromagnetic (AF) order, gapped saturated phase and a
critical incommensurate gapless phase. The external electric field modifies the
phase boundaries but does not lead to any new phases. Both external magnetic
fields and electric fields can be used to tune between the phases. We also show
that the transverse magnetic field induces a vector chiral order in the
N\'{e}el phase (even in the absence of an electric field) which can be
interpreted as an electric polarization in a direction parallel to the AF
order.",1801.10509v1
2018-02-20,Controlling magnetism in 2D CrI3 by electrostatic doping,"The atomic thickness of two-dimensional (2D) materials provides a unique
opportunity to control material properties and engineer new functionalities by
electrostatic doping. Electrostatic doping has been demonstrated to tune the
electrical and optical properties of 2D materials in a wide range, as well as
to drive the electronic phase transitions. The recent discovery of atomically
thin magnetic insulators has opened up the prospect of electrical control of
magnetism and new devices with unprecedented performance. Here we demonstrate
control of the magnetic properties of monolayer and bilayer CrI3 by
electrostatic doping using a dual-gate field-effect device structure. In
monolayer CrI3, doping significantly modifies the saturation magnetization,
coercive force and Curie temperature, showing strengthened (weakened) magnetic
order with hole (electron) doping. Remarkably, in bilayer CrI3 doping
drastically changes the interlayer magnetic order, causing a transition from an
antiferromagnetic ground state in the pristine form to a ferromagnetic ground
state above a critical electron density. The result reveals a strongly
doping-dependent interlayer exchange coupling, which enables robust switching
of magnetization in bilayer CrI3 by small gate voltages.",1802.07355v1
2018-11-29,Magnetic field effect on the chiral magnetism of noncentrosymmetric UPtGe: experiment and theory,"The effect of differently oriented magnetic field on chiral incommensurate
helimagnet UPtGe is studied both experimentally and theoretically. The
magnetization measurements up to the field above the saturation have revealed
an isotropic magnetic response below 20 T and a remarkable nonmonotonic
anisotropy in high fields. Moreover, the two principally different phase
transitions from the noncollinear incommensurate to the field-induced
ferromagnetic state have been observed. These properties are successfully
explained by density-functional theory calculations taking into account the
noncollinearity of the magnetic structures, arbitrary directed magnetic field,
and relativistic effects. We also estimate the strength of different competing
magnetic interactions and discuss possible scenarios of the field-induced phase
transformations.",1811.11952v1
2019-02-20,Interplay of magnetization dynamics with microwave waveguide at cryogenic temperatures,"In this work, magnetization dynamics is studied at low temperatures in a
hybrid system that consists of thin epitaxial magnetic film coupled with
superconducting planar microwave waveguide. The resonance spectrum was observed
in a wide magnetic field range, including low fields below the saturation
magnetization and both polarities. Analysis of the spectrum via a developed
fitting routine allowed to derive all magnetic parameters of the film at
cryogenic temperatures, to detect waveguide-induced uniaxial magnetic
anisotropies of the first and the second order, and to uncover a minor
misalignment of magnetic field. A substantial influence of the superconducting
critical state on resonance spectrum is observed and discussed.",1902.07566v2
2019-09-16,Flare Activity and Magnetic Feature Analysis of the Flare Stars,"We analyze the light curve of 1740 flare stars to study the relationship
between the magnetic feature characteristics and the identified flare activity.
Coverage and stability of magnetic features are inspired by rotational
modulation of light curve variations and flare activity of stars are obtained
using our automated flare detection algorithm. The results show that (i) Flare
time occupation ratio (or flare frequency) and total power of flares increase
by increasing relative magnetic feature coverage and contrast in F-M type stars
(ii) Magnetic feature stability is highly correlated with the coverage and the
contrast of the magnetic structures as this is the case for the Sun (iii)
Stability, coverage and contrast of the magnetic features, time occupation
ratio and total power of flares increases for G, K and M-type stars by
decreasing Rossby number due to the excess of produced magnetic field from
dynamo procedure until reaching to saturation level.",1909.07044v1
2019-10-03,Magnetization process of the breathing pyrochlore magnet CuInCr$_4$S$_8$ in ultra-high magnetic fields up to 150 T,"The magnetization process of the breathing pyrochlore magnet CuInCr4S8 has
been investigated in ultra-high magnetic fields up to 150 T. Successive phase
transitions characterized with a substantially wide 1/2-plateau from 55 T to
110 T are observed in this system, resembling those reported in chromium spinel
oxides. In addition to the 1/2-plateau phase, the magnetization is found to
exhibit two inherent behaviors: a slight change in the slope of the M-H curve
at ~ 85 T and a shoulder-like shape at ~ 130 T prior to the saturation. Both of
them are accompanied by a hysteresis, suggesting first-order transitions. The
theoretical calculation applicable to CuInCr4S8 is also shown, based on the
microscopic model with the spin-lattice coupling. The calculation fairly well
reproduces the main features of the experimentally observed magnetization
process, including a relatively wide cant 2:1:1 phase clearly observed in the
previous work [Y. Okamoto et al., J. Phys. Soc. Jpn. 87, 034709 (2018)]. The
robust 1/2-plateau on CuInCr4S8 seems to be originated from the dominant
antiferromagnetic interactions and the strong spin-lattice coupling.",1910.01315v1
2020-02-04,Accelerated design of Fe-based soft magnetic materials using machine learning and stochastic optimization,"Machine learning was utilized to efficiently boost the development of soft
magnetic materials. The design process includes building a database composed of
published experimental results, applying machine learning methods on the
database, identifying the trends of magnetic properties in soft magnetic
materials, and accelerating the design of next-generation soft magnetic
nanocrystalline materials through the use of numerical optimization. Machine
learning regression models were trained to predict magnetic saturation ($B_S$),
coercivity ($H_C$) and magnetostriction ($\lambda$), with a stochastic
optimization framework being used to further optimize the corresponding
magnetic properties. To verify the feasibility of the machine learning model,
several optimized soft magnetic materials -- specified in terms of compositions
and thermomechanical treatments -- have been predicted and then prepared and
tested, showing good agreement between predictions and experiments, proving the
reliability of the designed model. Two rounds of optimization-testing
iterations were conducted to search for better properties.",2002.05225v2
2020-09-26,Magnetization Plateau Observed by Ultra-High Field Faraday Rotation in a Kagomé Antiferromagnet Herbertsmithite,"To capture the high-field magnetization process of herbertsmithite
(ZnCu3(OH)6Cl2), Faraday rotation (FR) measurements were carried out on a
single crystal in magnetic fields of up to 190 T. The magnetization data
evaluated from the FR angle exhibited a saturation behavior above 150 T at low
temperatures, which was attributed to the 1/3 magnetization plateau. The
overall behavior of the magnetization process was reproduced by theoretical
models based on the nearest-neighbor Heisenberg model. This suggests that
herbertsmithite is a proximate kagome antiferromagnet hosting an ideal quantum
spin liquid in the ground state. A distinguishing feature is the superlinear
magnetization increase, which is in contrast to the Brillouin function-type
increase observed by conventional magnetization measurements and indicates a
reduced contribution from free spins located at the Zn sites to the FR signal.",2009.12476v1
2021-06-17,Magnetization process and ordering of the $S=1/2$ pyrochlore magnet in a field,"We study the $S=1/2$ pyrochlore Heisenberg antiferromagnet in a magnetic
field. Using large scale density-matrix renormalization group (DMRG)
calculations for clusters up to $128$ spins, we find indications for a finite
triplet gap, causing a threshold field to nonzero magnetization in the
magnetization curve. We obtain a robust saturation field consistent with a
magnon crystal, although the corresponding $5/6$ magnetization plateau is very
slim and possibly unstable. Most remarkably, there is a pronounced and
apparently robust $\frac 1 2$ magnetization plateau where the groundstate
breaks (real-space) rotational symmetry, exhibiting oppositely polarised spins
on alternating kagome and triangular planes. Reminiscent of the kagome ice
plateau of the pyrochlore Ising magnet known as spin ice, it arises via a much
more subtle `quantum order by disorder' mechanism.",2106.09722v2
2022-01-10,Soft Magnetic Properties of Ultra-Strong and Nanocrystalline Pearlitic Wires,"The paper describes the capability of magnetic softening of a coarse grained
bulk material by a severe deformation technique. Connecting the microstructure
with magnetic properties, the coercive field decreases dramatically for grains
smaller than the magnetic exchange length. This makes the investigation of soft
magnetic properties of severely drawn pearlitic wires very interesting. With
the help of the starting two phase microstructure, it is possible to
substantially refine the material, which allows the investigation of magnetic
properties for nanocrystalline bulk material. Compared to the coarse grained
initial, pearlitic state, the coercivities of the highly deformed wires
decrease while the saturation magnetization values increase, even beyond the
value expectable from the individual constituents. The lowest coercivity in the
drawn state is found to be 520 A m for a wire of 24 um thickness and an
annealing treatment has a further positive effect on it. The decreasing
coercivity is discussed in the framework of two opposing models: grain
refinement on the one hand and dissolution of cementite on the other hand.
Auxiliary measurements give a clear indication for the latter model, delivering
a sufficient description of the observed evolution of magnetic properties.",2201.03302v1
2022-01-18,In-situ alignment of anisotropic hard magnets of 3D printed magnets,"Within this work, we demonstrate in-situ easy-axis alignment of
single-crystal magnetic particles inside a polymer matrix using fused filament
fabrication. Two different magnetic materials are investigated: (i) Strontium
hexaferrite inside a PA6 matrix, fill grade: 49 vol% and (ii) Samarium iron
nitride inside a PA12 matrix, fill grade: 44 vol%. In the presence of the
external alignment field, the strontium hexaferrite particles inside the PA6
matrix can be well aligned with a ratio of remanent magnetization to saturation
magnetization of 0.7. No significant alignment for samarium iron nitride could
be achieved. The results show the feasibility to fabricate magnets with
arbitrary and locally defined easy axis using fused filament fabrication since
the permanent magnets used for the alignment (or alternatively an
electromagnet) can be mounted on a rotatable platform.",2201.07111v1
2022-02-02,Defect Controlled Ferromagnetic Ordering in Au Implanted TiSe$_2$ Nanocrystals,"Layered transition metal dichalcogenides (TMDs) are attracting increasing
attention because they exhibit unconventional magnetic properties due to
crystal imperfections in their usually non-magnetic 2D structure. This work
aims to investigate the magnetic response of self-engineered Se deficient
TiSe$_2$ thin films, synthesized using chemical vapour deposition. We
demonstrate tunability of the ferromagnetic order with the introduction of Au
atoms using low energy Au ion implantation, which works as a controlling knob
to vary the stoichiometry of Se in TiSe$_{2-x}$. The corresponding isothermal
field-magnetization curves fit well with a modified Brillouin J function with J
value of 1.5 for Ti$^{3+}$, and 4 for Au$^{3+}$, accounting for the
diamagnetism that arises from Au implantation. We propose a qualitative model
for the experimentally observed magnetization as a function of ion fluence,
corroborated with high-resolution transmission electron microscopy. Depending
on the Au nanoparticle size in the implanted samples, magnetization saturates
faster at a much lower applied magnetic field than the pristine sample. Our
findings hold potential to expand the range of 2D ferromagnetic materials for
spintronics and magnetic sensing applications.",2202.01152v1
2023-04-28,Magnetic phase diagram in three-dimensional triangular-lattice antiferromagnet Sr$_3$CoTa$_2$O$_9$ with small easy-axis anisotropy,"We report the results of low-temperature magnetization and specific heat
measurements of Sr$_3$CoTa$_2$O$_9$ powder, in which Co$^{2+}$ ions with
effective spin-1/2 form a uniform triangular lattice in the $ab$ plane. It was
found that Sr$_3$CoTa$_2$O$_9$ undergoes successive antiferromagnetic
transitions at $T_{\rm N1}\,{=}\,0.97~{\rm K}$ and $T_{\rm N2}\,{=}\,0.79~{\rm
K}$ at zero magnetic field. As the magnetic field increases, both $T_{\rm N1}$
and $T_{\rm N2}$ decrease monotonically. The obtained magnetic field vs
temperature phase diagram together with a sharp magnetization anomaly at a
saturation field of ${\mu_0}H_{\rm s}\,{=}\,2.3~{\rm T}$ indicates that
Sr$_3$CoTa$_2$O$_9$ is described as a spin-1/2 three-dimensional
triangular-lattice antiferromagnet with a weak easy-axis anisotropy. We discuss
the characteristics of the magnetic phase diagram, which approximates the phase
diagram for the magnetic field perpendicular to the $c$ axis.",2304.14693v1
2023-12-27,Global gyrokinetic simulation of magnetic island induced ion temperature gradient turbulence in toroidal plasma,"The characteristics of ion temperature gradient (ITG) turbulence in the
presence of a magnetic island are numerically investigated using a gyrokinetic
model. We observe that in the absence of the usual ITG drive gradient, a
solitary magnetic island alone can drive ITG instability. The magnetic island
not only drives high-n modes of ITG instability but also induces low-n modes of
vortex flow. Moreover, as the magnetic island width increases, the width of the
vortex flow also increases. This implies that wider islands may more easily
induce vortex flows. The study further indicates that the saturated amplitude
and transport level of MI-induced ITG turbulence vary with different magnetic
island widths. In general, larger magnetic islands enhance both particle and
heat transport. When the magnetic island is of the order of 21 times the ion
gyroradius (21\{rho}_i), the turbulence-driven transport level can reach the
same level in cases where ITG is driven by pressure gradients.",2312.16514v1
2024-02-22,Barium hexaferrite-based nanocomposites as Random Magnets for microwave absorption H,"The present work reports experimental evidence of random magnetic behavior
observed in modified barium hexagonal ferrites. A significant transition in the
magnetic properties of this system is observed when divalent cations (Ni2+,
Cu2+, Mn2+) are introduced in the structure and give rise to a magnetic
nanocomposite. Such introduction takes place in a random manner throughout each
sample and creates the conditions for such materials to behave as random
magnets. We verify the occurrence of such behavior in our samples by fitting
the magnetization in approaching saturation to the corresponding theoretical
model. We therefore analyze the microwave absorption capacities of random
magnets in the GHz range and predict large and broad absorption signals under
certain conditions. The findings presented here postulate, for the first time,
ceramic materials as promising random magnets and underline their potential as
microwave absorbers, in good agreement with recent theoretical models.",2402.14324v1
2024-02-24,A simple model of globally magnetized accretion discs,"We present an analytic, quasi-local dynamo model for accretion discs threaded
by net, vertical magnetic flux. In a simple slab geometry and ignoring
stochastic mean-field dynamo effects, we calculate the large-scale field
resulting from the balance between kinematic field amplification and turbulent
resistive diffusion. The ability of the disc to accumulate magnetic flux is
sensitive to a single parameter dependent on the ratio of the vertical
resistive diffusion time to the Alfv\'en crossing time, and we show how the
saturation levels of magnetorotational and other instabilities can govern disc
structure and evolution. Under wide-ranging conditions, inflow is governed by
large-scale magnetic stresses rather than internal viscous stress. We present
models of such ""magnetically boosted"" discs and show that they lack a radiation
pressure-dominated zone. Our model can account for ""magnetically elevated""
discs as well as instances of midplane outflow and field reversals with height
that have been seen in some global simulations. Using the time-dependent
features of our model, we find that the incorporation of dynamo effects into
disc structure can lead to steady or episodic ""magnetically arrested discs""
(MADs) that maximize the concentration of magnetic flux in their central
regions.",2402.15657v1
2003-03-02,"Hyperdiffusion in non-linear, large and small-scale turbulent dynamos","The generation of large-scale magnetic fields is generically accompanied by
the more rapid growth of small-scale fields. The growing Lorentz force due to
these fields back reacts on the turbulence to saturate the mean-field and
small-scale dynamos. For the mean-field dynamo, in a quasi-linear treatment of
this saturation, it is generally thought that, while the alpha-effect gets
renormalised and suppressed by non-linear effects, the turbulent diffusion is
left unchanged. We show here that this is not true and the effect of the
Lorentz forces, is also to generate additional non-linear hyperdiffusion of the
mean field. A combination of such non-linear hyperdiffusion with diffusion at
small scales, also arises in a similar treatment of small-scale dynamos, and is
crucial to understand its saturation.",0303015v2
2003-02-13,Anisotropic Caging of Interstitial Vortices in Superconductors with a Square Array of Rectangular Antidots,"We investigate anisotropy in the vortex pinning in thin superconducting films
with a square array of rectangular submicron holes (""antidots""). The size of
the antidots is chosen in such a way that it corresponds to a saturation number
n_s=1, i.e. each antidot can trap at most one flux quantum. Therefore,
interstitial vortices, appearing when the magnetic field exceeds the first
matching field, are ""caged"" at the interstitial positions by the repulsion from
the saturated antidots. We observe an overall higher critical current Ic(H)
when it is measured parallel to the long side of the antidots than the Ic(H)
along the short side of the antidots. Although the pinning force, exerted by
the empty antidot on the vortex, turns out to be isotropic, our I_c(H) data
indicate that the caging force, experienced by the interstitial vortices and
provided by the array of saturated antidots, is strongly anisotropic.",0302252v1
2003-12-01,Non-saturating magnetoresistance in heavily disordered semiconductors,"The resistance of a homogeneous semiconductor increases quadratically with
magnetic field at low fields and, except in very special cases, saturates at
fields much larger than the inverse of the carrier mobility, a number typically
of order 1 Tesla. Here, we argue that a macroscopically disordered and strongly
inhomogeneous semiconductor will instead show a non-saturating
magnetoresistance, with typically a quasi-linear behaviour up to very large
fields, and possibly also extending down to very low fields, depending on the
degree of inhomogeneity. We offer this as a possible explanation of the
observed anomalously large magnetoresistance in doped silver chalcogenides.
Furthermore, our model of an inhomogeneous semiconductor can be developed into
magnetoresistive devices that possess a large, controllable, linear response.",0312020v1
2004-04-08,Finite low-temperature entropy of some strongly frustrated quantum spin lattices in the vicinity of the saturation field,"For a class of highly frustrated antiferromagnetic quantum spin lattices the
ground state exhibits a huge degeneracy in high magnetic fields due to the
existence of localized magnon states. For some of these spin lattices (in
particular, the 1D dimer-plaquette, sawtooth and kagom\'{e}-like chains as well
as the 2D kagom\'{e} lattice) we calculate rigorously the ground-state entropy
at the saturation field. We find that the ground-state entropy per site remains
finite at saturation. This residual ground-state entropy produces a maximum in
the field dependence of the isothermal entropy at low temperatures. By
numerical calculation of the field dependence of the low-temperature entropy
for the sawtooth chain we find that the enhancement of isothermal entropy is
robust against small deviations in exchange constants. Moreover, the effect is
most pronounced in the extreme quantum case of spin 1/2.",0404204v1
2005-09-12,Two component butterfly hysteresis in Ru1222 ruthenocuprate,"We report detailed studies of the ac susceptibility butterfly hysteresis on
the Ru1222 ruthenocuprate compounds. Two separate contributions to these
hysteresis have been identified and studied. One contribution is
ferromagnetic-like and is characterized by the coercive field maximum. Another
contribution, represented by the so called inverted maximum, is related to the
unusual inverted loops, unique feature of Ru1222 butterfly hysteresis. The
different nature of the two identified magnetic contributions is proved by the
different temperature dependences involved. By lowering the temperature the
inverted peak gradually disappears while the coercive field slowly raises. If
the maximum dc field for the hysteresis is increased, the size of the inverted
part of the butterfly hysteresis monotonously grows while the position of the
peak saturates. In reaching saturation exponential field dependence has been
demonstrated to take place. At T = 78 K the saturation field is 42 Oe.",0509295v1
2006-09-15,Surfactant effects in monodisperse magnetite nanoparticles of controlled size,"Monodisperse magnetite Fe3O4 nanoparticles of controlled size within 6 and 20
nm in diameter were synthesized by thermal decomposition of an iron organic
precursor in an organic medium. Particles were coated with oleic acid. For all
samples studied, saturation magnetization Ms reaches the expected value for
bulk magnetite, in contrast to results in small particle systems for which Ms
is usually much smaller due to surface spin disorder. The coercive field for
the 6 nm particles is also similar to that of bulk magnetite. Both results
suggest that the oleic acid molecules covalently bonded to the nanoparticle
surface yield a strong reduction in the surface spin disorder. However,
although the saturated state may be similar, the approach to saturation is
different and, in particular, the high-field differential susceptibility is one
order of magnitude larger than in bulk materials. The relevance of these
results in biomedical applications is discussed.",0609384v1
2005-02-24,BPS saturation of the N=4 monopole by infinite composite-operator renormalization,"Quantum corrections to the magnetic central charge of the monopole in N=4
supersymmetric Yang-Mills theory are free from the anomalous contributions that
were crucial for BPS saturation of the two-dimensional supersymmetric kink and
the N=2 monopole. However these quantum corrections are nontrivial and they
require infinite renormalization of the supersymmetry current, central charges,
and energy-momentum tensor, in contrast to N=2 and even though the N=4 theory
is finite. Their composite-operator renormalization leads to counterterms which
form a multiplet of improvement terms. Using on-shell renormalization
conditions the quantum corrections to the mass and the central charge then
vanish both, thus verifying quantum BPS saturation.",0502221v3
2007-01-30,Saturable discrete vector solitons in one-dimensional photonic lattices,"Localized vectorial modes, with equal frequencies and mutually orthogonal
polarizations, are investigated both analytically and experimentally in a
one-dimensional photonic lattice with saturable nonlinearity. It is shown that
these modes may span over many lattice elements and that energy transfer among
the two components is both phase and intensity dependent. The transverse
electrically polarized mode exhibits a single-hump structure and spreads in
cascades in saturation, while the transverse magnetically polarized mode
exhibits splitting into a two-hump structure. Experimentally such discrete
vector solitons are observed in lithium niobate lattices for both coherent and
mutually incoherent excitations.",0701060v1
2006-03-24,Rigorous approach to the nonlinear saturation of the tearing mode in cylindrical and slab geometry,"The saturation of the tearing mode instability is described within the
standard framework of reduced magnetohydrodynamics (RMHD) in the case of an
$r$-dependent or of a uniform resistivity profile. Using the technique of
matched asymptotic expansions, where the perturbation parameter is the island
width $w$, the problem can be solved in two ways: with the so-called flux
coordinate method, which is based on the fact that the current profile is a
flux function, and with a new perturbative method that does not use this
property. The latter is applicable to more general situations where an external
forcing or a sheared velocity profile are involved. The calculation provides a
new relationship between the saturated island width and the $\Delta '$
stability parameter that involves a $\ln{w/w_{0}}$ term, where $w_{0}$ is a
nonlinear scaling length that was missing in previous work. It also yields the
modification of the equilibrium magnetic flux function.",0603204v1
2007-09-07,Flux saturation number of superconducting rings,"The distributions of electrical current and magnetic field in a thin-film
superconductor ring is calculated by solving the London equation. The maximum
amount of flux trapped by the hole, the fluxoid saturation number, is obtained
by limiting the current density by the depairing current. The results are
compare it with similar results derived for the bulk case of a long hollow
cylinder [Nordborg & Vinokur, Phys. Rev. B 62, 12408 (2000)]. In the limit of
small holes our result reduces to the Pearl solution for an isolated vortex in
a thin film. For large hole radius, the ratio between saturation numbers in
bulk and film superconductors is proportional to the square root of the hole
size.",0709.1086v3
2010-07-27,Vertical Structure and Turbulent Saturation Level in Fully Radiative Protoplanetary Disc Models,"We investigate a massive ($\varSigma \sim 10000 g cm^{-2}$ at 1 AU)
protoplanetary disc model by means of 3D radiation magnetohydrodynamics
simulations. The vertical structure of the disc is determined self-consistently
by a balance between turbulent heating caused by the MRI and radiative cooling.
Concerning the vertical structure, two different regions can be distinguished:
A gas-pressure dominated, optically thick midplane region where most of the
dissipation takes place, and a magnetically dominated, optically thin corona
which is dominated by strong shocks. At the location of the photosphere, the
turbulence is supersonic ($M \sim 2$), which is consistent with previous
results obtained from the fitting of spectra of YSOs. It is known that the
turbulent saturation level in simulations of MRI-induced turbulence does depend
on numerical factors such as the numerical resolution and the box size.
However, by performing a suite of runs at different resolutions (using up to
64x128x512 grid cells) and with varying box sizes (with up to 16 pressure
scaleheights in the vertical direction), we find that both the saturation
levels and the heating rates show a clear trend to converge once a sufficient
resolution in the vertical direction has been achieved.",1007.4747v1
2010-08-25,Alleviating alpha quenching by solar wind and meridional flow,"We study the ability of magnetic helicity expulsion to alleviate catastrophic
$\alpha$-quenching in mean field dynamos in two--dimensional spherical wedge
domains. Motivated by the physical state of the outer regions of the Sun, we
consider $\alpha^2\Omega$ mean field models with a dynamical $\alpha$
quenching. We include two mechanisms which have the potential to facilitate
helicity expulsion, namely advection by a mean flow (""solar wind"") and
meridional circulation. We find that a wind alone can prevent catastrophic
quenching, with the field saturating at finite amplitude. In certain parameter
ranges, the presence of a large-scale meridional circulation can reinforce this
alleviation. However, the saturated field strengths are typically below the
equipartition field strength. We discuss possible mechanisms that might
increase the saturated field.",1008.4226v2
2011-02-22,The effect of magnetic activity saturation in chromospheric flux-flux relationships,"We present a homogeneous study of chromospheric and coronal flux-flux
relationships using a sample of 298 late-type dwarf active stars with spectral
types F to M. The chromospheric lines were observed simultaneously in each star
to avoid spread due to long term variability. Unlike other works, we subtract
the basal chromospheric contribution in all the spectral lines studied. For the
first time, we quantify the departure of dMe stars from the general relations.
We show that dK and dKe stars also deviate from the general trend. Studying the
flux-colour diagrams we demonstrate that the stars deviating from the general
relations are those with saturated X-ray emission and that those stars also
present saturation in the H$\alpha$ line. Using several age spectral
indicators, we show that they are younger stars than those following the
general relationships. The non-universality of flux-flux relationships found in
this work should be taken into account when converting between fluxes in
different chromospheric activity indicators.",1102.4506v1
2012-10-19,Non-Dissipative Saturation of the Magnetorotational Instability in Thin Disks,"A new non-dissipative mechanism is proposed for the saturation of the
axisymmetric magnetorotational (MRI) instability in thin Keplerian disks that
are subject to an axial magnetic field. That mechanism relies on the energy
transfer from the MRI to stable magnetosonic (MS) waves. Such mode interaction
is enabled due to the vertical stratification of the disk that results in the
discretization of its MRI spectrum, as well as by applying the appropriate
boundary conditions. A second order Duffing-like amplitude equation for the
initially unstable MRI modes is derived. The solutions of that equation exhibit
bursty nonlinear oscillations with a constant amplitude that signifies the
saturation level of the MRI. Those results are verified by a direct numerical
solution of the full nonlinear reduced set of thin disk magnetohydrodynamics
equations.",1210.5343v1
2014-07-03,Theoretical aspect of enhancement and saturation in emission from laser produced plasma,"This paper presents a simplified theoretical model for the study of emission
from laser produced plasma to better understand the processes and the factors
involved in the onset of saturation in plasma emission as well as in increasing
emission due to plasma confinement. This model considers that plasma emission
is directly proportional to the square of plasma density, its volume and the
fraction of laser pulse absorbed through inverse Bremsstrahlung in the
pre-formed plasma plume produced by the initial part of the laser. This shows
that plasma density and temperature decide the threshold for saturation in
emission, which occurs for electron ion collision frequency more than 10E13 Hz,
beyond which plasma shielding effects become dominant. Any decrease in plasma
sound (expansion) velocity shows drastic enhancement in emission supporting the
results obtained by magnetic as well as spatial confinement of laser produced
plasma. The temporal evolution of plasma emission in the absence and presence
of plasma confinement along with the effect of laser pulse duration are also
discussed in the light of this model.",1407.0775v1
2016-12-05,Numerical simulations of the Princeton magneto-rotational instability experiment with conducting axial boundaries,"We investigate numerically the Princeton magneto-rotational instability (MRI)
experiment and the effect of conducting axial boundaries or endcaps. MRI is
identified and found to reach a much higher saturation than for insulating
endcaps. This is probably due to stronger driving of the base flow by the
magnetically rather than viscously coupled boundaries. Although the
computations are necessarily limited to lower Reynolds numbers ($\Re$) than
their experimental counterparts, it appears that the saturation level becomes
independent of $\Re$ when $\Re$ is sufficiently large, whereas it has been
found previously to decrease roughly as $\Re^{-1/4}$ with insulating endcaps.
The much higher saturation levels will allow for the first positive detection
of MRI beyond its theoretical and numerical predictions.",1612.01224v1
2019-06-08,Area Law Saturation of Entropy Bound from Perturbative Unitarity in Renormalizable Theories,"We study the quantum information storage capacity of solitons and baryons in
renormalizable quantum field theories that do not include gravity. We observe
that a 't Hooft-Polyakov magnetic monopole saturates the Bekenstein bound on
information when the theory saturates the bound on perturbative unitarity. In
this very limit the monopole entropy assumes the form of an area-law,
strikingly similar to a black hole entropy in gravity. The phenomenon appears
universal and takes place for other solitons and non-perturbative objects. We
observe the same behaviour of entropy of a baryon in QCD with large number of
colors. These observations indicate that the area-law form of the entropy bound
extends beyond gravity and is deeply rooted in concepts of weak coupling and
perturbative unitarity. One provoked idea is that confinement in QCD may be
understood as a prevention mechanism against violation of Bekenstein entropy
bound by colored states.",1906.03530v1
2022-07-06,Evidence of decoupling of surface and bulk states in Dirac semimetal $Cd_{3}As_{2}$,"Dirac semimetals have attracted a great deal of current interest due to their
potential applications in topological quantum computing, low-energy electronic
applications, and single photon detection in the microwave frequency range.
Herein are results from analyzing the low magnetic (B) field
weak-antilocalization behaviors in a Dirac semimetal $Cd_{3}As_{2}$ thin flake
device. At high temperatures, the phase coherence length $l_{\phi}$ first
increases with decreasing temperature (T) and follows a power law dependence of
$l_{\phi}\propto$ T$^{-0.4}$. Below ~ 3K, $l_{\phi}$ tends to saturate to a
value of ~ 180 nm. Another fitting parameter $\alpha$, which is associated with
independence transport channels, displays a logarithmic temperature dependence
for T > 3K, but also tends to saturate below ~ 3K. The saturation value, ~
1.45, is very close to 1.5, indicating three independent electron transport
channels, which we interpret as due to decoupling of both the top and bottom
surfaces as well as the bulk. This result, to our knowledge, provides first
evidence that the surfaces and bulk states can become decoupled in electronic
transport in Dirac semimetal $Cd_{3}As_{2}$.",2207.02461v1
2023-06-26,A Way of Determination of Axion Mass with Quantum Hall Effect,"Axion dark matter is converted to electromagnetic radiations in the presence
of strong magnetic field. The radiations possibly give rise to non trivial
phenomena in condensed matter physics. Especially, we discuss that saturation
of plateau-plateau transition width observed at low temperature in integer
quantum Hall effect is caused by the axion. The radiations from axions are
inevitably present in the experiment. Although the radiations generated by
axion is extremely weak, Hall conductivity jumps up to next plateau even if
only a single electron occupies an extended state; a localized electron is
transited to the extended state by absorbing the radiation. According to our
analysis, previous experiment\cite{sat6} of the saturation in detail suggests
that the axion mass is in the range $10^{-5}\mbox{eV}\sim 10^{-6}$eV. We
propose a way of the determination of the axion mass by imposing microwaves on
Hall bar and also a way of the confirmation that the axion really causes the
saturation of the width.",2306.14475v3
1997-07-25,Can the turbulent galactic dynamo generate large-scale magnetic fields?,"Large-scale magnetic fields in galaxies are thought to be generated by a
turbulent dynamo. However the same turbulence also leads to a small-scale
dynamo which generates magnetic noise at a more rapid rate. The efficiency of
the large-scale dynamo depends on how this noise saturates. We examine this
issue taking into account ambipolar drift, which obtains in a galaxy with
significant neutral gas. We argue that, (1) the small-scale dynamo generated
field does not fill the volume, but is concentrated into intermittent rope like
structures. The flux ropes are curved on the turbulent eddy scales. Their
thickness is set by the diffusive scale determined by the effective ambipolar
diffusion; (2) For a largely neutral galactic gas, the small-scale dynamo
saturates, due to inefficient random stretching, when the peak field in a flux
rope has grown to a few times the equipartition value; (3) The average energy
density in the saturated small-scale field is sub equipartition, since it does
not fill the volume; (4) Such fields neither drain significant energy from the
turbulence nor convert eddy motion of the turbulence on the outer scale into
wavelike motion. The diffusive effects needed for the large-scale dynamo
operation are then preserved until the large-scale field itself grows to near
equipartition levels.",9707280v1
2003-02-12,Dephasing of Electrons in Mesoscopic Metal Wires,"We have extracted the phase coherence time $\tau_{\phi}$ of electronic
quasiparticles from the low field magnetoresistance of weakly disordered wires
made of silver, copper and gold. In samples fabricated using our purest silver
and gold sources, $\tau_{\phi}$ increases as $T^{-2/3}$ when the temperature
$T$ is reduced, as predicted by the theory of electron-electron interactions in
diffusive wires. In contrast, samples made of a silver source material of
lesser purity or of copper exhibit an apparent saturation of $\tau_{\phi}$
starting between 0.1 and 1 K down to our base temperature of 40 mK. By
implanting manganese impurities in silver wires, we show that even a minute
concentration of magnetic impurities having a small Kondo temperature can lead
to a quasi saturation of $\tau_{\phi}$ over a broad temperature range, while
the resistance increase expected from the Kondo effect remains hidden by a
large background. We also measured the conductance of Aharonov-Bohm rings
fabricated using a very pure copper source and found that the amplitude of the
$h/e$ conductance oscillations increases strongly with magnetic field. This set
of experiments suggests that the frequently observed ``saturation'' of
$\tau_{\phi}$ in weakly disordered metallic thin films can be attributed to
spin-flip scattering from extremely dilute magnetic impurities, at a level
undetectable by other means.",0302235v2
2005-06-14,High field properties of geometrically frustrated magnets,"Above the saturation field, geometrically frustrated quantum antiferromagnets
have dispersionless low-energy branches of excitations corresponding to
localized spin-flip modes. Transition into a partially magnetized state occurs
via condensation of an infinite number of degrees of freedom. The ground state
below the phase transition is a magnon crystal, which breaks only translational
symmetry and preserves spin-rotations about the field direction. We give a
detailed review of recent works on physics of such phase transitions and
present further theoretical developments. Specifically, the low-energy degrees
of freedom of a spin-1/2 kagom\'e antiferromagnet are mapped to a hard hexagon
gas on a triangular lattice. Such a mapping allows to obtain a quantitative
description of the magnetothermodynamics of a quantum kagom\'e antiferromagnet
from the exact solution for a hard hexagon gas. In particular, we find the
exact critical behavior at the transition into a magnon crystal state, the
universal value of the entropy at the saturation field, and the position of
peaks in temperature- and field-dependence of the specific heat. Analogous
mapping is presented for the sawtooth chain, which is mapped onto a model of
classical hard dimers on a chain. The finite macroscopic entropies of
geometrically frustrated magnets at the saturation field lead to a large
magnetocaloric effect.",0506327v2
2015-08-11,A unified large/small-scale dynamo in helical turbulence,"We use high resolution direct numerical simulations (DNS) to show that
helical turbulence can generate significant large-scale fields even in the
presence of strong small-scale dynamo action. During the kinematic stage, the
unified large/small-scale dynamo grows fields with a shape-invariant
eigenfunction, with most power peaked at small scales or large $k$, as in
\citet{SB14}. Nevertheless, the large-scale field can be clearly detected as an
excess power at small $k$ in the negatively polarized component of the energy
spectrum for a forcing with positively polarized waves. Its strength $bar{B}$,
relative to the total rms field $B_{rms}$, decreases with increasing magnetic
Reynolds number, $R_m$. However, as the Lorentz force becomes important, the
field generated by the unified dynamo orders itself by saturating on
successively larger scales. The magnetic integral scale for the positively
polarized waves, characterizing the small-scale field, increases significantly
from the kinematic stage to saturation. This implies that the small-scale field
becomes as coherent as possible for a given forcing scale, which averts the
$R_m$-dependent quenching of $\bar{B}/B_rms$. These results are obtained for
$1024^3$ DNS with magnetic Prandtl numbers of $P_m=0.1$ and $10$. For
$P_m=0.1$, $\bar{B}/B_{rms}$ grows from about $0.04$ to about $0.4$ at
saturation, aided in the final stages by helicity dissipation. For $P_m=10$,
$\bar{B}/B_{rms}$ grows from much less than 0.01 to values of the order the
$0.2$. Our results confirm that there is a unified large/small-scale dynamo in
helical turbulence.",1508.02706v2
2016-09-05,Inflows towards active regions and the modulation of the solar cycle: a parameter study,"Aims: We aim to investigate how converging flows towards active regions
affect the surface transport of magnetic flux, as well as their impact on the
generation of the Sun's poloidal field. The inflows constitute a potential
non-linear mechanism for the saturation of the global dynamo and may contribute
to the modulation of the solar cycle in the Babcock-Leighton framework.
  Methods: We build a surface flux transport code incorporating a parametrized
model of the inflows and run simulations spanning several cycles. We carry out
a parameter study to assess how the strength and extension of the inflows
affect the build-up of the global dipole field. We also perform simulations
with different levels of activity to investigate the potential role of the
inflows in the saturation of the global dynamo.
  Results: We find that the interaction of neighbouring active regions can lead
to the occasional formation of single-polarity magnetic flux clumps
inconsistent with observations. We propose the darkening caused by pores in
areas of high magnetic field strength as a plausible mechanism preventing this
flux-clumping. We find that inflows decrease the amplitude of the axial dipole
moment by a $\sim30\,\%$, relative to a no-inflows scenario. Stronger (weaker)
inflows lead to larger (smaller) reductions of the axial dipole moment. The
relative amplitude of the generated axial dipole is about $9\%$ larger after
very weak cycles than after very strong cycles. This supports the inflows as a
non-linear mechanism capable of saturating the global dynamo and contributing
to the modulation of the solar cycle within the Babcock-Leighton framework.",1609.01199v1
2022-06-30,Experimental Demonstration of a Spin-Wave Lens Designed with Machine Learning,"We present the design and experimental realization of a device that acts like
a spin-wave lens i.e., it focuses spin waves to a specified location. The
structure of the lens does not resemble any conventional lens design, it is a
nonintuitive pattern produced by a machine learning algorithm. As a spin-wave
design tool, we used our custom micromagnetic solver ""SpinTorch"" that has
built-in automatic gradient calculation and can perform backpropagation through
time for spin-wave propagation. The training itself is performed with the
saturation magnetization of a YIG film as a variable parameter, with the goal
to guide spin waves to a predefined location. We verified the operation of the
device in the widely used mumax3 micromagnetic solver, and by experimental
realization. For the experimental implementation, we developed a technique to
create effective saturation-magnetization landscapes in YIG by direct
focused-ion-beam irradiation. This allows us to rapidly transfer the nanoscale
design patterns to the YIG medium, without patterning the material by etching.
We measured the effective saturation magnetization corresponding to the FIB
dose levels in advance and used this mapping to translate the designed
scatterer to the required dose levels. Our demonstration serves as a proof of
concept for a workflow that can be used to realize more sophisticated spin-wave
devices with complex functionality, e.g., spin-wave signal processors, or
neuromorphic devices.",2207.00055v1
2023-02-26,How well can VMEC predict the initial saturation of external kink modes in near circular tokamaks and $l=2$ stellarators?,"The equilibrium code, VMEC, is used to study external kinks in low $\beta$
tokamaks and $l=2$ stellarators. The applicability of the code when modelling
nonlinear MHD effects is explored in an attempt to understand and predict how
the initial saturation of the MHD mode depends on the external rotational
transform. It is shown that helicity preserving, free boundary VMEC
computations do not converge to a single perturbed solution with increasing
spectral resolution. Additional constraints are therefore applied to narrow
down the numerical resolution parameters appropriate for physical scans. The
dependence of the modelled (4, 1) kink mode on the external rotational
transform and field periodicity is then studied. While saturated states can be
identified which decrease in amplitude with increasing external rotational
transform, bifurcated states are found that contradict this trend. It was
therefore not possible to use VMEC alone to identify the physical dependency of
the nonlinear mode amplitude on the magnetic geometry. The accuracy of the VMEC
solutions is nevertheless demonstrated by showing that the expected toroidal
mode coupling is captured in the magnetic energy spectrum for stellarator
cases. Comparing with the initial value code, JOREK, the predicted
redistribution of poloidal magnetic energy from the vacuum to plasma region in
VMEC is shown to be physical. This work is a first step towards using VMEC to
study MHD modes in stellarator geometry.",2302.13291v2
2023-07-17,Nonlinear mode coupling and energetics of driven magnetized shear-flow turbulence,"To comprehensively understand saturation of two-dimensional ($2$D) magnetized
Kelvin-Helmholtz-instability-driven turbulence, energy transfer analysis is
extended from the traditional interaction between scales to include eigenmode
interactions, by using the nonlinear couplings of linear eigenmodes of the
ideal instability. While both kinetic and magnetic energies cascade to small
scales, a significant fraction of turbulent energy deposited by unstable modes
in the fluctuation spectrum is shown to be re-routed to the conjugate-stable
modes at the instability scale. They remove energy from the forward cascade at
its inception. The remaining cascading energy flux is shown to attenuate
exponentially at a small scale, dictated by the large-scale stable modes.
Guided by a widely used instability-saturation assumption, a general
quasilinear model of instability is tested by retaining all nonlinear
interactions except those that couple to the large-scale stable modes. These
complex interactions are analytically removed from the magnetohydrodynamic
equations using a novel technique. Observations are: an explosive large-scale
vortex separation instead of the well-known merger of $2$D, a dramatic
enhancement in turbulence level and spectral energy fluxes, and a reduced
small-scale dissipation length-scale. These show critical role of the stable
modes in instability saturation. Possible reduced-order turbulence models are
proposed for fusion and astrophysical plasmas, based on eigenmode-expanded
energy transfer analyses.",2307.08895v1
2000-12-01,Two-dimensional disk dynamos with vertical outflows into a halo,"We study the effects of vertical outflows on mean-field dynamos in disks.
These outflows could be due to thermal winds or magnetic buoyancy. We analyse
numerical solutions of the nonlinear mean-field dynamo equations using a
two-dimensional finite-difference model. Contrary to expectations, a modest
vertical velocity can enhance dynamo action. This can lead to super-exponential
growth of the magnetic field and to higher magnetic energies at saturation in
the nonlinear regime.",0012013v1
2001-05-21,A Solvable Model for Nonlinear Mean Field Dynamo,"We formulate a solvable model that describes generation and saturation of
mean magnetic field in a dynamo with kinetic helicity, in the limit of large
magnetic Prandtl number. This model is based on the assumption that the
stochastic part of the velocity field is Gaussian and white in time (the
Kazantsev-Kraichnan ensemble), while the regular part describing the back
reaction of the magnetic field is chosen from balancing the viscous and Lorentz
stresses in the MHD Navier-Stokes equation. The model provides an analytical
explanation for previously obtained numerical results.",0105354v1
2002-07-25,A Taylor-Couette Dynamo,"Recent experiments have shown that it is possible to study a fundamental
astrophysical process such as dynamo action in controlled laboratory conditions
using simple MHD flows. In this paper we explore the possibility that
Taylor-Couette flow, already proposed as a model of the magneto-rotational
instability of accretion discs, can sustain generation of magnetic field.
Firstly, by solving the kinematic dynamo problem, we identify the region of
parameter space where the magnetic field's growth rate is higher. Secondly, by
solving simultaneously the coupled nonlinear equations which govern velocity
field and magnetic field, we find a self-consistent nonlinearly saturated
dynamo.",0207566v1
1998-09-09,Magnetization plateau and quantum phase transition of the S=1/2 trimerized XXZ spin chain,"We study the plateau of the magnetization curve at $M = M_{\rm s}/3$ ($M_{\rm
s}$ is the saturation magnetization) of the $S=1/2$ trimerized $XXZ$ spin
chain. By examining the level crossing of low-lying excitations obtained from
the numerical diagonalization, we precisely determine the phase boundary
between the plateau state and the no-plateau state on the $\Delta-t$ plane,
where $\Delta$ denotes the $XXZ$ anisotropy and $t$ the magnitude of the
trimerization. This quantum phase transition is of the
Berezinskii-Kosterlitz-Thouless type.",9809138v1
1998-09-22,Magnetization plateau in the spin ladder with the four-spin exchange,"The magnetization process of the $S$=1/2 antiferromagnetic spin ladder with
the four-spin cyclic exchange interaction at T=0 is studied by the exact
diagonalization of finite clusters and size scaling analyses. It is found that
a magnetization plateau appears at half the saturation value if the ratio of
the four- and two-spin exchange coupling constants $J_4$ is larger than the
critical value $J_{4c}=0.05\pm$0.04. The phase transition with respect to $J_4$
at $J_{4c}$ is revealed to be the Kosterlitz-Thouless-type.",9809291v1
1999-04-05,Spin Degree of Freedom in a Two-Dimensional Electron Liquid,"We have investigated correlation between spin polarization and
magnetotransport in a high mobility silicon inversion layer which shows the
metal-insulator transition. Increase in the resistivity in a parallel magnetic
field reaches saturation at the critical field for the full polarization
evaluated from an analysis of low-field Shubnikov-de Haas oscillations. By
rotating the sample at various total strength of the magnetic field, we found
that the normal component of the magnetic field at minima in the diagonal
resistivity increases linearly with the concentration of ``spin-up'' electrons.",9904058v1
2000-08-30,Hall Coefficient of a Dilute 2D Electron System in Parallel Magnetic Field,"Measurements in magnetic fields applied at a small angle with respect to the
2D plane of the electrons of a low-density silicon MOSFET indicate that the
Hall coefficient is independent of parallel field from H=0 to $H>H_{sat}$, the
field above which the longitudinal resistance saturates and the electrons have
reached full spin-polarization. This implies that the mobilities of the spin-up
and spin-down electrons remain comparable at all magnetic fields, and suggests
there is strong mixing of spin-up and spin-down electron states.",0008456v1
2000-11-02,Magnetization Plateau of an S=1 Frustrated Spin Ladder,"We study the magnetization plateau at 1/4 of the saturation magnetization of
the S=1 antiferromagnetic spin ladder both analytically and numerically, with
the aim of explaining recent experimental results on BIP-TENO by Goto et al. We
propose two mechanisms for the plateau formation and clarify the plateau phase
diagram on the plane of the coupling constants between spins.",0011034v1
2001-07-30,Field induced transitions in a kagome antiferromagnet,"The thermal order by disorder effect in magnetic field is studied for a
classical Heisenberg antiferromagnet on the kagome lattice. Using analytical
arguments we predict a unique H-T phase diagram for this strongly frustrated
magnet: states with a coplanar and a uniaxial triatic order parameters
respectively at low and high magnetic fields and an incompressible collinear
spin-liquid state at a one-third of the saturation field. We also present the
Monte Carlo data which confirm existence of these phases.",0107608v3
2001-09-03,Mechanisms for Non-Trivial Magnetization Plateaux of an S=1 Frustrated Spin Ladder,"We investigate the non-trivial magnetization plateau at 1/4 of the saturation
magnetization of S=1 spin ladder, especially with reference to recent
experimental results on a new organic tetraradical
3,3',5,5'-tetrakis(N-tert-butylaminoxyl)biphenyl, abbreviated as BIP-TENO. We
propose three mechanisms for the formation of the plateau; the Neel mechanism,
the dimer mechanism and the spin-Peierls mechanism. We also discuss the effect
of four-spin exchange interactions.",0109035v1
2002-10-13,Enhanced magnetocaloric effect in frustrated magnets,"The magnetothermodynamics of strongly frustrated classical Heisenberg
antiferromagnets on kagome, garnet, and pyrochlore lattices is examined. The
field induced adiabatic temperature change (dT/dH)_S is significantly larger
for such systems compared to ordinary non-frustrated magnets and also exceeds
the cooling rate of an ideal paramagnet in a wide range of fields. An
enhancement of the magnetocaloric effect is related to presence of a
macroscopic number of soft modes in frustrated magnets below the saturation
field. Theoretical predictions are confirmed with extensive Monte Carlo
simulations.",0210288v1
2003-10-06,"Ferromagnetism in (In,Mn)As alloy thin films grown by metalorganic vapor phase epitaxy","Ferromagnetic properties of In1-xMnxAs thin films were investigated. Room
temperature ferromagnetic order was observed in nominally single-phase films
with x = 0.01-0.10. Magnetization measurements indicated that these In1-xMnxAs
samples had a Curie temperature of 333 K. The Curie temperature was independent
of Mn concentration. The temperature dependent magnetization along with the
magnitude of the saturation magnetization and microstructural data indicate
that the source of the high-temperature ferromagnetism in single-phase films is
not attributable to MnAs nanoprecipitates. The high transition temperature is
attributed to the presence of near neighbor Mn pairs.",0310104v1
2005-09-15,Reduction of the ordered magnetic moment in YMnO3 with hydrostatic pressure,"YMnO3 exhibits a ferroelectric transition at high temperature (~ 900 K) and
magnetic ordering at T_N ~ 70 K where the dielectric constant shows an anomaly
indicative of the magneto-dielectric effect. Here we report powder neutron
diffraction experiments in this compound that show that the magnetic moment at
saturation is reduced by application of hydrostatic pressure. Our results yield
further insight about the nature of the spin-lattice interaction in ferroic
materials.",0509413v1
2005-10-21,Structural distortions of frustrated quantum spin lattices in high magnetic fields,"We study the stability of some strongly frustrated antiferromagnetic spin
lattices in high magnetic fields against lattice distortions. In particular, we
consider a spin-s anisotropic Heisenberg antiferromagnet on the
square-kagom\'{e} and kagom\'{e} lattices. The independent localized magnons
embedded in a ferromagnetic environment, which are the ground state at the
saturation field, imply lattice instabilities for appropriate lattice
distortions fitting to the structure of the localized magnons. We discuss in
detail the scenario of this spin-Peierls instability in high magnetic fields
which essentially depends on the values of the exchange interaction anisotropy
\Delta and spin s.",0510582v1
2006-03-24,Magnetic resonance in a pyrochlore antiferromagnet Gd2Ti2O7,"Electron spin resonance study of frustrated pyrochlore Gd2Ti2O7 is performed
in a wide frequency band for a temperature range 0.4-30 K, which covers
paramagnetic and magnetically ordered phases. The paramagnetic resonance
reveals the spectroscopic g-factor about 2.0 and a temperature dependent
linewidth. In ordered phases magnetic resonance spectra are distinctive for a
nonplanar cubic (or tetrahedral) antiferromagnet with an isotropic
susceptibility. In the high-field saturated phase, weakly-dispersive soft modes
are observed and their field evolution is traced.",0603653v1
2006-05-24,CVD of CrO2 Thin Films: Influence of the Deposition Parameters on their Structural and Magnetic Properties,"This work reports on the synthesis of CrO2 thin films by atmospheric pressure
CVD using chromium trioxide (CrO3) and oxygen. Highly oriented (100) CrO2 films
containing highly oriented (0001) Cr2O3 were grown onto Al2O3(0001) substrates.
Films display a sharp magnetic transition at 375 K and a saturation
magnetization of 1.92 Bohr magnetons per f.u., close to the bulk value of 2
Bohr magnetons per f.u. for the CrO2.
  Keywords: Chromium dioxide (CrO2), Atmospheric pressure CVD, Spintronics.",0605600v1
2006-07-03,Orbital contribution to the magnetic properties of nanowires: Is the orbital polarization ansatz justified?,"We show that considerable orbital magnetic moments and magneto-crystalline
anisotropy energies are obtained for a Fe monatomic wire described in a
tight-binding method with intra-atomic electronic interactions treated in a
full Hartree Fock (HF) decoupling scheme. Even-though the use of the orbital
polarization ansatz with simplified Hamiltonians leads to fairly good results
when the spin magnetization is saturated this is not the case of unsaturated
systems. We conclude that the full HF scheme is necessary to investigate low
dimensional systems.",0607047v2
1998-02-13,Transverse quasilinear relaxation in inhomogeneous magnetic field,"Transverse quasilinear relaxation of the cyclotron-Cherenkov instability in
the inhomogeneous magnetic field of pulsar magnetospheres is considered. We
find quasilinear states in which the kinetic cyclotron-Cherenkov instability of
a beam propagating through strongly magnetized pair plasma is saturated by the
force arising in the inhomogeneous field due to the conservation of the
adiabatic invariant. The resulting wave intensities generally have nonpower law
frequency dependence, but in a broad frequency range can be well approximated
by the power law with the spectral index -2. The emergent spectra and fluxes
are consistent with the one observed from pulsars.",9802026v1
2005-01-14,Unidirectional Magnetostatic Waves,"Dispersion characteristics of magnetostatic waves in tangentially magnetized
to saturation ferrite film with a ""magnetic wall"" condition (tangential
component of microwave magnetic field is equal to zero) on the one of the film
surface were calculated. It is found, that unidirectional magnetostatic waves
appear in this geometry: they can transfer energy only in one direction and
fundamentally cannot transfer energy in an opposite direction.",0501074v2
2006-12-28,"Helicity fluctuation, generation of linking number and effect on resistivity","The energy of the stochastic magnetic field is bounded from below by a
topological quantity expressing the degree of linkage of the field lines. When
the bound is saturated one can assume that the storage of a certain magnetic
energy requires a minimal degree of topological complexity. It is then possible
to infer a connection between the helicity content and the average curvature of
the magnetic field lines. The random curvature induce random drifts leading to
an additional dissipation and modified resistivity.",0612248v1
2007-04-05,Correlation functions and excitation spectrum of the frustrated ferromagnetic spin-1/2 chain in an external magnetic field,"Magnetic field effects on the one-dimensional frustrated ferromagnetic chain
are studied by means of effective field theory approaches in combination with
numerical calculations utilizing Lanczos diagonalization and the density matrix
renormalization group method. The nature of the ground state is shown to change
from a spin-density-wave region to a nematic-like one upon approaching the
saturation magnetization. The excitation spectrum is analyzed and the behavior
of the single spin-flip excitation gap is studied in detail, including the
emergent finite-size corrections.",0704.0764v2
2007-05-15,Excitation of MHD waves in magnetized anisotropic cosmologies,"The excitation of cosmological perturbations in an anisotropic cosmological
model and in the presence of a homogeneous magnetic field was studied, using
the resistive magnetohydrodynamic (MHD) equations. We have shown that
fast-magnetosonic modes, propagating normal to the magnetic field grow
exponentially and saturated at high values, due to the resistivity. We also
demonstrate that the jeans-like instabilities are enhanced inside a resistive
and the formation of condensations formed within an anisotropic fluid influence
the growing magnetosonic waves.",0705.2194v1
2008-06-12,Magnetic behavior of nanocrystalline LaMn2Ge2,"The compound, LaMn2Ge2, crystallizing in ThCr2Si2-type tetragonal crystal
structure, has been known to undergo ferromagnetic order below (T_C=) 326 K. In
this article, we report the magnetic behavior of nanocrystalline form of this
compound, obtained by high-energy ball-milling. T_C of this compound is reduced
maginally for the nanoform, whereas there is a significant reduction of the
magnitude of the saturation magnetic moment with increasing milling time. The
coercive field however increases with decreasing particle size. Thus, this work
provides a route to tune these parameters by reducing the particle size in this
ternary family.",0806.2030v1
2008-07-07,Effective Theory of Magnetization Plateaux in the Shastry-Sutherland Lattice,"We use the non-perturbative Contractor-Renormalization method (CORE) in order
to derive an effective model for triplet excitations on the Shastry-Sutherland
lattice. For strong enough magnetic fields, various magnetization plateaux are
observed, e.g. at 1/8, 1/4, 1/3 of the saturation, as found experimentally in a
related compound. Moreover, other stable plateaux are found at 1/9, 1/6 or 2/9.
We give a critical review of previous works and try to resolve some apparent
inconsistencies between various theoretical approaches.",0807.1071v2
2008-07-27,Magnetic-dipolar and electromagnetic vortices in quasi-2D ferrite disks,"Magnetic-dipolar-mode (MDM) oscillations in a quasi-2D ferrite disk show
unique dynamical symmetry properties resulting in appearance of topologically
distinct structures. Based on the magnetostatic (MS) spectral problem
solutions, in this paper we give an evidence for eigen MS power-flow-density
vortices in a ferrite disk. Due to these circular eigen power flows, the MDMs
are characterized by MS energy eigen states. It becomes evident that the reason
of stability of the vortex configurations in saturated ferrite samples is
completely different from the nature of stability in magnetically soft
cylindrical dots. We found a clear correspondence between analytically derived
MDM vortex states and numerically modeled electromagnetic vortices in quasi-2D
ferrite disks.",0807.4281v1
2008-08-01,Asymmetric Magnetization Reversal in a Single Exchange-Biased Micro Bar,"The asymmetric magnetization reversal is studied in a single exchange-biased
microbar of 1.5 x 13 micrometer with anisotropic magnetoresistance and magnetic
force microscopy. The particle has a moment of less than 10^-9 emu and is not
accessible with standard magnetometry. The asymmetric hysteresis loop of
CoFe/CrMnPt shows a repeatable rotation process, followed by an irreversible
nucleation process that is marked by jumps in the magnetoresistance. The
induced unidirectional anisotropy enhances the rotation process in one branch
of the hysteresis loop, followed by a sped up nucleation process. Imprinted
ferromagnetic domain patterns left behind by the antiferromagnet are observed
after the nucleation process occurred but before complete saturation is
reached.",0808.0057v1
2009-01-19,The ground state magnetic phase diagram of the ferromagnetic Kondo-lattice model,"The magnetic ground state phase diagram of the ferromagnetic Kondo-lattice
model is constructed by calculating internal energies of all possible bipartite
magnetic configurations of the simple cubic lattice explicitly. This is done in
one dimension (1D), 2D and 3D for a local moment of S = 3/2. By assuming
saturation in the local moment system we are able to treat all appearing higher
local correlation functions within an equation of motion approach exactly. A
simple explanation for the obtained phase diagram in terms of bandwidth
reduction is given. Regions of phase separation are determined from the
internal energy curves by an explicit Maxwell construction.",0901.2855v1
2009-02-14,Relaxation of hole spins in quantum dots via two-phonon processes,"We investigate theoretically spin relaxation in heavy hole quantum dots in
low external magnetic fields. We demonstrate that two-phonon processes and
spin-orbit interaction are experimentally relevant and provide an explanation
for the recently observed saturation of the spin relaxation rate in heavy hole
quantum dots with vanishing magnetic fields. We propose further experiments to
identify the relevant spin relaxation mechanisms in low magnetic fields.",0902.2457v1
2009-06-23,Resistance fluctuations and 1/f noise in single crystalline Ni nanowires,"We measured the low frequency (10mHz < f < 10Hz) resistance fluctuations
(Noise) in single crystalline ferromagnetic Ni nanowires (diameter ~35nm) in
the temperature range 80K-300K. The noise spectral power shows 1/f dependence.
The nanowires in an applied magnetic field show negative magetoresistance that
saturates for H <= HC. The noise spectral power shows a reduction in low
applied field and becomes field independent for H >= HC. This indicates that a
part of the observed 1/f noise arises from magnetic origin. The magnetic part
is associated with thermally activated domain wall fluctuations that couples to
the resistance fluctuations.",0906.4227v1
2010-05-10,Direct and inverse cascades in the geodynamo,"The rapid rotation of planets causes cyclonic thermal turbulence in their
cores which may generate the large-scale magnetic fields observed outside the
planets. We consider the model which enables us reproduce the typical features
of small-scale geostrophic flows in physical and wave spaces. We present
estimates of kinetic and magnetic energy fluxes as a function of the wave
number. The joint existence of forward and inverse cascades are demonstrated.
We also consider the mechanism of magnetic field saturation at the end of the
kinematic dynamo regime.",1005.1546v1
2010-08-30,Towards a quantum theory of chiral magnetic effect,"We discuss three possible ways to address quantum physics behind chiral
magnetic effect and electric charge fluctuation patterns in heavy ion
collisions. The first one makes use of P-parity violation probed by local order
parameters, the second considers CME in quantum measurement theory framework
and the third way is to study P-odd * P-odd contributions to P-even
observables. In the latter approach relevant form-factor is extracted and
computed for weak magnetic field in confinement region and for free quarks in
strong field regime. It is shown that the effect is negligible in the former
case. We also discuss saturation effect - charge fluctuation asymmetry for free
fermions reaches constant value at asymptotically large fields.",1008.4977v1
2010-11-29,Upper Critical Field in the Molecular Organic Superconductor (DMET)2I3,"We report the temperature dependence of the upper critical magnetic field in
the quasi-onedimensional molecular organic superconductor (DMET)2I3, for
magnetic field applied along the intrachain, interchain, and interplane
directions. The upper critical field tends to saturation at low temperature for
field in all directions and does not exceed the Pauli paramagnetic limit.
Superconductivity in (DMET)2I3 thus appears to be conventional spin singlet, in
contrast to the status of the isostructural Bechgaard salts. We also discuss a
magnetic field-induced dimensional crossover effect in the normal metallic
state which had previously appeared to be associated with superconductivity.",1011.6230v1
2010-12-02,Hybrid metal-dielectric ring resonators for optical magnetic metamaterials down to ultraviolet range,"In this paper, we derive a model from Maxwell equations for the magnetic
resonance of split-ring resonators. Using this model we revisit the scaling of
split-ring resonators. Inspired by our model, we propose a new type of
split-hybrid metal-dielectric ring resonator, of which the ring is made
composed of moderately high index dielectric material (e.g. SiC, TiO2, ZnS)
(for the major portion), while and metal (e.g. Ag) fills the gap. Such a new
magnetic metamaterial is able to overcome the saturation problem of split-ring
resonatorssaturation-free and therefore is able to operate at short wavelength
down to ultraviolet range.",1012.0400v2
2012-04-05,The influence of individual lattice defects on the domain structure in magnetic antidot lattices,"We numerically and experimentally investigate the influence of single defects
consisting of a missing antidot on the spin configurations in rectangular
permalloy antidot lattices. The introduction of such lattice defects leads to
the nucleation of complex domain structures after the decay of a saturating
magnetic field. Micromagnetic simulations yield four typical domain
configurations around the defect having distinct energy densities. The
existence of the four spin configurations is confirmed by magnetic force
microscopy on antidot lattices containing individual defects.",1204.1183v2
2012-07-10,Magnetic field induced localization in 2D topological insulators,"Localization of the helical edge states in quantum spin Hall insulators
requires breaking time reversal invariance. In experiments this is naturally
implemented by applying a weak magnetic field B. We propse a model based on
scattering theory that describes the localization of helical edge states due to
coupling to random magnetic fluxes. We find that the localization length is
proportional to B^{2} when B is small, and saturates to a constant when B is
sufficiently large. We estimate especially the localization length for the
HgTe/CdTe quantum wells with known experimental parameters.",1207.2400v1
2012-09-26,Ferromagnetic InMnAs on InAs Prepared by Ion Implantation and Pulsed Laser Annealing,"Ferromagnetic InMnAs has been prepared by Mn ion implantation and pulsed
laser annealing. The InMnAs layer reveals a saturated magnetization of 2.6
mu_B/Mn at 5 K and a perpendicular magnetic anisotropy. The Curie temperature
is determined to be 46 K, which is higher than those in previous reports with
similar Mn concentrations. Ferromagnetism is further evidenced by the large
magnetic circular dichroism.",1209.5865v1
2012-11-01,Spin Seebeck effect in antiferromagnets and compensated ferrimagnets,"We theoretically investigate the spin Seebeck effect (SSE) in
antiferromagnets and ferrimagnets, and show that the SSE vanishes in
antiferromagnets but survives in ferrimagnets even at the magnetization
compensation point despite the absence of its saturation magnetization. The
non-vanishing SSE in ferrimagnets stems from two non-degenerate magnons. We
demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across
the magnetization compensation point.",1211.0123v1
2013-02-02,Ground states of an Ising model on an extended Shastry-Sutherland lattice and the 1/2-magnetization plateau in some rare-earth-metal tetraborides,"A complete solution of the ground-state problem for an Ising model on the
Shastry-Sutherland lattice with an additional interaction along the diagonals
of ""empty"" squares in an applied magnetic field is presented. A rigorous proof
is given that this interaction gives rise to a plateau at one-half of the
saturation magnetization. Such a fractional plateau has been observed in some
rare-earth-metal tetraborides, in particular, in strong Ising magnets ErB4
(where it is the only one) and TmB4 (where it is the broadest one), but its
origin has remained unclear. Our study sheds new light on the solution of this
problem.",1302.0377v1
2013-03-27,Magnetism driven ferroelectricity above liquid nitrogen temperature in Y2CoMnO6,"We report multiferroic behavior in double perovskite Y2CoMnO6 with
ferroelectric transition temperature Tc = 80K. The origin of ferroelectricity
is associated with magnetic ordering of Co2+ and Mn4+ moments in a
up-up-down-down arrangement. The saturation polarization and magnetization are
estimated to be 65 uC/m2 and 6.2 Bohr magneton/f.u. respectively. The
magnetoelectric coupling parameter, on the other hand, is small as a 5 Tesla
field suppresses the electric polarization by only ~8%. This is corroborated
with observed hysteretic behaviour at 5K that remains unsaturated even upto 7
Tesla. A model based on exchange-striction is proposed to explain the observed
high temperature ferroelectricity.",1303.6921v1
2014-07-16,Averaged effective pinning potential in YBCO single crystals close to Tc,"In this paper we present our results on the low density magnetic flux pinning
characteristics, obtained though HTSC samples magnetization relaxation
measurements M(t) near the phase transition temperatures (0,8 < T/Tc > 0,99).As
the main object of investigation we have chosen pure YBa2Cu3O7-x (YBCO) single
crystal samples with optimal oxygen saturation. We note the presence of strong
pinning in the system of unidirectional planar defects and a significant
nonmonotonicity of the Up(T) dependence behavior for low density trapped
magnetic flux.",1407.4304v1
2016-11-15,Numerical study of magnetization plateaux in the spin-1/2 Heisenberg antiferromagnet on the checkerboard lattice,"We present numerical evidence that the spin-1/2 Heisenberg model on the
two-dimensional checkerboard lattice exhibits several magnetization plateaux
for m=0, 1/4, 1/2 and 3/4, where m is the magnetization normalized by its
saturation value. These incompressible states correspond to somehow similar
valence-bond crystal phases that break lattice symmetries, though they are
different from the already established plaquette phase for m=0. Our results are
based on Exact Diagonalization as well as Density Matrix Renormalization Group
large-scale simulations, and interpreted in terms of simple trial
wavefunctions.",1611.04873v2
2017-06-21,Quantum Phase Transition in the Twisted Three-Leg Spin Tube,"We investigate the spin-1/2 twisted three-leg antiferromagnetic quantum spin
tube in the presence of the easy-plane anisotropy, using the numerical
diagonalization of finite-size clusters. And we observe cases of the existence
and the absence of magnetization plateau at 1/3 height of saturation
magnetization when the anisotropy is tuned. The
phenomenological-renormalization analysis indicates a quantum phase transition
between the 1/3 magnetization plateau phase and the plateauless one. The phase
diagram is also presented.",1706.06947v1
2017-08-28,Evidence for field induced proximity type behavior in ferromagnetic nanofluid,"We report some unusual magnetic properties observed in CoFe2O4 based
ferrofluid (with an average particle size of D = 6 nm). More precisely, in
addition to the low-field ferromagnetic (FM) phase transition with an intrinsic
Curie temperature T_Cb=350K, a second phase transition with an extrinsic Curie
temperature T_Cw = 266K emerges at higher (saturating) magnetic field. The
transitions meet at the crossover point T_cr = 210 K. The origin of the second
transition is attributed to magnetic field induced proximity type interaction
between FM particles through non-FM layers.",1708.08373v1
2018-04-27,Angular Dependent Magnetization Dynamics with Mirror-symmetric Excitations in Artificial Quasicrystalline Nanomagnet Lattices,"We report angle-dependent spin-wave spectroscopy on aperiodic
quasicrystalline magnetic lattices, i.e., Ammann, Penrose P2 and P3 lattices
made of large arrays of interconnected Ni$_{80}$Fe$_{20}$ nanobars. Spin-wave
spectra obtained in the nearly saturated state contain distinct sets of
resonances with characteristic angular dependencies for applied in-plane
magnetic fields. Micromagnetic simulations allow us to attribute detected
resonances to mode profiles with specific mirror symmetries. Spectra in the
reversal regime show systematic emergence and disappearance of spin wave modes
indicating reprogrammable magnonic characteristics.",1804.10630v1
2018-06-04,Magnetic field-tuned superconductor/insulator transition in TiN nanostrips,"We have measured the electric transport properties of TiN nanostrips with
different widths. At zero magnetic field the temperature dependent resistance
R(T) saturates at a finite resistance towards low temperatures, which results
from quantum phase slips in the narrower strips. We find that the
current-voltage (I-V) characteristics of the narrowest strips are equivalent to
those of small Josephson junctions. Applying a transverse magnetic field drives
the devices into a reentrant insulating phase, with I-V-characteristics dual to
those in the superconducting regime. The results evidence that our critically
disordered superconducting nanostrips behave like small self-organized random
Josephson networks.",1806.01335v1
2018-06-18,Large anomalous Nernst effect across the magneto-structural transition in bulk Ni-Co-Mn-Sn full Heusler alloy,"We report on the observation of temperature and field dependent anomalous
Nernst effect (ANE) in Ni-rich bulk Ni-Co-Mn-Sn full Heusler alloy. A large
change in the transverse Nernst coefficient (N) is obtained across the first
order magnetostructural transition from a tetragonal martensite to a cubic
austenite phase. The saturation of ANE and magnetic data appear to depend
largely on the magnetic anisotropy of the device. Such change in the Nernst
co-efficient may prove to be useful for switching applications controlled by
temperature and magnetic field changes.",1806.06675v1
2018-07-04,Control of multiferroic order by magnetic field in frustrated helimagnet MnI$_2$. Theory,"We provide a theoretical description of frustrated multiferroic $\rm MnI_2$
with a spiral magnetic ordering in magnetic field $\bf h$. We demonstrate that
subtle interplay of exchange coupling, dipolar forces, hexagonal anisotropy,
and the Zeeman energy account for the main experimental findings observed
recently in this material (Kurumaji, et al., Phys.\ Rev.\ Lett.\ {\bf 106},
167206 (2011)). We describe qualitatively the non-trivial evolution of electric
polarization $\bf P$ upon $\bf h$ rotation, changing $\bf P$ direction upon $h$
increasing, and disappearance of ferroelectricity at $h>h_c$, where $h_c$ is
smaller than the saturation field.",1807.01693v2
2020-04-22,Experimental realization of Lieb-Mattis plateau in a quantum spin chain,"We present a mixed spin-(1/2, 5/2) chain composed of a charge-transfer salt
(4-Br-$o$-MePy-V)FeCl$_4$. We observe the entire magnetization curve up to
saturation, which exhibits a clear Lieb-Mattis magnetization plateau and
subsequent quantum phase transition towards the gapless Luttinger-liquid phase.
The observed magnetic behavior is quantitatively explained by a mixed
spin-(1/2, 5/2) chain model. The present results demonstrate a quantum
many-body effect based on quantum topology and provide a new stage in the
search for topological properties in condensed matter physics.",2004.10416v1
2020-08-10,Phase competition in frustrated anisotropic antiferromagnet in strong magnetic field,"We discuss theoretically a frustrated Heisenberg antiferromagnet in magnetic
field close to the saturation one. It is demonstrated that a small biaxial
anisotropy and/or the magnetic dipolar interaction produce a delicate balance
between phases with a commensurate canted, incommensurate helical (conical),
and fan spin orderings. As a result, different sequences of phase transitions
are realized depending on values of these small anisotropic interactions. We
derive analytical expressions for critical fields and ground-state energies of
the phases which are in a quantitative agreement with our and previous
Monte-Carlo simulations.",2008.04234v1
2020-10-20,On the growth of the thermally modified non-resonant streaming instability,"The cosmic rays non-resonant streaming instability is believed to be the
source of substantial magnetic field amplification. In this work we investigate
the effects of the ambient plasma temperature on the instability and derive
analytical expressions of its growth rate in the hot, demagnetized regime of
interaction. To study its non-linear evolution we perform hybrid-PIC
simulations for a wide range of temperatures. We find that in the cold limit
about two-thirds of the cosmic rays drift kinetic energy is converted into
magnetic energy. Increasing the temperature of the ambient plasma can
substantially reduce the growth rate and the magnitude of the saturated
magnetic field.",2010.10237v1
2020-11-14,Gated two-dimensional electron gas in magnetic field: nonlinear versus linear regimes,"We study the effect of magnetic field on the properties of a high mobility
gated two-dimensional electron gas in a field effect transistor with the Hall
bar geometry. When approaching the current saturation when the drain side of
the channel becomes strongly depleted, we see a number of unusual effects
related to the magnetic field induced re-distribution of the electron density
in the conducting channel. The experimental results obtained in the non-linear
regime have been interpreted based on the results obtained in the linear regime
by a simple theoretical model, which describes quite well our observations.",2011.07292v1
2021-11-04,Sequence of superconducting states in field cooled $FeCr_2S_4$,"In the present article we discuss theoretically the emergence of
superconductivity in field cooled $FeCr_2S_4$. The chromium electrons form a
triplet $t_{2g}$ states and due to antiferromagnetic exchange with the iron
spins have Zeeman splitting. Applied, during preparation, magnetic field along
the moment of iron ions, successively compensates the Zeeman splittings. The
chromium electrons with zero Zeeman energy form Cooper pairs induced by iron
magnons. In that way, we predict theoretically the existence of sequence of
superconducting states in field cooled $FeCr_2S_4$. Actually there are three
different superconductors prepared applying, during preparation, different
magnetic fields. In these compounds superconductivity coexist with the
saturated magnetism of iron ions.",2111.02765v1
2022-05-14,Magnetization Plateau of the Distorted Diamond Spin Chain with Anisotropic Ferromagnetic Interaction,"The $S=1/2$ distorted diamond spin chain with the anisotropic ferromagnetic
interaction is investigated using the numerical diagonalization and the level
spectroscopy analysis. It is known that the system exhibits a plateau of the
magnetization curve at the 1/3 of the saturation. The present study indicates
that as the anisotropy is varied the quantum phase transition occurs between
two different mechanisms of the 1/3 magnetization plateau. The phase diagram
with respect to the anisotropy and the ferromagnetic coupling is also
presented.",2205.07027v1
2023-05-22,Skyrmions and antiskyrmions in monoaxial chiral magnets,"We show that competition between local interactions in monoaxial chiral
magnets provides the stability of two-dimensional (2D) solitons with identical
energies but opposite topological charges. These skyrmions and antiskyrmions
represent metastable states in a wide range of parameters above the transition
into the saturated ferromagnetic phase. The symmetry of the underlying
micromagnetic functional gives rise to soliton zero modes allowing efficient
control of their translational movement by the frequency of the circulating
external magnetic field. We also discuss the role of demagnetizing fields in
the energy balance between skyrmion and antiskyrmion and in their stability.",2305.13003v1
2000-01-10,The Effect of Resistivity on the Nonlinear Stage of the Magnetorotational Instability in Accretion Disks,"We present three-dimensional magnetohydrodynamic simulations of the nonlinear
evolution of the magnetorotational instability (MRI) with a non-zero Ohmic
resistivity. The properties of the saturated state depend on the initial
magnetic field configuration. In simulations with an initial uniform vertical
field, the MRI is able to support angular momentum transport even for large
resistivities through the quasi-periodic generation of axisymmetric radial
channel solutions rather than through the maintenance of anisotropic
turbulence. Simulations with zero net flux show that the angular momentum
transport and the amplitude of magnetic energy after saturation are
significantly reduced by finite resistivity, even at levels where the linear
modes are only slightly affected. This occurs at magnetic Reynolds numbers
expected in low, cool states of dwarf novae, these results suggest that finite
resistivity may account for the low and high angular momentum transport rates
inferred for these systems.",0001164v1
1998-06-24,Magnetization plateaus in weakly coupled dimer spin system,"I study a spin system consisting of strongly coupled dimers which are in turn
weakly coupled in a plane by zigzag interactions. The model can be viewed as
the strong-coupling limit of a two-dimensional zigzag chain structure typical,
e.g., for the $(ac)$-planes of KCuCl_3. It is shown that the magnetization
curve in this model has plateaus at 1/3 and 2/3 of the saturation
magnetization, and an additional plateau at 1/2 can appear in a certain range
of the model parameters; the critical fields are calculated perturbatively. It
is argued that for the three-dimensional lattice structure of the KCuCl_3
family the plateaus at 1/4 and 3/4 of the saturation can be favored in a
similar way, which might be relevant to the recent experiments on NH_4CuCl_3 by
Shiramura et al., J. Phys. Soc. Jpn. {\bf 67}, 1548 (1998).",9806292v3
2003-06-11,Electron Coherence in Mesoscopic Kondo Wires,"We present measurements of the magnetoresistance of long and narrow quasi
one-dimensional gold wires containing magnetic iron impurities. The electron
phase coherence time extracted from the weak antilocalisation shows a
pronounced plateau in a temperature region of 300 mK - 800 mK, associated with
the phase breaking due to the Kondo effect. Below the Kondo temperature, the
phase coherence time increases, as expected in the framework of Kondo physics.
At much lower temperatures, the phase coherence time saturates again, in
contradiction with standard Fermi liquid theory. In the same temperature
regime, the resistivity curve displays a characteristic maximum at zero
magnetic field, associated with the formation of a spin glass state. We argue
that the interactions between the magnetic moments are responsible for the low
temperature saturation of the phase coherence time.",0306276v1
2003-08-14,Low temperature dephasing saturation from elastic magnetic spin disorder and interactions,"We treat the question of the low temperature behavior of the dephasing rate
of the electrons in the presence of elastic spin disorder scattering and
interactions. In the frame of a self-consistent diagrammatic treatment, we
obtain saturation of the dephasing rate in the limit of low temperature for
magnetic scattering, in agreement with the non-interacting case. The magnitude
of the dephasing rate is set by the strength of the magnetic scattering rate.
We discuss the agreement of our results with relevant experiments.",0308300v7
2003-11-13,"Structural, magnetic and transport properties of thin films of the Heusler alloy Co2MnSi","Thin films of Co2MnSi have been grown on a-plane sapphire substrates from
three elemental targets by dc magnetron co-sputtering. These films are single
phase, have a strong (110) texture and a saturation magnetization of 4.95
uB/formula unit at 10 K. Films grown at the highest substrate temperature of
715 K showed the lowest resistivity (47 uOhm cm at 4.2 K) and the lowest
coercivity (18 Oe). The spin polarization of the transport current was found to
be of the order of 54% as determined by point contact Andreev reflection
spectroscopy. A decrease in saturation magnetization with decreasing film
thickness and different transport behaviour in thinner films indicate a graded
disorder in these films grown on non-lattice matched substrates.",0311316v1
2003-12-02,Frustrated antiferromagnets at high fields: the Bose-Einstein condensation in degenerate spectra,"Quantum phase transition at the saturation field is studied for a class of
frustrated quantum antiferromagnets. The considered models include (i) the
$J_1$-$J_2$ frustrated square-lattice antiferromagnet with $J_2={1/2}J_1$ and
(ii) the nearest-neighbor Heisenberg antiferromagnet on a face centered cubic
lattice. In the fully saturated phase the magnon spectra for the two models
have lines of degenerate minima. Transition into partially magnetized state is
treated via a mapping to a dilute gas of hard core bosons and by complementary
spin-wave calculations. Momentum dependence of the exact four-point boson
vertex removes the degeneracy of the single-particle excitation spectra and
selects the ordering wave-vectors at $(\pi,\pi)$ and $(\pi,0,0)$ for the two
models. The asymptotic behavior of the magnetization curve differs
significantly from that of conventional antiferromagnet in $d$-spatial
dimensions. We predict a unique form for the magnetization curve $\Delta
M=S-M\simeq \mu^{(d-1)/2}(\log\mu)^{(d-1)}$, where $\mu$ is a distance from the
quantum critical point.",0312076v2
2005-09-21,Bose-Einstein condensation of magnons in Cs$_{2}$CuCl$_{4}$: a dilute gas limit near the saturation magnetic field,"Based on a realistic spin Hamiltonian for a frustrated quasi-two dimensional
spin-1/2 antiferromagnet Cs$_{2}$CuCl$_{4}$, a three-dimensional spin ordering
in the applied magnetic field $B$ near the saturation value $B_{c}$ is studied
within the magnon Bose-Einstein condensation (BEC) scenario. With the use of a
hard-core boson formulation of the spin model, a strongly anysotropic magnon
dispersion in Cs$_{2}$CuCl$_{4}$ is calculated. In the dilute magnon limit near
$B_{c}$, the hard-core boson constraint is resulted in an effective magnon
interaction which is treated in the Hartree-Fock approximation. The critical
temperature $T_{c}$ is calculated as a function of a magnetic field $B$ and
compared with the phase boundary $T_{c}(B) $ experimentally determined in
Cs$_{2}$CuCl$_{4}$ [Phys. Rev. Lett. \textbf{95}, 127202 (2005)].",0509552v1
2006-06-22,Enhanced low field magnetoresistance of Fe3O4 nano-sphere compact,"Unusually large low field magetoresistance (LFMR), ~ 10 %, at 300 K has been
observed with the sample of mono-dispersed Fe3O4 magnetite nanospheres, ~ 200
nm, compactly cold-pressed and sintered at 800 C. A detailed analysis on the
transport and magnetic measurements indicates that the electron conduction is
dominated by the spin-dependent scattering or tunneling at the grain
boundaries. At low temperature, 140 K and 100 K near the Verwey transition, ~
115 K, the LFMR (below 2 kOe) does not show any sign of dependence on the
transition, and does not follow the variation of magnetization to reach the
saturation region either. On the other hand, at 300 K, the MR saturates fast
with the magnetization below 2 kOe. This temperature dependent property in LFMR
is very likely attributed to the scattering or tunneling of the conduction
electron passing through the grain boundary layer with spin disordered state.",0606565v1
2007-05-22,Magnetocaloric effect in the frustrated square lattice J1-J2 model,"We investigate the magnetocaloric properties of the two-dimensional
frustrated J1-J2 model on a square lattice. This model describes well the
magnetic behavior of two classes of quasi-two-dimensional S = 1/2 vanadates,
namely the Li2VOXO4 (X = Si, Ge) and AA'VO(PO4)2 (A, A' = Pb, Zn, Sr, Ba)
compounds. The magnetocaloric effect (MCE) consists in the adiabatic
temperature change upon changing the external magnetic field. In frustrated
systems, the MCE can be enhanced close to the saturation field because of
massive degeneracies among low lying excitations. We discuss results for the
MCE in the two distinct antiferromagnetic regimes of the phase diagram.
Numerical finite temperature Lanczos as well as analytical methods based on the
spin wave expansion are employed and results are compared. We give explicit
values for the saturation fields of the vanadium compounds. We predict that at
subcritical fields there is first a (positive) maximum followed by sign change
of the MCE, characteristic of all magnetically ordered phases.",0705.3094v2
2008-11-12,Spin-Dynamics of the antiferromagnetic S=1/2-Chain at finite magnetic Fields and intermediate Temperatures,"We present a study of the dynamic structure factor of the antiferromagnetic
spin-1/2 Heisenberg chain at finite temperatures and finite magnetic fields.
Using Quantum-Monte-Carlo based on the stochastic series expansion and
Maximum-Entropy methods we evaluate the longitudinal and the transverse dynamic
structure factor from vanishing magnetic fields up to and above the threshold
$B_c$ for ferromagnetic saturation, as well as for high and for intermediate
temperatures. We study the field-induced redistribution of spectral weight
contrasting longitudinal versus transverse excitations. At finite fields below
saturation incommensurate low-energy modes are found consistent with zero
temperature Bethe-Ansatz. The crossover between the field induced ferromagnet
above $B_c$ and the Luttinger liquid below $B_c$ is analyzed in terms of the
transverse spin-dynamics. Evaluating sum-rules we assess the quality of the
analytic continuation and demonstrate excellent consistency of the
Maximum-Entropy results.",0811.1956v2
2009-03-13,Magnetoconductivity of low-dimensional disordered conductors at the onset of the superconducting transition,"Magnetoconductivity of the disordered two- and three-dimensional
superconductors is addressed at the onset of superconducting transition. In
this regime transport is dominated by the fluctuation effects and we account
for the interaction corrections coming from the Cooper channel. In contrast to
many previous studies we consider strong magnetic fields and various
temperature regimes, which allow to resolve the existing discrepancies with the
experiments. Specifically, we find saturation of the fluctuations induced
magneto-conductivity for both two- and three-dimensional superconductors at
already moderate magnetic fields and discuss possible dimensional crossover at
the immediate vicinity of the critical temperature. The surprising observation
is that closer to the transition temperature weaker magnetic field provides the
saturation. It is remarkable also that interaction correction to
magnetoconductivity coming from the Cooper channel, and specifically the so
called Maki-Thompson contribution, remains to be important even away from the
critical region.",0903.2467v2
2009-04-18,From fibril to diffuse fields during dynamo saturation,"The degree of intermittency of the magnetic field of a large-scale dynamo is
considered. Based on simulations it is argued that there is a tendency for the
field to become more diffuse and non-intermittent as the dynamo saturates. The
simulations are idealized in that the turbulence is strongly helical and shear
is strong, so the tendency for the field to become more diffuse is somewhat
exaggerated. Earlier results concerning the effects of magnetic buoyancy are
discussed. It is emphasized that the resulting magnetic buoyancy is weak
compared with the stronger effects of simultaneous downward pumping. These
findings are used to support the notion that the solar dynamo might operate in
a distributed fashion where the near-surface shear layer could play an
important role.",0904.2842v1
2009-05-14,PIC simulations of the Thermal Anisotropy-Driven Weibel Instability: Field growth and phase space evolution upon saturation,"The Weibel instability is investigated with PIC simulations of an initially
unmagnetized and spatially uniform electron plasma. This instability, which is
driven by the thermally anisotropic electron distribution, generates
electromagnetic waves with wave vectors perpendicular to the direction of the
higher temperature. Two simulations are performed: A 2D simulation, with a
simulation plane that includes the direction of higher temperature,
demonstrates that the wave spectrum is initially confined to one dimension. The
electric field components in the simulation plane generated by the instability
equalize at the end of the simulation through a secondary instability. A 1D PIC
simulation with a high resolution, where the simulation box is aligned with the
wave vectors of the growing waves, reveals details of the electron phase space
distribution and permits a comparison of the magnetic and electric fields when
the instability saturates. It is shown that the electrostatic field is driven
by the magnetic pressure gradient and that it and the magnetic field
redistribute the electrons in space.",0905.2282v1
2009-12-01,Heavy Fermion-like metal alpha double prime-Fe16N2 with giant saturation magnetization,"A new model is proposed for the strong ferromagnetism associated with
partially localized orbitals in the Fe16N2 metallic system which draws
substantially from models of heavy fermion metals. We demonstrated that an
unusual correlation effect is brought up within the Fe-N octahedral cluster
region and the effective on-site 3d-3d Coulomb interaction increases due to a
substantial 3d electrons charge density difference between the clusters and its
surroundings, which leads to a partially localized high spin electron
configuration with a long range ferromagnetic order. First principle
calculation based on LDA+U method shows that giant magnetic moment can be
achieved at sufficiently large Hubbard U value. The feature of the coexistence
of the localized and itinerant electron states plays a key role on the
formation of the giant saturation magnetization.",0912.0276v1
2010-05-31,Can catastrophic quenching be alleviated by separating shear and alpha effect?,"The small-scale magnetic helicity produced as a by-product of the large-scale
dynamo is believed to play a major role in dynamo saturation. In a mean-field
model the generation of small-scale magnetic helicity can be modelled by using
the dynamical quenching formalism. Catastrophic quenching refers to a decrease
of the saturation field strength with increasing Reynolds number. It has been
suggested that catastrophic quenching only affects the region of non-zero
helical turbulence (i.e. where the kinematic alpha operates) and that it is
possible to alleviate catastrophic quenching by separating the region of strong
shear from the alpha layer. We perform a systematic study of a simple
axisymmetric two-layer alpha-omega dynamo in a spherical shell for Reynolds
numbers in the range 1 < Rm < 10^5. In the framework of dynamical quenching we
show that this may not be the case, suggesting that magnetic helicity fluxes
would be necessary.",1005.5708v1
2010-10-09,The High Field Magnetization in the RF Sputter Deposited Copper Ferrite Thin Films,"Copper ferrite thin films were deposited on amorphous quartz substrates. The
as deposited films were annealed in air and either quenched or slow cooled.
Magnetization studies were carried out on the as deposited as well as annealed
films using a SQUID magnetometer. The M-H curves were measured up to a field of
7T, at temperatures varying from 5K to 300K. The magnetization in the films did
not saturate, even at the highest field. The expression, M(H)= Q(1- a/H^n)
fitted the approach to saturation best with n=1/2, for all films and at all
temperatures. The coefficient a was the highest for the as deposited film and
was the smallest for the quenched film. In the case of as deposited film, the
value of coefficient a increased with increasing temperature, while for the
annealed films, the value of a showed a decrease as temperature increases.",1010.1881v1
2012-11-02,Polarized neutron reflectometry study of Fe16N2 with Giant Saturation Magnetization prepared by N Inter-diffusion in Annealed Fe-N Thin Films,"We report a synthesis route to grow iron nitride thin films with giant
saturation magnetization (Ms) through an N inter-diffusion process. By post
annealing Fe/Fe-N structured films grown on GaAs(001) substrates, nitrogen
diffuses from the over-doped amorphous-like Fe-N layer into strained
crystalline Fe layer and facilitates the development of metastable Fe16N2
phase. As explored by polarized neutron reflectometry, the depth-dependent Ms
profile can be well described by a model with the presence of a giant Ms up to
2360 emu/cm3 at near-substrate interface, corresponding to the strained regions
of these annealed films. This is much larger than the currently known limit
(Fe65Co35 with Ms \sim 1900 emu/cm3). The present synthesis method can be used
to develop writer materials for future magnetic recording application.",1211.0551v1
2012-12-19,Realizing a High Magnetic Moment in Gd/Cr/FeCo: The Role of the Rare Earth,"The search for materials or systems exhibiting a high magnetic saturation has
been of longstanding importance. It has been suggested that increased
saturation could be achieved by coupling a transition metal via a spacer to a
rare earth. We report Gd/Cr/Fe70Co30 multilayer stacks and find reduced yet
modulating magnetic moment as a function of Cr thickness. Through a micro
structural analysis the lowered moment is indicated by the nucleation of the
ultrathin Gd films into an fcc phase. We discuss the possible solution in terms
of quasi-perfect lattice match seed material to promote growth of hcp Gd.",1212.4859v1
2013-05-28,Magnonic band gaps in waveguides with a periodic variation of the saturation magnetization,"We present a micromagnetic analysis of spin-wave propagation in a magnonic
crystal realized as a permalloy spin-wave waveguide with a spatial periodical
variation of its saturation magnetization. Frequency band gaps were clearly
observed in the spin-wave transmission spectra and their origin is traced back
to an overlap of individual band gaps of the fundamental and the higher order
spin-wave width modes. The control of the depth, width and the position in
frequency and space of the rejection band gaps by the width areas with a
reduced magnetization and by the modulation level, are discussed in this study.",1305.6619v1
2013-10-28,Temperature dependent weak value of dwell time for a two state particle tunneling through a thermal magnetic barrier,"Dwell time for a two state particle tunneling through a noisy thermal
magnetic barrier has been calculated by studying the time evolution of the
system. The effect of temperature has been included by averaging over the
environmental magnetic modes. The time scale has been calculated in the
framework of weak measurement. The dwell time initially increases with the rise
of temperature and finally saturates. The increment of dwell time can be
explained by the phenomena of quantum memory loss caused by efficient energy
exchange with the environmental modes. The saturation region at higher
temperature corresponds to the process of thermal hopping of the barrier.",1310.7338v2
2014-01-23,Saturated-absorption spectroscopy revisited: atomic transitions in strong magnetic fields ($>$20 mT) with a micrometer-thin cell,"The existence of cross-over resonances makes saturated-absorption spectra
very complicated when external magnetic field B is applied. It is demonstrated
for the first time that the use of micrometric-thin cells (MTC,
$L\approx40\,\mu$m) allows application of SA for quantitative studies of
frequency splittings and shifts of the Rb atomic transitions in a wide range of
external magnetic fields, from 0.2 up to 6 kG (20-600 mT). We compare the SA
spectra obtained with the MTC with those obtained with other techniques, and
present applications for optical magnetometry with micrometer spatial
resolution and a broadly tunable optical frequency reference.",1401.6208v2
2014-05-05,The change of GRB polarization angles in the magnetic-dominated jet model,"The polarimetric measurement on the prompt phase of GRB 100826A shows that
the polarization angle changes $\sim 90^{\circ}$ between two adjacent time
intervals. We will show that this phenomenon can be naturally interpreted in
the framework of the magnetic-dominated jet (MDJ) model. The MDJ model suggests
that the bulk Lorentz factor of the outflow increases as $\Gamma\propto
r^{1/3}$, until reaching a saturated value $\Gamma_{\rm sat}$. Electrons move
in the globally ordered magnetic field advected by the jet from the central
engine and produce synchrotron photons. The polarized synchrotron photons
travel alone the jet direction and then collide with the cold electrons at the
front of the jet. After the Compton scattering process, these photons escape
from the jet and are detected by the observer locating slightly off-axis. If
photons are emitted before the bulk Lorentz factor saturates, the change of
polarization angle is a natural result of the acceleration of the outflow.",1405.0844v2
2015-09-07,Influence of spin dynamics of defects on weak localization in paramagnetic 2D metals,"Spin-flip scattering of charge carriers in metals with magnetic defects leads
to the low-temperature saturation of the decoherence time, $\tau_\varphi$, of
electrons at the value comparable to their spin relaxation time, $\tau_s$. In
two-dimensional (2D) conductors such a saturation can be lifted by an in-plane
magnetic field, $B_\parallel$, which polarizes spins of scatterers without
affecting orbital motion of free carriers. Here, we show that in 2D conductors
with substantially different values of the g-factors of electrons ($g_e$) and
magnetic defects ($g_i$), the decoherence time $\tau_\varphi(B_\parallel)$
(reflected by the curvature of magnetoconductance) displays an anomaly: it
first gets shorter, decaying on the scale $B_\parallel\sim \hbar/|g_i-g_e|\mu_B
\tau_s$, before becoming longer at higher values of $B_\parallel$.",1509.01955v2
2015-10-07,"Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films","The half-metallic half-Heusler alloy NiMnSb is a promising candidate for
applications in spintronic devices due to its low magnetic damping and its rich
anisotropies. Here we use ferromagnetic resonance (FMR) measurements and
calculations from first principles to investigate how the composition of the
epitaxially grown NiMnSb influences the magnetodynamic properties of saturation
magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$.
$M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while
the Gilbert damping is minimum. We find excellent quantitative agreement
between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows
the same trend as the experimental data, but has a larger magnitude.
Additionally to the unique in-plane anisotropy of the material, these
tunabilities of the magnetodynamic properties can be taken advantage of when
employing NiMnSb films in magnonic devices.",1510.01894v1
2016-02-19,Complete mapping of the spin-wave spectrum in vortex state nano-disk,"We report a study on the complete spin-wave spectrum inside a vortex state
nano-disk. Transformation of this spectrum is continuously monitored as the
nano-disk becomes gradually magnetized by a perpendicular magnetic field and
encouters a second order phase transition to the uniformly magnetized state.
This reveals the bijective relationship that exists between the eigen-modes in
the vortex state with the ones in the saturated state. It is found that the
gyrotropic mode can be continuously viewed as a uniform phase precession, which
uniquely softens (its frequency vanishes) at the saturation field to transform
above into the Kittel mode. By contrast the other spin-wave modes remain finite
as a function of the applied field while their character is altered by level
anti-crossing.",1602.06336v2
2016-07-01,Saturation magnetization and band gap tuning in BiFeO$_3$ nanoparticles via co-substitution of Gd and Mn,"In this investigation, Gd and Mn co-doped
Bi$_{0.85}$Gd$_{0.15}$Fe$_{1-x}$Mn$_x$O$_3$ (x=0.0-0.15) nanoparticles have
been prepared to report the influence of co-substitution on their structural,
optical, magnetic and electrical properties. Due to simultaneous substitution
of Gd and Mn in BiFeO$_3$, the crystal structure has been modified from
rhombohedral (R3c) to orthorhombic (Pn21a) and the Fe-O-Fe bond angle and Fe-O
bond length have been changed. For Mn doping up to 10 % in
Bi$_{0.85}$Gd$_{0.15}$Fe$_{1-x}$Mn$_x$O$_3$ nanoparticles, the saturation
magnetization (Ms) has been enhanced significantly, however, for a further
increase of doping up to 15 %, the Ms has started to reduce again. The
co-substitution of Gd and Mn in BiFeO$_3$ nanoparticles also demonstrates a
strong reduction in the optical band gap energy and electrical resistivity
compared to that of undoped BiFeO$_3$.",1607.00158v1
2017-05-18,Enhanced Ferromagnetism in Lacey Reduced Graphene Oxide Nano-ribbon,"Incorporation of magnetism in graphene based compounds holds great promise
for potential spintronic applications. By optimizing point defects and high
edge density of defects, we report many-fold increase in the ferromagnetic
saturation moment in lacey reduced graphene oxide nanoribbons (LRGONR) as
compared to other graphene derivatives. The samples were synthesized using
chemical unzipping methodology. Detailed structural and morphological
characterizations are discussed that include XRD, Raman, SEM, HRTEM and XPS
measurements. Brilluoin function analysis to magnetization data reflects best
fit for J = 7/2 with a saturation moment of 1.1 emu/g. The microscopic origin
of magnetization in LRGONR is assigned to high edge defect density which has
also been correlated to microstructure.",1705.06531v1
2018-01-23,"Polyaniline (C_{3}N) nanoribbons: Magnetic metal, Semiconductor, and Half-Metal","Two-dimensional polyaniline sheet has been recently synthesized and found
that it is a semiconductor with indirect band gap. Polyaniline nanoribbons
decomposed from two-dimensional polyaniline sheet (C3N sheet) are investigated
using density functional theory. The existence of nitrogen atoms in the edge of
the ribbons increases stability and magnetization of the ribbons and make them
different from graphene nanoribbons. Unsaturated nanoribbons are magnetic
metals so that armchair C3N nanoribbons are gap-less spin semicon- ductors in
the antiferromagnetic state and half-metals in the ferromagnetic state. A
transition from metal to semiconductor is observed in the armchair C3N
nanoribbons when the edge atoms are passivated by hy- drogen. The band gap of
hydrogen saturated armchair C3N nanoribbons can be controlled using an external
transverse electric field so that its magnitude is dependent on the direction
of the electric field. Being metal or semiconductor in hydrogen saturated
zigzag C3N nanoribbons is strongly dependent on the edge atoms so that just
ribbons having nitrogen atoms in both edges are semiconductor. An external
electric field cannot induce any spin polarization in the zigzag nanoribbons
which is in contrast with what was observed in zigzag",1801.07540v2
2018-09-19,Structure-property relationship of Co$_2$MnSi thin films in response to He$^+$ -irradiation,"We investigated the structure-property relationship of Co$_2$MnSi Heusler
thin films upon the irradiation with He$^+$ ions. The variation of the crystal
structure with increasing ion fluence has been probed using nuclear magnetic
resonance (NMR) and transmission electron microscopy (TEM), and associated with
the corresponding changes of the magnetic behavior. A decrease of both the
structural order and the moment in saturation is observed. Specifically, we
detect a direct transition from a highly $L2_1$-ordered to a fully
$A2$-disordered structure type and quantify the evolution of the $A2$
structural contribution as a function of ion fluence. Complementary TEM
analysis reveals a spatially-resolved distribution of the $L2_1$ and $A2$
phases showing that the $A2$ disorder starts at the upper part of the films.
The structural degradation in turn leads to a decreasing magnetic moment in
saturation in response to the increasing fluence.",1809.07097v1
2018-11-06,Phase programming in coupled spintronic oscillators,"Neurons in the brain behave as a network of coupled nonlinear oscillators
processing information by rhythmic activity and interaction. Several
technological approaches have been proposed that might enable mimicking the
complex information processing of neuromorphic computing, some of them relying
on nanoscale oscillators. For example, spin torque oscillators are promising
building blocks for the realization of artificial high-density, low-power
oscillatory networks (ON) for neuromorphic computing. The local external
control and synchronization of the phase relation of oscillatory networks are
among the key challenges for implementation with nanotechnologies. Here we
propose a new method of phase programming in ONs by manipulation of the
saturation magnetization, and consequently the resonance frequency of a single
oscillator via Joule heating by a simple DC voltage input. We experimentally
demonstrate this method in a pair of stray field coupled magnetic vortex
oscillators. Since this method only relies on the oscillatory behavior of
coupled oscillators, and the temperature dependence of the saturation
magnetization, it allows for variable phase programming in a wide range of
geometries and applications that can help advance the efforts of high frequency
neuromorphic spintronics up to the GHz regime.",1811.02154v1
2019-10-08,Analytic solutions of the modified Langevin equation in a mean-field model,"Approximate analytical solutions of the modified Langevin equation are
obtained. These solutions are relatively simple and enough accurate. They are
illustrated by considering a mean-field model of a system with interacting
superparamagnetic particles. Within the framework of this model system we
derived analytical approximate formulas for the temperature dependencies of the
saturation and remnant magnetization, coercive force, initial magnetic
susceptibility as well as for the law of approach to saturation. We obtained
also some exact analytical relationships for the coercive force. We found
remarkable similarity between the approximate cubic equation, which is resulted
from the modified Langevin equation, and the exact equation resulting from the
divergence condition of a solution derivative. The analytical formulas obtained
in this work can be used in various models (not only magnetic ones), where the
modified Langevin equation is applied.",1910.08401v1
2020-05-20,Correlating magnetic structure and magnetotransport in semimetal thin films of Eu$_{1-x}$Sm$_x$TiO$_3$,"We report on the evolution of the average and depth-dependent magnetic order
in thin film samples of biaxially stressed and electron-doped EuTiO$_3$ for
samples across a doping range $<$0.1 to 7.8 $\times 10^{20}$ cm$^{-3}$. Under
an applied in-plane magnetic field, the G-type antiferromagnetic ground state
undergoes a continuous spin-flop phase transition into in-plane,
field-polarized ferromagnetism. The critical field for ferromagnetism slightly
decreases with an increasing number of free carriers, yet the field evolution
of the spin-flop transition is qualitatively similar across the doping range.
Unexpectedly, we observe interfacial ferromagnetism with saturated Eu$^{2+}$
moments at the substrate interface at low fields preceding ferromagnetic
saturation throughout the bulk of the degenerate semiconductor film. We discuss
the implications of these findings for the unusual magnetotransport properties
of this compound.",2005.10339v1
2020-07-23,Effect of external electromagnetic radiation on the anomalous metallic behaviors in Ta thin films,"We investigated transport characteristics of superconducting Ta thin films
with three configurations in rf radiation filters; no filter, only
room-temperature filters, and low-temperature filters in addition to
room-temperature filters. The transport properties near the transition
temperature are strongly dependent on whether the room-temperature filter is
installed or not. The entire transition is shifted to higher temperature with
loading layers of the room-temperature filters. Once the zero-resistance state
is achieved at B=0, no strong radiation effect is observed even with
low-temperature filters installed. When magnetic field is turned on, the
nonzero-resistance saturation at low temperatures is revealed without
low-temperature filters, which has been considered to be magnetic-field-induced
quantum metallic phase. However, the insertion of the additional
low-temperature filter weakens the saturation of the resistance, the signature
of the metallic behavior. This observation suggests that the previously
reported anomalous metallic state in Ta films is mainly induced by the
unfiltered radiation and, thus, the intrinsic metallic ground state should be
limited to the narrow range of magnetic fields near the critical point, if
exists.",2007.11923v1
2020-08-21,Robust anomalous metallic states and vestiges of self duality in two-dimensional granular In-InOx composites,"Many experiments investigating magnetic field tuned superconductor-insulator
transition (H-SIT), often exhibit low-temperature resistance saturation, which
is interpreted as an anomalous metallic phase emerging from a ""failed
superconductor,"" thus challenging conventional theory. Here we study a random
granular array of indium islands grown on a gateable layer of indium-oxide. By
tuning the intergrain couplings, we reveal a wide range of magnetic fields
where resistance saturation is observed, under conditions of careful
electromagnetic filtering and within a wide range of linear response. Exposure
to external broadband noise or microwave radiation is shown to strengthen the
tendency of superconductivity, where at low field a global superconducting
phase is restored. Increasing magnetic field unveils an ""avoided H-SIT,"" that
exhibits granularity-induced logarithmic divergence of the
resistance/conductance above/below that transition, pointing to possible
vestiges of the original emergent duality observed in a true H-SIT. We conclude
that anomalous metallic phase is intimately associated with inherent
inhomogeneities, exhibiting robust behavior at attainable temperatures for
strongly granular two-dimensional systems.",2008.09325v2
2020-11-19,Measurements of the growth and saturation of electron Weibel instability in optical-field ionized plasmas,"The temporal evolution of the magnetic field associated with electron thermal
Weibel instability in optical-field ionized plasmas is measured using
ultrashort (1.8 ps), relativistic (45 MeV) electron bunches from a linear
accelerator. The self-generated magnetic fields are found to self-organize into
a quasi-static structure consistent with a helicoid topology within a few ps
and such a structure lasts for tens of ps in underdense plasmas. The measured
growth rate agrees well with that predicted by the kinetic theory of plasmas
taking into account collisions. Magnetic trapping is identified as the dominant
saturation mechanism.",2011.09979v1
2022-06-03,Development of Ni doped SnO$_2$ Dilute magnetic oxides for electronics and spintronics applications,"We used a solid-state reaction method to prepare Sn$_{1-x}$Ni$_x$O$_2$ with
$x$ = 0, 0.05, 0.1, 0.15 polycrystalline compounds. A rutile phase with
tetragonal crystal structure was confirmed by X-ray diffraction. At room
temperature, the magnetisation study shows that the saturation magnetization
increases with Ni doping content whereas the coercive field decreases after
$x$=0.1. The spin number increases as the Ni doping concentration increases,
indicating that the incorporation of Ni into the Sn sites increases the number
of spins interacting to improve the ferromagnetic phase , which is like
saturation magnetization and coercive field.",2206.01525v1
2022-12-26,Optimal design of nanomagnets for on-chip field gradients,"The generation of localized magnetic field gradients by on-chip nanomagnets
is important for a variety of technological applications, in particular for
spin qubits. To advance beyond the empirical design of these nanomagnets, we
propose a systematic and general approach based on the micromagnetic
formulation of an optimal field gradient source. We study the different field
configurations that can be realized and find out quantitatively the most
suitable ferromagnetic layer geometries. Using micromagnetic simulations, we
then investigate the minimum requirements for reaching magnetic saturation in
these nanomagnets. In terms of either longitudinal or transverse field
gradient, the results provide an optimal solution for uniform, saturated
nanomagnets, where the magnetic material can be selected according to the
strength of the external fields that can be used.",2212.13156v1
2023-05-04,Small-scale dynamos: From idealized models to solar and stellar applications,"In this article we review small-scale dynamo processes that are responsible
for magnetic field generation on scales comparable to and smaller than the
energy carrying scales of turbulence. We provide a review of critical
observation of quiet Sun magnetism, which have provided strong support for the
operation of a small-scale dynamo in the solar photosphere and convection zone.
After a review of basic concepts we focus on numerical studies of kinematic
growth and non-linear saturation in idealized setups, with special emphasis on
the role of the magnetic Prandtl number for dynamo onset and saturation. Moving
towards astrophysical applications we review convective dynamo setups that
focus on the deep convection zone and the photospheres of solar-like stars. We
review the critical ingredients for stellar convection setups and discuss their
application to the Sun and solar-like stars including comparison against
available observations.",2305.02787v1
2015-05-18,Simulating Astrophysical Magnetic Fields with Smoothed Particle Magnetohydrodynamics,"Numerical methods to improve the treatment of magnetic fields in smoothed
field magnetohydrodynamics (SPMHD) are developed and tested. Chapter 2 is a
review of SPMHD. In Chapter 3, a mixed hyperbolic/parabolic scheme is developed
which cleans divergence error from the magnetic field. Average divergence error
is an order of magnitude lower for all test cases considered, and allows for
the stable simulation of the gravitational collapse of magnetised molecular
cloud cores. The effectiveness of the cleaning may be improved by explicitly
increasing the hyperbolic wave speed or by cycling the cleaning equations
between timesteps. In the latter, it is possible to achieve DivB=0. Chapter 4
develops a switch to reduce dissipation of the magnetic field from artificial
resistivity. Compared to the existing switch in the literature, this leads to
sharper shock profiles in shocktube tests, lower overall dissipation of
magnetic energy, and importantly, is able to capture magnetic shocks in the
highly super-Alfvenic regime. Chapter 5 compares these numerical methods
against grid-based MHD methods (using the Flash code) in simulations of the
small-scale dynamo amplification of a magnetic field in driven, isothermal,
supersonic turbulence. Both codes exponentially amplify the magnetic energy at
a constant rate, though SPMHD shows a resolution dependence that arises from
the scaling of the numerical dissipation terms. The time-averaged saturated
magnetic spectra have similar shape, and both codes have PDFs of magnetic field
strength that are log-normal, which become lopsided as the magnetic field
saturates. We conclude that SPMHD is able to reliably simulate the small-scale
dynamo amplification of magnetic fields. Chapter 6 concludes the thesis and
presents some preliminary work demonstrating that SPMHD can activate the
magneto-rotational instability in 2D shearing box tests.",1505.04494v1
2018-06-28,"Fluctuation Dynamo in a Collisionless, Weakly Magnetized Plasma","Results from a numerical study of fluctuation dynamo in a collisionless,
weakly magnetized plasma are presented. The key difference between this dynamo
and its magnetohydrodynamic (MHD) counterpart is the adiabatic production of
magnetic-field-aligned pressure anisotropy by the amplification of a weak seed
field. This in turn drives kinetic instabilities on the ion-Larmor
scale---namely, firehose and mirror---which sever the adiabatic link between
the thermal and magnetic pressures, thereby allowing the dynamo to proceed.
After an initial phase of rapid growth driven by these instabilities, the
magnetic energy grows exponentially and exhibits a $k^{3/2}$ spectrum that
peaks near the resistive scale, similar to the large-magnetic-Prandtl-number
($\mathrm{Pm}\gg{1}$) MHD dynamo. The magnetic field self-organizes into a
folded-sheet topology, with direction reversals at the resistive scale and
field lines curved at the parallel scale of the flow. The effective
$\mathrm{Pm}$ is determined by whether the ion-Larmor scale is above or below
the field-reversing scale: in the former case, particles undergo Bohm-like
diffusion; in the latter case, particles scatter primarily off firehose
fluctuations residing at the ends of the magnetic folds, and the viscosity
becomes anisotropic. The magnetic field ultimately saturates at dynamical
strengths, with its spectral peak migrating towards larger scales. This
feature, along with an anti-correlation of magnetic-field strength and
field-line curvature and a gradual thinning of magnetic sheets into ribbons,
resemble the saturated state of the large-$\mathrm{Pm}$ dynamo, the primary
differences manifesting in firehose/mirror-unstable regions. These results have
implications for magnetic-field growth in the weakly collisional intracluster
medium of galaxy clusters.",1806.11162v3
2023-10-03,The effect of surface oxidation and crystal thickness on magnetic properties and magnetic domain structures of Cr2Ge2Te6,"Van der Waals (vdW) magnetic materials such as Cr2Ge2Te6 (CGT) show promise
for novel memory and logic applications. This is due to their broadly tunable
magnetic properties and the presence of topological magnetic features such as
skyrmionic bubbles. A systematic study of thickness and oxidation effects on
magnetic domain structures is important for designing devices and vdW
heterostructures for practical applications. Here, we investigate thickness
effects on magnetic properties, magnetic domains, and bubbles in
oxidation-controlled CGT crystals. We find that CGT exposed to ambient
conditions for 5 days forms an oxide layer approximately 5 nm thick. This
oxidation leads to a significant increase in the oxidation state of the Cr
ions, indicating a change in local magnetic properties. This is supported by
real space magnetic texture imaging through Lorentz transmission electron
microscopy. By comparing the thickness dependent saturation field of oxidized
and pristine crystals, we find that oxidation leads to a non-magnetic surface
layer which is thicker than the oxide layer alone. We also find that the stripe
domain width and skyrmionic bubble size are strongly affected by the crystal
thickness in pristine crystals. These findings underscore the impact of
thickness and surface oxidation on the properties of CGT such as saturation
field and domain/skyrmionic bubble size and suggest a pathway for manipulating
magnetic properties through a controlled oxidation process.",2310.02319v2
2001-08-05,Low Energy Behaviour of XXZ Antiferromagnetic Spin Chain,"Zero temperature phase diagram of XXZ spin chain in external magnetic field
is investigated at low energies using path integral approach.It has been shown
by spin wave analysis and then by nonlinear sigma model transformation that
below some critical field the system undergoes quantum Kosterlitz-Thouless
phase transition.Above that critical field for low anisotropies the system is
saturated while at strong anisotropy the system has Ising antiferromagnetic
order.",0108086v1
2007-09-03,On the magnetic fields generated by experimental dynamos,"We review the results obtained by three successful fluid dynamo experiments
and discuss what has been learnt from them about the effect of turbulence on
the dynamo threshold and saturation. We then discuss several questions that are
still open and propose experiments that could be performed to answer some of
them.",0709.0234v1
2016-09-26,Energy-based Modeling of AC Motors,"We propose an approach to modeling of AC motors entirely based on analytical
mechanics. Symmetry and connection constraints are moreover incorporated in the
energy function from which the models are derived. The approach is especially
suited to handle magnetic saturation, but also directly recovers the standard
unsaturated models of the literature. The theory is illustrated by some
experimental data.",1609.08050v1
2017-04-25,Characterization of Zinc oxide & Aluminum Ferrite and Simulation studies of M-H plots of Cobalt/Cobaltoxide,"Zinc oxide and Aluminum Ferrite were prepared Chemical route. The samples
were characterized by XRD and VSM. Simulation of M-H plots of Co/CoO thin films
were performed. Effect of parameters was observed on saturation magnetization.",1705.00525v2
2020-02-04,Amplitude of vortical turbulence in crossed fields in mass-separator at optimum parameters,"Properties and excitation of the vortical turbulence, excited in a
cylindrical radially inhomogeneous plasma in crossed radial electric and
longitudinal magnetic fields, are considered. The expression for the vortex
amplitude of saturation has been derived.",2002.01280v1
2006-01-11,"Turbulence, magnetic fields and plasma physics in clusters of galaxies","Observations of galaxy clusters show that the intracluster medium (ICM) is
likely to be turbulent and is certainly magnetized. The properties of this
magnetized turbulence are determined both by fundamental nonlinear
magnetohydrodynamic interactions and by the plasma physics of the ICM, which
has very low collisionality. Cluster plasma threaded by weak magnetic fields is
subject to firehose and mirror instabilities. These saturate and produce
fluctuations at the ion gyroscale, which can scatter particles, increasing the
effective collision rate and, therefore, the effective Reynolds number of the
ICM. A simple way to model this effect is proposed. The model yields a
self-accelerating fluctuation dynamo whereby the field grows explosively fast,
reaching the observed, dynamically important, field strength in a fraction of
the cluster lifetime independent of the exact strength of the seed field. It is
suggested that the saturated state of the cluster turbulence is a combination
of the conventional isotropic magnetohydrodynamic turbulence, characterized by
folded, direction-reversing magnetic fields and an Alfv\'en-wave cascade at
collisionless scales. An argument is proposed to constrain the reversal scale
of the folded field. The picture that emerges appears to be in qualitative
agreement with observations of magnetic fields in clusters.",0601246v2
2009-03-09,Interacting Superparamagnetism in La0.7Sr0.3MnO3 Nanoparticles,"The magnetic order of La0.7Sr0.3MnO3 nanoparticles (NPs) fabricated in a SPEX
D8000 mill was systematically studied. The La0.7Sr0.3MnO3 nanocrystals grow
from the milled constituent oxides during the milling processes. The
magnetization data obtained by using a SQUID magnetometer show the NPs as a
superparamagnet in terms of anhysteretic curves near room temperature.
Unoverlaping of the scaled M(H-ext, T)/M-s vs. H-ext, T plots and the dc
susceptibility obeying the Curie-Weiss behavior rather than the Curie law at
high temperatures provide evidence that the NPs are interacting
superparamagnetic ensembles. A mean-field correction to the Langevin function L
([H-ext + alpha M]/k(B)T) worked well for the magnetic ordering of the NPs. By
means of the Langevin fitting, the diameter of the NP was estimated to be lower
than 15 nm, depending oil the milling time. The saturation magnetization of NPs
varied from 48.5 em/g to 19 emu/g, with the higher value corresponding to a
larger particle size. A core-shell structure of the NP was adopted, with the NP
having the core-shell magnetically-effective mass density. This is applicable
to the variation of the saturation magnetization with particle size.",0903.1565v1
2009-05-03,Simulation study of the filamentation of counter-streaming beams of the electrons and positrons in plasmas,"The filamentation instability driven by two spatially uniform and
counter-streaming beams of charged particles in plasmas is modelled by a
particle-in-cell (PIC) simulation. Each beam consists of the electrons and
positrons. The four species are equally dense and they have the same
temperature. The one-dimensional simulation direction is orthogonal to the beam
velocity vector. The magnetic field grows spontaneously and rearranges the
particles in space, such that the distributions of the electrons of one beam
and the positrons of the second beam match. The simulation demonstrates that as
a result no electrostatic field is generated by the magnetic field through its
magnetic pressure gradient prior to its saturation. This electrostatic field
would be repulsive at the centres of the filaments and limit the maximum charge
and current density. The filaments of electrons and positrons in this
simulation reach higher charge and current densities than in one with no
positrons. The oscillations of the magnetic field strength induced by the
magnetically trapped particles result in an oscillatory magnetic pressure
gradient force. The latter interplays with the statistical fluctuations in the
particle density and it probably enforces a charge separation, by which
electrostatic waves grow after the filamentation instability has saturated.",0905.0276v1
2010-08-30,"Intriguing complex magnetism of Co in RECoAsO (RE=La, Nd and Sm)","We synthesized bulk polycrystalline samples of RECoAsO (RE=La, Nd and Sm) by
solid state reaction route in an evacuated sealed quartz tube. All these
compounds are crystallized in a tetragonal structure with space group P4/nmm.
The Co, in these compounds is in itinerant ferromagnetic state with its
paramagnetic moment above 1.5 microB and the same orders ferromagnetically (FM)
with small saturation moment of around 0.20 microB below say 80K. This bulk
intrinsic magnetism of Co changes dramatically when nonmagnetic La is changed
by magnetic Sm and Nd. Although the itinerant ferromagnetism occurs below
80-100K with small saturation moment, typical anti-ferromagnetic (AFM)
transitions (TN1, TN2) are observed at 57K and 45K for Sm and at 69K and 14K
for Nd. The transition of Co spins from FM to AFM, for magnetic Sm and Nd in
RECoAsO is both field and temperature dependent. For applied fields below
100Oe, both TN1 and TN2 are seen, with intermediate fields below 1-2kOe only
TN1 and above say 5kOe the AFM transition is not observed. This is evidenced in
isothermal magnetization (MH) plots as well. It is clear that Sm/Nd magnetic
moments interact with the ordered Co spins in adjacent layer and thus
transforms the FM ordering to AFM. All the studied compounds are metallic in
nature, and their magneto-transport R(T)H follows the temperature and field
dependent FM-AFM transition of ordered Co spins.",1008.4999v3
2010-12-17,"Radially Extended, Stratified, Local Models of Isothermal Disks","We consider local, stratified, numerical models of isothermal accretion
disks. The novel feature of our treatment is that radial extent L_x and
azimuthal extent L_y satisfy H << L_x, L_y << R, where H is the scale height
and R is the local radius. This enables us to probe mesoscale structure in
stratified thin disks. We evolve the model at several resolutions, sizes, and
initial magnetic field strengths. Consistent with earlier work, we find that
the saturated, turbulent state consists of a weakly magnetized disk midplane
coupled to a strongly magnetized corona, with a transition at |z| ~ 2H. The
saturated \alpha ~ 0.01 - 0.02. A two-point correlation function analysis
reveals that the central 4H of the disk is dominated by small scale turbulence
that is statistically similar to unstratified disk models, while the coronal
magnetic fields are correlated on scales ~ 10 H. Nevertheless angular momentum
transport through the corona is small. A study of magnetic field loops in the
corona reveals few open field lines and predominantly toroidal loops with a
characteristic distance between footpoints that is ~ H. Finally we find
quasi-periodic oscillations with characteristic timescale ~ 30 \Omega^{-1} in
the magnetic field energy density. These oscillations are correlated with
oscillations in the mean azimuthal field; we present a phenomenological,
alpha-dynamo model that captures most aspects of the oscillations.",1012.3789v1
2011-03-25,Numerical simulation of laminar plasma dynamos in a cylindrical von Kármán flow,"The results of a numerical study of the magnetic dynamo effect in cylindrical
von K\'arm\'an plasma flow are presented with parameters relevant to the
Madison Plasma Couette Experiment. This experiment is designed to investigate a
broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl
number Pm can be of order unity (i.e., the fluid Reynolds number Re is
comparable to the magnetic Reynolds number Rm). This is in contrast to liquid
metal experiments, where Pm is small (so, Re>>Rm) and the flows are always
turbulent. We explore dynamo action through simulations using the extended
magnetohydrodynamic NIMROD code for an isothermal and compressible plasma
model.We also study two-fluid effects in simulations by including the Hall term
in Ohm's law. We find that the counter-rotating von K\'arm\'an flow results in
sustained dynamo action and the self-generation of magnetic field when the
magnetic Reynolds number exceeds a critical value. For the plasma parameters of
the experiment, this field saturates at an amplitude corresponding to a new
stable equilibrium (a laminar dynamo). We show that compressibility in the
plasma results in an increase of the critical magnetic Reynolds number, while
inclusion of the Hall term in Ohm's law changes the amplitude of the saturated
dynamo field but not the critical value for the onset of dynamo action.",1103.5041v1
2011-10-03,Small-scale dynamo action in rotating compressible convection,"We study dynamo action in a convective layer of electrically-conducting,
compressible fluid, rotating about the vertical axis. At the upper and lower
bounding surfaces, perfectly-conducting boundary conditions are adopted for the
magnetic field. Two different levels of thermal stratification are considered.
If the magnetic diffusivity is sufficiently small, the convection acts as a
small-scale dynamo. Using a definition for the magnetic Reynolds number $R_M$
that is based upon the horizontal integral scale and the horizontally-averaged
velocity at the mid-layer of the domain, we find that rotation tends to reduce
the critical value of $R_M$ above which dynamo action is observed. Increasing
the level of thermal stratification within the layer does not significantly
alter the critical value of $R_M$ in the rotating calculations, but it does
lead to a reduction in this critical value in the non-rotating cases. At the
highest computationally-accessible values of the magnetic Reynolds number, the
saturation levels of the dynamo are similar in all cases, with the mean
magnetic energy density somewhere between 4 and 9% of the mean kinetic energy
density. To gain further insights into the differences between rotating and
non-rotating convection, we quantify the stretching properties of each flow by
measuring Lyapunov exponents. Away from the boundaries, the rate of stretching
due to the flow is much less dependent upon depth in the rotating cases than it
is in the corresponding non-rotating calculations. It is also shown that the
effects of rotation significantly reduce the magnetic energy dissipation in the
lower part of the layer. We also investigate certain aspects of the saturation
mechanism of the dynamo.",1110.0374v1
2012-01-12,Local Simulations of Instabilities in Relativistic Jets I: Morphology and Energetics of the Current-Driven Instability,"We present the results of a numerical investigation of current-driven
instability in magnetized jets. Utilizing the well-tested, relativistic
magnetohydrodynamic code Athena, we construct an ensemble of local, co-moving
plasma columns in which initial radial force balance is achieved through
various combinations of magnetic, pressure, and rotational forces. We then
examine the resulting flow morphologies and energetics to determine the degree
to which these systems become disrupted, the amount of kinetic energy
amplification attained, and the non-linear saturation behaviors. Our most
significant finding is that the details of initial force balance have a
pronounced effect on the resulting flow morphology. Models in which the initial
magnetic field is force-free deform, but do not become disrupted. Systems that
achieve initial equilibrium by balancing pressure gradients and/or rotation
against magnetic forces, however, tend to shred, mix, and develop turbulence.
In all cases, the linear growth of current-driven instabilities is
well-represented by analytic models. CDI-driven kinetic energy amplification is
slower and saturates at a lower value in force-free models than in those that
feature pressure gradients and/or rotation. In rotating columns, we find that
magnetized regions undergoing rotational shear are driven toward equipartition
between kinetic and magnetic energies. We show that these results are
applicable for a large variety of physical parameters, but we caution that
algorithmic decisions (such as choice of Riemann solver) can affect the
evolution of these systems more than physically motivated parameters.",1201.2681v2
2012-04-03,The Small-Scale Dynamo and Non-Ideal MHD in Primordial Star Formation,"We study the amplification of magnetic fields during the formation of
primordial halos. The turbulence generated by gravitational infall motions
during the formation of the first stars and galaxies can amplify magnetic
fields very efficiently and on short timescales up to dynamically significant
values. Using the Kazantsev theory, which describes the so-called small-scale
dynamo - a magnetohydrodynamical process converting kinetic energy from
turbulence into magnetic energy - we can then calculate the growth rate of the
small-scale magnetic field. Our calculations are based on a detailed chemical
network and we include non-ideal magnetohydrodynamical effects such as
ambipolar diffusion and Ohmic dissipation. We follow the evolution of the
magnetic field up to larger scales until saturation occurs on the Jeans scale.
Assuming a weak magnetic seed field generated by the Biermann battery process,
both Burgers and Kolmogorov turbulence lead to saturation within a rather small
density range. Such fields are likely to become relevant after the formation of
a protostellar disk and, thus, could influence the formation of the first stars
and galaxies in the Universe.",1204.0658v2
2014-01-31,PIC Simulations of Continuously Driven Mirror and Ion Cyclotron Instabilities in High Beta Astrophysical and Heliospheric Plasmas,"We use particle-in-cell (PIC) simulations to study the nonlinear evolution of
ion velocity space instabilities in an idealized problem in which a background
velocity shear continuously amplifies the magnetic field. We simulate the
astrophysically relevant regime where the shear timescale is long compared to
the ion cyclotron period, and the plasma beta is ~ 1-100. The background field
amplification in our calculation is meant to mimic processes such as turbulent
fluctuations or MHD-scale instabilities. The field amplification continuously
drives a pressure anisotropy with the perpendicular pressure larger than the
parallel pressure, and the plasma becomes unstable to the mirror and ion
cyclotron instabilities. In all cases, the nonlinear state is dominated by the
mirror instability, not the ion cyclotron instability, and the plasma pressure
anisotropy saturates near the threshold for the linear mirror instability. The
magnetic field fluctuations initially undergo exponential growth but saturate
in a secular phase in which the fluctuations grow on the same timescale as the
background magnetic field (with \delta B ~ 0.3 <B> in the secular phase). At
early times, the ion magnetic moment is well-conserved but once the fluctuation
amplitudes exceed \delta B ~ 0.1 <B>, the magnetic moment is no longer
conserved but instead changes on a timescale comparable to that of the mean
magnetic field. We discuss the implications of our results for
low-collisionality astrophysical plasmas, including the near-Earth solar wind
and low-luminosity accretion disks around black holes.",1402.0014v2
2017-04-20,Spectral Scaling Technique to Determine Extreme Carrington-level Geomagnetically Induced Currents Effects,"Space weather events produce variations in the electric current in the
Earth's magnetosphere and ionosphere. From these high altitude atmospheric
regions, resulting geomagnetically induced currents (GICs) can lead to
fluctuations in ground currents that affect the electric power grid and
potentially overload transformers during extreme storms. The most extreme
geomagnetic storm on record, known as the 1859 Carrington event, was so intense
that ground-based magnetometers were saturated at high magnetic latitudes. The
most reliable, un-saturated observation is the hour-resolution data from the
Colaba Magnetic Observatory in India. However, higher frequency components --
fluctuations at second through minute time cadence -- to the magnetic field can
play a significant role in GIC-related effects. We present a new method for
scaling higher frequency observations to create a realistic Carrington-like
event magnetic field model, using modern magnetometer observations. Using the
magnetic field model and ground conductivity models, we produce an electric
field model. This method can be applied to create similar magnetic and electric
field models for studies of GIC effects on power-grids.",1705.05325v1
2019-01-07,Field-induced phases in a heavy-fermion U(Ru$_{0.92}$Rh$_{0.08}$)$_{2}$Si$_{2}$ single crystal,"We report the high-field induced magnetic phases and phase diagram of a high
quality \urxrs~single crystal prepared using a modified Czochralski method. Our
study, that combines high-field magnetization and electrical resistivity
measurements, shows for fields applied along the $c$-axis direction three
field-induced magnetic phase transitions at $\mu_{0} H_{c1}$ = 21.60 T,
$\mu_{0} H_{c2}$ = 37.90 T and $\mu_{0} H_{c3}$ = 38.25 T, respectively. In
agreement with a microscopic up-up-down arrangement of the U magnetic moments
the phase above $H_{c1}$ has a magnetization of about one third of the
saturated value. In contrast the phase between $H_{c2}$ and $H_{c3}$ has a
magnetization that is a factor of two lower than above the $H_{c3}$, where a
polarized Fermi-liquid state with a saturated moment $M_{s}$ $\approx$ 2.1
$\mu_{B}$/U is realized. Most of the respective transitions are reflected in
the electrical resistivity as sudden drastic changes. Most notably, the phase
between $H_{c1}$ and $H_{c2}$ exhibits substantially larger values. As the
temperature increases, transitions smear out and disappear above $\approx$ 15
K. However, a substantial magnetoresistance is observed even at temperatures as
high as 80 K. Due to a strong uniaxial magnetocrystalline anisotropy a very
small field effect is observed for fields apllied perpendicular to the $c$-axis
direction.",1901.01750v1
2019-06-13,Electrodynamic improvements to the theory of magnetostatic modes in ferrimagnetic spheres and their applications to saturation magnetization measurements,"Electrodynamic theory applied to the analysis of TEn0p mode resonances in
ferromagnetic spheres placed either in metallic cavities or in the free space
is compared with Walker-Fletcher's theory of so-called magnetostatic modes. The
influence of the diameter of the sample, its permittivity and the permittivity
of the surrounding media on the resonance frequencies of a few modes is
analyzed. It is shown that the dominant resonances are essentially related
either to negative values of the diagonal component of the permeability tensor
or, for clockwise circularly polarized magnetic fields, to negative effective
permeability. The electrodynamic theory is used to determine the saturation
magnetization (Ms) from measured TEn01 frequency differences. Measurements on
different samples confirmed that Ms can be determined using an electrodynamic
approach with uncertainties of the order of 2% regardless of sample sizes,
metal enclosures or static magnetic field values.",1906.05559v1
2020-02-10,On the anisotropies of magnetization and electronic transport of magnetic Weyl semimetal Co3Sn2S2,"Co3Sn2S2, a quasi-two-dimensional system with kagome lattice, has been found
as a magnetic Weyl semimetal recently. In this work, the anisotropies of
magnetization and transport properties of Co3Sn2S2 were investigated. The high
field measurements reveal a giant magnetocrystalline anisotropy with an
out-of-plane saturation field of 0.9 kOe and an in-plane saturation field of
230 kOe at 2 K, showing a magnetocrystalline anisotropy coefficient Ku up to
8.3 * 10^5 J m-3, which indicates that it is extremely difficult to align the
small moment of 0.29 {\mu}B/Co on the kagome lattice from c axis to ab plane.
The out-of-plane angular dependences of Hall conductivity further reveal strong
anisotropies in Berry curvature and ferromagnetism, and the vector directions
of both are always parallel with each other. For in-plane situation, the
longitudinal and transverse measurements for both I parallel a and I
perpendicular a cases show that the transport on the kagome lattice is
isotropic. These results provide essential understanding on the magnetization
and transport behaviors for the magnetic Weyl semimetal Co3Sn2S2.",2002.03940v1
2020-08-29,Characteristics of Pumping Current in a YBCO Coil by a Pulse-Type Magnetic Flux Pump,"2G high temperature superconducting (HTS) wires, YBCO coated conductors,
perform a better carrying current capability, which is potentially applied in
the manufacture of HTS magnets. This paper presents the experimental results of
the pumping current for YBCO coils using a pulse-type magnetic flux pump in the
conduction-cooling system and liquid nitrogen bath (LN2) cryogenic environment.
Optimization of the flux pump used in the conduction-cooling system is that a
constantan heater was added to keep the temperature of the pumping bridge at a
certain value. Excitation effects of the YBCO coil at different temperatures
were investigated in the conduction-cooling system. A fast-increasing of
pumping current in the YBCO coil occurs when the temperature of the YBCO sheet
(i.e., pumping bridge) is in the range of 50 K to 80 K. The relationships
between saturated pumping current and input voltage, working frequency, numbers
of magnetic poles were also studied. Using the seven-pole configuration, the
saturated current can reach 155 A when the frequency is 20 Hz and the voltage
is 6 V. The excitation characteristics of the flux pump in the LN2 cooling
system show the possibility of the pulse-type magnetic flux pump for the
practical application of HTS magnets.",2008.12941v2
2020-09-21,Influence of ambipolar and Hall effects on vorticity in 3D simulations of magneto-convection,"This paper presents the results of the analysis of 3D simulations of solar
magneto-convection that include the joint action of the ambipolar diffusion and
the Hall effect. Three simulation-runs are compared: one including both
ambipolar diffusion and Hall effect; one including only ambipolar diffusion;
and one without any of these two effects. The magnetic field is amplified from
initial field to saturation level by the action of turbulent local dynamo. In
each of these cases, we study 2 hours of simulated solar time after the local
dynamo reaches the saturation regime. We analyze the power spectra of
vorticity, of magnetic field fluctuations and of the different components of
the magnetic Poynting flux responsible for the transport of vertical or
horizontal perturbations. Our preliminary results show that the ambipolar
diffusion produces a strong reduction of vorticity in the upper chromospheric
layers and that it dissipates the vortical perturbations converting them into
thermal energy. The Hall effect acts in the opposite way, strongly enhancing
the vorticity. When the Hall effect is included, the magnetic field in the
simulations becomes, on average, more vertical and long-lived flux tube-like
structures are produced. We trace a single magnetic structure to study its
evolution pattern and the magnetic field intensification, and their possible
relation to the Hall effect.",2009.09753v1
2020-11-10,Saturation of Energy Levels of the Hydrogen Atom in Strong Magnetic Field,"We demonstrate that the finiteness of the limiting values of the lower energy
levels of a hydrogen atom under an unrestricted growth of the magnetic field,
into which this atom is embedded, is achieved already when the vacuum
polarization (VP) is calculated in the magnetic field within the approximation
of the local action of Euler--Heisenberg. We find that the mechanism for this
saturation is different from the one acting, when VP is calculated via the
Feynman diagram in the Furry picture. We study the effective potential that
appears when the adiabatic (diagonal) approximation is exploited for solving
the Schr\""{o}dinger equation for the longitudinal degree of freedom of the
electron on the lowest Landau level in the atom. We find that the (effective)
potential of a point-like charge remains nonsingular thanks to the growing
screening provided by VP. The regularizing length turns out to be $\sqrt{\alpha
/3\pi }\lambdabar_{\mathrm{C}}$, where $\lambdabar_{\mathrm{C}}$ is the
electron Compton length. The family of effective potentials, labeled by growing
values of the magnetic field condenses towards a certain limiting,
magnetic-field-independent potential-distance curve. The~limiting values of
even ground-state energies are determined for four magnetic quantum numbers
using the Karnakov--Popov method.",2011.12422v1
2021-07-24,Anomalous Nernst thermopower and giant magnetostriction in microwave synthesized La0.5Sr0.5CoO3,"Ferromagnetic metallic oxides have potential applications in spincaloric
devices which utilize the spin property of charge carriers for interconversion
of heat and electricity through the spin Seebeck or the anomalous Nernst effect
or both. In this work, we synthesized polycrystalline La0.5S0.5CoO3 by
microwave irradiation method and studied its transverse thermoelectric voltage
(Nernst thermopower) and change in the linear dimension of the sample (Joule
magnetostriction) in response to external magnetic fields. In addition,
magnetization, temperature dependences of electrical resistivity, and
longitudinal Seebeck coefficient (Sxx) in absence of an external magnetic field
were also measured. The sample is ferromagnetic with a Curie temperature of TC
= 247 K and shows a metal-like resistivity above and below TC with a negative
sign of Sxx suggesting charge transport due to electrons. Magnetic field
dependence of the Nernst thermopower (Sxy) at a fixed temperature shows a rapid
increase at low fields and a tendency to saturate at high fields as like the
magnetization. Anomalous contribution to Sxy was extracted from total Sxy
measured and it exhibits a maximum value of ~ 0.21 microV/K at 180 K for H = 50
kOe, which is comparable to the value found in a single crystal for a lower Sr
content. The Joule magnetostriction is positive, i.e., the length of the sample
expands along the direction of the magnetic field and it does not saturate even
at 50 kOe. The magnetostriction increases with decreasing temperature below TC
and reaches a maximum value of 500 ppm at T = 40 K and below. Coexistence of
the anomalous Nernst thermopower and giant magnetostriction in a single
compound has potential applications for thermal energy harvesting and
low-temperature actuators, respectively.",2107.11535v1
2022-10-10,The small-scale dynamo in a multiphase supernova-driven medium,"Magnetic fields grow quickly, even at early cosmological times, suggesting
the action of a small-scale dynamo (SSD) in the interstellar medium (ISM) of
galaxies. Many studies have focused on idealized, isotropic, homogeneous,
turbulent driving of the SSD. Here we analyze more realistic simulations of
supernova-driven turbulence to understand how it drives an SSD. We find that
SSD growth rates are intermittently variable as a result of the evolving
multiphase ISM structure. Rapid growth in the magnetic field typically occurs
in hot gas, with the highest overall growth rates occurring when the fractional
volume of hot gas is large. SSD growth rates correlate most strongly with
vorticity and fluid Reynolds number, which also both correlate strongly with
gas temperature. Rotational energy exceeds irrotational energy in all phases,
but particularly in the hot phase while SSD growth is most rapid. Supernova
(SN) rate does not significantly affect the ISM average kinetic energy density.
Rather, higher temperatures associated with high SN rates tend to increase SSD
growth rates. SSD saturates with total magnetic energy density around 5% of
equipartition to kinetic energy density, increasing slightly with magnetic
Prandtl number. While magnetic energy density in the hot gas can exceed that of
the other phases when SSD grows most rapidly, it saturates below 5% of
equipartition with kinetic energy in the hot gas, while in the cold gas it
attains 100%. Fast, intermittent growth of the magnetic field appears to be a
characteristic behavior of SN-driven, multiphase turbulence.",2210.04460v2
2023-02-25,Effect of time-varying electromagnetic field on Wiedemann-Franz law in a hot hadronic matter,"We have estimated the electrical and thermal conductivity of a hadron
resonance gas for a time-varying magnetic field, which is also compared with
constant and zero magnetic field cases. Considering the exponential decay of
electromagnetic fields with time, a kinetic theory framework can provide the
microscopic expression of electrical and thermal conductivity in terms of
relaxation and decay times. In the absence of the magnetic field, only a single
time scale appears, and in the finite magnetic field case, their expressions
carry two-time scales, relaxation time and cyclotron time period. Estimating
the conductivities for HRG matter in three cases -- zero, constant, and
time-varying magnetic fields, we have studied the validity of the
Wiedemann-Franz law. We noticed that at a high-temperature domain, the ratio
saturates at a particular value, which may be considered as Lorenz number of
the hadron resonance gas. With respect to the saturation values, the deviation
of the Wiedemann-Franz law has been quantified at the low-temperature domain.
For the first time, the present work sketches this quantitative deviation of
the Wiedemann-Franz law for hadron resonance gas at a constant and a
time-varying magnetic field.",2302.13042v2
2023-04-24,Magnetic plateaus and jumps in a spin-1/2 ladder with alternate Ising-Heisenberg rungs: a field dependent study,"We study a frustrated two-leg spin-1/2 ladder with alternate Ising and
isotropic Heisenberg rung exchange interactions, whereas, interactions along
legs and diagonals are Ising type. The ground-state (GS) of this model has four
exotic phases: (i) the stripe-rung ferromagnet (SRFM), (ii) the anisotropic
anti-ferromagnet (AAFM), (iii) the Dimer, and (iv) the stripe-leg ferromagnet
(SLFM) in absence of any external magnetic field. In this work, the effect of
externally applied longitudinal and transverse fields on quantum phases are
studied. In both cases, we show that there exist two plateau phases at $1/4$,
and $1/2$ of the saturation of magnetization. Due to the strong rung dimer
formation, the system opens a finite spin gap for all the phases resulting in
zero magnetization plateau in presence of a longitudinal field. The mechanism
of plateau formation is analyzed using spin density, quantum fidelity, and
quantum concurrence. In the (i) SRFM phase, Ising exchanges are dominant for
all spins but the Heisenberg rungs are weak, and therefore, the magnetization
shows a continuous transition as a function of transverse field. In the other
three phases [(ii)-(iv)], Ising dimer rungs are weak and broken first to reach
the plateau at $1/2$ of the saturation magnetization, having a large gap, which
is closed by further application of the field. We use the exact diagonalization
(ED) and the transfer matrix method (TM) to solve the Hamiltonian.",2304.12266v2
2023-10-01,Inflows towards Bipolar Magnetic Active Regions and Their Nonlinear Impact on a Three-Dimensional Babcock-Leighton Solar Dynamo Model,"The changing magnetic fields of the Sun are generated and maintained by a
solar dynamo, the exact nature of which remains an unsolved fundamental problem
in solar physics. Our objective in this paper is to investigate the role and
impact of converging flows toward Bipolar Magnetic Regions (BMR inflows) on the
Sun's global solar dynamo. These flows are large scale physical phenomena that
have been observed and so should be included in any comprehensive solar dynamo
model. We have augmented the Surface flux Transport And Babcock LEighton
(STABLE) dynamo model to study the nonlinear feedback effect of BMR inflows
with magnitudes varying with surface magnetic fields. This fully 3D realistic
dynamo model produces the sunspot butterfly diagram and allows a study of the
relative roles of dynamo saturation mechanisms such as tilt angle quenching and
BMR inflows. The results of our STABLE simulations show that magnetic field
dependent BMR inflows significantly affect the evolution of the BMRs themselves
and result in a reduced buildup of the global poloidal field due to local flux
cancellation within the BMRs, to an extent that is sufficient to saturate the
dynamo. As a consequence, for the first time, we have achieved fully 3D solar
dynamo solutions in which BMR inflows alone regulate the amplitudes and periods
of the magnetic cycles.",2310.00738v1
2005-04-29,Saturated-State Turbulence and Structure from Thermal and Magnetorotational Instability in the ISM: Three-Dimensional Numerical Simulations,"This paper reports on 3D numerical simulations of dynamics and thermodynamics
in the diffuse ISM. Our models are local, account for sheared galactic
rotation, magnetic fields, and realistic cooling, and resolve scales ~1-200 pc.
This combination permits the study of quasi-steady turbulence in a cloudy
medium representing the warm/cold atomic ISM. Turbulence is driven by the
magnetorotational instability (MRI); our models are the first to study the
saturated state of MRI under strongly inhomogeneous conditions, with
cloud/intercloud contrasts of about 100. For volume-averaged densities n=0.25 -
4 cm^3, the saturated-state velocity dispersion ranges from 8-1 km/s, scaling
as n^-0.77. The MRI is therefore likely quite important in driving turbulence
in low-density ISM regions, both at high latitudes in the inner Galaxy,and
throughout the far outer Galaxy. The MRI may be key to suppressing star
formation at large radii in spiral galaxies, where without MRI-driven
turbulence, a thin, cold layer could form and become gravitationally instable.
Our presentation also includes analysis of thermal structure (temperature and
density PDFs are broadened and include extreme departures from equilibrium, but
retain the classical two-phase bimodal character); results on the distribution
of clump masses (the mass spectrum peaks at about 100 solar masses);
comparisons of saturated-state MRI scalings with single-phase simulation
results (we find B^2 is independent of n); and examples of synthetic HI line
profile maps (showing that physical clumps are not easily distinguished in
velocity components, and vice versa).",0504669v1
2016-11-09,Unusual non saturating Giant Magneto-resistance in single crystalline Bi2Te3 topological insulator,"We report synthesis, structural details and electrical transport properties
of topological insulator Bi2Te3. The single crystalline specimens of Bi2Te3 are
obtained from high temperature (950C) melt and slow cooling (2C/hour). The
resultant crystals were shiny, one piece (few cm) and of bright silver color.
The Bi2Te3 crystal is found to be perfect with clear [00l] alignment. The
powder XRD pattern being carried out on crushed crystals showed that Bi2Te3
crystallized in R3m symmetry with a = b = 4.3866(2) A, c = 30.4978(13) A and
Gamma = 120degree. The Bi position is refined to (0, 0, 0.4038 (9)) at Wyckoff
position 6c and of Te are (0, 0, 0) at Wyckoff position 3a and at (0, 0,
0.2039(8)) at 6c. Ambient pressure and low temperature (down to 2K) electrical
transport measurements revealed metallic behavior. Magneto transport
measurements under magnetic field showed huge non saturating magneto resistance
(MR) reaching up to 250% at 2.5K and under 50KOe field. Summarily, the short
communication clearly demonstrates that Bi2Te3 topological insulator exhibit
non-saturating large positive MR at low temperature of say below 10K. The non
saturating MR is seen right up to room temperature albeit with much decreased
magnitude. Worth mentioning is the fact that these crystals are bulk in nature
and hence the anomalous MR is clearly an intrinsic property and not due to the
size effect as reported for nano-wires or thin films of the same.",1611.02859v2
2018-10-03,Evolution and characteristics of forced shear flows in polytropic atmospheres: Large and small Péclet number regimes,"Complex mixing and magnetic field generation occurs within stellar interiors
particularly where there is a strong shear flow. To obtain a comprehensive
understanding of these processes, it is necessary to study the complex dynamics
of shear regions. Due to current observational limitations, it is necessary to
investigate the inevitable small-scale dynamics via numerical calculations.
Here, we examine direct numerical calculations of a local model of unstable
shear flows in a compressible polytropic fluid primarily in a two-dimensional
domain, where we focus on determining how key parameters affect the global
properties and characteristics of the resulting saturated turbulent phase. We
consider the effect of varying both the viscosity and the thermal diffusivity
on the non-linear evolution. Moreover, our main focus is to understand the
global properties of the saturated phase, in particular estimating for the
first time the spread of the shear region from an initially hyperbolic tangent
velocity profile. We find that the vertical extent of the mixing region in the
saturated regime is generally determined by the initial Richardson number of
the system. Further, the characteristic quantities of the turbulence, i.e.
typical length-scale and the root-mean-square velocity are found to depend on
both the Richardson number, and the thermal diffusivity. Finally, we present
our findings of our investigation into saturated flows of a `secular' shear
instability in the low P\'eclet number regime with large Richardson numbers.",1810.01706v1
2021-03-23,Improving the Precision of Optical Metrology by Detecting Fewer Photons,"In optical metrological protocols to measure physical quantities, it is, in
principle, always beneficial to increase photon number to improve measurement
precision. However, practical constraints prevent arbitrary increase of n due
to the imperfections of a practical detector, especially when the detector
response is dominated by saturation effect. In this work, we show that a
modified weak measurement protocol, namely, biased weak measurement
significantly improves the precision of optical metrology in the presence of
saturation effect. This method detects an ultra-small fraction of photons while
maintains considerable amount of metrological information. The biased
pre-coupling leads to an additional reduction of photons in the post-selection
and generates an extinction point in the spectrum distribution, which is
extremely sensitive to the estimated parameter and difficult to be saturated.
Therefore, the Fisher information can be persistently enhanced by increasing
the photon number. In our magnetic-sensing experiment, biased weak measurement
achieves precision approximately one order of magnitude better than those of
previously used methods. The proposed method can be applied in various optical
measurement schemes to circumvent detector saturation effect with low-cost
apparatuses.",2103.12373v1
2022-03-13,"Comment on ""Resonance-induced growth of number entropy in strongly disordered systems""","We comment on the recent paper by Ghosh and \v{Z}nidari\v{c} (Phys. Rev. B
105, 144203 (2022)) which studies the growth of the number entropy $S_N$ in the
Heisenberg model with random magnetic fields after a quantum quench. The
authors present arguments for an intermediate power-law growth in time $t$ and
a sub-ergodic saturation value, claiming consistency of their results with
many-body localization (MBL) for strong disorder. We show that these
interpretations are inconsistent with other recent studies and discuss specific
issues with the analysis of the numerical data. We point out, in particular,
that (i) the saturation values $\widetilde{S}_N(L,W)$ for fixed length $L$ are
only bounded from above by 'the ergodic value' and are already far below this
value for $W\ll 1$. Furthermore, the saturation values can show non-monotonic
scaling with $L$. (ii) Power-law fits $S_N(t)\sim 1/t^\alpha$ -- with
$\alpha=1$ expected based on the resonance model described in the paper --
yield a system-size dependent exponent $\alpha$ while fits $S_N\sim
\frac{1}{W^3}\ln\ln t$ do hold independent of system size and over several
orders of magnitude in time. (iii) We also argue that for the cases where the
effective resonance model works best and predicts a saturation of the number
entropy, the same applies to the von-Neumann entropy, i.e.~the dynamics at the
considered scales is of single particle type and unrelated to MBL.",2203.06689v2
2007-06-19,Synthesis and magnetic properties of NiFe_{2-x}Al_{x}O_{4} nanoparticles,"Nanocrystalline Al-doped nickel ferrite powders have been synthesized by
sol-gel auto-ignition method and the effect of non-magnetic aluminum content on
the structural and magnetic properties has been studied. The X-ray diffraction
(XRD) revealed that the powders obtained are single phase with inverse spinel
structure. The calculated grain sizes from XRD data have been verified using
transmission electron microscopy (TEM). TEM photographs show that the powders
consist of nanometer-sized grains. It was observed that the characteristic
grain size decreases from 29 to 6 nm as the non-magnetic Al content increases,
which was attributed to the influence of non-magnetic Al concentration on the
grain size. Magnetic hysteresis loops were measured at room temperature with a
maximum applied magnetic field of 1T. As aluminum content increases, the
measured magnetic hysteresis curves become more and more narrow and the
saturation magnetization and remanent magnetization both decreased. The
reduction of agnetization compared to bulk is a consequence of spin
non-collinearity. Further reduction of magnetization with increase of aluminum
content is caused by non-magnetic Al^{3+} ions and weakened interaction between
sublattices. This, as well as the decrease in hysteresis was understood in
terms of the decrease in particle size.",0706.2794v1
2014-05-29,Influence of small scale $E_M$ and $H_M$ on the growth of large scale magnetic field,"We investigated the influence of small scale magnetic energy ($E_M$) and
magnetic helicity ($H_M$) on the growth rate ($\gamma$) of large scale magnetic
field ($\overline{{\bf B}}$). $H_M$ that plays a key role in MHD dynamo is a
topological concept describing the structural properties of magnetic fields.
So, it is not possible to differentiate the intrinsic properties of $H_M$ from
the influence of $E_M$, and vice versa. However, to understand MHD dynamo the
features of helical and nonhelical magnetic field should be made clear. For
this, we made a detour: we gave each simulation set its own initial condition
($IC$, same $E_M$(0) and specific $H_M$(0) at $k_f=5$), and then drove the
system with positive helical kinetic energy($k_f=5$). According to the
simulation results, $E_M$(0), whether or not helical, increases the growth rate
of $\overline{{\bf B}}$. The positive $H_M$(0) boosts the increased growth
rate, but the negative $H_M$(0) decreases it. To explain these results two
coupled equations of $H_M$ and $E_M$ were derived and solved using a simple
approximate method. The equations imply that helical magnetic field generates
the whole (helical and nonhelical) magnetic field but quenches itself.
Nonhelical magnetic field also generates the whole magnetic field but quenches
itself. The initially given $E_M$(0) modifies the electromotive force ($\langle
{\bf v}{\bf \times} {\bf b}\rangle$, $EMF$) and generates new terms. The
effects of these terms depend on the magnetic diffusivity $\eta$, position of
initial conditions $k_f$, and time. But the influence disappears as time passes
($\sim e^{-\eta k_f^2 t}$), so the saturated magnetic fields are independent of
the initial conditions.",1405.7467v1
2016-11-29,Calculation of Evaluation Variables for High Gradient Magnetic Separation with an Idealized Capture Model,"This paper regards feed mine as a mixture of intergrowths and pure
non-magnetic mineral particles, presents a method to calculate the evaluation
variables such as grade and recovery in high gradient magnetic separation
(HGMS). A idealized capture model is constructed in which the interaction
between particles is not taken into account and only for the initial
aggregation condition that the separator has the highest capture efficiency. In
the model we adopt the functions that use nominal particle radius and magnetic
mineral content as independent variables to describe volume fraction
distribution and capture efficiency of intergrowths respectively. Through
adding multi-wire magnetic fields and setting periodic boundary conditions in
flow field analysis, we modify the computational domain of the single-wire
capture theory to a element domain that periodically appears in the multi-wire
matrix. By means of finite element software, particle trajectories, flow field
and magnetic field are clearly exhibited, and then capture efficiency function
is obtained by interpolation method. The calculated evaluation variables
theoretically represent the best performance of magnetic separator for a given
feed. They can assist mineral engineers to evaluate or compare the effects of
different magnetic separation systems in advance. We use removal of iron
impurity from kaolin as an example to illustrate the presented calculation
method. The results quantitatively compare the evaluation variables of the
separation at different magnetic fields and show that the advantage of higher
magnetic field in separation efficiency decreases with the increase of
saturation magnetization of magnetic mineral.",1611.09481v1
2017-12-26,Magnetic field amplification by the r-mode instability,"We discuss magnetic field enhancement by unstable r-modes (driven by the
gravitational radiation reaction force) in rotating stars. In the absence of a
magnetic field, gravitational radiation exponentially increases the r-mode
amplitude $\alpha$, and accelerates differential rotation (secular motion of
fluid elements). For a magnetized star, differential rotation enhances the
magnetic field energy. Rezzolla et al. (2000--2001) argued that if the magnetic
energy grows faster than the gravitational radiation reaction force pumps
energy into the r-modes, then the r-mode instability is suppressed. Chugunov
(2015) demonstrated that without gravitational radiation, differential rotation
can be treated as a degree of freedom decoupled from the r-modes and controlled
by the back reaction of the magnetic field. In particular, the magnetic field
windup does not damp r-modes. Here we discuss the effect of the back reaction
of the magnetic field on differential rotation of unstable r-modes, and show
that it limits the generated magnetic field and the magnetic energy growth rate
preventing suppression of the r-mode instability by magnetic windup at low
saturation amplitudes, $\alpha \ll 1$, predicted by current models.",1712.09224v1
2019-07-12,New method for characterization of magnetic nanoparticles by scanning magnetic microscopy,"In this paper, we present a new method for the magnetic characterization of
bulk materials, microstructures, and nanostructures. We investigated the
magnetic and morphological properties of two colloidal dispersions of iron
oxide (Fe3O4) magnetic nanoparticles (MNPs), synthesized by chemical
precipitation (co-precipitation) and pulsed laser ablation (PLA) in liquid, by
scanning magnetic microscopy (SMM) applied to a small sample with mass on the
order of tens of {\mu}g. We evaluated the performance of this technique by
comparing magnetization curves and measurements obtained with commercial
magnetometers, considered standard. The errors obtained for the saturation and
remanent magnetization were approximately 0.18 Am2/kg and 0.6 Am2/kg,
respectively. The average size distribution of the NPs estimated from the
magnetization curve measurements is consistent with the results obtained by
traditional transmission electron microscopy (TEM). The technique can be
extended to measure and analyze magnetization curves (hysteresis loops), thus
enabling an even more accurate estimation of overall NP sizes.",1907.05908v1
2009-11-23,Open and closed boundaries in large-scale convective dynamos,"Context. Earlier work has suggested that large-scale dynamos can reach and
maintain equipartition field strengths on a dynamical time scale only if
magnetic helicity of the fluctuating field can be shed from the domain through
open boundaries. Aims. Our aim is to test this scenario in convection-driven
dynamos by comparing results for open and closed boundary conditions. Methods.
Three-dimensional numerical simulations of turbulent compressible convection
with shear and rotation are used to study the effects of boundary conditions on
the excitation and saturation of large-scale dynamos. Open (vertical-field) and
closed (perfect-conductor) boundary conditions are used for the magnetic field.
The shear flow is such that the contours of shear are vertical, crossing the
outer surface, and are thus ideally suited for driving a shear-induced magnetic
helicity flux. Results. We find that for given shear and rotation rate, the
growth rate of the magnetic field is larger if open boundary conditions are
used. The growth rate first increases for small magnetic Reynolds number, Rm,
but then levels off at an approximately constant value for intermediate values
of Rm. For large enough Rm, a small-scale dynamo is excited and the growth rate
of the field in this regime increases as Rm^(1/2). Regarding the nonlinear
regime, the saturation level of the energy of the total magnetic field is
independent of Rm when open boundaries are used. In the case of perfect
conductor boundaries, the saturation level first increases as a function of Rm,
but then decreases proportional to Rm^(-1) for Rm > 30, indicative of
catastrophic quenching. These results suggest that the shear-induced magnetic
helicity flux is efficient in alleviating catastrophic quenching when open
boundaries are used. The horizontally averaged mean field is still weakly
decreasing as a function of Rm even for open boundaries.",0911.4120v2
2023-06-12,"Transition from small-scale to large-scale dynamo in a supernova-driven, multiphase medium","Magnetic fields are widely recognised as critical at many scales to galactic
dynamics and structure, including multiphase pressure balance, dust processing,
and star formation. Using imposed magnetic fields cannot reliably model the
interstellar medium's (ISM) dynamical structure nor phase interactions. Dynamos
must be modelled. ISM models exist of turbulent magnetic fields using
small-scale dynamo (SSD). Others model the large-scale dynamo (LSD) organising
magnetic fields at scale of the disc or spiral arms. Separately, neither can
fully describe the galactic magnetic field dynamics nor topology. We model the
LSD and SSD together at sufficient resolution to use the low explicit
Lagrangian resistivity required. The galactic SSD saturates within 20 Myr. We
show that the SSD is quite insensitive to the presence of an LSD and is even
stronger in the presence of a large-scale shear flow. The LSD grows more slowly
in the presence of SSD, saturating after 5 Gyr vs. 1--2 Gyr in studies where
the SSD is weak or absent. The LSD primarily grows in warm gas in the galactic
midplane. Saturation of the LSD occurs due to ${\alpha}$-quenching near the
midplane as the growing mean field produces a magnetic ${\alpha}$ that opposes
the kinetic ${\alpha}$. The magnetic energy in our models of the LSD shows
slightly sublinear response to increasing resolution, indicating that we are
converging towards the physical solution at 1 pc resolution. Clustering
supernovae in OB associations increases the growth rates for both the SSD and
the LSD, compared to a horizontally uniform supernova distribution.",2306.07051v3
2007-02-26,A solar surface dynamo,"Context: Observations indicate that the `quiet' solar photosphere outside
active regions contains considerable amounts of magnetic energy and magnetic
flux, with mixed polarity on small scales. The origin of this flux is unclear.
Aims: We test whether local dynamo action of the near-surface convection
(granulation) can generate a significant contribution to the observed magnetic
flux. Methods: We have carried out MHD simulations of solar surface convection,
including the effects of strong stratification, compressibility, partial
ionization, radiative transfer, as well as an open lower boundary. Results:
Exponential growth of a weak magnetic seed field (with vanishing net flux
through the computational box) is found in a simulation run with a magnetic
Reynolds number of about 2600. The magnetic energy approaches saturation at a
level of a few percent of the total kinetic energy of the convective motions.
Near the visible solar surface, the (unsigned) magnetic flux density reaches at
least a value of about 25 G. Conclusions: A realistic flow topology of
stratified, compressible, non-helical surface convection without enforced
recirculation is capable of turbulent local dynamo action near the solar
surface.",0702681v1
2002-05-28,"Ferromagnetism in (In,Mn)As Diluted Magnetic Semiconductor Thin Films Grown by Metalorganic Vapor Phase Epitaxy","In1-xMnxAs diluted magnetic semiconductor (DMS) thin films have been grown
using metalorganic vapor phase epitaxy (MOVPE).
Tricarbonyl(methylcyclopentadienyl)manganese was used as the Mn source.
Nominally single-phase, epitaxial films were achieved with Mn content as high
as x=0.14 using growth temperatures Tg>475 C. For lower growth temperatures and
higher Mn concentrations, nanometer scale MnAs precipitates were detected
within the In1-xMnxAs matrix. Magnetic properties of the films were
investigated using a superconducting quantum interference device (SQUID)
magnetometer. Room-temperature ferromagnetic order was observed in a sample
with x=0.1. Magnetization measurements indicated a Curie temperature of 333 K
and a room-temperature saturation magnetization of 49 emu/cm^3. The remnant
magnetization and the coercive field were small, with values of 10 emu/cm^3 and
400 Oe, respectively. A mechanism for this high-temperature ferromagnetism is
discussed in light of the recent theory based on the formation of small
clusters of a few magnetic atoms.",0205602v1
2003-01-27,Specific Heat of the S=1/2 Two-Dimensional Shastry-Sutherland Antiferromagnet SrCu2(BO3)2 in High Magnetic Fields,"We characterize the field-induced magnetic phases of SrCu2(BO3)2, a
frustrated spin-1/2 Heisenberg antiferromagnet in the two-dimensional
Shastry-Sutherland lattice, using specific heat in magnetic fields up to 33 T.
We find that the spin gap persists above the expected critical field Hc =
Delta/g*mu_B of 21 T despite the appearance of magnetic moment in the ground
state. At the magnetization plateau at 1/8 of the saturation, the Sz = +1
triplets that carry the magnetization of the ground state are observed to form
a two-dimensional spin gas of massive bosons. A spin gas consisting of the same
number of massive particles continues to completely dominate the specific heat
in the field region above the plateau, although the magnetization increases
with increasing field. Ordering is observed at a temperature immediately below
the spin-gas regime.",0301509v3
2004-04-05,Distribution of the sheet current in a magnetically shielded superconducting filament,"The distribution of the transport current in a superconducting filament
aligned parallel to the flat surface of a semi-infinite bulk magnet is studied
theoretically. An integral equation governing the current distribution in the
Meissner state of the filament is derived and solved numerically for various
filament-magnet distances and different relative permeabilities. This reveals
that the current is depressed on the side of the filament adjacent to the
surface of the magnet and enhanced on the averted side. Substantial current
redistributions in the filament can already occur for low values of the
relative permeability of the magnet, when the distance between the filament and
the magnet is short, with evidence of saturation at moderately high values of
this quantity, similar to the findings for magnetically shielded strips.",0404094v1
2004-04-13,Quantum kagome antiferromagnet in a magnetic field: Low-lying non-magnetic excitations versus valence-bond crystal order,"We study the ground state properties of a quantum antiferromagnet on the
kagome lattice in the presence of a magnetic field, paying particular attention
to the stability of the plateau at magnetization 1/3 of saturation and the
nature of its ground state. We discuss fluctuations around classical ground
states and argue that quantum and classical calculations at the harmonic level
do not lead to the same result in contrast to the zero-field case. For spin
S=1/2 we find a magnetic gap below which an exponential number of non-magnetic
excitations are present. Moreover, such non-magnetic excitations also have a
(much smaller) gap above the three-fold degenerate ground state. We provide
evidence that the ground state has long-range order of valence-bond crystal
type with nine spins in the unit cell.",0404279v2
2004-05-07,Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys,"A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19)
Heusler alloys undergoing structural martensite-austenite transformations while
in ferromagnetic state has been performed. From measurements of spontaneous
magnetization, Ms(T), jumps \Delta M at structural phase transitions were
determined. Virtual Curie temperatures of the martensite were estimated from
the comparison of magnetization in martensitic and austenitic phases. Both
saturation magnetic moments in ferromagnetic state and effective magnetic
moments in paramagnetic state of Mn and Ni atoms were estimated and the
influence of delocalization effects on magnetism in these alloys was discussed.
The experimental results obtained show that the shift of martensitic transition
temperature depends weakly on composition. The values of this shift are in good
correspondence with Clapeyron-Clausius formalism taking into account the
experimental data on latent heat at martensite-austenite transformations.",0405134v1
2005-05-30,Spin Disorder and Magnetic Anisotropy in Fe3O4 Nanoparticles,"We have studied the magnetic behavior of dextran-coated magnetite
(Fe$_3$O$_4$) nanoparticles with median particle size $\left<d\right>=8$ $nm$.
Magnetization curves and in-field M\""ossbauer spectroscopy measurements showed
that the magnetic moment $M_S$ of the particles was much smaller than the bulk
material. However, we found no evidence of magnetic irreversibility or
non-saturating behavior at high fields, usually associated to spin canting. The
values of magnetic anisotropy $K_{eff}$ from different techniques indicate that
surface or shape contributions are negligible. It is proposed that these
particles have bulk-like ferrimagnetic structure with ordered A and B
sublattices, but nearly compensated magnetic moments. The dependence of the
blocking temperature with frequency and applied fields, $T_B(H,\omega)$,
suggests that the observed non-monotonic behavior is governed by the strength
of interparticle interactions.",0505682v5
2005-05-29,Dynamical Aspects of Photoinduced Magnetism and Spin-Crossover phenomena in Prussian Blue Analogs,"We present dynamical properties of spin crossover compounds with
photomagnetization, proposing a new model in which the spin-crossover phenomena
and magnetic ordering are incorporated in a unified way. By using this model,
the novel characteristics observed in Prussian blue analogs are qualitatively
well reproduced. We investigate the time evolution of the magnetization and
high spin fraction taking into account multi-time scales in a master equation
approach for the magnetic relaxation, the lattice (electronic) relaxation, and
the photoexcitation process. In particular, processes with different
temperature cycles starting from the photoinduced saturated magnetic state are
studied including the effect of photoirradiation. In the temperature cycle in
the low temperature region where the high spin state has a strong
metastability, the magnetization almost exactly follows the quasi-static
process. On the other hand, when the temperature is raised above the region,
the dynamics of the spin state and the magnetization couple and exhibit various
types of dynamical cooperative phenomena under time-dependent control of
temperature and photoirradiation.",0505702v1
2006-06-26,Epitaxial film growth and magnetic properties of Co_2FeSi,"We have grown thin films of the Heusler compound Co_2FeSi by RF magnetron
sputtering. On (100)-oriented MgO substrates we find fully epitaxial
(100)-oriented and L2_1 ordered growth. On Al_2O_3 (11-20) substrates, the film
growth is (110)-oriented, and several in-plane epitaxial domains are observed.
The temperature dependence of the electrical resistivity shows a power law with
an exponent of 7/2 at low temperatures. Investigation of the bulk magnetic
properties reveals an extrapolated saturation magnetization of 5.0 mu_B/fu at 0
K. The films on Al_2O_3 show an in-plane uniaxial anisotropy, while the
epitaxial films are magnetically isotropic in the plane. Measurements of the
X-ray magnetic circular dichroism of the films allowed us to determine element
specific magnetic moments. Finally we have measured the spin polarization at
the surface region by spin-resolved near-threshold photoemission and found it
strongly reduced in contrast to the expected bulk value of 100%. Possible
reasons for the reduced magnetization are discussed.",0606666v2
2006-10-19,Bose-Einstein condensation of magnons in magnets with predominant ferromagnetic interaction,"We discuss Bose-Einstein condensation of magnons (BEC) in magnets with
predominant ferromagnetic (FM) interaction in magnetic field $H$ near
saturation ($H_c$). Because $H_c$ is independent of FM couplings, magnetic
materials of this type can have small $H_c$ that makes them promising
candidates for experimental investigation of BEC. Ferromagnets with easy-plane
anisotropy and antiferromagnets (AFs) containing weakly coupled FM planes or
chains are discussed in detail. We observe small effective interaction between
magnons near the QCP in such magnets, in contrast to AFs with strong AF
coupling previously discussed. In particular, this smallness allows us to find
crossovers in the critical temperature $T_c(H)\propto (H_c-H)^{1/\phi}$ from
$\phi=3/2$ to $\phi=1$ in quasi-1D magnets, and from $\phi=3/2$ to
$\phi\approx1$ ($T_c\ln T_c\propto H_c-H$) in quasi-2D ones.",0610536v4
2007-07-23,"Magnetocrystalline anisotropy controlled local magnetic configurations in (Ga,Mn)As spin-transfer-torque microdevices","The large saturation magnetization in conventional dense moment ferromagnets
offers flexible means of manipulating the ordered state through demagnetizing
shape anisotropy fields but these dipolar fields, in turn, limit the
integrability of magnetic elements in information storage devices. We show that
in a (Ga,Mn)As dilute moment ferromagnet, with comparatively weaker magnetic
dipole interactions, locally tunable magnetocrystalline anisotropy can take the
role of the internal field which determines the magnetic configuration.
Experiments and theoretical modeling are presented for lithographically
patterned microchannels and the phenomenon is attributed to lattice relaxations
across the channels. The utility of locally controlled magnetic anisotropies is
demonstrated in current induced switching experiments. We report structure
sensitive, current induced in-plane magnetization switchings well below the
Curie temperature at critical current densities 10^5 Acm^-2. The observed
phenomenology shows signatures of a contribution from domain-wall
spin-transfer-torque effects.",0707.3329v1
2007-12-04,Magnetic structure and phase diagram of TmB4,"Magnetic structure of single crystalline TmB4 has been studied by
magnetization, magnetoresistivity and specific heat measurements. A complex
phase diagram with different antiferromagnetic (AF) phases was observed below
TN1 = 11.7 K. Besides the plateau at half-saturated magnetization (1/2 MS),
also plateaus at 1/9, 1/8 and 1/7 of MS were observed as function of applied
magnetic field B//c. From additional neutron scattering experiments on TmB4, we
suppose that those plateaus arise from a stripe structure which appears to be
coherent domain boundaries between AF ordered blocks of 7 or 9 lattice
constants. The received results suggest that the frustration among the Tm3+
magnetic ions, which maps to a geometrically frustrated Shastry-Sutherland
lattice lead to strong competition between AF and ferromagnetic (FM) order.
Thus, stripe structures in intermediate field appear to be the best way to
minimize the magnetostatic energy against other magnetic interactions between
the Tm ions combined with very strong Ising anisotropy.",0712.0519v1
2007-12-13,Breakdown of an intermediate plateau in the magnetization process of anisotropic spin-1 Heisenberg dimer: theory vs. experiment,"The magnetization process of the spin-1 Heisenberg dimer model with axial and
rhombic single-ion anisotropy terms is particularly investigated in connection
with recent experimental high-field measurements performed on the
single-crystal sample of the homodinuclear nickel(II) compound
[Ni2(Medpt)2(ox)(H2O)2](ClO4)2.2H2O (Medpt=methyl-bis(3-aminopropyl)amine). The
results obtained from the exact numerical diagonalization reveal a striking
magnetization process with a marked spatial dependence on the applied magnetic
field for arbitrary but non-zero single-ion anisotropy. It is demonstrated that
the field range, which corresponds to an intermediate magnetization plateau
emerging at a half of the saturation magnetization, basically depends on
single-ion anisotropy terms as well as a spatial orientation of the applied
field. The breakdown of the intermediate magnetization plateau is discussed at
length in relation to the single-ion anisotropy strength.",0712.2109v2
2008-06-06,Magnetic moment of hyperons in nuclear matter by using quark-meson coupling models,"We calculate the magnetic moments of hyperons in dense nuclear matter by
using relativistic quark models. Hyperons are treated as MIT bags, and the
interactions are considered to be mediated by the exchange of scalar and vector
mesons which are approximated as mean fields. Model dependence is investigated
by using the quark-meson coupling model and the modified quark-meson coupling
model; in the former the bag constant is independent of density and in the
latter it depends on density. Both models give us the magnitudes of the
magnetic moments increasing with density for most octet baryons. But there is a
considerable model dependence in the values of the magnetic moments in dense
medium. The magnetic moments at the nuclear saturation density calculated by
the quark meson coupling model are only a few percents larger than those in
free space, but the magnetic moments from the modified quark meson coupling
model increase more than 10% for most hyperons. The correlations between the
bag radius of hyperons and the magnetic moments of hyperons in dense matter are
discussed.",0806.1099v2
2008-07-11,Magnetic interactions and high-field properties of Ag(2)VOP(2)O(7): frustrated alternating chain close to the dimer limit,"We report on high-field magnetic properties of the silver vanadium phosphate
Ag(2)VOP(2)O(7). This compound has a layered crystal structure, but the
specific topology of the V-P-O framework gives rise to a one-dimensional spin
system, a frustrated alternating chain. Low-field magnetization measurements
and band structure calculations show that Ag(2)VOP(2)O(7) is close to the dimer
limit with the largest nearest-neighbor interaction of about 30 K. High-field
magnetization data reveal the critical fields \mu_0H_{c1} of about 23 T
(closing of the spin gap) and \mu_0H_{c2} of about 30 T (saturation by full
alignment of the magnetic moments). From H_{c1} to H_{c2} the magnetization
increases sharply similar to the system of isolated dimers. Thus, the magnetic
frustration in Ag(2)VOP(2)O(7) bears little influence on the high-field
properties of this compound.",0807.1849v1
2008-08-20,Low-temperature magnetic ordering in SrEr$_2$O$_4$,"SrEr$_2$O$_4$ has been characterised by low-temperature powder neutron
diffraction, as well as single crystal specific heat and magnetisation
measurements. Magnetisation measurements show that the magnetic system is
highly anisotropic at temperature above ordering. A magnetic field of 280 kOe
applied at $T=1.6$ K does not overcome the anisotropic magnetisation and fails
to fully saturate the system. Long range antiferromagnetic ordering develops
below $T_N=0.75$ K, identified by magnetic Bragg reflections with propagation
vector ${\bf k}=0$ and a lambda anomaly in the specific heat. The magnetic
structure consists of ferromagnetic chains running along the \textit{c} axis,
two adjacent chains being stacked antiferromagnetically. The moments point
along the \textit{c} direction, but only one of the two crystallographically
in-equivalent Er sites has a sizeable ordered magnetic moment, 4.5 $\rm \mu_B$
at 0.55 K. The magnetic properties of SrEr$_2$O$_4$ are discussed in terms of
the interplay between the low-dimensionality, competing exchange interactions,
dipolar interactions and low lying crystal field levels.",0808.2675v1
2008-11-21,Magnetic Domains and Surface Effects in Hollow Maghemite Nanoparticles,"In the present work, we investigate the magnetic properties of ferrimagnetic
and noninteracting maghemite (g-Fe2O3) hollow nanoparticles obtained by the
Kirkendall effect. From the experimental characterization of their magnetic
behavior, we find that polycrystalline hollow maghemite nanoparticles are
characterized by low superparamagnetic-to-ferromagnetic transition
temperatures, small magnetic moments, significant coercivities and
irreversibility fields, and no magnetic saturation on external magnetic fields
up to 5 T. These results are interpreted in terms of the microstructural
parameters characterizing the maghemite shells by means of an atomistic Monte
Carlo simulation of an individual spherical shell model. The model comprises
strongly interacting crystallographic domains arranged in a spherical shell
with random orientations and anisotropy axis. The Monte Carlo simulation allows
discernment between the influence of the structure polycrystalline and its
hollow geometry, while revealing the magnetic domain arrangement in the
different temperature regimes.",0811.3592v2
2009-03-15,Direct Observation of Magnetic Gradient in Co/Pd Pressure-Graded Media,"Magnetometry and neutron scattering have been used to study the magnetic
properties of pressure graded Co/Pd multilayers. The grading of the multilayer
structure was done by varying the deposition pressure during sputtering of the
samples. Magnetic depth profiling by polarized neutron reflectometry directly
shows that for pressure-graded samples, the magnetization changes significantly
from one pressure region to the next, while control samples sputtered at
uniform pressure exhibit essentially uniform magnetic depth profiles.
Complementary magnetometry results suggest that the observed graded magnetic
profiles are due in part to a decrease in saturation magnetization for regions
deposited at progressively higher pressure. Increased deposition pressure is
shown to increase coercivity, and for graded samples, the absence of discrete
steps in the hysteresis loops implies exchange coupling among regions deposited
at different pressures.",0903.2650v1
2009-08-15,Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions,"Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to
measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel
junctions (MTJs). For this purpose, T-FMR measurements were conducted with an
external magnetic field up to 14 kOe applied perpendicular to the film surface
of MgO-based MTJs under a dc bias. The observed frequency-field relationship
suggests that a 20 A CoFeB free layer has an effective demagnetization field
much smaller than the intrinsic bulk value of CoFeB, with 4PiMeff = (6.1 +/-
0.3) kOe. This value is consistent with the saturation field obtained from
magnetometry measurements on extended films of the same CoFeB thickness.
In-plane T-FMR on the other hand shows less consistent results for the
effective demagnetization field, presumably due to excitations of more complex
modes. These experiments suggest that the perpendicular T-FMR is preferred for
quantitative magnetic characterization of nanoscale MTJs.",0908.2164v1
2009-09-24,The critical role of magnetic helicity in astrophysical large-scale dynamos,"The role of magnetic helicity in astrophysical large-scale dynamos is
reviewed and compared with cases where there is no energy supply and an initial
magnetic field can only decay. In both cases magnetic energy tends to get
redistributed to larger scales. Depending on the efficiency of magnetic
helicity fluxes, the decay of a helical field can speed up. Likewise, the
saturation of a helical dynamo can speed up through magnetic helicity fluxes.
The astrophysical importance of these processes is reviewed in the context of
the solar dynamo and an estimated upper limit for the magnetic helicity flux of
10^46 Mx^2/cycle is given.",0909.4377v1
2010-01-02,Surface magnetic states of Ni nanochains modified by using different organic surfactants,"Three powder samples of Ni nanochains formed of polycrystalline Ni
nanoparticles with an estimated diameter of about 30 nm have been synthesized
by a wet chemical method using different organic surfactants. These samples,
having magnetically/structurally core-shell structures, all with a
ferromagnetic Ni core, are Ni@Ni3C nanochains, Ni@NiSG nanochains with a spin
glass (SG) surface layer, and Ni@NiNM nanochains with a nonmagnetic (NM)
surface layer. The average thickness of the shell for these three samples is
determined as about 2 nm. Magnetic properties tailored by the different surface
magnetism are studied. In particular, suppression in saturation magnetization
usually observed with magnetic nanoparticles is revealed to arise from the
surface magnetic states with the present samples.",1001.0298v1
2010-04-13,Numerical study of magnetization processes in rare-earth tetraborides,"We present a simple model for a description of magnetization processes in
rare-earth tetraborides. The model is based on the coexistence of two
subsystems, and namely, the spin subsystem described by the Ising model and the
electronic subsystem described by the Falicov-Kimball model on the
Shastry-Sutherland lattice (SSL). Moreover, both subsystems are coupled by the
anisotropic spin-dependent interaction of the Ising type. We have found, that
the switching on the spin-dependent interaction ($J_z$) between the electron
and spin subsystems and taking into account the electron hopping on the nearest
($t$) and next-nearest ($t'$) lattice sites of the SSL leads to a stabilization
of new magnetization plateaus. In addition, to the Ising magnetization plateau
at $m^{sp}/m_s^{sp}=1/3$ we have found three new magnetization plateaus located
at $m^{sp}/m_s^{sp}=1/2$, 1/5 and 1/7 of the saturated spin magnetization
$m_s^{sp}$. The ground-states corresponding to magnetization plateaus have the
same spin structure consisting of parallel antiferromagnetic bands separated by
ferromagnetic stripes.",1004.2128v1
2010-05-20,Metastable magnetization behavior in magnetocaloric R6Co1.67Si3 (R=Tb and Nd) compounds,"Magnetic field and time induced steps have been observed in the recently
discovered ternary silicide R6Co1.67Si3. Huge relaxation steps are observed
across different loops in the low temperature magnetization isotherms. Giant
relaxation present in this system indicates the existence of incubation time to
get the saturated moment at a certain field. Measurement protocol sensitive
magnetization behavior observed in this system may arise from the strong
magnetostructural coupling and/or magnetic frustration. Electrical resistivity
and magnetoresistance also reflect the magnetic state of the compound.
Magnetocaloric effect is found to be large at temperatures close to the
magnetic transition temperature.",1005.3671v1
2010-12-22,Magnetic Structure in Fe/Sm-Co Exchange Spring Bilayers with Intermixed Interfaces,"The depth profile of the intrinsic magnetic properties in an Fe/Sm-Co bilayer
fabricated under nearly optimal spring-magnet conditions was determined by
complementary studies of polarized neutron reflectometry and micromagnetic
simulations. We found that at the Fe/Sm-Co interface the magnetic properties
change gradually at the length scale of 8 nm. In this intermixed interfacial
region, the saturation magnetization and magnetic anisotropy are lower and the
exchange stiffness is higher than values estimated from the model based on a
mixture of Fe and Sm-Co phases. Therefore, the intermixed interface yields
superior exchange coupling between the Fe and Sm-Co layers, but at the cost of
average magnetization.",1012.5086v1
2011-03-30,Giant coercivity of dense nanostructured spark plasma sintered barium hexaferrite,"Due to the limited rare-earth elements resources, ferrite magnets need to be
improved drastically. Ideally, for a true hard magnet, the coercive field
should be larger than the saturation magnetization, which is not yet realized
for ferrites. Thus, an alternative can be found in making very fine grain
ferrite magnets, but it is usually impossible to get small grains and dense
material together. In this paper, it is shown that the spark plasma sintering
method is able to produce approximately 80% of dense material with crystallites
smaller than 100 nm. The as-prepared bulk sintered anisotropic magnets exhibits
coercive field of 0.5 T which is approximately 60% of the theoretical limit and
only a few percentage below that of loose nanopowders. As a result, the magnets
behave nearly ideal (-1.18 slope in the BH plane second quadrant) and the
energy product reaches 8.8 kJ m-3, the highest value achieved in the isotropic
ferrite magnet to our knowledge.",1103.5840v1
2011-08-08,Dimensional crossover in spin-1 Heisenberg antiferromagnets: a quantum Monte Carlo study,"We present results of large scale simulations of the spin-1 Heisenberg
antiferromagnet on a tetragonal lattice. The stochastic series expansion
quantum Monte Carlo method is used to calculate equilibrium thermodynamic
variables in the presence of an external magnetic field. In particular, the low
temperature magnetization curve is investigated in the quasi-one-dimensional
(Q1D), quasi-two-dimensional (Q2D), and three-dimensional (3D) limits. Starting
from the 3D limit, the Q1D (Q2D) limit is achieved by reducing the in-plane
(out-of-plane) spin coupling strength towards zero. In the Q1D limit, a Haldane
gap appears in the magnetization curve at low magnetic field. Additionally,
near the saturation field the slope of the magnetization curve increases
substantially, approaching the infinite-slope behavior of a one-dimensional
spin-1 chain. A similar (though less pronounced) effect is seen in the Q2D
limit. We also study the effect of uniaxial single-ion anisotropy on the
magnetization curve for Q1D and Q2D systems. Our results will be important in
understanding the field-induced behavior of a class of low-dimensional Ni-based
quantum magnets.",1108.1648v1
2011-12-05,Magnetic field estimates for accreting neutron stars in massive binary systems and models of magnetic field decay,"Some modern models of neutron star evolution predict that initially large
magnetic fields rapidly decay down to some saturation value $\sim {\rm
few}\times 0^{13}$ G and weaker magnetic fields do not decay significantly
(Pons). It is difficult to check the predictions of this model for initially
highly magnetized objects on the time scale of a few million years. We propose
to use Be/X-ray binaries for this purpose. We apply several methods to estimate
magnetic fields of neutron stars in these accreting systems using the data
obtained by the RXTE satellite (Galache). Only using the most modern approach
for estimating the magnetic field strengths of long period NSs as proposed by
Shakura we are able to obtain a field distribution compatible with predictions
of the theoretical model of field decay of Pons.",1112.1123v2
2012-06-22,How is the magnetic reconnection derived from magnetohydrodynamics equations?,"We clarify how magnetic reconnection can be derived from magnetohydrodynamics
(MHD) equations in a way that is easily understandable to university students.
The essential mechanism governing the time evolution of the magnetic field is
diffusion dynamics. The magnetic field is represented by two components. It is
clarified that the diffusion of a component causes a generation of another
component that is initially zero and, accordingly, that the magnetic force
lines are reconnected. For this reconnection to occur correctly, the initial
magnetic field must be directed oppositely in the two regions, e.g., $y>0$ and
$y<0$; must be concave (convex) for $y>0$ ($y<0$); and must be saturated for
$y$ far from the x axis, which would indicate the existence of the current
sheet. It will be clear that our comprehension based on diffusion runs parallel
to the common qualitative explanation about the magnetic reconnection.",1206.5161v1
2013-05-29,Enhanced interface perpendicular magnetic anisotropy in Ta|CoFeB|MgO using nitrogen doped Ta underlayers,"We show that the magnetic characteristics of Ta|CoFeB|MgO magnetic
heterostructures are strongly influenced by doping the Ta underlayer with
nitrogen. In particular, the saturation magnetization drops upon doping the Ta
underlayer, suggesting that the doped underlayer acts as a boron diffusion
barrier. In addition, the thickness of the magnetic dead layer decreases with
increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy
increases to ~1.8 erg/cm2 when an optimum amount of nitrogen is introduced into
the Ta underlayer. These results show that nitrogen doped Ta serves as a good
underlayer for Spintronics applications including magnetic tunnel junctions and
domain wall devices.",1305.6660v1
2013-08-30,Magnetocapacitance as a sensitive probe of magnetostructural changes in NiCr$_2$O$_4$,"The spinel NiCr$_2$O$_4$ is characterized using dielectric and high magnetic
field measurements. The trends in the magnetodielectric response fall into
three clear temperature regimes corresponding to known magnetic and structural
transitions. Above 65\,K, weak magnetic field dependence of the dielectric
constant is observed with no hysteresis. When 30\,K\,$\leq\,T\,\leq$\,65\,K, a
strong dependence of the dielectric constant on the magnetic field is observed
and hysteresis develops resulting in so called butterfly loops. Below 30\,K,
magnetodielectric hysteresis is enhanced. Magnetodielectric hysteresis mirrors
magnetic hysteresis suggesting that spin-spin interactions are the mechanism
for the magnetoelectric effect in NiCr$_2$O$_4$. At high fields however, the
magnetization continues to increase while the dielectric constant saturates.
Magnetodielectric measurements of NiCr$_2$O$_4$ suggest an additional,
previously unobserved transition at 20\,K. Subtle changes in magnetism and
structure suggest that this 20\,K anomaly corresponds to the completion of
ferrimagnetic ordering and the spin driven structural distortion. We
demonstrate that magnetocapacitance is a sensitive probe of magnetostructural
distortion.",1309.0016v1
2014-01-22,Cooling a magnetic nanoisland by spin-polarized currents,"We investigate cooling of a vibrational mode of a magnetic quantum dot by a
spin-polarized tunneling charge current, exploiting the interaction between the
magnetization and the vibration. The spin-polarized charge current polarizes
the magnetic nanoisland, lowering its energy. Inevitable Ohmic energy losses
due to the charge current flow will heat up the vibration. A small but finite
coupling between the vibration and the local magnetic moment then permits an
energy exchange, resulting in a lower energy, i.e., cooling, of the vibrational
mode. We determine parameter regimes for the cooling of the vibration below
$50\%$ of its initial value. Lowest final phonon temperature is observed for
weak electron-phonon-coupling but similar magnetization-phonon coupling
strength. The cooling rate, thereby, increases at first with the
magnetization-phonon coupling and then saturates.",1401.5724v3
2014-03-24,Magnetic structure and dynamics of a strongly one-dimensional cobalt$^{II}$ metal-organic framework,"We investigate the magnetism of the
Co$^{II}_4$(OH)$_2$(C$_1$$_0$H$_1$$_6$O$_4$)$_3$ metal-organic framework which
displays complex inorganic chains separated from each other by distances of 1
to 2 nm, and which orders at ~5.4 K. The zero-field magnetic structure is
determined using neutron powder diffraction: it is mainly antiferromagnetic but
posseses a ferromagnetic component along the $\textbf{c}$-axis. This magnetic
structure persists in presence of a magnetic field. Ac susceptibility
measurements confirm the existence of a single thermally activated regime over
7 decades in frequency ($E/k_B\approx64 K$) whereas time-dependent relaxation
of the magnetization after saturation in an external field leads to a two times
smaller energy barrier. These experiments probe the slow dynamics of domain
walls within the chains: we propose that the ac measurements are sensitive to
the motion of existing domain walls within the chains, while the magnetization
measurements are governed by the creation of domain walls.",1403.5931v1
2014-07-24,Successive magnetic transitions of Ca$_2$CoSi$_2$O$_7$ in high magnetic fields,"Magnetic and dielectric properties of \aa kermanite Ca$_2$CoSi$_2$O$_7$
single crystals were investigated in pulsed high magnetic fields. In magnetic
fields along the $c$ axis, this material shows a magnetization plateau in a
wide range of field below the saturation. Magnetization processes for fields
along the $a$ and $b$ axes show multiple anomalies but different traces to each
other, indicating the breaking of four-fold symmetry. Measurements of the
magnetoelectric effects exhibit the changes in electric polarization according
to the changes in the spin system. The experimentally determined quadratic
magnetoelectric tensor is consistent with that expected in the crystal symmetry
of orthorhombic $P2_12_12$.",1407.6450v1
2015-12-24,Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca$_3$CoNb$_2$O$_9$,"We synthesized a quasi-two-dimensional distorted triangular lattice
antiferromagnet Ca$_3$CoNb$_2$O$_9$, in which the effective spin of Co$^{2+}$
is 1/2 at low temperatures, whose magnetic properties were studied by dc
susceptibility and magnetization techniques. The x-ray diffraction confirms the
quality of our powder samples. The large Weiss constant $\theta_{CW}\sim$ $-55$
K and the low Neel temperature($T_N\sim$ 1.45 K) give a frustration factor $f$
($=\mid\theta_{CW}/T_N \mid$) $\approx$ 38, suggesting that Ca$_3$CoNb$_2$O$_9$
resides in strong frustration regime. Slightly below $T_N$, deviation between
the susceptibility data under zero-field cooling (ZFC) and field cooling (FC)
is observed. A new magnetic state with 1/3 of the saturate magnetization $M_s$
is suggested in the magnetization curve at 0.46 K. Our study indicates that
Ca$_3$CoNb$_2$O$_9$ is an interesting material to investigate magnetism in
triangular lattice antiferromagnets with weak anisotropy.",1512.07792v1
2016-08-30,Multiple Magnetization Plateaus and the Magnetic Structures in $S=1/2$ Heisenberg Model on the Checkerboard Lattice,"We study the ground state of $S = 1/2$ Heisenberg model on the checkerboard
lattice in a magnetic field by the density matrix renormalization group (DMRG)
method with the sine-square deformation. We obtain magnetization plateaus at
$M/M_{\rm sat}=$0, 1/4, 3/8, 1/2, and 3/4 where $M_{\rm sat}$ is the saturated
magnetization. The obtained 3/4 plateau state is consistent with the exact
result, and the 1/2 plateau is found to have a four-spin resonating loop
structure similar to the six-spin loop structure of the 1/3 plateau of the
kagome lattice. Different four-spin loop structures are obtained in the 1/4 and
3/8 plateaus but no corresponding states exist in the kagome lattice. The 3/8
plateau has a unique magnetic structure of three types of four-spin local
quantum states in a $4\sqrt{2}\times2\sqrt{2}$ magnetic unit cell with a
16-fold degeneracy.",1608.08327v1
2016-10-13,Nanoscale distribution of magnetic anisotropies in bimagnetic soft core-hard shell MnFe$_2$O$_4$@CoFe$_2$O$_4$ nanoparticles,"The nanoscale distribution of magnetic anisotropies was measured in
core@shell MnFe$_2$O$_4$@CoFe$_2$O$_4$ 7.0 nm particles using a combination of
element selective magnetic spectroscopies with different probing depths. As
this picture is not accessible by any other technique, emergent magnetic
properties were revealed. The coercive field is not constant in a whole
nanospinel. The very thin (0.5 nm) CoFe$_2$O$_4$ hard shell imposes a strong
magnetic anisotropy to the otherwise very soft MnFe$_2$O$_4$ core: a large
gradient in coercivity was measured inside the MnFe$_2$O$_4$ core with lower
values close to the interface region, while the inner core presents a
substantial coercive field (0.54 T) and a very high remnant magnetization (90%
of the magnetization at saturation).",1610.04263v2
2016-12-16,Macroscopic magnetic field generated in laser atom interaction,"We observe shift in the zero magnetic field resonance as the handedness of
resonantly interacting circularly polarized light is changed. The
characteristic of the shift resembles with the Zeeman light shift that arises
due to interaction of non-resonant circularly polarized light with atom.
However many attributes of our observed resonant phenomena like dependence on
buffer gas, saturation of the shift with light intensity and involved time
constant in evolution of the shift contradicts to the fictitious magnetic field
model. We propose collective alignment of atomic magnetic moment giving rise to
a real magnetic field as a possible mechanism behind the observed shift. The
characteristic changes in the signal profile with respect to the three axis
magnetic field have been established that can reveal many subtle issues
pertaining to the phenomenon.",1612.05411v3
2017-01-07,Magnetization and the Concurrence of the Spin-1/2 Ising-Heisenberg Pyrochlore Ladder,"We have established a quantum antiferromagnetic Heisenberg-Ising model on a
spin-1/2 pyrochlore edge-shared ladder with Heisenberg intra-rung and Ising
inter-rung interactions as a perspicuous candidate to exhibit magnetization mid
and zero plateaus, characteristic peaks of magnetic susceptibility, and thermal
entanglement mid plateau. The model is exactly solvable and thus, all the
essential properties such as the thermal entanglement and the magnetic
properties of the system can be exactly calculated. The calculations are done
both through the transfer matrix technique and through the reduced density
matrix. The magnetization plateaus are observed at zero and half the saturation
value and the magnetic susceptibility exhibits a clear demonstration of the
associated characteristic peaks. The model also displays the mid plateau of the
thermal entanglement as a function of the external magnetic field at low
temperatures.",1701.01880v1
2017-01-09,"Magnetic properties of ultra-thin 3d transition-metal binary alloys I: spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior","The structure and static magnetic properties - saturation magnetization,
perpendicular anisotropy, spectroscopic g-factor, and orbital magnetization -
of thin-film 3d transition metal alloys are determined over the full range of
alloy compositions via X-ray diffraction, magnetometry, and ferromagnetic
resonance measurements. We determine the interfacial perpendicular magnetic
anisotropy by use of samples sets with varying thickness for specific alloy
concentrations. The results agree with prior published data and theoretical
predictions. They provide a comprehensive compilation of the magnetic
properties of thin-film Ni-Co, Ni-Fe and Co-Fe alloys that goes well beyond the
often-cited Slater-Pauling dependence of magnetic moment on alloy
concentration.",1701.02177v1
2017-01-10,Current-driven skyrmion expulsion from magnetic nanostrips,"We study the current-driven skyrmion expulsion from magnetic nanostrips using
micromagnetic simulations and analytic calculations. We explore the threshold
current density for the skyrmion expulsion, and show that this threshold is
determined by the critical boundary force as well as the spin-torque
parameters. We also find the dependence of the critical boundary force on the
magnetic parameters; the critical boundary force decreases with increasing the
exchange stiffness and perpendicular anisotropy constants, while it increases
with increasing Dzyaloshinskii-Moriya interaction and saturation magnetization
constants. Using a simple model describing the skyrmion and locally-tilted edge
magnetization, we reveal the underlying physics of the dependence of the
critical boundary force on the magnetic parameters based on the relation
between the scaled Dzyaloshinskii-Moriya-interaction parameter and the critical
boundary force. This work provides a fundamental understanding of the skyrmion
expulsion and the interaction between the skymion and boundaries of devices and
shows that the stability of the skyrmion in devices can be related to the
scaled Dzyaloshinskii-Moriya-interaction parameter of magnetic materials.",1702.05672v2
2017-03-13,Field dependence of the magnetic correlations of the frustrated magnet SrDy$_2$O$_4$,"The frustrated magnet SrDy$_2$O$_4$ exhibits a field-induced phase with a
magnetization plateau at $1/3$ of the saturation value for magnetic fields
applied along the $b$-axis. We report here a neutron scattering study of the
nature and symmetry of the magnetic order in this field-induced phase. Below
$T\approx 0.5$ K, there are strong hysteretic effects, and the order is short
or long ranged for zero-field and field cooling, respectively. We find that the
long-range ordered magnetic structure within the zig-zag chains is identical to
that expected for the one-dimensional axial next-nearest neighbour Ising
(ANNNI) model in longitudinal field. The long-range ordered structure in field
contrasts with the short-range order found at zero field, and is probably
reached through enhanced quantum fluctuations with increasing fields.",1703.04430v2
2017-10-18,Magnetization plateau as a result of the uniform and gradual electron doping in a coupled spin-electron double-tetrahedral chain,"The double-tetrahedral chain in a longitudinal magnetic field, whose nodal
lattice sites occupied by the localized Ising spins regularly alternate with
triangular plaquettes with the dynamics described by the Hubbard model, is
rigorously investigated. It is demonstrated that the uniform change of electron
concentration controlled by the chemical potential in a combination with the
competition between model parameters and the external magnetic field leads to
the formation of one chiral and seven non-chiral phases at the absolute zero
temperature. Rational plateaux at one-third and one-half of the saturation
magnetization can also be identified in the low-temperature magnetization
curves. On the other hand, the gradual electron doping results in eleven
different ground-state regions which distinguish from each other by the
evolution of the electron distribution during this process. Several
doping-dependent magnetization plateaux are observed in the magnetization
process as a result of the continuous change of electron content in the model.",1710.06822v1
2017-10-20,Magnetic field amplification in supernova remnants,"Based on the new findings on the turbulent dynamo in \citet{XL16}, we examine
the magnetic field amplification in the context of supernova remnants. Due to
the strong ion-neutral collisional damping in the weakly-ionized interstellar
medium, the dynamo in the preshock turbulence remains in the damping kinematic
regime, which leads to {\it a linear-in-time growth of the magnetic field
strength}. The resultant magnetic field structure enables effective diffusion
upstream and shock acceleration of cosmic rays to energies above the ""knee"".
Differently, the nonlinear dynamo in the postshock turbulence leads to {\it a
linear-in-time growth of the magnetic energy} due to the turbulent magnetic
diffusion. Given a weak initial field strength in the postshock region, the
magnetic field saturates at a significant distance from the shock front as a
result of the inefficiency of the nonlinear dynamo. This result is in a good
agreement with existing numerical simulations and well explains the X-ray spots
detected far behind the shock front.",1710.07717v1
2019-09-23,Giant magnetocaloric effect in Co2FeAl Heusler alloy nanoparticles,"A giant magnetocaloric effect across the ferromagnetic (FM) to paramagnetic
(PM) phase transition was observed in chemically synthesized Co2FeAl Heusler
alloy nanoparticles with a mean diameter of 16 nm. In our previous report, we
have observed a significant enhancement in its saturation magnetization (Ms)
and Curie temperature (Tc) as compared with the bulk counterpart. Motivated
from those results, here, we aim to explore its magnetocaloric properties near
the Tc. The magnetic entropy change shows a positive anomaly at 1252 K.
Magnetic entropy change increases linearly with the magnetic field, and a large
value of ~15 J/Kg-K is detected under a moderate field of 14 kOe. It leads to a
net relative cooling power of 89 J/Kg for the magnetic field change of 14 kOe.
To confirm the nature of magnetic phase transition, a detailed study of its
magnetization is performed. The Arrott plot and nature of the universal curve
conclude that FM to PM phase transition in the present system is of
second-order.",1909.10201v4
2019-10-23,Computational screening of Fe-Ta hard magnetic phases,"In this work we perform a systematic calculation of the Fe-Ta phase diagram
to discover novel hard magnetic phases. By using structure prediction methods
based on evolutionary algorithms, we identify two new energetically stable
magnetic structures: a tetragonal Fe$_3$Ta (space group 122) and cubic Fe$_5$Ta
(space group 216) binary phases. The tetragonal structure is estimated to have
both high saturation magnetization ($\mu_0$M$_s$=1.14 T) and magnetocrystalline
anisotropy (K$_1$=2.17 MJ/m$^3$) suitable for permanent magnet applications.
The high-throughput screening of magneto-crystalline anisotropy also reveals
two low energy metastable hard magnetic phases: Fe$_5$Ta$_2$ (space group 156)
and Fe$_{6}$Ta (space group 194), that may exhibit intrinsic magnetic
properties comparable to SmCo$_5$ and Nd$_2$Fe$_{14}$B, respectively.",1910.10531v1
2019-11-12,Two Coupled Chains are Simpler than One: Field-induced Chirality in a Frustrated Quantum Spin Ladder,"Although the frustrated spin chain (zigzag chain) is a Drosophila of
frustrated magnetism, the understanding of a pair of coupled zigzag chains
(frustrated spin ladder) in a magnetic field is incomplete. We address this
problem through nuclear magnetic resonance (NMR) experiments on
$\text{BiCu}_2\text{PO}_6$ in magnetic fields up to 45 T, revealing a
field-induced spiral magnetic structure. Conjointly, we present advanced
numerical calculations showing that even moderate rung coupling dramatically
simplifies the phase diagram below half-saturation magnetization by stabilizing
a field-induced chiral phase. Surprisingly for a one-dimensional model, this
phase and its response to Dzyaloshinskii-Moriya (DM) interactions adhere to
classical expectations. While explaining the behavior at the highest accessible
magnetic fields, our results imply a different origin for the solitonic phases
occurring at lower fields in $\text{BiCu}_2\text{PO}_6$. An exciting
possibility is that the known, DM-mediated coupling between chirality and
crystal lattice gives rise to a new kind of spin-Peierls instability.",1911.05011v1
2020-01-07,Growth-sequence-dependent interface magnetism of SrIrO$_3$ - La$_{0.7}$Sr$_{0.3}$MnO$_3$ bilayers,"Bilayers of the oxide 3d ferromagnet La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) and
the 5d paramagnet SrIrO$_{3}$ (SIO) with large spin-orbit coupling (SOC) have
been investigated regarding the impact of interfacial SOC on magnetic order.
For the growth sequence of LSMO on SIO, ferromagnetism is strongly altered and
large out-of-plane-canted anisotropy associated with lacking magnetic
saturation up to 4 T has been observed. Thin bilayer films have been grown
coherently in both growth sequences on SrTiO$_3$ (001) by pulsed laser
deposition and structurally characterized by scanning transmission electron
microscopy (STEM) and x-ray diffraction (XRD). Measurements of magnetization
and field-dependent Mn L$_{2,3}$ edge x-ray magnetic circular dichroism (XMCD)
reveal changes of LSMO magnetic order which are strong in LSMO on SIO and weak
in LSMO underneath of SIO. We attribute the impact of the growth sequence to
the interfacial lattice structure/symmetry which is known to influence the
interfacial magnetic coupling.",2001.02083v1
2020-03-25,Two-photon driven magnon-pair resonance as a signature of spin-nematic order,"We theoretically study the nonlinear magnetic resonance driven by intense
laser or electromagnetic wave in a fully polarized frustrated magnet near a
less-visible spin-nematic ordered phase. In general, both magnons and magnon
pairs (two-magnon bound state) appear as the low-energy excitation in the
saturated state of spin-nematic magnets. Their excitation energies are usually
in terahertz (THz) or gigahertz range. Magnon pairs with angular momentum
2$\hbar$ can be excited by the simultaneous absorption of two photons, and such
multi-photon processes occur if the applied THz laser is strong enough. We
compute laser-driven magnetic dynamics of a frustrated four-spin system with
both magnon ($\hbar$) and magnon-pair (2$\hbar$) like excitations which is
analogous to a macroscopic frustrated magnet with a spin nematic phase. We
estimate the required strength of magnetic field of laser for the realization
of two photon absorption, taking into account dissipation effects with the
Lindblad equation. We show that intense THz laser with ac magnetic field of
0.1-1.0 Tesla is enough to observe magnon-pair resonance.",2003.11240v2
2020-04-28,Chiral symmetry breaking for deterministic switching of perpendicular magnetization by spin-orbit torque,"Symmetry breaking is a characteristic to determine which branch of a
bifurcation system follows upon crossing a critical point. Specifically, in
spin-orbit torque (SOT) devices, a fundamental question arises: how to break
the symmetry of the perpendicular magnetic moment by the in-plane spin
polarization? Here, we show that the chiral symmetry breaking by the DMI can
induce the deterministic SOT switching of the perpendicular magnetization. By
introducing a gradient of saturation magnetization or magnetic anisotropy,
non-collinear spin textures are formed by the gradient of effective SOT
strength, and thus the chiral symmetry of the SOT-induced spin textures is
broken by the DMI, resulting in the deterministic magnetization switching. We
introduce a strategy to induce an out-of-plane (z) gradient of magnetic
properties, as a practical solution for the wafer-scale manufacture of SOT
devices.",2004.13872v1
2020-06-29,Domain switching and exchange bias control by electric field in multiferroic conical magnet Mn$_2$GeO$_4$,"The electric field effect on magnetism was examined in the multiferroic
conical magnet Mn$_2$GeO$_4$, which shows a strong coupling between
ferromagnetic and ferroelectric order parameters. The systematic evaluation of
the electric polarization in the multiferroic phase below 5.5 K under various
field cooling conditions reveals that small magnetic fields of 0.1 T
significantly reduce the required electric fields needed to reach saturation.
By applying electric fields during magnetic field dependent hysteresis
measurements of magnetization M and polarization P an electrically controllable
exchange bias was observed, a phenomenon exceedingly rare in single phase
multiferroics. Furthermore, non-reversible electric switching of P and M
domains was achieved under specific magnetic field conditions.",2006.16080v1
2020-08-12,Prediction on Properties of Rare-earth 2-17-X Magnets Ce2Fe17-xCoxCN : A Combined Machine-learning and Ab-initio Study,"We employ a combination of machine learning and first-principles calculations
to predict magnetic properties of rare-earth lean magnets. For this purpose,
based on training set constructed out of experimental data, the machine is
trained to make predictions on magnetic transition temperature (Tc), largeness
of saturation magnetization ({\mu}0Ms), and nature of the magnetocrystalline
anisotropy (Ku). Subsequently, the quantitative values of {\mu}0Ms and Ku of
the yet-to-be synthesized compounds, screened by machine learning, are
calculated by first-principles density functional theory. The applicability of
the proposed technique of combined machine learning and first-principles
calculations is demonstrated on 2-17-X magnets, Ce2Fe17-xCoxCN. Further to this
study, we explore stability of the proposed compounds by calculating vacancy
formation energy of small atom interstitials (N/C). Our study indicates a
number of compounds in the proposed family, offers the possibility to become
solution of cheap, and efficient permanent magnet.",2008.05125v1
2020-09-24,Phase diagram of multi-layer ferromagnet system with dipole-dipole interaction,"We investigate various magnetic configurations caused by the dipole-dipole
interaction (DDI) in the thin-film magnet with the perpendicular anisotropy
under the open boundary conditions. Two different approaches are simulated: one
starts from a random magnetic configuration and decreases temperatures
step-wisely; the other starts from the saturated out-of-plane ferromagnetic
state to evaluate its metastability. As typical patterns of magnetic
configuration, five typical configurations are found: an out-of-plane
ferromagnetic, in-plane ferromagnetic, vortex, multi-domain, and canted
multi-domain states. Notably, the canted multi-domain forms a concentric
magnetic-domain-pattern with an in-plane vortex structure, resulting from the
open boundary conditions. Concerning to the coercivity, a comparison of the
magnetic configurations in both processes reveals that the out-of-plane
ferromagnetic state exhibits metastability in the multi-domain state, while not
in the vortex state. We also confirm that the so-called Neel-cap
magnetic-domain-wall structure, which is originally discussed in the in-plane
anisotropy system, appears at the multi-domain state.",2009.11574v1
2021-02-11,Defect-driven ferrimagnetism and hidden magnetization in MnBi$_2$Te$_4$,"MnBi$_2$Te$_4$ (MBT) materials are promising antiferromagnetic topological
insulators where field driven ferromagnetism is predicted to cause a transition
between axion insulator and Weyl semimetallic states. However, the presence of
antiferromagnetic coupling between Mn/Bi antisite defects and the main Mn layer
can reduce the low-field magnetization, and it has been shown that such defects
are more prevalent in the structurally identical trivial magnetic insulator
MnSb$_2$Te$_4$ (MST). We use high-field magnetization measurements to show that
the magnetization of MBT and MST occur in stages and full saturation requires
fields of~$\sim$~60 Tesla. As a consequence, the low-field magnetization
plateau state in MBT, where many determinations of quantum anomalous Hall state
are studied, actually consists of ferrimagnetic septuple blocks containing both
a uniform and staggered magnetization component.",2102.05797v2
2021-03-04,Strange electrical transport: Colossal magnetoresistance via avoiding fully polarized magnetization in ferrimagnetic insulator Mn3Si2Te6,"Colossal magnetoresistance is of great fundamental and technological
significance and exists mostly in the manganites and a few other materials.
Here we report colossal magnetoresistance that is starkly different from that
in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring
a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of
magnitude with an applied magnetic field above 9 Tesla, leading to an
insulator-metal transition at up to 130 K. However, the colossal
magnetoresistance occurs only when the magnetic field is applied along the
magnetic hard axis and is surprisingly absent when the magnetic field is
applied along the magnetic easy axis where magnetization is fully saturated.
The anisotropy field separating the easy and hard axes is 13 Tesla, unexpected
for the Mn ions with nominally negligible orbital momentum and spin-orbit
interactions. Double exchange and Jahn-Teller distortions that drive the
hole-doped manganites do not exist in Mn3Si2Te6. The phenomena fit no existing
models, suggesting a unique, intriguing type of electrical transport.",2103.02764v1
2021-09-13,Gradient soft magnetic materials produced by additive manufacturing from non-magnetic powders,"Additive manufacturing (AM) allows printing parts of complex geometries that
cannot be produced by standard technologies. Besides, AM provides the
possibility to create gradient materials with different structural and physical
properties. We, for the first time, printed gradient soft magnetic materials
from paramagnetic powders (316L steel and Cu-12Al-2Fe (in wt.%) aluminium
bronze)). The magnetic properties can be adjusted during the in-situ printing
process. The saturated magnetization value of alloys reaches 49 emu g^{-1}. The
changes in the magnetic properties have been attributed to the formation of the
BCC phase after mixing two FCC-dominated powders. Moreover, the phase
composition of the obtained gradient materials can be predicted with reasonable
accuracy by the CALPHAD approach, thus providing efficient optimization of the
performance. The obtained results provide new prospects for printing gradient
magnetic alloys.",2109.05947v1
2022-09-19,Dissipative magnetic structures and scales in small-scale dynamos,"Small-scale dynamos play important roles in modern astrophysics, especially
on Galactic and extragalactic scales. Owing to dynamo action, purely
hydrodynamic Kolmogorov turbulence hardly exists and is often replaced by
hydromagnetic turbulence. Understanding the size of dissipative magnetic
structures is important in estimating the time scale of Galactic scintillation
and other observational and theoretical aspects of interstellar and
intergalactic small-scale dynamos. Here we show that, during the kinematic
phase of the small-scale dynamo, the cutoff wavenumber of the magnetic energy
spectra scales as expected for large magnetic Prandtl numbers, but continues in
the same way also for moderately small values - contrary to what is expected.
For a critical magnetic Prandtl number of about 0.3, the dissipative and
resistive cutoffs are found to occur at the same wavenumber. In the nonlinearly
saturated regime, the critical magnetic Prandtl number becomes unity. The
cutoff scale now has a shallower scaling with magnetic Prandtl number below a
value of about three, and a steeper one otherwise compared to the kinematic
regime.",2209.08717v2
2022-12-22,Magnetic braking with MESA evolutionary models in the single star and LMXB regimes,"Magnetic braking has a prominent role in driving the evolution of close low
mass binary systems and heavily influences the rotation rates of low mass F-
and later type stars with convective envelopes. Several possible prescriptions
that describe magnetic braking in the context of 1D stellar evolution models
currently exist. We test four magnetic braking prescriptions against both low
mass X-ray binary orbital periods from the Milky Way and single star rotation
periods observed in open clusters. We find that data favors a magnetic braking
prescription that follows a rapid transition from fast to slow rotation rates,
exhibits saturated (inefficient) magnetic braking below a critical Rossby
number, and that is sufficiently strong to reproduce ultra compact X-ray binary
systems. Of the four prescriptions tested, these conditions are satisfied by a
braking prescription that incorporates the effect of high order magnetic field
topology on angular momentum loss. None of the braking prescriptions tested are
able to replicate the stalled spin down observed in open cluster stars aged 700
- 1000 Myr or so, with masses $\lesssim$ 0.8 $\rm M_{\odot}$.",2212.12037v3
2024-01-31,Tailoring magnetic and hyperthermia properties of biphase iron oxide nanocubes through post-annealing,"Tailoring the magnetic properties of iron oxide nanosystems is essential to
expand their biomedical applications. In this study, the 34 nm iron oxide
nanocubes with two phases consisting of Fe3O4 and alpha-Fe2O3 were annealed for
2 hours in the presence of O2, N2, He, and Ar to tune the respective phase
volume fractions and control the magnetic properties. X-ray diffraction and
magnetic measurements were carried out post-treatment to evaluate the changes
of the treated samples compared to the as-prepared, which showed an enhancement
of the alpha-Fe2O3 phase in the samples annealed with O2, while the others
indicated Fe3O4 enhancement. Furthermore, the latter samples indicated
enhancements in the crystallinity and saturation magnetization while coercivity
enhancement was most significant in the samples annealed with O2, resulting in
the highest specific absorption rates (up to 1000 W/g) in all the applied
fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia
measurements. The general enhancement in the specific absorption rate
post-annealing underscores the importance of the annealing atmosphere in the
enhancement of the magnetic and structural properties of nanostructures.",2401.18009v1
2024-02-05,Comprehensive study of magnetic field evolution in relativistic jets based on 2D simulations,"We use two-dimensional particle-in-cell simulations to investigate the
generation and evolution of the magnetic field associated with the propagation
of a jet for various initial conditions. We demonstrate that, in general, the
magnetic field is initially grown by the Weibel and Mushroom instabilities.
However, the field is saturated by the Alfv'en current limit. For initially
non-magnetized plasma, we show that the growth of the magnetic field is delayed
when the matter density of the jet environment is lower, which are in agreement
with simple analytical predictions. We show that the higher Lorentz factor
($\gtrsim 2$) prevents rapid growth of the magnetic fields. When the initial
field is troidal, the position of the magnetic filaments moves away from the
jet as the field strength increases. The axial initial field helps the jet
maintain its shape more effectively than the troidal initial field.",2402.02737v1
2022-12-07,Electronic and magnetic phase diagrams of Kitaev quantum spin liquid candidate Na$_2$Co$_2$TeO$_6$,"The 3$d^7$ Co$^{2+}$-based insulating magnet \NCTO{} has recently been
reported to have strong Kitaev interactions on a honeycomb lattice, and is thus
being considered as a Kitaev quantum spin liquid candidate. However, due to the
existence of other types of interactions, a spontaneous long-range magnetic
order occurs. This order is suppressed by applied magnetic fields leading to a
succession of phases and ultimately saturation of the magnetic moments. The
precise phase diagram, the nature of the phases, and the possibility that one
of the field-induced phases is a Kitaev quantum spin liquid phase are still a
matter of debate. Here we measured an extensive set of physical properties to
build the complete temperature-field phase diagrams to magnetic saturation at
10 T for magnetic fields along the $a$- and $a^*$-axes, and a partial phase
diagram up to 60 T along $c$. We probe the phases using magnetization, specific
heat, magnetocaloric effect, magnetostriction, dielectric constant, and
electric polarization, which is a symmetry-sensitive probe. With these
measurements we identify all the previously incomplete phase boundaries and
find new high-field phase boundaries. We find strong magnetoelectric coupling
in the dielectric constant and moderate magnetostrictive coupling at several
phase boundaries. Furthermore, we detect the symmetry of the magnetic order
using electrical polarization measurements under magnetic fields. Based on our
analysis, the absence of electric polarization under zero or finite magnetic
field in any of the phases or after...",2212.03849v3
2009-12-16,Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry,"A ratchet effect (the rectification of an ac injected current) which is
purely magnetic in origin has been observed in a superconducting-magnetic
nanostructure hybrid. The hybrid consists of a superconducting Nb film in
contact with an array of nanoscale magnetic triangles, circular rings or
elliptical rings. The arrays were placed into well-defined remanent magnetic
states by application of different magnetic field cycles. The stray fields from
these remanent states provide a magnetic landscape which influences the motion
of superconducting vortices. We examined both randomly varying landscapes from
demagnetized samples, and ordered landscapes from samples at remanence after
saturation in which the magnetic rings form parallel onion states containing
two domain walls. The ratchet effect is absent if the rings are in the
demagnetized state or if the vortices propagate parallel to the magnetic
reflection symmetry axis (perpendicular to the magnetic domain walls) in the
ordered onion state. On the other hand, when the vortices move perpendicular to
the magnetic reflection symmetry axis in the ordered onion state (parallel to
the domain walls) a clear ratchet effect is observed. This behavior differs
qualitatively from that observed in samples containing arrays of triangular Ni
nanostructures, which show a ratchet of structural origin.",0912.3193v1
2015-11-14,Magnetic field induced augmented thermal conduction phenomenon in magneto nanocolloids,"Magnetic field induced drastically augmented thermal conductivity of magneto
nanocolloids involving magnetic oxide nanoparticles, viz. Fe2O3, Fe3O4, Nickel
oxide (NiO), Cobalt oxide (Co3O4), dispersed in different base fluids (heat
transfer oil, kerosene, and ethylene glycol) have been reported. Experiments
reveal the augmented thermal transport under the external applied magnetic
field, with kerosene based MNCs showing at relatively low magnetic field
intensities as compared to the heat transfer oil and EG based MNCs. A maximum
thermal conductivity enhancement of 114 % is attained at 7.0 vol. %
concentration and 0.1 T field intensity for Fe3O4/EG magneto nanocolloid.
However, a maximum of 82% thermal conductivity enhancement is observed for
Fe3O4/Kerosene magneto nanocolloid for the same concentration but relatively at
low magnetic field (600 G). Thereby, a strong effect of fluid as well as
particle physical properties on the chain formation propensity, leading to
enhanced conduction, in such systems is observed. Co3O4 nanoparticles show
insignificant effect on the thermal conductivity enhancement of MNCs due to
their minimal magnetic moment. An analytical approach has been proposed to
understand the mechanism and physics behind the thermal conductivity
enhancement under external applied magnetic field, in tune with near field
magnetostatic interactions as well as Neel relaxivity of the magnetic
nanoparticles. Furthermore, the analytical model is able to predict the
phenomenon of enhanced thermal conductivity as a function of physical
parameters such as chain length, size and types of nanoparticles, fluid
characteristics, magnetic field intensity, saturation magnetic moment,
nanoparticle concentration etc. and good agreement with the experimental
results has been observed.",1511.04560v1
2015-12-23,Magnetic Ordering and Crystal Field Effects in Quasi Caged Structure Compound PrFe$_2$Al$_8$,"The compound PrFe$_2$Al$_8$ possesses a three-dimensional network structure
resulting from the packing of Al polyhedra centered at the transition metal
element Fe and the rare earth Pr. Along the $c$-axis, Fe and Pr form {\em
chains} which are separated from each other by the Al-network. In this paper,
the magnetism and crystalline electric field effects in PrFe$_2$Al$_8$ are
investigated through the analysis of magnetization and specific heat data. A
magnetic phase transition in the Pr lattice is identified at
$T^{Pr}_{N}\approx$ 4~K in dc magnetization and ac susceptibility data. At 2~K,
the magnetization isotherm presents a ferromagnetic saturation, however,
failing to reach full spin-only ferromagnetic moment of Pr$^{3+}$. Metamagnetic
step-like low-field features are present in the magnetization curve at 2~K
which is shown to shift upon field-cooling the material. Arrott plots centered
around $T^{Pr}_{N}$ display ""S""-like features suggestive of an inhomogeneous
magnetic state. The magnetic entropy, $S_m$, estimated from specific heat
outputs a value of $R$ ln(2) at $T_{N2}$ suggesting a doublet state for
Pr$^{3+}$. The magnetic specific heat is modeled by using a 9-level Schottky
equation pertinent to the Pr$^{3+}$ ion with $J$ = 4. Given the crystalline
electric field situation of Pr$^{3+}$, the inference of a doublet state from
specific heat and consequent long-range magnetic order is an unexpected result.",1512.07488v1
2018-06-02,Mechanically Induced Thermal Breakdown in Magnetic Shuttle Structures,"A theory of a thermally induced single-electron ""shuttling"" instability in a
magnetic nanomechanical device subject to an external magnetic field is
presented in the Coulomb blockade regime of electron transport. The model
magnetic shuttle device considered comprises a movable metallic grain suspended
between two magnetic leads, which are kept at different temperatures and
assumed to be fully spin polarized with antiparallel magnetizations. For a
given temperature difference shuttling is found to occur for a region of
external magnetic fields between a lower and an upper critical field strength,
which separate the shuttling regime from normal small-amplitude ""vibronic""
regimes. We find that (i) the upper critical magnetic field saturates to a
constant value in the high temperature limit and that the shuttle instability
domain expands with a decrease of the temperature, (ii) the lower critical
magnetic field depends not only on the temperature independent phenomenological
friction coefficient used in the model but also on intrinsic friction (which
vanishes in the high temperature limit) caused by magnetic exchange forces and
electron tunneling between the quantum dot and the leads. The feasibility of
using thermally driven magnetic shuttle systems to harvest thermal breakdown
phenomena is discussed.",1806.00633v1
2018-06-08,Real-Space Magnetic Imaging of the Multiferroic Spinels MnV2O4 and Mn3O4,"Controlling multiferroic behavior in materials will enable the development of
a wide variety of technological applications. However, the exact mechanisms
driving multiferroic behavior are not well understood in most materials. Two
such materials are the spinels MnV2O4 and Mn3O4, where mechanical strain is
thought to play a role in determining magnetic behavior. Bulk studies of MnV2O4
have yielded conflicting and inconclusive results, due in part to the presence
of mesoscale magnetic inhomogeneity, which complicates the interpretation of
bulk measurements. To study the sub-micron-scale magnetic properties of
Mn-based spinel materials, we performed magnetic force microscopy (MFM) on
MnV2O4 samples subject to different levels of mechanical strain. We also used a
crystal grain mapping technique to perform spatially registered MFM on Mn3O4.
These local investigations revealed 100-nm-scale ""stripe"" modulations in the
magnetic structure of both materials. In MnV2O4, the magnetization of these
stripes is estimated to be Mz $\approx$ 105 A/m, which is on the order of the
saturation magnetization reported previously. Cooling in a strong magnetic
field eliminated the stripe patterning only in the low-strain sample of MnV2O4.
The discovery of nanoscale magnetostructural inhomogeneity that is highly
susceptible to magnetic field control in these materials necessitates both a
revision of theoretical proposals and a reinterpretation of experimental data
regarding the low-temperature phases and magnetic-field-tunable properties of
these Mn-based spinels.",1806.03148v1
2019-03-02,Microwave excitations and hysteretic magnetization dynamics of stripe domain films,"FeNi films with the stripe domain (SD) pattern are prepared by
electrodeposition and sputtering methods. The magnetic domain, static magnetic
parameters, and quality factor, as well as dynamic properties of the two films,
are respectively performed. The results show the magnetizations of the film
were dependent on the direction of SD, and the rotation of the SD is lagging
behind the magnetization reversal. The microwave properties of the SD emerge
dynamic hysteresis before the saturation magnetic field. These microwave
properties are selectively excited with acoustic mode, optical mode, and
spin-wave mode. The frequency and intensity of different resonance modes of
stripe domain are determined by the local magnetization. The magnetization
variations and the rotation of SD of different modes are further illuminated by
the micromagnetic simulation. The magnetic anisotropy and the resonance
intensity of permeability of different modes were finally described by the
modified resonance equations.",1903.00656v2
2019-04-09,On the origin of the magnetic energy in the quiet solar chromosphere,"The presence of magnetic field is crucial in the transport of energy through
the solar atmosphere. Recent ground-based and space-borne observations of the
quiet Sun have revealed that magnetic field accumulates at photospheric
heights, via a local dynamo or from small-scale flux emergence events. However,
most of this small-scale magnetic field may not expand into the chromosphere
due to the entropy drop with height at the photosphere. Here we present a study
that uses a high resolution 3D radiative MHD simulation of the solar atmosphere
with non-grey and non-LTE radiative transfer and thermal conduction along the
magnetic field to reveal that: 1) the net magnetic flux from the simulated
quiet photosphere is not sufficient to maintain a chromospheric magnetic field
(on average), 2) processes in the lower chromosphere, in the region dominated
by magneto-acoustic shocks, are able to convert kinetic energy into magnetic
energy, 3) the magnetic energy in the chromosphere increases linearly in time
until the r.m.s. of the magnetic field strength saturates at roughly 4 to 30 G
(horizontal average) due to conversion from kinetic energy, 4) and that the
magnetic features formed in the chromosphere are localized to this region.",1904.04464v2
2019-05-31,Magnetic Anisotropy and Low Field Magnetic Phase Diagram of Quasi Two-Dimensional Ferromagnet Cr$_2$Ge$_2$Te$_6$,"In this work we present a comprehensive investigation on magnetic and
thermodynamic properties of the two-dimensional layered honeycomb system
Cr$_2$Ge$_2$Te$_6$. Using magnetization and specific heat measurements under
magnetic field applied along two crystallographic directions we obtain the
magnetic phase diagram for both directions. Cr$_2$Ge$_2$Te$_6$ is a ferromagnet
with a Curie temperature $T_C=65$ K and exhibits an easy magnetization axis
perpendicular to the structural layers in the $ab$-plane. Under magnetic fields
applied parallel to the hard plane $ab$ below the magnetic saturation, a
downturn with an onset temperature $T\textrm{*}$ is observed in the temperature
dependent magnetization curve. $T\textrm{*}$ shows a monotonous shift towards
lower temperatures with increasing field. The nature of this anisotropic and
specific behavior for fields in the hard plane is discussed as an interplay
among field, temperature and effective magnetic anisotropy. Similarities to
structurally related compounds such as CrX$_3$ (X = Br, I) hint towards a
universality of this behavior in ferromagnetic quasi two-dimensional honeycomb
materials.",1905.13609v2
2019-07-04,Micromagnetic modelling of magnetic domain walls and domains in cylindrical nanowires,"Magnetic cylindrical nanowires are very fascinating objects where the curved
geometry allows many novel magnetic effects and a variety of non-trivial
magnetic structures. Micromagnetic modelling plays an important role in
revealing the magnetization distribution in magnetic nanowires, often not
accessible by imaging methods with sufficient details. Here we review the
magnetic properties of the shape anisotropy-dominated nanowires and the
nanowires with competing shape and magnetocrystalline anisotropies, as revealed
by micromagnetic modelling. We discuss the variety of magnetic walls and
magnetic domains reported by micromagnetic simulations in cylindrical
nanowires. The most known domain walls types are the transverse and vortex
(Bloch point) domain walls and the transition between them is materials and
nanowire diameter dependent. Importantly, the field or current-driven domain
walls in cylindrical nanowires can achieve very high velocities. In recent
simulations of nanowires with larger diameter the skyrmion tubes are also
reported. In nanowires with large saturation magnetization the core of these
tubes may form a helicoidal ('corkscrew') structure. The topology of the
skyrmion tubes play an important role in the pinning mechanism, discussed here
on the example of FeCo modulated nanowires. Other discussed examples include
the influence of antinotches ('bamboo' nanowires) on the remanent magnetization
configurations for hcp Co and FeCo nanowires and Co-Ni multisegmented
nanowires.",1907.02318v1
2019-08-28,Non-monotonic response of a sheared magnetic liquid crystal to an external field,"Utilizing molecular dynamics simulations, we report a non-monotonic
dependence of the shear stress on the strength of an external magnetic field
($H$) in a liquid-crystalline mixture of magnetic and non-magnetic anisotropic
particles. This non-monotonic behavior is in sharp contrast with the
well-studied monotonic $H$-dependency of the shear stress in conventional
ferrofluids, where the shear stress increases with $H$ until it reaches a
saturation value. We relate the origin of this non-monotonicity to the
competing effects of particle alignment along the shear-induced direction, on
the one hand, and the magnetic field direction, on the other hand. To isolate
the role of these competing effects, we consider a two-component mixture
composed of particles with effectively identical steric interactions, where the
orientations of a small fraction, i.e.\ the magnetic ones, are coupled to the
external magnetic field. By increasing $H$ from zero, the orientations of the
magnetic particles show a Fr\'{e}ederickz-like transition and eventually start
deviating from the shear-induced orientation, leading to an increase in shear
stress. Upon further increase of $H$, a demixing of the magnetic particles from
the non-magnetic ones occurs which leads to a drop in shear stress, hence
creating a non-monotonic response to $H$. Unlike the equilibrium demixing
phenomena reported in previous studies, the demixing observed here is neither
due to size-polydispersity nor due to a wall-induced nematic transition. Based
on a simplified Onsager analysis, we rather argue that it occurs solely due to
packing entropy of particles with different shear- or magnetic-field-induced
orientations.",1908.10815v1
2019-12-10,Magnetic properties of thin epitaxial Pd$_{1-x}$Fe$_x$ alloy films,"In the paper we present the results of extensive studies of palladium-rich
Pd1-xFex alloy films epitaxially grown on MgO single-crystal substrate. In a
composition range of x = 0.01-0.07 these materials are soft ferromagnets, the
saturation magnetization and magnetic anisotropy of which can be tuned by its
composition. Vibrating sample magnetometry was used to study temperature
dependences of spontaneous magnetic moment and to establish the temperature of
magnetic ordering (Curie temperature). Ferromagnetic resonance (FMR)
measurements at low temperatures in the in-plane and out-of-plane geometries
revealed the four-fold in-plane magnetic anisotropy with the easy directions
along the <110> axes of the substrate. The modelling of the angular dependence
of the field for resonance allowed to extract the cubic and tetragonal
contributions to the magnetic anisotropy of the films and establish their
dependence on the concentration of iron in the alloy. Experimental data are
discussed in the framework of existing theories of dilute magnetic alloys.
Using the anisotropy constants established from FMR, the magnetic hysteresis
loops are reproduced utilizing the Stoner-Wohlfarth model thus indicating the
predominant coherent magnetic moment rotation at low temperatures. The obtained
results compile a database of magnetic properties of a palladium-iron alloy
considered as a material for superconducting spintronics.",1912.04852v1
2020-04-15,Synthesis optimization of Zn-Mn ferrites for magnetic fluid aplications,"Mn-Zn ferrite nanoparticles have been subject of increasing research due to
their desired properties for a wide range of applications. These properties
include nanometer particle size control, tunable magnetic properties and low
toxicity, providing these ferrites with the necessary requirements for cancer
treatment via magnetic hyperthermia. During this master thesis, powders of
Mn1-xZnxFe2O4 (x=0; 0.5; 0.8; 1) were synthesized via the sol-gel
autocombustion and hydrothermal methods, aiming to optimize their structural
and magnetic properties for further application in a ferrofluid. Samples were
characterized by XRD, SQUID, SEM, TEM and magnetic induction heating (MIH)
techniques. The XRD diffractograms of hydrothermally produced samples present
spinel crystal structure with high single-phase percentage (>88%). Rietveld
refinement and Williamson-Hall analysis reveal a decrease of lattice constant
and crystallite size with increase of Zn/Mn ratio. TEM images reveal narrow
particle size distributions and decrease of the mean particle size with
increase of Zn/Mn. SQUID results show that the increase of Zn results in a
decrease of saturation magnetization and remnant magnetization. More
noticeably, the M(T) curves present a shift in the samples magnetic ordering
temperature towards lower temperatures with the increase of Zn content, from
~556 to ~284 K. The MIH experiment also unveil a decrease in the heating rate
with the increase of Zn. Nanocrystals of Mn-Zn ferrite produced by hydrothermal
method present better crystallinity and magnetic properties than the sol-gel
auto-combustion samples. The hydrothermally synthesized samples revealed
dependence of its structural and magnetic properties with Mn/Zn ratio.The
magnetic ordering temperature of these ferrites can be used as a
self-controlled mechanism of heating, raising these ferrites to a class of
smart materials.",2004.07006v2
2021-04-08,Tailoring magnetization reversal of a single-domain bar nanomagnet via its end geometry,"Nanoscale single-domain bar magnets are building blocks for a variety of
fundamental and applied mesoscopic magnetic systems, such as artificial spin
ices, magnetic shape-morphing microbots as well as magnetic majority logic
gates. The magnetization reversal switching field of the bar nanomagnets is a
crucial parameter that determines the physical properties and functionalities
of their constituted artificial systems. Previous methods on tuning the
magnetization reversal switching field of a bar nanomagnet usually rely on
modifying its aspect ratio, such as its length, width and/or thickness. Here,
we show that the switching field of a bar nanomagnet saturates when extending
its length beyond a certain value, preventing further tailoring of the
magnetization reversal via aspect ratios. We showcase highly tunable switching
field of a bar nanomagent by tailoring its end geometry without altering its
size. This provides an easy method to control the magnetization reversal of a
single-domain bar nanomagnet. It would enable new research and/or applications,
such as designing artificial spin ices with additional tuning parameters,
engineering magnetic microbots with more flexibility as well as developing
magnetic quantum-dot cellular automata systems for low power computing.",2104.03517v1
2021-08-05,Metamagnetic Transitions in Few-Layer CrOCl Controlled by Magnetic Anisotropy Flipping,"The pivotal role of magnetic anisotropy in stabilising two-dimensional (2D)
magnetism has been widely accepted, however, direct correlation between
magnetic anisotropy and long-range magnetic ordering in the 2D limit is yet to
be explored. Here, using angle- and temperature-dependent tunnelling
magnetoresistance, we report unprecedented metamagnetic phase transitions in
atomically-thin CrOCl, triggered by magnetic easy-axis flipping instead of the
conventional spin flop mechanism. Few-layer CrOCl tunnelling devices of various
thicknesses consistently show an in-plane antiferromagnetic (AFM) ground state
with the easy axis aligned along the Cr-O-Cr direction (b-axis). Strikingly,
with the presence of a magnetic field perpendicular to the easy-axis (H||c),
magnetization of CrOCl does not follow the prevalent spin rotation and
saturation pattern, but rather exhibits an easy-axis flipping from the in-plane
to out-of-plane directions. Such magnetic anisotropy controlled metamagnetic
phase transitions are manifested by a drastic upturn in tun- nelling current,
which shows anomalous shifts towards higher H when temperature increases. By 2D
mapping of tunnelling currents as a function of both temperature and H, we
determine a unique ferrimagnetic state with a superstructure periodicity of
five unit cells after the field-induced metam- agnetic transitions. The
feasibility to control 2D magnetism by manipulating magnetic anisotropy may
open enormous opportunities in spin-based device applications.",2108.02825v1
2021-10-05,Thermal transport of the frustrated spin-chain mineral linarite: Magnetic heat transport and strong spin-phonon scattering,"The mineral linarite (PbCuSO$_4$(OH)$_2$) forms a monoclinic structure where
a sequence of Cu(OH)$_2$ units forms a spin-$\frac{1}{2}$ chain. Competing
ferromagnetic nearest-neighbor ($J_1$) and antiferromagnetic
next-nearest-neighbor interactions ($J_2$) in this quasi-one-dimensional spin
structure imply magnetic frustration and lead to magnetic ordering below $T_N
=$2.8 K in a mutliferroic elliptical spin-spiral ground state. Upon the
application of a magnetic field along the spin-chain direction, distinct
magnetically ordered phases can be induced. We studied the thermal conductivity
$\kappa$ in this material across the magnetic phase diagram as well as in the
paramagnetic regime in the temperature ranges 0.07-1 K and 9-300 K. We found
that in linarite the heat is carried mainly by phonons but shows a peculiar
non-monotonic behavior in field. In particular, $\kappa$ is highly suppressed
at the magnetic phase boundaries, indicative of strong scattering of the
phonons off critical magnetic fluctuations. Even at temperatures far above the
magnetically ordered phases, the phononic thermal conductivity is reduced due
to scattering off magnetic fluctuations. The mean free path due to spin-phonon
scattering ($l_{\text{spin-phonon}}$) was determined as function of
temperature. A power law behavior was observed mainly above 0.5 K indicating
the thermal activation of spin fluctuations. In the critical regime close to
the saturation field, $l_{\text{spin-phonon}}$ shows a $1/T$ dependence.
Furthermore, a magnon thermal transport channel was verified in the helical
magnetic phase. We estimate a magnon mean free path which corresponds to about
1000 lattice spacings.",2110.01865v1
2021-10-21,Shaping Magnetic Fields with Zero-Magnetic-Permeability Media,"Some of the most important technological challenges of today's society, such
as fusion reactors for future clean unlimited energy or the next generation of
medical imaging techniques, require precise spatial shapes of strong magnetic
fields. Achieving these high fields is currently hindered by limitations such
as large forces damaging the wires in coils or the saturation of ferromagnets
at high fields. Here we demonstrate a novel paradigm for creating magnetic
landscapes. By enclosing magnetic sources within zero-magnetic-permeability
(ZMP) media, a set of novel properties is unveiled. The magnetic field shape
directly results from the contour of the outer surface of the ZMP enclosure,
which allows the realization of basically any imaginable field landscape. Also,
currents embedded in ZMP media can be fully magnetically isolated, which
eliminates the forces in the wires, one of the main factors that currently
impedes achieving very high magnetic fields. We confirm these properties,
rooted in fundamental laws of electromagnetism, by numerical simulations and by
proof-of-principle experiments using conventional high-temperature
superconductors as ZMP materials, which showcase the practical applicability of
our ideas. The freedom in the design of magnetic fields provided by ZMP media
enables to concentrate and homogenize magnetic fields with unprecedented
precision, as needed in medical imaging techniques and particle-physics
experiments, and to realize devices like perfect electromagnetic absorbers of
mechanical vibrations.",2110.11257v1
2022-07-15,Controlling polarization of spintronic THz emitter by remanent magnetization texture,"Terahertz (THz) sciences and technologies have contributed to a rapid
development of a wide range of applications and expanded the frontiers in
fundamental science. Spintronic terahertz emitters offer conceptual advantages
since the spin orientation in the magnetic layer can be easily controlled
either by the externally applied magnetic field or by the internal magnetic
field distribution determined by the specific shape of the magnetic elements.
Here, we report a switchable terahertz source based on micropatterned magnetic
heterostructures driven by femtosecond laser pulses. We show that the precise
tunability of the polarization state is facilitated by the underlying
magnetization texture of the magnetic layer that is dictated by the shape of
the microstructure. These results also reveal the underlying physical
mechanisms of a nonuniform magnetization state on the generation of ultrafast
spin currents in the magnetic heterostructures. Our findings indicate that the
emission of the linearly polarized THz waves can be switched on and off by
saturating the sample using a biasing magnetic field, opening fascinating
perspectives for integrated on-chip THz devices with wide-ranging potential
applications.",2207.07707v1
2023-06-19,Transition between radial and toroidal orders in a trimer-based magnetic metasurface,"The change in the arrangement of magnetic dipole moments in a magnetic
metasurface, due to the influence of an external static magnetic field, is
discussed. Each meta-atom of the metasurface is composed of three identical
disk-shaped resonators (trimer) made of magnetically saturated ferrite. To
provide physical insight, full-wave numerical simulations of the near-fields
and transmission characteristics of the metasurface are complemented by the
theoretical description based on the multipole decomposition method. With these
methods, the study of eigenmodes and scattering conditions of a single magnetic
resonator, trimer, and their array forming the metasurface is performed. It is
found that the magnetic dipole-based collective hybrid mode of the trimer can
be gradually transformed from the radial (pseudomonopole) to azimuthal
(toroidal) order and vice versa by varying the bias magnetic field strength.
This is because the magnetic dipole moment of each individual disk constituting
the trimer undergoes rotation as the bias magnetic field strength changes. This
transition between two orders is accompanied by various patterns of
localization of the electric field inside the meta-atoms. Due to the unique
field configuration of these modes, the proposed metasurface can be considered
for designing magnetic field sensors and nonreciprocal devices.",2306.10776v2
2016-10-27,Magnetic activity in the HARPS M-dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK,"Atmospheric magnetic fields in stars with convective envelopes heat stellar
chromospheres. Starting with the historical Mount Wilson monitoring program,
CaH&K lines have been widely used to trace stellar magnetic activity, and as a
proxy for rotation period and consequently for stellar age. Monitoring stellar
activity has also become essential in filtering out false-positives due to
magnetic activity in extra-solar planet surveys. The Ca H&Kemission is
traditionally quantified through the R'HK-index, which compares the
chromospheric flux in the doublet to the overall bolometric flux of the star.
Much work has been done to characterize this index for FGK-dwarfs, but M-dwarfs
were left out of these analyses and no calibration of their Ca ii H&K emission
to an R'HK exists to date. We set out to characterize the magnetic activity of
the low and very low-mass stars by providing a calibration of the R'HK-index
that extends to the realm of M-dwarfs, and by evaluating the relation between
R'HK and the rotation period. We calibrated the bolometric and photospheric
factors for M-dwarfs to properly transform the S-index into the R'HK. We
monitored magnetic activity through the Ca ii H&K emission lines in the HARPS
M-dwarf sample. The R'HK index, like the fractional X-ray luminosity L_X/Lbol,
shows a saturated correlation with rotation, with saturation setting in around
a ten days rotation period. Above that period, slower rotators show weaker Ca
ii activity, as expected. Under that period, the R'HK index saturates to
~10^-4. Stellar mass modulates the Ca ii activity, with R'HK showing a constant
basal activity above 0.6Msun and then decreasing with mass between 0.6Msun and
the fully-convective limit of 0.35Msun. Short-term variability of the activity
correlates with its mean level, stars with higher R'HK index show larger R'HK
variability, as previously observed for earlier spectral types.",1610.09007v2
2023-04-14,Effect of magnetic fields on the dynamics and gravitational wave emission of PPI-saturated self-gravitating accretion disks: simulations in full GR,"We explore the effect magnetic fields have on self-gravitating accretion
disks around spinning black holes via numerical evolutions in full dynamical
magnetohydrodynamic spacetimes. The configurations we study are unstable to the
Papaloizou-Pringle Instability (PPI). PPI-saturated accretion tori have been
shown to produce gravitational waves, detectable to cosmological distances by
third-generation gravitational wave (GW) observatories. While the PPI operates
strongly for purely hydrodynamic disks, the situation can be different for
disks hosting initially small magnetic fields. Evolutions of disks without
self-gravity in fixed BH spacetimes have shown that small seed fields can
initiate the rapid growth of the magneto-rotational instability (MRI), which
then strongly suppresses the PPI. Since realistic astrophysical disks are
expected to be magnetized, PPI-generated GW signals may be suppressed as well.
However, it is unclear what happens when the disk self-gravity is restored.
Here, we study the impact of magnetic fields on the PPI-saturated state of a
self-gravitating accretion disk around a spinning BH ($\chi = 0.7$) aligned
with the disk angular momentum, as well as one around a non-spinning BH. We
find the MRI is effective at reducing the amplitude of PPI modes and their
associated GWs, but the systems still generate GWs. Estimating the
detectability of these systems accross a wide range of masses, we show that
magnetic fields reduce the maximum detection distance by Cosmic Explorer from
300Mpc (in the pure hydrodynamic case) to 45Mpc for a $10 M_{\odot}$ system, by
LISA from 11500Mpc to 2700Mpc for a $2 \times 10^{5} M_{\odot}$ system, and by
DECIGO from $z \approx 5$ down to $z \approx 2$ for a $1000 M_{\odot}$ system.",2304.07282v2
2002-10-29,Evidence for the formation of magnetic moments in the cuprate superconductor Hg$_{0.8}$Cu$_{0.2}$Ba$_2$Ca$_2$Cu$_3$O$_{8+δ}$ below $T_c$ seen by NQR,"We report pure zero field nuclear magnetic resonance (NQR) measurements on
the optimally doped three layer high-$ T_{c} $-compounds HgBaCaCuO and
HgBaCaCuO(F) with $T_c$ 134 K. Above $ T_{c}$ two Cu NQR line pairs are
observed in the spectra corresponding to the two inequivalent Cu lattice sites.
Below $ T_{c}$ the Cu NQR spectra show additional lines leading to the extreme
broadened Cu NQR spectra at 4.2 K well known for the HgBaCaCuO compounds. The
spin-lattice relaxation curves follow a triple exponential function with
coefficients depend onto the saturation time (number of saturation pulses),
whereas the spin-spin relaxation curve is described by a single exponential
function. From the spin-lattice relaxation we deduced a complete removal of the
Kramers degeneracy of the Cu quadrupole indicating that the additional lines
are due to a Zeemann splitting of the $^{63/65}$Cu lines due to the spontaneous
formation of magnetic moments within the CuO layers. Below 140 K, the spectra
are well fitted by a number of 6 $^{63/65}$Cu line pairs. From the number of
the Cu lines, the position of the lines relative to each other and the complete
removal of the Kramers degeneracy we deduced an orientation of the magnetic
moments parallel to the symmetry axis of the electric field gradient tensor
with magnitudes of the order of 1000 G. We also discuss the possible
microscopic origin of the observed internal magnetic fields.",0210652v2
2006-12-27,"Peculiarities of the transport properties of InMnAs layers, produced by the laser deposition, in strong magnetic fields","Magnetotransport properties of p-InMnAs layers are studied in pulsed magnetic
fields up to 30 T. Samples were prepared by the laser deposition and annealed
by ruby laser pulses. Well annealed samples show p-type conductivity while they
were n-type before the annealing. Surprisingly the anomalous Hall effect
resistance in paramagnetic state (T>40 K) and in strong magnetic fields (B > 20
T) appears to be greater than that in ferromagnetic state (T <= 40 K), while
the longitudinal resistance rises with the temperature decrease. The negative
magnetoresistance saturates in magnetic fields higher then 10T at T near 4 K
only, whereas the saturation fields of the anomalous Hall effect resistance are
much less (around 2 T at 30K). The total reduction of resistance exceeds 10
times in magnetic fields around of 10T. The obtained results are interpreted on
the base of the assumptions of the non-uniform distribution of Mn atoms acting
as acceptors, the local ferromagnetic transition and the percolation-like
character of the film conductivity, which prevailed under conditions of the
strong fluctuations of the exchange interaction. Characteristic scales of the
magneto-electric nonuniformity are estimated using analysis of the mesoscopic
fluctuations of the non-diagonal components of the magnetoresistivity tensor.",0612641v1
2007-12-19,Nonlinear Simulations of the Heat Flux Driven Buoyancy Instability and its Implications for Galaxy Clusters,"In low collisionality plasmas heat flows almost exclusively along magnetic
field lines, and the condition for stability to convection is modified from the
standard Schwarzschild criterion. We present local two and three-dimensional
simulations of a new heat flux driven buoyancy instability (the HBI) that
occurs when the temperature in a plasma decreases in the direction of gravity.
We find that the HBI drives a convective dynamo that amplifies an initially
weak magnetic field by a factor of ~20. In simulations that begin with the
magnetic field aligned with the temperature gradient, the HBI saturates by
rearranging the magnetic field lines to be almost purely perpendicular to the
initial temperature gradient. This magnetic field reorientation results in a
net heat flux through the plasma that is less than 1% of the field-free
(Spitzer) value. We show that the HBI is likely to be present in the cool cores
of clusters of galaxies between ~0.1-100 kpc, where the temperature increases
outwards. The saturated state of the HBI suggests that inward thermal
conduction from large radii in clusters is unlikely to solve the cooling flow
problem. Finally, we also suggest that the HBI may contribute to suppressing
conduction across cold fronts in galaxy clusters.",0712.3048v1
2012-10-01,Unconventional quantum ordered and disordered states in the highly frustrated spin-1/2 Ising-Heisenberg model on triangles-in-triangles lattices,"Ground state and thermodynamics of geometrically frustrated spin-1/2
Ising-Heisenberg model on two different but topologically related
triangles-in-triangles lattices is investigated in particular. A rigorous
mapping based on generalized star-triangle transformations enables one to
derive exact analytical results for the free and internal energy, spontaneous
magnetization, entropy and specific heat from the known exact results for the
corresponding spin-1/2 Ising model on a triangular lattice. It is demonstrated
that several unconventional quantum ordered and disordered phases may become
the ground state in addition to the classical ferromagnetic phase with a
perfect alignment of all constituent spins. A mutual competition between the
ferromagnetic Ising and XXZ Heisenberg interactions may lead to an appearance
of a peculiar quantum ferromagnetic phase, in which the magnetic moment of the
Heisenberg spins undergoes a quantum reduction to one third of the saturation
value in contrast with the fully saturated magnetic moment of the classical
Ising spins. In the highly frustrated regime, we have found either the
disordered quantum paramagnetic phase with the substantial residual entropy or
a similar but strikingly spontaneously long-range ordered phase, in which a
quantum reduction of the magnetic moment of the Heisenberg spins causes a small
quantum reduction of the magnetic moment of otherwise purely classical Ising
spins. It is evidenced that the specific heat exhibits diverse thermal
dependences with or without a logarithmic divergence superimposed either on one
or two round Schottky-type maxima.",1210.0337v3
2013-05-15,"Structural ordering driven anisotropic magnetoresistance, anomalous Hall resistance and its topological overtones in full-Heusler Co2MnSi thin films","We report the evolution of crystallographic structure, magnetic ordering and
electronic transport in thin films of full-Heusler alloy Co$_2$MnSi deposited
on (001) MgO with annealing temperatures ($T_A$). By increasing the $T_A$ from
300$^\circ$C to 600$^\circ$C, the film goes from a disordered nanocrystalline
phase to $B2$ ordered and finally to the $L2_1$ ordered alloy. The saturation
magnetic moment improves with structural ordering and approaches the
Slater-Pauling value of $\approx 5.0 \mu_B$ per formula unit for $T_A$ =
600$^\circ$C. At this stage the films are soft magnets with coercive and
saturation fields as low as $\approx$ 7 mT and 350 mT, respectively. Remarkable
effects of improved structural order are also seen in longitudinal resistivity
($\rho_{xx}$) and residual resistivity ratio. A model based upon electronic
transparency of grain boundaries illucidates the transition from a state of
negative $d\rho/dT$ to positive $d\rho/dT$ with improved structural order. The
Hall resistivity ($\rho_{xy}$) derives contribution from the normal scattering
of charge carriers in external magnetic field, the anomalous effect originating
from built-in magnetization and a small but distinct topological Hall effect in
the disordered phase. The carrier concentration ($n$) and mobility ($\mu$) have
been extracted from the high field $\rho_{xy}$ data. The highly ordered films
are characterized by $n$ and $\mu$ of 1.19$\times$ 10$^{29}$ m$^{-3}$ and 0.4
cm$^2V^{-1}s^{-1}$ at room temperature. The dependence of $\rho_{xy}$ on
$\rho_{xx}$ indicates the dominance of skew scattering in our films, which
shows a monotonic drop on raising the $T_A$. The topological Hall effect is
analyzed for the films annealed at 300$^\circ$C. ......",1305.3453v1
2016-11-29,Critical quench dynamics of random quantum spin chains: Ultra-slow relaxation from initial order and delayed ordering from initial disorder,"By means of free fermionic techniques combined with multiple precision
arithmetic we study the time evolution of the average magnetization,
$\overline{m}(t)$, of the random transverse-field Ising chain after global
quenches. We observe different relaxation behaviors for quenches starting from
different initial states to the critical point. Starting from a fully ordered
initial state, the relaxation is logarithmically slow described by
$\overline{m}(t) \sim \ln^a t$, and in a finite sample of length $L$ the
average magnetization saturates at a size-dependent plateau $\overline{m}_p(L)
\sim L^{-b}$; here the two exponents satisfy the relation $b/a=\psi=1/2$.
Starting from a fully disordered initial state, the magnetization stays at zero
for a period of time until $t=t_d$ with $\ln t_d \sim L^{\psi}$ and then starts
to increase until it saturates to an asymptotic value $\overline{m}_p(L) \sim
L^{-b'}$, with $b'\approx 1.5$. For both quenching protocols, finite-size
scaling is satisfied in terms of the scaled variable $\ln t/L^{\psi}$.
Furthermore, the distribution of long-time limiting values of the magnetization
shows that the typical and the average values scale differently and the average
is governed by rare events. The non-equilibrium dynamical behavior of the
magnetization is explained through semi-classical theory.",1611.09495v2
2018-09-22,Large magnetic thermal conductivity induced by frustration in low-dimensional quantum magnets,"We study the magnetic field-dependence of the thermal conductivity due to
magnetic excitations in frustrated spin-1/2 Heisenberg chains. Near the
saturation field, the system is described by a dilute gas of weakly-interacting
fermions (free-fermion fixed point). We show that in this regime the thermal
conductivity exhibits a non-monotonic behavior as a function of the ratio
$\alpha= J_2/J_1$ between second and first nearest-neighbor antiferromagnetic
exchange interactions. This result is a direct consequence of the splitting of
the single-particle dispersion minimum into two minima that takes place at the
Lifshitz point $\alpha=1/4$. Upon increasing $\alpha$ from zero, the inverse
mass vanishes at $\alpha=1/4$ and it increases monotonically from zero for
$\alpha \geq 1/4$. By deriving an effective low-energy theory of the dilute gas
of fermions, we demonstrate that the Drude weight $K_{\rm th}$ of the thermal
conductivity exhibits a similar dependence on $\alpha$ near the saturation
field. Moreover, this theory predicts a transition between a two-component
Tomonaga-Luttinger liquid and a vector-chiral phase at a critical value
$\alpha=\alpha_c$ that agrees very well with previous density matrix
renormalization group results. We also show that the resulting curve $K_{\rm
th}(\alpha)$ is in excellent agreement with exact diagonalization (ED) results.
Our ED results also show that $K_{\rm th}(\alpha)$ has a pronounced minimum at
$\alpha\simeq 0.7$ and it decreases for sufficiently large $\alpha$ at lower
magnetic field values. We also demonstrate that the thermal conductivity is
significantly affected by the presence of magnetothermal coupling.",1809.08429v1
2018-11-29,"High Saturation Magnetization, Low Coercivity and Fine YIG Nanoparticles Prepared by Modifying Co-Precipitation Method","Nanoparticles with their specific properties newly have drawn a great deal of
attention of researchers [1-3]Yttrium iron Garnet magnetic nanoparticles
(YIG-NPs) are promising materials with novel applications in microwave,
spintronics, magnonics, and magneto-optical devices. However, achieving stable
and remarkable magnetic YIG-NPs has been remaining as a great challenge. In
this paper, synthesized YIG-NPs by modifying co-precipitation (MCP) method is
reported. Structural and magnetic properties of final products are compared to
those of the materials prepared by citrate-nitrate (CN) method. Smaller
crystals and particle size have been found by MCP method comparing to that of
synthesized by CN method. Using a relatively low annealing temperatures for
both sets of samples (~700 {\deg}C), the final YIG samples prepared by MCP
method show more structural purity than those made by CN method. Higher
saturation magnetization (Ms) and lower coercivity (Hc) are observed in MCP YIG
sample (23.23 emu/g 36 and 30.1 Oe) than the CN prepared YIG sample (16.43
emu/g and 44.95 Oe). The Curie temperature is measured to be 569 {\deg}C for
the MCP YIG sample determined from set of Ms measurement at different
temperatures ranging from 80-600 K. These findings lead to significant
improvement in quality of synthesized (synthetic methods) of YIG-NPs.",1811.12511v1
2018-11-29,Structural and Magnetic Study of Metallo-Organic YIG Powder Using 2-ethylhexanoate Carboxylate Based Precursors,"The crystallization and magnetic behavior of yttrium iron garnet (YIG)
prepared by metallo-organic decomposition (MOD) method are discussed. The
chemistry and physics related to synthesis of iron and yttrium carboxylates
based on 2-ethylhexanoic acid (2EHA) are studied, since no literature was found
which elucidates synthesis of metallo-organic precursor of YIG in spite of the
literatures of doped YIG samples such as Bi-YIG. Typically, the metal
carboxylates used in preparation of ceramic oxide materials are
2-ethylhexanoate (2EH) solvents. Herein, the synthesis, thermal behavior and
solubility of yttrium and iron 2EH used in synthesis of YIG powder by MOD are
reported. The crystallization and magnetic parameters, including saturation
magnetization and coercivity of these samples, smoothly change as a function of
the annealing temperature. It is observed that high sintering temperature of
1300 to 1400 {\deg}C promotes the diffraction peaks of YIG, therefore, we can
conclude that the formation of YIG in MOD method increases the crystallization
temperature. The maximum value of saturation magnetization and minimum value of
coercivity and remanence are observed for the sample sintered at 1200{\deg}C
which are 13.7 emu/g, 10.38 Oe and 1.5 emu/g, respectively. This study cites
the drawbacks in chemical synthesis of metallo-organic based YIG production.",1811.12514v1
2019-01-09,"The magnetic phase diagram of the frustrated spin chain compound linarite, PbCuSO$_4$(OH)$_2$, as seen by neutron diffraction and $^1$H-NMR","We report on a detailed neutron diffraction and $^1$H-NMR study on the
frustrated spin-1/2 chain material linarite, PbCuSO$_4$(OH)$_2$, where
competing ferromagnetic nearest neighbor and antiferromagnetic next-nearest
neighbor interactions lead to frustration. From the magnetic Bragg peak
intensity studied down to 60 mK, the magnetic moment per Cu atom is obtained
within the whole magnetic phase diagram for $H \parallel b$ axis. Further, we
establish the detailed configurations of the shift of the SDW propagation
vector in phase V with field and temperature. Finally, combining our neutron
diffraction results with those from a low-temperature/high-field NMR study we
find an even more complex phase diagram close to the quasi-saturation field
suggesting that bound two-magnon excitations are the lowest energy excitations
close to and in the quasi-saturation regime. Qualitatively and
semi-quantitatively, we relate such behavior to $XYZ$ exchange anisotropy and
contributions from the Dzyaloshinsky-Moriya interaction to affect the magnetic
properties of linarite.",1901.02842v1
2019-06-02,"Structural and magnetic properties of $La_{0.67}Ca_{0.33}MnO_3$ (D = Ca, Sr, Ba) manganites prepared by Ball milling","In this research, we report on the synthesis and characterization of
$La_{0.67}Ca_{0.33}MnO_3$ (LCMO), $La_{0.67}Ba_{0.33}MnO_3$ (LBMO), and
$La_{0.67}Sr_{0.33}MnO_3$ (LSMO) perovskites. Precursor powders for the
perovskite samples were prepared using ball mailing technique. The resulting
powder was pressed into disks which were subsequently sintered at 1000 C for
2h. The structural characteristics of the prepared samples were investigated
using X-ray diffraction (XRD) and scanning electron microscope (SEM), and the
magnetic properties were investigated using vibrating sample magnetometry
(VSM). XRD pattern of LCMO sample revealed a pure perovskite phase with Pnma
space group, while the pattern of LSMO sample revealed a pure perovskite with
R3c$^-$ space group. XRD pattern of LBMO sample, however, demonstrated the
presence of a major perovskite phase with R3c$^-$ symmetry, together with a
secondary $BaMnO_3$ phase. This secondary phase disappeared upon sintering LBMO
at a higher temperature of 1100 C. Isothermal magnetic measurements and
thermomagnetic curves revealed that LCMO was paramagnetic at room temperature.
However, LSMO exhibited soft ferromagnetic behavior at room temperature, with
Tc = 380 K and Ms = 50.9 emu/g. Also, LBMO sample sintered at 1000 C exhibited
soft ferromagnetic behavior at room temperature, with Curie temperature Tc =
343 K and a rather low saturation magnetization of Ms = 30.7 emu/g. The higher
sintering temperature of LBMO compound resulted in a significant increase of
the saturation magnetization to 50.8 emu/g for the sample sintered at 1100 C.",1906.00407v1
2020-02-06,"Effects of transition-metal spacers on the spin-orbit torques, spin Hall magnetoresistance, and magnetic anisotropy of Pt/Co bilayers","We studied the effect of inserting 0.5 nm-thick spacer layers (Ti, V, Cr, Mo,
W) at the Pt/Co interface on the spin-orbit torques, Hall effect,
magnetoresistance, saturation magnetization, and magnetic anisotropy. We find
that the damping-like spin-orbit torque decreases substantially for all samples
with a spacer layer compared to the reference Pt/Co bilayer, consistently with
the opposite sign of the atomic spin-orbit coupling constant of the spacer
elements relative to Pt. The reduction of the damping-like torque is monotonic
with atomic number for the isoelectronic 3d, 4d, and 5d elements, with the
exception of V that has a stronger effect than Cr. The field-like spin-orbit
torque almost vanishes for all spacer layers irrespective of their composition,
suggesting that this torque predominantly originates at the Pt/Co interface.
The anomalous Hall effect, magnetoresistance, and saturation magnetization are
also all reduced substantially, whereas the sheet resistance is increased in
the presence of the spacer layer. Finally, we evidence a correlation between
the amplitude of the spin-orbit torques, the spin Hall-like magnetoresistance,
and the perpendicular magnetic anisotropy. These results highlight the
significant influence of ultrathin spacer layers on the magnetotransport
properties of heavy metal/ferromagnetic systems.",2002.02162v1
2020-12-15,Induced anomalous Hall effect of massive Dirac fermions in ZrTe5 and HfTe5 thin flakes,"Researches on anomalous Hall effect (AHE) have been lasting for a century to
make clear the underlying physical mechanism. Generally, the AHE appears in
magnetic materials, in which extrinsic process related to scattering effects
and intrinsic contribution connected with Berry curvature are crucial.
Recently, AHE has been counterintuitively observed in non-magnetic topological
materials and attributed to the existence of Weyl points. However, the Weyl
point scenario would lead to unsaturated AHE even in large magnetic fields and
contradicts the saturation of AHE in several tesla (T) in experiments. In this
work, we investigate the Hall effect of ZrTe5 and HfTe5 thin flakes in static
ultrahigh magnetic fields up to 33 T. We find the AHE saturates to 55 (70)
Ohm^-1*cm^-1 for ZrTe5 (HfTe5) thin flakes above ~ 10 T. Combining detailed
magnetotransport experiments and Berry curvature calculations, we clarify that
the splitting of massive Dirac bands without Weyl points can be responsible for
AHE in non-magnetic topological materials ZrTe5 and HfTe5 thin flakes. This
model can identify our thin flake samples to be weak topological insulators and
serve as a new tool to probe the band structure topology in topological
materials.",2012.08188v1
2021-09-15,Formation and evolution of protostellar accretion discs. II. From 3D simulation to a simple semi-analytic model of Class 0/I discs,"We use a 3D radiative non-ideal magnetohydrodynamic (MHD) simulation to
investigate the formation and evolution of a young protostellar disc from a
magnetized pre-stellar core. The simulation covers the first ${\sim}10~{\rm
kyr}$ after protostar formation, and shows a massive, weakly magnetized disc
with radius that initially grows and then saturates at ${\sim}30~{\rm au}$. The
disc is gravitationally unstable with prominent large-amplitude spiral arms. We
use our simulation results and a series of physical arguments to construct a
predictive and quantitative physical picture of Class 0/I protostellar disc
evolution from several aspects, including (i) the angular-momentum
redistribution in the disc, self-regulated by gravitational instability to make
most of the disc marginally unstable; (ii) the thermal profile of the disc,
well-approximated by a balance between radiative cooling and accretion heating;
and (iii) the magnetic-field strength and magnetic-braking rate inside the
disc, regulated by non-ideal magnetic diffusion. Using these physical insights,
we build a simple 1D semi-analytic model of disc evolution. We show that this
1D model, when coupled to a computationally inexpensive simulation for the
evolution of the surrounding pseudodisc, can be used reliably to predict disc
evolution in the Class 0/I phase. The predicted long-term evolution of disc
size, which saturates at ${\sim}30~{\rm au}$ and eventually shrinks, is
consistent with a recent observational survey of Class 0/I discs. Such
hierarchical modelling of disc evolution circumvents the computational
difficulty of tracing disc evolution through Class 0/I phase with direct,
numerically converged simulations.",2109.07535v1
2023-09-01,Saturation of the anomalous Hall effect at high magnetic fields in altermagnetic RuO2,"Observations of the anomalous Hall effect in RuO$_2$ and MnTe have
demonstrated unconventional time-reversal symmetry breaking in the electronic
structure of a recently identified new class of compensated collinear magnets,
dubbed altermagnets. While in MnTe the unconventional anomalous Hall signal
accompanied by a vanishing magnetization is observable at remanence, the
anomalous Hall effect in RuO$_2$ is excluded by symmetry for the N\'eel vector
pointing along the zero-field [001] easy-axis. Guided by a symmetry analysis
and ab initio calculations, a field-induced reorientation of the N\'eel vector
from the easy-axis towards the [110] hard-axis was used to demonstrate the
anomalous Hall signal in this altermagnet. We confirm the existence of an
anomalous Hall effect in our RuO$_2$ thin-film samples whose set of magnetic
and magneto-transport characteristics is consistent with the earlier report. By
performing our measurements at extreme magnetic fields up to 68 T, we reach
saturation of the anomalous Hall signal at a field $H_{\rm c} \simeq$ 55 T that
was inaccessible in earlier studies, but is consistent with the expected
N\'eel-vector reorientation field.",2309.00568v1
2017-10-17,Rapid and Quantitative Chemical Exchange Saturation Transfer (CEST) Imaging with Magnetic Resonance Fingerprinting (MRF),"Purpose: To develop a fast magnetic resonance fingerprinting (MRF) method for
quantitative chemical exchange saturation transfer (CEST) imaging.
  Methods: We implemented a CEST-MRF method to quantify the chemical exchange
rate and volume fraction of the N${\alpha}$-amine protons of L-arginine (L-Arg)
phantoms and the amide and semi-solid exchangeable protons of in vivo rat brain
tissue. L-Arg phantoms were made with different concentrations (25-100 mM) and
pH (pH 4-6). The MRF acquisition schedule varied the saturation power randomly
for 30 iterations (phantom: 0-6 ${\mu}$T; in vivo: 0-4 ${\mu}$T) with a total
acquisition time of <=2 minutes. The signal trajectories were pattern-matched
to a large dictionary of signal trajectories simulated using the
Bloch-McConnell equations for different combinations of exchange rate,
exchangeable proton volume fraction, and water T1 and T2* relaxation times.
  Results: The chemical exchange rates of the N${\alpha}$-amine protons of
L-Arg were significantly (p<0.0001) correlated with the rates measured with the
Quantitation of Exchange using Saturation Power method. Similarly, the L-Arg
concentrations determined using MRF were significantly (p<0.0001) correlated
with the known concentrations. The pH dependence of the exchange rate was well
fit (R2=0.9186) by a base catalyzed exchange model. The amide proton exchange
rate measured in rat brain cortex (36.3+-12.9 Hz) was in good agreement with
that measured previously with the Water Exchange spectroscopy method (28.6+-7.4
Hz). The semi-solid proton volume fraction was elevated in white (11.2+-1.7%)
compared to gray (7.6+-1.8%) matter brain regions in agreement with previous
magnetization transfer studies.
  Conclusion: CEST-MRF provides a method for fast, quantitative CEST imaging.",1710.06054v2
2022-08-10,Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF,"We constrain the orbital period ($P_{\rm orb}$) distribution of low-mass
detached main-sequence eclipsing binaries (EBs) with light curves from the
Zwicky Transient Facility (ZTF), which provides a well-understood selection
function and sensitivity to faint stars. At short periods ($P_{\rm orb}\lesssim
2$ days), binaries are predicted to evolve significantly due to magnetic
braking (MB), which shrinks orbits and ultimately brings detached binaries into
contact. The period distribution is thus a sensitive probe of MB. We find that
the intrinsic period distribution of low-mass ($0.1\lesssim M_1/M_{\odot} <
0.9$) binaries is basically flat (${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm
orb}^0$), from $P_{\rm orb}=10$ days down to the contact limit. This is
strongly inconsistent with predictions of classical MB models based on the
Skumanich relation, which are widely used in binary evolution calculations and
predict ${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm orb}^{7/3}$ at short
periods. The observed distributions are best reproduced by models in which the
magnetic field saturates at short periods, with a MB torque that scales roughly
as $\dot{J}\propto P_{\rm orb}^{-1}$, as opposed to $\dot{J} \propto P_{\rm
orb}^{-3}$ in the standard Skumanich law. We also find no significant
difference between the period distributions of binaries containing fully and
partially convective stars. Our results confirm that a saturated MB law, which
was previously found to describe the spin-down of rapidly rotating isolated M
dwarfs, also operates in tidally locked binaries. We advocate using saturated
MB models in binary evolution calculations. Our work supports previous
suggestions that MB in cataclysmic variables (CVs) is much weaker than assumed
in the standard evolutionary model, unless mass transfer leads to significant
additional angular momentum loss in CVs.",2208.05488v2
2017-01-24,Magnetic field formation in the Milky Way-like disk galaxies of the Auriga project,"The magnetic fields observed in the Milky~Way and nearby galaxies appear to
be in equipartition with the turbulent, thermal, and cosmic ray energy
densities, and hence are expected to be dynamically important. However, the
origin of these strong magnetic fields is still unclear, and most previous
attempts to simulate galaxy formation from cosmological initial conditions have
ignored them altogether. Here, we analyse the magnetic fields predicted by the
simulations of the Auriga Project, a set of 30 high-resolution cosmological
zoom simulations of Milky~Way-like galaxies, carried out with a moving-mesh
magneto-hydrodynamics code and a detailed galaxy formation physics model. We
find that the magnetic fields grow exponentially at early times owing to a
small-scale dynamo with an e-folding time of roughly $100\,\rm{Myr}$ in the
center of halos until saturation occurs around $z=2-3$, when the magnetic
energy density reaches about $10\%$ of the turbulent energy density with a
typical strength of $10-50\,\rm{\mu G}$. In the galactic centers the ratio
between magnetic and turbulent energy remains nearly constant until $z=0$. At
larger radii, differential rotation in the disks leads to linear amplification
that typically saturates around $z=0.5$ to $z=0$. The final radial and vertical
variations of the magnetic field strength can be well described by two joint
exponential profiles, and are in good agreement with observational constraints.
Overall, the magnetic fields have only little effect on the global evolution of
the galaxies as it takes too long to reach equipartition. We also demonstrate
that our results are well converged with numerical resolution.",1701.07028v2
2020-12-03,Magnetic fields in elliptical galaxies: an observational probe of the fluctuation dynamo action,"Fluctuation dynamos are thought to play an essential role in magnetized
galaxy evolution, saturating within $\sim0.01~$Gyr and thus potentially acting
as seeds for large-scale dynamos. However, unambiguous observational
confirmation of the fluctuation dynamo action in a galactic environment is
still missing. This is because, in spiral galaxies, it is difficult to
differentiate between small-scale magnetic fields generated by a fluctuation
dynamo and those due to the tangling of the large-scale field. We propose that
observations of magnetic fields in elliptical galaxies would directly probe the
fluctuation dynamo action. This is motivated by the fact that in ellipticals,
due to their lack of significant rotation, the conventional large-scale dynamo
is absent and the fluctuation dynamo is responsible for controlling the
magnetic field strength and structure. By considering turbulence injected by
Type Ia supernova explosions and possible magnetic field amplification by
cooling flows, we estimate expected magnetic field strengths of $0.2~-~1
\,\mu{\rm G}$ in quiescent elliptical galaxies. We use a semi-analytic model of
galaxy formation to estimate the distribution and redshift evolution of field
strengths, tentatively finding a decrease in magnetic field strength with
decreasing redshift. We analyse a sample of radio sources that exhibit the
Laing-Garrington (LG) effect (radio polarization asymmetry in jets) and infer
magnetic field strengths between $0.14~-~1.33 \,\mu{\rm G}$ for a uniform
thermal electron density and between $1.36~-~6.21\,\mu{\rm G}$ for the thermal
electron density following the King profile. We examine observational
techniques for measuring the magnetic field saturation state in elliptical
galaxies, focusing on Faraday RM grids, the LG effect, synchrotron emission,
and gravitational lensing, finding appealing prospects for future empirical
analysis.",2012.02329v1
2021-01-26,Data-driven design of a new class of rare-earth free permanent magnets,"A new class of rare-earth-free permanent magnets is proposed. The parent
compound of this class is Co$_3$Mn$_2$Ge, and its discovery is the result of
first principles theory combined with experimental synthesis and
characterisation. The theory is based on a high-throughput/data-mining search
among materials listed in the ICSD database. From ab-initio theory of the
defect free material it is predicted that the saturation magnetization is 1.71
T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m$^3$, and the Curie
temperature is 700 K. Co$_3$Mn$_2$Ge samples were then synthesized and
characterised with respect to structure and magnetism. The crystal structure
was found to be the MgZn$_2$-type, with partial disorder of Co and Ge on the
crystallographic lattice sites. From magnetization measurements a saturation
polarization of 0.86 T at 10 K was detected, together with a uniaxial
magnetocrystalline anisotropy constant of 1.18 MJ/m$^3$, and the Curie
temperature of $T_{\rm C}$ = 359 K. These magnetic properties make
Co$_3$Mn$_2$Ge a very promising material as a rare-earth free permanent magnet,
and since we can demonstrate that magnetism depends critically on the amount of
disorder of the Co and Ge atoms, a further improvement of the magnetism is
possible. From the theoretical works, a substitution of Ge by neighboring
elements suggest two other promising materials - Co$_3$Mn$_2$Al and
Co$_3$Mn$_2$Ga. We demonstrate here that the class of compounds based on
$T_3$Mn$_2$X (T = Co or alloys between Fe and Ni; X=Ge, Al or Ga) in the
MgZn$_2$ structure type, form a new class of rare-earth free permanent magnets
with very promising performance.",2101.10773v1
2021-09-06,"The planar triangular $S=3/2$ magnet AgCrSe$_2$: magnetic frustration, short range correlations, and field tuned anisotropic cycloidal magnetic order","Our studies evidence an anisotropic magnetic order below $T_N = 32$~K.
Susceptibility data in small fields of about 1~T reveal an antiferromagnetic
(AFM) order for $H \perp c$, whereas for $H \parallel c$ the data are
reminiscent of a field-induced ferromagnetic (FM) structure. At low
temperatures and for $H \perp c$, the field-dependent magnetization and AC
susceptibility data evidence a metamagnetic transition at $H^+ = 5$~T, which is
absent for $H \parallel c$. We assign this to a transition from a planar
cycloidal spin structure at low fields to a planar fan-like arrangement above
$H^+$. A fully FM polarized state is obtained above the saturation field of
$H_{\perp S} = 23.7$~T at 2~K with a magnetization of $M_s = 2.8$~$\mu_{\rm
B}{\rm /Cr}$. For $H \parallel c$, $M(H)$ monotonously increases and saturates
at the same $M_s$ value at $H_{\parallel S} = 25.1$~T at 4.2~K. Above $T_N $,
the magnetic susceptibility and specific heat indicate signatures of two
dimensional (2D) frustration related to the presence of planar ferromagnetic
and antiferromagnetic exchange interactions. We found a pronounced nearly
isotropic maximum in both properties at about $T^* = 45$~K, which is a clear
fingerprint of short-range correlations and emergent spin fluctuations.
Calculations based on a planar 2D Heisenberg model support our experimental
findings and suggest a predominant FM exchange among nearest and AFM exchange
among third-nearest neighbors. Only a minor contribution might be assigned to
the antisymmetric Dzyaloshinskii-Moriya interaction possible related to the
non-centrosymmetric polar space group $R3m$. Due to these competing
interactions, the magnetism in AgCrSe$_{2}$, in contrast to the oxygen based
delafossites, can be tuned by relatively small, experimentally accessible,
magnetic fields, allowing us to establish the complete anisotropic magnetic
$H-T$ phase diagram in detail.",2109.02582v1
2022-01-19,Tearing instability and current-sheet disruption in the turbulent dynamo,"Turbulence in a conducting plasma can amplify seed magnetic fields in what is
known as the turbulent, or small-scale, dynamo. The associated growth rate and
emergent magnetic-field geometry depend sensitively on the material properties
of the plasma, in particular on the Reynolds number ${\rm Re}$, the magnetic
Reynolds number ${\rm Rm}$, and their ratio ${\rm Pm}\equiv{\rm Rm}/{\rm Re}$.
For ${\rm Pm} > 1$, the amplified magnetic field is gradually arranged into a
folded structure, with direction reversals at the resistive scale and field
lines curved at the larger scale of the flow. As the mean magnetic energy grows
to come into approximate equipartition with the fluid motions, this folded
structure is thought to persist. Using analytical theory and high-resolution
MHD simulations with the Athena++ code, we show that these magnetic folds
become unstable to tearing during the nonlinear stage of the dynamo for ${\rm
Rm}\gtrsim 10^4$ and ${\rm Re}\gtrsim 10^3$. An ${\rm Rm}$- and ${\rm
Pm}$-dependent tearing scale, at and below which folds are disrupted, is
predicted theoretically and found to match well the characteristic
field-reversal scale measured in the simulations. The disruption of folds by
tearing increases the ratio of viscous-to-resistive dissipation. In the
saturated state, the magnetic-energy spectrum exhibits a sub-tearing-scale
steepening to a slope consistent with that predicted for tearing-mediated
Alfv\'enic turbulence. Its spectral peak appears to be independent of the
resistive scale and comparable to the driving scale of the flow, while the
magnetic energy resides in a broad range of scales extending down to the
field-reversal scale set by tearing. Emergence of a degree of large-scale
magnetic coherence in the saturated state of the turbulent dynamo may be
consistent with observations of magnetic-field fluctuations in galaxy clusters
and recent laboratory experiments.",2201.07757v2
1999-04-09,Electron-Cyclotron-Maser Observable Modes,"We investigated wave amplification through the Electron-Cyclotron-Maser
mechanism.
  We calculated absorption and emission coefficients without any
approximations, also taking into account absorption by the ambient thermal
plasma. A power-law energy distribution for the fast electrons was used, as is
indicated by X-ray and microwave observations.
  We developed a model for the saturation length and amplification ratio of the
maser, scanned a large parameter space, and calculated the absorption and
emission coefficients for every frequency and angle.
  Previous studies concluded that the unobservable Z-mode dominates in the nu_p
\~ nu_B region, and that millisecond spikes are produced in the region nu_p /
nu_B<0.25. We find that the observable O-mode and X-mode can produce emission
in the 0.8<nu_p / nu_B<2 region, which is expected at the footpoints of a
flaring magnetic loop.
  The important criterion for observability is the saturation length and not
the growth rate, as was assumed previously, and even when the Z-mode is the
most strongly amplified, less strongly amplified O-mode or X-mode are still
intense enough to be observed.
  The brightness temperature computed with our model for the saturation length
is found to be of order 10^{16} K and higher. The emission is usually at a
frequency of 2.06 nu_B, and at angles 30-60 degrees to the magnetic field. The
rise time of the amplified emission to maximum is a few tenths of a millisecond
to a few milliseconds, and the emission persists for as long as new fast
electrons arrive into the maser region.",9904119v1
2004-02-23,Stellar models of evolved secondaries in CVs,"In this paper we study the impact of chemically evolved secondaries on CV
evolution. We find that when evolved secondaries are included a spread in the
secondary mass-orbital period plane comparable to that seen in the data is
produced for either the saturated prescription for magnetic braking or the
unsaturated model commonly used for CVs. We argue that in order to explain this
spread a considerable fraction of all CVs should have evolved stars as the
secondaries. The evolved stars become fully convective at lower orbital
periods. Therefore, even if there was an abrupt decrease in magnetic braking
for fully convective stars (contrary to open cluster data) it would not be
expected to produce a sharp break in the period distribution for CVs. We also
explore recent proposed revisions to the angular momentum loss rate for single
stars, and find that only modest increases over the saturated prescription are
consistent with the overall observed spindown pattern. We compare predictions
of our models with diagnostics of the mass accretion rate in WDs and find
results intermediate between the saturated and the older braking prescription.
Taken together these suggest that the angular momentum loss rate may be higher
in CV secondaries than in single stars of the same rotation period, but is
still significantly lower than in the traditional model. Alternative
explanations for the CV period gap are discussed.",0402536v2
1999-08-10,Existence of Saturated Ferromagnetic and Spiral States in 1D Lieb-Ferrimagnetic Models away from Half-Filling,"In order to study conditions for the appearance of ferromagnetism in a wide
filling region, we investigate numerically three types of one-dimensional
Lieb-ferrimagnetic Hubbard models: a periodic diamond (PD) chain, a periodic
alternately-attached leg (PAAL) chain and an open diamond (OD) chain. All of
these models have a flat band (or equivalently, degenerate single-electron
eigenvalues). The PD and OD chains commonly have a local-loop structure.
Nagaoka's theorem holds only in the PD chain. At half-filling, it have been
rigorously proven that all of these models are ferrimagnet. Away from
half-filling, however, quite different magnetic properties are found. In the
fillings 1/3< rho_e <1/2, the ground state of the PD chain for a
infinitely-large U is the extended ferromagnetic state, that is, the saturated
ferromagnetic state or the spiral state for odd or even number of electrons,
respectively. In the PAAL chain, on the other hand, there is no magnetic order.
Thus, the flat band is found to be not a sufficient condition of the extended
ferromagnetic state. We find, moreover, that the saturated ferromagnetism
appears in the OD chain, although the Nagaoka theorem does not hold on this
chain. This indicates that the local-loop structure plays an important role on
the appearance of the extended ferromagnetic state.",9908144v1
2013-09-26,Stellar Magnetic Dynamos and Activity Cycles,"Using a new uniform sample of 824 solar and late-type stars with measured
X-ray luminosities and rotation periods we have studied the relationship
between rotation and stellar activity that is believed to be a probe of the
underlying stellar dynamo. Using an unbiased subset of the sample we calculate
the power law slope of the unsaturated regime of the activity -- rotation
relationship as $L_X/L_{bol}\propto Ro^\beta$, where $\beta=-2.70\pm0.13$. This
is inconsistent with the canonical $\beta = -2$ slope to a confidence of
5$\sigma$ and argues for an interface-type dynamo. We map out three regimes of
coronal emission as a function of stellar mass and age, using the empirical
saturation threshold and theoretical super-saturation thresholds. We find that
the empirical saturation timescale is well correlated with the time at which
stars transition from the rapidly rotating convective sequence to the slowly
rotating interface sequence in stellar spin-down models. This may be hinting at
fundamental changes in the underlying stellar dynamo or internal structure. We
also present the first discovery of an X-ray unsaturated, fully convective M
star, which may be hinting at an underlying rotation - activity relationship in
fully convective stars hitherto not observed. Finally we present early results
from a blind search for stellar X-ray cycles that can place valuable
constraints on the underlying ubiquity of solar-like activity cycles.",1309.6970v1
2016-10-05,The weakly nonlinear magnetorotational instability in a local geometry,"The magnetorotational instability (MRI) is a fundamental process of accretion
disk physics, but its saturation mechanism remains poorly understood despite
considerable theoretical and computational effort. We present a multiple scales
analysis of the non-ideal MRI in the weakly nonlinear regime -- that is, when
the most unstable MRI mode has a growth rate asymptotically approaching zero
from above. Here, we develop our theory in a local, Cartesian channel. Our
results confirm the finding by Umurhan et al. (2007) that the perturbation
amplitude follows a Ginzburg-Landau equation. We further find that the
Ginzburg-Landau equation will arise for the local MRI system with
shear-periodic boundary conditions when the effects of ambipolar diffusion are
considered. A detailed force balance for the saturated azimuthal velocity and
vertical magnetic field demonstrates that even when diffusive effects are
important, the bulk flow saturates via the combined processes of reducing the
background shear and rearranging and strengthening the background vertical
magnetic field. We directly simulate the Ginzburg-Landau amplitude evolution
for our system and demonstrate the pattern formation our model predicts on long
length and time scales. We compare the weakly nonlinear theory results to a
direct numerical simulation of the MRI in a thin-gap Taylor Couette flow.",1610.01616v2
2019-05-13,"Characterizing maser polarization: effects of saturation, anisotropic pumping and hyperfine structure","The polarization of masers contains information on the magnetic field
strength and direction of the regions they occur in. Many maser polarization
observations have been performed over the last 30 years. However, versatile
maser polarization models that can aide in the interpretation of these
observations are not available. We aim to develop a program suite that can
compute the polarization by a magnetic field of any non-paramagnetic maser
specie at arbitrarily high maser saturation. Furthermore, we aim to investigate
the polarization of masers by non-Zeeman polarizing effects. We aim to present
a general interpretive structure for maser polarization observations. We expand
existing maser polarization theories of non-paramagnetic molecules and
incorporate these in a numerical modeling program suite. We present a modeling
program that CHAracterizes Maser Polarization (CHAMP) that can examine the
polarization of masers of arbitrarily high maser saturation and high angular
momentum. Also, hyperfine multiplicity of the maser-transition can be
incorporated. The user is able to investigate non-Zeeman polarizing mechanisms
such as anisotropic pumping and polarized incident seed radiation. We present
an analysis of the polarization of v = 1 SiO masers and the 22 GHz water maser.
We comment on the underlying polarization mechanisms, and also investigate
non-Zeeman effects. We identify the regimes where different polarizing
mechanisms will be dominant and present the polarization characteristics of the
SiO and water masers. From the results of our calculations, we identify markers
to recognize alternative polarization mechanisms.",1905.04868v1
2020-12-22,A two-dimensional disordered magnetic metamaterial,"We study the effect of a resonant frequency disorder on the eigenstates and
the transport of magnetic energy in a two-dimensional (square) array of
split-ring resonators (SRRs). In the absence of disorder, we find the
dispersion relation of magneto-inductive waves and the mean square displacement
(MSD) in closed form, showing that at long times the MSD is ballistic. When
disorder is present, we consider two types: the usual Anderson distribution
(uncorrelated monomers) and $2 \times 2$ units assigned at random to lattice
sites (correlated tetramers). This is a direct extension to two dimensions of
the one-dimensional random dimer model (RDM). For the uncorrelated case, we see
saturation of the MSD for all disorder widths, while for the correlated case we
find a disorder window, inside which the MSD does not saturate at long times,
with an asymptotic sub-diffusive behavior $MSD\sim t^{0.26}$. Outside this
disorder window, the MSD shows the same kind of saturation as in the monomer
case. We conjecture that the sub-diffusive behavior is a remanent of a weak
resonant transmission of a 2D plane wave across a tetramer unit.",2012.12043v4
2021-06-09,Scaling of Small-Scale Dynamo Properties in the Rayleigh-Taylor Instability,"We derive scaling relations based on free-fall and isotropy assumptions for
the kinematic small-scale dynamo growth rate and amplification factor over the
course of the mixing, saturation, and decay phases of the Rayleigh-Taylor
instability (RTI) in a fully-ionized plasma. The scaling relations are tested
using sets of three dimensional, visco-resistive MHD simulations of the RTI and
found to hold in the saturation phase, but exhibit discrepancies during the
mixing and decays phases, suggesting a need to relax either the free-fall or
isotropy assumptions. Application of the scaling relations allows for
quantitative prediction of the net amplification of magnetic energy in the
kinematic dynamo phase and therefore a determination of whether the magnetic
energy either remains sub-equipartition at all velocity scales or reaches
equipartition with at least some scales of the turbulent kinetic energy in
laboratory and astrophysical scenarios. As an example, we consider the dynamo
in RTI-unstable regions of the outer envelope of a binary neutron star merger
and predict that the kinematic regime of the small-scale dynamo ends on the
time scale of nanoseconds and then reaches saturation on a timescale of
microseconds, which are both fast compared to the millisecond relaxation time
of the post-merger.",2106.04787v2
2022-12-04,"Effects of geometry, boundary condition and dynamical rules on the magnetic relaxation of Ising ferromagnet","We have studied the magnetic relaxation behavior of a two-dimensional Ising
ferromagnet by Monte Carlo simulation. Our primary goal is to investigate the
effects of the system's geometry (area preserving) , boundary conditions, and
dynamical rules on the relaxation behavior. The Glauber and Metropolis
dynamical rules have been employed. The systems with periodic and open boundary
conditions are studied. The major findings are the exponential relaxation and
the dependence of relaxation time ($\tau$) on the aspect ratio $R$ (length over
breadth having fixed area). A power law dependence ($\tau \sim R^{-s}$) has
been observed for larger values of aspect ratio ($R$). The exponent ($s$) has
been found to depend linearly ($s=aT+b$) on the system's temperature ($T$). The
transient behaviours of the spin-flip density have been investigated for both
surface and bulk/core. The size dependencies of saturated spin-flip density
significantly differ for the surface and the bulk/core. Both the saturated
bulk/core and saturated surface spin-flip density was found to follow the
logarithmic dependence $f_d = a + b~log(L)$ with the system size. The faster
relaxation was observed for open boundary condition with any kind
(Metropolis/Glauber) of dynamical rule. Similarly, Metropolis algorithm yields
faster relaxation for any kind (open/periodic) of boundary condition.",2212.01858v2
2022-07-25,On the centeredness of saturated ideals,"We show that Kunen's saturated ideal over $\aleph_1$ is not centered. We also
evaluate the extent of saturation of Laver's saturated ideal in terms of
$(\kappa,\lambda,<\nu)$-saturation.",2207.11959v1
2006-01-17,Global Three-Dimensional MHD Simulations of Galactic Gaseous Disks: I. Amplification of Mean Magnetic Fields in Axisymmetric Gravitational Potential,"We carried out global three-dimensional resistive magnetohydrodynamic
simulations of galactic gaseous disks to investigate how the galactic magnetic
fields are amplified and maintained. We adopt a steady axisymmetric
gravitational potential given by \cite*{Miy80}. As the initial condition, we
assume a warm ($T\sim10^{5} \mathrm{K}$) rotating gas torus centered at
$\varpi=10 \mathrm{kpc}$ threaded by weak azimuthal magnetic fields. Numerical
results indicate that in differentially rotating galactic gaseous disks,
magnetic fields are amplified due to magneto-rotational instability and
magnetic turbulence develops. After the amplification of magnetic energy
saturates, the disk stays in a quasi-steady state. The mean azimuthal magnetic
field increases with time and shows reversals with period of 1Gyr (2Gyr for a
full cycle). The amplitude of $B_{\phi}$ near the equatorial plane is
$B_{\phi}\sim1.5\mu \mathrm{G}$ at $\varpi=5 \mathrm{kpc}$. The magnetic fields
show large fluctuations whose standard deviation is comparable to the mean
field. The mean azimuthal magnetic field in the disk corona has direction
opposite to the mean magnetic field inside the disk. The mass accretion rate
driven by the Maxwell stress is $\sim10^{-3}M_{\odot}/ \mathrm{yr}$ at
$\varpi=2.5 \mathrm{kpc}$ when the mass of the initial torus is
$\sim5\times10^{8}M_{\odot}$.",0601358v2
2006-09-10,Nonlinear shear-current dynamo and magnetic helicity transport in sheared turbulence,"The nonlinear mean-field dynamo due to a shear-current effect in a nonhelical
homogeneous turbulence with a mean velocity shear is discussed. The transport
of magnetic helicity as a dynamical nonlinearity is taken into account. The
shear-current effect is associated with the ${\bf W} {\bf \times} {\bf J}$ term
in the mean electromotive force, where ${\bf W}$ is the mean vorticity due to
the large-scale shear motions and ${\bf J}$ is the mean electric current. This
effect causes the generation of large-scale magnetic field in a turbulence with
large hydrodynamic and magnetic Reynolds numbers. The dynamo action due to the
shear-current effect depends on the spatial scaling of the correlation time
$\tau(k)$ of the background turbulence, where $k$ is the wave number. For
Kolmogorov scaling, $\tau(k) \propto k^{-2/3}$, the dynamo instability occurs,
while when $\tau(k) \propto k^{-2}$ (small hydrodynamic and magnetic Reynolds
numbers) there is no the dynamo action in a sheared nonhelical turbulence. The
magnetic helicity flux strongly affects the magnetic field dynamics in the
nonlinear stage of the dynamo action. Numerical solutions of the nonlinear
mean-field dynamo equations which take into account the shear-current effect,
show that if the magnetic helicity flux is not small, the saturated level of
the mean magnetic field is of the order of the equipartition field determined
by the turbulent kinetic energy. Turbulence with a large-scale velocity shear
is a universal feature in astrophysics, and the obtained results can be
important for elucidation of origin of the large-scale magnetic fields in
astrophysical sheared turbulence.",0609256v1
2006-07-12,Title Cluster-Variational Treatment of Disordered Mixed Spin Ising Model,"A disordered alloy Ap B1-p where both A and B represent the magnetic atoms
with respective spin SA =1/2 and SB =1 and whose magnetic interaction can be
described through Ising Hamiltonian is treated using the cluster-variational
method. In this method it is assumed that the system is built out of building
block which is embedded in an effective field. Taking building block as 4-atom
cluster the approximate free energy of the alloy is then obtained by treating
the interactions between spins within the cluster of all possible
configurations in exact manner and the rest of the interaction by an effective
variational field . The magnetization M and transition temperature Tc are then
calculated for different concentration and exchange parameters (JAA, JBB and
JAB). The magnetization M exhibits different kinds of ferrimagnetic behaviour
depending on concentration and relative strength of intra- and inter-
sub-network exchange interactions. For antiferromagnetic JAB, the sub-network
magnetization saturates and aligned antiferromagnetically at low temperature.
The existence of compensation temperature Tcm, where total magnetization
reverses its direction, depends sensitively on relative values of JAA/ JAB and
JBB/ JAB and p. For B (A)-rich alloy with small JAB, the direction of net
magnetization remains same upto Tc and a maximum of M appears at intermediate T
< Tc when JBB>> JAA (JBB<< JAA).When magnitude of JAB > JAA, JBB, Tc exhibits a
maximum with p. The transition temperature is much less than the mean-field
value for all cases. The magnetic susceptibility for diverges and is
Curie-Wiess like at T >>Tc. The meta-magnetic behaviour at high magnetic field
has been found. Some of these results are in tune with experimental observation
in amorphous rare-earth-transition metal alloys.",0607299v1
2006-02-17,"Numerical simulations of current generation and dynamo excitation in a mechanically-forced, turbulent flow","The role of turbulence in current generation and self-excitation of magnetic
fields has been studied in the geometry of a mechanically driven, spherical
dynamo experiment, using a three dimensional numerical computation. A simple
impeller model drives a flow which can generate a growing magnetic field,
depending upon the magnetic Reynolds number, Rm, and the fluid Reynolds number.
When the flow is laminar, the dynamo transition is governed by a simple
threshold in Rm, above which a growing magnetic eigenmode is observed. The
eigenmode is primarily a dipole field tranverse to axis of symmetry of the
flow. In saturation the Lorentz force slows the flow such that the magnetic
eigenmode becomes marginally stable. For turbulent flow, the dynamo eigenmode
is suppressed. The mechanism of suppression is due to a combination of a time
varying large-scale field and the presence of fluctuation driven currents which
effectively enhance the magnetic diffusivity. For higher Rm a dynamo reappears,
however the structure of the magnetic field is often different from the laminar
dynamo; it is dominated by a dipolar magnetic field which is aligned with the
axis of symmetry of the mean-flow, apparently generated by fluctuation-driven
currents. The fluctuation-driven currents have been studied by applying a weak
magnetic field to laminar and turbulent flows. The magnetic fields generated by
the fluctuations are significant: a dipole moment aligned with the symmetry
axis of the mean-flow is generated similar to those observed in the experiment,
and both toroidal and poloidal flux expulsion are observed.",0602126v2
2007-10-21,New mechanism of generation of large-scale magnetic field in a sheared turbulent plasma,"A review of recent studies on a new mechanism of generation of large-scale
magnetic field in a sheared turbulent plasma is presented. This mechanism is
associated with the shear-current effect which is related to the W x J-term in
the mean electromotive force. This effect causes the generation of the
large-scale magnetic field even in a nonrotating and nonhelical homogeneous
sheared turbulent convection whereby the alpha effect vanishes. It is found
that turbulent convection promotes the shear-current dynamo instability, i.e.,
the heat flux causes positive contribution to the shear-current effect.
However, there is no dynamo action due to the shear-current effect for small
hydrodynamic and magnetic Reynolds numbers even in a turbulent convection, if
the spatial scaling for the turbulent correlation time is k^{-2}, where k is
the small-scale wave number. We discuss here also the nonlinear mean-field
dynamo due to the shear-current effect and take into account the transport of
magnetic helicity as a dynamical nonlinearity. The magnetic helicity flux
strongly affects the magnetic field dynamics in the nonlinear stage of the
dynamo action. When the magnetic helicity flux is not small, the saturated
level of the mean magnetic field is of the order of the equipartition field
determined by the turbulent kinetic energy. The obtained results are important
for elucidation of origin of the large-scale magnetic fields in astrophysical
and cosmic sheared turbulent plasma.",0710.3934v1
2008-12-11,Magnetic properties of undoped Cu2O fine powders with magnetic impurities and/or cation vacancies,"Fine powders of micron- and submicron-sized particles of undoped Cu2O
semiconductor, with three different sizes and morphologies have been
synthesized by different chemical processes. These samples include nanospheres
200 nm in diameter, octahedra of size 1 micron, and polyhedra of size 800 nm.
They exhibit a wide spectrum of magnetic properties. At low temperature, T = 5
K, the octahedron sample is diamagnetic. The nanosphere is paramagnetic. The
other two polyhedron samples synthesized in different runs by the same process
are found to show different magnetic properties. One of them exhibits weak
ferromagnetism with T_C = 455 K and saturation magnetization, M_S = 0.19 emu/g
at T = 5 K, while the other is paramagnetic. The total magnetic moment
estimated from the detected impurity concentration of Fe, Co, and Ni, is too
small to account for the observed magnetism by one to two orders of magnitude.
Calculations by the density functional theory (DFT) reveal that cation
vacancies in the Cu2O lattice are one of the possible causes of induced
magnetic moments. The results further predict that the defect-induced magnetic
moments favour a ferromagnetically coupled ground state if the local
concentration of cation vacancies, n_C, exceeds 12.5%. This offers a possible
scenario to explain the observed magnetic properties. The limitations of the
investigations in the present work, in particular in the theoretical
calculations, are discussed and possible areas for further study are suggested.",0812.2079v1
2012-01-30,High--field NMR of the quasi--1D antiferromagnet LiCuVO$_4$,"We report on NMR studies of the quasi one--dimensional (1D) antiferromagnetic
$S=1/2$ chain cuprate LiCuVO$_4$ in magnetic fields $H$ up to $\mu_0H$ = 30 T
($\approx 70$% of the saturation field $H_{\rm sat}$). NMR spectra in fields
higher than $H_{\rm c2}$ ($\mu_0H_{\rm c2} \approx 7.5$ T) and temperatures
$T<T_{\rm N}$ can be described within the model of a spin-modulated phase in
which the magnetic moments are aligned parallel to the applied field $H$ and
their values alternate sinusoidally along the magnetic chains. Based on
theoretical concepts about magnetically frustrated 1D chains, the field
dependence of the modulation strength of the magnetic structure is deduced from
our experiments. Relaxation time $T_2$ measurements of the $^{51}$V nuclei show
that $T_2$ depends on the particular position of the probing $^{51}$V nucleus
with respect to the magnetic copper moments within the 1D chains: the largest
$T_2$ value is observed for the vanadium nuclei which are very next to the
magnetic Cu$^{2+}$ ion with largest ordered magnetic moment. This observation
is in agreement with the expectation for the spin-modulated magnetic structure.
The $(H,T)$ magnetic phase diagram of LiCuVO$_4$ is discussed.",1201.6182v1
2014-03-28,Magnetization scaling in the paramagnetic phase of Mn1-xFexSi solid solutions,"The magnetization field and temperature dependences in the paramagnetic phase
of Mn1-xFexSi solid solutions with x<0.3 are investigated in the range B<5 T
and T<60 K. It is found that field dependences of the magnetization
M(B,T=const) exhibit scaling behavior of the form B\partial M/\partial
B-M=F(B/(T-Ts)), where Ts denotes an empirically determined temperature of the
transition into the magnetic phase with fluctuation driven short-range magnetic
order and F(\c{hi}) is a universal scaling function for given composition. The
scaling relation allowed concluding that the magnetization in the paramagnetic
phase of Mn1-xFexSi is represented by the sum of two terms. The first term is
saturated by the scaling variable \c{hi}=B/(T-Ts), whereas the second is
linearly dependent on the magnetic field. A simple analytical formula
describing the magnetization is derived and applied to estimates of the
parameters characterizing localized magnetic moments in the studied system. The
obtained data may be qualitatively interpreted assuming magnetic inhomogeneity
of the paramagnetic phase on the nanoscale.",1403.7332v2
2014-10-11,Spin wave free spectrum and magnetic field gradient of nanopatterned planes of ferromagnetic cobalt nanoparticles: key properties for magnetic resonance based quantum computing,"We present a study by ferromagnetic resonance at microwave Q band of two
sheets of cobalt nanoparticles obtained by annealing SiO2 layers implanted with
cobalt ions. This ex- perimental study is performed as a function of the
applied magnetic field orientation, tempera- ture, and dose of implanted cobalt
ions. We demonstrate that each of those magnetic sheet of cobalt nanoparticles
can be well modelled by a nearly two dimensional ferromagnetic sheet hav- ing a
reduced effective saturation magnetization, compared to a regular thin film of
cobalt. The nanoparticles are found superparamagnetic above around 210 K and
ferromagnetic below this blocking temperature. Magnetostatic calculations show
that a strong magnetic field gradient of around 0.1 G/nm could be produced by a
ferromagnetic nanostripe patterned in such magnetic sheet of cobalt
nanoparticles. Such a strong magnetic field gradient combined with electron
para- magnetic resonance may be relevant for implementing an intermediate scale
quantum computer based on arrays of coupled electron spins, as previously
reported (Eur. Phys. J. B (2014) 87, 183). However, this new approach only
works if no additional spin decoherence is introduced by the spin waves
exitations of the ferromagnetic nanostructure. We thus suggest theoretically
some possible magnetic anisotropy engineering of cobalt nanoparticles that
could allow to suppress the spin qubit decoherence induced by the unwanted
collective excitation of their spins.",1410.3005v1
2015-04-12,Evolution of Kinetic and Magnetic Energy in Intra Cluster Media,"Intra Cluster Media (ICMs) located at galaxy clusters is in the state of hot,
tenuous, magnetized, and highly ionized X-ray emitting plasmas. This overall
collisionless, viscous, and conductive magnetohydrodynamic (MHD) turbulence in
ICM is simulated using hyper and physical magnetic diffusivity. The results
show that fluctuating random plasma motion amplifies the magnetic field, which
cascades toward the diffusivity scale passing through the viscous scale. The
kinetic eddies in the subviscous scale are driven and constrained by the
magnetic tension which finally gets balanced with the highly damping effect of
the kinetic eddies. However, the saturated kinetic energy spectrum is deeper
than that of the incompressible or compressible hydrodynamics fluid. To explain
this unusual field profile we set up two simultaneous differential equations
for the kinetic and magnetic energy spectrum using an Eddy Damped Quasi Normal
Markovianized (EDQNM) approximation. The analytic solution tells us that the
magnetic energy in addition to the viscous damping effect constrains the plasma
motion leading to the power spectra: kinetic energy spectrum $E_V^k\sim k^{-3}$
and corresponding representative magnetic energy spectrum $E_M^k\sim k^{-1/2}$.
Also the comparison of simulation results with different resolutions and
magnetic diffusivities implies the role of small scale magnetic energy in
dynamo.",1504.02940v3
2016-05-03,Field-induced transition of the magnetic ground state from A-type antiferromagnetic to ferromagnetic order in CsCo2Se2,"We report on the magnetic properties of CsCo$_2$Se$_2$ with ThCr$_2$Si$_2$
structure, which we have characterized through a series of magnetization and
neutron diffraction measurements. We find that CsCo$_2$Se2$_2$ undergoes a
phase transition to an antiferromagnetically ordered state with a N\'eel
temperature of $T_{\rm N} \approx$ 66 K. The nearest neighbour interactions are
ferromagnetic as observed by the positive Curie-Weiss temperature of $\Theta
\approx$ 51.0 K. We find that the magnetic structure of CsCo$_2$Se$_2$ consists
of ferromagnetic sheets, which are stacked antiferromagnetically along the
tetragonal \textit{c}-axis, generally referred to as A-type antiferromagnetic
order. The observed magnitude of the ordered magnetic moment at $T$ = 1.5 K is
found to be only 0.20(1)$\mu_{\rm Bohr}$/Co. Already in comparably small
magnetic fields of $\mu_0 H_{MM}$(5K) $\approx$ 0.3 T, we observe a
metamagnetic transition that can be attributed to spin-rearrangements of
CsCo$_2$Se$_2$, with the moments fully ferromagnetically saturated in a
magnetic field of $\mu_0 H_{\rm FM}$(5K) $\approx$ 6.4 T. We discuss the entire
experimentally deduced magnetic phase diagram for CsCo$_2$Se$_2$ with respect
to its unconventionally weak magnetic coupling. Our study characterizes
CsCo$_2$Se$_2$, which is chemically and electronically posed closely to the
$A_xFe_{2-y}Se_2$ superconductors, as a host of versatile magnetic
interactions.",1605.01113v1
2016-09-20,Magnetic anisotropy and the phase diagram of chiral MnSb2O6,"The magnetic phase diagram and low-energy magnon excitations of structurally
and magnetically chiral MnSb2O6 are reported. The specific heat and the static
magnetization are investigated in magnetic fields up to 9 and 30 T,
respectively, while the dynamicmagnetic properties are probed by X-band as well
as tunable high-frequency electron spin-resonance spectroscopy. Below TN = 11.5
K, we observe antiferromagnetic resonance modes which imply small but finite
planar anisotropy showing up in a zero-field splitting of 20 GHz. The data are
well described by means of an easy-plane two-sublattice model with the
anisotropy field BA = 0.02 T. The exchange field BE = 13 T is obtained from the
saturation field derived from the pulsed-field magnetization. A crucial role of
the small anisotropy for the spin structure is reflected by competing
antiferromagnetic phases appearing, at T = 2 K, in small magnetic fields at BC1
$\approx$ 0.5 T and BC2 = 0.9 T. We discuss the results in terms of spin
reorientation and of small magnetic fields favoring helical spin structure over
the cycloidal ground state which, at B = 0, is stabilized by the planar
anisotropy. Above TN, short-range magnetic correlations up to >=60 K and
magnetic entropy changes well above TN reflect the frustrated triangular
arrangement of Mn2+ ions in MnSb2O6.",1609.06105v1
2017-04-13,Extreme Magnetoresistance in Magnetic Rare Earth Monopnictides,"The acute sensitivity of the electrical resistance of certain systems to
magnetic fields known as extreme magnetoresistance (XMR) has recently been
explored in a new materials context with topological semimetals. Exemplified by
WTe$_{2}$ and rare earth monopnictide La(Sb,Bi), these systems tend to be
non-magnetic, nearly compensated semimetals and represent a platform for large
magnetoresistance driven by intrinsic electronic structure. Here we explore
electronic transport in magnetic members of the latter family of semimetals and
find that XMR is strongly modulated by magnetic order. In particular, CeSb
exhibits XMR in excess of $1.6 \times 10^{6}$ % at fields of 9 T while the
magnetoresistance itself is non-monotonic across the various magnetic phases
and shows a transition from negative magnetoresistance to XMR with field above
magnetic ordering temperature $T_{N}$. The magnitude of the XMR is larger than
in other rare earth monopnictides including the non-magnetic members and
follows an non-saturating power law to fields above 30 T. We show that the
overall response can be understood as the modulation of conductivity by the Ce
orbital state and for intermediate temperatures can be characterized by an
effective medium model. Comparison to the orbitally quenched compound GdBi
supports the correlation of XMR with the onset of magnetic ordering and
compensation and highlights the unique combination of orbital inversion and
type-I magnetic ordering in CeSb in determining its large response. These
findings suggest a paradigm for magneto-orbital control of XMR and are relevant
to the understanding of rare earth-based correlated topological materials.",1704.04226v1
2017-07-30,Effect of magnetic field on the burning of a neutron star,"In this article, we present the effect of a strong magnetic field in the
burning of a neutron star (NS). We have used relativistic magneto-hydrostatic
(MHS) conservation equations for studying the PT from nuclear matter (NM) to
quark matter (QM). We found that the shock-induced phase transition (PT) is
likely if the density of the star core is more than three times nuclear
saturation ($\rho_s$) density. The conversion process from NS to quark star
(QS) is found to be an exothermic process beyond such densities. The burning
process at the star center most likely starts as a deflagration process.
However, there can be a small window at lower densities where the process can
be a detonation one. At small enough infalling matter velocities the resultant
magnetic field of the QS is lower than that of the NS. However, for a higher
value of infalling matter velocities, the magnetic field of QM becomes larger.
Therefore, depending on the initial density fluctuation and on whether the PT
is a violent one or not the QS could be more magnetic or less magnetic. The PT
also have a considerable effect on the tilt of the magnetic axis of the star.
For smaller velocities and densities the magnetic angle are not affected much
but for higher infalling velocities tilt of the magnetic axis changes suddenly.
The magnetic field strength and the change in the tilt axis can have a
significant effect on the observational aspect of the magnetars.",1707.09590v3
2018-05-11,Anisotropic superconductivity and magnetism in single-crystal RbEuFe$_4$As$_4$,"We investigate the anisotropic superconducting and magnetic properties of
single-crystal RbEuFe$_4$As$_4$ using magnetotransport and magnetization
measurements. We determine a magnetic ordering temperature of the Eu-moments of
$T_m$ = 15 K and a superconducting transition temperature of $T_c$ = 36.8 K.
The superconducting phase diagram is characterized by high upper critical field
slopes of -70 kG/K and -42 kG/K for in-plane and out-of-plane fields,
respectively, and a surprisingly low superconducting anisotropy of $\Gamma$ =
1.7. Ginzburg-Landau parameters of $\kappa_c \sim 67$ and $\kappa_{ab} \sim
108$ indicate extreme type-II behavior. These superconducting properties are in
line with those commonly seen in optimally doped Fe-based superconductors. In
contrast, Eu-magnetism is quasi-two dimensional as evidenced by highly
anisotropic in-plane and out-of-plane exchange constants of 0.6 K and $<$ 0.04
K. A consequence of the quasi-2D nature of the Eu-magnetism are strong magnetic
fluctuation effects, a large suppression of the magnetic ordering temperature
as compared to the Curie-Weiss temperature, and a cusp-like anomaly in the
specific heat devoid of any singularity. Magnetization curves reveal a clear
magnetic easy-plane anisotropy with in-plane and out-of-plane saturation fields
of 2 kG and 4 kG.",1805.04216v1
2018-05-14,Magnetic heating across the cosmological recombination era: Results from 3D MHD simulations,"The origin of cosmic magnetic fields is an unsolved problem and
magnetogenesis could have occurred in the early Universe. We study the
evolution of such primordial magnetic fields across the cosmological
recombination epoch via 3D magnetohydrodynamic numerical simulations. We
compute the effective or net heating rate of baryons due to decaying magnetic
fields and its dependence on the magnetic field strength and spectral index. In
the drag-dominated regime ($z \gtrsim 1500$), prior to recombination, we find
no real heating is produced. Our simulations allow us to smoothly trace a new
transition regime ($600 \lesssim z \lesssim 1500$), where magnetic energy
decays, at first, into the kinetic energy of baryons. A turbulent velocity
field is built up until it saturates, as the net heating rate rises from a low
value at recombination to its peak towards the end of the transition regime.
This is followed by a turbulent decay regime ($z \lesssim 600$) where magnetic
energy dissipates via turbulent decay of both magnetic and velocity fields
while net heating remains appreciable and declines slowly. Both the peak of the
net heating rate and the onset of turbulent decay are delayed significantly
beyond recombination, by up to 0.5 Myr (until $z\simeq 600-700$), for
scale-invariant magnetic fields. We provide analytic approximations and present
numerical results for a range of field strengths and spectral indices,
illustrating the redshift-dependence of dissipation and net heating rates.
These can be used to study cosmic microwave background constraints on
primordial magnetic fields.",1805.05315v1
2018-06-19,"Magnetic, electronic and transport properties of high-pressure-synthesized chiralmagnets Mn$_{1-x}$Rh$_x$Ge (B20)","We report on structural, magnetic and transport properties of a new set of
the high-pressuresynthesized compounds Mn$_{1-x}$Rh$x$Ge ($0 \leq x \leq 1$)
with the chiral magnetic ordering. The magnetic and transport properties depend
substantially on the concentration of rhodium (x) and the pressure. The
saturation magnetic moment corresponds to a known high-spin value for pristine
MnGe (x = 0) and decreases almost linearly with increasing concentration $x$.
In addition, XMCD spectra taken at 10 K and 2 T indicate magnetic polarization
of the Rh 4d electron states and Ge $4p$ states, which decreases with $x$, too.
In rhodium rich compounds ($x \geq 0.5$) the temperature of the magnetic
ordering increases significantly with pressure, whereas in manganese rich
compounds ($x < 0.5$) the temperature decreases. Three different tendencies are
also found for several structural and transport properties. In the intermediate
range ($0.3 \leq x \leq 0.7$) samples are semiconducting in the paramagnetic
phase, but become metallic in the magnetically ordered state. We carried out ab
initio density-functional calculations of Mn$_{1-x}$Rh$_x$Ge at various
concentrations $x$ and traced the evolution of electronic and magnetic
properties. The calculation results are in good agreement with the measured
magnetic moments and qualitatively explain the observed trends in transport
properties.",1806.07165v1
2018-09-20,Three-dimensional kinetic simulations of relativistic magnetostatic equilibria,"We present the results of three-dimensional kinetic particle-in-cell (PIC)
simulations of isotropic periodic relativistically magnetized pair-plasma
equilibria known as the ABC fields. We performed several simulations for
initial wavenumbers k_ini = 2 or k_ini = 4, different efficiencies of radiative
cooling (including radiation reaction from synchrotron and inverse Compton
processes), and different mean magnetization values. These equilibria evolve by
means of ideal coalescence instability, the saturation of which generates ab
initio localized kinetically-thin current layers -- sites of magnetic
reconnection and non-thermal particle acceleration -- eventually relaxing to a
state of lower magnetic energy at conserved total magnetic helicity. We
demonstrate that magnetic relaxation involves in addition localized collapses
of magnetic minima and bulk mergers of current layer pairs, which represents a
novel scenario of spontaneous magnetic dissipation with application to the
rapid gamma-ray flares of blazars and of the Crab Nebula. Particle acceleration
under strong radiative losses leads to formation of power-law indices N(gamma)
~ gamma^(-p) up to p ~= -2.3 at mean hot magnetization values of <sigma_hot> ~
6. Individual energetic particles can be accelerated within one light-crossing
time by electric fields that are largely perpendicular to the local magnetic
fields. The energetic particles are highly anisotropic due to the kinetic
beaming effect, implying complex patterns of rapid variability. A significant
fraction of the initial total energy can be radiated away in the overall
process of magnetoluminescence.",1809.07773v1
2018-10-02,Building traps for skyrmions by the incorporation of magnetic defects into nanomagnets: pinning and scattering traps by magnetic properties engineering,"In this work we have used micromagnetic simulations to report four ways to
build traps for magnetic skyrmions. Magnetic defects have been modeled as local
variations in the material parameters, such as the exchange stiffness,
saturation magnetization, magnetocrystalline anisotropy and
Dzyaloshinskii-Moriya constant. We observe both pinning (potential well) and
scattering (potential barrier) traps when tuning either a local increase or a
local reduction for each one of these magnetic properties. It is found that the
skyrmion-defect aspect ratio is a crucial parameter to build traps for
skyrmions. In particular, the efficiency of the trap is compromised if the
defect size is smaller than the skyrmion size, because they interact weakly. On
the other hand, if the defect size is larger than the skyrmion diameter, the
skyrmion-defect interaction becomes evident. Thus, the strength of the
skyrmion-defect interaction can be tuned by the modification of the magnetic
properties within a region with suitable size. Furthermore, the basic physics
behind the mechanisms for pinning and for scattering is discussed. In
particular, we discover that skyrmions move towards the magnetic region which
tends to maximize its diameter; it enables the magnetic system to minimize its
energy. Thus, we are able to explain why skyrmions are either attracted or
repelled by a region with modified magnetic properties. Results here presented
are of utmost significance for the development and realization of future
spintronic devices, in which skyrmions will work as information carriers.",1810.03754v2
2019-01-16,"Magnetic properties of double perovskite $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho): hetero-tri-spin $3d$-$5d$-$4f$ systems","The field of double perovskites is now advancing to three magnetic elements
on the A, B and B$'$ sites. A series of iridium-based double perovskite
compounds, $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho) with three magnetic elements
were synthesized as polycrystalline samples. The compounds crystalize in
monoclinic structures with the space group $P2_1/n$. Magnetic properties of
these hetero-tri-spin $3d$-$5d$-$4f$ systems were studied by magnetic
susceptibility and field dependent magnetization in both DC and pulsed magnetic
fields. All these compounds show ferrimagnetic transitions at temperatures
$T_C$ above 100 K, which are attributable to antiferromagnetic coupling between
Co$^{2+}$ and Ir$^{4+}$ spins. For Eu$_2$CoIrO$_6$, the magnetic properties are
similar to those of La$_2$CoIrO$_6$. The Eu$^{3+}$ spins show Van Vleck
paramagnetism that don't significantly interact with transition-metal cations.
By contrast, Tb$_2$CoIrO$_6$ and Ho$_2$CoIrO$_6$ reveal a second transition to
antiferromagnetic order below a lower temperature $T_N$. The
temperature-induced ferrimagnetic-to-antiferromagnetic phase transition might
be explained by a spin-reorientation transition. Moreover, a
magnetic-field-induced spin-flop transition with a small hysteresis was
observed below $T_N$ in these two compounds. The magnetic moment of all three
compounds do not saturate up to 60 T at low temperatures. Moderate
magnetocaloric effect was also observed in all three compounds. Our results
should motivate further investigation of the spin configuration on single
crystals of these iridium-based double perovskites.",1901.05412v1
2019-05-14,Versatile Hall magnetometer with variable sensitivity assembly for characterization of the magnetic properties of nanoparticles,"A Hall magnetometer with variable sensitivity is constructed to measure the
magnetic properties of magnetic nanoparticles manufactured by different
methods. This novel magnetometer can also be used to measure bulk materials and
samples in liquids. The magnetometer is constructed with two commercial
Hall-effect sensors in an acrylic structure, which serves as the support for a
micrometer and the circuit board with the sensors. For operation, the
magnetometer it acquires a complete magnetization curve in a few minutes. If
has a magnetic moment sensitivity of 1.3*10-9 Am2 to sensitivity of 493 mV/mT,
the sensitivity can be adjustable in the range of 10 to 493 mV/mT. Its
performance is tested with magnetic nanoparticles. As an application example,
we estimate the mean diameter of the nanoparticles using the magnetic curves.
The results are compared with those obtained by other techniques, such as
transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic
light scattering (DLS). The magnetization results are also compared with those
obtained by independent commercial magnetometers, which reveals errors of
approximately 0.31 Am2/kg (i.e., 0.6%) in the saturation region.",1905.05741v2
2019-10-15,Irregularly Shaped γ'-Fe4N Nanoparticles for Hyperthermia Treatment and T2 Contrast-Enhanced Magnetic Resonance Imaging with Minimum Dose,"Magnetic nanoparticles (MNPs) have been extensively used in drug/gene
delivery, hyperthermia therapy, magnetic particle imaging (MPI), magnetic
resonance imaging (MRI), magnetic bioassays, etc. With proper surface chemical
modifications, physicochemically stable and non-toxic MNPs are emerging
contrast agents and tracers for in vivo MRI and MPI applications. Herein, we
report the high magnetic moment, irregularly shaped {\gamma}'-Fe4N
nanoparticles for enhanced hyperthermia therapy and T2 contrast agent for MRI
application. The static and dynamic magnetic properties of {\gamma}'-Fe4N
nanoparticles are characterized by vibrating sample magnetometer (VSM) and
magnetic particle spectroscopy (MPS) systems, respectively. Compared to the
{\gamma}-Fe2O3 nanoparticles, {\gamma}'-Fe4N show at least 3 times higher
saturation magnetization (in emu/g), which, as a result, gives rise to the
stronger dynamic magnetic responses as proved in the MPS measurement results.
In addition, {\gamma}'-Fe4N nanoparticles are functionalized with oleic acid
layer by a wet mechanical milling process, the morphologies of as-milled
nanoparticles are characterized by transmission electron microscopy (TEM),
dynamic light scattering (DLS) and nanoparticle tracking analyzer (NTA). We
report that with proper surface chemical modification and tuning on
morphologies, {\gamma}'-Fe4N nanoparticles could be used as tiny heating
sources for hyperthermia and contrast agents for MRI applications with minimum
dose.",1910.06842v1
2020-01-15,Meson masses in external magnetic fields with HISQ fermions,"We studied the temporal correlation function of mesons in the pseudo-scalar
channel in (2+1)-flavor QCD in the presence of external magnetic fields at zero
temperature. The simulations were performed on $32^3 \times 96$ lattices using
the Highly Improved Staggered Quarks (HISQ) action with $m_{\pi} \approx $ 230
MeV. The strength of magnetic fields $|eB|$ ranges from 0 to around 3.3 GeV$^2$
($\sim 60 m_\pi^2$). We found that the masses of neutral pseudo-scalar
particles, e.g. neutral pion and kaon, monotonouslly decrease as the magnetic
field grows and then saturate at a nonzero value. It is observed that heavier
neutral pseudo-scalars are less affected by magnetic fields. Moreover, we found
a non-monotonous behavior of charged pion and kaon mass in magnetic field for
the first time. In the case of small magnetic field (0 $\leq~|eB| \lesssim$ 0.3
GeV$^2~\sim 6m_\pi^2$ ) the mass of charged pseudo-scalar grows with magnetic
field and can be well described by the Lowest Landau Level approximation, while
for $|eB|$ larger than 0.3 GeV$^2$ the mass starts to decrease. The possible
connection between $|eB|$ dependences of neutral pion mass and the decreasing
behavior of pseudo-critical temperature in magnetic field is discussed. Due to
the nonzero value of neutral pion mass our simulation indicates that the
superconducting phase of QCD does not exist in the current window of magnetic
field.",2001.05322v1
2020-02-18,Magnetic and all-optical switching properties of amorphous Tb$_x$Co$_{100-x}$ alloys,"Amorphous Tb$_{x}$Co$_{100-x}$ magnetic alloys exhibit a list of intriguing
properties, such as perpendicular magnetic anisotropy, high magneto-optical
activity and magnetization switching using ultrashort optical pulses. Varying
the Tb:Co ratio in these alloys allows for tuning properties such as the
saturation magnetic moment, coercive field and the performance of the
light-induced magnetization switching. In this work, we investigate the
magnetic, optical and magneto-optical properties of various
Tb$_{x}$Co$_{100-x}$ thin film alloy compositions. We report on the effect the
choice of different seeding layers has on the structural and magnetic
properties of Tb$_{x}$Co$_{100-x}$ layers. We also demonstrate that for a range
of alloys, deposited on fused silica substrates, with Tb content of 24-30
at.$\%$, helicity dependent all-optical switching of magnetization can be
achieved, albeit in a multi-shot framework. We explain this property to arise
from the helicity-dependent laser induced magnetization on the Co sublattice
due to the inverse Faraday effect. Our study provides an insight into material
aspects for future potential hybrid magneto-plasmonic TbCo-based architectures.",2002.07544v3
2020-07-06,Ferrimagnetism in EuFe4As12 revealed by 153Eu NMR and 75As NQR measurements,"Filled skutterudite compound EuFe$_4$As$_{12}$ shows the highest magnetic
ordering temperature of $T_{\rm C}$ = 154 K among Eu-based skutterudite
compounds, but its magnetic ground state has not been determined yet. Here, we
performed $^{153}$Eu nuclear magnetic resonance (NMR) and $^{75}$As nuclear
quadrupole resonance (NQR) measurements on EuFe$_4$As$_{12}$ to reveal its
magnetic ground state as well as the physical properties from a microscopic
point of view. From the temperature and magnetic field dependence of $^{153}$Eu
NMR spectrum in the magnetically ordered state, we found that the Eu ions are
in Eu$^{2+}$ state with a nearly 7 $\mu_{\rm B}$ corresponding to $S$ = 7/2
spins. Combined with the magnetization measurements which show the reduced
saturation moments of 4.5 $\mu_{\rm B}$/f.u., we determined the ground magnetic
structure in EuFe$_4$As$_{12}$ to be ferrimagnetic where the Eu$^{2+}$ 4$f$ and
the Fe 3$d$ ordered moments are ferromagnetically aligned in each sublattice
but the moments between the sublattices are antiferromagnetically aligned. We
also found the local distortion at the Eu site from the cubic symmetry in the
magnetically ordered state. The relationship between the rattling motion of Eu
atoms and the local symmetry of the Eu ions is discussed. From the $^{75}$As
NQR nuclear spin-lattice relaxation time measurements as well as $^{153}$Eu NMR
measurements, we found that the 4$f$ electrons of the Eu ions are well
described by the local moment picture in both the magnetic and paramagnetic
metallic states.",2007.02983v1
2020-10-07,Magnetostriction in elastomers with mixtures of magnetically hard and soft microparticles: effects of non-linear magnetization and matrix rigidity,"In this contribution a magnetoactive elastomer (MAE) of mixed content, i.e.,
a polymer matrix filled with a mixture of magnetically soft and magnetically
hard spherical particles, is considered. The object we focus at is an
elementary unit of this composite, for which we take a set consisting of a
permanent spherical micromagnet surrounded by an elastomer layer filled with
magnetically soft microparticles. We present a comparative treatment of this
unit from two essentially different viewpoints. The first one is a
coarse-grained molecular dynamics simulation model, which presents the
composite as a bead-spring assembly and is able to deliver information of all
the microstructural changes of the assembly. The second approach is entirely
based on the continuum magnetomechanical description of the system, whose
direct yield is the macroscopic field-induced response of the MAE to external
field, as this model ignores all the microstructural details of the
magnetization process. We find that, differing in certain details, both
frameworks are coherent in predicting that a unit comprising magnetically soft
and hard particles may display a non-trivial re-entrant
(prolate/oblate/prolate) axial deformation under variation of the applied field
strength.
  The flexibility of the proposed combination of the two complementary
frameworks enables us to look deeper into the manifestation of the magnetic
response: with respect to the magnetically soft particles, we compare the
linear regime of magnetization to that with saturation, which we describe by
the Fr\""{o}hlich-Kennelly approximation; with respect to the polymer matrix, we
analyze the dependence of the re-rentrant deformation on its rigidity.",2010.03684v1
2021-05-18,Asteroid Magnetization from the Early Solar Wind,"Magnetic fields provide an important probe of the thermal, material, and
structural history of planetary and sub-planetary bodies. Core dynamos are a
potential source of magnetic fields for differentiated bodies, but evidence of
magnetization in undifferentiated bodies requires a different mechanism. Here
we study the amplified field provided by the stellar wind to an initially
unmagnetized body using analytic theory and numerical simulations, employing
the resistive MHD AstroBEAR adaptive mesh refinement (AMR) multiphysics code.
We obtain a broadly applicable scaling relation for the peak magnetization
achieved once a wind advects, piles-up, and drapes a body with magnetic field,
reaching a quasi-steady state. We find that the dayside magnetic field for a
sufficiently conductive body saturates when it balances the sum of incoming
solar wind ram, magnetic, and thermal pressures. Stronger amplification results
from pileup by denser and faster winds. Careful quantification of numerical
diffusivity is required for accurately interpreting the peak magnetic field
strength from simulations, and corroborating with theory. As specifically
applied to the Solar System, we find that early solar wind-induced field
amplification is a viable source of magnetization for observed paleointensities
in meteorites from some undifferentiated bodies. This mechanism may also be
applicable to other Solar System bodies, including metal-rich bodies to be
visited in future space missions such as the asteroid (16) Psyche.",2105.08852v3
2021-05-24,Magneto-rotational instability in magnetically polarized discs,"The magneto-rotational instability (MRI) is the most likely mechanism for
transportation of angular momentum and dissipation of energy within hot,
ionized accretion discs. This instability is produced through the interactions
of a differentially rotating plasma with an embedded magnetic field. Like all
substances in nature, the plasma in an accretion disc has the potential to
become magnetically polarized when it interacts with the magnetic field. In
this paper, we study the effect of this magnetic susceptibility, parameterized
by $\chi_m$, on the MRI, specifically within the context of black hole
accretion. We find from a linear analysis within the Newtonian limit that the
minimum wavelength of the first unstable mode and the wavelength of the fastest
growing mode are shorter in paramagnetic ($\chi_m>0$) than in diamagnetic
($\chi_m<0$) discs, all other parameters being equal. Furthermore, the
magnetization parameter (ratio of gas to magnetic pressure) in the saturated
state should be smaller when the magnetic susceptibility is positive than when
it is negative. We confirm this latter prediction through a set of numerical
simulations of magnetically polarized black hole accretion discs. We
additionally find that the vertically integrated stress and mass accretion rate
are somewhat larger when the disc is paramagnetic than when it is diamagnetic.
If astrophysical discs are able to become magnetically polarized to any
significant degree, then our results would be relevant to properly interpreting
observations.",2105.11329v1
2021-12-15,Effect of magnetocrystalline anisotropy on magnetocaloric properties of AlFe$_{2}$B$_{2}$ compound,"It is well known that the temperature dependence of the effective
magnetocrystalline anisotropy energy obeys the $l(l+1)/2$ power law of
magnetization in the Callen-Callen theory. Therefore, according to the
Callen-Callen theory, the magnetocrystalline anisotropy energy is assumed to be
zero at the critical temperature where the magnetization is approximately zero.
This study estimates the temperature dependence of the magnetocrystalline
anisotropy energy by integrating the magnetization versus magnetic field
($M$--$H$) curves, and found that the magnetocrystalline anisotropy is still
finite even above the Curie temperature in the uniaxial anisotropy, whereas
this does not appear in the cubic anisotropy case. The origin is the fast
reduction of the anisotropy field, which is the magnetic field required to
saturate the magnetization along the hard axis, in the case of cubic
anisotropy. Therefore, the magnetization anisotropy and anisotropic magnetic
susceptibility, those are the key factors of magnetic anisotropy, could not be
established in the case of cubic anisotropy. In addition, the effect of
magnetocrystalline anisotropy on magnetocaloric properties, as the difference
between the entropy change curves of AlFe$_{2}$B$_{2}$ appears above the Curie
temperature, which is in good agreement with a previous experimental study.
This is proof of magnetic anisotropy at slightly above Curie temperature.",2112.08154v1
2023-02-07,Masterthesis: Ab Initio Magnetic Properties of Rare-Earth Lean Nd-based Hard Magnets,"Due to the resource criticality of rare-earths (RE), an alternative to the
well-known Nd$_2$Fe$_{14}$B magnets with a lower amount of critical elements is
required. In this work, density functional theory (DFT) calculations to
investigate the influence of partial Nd substitution with more abundant
elements (X: Y and Ce) in ThMn$_{12}$-type (Nd,X)Fe$_{11}$Ti compounds were
performed. In order to have a systematic understanding, the intrinsic magnetic
properties such as the saturation magnetization $M_S$, Curie temperature $T_C$
and magnetocrystalline anisotropy energy, are screened starting from binaries
RFe$_{12}$ (R: Y, Ce and Nd), and only considering the spin magnetic
contribution in case of the $f$ electrons. Ti is considered for the
thermodynamic stabilization and different concentrations of Ti are taken into
account for ternaries RFe$_{12-y}$Ti$_y$ and quaternaries
(Nd,X)Fe$_{12-y}$Ti$_y$ (0.5$\le$ $y$ $\le$1). In addition, the effect of
nitrogenation is examined for each considered compound. In case of
(Nd,Y)Fe$_{11}$Ti, $|BH|$$_{max}$ is found to be 384 kJ/m$^3$ and $T_C$ is
calculated to be 595 K. Similarly, $|BH|$$_{max}$ and $T_C$ are calculated to
be 365 kJ/m$^3$ and 593 K for (Nd,Ce)Fe$_{11}$Ti magnet, respectively. Both 50
% Nd-lean magnets exhibit higher $|BH|$$_{max}$ compared to Sm$_2$Co$_{17}$ and
$T_C$ than Nd$_2$Fe$_{14}$B. For both cases, the theoretical magnetic hardness
factor $\kappa$ is calculated to be 1.20, which qualifies them as good
candidates for RE-lean permanent magnets.",2302.03417v1
2023-02-21,Exploring the magnetic properties of individual barcode nanowires using wide-field diamond microscopy,"Barcode magnetic nanowires typically comprise a multilayer magnetic structure
in a single body with more than one segment type. Interestingly, owing to
selective functionalization and novel interactions between the layers, barcode
magnetic nanowires have attracted significant attention, particularly in the
field of bioengineering. However, an analysis of their magnetic properties at
the individual nanowire level remains challenging. With this background,
herein, we investigated the characterization of magnetic nanowires at room
temperature under ambient conditions based on magnetic images obtained via
wide-field quantum microscopy with nitrogen-vacancy centers in diamond.
Consequently, we could extract critical magnetic properties, such as the
saturation magnetization and coercivity, of single nanowires by comparing the
experimental results with those of micromagnetic simulations. This study opens
up the possibility for a versatile characterization method suited to individual
magnetic nanowires.",2302.10547v1
2023-12-07,Features of magnetization and spin reorientation in weak ferrimagnets of the YFe$_{1-x}$Cr$_x$O$_3$ type,"A brief critical review is given of the 50-year history of experimental and
theoretical studies of the magnetic properties of a new promising class of weak
ferrimagnets such as RFe$_{1-x}$Cr$_x$O$_3$ with a non-magnetic R-ion (R = La ,
Y, Lu), i.e. systems with competing signs of the Dzyaloshinsky vectors Fe-Fe,
Cr-Cr and Fe-Cr. The spin Hamiltonian of the system is considered taking into
account isotropic exchange, antisymmetric Dzyaloshinsky-Moriya exchange, and
second- and fourth-order single-ion anisotropy. Within the framework of the
molecular field approximation, calculations were made of the Neel temperatures,
the average magnetic moments of $3d$ ions, total and partial magnetizations,
and effective anisotropy constants. The existence in the model system
YFe$_{1-x}$Cr$_x$O$_3$ of two regions of negative magnetization $0.25 \leq
x\leq 0.5$ and $x\approx 0.8$ with the corresponding magnetization reversal
points reaching room temperature at $x\approx 0.45$. The phenomenon of spin
reorientation observed for single-crystal samples in a wide range of
concentrations is explained by a sharp decrease in the contribution of
antisymmetric exchange to magnetic anisotropy with increasing deviation from
the parent compositions and competition between the contributions of single-ion
anisotropy of Fe and Cr ions. It has been suggested that the spatial
orientation of the Neel ${\bf G}$ vector and the $G_{xyz}$ configuration are
the reason for the small value of saturation magnetization observed
experimentally for compositions inside or near the region of negative
magnetization.",2312.04381v2
2024-03-01,Spin current control of magnetism,"Exploring novel strategies to manipulate the order parameter of magnetic
materials by electrical means is of great importance, not only for advancing
our understanding of fundamental magnetism, but also for unlocking potential
practical applications. A well-established concept to date uses gate voltages
to control magnetic properties, such as saturation magnetization, magnetic
anisotropies, coercive field, Curie temperature and Gilbert damping, by
modulating the charge carrier population within a capacitor structure. Note
that the induced carriers are non-spin-polarized, so the control via the
electric-field is independent of the direction of the magnetization. Here, we
show that the magnetocrystalline anisotropy (MCA) of ultrathin Fe films can be
reversibly modified by a spin current generated in Pt by the spin Hall effect.
The effect decreases with increasing Fe thickness, indicating that the origin
of the modification can be traced back to the interface. Uniquely, the change
in MCA due to the spin current depends not only on the polarity of the charge
current but also on the direction of magnetization, i.e. the change in MCA has
opposite sign when the direction of magnetization is reversed. The control of
magnetism by the spin current results from the modified exchange splitting of
majority- and minority-spin bands, and differs significantly from the
manipulation by gate voltages via a capacitor structure, providing a
functionality that was previously unavailable and could be useful in advanced
spintronic devices.",2403.00709v1
2002-10-18,Nonlinear Magnetic Diffusion and Magnetic Helicity Transport in Galactic Dynamos,"We have extended our previous mean-field galactic dynamo model which included
algebraic and dynamic alpha nonlinearities (Kleeorin et al., A&A, v. 387, 453,
2002), to include also a quenching of turbulent diffusivity. We readily obtain
equilibrium states for the large-scale magnetic field in the local disc dynamo
model, and these fields have strengths that are comparable to the equipartition
field strength. We find that the algebraic nonlinearity alone (i.e. quenching
of both the alpha effect and turbulent magnetic diffusion) cannot saturate the
growth of the mean magnetic field; only the combined effect of algebraic and
dynamic nonlinearities can limit the growth of the mean magnetic field.
However, in contrast to our earlier work without quenching of the turbulent
diffusivity, we cannot now find satisfactory solutions in the no-z
approximation to the axisymmetric galactic dynamo problem.",0210430v1
2005-04-15,On the Sr I 4607 A Hanle depolarization signals in the quiet Sun,"The Hanle depolarization signals of Sr 4607 A have been used to estimate the
unsigned magnetic flux and magnetic energy existing in the quiet Sun
photosphere. However, the Sr 4607 A Hanle signals are not sensitive to the
unsigned flux and energy. They only bear information on the fraction of
photosphere occupied by magnetic field strengths smaller than the Hanle
saturation, which do not contribute to the unsigned flux and energy. We deduce
an approximate expression for the relationship between magnetic fill factor and
Hanle signal. When applied to existing Hanle depolarization measurements, it
indicates that only 40% of the quiet Sun is filled by magnetic fields with a
strength smaller than 60 G. The remaining 60% of the surface has field
strengths above this limit. Such constraint will be needed to determine the
distribution of magnetic field strengths existing in the quiet Sun.",0504339v1
2005-07-16,Magnetohydrodynamics in full general relativity: Formulation and tests,"A new implementation for magnetohydrodynamics (MHD) simulations in full
general relativity (involving dynamical spacetimes) is presented. In our
implementation, Einstein's evolution equations are evolved by a BSSN formalism,
MHD equations by a high-resolution central scheme, and induction equation by a
constraint transport method. We perform numerical simulations for standard test
problems in relativistic MHD, including special relativistic magnetized shocks,
general relativistic magnetized Bondi flow in stationary spacetime, and a
longterm evolution for self-gravitating system composed of a neutron star and a
magnetized disk in full general relativity. In the final test, we illustrate
that our implementation can follow winding-up of the magnetic field lines of
magnetized and differentially rotating accretion disks around a compact object
until saturation, after which magnetically driven wind and angular momentum
transport inside the disk turn on.",0507383v1
1996-11-19,Magnetic phase diagram and transport properties of FeGe_2,"We have used resistivity measurements to study the magnetic phase diagram of
the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K
in magnetic fields up to 16 T. In contrast to theoretical predictions, the
incommensurate spin density wave phase is found to be stable at least up to 16
T, with an estimated critical field \mu _0H_c of ~ 30 T. We have also studied
the low temperature magnetoresistance in the [100], [110], and [001]
directions. The transverse magnetoresistance is well described by a power law
for magnetic fields above 1 T with no saturation observed at high fields. We
discuss our results in terms of the magnetic structure and the calculated
electronic bandstructure of FeGe_2. We have also observed, for the first time
in this compound, Shubnikov-de Haas oscillations in the transverse
magnetoresistance with a frequency of 190 +- 10 T for a magnetic field along
[001].",9611144v1
2000-02-17,"Silence of magnetic layers to magnetoresistive process and electronic separation at low temperatures in (La, Sm)Mn$_2$Ge$_2$","A closer look at the temperature (T) dependence of magnetoresistance (MR) of
two polycrystalline magnetic compounds, LaMn$_2$Ge$_2$ and SmMn$_2$Ge$_2$,
previously reported by us, is made. A common feature for both these compounds
is that the low temperature MR is positive (say, below, 30 K) in spite of the
fact that both are ferromagnetic at such low temperatures; in addition, MR as a
function of magnetic field (H) does not track magnetization (M) in the sense
that M saturates at low fields, while MR varies linearly with H. These
observations suggest that the magnetic layers interestingly do not dominate low
temperature magnetotransport process. Interestingly enough, as the T is
increased, say around 100 K, these magnetic layers dominate MR process as
evidenced by the tracking of M and MR in SmMn$_2$Ge$_2$. These results tempts
us to propose that there is an unusual ""electronic separation"" for MR process
as the T is lowered in this class of compounds.",0002275v1
2002-10-14,Magnetic Superstructure in the Two-Dimensional Quantum Antiferromagnet SrCu2(BO3)2,"We report the observation of magnetic superstructure in a magnetization
plateau state of SrCu2(BO3)2, a frustrated quasi-two-dimensional quantum spin
system. The Cu and B nuclear magnetic resonance (NMR) spectra at 35 mllikelvin
indicate an apparently discontinuous phase transition from uniform
magnetization to a modulated superstructure near 27 tesla, above which a
magnetization plateau at 1/8 of the full saturation has been observed.
Comparison of the Cu NMR spectrum and the theoretical analysis of a Heisenberg
spin model demonstrates the crystallization of itinerant triplets in the
plateau phase within a large rhomboid unit cell (16 spins per layer) showing
oscillations of the spin polarization. Thus we are now in possession of an
interesting model system to study a localization transition of strongly
interacting quantum particles.",0210294v1
2003-05-18,A disordered RKKY lattice mean field theory for ferromagnetism in diluted magnetic semiconductors,"We develop a lattice mean field theory for ferromagnetic ordering in diluted
magnetic semiconductors by taking into account the spatial fluctuations
associated with random disorder in the magnetic impurity locations and the
finite mean free path associated with low carrier mobilities. Assuming a
carrier-mediated indirect RKKY exchange interaction among the magnetic
impurities, we find substantial deviation from the extensively used continuum
Zener model Weiss mean-field predictions. Our theory allows accurate analytic
predictions for Tc, and provides simple explanations for a number of observed
anomalies including the non-Brillouin function magnetization curves, the
suppressed low-temperature magnetization saturation, and the dependence of Tc
on conductivity.",0305413v1
2003-12-18,Current induced magnetization dynamics in current perpendicular to the plane spin valves,"We observe magnetization dynamics induced by spin momentum transfer in the
noise spectra of current perpendicular to the plane giant magnetoresistance
spin valves. The dynamics are observable only for those combinations of current
direction and magnetic configuration in which spin transfer acts to reorient
the free layer magnetization away from the direction set by the net magnetic
field. Detailed measurements as a function of magnetic configuration reveal an
evolution of the noise spectra, going from a spectrum with a well-defined noise
peak when the free layer is roughly collinear with the pinned layer to a
spectrum dominated by 1/f noise when the free layer is in an orthogonal
configuration. Finally, the amplitude of the corresponding resistance noise
increases rapidly with increasing current until it saturates at a value that is
a substantial fraction of the magnetoresistance between parallel and
antiparallel states.",0312504v2
2004-04-18,Magnetization process of spin ice in a [111] magnetic field,"Spin ice in a magnetic field in the [111] direction displays two
magnetization plateaux, one at saturation and an intermediate one with finite
entropy. We study the crossovers between the different regimes from a point of
view of (entropically) interacting defects. We develop an analytical theory for
the nearest-neighbor spin ice model, which covers most of the magnetization
curve. We find that the entropy is non-monotonic, exhibiting a giant spike
between the two plateaux. This regime is described by a monomer-dimer model
with tunable fugacities. At low fields, we develop an RG treatment for the
extended string defects, and we compare our results to extensive Monte Carlo
simulations. We address the implications of our results for cooling by
adiabatic (de)magnetization.",0404417v2
2004-08-06,Relevance of a magnetic moment distribution and scaling law methods to study the magnetic behavior of antiferromagnetic nanoparticles,"In antiferromagnetic nanoparticles magnetization the linear component,
$\chi_{AF}$H superposed to the saturation one usually complicates the fit of
experimental data. We present a method based on scaling laws to determine the
variation of $\chi_{AF}$ with temperature and to find the temperature
dependence of the average magnetic moment $<\mu>$, without any assumption on
both the magnetization dependence on field or the moment distribution function,
whose relevance can also be estimated. We have applied this method to ferritin
and found that $<\mu>$ decreases with increasing temperature and that a
distribution function cannot be ignored. The fit with Langevin magnetization
law and lognormal moment distribution functions yielded parameters close to
those estimated with the scaling method. We also show that in general if the
distribution is ignored, and a single particle moment $\mu_p$ is used, $\mu_p$
presents an artificial systematic increase with temperature. This calls the
attention to the necessity of evaluating the effect of a size distribution
before concluding about the physical nature of the parameters variation.",0408134v1
2004-12-22,Ground state and low-lying excitations of the spin-1/2 XXZ model on the kagome lattice at magnetization 1/3,"We study the ground state and low-lying excitations of the S=1/2 XXZ
antiferromagnet on the kagome lattice at magnetization one third of the
saturation. An exponential number of non-magnetic states is found below a
magnetic gap. The non-magnetic excitations also have a gap above the ground
state, but it is much smaller than the magnetic gap. This ground state
corresponds to an ordered pattern with resonances in one third of the hexagons.
The spin-spin correlation function is short ranged, but there is long-range
order of valence-bond crystal type.",0412608v1
2005-07-05,Suppressed magnetization in La$_{0.7}$Ca$_{0.3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-δ}$ superlattices,"We studied the magnetic properties of La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ superlattices. Magnetometry showed that with
increasing YBa$_2$Cu$_3$O$_{7-\delta}$ layer thickness the saturation
magnetization per La$_{0.7}$Ca$_{0.3}$MnO$_3$ layer decreases. From polarized
neutron reflectometry we determined that this magnetization reduction is due to
an inhomogenous magnetization depth profile arising from the suppression of
magnetization near the La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ interface. Electron energy loss spectroscopy
indicates an increased 3d band occupation of the Mn atoms in the
La$_{0.7}$Ca$_{0.3}$MnO$_3$ layers at the interface. Thus, the suppression of
ferromagnetic order at the La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ interface is most likely due to charge transfer
between the two materials.",0507123v2
2005-09-07,Specific heat of the $S = 1$ spin-dimer antiferromagnet Ba$_3$Mn$_2$O$_8$ in high magnetic fields,"We have measured the specific heat of the coupled spin-dimer antiferromagnet
Ba$_3$Mn$_2$O$_8$ to 50 mK in temperature and to 29 T in the magnetic field.
The experiment extends to the midpoint of the field region (25.9 T $\leq H
\leq$ 32.3 T) of the magnetization plateau at 1/2 of the saturation
magnetization, and reveals the presence of three ordered phases in the field
region between that of the magnetization plateau and the low-field spin-liquid
region. The exponent of the phase boundary with the thermally disordered region
is smaller than the theoretical value based on the Bose-Einstein condensation
of spin triplets. At zero field and 29 T, the specific-heat data show gapped
behaviors characteristic of spin liquids. The zero-field data indicate that the
gapped triplet excitations form two levels whose energies differ by nearly a
factor of two. At least the lower level is well localized. The data at 29 T
reveal that the low-lying excitations at the magnetization plateau are weakly
delocalized.",0509169v2
2006-03-07,Magnetization plateau in the S=1/2 spin ladder with alternating rung exchange,"We have studied the ground state phase diagram of a spin ladder with
alternating rung exchange $J^{n}_{\perp} = J_{\perp}[1 + (-1)^{n} \delta ]$ in
a magnetic filed, in the limit where the rung coupling is dominant. In this
limit the model is mapped onto an $XXZ$ Heisenberg chain in a uniform and
staggered longitudinal magnetic fields, where the amplitude of the staggered
field is $\sim \delta$. We have shown that the magnetization curve of the
system exhibits a plateau at magnetization equal to the half of the saturation
value. The width of a plateau scales as $\delta^{\nu}$, where $\nu =4/5$ in the
case of ladder with isotropic antiferromagnetic legs and $\nu =2$ in the case
of ladder with isotropic ferromagnetic legs. We have calculated four critical
fields ($H^{\pm}_{c1}$ and $H^{\pm}_{c2}$) corresponding to transitions between
different magnetic phases of the system. We have shown that these transitions
belong to the universality class of the commensurate-incommensurate transition.",0603153v1
2006-07-19,Magnetic-field dependence of valley splitting for Si quantum wells grown on tilted SiGe substrates,"The valley splitting of the first few Landau levels is calculated as a
function of the magnetic field for electrons confined in a strained silicon
quantum well grown on a tilted SiGe substrate, using a parameterized
tight-binding method. For a zero substrate tilt angle, the valley splitting
slightly decreases with increasing magnetic field. In contrast, the valley
splitting for a finite substrate tilt angle exhibits a strong and
non-monotonous dependence on the magnetic field strength. The valley splitting
of the first Landau level shows an exponential increase followed by a slow
saturation as the magnetic field strength increases. The valley splitting of
the second and third Landau levels shows an oscillatory behavior. The
non-monotonous dependence is explained by the phase variation of the Landau
level wave function along the washboard-like interface between the tilted
quantum well and the buffer material. The phase variation is the direct
consequence of the misorientation between the crystal axis and the confinement
direction of the quantum well. This result suggests that the magnitude of the
valley splitting can be tuned by controlling the Landau-level filling factor
through the magnetic field and the doping concentration.",0607462v1
2006-08-01,Non-collinear long-range magnetic ordering in HgCr2S4,"The low-temperature magnetic structure of \HG has been studied by
high-resolution powder neutron diffraction. Long-range incommensurate magnetic
order sets in at T$_N\sim$22K with propagation vector
\textbf{k}=(0,0,$\sim$0.18). On cooling below T$_N$, the propagation vector
increases and saturates at the commensurate value \textbf{k}=(0,0,0.25). The
magnetic structure below T$_N$ consists of ferromagnetic layers in the
\textit{ab}-plane stacked in a spiral arrangement along the \textit{c}-axis.
Symmetry analysis using corepresentations theory reveals a point group symmetry
in the ordered magnetic phase of 422 (D$_4$), which is incompatible with
macroscopic ferroelectricity. This finding indicates that the spontaneous
electric polarization observed experimentally cannot be coupled to the magnetic
order parameter.",0608031v2
2006-08-14,Simultaneous Antiferromagnetic Fe3+ and Nd3+ Ordering in NdFe3(11BO3)4,"By means of magnetic susceptibility and specific heat measurements, x-ray and
unpolarised neutron diffraction investigations on powder and single-crystal
samples, simultaneous long-range antiferromagnetic Fe and Nd ordering in
NdFe3(11BO3)4 with R 3 2 chemical structure has been found at temperatures
below TN = 30.5(5) K down to 1.6 K. At temperatures down to 20 K to the
propagation vector is khex = [0,0,3/2] and becomes slightly incommensurate at
lower temperatures. Symmetry analysis yields magnetic spiral configurations
with the magnetic moments oriented parallel to hexagonal basal plane according
to the irreducible representations tau_3 in the commensurate case. This is in
agreement with the easy directions of magnetisation perpendicular to the c-axis
as determined by magnetic susceptibility measurements. At 1.6 K the magnetic Fe
moment amounts to 4.9 muB close to the free ion moment of Fe3+. The magnetic
Nd3+ moment saturates presumably due to crystal-field effects at 2.7 muB.",0608304v1
2007-07-21,Toward Coupling Flow Driven and Magnetically Driven Dynamos,"Most large scale dynamo research for astrophysical rotators focuses on
interior flow driven helical dynamos (FDHDs), but larger scale coronal fields
most directly influence observations. It is thus important to understand the
relationship between coronal and interior fields. Coronal field relaxation is
actually a type of magnetically dominated helical dynamo (MDHD). MDHDs also
occur in fusion plasma devices where they drive a system toward its relaxed
state in response to magnetic helicity injection that otherwise drives the
system away from this state. Global scale fields of astrophysical rotators and
jets are thus plausibly produced by a direct coupling between an interior FDHD
and a coronal MDHD, interfaced by magnetic helicity transport through their
mutual boundary. Tracking the magnetic helicity also elucidates how both FDHD
and MDHDs evolve and saturate. The utility of magnetic helicity is unhampered
by its non-gauge invariance since physical fields can always be recovered.",0707.3191v2
2008-02-18,Evolution of Unmagnetized and Magnetized Shear Layers,"We present numerical simulations of the growth and saturation of the
Kelvin-Helmholtz instability in a compressible fluid layer with and without a
weak magnetic field. In the absence of a magnetic field, the instability
generates a single eddy which flattens the velocity profile, stabilizing it
against further perturbations. Adding a weak magnetic field - weak in the sense
that it has almost no effect on the linear instability - leads to a complex
flow morphology driven by MHD forces and to enhanced broadening of the layer,
due to Maxwell stresses. We corroborate earlier studies which showed that
magnetic fields destroy the large scale eddy structure through periodic cycles
of windup and resistive decay, but we show that the rate of decay decreases
with decreasing plasma resistivity, at least within the range of resistivity
accessible to our simulations. Magnetization increases the efficiency of
momentum transport, and the transport increases with decreasing resistivity.",0802.2497v1
2008-07-22,On Fermi acceleration and MHD-instabilities at ultra-relativistic magnetized shock waves,"Fermi acceleration can take place at ultra-relativistic shock waves if the
upstream or downstream magnetic field has been remodeled so that most of the
magnetic power lies on short spatial scales. The relevant conditions under
which Fermi acceleration become efficient in the presence of both a coherent
and a short scale turbulent magnetic field are addressed. Within the MHD
approximation, this paper then studies the amplification of a pre-existing
magnetic field through the streaming of cosmic rays upstream of a relativistic
shock wave. The magnetic field is assumed to be perpendicular in the shock
front frame, as generally expected in the limit of large shock Lorentz factor.
In the MHD regime, compressive instabilities seeded by the net cosmic-ray
charge in the shock precursor (as seen in the shock front frame) develop on the
shortest spatial scales but saturate at a moderate level deltaB/B ~ 1, which is
not sufficient for Fermi acceleration. As we argue, it is possible that other
instabilities outside the MHD range provide enough amplification to allow
successful Fermi acceleration.",0807.3459v3
2009-02-08,Magnetic and magnetoelectric studies in pure and cation doped BiFeO3,"We report magnetic and magnetoelectric studies on BiFeO3 and divalent cation
(A) suvtitute Bi0.7A0.3FeO3 (A = Sr,Ba, and Sr0.5Ba0.5). It is shown that the
rapid increase of magnetization at the Neel temperature (TN = 642 K) is
suppressed in the co-doped compound A = Sr0.5Ba0.5. All the divalent subtituted
compounds show enhanced magnetization and hysteresis loop. Both longitudinal
and transverse magnetoelectric coefficients were measured using the dynamical
lock-in technique. The co-doped compound shows the highest magnetoelectric
coefficient at room temperature although it is not the compound with the
highest saturation magnetization. It is found that as the size of the A-site
cation increses, the transverse magnetoelectric coeffient increases and exceeds
the longitudinal magnetoelectric coefficient. It is suggested that changes in
magnetic domain structure and magnetostriction are possible reasons for the
observed changes in the magnetoelectric coefficients.",0902.1283v1
2009-03-11,Magnetization plateaux in the classical Shastry-Sutherland lattice,"We investigated the classical Shastry-Sutherland lattice under an external
magnetic field in order to understand the recently discovered magnetization
plateaux in the rare-earth tetraborides compounds RB$_4$. A detailed study of
the role of thermal fluctuations was carried out by mean of classical spin
waves theory and Monte-Carlo simulations. Magnetization quasi-plateaux were
observed at 1/3 of the saturation magnetization at non zero temperature. We
showed that the existence of these quasi-plateaux is due to an entropic
selection of a particular collinear state. We also obtained a phase diagram
that shows the domains of existence of different spin configurations in the
magnetic field versus temperature plane.",0903.1985v1
2009-05-27,Transport and Magnetic properties of PrCoIn_5,"Structural, electrical and magnetic measurements of 115 single crystals of
PrIn$_5$ are reported. It has a tetragonal structure and has slightly lower
cell volume than its isomorphic counter part CeCoIn_5. The resistivity
saturates for T\geq 10K. Analysis of the resistivity for 10K<T< 60K indicates a
regular fermi liquid behavior. It does not exhibit superconductivity down to
T\sim 1K. The magnetic susceptibility analysis yielded the moment to be
4.00\mu_B indicating that the magnetism of PrCoIn_5 is dominated by Pr^{3+}
free ions with some admixture of the magnetic moment of the Co sublattice. The
paramagnetic Curie temperature \theta \sim-40K. At low temperatures the
susceptibility follows a broad maximum around T_N \sim 14.5K, and increases as
the temperature is lowered. The disappearance of superconductivity for T>1K is
attributed to chemical pressure effects and magnetic pair breaking.",0905.4536v1
2009-07-23,Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes,"We report on the magnetic hyperthermia properties of chemically synthesized
ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the
saturation magnetization of bulk iron. The specific absorption rate measured on
16 nm nanocubes is 1690+-160 W/g at 300 kHz and 66 mT. This corresponds to
specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in
other systems. A way to quantify the degree of optimization of any system with
respect to hyperthermia applications is proposed. Applied here, this method
shows that our nanoparticles are not fully optimized, probably due to the
strong influence of magnetic interactions on their magnetic response. Once
protected from oxidation and further optimized, such nano-objects could
constitute efficient magnetic cores for biomedical applications requiring very
large heating power.",0907.4063v3
2009-08-26,Influence of an external magnetic field on forced turbulence in a swirling flow of liquid metal,"We report an experimental investigation on the influence of an external
magnetic field on forced 3D turbulence of liquid gallium in a closed vessel. We
observe an exponential damping of the turbulent velocity fluctuations as a
function of the interaction parameter N (ratio of Lorentz force over inertial
terms of the Navier-Stokes equation). The flow structures develop some
anisotropy but do not become bidimensional. From a dynamical viewpoint, the
damping first occurs homogeneously over the whole spectrum of frequencies. For
larger values of N, a very strong additional damping occurs at the highest
frequencies. However, the injected mechanical power remains independent of the
applied magnetic field. The simultaneous measurement of induced magnetic field
and electrical potential differences shows a very weak correlation between
magnetic field and velocity fluctuations. The observed reduction of the
fluctuations is in agreement with a previously proposed mechanism for the
saturation of turbulent dynamos and with the order of magnitude of the Von
Karman Sodium dynamo magnetic field.",0908.3821v1
2010-01-07,Magnetic response of nanoscale left-handed metamaterials,"Using detailed simulations we investigate the magnetic response of
metamaterials consisting of pairs of parallel slabs or combinations of slabs
with wires (including the fishnet design) as the length-scale of the structures
is reduced from mm to nm. We observe the expected saturation of the magnetic
resonance frequency when the structure length-scale goes to the sub-micron
regime, as well as weakening of the effective permeability resonance and
reduction of the spectral width of the negative permeability region. All these
results are explained by using an equivalent resistor-inductor-capacitor (RLC)
circuit model, taking into account the current-connected kinetic energy of the
electrons inside the metallic parts through an equivalent inductance, added to
the magnetic field inductance in the unit-cell. Using this model we derive
simple optimization rules for achieving optical negative permeability
metamaterials of improved performance. Finally, we analyze the magnetic
response of the fishnet design and we explain its superior performance
regarding the high attainable magnetic resonance frequency, as well as its
inferior performance regarding the width of the negative permeability region.",1001.1073v1
2010-04-07,Magnetization plateau and incommensurate spin modulation in Ca3Co2O6,"The magnetic properties of a trigonal prism unit of the spin-2 frustrated
compound Ca3Co2O6 are studied by means of the density-matrix renormalization
group method. A magnetization plateau at $ms/3$ ($ms$ is the saturation
magnetization) with ferrimagnetic structure is observed. By fitting the
experimental data of magnetic curve, an estimation of the couplings gives
J1=-26.84K, J_{2}=0.39K, and J_{3}=0.52K. The local magnetic moments are
unveiled to exhibit an incommensurate sinusoidally modulation along the three
chains of the trigonal prism, which gives a strong theoretical support to the
experimentally observed incommensurate partially disordered antiferromagnetic
state for Ca3Co2O6. The present result suggests that the modulation indeed
originates from the competition of antiferromagnetic and ferromagnetic
couplings.",1004.1031v1
2010-09-20,Variations in magnetic properties of nanostructured nickel,"The magnetic properties of carbon nanotube encapsulated nickel nanowires
(C.E. nanowires of diameter ~ 10 nm), and its comparison to other forms of Ni
are carried out in this work. The saturation magnetization (M_s) and coercivity
(H_c) for C.E. nanowires are 1.0 emu/g and 230 Oe. The temperature dependence
of coercivity follows T^0.77 dependence indicating a superparamagnetic
behavior. The field-cooled and zero-field-cooled plots indicate that the
blocking temperature (T_B) ~ 300 K. These altered magnetic properties of C.E.
nanowires are mainly due to the nanoscale confinement effect from carbon
nanotube encapsulation. The shape and magnetic environment enhance the total
magnetic anisotropy of C.E. nanowires by a factor of four.",1009.3761v1
2011-01-13,Frustrated couplings between alternating spin-1/2 chains in AgVOAsO4,"We report on the crystal structure and magnetic behavior of the spin-1/2
compound AgVOAsO4. Magnetic susceptibility, high-field magnetization, and
electron spin resonance measurements identify AgVOAsO4 as a gapped quantum
magnet with a spin gap Delta ~ 13 K and a saturation field H_s ~ 48.5 T.
Extensive band structure calculations establish the microscopic magnetic model
of spin chains with alternating exchange couplings J ~ 40 K and J' ~ 26 K.
However, the precise evaluation of the spin gap emphasizes the role of
interchain couplings which are frustrated due to the peculiar crystal structure
of the compound. The unusual spin model and the low energy scale of the
exchange couplings make AgVOAsO4 a promising candidate for an experimental
investigation of Bose-Einstein condensation and other exotic ground states in
high magnetic fields.",1101.2546v2
2011-02-13,Magnetization and Lyapunov exponents on a kagome chain with multi-site exchange interaction,"The Ising approximation of the Heisenberg model in a strong magnetic field,
with two, three and six spin exchange interactions is studied on a kagome
chain. The kagome chain can be considered as an approximation of the third
layer of 3He absorbed on the surface of graphite (kagome lattice). By using
dynamical approach we have found one and multi-dimensional mappings (recursion
relations) for the partition function. The magnetization diagrams are plotted
and they show that the kagome chain is separating into four sublattices with
different magnetizations. Magnetization curves of two sublattices exhibit
plateaus at zero and 2/3 of the saturation field. The maximal Lyapunov exponent
for multi-dimensional mapping is considered and it is shown that near the
magnetization plateaus the maximal Lyapunov exponent also exhibits plateaus.",1102.2589v1
2011-03-31,Bulk and Surface Magnetization of Co atoms in Rutile Ti_[1-x]Co_xO_[2-delta] Thin Films Revealed by X-Ray Magnetic Circular Dichroism,"We have studied magnetism in Ti_[1-x]Co_xO_[2-\delta] thin films with various
x and \delta by soft x-ray magnetic circular dichroism (XMCD) measurements at
the Co L_[2,3] absorption edges. The estimated ferromagnetic moment by XMCD was
0.15-0.24 \mu\beta/Co in the surface, while in the bulk it was 0.82-2.25
\mu\beta/Co, which is in the same range as the saturation magnetization of
1.0-1.5 \mu\beta/Co. Theseresults suggest that the intrinsic origin of the
erromagnetism. The smaller moment of Co atom at surface is an indication of a
magnetically dead layer of a few nm thick at the surface of the thin films.",1103.6092v2
2012-03-21,High-field magnetization and magnetoresistance of the $A$-site ordered perovskite oxide CaCu$_{3}$Ti$_{4-x}$Ru$_{x}$O$_{12}$~($0 \le x \le 4$),"We have measured high-field magnetization and magnetoresistance of
polycrystalline samples of the A-site ordered perovskite CaCu3Ti4-xRuxO12 (x=0
- 4) utilizing a non-destructive pulsed magnet. We find that the magnetization
for x=0.5, 1.0 and 1.5 is nonlinear, and tends to saturate in high fields. This
is highly nontrivial because the magnetization for x=0 and 4 is linear in
external field up to the highest one. We have analyzed this field dependence
based on the thermodynamics of magnetic materials, and propose that the
external fields delocalize the holes on the Cu2+ ions in order to maximize the
entropy. This scenario is qualitatively consistent with a large
magnetoresistance of -70% observed at 4.2 K at 52 T for x=1.5.",1203.4660v1
2012-04-11,Frustrated magnets and quantum paramagnetic phases at finite temperature,"We develop a general framework, which combines exact diagonalization in small
clusters with a density matrix variational principle, to study frustrated
magnets at finite temperature. This thermodynamic hierarchical mean-field
technique is used to determine the phase diagram and magnetization process of
the three-dimensional spin-1/2 $J_1$-$J_2$ antiferromagnet on a stacked square
lattice. Its non-magnetic phase exhibits a thermal crossover from a quantum to
a classical paramagnet at a temperature $T=T_0$ which can be extracted from
thermodynamic measurements. At low temperature an applied magnetic field
stabilizes, through order-by-disorder, a variety of phases with non-trivial
spin textures and a magnetization plateau at half-saturation which continuously
disappears at $T\sim T_0$. Our results are relevant for frustrated vanadium
oxides.",1204.2559v2
2012-06-02,Ferromagnetism of cobalt-doped anatase TiO$_2$ studied by bulk- and surface-sensitive soft x-ray magnetic circular dichroism,"We have studied magnetism in anatase Ti$_{1-x}$Co$_x$O$_{2-\delta}$ ({\it x}
= 0.05) thin films with various electron carrier densities, by soft x-ray
magnetic circular dichroism (XMCD) measurements at the Co $L_{2,3}$ absorption
edges. For electrically conducting samples, the magnetic moment estimated by
XMCD was $<$ 0.3 $\mu_B$/Co using the surface-sensitive total electron yield
(TEY) mode, while it was 0.3-2.4 $\mu_B$/Co using the bulk-sensitive total
fluorescence yield (TFY) mode. The latter value is in the same range as the
saturation magnetization 0.6-2.1 $\mu_B$/Co deduced by SQUID measurement. The
magnetization and the XMCD intensity increased with carrier density, consistent
with the carrier-induced origin of the ferromagnetism.",1206.0339v1
2012-06-12,A cascade of magnetic field induced spin transitions in LaCoO3,"We present magnetization and magnetostriction studies of the insulating
perovskite LaCoO3 in magnetic fields approaching 100 T. In marked contrast with
expectations from single-ion models, the data reveal two distinct first-order
spin transitions and well-defined magnetization plateaux. The magnetization at
the higher plateau is only about half the saturation value expected for spin-1
Co3+ ions. These findings strongly suggest collective behavior induced by
strong interactions between different electronic -- and therefore spin --
configurations of Co3+ ions. We propose a model of these interactions that
predicts crystalline spin textures and a cascade of four magnetic phase
transitions at high fields, of which the first two account for the experimental
data.",1206.2603v1
2012-12-19,Spontaneous atomic ordering and magnetism in epitaxially stabilized double perovskites,"We have studied the atomic ordering of B-site transition metals and magnetic
properties in the pulsed-laser deposited films of La2CrFeO6 (LCFO) and La2VMnO6
(LVMO), whose bulk materials are known to be single perovskites with random
distribution of the B-site cations. Despite similar ionic characters of
constituent transition metals in each compound, the maximum B-site order
attained was surprisingly high, ~90% for LCFO and ~80% for LVMO, suggesting a
significant role of epitaxial stabilization in the spontaneous ordering
process. Magnetization and valence state characterizations revealed that the
magnetic ground state of both compounds was coincidently ferrimagnetic with
saturation magnetization of ~2myuB per formula unit, unlike those predicted
theoretically. In addition, they were found to be insulating with optical band
gaps of 1.6 eV and 0.9 eV for LCFO and LVMO, respectively. Our results present
a wide opportunity to explore novel magnetic properties of binary
transition-metal perovskites upon epitaxial stabilization of the ordered phase.",1212.4622v1
2013-03-21,Tuning magnetic anisotropy in (001) oriented L10 (Fe1-xCux)55Pt45 films,"We have achieved (001) oriented L10 (Fe1-xCux)55Pt45 thin films, with
magnetic anisotropy up to 3.6x10^7 erg/cm^3, using atomic-scale multilayer
sputtering and post annealing at 400 {\deg}C for 10 seconds. By fixing the Pt
concentration, structure and magnetic properties are systematically tuned by
the Cu addition. Increasing Cu content results in an increase in the tetragonal
distortion of the L10 phase, significant changes to the film microstructure,
and lowering of the saturation magnetization and anisotropy. The relatively
convenient synthesis conditions, along with the tunable magnetic properties,
make such materials highly desirable for future magnetic recording
technologies.",1303.5208v1
2013-04-08,Reentrant cluster glass behavior in La2CoMnO6 nanoparticles,"Magnetic study on La2CoMnO6 nanoparticles revealed multiple magnetic
transitions at 218 K, 135 K and below 38 K and the nature of the low
temperature transition was unclear [J Appl Phys 111, 024102 2012]. Presence of
mixed valance states of Co and Mn has been confirmed from the XPS measurement
and its presence along with antisite disorder affects in reducing the
saturation magnetization of the nanoparticles. The zero field cooled and field
cooled bifurcation in dc magnetization, relaxation in zero field cooled
magnetization and large enhancement in coercive field below the glassy
temperature has been discussed. Frequency dependence of ac susceptibility using
power law has revealed cluster glass behavior. Further, the dc field
superimposed on ac susceptibility and absence of memory effect in ac
susceptibility has suggested the existence of non interacting clusters
comprising of competing interactions below 38 K. Competing magnetic
interactions due to the presence of mixed valances and antisite disorder found
to establish a reentered cluster glassy state in the nanoparticles.",1304.2267v1
2013-06-13,"Investigation of the quaternary Fe2-xCoxMnSi alloys by structural, magnetic, resistivity and spin polarization measurements","Effects of the Co substitution have been observed on the structural, magnetic
and magneto-transport properties of Fe2-xCoxMnSi alloy. Curie temperature (TC)
and saturation magnetization (MS) of these alloys increased linearly with the
Co substitution. Competitive magnetic interaction between ferromagnetic (FM)
and anti-ferromagnetic (AFM) phases exists in Fe2-xCoxMnSi for x less than 0.2,
AFM phase is completely disappears for x greater than or equal to 0.2. The
value of Rhodes-Wohlfarth ratio pc/ps is greater than one for these alloys
which is the characteristics of iterant magnetism present in the system.
M\""ossbauer spectroscopic measurements have been done to investigate the atomic
disorder and local magnetic moment for some x values. Resistivity measurements
also confirm the stability of ferromagnetism with the concentration of Co and
also show a sign of half metallicity. Resistivity shows semiconducting
behaviour for x = 0.4 which is interesting in view of spin gapless
semiconductors.",1306.3086v3
2013-07-18,Correlation between defect and magnetism of Ar9+ implanted and un-implanted Zn0.95Mn0.05O thin films suitable for electronic application,"Sol-gel derived thin films of Zn0.95Mn0.05O have been implanted with Ar9+
ions with doses viz. 5x10e14 ions/cm2 (low), 1x10e15 ions/cm2 (intermediate)
and 1x10e16 ions/cm2 (high). Structural, morphological, optical and magnetic
properties of the films have been investigated. Structural study confirmed
single phase, wurtzite structure of the films. The absence of impurity phase
has been confirmed from several measurements. Ion implantation induces a large
concentration of point defects into the films as identified from optical study.
All films exhibit well above room temperature (RT) intrinsic ferromagnetism
(FM) as evidenced from field and temperature dependent magnetization
measurements. The magnetization attains the maximum value for high dose of Ar9+
ion implanted film. It shows RT saturation magnetization (MS) value of
0.69emu/gm. The observed FM has been correlated with proportion of intrinsic
defects, such as, zinc and oxygen vacancies and the values of MS. Defect
induced formation of bound magnetic polaron actually controls the FM. The
utility of these films in transparent spin electronic device has also been
exhibited.",1307.4895v1
2013-10-24,Towards wafer scale inductive determination of magnetostatic and dynamic parameters of magnetic thin films and multilayers,"We investigate an inductive probe head suitable for non-invasive
characterization of the magnetostatic and dynamic parameters of magnetic thin
films and multilayers on the wafer scale. The probe is based on a planar
waveguide with rearward high frequency connectors that can be brought in close
contact to the wafer surface. Inductive characterization of the magnetic
material is carried out by vector network analyzer ferromagnetic resonance.
Analysis of the field dispersion of the resonance allows the determination of
key material parameters such as the saturation magnetization MS or the
effective damping parameter Meff. Three waveguide designs are tested. The
broadband frequency response is characterized and the suitability for inductive
determination of MS and Meff is compared. Integration of such probes in a wafer
prober could in the future allow wafer scale in-line testing of magnetostatic
and dynamic key material parameters of magnetic thin films and multilayers.",1310.6578v1
2014-08-18,Magnetic Spiral Arms and Galactic Outflows,"Galactic magnetic arms have been observed between the gaseous arms of some
spiral galaxies; their origin remains unclear. We suggest that magnetic spiral
arms can be naturally generated in the interarm regions because the galactic
fountain flow or wind is likely to be weaker there than in the arms. Galactic
outflows lead to two countervailing effects: removal of small-scale magnetic
helicity, which helps to avert catastrophic quenching of the dynamo, and
advection of the large-scale magnetic field, which suppresses dynamo action.
For realistic galactic parameters, the net consequence of outflows being
stronger in the gaseous arms is higher saturation large-scale field strengths
in the interarm regions as compared to in the arms. By incorporating rather
realistic models of spiral structure and evolution into our dynamo models, an
interlaced pattern of magnetic and gaseous arms can be produced.",1408.3937v2
2014-09-02,Anisotropic magnetodielectric coupling behavior of Ca3Co1.4Rh0.6O6 due to geometrically frustrated magnetism,"We have investigated the magnetic, dielectric and magnetodielectric (MDE)
behavior of a geometrically frustrated spin-chain system, Ca3Co1.4Rh0.6O6, in
the single crystalline form for different orientations. The results bring out
that the magnetic behavior of this compound is by itself interesting in the
sense that this compound exhibits an anisotropic glassy-like magnetic behavior
with a huge frequency dependence of ac susceptibility peak for an orientation
along the spin-chain in the range 30-60 K; this behavior is robust to
applications of large external magnetic fields (H) unlike in canonical
spin-glasses. The temperature dependence of dielectric constant also shows
strong frequency dependence with similar robustness to H. The isothermal
H-dependent dielectric results at low temperatures establishes anisotropic MDE
coupling. It is intriguing to note that there is a 'step' roughly at one-third
of saturation values as in the case of isothermal magnetization curves for same
temperatures (for orientation along spin-chain), a correlation hitherto
unrealized for geometrically frustrated systems.",1409.0783v1
2014-10-21,Investigation of Force-Freeness of Solar Emerging Magnetic Field via Application of the Virial Theorem to MHD Simulations,"Force-freeness of a solar magnetic field is a key to reconstructing invisible
coronal magnetic structure of an emerging flux region on the Sun where active
phenomena such as flares and coronal mass ejections frequently occur. We have
performed magnetohydrodynamic (MHD) simulations which are adjusted to
investigate force-freeness of an emerging magnetic field by using the virial
theorem. Our focus is on how the force-free range of an emerging flux region
develops and how it depends on the twist of a pre-emerged magnetic field. As an
emerging flux region evolves, the upper limit of the force-free range
continuously increases while the lower limit is asymptotically reduced to the
order of a photospheric pressure scale height above the solar surface. As the
twist becomes small the lower limit increases and then seems to be saturated.
We also discuss the applicability of the virial theorem to an evolving magnetic
structure on the Sun.",1410.5542v1
2014-11-04,Magnetoimpedance effect at the high frequency range for the thin film geometry: Numerical calculation and experiment,"The magnetoimpedance effect is a versatile tool to investigate ferromagnetic
materials, revealing aspects on the fundamental physics associated to
magnetization dynamics, broadband magnetic properties, important issues for
current and emerging technological applications for magnetic sensors, as well
as insights on ferromagnetic resonance effect at non-saturated magnetic states.
Here, we perform a theoretical and experimental investigation of the
magnetoimpedance effect for the thin film geometry in a wide frequency range.
We calculate the longitudinal magnetoimpedance for single layered, multilayered
or exchange biased systems from an approach that considers a magnetic
permeability model for planar geometry and the appropriate magnetic free energy
density for each structure. From numerical calculations and experimental
results found in literature, we analyze the magnetoimpedance behavior, and
discuss the main features and advantages of each structure. To test the
robustness of the approach, we directly compare theoretical results with
experimental magnetoimpedance measurements obtained in a wide range of
frequencies for an exchange biased multilayered film. Thus, we provide
experimental evidence to confirm the validity of the theoretical approach
employed to describe the magnetoimpedance in ferromagnetic films, revealed by
the good agreement between numerical calculations and experimental results.",1411.0971v1
2014-11-23,Studying the Magnetic Properties of CoSi Single Crystals,"The magnetic properties of CoSi single crystals have been measured in a range
of temperatures $T = 5.5 - 450$ K and magnetic field strengths $H \leq 11$ kOe.
A comparison of the results for crystals grown in various laboratories allowed
the temperature dependence of magnetic susceptibility $\chi(T) = M(T)/H$ to be
determined for a hypothetical ""ideal"" (free of magnetic impurities and defects)
CoSi crystal. The susceptibility of this ideal crystal in the entire
temperature range exhibits a diamagnetic character. The $\chi(T)$ value
significantly increases in absolute value with decreasing temperature and
exhibits saturation at the lowest temperatures studied. For real CoSi crystals
of four types, paramagnetic contributions to the susceptibility have been
evaluated and nonlinear (with respect to the field) contributions to the
magnetization have been separated and taken into account in the calculations of
$\chi(T)$.",1411.6242v1
2014-12-15,High pressure neutron scattering of the magnetoelastic Ni-Cr Prussian blue analogue,"This paper summarizes 0 GPa to 0.6 GPa neutron diffraction measurements of a
nickel hexacyanochromate coordination polymer (NiCrPB) that has the
face-centered cubic, Prussian blue structure. Deuterated powders of NiCrPB
contain ~100 nm sided cubic particles. The application of a large magnetic
field shows the ambient pressure, saturated magnetic structure. Pressures of
less than 1 GPa have previously been shown to decrease the magnetic
susceptibility by as much as half, and we find modifications to the nuclear
crystal structure at these pressures that we quantify. Bridging cyanide
molecules isomerize their coordination direction under pressure to change the
local ligand field and introduce inhomogeneities in the local (magnetic)
anisotropy that act as pinning sites for magnetic domains, thereby reducing the
low field magnetic susceptibility.",1412.4712v1
2015-06-09,Spin dynamics in a Curie-switch,"Ferromagnetic resonance properties of F$_1$/f/F$_2$/AF multilayers, where
weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic
layers F$_1$ and F$_2$, with F$_1$ being magnetically soft and F$_2$ -
magnetically hard due to exchange pinning to antiferromagnetic layer AF, are
investigated. Spacer-mediated exchange coupling is shown to strongly affect the
resonance fields of both F$_1$ and F$_2$ layers. Our theoretical calculations
as well as measurements show that the key magnetic parameters of the spacer,
which govern the ferromagnetic resonance in F$_1$/f/F$_2$/AF, are the magnetic
exchange length ($\Lambda$), effective saturation magnetization at $T=0$
$(m_0)$, and effective Curie temperature ($T_{\text{C}}^{\text{eff}}$). The
values of these key parameters are deduced from the experimental data for
multilayers with f = Ni$_x$Cu$_{100-x}$, for the key ranges in Ni-concentration
($x=54\div70$ at. %) and spacer thickness ($d=3\div 6$ nm). The results
obtained provide a deeper insight into thermally-controlled spin precession and
switching in magnetic nanostructures, with potential applications in spin-based
oscillators and memory devices.",1506.02928v1
2015-07-02,Macroscopic Simulation of Isotropic Permanent Magnets,"Accurate simulations of isotropic permanent magnets require to take the
magnetization process into account and consider the anisotropic, nonlinear, and
hysteretic material behaviour near the saturation configuration. An efficient
method for the solution of the magnetostatic Maxwell equations including the
description of isotropic permanent magnets is presented. The algorithm can
easily be implemented on top of existing finite element methods and does not
require a full characterization of the hysteresis of the magnetic material.
Strayfield measurements of an isotropic permanent magnet and simulation results
are in good agreement and highlight the importance of a proper description of
the isotropic material.",1507.00450v1
2015-08-10,Field dependent magnetization of BiFeO3 in ultrathin La0.7Sr0.3MnO3/BiFeO3 superlattice,"We report the observation of field-induced magnetization of BiFeO3 (BFO) in
an ultrathin BFO/La0.7Sr0.3MnO3 (LSMO) superlattice using polarized neutron
reflectivity (PNR). Our PNR results indicate parallel alignment of
magnetization across BFO/LSMO interfaces. The study showed an increase in
average magnetization on increasing applied magnetic field at 10K. We observed
a saturation magnetization of 110 \pm 15 kA/m (~0.8 {\mu}B/Fe) for ultrathin
BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit
cell), which is much higher than the canted moment (0.03 {\mu}B/Fe) in the bulk
BFO. The macroscopic VSM results on superlattice clearly indicate
superparamagnetic behavior typically observed in nanoparticles of manganites.",1508.02218v1
2015-08-31,Surface functionalization enhanced magnetism in SnO_2 nanoparticles and its correlation to photoluminescence properties,"High value of magnetic moment 0.08 emu/g at room temperature for SnO_2
nanoparticles (NPs) was observed. Surface functionalization with
octadecyltrichlorosilane (OTS) enhanced the saturation magnetic moment of NPs
to an anomalously high value of 0.187 emu/g by altering the electronic
configuration on NPs surface. Surface functionalization also suppressed
photoluminescence (PL) peaks arising from oxygen defects around 2 eV and caused
an increase in the intensities of two peaks near violet region (2.6 - 3 eV). PL
studies under uniform external magnetic field enriched understanding of the
role of OTS. Both OTS and external magnetic field significantly modulated the
luminescence spectra, by altering the surface electronic structure of NPs.
Extra spins on the surface of SnO2 NPs created by the surface functionalization
process and their influence on resultant magnetic moment and luminescence
properties are discussed in details.",1508.07791v1
2015-11-06,"Structural, magnetic and electrical properties of sputter deposited Mn-Fe-Ga thin films","We investigated structural, magnetic and electrical properties of sputter
deposited Mn-Fe-Ga compounds. The crystallinity of the Mn-Fe-Ga thin films was
confirmed using x-ray diffraction. X-ray reflection and atomic force microscopy
measurements were utilized to investigate the surface properties, roughness,
thickness and density of the deposited Mn-Fe-Ga. Depending on the
stoichiometry, as well as the used substrates (SrTiO3 (001) and MgO (001)) or
buffer layer (TiN) the Mn-Fe-Ga crystallizes in the cubic or the tetragonally
distorted phase. Anomalous Hall effect and alternating gradient magnetometry
measurements confirmed strong perpendicular magnetocrystalline anisotropy. Low
saturation magnetization and hard magnetic behavior was reached by tuning the
composition. Temperature dependent anomalous Hall effect measurements in a
closed cycle He-cryostat showed a slight increase in coercivity with decreasing
temperature (300K to 2K). TiN buffered Mn2.7Fe0.3Ga revealed sharper switching
of the magnetization compared to the unbuffered layers.",1511.02097v2
2016-04-18,Spontaneous Formation of Surface Magnetic Structure from Large-scale Dynamo in Strongly-stratified Convection,"We report the first successful simulation of spontaneous formation of surface
magnetic structures from a large-scale dynamo by strongly-stratified thermal
convection in Cartesian geometry. The large-scale dynamo observed in our
strongly-stratified model has physical properties similar to those in earlier
weakly-stratified convective dynamo simulations, indicating that the
$\alpha^2$-type mechanism is responsible for it. Additionally to the
large-scale dynamo, we find that large-scale structures of the vertical
magnetic field are spontaneously formed in the convection zone surface only for
the case of strongly-stratified atmosphere. The organization of the vertical
magnetic field proceeds in the upper convection zone within tens of convective
turn-over time and band-like bipolar structures are recurrently-appeared in the
dynamo-saturated stage. We examine possibilities of several candidates as the
origin of the surface magnetic structure formation, and then suggest the
existence of an as-yet-unknown mechanism for the self-organization of the
large-scale magnetic structure, which should be inherent in the
strongly-stratified convective atmosphere.",1604.05374v1
2016-07-13,"Breakdown of a Magnetization Plateau in Ferrimagnetic Mixed Spin-(1/2,S) Heisenberg Chains Due to a Quantum Phase Transition Towards the Luttinger Spin Liquid","Magnetization curves of the ferrimagnetic mixed spin-(1/2,S) Heisenberg
chains are calculated with the help of density-matrix renormalization group
method for several quantum spin numbers S=1, 3/2, 2 and 5/2. It is shown that
the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains exhibit irrespective of
the spin value S exactly one intermediate magnetization plateau, which can be
identified with the gapped Lieb-Mattis ferrimagnetic ground state. The
magnetization plateau due to the Lieb-Mattis ferrimagnetism breaks down at a
quantum phase transition towards the Luttinger spin liquid, which is
characterized by a continuous change of the magnetization with the magnetic
field until another quantum critical point is reached at the saturation field.",1607.03617v1
2016-08-09,Infinitely Multiple Steps in Magnetization of Ferro- and Antiferromagnetic Ising Models with Frustration on a Diamond Hierarchical Lattice,"Magnetizations of ferro- and antiferromagnetic Ising models with frustration
on diamond hierarchical lattices are exactly obtained at zero temperature. For
the zero-field classical spin-liquid phase found in [Kobayashi {\it et al}, J.
Phys. Soc. Jpn. 78, 074004 (2009) ], for which frustrating interactions play an
important role, an infinitely small applied magnetic field can induce an
infinitely small magnetization, despite classical Ising models that have
discrete energy levels. In antiferromagnetic systems, the magnetization cannot
saturate under finite magnetic fields owing to the competition between the
unfrustrating antiferromagnetic interaction and the Zeeman interaction and an
intrinsic long-range nature of hierarchical lattices.",1608.02865v1
2016-08-09,Exact Solutions on the Ground States of Ising Models in Magnetic Fields with Frustration on a Diamond Hierarchical Lattice,"Magnetization processes of Ising models with frustration on diamond
hierarchical lattices, which contain vertices with high coordination numbers,
are exactly obtained at zero temperature. In antiferromagnetic systems, the
magnetization cannot saturate under finite magnetic fields owing to the
competition between the antiferromagnetic and Zeeman interactions and the
intrinsic long-range nature of hierarchical lattices. For the zero-field
classical spin-liquid phase found in [Kobayashi et al., J. Phys. Soc. Jpn. 78,
074004 (2009)], an infinitely small applied magnetic field can induce an
infinitely small magnetization, despite Ising models that have discrete energy
levels. By examining the structure of the partition function, we obtain the
ground state spin-configurations and clarify the mechanism of the ""gapless like
behavior"".",1608.02878v1
2016-10-21,Tailoring non-collinear magnetism by misfit dislocation lines,"The large epitaxial stress induced by the misfit between a triple atomic
layer Fe film and an Ir(111) substrate is relieved by the formation of a dense
dislocation line network. Spin-polarized scanning tunneling microscopy (SP-STM)
investigations show that the strain is locally varying within the Fe film and
that this variation affects the magnetic state of the system. Two types of
dislocation line regions can be distinguished and both exhibit spin spirals
with strain-dependent periods (ranging from 3 nm to 10 nm). Using a simple
micromagnetic model, we attribute the changes of the period of the spin spirals
to variations of the effective exchange coupling in the magnetic film. This
assumption is supported by the observed dependence of the saturation magnetic
field on the spin spiral period. Moreover, magnetic skyrmions appear in an
external magnetic field only in one type of dislocation line area, which we
impute to the different pinning properties of the dislocation lines.",1610.06785v1
2016-11-09,Voltage control of magnetic anisotropy in epitaxial Ru/Co2FeAl/MgO heterostructures,"Voltage control of magnetic anisotropy (VCMA) in magnetic heterostructures is
a key technology for achieving energy-efficiency electronic devices with
ultralow power consumption. Here, we report the first demonstration of the VCMA
effect in novel epitaxial Ru/Co2FeAl(CFA)/MgO heterostructures with interfacial
perpendicular magnetic anisotropy (PMA). Perpendicularly magnetized tunnel
junctions with the structure of Ru/CFA/MgO were fabricated and exhibited an
effective voltage control on switching fields for the CFA free layer. A large
VCMA coefficient of 108 (139) fJ/Vm for the CFA film was achieved at room
temperature (4 K). The interfacial stability in the heterostructure was
confirmed by repeating measurements. Temperature dependences of both the
interfacial PMA and the VCMA effect were also investigated. It is found that
the temperature dependences follow power laws of the saturation magnetization
with an exponent of ~2. The significant VCMA effect observed in this work
indicates that the Ru/CFA/MgO heterostructure could be one of the promising
candidates for spintronic devices with voltage control.",1611.02827v1
2016-12-30,Nuclear magnetic resonance signature of the spin-nematic phase in LiCuVO$_{4}$ at high magnetic fields,"We report a 51V nuclear magnetic resonance investigation of the frustrated
spin-1/2 chain compound LiCuVO4, performed in pulsed magnetic fields and
focused on high-field phases up to 55 T. For the crystal orientations H // c
and H // b we find a narrow field region just below the magnetic saturation
where the local magnetization remains uniform and homogeneous, while its value
is field dependent. This behavior is the first microscopic signature of the
spin-nematic state, breaking spin-rotation symmetry without generating any
transverse dipolar order, and is consistent with theoretical predictions for
the LiCuVO4 compound.",1612.09483v3
2017-02-19,The population of highly magnetized neutron stars,"In this work, we study the effects of strong magnetic field configurations on
the population of neutron stars. The stellar matter is described within a
relativistic mean field formalism which considers many-body force contributions
in the scalar couplings. We choose the parametrization of the model that
reproduces nuclear matter properties at saturation and also describes massive
hyperon stars. Hadronic matter is modeled at zero temperature, in
beta-equilibrium, charge neutral and populated by the baryonic octet, electrons
and muons. Magnetic effects are taken into account in the structure of stars by
the solution of the Einstein-Maxwell equations with the assumption of a
poloidal magnetic field distribution. Our results show that magnetic neutron
stars are populated essencialy by nucleons and leptons, due to the fact that
strong magnetic fields decrease the central density of stars and, hence,
supress the appearance of exotic particles.",1702.05684v2
2017-03-15,Anisotropic super-paramagnetism in cobalt implanted rutile-TiO2 single crystals,"We study the magnetic properties of single crystals of rutile TiO2 implanted
with cobalt for various fluences. The temperature variation of zero field
cooled(ZFC) and field cooled (FC) magnetization shows a much higher blocking
temperature (TB) along [1-10]. Similarly the scaling of magnetization isotherms
above TB is seen only when the field is parallel to [1-10] direction. With
field along this direction, the magnetization shows near saturation at a much
smaller field compared to that of[001] direction. The Co nanoclusters possess
an ""easy"" and ""hard axis"" of magnetization coupled by the magneto crystalline
anisotropy of secondary phases of cobalt with TiO2. In addition, at T=2 K we
observe a crossover in the magnetization vs field isotherms between the two
field directions in the samples which has been attributed to the anisotropic
paramagnetism arising from cobalt present in 2+ ionic state with S = 3/2.",1703.04965v1
2017-06-23,Detection of induced paramagnetic moments in Pt on Y$_3$Fe$_5$O$_{12}$ via x-ray magnetic circular dichroism,"Magnetic moments in an ultra-thin Pt film on a ferrimagnetic insulator
Y$_3$Fe$_5$O$_{12}$ (YIG) have been investigated at high magnetic fields and
low temperatures by means of X-ray magnetic circular dichroism (XMCD). We
observed an XMCD signal due to the magnetic moments in a Pt film at the Pt
$L_{3}$- and $L_{2}$-edges. By means of the element-specific magnetometry, we
found that the XMCD signal at the Pt $L_{3}$-edge gradually increases with
increasing the magnetic field even when the field is much greater than the
saturation field of YIG. Importantly, the observed XMCD intensity was found to
be much greater than the intensity expected from the Pauli paramagnetism of Pt
when the Pt film is attached to YIG. These results imply the emergence of
induced paramagnetic moments in Pt on YIG and explain the characteristics of
the unconventional Hall effect in Pt/YIG systems.",1706.07559v1
2017-09-07,Could the low braking index pulsar PSR J1734-3333 evolve into a magnetar?,"The low braking-index pulsar PSR J1734$-$3333 could be born with superhigh
internal magnetic fields $B_{\rm in}\sim10^{15}-10^{16}$ G, and undergo a
supercritical accretion soon after its formation in a supernova explosion. The
buried multipole magnetic fields will merger into a dipole magnetic field.
Since the magnetic flow transfers from the core to the crust of the pulsar, its
surface dipole field grows quickly at a power-law form assumed until it
saturates at the level of internal dipole field. The increase in surface dipole
magnetic field results in the observed low braking index of $n=0.9(2)$. Keeping
an average field growth index $\varepsilon=1.34(6)$, this pulsar will become a
magnetar with surface dipole magnetic field at the equator $B_{\rm d}\sim
2.6(1)\times 10^{14}$\,G and $\sim 5.3(2)\times 10^{14}$\,G after next 50\,kyrs
and 100\,kys, respectively.",1709.02734v3
2017-10-12,Frustrated two dimensional quantum magnets,"We overview physical effects of exchange frustration and quantum spin
fluctuations in (quasi-) two dimensional (2D) quantum magnets ($S=1/2$) with
square, rectangular and triangular structure. Our discussion is based on the
$J_1$-$J_2$ type frustrated exchange model and its generalizations. These
models are closely related and allow to tune between different phases,
magnetically ordered as well as more exotic nonmagnetic quantum phases by
changing only one or two control parameters. We survey ground state properties
like magnetization, saturation fields, ordered moment and structure factor in
the full phase diagram as obtained from numerical exact diagonalization
computations and analytical linear spin wave theory. We also review finite
temperature properties like susceptibility, specific heat and magnetocaloric
effect using the finite temperature Lanczos method. This method is powerful to
determine the exchange parameters and g-factors from experimental results. We
focus mostly on the observable physical frustration effects in magnetic phases
where plenty of quasi-2D material examples exist to identify the influence of
quantum fluctuations on magnetism.",1710.04399v1
2018-01-23,Correlation between Magnetic Properties and Depinning Field in Field-Driven Domain Wall Dynamics in GdFeCo Ferrimagnets,"The influence of temperature on the magnetic-field-driven domain wall (DW)
motion is investigated in GdFeCo ferrimagnets with perpendicular magnetic
anisotropy (PMA). We find that the depinning field strongly depends on
temperature. Moreover, it is also found that the saturation magnetization
exhibits a similar dependence on temperature to that of depinning field. From
the creep-scaling criticality, a simple relation between the depinning field
and the properties of PMA is clearly identified theoretically as well as
experimentally. Our findings open a way for a better understanding how the
magnetic properties influence on the depinning field in magnetic system and
would be valuably extended to depinning studies in other system.",1801.07436v1
2018-02-26,Small-scale dynamos in simulations of stratified turbulent convection,"Small-scale dynamo action is often held responsible for the generation of
quiet-Sun magnetic fields. We aim to determine the excitation conditions and
saturation level of small-scale dynamos in non-rotating turbulent convection at
low magnetic Prandtl numbers. We use high resolution direct numerical
simulations of weakly stratified turbulent convection. We find that the
critical magnetic Reynolds number for dynamo excitation increases as the
magnetic Prandtl number is decreased, which might suggest that small-scale
dynamo action is not automatically evident in bodies with small magnetic
Prandtl numbers as the Sun. As a function of the magnetic Reynolds number
(${\rm Rm}$), the growth rate of the dynamo is consistent with an ${\rm
Rm}^{1/2}$ scaling. No evidence for a logarithmic increase of the growth rate
with ${\rm Rm}$ is found.",1802.09607v1
2018-04-10,Force-detected high-frequency electron spin resonance spectroscopy using magnet-mounted nanomembrane: robust detection of thermal magnetization modulation,"In this study, we report a conceptually novel broadband high-frequency
electron spin resonance (HFESR) spectroscopic technique. In contrast to the
ordinary force-detected ESR technique, which detects the magnetization change
due to the saturation effect, this method measures the magnetization change due
to the change of the sample temperature at resonance. To demonstrate its
principle, we developed a silicon nitride nanomembrane-based force-detected ESR
spectrometer, which can be stably operated even at high magnetic fields. Test
measurements were performed for samples with different spin relaxation times.
We succeeded in obtaining a seamless ESR spectrum in magnetic fields of 15~T
and frequencies of 636~GHz without significant spectral distortion. A high spin
sensitivity of $10^{12}$~spins/G$\cdot$s was obtained, which was independent of
the spin relaxation time. These results show that this technique can be used as
a practical method in research fields where the HFESR technique is applicable.",1804.03345v3
2018-07-05,Domain wall dynamics for an in-plane magnetized thin film with large perpendicular hard axis anisotropy including Dzyaloshinskii-Moriya interaction,"We consider a thin ferromagnetic layer to which an external field or a
current are applied along an in plane easy axis. The perpendicular hard axis
anisotropy constant is large so that the out of plane magnetization component
is smaller than the in plane components. A perturbation approach is used to
obtain the profile and velocity of the moving domain wall. The dynamics of the
in plane components of the magnetization is governed by a reaction diffusion
equation which determines the speed of the profile. We find a simple analytic
expression for the out of plane magnetization showing a symmetric distortion
due to the motion in addition to the asymmetric component due to the
Dzyaloshinskii--Moriya interaction. The results obtained complement previous
studies in which either the Dzyalozhinskii vector or the out of plane hard axis
anisotropy were assumed small. In the regime studied the Walker breakdown is
not observed but the reaction diffusion dynamics predicts a slowing down of the
domain wall for sufficiently large magnetic field. The transition point depends
on the applied field, saturation magnetization and easy axis anisotropy.",1807.02032v1
2018-07-25,Thermodynamics of a frustrated quantum magnet on a square lattice,"We report the magnetic and calorimetric measurements in single crystal
samples of the square lattice $J_{1}-J_{2}$ quantum antiferromagnet
BaCdVO(PO$_4$)$_2$. An investigation of the scaling of magnetization reveals a
""dimensionality reduction"" indicative of a strong degree of geometric
frustration. Below a characteristic temperature of $T^{\ast}\simeq150$~mK we
observe the emergence of an additional strongly fluctuating quantum phase close
to full magnetic saturation. It is separated from the magnetically ordered
state by first- and second-order phase transitions, depending on the
orientation of the applied magnetic field. We suggest that this phase may
indeed be related to the theoretically predicted spin-nematic state.",1807.09549v2
2018-12-11,"Enhanced mixing in magnetized fingering convection, and implications for RGB stars","Double-diffusive convection has been well studied in geophysical contexts,
but detailed investigations of the regimes characteristic of stellar or
planetary interiors have only recently become feasible. Since most
astrophysical fluids are electrically conducting, it is possible that magnetic
fields play a role in either enhancing or suppressing double-diffusive
convection, but to date there have been no numerical investigations of such
possibilities. Here we study the effects of a vertical background magnetic
field (aligned with the gravitational axis) on the linear stability and
nonlinear saturation of fingering (thermohaline) convection, through a
combination of theoretical work and direct numerical simulations (DNSs). We
find that a vertical magnetic field rigidifies the fingers along the vertical
direction which has the remarkable effect of enhancing vertical mixing. We
propose a simple analytical model for mixing by magnetized fingering
convection, and argue that magnetic effects may help explain discrepancies
between theoretical and observed mixing rates in low-mass red giant branch
(RGB) stars. Other implications of our findings are also discussed.",1812.04687v1
2019-03-29,Putative spin-nematic phase in BaCdVO(PO$_{4}$)$_{2}$,"We report neutron scattering and AC magnetic susceptibility measurements of
the 2D spin-1/2 frustrated magnet BaCdVO(PO$_{4}$)$_{2}$. At temperatures well
below $T_{\sf N}\approx 1K$, we show that only 34 % of the spin moment orders
in an up-up-down-down strip structure. Dominant magnetic diffuse scattering and
comparison to published $\mu$sr measurements indicates that the remaining 66 %
is fluctuating. This demonstrates the presence of strong frustration,
associated with competing ferromagnetic and antiferromagnetic interactions, and
points to a subtle ordering mechanism driven by magnon interactions. On
applying magnetic field, we find that at $T=0.1$ K the magnetic order vanishes
at 3.8 T, whereas magnetic saturation is reached only above 4.5 T. We argue
that the putative high-field phase is a realization of the long-sought
bond-spin-nematic state.",1903.12462v1
2019-07-27,Magnetization plateau of the $S=2$ antiferromagnetic Heisenberg chain with anisotropies,"We investigate the $S=2$ antiferromagnetic quantum spin chain with the
exchange and single-ion anisotropies in a magnetic field, using the numerical
exact diagonalization of finite-size clusters and the level spectroscopy
analysis. It is found that a magnetization plateau possibly appears at a half
of the saturation magnetization for some suitable anisotropy parameters. The
level spectroscopy analysis indicates that the 1/2 magnetization plateau is
formed by two different mechanisms, depending on the anisotropy parameters. The
phase diagram of the 1/2 plateau states and some typical magnetization curves
are also presented. In addition the biquadratic interaction is revealed to
enhance the plateau induced by the Haldane mechanism.",1907.11931v2
2019-09-04,Density wave and topological reconstruction of an isotropic two-dimensional electron band in external magnetic field,"We predict a mechanism of spontaneous stabilization of a uniaxial density
wave in a two-dimensional metal with an isotropic Fermi surface in the presence
of external magnetic field. The topological transformation of a closed Fermi
surface into an open one decreases the electron band energy due to
delocalization of electrons initially localized by magnetic field, additionally
affected by the magnetic breakdown effect. The driving mechanism of such
reconstruction is a periodic potential due to the self-consistently formed
electron density wave. It is accompanied with quantum oscillations periodic in
inverse magnetic field, similar to the standard de Haas - van Alphen effect,
due to Landau level filling. The phase transition appears as a quantum one at
T=0, provided the relevant coupling constant is above the critical one. This
critical value rapidly decreases, and finally saturates toward zero on the
scale of tens of Tesla. Thus, a strong enough magnetic field can induce the
density wave in the system in which it was absent in zero field.",1909.01781v1
2019-11-18,Chemical synthesis and magnetic properties of monodisperse cobalt ferrite nanoparticles,"In this work, a successful synthesis of magnetic cobalt ferrite (CoFe2O4)
nanoparticles is presented. The synthesized CoFe2O4 nanoparticles have a
spherical shape and highly monodisperse in the selected solvent. The effect of
different reaction conditions such as temperature, reaction time and varying
capping agents on the phase and morphology is studied. Scanning transmission
electron microscopy showed that the size of these nanoparticles can be
controlled by varying reaction conditions. Both X-ray diffraction and energy
dispersive X-ray spectroscopy corroborate the formation of CoFe2O4 spinel
structure with cubic symmetry. Due to optimized reaction parameters, each
nanoparticle was shown to be a single magnetic domain with diameter ranges from
6 to 16 nm. Finally, the magnetic investigations showed that the obtained
nanoparticles are superparamagnetic with a small coercivity value of about 315
Oe and a saturation magnetization of 58 emu/g at room temperature. These
results make the cobalt ferrite nanoparticles promising for advanced magnetic
nanodevices and biomagnetic applications.",1911.07496v1
2020-02-07,Half-magnetization plateau and the origin of threefold symmetry breaking in an electrically-switchable triangular antiferromagnet,"We perform high-field magnetization measurements on the triangular lattice
antiferromagnet Fe$_{1/3}$NbS$_2$. We observe a plateau in the magnetization
centered at approximately half the saturation magnetization over a wide range
of temperature and magnetic field. From density functional theory calculations,
we determine a likely set of magnetic exchange constants. Incorporating these
constants into a minimal Hamiltonian model of our material, we find that the
plateau and of the $Z_3$ symmetry breaking ground state both arise from
interplane and intraplane antiferromagnetic interactions acting in competition.
These findings are pertinent to the magneto-electric properties of
Fe$_{1/3}$NbS$_2$, which allow electrical switching of antiferromagnetic
textures at relatively low current densities.",2002.02960v2
2020-04-09,Magnetic field-dependent resistance crossover and logarithmic to non-saturating magnetoresistance in topological insulator Bi$_2$Te$_3$,"We report a metal-insulator like transition in single crystalline 3D
topological insulator Bi2Te3 at a temperature of 230K in presence of an
external magnetic field applied normal to the surface. This transition becomes
more prominent at larger magnetic field strength with the residual resistance
value increasing linearly with the magnetic field. At low temperature, the
magnetic field dependence of the magnetoresistance shows a transition from
logarithmic to linear behavior and the onset magnetic field value for this
transition decreases with increasing temperature. The logarithmic
magnetoresistance indicates the weak anti-localization of the surface Dirac
electrons while the high temperature behavior originates from the bulk carriers
due to intrinsic impurities. At even higher temperatures beyond~230 K, a
completely classical Lorentz model type quadratic behavior of the
magnetoresistance is observed. We also show that the experimentally observed
anomalies at ~230K in the magneto-transport properties do not originate from
any stacking fault in Bi2Te3.",2004.04375v2
2020-04-14,High-intensity pulsed ion beam treatment of amorphous iron-based metal alloy,"Abstract The results of intense pulsed ion beam (IPIB) treatment of the soft
magnetic amorphous alloy of a FINEMET-type are presented. Foil produced from
the alloy was irradiated with short (about 100 ns) pulses of carbon ions and
protons with energy of up to 300 keV and an energy density of up to 7 J/cm2.
X-ray diffraction, M\""ossbauer spectroscopy and magnetic measurements were used
to investigate structural and magnetic properties of irradiated foils. It is
shown that the foil remains intact after the treatment, and the crystal
structure still amorphous. Spontaneous magnetization vector is found to lie
almost along perpendicular to the foil plane after irradiation, whereas for the
initial amorphous foil it belongs to the plane. The magnetic properties of the
foil undergo changes: the coercive force decreases, the saturation induction
increases slightly, and the magnetization curve has shallower slope.",2004.06410v1
2021-02-04,Classical Spin Liquid State in the $S=\frac{5}{2}$ Heisenberg Kagomé Antiferromagnet Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$,"We investigate the low temperature magnetic properties of a $S=\frac{5}{2}$
Heisenberg kagom\'e antiferromagnet, the layered monodiphosphate
Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$, using magnetization measurements and
$^{31}$P nuclear magnetic resonance. An antiferromagnetic-type order sets in at
$T_{\rm N}=1.3$ K and a characteristic magnetization plateau is observed at 1/3
of the saturation magnetization below $T^* \sim 5$ K. A moderate $^{31}$P NMR
line broadening reveals the development of anisotropic short-range correlations
within the plateau phase concomitantly with a gapless spin-lattice relaxation
time $T_1 \sim k_B T / \hbar S$, which both point to the presence of a
semiclassical nematic spin liquid state predicted for the Heisenberg kagom\'e
antiferromagnetic model or to the persistence of the zero-energy modes of the
kagome lattice under large magnetic fields.",2102.02882v2
2021-03-26,Schwinger pair production of magnetic monopoles: momentum distribution for heavy-ion collisions,"Magnetic monopoles may be produced by the dual Schwinger effect in strong
magnetic fields. Today, the strongest known magnetic fields in the universe are
produced fleetingly in heavy-ion collisions. We use the complex worldline
instanton method to calculate the momentum distribution of magnetic monopoles
produced in heavy-ion collisions, in an approximation that includes the effect
of the magnetic field to all orders but neglects monopole self-interactions.
The result saturates the preparation time-energy uncertainty principle, and
yields a necessary ingredient for experimental monopole searches in heavy-ion
collisions.",2103.14454v2
2021-04-05,Competing ferromagnetic and antiferromagnetic interactions drive the magnetocaloric tunability in Gd55Co30NixAl15-x microwires,"We have employed Gd55Co30NixAl15-x (x = 10, 5 and 0) amorphous microwires as
a model system to unravel the impact of multiple magnetic interactions on the
magnetism and the magnetocaloric behavior in Gd-alloy microwire systems. Our
study shows that in addition to the RKKY ferromagnetic (FM) interaction
(Gd-Gd), antiferromagnetic (AFM) interactions (Gd-Co, Gd-Ni) coexist and
contribute to the magnetic and magnetocaloric response of the system. The
dilution effect of Al element on the FM Gd-Gd interaction is responsible for
the decrease of the Curie temperature (TC), whereas the increase of the
saturation magnetization (MS) is originated from the reduced AFM Gd-Ni
interaction. A thorough analysis of critical exponents suggests that the
presence of the AFM interactions hinders the system to exhibit a long-range FM
order below the TC. Adjusting these interactions is shown to preserve the large
refrigerant capacity (RC) while tuning the TC over a wide temperature range,
which is desirable for active magnetic refrigeration.",2104.01790v1
2021-05-20,Rectangle-like hysteresis in a Dysprosium Metallacrown Magnet with Linear F-Dy-F Anisotropic Moiety,"Single-molecule magnets (SMMs) exhibiting open hysteresis loops may
potentially apply to molecule-based information processing and storage.
However, the capacity to retain magnetic memory is always limited by zero-field
quantum tunneling of magnetization (QTM). Herein, a well-designed dysprosium
metallacrown SMM, consisting of an endohedral approximate linear F-Dy-F strong
anisotropic moiety in a peripheral [15-MCNi-5] metallacrown (MC), is reported
with the largest reversal barrier of 1060 cm-1 among d-f SMMs. Rectangle-like
hysteresis loops are observed with the huge squareness (remanence/saturation
magnetization) up to 97% at 2 K. More importantly, zero-field QTM step is
phenomenologically removed by minimizing the dipole coupling and hyperfine
interactions. The results demonstrate for the first time that zero-field QTM
step can be eliminated via manipulating the ligand field and vanishing the
external magnetic perturbations, which illuminates a promising blueprint for
developing high-performance SMMs.",2105.09586v1
2021-09-03,Magnetization Plateaus of a Double Fullerene Core/Shell Like-Nanostructure in an External Magnetic Field: Monte Carlo Study,"This paper concerns the investigation of the critical (HC) and the saturation
(HS) magnetic fields behavior of the studied system as a function of different
physical parameters. The Monte Carlo method has been used to study the magnetic
properties of a ferrimagnetic behavior of a double fullerene X60 core/shell
like-nanostructure, where the symbol X can be assigned to any magnetic atom.
Based on the Ising model, we focus our study on a system formed by a double
sphere core/shell. The two spheres are containing the spins: $\sigma=\pm 1/2$
in the core are surrounded by the spin $S=\pm 1, 0$ in the shell. Many types of
magnetization curves have been found, depending on the competitions among the
exchange couplings, the crystal fields and the temperature.",2109.01453v1
2021-09-14,Quantum magnetism of ferromagnetic spin dimers in $α$-KVOPO$_4$,"Magnetism of the spin-$\frac12$ $\alpha$-KVOPO$_4$ is studied by
thermodynamic measurements, $^{31}$P nuclear magnetic resonance (NMR), neutron
diffraction, and density-functional band-structure calculations. Ferromagnetic
Curie-Weiss temperature of $\theta_{\rm CW}\simeq 15.9$ K and the saturation
field of $\mu_0H_s\simeq 11.3$ T suggest the predominant ferromagnetic coupling
augmented by a weaker antiferromagnetic exchange that leads to a short-range
order below 5 K and the long-range antiferromagnetic order below $T_{\rm
N}\simeq 2.7$ K in zero field. Magnetic structure with the propagation vector
$\mathbf k=(0,\frac12,0)$ and the ordered magnetic moment of 0.58 $\mu_B$ at
1.5 K exposes a non-trivial spin lattice where strong ferromagnetic dimers are
coupled antiferromagnetically. The reduction in the ordered magnetic moment
with respect to the classical value (1 $\mu_{\rm B}$) indicates sizable quantum
fluctuations in this setting, despite the predominance of ferromagnetic
exchange. We interpret this tendency toward ferromagnetism as arising from the
effective orbital order in the folded chains of the VO$_6$ octahedra.",2109.06840v1
2021-09-15,Confining and chiral properties of QCD in extremely strong magnetic fields,"We investigate, by numerical lattice simulations, the static quark-antiquark
potential, the flux tube properties and the chiral condensate for $N_f = 2+1$
QCD with physical quark masses in the presence of strong magnetic fields, going
up to $eB = 9$ GeV$^2$, with continuum extrapolated results. The string tension
for quark-antiquark separations longitudinal to the magnetic field is
suppressed by one order of magnitude at the largest explored magnetic field
with respect to its value at zero magnetic background, but is still
non-vanishing; in the transverse direction, instead, the string tension is
enhanced but seems to reach a saturation at around 50 % of its value at $B =
0$. The flux tube shows a consistent suppression/enhancement of the overall
amplitude, with mild modifications of its profile. Finally, we observe magnetic
catalysis in the whole range of explored fields with a behavior compatible with
a lowest Landau level approximation, in particular with a linear dependence of
the chiral condensate on $B$ which is in agreement, within errors, with that
already observed for $eB \sim 1$ GeV$^2$.",2109.07456v2
2021-11-29,Current driven kink instabilities in relativistic jets: dissipation properties,"We analyze the evolution of current driven kink instabilities of a highly
magnetized relativistic plasma column, focusing in particular on its
dissipation properties. The instability evolution leads to the formation of
thin current sheets where the magnetic energy is dissipated. We find that the
total amount of dissipated magnetic energy is independent of the dissipation
properties. Dissipation occurs in two stages: a peak when the instability
saturates, which is characterized by the formation of a helicoidal current
sheet at the boundary of the deformed plasma column, followed by a weaker
almost flat phase, in which turbulence develops. The detailed properties of
these two phases depend on the equilibrium configuration and other parameters,
in particular on the steepness of the pitch radial profile, on the presence of
an external axial magnetic field and on the amount of magnetization. These
results are relevant for high energy astrophysical sources, since current
sheets can be the sites of magnetic reconnection where particles can be
accelerated to relativistic energies and give rise to the observed radiation.",2111.14575v1
2021-12-21,Magnetically tunable Shubnikov-de Hass oscillations in MnBi2Te4,"Shubnikov-de Hass oscillations are directly observed in undoped
antiferromagnetic topological insulator MnBi2Te4. With increasing magnetic
fields, the oscillation period decreases gradually in the magnetic transition
from canted antiferromagnetism to ferromagnetism and then saturates in high
magnetic fields, indicating the field-induced evolution of the band structure.
From the analysis of the high-field oscillations, a nontrivial Berry phase and
a small effective mass are extracted, in agreement with the predicted Weyl
semimetal phase in ferromagnetic MnBi2Te4. Furthermore, rotating the
magnetization of MnBi2Te4 can lead to a splitting of the high-field
oscillations, which suggests the enhanced asymmetry of the Weyl cones in tilted
fields. Therefore, the observation of these magnetically tunable quantum
oscillations clearly demonstrates the indispensable role of field in tuning the
band structure or physical properties of MnBi2Te4.",2112.10962v1
2021-12-23,Control of site occupancy by variation of the Zn and Al content in NiZnAl ferrite epitaxial films with low magnetic damping,"The structural and magnetic properties of Zn/Al doped nickel ferrite thin
films can be adjusted by changing the Zn and Al content. The films are
epitaxially grown by reactive magnetron sputtering using a triple cluster
system to sputter simultaneously from three different targets. Upon the
variation of the Zn content the films remain fully strained with similar
structural properties, while the magnetic properties are strongly affected. The
saturation magnetization and coercivity as well as resonance position and
linewidth from ferromagnetic resonance (FMR) measurements are altered depending
on the Zn content in the material. The reason for these changes can be
elucidated by investigation of the x-ray magnetic circular dichroism spectra to
gain site and valence specific information with elemental specificity.
Additionally, from a detailed investigation by broadband FMR a minimum in
g-factor and linewidth could be found as a function of film thickness.
Furthermore, the results from a variation of the Al content using the same set
of measurement techniques is given. Other than for Zn, the variation of Al
affects the strain and even more pronounced changes to the magnetic properties
are apparent.",2112.12456v1
2022-01-31,Anomalous Nernst effect in La0.5Ca0.5Coo3,"We report the occurrence of the anomalous Nernst effect (ANE) in
polycrystalline perovskite La0.5Ca0.5CoO3. The sample is ferromagnetic below TC
= 147 K and resistivity shows non-metallic behavior above and below the TC with
only a small negative magnetoresistance (~2%) around TC. Field dependence of
magnetization at 10 K shows large hysteresis with a coercive field of 6 kOe but
a small magnetization ~ 0.64 Bohr magneton/Co even in a field of 50 kOe, which
indicates the presence of magnetically heterogeneous ground state consisting of
ferromagnetic and non-ferromagnetic phases. The field dependence of the Nernst
thermopower (Sxy) at low temperatures shows complete saturation but the
magnetization does not. This indicates that the ANE in La0.5Ca0.5CoO3 depends
only on the transport properties of the ferromagnetic phase, while it is not
affected by the non-ferromagnetic phase. Due to the higher value of remnant
Sxy, the magnetized polycrystalline sample exhibits ANE in absence of an
external magnetic field.",2201.12982v1
2022-04-22,Resistive instabilities in sinusoidal shear flows with a streamwise magnetic field,"We investigate the linear stability of a sinusoidal shear flow with an
initially uniform streamwise magnetic field in the framework of incompressible
magnetohydrodynamics (MHD) with finite resistivity and viscosity. This flow is
known to be unstable to the Kelvin-Helmholtz instability in the hydrodynamic
case. The same is true in ideal MHD, where dissipation is neglected, provided
the magnetic field strength does not exceed a critical threshold beyond which
magnetic tension stabilizes the flow. Here, we demonstrate that including
viscosity and resistivity introduces two new modes of instability. One of these
modes, which we call a resistively-unstable Alfv\'en wave due to its connection
to shear Alfv\'en waves, exists for any nonzero magnetic field strength as long
as the magnetic Prandtl number $Pm < 1$. We present a reduced model for this
instability that reveals its excitation mechanism to be the negative eddy
viscosity of periodic shear flows described by Dubrulle & Frisch (1991).
Finally, we demonstrate numerically that this mode saturates in a
quasi-stationary state dominated by counter-propagating solitons.",2204.10875v1
2022-06-23,Primordial magnetic fields in Population III star formation: a magnetised resolution study,"Population III stars form in groups due to the fragmentation of primordial
gas. While uniform magnetic fields have been shown to support against
fragmentation in present day star formation, it is unclear whether realistic
k^3/2 primordial fields can have the same effect. We bypass the issues
associated with simulating the turbulent dynamo by introducing a saturated
magnetic field at equipartition with the velocity field when the central
densities reaches 10-13 g cm-3. We test a range of sink particle creation
densities from 10-10-10-8 g cm-3. Within the range tested, the fields did not
suppress fragmentation of the gas and hence could not prevent the degree of
fragmentation from increasing with increased resolution. The number of sink
particles formed and total mass in sink particles was unaffected by the
magnetic field across all seed fields and resolutions. The magnetic pressure
remained sub-dominant to the gas pressure except in the highest density regions
of the simulation box, where it became equal to but never exceeded gas
pressure. Our results suggest that the inclusion of magnetic fields in
numerical simulations of Pop III star formation is largely unimportant.",2206.11919v1
2022-11-16,BPS solitons with internal structures in a restricted baby Skyrme-Maxwell theory in a magnetic medium,"We consider a restricted baby Skyrme-Maxwell scenario enlarged via the
inclusion of a nontrivial magnetic permeability. We then proceed with the
minimization of its total energy by means of the Bogomol'nyi-Prasad-Sommerfield
(BPS) prescription, from which we get that the self-dual potential now depends
on the magnetic permeability itself. As a result, we obtain not only the lower
bound for the energy, but also the self-dual equations whose solutions saturate
that bound. In such a context, we focus our attention on those time-independent
gauged skyrmions with radial symmetry and no electric charge. We solve the
effective self-dual equations numerically for different choices of the magnetic
permeability, from which we obtain BPS magnetic fields whose internal
structures form concentric rings. We also explain analytically the formation of
these structures based on the values of a single real parameter which
characterizes the respective magnetic permeabilities.",2211.09216v1
2023-03-03,Magneto-optical sensing of the pressure driven magnetic ground states in bulk CrSBr,"Competition between exchange interactions and magnetocrystalline anisotropy
may bring new magnetic states that are of great current interest. An applied
hydrostatic pressure can further be used to tune their balance. In this work we
investigate the magnetization process of a biaxial antiferromagnet in an
external magnetic field applied along the easy axis. We find that the single
metamagnetic transition of the Ising type observed in this material under
ambient pressure transforms under hydrostatic pressure into two transitions, a
first-order spin flop transition followed by a second order transition towards
a polarized ferromagnetic state near saturation. This reversible tuning into a
new magnetic phase is obtained in layered bulk CrSBr at low temperature by
varying the interlayer distance using high hydrostatic pressure, which
efficiently acts on the interlayer magnetic exchange, and is probed by
magneto-optical spectroscopy.",2303.01823v2
2023-06-01,Structural Trends and Itinerant Magnetism of the New Cage-structured Compound HfMn$_{2}$Zn$_{20}$,"A new cage-structured compound - HfMn$_{2}$Zn$_{20}$ - belonging to the
AB$_{2}$C$_{20}$ (A, B = transition or rare earth metals, and C = Al, Zn, or
Cd) family of structures has been synthesized via the self-flux method. The new
compound crystallizes in the space group Fd-3m with lattice parameter a =
14.0543(2) \r{A} (Z = 8) and exhibits non-stoichiometry due to Mn/Zn mixing on
the Mn-site and an underoccupied Hf-site. The structure refines to
Hf$_{0.93}$Mn$_{1.63}$Zn$_{20.37}$ and follows lattice size trends when
compared to other HfM$_{2}$Zn$_{20}$ (M = Fe, Co, and Ni) structures. The
magnetic measurements show that this compound displays a modified Curie-Weiss
behavior with a transition temperature around 22 K. The magnetization shows no
saturation, a small magnetic moment, and near negligible hysteresis, all signs
of the itinerant magnetism. The Rhodes-Wohlfarth ratio and the spin fluctuation
parameters ratio both confirm the itinerant nature of the magnetism in
HfMn$_{2}$Zn$_{20}$.",2306.01146v3
2023-10-16,Emergent spin-gapped magnetization plateaus in a spin-1/2 perfect kagome antiferromagnet,"The two-dimensional (2D) spin-1/2 kagome Heisenberg antiferromagnet is
believed to host quantum spin liquid (QSL) states with no magnetic order, but
its ground state remains largely elusive. An important outstanding question
concerns the presence or absence of the 1/9 magnetization plateau, where exotic
quantum states, including topological ones, are expected to emerge. Here we
report the magnetization of a recently discovered kagome QSL candidate
YCu$_3$(OH)$_{6.5}$Br$_{2.5}$ up to 57 T. Above 50 T, a clear magnetization
plateau at 1/3 of the saturation moment of Cu$^{2+}$ ions is observed,
supporting that this material provides an ideal platform for the kagome
Heisenberg antiferromagnet. Remarkably, we found another magnetization plateau
around 20 T, which is attributed to the 1/9 plateau. The temperature dependence
of this plateau reveals the distinct spin gap, whose magnitude estimated by the
plateau width is approximately 10% of the exchange interaction. The observation
of 1/9 and 1/3 plateaus highlights the emergence of novel states in quantum
spin systems.",2310.10069v1
2005-08-24,Shearing Box Simulations of the MRI in a Collisionless Plasma,"We describe local shearing box simulations of turbulence driven by the
magnetorotational instability (MRI) in a collisionless plasma. Collisionless
effects may be important in radiatively inefficient accretion flows, such as
near the black hole in the Galactic Center. The MHD version of ZEUS is modified
to evolve an anisotropic pressure tensor. A fluid closure approximation is used
to calculate heat conduction along magnetic field lines. The anisotropic
pressure tensor provides a qualitatively new mechanism for transporting angular
momentum in accretion flows (in addition to the Maxwell and Reynolds stresses).
We estimate limits on the pressure anisotropy due to pitch angle scattering by
kinetic instabilities. Such instabilities provide an effective ``collision''
rate in a collisionless plasma and lead to more MHD-like dynamics. We find that
the MRI leads to efficient growth of the magnetic field in a collisionless
plasma, with saturation amplitudes comparable to those in MHD. In the saturated
state, the anisotropic stress is comparable to the Maxwell stress, implying
that the rate of angular momentum transport may be moderately enhanced in a
collisionless plasma.",0508502v2
2006-04-21,Flux-transport dynamos with Lorentz force feedback on differential rotation and meridional flow: Saturation mechanism and torsional oscillations,"In this paper we discuss a dynamic flux-transport dynamo model that includes
the feedback of the induced magnetic field on differential rotation and
meridional flow. We consider two different approaches for the feedback:
meanfield Lorentz force and quenching of transport coefficients such as
turbulent viscosity and heat conductivity. We find that even strong feedback on
the meridional flow does not change the character of the flux-transport dynamo
significantly; however it leads to a significant reduction of differential
rotation. To a large degree independent from the dynamo parameters, the
saturation takes place when the toroidal field at the base of the convection
zone reaches between 1.2 an 1.5 T, the energy converted intomagnetic energy
corresponds to about 0.1 to 0.2% of the solar luminosity. The torsional
oscillations produced through Lorentz force feedback on differential rotation
show a dominant poleward propagating branch with the correct phase relation to
the magnetic cycle. We show that incorporating enhanced surface cooling of the
active region belt (as proposed by Spruit) leads to an equatorward propagating
branch in good agreement with observations.",0604446v2
1999-08-31,NMR Detection of Temperature-Dependent Magnetic Inhomogeneities in URu2Si2,"We present 29Si-NMR relaxation and spectral data in URu2Si2. Our echo-decay
experiments detect slowly fluctuating magnetic field gradients. In addition, we
find that the echo-decay shape (time dependence) varies with temperature T and
its rate behaves critically near the Neel temperature TN, indicating a
correlation between the gradient fluctuations and the transition to
small-moment order. T-dependent broadening contributions become visible below
100 Kelvin and saturate somewhat above TN, remaining saturated at lower
temperatures. Together, the line width and shift suggest partial lattice
distortions below TN. We propose an intrinsic minority phase below $T_{\rm N}$
and compare our results with one of the current theoretical models.",9908460v1
2000-03-21,Field induced ordering in highly frustrated antiferromagnets,"We predict that an external field can induce a spin order in highly
frustrated classical Heisenberg magnets. We find analytically stabilization of
collinear states by thermal fluctuations at a one-third of the saturation field
for kagome and garnet lattices and at a half of the saturation field for
pyrochlore and frustrated square lattices. This effect is studied numerically
for the frustrated square-lattice antiferromagnet by Monte Carlo simulations
for classical spins and by exact diagonalization for $S=1/2$. The field induced
collinear states have a spin gap and produce magnetization plateaus.",0003343v2
2000-04-12,Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high mobility (100) Si-inversion layers,"We report studies of the magnetoresistance (MR) in a two-dimensional electron
system in (100) Si-inversion layers, for perpendicular and parallel
orientations of the current with respect to the magnetic field in the 2D-plane.
The magnetoresistance is almost isotropic; this result does not support the
suggestion of the orbital origin of the MR in Si-inversion layer. In the
hopping regime, however, the MR contains a weak anisotropic component that is
non-monotonic in magnetic field. We found that the field, at which the MR
saturates, for different samples varies by a factor of two, being lower or
higher than the field of complete spin polarization of free carriers.
Therefore, the saturation of the MR can not be identified with the spin
polarization of free carriers.",0004206v3
2000-06-22,Magnetoresistance of Three-Constituent Composites: Percolation Near a Critical Line,"Scaling theory, duality symmetry, and numerical simulations of a random
network model are used to study the magnetoresistance of a
metal/insulator/perfect conductor composite with a disordered columnar
microstructure. The phase diagram is found to have a critical line which
separates regions of saturating and non-saturating magnetoresistance. The
percolation problem which describes this line is a generalization of
anisotropic percolation. We locate the percolation threshold and determine the
t = s = 1.30 +- 0.02, nu = 4/3 +- 0.02, which are the same as in
two-constituent 2D isotropic percolation. We also determine the exponents which
characterize the critical dependence on magnetic field, and confirm numerically
that nu is independent of anisotropy. We propose and test a complete scaling
description of the magnetoresistance in the vicinity of the critical line.",0006338v3
2001-03-21,Magneto-transport Properties near the Superconductor-Insulator Transition in 2D,"We analyze here the behavior near the 2D insulator-superconductor quantum
critical point in the presence of a perpendicular magnetic field. We show that
with increasing field $H$, the quantum disordered and quantum critical regimes,
in which vortex degrees of freedom are suppressed, crossover to a new
magnetically activated (MA) regime, where the correlation length $\xi \sim
1/\sqrt{H}$. In this regime, we show that the conductivity decreases
monotonically as opposed to the anticipated saturation predicted from
hyperuniversality arguments. This discrepancy arises from the lack of
commutativity of the frequency and temperature tending to zero limits of the
conductivity. In the low-field regime such that $\sqrt{H}\ll\Delta$, and in the
absence of Ohmic dissipation, where $\Delta$ is a measure of the distance from
the quantum critical point, the resistivity saturates to the Bose metal value
found previously for Cooper pairs lacking phase coherence.",0103433v2
2001-09-26,Ferromagnetic Domain Walls in finite systems: mean-field critical exponents and applications,"The distribution of magnetic moments in finite ferromagnetic bodies was first
investigated by Landau and Lifshitz in a famous paper [\textit{Phys. Z. Soviet
Union}, \textbf{8}, 153 (1935)], where they obtained the domain structure of a
ferromagnetic crystal at low temperatures, in the regime of saturated
magnetization. In this article, we investigate the general properties of
ferromagnetic domain walls of uniaxial crystals from the view point of the
Landau free energy. We present the basic ideas at an introductory level, for
non-experts. Extending the formalism to the vicinity of the Curie temperature,
where a general qualitative description by the Landau theory of phase
transitions can be applied, we find that domain walls tend to suppress the
layers, leading to a continuous vanishing of the domain structure with
anomalous critical exponents. In the saturated regime, we discuss the role of
domain walls in mesoscopic systems and ferromagnetic nanojunctions, relating
the observed magnetoresistance with promising applications in the recent area
of spintronics.",0109499v2
2001-10-11,The Parallel Magnetoconductance of Interacting Electrons in a Two Dimensional Disordered System,"The transport properties of interacting electrons for which the spin degree
of freedom is taken into account are numerically studied for small two
dimensional diffusive clusters. On-site electron-electron interactions tend to
delocalize the electrons, while long-range interactions enhance localization.
On careful examination of the transport properties, we reach the conclusion
that it does not show a two dimensional metal insulator transition driven by
interactions. A parallel magnetic field leads to enhanced resistivity, which
saturates once the electrons become fully spin polarized. The strength of the
magnetic field for which the resistivity saturates decreases as electron
density goes down. Thus, the numerical calculations capture some of the
features seen in recent experimental measurements of parallel
magnetoconductance.",0110235v1
2003-05-08,Photoemission spectra of a two-dimensional S=1/2 quantum antiferromagnet in magnetic fields: a theoretical study,"We calculate the angular resolved photoemission spectra (ARPES) of a spin-1/2
Heisenberg antiferromagnet as a function of magnetic fields using both the
exact diagonalization method and self-consistent Born approximation. Below the
saturation field $B_C$, strong scattering between spin waves and a hole,
created by photoemission of an electron, significantly narrows the
quasiparticle band that is characterized by the lowering of the quasiparticle
energy at $(\pi,\pi)$ with increasing field. Accordingly, in ARPES the
quasiparticle peak gets shaper near $(\pi,\pi)$ and broader elsewhere.
Furthermore, we observe that an anomalous extended van Hove region (EVHR)
around $(\pi,\pi)$ appears in a half saturation field, while EVHRs around
$(\pi,0)$ and $(0,\pi)$ in zero field gradually disappear with increasing
field.",0305174v1
2004-04-22,Magnetocaloric effect in pyrochlore antiferromagnet Gd2Ti2O7,"An adiabatic demagnetization process is studied in Gd2Ti2O7, a geometrically
frustrated antiferromagnet on a pyrochlore lattice. In contrast to conventional
paramagnetic salts, this compound can exhibit a temperature decrease by a
factor of ten in the temperature range below the Curie-Weiss constant. The most
efficient cooling is observed in the field interval between 120 and 60 kOe
corresponding to a crossover between saturated and spin-liquid phases. This
phenomenon indicates that a considerable part of the magnetic entropy survives
in the strongly correlated state. According to the theoretical model, this
entropy is associated with a macroscopic number of local modes remaining
gapless till the saturation field. Monte Carlo simulations on a classical spin
model demonstrate good agreement with the experiment. The cooling power of the
process is experimentally estimated with a view to possible technical
applications. The results for Gd2Ti2O7 are compared to those for Gd3Ga5O12, a
well-known material for low temperature magnetic refrigeration.",0404529v2
2004-11-26,Metastable states and T=0 hysteresis in the random-field Ising model on random graphs,"We study the ferromagnetic random-field Ising model on random graphs of fixed
connectivity z (Bethe lattice) in the presence of an external magnetic field
$H$. We compute the number of single-spin-flip stable configurations with a
given magnetization m and study the connection between the distribution of
these metastable states in the H-m plane (focusing on the region where the
number is exponentially large) and the shape of the saturation hysteresis loop
obtained by cycling the field between $-\infty$ and $+\infty$ at T=0. The
annealed complexity $\Sigma_A(m,H)$ is calculated for z=2,3,4 and the quenched
complexity $\Sigma_Q(m,H)$ for z=2. We prove explicitly for z=2 that the
contour $\Sigma_Q(m,H)=0$ coincides with the saturation loop. On the other
hand, we show that $\Sigma_A(m,H)$ is irrelevant for describing, even
qualitatively, the observable hysteresis properties of the system.",0411677v2
2006-02-26,Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB,"The temperature dependence of saturation and spin-flop fields for artificial
ferrimagnets (AFi) based on antiparallel coupled CoFeB/Ru/CoFeB trilayers has
been investigated in a temperature range between 80K and 600K. The results
presented in this paper are relevant for magnetic devices using this system,
e.g. magnetic-random access memory based on spin-flop switching. In good
accordance to the theory, the saturation field Hsat behaves like Hsat ~ H_0
(T/T_0)/sinh(T/T_0) with a characteristic temperature of T_0 = 150K. Within
this model, the Fermi velocity for the Ru layer is of the order of 10^5m/s,
therefore, explaining the strong variation of the coupling strength with the
temperature in Ru based AFi. Furthermore, a strong uniaxial anisotropy of K_u =
2x10^3 J/m^3 with a small angular distribution of the anisotropy axes is
observed for the AFi trilayers based on amorphous CoFeB alloys.",0602609v2
1995-04-21,``GLUELUMP'' SPECTRUM AND ADJOINT SOURCE POTENTIAL IN LATTICE QCD$_3$,"We calculate the potential between ``quarks'' which are in the adjoint
representation of SU(2) color in the three-dimensional lattice theory. We work
in the scaling region of the theory and at large quark separations $R$. We also
calculate the masses $M_{Qg}$ of color-singlet bound states formed by coupling
an adjoint quark to adjoint glue (``gluelumps''). Good scaling behavior is
found for the masses of both magnetic (angular momentum $J=0$) and electric
($J=1$) gluelumps, and the magnetic gluelump is found to be the lowest-lying
state. It is naively expected that the potential for adjoint quarks should
saturate above a separation $R_{\rm scr}$ where it becomes energetically
favorable to produce a pair of gluelumps. We obtain a good estimate of the
naive screening distance $R_{\rm scr}$. However we find little evidence of
saturation in the potential out to separations $R$ of about twice $R_{\rm
scr}$.",9504015v1
1994-02-01,Strong-Weak Coupling Duality in Four Dimensional String Theory,"We present several pieces of evidence for strong-weak coupling duality
symmetry in the heterotic string theory, compactified on a six dimensional
torus. These include symmetry of the 1) low energy effective action, 2) allowed
spectrum of electric and magnetic charges in the theory, 3) allowed mass
spectrum of particles saturating the Bogomol'nyi bound, and 4) Yukawa couplings
between massless neutral particles and massive charged particles saturating the
Bogomol'nyi bound. This duality transformation exchanges the electrically
charged elementary string excitations with the magnetically charged soliton
states in the theory. It is shown that the existence of a strong-weak coupling
duality symmetry in four dimensional string theory makes definite prediction
about the existence of new stable monopole and dyon states in the theory with
specific degeneracies, including certain supersymmetric bound states of
monopoles and dyons. The relationship between strong-weak coupling duality
transformation in string theory and target space duality transformation in the
five-brane theory is also discussed. (Based on a talk given at the workshop on
Strings and Gravity, Madras, India.)",9402002v2
2002-05-08,The alpha effect and its saturation in a turbulent swirling flow generated in the VKS experiment,"We report the experimental observation of the alpha-effect. It consists in
the generation of a current parallel to a magnetic field B0 applied to a
turbulent swirling flow of liquid sodium. At low magnetic Reynolds number, Rm,
we show that the magnitude of the alpha-effect increases like Rm2 and that its
sign is determined by the flow helicity. It saturates and then decreases at
large Rm, primarily because of the expulsion of the applied field B0 from the
bulk of the flow. We show how this expulsion is affected by the flow geometry
by varying the relative amplitudes of the azimuthal and axial flows.",0205019v1
2004-12-08,Zero-Temperature Theory of Collisionless Rapid Adiabatic Passage from a Fermi Degenerate Gas of Atoms to a Bose-Einstein Condensate of Molecules,"We theoretically examine a zero-temperature system of Fermi degenerate atoms
coupled to bosonic molecules via collisionless rapid adiabatic passage across a
Feshbach resonance, focusing on saturation of the molecular conversion
efficiency at the slowest magnetic-field sweep rates. Borrowing a novel
MANY-FERMION Fock-state theory, we find that a proper model of the
magnetic-field sweep can systematically remove saturation. We also debunk the
common misconception that many-body effects are responsible for molecules
existing above the two-body threshold.",0412048v2
2009-06-25,Frustration Driven Stripe Domain Formation in Co/Pt Multilayer Films,"We report microscopic mechanisms for an unusual magnetization reversal
behavior in Co/Pt multilayers where some of the first-order reversal curves
protrude outside of the major loop. Transmission x-ray microscopy reveals a
fragmented stripe domain topography when the magnetic field is reversed prior
to saturation, in contrast to an interconnected pattern when reversing from a
saturated state. The different domain nucleation and propagation behaviors are
due to unannihilated domains from the prior field sweep. These residual domains
contribute to random dipole fields that impede the subsequent domain growth and
prevent domains from growing as closely together as for the interconnected
pattern.",0906.4744v1
2009-07-02,Thermal expansion of the spin-1/2 Heisenberg-chain compound Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$,"Compounds containing magnetic subsystems representing simple model spin
systems with weak magnetic coupling constants are ideal candidates to test
theoretical predictions for the generic behavior close to quantum phase
transitions. We present measurements of the thermal expansion and
magnetostriction of the spin-1/2-chain compound copper pyrazine dinitrate
Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$. Of particular interest is the low-temperature
thermal expansion close to the saturation field $H_c \simeq 13.9 \mathrm{T}$,
which defines a quantum phase transition from the gapless Luttinger liquid
state to the fully saturated state with a finite excitation gap. We observe a
sign change of the thermal expansion for the different ground states, and at
the quantum critical point $H_c$ the low-temperature expansion approaches a
$1/\sqrt{T}$ divergence. Thus, our data agree very well with the expected
quantum critical behaviour.",0907.0400v1
2009-07-08,On the theory of astronomical maser. II. Polarization of maser radiation,"In this paper we investigate the polarization property of the radiation
amplified by astronomical masers in the presence of a strong magnetic field.
Our model explicitly takes into account the broadband nature of the radiation
field and the interaction of the radiation with the maser transition J=1--0.
The amplification of different realisations of the background continuum
radition by the maser is directly simulated and the Stokes parameters of the
radiation field are then obtained by averaging over the ensemble of emerging
maser radiation. For isotropic pumping and partially saturated masers we find
that the maser radiation is linearly polarized in two representative cases
where the magnetic field {\bf B} makes an angle $\theta$=30$^0$ and
$\theta$=90$^0$ to the maser axis. The linear polarization for maser radiation
obtained in our simulations for both cases are in agreement with the results of
the standard model. Furthermore, no instability during amplification is seen in
our simulations. Therefore, we conclude that there is no problem with the
previous numerical investigations of maser polarization in the unsaturated and
partially saturated regime.",0907.1327v1
2010-01-05,Radiative Signatures of Relativistic Shocks,"(Abbreviated) Particle-in-cell simulations of relativistic, weakly magnetized
collisionless shocks show that particles can gain energy by repeatedly crossing
the shock front. This requires scattering off self-generated small length-scale
magnetic fluctuations. The radiative signature of this first-order Fermi
acceleration mechanism is important for models of both the prompt and afterglow
emission in gamma-ray bursts and depends on the strength parameter ""a"" of the
fluctuations. For electrons (and positrons), acceleration saturates when the
radiative losses produced by the scattering cannot be compensated by the energy
gained on crossing the shock. We show that this sets an upper limit on both the
electron Lorentz factor and on the energy of the photons radiated during the
scattering process. This rules out ""jitter"" radiation on self-excited
fluctuations with a < 1 as a source of gamma-rays, although high-energy photons
might still be produced when the jitter photons are upscattered in an analog of
the synchrotron self-Compton process. In fluctuations with a > 1, radiation is
generated by the standard synchrotron mechanism, and the maximum photon energy
rises linearly with a, until saturating at approximately 70 MeV.",1001.0687v1
2010-01-21,Control of the amplification process in baseline XFEL undulator with mechanical SASE switchers,"The magnetic gap of the baseline XFEL undulators can be varied mechanically
for wavelength tuning. In particular, the wavelength range 0.1 nm - 0.4 nm can
be covered by operating the European XFEL with the SASE2 undulator. The length
of the SASE2 undulator (256.2 m) is sufficient to independently generate three
pulses of different radiation wavelengths at saturation. Normally, if a SASE
FEL operates in saturation, the quality of the electron beam is too bad for
generation of SASE radiation in the subsequent part of undulator which is
resonant at a few times longer wavelength. The new method of SASE
undulator-switching based on the rapid switching of the FEL amplification
process proposed in this paper is an attempt to get around this obstacle. Using
mechanical SASE shutters installed within short magnetic chicanes in the
baseline undulator, it is possible to rapidly switch the FEL photon beam from
one wavelength to another, providing simultaneous multi-color capability.
Combining this method with a photon-beam distribution system can provide an
efficient way to generate a multi-user facility.",1001.3812v1
2011-09-08,Mach Number Dependence of Turbulent Magnetic Field Amplification: Solenoidal versus Compressive Flows,"We study the growth rate and saturation level of the turbulent dynamo in
magnetohydrodynamical simulations of turbulence, driven with solenoidal
(divergence-free) or compressive (curl-free) forcing. For models with Mach
numbers ranging from 0.02 to 20, we find significantly different magnetic field
geometries, amplification rates, and saturation levels, decreasing strongly at
the transition from subsonic to supersonic flows, due to the development of
shocks. Both extreme types of turbulent forcing drive the dynamo, but
solenoidal forcing is more efficient, because it produces more vorticity.",1109.1760v1
2012-03-14,Oxygen vacancy enhanced room temperature ferromagnetism in Al-doped MgO nanoparticles,"We have investigated the room temperature ferromagnetic order that develops
in Al-substituted magnesium oxide, Mg(Al)O, nanoparticles with Al fractions of
up to 5 at.%. All samples, including undoped MgO nanoparticles, exhibit room
temperature ferromagnetism, with the saturation magnetization reaching a
maximum of 0.023 emu/g at 2 at.% of Al. X-ray photoelectron spectroscopy
identifies the presence of oxygen vacancies in both doped and undoped MgO
nanoparticles, with the vacancy concentration increasing upon vacuum annealing
of Mg(Al)O, resulting in two-fold enhancement of the saturation magnetization
for 2 at.% Al-doped MgO. Our results suggest that the oxygen vacancies are
largely responsible for room temperature ferromagnetism in MgO.",1203.2991v3
2013-02-15,Equatorial trench at the magnetopause under saturation,"Magnetic data from GOES geosynchronous satellites were applied for
statistical study of the low-latitude dayside magnetopause under a strong
interplanetary magnetic field of southward orientation when the reconnection at
the magnetopause was saturated. From minimum variance analysis, we determined
the magnetopause orientation and compared it with predictions of a reference
model. The magnetopause shape was found to be substantially distorted by a
duskward shifting such that the nose region appeared in the postnoon sector. At
equatorial latitudes, the shape of magnetopause was characterized by a
prominent bluntness and by a trench formed in the postnoon sector. The origin
of distortions was regarded in the context of the storm-time magnetospheric
currents and the large-scale quasi-state reconnection at the dayside
magnetopause.",1302.3735v1
2013-04-26,A micro-structured ion-implanted magnonic crystal,"We investigate spin-wave propagation in a microstructured magnonic-crystal
waveguide fabricated by localized ion implantation. The irradiation caused a
periodic variation in the saturation magnetization along the waveguide. As a
consequence, the spin-wave transmission spectrum exhibits a set of frequency
bands, where spin-wave propagation is suppressed. A weak modification of the
saturation magnetization by 7% is sufficient to decrease the spin-wave
transmission in the band gaps by a factor of 10. These results evidence the
applicability of localized ion implantation for the fabrication of efficient
micron- and nano-sized magnonic crystals for magnon spintronic applications.",1304.7122v1
2016-09-08,On the Origin of Non-Saturating Linear Magnetoresistivity,"The observation of non-saturating classical linear magnetoresistivity has
been an enigmatic phenomenon in solid state physics. We present a study of a
two-dimensional ohmic conductor, including local Hall effect and a
self-consistent consideration of the environment. An equivalent-circuit scheme
delivers a simple and convincing argument why the magnetoresistivity is linear
in strong magnetic field, provided that current and biasing electric field are
misaligned by a nonlocal mechanism. A finite-element model of a two-dimensional
conductor is suited to display the situations that create such deviating
currents. Besides edge effects next to electrodes, charge carrier density
fluctuations are efficiently generating this effect. However, mobility
fluctuations that have frequently been related to linear magnetoresistivity are
barely relevant. Despite its rare observation, linear magnetoresitivity is
rather the rule than the exception in a regime of low charge carrier densities,
misaligned current pathways and strong magnetic field.",1609.02418v1
2016-11-21,Quantum phase transitions in Heisenberg $J_1-J_2$ triangular antiferromagnet in a magnetic field,"We present the zero temperature phase diagram of a Heisenberg antiferromagnet
on a frustrated triangular lattice with nearest neighbor ($J_1$) and next
nearest neighbor ($J_2$) interactions, in a magnetic field. We show that the
classical model has an accidental degeneracy for all $J_2/J_1$ and all fields,
but the degeneracy is lifted by quantum fluctuations. We show that at large
$S$, for $J_2/J_1 <1/8$, quantum fluctuations select the same sequence of three
sublattice co-planar states in a field as for $J_2 =0$, and for $1/8<J_2/J_1
<1$ they select the canted stripe state for all non-zero fields. The transition
between the two states is first order in all fields, with the hysteresis width
set by quantum fluctuations. We study the model with arbitrary $S$, including
$S=1/2$, near the saturation field by exploring the fact that near saturation
the density of bosons is small for all $S$. We show that for $S >1$, the
transition remains first order, with a finite hysteresis width, but for $S=1/2$
and, possibly, $S=1$, there appears a new intermediate phase, likely without a
spontaneous long-range order.",1611.06920v2
2017-04-11,Long range interactions in antiferromagnetic quantum spin chains,"We study the role of long range dipolar interactions on antiferromagnetic
spin chains, from the classical $S\to \infty$ limit to the deep quantum case
$S=1/2$, including a transverse magnetic field. To this end, we combine
different techniques such as classical energy minima, classical Monte Carlo,
linear spin waves, bosonization and DMRG. We find a phase transition from the
already reported dipolar ferromagnetic region to an antiferromagnetic region
for high enough antiferromagnetic exchange. Thermal and quantum fluctuations
destabilize the classical order before reaching magnetic saturation in both
phases, and also close to zero field in the antiferromagnetic phase. In the
extreme quantum limit $S=1/2$, extensive DMRG computations show that the main
phases remain present with transition lines to saturation significatively
shifted to lower fields, in agreement with the bosonization analysis. The
overall picture keeps close analogy with the phase diagram of the anisotropic
XXZ spin chain in a transverse field.",1704.03420v3
2017-07-06,Switching from pyroelectric to ferroelectric order in Ni doped CaBaCo4O7,"We report ferroelectric ordering in Ni substituted CaBaCo4O7. Magnetization
showed ferrimagnetic transition at 60 K and an additional transition is found ~
82 K, further, enhanced antiferromagnetic interactions and decrease in
saturation magnetization are noticed with Ni substitution. The dielectric and
pyroelectric measurements illustrate a strong coupling between spin and charge
degrees of freedom; ferroelectric behavior is confirmed with enhanced ordering
temperature (~82 K) and saturation polarization (250 muC/m2. Neutron
diffraction has revealed an increase in c-lattice parameter in Ni sample and
all the Co/Ni moments are reoriented in a- direction; evidently a non-collinear
ferrimagnetic to collinear ferrimagnetic spin order is observed. The coupling
between the triangular and Kagome layers weakens and leads to up-up-down-down
AFM ordering in the Kagoma layer. This can be viewed as a 2D-collinear layer
with unequal bond distances and most likely responsible for the switching of
electric polarization.",1707.01712v1
2018-07-09,Magnetic quenching of the inverse cascade in rapidly rotating convective turbulence,"We present results from an asymptotic magnetohydrodynamic model that is
suited for studying the rapidly rotating, low viscosity regime typical of the
electrically conducting fluid interiors of planets and stars. We show that the
presence of sufficiently strong magnetic fields prevents the formation of
large-scale vortices and saturates the inverse cascade at a finite
length-scale. This saturation corresponds to an equilibrated state in which the
energetics of the depth-averaged flows are characterized by a balance of
convective power input and ohmic dissipation. A quantitative criteria
delineating the transition between finite-size flows and domain-filling
(large-scale) vortices in electrically conducting fluids is found. By making
use of the inferred and observed properties of planetary interiors, our results
suggest that convection-driven large-scale vortices do not form in the
electrically conducting regions of many bodies.",1807.03268v2
2019-02-22,Temperature-dependent Saturation of Weibel-type Instabilities in Counter-streaming Plasmas,"We present the first 2X2V continuum Vlasov-Maxwell simulations of
interpenetrating, unmagnetized plasmas to study the competition between
two-stream, Oblique, and filamentation modes in the weakly relativistic regime.
We find that after nonlinear saturation of the fastest-growing two-stream and
Oblique modes, the effective temperature anisotropy, which drives current
filament formation via the secular Weibel instability, has a strong dependence
on the internal temperature of the counter-streaming plasmas. The effective
temperature anisotropy is significantly more reduced in colder than in hotter
plasmas, leading to orders of magnitude lower magnetization for colder plasmas.
A strong dependence of the energy conversion efficiency of Weibel-type
instabilities on internal beam temperature has implications for determining
their contribution to the observed magnetization of many astrophysical and
laboratory plasmas.",1902.08672v1
2019-05-20,Efficient quasi-kinematic large-scale dynamo as the small-scale dynamo saturates,"Large-scale magnetic fields in stars and galaxies are thought to arise by
mean-field dynamo action due to the combined influence of both helical
turbulence and shear. Those systems are also highly conducting and the
turbulence therein leads to a fluctuation (or small-scale) dynamo which more
rapidly amplifies magnetic field fluctuations on the eddy scales and smaller.
Will this then interfere with and suppress the mean (or large-scale) field
growth? Using direct numerical simulations of helical turbulence (with and
without shear), we identify a novel quasi-kinematic large-scale dynamo which
operates as the small-scale dynamo saturates. Thus both dynamos operate
efficiently, one after the other, and lead to the generation of significant
large-scale fields.",1905.08278v1
2019-08-23,A Correlation in the Waiting-time Distributions of Solar Flares,"In isolated solar active regions, we find that the waiting times between
flares correlate with flare magnitudes as determined by the GOES soft X-ray
fluxes. A ""build-up and release"" scenario (BUR) for magnetic energy storage in
the solar corona suggests the existence of such a relationship, relating the
slowly varying subphotospheric energy sources to the sudden coronal energy
releases of flares and CMEs. Substantial amounts of research effort had not
previously found any obvious observational evidence for such a BUR process.
This has posed a puzzle since coronal magnetic energy storage represents the
consensus view of the basic flare mechanism. We have revisited the GOES soft
X-ray flare statistics for any evidence of correlations, using two isolated
active regions, and have found significant evidence for a ""saturation""
correlation. Rather than a ""reset"" form of this relaxation, in which the time
\textit{before} a flare correlates with its magnitude, the ""saturation""
relationship results in the time \textit{after} the flare showing the
correlation. The observed correlation competes with the effect of reduced GOES
sensitivity, in which weaker events can be under-reported systematically. This
complicates the observed correlation, and we discuss several approaches to
remedy this.",1908.08749v2
2019-09-10,Transport properties of Keplerian flows in extended local domains with no imposed field,"We compare transport statistics of elongated incompressible shearing boxes
for different Reynolds and magnetic Prandtl numbers, $Re$ and $Pm$, and aspect
ratios, $L_z/L_x$. We find that at fixed aspect ratio $L_z/L_x=4$ and $Re =
10,000$, the turbulent stresses for $Pm \lesssim 1$ do not show considerable
variation and follow a power law $\sim Pm^{3/2}$ for $Pm > 1$. This is
qualitatively consistent with previous results based on net imposed flux and
small box $L_z/L_x \sim 1$ simulations but the power law exponent is different.
The saturated level of stresses, the ratio of Maxwell stress to the magnetic
energy and Reynolds to Maxwell stress ratio are roughly invariant as $L_z/L_x$
is increased. For cases where the boxes are elongated in both the azimuth and
vertical direction, the transport coefficient $\alpha \in [0.1,1.0]$ that is
$10-100$ times larger than the case with $L_y/L_x = 2$ and large $L_z/L_x$.
Overall, our results suggest that the saturated state of turbulence is
sensitive to both dissipation coefficients and aspect ratio (both $L_z/L_x$,
$L_y/L_x$) motivating further work on this problem.",1909.04290v1
2022-01-21,Cavity Ferromagnetic Resonance Study of Acoustic and Optic excitations in Ru/Cr/Co and Ru/Co multilayers,"Two series of [Ru10/Cox)]12 and [Ru6/Cr3/Cox)]12 x=16-60 easy-plane
anisotropy multilayers (all thicknesses in {\AA}), prepared by sputter
deposition, are studied by cavity FMR. The acoustic modes are excited by
setting the RF field perpendicular to the saturating in-plane field. Their
resonance fields are in good agreement with the values predicted for acoustic
modes by macrospin models, using the interlayer RKKY exchange and anisotropy
fields derived by the magnetic measurements. The resonance fields of the modes
excited by setting the RF field parallel to the saturating field, are lower
than those expected for optical modes. This and could attributed to the
existence of hybridized mixed modes, according to results of micromagnetic
simulations which also show that the mode mixing is related to the
inhomogeneous magnetization profile along the multilayer thickness.",2201.08630v1
2022-09-29,"Magnetic properties, electrical resistivity, and hardness of high-entropy alloys FeCoNiPd and FeCoNiPt","We report the magnetic properties, electrical resistivity, and Vickers
microhardness of as-cast and annealed high-entropy alloys (HEAs) FeCoNiPd and
FeCoNiPt with the face-centered cubic structure. The heat treatment at 800
$^{\circ}$C does not largely affect the physical properties in each HEA. The
values of the Curie temperature and the saturation moment at 50 K are 955 K and
1.458 $\mu_\mathrm{B}$/f.u. for the annealed FeCoNiPd, and 851 K and 1.456
$\mu_\mathrm{B}$/f.u. for the annealed FeCoNiPt, respectively. Each HEA is a
soft ferromagnet and shows metallic resistivity. The electronic structure
calculations of both HEAs support the ferromagnetic ground states. The
comparisons between experimental and theoretical values are made for the Curie
temperature, the saturation moment, and the residual resistivity. The Vickers
microhardness of annealed FeCoNiPd and FeCoNiPt are both 188 HV. The hardness
vs. valence electron count (VEC) per atom plot of these HEAs does not largely
deviate from an expected universal relation forming a broad peak at
VEC$\sim$6.8. This study would give some hints on designing a soft
ferromagnetic HEA with high hardness.",2209.14506v1
2023-03-06,Neutron star mass-radius constraints using the high-frequency QPOs of GRB 200415A,"Quasi-periodic oscillations (QPOs) observed in a giant flare of a strongly
magnetized neutron star (magnetar), are carrying crucial information for
extracting the neutron star properties. The aim of the study is to constrain
the mass and radius of the neutron star model for GRB 200415A, by identifying
the observed QPOs with the crustal torsional oscillations together with the
experimental constraints on the nuclear matter properties. The frequencies of
the crustal torsional oscillations are determined by solving the eigenvalue
problem with the Cowling approximation, assuming a magnetic field of about
$10^{15}$G. We find that the observed QPOs can be identified with several
overtones of crustal oscillations, for carefully selected combinations of the
nuclear saturation parameters. Thus, we can inversely constrain the neutron
star mass and radius for GRB 200415A by comparing them to the values of nuclear
saturation parameters obtained from terrestrial experiments. We impose further
constraints on the neutron star mass and radius while the candidate neutron
star models are consistent with the constraints obtained from other available
astronomical and experimental observations.",2303.03150v2
2023-03-22,Role of alkaline metal in the rare-earth triangular antiferromagnet KYbO$_2$,"We report crystal structure and magnetic behavior of the triangular
antiferromagnet KYbO$_2$, the A-site substituted version of the quantum spin
liquid candidate NaYbO$_2$. The replacement of Na by K introduces an
anisotropic tensile strain with 1.6% in-plane and 12.1% out-of-plane lattice
expansion. Compared to NaYbO$_2$, both Curie-Weiss temperature and saturation
field are reduced by about 20% as the result of the increased Yb--O--Yb angles,
whereas the $g$-tensor of Yb$^{3+}$ becomes isotropic with $g=3.08(3)$.
Field-dependent magnetization shows the plateau at 1/2 of the saturated value
and suggests the formation of the up-up-up-down field-induced order in the
triangular AYbO$_2$ oxides (A = alkali metal), in contrast to the isostructural
selenides that exhibit the 1/3 plateau and the up-up-down field-induced order.",2303.12448v2
2023-05-04,Dynamics of magnetoelastic robots in water-saturated granular beds,"We investigate the dynamics of a magnetoelastic robot with a dipolar magnetic
head and a slender elastic body as it performs undulatory strokes and burrows
through water-saturated granular beds. The robot is actuated by an oscillating
magnetic field and moves forward when the stroke amplitude increases above a
critical threshold. By visualizing the medium, we show that the undulating body
fluidizes the bed, resulting in the appearance of a dynamic burrow, which
rapidly closes in behind the moving robot as the medium loses energy. We
investigate the applicability of Lighthill's elongated body theory of fish
locomotion, and estimate the contribution of thrust generated by the undulating
body and the drag incorporating the granular volume fraction-dependent
effective viscosity of the medium. The projected speeds are found to be
consistent with the measured speeds over a range of frequencies and amplitudes
above the onset of forward motion. However, systematic deviations are found to
grow with increasing driving, pointing to a need for further sophisticated
modelling of the medium-structure interactions.",2305.02903v2
2024-01-24,"Hybrid Dynamical Model for Reluctance Actuators Including Saturation, Hysteresis and Eddy Currents","A novel hybrid dynamical model for single-coil, short-stroke reluctance
actuators is presented in this paper. The model, which is partially based on
the principles of magnetic equivalent circuits, includes the magnetic phenomena
of hysteresis and saturation by means of the generalized Preisach model. In
addition, the eddy currents induced in the iron core are also considered, and
the flux fringing effect in the air is incorporated by using results from
finite element simulations. An explicit solution of the dynamics without need
of inverting the Preisach model is derived, and the hybrid automaton that
results from combining the electromagnetic and motion equations is presented
and discussed. Finally, an identification method to determine the model
parameters is proposed and experimentally illustrated on a real actuator. The
results are presented and the advantages of our modeling method are emphasized.",2402.00049v1
2011-08-01,The Radio Activity-Rotation Relation of Ultracool Dwarfs,"[Abridged] We present a new radio survey of about 100 late-M and L dwarfs
undertaken with the VLA. The sample was chosen to explore the role of rotation
in the radio activity of ultracool dwarfs. Combining the new sample with
results from our previous studies and from the literature, we compile the
largest sample to date of ultracool dwarfs with radio observations and measured
rotation velocities (167 objects). In the spectral type range M0-M6 we find a
radio activity-rotation relation, with saturation at log(L_rad/L_bol) 10^(-7.5)
above vsini~5 km/s, similar to the relation in H-alpha and X-rays. However, at
spectral types >M7 the ratio of radio to bolometric luminosity increases
regardless of rotation velocity, and the scatter in radio luminosity increases.
In particular, while the most rapid rotators (vsini>20 km/s) exhibit
""super-saturation"" in X-rays and H-alpha, this effect is not seen in the radio.
We also find that ultracool dwarfs with vsini>20 km/s have a higher radio
detection fraction by about a factor of 3 compared to objects with vsini<10
km/s. When measured in terms of the Rossby number (Ro), the radio
activity-rotation relation follows a single trend and with no apparent
saturation from G to L dwarfs and down to Ro~10^-3; in X-rays and H-alpha there
is clear saturation at Ro<0.1, with super-saturation beyond M7. A similar trend
is observed for the radio surface flux (L_rad/R^2) as a function of Ro. The
continued role of rotation in the overall level of radio activity and in the
fraction of active sources, and the single trend of L_rad/L_bol and L_rad/R^2
as a function of Ro from G to L dwarfs indicates that rotation effects are
important in regulating the topology or strength of magnetic fields in at least
some fully-convective dwarfs. The fact that not all rapid rotators are detected
in the radio provides additional support to the idea of dual dynamo states.",1108.0415v1
2008-04-08,Spherical Accretion with Anisotropic Thermal Conduction,"We study the effects of anisotropic thermal conduction on magnetized
spherical accretion flows using global axisymmetric MHD simulations. In low
collisionality plasmas, the Bondi spherical accretion solution is unstable to
the magnetothermal instability (MTI). The MTI grows rapidly at large radii
where the inflow is subsonic. For a weak initial field, the MTI saturates by
creating a primarily radial magnetic field, i.e., by aligning the field lines
with the background temperature gradient. The saturation is quasilinear in the
sense that the magnetic field is amplified by a factor of $\sim 10-30$
independent of the initial field strength (for weak fields). In the saturated
state, the conductive heat flux is much larger than the convective heat flux,
and is comparable to the field-free (Spitzer) value (since the field lines are
largely radial). The MTI by itself does not appreciably change the accretion
rate $\dot M$ relative to the Bondi rate $\dot M_B$. However, the radial field
lines created by the MTI are amplified by flux freezing as the plasma flows in
to small radii. Oppositely directed field lines are brought together by the
converging inflow, leading to significant resistive heating. When the magnetic
energy density is comparable to the gravitational potential energy density, the
plasma is heated to roughly the virial temperature; the mean inflow is highly
subsonic; most of the energy released by accretion is transported to large
radii by thermal conduction; and the accretion rate $\dot M \ll \dot M_B$. The
predominantly radial magnetic field created by the MTI at large radii in
spherical accretion flows may account for the stable Faraday rotation measure
towards Sgr A* in the Galactic Center.",0804.1353v2
2008-08-27,Epitaxial Zn(x)Fe(3-x)O(4) Thin Films: A Spintronic Material with Tunable Electrical and Magnetic Properties,"The ferrimagnetic spinel oxide Zn(x)Fe(3-x)O(4) combines high Curie
temperature and spin polarization with tunable electrical and magnetic
properties, making it a promising functional material for spintronic devices.
We have grown epitaxial thin films with 0<=x<=0.9 on MgO(001) substrates with
excellent structural properties both in pure Ar atmosphere and an Ar/O2 mixture
by laser molecular beam epitaxy. We find that the electrical conductivity and
the saturation magnetization can be tuned over a wide range during growth. Our
extensive characterization of the films provides a clear picture of the
underlying physics of this spinel ferrimagnet with antiparallel Fe moments on
the A and B sublattice: (i) Zn substitution removes both Fe3+ moments from the
A sublattice and itinerant charge carriers from the B sublattice, (ii) growth
in finite oxygen partial pressure generates Fe vacancies on the B sublattice
also removing itinerant charge carriers, and (iii) application of both Zn
substitution and excess oxygen results in a compensation effect as Zn
substitution partially removes the Fe vacancies. A decrease (increase) of
charge carrier density results in a weakening (strengthening) of double
exchange and thereby a decrease (increase) of conductivity and the saturation
magnetization. This scenario is confirmed by the observation that the
saturation magnetization scales with the longitudinal conductivity. The
combination of tailored films with semiconductor materials such as ZnO in
multi-functional heterostructures seems to be particularly appealing.",0808.3642v3
2008-10-26,Non-linear Study of Bell's Cosmic Ray Current-driven Instability,"The cosmic ray current-driven (CRCD) instability, predicted by Bell (2004),
consists of non-resonant, growing plasma waves driven by the electric current
of cosmic rays (CRs) that stream along the magnetic field ahead of both
relativistic and non-relativistic shocks. Combining an analytic, kinetic model
with one-, two-, and three-dimensional particle-in-cell simulations, we confirm
the existence of this instability in the kinetic regime and determine its
saturation mechanisms. In the linear regime, we show that, if the background
plasma is well magnetized, the CRCD waves grow exponentially at the rates and
wavelengths predicted by the analytic dispersion relation. The magnetization
condition implies that the growth rate of the instability is much smaller than
the ion cyclotron frequency. As the instability becomes non-linear, significant
turbulence forms in the plasma. This turbulence reduces the growth rate of the
field and damps the shortest wavelength modes, making the dominant wavelength,
\lambda_d, grow proportional to the square of the field. At constant CR
current, we find that plasma acceleration along the motion of CRs saturates the
instability at the magnetic field level such that v_A ~ v_{d,cr}, where v_A is
the Alfven velocity in the amplified field, and v_{d,cr} is the drift velocity
of CRs. The instability can also saturate earlier if CRs get strongly deflected
by the amplified field, which happens when their Larmor radii get close to
\lambda_d. We apply these results to the case of CRs in the upstream medium of
supernova remnants. Considering only the most energetic CRs that escape from
the shock, we obtain that the field amplification factor of ~10 can be reached.
This confirms the CRCD instability as a potentially important component of
magnetic amplification process in astrophysical shocks.",0810.4565v1
2011-07-23,Dephasing and Hyperfine Interaction in Carbon Nanotubes Double Quantum Dots: The Clean Limit,"We consider theoretically ${}^{13}$C-hyperfine interaction induced dephasing
in carbon nanotubes double quantum dots with curvature induced spin-orbit
coupling. For two electrons initially occupying a single dot, we calculate the
average return probability after separation into the two dots, which have
random nuclear-spin configurations. We focus on the long time saturation value
of the return probability, $P_\infty$. Because of the valley degree of freedom,
the analysis is more complex than in, for example, GaAs quantum dots, which
have two distinct $P_\infty$ values depending on the magnetic field. Here the
prepared state and the measured state is non-unique because two electrons in
the same dot are allowed in six different states. Moreover, for one electron in
each dot sixteen states exist and therefore are available for being mixed by
the hyperfine field. The return probability experiment is found to be strongly
dependent on the prepared state, on the external magnetic field---both Zeeman
and orbital effects - and on the spin-orbit splitting. The lowest saturation
value, being $P_\infty$=1/3, occurs at zero magnetic field for nanotubes with
spin-orbit coupling and the initial state being the groundstate, this situation
is equivalent to double dots without the valley degree of freedom. In total, we
report nine dynamically different situations that give $P_\infty$=1/3, 3/8,
2/5, 1/2 and for valley anti-symmetric prepared states in an axial magnetic
field, $P_\infty$=1. When the groundstate is prepared the ratio between the
spin-orbit splitting and the Zeeman energy due to a perpendicular magnetic
field can tune the effective hyperfine field continuously from being three
dimensional to two dimensional giving saturation values from $P_\infty$=1/3 to
3/8.",1107.4710v1
2012-10-11,Fluctuation dynamos and their Faraday rotation signatures,"Turbulence is ubiquitous in many astrophysical systems like galaxies, galaxy
clusters and possibly even the IGM filaments. We study fluctuation dynamo
action in turbulent systems focusing on one observational signature; the
Faraday rotation measure (RM) from background radio sources seen through the
magnetic field generated by such a dynamo. We simulate the fluctuation dynamo
(FD) in periodic boxes up to resolutions of 512^3, with varying fluid and
magnetic Reynolds numbers, and measure the resulting random RMs. We show that,
even though the magnetic field generated is intermittent, it still allows for
contributions to the RM to be significant. When the dynamo saturates, it is of
order 40%-50% of the value expected in a model where fields of strength B_rms
uniformly fill cells of the largest turbulent eddy but are randomly oriented
from one cell to another. This level of RM dispersion obtains across different
values of magnetic Reynolds number and Prandtl number explored. We also use the
random RMs to probe the structure of the generated fields to distinguish the
contribution from intense and diffuse field regions. We find that the strong
field regions (say with B > 2B_rms) contribute only of order 15%-20% to the RM.
Thus rare structures do not dominate the RM; rather the general 'sea' of volume
filling fluctuating fields are the dominant contributors. We also show that the
magnetic integral scale, L_{int}, which is directly related to the RM
dispersion, increases in all the runs, as Lorentz forces become important to
saturate the dynamo. It appears that due to the ordering effect of the Lorentz
forces, L_{int} of the saturated field tends to a modest fraction, 1/2-1/3 of
the integral scale of the velocity field, for all our runs. These results are
then applied to discuss the RM signatures of FD generated fields in young
galaxies, galaxy clusters and intergalactic filaments.",1210.3243v2
2020-02-06,A Non-Linear Magnetic Field Calibration Method for Filter-Based Magnetographs by Multilayer Perceptron,"For filter-based magnetographs, the linear calibration method under the
weak-field assumption is usually adopted; this leads to magnetic saturation
effect in the regions with strong magnetic field. This article explores a new
method to overcome the above disadvantage using a multilayer perceptron
network, which we call MagMLP, based on a back-propagation algorithm with one
input layer, five hidden layers, and one output layer. We use the data from the
\textit{Spectropolarimeter} (SP) on board \textit{Hinode} to simulate
single-wavelength observations for the model training, and take into account
the influence of the Doppler velocity field and the filling factor. The
training results show that the linear fitting coefficient (LFC) of the
transverse field reaches above 0.91, and that of the longitudinal field is
above 0.98. The generalization of the models is good because the corresponding
LFCs are above 0.9 for the test subsets. Compared with the linear calibration
method, the MagMLP is much more effective on dealing with the magnetic
saturation effect. Analyzing an active region, the results of the linear
calibration present an evident magnetic saturation effect in the umbra regions;
the corresponding systematic error reaches values greater than 1000 G in most
areas, or even exceeds 2000 G at some pixels. However, the results of MagMLP at
these locations are very close to the inversion results, and the systematic
errors are basically within 300 G. In addition, we find that there are many
""bright spots"" and ""dark spots"" on the inclination angle images from the
inversion results of \textit{Hinode}/SP with values of 180 and 0 degrees,
respectively, where the inversion is not reliable and does not produce a good
result; the MagMLP handles these points well.",2002.02249v1
2014-01-30,Mixing in Magnetized Turbulent Media,"Turbulent motions are essential to the mixing of entrained fluids and are
also capable of amplifying weak initial magnetic fields by small-scale dynamo
action. Here we perform a systematic study of turbulent mixing in magnetized
media, using three-dimensional magnetohydrodynamic simulations that include a
scalar concentration field. We focus on how mixing depends on the magnetic
Prandtl number, Pm, from 1 to 4 and the Mach number, M}, from 0.3 to 2.4. For
all subsonic flows, we find that the velocity power spectrum has a k^-5/3 slope
in the early, kinematic phase, but steepens due to magnetic back reactions as
the field saturates. The scalar power spectrum, on the other hand, flattens
compared to k^-5/3 at late times, consistent with the Obukohov-Corrsin picture
of mixing as a cascade process. At higher Mach numbers, the velocity power
spectrum also steepens due to the presence of shocks, and the scalar power
spectrum again flattens accordingly. Scalar structures are more intermittent
than velocity structures in subsonic turbulence while for supersonic
turbulence, velocity structures appear more intermittent than the scalars only
in the kinematic phase. Independent of the Mach number of the flow, scalar
structures are arranged in sheets in both the kinematic and saturated phases of
the magnetic field evolution. For subsonic turbulence, scalar dissipation is
hindered in the strong magnetic field regions, probably due to Lorentz forces
suppressing the buildup of scalar gradients, while for supersonic turbulence,
scalar dissipation increases monotonically with increasing magnetic field
strength. At all Mach numbers, mixing is significantly slowed by the presence
of dynamically-important small-scale magnetic fields, implying that mixing in
the interstellar medium and in galaxy clusters is less efficient than modeled
in hydrodynamic simulations.",1401.8001v2
2015-12-25,Collective magnetic response of inhomogeneous nanoisland FeNi films around the percolation transition,"By using superconducting quantum interference device (SQUID) magnetometry we
investigated anisotropic high-field (H < 7 T) low-temperature (10 K)
magnetization response of inhomogeneous nanoisland FeNi films grown by rf
sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi
films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the
percolation transition at the d_c=1.8 nm. We discovered that, beyond
conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane
magnetization response of the nanoisland FeNi films is not saturated in the
range of investigated magnetic fields and exhibits paramagnetic-like behavior.
We found that the anomalous out-of-plane magnetization response exhibits an
escalating slope with increase in the nominal film thickness from 0.6 to 1.1
nm, however, it decreases with further increase in the film thickness, and then
practically vanishes on approaching the FeNi film percolation threshold. At the
same time, the in-plane response demonstrates saturation behavior above 1.5-2
T, competing with anomalously large diamagnetic-like response, which becomes
pronounced at high magnetic fields. It is possible that the supported-metal
interaction leads to the creation of a thin charge-transfer (CT) layer and a
Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system
with nanoscale circular domains, the observed anomalous paramagnetic-like
magnetization response can be associated with a large orbital moment of the
localized electrons. The observed magnetization response is determined by the
interplay between the paramagnetic- and diamagnetic-like contributions.",1512.07993v3
2017-07-21,Magnetism out of disorder in a J=0 compound Ba2YIrO6,"We systematically investigate the magnetic properties and local structure of
Ba2YIrO6 to demonstrate that Y and Ir lattice defects in the form of antiphase
boundary or clusters of antisite disorder affect the magnetism observed in this
$d^4$ compound. We compare the magnetic properties and atomic imaging of (1) a
slow cooled crystal, (2) a crystal quenched from 900\degree C after growth, and
(3) a crystal grown using a faster cooling rate than the slow cooled one.
Atomic imaging by scanning transmission electron microscopy (STEM) shows that
quenching from 900oC introduces antiphase boundary to the crystals, and a
faster cooling rate during crystal growth leads to clusters of Y and Ir
antisite disorder. STEM study suggests the antiphase boundary region is Ir-rich
with a composition of Ba2YIrO6. The magnetic measurements show that Ba2YIrO6
crystals with clusters of antisite defects have a larger effective moment and a
larger saturation moment than the slow-cooled crystals. Quenched crystals with
Ir-rich antiphase boundary shows a slightly suppressed saturation moment than
the slow cooled crystals, and this seems to suggest that antiphase boundary is
detrimental to the moment formation. Our DFT calculations suggest magnetic
condensation is unlikely as the energy to be gained from superexchange is small
compared to the spin-orbit gap. However, once Y is replaced by Ir in the
antisite disordered region, the picture of local non-magnetic singlets breaks
down and magnetism can be induced. This is because of (a) enhanced interactions
due to increased overlap of orbitals between sites, and, (b) increased number
of orbitals mediating the interactions. Our work highlights the importance of
lattice defects in understanding the experimentally observed magnetism in
Ba2YIrO6 and other J=0 systems.",1707.06980v1
2022-04-01,"Magnetism, rotation, and nonthermal emission in cool stars -- Average magnetic field measurements in 292 M dwarfs","Stellar dynamos generate magnetic fields that are of fundamental importance
to the variability and evolution of Sun-like and low-mass stars, and for the
development of their planetary systems. We report measurements of
surface-average magnetic fields in 292 M dwarfs from a comparison with
radiative transfer calculations; for 260 of them, this is the first measurement
of this kind. Our data were obtained from more than 15,000 high-resolution
spectra taken during the CARMENES project. They reveal a relation between
average field strength, <B>, and Rossby number, $Ro$, resembling the
well-studied rotation-activity relation. Among the slowly rotating stars, we
find that magnetic flux, $\Phi_\textrm{B}$, is proportional to rotation period,
$P$, and among the rapidly rotating stars that average surface fields do not
grow significantly beyond the level set by the available kinetic energy.
Furthermore, we find close relations between nonthermal coronal X-ray emission,
chromospheric H$\alpha$ and Ca H&K emission, and magnetic flux. Taken together,
these relations demonstrate empirically that the rotation-activity relation can
be traced back to a dependence of the magnetic dynamo on rotation. We advocate
the picture that the magnetic dynamo generates magnetic flux on the stellar
surface proportional to rotation rate with a saturation limit set by the
available kinetic energy, and we provide relations for average field strengths
and nonthermal emission that are independent of the choice of the convective
turnover time. We also find that Ca H&K emission saturates at average field
strengths of $\langle B \rangle \approx 800$ G while H$\alpha$ and X-ray
emission grow further with stronger fields in the more rapidly rotating stars.
This is in conflict with the coronal stripping scenario predicting that in the
most rapidly rotating stars coronal plasma would be cooled to chromospheric
temperatures.",2204.00342v1
2023-07-03,Interplay between local moment and itinerant magnetism in the layered metallic antiferromagnet TaFe$_{1.14}$Te$_3$,"Two-dimensional (2D) antiferromagnets have garnered considerable interest for
the next generation of functional spintronics. However, many available bulk
materials from which 2D antiferromagnets are isolated are limited by their
sensitivity to air, low ordering temperatures, and insulating transport
properties. TaFe$_{1+y}$Te$_3$ offers unique opportunities to address these
challenges with increased air stability, metallic transport properties, and
robust antiferromagnetic order. Here, we synthesize TaFe$_{1+y}$Te$_3$ ($y$ =
0.14), identify its structural, magnetic, and electronic properties, and
elucidate the relationships between them. Axial-dependent high-field
magnetization measurements on TaFe$_{1.14}$Te$_3$ reveal saturation magnetic
fields ranging between 27-30 T with a saturation magnetic moment of 2.05-2.12
$\mu_B$. Magnetotransport measurements confirm TaFe$_{1.14}$Te$_3$ is metallic
with strong coupling between magnetic order and electronic transport.
Angle-resolved photoemission spectroscopy measurements across the magnetic
transition uncover a complex interplay between itinerant electrons and local
magnetic moments that drives the magnetic transition. We further demonstrate
the ability to isolate few-layer sheets of TaFe$_{1.14}$Te$_3$ through
mechanical exfoliation, establishing TaFe$_{1.14}$Te$_3$ as a potential
platform for 2D spintronics based on metallic layered antiferromagnets.",2307.01397v1
2000-05-08,Particle Heating by Nonlinear Alfvenic Turbulence in ADAFs,"Particle heating in advection-dominated accretion flows (ADAFs) by nonlinear
MHD (Alfvenic) turbulence is investigated. Such turbulence with
highly-fluctuating magnetic fields, $\tilde B\sim B_0$, is believed to be
naturally produced by the magnetic shearing instability near the nonlinear
saturation. It is shown that the energy is dissipated in the parallel cascade,
which occurs due to nonlinear compressibility of high-amplitude turbulence, and
predominantly heats protons, but not electrons. The conservative limit on the
electron--to--proton heating fraction is $\delta\lesssim{\rm
few}\times10^{-2}$.",0005119v1
2000-12-04,On the pre-RLO spin-orbit couplings in LMXBs,"We investigate the effect of orbital decay caused by nuclear expansion of a
(sub)giant star in synchronous binary system. We compare this effect with the
presence of a magnetic stellar wind and show that the additional transfer of
orbital angular momentum into spin angular momentum is relatively important --
especially since it has been shown that the effect of magnetic braking
saturates at short orbital periods.",0012077v1
2006-07-14,Intrinsic properties of the magnetically collimated water maser jet of W43A,"Water maser polarization observations in the precessing jet of W43A have
revealed that it is magnetically collimated. Here we present a detailed
description of the physical properties of the water maser environment in the
jet. We discuss the maser saturation level and beaming angle as well as the
intrinsic temperatures and densities. Additionally, we show that the
polarization angle of the strongest red-shifted maser feature undergoes a fast
rotation of 90 degrees across the maser. Along with the variation of linear
polarization fraction, this strongly supports the current theoretical
description of maser linear polarization.",0607337v1
1993-03-25,Critical Exponents of the Three Dimensional Random Field Ising Model,"The phase transition of the three--dimensional random field Ising model with
a discrete ($\pm h$) field distribution is investigated by extensive Monte
Carlo simulations. Values of the critical exponents for the correlation length,
specific heat, susceptibility, disconnected susceptibility and magnetization
are determined simultaneously via finite size scaling. While the exponents for
the magnetization and disconnected susceptibility are consistent with a first
order transition, the specific heat appears to saturate indicating no latent
heat. Sample to sample fluctuations of the susceptibilty are consistent with
the droplet picture for the transition.",9303045v1
1995-11-07,Influence of frustration on a d=3 diluted antiferromagnet: $Fe_{x}Zn_{1-x}F_{2}$,"The influence of a frustrated bond on the magnetic properties of a d=3
uniaxial (Ising) b.c.c. diluted antiferromagnet, with emphasis in the compound
$Fe_{x}Zn_{1-x}F_{2}$, is investigated by a local mean-field numerical
simulation. In particular we find that the initial drop of the saturation
staggered magnetization ($M_{S}$) with concentration follows a percolation-like
phenomenon characterized by an exponent $\beta_{p}$. For the frustrated
samples, however, this regime is followed by a second one identified by a
``long tail"" effect such that $M_{S}$ is zero only at the percolation
threshold. Our numerical data also confirms a spin-glass phase near this
threshold.",9511036v1
1997-12-08,A Theory of Magnets with Competing Double Exchange and Superexchange Interactions,"We study the competition between ferromagnetic double exchange (DE) and
nearest-neighbour antiferromagnetic exchange in CMR materials. Towards this
end, a single site mean field theory is proposed which emphasizes the
hopping-mediated nature of the DE contribution. We find that the competition
between these two exchange interactions leads to ferro- or antiferromagnetic
order with incomplete saturation of the (sub)lattice magnetization. This
conclusion is in contrast to previous results in the literature which find a
canted spin arrangement under similar circumstances. We attribute this
difference to the highly anisotropic exchange interactions used elsewhere. The
associated experimental implications are discussed.",9712094v1
1997-12-25,Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain,"The low temperature magnetization process of the
ferromagnetic-antiferromagnetic Heisenberg chain is studied using the
interacting boson approximation. In the low field regime and near the
saturation field, the spin wave excitations are approximated by the $\delta$
function boson gas for which the Bethe ansatz solution is available. The finite
temperature properties are calculated by solving the integral equation
numerically. The comparison is made with Monte Carlo calculation and the limit
of the applicability of the present approximation is discussed.",9712289v1
1999-11-27,Coherent vs incoherent pairing in 2D systems near magnetic instability,"We study the superconductivity in 2D fermionic systems near antiferromagnetic
instability, assuming that the pairing is mediated by spin fluctuations. This
pairing involves fully incoherent fermions and diffusive spin excitations. We
show that the competition between fermionic incoherence and strong pairing
interaction yields the pairing instability temperature $T_{ins}$ which
increases and saturates as the magnetic correlation length $\xi \to \infty$. We
argue that in this quantum-critical regime the pairing problem is qualitatively
different from the BCS one.",9911445v2
2000-08-23,Field-Induced Gaps in the Frustrated Spin Ladder,"We study the magnetization process of the $S=1/2$ antiferromagnetic spin
ladder in the presence of the second and the third-neighbor couplings which
lead to frustration with the typical nearest-neighbor coupling. We use
degenerate perturbation theory and level spectroscopy analysis of the numerical
diagonalization data of the Hamiltonian for finite systems. We find two kinds
of plateaux at half the saturation moment in the magnetization curve. One is
mainly due to the second-neighbor couplings and the other to the third-neighbor
couplings. The mechanisms of these two plateaux are quite different with each
other.",0008328v1
2001-01-12,Spin Polarization of Two-Dimensional Electrons Determined from Shubnikov-de Haas Oscillations as a Function of Angle,"Recent experiments in the two dimensional electron systems in silicon MOSFETs
have shown that the in-plane magnetic field $H_{sat}$ required to saturate the
conductivity to its high-field value and the magnetic field $H_s$ needed to
completely align the spins of the electrons are comparable. By small-angle
Shubnikov-de Haas oscillation measurements that allow separate determinations
of the spin-up and spin-down subband populations, we show that $H_{sat}=H_s$ to
an accuracy of 5% for electron densities $n_s > 3 \times 10^{11}$ cm$^{-2}$.",0101196v2
2001-02-21,Magnetization plateaus of SrCu_2(BO_3)_2 from a Chern-Simons theory,"The antiferromagnetic Heisenberg model on the frustrated Shastry-Sutherland
lattice is studied by a mapping onto spinless fermions carrying one quantum of
statistical flux. Using a mean-field approximation these fermions populate the
bands of a generalized Hofstadter problem. Their filling leads to the
magnetization curve. For SrCu_2(BO_3)_2 we reproduce plateaus at 1/3 and 1/4 of
the saturation moment and predict a new one at 1/2. Gaussian fluctuations are
shown to be massive at these plateau values.",0102377v1
2001-07-27,"Noncollinear Ferromagnetism in (III,Mn)V Semiconductors","We investigate the stability of the collinear ferromagnetic state in kinetic
exchange models for (III,Mn)V semiconductors with randomly distributed Mn ions
>. Our results suggest that {\em noncollinear ferromagnetism} is commom to
these semiconductor systems. The instability of the collinear state is due to
long-ranged fluctuations invloving a large fraction of the localized magnetic
moments. We address conditions that favor the occurrence of noncollinear
groundstates and discuss unusual behavior that we predict for the temperature
and field dependence of its saturation magnetization.",0107573v2
2001-10-30,Localization corrections and small-q phonon-mediated unconventional superconductivity in the cuprates,"Taking into account the first localization corrections in the
electron-impurity self-energy we study the effect of non-magnetic impurities on
unconventional superconductivity (SC) mediated by small-q electron-phonon
scattering. We show that when van Hove singularities are close to the Fermi
level making the electronic system anisotropic as in the high-$T_c$ oxides,
both the d-wave and s-wave states are sensitive to non-magnetic impurities and
beyond a critical impurity concentration SC disappears in {\it both gap
symmetry channels}. Impurity doping may induce a first order transition from
d-wave to s-wave SC, but no saturation of the impuruty effect is reported due
to the intrinsically anisotropic character of the localization corrections in
this context.",0110637v1
2001-11-12,Itinerant-electron Ferromagnetism in W(Nb)O3-d,"The crystal structure and the magnetic properties of the W1-xNbxO3-d,
(x<0.03) system have been investigated. In contrast to the orthorhombic
diamagnetic WO3, the material with x=0.01 is paramagnetic down to 5 K.
Introducing of 2.5 at. % of Nb into WO3 leads to a tetragonal structure and to
a weak itinerant ferromagnetic ordering below TC= 225 K. The saturation
magnetic moment at 5 K is 1.07*10-3 mB, whereas the paramagnetic effective
moment is 0.06 mB per mole. This high ratio indicates itinerant ferromagnetism
in W0.975Nb0.025O3-d.",0111210v1
2001-12-11,Rayleigh loops in the random-field Ising model on the Bethe lattice,"We analyze the demagnetization properties of the random-field Ising model on
the Bethe lattice focusing on the beahvior near the disorder induced phase
transition. We derive an exact recursion relation for the magnetization and
integrate it numerically. Our analysis shows that demagnetization is possible
only in the continous high disorder phase, where at low field the loops are
described by the Rayleigh law. In the low disorder phase, the saturation loop
displays a discontinuity which is reflected by a non vanishing magnetization
m_\infty after a series of nested loops. In this case, at low fields the loops
are not symmetric and the Rayleigh law does not hold.",0112190v1
2003-06-13,Scaling of the magnetic response in doped antiferromagnets,"A theory of the anomalous $\omega/T$ scaling of the dynamic magnetic response
in cuprates at low doping is presented. It is based on the memory function
representation of the dynamical spin suceptibility in a doped antiferromagnet
where the damping of the collective mode is constant and large, whereas the
equal-time spin correlations saturate at low $T$. Exact diagonalization results
within the t-J model are shown to support assumptions. Consequences, both for
the scaling function and the normalization amplitude, are well in agreement
with neutron scattering results.",0306366v2
2003-11-14,Dynamic roughening and fluctuations of dipolar chains,"Nonmagnetic particles in a carrier ferrofluid acquire an effective dipolar
moment when placed in an external magnetic field. This fact leads them to form
chains that will roughen due to Brownian motion when the magnetic field is
decreased. We study this process through experiments, theory and simulations,
three methods that agree on the scaling behavior over 5 orders of magnitude.
The RMS width goes initially as $t^{1/2}$, then as $t^{1/4}$ before it
saturates. We show how these results complement existing results on polymer
chains, and how the chain dynamics may be described by a recent non-Markovian
formulation of anomalous diffusion.",0311340v1
2004-02-20,Low-frequency incommensurate magnetic response in strongly correlated systems,"It is shown that in the t-J model of Cu-O planes at low frequencies the
dynamic spin structure factor is peaked at incommensurate wave vectors
(1/2+-delta,1/2)$, (1/2,1/2+-delta). The incommensurability is connected with
the momentum dependencies of the magnon frequency and damping near the
antiferromagnetic wave vector. The behavior of the incommensurate peaks is
similar to that observed in La_{2-x}(Ba,Sr)_xCuO_{4+y} and YBa_2Cu_3O_{7-y}:
for hole concentrations 0.02<x<=0.12 we find that delta is nearly proportional
to x, while for x>0.12 it tends to saturation. The incommensurability
disappears with increasing temperature. Generally the incommensurate magnetic
response is not accompanied by an inhomogeneity of the carrier density.",0402512v1
2004-05-29,Optical Spectroscopy of the Hole Spin in GaMnAs Acceptors,"The spin state of holes bound to Mn acceptors in GaMnAs is investigated by
optical spectroscopy. Concentrations of Mn from 10^17 to 10^19 cm^-3 were
studied as a function of magnetic field and temperature. The photoluminescence
from recombination of electrons with holes bound in the Mn-acceptor complex
(MAC) displays multiple spectral peaks. The circular polarization rho of these
peaks increases with increasing magnetic field and saturates at rho ~= 1/3.
This value of polarization is expected from modeling the addition of spin
angular momentum and interband optical transition matrix elements.",0405692v1
2004-06-08,Properties of magnetite nanoparticles synthesized through a novel chemical route,"We have developed a simple precipitation route to synthesize magnetite
(Fe3O4) nano-particles with controlled size without any requirement of
calcination step at high temperatures. The study of these nano-particles
indicates an enhancement in saturation magnetization with reduction in size
down to ~10 nm beyond which the magnetization reduces. The latter is attributed
to surface effects becoming predominant as surface to core volume ratio
increases. From the view -point of applications, 10 nm size of magnetite
particles seems to be the optimum.",0406184v1
2004-07-27,Composition dependent magnetic properties of iron oxide - polyaniline nanoclusters,"Gamma - Iron Oxide prepared by sol -gel process was used to produce
nanocomposites with polyaniline of varying aniline concentrations. TEM shows
the presence of chain like structure for lower polyaniline concentration. The
room temperature hysteresis curves show finite coercivity of 160 Oe for all the
composites while the saturation magnetization was found to decrease with
increasing polymer content. ZFC - FC magnetisation measurements indicate high
blocking temperatures. It is believed that this indicates a strongly
interacting system, which is also shown by our TEM results. Monte Carlo
simulations performed on a random anisotropy model with dipolar and exchange
inteactions match well with experimental results.",0407693v1
2005-03-16,Nonuniqueness in spin-density-functional theory on lattices,"In electronic many-particle systems, the mapping between densities and spin
magnetizations, {n(r), m(r)}, and potentials and magnetic fields, {v(r), B(r)},
is known to be nonunique, which has fundamental and practical implications for
spin-density-functional theory (SDFT). This paper studies the nonuniqueness
(NU) in SDFT on arbitrary lattices. Two new, non-trivial cases are discovered,
here called local saturation and global noncollinear NU, and their properties
are discussed and illustrated. In the continuum limit, only some well-known
special cases of NU survive.",0503384v1
2005-09-05,CeMnNi4: A soft ferromagnet with a high degree of transport spin polarization,"In this letter we introduce a new soft ferromagnetic compound, i.e. CeMnNi4,
which exhibits a large moment (~4.95mu_B/Mn) and high degree of spin
polarization. The system has a ferromagnetic transition temperature of 148K.
Isothermal magnetization measurements at 5K reveal that the material is a soft
ferromagnet with a magnetization saturating at about 500Oe and a coercive field
of < 5 Oe. We determine the transport spin polarization of this material from
Point Contact Andreev Reflection measurements to be 66% thereby making this
material potentially important for spintronic applications.",0509101v2
2005-12-15,"Control of Coercivities in (Ga,Mn)As Thin Films by Small Concentrations of MnAs Nanoclusters","We demonstrate that low concentrations of a secondary magnetic phase in
(Ga,Mn)As thin films can enhance the coercivity by factors up to ~100 without
significantly degrading the Curie temperature or saturation magnetisation.
Magnetic measurements indicate that the secondary phase consists of MnAs
nanoclusters, of average size ~7nm. This approach to controlling the coercivity
while maintaining high Curie temperature, may be important for realizing
ferromagnetic semiconductor based devices.",0512353v1
2006-03-03,Asymmetric Reversal in Inhomogeneous Magnetic Heterostructures,"Asymmetric magnetization reversal is an unusual phenomenon in antiferromagnet
/ ferromagnet (AF/FM) exchange biased bilayers. We investigated this phenomenon
in a simple model system experimentally and by simulation assuming
inhomogeneously distributed interfacial AF moments. The results suggest that
the observed asymmetry originates from the intrinsic broken symmetry of the
system, which results in local incomplete domain walls parallel to the
interface in reversal to negative saturation of the FM. Magneto-optic Kerr
effect unambiguously confirms such an asymmetric reversal and a depth-dependent
FM domain wall in accord with the magnetometry and simulations.",0603060v1
2006-09-15,Two-dimensional frustrated spin systems in high magnetic fields,"We discuss our numerical results on the properties of the S = 1/2 frustrated
J1-J2 Heisenberg model on a square lattice as a function of temperature and
frustration angle phi = atan(J2/J1) in an applied magnetic field. We cover the
full phase diagram of the model in the range -pi <= phi <= pi. The discussion
includes the parameter dependence of the saturation field itself, and addresses
the instabilities associated with it. We also discuss the magnetocaloric effect
of the model and show how it can be used to uniquely determine the effective
interaction constants of the compounds which were investigated experimentally.",0609381v1
1993-04-13,Critical Exponents of the Three Dimensional Random Field Ising Model,"The phase transition of the three--dimensional random field Ising model with
a discrete ($\pm h$) field distribution is investigated by extensive Monte
Carlo simulations. Values of the critical exponents for the correlation length,
specific heat, susceptibility, disconnected susceptibility and magnetization
are determined simultaneously via finite size scaling. While the exponents for
the magnetization and disconnected susceptibility are consistent with a first
order transition, the specific heat appears to saturate indicating no latent
heat. Sample to sample fluctuations of the susceptibilty are consistent with
the droplet picture for the transition.",9304007v1
2000-10-09,Origin of the Nucleon Electromagnetic Form Factors Dipole Formula,"Starting with the VMD parametrization of the electric and magnetic nucleon
form factors, which are saturated just by the ground state vector-mesons rho,
omega and phi, then aplying the strict OZI rule and the asymptotic behaviour of
form factors as predicted by quark model of hadrons, the famous one parameter
dipole formula is derived. By its comparison with space-like data up to t = -5
GeV^2 the most optimal value of the parameter under consideration is
determined. Finaly, charge and magnetization distributions in proton and
neutron are predicted.",0010084v1
1995-03-20,The Bogomol'nyi Bound of Lee-Weinberg Magnetic Monopoles,"The Lee-Weinberg $U(1)$ magnetic monopoles, which have been reinterpreted as
topological solitons of a certain non-Abelian gauged Higgs model recently, are
considered for some specific choice of Higgs couplings. The model under
consideration is shown to admit a Bogomol'nyi-type bound which is saturated by
the configurations satisfying the generalized BPS equations. We consider the
spherically symmetric monopole solutions in some detail.",9503123v1
1995-12-29,Solitonic Black Holes in Gauged N=2 Supergravity,"A sequence of zero-temperature black-hole spacetimes with angular momentum
and electric and magnetic charges is shown to exist in gauged $N=2$
supergravity. Stability of a subset of these spacetimes is demonstrated by
saturation of the Bogomol'nyi bound arising from the supersymmetry algebra. The
mass of the resulting solitonic black holes is given in terms of the
cosmological constant and the angular momentum. We conjecture that at the
quantum level these solitons are dyons with angular momentum determined by the
electric and magnetic charges.",9512222v1
1994-11-29,The Drell-Hearn-Gerasimov Sum Rule,"The Drell-Hearn-Gerasimov (DHG) sum rule relates the helicity structure of
the photoabsorption cross section to the anomalous magnetic moment of the
nucleon. It is based on Lorentz and gauge invariance, crossing symmetry,
causality and unitarity. A generalized DHG sum rule my be derived for virtual
photons. At low momentum transfer this generalized sum rule is saturated by the
resonance region, at high momentum transfer it may be expressed by the parton
spin distributions measured in deep inelastic scattering. The
longitudinal-transverse interference determines the Cottingham sum rule, which
is related to the electric and magnetic form factors over the whole range of
momentum transfer.",9411034v1
2000-01-07,New tests for a singularity of ideal MHD,"Analysis using new calculations with 3 times the resolution of the earlier
linked magnetic flux tubes confirms the transition from singular to saturated
growth rate reported by Grauer and Marliani \cite{GrauerMar99} for the
incompressible cases is confirmed. However, all of the secondary tests point to
a transition back to stronger growth rate at a different location at late
times. Similar problems in ideal hydrodynamics are discussed, pointing out that
initial negative results eventually led to better initial conditions that did
show evidence for a singularity of Euler. Whether singular or near-singular
growth in ideal MHD is eventually shown, this study could have bearing on fast
magnetic reconnection, high energy particle production and coronal heating.",0001016v1
2007-08-14,Formation of bulk ferromagnetic nanostructured Fe40Ni40P14B6 alloys by metastable liquid spinodal decomposition,"Nanostructured Fe40Ni40P14B6 alloys ingots of diameter 3~5 mm could be
synthesised by a metastable liquid state spinodal decomposition method. The
molten Fe40Ni40P14B6 alloy was purified by means of the fluxing technique and
thus a large undercooling could be achieved. For undercooling Delta T > 260 K,
the microstructure of the undercooled specimen had exhibited liquid state
spinodal decomposition in the undercooled liquid state. The microstructure
could be described as two intertwining networks with small grains dispersed in
them. For undercooling Delta T > 290 K, the overall microstructure of the
specimen changed into a granular morphology. The average grain sizes of the
small and large grains are ~ 30 nm and ~ 80 nm, respectively. These prepared
samples are soft magnets with saturation magnetization Bs ~0.744 T.",0708.1809v1
2007-10-06,Spin Anisotropy in ZnCu_3(OH)_6Cl_2,"The spin anisotropic exchange interaction is suggested to contribute
significantly to the abnormal upturn of the magnetic susceptibility in the
ZnCu$_3$(OH)$_6$Cl$_2$. The saturation of the magnetic susceptibility below 300
mK observed in the muon spin resonance ($\mu$SR) experiment is the quantum
effect of the spin flipping process.",0710.1334v3
2007-12-01,Solitons in isotropic antiferromagnets: beyond a sigma model,"Isotropic antiferromagnets shows a reach variety of magnetic solitons with
non-trivial static and dynamic properties. One-dimensional soliton elementary
excitations have a periodic dispersion law. For two-dimensional case, planar
antiferromagnetic vortices having non-singular macroscopic core with the
saturated magnetic moment are present. The dynamic properties of these planar
antiferromagnetic vortex are characterized by presence of a gyroforce",0712.0073v1
2008-04-22,Evolution of entanglement entropy following a quantum quench: Analytic results for the XY chain in a transverse magnetic field,"The non-equilibrium evolution of the block entanglement entropy is
investigated in the XY chain in a transverse magnetic field after the
Hamiltonian parameters are suddenly changed from and to arbitrary values. Using
Toeplitz matrix representation and multidimensional phase methods, we provide
analytic results for large blocks and for all times, showing explicitly the
linear growth in time followed by saturation. The consequences of these
analytic results are discussed and the effects of a finite block length is
taken into account numerically.",0804.3559v1
2008-06-10,Inelastic Scattering from Local Vibrational Modes,"We study a nonuniversal contribution to the dephasing rate of conduction
electrons due to local vibrational modes. The inelastic scattering rate is
strongly influenced by multiphonon excitations, exhibiting oscillatory
behaviour. For higher frequencies, it saturates to a finite, coupling dependent
value. In the strong coupling limit, the phonon is almost completely softened,
and the inelastic cross section reaches its maximal value. This represents a
magnetic field insensitive contribution to the dephasing time in mesoscopic
systems, in addition to magnetic impurities.",0806.1680v1
2008-12-15,Dynamically dominant excitations of string solutions in the spin-1/2 antiferromagnetic Heisenberg chain in magnetic fields,"Using Bethe-ansatz solutions, we uncover a well-defined continuum in
dynamical structure factor $S^{+-}(k,\omega)$ of the spin-1/2 antiferromagnetic
Heisenberg chain in magnetic fields. It comes from string solutions which
continuously connect the mode of the lowest-energy excitations in the
zero-field limit and that of bound states of overturned spins from the
ferromagnetic state near the saturation field. We confirm the relevance to real
materials through comparisons with experimental results.",0812.2707v1
2009-05-13,Pair Creation of Massless Fermions in Electric Flux Tube,"Using chiral anomaly, we discuss the pair creation of massless fermions in an
electric flux tube $\vec{E}$ under homogeneous magnetic field $\vec{B}$
parallel to $\vec{E}$. The tube is axial symmetric and infinitely long in
longitudinal direction. In the limit $B\gg E$, we can analytically obtain the
spatial and temporal behaviors of the electric field and azimuthal magnetic
field generated by the produced fermions. We find that the life time $t_c$ of
the electric field is shorter as the width of the tube is narrower. Applying it
to the glasma in high-energy heavy-ion collisions, we find that color electric
field decays fast such as $t_c\simeq Q_s^{-1}$ with saturation momentum $Q_s$.",0905.2003v1
2009-07-21,Magnetocaloric effect in quantum spin-s chains,"We compute the entropy of antiferromagnetic quantum spin-s chains in an
external magnetic field using exact diagonalization and Quantum Monte Carlo
simulations. The magnetocaloric effect, i.e., temperature variations during
adiabatic field changes, can be derived from the isentropes. First, we focus on
the example of the spin-s=1 chain and show that one can cool by closing the
Haldane gap with a magnetic field. We then move to quantum spin-s chains and
demonstrate linear scaling with $s$ close to the saturation field. In passing,
we propose a new method to compute many low-lying excited states using the
Lanczos recursion.",0907.3736v1
2009-09-11,Resistive g-modes in a reversed field pinch plasma,"First direct experimental evidence of high frequency, high toroidal mode
number (n>20), magnetic fluctuations due to unstable resistive interchange
modes (g-modes) resonant in the edge region of a reversed field pinch (RFP)
plasma is presented. Experimental characterization of time and space
periodicities of the modes is provided by means of highly resolved in-vessel
edge and insertable magnetic diagnostics. It is found that the spectral mode
properties are in good agreement with the predictions of the theoretical linear
resistive magnetohydrodynamic stability analysis. A simple model is proposed
for the observed saturation levels of the modes.",0909.2153v1
2010-06-03,Obtaining and Application of the Reduced Bloch Equations,"Well-known Bloch equations describe the spin systems (electronic and nuclear)
for any scale of time, from transient processes to steady states. Usually in
solids T_2 << T_1. The question arises: what are the approximations that should
be made in order the ""roughen"" Bloch equations to describe the processes at the
time T_2 < t < T_1? The answer to this question is given in this article. As an
example, the saturation of magnetic resonance is considered under the
conditions of harmonic modulation of a constant magnetic field.",1006.1143v1
2011-04-12,Interactions and magnetic moments near vacancies and resonant impurities in graphene,"The effect of electronic interactions in graphene with vacancies or resonant
scatterers is investigated. We apply dynamical mean-field theory in combination
with quantum Monte Carlo simulations, which allow us to treat
non-perturbatively quantum fluctuations beyond Hartree-Fock approximations. The
interactions narrow the width of the resonance and induce a Curie magnetic
susceptibility, signaling the formation of local moments. The absence of
saturation of the susceptibility at low temperatures suggests that the coupling
between the local moment and the conduction electrons is ferromagnetic.",1104.2207v1
2011-05-20,"Magnetization Dissipation in the Ferromagnetic Semiconductor (Ga,Mn)As","We compute the Gilbert damping in (Ga,Mn)As based on the scattering theory of
magnetization relaxation. The disorder scattering is included
non-perturbatively. In the clean limit, the spin-pumping from the localized
d-electrons to the itinerant holes dominates the relaxation processes. In the
diffusive regime, the breathing Fermi-surface effect is balanced by the effects
of interband scattering, which cause the Gilbert damping constant to saturate
at around 0.005. In small samples, the system shape induces a large anisotropy
in the Gilbert damping.",1105.4148v2
2011-08-09,Evidence for spin memory in the electron phase coherence in graphene,"We measure the dependence of the conductivity of graphene as a function of
magnetic field, temperature and carrier density and discover a saturation of
the dephasing length at low temperatures that we ascribe to spin memory
effects. Values of the spin coherence length up to eight microns are found to
scale with the mean free path. We consider different origins of this effect and
suggest that it is controlled by resonant states that act as magnetic-like
defects. By varying the level of disorder, we demonstrate that the spin
coherence length can be tuned over an order of magnitude.",1108.2067v1
2012-01-08,Effect of mechanical stresses on the coercive force of the heterophase non-interacting nanoparticles,"The theoretical analysis of the effect of uniaxial stress on the
magnetization of the system of noninteracting nanoparticles is done by an
example of heterophase particles of maghemite, epitaxially coated with cobalt
ferrite. It is shown that stretching leads to a decrease in the coercive force
$H_c$, and compression leads to its growth. The residual saturation
magnetization $I_{rs}$ of nanoparticles does not change. With increasing of
interfacial exchange interaction, coercive force varies nonmonotonically",1201.1629v1
2012-08-29,Exploring the physical limits of saturation contrast in Magnetic Resonance Imagign,"Magnetic Resonance Imaging has become nowadays an indispensable tool with
applications ranging from medicine to material science. However, so far the
physical limits of the maximum achievable experimental contrast were unknown.
We introduce an approach based on principles of optimal control theory to
explore these physical limits, providing a benchmark for numerically optimized
robust pulse sequences which can take into account experimental imperfections.
This approach is demonstrated experimentally using a model system of two
spatially separated liquids corresponding to blood in its oxygenated and
deoxygenated forms.",1208.5865v1
2013-06-28,Particle Acceleration during Magnetorotational Instability in a Collisionless Accretion Disk,"Particle acceleration during the magnetorotational instability (MRI) in a
collisionless accretion disk was investigated by using a particle-in-cell (PIC)
simulation. We discuss the important role that magnetic reconnection plays not
only on the saturation of MRI but also on the relativistic particle generation.
The plasma pressure anisotropy of $p_{\perp} > p_{\para}$ induced by the action
of MRI dynamo leads to rapid growth in magnetic reconnection, resulting in the
fast generation of nonthermal particles with a hard power-law spectrum. This
efficient particle acceleration mechanism involved in a collisionless accretion
disk may be a possible model to explain the origin of high energy particles
observed around massive black holes.",1306.6720v1
2013-07-03,Low-temperature thermodynamics of spin-1/2 orthogonal-dimer chain with Ising and Heisenberg interactions,"We consider an exactly solvable version of the quantum spin-1/2
orthogonal-dimer chain with the Heisenberg intra-dimer and Ising inter-dimer
couplings. The investigated quantum spin system exhibits at zero temperature
fractional plateaux at 1/4 and 1/2 of the saturation magnetization and it has a
highly degenerate ground state at critical fields where the magnetization
jumps. We study the field dependence of the specific heat at low temperature.
The lattice-gas description is formulated in a vicinity of critical fields to
explain the low-temperature behaviour of specific heat.",1307.1005v1
2013-07-06,Iterative Deconvolution of Quadrupole Split NMR Spectra,"We propose a simple method to deconvolute NMR spectra of quadrupolar nuclei
in order to separate the distribution of local magnetic hyperfine field from
the quadrupole splitting. It is based on an iterative procedure which allows to
express the intensity of a single NMR line directly as a linear combination of
the intensities of the total experimental spectrum at a few related
frequencies. This procedure is argued to be an interesting complement to
Fourier transformation since it can lead to a significant noise reduction in
some frequency ranges. This is demonstrated in the case of the 11B-NMR spectrum
in SrCu2(BO3)2 at a field of 31.7 T, where a magnetization plateau at 1/6 of
the saturation has been observed.",1307.1752v1
2013-10-04,A Classical Nernst Engine,"We introduce a simple model for an engine based on the Nernst effect. In the
presence of a magnetic field, a vertical heat current can drive a horizontal
particle current against a chemical potential. For a microscopic model invoking
classical particle trajectories subject to the Lorentz force, we prove a
universal bound 3-2*sqrt(2) simeq 0.172 for the ratio between maximum
efficiency and Carnot efficiency. This bound, as the slightly lower one 1/6 for
efficiency at maximum power, can indeed be saturated for large magnetic field
and small fugacity irrespective of the aspect ratio.",1310.1195v1
2013-12-05,Magnetic properties of ferromagnetic Pu2Pt3Si5,"The structural, magnetic, and thermodynamic properties of a new plutonium
based compound, Pu2Pt3Si5, are reported. Single crystals produced by a Sn-flux
technique have been analyzed showing a ferromagnetic behavior at 58 K.
Pu2Pt3Si5 crystallizes in the U2Co3Si5-type orthorhombic Iabm structure (72)
with atomic parameters a = 9.9226(2) \AA, b = 11.4436(2) \AA and c = 6.0148(1)
\AA. The effective (\mu_eff ~0.74 \mu_B) and saturated (\mu_sat ~0.32 B/Pu)
moments as well as the Sommerfeld coefficient (\gamma_e ~2 mJ.mol-1.K-2/Pu)
could point towards 5f localization in this material.",1312.1576v1
2014-01-16,Low-temperature large-distance asymptotics of the transversal two-point functions of the XXZ chain,"We derive the low-temperature large-distance asymptotics of the transversal
two-point functions of the XXZ chain by summing up the asymptotically dominant
terms of their expansion into form factors of the quantum transfer matrix. Our
asymptotic formulae are numerically efficient and match well with known results
for vanishing magnetic field and for short distances and magnetic fields below
the saturation field.",1401.4132v1
2014-07-03,Inhomogeneous ordering in weakly coupled Heisenberg $S=1/2$ chains with random bonds,"Long range magnetic ordering in the quasi-one-dimensional random-bond
antiferromagnet BaCu$_2$(Si$_{1-x}$Ge$_{x}$)$_2$O$_7$ is studied in $\mu$SR
experiments as a function of disorder strength. Compared to the disorder-free
parent materials, the saturation ordered moment is found to be considerably
reduced. Moreover, even in weakly disordered species, the magnetically ordered
state is shown to be highly inhomogeneous. The results are interpreted in terms
of weakly coupled random spin chains, governed by the ``infinite randomness``
fixed point.",1407.0813v2
2014-07-18,Structural and electronic properties of epitaxial YBaCuO/LaCaMnO bilayers grown on SrTiO$_3$ (110) substrates,"Epitaxial bilayers of the high-temperature-superconductor YBa2Cu3O7-d (YBCO)
and the ferromagnetic metal La0.67Ca0.33MnO3 (LCMO) were prepared by pulsed
laser deposition on (110)-oriented SrTiO3 substrates, such that the CuO2 planes
of YBCO are perpendicular to the YBCO-LCMO interface. X-ray diffraction and
Raman scattering demonstrate complete (110) orientation of both YBCO and LCMO
overlayers. The resistivity and magnetization of the bilayer films are highly
anisotropic. The critical temperatures for superconductivity and ferromagnetism
as well as the saturation magnetization exhibit modest reductions compared to
corresponding bulk values.",1407.5049v1
2016-01-14,Optimal Current Waveforms for Switched-Reluctance Motors,"In this paper, we address the problem of finding current waveforms for a
switched reluctance motor that minimize a user-defined combination of torque
ripple and RMS current. The motor model we use is fairly general, and includes
magnetic saturation, voltage and current limits, and highly coupled magnetics
(and therefore, unconventional geometries and winding patterns). We solve this
problem by approximating it as a mixed-integer convex program, which we solve
globally using branch and bound. We demonstrate our approach on an
experimentally verified model of a fully pitched switched reluctance motor, for
which we find the globally optimal waveforms, even for high rotor speeds.",1601.03768v1
2016-02-02,Magnetization Dynamics of Topological Defects and the Spin Solid in Kagome Artificial Spin Ice,"We report broadband spin-wave spectroscopy on kagome artificial spin ice
(ASI) made of large arrays of interconnected Ni$_{80}$Fe$_{20}$ nanobars.
Spectra taken in saturated and disordered states exhibit a series of resonances
with characteristic magnetic field dependencies. Making use of micromagnetic
simulations, we identify resonances that reflect the spin-solid-state and
monopole-antimonopole pairs on Dirac strings. The latter resonances allow for
the generation of highly-charged vertices in ASIs via microwave assisted
switching. Our findings open further perspectives for fundamental studies on
ASIs and their usage in reprogrammable magnonics.",1602.00918v1
2016-02-22,Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators,"We investigate magnetization dynamics in a spin-Hall oscillator using a
direct current measurement as well as conventional microwave spectrum analysis.
When the current applies an anti-damping spin-transfer torque, we observe a
change in resistance which we ascribe to the excitation of incoherent exchange
magnons. A simple model is developed based on the reduction of the effective
saturation magnetization, quantitatively explaining the data. The observed
phenomena highlight the importance of exchange magnons on the operation of
spin-Hall oscillators.",1602.06710v1
2017-03-28,Gauged BPS baby Skyrmions with quantised magnetic flux,"A new type of gauged BPS baby Skyrme model is presented, where the derivative
term is just the Schroers current (i.e., gauge invariant and conserved version
of the topological current) squared. This class of models has a topological
bound saturated for solutions of the pertinent Bogomolnyi equations
supplemented by a so-called superpotential equation. In contrast to the gauged
BPS baby Skyrme models considered previously, the superpotential equation is
linear and, hence, completely solvable. Furthermore, the magnetic flux is
quantized in units of $2\pi$, which allows, in principle, to define this theory
on a compact manifold without boundary, unlike all gauged baby Skyrme models
considered so far.",1703.09672v1
2018-04-12,Peculiar magnetic properties of NC6 and NC12 layered compounds from first principles,"In the context of characterizing nitrogen poor carbo-nitrides for different
applications, identification of an unusual onset of spin polarization of N(p)
states has been shown. A full saturation up to 3 Bohr magnetons is demonstrated
in extended two-dimensional carbon networks of C6N and C12N hexagonal
structures refined based on density functional theory calculations. From
establishing the energy-volume equations of states in both compounds assuming
spin degenerate (non spin polarized) and spin-polarized configurations, the
ground state is identified as ferromagnetic. The variation of magnetization
with volume points to strongly ferromagnetic behavior",1804.04441v1
2018-05-01,Optoelectronic spin memories of electrons in semiconductors,"We optically generate electron spins in semiconductors and apply an external
magnetic field perpendicularly to them. Time-resolved photoluminescence
measurements, pumped with a circularly polarized light, are performed to study
the spin polarization and spin memory times in the semiconducting host. The
measured spin polarization is found to be an exponential decay with the time
delay of the probe. It is also found that the spin memory times, extracted from
the polarization decays, enhance with the strength of the external magnetic
field. However, at higher fields, the memory times get saturated to sub-{\mu}s
because of the coupling for interacting electrons with the local nuclear field.",1805.00171v1
2018-05-04,Modeling of graphene Hall effect sensors for microbead detection,"This paper deals with the modeling of sensitivity of epitaxial graphene Hall
bars, from sub-micrometer to micrometer size, to the stray field generated by a
magnetic microbead. To demonstrate experiment feasibility, the model is first
validated by comparison to measurement results, considering an ac-dc detection
scheme. Then, an exhaustive numerical analysis is performed to investigate
signal detriment caused by material defects, saturation of bead magnetization
at high fields, increment of bead distance from sensor surface and device width
increase.",1805.01779v1
2018-06-04,Dynamical quadrupole structure factor of frustrated ferromagnetic chain,"We investigate the dynamical quadrupole structure factor of a spin-1/2
$J_{1}$-$J_{2}$ Heisenberg chain with competing ferromagnetic $J_{1}$ and
antiferromagnetic $J_{2}$ in a magnetic field by exploiting density-matrix
renormalization group techniques. In a field-induced spin nematic regime, we
observe gapless excitations at $q=\pi$ according to quasi-long-range
antiferro-quadrupole correlations. The gapless excitation mode has a quadratic
form at the saturation, while it changes into a linear dispersion as the
magnetization decreases.",1806.01434v1
2019-05-19,Path-integral Monte Carlo study of electronic states in quantum dots in an external magnetic field,"We explore correlated electron states in harmonically confined few-electron
quantum dots in an external magnetic field by the path-integral Monte Carlo
method for a wide range of the field and the Coulomb interaction strength.
Using the phase structure of a preceding unrestricted Hartree-Fock calculation
for phase fixing, we find a rich variety of correlated states, often completely
different from the prediction of mean-field theory. These are finite
temperature results, but sometimes the correlations saturate with decreasing
temperature, providing insight into the ground-state properties.",1905.07802v2
2019-06-24,Graded index lenses for spin wave steering,"We use micromagnetic modelling to demonstrate the operation of graded index
lenses designed to steer forward-volume magnetostatic spin waves by 90 and 180
degrees. The graded index profiles require the refractive index to diverge in
the lens center, which, for spin waves, can be achieved by modulating the
saturation magnetization or external magnetic field in a ferromagnetic film by
a small amount. We also show how the 90$^\circ$ lens may be used as a beam
divider. Finally, we analyse the robustness of the lenses to deviations from
their ideal profiles.",1906.09985v1
2020-09-30,Exploring zonal flow mediated saturation on stellarators,"In stellarators, zonal flow activity depends sensitively on geometry of the
three dimensional magnetic field, via an interplay of mechanisms that is not
fully understood. In this work, we investigate this by studying three magnetic
configurations of the Wendelstein 7-X stellarator. We find that variation in
linear zonal flow damping is accompanied by variation in nonlinear drive, and
identify key geometric features that control these effects. Understanding the
resulting balance is important for the development of reduced models of
turbulent transport.",2009.14750v1
2022-04-19,Spin correlations in the frustrated ferro-antiferromagnet SrZnVO(PO4)2 near saturation,"Single crystal elastic and inelastic neutron scattering experiments are
performed on the frustrated ferro-antiferromagnet SrZnVO(PO4)2 in high magnetic
fields. The fully polarized state, the presaturation phase and the
columnar-antiferromagnetic phase just bellow the presaturation phase were
investigated. The observed renormalization of spin wave bandwidths,
re-distribution of intensities between different branches and non-linearities
in the magnetization curve are all indicative of strong deviations from
classical spin wave theory. The previously observed presaturation transition is
attributed to a staggered pattern of Dzyaloshinskii-Moriya interactions.",2204.08778v2
2011-02-16,{Rearrangement of the antiferromagnetic ordering at high magnetic fields in SmFeAsO and SmFeAsO$_{0.9}$F$_{0.1}$ single crystals,"The low-temperature antiferromagnetic state of the Sm-ions in both
nonsuperconducting SmFeAsO and superconducting SmFeAsO$_{0.9}$F$_{0.1}$ single
crystals was studied by magnetic torque, magnetization, and magnetoresistance
measurements in magnetic fields up to 60~T and temperatures down to 0.6~K. We
uncover in both compounds a distinct rearrangement of the antiferromagnetically
ordered Sm-moments near $35-40$~T. This is seen in both, static and pulsed
magnetic fields, as a sharp change in the sign of the magnetic torque, which is
sensitive to the magnetic anisotropy and hence to the magnetic moment in the
$ab$-plane, ({\it i.e.} the FeAs-layers), and as a jump in the magnetization
for magnetic fields perpendicular to the conducting planes. This rearrangement
of magnetic ordering in $35-40$~T is essentially temperature independent and
points towards a canted or a partially polarized magnetic state in high
magnetic fields. However, the observed value for the saturation moment above
this rearrangement, suggests that the complete suppression of the
antiferromagnetism related to the Sm-moments would require fields in excess of
60~T. Such a large field value is particularly remarkable when compared to the
relatively small N\'{e}el temperature $T_{\rm N}\simeq5$~K, suggesting very
anisotropic magnetic exchange couplings. At the transition, magnetoresistivity
measurements show a crossover from positive to negative field-dependence,
indicating that the charge carriers in the FeAs planes are sensitive to the
magnetic configuration of the rare-earth elements. This is indicates a finite
magnetic/electronic coupling between the SmO and the FeAs layers which are
likely to mediate the exchange interactions leading to the long range
antiferromagnetic order of the Sm ions.",1102.3312v1
2006-09-27,Simulation of the Magnetothermal Instability,"In many magnetized, dilute astrophysical plasmas, thermal conduction occurs
almost exclusively parallel to magnetic field lines. In this case, the usual
stability criterion for convective stability, the Schwarzschild criterion,
which depends on entropy gradients, is modified. In the magnetized long mean
free path regime, instability occurs for small wavenumbers when (dP/dz)(dln
T/dz) > 0, which we refer to as the Balbus criterion. We refer to the
convective-type instability that results as the magnetothermal instability
(MTI). We use the equations of MHD with anisotropic electron heat conduction to
numerically simulate the linear growth and nonlinear saturation of the MTI in
plane-parallel atmospheres that are unstable according to the Balbus criterion.
The linear growth rates measured from the simulations are in excellent
agreement with the weak field dispersion relation. The addition of isotropic
conduction, e.g. radiation, or strong magnetic fields can damp the growth of
the MTI and affect the nonlinear regime. The instability saturates when the
atmosphere becomes isothermal as the source of free energy is exhausted. By
maintaining a fixed temperature difference between the top and bottom
boundaries of the simulation domain, sustained convective turbulence can be
driven. MTI-stable layers introduced by isotropic conduction are used to
prevent the formation of unresolved, thermal boundary layers. We find that the
largest component of the time-averaged heat flux is due to advective motions as
opposed to the actual thermal conduction itself. Finally, we explore the
implications of this instability for a variety of astrophysical systems, such
as neutron stars, the hot intracluster medium of galaxy clusters, and the
structure of radiatively inefficient accretion flows.",0609732v1
2005-09-04,Itinerant Ferromagnetism and Metamagnetism in Cr Doped Perovskite Ruthenates,"We report results of structural, magnetic and transport properties of single
crystal CaRu1-xCrxO3 (0&#8804;x&#8804;0.36) and SrRu1-xCrxO3
(0&#8804;x&#8804;0.30). Cr substitution as low as x=0.08 drives CaRu1-xCrxO3
from the paramagnetic state to an itinerant ferromagnetic state with
field-driven first-order metamagnetic transitions leading to a sizeable
saturation moment (~0.4&#61549;B/f.u.within the ab plane). The ferromagnetism
occurs abruptly and reaches as high as TC=123 K for x=0.22. The Cr-driven
ferromagnetism is highly anisotropic, suggesting an important role for
spin-orbit coupling. Lattice constant and magnetic measurements strongly
support the valence of the Cr as tetravalent (Cr4+, 3d2 configuration). Cr
substitution for Ru in SrRuO3 (TC=165 K) enhances the itinerant ferromagnetism,
with TC reaching 290 K for x=0.30, consistent with Cr-induced ferromagnetism in
paramagnetic CaRuO3. Preliminary pressure-dependent magnetization of
CaRu0.85Cr0.15O3 shows strong enhancement of the saturation magnetization (25%
for P~0.7 GPa). All results indicate a coupling of Ru 4d and Cr 3d electrons
that is unexpectedly favorable for itinerant ferromagnetism which often exists
delicately in the ruthenates.",0509084v1
1995-07-31,Singular BPS Saturated States and Enhanced Symmetries of Four-Dimensional N=4 Supersymmetric String Vacua,"A class of supersymmetric (BPS saturated), static, spherically symmetric
solutions of four-dimensional effective N=4 supersymmetric superstring vacua,
which become massless at special points of moduli space, is studied in terms of
the fields of the effective heterotic string theory compactified on a
six-torus. Those are singular four-dimensional solutions corresponding to
$O(6,22,Z)$ orbits of dyonic configurations (with zero axion), whose
left-moving as well as right-moving electric and magnetic charges are
orthogonal (light-like in the $O(6,22,Z)$ sense), while the $O(6,22,Z)$ norms
of both the electric and magnetic charges are negative. Purely electric [or
purely magnetic] and dyonic configurations preserve $1\over 2$ and $1\over 4$
of N=4 supersymmetry, respectively, thus belonging to the vector and the
highest spin $3\over 2$ supermultiplets, respectively. Purely electric [or
purely magnetic] solutions (along with an infinite tower of $SL(2,Z)$
transformed states) become massless at a point of the corresponding
``one-torus'', thus may contribute to the enhancement of non-Abelian gauge
symmetry, while dyonic solutions become simultaneously massless at a point of
the corresponding two-torus, and thus may in addition contribute to the
enhancement of the local supersymmetry there.",9507160v3
2007-05-02,Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence,"We present a scaling law that predicts the values of the stresses obtained in
numerical simulations of saturated MRI-driven turbulence in non-stratified
shearing boxes. It relates the turbulent stresses to the strength of the
vertical magnetic field, the sound speed, the vertical size of the box, and the
numerical resolution and predicts accurately the results of 35 numerical
simulations performed for a wide variety of physical conditions. We use our
result to show that the saturated stresses in simulations with zero net
magnetic flux depend linearly on the numerical resolution and would become
negligible if the resolution were set equal to the natural dissipation scale in
astrophysical disks. We conclude that, in order for MRI-driven turbulent
angular momentum transport to be able to account for the large value of the
effective alpha viscosity inferred observationally, the disk must be threaded
by a significant vertical magnetic field and the turbulent magnetic energy must
be in near equipartition with the thermal energy. This result has important
implications for the spectra of accretion disks and their stability.",0705.0352v2
2008-01-08,"Nano granular metallic Fe - oxygen deficient TiO$_{2-δ}$ composite films: A room temperature, highly carrier polarized magnetic semiconductor","Nano granular metallic iron (Fe) and titanium dioxide (TiO$_{2-\delta}$) were
co-deposited on (100) lanthanum aluminate (LaAlO$_3$) substrates in a low
oxygen chamber pressure using a pulsed laser ablation deposition (PLD)
technique. The co-deposition of Fe and TiO$_2$ resulted in $\approx$ 10 nm
metallic Fe spherical grains suspended within a TiO$_{2-\delta}$ matrix. The
films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss
at room temperature. Our estimate of the saturation magnetization based on the
size and distribution of the Fe spheres agreed well with the measured value.
The film composite structure was characterized as p-type magnetic semiconductor
at 300 K with a carrier density of the order of $ 10^{22} /{\rm cm^3}$. The
hole carriers were excited at the interface between the nano granular Fe and
TiO$_{2-\delta}$ matrix similar to holes excited in the metal/n-type
semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS)
devices. From the large anomalous Hall effect directly observed in these films
it follows that the holes at the interface were strongly spin polarized.
Structure and magneto transport properties suggested that these PLD films have
potential nano spintronics applications.",0801.1285v1
2009-01-28,Detailed Analysis of Filamentary Structure in the Weibel Instability,"We present results of a 2D3V kinetic Vlasov simulation of the Weibel
instability. The kinetic Vlasov simulation allows us to investigate the
velocity distribution of dilute plasmas, in which the effect of collisions
between particles is negligible, and has the advantage that the accuracy of the
calculated velocity distribution does not depend on the density of plasmas at
each point in the physical space. We succeed in reproducing some features of
the Weibel instability shown by other simulations, for example, the
exponentially growing phase, the saturation of the magnetic field strength, the
formation of filamentary structure, and the coalescence of the filaments.
Especially, we concentrate on the behavior of the filaments after the
saturation of the magnetic field strength and find that there is a kind of
quasi-equilibrium states before the coalescence occurs. Furthermore, it is
found that an analytical solution for stationary states of the 2D3V
Vlasov-Maxwell system can reproduce some dominant features of the
quasi-equilibrium, e.g, the configuration of the magnetic field and the
velocity distribution at each point. The analytical expression could give a
plausible model for the transition layer of a collisionless shock where a
strong magnetic field generated by the Weibel instability provides an effective
dissipation process instead of collisions between particles.",0901.4402v1
2012-08-22,The kinetic helicity needed to drive large-scale dynamos,"Magnetic field generation on scales large compared with the scale of the
turbulent eddies is known to be possible via the so-called $\alpha$ effect when
the turbulence is helical and if the domain is large enough for the $\alpha$
effect to dominate over turbulent diffusion. Using three-dimensional turbulence
simulations, we show that the energy of the resulting mean magnetic field of
the saturated state increases linearly with the product of normalized helicity
and the ratio of domain scale to eddy scale, provided this product exceeds a
critical value of around unity. This implies that large-scale dynamo action
commences when the normalized helicity is larger than the inverse scale ratio.
Our results show that the emergence of small-scale dynamo action does not have
any noticeable effect on the large-scale dynamo. Recent findings by Pietarila
Graham et al. (2012, Phys. Rev. E85, 066406) of a smaller minimal helicity may
be an artifact due to the onset of small-scale dynamo action at large magnetic
Reynolds numbers. However, the onset of large-scale dynamo action is difficult
to establish when the kinetic helicity is small. Instead of random forcing,
they used an ABC-flow with time-dependent phases. We show that such dynamos
saturate prematurely in a way that is reminiscent of inhomogeneous dynamos with
internal magnetic helicity fluxes. Furthermore, even for very low fractional
helicities, such dynamos display large-scale fields that change direction,
which is uncharacteristic of turbulent dynamos.",1208.4529v2
2012-12-06,"Equilibrium disks, MRI mode excitation, and steady state turbulence in global accretion disk simulations","Global three dimensional magnetohydrodynamic (MHD) simulations of turbulent
accretion disks are presented which start from fully equilibrium initial
conditions in which the magnetic forces are accounted for and the induction
equation is satisfied. The local linear theory of the magnetorotational
instability (MRI) is used as a predictor of the growth of magnetic field
perturbations in the global simulations. The linear growth estimates and global
simulations diverge when non-linear motions - perhaps triggered by the onset of
turbulence - upset the velocity perturbations used to excite the MRI. The
saturated state is found to be independent of the initially excited MRI mode,
showing that once the disk has expelled the initially net flux field and
settled into quasi-periodic oscillations in the toroidal magnetic flux, the
dynamo cycle regulates the global saturation stress level. Furthermore,
time-averaged measures of converged turbulence, such as the ratio of magnetic
energies, are found to be in agreement with previous works. In particular, the
globally averaged stress normalized to the gas pressure, <\alpha_{\rm P}> =
0.034, with notably higher values achieved for simulations with higher
azimuthal resolution. Supplementary tests are performed using different
numerical algorithms and resolutions. Convergence with resolution during the
initial linear MRI growth phase is found for 23-35 cells per scaleheight (in
the vertical direction).",1212.1306v1
2013-08-28,Quantum phase diagram of the $S=1/2$ triangular-lattice antiferromagnet Ba$_3$CoSb$_2$O$_9$,"The magnetic phases of the ideal spin-1/2 triangular-lattice antiferromagnet
Ba$_3$CoSb$_2$O$_9$ are identified and studied using $^{135,137}$Ba nuclear
magnetic resonance (NMR) spectroscopy in magnetic fields ranging to 30T,
oriented parallel and near perpendicular to the crystallographic $ab$-plane.
For both directions, the saturation field is approximately 33T. Notably, the
NMR spectra provide microscopic evidence for the stabilization of an up-up-down
spin configuration for in-plane fields, giving rise to an one-third
magnetization plateau ($M_\text{sat}/3$), as well as for a higher field phase
transition near to $\sim (3/5)M_\text{sat}$ for both field orientations. Phase
transitions are signaled by the evolution of the NMR spectra, and in some cases
through spin-lattice relaxation measurements. The results are compared with
expectations obtained from a semi-classical energy density modeling, in which
quantum effects are incorporated by effective interactions extracted from the
spin-wave analysis of the two-dimensional model. The interlayer coupling also
plays a significant role in the outcome. Good agreement between the model and
the experimental results is achieved, except for the case of fields approaching
the saturation value applied along the c-axis.",1308.6331v2
2015-07-17,Hard-core boson approach to the spin-1/2 triangular-lattice antiferromagnet Cs$_2$CuCl$_4$ at finite temperatures in magnetic fields higher than the saturation field,"We study the high magnetic field regime of the antiferromagnetic insulator
Cs$_2$CuCl$_4$ by expressing the spin-1/2 operators in the relevant Heisenberg
model in terms of hard-core bosons and implementing the hard-core constraint
via an infinite on-site interaction. We focus on the case where the external
magnetic field exceeds the saturation field $B_{c}\approx8.5\;\mathrm{T}$ and
is oriented along the crystallographic $a$ axis perpendicular to the lattice
plane. Because in this case the excited states are separated by an energy gap
from the ground state, we may use the self-consistent ladder approximation to
take the strong correlations due to the hard-core constraint into account. In
Cs$_2$CuCl$_4$ there are additional interactions besides the hard-core
interaction which we treat in self-consistent Hartree-Fock approximation. We
calculate the spectral function of the hard-core bosons from which we obtain
the in-plane components of the dynamic structure factor, the magnetic
susceptibility, and the specific heat. Our results for the specific heat are in
good agreement with the available experimental data. We conclude that the
self-consistent ladder approximation in combination with a self-consistent
Hartree-Fock decoupling of the non-hard-core interactions gives an accurate
description of the physical properties of gapped hard-core bosons in two
dimensions at finite temperatures.",1507.04957v2
2019-04-05,"Cluster-based Haldane phases, bound magnon crystals and quantum spin liquids of a mixed spin-1 and spin-1/2 Heisenberg octahedral chain","The mixed spin-1 and spin-1/2 Heisenberg octahedral chain with regularly
alternating monomeric spin-1 sites and square-plaquette spin-1/2 sites is
investigated using variational technique, localized-magnon approach, exact
diagonalization (ED) and density-matrix renormalization group (DMRG) method.
The investigated model has in a magnetic field an extraordinarily rich
ground-state phase diagram, which includes the uniform and cluster-based
Haldane phases, two ferrimagnetic phases of Lieb-Mattis type, two quantum spin
liquids and two bound magnon crystals in addition to the fully polarized
ferromagnetic phase. The lowest-energy eigenstates in a highly-frustrated
parameter region belong to flat bands and hence, low-temperature thermodynamics
above the bound magnon-crystal ground states can be satisfactorily described
within the localized-magnon approach. The variational method provides an exact
evidence for the magnon-crystal phase with a character of the monomer-tetramer
ground state at zero field, while another magnon-crystal phase with a single
bound magnon at each square plaquette is found in a high-field region. A
diversity of quantum ground states gives rise to manifold zero-temperature
magnetization curves, which may involve up to four wide intermediate plateaus
at zero, one-sixth, one-third and two-thirds of the saturation magnetization,
two quantum spin-liquid regions and two tiny plateaus at one-ninth and
one-twelfth of the saturation magnetization corresponding to the fragmentized
cluster-based Haldane phases.",1904.02889v2
2021-03-06,Exceptional spectrum and dynamic magnetization,"A macroscopic effect can be induced by a local non-Hermitian term in a
many-body system, when it manifests simultaneously level coalescence of a full
real degeneracy spectrum, leading to exceptional spectrum. In this paper, we
propose a family of systems that support such an intriguing property. It is
generally consisted of two arbitrary identical Hermitian sub-lattices in
association with unidirectional couplings between them. We show exactly that
all single-particle eigenstates coalesce in pairs even only single
unidirectional coupling appears. It means that all possible initial states obey
the exceptional dynamics, resulting in some macroscopic phenomena, which never
appears in a Hermitian system. As an application, we study the dynamic
magnetization induced by complex fields in an itinerant electron system. It
shows that an initial saturated ferromagnetic state at half-filling can be
driven into its opposite state according to the dynamics of high-order
exceptional point. Any Hermitian quench term cannot realize a steady opposite
saturated ferromagnetic state. Numerical simulations for the dynamical
processes of magnetization are performed for several representative situations,
including lattice dimensions, global random and local impurity distributions.
It shows that the dynamic magnetization processes exhibit universal behavior.",2103.04109v2
2021-03-29,Topological response of the anomalous Hall effect in MnBi2Te4 due to magnetic canting,"Three-dimensional (3D) compensated MnBi2Te4 is antiferromagnetic, but
undergoes a spin-flop transition at intermediate fields, resulting in a canted
phase before saturation. In this work, we experimentally show that the
anomalous Hall effect (AHE) in MnBi2Te4 originates from a topological response
that is sensitive to the perpendicular magnetic moment and to its canting
angle. Synthesis by molecular beam epitaxy allows us to obtain a large-area
quasi-3D 24-layer MnBi2Te4 with near-perfect compensation that hosts the phase
diagram observed in bulk which we utilize to probe the AHE. This AHE is seen to
exhibit an antiferromagnetic response at low magnetic fields, and a clear
evolution at intermediate fields through surface and bulk spin-flop transitions
into saturation. Throughout this evolution, the AHE is super-linear versus
magnetization rather than the expected linear relationship. We reveal that this
discrepancy is related to the canting angle, consistent with the symmetry of
the crystal. Our findings suggests that novel topological responses may be
found in non-collinear ferromagnetic, and antiferromagnetic phases.",2103.15801v3
2021-10-26,Magneto-Thermal Instability In Galaxy Clusters I: Theory and Two-Dimensional Simulations,"Determining the origin of turbulence in galaxy clusters, and quantifying its
transport of heat, is an outstanding problem, with implications for our
understanding of their thermodynamic history and structure. As the dilute
plasma of the intracluster medium (ICM) is magnetized, heat and momentum travel
preferentially along magnetic field lines. This anisotropy triggers a class of
buoyancy instabilities that destabilize the ICM, and whose turbulent motions
can augment or impede heat transport. We focus on the magneto-thermal
instability (MTI), which may be active in the periphery of galaxy clusters. We
aim to take a fresh look at the problem and construct a general theory that
explains the MTI saturation mechanism and provides scalings and estimates for
the turbulent kinetic energy, magnetic energy, and heat flux. We simulate MTI
turbulence with a Boussinesq code, SNOOPY, which, in contrast to previous work,
allows us to perform an extensive sampling of the parameter space. In two
dimensions the saturation mechanism involves an inverse cascade carrying
kinetic energy from the short MTI injection scales to larger scales, where it
is arrested by the stable entropy stratification; at a characteristic ""buoyancy
scale"", the energy is dumped into large-scale g-modes, which subsequently
dissipate. Consequently, the entropy stratification sets an upper limit on the
size and strength of turbulent eddies. Meanwhile, the MTI conveys a substantial
fraction of heat, despite the tangled geometry of the magnetic field. In a
companion paper, these results are extended to three-dimensional flows, and
compared to real cluster observations.",2110.13918v1
2021-11-05,Interlayer exciton valley polarization dynamics in large magnetic fields,"In van der Waals heterostructures (HS) consisting of stacked MoSe$_2$ and
WSe$_2$ monolayers, optically bright interlayer excitons (ILE) can be observed
when the constituent layers are crystallographically aligned. The symmetry of
the monolayers allows for two different types of alignment, in which the
momentum-direct interlayer transitions are either valley-conserving (R-type
alignment) or changing the valley index (H-type anti-alignment). Here, we study
the valley polarization dynamics of ILE in magnetic fields up to 30~Tesla by
time-resolved photoluminescence (PL). For all ILE types, we find a finite
initial PL circular degree of polarization ($DoP$) after unpolarized excitation
in applied magnetic fields. For ILE in H-type HS, we observe a systematic
increase of the PL $DoP$ with time in applied magnetic fields, which saturates
at values close to unity for the largest fields. By contrast, for ILE in R-type
HS, the PL $DoP$ shows a decrease and a zero crossing before saturating with
opposite polarization. This unintuitive behavior can be explained by a model
considering the different ILE states in H- and R-type HS and their selection
rules coupling PL helicity and valley polarization.",2111.03336v1
2022-01-31,Magnetostriction in microwave synthesized La0.5Ba0.5CoO3,"A single-phase polycrystalline La0.5Ba0.5CoO3-d sample was synthesized by
microwave irradiation within 20 minutes of processing time and its structural,
magnetic, electrical, and magnetostrictive properties were investigated. While
the temperature dependence of field-cooled magnetization (M) in a field of H =
0.5 kOe indicates the onset of ferromagnetic transition at TC = 177 K,
irreversibility between the zero field-cooled and field cooled M(T) persists
even at H = 3 kOe. M(H) at 10 K does not saturate at the maximum available
field and has a much smaller value (0.87 {\mu}B/Co in a field of 50 kOe) than
1.9 {\mu}B/Co expected for spin-only contribution from intermediate Co3+ and
Co4+ spins. The resistivity shows insulating behavior down to 10 K and only a
small magnetoresistance (~ 2% for H = 70 kOe) occurs around TC. All these
results suggest a magnetically heterogeneous ground state with weakly
interacting ferromagnetic clusters coexisting with a non-ferromagnetic phase.
The length of the sample expands in the direction of the applied magnetic field
(positive magnetostriction) and does not show saturation even at 50 kOe. The
magnetostriction has a maximum value (= 252 ppm) at 10 K and it decreases with
increasing temperature. The smaller value of magnetostriction compared to the
available data on La0.5Sr0.5CoO3 suggests that non-ferromagnetic matrix is most
likely antiferromagnetic and it restrains the field-induced expansion of
ferromagnetic clusters in the microwave synthesized La0.5Ba0.5CoO3-d sample.",2201.12979v1
2022-03-22,Unconventional spin frustration due to two competing ferromagnetic interactions of a spin-1/2 Ising-Heisenberg model on martini and martini-diced lattice,"The spin-1/2 Ising-Heisenberg model on martini and martini-diced lattice is
exactly solved using a star-triangle transformation, which affords an exact
mapping correspondence to an effective spin-1/2 Ising model on a triangular
lattice. The ground-state phase diagram of both investigated quantum spin
models display two spontaneously ordered ferromagnetic phases and one
macroscopically degenerate disordered phase. In contrast to a classical
ferromagnetic phase where the spontaneous magnetization of the Ising as well as
Heisenberg spins acquire fully saturated values the spontaneous magnetization
of the Heisenberg spins is subject to a quantum reduction to one-third of its
saturated value within a quantum ferromagnetic phase. The spontaneous
magnetization and logarithmic divergence of the specific heat as the most
essential features of both ferromagnetic phases disappear whenever the
investigated quantum spin model is driven to the highly degenerate disordered
phase. The disordered phase with nonzero residual entropy originates either
from a geometric spin frustration caused by antiferromagnetic interactions or
more strikingly it may also alternatively arise from a competition of the
ferromagnetic Ising and Heisenberg interactions of easy-axis and easy-plane
type, respectively. All three available ground states coexist together at a
single triple point, around which anomalous magnetic and thermodynamic behavior
can be detected.",2203.11582v1
2022-05-04,Magnetized oscillatory double-diffusive convection,"We study the properties of oscillatory double-diffusive convection (ODDC) in
the presence of a uniform vertical background magnetic field. ODDC takes place
in stellar regions that are unstable according to the Schwarzschild criterion
and stable according to the Ledoux criterion (sometimes called semiconvective
regions), which are often predicted to reside just outside the core of
intermediate-mass main sequence stars. Previous hydrodynamic studies of ODDC
have shown that the basic instability saturates into a state of weak wave-like
convection, but that a secondary instability can sometimes transform it into a
state of layered convection, where layers then rapidly merge and grow until the
entire region is fully convective. We find that magnetized ODDC has very
similar properties overall, with some important quantitative differences. A
linear stability analysis reveals that the fastest-growing modes are unaffected
by the field, but that other modes are. Numerically, the magnetic field is seen
to influence the saturation of the basic instability, overall reducing the
turbulent fluxes of temperature and composition. This in turn affects layer
formation, usually delaying it, and occasionally suppressing it entirely for
sufficiently strong fields. Further work will be needed, however, to determine
the field strength above which layer formation is actually suppressed in stars.
Potential observational implications are briefly discussed.",2205.02251v2
2022-11-17,Delayed Hopf bifurcation and control of a ferrofluid interface via a time-dependent magnetic field,"A ferrofluid droplet confined in a Hele-Shaw cell can be deformed into a
stably spinning ``gear,'' using crossed magnetic fields. Previously, fully
nonlinear simulation revealed that the spinning gear emerges as a stable
traveling wave along the droplet's interface bifurcates from the trivial
(equilibrium) shape. In this work, a center manifold reduction is applied to
show the geometrical equivalence between a two-harmonic-mode coupled system of
ordinary differential equations arising from a weakly nonlinear analysis of the
interface shape and a Hopf bifurcation. The rotating complex amplitude of the
fundamental mode saturates to a limit circle as the periodic traveling wave
solution is obtained. An amplitude equation is derived from a
multiple-time-scale expansion as a reduced model of the dynamics. Then,
inspired by the well-known delay behavior of time-dependent Hopf bifurcations,
we design a slowly time-varying magnetic field such that the timing and
emergence of the interfacial traveling wave can be controlled. The proposed
theory allows us to determine the time-dependent saturated state resulting from
the dynamic bifurcation and delayed onset of instability. The amplitude
equation also reveals hysteresis-like behavior upon time reversal of the
magnetic field. The state obtained upon time reversal differs from the state
obtained during the initial (forward-time) period, yet it can still be
predicted by the proposed reduced-order theory.",2211.09758v3
2004-06-14,"Nonlinear theory of a ""shear-current"" effect and mean-field magnetic dynamos","The nonlinear theory of a ""shear-current"" effect in a nonrotating and
nonhelical homogeneous turbulence with an imposed mean velocity shear is
developed. The ''shear-current"" effect is associated with the $\bar{\bf W} {\bf
\times} \bar{\bf J}$-term in the mean electromotive force and causes the
generation of the mean magnetic field even in a nonrotating and nonhelical
homogeneous turbulence (where $\bar{\bf W}$ is the mean vorticity and $\bar{\bf
J}$ is the mean electric current). It is found that there is no quenching of
the nonlinear ""shear-current"" effect contrary to the quenching of the nonlinear
$\alpha$-effect, the nonlinear turbulent magnetic diffusion, etc. During the
nonlinear growth of the mean magnetic field, the ''shear-current"" effect only
changes its sign at some value $\bar{\bf B}_\ast$ of the mean magnetic field.
The magnitude $\bar{\bf B}_\ast$ determines the level of the saturated mean
magnetic field which is less than the equipartition field. It is shown that the
background magnetic fluctuations due to the small-scale dynamo enhance the
""shear-current"" effect, and reduce the magnitude $\bar{\bf B}_\ast$. When the
level of the background magnetic fluctuations is larger than 1/3 of the kinetic
energy of the turbulence, the mean magnetic field can be generated due to the
""shear-current"" effect for an arbitrary exponent of the energy spectrum of the
velocity fluctuations.",0406328v2
2002-09-19,"Magnetic Interactions and Transport in (Ga,Cr)As","The magnetic, transport, and structural properties of (Ga,Cr)As are reported.
Zincblende Ga$_{1-x}$Cr$_{x}$As was grown by low-temperature molecular beam
epitaxy (MBE). At low concentrations, x$\sim$0.1, the materials exhibit unusual
magnetic properties associated with the random magnetism of the alloy. At low
temperatures the magnetization M(B) increases rapidly with increasing field due
to the alignment of ferromagnetic units (polarons or clusters) having large
dipole moments of order 10-10$^2$$\mu_B$. A standard model of
superparamagnetism is inadequate for describing both the field and temperature
dependence of the magnetization M(B,T). In order to explain M(B) at low
temperatures we employ a distributed magnetic moment (DMM) model in which
polarons or clusters of ions have a distribution of moments. It is also found
that the magnetic susceptibility increases for decreasing temperature but
saturates below T=4 K. The inverse susceptibility follows a linear-T
Curie-Weiss law and extrapolates to a magnetic transition temperature
$\theta$=10 K. In magnetotransport measurements, a room temperature resistivity
of $\rho$=0.1 $\Omega$cm and a hole concentration of $\sim10^{20}$ cm$^{-3}$
are found, indicating that Cr can also act as a acceptor similar to Mn. The
resistivity increases rapidly for decreasing temperature below room
temperature, and becomes strongly insulating at low temperatures. The
conductivity follows exp[-(T$_1$/T)$^{1/2}$] over a large range of
conductivity, possible evidence of tunneling between polarons or clusters.",0209477v2
2005-11-04,Magnetic Inhomogeneity and Magnetotransport in Electron-Doped Ca(1-x)La(x)MnO(3) (0<=x<=0.10),"The dc magnetization (M) and electrical resistivity (\rho) as functions of
magnetic field and temperature are reported for a series of lightly electron
dopedCa(1-x)La(x)MnO(3) (0<=x<=0.10) specimens for which magnetization [Phys.
Rev. B {\bf 61}, 14319 (2000)] and scattering studies [Phys. Rev. B {\bf 68},
134440 (2003)] indicate an inhomogeneous magnetic ground state composed of
ferromagnetic (FM) droplets embedded in a G-type antiferromagnetic matrix. A
change in the magnetic behavior near x=0.02 has been suggested to be the
signature of a crossover to a long-ranged spin-canted phase. The data reported
here provide further detail about this crossover in the magnetization, and
additional insight into the origin of this phenomenon through its manifestation
in the magnetotransport. In the paramagnetic phase (T>=125 K) we find a
magnetoresistance =-C(M/M_S)^2 (M_S is the low-T saturation magnetization), as
observed in many manganites in the ferromagnetic (FM), colossal
magnetoresistance (CMR) region of the phase diagram, but with a value of C that
is two orders of magnitude smaller than observed for CMR materials. The doping
behavior C(x) follows that of M_S(x), indicating that electronic inhomogeneity
associated with FM fluctuations occurs well above the magnetic ordering
transition.",0511117v1
2007-12-06,Magnetohydrodynamic Simulations of Disk Galaxy Formation: the Magnetization of The Cold and Warm Medium,"Using magnetohydrodynamic (MHD) adaptive mesh refinement simulations, we
study the formation and early evolution of disk galaxies with a magnetized
interstellar medium. For a $10^{10}$ \msun halo with initial NFW dark matter
and gas profiles, we impose a uniform $10^{-9}$ G magnetic field and follow its
collapse, disk formation and evolution up to 1 Gyr. Comparing to a purely
hydrodynamic simulation with the same initial condition, we find that a
protogalactic field of this strength does not significantly influence the
global disk properties. At the same time, the initial magnetic fields are
quickly amplified by the differentially rotating turbulent disk. After the
initial rapid amplification lasting $\sim500$ Myr, subsequent field
amplification appears self-regulated. As a result, highly magnetized material
begin to form above and below the disk. Interestingly, the field strengths in
the self-regulated regime agrees well with the observed fields in the Milky Way
galaxy both in the warm and the cold HI phase and do not change appreciably
with time. Most of the cold phase shows a dispersion of order ten in the
magnetic field strength. The global azimuthal magnetic fields reverse at
different radii and the amplitude declines as a function of radius of the disk.
By comparing the estimated star formation rate (SFR) in hydrodynamic and MHD
simulations, we find that after the magnetic field strength saturates, magnetic
forces provide further support in the cold gas and lead to a decline of the
SFR.",0712.0872v1
2008-09-25,"Experimental magnetic form factors in Co3V2O8: A combined study of ab initio calculations, magnetic Compton scattering and polarized neutron diffraction","We present a combination of ab initio calculations, magnetic Compton
scattering and polarized neutron experiments, which elucidate the density
distribution of unpaired electrons in the kagome staircase system Co3V2O8. Ab
initio wave functions were used to calculate the spin densities in real and
momentum space, which show good agreement with the respective experiments. It
has been found that the spin polarized orbitals are equally distributed between
the t2g and the eg levels for the spine (s) Co ions, while the eg orbitals of
the cross-tie (c) Co ions only represent 30% of the atomic spin density.
Furthermore, the results reveal that the magnetic moments of the cross-tie Co
ions, which are significantly smaller than those of the spine Co ions in the
zero-field ferromagnetic structure, do not saturate by applying an external
magnetic field of 2 T along the easy axis a, but that the increasing bulk
magnetization originates from induced magnetic moments on the O and V sites.
The refined individual magnetic moments are mu(Co_c)=1.54(4) mu_B,
mu(Co_s)=2.87(3) mu_B, mu(V)=0.41(4) mu_B, mu(O1)=0.05(5) mu_B, mu(O2)=0.35(5)
mu_B, and; mu(O3)=0.36(5) mu_B combining to the same macroscopic magnetization
value, which was previously only attributed to the Co ions.",0809.4404v2
2009-06-17,Interplay of frustration and magnetic field in the two-dimensional quantum antiferromagnet Cu(tn)Cl$_2$,"Specific heat and ac magnetic susceptibility measurements, spanning low
temperatures ($T \geq 40$ mK) and high magnetic fields ($B \leq 14$ T), have
been performed on a two-dimensional (2D) antiferromagnet Cu(tn)Cl$_{2}$ (tn =
C$_{3}$H$_{10}$N$_{2}$). The compound represents an $S = 1/2$ spatially
anisotropic triangular magnet realized by a square lattice with
nearest-neighbor ($J/k_{B} = 3$ K), frustrating next-nearest-neighbor ($0 <
J^{\prime}/J < 0.6$), and interlayer ($|J^{\prime \prime}/J| \approx 10^{-3}$)
interactions. The absence of long-range magnetic order down to $T = $ 60 mK in
$B = 0$ and the $T^{2}$ behavior of the specific heat for $T \leq 0.4$ K and $B
\geq 0$ are considered evidence of high degree of 2D magnetic order. In fields
lower than the saturation field, $B_{\text{sat}} = 6.6$ T, a specific heat
anomaly, appearing near 0.8 K, is ascribed to bound vortex-antivortex pairs
stabilized by the applied magnetic field. The resulting magnetic phase diagram
is remarkably consistent with the one predicted for the ideal square lattice,
except that $B_{\text{sat}}$ is shifted to values lower than expected.
Potential explanations for this observation, as well as the possibility of a
Berezinski-Kosterlitz-Thouless (BKT) phase transition in a spatially
anisotropic triangular magnet with the N\'{e}el ground state, are discussed.",0906.3181v1
2009-12-01,Aperiodic magnetic turbulence produced by relativistic ion beams,"Magnetic-field generation by a relativistic ion beam propagating through an
electron-ion plasma along a homogeneous magnetic field is investigated with
2.5D high-resolution particle-in-cell (PIC) simulations. The studies test
predictions of a strong amplification of short-wavelength modes of magnetic
turbulence upstream of nonrelativistic and relativistic parallel shocks
associated with supernova remnants, jets of active galactic nuclei, and
gamma-ray bursts. We find good agreement in the properties of the turbulence
observed in our simulations compared with the dispersion relation calculated
for linear waves with arbitrary orientation of ${\vec k}$. Depending on the
parameters, the backreaction on the ion beam leads to filamentation of the
ambient plasma and the beam, which in turn influences the properties of the
magnetic turbulence. For mildly- and ultra-relativistic beams, the instability
saturates at field amplitudes a few times larger than the homogeneous magnetic
field strength. This result matches our recent studies of nonrelativistically
drifting, hot cosmic-ray particles upstream of supernova-remnant shocks which
indicated only a moderate magnetic-field amplification by nonresonant
instabilities. We also demonstrate that the aperiodic turbulence generated by
the beam can provide efficient particle scattering with a rate compatible with
Bohm diffusion. Representing the ion beam as a constant external current, i.e.
excluding a backreaction of the magnetic turbulence on the beam, we observe
non-resonant parallel modes with wavelength and growth rate as predicted by
analytic calculations. In this unrealistic setup the magnetic field is
amplified to amplitudes far exceeding the homogeneous field, as observed in
recent MHD and PIC simulations.",0912.0101v1
2010-04-26,Magnetic helicity fluxes in an alpha-squared dynamo embedded in a halo,"We present the results of simulations of forced turbulence in a slab where
the mean kinetic helicity has a maximum near the mid-plane, generating
gradients of magnetic helicity of both large and small-scale fields. We also
study systems that have poorly conducting buffer zones away from the midplane
in order to assess the effects of boundaries. The dynamical alpha quenching
phenomenology requires that the magnetic helicity in the small-scale fields
approaches a nearly static, gauge independent state. To stress-test this steady
state condition we choose a system with a uniform sign of kinetic helicity, so
that the total magnetic helicity can reach a steady state value only through
fluxes through the boundary, which are themselves suppressed by the velocity
boundary conditions. Even with such a set up, the small-scale magnetic helicity
is found to reach a steady state. In agreement with earlier work, the magnetic
helicity fluxes of small-scale fields are found to be turbulently diffusive. By
comparing results with and without halos, we show that artificial constraints
on magnetic helicity at the boundary do not have a significant impact on the
evolution of the magnetic helicity, except that ""softer"" (halo) boundary
conditions give a lower energy of the saturated mean magnetic field.",1004.4591v1
2011-04-13,The spin-half Heisenberg antiferromagnet on two Archimedian lattices: From the bounce lattice to the maple-leaf lattice and beyond,"We investigate the ground state of the two-dimensional Heisenberg
antiferromagnet on two Archimedean lattices, namely, the maple-leaf and bounce
lattices as well as a generalized $J$-$J'$ model interpolating between both
systems by varying $J'/J$ from $J'/J=0$ (bounce limit) to $J'/J=1$ (maple-leaf
limit) and beyond. We use the coupled cluster method to high orders of
approximation and also exact diagonalization of finite-sized lattices to
discuss the ground-state magnetic long-range order based on data for the
ground-state energy, the magnetic order parameter, the spin-spin correlation
functions as well as the pitch angle between neighboring spins. Our results
indicate that the ""pure"" bounce ($J'/J=0$) and maple-leaf ($J'/J=1$) Heisenberg
antiferromagnets are magnetically ordered, however, with a sublattice
magnetization drastically reduced by frustration and quantum fluctuations. We
found that magnetic long-range order is present in a wide parameter range $0
\le J'/J \lesssim J'_c/J $ and that the magnetic order parameter varies only
weakly with $J'/J$. At $J'_c \approx 1.45 J$ a direct first-order transition to
a quantum orthogonal-dimer singlet ground state without magnetic long-range
order takes place. The orthogonal-dimer state is the exact ground state in this
large-$J'$ regime, and so our model has similarities to the Shastry-Sutherland
model. Finally, we use the exact diagonalization to investigate the
magnetization curve. We a find a 1/3 magnetization plateau for $J'/J \gtrsim
1.07$ and another one at 2/3 of saturation emerging only at large $J'/J \gtrsim
3$.",1104.2572v1
2012-12-06,Simulations of magnetic fields in isolated disk galaxies,"Magnetic fields are known to be dynamically important in the interstellar
medium of our own Galaxy, and they are ubiquitously observed in diffuse gas in
the halos of galaxies and galaxy clusters. Yet, magnetic fields have typically
been neglected in studies of the formation of galaxies, leaving their global
influence on galaxy formation largely unclear. We extend our MHD implementation
in the moving-mesh code Arepo to cosmological problems which include radiative
cooling and the formation of stars. In particular, we replace our previously
employed divergence cleaning approach with a Powell 8-wave scheme, which turns
out to be significantly more stable, even in very dynamic environments. We
verify the improved accuracy through simulations of the MRI in accretion disks,
that reproduce its correct linear growth rate. Using this new MHD code, we
simulate the formation of isolated disk galaxies similar to the Milky Way using
idealized initial conditions with and without magnetic fields. We find that the
magnetic field is quickly amplified in the initial starburst and the
differential rotation of the forming disk until it eventually saturates when it
becomes comparable to the thermal pressure. The additional pressure component
leads to a lower star formation rate at late times compared to simulations
without magnetic fields, and induces changes in the spiral arm structures of
the gas disk. In addition, we observe highly magnetized fountain-like outflows
from the disk. These results are robust with numerical resolution and are
largely independent of the initial magnetic seed field assumed in the initial
conditions, as the amplification process is rapid and self-regulated. Our
findings suggest an important influence of magnetic fields on galaxy formation
and evolution, cautioning against their neglect in theoretical models of
structure formation.",1212.1452v1
2014-01-10,Investigation of the strongly correlated one-dimensional magnetic behavior of NiTa2O6,"The magnetic properties of NiTa$_2$O$_6$ were investigated by magnetic
susceptibility, specific heat, electron paramagnetic resonance, neutron powder
diffraction and pulse field magnetization measurements. Accompanying \textit{ab
initio} DFT calculations of the spin-exchange constants complemented and
supported our experimental findings that NiTa$_2$O$_6$ must be described as a
quasi-1D Heisenberg $S$ = 1 spin chain system with a nearest-neighbor only
anti-ferromagnetic spin-exchange interaction of 18.92(2) K. Inter-chain
coupling is by about two orders of magnitude smaller. Electron paramagnetic
resonance measurements on Mg$_{1-x}$Ni$_x$Ta$_2$O$_6$ ($x \approx$ $1\%$)
polycrystalline samples enabled us to estimate the single-ion zero-field
splitting of the $S$ = 1 states which amounts to less than $4\%$ of the
nearest-neighbor spin-exchange interaction. At 0 T NiTa$_2$O$_6$ undergoes
long-range anti-ferromagnetic ordering at 10.3(1) K evidenced by a
$\lambda$-type anomaly in the specific heat capacity. On application of a
magnetic field the specific heat anomaly is smeared out. We confirmed the
magnetic structure by neutron powder diffraction measurements and at 2.00(1) K
refined a magnetic moment of 1.93(5) $\mu_{\rm{B}}$ per Ni$^{2+}$ ion.
Additionally, we followed the magnetic order parameter as a function of
temperature. Lastly we found saturation of the magnetic moment at 55.5(5) T
with a $g$-factor of 2.14(1), with an additional high field phase above 12.8(1)
T. The onset of the new high field phase is not greatly effected by
temperature, but rather smears out as one approaches the long-range ordering
temperature.",1401.2401v1
2015-02-11,Anisotropic defect-induced ferromagnetism and transport in Gd-doped GaN two-dimensional electron gasses,"Here we report on the effect of rare earth Gd-doping on the magnetic
properties and magnetotransport of GaN two-dimensional electron gasses (2DEGs).
Samples are grown by plasma-assisted molecular beam epitaxy and consist of
AlN/GaN heterostructures where Gd is delta-doped within a polarization-induced
2DEG. Ferromagnetism is observed in these Gd-doped 2DEGs with a Curie
temperature above room temperature and an anisotropic spontaneous magnetization
preferring an out-of-plane (c-axis) orientation. At magnetic fields up to 50
kOe, the magnetization remains smaller for in-plane configuration than for
out-of-plane, which is indicative of exchange coupled spins locked along the
polar c-axis. The sample with the lowest Gd concentration (2.3 $\times$
$10^{14}$ cm$^{-2}$) exhibits a saturation magnetization of 41.1
$\mu_B/Gd^{3+}$ at 5 K revealing that the Gd ion spins (7 ${\mu}_B$) alone do
not account for the magnetization. Surprisingly, control samples grown without
any Gd display inconsistent magnetic properties; in some control samples weak
ferromagnetism is observed and in others paramagnetism. The ferromagnetic 2DEGs
do not exhibit the anomalous Hall effect; the Hall resistance varies
non-linearly with the magnetic field, but does not track the magnetization
indicating the lack of coupling between the ferromagnetic phase and the
conduction band electrons within the 2DEG.",1502.03478v2
2015-10-05,Absence of magnetic proximity effects in magnetoresistive Pt/CoFe2O4 hybrid interfaces,"Ultra-thin Pt films grown on insulating ferrimagnetic CoFe2O4 (111) epitaxial
films display a magnetoresistance upon rotating the magnetization of the
magnetic layer. We report here X-ray magnetic circular dichroism (XMCD)
recorded at Pt-L2,3 and Pt-M3 edges. The results indicate that the Pt magnetic
moment, if any, is below the detection limit (< 0.001 {\mu}$_B$/Pt), thus
strongly favoring the view that the presence of CoFe2O4 does not induce the
formation of magnetic moments in Pt. Therefore, the observed magnetoresistance
cannot be attributed to some sort of proximity-induced magnetic moments at Pt
ions and subsequent magnetic-field dependent scattering. It thus follows that
either bulk (spin Hall and Inverse spin Hall Effects) or interface (Rashba)
spin-orbit related effects dominate the observed magnetoresistance.
Furthermore, comparison of bulk magnetization and XMCD data at (Fe,Co)-L2,3
edges suggests the presence of some spin disorder in the CoFe2O4 layer which
may be relevant for the observed anomalous non-saturating field-dependence of
spin Hall magnetoresistance.",1510.01080v4
2015-12-14,The magnetic shear-current effect: generation of large-scale magnetic fields by the small-scale dynamo,"A novel large-scale dynamo mechanism, the magnetic shear-current effect, is
discussed and explored. The effect relies on the interaction of magnetic
fluctuations with a mean shear flow, meaning the saturated state of the
small-scale dynamo can drive a large-scale dynamo -- in some sense the inverse
of dynamo quenching. The dynamo is nonhelical, with the mean-field $\alpha$
coefficient zero, and is caused by the interaction between an off-diagonal
component of the turbulent resistivity and the stretching of the large-scale
field by shear flow. Following up on previous numerical and analytic work, this
paper presents further details of the numerical evidence for the effect, as
well as an heuristic description of how magnetic fluctuations can interact with
shear flow to produce the required electromotive force. The pressure response
of the fluid is fundamental to this mechanism, which helps explain why the
magnetic effect is stronger than its kinematic cousin, and the basic idea is
related to the well-known lack of turbulent resistivity quenching by magnetic
fluctuations. As well as being interesting for its applications to general high
Reynolds number astrophysical turbulence, where strong small-scale magnetic
fluctuations are expected to be prevalent, the magnetic shear-current effect is
a likely candidate for large-scale dynamo in the unstratified regions of
ionized accretion disks. Evidence for this is discussed, as well as future
research directions and the challenges involved with understanding details of
the effect in astrophysically relevant regimes.",1512.04511v2
2016-12-17,Magnetic resonance study of bulk and thin film EuTiO3,"Magnetic resonance spectra of EuTiO3 in both bulk and thin film form were
taken at temperatures from 3-350 K and microwave frequencies from 9.2-9.8 and
34 GHz. In the paramagnetic phase, magnetic resonance spectra are determined by
magnetic dipole and exchange interactions between Eu2+ spins. In the film, a
large contribution arises from the demagnetization field. From detailed
analysis of the linewidth and its temperature dependence, the parameters of
spin-spin interactions were determined: the exchange frequency is 15-15.5 GHz
and the estimated critical exponent of the spin correlation length is ~ 0.5. In
the bulk samples, the spectra exhibited a distinct minimum in the linewidth at
the N\'eel temperature, T_N = 5.5 K, while the resonance field practically does
not change even on cooling below T_N. This is indicative of a small magnetic
anisotropy ~ 320 G in the antiferromagnetic phase. In the film, the magnetic
resonance spectrum is split below T_N into several components due to excitation
of the magnetostatic modes, corresponding to a non-uniform precession of
magnetization. Moreover, the film was observed to degrade over two years. This
was manifested by an increase of defects and a change in the domain structure.
The saturated magnetization in the film, estimated from the magnetic resonance
spectrum, was about 900 emu/cm3 or 5.5 mu_B/unit cell at T = 3.5 K.",1612.05781v1
2017-03-24,Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal YbFeO3,"The magnetic interaction between rare-earth and Fe ions in hexagonal
rare-earth ferrites (h-REFeO3), may amplify the weak ferromagnetic moment on
Fe, making these materials more appealing as multiferroics. To elucidate the
interaction strength between the rare-earth and Fe ions as well as the magnetic
moment of the rare-earth ions, element specific magnetic characterization is
needed. Using X-ray magnetic circular dichroism, we have studied the
ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb
separately. The results directly show anti-alignment of magnetization of Yb and
Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about
17 kOe. The magnetic moment of Yb is about 1.6 \muB at low-temperature,
significantly reduced compared with the 4.5 \muB moment of a free Yb3+. In
addition, the saturation magnetization of Fe in h-YbFeO3 has a sizable
enhancement compared with that in h-LuFeO3. These findings directly demonstrate
that ferrimagnetic order exists in h-YbFeO3; they also account for the
enhancement of magnetization and the reduction of coercivity in h-YbFeO3
compared with those in h-LuFeO3 at low temperature, suggesting an important
role for the rare-earth ions in tuning the multiferroic properties of h-REFeO3.",1703.08482v2
2017-06-09,Negative spin Hall magnetoresistance of Pt on the bulk easy-plane antiferromagnet NiO,"We report on spin Hall magnetoresistance (SMR) measurements of Pt Hall bars
on the antiferromagnetic NiO(111) single crystal. An SMR with a sign opposite
of conventional SMR is observed over a wide range of temperatures as well as
magnetic fields stronger than 0.25T. The negative sign of the SMR can be
explained by the alignment of magnetic moments being almost perpendicular to
the external magnetic field within the easy plane (111) of the antiferromagnet.
This correlation of magnetic moment alignment and external magnetic field
direction is realized just by the easy-plane nature of the material without the
need of any exchange coupling to an additional ferromagnet. The SMR signal
strength decreases with increasing temperature, primarily due to the decrease
in N\'eel order by including fluctuations. An increasing magnetic field
increases the SMR signal strength as there are less domains and the magnetic
moments are more strongly manipulated at high magnetic fields. The SMR is
saturated at an applied magnetic field of $6$~T resulting in a spin-mixing
conductance of $\sim10^{18}~ \Omega^{-1}$m$^{-2}$, which is comparable to that
of Pt on insulating ferrimagnets such as yttrium iron garnet. An argon plasma
treatment doubles the spin-mixing conductance.",1706.03004v1
2018-10-07,Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet $α$-Li$_2$IrO$_3$,"The layered honeycomb iridate $\alpha$-Li$_2$IrO$_3$ displays an
incommensurate magnetic structure with counterrotating moments on
nearest-neighbor sites, proposed to be stabilized by strongly-frustrated
anisotropic Kitaev interactions between spin-orbit entangled Ir$^{4+}$ magnetic
moments. Here we report powder inelastic neutron scattering measurements that
observe sharply dispersive low-energy magnetic excitations centered at the
magnetic ordering wavevector, attributed to Goldstone excitations of the
incommensurate order, as well as an additional intense mode above a gap
$\Delta\simeq2.3$ meV. Zero-field muon-spin relaxation measurements show clear
oscillations in the muon polarization below the N\'{e}el temperature $T_{\rm
N}\simeq15$ K with a time-dependent profile consistent with bulk incommensurate
long-range magnetism. Pulsed field magnetization measurements observe that only
about half the saturation magnetization value is reached at the maximum field
of 64 T. A clear anomaly near 25 T indicates a transition to a phase with
reduced susceptibility. The transition field has a Zeeman energy comparable to
the zero-field gapped mode, suggesting gap suppression as a possible mechanism
for the field-induced transition.",1810.03212v1
2019-02-14,Calculating temperature-dependent properties of Nd$_2$Fe$_{14}$B permanent magnets by atomistic spin model simulations,"Temperature-dependent magnetic properties of Nd$_2$Fe$_{14}$B permanent
magnets, i.e., saturation magnetization $M_\text{s}(T)$, effective magnetic
anisotropy constants $K_i^\text{eff}(T)$ ($i=1,2,3$), domain wall width
$\delta_w(T)$, and exchange stiffness constant $A_\text{e}(T)$, are calculated
by using \textit{ab-initio} informed atomistic spin model simulations. We
construct the atomistic spin model Hamiltonian for Nd$_2$Fe$_{14}$B by using
the Heisenberg exchange of Fe$-$Fe and Fe$-$Nd atomic pairs, the uniaxial
single-ion anisotropy of Fe atoms, and the crystal-field energy of Nd ions
which is approximately expanded into an energy formula featured by second,
fourth, and sixth-order phenomenological anisotropy constants. After applying a
temperature rescaling strategy, we show that the calculated Curie temperature,
spin-reorientation phenomenon, $M_\text{s}(T)$, $\delta_w(T)$, and
$K_i^\text{eff}(T)$ agree well with the experimental results. $A_\text{e}(T)$
is estimated through a general continuum description of the domain wall profile
by mapping atomistic magnetic moments to the macroscopic magnetization.
$A_\text{e}$ is found to decrease more slowly than $K_1^\text{eff}$ with
increasing temperature, and approximately scale with normalized magnetization
as $A_\text{e}(T) \sim m^{1.2}$. This work provokes a scale bridge between
\textit{ab-initio} calculations and temperature-dependent micromagnetic
simulations of Nd-Fe-B permanent magnets.",1902.05636v2
2019-04-08,Magnetism study on a triangular lattice antiferromagnet Cu$_2$(OH)$_3$Br,"Magnetism of Cu$_2$(OH)$_3$Br single crystals based on a triangular lattice
is studied by means of magnetic susceptibility, pulsed-field magnetization, and
specific heat measurements. There are two inequivalent Cu$^{2+}$ sites in an
asymmetric unit. Both Cu$^{2+}$ sublattices undergo a long-range
antiferromagnetic (AFM) order at $T\rm_N$ = 9.3 K. Upon cooling, an anisotropy
crossover from Heisenberg to $XY$ behavior is observed below 7.5 K from the
anisotropic magnetic susceptibility. The magnetic field applied within the $XY$
plane induces a spin-flop transition of Cu$^{2+}$ ions between 4.9 T and 5.3 T.
With further increasing fields, the magnetic moment is gradually increased but
is only about half of the saturation of a Cu$^{2+}$ ion even in 30 T. The
individual reorientation of the inequivalent Cu$^{2+}$ spins under field is
proposed to account for the magnetization behavior. The observed spin-flop
transition is likely related to one Cu site, and the AFM coupling among the
rest Cu spins is so strong that the 30-T field cannot overcome the anisotropy.
The temperature dependence of the magnetic specific heat, which is well
described by a sum of two gapped AFM contributions, is a further support for
the proposed scenario.",1904.03798v1
2019-05-09,Domain wall pinning and hard magnetic phase in Co-doped bulk single crystalline Fe3GeTe2,"We report the effects of cobalt doping on the magnetic properties of
two-dimensional van der Waals ferromagnet Fe3GeTe2. Single crystals of
(Fe{1-x}Cox)3GeTe2 with x=0-0.78 were successfully synthesized and
characterized with x-ray diffraction, energy dispersive x-ray spectroscopy and
magnetization measurements. Both the Curie-Weiss temperature and ferromagnetic
(FM) ordered moment of Fe3GeTe2 are gradually suppressed upon Co doping. A kink
in zero-field-cooling low field M(T) curve which is previously explained as an
antiferromagnetic transition is observed for samples with x=0-0.58. Our
detailed magnetization measurements and theoretical calculations strongly
suggest that this kink is originated from the pinning of magnetic domain walls.
The domain pinning effects are suddenly enhanced when the doping concentration
of cobalt is around 50%, both the coercive field Hc and the magnetic remanence
to saturated magnetization ratio MR/MS are largely improved and a hard magnetic
phase emerges in bulk single crystal samples. The strong doping dependent
magnetic properties suggest more spintronic applications of Fe3GeTe2.",1905.03458v1
2019-11-27,Field-induced magnetic transition and spin fluctuation in quantum spin liquid candidate CsYbSe$_2$,"Two-dimensional triangular-lattice materials with spin-1/2 are perfect
platforms for investigating quantum frustrated physics with spin fluctuations.
Here we report the structure, magnetization, heat capacity and inelastic
neutron scattering (INS) results on cesium ytterbium diselenide, CsYbSe$_2$.
There is no long-range magnetic order down to 0.4 K at zero field. The
temperature dependent magnetization, $M(T)$, reveals an easy-plane magnetic
anisotropy. A maximum is found in $M(T)$ around \emph{T}$\sim$1.5 K when
magnetic field $H$ is applied in the $ab$ plane, indicating the short-range
interaction. The low-temperature isothermal magnetization $M(H)$ shows a
one-third plateau of the estimated saturation moment, that is characteristic of
a two-dimensional frustrated triangular lattice. Heat capacity shows
field-induced long-range magnetic order for both $H||c$ and $H||ab$ directions.
The broad peak in heat capacity and highly damped INS magnetic excitation at
$T$=2 K suggests strong spin fluctuations. The dispersive in-plane INS,
centered at the (1/3 1/3 0) point, and the absence of dispersion along $c$
direction suggests 120$^{\circ}$ non-collinear 2D-like spin correlations. All
these results indicate that the two-dimensional frustrated material CsYbSe$_2$
can be in proximity to the triangular-lattice quantum spin liquid. We propose
an experimental low-temperature $H$-$T$ phase diagram for CsYbSe$_2$.",1911.12286v1
2020-05-01,Tunable Ferromagnetism and Thermally Induced Spin Flip in Vanadium-doped Tungsten Diselenide Monolayers at Room Temperature,"The outstanding optoelectronic and valleytronic properties of transition
metal dichalcogenides (TMDs) have triggered intense research efforts by the
scientific community. An alternative to induce long-range ferromagnetism (FM)
in TMDs is by introducing magnetic dopants to form a dilute magnetic
semiconductor. Enhancing ferromagnetism in these semiconductors not only
represents a key step towards modern TMD-based spintronics, but also enables
exploration of new and exciting dimensionality-driven magnetic phenomena. To
this end, we show tunable ferromagnetism at room temperature and a thermally
induced spin flip (TISF) in monolayers of V-doped WSe2. As vanadium
concentrations increase within the WSe2 monolayers the saturation magnetization
increases, and it is optimal at ~4at.% vanadium; the highest doping/alloying
level ever achieved for V-doped WSe2 monolayers. The TISF occurs at ~175 K and
becomes more pronounced upon increasing the temperature towards room
temperature. We demonstrate that TISF can be manipulated by changing the
vanadium concentration within the WSe2 monolayers. We attribute TISF to the
magnetic field and temperature dependent flipping of the nearest W-site
magnetic moments that are antiferromagnetically coupled to the V magnetic
moments in the ground state. This is fully supported by a recent spin-polarized
density functional theory calculation. Our findings pave the way for the
development of novel spintronic and valleytronic nanodevices based on
atomically thin magnetic semiconductors and stimulate further studies in this
rapidly expanding research field of 2D magnetism.",2005.00493v1
2020-10-07,Correlation of uniaxial magnetic anisotropy axes and principal resistivities in polycrystalline ferromagnetic films,"In the present study, we demonstrate the measurement of resistivity tensor
($\rho$) along the magnetic axes of a polycrystalline film of ferromagnetic
permalloy (Py). To this end, conventional Hall-bar and a more recent extended
van der Pauw methods were utilized for determining 2D $\rho$ in the film plane.
The samples were prepared by normal incidence sputter deposition within an
in-situ magnetic field to induce in-plane uniaxial magnetic anisotropy in the
film. Since $\rho$ might be affected by the internal magnetization of the film,
we performed measurements by rotation of a saturating magnetic field in the
film plane. Both methods indicate that the average resistivity is lower along
the easy axis of the film compared to the hard axis. Since X-ray diffraction
results indicated no dominating texture in the film, we concluded that there is
a correlation between uniaxial magnetic axes and principal resistivity axes.
This is an important finding that allows determining the direction of magnetic
anisotropy axes without magnetometry. The results also verify atomic or pair
ordering to be the origin of uniaxial magnetic anisotropy in the Py since
resistivity is sensitive to the level of order in solids. The extended van der
Pauw utilized here can be easily performed on the as-received samples which is
of practical interest.",2010.03554v3
2020-12-31,Neutron diffraction study of magnetism in van der Waals layered MnBi$_{2n}$Te$_{3n+1}$,"Two-dimensional van der Waals MnBi$_{2n}$Te$_{3n+1}$ (n = 1, 2, 3, 4)
compounds have been recently found to be intrinsic magnetic topological
insulators rendering quantum anomalous Hall effect and diverse topological
states. Here, we summarize and compare the crystal and magnetic structures of
this family, and discuss the effects of chemical composition on their
magnetism. We found that a considerable fraction of Bi occupies at the Mn sites
in MnBi$_{2n}$Te$_{3n+1}$ (n = 1, 2, 3, 4) while Mn is no detectable at the
non-magnetic atomic sites within the resolution of neutron diffraction
experiments. The occupancy of Mn monotonically decreases with the increase of
n. The polarized neutron diffraction on the representative MnBi$_{4}$Te$_{7}$
reveals that its magnetization density is exclusively accumulated at the Mn
site, in good agreement with the results from the unpolarized neutron
diffraction. The defects of Bi at the Mn site naturally explain the
continuously reduced saturated magnetic moments from n = 1 to n = 4. The
experimentally estimated critical exponents of all the compounds generally
suggest a three-dimensional character of magnetism. Our work provides
material-specified structural parameters that may be useful for band structure
calculations to understand the observed topological surface states and for
designing quantum magnetic materials through chemical doping.",2012.15415v2
2021-02-22,"Structural, magnetic, and magnetocaloric properties of Fe2CoAl Heusler nanoalloy","Spherical nanoparticles (NPs) of size 14 nm, made of intermetallic Fe2CoAl
(FCA) Heusler alloy, are synthesized via the co-precipitation and thermal
deoxidization method. X-ray diffraction (XRD) and selected area electron
diffraction (SAED) patterns confirm that the present nanoalloy is crystallized
in A2-disordered cubic Heusler structure. Magnetic field (H) and temperature
(T) dependent magnetization (M) results reveal that the NPs are soft
ferromagnetic (FM) with high saturation magnetization (Ms) and Curie
temperature (Tc). Fe2CoAl nanoalloy does not follow the Slater Pauling (SP)
rule, possibly because of the disorder present in the system. We also
investigate its magnetic phase transition (MPT) and magnetocaloric (MC)
properties. The peak value of the magnetic entropy change vs T curve at a
magnetic field change of 20 kOe corresponds to about 2.65 J/kg-K, and the
observed value of refrigeration capacity (RCP) is as large as 44 J/kg,
suggesting a large heat conversion in magnetic refrigeration cycle. The Arrott
plot and the nature of the universal curve accomplish that the FM to
paramagnetic (PM) phase transition in Fe2CoAl nanoalloy is of second-order. The
present study suggests that the Fe2CoAl nanoscale system is proficient, useful
and a good candidate for the spintronics application and opens up a window for
further research on full-Heusler based magnetic refrigerants.",2102.11195v2
2021-04-14,"On the complexity of spinels: Magnetic, electronic, and polar ground states","This review summarizes more than 100 years of research on spinel compounds,
mainly focusing on the progress in understanding their magnetic, electronic,
and polar properties during the last two decades. Many spinel compounds are
magnetic insulators or semiconductors; however, a number of spinel-type metals
exists including superconductors and some rare examples of d-derived
heavy-fermion compounds. In the early days, they gained importance as
ferrimagnetic or even ferromagnetic insulators with relatively high saturation
magnetization and high ordering temperatures, with magnetite being the first
magnetic mineral known to mankind. However, spinels played an outstanding role
in the development of concepts of magnetism, in testing and verifying the
fundamentals of magnetic exchange, in understanding orbital-ordering and
charge-ordering phenomena. In addition, the A- site as well as the B-site
cations in the spinel structure form lattices prone to strong frustration
effects resulting in exotic ground-state properties. In case the A-site cation
is Jahn-Teller active, additional entanglements of spin and orbital degrees of
freedom appear, which can give rise to a spin-orbital liquid or an orbital
glass state. The B-site cations form a pyrochlore lattice, one of the strongest
contenders of frustration in three dimensions. In addition, in spinels with
both cation lattices carrying magnetic moments, competing magnetic exchange
interactions become important, yielding ground states like the time-honoured
triangular Yafet-Kittel structure. Finally, yet importantly, there exists a
long-standing dispute about the possibility of a polar ground state in spinels,
despite their reported overall cubic symmetry. Indeed, over the years number of
multiferroic spinels were identified.",2104.06889v1
2021-05-29,Magnetic Field and Frequency Dependent AC Susceptibility of High-Tc YBCO Single Crystal,"The temperature dependence of AC susceptibility (ACS) has been measured for a
very high-quality plate-like slightly overdoped YBCO single crystal for
different frequencies and AC magnetic field amplitudes. Frequency dependence of
the ACS is weak irrespective of the magnetic field orientation but significant
effects of field orientation with respect to the CuO2 planes and field
magnitude on real and imaginary components of fundamental ACS were observed.
The height of the loss peak saturates as full penetration of magnetic field is
achieved. The peak temperature, Tp, in \c{hi}"" shifts to lower temperatures
with increasing magnetic field amplitude for both HIIc and HIIab. The value of
Tp depends on the orientation of the magnetic field with respect to the
crystallographic axes, illustrating the anisotropy in the magnetic flux
dynamics. The superconducting transition width increases weakly with increasing
magnetic field. The Cole-Cole plot [\c{hi}""(\c{hi}')] shows qualitatively and
quantitatively identical features for HIIc and HIIab, independent of the
orientation of the magnetic field with respect to the sample geometry and
shielding current paths. The general features of \c{hi}""(\c{hi}') implies that,
there is no flux creep for the range of frequencies and AC fields employed in
this investigation. The maximum value of the loss peak and its position with
respect to \c{hi}' in the Cole-Cole plot are largely consistent with the Bean
critical state model. Slightly increased peak value in comparison to the
predicted peak value within the Bean critical state model is probably due to a
weak field dependence of Jc. The results obtained here are compared with
various theoretical models and experimental findings. Prominent differences are
noted and discussed in details in this study.",2105.14321v1
2021-06-27,Relaxation in Ordered Assembly of Magnetic Nanoparticles,"We study the relaxation characteristics in the two-dimensional ($l^{}_x
\times l^{}_y$) array of magnetic nanoparticles (MNPs) as a function of aspect
ratio $A^{}_r=l^{}_y/l^{}_x$, dipolar interaction strength $h^{}_d$ and
anisotropy axis orientation using computer simulation. The anisotropy axes of
all the MNPs are assumed to have the same direction, $\alpha$ being the
orientational angle. Irrespective of $\alpha$ and $A^{}_r$, the functional form
of the magnetization-decay curve is perfectly exponentially decaying with
$h^{}_d\leq0.2$. There exists a transition in relaxation behaviour at
$h^{}_d\approx0.4$; magnetization relaxes slowly for $\alpha\leq45^\circ$; it
relaxes rapildy with $\alpha>45^\circ$. Interestingly, it decays rapidly for
$h^{}_d>0.6$, irrespective of $\alpha$. It is because the dipolar interaction
promotes antiferromagnetic coupling in such cases. There is a strong effect of
$\alpha$ on the magnetic relaxation in the highly anisotropic system
($A^{}_r\geq25$). Interesting physics unfolds in the case of a huge aspect
ratio $A^{}_r=400$. There is a rapid decay of magnetization with $\alpha$, even
for weakly interacting MNPs. Remarkably, magnetization does not relax even with
a moderate value of $h^{}_d=0.4$ and $\alpha=0^\circ$ because of ferromagnetic
coupling dominance. Surprisingly, there is a complete magnetization reversal
from saturation (+1) to $-1$ state with $\alpha>60^\circ$. The dipolar field
and anisotropy axis tend to get aligned antiparallel to each other in such a
case. The effective N\'eel relaxation time $\tau^{}_N$ depends weakly on
$\alpha$ for small $h^{}_d$ and $A^{}_r\leq25.0$. For large $A^{}_r$, there is
a rapid fall in $\tau^{}_N$ as $\alpha$ is incremented from 0 to $90^\circ$.
These results benefit applications in data and energy storages where such
controlled magnetization alignment and desired structural anisotropy are
desirable.",2106.14271v1
2022-01-25,Collinear antiferromagnetic order in spin-$\frac52$ triangle lattice antiferromagnet Na$_3$Fe(PO$_4$)$_2$,"We set forth the structural and magnetic properties of the frustrated
spin-$5/2$ triangle lattice antiferromagnet Na$_3$Fe(PO$_4$)$_2$ examined via
x-ray diffraction, magnetization, heat capacity, and neutron diffraction
measurements on the polycrystalline sample. No structural distortion was
detected from the temperature-dependant x-ray diffraction down to 12.5 K,
except a systematic lattice contraction. The magnetic susceptibility at high
temperatures agrees well with the high-temperature series expansion for a
spin-$5/2$ isotropic triangular lattice antiferromagnet with an average
exchange coupling of $J/k_{\rm B} \simeq 1.8$ K rather than a one-dimensional
spin-$5/2$ chain model. This value of the exchange coupling is consistently
reproduced by the saturation field of the pulse field magnetization data. It
undergoes a magnetic long-range-order at $T_{\rm N} \simeq 10.4$ K. Neutron
diffraction experiments elucidate a collinear antiferromagnetic ordering below
$T_{\rm N}$ with the propagation vector $k = (1,0,0)$. An intermediate value of
frustration ratio ($f \simeq 3.6$) reflects moderate frustration in the
compound which is corroborated by a reduced ordered magnetic moment of $\sim
1.52$ $\mu_{\rm B}$ at 1.6 K, compared to its classical value ($5 \mu_{\rm
B}$). Magnetic isotherms exhibit a change of slope envisaging a field induced
spin-flop transition at $H_{\rm SF}\simeq3.2$ T. The magnetic field vs
temperature phase diagram clearly unfold three distinct phase regimes,
reminiscent of a frustrated magnet with in-plane (XY-type) anisotropy.",2201.10467v1
2023-02-01,Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning,"Thin garnet films are becoming central for magnon-spintronics and
spin-orbitronics devices as they show versatile magnetic properties together
with low magnetic losses. These fields would benefit from materials in which
heat does not affect the magnetization dynamics, an effect known as the
non-linear thermal frequency shift. In this study, low damping Bi substituted
Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser
Deposition. Through a fine tuning of the growth parameters, the precise control
of the perpendicular magnetic anisotropy allows to achieve a full compensation
of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are
optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as
the only tuning parameter induces the easy-axis to go from out-of-plane to
in-plane. For films that are close to the dipolar compensation, Ferromagnetic
Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$
that has almost no temperature dependence over a large temperature range (260 K
to 400 K) resulting in an anisotropy temperature exponent of 2. These findings
put Bi:YIG system among the very few materials in which the temperature
dependence of the magnetic anisotropy varies at the same rate than the
saturation magnetization. This interesting behavior is ascribed
phenomenologically to the sizable orbital moment of $Bi^{3+}$.",2302.00585v1
2023-02-23,First-principles based Monte Carlo modeling of oxygen deficient Fe-substituted SrTiO$_3$ experimental magnetization,"Ferroics based on transition-metal (TM) substituted SrTiO$_{3}$ have called
much attention as magnetism and/or ferroelectricity can be tuned by using
cations substitution and defects, strain and/or oxygen deficiency. C. A. Ross
et al. [Phys. Rev. Applied 7, 024006 (2017)] demonstrated the
SrTi$_{1-x}$Fe$_{x}$O$_{3-\delta}$ (STF) magnetization behavior for different
deposition oxygen-pressures, substrates and magnetic fields. The relation
between oxygen deficiency and ferroic orders is yet to be well understood, for
which the full potential of oxygen-stoichiometry engineered materials remain an
open question. Here, we use hybrid-DFT to calculate different oxygen vacancy
($v_{o}$) states in STF with a variety of TM distributions. The resulting
cations' magnetic states and alignments associated to the $v_{o}$ ground-states
for $x=\{0.125,0.25\}$ are used within a Monte Carlo scope for collinear
magnetism to simulate the spontaneous magnetization. Our model captures several
experimental STF features i.e., display a maximum of the magnetization at
intermediate number of vacancies, a monotonous quenching from
$\sim{0.35}\mu{_{B}}$ for small ${\delta}$, and a slower decreasing of such
saturation for larger number of vacancies. Moreover, our approach gives a
further insight into the relations between defects stabilization and
magnetization, vacancy density and the oxygen pressure required to maximize
such ferroic order, and sets guidelines for future Machine Learning based
computational synthesis of multiferroic oxides.",2302.12174v1
2023-04-16,Anomalous and Topological Hall Resistivity in Ta/CoFeB/MgO Magnetic Systems for Neuromorphic Computing Applications,"Topologically protected spin textures, such as magnetic skyrmions, have the
potential for dense data storage as well as energy-efficient computing due to
their small size and a low driving current. The evaluation of the writing and
reading of the skyrmion's magnetic and electrical characteristics is a key step
toward the implementation of these devices. In this paper, we present the
magnetic heterostructure Hall bar device and study the anomalous Hall and
topological Hall signals in the device. Using the combination of different
measurements like magnetometry at different temperatures, Hall effect
measurement from 2K to 300K, and magnetic force microscopy imaging, we
investigate the magnetic and electrical characteristics of the magnetic
structure. We measure the skyrmion topological resistivity at different
temperatures as a function of the magnetic field. The topological resistivity
is maximum around the zero magnetic field and it decreases to zero at the
saturating field. This is further supported by MFM imaging. Interestingly the
resistivity decreases linearly with the field, matching the behavior observed
in the corresponding micromagnetic simulations. We combine the experimental
results with micromagnetic simulations, thus propose a skyrmion-based synaptic
device and show spin-orbit torque-controlled potentiation/depression in the
device. The device performance as the synapse for neuromorphic computing is
further evaluated in a convolutional neural network CNN. The neural network is
trained and tested on the MNIST data set we show devices acting as synapses
achieving a recognition accuracy close to 90%, on par with the ideal
software-based weights which offer an accuracy of 92%.",2304.07742v1
2023-08-09,1/3 plateau and 3/5 discontinuity in the magnetization and the magnetic phase diagram of hexagonal GdInO$_3$,"We report the high-pressure optical floating-zone growth of GdInO$_3$ single
crystals and show its magnetic phase diagram down to the mK-regime as
determined by magnetization measurements. The centered-honeycomb lattice
structure shows considerable magnetic frustration ($\lvert\Theta\rvert /T_{\rm
N}\simeq 5$) and develops long-range magnetic order below $T_{\rm N}$~=~2.1 K
from a short-range ordered paramagnetic phase. Concomitantly, a small net
magnetic moment evolves at $T_{\rm N}$ which points along the crystallographic
$c$ direction. Upon cooling, the net moment reorients at $T^{**}\simeq 1.7$ K
and $T^{*}\simeq 1$ K. A broad 1/3 plateau indicative of the up-up-down ($uud$)
spin configuration appears for $B||c$ but is absent for $B||ab$, thereby
suggesting easy axis anisotropy. At $T=0.4$ K, a jump in magnetization at
$\simeq 3/5$ of the saturation magnetization signals a discontinuous transition
to a high field phase and we find evidence for a possible tricritical point.
Small energy and field scales in the accessible regimes render GdInO$_3$ a
prime example to study the phase diagram of a semiclassical frustrated
hexagonal lattice in the presence of weak easy axis anisotropy of mainly
dipolar origin.",2308.04935v1
2012-09-24,The evolution of the f-mode instability in neutron stars and gravitational wave detectability,"We study the dynamical evolution of the gravitational-wave driven instability
of the f-mode in rapidly rotating relativistic stars. With an approach based on
linear perturbation theory we describe the evolution of the mode amplitude and
follow the trajectory of a newborn neutron star through its instability window.
The influence on the f-mode instability of the magnetic field and the presence
of an unstable r-mode is also considered. Two different configurations are
studied in more detail; an N = 1 polytrope with a typical mass and radius and a
more massive polytropic N = 0.62 model with gravitational mass M = 1.98 Msun.
We study several evolutions with different initial rotation rates and
temperature and determine the gravitational waves radiated during the
instability. In more massive models, an unstable f-mode with a saturation
energy of about 1e-6 Msun c^2 may generate a gravitational-wave signal which
can be detected by the Advanced LIGO/Virgo detector from the Virgo cluster. The
magnetic field affects the evolution and then the detectability of the
gravitational radiation when its strength is higher than 1e12 G, while the
effects of an unstable r-mode become dominant when this mode reaches the
maximum saturation value allowed by non-linear mode couplings. However, the
relative saturation amplitude of the f- and r-modes must be known more
accurately in order to provide a definitive answer to this issue. From the
thermal evolution we find also that the heat generated by shear viscosity
during the saturation phase completely balances the neutrinos' cooling and
prevents the star from entering the regime of mutual friction. The evolution
time of the instability is therefore longer and the star loses significantly
larger amounts of angular momentum via gravitational waves.",1209.5308v2
2013-03-07,Saturation of the MRI in Strongly Radiation Dominated Accretion Disks,"The saturation level of the magneto-rotational instability (MRI) in a
strongly radiation dominated accretion disk is studied using a new Godunov
radiation MHD code in the unstratified shearing box approximation. Since
vertical gravity is neglected in this work, our focus is on how the MRI
saturates in the optically thick mid-plane of the disk. We confirm that
turbulence generated by the MRI is very compressible in the radiation dominated
regime, as found by previous calculations using the flux-limited diffusion
approximation. We also find little difference in the saturation properties in
calculations that use a larger horizontal domain (up to four times the vertical
scale height in the radial direction). However, in strongly radiation pressure
dominated disks (one in which the radiation energy density reaches 1% of the
rest mass energy density of the gas), we find Maxwell stress from the MRI
turbulence is larger than the value produced when radiation pressure is
replaced with the same amount of gas pressure. At the same time, the ratio
between Maxwell stress and Reynolds stress is increased by almost a factor of 8
compared with the gas pressure dominated case. We suggest that this effect is
caused by radiation drag, which acts like bulk viscosity and changes the
effective magnetic Prandtl number of the fluid. Radiation viscosity
significantly exceeds both the microscopic plasma viscosity and resistivity,
ensuring that radiation dominated systems occupy the high magnetic Prandtl
number regime. Nevertheless, we find radiative shear viscosity is negligible
compared to the Maxwell and Reynolds stress in the flow. This may have
important implications for the structure of radiation dominated accretion
disks.",1303.1823v1
2022-03-09,Modelling of saturated external MHD instabilities in tokamaks: a comparison of 3D free boundary equilibria and nonlinear stability calculations,"3D free boundary equilibrium computations have recently been used to model
external kinks and edge harmonic oscillations (EHOs), comparing with linear MHD
stability codes, and nonlinear analytic theory [Kleiner et al, PPCF 61 084005
(2019)]. In this study, results of the VMEC equilibrium code are compared
further with nonlinear reduced MHD simulations, using the JOREK code. The
purpose of this investigation is to understand the extent to which the
modelling approaches agree, and identify the important physical effects which
can modify the dynamics. For the simulated external kink, which is dominated by
a single toroidal harmonic, good agreement is found when a large Lundquist
number is used in the JOREK simulation, such that resistive effects are
sub-dominant. Modelling EHOs where multiple toroidal harmonics are linearly
unstable, the saturated perturbation observed can differ in the dominant
toroidal harmonic. On the ideal timescale, a n=2 EHO is observed in JOREK,
while the saturated perturbation predicted by VMEC is a n=1 mode. Extending
simulations into timescales where resistive effects can play a role, similar
n=1 perturbations can be found. The coupling of different linearly unstable
toroidal harmonics in the JOREK simulation broadens the magnetic energy
spectrum and ergodises the plasma edge region, resulting in a more localised
pressure perturbation. These effects are not observed in VMEC, because closed
magnetic flux surfaces are enforced. Despite the sensitivity of JOREK results
on the assumed resistivity, saturated states can be found using both approaches
that are in reasonable agreement, even for this more advanced case.",2203.04772v2
2005-10-18,"Domain imaging, MOKE and magnetoresistance studies of CoFeB films for MRAM applications","We present a detailed study on domain imaging, Kerr effect magnetometry
(MOKE) and magnetoresistance (MR), for a series of 20 nm
Co$_{73.8}$Fe$_{16.2}$B$_{10}$ thin films, both as-deposited (amorphous) and
annealed (crystalline). By considering the two different (orthogonal) in-plane
magnetization components, obtained by MOKE measurements, we were able to study
the uniaxial anisotropy induced during CoFeB-deposition and to discriminate the
magnetization processes under a magnetic field parallel and perpendicular to
such axis. MOKE magnetic imaging enabled us to observe the dominant
magnetization processes, namely domain wall motion and moment rotation. These
processes were correlated with the behavior of the magnetoresistance, which
depends both on short-range spin disorder electron scattering and on the angle
between the electrical current and the spontaneous magnetization
($\emph{\textbf{M}}_{S}$). A simple numerical treatment based on
Stoner-Wolfarth model enables us to satisfactorily predict the magnetization
behaviour observed in these films. A comparison between the results in
Co$_{73.8}$Fe$_{16.2}$B$_{10}$ films and the previous ones obtained in annealed
Co$_{80}$Fe$_{20}$ films, show that the introduction of boron in CoFe reduces
significatively the coercive and saturation fields along the easy axis (e.g.
$H_{c}$ from $\sim$ 2 down to $\sim$ 0.5 kAm$^{-1}$). Also, the magnetization
along the hard axis saturates at lower fields. We conclude that amorphous and
nanocrystalline CoFeB films show low coercive fields and abrupt switching, as
well as absence of short range spin disorder effects after switching when
compared with Co$_{80}$Fe$_{20}$.",0510479v2
2011-02-10,Effects of hydrogen/deuterium absorption on the magnetic properties of Co/Pd multilayers,"The effects of hydrogen (H2) and deuterium (D2) absorption were studied in
two Co/Pd multilayers with perpendicular magnetic anisotropy (PMA) using
polarized neutron reflectivity (PNR). PNR was measured in an external magnetic
field H applied in the plane of the sample with the magnetization M confined in
the plane for {\mu}_o H= 6.0 T and partially out of plane at 0.65 T. Nominal
thicknesses of the Co and Pd layers were 2.5 {\AA} and 21 {\AA}, respectively.
Because of these small values, the actual layer chemical composition,
thickness, and interface roughness parameters were determined from the nuclear
scattering length density profile ({\rho}_n) and its derivative obtained from
both x-ray reflectivity and PNR, and uncertainties were determined using Monte
Carlo analysis. The PNR {\rho}_n showed that although D2 absorption occurred
throughout the samples, absorption in the multilayer stack was modest (0.02 D
per Pd atom) and thus did not expand. Direct magnetometry showed that H2
absorption decreased the total M at saturation and increased the component of M
in the plane of the sample when not at saturation. The PNR magnetic scattering
length density ({\rho}_m) revealed that the Pd layers in the multilayer stack
were magnetized and that their magnetization was preferentially modified upon
D2 absorption. In one sample, a modulation of M with twice the multilayer
period was observed at {\mu}_o H= 0.65 T, which increased upon D2 absorption.
These results indicate that H2 or D2 absorption decreases both the PMA and
total magnetization of the samples. The lack of measurable expansion during
absorption indicates that these changes are primarily governed by modification
of the electronic structure of the material.",1102.2260v1
2016-09-12,"Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM$_2$Al$_{20}$ [R = Eu,Gd and La ; TM = V,Ti]","Single crystals of Frank-Kasper compounds RTM$_2$Al$_{20}$ (R = Eu, Gd and
La; TM = V and Ti) were grown by self-flux method and their physical properties
were investigated through magnetization ($M$), magnetic susceptibility
($\chi$), specific heat ($C_P$) and electrical resistivity ($\rho$)
measurements. Powder x-ray diffraction studies and structural analysis showed
that these compounds crystallize in the cubic crystal structure with the space
group $Fd\overline{3}m$. The magnetic susceptibility for the compounds
EuTi$_2$Al$_{20}$ and GdTi$_2$Al$_{20}$ showed a sudden jump below the N{\'e}el
temperature $T_N$ indicative of plausible double magnetic transition. Specific
heat ($C_P$) and electrical resistivity ($\rho$) measurements also confirm the
first-order magnetic transition (FOMT) and possible double magnetic
transitions. Temperature variation of heat capacity showed a sharp phase
transition and huge $C_P$ value for the (Eu/Gd)Ti$_2$Al$_{20}$ compounds Full
width at half-maximum (FWHM) $<$ 0.2 K) which is reminiscent of a first-order
phase transition and a unique attribute among RTM$_2$Al$_{20}$ compounds. We
observed clear anomaly between heating and cooling cycle in temperature-time
relaxation curve for the compounds GdTi$_2$Al$_{20}$ (2.38 $K$) and
EuTi$_2$Al$_{20}$ (3.2 $K$) which is indicating a thermal arrest due to the
latent heat. The temperature variation of $S_{mag}$ for GdTi$_2$Al$_{20}$
saturates to a value $0.95R\ln8$ while the other magnetic systems exhibited
still lower entropy saturation values in the high temperature limit.
Resistivity measurements showed that all the samples behave as normal Fermi
liquid type compounds and $\rho(T)$ due to electron-phonon scattering follows
Bloch-Gr$\ddot{\textrm u}$neisen-Mott relation in the paramagnetic region.",1609.03458v1
2022-03-21,Accurate Determination of the Electron Spin Polarization In Magnetized Iron and Nickel Foils for Møller Polarimetry,"The M{\o}ller polarimeter in Hall A at Jefferson Lab in Newport News, VA, has
provided reliable measurements of electron beam polarization for the past two
decades reaching the typically required $\pm$1\% level of absolute uncertainty.
However, the upcoming proposed experimental program including MOLLER and SoLID
have stringent requirements on beam polarimetry precision at the level of 0.4\%
\cite{MOLLER2014, SoLID2019}, requiring a systematic re-examination of all the
contributing uncertainties.
  M{\o}ller polarimetry uses the double polarized scattering asymmetry of a
polarized electron beam on a target with polarized atomic electrons. The target
is a ferromagnetic material magnetized to align the spins in a given direction.
In Hall A, the target is a pure iron foil aligned perpendicular to the beam and
magnetized out of plane parallel or antiparallel to the beam direction. The
acceptance of the detector is engineered to collect scattered electrons close
to 90$^{\circ}$ in the center of mass frame where the analyzing power is a
maximum (-7/9).
  One of the leading systematic errors comes from determination of the target
foil polarization. Polarization of a magnetically saturated target foil
requires knowledge of both the saturation magnetization and $g^\prime$, the
electron $g$-factor which includes components from both spin and orbital
angular momentum from which the spin fraction of magnetization is determined.
This paper utilizes the existing world data to provide a best estimate for
target polarization for both nickel and iron foils including uncertainties in
magnetization, high-field and temperature dependence, and fractional
contribution to magnetization from orbital effects. We determine the foil
electron spin polarization at 294~K to be 0.08020$\pm$0.00018 (@4~T applied
field) for iron and 0.018845$\pm0.000053$ (@2~T applied field) for nickel.",2203.11238v2
2024-01-15,Sensing magnetic flux of Langmuir-Blodgett films of a molecular magnetic system using superconducting films and nano-SQUID devices,"We report a study on the response of superconducitng micro-tracks and quantum
interference devices (SQUIDs) to a proximal SMM film. As a test case,
Langmuir-Blodgett $Mn_{12}$-ac SMM films have been grown on 2 $\mu$m wide Nb
tracks and Nb nano-SQUIDs to observe the proximity effect of magnetic moment
and magnetization tunneling, respectively. The superconducting critical
temperature of thin Nb tracks (thinner than the coherence length of Nb) were
found to decrease by the magnetic moment of $Mn_{12}$-ac SMM. Following the
thermally activated flux flow (TAFF) model, we found an increase in the vortex
unbinding energy of the SMM coated Nb tracks, near critical temperature. More
importantly, the random alignment of moments of the $Mn_{12}$-ac molecules at
low fields seemed to have the enhancing effect on vortex unbinding energy
rather than the saturated state of $Mn_{12}$-ac molecules at high fields. In
the fully superconducting state, on the other hand, the vortex pinning effects
were found to be more effective in the saturated state of the $Mn_{12}$-ac
molecules, as seen from magnetoresistance and field dependent critical current
measurements. In a separate experiment, a Langmuir-Blodgett film of SMM was
grown on a nano-SQUID to look for local changes in magnetization arising from
magnetizatin tunnelling phenomenon in SMMs. Upon magnetizing the SMM (deposited
on SQUIDs) at 2 K along the plane of the film and allowing it to relax, we
found occasional jumps in the underlying SQUID voltage, unlike bare
nano-SQUIDs, which did not show any such jumps over several hours. Therefore,
we believe that the jumps in the SQUID voltage are the signatures of random
tunneling of magnetization in the SMM layer.",2401.07566v2
2014-05-05,Titanic Magnetoresistance in WTe2,"Magnetoresistance is the change of a material's electrical resistance in
response to an applied magnetic field. In addition to its intrinsic scientific
interest, it is a technologically important property, placing it in ""Pasteur's
quadrant"" of research value: materials with large magnetorsistance have found
use as magnetic sensors 1, in magnetic memory 2, hard drives 3, transistors 4,
and are the subject of frequent study in the field of spintronics 5, 6. Here we
report the observation of an extremely large one-dimensional positive
magnetoresistance (XMR) in the layered transition metal dichalcogenide (TMD)
WTe2; 452,700 percent at 4.5 Kelvin in a magnetic field of 14.7 Tesla, and 2.5
million percent at 0.4 Kelvin in 45 Tesla, with no saturation. The XMR is
highly anisotropic, maximized in the crystallographic direction where small
pockets of holes and electrons are found in the electronic structure. The
determination of the origin of this effect and the fabrication of
nanostructures and devices based on the XMR of WTe2 will represent a
significant new direction in the study and uses of magnetoresistivity.
  *The published version of the paper includes co-authors Tian Liang and Max
Hirschberger.
  **This paper has been published with new MR data to 60T where the MR of WTe2
reaches 13 million percent (at 0.5K) and still shows no signs of saturation. We
also have new electron diffraction patterns to lower temperature (10K). We
discuss the possible origin of the MR as coming from an electron-hole
'resonance' condition established by a perfect n/p ratio of 1 (more details in
a new ""extended data"" section). This makes WTe2, possibly, the first
realization of a perfectly balanced semimetal.
  ***The paper is published as ""Large non-saturating magnetoresistance in WTe2""
in Nature (2014), DOI:10.1038/nature13763",1405.0973v3
2001-01-22,Magnetically driven superluminal motion from rotating black holes,"We have investigated magnetically driven superluminal jets originating from
rotating black holes. The stationary, general relativistic, magnetohydrodynamic
wind equation along collimating magnetic flux surfaces has been solved
numerically. In particular, we apply our results to the Galactic superluminal
sources GRS 1915+105 and GRO 1655-40. Our results show that the observed speed
of more than 0.9 c can be achieved in general by magnetohydrodynamic
acceleration. The velocity distribution along the magnetic field has a
saturating profile. Further, we find that highly relativistic speeds can be
reached also for jets not emerging from a region close to the black hole, if
the flow magnetization is sufficiently large. The plasma temperature rapidly
decreases from about 10**10 K at the foot point of the jet to about 10**6 K at
a distance of 5000 gravitational radii from the source. Temperature and the
mass density follow a power law distribution with the radius.",0101373v1
2003-06-03,Dynamo action in turbulent flows,"We present results from numerical simulations of nonlinear MHD dynamo action
produced by three-dimensional flows that become turbulent for high values of
the fluid Reynolds number. The magnitude of the forcing function driving the
flow is allowed to evolve with time in such way as to maintain an approximately
constant velocity amplitude (and average kinetic energy) when the flow becomes
hydrodynamically unstable. It is found that the saturation level of the dynamo
increases with the fluid Reynolds number (at constant magnetic Prandtl number),
and that the average growth rate approaches an asymptotic value for high fluid
Reynolds number. The generation and destruction of magnetic field is examined
during the laminar and turbulent phase of the flow and it is found that in the
neighborhood of strong magnetic ""flux cigars"" Joule dissipation is balanced by
the work done against the Lorentz force, while the steady increase of magnetic
energy occurs mainly through work done in the weak part of the magnetic field.",0306069v3
2006-08-31,Nonlinear simulations of magnetic Taylor-Couette flow with current-free helical magnetic fields,"The magnetorotational instability (MRI) in cylindrical Taylor-Couette flow
with external helical magnetic field is simulated for infinite and finite
aspect ratios. We solve the MHD equations in their small Prandtl number limit
and confirm with time-dependent nonlinear simulations that the additional
toroidal component of the magnetic field reduces the critical Reynolds number
from $O(10^6)$ (axial field only) to $O(10^3)$ for liquid metals with their
small magnetic Prandtl number. Computing the saturated state we obtain velocity
amplitudes which help designing proper experimental setups. Experiments with
liquid gallium require axial field $\sim 50$ Gauss and axial current $\sim 4$
kA for the toroidal field. It is sufficient that the vertical velocity $u_z$ of
the flow can be measured with a precision of 0.1mm/s.
  We also show that the endplates enclosing the cylinders do not destroy the
traveling wave instability which can be observed as presented in earlier
studies. For TC containers without and with endplates the angular momentum
transport of the MRI instability is shown as to be outwards.",0608703v1
1996-06-11,On Magnetic Impurities in Gapless Fermi Systems,"In ordinary metals, antiferromagnetic exchange between conduction electrons
and a magnetic impurity leads to screening of the impurity spin below the Kondo
temperature, $T_K$. In systems such as semimetals, small-gap semiconductors and
unconventional superconductors, a reduction in available conduction states near
the chemical potential can greatly depress $T_K$. The behavior of an Anderson
impurity in a model with a power-law density of states, $N(\epsilon) \sim
|\epsilon|^r$, $r>0$, for $|\epsilon| < \Delta$, where $\Delta \ll D$, is
studied using the non-crossing approximation. The transition from the Kondo
singlet to the magnetic ground state can be seen in the behavior of the
impurity magnetic susceptibility $\chi$. The product $T\chi$ saturates at a
finite value at low temperature for coupling smaller than the critical one. For
sufficiently large coupling $T\chi \to 0$, as $T \to 0$, indicating complete
screening of the impurity spin.",9606075v1
1998-02-23,Magnetization under High Pressure in MnSi,"The magnetization M(H) has been measured in the weakly helimagnetic itinerant
compound MnSi under high pressure up to 10.2 kbar and high magnetic field up to
9 Tesla. We interpret the simultaneous decrease under pressure of the saturated
magnetization, $p_s$, and the Curie temperature, $% T_c$ in the frame of the
self-consistent renormalization theory (SCR) of spin fluctuations. From the
analysis of the so-called Arrot-plot ($H/p [ H,T ] $ versus $p^2[ H,T ] $) and
the respective volume dependence of $p_s$ and $T_c$, we estimate the evolution
of the characteristic spin fluctuation temperatures, $T_0$ and $T_A$ when the
system approaches its critical pressure, $P_c$=15 kbar, corresponding to the
disappearance of the long range magnetic order at T=0.",9802238v1
1998-08-27,Magnetization Plateaus in One Dimensional $Š=1/2$ Heisenberg Model with Dimerization and Quadrumerization,"The one dimensional $S=1/2$ Heisenberg model with dimerization ($1-j$) and
quadrumerization ($\delta$) in the magnetic field is studied by means of the
numerical exact diagonalization of finite size systems and the conformal field
theory. It is found that the magnetization plateau at half of the saturation
value exists for $\delta \neq 0$. For $\delta = 0$, this model is described by
the conformal field theory with central charge $c=1$ at this value of
magnetization. The critical exponent $\nu$ which characterizes the
$\delta$-dependence of the width of the plateau is calculated using the level
spectroscopy method. The $j$-dependence of the critical exponent $\nu$ is found
to be non-monotonic and discontinuous at $j = 0$. The effective theory of the
magnetization plateau is also presented for various limiting cases.",9808300v2
1999-09-29,Magnetic Field Dependent Tunneling in Glasses,"We report on experiments giving evidence for quantum effects of
electromagnetic flux in barium alumosilicate glass. In contrast to expectation,
below 100 mK the dielectric response becomes sensitive to magnetic fields. The
experimental findings include both, the complete lifting of the dielectric
saturation by weak magnetic fields and oscillations of the dielectric response
in the low temperature resonant regime. As origin of these effects we suggest
that the magnetic induction field violates the time reversal invariance leading
to a flux periodicity in the energy levels of tunneling systems. At low
temperatures, this effect is strongly enhanced by the interaction between
tunneling systems and thus becomes measurable.",9909425v1
1999-10-26,Magnetotransport in nearly antiferromagnetic metals,"We present a theory of the magnetotransport in weakly disordered metals close
to an antiferromagnetic quantum-critical point. The anisotropic scattering from
critical spin fluctuations is strongly influenced by weak but isotropic
scattering from small amounts of disorder. This leads to a large regime where
the resistivity obeys a scaling form rho=rho_0+Delta rho = rho_0+T^{3/2}
f(T/\rho_0,(p-p_c)/rho_0,B/rho_0^{3/2}), where rho_0 is the residual
resistivity, B the magnetic field and p-p_c>0 measures the distance from the
quantum-critical point on the paramagnetic side of the phase diagram. Orbital
effects of the magnetic field are most pronounced in very clean samples for not
too low temperatures, where the resistivity for increasing magnetic field
crosses over from a linear temperature dependence Delta rho =T*sqrt{rho_0} to a
resistivity linear in B and independent of T and rho_0. At higher magnetic
fields Delta rho saturates at a value proportional to T^{1.5} or T^2/(p-p_c).
Deviations from scaling, the interplay of orbital and spin contributions of the
magnetic field and experimental test of the spin-fluctuation model are
discussed in detail.",9910432v1
2000-04-11,Antiferromagnetic Zigzag Spin Chain in Magnetic Fields at Finite Temperatures,"We study thermodynamic behaviors of the antiferromagnetic zigzag spin chain
in magnetic fields, using the density-matrix renormalization group method for
the quantum transfer matrix. We focus on the thermodynamics of the system near
the critical fields in the ground-state magnetization process($M$-$H$ curve):
the saturation field, the lower critical field associated with excitation gap,
and the field at the middle-field cusp singularity. We calculate magnetization,
susceptibility and specific heat of the zigzag chain in magnetic fields at
finite temperatures, and then discuss how the calculated quantities reflect the
low-lying excitations of the system related with the critical behaviors in the
$M$-$H$ curve.",0004159v2
2000-10-25,"Susceptibility, Magnetization Process and ESR Studies on the Helical Spin System RbCuCl$_{3}$","The static and dynamic magnetic properties of an $S=1/2$ stacked triangular
antiferromagnet RbCuCl$_{3}$ with a helical spin structure due to lattice
distortion were investigated by susceptibility, high-field magnetization
process and ESR measurements. The susceptibilities were analyzed by
high-temperature expansion approximation in terms of ferromagnetic intrachain
coupling and the antiferromagnetic interchain coupling. The magnetization
saturates at $H_{\rm s}\approx 66.8$ T at 1.5 K, the value of which is twice
that of CsCuCl$_3$. A small magnetization jump indicative of a phase transition
was observed at $H_{\rm c}=21.2$ T $\approx (1/3)H_{\rm s}$ for $H{\perp}c$.
ESR modes observed for $H\parallel c$ are well described by the calculation
based on the helical spin structure. From the present measurements, the
ferromagnetic intrachain and two kinds of antiferromagnetic interchain exchange
interactions, and the planar anisotropy energy were determined as $J_0/k_{\rm
B}=25.7$ K, $J_1/k_{\rm B}=-10.6$ K, $J_1'/k_{\rm B}=-17.4$ K, and
${\Delta}J_0/k_{\rm B}=-0.45$ K, respectively.",0010388v2
2001-09-04,Magnetolocalization in disordered quantum wires,"The magnetic field dependent localization in a disordered quantum wire is
considered nonperturbatively.
  An increase of an averaged localization length with the magnetic field is
found, saturating at twice its value without magnetic field.
  The crossover behavior is shown to be governed both in the weak and strong
localization regime by the magnetic diffusion length L_B. This function is
derived analytically in closed form as a function of the ratio of the mean free
path l, the wire thickness W, and the magnetic length l_B for a two-dimensional
wire with specular boundary conditions, as well as for a parabolic wire. The
applicability of the analytical formulas to resistance measurements in the
strong localization regime is discussed. A comparison with recent experimental
results on magnetolocalization is included.",0109060v1
2001-11-28,Random Magnetism in $S=1/2$ Heisenberg Chains with Bond Alternation and Randomness on the Strong Bonds,"The $S=1/2$ Heisenberg chains with bond alternation and randomness on the
strong bonds are studied by the density matrix renormalization group method. It
is assumed that the odd-th bond is antiferromagnetic with strength $J$ and
even-th bond can take the values $\JA$ and $\JF$ $ (\JA > J > 0 > \JF)$
randomly. The ground state of this model interpolates between the Haldane and
dimer phases via a randomness dominated intermediate phase. Based on the
scaling of the low energy spectrum and mean field treatment of the interchain
coupling, it is found that the magnetic long range order is induced by
randomness in the intermediate regime. In the magnetization curves, there
appears a plateau at the fractional value of the saturated magnetization. The
fine structures of the magnetization curves and low energy spectrum are
understood based on the cluster picture. The relation with the recent
experiment for (CH$_3)_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x})_3$ is discussed.",0111521v2
2002-04-19,Optical and magnetic properties of Co-TiO2 sandwich Composite films grown by magnetron sputtering,"The transition metal ions doped with TiO2 films are of magnetic properties at
room temperatures and have stimulated many scientists to study other
properties. The Co-TiO2 sandwich composite films have been recently grown on
glass and silicon substrates by using alternately radio frequency reactive and
direct current magnetron sputtering. The microstructural properties of these
films were characterized with Raman spectra and X-ray photoemission spectra
(XPS). It shows an anatase TiO2 containing Co nano-layer. Optical absorption
spectra have red shift with Co nano-layer increasing, which originated from the
quantum confinement and tunnel effects. Magnetic properties show that the
saturation magnetization, remanent magnetic induction and coercivity are about
4.35 emu /g, 1.02 emu/g and 569.6 Oe respectively for 12 nm Co layer between
the two TiO2 layers.",0204419v1
2002-05-13,Direct visualization of iron sheath shielding effect in MgB_2 superconducting wires,"Local magneto-optical imaging and global magnetization measurement techniques
were used in order to visualize shielding effects in the superconducting core
of MgB_2 wires sheathed by ferromagnetic iron (Fe). The magnetic shielding can
provide a Meissner-like state in the superconducting core in applied magnetic
fields up to ~1T. The maximum shielding fields are shown to correlate with the
saturation fields of magnetization in Fe-sheaths. The shielding has been found
to facilitate the appearance of an overcritical state, which is capable of
achieving a critical current density (J_c) in the core which is larger than J_c
in the same wire without the sheath by a factor of ~2. Other effects caused by
the magnetic interaction between the sheath and the superconducting core are
discussed.",0205253v2
2003-02-24,Magnetization study of RuSr2Y1.5Ce 0.5Cu2O10 (Ru-1222),"We have studied the magnetic properties of the non-superconducting
RuSr2Ln1.5Ce0.5Cu2O10 (Ln=Y, Dy and Ho, Ru-1222) compounds synthesized under
high pressure (6 Gpa) at elevated temperature. The materials become
magnetically ordered at TM =152(2) K regardless of Ln. The wide
ferromagnetic-like hysteresis loops which open at 5 K, close themselves around
Tirr= 90-100 K and the remanent magnetizations (Mrem) and the coercive fields
(HC) become zero. Surprisingly, at Tirr<T< TM a reappearance of the Mrem and HC
(with a peak at 120-130 K) is observed for all three samples studied. For the
non-magnetic Ln=Y compound, the extracted saturation moment at 5 K and the
effective paramagnetic moment are is 0.75 and 2.05 mB /Ru, values which are
close to the expected 1 mB and 1.73 mB respectively, for the low-spin state of
Ru5+. We argue that the Ru-1222 system becomes (i) anti-ferromagnetically (AFM)
ordered at TM. In this range a metamagnetic transition is induced by the
applied field (ii). At Tirr < TM, weak-ferromagnetism (W-FM) is induced by the
canting of the Ru moments.",0302475v1
2004-04-27,Field-induced gap in ordered Heisenberg antiferromagnets,"Heisenberg antiferromagnets in a strong uniform magnetic field $H$ are
expected to exhibit a gapless phase with a global O(2) symmetry. In many real
magnets, a small energy gap is induced by additional interactions that can be
viewed as a staggered transverse magnetic field $h = c H$, where $c$ is a small
proportionality constant. We study the effects of such a perturbation,
particularly for magnets with long-range order, by using several complimentary
approaches: numerical diagonalizations of a model with long-range interactions,
classical equations of motion, and scaling arguments. In an ordered state at
zero temperature, the energy gap at first grows as $(cH)^{1/2}$ and then may
dip to a smaller value, of order $(cH)^{2/3}$, at the quantum critical point
separating the ``gapless'' phase from the gapped state with saturated
magnetization. In one spatial dimension, the latter exponent changes to 4/5.",0404636v2
2004-06-10,Influence of randomly distributed magnetic nanoparticles on surface superconductivity in Nb films,"We report on combined resistance and magnetic measurements in a hybrid
structure (HS) of randomly distributed anisotropic CoPt magnetic nanoparticles
(MN) embedded in a 160 nm Nb thick film. Our resistance measurements exhibited
a sharp increase at the magnetically determined bulk upper-critical fields
Hc2(T). Above these points the resistance curves are rounded, attaining the
normal state value at much higher fields identified as the surface
superconductivity fields Hc3(T). When plotted in reduced temperature units, the
characteristic field lines Hc3(T) of the HS and of a pure Nb film, prepared at
exactly the same conditions, coincide for H<10 kOe, while for fields H>10 kOe
they strongly segregate. Interestingly, the characteristic value H=10 kOe is
equal to the saturation field of the MN. The behavior mentioned above is
observed only for the case where the field is normal to the HS, while is absent
when the field is parallel to the film. Our experimental results suggest that
the observed enhancement of surface superconductivity field Hc3(T) is possibly
due to the not uniform local reduction of the external magnetic field by the
dipolar fields of the MN.",0406235v1
2004-12-09,Finite-Field Ground State of the S=1 Antiferromagnetic-Ferromagnetic Bond-Alternating Chain,"We investigate the finite-field ground state of the S=1
antiferromagnetic-ferromagnetic bond-alternating chain described by the
Hamiltonian
${\calH}=\sum\nolimits_{\ell}\bigl\{\vecS_{2\ell-1}\cdot\vecS_{2\ell}
+J\vecS_{2\ell}\cdot\vecS_{2\ell+1}\bigr\} +D\sum\nolimits_{\ell}
\bigl(S_{\ell}^z)^2 -H\textstyle\sum\nolimits_\ell S_\ell^z$, where
\hbox{$J\leq0$} and \hbox{$-\infty<D<\infty$}. We find that two kinds of
magnetization plateaux at a half of the saturation magnetization, the
1/2-plateaux, appear in the ground-state magnetization curve; one of them is of
the Haldane type and the other is of the large-$D$-type. We determine the
1/2-plateau phase diagram on the $D$ versus $J$ plane, applying the
twisted-boundary-condition level spectroscopy methods developed by Kitazawa and
Nomura. We also calculate the ground-state magnetization curves and the
magnetization phase diagrams by means of the density-matrix
renormalization-group method.",0412234v1
2005-10-07,The many-electron ground-state determines uniquely the potential in Spin-Density-Functional Theory for non-collinear magnetism,"Since Spin Density Functional Theory was first proposed, but also recently,
examples were constructed to show that a spin-potential may share its ground
state with other spin-potentials. In fact, for collinear magnetic fields and
systems with fixed magnetization, the mapping between potentials and ground
states is invertible, provided the magnetization is not saturated and that
spin-potentials are determined within a spin-constant. We complete the proof
that the mapping is invertible also for non-collinear magnetic fields and
systems with more than one electron. We then discuss the non-collinear exchange
and correlation energy functional and suggest improvements.",0510199v4
2005-10-20,Current-driven magnetization switching in CoFeB/MgO/CoFeB magnetic tunnel junctions,"Current-driven magnetization switching in low-resistance
Co40Fe40B20/MgO/Co40Fe40B20 magnetic tunnel junctions (MTJs) is reported. The
critical-current densities Jc required for current-driven switching in samples
annealed at 270C and 300C are found to be as low as 7.8 x 10^5 A/cm^2 and 8.8 x
10^5 A/cm^2 with accompanying tunnel magnetoresistance (TMR) ratios of 49% and
73 %, respectively. Further annealing of the samples at 350C increases TMR
ratio to 160 %, while accompanying Jc increases to 2.5 x 10^6 A/cm^2. We
attribute the low Jc to the high spin-polarization of tunnel current and small
MsV product of the CoFeB single free layer, where Ms is the saturation
magnetization and V the volume of the free layer.",0510538v1
2006-04-05,Interparticle interaction and size effect in polymer coated magnetite nanoparticles,"Magnetization and Mossbauer studies have been performed on the polymer coated
magnetite nanoparticles with particle size from 5.1 to 14.7 nm. The maximum in
the temperature dependence of magnetization (TM) is found to be inconsistent
with the particle size (DTEM). The effective magnetic anisotropy (Kan) is found
to increase with the decrease of DTEM, which is attributed to the increase of
surface anisotropy. The absence of coercivity and remanence of magnetization
noticed well above TM indicates the superparamagnetic behaviour, which has also
been observed in the temperature dependent Mossbauer results. The temperature
dependence of hyperfine field is found to follow similar dependence of
saturation magnetization for bulk magnetite.",0604119v2
2006-12-06,Coexistence of vector chiral order and Tomonaga-Luttinger liquid in the frustrated three-leg spin tube in a magnetic field,"The frustrated three-leg antiferromagnetic spin-1/2 tube with a weak
interchain coupling in a magnetic field is investigated by means of Abelian
bosonization techniques. It is clearly shown that a vector chiral order and a
one-component Tomonaga-Luttinger liquid coexist in a wide magnetic-field region
from a state with a small magnetization to a nearly saturated one. The chiral
order is predicted to still survive in the intermediate plateau state. We
further predict that (even) when the strength of one bond in the three rung
couplings is decreased (increased), an Ising type quantum phase transition
takes place and the chirality vanishes (no singular phenomena occur and the
chiral order is maintained). Even without magnetic fields, the chiral order
would also be present, if the spin tube possess easy-plane anisotropy.",0612165v3
2007-02-14,Vortices and chirality of magnetostatic modes in quasi-2D ferrite disk particles,"In this paper we show that the vortex states can be created not only in
magnetically soft ""small"" (with the dipolar and exchange energy competition)
cylindrical dots, but also in magnetically saturated ""big"" (when the exchange
is neglected) cylindrical dots. A property associated with a vortex structure
becomes evident from an analysis of confinement phenomena of magnetic
oscillations in a ferrite disk with a dominating role of magnetic-dipolar
(non-exchange-interaction) spectra. In this case the scalar
(magnetostatic-potential) wave functions may have a phase singularity in a
center of a dot. A non-zero azimuth component of the flow velocity demonstrates
the vortex structure. The vortices are guaranteed by the chiral edge states of
magnetic-dipolar modes in a quasi-2D ferrite disk.",0702327v1
1992-09-26,Saddle point solutions in Yang-Mills-dilaton theory,"The coupling of a dilaton to the $SU(2)$-Yang-Mills field leads to
interesting non-perturbative static spherically symmetric solutions which are
studied by mixed analitical and numerical methods. In the abelian sector of the
theory there are finite-energy magnetic and electric monopole solutions which
saturate the Bogomol'nyi bound. In the nonabelian sector there exist a
countable family of globally regular solutions which are purely magnetic but
have zero Yang-Mills magnetic charge. Their discrete spectrum of energies is
bounded from above by the energy of the abelian magnetic monopole with unit
magnetic charge. The stability analysis demonstrates that the solutions are
saddle points of the energy functional with increasing number of unstable
modes. The existence and instability of these solutions are ""explained"" by the
Morse-theory argument recently proposed by Sudarsky and Wald.",9209106v1
2007-05-24,Magnetic helicity effects in astrophysical and laboratory dynamos,"Magnetic helicity effects are discussed in laboratory and astrophysical
settings. First, dynamo action in Taylor-Green flows is discussed for different
boundary conditions. However, because of the lack of scale separation with
respect to the container, no large scale field is being produced and there is
no resistively slow saturation phase as otherwise expected. Second, the
build-up of a large scale field is demonstrated in a simulation where a
localized magnetic eddy produces field on a larger scale if the eddy possesses
a swirl. Such a set-up might be realizable experimentally through coils.
Finally, new emerging issues regarding the connection between magnetic helicity
and the solar dynamo are discussed. It is demonstrated that dynamos with a
non-local (Babcock-Leighton type) alpha effect can also be catastrophically
quenched, unless there are magnetic helicity fluxes.",0705.3507v1
2007-06-19,Quenched magnetic moment in Mn-doped amorphous Si (\textit{a}-Mn$_{x}$Si$_{1-x}$) across the metal-insulator transition,"The magnetic and electrical transport properties of Mn-doped amorphous
silicon (\textit{a-}Mn$_{x}$Si$_{1-x}$) thin films have been measured. The
magnetic susceptibility obeys the Curie-Weiss law for a wide range of $x$
(0.005-0.175) and the saturation moment is small. While all Mn atoms contribute
to the electrical transport, only a small fraction (interstitial Mn$^{2+}$
states with $J$=$S$=5/2) contribute to the magnetization. The majority of the
Mn atoms do not possess any magnetic moment, contrary to what is predicted by
the Ludwig-Woodbury model for Mn in crystalline silicon. Unlike
\textit{a-}Gd$_{x}$Si$_{1-x}$ films which have an enormous \textit{negative}
magnetoresistance, \textit{a-}Mn$_{x}$Si$_{1-x}$ films have only a small
\textit{positive} magnetoresistance, which can be understood by this quenching
of the Mn moment.",0706.2847v1
2008-02-20,Magnetizing the universe,"The origin of cosmic magnetism is an issue of fundamental importance in
astrophysics. We review here some of the ideas of how large scale magnetic
fields in the universe, particularly in galaxies and galaxy clusters could
arise. The popular paradigm involves the generation of a seed magnetic field
followed by turbulent dynamo amplification of the seed field. We first outline
various seed field generation mechanisms including Biermann batteries. These in
general give a field much smaller than the observed field and so they require
further amplification by dynamo action. The basic idea behind fluctuation
dynamos, as applied to cluster magnetism and the mean-field helical dynamo as
applied to disk galaxies, are outlined. Major difficulties with the dynamo
paradigm are considered. It is particularly important to understand the
nonlinear saturation of dynamos, and whether the fields produced are coherent
enough on large-scales to explain the observed fields in galaxies and clusters.
At the same time the alternative possibility of a primordial field lacks firm
theoretical support but can have very interesting observational consequences.",0802.2804v1
2008-03-25,Magnetic properties of BaCdVO(PO_4)_2: a strongly frustrated spin-1/2 square lattice close to the quantum critical regime,"We report magnetization and specific heat measurements on polycrystalline
samples of BaCdVO(PO_4)_2 and show that this compound is a S=1/2 frustrated
square lattice with ferromagnetic nearest-neighbor (J_1) and antiferromagnetic
next-nearest-neighbor (J_2) interactions. The coupling constants J_1\simeq -3.6
K and J_2\simeq 3.2 K are determined from a fitting of the susceptibility data
and confirmed by an analysis of the saturation field (H_s=4.2 T), the specific
heat, and the magnetic entropy. BaCdVO(PO_4)_2 undergoes magnetic ordering at
about 1 K, likely towards a columnar antiferromagnetic state. We find that
BaCdVO(PO_4)_2 with the frustration ratio \alpha=J_2/J_1\simeq -0.9 is closer
to a critical (quantum spin liquid) region of the frustrated square lattice
than any of the previously reported compounds. Positive curvature of the
magnetization curve is observed in agreement with recent theoretical
predictions for high-field properties of the frustrated square lattice close to
the critical regime.",0803.3535v2
2008-05-02,Commensurate Spin Density Wave in LaOFeAs: A Local Probe Study,"We present a detailed study on the magnetic order in the undoped mother
compound LaOFeAs of the recently discovered Fe-based superconductor
LaO$_{1-x}$F$_x$FeAs. In particular, we present local probe measurements of the
magnetic properties of LaOFeAs by means of $^{57}$Fe M\""ossbauer spectroscopy
and muon spin relaxation in zero external field along with magnetization and
resistivity studies. These experiments prove a commensurate static magnetic
order with a strongly reduced ordered moment of 0.25(5) $\mu_B$ at the iron
site below T_N = 138 K, well separated from a structural phase transition at
T_N = 156 K. The temperature dependence of the sublattice magnetization is
determined and compared to theory. Using a four-band spin density wave model
both, the size of the order parameter and the quick saturation below T_N are
reproduced.",0805.0264v2
2008-08-03,Magnetic and Transport Studies on Electron-doped CeFeAsO1-xFx Superconductor,"The magnetic and transport behaviors of cerium substituted iron oxy-arsenide
superconductor with x = 0.1 to 0.4 fluoride (F) doping have been investigated
in this report. Temperature dependent susceptibility and resistivity
measurements showed the 0.1 F-doped sample (CeFeAsO0.9F0.1) has a
superconducting transition temperature (Tc) of around 30 K. With increasing
doping beyond x = 0.2 Tc saturates to around 40 K. Temperature dependent
susceptibility measured in different magnetic fields for the under-doped sample
showed Meissner effect in low field and the diamagnetism is still visible up to
1 Tesla, with an obvious magnetic transition below 5 K, perhaps originating
from magnetic ordering of the rare earth cerium. The corresponding field
dependent resistance versus temperature measurements indicated a broadening of
less than 3 K for Tc at mid-point by increasing the field to 5 Tesla indicating
rather low anisotropy. An estimated upper critical field of more than 48 Tesla
and accordingly an estimated maximum coherence length of 2.6 nm were obtained
confirming the high upper critical field with a short coherence length for this
superconductor.",0808.0296v1
2008-08-07,The dual role of shear in large-scale dynamos,"The role of shear in alleviating catastrophic quenching by shedding
small-scale magnetic helicity through fluxes along contours of constant shear
is discussed. The level of quenching of the dynamo effect depends on the
quenched value of the turbulent magnetic diffusivity. Earlier estimates that
might have suffered from the force-free degeneracy of Beltrami fields are now
confirmed for shear flows where this degeneracy is lifted. For a dynamo that is
saturated near equipartition field strength those estimates result in a 5-fold
decrease of the magnetic diffusivity as the magnetic Reynolds number based on
the wavenumber of the energy-carrying eddies is increased from 2 to 600.
Finally, the role of shear in driving turbulence and large-scale fields by the
magneto-rotational instability is emphasized. New simulations are presented and
the 3pi/4 phase shift between poloidal and toroidal fields is confirmed. It is
suggested that this phase shift might be a useful diagnostic tool in
identifying mean-field dynamo action in simulations and to distinguish this
from other scenarios invoking magnetic buoyancy as a means to explain migration
away from the midplane.",0808.0959v1
2008-09-30,Magnetization Process of the Classical Heisenberg Model on the Shastry-Sutherland Lattice,"We investigate classical Heisenberg spins on the Shastry-Sutherland lattice
and under an external magnetic field. A detailed study is carried out both
analytically and numerically by means of classical Monte-Carlo simulations.
Magnetization pseudo-plateaux are observed around 1/3 of the saturation
magnetization for a range of values of the magnetic couplings. We show that the
existence of the pseudo-plateau is due to an entropic selection of a particular
collinear state. A phase diagram that shows the domains of existence of those
pseudo-plateaux in the $(h, T)$ plane is obtained.",0809.5249v2
2008-11-26,The Fate of the Sound and Diffusion in Holographic Magnetic Field,"It was shown in arXiv:0810.4094 [hep-th] that in the presence of the magnetic
field the sound waves in (2+1) dimensional plasma disappear and are replaces by
a diffusive mode. Similarly, the shear and charge diffusion fluctuations form a
subdiffusive mode. However, since the limit of small magnetic field does not
commute with the hydrodynamic limit it is not obvious whether or not these
modes are stable under higher order corrections. Using AdS/CFT correspondence
we show that in the case of M2-brane plasma these modes do exist as we find the
corresponding supergravity solutions. This allowed us to compute the
conductivity and the shear viscosity to all orders in magnetic field. We find
that the viscosity to entropy ratio saturates the Kovtun-Son-Starinets bound.
This extends the universality property of the shear viscosity to the case of
the strongly coupled plasma in external magnetic field.",0811.4325v2
2009-01-28,Epitaxial growth and magnetic properties of Sr2CrReO6 thin films,"The double perovskite Sr2CrReO6 is an interesting material for spintronics,
showing ferrimagnetism up to 635 K with a predicted high spin polarization of
about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition
on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum
crystallographic and magnetic properties were obtained by growing at a
substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films
are c-axis oriented, coherently strained, and show less than 20% anti-site
defects. The magnetization curves reveal high saturation magnetization of 0.8
muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic
anisotropy.",0901.4499v1
2009-01-30,Hysteresis and complexity in the zero-temperature mean-field RFIM: the soft-spin version,"We study the energy landscape of the soft-spin random field model in the
mean-field limit and compute analytically the quenched complexity of the
metastable states as a function of their magnetization and energy at a given
external magnetic field. The shape of the domain within which the complexity is
positive (and the number of typical metastable states grows exponentially with
system size) changes with the amount of disorder and becomes non-convex and
disconnected at low disorder. As a consequence, phase transitions occur both at
equilibrium and out of equilibrium along the saturation hysteresis loop. We
focus on the zero complexity curve in the field-magnetization plane and its
relationship with the hysteresis loop. We also study the response of the system
when the magnetization is externally controlled instead of the magnetic field.
The main features of the model that should survive in finite dimensions are
discussed.",0901.4852v1
2009-04-27,Effect of resistance feedback on spin torque-induced switching of nanomagnets,"In large magnetoresistance devices spin torque-induced changes in resistance
can produce GHz current and voltage oscillations which can affect magnetization
reversal. In addition, capacitive shunting in large resistance devices can
further reduce the current, adversely affecting spin torque switching. Here, we
simultaneously solve the Landau-Lifshitz-Gilbert equation with spin torque and
the transmission line telegrapher's equations to study the effects of
resistance feedback and capacitance on magnetization reversal of both spin
valves and magnetic tunnel junctions. While for spin valves parallel (P) to
anti-parallel (AP) switching is adversely affected by the resistance feedback
due to saturation of the spin torque, in low resistance magnetic tunnel
junctions P-AP switching is enhanced. We study the effect of resistance
feedback on the switching time of MTJ's, and show that magnetization switching
is only affected by capacitive shunting in the pF range.",0904.4159v2
2009-09-25,Effect of Fe substitution on magnetocaloric effect in La0.7Sr0.3Mn1-xFexO3 (x = 0 to 0.2),"We have studied the effect of Fe substitution on magnetic and magnetocaloric
properties in La0.7Sr0.3Mn1-xFexO3 (x = 0.05, 0.07, 0.10, 0.15, and 0.20) over
a wide temperature range (T = 10-400 K). It is shown that substitution by Fe
gradually decreases the ferromagnetic Curie temperature (Tc) and saturation
magnetization up to x = 0.15 but a dramatic change occurs for x = 0.2. The x =
0.2 sample can be considered as a phase separated compound in which both
short-range ordered ferromagnetic and antiferromagnetic phases coexist. The
magnetic entropy change (DSm) was estimated from isothermal magnetization
curves and it decreases with increase of Fe content from 4.4 J/KgK at 343 K (x
= 0.05) to 1.3 J/KgK at 105 K (x = 0.2), under H = 5 T. The
La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating
temperature over 60 K range around room temperature with refrigerant capacity
of 225 J/Kg, and magnetic entropy of 4 J/kgK which will be an interesting
compound for application in room temperature refrigeration.",0909.4619v1
2009-10-21,Magnetic properties of the spin-1/2 XXZ model on the Shastry-Sutherland lattice: Effect of long-range interactions,"We study magnetic properties of the $S=1/2$ Ising-like XXZ model on the
Shastry-Sutherland lattices with long-range interactions, using the quantum
Monte Carlo method. This model shows magnetization plateau phases at one-half
and one-third of the saturation magnetization when additional couplings are
considered. We investigate the finite temperature transition to one-half and
one-third plateau phases. The obtained results suggest that the former case is
of the first order and the latter case is of the second order. We also find
that the system undergoes two successive transitions with the 2D Ising model
universality, although there is a single phase transition in the Ising limit
case. Finally, we estimate the coupling ratio to explain the magnetization
process observed in ${\rm TmB_4}$",0910.4162v1
2010-01-21,Magnetic phase transitions in SmCoAsO,"Magnetization, x-ray diffraction and specific-heat measurements reveal that
SmCoAsO undergoes three magnetic phase transitions. A ferromagnetic transition
attributed to the Co ions, emerges at TC=57 K with a small saturation moment of
0.15muB/Co. Reorientation of the Co moment to an antiferromagnetic state is
obtained at TN2=45 K. The relative high paramagnetic effective moment Peff=1.57
MuB/Co indicates an itinerant ferromagnetic state of the Co sublattice. The
third magnetic transition at TN1=5 K is observed clearly in the specific-heat
study only. Both magnetic and 57Fe Mossbauer studies show that substitution of
small quantities of Fe for Co was unsuccessful.",1001.3719v3
2010-04-14,Magnetorotational instability driven dynamos at low magnetic Prandtl numbers,"Numerical simulations of the magnetorotational instability (MRI) with zero
initial net flux in a non-stratified isothermal cubic domain are used to
demonstrate the importance of magnetic boundary conditions.In fully periodic
systems the level of turbulence generated by the MRI strongly decreases as the
magnetic Prandtl number (Pm), which is the ratio of kinematic viscosity and
magnetic diffusion, is decreased. No MRI or dynamo action below Pm=1 is found,
agreeing with earlier investigations. Using vertical field conditions, which
allow the generation of a net toroidal flux and magnetic helicity fluxes out of
the system, the MRI is found to be excited in the range 0.1 < Pm < 10, and that
the saturation level is independent of Pm. In the vertical field runs strong
mean-field dynamo develops and helps to sustain the MRI.",1004.2417v2
2010-05-03,Giant magnetic moment enhancement of nickel nanoparticles embedded in multi-walled carbon nanotubes,"We report a giant magnetic moment enhancement of ferromagnetic nickel
nanoparticles (11 nm) embedded in multi-walled carbon nanotubes. High-energy
synchrotron x-ray diffraction experiment and chemical analysis are used to
accurately determine the ferromagnetic nickel concentration. Magnetic
measurements up to 900 K show an intriguing result-the saturation magnetization
of the nickel nanoparticles embedded in the multi-walled carbon nanotubes is
about 3.4 times as much as the value expected from the measured nickel
concentration while the Curie temperature is the same as that of bulk nickel.
The implication of this giant magnetic moment enhancement, whatever its origin,
is likely to be far reaching-it opens a new avenue for implementing
spin-electronics at the molecular level.",1005.0350v1
2010-06-01,"Synthesis, structural and physical properties of $δ'$-FeSe$_{1-x}$","We report on synthesis, structural characterization, resistivity, magnetic
and thermal expansion measurements on the as yet unexplored $\delta'$-phase of
FeSe$_{1-x}$, here synthesized under ambient- (AP) and high-pressure (HP)
conditions. We show that in contrast to $\beta$-FeSe$_{1-x}$, monophasic
superconducting $\delta'$-FeSe$_{1-x}$ can be obtained in off-stoichiometric
samples with excess Fe atoms preferentially residing in the van der Waals gap
between the FeSe layers. The AP $\delta'$-FeSe$_{1-x}$ sample studied here
($T_c$ $\simeq$ 8.5\,K) possesses an unprecedented residual resistivity ratio
RRR $\simeq$ 16. Thermal expansion data reveal a small feature around
$\sim$90\,K, which resembles the anomaly observed at the structural and
magnetic transitions for other Fe-based superconductors, suggesting that some
kind of ""magnetic state"" is formed also in FeSe. %indicative of a fluctuating
magnetic ordering. For HP samples (RRR $\simeq$ 3), the disorder within the
FeSe layers is enhanced through the introduction of vacancies, the saturated
magnetic moment of Fe is reduced and only spurious superconductivity is
observed.",1006.0073v2
2010-06-08,Effect of pressure on magnetization and magnetostriction jumps in the manganite Eu$_{0.58}$Sr$_{0.42}$MnO$_{3}$,"We have demonstrated the effect of pressure on magnetization jump and its
associated magnetostriction in Eu$_{0.58}$Sr$_{0.42}$MnO$_{3}$. The critical
field lowered by the applied pressure is explained by a suppression of the
metastable blocked state, which is inherent to the phase separated manganite
system exhibiting the magnetic avalanche. To reduce a factor of the bad thermal
coupling in the bulk sample, and to further examine the nature of the
magnetization jump, we have performed the influence of pressure on the
isothermal magnetization of the powder sample. There is no discrepancy in the
critical field between the bulk and powder samples although the $MH$ curve of
the latter is not saturated at high fields. These findings indicate a crucial
role of the frozen phase separated state in the abrupt transition.",1006.1459v3
2010-06-15,PIC Simulations of the Temperature Anisotropy-Driven Weibel Instability: Analyzing the perpendicular mode,"An instability driven by the thermal anisotropy of a single electron species
is investigated in a 2D particle-in-cell (PIC) simulation. This instability is
the one considered by Weibel and it differs from the beam driven filamentation
instability. A comparison of the simulation results with analytic theory
provides similar exponential growth rates of the magnetic field during the
linear growth phase of the instability. We observe in accordance with previous
works the growth of electric fields during the saturation phase of the
instability. Some components of this electric field are not accounted for by
the linearized theory. A single-fluid-based theory is used to determine the
source of this nonlinear electric field. It is demonstrated that the magnetic
stress tensor, which vanishes in a 1D geometry, is more important in this
2-dimensional model used here. The electric field grows to an amplitude, which
yields a force on the electrons that is comparable to the magnetic one. The
peak energy density of each magnetic field component in the simulation plane
agrees with previous estimates. Eddy currents develop, which let the amplitude
of the third magnetic field component grow, which is not observed in a 1D
simulation.",1006.3057v1
2010-12-25,Magnetic Properties and Thermal Entanglement on a Triangulated Kagome Lattice,"The magnetic and entanglement thermal (equilibrium) properties in spin-1/2
Ising-Heisenberg model on a triangulated Kagome lattice are analyzed by means
of variational mean-field like treatment based on Gibbs-Bogoliubov inequality.
Because of the separable character of Ising-type exchange interactions between
the Heisenberg trimers the calculation of quantum entanglement in a
self-consistent field can be performed for each of the trimers individually.
The concurrence in terms of three qubit isotropic Heisenberg model in effective
Ising field is non-zero even in the absence of a magnetic field. The magnetic
and entanglement properties exhibit common (plateau and peak) features
observable via (antferromagnetic) coupling constant and external magnetic
field. The critical temperature for the phase transition and threshold
temperature for concurrence coincide in the case of antiferromagnetic coupling
between qubits. The existence of entangled and disentangled phases in saturated
and frustrated phases is established.",1012.5478v1
2011-03-22,Magnetic Interactions in Ball-Milled Spinel Ferrites,"Spinel Fe3O4 nanoparticles have been produced through ball milling in
methyl-alcohol (CH3OH), aiming to obtain samples with similar average particle
sizes <d> and different interparticle interactions. Three samples having
Fe3O4/CH3(OH) mass ratios R of 3 %, 10 % and 50 % wt. were milled for several
hours until particle size reached a steady value (<d> ~ 7-10 nm). A detailed
study of static and dynamic magnetic properties has been undertaken by
measuring magnetization, ac susceptibility and M\""ossbauer data. As expected
for small particles, the Verwey transition was not observed, but instead
superparamagnetic (SPM) behavior was found with transition to a blocked state
at TB ~ 10-20 K. Spin disorder of the resulting particles, independent of its
concentration, was inferred from the decrease of saturation magnetization MS at
low temperatures. For samples having 3% wt. of magnetic particles, dynamic ac
susceptibility measurements show a thermally activated Arrhenius dependence of
the blocking temperature with applied frequency. This behaviour is found to
change as interparticle interactions begin to rule the dynamics of the system,
yielding a spin-glass-like state at low temperatures for R = 50 wt.% sample.",1103.4390v1
2011-04-08,Magnetic nanocomposites at microwave frequencies,"Most conventional magnetic materials used in the electronic devices are
ferrites, which are composed of micrometer-size grains. But ferrites have small
saturation magnetization, therefore the performance at GHz frequencies is
rather poor. That is why functionalized nanocomposites comprising magnetic
nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm,
and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have
a significant potential for the electronics industry. When the size of the
nanoparticles is smaller than the critical size for multidomain formation,
these nanocomposites can be regarded as an ensemble of particles in
single-domain states and the losses (due for example to eddy currents) are
expected to be relatively small. Here we review the theory of magnetism in such
materials, and we present a novel measurement method used for the
characterization of the electromagnetic properties of composites with
nanomagnetic insertions. We also present a few experimental results obtained on
composites consisting of iron nanoparticles in a dielectric matrix.",1104.1535v1
2011-07-01,Catastrophic quenching in alpha-Omega dynamos revisited,"At large magnetic Reynolds numbers, magnetic helicity evolution plays an
important role in astrophysical large-scale dynamos. The recognition of this
fact led to the development of the dynamical alpha quenching formalism, which
predicts catastrophically low mean fields in open systems. Here we show that in
oscillatory alpha-Omega dynamos this formalism predicts an unphysical magnetic
helicity transfer between scales. An alternative technique is proposed where
this artifact is removed by using the evolution equation for the magnetic
helicity of the total field in the shearing--advective gauge. In the
traditional dynamical alpha quenching formalism, this can be described as an
additional magnetic helicity flux of small-scale fields that does not appear in
homogeneous alpha-squared dynamos. In alpha-Omega dynamos, the alternative
formalism is shown to lead to larger saturation fields than previously obtained
with the traditional formalism.",1107.0238v2
2011-08-31,Multicore magnetite nanoparticles prepared by glass crystallisation and their magnetic properties,"A potassium alumina borosilicate glass with the composition
13K2O*13Al2O3*16B2O3*43SiO2*15Fe2O3-x was melted using Fe2O3 as raw material.
The melt was dumped from a Pt-crucible with a downpipe in water which resulted
in the formation of phase separated droplets with a size of around 100 - 150
nm. In this droplets, magnetite crystals with a size of around 10-20 nm were
observed. These magnetite nanoparticles with superparamagnetic behaviour are
arranged to larger aggregates. This leads to a higher effective magnetic
radius. According to magnetisation measurements the particles show hysteresis.
The ratio of remanent vs. saturation magnetisation is not as high as it is
necessary for uniaxial anisotropy. It is possible to elude the phase
separations by cooking the pulverized glass in concentrated sodium hydroxide.
Additional temperature dependent magnetorelaxometry (TMRX) measurements show in
the distribution of the relaxation of magnetic moments over the course of
temperature two peaks at 13 and 39 K. According to an interparticle distance
smaller than 5 dC (the core diameter) could that be a result of strong magnetic
interactions. Other magnetic relaxation processes also explain this measured
effect.",1108.6201v1
2011-09-19,Axial dipolar dynamo action in the Taylor-Green vortex,"We present a numerical study of the magnetic field generated by the
Taylor-Green vortex. We show that periodic boundary conditions can be used to
mimic realistic boundary conditions by prescribing the symmetries of the
velocity and magnetic fields. This gives insight in some problems of central
interest for dynamos: the possible effect of velocity fluctuations on the
dynamo threshold, the role of boundary conditions on the threshold and on the
geometry of the magnetic field generated by dynamo action. In particular, we
show that an axial dipolar dynamo similar to the one observed in a recent
experiment can be obtained with an appropriate choice of the symmetries of the
magnetic field. The nonlinear saturation is studied and a simple model
explaining the magnetic Prandtl number dependence of the super/sub critical
nature of the dynamo transition is given.",1109.4063v2
2011-11-04,Orthogonal spin arrangement as possible ground state of three - dimensional Shastry - Sutherland network in Ba3Cu3In4O12,"The Ba3Cu3In4O12 stands for unique topology of the magnetic subsystem. It
consists of rotated by 90\Box$^b$ relative to each other ""paper-chain"" columns
made of vertex-sharing CuIO4 and CuIIO4 planar units. The overall pattern of
the copper ions is that of a three-dimensional Shastry-Sutherland network. At
high temperatures, the magnetic susceptibility follows the Curie-Weiss law with
positive Weiss temperature indicating strong predominance of ferromagnetic
coupling. At low temperatures, however, this compound reaches the
antiferromagnetically ordered state and experiences non-trivial succession of
two spin-flop and two spin-flip transitions reaching full saturation in modest
magnetic fields. Here we show that the possible ground state in Ba3Cu3In4O12
can be three-dimensional orthogonal arrangement of the Cu2+ (S = 1/2) magnetic
moments forming three virtually independent antiferromagnetic subsystems. In
this arrangement, favored by anisotropic exchange interactions, the quantum
fluctuations provide the coupling between three mutually orthogonal magnetic
subsystems resulting in an impressive ""order by disorder"" effect.",1111.1186v1
2011-12-13,Magnetic Phase transitions in Plasmas and Transport Barriers,"A model of magnetic phase transitions in plasmas is presented: plasma blobs
with pressure excess or defect are dia- or para-magnets and move radially under
the influence of the background plasma magnetisation. It is found that magnetic
phase separation could be the underlying mechanism of L to H transitions and
drive transport barrier formation. Magnetic phase separation and associated
pedestal build up, as described here, can be explained by the well known
interchange mechanism, now reinterpreted as a magnetisation interchange which
remains relevant even when stable or saturated. A testable necessary criterion
for the L to H transition is presented.",1112.2977v4
2012-03-30,A correlator product state study of molecular magnetism in the giant Keplerate Mo72Fe30,"We have studied the properties of the giant Keplerate molecular magnet
Mo72Fe30, as a function of applied magnetic field, using the correlator product
state (CPS) tensor network ansatz. The magnet is modeled with an S = 5/2
antiferromagnetic Heisenberg Hamiltonian on the 30-site icosidodecahedron
lattice, a model for which exact diagonalization is infeasible. The CPS ansatz
produces significant improvements in variational energies relative to previous
studies using the density matrix renormalization group, a result of its
superior ability to handle strong correlation in two dimensional spin systems.
The CPS results reaffirm that the ground state energies adhere qualitatively to
the parabolic progression of the rotational band model (RBM), but show
important deviations near 1/3 of the saturation field. These deviations predict
anomalous behavior in the differential magnetization and heat capacity that
cannot be explained by the RBM alone. Finally, we show that these energetic
deviations originate from a qualitative change in the ground state that
resembles a finite size analogue of a phase transition.",1203.6883v1
2012-04-04,Martensite-like transition and spin-glass behavior in nanocrystalline Pr0.5Ca0.5MnO3,"We report on isothermal pulsed (20 ms) field magnetization, temperature
dependent AC - susceptibility, and the static low magnetic field measurements
carried out on 10 nm sized Pr0.5Ca0.5MnO3 nanoparticles (PCMO10). The
saturation field for the magnetization of PCMO10 (~ 250 kOe) is found to be
reduced in comparison with that of bulk PCMO (~300 kOe). With increasing
temperature, the critical magnetic field required to 'melt' the residual
charge-ordered phase decays exponentially while the field transition range
broadens, which is indicative of a Martensite-like transition. The AC -
susceptibility data indicate the presence of a frequency-dependent freezing
temperature, satisfying the conventional Vogel-Fulcher and power laws, pointing
to the existence of a spin-glass-like disordered magnetic phase. The present
results lead to a better understanding of manganite physics and might prove
helpful for practical applications.",1204.1014v1
2012-04-08,Two successive field-induced spin-flop transitions in single-crystalline CaCo$_{2}$As$_{2}$,"CaCo$_{2}$As$_{2}$, a ThCr$_{2}$Si$_{2}$-structure compound, undergoes an
antiferromagnetic transition at \emph{T$_{N}$}=76K with the magnetic moments
being aligned parallel to the \emph{c} axis. Electronic transport measurement
reveals that the coupling between conducting carriers and magnetic order in
CaCo$_{2}$As$_{2}$ is much weaker comparing to the parent compounds of iron
pnictide. Applying magnetic field along \emph{c} axis induces two successive
spin-flop transitions in its magnetic state. The magnetization saturation
behaviors with \emph{\textbf{H}$\parallel$c} and \emph{\textbf{H}$\parallel$ab}
at 10K indicate that the antiferromagnetic coupling along \emph{c} direction is
very weak. The interlayer antiferromagntic coupling constant \emph{J$_{c}$} is
estimated to be about 2 meV.",1204.1736v1
2012-04-09,Evidence for spin-flip scattering and local moments in dilute fluorinated graphene,"The issue of whether local magnetic moments can be formed by introducing
adatoms into graphene is of intense research interest because it opens the
window to fundamental studies of magnetism in graphene, as well as of its
potential spintronics applications. To investigate this question we measure, by
exploiting the well-established weak localization physics, the phase coherence
length L_phi in dilute fluorinated graphene. L_phi reveals an unusual
saturation below ~ 10 K, which cannot be explained by non-magnetic origins. The
corresponding phase breaking rate increases with decreasing carrier density and
increases with increasing fluorine density. These results provide strong
evidence for spin-flip scattering and points to the existence of adatom-induced
local magnetic moment in fluorinated graphene. Our results will stimulate
further investigations of magnetism and spintronics applications in
adatom-engineered graphene.",1204.1775v1
2012-05-17,Simulations of Magnetic Field Generation in Unmagnetized Plasmas via Beat Wave Current Drive,"This work describes the scientific basis and associated simulation results
for the magnetization of an unmagnetized plasma via beat wave current drive.
Two-dimensional electromagnetic particle-in-cell simulations have been
performed for a variety of angles between the injected waves to demonstrate
beat wave generation in agreement with theoretical predictions of the beat-wave
wave vector and saturation time, revealing new 2D effects. The simulations
clearly demonstrate electron acceleration by the beat waves and resultant
current drive and magnetic field generation. The basic process depends entirely
on the angle between the parent waves and the ratio of the beat-wave phase
velocity to the electron thermal velocity. The wave to magnetic energy
conversion efficiency of the cases examined is as high as 0.2%. The technique
could enable novel plasma experiments in which the use of magnetic coils is
infeasible.",1205.3920v2
2012-09-01,Incomplete devil's staircase in the magnetization curve of SrCu2(BO3)2,"We report on NMR and torque measurements on the frustrated
quasi-two-dimensional spin-dimer system SrCu2(BO3)2 in magnetic fields up to 34
T that reveal a sequence of magnetization plateaus at 1/8, 2/15, 1/6, and 1/4
of the saturation and two incommensurate phases below and above the 1/6
plateau. The magnetic structures determined by NMR involve a stripe order of
triplets in all plateaus, suggesting that the incommensurate phases originate
from proliferation of domain walls. We propose that the magnetization process
of SrCu2(BO3)2 is best described as an incomplete devil's staircase.",1209.0069v2
2012-09-05,Magnetic Field Amplification Associated with the Richtmyer-Meshkov Instability,"The amplification of a magnetic field due to the Richtmyer-Meshkov
instability (RMI) is investigated by two-dimensional MHD simulations.
Single-mode analysis is adopted to reveal definite relation between the
nonlinear evolution of RMI and the field enhancement. It is found that an
ambient magnetic field is stretched by fluid motions associated with the RMI,
and the strength is amplified significantly by more than two orders of
magnitude. The saturation level of the field is determined by a balance between
the amplified magnetic pressure and the thermal pressure after shock passage.
This effective amplification can be achieved in a wide range of the conditions
for the RMI such as the Mach number of an incident shock and the density ratio
at a contact discontinuity. The results suggest that the RMI could be a robust
mechanism of the amplification of interstellar magnetic fields and cause the
origin of localized strong fields observed at the shock of supernova remnants.",1209.0961v1
2012-09-25,Magnetization of 2.6T in gadolinium thin films,"There is renewed interest in rare-earth elements and gadolinium in particular
for a range of studies in coupling physics and applications. However, it is
still apparent that synthesis impacts understanding of the intrinsic magnetic
properties of thin gadolinium films, particularly for thicknesses of
topicality. We report studies on 50nm thick nanogranular polycrystalline
gadolinium thin films on SiO2 wafers that demonstrate single-crystal like
behavior. The maximum in-plane saturation magnetization at 4K was found to be
4{\pi}MS4K = (2.61{\pm}0.26)T with a coercivity of HC4K = (160{\pm}5)Oe. A
maximum Curie point of TC = (293{\pm}2)K was measured via zero-field-cooled -
field- cooled magnetization measurements in close agreement with values
reported in bulk single crystals. Our measurements revealed magnetic
transitions at T1 = (12{\pm}2)K (as deposited samples) and T2 = (22{\pm}2)K
(depositions on heated substrates) possibly arising from the interaction of
paramagnetic fcc grains with their ferromagnetic hcp counterparts.",1209.5617v1
2012-11-05,Exact asymptotic behavior of magnetic stripe domain arrays,"The classical problem of magnetic stripe domain behavior in films and plates
with uniaxial magnetic anisotropy is treated. Exact analytical results are
derived for the stripe domain widths as function of applied perpendicular
field, $H$, in the regime where the domain period becomes large. The stripe
period diverges as $(H_c-H)^{-1/2}$, where $H_c$ is the critical (infinite
period) field, an exact result confirming a previous conjecture. The
magnetization approaches saturation as $(H_c-H)^{1/2}$, a behavior which
compares excellently with experimental data obtained for a $4 \mu$m thick
ferrite garnet film. The exact analytical solution provides a new basis for
precise characterization of uniaxial magnetic films and plates, illustrated by
a simple way to measure the domain wall energy. The mathematical approach is
applicable for similar analysis of a wide class of systems with competing
interactions where a stripe domain phase is formed.",1211.1366v1
2012-12-03,Successive magnetic phase transitions and multiferroicity in Spin-1 triangular lattice antiferromagnet Ba$_3$NiNb$_2$O$_9$,"We report the magnetic and electric properties of Ba$_3$NiNb$_2$O$_9$, which
is a quasi-two-dimensional spin-1 triangular lattice antiferromagnet (TLAF)
with trigonal structure. At low $T$ and with increasing magnetic field, the
system evolves from a 120 degree magnetic ordering phase (A phase) to an
up-up-down ($uud$) phase (B phase) with a change of slope at 1/3 of the
saturation magnetization, and then to an ""oblique"" phase (C phase).
Accordingly, the ferroelectricity switches on at each phase boundary with
appearance of spontaneous polarization. Therefore, Ba$_3$NiNb$_2$O$_9$ is a
unique TLAF exhibiting both $uud$ phase and multiferroicity.",1212.0485v1
2012-12-04,Spinodal Decomposition of Magnetic Ions in Eu-Codoped Ge/1-x/Cr/x/Te,"We present the experimental evidence for the presence of spinodal
decomposition of the magnetic ions in the Ge/1-x-y/Cr/x/Eu/y/Te samples with
chemical composition varying in the range of 0.015 < x < 0.057 and 0.003 < y <
0.042. The ferromagnetic transition at temperatures 50 < T < 57 K was observed,
independent of the chemical composition. The long-range carrier mediated
itinerant magnetic interactions seem to be responsible for the observed
ferromagnetic order. The magnetic irreversibility with coercive field H/C/ =
5?63 mT and the saturation magnetization M/S/ <? 2?6 emu/g are found to
strongly depend on the chemical composition of the alloy.",1212.0666v1
2012-12-11,Exact ground state of the Shastry-Sutherland lattice with classical Heisenberg spins,"An exact analytical solution of the ground state problem of the isotropic
classical Heisenberg model on the Shastry-Sutherland lattice in external
magnetic field $H$ is found for arbitrary ratio of diagonal to edge exchange
constants $J_2/J_1$. The phase diagram of this model in the ($J_2/J_1, H/J_1$)
plane is presented. It includes spin-flop, spin-flip and umbrella phases. The
magnetization curves are found to be linear until saturation. It is shown
numerically that the inclusion of the easy-axis anisotropy into the model leads
to the appearance of the 1/3 magnetization plateau, corresponding to the
collinear up-up-down spin structure. This explains the appearance of the 1/3
magnetization plateau in rare earth tetraborides RB$_4$. In particular,
magnetization curve of the compound HoB$_4$ is explained.",1212.2320v2
2012-12-13,Material Targets for Scaling All Spin Logic,"All-spin logic devices are promising candidates to augment and complement
beyond-CMOS integrated circuit computing due to non-volatility, ultra-low
operating voltages, higher logical efficiency, and high density integration.
However, the path to reach lower energy-delay product performance compared to
CMOS transistors currently is not clear. We show that scaling and engineering
the nanoscale magnetic materials and interfaces is the key to realizing spin
logic devices that can surpass energy-delay performance of CMOS transistors.
With validated stochastic nano-magnetic and vector spin transport numerical
models, we derive the target material and interface properties for the
nanomagnets and channels. We identified promising new directions for material
engineering/discovery focusing on systematic scaling of magnetic anisotropy
(Hk) with saturation magnetization (Ms), use of perpendicular magnetic
anisotropy, and interface spin mixing conductance of ferromagnet/spin channel
interface (Gmix). We provide systematic targets for scaling spin logic
energy-delay product toward a 2 aJ.ns energy-delay product, comprehending the
stochastic noise for nanomagnets.",1212.3362v1
2012-12-25,"Magnetic properties, Lyapunov exponent and superstability of the spin-1/2 Ising-Heisenberg model on diamond chain","The exactly solvable spin-1/2 Ising-Heisenberg model on diamond chain has
been considered. We have found the exact results for the magnetization by using
recursion relation method. The existence of the magnetization plateau has been
observed at one third of the saturation magnetization in the antiferromagnetic
case. Some ground-state properties of the model are examined. At low
temperatures, the system has two ferrimagnetic (FRI1 and FRI2) phases and one
paramagnetic (PRM) phase. Lyapunov exponents for the various values of the
exchange parameters and temperatures have been analyzed. It have also been
shown that the maximal Lyapunov exponent exhibits plateau. Lyapunov exponents
exhibit different behavior for two ferrimagnetic phases. We have found the
existence of the supercritical point for the multi-dimensional rational mapping
of the spin-1/2 Ising-Heisenberg model on diamond chain for the first time at
absence of the external magnetic field and $T \rightarrow 0$ in the
antiferromagnetic case.",1212.6008v1
2012-12-31,Effects of lateral device size and material properties on the ferromagnetic resonance response of spinwave eigen-modes in magnetic devices,"We analyze the effects of lateral device size and magnetic material
parameters on the ferromagnetic resonance (FMR) response. Results presented are
directly relevant to widely used FMR experimental techniques for extracting
magnetic parameters from thin films, the results of which are often assumed to
carry over to corresponding nanometer-sized patterned devices. We show that
there can be significant variation in the FMR response with device size, and
that the extent of the variation depends on the magnetic material properties.
This explains, for example, why different experiments along these lines have
yielded different size-dependent trends from damping measurements. Observed
trends with increasing size and different material parameters are explained
through the evolution of three distinct eigen-modes, demonstrating the
respective roles of demagnetization and exchange. It is also shown that there
is a crossover of dominant eigen-modes in the response signal, accompanied by
conjugating edge-type modes, leading to evident effects in measured linewidth
and damping. Among the sizes considered, in higher saturation magnetization, we
observe as much as a 40% increase in apparent damping, due solely to device
size variation.",1212.6835v1
2013-01-28,Structural and magnetic properties of Pr-alloyed MnBi nanostructures,"The structural and magnetic properties of Pr-alloyed MnBi (short MnBi-Pr)
nanostructures with a range of Pr concentrations have been investigated. The
nanostructures include thin films having Pr concentrations 0, 2, 3, 5 and 9
atomic percent and melt-spun ribbons having Pr concentrations 0, 2, 4 and 6
percent respectively. Addition of Pr into the MnBi lattice has produced a
significant change in the magnetic properties of these nanostructures including
an increase in coercivity and structural phase transition temperature, and a
decrease in saturation magnetization and anisotropy energy. The highest value
of coercivity measured in the films is 23 kOe and in the ribbons is 5.6 kOe.
The observed magnetic properties are explained as the consequences of competing
ferromagnetic and antiferromagnetic interactions.",1301.6782v1
2013-02-08,Magnetic flux loop in high-energy heavy-ion collisions,"We consider the expectation value of a magnetic flux loop in the immediate
forward light cone of collisions of heavy nuclei at high energies. Such
collisions are characterized by a non-linear scale Q_s where color fields
become strong. We find that loops of area greater than ~2/Q_s^2 exhibit area
law behavior, which determines the scale of elementary flux excitations
(""vortices""). We also estimate the magnetic string tension, sigma_M = 0.12
Q_s^2. By the time t ~ 1/Q_s even small loops satisfy an area law. We describe
corrections to the propagator of semi-hard gluons at very early times in the
background of fluctuating magnetic fields.",1302.2064v4
2013-02-27,Magnetic Hyperthermia with Fe3O4 nanoparticles: the Influence of Particle Size on Energy Absorption,"We have studied the magnetic and power absorption properties of a series of
magnetic nanoparticles (MNPs) of Fe3O4 with average sizes <d> ranging from 3 to
26 nm. Heating experiments as a function of particle size revealed a strong
increase in the specific power absorption (SPA) values for particles with <d> =
25-30 nm. On the other side saturation magnetization MS values of these MNPs
remain essentially constant for particles with <d> above 10 nm, suggesting that
the absorption mechanism is not determined by MS. The largest SPA value
obtained was 130 W/g, corresponding to a bimodal particle distribution with
average size values of 17 and 26 nm.",1302.6912v1
2013-03-05,"Angle-Dependent Spin-Wave Resonance Spectroscopy of (Ga,Mn)As Films","A modeling approach for standing spin-wave resonances based on a
finite-difference formulation of the Landau-Lifshitz-Gilbert equation is
presented. In contrast to a previous study [Bihler et al., Phys. Rev. B 79,
045205 (2009)], this formalism accounts for elliptical magnetization precession
and magnetic properties arbitrarily varying across the layer thickness,
including the magnetic anisotropy parameters, the exchange stiffness, the
Gilbert damping, and the saturation magnetization. To demonstrate the
usefulness of our modeling approach, we experimentally study a set of (Ga,Mn)As
samples grown by low-temperature molecular-beam epitaxy by means of
electrochemical capacitance-voltage measurements and angle-dependent standing
spin-wave resonance spectroscopy. By applying our modeling approach, the angle
dependence of the spin-wave resonance data can be reproduced in a simulation
with one set of simulation parameters for all external field orientations. We
find that the approximately linear gradient in the out-of-plane magnetic
anisotropy is related to a linear gradient in the hole concentrations of the
samples.",1303.1192v1
2013-10-02,Coronal influence on dynamos,"We report on turbulent dynamo simulations in a spherical wedge with an outer
coronal layer. We apply a two-layer model where the lower layer represents the
convection zone and the upper layer the solar corona. This setup is used to
study the coronal influence on the dynamo action beneath the surface.
Increasing the radial coronal extent gradually to three times the solar radius
and changing the magnetic Reynolds number, we find that dynamo action benefits
from the additional coronal extent in terms of higher magnetic energy in the
saturated stage. The flux of magnetic helicity can play an important role in
this context.",1310.0787v1
2013-11-05,Chiral skyrmions in cubic helimagnet films: the role of uniaxial anisotropy,"This paper reports on magnetometry and magnetoresistance measurements of MnSi
epilayers performed in out-of-plane magnetic fields. We present a theoretical
analysis of the chiral modulations that arise in confined cubic helimagnets
where the uniaxial anisotropy axis and magnetic field are both out-of-plane. In
contrast to in-plane field measurements (Wilson et al., Phys. Rev. B 86, 144420
(2012)), the hard-axis uniaxial anisotropy in MnSi/Si(111) increases the energy
of (111)-oriented skyrmions and in-plane helicoids relative to the cone phase,
and makes the cone phase the only stable magnetic texture below the saturation
field. While induced uniaxial anisotropy is important in stabilizing skyrmion
lattices and helicoids in other confined cubic helimagnets, the particular
anisotropy in MnSi/Si(111) entirely suppresses these states in an out-of-plane
magnetic field. However, it is predicted that isolated skyrmions with enlarged
sizes exist in MnSi/Si(111) epilayers in a broad range of out-of-plane magnetic
fields.",1311.1191v2
2013-11-26,Transition from insulating to metallic phase induced by in-plane magnetic field in HgTe quantum wells,"We report transport measurements in HgTe-based quantum wells with well width
of 8 nm, corresponding to quantum spin Hall state, subject to in-plane magnetic
field. In the absence of the magnetic field the local and nonlocal resistances
behave very similar, which confirms the edge state transport in our system. In
the magnetic field, we observe a monotonic decrease of the resistance with
saturation of local resistance, while nonlocal resistance disappears
completely, independent of the gate voltage. We believe that these evidences of
metallic behavior indicate a transition to a gapless two-dimensional phase,
according to theoretical predictions. The influence of disorder on resistivity
properties of HgTe quantum wells under in-plane magnetic field is discussed.",1311.6775v1
2013-12-12,Exact results for a generalized spin-1/2 Ising-Heisenberg diamond chain with the second-neighbor interaction between nodal spins,"The ground state and thermodynamics of a generalized spin-1/2
Ising-Heisenberg diamond chain with the second-neighbor interaction between
nodal spins are calculated exactly using the mapping method based on the
decoration-iteration transformation. Rigorous results for the magnetization,
susceptibility, and heat capacity are investigated in dependence on temperature
and magnetic field for the frustrated diamond spin chain with the
antiferromagnetic Ising and Heisenberg interactions. It is demonstrated that
the second-neighbor interaction between nodal spins gives rise to a greater
diversity of low-temperature magnetization curves, which may include an
intermediate plateau at two-third of the saturation magnetization related to
the classical ferrimagnetic (up-up-up-down-up-up-...) ground state with
translationally broken symmetry besides an intermediate one-third magnetization
plateau reflecting the translationally invariant quantum ferrimagnetic
(monomer-dimer) spin arrangement.",1312.3439v1
2014-02-11,Thermodynamic Properties of the Quantum Spin Liquid Candidate ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ in High Magnetic Fields,"We report measurements of the specific heat and magnetization of single
crystal samples of the spin-1/2 kagome compound ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$
(herbertsmithite), a promising quantum spin-liquid candidate, in high magnetic
fields and at low temperatures. The magnetization was measured up to $\mu_{0}H$
= 55 T at $T$ = 0.4 K, showing a saturation of the weakly interacting impurity
moments in fields above $\sim10$ T. The specific heat was measured down to $T <
0.4$ K in magnetic fields up to 18 T, revealing $T$-linear and $T$-squared
contributions. The $T$-linear contribution is surprisingly large and indicates
the presence of gapless excitations in large applied fields. These results
further highlight the unusual excitation spectrum of the spin liquid ground
state of herbertsmithite.",1402.2693v1
2014-03-26,Manipulation of the magnetic order parameter and the metal-insulator-transition of a manganite thin film with applied elastic stress,"We measured the temperature dependence of the saturation magnetization (Ms)
of a (La1-xPrx)1-yCayMnO3 (x ~ 0.60, y ~ 0.33) film as a function of applied
bending stress. Stress producing a compressive strain of -0.01% along the
magnetic easy axis increased the Curie temperature by ~6 K and the
metal-insulator-transition by ~4 K. Regardless of whether or not stress is
applied to the film, magnetic ordering occurs at temperatures significantly
higher than the metal-insulator-transition temperature. The magnetization of
the sample at the temperature of the metal-insulator-transition is
approximately the site percolation threshold for a two-dimensional spin
lattice.",1403.6755v1
2014-04-08,Almost Perfect Frustration in the Dimer Magnet Ba$_2$CoSi$_2$O$_6$Cl$_2$,"We determined the crystal structure of Ba$_2$CoSi$_2$O$_6$Cl$_2$, which was
synthesized in this work, and investigated its quantum magnetic properties
using single crystals. This compound should be described as a two-dimensionally
coupled spin-1/2 XY-like spin dimer system. Ba$_2$CoSi$_2$O$_6$Cl$_2$ exhibits
a stepwise magnetization process with a plateau at half of the saturation
magnetization, irrespective of the field direction, although all the Co$^{2+}$
sites are equivalent. This indicates that spin triplets are localized owing to
the almost perfect frustration of interdimer exchange interactions. Thus, the
spin states for the zero and 1/2 magnetization-plateau states are almost
exactly given by the simple product of singlet dimers and the alternate product
of singlet and triplet dimers, respectively.",1404.2033v2
2014-05-03,Theory of field-induced quantum phase transition in spin dimer system Ba$_3$Cr$_2$O$_8$,"Motivated by recent experiments on Ba$_3$Cr$_2$O$_8$, we propose a theory
describing low-temperature properties in magnetic field $h$ of dimer
spin-$\frac12$ systems on a stacked triangular lattice with spatially
anisotropic exchange interactions. Considering the interdimer interaction as a
perturbation we derive in the second order the elementary excitations (triplon)
spectrum and the effective interaction between triplons at the quantum critical
point $h=h_c$ separating the paramagnetic phase ($h<h_c$) and a magnetically
ordered one ($h_c<h<h_s$, where $h_s$ is the saturation field). Expressions are
derived for $h_c(T)$ and the staggered magnetization $M_\perp(h)$ at $h$ close
to $h_c$. We apply the theory to Ba$_3$Cr$_2$O$_8$ and determine exchange
constants of the model by fitting the triplon spectrum obtained experimentally.
It is demonstrated that in accordance with experimental data the system follows
the 3D BEC scenario at $T<1$ K only due to a pronounced anisotropy of the
spectrum near its minimum. Our expressions for $h_s$, $h_c(T)$ and $M_\perp(h)$
fit well available experimental data.",1405.0564v1
2014-10-27,Hysteretic Magnetotransport in SmB6 at Low Magnetic Fields,"Utilizing Corbino disc structures, we have examined the magnetic field
response of resistivity for the surface states of SmB6 on different crystalline
surfaces at low temperatures. Our results reveal a hysteretic behavior whose
magnitude depends on the magnetic field sweep rate and temperature. Although
this feature becomes smaller when the field sweep is slower, a complete
elimination or saturation is not observed in our slowest sweep-rate
measurements, which is much slower than a typical magnetotransport trace. These
observations cannot be explained by quantum interference corrections such as
weak anti-localization. Instead, they are consistent with behaviors of glassy
surface magnetic ordering, whose magnetic origin is most likely from samarium
oxide (Sm2O3) forming on the surface during exposure to ambient conditions.",1410.7430v1
2014-11-27,"Magnetism of Hexagonal Mn1.5X0.5Sn (X = Cr, Mn, Fe, Co) Nanomaterials","Mn1.5X0.5Sn (X = Cr, Mn, Fe, Co) nanomaterials in the hexagonal Ni2In-type
crystal structure have been prepared using arc-melting and melt spinning. All
the rapidly quenched Mn1.5X0.5Sn alloys show moderate saturation magnetizations
with the highest value of 458 emu/cm3 for Mn1.5Fe0.5Sn, but their Curie
temperatures are less than 300 K. All samples except the Cr containing one show
spin-glass-like behavior at low temperature. The magnetic anisotropy constants
calculated from the high-field magnetization curves at 100 K are on the order
of 1 Merg/cm3. The vacuum annealing of the ribbons at 550 oC significantly
improved their magnetic properties with the Curie temperature increasing from
206 K to 273 K for Mn1.5Fe0.5Sn.",1411.7689v1
2014-12-09,Low-temperature ordered phases of the spin-$\frac{1}{2}$ XXZ chain system Cs$_2$CoCl$_4$,"In this study the magnetic order of the spin-1/2 XXZ chain system
Cs$_2$CoCl$_4$ in a temperature range from 50 mK to 0.5 K and in applied
magnetic fields up to 3.5 T is investigated by high-resolution measurements of
the thermal expansion and the specific heat. Applying magnetic fields along a
or c suppresses $T_\textrm{N}$ completely at about 2.1 T. In addition, we find
an adjacent intermediate phase before the magnetization saturates close to 2.5
T. For magnetic fields applied along b, a surprisingly rich phase diagram
arises. Two additional transitions are observed at critical fields $\mu_0
H_{SF1}\simeq 0.25$ T and $\mu_0 H_{SF2}\simeq 0.7$ T, which we propose to
arise from a two-stage spin-flop transition.",1412.2988v1
2014-12-17,Collinear order in a frustrated three-dimensional spin-$\frac12$ antiferromagnet Li$_2$CuW$_2$O$_8$,"Magnetic frustration in three dimensions (3D) manifests itself in the
spin-$\frac12$ insulator Li$_2$CuW$_2$O$_8$. Density-functional band-structure
calculations reveal a peculiar spin lattice built of triangular planes with
frustrated interplane couplings. The saturation field of 29 T contrasts with
the susceptibility maximum at 8.5 K and a relatively low N\'eel temperature
$T_N\simeq 3.9$ K. Magnetic order below $T_N$ is collinear with the propagation
vector $(0,\frac12,0)$ and an ordered moment of 0.65(4) $\mu_B$ according to
neutron diffraction data. This reduced ordered moment together with the low
maximum of the magnetic specific heat ($C^{\max}/R\simeq 0.35$) pinpoint strong
magnetic frustration in 3D. Collinear magnetic order suggests that quantum
fluctuations play crucial role in this system, where a non-collinear spiral
state would be stabilized classically.",1412.5578v2
2015-02-16,"Giant magnetocaloric effect, magnetization plateaux and jumps of the regular Ising polyhedra","Magnetization process and adiabatic demagnetization of the antiferromagnetic
Ising spin clusters with the shape of regular polyhedra (Platonic solids) are
exactly examined within the framework of a simple graph-theoretical approach.
While the Ising cube as the only unfrustrated (bipartite) spin cluster shows
just one trivial plateau at zero magnetization, the other regular Ising
polyhedra (tetrahedron, octahedron, icosahedron and dodecahedron) additionally
display either one or two intermediate plateaux at fractional values of the
saturation magnetization. The nature of highly degenerate ground states
emergent at intermediate plateaux owing to a geometric frustration is
clarified. It is evidenced that the regular Ising polyhedra exhibit a giant
magnetocaloric effect in a vicinity of magnetization jumps, whereas the Ising
octahedron and dodecahedron belong to the most prominent geometrically
frustrated spin clusters that enable an efficient low-temperature refrigeration
by the process of adiabatic demagnetization.",1502.04449v1
2015-02-27,Accurate calculation of the transverse anisotropy in perpendicularly magnetized multilayers,"The transverse anisotropy constant and the related D\""oring mass density are
key parameters of the one-dimensional model to describe the motion of magnetic
domain walls. So far, no general framework is available to determine these
quantities from static characterizations such as magnetometry measurements.
Here, we derive a universal analytical expression to calculate the transverse
anisotropy constant for the important class of perpendicular magnetic
multilayers. All the required input parameters of the model, such as the number
of repeats, the thickness of a single magnetic layer, and the layer
periodicity, as well as the effective perpendicular anisotropy, the saturation
magnetization, and the static domain wall width are accessible by static sample
characterizations. We apply our model to a widely used multilayer system and
find that the effective transverse anisotropy constant is a factor 7 different
from the when using the conventional approximations, showing the importance of
using our analysis scheme.",1502.07937v1
2015-03-11,Investigation of Magnetic Domain Structure in Bi0.7Dy0.3FeO3 thin films integrated with ZnO film,"The magnetic domain structure of the multiferroic Bi1-xDyxFeO3 (BDFO)
deposited on ZnO at the macroscopic level has been demonstrated in this paper.
Magnetic properties are observed by saturated magnetic and ferroelectric
hysteresis loops at room temperature. The coupling behaviour and magnetic
transition are verified using Multimode Atomic Force Microscope by applying
bias between sample and MFM tip. ZnO thin film of 300 nm was deposited by
dielectric sputtering using a ZnO target on Si p-type conducting (.0001-0005
{\Omega} cm) substrate. BDFO thin films of 300 nm were deposited on Si/ZnO
using PLD (Pulsed laser deposition) technique. It is observed that BDFO thin
films integrated with ZnO film shows the coexistence of ferromagnetic and
ferroelectric ordering with significant coupling at room temperature.
Integration of BDFO films with ZnO piezoelectric thin film shows the potential
in MEMS applications as well as in Memory devices and strong history dependent
systems.",1503.03237v1
2015-06-20,Effect of Sintering Temperature on Structural and Magnetic Properties of Ni0.6Zn0.4Fe2O4 Ferrite: Synthesized from Nanocrystalline Powders,"The effect of sintering temperatures (Ts) on the structural and magnetic
properties of Ni0.6Zn0.4Fe2O4 (NZFO) ferrites synthesized by conventional
double sintering method has been reported. The samples are sintered at 1200,
1250 and 1300 {\deg}C. The X-ray diffraction (XRD) analysis reveals the
formation of a single phase cubic spinel structure of the sample. The magnetic
parameters such as saturation magnetization, Ms; coercive field, Hc; remanent
magnetization, Mr and Bohr magneton, {\mu}B are determined and well compared
with reported values. The obtained values are found to be 71.94 emu/gm and 1.2
Oe for Ms and Hc, respectively at Ts=1300 oC. Curie temperature (Tc) at various
Ts has also been calculated. It is noteworthy to note that the sample with a
very low Hc could be used in transformer core and inductor applications.",1506.06280v2
2015-06-27,Do Magnetic Fields Destroy Black Hole Accretion Disk g-Modes?,"Diskoseismology, the theoretical study of normal mode oscillations in
geometrically thin, optically thick accretion disks, is a strong candidate to
explain some QPOs in the power spectra of many black hole X-ray binary systems.
The existence of g-modes, presumably the most robust and visible of the modes,
depends on general relativistic gravitational trapping in the hottest part of
the disk. As the existence of the required cavity in the presence of magnetic
fields has been put into doubt by theoretical calculations, we will explore in
greater generality what the inclusion of magnetic fields has to say on the
existence of g-modes. We use an analytical perturbative approach on the
equations of MHD to assess the impact of such effects. Our main conclusion is
that there appears to be no compelling reason to discard g-modes. In
particular, the inclusion of a non-zero {\it radial} component of the magnetic
field enables a broader scenario for cavity non-destruction, especially taking
into account recent simulations' saturation values for the magnetic field.",1506.08314v1
2015-09-02,Magnetization Jump in the Magnetization Process of the spin-1/2 Heisenberg Antiferromagnet on a Distorted Square-Kagome Lattice,"We study the magnetization process of the spin-$1/2$ Heisenberg
antiferromagnet on a distorted square-kagome lattice by the
numerical-diagonalization method. The magnetization jump at one-third of the
height of the saturation is examined in detail; we find that the jump becomes
larger when a small distortion is switched on and that it is accompanied by an
abrupt change in lines along microscopic spin directions. Our finite-size
results successfully confirm that the magnetization jump in a spin-isotropic
system is a macroscopic jump that survives in the thermodynamic limit and that
the changes in spin directions are common to a spin-flop phenomenon observed in
spin-anisotropic systems.",1509.00587v1
2015-10-16,Effect of monomer-monomer interactions on the phase diagrams of the S=1/2 distorted diamond type quantum spin chain,"By use of mainly the exact diagonalization and the level spectroscopy method,
we investigate the ground-state phase diagrams of the $S=1/2$ distorted diamond
type quantum spin chain with the monomer-monomer interactions and/or
ferromagnetic interactions for the zero magnetic field case, as well as the
$M=M_{\rm s}/3$ case and the $M=(2/3)M_{\rm s}$ case, where $M$ is the total
magnetization and $M_{\rm s}$ is the saturation magnetization. The
magnetization plateau at $M=M_{\rm s}/3$ vanishes in the region where the
ferromagnetic interaction is rather strong. The monomer-monomer interaction
remarkably stabilizes the magnetization plateau at $M=(2/3)M_{\rm s}$.",1510.04913v1
2015-11-05,Perpendicular standing spin wave and magnetic anisotropic study on amorphous FeTaC films,"Magnetic anisotropy, spin wave (SW) excitation and exchange stiffness
constant of amorphous FeTaC ($d$ = 20-200 nm) films were studied as a function
of thickness using micro-strip ferromagnetic resonance (MS-FMR) technique. The
MS-FMR spectra for in-plane applied magnetic field show the presence of uniform
precessional mode ($n$ = 0) along with first perpendicular standing spin wave
(PSSW) mode ($n$ = 1) especially for $d$ = 50, 100 and 200 nm films. The
angular ($\varphi_{H}$) dependence of resonance field ($H_{r}$) and magnetic
field dependence of resonance frequencies ($f_{r}$) in planar configuration for
the uniform and PSSW modes were modeled successfully by using dispersion
relation which arises from a combination of exchange and dipolar interactions.
The relevant parameters such as saturation magnetization ($4\pi M_{S}$),
uniaxial anisotropic constant ($K_{u}$), $g$-factor, and exchange stiffness
constants ($A_{ex}$) are estimated for different FeTaC film thickness. $A_{ex}$
is found to increase from 1.52(4)$\times$10$^{-7}$ to 5.0(5)$\times$10$^{-6}$
erg/cm as the thickness of film increases from 50 to 200 nm, possibly due to
surface pinning effect or significant inhomogeneity especially at higher
thickness films.",1511.01722v2
2015-11-24,Ferromagnetic Resonance of a YIG film in the Low Frequency Regime,"An improved method for characterizing the magnetic anisotropy of films with
cubic symmetry is described and is applied to an yttrium iron garnet (111)
film. Analysis of the FMR spectra performed both in-plane and out-of-plane from
0.7 to 8 GHz yielded the magnetic anisotropy constants as well as the
saturation magnetization. The field at which FMR is observed turns out to be
quite sensitive to anisotropy constants (by more than a factor ten) in the low
frequency (< 2 GHz) regime and when the orientation of the magnetic field is
nearly normal to the sample plane; the restoring force on the magnetization
arising from the magnetocrystalline anisotropy fields is then comparable to
that from the external field, thereby allowing the anisotropy constants to be
determined with greater accuracy. In this region, unusual dynamical behaviors
are observed such as multiple resonances and a switching of FMR resonance with
only a 1 degree change in field orientation at 0.7 GHz.",1511.07892v1
2015-12-16,The generation of magnetic fields by the Biermann battery and the interplay with the Weibel instability,"An investigation of magnetic fields generated in an expanding bubble of
plasma with misaligned temperature and density gradients (driving the Biermann
battery mechanism) is performed. With gradient scales $L$, large-scale magnetic
fields are generated by the Biermann battery mechanism with plasma $\beta \sim
1$, as long as $L$ is comparable to the ion inertial length $d_i$. For larger
system sizes, $L/d_e > 100$ (where $d_e$ is the electron inertial length), the
Weibel instability generates magnetic fields of similar magnitude but with
wavenumber $k d_e \sim 0.2$. In both cases, the growth and saturation of these
fields have a weak dependence on mass ratio $m_i/m_e$, indicating electron
mediated physics. A scan in system size is performed at $m_i/m_e = 2000$,
showing agreement with previous results with $m_i/m_e = 25$. In addition, the
instability found at large system sizes is quantitatively demonstrated to be
the Weibel instability. Furthermore, magnetic and electric energy spectra at
scales below the electron Larmor radius are found to exhibit power law behavior
with spectral indices $-16/3$ and $-7/3$, respectively.",1512.05158v2
2016-01-04,Influence of magnetic quantum confined Stark effect on the spin lifetime of indirect excitons,"We report on the unusual and counter-intuitive behaviour of spin lifetime of
excitons in coupled semiconductor quantum wells (CQWs) in the presence of
in-plane magnetic field. Instead of conventional acceleration of spin
relaxation due to the Larmor precession of electron and hole spins we observe a
strong increase of the spin relaxation time at low magnetic fields followed by
saturation and decrease at higher fields. We argue that this non-monotonic spin
relaxation dynamics is a fingerprint of the magnetic quantum confined Stark
effect. In the presence of electric field along the CQW growth axis, an applied
magnetic field efficiently suppresses the exciton spin coherence, due to
inhomogeneous broadening of the $g$-factor distribution.",1601.00427v1
2016-02-08,Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB_4,"We study TmB_4, a frustrated magnet on the Archimedean Shastry-Sutherland
lattice, through magnetization and transport experiments. The lack of
anisotropy in resistivity shows that TmB_4 is an electronically
three-dimensional system. The magnetoresistance (MR) is hysteretic at
low-temperature even though a corresponding hysteresis in magnetization is
absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE)
and is linear above saturation despite a large MR. We propose that complex
structures at magnetic domain walls may be responsible for the hysteretic MR
and may also lead to the AHE.",1602.02679v2
2016-04-21,Achieving sub-shot-noise sensing at finite temperatures,"We investigate sensing of magnetic fields using quantum spin chains at finite
temperature and exploit quantum phase crossovers to improve metrological bounds
on the estimation of the chain parameters. In particular, we analyze the $ XX $
spin chain and show that the magnetic sensitivity of this system is dictated by
its adiabatic magnetic susceptibility, which scales extensively (linearly) in
the number of spins $ N $. Next, we introduce an iterative feedforward protocol
that actively exploits features of quantum phase crossovers to enable
super-extensive scaling of the magnetic sensitivity. Moreover, we provide
experimentally realistic observables to saturate the quantum metrological
bounds. Finally, we also address magnetic sensing in the Heisenberg $ XY $ spin
chain.",1604.06400v2
2016-04-28,"Magnetization Saturation Process in the Magnonic Anti-dot Structures Based on (Ga,Mn)As: A Magnetometric Study","Applicability of dilute magnetic semiconductors (DMS) in electronic devices
relies upon the understanding and control of their magnetic anisotropy. This
paper explores one of the ways in engineering magnetic anisotropy in epitaxial
layers of DMS by forming them into magnonic structures. For this purpose the
canonical ferromagnetic DMS, namely (Ga,Mn)As, is employed. The anti-dot
systems based on (Ga,Mn)As layers of various thicknesses are fabricated with
focused ion beam apparatus and studied by means of microscopy as well as
magnetometry. The magnetometric data - collected along two nonequivalent
in-plane crystallographic directions of (Ga,Mn)As: [110] and [1-10] - shows the
effect of structuring on high-field magnetization process, whereas no
significant change of the width of hysteresis loop in anti-dot samples is
observed.",1604.08607v1
2016-05-09,Self-heating effects of the surface oxidized FeCo nanoparticles colloid under alternating magnetic field,"To evaluate the self-heating effects of FeCo magnetic nanoparticles, the
surface oxidized FeCo nanoparticles were synthesized by co-precipitation method
with the reduction reaction without any post treatments. As-synthesized FeCo
nanoparticles exhibited the mean diameter of about 39 nm with the oxidized
shell thickness of about 4-5 nm. The saturation magnetization and coercivity
were obtained 172 emu/g and 268 Oe at 300 K, respectively. The heat elevation
of the FeCo magnetic colloid was measured under alternating magnetic fields of
76, 102, and 127 Oe with selectable frequencies of 190, 250 and 355 kHz. The
heat temperature increased up to about 45 oC from initial temperature of 24 oC
under 127 Oe and 355 kHz, which the specific absorption exhibited about 35.7
W/g.",1605.02806v1
2016-05-25,Effect of further-neighbor interactions on the magnetization behaviors of the Ising model on a triangular lattice,"In this work, we study the magnetization behaviors of the classical Ising
model on the triangular lattice using Monte Carlo simulations, and pay
particular attention to the effect of further-neighbor interactions. Several
fascinating spin states are identified to be stabilized in certain magnetic
field regions, respectively, resulting in the magnetization plateaus at 2/3,
5/7, 7/9 and 5/6 of the saturation magnetization MS, in addition to the well
known plateaus at 0, 1/3 and 1/2 of MS. The stabilization of these interesting
orders can be understood as the consequence of the competition between Zeeman
energy and exchange energy.",1605.07794v1
2016-06-30,Magnetic flux stabilizing thin accretion disks,"We calculate the minimal amount of large-scale poloidal magnetic field that
has to thread the inner, radiation-over-gas pressure dominated region of a thin
disk for its thermal stability. Such a net field amplifies the magnetization of
the saturated turbulent state and makes it locally stable. For a $10 M_\odot$
black hole the minimal magnetic flux is $10^{24}(\dot M/\dot M_{\rm
Edd})^{20/21}\,\rm G\cdot cm^{2}$. This amount is compared with the amount of
uniform magnetic flux that can be provided by the companion star -- estimated
to be in the range $10^{22}-10^{24}\,\rm G\cdot cm^2$. If accretion rate is
large enough, the companion is not able to provide the required amount and such
a system, if still sub-Eddington, must be thermally unstable. The peculiar
variability of GRS 1915+105, an X-ray binary with the exceptionally high BH
mass and near-Eddington luminosity, may result from the shortage of large scale
poloidal field of uniform polarity.",1606.09566v1
2016-07-25,Particles trajectories in Weibel magnetic filaments with a flow-aligned magnetic field,"For a Weibel shock to form, two plasma shells have to collide and trigger the
Weibel instability. At saturation, this instability generates in the
overlapping region magnetic filaments with peak field $B_f$. In the absence of
an external guiding magnetic field, these filaments can block the incoming
flow, initiating the shock formation, if their size is larger than the Larmor
radius of the incoming particles in the peak field. Here we show that this
results still holds in the presence of an external magnetic field $B_0$,
provided it is not too high. Yet, for $B_0 \gtrsim B_f/2$, the filaments become
unable to stop any particle, regardless of its initially velocity.",1607.07442v1
2016-09-29,Magnetotransport properties and evidence of topological insulating state in LaSbTe,"In this report, we present the magnetotransport and magnetization properties
of LaSbTe single crystals. Magnetic field-induced turn-on behavior and
low-temperature resistivity plateau have been observed. By adopting both
metal-semiconductor crossover and Kohler scaling analysis, we have discussed
the possible origin of the temperature and magnetic field dependence of
resistivity. At 5 K and 9 T, a large, non-saturating transverse
magnetoresistance (MR) $\sim$ 5$\times$10$^{3}$ \% has been obtained. The MR
shows considerable anisotropy, when the magnetic field is applied along
different crystallographic directions. The non-linear field dependence of the
Hall resistivity confirms the presence of two types of charge carriers. From
the semiclassical two-band fitting of Hall conductivity and longitudinal
conductivity, very high carrier mobilities and almost equal electron and hole
densities have been deduced, which result in large MR. The Fermi surface
properties have been analyzed from de Haas-van Alphen oscillation. From the
magnetization measurement, the signature of non-trivial surface state has been
detected, which confirms that LaSbTe is a topological insulator, consistent
with the earlier first-principles calculations.",1609.09397v3
2016-12-14,"Exactly solved mixed spin-(1,1/2) Ising-Heisenberg distorted diamond chain","The mixed spin-(1,1/2) Ising-Heisenberg model on a distorted diamond chain
with the spin-1 nodal atoms and the spin-1/2 interstitial atoms is exactly
solved by the transfer-matrix method. An influence of the geometric spin
frustration and the parallelogram distortion on the ground state,
magnetization, susceptibility and specific heat of the mixed-spin
Ising-Heisenberg distorted diamond chain are investigated in detail. It is
demonstrated that the zero-temperature magnetization curve may involve
intermediate plateaus just at zero and one-half of the saturation
magnetization. The temperature dependence of the specific heat may have up to
three distinct peaks at zero magnetic field and up to four distinct peaks at a
non-zero magnetic field. The origin of multipeak thermal behavior of the
specific heat is comprehensively studied.",1612.04841v1
2017-03-28,Temperature dependent magnetic damping of yttrium iron garnet spheres,"We investigate the temperature dependent microwave absorption spectrum of an
yttrium iron garnet sphere as a function of temperature (5 K to 300 K) and
frequency (3 GHz to 43.5 GHz). At temperatures above 100 K, the magnetic
resonance linewidth increases linearly with temperature and shows a
Gilbert-like linear frequency dependence. At lower temperatures, the
temperature dependence of the resonance linewidth at constant external magnetic
fields exhibits a characteristic peak which coincides with a non-Gilbert-like
frequency dependence. The complete temperature and frequency evolution of the
linewidth can be modeled by the phenomenology of slowly relaxing rare-earth
impurities and either the Kasuya-LeCraw mechanism or the scattering with
optical magnons. Furthermore, we extract the temperature dependence of the
saturation magnetization, the magnetic anisotropy and the g-factor.",1703.09444v2
2017-05-26,Static and Dynamic Magnetic Properties of FeMn/Pt Multilayers,"Recently we have demonstrated the presence of spin-orbit toque in FeMn/Pt
multilayers which, in combination with the anisotropy field, is able to rotate
its magnetization consecutively from 0o to 360o without any external field.
Here, we report on an investigation of static and dynamic magnetic properties
of FeMn/Pt multilayers using combined techniques of magnetometry, ferromagnetic
resonance, inverse spin Hall effect and spin Hall magnetoresistance
measurements. The FeMn/Pt multilayer was found to exhibit ferromagnetic
properties, and its temperature dependence of saturation magnetization can be
fitted well using a phenomenological model by including a finite distribution
in Curie temperature due to subtle thickness variations across the multilayer
samples. The non-uniformity in static magnetic properties is also manifested in
the ferromagnetic resonance spectra, which typically exhibit a broad resonance
peak. A damping parameter of around 0.106 is derived from the frequency
dependence of ferromagnetic resonance linewidth, which is comparable to the
reported values for other types of Pt-based multilayers. Clear inverse spin
Hall signals and spin Hall magnetoresistance have been observed in all samples
below the Curie temperature, which corroborate the strong spin-orbit torque
effect observed previously.",1705.09423v1
2017-05-30,Heteroepitaxial growth of tetragonal Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ (0 $\leqslant$ x $\leqslant$ 1.2) Heusler films with perpendicular magnetic anisotropy,"This work reports on the structural and magnetic properties of
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ Heusler films with different Fe content x (0
$\leqslant$ x $\leqslant$ 1.2). The films were deposited heteroepitaxially on
MgO single crystal substrates, by magnetron sputtering.
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films with the thickness of 35 nm were
crystallized in tetragonal D0$_{22}$ structure with (001) preferred
orientation. Tunable magnetic properties were achieved by changing the Fe
content x. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ thins films exhibit high uniaxial
anisotropy Ku $\geqslant$ 1.4 MJ/m3, coercivity from 0.95 to 0.3 T and
saturation magnetization from 290 to 570 kA/m. The film with
Mn$_{1.6}$Fe$_{1.1}$Ga$_{1.3}$ composition shows high Ku of 1.47 MJ/m3 and
energy product ${(BH)_{max}}$ of 37 kJ/m3, at room temperature. These findings
demonstrate that Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films have promising properties
for mid-range permanent magnet and spintronic applications.",1705.10668v1
2017-10-03,d-zero Magnetism in Nanoporous Amorphous Alumina Membranes,"Nanoporous alumina membranes produced by mild or hard anodisation in oxalic
acid at potentials ranging from 5 - 140 V have a controllable pore surface area
of up to 200 times the membrane area. They exhibit a saturating magnetic
response that is temperature-independent and almost anhysteretic below room
temperature. The magnetism cannot be explained by the ~1 ppm of
transition-metal impurities present in the membranes. The magnetic moment
increases with the area of the open nanopores, reaching values of 0.6 Bohr
magnetons per square nanometer for mild anodisation and 8 muB/nm2 for hard
anodisation where the growth rate is faster. Crystallization of the membrane or
chemical treatment with salicylic acid reduces the effect by up to 90 %. The
magnetism is therefore associated with the open pore surfaces of the amorphous
Al2O3, and it is independent of the orientation of the applied field with
respect to the membrane surface. Possible explanations in terms of electrons
associated with oxygen vacancies (F or F+ centres) are discussed and it is
concluded that the effect is due to giant orbital paramagnetism rather than
collective ferromagnetic spin order.",1710.01232v2
2017-11-19,Room-temperature observation and current control of skyrmions in Pt/Co/Os/Pt thin films,"We report the observation of room-temperature magnetic skyrmions in
Pt/Co/Os/Pt thin-film heterostructures and their response to electric currents.
The magnetic properties are extremely sensitive to inserting thin Os layers
between the Co-Pt interface resulting in reduced saturation magnetization,
magnetic anisotropy and Curie temperature. The observed skyrmions exist in a
narrow temperature, applied-field and layer-thickness range near the
spin-reorientation transition from perpendicular to in-plane magnetic
anisotropy. The skyrmions have an average diameter of 2.3{\mu}m and transport
measurements demonstrate these features can be displaced with current densities
as low as J = 2x10^4 A/cm^2 and display a skyrmion Hall effect.",1711.07101v1
2017-11-26,Magnetization and Thermal Entanglement of the Spin-1 Ising-Heisenberg Polymer Chain,"We establish a solvable Heisenberg-Ising model on a spin-1 Ni-containing
polymer chain, $[Ni (NN'-dmen) (\mu-N_3)_2]$, with $NN'-dmen$ being
$NN'-dimethylethylenediamine$, that fully covers the interaction
characteristics of the material and by which, we can characterize all the
peculiar magnetic features of the polymer, which has been partly studied in
experiment. By purely analytical calculations, we can see that the
magnetization exhibits three plateaus at zero, mid, and 3/4 of the saturation
value at low temperatures below 2 K. The corresponding featuring peaks of
magnetic susceptibility are clearly shown. The model also displays plateaus in
thermal entanglement that captures the one-to-one correspondence between
thermal entanglement plateaus and those of the magnetization. The calculations
are done by the transfer matrix technique.",1711.09350v1
2018-04-18,Large perpendicular magnetic anisotropy in epitaxial Fe/MgAl2O4(001) heterostructures,"We investigated perpendicular magnetic anisotropy (PMA) and related
properties of epitaxial Fe (0.7 nm)/MgAl2O4(001) heterostructures prepared by
electron-beam evaporation. Using an optimized structure, we obtained a large
PMA energy ~1 MJ/m3 at room temperature, comparable to that in
ultrathin-Fe/MgO(001) heterostructures. Both the PMA energy and saturation
magnetization show weak temperature dependence, ensuring wide working
temperature in application. The effective magnetic damping constant of the 0.7
nm Fe layer was ~0.02 using time-resolved magneto-optical Kerr effect. This
study demonstrates capability of the Fe/MgAl2O4 heterostructure for
perpendicular magnetic tunnel junctions, as well as a good agreement with
theoretical predictions.",1804.06526v2
2018-06-18,Magnetic properties of cobalt doped ZrO$_2$ nanoparticles: Evidence of Co segregation,"We synthesized pure and Co-doped (6.25 12.5 at.) ZrO$_2$ nanopowders in order
to study their magnetic properties.We analyzed magnetic behavior as a function
of the amount of Co and the oxygenation, which was controlled by low pressure
thermal treatments. As prepared pure and Co-doped samples are diamagnetic and
paramagnetic respectively. Ferromagnetism can be induced by performing low
pressure thermal treatments, which becomes stronger as the dwell time of the
thermal treatment is increased. This behavior can be reversed, recovering the
initial diamagnetic or paramagnetic behavior, by performing reoxidizing thermal
treatments. Also, a cumulative increase can be observed in the saturation of
the magnetization with the number of low pressure thermal treatments performed.
We believe that this phenomenon indicates that cobalt segregation induced by
the thermal treatments is the responsible for the magnetic properties of the
ZrO$_2$ Co system.",1806.06839v1
2018-07-23,Magnetization curves and low-temperature thermodynamics of two spin-1/2 Heisenberg edge-shared tetrahedra,"A full energy spectrum, magnetization and susceptibility of a spin-1/2
Heisenberg model on two edge-shared tetrahedra are exactly calculated by
assuming two different coupling constants. It is shown that a ground state in
zero field is either a singlet or a triplet state depending on a relative
strength of both coupling constants. Low-temperature magnetization curves may
exhibit three different sequences of intermediate plateaux at the following
fractional values of the saturation magnetization: 1/3-2/3-1, 0-1/3-2/3-1 or
0-2/3-1. The inverse susceptibility displays a marked temperature dependence
significantly influenced by a character of the zero-field ground state. The
obtained theoretical results are confronted with recent high-field
magnetization data of the mineral crystal fedotovite K2Cu3(SO4)3.",1807.08821v1
2018-09-25,Feasibility of imaging using Boltzmann polarization in nuclear Magnetic Resonance Force Microscopy,"We report on Magnetic Resonance Force Microscopy measurements of the
Boltzmann polarization of the nuclear spins in copper by detecting the
frequency shift of a soft cantilever. We use the time-dependent solution of the
Bloch equations to derive a concise equation describing the effect of rf
magnetic fields on both on- and off-resonant spins in high magnetic field
gradients. We then apply this theory to saturation experiments performed on a
100 nm thick layer of copper, where we use the higher modes of the cantilever
as source of the rf field. We demonstrate a detection volume sensitivity of
only (40 nm)$^3$, corresponding to about 1.6$\cdot 10^4$ polarized copper
nuclear spins. We propose an experiment on protons where, with the appropriate
technical improvements, frequency-shift based magnetic resonance imaging with a
resolution better than (10 nm)$^3$ could be possible. Achieving this resolution
would make imaging based on the Boltzmann polarization competitive with the
more traditional stochastic spin-fluctuation based imaging, with the
possibility to work at milliKelvin temperatures.",1809.09351v1
2018-11-03,Ferromagnetic resonance in the complex permeability of an Fe$_3$O$_4$ nanosuspension at radio and microwave frequencies,"The complex permeability of an iron-oxide nanosuspension has been measured as
a function of magnetic field strength at RF and microwave frequencies using a
loop-gap resonator. The particles were suspended in water and had an 8-nm
diameter Fe$_3$O$_4$ core that was coated by Dextran. The real part of the
permeability increased sharply beyond a frequency-dependent threshold value of
the static magnetic field before saturating. Just beyond this threshold field,
there was a peak in the imaginary part of the permeability. The permeability
measurements, which exhibited features associated with ferromagnetic resonance,
were used to determine the dependence of the microwave absorption on static
magnetic field strength. Using the absorption data, the $g$-factor of the
nanosuspension was found to be $1.86\pm 0.07$.",1811.01168v1
2018-12-04,Optical excitation of single- and multi-mode magnetization precession in Galfenol nanolayers,"We demonstrate a variety of precessional responses of the magnetization to
ultrafast optical excitation in nanolayers of Galfenol (Fe,Ga), which is a
ferromagnetic material with large saturation magnetization and enhanced
magnetostriction. The particular properties of Galfenol, including cubic
magnetic anisotropy and weak damping, allow us to detect up to 6 magnon modes
in a 120-nm layer, and a single mode with effective damping ${\alpha}_{eff}$ =
0.005 and frequency up to 100 GHz in a 4-nm layer. This is the highest
frequency observed to date in time-resolved experiments with metallic
ferromagnets. We predict that detection of magnetization precession approaching
THz frequencies should be possible with Galfenol nanolayers.",1812.01237v1
2018-12-17,Magnetized Current Filaments as a Source of Circularly Polarized Light,"We show that the Weibel or currente filamentation instability can lead to the
emission of circularly polarized radiation. Using particle-in-cell (PIC)
simulations and a radiation post-processing numerical algorithm, we demonstrate
that the level of circular polarization increases with the initial plasma
magnetization, saturating at ~13% when the magnetization, given by the ratio of
magnetic energy density to the electron kinetic energy density, is larger than
0.05. Furthermore, we show that this effect requires an ion-electron mass ratio
greater than unity. These findings, which could also be tested in currently
available laboratory conditions, show that the recent observation of circular
polarization in gamma ray burst afterglows could be attributed to the presence
of magnetized current filaments driven by the Weibel or the current
filamentation instability.",1812.06889v1
2019-01-30,Spin freezing and Field induced transition in (Tb1-xEux)2Ti2O7 : A Magnetic Property study,"The structural, magnetic and Raman effect have been investigated on
(Tb1-xEux)2Ti2O7. From structural study it is clear that Eu substitutes the Tb
in Tb2Ti2O7. Raman effect study indicates the existence of hardening due to
phonon-phonon anharmonic interaction. From dc-magnetic measurement it is
observed that in Eu rich samples contribution of dipolar interaction is
significant. From ac magnetic measurement of (Tb1-xEux)2Ti2O7 a new single ion
weak spin freezing ~ 33K at zero magnetic field is observed. On applying a
field of 1T, all the compounds show a field induced transition (T*) which
shifts towards higher temperature with increase of Eu content. This field
induced transition corresponds to single moment saturation.",1901.10899v1
2019-06-18,Discovery of room temperature ferromagnetism in metal-free organic semiconductors,"Creating magnetic semiconductors that work at warm circumstance is still a
great challenge in the physical sciences. Here, we report the discovery of
ferromagnetism in the metal-free perylene diimide semiconductor, whose Curie
temperature is higher than 400 Kelvin. A solvothermal approach is used to
reduce and dissolve the rigid-backbone perylene diimide crystallites, and
radical anion aggregates were fabricated by the subsequent self-assembly and
oxidation process. Magnetic measurements exhibit the ferromagnetic ordering
with the saturated magnetization of 0.48 $\mu_{\rm B}$ per molecule and the
appreciable magnetic anisotropy. X-ray magnetic circular dichroism spectra
suggest the ferromagnetism stems from $\pi$ orbitals of radicals. Our findings
unambitiously demonstrate the long-range ferromagnetic ordering can survive at
room temperature in organic semiconductors, although which are intuitively
regarded to be nonmagnetic.",1906.07531v2
2019-10-03,Shaping Magnetite Nanoparticles from First-principles,"Iron oxide magnetic nanoparticles (NPs) are stimuli-responsive materials at
the forefront of nanomedicine. Their realistic finite temperature simulations
are a formidable challenge for first-principles methods. Here, we use density
functional tight binding to open up the required time and length scales and
obtain global minimum structures of Fe3O4 NPs of realistic size (1400 atoms,
2.5 nm) and of different shapes, which we then refine with hybrid density
functional theory methods to accomplish proper electronic and magnetic
properties, which have never been accurately described in simulations. On this
basis, we develop a general empirical formula and prove its predictive power
for the evaluation of the total magnetic moment of Fe3O4 NPs. By converting the
total magnetic moment into the macroscopic saturation magnetization, we
rationalize the experimentally observed dependence with shape. We also reveal
interesting reconstruction mechanisms and unexpected patterns of charge
ordering.",1910.01704v2
2019-11-07,New neutron transmission supermirror remanent polarizer,"A new neutron transmission supermirror remanent polarizer is proposed. The
polarizer is compact. It consists of two solid state polarizing parts. Parts of
the polarizer have antiparallel magnetization of magnetic layers of supermirror
structures. Both parts of the polarizer have magnetic remanence. This allows it
to be used as a polarizer and analyzer in small magnetic fields. The polarizer
can be used when working with beams of large cross-section and with a wide
angular distribution. Assembly of the device is greatly simplified, because it
is not required to bend a large stack of short plates along the radius, but
only to compress of its. The width of the angular profile of the beam passed
through the polarizer does not change! The polarizer has a high transmittance
for the (-) spin component of the beam. The beam passed through the polarizer
is highly polarized. Properties of neutron polarizing CoFe/TiZr and Fe/Si
remanent supermirrors (m = 2.0 and 2.5) are discussed. A variant of effective
use of the proposed polarizer with a spin-flipper for operation in saturating
magnetic fields is proposed.",1911.02936v1
2019-12-18,Magnetization and magneto-transport measurements on CeBi single crystals,"We report the synthesis of CeBi single crystals out of Bi self flux and a
systematic study of the magnetic and transport properties with varying
temperature and applied magnetic fields. From these $R(T,H)$ and $M(T,H)$ data
we could assemble the field-temperature ($H-T$) phase diagram for CeBi and
visualize the three dimensional $M-T-H$ surface. In the phase diagram, we
identify regions with well defined magnetization values, and identify a new
phase region. The magnetoresistance (MR) in the low temperature regime shows,
above $6~$T a power-law, non-saturated behavior with large MR ($\sim
3\times10^5 \%$ at $2~$K and $13.95~$T), along with Shubnikov-de Haas
oscillations. With increasing temperatures, MR decreases, and then becomes
negative for $T\gtrsim 10~$K. This crossover in MR seems to be unrelated to any
specific magnetic or metamagnetic transitions, but rather is associated with
changing from a low-temperature normal metal regime with little or no
scattering from the Ce$^{3+}$ moments and an anomalously large MR, to an
increased scattering from local Ce moments and a negative MR as temperature
increases.",1912.08896v2
2020-01-21,Huge linear magnetoresistance due to open orbits in $γ$-PtBi$_2$,"Some single-crystalline materials present an electrical resistivity which
decreases between room temperature and low temperatures at zero magnetic field
as in a good metal and switches to a nearly semiconductinglike behavior at low
temperatures with the application of a magnetic field. Often, this is
accompanied by a huge and nonsaturating linear magnetoresistance which remains
difficult to explain. Here we present a systematic study of the
magnetoresistance in single-crystal $\gamma$-PtBi$_2$. We observe that the
angle between the magnetic field and the crystalline $c$ axis fundamentally
changes the magnetoresistance, going from a saturating to a nonsaturating
magnetic field dependence. In between, there is one specific angle where the
magnetoresistance is perfectly linear with the magnetic field. We show that the
linear dependence of the nonsaturating magnetoresistance is due to the
formation of open orbits in the Fermi surface of $\gamma$-PtBi$_2$.",2001.07674v2
2020-02-26,Enhanced Ferroelectricity and Spin Current Waves in M-Type Barium Hexaferrite,"The intrinsic ferroelectricity and related dielectric properties of M-type
Barium Hexaferrite (BaFe12O19) with excellent magnetic performance are reported
in this paper. A classic electric polarization (P-E) hysteresis loop with full
saturation, together with two nonlinear reversal current peaks in the I-V curve
and huge change of dielectric constant in the vicinity of Curie temperature,
have all demonstrated themselves as sufficient experimental evidences to verify
the ferroelectricity of BaFe12O19 ceramics. It holds a large remnant
polarization at 108 uC/cm2 and a suitable coercive field at 117 kV/cm. Two
peaks at 194C and 451C in the temperature-dependent dielectric spectrum of
BaFe12O19 ceramics are considered to be the phase transition from ferro- to
antiferro- and antiferro- to para-electric structures. A conventional strong
magnetic hysteresis loop was also observed. The magnetically induced
polarization upon the BaFe12O19 ceramics was achieved in the form of
alternating spin current waves. A ME-coupling voltage with an amplitude of 23mV
on an applied magnetic field at 500mT was achieved. These combined multiple
functional responses of large ferroelectrics and strong ferromagnetism reveal
the excellent multiferroic features of BaFe12O19, which would bring forth the
great opportunity to create novel electric devices with active coupling effect
between magnetic and electric orders.",2002.11412v1
2020-03-31,Magnetic field evolution in solar-type stars,"We discuss selected aspects regarding the magnetic field evolution of
solar-type stars. Most of the stars with activity cycles are in the range where
the normalized chromospheric Calcium emission increases linearly with the
inverse Rossby number. For Rossby numbers below about a quarter of the solar
value, the activity saturates and no cycles have been found. For Rossby numbers
above the solar value, again no activity cycles have been found, but now the
activity goes up again for a major fraction of the stars. Rapidly rotating
stars show nonaxisymmetric large-scale magnetic fields, but there is
disagreement between models and observations regarding the actual value of the
Rossby number where this happens. We also discuss the prospects of detecting
the sign of magnetic helicity using various linear polarization techniques both
at the stellar surface using the parity-odd contribution to linear polarization
and above the surface using Faraday rotation.",2004.00439v1
2020-06-12,"Enhanced magnetocaloric effect in a mixed spin-(1/2, 1) Ising-Heisenberg two-leg ladder with strong-rung interaction","The magnetic and magnetocaloric properties of the mixed spin-(1/2,1)
Ising-Heisenberg model on a two-leg ladder with dimer-rung alternation are
exactly examined under an adiabatic demagnetization process using the
transfer-matrix formalism. We notify that the magnetization curve of the model
exhibits plateaux as a function of the applied magnetic field and cyclic
four-spin Ising interaction at certain rational fractions of the saturation
value. We precisely investigate the ability of cooling/heating of the model
nearby the critical points at which discontinuous ground-state phase transition
occurs. It is evidenced that the model manifests an enhanced magnetocaloric
effect in a proximity of the magnetization steps and jumps, accompanying with
the plateaux and jumps of correlation function of the dimer spins. We conclude
that not only the cooling/heating capability of the model could be pleasantly
demonstrated by the applied magnetic field variations, but also a typical
cyclic four-spin Ising interaction plays essential role to determine an
efficiency of the magnetocaloric effect of the model.",2006.07208v2
2020-08-02,Thermal stability for domain wall mediated magnetization reversal in perpendicular STT MRAM cells with W insertion layers,"We present an analytical model for calculating energy barrier for the
magnetic field-driven domain wall-mediated magnetization reversal of a
magneto-resistive random access memory (MRAM) cell and apply it to study
thermal stability factor $\Delta$ for various thicknesses of W layers inserted
into the free layer (FL) as a function of the cell size and temperature. We
find that, by increasing W thickness, the effective perpendicular magnetic
anisotropy (PMA) energy density of the FL film monotonically increases, but at
the same time, $\Delta$ of the cell mainly decreases. Our analysis shows that,
in addition to saturation magnetization $M_s$ and exchange stiffness constant
$A_\mathrm{ex}$ of the FL film, the parameter that quantifies the $\Delta$ of
the cell is its coercive field $H_c$, rather than the net PMA field $H_k$ of
the FL film comprising the cell.",2008.00412v2
2020-09-23,Effect of reduced local lattice disorder on the magnetic properties of B-site substituted La0.8Sr0.2MnO3,"Disorder induced by chemical inhomogeneity and Jahn-Teller (JT) distortions
is often observed in mixed valence perovskite manganites. The main reasons for
the evolution of this disorder are connected with the cationic size differences
and the ratio between JT active and non-JT active ions. The quenched disorder
leads to a spin-cluster state above the magnetic transition temperature. The
effect of Cu, a B-site substitution in the La0.8Sr0.2MnO3 compound, on the
disordered phase has been addressed here. X-ray powder diffraction reveals
rhombohedral (R-3c) structures for the two compounds with negligible change of
lattice volume. The chemical compositions of the two compounds were verified by
ion beam analysis technique. With the change of electronic bandwidth, the
magnetic phase transition temperature has been tuned towards room temperature
(318 K), an important requirement for room temperature magnetic refrigeration.
However, a small decrease of the isothermal entropy was observed with
Cu-substitution, related to the decrease of the saturation magnetization.",2009.11157v2
2020-10-30,Critical dielectric susceptibility at a magnetic BEC quantum critical point,"Magnetic-field-induced phase transitions are investigated in the frustrated
gapped quantum paramagnet Rb$_{2}$Cu$_{2}$Mo$_3$O$_{12}$ through dielectric and
calorimetric measurements on single-crystal samples. It is clarified that the
previously reported dielectric anomaly at 8~K in powder samples is not due to a
chiral spin liquid state as has been suggested, but rather to a tiny amount of
a ferroelectric impurity phase. Two field-induced quantum phase transitions
between paraelectric and paramagnetic and ferroelectric and magnetically
ordered states are clearly observed. It is shown that the electric polarization
is a secondary order parameter at the lower-field (gap closure) quantum
critical point but a primary one at the saturation transition. Having clearly
identified the magnetic Bose-Einstein condensation (BEC) nature of the latter,
we use the dielectric channel to directly measure the critical divergence of
BEC susceptibility. The observed power-law behavior is in very good agreement
with theoretical expectations for three-dimensional BEC. Finally, dielectric
data reveal magnetic presaturation phases in this compound that may feature
exotic order with unconventional broken symmetries.",2011.00107v2
2021-01-20,Efficient highly-subsonic turbulent dynamo and growth of primordial magnetic fields,"We present the first study on the amplification of magnetic fields by the
turbulent dynamo in the highly subsonic regime, with Mach numbers ranging from
$10^{-3}$ to $0.4$. We find that for the lower Mach numbers the saturation
efficiency of the dynamo, $(E_{\mathrm{mag}}/E_{\mathrm{kin}})_{\mathrm{sat}}$,
increases as the Mach number decreases. Even in the case when injection of
energy is purely through longitudinal forcing modes,
$(E_{\mathrm{mag}}/E_{\mathrm{kin}})_{\mathrm{sat}}$ $\gtrsim 10^{-2}$ at a
Mach number of $10^{-3}$. We apply our results to magnetic field amplification
in the early Universe and predict that a turbulent dynamo can amplify
primordial magnetic fields to $\gtrsim$ $10^{-16}$ Gauss on scales up to 0.1 pc
and $\gtrsim$ $10^{-13}$ Gauss on scales up to 100 pc. This produces fields
compatible with lower limits of the intergalactic magnetic field inferred from
blazar $\gamma$-ray observations.",2101.08256v1
2021-04-14,Control of a polar order via magnetic field in a vector-chiral magnet,"Vector-chiral (VC) antiferromagnetism is a spiral-like ordering of spins
which may allow ferroelectricity to occur due to loss of space inversion
symmetry. In this paper we report direct experimental observation of
ferroelectricity in the VC phase of $\beta$-TeVO$_4$, a frustrated spin chain
system with pronounced magnetic anisotropy and a rich phase diagram. Saturation
polarization is proportional to neutron scattering intensities that correspond
to the VC magnetic reflection. This implies that inverse Dzyaloshinskii-Moriya
mechanism is responsible for driving electric polarization. Linear
magnetoelectric coupling is absent, however an unprecedented dependence of
electric coercive field on applied magnetic field reveals a novel way of
manipulating multiferroic information.",2104.06726v3
2021-06-22,Incommensurate magnetic order in rare earth and transition metal compounds with local moments,"Within the framework of the $s$-$d(f)$ exchange model in the mean-field
approximation for square, simple cubic, body-centered and face-centered cubic
lattices, the formation of a ferromagnetic, spiral, and commensurate
antiferromagnetic order is investigated. The possibility of the formation of
inhomogeneous states (magnetic phase separation), which necessarily arises
during first-order phase transitions in the electron filling parameter, is
taken into account. The saturation of the antiferromagnetic and spiral states
is studied depending on the parameters of the model. The results obtained
include a rich variety of magnetic structures and phase transitions, allowing
the interpretation of magnetic properties of semiconducting and metallic
systems containing magnetic atoms.",2106.11697v2
2021-09-02,Multifold enhancement in magnetization of atomically thin Cobalt Telluride,"Magnetism in semiconductor two-dimensional (2D) materials is gaining
popularity due to its potential application in memory devices, sensors,
spintronic and biomedical applications. Here, 2D Cobalt Telluride (CoTe) has
been synthesized from its bulk crystals using a simple and scalable
liquid-phase exfoliation method. The atomically thin CoTe shows over four
hundred times enhancement in its magnetic saturation values compared to the
bulk form. The UV-Vis absorption spectra reveal superior absorption in the high
energy region, suggesting a semiconducting nature. Furthermore, we explain
bandgap and origin of high magnetic behavior by density functional theory (DFT)
calculations. The 2D CoTe shows a larger magnetism compared to bulk CoTe due to
the reduced coordination number of the surface atoms, shape anisotropy and
surface charge effect.",2109.02783v1
2021-11-09,Quantum oscillations in Noncentrosymmetric Weyl semimetals RAlSi (R = Sm and Ce),"Weyl semimetal (WSM) as a new type of quantum state of matter hosting low
energy relativistic quasiparticles, has attracted significant attention for
both scientific community and potential quantum device applications. Here, we
report a comprehensive investigation of the structural, magnetic and transport
properties of noncentrosymmetric RAlSi (R = Sm, Ce), which have been predicted
to be new magnetic WSM candidates. Both samples exhibit non-saturated
magnetoresistance (MR), with ~ 900% for SmAlSi and 80% for CeAlSi at 1.8 K, 9
T. The carrier densities of SmAlSi and CeAlSi display remarkable change around
magnetic transition temperatures, signifying that the electronic states are
sensitive to magnetic ordering of rare earth elements. At low temperatures,
SmAlSi reveals prominent Shubnikov-de Haas (SdH) oscillations associated with
the nontrivial Berry phase. High pressure experiments demonstrate that the
magnetic order is robust and survival under high pressure. Our results would
yield valuable insights of WSM physics and potentials in application to the
next-generation spintronic devices in RAX family.",2111.05235v1
2022-03-15,Magnetic field-controlled lattice thermal conductivity in MnBi2Te4,"Phonon properties and the lattice thermal conductivity are not generally
understood to be sensitive to magnetic fields. Using an applied field to change
MnBi2Te4 between antiferromagnetic (AFM), canted (CAFM) and ferromagnetic (FM)
phases we discovered a new way to control the lattice thermal conductivity,
generating both a positive and a negative magnetic field dependence. We report
the field dependence of the thermal conductivity, k, in the in-plane direction
under an applied magnetic field along the cross-plane direction in MnBi2Te4
from 2K to 30K. k decreases with field in the AFM phase, saturates in the CAFM
phase, and increases with field in the FM phase. We explain this in terms of
the field-induced changes of the magnon gap which modifies which magnon-phonon
scattering processes are allowed by energy conservation. We also report
magneto-Seebeck coefficient, Nernst coefficient and thermal Hall data measured
in the same configuration. This finding may open a way to design magnetically
controlled heat switches.",2203.08032v2
2022-03-18,Domain-knowledge-aided machine learning method for properties prediction of soft magnetic metallic glasses,"A machine learning (ML) method aided by domain knowledge was proposed to
predict saturated magnetization (Bs) and critical diameter (Dmax) of soft
magnetic metallic glass (MGs). Two datasets were established based on published
experimental works about soft magnetic MGs. A general feature space was
proposed and proved to be adaptive for ML model training for different
prediction tasks. It was found that the predictive performance of ML models was
better than traditional physical knowledge-based estimation methods. In
addition, domain knowledge aided feature selection can greatly reduce the
number of features without significantly reducing the prediction accuracy.
Finally, binary classification of the critical size of soft magnetic metallic
glass was studied.",2203.10951v1
2022-06-08,SmI3: 4f5 honeycomb magnet with spin-orbital entangled Γ7 Kramers doublet,"We report magnetic properties of a 4f-honeycomb iodide SmI3 made up of
edge-shared network of SmI6 octahedra. High temperature magnetic susceptibility
indicates {\Gamma}7 Kramers doublet ground state of Sm3+ (4f5) ions stabilized
by the spin-orbit coupling and octahedral crystal electric field, which
interact with Sm-I-Sm bond angle nearly 90 degree. Magnetization measurements
down to 0.1 K detected antiferromagnetic correlations and an anomaly in the
magnetization curve before saturation without a sign of long-range order.
Relevance between SmI3 and the antiferromagnetic Kitaev material proposed in
the 4f-electron system is discussed.",2206.03628v1
2022-08-23,Translational Symmetry Broken Magnetization Plateau of the $S=2$ Antiferromagnetic Chain with Anisotropies,"The magnetization plateau of the $S=2$ antiferromagnetic chain with
interaction and single-ion anisotropies is investigated using the numerical
diagonalization of finite-size clusters and some size scaling analyses. The
previous level spectroscopy analysis indicated that two different magnetization
plateau phases appear at half of the saturation magnetization. One is due to
the large-$D$ mechanism and the other is due to the Haldane one. In the present
study the phase diagram is extended to wider region of the anisotropies. As a
result we find another half magnetization plateau phase, where the
translational symmetry is spontaneously broken .",2208.10983v1
2022-12-07,Acoustic Frequency Multiplication and Pure Second Harmonic Generation of Phonons by Magnetic Transducers,"We predict frequency multiplication of surface acoustic waves in dielectric
substrates via the ferromagnetic resonance of adjacent magnetic transducers
when driven by microwaves. We find pure second harmonic generation (SHG)
without any linear and third harmonic components by a magnetic nanowire. The
SHG and linear phonon pumping are switched by varying the saturated
magnetization direction of the wire, or resolved directionally when pumped by
magnetic nano-disc. We address the high efficiency of SHG with comparable
magnitude to that of linear response, as well as unique non-reciprocal phonon
transport that is remarkably distinct in different phonon harmonics. Such
acoustic frequency comb driven by microwaves should bring unprecedented
tunability for the miniaturized phononic and spintronic devices.",2212.03451v1
2023-01-09,Long distance magnon transport in the van der Waals antiferromagnet CrPS$_4$,"We demonstrate the potential of van der Waals magnets for spintronic
applications by reporting long-distance magnon spin transport in the
electrically insulating antiferromagnet chromium thiophosphate (CrPS$_4$) with
perpendicular magnetic anisotropy. We inject and detect magnon spins
non-locally by Pt contacts and monitor the non-local resistance as a function
of an in-plane magnetic field up to 7 Tesla. We observe a non-local resistance
over distances up to at least a micron below the Neel temperature (T$_{\rm N}$
= 38 Kelvin) close to magnetic field strengths that saturate the sublattice
magnetizations.",2301.03268v1
2023-02-20,Magnetic Breakdown and Chiral Magnetic Effect at Weyl-Semimetal Tunnel Junctions,"We investigate magnetotransport across an interface between two Weyl
semimetals whose Weyl nodes project onto different interface momenta. Such an
interface generically hosts Fermi arcs that connect Weyl nodes of identical
chirality in different Weyl semimetals (homochiral connectivity) -- in contrast
to surface Fermi arcs that connect opposite-chirality Weyl nodes within the
same Weyl semimetal (heterochiral connectivity). We show that electron
transport along the arcs with homochiral connectivity, in the presence of a
longitudinal magnetic field, leads to a universal longitudinal
magnetoconductance of $e^2/h$ per magnetic flux quantum. Furthermore, a weak
tunnel coupling can result in a close encounter of two homochiral-connectivity
Fermi arcs, enabling magnetic breakdown. Above the breakdown field the
interface Fermi arc connectivity is effectively heterochiral, leading to a
saturation of the conductance.",2302.09896v1
2023-04-01,Pulsed $^{87}$Rb vector magnetometer using a fast rotating field,"There are diverse set approaches for vector magnetic field measurements
involving condensed matter and atomic physics systems. However, they all suffer
from various limitations, so the most widely used high-sensitivity vector
magnetometers are fluxgates using soft magnetically-saturable materials. Here
we describe a vector magnetometer by applying an external rotating magnetic
field to a scalar atomic magnetometer. Such an approach provides simultaneous
measurements of the total magnetic field and two polar angles relative to the
plane of magnetic field rotation. Crucially, it avoids several metrological
difficulties associated with vector magnetometers and gradiometers. We describe
in detail the fundamental, systematic, and practical limits of such vector
magnetometers. We use a field rotation rate faster than the spin relaxation
rate. We show that it eliminates a class of systematic effects associated with
heading errors in alkali-metal scalar magnetometers. We investigate several
other systematic effects, such as Berry's phase frequency shift and the effects
of eddy currents in nearby conductors. We also derive fundamental limits on the
sensitivity of such sensors and show that the vector sensitivity can approach
the sensitivity of scalar atomic magnetometers.",2304.00214v1
2023-11-20,Surface spin polarization in the magnetic response of GeTe Rashba ferroelectric,"We experimentally investigate magnetization reversal curves for a GeTe
topological semimetal. In addition to the known lattice diamagnetic response,
we observe narrow magnetization loop in low fields, which should not be
expected for non-magnetic GeTe. The hysteresis is unusual, so the saturation
level is negative in positive fields, and the loop is passed clockwise, in
contrast to standard ferromagnetic behavior. The experimental hysteresis curves
can not be obtained from usual ferromagnetic ones by adding/subtracting of any
linear dependence, or even by considering several interacting magnetic phases.
The possibility of several phases is also eliminated by the remanence plots
technique (Henkel or {\delta}M plots). We explain our results as a direct
consequence of the correlation between ferroelectricity and spin-polarized
surface states in GeTe, similarly to magnetoelectric structures.",2311.11831v1
2023-11-30,Growth of high-quality CrI3 single crystals and engineering of its magnetic properties via V and Mn doping,"CrI3, as a soft van der Waals layered magnetic material, has been widely
concerned and explored for its magnetic complexity and tunability. In this
work, high quality and large size thin CrI3, V and Mn doped single crystals
were prepared by chemical vapor transfer method. A remarkable irreversible
Barkhausen effect was observed in CrI3 and CrMn0.06I3, which can be attributed
to the low dislocation density that facilitates movement of the domain walls.
In addition, the introduction of the doping element Mn allows higher saturation
magnetization intensity. Cr0.5V0.5I3 exhibits substantially increased
coercivity force and larger magnetocrystalline anisotropy compared to CrI3,
while kept similar Curie temperature and good environmental stability. The
first principles calculations suggest direct and narrowed band gaps in
Cr0.5V0.5I3 and VI3 comparing to CrI3. The smaller band gaps and good hard
magnetic property make Cr0.5V0.5I3 an alternative choice to future research of
spintronic devices.",2311.18360v1
2009-10-06,Diffusion of magnetic field and removal of magnetic flux from clouds via turbulent reconnection,"The diffusion of astrophysical magnetic fields in conducting fluids in the
presence of turbulence depends on whether magnetic fields can change their
topology via reconnection in highly conducting media. Recent progress in
understanding fast magnetic reconnection in the presence of turbulence is
reassuring that the magnetic field behavior in computer simulations and
turbulent astrophysical environments is similar, as far as magnetic
reconnection is concerned. Our studies of magnetic field diffusion in turbulent
medium reveal interesting new phenomena. In the presence of gravity and
turbulence, our 3D simulations show the decrease of the magnetic flux-to-mass
ratio as the gaseous density at the center of the gravitational potential
increases. We observe this effect both in the situations when we start with
equilibrium distributions of gas and magnetic field and when we follow the
evolution of collapsing dynamically unstable configurations. Thus the process
of turbulent magnetic field removal should be applicable both to quasi-static
subcritical molecular clouds and cores and violently collapsing supercritical
entities. The increase of the gravitational potential as well as the
magnetization of the gas increases the segregation of the mass and magnetic
flux in the saturated final state of the simulations, supporting the notion
that the reconnection-enabled diffusivity relaxes the magnetic field + gas
system in the gravitational field to its minimal energy state. This effect is
expected to play an important role in star formation, from its initial stages
of concentrating interstellar gas to the final stages of the accretion to the
forming protostar.",0910.1117v3
2020-05-07,A global model of the magnetorotational instability in protoneutron stars,"Magnetars are highly magnetized neutron stars whose magnetic dipole ranges
from $10^{14}$ to $10^{15}$ G. The MRI is considered to be a promising
mechanism to amplify the magnetic field in fast-rotating protoneutron stars and
form magnetars. This scenario is supported by many local studies showing that
magnetic fields could be amplified by the MRI on small scales. However, the
efficiency of the MRI at generating a dipole field is still unknown. To answer
this question, we study the MRI dynamo in an idealized global model of a fast
rotating protoneutron star with differential rotation. We perform 3D
incompressible MHD simulations in spherical geometry with explicit
diffusivities where the differential rotation is forced at the outer boundary.
We vary the initial magnetic field and investigated different magnetic boundary
conditions. These simulations were compared to local shearing box simulations.
We obtain a self-sustained turbulent MRI-driven dynamo, whose saturated state
is independent of the initial magnetic field. The MRI generates a strong
turbulent magnetic field of $B \geq 2\times 10^{15}$ G and a non-dominant
magnetic dipole, which represents systematically about $5\%$ of the averaged
magnetic field strength. Interestingly, this dipole is tilted towards the
equatorial plane. We find that local shearing box models can reproduce fairly
well several characteristics of global MRI turbulence such as the kinetic and
magnetic spectra. The turbulence is nonetheless more vigorous in the local
models than in the global ones. Overall, our results support the ability of the
MRI to form magnetar-like large-scale magnetic fields. They furthermore predict
the presence of a stronger small-scale magnetic field. The resulting magnetic
field could be important to power outstanding stellar explosions, such as
superluminous supernovae and GRBs.",2005.03567v2
2000-09-06,"Two-Dimensional MHD Numerical Simulations of Magnetic Reconnection Triggered by A Supernova Shock in Interstellar Medium, Generation of X-Ray Gas in Galaxy","We examine the magnetic reconnection triggered by a supernova (or a point
explosion) in interstellar medium, by performing two-dimensional resistive
magnetohydrodynamic (MHD) numerical simulations with high spatial resolution.
We found that the magnetic reconnection starts long after a supernova shock
(fast-mode MHD shock) passes a current sheet. The current sheet evolves as
follows: (i) Tearing-mode instability is excited by the supernova shock, and
the current sheet becomes thin in its nonlinear stage. (ii) The current-sheet
thinning is saturated when the current-sheet thickness becomes comparable to
that of Sweet-Parker current sheet. After that, Sweet-Parker type reconnection
starts, and the current-sheet length increases. (iii) ``Secondary tearing-mode
instability'' occurs in the thin Sweet-Parker current sheet. (iv) As a result,
further current-sheet thinning occurs and anomalous resistivity sets in,
because gas density decreases in the current sheet. Petschek type reconnection
starts and heats interstellar gas. Magnetic energy is released quickly while
magnetic islands are moving in the current sheet during Petschek type
reconnection. The released magnetic energy is determined by the interstellar
magnetic field strength, not energy of initial explosion nor distance to
explosion. We suggest that magnetic reconnection is a possible mechanism to
generate X-ray gas in Galaxy.",0009088v2
1999-10-25,Finite-size versus Surface effects in nanoparticles,"We study the finite-size and surface effects on the thermal and spatial
behaviors of the magnetisation of a small magnetic particle. We consider two
systems: 1) A box-shaped isotropic particle of simple cubic structure with
either periodic or free boundary conditions. This case is treated analytically
using the isotropic model of D-component spin vectors in the limit $D\to
\infty$, including the magnetic field. 2) A more realistic particle ($\gamma
$-Fe$_{2}$O$_{3}$) of ellipsoidal (or spherical) shape with open boundaries.
The magnetic state in this particle is described by the anisotropic classical
Dirac-Heisenberg model including exchange and dipolar interactions, and bulk
and surface anisotropy. This case is dealt with by the classical Monte Carlo
technique. It is shown that in both systems finite-size effects yield a
positive contribution to the magnetisation while surface effects render a
larger and negative contribution, leading to a net decrease of the
magnetisation of the small particle with respect to the bulk system. In the
system 2) the difference between the two contributions is enhanced by surface
anisotropy. The latter also leads to non saturation of the magnetisation at low
temperatures, showing that the magnetic order in the core of the particle is
perturbed by the magnetic disorder on the surface. This is confirmed by the
profile of the magnetisation.",9910393v1
2001-07-23,"New two dimensional S=1/2 Heisenberg antiferromagnets: synthesis, structure and magnetic properties","The magnetic susceptibility and magnetization of two new layered S=1/2
Heisenberg antiferromagnets with moderate exchange are reported. The two
isostructural compounds, (2-amino-5-chloropyridinium)2CuBr4 ((5CAP)2CuBr4) and
(2-amino-5-methylpyridinium)2CuBr4 ((5MAP)2CuBr4), contain S=1/2, Cu(II) ions
related by C-centering, yielding four equivalent nearest neighbors. The crystal
structure of newly synthesized compound, (5CAP)2CuBr4, shows the existence of
layers of distorted copper(II)-bromide tetrahedra parallel to the ab plane,
separated by the organic cations along the c axis. Magnetic pathways are
available through the bromide-bromide contacts within the layers and provide
for moderate antiferromagnetic exchange. Susceptibility measurements indicate
interaction strengths to be 8.5(1) K, and 6.5(1) K and ordering temperatures of
5.1(2) K and 3.8(2) K for (5CAP)2CuBr4 and (5MAP)2CuBr4 respectively. High
field magnetization experiments on both compounds show upward curvature of
M(H,T). Magnetization measurements made at T = 1.3 K show saturation occurs in
(5MAP)2CuBr4 at 18.8 T and in (5CAP)2CuBr4 at 24.1 T. The magnetization curves
are consistent with recent theoretical predictions. Single crystal
magnetization measured at 2.0 K indicate a spin flop transition at 0.38 T and
0.63 T for (5CAP)2CuBr4 and (5MAP)2CuBr4 respectively.",0107483v3
2003-05-13,Thermal Remagnetization in Polycrystalline Permanent Magnets,"The thermal remagnetization (TR), i.e. the reentrance of magnetization upon
heating in a steady-field demagnetized sample, is a common feature to the four
types of polycrystalline permanent magnets, mainly utilized for practical
purposes, i.e. barium ferrites, SmCo5, Sm2Co17 and NdFeB magnets. The effect is
small for pinning controlled and large for nucleation controlled magnets. The
effect is strongly dependent on the demagnetization factor and may reach nearly
100 per cent in SmCo5 samples measured in a closed circuit. The TR is very
sensitive to a small superimposed steady field. The maximum effect and the
position of the peak is dependent on the initial temperature. The direction of
the TR is correlated with the temperature coefficient of the coercivity,
resulting in a inverse TR in barium ferrite. The susceptibility of the
thermally remagnetized samples is increased. Repeated cycles of steady-field
demagnetization followed by heating result in the same TR. The phenomenology of
TR and ITR is explained by means of a model taking into account both the
internal field fluctuations due to grain interactions and the decay of single
domain grains into multi-domain state. By taking the measured temperature
dependencies of the coercivity and the saturation magnetization the theory is
able to reproduce the experiments very well, allowing to determine the width of
the field fluctuations, the width of the switching field distribution and an
internal demagnetization factor as characteristics of the materials by fitting.",0305292v1
2004-03-22,Magnetic properties of a helical spin chain with alternating isotropic and anisotropic spins: magnetization plateaus and finite entropy,"We study a model which could explain some of the unusual magnetic properties
observed for the one-dimensional helical spin system Co(hfac)_2 NITPhOMe. One
of the properties observed is that the magnetization shows plateaus near zero
and near one-third of the saturation value if a magnetic field is applied along
the helical axis, but not if the field is applied in the plane perpendicular to
that axis. The system consists of a spin-1/2 chain in which cobalt ions (which
are highly anisotropic with an easy axis e_i) and organic radicals (which are
isotropic) alternate with each other. The easy axis of the cobalts e_i lie at
an angle theta_i with respect to the helical axis, while the projection of
e_{i+1} - e_i on the plane perpendicular to the helical axis is given by 2 pi
/3. For temperatures and magnetic fields which are much smaller than the
coupling between the nearest-neighbor cobalts and radicals, one can integrate
out the radicals to obtain an Ising model for the cobalts; this enables one to
compute the thermodynamic properties of the system using the transfer matrix
approach. We consider a model in which the tilt angles theta_i are allowed to
vary with i with period three; we find that for certain patterns of theta_i,
the system shows the magnetization plateaus mentioned above. At the ends of the
plateaus, the entropy is finite even at very low temperatures, while the
magnetic susceptibility and specific heat also show some interesting features.",0403555v1
2004-08-27,Spin reorientation and in-plane magnetoresistance of lightly doped La_{2-x}Sr_{x}CuO_{4} in magnetic fields up to 55 T,"The magnetoresistance (MR) in the in-plane resistivity is measured in
magnetic fields up to 55 T in lightly doped La_{2-x}Sr_{x}CuO_{4} in the N\'eel
state (x = 0.01) and in the spin-glass state (x = 0.03) using high-quality
untwinned single crystals. In both cases, a large negative MR is observed to
appear when the magnetic order is established. For x = 0.01, it is found that
the MR is indicative of a one-step transition into a high-field
weak-ferromagnetic state at around 20 T when the magnetic field is applied from
the spin easy axis (b axis), which means that there is no spin-flop transition
in the N\'eel state of this material; this is contrary to a previous report,
but is natural in light of the peculiar in-plane magnetic susceptibility
anisotropy recently found in this system. In the spin-glass state, we observe
that the large (up to \sim20%) negative MR saturates at around 40 T, and this
MR is found to be essentially isotropic when the magnetic field is rotated
within the ab plane. Our data show that the large negative MR is inherent to
LSCO in a magnetically ordered state, in which the weak-ferromagnetic (WF)
moment becomes well-defined; we discuss that the observed MR is essentially due
to the reorientation of the WF moments towards the magnetic field direction
both in the N\'eel state and in the spin-glass state.",0408604v1
2009-05-06,Formation of gaseous arms in barred galaxies with dynamically important magnetic field : 3D MHD simulations,"We present results of three-dimensional nonlinear MHD simulations of a
large-scale magnetic field and its evolution inside a barred galaxy with the
back reaction of the magnetic field on the gas. The model does not consider the
dynamo process. To compare our modeling results with observations, we construct
maps of the high-frequency (Faraday-rotation-free) polarized radio emission on
the basis of simulated magnetic fields. The model accounts for the effects of
projection and the limited resolution of real observations. We performed 3D MHD
numerical simulations of barred galaxies and polarization maps. The main result
is that the modeled magnetic field configurations resemble maps of the
polarized intensity observed in barred galaxies. They exhibit polarization
vectors along the bar and arms forming coherent structures similar to the
observed ones. In the paper, we also explain the previously unsolved issue of
discrepancy between the velocity and magnetic field configurations in this type
of galaxies. The dynamical influence of the bar causes gas to form spiral waves
that travel outwards. Each gaseous spiral arm is accompanied by a magnetic
counterpart, which separates and survives in the inter-arm region. Because of a
strong compression, shear of non-axisymmetric bar flows and differential
rotation, the total energy of modeled magnetic field grows constantly, while
the azimuthal flux grows slightly until $0.05\Gyr$ and then saturates.",0905.0845v1
2009-10-19,Magnetic properties of EuPtSi$_3$ single crystals,"Single crystals of EuPtSi$_3$, which crystallize in the BaNiSn$_3$-type
crystal structure, have been grown by high temperature solution growth method
using molten Sn as the solvent. EuPtSi$_3$ which lacks the inversion symmetry
and has only one Eu site in the unit cell is found to be an antiferromagnet
with two successive magnetic transitions at $T_{\rm N1}$ = 17 K and $T_{\rm
N2}$ = 16 K, as inferred from magnetic susceptibility, heat capacity and
$^{151}$Eu M\""ossbauer measurements. The isothermal magnetization data for $H
\parallel$ [001] reveal a metamagnetic transition at a critical field $H_{\rm
c}$ = 1 T. The magnetization saturates to a moment value of 6.43 $\mu_{\rm
B}$/Eu above 5.9 T (9.2 T) for $H \parallel $ [001] ([100]), indicating that
these fields are spin-flip fields for the divalent Eu moments along the two
axes. The origin of this anisotropic behaviour is discussed. A magnetic (H, T)
phase diagram has been constructed from the temperature dependence of
isothermal magnetization data. The reduced jump in the heat capacity at $T_{\rm
N1}$ indicates a transition to an incommensurate, amplitude modulated
antiferromagnetic structure. The shape of the hyperfine field split M\""ossbauer
spectrum at $T_{\rm N1}$ provides additional support for the proposed nature of
this magnetic transition.",0910.3517v2
2011-10-20,Magnetic properties of the spin $S=1/2$ Heisenberg chain with hexamer modulation of exchange,"We consider the spin-1/2 Heisenberg chain with alternating spin exchange %on
even and odd sites in the presence of additional modulation of exchange on odd
bonds with period three. We study the ground state magnetic phase diagram of
this hexamer spin chain in the limit of very strong antiferromagnetic (AF)
exchange on odd bonds using the numerical Lanczos method and bosonization
approach. In the limit of strong magnetic field commensurate with the
dominating AF exchange, the model is mapped onto an effective $XXZ$ Heisenberg
chain in the presence of uniform and spatially modulated fields, which is
studied using the standard continuum-limit bosonization approach. In absence of
additional hexamer modulation, the model undergoes a quantum phase transition
from a gapped string order into the only one gapless L\""uttinger liquid (LL)
phase by increasing the magnetic field. In the presence of hexamer modulation,
two new gapped phases are identified in the ground state at magnetization equal
to 1/3 and 2/3 of the saturation value. These phases reveal themselves also in
magnetization curve as plateaus at corresponding values of magnetization. As
the result, the magnetic phase diagram of the hexamer chain shows seven
different quantum phases, four gapped and three gapless and the system is
characterized by six critical fields which mark quantum phase transitions
between the ordered gapped and the LL gapless phases.",1110.4467v3
2013-05-23,Holographic Photon Production with Magnetic Field in Anisotropic Plasmas,"We investigate the thermal photon production from constant magnetic field in
a strongly coupled and anisotropic plasma via the gauge/gravity duality. The
dual geometry with pressure anisotropy is generated from the axion-dilaton
gravity action introduced by Mateos and Trancancelli and the magnetic field is
coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find
that the photon spectra with different quark mass are enhanced at large
frequency when the photons are emitted parallel to the anisotropic direction
with larger pressure or perpendicular to the magnetic field. However, in the
opposite conditions for the emitted directions, the spectra approximately
saturate isotropic results in the absence of magnetic field. On the other hand,
a resonance emerges at moderate frequency for the photon spectrum with heavy
quarks when the photons move perpendicular to the magnetic field. The resonance
is more robust when the photons are polarized along the magnetic field. On the
contrary, in the presence of pressure anisotropy, the resonance will be
suppressed. There exist competing effects of magnetic field and pressure
anisotropy on meson melting in the strongly coupled super Yang-Mills plasma,
while we argue that the suppression led by anisotropy may not be applied to the
quark gluon plasma.",1305.5509v3
2013-08-01,Magnetostatic wave analog of integer quantum Hall state in patterned magnetic films,"A magnetostatic spin wave analog of integer quantum Hall (IQH) state is
proposed in realistic patterned ferromagnetic thin films. Due to magnetic shape
anisotropy, magnetic moments in a thin film lie within the plane, while all
spin-wave excitations are fully gapped. Under an out-of-plane magnetic field,
the film acquires a finite magnetization, where some of the gapped magnons
become significantly softened near a saturation field. It is shown that, owing
to a spin-orbit locking nature of the magnetic dipolar interaction, these soft
spin-wave volume-mode bands become chiral volume-mode bands with finite
topological Chern integers. A bulk-edge correspondence in IQH physics suggests
that such volume-mode bands are accompanied by a chiral magnetostatic spin-wave
edge mode. The existence of the edge mode is justified both by micromagnetic
simulations and by band calculations based on a linearized Landau-Lifshitz
equation. Employing intuitive physical arguments, we introduce proper
tight-binding models for these soft volume-mode bands. Based on the
tight-binding models, we further discuss possible applications to other systems
such as magnetic ultrathin films with perpendicular magnetic anisotropy (PMA).",1308.0199v3
2013-08-31,Nature of the magnetic ground state in the mixed valence compound CeRuSn: a single-crystal study,"We report on detailed low temperature measurements of the magnetization, the
specific heat and the electrical resistivity on high quality CeRuSn single
crystals. The compound orders antiferromagnetically at $T_{\rm N} = 2.8$ K with
the Ce$^{3+}$ ions locked within the $a-c$ plane of the monoclinic structure.
Magnetization shows that below $T_{\rm N}$ CeRuSn undergoes a metamagnetic
transition when applying a magnetic field of 1.5 and 0.8 T along the $a$ and
$c$--axis, respectively. This transition manifests in a tremendous negative
jump of $\sim 25$% in the magnetoresistance. The value of the saturated
magnetization along the easy magnetization direction ($c$--axis) and the
magnetic entropy above $T_{\rm N}$ derived from specific heat data correspond
to the scenario where only one third of the Ce ions in the compound being
trivalent and carrying a stable Ce$^{3+}$ magnetic moment, whereas the other
two thirds of the Ce ions are in a nonmagnetic tetravalent and/or mixed valence
state. This is consistent with the low temperature CeRuSn crystal structure
i.\,e.\,, a superstructure consisting of three unit cells of the CeCoAl-type
piled up along the $c$--axis, and in which the Ce$^{3+}$ ions are characterized
by large distances from the Ru ligands while the Ce-Ru distances of the other
Ce ions are much shorter causing a strong 4{\it f}-ligand hybridization and
hence leading to tetravalent and/or mixed valence Ce ions.",1309.0106v1
2017-03-21,Microstrain induced deviation from Néel's 1/d behaviour: Size-dependent magnetization in Bi1-xCaxFe1-yTiyO3-delta nanoparticles,"Magnetization of antiferromagnetic nanoparticles is known to generally scale
up inversely to their diameter (d) according to N\'eel's model. Here we report
a deviation from this conventional linear 1/d dependence, altered significantly
by the microstrain, in Ca and Ti substituted BiFeO3 nanoparticles. Magnetic
properties of microstrain-controlled Bi1-xCaxFe1-yTiyO3-delta (y = 0 and x = y)
nanoparticles are analyzed as a function of their size ranging from 18 nm to
200 nm. A complex interdependence of doping concentration (x or y), annealing
temperature (T), microstrain (epsilon) and particle size (d) is established.
X-ray diffraction studies reveal a linear variation of microstrain with inverse
particle size, 1/d nm-1 (i.e. epsilon.d = 16.5 nm.%). A rapid increase in the
saturation magnetization below a critical size dc ~ 35 nm, exhibiting a
(1/d)^alpha (alpha ~ 2.6) dependence, is attributed to the influence of
microstrain. We propose an empirical formula M is proportional to
(1/d)epsilon^beta (beta ~ 1.6) to highlight the contributions from both the
size and microstrain towards the total magnetization in the doped systems. The
magnetization observed in nanoparticles is thus, a result of competing magnetic
contribution from the terminated spin cycloid on the surface and counteracting
microstrain present at a given size. Large magnetodielectric response of ~ 9.5
% is observed in spark plasma sintered pellets with optimal size and doping
concentration, revealing a strong correlation between magnetic and
ferroelectric order parameters.",1703.07190v1
2017-06-06,Magnetic order and interactions in ferrimagnetic Mn3Si2Te6,"The magnetism in Mn$_3$Si$_2$Te$_6$ has been investigated using thermodynamic
measurements, first principles calculations, neutron diffraction and diffuse
neutron scattering on single crystals. These data confirm that
Mn$_3$Si$_2$Te$_6$ is a ferrimagnet below a Curie temperature of $T_C$
approximately 78K. The magnetism is anisotropic, with magnetization and neutron
diffraction demonstrating that the moments lie within the basal plane of the
trigonal structure. The saturation magnetization of approximately 1.6$\mu_B$/Mn
at 5K originates from the different multiplicities of the two
antiferromagnetically-aligned Mn sites. First principles calculations reveal
antiferromagnetic exchange for the three nearest Mn-Mn pairs, which leads to a
competition between the ferrimagnetic ground state and three other magnetic
configurations. The ferrimagnetic state results from the energy associated with
the third-nearest neighbor interaction, and thus long-range interactions are
essential for the observed behavior. Diffuse magnetic scattering is observed
around the 002 Bragg reflection at 120K, which indicates the presence of strong
spin correlations well above $T_C$. These are promoted by the competing ground
states that result in a relative suppression of $T_C$, and may be associated
with a small ferromagnetic component that produces anisotropic magnetism below
$\approx$330K.",1706.01925v1
2017-06-13,Novel Exotic Magnetic Spin-order in Co5Ge3 Nano-size Materials,"The Cobalt-germanium (Co-Ge) is a fascinating complex alloy system that has
unique structure and exhibit range of interesting magnetic properties which
would change when reduce to nanoscale dimension. At this experimental work, the
high-aspect-ratio Co5Ge3 nanoparticle with average size of 8nm was synthesized
by gas aggregation-type cluster-deposition technology. The nanostructure
morphology of the as-made binary Co5Ge3 nanoparticles demonstrate excellent
single-crystalline hexagonal structure with mostly preferable growth along
(110) and (102) directions. In contrast the bulk possess Pauli paramagnetic
spin-order at all range of temperature, here we discover size-driven new
magnetic ordering of as-synthesized Co5Ge3 nanoparticles exhibiting
ferromagnetism at room temperature with saturation magnetization of Ms = 32.2
emu/cm3. This is first report of observing such new magnetic spin ordering in
this kind of material at nano-size which the magnetization has lower
sensitivity to thermal energy fluctuation and exhibit high Curie temperature
close to 850 K. This ferromagnetic behavior along with higher Curie temperature
at Co5Ge3 nanoparticles are attributes to low-dimension and quantum-confinement
effect which imposes strong spin coupling and provides a new set of size-driven
spin structures in Co5Ge3 nanoparticle which no such magnetic behavior being
present in the bulk of same material. This fundamental scientific study
provides important insights into the formation, structural, and the magnetic
property of sub 10nm Co5Ge3 nanostructure which shall lead to promising
practical versatile applications for magneto- germanide based nano-devices.",1706.04271v2
2017-09-04,Many-body forces in magnetic neutron stars,"In this work, we study in detail the effects of many-body forces on the
equation of state and the structure of magnetic neutron stars. The stellar
matter is described within a relativistic mean field formalism that takes into
account many-body forces by means of a non-linear meson field dependence on the
nuclear interaction coupling constants. We assume that matter is at zero
temperature, charge neutral, in beta-equilibrium, and populated by the baryon
octet, electrons, and muons. In order to study the effects of different degrees
of stiffness in the equation of state, we explore the parameter space of the
model, which reproduces nuclear matter properties at saturation, as well as
massive neutron stars. Magnetic field effects are introduced both in the
equation of state and in the macroscopic structure of stars by the
self-consistent solution of the Einstein-Maxwell equations. In addition,
effects of poloidal magnetic fields on the global properties of stars, as well
as density and magnetic field profiles are investigated. We find that not only
different macroscopic magnetic field distributions, but also different
parameterizations of the model for a fixed magnetic field distribution impact
the gravitational mass, deformation and internal density profiles of stars.
Finally, we also show that strong magnetic fields affect significantly the
particle populations of stars",1709.01017v1
2018-05-19,Frustration of square cupola in Sr(TiO)Cu$_{4}$(PO$_{4}$)$_{4}$,"The structural and magnetic properties of the square-cupola antiferromagnet
Sr(TiO)Cu$_{4}$(PO$_{4}$)$_{4}$ are investigated via x-ray diffraction,
magnetization, heat capacity, and $^{31}$P nuclear magnetic resonance
experiments on polycrystalline samples, as well as density-functional
band-structure calculations. The temperature-dependent unit cell volume could
be described well using the Debye approximation with the Debye temperature of
$\theta_{\rm D} \simeq $ 550~K. Magnetic response reveals a pronounced
two-dimensionality with a magnetic long-range-order below $T_{\rm N} \simeq
6.2$~K. High-field magnetization exhibits a kink at $1/3$ of the saturation
magnetization. Asymmetric $^{31}$P NMR spectra clearly suggest strong in-plane
anisotropy in the magnetic susceptibility, as anticipated from the crystal
structure. From the $^{31}$P NMR shift vs bulk susceptibility plot, the
isotropic and axial parts of the hyperfine coupling between $^{31}$P nuclei and
the Cu$^{2+}$ spins are calculated to be $A_{\rm hf}^{\rm iso} \simeq 6539$ and
$A_{\rm hf}^{\rm ax} \simeq 952$~Oe/$\mu_{\rm B}$, respectively. The
low-temperature and low-field $^{31}$P NMR spectra indicate a commensurate
antiferromagnetic ordering. Frustrated nature of the compound is inferred from
the temperature-dependent $^{31}$P NMR spin-lattice relaxation rate and
confirmed by our microscopic analysis that reveals strong frustration of the
square cupola by next-nearest-neighbor exchange couplings.",1805.07497v1
2018-05-22,Small-scale dynamo simulations: Magnetic field amplification in exploding granules and the role of deep and shallow recirculation,"We analyze recent high resolution photospheric small-scale dynamo simulations
that were computed with the MURaM radiative MHD code. We focus the analysis on
newly forming downflow lanes in exploding granules since they show how weakly
magnetized regions in the photosphere (center of granules) evolve into strongly
magnetized regions (downflow lanes). We find that newly formed downflow lanes
exhibit initially mostly a laminar converging flow that amplifies the vertical
magnetic field embedded in the granule from a few 10 G to field strengths
exceeding 800 G. This results in extended magnetic sheets that have a length
comparable to granular scales. Field amplification by turbulent shear happens
first a few 100 km beneath the visible layers of the photosphere. Shallow
recirculation transports the resulting turbulent field into the photosphere
within minutes, after which the newly formed downflow lane shows a mix of
strong magnetic sheets and turbulent field components. We stress in particular
the role of shallow and deep recirculation for the organization and strength of
magnetic field in the photosphere and discuss the photospheric and
sub-photospheric energy conversion associated with the small-scale dynamo
process. While the energy conversion through the Lorentz force depends only
weakly on the saturation field strength (and therefore deep or shallow
recirculation), it is strongly dependent on the magnetic Prandtl number. We
discuss the potential of these findings for further constraining small-scale
dynamo models through high resolution observations.",1805.08390v1
2019-01-28,Study of Dynamo Action in Three Dimensional Magnetohydrodynamic Plasma with Arnold-Beltrami-Childress Flow,"For a three dimensional magnetohydrodynamic (MHD) plasma the dynamo action
with ABC flow as initial condition has been studied. The study delineates
crucial parameter that gives a transition from coherent nonlinear oscillation
to dynamo. Further, for both kinematic and dynamic models at magnetic Prandtl
number equal to unity the dynamo action is studied for driven ABC flows. The
magnetic resistivity has been chosen at a value where the fast dynamo occurs
and the growth rate shows no further variation with the change of magnetic
Reynold's number. The exponent of growth of magnetic energy increases,
indicating a faster dynamo, if a higher wave number is excited compared to the
one with a lower wave number. The result has been found to hold good for both
kinematic and externally forced dynamic dynamos where the backreaction of
magnetic field on the velocity field is no more negligible. In case of an
externally forced dynamic dynamo, the super Alfvenic flows have been found to
excite strong dynamos giving rise to the growth of magnetic energy of seven
orders of magnitude. The back-reaction of magnetic field on the velocity field
through Lorentz force term has been found to affect the dynamics of the
velocity field and in turn the dynamics of magnetic field, leading to a
saturation, when the dynamo action is very prominent.",1901.09610v1
2019-02-11,"Magnetization process of the insulating ferromagnetic semiconductor (Al,Fe)Sb","We have studied the magnetization process of the new insulating ferromagnetic
semiconductor (Al,Fe)Sb by means of x-ray magnetic circular dichroism. For an
optimally doped sample with 10% Fe, a magnetization was found to rapidly
increase at low magnetic fields and to saturate at high magnetic fields at room
temperature, well above the Curie temperature of 40 K. We attribute this
behavior to the existence of nanoscale Fe-rich ferromagnetic domains acting as
superparamagnets. By fitting the magnetization curves using the Langevin
function representing superparamagnetism plus the paramagnetic linear function,
we estimated the average magnetic moment of the nanoscale ferromagnetic domain
to be 300-400 $\mu_{B}$, and the fraction of Fe atoms participating in the
nano-scale ferromagnetism to be $\sim$50%. Such behavior was also reported for
(In,Fe)As:Be and Ge:Fe, and seems to be a universal characteristic of the
Fe-doped ferromagnetic semiconductors. Further Fe doping up to 14% led to the
weakening of the ferromagnetism probably because antiferromagnetic
superexchange interaction between nearest-neighbor Fe-Fe pairs becomes
dominant.",1902.03742v1
2019-08-15,Breakdown of intermediate one-half magnetization plateau of spin-1/2 Ising-Heisenberg and Heisenberg branched chains at triple and Kosterlitz-Thouless critical points,"The spin-1/2 Ising-Heisenberg branched chain composed of regularly
alternating Ising spins and Heisenberg dimers involving an additional side
branching is rigorously solved in a magnetic field by the transfer-matrix
approach. The ground-state phase diagram, the magnetization process and the
concurrence measuring a degree of bipartite entanglement within the Heisenberg
dimers are examined in detail. Three different ground states were found
depending on a mutual interplay between the magnetic field and two different
coupling constants: the modulated quantum antiferromagnetic phase, the quantum
ferrimagnetic phase and the classical ferromagnetic phase. Two former quantum
ground states are manifested in zero-temperature magnetization curves as
intermediate plateaus at zero and one-half of the saturation magnetization,
whereas the one-half plateau disappears at a triple point induced by a strong
enough ferromagnetic Ising coupling. The ground-state phase diagram and
zero-temperature magnetization curves of the analogous spin-1/2 Heisenberg
branched chain were investigated using DMRG calculations. The latter fully
quantum Heisenberg model involves, besides two gapful phases manifested as zero
and one-half magnetization plateaus, gapless quantum spin-liquid phase. The
intermediate one-half plateau of the spin-1/2 Heisenberg branched chain
vanishes at Kosterlitz-Thouless quantum critical point between gapful and
gapless quantum ground states unlike the triple point of the spin-1/2
Ising-Heisenberg branched chain.",1908.05639v1
2019-12-23,Fluctuation Dynamo in Collisionless and Weakly Collisional Magnetized Plasmas,"In weakly collisional astrophysical plasmas, such as the intracluster medium
of galaxy clusters, the amplification of cosmic magnetic fields by chaotic
fluid motions is hampered by the adiabatic production of magnetic-field-aligned
pressure anisotropy. This anisotropy drives a viscous stress parallel to the
field that inhibits the plasma's ability to stretch magnetic-field lines. I
demonstrate through the use of kinetic simulations that in high-$\beta$
plasmas, kinetic ion-Larmor scale instabilities sever the adiabatic link
between the thermal and magnetic pressures, reducing this viscous stress and
thereby allowing the dynamo to operate. Two distinct regimes of the fluctuation
dynamo in a magnetized plasma are identified: one in which these instabilities
efficiently regulate the pressure anisotropy and one in which this regulation
is imperfect. I elucidate the role of these kinetic instabilities on the plasma
viscosity and determine how the fields and flows self-organize to allow the
dynamo to operate in the face of parallel viscous stresses. In the case of
efficient pressure-anisotropy regulation, the plasma dynamo closely resembles
its more traditional Pm ~ 1 MHD counterpart. When the regulation is imperfect,
the dynamo exhibits characteristics remarkably similar to those found in the
saturated state of the MHD dynamo. A novel set of microphysical closures for
fluid simulations that bridges these two regimes are constructed, exhibiting
explosive magnetic-field growth caused by a field-strength-dependent viscosity.
The dynamos in both collisionless and weakly collisional plasmas are then
closely compared to each other, revealing substantial differences in how
sub-parallel viscous motions behave. The former (collisionless) scenario
experiences a cascade of stretching motions to sub-Larmor scales that lead to
increasingly fast dynamo as the magnetic Reynolds number is increased.",1912.11072v1
2020-01-22,Generation of strong magnetic fields in a nascent neutron star accounting for the chiral magnetic effect,"We propose the mean field dynamo model for the generation of strongest
magnetic fields, $B\sim 10^{15}\,{\rm G}$, in a neutron star (NS) accounting
for the chiral magnetic effect (CME) driven by the shock in a supernova (SN)
progenitor of that NS. The temperature jump at a narrow shock front, where an
initial magnetic field existing in inflowing matter rises sharply, is the
source of the CME that prevails significantly the erasure of the CME due to the
spin-flip through Coulomb collisions in plasma. The growth of the magnetic
field just behind the shock given by the instability term $\nabla\times (\alpha
{\bf B})$ in induction equation, stops after a successful SN explosion that
throws out the mantle of a protoneutron star. As a result, such an explosion
interrupts the transfer of strongly magnetized plasma from the shock onto NS
surface and leads to the saturation of the magnetic field. Assuming the rigid
protostar rotation, we employ the mean field dynamo, which is similar to the
$\alpha^2$-dynamo known in the standard magnetohydrodynamics (MHD). The novelty
of our model is that $\alpha^2$-dynamo is based on concepts of particle
physics, applied in MHD, rather than by a mirror asymmetry of convective
vortices in the rotating convection.",2001.08139v1
2020-06-05,Sgr A* near-infrared flares from reconnection events in a magnetically arrested disc,"Large-amplitude Sgr A* near-infrared flares result from energy injection into
electrons near the black hole event horizon. Astrometry data show continuous
rotation of the emission region during bright flares, and corresponding
rotation of the linear polarization angle. One broad class of physical flare
models invokes magnetic reconnection. Here we show that such a scenario can
arise in a general relativistic magnetohydrodynamic simulation of a
magnetically arrested disc. Saturation of magnetic flux triggers eruption
events, where magnetically dominated plasma is expelled from near the horizon
and forms a rotating, spiral structure. Dissipation occurs via reconnection at
the interface of the magnetically dominated plasma and surrounding fluid. This
dissipation is associated with large increases in near-infrared emission in
models of Sgr A*, with durations and amplitudes consistent with the observed
flares. Such events occur at roughly the timescale to re-accumulate the
magnetic flux from the inner accretion disc, 10h for Sgr A*. We study
near-infrared observables from one sample event to show that the emission
morphology tracks the boundary of the magnetically dominated region. As the
region rotates around the black hole, the near-infrared centroid and linear
polarization angle both undergo continuous rotation, similar to the behavior
seen in Sgr A* flares.",2006.03657v2
2020-09-15,Dynamo saturation through the latitudinal variation of bipolar magnetic regions in the Sun,"Observations of the solar magnetic cycle showed that the amplitude of the
cycle did not grow all the time in the past. Thus, there must be a mechanism to
halt the growth of the magnetic field in the Sun. We demonstrate a recently
proposed mechanism for this under the Babcock--Leighton dynamo framework, which
is believed to be the most promising paradigm for the generation of the solar
magnetic field at present. This mechanism is based on the observational fact
that the stronger solar cycles produce bipolar magnetic regions (BMRs) at
higher latitudes and thus have higher mean latitudes than the weaker ones. We
capture this effect in our three-dimensional Babcock--Leighton solar dynamo
model and show that when the toroidal magnetic field tries to grow, it produces
BMRs at higher latitudes. The BMRs at higher latitudes generate a less poloidal
field, which consequently limits the overall growth of the magnetic field in
our model. Thus, our study suggests that the latitudinal variation of BMRs is a
potential mechanism for limiting the magnetic field growth in the Sun.",2009.06969v2
2020-12-02,"Synthesis, structure and magnetic properties of honeycomb-layered Li3Co2SbO6 with new data on its sodium precursor, Na3Co2SbO6","Li3Co2SbO6 is prepared by molten salt ion exchange and its structure refined
by the Rietveld method confirming the honeycomb-type Co/Sb ordering of its Na
precursor. Monoclinic rather than trigonal symmetry of Na3Co2SbO6 is directly
demonstrated for the first time by peak splitting in the high-resolution
synchrotron XRD pattern. The long-range antiferromagnetic order is established
at TN about 6.7 K and 9.9 K in Na3Co2SbO6 and Li3Co2SbO6, respectively,
confirmed by both the magnetic susceptibility and specific heat. Spin-wave
analysis of specific heat data indicates the presence of 3D AFM magnons in
Na3Co2SbO6 and 2D AFM magnons in Li3Co2SbO6. The field dependence of the
magnetization almost reaches saturation in moderate magnetic fields up to 9 T
and demonstrates characteristic features of magnetic field induced
spin-reorientation transitions for both A3Co2SbO6 (A = Na, Li). Overall
thermodynamic studies show that the magnetic properties of both compounds are
very sensitive to an external magnetic field, thus predicting a non-trivial
ground state with a rich magnetic phase diagram. The ground state spin
configuration of Li3Co2SbO6 has been determined by low-temperature neutron
powder diffraction. It represents a ferromagnetic arrangement of moments in the
honeycomb layers with antiferromagnetic coupling between adjacent layers.",2012.01093v1
2021-02-28,Flare Activity and Magnetic Feature Analysis of the Flare Stars II: Sub-Giant Branch,"We present an investigation of the magnetic activity and flare
characteristics of the sub-giant stars mostly from F and G spectral types and
compare the results with the main-sequence (MS) stars. The light curve of 352
stars on the sub-giant branch (SGB) from the Kepler mission is analyzed in
order to infer stability, relative coverage and contrast of the magnetic
structures and also flare properties using three flare indexes. The results
show that: (i) Relative coverage and contrast of the magnetic features along
with rate, power and magnitude of flares increase on the SGB due to the
deepening of the convective zone and more vigorous magnetic field production
(ii) Magnetic activity of the F and G-type stars on the SGB does not show
dependency to the rotation rate and does not obey the saturation regime. This
is the opposite of what we saw for the main sequence, in which the G-, K- and
M-type stars show clear dependency to the Rossby number; (iii) The positive
relationship between the magnetic features stability and their relative
coverage and contrast remains true on the SGB, though it has lower dependency
coefficient in comparison with the MS; (iv) Magnetic proxies and flare indexes
of the SGB stars increase with increasing the relative mass of the convective
zone.",2103.00478v1
2021-06-14,Yb delafossites: unique exchange frustration of 4f spin 1/2 moments on a perfect triangular lattice,"While the Heisenberg model for magnetic Mott insulators on planar lattice
structures is comparatively well understood in the case of transition metal
ions, the intrinsic spin-orbit entanglement of 4f magnetic ions on such
lattices shows fascinating new physics largely due to corresponding strong
anisotropies both in their single-ion and their exchange properties. We show
here that the Yb delafossites, containing perfect magnetic Yb$^{3+}$ triangular
lattice planes with pseudospin $s=1/2$ at low temperatures, are an ideal
platform to study these new phenomena. Competing frustrated interactions may
lead to an absence of magnetic order associated to a gapless spin liquid ground
state with a huge linear specific heat exceeding that of many heavy fermions,
whereas the application of a magnetic field induces anisotropic magnetic order
with successive transitions into different long ranged ordered structures. In
this comparative study, we discuss our experimental findings in terms of a
unified crystal-field and exchange model. We combine electron paramagnetic
resonance (EPR) experiments and results from neutron scattering with
measurements of the magnetic susceptibility, isothermal magnetization up to
full polarization, and specific heat to determine the relevant model
parameters. The impact of the crystal field is discussed as well as the
symmetry-compatible form of the exchange tensor, and we give explicit
expressions for the anisotropic g factor, the temperature dependence of the
susceptibility, the exchange-narrowed EPR linewidth and the saturation field.",2106.07576v1
2021-07-23,Intermixing Induced Anisotropy Variations in CoB-based Chiral Multilayer Films,"We examine the atomic intermixing phenomenon in three distinct amorphous
CoB-based multilayer thin film platforms - Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO
- which are shown to stabilise room-temperature chiral magnetic textures.
Intermixing occurs predominantly between adjacent metallic layers. Notably, it
is stack-order dependent, and particularly extensive when Ir sits atop CoB.
Intermixing induced variations in magnetic properties are ascribed to the
formation of magnetic dead layer arising from CoIr alloying in the metallic
stacks. It also produces systematic variations in saturation magnetization, by
as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness
for the transition from perpendicular to in-plane magnetic anisotropy differs
by more than 2x across the stacks. Finally, with thermal annealing treatment
over moderate temperatures of 150-300 degree Celsius, the magnetic anisotropy
increases monotonically across all stacks, coupled with discernibly larger Hc
for the metallic stacks. These are attributed to thermally induced CoPt
alloying and MgO crystallization in the metallic and oxide stacks,
respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its
amorphous nature after annealing. Our results set the stage for harnessing the
collective attributes of amorphous CoB-based material platforms and associated
annealing processes for modulating magnetic interactions, enabling the tuning
of chiral magnetic texture properties in ambient conditions.",2107.11034v1
2022-03-18,Structural and Magnetic Properties of Pt/Co/Mn-Based Multilayers,"Magnetic multilayers are a rich class of materials systems with numerous
highly tunable physical parameters that determine both their magnetic and
electronic properties. Here we present a comprehensive experimental study of a
novel system, Pt/Co/Mn, which extends the group of Pt/Co/X ($\mathrm{X}=$
metal) multilayers that have been investigated thus far. We demonstrate that an
increasing Co layer thickness changes the magnetic anisotropy from out-of-plane
to in-plane, whereas the deposition of thicker Mn layers leads to a decrease in
the saturation magnetization. Temperature-dependent magnetometry measurements
reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces
being responsible for the observed Mn thickness dependence of the magnetization
reversal. Moreover, magneto-optical imaging experiments indicate systematic
changes in magnetic domain patterns as a function of the Co and Mn layer
thickness, suggesting the existence of bubble-like domains -- potentially even
magnetic skyrmions -- in the case of sufficiently thick Mn layers, which are
expected to contribute to a sizeable Dzyaloshinskii-Moriya interaction in the
multilayer stacks. We identify Pt/Co/Mn as a highly complex multilayer system
with strong potential for further fundamental studies and possible
applications.",2203.10059v2
2022-05-24,Competing magnetic phases in the frustrated spin-1/2 chain compound $β$-TeVO$_4$ probed by NMR,"In frustrated spin-1/2 chains the competition between the nearest- and
next-nearest-neighbor exchange interactions leads to a rich phase diagram that
becomes even richer in the presence of perturbations in their material
realizations. These effects are still largely unexplored, so that new insight
into static and dynamic magnetism, in particular by sensitive local probes, is
highly desired. Here we present a comprehensive $^{17}$O nuclear magnetic
resonance study of $\beta$-TeVO$_4$, where the anisotropy of the main exchange
interactions and additional weak interchain exchange interactions complement
the theoretical phase diagram. Our results confirm the dynamical nature of the
intriguing spin-stripe phase that has been reported in previous studies. In
addition, we find that the magnetic order in the high-field phase, which
develops just below the magnetization saturation, is consistent with an unusual
type of spin-density-wave (SDW) order with different alignments of the magnetic
moments on the neighboring chains. This is reminiscent of the ordering in the
SDW phase, realized in the absence of the magnetic field, and is thus most
likely stabilized by magnetic anisotropy.",2205.11875v1
2022-06-02,A mechanically strong and ductile soft magnet with extremely low coercivity,"Soft magnetic materials (SMMs) serve in electrical applications and
sustainable energy supply, allowing magnetic flux variation in response to
changes in applied magnetic field, at low energy loss1. The electrification of
transport, households and manufacturing leads to an increase in energy
consumption due to hysteresis losses2. Therefore, minimizing coercivity, which
scales these losses, is crucial3. Yet, meeting this target alone is not enough:
SMMs in electrical engines must withstand severe mechanical loads, i.e., the
alloys need high strength and ductility4. This is a fundamental design
challenge, as most methods that enhance strength introduce stress fields that
can pin magnetic domains, thus increasing coercivity and hysteretic losses5.
Here, we introduce an approach to overcome this dilemma. We have designed a
Fe-Co-Ni-Ta-Al multicomponent alloy with ferromagnetic matrix and paramagnetic
coherent nanoparticles (~91 nm size, ~55% volume fraction). They impede
dislocation motion, enhancing strength and ductility. Their small size, low
coherency and small magnetostatic energy create an interaction volume below the
magnetic domain wall width, leading to minimal domain wall pinning, thus
maintaining the soft magnetic properties. The alloy has a tensile strength of
1336 MPa at 54% tensile elongation, extremely low coercivity of 78 A/m (<1 Oe),
moderate saturation magnetization of 100 Am2/kg, and high electrical
resistivity of 103 {\mu}{\Omega} u Ohm cm.",2207.05686v1
2022-11-10,Field induced non-BEC transitions in frustrated magnets,"Frustrated spin-systems have traditionally proven challenging to understand,
owing to a scarcity of controlled methods for their analyses. By contrast,
under strong magnetic fields, certain aspects of spin systems admit simpler and
universal description in terms of hardcore bosons. The bosonic formalism is
anchored by the phenomenon of Bose-Einstein condensation (BEC), which has
helped explain the behaviors of a wide range of magnetic compounds under
applied magnetic fields. Here, we focus on the interplay between frustration
and externally applied magnetic field to identify instances where the BEC
paradigm is no longer applicable. As a representative example, we consider the
antiferromagnetic $J_1 - J_2 - J_3$ model on the square lattice in the presence
of a uniform external magnetic field, and demonstrate that the
frustration-driven suppression of the N\'{e}el order leads to a Lifshitz
transition for the hardcore bosons. In the vicinity of the Lifshitz point, the
physics becomes unmoored from the BEC paradigm, and the behavior of the system,
both at and below the saturation field, is controlled by a Lifshitz
multicritical point. We obtain the resultant universal scaling behaviors, and
provide strong evidence for the existence of a frustration and magnetic-field
driven correlated bosonic liquid state along the entire phase boundary
separating the N\'{e}el phase from other magnetically ordered states.",2211.05771v3
2023-01-04,Magnetic properties of the layered heavy fermion antiferromagnet CePdGa$_6$,"We report the magnetic properties of the layered heavy fermion
antiferromagnet CePdGa$_{6}$, and their evolution upon tuning with the
application of magnetic field and pressure. CePdGa$_{6}$ orders
antiferromagnetically below $T\rm_{N}$ = 5.2 K, where there is evidence for
heavy fermion behavior from an enhanced Sommerfeld coefficient. Our results are
best explained by a magnetic ground state of ferromagnetically coupled layers
of Ce $4f$-moments orientated along the $c$-axis, with antiferromagnetic
coupling between layers. At low temperatures we observe two metamagnetic
transitions for fields applied along the $c$-axis corresponding to spin-flip
transitions, where the lower transition is to a different magnetic phase with a
magnetization one-third of the saturated value. From our analysis of the
magnetic susceptibility, we propose a CEF level scheme which accounts for the
Ising anisotropy at low temperatures, and we find that the evolution of the
magnetic ground state can be explained considering both antiferromagnetic
exchange between nearest neighbor and next nearest neighbor layers, indicating
the influence of long-range interactions. Meanwhile we find little change of
$T\rm_{N}$ upon applying hydrostatic pressures up to 2.2 GPa, suggesting that
significantly higher pressures are required to examine for possible quantum
critical behaviors.",2301.01444v1
2023-03-03,Room-Temperature Magnetic Skyrmions in Pt/Co/Cu Multilayers,"Magnetic skyrmions are promising for next-generation information storage and
processing owing to their potential advantages in data storage density,
robustness, and energy efficiency. The magnetic multilayers consisting of Pt,
Co, and a third metal element $X$ provide an ideal platform to study the
skyrmions due to their highly tunable magnetic properties. Here, we report the
observation of room-temperature bubble-like N\'eel skyrmions in epitaxial
Pt/Co/Cu multilayers in samples with multidomain states in zero field. The
magneto-optic Kerr effect (MOKE) and superconducting quantum interference
device (SQUID) magnetometry are applied to investigate the shapes of the
hysteresis loops, the magnetic anisotropy, and the saturation magnetization. By
tuning the Co thickness and the number of periods, we achieve perpendicular and
in-plane magnetized states and multidomain states that are identified by a
wasp-waisted hysteresis loop. Skyrmions are directly imaged by magnetic force
microscopy (MFM) and Lorentz transmission electron microscopy (LTEM). The
development of room-temperature skyrmions in Pt/Co/Cu multilayers may lead to
advances in skyrmion-related research and applications.",2303.02117v2
2023-04-29,Evolution of medium-range order and its correlation with magnetic nanodomains in Fe-Dy-B-Nb bulk metallic glasses,"Fe-based metallic glasses are promising functional materials for advanced
magnetism and sensor fields. Tailoring magnetic performance in amorphous
materials requires a thorough knowledge of the correlation between structural
disorder and magnetic order, which remains ambiguous. Two practical
difficulties remain: the first is directly observing subtle magnetic structural
changes on multiple scales, and the second is precisely regulating the various
amorphous states. Here we propose a novel approach to tailor the amorphous
structure through the liquid liquid phase transition. In-situ synchrotron
diffraction has unraveled a medium-range ordering process dominated by
edge-sharing cluster connectivity during the liquid-liquid phase transition.
Moreover, nanodomains with topological order have been found to exist in
composition with liquid-liquid phase transition, manifesting as hexagonal
patterns in small-angle neutron scattering profiles. The liquid-liquid phase
transition can induce the nanodomains to be more locally ordered, generating
stronger exchange interactions due to the reduced Fe-Fe bond and the enhanced
structural order, leading to the increment of saturation magnetization.
Furthermore, the increased local heterogeneity in the medium range scale
enhances the magnetic anisotropy, promoting the permeability response under
applied stress and leading to a better stress-impedance effect. These
experimental results pave the way to tailor the magnetic structure and
performance through the liquid-liquid phase transition.",2305.00274v1
2023-07-16,Long-term variations of the Sun's photospheric magnetic field,"Variations of the weak magnetic fields of the photosphere with periods of the
order of the solar magnetic cycle were investigated. Synoptic maps of the
photospheric magnetic field produced by NSO Kitt Peak for the period from 1978
to 2016 were used as initial data. In order to study weak magnetic fields, the
saturation threshold for synoptic maps was set at 5 G. On the base of
transformed synoptic maps the time-latitude chart was built. 18 profiles of the
magnetic field evenly distributed along the sine of latitude from the north to
the south pole were selected in the diagram for the further analysis. Time
dependencies were averaged by sliding smoothing over 21 Carrington rotations.
The approximation of averaged time dependencies by the sinusoidal function made
it possible to distinguish in weak magnetic fields a cyclic component with a
period of about 22 years (the period of the Hale magnetic cycle). The
dependence of 22-year variation on latitude was studied. In addition to the
well-known 22-year change in the near-polar field, similar variations were
found for the fields at all latitudes. The exception was latitudes $26^\circ$
and $33^\circ$ in the northern and $26^\circ$ in the southern hemisphere. These
mid-latitude intervals were characterized by a predominance of short-period
variations. The amplitude of the long-term variation decreased from the poles
to the equator, with the period of variation remaining almost constant (T =
22.3 years).",2307.08009v1
2023-08-28,Magnetic kagome materials RETi3Bi4 family with weak interlayer interactions,"Kagome materials have attracted a surge of research interest recently,
especially for the ones combining with magnetism, and the ones with weak
interlayer interactions which can fabricate thin devices. However, kagome
materials combining both characters of magnetism and weak interlayer
interactions are rare. Here we investigate a new family of titanium based
kagome materials RETi3Bi4 (RE = Eu, Gd and Sm). The flakes of nanometer
thickness of RETi3Bi4 can be obtained by exfoliation due to the weak interlayer
interactions. According to magnetic measurements, out-of-plane ferromagnetism,
out-of-plane anti-ferromagnetism, and in-plane ferromagnetism are formed for RE
= Eu, Gd, and Sm respectively. The magnetic orders are simple and the
saturation magnetizations can be relatively large since the rare earth elements
solely provide the magnetic moments. Further by angle-resolved photoemission
spectroscopy (ARPES) and first-principles calculations, the electronic
structures of RETi3Bi4 are investigated. The ARPES results are consistent with
the calculations, indicating the bands characteristic with kagome sublattice in
RETi3Bi4. We expect these materials to be promising candidates for observation
of the exotic magnetic topological phases and the related topological quantum
transport studies.",2308.14509v1
2023-12-01,Magnetic phase diagram and magneto-elastic coupling of NdB$_4$ studied by high-resolution capacitance dilatometry up to 35~T,"We report high-resolution dilatometry studies on single crystals of the
Shastry-Sutherland-lattice magnet NdB$_4$ supported by specific heat and
magnetometry data. Our dilatometric studies evidence pronounced anomalies at
the phase boundaries which imply strong magneto-elastic coupling. The evolution
of the three zero-field phase transitions separating distinct antiferromagnetic
phases at $TN=17.2$~K, $TIT=6.8$~K and $TLT=4.8$~K can thus be traced in
applied magnetic fields which provides the magnetic phase diagrams for
$B\parallel c$ up to 15~T and for $B\parallel [110]$ up to 35~T. New in-field
phases are discovered for both field directions and already known phases are
confirmed. In particular, phase boundaries between different phases are
unambiguously shown by sign changes of observed anomalies and corresponding
changes in uniaxial pressure effects. For $B||c$, we find a 1/4-magnetization
plateau in addition to a previously reported plateau at 1/5 of the saturation
magnetization. TN increases for $B\parallel c$ in fields up to 15~T implying
that magnetic moments of the all-in/all-out structure in the high temperature
AFM ordered phase are driven towards the $c$ axis in high magnetic fields.
Uniaxial pressure dependencies
${\partial}T_{\mathrm{crit}}/{\partial}p_{\mathrm{c}}$ of the phase transition
temperatures for magnetic fields and pressure applied along the $c$ axis are
derived from the data.",2312.00715v1
2024-03-25,Stellar Spin Down in Post-Mass Transfer Binary Systems,"Motivated by measurements of the rotation speed of accretor stars in
post-mass-transfer (post-MT) systems, we investigate how magnetic braking
affects the spin-down of individual stars during binary evolution with the
\texttt{MESAbinary} module. Unlike the conventional assumption of tidal
synchronization coupled with magnetic braking in binaries, we first calculate
whether tides are strong enough to synchronize the orbit. Subsequently, this
influences the spin-down of stars and the orbital separation. In this study, we
apply four magnetic braking prescriptions to reduce the spin angular momentum
of the two stars throughout the entire binary evolution simulation. Our
findings reveal that despite magnetic braking causing continuous spin-down of
the accretor, when the donor begins to transfer material onto the accretor, the
accretor can rapidly spin up to its critical rotation rate. After MT, magnetic
braking becomes more important in affecting the angular momentum evolution of
the stars. Post-MT accretor stars thus serve as a valuable testbed for
observing how the magnetic braking prescriptions operate in spinning down stars
from their critical rotation, including the saturation regimes of the magnetic
braking. The rotation rate of the accretor star, combined with its mass, could
provide age information since the cessation of MT. By comparing the models
against observation, the magnetic braking prescription by Garraffo et al.
(2018b) is found to better align with the rotation data of post-MT accretors.",2403.17279v1
2004-08-27,Progress in Anisotropic Plasma Physics,"In 1959 Weibel demonstrated that when a QED plasma has a temperature
anisotropy there exist unstable transverse magnetic excitations which grow
exponentially fast. In this paper we will review how to determine the growth
rates for these unstable modes in the weak-coupling and ultrarelativistic
limits in which the collective behavior is describable in terms are so-called
""hard-loops"". We will show that in this limit QCD is subject to instabilities
which are analogous to the Weibel instability in QED. The presence of such
instabilities dominates the early time evolution of a highly anisotropic
plasma; however, at longer times it is expected that these instabilities will
saturate (condense). I will discuss how the presence of non-linear interactions
between the gluons complicates the determination of the saturated state. In
order to discuss this I present the generalization of the Braaten-Pisarski
isotropic hard-thermal-loop effective action to a system with a temperature
anisotropy in the parton distribution functions. The resulting hard-loop
effective action can be used to determine the time and energy scales associated
with the possible saturation (condensation) of the gluonic modes. We will also
discuss the effects of anisotropies on observables, in particular on the heavy
quark energy loss.",0408314v2
2014-02-26,Anomalous temperature dependence of current induced torques in CoFeB|MgO heterostructures with Ta based underlayers,"We have studied the underlayer thickness and temperature dependences of the
current induced effective field in CoFeB|MgO heterostructures with Ta based
underlayers. The underlayer thickness at which the effective field saturates is
found to be different between the two orthogonal components of the effective
field, i.e. the damping-like term tends to saturate at smaller underlayer
thickness than the field-like term. For large underlayer thickness films in
which the effective field saturates, we find that the temperature significantly
influences the size of the effective field. A striking difference is found in
the temperature dependence of the two components: the damping-like term
decreases whereas the field-like term increases with increasing temperature.
Using a simple spin diffusion-spin transfer model, we find that all of these
results can be accounted for provided the real and imaginary parts of an
effective spin mixing conductance are negative. These results imply that either
spin transport in this system is different from conventional metallic
interfaces or effects other spin diffusion into the magnetic layer need to be
taken account in order to model the system accurately.",1402.6388v1
2017-03-07,MHD modeling of a DIII-D low-torque QH-mode discharge and comparison to observations,"Extended-MHD modeling of DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614
(2002)] quiescent H-mode (QH-mode) discharges with nonlinear NIMROD [C. R.
Sovinec et al., J. Comput. Phys. 195, 355 (2004)] simulations saturates into a
turbulent state but does not saturate when the steady-state flow inferred from
measurements is not included. This is consistent with the experimental
observations of the quiescent regime on DIII-D. The simulation with flow
develops into a saturated turbulent state where the n=1 and 2 toroidal modes
become dominant through an inverse cascade. Each mode in the range of n=1-5 is
dominant at a different time. Consistent with experimental observations during
QH-mode, the simulated state leads to large particle transport relative to the
thermal transport. Analysis shows that the amplitude and phase of the density
and temperature perturbations differ resulting in greater fluctuation-induced
convective particle transport relative to the convective thermal transport.
Comparison to magnetic-coil measurements shows that rotation frequencies differ
between the simulation and experiment, which indicates that more sophisticated
extended-MHD two-fluid modeling is required.",1703.02584v1
2018-03-30,Quasi-linear Transport in a Sheared Flow Field,"The evolution of a passive scalar field is considered for a slowly varying
stratified medium, which is convected in an incompressible sheared flow with
many overlapping static flux islands. Within the quasilinear/random phase
approximation, a multiple scale expansion is made. Due to the rapid spatial
variation of the temperature, the ""ensemble"" averaged/ slowly varying part of
the solution is not described by the arithmetic average of the oscillatory
evolution equation. The standard Markovian and continuum approximations are
shown to be invalid. For times of order $N$, where there are $O(N^2)$ excited
modes, most of the time dependent perturbation phase mixes away and the fluid
reaches a new saturated state with small time oscillations about the
temperature. This saturated state has smaller resonance layers, (corresponding
to magnetic islands) than those that occur in the isolated resonant
perturbation case. Thus the quasilinear response to the resonant interactions
reduces the effective size of the perturbations. The temperature gradient of
the saturated state vanishes at all the excited resonance surfaces but has a
nonzero average. Thus either the quasi-linear approximation ceases to be valid
on long time scales, or the fluid remains essentially in this modified
equilibrium and does not evolve diffusively. Thus collisionless, driftless fast
particles will not be lost rapidly in equilibria with many small islands.",1804.00042v1
2018-04-13,Tuning Rashba Spin-Orbit Coupling in Gated Multilayer InSe,"Manipulating the electron spin with the aid of spin-orbit coupling (SOC) is
an indispensable element of spintronics. Electrostatically gating a material
with strong SOC results in an effective magnetic field which can in turn be
used to govern the electron spin. In this work, we report the existence and
electrostatic tunability of Rashba SOC in multilayer InSe. We observed a
gate-voltage-tuned crossover from weak localization (WL) to weak
antilocalization (WAL) effect in quantum transport studies of InSe, which
suggests an increasing SOC strength. Quantitative analyses of magneto-transport
studies and energy band diagram calculations provide strong evidence for the
predominance of Rashba SOC in electrostatically gated InSe. Furthermore, we
attribute the tendency of the SOC strength to saturate at high gate voltages to
the increased electronic density of states-induced saturation of the electric
field experienced by the electrons in the InSe layer. This explanation of
nonlinear gate voltage control of Rashba SOC can be generalized to other
electrostatically gated semiconductor nanomaterials in which a similar tendency
of spin-orbit length saturation was observed (e.g. nanowire field effect
transistors), and is thus of broad implications in spintronics. Identifying and
controlling the Rashba SOC in InSe may serve pivotally in devising III-VI
semiconductor-based spintronic devices in the future.",1804.04992v2
2020-04-08,Zonally dominated dynamics and Dimits threshold in curvature-driven ITG turbulence,"The saturated state of turbulence driven by the ion-temperature-gradient
instability is investigated using a two-dimensional long-wavelength fluid model
that describes the perturbed electrostatic potential and perturbed ion
temperature in a magnetic field with constant curvature (a $Z$-pinch) and an
equilibrium temperature gradient. Numerical simulations reveal a well-defined
transition between a finite-amplitude saturated state dominated by strong
zonal-flow and zonal-temperature perturbations, and a blow-up state that fails
to saturate on a box-independent scale. We argue that this transition is
equivalent to the Dimits transition from a low-transport to a high-transport
state seen in gyrokinetic numerical simulations. A quasi-static staircase-like
structure of the temperature gradient intertwined with zonal flows, which have
patch-wise constant shear, emerges near the Dimits threshold. The turbulent
heat flux in the low-collisionality near-marginal state is dominated by
turbulent bursts, triggered by coherent long-lived structures closely
resembling those found in gyrokinetic simulations with imposed equilibrium flow
shear. The break up of the low-transport Dimits regime is linked to a
competition between the two different sources of poloidal momentum in the
system -- the Reynolds stress and the advection of the diamagnetic flow by the
$\boldsymbol{E}\times\boldsymbol{B}$ flow. By analysing the linear ITG modes,
we obtain a semi-analytic model for the Dimits threshold at large
collisionality.",2004.04047v2
2021-12-18,Magnetograph Saturation and the Open Flux Problem,"Extrapolations of line-of-sight photospheric field measurements predict
radial interplanetary magnetic field (IMF) strengths that are factors of ~2--4
too low. To address this ""open flux problem,'' we reanalyze the magnetograph
measurements from different observatories, with particular focus on those made
in the saturation-prone Fe I 525.0 nm line by the Mount Wilson Observatory
(MWO) and the Wilcox Solar Observatory (WSO). The total dipole strengths, which
determine the total open flux, generally show large variations among
observatories, even when their total photospheric fluxes are in agreement.
However, the MWO and WSO dipole strengths, as well as their total fluxes, agree
remarkably well with each other, suggesting that the two data sets require the
same scaling factor. As shown earlier by Ulrich et al., the saturation
correction $\delta^{-1}$ derived by comparing MWO measurements in the 525.0 nm
line with those in the nonsaturating Fe I 523.3 nm line depends sensitively on
where along the irregularly shaped 523.3 nm line wings the exit slits are
placed. If the slits are positioned so that the 523.3 and 525.0 nm signals
originate from the same height, $\delta^{-1}$ ~ 4.5 at disk center, falling to
~2 near the limb. When this correction is applied to either the MWO or WSO
maps, the derived open fluxes are consistent with the observed IMF magnitude.
Other investigators obtained scaling factors only one-half as large because
they sampled the 523.3 nm line farther out in the wings, where the shift
between the right- and left-circularly polarized components is substantially
smaller.",2112.09969v1
2023-03-31,Particle-In-Cell Simulations of Sunward and Anti-sunward Whistler Waves in the Solar Wind,"Spacecraft observations showed that electron heat conduction in the solar
wind is probably regulated by whistler waves, whose origin and efficiency in
electron heat flux suppression is actively investigated. In this paper, we
present Particle-In-Cell simulations of a combined whistler heat flux and
temperature anisotropy instability that can operate in the solar wind. The
simulations are performed in a uniform plasma and initialized with core and
halo electron populations typical of the solar wind. We demonstrate that the
instability produces whistler waves propagating both along (anti-sunward) and
opposite (sunward) to the electron heat flux. The saturated amplitudes of both
sunward and anti-sunward whistler waves are strongly correlated with their {\it
initial} linear growth rates, $B_{w}/B_0\sim (\gamma/\omega_{ce})^{\nu}$, where
for typical electron betas we have $0.6\lesssim \nu\lesssim 0.9$. The
correlations of whistler wave amplitudes and spectral widths with plasma
parameters (electron beta and temperature anisotropy) revealed in the
simulations are consistent with those observed in the solar wind. The
efficiency of electron heat flux suppression is positively correlated with the
saturated amplitude of sunward whistler waves. The electron heat flux can be
suppressed by 10--60% provided that the saturated amplitude of sunward whistler
waves exceeds about 1% of background magnetic field. Other experimental
applications of the presented results are discussed.",2303.18214v1
2023-06-27,Gyrokinetic theory of toroidal Alfvén eigenmode saturation via nonlinear wave-wave coupling,"Nonlinear wave-wave coupling constitutes an important route for the
turbulence spectrum evolution in both space and laboratory plasmas. For
example, in a reactor relevant fusion plasma, a rich spectrum of symmetry
breaking shear Alfv\'en wave (SAW) instabilities are expected to be excited by
energetic fusion alpha particles, and self-consistently determine the anomalous
alpha particle transport rate by the saturated electromagnetic perturbations.
In this work, we will show that the nonlinear gyrokinetic theory is a necessary
and powerful tool in qualitatively and quantitatively investigating the
nonlinear wave-wave coupling processes. More specifically, one needs to employ
the gyrokinetic approach in order to account for the breaking of the ``pure
Alfv\'enic state"" in the short wavelength kinetic regime, due to the short
wavelength structures associated with nonuniformity intrinsic to magnetically
confined plasmas.
  Using well-known toroidal Alfv\'en eigenmode (TAE) as a paradigm case, three
nonlinear wave-wave coupling channels expected to significantly influence the
TAE nonlinear dynamics are investigated to demonstrate the strength and
necessity of nonlinear gyrokinetic theory in predicting crucial processes in a
future reactor burning plasma. These are: 1. the nonlinear excitation of
meso-scale zonal field structures via modulational instability and TAE
scattering into short-wavelength stable domain; 2. the TAE frequency cascading
due to nonlinear ion induced scattering and the resulting saturated TAE
spectrum; and 3. the cross-scale coupling of TAE with micro-scale ambient drift
wave turbulence and its effect on TAE regulation and anomalous electron
heating.",2306.15579v1
2024-01-05,Effects of multi-dimensionality and energy exchange on electrostatic current-driven plasma instabilities and turbulence,"Large-amplitude current-driven plasma instabilities, which can transition to
the Buneman instability, were observed in one-dimensional (1D) simulations to
generate high-energy backstreaming ions. We investigate the saturation of
multi-dimensional plasma instabilities and its effects on energetic ion
formation. Such ions directly impact spacecraft thruster lifetimes and are
associated with magnetic reconnection and cosmic ray inception. An Eulerian
Vlasov--Poisson solver employing the grid-based direct kinetic method is used
to study the growth and saturation of 2D2V collisionless, electrostatic
current-driven instabilities spanning two dimensions each in the configuration
(D) and velocity (V) spaces supporting ion and electron phase-space transport.
Four stages characterise the electric potential evolution in such
instabilities: linear modal growth, harmonic growth, accelerated growth via
quasi-linear mechanisms alongside non-linear fill-in, and saturated turbulence.
Its transition and isotropisation process bears considerable similarities to
the development of hydrodynamic turbulence. While a tendency to isotropy is
observed in the plasma waves, followed by electron and then ion phase space
after several ion-acoustic periods, the formation of energetic backstreaming
ions is more limited in the 2D2V than in the 1D1V simulations. Plasma waves
formed by two-dimensional electrostatic kinetic instabilities can propagate in
the direction perpendicular to the net electron drift. Thus, large-amplitude
multi-dimensional waves generate high-energy transverse-streaming ions and
eventually limit energetic backward-streaming ions along the longitudinal
direction. The multi-dimensional study sheds light on interactions between
longitudinal and transverse electrostatic plasma instabilities, as well as
fundamental characteristics of the inception and sustenance of unmagnetised
plasma turbulence.",2401.05428v1
2006-08-08,Comparison of Magnetic Field Structures on Different Scales in and around the Filamentary Dark Cloud GF 9,"New visible polarization data combined with existing IR and FIR polarization
data are used to study how the magnetic field threading the filamentary
molecular cloud GF 9 connects to larger structures in its general environment.
We find that when both visible and NIR polarization data are plotted as a
function of extinction, there is no evidence for a plateau or a saturation
effect in the polarization at Av ~ 1.3 as seen in dark clouds in Taurus. This
lack of saturation effect suggests that even in the denser parts of GF 9 we are
still probing the magnetic field. The visible polarization is smooth and has a
well-defined orientation. The IR data are also well defined but with a
different direction, and the FIR data in the core region are well defined and
with yet another direction, but are randomly distributed in the filament
region. On the scale of a few times the mean radial dimension of the molecular
cloud, it is as if the magnetic field were `blind' to the spatial distribution
of the filaments while on smaller scales within the cloud, in the core region
near the IRAS point source PSC 20503+6006, polarimetry shows a rotation of the
magnetic field lines in these denser phases. Hence, in spite of the fact that
the spatial resolution is not the same in the visible/NIR and in the FIR data,
all the data put together indicate that the field direction changes with the
spatial scale. Finally, the Chandrasekhar and Fermi method is used to evaluate
the magnetic field strength, indicating that the core region is approximately
magnetically critical. A global interpretation of the results is that in the
core region an original poloidal field could have been twisted by a rotating
elongated (core+envelope) structure. There is no evidence for turbulence and
ambipolar diffusion does not seem to be effective at the present time.",0608188v1
2008-06-03,Euler-Lagrange models with complex currents of three-phase electrical machines and observability issues,"A new Lagrangian formulation with complex currents is developed and yields a
direct and simple method for modeling three-phase permanent-magnet and
induction machines. The Lagrangian is the sum a mechanical one and of a
magnetic one. This magnetic Lagrangian is expressed in terms of rotor angle,
complex stator and rotor currents. A complexification procedure widely used in
quantum electrodynamic is applied here in order to derive the Euler-Lagrange
equations with complex stator and rotor currents. Such complexification process
avoids the usual separation into real and imaginary parts and simplifies
notably the calculations. Via simple modifications of such magnetic Lagrangians
we derive new dynamical models describing permanent-magnet machines with both
saturation and saliency, and induction machines with both magnetic saturation
and space harmonics. For each model we also provide its Hamiltonian thus its
magnetic energy. This energy is also expressed with complex currents and can be
directly used in Lyapunov and/or passivity based control. Further, we briefly
investigate the observability of this class of Euler-Lagrange models, in the
so-called sensorless case when the measured output is the stator current and
the load torque is constant but unknown. For all the dynamical models obtained
via such variational principles, we prove that their linear tangent systems are
unobservable around a one-dimensional family of steady-states attached to the
same constant stator voltage and current. This negative result explains why
sensorless control of three-phase electrical machines around zero stator
frequency remains yet a difficult control problem.",0806.0387v4
2012-10-24,Local Study of Accretion Disks with a Strong Vertical Magnetic Field: Magnetorotational Instability and Disk Outflow,"We perform 3D vertically-stratified local shearing-box ideal MHD simulations
of the magnetorotational instability (MRI) that include a net vertical magnetic
flux, which is characterized by beta_0 (ratio of gas pressure to magnetic
pressure of the net vertical field at midplane). We have considered
beta_0=10^2, 10^3 and 10^4 and in the first two cases the most unstable linear
MRI modes are well resolved in the simulations. We find that the behavior of
the MRI turbulence strongly depends on beta_0: The radial transport of angular
momentum increases with net vertical flux, achieving alpha=0.08 for beta_0=10^4
and alpha>1.0 for beta_0=100, where alpha is the Shakura-Sunyaev parameter. A
critical value lies at beta_0=10^3: For beta_0>10^3, the disk consists of a gas
pressure dominated midplane and a magnetically dominated corona. The turbulent
strength increases with net flux, and angular momentum transport is dominated
by turbulent fluctuations. The magnetic dynamo that leads to cyclic flips of
large-scale fields still exists, but becomes more sporadic as net flux
increases. For beta_0<10^3, the entire disk becomes magnetic dominated. The
turbulent strength saturates, and the magnetic dynamo is quenched. Stronger
large-scale fields are generated with increasing net flux, which dominates
angular momentum transport. A strong outflow is launched from the disk by the
magnetocentrifugal mechanism, and the mass flux increases linearly with net
vertical flux and shows sign of saturation at beta_0=10^2. However, the outflow
is unlikely to be directly connected to a global wind: for beta_0>10^3, the
large-scale field has no permanent bending direction due to dynamo activities,
while for beta_0<10^3, the outflows from the top and bottom sides of the disk
bend towards opposite directions, inconsistent with a physical disk wind
geometry. Global simulations are needed to address the fate of the outflow.",1210.6661v2
2013-01-18,The small-scale dynamo: Breaking universality at high Mach numbers,"(Abridged) The small-scale dynamo may play a substantial role in magnetizing
the Universe under a large range of conditions, including subsonic turbulence
at low Mach numbers, highly supersonic turbulence at high Mach numbers and a
large range of magnetic Prandtl numbers Pm, i.e. the ratio of kinetic viscosity
to magnetic resistivity. Low Mach numbers may in particular lead to the
well-known, incompressible Kolmogorov turbulence, while for high Mach numbers,
we are in the highly compressible regime, thus close to Burgers turbulence. In
this study, we explore whether in this large range of conditions, a universal
behavior can be expected. Our starting point are previous investigations in the
kinematic regime. Here, analytic studies based on the Kazantsev model have
shown that the behavior of the dynamo depends significantly on Pm and the type
of turbulence, and numerical simulations indicate a strong dependence of the
growth rate on the Mach number of the flow. Once the magnetic field saturates
on the current amplification scale, backreactions occur and the growth is
shifted to the next-larger scale. We employ a Fokker-Planck model to calculate
the magnetic field amplification during the non-linear regime, and find a
resulting power-law growth that depends on the type of turbulence invoked. For
Kolmogorov turbulence, we confirm previous results suggesting a linear growth
of magnetic energy. For more general turbulent spectra, where the turbulent
velocity v_t scales with the characteristic length scale as u_\ell\propto
\ell^{\vartheta}, we find that the magnetic energy grows as
(t/T_{ed})^{2\vartheta/(1-\vartheta)}, with t the time-coordinate and T_{ed}
the eddy-turnover time on the forcing scale of turbulence. For Burgers
turbulence, \vartheta=1/2, a quadratic rather than linear growth may thus be
expected, and a larger timescale until saturation is reached.",1301.4371v1
2014-10-01,Search for a spin-nematic phase in the quasi-one-dimensional frustrated magnet LiCuVO$_4$,"We have performed NMR experiments on the quasi one-dimensional frustrated
spin-1/2 system LiCuVO$_4$ in magnetic fields $H$ applied along the c-axis up
to field values near the saturation field $H_{\rm sat}$. For the field range
$H_{\rm c2}<H<H_{\rm c3}$ ($\mu_0H_{\rm c2}\approx 7.5$T and $\mu_0H_{\rm c3} =
[40.5 \pm 0.2]$T) the $^{51}$V NMR spectra at $T$ = 380mK exhibit a
characteristic double-horn pattern, as expected for a spin-modulated phase in
which the magnetic moments of Cu$^{2+}$ ions are aligned parallel to the
applied field $H$ and their magnitudes change sinusoidally along the magnetic
chains. For higher fields, the $^{51}$V NMR spectral shape changes from the
double-horn pattern into a single Lorentzian line. For this Lorentzian line,
the internal field at the $^{51}$V nuclei stays constant for $\mu_0 H > 41.4$T,
indicating that the majority of magnetic moments in LiCuVO$_4$ are already
saturated in this field range. This result is inconsistent with the previously
observed linear field dependence of the magnetization $M(H)$ for $H_{\rm
c3}<H<H_{\rm sat}$ with $\mu_0H_{\rm sat}=45$T [L. E. Svistov {\it et al}.,
JETP Letters {\bf 93}, 21 (2011)]. We argue that the discrepancy is due to
non-magnetic defects in the samples. The results of the spin-lattice relaxation
rate of $^7$Li nuclei indicate an energy gap which grows with field twice as
fast as the Zeeman energy of a single spin, therefore, suggesting that the
two-magnon bound state is the lowest energy excitation. The energy gap tends to
close at $\mu_0H \approx 41$T. Our results suggest that the theoretically
predicted spin-nematic phase, if it exists in LiCuVO$_4$, can be established
only within the narrow field range $40.5 < \mu_0 H < 41.4$T .",1410.0160v1
2019-10-16,The rotation angle distribution underlying magnetic field fluctuations in the 1/f range of solar wind turbulent spectra,"We discuss properties of large amplitude magnetic field fluctuations during
fast Alfvenic solar wind streams, focussing on the statistics of the rotation
angle between consecutive magnetic field vector measurements for different
scales in the plasma. Since in the fast solar wind fluctuations preserve the
modulus of the magnetic field to a good approximation, the tip of the magnetic
field vector is observed to move on a sphere of approximately constant radius
|B|. We then compare statistics of solar wind measurements with that of a
simple model of a random walk bounded on a spherical surface. The analogy
consists in the fact that in both systems the geometrical constraint imposes a
limiting amplitude at large separations and thus introduces a break scale in
the power spectrum of the fluctuations, leading to a shallower slope for scales
where the fluctuations amplitude becomes scale-independent. However, while in
the case of the random walk the saturation of the fluctuations occurs when the
pattern becomes uniform on the sphere (flat distribution of the cosine of the
rotation angle), transitioning then to a white noise regime, in the solar wind
magnetic field fluctuations saturate in amplitude maintaining a preferential
direction. We suggest that this behaviour is due to the presence of the
background interplanetary magnetic field, which keeps some long-range memory in
the system also when the fluctuations becomes independent of the scale. This
long-range correlation is a necessary ingredient in order to produce the 1/f
spectrum observed at large scales in the solar wind.",1910.07285v1
2020-03-21,Fluctuation dynamo in a weakly collisional plasma,"The turbulent amplification of cosmic magnetic fields depends upon the
material properties of the host plasma. In many hot, dilute astrophysical
systems, such as the intracluster medium (ICM) of galaxy clusters, the rarity
of particle--particle collisions allows departures from local thermodynamic
equilibrium. These departures exert anisotropic viscous stresses on the plasma
motions that inhibit their ability to stretch magnetic-field lines. We present
a numerical study of the fluctuation dynamo in a weakly collisional plasma
using magnetohydrodynamic (MHD) equations endowed with a field-parallel viscous
(Braginskii) stress. When the stress is limited to values consistent with a
pressure anisotropy regulated by firehose and mirror instabilities, the
Braginskii-MHD dynamo largely resembles its MHD counterpart. If instead the
parallel viscous stress is left unabated -- a situation relevant to recent
kinetic simulations of the fluctuation dynamo and to the early stages of the
dynamo in a magnetized ICM -- the dynamo changes its character, amplifying the
magnetic field while exhibiting many characteristics of the saturated state of
the large-Prandtl-number (${\rm Pm}\gtrsim{1}$) MHD dynamo. We construct an
analytic model for the Braginskii-MHD dynamo in this regime, which successfully
matches magnetic-energy spectra. A prediction of this model, confirmed by our
simulations, is that a Braginskii-MHD plasma without pressure-anisotropy
limiters will not support a dynamo if the ratio of perpendicular and parallel
viscosities is too small. This ratio reflects the relative allowed rates of
field-line stretching and mixing, the latter of which promotes resistive
dissipation of the magnetic field. In all cases that do exhibit a dynamo, the
generated magnetic field is organized into folds that persist into the
saturated state and bias the chaotic flow to acquire a scale-dependent spectral
anisotropy.",2003.09760v2
2023-04-24,Vorticity and magnetic dynamo from subsonic expansion waves,"This work concentrates on the effect of an irrotational forcing on a
magnetized flow in the presence of rotation, baroclinicity, shear, or a
combination of them. By including magnetic field in the model we can evaluate
the occurrence of dynamo on both small and large scales. We aim at finding what
are the minimum ingredients needed to trigger a dynamo instability and what is
the relation between dynamo and the growth of vorticity.
  We use the Pencil code to run resistive MHD direct numerical simulations. We
report no dynamo in all cases where only rotation is included, regardless on
the equation of state. Conversely, the inclusion of a background sinusoidal
shearing profile leads to an hydrodynamic instability that produces an
exponential growth of the vorticity at all scales, starting from small ones.
This is know as vorticity dynamo. The onset of this instability occurs after a
rather long temporal evolution of several thousand turbulent turnover times.
The vorticity dynamo in turn drives an exponential growth of the magnetic
field, first at small scales, then also at large one. The instability then
saturates and the magnetic field approximately reaches equipartition with the
turbulent kinetic energy. During the saturation phase we can observe a winding
of the magnetic field in the direction of the shearing flow. By varying the
intensity of the shear we see that the growth rates of this instability change.
The inclusion of the baroclinic term delays the onset of the vorticity dynamo
but leads to a more rapid growth.
  We demonstrate how in the presence of shear, even a purely irrotational
forcing amplifies the field to equipartition. At the same time, we confirm how
this forcing alone does not lead to vorticity nor magnetic field growth, and
this picture does not change in the presence of rotation or baroclinicity up to
$256^3$ meshpoints.",2304.11929v2
2003-08-20,Magnetic Braking Revisited,"We present a description for the angular momentum loss rate due to magnetic
braking for late type stars taking into account recent observational data on
the relationship between stellar activity and rotation. The analysis is based
on an idealized two component coronal model subject to constraints imposed on
the variation of the coronal gas density with rotation period inferred from the
observed variation of X-ray luminosity, L_x, with rotation rate, Omega, (L_x
\propto Omega^2) for single rotating dwarfs. An application of the model to
high rotation rates leads to a gradual turnover of the X-ray luminosity which
is similar to the saturation recently observed in rapidly rotating dwarfs. The
resulting angular momentum loss rate, \dot J, depends on Omega in the form \dot
J \propto Omega^beta where beta ~ 3 for slow rotators and ~ 1.3 for fast
rotators. The relation at high rotation rates significantly differs from the
power law exponent for slowly rotating stars, depressing the angular momentum
loss rate without necessarily requiring the saturation of the magnetic field.
The application of this model to the evolution of cataclysmic variable binary
systems leads to mass transfer rates that are in approximate accord with those
observed in comparison to rates based on either a Skumanich law or an empirical
law based on beta=1.",0308361v1
2005-08-30,A further 'degree of freedom' in the rotational evolution of stars,"Observational and theoretical investigations provide evidence for non-uniform
spot and magnetic flux distributions on rapidly rotating stars, which have a
significant impact on their angular momentum loss rate through magnetised
winds. Supplementing the formalism of MacGregor & Brenner (1991) with a
latitude-dependent magnetised wind model, we analyse the effect of analytically
prescribed surface distributions of open magnetic flux with different shapes
and degrees of non-uniformity on the rotational evolution of a solar-like star.
The angular momentum redistribution inside the star is treated in a qualitative
way, assuming an angular momentum transfer between the rigidly-rotating
radiative and convective zones on a constant coupling timescale of 15 Myr; for
the sake of simplicity we disregard interactions with circumstellar disks. We
find that non-uniform flux distributions entail rotational histories which
differ significantly from those of classical approaches, with differences
cumulating up to 200% during the main sequence phase. Their impact is able to
mimic deviations of the dynamo efficiency from linearity of up to 40% and
nominal dynamo saturation limits at about 35 times the solar rotation rate.
Concentrations of open magnetic flux at high latitudes thus assist in the
formation of very rapidly rotating stars in young open clusters, and ease the
necessity for a dynamo saturation at small rotation rates. However, since our
results show that even minor amounts of open flux at intermediate latitudes, as
observed with Zeeman-Doppler imaging techniques, are sufficient to moderate
this reduction of the AM loss rate, we suggest that non-uniform flux
distributions are a complementary rather than an alternative explanation for
very rapid stellar rotation.",0508643v1
2003-06-13,Structural and doping effects in the half-metallic double perovskite $A_2$CrWO$_6$,"he structural, transport, magnetic and optical properties of the double
perovskite $A_2$CrWO$_6$ with $A=\text{Sr, Ba, Ca}$ have been studied. By
varying the alkaline earth ion on the $A$ site, the influence of steric effects
on the Curie temperature $T_C$ and the saturation magnetization has been
determined. A maximum $T_C=458$ K was found for Sr$_2$CrWO$_6$ having an almost
undistorted perovskite structure with a tolerance factor $f\simeq 1$. For
Ca$_2$CrWO$_6$ and Ba$_2$CrWO$_6$ structural changes result in a strong
reduction of $T_C$. Our study strongly suggests that for the double perovskites
in general an optimum $T_C$ is achieved only for $f \simeq 1$, that is, for an
undistorted perovskite structure. Electron doping in Sr$_2$CrWO$_6$ by a
partial substitution of Sr$^{2+}$ by La$^{3+}$ was found to reduce both $T_C$
and the saturation magnetization $M_s$. The reduction of $M_s$ could be
attributed both to band structure effects and the Cr/W antisites induced by
doping. Band structure calculations for Sr$_2$CrWO$_6$ predict an energy gap in
the spin-up band, but a finite density of states for the spin-down band. The
predictions of the band structure calculation are consistent with our optical
measurements. Our experimental results support the presence of a kinetic energy
driven mechanism in $A_2$CrWO$_6$, where ferromagnetism is stabilized by a
hybridization of states of the nonmagnetic W-site positioned in between the
high spin Cr-sites.",0306357v1
2005-06-09,Magnetoresistance Anisotropy of Polycrystalline Cobalt Films: Geometrical-Size- and Domain-Effects,"The magnetoresistance (MR) of 10 nm to 200 nm thin polycrystalline Co-films,
deposited on glass and insulating Si(100), is studied in fields up to 120 kOe,
aligned along the three principal directions with respect to the current:
longitudinal, transverse (in-plane), and polar (out-of-plane). At technical
saturation, the anisotropic MR (AMR) in polar fields turns out to be up to
twice as large as in transverse fields, which resembles the yet unexplained
geometrical size-effect (GSE), previously reported for Ni- and Permalloy films.
Upon increasing temperature, the polar and transverse AMR's are reduced by
phonon-mediated sd-scattering, but their ratio, i.e. the GSE remains unchanged.
Basing on Potters's theory [Phys.Rev.B 10, 4626(1974)], we associate the GSE
with an anisotropic effect of the spin-orbit interaction on the sd-scattering
of the minority spins due to a film texture. Below magnetic saturation, the
magnitudes and signs of all three MR's depend significantly on the domain
structures depicted by magnetic force microscopy. Based on hysteresis loops and
taking into account the GSE within an effective medium approach, the three MR's
are explained by the different magnetization processes in the domain states.
These reveal the importance of in-plane uniaxial anisotropy and out-of-plane
texture for the thinnest and thickest films, respectively.",0506232v1
2007-03-02,Nuclear-induced time evolution of entanglement of two-electron spins in anisotropically coupled quantum dot,"We study the time evolution of entanglement of two spins in anisotropically
coupled quantum dot interacting with the unpolarized nuclear spins environment.
We assume that the exchange coupling strength in the z-direction $J_z$ is
different from the lateral one $J_l$. We observe that the entanglement decays
as a result of the coupling to the nuclear environment and reaches a saturation
value, which depends on the value of the exchange interaction difference $J=\|
J_l-J_z\|$ between the two spins and the strength of the applied external
magnetic field. We find that the entanglement exhibits a critical behavior
controlled by the competition between the exchange interaction $J$ and the
external magnetic field. The entanglement shows a quasi-symmetric behavior
above and below a critical value of the exchange interaction. It becomes more
symmetric as the external magnetic field increases. The entanglement reaches a
large saturation value, close to unity, when the exchange interaction is far
above or below its critical value and a small one as it closely approaches the
critical value. Furthermore, we find that the decay rate profile of
entanglement is linear when the exchange interaction is much higher or lower
than the critical value but converts to a power law and finally to a Gaussian
as the critical value is approached from both directions. The dynamics of
entanglement is found to be independent of the exchange interaction for
isotropically coupled quantum dot.",0703054v3
2011-03-07,Effect of Ambipolar Diffusion on the Non-linear Evolution of Magnetorotational Instability in Weakly Ionized Disks,"We study the role of ambipolar diffusion (AD) on the non-linear evolution of
the MRI in protoplanetary disks using the strong coupling limit, which applies
when the electron recombination time is much shorter than the orbital time. The
effect of AD in this limit is characterized by the dimensionless number Am, the
frequency of which neutral particles collide with ions normalized to the
orbital frequency. We perform three-dimensional unstratified shearing-box
simulations of the MRI over a wide range of Am as well as different magnetic
field strengths and geometries. The saturation level of the MRI turbulence
depends on the magnetic geometry and increases with the net magnetic flux.
There is an upper limit to the net flux for sustained turbulence, corresponding
to the requirement that the most unstable vertical wavelength be less than the
disk scale height. Correspondingly, at a given Am, there exists a maximum value
of the turbulent stress alpha_max. For Am<1, the largest stress is associated
with a field geometry that has both net vertical and toroidal flux. In this
case, we confirm the results of linear analyses that show the fastest growing
mode has a non-zero radial wave number with growth rate exceeding the pure
vertical field case. We find there is a very tight correlation between the
turbulent stress (alpha) and the plasma beta=P_gas/P_mag~1/(2alpha) at the
saturated state of the MRI turbulence regardless of field geometry, and
alpha_max rapidly decreases with decreasing Am. In particular, we quote
alpha_max~0.007 for Am=1 and alpha_max~0.0006 for Am=0.1.",1103.1380v1
2014-01-27,Direct determination of exchange parameters in Cs2CuBr4 and Cs2CuCl4: high-field ESR studies,"Spin-1/2 Heisenberg antiferromagnets Cs$_2$CuCl$_4$ and Cs$_2$CuBr$_4$ with
distorted triangular-lattice structures are studied by means of electron spin
resonance spectroscopy in magnetic fields up to the saturation field and above.
In the magnetically saturated phase, quantum fluctuations are fully suppressed,
and the spin dynamics is defined by ordinary magnons. This allows us to
accurately describe the magnetic excitation spectra in both materials and,
using the harmonic spin-wave theory, to determine their exchange parameters.
The viability of the proposed method was proven by applying it to
Cs$_2$CuCl$_4$, yielding $J/k_B=4.7(2)$ K, $J'/k_B=1.42(7)$ K [$J'/J\simeq
0.30$] and revealing good agreement with inelastic neutron-scattering results.
For the isostructural Cs$_2$CuBr$_4$, we obtain $J/k_B=14.9(7)$ K,
$J'/k_B=6.1(3)$ K, [$J'/J\simeq 0.41$], providing exact and conclusive
information on the exchange couplings in this frustrated spin system.",1401.6793v2
2014-10-01,Spin gapless semiconducting behavior in equiatomic quaternary CoFeMnSi Heusler alloy,"Spin gapless semiconductors (SGS) form a new class of magnetic
semiconductors, which has a band gap for one spin sub band and zero band gap
for the other, and thus are useful for tunable spin transport based
applications. In this paper, we report the first experimental evidence for spin
gapless semiconducting behavior in CoFeMnSi Heusler alloy. Such a behavior is
also confirmed by first principles band structure calculations. The most stable
configuration obtained by the theoretical calculation is verified by
experiment. The alloy is found to crystallize in the cubic Heusler structure
(LiMgPdSn type) with some amount of disorder and has a saturation magnetization
of 3.7 Bohr's magneton/f.u.. and Curie temperature of 620 K. The saturation
magnetization is found to follow the Slater-Pauling behavior, one of the
prerequisites for SGS. Nearly temperature-independent carrier concentration and
electrical conductivity is observed from 5 to 300 K. An anomalous Hall
coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection
data has yielded the current spin polarization value of 0.64, which is found to
be robust against the structural disorder. All these properties are quite
promising for the spintronic applications such as spin injection and can bridge
a gap between the contrasting behavior of half-metallic ferromagnets and
semiconductors.",1410.0177v1
2015-07-19,Unsaturated both large positive and negative magnetoresistance in Weyl Semimetal TaP,"After growing successfully TaP single crystal, we measured its longitudinal
resistivity (rhoxx) and Hall resistivity (rhoyx) at magnetic fields up to 9T in
the temperature range of 2-300K. It was found that at 2K its magnetoresistivity
(MR) reaches to 328000 percent, at 300K to 176 percent at 8T, and both do not
appear saturation. We confirmed that TaP is indeed a low carrier concentration,
hole-electron compensated semimetal, with a high mobility of hole muh=371000
cm2V-1s-1, and found that a magnetic-field-induced metal-insulator transition
occurs at room temperature. Remarkably, as a magnetic field (H) is applied in
parallel to the electric field (E), the negative MR due to chiral anomaly is
observed, and reaches to -3000 percent at 9T without any signature of
saturation, too, which distinguishes with other Weyl semimetals (WSMs). The
analysis on the Shubnikov-de Haas (SdH) oscillations superimposing on the MR
reveals that a nontrivial Berry phase with strong offset of 0.3958 realizes in
TaP, which is the characteristic feature of the charge carriers enclosing a
Weyl nodes. These results indicate that TaP is a promising candidate not only
for revealing fundamental physics of the WSM state but also for some novel
applications.",1507.05246v1
2016-08-29,Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses,"Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG)
films with thicknesses of ~100 nm and surface roughnesses as low as 0.3 nm have
been grown as a basic material for spin-wave propagation experiments in
microstructured waveguides. The continuously strained films exhibit nearly
perfect crystallinity without significant mosaicity and with effective lattice
misfits of delta a(perpendicular)/a(substrate) ~10-4 and below. The
film/substrate interface is extremely sharp without broad interdiffusion layer
formation. All LPE films exhibit a nearly bulk-like saturation magnetization of
(1800+-20) Gs and an `easy cone' anisotropy type with extremely small in-plane
coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy
with a pronounced six-fold symmetry observed for saturation field <1.5 Oe. No
significant out-of-plane anisotropy is observed, but a weak dependence of the
effective magnetization on the lattice misfit is detected. The narrowest
ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is
the lowest value reported so far for YIG films of 100 nm thicknesses and below.
The Gilbert damping coefficient for investigated LPE films is estimated to be
close to 1 x 10-4.",1608.08043v1
2017-08-24,Stochastic Electron Acceleration by the Whistler Instability in a Growing Magnetic Field,"We use 2D particle-in-cell (PIC) simulations to study the effect of the
saturated whistler instability on the viscous heating and nonthermal
acceleration of electrons in a shearing, collisionless plasma with a growing
magnetic field, \textbf{B}. In this setup, an electron pressure anisotropy with
$p_{\perp,e} > p_{||,e}$ naturally arises due to the adiabatic invariance of
the electron magnetic moment ($p_{||,e}$ and $p_{\perp,e}$ are the pressures
parallel and perpendicular to \textbf{B}). If the anisotropy is large enough,
the whistler instability arises, efficiently scattering the electrons and
limiting $\Delta p_e$ ($\equiv p_{\perp,e}-p_{||,e}$). In this context, $\Delta
p_e$ taps into the plasma velocity shear, producing electron heating by the so
called anisotropic viscosity. In our simulations, we permanently drive the
growth of $|\textbf{B}|$ by externally imposing a plasma shear, allowing us to
self-consistently capture the long-term, saturated whistler instability
evolution. We find that besides the viscous heating, the scattering by whistler
modes can stochastically accelerate electrons to nonthermal energies. This
acceleration is most prominent when initially $\beta_e\sim 1$, gradually
decreasing its efficiency for larger values of $\beta_e$ ($\equiv 8\pi
p_e/|\textbf{B}|^2$). If initially $\beta_e \sim 1$, the final electron energy
distribution can be approximately described by a thermal component, plus a
power-law tail with spectral index $\sim 3.7$. In these cases, the nonthermal
tail accounts for $\sim 5\%$ of the electrons, and for $\sim 15\%$ of their
kinetic energy. We discuss the implications of our results for electron heating
and acceleration in low-collisionality astrophysical environments, such as
low-luminosity accretion flows.",1708.07254v2
2019-03-02,"A spin dynamics study in layered van der Waals single crystal, Cr$_2$Ge$_2$Te$_6$","We study the magnetisation dynamics of a bulk single crystal
Cr$_2$Ge$_2$Te$_6$ (CGT), by means of broadband ferromagnetic resonance (FMR),
for temperatures from 60 K down to 2 K. We determine the Kittel relations of
the fundamental FMR mode as a function of frequency and static magnetic field
for the magnetocrystalline easy - and hard - axis. The uniaxial
magnetocrystalline anisotropy constant is extracted and compared with the
saturation magnetisation, when normalised with their low temperature values.
The ratios show a clear temperature dependence when plotted in the logarithmic
scale, which departs from the predicted Callen-Callen power law fit of a
straight line, where the scaling exponent \textit{n}, $K_{u}(T) \propto
[M_s(T)/M_s(2$ K$)]^n$, contradicts the expected value of 3 for uniaxial
anisotropy. Additionally, the spectroscopic g-factor for both the magnetic easy
- and hard - axis exhibits a temperature dependence, with an inversion between
20 K and 30 K, suggesting an influence by orbital angular momentum. Finally, we
qualitatively discuss the observation of multi-domain resonance phenomena in
the FMR spectras, at magnetic fields below the saturation magnetisation.",1903.00584v2
2021-03-26,Magnetization Reversal Signatures of Hybrid and Pure Néel Skyrmions in Thin Film Multilayers,"We report a study of the magnetization reversals and skyrmion configurations
in two systems - Pt/Co/MgO and Ir/Fe/Co/Pt multilayers, where magnetic
skyrmions are stabilized by a combination of dipolar and Dzyaloshinskii-Moriya
interactions (DMI). First Order Reversal Curve (FORC) diagrams of low-DMI
Pt/Co/MgO and high-DMI Ir/Fe/Co/Pt exhibit stark differences, which are
identified by micromagnetic simulations to be indicative of hybrid and pure
N\'eel skyrmions, respectively. Tracking the evolution of FORC features in
multilayers with dipolar interactions and DMI, we find that the negative FORC
valley, typically accompanying the positive FORC peak near saturation,
disappears under both reduced dipolar interactions and enhanced DMI. As these
conditions favor the formation of pure Neel skyrmions, we propose that the
resultant FORC feature - a single positive FORC peak near saturation - can act
as a fingerprint for pure N\'eel skyrmions in multilayers. Our study thus
expands on the utility of FORC analysis as a tool for characterizing spin
topology in multilayer thin films.",2103.14527v1
2021-11-08,Magnetic properties of a capped kagome molecule with 60 quantum spins,"We compute ground-state properties of the isotropic, antiferromagnetic
Heisenberg model on the sodalite cage geometry. This is a 60-spin spherical
molecule with 24 vertex-sharing tetrahedra which can be regarded as a molecular
analogue of a capped kagome lattice and which has been synthesized with
high-spin rare-earth atoms. Here, we focus on the $S=1/2$ case where quantum
effects are strongest. We employ the SU(2)-symmetric density-matrix
renormalization group (DMRG).
  We find a threefold degenerate ground state that breaks the spatial symmetry
and that splits up the molecule into three large parts which are almost
decoupled from each other. This stands in sharp contrast to the behaviour of
most known spherical molecules. On a methodological level, the disconnection
leads to ""glassy dynamics"" within the DMRG that cannot be targeted via standard
techniques.
  In the presence of finite magnetic fields, we find broad magnetization
plateaus at 4/5, 3/5, and 1/5 of the saturation, which one can understand in
terms of localized magnons, singlets, and doublets which are again nearly
decoupled from each other. At the saturation field, the zero-point entropy is
$S=\ln(182)\approx 5.2$ in units of the Boltzmann constant.",2111.04549v4
2022-01-07,Nonlinear evolution of the magnetorotational instability in eccentric disks,"The magnetorotational instability (MRI) has been extensively studied in
circular magnetized disks, and its ability to drive accretion has been
demonstrated in a multitude of scenarios. There are reasons to expect eccentric
magnetized disks to also exist, but the behavior of the MRI in these disks
remains largely uncharted territory. Here we present the first simulations that
follow the nonlinear development of the MRI in eccentric disks. We find that
the MRI in eccentric disks resembles circular disks in two ways, in the overall
level of saturation and in the dependence of the detailed saturated state on
magnetic topology. However, in contrast with circular disks, the Maxwell stress
in eccentric disks can be negative in some disk sectors, even though the
integrated stress is always positive. The angular momentum flux raises the
eccentricity of the inner parts of the disk and diminishes the same of the
outer parts. Because material accreting onto a black hole from an eccentric
orbit possesses more energy than material tracing the innermost stable circular
orbit, the radiative efficiency of eccentric disks may be significantly lower
than circular disks. This may resolve the ""inverse energy problem"" seen in many
tidal disruption events.",2201.03728v2
2022-07-06,Control of magnetoelastic coupling in Ni/Fe multilayers using He$^+$ ion irradiation,"This study reports the effects of post-growth He$^+$ irradiation on the
magneto-elastic properties of a $Ni$ /$Fe$ multi-layered stack. The progressive
intermixing caused by He$^+$ irradiation at the interfaces of the multilayer
allows us to tune the saturation magnetostriction value with increasing He$^+$
fluences, and even to induce a reversal of the sign of the magnetostrictive
effect. Additionally, the critical fluence at which the absolute value of the
magnetostriction is dramatically reduced is identified. Therefore insensitivity
to strain of the magnetic stack is nearly reached, as required for many
applications. All the above mentioned effects are attributed to the combination
of the negative saturation magnetostriction of sputtered Ni, Fe layers and the
positive magnetostriction of the Ni$_{x}$Fe$_{1-x}$ alloy at the intermixed
interfaces, whose contribution is gradually increased with irradiation.
Importantly the irradiation does not alter the layers polycrystalline
structure, confirming that post-growth He$^+$ ion irradiation is an excellent
tool to tune the magneto-elastic properties of magnetic samples. A new class of
spintronic devices can be envisioned with a material treatment able to
arbitrarily change the magnetostriction with ion-induced ""magnetic patterning"".",2207.02493v1
2022-12-06,Steady states of the Parker instability,"We study the linear properties, nonlinear saturation and a steady, strongly
nonlinear state of the Parker instability in galaxies. We consider magnetic
buoyancy and its consequences with and without cosmic rays. Cosmic rays are
described using the fluid approximation with anisotropic, non-Fickian
diffusion. To avoid unphysical constraints on the instability (such as boundary
conditions often used to specify an unstable background state), nonideal MHD
equations are solved for deviations from a background state representing an
unstable magnetohydrostatic equilibrium. We consider isothermal gas and neglect
rotation. The linear evolution of the instability is in broad agreement with
earlier analytical and numerical models; but we show that most of the
simplifying assumptions of the earlier work do not hold, such that they provide
only a qualitative rather than quantitative picture. In its nonlinear stage the
instability has significantly altered the background state from its initial
state. Vertical distributions of both magnetic field and cosmic rays are much
wider, the gas layer is thinner, and the energy densities of both magnetic
field and cosmic rays are much reduced. The spatial structure of the nonlinear
state differs from that of any linear modes. A transient gas outflow is driven
by the weakly nonlinear instability as it approaches saturation.",2212.03215v1
2023-05-15,Influence of amorphous phase on coercivity in SmCo5-Cu nanocomposites,"Severe plastic deformation of powder blends consisting of SmCo5-Cu results in
magnetically hardened nanocomposite bulk materials. The microstructure is
continuously refined with increasing torsional deformation, yet, coercivity
saturates at a certain level of strain. Transmission electron microscopy (TEM)
investigation of the microstructure reveals a partial amorphization of the
SmCo5 phase due to high-pressure torsion by 20 applied rotations. In this
amorphous matrix nanocrystals are embedded. The effect of these experimentally
observed microstructural features on the magnetic properties are investigated
by micromagnetic simulations, which show that an increasing volume fraction of
nanocrystals is beneficial for higher coercivities. For a fixed volume fraction
of nanocrystals the simulations reveal an increasing coercivity with decreasing
the size of the nanocrystals due to increasing number of interfaces acting as
pinning sites. Furthermore, our micromagnetic simulations disclose the
mechanisms of the saturation and decline of magnetic hardening due to the
strain induced by high-pressure torsion. The calculated coercivity fits very
well to the experimentally observed coercivity of Hc=1.34 T. The knowledge can
also be used to develop and provide optimization strategies from the
microstructure perspective.",2305.08948v1
2023-09-27,Helical and nonhelical large-scale dynamos in thin accretion discs,"The dynamics of accreting and outgoing flows around compact objects depends
crucially on the strengths and configurations of the magnetic fields therein,
especially of the large-scale fields that remain coherent beyond turbulence
scales. Possible origins of these large-scale magnetic fields include flux
advection and disc dynamo actions. However, most numerical simulations have to
adopt an initially strong large-scale field rather than allow them to be
self-consistently advected or amplified, due to limited computational
resources. The situation can be partially cured by using sub-grid models where
dynamo actions only reachable at high resolutions are mimicked by artificial
terms in low-resolution simulations. In this work, we couple thin-disc models
with local shearing-box simulation results to facilitate more realistic
sub-grid dynamo implementations. For helical dynamos, detailed spatial profiles
of dynamo drivers inferred from local simulations are used, and the nonlinear
quenching and saturation is constrained by magnetic helicity evolution. In the
inner disc region, saturated fields have dipole configurations and the plasma
$\beta$ reaches $\simeq 0.1$ to $100$, with correlation lengths $\simeq h$ in
the vertical direction and $\simeq 10h$ in the radial direction, where $h$ is
the disc scale height. The dynamo cycle period is $\simeq 40$ orbital time
scale, compatible with previous global simulations. Additionally, we explore
two dynamo mechanisms which do not require a net kinetic helicity and have only
been studied in shearing-box setups. We show that such dynamos are possible in
thin accretion discs, but produce field configurations that are incompatible
with previous results. We discuss implications for future general-relativistic
magnetohydrodynamics simulations.",2309.15565v2
1996-07-28,The Protogalactic Origin for Cosmic Magnetic Fields,"It is demonstrated that strong magnetic fields are produced from a zero
initial magnetic field during the pregalactic era, when galaxies are first
forming. Their development proceeds in three phases. In the first phase, weak
magnetic fields are created by the Biermann battery mechanism, acting in
shocked parts of the intergalactic medium where caustics form and intersect. In
the second phase, these weak magnetic fields are amplified to strong magnetic
fields by the Kolmogoroff turbulence endemic to gravitational structure
formation of galaxies. During this second phase, the magnetic fields reach
saturation with the turbulent power, but they are coherent only on the scale of
the smallest eddy. In the third phase, the magnetic field strength increases to
equipartition with the turbulent energy, and the coherence length of the
magnetic fields increases to the scale of the largest turbulent eddy,
comparable to the scale of the entire galaxy. The resulting magnetic field
represents a galactic magnetic field of primordial origin. No further dynamo
action is necessary, after the galaxy forms, to explain the origin of magnetic
fields. However, the magnetic field may be altered by dynamo action once the
galaxy and the galactic disk have formed. It is first shown by direct numerical
simulations, that thermoelectric currentsassociated with the Biermann battery,
build the field up from zero to $10^{-21}$ G in the regions about to collapse
into galaxies, by $z\sim3$. For weak fields, in the absence of dissipation, the
cyclotron frequency ${\bf \omega_{cyc}}=e{\bf B } /m_H c $ and $ {\bf
\omega}/(1+ \chi )$, where ${\bf \omega = \nabla \times v }$ is the vorticity
and $\chi$ is the degree of ionization, satisfy the same equations, and initial
conditions ${\bf \omega_{cyc}=\omega}=0$, so that, ${\bf \omega_{cyc}}({\bf",9607141v1
2010-11-26,Galactic ménage à trois: Simulating magnetic fields in colliding galaxies,"We present high resolution simulations of a multiple merger of three disk
galaxies including the evolution of magnetic fields performed with the
N-body/SPH code Gadget. For the first time, we embed the galaxies in a
magnetized, low-density medium, thus modeling an ambient IGM. The simulations
include radiative cooling and a model for star formation and supernova
feedback. The progenitor disks have initial magnetic seed fields in the range
of 10e-9 to 10e-6 G and the IGM has initial fields of 10e-12 to 10e-9 G. The
simulations are compared to a run excluding magnetic fields. We show that the
propagation of interaction-driven shocks depends significantly on the initial
magnetic field strength. The shocks propagate faster in simulations with
stronger initial field, suggesting that the shocks are supported by magnetic
pressure. The Mach numbers of the shocks range from approximately M=1.5 for the
non-magnetized case up to M=6 for the highest initial magnetization, resulting
in higher temperatures of the shock heated IGM gas. The magnetic field in the
system saturates rapidly after the mergers at ~ 10e-6 G within the galaxies and
~ 10e-8 G in the IGM independent of the initial value. These field strengths
agree with observed values and correspond to the equipartition value of the
magnetic pressure with the turbulent pressure in the system. We also present
synthetic radio and polarization maps for different phases of the evolution
showing that shocks driven by the interaction produce a high amount of
polarized emission. These idealized simulations indicate that magnetic fields
play an important role for the hydrodynamics of the IGM during galactic
interactions. We also show that even weak seed fields are efficiently
strengthened during multiple galactic mergers. This interaction driven
amplification might have been a key process for the magnetization of the
Universe.",1011.5735v2
2018-03-16,Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation,"The Magnetospheric Multiscale (MMS) mission has observed electron whistler
waves at the center and at the edges of magnetic holes in the dayside
magnetosheath. The magnetic holes are nonlinear mirror structures since their
magnitude is anti-correlated with particle density. In this article, we examine
the growth mechanisms of these whistler waves and their interaction with the
host magnetic hole. In the observations, as magnetic holes develop and get
deeper, an electron population gets trapped and develops a temperature
anisotropy favorable for whistler waves to be generated. In addition, the
decrease in magnetic field magnitude and the increase in density reduces the
electron resonance energy, which promotes the electron cyclotron resonance. To
investigate this process, we used an expanding box particle-in-cell simulations
to produce the mirror instability, which then evolves into magnetic holes. The
simulation shows that whistler waves can be generated at the center and edges
of magnetic holes, which reproduces the primary features of the MMS
observations. The simulation shows that the electron temperature anisotropy
develops in the center of the magnetic hole once the mirror instability reaches
its nonlinear stage of evolution. The plasma is then unstable to whistler waves
at the minimum of the magnetic field structures. In the saturation regime of
mirror instability, when magnetic holes are developed, the electron temperature
anisotropy appears at the edges of the holes and electron distributions become
more isotropic at the magnetic field minimum. At the edges, the expansion of
magnetic holes decelerates the electrons which leads to temperature
anisotropies.",1803.06399v1
2023-03-21,Robust intralayer antiferromagnetism and tricriticality in a van der Waals compound: VBr3 case,"We studied magnetic states and phase transitions in the van der Waals
antiferromagnet VBr3 by specific heat and magnetization measurements of single
crystals in high magnetic fields and by ab initio density functional theory
calculations focused on exchange interactions. The magnetization behavior
resembles Ising antiferromagnets with magnetic moments kept in the out-of-plane
direction by strong uniaxial magnetocrystalline anisotropy. The out-of-plane
magnetic field induces a spin-flip metamagnetic transition, which is of
first-order type at low temperatures while at higher temperatures the
transition becomes continuous. The first-order and continuous transition
segments in the field-temperature phase diagram meet at a tricritical point at
= 12 K. The magnetization response to the in-plane field manifests a continuous
spin-flop transition, which at 2 K terminates at a field mu0Hc = 27 T that can
serve as an estimate of the anisotropy field in VBr3. The magnetization curves
above the metamagnetic transition saturate at the same value of magnetic moment
musat = 1.2 muB/f.u., which is much smaller than the spin-only (S = 1) moment
of the V3+ ion. The reduced moment can be explained by the existence of a
significant orbital magnetic moment antiparallel to the spin. The orbital
moment is a key ingredient of a mechanism responsible for the observed large
anisotropy. The exact energy evaluation of possible magnetic orders
unambiguously shows that the magnetic ground state of VBr3 is the intralayer
zigzag antiferromagnetic order that renders the antiferromagnetic ground state
significantly more stable against the spin-flip transition than the other
options. The calculations also predict that a minimal distortion of the Br ion
sublattice causes a radical change of the orbital occupation in the ground
state, connected with the formation of the orbital moment and the stability of
magnetic order.",2303.11794v2
2011-08-30,Comparison Between Turbulent Helical Dynamo Simulations and a Nonlinear Three-Scale Theory,"Progress toward understanding principles of nonlinear growth and saturation
of large scale magnetic fields has emerged from comparison of theoretical
models that incorporate the evolution of magnetic helicity with numerical
simulations for problems that are more idealized than expected in astrophysical
circumstances, but still fully non-linear. We carry out a new comparison of
this sort for the magnetic field growth from forced isotropic helical
turbulence in a periodic box. Previous comparisons be- tween analytic theory
and simulations of this problem have shown that a two-scale model compares well
with the simulations in agreeing that the driver of large scale field growth is
the difference between kinetic and current helicities associated with the small
scale field, and that the backreaction that slows the growth of the large scale
field as the small scale current helicity grows. However, the two-scale model
artificially re- stricts the small scale current helicity to reside at the same
scale as the driving kinetic helicity. In addition, previous comparisons have
focused on the late time saturation regime, and less on the early-time growth
regime. Here we address these issues by comparing a three scale model to new
simulations for both early and late time growth regimes. We find that the
minimalist extension to three scales provides a better model for the field
evolution than the two-scale model because the simulations show that the small
scale current helicity does not reside at the same scale as that of the driving
kinetic helicity. The simulations also show that the peak of the small scale
current helicity migrates toward lower wave numbers as the growth evolves from
the fast to saturated growth regimes.",1108.6079v2
2012-01-03,The Effects of Anisotropic Viscosity on Turbulence and Heat Transport in the Intracluster Medium,"In the intracluster medium (ICM) of galaxy clusters, heat and momentum are
transported almost entirely along (but not across) magnetic field lines. We
perform the first fully self-consistent Braginskii-MHD simulations of galaxy
clusters including both of these effects. Specifically, we perform local and
global simulations of the magnetothermal instability (MTI) and the
heat-flux-driven buoyancy instability (HBI) and assess the effects of viscosity
on their saturation and astrophysical implications. We find that viscosity has
only a modest effect on the saturation of the MTI. As in previous calculations,
we find that the MTI can generate nearly sonic turbulent velocities in the
outer parts of galaxy clusters, although viscosity somewhat suppresses the
magnetic field amplification. At smaller radii in cool-core clusters, viscosity
can decrease the linear growth rates of the HBI. However, it has less of an
effect on the HBI's nonlinear saturation, in part because three-dimensional
interchange motions (magnetic flux tubes slipping past each other) are not
damped by anisotropic viscosity. In global simulations of cool core clusters,
we show that the HBI robustly inhibits radial thermal conduction and thus
precipitates a cooling catastrophe. The effects of viscosity are, however, more
important for higher entropy clusters. We argue that viscosity can contribute
to the global transition of cluster cores from cool-core to non cool-core
states: additional sources of intracluster turbulence, such as can be produced
by AGN feedback or galactic wakes, suppress the HBI, heating the cluster core
by thermal conduction; this makes the ICM more viscous, which slows the growth
of the HBI, allowing further conductive heating of the cluster core and a
transition to a non cool-core state.",1201.0754v1
2012-12-30,Saturation of Stellar Winds from Young Suns,"We investigate mass losses via stellar winds from sun-like main sequence
stars with a wide range of activity levels. We perform forward-type
magnetohydrodynamical numerical experiments for Alfven wave-driven stellar
winds with a wide range of the input Poynting flux from the photosphere.
Increasing the magnetic field strength and the turbulent velocity at the
stellar photosphere from the current solar level, the mass loss rate rapidly
increases at first owing to the suppression of the reflection of the Alfven
waves. The surface materials are lifted up by the magnetic pressure associated
with the Alfven waves, and the cool dense chromosphere is intermittently
extended to 10 -- 20 % of the stellar radius. The dense atmospheres enhance the
radiative losses and eventually most of the input Poynting energy from the
stellar surface escapes by the radiation. As a result, there is no more
sufficient energy remained for the kinetic energy of the wind; the stellar wind
saturates in very active stars, as observed in Wood et al. The saturation level
is positively correlated with B_{r,0}f_0, where B_{r,0} and f_0 are the
magnetic field strength and the filling factor of open flux tubes at the
photosphere. If B_{r,0}f_0 is relatively large >~ 5 G, the mass loss rate could
be as high as 1000 times. If such a strong mass loss lasts for ~ 1 billion
years, the stellar mass itself is affected, which could be a solution to the
faint young sun paradox. We derive a Reimers-type scaling relation that
estimates the mass loss rate from the energetics consideration of our
simulations. Finally, we derive the evolution of the mass loss rates, \dot{M}
t^{-1.23}, of our simulations, combining with an observed time evolution of
X-ray flux from sun-like stars, which is shallower than \dot{M}
t^{-2.33+/-0.55} in Wood et al.(2005).",1212.6713v4
2000-12-22,Large scale dynamos with helicity loss through boundaries,"Dynamo action is investigated in simulations of locally isotropic and
homogeneous turbulence in a slab between open boundaries. It is found that a
`pseudo-vacuum' boundary condition (where the field is vertical) leads to
strong helicity fluxes which significantly reduce the amplitude of the
resulting large scale field. On the other hand, if there is a conducting halo
outside the dynamo-active region the large scale field amplitude can reach
larger values, but the time scale after which this field is reached increases
linearly with the magnetic Reynolds number. In both cases most of the helicity
flux is found to occur on large scales. From the variety of models considered
we conclude that open boundaries tend to lower the saturation field strength
compared to the case with periodic boundaries. The rate at which this lower
saturation field strength is attained is roughly independent of the strength of
the turbulence and of the boundary conditions. For dynamos with less helicity,
however, significant field strengths could be reached in a shorter time.",0012472v2
2005-03-24,Surface imaging of late-type contact binaries II: Halpha 6563 A emission in AE Phoenicis and YY Eridani,"We present and discuss the Halpha (6563 A) observations of the contact (W UMa
type) binaries AE Phoenicis and YY Eridani, obtaineded in 1989, 1990 and 1995
with the CAT/CES telescope of the Southern European Observatory (ESO). In
particular, we compare the intrinsic equivalent widths of both components with
the NextGen theoretical models and the saturation limit. We find that the
average Halpha equivalent widths are close to the saturation border and that
the primary components have excess Halpha-emission, indicating enhanced
chromospheric activity. This is compatible with both theoretical and
observational suggestions that the primary is the more magnetically active
component and is filled with (mostly unresolvable) dark spots and associated
chromospheric plages.",0503548v1
1998-03-05,Decoherence and the Thouless Crossover in One-Dimensional Conductors,"The temperature and magnetic-field dependences of the resistance of
one-dimensional (1D) conductors have been studied in the vicinity of the
Thouless crossover. We find that on the weak localization (WL) side of the
crossover, these dependences are consistent with the theory of quantum
corrections to the resistance, and the phase breaking is due to the
quasi-elastic electron-electron interactions (the Nyquist noise). The
temperature dependence of the phase coherence time does not saturate, and the
quasiparticle states remain well defined over the whole WL temperature range.
This fact, as well as observation of the Thouless crossover in 1D samples,
argues against the idea of intrinsic decoherence by zero-point fluctuations of
the electrons (Mohanty et al., Phys.Rev.Lett. 78, 3366 (1997)). We believe that
frequently observed saturation of the phase coherence time is caused by the
external microwave noise.",9803067v2
1999-02-11,Dephasing in Metals by Two-Level Systems in the 2-Channel-Kondo Regime,"We point out a novel, non-universal contribution to the dephasing rate
1/\tau_\phi \equiv \gamma_\phi of conduction electrons in metallic systems:
scattering off non-magnetic two-level systems (TLSs) having almost degenerate
Kondo ground states. In the regime \Delta_{ren} < T < T_K (\Delta_{ren} =
renormalized level splitting, T_K = Kondo temperature), such TLSs exhibit
non-Fermi-liquid physics that can cause \gamma_\phi, which generally decreases
with decreasing T, to seemingly saturate in a limited temperature range before
vanishing for T \to 0. This could explain the saturation of dephasing recently
observed in gold wires [Mohanty et al. Phys. Rev. Lett. 78, 3366 (1997)].",9902176v2
2000-06-22,High field magnetotransport in composite conductors: the effective medium approximation revisited,"The self consistent effective medium approximation (SEMA) is used to study
three-dimensional random conducting composites under the influence of a strong
magnetic field {\bf B}, in the case where all constituents exhibit isotropic
response. Asymptotic analysis is used to obtain almost closed form results for
the strong field magnetoresistance and Hall resistance in various types of two-
and three-constituent isotropic mixtures for the entire range of compositions.
Numerical solutions of the SEMA equations are also obtained, in some cases, and
compared with those results. In two-constituent
free-electron-metal/perfect-insulator mixtures, the magnetoresistance is
asymptotically proportional to $|{\bf B}|$ at {\em all concentrations above the
percolation threshold}. In three-constituent metal/insulator/superconductor
mixtures a line of critical points is found, where the strong field
magnetoresistance switches abruptly from saturating to non-saturating
dependence on $|{\bf B}|$, at a certain value of the
insulator-to-superconductor concentration ratio. This transition appears to be
related to the phenomenon of anisotropic percolation.",0006351v1
2000-06-23,Critical point for the strong field magnetoresistance of a normal conductor/perfect insulator/perfect conductor composite with a random columnar microstructure,"A recently developed self-consistent effective medium approximation, for
composites with a columnar microstructure, is applied to such a
three-constituent mixture of isotropic normal conductor, perfect insulator, and
perfect conductor, where a strong magnetic field {\bf B} is present in the
plane perpendicular to the columnar axis. When the insulating and perfectly
conducting constituents do not percolate in that plane, the
microstructure-induced in-plane magnetoresistance is found to saturate for
large {\bf B}, if the volume fraction of the perfect conductor $p_S$ is greater
than that of the perfect insulator $p_I$. By contrast, if $p_S<p_I$, that
magnetoresistance keeps increasing as ${\bf B}^2$ without ever saturating. This
abrupt change in the macroscopic response, which occurs when $p_S=p_I$, is a
critical point, with the associated critical exponents and scaling behavior
that are characteristic of such points. The physical reasons for the singular
behavior of the macroscopic response are discussed. A new type of percolation
process is apparently involved in this phenomenon.",0006376v1
2001-11-23,Possible Superconductivity at 37 K in Graphite-Sulfur Composite,"Sulfur intercalated graphite composites with diamagnetic transitions at 6.7 K
and 37 K are prepared. The magnetization hysteresis loops (MHL), Xray
diffraction patterns, and resistance were measured. From the MHL, a slight
superconducting like penetration process is observed at 15 K in low field
region. The XRD shows no big difference from the mixture of graphite and sulfur
indicating that the volume of the superconducting phase (if any) is very small.
The temperature dependence of resistance shows a typical semiconducting
behavior with a saturation in low temperature region. This saturation is either
induced by the de-localization of conducting electrons or by possible
superconductivity in this system.",0111445v1
2001-12-21,Effect of annealing on electron dephasing in three-dimensional polycrystalline metals,"We have studied the effect of thermal annealing on electron dephasing times
$\tau_\phi$ in three-dimensional polycrystalline metals. Measurements are
performed on as-sputtered and annealed AuPd and Sb thick films, using
weak-localization method. In all samples, we find that $\tau_\phi$ possesses an
extremely weak temperature dependence as $T \to 0$. Our results show that the
effect of annealing is non-universal, and it depends strongly on the amount of
disorder quenched in the microstructures during deposition. The observed
""saturation"" behavior of $\tau_\phi$ cannot be easily explained by magnetic
scattering. We suggest that the issue of saturation can be better addressed in
three-dimensional, rather than lower-dimensional, structures.",0112421v1
2003-02-20,Optimal Size of a Complex Network,"We investigate the response behavior of an Ising system, driven by an
oscillating field, on a small-world network, with particular attention to the
effects of the system size. The responses of the magnetization to the driving
field are probed by means of Monte Carlo dynamic simulations with the rewiring
probability varied. It is found that at low and high temperatures the occupancy
ratio, measuring how many spins follow the driving field, behaves monotonically
with the system size. At intermediate temperatures, on the other hand, the
occupancy ratio first grows and then reduces as the size is increased,
displaying a resonance-like peak at a finite value of the system size. In all
cases, further increase of the size eventually leads to saturation to finite
values; the size at which saturation emerges is observed to depend on the
temperature, similarly to the correlation length of the system.",0302400v1
2005-06-01,Spin polarization induced tenfold magneto-resistivity of highly metallic 2D holes in a narrow GaAs quantum well,"We observe that an in-plane magnetic field ($B_{||}$) can induce an order of
magnitude enhancement in the low temperature ($T$) resistivity ($\rho$) of
metallic 2D holes in a narrow (10nm) GaAs quantum well. Moreover, we show the
first observation of saturating behavior of $\rho(B_{||})$ at high $B_{||}$ in
GaAs system, which suggests our large positive $\rho(B_{||})$ is due to the
spin polarization effect alone. We find that this tenfold increase in
$\rho(B_{||})$ even persists deeply into the 2D metallic state with the high
$B_{||}$ saturating values of $\rho$ lower than 0.1$\times$h/e$^2$. The
dramatic effect of $B_{||}$ we observe on the highly conductive 2D holes (with
$B$=0 conductivity as high as 75e$^2$/h) sets strong constraint on models for
the spin dependent transport in dilute metallic 2D systems.",0506031v3
2007-01-24,Berezinskii-Kosterlitz-Thouless transition in two-dimensional lattice gas models,"We have considered two classical lattice-gas models, consisting of particles
that carry multicomponent magnetic momenta, and associated with a
two-dimensional square lattices; each site can host one particle at most, thus
implicitly allowing for hard-core repulsion; the pair interaction, restricted
to nearest neighbors, is ferromagnetic and involves only two components. The
case of zero chemical potential has been investigated by Grand--Canonical Monte
Carlo simulations; the fluctuating occupation numbers now give rise to
additional fluid-like observables in comparison with the usual
saturated--lattice situation; these were investigated and their possible
influence on the critical behaviour was discussed. Our results show that the
present model supports a Berezinskii-Kosterlitz-Thouless phase transition with
a transition temperature lower than that of the saturated lattice counterpart
due to the presence of ``vacancies''; comparisons were also made with similar
models studied in the literature.",0701584v1
1997-03-28,Non-threshold D-brane bound states and black holes with non-zero entropy,"We start with BPS-saturated configurations of two (orthogonally) intersecting
M-branes and use the electro-magnetic duality or dimensional reduction along a
boost, in order to obtain new p-brane bound states. In the first case the
resulting configurations are interpreted as BPS-saturated non-threshold bound
states of intersecting p-branes, and in the second case as p-branes
intersecting at angles and their duals. As a by-product we deduce the
enhancement of supersymmetry as the angle approaches zero. We also comment on
the D-brane theory describing these new bound states, and a connection between
the angle and the world-volume gauge fields of the D-brane system. We use these
configurations to find new embeddings of the four and five dimensional black
holes with non-zero entropy, whose entropy now also depends on the angle and
world-volume gauge fields. The corresponding D-brane configuration sheds light
on the microscopic entropy of such black holes.",9703204v4
2007-05-03,Non-saturating magnetoresistance of inhomogeneous conductors: comparison of experiment and simulation,"The silver chalcogenides provide a striking example of the benefits of
imperfection. Nanothreads of excess silver cause distortions in the current
flow that yield a linear and non-saturating transverse magnetoresistance (MR).
Associated with the large and positive MR is a negative longitudinal MR. The
longitudinal MR only occurs in the three-dimensional limit and thereby permits
the determination of a characteristic length scale set by the spatial
inhomogeneity. We find that this fundamental inhomogeneity length can be as
large as ten microns. Systematic measurements of the diagonal and off-diagonal
components of the resistivity tensor in various sample geometries show clear
evidence of the distorted current paths posited in theoretical simulations. We
use a random resistor network model to fit the linear MR, and expand it from
two to three dimensions to depict current distortions in the third (thickness)
dimension. When compared directly to experiments on Ag$_{2\pm\delta}$Se and
Ag$_{2\pm\delta}$Te, in magnetic fields up to 55 T, the model identifies
conductivity fluctuations due to macroscopic inhomogeneities as the underlying
physical mechanism. It also accounts reasonably quantitatively for the various
components of the resistivity tensor observed in the experiments.",0705.0393v1
2007-11-11,Saturated absorption spectroscopy: elimination of crossover resonances by use of a nanocell,"It is demonstrated that velocity selective optical pumping/saturation
resonances of reduced absorption in a Rb vapor nanocell with thickness
\textit{L=} $\lambda $, 2$\lambda $, and 3$\lambda $ (resonant wavelength
$\lambda $ = 780 nm) allow the complete elimination of crossover (CO)
resonances. We observe well pronounced resonances corresponding to the
F$_{g}=3$ $\to $ F$_{e}=2,3,4$ hyperfine transitions of the $^{85}$Rb D$_{2}$
line with linewidths close to the natural width. A small CO resonance located
midway between F$_{g}=3$ $\to $ F$_{e}=3$ and F$_{g}=3$ $\to$ F$_{e}=4$
transitions appears only for \textit{L} = 4$\lambda $. The D$_{2}$ line
($\lambda $ = 852 nm) in a Cs nanocell exhibits a similar behavior. From the
amplitude ratio of the CO and VSOP resonances it is possible to determine the
thickness of the column of alkali vapor in the range of 1 - 1000 $\mu $m. The
absence of CO resonances for nanocells with $L \sim \lambda $ is attractive for
frequency reference application and for studying transitions between Zeeman
sublevels in external magnetic fields.",0711.1684v1
2008-08-15,A growing dynamo from a saturated Roberts flow dynamo,"Using direct simulations, weakly nonlinear theory and nonlinear mean-field
theory, it is shown that the quenched velocity field of a saturated nonlinear
dynamo can itself act as a kinematic dynamo. The flow is driven by a forcing
function that would produce a Roberts flow in the absence of a magnetic field.
This result confirms an analogous finding by F. Cattaneo & S. M. Tobias
(arXiv:0809.1801) for the more complicated case of turbulent convection,
suggesting that this may be a common property of nonlinear dynamos; see also
the talk given also online at the Kavli Institute for Theoretical Physics
(http://online.kitp.ucsb.edu/online/dynamo_c08/cattaneo). It is argued that
this property can be used to test nonlinear mean-field dynamo theories.",0808.2141v2
2008-10-31,Diffusion-limited exciton-exciton annihilation in single-walled carbon nanotubes: A time-dependent analysis,"To provide physical insight into the recently observed photoluminescence
saturation behaviors in single-walled carbon nanotubes implying the existence
of an upper limit of exciton densities, we have performed a time-dependent
theoretical study of diffusion-limited exciton-exciton annihilation in the
general context of reaction-diffusion processes, for which exact treatments
exist. By including the radiative recombination decay as a Poissonian process
in the exactly-solvable problem of one-dimensional diffusion-driven
two-particle annihilation, we were able to correctly model the dynamics of
excitons as a function of time with different initial densities, which in turn
allowed us to reproduce the experimentally observed photoluminescence
saturation behavior at high exciton densities. We also performed Monte Carlo
simulations of the purely stochastic, Brownian diffusive motion of
one-dimensional excitons, which validated our analytical results. Finally, we
consider the temperature-dependence of this diffusion-limited exciton-exciton
annihilation and point out that high excitonic densities in SWNTs could be
achieved at low temperature in an external magnetic field.",0810.5748v1
2010-08-19,Precise measurement of hyperfine structure in the ${2P}_{1/2}$ state of $^{7}$Li using saturated-absorption spectroscopy,"We report a precise measurement of the hyperfine interval in the ${2P}_{1/2}$
state of $^{7}$Li. The transition from the ground state ($D_1$ line) is
accessed using a diode laser and the technique of saturated-absorption
spectroscopy in hot Li vapor. The interval is measured by locking an
acousto-optic modulator to the frequency difference between the two hyperfine
peaks. The measured interval of 92.040(6)~MHz is consistent with an earlier
measurement reported by us using an atomic-beam spectrometer [Das and
Natarajan, J.\ Phys.\ B {\bf 41}, 035001 (2008)]. The interval yields the
magnetic dipole constant in the $P_{1/2}$ state as $A=46.047(3)$, which is
discrepant from theoretical calculations by $>80$~kHz.",1008.3228v1
2011-05-11,Linear magnetoresistance in commercial n-type silicon due to inhomogeneous doping,"Free electron theory tells us that resistivity is independent of magnetic
field. In fact, most observations match the semiclassical prediction of a
magnetoresistance that is quadratic at low fields before saturating. However, a
non-saturating linear magnetoresistance has been observed in exotic
semiconductors such as silver chalcogenides, lightly-doped InSb, N-doped InAs,
MnAs-GaAs composites, PrFeAsO, and epitaxial graphene. Here we report the
observation of a large linear magnetoresistance in the ohmic regime in
commonplace commercial n-type silicon wafer. It is well-described by a
classical model of spatially fluctuating donor densities, and may be amplified
by altering the aspect ratio of the sample to enhance current-jetting:
increasing the width tenfold increased the magnetoresistance at 8 T from 445 %
to 4707 % at 35 K. This physical picture may well offer insights into the large
magnetoresistances recently observed in n-type and p-type Si in the non-ohmic
regime.",1105.2174v1
2011-10-31,Resistivity saturation in a weakly interacting 2D Fermi liquid at intermediate temperatures,"We report a highly unusual temperature dependence in the magnetoresistance of
a weakly interacting high mobility 2D electron gas (2DEG) under a parallel
magnetic field and when the current is perpendicular to the field. While the
linear temperature dependence below 10 K and the exponential temperature
dependence above 40 K agree with existing theory of electron-phonon scattering,
a field induced resistivity saturation behaviour characterized by an almost
complete suppression of the temperature dependence is observed from
approximately 20 to 40 K, which is in sharp contrast to the phenomenology
observed when the current is parallel to the field. Possible origins of this
intriguing intermediate temperature phenomenon are discussed.",1111.0011v2
2012-08-27,Anomalous Gluon Production and Condensation in Glasma,"The collinear color electric and magnetic fields have been discussed to be
produced immediately after high energy heavy ion collisions. We discuss
anomalous gluon production under the background gauge fields. The gluons are
Nielsen-Olesen unstable modes. The production rate of the modes by Schwinger
mechanism has recently been found to be anomalously larger than the rate of
quarks or other stable gluons. Analyzing classical evolutions of the modes with
initial conditions given by vacuum fluctuations, we find that their production
makes the color electric field decay very rapidly. The life time of the field
is approximately given by the inverse of saturation momentum in the collisions.
We also show that the mode with zero momentum form a Bose condensate and its
gluon number density grows up to be of the order of $1/\alpha_g$. After the
saturation of the gluon number density, the condensate melts into quark gluon
plasma owing to nonlinear interactions in QCD.",1208.5320v2
2012-09-29,Realization of spin gapless semiconductors: the Heusler compound Mn2CoAl,"Recent studies have reported an interesting class of semiconductor materials
that bridge the gap between semiconductors and halfmetallic ferromagnets. These
materials, called spin gapless semiconductors, exhibit a bandgap in one of the
spin channels and a zero bandgap in the other and thus allow for tunable spin
transport. Here, a theoretical and experimental study of the spin gapless
Heusler compound Mn2CoAl is presented. It turns out that Mn2CoAl is a very
peculiar ferrimagnetic semiconductor with a magnetic moment of 2 {\mu}B and a
high Curie temperature of 720 K. Below 300 K, the compound exhibits nearly
temperature-independent conductivity, very low, temperature-independent carrier
concentration, and a vanishing Seebeck coefficient. The magnetoresistance
changes sign with temperature. In high fields, it is positive and
non-saturating at low temperatures, but negative and saturating at high
temperatures. The anomalous Hall effect is comparatively low, which is
explained by the close antisymmetry of the Berry curvature for kz of opposite
sign.",1210.0148v1
2012-10-02,Amplification of a surface electromagnetic wave by running over plasma surface ultrarelativistic electron bunch as a new scheme for generation of Teraherz radiation,"The amplification of a surface electromagnetic wave by means of
ultrarelativistic monoenergetic electron bunch running over the flat plasma
surface in absence of a magnetic field is studied theoretically. It is shown
that when the ratio of electron bunch number density to plasma electron number
density multiplied by a powered to 5 relativity factor is much higher than 1,
i.e $\gamma^5 n_b/n_p>> 1$, the saturation field of the surface electromagnetic
wave induced by trapping of bunch electrons gains the magnitude:
$E_x=B_y\approx 0.16 \frac{\omega_p m c}{e} (\frac{2n_b}{\gamma^2 n_p})^{1/7}$
and does not approache the surface electromagnetic wave front breakdown
threshold in plasma. The surface electromagnetic wave saturation energy density
in plasma can exceed the electron bunch energy density. Here, we discuss the
possibility of generation of superpower Teraherz radiation on a basis of such
scheme.",1210.0610v2
2012-10-11,Optical orientation of nuclei in nitrogen alloys GaAsN at room temperature,"The intensity and the giant circular polarization of edge luminescence in a
longitudinal magnetic field have been measured in nitrogen alloys GaAsN under
circularly polarized pumping. It has been found that these dependences are
shifted with respect to zero field by a value Beff. The magnitude of the
internal field Beff increases with increase in pumping intensity and reaches
saturation (~250 Gauss) at great densities of excitation. The saturation of the
Beff field with growth of pumping indicates that this is a field of nuclei,
polarized dynamically due to hyperfine interaction with optically oriented deep
paramagnetic centers, rather than a field of exchange interaction created on
the center by spin-polarized photo-excited conduction electrons. The short time
of nuclear polarization by electrons (<15 mks), measured under modulation of
circular polarization of the exciting light with high frequency, points to a
small number of nuclei undergoing hyperfine interaction with an electron
localized at a center.",1210.3302v1
2012-10-12,Organic magnetoresistance near saturation: mesoscopic effects in small devices,"In organic light emitting diodes with small area the current may be dominated
by a finite number, N of sites in which the electron-hole recombination occurs.
As a result, averaging over the hyperfine magnetic fields, b_h, that are
generated in these sites by the environment nuclei is incomplete. This creates
a random (mesoscopic) current component, {\Delta}I(B), at field B having
relative magnitude ~ N^(-1/2). To quantify the statistical properties of
{\Delta}I(B) we calculate the correlator K(B, {\Delta}B)= <{\delta}I(B -
{\Delta}B/2){\delta}I(B + {\Delta}B/2)> for parallel and perpendicular
orientations of {\Delta}B. We demonstrate that mesoscopic fluctuations develop
at fields B>>b_h, where the average magnetoresistance is near saturation. These
fluctuations originate from the slow beating between S and T_0 states of the
recombining e-h spin pair-partners. We identify the most relevant processes
responsible for the current fluctuations as due to anomalously slow beatings
that develop in sparse e-h polaron pairs at sites for which the b_h projections
on the external field direction almost coincide.",1210.3443v2
2013-08-05,Implications of Resonant Inelastic X-ray Scattering Data for Theoretical Models of Cuprates,"There are two commonly discussed points of view in theoretical description of
cuprate superconductors, (i) Cuprates can be described by the modified t-J
model. (ii) Overdoped cuprates are close to the regime of normal Fermi liquid
(NFL). We argue that recent resonant inelastic X-ray scattering data challenge
both points. While the modified t-J model describes well the strongly
underdoped regime, it fails to describe high energy magnetic excitations when
approaching optimal doping. This probably indicates failure of the Zhang-Rice
singlet picture. In the overdoped regime the momentum-integrated spin structure
factor S(\omega) has the same intensity and energy distribution as that in an
undoped parent compound. This implies that the entire spin spectral sum rule is
saturated at \omega ~ 2J, while in a NFL the spectral weight should saturate
only at the total bandwidth which is much larger than 2J.",1308.0987v1
2014-01-11,Resonant instability of the nonlinearly-saturated magnetorotational mode in thin Keplerian discs,"The magneto-rotational decay instability (MRDI) of thin Keplerian discs
threaded by poloidal magnetic fields is introduced and studied. The linear
magnetohydrodynamic problem decouples into eigenvalue problems for in-plane
slow- and fast- Alfv'een-Coriolis (AC), and vertical magnetosonic (MS)
eigenmodes. The magnetorotational instability (MRI) is composed of a discrete
number of unstable slow AC eigenmodes that is determined for each radius by the
local beta. In the vicinity of the first beta threshold a parent MRI eigenmode
together with a stable AC eigenmode (either slow or fast) and a stable MS
eigenmode form a resonant triad. The three-wave MRDI relies on the nonlinear
saturation of the parent MRI mode and the exponential growth of two daughter
linearly stable waves, slow-AC and MS modes with an effective growth rate that
is comparable to that of the parent MRI. If, however, the role of the AC
daughter wave is played by a stable fast mode, all three modes remain bounded.",1401.2528v1
2014-01-17,Computation of dynamical correlation functions of the spin-1 Babujan-Takhtajan chain,"The dynamical structure factor of the Babujan-Takhtajan antiferromagnetic
spin-1 chain is computed numerically at zero temperature and zero magnetic
field, using the higher-spin generalization of an Algebraic Bethe Ansatz-based
method previously used for spin-1/2 integrable chains. This method, which
consists in the explicit construction of eigenstates and the summation of the
Lehmann representation of the correlator, is here particularly challenging to
implement in view of the presence of strongly deviated string solutions to the
Bethe equations. We show that a careful treatment of these deviations makes it
possible to obtain perfect saturation of sum rules for small system sizes, and
extremely good saturation for large system sizes where the dynamical structure
factor is computed by including all two-spinon and four-spinon contributions.
The real-space spin-spin correlation, obtained by Fourier transforming our
results, displays asymptotics fitting predictions from conformal field theory.",1401.4450v1
2014-04-03,Phases of triangular lattice antiferromagnet near saturation,"We consider 2D Heisenberg antiferromagnets on a triangular lattice with
spatially anisotropic interactions in a high magnetic field close to the
saturation. We show that this system possess rich phase diagram in
field/anisotropy plane due to competition between classical and quantum orders:
an incommensurate non-coplanar spiral state, which is favored classically, and
a commensurate co-planar state, which is stabilized by quantum fluctuations. We
show that the transformation between these two states is highly non-trivial and
involves two intermediate phases -- the phase with co-planar incommensurate
spin order and the one with non-coplanar double-${\bf Q}$ spiral order. The
transition between the two co-planar states is of commensurate- incommensurate
type, not accompanied by softening of spin-wave excitations. We show that a
different sequence of transitions holds in triangular antiferromagnets with
exchange anisotropy, such as Ba3CoSb2O9.",1404.1046v1
2014-08-21,Anyonic Liquids in Nearly Saturated Spin Chains,"Most Heisenberg-like spin chains flow to a universal free-fermion fixed point
near the magnetic-field induced saturation point. Here we show that an exotic
fixed point, characterized by two species of low-energy excitations with mutual
anyonic statistics, may also emerge in such spin chains if the dispersion
relation has two minima. By using bosonization, two-magnon exact calculations,
and numerical density-matrix-renormalization-group, we demonstrate the
existence of this anyonic-liquid fixed point in an XXZ spin chain with up to
second neighbor interactions. We also identify a range of microscopic
parameters, which support this phase.",1408.5151v2
2014-12-12,Linear magnetoresistance caused by mobility fluctuations in the n-doped Cd3As2,"Cd3As2 is a candidate three-dimensional Dirac semi-metal which has
exceedingly high mobility and non-saturating linear magnetoresistance that may
be relevant for future practical applications. We report magnetotransport and
tunnel diode oscillation measurements on Cd3As2, in magnetic fields up to 65 T
and temperatures between 1.5K to 300K. We find the non-saturating linear
magnetoresistance persist up to 65T and it is likely caused by disorder effects
as it scales with the high mobility, rather than directly linked to Fermi
surface changes even when approaching the quantum limit. From the observed
quantum oscillations, we determine the bulk three-dimensional Fermi surface
having signatures of Dirac behaviour with non-trivial Berry's phase shift, very
light effective quasiparticle masses and clear deviations from the
band-structure predictions. In very high fields we also detect signatures of
large Zeeman spin-splitting (g~16).",1412.4105v1
2016-02-09,Mechanical energy fluxes associated with saturated coronal heating in M dwarfs: comparison with predictions of a turbulent dynamo,"Empirically, the X-ray luminosity LX from M dwarfs has been found to have an
upper limit of about 0.2% of the bolometric flux Lbol. In the limit where
magnetic fields in M dwarfs are generated in equipartition with convective
motions, we use stellar models to calculate the energy flux of Alfven waves FA
as a function of depth in the sub-surface convection zone. Since Alfven waves
have the optimal opportunity for wave modes to reach the corona, we suggest
that FA sets an upper limit on the mechanical flux Fmech which causes coronal
heating. This suggestion accounts quantitatively for the saturated values of
LX/Lbol which have been reported empirically for M dwarfs.",1602.03079v1
2017-01-10,Saturation of resistivity and Kohler's rule in Ni-doped La$_{1.85}$Sr$_{0.15}$CuO$_{4}$ cuprate,"We present the results of electrical transport measurements of
La$_{1.85}$Sr$_{0.15}$Cu$_{1-y}$Ni$_{y}$O$_{4}$ thin single-crystal films at
magnetic fields up to 9 T. Adding Ni impurity with strong Coulomb scattering
potential to slightly underdoped cuprate makes the signs of resistivity
saturation at $\rho_{sat}$ visible in the measurement temperature window up to
350 K. Employing the parallel-resistor formalism reveals that $\rho_{sat}$ is
consistent with classical Ioffe-Regel-Mott limit and changes with carrier
concentration $n$ as $\rho_{sat}\propto 1/\sqrt{n}$. Thermopower measurements
show that Ni tends to localize mobile carriers, decreasing their effective
concentration as $n\!\cong0.15\!-\!y$. The classical unmodified Kohler's rule
is fulfilled for magnetoresistance in the nonsuperconducting part of the phase
diagram when applied to the ideal branch in the parallel-resistor model.",1701.02568v1
2017-08-21,Properties of $(TiZrNbCu)_{1-x}$$Ni_{x}$ Metallic Glasses,"Recent studies (J. Alloys Compd. 695 (2017) 2661) of the electronic structure
and properties of $(TiZrNbCu)_{1-x}$$Ni_{x}$ (x$\leq$0.25) amorphous high
entropy alloys (a-HEA) have been extended to x=0.5 in order to compare
behaviours of a-HEA and conventional Ni-base metallic glasses (MG). The
amorphous state of all samples was verified by thermal analysis and X-ray
diffraction (XRD). XRD indicated a probable change in local atomic
arrangements, i.e. short-range-order (SRO) for x$\geq$0.35. Simultaneously,
thermal parameters, such as the first crystallization temperature $T_{x}$ and
the liquidus temperature showed a tendency to saturate for x$\geq$0.35 . The
same tendency also appeared in the magnetic susceptibility $\chi_{exp}$ and the
linear term in the low temperature specific heat {\gamma}. The Debye
temperatures and Youngs moduli also tend to saturate for x$\geq$0.35. These
unusual changes in SRO and all properties within the amorphous phase seem
correlated with the change of valence electron number (VEC) on increasing x.",1708.06171v2
2017-12-04,Particle-hole symmetry reveals failed superconductivity in the metallic phase of two-dimensional superconducting films,"Electrons confined to two dimensions display an unexpected diversity of
behaviors as they are cooled to absolute zero. Noninteracting electrons are
predicted to eventually ""localize"" into an insulating ground state, and it has
long been supposed that electron correlations stabilize only one other phase:
superconductivity. However, many two-dimensional (2D) superconducting materials
have shown surprising evidence for metallic behavior, where the electrical
resistivity saturates in the zero-temperature limit, the nature of this
unexpected metallic state remains under intense scrutiny. We report electrical
transport properties for two disordered 2D superconductors, indium oxide and
tantalum nitride, and observe a magnetic field-tuned transition from a true
superconductor to a metallic phase with saturated resistivity. This metallic
phase is characterized by a vanishing Hall resistivity, suggesting that it
retains particle-hole symmetry from the disrupted superconducting state.",1712.00947v1
2019-01-14,BPS soliton-impurity models and supersymmetry,"We find supersymmetric extensions of the half-BPS soliton-impurity models in
(1+1) dimensions which preserve half of the $\mathcal{N}=1$ supersymmetry. This
is related to the fact that in the bosonic sector (i.e., the half-BPS
soliton-impurity model), only one soliton (for example, the kink) is a BPS
configuration which solves the pertinent Bogomolnyi equation and saturates the
topological energy bound. On the other hand, the topological charge conjugate
state (the antikink) is not a BPS solution. This means that it obeys the full
Euler-Lagrange equation and does not saturate the topological energy bound. The
supersymmetric approach also allows us to construct half-BPS soliton-impurity
models in (2+1) dimensions. Concretely, in the case of the $CP^1$ model, its
BPS impurity generalisation preserves one-quarter of the $\mathcal{N}=2$ SUSY,
while for the Abelian Higgs model at critical coupling both impurity
generalisations preserving one-quarter (the case of a new, so-called Higgs
impurity) as well as one-half of the $\mathcal{N}=2$ SUSY (the case of the
previously known magnetic impurity) are possible. We also discuss a possible
relation between the BPS $CP^1$-impurity model and the Dzyaloshinskii-Moriya
interaction energy.",1901.04501v1
2019-05-21,Boundary-limited and glassy-like phonon thermal conduction in EtMe$_3$Sb[Pd(dmit)$_2$]$_2$,"In molecular-based quantum-spin-liquid candidate EtMe$_3$Sb[Pd(dmit)$_2$]$_2$
with two-dimensional $S$=1/2 triangular lattice, a finite residual linear term
in the thermal conductivity, $\kappa_0/T\equiv\kappa/T (T \rightarrow 0)$, has
been observed and attributed to the presence of itinerant gapless excitations.
Here we show that the data of $\kappa$ measured in several single crystals are
divided into two groups with and without the residual linear term. In the first
group with finite $\kappa_0/T$, the phonon thermal conductivity $\kappa_{ph}$
is comparable to that of other organic compounds. In these crystals, the phonon
mean free path $\ell_{ph}$ saturates at low temperatures, being limited by
sample size. On the other hand, in the second group with zero $\kappa_0/T$,
$\kappa_{ph}$ is one order of magnitude smaller than that in the first group,
comparable to that of amorphous solids. In contrast to the first group,
$\ell_{ph}$ shows a glassy-like non-saturating behavior at low temperatures.
These results suggest that the crystals with long $\ell_{ph}$ are required to
discuss the magnetic excitations by thermal conductivity measurements.",1905.08420v1
2020-01-29,Extremely slow non-equilibrium monopole dynamics in classical spin ice,"We report on the non-equilibrium monopole dynamics in the classical spin ice
Dy$_2$Ti$_2$O$_7$ detected by means of high-resolution magnetostriction
measurements. Significant lattice changes occur at the transition from the
kagome-ice to the saturated-ice phase, visible in the longitudinal and
transverse magnetostriction. A hysteresis opening at temperatures below 0.6 K
suggests a first-order transition between the kagome and saturated state.
Extremely slow lattice relaxations, triggered by changes of the magnetic field,
were observed. These lattice-relaxation effects result from non-equilibrium
monopole formation or annihilation processes. The relaxation times extracted
from our experiment are in good agreement with theoretical predictions with
decay constants of the order of $10{^4}$ s at 0.3 K.",2001.10844v1
2020-05-11,Pressure tuning of the anomalous Hall effect in the chiral antiferromagnet Mn3Ge,"We report on the pressure evolution of the giant anomalous Hall effect (AHE)
in the chiral antiferromagnet Mn$_3$Ge. The AHE originating from the
non-vanishing Berry curvature in Mn$_3$Ge can be continuously tuned by
application of hydrostatic pressure. At room temperature, the Hall signal
changes sign as a function of pressure and vanishes completely at $p=1.53$ GPa.
Even though the Hall conductivity changes sign upon increasing pressure, the
room-temperature saturation value of 23 ${\rm \Omega^{-1}cm^{-1}}$ at 2.85 GPa
is remarkably high and comparable to the saturation value at ambient pressure
of about 40 ${\rm \Omega^{-1}cm^{-1}}$. The change in the Hall conductivity can
be directly linked to a gradual change of the size of the in-plane components
of the Mn moments in the non-collinear triangular magnetic structure. Our
findings, therefore, provide a route for tuning of the AHE in the chiral
antiferromagnetic Mn$_3$Ge.",2005.04967v1
2020-06-05,Effect of Oxygen Saturation on AFM-WFM-HTSC Transition Temperatures in RuSr2(Eu1.5Ce0.5)Cu2O10-δ Ceramic Samples,"The effect of annealing in high pressure oxygen atmosphere on superconducting
transition temperatures for ceramic samples of magnetic superconductor europium
based 1222 ruthenocuprate was studied. It was shown that the properties of the
samples are consistent with the behavior of granular superconducting system. As
a result of oxygen saturation the superconducting transition temperatures
become higher. Particularly, the shift of superconducting transition
temperature for the intergranular medium is 9.2 K and for the matter within the
granules 6.8 K. This difference is supposed due to the mechanism of oxygen
diffusion along the grain boundaries. In the temperature range between 135 K
and 350 K the behavior of resistance obeyed the Mott law of variable range
hopping for three dimensional case.",2006.03436v1
2020-11-27,PFG NMR time-dependent diffusion coefficient analysis of confined emulsion: post drainage phase conformation,"In this work, we present a characterization of phase configuration in
water-saturated sintered glass bead samples after oil injection, through the
analysis of time-dependent diffusion coefficients obtained from sets of
one-dimensional pulsed field gradient nuclear magnetic resonance (PFG NMR)
measurements, pre and post drainage. Estimates of samples surface-to-volume
ratio and permeability from pre drainage PFG measurements in a water-saturated
sample were compared with analytical and reported values, respectively, and a
fair agreement was found in both cases. Short-time analysis of diffusion
coefficients extracted from PFG measurements was used to quantify the increase
in surface-to-volume ratio probed by the wetting phase after drainage. Analysis
of water and oil diffusion coefficients from post drainage PFG experiments were
carried out using a bi-Gaussian model, and two distinct scenarios were
considered to describe fluids conformation within pores. For the case where
non-wetting phase was considered to exhibit a poorly connected geometry, an
analysis assuming the formation of oi-in-water droplets within pores was
performed, and a Gaussian distribution of droplets radii was determined.",2011.13703v1
2021-06-30,Temperature dependent equilibration of spin orthogonal quantum Hall edge modes,"Conductance of the edge modes as well as conductance across the
co-propagating edge modes around the \nu = 4/3, 5/3 and 2 quantum Hall states
are measured by individually exciting the modes. Temperature dependent
equilibration rates of the outer unity conductance edge mode are presented for
different filling fractions. We find that the equilibration rate of the outer
unity conductance mode at \nu = 2 is higher and more temperature sensitive
compared to the mode at fractional filling 5/3 and 4/3. At lowest temperature,
equilibration length of the outer unity conductance mode tends to saturate with
lowering filling fraction \nu by increasing magnetic field B. We speculate this
saturating nature of equilibration length is arising from an interplay of
Coulomb correlation and spin orthogonality.",2106.15848v1
2021-10-17,Effective two-level approximation of a multi-level system driven by coherent and incoherent fields,"The numerical simulation of multiple scattering in dense ensembles is the
mostly adopted solution to predict their complex optical response. While the
scalar and vectorial light mediated interactions are accurately taken into
account, the computational complexity still limits current simulations to the
low saturation regime and ignores the internal structure of atoms. Here, we
propose to go beyond these restrictions, at constant computational cost, by
describing a multi-level system (MLS) by an effective two-level system (TLS)
that best reproduces the coherent and total scattering properties in any
saturation regime. The correspondence of our model is evaluated for different
experimentally realistic conditions such as the modification of the driving
field polarization, the presence of stray magnetic fields or an incoherent
resonant electromagnetic field background. The trust interval of the model is
quantified for the D2-line of 87Rb atoms but it could be generalized to any
closed transition of a multi-level quantum system.",2110.08894v1
2022-07-19,Microtearing turbulence saturation via electron temperature flattening at low-order rational surfaces,"Microtearing instability is one of the major sources of turbulent transport
in high-$\beta$ tokamaks. These modes lead to very localized transport at
low-order rational magnetic field lines, and we show that flattening of the
local electron temperature gradient at these rational surfaces plays an
important role in setting the saturated flux level in microtearing turbulence.
This process depends crucially on the density of rational surfaces, and thus
the system-size, and gives rise to a worse-than-gyro-Bohm transport scaling for
system-sizes typical of existing tokamaks and simulations.",2207.09211v4
2024-02-09,Simulation of ion temperature gradient driven modes with 6D kinetic Vlasov code,"With the increase in computational capabilities over the last years it
becomes possible to simulate more and more complex and accurate physical
models. Gyrokinetic theory has been introduced in the 1960s and 1970s in the
need of describing a plasma with more accurate models than fluid equations, but
eliminating the complexity of the fast gyration about the magnetic field lines.
Although results from current gyrokinetic computer simulations are in fair
agreement with experimental results in core physics, crucial assumptions made
in the derivation make it unreliable in regimes of higher fluctuations and
stronger gradient, such as the tokamak edge. With our novel optimized and
scalable semi-Lagrangian solver we are able to simulate ion-temperature
gradient modes with the 6D kinetic model including the turbulent saturation.
After thoroughly testing our simulation code against analytical computations
and gyrokinetic simulations (with the gyrokinetic code GYRO), it has been
possible to show first plasma properties that go beyond standard gyrokinetic
simulations. This includes the explicit description of the complete
perpendicular energy fluxes and the excitation of high frequency waves (around
the Larmor frequency) in the nonlinear saturation phase.",2402.06605v1
2005-01-18,Plasma instabilities and magnetic-field growth in clusters of galaxies,"We show that under very general conditions, cluster plasmas threaded by weak
magnetic fields are subject to very fast growing plasma instabilities driven by
the anisotropy of the plasma pressure (viscous stress) with respect to the
local direction of the magnetic field. Such an anisotropy will naturally arise
in any weakly magnetized plasma that has low collisionality and is subject to
stirring. The magnetic field must be sufficiently weak for the instabilities to
occur, viz., beta>Re^{1/2}. The instabilities are captured by the extended MHD
model with Braginskii viscosity. However, their growth rates are proportional
to the wavenumber down to the ion gyroscale, so MHD equations with Braginskii
viscosity are not well posed and a fully kinetic treatment is necessary. The
instabilities can lead to magnetic fields in clusters being amplified from seed
strength of ~10^{-18} G to dynamically important strengths of ~10 microG on
cosmologically trivial time scales (~10^8 yr). The fields produced during the
amplification stage are at scales much smaller than observed. Predicting the
saturated field scale and structure will require a kinetic theory of magnetized
cluster turbulence.",0501362v3
2001-11-12,Magnetic-Superconducting phase-diagram of Eu2-xCexRuSr2Cu2O10,"Eu2-xCexRuSr2Cu2O10-d (Ru-2122) is the first Cu-O based system in which
superconductivity (SC) in the CuO2 planes and weak-ferromagnetism (W-FM) in the
Ru sub-lattice coexists. The hole doping in the CuO2 planes, is controlled by
appropriate variation of the Ce concentration. SC occurs for Ce contents of
0.4-0.8, with the highest TC=35 K for Ce=0.6. The as-prepared non-SC
EuCeRuSr2Cu2O10 (x=1) sample exhibits magnetic irreversibility below Tirr=125 K
and orders anti-ferromagnetically (AFM) at TM =165 K. The saturation moment at
5 K is Msat=0.89 mB /Ru close to the expected 1 mB for the low-spin state of
Ru5+. Annealing under oxygen pressures, does not affect these parameters,
whereas depletion of oxygen shifts both Tirr and TM up to 169 and 215 K
respectively. Systematic magnetic studies on Eu2-xCexRuSr2Cu2O10-d show that
TM, Tirr and Msat decrease with x, and the Ce dependent magnetic-SC phase
diagram is presented. A simple model for the SC state is proposed. We interpret
the magnetic behavior in the framework of our ac and dc magnetic studies, and
argue that: (i) the system becomes AFM ordered at TM; (b) at Tirr < TM, W-FM is
induced by the canting of the Ru moments, and (c), at lower temperatures the
appropriate samples become SC at TC. The magnetic features are not affected by
the SC state, and the two states coexist.",0111217v1
2003-05-03,Magnetic properties of the $S=1/2$ distorted diamond chain at T=0,"We explore, at T=0, the magnetic properties of the $S=1/2$ antiferromagnetic
distorted diamond chain described by the Hamiltonian ${\cal H}
  = \sum_{j=1}^{N/3}{J_1 ({\bi S}_{3j-1} \cdot {\bi S}_{3j}
  + {\bi S}_{3j} \cdot {\bi S}_{3j+1})
  + J_2 {\bi S}_{3j+1} \cdot {\bi S}_{3j+2}
  + J_3 ({\bi S}_{3j-2} \cdot {\bi S}_{3j}
  + {\bi S}_{3j} \cdot {\bi S}_{3j+2})}
  \allowbreak - H \sum_{l=1}^{N} S_l^z $ with $J_1, J_2, J_3\ge0$, which well
models ${\rm A_3 Cu_3 (PO_4)_4}$ with ${\rm A = Ca, Sr}$, ${\rm Bi_4 Cu_3 V_2
O_{14}}$ and azurite $\rm Cu_3(OH)_2(CO_3)_2$. We employ the physical
consideration, the degenerate perturbation theory, the level spectroscopy
analysis of the numerical diagonalization data obtained by the Lanczos method
and also the density matrix renormalization group (DMRG) method. We investigate
the mechanisms of the magnetization plateaux at $M=M_s/3$ and $M=(2/3)M_s$, and
also show the precise phase diagrams on the $(J_2/J_1, J_3/J_1)$ plane
concerning with these magnetization plateaux, where $M=\sum_{l=1}^{N} S_l^z$
and $M_s$ is the saturation magnetization. We also calculate the magnetization
curves and the magnetization phase diagrams by means of the DMRG method.",0305057v1
2003-09-26,Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers,"In antiferromagnetically coupled superlattices grown on (001) faces of cubic
substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or
Fe/Cr, the magnetic states evolve under competing influence of bilinear and
biquadratic exchange interactions, surface-enhanced four-fold in-plane
anisotropy, and specific finite-size effects. Using phenomenological
(micromagnetic) theory, a comprehensive survey of the magnetic states and
reorientation transitions has been carried out for multilayer systems with even
number of ferromagnetic sub-layers and magnetizations in the plane. In
two-layer systems (N=2) the phase diagrams in dependence on components of the
applied field in the plane include ``swallow-tail'' type regions of
(metastable) multistate co-existence and a number of continuous and
discontinuous reorientation transitions induced by radial and transversal
components of the applied field. In multilayers (N \ge 4) noncollinear states
are spatially inhomogeneous with magnetization varying across the multilayer
stack. For weak four-fold anisotropy the magnetic states under influence of an
applied field evolve by a complex continuous reorientation into the saturated
state. At higher anisotropy they transform into various inhomogeneous and
asymmetric structures. The discontinuous transitions between the magnetic
states in these two-layers and multilayers are characterized by broad ranges of
multi-phase coexistence of the (metastable) states and give rise to specific
transitional domain structures.",0309621v1
2005-08-17,Magnetic properties in a partially oxidized nanocomposite of Cu-CuCl,"Magnetism of a very thin antiferromagnetic (AFM) surface CuO has been
investigated with the partially oxidized nanocomposites of Cu-CuCl, ~ 200 nm.
The samples are characterized by X-ray diffraction, X-ray photoelectron
spectroscopy, X-ray-excited Auger electron spectroscopy, transmission electron
microscope and magnetic measurements. The characterizations indicate that the
composites have a core-shell structure. Before the oxidation, it is
(Cu)core/(CuCl)shell, and after the oxidation,
(Cu)core/(Cu2O+CuCl+minuteCuO)shell. The magnetic measurements have revealed
that a ferromagnetic (FM) like open hysteresis exists at the temperature below
the freezing point, TF. In the high field region, a paramagnetic (PM) response
appears without showing a sign of saturation. Also, the field dependent
magnetization (M-H) measurement is PM-like at T > TF. These interesting
magnetic properties are evident to arise from the AFM CuO on the outer surface.
They are attributed to the uncompensated surface spins of Cu2+ and the effect
of surface random potential. More interestingly, the magnetic susceptibility is
greatly enhanced in the presence of Cl- anions at T < TF, according to the
field-cooled/zero-field-cooled (FC/ZFC) measurements. This further supports the
point that the disorder or frustration effect of the impurity would reduce the
AFM ordering of CuO and increase the level of uncompensated spins.",0508387v2
2005-08-29,"Magnetic Properties of J-J-J' Quantum Heisenberg Chains with Spin S=1/2, 1, 3/2 and 2 in a Magnetic Field","By means of the density matrix renormalization group (DMRG) method, the
magnetic properties of the J-J-J$^{\prime}$ quantum Heisenberg chains with spin
$S=1/2$, 1, 3/2 and 2 in the ground states are investigated in the presence of
a magnetic field. Two different cases are considered: (a) when $J$ is
antiferromagnetic and $J^{\prime}$ is ferromagnetic (i.e. the AF-AF-F chain),
the system is a ferrimagnet. The plateaus of the magnetization are observed. It
is found that the width of the plateaus decreases with increasing the
ferromagnetic coupling, and disappears when $% J^{\prime}/J$ passes over a
critical value. The saturated field is observed to be independent of the
ferromagnetic coupling; (b) when $J$ is ferromagnetic and $J^{\prime}$ is
antiferromagnetic (i.e. the F-F-AF chain), the system becomes an
antiferromagnet. The plateaus of the magnetization are also seen. The width of
the plateaus decreases with decreasing the antiferromagnetic coupling, and
disappears when $J^{\prime}/J $ passes over a critical value. Though the ground
state properties are quite different, the magnetization plateaus in both cases
tend to disappear when the ferromagnetic coupling becomes more dominant.
Besides, no fundamental difference between the systems with spin half-integer
and integer has been found.",0508685v1
2006-06-15,Exact eigenstates of highly frustrated spin lattices probed in high fields,"Strongly frustrated antiferromagnets such as the magnetic molecule
{Mo72Fe30}, the kagome, or the pyrochlore lattice exhibit a variety of
fascinating properties like low-lying singlets, magnetization plateaus as well
as magnetization jumps. During recent years exact many-body eigenstates could
be constructed for several of these spin systems. These states become ground
states in high magnetic fields, and they also lead to exotic behavior. A key
concept to an understanding of these properties is provided by independent
localized magnons. The energy eigenvalue of these n-magnon states scales
linearly with the number n of independent magnons and thus with the total
magnetic quantum number M=Ns-n. In an applied field this results in a giant
magnetization jump which constitutes a new macroscopic quantum effect. It will
be demonstrated that this behavior is accompanied by a massive degeneracy, an
extensive (T=0)-entropy, and thus a large magnetocaloric effect at the
saturation field. The connection to flat band ferromagnetism will be outlined.",0606401v2
2007-08-11,Relationship between macroscopic physical properties and local distortions of low doping La{1-x}Ca{x}MnO3: an EXAFS study,"A temperature-dependent EXAFS investigation of La{1-x}Ca{x}MnO3 is presented
for the concentration range that spans the ferromagnetic-insulator (FMI) to
ferromagnetic-metal (FMM) transition region, x = 0.16-0.22. The samples are
insulating for x = 0.16-0.2 and show a metal/insulator transition for x = 0.22.
All samples are ferromagnetic although the saturation magnetization for the 16%
Ca sample is only ~ 70% of the expected value at 0.4T. We find that the FMI
samples have similar correlations between changes in the local Mn-O distortions
and the magnetization as observed previously for the colossal magnetoresistance
(CMR) samples (0.2 < x < 0.5) - except that the FMI samples never become fully
magnetized. The data show that there are at least two distinct types of
distortions. The initial distortions removed as the insulating sample becomes
magnetized are small and provides direct evidence that roughly 50% of the Mn
sites have a small distortion/site and are magnetized first. The large
remaining Mn-O distortions at low T are attributed to a small fraction of
Jahn-Teller-distorted Mn sites that are either antiferromagnetically ordered or
unmagnetized. Thus the insulating samples are very similar to the behavior of
the CMR samples up to the point at which the M/I transition occurs for the CMR
materials. The lack of metallic conductivity for x <= 0.2, when 50% or more of
the sample is magnetic, implies that there must be preferred magnetized Mn
sites and that such sites do not percolate at these concentrations.",0708.1546v1
2008-03-24,Effect of static and dynamic disorder on electronic transport of $RCo_2$ compounds: a study of $Ho(Al_xCo_{1-x})_2$ alloys,"We present experimental results on thermoelectric power ({\em S}) and
electrical resistivity ($\rho $) of pseudobinary alloys
Ho(Al$_x$Co$_{1-x}$)$_2$ ($0 \leq x \leq 0.1 $), in the temperature range 4.2 K
to 300 K. The work focuses on the effects of static (induced by alloying) and
dynamic (induced by temperature) disorder on the magnetic state and electronic
transport in a metallic system with itinerant metamagnetic instability. Spatial
fluctuations of the local magnetic susceptibility in the alloys lead to a
development of a partially ordered magnetic ground state of the itinerant 3d
electron system. This results in a strong increase of the residual resistivity
and a suppression of the temperature-dependent resistivity. Thermopower
exhibits a complex temperature variation in both the magnetically ordered and
in the paramagnetic state. This complex temperature variation is referred to
the electronic density of states features in vicinity of Fermi energy and to
the interplay of magnetic and impurity scattering. Our results indicate that
the magnetic enhancement of the Co 3d-band in RCo$_{\rm 2}$--based alloys upon
a substitution of Co by non-magnetic elements is mainly related to a
progressive localization of the Co -- 3d electrons caused by disorder. We show
that the magnitude of the resistivity jump at the Curie temperature for
RCo$_{\rm 2}$ compounds exhibiting a first order phase transition is a
non-monotonic function of the Curie temperature due to a saturation of the
3d--band spin fluctuation magnitude at high temperatures.",0803.3380v3
2008-06-03,Magnetic Anomalies in a New Manganocuprate Gd3Ba2Mn2Cu2O12,"The manganocuprate compound Gd3Ba2Mn2Cu2O12 (Gd-3222) has been synthesized by
conventional solid state reaction method and its magnetic behavior has been
studied by dc and ac magnetization (M) and heat capacity (C) measurements as a
function of temperature (T). This compound crystallizes in a tetragonal
structure (space group I4/mmm). We find that this compound exhibits three
magnetic transitions, around 2.5, 4.8 and 9 K, as inferred from dc and ac
magnetic susceptibility (chi) data. However, no evidence for a well-defined
lambda-anomaly is found in C(T) above 1.8 K, though there is a gradual upturn
below about 10 K. An application of a magnetic field results in a peak around
5K, while ac chi appears to show a very weak frequency dependence below 9 K.
Isothermal M curve at 1.8 K exhibits a weak hysteresis without any evidence for
saturation even at fields as high as 120 kOe. These results imply that this
compound undergoes a spin-glass-like freezing at low temperatures, though the
exact nature of the magnetic transition at 10 K is not clear. The magnitude of
the magnetocaloric effect, as inferred from M and C data, is quite large over a
wide temperature range below 50 K peaking around 4 K.",0806.0456v1
2008-10-14,Field induced magnetic order in the frustrated magnet Gadolinium Gallium Garnet,"Gd3Ga5O12, (GGG), has an extraordinary magnetic phase diagram, where no long
range order is found down to 25 mK despite \Theta_CW \approx 2 K. However, long
range order is induced by an applied field of around 1 T. Motivated by recent
theoretical developments and the experimental results for a closely related
hyperkagome system, we have performed neutron diffraction measurements on a
single crystal sample of GGG in an applied magnetic field. The measurements
reveal that the H-T phase diagram of GGG is much more complicated than
previously assumed. The application of an external field at low T results in an
intensity change for most of the magnetic peaks which can be divided into three
distinct sets: ferromagnetic, commensurate antiferromagnetic, and
incommensurate antiferromagnetic. The ferromagnetic peaks (e.g. (112), (440)
and (220)) have intensities that increase with the field and saturate at high
field. The antiferromagnetic reflections have intensities that grow in low
fields, reach a maximum at an intermediate field (apart from the (002) peak
which shows two local maxima) and then decrease and disappear above 2 T. These
AFM peaks appear, disappear and reach maxima in different fields. We conclude
that the competition between magnetic interactions and alternative ground
states prevents GGG from ordering in zero field. It is, however, on the verge
of ordering and an applied magnetic field can be used to crystallise ordered
components. The range of ferromagnetic and antiferromagnetic propagation
vectors found reflects the complex frustration in GGG.",0810.2410v1
2009-10-28,Fluctuation dynamo based on magnetic reconnections,"We develop a new model of the fluctuation dynamo in which the magnetic field
is confined to thin flux ropes advected by a multi-scale flow which models
turbulence. Magnetic dissipation occurs only via reconnections of flux ropes.
The model is particularly suitable for rarefied plasma, such as the Solar
corona or galactic halos. We investigate the kinetic energy release into heat,
mediated by dynamo action, both in our model and by solving the induction
equation with the same flow. We find that the flux rope dynamo is more than an
order of magnitude more efficient at converting mechanical energy into heat.
The probability density of the magnetic energy released during reconnections
has a power-law form with the slope -3, consistent with the Solar corona
heating by nanoflares. We also present a nonlinear extension of the model. This
shows that a plausible saturation mechanism of the fluctuation dynamo is the
suppression of turbulent magnetic diffusivity, due to suppression of random
stretching at the location of the flux ropes. We confirm that the probability
distribution function of the magnetic line curvature has a power-law form
suggested by (Schekochihin et al., 2002). We argue, however, using our results
that this does not imply a persistent folded structure of magnetic field, at
least in the nonlinear stage.",0910.5392v2
2009-11-23,Magnetic anisotropy determination and magnetic hyperthermia properties of small Fe nanoparticles in the superparamagnetic regime,"We report on the magnetic and hyperthermia properties of iron nanoparticles
synthesized by organometallic chemistry. They are 5.5 nm in diameter and
display a saturation magnetization close to the bulk one. Magnetic properties
are dominated by the contribution of aggregates of nanoparticles with respect
to individual isolated nanoparticles. Alternative susceptibility measurements
are been performed on a low interacting system obtained after eliminating the
aggregates by centrifugation. A quantitative analysis using the Gittleman s
model allow a determination of the effective anisotropy Keff = 1.3 * 10^5
J.m^{-3}, more than two times the magnetocristalline value of bulk iron.
Hyperthermia measurements are performed on agglomerates of nanoparticles at a
magnetic field up to 66 mT and at frequencies in the range 5-300 kHz. Maximum
measured SAR is 280 W/g at 300 kHz and 66 mT. Specific absorption rate (SAR)
displays a square dependence with the magnetic field below 30 mT but deviates
from this power law at higher value. SAR is linear with the applied frequency
for mu_0H=19 mT. The deviations from the linear response theory are discussed.
A refined estimation of the optimal size of iron nanoparticles for hyperthermia
applications is provided using the determined effective anisotropy value.",0911.4413v1
2010-02-02,"Magnetic anisotropy of epitaxial (Ga,Mn)As on (113)A GaAs","The temperature dependence of magnetic anisotropy in (113)A (Ga,Mn)As layers
grown by molecular beam epitaxy is studied by means of superconducting quantum
interference device (SQUID) magnetometry as well as by ferromagnetic resonance
(FMR) and magnetooptical effects. Experimental results are described
considering cubic and two kinds of uniaxial magnetic anisotropy. The magnitude
of cubic and uniaxial anisotropy constants is found to be proportional to the
fourth and second power of saturation magnetization, respectively. Similarly to
the case of (001) samples, the spin reorientation transition from uniaxial
anisotropy with the easy along the [-1, 1, 0] direction at high temperatures to
the biaxial <100> anisotropy at low temperatures is observed around 25 K. The
determined values of the anisotropy constants have been confirmed by FMR
studies. As evidenced by investigations of the polar magnetooptical Kerr
effect, the particular combination of magnetic anisotropies allows the
out-of-plane component of magnetization to be reversed by an in-plane magnetic
field. Theoretical calculations within the p-d Zener model explain the
magnitude of the out-of-plane uniaxial anisotropy constant caused by epitaxial
strain, but do not explain satisfactorily the cubic anisotropy constant. At the
same time the findings point to the presence of an additional uniaxial
anisotropy of unknown origin. Similarly to the case of (001) films, this
additional anisotropy can be explained by assuming the existence of a shear
strain. However, in contrast to the (001) samples, this additional strain has
an out-of-the-(001)-plane character.",1002.0563v2
2011-02-25,Dynamo in the Intra-Cluster Medium: Simulation of CGL-MHD Turbulent Dynamo,"The standard magnetohydrodynamic (MHD) description of the plasma in the hot,
magnetized gas of the intra-cluster (ICM) medium is not adequate because it is
weakly collisional. In such collisionless magnetized gas, the microscopic
velocity distribution of the particles is not isotropic, giving rise to kinetic
effects on the dynamical scales. These kinetic effects could be important in
understanding the turbulence, as so as the amplification and maintenance of the
magnetic fields in the ICM. It is possible to formulate fluid models for
collisonless or weakly collisional gas by introducing modifications in the MHD
equations. These models are often referred as kinetic MHD (KMHD). Using a KMHD
model based on the CGL-closure, which allows the adiabatic evolution of the two
components of the pressure tensor (the parallel and perpendicular components
with respect to the local magnetic field), we performed 3D numerical
simulations of forced turbulence in order to study the amplification of an
initially weak seed magnetic field. We found that the growth rate of the
magnetic energy is comparable to that of the ordinary MHD turbulent dynamo, but
the magnetic energy saturates in a level smaller than of the MHD case. We also
found that a necessary condition for the dynamo works is to impose limits to
the anisotropy of the pressure.",1102.5139v1
2011-12-20,The Ly-alpha Lines of H I and He II: A Differential Hanle Effect for Exploring the Magnetism of the Solar Transition Region,"The Ly-alpha line of He II at 304 \AA\ is one of the spectral lines of choice
for EUV channels of narrow-band imagers on board space telescopes, which
provide spectacular intensity images of the outer solar atmosphere. Since the
magnetic field information is encoded in the polarization of the spectral line
radiation, it is important to investigate whether the He II line radiation from
the solar disk can be polarized, along with its magnetic sensitivity. Here we
report some theoretical predictions concerning the linear polarization signals
produced by scattering processes in this strong emission line of the solar
transition region, taking into account radiative transfer and the Hanle effect
caused by the presence of organized and random magnetic fields. We find that
the fractional polarization amplitudes are significant (${\sim}1%$), even when
considering the wavelength-integrated signals. Interestingly, the scattering
polarization of the Ly-alpha line of He II starts to be sensitive to the Hanle
effect for magnetic strengths B>100 G (i.e., for magnetic strengths of the
order of and larger than the Hanle saturation field of the hydrogen Ly-alpha
line at 1216 \AA). We therefore propose simultaneous observations of the
scattering polarization in both Ly-alpha lines to facilitate magnetic field
measurements in the upper solar chromosphere. Even the development of a
narrow-band imaging polarimeter for the He II 304 \AA\ line alone would be
already of great diagnostic value for probing the solar transition region.",1112.4746v1
2012-01-13,Preisach images of a simple mechanical system,"This work is an an early stage of a larger project aiming at answering the
question whether or not the Preisach map is really fingerprinting magnetic
materials. More precisely, we are interested whether Preisach model of magnetic
hysteresis indeed contains any physics or is just a convenient modeling tool.
To this extent we study a very simple mechanical system, thus fully tractable,
subjected to the external force. Despite of its simplicity, our model captures
all the fundamental features of real magnetic materials, namely their
hysteretic behavior, coercivity, remanent magnetization and saturation at high
fields. Both the overall shape of major hysteresis loop as well as First Order
Reversal Curves (FORC's) are reproduced quite correctly; they are very similar
to those observed in magnetic materials. The model essentially consists of a
single, spring loaded, rigid and rotative bar with non-zero friction torque.
The length of a projection of this bar onto the direction of an external force
is identified with magnetization. The friction torque and the spring constant
are the only freely adjustable parameters of our model. Here we investigate,
and present, their influence on the inferred Preisach maps.",1201.2811v1
2012-07-09,Coronal Structure of Low-Mass Stars,"We investigate the change in stellar magnetic topology across the
fully-convective boundary and its effects on coronal properties. We consider
both the magnitude of the open flux that influences angular momentum loss in
the stellar wind and X-ray emission measure. We use reconstructed maps of the
radial magnetic field at the stellar surface and the potential-field source
surface method to extrapolate a 3D coronal magnetic field for a sample of
early-to-mid M dwarfs. During the magnetic reconstruction process it is
possible to force a solution towards field geometries that are symmetric or
antisymmetric about the equator but we demonstrate that this has only a modest
impact on the coronal tracers mentioned above. We find that the dipole
component of the field, which governs the large-scale structure, becomes
increasingly strong as the stellar mass decreases, while the magnitude of the
open (wind-bearing) magnetic flux is proportional to the magnitude of the
reconstructed magnetic flux. By assuming a hydrostatic and isothermal corona we
calculate X-ray emission measures (in magnitude and rotational modulation) for
each star and, using observed stellar densities as a constraint, we reproduce
the observed X-ray saturation at Ro < 0.1. We find that X-ray rotational
modulation is not a good indicator of magnetic structure as it shows no trend
with Rossby number but can be useful in discriminating between different
assumptions on the field geometry.",1207.2165v1
2012-12-12,Ferrimagnetism and spin canting of ZnFe2O4 nanoparticles embedded in ZnO matrix,"The structural and magnetic properties of ZnFe2O4 nanoparticles embedded in a
non-magnetic ZnO matrix are presented. X-ray diffractograms and Transmission
Electron Microscopy (TEM) images showed that the resulting samples are composed
of crystalline ferrite nanoparticles with average crystallite size <D> =
23.4(0.9) nm, uniformly dispersed within the ZnO matrix. Magnetization data
indicated a superparamagnetic-like behavior from room temperature down to T_{M}
~ 20 K, where a transition to a frozen state is observed. The M(H) curves
displayed nearly zero coercive field down to TM, where a sharp increase in the
H_C value is observed. The measured saturation magnetization M_S values at 200
and 2 K were M_S = 0.028(3) and 0.134(7) muB/f.u. ZnFe2O4 respectively, showing
the existence of small amounts of non compensated atomic moments. M\""ossbauer
measurements at low temperatures confirmed the transition to a magnetically
ordered state for T < 25 K, where two magnetically split sextets develop.
Whereas these two sextets show strong overlap due to the similar hyperfine
fields, in-field M\""ossbauer spectra clearly showed two different Fe3+ sites,
demonstrating that the sample is ferrimagnetically ordered. The two spinel
sites are found to behave differently under an external field of 12 T: whereas
the moments located at A sites show a perfect alignment with the external
field, spins at B sites are canted by an angle alpha_B = 49(2){\deg}. We
discuss the significance of this particle structure for the observed magnetic
behavior.",1212.2798v1
2013-01-22,The Maximum Energy of Accelerated Particles in Relativistic Collisionless Shocks,"The afterglow emission from gamma-ray bursts (GRBs) is usually interpreted as
synchrotron radiation from electrons accelerated at the GRB external shock,
that propagates with relativistic velocities into the magnetized interstellar
medium. By means of multi-dimensional particle-in-cell simulations, we
investigate the acceleration performance of weakly magnetized relativistic
shocks, in the magnetization range 0<sigma<1e-1. The pre-shock magnetic field
is orthogonal to the flow, as generically expected for relativistic shocks. We
find that relativistic perpendicular shocks propagating in electron-positron
plasmas are efficient particle accelerators if the magnetization is sigma<1e-3.
For electron-ion plasmas, the transition to efficient acceleration occurs for
sigma<3e-5. Here, the acceleration process proceeds similarly for the two
species, since the electrons enter the shock nearly in equipartition with the
ions, as a result of strong pre-heating in the self-generated upstream
turbulence. In both electron-positron and electron-ion shocks, we find that the
maximum energy of the accelerated particles scales in time as t^(1/2). This
scaling is shallower than the so-called (and commonly assumed) Bohm limit, and
it naturally results from the small-scale nature of the Weibel turbulence
generated in the shock layer. In magnetized plasmas, the energy of the
accelerated particles increases until it reaches a saturation value that scales
with the magnetization as sigma^(-1/4). Further energization is prevented by
the fact that the self-generated turbulence is confined within a finite region
of thickness proportional to sigma^(-1/2) around the shock. Our results can
provide physically-grounded inputs for models of non-thermal emission from a
variety of astrophysical sources, with particular relevance to GRB afterglows.",1301.5333v1
2013-06-03,Exact solution for quantum spin-1/2 Ising-Heisenberg orthogonal-dimer chain with the Heisenberg intra-dimer and Ising inter-dimer interactions,"The quantum spin-1/2 orthogonal-dimer chain with the Heisenberg intra-dimer
and Ising inter-dimer interactions in a magnetic field is considered by a
rigorous approach. The model conserves the z-component of total spin on
vertical Heisenberg bonds and this property is used to calculate exactly the
partition function using the transfer-matrix method. We have found the
ground-state phase diagram of the given model in a magnetic field as well as
the macroscopic degeneracy along field-induced transitions accompanied with the
magnetization jumps. The model exhibits two intermediate fractional plateaux at
one-quarter and one-half of the saturation magnetization. We have examined the
effect of the exchange anisotropy in the XXZ Heisenberg intra-dimer interaction
on the ground state. It is shown that the one-quarter and one-half plateaux may
disappear from the magnetization curve for the ferromagnetic Heisenberg
intra-dimer interaction. We have also rigorously studied the effect of
frustrated interactions on the thermodynamic and magnetic properties of the
model and show how the macroscopic degeneracy of the ground state is reflected
in the low-temperature behavior of the magnetization, entropy and specific
heat. A possibility of observing enhanced magnetocaloric effect during the
adiabatic demagnetization is discussed in detail.",1306.0487v2
2013-12-20,Exciton spin dynamics of colloidal CdTe nanocrystals in magnetic field,"The recombination and spin dynamics of excitons in colloidal CdTe
nanocrystals (NCs) are studied by time-resolved photoluminescence in high
magnetic fields up to 15 T and at cryogenic temperatures. The recombination
decay shows a nonexponential temporal behavior, with the longest component
corresponding to the dark excitons having 260 ns decay time at zero magnetic
field and 4.2 K temperature. This long component shortens to 150 ns at 15 T due
to the magnetic-field-induced mixing of the bright and dark exciton states. The
spin dynamics, assessed through the evolution of the magnetic-field-induced
circular polarization degree of the photoluminescence, has a fast component
shorter than 1 ns related to the bright excitons and a slow component of 5-10
ns associated with the dark excitons. The latter shortens with increasing
magnetic field, which is characteristic for a phonon-assisted spin relaxation
mechanism. The relatively low saturation level of the associated
magnetic-field-induced circular polarization degree of -30 % is explained by a
model that suggests the CdTe NCs to constitute an ensemble of prolate and
oblate NCs, both having a structural quantization axis. The exciton g-factor of
2.4-2.9 evaluated from fitting the experimental data in the frame of the
suggested approach is in good agreement with the expected value for the dark
excitons in CdTe NCs.",1312.5929v1
2014-06-23,Anisotropic shear viscosity of a strongly coupled non-Abelian plasma from magnetic branes,"Recent estimates for the electromagnetic fields produced in the early stages
of non-central ultra-relativistic heavy ion collisions indicate the presence of
magnetic fields $B\sim \mathcal{O}(0.1-15\,m_\pi^2)$, where $m_\pi$ is the pion
mass. It is then of special interest to study the effects of strong (Abelian)
magnetic fields on the transport coefficients of strongly coupled non-Abelian
plasmas, such as the quark-gluon plasma formed in heavy ion collisions. In this
work we study the anisotropy in the shear viscosity induced by an external
magnetic field in a strongly coupled $\mathcal{N} = 4$ SYM plasma. Due to the
spatial anisotropy created by the magnetic field, the most general viscosity
tensor of a magnetized plasma has 5 shear viscosity coefficients and 2 bulk
viscosities. We use the holographic correspondence to evaluate two of the shear
viscosities, $\eta_{\perp} \equiv \eta_{xyxy}$ (perpendicular to the magnetic
field) and $\eta_{\parallel} \equiv \eta_{xzxz}=\eta_{yzyz}$ (parallel to the
field). When $B\neq 0$ the shear viscosity perpendicular to the field saturates
the viscosity bound $\eta_{\perp}/s = 1/(4\pi)$ while in the direction parallel
to the field the bound is violated since $\eta_{\parallel}/s < 1/(4\pi)$.
However, the violation of the bound in the case of strongly coupled SYM is
minimal even for the largest value of $B$ that can be reached in heavy ion
collisions.",1406.6019v2
2015-01-16,State of Co and Mn in half-metallic ferromagnet Co$_2$MnSi explored by magnetic circular dichroism in hard X-ray photoelectron emission and soft X-ray absorption spectroscopies,"The half-metallic Heusler compound Co$_2$MnSi is a very attractive material
for spintronic devices because it exhibits very high tunnelling
magnetoresistance ratios. This work reports on a spectroscopic investigation of
thin Co$_2$MnSi films as they are used as electrodes in magnetic tunnel
junctions. The investigated films exhibit a remanent in-plane magnetisation
with a magnetic moment of about 5~$\mu_B$ when saturated, as expected. The low
coercive field of only 4~mT indicates soft magnetic behaviour. Magnetic
dichroism in emission and absorption was measured at the Co and Mn $2p$ core
levels. The photoelectron spectra were excited by circularly polarised hard
X-rays with an energy of of 6~keV and taken from the remanently magnetised
film. The soft X-ray absorption spectra were taken in an induction field of
4~T. Both methods yielded large dichroism effects. An analysis reveals the
localised character of the electrons and magnetic moments attributed to the Mn
atoms, whereas the electrons related to the Co atoms contribute an itinerant
part to the total magnetic moment.",1501.03966v1
2015-06-29,Frustrated magnetic planes with intricate interaction pathways in the mineral langite Cu$_4$(OH)$_6$SO$_4\cdot 2$H$_2$O,"Magnetic and crystallographic properties of the mineral langite
Cu$_4$(OH)$_6$SO$_4\cdot 2$H$_2$O are reported. Its layered crystal structure
features a peculiar spatial arrangement of spin-$\frac12$ Cu$^{2+}$ ions that
arises from a combination of corner- and edge-sharing chains. Experimentally,
langite orders antiferromagnetically at $T_N\simeq 5.7$ K as revealed by
magnetization and specific heat measurements. Despite this very low energy
scale of the magnetic transition, langite features significantly stronger
couplings on the order of 50-70 K. Half of the Cu$^{2+}$ spins are weakly
coupled and saturate around 12T, where the magnetization reaches 0.5$\mu_B$/Cu.
These findings are rationalized by density-functional band-structure
calculations suggesting a complex interplay of frustrated exchange couplings in
the magnetic planes. A simplified model of coupled magnetic sublattices
explains the experimental features qualitatively. To start from reliable
structural data, the crystal structure of langite in the 100-280 K temperature
range has been determined by single-crystal x-ray diffraction, and the hydrogen
positions were refined computationally.",1506.08562v3
2015-07-23,Negative Magnetoresistance in Dirac Semimetal Cd3As2,"A large negative magnetoresistance is anticipated in topological semimetals
in the parallel magnetic and electric field configuration as a consequence of
the nontrivial topological properties. The negative magnetoresistance is
believed to demonstrate the chiral anomaly, a long-sought high-energy physics
effect, in solid-state systems. Recent experiments reveal that Cd3As2, a Dirac
topological semimetal, has the record-high mobility and exhibits positive
linear magnetoresistance in the orthogonal magnetic and electric field
configuration. However, the negative magnetoresistance in the parallel magnetic
and electric field configuration remains unveiled. Here, we report the
observation of the negative magnetoresistance in Cd3As2 microribbons in the
parallel magnetic and electric field configuration as large as 66% at 50 K and
even visible at room temperatures. The observed negative magnetoresistance is
sensitive to the angle between magnetic and electrical field, robust against
temperature, and dependent on the carrier density. We have found that carrier
densities of our Cd3As2 samples obey an Arrhenius's law, decreasing from
3.0x10^17 cm^-3 at 300 K to 2.2x10^16 cm^-3 below 50 K. The low carrier
densities result in the large values of the negative magnetoresistance. We
therefore attribute the observed negative magnetoresistance to the chiral
anomaly. Furthermore, in the perpendicular magnetic and electric field
configuration a positive non-saturating linear magnetoresistance up to 1670% at
14 T and 2 K is also observed. This work demonstrates potential applications of
topological semimetals in magnetic devices.",1507.06470v1
2015-08-10,Efficiency of Super-Eddington Magnetically-Arrested Accretion,"The radiative efficiency of super-Eddington accreting black holes (BHs) is
explored for magnetically-arrested disks (MADs), where magnetic flux builds-up
to saturation near the BH. Our three-dimensional general relativistic radiation
magnetohydrodynamic (GRRMHD) simulation of a spinning BH (spin $a/M=0.8$)
accreting at $\sim 50$ times Eddington shows a total efficiency $\sim 50\%$
when time-averaged and total efficiency $\gtrsim 100\%$ in moments. Magnetic
compression by the magnetic flux near the rotating BH leads to a thin disk,
whose radiation escapes via advection by a magnetized wind and via transport
through a low-density channel created by a Blandford-Znajek (BZ) jet. The BZ
efficiency is sub-optimal due to inertial loading of field lines by optically
thick radiation, leading to BZ efficiency $\sim 40\%$ on the horizon and BZ
efficiency $\sim 5\%$ by $r\sim 400r_g$ (gravitational radii) via absorption by
the wind. Importantly, radiation escapes at $r\sim 400r_g$ with efficiency
$\eta\approx 15\%$ (luminosity $L\sim 50L_{\rm Edd}$), similar to $\eta\approx
12\%$ for a Novikov-Thorne thin disk and beyond $\eta\lesssim 1\%$ seen in
prior GRRMHD simulations or slim disk theory. Our simulations show how BH spin,
magnetic field, and jet mass-loading affect the radiative and jet efficiencies
of super-Eddington accretion.",1508.02433v1
2015-09-11,Theoretical investigation of the behavior of CuSe2O5 compound in high magnetic fields,"Based on analytical and numerical approaches, we investigate thermodynamic
properties of CuSe2O5 at high magnetic fields which is a candidate for the
strong intra-chain interaction in quasi one-dimensional (1D) quantum magnets.
Magnetic behavior of the system can be described by the 1D spin-1/2 XXZ model
in the presence of the Dzyaloshinskii-Moriya (DM) interaction. Un- der these
circumstances, there is one quantum critical field in this compound. Below the
quantum critical field the spin chain system is in the gapless Luttinger liquid
(LL) regime, whereas above it one observes a crossover to the gapped saturation
magnetic phase. Indications on the thermodynamic curves confirm the occurrence
of such a phase transition. The main characteristics of the LL phase are
gapless and spin-spin correlation functions decay algebraic. The effects of
zero-temperature quantum phase transition are observed even at rather high
temperatures in comparison with the counterpart compounds. In addition, we
calculate the Wilson ratio in the model. The Wilson ratio at a fixed
temperature remains almost independent of the field in the LL region. In the
vicinity of the quantum critical field, the Wilson ratio increases and exhibits
anomalous enhancement.",1509.03414v1
2016-02-17,Modeling of screening currents in coated conductor magnets containing up to 40000 turns,"Screening currents caused by varying magnetic fields degrade the homogeneity
and stability of the magnetic fields created by $RE$BCO coated conductor coils.
They are responsible for the AC loss, which is also important for other power
applications containing windings. Since real magnets contain coils exceeding
10000 turns, accurate modeling tools for this number of turns are necessary for
magnet design. This article presents a fast numerical method to model coils
with no loss of accuracy. We model a 10400-turn coil for its real geometry and
coils of up to 40000 turns with the continuous approximation, which we checked
that introduces negligible errors. The screening currents, the Screening
Current Induced Field (SCIF) and the AC loss is analyzed in detail. The SCIF is
maximum at the remnant state with a considerably large value and decreases
substantially after one day of relaxation. The instantaneous AC loss for an
anisotropic magnetic-field dependent $J_c$ is qualitatively different than for
a constant $J_c$, although the loss per cycle is similar. Saturation of the
magnetization currents at the end pancakes causes that the maximum AC loss at
the first ramp increases with $J_c$. The presented modeling tool can accurately
calculate the SCIF and AC loss in practical computing times for coils with any
number of turns used in real windings, enabling parameter optimization.",1602.05433v2
2016-03-15,Instability of Non-uniform Toroidal Magnetic Fields in Accretion Disks,"A new type of instability that is expected to drive magnetohydrodynamic (MHD)
turbulence from a purely toroidal magnetic field in an accretion disk is
presented. It is already known that in a differentially rotating system, the
uniform toroidal magnetic field is unstable due to a magnetorotational
instability (MRI) under a non-axisymmetric and vertical perturbation, while it
is stable under a purely vertical perturbation. Contrary to the previous study,
this paper proposes an unstable mode completely confined to the equatorial
plane, driven by the expansive nature of the magnetic pressure gradient force
under a non-uniform toroidal field. The basic nature of this growing eigenmode,
to which we give a name ""magneto-gradient driven instability"", is studied using
linear analysis, and the corresponding nonlinear evolution is then investigated
using two-dimensional ideal MHD simulations. Although a single localized
magnetic field channel alone cannot provide sufficient Maxwell stress to
contribute significantly to the angular momentum transport, we find that the
mode coupling between neighboring toroidal fields under multiple localized
magnetic field channels drastically generates a highly turbulent state and
leads to the enhanced transport of angular momentum, comparable to the
efficiency seen in previous studies on MRIs. This horizontally confined mode
may play an important role in the saturation of an MRI through complementray
growth with the toroidal MHDs and coupling with magnetic reconnection.",1603.04638v1
2016-03-15,Kinetic simulations of the lowest-order unstable mode of relativistic magnetostatic equilibria,"We present the results of particle-in-cell numerical pair plasma simulations
of relativistic 2D magnetostatic equilibria known as the 'ABC' fields. In
particular, we focus on the lowest-order unstable configuration consisting of
two minima and two maxima of the magnetic vector potential. Breaking of the
initial symmetry leads to exponential growth of the electric energy and to the
formation of two current layers, which is consistent with the picture of
'X-point collapse' first described by Syrovatskii. Magnetic reconnection within
the layers heats a fraction of particles to very high energies. After the
saturation of the linear instability, the current layers are disrupted and the
system evolves chaotically, diffusing the particle energies in a stochastic
second-order Fermi process leading to the formation of power-law energy
distributions. The power-law slopes harden with the increasing mean
magnetization, but they are significantly softer than those produced in
simulations initiated from Harris-type layers. The maximum particle energy is
proportional to the mean magnetization, which is attributed partly to the
increase of the effective electric field and partly to the increase of the
acceleration time scale. We describe in detail the evolving structure of the
dynamical current layers, and report on the conservation of magnetic helicity.
These results can be applied to highly magnetized astrophysical environments,
where ideal plasma instabilities trigger rapid magnetic dissipation with
efficient particle acceleration and flares of high-energy radiation.",1603.04850v1
2016-08-18,Turbulent dynamo in a conducting fluid and partially ionized gas,"By following the Kazantsev theory and taking into account both microscopic
and turbulent diffusion of magnetic fields, we develop a unified treatment of
the kinematic and nonlinear stages of turbulent dynamo, and study the dynamo
process for a full range of magnetic Prandtl number Pm and ionization
fractions. We find a striking similarity between the dependence of dynamo
behavior on Pm in a conducting fluid and R (a function of ionization fraction)
in partially ionized gas. In a weakly ionized medium, the kinematic stage is
largely extended, including not only exponential growth but a new regime of
dynamo characterized by linear-in-time growth of magnetic field strength, and
the resulting magnetic energy is much higher than the kinetic energy carried by
viscous-scale eddies. Unlike the kinematic stage, the subsequent nonlinear
stage is unaffected by microscopic diffusion processes and has a universal
linear-in-time growth of magnetic energy with the growth rate as a constant
fraction $3/38$ of the turbulent energy transfer rate, showing good agreement
with earlier numerical results. Applying the analysis to the first stars and
galaxies, we find that the kinematic stage is able to generate a field strength
only an order of magnitude smaller than the final saturation value. But the
generation of large-scale magnetic fields can only be accounted for by the
relatively inefficient nonlinear stage and requires longer time than the
free-fall time. It suggests that magnetic fields may not have played a
dynamically important role during the formation of the first stars.",1608.05161v2
2016-09-06,Universal fluctuations in orbital diamagnetism: A surprise in theoretical physics,"Over the last century Bohr van Leuween theorem attracted the notice of
physicists. The theorem states about the absence of magnetization in classical
systems in thermal equilibrium. In this paper, we discuss about fluctuations of
magnetic moment in classical systems. In recent years this topic has been
investigated intensively and it is not free from controversy. We a have
considered a system consisting of a single particle moving in a plane. A
magnetic field is applied perpendicular to the plane. The system is in contact
with a thermal bath. We have considered three cases: (a) particle moving in a
homogeneous medium, (b) particle moving in a medium with space dependent
friction and (c) particle moving in a medium with space dependent temperature.
For all the three cases average magnetic moment and fluctuations in magnetic
moment has been calculated. Average magnetic moment saturates to a finite value
in case of free particle but goes to zero when the particle is confined by a
2-D harmonic potential. Fluctuations in magnetic moment shows universal
features in the presence of arbitrary friction inhomogeneity. For this case the
system reaches equilibrium asymptotically. In case of space dependent
temperature profile, the stationary distribution is non-Gibbsian and
fluctuations deviate from universal value for the bounded system only.",1609.01603v1
2017-04-11,Prediction of helium vapor quality in steady state Two-phase operation for SST-1 Toroidal field magnets,"Steady State Superconducting Tokamak (SST-1) at the Institute for Plasma
Research (IPR) is an operational device and is the first superconducting
Tokamak in India. Superconducting Magnets System (SCMS) in SST-1 comprises of
sixteen Toroidal field (TF) magnets and nine Poloidal Field (PF) magnets
manufactured using NbTi/Cu based cable-in-conduit-conductor (CICC) concept.
SST-1, superconducting TF magnets are operated in a Cryo-stable manner being
cooled with two-phase (TP) flow helium. The typical operating pressure of the
TP helium is 1.6 bar (a) at corresponding saturation temperature. The SCMS has
a typical cool-down time of about 14 days from 300 K down to 4.5 K using Helium
plant of equivalent cooling capacity of 1350 W at 4.5 K. Using the onset of
experimental data from the HRL, we estimated the vapor quality for the input
heat load on to the TF magnets system. In this paper, we report the
characteristics of two-phase flow for given thermo-hydraulic conditions during
long steady state operation of the SST-1 TF magnets. Finally, the
experimentally obtained results have been compared with the well-known
correlations of two-phase flow.",1704.08107v2
2017-04-27,Are chains of type I radio bursts generated by similar processes as drifting pulsation structures observed during solar flares?,"We present examples of the both types of bursts and show their similarities
and differences. Then for chains of type I bursts a similar model as for
drifting pulsation structures (DPSs) is proposed. We show that similarly as in
the DPS, the chains of type I bursts can be generated by the fragmented
magnetic reconnection associated with plasmoids interactions. To support this
new model of chains of type I bursts, we present an effect of merging of two
plasmoids to one larger plasmoid on the radio spectrum of DPS. This process can
also explain the ""wavy"" appearance of some chains of type I bursts. Then we
show that the chains of type I bursts with the ""wavy"" appearance can be used
for estimation of the magnetic field strength in their sources. We think that
differences of chains of type I bursts and DPSs are mainly owing to different
regimes of the magnetic field reconnection. While in the case of chains of type
I bursts the magnetic reconnection and plasmoid interactions are in the
quasi-separatrix layer of the active region in more or less quasi-saturated
regime, in the case of DPSs, observed in the impulsive phase of eruptive
flares, the magnetic reconnection and plasmoids interactions are in the current
sheet formed under the flare magnetic rope, which moves upwards and forces this
magnetic reconnection.",1704.08532v1
2017-06-16,"Magnetic order, hysteresis and phase coexistence in magnetoelectric LiCoPO$_4$","The magnetic phase diagram of magnetoelectric LiCoPO$_4$ is established using
neutron diffraction and magnetometry in fields up to 25.9T applied along the
crystallographic $b$-axis. For fields greater than 11.9T the magnetic unit cell
triples in size with propagation vector Q = (0, 1/3, 0). A magnetized elliptic
cycloid is formed with spins in the $(b,c)$-plane and the major axis oriented
along $b$. Such a structure allows for the magnetoelectric effect with an
electric polarization along $c$ induced by magnetic fields applied along $b$.
Intriguingly, additional ordering vectors Q $\approx$ (0, 1/4, 0) and Q
$\approx$ (0, 1/2, 0) appear for increasing fields in the hysteresis region
below the transition field. Traces of this behavior are also observed in the
magnetization. A simple model based on a mean-field approach is proposed to
explain these additional ordering vectors. In the field interval 20.5-21.0T,
the propagation vector Q = (0, 1/3, 0) remains but the spins orient differently
compared to the cycloid phase. Above 21.0T and up until saturation a
commensurate magnetic structure exists with a ferromagnetic component along $b$
and an antiferromagnetic component along $c$.",1706.05203v2
2017-10-27,"Near total magnetic moment compensation without reduction in T_C of Mn_2 V_0.5 Co_0.5 Z (Z=Ga,Al) Heusler compounds","Mn_2V_1-xCo_xZ (Z=Ga,Al and x=0, 0.25, 0.5, 0.75, 1) Heusler compounds have
been synthesized to investigate the effect of Co substitution at the V site on
the magnetic moment and Curie temperatures of half-metallic ferrimagnets
Mn_2VGa and Mn_2VAl. The Co substituted compounds show a non linear decrease in
lattice parameter without altering the crystal structure of the parent
compounds. The end members Mn_2VGa and Mn_2CoGa have the saturation
magnetization of 1.80 {\mu}_B/f.u and 2.05 {\mu}_B/f.u respectively whereas for
the Mn_2V_0.5Co_0.5Ga compound, a near total magnetic moment compensation (0.10
{\mu}_B/f.u) was observed due to the ferrimagnetic coupling of Mn with
parallelly aligned V and Co. The Co substituted Mn_2VAl has also shown the
similar trend with compensated magnetic moment value of 0.06 {\mu}_B/f.u for
x=0.5. The Curie temperatures of the compounds including the x=0.5 composition
are well above the room temperature (more than 700 K) which is in sharp
contrast to the earlier reported values of 171 K for the (MnCo)VGa and 105 K
for the (MnCo)VAl compounds (substitution at the Mn site). The magnetic moment
compensation without significant reduction in T_C indicates that the V site
substitution of Co does not weaken the magnetic interaction in Mn_2VZ (Z=Ga,
Al) compounds which is in contrary to the earlier experimental reports on Mn
site substitution.",1710.09971v1
2018-05-29,Spin-Hall magnetoresistance in a low-dimensional magnetic insulator,"We observe an unusual behavior of the spin Hall magnetoresistance (SMR)
measured in a Pt ultra-thin film deposited on a ferromagnetic insulator, which
is a tensile-strained LaCoO3 (LCO) thin film with the Curie temperature Tc=85K.
The SMR displays a strong magnetic-field dependence below Tc, with the SMR
amplitude continuing to increase (linearly) with increasing the field far
beyond the saturation value of the ferromagnet. The SMR amplitude decreases
gradually with raising the temperature across Tc and remains measurable even
above Tc. Moreover, no hysteresis is observed in the field dependence of the
SMR. These results indicate that a novel low-dimensional magnetic system forms
on the surface of LCO and that the Pt/LCO interface decouples magnetically from
the rest of the LCO thin film. To explain the experiment, we revisit the
derivation of the SMR corrections and relate the spin-mixing conductances to
the microscopic quantities describing the magnetism at the interface. Our
results can be used as a technique to probe quantum magnetism on the surface of
a magnetic insulator.",1805.11225v2
2019-03-12,High-magnetic field phase diagram and failure of magnetic Grüneisen scaling in LiFePO$_4$,"We report the magnetic phase diagram of single-crystalline LiFePO$_4$ in
magnetic fields up to 58~T and present a detailed study of magneto-elastic
coupling by means of high-resolution capacitance dilatometry. Large anomalies
at \tn\ in the thermal expansion coefficient $\alpha$ imply pronounced
magneto-elastic coupling. Quantitative analysis yields the magnetic Gr\""uneisen
parameter $\gamma_{\rm mag}=6.7(5)\cdot 10^{-7}$~mol/J. The positive
hydrostatic pressure dependence $dT_{\rm N}/dp = 1.46(11)$~K/GPa is dominated
by uniaxial effects along the $a$-axis. Failure of Gr\""uneisen scaling below
$\approx 40$~K, i.e., below the peak temperature in the magneto-electric
coupling coefficient [\onlinecite{toft2015anomalous}], implies several
competing degrees of freedom and indicates relevance of recently observed
hybrid excitations~[\onlinecite{yiu2017hybrid}]. A broad and strongly
magnetic-field-dependent anomaly in $\alpha$ in this temperature regime
highlight the relevance of structure changes. Upon application of magnetic
fields $B||b$-axis, a pronounced jump in the magnetisation implies
spin-reorientation at $B_{\rm SF} = 32$~T as well as a precursing phase at 29~T
and $T=1.5$~K. In a two-sublattice mean-field model, the saturation field
$B_{\rm sat,b} = 64(2)$~T enables the determination of the effective
antiferromagnetic exchange interaction $J_{\rm af} = 2.68(5)$~meV as well as
the anisotropies $D_{\rm b} = -0.53(4)$~meV and $D_{\rm c} = 0.44(8)$~meV.",1903.05169v1
2019-09-10,Magnetic phase diagram of a spin S=1/2 antiferromagnetic two-leg ladder in the presence of modulated along legs Dzyaloshinskii-Moriya interaction,"We study the ground-state magnetic phase diagram of a spin S=1/2
antiferromagnetic two-leg ladder in the presence of period two lattice units
modulated, Dzyaloshinskii-Moriya (DM) interaction along the legs. We consider
the case of collinear DM vectors and strong rung exchange and magnetic field.
In this limit we map the initial ladder model onto the effective spin
$\sigma=1/2$ XXZ chain and study the latter using the continuum-limit
bosonization approach. We identified four quantum phase transitions and
corresponding critical magnetic fields, which mark transitions from the spin
gapped regimes into the gapless quantum spin-liquid regimes. In the gapped
phases the magnetization curve of the system shows plateaus at magnetisation
M=0 and to its saturation value per rung M=1. We have shown that the very
presence of alternating DM interaction leads to opening of a gap in the
excitation spectrum at magnetization M=0.5. The width of the magnetization
plateau at M=0.5, is determined by the associated with the dynamical generation
of a gap in the spectrum is calculated and is shown that its length scales as
$(D_{0}D_{1}/J^{2})^{\alpha}$ where $D_{0},D_{1}$ are uniform and staggered
components of the DM term, $J$ is the intraleg exchange and $\alpha \leq 3/4$
and weakly depends on the DM couplings.",1909.04618v1
2019-12-11,Magnetic field effects on electron transport in nanoring with orbital Rashba coupling,"We study the effects of a Zeeman magnetic field on the electron transport of
one-dimensional quantum rings which are marked by electronic states with
$d-$orbital symmetry in the presence of spin-orbit and orbital Rashba
couplings. By considering phase-coherent propagation, we analyse the geometric
Aharonov-Anandan (AA) phase of the channels which is acquired in a closed path,
by demonstrating that the orbital polarization can influence the electronic
transport when amplitude and magnetic field directions are varied. We explore
all the possible cases for the injection of electrons at various energies in
the regime of low electron filling. The magnetic field can allow the selection
of only one channel where the transmission is uniquely affected by the AA
phase. Conversely, when more orbital channels are involved there is also a
dynamical contribution that lead to oscillations in the transmission as the
magnetic field is varied. In particular, the transmission is chiral when the
energy states are close to the absolute minimum of the energy bands. Instead,
when an interference between the channels occurs the orbital and spin
contributions tend to balance each other with the increasing of the magnetic
field amplitude resulting in a trivial AA phase. This saturation effect does
not occur in the high magnetic field regime when orbital and spin properties of
the channels exhibit sharp variations with direct consequences on the
transport.",1912.05602v1
2020-01-16,Random singlet state in Ba$_5$CuIr$_3$O$_{12}$ single crystals,"We study the thermodynamic and high-magnetic-field properties of the magnetic
insulator Ba$_5$CuIr$_3$O$_{12}$, which shows no magnetic order down to 2 K
consistent with a spin liquid ground state. While the temperature dependence of
the magnetic susceptibility and the specific heat shows only weak
antiferromagnetic correlations, we find that the magnetization does not
saturate up to a field of 59 Tesla, leading to an apparent contradiction. We
demonstrate that the paradox can be resolved, and all of the experimental data
can be consistently described within the framework of random singlet states. We
demonstrate a generic procedure to derive the exchange coupling distribution
$P(J)$ from the magnetization measurements and use it to show that the
experimental data is consistent with the power-law form $P(J)\sim J^{-\alpha}$
with $\alpha \approx 0.6 $. Thus, we reveal that high-magnetic-field
measurements can be essential to discern quantum spin liquid candidates from
disorder dominated states that do not exhibit long-range order.",2001.06013v1
2020-02-06,Temperature scaling of two-ion anisotropy in pure and mixed anisotropy systems,"Magnetic anisotropy plays an essential role in information technology
applications of magnetic materials, providing a means to retain the long-term
stability of a magnetic state in the presence of thermal fluctuations.
Anisotropy consists of a single-ion contribution stemming from the crystal
structure and two-ion terms attributed to the exchange interactions between
magnetic atoms. A lack of robust theory crucially limits the understanding of
the temperature dependence of the anisotropy in pure two-ion and mixed
single-ion and two-ion systems. Here, we use Green's function theory and
atomistic Monte Carlo simulations to determine the temperature scaling of the
effective anisotropy in ferromagnets in these pure and mixed cases, from
saturated to vanishing magnetization. At low temperature, we find that the pure
two-ion anisotropy scales with the reduced magnetization as $k(m) \sim
m^{2.28}$, while the mixed scenario describes the diversity of the temperature
dependence of the anisotropy observed in real materials. The temperature
dependence of the mixed anisotropy determined here is expected to considerably
contribute to the understanding and the control of the thermal properties of
magnetic materials.",2002.02548v2
2020-02-25,Strain-Tuned Magnetic Anisotropy in Sputtered Thulium Iron Garnet Ultrathin Films and TIG/Au/TIG Valve Structures,"Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in
ferrimagnetic insulators films by controlling the strain, while maintaining
high-quality surfaces, is desirable for spintronic and magnonic applications.
We investigate ways to tune the anisotropy of amorphous sputtered ultrathin
thulium iron garnet (TIG) films, and thus tailor their magnetic properties by
the thickness (7.5 to 60 nm), substrate choice (GGG and SGGG), and
crystallization process. We correlate morphological and structural properties
with the magnetic anisotropy of post-growth annealed films. 30 nm thick films
annealed at 600 {\deg}C show compressive strain favoring an in-plane magnetic
anisotropy (IPMA), whereas films annealed above 800 {\deg}C are under a tensile
strain leading to a perpendicular magnetic anisotropy (PMA). Air-annealed films
present a high degree of crystallinity and magnetization saturation close to
the bulk value. These results lead to successful fabrication of trilayers
TIG/Au/TIG, with coupling between the TIG layers depending on Au thickness.
These results will facilitate the use of TIG to create various in situ clean
hybrid structures for fundamental interface exchange studies, and towards the
development of complex devices. Moreover, the sputtering technique is
advantageous as it can be easily scaled up for industrial applications.",2002.10608v2
2020-02-28,Traps for pinning and scattering of antiferromagnetic skyrmions via magnetic properties engineering,"Micromagnetic simulations have been performed to investigate the
controllability of the skyrmion position in antiferromagnetic nanotracks with
their magnetic properties modified spatially. In this study we have modeled
magnetic defects as local variations on the material parameters, such as the
exchange stiffness, saturation magnetization, perpendicular magnetocrystalline
anisotropy and Dzyaloshinskii-Moriya constant. Thus, we have observed not only
pinning (potential well) but also scattering (potential barrier) of
antiferromagnetic skyrmions, when adjusting either a local increase or a local
reduction for each material parameter. In order to control of the skyrmion
motion it is very important to impose certain positions along the nanotrack
where the skyrmion can stop. Magnetic defects incorporated intentionally in
antiferromagnetic racetracks can be useful for such purpose. In order to
provide guidelines for experimental studies, we vary both material parameters
and size of the modified region. The found results show that the efficiency of
skyrmion trap depends on a suitable combination of magnetic defect parameters.
Furthermore, we discuss the reason why skyrmions are either attracted or
repelled by a region magnetically modified.",2003.00907v2
2020-04-28,Crystal Growth and characterization of possible New Magnetic Topological Insulators FeBi2Te4,"Here we report successful single crystal growth of new possible magnetic
topological insulator (MTI) FeBi2Te4 by self-flux method via vacuum
encapsulation process. The detailed Rietveld analysis of Powder XRD data shows
the as grown MTI crystal to be mainly dominated by FeBi2Te4 phase along with
minority phases of Bi2Te3 and FeTe. Scanning electron microscope (SEM) image
shows the morphology of as grown MTI single crystal to be of layered type
laminar structure. Raman spectroscopy of the crystal exhibited three distinct
phonon modes at 65, 110, and 132 cm-1 along with two split secondary modes at
90, and 144cm-1. The secondary split modes are result of FeTe intercalation in
Bi2Te3 unit cell. Magneto-resistance measurement has been performed at
different temperatures i.e. 200K, 20K and 2K in applied magnetic fields up to
12 Tesla, which showed very low MR in comparison to pure Bi2Te3 crystal.
Temperature dependence of DC magnetization measurements show the FeBi2Te4
crystal to be mainly of ferromagnetic (FM) or ferri-magnetic nature above 295
K, albeit a secondary weak magnetic transition is seen at 54-46K as well.
Detailed isothermal magnetization (MH) results showed that FM saturation moment
at 295K is 0.00213emu/g, which is nearly invariant till 400 K. Summary, we had
grown an MTI FeBi2Te4 single crystal, which may be a possible entrant for
Quantum Anomalous Hall (QAH) effect at room temperature or above.",2004.13584v1
2020-06-21,"Crystal Structure, Magnetism, and Electronic Properties of New Rare-Earth-Free Ferromagnetic MnPt5As","The design and synthesis of targeted functional materials have been a
long-term goal for material scientists. Although a universal design strategy is
difficult to generate for all types of materials, however, it is still helpful
for a typical family of materials to have such design rules. Herein, we
incorporated several significant chemical and physical factors regarding
magnetism, such as structure type, atom distance, spin-orbit coupling, and
successfully synthesized a new rare-earth-free ferromagnet, MnPt5As, for the
first time. MnPt5As can be prepared by using high-temperature pellet methods.
According to X-ray diffraction results, MnPt5As crystallizes in a tetragonal
unit cell with the space group P4/mmm (Pearson symbol tP7). Magnetic
measurements on MnPt5As confirm ferromagnetism in this phase with a Curie
temperature of ~301 K and a saturated moment of 3.5 uB per formula. Evaluation
by applying the Stoner Criterion also indicates that MnPt5As is susceptible to
ferromagnetism. Electronic structure calculations using the WIEN2k program with
local spin density approximation imply that the spontaneous magnetization of
this phase arises primarily from the hybridization of d orbitals on both Mn and
Pt atoms. The theoretical assessments are consistent with the experimental
results. Moreover, the spin-orbit coupling effects heavily influence on
magnetic moments in MnPt5As. MnPt5As is the first high-performance magnetic
material in this structure type. The discovery of MnPt5As offers a platform to
study the interplay between magnetism and structure.",2006.11897v1
2020-07-22,Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method,"Modeling blocking temperature in molecular magnets has been a long standing
problem in the field of molecular magnetism. We investigate this problem using
a kinetic Monte Carlo (kMC) approach on an assembly of 100,000 short molecular
magnetic chains (SMMCs), each of six identical spins with nearest neighbour
anisotropic ferromagnetic exchange interactions. Each spin is also anisotropic
with an uniaxial anisotropy. The site spin on these SMMCs take values $1$,
$3/2$ or $2$. Using eigenstates of these SMMCs as the states of Markov chain,
we carry out a kMC simulation starting with an initial state in which all SMMCs
are completely spin polarized and assembled on a one-dimensional lattice so as
to experience ferromagnetic spin-dipolar interaction with each other. From
these simulations we obtain the relaxation time $\tau_r$ as a function of
temperature and the associated blocking temperature. We study this for
different exchange anisotropy, on-site anisotropy and strength of dipolar
interactions. The magnetization relaxation times show non-Arrhenius behaviour
for weak on-site interactions. The energy barrier to magnetization relaxation
increases with increase in on-site anisotropy, exchange anisotropy and strength
of spin dipolar interactions; more strongly on the last parameter. In all cases
the barrier saturates at large on-site anisotropy. The barrier also increases
with site spin. The large barrier observed in rare-earth single ion magnets can
be attributed to large dipolar interactions due to short intermolecular
distances, owing to their small size and large spin of the rare earth ion in
the molecule.",2007.11342v4
2020-09-29,Magnetic proximity effect on excitonic spin states in Mn-doped layered hybrid perovskites,"Materials combining the optoelectronic functionalities of semiconductors with
control of the spin degree of freedom are highly sought after for the
advancement of quantum technology devices. Here, we report the paramagnetic
Ruddlesden-Popper hybrid perovskite Mn:(PEA)2PbI4 (PEA = phenethylammonium) in
which the interaction of isolated Mn2+ ions with magnetically brightened
excitons leads to circularly polarized photoluminescence. Using a combination
of superconducting quantum interference device (SQUID) magnetometry and
magneto-optical experiments, we find that the Brillouin-shaped polarization
curve of the photoluminescence follows the magnetization of the material. This
indicates coupling between localized manganese magnetic moments and exciton
spins via a magnetic proximity effect. The saturation polarization of 15% at 4
K and 6 T indicates a highly imbalanced spin population and demonstrates that
manganese doping enables efficient control of excitonic spin states in
Ruddlesden-Popper perovskites. Our finding constitutes the first example of
polarization control in magnetically doped hybrid perovskites and will
stimulate research on this highly tuneable material platform that promises
tailored interactions between magnetic moments and electronic states.",2009.13867v1
2021-01-28,Modified strong-coupling treatment of a spin-1/2 Heisenberg trimerized chain developed from the exactly solved Ising-Heisenberg diamond chain,"Quantum spin-1/2 antiferromagnetic Heisenberg trimerized chain with strong
intradimer and weak monomer-dimer coupling constants is studied using the novel
many-body perturbation expansion, which is developed from the exactly solved
spin-1/2 Ising-Heisenberg diamond chain preserving correlations between all
interacting spins of the trimerized chain unlike the standard perturbation
scheme developed on the grounds of noninteracting spin monomers and dimers. The
Heisenberg trimerized chain shows the intermediate one-third plateau, which was
also observed in the magnetization curve of the polymeric compound
Cu$_3$(P$_2$O$_6$OH)$_2$ affording its experimental realization. Within the
modified strong-coupling method we have obtained the effective Hamiltonians for
the magnetic-field range from zero to one-third plateau, and from one-third
plateau to the saturation magnetization. The second-order perturbation theory
shows reliable results even for the moderate ratio between weaker dimer-monomer
and stronger intradimer coupling constants. We have also examined thermodynamic
properties and recovered the low-temperature peak in the specific heat. The
accuracy of the developed method is tested through a comparison with numerical
density-matrix renormalization group and quantum Monte Carlo simulations. Using
the results for the effective Hamiltonian we suggest straightforward procedure
for finding the microscopic parameters of one-dimensional trimerized magnetic
compounds with strong intradimer and weak monomer-dimer couplings. We found the
refined values for the coupling constants of Cu$_3$(P$_2$O$_6$OH)$_2$ by
matching the theoretical results with the available experimental data for the
magnetization and magnetic susceptibility in a wide range of temperatures and
magnetic fields.",2101.11926v3
2021-02-19,Effects of Topological Defect on the Energy Spectra and Thermo-magnetic Properties of CO Diatomic Molecule,"Confinement effects of Aharonov-Bohm (AB) flux and magnetic fields with
topological defect on CO diatomic molecule modeled by screened modified Kratzer
potential is investigated in this paper. The all-encompassing effects of the
fields and topological defect result in a strongly repulsive system. We
discover that the collective effect of the fields and defect is intense than
the lone and dual effect and consequently there is a substantial shift in the
bound state energy of the system. We also find that to sustain a low-energy
medium for the molecule modeled by SMKP, the topological defect and weak AB
field are required, whereas the Magnetic field can be used as a control
parameter or enhancer. The effects of the topological defect and magnetic and
AB fields on the thermal and magnetic properties of the system are duly
analyzed. We observe that the system tends to exhibit both a paramagnetic and
diamagnetic behavior for weak and intense magnetic field respectively and some
sort of saturation at large magnetic field. To further validate our findings,
we map our result to 3D and a comparison of our results with what obtains in
literature reveals an excellent agreement.",2102.09842v1
2021-06-07,Crust-core transition of a neutron star: effect of the temperature under strong magnetic fields,"The effect of temperature on the crust-core transition of a magnetar is
studied. The thermodynamical spinodals are used to calculate the transition
region within a relativistic mean-field approach for the equation of state.
Magnetic fields with intensities $5\times 10^{16}$ G and $5\times 10 ^{17}$ G
are considered. It is shown that the effect on the extension of the crust-core
transition is washed away for temperatures above $10^{9}$ K for magnetic field
intensities $ \lesssim 5\times 10^{16}$ G but may still persist if a magnetic
field as high as $5\times 10 ^{17}$G is considered. For temperatures below that
value, the effect of the magnetic field on crust-core transition is noticeable
and grows as the temperature decreases and, in particular, it is interesting to
identify the existence of disconnected non-homogeneous matter above the $B=0$
crust core transition density. Models with different symmetry energy slopes at
saturation show quite different behaviors. In particular, a model with a large
slope, as suggested by the recent results of PREX-2, predicts the existence of
up to four disconnected regions of non-homogeneous matter above the zero
magnetic field crust-core transition density.",2106.03590v2
2021-08-26,Helical turbulent nonlinear dynamo at large magnetic Reynolds numbers,"The excitation and further sustenance of large-scale magnetic fields in
rotating astrophysical systems, including planets, stars and galaxies, is
generally thought to involve a fluid magnetic dynamo effect driven by helical
magnetohydrodynamic turbulence. While this scenario is appealing on general
grounds, it however currently remains largely unconstrained, notably because a
fundamental understanding of the nonlinear asymptotic behaviour of large-scale
fluid magnetism in the astrophysically-relevant but treacherous regime of large
magnetic Reynolds number $Rm$ is still lacking. We explore this problem using
local high-resolution simulations of turbulent magnetohydrodynamics driven by
an inhomogeneous helical forcing generating a sinusoidal profile of kinetic
helicity, mimicking the hemispheric distribution of kinetic helicity in
rotating turbulent fluid bodies. We identify a transition at large $Rm$ to a
nonlinear state, followed up to $Rm\simeq 3\times 10^3$, consisting of strong,
saturated small-scale magnetohydrodynamic turbulence and a weaker, travelling
coherent large-scale field oscillation. This state is characterized by an
asymptotically small resistive dissipation of magnetic helicity, by its spatial
redistribution across the equator through turbulent fluxes driven by the
hemispheric distribution of kinetic helicity, and by the tentative presence in
the tangled dynamical magnetic field of plasmoids typical of reconnection at
large $Rm$.",2108.12037v2
2021-09-10,Electrical spectroscopy of the spin-wave dispersion and bistability in gallium-doped yttrium iron garnet,"Yttrium iron garnet (YIG) is a magnetic insulator with record-low damping,
allowing spin-wave transport over macroscopic distances. Doping YIG with
gallium ions greatly reduces the demagnetizing field and introduces a
perpendicular magnetic anisotropy, which leads to an isotropic spin-wave
dispersion that facilitates spin-wave optics and spin-wave steering. Here, we
characterize the dispersion of a gallium-doped YIG (Ga:YIG) thin film using
electrical spectroscopy. We determine the magnetic anisotropy parameters from
the ferromagnetic resonance frequency and use propagating spin wave
spectroscopy in the Damon-Eshbach configuration to detect the small spin-wave
magnetic fields of this ultrathin weak magnet over a wide range of wavevectors,
enabling the extraction of the exchange constant $\alpha=1.3(2)\times10^{-12}$
J/m. The frequencies of the spin waves shift with increasing drive power, which
eventually leads to the foldover of the spin-wave modes. Our results shed light
on isotropic spin-wave transport in Ga:YIG and highlight the potential of
electrical spectroscopy to map out the dispersion and bistability of
propagating spin waves in magnets with a low saturation magnetization.",2109.05045v1
2022-02-19,Control and tunability of magnetic bubble states in multilayers with strong perpendicular magnetic anisotropy at ambient conditions,"The reversal of magnetic bubble helicity through topologically trivial
transient states provides an additional degree of freedom that promises the
development of multidimensional magnetic memories. A key requirement for this
concept is the stabilization of bubble states at ambient conditions on
application-compatible substrates. In the present work we demonstrate a
stabilization routine for remanent bubble states in high perpendicular magnetic
anisotropy [(Co(0.44\,nm)/Pt(0.7\,nm)]$_X$, X = 48, 100, 150 multilayers on
Si/SiO$_2$ substrates by exploring the effect of external magnetic fields
($H_\mathrm{m}$) of different strength and angles ($\theta$) with respect to
the film surface normal. By systematic variation of these two parameters, we
demonstrate that remanent bubble density and mean bubble diameter can be
carefully tuned and optimized for each sample. Our protocol based on
magnetometry only reveals the densest remanent bubble states at $H_\mathrm{m} =
0.87 H_\mathrm{s}$ ($H_\mathrm{s}$ is the magnetic saturation field) and
$\theta=60^\circ - 75^\circ$ for all $X$ with a maximum of 3736 domains/100
$\mu$m$^2$ for the X = 48 sample. The experimental observations are supported
by micromagnetic simulations taking into account the nanoscale lateral grain
structure of multilayers synthesized by magnetron sputter deposition, and thus
helping understand the different density of the bubble states found in these
systems.",2202.09564v1
2022-06-15,Deformed spin-$\frac12$ square lattice in antiferromagnetic NaZnVOPO$_4$(HPO$_4$),"We report the structural and magnetic properties of a new spin-$\frac12$
antiferromagnet NaZnVOPO$_4$(HPO$_4$) studied via x-ray diffraction, magnetic
susceptibility, high-field magnetization, specific heat, and $^{31}$P nuclear
magnetic resonance (NMR) measurements, as well as density-functional
band-structure calculations. While thermodynamic properties of this compound
are well described by the $J_1-J_2$ square-lattice model, \textit{ab initio}
calculations suggest a significant deformation of the spin lattice. From fits
to the magnetic susceptibility we determine the averaged nearest-neighbor and
second-neighbor exchange couplings of $\bar J_1\simeq -1.3$ K and $\bar
J_2\simeq 5.6$ K, respectively. Experimental saturation field of 15.3\,T is
consistent with these estimates if 20\% spatial anisotropy in $J_1$ is taken
into account. Specific heat data signal the onset of a magnetic long-range
order at $T_{\rm N} \simeq 2.1$ K, which is further supported by a sharp peak
in the NMR spin-lattice relaxation rate. The NMR spectra mark the superposition
of two P lines due to two noneqivalent P sites where the broad line with the
strong hyperfine coupling and short $T_1$ is identified as the P(1) site
located within the magnetic planes, while the narrow line with the weak
hyperfine coupling and long $T_1$ is designated as the P(2) site located
between the planes.",2206.07299v1
2022-06-29,Inertial active Ornstein-Uhlenbeck particle in the presence of magnetic field,"We consider an inertial active Ornstein-Uhlenbeck particle in an athermal
bath. The particle is charged, constrained to move in a two-dimensional
harmonic trap, and a magnetic field is applied perpendicular to the plane of
motion. The steady state correlations and the mean square displacement are
studied when the particle is confined as well as when it is set free from the
trap. With the help of both numerical simulation and analytical calculations,
we observe that inertia plays a crucial role in the dynamics in the presence of
a magnetic field. In a highly viscous medium where the inertial effects are
negligible, the magnetic field has no influence on the correlated behaviour of
position as well as velocity. In the time asymptotic limit, the overall
displacement of the confined harmonic particle gets enhanced by the presence of
magnetic field and saturates for a stronger magnetic field. On the other hand,
when the particle is set free, the overall displacement gets suppressed and
approaches zero when strength of the field is very high. Interestingly, it is
seen that in the time asymptotic limit, the confined harmonic particle behaves
like a passive particle and becomes independent of the activity, especially in
the presence of a very strong magnetic field. Similarly, for a free particle
the mean square displacement in the long time limit becomes independent of
activity even for a longer persistence of noise correlation in the dynamics.",2206.14715v1
2022-10-12,Current-induced switching of thin film $α$-Fe$_2$O$_3$ devices imaged using a scanning single-spin microscope,"Electrical switching of N\'eel order in an antiferromagnetic insulator is
desirable as a basis for memory applications. Unlike electrically-driven
switching of ferromagnetic order via spin-orbit torques, electrical switching
of antiferromagnetic order remains poorly understood. Here we investigate the
low-field magnetic properties of 30 nm thick, c-axis oriented
$\alpha$-Fe$_2$O$_3$ Hall devices using a diamond nitrogen-vacancy (NV) center
scanning microscope. Using the canted moment of $\alpha$-Fe$_2$O$_3$ as a
magnetic handle on its N\'eel vector, we apply a saturating in-plane magnetic
field to create a known initial state before letting the state relax in low
field for magnetic imaging. We repeat this procedure for different in-plane
orientations of the initialization field. We find that the magnetic field
images are characterized by stronger magnetic textures for fields along
$[\bar{1}\bar{1}20]$ and $[11\bar{2}0]$, suggesting that despite the expected
3-fold magneto-crystalline anisotropy, our $\alpha$-Fe$_2$O$_3$ thin films have
an overall in-plane uniaxial anisotropy. We also study current-induced
switching of the magnetic order in $\alpha$-Fe$_2$O$_3$. We find that the
fraction of the device that switches depends on the current pulse duration,
amplitude and direction relative to the initialization field. Specifically, we
find that switching is most efficient when current is applied along the
direction of the initialization field.",2210.06233v1
2022-10-14,Flux eruption events drive angular momentum transport in magnetically arrested accretion flows,"We evolve two high-resolution general relativistic magnetohydrodynamic
(GRMHD) simulations of advection-dominated accretion flows around non-spinning
black holes (BHs), each over a duration $\sim 3\times 10^5\,GM_{\rm BH}/c^3$.
One model captures the evolution of a weakly magnetized (SANE) disk and the
other a magnetically arrested disk (MAD). Magnetic flux eruptions in the MAD
model push out gas from the disk and launch strong winds with outflow
efficiencies at times reaching $10\%$ of the incoming accretion power. Despite
the substantial power in these winds, average mass outflow rates remain small
out to a radius $\sim100\,GM_{\rm BH}/c^2$, only reaching $\sim 60-80\%$ of the
horizon accretion rate. The average outward angular momentum transport is
primarily radial in both modes of accretion, but with a clear distinction:
magnetic flux eruption-driven disk winds cause a strong vertical flow of
angular momentum in the MAD model, while for the SANE model, the
magnetorotational instability (MRI) moves angular momentum mostly equatorially
through the disk. Further, we find that the MAD state is highly transitory and
non-axisymmetric, with the accretion mode often changing to a SANE-like state
following an eruption before reattaining magnetic flux saturation with time.
The Reynolds stress changes direction during such transitions, with the MAD
(SANE) state showing an inward (outward) stress, possibly pointing to
intermittent MRI-driven accretion in MADs. Pinning down the nature of flux
eruptions using next-generation telescopes will be crucial in understanding the
flow of mass, magnetic flux and angular momentum in sub-Eddington accreting BHs
like M87$^*$ and Sagittarius A$^*$.",2210.08045v1
2022-11-07,Galactic Dynamos,"Spiral galaxies, including the Milky Way, have large-scale magnetic fields
with significant energy densities. The dominant theory attributes these
magnetic fields to a large-scale dynamo. We review the current status of dynamo
theory and discuss various numerical simulations designed to explain either
particular aspects of the problem or to reproduce galactic magnetic fields
globally. Our main conclusions can be summarized as follows. Idealized direct
numerical simulations produce mean magnetic fields, whose saturation energy
density tends to decline with increasing magnetic Reynolds number. This is
still an unsolved problem. Large-scale galactic magnetic fields of microgauss
strengths can probably only be explained if helical magnetic fields of small or
moderate length scales can rapidly be ejected or destroyed. Small-scale dynamos
are important throughout a galaxy's life, and probably provide strong seed
fields at early stages. The circumgalactic medium (CGM) may play an important
role in driving dynamo action at small and large length scales. These
interactions between the galactic disk and the CGM may provide important
insights into our understanding of galactic dynamos. We expect future research
in galactic dynamos to focus on the cosmological history of galaxies and the
interaction with the CGM as means of replacing the idealized boundary
conditions used in earlier work.",2211.03476v2
2023-02-06,Large ordered moment with strong easy-plane anisotropy and vortex-domain pattern in the kagome ferromagnet Fe$_3$Sn,"We report the structural and magnetic properties of high-quality bulk single
crystals of the kagome ferromagnet Fe$_3$Sn. The dependence of magnetisation on
the magnitude and orientation of the external field reveals strong easy-plane
type uniaxial magnetic anisotropy, which shows a monotonous increase from
$K_1=-0.99\times 10^6 J/m^3$ at 300\,K to $-1.23\times10^6 J/m^3$ at 2\,K. Our
\textit{ab initio} electronic structure calculations yield the value of total
magnetic moment of about 6.9 $\mu_B$/f.u. and a magnetocrystalline anisotropy
energy density of 0.406\,meV/f.u. ($1.16\times10^6 J/m^3$) both being in good
agreement with the experimental values. The self-consistent DFT computations
for the components of the spin/orbital moments indicate that the small
difference between the saturation magnetisations measured along and
perpendicular to the kagome layers results from the subtle balance between the
Fe and Sn spin/orbital moments on the different sites. In zero field, magnetic
force microscopy reveals micrometer-scale magnetic vortices with weakly pinned
cores that vanish at $\sim$3\,T applied perpendicular to the kagome plane. Our
micromagnetic simulations, using the experimentally determined value of
anisotropy, well reproduce the observed vortex-domain structure. The present
study, in comparison with the easy-axis ferromagnet Fe$_3$Sn$_2$, shows that
varying the stacking of kagome layers provides an efficient control over
magnetic anisotropy in this family of Fe-based kagome magnets.",2302.13810v1
2023-03-07,Effects of Magnetic Fields on Gas Dynamics and Star Formation in Nuclear Rings,"Nuclear rings at the centers of barred galaxies are known to be strongly
magnetized. To explore the effects of magnetic fields on star formation in
these rings and nuclear gas flows, we run magnetohydrodynamic simulations in
which there is a temporally-constant magnetized inflow to the ring,
representing a bar-driven inflow. The mass inflow rate is
$1\,M_\odot\,\mathrm{yr}^{-1}$, and we explore models with a range of field
strength in the inflow. We adopt the TIGRESS framework developed by Kim &
Ostriker to handle radiative heating and cooling, star formation, and resulting
supernova (SN) feedback. We find that magnetic fields are efficiently amplified
in the ring due to rotational shear and SN feedback. Within a few
$100\,\mathrm{Myr}$, the turbulent component $B_\mathrm{trb}$ in the ring
saturates at $\sim 35\,\mu\mathrm{G}$ (in rough equipartition with the
turbulent kinetic energy density), while the regular component $B_\mathrm{reg}$
exceeds $50\,\mu\mathrm{G}$. Expanding superbubbles created by clustered SN
explosions vertically drag predominantly-toroidal fields from near the midplane
to produce poloidal fields in high-altitude regions. The growth of magnetic
fields greatly suppresses star formation at late times. Simultaneously, strong
magnetic tension in the ring drives radially inward accretion flows from the
ring to form a circumnuclear disk in the central region; this feature is absent
in the unmagnetized model.",2303.04206v1
2023-08-10,Budget equations and astrophysical nonlinear mean-field dynamos,"Solar, stellar and galactic large-scale magnetic fields are originated due to
a combined action of non-uniform (differential) rotation and helical motions of
plasma via mean-field dynamos. Usually, nonlinear mean-field dynamo theories
take into account algebraic and dynamic quenching of alpha effect and algebraic
quenching of turbulent magnetic diffusivity. However, the theories of the
algebraic quenching do not take into account the effect of modification of the
source of turbulence by the growing large-scale magnetic field. This phenomenon
is due to the dissipation of the strong large-scale magnetic field resulting in
an increase of the total turbulent energy. This effect has been studied using
the budget equation for the total turbulent energy (which takes into account
the feedback of the generated large-scale magnetic field on the background
turbulence) for (i) a forced turbulence, (ii) a shear-produced turbulence and
(iii) a convective turbulence. As the result of this effect, a nonlinear dynamo
number decreases with increase of the large-scale magnetic field, so that that
the mean-field $\alpha\Omega$, $\alpha^2$ and $\alpha^2\Omega$ dynamo
instabilities are always saturated by the strong large-scale magnetic field.",2308.05590v3
2023-09-11,Dynamics of photospheric magnetic flux distribution and variations in solar RVs -- a study using HARPS-N solar and SDO observations,"The distribution and evolution of photospheric magnetic field in sunspots,
plages and network, and variations in their relative flux content, play key
roles in radial velocity (RV) fluctuations observed in Sun-as-a-star spectra.
Differentiating and disentangling such magnetic contributions to RVs help in
building models to account for stellar activity signals in high precision RV
exoplanet searches. In this work, as earlier authors, we employ high-resolution
images of the solar magnetic field and continuum intensities from SDO/HMI to
understand the activity contributions to RVs from HARPS-N solar observations.
Using well observed physical relationships between strengths and fluxes of
photospheric magnetic fields, we show that the strong fields (spots, plages and
network) and the weak internetwork fields leave distinguishing features in
their contributions to the RV variability. We also find that the fill-factors
and average unsigned magnetic fluxes of different features correlate
differently with the RVs and hence warrant care in employing either of them as
a proxy for RV variations. In addition, we examine disk averaged UV intensities
at 1600 \r{A} and 1700 \r{A} wavelength bands imaged by SDO/AIA and their
performances as proxies for variations in different magnetic features. We find
that the UV intensities provide a better measure of contributions of plage
fields to RVs than the Ca II H-K emission indices, especially during high
activity levels when the latter tend to saturate.",2309.05428v1
2023-10-03,Complex magnetic interactions and critical behavior analysis in quaternary CoFeV$_{0.8}$Mn$_{0.2}$Si Heusler alloy,"We investigate the magnetic behavior and critical exponents of quaternary
CoFeV$_{0.8}$Mn$_{0.2}$Si Heusler alloy to understand the interactions across
the Curie temperature ($T_{\rm C}$). The Rietveld refinement of the x-ray
diffraction pattern with the space group F$\bar{4}$3m confirms a single-phase
cubic Y-type crystal structure. The magnetic susceptibility $\chi (T)$ data
show a ferromagnetic nature with a second-order phase transition from
paramagnetic to ferromagnetic at $446\pm1$~K. The saturation magnetization at
5~K is determined to be 2.2~$\mu_B$/f.u., which found to be close to the
Slater--Pauling rule and indicates its half-metallic nature. The values of
asymptotic critical exponents ($\beta$, $\gamma$, and $\delta$) and the $T_{\rm
C}$ are extracted through detailed analytical analysis including the Modified
Arrott plot, the Kouvel-Fisher (K--F) method, and the Widom scaling relation.
Interestingly, the estimated values of $\beta$ = 0.369 and $\gamma$ = 1.445
closely approximate the theoretical values of the 3D Heisenberg model and
second-order thermodynamic phase transition across the $T_{\rm C}$. The
obtained exponents lead to the collapse of renormalized isotherms, represented
by the relationship between the magnetization (m) and the applied magnetic
field (h), into two distinct branches above and below the $T_{\rm C}$, which
validates the reliability of the analysis. Furthermore, these exponents suggest
that the spin interaction follows a decay pattern of $J(r) \sim r^{-4.99}$,
indicating a short-range magnetic ordering, akin to the itinerant-electron 3D
Heisenberg model.",2310.01790v1
2024-01-08,Computational approaches to modeling dynamos in galaxies,"Galaxies are observed to host magnetic fields with a typical total strength
of around 15microgauss. A coherent large-scale field constitutes up to a few
microgauss of the total, while the rest is built from strong magnetic
fluctuations over a wide range of spatial scales. This represents sufficient
magnetic energy for it to be dynamically significant. Several questions
immediately arise: What is the physical mechanism that gives rise to such
magnetic fields? How do these magnetic fields affect the formation and
evolution of galaxies? In which physical processes do magnetic fields play a
role, and how can that role be characterized? Numerical modelling of magnetized
flows in galaxies is playing an ever-increasing role in finding those answers.
We review major techniques used for these models. Current results strongly
support the conclusion that field growth occurs during the formation of the
first galaxies on timescales shorter than their accretion timescales due to
small-scale turbulent dynamos. The saturated small-scale dynamo maintains field
strengths at a few percent of equipartition with turbulence. The subsequent
action of large-scale dynamos in differentially rotating discs produces
observed modern field strengths in equipartition with the turbulence and having
power at large scales. The field structure resulting appears consistent with
observations including Faraday rotation and polarisation from synchrotron and
dust thermal emission. Major remaining challenges include scaling numerical
models toward realistic scale separations and Prandtl and Reynolds numbers.",2401.04015v1
2024-04-02,Isotropic to nematic transition in alcohol ferrofluids of barium hexaferrite nanoplatelets,"Alcohol ferrofluids made of ferrimagnetic barium hexaferrite (BHF)
nanoplatelets (NPLs) form a unique example of a dipolar fluid - a liquid
magnet. Its formation is induced at a high enough concentration of the NPLs.
The key interactions between the NPLs are long-ranged dipolar magnetic and
screened anisotropic electrostatic. Herein, we report the results on tuning the
isotropic-nematic phase transition (i.e., the NPLs threshold concentration) in
1-butanol ferrofluids of BHF NPLs by affecting the interactions in the
ferrofluids. The threshold concentration was determined by polarizing optical
microscopy (POM) combined with a system for magnetic field manipulation and was
in the range between 4.6 and 6.6 \% (v/v) depending on the ferrofluid. We
observed that the threshold concentration decreased for 0.6 \% (v/v) with a
larger mean diameter of the NPLs, up to 0.6 \% (v/v) with increased ionic
strength of the ferrofluid, and for $\sim$ 2 \% (v/v) with higher saturation
magnetization of the NPLs. We showed that by tuning the parameters affecting
the ferrofluid's interplatelet interactions, we can alter the threshold
concentration for the liquid magnet formation. The results elucidate the
importance of a delicate balance between the repulsive screened electrostatic
and attractive dipolar magnetic interactions for the liquid magnet formation.",2404.01956v1
1995-10-06,An Incoherent $α-Ω$ Dynamo in Accretion Disks,"We use the mean-field dynamo equations to show that an incoherent alpha
effect in mirror-symmetric turbulence in a shearing flow can generate a large
scale, coherent magnetic field. We illustrate this effect with simulations of a
few simple systems. In accretion disks, this process can lead to axisymmetric
magnetic domains whose radial and vertical dimensions will be comparable to the
disk height. This process may be responsible for observations of dynamo
activity seen in simulations of dynamo-generated turbulence involving, for
example, the Balbus-Hawley instability. In this case the magnetic field
strength will saturate at $\sim (h/r)^2$ times the ambient pressure in real
accretion disks. The resultant dimensionless viscosity will be of the same
order. In numerical simulations the azimuthal extent of the simulated annulus
should be substituted for $r$. We compare the predictions of this model to
numerical simulations previously reported by Brandenburg et al. (1995). In a
radiation pressure dominated environment this estimate for viscosity should be
reduced by a factor of $(P_{gas}/P_{radiation})^6$ due to magnetic buoyancy.",9510038v1
2000-01-24,The Magnetic Fields of the Universe and Their Origin,"Recent rotation measure observations of a dozen or so galaxy clusters have
revealed a surprisingly large amount of magnetic fields, whose estimated energy
and flux are, on average, $\sim 10^{58}$ ergs and $\sim 10^{41}$ G cm$^2$,
respectively. These quantities are so much larger than any coherent sums of
individual galaxies within the cluster that an efficient galactic dynamo is
required. We associate these fields with single AGNs within the cluster and
therefore with all galaxies during their AGN phase. Only the central, massive
black hole (BH) has the necessary binding energy, $\sim 10^{61}$ ergs. Only the
accretion disk during the BH formation has the winding number, $\sim 10^{11}$
turns, necessary to make the gain and magnetic flux. We present a model of the
BH accretion disk dynamo that might create these magnetic fields, where the
helicity of the $\alpha - \Omega$ dynamo is driven by star-disk collisions. The
back reaction of the saturated dynamo forms a force-free field helix that
carries the energy and flux of the dynamo and redistributes them within the
clusters.",0001418v1
2002-08-09,Circular Polarization of Water Masers in the Circumstellar Envelopes of Late Type Stars,"We present circular polarization measurements of circumstellar H_2O masers.
The circular polarization detected in the (6_{16}-5_{23}) rotational transition
of the H_{2}O maser can be attributed to Zeeman splitting in the intermediate
temperature and density regime. The magnetic fields are derived using a
general, LTE Zeeman analysis as well as a full radiative transfer method
(non-LTE), which includes a treatment of all hyperfine components
simultaneously as well as the effects of saturation and unequal populations of
the magnetic substates. The differences and relevances of these interpretations
are discussed extensively. The field strengths are compared with previous
detections of the magnetic field on the SiO and OH masers. We show that the
magnetic pressure dominates the thermal pressure by a factor of 20 or more.",0208197v1
2004-05-04,Astrophysical magnetic fields and nonlinear dynamo theory,"The current understanding of astrophysical magnetic fields is reviewed,
focusing on their generation and maintenance by turbulence. In the
astrophysical context this generation is usually explained by a self-excited
dynamo, which involves flows that can amplify a weak 'seed' magnetic field
exponentially fast. Particular emphasis is placed on the nonlinear saturation
of the dynamo. Analytic and numerical results are discussed both for small
scale dynamos, which are completely isotropic, and for large scale dynamos,
where some form of parity breaking is crucial. Central to the discussion of
large scale dynamos is the so-called alpha effect which explains the generation
of a mean field if the turbulence lacks mirror symmetry, i.e. if the flow has
kinetic helicity. Large scale dynamos produce small scale helical fields as a
waste product that quench the large scale dynamo and hence the alpha effect.
With this in mind, the microscopic theory of the alpha effect is revisited in
full detail and recent results for the loss of helical magnetic fields are
reviewed.",0405052v2
2006-10-30,Green Bank Telescope observations of the water masers of NGC 3079: accretion disk magnetic field and maser scintillation,"We present observations of the 22 GHz water megamasers in the circumnuclear
disk of NGC 3079 obtained with the Green Bank Telescope. The data are analyzed
for circular polarization due to the Zeeman-induced splitting of the water
maser lines. No circular polarization is detected and we derive a 1 sigma upper
limit of 11 mG for the toroidal magnetic field at ~0.64 pc from the central
black hole. This is the tightest upper limit for the magnetic field around a
black hole to date. We use the magnetic field limit to derive an estimate of
the mass accretion onto the central black hole. In addition to the polarimetric
results, we present an observation of rapid variability in the maser lines,
which we explain as weak interstellar scintillation. From the scintillation
parameters, we estimate an intrinsic size of the mostly saturated maser
features of ~12 microarcseconds. This is consistent with models assuming a
thick, clumpy accretion disk.",0610912v1
1998-05-04,Phase diagram of the anti-ferromagnetic xxz model in the presence of an external magnetic field,"The anisotropic s=1/2 anti-ferromagnetic Heisenberg chain in the presence of
an external magnetic field is studied by using the standard quantum
renormalization group. We obtain the critical line of the transition from
partially magnetized (PM) phase to the saturated ferromagnetic (SFM) phase. The
crossover exponent between the PM phase and anti-ferromagnetic Ising (AFI)
phase is evaluated. Our results show that the anisotropy($\d$) term is relevant
and causes crossover. These results indicate that the standard RG approach
yields fairly good values for the critical points and their exponents. The
magnetization curve, correlation functions and the ground state energy per site
are obtained and compared with the known exact results.",9805024v2
1998-12-30,Giant transverse magnetoresistance in an asymmetric system of three GaAs/AlGaAs quantum wells in a strong magnetic field at room temperature,"The giant transverse magnetoresistance is observed in the case of
photoinduced nonequilibrium carriers in an asymmetric undoped system of three
GaAs/AlGaAs quantum wells at room temperature. In a magnetic field of 75 kOe,
the resistance of nanostructure being studied increases by a factor of 1.85.
The magnetoresistance depends quadratically on the magnetic field in low fields
and tends to saturation in high fields. This phenomenon is attributed to the
rearrangement of the electron wave function in magnetic field. Using the fact
that the incoherent part of the scattering probability for electron scattering
on impurities and bulk defects is proportional to the integral of the forth
power of the envelope wave function, the calculated field dependence of the
magnetoresistance is shown to be similar to that observed experimentally.",9812426v1
1999-08-02,Breakdown of the magnetization plateau of the S=1/2 ferromagnetic-ferromagnetic-antiferromagnetic trimerized spin chain with anisotropy,"We study the breakdown of the magnetization plateau at the magnetization
M=M_{S}/3 (M_{S} is the saturation magnetization) of the S=1/2 anisotropic spin
chain with ferromagnetic-ferromagnetic-antiferromagnetic interactions. We
consider the model with the isotropic ferromagnetic (trimer) coupling J_{F},
and anisotropic antiferromagnetic coupling (J_{x}=J_{y}=J_{AF} and J_{z}=\Delta
J_{AF}). For the limit of large \gamma\equiv J_{F}/J_{AF}, the model is
equivalent to the S=3/2 XXZ chain with the exchange anisotropy \Delta. There is
a phase transition between the plateau (small-\gamma) and the no-plateau
(large-\gamma) regions. This phase transition is of the
Berezinskii-Kosterlitz-Thouless type, and we determine the phase boundary from
the numerical diagonalization data. For \Delta=1, in particular, the phase
transition between the plateau and the no-plateau regions occurs at the point
\gamma_{c}=15.4.",9908027v2
1999-08-03,Spin Chains in an External Magnetic Field. Closure of the Haldane Gap and Effective Field Theories,"We investigate both numerically and analytically the behaviour of a spin-1
antiferromagnetic (AFM) isotropic Heisenberg chain in an external magnetic
field. Extensive DMRG studies of chains up to N=80 sites extend previous
analyses and exhibit the well known phenomenon of the closure of the Haldane
gap at a lower critical field H_c1. We obtain an estimate of the gap below
H_c1. Above the lower critical field, when the correlation functions exhibit
algebraic decay, we obtain the critical exponent as a function of the net
magnetization as well as the magnetization curve up to the saturation (upper
critical) field H_c2. We argue that, despite the fact that the SO(3) symmetry
of the model is explicitly broken by the field, the Haldane phase of the model
is still well described by an SO(3) nonlinear sigma-model. A mean-field theory
is developed for the latter and its predictions are compared with those of the
numerical analysis and with the existing literature.",9908044v1
2000-04-13,NMR and Neutron Scattering Studies of Quasi One-Dimensional Magnet CuV_2O_6,"Magnetic properties of a quasi one-dimensional magnet CuV_2O_6 have been
studied by means of susceptibility measurement, NMR and powder neutron
diffraction. Cu^{2+} spins (S=1/2) order antiferromagnetically below 22.6 K,
and the saturation moment is about 0.70 \mu_{B} at 0 K. The magnetic structure
determined in the present study indicates that in CuV_2O_6 one-dimensional
antiferromagnetic spin chains are along [110], suggesting a dominant
antiferromagnetic exchange interaction between the next-nearest-neighbor spins
rather than the nearest-neighbor ones.",0004213v2
2001-03-19,Time decay of the remanent magnetization in the $\pm J$ spin glass model at T=0,"Using the zero-temperature Metropolis dynamics, the time decay of the
remanent magnetization in the $\pm J$ Edward-Anderson spin glass model with a
uniform random distribution of ferromagnetic and antiferromagnetic interactions
has been investigated. Starting from the saturation, the magnetization per spin
$m$ reveals a slow decrease with time, which can be approximated by a power
law:$m(t)=m_{\infty}+ ({t\over a_{0}})^{a_{1}}$, $a_{1} < 0$. Moreover, its
relaxation does not lead it into one of the ground states, and therefore the
system is trapped in metastable isoenergetic microstates remaining magnetized.
Such behaviour is discussed in terms of a random walk the system performs on
its available configuration space.",0103382v4
2001-07-03,"Sr$_3$CuIrO$_6$, a spin-chain compound with random ferromagnetic-antiferromagnetic interactions","Ac and dc magnetization and heat-capacity (C) measurements performed on the
pseudo-one-dimensional compound Sr$_3$CuIrO$_6$ reveal a competition between
antiferromagnetic (AF) and ferromagnetic (F) exchange couplings, as evidenced
by frequency dependence of ac susceptibility and by the absence of a C anomaly
at the magnetic transition. The value of the saturation moment (about 0.35
$\mu_B$/formula unit) is much smaller than expected for ferromagnetism from the
two S=1/2 ions (Cu and Ir). Thus, this compound is not a ferromagnet in zero
magnetic field, in contrast to earlier beliefs. Of particular importance is the
finding that the value of the magnetic ordering temperature is sample
dependent, sensitive to synthetic conditions resulting from deviations in
oxygen/Cu content. We propose that this compound serves as a unique model
system to test theories on random AF-F interaction in a chain system,
considering that this competition can be tuned without any chemical
substitution.",0107069v1
2001-11-08,Magnetic structures of RbCuCl_3 in a transverse field,"A recent high-field magnetization experiment found a phase transition of
unknown character in the layered, frustrated antiferromagnet RbCuCl_3, in a
transverse field (in the layers). Motivated by these results, we have examined
the magnetic structures predicted by a model of RbCuCl_3, using the classical
approximation. At small fields, we obtain the structure already known to be
optimal, an incommensurate (IC) spiral with wave vector q in the layers. At
higher fields, we find a staircase of long-period commensurate (C) phases
(separated initially by the low-field IC phase), then two narrow IC phases,
then a fourth IC phase (also with intermediate C phases), and finally the
ferromagnetically aligned phase at the saturation field H_S. The
three-sublattice C states familiar from the theory of the triangular
antiferromagnet are never optimal. The C phases and the two intermediate IC
phases were previously unknown in this context. The magnetization is
discontinuous at a field \approx 0.4H_S, in qualitative agreement with
experiment, though we find much fine structure not reported.",0111146v1
2002-04-17,Quantum magnetization plateaux of an anisotropic ferrimagnetic spin chain,"The magnetization curve of the $(S,s)=(1,1/2)$ ferrimagnetic alternating spin
chain with the single-ion anisotropy $D$ is investigated with the numerical
exact diagonalization of finite clusters and size-scaling analyses. The system
has a plateau at 1/3 of the saturation moment, which corresponds to the
spontaneous magnetization for D=0. Varying $D$ in the 1/3-magnetized ground
state under the external field along the axis of $D$, a quantum phase
transition is revealed to occur at the critical value $D/J=1.114 \pm 0.001$
where the plateau vanishes. Except for the critical point, the plateau is
always opening, but the mechanism is different between $D<D_c$ and $D>D_c$. The
change of mechanisms is an evidence to clarify that the plateau originates from
the quantization of magnetization.",0204375v2
2002-07-15,Low temperature annealing studies of Ga1-xMnxAs,"High- and low-field magneto-transport measurements, as well as SQUID
measurements of magnetization, were carried out on Ga1-xMnxAs epilayers grown
by low temperature molecular beam epitaxy, and subsequently annealed under
various conditions. We observe a large enhancement of ferromagnetism when the
samples are annealed at an optimal temperature, typically about 280 0C. Such
optimal annealing leads to an increase of Curie temperature, accompanied by an
increase of both the conductivity and the saturation magnetization. A decrease
of the coercive field and of magnetoresistivity is also observed for Ga1-xMnxAs
annealed at optimal conditions. We suggest that the experimental results
reported in this paper are related to changes in the domain structure of
Ga1-xMnxAs.",0207354v1
2002-11-18,"Synthesis of RuSr2(Ln3/4Ce1/4)2Cu2O10 magneto-superconducting compounds with Ln = Ho, Y and Dy by high-pressure high-temperature (HPHT) technique","The samples of composition RuSr2(Ln3/4Ce1/4)2Cu2O10 with Ln = Ho, Y and Dy.
being synthesized by high pressure high temperature (6Gpa, 1200 0C) solid state
synthesis route do crystallize in space group I4/mmm. These samples exhibit
magnetic transitions at ~150 K with significant branching of zfc
(zero-field-cooled) and fc (field-cooled) magnetization and a sharp cusp in zfc
at ~ 100 K, followed by a superconducting transition at lower temperatures. All
the compounds show typical ferromagnetic hysteresis loops in magnetic moment
(M) versus field (H) magnetization at 5 K. Near saturation of the moments at 5
K is achieved in above 5 T (Tesla) applied fields with a value of ~ 0.80 muB.
At low temperatures (5 K) these compounds exhibit both superconductivity and
ferromagnetism. To our knowledge these are first successfully synthesized
Ru-1222 compounds with various lanthanides including Y, Dy, and Ho. The results
are compared with widely reported Gd/Ru-1222 compound.",0211359v1
2002-12-11,Coercive Field and Magnetization Deficit in Ga(1-x)Mn(x)As Epilayers,"We have studied the field dependence of the magnetization in epilayers of the
diluted magnetic semiconductor Ga(1-x)Mn(x)As for 0.0135 < x < 0.083.
Measurements of the low temperature magnetization in fields up to 3 T show a
significant deficit in the total moment below that expected for full saturation
of all the Mn spins. These results suggest that the spin state of the
non-ferromagnetic Mn spins is energetically well separated from the
ferromagnetism of the bulk of the spins. We have also studied the coercive
field (Hc) as a function of temperature and Mn concentration, finding that Hc
decreases with increasing Mn concentration as predicted theoretically.",0212260v1
2003-08-24,Anomalous magnetization process in frustrated spin ladders,"We study, at T=0, the anomalies in the magnetization curve of the S=1 two-leg
ladder with frustrated interactions. We focus mainly on the existence of the
$M=\Ms/2$ plateau, where $\Ms$ is the saturation magnetization. We use
analytical methods (degenerate perturbation theory and non-Abelian
bosonization) as well as numerical methods (level spectroscopy and density
matrix renormalization group), which lead to the consistent conclusion with
each other. We also touch on the $M=\Ms/4$ and $M=(3/4)\Ms$ plateaux and cusps.",0308473v2
2003-09-19,Exact eigenstates and macroscopic magnetization jumps in strongly frustrated spin lattices,"For a class of frustrated spin lattices including e.g. the 1D sawtooth chain,
the 2D kagom\'e and checkerboard, as well as the 3D pyrochlore lattices we
construct exact product eigenstates consisting of several independent,
localized one-magnon states in a ferromagnetic background. Important
geometrical elements of the relevant lattices are triangles being attached to
polygons or lines. Then the magnons can be trapped on these polygons/lines. If
the concentration of localized magnons is small they can be distributed
randomly over the lattice. Increasing the number of localized magnons their
distribution over the lattice becomes more and more regular and finally the
magnons condensate in a crystal-like state. The physical relevance of these
eigenstates emerges in high magnetic fields where they become groundstates of
the system. As a result a macroscopic magnetization jump appears in the
zero-temperature magnetization curve just below the saturation field. The
height of the jump decreases with increasing spin quantum number and vanishes
in the classical limit. Thus it is a true macroscopic quantum effect.",0309455v1
2003-10-31,Unconventional magnetism in all-carbon nanofoam,"We report production of nanostructured carbon foam by a high-repetition-rate,
high-power laser ablation of glassy carbon in Ar atmosphere. A combination of
characterization techniques revealed that the system contains both sp2 and sp3
bonded carbon atoms. The material is a novel form of carbon in which
graphite-like sheets fill space at very low density due to strong hyperbolic
curvature, as proposed for ?schwarzite?. The foam exhibits ferromagnetic-like
behaviour up to 90 K, with a narrow hysteresis curve and a high saturation
magnetization. Such magnetic properties are very unusual for a carbon
allotrope. Detailed analysis excludes impurities as the origin of the magnetic
signal. We postulate that localized unpaired spins occur because of topological
and bonding defects associated with the sheet curvature, and that these spins
are stabilized due to the steric protection offered by the convoluted sheets.",0310751v1
2004-11-26,The spin-half Heisenberg antiferromagnet on the square-kagomé lattice: Ground state and low-lying excitations,"We discuss the ground state and the low-lying excitations of the spin-half
Heisenberg antiferromagnet on the two-dimensional square-kagome lattice. This
magnetic system belongs to the class of highly frustrated spin systems with an
infinite non-trivial degeneracy of the classical ground state as it is known
also for the Heisenberg antiferromagnet on the kagome and on the star lattice.
The quantum ground state of the spin-half system is a quantum paramagnet likely
with a finite spin gap and with a large number of non-magnetic excitations
within this gap. The magnetization versus field curve shows plateaux as well as
a macroscopic magnetization jump to saturation due to independent localized
magnon states.",0411673v1
2004-11-26,Study of the magnetic penetration depth in RbOs_2O_6,"Measurements of the magnetic field penetration depth \lambda in the
pyrochlore superconductor RbOs_2O_6 (T_c\simeq6.3 K) were carried out by means
of the muon-spin-rotation (\muSR) technique. At low temperatures
\lambda^{-2}(T) saturates and becomes constant below T\simeq 0.2T_c, in
agreement with what is expected for weak-coupled s-wave BCS superconductors.
The value of \lambda at T=0 was found to be in the range of 250 nm to 300 nm.
\muSR and equilibrium magnetization measurements both reveal that at low
temperatures $\lambda$ is almost (at the level of 10%) independent of the
applied magnetic field. This result suggests that the superconducting energy
gap in RbOs_2O_6 is isotropic.",0411674v1
2004-12-22,Investigation of the growth and magnetic properties of highly oriented films of the Heusler alloy Co2MnSi on GaAs(001),"Highly (001) oriented thin films of Co2MnSi have been grown on lattice
matched GaAs(001) without a buffer layer. Stoichiometric films exhibited a
saturation magnetization slightly reduced from the bulk value and films grown
at the highest substrate temperature of 689 K showed the lowest resistivity (33
micro.ohm.cm at 4.2 K) and the lowest coercivity (14 Oe). The spin polarization
of the transport current was found to be of the order of 55% as determined by
point contact Andreev reflection spectroscopy. The reduced magnetization
obtained was attributed to the antiferromagnetic Mn2As phase. Twofold in-plane
magnetic anisotropy was observed due to the inequivalence of the <110>
directions, and this was attributed to the nature of the bonding at the
reconstructed GaAs surface.",0412636v1
2005-01-14,Ground states of a frustrated spin-1/2 antifferomagnet: Cs_2CuCl_4 in a magnetic field,"We present detailed calculations of the magnetic ground state properties of
Cs$_2$CuCl$_4$ in an applied magnetic field, and compare our results with
recent experiments. The material is described by a spin Hamiltonian, determined
with precision in high field measurements, in which the main interaction is
antiferromagnetic Heisenberg exchange between neighboring spins on an
anisotropic triangular lattice. An additional, weak Dzyaloshinkii-Moriya
interaction introduces easy-plane anisotropy, so that behavior is different for
transverse and longitudinal field directions. We determine the phase diagram as
a function of field strength for both field directions at zero temperature,
using a classical approximation as a first step. Building on this, we calculate
the effect of quantum fluctuations on the ordering wavevector and components of
the ordered moments, using both linear spinwave theory and a mapping to a Bose
gas which gives exact results when the magnetization is almost saturated. Many
aspects of the experimental data are well accounted for by this approach.",0501347v1
2005-09-09,Magnetic Chains Created by Polymer-Induced Assembly of Hollow Cobalt Nanoparticles,"Magnetic chains of hollow cobalt nanoparticles (450-750 nm) have been
synthesized by using poly(vinyl pyrrolidone) (PVP) as a template in an ethylene
glycol solution. In this process, CoCl2.6H2O was reduced by N2H4.H2O in the
presence of PVP. All of the Co nanoparticles are hollow with a shell of 40 nm
and self-assembled into a chainlike structure that is as long as ~10 micron. At
300 K, the branched hollow Co nanoparticle chains exhibit a saturation
magnetization of 37.5 emu/g, a remnant magnetization of approximately 1.55
emu/g, and a coercivity of about 66 Oe, which is more than an order of
magnitude larger than that of the bulk",0509237v1
2005-11-04,Low Temperature Thermodynamic Properties of the Heavy Fermion Compound YbAgGe Close to the Field-Induced Quantum Critical Point,"We present temperature and field dependent heat capacity and magnetization
data taken at temperatures down to 50 mK and in an applied magnetic field up to
11.5 Tesla for YbAgGe, a heavy-fermion compound with a field induced quantum
critical point. These data clearly indicate that the same electronic degrees of
freedom are responsible for the features seen in both specific heat and
magnetization data. In addition, they further refine the different boundaries
suggested for the H - T phase diagram of YbAgGe through previous,
magneto-transport measurements, and allow for further understanding of
different phases on the H - T phase diagram, in particular, clearly
disconnecting the field-induced quantum critical point in YbAgGe from any sort
of saturation of the Yb moment in higher applied magnetic field.",0511125v1
2006-01-12,"Electronic structure, magnetic and optical properties of intermetallic compounds R2Fe17 (R=Pr,Gd)","In this paper we report comprehensive experimental and theoretical
investigation of magnetic and electronic properties of the intermetallic
compounds Pr2Fe17 and Gd2Fe17. For the first time electronic structure of these
two systems was probed by optical measurements in the spectral range of 0.22-15
micrometers. On top of that charge carriers parameters (plasma frequency and
relaxation frequency) and optical conductivity s(w) were determined.
Self-consistent spin-resolved bandstructure calculations within the
conventional LSDA+U method were performed. Theoretical interpetation of the
experimental s(w) dispersions indicates transitions between 3d and 4p states of
Fe ions to be the biggest ones. Qualitatively the line shape of the theoretical
optical conductivity coincides well with our experimental data. Calculated by
LSDA+U method magnetic moments per formula unit are found to be in good
agreement with observed experimental values of saturation magnetization.",0601247v1
2006-01-12,Commensurate and incommensurate ground states of Cs_2CuCl_4 in a magnetic field,"We present calculations of the magnetic ground state of Cs_2CuCl_4 in an
applied magnetic field, with the aim of understanding the commensurately
ordered state that has been discovered in recent experiments. This layered
material is a realization of a Heisenberg antiferromagnet on an anisotropic
triangular lattice. Its behavior in a magnetic field depends on field
orientation, because of weak Dzyaloshinskii-Moriya interactions.We study the
system by mapping the spin-1/2 Heisenberg Hamiltonian onto a Bose gas with hard
core repulsion. This Bose gas is dilute, and calculations are controlled, close
to the saturation field. We find a zero-temperature transition between
incommensurate and commensurate phases as longitudinal field strength is
varied, but only incommensurate order in a transverse field. Results for both
field orientations are consistent with experiment.",0601268v1
2006-01-12,Magnetic phase transitions in the two-dimensional frustrated quantum antiferromagnet Cs2CuCl4,"We report magnetization and specific heat measurements in the 2D frustrated
spin-1/2 Heisenberg antiferromagnet Cs2CuCl4 at temperatures down to 0.05 K and
high magnetic fields up to 11.5 T applied along a, b and c-axes. The low-field
susceptibility chi (T) M/B shows a broad maximum around 2.8 K characteristic of
short-range antiferromagnetic correlations and the overall temperature
dependence is well described by high temperature series expansion calculations
for the partially frustrated triangular lattice with J=4.46 K and J'/J=1/3. At
much lower temperatures (< 0.4 K) and in in-plane field (along b and c-axes)
several new intermediate-field ordered phases are observed in-between the
low-field incommensurate spiral and the high-field saturated ferromagnetic
state. The ground state energy extracted from the magnetization curve shows
strong zero-point quantum fluctuations in the ground state at low and
intermediate fields.",0601272v2
2006-02-23,Quantum Metallicity on the High-Field Side of the Superconductor-Insulator Transition,"We investigate ultrathin superconducting TiN films, which are very close to
the localization threshold. Perpendicular magnetic field drives the films from
the superconducting to an insulating state, with very high resistance. Further
increase of the magnetic field leads to an exponential decay of the resistance
towards a finite value. In the limit of low temperatures, the saturation value
can be very accurately extrapolated to the universal quantum resistance h/e^2.
Our analysis suggests that at high magnetic fields a new ground state, distinct
from the normal metallic state occurring above the superconducting transition
temperature, is formed. A comparison with other studies on different materials
indicates that the quantum metallic phase following the magnetic-field-induced
insulating phase is a generic property of systems close to the disorder-driven
superconductor-insulator transition.",0602557v2
2006-03-21,Excitations of a low-dimensional dimerized spin ladder under a magnetic field,"We study the dimerized spin ladder with nearest-neighbor ($J_1$) and
next-nearest-neighbor ($J_2$) anti-ferromagnetic interaction under a magnetic
field. We predict the existence of different magnetization plateaus for the
presence of spin-Peierls interaction on both $J_1$ and $J_2$. Magnetization
plateau at $m=0$ for $J_1$ dimerization is spontaneous due to XY interaction,
but it is absent for $J_2$ dimerization, only intrinsic umklapp term leads to
plateau (spin gap) state for some specific values of XXZ anisotropy ($\Delta$)
and $J_2$. Here we predict a saturation plateau which is the classical phase of
the system. There are some numerical support of our analytical approach already
existing in the literature. The transition from commensurate gapped phase to
incommensurate Luttinger liquid phase is the Mott-$\delta$ type of transition.",0603545v1
2006-04-11,Antiferromagnetic coupling and enhanced magnetization in all-ferromagnetic superlattices,"The structural and magnetic properties of a series of superlattices
consisting of two ferromagnetic metals La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) and
SrRuO$_3$ (SRO) grown on (001) oriented SrTiO$_3$ are studied. Superlattices
with a fixed LSMO layer thickness of 20 unit cells (u.c.) and varying SRO layer
thickness show a sudden drop in magnetization on cooling through temperature
where both LSMO and SRO layers are ferromagnetic. This behavior suggests an
antiferromagnetic coupling between the layers. In addition, the samples having
thinner SRO layers (n \TEXTsymbol{<} 6) exhibit enhanced saturation
magnetization at 10 K. These observations are attributed to the possible
modification in the stereochemistry of the Ru and Mn ions in the interfacial
region.",0604266v1
2006-06-09,Magnetic resonance studies of the fundamental spin-wave modes in individual submicron Cu/NiFe/Cu perpendicularly magnetized disks,"Spin wave spectra of perpendicularly magnetized disks with trilayers
consisting of a 100 nm permalloy (Py) layer sandwiched by two Cu layers of 30
nm, are measured individually with a Magnetic Resonance Force Microscope
(MRFM). It is demonstrated by 3D micromagnetic simulations that in disks having
sub-micron size diameters, the lowest energy spin wave mode of the saturated
state is not spatially uniform but rather is localized at the center of the
Py/Cu interface in the region of a minimum demagnetizing field.",0606245v3
2006-08-26,Ferrimagnetic States in S=1/2 Frustrated Heisenberg Chains with Period 3 Exchange Modulation,"Ground state properties of the S=1/2 frustrated Heisenberg chain with period
3 exchange modulation are investigated using the numerical diagonalization and
DMRG method. It is known that this model has a magnetization plateau at 1/3 of
the saturation magnetization M_s. On the other hand, the ground state is
ferrimagnetic even in the absence of frustration if one of the nearest
neighbour bond is ferromagnetic and others are antiferromagnetic. In the
present work, we show that this ferrimagnetic state continues to the region in
which all bonds are antiferromagnetic if frustration is strong. This state
further continues to the above mentioned 1/3-plateau state. In between, we also
find the noncollinear ferrimagnetic phase in which the spontaneous
magnetization is finite but less than M_s/3. The intuitive interpretation for
the phase diagram is given and the physical properties of these phases are
discussed.",0608582v1
2006-10-05,Magnetic Domain Patterns Depending on the Sweeping Rate of Magnetic Fields,"The domain patterns in a thin ferromagnetic film are investigated in both
experiments and numerical simulations. Magnetic domain patterns under a zero
field are usually observed after an external magnetic field is removed. It is
demonstrated that the characteristics of the domain patterns depend on the
decreasing rate of the external field, although it can also depend on other
factors. Our numerical simulations and experiments show the following
properties of domain patterns: a sea-island structure appears when the field
decreases rapidly from the saturating field to the zero field, while a
labyrinth structure is observed for a slowly decreasing field. The mechanism of
the dependence on the field sweeping rate is discussed in terms of the concepts
of crystallization.",0610142v3
2006-10-24,Ferrimagnetic and Long Period Antiferromagnetic Phases in High Spin Heisenberg Chains with D-Modulation,"The ground state properties of the high spin Heisenberg chains with
alternating single site anisotropy are investigated by means of the numerical
exact daigonaization and DMRG method. It is found that the ferrimagnetic state
appears between the Haldane phase and period doubled N\'eel phase for the
integer spin chains. On the other hand, the transition from the
Tomonaga-Luttinger liquid state into the ferrimagnetic state takes place for
the half-odd-integer spin chains. In the ferrimagnetic phase, the spontaneous
magnetization varies continuously with the modulation amplitude of the single
site anisotropy. Eventually, the magnetization is locked to fractional values
of the saturated magnetization. These fractional values satisfy the
Oshikawa-Yamanaka-Affleck condition. The local spin profile is calculated to
reveal the physical nature of each state. In contrast to the case of
frustration induced ferrimagnetism, no incommensurate magnetic superstructure
is found.",0610660v1
2006-10-30,"Nucleation of magnetisation reversal, from nanoparticles to bulk materials","We review models for the nucleation of magnetisation reversal, i.e. the
formation of a region of reversed magnetisation in an initially magnetically
saturated system. For small particles models for collective reversal, either
uniform (Stoner-Wohlfarth model) or non-uniform like curling, provide good
agreement between theory and experiment. For microscopic objects and thin
films, we consider two models, uniform (Stoner-Wohlfarth) reversal inside a
nucleation volume and a droplet model, where the free energy of an inverse
bubble is calculated taking into account volume energy (Zeeman energy) and
surface tension (domain wall energy). In macroscopic systems, inhomogeneities
in magnetic properties cause a distribution of energy barriers for nucleation,
which strongly influences effects of temperature and applied field on
magnetisation reversal. For these systems, macroscopic material parameters like
exchange interaction, spontaneous magnetisation and magnetic anisotropy can
give an indication of the magnetic coercivity, but exact values for nucleation
fields are, in general, hard to predict.",0610840v2
2006-12-04,"Structural, magnetic, and transport properties of Co$_2$FeSi Heusler films","We report the deposition of thin Co$_2$FeSi films by RF magnetron sputtering.
Epitaxial (100)-oriented and L2$_1$ ordered growth is observed for films grown
on MgO(100) substrates. (110)-oriented films on Al$_2$O$_3$(110) show several
epitaxial domains in the film plane. Investigation of the magnetic properties
reveals a saturation magnetization of 5.0 $mu_B/f.u.$ at low temperatures. The
temperature dependence of the resistivity $rho_{xx}(T)$ exhibits a crossover
from a T^3.5 law at T<50K to a T^1.65 behaviour at elevated temperatures.
$rho_{xx}(H)$ shows a small anisotropic magnetoresistive effect. A weak
dependence of the normal Hall effect on the external magnetic field indicates
the compensation of electron and hole like contributions at the Fermi surface.",0612073v1
1998-11-19,Spectrum of Neutral Helium in Strong Magnetic Fields,"We present extensive and accurate calculations for the excited state spectrum
of spin-polarized neutral helium in a range of magnetic field strengths up to
$10^{12}$ G. Of considerable interest to models of magnetic white dwarf stellar
atmospheres, we also present results for the dipole strengths of the low lying
transitions among these states. Our methods rely on a systematically saturated
basis set approach to solving the Hartree--Fock self-consistent field
equations, combined with an ``exact'' stochastic method to estimate the
residual basis set truncation error and electron correlation effects. We also
discuss the applicability of the adiabatic approximation to strongly magnetized
multi-electron atoms.",9811041v1
2002-12-20,Orbital magnetism in axially deformed sodium clusters: From scissors mode to dia-para magnetic anisotropy,"Low-energy orbital magnetic dipole excitations, known as scissors mode (SM),
are studied in alkali metal clusters. Subsequent dynamic and static effects are
explored. The treatment is based on a self-consistent microscopic approach
using the jellium approximation for the ionic background and the Kohn-Sham mean
field for the electrons. The microscopic origin of SM and its main features
(structure of the mode in light and medium clusters, separation into low- and
high-energy plasmons, coupling high-energy M1 scissors and E2 quadrupole
plasmons, contributions of shape isomers, etc) are discussed. The scissors M1
strength acquires large values with increasing cluster size. The mode is
responsible for the van Vleck paramagnetism of spin-saturated clusters. Quantum
shell effects induce a fragile interplay between Langevin diamagnetism and van
Vleck paramagnetism and lead to a remarkable dia-para anisotropy in magnetic
susceptibility of particular light clusters. Finally, several routes for
observing the SM experimentally are discussed.",0212084v1
2004-10-07,Numerical study of dynamo action at low magnetic Prandtl numbers,"We present a three--pronged numerical approach to the dynamo problem at low
magnetic Prandtl numbers $P_M$. The difficulty of resolving a large range of
scales is circumvented by combining Direct Numerical Simulations, a
Lagrangian-averaged model, and Large-Eddy Simulations (LES). The flow is
generated by the Taylor-Green forcing; it combines a well defined structure at
large scales and turbulent fluctuations at small scales. Our main findings are:
(i) dynamos are observed from $P_M=1$ down to $P_M=10^{-2}$; (ii) the critical
magnetic Reynolds number increases sharply with $P_M^{-1}$ as turbulence sets
in and then saturates; (iii) in the linear growth phase, the most unstable
magnetic modes move to small scales as $P_M$ is decreased and a Kazantsev
$k^{3/2}$ spectrum develops; then the dynamo grows at large scales and modifies
the turbulent velocity fluctuations.",0410046v1
2005-09-08,On the inverse cascade of magnetic helicity,"We study the inverse cascade of magnetic helicity in conducting fluids by
investigating the detailed transfer of helicity between different spherical
shells in Fourier space in direct numerical simulations of three-dimensional
magnetohydrodynamics (MHD). Two different numerical simulations are used, one
where the system is forced with an electromotive force in the induction
equation, and one in which the system is forced mechanically with an ABC flow
and the magnetic field is solely sustained by a dynamo action. The magnetic
helicity cascade at the initial stages of both simulations is observed to be
inverse and local (in scale space) in the large scales, and direct and local in
the small scales. When saturation is approached most of the helicity is
concentrated in the large scales and the cascade is non-local. Helicity is
transfered directly from the forced scales to the largest scales. At the same
time, a smaller in amplitude direct cascade is observed from the largest scale
to small scales.",0509069v1
2007-04-02,Quasi-quartet crystal electric field ground state in a tetragonal CeAg$_2$Ge$_2$ single crystal,"We have successfully grown the single crystals of CeAg$_2$Ge$_2$, for the
first time, by flux method and studied the anisotropic physical properties by
measuring the electrical resistivity, magnetic susceptibility and specific
heat. We found that CeAg$_2$Ge$_2$ undergoes an antiferromagnetic transition at
$T_{\rm N}$ = 4.6 K. The electrical resistivity and susceptibility data reveal
strong anisotropic magnetic properties. The magnetization measured at $T$ = 2 K
exhibited two metamagnetic transitions at $H_{\rm m1}$ = 31 kOe and $H_{\rm
m2}$ = 44.7 kOe, for $H \parallel$ [100] with a saturation magnetization of 1.6
$\mu_{\rm B}$/Ce. The crystalline electric field (CEF) analysis of the inverse
susceptibility data reveals that the ground state and the first excited states
of CeAg$_2$Ge$_2$ are closely spaced indicating a quasi-quartet ground state.
The specific heat data lend further support to the presence of closely spaced
energy levels.",0704.0119v1
2007-05-17,Ferromagnetism in nanoscale BiFeO3,"A remarkably high saturation magnetization of ~0.4mu_B/Fe along with room
temperature ferromagnetic hysteresis loop has been observed in nanoscale (4-40
nm) multiferroic BiFeO_3 which in bulk form exhibits weak magnetization
(~0.02mu_B/Fe) and an antiferromagnetic order. The magnetic hysteresis loops,
however, exhibit exchange bias as well as vertical asymmetry which could be
because of spin pinning at the boundaries between ferromagnetic and
antiferromagnetic domains. Interestingly, like in bulk BiFeO_3, both the
calorimetric and dielectric permittivity data in nanoscale BiFeO_3 exhibit
characteristic features at the magnetic transition point. These features
establish formation of a true ferromagnetic-ferroelectric system with a
coupling between the respective order parameters in nanoscale BiFeO_3.",0705.2498v1
2007-08-23,Sharp Magnetic Field Dependence of the 2D Hall Coefficient Induced by Classical Memory Effects,"We show that a sharp dependence of the Hall coefficient $R$ on the magnetic
field $B$ arises in two-dimensional electron systems with randomly located
strong scatterers. The phenomenon is due to classical memory effects. We
calculate analytically the dependence $R(B)$ for the case of scattering by hard
disks of radius $a$, randomly distributed with concentration $n_0\ll1/a^2$. We
demonstrate that in very weak magnetic fields ($\omega_c\tau \lesssim n_0a^2$)
memory effects lead to a considerable renormalization of the Boltzmann value of
the Hall coefficient: $\delta R / R \sim 1 .$ With increasing magnetic field,
the relative correction to $R$ decreases, then changes sign, and saturates at
the value $\delta R / R \sim -n_0a^2 .$ We also discuss the effect of the
smooth disorder on the dependence of $R$ on $B$.",0708.3165v1
2008-01-09,"Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb","Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb
are presented and analyzed in terms of current models of charge conversion at a
superconductor-ferromagnet interface. We investigate the influence of surface
transparency, and study the crossover from ballistic to diffusive transport
regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample
with Curie temperature Tc of 5.4 K allowed the determination of
spin-polarization when the ferromagnetic phase transition temperature is
crossed. We find a striking difference between the temperature dependence of
the local spin polarization and of the macroscopic magnetization, and
demonstrate that nanoscale clusters with magnetization close to the saturated
value are present even well above the magnetic phase transition temperature.",0801.1464v1
2008-05-14,Persistent Spin Dynamics in the $S=1/2$ V$_{15}$ Molecular Nano-Magnet,"We present muon spin lattice relaxation measurements in the V15 spin 1/2
molecular nano-magnet. We find that the relaxation rate in low magnetic fields
(<5 kG) is temperature independent below ~10 K, implying that the molecular
spin is dynamically fluctuating down to 12 mK. These measurements show that the
fluctuation time increases as the temperature is decreased and saturates at a
value of ~6 nsec at low temperatures. The fluctuations are attributed to V15
molecular spin dynamics perpendicular to the applied magnetic field direction,
induced by coupling between the molecular spin and nuclear spin bath in the
system.",0805.2164v1
2008-08-11,Monitoring of band gap and magnetic state of graphene nanoribbons through vacancies,"Using first-principles plane wave calculations we predict that electronic and
magnetic properties of graphene nanoribbons can be affected by defect-induced
itinerant states. The band gaps of armchair nanoribbons can be modified by
hydrogen saturated holes. Defects due to periodically repeating vacancy or
divacancies induce metallization, as well as magnetization in non-magnetic
semiconducting nanoribbons due to the spin-polarization of local defect states.
Antiferromagnetic ground state of semiconducting zigzag ribbons can change to
ferrimagnetic state upon creation of vacancy defects, which reconstruct and
interact with edge states. Even more remarkable is that all these effects of
vacancy defects are found to depend on their geometry and position relative to
edges. It is shown that these effects can, in fact, be realized without really
creating defects.",0808.1468v1
2008-08-15,19F nuclear spin relaxation and spin diffusion effects in the single ion magnet LiYF4:Ho3+,"Temperature and magnetic field dependences of the 19F nuclear spin-lattice
relaxation in a single crystal of LiYF4 doped with holmium are described by an
approach based on a detailed consideration of the magnetic dipole-dipole
interactions between nuclei and impurity paramagnetic ions and nuclear spin
diffusion processes. The observed non-exponential long time recovery of the
nuclear magnetization after saturation at intermediate temperatures is in
agreement with predictions of the spin-diffusion theory in a case of the
diffusion limited relaxation. At avoided level crossings in the spectrum of
electron-nuclear states of the Ho3+ ion, rates of nuclear spin-lattice
relaxation increase due to quasi-resonant energy exchange between nuclei and
paramagnetic ions, in contrast to the predominant role played by electronic
cross-relaxation processes in the low-frequency ac-susceptibility.",0808.2137v1
2008-09-23,Localized magnetorotational instability and its role in the accretion disc dynamo,"(Abriged) The magnetorotational instability (MRI) is believed to be an
efficient way to transport angular momentum in accretion discs. It has also
been suggested as a way to amplify magnetic fields in discs, the instability
acting as a nonlinear dynamo. Recent numerical work has shown that a
large-scale magnetic field, which is predominantly azimuthal, can be sustained
by motions driven by the MRI of this same field. Following this idea, we
present an analytical calculation of the MRI in the presence of an azimuthal
field with a non-trivial vertical structure. We find that the mean radial EMF
associated to MRI modes tends to reduce the magnetic energy, acting like a
turbulent resistivity by mixing the non-uniform azimuthal field. Meanwhile, the
azimuthal EMF generates a radial field that, in combination with the Keplerian
shear, tends to amplify the azimuthal field and can therefore assist in the
dynamo process. This effect, however, is reversed for sufficiently strong
azimuthal fields, naturally leading to a saturation of the dynamo and possibly
to a cyclic behaviour of the magnetic field, as found in previous numerical
works.",0809.3871v1
2008-10-11,The bifurcation periods in low-mass X-ray binaries: the effect of magnetic braking and mass loss,"The bifurcation period in low-mass X-ray binaries is the initial orbital pe-
riod which separates the formation of converging systems (which evolve with
decreasing orbital periods until the donor becomes degenerate) from the
diverging systems (which evolve with increasing orbital periods until the donor
star loses its envelope and a wide detached binary is formed). We calculate
systematically the bifurcation periods of binary systems with a 1.4M_\sun
neutron star and a 0.5-2M_\sun donor star, taking into account different kinds
of magnetic braking and mass loss mechanisms. Our results show that the
saturated magnetic braking can considerably decrease the values of bifurcation
period compared to the traditional magnetic braking, while the influence of
mass loss mechanisms on bifurcation periods is quite weak. We also develop a
semi-analytical method to compute the bifurcation period, the result of which
agrees well with the numerical method in the leading order.",0810.2009v2
2008-10-14,Turbulent dynamos with shear and fractional helicity,"Dynamo action owing to helically forced turbulence and large-scale shear is
studied using direct numerical simulations. The resulting magnetic field
displays propagating wave-like behavior. This behavior can be modelled in terms
of an \alpha\Omega dynamo. In most cases super-equipartition fields are
generated. By varying the fraction of helicity of the turbulence the
regeneration of poloidal fields via the helicity effect (corresponding to the
\alpha-effect) is regulated. The saturation level of the magnetic field in the
numerical models is consistent with a linear dependence on the ratio of the
fractional helicities of the small and large-scale fields, as predicted by a
simple nonlinear mean-field model. As the magnetic Reynolds number (Rm) based
on the wavenumber of the energy-carrying eddies is increased from 1 to 180, the
cycle frequency of the large-scale field is found to decrease by a factor of
about 6 in cases where the turbulence is fully helical. This is interpreted in
terms of the turbulent magnetic diffusivity, which is found to be only weakly
dependent on Rm.",0810.2298v2
2008-11-26,"Magnetic order in CaFe1-xCoxAsF (x = 0, 0.06, 0.12) superconductor compounds","A Neutron Powder Diffraction (NPD) experiment has been performed to
investigate the structural phase transition and magnetic order in CaFe1-xCoxAsF
superconductor compounds (x = 0, 0.06, 0.12). The parent compound CaFeAsF
undergoes a tetragonal to orthorhombic phase transition at 134(3) K, while the
magnetic order in form of a spin-density wave (SDW) sets in at 114(3) K. The
antiferromagnetic structure of the parent compound has been determined with a
unique propagation vector k = (1,0,1) and the Fe saturation moment of 0.49(5)uB
aligned along the long a-axis. With increasing Co doping, the long range
antiferromagnetic order has been observed to coexist with superconductivity in
the orthorhombic phase of the underdoped CaFe0.94Co0.06AsF with a reduced Fe
moment (0.15(5)uB). Magnetic order is completely suppressed in optimally doped
CaFe0.88Co0.12AsF. We argue that the coexistence of SDW and superconductivity
might be related to mesoscopic phase separation.",0811.4418v2
2008-12-31,Cosmic-ray driven dynamo in galactic disks,"We present new developments on the Cosmic--Ray driven, galactic dynamo,
modeled by means of direct, resistive CR--MHD simulations, performed with ZEUS
and PIERNIK codes. The dynamo action, leading to the amplification of
large--scale galactic magnetic fields on galactic rotation timescales, appears
as a result of galactic differential rotation, buoyancy of the cosmic ray
component and resistive dissipation of small--scale turbulent magnetic fields.
Our new results include demonstration of the global--galactic dynamo action
driven by Cosmic Rays supplied in supernova remnants. An essential outcome of
the new series of global galactic dynamo models is the equipartition of the gas
turbulent energy with magnetic field energy and cosmic ray energy, in saturated
states of the dynamo on large galactic scales.",0901.0111v1
2009-06-09,Partial ferromagnetic ordering and indirect exchange interaction in spatially anisotropic kagome antiferromagnet Cs_2Cu_3CeF_{12},"We report the crystal structure and unconventional magnetic ordering of
Cs_2Cu_3CeF_{12}, which is composed of buckled kagome lattice of Cu^{2+} ions.
The exchange network in the buckled kagome lattice is fairly anisotropic, so
that the present spin system can be divided into two subsystems: alternating
Heisenberg chains with strong antiferromagnetic exchange interactions and
dangling spins. Although the direct exchange interactions between neighboring
spins were found to be all antiferromagnetic, ferromagnetic magnetic ordering
of the dangling spins was observed. Magnetization exhibits a plateau at
one-third of the saturation magnetization. These observations can be understood
in terms of the indirect interaction between dangling spins mediated by the
chain spin.",0906.1628v2
2009-06-11,Magnetization study on the field-induced quantum critical point in YbRh_2Si_2,"We study the field-induced quantum critical point (QCP) in YbRh$_2$Si$_2$ by
low-temperature magnetization, $M(T)$, and magnetic Gr\""uneisen ratio,
$\Gamma_{\rm mag}$, measurements and compare the results with previous thermal
expansion, $\beta(T)$, and critical Gr\""uneisen ratio, $\Gamma^{cr}(T)$, data
on YbRh$_2$(Si$_{0.95}$Ge$_{0.05}$)$_2$. In the latter case, a slightly
negative chemical pressure has been used to tune the system towards its
zero-field QCP. The magnetization derivative $-dM/dT$ is far more singular than
thermal expansion, reflecting a strongly temperature dependent pressure
derivative of the field at constant entropy, $(dH/dP)_S=V_m\beta/(dM/dT)$
($V_m$: molar volume), which saturates at $(0.15\pm 0.04)$ T/GPa for $T\to 0$.
The line $T^\star(H)$, previously observed in Hall- and thermodynamic
measurements, separates regimes in $T$-$H$ phase space of stronger
$(\epsilon>1$) and weaker $(\epsilon<1$) divergent $\Gamma_{\rm mag}(T)\propto
T^{-\epsilon}$.",0906.2097v1
2009-07-02,Exploring the spin-1/2 frustrated square lattice model with high-field magnetization measurements,"We report on high-field magnetization measurements for a number of layered
vanadium phosphates that were recently recognized as spin-1/2 frustrated square
lattice compounds with ferromagnetic nearest-neighbor couplings (J_1) and
antiferromagnetic next-nearest-neighbor couplings (J_2). The saturation fields
of the materials lie in the range from 4 to 24 T and show excellent agreement
with the previous estimates of the exchange couplings deduced from low-field
thermodynamic measurements. The consistency of the high-field data with the
regular frustrated square lattice model provides experimental evidence for a
weak impact of spatial anisotropy on the nearest-neighbor couplings in layered
vanadium phosphates. The variation of the J_2/J_1 ratio within the compound
family facilitates the experimental access to the evolution of the
magnetization curve upon the change of the frustration magnitude. Our results
support the recent theoretical prediction by Thalmeier et al. [Phys. Rev. B,
77, 104441 (2008)] and give evidence for the enhanced bending of the
magnetization curves due to the increasing frustration of the underlying spin
system.",0907.0391v1
2009-10-28,Novel electronic and magnetic properties of BN sheet decorated with hydrogen and fluorine,"First principles calculations based on density functional theory reveal some
unusual properties of BN sheet functionalized with hydrogen and fluorine. These
properties differ from those of similarly functionalized graphene even though
both share the same honeycomb structure. (1) Unlike graphene which undergoes a
metal to insulator transition when fully hydrogenated, the band gap of the BN
sheet significantly narrows when fully saturated with hydrogen. Furthermore,
the band gap of the BN sheet can be tuned from 4.7 eV to 0.6 eV and the system
can be a direct or an indirect semiconductor or even a half-metal depending
upon surface coverage. (2) Unlike graphene, BN sheet has hetero-atomic
composition, when co-decorated with H and F, it can lead to anisotropic
structures with rich electronic and magnetic properties. (3) Unlike graphene,
BN sheets can be made ferromagnetic, antiferromagnetic, or magnetically
degenerate depending upon how the surface is functionalized. (4) The stability
of magnetic coupling of functionalized BN sheet can be further modulated by
applying external strain. Our study highlights the potential of functionalized
BN sheets for novel applications.",0910.5287v1
2009-11-11,Dilute-Bose-Gas Approach to ground state phases of 3D quantum helimagnets under high magnetic field,"We study high-field phase diagram and low-energy excitations of
three-dimensional quantum helimagnets. Slightly below the saturation field, the
emergence of magnetic order may be mathematically viewed as Bose-Einstein
condensation (BEC) of magnons. The method of dilute Bose gas enables an
unbiased quantitative analysis of quantum effects in three-dimensional
helimagnets and thereby three phases are found: cone, coplanar fan and an
attraction-dominant one. To investigate the last phase, we extend the usual BEC
approach so that we can handle 2-magnon bound states. In the case of 2-magnon
BEC, the transverse magnetization vanishes and long-range order occurs in the
quadrupolar channel (spin-nematic phase). As an application, we map out the
phase diagram of a 3D helimagnet which consists of frustrated J1-J2 chains
coupled by an interchain interaction J3.",0911.2186v2
2009-11-22,Structural and magnetic study of a dilute magnetic semiconductor: Fe doped CeO2 nanoparticles,"This paper reports the effect of Fe doping on the structure and room
temperature ferromagnetism of CeO2 nanoparticles. X-ray diffraction and
selective area electron diffraction measurement reflects that Ce1-xFexO2 (x =
0.0 - 0.07) nanoparticles exhibit single phase nature with cubic structure and
none of the sample showed the presence of any secondary phase. The mean
particle size calculated by using a transmission electron microscopy
measurement was found to increase with increase in Fe content. DC magnetization
measurements performed at room temperature indicates that all the samples
exhibit ferromagnetism. The saturation magnetic moment has been found to
increase with an increase in the Fe content.",0911.4225v1
2009-11-24,Magnetic properties and atomic structure of La(2/3)Ca(1/3)MnO(3)-YBa(2)Cu(3)O(7) heterointerfaces,"A heterostructure comprised of a 2.7 nm (7 unit-cell) thick layer of the
metallic ferromagnet La(2/3)Ca(1/3)MnO(3) and two 50 nm thick layers of the
high-temperature superconductor YBa(2)Cu(3)O(7) epitaxially grown on (100)
SrTiO3 by pulsed-laser deposition was characterized by magnetization
measurements and spherical-aberration-corrected high-resolution transmission
electron microscopy (HRTEM). The saturation magnetization is about half of that
in bulk La(2/3)Ca(1/3)MnO(3). A massive reduction of the magnetization
previously inferred from sputter-deposited La(2/3)Ca(1/3)MnO(3)-YBa(2)Cu(3)O(7)
heterostructures can be ruled out. HRTEM image analysis, combined with image
simulation and a focus series reconstruction, revealed atomically sharp
epitaxial structures with stacking sequences -(La,Ca)O-CuO2- and -BaO-MnO- at
the top and bottom interface.",0911.4606v1
2009-12-21,Magnetic Phase Transitions in NdCoAsO,"Magnetization measurements reveal that NdCoAsO undergoes three magnetic phase
transitions below room temperature. The crystal and magnetic structures of
NdCoAsO have been determined by powder neutron diffraction, and the effects of
the phase transitions on physical properties are reported. Near 69 K a
ferromagnetic state emerges with a small saturation moment of about 0.2 Bohr
magnetons, likely on Co atoms. At 14 K the material enters an antiferromagnetic
state with propagation vector (0 0 1/2) and small ordered moments (~0.4 Bohr
magnetons) on Co and Nd. Near 3.5 K a third transition is observed, and
corresponds to the antiferromagnetic ordering, with the same propagation
vector, of larger moments on Nd reaching 1.30(2) Bohr magnetons at 1.4 K. In
addition, transport properties and heat capacity results are presented, and
show anomalies at all three phase transitions.",0912.4237v2
2010-02-12,The Parker Scenario for Coronal Heating as an MHD Turbulence Problem,"The Parker or field line tangling model of coronal heating is investigated
through long-time high-resolution simulations of the dynamics of a coronal loop
in cartesian geometry within the framework of reduced magnetohydrodynamics
(RMHD). Slow photospheric motions induce a Poynting flux which saturates by
driving an anisotropic turbulent cascade dominated by magnetic energy and
characterized by current sheets elongated along the axial magnetic field.
Increasing the value of the axial magnetic field different regimes of MHD
turbulence develop with a bearing on coronal heating rates. In physical space
magnetic field lines at the scale of convection cells appear only slightly
bended in agreement with observations of large loops of current (E)UV and X-ray
imagers.",1002.2631v1
2010-03-11,Structural and Magnetic Properties of Nanosized Barium Hexaferrite Powders Obtained by Microemulsion Technique,"Thin hexagonal barium hexaferrite particles synthesized using the
microemulsion technique were studied. A water-in-oil reverse microemulsion
system with cetyltrimethylammonium bromide (CTAB) as a cationic surfactant,
n-butanol as a co-surfactant, n-hexanol as a continuous oil phase, and an
aqueous phase were used. The microstructural and magnetic properties were
investigated. The particles obtained were mono-domain with average particle
size 280 nm. The magnetic properties of the powder were investigated at 4.2 K
and at room temperature. The saturation magnetization was 48.86 emu/g and the
coercivity, 2.4 x 105 A/m at room temperature. The anisotropy field Ha and
magneto-crystalline anisotropy K1 were 1.4 x 106 A/m and 2.37 x 105 J/m3,
respectively.",1003.2276v1
2010-05-31,Driven weak to strong pinning crossover in partially nanopatterned 2H-NbSe2 single crystal,"Investigations into the heterogeneous pinning properties of the vortex state
created by partially nano-patterning single crystals of 2H-NbSe2 reveal an
atypical magnetization response which is significantly drive dependent.
Analysis of the magnetization response shows non-monotonic behavior of the
magnetization relaxation rate with varying magnetic field sweep rate. With all
the patterned pinning centers saturated with vortices, we find that the pinning
force experienced by the vortices continues to increase with increasing drive.
Our studies reveal an unconventional dynamic weak to strong pinning crossover
where the flow of the vortex state appears to be hindered or jammed as it is
driven harder through the interstitial voids in the patterned pinning lattice.",1005.5641v1
2010-05-31,New high magnetic field phase of the frustrated $S=1/2$ chain compound LiCuVO$_4$,"Magnetization of the frustrated $S=1/2$ chain compound LiCuVO$_4$, focusing
on high magnetic field phases, is reported. Besides a spin-flop transition and
the transition from a planar spiral to a spin modulated structure observed
recently, an additional transition was observed just below the saturation
field. This newly observed magnetic phase is considered as a spin nematic
phase, which was predicted theoretically but was not observed experimentally.
The critical fields of this phase and its dM/dH curve are in good agreement
with calculations performed in a microscopic model (M. E. Zhitomirsky and H.
Tsunetsugu, preprint, arXiv:1003.4096v2).",1005.5668v2
2010-06-08,Linear-Temperature Dependence of Static Magnetic Susceptibility in LaFeAsO from Dynamical Mean-Field Theory,"In this Letter we report the LDA+DMFT (method combining Local Density
Approximation with Dynamical Mean-Field Theory) results for magnetic properties
of parent superconductor LaFeAsO in paramagnetic phase. Calculated uniform
magnetic susceptibility shows linear dependence at intermediate temperatures in
agreement with experimental data. For high temperatures ($>$1000 K)
calculations show saturation and then susceptibility decreases with
temperature. Contributions to temperature dependence of the uniform
susceptibility are strongly orbitally dependent. It is related to the form of
the orbitally-resolved spectral functions near the Fermi energy with strong
temperature dependent narrow peaks for some of the orbitals. Our results
demonstrate that linear-temperature dependence of static magnetic
susceptibility in pnictide superconductors can be reproduced without invoking
antiferromagnetic fluctuations.",1006.1509v2
2010-06-29,Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study,"Microstrip ferromagnetic resonance and Brillouin scattering are used to
provide a comparative determination of the magnetic parameters of thin
permalloy layers interfaced with a non-magnetic (Al2O3) or with an
antiferromagnetic oxide (NiO). It is shown that the perpendicular anisotropy is
monitored by an interfacial surface energy term which is practically
independent of the nature of the interface. In the investigated interval of
thicknesses (5-25 nm) the saturation magnetisation does not significantly
differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy
and exchange-bias anisotropy are also derived from this study of the dynamic
magnetic excitations and compared to our independent evaluations using
conventional magnetometry",1006.5598v1
2010-09-06,Energy oscillations and a possible route to chaos in a modified Riga dynamo,"Starting from the present version of the Riga dynamo experiment with its
rotating magnetic eigenfield dominated by a single frequency we ask for those
modifications of this set-up that would allow for a non-trivial magnetic field
behaviour in the saturation regime. Assuming an increased ratio of azimuthal to
axial flow velocity, we obtain energy oscillations with a frequency below the
eigenfrequency of the magnetic field. These new oscillations are identified as
magneto-inertial waves that result from a slight imbalance of Lorentz and
inertial forces. Increasing the azimuthal velocity further, or increasing the
total magnetic Reynolds number, we find transitions to a chaotic behaviour of
the dynamo.",1009.1051v1
2010-09-14,Uncompensated magnetization and exchange-bias field in La$_{0.7}$Sr$_{0.3}$MnO$_3$/YMnO$_3$ bilayers: The influence of the ferromagnetic layer,"We studied the magnetic behavior of bilayers of multiferroic and nominally
antiferromagnetic o-YMnO$_3$ (375~nm thick) and ferromagnetic
La$_{0.7}$Sr$_{0.3}$MnO$_3$ and La$_{0.67}$Ca$_{0.33}$MnO$_3$ ($8 \ldots
225~$nm), in particular the vertical magnetization shift $M_E$ and exchange
bias field $H_E$ for different thickness and magnetic dilution of the
ferromagnetic layer at different temperatures and cooling fields. We have found
very large $M_E$ shifts equivalent to up to 100\% of the saturation value of
the o-YMO layer alone. The overall behavior indicates that the properties of
the ferromagnetic layer contribute substantially to the $M_E$ shift and that
this does not correlate straightforwardly with the measured exchange bias field
$H_E$.",1009.2619v1
2010-11-29,Lagrangian coherent structures in nonlinear dynamos,"Turbulence and chaos play a fundamental role in stellar convective zones
through the transportof particles, energy and momentum, and in fast dynamos,
through the stretching, twisting and folding of magnetic flux tubes. A
particularly revealing way to describe turbulent motions is through the
analysis of Lagrangian coherent structures (LCS), which are material lines or
surfaces that act as transport barriers in the fluid. We report the detection
of Lagrangian coherent structures in helical MHD dynamo simulations with scale
separation. In an ABC--flow, two dynamo regimes, a propagating coherent
mean--field regime and an intermittent regime, are identified as the magnetic
diffusivity is varied. The sharp contrast between the chaotic tangle of
attracting and repelling LCS in both regimes permits a unique analysis of the
impact of the magnetic field on the velocity field. In a second example, LCS
reveal the link between the level of chaotic mixing of the velocity field and
the saturation of a large--scale dynamo when the magnetic field exceeds the
equipartition value.",1011.6327v2
2010-12-13,Three-Dimensional Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. II. Relaxation of Pulsar Wind Nebula,"We have investigated the relaxation of a hydrostatic hot plasma column
containing toroidal magnetic field by the Current-Driven (CD) kink instability
as a model of pulsar wind nebulae. In our simulations the CD kink instability
is excited by a small initial velocity perturbation and develops turbulent
structure inside the hot plasma column. We demonstrate that, as envisioned by
Begelman, the hoop stress declines and the initial gas pressure excess near the
axis decreases. The magnetization parameter \sigma, the ratio of the Poynting
to the kinetic energy flux, declines from an initial value of 0.3 to about 0.01
when the CD kink instability saturates. Our simulations demonstrate that
axisymmetric models strongly overestimate the elongation of the pulsar wind
nebulae. Therefore, the previous requirement for an extremely low pulsar wind
magnetization can be abandoned. The observed structure of the pulsar wind
nebulae do not contradict the natural assumption that the magnetic energy flux
still remains a good fraction of the total energy flux after dissipation of
alternating fields.",1012.2770v1
2011-01-11,Solving relativistic hydrodynamic equation in presence of magnetic field for phase transition in a neutron star,"Hadronic to quark matter phase transition may occur inside neutron stars (NS)
having central densities of the order of 3-10 times normal nuclear matter
saturation density ($n_0$). The transition is expected to be a two-step
process; transition from hadronic to 2-flavour matter and two-flavour to
$\beta$ equilibrated charge neutral three-flavour matter. In this paper we
concentrate on the first step process and solve the relativistic hydrodynamic
equations for the conversion front in presence of high magnetic field. Lorentz
force due to magnetic field is included in the energy momentum tensor by
averaging over the polar angles. We find that for an initial dipole
configuration of the magnetic field with a sufficiently high value at the
surface, velocity of the front increases considerably.",1101.2030v3
2011-02-13,Kagome Approximation for 3He on Husimi Lattice with Two- and Three-Site Exchange Interactions,"The Ising approximation of the Heisenberg model in a strong magnetic field,
with two-, and three-spin exchange interactions are studied on a Husimi
lattice. This model can be considered as an approximation of the third layer of
3He absorbed on the surface of graphite (kagome lattice). Using dynamic
approach we have found exact recursion relation for the partition function. For
different values of exchange parameters and temperature the diagrams of
magnetization are plotted and showed that magnetization properties of the model
vary from ferromagnetic to antiferromagnetic depending from the value of model
parameters. For antiferromagnetic case magnetization plateau at 1/3 of
saturation field is obtained. Lyapunov exponent for recursion relation are
considered and showed absents of bifurcation points in thermodynamic limit. The
Yang-Lee zeros are analyzed in terms of neutral fixed points and showed that
Yang-Lee zeros of the model are located on the arcs of the circle with the
radius R=1.",1102.2607v1
2011-04-28,Buneman instability in a magnetized current-carrying plasma with velocity shear,"Buneman instability is often driven in magnetic reconnection. Understanding
how velocity shear in the beams driving the Buneman instability affects the
growth and saturation of waves is relevant to turbulence, heating, and
diffusion in magnetic reconnection. Using a Mathieu-equation analysis for weak
cosine velocity shear together with Vlasov simulations, the effects of shear on
the kinetic Buneman instability are studied in a plasma consisting of strongly
magnetized electrons and cold unmagnetized ions. In the linearly unstable
phase, shear enhances the coupling between oblique waves and the sheared
electron beam, resulting in a wider range of unstable eigenmodes with common
lower growth rates. The wave couplings generate new features of the electric
fields in space, which can persist into the nonlinear phase when electron holes
form. Lower hybrid instabilities simultaneously occur at
$k_{\shortparallel}/k_{\perp} \sim \sqrt{m_e/m_i}$ with a much lower growth
rate, and are not affected by the velocity shear.",1104.5283v2
2011-06-07,Effect of Zn substitution on morphology and magnetic properties of copper ferrite nanofibers,"Spinel ferrite Cu1-xZnxFe2O4 nanofibers over a compositional range 0 < x < 1
were prepared by electrospinning combined with sol-gel method. The influence of
Zn2+ ions substitution on morphology, structure, and magnetic properties of
copper ferrite has been investigated. The results show that surface of CuFe2O4
nanofibers consists of small open porosity, while surface of doped nanofibers
reveals smooth and densified nature. With increasing Zn substitution,
saturation magnetization initially increases and then decreases with a maximum
value of 58.4 emu/g at x = 0.4, coercivity and square ratio all decrease. The
influence of substitution on magnetic properties is related with the cation
distraction and exchange interactions between spinel lattices.",1106.1269v1
2011-06-17,Magnetic susceptibility of Ce: an LDA+DMFT study,"The magnetic properties of Ce in the $\alpha$ and $\gamma$ phase are
calculated within the LDA+DMFT approach. The magnetic susceptibility in these
two phases shows a similar behavior over a wide temperature range: a
Curie-Weiss law at high temperatures, indicating the presence of local moments,
followed by a maximum in a crossover regime, and a saturation characteristic of
a state with screened local moments at low temperature. The difference in
experimentally observable magnetic properties is caused by the shift of the
susceptibility to higher temperatures in the $\alpha-$phase compared to the
$\gamma-$phase, due to the larger hybridization between localized $4f-$states
and conductive $spd-$electrons.",1106.3470v2
2011-06-24,Hydrogen-induced ferromagnetism in ZnO single crystals investigated by Magnetotransport,"We investigated the electrical and magnetic properties of low-energy
hydrogen-implanted ZnO single crystals with hydrogen concentrations up to 3
at.% in the first 20 nm surface layer between 10 K and 300 K. All samples
showed clear ferromagnetic hysteresis loops at 300 K with a saturation
magnetization up to 4 emu/g. The measured anomalous Hall effect agrees with the
hysteresis loops measured by superconducting quantum interferometer device
magnetometry. All the H-treated ZnO crystals exhibited a negative
magnetoresistance up to the room temperature. The relative magnitude of the
anisotropic magnetoresistance reaches 0.4 % at 250 K and 2 % at 10 K,
exhibiting an anomalous, non-monotonous behavior and a change of sign below 100
K. All the experimental data indicate that hydrogen atoms alone in a few
percent range trigger a magnetic order in a ZnO crystalline state. Hydrogen
implantation turns out to be a simpler and effective method to generate a
magnetic order in ZnO, which provides interesting possibilities for future
applications due to the strong reduction of the electrical resistance.",1106.4951v1
2011-07-12,Magnetic and electric dipole moments of the $H\ {}^3Δ_1$ state in ThO,"The metastable $H \ {}^3\Delta_1$ state in the thorium monoxide (ThO)
molecule is highly sensitive to the presence of a CP-violating permanent
electric dipole moment of the electron (eEDM). The magnetic dipole moment
$\mu_H$ and the molecule-fixed electric dipole moment $D_H$ of this state are
measured in preparation for a search for the eEDM. The small magnetic moment
$\mu_H = 8.5(5) \times 10^{-3} \ \mu_B$ displays the predicted cancellation of
spin and orbital contributions in a ${}^3 \Delta_1$ paramagnetic molecular
state, providing a significant advantage for the suppression of magnetic field
noise and related systematic effects in the eEDM search. In addition, the
induced electric dipole moment is shown to be fully saturated in very modest
electric fields ($<$ 10 V/cm). This feature is favorable for the suppression of
many other potential systematic errors in the ThO eEDM search experiment.",1107.2287v1
2011-07-29,Ferrimagnetism and spontaneous ordering of transition-metals in La2CrFeO6 double-perovskite films,"We report on atomic ordering of B-site transition-metals and magnetic
properties of epitaxial La2CrFeO6 double-perovskite films grown by pulsed-laser
deposition under various conditions. The highest ordered sample exhibited a
fraction of antisite-disorder of only 0.05 and a saturation magnetization of
~2\mu_{B} per formula unit at 5 K. The result is consistent with the
antiferromagnetic ordering of local spin moment
(3d^{3}_{\downarrow}3d^{5}_{\uparrow}; S = -3/2+5/2 = 1). Therefore, the
magnetic ground state of La2CrFeO6 double-perovskite that has been long debate
is unambiguously revealed to be ferrimagnetic. Our results present a wide
opportunity to explore novel magnetic properties of binary transition-metal
perovskites upon epitaxial stabilization of the ordered phase.",1107.5891v1
2011-09-14,Antiferromagnetic coupling across silicon regulated by tunneling currents,"We report on the enhancement of antiferromagnetic coupling in epitaxial
Fe/Si/Fe structures by voltage-driven spin-polarized tunneling currents. Using
the ballistic electron magnetic microscopy we established that the hot-electron
collector current reflects magnetization alignment and the magnetocurrent
exceeds 200% at room temperature. The saturation magnetic field for collector
current corresponding to parallel alignment of magnetizations rises up with the
tunneling current, thus demonstrating stabilization of the antiparallel
alignment and increasing antiferromagnetic coupling. We connect the enhancement
of antiferromagnetic coupling with local dynamic spin torques mediated by
tunneling electrons",1109.3106v1
2012-01-04,Quasiparticles of string solutions in the spin-1/2 antiferromagnetic Heisenberg chain in a magnetic field,"Spectral properties of the spin-1/2 antiferromagnetic Heisenberg chain in a
magnetic field are investigated by using exact Bethe-ansatz solutions. We argue
that not only quasiparticles called psinon and antipsinon but also a
quasiparticle representing a 2-string in the Bethe ansatz plays an important
role for dynamical properties in a magnetic field. Combined with psinon and
antipsinon, the quasiparticle for a 2-string forms a continuum in the
high-energy regime for transverse dynamical structure factor
$S^{+-}(k,\omega)$. In the zero-field limit, the continuum is located on the
mode of the lowest excited states in zero field called the des
Cloizeaux-Pearson mode. In a magnetic field, the continuum separates from other
low-energy continua, and reduces to the mode of bound states of overturned
spins from the fully polarized state near the saturation field. We confirm the
relevance through comparisons with available experimental results on the
quasi-one-dimensional antiferromagnet CuCl$_2\cdot$2N(C$_5$D$_5$).",1201.0844v1
2012-08-15,Current-induced synchronized switching of magnetization,"We investigate current-induced magnetization switching for a multilayer
structure that allows a reduced switching current while maintaining high
thermal stability of the magnetization. The structure consists of a
perpendicular polarizer, a perpendicular free-layer, and an additional
free-layer having in-plane magnetization. When the current runs perpendicular
to the structure, the in-plane free-layer undergoes a precession and supplies
an internal rf field to the perpendicular free-layer, resulting in a reduced
switching current for one current polarity. For the other polarity, the
in-plane free-layer almost saturates perpendicular to the plane and acts as
another perpendicular polarizer, which also reduces the switching current.",1208.3050v1
2012-09-12,Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements,"We determine experimentally the spin structure of half-metallic
Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following
magnetic saturation, the dominant magnetic states consist of quasi-uniform
configurations, where a strong influence from the magnetocrystalline anisotropy
is visible. Heating experiments show the stability of the spin configuration of
domain walls in confined geometries up to 800 K. The switching temperature for
the transition from transverse to vortex walls in ring elements is found to
increase with ring width, an effect attributed to structural changes and
consequent changes in magnetic anisotropy, which start to occur in the narrower
elements at lower temperatures.",1209.2702v1
2012-09-24,Theory of magnetic enhancement in strontium hexaferrite through Zn-Sn pair substitution,"We study the site occupancy and magnetic properties of Zn-Sn substituted
M-type Sr-hexaferrite SrFe$_{12-x}$(Zn$_{0.5}$Sn$_{0.5}$)$_x$O$_{19}$ with x =
1 using first-principles total-energy calculations. We find that in a
ground-state configuration Zn-Sn ions preferentially occupy $4f_1$ and $4f_2$
sites unlike the model previously suggested by Ghasemi et al. [J. Appl. Phys,
\textbf{107}, 09A734 (2010)], where Zn$^{2+}$ and Sn$^{4+}$ ions occupy the
$2b$ and $4f_2$ sites. Density-functional theory calculations show that our
model has a lower total energy by more than 0.2 eV per unit cell compared to
Ghasemi's model. More importantly, the latter does not show an increase in
saturation magnetization ($M_s$) compared to the pure $M$-type Sr-hexaferrite,
in disagreement with the experiment. On the other hand, our model correctly
predicts a rapid increase in $M_s$ as well as a decrease in magnetic anisotropy
compared to the pure $M$-type Sr-hexaferrite, consistent with experimental
measurements.",1209.5143v2
2012-10-16,High temperature magnetic insulating phase in ultrathin La0.67Sr0.33MnO3 films,"We present a study of the thickness dependence of magnetism and electrical
conductivity in ultra thin La0.67Sr0.33MnO3 films grown on SrTiO3 (110)
substrates. We found a critical thickness of 10 unit cells below which the
conductivity of the films disappeared and simultaneously the Curie temperature
(TC) increased, indicating a magnetic insulating phase at room temperature.
These samples have a TC of about 560 K with a significant saturation
magnetization of 1.2 +- 0.2 muB/Mn. The canted antiferromagnetic insulating
phase in ultra thin films of n< 10 coincides with the occurrence of a higher
symmetry structural phase with a different oxygen octahedra rotation pattern.
Such a strain engineered phase is an interesting candidate for an insulating
tunneling barrier in room temperature spin polarized tunneling devices.",1210.4435v1
2012-11-11,Perpendicularly magnetized Mn-Co-Ga-based thin films with high coercive field,"Mn$_{3-x}$Co$_{x}$Ga epitaxial thin films were grown on MgO substrates by
magnetron co-sputtering. Structures were tetragonal or cubic depending on Co
content. Composition dependence of saturation magnetization and uniaxial
magnetic anisotropy $K_u$ of the films were investigated. A high $K_u$ (1.2 MJ
m$^{-3}$) was achieved for the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film with the
magnetic moment 0.84$\mu_B$. Valence band spectra were obtained by hard X-ray
photoelectron spectroscopy. Sharp peaks in the cubic case, which were absent in
the tetragonal case, prove that a van Hove singularity causes a band
Jahn-Teller effect with tetragonal distortion. Observations agree well with the
first-principles calculations.",1211.2440v1
2013-01-02,Fast collisionless reconnection and electron heating in strongly magnetized plasmas,"Magnetic reconnection in strongly magnetized (low-beta), weakly collisional
plasmas is investigated using a novel fluid-kinetic model [Zocco &
Schekochihin, Phys. Plasmas 18, 102309 (2011)] which retains non-isothermal
electron kinetics. It is shown that electron heating via Landau damping (linear
phase mixing) is the dominant dissipation mechanism. In time, electron heating
occurs after the peak of the reconnection rate; in space, it is concentrated
along the separatrices of the magnetic island. For sufficiently large systems,
the peak reconnection rate is $cE_{max}\approx 0.2v_AB_{y,0}$, where $v_A$ is
the Alfv\'en speed based on the reconnecting field $B_{y,0}$. The island
saturation width is the same as in MHD models except for small systems, when it
becomes comparable to the kinetic scales.",1301.0338v1
2013-02-03,Effects of Strong Interactions in a Half Metallic Magnet: a Determinant Quantum Monte Carlo Study,"Understanding the effects of electron-electron interactions in half metallic
magnets (HMs), which have band structures with one gapped spin channel and one
metallic channel, poses fundamental theoretical issues as well as having
importance for their potential applications. Here we use determinant quantum
Monte Carlo to study the impacts of an on-site Hubbard interaction $U$, finite
temperature, and an external (Zeeman) magnetic field on a bilayer tight-binding
model which is a half-metal in the absence of interactions, by calculating the
spectral density, conductivity, spin polarization of carriers, and local
magnetic properties. We quantify the effect of $U$ on the degree of thermal
depolarization, and follow relative band shifts and monitor when significant
gap states appear, each of which can degrade the HM character. For this model,
Zeeman coupling induces, at fixed particle number, two successive transitions:
compensated half-metal with spin-down band gap $\rightarrow$ metallic
ferromagnet $\rightarrow$ saturated ferromagnetic insulator. However, over much
of the more relevant parameter regime, the half-metallic properties are rather
robust to $U$.",1302.0550v1
2013-02-26,R-M interactions in R2BaMO5 (R=Y or Gd and M=Cu or Zn),"R2BaMO5 (R = Gd, Y and M = Cu, Zn) oxides have been studied by specific heat,
dc magnetic susceptibility, and electron paramagnetic resonance (EPR). For one
member of the series without magnetic moment at M, namely Gd2BaZnO5,
measurements reveal long range antiferromagnetic order at TN(Gd2BaZnO5) =
2.3(0.1)K, much lower than the Curie Weiss temperature of {\Theta}=15.9(0.3)K.
This indicates the existence of competing interactions that introduce a large
degree of magnetic frustration in the system. For Y2BaCuO5 the Cu Cu
interactions are responsible for the broad maximum in the magnetic contribution
to the specific heat centered at 18.5(0.01)K that stretches beyond the
instrumental limit of 25K. The strong Cu Cu interactions also present in
Gd2BaCuO5, combined with the Gd-Cu interaction, polarize the Gd sublattice
giving measurable contributions to the specific heat in the same temperature
range. In addition, they broaden the Gd EPR line and saturate its integrated
intensity. The ordering temperature of Gd ions is raised to
TN(Gd2BaCuO5)=12.0(0.1)K.",1302.6327v1
2013-05-03,Non-resonant magnetohydrodynamics streaming instability near magnetized relativistic shocks,"We present in this paper both a linear study and numerical relativistic MHD
simulations of the non-resonant streaming instability occurring in the
precursor of relativistic shocks. In the shock front restframe, we perform a
linear analysis of this instability in a likely configuration for
ultra-relativistic shock precursors. This considers magneto-acoustic waves
having a wave vector perpendicular to the shock front and the large scale
magnetic field. Our linear analysis is achieved without any assumption on the
shock velocity and is thus valid for all velocity regimes. In order to check
our calculation, we also perform relativistic MHD simulations describing the
propagation of the aforementioned magneto-acoustic waves through the shock
precursor. The numerical calculations confirm our linear analysis, which
predicts that the growth rate of the instability is maximal for
ultra-relativistic shocks and exhibits a wavenumber dependence $\propto
k_x^{1/2}$. Our numerical simulations also depict the saturation regime of the
instability where we show that the magnetic amplification is moderate but
nevertheless significant ($\delta B/B\leq 10$). This latter fact may explain
the presence of strong turbulence in the vicinity of relativistic magnetized
shocks. Our numerical approach also introduces a convenient means to handle
isothermal (ultra-)relativistic MHD conditions.",1305.0847v1
2013-05-21,Contrasting behavior of the structural and magnetic properties in Mn- and Fe-doped In$_2$O$_3$ films,"We have observed room temperature ferromagnetism (FM) in In$_2$O$_3$ thin
films doped with either 5 at.% Mn or Fe, prepared by pulsed laser deposition
(PLD) at substrate temperatures ranging from 300 to 600$\,^{\circ}{\rm C}$. The
dependence of saturation magnetization on grain size was investigated for both
types of In$_2$O$_3$ films. It is revealed that, for the Mn-doped films, the
magnetization was largest with small grains, indicating the importance of grain
boundaries. In contrast, for Fe-doped films, the largest magnetization was
observed with large grains.",1305.4831v1
2013-10-04,Driven isotropic Heisenberg spin chain with arbitrary boundary twisting angle: exact results,"We consider an open isotropic Heisenberg quantum spin chain, coupled at the
ends to boundary reservoirs polarized in different directions, which sets up a
twisting gradient across the chain. Using a matrix product ansatz, we calculate
the exact magnetization profiles and magnetization currents in the
nonequilibrium steady steady state of a chain with N sites. The magnetization
profiles are harmonic functions with a frequency proportional to the twisting
angle {\theta}. The currents of the magnetization components lying in the
twisting plane and in the orthogonal direction behave qualitatively
differently: In-plane steady state currents scale as 1/N^2 for fixed and
sufficiently large boundary coupling, and vanish as the coupling increases,
while the transversal current increases with the coupling and saturates to
2{\theta}/N.",1310.1315v2
2014-02-18,Switching Properties in Magnetic Tunnel Junctions with Interfacial Perpendicular Anisotropy: Micromagnetic Study,"The role of universal memory can be successfully satisfied by magnetic tunnel
junctions (MTJs) where the writing mechanism is based on spin-transfer torque
(STT). An improvement in the switching properties (lower switching current
density maintaining the thermal stability) has been achieved in MTJs with
interfacial perpendicular anisotropy (IPA) at the interface between CoFeB and
MgO. In this paper, micromagnetic simulations point out the influence of IPA
and saturation magnetization (MS) on the properties of fast magnetization
reversal achieved in 5, 10 and 20 ns. Both cases of in-plane and out-of-plane
free layer are considered. In addition, the thermal effect is included for the
in-plane switching at 20 ns and a complete analysis of energy dissipation
during the switching is illustrated. This study can provide useful information
for the design of STT-based memories.",1402.4352v1
2014-03-20,Magnetization Process of the S=1/2 Heisenberg Antiferromagnet on the Cairo Pentagon Lattice,"We study the S=1/2 Heisenberg antiferromagnet on the Cairo pentagon lattice
by the numerical-diagonalization method. We tune the ratio of two
antiferromagnetic interactions coming from two kinds of inequivalent sites in
this lattice, examining the magnetization process of the antiferromagnet;
particular attention is given to one-third of the height of the saturation. We
find that quantum phase transition occurs at a specific ratio and that a
magnetization plateau appears in the vicinity of the transition. The plateau is
accompanied by a magnetization jump on one side among the edges due to the
spin-flop phenomenon. Which side the jump appears depends on the ratio.",1403.5008v1
2014-04-02,Mechanical magnetometry of Cobalt nanospheres deposited by focused electron beam at the tip of ultra-soft cantilevers,"Using focused-electron-beam-induced deposition, Cobalt magnetic nanospheres
with diameter ranging between 100 nm and 300 nm are grown at the tip of
ultra-soft cantilevers. By monitoring the mechanical resonance frequency of the
cantilever as a function of the applied magnetic field, the hysteresis curve of
these individual nanospheres are measured. This enables to evaluate their
saturation magnetization, found to be around 430 emu/cm^3 independently of the
size of the particle, and to infer that the magnetic vortex state is the
equilibrium configuration of these nanospheres at remanence.",1404.0492v1
2014-04-03,Magnetic Field Tunable Small-scale Mechanical Properties of Nickel Single Crystals Measured by Nanoindentation Technique,"Nano- and micromagnetic materials have been extensively employed in
micro-functional devices. However, measuring small-scale mechanical and
magnetomechanical properties is challenging, which restricts the design of new
products and the performance of smart devices. A new magnetomechanical
nanoindentation technique is developed and tested on a nickel single crystal in
the absence and presence of a saturated magnetic field. Small-scale parameters
such as Young's modulus, indentation hardness, and plastic index are dependent
on the applied magnetic field, which differ greatly from their macroscale
counterparts. Possible mechanisms that induced 31% increase in modulus and 7%
reduction in hardness (i.e., the flexomagnetic effect and the interaction
between dislocations andmagnetic field, respectively) are analyzed and
discussed. Results could be useful in the microminiaturization of applications,
such as tunable mechanical resonators and magnetic field sensors.",1404.0884v1
2014-07-05,Atomistic modeling of magnetization reversal modes in $L1_{0}$ FePt nanodots with magnetically soft edges,"Nanopatterned FePt nano-dots often exhibit low coercivity and a broad
switching field distribution, which could arise due to edge damage during the
patterning process causing a reduction in the $L1_{0}$ ordering required for a
high magnetocrystalline anisotropy. Using an atomistic spin model, we study the
magnetization reversal behavior of $L1_{0}$ FePt nanodots with soft magnetic
edges. We show that reversal is initiated by nucleation for the whole range of
edge widths studied. For narrow soft edges the individual nucleation events
dominate reversal; for wider edges, multiple nucleation at the edge creates a
circular domain wall at the interface which precedes complete reversal. Our
simulations compare well with available analytical theories. The increased edge
width further reduces and saturates the required nucleation field. The
nucleation field and the activation volume manipulate the thermally induced
switching field distribution. By control of the properties of dot edges using
proper patterning methods, it should be possible to realize exchange spring bit
patterned media without additional soft layers.",1407.1363v2
2014-07-17,Nonlinear mirror instability,"Slow dynamical changes in magnetic-field strength and invariance of the
particles' magnetic moments generate ubiquitous pressure anisotropies in weakly
collisional, magnetized astrophysical plasmas. This renders them unstable to
fast, small-scale mirror and firehose instabilities, which are capable of
exerting feedback on the macroscale dynamics of the system. By way of a new
asymptotic theory of the early nonlinear evolution of the mirror instability in
a plasma subject to slow shearing or compression, we show that the instability
does not saturate quasilinearly at a steady, low-amplitude level. Instead, the
trapping of particles in small-scale mirrors leads to nonlinear secular growth
of magnetic perturbations, $\delta B/B \propto t^{2/3}$. Our theory explains
recent collisionless simulation results, provides a prediction of the mirror
evolution in weakly collisional plasmas and establishes a foundation for a
theory of nonlinear mirror dynamics with trapping, valid up to $\delta B/B
=O(1)$.",1407.4707v1
2014-07-23,Effect of Eu magnetism on the electronic properties of the candidate Dirac material EuMnBi2,"The crystal structure and physical properties of the layered material EuMnBi2
have been characterized by measurements on single crystals. EuMnBi2 is
isostructural with the Dirac material SrMnBi2 based on single crystal x-ray
diffraction, crystallizing in the I4/mmm space group (No. 139). Magnetic
susceptibility measurements suggest antiferromagnetic (AFM) ordering of moments
on divalent Eu ions near T_N=22K. For low fields, the ordered Eu moments are
aligned along the c-axis, and a spin-flop is observed near 5.4T at 5K. The
moment is not saturated in an applied field of 13T at 5K, which is uncommon for
compounds containing Eu^{2+}. The magnetic behavior suggests an anisotropy
enhancement via interaction between Eu and the Mn moments that appear to be
order antiferromagnetically below approximately 310K. A large increase in the
magnetoresistance is observed across the spin-flop, with absolute
magnetoresistance reaching approximately 650% at 5K and 12T. Hall effect
measurements reveal a decrease in the carrier density below T_N, which implies
a manipulation of the Fermi surface by magnetism on the sites surrounding the
Bi square nets that lead to Dirac cones in this family of materials.",1407.6203v1
2014-10-03,Unexpected impact of magnetic disorder on multiband superconductivity,"We analyze how the magnetic disorder affects the properties of the two-band
$s_\pm$ and $s_{++}$ models, which are subject of hot discussions regarding
iron-based superconductors and other multiband systems like MgB$_2$. We show
that there are several cases when the transition temperature $T_c$ is not fully
suppressed by magnetic impurities in contrast to the Abrikosov-Gor'kov theory,
but a saturation of $T_c$ takes place in the regime of strong disorder. These
cases are: (1) the purely interband impurity scattering, (2) the unitary
scattering limit. We show that in the former case the $s_\pm$ gap is preserved,
while the $s_{++}$ state transforms into the $s_\pm$ state with increasing
magnetic disorder. For the case (2), the gap structure remains intact.",1410.0832v2
2014-10-30,Magnetoresistance of layered conductors under conditions of topological phase transition,"The resistance of layered conductors with a multisheet Fermi surface (FS), in
a high magnetic field, in the immediate vicinity of Lifshic's topological
transition when the separate FS sheets are drown together by an external
action, pressure in part (and eventual change of the FS connectivity) is
studied theoretically. Analysis of magnetoresistance near topological
transition is illustrated for the case of FS in the shape of lightly corrugated
cylinder and two corrugated planes distributed with a repeated period in the
pulse space. It yields, that as the FS plane sheets approach sufficiently the
cylinder, the charge carriers produce a magnetic breakdown of one FS sheet to
another, decreasing a sharp anisotropy of magnetoresistance to the in-plane
current. Instead of square increase with a magnetic field, the slower
resistance growth remains linear in the field within a broad magnetic-field
range. In the intimate vicinity of topological transition, when the energy gap
between FS layers is negligibly small, the resistance is saturated.",1410.8330v1
2014-12-26,Topological Order Parameters of the Spin-1/2 Dimerized Heisenberg Ladder in Magnetic Field,"Topological properties of the spin-1/2 dimerized Heisenberg ladder are
investigated focusing on the plateau phase in the magnetic field whose
magnetization is half of the saturation value. Although the applied magnetic
field removes most of the symmetries of the system, there is a symmetry
protected topological phase supported by the spatial inversion symmetry. The
Z_2 Berry phase associated with a symmetry respecting boundary and quantized
into 0 and \pi is used as a symmetry protected topological order parameter.
Edge states are also analyzed to confirm the bulk-edge correspondence. In
addition, a symmetry breaking boundary is considered. Then, we observe a unique
type of quantization of the Berry phase, a quantization into +-\pi/2 of the
Berry phase. In this case, the bulk-edge correspondence is also unique, namely,
there emerge ""polarized"" edge states for the case with +-\pi/2 quantization. We
also evaluate the entanglement entropy by the infinite time-evolving block
decimation (iTEBD) to complement the Berry phase based arguments. Further, a
different type of the topological order parameter is extracted from the matrix
product state representation of the ground state given by the iTEBD.",1412.7901v2
2015-01-19,Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$,"We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler
alloy Ni$_{50}$Mn$_{35}$In$_{15}$ by direct measurements in pulsed magnetic
fields up to 6 and 20 T. The results in 6 T are compared with data obtained
from heat-capacity experiments. We find a saturation of the inverse MCE,
related to the first-order martensitic transition, with a maximum adiabatic
temperature change of $\Delta T_{ad} = -7$ K at 250 K and a conventional
field-dependent MCE near the second-order ferromagnetic transition in the
austenitic phase. The pulsed magnetic field data allow for an analysis of the
temperature response of the sample to the magnetic field on a time scale of
$\sim 10$ to 100 ms which is on the order of typical operation frequencies (10
to 100 Hz) of magnetocaloric cooling devices. Our results disclose that in
shape-memory alloys the different contributions to the MCE and hysteresis
effects around the martensitic transition have to be carefully considered for
future cooling applications.",1501.04430v1
2015-02-20,Magnetic and Dielectric Properties of Multiferroic BiFeO3 Nanoparticles Synthesized by a Novel Citrate Combustion Method,"Single phase BiFeO3 nanoparticles have been successfully synthesized for the
first time by a novel citrate combustion method without using any solvent. Well
mixed metal nitrates along with citric acid which is used as fuel combust to
give BiFeO3 nanoparticles after annealing. These particles are single phase in
nature and crystallize in the rhombohedral distorted perovskite structure
(space group-R3c) which has been confirmed by the Rietveld refinement of the
room temperature powder x-ray diffraction data. Nearly spherical particles of
average particle size 47 nm have been seen from transmission electron
micrograph. Room temperature magnetic hysteresis measurement shows weak
ferromagnetism though the magnetization does not saturate upto 1.75 T applied
field. The coercive field value is calculated to be 180 Oe which is 3 times
higher than that prepared by solvent free combustion method using Glycine. 57Fe
M\""ossbauer spectrum can be fitted with a sextet corresponding to single
magnetic state of hyperfine field about 49.5 T corresponding to Fe3+ state of
the iron atom. The dielectric relaxation and ac conductivity as a function of
frequency have been discussed. High dielectric permittivity has not been found
in these nanoparticles like other reported BiFeO3 ceramics.",1502.05797v1
2015-04-09,Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates,"In this study we investigate magnetic properties, surface morphology and
crystal structure in iron nanoclusters electrodeposited on lightly-doped (100)
n-type silicon substrates. Our goal is to investigate the spin injection and
detection in the Fe/Si lateral structures. The samples obtained under electric
percolation were characterized by magnetoresistive and magnetic resonance
measurements with cycling the sweeping applied field in order to understand the
spin dynamics in the as-produced samples. The observed hysteresis in the
magnetic resonance spectra, plus the presence of a broad peak in the
non-saturated regime confirming the low field microwave absorption (LFMA), were
correlated to the peaks and slopes found in the magnetoresistance curves. The
results suggest long range spin injection and detection in low resistive
silicon and the magnetic resonance technique is herein introduced as a
promising tool for analysis of electric contactless magnetoresistive samples.",1504.02508v1
2015-05-28,Steady shear magnetorheology in Co0.9Ni0.1 nanocluster-based MR fluids at elevated temperatures,"In this paper, we present the study of magnetorheological properties of
magnetic fluids containing Co0.9Ni0.1 nanocluster that have been measured as a
function of both magnetic field and temperature. Co-rich nanoclusters were
synthesized by conventional homogeneous nucleation in liquid polyol.
Morphological characterization using FESEM revealed the non-aggregated nature
of nanoclusters with an average diameter of 450 nm. Crystal structure and room
temperature magnetization measurements were performed by powder XRD and
vibrating sample magnetometry (VSM). Two MR samples of different particle
volume fractions were prepared. Temperature-dependent steady shear MR
characterizations for both the samples in the range of 250C-550C demonstrated
systematic decline of MR parameters with increasing temperatures. The
temperature-induced thinning of shear stress and viscosity was explained in
terms of change in effective volume fraction and magnetic saturation. To
analyze the measured variation in MR response with increasing temperature,
suitable temperature-sensitive scaling parameters were also constructed.
Finally to generalize the trend, rheological master curves were constructed by
using time-temperature-field superposition method.",1505.07567v1
2015-07-11,Coherent nonhelical shear dynamos driven by magnetic fluctuations at low Reynolds numbers,"Nonhelical shear dynamos are studied with a particular focus on the
possibility of coherent dynamo action. The primary results -- serving as a
follow up to the results of Squire & Bhattacharjee [arXiv:1506.04109 (2015)] --
pertain to the ""magnetic shear-current effect"" as a viable mechanism to drive
large-scale magnetic field generation. This effect raises the interesting
possibility that the saturated state of the small-scale dynamo could drive
large-scale dynamo action, and is likely to be important in the unstratified
regions of accretion disk turbulence. In this paper, the effect is studied at
low Reynolds numbers, removing the complications of small-scale dynamo
excitation and aiding analysis by enabling the use of quasi-linear statistical
simulation methods. In addition to the magnetically driven dynamo, new results
on the kinematic nonhelical shear dynamo are presented. These illustrate the
relationship between coherent and incoherent driving in such dynamos,
demonstrating the importance of rotation in determining the relative dominance
of each mechanism.",1507.03154v1
2015-08-04,Acoustic signatures of the phases and phase transitions in Yb$_2$Ti$_2$O$_7$,"We report on measurements of the sound velocity and attenuation in a single
crystal of the candidate quantum- spin-ice material Yb$_2$Ti$_2$O$_7$ as a
function of temperature and magnetic field. The acoustic modes couple to the
spins magneto-elastically and, hence, carry information about the spin
correlations that sheds light on the intricate magnetic phase diagram of
Yb$_2$Ti$_2$O$_7$ and the nature of spin dynamics in the material.
Particularly, we find a pronounced thermal hysteresis in the acoustic data with
a concomitant peak in the specific heat indicating a possible first-order phase
transition at about $0.17$ K. At low temperatures, the acoustic response to
magnetic field saturates hinting at the development of magnetic order.
Furthermore, mean-field calculations suggest that Yb$_2$Ti$_2$O$_7$ undergoes a
first-order phase transition from a cooperative paramagnetic phase to a
ferromagnet below $T\approx 0.17$ K.",1508.00925v1
2015-08-05,Inverse proximity effect at superconductor-ferromagnet interfaces: Evidence for induced triplet pairing in the superconductor,"Considerable evidence for proximity-induced triplet superconductivity on the
ferromagnetic side of a superconductor-ferromagnet (S-F) interface now exists;
however, the corresponding effect on the superconductor side has hardly been
addressed. We have performed scanning tunneling spectroscopy measurements on
NbN superconducting thin films proximity coupled to the half-metallic
ferromagnet La2/3Ca1/3MnO3 (LCMO) as a function of magnetic field. We have
found that at zero and low applied magnetic fields the tunneling spectra on NbN
typically show an anomalous gap structure with suppressed coherence peaks and,
in some cases, a zero-bias conductance peak. As the field increases to the
magnetic saturation of LCMO where the magnetization is homogeneous, the spectra
become more BCS-like and the critical temperature of the NbN increases,
implying a reduced proximity effect. Our results therefore suggest that
triplet-pairing correlations are also induced in the S side of an S-F bilayer.",1508.01070v1
2015-08-28,Rigorous determination of the ground-state phases and thermodynamics in an Ising-type multiferroic Ca3CoMnO6 chain,"To understand the collinear-magnetism-driven ferroelectricity in multiferroic
Ca3CoMnO6 compound, we have established an elastic diatomic Ising spin-chain
model with axial-next-nearest-neighbor interaction to describe its
magnetoelectric properties. By employing magneto-phonon decoupling and
transfer-matrix method, the possible ground-state configurations and
thermodynamic behaviors of the system have been exactly determined. From the
perspective of the ground-state configuration, we analyze the computational
results and make a detail comparison with experimental data. The parameter
relation for the appearance of electric polarization has been discussed. Our
data indicate that the magnetic coupling between nearest-neighbor spin pair is
antiferromagnetic rather than ferromagnetic. The system under the driven of
external magnetic field undergoes a different series of transitions from the
up-up-down-down spin configuration to the up-down-up state with peculiar 1/3
magnetization plateau, then to the up-up-up-down state, and finally saturated
at up-up-up-up state.",1508.07072v1
2015-09-02,Effect of Chemical Pressure on High Temperature Ferrimagnetic Double Perovskites Sr2CrOsO6 and Ca2CrOsO6,"The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized
and characterized with neutron powder diffraction, electrical transport
measurements, and high field magnetization experiments. Sr2CrOsO6 and Ca2CrOsO6
crystallize with R-3 and P21/n space group symmetry, respectively. Both
materials are found to be ferrimagnetic insulators with saturation
magnetizations near 0.2 {\mu}B. Sr2CrOsO6 orders at 660 K, showing
non-monotonic magnetization temperature dependence, while Ca2CrOsO6 orders at
490 K and does not show non-monotonic behavior. Evidence for a theoretically
predicted canted magnetic structure in Sr2CrOsO6 is sought and not found.",1509.00901v1
2015-09-13,Effects of Cr substitution on the magnetic and transport properties and electronic states of SrRuO3 epitaxial thin films,"The effect of Cr substitution in a SrRuO3 epitaxial thin film on SrTiO3
substrate was investigated by measuring the magnetic and transport properties
and the electronic states. The ferromagnetic transition temperature of the
SrRu0.9Cr0.1O3 film (166 K) was higher than that of the SrRuO3 film (147 K).
Resonant photoemission spectroscopy experimentally revealed that the Cr 3dt2g
orbital is hybridized with the Ru 4dt2g orbital in the SrRu0.9Cr0.1O3 film,
supporting the assumption that the enhancement of the ferromagnetic transition
temperature through Cr substitution stems from the widening of energy bands due
to the hybridization of Cr 3dt2g and Ru 4dt2g orbitals. Furthermore, we found
that the Hall resistivity of the SrRu0.9Cr0.1O3 film at low temperature is not
a linear function of magnetic field in the high-field region where the
out-of-plane magnetization was saturated; this result suggests that the
SrRu0.9Cr0.1O3 film undergoes a structural transition at low temperature
accompanied with the modulation of the Fermi surface.",1509.03804v1
2015-09-20,"Electronic structure, magnetism and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys","We present a combined theoretical and experimental study of two quaternary
Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for
spintronics applications. Magnetization measurement shows the saturation
magnetization and transition temperature to be $3\; \mu_B$, $866$ K and $0.9 \;
\mu_B$, $358$ K for CFCG and CMCA respectively. The magnetization values agree
fairly well with our theoretical results and also obey the Slater-Pauling rule,
a prerequisite for half metallicity. A striking difference between the two
systems is their structure; CFCG crystallizes in fully ordered Y-type structure
while CMCA has L2$_1$ disordered structure. The antisite disorder adds a
somewhat unique property to the second compound, which arises due to the
probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is
possibly expected due to comparable electronegativities of Al and Cr/Mn. {\it
Ab-initio} simulation predicted a unique transition from half metallic
ferromagnet to metallic antiferromagnet beyond a critical excess amount of Al
in the alloy.",1509.05971v2
2015-09-30,Efficient magnetic-field amplification due to the Kelvin-Helmholtz instability in binary neutron star mergers,"We explore magnetic-field amplification due to the Kelvin-Helmholtz
instability during binary neutron star mergers. By performing high-resolution
general relativistic magnetohydrodynamics simulations with a resolution of
$17.5$ m for $4$--$5$ ms after the onset of the merger on the Japanese
supercomputer ""K"", we find that an initial magnetic field of moderate maximum
strength $10^{13}$ G is amplified at least by a factor of $\approx 10^3$. We
also explore the saturation of the magnetic-field energy and our result shows
that it is likely to be $\gtrsim 4 \times 10^{50}$ erg, which is $\gtrsim
0.1\%$ of the bulk kinetic energy of the merging binary neutron stars.",1509.09205v2
2016-02-26,Water dispersible CoFe2O4 nanoparticles with improved colloidal stability for biomedical applications,"Single phase cobalt ferrite (CoFe2O4, CFO) nanoparticles of a controlled size
(~ 6 nm) exhibiting superparamagnetic properties have been synthesized by
hydrothermal technique using oleic acid (OA) as surfactant. The oleic acid
coated CFO nanoparticles are stable in non-polar organic media, such as hexane
but are not well dispersible in water. The surface of these snanoparticles has
been further modified by citric acid using ligand exchange process, which makes
CFO nanoparticles more stable colloidal solution in water. Citric acid coated
CFO nanoparticles exhibits high dispersibility in water, high zeta potential,
very low coercivity and moderate saturation magnetization. Biocompatibility of
these CFO nanoparticles is demonstrated through cytotoxicity test in L929 cell
line.",1602.08415v1
2016-03-15,Colossal Magnetocapacitance Effect and Multiferroism of Polycrystalline La0.2Pb0.7Fe12O19,"The mutual control of the electric and magnetic properties of a multiferroic
solid is of fundamental and great technological importance. We report here on
the colossal magnetoelectric coupling effect of polycrystalline
La0.2Pb0.7Fe12O19. A large classic ferroelectric hysteresis loop with full
saturation and a strong magnetic hysteresis loop were observed simultaneously
in polycrystalline La0.2Pb0.7Fe12O19 due to the coexistence of an off-centered
FeO6 octahedron in its unit cell and electron spins in the partially filled 3d
orbits of the Fe3+ ions. The coupling voltage and capacity demonstrate giant
oscillations, along with magnetic field; the maximum magnetocapacitance ratio
exceeds 1.9E5 at 80 Hz. The substitution of La ions with Pb ions progressively
stabilized the conical spin structure, which gave rise to the spin-current
induced capacity oscillations upon magnetic field.",1603.04508v1
2016-06-02,The small-scale turbulent dynamo in smoothed particle magnetohydrodynamics,"Supersonic turbulence is believed to be at the heart of star formation. We
have performed smoothed particle magnetohydrodynamics (SPMHD) simulations of
the small-scale dynamo amplification of magnetic fields in supersonic
turbulence. The calculations use isothermal gas driven at rms velocity of Mach
10 so that conditions are representative of star-forming molecular clouds in
the Milky Way. The growth of magnetic energy is followed for 10 orders in
magnitude until it reaches saturation, a few percent of the kinetic energy. The
results of our dynamo calculations are compared with results from grid-based
methods, finding excellent agreement on their statistics and their qualitative
behaviour. The simulations utilise the latest algorithmic developments we have
developed, in particular, a new divergence cleaning approach to maintain the
solenoidal constraint on the magnetic field and a method to reduce the
numerical dissipation of the magnetic shock capturing scheme. We demonstrate
that our divergence cleaning method may be used to achieve $\nabla \cdot {\bf
B}=0$ to machine precision, albeit at significant computational expense.",1606.00767v1
2016-08-22,Optimization of infrared and magnetic shielding of superconducting TiN and Al coplanar microwave resonators,"We present a systematic study of the effects of shielding on the internal
quality factors (Qi) of Al and TiN microwave resonators designed for use in
quantum coherent circuits. Measurements were performed in an adiabatic
demagnetization refrigerator, where typical magnetic fields of 200 {\mu}T are
present at the unshielded sample stage. Radiation shielding consisted of 100 mK
and 500 mK Cu cans coated with infrared absorbing epoxy. Magnetic shields
consisted of Cryoperm 10 and Sn plating of the Cu cans. A 2.7 K radiation can
and coaxial thermalization filters were present in all measurements. TiN
samples with Qi = $1.3*10^6$ at 100 mK exhibited no significant variation in
quality factor when tested with limited shielding. In contrast, Al resonators
showed improved Qi with successive shielding, with the largest gains obtained
from the addition of the first radiation and magnetic shields and saturating
before the addition of Sn plating infrared absorbing epoxy.",1608.06273v1
2016-09-20,A coupled spin-electron diamond chain with different Landé g-factors of localized Ising spins and mobile electrons,"A coupled spin-electron diamond chain with localized Ising spins placed on
its nodal sites and mobile electrons delocalized over interstitial sites is
explored in a magnetic field taking into account the difference between Land\'e
g-factors of the localized spins and mobile electrons. The ground-state phase
diagram is constituted by two classical ferrimagnetic phases, the quantum
unsaturated paramagnetic phase and the saturated paramagnetic phase. Both
classical ferrimagnetic phases as well as the unsaturated paramagnetic phase
are reflected in a low-temperature magnetization curve as intermediate
magnetization plateaus. The unsaturated paramagnetic phase is quantum in its
character as evidenced by the fermionic concurrence calculated for a pair of
the mobile electrons hopping in between the interstitial sites. It is shown
that the magnetic field can under certain conditions induce a quantum
entanglement above the disentangled ground state.",1609.06072v2
2016-09-21,Evolution of the magnetorotational instability on initially tangled magnetic fields,"The initial magnetic field of previous magnetorotational instability (MRI)
simulations has always included a significant system-scale component, even if
stochastic. However, it is of conceptual and practical interest to assess
whether the MRI can grow when the initial field is turbulent. The ubiquitous
presence of turbulent or random flows in astrophysical plasmas generically
leads to a small-scale dynamo (SSD), which would provide initial seed turbulent
velocity and magnetic fields in the plasma that becomes an accretion disc. Can
the MRI grow from these more realistic initial conditions? To address this we
supply a standard shearing box with isotropically forced SSD generated magnetic
and velocity fields as initial conditions, and remove the forcing. We find that
if the initially supplied fields are too weak or too incoherent, they decay
from the initial turbulent cascade faster than they can grow via the MRI. When
the initially supplied fields are sufficient to allow MRI growth and
sustenance, the saturated stresses, large-scale fields, and power spectra match
those of the standard zero net flux MRI simulation with an initial large scale
vertical field.",1609.06745v2
2016-09-30,The Tricritical Point of the f-electron Antiferromagnet USb2 Driven by High Magnetic Fields,"In pulsed magnetic fields up to 65T and at temperatures below the N\'eel
transition, our magnetization and magnetostriction measurements reveal a
field-induced metamagnetic-like transition that is suggestive of an
antiferromagnetic to polarized paramagnetic or ferrimagnetic ordering. Our data
also suggests a change in the nature of this metamagnetic-like transition from
second- to first-order-like near a tricritical point at T_{tc} ~145K and
H_{c}~52T. At high fields for H>H_{c} we found a decreased magnetic moment
roughly half of the moment reported in low field measurements. We propose that
\mathit{f-p} hybridization effects and magnetoelastic interactions drive the
decreased moment, lack of saturation at high fields, and the decreased phase
boundary.",1609.09845v1
2016-11-08,Thermal and Magnetic Properties of Nanostructured Ferrimagnetic Composites with Graphene - Graphite Fillers,"We report the results of an experimental study of thermal and magnetic
properties of nanostructured ferrimagnetic iron oxide composites with graphene
and graphite fillers synthesized via the current activated pressure assisted
densification. The thermal conductivity was measured using the laser-flash and
transient plane source techniques. It was demonstrated that addition of 5 wt. %
of equal mixture of graphene and graphite flakes to the composite results in a
factor of x2.6 enhancement of the thermal conductivity without significant
degradation of the saturation magnetization. The microscopy and spectroscopic
characterization reveal that sp2 carbon fillers preserve their crystal
structure and morphology during the composite processing. The strong increase
in the thermal conductivity was attributed to the excellent phonon heat
conduction properties of graphene and graphite. The results are important for
energy and electronic applications of the nanostructured permanent magnets.",1611.02359v1
2017-01-16,Electric field modulation of the non-linear areal magnetic anisotropy energy,"We study the ferromagnetic layer thickness dependence of the
voltage-controlled magnetic anisotropy (VCMA) in gated CoFeB/MgO
heterostructures with heavy metal underlayers. When the effective CoFeB
thickness is below ~1 nm, the VCMA efficiency of Ta/CoFeB/MgO heterostructures
considerably decreases with decreasing CoFeB thickness. We find that a high
order phenomenological term used to describe the thickness dependence of the
areal magnetic anisotropy energy can also account for the change in the areal
VCMA efficiency. In this structure, the higher order term competes against the
common interfacial VCMA, thereby reducing the efficiency at lower CoFeB
thickness. The areal VCMA efficiency does not saturate even when the effective
CoFeB thickness exceeds ~1 nm. We consider the higher order term is related to
the strain that develops at the CoFeB/MgO interface: as the average strain of
the CoFeB layer changes with its thickness, the electronic structure of the
CoFeB/MgO interface varies leading to changes in areal magnetic anisotropy
energy and VCMA efficiency.",1701.04150v1
2017-02-19,Highly magnetized neutron stars in a many-body forces formalism,"In this work, we study the effects of different magnetic field configurations
in neutron stars described by a many-body forces formalism (MBF model). The MBF
model is a relativistic mean field formalism that takes into account many-body
forces by means of a meson field dependence of the nuclear interaction coupling
constants. We choose the best parametrization of the model that reproduces
nuclear matter properties at saturation and also describes massive neutron
stars. We assume matter to be in beta-equilibrium, charge neutral and at zero
temperature. Magnetic fields are taken into account both in the equation of
state and in the structure of the stars by the self-consistent solution of the
Einstein-Maxwell equations. We assume a poloidal magnetic field distribution
and calculate its effects on neutron stars, showing its influence on the
gravitational mass and deformation of the stars.",1702.05685v1
2017-04-11,CoFeAlB alloy with low damping and low magnetization for spin transfer torque switching,"We investigate the effect of Al doping on the magnetic properties of the
alloy CoFeB. Comparative measurements of the saturation magnetization, the
Gilbert damping parameter $\alpha$ and the exchange constant as a function of
the annealing temperature for CoFeB and CoFeAlB thin films are presented. Our
results reveal a strong reduction of the magnetization for CoFeAlB in
comparison to CoFeB. If the prepared CoFeAlB films are amorphous, the damping
parameter $\alpha$ is unaffected by the Al doping in comparison to the CoFeB
alloy. In contrast, in the case of a crystalline CoFeAlB film, $\alpha$ is
found to be reduced. Furthermore, the x-ray characterization and the evolution
of the exchange constant with the annealing temperature indicate a similar
crystallization process in both alloys. The data proves the suitability of
CoFeAlB for spin torque switching properties where a reduction of the switching
current in comparison with CoFeB is expected.",1704.03326v1
2017-05-29,"Contributions of Co and Fe orbitals to Perpendicular Magnetic Anisotropy of MgO/CoFeB Bilayers with Spin-Orbit-Torque-Related (Ta, W, IrMn, and Ti) Underlayers","We study the perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO
bilayers in contact with W, Ta, IrMn and Ti which has been suggested as the
spin-orbit-torque-related underlayers. The saturation magnetization of the
CoFeB depends on the underlayer materials due to formation of a dead-layer,
affecting PMA strength of each film. The x-ray magnetic circular dichroism
measurement reveals that the interfacial intermixing suppresses only the
perpendicular orbital moment of Fe, while the intermixing simultaneously
suppresses both the perpendicular and in-plane orbital moments of Co.",1705.10064v1
2017-06-24,Magnetization process of the S = 1/2 two-leg organic spin-ladder compound BIP-BNO,"We have measured the magnetization of the organic compound BIP-BNO
(3,5'-bis(N-tert-butylaminoxyl)-3',5-dibromobiphenyl) up to 76 T where the
magnetization is saturated. The S = 1/2 antiferromagnetic Heisenberg two-leg
spin-ladder model accounts for the obtained experimental data regarding the
magnetization curve, which is clarified using the quantum Monte Carlo method.
The exchange constants on the rung and the side rail of the ladder are
estimated to be J(rung)/kB = 65.7 K and J(leg)/kB = 14.1 K, respectively,
deeply in the strong coupling region: J(rung)/J(leg) > 1.",1706.08008v1
2017-06-28,Monte Carlo study of magnetic nanoparticles adsorbed on halloysite $Al_2Si_2O_5(OH)_4$ nanotubes,"We study properties of magnetic nanoparticles adsorbed on the halloysite
surface. For that a distinct magnetic Hamiltonian with random distribution of
spins on a cylindrical surface was solved by using a nonequilibrium Monte Carlo
method. The parameters for our simulations: anisotropy constant, nanoparticle
size distribution, saturated magnetization and geometrical parameters of the
halloysite template were taken from recent experiments. We calculate the
hysteresis loops and temperature dependence of the zero field cooling (ZFC)
susceptibility, which maximum determines the blocking temperature. It is shown
that the dipole-dipole interaction between nanoparticles moderately increases
the blocking temperature and weakly increases the coercive force. The obtained
hysteresis loops (e.g., the value of the coercive force) for Ni nanoparticles
are in reasonable agreement with the experimental data. We also discuss the
sensitivity of the hysteresis loops and ZFC susceptibilities to the change of
anisotropy and dipole-dipole interaction, as well as the 3d-shell occupation of
the metallic nanoparticles; in particular we predict larger coercive force for
Fe, than for Ni nanoparticles.",1706.09213v2
2017-07-05,Indications of spin polarized transport in Ba$_2$FeMoO$_6$ thin films,"We have investigated the magnetic and magnetotransport properties of
Ba$_2$FeMoO$_6$ thin films produced by pulsed laser deposition from optimized
bulk material. The films are comprised of grains of crystalline Ba$_2$FeMoO$_6$
with a disordered grain boundary region that lowers the net saturation
magnetization of the film and prevents full magnetic alignment below a Curie
temperature $T_C$$\sim$305 K. Magnetotransport measurements point to the
Ba$_2$FeMoO$_6$ grains retaining the high spin polarization of a half-metal up
to $T_C$, while the grain boundaries greatly reduce the spin polarization of
the intergrain electrical current due to spin-flip scattering. Our results show
that a strong spin polarization of the electronic charge carriers is present
even in Ba$_2$FeMoO$_6$ films that do not show the ideal bulk magnetic
character.",1707.01208v1
2017-09-21,Tricritical point and phase diagram based on critical scaling in monoaxial chiral helimagnet Cr1/3NbS2,"In this work, the magnetism of the single crystal Cr$_{1/3}$NbS$_{2}$, which
exhibits chiral magnetic soliton lattice (CSL) state, is investigated. The
magnetization displays strong magnetic anisotropy when the field is applied
perpendicularly and parallel to the $c$-axis in low field region ($H<H_{S}$,
$H_{S}$ is the saturation field). The critical exponents of Cr$_{1/3}$NbS$_{2}$
are obtained as $\beta=$ 0.370(4), $\gamma=$ 1.380(2), and $\delta=$ 4.853(6),
which are close to the theoretical prediction of three-dimensional Heisenberg
model. Based on the scaling equation and the critical exponents, the $H-T$
phase diagram in the vicinity of the phase transition is constructed, where two
critical points are determined. One is a tricritical point which locates at the
intersection between the CSL, forced ferromagnetic (FFM), and paramagnetic (PM)
states. The other one is a critical point situated at the boundaries between
CSL, helimagnetic (HM), and PM states.",1709.07740v1
2017-11-15,Structural and Magnetic Characterizations of Co2FeGa/SiO2 Nanoparticles Prepared via Chemical Route,"We report the synthesis of Co2FeGa/SiO2 nanoparticles by sol-gel method and
characterization using x-ray diffraction (XRD), transmission electron
microscopy (TEM) and magnetic measurements. The Rietveld refinements of XRD
data with space group Fm-3m clearly show the formation of A2 disorder single
phase and the lattice constant is found to be 5.738 {\AA}. The
energy-dispersive x-ray spectroscopy (EDX) confirm the elemental composition
close the desired values. The value of coercivity is found to be around 283 Oe
and 126 Oe, measured at 10 K and 300 K, respectively. We observed the
saturation magnetization significantly lower than expected from Slater-Pauling
rule. This decrease in the magnetic moment might be due to the presence of
amorphous SiO2 during the synthesis process. A large content of small size SiO2
particles along with Co2FeGa nanoparticles are also found in TEM study.",1711.05404v1
2017-11-23,"Structural and magnetic properties of (Mg,Co)2W hexaferrites","Precursor powders of BaMg2-xCoxFe16O27 with (x = 0.0, 1.0, and 2.0) were
prepared using high-energy ball milling, and the effects of chemical
composition and sintering temperature on the structural and magnetic properties
were investigated using x-ray diffractometer (XRD), scanning electron
microscopy (SEM), and vibrating sample magnetometry (VSM). XRD patterns of the
prepared samples indicated that crystallization of pure BaW hexaferrite phase
was achieved at sintering temperature of 1300{\deg} C, while BaM and cubic
spinel phase intermediate phases were obtained at lower sintering temperatures
of 1100{\deg} C and 1200{\deg} C. SEM images revealed improvement of the
crystallization of the structural phases, and growth of the particle size with
increasing the sintering temperature. The magnetic data of the samples sintered
at 1300{\deg} C revealed an increase of the saturation magnetization from 59.44
emu/g to 72.56 emu/g with increasing Co concentration (x) from 0.0 to 2.0. The
coercive field Hc decreased from 0.07 kOe at x = 0.0, to 0.03 kOe at x = 1.0,
and then increases to 0.09 kOe at x = 2.0. The thermomagnetic curves of the
samples sintered at 1300{\deg} C confirmed the existence of the W-type phase,
and revealed spin reorientation transitions above room temperature.",1711.08581v1
2017-11-27,Extreme magnetoresistance induced by Zeeman effect-driven electron-hole compensation and topological protection in MoSi$_2$,"The magnetoresistance is the magnetic field induced change of electrical
resistivity of a material. Recent studies have revealed extremely large
magnetoresistance in several non-magnetic semimetals, which has been explained
on the basis of either electron-hole compensation or the Fermi surface
topology, or the combination of both. Here, we present a single crystal study
on MoSi$_2$, which exhibits extremely large magnetoresistance, approaching
almost 10$^7$ % at 2 K and 14 T magnetic field. It is found that the
electron-hole compensation level in MoSi$_2$ evolves with magnetic field, which
is resulted from strong Zeeman effect, and found beneficial in boosting the
large non-saturating magnetoresistance. The non-trivial Berry phase in the de
Haas-van Alphen oscillations and the moderate suppression of backward
scattering of the charge carriers lend support for the topological nature of
this semimetal. The ultra-large carrier mobility of the topologically protected
charge carriers reinforces the magnetoresistance of MoSi2 to an unprecedented
large value.",1711.09646v1
2017-11-30,Prompt photon yield and $v_2$ coefficient from gluon fusion induced by magnetic field in heavy-ion collision,"We compute the production of prompt photons and the $v_2$ harmonic
coefficient in relativistic heavy-ion collisions induced by gluon fusion in the
presence of an intense magnetic field, during the early stages of the reaction.
The calculations take into account several parameters which are relevant to the
description of the experimental transverse momentum distribution, and elliptic
flow for RHIC and LHC energies. The main imput is the strength of the magnetic
field which varies in magnitude from 1 to 3 times the pion mass squared, and
allows the gluon fusion that otherwise is forbidden in the absence of the
field. The high gluon occupation number and the value of the saturation scale
also play an important role in our calculation, as well as a flow velocity and
geometrical factors. Our results support the idea that the origin of at least
some of the photon excess observed in heavy-ion experiments may arise from
magnetic field induced processes, and gives a good description of the
experimental data.",1711.11163v1
2017-12-13,Co$_{2}$PtGa: A promising magnetic shape memory alloy with high martensite transition temperature,"In the present work, a combined theoretical and experimental study on
Co$_{2}$PtGa Heusler alloy shows that it exhibits a martensite transition
around 1320 K with a small thermal hysteresis (10 K). Dynamical stability of
Co$_2$PtGa in the tetragonal phase has been established by the theoretically
calculated phonon dispersion curves. Magnetization measurements suggest that
this alloy is a ferromagnetic material with a saturation magnetic moment of
2.83 $\mu_B$/f.u. at 2 K, which is in excellent agreement with the value
obtained from \textit{ab-initio} calculations (2.87 $\mu_B$/f.u.). Our present
study demonstrates that Co$_{2}$PtGa is a promising material for high
temperature magnetic shape memory application.",1712.04765v4
2018-02-15,Damping's effect on the magnetodynamics of spin Hall nano-oscillators,"We study the impact of spin wave damping ($\alpha$) on the auto-oscillation
properties of nano-constriction based spin Hall nano-oscillators (SHNOs). The
SHNOs are based on a 5 nm Pt layer interfaced to a 5 nm
Py$_{100-x-y}$Pt$_{x}$Ag$_{y}$ magnetic layer, where the Pt and Ag contents are
co-varied to keep the saturation magnetization constant (within 10 %), while
$\alpha$ varies close to a factor of three. We systematically investigate the
influence of the Gilbert damping on the magnetodynamics of these SHNOs by means
of electrical microwave measurements. Under the condition of a constant field,
the threshold current scales with the damping in the magnetic layer. The
threshold current as a function of field shows a parabolic-like behavior, which
we attribute to the evolution of the spatial profile of the auto-oscillation
mode. The signal linewidth is smaller for the high-damping materials in low
magnetic fields, although the lowest observed linewidth was measured for the
alloy with least damping.",1802.05548v1
2018-05-16,Magnetic properties of single crystalline itinerant ferromagnet AlFe2B2,"Single crystals of AlFe$_{2}$B$_{2}$ have been grown using the self flux
growth method and then measured the structural properties, temperature and
field dependent magnetization, and temperature dependent electrical resistivity
at ambient as well as high pressure. The Curie temperature of AlFe$_{2}$B$_{2}$
is determined to be $274$~K. The measured saturation magnetization and the
effective moment for paramagnetic Fe-ion indicate the itinerant nature of the
magnetism with a Rhode-Wohlfarth ratio $ \frac{M_{C}}{M_{sat}}\approx 1.14$.
Temperature dependent resistivity measurements under hydrostatic pressure shows
that transition temperature \textit{T$_C$} is suppressed down to 255 K for $p =
2.24$~GPa pressure with a suppression rate of $\sim -8.9$~K/GPa. The anisotropy
fields and magnetocrystalline anisotropy constants are in reasonable agreement
with density functional theory calculations.",1805.06373v1
2018-06-06,Pressure Evolution of Magnetism in URhGa,"In this paper, we report the results of an ambient and high pressure study of
a 5f-electron ferromagnet URhGa. The work is focused on measurements of
magnetic and thermodynamic properties of a single crystal sample and on the
construction of the p-T phase diagram. Diamond anvil cells were employed to
measure the magnetization and electrical resistivity pressures up to ~ 9 GPa.
At ambient pressure, URhGa exhibits collinear ferromagnetic ordering of uranium
magnetic moments {\mu}U ~ 1.1 {\mu}B (at 2 K) aligned along the c-axis of the
hexagonal crystal structure below the Curie temperature TC = 41K. With the
application of pressure up to 5GPa the ordering temperature TC initially
increases whereas the saturated moment slightly decreases. The rather
unexpected evolution is put in the context of the UTX family of compounds.",1806.02686v1
2018-07-31,Tunable Half-Metallicity and Edge Magnetism of H-saturated InSe Nanoribbons,"We report on a theoretical study of electronic and magnetic properties of
hydrogen-saturated InSe nanoribbons (H-ZISNs). Based on hybrid-functional
first-principles calculations, we find that H-ZISNs exhibit tunable
half-metallicity and short-range ferromagnetic order. We first show that p-type
doping turns narrow H-ZISNs from semimetal to half-metal with spin-polarization
along In-terminated edge. This behavior is further analyzed in terms of a
two-band tight-binding model, which provides a tractable description of the
H-ZISN electronic structure, and serves as a starting point for the
determination of magnetic interactions. The dominant exchange interaction
determined within the Heisenberg model is found to be ferromagnetic
independently of the ribbon width and charge doping. Short-range stability of
magnetic order is assessed in terms of the zero-field spin correlation length,
which is found to be about 1 nm at liquid nitrogen temperatures. Finally, by
calculating spin-dependent transport properties, we find a doping regime in
which strongly spin-selective electrical conductivities can be observed. Our
findings suggest that H-ZISNs are appealing candidates for the realization of
spintronic effects at the nanoscale.",1807.11715v2
2018-09-06,Epitaxial growth and magnetic properties of NiMnAs film on GaAs substrate,"Single-phase Ni0.46Mn0.54As films with strained C1b symmetry have been
successfully grown on GaAs (001) substrates by molecular-beam epitaxy. The
epitaxial relationship between the film and the substrate has been studied
using synchrotron radiation, and a preferred configuration of (110)-orientated
Ni0.46Mn0.54As on (001)-orientated GaAs was revealed. In addition, the magnetic
properties of the films were found to be significantly influenced by the growth
temperature. The optimized growth temperature is determined to be ~370 degree
Celsius , for which relatively high Curie temperature, large saturation
magnetization and coercive field, as well as the pronounced in-plane magnetic
anisotropy were obtained. According to the results of X-ray absorption
spectroscopy, the above phenomenon can be attributed to the variation of the
local electronic structure of the Mn atoms. Our work provides useful
information for the further investigations of NiMnAs, which is theoretically
predicted to host robust half-metallicity.",1809.01976v2
2018-11-08,Sensitivity enhancement for a light axion dark matter search with magnetic material,"The sensitivity of experimental searches for axion dark matter coupled to
photons is typically proportional to the strength of the applied static
magnetic field. We demonstrate how a permeable material can be used to enhance
the magnitude of this static magnetic field, and therefore improve the
sensitivity of such searches in the low frequency lumped-circuit limit. Using
gadolinium iron garnet toroids at temperature 4.2 K results in a factor of 4
enhancement compared to an air-core toroidal design. The enhancement is limited
by magnetic saturation. Correlation of signals from three such toroids allows
efficient rejection of systematics due to electromagnetic interference. The
sensitivity of a centimeter-scale axion dark matter search based on this
approach is on the order of $g_{a\gamma\gamma}\approx10^{-9}$ GeV$^{-1}$ after
8 hours of data collection for axion masses near $10^{-10}$ eV. This approach
may substantially extend the sensitivity reach of large-volume lumped element
axion dark matter searches.",1811.03231v1
2019-02-21,Slowing the Spins of Stellar Cores,"The angular momentum (AM) evolution of stellar interiors, along with the
resulting rotation rates of stellar remnants, remains poorly understood.
Asteroseismic measurements of red giant stars reveal that their cores rotate
much faster than their surfaces, but much slower than theoretically predicted,
indicating an unidentified source of AM transport operates in their radiative
cores. Motivated by this, we investigate the magnetic Tayler instability and
argue that it saturates when turbulent dissipation of the perturbed magnetic
field energy is equal to magnetic energy generation via winding. This leads to
larger magnetic field amplitudes, more efficient AM transport, and smaller
shears than predicted by the classic Tayler-Spruit dynamo. We provide
prescriptions for the effective AM diffusivity and incorporate them into
numerical stellar models, finding they largely reproduce (1) the nearly rigid
rotation of the Sun and main sequence stars, (2) the core rotation rates of
low-mass red giants during hydrogen shell and helium burning, and (3) the
rotation rates of white dwarfs. We discuss implications for stellar rotational
evolution, internal rotation profiles, rotational mixing, and the spins of
compact objects.",1902.08227v2
2019-03-14,Thermoelectric property of a one dimensional channel in the presence of a transverse magnetic field,"We studied the thermal conduction through a quantum point contact (QPC),
defined in GaAs-AlGaAs heterostructure, in the presence of a transverse
magnetic field. A shift in the position of thermo-voltage peak is observed with
increasing field. The position of the thermo-voltage peak follows the
Cutler-Mott relation in the small field regime (B < 0.5 T); it starts diverging
from the Cutler-Mott relation in the moderate field regime, where a cubic
magnetic field term dominates over the trivial quadratic term; eventually the
shift saturates in the large field regime (B > 3.0 T). Our results suggest that
additional calibration is necessary when using QPC as thermometry, especially
when the transverse magnetic field is applied.",1903.06096v6
2019-04-05,Centrality dependence of photon yield and elliptic flow from gluon fusion and splitting induced by magnetic fields in relativistic heavy-ion collisions,"We compute the photon yield and elliptic flow coefficient in relativistic
heavy-ion collisions from gluon fusion and splitting processes induced by a
magnetic field for different centralities. The calculation accounts for the
intense magnetic field and the high gluon occupation number at early times. The
photon production induced by these process represents an excess contribution
over calculations without magnetic field effects. We compare this excess to the
difference between PHENIX data and recent hydrodynamic calculations for the
photon transverse momentum distribution and elliptic flow coefficient $v_2$.
The time evolution of the field strength and reaction volume is computed using
UrQMD. We show that with reasonable values for the saturation scale, the
calculation helps to better describe the experimental results obtained at RHIC
energies for the lowest part of the transverse photon momentum at different
centralities.",1904.02938v2
2019-05-27,Magnetocaloric properties of an Ising antiferromagnet on a kagome lattice,"Owing to a high degree of geometrical frustration an Ising antiferromagnet on
a kagome lattice (IAKL) is known to exhibit no long-range ordering at any
temperature, including the ground state. Nevertheless, at low temperatures it
shows a strongly correlated, highly fluctuating regime known as a cooperative
paramagnet or classical spin liquid. In the ground state it is characterized by
a macroscopic degeneracy which translates to a relatively large value of the
residual entropy. It has been shown that the presence of a macroscopic
degeneracy associated with geometrical frustration below the saturation field
can facilitate an enhanced magnetocaloric effect (MCE), which can exceed that
of an ideal paramagnet with equivalent spin by more than an order of magnitude.
In the present study we investigate magnetic and magnetocaloric properties of
IAKL by Monte Carlo simulation. In particular, we calculate the entropy of the
system using the thermodynamic integration method and evaluate quantities which
characterize MCE, such as the isothermal entropy and adiabatic temperature
changes in a varying magnetic field. It is found that IAKL shows the most
interesting magnetocaloric properties at low temperatures and moderate magnetic
fields, suggesting its potential to be used in technological applications for
low-temperature magnetic refrigeration.",1905.11494v1
2019-05-30,Predicting New Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy,"Perpendicular magnetic anisotropy (PMA) is a necessary condition for many
spintronic applications like spin-orbit torques switching, logic and memory
devices. An important class of magnetic insulators with low Gilbert damping at
room temperature are iron garnets, which only have a few PMA types such as
terbium and samarium iron garnet. More and stable PMA garnet options are
necessary for researchers to be able to investigate new spintronic phenomena.
In this study, we predict 20 new substrate/magnetic iron garnet film pairs with
stable PMA at room temperature. The effective anisotropy energies of 10
different garnet films that are lattice-matched to 5 different commercially
available garnet substrates have been calculated using shape, magnetoelastic
and magnetocrystalline anisotropy terms. Strain type, tensile or compressive
depending on substrate choice, as well as the sign and the magnitude of the
magnetostriction constants of garnets determine if a garnet film may possess
PMA. We show the conditions in which Samarium, Gadolinium, Terbium, Holmium,
Dysprosium and Thulium garnets may possess PMA on the investigated garnet
substrate types. Guidelines for obtaining garnet films with low damping are
presented. New PMA garnet films with tunable saturation moment and field may
improve spin-orbit torque memory and compensated magnonic thin film devices.",1905.13042v1
2019-07-04,Dynamics of the magnetoelastic phase transition and adiabatic temperature change in Mn1.3Fe0.7P0.5Si0.55,"The adiabatic temperature change DTad of a Mn1.3Fe0.7P0.5Si0.55 Fe2P-type
alloy was measured under different magnetic field-sweep rates from 0.93 Ts-1 to
2870 Ts-1. We find a field-sweep-rate independent magnetocaloric effect due to
a partial alignment of magnetic moments in the paramagnetic region overlapping
with the magnetocaloric effect of the first-order phase transition.
Additionally, the first-order phase transition is not completed even in fields
up to 20 T leading to a non-saturating behavior of DTad. Measurements in
different pulsed fields reveal that the first-order phase transition cannot
follow the fast field changes as previously assumed, resulting in a distinct
field-dependent hysteresis in DTad.",1907.02307v1
2019-07-10,The superior role of the Gilbert damping on the signal-to-noise ratio in heat-assisted magnetic recording,"In magnetic recording the signal-to-noise ratio (SNR) is a good indicator for
the quality of written bits. However, a priori it is not clear which parameters
have the strongest influence on the SNR. In this work, we investigate the role
of the Gilbert damping on the SNR. Grains consisting of FePt like hard magnetic
material with two different grain sizes $d_1=5\,$nm and $d_2=7\,$nm are
considered and simulations of heat-assisted magnetic recording (HAMR) are
performed with the atomistic simulation program VAMPIRE. The simulations
display that the SNR saturates for damping constants larger or equal than 0.1.
Additionally, we can show that the Gilbert damping together with the bit length
have a major effect on the SNR whereas other write head and material parameters
only have a minor relevance on the SNR.",1907.04577v2
2019-10-27,On a variational formulation of the weakly nonlinear magnetic Rayleigh--Taylor instability,"The magnetic-Rayleigh--Taylor (MRT) instability is a ubiquitous phenomenon
that occurs in magnetically-driven Z-pinch implosions. It is important to
understand this instability since it can decrease the performance of such
implosions. In this work, I present a theoretical model for the weakly
nonlinear MRT instability. I obtain such model by asymptotically expanding an
action principle, whose Lagrangian leads to the fully nonlinear MRT equations.
After introducing a suitable choice of coordinates, I show that the theory can
be cast as a Hamiltonian system, whose Hamiltonian is calculated up to sixth
order in a perturbation parameter. The resulting theory captures the harmonic
generation of MRT modes. In particular, it is shown that the saturation
amplitude of the linear MRT instability grows as the stabilization effect of
the magnetic-field tension increases. Overall, the theory provides an intuitive
interpretation of the weakly nonlinear MRT instability and provides a
systematic approach for studying this instability in more complex settings.",1910.12167v1
2020-02-24,Magnetic field configurations in neutron stars from MHD simulations,"We have studied numerically the evolution of magnetic fields in barotropic
neutron stars, by performing nonlinear magnetohydrodynamical simulations with
the code PLUTO. For both initially predominantly poloidal and toroidal fields,
with varying strengths, we find that the field settles down to a mixed
poloidal-toroidal configuration, where the toroidal component contributes
between 10% and 20% of the total magnetic energy. This is, however, not a
strict equilibrium, as the instability leads to the development of turbulence,
which in turn gives rise to an inverse helicity cascade, which determines the
final 'twisted torus' setup. The final field configuration is thus dictated by
the non-linear saturation of the instability and is not stationary. The average
energy of the poloidal and toroidal components, however, is approximately
stable in our simulations, and a complex multipolar structure emerges at the
surface, while the magnetic field is dipolar at the exterior boundary, outside
the star.",2002.10357v2
2020-03-17,Domain wall dynamics in stepped magnetic nanowire with perpendicular magnetic anisotropy,"Micromagnetic simulation is carried out to investigate the current-driven
domain wall (DW) in a nanowire with perpendicular magnetic anisotropy (PMA). A
stepped nanowire is proposed to pin DW and achieve high information storage
capacity based on multi-bit per cell scheme. The DW speed is found to increase
for thicker and narrower nanowires. For depinning DW from the stepped region,
the current density Jdep is investigated with emphasis on device geometry and
materials intrinsic properties. The Jdep could be analytically determined as a
function of the nanocontriction dimension and the thickness of the nanowire.
Furthermore, Jdep is found to exponential dependent on the anisotropy energy
and saturation magnetization, offering thus more flexibility in adjusting the
writing current for memory applications.",2003.07721v1
2020-03-26,Bipolar spin Hall nano-oscillators,"We demonstrate a novel type of spin Hall nano-oscillator (SHNO) that allows
for efficient tuning of magnetic auto-oscillations over an extended range of
gigahertz frequencies, using bipolar direct currents at constant magnetic
fields. This is achieved by stacking two distinct ferromagnetic layers with a
platinum interlayer. In this device, the orientation of the spin polarised
electrons accumulated at the top and bottom interfaces of the platinum layer is
switched upon changing the polarity of the direct current. As a result, the
effective anti-damping required to drive large amplitude auto-oscillations can
appear either at the top or bottom magnetic layer. Tuning of the
auto-oscillation frequencies by several gigahertz can be obtained by combining
two materials with sufficiently different saturation magnetization. Here we
show that the combination of NiFe and CoFeB can result in 3 GHz shifts in the
auto-oscillation frequencies. Bipolar SHNOs as such may bring enhanced
synchronisation capabilities to neuromorphic computing applications.",2003.11776v1
2020-04-07,Quantum and Thermal Phase Transitions of the Triangular SU(3) Heisenberg Model under Magnetic Fields,"We study the quantum and thermal phase transition phenomena of the SU(3)
Heisenberg model on triangular lattice in the presence of magnetic fields.
Performing a scaling analysis on large-size cluster mean-field calculations
endowed with a density-matrix-renormalization-group solver, we reveal the
quantum phases selected by quantum fluctuations from the massively degenerate
classical ground-state manifold. The magnetization process up to saturation
reflects three different magnetic phases. The low- and high-field phases have
strong nematic nature, and especially the latter is found only via a nontrivial
reconstruction of symmetry generators from the standard spin and quadrupolar
description. We also perform a semiclassical Monte Carlo simulations to show
that thermal fluctuations prefer the same three phases as well. Moreover, we
find that exotic topological phase transitions driven by the binding-unbinding
of fractional (half-)vortices take place, due to the nematicity of the low- and
high-field phases. Possible experimental realization with alkaline-earth-like
cold atoms is also discussed.",2004.03250v2
2020-04-22,Magnetic phase diagram of the linear quantum ferro-antiferromagnet Cs$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$,"A single-crystal sample of the frustrated quasi one-dimensional quantum
magnet Cs$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$ is investigated by magnetic and
thermodynamic measurements.A combination of specific heat and magnetic torque
measurements maps out the entire $H$-$T$ phase diagram for three
orientations.Remarkably, a new phase emerges below the saturation field,
irrespective of the crystal orientation. It is suggested that the presaturation
phase represents spin-nematic order or other multi-magnon condensate. The phase
diagrams within the long-range ordered dome are qualitatively different for
each geometry. In particular, multiple transitions are identified in the field
along the chain direction.",2004.10636v3
2020-05-15,Multiple magnon modes in spin-1/2 Heisenberg antiferromagnet on simple square lattice in strong magnetic field,"We discuss spin-$\frac12$ Heisenberg antiferromagnet on simple square lattice
in magnetic field $H$ using recently proposed bond-operator technique. It is
well known that magnetically ordered phases of quantum magnets are well
described at least qualitatively by the conventional spin-wave theory that only
introduces quantum corrections into the classical solution of the problem. We
observe that quantum fluctuations change drastically dynamical properties of
the considered model at $H$ close to its saturation value: the dynamical
structure factor shows anomalies corresponding to Green's function poles which
have no counterparts in the spin-wave theory. That is, quantum fluctuations
produce multiple short-wavelength magnon modes not changing qualitatively the
long-wavelength spin dynamics. Our results are in agreement with previous
quantum Monte-Carlo simulations and exact diagonalization of finite clusters.",2005.07537v3
2020-07-12,Three-Dimensional Chiral Magnetization Structures in FeGe Nanospheres,"Skyrmions, spin spirals, and other chiral magnetization structures developing
in materials with intrinsic Dzyaloshinsky-Moriya Interaction display unique
properties that have been the subject of intense research in thin-film
geometries. Here we study the formation of three-dimensional chiral
magnetization structures in FeGe nanospheres by means of micromagnetic
finite-element simulations. In spite of the deep sub-micron particle size, we
find a surprisingly large number of distinct equilibrium states, namely,
helical, meron, skyrmion, chiral-bobber and quasi-saturation state. The
distribution of these states is summarized in a phase diagram displaying the
ground state as a function of the external field and particle radius. This
unusual multiplicity of possible magnetization states in individual
nanoparticles could be a useful feature for multi-state memory devices. We also
show that the magneto-dipolar interaction is almost negligible in these
systems, which suggests that the particles could be arranged at high density
without experiencing unwanted coupling.",2007.05939v1
2020-09-02,Non-local spin Seebeck effect in the bulk easy-plane antiferromagnet NiO,"We report the observation of magnon spin currents generated by the Spin
Seebeck effect (SSE) in a bulk single crystal of the easy-plane antiferromagnet
NiO. A magnetic field induces a non-degeneracy and thereby an imbalance in the
population of magnon modes with opposite spin. A temperature gradient then
gives rise to a non-zero magnon spin current. This SSE is measured both in a
local and a non-local geometry at 5$\,$K in bulk NiO. The magnetic field
dependence of the obtained signal is modelled by magnetic field splitting of
the low energy magnon modes, affecting the spin Seebeck coefficient. The
relevant magnon modes at this temperature are linked to cubic anisotropy and
magnetic dipole-dipole interactions. The non-local signal deviates from the
expected quadratic Joule heating by saturating at a current from around
75$\,\mu A$ in the injector. The magnon chemical potential does not decay
exponentially with distance and inhomogeneities may be the result of local
magnon accumulations.",2009.01160v1
2020-09-03,Thermal effects in spin torque switching of perpendicular magnetic tunnel junctions at cryogenic temperatures,"Temperature plays an important role in spin torque switching of magnetic
tunnel junctions causing magnetization fluctuations that decrease the switching
voltage but also introduce switching errors. Here we present a systematic study
of the temperature dependence of the spin torque switching probability of
state-of-the-art perpendicular magnetic tunnel junction nanopillars (40 to 60
nm in diameter) from room temperature down to 4 K, sampling up to a million
switching events. The junction temperature at the switching voltage---obtained
from the thermally assisted spin torque switching model---saturates at
temperatures below about 75 K, showing that junction heating is significant
below this temperature and that spin torque switching remains highly stochastic
down to 4 K. A model of heat flow in a nanopillar junction shows this effect is
associated with the reduced thermal conductivity and heat capacity of the
metals in the junction.",2009.01743v1
2020-11-16,Electrically induced strong modulation of magnons transport in ultrathin magnetic insulator films,"Magnon transport through a magnetic insulator can be controlled by
current-biased heavy-metal gates that modulate the magnon conductivity via the
magnon density. Here, we report nonlinear modulation effects in 10$\,$nm thick
yttrium iron garnet (YIG) films. The modulation efficiency is larger than
40\%/mA. The spin transport signal at high DC current density (2.2$\times
10^{11}\,$A/m$^{2}$) saturates for a 400$\,$nm wide Pt gate, which indicates
that even at high current levels a magnetic instability cannot be reached in
spite of the high magnetic quality of the films.",2011.07800v1
2021-01-07,Quantum annealing simulation of out-of-equilibrium magnetization in a spin-chain compound,"Geometrically frustrated spin-chain compounds such as Ca3Co2O6 exhibit
extremely slow relaxation under a changing magnetic field. Consequently, both
low-temperature laboratory experiments and Monte Carlo simulations have shown
peculiar out-of-equilibrium magnetization curves, which arise from trapping in
metastable configurations. In this work we simulate this phenomenon in a
superconducting quantum annealing processor, allowing us to probe the impact of
quantum fluctuations on both equilibrium and dynamics of the system. Increasing
the quantum fluctuations with a transverse field reduces the impact of
metastable traps in out-of-equilibrium samples, and aids the development of
three-sublattice ferrimagnetic (up-up-down) long-range order. At equilibrium we
identify a finite-temperature shoulder in the 1/3-to-saturated phase
transition, promoted by quantum fluctuations but with entropic origin. This
work demonstrates the viability of dynamical as well as equilibrium studies of
frustrated magnetism using large-scale programmable quantum systems, and is
therefore an important step toward programmable simulation of dynamics in
materials using quantum hardware.",2101.02769v1
2021-01-26,Hydrodynamical study of Terahertz emission in magnetized graphene field-effect transistors,"Several hydrodynamic descriptions of charge transport in graphene have been
presented in the late years. We discuss a general hydrodynamic model governing
the dynamics of a two-dimensional electron gas in a magnetized field-effect
transistor in the slow drift regime. The Dyakonov--Shur instability is
investigated including the effect of weak magnetic fields (i.e. away from
Landau levels). We show that the gap on the dispersion relation prevents the
instability to reach the lower frequencies thus imposing a limit on the Mach
number of the electronic flow. Furthermore, we discuss that the presence of the
external magnetic field decreases the growth rate of the instability, as well
as the saturation amplitude. The numerical results from our simulations and the
presented higher order dynamic mode decomposition support such reasoning.",2101.10786v2
2021-02-19,Critical Energy Dissipation in a Binary Superfluid Gas by a Moving Magnetic Obstacle,"We study the critical energy dissipation in an atomic superfluid gas with two
symmetric spin components by an oscillating magnetic obstacle. Above a certain
critical oscillation frequency, spin-wave excitations are generated by the
magnetic obstacle, demonstrating the spin superfluid behavior of the system.
When the obstacle is strong enough to cause density perturbations via local
saturation of spin polarization, half-quantum vortices (HQVs) are created for
higher oscillation frequencies, which reveals the characteristic evolution of
critical dissipative dynamics from spin-wave emission to HQV shedding. Critical
HQV shedding is further investigated using a pulsed linear motion of the
obstacle, and we identify two critical velocities to create HQVs with different
core magnetization.",2102.09826v2
2021-02-24,Quantum paramagnetism and magnetization plateaus in a kagome-honeycomb Heisenberg antiferromagnet,"A spin-1/2 Heisenberg model on honeycomb lattice is investigated by doing
triplon analysis and quantum Monte Carlo calculations. This model, inspired by
Cu$_2$(pymca)$_3$(ClO$_4$), has three different antiferromagnetic exchange
interactions ($J_A$, $J_B$, $J_C$) on three different sets of nearest-neighbour
bonds which form a kagome superlattice. While the model is bipartite and
unfrustrated, its quantum phase diagram is found to be dominated by a quantum
paramagnetic phase that is best described as a spin-gapped hexagonal-singlet
state. The N\'eel antiferromagnetic order survives only in a small region
around $J_A=J_B=J_C$. The magnetization produced by external magnetic field is
found to exhibit plateaus at 1/3 and 2/3 of the saturation value, or at 1/3
alone, or no plateaus. Notably, the plateaus exist only inside a bounded region
within the hexagonal-singlet phase. This study provides a clear understanding
of the spin-gapped behaviour and magnetization plateaus observed in
Cu$_2$(pymca)$_3$(ClO$_4$), and also predicts the possible disappearance of 2/3
plateau under pressure.",2102.12291v2
2021-03-24,Effective strain manipulation of the antiferromagnetic state of polycrystalline NiO,"As a candidate material for applications such as magnetic memory,
polycrystalline antiferromagnets offer the same robustness to external magnetic
fields, THz spin dynamics, and lack of stray field as their single crystalline
counterparts, but without the limitation of epitaxial growth and lattice
matched substrates. Here, we first report the detection of the average Neel
vector orientiation in polycrystalline NiO via spin Hall magnetoresistance
(SMR). Secondly, by applying strain through a piezo-electric substrate, we
reduce the critical magnetic field required to reach a saturation of the SMR
signal, indicating a change of the anisotropy. Our results are consistent with
polycrystalline NiO exhibiting a positive sign of the in-plane
magnetostriction. This method of anisotropy-tuning offers an energy efficient,
on-chip alternative to manipulate a polycrystalline antiferromagnets magnetic
state.",2103.13105v1
2021-04-22,Impact of Fe$_{80}$B$_{20}$ insertion on the properties of dual-MgO perpendicular magnetic tunnel junctions,"We explore the impact of Fe80B20 inserted at both
Co$_{20}$Fe$_{80}$B$_{20}$/MgO interfaces of dual-MgO free layers (FLs) in
bottom-pinned magnetic tunnel junctions (MTJs). MTJ stacks are annealed for 30
min at 350 $^\circ$C and 400 $^\circ$C in a vacuum after film deposition.
Current-in-plane tunneling measurements are carried out to characterize
magnetotransport properties of the MTJs. Conventional magnetometry measurements
and ferromagnetic resonance are conducted to estimate the saturation
magnetization, the effective perpendicular anisotropy field and the Gilbert
damping of dual-MgO FLs as a function of the Fe$_{80}$B$_{20}$ thickness and
annealing temperatures. With ultrathin Fe$_{80}$B$_{20}$ (0.2 - 0.4 nm)
inserted, perpendicular magnetic anisotropy (PMA) of FLs increases with similar
tunnel magneto-resistance (TMR) and low damping values. As Fe$_{80}$B$_{20}$
layer thickness further increases (0.6 - 1.2 nm), both TMR and PMA degrade, and
damping increases dramatically. This study demonstrates a novel approach to
tune properties of MTJ stacks with dual-MgO FLs up to 400 $^\circ$C annealing,
which enables MTJ stacks for various applications.",2104.10918v1
2021-05-09,Planar topological Hall effect in a hexagonal ferromagnetic Fe5Sn3 single crystal,"The planar topological Hall effect (PTHE), appeared when the magnetic field
tended to be along the current, is believed to result from the real-space Berry
curvature of the spin spiral structure and has been experimentally observed in
skyrmion-hosting materials. In this paper, we report an experimental
observation of the PTHE in a hexagonal ferromagnetic Fe5Sn3 single crystal.
With a current along the c axis of Fe5Sn3, the transverse resistivity curves
exhibited obvious peaks near the saturation field as the magnetic field rotated
to the current and appeared more obvious with increasing temperature, which was
related to the noncoplanar spin structure in Fe5Sn3. This spin structure
induced nonzero scalar spin chirality, which acted as fictitious magnetic
fields to conduction electrons and contributed the additional transverse
signal. These findings deepen the understanding of the interaction between
conduction electrons and complex magnetic structures and are instructive for
the design of next-generation spintronic devices.",2105.03898v1
2021-05-10,Nonlinear MHD simulation of core plasma collapse events in stellarators,"The core collapse events observed in a stellarator experiment are studied by
a three-dimensional nonlinear MHD simulations. In the low magnetic shear
configuration like the Wendelstein 7-X, the rotational transform profile is
very sensitive to the toroidal current density. The 3D equilibrium with
localized toroidal current density is studied. If the toroidal current density
follows locally in the middle of the plasma minor radius, the rotational
transform is also changed locally. Sometimes, the magnetic topology changes due
to appearing the magnetic island. The nonlinear behaviors of the MHD
instability are studied by a full three-dimensional nonlinear MHD code. It was
found that a following sequence. At first, the high-n ballooning-type mode
structure appears in the plasma core, and then the mode linearly grows. The
high-n ballooning modes nonlinearly couple and saturate. The mode structure
changes to the low-n mode. In that phase, the magnetic field structure becomes
strongly stochastic into the plasma core due to the nonlinear coupling.
Finally, the plasma pressure diffuses along the stochastic field lines, and
then the core plasma pressure drops. This is an important results to interpret
the core collapse event by strong nonlinear coupling.",2105.04119v2
2021-06-24,Low-dimensional antiferromagnetic fluctuations in the heavy-fermion paramagnetic ladder UTe$_2$,"Inelastic-neutron-scattering measurements were performed on a single crystal
of the heavy-fermion paramagnet UTe$_2$ above its superconducting temperature.
We confirm the presence of antiferromagnetic fluctuations with the
incommensurate wavevector $\mathbf{k}_1=(0,0.57,0)$. A quasielastic signal is
found, whose momentum-transfer dependence is compatible with fluctuations of
magnetic moments $\mu\parallel\mathbf{a}$, with a sine-wave modulation of
wavevector $\mathbf{k}_1$ and in-phase moments on the nearest U atoms. Low
dimensionality of the magnetic fluctuations, consequence of the ladder
structure, is indicated by weak correlations along the direction $\mathbf{c}$.
These fluctuations saturate below the temperature $T_1^*\simeq15$~K, in
possible relation with anomalies observed in thermodynamic,
electrical-transport and nuclear-magnetic-resonance measurements. The absence
or weakness of ferromagnetic fluctuations, in our data collected at
temperatures down to 2.1 K and energy transfers from 0.6 to 7.5 meV, is
emphasized. These results constitute constraints for models of
magnetically-mediated superconductivity in UTe$_2$.",2106.13087v1
2021-08-22,Chiral vortical catalysis,"Gluon interaction introduces remarkable corrections to the magnetic
polarization effects on the chiral fermions, which is known as the inverse
magnetic catalysis. It is a natural speculation that the vorticity, which has
many similar properties as magnetic field, would bring non-negligible
contribution to the chiral rotational suppression. Using the intuitive
semi-classical background field method we studied the rotation dependence of
the effective strong interaction coupling. Contrary to the magnetic field case
the rotation increases the effective coupling which leads to slowing down the
condensate melting procedure with temperature. This could be named as the
chiral vortical catalysis or inverse rotation suppression. Imposing such
dependence to the coupling in the NJL model, we numerically checked this
analysis qualitatively. The pseudo critical temperature is shown to rise with
the rotation and approach saturation eventually which may be induced by the
model cutoff.",2108.09622v1
2021-11-09,Design of soft magnetic materials,"We present a strategy for the design of ferromagnetic materials with
exceptionally low magnetic hysteresis, quantified by coercivity. In this
strategy, we use a micromagnetic algorithm that we have developed in previous
research and which has been validated by its success in solving the ""Permalloy
Problem"" -- the well-known difficulty of predicting the composition 78.5% Ni of
lowest coercivity in the Fe-Ni system -- and by the insight, it provides into
the ""Coercivity Paradox"" of W. F. Brown. Unexpectedly, the design strategy
predicts that cubic materials with large saturation magnetization $m_s$ and
large magnetocrystalline anisotropy constant $\kappa_1$ will have low
coercivity on the order of that of Permalloy, as long as the magnetostriction
constants $\lambda_{100}, \lambda_{111}$ are tuned to special values. The
explicit prediction for a cubic material with low coercivity is the
dimensionless number $(c_{11}-c_{12}) \lambda_{100}^2/\kappa_1 = 81$ for
$\langle 100 \rangle$ easy axes. The results would seem to have a broad
potential application, especially to magnetic materials of interest in energy
research.",2111.05456v1
2021-12-14,"Ground State, Magnetization Process and Bipartite Quantum Entanglement of a Spin-1/2 Ising-Heisenberg Model on Planar Lattices of Interconnected Trigonal Bipyramids","The ground state, magnetization scenario and the local bipartite quantum
entanglement of a mixed spin-$1/2$ Ising--Heisenberg model in a magnetic field
on planar lattices formed by identical corner-sharing bipyramidal plaquettes is
examined by combining the exact analytical concept of generalized
decoration-iteration mapping transformations with Monte Carlo simulations
utilizing the Metropolis algorithm. The ground-state phase diagram of the model
involves six different phases, namely, the standard ferrimagnetic phase, fully
saturated phase, two unique quantum ferrimagnetic phases, and two
macroscopically degenerate quantum ferrimagnetic phases with two chiral degrees
of freedom of the Heisenberg triangular clusters. The diversity of ground-state
spin arrangement is manifested themselves in seven different magnetization
scenarios with one, two or three fractional plateaus whose values are
determined by the number of corner-sharing plaquettes. The low-temperature
values of the concurrence demonstrate that the bipartite quantum entanglement
of the Heisenberg spins in quantum ferrimagnetic phases is field independent,
but twice as strong if the Heisenberg spin arrangement is unique as it is
two-fold degenerate.",2112.07233v1
2022-03-09,The Ca II H&K Rotation-Activity Relation in 53 mid-to-late type M-Dwarfs,"In the canonical theory of stellar magnetic dynamo, the tachocline in
partially convective stars serves to arrange small-scale fields, generated by
stochastic movement of plasma into a coherent large-scale field. Mid-to-late
M-dwarfs, which are fully convective, show more magnetic activity than
classical magnetic dymano theory predicts. However, mid-to-late M-dwarfs show
tight correlations between rotation and magnetic activity, consistent with
elements of classical dynamo theory. We use data from Magellan Inamori Kyocera
Echelle (MIKE) Spectrograph to detail the relation between Ca II H\&K flux and
rotation period for these low-mass stars. We measure $R'_{HK}$ values for 53
spectroscopically identified M-dwarfs selected from the MEarth survey; these
stars span spectral classes from M5.0 to M3.5 and have rotation periods ranging
from hours to months. We present the rotation--activity relationship as traced
through these data. We find power law and saturated regimes consistent to
within one sigma of previously published results and observe a mass dependence
in $R'_{HK}$.",2203.04999v1
2022-03-14,Magnetic-field and pressure phase diagram of the triangular lattice antiferromagnet CsCuCl$_3$ clarified by magnetic susceptibility measured with a proximity detector oscillator,"The effect of pressure ($P$) on magnetic susceptibility of CsCuCl$_3$ was
examined in magnetic fields ($\rm \mu_0$$H$) of up to 51 T using a proximity
detector oscillator (PDO), and the $H$-$P$ phase diagram of CsCuCl$_3$ was
constructed over the saturation field ($H_{\rm sat}$). We found that, with
increasing $P$, $H_{\rm sat}$ increases and the uud-phase that appeared at $P$
= 0.7 GPa widened. Based on comparison between the experimental and calculated
$H$-$P$ phase diagrams, the Y-phase was predicted to appear above 1.7 GPa. The
interchain antiferromagnetic exchange interaction in the $ab$-plane was
evaluated and found to increase with increasing $P$, which is consistent with a
previous study under high pressure [D. Yamamoto {\it et al.}, Nat. Commun. {\bf
12}, 4263 (2021).]. Moreover, an anomaly was observed below $P$ = 0.6 GPa just
below $H_{\rm sat}$ and might be a new phase transition derived from nonlinear
response caused by the PDO technique.",2203.06869v1
2022-04-16,Entanglement and quantum correlations in the XX spin-$1/2$ honeycomb lattice,"The ground state phase diagram of the dimerized spin-1/2 XX honeycomb model
in presence of a transverse magnetic field (TF) is known. With the absence of
the magnetic field, two quantum phases, namely, the N\'eel and the dimerized
phases have been identified. Moreover, canted N\'eel and the paramagnetic (PM)
phases also emerge by applying the magnetic field. In this paper, using two
complementary numerical exact techniques, Lanczos exact diagonalization, and
Density matrix renormalization group (DMRG) methods, we study this model by
focusing on the quantum correlations, the concurrence, and the quantum discord
(QD) among nearest-neighbor spins. We show that the quantum correlations can
capture the position of the quantum critical points in the whole range of the
ground state phase diagram consistent with previous results. Although the
concurrence and the QD are short-range, informative about long-ranged critical
correlations. In addition, we address a ""magnetic-entanglement"" behavior that
starts from an entangled field around the saturation field.",2204.07708v1
2022-05-02,Novel quantum phase of the chromium spinel oxide HgCr$_{\rm 2}$O$_{\rm 4}$ in high magnetic fields,"In this study, we have performed the magnetocaloric effect and the specific
heat measurements of chromium spinel oxide HgCr$_2$O$_4$, wherein the magnetic
Cr$^{3+}$ ions form a highly frustrated pyrochlore lattice with significant
spin-lattice coupling. In addition to the known magnetic-field-induced phases,
our thermodynamic measurements detect a novel quantum phase just before the
saturation of the magnetization, which has not been expected from the classical
theories of the pyrochlore lattice antiferromagnet with spin-lattice coupling.
Based on recent theoretical model calculation, we discuss the possibility of a
spin nematic state appearing for this quantum phase.",2205.00810v1
2022-07-28,Magnetic properties of CrSnS3: A new Van der Waals ferromagnet,"We report an experimental discovery of CrSnS3, a new Van der Waals
ferromagnetic (FM) with Curie temperature TC ~119K. The Curie temperature is in
qualitative agreement of Chittari et. al. DFT prediction (TC =112.3K) for an
Ising model with the addition of Coulomb potential. The FM ordering temperature
in CrSnS3 is the highest among Cr-based Van der Waals materials: CrI3, CrSiTe3
and CrGeTe3. The dc-susceptibility revealed a sharp increase at Tc (~119K)
indicative of a first order transition; then raises to a wide maximum at AFM
Neel temperature TN~90K.The ac-susceptibility reveals the presence of two sharp
peaks; one close to Tc (119K) and the other at TN~90K. Ac-susceptibility
measurements in an applied dc-magnetic field indicates that CrSnS3 undergoes
two successive phase transitions: a sharp increase in the susceptibility
indicates a first order PM to FM at 119K, followed by more gradual decrease at
the onset of AFM transition at TN~90K. The magnetization isotherms below 30K
indicates that the materials orders in an AFM state; while the magnetic
isotherms at T >30K rises sharply to its saturated values confirming the
ferromagnetic state.",2207.14129v1
2022-08-22,Nonlinear transport due to magnetic-field-induced flat bands in the nodal-line semimetal ZrTe5,"The Dirac material ZrTe$_5$ at very low carrier density was recently found to
be a nodal-line semimetal, where ultra-flat bands are expected to emerge in
magnetic fields parallel to the nodal-line plane. Here we report that in very
low carrier-density samples of ZrTe$_5$, when the current and the magnetic
field are both along the crystallographic $a$ axis, the current-voltage
characteristics presents a pronounced nonlinearity which tends to saturate in
the ultra quantum limit. The magnetic-field dependence of the nonlinear
coefficient is well explained by the Boltzmann theory for flat-band transport,
and we argue that this nonlinear transport is likely due to the combined effect
of flat bands and charge puddles, the latter appear due to very low carrier
densities.",2208.10314v3
2022-09-02,Magnetic phase diagram and possible Kitaev-like behavior of honeycomb-lattice antimonate Na3Co2SbO6,"Recent theoretical studies have suggested that Kitaev physics and such
effects as formation of a mysterious spin-liquid state can be expected not only
in RuCl3 and iridates, but also in conventional $3d$ transition metal
compounds. Using DC and AC magnetometry, thermodynamic and $^{23}$Na nuclear
magnetic resonance measurements (NMR) we studied such a candidate material
Na3Co2SbO6. A full phase diagram of Na3Co2SbO6 in a wide range of magnetic
fields and temperatures is presented. The results demonstrate transformation of
the antiferromagnetic structure under the external magnetic field, gradual
development of the saturation phase, as well as evidence of gapped behavior in
certain parts of the phase diagram",2209.00846v2
2022-10-30,Evaporation of water in a microfluidic channel under magnetic field,"The evaporation of drops of water placed at the center of long poly(methyl
methacrylate) microfluidic channels with a rectangular cross section of 0.38
mm2 is studied by simultaneously monitoring the shapes of two samples, one is
in a 300 mT magnetic field, the other is in no field. A magnetic enhancement of
the evaporation rate of up to 140 % is observed, which can be understood by
treating the ortho and para nuclear isomers of water vapor as quasi-independent
gasses with an ortho:para ratio in fresh vapor close to 2:3. It would take much
longer than the 2 - 4 h duration of an experiment in the channel, for the ratio
to approach the 3:1 equilibrium value. Magnetic field influences evaporation
rate by equalizing the isomeric populations in the vapor phase. The atmosphere
in the channel is saturated with water vapor yet the evaporation rate far
exceeds that in open beakers.",2210.16962v1
2023-02-13,Helical dynamo growth at modest versus extreme magnetic Reynolds numbers,"Understanding large-scale magnetic field growth in astrophysical objects is a
persistent challenge. We tackle the long-standing question of how much helical
large-scale dynamo growth occurs independent of the magnetic Reynolds number
(Rm) in a closed volume. From modest-Rm numerical simulations, we identify a
pre-saturation regime when the large-scale field grows independently of Rm, but
to an Rm-dependent magnitude. For plausible magnetic spectra however, the
analysis predicts the magnitude to be Rm-independent and substantial as
Rm$\to\infty$. This gives renewed optimism for the relevance of closed dynamos
and pinpoints how modest Rm and hyper-diffusive simulations can cause
misapprehension of the Rm$\to\infty$ behavior.",2302.06042v2
2023-02-21,Aluminium substituted yttrium iron garnet thin films with reduced Curie temperature,"Magnetic garnets such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG) are
widely used in spintronic and magnonic devices. Their magnetic and
magneto-optical properties can be modified over a wide range by tailoring their
chemical composition. Here, we report the successful growth of Al-substituted
yttrium iron garnet (YAlIG) thin films via radio frequency sputtering in
combination with an ex situ annealing step. Upon selecting appropriate process
parameters, we obtain highly crystalline YAlIG films with different Al$^{3+}$
substitution levels on both, single crystalline Y$_3$Al$_5$O$_{12}$ (YAG) and
Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates. With increasing Al$^{3+}$ substitution
levels, we observe a reduction of the saturation magnetisation as well as a
systematic decrease of the magnetic ordering temperature to values well below
room temperature. YAlIG thin films thus provide an interesting material
platform for spintronic and magnonic experiments in different magnetic phases.",2302.10517v2
2023-09-11,Experimental realization of a high Curie temperature CoFeRuSn quaternary Heusler alloy for spintronic applications,"We synthesize CoFeRuSn equiatomic quaternary Heusler alloy using arc-melt
technique and investigate its structural, magnetic and transport properties.
The room temperature powder X-ray diffraction analysis reveals that CoFeRuSn
crystallizes in cubic crystal structure with small amount of DO3 - disorder.
The field dependence of magnetization shows non-zero but small hysteresis and
saturation behavior up to room temperature, indicating soft ferromagnetic
nature of CoFeRuSn. The magnetic moment estimated from the magnetization data
is found to be 4.15 {\mu}B / f.u., which is slightly less than the expected
Slater-Pauling rule. The deviation in the value of experimentally observed
moment from the theoretical value might be due to small disorder in the
crystal. The low temperature fit to electrical resistivity data show absence of
quadratic temperature dependence of resistivity, suggesting half-metallic
behavior of CoFeRuSn. The high Curie temperature and possible half-metallic
behavior of CoFeRuSn make it a highly promising candidate for room temperature
spintronic applications.",2309.05493v1
2023-11-24,Local temperature control of magnon frequency and direction of supercurrents in a magnon Bose-Einstein condensate,"The creation of temperature variations in magnetization, and hence in the
frequencies of the magnon spectrum in laser-heated regions of magnetic films,
is an important method for studying Bose-Einstein condensation of magnons,
magnon supercurrents, Bogoliubov waves, and similar phenomena. In our study, we
demonstrate analytically, numerically, and experimentally that, in addition to
the magnetization variations, it is necessary to consider the connected
variations of the demagnetizing field. In case of a heat induced local minimum
of the saturation magnetization, the combination of these two effects results
in a local increase in the minimum frequency value of the magnon dispersion at
which the Bose-Einstein condensate emerges. As a result, a magnon supercurrent
directed away from the hot region is formed.",2311.14476v1
2023-11-30,Highly sensitive magnetic properties and large linear magnetoresistance in antiferromagnetic CrxSe(0.875\lex\le1)single crystals,"CrxSe (x\le1) is a class of quasi-layered binary compounds with potential
applications in spintronics due to its intriguing antiferromagnetic properties.
In this work, CrxSe single crystals with high Cr content (x=0.87, 0.91 and
0.95) were grown, and their magnetic and transport properties were investigated
in detail. It is found that with small increase of Cr content, the N\'eel
temperature (TN) of the samples can dramatically increase from 147 K to 257 K,
accompanied with obvious changes in the magnetic anisotropy and hysteresis. The
phenomena of field-induced spin-flop transitions were unveiled in these alloys,
indicating their comparatively low anisotropy. The magnetoresistance (MR) of
the three compounds showed positive dependence at low temperatures and
particularly, non-saturated linear positive MR was observed in Cr0.91Se and
Cr0.95Se, with a large value of 16.2% achieved in Cr0.91Se (10K, 9T). The
calculated Fermi surface and MR showed that the quasi-linear MR is a product of
carrier compensation. Our work revealed highly sensitive magnetic and transport
properties in the Cr-Se compounds, which can lay foundation when constructing
further antiferromagnetic spintronic devices based on them.",2311.18349v1
2024-03-15,Granular Aluminum Parametric Amplifier for Low-Noise Measurements in Tesla Fields,"Josephson junction parametric amplifiers have become essential tools for
microwave quantum circuit readout with minimal added noise. Even after
improving at an impressive rate in the last decade, they remain vulnerable to
magnetic field, which limits their use in many applications such as spin
qubits, Andreev and molecular magnet devices, dark matter searches, etc.
Kinetic inductance materials, such as granular aluminum (grAl), offer an
alternative source of non-linearity with innate magnetic field resilience. We
present a non-degenerate amplifier made of two coupled grAl resonators
resilient to in-plane magnetic field up to 1 T. It offers 20 dB of gain close
to the quantum limit of added noise, with a gain-bandwidth product of 28 MHz
and -110 dBm input saturation power.",2403.10669v2
2011-06-20,Global Simulations of Accretion Disks I: Convergence and Comparisons with Local Models,"Grid-based magnetohydrodynamic (MHD) simulations have proven invaluable for
the study of astrophysical accretion disks. However, the fact that angular
momentum transport in disks is mediated by MHD turbulence (with structure down
to very small scales) raises the concern that the properties of the modeled
accretion disks are affected by the finite numerical resolution of the
simulation. By implementing an orbital advection algorithm into the Athena code
in cylindrical geometry, we have performed a set of global (but unstratified)
Newtonian disk simulations extending up to resolutions previously unattained.
We study the convergence of these models as a function of spatial resolution
and initial magnetic field geometry. The usual viscosity parameter ($\alpha$)
or the ratio of thermal-to-magnetic pressure ($\beta$) are found to be poor
diagnostics of convergence, whereas the average tilt angle of the magnetic
field in the $(r,\phi)$-plane is a very good diagnostic of convergence. We
suggest that this is related to the saturation of the MHD turbulence via
parasitic modes of the magnetorotational instability. Even in the case of
zero-net magnetic flux, we conclude that our highest resolution simulations
(with 32-zones and 64-zones per vertical scale height) have achieved
convergence.
  Our global simulations reach resolutions comparable to those used in local,
shearing box models of MHD disk turbulence. We find that the saturation
predictors derived from local simulations correspond well to the instantaneous
correlations between local flux and stress found in our global simulations.
However, the conservation of magnetic flux implicit in local models is not
realized in our global disks. Thus, the magnetic connectivity of an accretion
disk represents physics that is truly global and cannot be captured in any
ab-initio local model.",1106.4019v1
2012-12-17,"M dwarf companions to white dwarfs I: relating magnetic activity, rotation and age","We make use of the largest and most homogeneous sample of white dwarf/M dwarf
(WD/dM) binaries from the Sloan Digital Sky Survey (SDSS DR7) to investigate
relations between magnetic activity, rotation, magnetic braking and age in M
stars. These relations are studied separately for close WD/dM binaries that
underwent a common envelope phase and thus contain tidally locked and hence
rapidly rotating M dwarfs, and for wide WD/dM binaries that never interacted.
For the wide WD/dM binary sample we find that the M dwarf activity fractions
are significantly higher than those measured in single M stars of spectral type
M0 to M5. We attribute this effect as a consequence of M dwarfs in wide SDSS
WD/dM binaries being, on average, significantly younger and hence more active
than the field M dwarf population. The measured M dwarf activity fractions in
wide WD/dM binaries show as well a significant increase from spectral types M3
to M5, where these low-mass stars become fully convective. This provides
additional observational evidence for magnetic braking being less efficient
below the fully convective boundary, in agreement with the hypothesis of fully
convective stars having considerably longer activity lifetimes than partially
convective stars. The M dwarfs in all our close binaries are active,
independently of the spectral type, giving robust observational evidence for
magnetic activity being enhanced due to fast rotation. The rotational
velocities of the M dwarfs in our close binary sample are significantly higher
than seen among field M dwarfs, however the strength of magnetic activity
remains saturated at log LHalpha/Lbol approximately -3.5. This unambiguously
confirms the M dwarf saturation-type rotation-activity relation.",1212.4189v1
2014-02-08,A dynamo model of magnetic activity in solar-like stars with different rotational velocities,"We attempt to provide a quantitative theoretical explanation for the
observations that Ca II H/K emission and X-ray emission from solar-like stars
increase with decreasing Rossby number (i.e., with faster rotation). Assuming
that these emissions are caused by magnetic cycles similar to the sunspot
cycle, we construct flux transport dynamo models of $1M_{\odot}$ stars rotating
with different rotation periods. We first compute the differential rotation and
the meridional circulation inside these stars from a mean-field hydrodynamics
model. Then these are substituted in our dynamo code to produce periodic
solutions. We find that the dimensionless amplitude $f_m$ of the toroidal flux
through the star increases with decreasing rotation period. The observational
data can be matched if we assume the emissions to go as the power 3-4 of $f_m$.
Assuming that the Babcock-Leighton mechanism saturates with increasing
rotation, we can provide an explanation for the observed saturation of emission
at low Rossby numbers. The main failure of our model is that it predicts an
increase of magnetic cycle period with increasing rotation rate, which is the
opposite of what is found observationally. Much of our calculations are based
on the assumption that the magnetic buoyancy makes the magnetic flux tubes to
rise radially from the bottom of the convection zone. On taking account of the
fact that the Coriolis force diverts the magnetic flux tubes to rise parallel
to the rotation axis in rapidly rotating stars, the results do not change
qualitatively.",1402.1874v3
2014-07-10,"Magnetic hyperthermia properties of nanoparticles inside lysosomes using kinetic Monte-Carlo simulations : influence of key parameters, of dipolar interactions and spatial variation of heating power","Understanding the influence of dipolar interactions in magnetic hyperthermia
(MH) experiments is of crucial importance for a fine optimization of
nanoparticle (NP) heating power. In this study, we use a kinetic Monte-Carlo
algorithm to calculate hysteresis loops, so both time and temperature are
correctly taken into account. It is demonstrated that this algorithm correctly
reproduces the high-frequency hysteresis loop of both superparamagnetic NPs and
ferromagnetic ones without any ad-hoc parameters. The algorithm is easily
parallelizable so calculation on several processors decreases considerably
calculation time. The specific absorption rate (SAR) of NPs dispersed inside
spherical lysosomes is studied as a function of several key parameters: volume
concentration, applied magnetic field, lysosome size, NP diameter and
anisotropy. The influence of these parameters is illustrated and
comprehensively explained. In summary, the effect of magnetic interactions is
to increase the coercive field, saturation field and hysteresis area of major
loops. However, for small amplitude magnetic field such as the ones used in MH,
the heating power as function of concentration can increase, decrease or
display a bell shape, depending of the relationship between the applied
magnetic field and the coercive/saturation fields of the NPs. The hysteresis
area is found to be well correlated to the parallel or antiparallel nature of
the dipolar field acting on each NP. It is shown that the heating power
increases or decreases sharply in the vicinity of the lysosome membrane. The
amplitude of variation reaches more than one order of magnitude in certain
conditions. Finally, implications of these various findings are discussed in
the framework of MH optimization. It is concluded that feedbacks on specific
points from biology experiments are required for further advance on the
optimization of NPs for MH.",1407.2737v2
2017-08-13,PIC Simulations of Velocity-Space Instabilities in a Decreasing Magnetic Field: Viscosity and Thermal Conduction,"We use particle-in-cell (PIC) simulations of a collisionless, electron-ion
plasma with a decreasing background magnetic field, $B$, to study the effect of
velocity-space instabilities on the viscous heating and thermal conduction of
the plasma. If $B$ decreases, the adiabatic invariance of the magnetic moment
gives rise to pressure anisotropies with $p_{||,j} > p_{\perp,j}$ ($p_{||,j}$
and $p_{\perp,j}$ represent the pressure of species $j$ ($=i$ or $e$) parallel
and perpendicular to the magnetic field). Linear theory indicates that, for
sufficiently large anisotropies, different velocity-space instabilities can be
triggered. These instabilities, which grow on scales comparable to the electron
and ion Larmor radii, in principle have the ability to pitch-angle scatter the
particles, limiting the growth of the anisotropies. Our PIC simulations focus
on the nonlinear, saturated regime of the instabilities. This is done through
the permanent decrease of the magnetic field by an imposed shear in the plasma.
Our results show that, in the regime $2 \lesssim \beta_j \lesssim 20$ ($\beta_j
\equiv 8\pi p_j/B^2$), the saturated ion and electron pressure anisotropies are
controlled by the combined effect of the oblique ion firehose (OIF) and the
fast magnetosonic/whistler (FM/W) instabilities. These instabilities grow
preferentially on the ion Larmor radius scale, and make the ion and electron
pressure anisotropies nearly equal: $\Delta p_e/p_{||,e} \approx \Delta
p_i/p_{||,i}$ (where $\Delta p_j=p_{\perp,j} - p_{||,j}$). We also quantify the
thermal conduction of the plasma by directly calculating the mean free path of
electrons along the mean magnetic field, which we find strongly depends on
whether $B$ decreases or increases. Our results can be applied in studies of
low collisionality plasmas such as the solar wind, the intracluster medium, and
some accretion disks around black holes.",1708.03926v2
2020-07-06,Spin-canting effects in GMR sensors with wide dynamic field range,"Magnetoresistive (xMR) sensors find extensive application in science and
industry, replacing Hall sensors in various low field environments. While there
have been some efforts in increasing the dynamic field range of xMR sensors,
Hall sensors remain to dominate high field applications due to their wide
linear range. Using a perpendicular magnetized reference system and an in-plane
free layer allows us to overcome this disadvantage of xMR sensors, and,
furthermore, investigate spin-canting effects in interlayer exchange coupled
perpendicular synthetic antiferromagnets (p-SAF). We created p-SAFs with
exchange coupling fields of up to 10 kOe, based on magnetic Co/Pt multilayer
systems. The p-SAFs are either designed as ""single"" p-SAFs, where two Co/Pt
multilayers are interlayer exchange coupled via a 4 {\AA} thick Ru spacer, or
as ""double"" p-SAFs, where an additional Co layer is interlayer exchange coupled
to the top multilayer. These p-SAFs are used for giant magnetoresistance (GMR)
sensors with wide dynamic field range. By using a p-SAF as the reference system
and employing an in-plane magnetic layer as the GMR's free layer, the linear
range can be effectively increased limited only by the p-SAF's switching
fields. Additionally, the magnetic anisotropy of the in-plane free layer is
fully controlled, which allows saturation fields by design. Different
configurations were investigated, ranging from free layer magnetic saturation
at lower to far higher fields than the p-SAF's switching fields. We can show
through micromagnetic simulations that certain GMR transfer curves are
dominated by spin-canting effects in the interlayer exchange coupled reference
system. Finally, our simulation results lay out the correlation of the p-SAF's
design parameters and its magnetization reversal behavior.",2007.02640v1
2021-08-27,"Jets in Magnetically Arrested Hot Accretion Flows: Geometry, Power and Black Hole Spindown","We present the results of nine simulations of radiatively-inefficient
magnetically arrested disks (MADs) across different values of the black hole
spin parameter $a_*$: $-0.9$, $-0.7$, $-0.5$, $-0.3$, 0, 0.3, 0.5, 0.7, and
0.9. Each simulation was run up to $t \gtrsim 100,000\,GM/c^3$ to ensure disk
inflow equilibrium out to large radii. We find that the saturated magnetic flux
level, and consequently also jet power, of MAD disks depends strongly on the
black hole spin, confirming previous results. Prograde disks saturate at a much
higher relative magnetic flux and have more powerful jets than their retrograde
counterparts. MADs with spinning black holes naturally launch jets with
generalized parabolic profiles whose widths vary as a power of distance from
the black hole. For distances up to $100\;GM/c^2$, the power-law index is $k
\approx 0.27-0.42$. There is a strong correlation between the disk-jet geometry
and the dimensionless magnetic flux, resulting in prograde systems displaying
thinner equatorial accretion flows near the black hole and wider jets, compared
to retrograde systems. Prograde and retrograde MADs also exhibit different
trends in disk variability: accretion rate variability increases with
increasing spin for $a_*>0$ and remains almost constant for $a_*\lesssim 0$,
while magnetic flux variability shows the opposite trend. Jets in the MAD state
remove more angular momentum from black holes than is accreted, effectively
spinning down the black hole. If powerful jets from MAD systems in Nature are
persistent, this loss of angular momentum will notably reduce the black hole
spin over cosmic time.",2108.12380v2
2023-06-26,Large saturation moment and high ferromagnetic transition temperature in a structurally disordered inverse Heusler alloy Fe2RuGe,"We report the successful synthesis of a new 4$d$ based polycrystalline
inverse Heusler alloy Fe$_2$RuGe by an arc melting process and have studied in
detail its structural, magnetic and transport properties complemented with
first principle calculations. X-ray and neutron diffraction, Extended X-ray
Absorption Fine Structure and $^{57}$Fe M\""{o}ssbauer spectroscopic studies
confirm the single phase nature of the system where the Fe and Ru atoms are
randomly distributed in the 4$c$ and 4$d$ Wyckoff positions in a ratio close to
50:50. The formation of the disordered structure is also confirmed by the
theoretical energy minimization calculation. Despite the random cross-site
disorder of Fe and Ru atoms, magnetic measurements suggest not only a high
Curie temperature of $\sim$860\,K, but also a large saturation magnetic moment
$\sim$4.9\,$\mu_B$ per formula unit at 5\,K, considerably exceeding the
theoretical limit (4\,$\mu_B$ per formula unit) predicted by the Slater-Pauling
rule. Only a few Fe-based inverse Heusler alloys are known to exhibit such high
Curie temperatures. Neutron diffraction analysis coupled with the isothermal
magnetization value indicates that the magnetic moments in Fe$_2$RuGe are
associated with Fe-atoms only, which is also confirmed by M\""ossbauer
spectrometry. Interestingly, in comparison to the cubic or hexagonal phase of
the parent compound, Fe$_3$Ge, the Curie temperature of Fe$_2$RuGe has
increased significantly despite the substitution of the nonmagnetic, yet
isoelectronic element Ru in this structurally disordered compound. Our
theoretical calculation reveals that the large Fe moment ($\sim2.8\mu_B$/Fe) on
the 4$b$ site can be attributed to a charge transfer from this Fe site towards
its Ru neighbours. Such a substantial increase in magnetic moment due to
electron charge transfer has not previously been reported in a Heusler alloy
system.",2306.14831v1
2023-08-25,High-susceptibility nanoparticles for micro-inductor core materials,"According to the laws of magnetism, the shape of magnetically soft objects
limits the effective susceptibility. For example, spherical soft magnets cannot
display an effective susceptibility larger than 3. Although true for
macroscopic multi-domain magnetic materials, we show that magnetic
nanoparticles in a single-domain state do not suffer from this limitation. This
is a consequence of the particle moment being forced to saturation by the
predominance of exchange forces, and only allowed to rotate coherently in
response to thermal and/or applied fields. We apply statistical mechanics to
determine the static and dynamic susceptibility of single-domain particles as a
function of size, temperature and material parameters. Our calculations reveal
that spherical single-domain particles with large saturation magnetisation and
small magneto-crystalline anisotropy, e.g. FeNi particles, can have very a
large susceptibility of 200 or more. We further show that susceptibility and
losses can be tuned by particle easy axis alignment with the applied field in
case of uniaxial anisotropy, but not for particles with cubic anisotropy. Our
model is validated experimentally by comparison with measurements on
nanocomposites containing spherical 11$\pm$3 nm $\gamma$-Fe$_2$O$_3$ particles
up to 45 vol% finely dispersed in a polymer matrix. In agreement with the
calculations for this specific material, the measured susceptibility of the
composites is up to 17 ($\gg$3) and depends linearly on the volume fraction of
particles. Based on these results, we predict that nanocomposites of 30 vol% of
superparamagnetic FeNi particles in an insulating non-magnetic matrix can have
a sufficiently large susceptibility to be used as micro-inductor core materials
in the MHz frequency range, while maintaining losses below state-of-the-art
ferrites.",2308.13407v2
2006-12-13,X-ray Emission from T Tauri Stars and the Role of Accretion: Inferences from the XMM-Newton Extended Survey of the Taurus Molecular Cloud,"T Tau stars display different X-ray properties depending on whether they are
accreting (classical T Tau stars; CTTS) or not (weak-line T Tau stars; WTTS).
We use data from the XMM-Newton Extended Survey of the Taurus Molecular Cloud
(XEST) to study differences in X-ray properties between CTTS and WTTS. We
perform correlation and regression analysis between X-ray parameters and
stellar properties. We confirm the existence of a X-ray luminosity (Lx) vs.
mass (M) relation, Lx ~ M^(1.69 +/- 0.11), but this relation is a consequence
of X-ray saturation and a mass vs. bolometric luminosity (L*) relation for the
TTS with an average age of 2.4 Myr. X-ray saturation indicates Lx = const L*,
although the constant is different for the two subsamples: const = 10^(-3.73
+/- 0.05) for CTTS and const = 10^(-3.39 +/- 0.06) for WTTS. Given a similar L*
distribution of both samples, the X-ray luminosity function also reflects a
real X-ray deficiency in CTTS, by a factor of ~ 2 compared to WTTS. The average
electron temperatures Tav are correlated with Lx in WTTS but not in CTTS; CTTS
sources are on average hotter than WTTS sources. The most fundamental
properties are the two saturation laws, indicating suppressed Lx for CTTS. We
speculate that some of the accreting material in CTTS is cooling active regions
to temperatures that may not significantly emit in the X-ray band, and if they
do, high-resolution spectroscopy may be required to identify lines formed in
such plasma, while CCD cameras do not detect these components. The similarity
of the Lx vs. Tav dependencies in WTTS and main-sequence stars as well as their
similar X-ray saturation laws suggests similar physical processes for the hot
plasma, i.e., heating and radiation of a magnetic corona.",0612338v1
2022-05-26,X-ray emission of contact binary variables within 1 kpc,"By assembling the largest sample to date of X-ray emitting EW-type binaries
(EWXs), we carried out correlation analyses for the X-ray luminosity
log$L_{\textrm{X}}$, and X-ray activity level
log($L_{\textrm{X}}$/$L_{\textrm{bol}}$) versus the orbital period $P$ and
effective temperature $T_{\rm eff}$. We find strong $P$-log$L_{\textrm{X}}$ and
$P$-log($L_{\textrm{X}}$/$L_{\textrm{bol}}$) correlations for EWXs with $P$ <
0.44 days and we provide the linear parametrizations for these relations, on
the basis of which the orbital period can be treated as a good predictor for
log$L_{\textrm{X}}$ and log($L_{\textrm{X}}$/$L_{\textrm{bol}}$). The
aforementioned binary stellar parameters are all correlated with
log$L_{\textrm{X}}$, while only $T_{\rm eff}$ exhibits a strong correlation
with log($L_{\textrm{X}}$/$L_{\textrm{bol}}$). Then, EWXs with higher
temperature show lower X-ray activity level, which could indicate the thinning
of the convective area related to the magnetic dynamo mechanism. The total
X-ray luminosity of an EWX is essentially consistent with that of an X-ray
saturated main sequence star with the same mass as its primary, which may imply
that the primary star dominates the X-ray emission. The monotonically
decreasing $P$-log($L_{\textrm{X}}$/$L_{\textrm{bol}}$) relation and the short
orbital periods indicate that EWXs could all be in the X-ray saturated state,
and they may inherit the changing trend of the saturated X-ray luminosities
along with the mass shown by single stars. For EWXs, the orbital period, mass,
and effective temperature increase in concordance. We demonstrate that the
period $P=0.44$ days corresponds to the primary mass of $\sim1.1 \rm M_\odot$,
beyond which the saturated X-ray luminosity of single stars will not continue
to increase with mass. This explains the break in the positive
$P$-log$L_{\textrm{X}}$ relation for EWXs with $P>0.44$ days.",2205.13210v1
2006-10-27,Magnetorotational collapse of massive stellar cores to neutron stars: Simulations in full general relativity,"We study magnetohydrodynamic (MHD) effects arising in the collapse of
magnetized, rotating, massive stellar cores to proto-neutron stars (PNSs). We
perform axisymmetric numerical simulations in full general relativity with a
hybrid equation of state. The formation and early evolution of a PNS are
followed with a grid of 2500 x 2500 zones, which provides better resolution
than in previous (Newtonian) studies. We confirm that significant differential
rotation results even when the rotation of the progenitor is initially uniform.
Consequently, the magnetic field is amplified both by magnetic winding and the
magnetorotational instability (MRI). Even if the magnetic energy E_EM is much
smaller than the rotational kinetic energy T_rot at the time of PNS formation,
the ratio E_EM/T_rot increases to 0.1-0.2 by the magnetic winding. Following
PNS formation, MHD outflows lead to losses of rest mass, energy, and angular
momentum from the system. The earliest outflow is produced primarily by the
increasing magnetic stress caused by magnetic winding. The MRI amplifies the
poloidal field and increases the magnetic stress, causing further angular
momentum transport and helping to drive the outflow. After the magnetic field
saturates, a nearly stationary, collimated magnetic field forms near the
rotation axis and a Blandford-Payne type outflow develops along the field
lines. These outflows remove angular momentum from the PNS at a rate given by
\dot{J} \sim \eta E_EM C_B, where \eta is a constant of order 0.1 and C_B is a
typical ratio of poloidal to toroidal field strength. As a result, the rotation
period quickly increases for a strongly magnetized PNS until the degree of
differential rotation decreases. Our simulations suggest that rapidly rotating,
magnetized PNSs may not give rise to rapidly rotating neutron stars.",0610840v1
2014-02-05,Magnetic Helicity and Large Scale Magnetic Fields: A Primer,"Magnetic fields of laboratory, planetary, stellar, and galactic plasmas
commonly exhibit significant order on large temporal or spatial scales compared
to the otherwise random motions within the hosting system. Such ordered fields
can be measured in the case of planets, stars, and galaxies, or inferred
indirectly by the action of their dynamical influence, such as jets. Whether
large scale fields are amplified in situ or a remnant from previous stages of
an object's history is often debated for objects without a definitive magnetic
activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic
field lines, is a unifying tool for understanding large scale field evolution
for both mechanisms of origin. Its importance stems from its two basic
properties: (1) magnetic helicity is typically better conserved than magnetic
energy; and (2) the magnetic energy associated with a fixed amount of magnetic
helicity is minimized when the system relaxes this helical structure to the
largest scale available. Here I discuss how magnetic helicity has come to help
us understand the saturation of and sustenance of large scale dynamos, the need
for either local or global helicity fluxes to avoid dynamo quenching, and the
associated observational consequences. I also discuss how magnetic helicity
acts as a hindrance to turbulent diffusion of large scale fields, and thus a
helper for fossil remnant large scale field origin models in some contexts. I
briefly discuss the connection between large scale fields and accretion disk
theory as well. The goal here is to provide a conceptual primer to help the
reader efficiently penetrate the literature.",1402.0933v2
2019-04-29,Magnetic fields in M dwarfs from the CARMENES survey,"M dwarfs are known to generate the strongest magnetic fields among
main-sequence stars with convective envelopes, but the link between the
magnetic fields and underlying dynamo mechanisms, rotation, and activity still
lacks a consistent picture. In this work we measure magnetic fields from the
high-resolution near-infrared spectra taken with the CARMENES radial-velocity
planet survey in a sample of 29 active M dwarfs and compare our results against
stellar parameters. We use the state-of-the-art radiative transfer code to
measure total magnetic flux densities from the Zeeman broadening of spectral
lines and filling factors. We detect strong kG magnetic fields in all our
targets. In 16 stars the magnetic fields were measured for the first time. Our
measurements are consistent with the magnetic field saturation in stars with
rotation periods P<4d. The analysis of the magnetic filling factors reveal two
different patterns of either very smooth distribution or a more patchy one,
which can be connected to the dynamo state of the stars and/or stellar mass.
Our measurements extend the list of M dwarfs with strong surface magnetic
fields. They also allow us to better constrain the interplay between the
magnetic energy, stellar rotation, and underlying dynamo action. The high
spectral resolution and observations at near-infrared wavelengths are the
beneficial capabilities of the CARMENES instrument that allow us to address
important questions about the stellar magnetism.",1904.12762v1
2021-11-23,Magnetism in Metastable and Annealed Compositionally Complex Alloys,"Compositionally complex materials (CCMs) present a potential paradigm shift
in the design of magnetic materials. These alloys exhibit long-range structural
order coupled with limited or no chemical order. As a result, extreme local
environments exist with a large opposing magnetic energy term, which can
manifest large changes in the magnetic behavior. In the current work, the
magnetic properties of (Cr, Mn, Fe, Ni) alloys are presented. These materials
were prepared by room-temperature combinatorial sputtering, resulting in a
range of compositions with a single BCC structural phase and no chemical
ordering. The combinatorial growth technique allows CCMs to be prepared outside
of their thermodynamically stable phase, enabling the exploration of otherwise
inaccessible order. The mixed ferromagnetic and antiferromagnetic interactions
in these alloys causes frustrated magnetic behavior, which results in an
extremely low coercivity (<1 mT), which increases rapidly at 50 K. At low
temperatures, the coercivity achieves values of nearly 500 mT, which is
comparable to some high-anisotropy magnetic materials. Commensurate with the
divergent coercivity is an atypical drop in the temperature dependent
magnetization. These effects are explained by a mixed magnetic phase model,
consisting of ferro-, antiferro , and frustrated magnetic regions, and are
rationalized by simulations. A machine-learning algorithm is employed to
visualize the parameter space and inform the development of subsequent
compositions. Annealing the samples at 600 {\deg}C orders the sample, more-than
doubling the Curie temperature and increasing the saturation magnetization by
as much as 5x. Simultaneously, the large coercivities are suppressed, resulting
in magnetic behavior that is largely temperature independent over a range of
350 K.",2111.12188v1
2022-08-23,Nearby galaxies in the LOFAR Two-metre Sky Survey II. The magnetic field-gas relation,"Context. Magnetic fields are key to understand galaxy evolution, regulating
stellar feedback and star formation in galaxies. Aims. We probe the origin of
magnetic fields in late-type galaxies, measuring magnetic field strengths,
exploring whether magnetic fields are only passive constituents of the
interstellar medium, or whether they are active constituents being part of the
local energy equilibrium. Methods. We measure equipartition magnetic field
strengths in 39 galaxies from LoTSS-DR2 using LOFAR observations at 144 MHz
with 6 arcsec angular resolution which (0.1-0.7 kpc). For a subset of 9
galaxies, we obtain atomic and molecular mass surface densities using HI and
CO(2-1) data, from the THINGS and HERACLES surveys, respectively. These data
are at 13 arcsec angular resolution, which corresponds to 0.3-1.2 kpc at the
distances of our galaxies. We measure kinetic energy densities using HI and CO
velocity dispersions. Results. We found a mean magnetic field strength of
3.6-12.5 $\mu$G with a mean of $7.9 \pm 2.0$ $\mu$G across the full sample. The
magnetic field strength has the tightest and steepest relation with the total
gas surface density with $B\propto \Sigma_{\rm HI+H2}^{0.309\pm0.006}$. The
relation with the star-formation rate surface density and molecular gas surface
density has significantly flatter slopes. After accounting for the influence of
cosmic-ray transport, we found an even steeper relation of $B\propto
\Sigma_{\rm HI+H2}^{0.393\pm0.009}$. Conclusions. These results suggest that
the magnetic field is regulated by a $B$-$\rho$ relation, which has its origin
in the saturation of the small-scale dynamo. This is borne out by an agreement
of kinetic and magnetic energy densities although local deviations do exist in
particular in areas of high kinetic energy densities where the magnetic field
is sub-dominant.",2208.11068v1
2010-04-13,Magnetic properties of Fe3O4 nanoparticles coated with oleic and dodecanoic acids,"Magnetic nanoparticles (NP) of magnetite (Fe3O4) coated with oleic acid (OA)
and dodecanoic acid (DA) were synthesized and investigated through Transmission
Electron Microscopy (TEM),magnetization M, and ac magnetic susceptibility
measurements. The OA coated samples were produced with different magnetic
concentrations (78, 76, and 65%) and the DA sample with 63% of Fe3O4. Images
from TEM indicate that the NP have a nearly spherical geometry and mean
diameter ~ 5.5 nm. Magnetization measurements, performed in zero field cooled
(ZFC) and field cooled (FC) processes under different external magnetic fields
H, exhibited a maximum at a given temperature TB in the ZFC curves, which
depends on the NP coating (OA or DA), magnetite concentration, and H. The
temperature TB decreases monotonically with increasing H and, for a given H,
the increase in the magnetite concentration results in an increase of TB. The
observed behavior is related to the dipolar interaction (DI) between NP which
seems to be an important mechanism in all samples studied. This is supported by
the results of the ac magnetic susceptibility Xac measurements, where the
temperature in which X' peaks for different frequencies follows the
Vogel-Fulcher model, a feature commonly found in systems with dipolar
interactions. Curves of H vs. TB/TB(H=0) for samples with different coatings
and magnetite concentrations collapse into a universal curve, indicating that
the qualitative magnetic behavior of the samples may be described by the NP
themselves, instead of the coating or the strength of the dipolar interaction.
Below TB, M vs. H curves show a coercive field (HC) that increases
monotonically with decreasing temperature. The saturation magnetization (MS)
follows the Bloch's law and values of MS at room temperature as high as 78
emu/g were estimated, a result corresponding to ~80% of the bulk value. The
overlap of M/MS vs. H/T curves for a given sample and the low HC at high
temperatures suggest superparamagnetic behavior in all samples studied. The
overlap of M/MS vs. H curves at constant temperature for different samples
indicates that the NP magnetization behavior is preserved, independently of the
coating and magnetite concentration.",1004.2231v1
2012-08-03,"Spin dynamics, short-range order and superparamagnetism in superconducting ferromagnet RuSr2Gd1.4Ce0.6Cu2O10-δ","We report structural, detailed DC and linear/non-linear AC, isothermal and
thermoremanent magnetization study of the rutheno-cuprate superconducting
ferromagnet RuSr2Gd1.4Ce0.6Cu2O10-{\delta} (GdRu-1222). Structural analysis, by
employing Rietveld refinement of X-ray diffraction pattern, reveals that
GdRu-1222 crystallizes in tetragonal phase with I4/mmm space group. GdRu-1222
is a reported superconducting ferromagnet with Ru spins magnetic ordering at
around 110 K and superconductivity below 40 K in Cu-O2 planes. Detailed
linear/non-linear first and higher order harmonic of AC susceptibility studies
unveiled the complex magnetism of GdRu-1222. A frequency dependent cusp is
observed in AC susceptibility ({\chi}ac) vs. T measurements. The change in cusp
position with applied frequency followed the well known Vogel-Fulcher law,
which is a feature to describe a spin-glass (SG) system with possibility of
embedded homogeneous/non-homogeneous magnetically interacting/non-interacting
ferromagnetic clusters. Such an interpretation is also supported by
thermoremanent magnetization (TRM) study at T = 60 K. Detailed interpretation
of AC magnetization results revealed the formation of magnetic (ferromagnetic)
homogenous/non-homogenous clusters of different sizes embedded in spin-glass
(SG) matrix. The magnetization vs. applied field loops do not saturate, even at
high applied fields (50 kOe), resulting in the short-range magnetic ordering in
the system, which causes the formation of clusters that freeze at low
temperatures. Temperature variation of first- and third-order susceptibility
harmonics show good agreement with Wohlfarth's model (WM), leading to the
superparamagnetism (SPM) state. Detailed magnetization (DC and AC both) results
and their analysis helped in explaining the temperature dependent magnetism of
the GdRu-1222 system.",1208.0760v2
2015-11-11,Polarization of Magnetic Dipole Emission and Spinning Dust Emission from Magnetic Nanoparticles,"Magnetic dipole emission (MDE) from interstellar magnetic nanoparticles is an
important Galactic foreground in the microwave frequencies, and its
polarization level may pose great challenges for achieving reliable
measurements of cosmic microwave background (CMB) B-mode signal. To obtain
theoretical constraints on the polarization of MDE, we first compute the degree
of alignment of big silicate grains incorporated with magnetic inclusions. We
find that, in realistic conditions of the interstellar medium, thermally
rotating big grains with magnetic inclusions are weakly aligned and achieve
{\it alignment saturation} when the magnetic alignment rate becomes much faster
than the rotational damping rate. We then compute the degree of alignment for
free-flying magnetic nanoparticles, taking into account various interaction
processes of grains with the ambient gas and radiation field, including neutral
collisions, ion collisions, and infrared emission. We find that the rotational
damping by infrared emission can significantly decrease the degree of alignment
of small particles from the saturation level, whereas the excitation by ion
collisions can enhance the alignment of ultrasmall particles. Using the
computed degrees of alignment, we predict the polarization level of MDE from
free-flying magnetic nanoparticles to be rather low. Such a polarization level
is within the upper limits measured for anomalous microwave emission (AME),
which indicates that MDE from free-flying iron particles may not be ruled out
as a source of AME. We also quantify spinning dust emission from free-flying
iron nanoparticles with permanent magnetic moments and find that its emissivity
is one order of magnitude lower than that from spinning polycyclic aromatic
hydrocarbons (PAHs). Finally, we compute the polarization spectra of spinning
dust emission from PAHs for the different interstellar magnetic fields.",1511.03691v1
2017-01-05,Effect of single-particle magnetostriction on the shear modulus of compliant magnetoactive elastomers,"The influence of an external magnetic field on the static shear strain and
the effective shear modulus of a magnetoactive elastomer (MAE) is studied
theoretically in the framework of a recently introduced approach to the
single-particle magnetostriction mechanism [V. M. Kalita et al, Phys. Rev. E
93, 062503 (2016)]. The planar problem of magnetostriction in an MAE with soft
magnetic inclusions in the form of a thin disk (platelet) having the magnetic
anisotropy in the plane of this disk is solved analytically. An external
magnetic field acts with torques on magnetic filler particles, creates
mechanical stresses in the vicinity of inclusions, induces shear strain and
increases the effective shear modulus of these composite materials. It is shown
that the largest effect of the magnetic field on the effective shear modulus
should be expected in MAEs with soft elastomer matrices, where the shear
modulus of the matrix is less than the magnetic anisotropy constant of
inclusions. It is derived that the effective shear modulus is non-linearly
dependent on the external magnetic field and approaches the saturation value in
magnetic fields exceeding the field of particle anisotropy. It is shown that
model calculations of the effective shear modulus correspond to a
phenomenological definition of effective elastic moduli and magnetoelastic
coupling constants. Obtained theoretical results compare well with known
experimental data. Determination of effective elastic coefficients in MAEs and
their dependence on magnetic field is discussed. The concentration dependence
of the effective shear modulus at higher filler concentrations has been
estimated using the method of Pad\'e approximants, which correctly predicts
that both the absolute and relative changes of the magnetic-field dependent
effective shear modulus will significantly increase with the growing
concentration of filler particles.",1701.01305v1
2021-09-29,The relationship between bipolar magnetic regions and their sunspots,"The relationship between bipolar magnetic regions (BMRs) and their sunspots
is an important property of the solar magnetic field, but it is not well
constrained. One consequence is that it is a challenge for surface flux
transport models (SFTMs) based on sunspot observations to determine the details
of BMR emergence, which they require as input, from such data. We aimed to
establish the relationship between the amount of magnetic flux in newly emerged
BMRs and the area of the enclosed sunspots. Earlier attempts to constrain BMR
magnetic flux were hindered by the fact that there is no proper database of the
magnetic and physical properties of newly emerged BMRs currently available. We
made use of the empirical model of the relationship between the disc-integrated
facular and network magnetic flux and the total surface coverage by sunspots
reported in a recent study. The structure of the model is such that it enabled
us to establish, from these disc-integrated quantities, an empirical
relationship between the magnetic flux and sunspot area of individual newly
emerged BMRs, circumventing the lack of any proper BMR database. Applying the
constraint on BMR magnetic flux derived here to an established SFTM retained
its ability to replicate various independent datasets and the correlation
between the model output polar field at the end of each cycle and the observed
strength of the following cycle. The SFTM output indicates that facular and
network magnetic flux rises with increasing sunspot magnetic flux at a slowing
rate such that it appears to gradually saturate, analogous to earlier studies.
The activity dependence of the ratio of facular and network flux to sunspot
flux is consistent with the findings of recent studies: although the Sun is
faculae-dominated, it is only marginally so as facular and network brightening
and sunspot darkening appear to be closely balanced.",2109.14313v1
2022-01-12,Magneto-transport and magnetic textures in Ho/FeCoGd/β-W multilayers,"The enhancement of interfacial Dzyaloshinskii-Moriya Interaction (DMI) in
magnetic multilayers results in the stabilization of topological spin textures
like chiral domain walls and skyrmions. Here we report on the evaluation of
interface-driven magnetic interactions in a uniquely designed multilayer where
each magnetic layer of two AFM coupled sublattices of 3d and 4f moments is
sandwiched between the layers of \beta-tungsten and holmium whose spin Hall
angles are large but opposite in sign. The atomic and magnetic periodicity of
these multilayers is established by polarized neutron reflectivity measurements
and the presence of a labyrinth domain spin texture of zero remanence with
x-ray photoelectron microscopy. Measurements of the Hall resistivity
(\rho_{xy}(T, H)) together with static magnetization (M(T,H)) over a broad
range of temperature (T) and magnetic field (H) indicate impending compensation
between 3d and 4f sublattices at T>350 K. These multilayers are characterized
by a small (0.04 %) but positive magnetoresistance indicative of interface
enhance scattering and a large (40 n\Omega.m) and negative anomalous
\rho_{xy}(T,H) which results from a parallel alignment of 4f moments with the
external magnetic field. No distinct scaling is seen between \rho_{xy}(T,H),
\rho_{xx}(T, H) and M(T,H) at temperatures above 200K where the magnetization
develops out-of-plane anisotropy. The field scans of \rho_{xy} at T>200K show a
distinct cusp in the vicinity of magnetic saturation. These Hall data have been
analyzed in the framework of a model where a distinct topological contribution
to \rho_{xy} rides over the anomalous Hall resistivities of the 3d and 4f
magnetic sublattices. It is suggested that this apparent topological effect
results from an interfacial DMI and dominates \rho_{xy}(T,H) in the temperature
regime where the 3d and 4f lattices are nearly compensated.",2201.04696v1
1998-02-13,Induced Raman Scattering in Pulsar Magnetospheres,"It is shown that induced Raman scattering of electromagnetic waves in the
strongly magnetized electron-positron plasma of pulsar magnetosphere may be
important for wave propagation and as an effective saturation mechanism for
electromagnetic instabilities. The frequencies, at which strong Raman
scattering occurs in the outer parts of magnetosphere, fall into the observed
radio band. The typical threshold intensities for the strong Raman scattering
are of the order of the observed intensities, implying that pulsar
magnetosphere may be optically thick to Raman scattering of electromagnetic
waves.",9802195v1
1996-07-02,Phase separation in the one-dimensional Hubbard model,"The Hartree-Fock ground-state phase diagram of the one-dimensional Hubbard
model is calculated in the $\mu-U$ plane, restricted to phases with no charge
density modulation, extending the results presented in cond-mat/9511116. This
allows antiferromagnetism, saturated ferromagnetism, spiral spin density waves
and a collinear structure with unit cell $\uparrow \uparrow \downarrow
\downarrow$. The spiral phase is unstable against phase separation near
quarter-, half- and three-quarter-filling. For large $U$ this occurs at hole
(or electron) doping of $(3t/\pi^{2}U)^{1/3}$ from half filling.",9607011v1
1998-08-10,Instability of antiferromagnetic magnons in strong fields,"We predict that spin-waves in an ordered quantum antiferromagnet (AFM) in a
strong magnetic field become unstable with respect to spontaneous two-magnon
decays. At zero temperature, the instability occurs between the threshold field
$H^*$ and the saturation field $H_c$. As an example, we investigate the
high-field dynamics of a Heisenberg antiferromagnet on a square lattice and
show that the single-magnon branch of the spectrum disappears in the most part
of the Brillouin zone.",9808100v2
1999-03-15,Giant Mutual Proximity Effects in Ferromagnetic/Superconducting Nanostructures,"A strong mutual influence of superconductors (S) and ferromagnetic (F)
conductors in hybrid F/S (Ni/Al) nanostructures is observed. The magnitude of a
proximity-induced conductance on the F-side is more than two orders larger than
that predicted by theory. Re-entrance of the superconductors to the normal
state reciprocated by changes on the F-side has been found in low applied
magnetic fields with new peaks in the differential resistance as an effect of
the saturation magnetisation. An analysis has been developed providing a base
for a numerical description of the system. PACS numbers: 74.50.+r, 74.80.Fp,
85.30St",9903237v1
1999-05-08,H_c_3 for a thin-film superconductor with a ferromagnetic dot,"We investigate the effect of a ferromagnetic dot on a thin-film
superconductor. We use a real-space method to solve the linearized
Ginzburg-Landau equation in order to find the upper critical field, H_c_3. We
show that H_c_3 is crucially dependent on dot composition and geometry, and may
be significantly greater than H_c_2. H_c_3 is maximally enhanced when (1) the
dot saturation magnetization is large, (2) the ratio of dot thickness to dot
diameter is of order one, and (3) the dot thickness is large.",9905107v1
2000-06-27,Energy separation of single-particle and continuum states in a S=1/2 weakly-coupled chains antiferromagnet,"Inelastic neutron scattering is used to study transverse-polarized magnetic
excitations in the quasi-one-dimensional S=1/2 antiferromagnet BaCu_2Si_2O_7,
where the saturation value for the N\'eel order parameter is $m_0=0.12 \mu_{\rm
B}$ per spin. At low energies the spectrum is totally dominated by
resolution-limited spin wave-like excitations. An excitation continuum sets in
above a well-defined threshold frequency. Experimental results are discussed in
the context of current theories for weakly-interacting quantum half-integer
spin chains.",0006426v1
2000-12-10,Out-of-Equilibrium Kondo Effect: Response to Pulsed Fields,"The current in response to a rectangular pulsed bias potential is calculated
exactly for a special point in the parameter space of the nonequilibrium Kondo
model. Our simple analytical solution shows the all essential features
predicted by the noncrossing approximation, including a hierarchy of time
scales for the rise, saturation, and fall-off of the current; current
oscillations with a frequency of eV/hbar; and the instantaneous reversal of the
fall-off current for certain pulse lengths. Rich interference patterns are
found for a nonzero magnetic field (either dc or pulsed), with several
underlying time scales. These features should be observable in ultra small
quantum dots.",0012163v1
2001-02-23,Pressure dependence of the spin dynamics around a quantum critical point : An inelastic neutron scattering study of Ce0.87La0.13Ru2Si2,"Inelastic neutron scattering experiments performed on a single crystal of the
antiferromagnetic compound Ce$_{0.87}$La$_{0.13}$Ru$_{2}$Si$_{2}$ under applied
pressures of up to 5 kbar are reported. A quantum critical point is reached at
around 2.6 kbar where long-range magnetic order disappears. The variation of
the characteristic energy scales with respect to temperature and pressure is
followed and found to saturate in the ordered phase.",0102427v1
2001-04-27,Realization of Bose-Einstein condensates in lower dimensions,"Bose-Einstein condensates of sodium atoms have been prepared in optical and
magnetic traps in which the energy-level spacing in one or two dimensions
exceeds the interaction energy between atoms, realizing condensates of lower
dimensionality. The cross-over into two-dimensional and one-dimensional
condensates was observed by a change in aspect ratio and saturation of the
release energy when the number of trapped atoms was reduced.",0104549v1
2001-06-22,(13)C NMR investigation of the superconductor MgCNi_3 up to 800K,"We report (13)C NMR characterization of the new superconductor MgCNi_3 (He et
al., Nature (411), 54 (2001)). We found that both the uniform spin
susceptibility and the spin fluctuations show a strong enhancement with
decreasing temperature, and saturate below ~50K and ~20K respectively. The
nuclear spin-lattice relaxation rate 1/(13)T_1T exhibits typical behaviour for
isotropic s-wave superconductivity with a coherence peak below Tc=7.0K that
grows with decreasing magnetic field.",0106476v3
2002-03-14,Spin dynamics in a hole-doped S=1/2 Heisenberg antiferromagnet with a disordered ground state,"Only 3% hole doping by Li is sufficient to suppress the long-range
antiferromagnetic order in La2CuO4. Spin dynamics in such a disordered state
was investigated with measurements of the dynamic magnetic structure factor
S(omega,q), using cold neutron spectroscopy, for La2(Cu0.94Li0.06)O4. The
S(omega,q) is found to sharply peak at (pi,pi), and its dynamics to be
relaxational. Confirming theoretical expectation for the quantum disordered 2D
S=1/2 Heisenberg antiferromagnet, the energy scale saturates at a finite value
at low temperatures. Possible connection to the ``pseudo spin gap'' phenomenon
observed in the NMR/NQR studies on underdoped cuprates is discussed.",0203318v1
2002-05-01,Barkhausen Noise and Critical Scaling in the Demagnetization Curve,"The demagnetization curve, or initial magnetization curve, is studied by
examining the embedded Barkhausen noise using the non-equilibrium, zero
temperature random-field Ising model. The demagnetization curve is found to
reflect the critical point seen as the system's disorder is changed. Critical
scaling is found for avalanche sizes and the size and number of spanning
avalanches. The critical exponents are derived from those related to the
saturation loop and subloops. Finally, the behavior in the presence of long
range demagnetizing fields is discussed. Results are presented for simulations
of up to one million spins.",0205021v1
2002-08-21,A key to room-temperature ferromagnetism in Fe-doped ZnO: Cu,"Successful synthesis of room-temperature ferromagnetic semiconductors,
Zn$_{1-x}$Fe$_{x}$O, is reported. The essential ingredient in achieving
room-temperature ferromagnetism in bulk Zn$_{1-x}$Fe$_{x}$O was found to be
additional Cu doping. A transition temperature as high as 550 K was obtained in
Zn$_{0.94}$Fe$_{0.05}$Cu$_{0.01}$O; the saturation magnetization at room
temperature reached a value of $0.75 \mu_{\rm B}$ per Fe. Large
magnetoresistance was also observed below $100 $K.",0208399v1
2002-10-14,Phase diagram and influence of defects in the double perovskites,"The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo
O_6 is analyzed, with and without disorder due to antisites. In addition to an
homogeneous half metallic ferrimagnetic phase in the absence of doping and
disorder, we find antiferromagnetic phases at large dopings, and other
ferrimagnetic phases with lower saturation magnetization, in the presence of
disorder.",0210303v2
2002-11-14,Electron Spin Polarization in Resonant Interband Tunneling Devices,"We study spin-dependent interband resonant tunneling in double-barrier
InAs/AlSb/ GaMnSb heterostructures. We demonstrate that these structures can be
used as spin filters utilizing spin-selective tunneling of electrons through
the light-hole resonant channel. High densities of the spin polarized electrons
injected into bulk InAs make spin resonant tunneling devices a viable
alternative for injecting spins into a semiconductor. Another striking feature
of the proposed devices is the possibility of inducing additional resonant
channels corresponding to the heavy holes. This can be implemented by
saturating the in-plane magnetization in the quantum well.",0211300v1
2003-07-04,Electronic and magnetic properties of GaMnAs: Annealing effects,"The effect of short-time and long-time annealing at 250C on the conductivity,
hole density, and Curie temperature of GaMnAs single layers and GaMnAs/InGaMnAs
heterostructures is studied by in-situ conductivity measurements as well as
Raman and SQUID measurements before and after annealing. Whereas the
conductivity monotonously increases with increasing annealing time, the hole
density and the Curie temperature show a saturation after annealing for 30
minutes. The incorporation of thin InGaMnAs layers drastically enhances the
Curie temperature of the GaMnAs layers.",0307102v1
2003-07-08,"Induced currents, frozen charges and the quantum Hall effect breakdown","Puzzling results obtained from torque magnetometry in the quantum Hall effect
(QHE) regime are presented, and a theory is proposed for their explanation.
Magnetic moment saturation, which is usually attributed to the QHE breakdown,
is shown to be related to the charge redistribution across the sample.",0307180v2
2003-12-02,The Efficiency of Defect Production in Planar Superconductors and Liquid Crystals,"A recent experiment that sees the spontaneous creation of magnetic flux on
quenching high-$T_c$ films has shown that earlier null results were a
consequence of the lack of saturation of the Zurek-Kibble causal bounds against
which flux density was measured. In this letter we estimate how efficient the
production of topological charge is in planar systems, both for the
aforementioned experiment (when flux measures topological charge) and for an
earlier experiment on planar liquid crystals. Agreement is good.",0312082v1
2004-03-17,Hall effect in Fe$_3$O$_4$ epitaxial thin films,"Magnetite epitaxial thin films have been prepared by pulsed laser deposition
at 340 C on MgO and Si substrates. One key result is that the thin film
properties are almost identical to the properties of bulk material. For 40 - 50
nm thick films, the saturation magnetization and conductivity are respectively
453 emu/cm^3 and 225 1/(Ohm cm) at room temperature. The Verwey transition is
at 117 K. The Hall effect indicates an electron concentration corresponding to
0.22 electrons per formula unit at room temperature. Normal and anomalous Hall
effect both have a negative sign.",0403422v2
2004-04-19,High Curie temperatures in ferromagnetic Cr-doped AlN thin films,"Al1-xCrxN thin films with $0.02\le x \le 0.1$ were deposited by reactive
co-sputtering onto c-plane (001) sapphire. Room-temperature ferromagnetism with
a coercive field of 85 Oe was observed in samples with chromium contents as low
as x = 0.027 (2.7%). With increasing Cr content the mean magnetic moment is
strongly suppressed, with a maximum saturation moment of 0.62 and 0.71 $\mu_B$
per Cr atom at 300 and 50 K respectively. We show that the Curie temperature of
Al1-xCrxN for x = 0.027 is greater than 900 K.",0404436v1
2004-05-13,Magnetization reduction induced by nonlinear effects,"This letter reports the first detailed measurement of $M_z$, the component
parallel to the effective field direction, when ferromagnets are excited by
microwave fields at high power levels. It is found that $M_z$ drops
dramatically at the saturation of the main resonance. Simultaneous measurements
of $M_z$ and absorption power show that this drop corresponds to a diminution
of the spin-lattice relaxation rate. These changes are interpreted as
reflecting the properties of longitudinal spinwaves excited above Suhl's
instability. Similar behavior should be expected in spinwave emission by
currents.",0405301v3
2004-07-23,"High Pressure Effects on Superconductivity in the beta-pyrochlore Oxides AOs2O6 (A=K, Rb, Cs)","Recently new pyrochlore oxides superconductors AOs2O6 (A=K,Rb,Cs) were found
and we measured the pressure dependence of magnetization up to 1.2 GPa in order
to deduce the pressure effect of Tc in the three beta-pyrochlore oxides. It is
found that the initial pressure dependence of Tc is positive for all the
compounds. Only KOs2O6 exhibits a saturation in Tc at 0.56 GPa and the downturn
at higher pressure",0407610v1
2004-08-31,Current fluctuations of an interacting quantum dot,"We calculate the counting statistics of electron transfer through an open
quantum dot with charging interaction. A dot that is connected to leads by two
single-channel quantum point contacts in an in-plane magnetic field is
described by a Luttinger liquid with impurity at the Toulouse point. We find
that the fluctuations of the current through this conductor exhibit distinctive
interaction effects. Fluctuations saturate at high voltages, while the mean
current increases linearly with the bias voltage. All cumulants higher than the
second one reach at large bias a temperature independent limit.",0408666v2
2004-10-12,High-Tc Superconductors - based Nanocomposites with Improved Intergrain Coupling and Enhanced Bulk Pinning,"Heterogeneous sonochemical synthesis was used to modify superconducting
properties of granular YBa2Ca3CuO7-y and Bi2Sr2CaCu2O8+x. Sonication of
liquid-powder alkane slurries produces material with enhanced intergrain
coupling and improved current-carrying capabilities. Co-sonication with metals
and organometallics results in highly compact nanocomposites with increased
magnetic irreversibility. Ultrasonic irradiation of YBa2Ca3CuO7-y carried under
partial oxygen atmosphere produces similar morphological effects and increases
superconducting transition temperature due to effective surface saturation with
oxygen. Detailed chemical and physical characterization of sonochemically
prepared high-Tc nanocomposites is presented.",0410267v1
2005-02-15,Computation of dynamical correlation functions of Heisenberg chains in a field,"We compute the momentum- and frequency-dependent longitudinal spin structure
factor for the one-dimensional spin-1/2 $XXZ$ Heisenberg spin chain in a
magnetic field, using exact determinant representations for form factors on the
lattice. Multiparticle contributions are computed numerically throughout the
Brillouin zone, yielding saturation of the sum rule to high precision.",0502365v1
2005-09-28,Magnetic properties of antiferromagnetically coupled CoFeB/Ru/CoFeB,"This work reports on the thermal stability of two amorphous CoFeB layers
coupled antiferromagnetically via a thin Ru interlayer. The saturation field of
the artificial ferrimagnet which is determined by the coupling, J, is almost
independent on the annealing temperature up to more than 300 degree C. An
annealing at more than 325 degree C significantly increases the coercivity, Hc,
indicating the onset of crystallization.",0509753v1
2005-11-29,Slow spin relaxation in a highly polarized cooperative paramagnet,"We report measurements of the ac susceptibility of the cooperative paramagnet
Tb2Ti2O7 in a strong magnetic field. Our data show the expected saturation
maximum in chi(T) and also an unexpected low frequency dependence (< 1 Hz) of
this peak, suggesting very slow spin relaxations are occurring. Measurements on
samples diluted with nonmagnetic Y3+ or Lu3+ and complementary measurements on
pure and diluted Dy2Ti2O7 strongly suggest that the relaxation is associated
with dipolar spin correlations, representing unusual cooperative behavior in a
paramagnetic system.",0511716v1
2007-01-12,Spectroscopy of the parametric magnons excited by 4-wave process,"Using a Magnetic Resonace Force Microscope, we have performed ferromagnetic
resonance (FMR) spectroscopy on parametric magnons created by 4-wave process.
This is achieved by measuring the differential response to a small source
modulation superimposed to a constant excitation power that drives the dynamics
in the saturation regime of the transverse component. By sweeping the applied
field, we observe abrupt readjustement of the total number of magnons each time
the excitation coincides with a parametric mode. This gives rise to
ultra-narrow peaks whose linewith is lower than $5~10^{-6}$ of the applied
field.",0701287v1
2007-03-07,Theory of resonant spin Hall effect,"A biref review is presented on resonant spin Hall effect, where a tiny
external electric field induces a saturated spin Hall current in a
2-dimensional electron or hole gas in a perpendicular magnetic field. The
phenomenon is attributted to the energy level crossing associated with the
spin-orbit coupling and the Zeeman splitting. We summarize recent theoretical
development of the effect in various systems and discuss possible experiments
to observe the effect.",0703176v1
1999-11-11,Inertial Control of the VIRGO Superattenuator,"The VIRGO superattenuator (SA) is effective in depressing the seismic noise
below the thermal noise level above 4 Hz. On the other hand, the residual
mirror motion associated to the SA normal modes can saturate the dynamics of
the interferometer locking system. This motion is reduced implementing a
wideband (DC-5 Hz) multidimensional control (the so called inertial damping)
which makes use of both accelerometers and position sensors and of a DSP
system. Feedback forces are exerted by coil-magnet actuators on the top of the
inverted pendulum. The inertial damping is successful in reducing the mirror
motion within the requirements. The results are presented.",9911044v1
1996-02-28,Charged Pion Polarizabilities to two Loops,"We evaluate the electric and magnetic polarizabilities of charged pions in
the framework of chiral perturbation theory at next-to-leading order. This
requires a two-loop evaluation of the Compton amplitude near threshold. We
estimate the two new low-energy constants which enter the chiral expansion at
this order with resonance saturation. The numerical results are compared with
presently available experimental information.",9602421v1
1994-07-28,Spontaneous Breakdown of the Lorentz Invariance and the Nambu-Goldstone Theorem,"In a class of three-dimensional abelian gauge theory the Lorentz invariance
is spontaneously broken by dynamical generation of a magnetic field. An
originally topologically massive photon becomes gapless, i.e. p_0=0 at {\vec
p}=0. Indeed, the photon is the Nambu-Goldstone boson associated with the
spontaneous breaking of the Lorentz invariance. Although symmetry generated by
two Lorentz boost generators is broken, there seems to appear only one physical
Nambu-Goldstone boson, namely a photon. We argue that the Ward identities in
the Nambu-Goldstone theorem are saturated by the photon pole.",9407188v1
1995-10-18,Discontinuous BPS spectra in $N = 2$ gauge theory,"We consider the spectrum of BPS saturated states in $N = 2$ gauge theories in
four dimensions. This spectrum may be discontinuous across real codimension one
submanifolds of marginal stability in the moduli space of vacua. An example,
which can be treated with semiclassical methods in the weak coupling limit, is
the decay of quark-soliton bound states. For a quark and a soliton of
electric-magnetic charge vectors $Q$ and $Q^\prime$ respectively, we find that
as the manifold of marginal stability is crossed, the number of soliton states
changes by a factor of $2^{Q \cdot Q^\prime}$, where the dot denotes the
symplectic product.",9510138v1
1996-06-02,More on Four-Dimensional Extremal Black Holes,"We consider an embedding of the extremal four-dimensional
Reissner-Nordstr\""om black hole into type $IIB$ string theory. The equivalent
type $IIB$ configuration, in the D-brane weak-coupling picture, is a bound
state of D1- and D5-branes threaded by fundamental type $IIB$ strings. The
bound state involves also a NSNS solitonic 5-brane, mimicking the role of the
Kaluza-Klein magnetic monopole. The statistical entropy derived by counting the
degeneracy of the BPS-saturated excitations of this bound state agrees
perfectly with the (semiclassical) Bekenstein-Hawking formula.",9605236v1
1997-03-27,Self-dual Chern-Simons Solitons in the Planar Ferromagnet,"We consider a uniaxial planar ferromagnet coupled minimally to an Abelian
Chern-Simons gauge field and study self-dual solitons which saturate the
Bogomol'nyi bound. We find a rich structure of rotationally symmetric static
soliton solutions for various uniform background charge densities. For a given
ferromagnet material, the properties of these solitons are controlled only by
the external magnetic field and the background charge.",9703193v1
1998-05-18,On N=2 MQCD,"We review M-theory description of 4d N=2 SQCD. Configurations of M-theory
fivebranes relevant to describe the moduli spaces of the Coulomb and Higgs
branches are studied using the Taub-NUT geometry. Minimal area membranes
related with the BPS states of N=2 SQCD are given explicitly. They almost
saturate the BPS bounds. The deviation from the bounds is due to their boundary
condition constrained by the fivebrane. The electric-magnetic duality at the
baryonic branch root is also examined from the M-theory viewpoint. In this
course, novel concepts such as creation of brane and exchange of branes in Type
II theory are explained in the framework of M-theory.",9805107v1
2006-01-27,Signature of directed chaos in the conductance of a nanowire,"We study the conductance of chaotic or disordered wires in a situation where
equilibrium transport decomposes into biased diffusion and a counter-moving
regular current. A possible realization is a semiconductor nanostructure with
transversal magnetic field and suitably patterned surfaces. We find a
non-trivial dependence of the conductance on the wire length which differs
qualitatively from Ohm's law by the existence of a characteristic length scale
and a finite saturation value.",0601058v2
2006-05-02,Isospin violation in the vector form factors of the nucleon,"A quantitative understanding of isospin violation is an increasingly
important ingredient for the extraction of the nucleon's strange vector form
factors from experimental data. We calculate the isospin violating electric and
magnetic form factors in chiral perturbation theory to leading and
next-to-leading order respectively, and we extract the low-energy constants
from resonance saturation. Uncertainties are dominated largely by limitations
in the current knowledge of some vector meson couplings. The resulting bounds
on isospin violation are sufficiently precise to be of value to on-going
experimental studies of the strange form factors.",0605006v1
2007-04-25,Quantized spin excitations in a ferromagnetic microstrip from microwave photovoltage measurements,"Quantized spin excitations in a single ferromagnetic microstrip have been
measured using the microwave photovoltage technique. Several kinds of spin wave
modes due to different contributions of the dipole-dipole and the exchange
interactions are observed. Among them are a series of distinct dipole-exchange
spin wave modes, which allow us to determine precisely the subtle spin boundary
condition. A comprehensive picture for quantized spin excitations in a
ferromagnet with finite size is thereby established. The dispersions of the
quantized spin wave modes have two different branches separated by the
saturation magnetization.",0704.3397v1
2007-04-26,Spin effects in single-electron transport through carbon nanotube quantum dots,"We investigate the total spin in an individual single-wall carbon nanotube
quantum dot with various numbers of electrons in a shell by using the ratio of
the saturation currents of the first steps of Coulomb staircases for positive
and negative biases. The current ratio reflects the total-spin transition that
is increased or decreased when the dot is connected to strongly asymmetric
tunnel barriers. Our results indicate that total spin states with and without
magnetic fields can be traced by this method.",0704.3505v2
2007-06-19,Proximity effects induced by a gold layer on La0.67Sr0.33MnO3 thin films,"We report about La0.67Sr0.33MnO3 single crystal manganite thin films in
interaction with a gold capping layer. With respect to uncoated manganite
layers of the same thickness, Au-capped 4 nm-thick manganite films reveal a
dramatic reduction (about 185 K) of the Curie temperature TC and a lower
saturation low-temperature magnetization M0. A sizeable TC reduction (about 60
K) is observed even when an inert SrTiO3 layer is inserted between the gold
film and the 4 nm-thick manganite layer, suggesting that this effect might have
an electrostatic origin.",0706.2688v1
2007-08-06,Multi-magnon bound states in the frustrated ferromagnetic 1D chain,"We study a one-dimensional Heisenberg chain with competing ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest neighbor interactions in
magnetic field. Starting from the fully polarized high-field state, we
calculate the dispersions of the lowest-lying $n$-magnon excitations and the
saturation field (n=2,3,4). We show that the lowest-lying excitations are
always bound multi-magnon states with a total momentum of $\pi$ except for a
small parameter range. We argue that bose condensation of the bound $n$ magnons
leads to novel Tomonaga-Luttinger liquids with multi-polar correlations;
nematic and triatic ordered liquids correspond to n=2 and n=3.",0708.0701v1
2007-11-21,"Electron-electron interaction in 2D and 1D ferromagnetic (Ga,Mn)As","We investigated the magnetotransport in high quality ferromagnetic (Ga,Mn)As
films and wires. At low temperature the conductivity decreases with decreasing
temperature without saturation down to 20 mK. Here we show, that the
conductivity decrease follows a ln($T/T_0$) dependency in 2D films and a
$-1/\sqrt{T}$ dependency in 1D wires and is independent of an applied magnetic
field. This behavior can be explained by the theory of electron-electron
interaction.",0711.3278v2
2008-03-05,Vanishing Hall Coefficient in the Extreme Quantum Limit in Photocarrier-Doped SrTiO3,"We have investigated the extreme quantum limit of photogenerated electrons in
quantum paraelectric SrTiO3. This regime is distinct from conventional
semiconductors, due to the large electron effective mass and large lattice
dielectric constant. At low temperature, the magnetoresistance and Hall
resistivity saturate at high magnetic field, deviating from conventional
behavior. As a result, the Hall coefficient vanishes on the scale of the ratio
of the Landau level splitting to the thermal energy, indicating the essential
role of lowest Landau level occupancy, as limited by thermal broadening.",0803.0723v1
2008-07-02,History and results of the Riga dynamo experiments,"On 11 November 1999, a self-exciting magnetic eigenfield was detected for the
first time in the Riga liquid sodium dynamo experiment. We report on the long
history leading to this event, and on the subsequent experimental campaigns
which provided a wealth of data on the kinematic and the saturated regime of
this dynamo. The present state of the theoretical understanding of both regimes
is delineated, and some comparisons with other laboratory dynamo experiments
are made.",0807.0305v1
2008-07-25,Gluon Saturation and the Formation Stage of Heavy Ion Collisions,"The high energy limit of QCD is controlled by very high energy density
gluonic matter, the Color Glass Condensate. In the first instants of the
collisions of two sheets of Colored Glass Condensate, a Glasma is formed with
longitudinal flux tubes of color electric and magnetic fields. These flux tubes
decay and might form a turbulent liquid that eventually thermalizes into a
Quark Gluon Plasma",0807.4095v1
2009-02-09,Modulation-free pump-probe spectroscopy of strontium atoms,"We have performed polarization spectroscopy and sub-Doppler DAVLL on the
(5s5s) 1^S_0 -> (5s5p) 1^P_1 transition of atomic strontium. Both techniques
generated a dispersion-type lineshape suitable for laser stabilization, without
the need for frequency modulation. In both cases the signal is generated
primarily by saturation effects, rather than optical pumping. The dependence of
the amplitude and gradient on intensity and magnetic field were also
investigated.",0902.1430v1
2009-04-09,Chiral Anomaly and Decay of Color Electric Field,"Using the formula of chiral anomaly, we discuss the pair production of quarks
under color electric field $\vec{E}$ without addressing explicit formula of
quark's wavefunctions. The production is assumed to occur under the effect of
color magnetic field $\vec{B}$ as well as the color electric field. We obtain
the life time $t_c$ of the color electric field in the limit of $B\gg E$.
Applying it to the glasma in high-energy heavy-ion collisions, we find that
$t_c\simeq 10Q_s^{-1}$ with saturation momentum $Q_s$.",0904.1449v2
2009-05-01,Self-organization of dissipationless solitons in negative refractive index materials,"General nonlinear and nonparaxial dissipative complex Helmholtz equations for
magnetic and electric fields propagating in negative refractive index materials
(NIMs) are derived ab initio from Maxwell equations. In order to describe
nonconservative soliton dynamics in NIMs, such coupled equations are reduced
into generalized Ginzburg-Landau equation. Cross-compensation between the
excess of saturating nonlinearity, losses, and gain renders these
self-organized solitons dissipationless and exceptionally robust. The presence
of such solitons makes NIMs effectively dissipationless.",0905.0037v1
2010-03-14,Direct Measurement of Cyclotron Coherence Times of High-Mobility Two-Dimensional Electron Gases,"We have observed long-lived (~30 ps) coherent oscillations of charge carriers
due to cyclotron resonance (CR) in high-mobility two-dimensional electrons in
GaAs in perpendicular magnetic fields using time-domain terahertz spectroscopy.
The observed coherent oscillations were fitted well by sinusoids with
exponentially-decaying amplitudes, through which we were able to provide direct
and precise measures for the decay times and oscillation frequencies
simultaneously. This method thus overcomes the CR saturation effect, which is
known to prevent determination of true CR linewidths in high-mobility electron
systems using Fourier-transform infrared spectroscopy.",1003.2795v1
2010-06-08,Possible evidence for two-gap superconductivity in TiSe_2Cu_x,"We report a comprehensive TF-muSR study of TiSe_2Cu_2. The magnetic
penetration depth was found to saturate at low temperature as expected in an
s-wave SC. As x is increased we find that the superfluid density increases and
the size of the superconducting gap, calculated from the temperature dependence
of the superfluid density, is approaching the BCS value. However, for low
values of x, the gap is smaller than the weak-coupling BCS prediction
suggesting that two superconducting gaps are present in the sample.",1006.1630v1
2010-08-25,Colossal negative magnetoresistance in dilute fluorinated graphene,"Adatoms offer an effective route to modify and engineer the properties of
graphene. In this work, we create dilute fluorinated graphene using a clean,
controlled and reversible approach. At low carrier densities, the system is
strongly localized and exhibits an unexpected, colossal negative
magnetoresistance. The zero-field resistance is reduced by a factor of 40 at
the highest field of 9 T and shows no sign of saturation. Unusual ""staircase""
field dependence is observed below 5 K. The magnetoresistance is highly
anisotropic. We discuss possible origins, considering quantum interference
effects and adatom-induced magnetism in graphene.",1008.4387v1
2010-10-23,High spin polarization in epitaxial films of ferrimagnetic Mn3Ga,"Ferrimagnetic Mn3Ga exhibits a unique combination of low saturation
magnetization (Ms = 0.11 MA m-1) and high perpendicular anisotropy with a
uniaxial anisotropy constant of Ku = 0.89 MJ m-3. Epitaxial c-axis films
exhibit spin polarization as high as 58%, measured using point contact Andreev
reflection. These epitaxial films will be able to support thermally stable
sub-10 nm bits for spin transfer torque memories.",1010.4872v1
2010-12-27,Disorder induced superconducting ratchet effect in nanowires,"A dc voltage drop develops along amorphous indium oxide nanowires that are
exposed to an ac bias source. This voltage is anti-symmetric with magnetic
field and is characterized by sample specific quasi-periodic magneto-voltage
oscillations. The voltage magnitude increases with decreasing temperature below
$T_{C}$ but saturates at low T. As the disorder of the sample is decreased, the
dc voltage is suppressed. We suggest that this rectification is a manifestation
of the superconducting ratchet effect in which disorder and geometrical
confinement play the role of asymmetric pinning centers. This effect
demonstrates the importance of inherent inhomogeneity and vortex motion in the
superconductor-insulator transition of disordered superconductors.",1012.5609v1
2011-03-25,Magnetic Neutron Scattering in Solid Oxygen and its Applications to Ultracold Neutron Production,"Using neutron scattering, we investigate the static and dynamic structure
functions $S(Q,\omega)$ of 3 distinct solid phases (using powder average
techniques), and characterize the corresponding modes of energy excitation,
focusing primarily on the dynamics of spin interaction. With the $S(Q,\omega)$
maps, we extract the temperature dependent production rate and upscattering
cross section, that are relevant for understanding experimental data on
ultracold neutron production in solid oxygen at the saturated vapor pressure.",1103.5091v1
2011-07-31,Electrolyte gate-controlled Kondo effect in SrTiO3,"We report low-temperature, high-field magnetotransport measurements of SrTiO3
gated by an ionic gel electrolyte. A saturating resistance upturn and negative
magnetoresistance that signal the emergence of the Kondo effect appear for
higher applied gate voltages. This observation, enabled by the wide tunability
of the ionic gel-applied electric field, promotes the interpretation of the
electric field-effect induced 2D electron system in SrTiO3 as an admixture of
magnetic Ti3+ ions, i.e. localized and unpaired electrons, and delocalized
electrons that partially fill the Ti 3d conduction band.",1108.0139v2
2011-08-03,Parametric amplification of magnetoplasmons in semiconductor quantum dots,"We show that the magnetoplasmon collective modes in quasi-two-dimensional
semiconductor quantum dots can be parametrically amplified by periodically
modulating the magnetic field perpendicular to the nanostructure. The two
magnetoplasmon modes are excited and amplified simultaneously, leading to an
exponential growth of the number of bosonic excitations in the system. We
further demonstrate that damping mechanisms as well as anharmonicities in the
confinement of the quantum dot lead to a saturation of the parametric
amplification. This work constitutes a first step towards parametric
amplification of collective modes in many-body fermionic systems beyond one
dimension.",1108.0891v3
2011-10-11,Uncertainty relation for photons,"Uncertainty relation for photons that overcomes the difficulties caused by
the nonexistence of the photon position operator is derived in quantum
electrodynamics. The photon energy density plays the role of the probability
density in configuration space. It is shown that the measure of the spatial
extension based on the energy distribution in space combined with a measure of
the spread in the photon momentum leads to an inequality that is a natural
counterpart of the standard Heisenberg relation. Unexpectedly, the equation
satisfied by the photon wave function in momentum space which saturates the
uncertainty relations has the form of the Schr\""odinger equation in coordinate
space in the presence of electric and magnetic charges.",1110.2415v2
2011-11-22,z/-z Symmetry of spin-orbit coupling and weak localization in graphene,"We show that the influence of spin-orbit (SO) coupling on the weak
localization effect for electrons in graphene depends on the lack or presence
of z/-z symmetry in the system. While for z/-z asymmetric SO coupling,
disordered graphene should display a weak anti-localization behavior at lowest
temperature, z/-z symmetric coupling leads to an effective saturation of
decoherence time which can be partially lifted by an in-plane magnetic field,
thus, tending to restore the weak localization effect.",1111.5267v1
2012-05-11,Magnetic penetration depth in the presence of a spin-density wave in multiband superconductors at zero temperature,"We present a theoretical description of the London penetration depth of a
multi-band superconductor in the case when both superconducting and
spin-density wave orders coexist. We focus on clean systems and zero
temperature to emphasize the effect of the two competing orders. Our
calculation shows that the supefluid density closely follows the evolution of
the superconducting order parameter as doping is increased, saturating to a BCS
value in the pure superconducting state. Furthermore, we predict a strong
anisotropic in-pane penetration depth induced by the spin-density wave order.",1205.2564v1
2012-07-05,Magnetoresistance from quenching of spin quantum correlation in organic semiconductors,"We present a theory of organic magnetoresistance (OMR) based on the quenching
of the quantum correlation between the carrier's spin and its local environment
when the incoherent hopping takes place. We prove that this process contributes
a spin-dependent prefactor to the attempt-to-escape frequency in the hopping
rate, with its value modulated by the magnetic field. The resulting OMR
exhibits a positive Lorentzian saturation component and a negative small-field
component, which are independent of model parameters. These behaviors, with
their isotope effects, are in good agreement with experimental results.",1207.1152v2
2012-07-24,Exact results on the Kondo-lattice magnetic polaron,"In this work we revise the theory of one electron in a ferromagnetically
saturated local moment system interacting via a Kondo-like exchange
interaction. The complete eigenstates for the finite lattice are derived. It is
then shown, that parts of these states lose their norm in the limit of an
infinite lattice. The correct (scattering) eigenstates are calculated in this
limit. The time-dependent Schr\""odinger equation is solved for arbitrary
initial conditions and the connection to the down-electron Green's function and
the scattering states is worked out. A detailed analysis of the down-electron
decay dynamics is given.",1207.5623v1
2012-08-27,Linear magnetoresistance on the topological surface,"A positive, non-saturating and dominantly linear magnetoresistance is
demonstrated to occur in the surface state of a topological insulator having a
wavevector-linear energy dispersion together with a finite positive Zeeman
energy splitting. This linear magnetoresistance shows up within quite wide
magnetic-field range in a spatially homogenous system of high carrier density
and low mobility in which the conduction electrons are in extended states and
spread over many smeared Landau levels, and is robust against increasing
temperature, in agreement with recent experimental findings in Bi$_2$Se$_3$
nanoribbons.",1208.5351v1
2014-03-14,Multiferroic Studies on La0.7Bi0.3CrO3 Perovskite,"Magnetic and dielectric properties on a polycrystalline La0.7Bi0.3CrO3 have
been investigated. A canted antiferromagnetic (CAF) phase transition giving
weak ferromagnetism at TN = 230K has been observed. M-H at 10K shows
non-saturating trend, even up to 5T, confirms the CAF ordering. The
permittivity ({\epsilon}')-vs-temperature (T) variation shows a relaxor
ferroelectric (RFE) nature accompanied by a pronounced anomaly in {\epsilon}'-T
at TN. The anomaly in {\epsilon}'-T at TN indicates the presence of
magentoelectric (ME) coupling in this material.",1403.3520v1
2014-03-26,Energy-based modeling of electric motors,"We propose a new approach to model electrical machines based on energy
considerations and construction symmetries of the motor. We detail the approach
on the Permanent-Magnet Synchronous Motor and show that it can be extended to
Synchronous Reluctance Motor and Induction Motor. Thanks to this approach we
recover the usual models without any tedious computation. We also consider
effects due to non-sinusoidal windings or saturation and provide experimental
data.",1403.6641v1
2014-07-23,Organic magnetoresistance from deep traps,"We predict that singly-occupied carrier traps, produced by electrical stress
or irradiation within organic semiconductors, can cause spin blockades and the
large room-temperature magnetoresistance known as organic magnetoresistance.
The blockade occurs because many singly-occupied traps can only become doubly
occupied in a spin-singlet configuration. Magnetic-field effects on spin mixing
during transport dramatically modify the effects of this blockade and produce
magnetoresistance.We calculate the quantitative effects of these traps on
organic magnetoresistance from percolation theory and find a dramatic nonlinear
dependence of the saturated magnetoresistance on trap density, leading to
values $\sim$ 20%, within the theory's range of validity.",1407.6277v1
2014-08-19,Magnetoresistive property study of direct and indirect band gap thermoelectric Bi-Sb alloys,"We report magnetoresistive properties of direct and indirect band gap
Bismuth-Antimony (Bi-Sb) alloys. Band gap increases with magnetic field. Large
positive magnetoresistance (MR) approaching to 400 % is observed. Low field MR
experiences quadratic growth and at high field it follows a nearly linear
behavior without sign of saturation. Carrier mobility extracted from low field
MR data, depicts remarkable high value. Correlation between MR and mobility is
revealed. We demonstrate that the strong nearly linear MR at high field can be
well understood by classical method, co-build by Parish and Littlewood.",1408.4305v1
2014-09-16,Tuning ferromagnetism at interfaces between insulating perovskite oxides,"We use density functional theory calculations to show that the LaAlO3|SrTiO3
interface between insulating perovskite oxides is borderline in satisfying the
Stoner criterion for itinerant ferromagnetism and explore other oxide
combinations with a view to satisfying it more amply. The larger lattice
parameter of an LaScO3|BaTiO3 interface is found to be less favorable than the
greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the
latter is predicted to exhibit robust magnetism with a larger saturation moment
and a higher Curie temperature. Our results provide support for a ""two phase""
picture of coexistent superconductivity and ferromagnetism.",1409.4554v1
2015-09-27,Exchange Bias following Kinetic Arrest,"Exchange bias is often observed when anti-ferromagnetic and ferromagnetic
phases coexist. The coexistence of two competing magnetic phases can persist to
the lowest temperatures if the disorder-broadened 1st order transition
separating them is interrupted, as is proposed in the kinetic arrest
phenomenon. The fractions of coexisting phases can, in this phenomenon, be
tuned by following different cooling protocols. We discuss predicted behaviours
of exchange bias resulting from the kinetic arrest phenomenon. Specifically,
for appropriate values of cycling field Hmax and measuring temperature T0 there
will be no exchange bias under cooling in zero field, while it will manifest
with increasing cooling field, and then saturate.",1509.08052v1
2016-01-05,Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor Belt,"We study propulsion arising from microscopic colloidal rotors dynamically
assembled and driven in a viscous fluid upon application of an elliptically
polarized rotating magnetic field. Close to a confining plate, the motion of
this self-assembled microscopic worm results from the cooperative flow
generated by the spinning particles which act as a hydrodynamic ""conveyor
belt."" Chains of rotors propel faster than individual ones, until reaching a
saturation speed at distances where induced-flow additivity vanishes. By
combining experiments and theoretical arguments, we elucidate the mechanism of
motion and fully characterize the propulsion speed in terms of the field
parameters.",1601.00806v1
2016-09-07,Magnetodielectric and spin-lattice coupling in quasi 1D Ising spin chain CoNb$_{2}$O$_{6}$,"We have studied magnetodielectric and spin-lattice coupling in
CoNb$_{2}$O$_{6}$ single crystals. Magnetostriction and magnetodielectric
experiments are performed at temperatures in and above antifferomagnetic phase
of quasi 1D Ising spin chain CoNb$_{2}$O$_{6}$. Field induced magnetic
transitions are clearly reflected in magnetodielectric measurement as well as
magnetostriction measurement also. Two sharp anomalies are found around the
critical fields of antiferromagnetic to ferrimagnetic transition and
ferrimagnetic to saturated paramagnetic transition in both magnetodielectric
and magnetostriction experiments. High field anomaly is more pronounced for
magnetodielectric response and magnetostriction also. So, in CoNb$_{2}$O$_{6}$,
spins are strongly coupled with lattice as well as charges also.",1609.02048v1
2016-10-21,Electromotive forces generated in 3d-transition ferromagnetic metal films themselves under their ferromagnetic resonance,"We report the electromotive force (EMF) properties generated in 3d-transition
ferromagnetic metal (FM = Fe, Co, and Ni80Fe20) films themselves under their
ferromagnetic resonance (FMR). For Fe and Co films, the EMF due to the
anomalous-Hall effect is dominantly generated under their FMR. Meanwhile, for a
Ni80Fe20 film, the EMF due to the inverse spin-Hall effect in the Ni80Fe20 film
itself under the FMR is mainly generated. This tendency is qualitatively
explained with differences of the spin polarization, the spin Hall
conductivity, the anomalous Hall conductivity, the magnetization saturation,
and the resistivity of the FM films.",1610.06695v2
2017-09-26,Three-dimensional Bose-Einstein Condensation in the Spin-1/2 Ferromagnetic-leg Ladder 3-Br-4-F-V,"The critical exponent of the phase boundary has been examined on the
three-dimensional incommensurate ordering phase in the spin-1/2
ferromagnetic-leg ladder 3-Br-4-F-V
[=3-(3-bromo-4-fluorophenyl)-1,5-diphenylverdazyl]. Using the
temperature-window fitting technique, we obtained the critical exponents which
agreed with the three-dimensional (3D) Bose-Einstein condensation (BEC)
universality class at both sides of the lower critical field and the saturation
field. 3-Br-4-F-V thus becomes a new member of the quantum magnets which prove
the universality of the 3D BEC exponent.",1709.08849v1
2018-05-09,Crossover of skyrmion and helical modulations in noncentrosymmetric ferromagnets,"The coupling between angular (twisting) and longitudinal modulations arising
near the ordering temperature of noncentrosymmetric ferromagnets strongly
influences the structure of skyrmion states and their evolution in an applied
magnetic field. In the precursor states of cubic helimagnets, a continuous
transformation of skyrmion lattices into the saturated state is replaced by the
first-order processes accompanied by the formation of multidomain states.
Recently the effects imposed by dominant longitudinal modulations have been
reported in bulk MnSi and FeGe. Similar phenomena can be observed in the
precursor regions of cubic helimagnet epilayers and in easy-plane chiral
ferromagnets (e.g. in the hexagonal helimagnet CrNb3S6).",1805.03360v1
2018-07-17,A Luneburg lens for spin waves,"We report on the theory of a Luneburg lens for forward-volume magnetostatic
spin waves, and verify its operation via micromagnetic modelling. The lens
converts a plane wave to a point source (and vice versa) by a designed graded
index, realised here by either modulating the thickness or the saturation
magnetization in a circular region. We find that the lens enhances the wave
amplitude by 5 times at the lens focus, and 47% of the incident energy arrives
in the focus region. Furthermore, small deviations in the profile can still
result in good focusing, if the lens index is graded smoothly.",1807.06705v1
2018-11-14,On the background-gyroresonant character of the Bell instability,"We show that the Bell instability, which is widely considered potentially
important for cosmic-ray acceleration, is the low-frequency limit of a
gyroresonant interaction between the protons of the interstellar medium and
shear-Alfv\'en waves. At large cosmic-ray current densities, its growth rate is
therefore limited by the proton gyrofrequency, and two modes emerge from the
cold-beam dispersion relation. A third mode driven by electron gyroresonance is
only weakly unstable at low current densities. We discuss implications for
magnetic-field amplification and its saturation in the vicinity of supernova
remnants.",1811.05666v1
2019-05-21,Absolute frequency measurement of rubidium 5S-6P transitions,"We report on measurements on the 5S-6P rubidium transition frequencies for
rubidium isotopes with an absolute uncertainty of better than \SI{450}{kHz} for
the 5S $\rightarrow$ 6P$_{1/2}$ transition and \SI{20}{kHz} for the 5S
$\rightarrow$ 6P$_{3/2}$ transition, achieved by saturation absorption
spectroscopy. From the results we derive the hyperfine splitting with an
accuracy of \SI{460}{kHz} and \SI{30}{kHz}, respectively. We also verify the
literature values for the isotope shifts as well as magnetic dipole constant
and the electric quadrupole constant.",1905.08824v1
2019-08-30,Late-time large-distance asymptotics of the transverse correlation functions of the XX chain in the space-like regime,"We derive an explicit expression for the leading term in the late-time,
large-distance asymptotic expansion of a transverse dynamical two-point
function of the XX chain in the spacelike regime. This expression is valid for
all non-zero finite temperatures and for all magnetic fields below the
saturation threshold. It is obtained here by means of a straightforward
term-by-term analysis of a thermal form factor series, derived in previous
work, and demonstrates the usefulness of the latter.",1908.11555v1
2019-11-12,Pairwise entanglement in double-tetrahedral chain with different Landé g-factors of the Ising and Heisenberg spins,"The pairwise entanglement is exactly examined in the spin-1/2
Ising-Heisenberg double-tetrahedral chain with different Land\'e g-factors of
the Ising and Heisenberg spins at zero and finite temperatures. It is shown
that the phenomenon present in quantum non-chiral ground states is twice as
strong as in quantum chiral ground states and that it gradually diminishes with
increasing temperature until it completely vanishes at a certain threshold
temperature. It is also demonstrated that the strong magnetic field maintains a
weak thermal entanglement quite far from the saturation field, although the
ground state is non-entangled.",1911.04754v1
2019-12-02,"Slice collective dynamics, projected emittance deterioration and Free Electron Laser performances detrimental effects","The dynamical effects inducing geometrical and phase space misalignment of
bunch slice in X-ray operating Free Electron Lasers can be traced back to a
plethora of phenomena, both in the linac accelerating section or inside the
beam transport optic magnet. They are responsible for a spoiling of the beam
projected qualities and induce, if not properly corrected, an increase of the
saturation length and a decreasing of the output power. We discuss the
inclusion of these effects in models employing scaling formulae.",1912.00906v1
2020-03-03,Heat flux sensing by anomalous Nernst effect in Fe-Al thin films on a flexible substrate,"We performed a numerical analysis of the material parameters required for
realizing a heat flux sensor exploiting the anomalous Nernst effect (ANE). The
results showed the importance of high thermopower of ANE ($S_{\text{ANE}}$) and
small saturation magnetization. This motivated us to investigate the effect of
Al substitution of Fe on ANE and found $S_{\text{ANE}} =$ 3.4 $\mu$V/K in
Fe$_{81}$Al$_{19}$ because of the dominant intrinsic mechanism. Using this
material, we made a prototype ANE-based heat flux sensor on a thin flexible
polyimide sheet and demonstrated accurate sensing with it. This study gives
important information for enhancing sensor sensitivity.",2003.01459v1
2020-05-21,Theory of ground states for classical Heisenberg spin systems VI,"We formulate part VI of a rigorous theory of ground states for classical,
finite, Heisenberg spin systems. After recapitulating the central results of
the parts I - V previously published we consider a magnetic field and
analytically calculate the susceptibility at the saturation point. To this end
we have to distinguish between parabolic and non-parabolic systems, and for the
latter ones between two- and three-dimensional ground states. These results are
checked for a couple of examples.",2005.10487v1
2020-08-26,Quantum criticality in the 2d quasiperiodic Potts model,"Quantum critical points in quasiperiodic magnets can realize new universality
classes, with critical properties distinct from those of clean or disordered
systems. Here, we study quantum phase transitions separating ferromagnetic and
paramagnetic phases in the quasiperiodic $q$-state Potts model in $2+1d$. Using
a controlled real-space renormalization group approach, we find that the
critical behavior is largely independent of $q$, and is controlled by an
infinite-quasiperiodicity fixed point. The correlation length exponent is found
to be $\nu=1$, saturating a modified version of the Harris-Luck criterion.",2008.11742v1
2022-03-09,Vector cnoidal and solitary plasmon polariton waves in a planar waveguide,"The paper considers the dynamics of nonlinear surface plasmon polariton waves
in a planar plasmon waveguide, which is a heterostructure of non-magnetic
metallic and dielectric layers. The obtained in the work nonlinear equations
and their analytical solutions describe the vector cnoidal and solitary plasmon
polariton waves excited by single electromagnetic pulse at the waveguide.
Nonlinear plasmon polariton waves arise under the influence of the Kerr
nonlinearity of metal and the saturation of nonlinearity at the
heterostructure. The period and profile of envelope of the excited nonlinear
surface plasmon polariton wave vary depending on the conditions of excitation
and the power of exciting electromagnetic pulse.",2203.05011v1
2022-05-14,S=2 Quantum Spin Chain with the Biquadratic Exchange Interaction,"The $S=2$ quantum spin chain with the single-ion anisotropy $D$ and the
biquadratic exchange interaction $J_{\rm BQ}$ is investigated using the
numerical diagonalization of finite-size clusters and the level spectroscopy
analysis. It is found that the intermediate-$D$ phase corresponding to the
symmetry protected topological (SPT) phase appears in a wide region of the
ground state phase diagram. We also obtain the phase diagram at the half of the
saturation magnetization which includes the SPT plateau phase.",2205.07005v1
2022-06-06,Parameter estimation with the steady states of non-Hermitian spin chains,"We propose a scheme for parameter estimation with the steady states of
non-Hermitian spin chains. The parameters to be estimated are encoded in the
system via the external magnetic field that imposed on the first site of the
chain. We obtain the analytical spectrum for the spin chain of two sites. We
find that the quantum Fisher information (QFI) about the amplitude of the
imposing field diverges while the QFI about the azimuthal angle reaches to the
maximum at exceptional points. Moreover, the QFI is enhanced as the system size
increasing and saturates for sufficiently long spin chain because only
short-range correlations are induced by the imposing field.",2206.02322v1
2023-03-10,Weighted CLR type bounds in two dimensions,"We derive weighted versions of the Cwikel-Lieb-Rozenblum inequality for the
Schr\""odinger operator in two dimensions with a nontrivial Aharonov-Bohm
magnetic field. Our bounds capture the optimal dependence on the flux and we
identify a class of long-range potentials that saturate our bounds in the
strong coupling limit. We also extend our analysis to the two-dimensional
Schr\""odinger operator acting on antisymmetric functions and obtain similar
results.",2303.06104v1
2023-07-28,Analysis of magneto-optical Kerr spectra of ferrimagnetic Mn$_4$N,"Simulations of magneto-optical Kerr effect in biaxially strained Mn$_4$N are
performed using density functional theory and linear response theory. We
consider three ferrimagnetic phases, two collinear and one noncollinear, which
have been corroborated separately by earlier studies. The simulated spectra are
compared to magneto-optical data available in recent literature. A collinear
ferrimagnetic phase with a small saturation magentization, a large
perpendicular anisotropy, and Curie temperature above 700~K is found to be
consistent with the measured spectra. We hypothesise that an admixture of the
noncollinear phase, which could explain the lower than predicted net moment and
magnetic anisotropy observed experimentally, is also present.",2307.15246v1
2023-12-28,Cosmic-Ray-modified and driven instabilities,"These lectures address the effects of Cosmic Rays over macro-instabilities
which develop in the interstellar medium and the micro-instabilities the
particles are able to trigger themselves. The lectures are centered on the
derivation of linear growth rates but also discuss some numerical simulations
addressing the issue of magnetic field saturation. A particular emphasis is
made on the streaming instability, an instability driven by anisotropic
cosmic-ray distributions.",2312.17134v1
2024-03-18,"A new method to search for highly ionizing exotic particles, monopoles and beyond, using time projection chamber","Measuring the energy loss and mass of highly ionizing particles predicted by
theories from beyond the Standard Model pose considerable challenges to
conventional detection techniques. Such particles are predicted to experience
energy loss to matter they pass through that exceeds the dynamic range
specified for most readout chips, leading to saturation of the detectors'
electronics. Consequently, achieving precise energy loss and mass measurements
becomes unattainable. We present a new approach to detect such highly ionizing
particles using time projection chambers that overcomes this limitation and
provide a case study for triggering on magnetic monopoles.",2403.12299v1
1997-04-14,Hydrogen Phases on the Surface of a Strongly Magnetized Neutron Star,"The outermost layers of some neutron stars are likely to be dominated by
hydrogen, as a result of fast gravitational settling of heavier elements. These
layers directly mediate thermal radiation from the stars, and determine the
characteristics of X-ray/EUV spectra. For a neutron star with surface
temperature $T\lo 10^6$ K and magnetic field $B\go 10^{12}$ G, various forms of
hydrogen can be present in the envelope, including atom, poly-molecules, and
condensed metal. We study the physical properties of different hydrogen phases
on the surface of a strongly magnetized neutron star for a wide range of field
strength $B$ and surface temperature $T$. Depending on the values of $B$ and
$T$, the outer envelope can be either in a nondegenerate gaseous phase or in a
degenerate metallic phase. For $T\go 10^5$ K and moderately strong magnetic
field, $B\lo 10^{13}$ G, the envelope is nondegenerate and the surface material
gradually transforms into a degenerate Coulomb plasma as density increases. For
higher field strength, $B>> 10^{13}$ G, there exists a first-order phase
transition from the nondegenerate gaseous phase to the condensed metallic
phase. The column density of saturated vapor above the metallic hydrogen
decreases rapidly as the magnetic field increases or/and temperature decreases.
Thus the thermal radiation can directly emerge from the degenerate metallic
hydrogen surface. The characteristics of surface X-ray/EUV emission for
different phases are discussed. A separate study concerning the possibility of
magnetic field induced nuclear fusion of hydrogen on the neutron star surface
is also presented.",9704130v1
1999-12-02,Magnetic history dependence of metastable states in systems with dipolar interactions,"We present the results of a Monte Carlo simulation of the ground state and
magnetic relaxation of a model of a thin film consisting on a two-dimensional
square lattice of Heisenberg spins with perpendicular anisotropy K, exchange J
and long-range dipolar interactions g. We have studied the ground state
configurations of this system for a wide range of the interaction parameters
J/g, K/g by means of the simulated annealing procedure, showing that the model
is able to reproduce the different magnetic configurations found in real
samples. We have found the existence of a certain range of K/g, J/g values for
which in-plane and out-of-plane configurations are quasi-degenerated in energy.
We show that when a system in this region of parameters is perturbed by an
external force that is subsequently removed different kinds of ordering may be
induced depending on the followed procedure. In particular, simulations of
relaxations from saturation under an a.c. demagnetizing field or in zero field
are in qualitative agreement with recent experiments on epitaxial and granular
alloy thin films, which show a wide variety of magnetic patterns depending on
their magnetic history.",9912025v2
2004-12-14,Current-induced magnetization changes in a spin valve due to incoherent emission of non-equilibrium magnons,"We describe spin transfer in a ferromagnet/normal metal/ferromagnet
spin-valve point contact. Spin is transferred from the spin-polarized device
current to the magnetization of the free layer by the mechanism of incoherent
magnon emission by electrons. Our approach is based on the rate equation for
the magnon occupation, using Fermi's golden rule for magnon emission and
absorption and the non-equilibrium electron distribution for a biased spin
valve. The magnon emission reduces the magnetization of the free layer. For
anti-parallel alignment of the magnetizations of the layers and at a critical
bias a magnon avalanche occurs, characterized by a diverging effective magnon
temperature. This critical behavior can result in magnetization reversal and
consequently to suppression of magnon emission. However, magnon-magnon
scattering can lead to saturation of the magnon concentration at a large but
finite value. The further behavior depends on the parameters of the system. In
particular, gradual evolution of the magnon concentration followed by a
magnetization reversal is possible. Another scenario corresponds to a step-like
increase of the magnon concentration followed by a slow decrease. In the latter
case a spike in the differential resistance is expected due to a contribution
of electron-magnon scattering. A comparison of the obtained results to existing
experimental data and theoretical approches is given.",0412348v1
2005-03-27,Magnetic Vortex Resonance in Patterned Ferromagnetic Dots,"We report a high-resolution experimental detection of the resonant behavior
of magnetic vortices confined in small disk-shaped ferromagnetic dots. The
samples are magnetically soft Fe-Ni disks of diameter 1.1 and 2.2 um, and
thickness 20 and 40 nm patterned via electron beam lithography onto microwave
co-planar waveguides. The vortex excitation spectra were probed by a vector
network analyzer operating in reflection mode, which records the derivative of
the real and the imaginary impedance as a function of frequency. The spectra
show well-defined resonance peaks in magnetic fields smaller than the
characteristic vortex annihilation field. Resonances at 162 and 272 MHz were
detected for 2.2 and 1.1 um disks with thickness 40 nm, respectively. A
resonance peak at 83 MHz was detected for 20-nm thick, 2-um diameter disks. The
resonance frequencies exhibit weak field dependence, and scale as a function of
the dot geometrical aspect ratio. The measured frequencies are well described
by micromagnetic and analytical calculations that rely only on known properties
of the dots (such as the dot diameter, thickness, saturation magnetization, and
exchange stiffness constant) without any adjustable parameters. We find that
the observed resonance originates from the translational motion of the magnetic
vortex core.",0503632v1
2005-06-22,Spin configurations in circular and rectangular vertical quantum dots in a magnetic field: Three-dimensional self-consistent simulation,"The magnetic field dependence of the electronic properties of \textit{real}
single vertical quantum dots in circular and rectangular mesas is investigated
within a full three-dimensional multiscale self-consistent approach without any
{\it \'a priori} assumptions about the shape and strength of the confinement
potential. The calculated zero field electron addition energies are in good
agreement with available experimental data for both mesa geometries. Charging
diagrams in a magnetic field for number of electrons up to five are also
computed. Consistent with the experimental data, we found that the charging
curves for the rectangular mesa dot in a magnetic field are flatter and exhibit
less features than for a circular mesa dot. Evolution of the singlet-triplet
energy separation in the two electron system for both dot geometries in
magnetic field was also investigated. In the limit of large field, beyond the
singlet-triplet transition, the singlet-triplet energy difference continues to
become more negative in a circular mesa dot without any saturation within the
range of considered magnetic fields whilst it is predicted to asymptotically
approach zero for the rectangular mesa dot. This different behavior is
attributed to the symmetry ""breaking"" that occurs in the singlet wave-functions
in the rectangular mesa dot but not in the circular one.",0506585v1
2006-09-21,Universal emergence of the one-third plateau in the magnetization process of frustrated quantum spin chains,"We present a numerical study of the magnetization process of frustrated
quantum spin-S chains with S=1, 3/2, 2 as well as the classical limit. Using
the exact diagonalization and density-matrix renormalization techniques, we
provide evidence that a plateau at one third of the saturation magnetization
exists in the magnetization curve of frustrated spin-S chains with S>1/2.
Similar to the case of S=1/2, this plateau state breaks the translational
symmetry of the Hamiltonian and realizes an up-up-down pattern in the spin
component parallel to the external field. Our study further shows that this
plateau exists both in the cases of an isotropic exchange and in the easy-axis
regime for spin-S=1, 3/2, and 2, but is absent in classical frustrated spin
chains with isotropic interactions. We discuss the magnetic phase diagram of
frustrated spin-1 and spin-3/2 chains as well as other emergent features of the
magnetization process such as kink singularities, jumps, and even-odd effects.
A quantitative comparison of the one-third plateau in the easy-axis regime
between spin-1 and spin-3/2 chains on the one hand and the classical frustrated
chain on the other hand indicates that the critical frustration and the phase
boundaries of this state rapidly approach the classical result as the spin S
increases.",0609555v1
2007-03-22,Orbital contribution to the magnetic properties of iron as a function of dimensionality,"The orbital contribution to the magnetic properties of Fe in systems of
decreasing dimensionality (bulk, surfaces, wire and free clusters) is
investigated using a tight-binding hamiltonian in an $s, p,$ and $d$ atomic
orbital basis set including spin-orbit coupling and intra-atomic electronic
interactions in the full Hartree-Fock (HF) scheme, i.e., involving all the
matrix elements of the Coulomb interaction with their exact orbital dependence.
Spin and orbital magnetic moments and the magnetocrystalline anisotropy energy
(MAE) are calculated for several orientations of the magnetization. The results
are systematically compared with those of simplified hamiltonians which give
results close to those obtained from the local spin density approximation. The
full HF decoupling leads to much larger orbital moments and MAE which can reach
values as large as 1$\mu_B$ and several tens of meV, respectively, in the
monatomic wire at the equilibrium distance. The reliability of the results
obtained by adding the so-called Orbital Polarization Ansatz (OPA) to the
simplified hamiltonians is also discussed. It is found that when the spin
magnetization is saturated the OPA results for the orbital moment are in
qualitative agreement with those of the full HF model. However there are large
discrepancies for the MAE, especially in clusters. Thus the full HF scheme must
be used to investigate the orbital magnetism and MAE of low dimensional
systems.",0703576v1
2003-07-22,Interaction of Electromagnetic Radiation with Supercritical Magnetic Field,"It is pointed, that effects of refraction of electromagnetic radiation in the
medium, formed by the magnetized vacuum, become essential already for
relatively soft photons, not hard enough to create an electron-positron pair,
including those belonging to soft gamma-, X-ray, optic and radio- range, if the
magnetic field B exceeds the critical value of Bcr=m^2/e=4.4 10^13 Gauss. Three
leading terms in the asymptotic expansion of the one-loop polarization operator
in a constant magnetic field are found for B>>Bcr, and the corresponding
refraction index is shown to depend only on the propagation direction of the
photon relative to the external field. It is established, that the refraction
index for one of polarization modes unlimitedly grows with the field, while the
other is saturated at a moderate level. The photon capture effect is extended
to soft photons. The results may be essential in studying reflection,
refraction and splitting of X-rays, light and radio waves by magnetic fields of
magnetars, as well as in considering emission of such waves by charged
particles .",0307214v2
2007-08-27,Strain-driven elastic and orbital-ordering effects on thickness-dependent properties of manganite thin films,"We report on the structural and magnetic characterization of (110) and (001)
La2/3Ca1/3MnO3 (LCMO) epitaxial thin films simultaneously grown on (110) and
(001)SrTiO3 substrates, with thicknesses t varying between 8 nm and 150 nm. It
is found that while the in-plane interplanar distances of the (001) films are
strongly clamped to those of the substrate and the films remain strained up to
well above t=100 nm, the (110) films relax much earlier. Accurate determination
of the in-plane and out-of-plane interplanar distances has allowed concluding
that in all cases the unit cell volume of the manganite reduces gradually when
increasing thickness, approaching the bulk value. It is observed that the
magnetic properties (Curie temperature and saturation magnetization) of the
(110) films are significantly improved compared to those of (001) films. These
observations, combined with 55Mn-nuclear magnetic resonance data and X-ray
photoemission spectroscopy, signal that the depression of the magnetic
properties of the more strained (001)LCMO films is not caused by an elastic
deformation of the perovskite lattice but rather due to the electronic and
chemical phase separation caused by the substrate-induced strain. On the
contrary, the thickness dependence of the magnetic properties of the less
strained (110)LCMO films are simply described by the elastic deformation of the
manganite lattice. We will argue that the different behavior of (001) and
(110)LCMO films is a consequence of the dissimilar electronic structure of
these interfaces.",0708.3602v1
2008-05-15,Thickness dependent magnetic anisotropy of ultrathin LCMO epitaxial thin films,"The magnetic properties of La0.7Ca0.3MnO3 (LCMO) manganite thin films were
studied with magnetometry and ferromagnetic resonance as a function of film
thickness. They maintain the colossal magnetoresistance behavior with a
pronounced metal-insulator transition around 150-200 K, except for the very
thinnest films studied (3 nm). Nevertheless, LCMO films as thin as 3 nm remain
ferromagnetic, without a decrease in saturation magnetization, indicating an
absence of dead-layers, although below approx. 6 nm the films remain insulating
at low temperature. Magnetization hysteresis loops reveal that the magnetic
easy axes lie in the plane of the film for thicknesses in the range of 4-15 nm.
Ferromagnetic resonance studies confirm that the easy axes are in-plane, and
find a biaxial symmetry in-plane with two, perpendicular easy axes. The
directions of the easy axes with respect to the crystallographic directions of
the cubic SrTiO3 substrate differ by 45 degrees in 4 nm and 15 nm thick LCMO
films.",0805.2336v1
2008-07-05,Vector chiral and multipolar orders in the spin-1/2 frustrated ferromagnetic chain in magnetic field,"We study the one-dimensional spin-1/2 Heisenberg chain with competing
ferromagnetic nearest-neighbor J_1 and antiferromagnetic next-nearest-neighbor
J_2 exchange couplings in the presence of magnetic field. We use both numerical
approaches (the density matrix renormalization group method and exact
diagonalization) and effective field-theory approach, and obtain the
ground-state phase diagram for wide parameter range of the coupling ratio
J_1/J_2. The phase diagram is rich and has a variety of phases, including the
vector chiral phase, the nematic phase, and other multipolar phases. In the
vector chiral phase, which appears in relatively weak magnetic field, the
ground state exhibits long-range order (LRO) of vector chirality which
spontaneously breaks a parity symmetry. The nematic phase shows a quasi-LRO of
antiferro-nematic spin correlation, and arises as a result of formation of
two-magnon bound states in high magnetic fields. Similarly, the higher
multipolar phases, such as triatic (p=3) and quartic (p=4) phases, are formed
through binding of p magnons near the saturation fields, showing quasi-LRO of
antiferro-multipolar spin correlations. The multipolar phases cross over to
spin density wave phases as the magnetic field is decreased, before
encountering a phase transition to the vector chiral phase at a lower field.
The implications of our results to quasi-one-dimensional frustrated magnets
(e.g., LiCuVO_4) are discussed.",0807.0858v2
2008-11-26,Dirac equation description on the electronic states and magnetic properties of a square graphene quantum dot,"Electronic eigen-states of a square graphene quantum dot(GQD) terminated by
both zigzag and armchair edges are derived in the theoretical framework of
Dirac equation. We find that the Dirac equation can determine the eigen-energy
spectrum of a GQD with high accuracy even if its size is reduced to a few
nanometers. More importantly, from the Dirac equation description we can
readily work out the number and energy gap of the conjugate surface states,
which are intimately associated with the magnetic properties of the GQD. By
using the Hartree-Fock mean field approach, we study the size dependence of the
magnetic ordering formation in this square GQD. We find that there exists a
critical size of the width between the two zigzag edges to indicate the onset
of the stable magnetic ordering. On the other hand, when such a width increases
further, the magnetic ground state energy of a charge neutral GQD tends to a
saturated value. These results coincide with the previous results obtained from
the first principle calculation. Then, based on the Dirac equation solution
about the surface state, we establish a simple two-state model which can
quantitatively explain the size dependence of the magnetic ordering in the
square GQD.",0811.4312v1
2009-06-29,A novel wear-resistant magnetic thin film material based on a $Ti_{1-x}Fe_xC_{1-y}$ nanocomposite alloy,"In this study we report on the film growth and characterization of thin
(approximately 50 nm thick) Ti-Fe-C films deposited on amorphous quartz. The
experimental studies have been complemented by first principles density
functional theory (DFT) calculations. Upon annealing of as-prepared films, the
composition of the metastable Ti-Fe-C film changes. An iron-rich phase is first
formed close to the film surface, but with increasing annealing time this phase
is gradually displaced toward the film-substrate interface where its position
stabilizes. Both the magnetic ordering temperature and the saturation
magnetization changes significantly upon annealing. The DFT calculations show
that the critical temperature and the magnetic moment both increase with
increasing Fe and C-vacancy concentration. The formation of the metastable
iron-rich Ti-Fe-C compound is reflected in the strong increase of the magnetic
ordering temperature. Eventually, after enough annealing time ($\geq 10$
minutes), nano-crystalline $\alpha$-Fe starts to precipitate and the amount and
size of these precipitates can be controlled by the annealing procedure; after
20 minutes of annealing, the experimental results indicate a nano-crystalline
iron-film embedded in a wear resistant TiC compound. This conclusion is further
supported by transmission electron microscopy studies on epitaxial Ti-Fe-C
films deposited on single crystalline MgO substrates where, upon annealing, an
iron film embedded in TiC is formed. Our results suggest that annealing of
metastable Ti-Fe-C films can be used as an efficient way of creating a
wear-resistant magnetic thin film material.",0906.5386v1
2009-11-18,Kelvin-Helmholtz Instability of the Magnetopause of Disc-Accreting Stars,"This work investigates the short wavelength stability of the magnetopause
between a rapidly-rotating, supersonic, dense accretion disc and a
slowly-rotating low-density magnetosphere of a magnetized star. The
magnetopause is a strong shear layer with rapid changes in the azimuthal
velocity, the density, and the magnetic field over a short radial distance and
thus the Kelvin-Helmholtz (KH) instability may be important. The plasma
dynamics is treated using non-relativistic, compressible (isentropic)
magnetohydrodynamics. It is necessary to include the displacement current in
order that plasma wave velocities remain less than the speed of light. We focus
mainly on the case of a star with an aligned dipole magnetic field so that the
magnetic field is axial in the disc midplane and perpendicular to the disc flow
velocity. However, we also give results for cases where the magnetic field is
at an arbitrary angle to the flow velocity. For the aligned dipole case the
magnetopause is most unstable for KH waves propagating in the azimuthal
direction perpendicular to the magnetic field which tends to stabilize waves
propagating parallel to it. The wave phase velocity is that of the disc matter.
A quasi-linear theory of the saturation of the instability leads to a
wavenumber ($k$) power spectrum $\propto k^{-1}$ of the density and temperature
fluctuations of the magnetopause, and it gives the mass accretion and angular
momentum inflow rates across the magnetopause. For self-consistent conditions
this mass accretion rate will be equal to the disc accretion rate at large
distances from the magnetopause.",0911.3590v1
2009-12-26,Magnetic Amplification by Magnetized Cosmic Rays in SNR Shocks,"(Abridged) X-ray observations of synchrotron rims in supernova remnant (SNR)
shocks show evidence of strong magnetic field amplification (a factor of ~100
between the upstream and downstream medium). This amplification may be due to
plasma instabilities driven by shock-accelerated cosmic rays (CRs). One
candidate is the cosmic ray current-driven (CRCD) instability (Bell 2004),
caused by the electric current of large Larmor radii CRs propagating parallel
to the upstream magnetic field. Particle-in-cell (PIC) simulations have shown
that the back-reaction of the amplified field on CRs would limit the
amplification factor of this instability to less than ~10 in galactic SNRs. In
this paper, we study the possibility of further amplification driven near
shocks by ""magnetized"" CRs, whose Larmor radii are smaller than the length
scale of the field that was previously amplified by the CRCD instability. We
find that additional amplification can occur due to a new instability, driven
by the CR current perpendicular to the field, which we term the ""perpendicular
current-driven instability"" (PCDI). We derive the growth rate of this
instability, and, using PIC simulations, study its non-linear evolution and
saturation. We find that PCDI increases the amplification of the field
(amplification factor up to ~45, not including the shock compression) and
discuss its observational signatures. Our results strengthen the idea of CRs
driving a significant part of the magnetic field amplification observed in SNR
shocks.",0912.4990v1
2010-11-04,"Magnetic order, metamagnetic transitions, and low-temperature spin freezing in Ca3Co2O6: an NMR study","We report on a 59Co NMR investigation of the trigonal cobaltate Ca3Co2O6
carried out on a single crystal, providing precise determinations of the
electric field gradient and chemical shift tensors, and of the internal
magnetic fields at the non-magnetic Co I sites, unavailable from former studies
on powders. The magnetic field-induced ferri- and ferromagnetic phases at
intermediate temperature (e.g. 10 K) are identified by distinct internal
fields, well accounted for by purely dipolar interactions. The vanishing
transferred hyperfine field at the Co I site indicates that the Co3+(I)
orbitals do not participate in the intra-chain superexchange, in disagreement
with a previous theoretical model. The strong Ising character of the system is
confirmed experimentally by the field dependence of the resonance lines,
indicating that local moments are saturated even at the phase boundaries. In
the vicinity of the critical fields, nuclear spin-spin relaxations detect the
spin reversal dynamics of large magnetic assemblies, either Ising chain
fragments or finite size domains, which drive the metamagnetic transitions.
Such collective excitations exhibit a glassy behavior, slowing down to
subacoustic frequencies and freezing at low temperature. The relevance of such
slow fluctuation modes for the low-temperature multi-step behavior reported in
the magnetization is discussed.",1011.1142v2
2011-02-17,Magnetic fields during primordial star formation,"Recent FERMI observations provide a lower limit of 10^{-15} G for the
magnetic field strength in the intergalactic medium (IGM). This is consistent
with theoretical expectations based on the Biermann battery effect, which
predicts such IGM fields already at redshifts z~10. During gravitational
collapse, such magnetic fields can be amplified by compression and by
turbulence, giving rise to the small-scale dynamo. On scales below the Jeans
length, the eddy turnover timescale is much shorter than the free-fall
timescale, so that saturation can be reached during collapse. This scenario has
been tested and confirmed with magneto-hydrodynamical simulations following the
collapse of a turbulent, weakly magnetized cloud. Based on a spectral analysis,
we confirm that turbulence is injected on the Jeans scale. For the power
spectrum of the magnetic field, we obtain the Kazantsev slope which is
characteristic for the small-scale dynamo. A calculation of the critical length
scales for ambipolar diffusion and Ohmic dissipation shows that these scales
are always small enough to allow significant amplification of the magnetic
field by small-scale eddies. We discuss potential implications for the
protostellar accretion disk, with particular focus on the magneto-rotational
instability, which may change the morphology of the disk and reduce the
accretion rate by a factor of a few.",1102.3558v1
2011-03-15,Magnetohydrodynamic Simulations of Reconnection and Particle Acceleration: Three-Dimensional Effects,"The magnetic fields can change their topology through a process known as
magnetic reconnection. This process in not only important for understanding the
origin and evolution of the large-scale magnetic field, but is seen as a
possibly efficient particle accelerator producing cosmic rays mainly through
the first order Fermi process. In this work we study the properties of particle
acceleration in reconnection zones and show that the velocity component
parallel to the magnetic field of test particles inserted in nearly
non-resistive magnetohydrodynamic (MHD) domains of reconnection without
including kinetic effects, such as pressure anisotropy, the Hall term, or
anomalous effects, increases exponentially. Also, the acceleration of the
perpendicular component is always possible in such models. We have found that
within contracting magnetic islands or current sheets the particles accelerate
predominantly through the first order Fermi process, as previously described,
while outside the current sheets and islands the particles experience mostly
drift acceleration due to magnetic fields gradients. Considering two
dimensional MHD models without a guide field, we find that the parallel
acceleration stops at some level. This saturation effect is however removed in
the presence of an out-of-plane guide field or in three dimensional models.
Therefore, we stress the importance of the guide field and fully three
dimensional studies for a complete understanding of the process of particle
acceleration in astrophysical reconnection environments.",1103.2984v1
2011-07-05,Spindown of Isolated Neutron Stars: Gravitational Waves or Magnetic Braking?,"We study the spindown of isolated neutron stars from initially rapid rotation
rates, driven by two factors: (i) gravitational wave emission due to r-modes
and (ii) magnetic braking. In the context of isolated neutron stars, we present
the first study including self-consistently the magnetic damping of r-modes in
the spin evolution. We track the spin evolution employing the RNS code, which
accounts for the rotating structure of neutron stars for various equations of
state. We find that, despite the strong damping due to the magnetic field,
r-modes alter the braking rate from pure magnetic braking for B<10^{13}G. For
realistic values of the saturation amplitude, the r-mode can also decrease the
time to reach the threshold central density for quark deconfinement. Within a
phenomenological model, we assess the gravitational waveform that would result
from r-mode driven spindown of a magnetized neutron star. To contrast with the
persistent signal during the spindown phase, we also present a preliminary
estimate of the transient gravitational wave signal from an explosive
quark-hadron phase transition, which can be a signal for the deconfinement of
quarks inside neutron stars.",1107.1000v2
2011-07-16,Magnetic effects in heavy-ion collisions at intermediate energies,"The time-evolution and space-distribution of internal electromagnetic fields
in heavy-ion reactions at beam energies between 200 and 2000 MeV/nucleon are
studied within an Isospin-dependent Boltzmann-Uhling-Uhlenbeck transport model
IBUU11. While the magnetic field can reach about $7\times 10^{16}$ G which is
significantly higher than the estimated surface magnetic field ($\sim 10^{15}$
G) of magnetars, it has almost no effect on nucleon observables as the Lorentz
force is normally much weaker than the nuclear force. Very interestingly,
however, the magnetic field generated by the projectile-like (target-like)
spectator has a strong focusing/diverging effect on positive/negative pions at
forward (backward) rapidities. Consequently, the differential $\pi^-/\pi^+$
ratio as a function of rapidity is significantly altered by the magnetic field
while the total multiplicities of both positive and negative pions remain about
the same. At beam energies above about 1 GeV/nucleon, while the integrated
ratio of total $\pi^-$ to $\pi^+$ multiplicities is not, the differential
$\pi^-/\pi^+$ ratio is sensitive to the density dependence of nuclear symmetry
energy $E_{\rm{sym}}(\rho)$. Our findings suggest that magnetic effects should
be carefully considered in future studies of using the differential
$\pi^-/\pi^+$ ratio as a probe of the $E_{\rm{sym}}(\rho)$ at supra-saturation
densities.",1107.3192v1
2012-03-20,Ferromagnetism induced in anisotropic stacked kagome-lattice antiferromagnet Cs$_2$Cu$_3$CeF$_{12}$,"The magnetic properties of Cs$_2$Cu$_3$CeF$_{12}$ were investigated through
magnetization and specific heat measurements. Cs$_2$Cu$_3$CeF$_{12}$ is
composed of a buckled kagome lattice of Cu$^{2+}$, which is stacked along the b
axis. The exchange network in the buckled kagome lattice is strongly
anisotropic. Consequently, Cs$_2$Cu$_3$CeF$_{12}$ can be divided into two
subsystems: alternating Heisenberg chains with strong antiferromagnetic
exchange interactions and dangling spins. The dangling spins couple with one
another via effective exchange interactions, which are mediated by chain spins.
The dangling spins are further divided into two subsystems, DS1 and DS2. The
dangling spins in DS1 undergo three-dimensional ferromagnetic ordering at 3.14
K, while those in DS2 remain paramagnetic down to 0.35 K. The effective
interaction between the DS1 spins is approximately expressed by the
ferromagnetic $XXZ$ model with the $z$ direction parallel to the
crystallographic c axis. A magnetic phase diagram for $H {\parallel} c$ was
obtained and was analyzed within the framework of the molecular field
approximation. With increasing magnetic field, the dangling spins are polarized
and the magnetization curve exhibits a wide plateau at one-third of the
saturation magnetization.",1203.4453v1
2012-03-21,Magneto-thermal properties of the Heisenberg-Ising orthogonal-dimer chain with triangular XXZ-clusters,"We study a spin-1/2 model with triangular XXZ-clusters on the
orthogonal-dimer chain in the presence of an external magnetic field. First, we
discuss the case where the triangular clusters are coupled via intermediate
""classical"" Ising spins. Diagonalization of the triangular XXZ-clusters yields
the exact ground states; finite-temperature properties are computed exactly by
an additional transfer-matrix step. A detailed analysis reveals a large variety
of ground states at magnetization M equal to fractions 0, 1/4, and 1/2 of the
saturation magnetization M=1. Some of these ground states break translational
symmetry spontaneously and give rise to doubling of the unit cell. In a second
part we present complementary numerical data for the spin-1/2 Heisenberg model
on the orthogonal-dimer chain. We analyze several examples of T=0 magnetization
curves, entropy as a function of temperature T and magnetic field, and the
associated magnetic cooling rate. Comparison of the two models shows that in
certain situations the simplified exactly solvable model yields a qualitatively
or sometimes even quantitatively accurate description of the more challenging
quantum model, including a case which may be relevant to experimental
observations of an enhanced magnetocaloric effect in the two-dimensional
compound SrCu2(BO3)2.",1203.4741v2
2013-05-06,Study of Ni and Zn doped CeOFeAs: Effect on the structural transition and specific heat capacity,"We have systematically studied the substitution of nonmagnetic Zn and
magnetic Ni at iron sites in Ce based oxypnictide. The parent compound
(CeOFeAs) shows an anomaly in resistivity around 150 K due to structural
transition from tetragonal (space group: P4/nmm) to orthorhombic structure
(space group: Cmma). Substitution of Zn suppresses this anomaly to lower
temperature (~130 K) but Ni substitution does not show any anomaly around this
temperature and the compound behaves like a metal. Further, we find that non
magnetic (Zn) doping leads to higher impurity scattering as compared to
magnetic Ni doping. Similar to the resistivity measurement, the specific heat
shows another jump near 4 K for CeOFeAs. This is attributed to the ordering of
Ce3+ moments. This peak shifts to 3.8 K for Zn substituted compound and there
is no change in the ordering temperature in the Ni substituted CeOFeAs. These
peaks are broadened in applied magnetic field (5 T) and the calculated magnetic
entropy tends to saturate at the same value for 0 T and 5 T external magnetic
field.",1305.1088v2
2013-05-29,Thermodynamic Properties of the Anisotropic Frustrated Spin-chain Compound Linarite PbCuSO$_4$(OH)$_2$,"We present a comprehensive macroscopic thermodynamic study of the
quasi-one-dimensional (1D) $s = \tfrac{1}{2}$ frustrated spin-chain system
linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect,
magnetostriction, and thermal-expansion measurements were performed to
characterize the magnetic phase diagram. In particular, for magnetic fields
along the b axis five different magnetic regions have been detected, some of
them exhibiting short-range-order effects. The experimental magnetic entropy
and magnetization are compared to a theoretical modelling of these quantities
using DMRG and TMRG approaches. Within the framework of a purely 1D isotropic
model Hamiltonian, only a qualitative agreement between theory and the
experimental data can be achieved. Instead, it is demonstrated that a
significant symmetric anisotropic exchange of about 10% is necessary to account
for the basic experimental observations, including the 3D saturation field, and
which in turn might stabilize a triatic (three-magnon) multipolar phase.",1305.6731v3
2013-07-23,Study of the flux effect on nuclear pressure vessel steel by measurement of magnetic properties,"Since Reactor Pressure Vessel steels are ferromagnetic, they provide a
convenient means to monitor changes in the mechanical properties of the
material upon irradiation with high energy particles, by measuring their
magnetic properties. Here, we discuss the correlation between these two
properties (i.e. mechanical and magnetic properties) and microstructure, by
studying the flux effect on the nuclear pressure vessel steel used in reactors
currently under construction in Argentina. Charpy-V notched specimens of this
steel were irradiated in the RA1 experimental reactor at 275{\deg}C with two
lead factors (LFs), 93 and 183. The magnetic properties were studied by means
of DC magnetometry and ferromagnetic resonance. The results show that the
coercive field and magnetic anisotropy spatial distribution are sensitive to
the LF and can be explained by taking into account the evolution of the
microstructure with this parameter. The saturation magnetization shows a
dominant dependence on the accumulated damage. Consequently, the mentioned
techniques are suitable to estimate the degradation of the reactor vessel
steel.",1307.6124v2
2013-09-18,"Magnetization process, bipartite entanglement and enhanced magnetocaloric effect of the exactly solved spin-1/2 Ising-Heisenberg tetrahedral chain","The frustrated spin-1/2 Ising-Heisenberg ladder with Heisenberg intra-rung
and Ising inter-rung interactions is exactly solved in a longitudinal magnetic
field by taking advantage of the local conservation of the total spin on each
rung and the transfer-matrix method. We have rigorously calculated the
ground-state phase diagram, magnetization process, magnetocaloric effect and
basic thermodynamic quantities for the model, which can be alternatively viewed
as an Ising-Heisenberg tetrahedral chain. It is demonstrated that a stepwise
magnetization curve with an intermediate plateau at a half of the saturation
magnetization is also reflected in respective stepwise changes of the
concurrence serving as a measure of bipartite entanglement. The ground-state
phase diagram and zero-temperature magnetization curves of the Ising-Heisenberg
tetrahedral chain are contrasted with the analogous results of the purely
quantum Heisenberg tetrahedral chain, which have been obtained through
density-matrix renormalization group (DMRG) calculations. While both
ground-state phase diagrams fully coincide in the regime of weak inter-rung
interaction, the purely quantum Heisenberg tetrahedral chain develops Luttinger
spin-liquid and Haldane phases for strongly coupled rungs which are absent in
the Ising-Heisenberg counterpart model.",1309.4603v2
2014-03-18,Two-Fluid Description of Wave-Particle Interactions in Strong Buneman Turbulence,"To understand the nature of anomalous resistivity in magnetic reconnection,
we investigate turbulence-induced momentum transport and energy dissipation
while a plasma is unstable to the Buneman instability in force-free current
sheets. Using 3D particle-in-cell simulations, we find that the macroscopic
effects generated by wave-particle interactions in Buneman instability can be
approximately described by a set of electron fluid equations. We show that both
energy dissipation and momentum transport along electric current in the current
layer are locally quasi-static, but globally dynamic and irreversible.
Turbulent drag dissipates both the streaming energy of the current sheet and
the associated magnetic energy. The net loss of streaming energy is converted
into the electron component heat conduction parallel to the magnetic field and
increases the electron Boltzmann entropy. The growth of self-sustained Buneman
waves satisfies a Bernoulli-like equation that relates the turbulence-induced
convective momentum transport and thermal momentum transport. Electron trapping
and de-trapping drive local momentum transports, while phase mixing converts
convective momentum into thermal momentum. The drag acts like a micro-macro
link in the anomalous heating processes. The decrease of magnetic field
maintains an inductive electric field that re-accelerates electrons, but most
of the magnetic energy is dissipated and converted into the component heat of
electrons perpendicular to the magnetic field. This heating process is
decoupled from the heating of Buneman instability in the current sheets. Ion
heating is weak but ions plays an important role in assisting energy exchanges
between waves and electrons. Cold ion fluid equations together with our
electron fluid equations form a complete set of equations that describes the
occurrence, growth, saturation and decay of the Buneman instability.",1403.4552v2
2014-09-30,Producing Magnetar Magnetic Fields in the Merger of Binary Neutron Stars,"The merger of binary neutron stars (BNSs) can lead to large amplifications of
the magnetic field due to the development of turbulence and instabilities in
the fluid, such as the Kelvin-Helmholtz shear instability, which drive
small-scale dynamo activity. In order to properly resolve such instabilities
and obtain the correct magnetic field amplification, one would need to employ
resolutions that are currently unfeasible in global general relativistic
magnetohydrodynamic (GRMHD) simulations of BNS mergers. Here, we present a
subgrid model that allows global simulations to take into account the
small-scale amplification of the magnetic field which is caused by the
development of turbulence during BNS mergers. Assuming dynamo saturation, we
show that magnetar-level fields ($\sim 10^{16}\,{\rm G}$) can be easily
reached, and should therefore be expected from the merger of magnetized BNSs.
The total magnetic energy can reach values up to $\sim 10^{51}\,{\rm erg}$ and
the post-merger remnant can therefore emit strong electromagnetic signals and
possibly produce short gamma-ray bursts.",1410.0013v2
2014-11-18,The Turbulent Dynamo in Highly Compressible Supersonic Plasmas,"The turbulent dynamo may explain the origin of cosmic magnetism. While the
exponential amplification of magnetic fields has been studied for
incompressible gases, little is known about dynamo action in
highly-compressible, supersonic plasmas, such as the interstellar medium of
galaxies and the early Universe. Here we perform the first quantitative
comparison of theoretical models of the dynamo growth rate and saturation level
with three-dimensional magnetohydrodynamical simulations of supersonic
turbulence with grid resolutions of up to 1024^3 cells. We obtain numerical
convergence and find that dynamo action occurs for both low and high magnetic
Prandtl numbers Pm = nu/eta = 0.1-10 (the ratio of viscous to magnetic
dissipation), which had so far only been seen for Pm >= 1 in supersonic
turbulence. We measure the critical magnetic Reynolds number, Rm_crit = 129
(+43, -31), showing that the compressible dynamo is almost as efficient as in
incompressible gas. Considering the physical conditions of the present and
early Universe, we conclude that magnetic fields need to be taken into account
during structure formation from the early to the present cosmic ages, because
they suppress gas fragmentation and drive powerful jets and outflows, both
greatly affecting the initial mass function of stars.",1411.4707v2
2014-12-04,Cross-correlation Aided Transport in Stochastically Driven Accretion Flows,"Origin of linear instability resulting in rotating sheared accretion flows
has remained a controversial subject for long. While some explanations of such
non-normal transient growth of disturbances in the Rayleigh stable limit were
available for magnetized accretion flows, similar instabilities in absence of
magnetic perturbations remained unexplained. This dichotomy was resolved in two
recent publications by Chattopadhyay, {\it et al} where it was shown that such
instabilities, especially for non-magnetized accretion flows, were introduced
through interaction of the inherent stochastic noise in the system (even a
\enquote{cold} accretion flow at 3000K is too \enquote{hot} in the statistical
parlance and is capable of inducing strong thermal modes) with the underlying
Taylor-Couette flow profiles. Both studies, however, excluded the additional
energy influx (or efflux) that could result from nonzero cross-correlation of a
noise perturbing the velocity flow, say, with the noise that is driving the
vorticity flow (or equivalently the magnetic field and magnetic vorticity flow
dynamics). In this article we show that nonzero noise cross-correlations
essentially renormalize the strength of temporal correlations. Apart from an
overall boost in the energy rate (both for spatial and temporal correlations,
and hence in the ensemble averaged energy spectra), this results in mutual
competition in growth rates of affected variables often resulting in
suppression of oscillating Alfven waves at small times while leading to faster
saturations at relatively longer time scales. The effects are seen to be more
pronounced with magnetic field fluxes where the noise cross-correlation
magnifies the strength of the field concerned.",1412.1752v1
2015-01-30,Stability of magnetized strange quark matter in the MIT bag model with the density dependent bag pressure,"The stability of magnetized strange quark matter (MSQM) is studied in the MIT
bag model with the density dependent bag pressure. In the consistent
thermodynamic description of MSQM, the quark chemical potentials, the total
thermodynamic potential and the anisotropic pressure acquire the corresponding
additional term proportional to the density derivative of the bag pressure. The
model parameter space is determined, for which MSQM is absolutely stable, i.e.,
its energy per baryon is less than that of the most stable $^{56}$Fe nucleus
under the zero external pressure and vanishing temperature. It is shown that
there exists the magnetic field strength $H_{u\,max}$ at which the upper bound
$B_\infty^u$ on the asymptotic bag pressure $B_\infty\equiv B(\varrho_B\gg
\varrho_0$) ($\varrho_0$ being the nuclear saturation density) from the
absolute stability window vanishes. The value of this field,
\hbox{$H_{u\,max}\sim$$(1$--$3)\cdot10^{18}$}~G, represents the upper bound on
the magnetic field strength, which can be reached in a strongly magnetized
strange quark star. It is clarified how the absolute stability window and upper
bound on the magnetic field strength are affected by varying the parameters in
the Gaussian parametrization for the density dependence of the bag pressure.",1501.07772v1
2015-04-09,Site occupancy and magnetic properties of Al-substituted M-type strontium hexaferrite,"We use first-principles total-energy calculations based on density functional
theory to study the site occupancy and magnetic properties of Al-substituted
$M$-type strontium hexaferrite SrFe$_{12-x}$Al$_{x}$O$_{19}$ with $x=0.5$ and
$x=1.0$. We find that the non-magnetic Al$^{3+}$ ions preferentially replace
Fe$^{3+}$ ions at two of the majority spin sites, $2a$ and $12k$, eliminating
their positive contribution to the total magnetization causing the saturation
magnetization $M_s$ to be reduced as Al concentration $x$ is increased. Our
formation probability analysis further provides the explanation for increased
magnetic anisotropy field when the fraction of Al is increased. Although
Al$^{3+}$ ions preferentially occupy the $2a$ sites at a low temperature, the
occupation probability of the $12k$ site increases with the rise of the
temperature. At a typical annealing temperature ($> 700\,^{\circ}{\rm C}$)
Al$^{3+}$ ions are much more likely to occupy the $12k$ site than the $2a$
site. Although this causes the magnetocrystalline anisotropy $K_1$ to be
reduced slightly, the reduction in $M_s$ is much more significant. Their
combined effect causes the anisotropy field $H_a$ to increase as the fraction
of Al is increased, consistent with recent experimental measurements.",1504.02320v2
2015-10-06,Spin Hall magnetoresistance as a probe for surface magnetization in Pt/CoFe$_2$O$_4$ bilayers,"We study the spin Hall magnetoresistance (SMR) in Pt grown $\textit{in situ}$
on CoFe$_2$O$_4$ (CFO) ferrimagnetic insulating (FMI) films. A careful analysis
of the angle-dependent and field-dependent longitudinal magnetoresistance
indicates that the SMR contains a contribution that does not follow the bulk
magnetization of CFO but it is a fingerprint of the complex magnetism at the
surface of the CFO layer, thus signaling SMR as a tool for mapping surface
magnetization. A systematic study of the SMR for different temperatures and CFO
thicknesses gives us information impossible to obtain with any standard
magnetometry technique. On one hand, surface magnetization behaves
independently of the CFO thickness and does not saturate up to high fields,
evidencing that the surface has its own anisotropy. On the other hand,
characteristic zero-field magnetization steps are not present at the surface
while they are relevant in the bulk, strongly suggesting that antiphase
boundaries are the responsible of such intriguing features. In addition, a
contribution from ordinary magnetoresistance of Pt is identified, which is only
distinguishable due to the low resistivity of the $\textit{in-situ}$ grown Pt.",1510.01449v2
2016-02-18,Spin Liquid State in the 3D Frustrated Antiferromagnet PbCuTe2O6: NMR and muSR Studies,"PbCuTe2O6 is a rare example of a spin liquid candidate featuring a three
dimensional magnetic lattice. Strong geometric frustration arises from the
dominant antiferromagnetic interaction which generates a hyperkagome network of
Cu2+ ions although additional interactions enhance the magnetic lattice
connectivity. Through a combination of magnetization measurements and local
probe investigation by NMR and muSR down to 20 mK, we provide a robust evidence
for the absence of magnetic freezing in the ground state. The local spin
susceptibility probed by the NMR shift hardly deviates from the macroscopic one
down to 1 K pointing to a homogeneous magnetic system with a low defect
concentration. The saturation of the NMR shift and the sublinear power law
temperature (T) evolution of the 1/T1 NMR relaxation rate at low T point to a
non-singlet ground state favoring a gapless fermionic description of the
magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics
is witnessed, which may signal a reconstruction of spinon Fermi surface.
Nonetheless, the compound remains in a fluctuating spin liquid state down to
the lowest temperature of the present investigation.",1602.05818v1
2016-04-06,Universal behavior of dense clusters of magnetic nanoparticles,"A detailed numerical simulation of quasistatic hysteresis loops of dense
clusters of interacting magnetic nanoparticles is carried out. Both clusters of
magnetically soft and magnetically hard nanoparticles are considered. The
clusters are characterized by an average particle diameter D, the cluster
radius Rc, the particle saturation magnetization Ms, and the uniaxial
anisotropy constant K. The number of particles in the cluster varies between Np
= 30 - 120. The particle centers are randomly distributed within the cluster,
their easy anisotropy axes being randomly oriented. It is shown that a rare
assembly of identical random clusters of magnetic nanoparticles can be
characterized by two dimensionless parameters: 1) the relative strength of
magneto-dipole interaction, K/Ms^2, and the average particle concentration
within the cluster, {\eta} = VNp/Vc. Here V is the nanoparticle volume, and Vc
is the volume of the cluster, respectively. In the strong interaction limit,
Ms*{\eta}/Ha >> 1, where Ha = 2K/Ms is the anisotropy field, the ultimate
hysteresis loops of dilute assemblies of clusters have been constructed. In the
variables (M/Ms, H/Ms) these hysteresis loops depend only on the particle
volume fraction {\eta}. In the weak interaction limit, Ms*{\eta}/Ha << 1, the
assembly hysteresis loops in the variables (M/Ms, H/Ha) are close to the
standard Stoner-Wohlfarth hysteresis loop.",1604.01705v1
2016-06-30,Surface magnetism of strontium titanate,"SrTiO3 plays a central role in oxide electronics. It is the substrate of
choice for functional oxide heterostructures based on perovskite-structure
thin-film stacks, and its surface or interface with a polar oxide such as
LaAlO3 can become a two-dimensional conductor because of electronic
reconstruction or the presence of oxygen defects. Inconsistent reports of
magnetic order in SrTiO3 abound in the literature. Here we report a systematic
experimental study aimed at establishing how and when SrTiO3 can develop a
magnetic moment at room temperature. Polished 100, 110 or 111 crystal slices
from four different suppliers are characterized before and after vacuum
annealing at 750 {\deg}C, both in single-crystal and powdered form. Impurity
content is analysed at the surface and in the bulk. Besides the underlying
intrinsic diamagnetism of SrTiO3, magnetic signals are of three types-a Curie
law susceptibility due to dilute magnetic impurities at the ppm level, a
hysteretic, temperature-dependent ferromagnetic impurity contribution, and a
practically-anhysteretic, defect-related temperature-independent component that
saturates in about 200 mT. The latter component is intrinsic. It is often the
largest, reaching 10 Bohr magnetons per nm2 of surface area or more and
dominating the magnetic response in low fields at room temperature. It is
associated with defects near the surface, and can be destroyed by treatment
with Tiron (C6H4Na2O8S2), an electron donor molecule that forms a strong
complex with titanium at the surface. The origin of this unusual
high-temperature ferromagnetic-like response is discussed.",1606.09422v1
2016-07-04,First-principles investigations into the thermodynamics of cation disorder and it's impact on electronic structure and magnetic properties of spinel $Co\left(Cr_{1-x}Mn_{x} \right)_{2}O_{4}$,"Recent experiments on Mn doped multiferroic $CoCr_{2}O_{4}$ indicate that a
possible distribution of Mn atoms among tetrahedrally and octahedrally
coordinated sites in the spinel lattice give rise to different variations in
the structural parameters and saturation magnetisations in different
concentration regimes of Mn atoms substituting the Cr. A composition dependent
magnetic compensation behaviour points to the role conversions of the magnetic
constituents. In this work, we have investigated the thermodynamics of cation
disorder in $Co\left(Cr_{1-x}Mn_{x}\right)_{2}O_{4}$ system and it's
consequences on the structural, electronic and magnetic properties, using
results from first-principles electronic structure calculations. We have
computed the variations in the cation-disorder as a function of Mn
concentration and the temperature and found that at the annealing temperature
of the experiment many of the systems exhibit cation disorder. Our results
support the interpretations of the experimental results regarding the
qualitative variations in the sub-lattice occupancies and the associated
magnetisation behaviour, with composition. We have analysed the variations in
structural, magnetic and electronic properties of this system with variations
in the compositions and the degree of cation disorder from the variations in
their electronic structures and by using the ideas from crystal field theory.
Our study provides a complete microscopic picture of the effects that are
responsible for composition dependent behavioural differences of the properties
of this system. This work lays down a general framework, based upon results
from first-principles calculations, to understand and analyse the
substitutional magnetic spinel oxides $A\left(B_{1-x}C_{x} \right)_{2}O_{4}$ in
presence of cation disorder.",1607.00742v1
2016-10-19,Surface tension of highly magnetized degenerate quark matter,"We study the surface tension of highly magnetized three flavor quark matter
within the formalism of multiple reflection expansion (MRE). Quark matter is
described as a mixture of free Fermi gases composed by quarks $u$, $d$, $s$ and
electrons, in chemical equilibrium under weak interactions. Due to the presence
of strong magnetic fields the particles' transverse motion is quantized into
Landau levels, and the surface tension has a different value in the parallel
and transverse directions with respect to the magnetic field.
  We calculate the transverse and longitudinal surface tension for different
values of the magnetic field and for quark matter drops with different sizes,
from a few fm to the bulk limit. For baryon number densities between $2-10$
times the nuclear saturation density, the surface tension falls in the range $2
- 20$ MeV /fm$^{2}$. The largest contribution comes from strange quarks which
have a surface tension an order of magnitude larger than the one for $u$ or $d$
quarks and more than two orders of magnitude larger than for electrons. Our
results show that the total surface tension is quite insensitive to the size of
the drop. We also find that the surface tensions in the transverse and parallel
directions are almost unaffected by the magnetic field if $eB$ is below $\sim 5
\times 10^{-3} $ GeV$^2$. Nevertheless, for higher values of $eB$, there is a
significant increase in the parallel surface tension and a significant decrease
in the transverse one with respect to the unmagnetized case.",1610.05875v2
2016-11-10,Pressure-induced quantum phase transition in the itinerant ferromagnet UCoGa,"In this paper, we report the results of a high pressure study of the
itinerant 5f-electron ferromagnet UCoGa. The work is focused on probing the
expected ferromagnet-to-paramagnet quantum phase transition induced by high
pressure and on the general features of the P-T(-H) phase diagram. Diamond
anvil cells were employed to measure the magnetization and electrical
resistivity under pressures up to ~ 10 GPa.At ambient pressure, UCoGa exhibits
collinear ferromagnetic ordering of uranium magnetic moments {\mu}U ~ 0.74
{\mu}B (at 2 K) aligned along the c-axis of the hexagonal crystal structure
below Curie temperature TC = 48K. With the application of pressure, gradual
decrease of both, TC and the saturated magnetic moment, has been observed up to
pressures ~ 6 GPa. This is followed by a sharp drop of magnetic moment and a
sudden disappearance of the magnetic order at the pressure of 6.5 GPa,
suggesting a first-order phase transition, as expected for a clean system. The
low temperature power law dependence of the electrical resistivity shows
distinct anomalies around the ~ 6 GPa, consistent with the pressure evolution
of the magnetic moment and the ordering temperature. The tricritical point of
the UCoGa phase diagram is located at approximately ~ 30 K and ~ 6 GPa.",1611.03276v1
2017-04-08,Prompt photon yield and elliptic flow from gluon fusion induced by magnetic fields in relativistic heavy-ion collisions,"We compute photon production at early times in semi-central relativistic
heavy-ion collisions from non-equilibrium gluon fusion induced by a magnetic
field. The calculation accounts for the main features of the collision at these
early times, namely, the intense magnetic field and the high gluon occupation
number. The gluon fusion channel is made possible by the magnetic field and
would otherwise be forbidden due to charge conjugation invariance. Thus, the
photon yield from this process is an excess over calculations without magnetic
field effects. We compare this excess to the difference between PHENIX data and
recent hydrodynamic calculations for the photon transverse momentum
distribution and elliptic flow coefficient $v_2$. We show that with reasonable
values for the saturation scale and magnetic field strength, the calculation
helps to better describe the experimental results obtained at RHIC energies for
the lowest part of the transverse photon momentum.",1704.02433v4
2017-05-02,Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs): II The Relative Importance of MRI and Spiral Shocks,"We perform global three-dimensional MHD simulations of unstratified accretion
disks in cataclysmic variables (CVs). By including mass inflow via an accretion
stream, we are able to evolve the disk to a steady state. We investigate the
relative importance of spiral shocks and the magnetorotational instability
(MRI) in driving angular momentum transport and how each depend on the geometry
and strength of seed magnetic field and the Mach number of the disk (where Mach
number is ratio of the azimuthal velocity and the sound speed of gas). We use a
locally isothermal equation of state and adopt temperature profiles that are
consistent with CV disk observations. Our results indicate that the relative
importance of spiral shocks and MRI in driving angular momentum transport is
controlled by the gas Mach number and the seed magnetic field strength. MRI and
spiral shocks provide comparable efficiency of angular momentum transport when
the disk Mach number is around 10 and the seed magnetic field has plasma
$\beta=400$ (where $\beta$ is ratio of gas pressure and magnetic pressure). The
MRI dominates whenever the seed field strength, or the disk Mach number, is
increased. Among all of our simulations, the effective viscosity parameter
$\alpha_{eff} \sim 0.016-0.1$ after MRI saturates and the disk reaches steady
state. Larger values of $\alpha_{eff}$ are favored when the seed magnetic field
has vertical components or the flow has stronger magnetization ($1/\beta$). Our
models all indicate that the role of MRI in driving angular momentum transport
thus mass accretion in CV disks is indispensable, especially in cool disks with
weak spiral shocks.",1705.00779v1
2018-03-21,Sub-photospheric fluctuations in magnetized radiative envelopes: contribution from unstable magnetosonic waves,"We examine the excitation of unstable magnetosonic waves in the radiative
envelopes of intermediate- and high-mass stars with a magnetic field of ~kG
strength. Wind clumping close to the star and microturbulence can often be
accounted for when including small-scale, sub-photospheric density or velocity
perturbations. Compressional waves - with wavelengths comparable to or shorter
than the gas pressure scale height - can be destabilized by the radiative flux
in optically-thick media when a magnetic field is present, in a process called
the Radiation-Driven Magneto-Acoustic Instability (RMI). The instability does
not require radiation or magnetic pressure to dominate over gas pressure, and
acts independently of sub-surface convection zones. Here we evaluate the
conditions for the RMI to operate on a grid of stellar models covering a mass
range $3-40M_\odot$ at solar metallicity. For a uniform 1kG magnetic field,
fast magnetosonic modes are unstable down to an optical depth of a few tens,
while unstable slow modes extend beyond the depth of the iron convection zone.
The qualitative behavior is robust to magnetic field strength variations by a
factor of a few. When combining our findings with previous results for the
saturation amplitude of the RMI, we predict velocity fluctuations in the range
~0.1-10 km/s. These amplitudes are a monotonically increasing function of the
ratio of radiation to gas pressure, or alternatively, of the zero-age main
sequence mass.",1803.08053v1
2018-04-06,Effect of Substrate Temperature on Structural and Magnetic Properties of c-axis Ori-ented Spinel Ferrite Ni0.65Zn0.35Fe2O4 (NZFO) Thin Films,"Varying the substrate temperature changes structural and magnetic properties
of spinel ferrite NZFO thin films. XRD of films grown at different temperature
display only 004 reflections, without any secondary peaks, showing growth
orientation along the c axis. We find an increase in crystalline quality of
these thin films with the rise of substrate temperature. The surface topography
of the thin films grown on various growth temperatures conditions reveal that
these films are smooth with low roughness, however the thin films grown at 800
C exhibit lowest average and rms roughness among all thin films. We find iron
and nickel to be more oxidized i,e greater Fe and Ni content in films grown and
annealed at 700 C and 800 C, compared to those grown at lower temperatures. The
magnetic moment is observed to increase with an increase of substrate
temperature and all thin films possess high saturation magnetization and low
coercive field at room temperature. Films grown at 800 C exhibit a
ferrimagnetic paramagnetic phase transition well above room temperature. The
observed large magnetizations with soft magnetic behavior in NZFO thin films
above room temperature suggest potential application in memory, spintronics,
and multifunctional devices.",1804.02458v2
2018-05-13,Pressure-induced spin reorientation transition in layered ferromagnetic insulator Cr2Ge2Te6,"Anisotropic magnetoresistance (AMR) of Cr2Ge2Te6 (CGT), a layered
ferromagnetic insulator, is investigated under an applied hydrostatic pressure
up to 2 GPa. The easy axis direction of the magnetization is inferred from the
AMR saturation feature in the presence and absence of the applied pressure. At
zero applied pressure, the easy axis is along the c-direction or perpendicular
to the layer. Upon application of a hydrostatic pressure>1 GPa, the uniaxial
anisotropy switches to easy-plane anisotropy which drives the equilibrium
magnetization from the c-axis to the ab-plane at zero magnetic field, which
amounts to a giant magnetic anisotropy energy change (>100%). As the
temperature is increased across the Curie temperature, the characteristic AMR
effect gradually decreases and disappears. Our first-principles calculations
confirm the giant magnetic anisotropy energy change with moderate pressure and
assign its origin to the increased off-site spin-orbit interaction of Te atoms
due to a shorter Cr-Te distance. Such a pressure-induced spin reorientation
transition is very rare in three-dimensional ferromagnets, but it may be common
to other layered ferromagnets with similar crystal structures to CGT, and
therefore offers a unique way to control magnetic anisotropy.",1805.04937v1
2018-06-14,The specific heat and magnetic properties of a spin-1/2 ladder including butterfly-shaped unit blocks,"The specific heat, structural characterization, and magnetic property studies
of a new spin ladder with the geometry of butterfly-shaped configuration are
reported. The model introduced here is an infinite spin ladder-type including
spin-1/2 particle for which unit blocks consist of two butterflies connected
together through their bodies (Body-Body bridges). Localized spins on the wings
of butterflies have XXZ Heisenberg interaction with two extra spin-1/2
particles assumed in the center of each cage (unit block), while they have pure
Ising-type interaction with those spins that are localized on the bodies.
Hence, there are six interstitial spins and four nodal spins (Body-Body
interaction) per block. To obtain the partition function of this model, we use
the transfer matrix approach, then we examine the magnetization process, as
well as, the specific heat of the model. Interestingly, we see a wide plateau
at $\frac{5}{6}$ of the saturation magnetization that is strongly dependent on
the magnetic field and anisotropy variations. Moreover, some unexpected
phenomena are observed in the low-temperature limit, such as anomalous
triple-peak in the specific heat function which gradually turns to a
double-peak upon increasing the magnetic field and/or anisotropic Heisenberg
coupling, due to the ferromagnetic phase predomination.",1806.05391v2
2018-07-20,Ising versus Potts criticality in a low-temperature magnetothermodynamics of a frustrated spin-1/2 Heisenberg triangular bilayer,"Low-temperature magnetization curves and thermodynamics of a frustrated
spin-1/2 Heisenberg triangular bilayer with the antiferromagnetic intradimer
interaction and either ferromagnetic or antiferromagnetic interdimer
interaction are investigated in a highly frustrated parameter region, where
localized many-magnon eigenstates provide the most dominant contribution to
magnetothermodynamics. Low-energy states of the highly frustrated spin-1/2
Heisenberg triangular bilayer can be accordingly found from a mapping
correspondence with an effective triangular-lattice spin-1/2 Ising model in a
field. A description based on the effective Ising model implies that the
frustrated Heisenberg triangular bilayer with the ferromagnetic interdimer
coupling displays in a zero-temperature magnetization curve discontinuous
magnetization jump, which is reduced upon increasing of temperature until a
continuous field-driven phase transition from the Ising universality class is
reached at a certain critical temperature. The frustrated Heisenberg triangular
bilayer with the antiferromagnetic interdimer coupling contrarily exhibits
multistep magnetization curve with intermediate plateaus at one-third and
two-thirds of the saturation magnetization, whereas discontinuous magnetization
jumps observable at zero temperature change to continuous field-driven phase
transitions from the universality class of three-state Potts model at
sufficiently low temperatures. Exact results and Monte Carlo simulations of the
effective Ising model are confronted with full exact diagonalization data for
the Heisenberg triangular bilayer in order to corroborate these findings.",1807.08042v2
2018-08-10,Diamond magnetic microscopy of malarial hemozoin nanocrystals,"Magnetic microscopy of malarial hemozoin nanocrystals was performed using
optically detected magnetic resonance imaging of near-surface diamond
nitrogen-vacancy centers. Hemozoin crystals were extracted from
$Plasmodium$-$falciparum$-infected human blood cells and studied alongside
synthetic hemozoin crystals. The stray magnetic fields produced by individual
crystals were imaged at room temperature as a function of applied field up to
350 mT. More than 100 nanocrystals were analyzed, revealing the distribution of
their magnetic properties. Most crystals ($96\%$) exhibit a linear dependence
of stray field magnitude on applied field, confirming hemozoin's paramagnetic
nature. A volume magnetic susceptibility $\chi=3.4\times10^{-4}$ is inferred
using a magnetostatic model informed by correlated scanning electron microscopy
measurements of crystal dimensions. A small fraction of nanoparticles (4/82 for
$Plasmodium$-produced and 1/41 for synthetic) exhibit a saturation behavior
consistent with superparamagnetism. Translation of this platform to the study
of living malaria-infected cells may shed new light on hemozoin formation
dynamics and their interaction with antimalarial drugs.",1808.03636v2
2018-10-31,Transverse Magneto-Optical Kerr Effect at Narrow Optical Resonances,"Magneto-optical spectroscopy based on the transverse magneto-optical Kerr
effect (TMOKE) is a sensitive method for investigation of magnetically-ordered
media. However, in magnetic materials the optical transitions are usually
characterized by spectrally broad resonances with widths considerably exceeding
the Zeeman splitting in the magnetic field. Here we investigate experimentally
and theoretically the TMOKE in the vicinity of relatively narrow optical
resonances provided by confined quantum systems. For experimental demonstration
we use the exciton resonance in a (Cd,Mn)Te diluted magnetic semiconductor
quantum well, where the strong exchange interaction with magnetic ions enables
the giant Zeeman splitting of exciton spin states $\Delta$ in magnetic fields
of a few Tesla. In the weak coupling regime, when the splitting $\Delta$ is
smaller than the spectral broadening of the optical transitions $\Gamma$, the
TMOKE magnitude grows linearly with the increase of the Zeeman splitting and
its spectrum has an S-shape, which remains virtually unchanged in this range.
In the strong coupling regime ($\Delta>\Gamma$) the TMOKE magnitude saturates,
while its spectrum is strongly modified resulting in the appearance of two
separate peaks. The TMOKE is sensitive not only to the sample surface but can
be used to probe the confined electronic states in depth if the upper layer is
sufficiently transparent. Our results demonstrate that TMOKE of spectrally
narrow resonances serves as a versatile tool for probing the charge and spin
structure of electronic states in various confined quantum systems and can be
used for spin tomography in combination with the conventional polar Kerr
effect.",1810.13344v1
2018-12-28,High-order two-fluid plasma solver for direct numerical simulations of plasma flows with full transport phenomena,"The two-fluid plasma equations for a single ion species, with full transport
terms, including temperature and magnetic field dependent ion and electron
viscous stresses and heat fluxes, frictional drag force, and ohmic heating term
have been implemented in the CFDNS code and solved by using sixth-order
non-dissipative compact finite differences for plasma flows in several
different regimes. In order to be able to fully resolve all the dynamically
relevant time and length scales, while maintaining computational feasibility,
the assumptions of infinite speed of light and negligible electron inertia have
been made. Non-dimensional analysis of the two-fluid plasma equations shows
that, by varying the characteristic/background number density, length scale,
temperature, and magnetic strength, the corresponding Hall, resistive, and
ideal magnetohydrodynamics (MHD) equations can be recovered as limiting cases.
The accuracy and robustness of this two-fluid plasma solver in handling plasma
flows in different regimes have been validated against four canonical problems:
Alfven and whistler dispersion relations, electromagnetic plasma shock, and
magnetic reconnection. For all test cases, by using physical dissipation and
diffusion, with negligible numerical dissipation/diffusion, fully converged
Direct Numerical Simulations (DNS)-like solutions are obtained when the ion
Reynolds number based on grid size is smaller than a threshold value which is
about 2.3 in this study. For the magnetic reconnection problem, the results
show that the magnetic flux saturation time and value converge when the ion and
magnetic Reynolds numbers are large enough. Thus, the DNS-like results become
relevant to practical problems with much larger Reynolds numbers.",1812.11237v1
2019-03-27,Structural and magnetic properties of GdCo$_{5-x}$Ni$_x$,"GdCo$_5$ may be considered as two sublattices - one of Gd and one of Co -
whose magnetizations are in antiparallel alignment, forming a ferrimagnet.
Substitution of nickel in the cobalt sublattice of GdCo$_5$ has been
investigated to gain insight into how the magnetic properties of this prototype
rare-earth/transition-metal magnet are affected by changes in the transition
metal sublattice. Polycrystalline samples of GdCo$_{5-x}$Ni$_x$ for 0 $ \leq x
\leq $ 5 were synthesized by arc melting. Structural characterization was
carried out by powder x-ray diffraction and optical and scanning electron
microscope imaging of metallographic slides, the latter revealing a low
concentration of Gd$_2$(Co, Ni)$_7$ lamellae for $x \leq 2.5$. Compensation -
i.e. the cancellation of the opposing Gd and transition metal moments is
observed for $1 \leq x \leq 3$ at a temperature which increases with Ni
content; for larger $x$, no compensation is observed below 360 K. A peak in the
coercivity is seen at $x \approx 1$ at 10K coinciding with a minimum in the
saturation magnetization. Density-functional theory calculations within the
disordered local moment picture reproduce the dependence of the magnetization
on Ni content and temperature. The calculations also show a peak in the
magnetocrystalline anisotropy at similar Ni concentrations to the
experimentally observed coercivity maximum.",1903.11442v1
2020-08-13,Half-metallic ferromagnetism in layered CdOHCl induced by hole doping,"Next-generation spintronic devices will benefit from low-dimensionality,
ferromagnetism, and half-metallicity, possibly controlled by electric fields.
We find these technologically-appealing features to be combined with an exotic
microscopic origin of magnetism in doped CdOHCl, a van der Waals material from
which 2D layers may be exfoliated. By means of first principles simulations, we
predict homogeneous hole-doping to give rise to $p$-band magnetism in both the
bulk and monolayer phases and interpret our findings in terms of Stoner
instability: as the Fermi level is tuned via hole-doping through singularities
in the 2D-like density of states, ferromagnetism develops with large saturation
magnetization of 1 $\mu_B$ per hole, leading to a half-metallic behaviour for
layer carrier densities of the order of 10$^{14}$ cm$^{-2}$. Furthermore, we
put forward electrostatic doping as an additional handle to induce magnetism in
monolayers and bilayers of CdOHCl. Upon application of critical electric fields
perpendicular to atomically-thin-films (as low as 0.2 V/$A{\deg}$ and 0.5
V/$A{\deg}$ in the bilayer and monolayer case, respectively), we envisage the
emergence of a magnetic half-metallic state. The different behaviour of
monolayer vs bilayer systems, as well as an observed asymmetric response to
positive and negative electric fields in bilayers, are interpreted in terms of
intrinsic polarity of CdOHCl atomic stacks, a distinctive feature of the
material. In perspective, given the experimentally accessible magnitude of
critical fields in bilayer of CdOHCl, one can envisage $p$ band magnetism to be
exploited in miniaturized spintronic devices.",2008.05766v1
2020-09-28,Nanoscale transient magnetization gratings excited and probed by femtosecond extreme ultraviolet pulses,"We utilize coherent femtosecond extreme ultraviolet (EUV) pulses derived from
a free electron laser (FEL) to generate transient periodic magnetization
patterns with periods as short as 44 nm. Combining spatially periodic
excitation with resonant probing at the dichroic M-edge of cobalt allows us to
create and probe transient gratings of electronic and magnetic excitations in a
CoGd alloy. In a demagnetized sample, we observe an electronic excitation with
50 fs rise time close to the FEL pulse duration and ~0.5 ps decay time within
the range for the electron-phonon relaxation in metals. When the experiment is
performed on a sample magnetized to saturation in an external field, we observe
a magnetization grating, which appears on a sub-picosecond time scale as the
sample is demagnetized at the maxima of the EUV intensity and then decays on
the time scale of tens of picoseconds via thermal diffusion. The described
approach opens prospects for studying dynamics of ultrafast magnetic phenomena
on nanometer length scales.",2009.13330v1
2021-01-01,3D Simulations of Oxygen Shell Burning with and without Magnetic Fields,"We present a first 3D magnetohydrodynamic (MHD) simulation of convective
oxygen and neon shell burning in a non-rotating $18\, M_\odot$ star shortly
before core collapse to study the generation of magnetic fields in supernova
progenitors. We also run a purely hydrodynamic control simulation to gauge the
impact of the magnetic fields on the convective flow and on convective boundary
mixing. After about 17 convective turnover times, the magnetic field is
approaching saturation levels in the oxygen shell with an average field
strength of $\mathord{\sim}10^{10}\, \mathrm{G}$, and does not reach kinetic
equipartition. The field remains dominated by small to medium scales, and the
dipole field strength at the base of the oxygen shell is only $10^{9}\,
\mathrm{G}$. The angle-averaged diagonal components of the Maxwell stress
tensor mirror those of the Reynolds stress tensor, but are about one order of
magnitude smaller. The shear flow at the oxygen-neon shell interface creates
relatively strong fields parallel to the convective boundary, which noticeably
inhibit the turbulent entrainment of neon into the oxygen shell. The reduced
ingestion of neon lowers the nuclear energy generation rate in the oxygen shell
and thereby slightly slows down the convective flow. Aside from this indirect
effect, we find that magnetic fields do not appreciably alter the flow inside
the oxygen shell. We discuss the implications of our results for the subsequent
core-collapse supernova and stress the need for longer simulations, resolution
studies, and an investigation of non-ideal effects for a better understanding
of magnetic fields in supernova progenitors.",2101.00213v2
2021-01-04,Influence of the martensitic transformation kinetics on the magnetocaloric effect in Ni-Mn-In,"The inverse magnetocaloric effect (MCE) in Ni-Mn-based Heusler compounds
occurs during the magnetostructural transition between low-temperature,
low-magnetization martensite and high-temperature, high-magnetization
austenite. In this study, we analyze the metamagnetic transformation of a
$Ni_{49.8}Mn_{35}In_{15.2}$ compound by simultaneous adiabatic temperature
change and strain measurements in pulsed magnetic fields up to 10 T. We observe
an adiabatic temperature change of -10 K and a strain of -0.22 % when the
reverse martensitic transition is fully induced at a starting temperature of
285 K. By a variation of the magnetic field-sweep rates between 316 Ts$^{-1}$,
865 Ts$^{-1}$ and 1850 Ts$^{-1}$, the transitional dynamics of the reverse
martensitic transformation have been investigated. Our experiments reveal an
apparent delay upon the end of the reverse martensitic transformation at field
rates exceeding 865 Ts$^{-1}$ which is related to the annihilation of retained
martensite. As a consequence, the field hysteresis increases and higher fields
are required to saturate the transition. In contrast, no time-dependent effects
on the onset of the reverse martensitic transformation were observed in the
studied field-sweep range. Our results demonstrate that kinetic effects in
Heusler compounds strongly affect the magnetic cooling cycle, especially when
utilising a multicaloric ""exploiting-hysteresis cycle"" where high magnetic
field-sweep rates are employed.",2101.00840v1
2021-01-11,Strain Induced Anisotropic Magnetic Behaviour and Exchange Coupling Effect in Fe-SmCo$_{5}$ Permanent Magnets Generated by High Pressure Torsion,"High-pressure torsion (HPT), a technique of severe plastic deformation (SPD),
is shown as a promising processing method for exchange-spring magnetic
materials in bulk form. Powder mixtures of Fe and SmCo$_{5}$ are consolidated
and deformed by HPT exhibiting sample dimensions of several millimetres, being
essential for bulky magnetic applications. The structural evolution during HPT
deformation of Fe-SmCo$_{5}$ compounds at room- and elevated- temperatures of
chemical compositions consisting of 87, 47, 24 and 10 wt.% Fe is studied and
microstructurally analysed. Electron microscopy and synchrotron X-ray
diffraction reveal a dual-phase nanostructured composite for the as-deformed
samples with grain refinement after HPT deformation. SQUID magnetometry
measurements show hysteresis curves of an exchange coupled nanocomposite at
room temperature, while for low temperatures a decoupling of Fe and SmCo$_{5}$
is observed. Furthermore, exchange interactions between the hard- and
soft-magnetic phase can explain a shift of the hysteresis curve. Strong
emphasis is devoted to the correlation between the magnetic properties and the
evolving nano-structure during HPT deformation, which is conducted for a 1:1
composition ratio of Fe to SmCo$_{5}$. SQUID magnetometry measurements show an
increasing saturation magnetisation for increasing strain $\gamma$ and a
maximum of the coercive field strength at a shear strain of $\gamma$ = 75.",2101.03900v2
2021-01-13,Quasi-one-dimensional magnetism in the spin-$\frac12$ antiferromagnet BaNa$_{2}$Cu(VO$_{4}$)$_{2}$,"We report synthesis and magnetic properties of quasi-one-dimensional
spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain compound
BaNa$_2$Cu(VO$_4$)$_2$. This orthovanadate has a centrosymmetric crystal
structure, $C2/c$, where the magnetic Cu$^{2+}$ ions form spin chains. These
chains are arranged in layers, with the chain direction changing by 62$^0$
between the two successive layers. Alternatively, the spin lattice can be
viewed as anisotropic triangular layers upon taking the inter-chain
interactions into consideration. Despite this potential structural complexity,
temperature-dependent magnetic susceptibility, heat capacity, ESR intensity,
and NMR shift agree well with the uniform spin-$1/2$ Heisenberg chain model
with an intrachain coupling of $J/k_{\rm B} \simeq 5.6$ K. The saturation field
obtained from the magnetic isotherm measurement consistently reproduces the
value of $J/k_{\rm B}$. Further, the $^{51}$V NMR spin-lattice relaxation rate
mimics the 1D character in the intermediate temperature range, whereas magnetic
long-range order sets in below $T_{\rm N} \simeq 0.25$ K. The effective
interchain coupling is estimated to be $J_{\perp}/k_{\rm B} \simeq 0.1$ K. The
theoretical estimation of exchange couplings using band-structure calculations
reciprocate our experimental findings and unambiguously establish the 1D
character of the compound. Finally, the spin lattice of BaNa$_2$Cu(VO$_4$)$_2$
is compared with the chemically similar but not isostructural compound
BaAg$_2$Cu(VO$_4)_2$.",2101.05120v1
2021-02-04,Evaluating the reliability of a simple method to map the magnetic field azimuth in the solar chromosphere,"The Zeeman effect is of limited utility for probing the magnetism of the
quiet solar chromosphere. The Hanle effect in some spectral lines is sensitive
to such magnetism, but the interpretation of the scattering polarization
signals requires taking into account that the chromospheric plasma is highly
inhomogeneous and dynamic (i.e., that the magnetic field is not the only cause
of symmetry breaking). Here we investigate the reliability of a well-known
formula for mapping the azimuth of chromospheric magnetic fields directly from
the scattering polarization observed in the \ion{Ca}{2}~8542~\AA\, line, which
is typically in the saturation regime of the Hanle effect. To this end, we use
the Stokes profiles of the \ion{Ca}{2}~8542~\AA\, line computed with the PORTA
radiative transfer code in a three-dimensional (3D) model of the solar
chromosphere, degrading them to mimic spectropolarimetric observations for a
range of telescope apertures and noise levels. The simulated observations are
used to obtain the magnetic field azimuth at each point of the field of view,
which we compare with the actual values within the 3D model. We show that,
apart from intrinsic ambiguities, the method provides solid results. Their
accuracy depends more on the noise level than on the telescope diameter.
Large-aperture solar telescopes, like DKIST and EST, are needed to achieve the
required noise-to-signal ratios using reasonable exposure times.",2102.02880v1
2021-03-05,Ferromagnetic Composite Self-Arrangement in Iron-Implanted Epitaxial Palladium Thin Films,"We report on the formation of the dilute $Pd_{1-x}Fe_x$ compositions with
tunable magnetic properties under an ion-beam implantation of epitaxial Pd thin
films. Binary $Pd_{1-x}Fe_x$ alloys with a mean iron content $x$ of $0.025$,
$0.035$ or $0.075$ were obtained by the implantation of $40 keV$ $Fe^+$ ions
into the palladium films on MgO (001) substrate to the doses of
$0.5\cdot10^{16}, 1.0\cdot10^{16}$ and $3.0\cdot10^{16}$ $ions/cm^2$,
respectively. Structural and magnetic studies have shown that iron atoms occupy
regular fcc-lattice Pd-sites without the formation of any secondary
crystallographic phase. All the iron implanted Pd films reveal ferromagnetism
at low temperatures (below $200 K$) with both the Curie temperature and
saturation magnetization determined by the implanted iron dose. In contrast to
the magnetic properties of the molecular beam epitaxy grown $Pd_{1-x}Fe_x$
alloy films with the similar iron contents, the Fe-implanted Pd films possess
weaker in-plane magnetocrystalline anisotropy, and, accordingly, a lower
coercivity. The observed multiple ferromagnetic resonances in the implanted
$Pd_{1-x}Fe_x$ films indicate a formation of a magnetically inhomogeneous state
due to spinodal decomposition into regions, presumably layers, with identical
crystal symmetry but different iron contents. The multiphase magnetic structure
is robust with respect to the vacuum annealing at $770 K$, though develops
towards well-defined local $Pd-Fe$ compositions.",2103.03562v1
2021-05-20,Spin dynamics of the quantum dipolar magnet Yb$_3$Ga$_5$O$_{12}$ in an external field,"We investigate ytterbium gallium garnet Yb$_{3}$Ga$_{5}$O$_{12}$ in the
paramagnetic phase above the supposed magnetic transition at $T_{\lambda}
\approx 54$ mK. Our study combines susceptibility and specific heat
measurements with neutron scattering experiments and theoretical calculations.
Below 500 mK, the elastic neutron response is strongly peaked in the momentum
space. Along with that the inelastic spectrum develops flat excitation modes.
In magnetic field, the lowest energy branch follows a Zeeman shift in
accordance with the field-dependent specific heat data. An intermediate state
with spin canting away from the field direction is evidenced in small magnetic
fields. In the field of 2 T, the total magnetization almost saturates and the
measured excitation spectrum is well reproduced by the spin-wave calculations
taking into account solely the dipole-dipole interactions. The small positive
Curie-Weiss temperature derived from the susceptibility measurements is also
accounted for by the dipole spin model. Altogether, our results suggest that
Yb$_{3}$Ga$_{5}$O$_{12}$ is a quantum dipolar magnet.",2105.09817v1
2021-07-09,Electric field driven flat bands: Enhanced magnetoelectric and electrocaloric effects in frustrated quantum magnets,"The $J_1$-$J_2$ quantum spin sawtooth chain is a paradigmatic one-dimensional
frustrated quantum spin system exhibiting unconventional ground-state and
finite-temperature properties. In particular, it exhibits a flat energy band of
one-magnon excitations accompanied by an enhanced magnetocaloric effect for two
singular ratios of the basal interactions $J_1$ and the zigzag interactions
$J_2$. In our paper, we demonstrate that one can drive the spin system into a
flat-band scenario by applying an appropriate electric field, thus overcoming
the restriction of fine-tuned exchange couplings $J_1$ and $J_2$ and allowing
one to tune more materials towards flat-band physics, that is to show a
macroscopic magnetization jump when crossing the magnetic saturation field, a
residual entropy at zero temperature as well as an enhanced magnetocaloric
effect. While the magnetic field acts on the spin system via the ordinary
Zeeman term, the coupling of an applied electric field with the spins is given
by the sophisticated Katsura-Nagaosa-Balatsky (KNB) mechanism, where the
electric field effectively acts as a Dzyaloshinskii-Moriya spin-spin
interaction. The resulting novel features are corresponding reciprocal effects:
We find a magnetization jump driven by the electric field as well as a jump of
the electric polarization driven by the magnetic field, i.e.\ the system
exhibits an extraordinarily strong magnetoelectric effect. Moreover, in analogy
to the enhanced magnetocaloric effect the system shows an enhanced
electrocaloric effect.",2107.04371v2
2021-11-11,Tuning the Room Temperature Ferromagnetism in Fe5GeTe2 by Arsenic Substitution,"In order to tune the magnetic properties of the cleavable high-Curie
temperature ferromagnet Fe$_{5-x}$GeTe$_2$, the effect of increasing the
electron count through arsenic substitution has been investigated. Small
additions of arsenic (2.5 and 5%) seemingly enhance ferromagnetic order in
polycrystalline samples by quenching fluctuations on one of the three magnetic
sublattices, whereas larger As concentrations decrease the ferromagnetic Curie
temperature ($T_{\rm C}$) and saturation magnetization. This work also
describes the growth and characterization of Fe$_{4.8}$AsTe$_2$ single crystals
that are structurally analogous to Fe$_{5-x}$GeTe$_2$ but with some phase
stability complications. Magnetization measurements reveal dominant
antiferromagnetic behavior in Fe$_{4.8}$AsTe$_2$ with a N\'{e}el temperature of
$T_{\rm N}$ $\approx$42K. A field-induced spin-flop below $T_{\rm N}$ results
in a switch from negative to positive magnetoresistance, with significant
hysteresis causing butterfly-shaped resistance loops. In addition to reporting
the properties of Fe$_{4.8}$AsTe$_2$, this work shows the importance of
manipulating the individual magnetic sublattices in Fe$_{5-x}$GeTe$_2$ and
motivates further efforts to control the magnetic properties in related
materials by fine tuning of the Fermi energy or crystal chemistry.",2111.06439v1
2021-11-20,Exchange coupling in synthetic anion-engineered chromia heterostructures,"Control of magnetic states by external factors has garnered a mainstream
status in spintronic research for designing low power consumption and
fast-response information storage and processing devices. Previously,
magnetic-cation substitution is the conventional means to induce ferromagnetism
in an intrinsic antiferromagnet. Theoretically, the anion-doping is proposed to
be another effect means to change magnetic ground states. Here we demonstrate
the synthesis of high-quality single-phase chromium oxynitride thin films using
in-situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide
and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and
insulating state, as demonstrated by the combination of multiple magnetization
probes and theoretical calculations. With increasing the nitrogen content, the
crystal structure of chromium oxynitride transits from trigonal (R3c) to
tetragonal (4mm) phase and its saturation magnetization reduces significantly.
Furthermore, we achieve a large and controllable exchange bias field in the
chromia heterostructures by synthetic anion engineering. This work reflects the
anion engineering in functional oxides towards the potential applications in
giant magnetoresistance and tunnelling junctions of modern magnetic sensors and
read heads.",2111.10564v1
2021-11-23,"TaCo$_{2}$Te$_{2}$: An air-stable, magnetic van der Waals material with high mobility","Van der Waals (vdW) materials are an indispensable part of functional device
technology due to their versatile physical properties and ease of exfoliating
to the low-dimensional limit. Among all the compounds investigated so far, the
search for magnetic vdW materials has intensified in recent years, fueled by
the realization of magnetism in two dimensions (2D). However, metallic magnetic
vdW systems are still uncommon. In addition, they rarely host high-mobility
charge carriers, which is an essential requirement for high-speed electronic
applications. Another shortcoming of 2D magnets is that they are highly air
sensitive. Using chemical reasoning, we introduce TaCo2Te2 as an air-stable,
high-mobility, magnetic vdW material. It has a layered structure, which
consists of Peierls distorted Co chains and a large vdW gap between the layers.
We find that the bulk crystals can be easily exfoliated and the obtained thin
flakes are robust to ambient conditions after four months of monitoring using
an optical microscope. We also observe signatures of canted antiferromagntic
behavior at low-temperature. TaCo2Te2 shows a metallic character and a large,
non-saturating, anisotropic magnetoresistance. Furthermore, our Hall data and
quantum oscillation measurements reveal the presence of both electron- and
hole-type carriers and their high mobility.",2111.12079v1
2021-12-01,Pressure dependent magnetic properties on bulk CrBr3 single crystals,"The van der Waals class of materials offer an approach to two-dimensional
magnetism as their spin fluctuations can be tuned upon exfoliation of layers.
Moreover, it has recently been shown that spin-lattice coupling and long-range
magnetic ordering can be modified with pressure in van der Waals materials. In
this work, the magnetic properties of quasi two-dimensional CrBr3 are reported
applying hydrostatic pressure. The application of pressure (0 - 0.8 GPa) shows
a 72 % decrease in saturation magnetization with small decrease in the Curie
temperature from 33 to 29 K. Density functional theory calculations with
pressure up to 1 GPa show a reduction in volume and interplanar distance as
pressure increases. To further understand magnetic properties with applied
pressure, the magnetocrystalline anisotropy energy (MAE) and exchange coupling
parameter (J) are calculated. There is minimal decrease in MAE and the first
nearest neighbor interaction (J1) (U = 2.7 eV and J = 0.7 eV), shows an
increase in J1 with respect to pressure. Overall, CrBr3 displays ferromagnetic
interlayer coupling and the calculated exchange coupling and MAE parameters
match well with the observations from the experimental work.",2112.00233v1
2022-01-27,Robust antiferromagnetism in Y$_2$Co$_3$,"We report on a solution-growth based method to synthesise single crystals of
Y$_2$Co$_3$ and on its structural and magnetic properties. We find that
Y$_2$Co$_3$ crystallizes in the La2Ni3-type orthorhombic structure with space
group Cmce (No. 64), with Co forming distorted kagome lattices. Y$_2$Co$_3$
orders antiferromagnetically below $T_N$ = 252 K. Magnetization measurements
reveal that the moments are primarily aligned along the b axis with evidence
for some canting. Band-structure calculations indicate that ferromagnetic and
antiferromagnetic orders are nearly degenerate, at odds with experimental
results. Magnetization measurements under pressure up to 1 GPa reveal that the
N/'eel temperature decreases with the slope of -1.69 K/GPa. We observe a
field-induced spin-flop transition in the magnetization measurements at 1.5 K
and 21 T with magnetic field along the b direction. The magnetization is not
saturated up to 35 T, indicating that the antiferromagnetic ordering in
Y$_2$Co$_3$ is quite robust, which is surprising for such a Co-rich
intermetallic.",2201.11778v1
2022-03-03,On large-scale dynamos with stable stratification and the application to stellar radiative zones,"Our understanding of large-scale magnetic fields in stellar radiative zones
remains fragmented and incomplete. Such magnetic fields, which must be produced
by some form of dynamo mechanism, are thought to dominate angular-momentum
transport, making them crucial to stellar evolution. A major difficulty is the
effect of stable stratification, which generally suppresses dynamo action. We
explore the effects of stable stratification on mean-field dynamo theory with a
particular focus on a non-helical large-scale dynamo (LSD) mechanism known as
the magnetic shear-current effect. We find that the mechanism is robust to
increasing stable stratification as long as the original requirements for its
operation are met: a source of shear and non-helical magnetic fluctuations
(e.g. from a small-scale dynamo). Both are plausibly sourced in the presence of
differential rotation. Our idealized direct numerical simulations, supported by
mean-field theory, demonstrate the generation of near equipartition large-scale
toroidal fields. Additionally, a scan over magnetic Reynolds number shows no
change in the growth or saturation of the LSD, providing good numerical
evidence of a dynamo mechanism resilient to catastrophic quenching, which has
been an issue for helical dynamos. These properties -- the absence of
catastrophic quenching and robustness to stable stratification -- make the
mechanism a plausible candidate for generating in-situ large-scale magnetic
fields in stellar radiative zones.",2203.01943v2
2022-05-12,Magnetization of Zn1-xCoxO nanoparticles: single-ion anisotropy and spin clustering,"The magnetization of Zn1-xCoxO (0.0055 < x < 0.073) nanoparticles has been
measured as a function of temperature T (1.7 K < T , 10 K) and for magnetic
field up to 65 kOe using a SQUID magnetometer. Samples were synthesized by
three different growth methods: microwave-assisted hydrothermal, combustion
reaction and sol-gel. For all studied samples, the magnetic properties derive
from the antiferromagnetic (AF) spin clustering due to the Co2+ nearest
neighbors. At T >= 6 K, the magnetization of the Co2+ ions has a Brillouin-type
behavior, but below 6 K, it shows a notable deviation. We have shown that the
observed deviation may be derived from single-ion anisotropy (SIA) with
uniaxial symmetry. Results of fits show that the axial-SIA parameter D
(typically D = 4.4 K) is slightly larger that the bulk value D = 3.97 K. No
significant change of D has been observed as a function of the Co concentration
or the growth process. For each sample, the SIA fit gave also the effective
concentration (x) corresponding to the technical saturation value of the
magnetization. Comparison of the concentration dependence of x with predictions
based on cluster models shows an enhancement of the AF spin clustering
independent of the growth method. This is ascribed to a clamped non-random
distribution of the cobalt ions in the nanoparticles. The approach of the local
concentration (xL) has been used to quantify the observed deviation from
randomicity. Assuming a ZnO core/ Zn1-xCoxO shell nanoparticle, the thickness
of the shell has been determined from the ratio xL/x.",2205.06213v1
2022-08-09,"Structural, magnetic and transport properties of Co$_2$CrAl epitaxial thin films","We report the physical properties of Co$_2$CrAl Heusler alloy epitaxial thin
films grown on single crystalline MgO(001) substrate using pulsed laser
deposition technique. The x-ray diffraction pattern in $\theta$-2$\theta$ mode
showed the film growth in single phase B2-type ordered cubic structure with the
presence of (002) and (004) peaks, and the film oriented along the MgO(001)
direction. The $\phi$~scan along the (220) plane confirms the four-fold
symmetry and the epitaxial growth relation found to be
Co$_2$CrAl(001)[100]$\vert$$\vert$MgO(001)[110]. The thickness of about 12~nm
is extracted through the analysis of x-ray reflectivity data. The isothermal
magnetization (M--H) curves confirm the ferromagnetic (FM) nature of the thin
film having significant hysteresis at 5 and 300~K. From the in-plane M--H
curves, the saturation magnetization values are determined to be
2.1~$\mu$$_{\rm B}$/f.u.~at 5~K and 1.6~$\mu$$_{\rm B}$/f.u. at 300~K, which
suggests the soft FM behavior in the film having the coercive field $\approx$
522~Oe at 5~K. The thermo-magnetization measurements at 500~Oe magnetic field
show the bifurcation between field-cooled and zero-field-cooled curves below
about 100~K. The normalized field-cooled magnetization curve follows the T$^2$
dependency, and the analysis reveal the Curie temperature around 335$\pm$11~K.
Moreover, the low-temperature resistivity indicates semiconducting behavior
with the temperature, and we find a negative temperature coefficient of
resistivity (5.2 $\times$ 10$^{-4}$ /K).",2208.04687v1
2022-10-14,Linear colossal magnetoresistance driven by magnetic textures in LaTiO3 thin films on SrTiO3,"Linear magnetoresistance (LMR) is of particular interest for memory,
electronics, and sensing applications, especially when it does not saturate
over a wide range of magnetic fields. One of its principal origins is local
mobility or density inhomogeneities, often structural, which in the
Parish-Littlewood theory leads to an unsaturating LMR proportional to mobility.
Structural disorder, however, also tends to limit the mobility and hence the
overall LMR amplitude. An alternative route to achieve large LMR is via
non-structural inhomogeneities which do not affect the zero field mobility,
like magnetic domains. Here, linear positive magnetoresistance caused by
magnetic texture is reported in \ch{LaTiO3}/\ch{SrTiO3} heterostructures. The
LMR amplitude reaches up to 6500\% at 9T. This colossal value is understood by
the unusual combination of a very high thin film mobility, up to 40 000
cm$^2$/V.s, and a very large coverage of low-mobility regions. These regions
correlate with a striped magnetic structure, compatible with a spiral magnetic
texture in the \ch{LaTiO3} film, revealed by low temperature Lorentz
transmission electron microscopy. These results provide a novel route for the
engineering of large-LMR devices.",2210.07682v1
2022-11-01,Magnetically Dominated Disks in Tidal Disruption Events and Quasi-Periodic Eruptions,"The classical radiation pressure instability has been a persistent
theoretical feature of thin, radiatively efficient accretion disks with
accretion rates 1 to 100 per cent of the Eddington rate. But there is only
limited evidence of its occurrence in nature: rapid heartbeat oscillations of a
few X-ray binaries and now, perhaps, the new class of hourly X-ray transients
called quasi-periodic eruptions (QPEs). The accretion disks formed in tidal
disruption events (TDEs) have been observed to peacefully trespass through the
range of unstable accretion rates without exhibiting any clear sign of the
instability. We try to explain the occurrence or otherwise of this instability
in these systems, by constructing steady state 1D models of thin magnetic
accretion disks. The local magnetic pressure in the disk is assumed to be
dominated by toroidal fields arising from a dynamo sourced by
magneto-rotational instability (MRI). We choose a physically motivated
criterion of MRI saturation, validated by recent magnetohydrodynamic
simulations, to determine the strength of magnetic pressure in the disk. The
resulting magnetic pressure support efficiently shrinks: (1) the parameter
space of unstable mass accretion rates, explaining the absence of instability
in systems such as TDEs and (2) the range of unstable radii in the inner
accretion disk, which can shorten the quasi-periods of instability limit-cycles
by more than three orders of magnitude, explaining the observed periods ( a few
hrs) of QPEs. In addition to examining stability properties of strongly
magnetized disks, we predict other observational signatures such as spectral
hardening factors and jet luminosities to test the compatibility of our disk
models with observations of apparently stable TDE disks.",2211.00704v1
2022-12-21,Charge transfer and disorder-induced spin relaxation in La2NiMnO6 crystallites,"Investigation of the electronic and spin structure in double perovskites is
recently attracting significant attention, mainly driven by their unique
multifunctional properties and other underlying charge and spin dynamics.
Herein, using X-ray photoelectron spectroscopy (XPS), we explore the influence
of variable fractions of Mn3+/Mn4+ cation in different crystallite sizes of
La2NiMnO6 that control the various completing exchange interactions of Ni/Mn
cations responsible for multiple magnetic transitions. The enhanced itinerant
electron due to Mn4+ + Ni2+ to Mn3+ + Ni3+ charge transfer emerged as a
shoulder like characteristics at the low binding energy in the Mn-2P core-level
spectrum. The various approaches such as difference in saturation
magnetization, presence of multiple charge valance, and magnetic entropy
calculations confirm the presence of antisites disorder and it varies as a
function of milling. As milling provides excess energy that helps with
nucleation or cation ordering. Competing magnetic interactions driven by mixed
valences and disorder were established across a cluster glassy phase in the
crystallites. Electron spin resonance spectroscopy (ESR) was utilized to probe
the temperature-driven ferromagnetic-cluster spin-glass transition with
modified g-factor ranging from 2.050 to 2.037. The line width of the ESR
signals increases across the ferromagnetic to cluster-glass phase transition
due to spin freezing. This phase transition is further characterized by
temperature-dependent ac-magnetic susceptibility measurements. Argand diagram
for the ac-susceptibility of the interacting crystallites suggests a collective
magnetization relaxation dynamic in the proximity of spin-glass freezing
temperature of La2NiMnO6.",2212.10845v2
2023-02-22,Magnetized fingering convection in stars,"Fingering convection (also known as thermohaline convection) is a process
that drives the vertical transport of chemical elements in regions of stellar
radiative zones where the mean molecular weight increases with radius.
Recently, Harrington & Garaud (2019) used three-dimensional direct numerical
simulations to show that a vertical magnetic field can dramatically enhance the
rate of chemical mixing by fingering convection. Furthermore, they proposed a
so-called ""parasitic saturation"" theory to model this process. Here, we test
their model over a broad range of parameter space, using a suite of direct
numerical simulations of magnetized fingering convection varying the magnetic
Prandtl number, magnetic field strength, and composition gradient. We find that
the rate of chemical mixing measured in the simulations is not always predicted
accurately by their existing model, in particular when the magnetic diffusivity
is large. We then present an extension of the Harrington & Garaud (2019) model
which resolves this issue. When applied to stellar parameters, it recovers the
results of Harrington & Garaud (2019) except in the limit where fingering
convection becomes marginally stable, where the new model is preferred. We
discuss the implications of our findings for stellar structure and evolution.",2302.11610v3
2023-03-20,Constraining atmospheric parameters and surface magnetic fields with $\texttt{ZeeTurbo}$: an application to SPIRou spectra,"We report first results on a method aimed at simultaneously characterising
atmospheric parameters and magnetic properties of M dwarfs from high-resolution
nIR spectra recorded with SPIRou in the framework of the SPIRou Legacy Survey.
Our analysis relies on fitting synthetic spectra computed from MARCS model
atmospheres to selected spectral lines, both sensitive and insensitive to
magnetic fields. We introduce a new code, $\texttt{ZeeTurbo}$, obtained by
including the Zeeman effect and polarised radiative transfer capabilities to
$\texttt{Turbospectrum}$. We compute a grid of synthetic spectra with
$\texttt{ZeeTurbo}$ for different magnetic field strengths and develop a
process to simultaneously constrain $T_{\rm eff}$, $\log{g}$, [M/H],
[$\alpha$/Fe] and the average surface magnetic flux. In this paper, we present
our approach and assess its performance using simulations, before applying it
to six targets observed in the context of the SPIRou Legacy Survey (SLS),
namely AU Mic, EV Lac, AD Leo, CN Leo, PM J18482+0741, and DS Leo. Our method
allows us to retrieve atmospheric parameters in good agreement with the
literature, and simultaneously yields surface magnetic fluxes in the range 2-4
kG with a typical precision of 0.05 kG, in agreement with literature estimates,
and consistent with the saturated dynamo regime in which most of these stars
are.",2303.11241v1
2023-06-21,"First-principles prediction of structural, magnetic properties of Cr-substituted strontium hexaferrite, and its site preference","To investigate the structural and magnetic properties of Cr-doped M-type
strontium hexaferrite (SrFe$_{12}$O$_{19}$) with x = (0.0, 0.5, 1.0), we
perform first-principles total-energy calculations relied on density functional
theory. Based on the calculation of the substitution energy of Cr in strontium
hexaferrite and formation probability analysis, we conclude that the doped Cr
atoms prefer to occupy the 2a, 12k, and 4f$_{2}$ sites which is in good
agreement with the experimental findings. Due to Cr$^{3+}$ ion moment, 3
{$\mu_B$}, smaller than that of Fe$^{3+}$ ion, 5 {$\mu_B$}, saturation
magnetization (M$_{s}$) reduce rapidly as the concentration of Cr increases in
strontium hexaferrite. The magnetic anisotropic field $\left(H_{a}\right)$
rises with an increasing fraction of Cr despite a significant reduction of
magnetization and a slight increase of magnetocrystalline anisotropy
$\left(K_{1}\right)$.The cause for the rise in magnetic anisotropy field
$\left(H_{a}\right)$ with an increasing fraction of Cr is further emphasized by
our formation probability study. Cr$^{3+}$ ions prefer to occupy the 2a sites
at lower temperatures, but as the temperature rises, it is more likely that
they will occupy the 12k site. Cr$^{3+}$ ions are more likely to occupy the 12k
site than the 2a site at a specific annealing temperature (>700{\deg}C).",2306.11952v1
2023-06-27,MHD Simulation in Galactic Center Region with Radiative Cooling and Heating,"We investigate the role of magnetic field on the gas dynamics in a galactic
bulge region by three dimensional simulations with radiative cooling and
heating. While high-temperature corona with $T>10^6\ {\rm K}$ is formed in the
halo regions, the temperature near the mid-plane is $\lesssim 10^4\ {\rm K}$
following the thermal equilibrium curve determined by the radiative cooling and
heating. Although the thermal energy of the interstellar gas is lost by
radiative cooling, the saturation level of the magnetic field strength does not
significantly depend on the radiative cooling and heating. The magnetic field
strength is amplified to $10\ {\rm \mu G}$ on average, and reaches several
hundred ${\rm \mu G}$ locally. We find the formation of magnetically dominated
regions at mid-latitudes in the case with the radiative cooling and heating,
which is not seen in the case without radiative effect. The vertical thickness
of the mid-latitude regions is $50-150\ {\rm pc}$ at the radial location of
$0.4-0.8\ {\rm kpc}$ from the galactic center, which is comparable to the
observed vertical distribution of neutral atomic gas. When we take the average
of different components of energy density integrated over the galactic bulge
region, the magnetic energy is comparable to the thermal energy. We conclude
that the magnetic field plays a substantial role in controlling the dynamical
and thermal properties of the galactic bulge region.",2306.15761v2
2023-10-29,Bridging Scales in Black Hole Accretion and Feedback: Magnetized Bondi Accretion in 3D GRMHD,"Fueling and feedback couple supermassive black holes (SMBHs) to their host
galaxies across many orders of magnitude in spatial and temporal scales, making
this problem notoriously challenging to simulate. We use a multi-zone
computational method based on the general relativistic magneto-hydrodynamic
(GRMHD) code KHARMA that allows us to span $7$ orders of magnitude in spatial
scale, to simulate accretion onto a non-spinning SMBH from an external medium
with Bondi radius $R_B\approx 2\times 10^5 \,GM_\bullet/c^2$, where $M_\bullet$
is the SMBH mass. For the classic idealized Bondi problem, spherical gas
accretion without magnetic fields, our simulation results agree very well with
the general relativistic analytic solution. Meanwhile, when the accreting gas
is magnetized, the SMBH magnetosphere becomes saturated with a strong magnetic
field. The density profile varies as $\sim r^{-1}$ rather than $r^{-3/2}$ and
the accretion rate $\dot{M}$ is consequently suppressed by over 2 orders of
magnitude below the Bondi rate $\dot{M}_B$. We find continuous energy feedback
from the accretion flow to the external medium at a level of
$\sim10^{-2}\dot{M}c^2 \sim 5\times 10^{-5} \dot{M}_B c^2$. Energy transport
across these widely disparate scales occurs via turbulent convection triggered
by magnetic field reconnection near the SMBH. Thus, strong magnetic fields that
accumulate on horizon scales transform the flow dynamics far from the SMBH and
naturally explain observed extremely low accretion rates compared to the Bondi
rate, as well as at least part of the energy feedback.",2310.19135v2
2023-11-30,Induced quantum magnetism in CEF singlet ground state models: Thermodynamics and excitations,"We present a comparative investigation of singlet ground state induced
magnetism for singlet, doublet and triplet excited CEF states of non-Kramers
f-electrons relevant primarily for Pr- and U- based compounds. This type of
magnetic order is of intrinsic quantum nature because it requires the
superposition of singlet ground state with excited states due to non-diagonal
matrix elements of the effective intersite exchange to generate local moments.
In contrast to conventional magnets the local moments and their ordering appear
simultaneously at the transition temperature. It is finite only if the control
parameter proportional to the ratio of exchange strength to level splitting
exceeds a critical value marking the quantum critical point of the models. We
determine the dependence of transition temperature, saturation moment,
renormalised level splitting, specific heat jumps and low-temperature
susceptibility as function of control parameter. Furthermore the temperature
dependence of these quantities is calculated for control parameters above and
below the quantum critical point and the distinction to conventional magnetism
is discussed. In addition we investigate the dynamical properties of the three
models, deriving the magnetic exciton dispersion and their critical behaviour.
In particular the conditions for true and arrested soft-mode behaviour at the
ordering wave vector are identified.",2311.18416v2
2023-12-04,Survival of magnetic correlations above ordering temperature in a ferromagnetically ordered classical kagomé magnet: Li9Cr3(P2O7)3(PO4)2,"Motivated by the recent discovery of a semiclassical nematic spin liquid
state in a Heisenberg kagom\'e antiferromagnet Li9Fe3(P2O7)3(PO4)2 (LFPO) with
S=5/2 [Kermarrec et al. Phys. Rev. Lett. 127, 157202 (2021)], we now
investigate the impact of spin quantum number S on the ground state properties
by studying the isostructural kagom\'e magnet Li9Cr3(P2O7)3(PO4)2 (LCPO) with
active t2g orbitals and S = 3/2. Thermodynamic measurements reveal that the
ground state properties of LCPO is dominated by the ferromagnetic interactions
with a mean-field temperature $\theta \sim$ 3 K (J < 1 K) and the ordering
temperature, Tc ~ 2.7 K, and the size of the ordered moment $\sim 1.05 \pm 0.25
$ ~${\mu}_B$ is significantly reduced from that of a fully ordered moment. The
ab initio electronic structure calculations nicely corroborate the
thermodynamic results and suggest the presence of additional in and
out-of-plane further neighbor antiferromagnetic couplings, though significantly
weaker in comparison to the dominant first-nearest neighbor ferromagnetic
coupling. The spin-lattice relaxation rate measured with fields larger than the
saturation field shows a magnetic field induced gap ($\Delta \propto B$) in the
excitation spectrum, and in $B \rightarrow 0$ limit the gap has a finite
intercept ~ 3 K, equivalent to the mean-field scale. We interpret the origin of
this gap is associated with the magnetic interactions inherent to the material.
With our experimental results, we establish the stabilization of a
ferromagnetic like ground state and the persistence of magnetic-correlations
above the ordering temperature in LCPO.",2312.01731v1
2023-12-09,Bachelorthesis: Calculation of the magnetic properties of quarternary ThMn$_{12}$-type compounds with Zr as a substitution for Nd,"This research aims to identify an alternative solution for the
Nd$_2$Fe$_{14}$B magnet in light of the scarcity of rare earth (RE) resources.
The investigation uses density functional theory (DFT) calculations to assess
the effect of partial substitution of Nd with the transition metal (TM) Zr
within the ThMn$_{12}$ structure, focusing specifically on the
(Zr$_{0.5}$Nd$_{0.5}$)Fe$_{11}$Ti compound. In order to gain a comprehensive
understanding, an investigation of intrinsic and magnetic properties, including
saturation magnetisation ($M_S$), Curie temperature ($T_C$) and magnetic
anisotropy energy (MAE), is carried out on binary to quinary compounds
RFe$_{11-y}$Ti$_{y}$ (R: Nd, Zr and Zr$_{0.5}$Nd$_{0.5}$, y: $0 \leq y \leq 1$)
and (Zr$_{0.5}$Nd$_{0.5}$)Fe$_{10}$CoTi. The substitution of Ti at different
concentrations for thermodynamic stabilisation is studied in ternary and
quaternary compounds RFe$_{12-y}$Ti$_y$ ($0 \leq y \leq 1$). In addition, the
influence of Co on phase stability and intrinsic magnetic properties is studied
in the quinary compound (Zr$_{0.5}$Nd$_{0.5}$)Fe$_{10}$CoTi. Special attention
is given to the treatment of the 4$f$-electrons of Nd and their interaction
with the 3$d$-electrons. Theoretical results are compared with available
experimental data, although the limited availability of data, especially for
Zr-containing compounds, limits the scope of such comparisons. Based on the
literature and the calculations of binary and ternary compounds, the
calculations of quaternary and quinary compounds are encouraged. Promising
magnetic properties of an Nd-lean quaternary compound suitable for engineering
applications have been identified.",2312.14951v1
2024-01-22,The polarization of the solar Ba II D1 line with partial frequency redistribution and its magnetic sensitivity,"We investigate the main physical mechanisms that shape the intensity and
polarization of the Ba II D1 line at 4934 angstroms via radiative transfer
numerical experiments. We focus especially on the scattering linear
polarization arising from the spectral structure of the anisotropic radiation
in the wavelength interval spanned by the line's hyperfine structure (HFS)
components in the odd isotopes of barium. After verifying that the presence of
the low-energy metastable levels only impacts the amplitude, but not the shape,
of the D1 linear polarization, we relied on a two-term atomic model that
neglects such metastable levels but includes HFS. The D1 fractional linear
polarization shows a very small variation with the choice of atmospheric model,
enhancing its suitability for solar magnetic field diagnostics. Tangled
magnetic fields with strengths of tens of gauss reduce the linear polarization
and saturation is reached at roughly 300 G. Deterministic inclined magnetic
fields produce a U/I profile and, if they have a significant longitudinal
component, a V/I profile, whose modeling requires accounting for HFS and the
Paschen-Back effect. Because of the overlap between HFS components, the
magnetograph formula cannot be applied to infer the longitudinal magnetic
field. Accurately modeling the D1 intensity and polarization requires an atomic
system that includes the metastable levels and the HFS, the detailed spectral
structure of the radiation field, the incomplete Paschen-Back regime for
magnetic fields, and an accurate treatment of collisions.",2401.12303v1
2009-10-12,Frustrated square lattice with spatial anisotropy: crystal structure and magnetic properties of PbZnVO(PO4)2,"Crystal structure and magnetic properties of the layered vanadium phosphate
PbZnVO(PO4)2 are studied using x-ray powder diffraction, magnetization and
specific heat measurements, as well as band structure calculations. The
compound resembles AA'VO(PO4)2 vanadium phosphates and fits to the extended
frustrated square lattice model with the couplings J(1), J(1)' between
nearest-neighbors and J(2), J(2)' between next-nearest-neighbors. The
temperature dependence of the magnetization yields estimates of averaged
nearest-neighbor and next-nearest-neighbor couplings, J(1) ~ -5.2 K and J(2) ~
10.0 K, respectively. The effective frustration ratio alpha=J(2)/J(1) amounts
to -1.9 and suggests columnar antiferromagnetic ordering in PbZnVO(PO4)2.
Specific heat data support the estimates of J(1) and J(2) and indicate a likely
magnetic ordering transition at 3.9 K. However, the averaged couplings
underestimate the saturation field, thus pointing to the spatial anisotropy of
the nearest-neighbor interactions. Band structure calculations confirm the
identification of ferromagnetic J(1), J(1)' and antiferromagnetic J(2), J(2)'
in PbZnVO(PO4)2 and yield J(1)'-J(1) ~ 1.1 K in excellent agreement with the
experimental value of 1.1 K, deduced from the difference between the expected
and experimentally measured saturation fields. Based on the comparison of
layered vanadium phosphates with different metal cations, we show that a
moderate spatial anisotropy of the frustrated square lattice has minor
influence on the thermodynamic properties of the model. We discuss relevant
geometrical parameters, controlling the exchange interactions in these
compounds, and propose a new route towards strongly frustrated square lattice
materials.",0910.2258v1
2013-05-09,A study of large scale dynamo growth rates from numerical simulations and implications for mean field theories,"Understanding large scale magnetic field growth in turbulent plasmas in the
magnetohydrodynamic limit is a goal of magnetic dynamo theory. In particular,
assessing how well large scale helical field growth and saturation in
simulations matches that predicted by existing theories is important for
progress. Using numerical simulations of isotropically forced turbulence
without large scale shear with the implications, we focus on several aspects of
this comparison that have not been previously tested: (1) Leading mean field
dynamo theories which break the field into large and small scales predict that
large scale helical field growth rates are determined by the difference between
kinetic helicity and current helicity with no dependence on the non-helical
energy in small scale magnetic fields. Our simulations show that the growth
rate of the large scale field from fully helical forcing is indeed unaffected
by the presence or absence of small scale magnetic fields amplified in a
precursor non-helical dynamo. However, because the precursor non helical dynamo
in our simulations produced fields that were strongly sub-equipartition with
respect to the kinetic energy, we cannot yet rule out the potential influence
of stronger non- helical small scale fields. (2) We have identified two
features in our simulations which cannot be explained by the most minimalist
versions of two-scale mean field theory: (i) fully helical small scale forcing
produces significant non-helical large scale magnetic energy and (ii) the
saturation of the large scale field growth is time-delayed with respect to what
minimalist theory predicts. We comment on desirable generalizations to the
theory in this context and future desired work.",1305.2080v2
2015-10-30,"Vertical Equilibrium, Energetics, and Star Formation Rates in Magnetized Galactic Disks Regulated by Momentum Feedback from Supernovae","Recent hydrodynamic (HD) simulations have shown that galactic disks evolve to
reach well-defined statistical equilibrium states. The star formation rate
(SFR) self-regulates until energy injection by star formation feedback balances
dissipation and cooling in the interstellar medium (ISM), and provides vertical
pressure support to balance gravity. In this paper, we extend our previous
models to allow for a range of initial magnetic field strengths and
configurations, utilizing three-dimensional, magnetohydrodynamic (MHD)
simulations. We show that a quasi-steady equilibrium state is established as
rapidly for MHD as for HD models unless the initial magnetic field is very
strong or very weak, which requires more time to reach saturation. Remarkably,
models with initial magnetic energy varying by two orders of magnitude approach
the same asymptotic state. In the fully saturated state of the fiducial model,
the integrated energy proportions E_kin:E_th:E_mag,t:E_mag,o are
0.35:0.39:0.15:0.11, while the proportions of midplane support
P_turb:P_th:\Pi_mag,t:\Pi_mag,o are 0.49:0.18:0.18:0.15. Vertical profiles of
total effective pressure satisfy vertical dynamical equilibrium with the total
gas weight at all heights. We measure the ""feedback yields""
\eta_c=P_c/\Sigma_SFR (in suitable units) for each pressure component, finding
that \eta_turb~4 and \eta_th~1 are the same for MHD as in previous HD
simulations, and \eta_mag,t~1. These yields can be used to predict the
equilibrium SFR for a local region in a galaxy based on its observed gas and
stellar surface densities and velocity dispersions. As the ISM weight (or
dynamical equilibrium pressure) is fixed, an increase in $\eta$ from turbulent
magnetic fields reduces the predicted \Sigma_SFR by ~25% relative to the HD
case.",1511.00010v1
2016-08-05,Domain Wall Spin Structures in Mesoscopic Fe Rings probed by High Resolution SEMPA,"We present a combined theoretical and experimental study of the energetic
stability and accessibility of different domain wall spin configurations in
mesoscopic magnetic iron rings. The evolution is investigated as a function of
the width and thickness in a regime of relevance to devices, while Fe is chosen
as a material due to its simple growth in combination with attractive magnetic
properties including high saturation magnetization and low intrinsic
anisotropy. Micromagnetic simulations are performed to predict the lowest
energy states of the domain walls, which can be either the transverse or vortex
wall spin structure, in good agreement with analytical models, with simulations
revealing the expected low temperature configurations observable on relaxation
of the magnetic structure from saturation in an external field. In the latter
case, following the domain wall nucleation process, transverse domain walls are
found at larger widths and thicknesses than would be expected by comparing the
competing energy terms demonstrating the importance of metastability of the
states. The simulations are compared to high resolution experimental images of
the magnetization using scanning electron microscopy with polarization analysis
to provide a phase diagram of the various spin configurations. In addition to
the vortex and simple symmetric transverse domain wall, a significant range of
geometries are found to exhibit highly asymmetric transverse domain walls with
properties distinct from the symmetric transverse wall. Simulations of the
asymmetric walls reveal an evolution of the domain wall tilting angle with ring
thickness. Analysis of all the data reveals that in addition to the geometry,
the influence of materials properties, defects and thermal activation all need
to be taken into account in order to understand and reliably control the
experimentally accessible states, as needed for devices.",1608.01981v1
2017-08-21,Quasi-two-dimensional nonlinear evolution of helical magnetorotational instability in a magnetized Taylor-Couette flow,"Magnetorotational instability (MRI) is one of the fundamental processes in
astrophysics, driving angular momentum transport and mass accretion in a wide
variety of cosmic objects. Despite much theoretical/numerical and experimental
efforts over the last decades, its saturation mechanism and amplitude, which
sets the angular momentum transport rate, remains not well understood,
especially in the limit of high resistivity, or small magnetic Prandtl numbers
typical to interiors (dead zones) of protoplanetary disks, liquid cores of
planets and liquid metals in laboratory. Using direct numerical simulations, in
this paper we investigate the nonlinear development and saturation properties
of the helical magnetorotational instability (HMRI) -- a relative of the
standard MRI -- in a magnetized Taylor-Couette flow at very low magnetic
Prandtl number (correspondingly at low magnetic Reynolds number) relevant to
liquid metals. For simplicity, the ratio of azimuthal field to axial field is
kept fixed. From the linear theory of HMRI, it is known that the Elsasser
number, or interaction parameter determines its growth rate and plays a special
role in the dynamics. We show that this parameter is also important in the
nonlinear problem. By increasing its value, a sudden transition from weakly
nonlinear, where the system is slightly above the linear stability threshold,
to strongly nonlinear, or turbulent regime occurs. We calculate the azimuthal
and axial energy spectra corresponding to these two regimes and show that they
differ qualitatively. Remarkably, the nonlinear state remains in all cases
nearly axisymmetric suggesting that HMRI turbulence is quasi two-dimensional in
nature. Although the contribution of non-axisymmetric modes increases
moderately with the Elsasser number, their total energy remains much smaller
than that of the axisymmetric ones.",1708.06148v2
2021-12-20,One-dimensional magnetism in a facile spin 1/2 Heisenberg antiferromagnet with a low saturation field,"This work reports the synthesis, structure and magnetic properties of the
single crystal of a facile spin 1/2 one dimensional Heisenberg antiferromagnet
bis(4-aminopyridinium) bis(oxalato)cuprate(II) dihydrate, (C 5 H 7 N 2 ) 2
[Cu(C 2 O 4 ) 2 ].2H 2 O. Single crystals of large sizes of the title compound
were obtained using the technique of liquid-liquid diffusion or layer diffusion
with 100 % yield. Single crystal X-ray diffraction measurements revealed a very
good quality of the grown single crystals with small value of goodness of fit R
obtained at 1.058. The structure comprises corner-sharing CuO 6 octahedra
resulting in Cu-Cu chains in the a-direction that are very well isolated in the
b and c directions. Density functional theory (DFT) with three different basis
sets (B3LYP/6-311++G(d,p); B3LYP/LanL2DZ and B3LYP/6-311++G(d,p),
B3LYP/LanL2DZ) generated the optimized geometry of a monomeric unit as well as
its vibrational spectra. The vibrational frequency corresponding to the CuO 6
octahedron was found in the experimentally obtained IR spectrum that matched
very well with the theoretically obtained IR spectra incorporating the mixed
basis. Temperature dependent dc magnetic susceptibility revealed a low
temperature peak suggesting the presence of low dimensional magnetism in the
system. Bonner-Fisher fit confirmed the one dimensional nature of the magnetic
interaction with an exchange coupling constant of 1.23 K. Magnetisation
measurements along with Quantum Monte Carlo simulations confirm this
metal-organic crystal to be a very good spin-1/2 Heisenberg antiferromagnet
with a low saturation field H s of 1.75 T.",2112.10639v2
2022-08-05,Near-cancellation of up- and down-gradient momentum transport in forced magnetized shear-flow turbulence,"Visco-resistive magnetohydrodynamic turbulence, driven by a two-dimensional
unstable shear layer that is maintained by an imposed body force, is examined
by decomposing it into dissipationless linear eigenmodes of the initial
profiles. The down-gradient momentum flux, as expected, originates from the
large-scale instability. However, continual up-gradient momentum transport by
large-scale linearly stable but nonlinearly excited eigenmodes is identified,
and found to nearly cancel the down-gradient transport by unstable modes. The
stable modes effectuate this by depleting the large-scale turbulent
fluctuations via energy transfer to the mean flow. This establishes a physical
mechanism underlying the long-known observation that coherent vortices formed
from nonlinear saturation of the instability reduce turbulent transport and
fluctuations, as such vortices are composed of both the stable and unstable
modes, which are nearly equal in their amplitudes. The impact of magnetic
fields on the nonlinearly excited stable modes is then quantified. Even when
imposing a strong magnetic field that almost completely suppresses the
instability, the up-gradient transport by the stable modes is at least
two-thirds of the down-gradient transport by the unstable modes, whereas for
weaker fields, this fraction reaches up to $98\%$. These effects are persistent
with variations in magnetic Prandtl number and forcing strength. Finally,
continuum modes are shown to be energetically less important, but essential for
capturing the magnetic fluctuations and Maxwell stress. A simple analytical
scaling law is derived for their saturated turbulent amplitudes. It predicts
the fall-off rate as the inverse of the Fourier wavenumber, a property which is
confirmed in numerical simulations.",2208.03342v1
2022-10-10,Magnetic fields do not suppress global star formation in low metallicity dwarf galaxies,"Many studies concluded that magnetic fields suppress star formation in
molecular clouds and Milky Way like galaxies. However, most of these studies
are based on fully developed fields that have reached the saturation level,
with little work on investigating how an initial weak primordial field affects
star formation in low metallicity environments. In this paper, we investigate
the impact of a weak initial field on low metallicity dwarf galaxies. We
perform high-resolution AREPO simulations of five isolated dwarf galaxies. Two
models are hydrodynamical, two start with a primordial magnetic field of
10$^{-6} \mu$G and different sub-solar metallicities, and one starts with a
saturated field of 10$^{-2} \mu$G. All models include a non-equilibrium,
time-dependent chemical network that includes the effects of gas shielding from
the ambient ultraviolet field. Sink particles form directly from the
gravitational collapse of gas and are treated as star-forming clumps that can
accrete gas. We vary the ambient uniform far ultraviolet field, and cosmic ray
ionization rate between 1\% and 10\% of solar values. We find that the magnetic
field has little impact on the global star formation rate, which is in tension
with some previously published results. We further find that the initial field
strength has little impact on the global star formation rate. We show that an
increase in the mass fractions of both molecular hydrogen and cold gas, along
with changes in the perpendicular gas velocity dispersion and the magnetic
field acting in the weak-field model, overcome the expected suppression in star
formation.",2210.04922v2
2005-05-23,Strong mean field dynamos require supercritical helicity fluxes,"Several one and two dimensional mean field models are analyzed where the
effects of current helicity fluxes and boundaries are included within the
framework of the dynamical quenching model. In contrast to the case with
periodic boundary conditions, the final saturation energy of the mean field
decreases inversely proportional to the magnetic Reynolds number. If a
nondimensional scaling factor in the current helicity flux exceeds a certain
critical value, the dynamo can operate even without kinetic helicity, i.e. it
is based only on shear and current helicity fluxes, as first suggested by
Vishniac & Cho (2001, ApJ 550, 752). Only above this threshold is the current
helicity flux also able to alleviate catastrophic quenching. The fact that
certain turbulence simulations have now shown apparently non-resistively
limited mean field saturation amplitudes may be suggestive of the current
helicity flux having exceeded this critical value. Even below this critical
value the field still reaches appreciable strength at the end of the kinematic
phase, which is in qualitative agreement with dynamos in periodic domains.
However, for large magnetic Reynolds numbers the field undergoes subsequent
variations on a resistive time scale when, for long periods, the field can be
extremely weak.",0505457v2
2005-07-08,Nonlinear Evolution of the Magnetothermal Instability in Two Dimensions,"In weakly magnetized, dilute plasmas in which thermal conduction along
magnetic field lines is important, the usual convective stability criterion is
modified. Instead of depending on entropy gradients, instability occurs for
small wavenumbers when (dP/dz)(dln T/dz) > 0, which we refer to as the Balbus
criterion. We refer to the convective instability that results in this regime
as the magnetothermal instability (MTI). We use numerical MHD simulations which
include anisotropic electron heat conduction to follow the growth and
saturation of the MTI in two-dimensional, plane parallel atmospheres that are
unstable according to the Balbus criterion. The linear growth rates measured in
the simulations agree with the weak field dispersion relation. We investigate
the effect of strong fields and isotropic conduction on the linear properties
and nonlinear regime of the MTI. In the nonlinear regime, the instability
saturates and convection decays away, when the atmosphere becomes isothermal.
Sustained convective turbulence can be driven if there is a fixed temperature
difference between the top and bottom edges of the simulation domain, and if
isotropic conduction is used to create convectively stable layers that prevent
the formation of unresolved, thermal boundary layers. The largest component of
the time-averaged heat flux is due to advective motions. These results have
implications for a variety of astrophysical systems, such as the temperature
profile of hot gas in galaxy clusters, and the structure of radiatively
inefficient accretion flows.",0507212v2
2005-10-04,Large-scale alpha^2-dynamo in low-mass stars and brown dwarfs,"We develop a model based on 3D mean-field MHD for the generation of large
scale magnetic fields in fully convective objects like low-mass stars, brown
dwarfs and possibly gaseous planets. The dynamo process is of alpha^2 type and
thus differs from the shell-dynamo at work in more massive stars.The alpha^2
dynamo becomes supercritical for Rossby numbers Ro\la 10. It generates a
large-scale, non-axisymmetric, steady field that is symmetric with respect to
the equatorial plane. Saturation of the alpha^2-generated field at the
equipartition yields strengths of several kGauss, in agreement with
observations of active M dwarfs, and provides a qualitative explanation for the
observed activity saturation in late M stars. For brown dwarfs with a
conductive core, as occurs at the center of the most massive and oldest of
these objects, we have also studied an alpha^2-Omega dynamo, i.e. the effect of
differential rotation. In this case the field is predominantly toroidal,
axisymmetric and oscillatory, like the solar field. The topology of the field
in the fully convective objects exhibits a high order multipole character that
differs from the aligned dipole field generated by the alpha-Omega dynamo. The
strong reduction of the dipolar component due to the field non-axisymmetry
should considerably reduce the Alfven radius and thus the efficiency of
magnetic braking, providing an appealing explanation for the decreasing angular
momentum loss rate observed in low-mass stars and brown dwarfs. This may have
also implications for cataclysmic variables below the period gap. In spite of
this large-scale field, the decreasing conductivity in the dominantly neutral
atmosphere of these objects prevents the current generation necessary to
support a chromosphere and thus activity. (Abridged)",0510075v1
2000-08-01,SDW and FISDW transition of (TMTSF)$_2$ClO$_4$ at high magnetic fields,"The magnetic field dependence of the SDW transition in (TMTSF)$_2$ClO$_4$ for
various anion cooling rates has been measured, with the field up to 27T
parallel to the lowest conductivity direction $c^{\ast}$. For quenched
(TMTSF)$_2$ClO$_4$, the SDW transition temperature $T_{\rm {SDW}}$ increases
from 4.5K in zero field up to 8.4K at 27T. A quadratic behavior is observed
below 18T, followed by a saturation behavior. These results are consistent with
the prediction of the mean-field theory. From these behaviors, $T_{\rm {SDW}}$
is estimated as $T_{\rm {SDW_0}}$=13.5K for the perfect nesting case. This
indicates that the SDW phase in quenched (TMTSF)$_2$ClO$_4$, where $T_{\rm
{SDW}}$ is less than 6K, is strongly suppressed by the two-dimensionality of
the system. In the intermediate cooled state in which the SDW phase does not
appear in zero field, the transition temperature for the field-induced SDW
shows a quadratic behavior above 12T and there is no saturation behavior even
at 27T, in contrast to the FISDW phase in the relaxed state. This behavior can
probably be attributed to the difference of the dimerized gap due to anion
ordering.",0008011v1
2004-11-20,Studies of DC biasing of internal ring on plasma rotation and transport in a toroidal geometry,"We report results from experiments performed to study how a DC bias with
respect to the plasma potential is affecting the plasma states in the toroidal
geometry of the Blaamann device in Tromso. In the experiments discussed here, a
ring with smaller diameter than the limiter was centered inside the bulk of the
plasma and its bias varied with respect to the plasma potential. In the
electron saturation current regime of the ring, a significant reduction of the
fluctuation levels was observed, and a shear in the poloidal velocity occurred
at the low-field side of the ring. This shear was positioned at the same radial
position as the maximum of the radial transport when the ring was left floating
or biased in the ion saturation current regime. For the latter ring biases, the
poloidal velocities had no shear on the low-field side of the ring. Without the
velocity shear, the radial transport was similar to previous experiments
without ring. With the velocity shear, the radial transport was destroyed. This
plasma state, with very low radial transport and fluctuation levels as well as
plasma densities around 1017 m-3, is believed to provide a suitable plasma for
wave propagation studies in a magnetized plasma with curved magnetic field
lines without end effects.",0411193v1
2011-07-01,Faraday Rotation Measure due to the Intergalactic Magnetic Field II: the Cosmological Contribution,"We investigate the Faraday rotation measure (RM) due to the intergalactic
magnetic field (IGMF) through the cosmic web up to cosmological distances,
using a model IGMF based on turbulence dynamo in the large-scale structure of
the universe. By stacking the IGMF and gas density data up to redshift $z=5$
and taking account of the redshift distribution of polarized background radio
sources against which the RM is measured, we simulate the sky map of the RM.
The contribution from galaxy clusters is subtracted from the map, based on
several different criteria of X-ray brightness and temperature. Our findings
are as follows. The distribution of RM for radio sources of different redshifts
shows that the root-mean-square (rms) value increases with redshift and
saturates for $z \ga 1$. The saturated value is RM$_{\rm rms} \approx$ several
${\rm rad m^{-2}}$. The probability distribution function of $|{\rm RM}|$
follows the lognormal distribution. The power spectrum has a broad plateau over
the angular scale of $\sim 1 - 0.1^\circ$ with a peak around $\sim 0.15^\circ$.
The second-order structure function has a flat profile in the angular
separation of $\ga 0.2^\circ$. Our results could provide useful insights for
surveys to explore the IGMF with the Square Kilometer Array (SKA) and upcoming
SKA pathfinders.",1107.0142v1
2012-05-16,Constraining the Bulk Lorentz Factor of GRB Outflow in the Magnetic-dominated Jet Model,"Recent observations by the Fermi-LAT showed that there are delayed arrivals
of GeV photons relative to the onset of MeV photons in some GRBs. In order to
avoid a large optical depth, the minimal value of the Lorentz factor has been
estimated to be higher than 1000 in some brightest bursts. In this paper, we
present a detailed calculation of the time delay between the MeV and GeV
photons in the framework of the magnetic-dominated jet model. We find that the
time delay strongly depends on the saturated bulk Lorentz factor of the jet.
Inspired by this fact, we use this model to calculate the Lorentz factors of
the four brightest Fermi bursts. The results indicate that the Lorentz factors
are much smaller than that obtained from the ""single-zone"" scenario. The short
GRB 090510 has a minimal Lorentz factor 385, while the three long bursts GRB
080916c, GRB090902b and GRB 090926 have almost the same Lorentz factors, with
an average value near 260. Another interesting result is that, for long bursts,
GeV photons are emitted after the bulk Lorentz factor saturates. For the short
GRB, however, MeV and GeV photons are emitted at the same phase, i.e., either
at the expansion phase or at the coast phase.",1205.3572v3
2013-02-05,Implications of mass and energy loss due to coronal mass ejections on magnetically-active stars,"Analysis of a database of solar coronal mass ejections (CMEs) and associated
flares over the period 1996-2007 finds well-behaved power law relationships
between the 1-8 AA flare X-ray fluence and CME mass and kinetic energy. We
extrapolate these relationships to lower and higher flare energies to estimate
the mass and energy loss due to CMEs from stellar coronae, assuming that the
observed X-ray emission of the latter is dominated by flares with a frequency
as a function of energy dn/dE=kE^-alpha. For solar-like stars at saturated
levels of X-ray activity, the implied losses depend fairly weakly on the
assumed value of alpha and are very large: M_dot ~ 5x10^-10 M_sun/yr and E_dot
~ 0.1L_sun. In order to avoid such large energy requirements, either the
relationships between CME mass and speed and flare energy must flatten for
X-ray fluence >~ 10^31 erg, or the flare-CME association must drop
significantly below 1 for more energetic events. If active coronae are
dominated by flares, then the total coronal energy budget is likely to be up to
an order of magnitude larger than the canonical 10^-3 L_bol X-ray saturation
threshold. This raises the question of what is the maximum energy a magnetic
dynamo can extract from a star? For an energy budget of 1% of L_bol, the CME
mass loss rate is about 5x10^-11 M_sun/yr.",1302.1136v1
2014-02-25,Analysis of a drift-diffusion model with velocity saturation for spin-polarized transport in semiconductors,"A system of drift-diffusion equations with electric field under Dirichlet
boundary conditions is analyzed. The system of strongly coupled parabolic
equations for particle density and spin density vector describes the
spin-polarized semi-classical electron transport in ferromagnetic
semiconductors. The presence of a nonconstant and nonsmooth magnetization
vector, solution of the Landau-Lifshitz equation, causes the diffusion matrix
to be dependent from space and time and to have in general poor regularity
properties, thus making the analysis challenging. To partially overcome the
analytical difficulties the velocity saturation hypothesis is made, which
results in a bounded drift velocity. The global-in-time existence and
uniqueness of weak solutions is shown by means of a semi-discretization in
time, which yields an elliptic semilinear problem, and a quadratic entropy
inequality, which allow for the limit of vanishing time step size. The
convergence of the weak solutions to the steady state, under some restrictions
on the parameters and data, is shown. Finally the higher regularity of
solutions for a smooth magnetization in two space dimensions is shown through a
diagonalization argument, which allows to get rid of the cross diffusion terms
in the fluid equations, and the iterative application of Gagliardo-Nirenberg
inequalities and a generalized version of Aubin lemma.",1402.6230v1
2015-04-09,Impurity coupled to an artificial magnetic field in a Fermi gas in a ring trap,"The dynamics of a single impurity interacting with a many particle background
is one of the central problems of condensed matter physics. Recent progress in
ultracold atom experiments makes it possible to control this dynamics by
coupling an artificial gauge field specifically to the impurity. In this paper,
we consider a narrow toroidal trap in which a Fermi gas is interacting with a
single atom. We show that an external magnetic field coupled to the impurity is
a versatile tool to probe the impurity dynamics. Using Bethe Ansatz (BA) we
calculate the eigenstates and corresponding energies exactly as a function of
the flux through the trap. Adiabatic change of flux connects the ground state
to excited states due to flux quantization. For repulsive interactions, the
impurity disturbs the Fermi sea by dragging the fermions whose momentum matches
the flux. This drag transfers momentum from the impurity to the background and
increases the effective mass. The effective mass saturates to the total mass of
the system for infinitely repulsive interactions. For attractive interactions,
the drag again increases the effective mass which quickly saturates to twice
the mass of a single particle as a polaron of the impurity and one fermion is
formed. For excited states with momentum comparable to number of particles,
effective mass shows a resonant behavior. We argue that standard tools in cold
atom experiments can be used to test these predictions.",1504.02210v2
2015-06-10,Nonlinear Galactic Dynamos and the Magnetic Pitch Angle,"Pitch angles $p$ of the large-scale magnetic fields $\overline{\bf{\it{B}}}$
of spiral galaxies have previously been inferred from observations to be
systematically larger in magnitude than predicted by standard mean-field dynamo
theory. This discrepancy is more pronounced if dynamo growth has saturated,
which is reasonable to assume given that such fields are generally inferred to
be close to energy equipartition with the interstellar turbulence. This 'pitch
angle problem' is explored using local numerical mean-field dynamo solutions as
well as asymptotic analytical solutions. It is first shown that solutions in
the saturated or kinematic regimes depend on only five dynamo parameters, two
of which are tightly constrained by observations of galaxy rotation curves. The
remaining 3-dimensional (dimensionless) parameter space can be constrained to
some extent using theoretical arguments. Predicted values of $|p|$ can be as
large as $\sim40^\circ$, which is similar to the largest values inferred from
observations, but only for a small and non-standard region of parameter space.
We argue, based on independent evidence, that such non-standard parameter
values are plausible. However, these values are located toward the boundary of
the allowed parameter space, suggesting that additional physical effects may
need to be incorporated. We therefore suggest possible directions for extending
the basic model considered.",1506.03245v2
2015-09-21,Magnetization of underdoped YBa$_2$Cu$_3$O$_{y}$ above the irreversibility field,"Torque magnetization measurements on YBa$_2$Cu$_3$O$_{y}$ (YBCO) at doping
$y=6.67$($p=0.12$), in DC fields ($B$) up to 33 T and temperatures down to 4.5
K, show that weak diamagnetism persists above the extrapolated irreversibility
field $H_{\rm irr} (T=0) \approx 24$ T. The differential susceptibility
$dM/dB$, however, is more rapidly suppressed for $B\gtrsim 16$ T than expected
from the properties of the low field superconducting state, and saturates at a
low value for fields $B \gtrsim 24$ T. In addition, torque measurements on a
$p=0.11$ YBCO crystal in pulsed field up to 65 T and temperatures down to 8 K
show similar behaviour, with no additional features at higher fields. We
discuss several candidate scenarios to explain these observations: (a)
superconductivity survives but is heavily suppressed at high field by
competition with CDW order; (b) static superconductivity disappears near 24 T
and is followed by a region of fluctuating superconductivity, which causes
$dM/dB$ to saturate at high field; (c) the stronger 3D ordered CDW that sets in
above 15 T may suppress the normal state spin susceptibility sufficiently to
give an apparent diamagnetism of the magnitude observed.",1509.06206v1
2016-04-14,Magnetotransport of single crystalline YSb,"We report magnetic field dependent transport measurements on a single crystal
of cubic YSb together with first principles calculations of its electronic
structure. The transverse magnetoresistance does not saturate up to 9 T and
attains a value of 75,000 % at 1.8 K. The Hall coefficient is electron-like at
high temperature, changes sign to hole-like between 110 and 50 K, and again
becomes electron-like below 50 K. First principles calculations show that YSb
is a compensated semimetal with a qualitatively similar electronic structure to
that of isostructural LaSb and LaBi, but with larger Fermi surface volume. The
measured electron carrier density and Hall mobility calculated at 1.8 K, based
on a single band approximation, are 6.5$\times10^{20}/$cm$^{3}$ and
6.2$\times10^{4}$cm$^{2}$/Vs, respectively. These values are comparable with
those reported for LaBi and LaSb. Like LaBi and LaSb, YSb undergoes a magnetic
field-induced metal-insulator-like transition below a characteristic
temperature T$_{m}$, with resistivity saturation below 13 K. Thickness
dependent electrical resistance measurements show a deviation of the resistance
behavior from that expected for a normal metal; however, they do not
unambiguously establish surface conduction as the mechanism for the resistivity
plateau.",1604.04232v1
2016-09-02,Influence of Cu deposition potential on the giant magnetoresistance and surface roughness of electrodeposited Ni-Co/Cu multilayers,"It has been shown previously for electrodeposited Co/Cu multilayers that the
single-bath electrodeposition process can be optimized from an electrochemical
point of view in order to avoid unwanted Co dissolution and incorporation of Co
in the non-magnetic layer during the Cu deposition pulse. In the present work,
electrodeposition of Ni-Co/Cu multilayers has been studied to clarify if the
same optimization method is appropriate when two magnetic elements are present
and if this potential results in the largest giant magnetoresistance (GMR) for
the particular alloy system studied. For this purpose, several Ni-Co/Cu
multilayers were prepared by varying the deposition potential of the Cu layer.
The composition analysis of the deposits showed that the Ni:Co ratio exhibits a
minimum as a function of the Cu deposition potential, which can be explained by
considering both the dissolution of Co and the mass transport of the reactants.
Both the saturation GMR value and the intensity of the satellite peaks in the
X-ray diffractograms were highly correlated with the resulting surface
roughness of the deposits which was strongly varying with the Cu deposition
potential. Higher GMR values, lower saturation fields and more perfect
multilayer structure were observed for sufficiently positive Cu deposition
potentials only which enabled a partial Co dissolution resulting in a reduced
surface roughness. The results draw attention to the complexity of the
optimization procedure of the deposition of multilayers with several alloying
components.",1609.00597v1
2017-02-03,The Kinetically Dominated Quasar 3C~418,"The existence of quasars that are kinetically dominated, where the jet
kinetic luminosity, $Q$, is larger than the total (IR to X-ray) thermal
luminosity of the accretion flow, $L_{\rm{bol}}$, provides a strong constraint
on the fundamental physics of relativistic jet formation. Since quasars have
high values of $L_{\rm{bol}}$ by definition, only $\sim 10$ kinetically
dominated quasars (with $\overline{Q}/L_{\rm{bol}}>1$) have been found, where
$\overline{Q}$ is the long term time averaged jet power. We use low frequency
(151 MHz$-$1.66 GHz) observations of the quasar 3C\,418 to determine
$\overline{Q}\approx 5.5 \pm 1.3 \times 10^{46} \rm{ergs~s^{-1}}$. Analysis of
the rest frame ultraviolet spectrum indicates that this equates to $0.57 \pm
0.28$ times the Eddington luminosity of the central supermassive black hole and
$\overline{Q}/L_{\rm{bol}} \approx 4.8 \pm 3.1$, making 3C\,418 one of the most
kinetically dominated quasars found to date. It is shown that this maximal
$\overline{Q}/L_{\rm{bol}}$ is consistent with models of magnetically arrested
accretion of jet production in which the jet production reproduces the observed
trend of a decrement in the extreme ultraviolet continuum as the jet power
increases. This maximal condition corresponds to an almost complete saturation
of the inner accretion flow with vertical large scale magnetic flux (maximum
saturation).",1702.01157v1
2017-09-15,Reentrant Metallic Behavior in the Weyl Semimetal NbP,"We report the occurrence of reentrant metallic behavior in the Weyl semimetal
NbP. When the applied magnetic field $H$ is above a critical value $H_c$, a
reentrance appears as a peak in the temperature dependent resistivity
$\rho_{xx}(T)$ at $T$ = $T_p$, similar to that observed in graphite where it
was attributed to local superconductivity. The $T_p(H)$ relationship follows a
power-law dependence $T_p\sim(H-H_c)^{1/v}$ where $v$ can be derived from the
temperature dependence of the zero-field resistivity $\rho_0(T) \sim T^v$. From
concurrent measurements of the transverse $\rho_{xx}(T)$ and Hall
$\rho_{xy}(T)$ magnetoresistivities, we reveal a clear correlation between the
rapidly increasing $\rho_{xy}(T)$ and the occurrence of a peak in the
$\rho_{xx}(T)$ curve. Quantitative analysis indicates that the reentrant
metallic behavior arises from the competition of the magneto conductivity
$\sigma_{xx}(T)$ with an additional component
$\Delta\sigma_{xx}(T)=\kappa_H\sigma_{xx}(T)$ where
$\kappa_H=[\rho_{xy}(T)/\rho_{xx}(T)]^2$ is the Hall factor. We find that the
Hall factor ($\kappa_H \approx 0.4$) at peak temperature $T_p$ is nearly
field-independent, leading to the observed $T_p(H)$ relationship. Furthermore,
the reentrant metallic behavior in $\rho_{xx}(T)$ also is reflected in the
behavior of $\rho_{xx}(H)$ that ranges from non-saturating at $T>70$ K to
saturation at liquid helium temperatures. The latter can be explained with the
magnetic field dependence of the Hall factor $\kappa_H(H)$. Our studies
demonstrate that a semiclassical theory can account for the 'anomalies' in the
magnetotransport phenomena of NbP without invoking an exotic mechanism.",1709.05041v1
2018-11-13,Probing interacting two-level systems with rare-earth ions,"Two-level systems (TLS) in amorphous materials limit coherence times of a
number of solid-state quantum devices. Interactions between TLS become
prominent below 100 mK, but the coupling mechanism and statistical properties
are still unclear. Here we determine the homogeneous linewidth of ytterbium
ions (Yb$ ^{3+} $) in silica glass at 10-80 mK by using photon echo techniques
as a probe of TLS. First, the homogeneous linewidth can be reduced by applying
a magnetic field of 0.3 T. This effect is due to reduced magnetic interactions
between adjacent Yb$ ^{3+} $. Secondly, we observe saturation of the linewidth
below 50 mK to a level of approximately 30 kHz, which is much larger than the
lifetime-limited value of 0.2 kHz. This saturation behavior is in conflict with
the coupling to independent TLS. We show that this effect can be explained by
coherently coupled TLS.",1811.05248v3
2019-05-06,A van der Waals antiferromagnetic topological insulator with weak interlayer magnetic coupling,"Magnetic topological insulators (TI) provide an important material platform
to explore quantum phenomena such as quantized anomalous Hall (QAH) effect and
Majorana modes, etc. Their successful material realization is thus essential
for our fundamental understanding and potential technical revolutions. By
realizing a bulk van der Waals material MnBi4Te7 with alternating septuple
[MnBi2Te4] and quintuple [Bi2Te3] layers, we show that it is ferromagnetic in
plane but antiferromagnetic along the c axis with an out-of-plane saturation
field of ~ 0.22 T at 2 K. Our angle-resolved photoemission spectroscopy
measurements and first-principles calculations further demonstrate that
MnBi4Te7 is a Z2 antiferromagnetic TI with two types of surface states
associated with the [MnBi2Te4] or [Bi2Te3] termination, respectively.
Additionally, its superlattice nature may make various heterostructures of
[MnBi2Te4] and [Bi2Te3] layers possible by exfoliation. Therefore, the low
saturation field and the superlattice nature of MnBi4Te7 make it an ideal
system to investigate rich emergent phenomena.",1905.02154v2
2020-01-28,Stimulated-emission based model of fast radio bursts,"Fast radio bursts (FRBs) are bright, short-duration radio transients with
very high brightness temperatures implying highly coherent emission. We suggest
that the FRBs are caused by the self-focusing of an electron beam interacting
with an ambient plasma right beyond the light cylinder radius of a neutron
star. The magnetic field at the light cylinder radius is relatively high which
can accommodate both young Crab-like systems and old millisecond pulsars
addressing the diverse environments of FRBs. At the first stage, the intense
pulsed-beam passing through the background plasma causes instabilities such
that the trapped particles in local Buneman-type cavitons saturate the local
field. The beam is then radially self-focused due to the circular electric
field developed by the two-stream instability which leads to Weibel instability
in the transverse direction. Finally, the non-linear saturation of the Weibel
instability results in the self-modulational formation of solitons due to
plasmoid instability. The resonant solitary waves are the breather-type
solitons hosting relativistic particles with self-excited oscillations. The
analytical solutions obtained for non-linear dispersion and solitons suggest
that, near the current sheets, the relativistic bunches are
accelerated/amplified by klystron-like structures due to self-excited
oscillations by the induced local electric field. Boosted coherent radio
emission propagates through a narrow cone with strong focusing due to radial
electric field and magnetic pinching. The non-linear evolution of solitons and
the stimulated emission are associated with the Buneman instability and the
possibility of the presence of nanosecond shots in FRBs are investigated.",2001.10454v2
2020-06-30,Suppressed heat conductivity in the intracluster medium: implications for the magneto-thermal instability,"In the outskirts of the intracluster medium (ICM) in galaxy clusters, the
temperature decreases with radius. Due to the weakly collisional nature of the
plasma, these regions are susceptible to the magneto-thermal instability (MTI),
which can sustain turbulence and provide turbulent pressure support in the ICM.
This instability arises due to heat conduction directed along the magnetic
field, with a heat conductivity which is normally assumed to be given by the
Spitzer value. Recent numerical studies of the ion mirror and the electron
whistler instability using particle-in-cell codes have shown that microscale
instabilities can lead to a reduced value for the heat conductivity in the ICM.
This could in turn influence the efficiency with which the MTI drives
turbulence. In this paper we investigate the influence of reduced heat
transport on the nonlinear evolution of the MTI. We study plane-parallel,
initially static atmospheres and employ a subgrid model that mimics the
influence of the mirror instability on the heat conductivity. We use this
subgrid model to assess the effect of microscales on the large scale dynamics
of the ICM. We find that the nonlinear saturation of the MTI is surprisingly
robust in our simulations. Over a factor of $\sim 10^3$ in the
thermal-to-magnetic pressure ratio and collisionality we find at most modest
changes to the saturation of the MTI with respect to reference simulations
where heat transport is unsuppressed.",2007.00018v2
2020-08-24,Loop-gas description of the localized-magnon states on the kagome lattice with open boundary conditions,"The high-field regime of the spin-s XXZ antiferromagnet on the kagome lattice
gives rise to macroscopically degenerate ground states thanks to a completely
flat lowest single-magnon band. The corresponding excitations can be localized
on loops in real space and have been coined ""localized magnons"". Thus, the
description of the many-body ground states amounts to characterizing the
allowed classical loop configurations and eliminating the quantum mechanical
linear relations between them. Here, we investigate this loop-gas description
on finite kagome lattices with open boundary conditions and compare the results
with exact diagonalization for the spin-1/2 XY model on the same lattice. We
find that the loop gas provides an exact account of the degenerate ground-state
manifold while a hard-hexagon description misses contributions from nested loop
configurations. The densest packing of the loops corresponds to a magnon
crystal that according to the zero-temperature magnetization curve is a stable
ground state of the spin-1/2 XY model in a window of magnetic fields of about
4% of the saturation field just below this saturation field. We also present
numerical results for the specific heat obtained by the related methods of
thermal pure quantum (TPQ) states and the finite-temperature Lanczos method
(FTLM). For a field in the stability range of the magnon crystal, one finds a
low-temperature maximum of the specific heat that corresponds to a
finite-temperature phase transition into the magnon crystal at low
temperatures.",2008.10614v2
2021-03-04,Nodal superconducting gap in LiFeP revealed by NMR: contrast with LiFeAs,"Identifying the uniqueness of FeP-based superconductors may shed new lights
on the mechanism of superconductivity in iron-pnictides. Here, we report
nuclear magnetic resonance(NMR) studies on LiFeP and LiFeAs which have the same
crystal structure but different pnictogen atoms. The NMR spectrum is sensitive
to inhomogeneous magnetic fields in the vortex state and can provide the
information on the superconducting pairing symmetry through the temperature
dependence of London penetration depth $\lambda_L$. We find that $\lambda_L$
saturates below $T \sim 0.2$ $T_c$ in LiFeAs, where $T_c$ is the
superconducting transition temperature, indicating nodeless superconducting
gaps. Furthermore, by using a two-gaps model, we simulate the temperature
dependence of $\lambda_L$ and obtain the superconducting gaps of LiFeAs, as
$\Delta_1 = 1.2$ $k_B T_c$ and $\Delta_2 = 2.8$ $k_B T_c$, in agreement with
previous result from spin-lattice relaxation. For LiFeP, in contrast, the
London penetration depth $\lambda_L$ does not show any saturation down to $T
\sim 0.03 $ $T_c$, indicating nodes in the superconducting energy gap function.
Finally, we demonstrate that the strong spin fluctuations with diffusive
characteristics exist in LiFeP, as in some cuprate high temperature
superconductors.",2103.02991v1
2021-11-27,Antiferromagnetism and large magnetoresistance in GdBi single crystal,"Single crystal of the binary equi-atomic compound GdBi crystallizing in the
rock salt type cubic crystal structure with the space group $Fm\bar{3}m$ has
been grown by flux method. The electrical and magnetic measurements have been
performed on well oriented single crystals. The antiferromagnetic ordering of
the Gd moments is confirmed at $T_{\rm N} = 27.5$~K. The magnetization
measurement performed at $2$~K along the principal crystallographic direction
[100] did not show any metamagnetic transition and no sign of saturation up to
$7$~T. Zero field electrical resistivity reveals a sharp drop at $27.5$~K
suggesting a reduction in the spin disorder scattering due to the
antiferromagnetic alignment of the Gd moments. The residual resistivity at
$2$~K is 390~n$\Omega$cm suggesting a good quality of the grown crystal. The
magneto resistance attains a value of $1.0~\times~10^{4}\%$ with no sign of
saturation, in a field of $14$~T, at $T = 2$~K. Shubnikov de Hass (SdH)
oscillations have been observed in the high field range of the
magnetoresistance with five different frequencies corresponding to the extremal
areas of the Fermi surface. Analysis of the Hall data revealed a near
compensation of the charge carriers accounting for the extremely large
magnetoresistance.",2111.13836v1
2022-02-03,Exceptionally high saturation magnetisation in Eu-doped magnetite stabilised by spin-orbit interaction,"The significance of the spin-orbit interaction is very well known in
compounds containing heavier elements such as the rare-earth Eu ion. Here,
through density functional calculations, we investigated the effect of the
spin-orbit interaction on the magnetic ground state of Eu doped magnetite
($\mathrm{Fe_3O_4:Eu_{Fe}}$). By examining all possible spin alignments between
Eu and magnetite's Fe, we demonstrate that Eu, which is most stable when doped
at the tetrahedral site, adapts a spin almost opposite the substituted Fe.
Consequently, because of smaller spin cancellation between the cations on the
tetrahedral site ($\mathrm{Fe_{Tet}}$ and $\mathrm{Eu_{Tet}}$) and the cations
on the octahedral sites ($\mathrm{Fe_{Oct}}$), $\mathrm{Fe_3O_4:Eu_{Fe}}$
exhibits a maximum saturation magnetisation of 9.451 $\mu_B/$f.u. which is
significantly larger than that of undoped magnetite (calculated to be 3.929
$\mu_B/$f.u.). We further show that this large magnetisation persists through
additional electron doping. However, additional hole doping, which may
unintentionally occur in Fe deficient magnetite, can reduce the magnetisation
to values smaller than that of the undoped magnetite. The results presented
here can aid in designing highly efficient magnetically recoverable catalysts
for which both magnetite and rare earth dopants are common materials.",2202.01453v1
2022-03-13,The distribution of B-site in the perovskite for a d5-d3 superexchange system studied with Molecular field theory and Monte Carlo simulation,"The B-site disorder in the d5 - d3 system of perovskites has been analyzed
with molecular field theory and Monte Carlo method. The model is applicable to
RFe1-pCrpO3 at any p value. When the saturation magnetization MS and phase
transition temperature TP are known, a model can be built to calculate the
order or disorder distribution of lattice B-sites. We analyze the case that the
Fe-Cr superexchange is antiferromagnetic and ferromagnetic coupling
respectively. The simulation result shows that the theoretical calculation
formula is suitable for the calculation of different B-site distribution.
Through the simulation, we find that when the x and y are large, the system
will appear obvious long-range order. The DM interaction has a certain
influence on the saturation magnetization. Via calculation, we found that the
distribution states of Fe and Cr do not always conform to the uniform
distribution but rather exhibit an effect that reduces the Fe-Fe clustering.
The establishment of this model offers an explanation for several previously
contentious issues, e.g., what is the phase transition temperature range of
double perovskite, and why the different phase transition temperatures with the
same doping proportion. It provides theoretical guidance for the design of
functional materials with an arbitrary phase transition temperature.",2203.06599v1
2022-10-25,Planar Thermal Hall Effects in Kitaev Spin Liquid Candidate Na2Co2TeO6,"We investigate both the longitudinal thermal conductivity ($\kappa_{xx}$) and
the planar thermal Hall conductivity ($\kappa_{xy}$) in the Kitaev spin liquid
candidate of Co-based honeycomb antiferromagnet Na$_2$Co$_2$TeO$_6$ in a
magnetic field ($B$) applied along the $a$ and $a^*$ axes. A finite
$\kappa_{xy}$ is resolved for both field directions in the antiferromagnetic
(AFM) phase below the N\'eel temperature of 27 K. The temperature dependence of
$\kappa_{xy}/T$ shows the emergence of topological bosonic excitations. In
addition, the field dependence of $\kappa_{xy}$ shows sign reversals at the
critical fields in the AFM phase, suggesting the changes in the Chern number
distribution of the topological magnons. Remarkably, a finite $\kappa_{xy}$ is
observed in $B \parallel a^*$ between the first-order transition field in the
AFM phase and the saturation field, which is prohibited in a disordered state
by the two-fold rotation symmetry around the $a^*$ axis of the honeycomb
lattice, showing the presence of a magnetically ordered state that breaks the
two-fold rotation symmetry. Our results demonstrate the presence of topological
magnons in this compound in the whole field range below the saturation field.",2210.13798v1
2023-07-05,Available energy of trapped electrons in Miller tokamak equilibria,"Available energy (\AE{}), which quantifies the maximum amount of thermal
energy that may be liberated and converted into instabilities and turbulence,
has shown to be a useful metric for predicting saturated energy fluxes in
trapped-electron-mode-driven turbulence. Here, we calculate and investigate the
\AE{} in the analytical tokamak equilibria introduced by
\citet{Miller1998NoncircularModel}. The \AE{} of trapped electrons reproduces
various trends also observed in experiments; negative shear, increasing
Shafranov shift, vertical elongation, and negative triangularity can all be
stabilising, as indicated by a reduction in \AE{}, although it is strongly
dependent on the chosen equilibrium. Comparing \AE{} with saturated energy flux
estimates from the \textsc{tglf} model, we find fairly good correspondence,
showcasing that \AE{} can be useful to predict trends. We go on to investigate
\AE{} and find that negative triangularity is especially beneficial in
vertically elongated configurations with positive shear or low gradients. We
furthermore extract a gradient threshold-like quantity from \AE{} and find that
it behaves similarly to gyrokinetic gradient thresholds: it tends to increase
linearly with magnetic shear, and negative triangularity leads to an especially
high threshold. We next optimise the device geometry for minimal \AE{} and find
that the optimum is strongly dependent on equilibrium parameters, e.g. magnetic
shear or pressure gradient. Investigating the competing effects of increasing
the density gradient, the pressure gradient, and decreasing the shear, we find
regimes that have steep gradients yet low \AE{}, and that such a regime is
inaccessible in negative-triangularity tokamaks.",2307.02304v2
2023-10-13,Correcting for T1 bias in Magnetization Transfer Saturation (MTsat) Maps Using Sparse-MP2RAGE,"Purpose: Magnetization transfer saturation (MTsat) mapping is commonly used
to examine the macromolecular content of brain tissue. This study compared
variable flip angle (VFA) T1 mapping against compressed sensing (cs)MP2RAGE T1
mapping for accelerating MTsat imaging. Methods: VFA, MP2RAGE and csMP2RAGE
were compared against inversion recovery (IR) T1 in a phantom at 3 Tesla. The
same 1 mm VFA, MP2RAGE and csMP2RAGE protocols were acquired in four healthy
subjects to compare the resulting T1 and MTsat. Bloch-McConnell simulations
were used to investigate differences between the phantom and in vivo T1
results. Finally, ten healthy controls were imaged twice with the csMP2RAGE
MTsat protocol to quantify repeatability. Results: The MP2RAGE and csMP2RAGE
protocols were 13.7% and 32.4% faster than the VFA protocol, respectively. All
approaches provided accurate T1 values (<5% difference) in the phantom, but the
accuracy of the T1 times was more impacted by differences in T2 for VFA than
for MP2RAGE. In vivo, VFA generated longer T1 times than MP2RAGE and csMP2RAGE.
Simulations suggest that the bias in the T1 values between VFA and IR-based
approaches (MP2RAGE and IR) could be explained by the MT-effects from the
inversion pulse. In the test-retest experiment, we found that the csMP2RAGE has
a minimum detectable change of 3% for T1 mapping and 7.9% for MTsat imaging.
Conclusions: We demonstrated that csMP2RAGE can be used in place of VFA T1
mapping in an MTsat protocol. Furthermore, a shorter scan time and high
repeatability can be achieved using the csMP2RAGE sequence.",2310.09102v1
2022-01-07,The extent of saturation of induced ideals,"We construct a model with a saturated ideal $I$ over
$\mathcal{P}_{\kappa}\lambda$ and study the extent of saturation of $I$.",2201.02364v1
2003-03-20,"Bulk viscosity, r-modes, and the early evolution of neutron stars","We discuss the effect of nonlinear bulk viscosity and the associated
reheating on the evolution of newly born, rapidly rotating neutron stars with
r-modes destabilized through the Chandrasekhar-Friedman-Schutz (CFS) mechanism.
Bulk viscosity in these stars is due to the adjustment of the relative
abundances of different particle species as the density of a fluid element is
perturbed. It becomes nonlinear when the chemical potential difference
$\delta\mu$, measuring the chemical imbalance in the fluid element, becomes
larger than the temperature $T$, which is generally much smaller than the Fermi
energy. From this scale on, the bulk viscosity increases much faster with
$\delta\mu$ than predicted by the usual, linear approximation. This provides a
potential saturation mechanism for stellar oscillation modes at a small to
moderate amplitude. In addition, bulk viscosity dissipates energy, which can
lead to neutrino emission, reheating of the star, or both. This is the first
study to explicitly consider these effects in the evolution of the r-mode
instability. For stars with little or no hyperon bulk viscosity, these effects
are not strong enough to prevent the r-modes from growing to amplitudes
$\alpha\sim 1$ or higher, so other saturation mechanisms will probably set in
earlier. The reheating effect makes spin-down occur at a higher temperature
than would otherwise be the case, in this way possibly avoiding complications
associated with a solid crust or a core superfluid. On the other hand, stars
with a substantial hyperon bulk viscosity and a moderate magnetic field
saturate their mode amplitude at a low value, which makes them gravitational
radiators for hundreds of years, while they lose angular momentum through
gravitational waves and magnetic braking.",0303454v1
2011-12-19,X-ray activity and rotation of the young stars in IC 348,"The physical origin of the strong magnetic activity in T Tauri stars and its
relation to stellar rotation is not yet well understood. We investigate the
relation between the X-ray activity, rotation, and Rossby number for a sample
of 82 young stars in the ~3 Myr old cluster IC 348. We use the data of four
Chandra observations of IC 348 to derive the X-ray luminosities of the young
stars. The young stars in IC 348 show no correlation between X-ray activity and
rotation period. Considering the Rossby numbers, nearly all IC 348 stars are in
the saturated regime of the activity-rotation relation defined by main-sequence
stars. Searching for possible super-saturation effects, we find a marginal (but
statistically in-significant) trend that the stars with the smallest Rossby
numbers show slightly lower X-ray activity levels. We compare the dispersion of
fractional X-ray luminosities of the stars in the saturated rotation regime in
IC 348 to that seen in younger and older stellar populations. The scatter seen
in the ~3 Myr old IC 348 is considerably smaller than for the ~1 Myr old ONC,
but, at the same time, considerably larger than the dispersion seen in the ~30
Myr old cluster NGC 2547 and in main-sequence stars. The results of our X-ray
analysis of IC 348 show that neither the rotation rates nor the
presence/absence of circumstellar disks are of fundamental importance for
determining the level of X-ray activity in TTS. Our results suggest that the
scatter of X-ray activity levels shown by the fast-rotating members of young
clusters decreases with the age of the stellar population. We interpret this as
a signature of the changing interior structure of PMS stars and the consequent
changes in the dynamo mechanisms that are responsible for the magnetic field
generation.",1112.4290v2
2023-02-14,Optimization of acquisition parameters for cortical inhomogeneous magnetization transfer (ihMT) imaging using a rapid gradient echo readout,"Purpose: Imaging biomarkers with increased myelin specificity are needed to
better understand the complex progression of neurological disorders.
Inhomogeneous magnetization transfer (ihMT) imaging is an emergent technique
that has a high degree of specificity for myelin content but suffers from low
signal-to-noise ratio (SNR). This study used simulations to determine optimal
sequence parameters for ihMT imaging for use in high-resolution cortical
mapping. Methods: MT-weighted cortical image intensity and ihMT SNR were
simulated using modified Bloch equations for a range of sequence parameters.
The acquisition time was limited to 4.5 min/volume. A custom MT-weighted RAGE
sequence with center-out k-space encoding was used to enhance SNR at 3 Tesla.
Pulsed MT imaging was studied over a range of saturation parameters and the
impact of the turbo-factor on effective ihMT was investigated. 1 mm isotropic
ihMTsat maps were generated in 25 healthy adults using an optimized protocol.
Results: Greater SNR was observed for larger number of bursts consisting of 6-8
saturation pulses each, combined with a high readout turbo-factor. However,
that protocol suffered from a point spread function that was more than twice
the nominal resolution. For high-resolution cortical imaging, we selected a
protocol with a higher effective resolution at the cost of a lower SNR. We
present the first group-average ihMTsat whole-brain map at 1 mm isotropic
resolution. Conclusion: This study presents the impact of saturation and
excitation parameters on ihMTsat SNR and resolution. We demonstrate the
feasibility of high-resolution cortical myelin imaging using ihMTsat in less
than 20 minutes.",2302.07297v2
2023-07-30,Non-axisymmetric modes of magnetorotational and possible hydrodynamical instabilities in the upcoming DRESDYN-MRI experiments -- linear and nonlinear dynamics,"The quest for an unambiguous detection of magnetorotational instability (MRI)
in experiments is still ongoing despite recent promising results. To
conclusively identify MRI in the laboratory, a large cylindrical Taylor-Couette
experiment with liquid sodium is under construction within the DRESDYN project.
In this paper, we investigate the linear and nonlinear dynamics of
non-axisymmetric MRI in the magnetized Taylor-Couette flow of liquid sodium,
which is a model flow in this experiment. We show that the achievable highest
Lundquist $Lu = 10$ and magnetic Reynolds $Rm = 40$ numbers in this experiment
are large enough for the linear instability of non-axisymmetric modes with
azimuthal wavenumber $|m|=1$, although the corresponding critical values of
these numbers are usually higher than those for the axisymmetric mode. The
structure of the ensuing nonlinear saturated state and its scaling properties
with respect to Reynolds number $Re$ are analyzed, which are important for the
DRESDYN-MRI experiment having very high $Re \gtrsim 10^6$. It is shown that for
$Re \lesssim 4\times 10^4$, the non-axisymmetric MRI modes eventually decay,
since the modified shear profile of the mean azimuthal velocity due to the
nonlinear axisymmetric MRI appears to be stable against non-axisymmetric
instabilities. By contrast, for larger $Re \gtrsim 4\times 10^4$, a rapid
growth and saturation of the non-axisymmetric modes of nonmagnetic origin
occurs, which are radially localized near the inner cylinder wall, forming a
turbulent boundary layer. However, for all the parameters considered, the
saturation amplitude of these non-axisymmetric modes is always a few orders
smaller than that of the axisymmetric MRI mode. Therefore, the results of our
previous axisymmetric study on the scaling properties of nonlinear MRI states
also hold when non-axisymmetric modes are included.",2307.16295v2
2007-03-13,Behavior of bulk high-temperature superconductors of finite thickness subjected to crossed magnetic fields,"Crossed magnetic field effects on bulk high-temperature superconductors have
been studied both experimentally and numerically. The sample geometry
investigated involves finite-size effects along both (crossed) magnetic field
directions. The experiments were carried out on bulk melt-processed Y-Ba-Cu-O
(YBCO) single domains that had been pre-magnetized with the applied field
parallel to their shortest direction (i.e. the c-axis) and then subjected to
several cycles of the application of a transverse magnetic field parallel to
the sample ab plane. The magnetic properties were measured using orthogonal
pick-up coils, a Hall probe placed against the sample surface and
Magneto-Optical Imaging (MOI). We show that all principal features of the
experimental data can be reproduced qualitatively using a two-dimensional
finite-element numerical model based on an E-J power law and in which the
current density flows perpendicularly to the plane within which the two
components of magnetic field are varied. The results of this study suggest that
the suppression of the magnetic moment under the action of a transverse field
can be predicted successfully by ignoring the existence of flux-free
configurations or flux-cutting effects. These investigations show that the
observed decay in magnetization results from the intricate modification of
current distribution within the sample cross-section. It is also shown that the
model does not predict any saturation of the magnetic induction, even after a
large number (~ 100) of transverse field cycles. These features are shown to be
consistent with the experimental data.",0703330v2
2014-02-01,Anisotropic magnetic properties and giant magnetocaloric effect of PrSi single crystal,"Single crystal of PrSi was grown by Czochralski method in a tetra-arc
furnace. Powder x-ray diffraction of the as grown crystal revealed that PrSi
crystallizes in FeB$-$type structure with space group $Pnma$ (no. 62). PrSi
undergoes a ferromagnetic transition at 52 K with [010] direction as the easy
axis of magnetization. Heat capacity data confirm the bulk nature of the
transition at 52 K and exhibit a huge anomaly at the transition. A sharp rise
in the low temperature heat capacity has been observed (below 5 K) which is
attributed to the $^{141}$Pr nuclear Schottky heat capacity arising from the
hyperfine field of the Pr moment. The estimated Pr magnetic moment 2.88
$\mu_{\rm B}$/Pr from the hyperfine splitting is in agreement with the
saturation magnetization value obtained from the magnetization data measured at
2 K. From the crystal electric field (CEF) analysis of the magnetic
susceptibility, magnetization and the heat capacity data it is found that the
degenerate $J = 4$ Hund's rule derived state of Pr$^{3+}$-ion splits into nine
singlets with an overall splitting of 284 K, the first excited singlet state
separated by just 9 K from the ground state. The magnetic ordering in PrGe
appears to be due to the exchange generated admixture of low lying crystal
field levels. Magnetocaloric effect (MCE) has been investigated from
magnetization data along all the three principal crystallographic directions.
Large magnetic entropy change, $-\Delta S_M = $22.2 J/kg K, and the relative
cooling power, RCP = $460$ J/kg, characteristic of giant magneto caloric effect
are achieved near the transition temperature ($T_{\rm C}$ = 52 K) for $H =$~70
kOe along $[010]$. Furthermore, the PrSi single crystal exhibits a giant MCE
anisotropy.",1402.0095v1
2014-10-17,Ferromagnetic resonance in $ε$-Co magnetic composites,"We investigate the electromagnetic properties of assemblies of nanoscale
$\epsilon$-cobalt crystals with size range between 5 nm to 35 nm, embedded in a
polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate
the samples by transmission electron microscopy (TEM) imaging, demonstrating
that the particles aggregate and form chains and clusters. By using a broadband
coaxial-line method, we extract the magnetic permeability in the frequency
range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance
with respect to an externally applied magnetic field. We find that the
zero-magnetic field ferromagnetic resonant peak shifts towards higher
frequencies at finite magnetic fields, and the magnitude of complex
permeability is reduced. At fields larger than 2.5 kOe the resonant frequency
changes linearly with the applied magnetic field, demonstrating the transition
to a state in which the nanoparticles become dynamically decoupled. In this
regime, the particles inside clusters can be treated as non-interacting, and
the peak position can be predicted from Kittel's ferromagnetic resonance theory
for non-interacting uniaxial spherical particles combined with the
Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields
this magnetic order breaks down and the resonant frequency in zero magnetic
field reaches a saturation value reflecting the interparticle interactions as
resulting from aggregation. Our results show that the electromagnetic
properties of these composite materials can be tuned by external magnetic
fields and by changes in the aggregation structure.",1410.4789v2
2017-11-15,Laminar and turbulent dynamos in chiral magnetohydrodynamics. II. Simulations,"Using direct numerical simulations (DNS), we study laminar and turbulent
dynamos in chiral magnetohydrodynamics (MHD) with an extended set of equations
that accounts for an additional contribution to the electric current due to the
chiral magnetic effect (CME). This quantum phenomenon originates from an
asymmetry between left- and right-handed relativistic fermions in the presence
of a magnetic field and gives rise to a chiral dynamo. We show that the
magnetic field evolution proceeds in three stages: (1) a small-scale chiral
dynamo instability; (2) production of chiral magnetically driven turbulence and
excitation of a large-scale dynamo instability due to a new chiral effect
(alpha_mu effect); and (3) saturation of magnetic helicity and magnetic field
growth controlled by a conservation law for the total chirality. The
$\alpha_\mu$ effect becomes dominant at large fluid and magnetic Reynolds
numbers and is not related to kinetic helicity. The growth rate of the
large-scale magnetic field and its characteristic scale measured in the
numerical simulations agree well with theoretical predictions based on
mean-field theory. The previously discussed two-stage chiral magnetic scenario
did not include stage (2) during which the characteristic scale of magnetic
field variations can increase by many orders of magnitude. Based on the
findings from numerical simulations, the relevance of the CME and the chiral
effects revealed in the relativistic plasma of the early universe and of
proto-neutron stars are discussed.",1711.09733v3
2018-11-14,Intensity contrast of solar plage as a function of magnetic flux at high spatial resolution,"Magnetic elements have an intensity contrast that depends on the type of
region they are located in (e.g. quiet Sun, or active region plage). Observed
values also depend on the spatial resolution of the data. Here we investigate
the contrast-magnetic field dependence in active region plage observed near
disk center with Sunrise during its second flight in 2013. The wavelengths
under study range from the visible at 525\,nm to the near ultraviolet (NUV) at
300\,nm and 397\,nm. We use quasi-simultaneous spectropolarimetric and
photometric data from the Imaging Magnetograph eXperiment (IMaX) and the
Sunrise Filter Imager (SuFI), respectively. We find that in all wavelength
bands, the contrast exhibits a qualitatively similar dependence on the
line-of-sight magnetic field, $B_{\rm LOS}$, as found in the quiet Sun, with
the exception of the continuum at 525\,nm. There, the contrast of plage
magnetic elements peaks for intermediate values of $B_{\rm LOS}$ and decreases
at higher field strengths. By comparison, the contrast of magnetic elements in
the quiet Sun saturates at its maximum value at large $B_{\rm LOS}$. We find
that the explanation of the turnover in contrast in terms of the effect of
finite spatial resolution of the data is incorrect with the evidence provided
by the high-spatial resolution Sunrise data, as the plage magnetic elements are
larger than the quiet Sun magnetic elements and are well-resolved. The turnover
comes from the fact that the core pixels of these larger magnetic elements are
darker than the quiet Sun. We find that plages reach lower contrast than the
quiet Sun at disk center at wavelength bands formed deep in the photosphere,
such as the visible continuum and the 300\,nm band. This difference decreases
with formation height and disappears in the Ca\,{\sc ii} H core, in agreement
with empirical models of magnetic element atmospheres.",1811.05759v1
2020-09-02,New highly-anisotropic Rh-based Heusler compound for magnetic recording,"The development of high-density magnetic recording media is limited by the
superparamagnetism in very small ferromagnetic crystals. Hard magnetic
materials with strong perpendicular anisotropy offer stability and high
recording density. To overcome the difficulty of writing media with a large
coercivity, heat assisted magnetic recording (HAMR) has been developed, rapidly
heating the media to the Curie temperature Tc before writing, followed by rapid
cooling. Requirements are a suitable Tc, coupled with anisotropic thermal
conductivity and hard magnetic properties. Here we introduce Rh2CoSb as a new
hard magnet with potential for thin film magnetic recording. A
magnetocrystalline anisotropy of 3.6 MJm-3 is combined with a saturation
magnetization of {\mu}0Ms = 0.52 T at 2 K (2.2 MJm-3 and 0.44 T at
room-temperature). The magnetic hardness parameter of 3.7 at room temperature
is the highest observed for any rare-earth free hard magnet. The anisotropy is
related to an unquenched orbital moment of 0.42 {\mu}B on Co, which is
hybridized with neighbouring Rh atoms with a large spin-orbit interaction.
Moreover, the pronounced temperature-dependence of the anisotropy that follows
from its Tc of 450 K, together with a high thermal conductivity of 20 Wm-1K-1,
makes Rh2CoSb a candidate for development for heat assisted writing with a
recording density in excess of 10 Tb/in2.",2009.01034v1
2023-04-06,Microscopic characterization of the magnetic properties of the itinerant antiferromagnet La2Ni7 by 139La NMR/NQR measurements,"139La nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)
measurements have been performed to investigate the magnetic properties of the
itinerant magnet La2Ni7 which shows a series of antiferromagnetic (AFM) phase
transitions at $T_{N1}$=61 K, $T_{N2}$=56 K, and $T_{N3}$=42 K under zero
magnetic field. Two distinct La NMR signals were observed due to the two
crystallographically inequivalent La sites in La2Ni7 (La1 and La2 in the La2Ni4
and the LaNi5 sub-units of the La2Ni7 unit cell, respectively). From the 139La
NQR spectrum in the AFM state below $T_{N3}$, the AFM state was revealed to be
a commensurate state where Ni ordered moments align along the crystalline c
axis. Owing to the two different La sites, we were able to estimate the average
values of the Ni ordered moments ($\sim$0.09-0.10 $\mu_{B}$/Ni and
$\sim$0.17$\mu_{B}$/Ni around La1 and La2, respectively) from 139La NMR
spectrum measurements in the AFM state below $T_{N3}$, suggesting a non-uniform
distribution of the Ni-ordered moments in the AFM state. In contrast, a more
uniform distribution of the Ni-ordered moments in the saturated paramagnetic
state induced by the application of high magnetic fields is observed. The
temperature dependence of the sublattice magnetization measured by the internal
field at the La2 site in the AFM state was reproduced by a local moment model
better than the self-consistent renormalization (SCR) theory for weak itinerant
antiferromagnets. Given the small Ni-ordered moments in the magnetically
ordered state, our results suggest that La2Ni7 has characteristics of both
itinerant and localized natures in its magnetism. With this in mind, it is
noteworthy that the temperature dependence of nuclear spin-relaxation rates in
the paramagnetic state above $T_{N1}$ measured at zero magnetic field can be
explained qualitatively by both the SCR theory and the local-moment model.",2304.03157v2
2023-12-07,On the role of numerical diffusivity in MHD simulations of global accretion disc dynamos,"Observations, mainly of outbursts in dwarf novae, imply that the anomalous
viscosity in highly ionized accretion discs is magnetic in origin, and requires
that the plasma $\beta \sim 1$. Until now most simulations of the magnetic
dynamo in accretion discs have used a local approximation (known as the
shearing box). While these simulations demonstrate the possibility of a
self-sustaining dynamo, the magnetic activity generated in these models
saturates at $\beta \gg 1$. This long-standing discrepancy has previously been
attributed to the local approximation itself. There have been recent attempts
at simulating magnetic activity in global accretion discs with parameters
relevant to the dwarf novae. These too find values of $\beta \gg 1$. We
speculate that the tension between these models and the observations may be
caused by numerical magnetic diffusivity. As a pedagogical example, we present
exact time-dependent solutions for the evolution of weak magnetic fields in an
incompressible fluid subject to linear shear and magnetic diffusivity. We find
that the maximum factor by which the initial magnetic energy can be increased
depends on the magnetic Reynolds number as ${\mathcal R}_{\rm m}^{2/3}$. We
estimate that current global numerical simulations of dwarf nova discs have
numerical magnetic Reynolds numbers around 6 orders of magnitude less than the
physical value found in dwarf nova discs of ${\mathcal R}_{\rm m} \sim
10^{10}$. We suggest that, given the current limitations on computing power,
expecting to be able to compute realistic dynamo action in observable accretion
discs using numerical MHD is, for the time being, a step too far.",2312.04400v1
1998-05-11,Turbulence and angular momentum transport in a global accretion disk simulation,"The global development of magnetohydrodynamic turbulence in an accretion disk
is studied within a simplified disk model that omits vertical stratification.
Starting with a weak vertical seed field, a saturated state is obtained after a
few tens of orbits in which the energy in the predominantly toroidal magnetic
field is still subthermal. The efficiency of angular momentum transport,
parameterized by the Shakura-Sunyaev alpha parameter, is of the order of 0.1.
The dominant contribution to alpha comes from magnetic stresses, which are
enhanced by the presence of weak net vertical fields. The power spectra of the
magnetic fields are flat or decline only slowly towards the largest scales
accessible in the calculation, suggesting that the viscosity arising from MHD
turbulence may not be a locally determined quantity. I discuss how these
results compare with observationally inferred values of alpha, and possible
implications for models of jet formation.",9805133v1
1999-01-27,Non-linear dynamics of Kelvin-Helmholtz unstable magnetized jets: three-dimensional effects,"A numerical study of the Kelvin-Helmholtz instability in compressible
magnetohydrodynamics is presented. The three-dimensional simulations consider
shear flow in a cylindrical jet configuration, embedded in a uniform magnetic
field directed along the jet axis. The growth of linear perturbations at
specified poloidal and axial mode numbers demonstrate intricate non-linear
coupling effects. The physical mechanims leading to induced secondary
Kelvin-Helmholtz instabilities at higher mode numbers are identified. The
initially weak magnetic field becomes locally dominant in the non-linear
dynamics before and during saturation. Thereby, it controls the jet deformation
and eventual breakup. The results are obtained using the Versatile Advection
Code [G. Toth, Astrophys. Lett. Comm. 34, 245 (1996)], a software package
designed to solve general systems of conservation laws. An independent
calculation of the same Kelvin-Helmholtz unstable jet configuration using a
three-dimensional pseudo-spectral code gives important insights into the
coupling and excitation events of the various linear mode numbers.",9901383v1
1999-09-03,Effect of Expansion and Magnetic Field Configuration on Mass Entrainment of Jets,"We investigate the growth of jet plus entrained mass in simulations of
supermagnetosonic cylindrical and expanding jets. The entrained mass spatially
grows in three stages: from an initially slow spatial rate to a faster rate and
finally at a flatter rate. These stages roughly coincide with the similar rates
of expansion in simulated radio intensity maps, and also appear related to the
growth of the Kelvin-Helmholtz instability through linear, nonlinear, and
saturated regimes. In the supermagnetosonic cylindrical jets, we found that a
jet with an embedded primarily toroidal magnetic field is more stable than a
jet with a primarily axial magnetic field. Also, pressure-matched expanding
jets are more stable and entrain less mass than cylindrical jets with
equivalent inlet conditions.",9909077v1
2000-12-11,Sheared helical turbulence and the helicity constraint in large-scale dynamos,"The effect of shear on the growth of large scale magnetic fields in helical
turbulence is investigated. The resulting large-scale magnetic field is also
helical and continues to evolve, after saturation of the small scale field, on
a slow resistive time scale. This is a consequence of magnetic helicity
conservation. Because of shear, the time scale needed to reach an
equipartition-strength large scale field is shortened proportionally to the
ratio of the resulting toroidal to poloidal large scale fields.",0012240v1
2003-04-12,Magnetic Helicity Evolution During the Solar Activity Cycle: Observations and Dynamo Theory,"We study a simple model for the solar dynamo in the framework of the Parker
migratory dynamo, with a nonlinear dynamo saturation mechanism based on
magnetic helicity conservation arguments. We find a parameter range in which
the model demonstrates a cyclic behaviour with properties similar to that of
Parker dynamo with the simplest form of algebraic alpha-quenching. We compare
the nonlinear current helicity evolution in this model with data for the
current helicity evolution obtained during 10 years of observations at the
Huairou Solar Station of China. On one hand, our simulated data demonstrate
behaviour comparable with the observed phenomenology, provided that a suitable
set of governing dynamo parameters is chosen. On the other hand, the
observational data are shown to be rich enough to reject some other sets of
governing parameters. We conclude that, in spite of the very preliminary state
of the observations and the crude nature of the model, the idea of using
observational data to constrain our ideas concerning magnetic field generation
in the framework of the solar dynamo appears promising.",0304232v1
2003-10-09,A Magnetic Betelgeuse? Numerical Simulations of Non-linear Dynamo Action,"Betelgeuse is an example of a cool super-giant displaying brightness
fluctuations and irregular surface structures. Simulations by Freytag et al.
(2002) of the convective envelope of the star have shown that the fluctuations
in the star's luminosity may be caused by giant cell convection. A related
question regarding the nature of Betelgeuse and supergiants in general is
whether these stars may be magnetically active. If so, that may in turn also
contribute to their variability. By performing detailed numerical simulations,
I find that both linear kinematic and non-linear dynamo action are possible and
that the non-linear magnetic field saturates at a value somewhat below
equipartition: in the linear regime there are two modes of dynamo action.",0310279v1
2006-03-17,Local Kelvin-Helmholtz instability and synchrotron modulation in Pulsar Wind Nebulae,"We present here a series of numerical simulations of the development of
Kelvin-Helmholtz instability in a relativistically hot plasma. The physical
parameters in the unperturbed state are chosen to be representative of local
conditions encountered in Pulsar Wind Nebulae (PWNe), with a main magnetic
field perpendicular to a mildly relativistic shear layers. By using a numerical
code for Relativistic MHD, we investigate the effect of an additional magnetic
field component aligned with the shear velocity, and we follow the evolution of
the instability to the saturation and turbulent regimes. Based on the resulting
flow structure, we then compute synchrotron maps in order to evaluate the
signature of Kelvin-Helmholtz instability on the emission and we investigate
how the time scale and the amplitude of the synchrotron modulations depend on
shear velocity and magnetic field. Finally we compare our results to the
observed variable features in the Crab Nebula. We show that the
Kelvin-Helmholtz instability cannot account for the wisps variability, but it
might be responsible for the time dependent filamentary structure observed in
the main torus.",0603481v1
1995-10-13,Plateau of the Magnetization Curve of the S=1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic Spin Chain,"I analytically study the plateau of the magnetization curve at $M/M_{\rm S} =
1/3$ (where $M_{\rm S}$ is the saturation magnetization) of the one-dimensional
$S=1/2$ trimerized Heisenberg spin system with ferromagnetic ($J_{\rm
F}$)-ferromagnetic ($J_{\rm F}$)-antiferromagnetic ($J_{\rm A}$) interactions
at $T=0$. I use the bosonization technique for the fermion representation of
the spin Hamiltonian through the Jordan-Wigner transformation. The plateau
appears when $\gamma \equiv J_{\rm F}/J_{\rm A} \allowbreak < \gamma_{\rm C}$,
and vanishes when $\gamma > \gamma_{\rm C}$, where the critical value
$\gamma_{\rm C}$ is estimated as $\gamma_{\rm C} = 5 \sim 6$. The behavior of
the width of the plateau near $\gamma_{\rm C}$ is of the Kosterlitz-Thouless
type. The present theory well explains the numerical result by Hida.",9510070v1
1995-10-18,Metamagnetism and Fermi Surface in the Anderson Lattice Model,"We investigate magnetization as functions of external magnetic field $H$ in
the $U$-infinite Anderson lattice model within the leading order approximation
in the $1/N$-expansion. At $T=0$, at $H=H_M$ where the Zeeman energy is equal
to a certain characteristic energy in the system, the magnetization curve has a
kink and the differential susceptibility $dM/dH$ shows a jump. At finite
temperature, $dM/dH$ shows a peak around $H_M$. Its maximum value increases
with decreasing $T$ and saturates to a finite value at $T\to 0$. When $H<H_M$,
the $f$ and the conduction electrons form the renormalized bands with a large
Fermi surface determined by the Luttinger sum rule. On the other hand, when
$H>H_M$, the bands reform themselves significantly free from the Luttinger sum
rule, eventually leading to a small Fermi surface at $H \gg H_M$. The results
are consistent with the metamagnetic properties observed in the heavy fermion
CeRu$_2$Si$_2$.",9510095v1
1996-09-20,High Temperature Thermopower in La_{2/3}Ca_{1/3}MnO_3 Films: Evidence for Polaronic Transport,"Thermoelectric power, electrical resistivity and magnetization experiments,
performed in the paramagnetic phase of La_{2/3}Ca_{1/3}MnO_3, provide evidence
for polaron-dominated conduction in CMR materials. At high temperatures, a
large, nearly field-independent difference between the activation energies for
resistivity (rho) and thermopower (S), a characteristic of Holstein Polarons,
is observed, and ln(rho) ceases to scale with the magnetization. On approaching
T_c, both energies become field-dependent, indicating that the polarons are
magnetically polarized. Below T_c, the thermopower follows a law S(H) prop.
1/rho (H) as in non saturated ferromagnetic metals.",9609212v1
1997-05-30,Ferromagnetism in the Hubbard model: Influence of the lattice structure,"By use of the spectral density approach the influence of the lattice
structure on the possibility of ferromagnetism in the single band Hubbard model
is investigated. The d=\infty hypercubic lattice does not show magnetic phase
transitions of second order irrespective of the strength of the Coulomb
coupling. However, first order transitions to finite magnetic moments, not
visible as singularities of the paramagnetic susceptibility, may appear in the
very strong coupling regime. In d=3 second order transitions are found but only
for very strong couplings, where the non-locality of the electronic self-energy
acts in favour of the spontaneous magnetic moment. The influence of the
non-local part of the self-energy is particularly strong for lattices with
small coordination number. The non-bipartite fcc lattice exhibits saturated
ferromagnetism for all band occupations $1\le n\le 2$ while for less than half
filled bands ($0\le n\le 1$) the system remains in any case paramagnetic, and
that for d=3 as well as d=\infty. The Curie temperature runs through a maximum
at about $n=1.4$ and vanishes for $n\to 1$ and $n\to 2$.",9705305v1
1998-05-19,On the Theory of Magnets with Competing Double Exchange and Superexchange Interactions,"In the CMR materials, ferromagnetic double exchange (DE) presumably coexists
with a direct nearest-neighbour antiferromagnetic interaction. We construct a
single-site mean field theory that explicitly takes into account the different
nature of carrier-mediated ferromagnetism vs. Heisenberg-like superexchange. We
find, in contrast to previous results in the literature, that the competition
between these two exchange interactions leads to ferro- or antiferromagnetic
order with incomplete saturation of the magnetization (or sublattice
magnetization), rather than spin canting. The associated experimental
implications are discussed.",9805238v3
1998-10-19,Coupled Ladders in a Magnetic Field,"We investigate the phase transitions in two-leg ladders systems in the
incommensurate phase, for which the gap is destroyed by a magnetic field
($h_{c1}< h$) and the ladder is not yet totally saturated ($h < h_{c2}$). We
compute quantitatively the correlation functions as a function of the magnetic
field for an isolated strong coupling ladder $J_\perp \gg J_\parallel$ and use
it to study the phase transition occuring in a three dimensional array of
antiferromagnetically coupled ladders. The three dimensional ordering is in the
universality class of Bose condensation of hard core bosons. We compute the
critical temperature $T_c(h)$ as well as various physical quantities such as
the NMR relaxations rate. $T_c$ has an unusual camel-like shape with a local
minimum at $h=(h_{c1}+h_{c2})/2$ and behaves as $T_c \sim (h-h_{c1})^{2/3}$ for
$h\sim h_{c1}$. We discuss the experimental consequences for compounds such as
Cu_2(C_5H_{12}N_2)_2Cl_4",9810219v2
1999-03-10,Response to Parallel Magnetic Field of a Dilute 2D Electron System across the Metal-Insulator Transition,"The response to a parallel magnetic field of the very dilute insulating
two-dimensional system of electrons in silicon MOSFET's is dramatic and similar
to that found on the conducting side of the metal-insulator transition: there
is a large initial increase in resistivity with increasing field, followed by
saturation to a value that is approximately constant above a characteristic
magnetic field of about one Tesla. This is unexpected behavior in an insulator
that exhibits Efros-Shklovskii variable-range hopping in zero field, and
appears to be a general feature of very dilute electron systems.",9903179v3
1999-06-15,Separation of quadrupolar and magnetic contributions to spin-lattice relaxation in the case of a single isotope,"We present a NMR pulse double-irradiation method which allows one to separate
magnetic from quadrupolar contributions in the spin-lattice relaxation. The
pulse sequence fully saturates one transition while another is observed. In the
presence of a Delta m = 2 quadrupolar contribution, the intensity of the
observed line is altered compared to a standard spin-echo experiment. We
calculated analytically this intensity change for spins I=1, 3/2, 5/2, thus
providing a quantitative analysis of the experimental results. Since the pulse
sequence we used takes care of the absorbed radio-frequency power, no problems
due to heating arise. The method is especially suited when only one NMR
sensitive isotope is available. Different cross-checks were performed to prove
the reliability of the obtained results. The applicability of this method is
demonstrated by a study of the plane oxygen 17O (I = 5/2) in the
high-temperature superconductor YBa_2Cu_4O_8: the 17O spin-lattice relaxation
rate consists of magnetic as well as quadrupolar contributions.",9906216v1
1999-07-30,Quantum Phase Transition of S=1/2 Trimerized XXZ Spin Chain in Magnetic Field,"We study the magnetization plateau at a third of the saturation magnetization
of the S=1/2 trimerized XXZ spin chain at T=0. The appearance of the plateau
depends on the values of the XXZ anisotropy and the magnitude of the
trimerization. This plateauful-plateauless transition is a quantum phase
transition of the Berezinskii-Kosterlitz-Thouless type, which is difficult to
precisely detect from the numerical data. To determine the phase boundary line
of this transition precisely, we use the level crossing of low-lying
excitations obtained from the numerical diagonalization. We also discuss the
S=1/2 ferromagnetic-ferromagnetic-antiferromagnetic chain.",9907481v1
1999-12-10,Weak-localization corrections to the conductivity of double quantum wells,"The weak-localization contribution \delta\sigma(B) to the conductivity of a
tunnel-coupled double-layer electron system is evaluated and its behavior in
weak magnetic fields B perpendicular or parallel to the layers is examined. In
a perpendicular field B, \delta \sigma(B) increases and remains dependent on
tunneling as long as the magnetic field is smaller than \hbar/e D \tau_t, where
D is the in-plane diffusion coefficient and \tau_t the interlayer tunneling
time. If \tau_t is smaller than the inelastic scattering time, a parallel
magnetic field also leads to a considerable increase of the concuctivity
starting with a B**2 law and saturating at fields higher than \hbar/e Z (D
\tau_t)**(1/2), where Z is the interlayer distance. In the limit of coherent
tunneling, when \tau_t is comparable to elastic scattering time, \delta
\sigma(B) differs from that of a single-layer system due to ensuing
modifications of the diffusion coefficient. A possibility to probe the
weak-localization effect in double-layer systems by the dependence of the
conductivity on the gate-controlled level splitting is discussed.",9912169v1
2000-04-20,Dynamical response of a pinned two-dimensional Wigner crystal,"We re-examine a long-standing problem of a finite-frequency conductivity of a
weakly pinned two-dimensional classical Wigner crystal. In this system an
inhomogeneously broadened absorption line (pinning mode) centered at disorder
and magnetic field dependent frequency $\omega_p$ is known to appear. We show
that the relative linewidth $\Delta \omega_p / \omega_p$ of the pinning mode is
of the order of one in weak magnetic fields, exhibits a power-law decrease in
intermediate fields, and eventually saturates at a small value in strong
magnetic fields. The linewidth narrowing is due to a peculiar mechanism of
mixing between the stiffer longitudinal and the softer transverse components of
the collective excitations. The width of the high-field resonance proves to be
related to the density of states in the low-frequency tail of the zero-field
phonon spectrum. We find a qualitative agreement with recent experiments and
point out differences from the previous theoretical work on the subject.",0004343v1
2000-07-31,Carrier-induced ferromagnetism in p-Zn1-xMnxTe,"We present a systematic study of the ferromagnetic transition induced by the
holes in nitrogen doped Zn1-xMnxTe epitaxial layers, with particular emphasis
on the values of the Curie-Weiss temperature as a function of the carrier and
spin concentrations. The data are obtained from thorough analyses of the
results of magnetization, magnetoresistance and spin-dependent Hall effect
measurements. The experimental findings compare favorably, without adjustable
parameters, with the prediction of the Rudermann-Kittel-Kasuya-Yosida (RKKY)
model or its continuous-medium limit, that is, the Zener model, provided that
the presence of the competing antiferromagnetic spin-spin superexchange
interaction is taken into account, and the complex structure of the valence
band is properly incorporated into the calculation of the spin susceptibility
of the hole liquid. In general terms, the findings demonstrate how the
interplay between the ferromagnetic RKKY interaction, carrier localization, and
intrinsic antiferromagnetic superexchange affects the ordering temperature and
the saturation value of magnetization in magnetically and electrostatically
disordered systems.",0007502v1
2000-11-02,The Magnetic Spin Ladder (C_{5}H_{12}N)_{2}CuBr_{4}: High Field Magnetization and Scaling Near Quantum Criticality,"The magnetization, $M(H \leq 30$ T, 0.7 K $\leq T \leq 300$ K), from single
crystals and powder samples of (C$_{5}$H$_{12}$N)$_{2}$CuBr$_{4}$ has been used
to identify this system as an $S=1/2$ Heisenberg two-leg ladder in the strong
coupling limit, $J_{\perp} = 13.3$ K and $J_{\parallel} = 3.8$ K, with $H_{c1}
= 6.6$ T and $H_{c2} = 14.6$ T. An inflection point in $M(H, T = 0.7$ K) at
half-saturation, $M_{s}/2$, is described by an effective \emph{XXZ} chain. The
data exhibit universal scaling behavior in the vicinity of $H_{c1}$ and
$H_{c2}$, indicating the system is near a quantum critical point.",0011052v2
2000-12-09,"Staggered magnetization, critical behavior and weak ferromagnetic propert ies of LaMnO$_3$ by muon spin rotation","We present a study of a microtwinned single crystal of LaMnO$_3$ by means of
implanted muons. Two muon stopping sites are identified from the symmetry of
the internal field in the ordered phase. The temperature dependence of these
fields yields the behavior of the staggered magnetization from which a static
critical exponent ($\beta=0.36(2)$) is extracted and discussed. The muon
spin-spin relaxation rate shows a critical slowing down (contrary to
preliminary findings) with a critical exponent $n=0.7(1)$, witnessing the Ising
nature of the dynamic fluctuations. The muon precession frequencies vs. applied
magnetic field reveal the saturation of the weak ferromagnetic domain structure
originated by the Dzialoshinski-Moriya antisymmetric exchange.",0012158v2
2000-12-15,Alternating-Spin Ladders in a Magnetic Field: New Magnetization Plateaux,"We study numerically the formation of magnetization plateaux with the Lanczos
method in 2-leg ladders with mixed spins of magnitudes $(S_1,S_2)=(1,1/2)$
located at alternating positions along the ladder and with dimerization
$\gamma$. For interchain coupling $J'>0$ and $\gamma=0$, we find normalized
plateaux at $m=1/3$ starting at zero field and $m=1$ (saturation), while when
$\gamma \ne 0$ is columnar, another extra plateau at $m=2/3$ shows up. For
$J'<0$, when $\gamma<\gamma_c(J')$ we find no plateau while for
$\gamma>\gamma_c(J')$ we find four plateaux at $m=0,1/3,2/3,1$. We also apply
several approximate analytical methods (Spin Wave Theory, Low-Energy Effective
Hamiltonians and Bosonization) to understand these findings and to conjeture
the behaviour of ferrimagnetic ladders with a bigger number of legs.",0012278v1
2001-01-12,Superfluid-spiral state of quantum ferrimagnets in magnetic field,"We study the phase diagram of one-dimensional quantum ferrimagnets by using a
numerical exact diagonalization of a finite size system along with a
field-theoretical non-linear $\sigma$ model of the quantum ferrimagnets at zero
temperature and its effective description in the presence of the external
magnetic field in terms of the quantum XY-model. The low- and the high-field
phases correspond respectively to the classical N\'eel and the fully polarized
ferromagnetic states where in the intermediate magnetic field ($h_{c1} < h <
h_{c2}$), it is an XXZ+h model with easy plane anisotropy, which possess the
spiral (superfluid) states that carry the dissipationless spin-supercurrent. We
derive the critical exponents, and then will study the stability of the XY
spiral state against these spin-supercurrents and the hard axis fluctuations.
We will show a first order phase transition from the easy plane spiral state to
a saturated ferromagnetic state occurs at $h=h_{c2}$ if the spin-supercurrent
reaches to its critical value.",0101194v1
2001-04-02,Antiferromagnetic vortex state in a high-temperature superconductor,"There is strong evidence that magnetic interactions play a crucial role in
the mechanism driving high-temperature superconductivity in cuprate
superconductors. To investigate this further we have done neutron scattering
experiments on the simplest high-temperature superconductor La(2-x)Sr(x)CuO(4)
(LSCO) in an applied magnetic field. Below the superconducting transition
temperature (Tc), the field penetrates the material via an array of normal
state inclusions or vortices while phase coherent superconductivity
characterized by zero resistance is suppressed to the lower field-dependent
irreversibility temperature. The measurements described here were performed on
underdoped LSCO (x=0.10), which develops static incommensurate order below Tc
in zero field. Our results show that application of a magnetic field enhances
this response without changing the onset temperature. For H=5T the
field-induced signal saturates to three times the zero-field signal and phase
coherent superconductivity is established within the antiferromagnetic phase.",0104026v1
2001-08-29,Macroscopic magnetization jumps due to independent magnons in frustrated quantum spin lattices,"For a class of frustrated spin lattices including the kagome lattice we
construct exact eigenstates consisting of several independent, localized
one-magnon states and argue that they are ground states for high magnetic
fields. If the maximal number of local magnons scales with the number of spins
in the system, which is the case for the kagome lattice, the effect persists in
the thermodynamic limit and gives rise to a macroscopic jump in the
zero-temperature magnetization curve just below the saturation field. The
effect decreases with increasing spin quantum number and vanishes in the
classical limit. Thus it is a true macroscopic quantum effect.",0108498v2
2002-02-13,Field Suppression of the Density-of-States: A Mechanism for Large Linear Magnetoresistance,"Hall, resistivity, magnetization, and thermoelectric power measurements were
performed on single crystals of the highly anisotropic layered metal LaSb2. A
100-fold linear magnetoresistance (MR) was observed in fields up to 45 T, with
no indication of saturation. We show that the MR is associated with a
magnetic-field-dependent holelike carrier density, n(H) \propto 1/H. The effect
is orbital, depending upon the component of the magnetic field normal to the
layers. At low temperature, a field of 9 T reduces the carrier density by more
than an order of magnitude.",0202220v1
2002-08-12,"Fe/V and Fe/Co (001) superlattices: growth, anisotropy, magnetisation and magnetoresistance","Some physical properties of bcc Fe/V and Fe/Co (001) superlattices are
reviewed. The dependence of the magnetic anisotropy on the in-plane strain
introduced by the lattice mismatch between Fe and V is measured and compared to
a theoretical derivation. The dependence of the magnetic anisotropy (and
saturation magnetisation) on the layer thickness ratio Fe/Co is measured and a
value for the anisotropy of bcc Co is derived from extrapolation. The
interlayer exchange coupling of Fe/V superlattices is studied as a function of
the layer thickness V (constant Fe thickness) and layer thickness of Fe
(constant V thickness). A region of antiferromagnetic coupling and GMR is found
for V thicknesses 12-14 monolayers. However, surprisingly, a 'cutoff' of the
antiferromagnetic coupling and GMR is found when the iron layer thickness
exceeds about 10 monolayers.",0208229v1
2002-11-28,Magneto-superconductivity of 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10,"Studied 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10 (Ru-1222) compound
crystallized in a tetragonal I4/mmm space group crystal structure.
Thermo-gravemetric (TG) analysis of the compound showed the release of oxygen
and breaking to metallic constituents in two distinct steps at around 350 and
500 0C. The DC magnetization data (M vs. T) revealed magnetic transition at 100
K followed by superconducting transition at 40 K. Low field M vs. H hysteresis
loop showed a lower critical field (Hc1) value of around 25 Oe. Ferromagnetic
component is evidenced at 5, 10, 20 and 40 K. Near saturation field of above 5
Tesla is observed at 5 K. Zero-field returning moment (Mr) and zero-moment
coercive field (Hc) values at 5 K are 0.35mB and 250 Oe. The resistance vs.
temperature (R vs. T) behaviour of the sample confirmed superconductivity at
around 43 K. Superconductivity transition (Tc) is broadened under magnetic
field with strong granularity like steps.",0211644v1
2003-02-25,Two-dimensional Induced Ferromagnetism,"Magnetic properties of materials confined to nanometer length scales are
providing important information regarding low dimensional physics. Using
gadolinium based Langmuir-Blodgett films, we demonstrate that two-dimensional
ferromagnetic order can be induced by applying magnetic field along the
in-plane (perpendicular to growth) direction. Field dependent exchange coupling
is evident in the in-plane magnetization data that exhibit absence of
hysteresis loop and show reduction in field required to obtain saturation in
measured moment with decreasing temperature.",0302516v2
2003-07-28,Low temperature spin fluctuations in geometrically frustrated Yb3Ga5O12,"In the garnet structure compound Yb3Ga5O12, the Yb3+ ions (ground state
effective spin S' = 1/2) are situated on two interpenetrating corner sharing
triangular sublattices such that frustrated magnetic interactions are possible.
Previous specific heat measurements evidenced the development of short range
magnetic correlations below 0.5K and a lambda-transition at 54mK (Filippi et
al. J. Phys. C: Solid State Physics 13 (1980) 1277). From 170-Yb M""ossbauer
spectroscopy measurements down to 36mK, we find there is no static magnetic
order at temperatures below that of the lambda-transition. Below 0.3K, the
fluctuation frequency of the short range correlated Yb3+ moments progressively
slows down and as the temperature tends to 0, the frequency tends to a
quasi-saturated value of 3 x 10^9 s^-1. We also examined the Yb3+ paramagnetic
relaxation rates up to 300K using 172-Yb perturbed angular correlation
measurements: they evidence phonon driven processes.",0307676v1
2004-01-31,Bond Operator Mean Field Approach to the Magnetization Plateaux in Quantum Antiferromagnets -- Application to the S=1/2 Coupled Dimerized Zigzag Heisenberg Chains,"The magnetization plateaux in two dimensionally coupled S=1/2 dimerized
zigzag Heisenberg chains are investigated by means of the bond operator mean
field approximation. In the absence of the interchain coupling, this model is
known to have a plateau at half of the saturation magnetization accompanied by
the spontanuous translational symmetry breakdown. The parameter regime in which
the plateau appears is reproduced well within the present approximation. In the
presence of the interchain coupling, this plateau is shown to be suppressed.
This result is also supported by the numerical diagonalization calculation.",0402008v2
2004-06-04,Absence of magnetic order for the spin-half Heisenberg antiferromagnet on the star lattice,"We study the ground-state properties of the spin-half Heisenberg
antiferromagnet on the two-dimensional star lattice by spin-wave theory, exact
diagonalization and a variational mean-field approach. We find evidence that
the star lattice is (besides the \kagome lattice) a second candidate among the
11 uniform Archimedean lattices where quantum fluctuations in combination with
frustration lead to a quantum paramagnetic ground state. Although the classical
ground state of the Heisenberg antiferromagnet on the star exhibits a huge
non-trivial degeneracy like on the \kagome lattice, its quantum ground state is
most likely dimerized with a gap to all excitations. Finally, we find several
candidates for plateaux in the magnetization curve as well as a macroscopic
magnetization jump to saturation due to independent localized magnon states.",0406103v2
2004-06-24,"Magneto-transport studies on (Pr1/3Sm2/3)2/3A1/3MnO3 (A = Ca, Sr and Ba) compounds","Magnetic and transport properties of (Pr1/3Sm2/3)2/3A1/3MnO3 (A = Ca, Sr and
Ba) compounds, prepared by the citrate gel route, have been investigated. These
compounds are found to crystallize in the orthorhombic structure. Charge
ordering transport behavior is indicated only in Ca-substituted compound. The
Sr- and Ba-substituted compounds show metal-insulator transition and
semiconducting-like behavior, respectively. The magnetoresistance is highest in
the Ba substituted compound. All the three samples show irreversibility in
magnetization as a function of temperature in zero-field cooled (ZFC) and field
cooled (FC) plots. The non-saturating magnetization, even at 5K and 4 Tesla
field, are observed in Ca as well Ba-substituted compounds.",0406599v1
2005-01-28,Quantum vs. Classical Magnetization Plateaus of S=1/2 Frustrated Heisenberg Chains,"The competition between quantum and classical magnetization plateaus of S=1/2
frustrated Heisenberg chains with modified exchange couplings is investigated.
The conventional S=1/2 frustrated Heisenberg chains is known to exhibit a
3-fold degenerate udu-type classical plateau at 1/3 of the saturation
magnetization accompanied by the spontaneous Z_3 translational symmetry
breakdown. The stability of this plateau phase against period 3 exchange
modulation which favors the 00u-type quantum plateau state (00= singlet dimer)
is studied by bosonization, renormalization group and numerical diagonalization
methods. The ground state phase diagram and the spin configuration in each
phase are numerically determined. The translationally invariant Valence Bond
Solid-type model with 4-spin and third neighbor interactions, which has the
exact 00u-type quantum plateau state, is also presented. The phase transition
to the classical udu-type ground state is also observed by varying the strength
of 4-spin and third neighbor interactions. The relation between these two types
of models with quantum plateau states is discussed.",0501697v2
2005-07-08,Field-induced non-Fermi-liquid resistivity of stoichiometric YbAgGe single crystals,"We have investigated hexagonal YbAgGe down to 70 mK by measuring the
magnetic-field and temperature dependence of the resistivity rho of single
crystals in fields up to 14 T. Our results extend the H-T phase diagram to the
lowest temperatures for H applied in the basal plane and along the c-axis. In
particular, critical fields for the suppression of several magnetic phases are
determined. The temperature dependence of rho(T) is unusual: whereas at low H,
rho(T) reveals a temperature exponent n>=2, we find 1<=n<1.5 and strong
enhancement of the temperature dependence of rho(T) close to and beyond the
highest critical field for each field direction. For H applied in the basal
plane, at high fields a conventional T^2 dependence of rho(T) is reached above
10 T accompanied by an approach to saturation of a strong drop in the residual
resistivity. YbAgGe appears to be one of few Yb-based stoichiometric systems,
where quantum-critical behaviour may be induced by a magnetic field.",0507211v2
2005-09-05,Unified description of bulk and interface-enhanced spin pumping,"The dynamics of non-equilibrium spin accumulation generated in metals or
semiconductors by rf magnetic field pumping is treated within a diffusive
picture. The dc spin accumulation produced in a uniform system by a rotating
applied magnetic field or by a precessing magnetization of a weak ferromagnet
is in general given by a (small) fraction of hbar omega, where omega is the
rotation or precession frequency. With the addition of a neighboring,
field-free region and allowing for the diffusion of spins, the spin
accumulation is dramatically enhanced at the interface, saturating at the
universal value hbar omega in the limit of long spin relaxation time. This
effect can be maximized when the system dimensions are of the order of sqrt(2pi
D omega), where D is the diffusion constant. We compare our results to the
interface spin pumping theory of A. Brataas et al. [Phys. Rev. B 66, 060404(R)
(2002)].",0509100v1
2005-09-10,Theory of Magnetodynamics Induced by Spin Torque in Perpendicularly Magnetized Thin Films,"A nonlinear model of spin wave excitation using a point contact in a thin
ferromagnetic film is introduced. Large-amplitude magnetic solitary waves are
computed, which help explain recent spin-torque experiments. Numerical
simulations of the fully nonlinear model predict excitation frequencies in
excess of 0.2 THz for contact diameters smaller than 6 nm. Simulations also
predict a saturation and red shift of the frequency at currents large enough to
invert the magnetization under the point contact. The theory is approximated by
a cubic complex Ginzburg-Landau type equation. The mode's nonlinear frequency
shift is found by use of perturbation techniques, whose results agree with
those of direct numerical simulations.",0509265v1
2005-09-20,Magnetism and superconductivity of strongly correlated electrons on the triangular lattice,"We investigate the phase diagram of the \tj Model on a triangular lattice
using a Variational Monte-Carlo approach. We use an extended set of Gutzwiller
projected fermionic trial wave-functions allowing for simultaneous magnetic and
superconducting order parameters. We obtain energies at zero doping for the
spin-1/2 Heisenberg model in very good agreement with the best estimates. Upon
electron doping (with a hopping integral $t<0$) this phase is surprisingly
stable variationally up to $n\approx 1.4$, while the $d_{x^{2}-y^{2}}+i d_{xy}$
order parameter is rather weak and disappears at $n\approx 1.1$. For hole
doping however the coplanar magnetic state is almost immediately destroyed and
$d_{x^{2}-y^{2}}+i d_{xy}$ superconductivity survives down to $n\approx 0.8$.
For lower $n$, between 0.2 and 0.8, we find saturated ferromagnetism. Moreover,
there is evidence for a narrow spin density wave phase around $n\approx 0.8$.
Commensurate flux phases were also considered, but these turned out {\em not}
to be competitive at finite doping.",0509520v2
2006-03-10,A microspectroscopic study of the electronic homogeneity of ordered and disordered Sr2FeMoO6,"Besides a drastic reduction in saturation magnetization of disordered
Sr2FeMoO6 compared to highly ordered samples, magnetizations as a function of
the temperature for different disordered samples may also show qualitatively
different behaviors. We investigate the origin of such diversity by performing
spatially resolved photoemission spectroscopy on various disordered samples.
Our results establish that extensive electronic inhomogeneity, arising most
probably from an underlying chemical inhomogeneity in disordered samples is
responsible for the observed magnetic inhomogeneity. It is further pointed out
that these inhomogeneities are connected with composition fluctuations of the
type Sr2Fe1+xMo1-xO6 with Fe-rich (x>0) and Mo-rich (x<0) regions.",0603291v1
2006-04-15,Anisotropic Dependence of Giant Magneto-Impedance of Amorphous Ferromagnetic Ribbon on Biasing Field,"The magneto-impedance (MI) in amorphous ribbon of nominal composition
Fe73.5Nb3Cu1Si13.5B9 has been measured at 1MHz and at room temperature for
different configurations of exciting a.c and biasing d.c. fields. A large drop
in both resistance and reactance is observed as a function of d.c magnetic
field. When the d.c and a.c fields are parallel but normal to the axis of
ribbon, smaller magnetic field is needed to reduce the impedance to its small
saturated value compared to the situation when fields are along the axis of
ribbon. Larger d.c. field is required to lower the impedance when the d.c field
acts perpendicular to the plane of the ribbon. Such anisotropy in
magneto-impedance is related to the anisotropic response of the magnetization
of ribbon. The large change of impedance is attributed to large variation of
a.c permeability on the direction and magnitude of the dc biasing field.",0604382v2
2006-09-23,Epitaxial growth and the magnetic properties of orthorhombic YTiO3 thin films,"High-quality YTiO3 thin films were grown on LaAlO3 (110) substrates at low
oxygen pressures (<10-8 Torr) using pulsed laser deposition. The in-plane
asymmetric atomic arrangements at the substrate surface allowed us to grow
epitaxial YTiO3 thin films, which have an orthorhombic crystal structure with
quite different a- and b-axes lattice constants. The YTiO3 film exhibited a
clear ferromagnetic transition at 30 K with a saturation magnetization of about
0.7 uB/Ti. The magnetic easy axis was found to be along the [1-10] direction of
the substrate, which differs from the single crystal easy axis direction, i.e.,
[001].",0609602v1
2006-10-04,Cu-NMR study on the disordered quantum spin magnet with the Bose-glass ground state,"Cu-NMR study has been performed on the disordered spin-gap system
Tl1-xKxCuCl3 In the high-field H > HC=\Delta/\mu_B, where \Delta is the
spin-gap, the hyperfine field becomes extremely inhomogeneous at low
temperatures due to the field-induced magnetic order, indicating that the
ordered spin state must be different from the pure TlCuCl3. In the low field H
< HC, a saturating behavior in the longitudinal nuclear spin relaxation rate
1/T1 was observed at low temperatures, indicating existence of the magnetic
ground state proposed to be Bose-glass phase by Fisher.",0610101v1
2006-10-11,Engineering Exchange Coupling in Double Elliptic Quantum Dots,"Coupled elliptic quantum dots with different aspect ratios containing up to
two electrons are studied using a model confinement potential in the presence
of magnetic fields. Single and two particle Schroedinger equations are solved
using numerical exact diagonolization to obtain the exchange energy and
chemical potentials. As the ratio between the confinement strengths in
directions perpendicular and parallel to the coupling direction of the double
dots increases, the exchange energy at zero magnetic field increases, while the
magnetic field of the singlet-triplet transition decreases. By investigating
the charge stability diagram, we find that as inter-dot detuning increases, the
absolute value of the exchange energy increases superlinearly followed by
saturation. This behavior is attributed to the electron density differences
between the singlet and triplet states in the assymetric quantum dot systems.",0610281v1
2006-10-11,Proton-induced magnetic order in carbon: SQUID measurements,"In this work we have studied systematically the changes in the magnetic
behavior of highly oriented pyrolytic graphite (HOPG) samples after proton
irradiation in the MeV energy range. Superconducting quantum interferometer
device (SQUID) results obtained from samples with thousands of localized spots
of micrometer size as well on samples irradiated with a broad beam confirm
previously reported results. Both, the para- and ferromagnetic contributions
depend strongly on the irradiation details. The results indicate that the
magnetic moment at saturation of spots of micrometer size is of the order of
$10^{-10}$ emu.",0610293v1
2007-01-31,Nuclear Magnetic Resonance Study of Ultrananocrystalline Diamonds,"We report on a nuclear magnetic resonance (NMR) study of ultrananocrystalline
diamond (UNCD) materials produced by detonation technique. Analysis of the 13C
and 1H NMR spectra, spin-spin and spin-lattice relaxation times in purified
UNCD samples is presented. Our measurements show that UNCD particles consist of
a diamond core that is partially covered by a sp2-carbon fullerene-like shell.
The uncovered part of outer diamond surface comprises a number of hydrocarbon
groups that saturate the dangling bonds. Our findings are discussed along with
recent calculations of the UNCD structure. Significant increase in the
spin-lattice relaxation rate (in comparison with that of natural diamond), as
well as stretched exponential character of the magnetization recovery, are
attributed to the interaction of nuclear spins with paramagnetic centers which
are likely fabrication-driven dangling bonds with unpaired electrons. We show
that these centers are located mainly at the interface between the diamond core
and shell.",0701771v1
1992-08-31,Electric-Magnetic Duality and Supersymmetry in Stringy Black Holes,"We present a generalization of the $U(1)^{2}$ charged dilaton black holes
family whose main feature is that both $U(1)$ fields have electric and magnetic
charges, the axion field still being trivial. We show the supersymmetry of
these solutions in the extreme case, in which the corresponding generalization
of the Bogomolnyi bound is saturated and a naked singularity is on the verge of
being visible to external observers. Then we study the action of a subset of
the $SL(2,R)$ group of electric-magnetic duality rotations that generates a
non-trivial axion field on those solutions. This group of transformations is an
exact symmetry of the $N=4$ $d=4$ ungauged supergravity equations of motion. It
has been argued recently that it could be an exact symmetry of the full
effective string theory. The generalization of the Bogomolnyi bound is
invariant under the full $SL(2,R)$ and the solutions explicitly rotated are
shown to be supersymmetric if the originals are. We conjecture that any
$SL(2,R)$ transformation will preserve supersymmetry.",9208078v1
2000-07-11,Type-I strings on magnetised orbifolds and brane transmutation,"In the presence of internal magnetic fields, a D9 brane can acquire a D5 (or
anti-D5) R-R charge, and can therefore contribute to the corresponding tadpole.
In the resulting vacua, supersymmetry is generically broken and tachyonic
instabilities are present. However, suitable choices for the magnetic fields,
corresponding to self-dual configurations in the internal space, can yield new
chiral supersymmetric vacua with gauge groups of reduced rank, where the
magnetic energy saturates, partly or fully, the negative tension of the O5+
planes. These models contain Green-Schwarz couplings to untwisted R-R forms not
present in conventional orientifolds.",0007090v2
2000-09-15,Exact time-correlation functions of quantum Ising chain in a kicking transversal magnetic field,"Spectral analysis of the {\em adjoint} propagator in a suitable Hilbert space
(and Lie algebra) of quantum observables in Heisenberg picture is discussed as
an alternative approach to characterize infinite temperature dynamics of
non-linear quantum many-body systems or quantum fields, and to provide a bridge
between ergodic properties of such systems and the results of classical ergodic
theory. We begin by reviewing some recent analytic and numerical results along
this lines. In some cases the Heisenberg dynamics inside the subalgebra of the
relevant quantum observables can be mapped explicitly into the (conceptually
much simpler) Schr\"" odinger dynamics of a single one-(or few)-dimensional
quantum particle. The main body of the paper is concerned with an application
of the proposed method in order to work out explicitly the general spectral
measures and the time correlation functions in {\em a quantum Ising spin 1/2
chain in a periodically kicking transversal magnetic field}, including the
results for the simpler autonomous case of a static magnetic field in the
appropriate limit. The main result, being a consequence of a purely continuous
non-trivial part of the spectrum, is that the general time-correlation
functions decay to their saturation values as $t^{-3/2}$.",0009031v1
2003-06-28,Self-similar turbulent dynamo,"The amplification of magnetic fields in a highly conducting fluid is studied
numerically. During growth, the magnetic field is spatially intermittent: it
does not uniformly fill the volume, but is concentrated in long thin folded
structures. Contrary to a commonly held view, intermittency of the folded field
does not increase indefinitely throughout the growth stage if diffusion is
present. Instead, as we show, the probability-density function (PDF) of the
field strength becomes self-similar. The normalized moments increase with
magnetic Prandtl number in a powerlike fashion. We argue that the
self-similarity is to be expected with a finite flow scale and system size. In
the nonlinear saturated state, intermittency is reduced and the PDF is
exponential. Parallels are noted with self-similar behavior recently observed
for passive-scalar mixing and for map dynamos.",0306059v3
2007-04-29,Critical state analysis of orthogonal flux interactions in pinned superconductors,"We show that, based on the critical state model for flux-line pinning in hard
superconductors, one can assess the magnetic moment relaxation induced by the
oscillations of a perpendicular magnetic field. Our theory follows a recent
proposal of using phenomenological 2D modeling for the description of crossed
field dynamics in high-T$_c$ superconductors [{\tt arXiv:cond-mat/0703330}].
  Stationary regimes with either saturation to metastable configurations, or
complete decay to the thermodynamic equilibrium are obtained. The transition
between both types of response is related to the disappearance of a flux free
core within the sample. As a common feature, a step-like dependence in the time
relaxation is predicted for both cases. The theory may be applied to long bars
of arbitrary and non homogeneous cross section, under in-plane magnetic field
processes.",0704.3830v1
2007-05-24,Nonequilibrium Dynamics of Anisotropic Large Spins in the Kondo Regime: Time-Dependent Numerical Renormalization Group Analysis,"We investigate the time-dependent Kondo effect in a single-molecule magnet
(SMM) strongly coupled to metallic electrodes. Describing the SMM by a Kondo
model with large spin S > 1/2, we analyze the underscreening of the local
moment and the effect of anisotropy terms on the relaxation dynamics of the
magnetization. Underscreening by single-channel Kondo processes leads to a
logarithmically slow relaxation, while finite uniaxial anisotropy causes a
saturation of the SMM's magnetization. Additional transverse anisotropy terms
induce quantum spin tunneling and a pseudospin-1/2 Kondo effect sensitive to
the spin parity.",0705.3654v2
2007-06-28,Coherent Magnetization Precession in GaMnAs induced by Ultrafast Optical Excitation,"We use femtosecond optical pulses to induce, control and monitor
magnetization precession in ferromagnetic Ga0.965Mn0.035As. At temperatures
below ~40 K we observe coherent oscillations of the local Mn spins, triggered
by an ultrafast photoinduced reorientation of the in-plane easy axis. The
amplitude saturation of the oscillations above a certain pump intensity
indicates that the easy axis remains unchanged above ~TC/2. We find that the
observed magnetization precession damping (Gilbert damping) is strongly
dependent on pump laser intensity, but largely independent on ambient
temperature. We provide a physical interpretation of the observed light-induced
collective Mn-spin relaxation and precession.",0706.4270v2
2007-07-21,Ferromagnetism as a universal feature of nanoparticles of the otherwise nonmagnetic oxides,"Room-temperature ferromagnetism has been observed in the nanoparticles (7 -
30 nm dia) of nonmagnetic oxides such as CeO2, Al2O3, ZnO, In2O3 and SnO2. The
saturated magnetic moments in CeO_2 and Al_2O_3 nanoparticles are comparable to
those observed in transition metal doped wide band semiconducting oxides. The
other oxide nanoparticles show somewhat lower values of magnetization but with
a clear hysteretic behavior. Conversely, the bulk samples obtained by sintering
the nanoparticles at high temperatures in air or oxygen became diamagnetic. As
there were no magnetic impurities present, we assume that the origin of
ferromagnetism may be due to the exchange interactions between localized
electron spin moments resulting from oxygen vacancies at the surfaces of
nanoparticles. We suggest that ferromagnetism may be a universal characteristic
of nanopartilces of metal oxides",0707.3183v1
2007-08-08,"Magnetic properties of Gd_xY_{1-x}Fe_2Zn_{20}: dilute, large, $\textbf {S}$ moments in a nearly ferromagnetic Fermi liquid","Single crystals of the dilute, rare earth bearing, pseudo-ternary series,
Gd_xY_{1-x}Fe_2Zn_{20} were grown out of Zn-rich solution. Measurements of
magnetization, resistivity and heat capacity on Gd_xY_{1-x}Fe_2Zn_{20} samples
reveal ferromagnetic order of Gd^{3+} local moments across virtually the whole
series ($x \geq 0.02$). The magnetic properties of this series, including the
ferromagnetic ordering, the reduced saturated moments at base temperature, the
deviation of the susceptibilities from Curie-Weiss law and the anomalies in the
resistivity, are understood within the frame work of dilute, $\textbf {S}$
moments (Gd^{3+}) embedded in a nearly ferromagnetic Fermi liquid
(YFe_2Zn_{20}). The s-d model is employed to further explain the variation of
$T_{\mathrm{C}}$ with x as well as the temperature dependences of of the
susceptibilities.",0708.1170v1
2007-08-15,"Effects of selective dilution on the magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}M'_xO_3 (M' = Al, Ti)","The magnetic lattice of mixed-valence Mn ions in
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ is selectively diluted by partial substitution of
Al or Ti for Mn. The ferromagnetic transition temperature $T_\mathrm{c}$ and
the saturation magnetization $M_\mathrm{s}$ both decrease with substitution. By
presenting the data in terms of selective dilution, $T_\mathrm{c}$ in the
low-doping region is found to follow the relation
$T_\mathrm{c}=T_\mathrm{c0}(1-n_\mathrm{p})$, where $T_\mathrm{c0}$ refers to
the undiluted system and $n_\mathrm{p}$ is the dilution concentration defined
as $n_\mathrm{p}=x/0.7$ or $n_\mathrm{p}=x/0.3$ for $M^\prime=$ Al or Ti,
respectively. The scaling behavior of $T_\mathrm{c}(n_\mathrm{p})$ can be
analyzed in the framework of the molecular-field theory and still valid when Mn
is substituted by both Al and Ti. The results are discussed with respect to the
contributions from ferromagnetic double exchange and other possible
antiferromagnetic superexchange interactions coexisting in the material.",0708.2025v1
2007-08-21,Magnetic and transport properties of the one-dimensional ferromagnetic Kondo lattice model with an impurity,"We have studied the ferromagnetic Kondo lattice model (FKLM) with an Anderson
impurity on finite chains with numerical techniques. We are particularly
interested in the metallic ferromagnetic phase of the FKLM. This model could
describe either a quantum dot coupled to one-dimensional ferromagnetic leads
made with manganites or a substitutional transition metal impurity in a MnO
chain. We determined the region in parameter space where the impurity is empty,
half-filled or doubly-occupied and hence where it is magnetic or nonmagnetic.
The most important result is that we found, for a wide range of impurity
parameters and electron densities where the impurity is magnetic, a singlet
phase located between two saturated ferromagnetic phases which correspond
approximately to the empty and double-occupied impurity states. Transport
properties behave in general as expected as a function of the impurity
occupancy and they provide a test for a recently developed numerical approach
to compute the conductance. The results obtained could be in principle
reproduced experimentally in already existent related nanoscopic devices or in
impurity doped MnO nanotubes.",0708.2826v2
2007-08-24,Influence of the L21 ordering degree on the magnetic properties in Co2MnSi Heusler films,"We report on the influence of the improved L21 ordering degree on the
magnetic properties of Co2MnSi Heusler films. Different fractions of the L21
phase are obtained by different post-growth annealing temperatures ranging from
350 degC to 500 degC. Room temperature magneto-optical Kerr effect measurements
reveal an increase of the coercivity at an intermediate annealing temperature
of 425 degC, which is a fingerprint of an increased number of pinning centers
at this temperature. Furthermore, Brillouin light scattering studies show that
the improvement of the L21 order in the Co2MnSi films is correlated with a
decrease of the saturation magnetization by about 9%. The exchange stiffness
constant of Co2MnSi, however, increases by about 8% when the L21 order is
improved. Moreover, we observe a drop of the cubic anisotropy constant K1 by a
factor of 10 for an increasing amount of the L21 phase.",0708.3303v1
2007-11-13,Magnetism of one-dimensional Wigner lattices and its impact on charge order,"The magnetic phase diagram of the quarter-filled generalized Wigner lattice
with nearest- and next-nearest-neighbor hopping t_1 and t_2 is explored. We
find a region at negative t_2 with fully saturated ferromagnetic ground states
that we attribute to kinetic exchange. Such interaction disfavors
antiferromagnetism at t_2 <0 and stems from virtual excitations across the
charge gap of the Wigner lattice, which is much smaller than the Mott-Hubbard
gap proportional to U. Remarkably, we find a strong dependence of the charge
structure factor on magnetism even in the limit U to infinity, in contrast to
the expectation that charge ordering in the Wigner lattice regime should be
well described by spinless fermions. Our results, obtained using the
density-matrix renormalization group and exact diagonalization, can be
transparently explained by means of an effective low-energy Hamiltonian.",0711.1990v2
2008-01-08,Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures,"We report observations of tunneling anisotropic magnetoresitance (TAMR) in
vertical tunnel devices with a ferromagnetic multilayer-(Co/Pt) electrode and a
non-magnetic Pt counter-electrode separated by an AlOx barrier. In stacks with
the ferromagnetic electrode terminated by a Co film the TAMR magnitude
saturates at 0.15% beyond which it shows only weak dependence on the magnetic
field strength, bias voltage, and temperature. For ferromagnetic electrodes
terminated by two monolayers of Pt we observe order(s) of magnitude enhancement
of the TAMR and a strong dependence on field, temperature and bias. Discussion
of experiments is based on relativistic ab initio calculations of magnetization
orientation dependent densities of states of Co and Co/Pt model systems.",0801.1192v1
2008-03-04,Expanding color flux tubes and instabilities,"We present an analytic study of the physics of the glasma which is a strong
classical gluon field created at early stage of high-energy heavy-ion
collisions. Our analysis is based on the picture that the glasma just after the
collision is made of color electric and magnetic flux tubes extending in the
longitudinal direction with their diameters of the order of 1/Q_s (Q_s is the
saturation scale of the colliding nuclei). We find that both the electric and
magnetic flux tubes expand outwards and the field strength inside the flux tube
decays rapidly in time. Next we investigate whether there exist instabilities
against small rapidity-dependent perturbations for a fixed color configuration.
We find that the magnetic background field exhibits an instability induced by
the fluctuations in the lowest Landau level, and it grows in the time scale of
1/Q_s. For the electric background field we find no apparent instability while
the possible relation to the Schwinger mechanism for particle pair creations is
suggested.",0803.0410v3
2008-06-04,"Broadband electrical detection of spin excitations in (Ga,Mn)As using a photovoltage technique","We report on microwave photovoltage and simultaneous magnetotransport
measurements in a (Ga,Mn)As film oriented normal to the magnetic field. We
detect the ferromagnetic resonance over a broad frequency range of 2 GHz to
18.5 GHz and determine the spectroscopic g-factor and separate the Gilbert from
the inhomogeneous contribution to magnetization relaxation. Temperature
dependent measurements below the saturation magnetization indicate that the
photovoltage signal can serve as a sensitive tool to study the crystal
anisotropy. We demonstrate that the combination of spin dynamics with charge
transport is a promising tool to study microstructured ferromagnetic
semiconductor samples.",0806.0785v1
2008-07-09,Lattice and magnetic instabilities in CaFe2As2: A single crystal neutron diffraction study,"Neutron diffraction measurements of a high quality single crystal of CaFe2As2
are reported. A sharp transition was observed between the high temperature
tetragonal and low temperature orthorhombic structures at TS = 172.5K (on
cooling) and 173.5K (on warming). Coincident with the structural transition we
observe a rapid, but continuous, ordering of the Fe moments, in a commensurate
antiferromagnetic structure is observed, with a saturated moment of
0.80(5)muB/Fe directed along the orthorhombic a-axis. The hysteresis of the
structural transition is 1K between cooling and warming and is consistent with
previous thermodynamic, transport and single crystal x-ray studies. The
temperature onset of magnetic ordering shifts rigidly with the structural
transition providing the clearest evidence to date of the coupling between the
structural and magnetic transitions in this material and the broader class of
iron arsenides.",0807.1525v3
2008-08-22,Phases and magnetization process of an anisotropic Shastry-Sutherland model,"We examine ground state properties of the spin-1/2 easy-axis Heisenberg model
on the Shastry-Sutherland lattice with ferromagnetic transverse spin exchange
using quantum Monte Carlo and degenerate perturbation theory. For vanishing
transverse exchange, the model reduces to an antiferromagnetic Ising model that
besides Neel order harbors regions of extensive ground state degeneracy. In the
quantum regime, we find a dimerized phase of triplet states, separated from the
Neel ordered phase by a superfluid. The quantum phase transitions between these
phases are characterized. The magnetization process shows a magnetization
plateau at 1/3 of the saturation value, that persists down to the Ising limit,
and a further plateau at 1/2 only in the quantum regime. For both plateaus, we
determine the crystalline patterns of the localized triplet excitations. No
further plateaus nor supersolid phases are found in this model.",0808.3104v1
2008-09-05,Carrier-mediated antiferromagnetic interlayer exchange coupling in diluted magnetic semiconductor multilayers Ga$_{1-x}$Mn$_x$As/GaAs:Be,"We use neutron reflectometry to investigate the interlayer exchange coupling
between Ga$_{0.97}$Mn$_{0.03}$As ferromagnetic semiconductor layers separated
by non-magnetic Be-doped GaAs spacers. Polarized neutron reflectivity measured
below the Curie temperature of Ga$_{0.97}$Mn$_{0.03}$As reveals a
characteristic splitting at the wave vector corresponding to twice the
multilayer period, indicating that the coupling between the ferromagnetic
layers are antiferromagnetic (AFM). When the applied field is increased to
above the saturation field, this AFM coupling is suppressed. This behavior is
not observed when the spacers are undoped, suggesting that the observed AFM
coupling is mediated by charge carriers introduced via Be doping. The behavior
of magnetization of the multilayers measured by DC magnetometry is consistent
with the neutron reflectometry results.",0809.0955v1
2008-09-22,The T=0 random-field Ising model on a Bethe lattice with large coordination number: hysteresis and metastable states,"In order to elucidate the relationship between rate-independent hysteresis
and metastability in disordered systems driven by an external field, we study
the Gaussian RFIM at T=0 on regular random graphs (Bethe lattice) of finite
connectivity z and compute to O(1/z) (i.e. beyond mean-field) the quenched
complexity associated with the one-spin-flip stable states with magnetization m
as a function of the magnetic field H. When the saturation hysteresis loop is
smooth in the thermodynamic limit, we find that it coincides with the envelope
of the typical metastable states (the quenched complexity vanishes exactly
along the loop and is positive everywhere inside). On the other hand, the
occurence of a jump discontinuity in the loop (associated with an infinite
avalanche) can be traced back to the existence of a gap in the magnetization of
the metastable states for a range of applied field, and the envelope of the
typical metastable states is then reentrant. These findings confirm and
complete earlier analytical and numerical studies.",0809.3774v1
2008-09-24,Probing multi-band superconductivity and magnetism in SmFeAsO$_{0.8}$F$_{0.2}$ single crystals by high-field vortex torque magnetometry,"To probe manifestations of multiband superconductivity in oxypnictides, we
measured the angular dependence of magnetic torque $\tau(\theta)$ in the mixed
state of SmO$_{0.8}$F$_{0.2}$FeAs single crystals as functions of temperature
$T$ and high magnetic field $H$ up to 30 T. We show that the effective mass
anisotropy parameter $\gamma$ extracted from $\tau(\theta)$, can be greatly
overestimated if the strong paramagnetism of Sm or Fe ions is not properly
taken into account. The correctly extracted $\gamma$ depends on both $T$ and
$H$, saturating at $\gamma \simeq 9$ at lower temperatures. Neither the London
penetration depth nor the superfluid density is affected by high fields fields
up to the upper critical field. Our results indicate two strongly-coupled
superconducting gaps of nearly equal magnitudes.",0809.4223v2
2008-10-22,Magnetic hyperthermia in single-domain monodisperse FeCo nanoparticles: Evidences for Stoner-Wohlfarth behaviour and large losses,"We report on hyperthermia measurements on a colloidal solution of 15 nm
monodisperse FeCo nanoparticles (NPs). Losses as a function of the magnetic
field display a sharp increase followed by a plateau, which is what is expected
for losses of ferromagnetic single-domain NPs. The frequency dependence of the
coercive field is deduced from hyperthermia measurement and is in quantitative
agreement with a simple model of non-interacting NPs. The measured losses (1.5
mJ/g) compare to the highest of the literature, though the saturation
magnetization of the NPs is well below the bulk one.",0810.4109v1
2008-10-24,Hyperactivated resistance in TiN films on the insulating side of the disorder-driven superconductor-insulator transition,"We investigate the insulating phase that forms in a titanium nitride film in
a close vicinity of the disorder-driven superconductor-insulator transition. In
zero magnetic field the temperature dependence of the resistance reveals a
sequence of distinct regimes upon decreasing temperature crossing over from
logarithmic to activated behavior with the variable-range hopping squeezing in
between. In perpendicular magnetic fields below 2 T, the thermally activated
regime retains at intermediate temperatures, whereas at ultralow temperatures,
the resistance increases faster than that of the thermally activated type. This
indicates a change of the mechanism of the conductivity. We find that at higher
magnetic fields the thermally activated behavior disappears and the
magnetoresistive isotherms saturate towards the value close to quantum
resistance h/e^2.",0810.4351v2
2008-11-20,How the Kondo ground state avoids the orthogonality catastrophe,"In the presence of a magnetic impurity the spin-up and down band states are
modified differently by the impurity. If the multi-electron scalar product
(MESP) between the occupied spin-up and down states approaches zero then this
defines an orthogonality catastrophe. In the present paper the MESP is
investigated for the FAIR (Friedel Artificial Iserted Resonance) solution for a
Friedel-Anderson impurity. A basis of Wilson states is used. The MESP is
numerically determined for the (enforced) magnetic, the singlet, and the
triplet states as a function of the number N of Wilson states. The magnetic and
the triplet state show an exponentially decreasing MESP as a function of N.
Surprisingly it is not the number of states which causes this decrease. It is
instead the energy separation of the highest occupied state from the Fermi
energy which determines the reduction of the MESP. In the singlet state the
ground-state requires a finite MESP to optimize its energy. As a consequence
there is no orthogonality catastrophe. The MESP approaches a saturation value
as function of N.",0811.3259v1
2008-12-04,"Two-Dimensional particle-in-cell simulations of the nonresonant, cosmic-ray driven instability in SNR shocks","In supernova remnants, the nonlinear amplification of magnetic fields
upstream of collisionless shocks is essential for the acceleration of cosmic
rays to the energy of the ""knee"" at 10^{15.5}eV. A nonresonant instability
driven by the cosmic ray current is thought to be responsible for this effect.
We perform two-dimensional, particle-in-cell simulations of this instability.
We observe an initial growth of circularly polarized non-propagating magnetic
waves as predicted in linear theory. It is demonstrated that in some cases the
magnetic energy density in the growing waves, can grow to at least 10 times its
initial value. We find no evidence of competing modes, nor of significant
modification by thermal effects. At late times we observe saturation of the
instability in the simulation, but the mechanism responsible is an artefact of
the periodic boundary conditions and has no counterpart in the supernova-shock
scenario.",0812.0901v2
2008-12-11,Cascade of magnetic-field-induced quantum phase transitions in a spin $\bm{1/2}$ triangular-lattice antiferromagnet,"We report magnetocaloric and magnetic-torque evidence that in
Cs$_{2}$CuBr$_{4}$ -- a geometrically frustrated Heisenberg $S=1/2$
triangular-lattice antiferromagnet -- quantum fluctuations stabilize a series
of spin states at simple increasing fractions of the saturation magnetization
$M_{s}$. Only the first of these states -- at $M={1/3}M_{s}$ -- has been
theoretically predicted. We discuss how the higher fraction quantum states
might arise and propose model spin arrangements. We argue that the first-order
nature of the transitions into those states is due to strong lowering of the
energies by quantum fluctuations, with implications for the general character
of quantum phase transitions in geometrically frustrated systems.",0812.2077v2
2008-12-17,The antiferromagnetic spin-1/2 Heisenberg model on the square lattice in a magnetic field,"We study the field dependence of the antiferromagnetic spin-1/2 Heisenberg
model on the square lattice by means of exact diagonalizations. In a first
part, we calculate the spin-wave velocity, the spin-stiffness, and the magnetic
susceptibility and thus determine the microscopic parameters of the low-energy
long-wavelength description. In a second part, we present a comprehensive study
of dynamical spin correlation functions for magnetic fields ranging from zero
up to saturation. We find that at low fields, magnons are well defined in the
whole Brillouin zone, but the dispersion is substantially modified by quantum
fluctuations compared to the classical spectrum. At higher fields, decay
channels open and magnons become unstable with respect to multi-magnon
scattering. Our results directly apply to inelastic neutron scattering
experiments.",0812.3420v3
2009-03-02,Attenuation and damping of electromagnetic fields: Influence of inertia and displacement current,"New results for attenuation and damping of electromagnetic fields in rigid
conducting media are derived under the conjugate influence of inertia due to
charge carriers and displacement current. Inertial effects are described by a
relaxation time for the current density in the realm of an extended Ohm's law.
The classical notions of poor and good conductors are rediscussed on the basis
of an effective electric conductivity, depending on both wave frequency and
relaxation time. It is found that the attenuation for good conductors at high
frequencies depends solely on the relaxation time. This means that the
penetration depth saturates to a minimum value at sufficiently high
frequencies. It is also shown that the actions of inertia and displacement
current on damping of magnetic fields are opposite to each other. That could
explain why the classical decay time of magnetic fields scales approximately as
the diffusion time. At very small length scales, the decay time could be given
either by the relaxation time or by a fraction of the diffusion time, depending
whether inertia or displacement current, respectively, would prevail on
magnetic diffusion.",0903.0210v1
2009-04-15,"Unified description of pairing, trionic and quarteting states for one-dimensional SU(4) attractive fermions","Paired states, trions and quarteting states in one-dimensional SU(4)
attractive fermions are investigated via exact Bethe ansatz calculations. In
particular, quantum phase transitions are identified and calculated from the
quarteting phase into normal Fermi liquid, trionic states and spin-2 paired
states which belong to the universality class of linear field-dependent
magnetization in the vicinity of critical points. Moreover, unified exact
results for the ground state energy, chemical potentials and complete phase
diagrams for isospin $S=1/2, 1, 3/2$ attractive fermions with external fields
are presented. Also identified are the magnetization plateaux of $m^z=M_s/3$
and $m^z=2M_s/3$, where $M_s$ is the magnetization saturation value. The
universality of finite-size corrections and collective dispersion relations
provides a further test ground for low energy effective field theory.",0904.2269v1
2009-07-21,Incommensurate spin correlations induced by magnetic Fe ions substituted into overdoped Bi1.75Pb0.35Sr1.90CuO6+z,"Spin correlations in the overdoped region of Bi1.75Pb0.35Sr1.90CuO6+z have
been explored with Fe-doped single crystals characterized by neutron
scattering, muon-spin-rotation (muSR) spectroscopy, and magnetic susceptibility
measurements. Static incommensurate spin correlations induced by the Fe spins
are revealed by elastic neutron scattering. The resultant incommensurability
delta is unexpectedly large (~0.2 r.l.u.), as compared with delta ~ 1/8 in
overdoped superconductor La2-xSrxCuO4. Intriguingly, the large delta in this
overdoped region is close to the hole concentration p. This result is
reminiscent of the delta ~ p trend observed in underdoped La2-xSrxCuO4;
however, it is inconsistent with the saturation of delta in the latter compound
in the overdoped regime. While our findings in Fe-doped
Bi1.75Pb0.35Sr1.90CuO6+z support the commonality of incommensurate spin
correlations in high-Tc cuprate superconductors, they also suggest that the
magnetic response might be dominated by a distinct mechanism in the overdoped
region.",0907.3590v2
2009-08-04,Simulating Supersonic Turbulence in Magnetized Molecular Clouds,"We present results of large-scale three-dimensional simulations of weakly
magnetized supersonic turbulence at grid resolutions up to 1024^3 cells. Our
numerical experiments are carried out with the Piecewise Parabolic Method on a
Local Stencil and assume an isothermal equation of state. The turbulence is
driven by a large-scale isotropic solenoidal force in a periodic computational
domain and fully develops in a few flow crossing times. We then evolve the flow
for a number of flow crossing times and analyze various statistical properties
of the saturated turbulent state. We show that the energy transfer rate in the
inertial range of scales is surprisingly close to a constant, indicating that
Kolmogorov's phenomenology for incompressible turbulence can be extended to
magnetized supersonic flows. We also discuss numerical dissipation effects and
convergence of different turbulence diagnostics as grid resolution refines from
256^3 to 1024^3 cells.",0908.0378v1
2009-09-28,Kinetic simulations of turbulent magnetic-field growth by streaming cosmic rays,"Efficient acceleration of cosmic rays (via the mechanism of diffusive shock
acceleration) requires turbulent, amplified magnetic fields in the shock's
upstream region. We present results of multidimensional particle-in-cell
simulations aimed at observing the magnetic field amplification that is
expected to arise from the cosmic-ray current ahead of the shock, and the
impact on the properties of the upstream interstellar medium. We find that the
initial structure and peak strength of the amplified field is somewhat
sensitive to the choice of parameters, but that the field growth saturates in a
similar manner in all cases: the back-reaction on the cosmic rays leads to
modification of their rest-frame distribution and also a net transfer of
momentum to the interstellar medium, substantially weakening their relative
drift while also implying the development of a modified shock. The upstream
medium becomes turbulent, with significant spatial fluctuations in density and
velocity, the latter in particular leading to moderate upstream heating; such
fluctuations will also have a strong influence on the shock structure.",0909.5212v1
2009-10-08,Solar Magnetic Field Signatures in Helioseismic Splitting Coefficients,"Normal modes of oscillation of the Sun are useful probes of the solar
interior. In this work, we use the even-order splitting coefficients to study
the evolution of magnetic fields in the convection zone over solar cycle 23,
assuming that the frequency splitting is only due to rotation and a large scale
magnetic field. We find that the data are best fit by a combination of a
poloidal field and a double-peaked near-surface toroidal field. The toroidal
fields are centered at r=0.999R_solar and r=0.996R_solar and are confined to
the near-surface layers. The poloidal field is a dipole field. The peak
strength of the poloidal field is 124 +/- 17G. The toroidal field peaks at 380
+/- 30G and 1.4 +/- 0.2kG for the shallower and deeper fields respectively. The
field strengths are highly correlated with surface activity. The toroidal field
strength shows a hysteresis-like effect when compared to the global 10.7 cm
radio flux. The poloidal field strength shows evidence of saturation at high
activity.",0910.1597v1
2009-10-11,"Magnetic and electrical properties of RCo2Mn (R=Ho, Er) compounds","The RCo2Mn (R= Ho and Er) alloys, crystallizing in the cubic MgCu2-type
structure, are isostructural to RCo2 compounds. The excess Mn occupies both the
R and the Co atomic positions. Magnetic, electrical and heat capacity
measurements have been done in these comounds. The Curie temperature is found
to be 248 K and 222 K for HoCo2Mn and ErCo2Mn respectively, which are
considerably higher than that of the corresponding RCo2 compounds. Saturation
magnetization values calculated in these samples are less compared to that of
the corresponding RCo2 compounds. Heat capacity data have been fitted with the
nonmagnetic contribution with Debye temperature =250 K and electronic
coefficient=26 mJ mol^-1K^-2.",0910.2001v1
2009-11-11,Temperature dependent nucleation and annihilation of individual magnetic vortices,"We studied the temperature dependence of the magnetization reversal in
individual submicron permalloy disks with micro-Hall and bend-resistance
magnetometry. The nucleation field exhibits a nonmonotonic dependence with
positive and negative slopes at low and high temperatures, respectively, while
the annihilation field monotonically decreases with increasing temperature, but
with distinctly different slopes at low and high temperatures. Our analysis
suggests that at low temperatures vortex nucleation and annihilation proceeds
via thermal activation over an energy barrier, while at high temperatures they
are governed by a temperature dependence of the saturation magnetization.",0911.2267v1
2009-12-05,Electrical and magnetic transport properties of Fe3O4 thin films on GaAs (100) substrate,"Thin films of magnetite (Fe3O4) are grown on single crystal GaAs (100)
substrate by pulsed laser deposition. X ray diffraction (XRD) result shows the
(111) preferred orientation of the Fe3O4 film and x-ray photoelectron
spectroscopy confirm the presence of single phase Fe3O4 in the film. The
electrical transport property of the film shows the characteristic Verwey
transition at 122 K and below 110 K, the transport follows variable range
hopping type conduction mechanism. The film shows room temperature
magnetization hysteresis loop suggesting the ferrimagnetic behavior of the film
with saturation magnetization value close to 470 emu/cc.",0912.0979v1
2009-12-26,Theory of Combined Photoassociation and Feshbach Resonances in a Bose-Einstein Condensate,"We model combined photoassociation and Feshbach resonances in a Bose-Einstein
condensate, where the shared dissociation continuum allows for quantum
interference in losses from the condensate, as well as a dispersive-like shift
of resonance. A simple analytical model, based on the limit of weakly bound
molecules, agrees well with numerical experiments that explicitly include
dissociation to noncondensate modes. For a resonant laser and an off-resonant
magnetic field, constructive interference enables saturation of the
photoassociation rate at user-friendly intensities, at a value set by the
interparticle distance. This rate limit is larger for smaller condensate
densities and, near the Feshbach resonance, approaches the rate limit for
magnetoassociation alone. Also, we find agreement with the unitary limit--set
by the condensate size--only for a limited range of near-resonant magnetic
fields. Finally, for a resonant magnetic field and an off-resonant laser,
magnetoassociation displays similar quantum interference and a dispersive-like
shift. Unlike photoassociation, interference and the fieldshift in resonant
magnetoassociation is tunable with both laser intensity and detuning. Also, the
dispersive-like shift of the Feshbach resonance depends on the size of the
Feshbach molecule, and is a signature of non-universal physics in a strongly
interacting system.",0912.5035v1
2009-12-30,Spin torque and critical currents for magnetic vortex nano-oscillator in nanopillars,"We calculated the main dynamic parameters of the spin polarized current
induced magnetic vortex oscillations in nanopillars, such as the range of
current density, where a vortex steady oscillations exist, the oscillation
frequency and orbit radius. We accounted for both the non-linear vortex
frequency and non-linear vortex damping. To describe the vortex excitations by
the spin polarized current we used a generalized Thiele approach to motion of
the vortex core as a collective coordinate. All the calculation results are
represented via the free layer sizes, saturation magnetization, Gilbert damping
and the degree of the spin polarization of the fixed layer. Predictions of the
developed model can be checked experimentally.",0912.5521v1
2010-01-06,Properties of Light Flavour Baryons in Hypercentral quark model,"The light flavour baryons are studied within the quark model using the hyper
central description of the three-body system. The confinement potential is
assumed as hypercentral coulomb plus power potential ($hCPP_\nu$) with power
index $\nu$. The masses and magnetic moments of light flavour baryons are
computed for different power index, $\nu$ starting from 0.5 to 1.5. The
predicted masses and magnetic moments are found to attain a saturated value
with respect to variation in $\nu$ beyond the power index $\nu>$ 1.0. Further
we computed transition magnetic moments and radiative decay width of light
flavour baryons. The results are in good agreement with known experimental as
well as other theoretical models.",1001.0849v2
2010-01-15,Pressure-induced new magnetic phase in Tl(Cu$_{0.985}$Mg$_{0.015}$)Cl$_3$ probed by muon spin rotation,"We carried out zero-field muon-spin-rotation (ZF-$\mu$SR) measurements in
hydrostatic pressures in impurity-doped quantum spin gap system
Tl(Cu$_{0.985}$Mg$_{0.015}$)Cl$_3$ to investigate microscopic magnetic
properties of the pressure-induced phase. The spontaneous muon spin precession,
which indicates the existence of a long-range coherent order, is observed in
pressures. With decreasing temperature in 3.1 kbar, the internal static
magnetic field at the muon sites {\it H}$_{\rm int}$ tends to saturate to 280
Oe around 4 K, however, decreases to 240 Oe at 2.3 K. These results suggest a
rearrangement of ordered spins, and we speculate that the oblique
antiferromagnetic phase, which is observed in the pressure of 14 kbar on the
pure TlCuCl$_3$, appears in the Mg-doped system in lower pressures.",1001.2601v1
2010-02-09,Magnetic Effects on Dielectric and Polarization Behavior of Multiferroic Hetrostructures,"PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3(PZT/LSMO) bilayer with surface roughness ~
1.8 nm thin films have been grown by pulsed laser deposition on LaAlO3(LAO)
substrates. High remnant polarization (30-54 micro C/cm2), dielectric
constant(400-1700), and well saturated magnetization were observed depending
upon the deposition temperature of the ferromagnetic layer and applied
frequencies. Giant frequency-dependent change in dielectric constant and loss
were observed above the ferromagnetic-paramagnetic temperature. The frequency
dependent dielectric anomalies are attributed to the change in metallic and
magnetic nature of LSMO and also the interfacial effect across the bilayer; an
enhanced magnetoelectric interaction may be due to the Parish-Littlewood
mechanism of inhomogeneity near the metal-dielectric interface.",1002.1988v1
2010-02-15,Optical determination and magnetic manipulation of single nitrogen-vacancy color center in diamond nanocrystal,"The controlled and coherent manipulation of individual quantum systems is a
fundamental key for the development of quantum information processing. The
nitrogen-vacancy (NV) color center in diamond is a promising system since its
photoluminescence is perfectly stable at room temperature and its electron spin
can be optically read-out at the individual level. We review here the
experiments currently realized in our laboratory, concerning the use of single
NV color center as single photon source and the coherent magnetic manipulation
of the electron spin associated to a single NV color center. Furthermore, we
demonstrate a nanoscopy experiment based on saturation absorption effect, which
allows to optically pin-point single NV color center at a sub-? resolution.
This opens a possibility to independently address two or multiple
magnetically-coupled single NV color centers, which is a necessary step toward
the realization of a diamond-based quantum computer.",1002.2902v1
2010-03-05,Finite size effects with variable range exchange coupling in thin-film Pd/Fe/Pd trilayers,"The magnetic properties of thin-film Pd/Fe/Pd trilayers in which an embedded
~1.5 A-thick ultrathin layer of Fe induces ferromagnetism in the surrounding Pd
have been investigated. The thickness of the ferromagnetic trilayer is
controlled by varying the thickness of the top Pd layer over a range from 8 A
to 56 A. As the thickness of the top Pd layer decreases, or equivalently as the
embedded Fe layer moves closer to the top surface, the saturated magnetization
normalized to area and the Curie temperature decrease whereas the coercivity
increases. These thickness-dependent observations for proximity-polarized
thin-film Pd are qualitatively consistent with finite size effects that are
well known for regular thin-film ferromagnets. The critical exponent $\beta$ of
the order parameter (magnetization) is found to approach the mean field value
of 0.5 as the thickness of the top Pd layer increases. The functional forms for
the thickness dependences, which are strongly modified by the nonuniform
exchange interaction in the polarized Pd, provide important new insights to
understanding nanomagnetism in two-dimensions.",1003.1305v1
2010-03-23,Intrinsic Room Temperature Ferromagnetism in Boron-doped ZnO,"We report room temperature ferromagnetism in boron-doped ZnO both
experimentally and theoretically. The single phase Zn1-xBxO films deposited
under high oxygen pressure by pulsed-laser deposition show ferromagnetic
behavior at room temperature. The saturation magnetization increases
monotonously from 0 to 1.5 emu/cm3 with the increasing of B component x from 0
to 6.8%. The first-principles calculations based on density functional theory
demonstrate that the ferromagnetism in B-doped ZnO originates from the induced
magnetic moments of oxygen atoms in the nearest neighbor sites to the B-Zn
vacancy pair. The calculated total magnetic moment increasing tendency with B
component is well consistent with experiments.",1003.4423v1
2010-03-23,Low frequency spin dynamics in the quantum magnet copper pyrazine dinitrate,"The S=1/2 antiferromagnetic Heisenberg chain exhibits a magnetic field driven
quantum critical point. We study the low frequency spin dynamics in copper
pyrazine dinitrate (CuPzN), a realization of this model system of quantum
magnetism, by means of $^{13}$C-NMR spectroscopy. Measurements of the nuclear
spin-lattice relaxation rate $T_1^{-1}$ in the vicinity of the saturation field
are compared with quantum Monte Carlo calculations of the dynamic structure
factor. Both show a strong divergence of low energy excitations at temperatures
in the quantum regime. The analysis of the anisotropic $T_1^{-1}$-rates and
frequency shifts allows one to disentangle the contributions from transverse
and longitudinal spin fluctuations for a selective study and to determine the
transfer of delocalized spin moments from copper to the neighboring nitrogen
atoms.",1003.4535v1
2010-05-29,{\it Ab initio} calculations of magnetic structure and lattice dynamics of Fe/Pt multilayers,"The magnetization distribution, its energetic characterization by the
interlayer coupling constants and lattice dynamics of (001)-oriented Fe/Pt
multilayers are investigated using density functional theory combined with the
direct method to determine phonon frequencies. It is found that ferromagnetic
order between consecutive Fe layers is favoured, with the enhanced magnetic
moments at the interface. The bilinear and biquadratic coupling coefficients
between Fe layers are shown to saturate fast with increasing thickness of
nonmagnetic Pt layers which separate them. The phonon calculations demonstrate
a rather strong dependence of partial iron phonon densities of states on the
actual position of Fe monolayer in the multilayer structure.",1005.5454v1
2010-06-01,Magnetic and humidity sensing properties of nanostructured Cu[x]Co[1-x]Fe2O4 synthesized by auto combustion technique,"Magnetic nanomaterials (23-43 nm) of Cu$_x$Co$_{1-x}$Fe$_2$O$_4$\ (x = 0.0,
0.5 and 1.0) were synthesized by auto combustion method. The crystallite sizes
of these materials were calculated from X-ray diffraction peaks. The band
observed in Fourier transform infrared spectrum near 575 cm$^{-1}$ in these
samples confirm the presence of ferrite phase. Conductivity measurement shows
the thermal hysteresis and demonstrates the knee points at 475$^o$C, 525$^o$C
and 500$^o$C for copper ferrite, cobalt ferrite and copper-cobalt mixed ferrite
respectively. The hystersis M-H loops for these materials were traced using the
Vibrating Sample Magnetometer (VSM) and indicate a significant increase in the
saturation magnetization (M$_s$) and remanence (M$_r$) due to the substitution
of Cu$^{2+}$ ions in cobalt ferrite, while the intrinsic coercivity (H$_c$) was
decreasing. Among these ferrites, copper ferrite exhibits highest sensitivity
for humidity.",1006.0083v1
2010-06-29,Revealing the Exciton Fine Structure in PbSe Nanocrystal Quantum Dots,"We measure the photoluminescence (PL) lifetime, $\tau$, of excitons in
colloidal PbSe nanocrystals (NCs) at low temperatures to 270~mK and in high
magnetic fields to 15~T. For all NCs (1.3-2.3~nm radii), $\tau$ increases
sharply below 10~K but saturates by 500~mK. In contrast to the usual picture of
well-separated ``bright"" and ``dark"" exciton states (found, e.g., in CdSe NCs),
these dynamics fit remarkably well to a system having two exciton states with
comparable - but small - oscillator strengths that are separated by only
300-900 $\mu$eV. Importantly, magnetic fields reduce $\tau$ below 10~K,
consistent with field-induced mixing between the two states. Magnetic circular
dichroism studies reveal exciton g-factors from 2-5, and magneto-PL shows
$>$10\% circularly polarized emission.",1006.5673v1
2010-08-10,On the resistivity at low temperatures in electron-doped cuprate superconductors,"We measured the magnetoresistance as a function of temperature down to 20mK
and magnetic field for a set of underdoped PrCeCuO (x=0.12) thin films with
controlled oxygen content. This allows us to access the edge of the
superconducting dome on the underdoped side. The sheet resistance increases
with increasing oxygen content whereas the superconducting transition
temperature is steadily decreasing down to zero. Upon applying various magnetic
fields to suppress superconductivity we found that the sheet resistance
increases when the temperature is lowered. It saturates at very low
temperatures. These results, along with the magnetoresistance, cannot be
described in the context of zero temperature two dimensional
superconductor-to-insulator transition nor as a simple Kondo effect due to
scattering off spins in the copper-oxide planes. We conjecture that due to the
proximity to an antiferromagnetic phase magnetic droplets are induced. This
results in negative magnetoresistance and in an upturn in the resistivity.",1008.1682v1
2010-08-19,Josephson Coupling and Fiske Dynamics in Ferromagnetic Tunnel Junctions,"We report on the fabrication of Nb/AlO_x/Pd_{0.82}Ni_{0.18}/Nb
superconductor/insulator/ferromagnetic metal/superconductor (SIFS) Josephson
junctions with high critical current densities, large normal resistance times
area products, high quality factors, and very good spatial uniformity. For
these junctions a transition from 0- to \pi-coupling is observed for a
thickness d_F ~ 6 nm of the ferromagnetic Pd_{0.82}Ni_{0.18} interlayer. The
magnetic field dependence of the \pi-coupled junctions demonstrates good
spatial homogeneity of the tunneling barrier and ferromagnetic interlayer.
Magnetic characterization shows that the Pd_{0.82}Ni_{0.18} has an out-of-plane
anisotropy and large saturation magnetization, indicating negligible dead
layers at the interfaces. A careful analysis of Fiske modes provides
information on the junction quality factor and the relevant damping mechanisms
up to about 400 GHz. Whereas losses due to quasiparticle tunneling dominate at
low frequencies, the damping is dominated by the finite surface resistance of
the junction electrodes at high frequencies. High quality factors of up to 30
around 200 GHz have been achieved. Our analysis shows that the fabricated
junctions are promising for applications in superconducting quantum circuits or
quantum tunneling experiments.",1008.3341v1
2010-08-26,Modulation of the ferromagnetic insulating phase in Pr0.8Ca0.2MnO3 by Co substitution,"Ferromagnetic insulator Pr0.8Ca0.2Mn1-yCoyO3 (0 <= y <= 0.7) thin films were
epitaxially grown on (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (100) substrates by pulsed
laser deposition. To probe the ferromagnetic insulator state of hole-doped
manganites, the Co content dependences of the structural, magnetic, and
transport properties were studied. Variation of lattice constant by the
substitution of Co ions is well reproduced considering that divalent and
trivalent Co ions substitute for Mn ions at the perovskite B-sites. For 0 <= y
<= 0.3, the Curie temperature, saturation magnetization, and magnetoresistance
increase with increasing Co content, retaining the insulating properties.
Detailed analyses of transport and magnetic properties indicate the
contribution of both double exchange and superexchange interactions to the
appearance of the ferromagnetic insulating phase.",1009.1524v2
2010-09-20,Emergent Ising degrees of freedom in frustrated two-leg ladder and bilayer $s=1/2$ Heisenberg antiferromagnets,"Based on exact diagonalization data for finite quantum Heisenberg
antiferromagnets on two frustrated lattices (two-leg ladder and bilayer) and
analytical arguments we map low-energy degrees of freedom of the spin models in
a magnetic field on classical lattice-gas models. Further we use
transfer-matrix calculations and classical Monte Carlo simulations to give a
quantitative description of low-temperature thermodynamics of the quantum spin
models. The classical lattice-gas model yields an excellent description of the
quantum spin models up to quite large temperatures. The main peculiarity of the
considered frustrated bilayer is a phase transition which occurs at low
temperatures for a wide range of magnetic fields below the saturation magnetic
field and belongs to the two-dimensional Ising model universality class.",1009.3828v1
2010-10-09,Superparamagnetism in Nanocrystalline Copper Ferrite Thin Films,"The rf sputtered copper ferrite films contain nanocrystalline grains. In
these films, the magnetization does not saturate even in high magnetic fields.
This phenomenon of high field susceptibility is attributed to the defects
and/or superparamagnetic grains in the films. A simple model is developed to
describe the observed high field magnetization behavior of these films. The
model is found to fit well to the high field part for all the studied films. An
attempt is also made to explain the temperature variation of the ferrimagnetic
contribution on the basis of reported exchange constants.",1010.1877v1
2010-11-02,Upper-hybrid wave driven Alfvenic turbulence in magnetized dusty plasmas,"The nonlinear dynamics of coupled electrostatic upper-hybrid (UH) and Alfven
waves (AWs) is revisited in a magnetized electron-ion plasma with charged dust
impurities. A pair of nonlinear equations that describe the interaction of UH
wave envelopes (including the relativistic electron mass increase) and the
density as well as the compressional magnetic field perturbations associated
with the AWs is solved numerically to show that many coherent solitary patterns
can be excited and saturated due to modulational instability of unstable UH
waves. The evolution of these solitary patterns is also shown to appear in the
states of spatiotemporal coherence, temporal as well as spatiotemporal chaos
due to collision and fusion among the patterns in stochastic motion.
Furthermore, these spatiotemporal features are demonstrated by the analysis of
wavelet power spectra. It is found that a redistribution of wave energy takes
place to higher harmonic modes with small wavelengths which, in turn, results
into the onset of Alfvenic turbulence in dusty magnetoplasmas. Such a scenario
can occur in the vicinity of Saturn's magnetosphere as many electrostatic
solitary structures have been observed there by the Cassini spacecraft.",1011.0540v2
2010-11-11,"Anomalous galvanomagnetism, cyclotron resonance and microwave spectroscopy of topological insulators","The surface quantum Hall state, magneto-electric phenomena and their
connection to axion electrodynamics have been studied intensively for
topological insulators. One of the obstacles for observing such effects comes
from nonzero conductivity of the bulk. To overcome this obstacle we propose to
use an external magnetic field to suppress the conductivity of the bulk
carriers. The magnetic field dependence of galvanomagnetic and electromagnetic
responses of the whole system shows anomalies due to broken time-reversal
symmetry of the surface quantum Hall state, which can be used for its
detection. In particular, we find linear bulk dc magnetoresistivity and a
quadratic field dependence of the Hall angle, shifted rf cyclotron resonance,
nonanalytic microwave transmission coefficient and saturation of the Faraday
rotation angle with increasing magnetic field or wave frequency.",1011.2756v4
2010-12-08,Tailoring the magnetism of GaMnAs films by ion irradiation,"Ion irradiation of semiconductors is a well understood method to tune the
carrier concentration in a controlled manner. We show that the ferromagnetism
in GaMnAs films, known to be hole-mediated, can be modified by He ion
irradiation. The coercivity can be increased by more than three times. The
magnetization, Curie temperature and the saturation field along the
out-of-plane hard axis all decrease as the fluence increases. The electrical
and structural characterization of the irradiated GaMnAs layers indicates that
the controlled tailoring of magnetism results from a compensation of holes by
generated electrical defects.",1012.1678v1
2011-01-07,NMR relaxation rate in the field-induced octupolar liquid phase of spin-1/2 J1-J2 frustrated chains,"In the spin-1/2 frustrated chain with nearest-neighbor ferromagnetic exchange
J1 and next-nearest-neighbor antiferromagnetic exchange J2 under magnetic
field, magnetic multipolar-liquid (quadrupolar, octupolar, and hexadecapolar)
phases are widely expanded from the saturation down to a low-field regime.
Recently, we have clarified characteristic temperature and field dependence of
the NMR relaxation rate 1/T_1 in the quadrupolar phase. In this paper, we
examine those of 1/T_1 in the octupolar phase combining field theoretical
method with numerical data. The relevance of the results to quasi
one-dimensional J1-J2 magnets such as PbCuSO4(OH)2, Rb2Cu2Mo3O12 and Li2ZrCuO4
is shortly discussed.",1101.1375v2
2011-03-02,Switching dynamics of a magnetostrictive single-domain nanomagnet subjected to stress,"The temporal evolution of the magnetization vector of a single-domain
magnetostrictive nanomagnet, subjected to in-plane stress, is studied by
solving the Landau-Lifshitz-Gilbert equation. The stress is ramped up linearly
in time and the switching delay, which is the time it takes for the
magnetization to flip, is computed as a function of the ramp rate. For high
levels of stress, the delay exhibits a non-monotonic dependence on the ramp
rate, indicating that there is an {\it optimum} ramp rate to achieve the
shortest delay. For constant ramp rate, the delay initially decreases with
increasing stress but then saturates showing that the trade-off between the
delay and the stress (or the energy dissipated in switching) becomes less and
less favorable with increasing stress. All of these features are due to a
complex interplay between the in-plane and out-of-plane dynamics of the
magnetization vector induced by stress.",1103.0352v1
2011-03-07,Magnetic Susceptibility of the Quark Condensate and Polarization from Chiral Models,"We compute the magnetic susceptibility of the quark condensate and the
polarization of quarks at zero temperature and in a uniform magnetic
background. Our theoretical framework consists of two chiral models that allow
to treat self-consistently the spontaneous breaking of chiral symmetry: the
linear $\sigma-$model coupled to quarks, dubbed quark-meson model, and the
Nambu-Jona-Lasinio model. We also perform analytic estimates of the same
quantities within the renormalized quark-meson model, both in the regimes of
weak and strong fields. Our numerical results are in agreement with the recent
literature; moreover, we confirm previous Lattice findings, related to the
saturation of the polarization at large fields.",1103.1194v1
2011-03-24,Supernova remnants as cosmic ray factories,"In this work we investigate particle acceleration in supernova remnant shocks
within a semi-analytical formalism which self-consistently accounts for
particle acceleration, amplification of the magnetic field via streaming
instability and back-reaction of both accelerated particles and magnetic
turbulence on the shock dynamics. In particular, we study the interplay between
particle injection and magnetic field amplification, showing how a
phenomenological but reasonable saturation of the standard streaming
instability may lead to quite steep spectra for the accelerated particles. We
comment on the implications that such a scenario may have on the comprehension
of the diffuse spectrum of Galactic cosmic rays and of gamma-ray observations
of single remnants.",1103.4798v1
2011-03-28,From convective to stellar dynamos,"Convectively driven dynamos with rotation generating magnetic fields on
scales large compared with the scale of the turbulent eddies are being
reviewed. It is argued that such fields can be understood as the result of an
alpha effect. Simulations in Cartesian domains show that such large-scale
magnetic fields saturate on a time scale compatible with the resistive one,
suggesting that the magnitude of the alpha effect is here still constrained by
approximate magnetic helicity conservation. It is argued that, in the absence
of shear and/or any other known large-scale dynamo effects, these simulations
prove the existence of turbulent alpha^2-type dynamos. Finally, recent results
are discussed in the context of solar and stellar dynamos.",1103.5475v1
2011-04-29,Upper critical magnetic field in Ba_0.68K_0.32Fe_2As_2 and Ba(Fe_0.93Co_0.07)_2As_2,"We report measurements of the temperature dependence of the radio-frequency
magnetic penetration depth in Ba_0.68K_0.32Fe_2As_2 and
Ba(Fe_0.93Co_0.07)_2As_2 single crystals in pulsed magnetic fields up to 60 T.
From our data, we construct an H-T phase diagram for the inter-plane (H || c)
and in-plane (H || ab) directions for both compounds. For both field
orientations in Ba_0.68K_0.32Fe_2As_2, we find a concave curvature of the
Hc2(T) lines with decreasing anisotropy and saturation towards lower
temperature. Taking into account Pauli spin paramagnetism we can describe
Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair
breaking is not essential for Ba(Fe_0.93Co_0.07)_2As_2. For this electron-doped
compound, the data support a Hc2(T) dependence that can be described by the
Werthamer Helfand Hohenberg model for H || ab and a two-gap behavior for H ||
c.",1104.5619v1
2011-06-28,Nonlinear small-scale dynamos at low magnetic Prandtl numbers,"Saturated small-scale dynamo solutions driven by isotropic non-helical
turbulence are presented at low magnetic Prandtl numbers Pm down to 0.01. For
Pm < 0.1, most of the energy is dissipated via Joule heat and, in agreement
with earlier results for helical large-scale dynamos, kinetic energy
dissipation is shown to diminish proportional to Pm^{1/2} down to values of
0.1. In agreement with earlier work, there is, in addition to a short Golitsyn
k^{-11/3} spectrum near the resistive scale also some evidence for a short
k^{-1} spectrum on larger scales. The rms magnetic field strength of the
small-scale dynamo is found to depend only weakly on the value of Pm and
decreases by about a factor of 2 as Pm is decreased from 1 to 0.01. The
possibility of dynamo action at Pm=0.1 in the nonlinear regime is argued to be
a consequence of a suppression of the bottleneck seen in the kinetic energy
spectrum in the absence of a dynamo and, more generally, a suppression of
kinetic energy near the dissipation wavenumber.",1106.5777v2
2011-07-14,Anomalous Coexistence of Ferroelectric Phases ($P\parallel a$ and $P\parallel c$) in Orthorhombic Eu$_{1-y}$Y$_y$MnO$_3$ ($y>0.5$) Crystals,"We have investigated the magnetic and dielectric properties of orthorhombic
Eu$_{1-y}$Y$_y$MnO$_3$ ($0\leq y\leq 0.6$) single crystals without the presence
of the 4$f$ magnetic moments of the rare-earth ions. In $y\geq 0.2$, the
magnetic-structure driven ferroelectricity is observed. The ferroelectric
transition temperature is steeply reducing with increasing $y$. In $y\geq
0.52$, two ferroelectric phases ($P\parallel a$ and $P\parallel c$) are
coexistent at low temperatures. In these phases, ferroelectricity has different
origin, which is evidenced by the distinctive poling-electric-field dependence
of electric polarization. Namely, the electric polarization along the c axis
($P_c$) is easily saturated by a poling electric field, therefore $P_c$ is
caused by the $bc$ spiral antiferromagnetic order. On the other hand, the
electric polarization along the a axis ($P_a$) is probably attributed to the
collinear $E$-type antiferromagnetic order, because $P_a$ is unsaturated even
in a poling field of $10^6$ V/m.",1107.2733v1
2011-08-14,High pressure sequence of Ba_3NiSb_2O_9 structural phases: new $S = 1$ quantum spin-liquids based on Ni^{2+},"By using a high pressure, high temperature (HPHT) technique, the
antiferromagnetically ordered ($T_N$ = 13.5 K) 6H-A phase of
Ba$_3$NiSb$_2$O$_9$ was transformed into two new gapless quantum spin
liquid(QSL) candidates with S=1 (Ni$^{2+}$) moments: the 6H-B phase with a
Ni$^{2+}$-triangular lattice and the 3C-phase with a
Ni$^{2+}$-three-dimensional (3D) edge-shared tetrahedral lattice. Both
compounds show no magnetic order down to 0.35 K despite Curie-Weiss
temperatures $\theta_{CW}$ of -75.5 K (6H-B) and -182.5 K (3C), respectively.
Below $\sim 25$ K the magnetic susceptibility of the 6H-B phase saturates to a
constant value $\chi_0 = 0.013 $ emu/mol which is followed below 7 K, by a
linear-temperature dependent magnetic specific heat ($C_M$) displaying a giant
coefficient $\gamma$ = 168 mJ/mol-K$^2$. Both observations suggest the
development of a Fermi-liquid like ground state characterized by a Wilson ratio
of 5.6 in this insulating material. For the 3C phase, the $C_M \propto T^2$
behavior indicates a unique S=1, 3D QSL ground-state.",1108.2897v1
2011-12-20,The Effect of Anisotropic Conduction on the Thermal Instability in the Interstellar Medium,"Thermal instability (TI) can strongly affect the structure and dynamics of
the interstellar medium (ISM) in the Milky Way and other disk galaxies. Thermal
conduction plays an important role in the TI by stabilizing small scales and
limiting the size of the smallest condensates. In the magnetized ISM, however,
heat is conducted anisotropically (primarily along magnetic field lines). We
investigate the effects of anisotropic thermal conduction on the nonlinear
regime of the TI by performing two-dimensional magnetohydrodynamic simulations.
We present models with magnetic fields of different initial geometries and
strengths, and compare them to hydrodynamic models with isotropic conduction.
We find anisotropic conduction does not significantly alter the overall density
and temperature statistics in the saturated state of the TI. However, it can
strongly affect the shapes and sizes of cold clouds formed by the TI. For
example, for uniform initial fields long filaments of cold gas are produced
that are reminiscent of some observed HI clouds. For initially tangled fields,
such filaments are not produced. We also show that anisotropic conduction
suppresses turbulence generated by evaporative flows from the surfaces of cold
blobs, which may have implications for mechanisms for driving turbulence in the
ISM.",1112.4841v1
2012-02-27,Exact ground state of a frustrated integer-spin modified Shastry-Sutherland model,"We consider a two-dimensional geometrically frustrated integer-spin
Heisenberg system that admits an exact ground state. The system corresponds to
a decorated square lattice with two coupling constants J1 and J2, and it can be
understood as a generalized Shastry-Sutherland model. Main elements of the spin
model are suitably coupled antiferromagnetic spin trimers with integer spin
quantum numbers s and their ground state Phi will be the product state of the
local singlet ground states of the trimers. We provide exact numerical data for
finite lattices as well as analytical considerations to estimate the range of
the existence in dependence on the ratio of the two couplings constants J2 and
J1 and on the spin quantum number s. Moreover, we find that the magnetization
curves as a function of the applied magnetic field shows plateaus and jumps. In
the classical limit s \to \infty the model exhibits phases of three- and
two-dimensional ground states separated by a one-dimensional (collinear)
plateau state at 1/3 of the saturation magnetization.",1202.5854v1
2012-03-17,Magnetic Phase Transition and Relaxation Effects in LiFePO4,"We report the observation of para - antiferromagnetic transition at ~ 50 K in
lithium iron phosphate, LiFePO4 through DC magnetization and M\""ossbauer
spectroscopy. The Ferrous ion Fe2+ (3d6, 5D) in LiFePO4 exhibits relaxation
effects with a relaxation frequency ~1.076 \times 10(rise to 7) s-1 at 300 K.
The temperature dependence of the frequency suggests the origin of the
relaxation is spin-lattice type. The quadrupole splitting at low temperatures
indicates the excited orbital states mix strongly to the orbital doublet ground
state via spin-orbit coupling. Modified molecular field model analysis yields a
saturation value for hyperfine field ~125 kOe. The anomaly in magnetization and
M\""ossbauer parameters below 27 K may be ascribed to contribution of orbital
angular momentum. The high value of the asymmetry parameter ({\eta} ~ 0.8) of
the electric field gradient obtained in the antiferromagnetic regime indicates
a strongly distorted octahedral oxygen neighbourhood for the ferrous sites.",1203.3863v2
2012-04-15,Efect of magnetic Gd impurities on superconductivity in MoGe films with different thickness and morphology,"We studied the effect of magnetic doping with Gd atoms on the superconducting
properties of amorphous Mo70Ge30 films. We observed that in uniform films
deposited on amorphous Ge, the pair-breaking strength per impurity strongly
decreases with film thickness initially and saturates at a finite value in
films with thickness below the spin-orbit scattering length. The variation is
likely caused by surface induced magnetic anisotropy and is consistent with the
fermionic mechanism of superconductivity suppression. In thin films deposited
on SiN the pair-breaking strength becomes zero. Possible reasons for this
anomalous response are discussed. The morphological distinctions between the
films of the two types were identified using atomic force microscopy with a
carbon nanotube tip.",1204.3334v1
2012-05-10,DC magnetic field generation in unmagnetized shear flows,"The generation of DC magnetic fields in unmagnetized plasmas with velocity
shear is predicted for non relativistic and relativistic scenarios either due
to thermal effects or due to the onset of the Kelvin-Helmholtz instability
(KHI). A kinetic model describes the growth and the saturation of the DC field.
The predictions of the theory are confirmed by multidimensional
particle-in-cell simulations, demonstrating the formation of long lived
magnetic fields ($t \sim 100s \omega_{pi}^{-1}$) along the full longitudinal
extent of the shear layer, with transverse width on the electron length scale
($\sqrt{\gamma_0}c/\omega_{pe}$), reaching magnitudes
$eB_{\mathrm{DC}}/m_ec\omega_{pe}\sim \beta_0\sqrt{\gamma_0}$.",1205.2293v3
2012-05-21,Cyclic magnetic activity due to turbulent convection in spherical wedge geometry,"We report on simulations of turbulent, rotating, stratified,
magnetohydrodynamic convection in spherical wedge geometry. An initially
small-scale, random, weak-amplitude magnetic field is amplified by several
orders of magnitude in the course of the simulation to form oscillatory
large-scale fields in the saturated state of the dynamo. The differential
rotation is solar-like (fast equator), but neither coherent meridional poleward
circulation nor near-surface shear layer develop in these runs. In addition to
a poleward branch of magnetic activity beyond 50 degrees latitude, we find for
the first time a pronounced equatorward branch at around 20 degrees latitude,
reminiscent of the solar cycle.",1205.4719v2
2012-07-16,Influence of the magnetic field on the plasmonic properties of transparent Ni anti-dot arrays,"Extraordinary optical transmission is observed due to the excitation of
surface plasmon polaritons (SPPs) in 2-Dimensional hexagonal anti-dot patterns
of pure Ni thin films, grown on sapphire substrates. A strong enhancement of
the polar Kerr rotation is recorded at the surface plasmon related transmission
maximum. Angular resolved reflectivity measurements under an applied field,
reveal an enhancement and a shift of the normalized reflectivity difference
upon reversal of the magnetic saturation (transverse magneto-optical Kerr
effect-TMOKE). The change of the TMOKE signal clearly shows the magnetic field
modulation of the dispersion relation of SPPs launched in a 2D patterned
ferromagnetic Ni film.",1207.3697v1
2012-07-20,Three-Dimensional Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. III. Rotating Relativistic Jets,"We have investigated the influence of jet rotation and differential motion on
the linear and nonlinear development of the current-driven (CD) kink
instability of force-free helical magnetic equilibria via three-dimensional
relativistic magnetohydrodynamic simulations. In this study, we follow the
temporal development within a periodic computational box. Displacement of the
initial helical magnetic field leads to the growth of the CD kink instability.
We find that, in accord with linear stability theory, the development of the
instability depends on the lateral distribution of the poloidal magnetic field.
If the poloidal field significantly decreases outwards from the axis, the
initial small perturbations grow strongly, and if multiple wavelengths are
excited non-linear interaction eventually disrupts the initial cylindrical
configuration. When the profile of the poloidal field is shallow, the
instability develops slowly and eventually saturates. We briefly discuss
implications of our findings for Poynting dominated jets.",1207.4949v1
2012-10-03,Torsional Oscillations in a Global Solar Dynamo,"We characterize and analyze rotational torsional oscillations developing in a
large-eddy magnetohydrodynamical simulation of solar convection (Ghizaru,
Charbonneau, and Smolarkiewicz, Astrophys. J. Lett., 715, L133 (2010); Racine
et al., Astrophys. J., 735, 46 (2011)) producing an axisymmetric large-scale
magnetic field undergoing periodic polarity reversals. Motivated by the many
solar-like features exhibited by these oscillations, we carry out an analysis
of the large-scale zonal dynamics. We demonstrate that simulated torsional
oscillations are not driven primarily by the periodically-varying large-scale
magnetic torque, as one might have expected, but rather via the magnetic
modulation of angular-momentum transport by the large-scale meridional flow.
This result is confirmed by a straightforward energy analysis. We also detect a
fairly sharp transition in rotational dynamics taking place as one moves from
the base of the convecting layers to the base of the thin tachocline-like shear
layer formed in the stably stratified fluid layers immediately below. We
conclude by discussing the implications of our analyses with regards to the
mechanism of amplitude saturation in the global dynamo operating in the
simulation, and speculate on the possible precursor value of torsional
oscillations for the forecast of solar cycle characteristics.",1210.1209v1
2012-10-08,Sputter gas pressure effects on the properties of Sm-Co thin films deposited from a single target,"We grow epitaxial Sm-Co thin films by sputter deposition from an alloy target
with a nominal SmCo5 composition on Cr(100)-buffered MgO(100) single-crystal
substrates. By varying the Ar gas pressure, we can change the composition of
the film from a SmCo5-like to a Sm2Co7-like phase. The composition, crystal
structure, morphology and magnetic properties of these films have been
determined using Rutherford Backscattering, X-ray diffraction and magnetization
measurements. We find that the various properties are sensitive to the sputter
background pressure in different ways. In particular, the lattice parameter
changes in a continuous way, the coercive fields vary continuously with a
maximum value of 3.3 T, but the saturation magnetization peaks when the lattice
parameter is close to that of Sm2Co7. Moreover, we find that the Sm content of
the films is higher than expected from the expected stoichiometry.",1210.2240v1
2012-10-17,Turbulence in weakly-ionized proto-planetary disks,"We investigate the characteristic properties of self-sustained MRI turbulence
in low-ionized proto-planetary disks. We study the transition regime between
active and dead-zone, performing 3D global non-ideal MHD simulations of
stratified disk covering range of magnetic Reynolds number between 2700 < Rm <
6600. We found converged and saturated MRI turbulence for Rm > 5000 with a
strength of alpha ~ 0.01. Below Rm < 5000 the MRI starts to decay at the
midplane, having Elsasser numbers below one. We find a transition regime
between 3300 < Rm < 5000 where the MRI turbulence is still sustained but
damped. At around Rm < 3000 the MRI turbulence decays but could reestablished
due to the accumulation of toroidal magnetic field or the radial transport of
magnetic field from the active region. Below Rm < 3000 the MRI cannot be
sustained and is decaying. Here hydro-dynamical motions, like density waves
dominate. We observe anti-cyclonic vortices in the transition between dead-zone
and active zone.",1210.4669v1
2012-11-12,Magnetic and transport properties of tetragonal- or cubic-Heusler-type Co-substituted Mn-Ga epitaxial thin films,"The composition dependence of the structural, magnetic, and transport
properties of epitaxially grown Mn-Co-Ga films were investigated. The crystal
structure was observed to change from tetragonal to cubic as the Co content was
increased. In terms of the dependence of saturation magnetization on the Co
content, relatively small value was obtained for the
Mn$_{2.3}$Co$_{0.4}$Ga$_{1.3}$ film at a large {\it K}$_\textrm u$ value of 9.2
Merg/cm$^3$. Electrical resistivity of Mn-Co-Ga films was larger than that of
pure Mn-Ga film. The maximum value of the resistivity was 490 $\mu\Omega$cm for
Mn$_{2.2}$Co$_{0.6}$Ga$_{1.2}$ film. The high resistivity of Mn-Co-Ga might be
due to the presence of localized electron states in the films due to chemical
disordering caused by the Co substitution.",1211.2524v1
2012-11-20,Microscopic magnetic structuring of a spin-wave waveguide by ion implantation in a Ni(81)Fe(19) layer,"We investigate the spin-wave excitation in microscopic waveguides fabricated
by localized Cr+ ion implantation in a ferromagnetic Ni(81)Fe(19) film. We
demonstrate that spin-wave waveguides can be conveniently made by this
technique. The magnetic patterning technique yields an increased damping and a
reduction in saturation magnetization in the implanted regions that can be
extracted from Brillouin light scattering measurements of the spin-wave
excitation spectra. Furthermore, the waveguide performance as well as the
internal field of the waveguide depend on the doping fluence. The results prove
that localized ion implantation is a powerful tool for the patterning of magnon
spintronic devices.",1211.4786v1
2012-11-21,Spin-wave propagation and transformation in a thermal gradient,"The influence of a thermal gradient on the propagation properties of
externally excited dipolar spin waves in a magnetic insulator waveguide is
investigated. It is shown that spin waves propagating towards a colder region
along the magnetization direction continuously reduce their wavelength. The
wavelength increase of a wave propagating into a hotter region was utilized to
realize its decomposition in the partial waveguide modes which are reflected at
different locations. This influence of temperature on spin-wave properties is
mainly caused by a change in the saturation magnetization and yields promising
opportunities for the manipulation of spin waves in spin-caloritronic
applications.",1211.5017v1
2012-12-07,Current helicity constraints in solar dynamo models,"We investigate to what extent the current helicity distribution observed in
solar active regions is compatible with solar dynamo models. We use an advanced
2D mean-field dynamo model with dynamo action largely concentrated near the
bottom of the convective zone, and dynamo saturation based on the evolution of
the magnetic helicity and algebraic quenching. For comparison, we also studied
a more basic 2D mean-field dynamo model with simple algebraic alpha quenching
only. Using these numerical models we obtain butterfly diagrams for both the
small-scale current helicity and the large-scale magnetic helicity, and compare
them with the butterfly diagram for the current helicity in active regions
obtained from observations. This comparison shows that the current helicity of
active regions, as estimated by $-A \cdot B$ evaluated at the depth from which
the active region arises, resembles the observational data much better than the
small-scale current helicity calculated directly from the helicity evolution
equation. Here $B$ and $A$ are respectively the dynamo generated mean magnetic
field and its vector potential.",1212.1643v1
2013-01-07,Quantum Hall Effect in Hydrogenated Graphene,"The quantum Hall effect is observed in a two-dimensional electron gas formed
in millimeter-scale hydrogenated graphene, with a mobility less than 10
$\mathrm{cm^{2}/V\cdot s}$ and corresponding Ioffe-Regel disorder parameter
$(k_{F}\lambda)^{-1}\gg1$. In zero magnetic field and low temperatures, the
hydrogenated graphene is insulating with a two-point resistance of order of
$250 h/e^2$. Application of a strong magnetic field generates a negative
colossal magnetoresistance, with the two-point resistance saturating within
0.5% of $h/2e^{2}$ at 45T. Our observations are consistent with the opening of
an impurity-induced gap in the density of states of graphene. The interplay
between electron localization by defect scattering and magnetic confinement in
two-dimensional atomic crystals is discussed.",1301.1257v1
2013-01-18,Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:O$_{x}$,"We report an unusual persistence of superconductivity against high magnetic
fields in the iron chalcogenide film FeTe:O$_{x}$ below ~ 2.5 K. Instead of
saturating like a mean-field behavior with a single order parameter, the
measured low-temperature upper critical field increases progressively,
suggesting a large supply of superconducting states accessible via magnetic
field or low-energy thermal fluctuations. We demonstrate that superconducting
states of finite momenta can be realized within the conventional theory,
despite its questionable applicability. Our findings reveal a fundamental
characteristic of superconductivity and electronic structure in the
strongly-correlated iron-based superconductors.",1301.4487v3
2013-02-07,Three-dimensional artificial neural network model of the dayside magnetopause,"Artificial Neural Networks (ANN) from package NeuroShell 2 are applied for
modeling of dayside magnetopause. The model data set is based on the
magnetopause crossings and on the corresponding hour-averaged measurements of
solar wind plasma and interplanetary magnetic field. ANN model represents 3D
shape and size of the dayside magnetopause in dependence on solar wind dynamic
pressure, Bz and By components of interplanetary magnetic field. The model
permits firstly to describe dynamics of the magnetic cusp and global asymmetry
of the dayside magnetopause under wide range of the external conditions.
Slightly change of the magnetopause size with change of By absolute value is
presented quantitatively in the form of analytical expression. ANN model shows
three regimes of the magnetopause dynamics that controlled by Bz component:
pressure balance regime (Bz>0 nT), reconnection regime (0>Bz>-10 nT) and regime
of reconnection saturation (Bz<-10 nT). Three different regimes of magnetopause
dynamics at the subsolar point are described by modified pressure balance
equation obtained from ANN model.",1302.1704v1
2013-03-01,Parallel pumping of magnetic vortex gyrations in spin-torque nano-oscillators,"We experimentally demonstrate that large magnetic vortex oscillations can be
parametrically excited in a magnetic tunnel junction by the injection of
radio-frequency (rf) currents at twice the natural frequency of the gyrotropic
vortex core motion. The mechanism of excitation is based on the parallel
pumping of vortex motion by the rf orthoradial field generated by the injected
current. Theoretical analysis shows that experimental results can be
interpreted as the manifestation of parametric amplification when rf current is
small, and of parametric instability when rf current is above a certain
threshold. By taking into account the energy nonlinearities, we succeed to
describe the amplitude saturation of vortex oscillations as well as the
coexistence of stable regimes.",1303.0225v1
2013-03-08,Ultracold neutron accumulation in a superfluid-helium converter with magnetic multipole reflector,"We analyze accumulation of ultracold neutrons (UCN) in a superfluid-helium
converter vessel surrounded by a magnetic multipole reflector. We solved the
spin-dependent rate equation, employing formulas valid for adiabatic spin
transport of trapped UCN in mechanical equilibrium. Results for saturation UCN
densities are obtained in dependence of order and strength of the multipolar
field. The addition of magnetic storage to neutron optical potentials can
increase the density and energy of the low field seeking UCN produced and
serves to mitigate the effects of wall losses on the source performance. It
also can provide a highly polarized sample of UCN without need to polarize the
neutron beam incident on the converter. This work was performed in preparation
of the UCN source project SuperSUN at the ILL.",1303.1944v2
2013-03-25,First Study of Intersubband Absorption in Electrons on Helium under Quantizing Magnetic Fields,"We present the first measurements of inter-subband absorption of microwaves
in surface electrons on liquid helium subjected to perpendicular magnetic field
B. In quantizing B, the power absorption shows intermittent regions of enhanced
and suppressed absorption. This behavior is caused by strong variation of the
excited-electron decay rate with B. Particularly, fast decay due to elastic
scattering provides condition for strong absorption and overheating of the
electron system, while slow decay due to inelastic scattering limits absorption
and causes its saturation. An unexpected feature is the strong suppression of
absorption at magnetic fields where the inter-subband energy splitting is a
multiple number of the cyclotron energy.",1303.6044v1
2013-04-09,Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi,"In this paper, we investigate the half-metallicity of Heusler alloys
Fe2Co1-xCrxSi by first principles calculations and anisotropy magnetoresistance
measurements. It is found that, with the increase of Cr content x, the Fermi
level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of
conduction band, and a large half-metallic band gap of 0.75 eV is obtained for
x=0.75. We then successfully synthesized a series Heusler Fe2Co1-xCrxSi
polycrystalline ribbon samples. The results of X-ray diffraction indicate that
the Fe2Co1-xCrxSi series of samples are pure phase with a high degree of order
and the saturation magnetic moment follows half-metallic Slater-Pauling rule.
Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic
magnetoresistance of Fe2Co1-xCrxSi (x=0.25, 0.5, 0.75) show a negative value
suggesting they are stable half-metallic ferromagnets.",1304.2602v1
2013-05-22,Field-induced spin-structural transition and giant magnetostriction in Ising chain $α$-CoV$_2$O$_6$,"We have investigated the temperature and magnetic field dependence of
magnetization, specific heat ($C_p$), and relative sample length change
($\Delta L/L_0$) for understanding the field-induced spin-structural change in
quasi-one-dimensional spin chain $\alpha$-CoV$_2$O$_6$ which undergoes
antiferromagnetic (AFM) transition below $T_N$$=$15 K. Analysis of $C_p$($T$)
shows that an effective $S$$=$1/2 Ising state is realized below 20 K, though
the magnetic fluctuations persist well above $T_N$. $C_p$ and the coefficient
of linear thermal expansion ($\alpha$) exhibit strong $H$ dependence in the AFM
state. We also observe a huge positive magnetostriction [$\Delta L$($H$)/$L_0$]
below 20 K which does not show any tendency of saturation up to 9 T. With
increasing field, a sharp and symmetric peak emerges below $T_N$ in both
$C_p$($T$) and $\alpha$($T$) due to field-induced first order
ferrimagnetic/ferromagnetic-paramagnetic transitions. The large value of
magnetostriction below $T_N$ suggests strong spin-lattice coupling in
$\alpha$-CoV$_2$O$_6$.",1305.5027v2
2013-05-29,Exact Ground States of Frustrated Spin-1 Ising-Heisenberg and Heisenberg Ladders in a Magnetic Field,"Ground states of the frustrated spin-1 Ising-Heisenberg two-leg ladder with
Heisenberg intra-rung coupling and only Ising interaction along legs and
diagonals are rigorously found by taking advantage of local conservation of the
total spin on each rung. The constructed ground-state phase diagram of the
frustrated spin-1 Ising-Heisenberg ladder is then compared with the analogous
phase diagram of the fully quantum spin-1 Heisenberg two-leg ladder obtained by
density matrix renormalization group (DMRG) calculations. It is demonstrated
that both investigated spin models exhibit quite similar magnetization
scenarios, which involve intermediate plateaux at one-quarter, one-half and
three-quarters of the saturation magnetization.",1305.6703v1
2013-05-30,Suppression of ferromagnetism in the LaVxCr1-xGe3 system,"We report synthesis of hexagonal LaVxCr1-xGe3 (x = 0-0.21, 1.00) single
crystals, and present a systematic study of this series by measurements of
temperature and field dependent magnetic susceptibility, magnetization,
resistivity, and specific heat. Ferromagnetism has been observed for x =
0-0.21, and the system manifests a strong axial anisotropy in its ordered
state. The decrease of the saturated moment and the effective moment per Cr
with the increase of V-concentration suggests this is an itinerant
ferromagnetic system. The Curie temperature declines monotonically as the
V-concentration increases. Single crystalline samples could only be grown for
x-values up to 0.21 for which the transition temperature was suppressed down to
36 K. Although we could not fully suppress TC via V-substitution, for x = 0.16,
we performed magnetization measurements under pressure. The ferromagnetic state
is suppressed under pressure at an initial rate of dTC/dp = -11.7 K/GPa and
vanishes by 3.3 GPa.",1305.7258v1
2013-06-11,Magnetically Active Stars in Taurus-Auriga: Activity and Rotation,"A sample of 70 magnetically active stars toward the Taurus-Auriga
star-forming region has been investigated. The positions of the sample stars on
the Rossby diagram have been analyzed. All stars are shown to be in the regime
of a saturated dynamo, where the X-ray luminosity reaches its maximum and does
not depend on the Rossby number. A correlation has been found between the
lithium line equivalent width and the age of a solar-mass (from 0.7 to 1.2
Msun) pre-main-sequence star. The older the age, the smaller the Li line
equivalent width. Analysis of the long-term photometric variability of these
stars has shown that the photometric activity of the youngest stars is
appreciably higher than that of the older objects from the sample. This result
can be an indirect confirmation of the evolution of the magnetic field in
pre-main-sequence stars from predominantly dipole and axisymmetric to multipole
and nonaxisymmetric.",1306.2651v1
2013-07-11,"Stable Spin State Analysis of Fe, Co, Ni-modified Graphene-ribbon","Magnetic graphene-ribbon is a candidate for realizing future ultra high
density 100 tera bit/inch2 class data storage media. In order to increase the
saturation magnetization, first principles DFT analysis was done for Fe, Co,
Ni-modified zigzag edge graphene-ribbon. Typical unit cell is [C32H2Fe1],
[C32H2Co1] and [C32H2Ni1] respectively. Most stable spin state was Sz=4/2 for
Fe-modified case, whereas Sz=3/2 for Co-case and Sz=2/2 for Ni-case. Magnetic
moment of Fe,Co, and Ni were 3.63, 2.49 and 1.26 {\mu}B, which can be explained
by the Hund-rule considering charge donation to neighboring carbons. Band
calculation shows half-metal like structure with a large band gap (in Co-case,
0.55eV) for up-spin, whereas very small gap (0.05eV) for down-spin, which will
be useful for many featured application like information storage, spin filter
and magneto-resistance devices. Dual layer Fe-modified ribbon shows a tube like
curved structure, which may suggest a carbon nanotube creation by Fe catalyst.",1307.2960v1
2013-07-12,Singlet-triplet Crossover in the Two-dimensional Dimer Spin System YbAl3C3,"Low-temperature magnetization (M) measurements down to 0.1 K have been
performed in magnetic fields up to 14.5 T for a single piece of a tiny
single-crystalline sample (0.2 mg weight) of the spin-gap system YbAl3C3. At
the base temperature of 0.1 K, several metamagnetic transitions were clearly
observed for H // c in the range 6 T < H < 9 T whereas only two transitions
were observed, one at 4.8 T and the other at 6.6 T, for H // a. At fields above
9 T, the magnetization becomes almost saturated for both H // a and H // c. The
present results indicate that a singlet-triplet crossover occurs in a
relatively narrow field range, suggesting a rather weak interdimer interaction
in spite of the nearly triangular lattice of Yb ions.",1307.3494v1
2013-08-06,Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties,"A cluster deposition method was used to produce films of loosely aggregated
nanoclusters (NC) of Fe core-Fe3O4 shell or fully oxidized Fe3O4. Films of
these NC on Si(100) or MgO(100)/Fe3O4(100) were irradiated to 10^16 Si2+/cm2
near room temperature using an ion accelerator. Ion irradiation creates
structural change in the NC film with corresponding chemical and magnetic
changes which depend on the initial oxidation state of the cluster. Films were
characterized using magnetometry (hysteresis, first order reversal curves),
microscopy (transmission electron, helium ion), and x-ray diffraction. In all
cases, the particle sizes increased due to ion irradiation, and when a core of
Fe is present, irradiation reduces the oxide shells to lower valent Fe species.
These results show that ion irradiated behavior of the nanocluster films
depends strongly on the initial nanostructure and chemistry, but in general
saturation magnetization decreases slightly.",1308.1384v1
2013-08-15,Magnetic field generation and amplification in an expanding plasma,"Particle-in-cell simulations are used to investigate the formation of
magnetic fields, B, in plasmas with perpendicular electron density and
temperature gradients. For system sizes, L, comparable to the ion skin depth,
d_i, it is shown that B ~ d_i/L, consistent with the Biermann battery effect.
However, for large L/d_i, it is found that the Weibel instability (due to
electron temperature anisotropy) supersedes the Biermann battery as the main
producer of B. The Weibel-produced fields saturate at a finite amplitude
(plasma \beta \approx 100), independent of L. The magnetic energy spectra below
the electron Larmor radius scale is well fitted by power law with slope -16/3,
as predicted in Schekochihin et al., Astrophys. J. Suppl. Ser 182, 310 (2009).",1308.3421v2
2014-01-15,Large enhancement of emergent magnetic fields in MnSi with impurities and pressure,"We report a study of the topological Hall effect (THE) in Fe-doped MnSi and
compare with results from pure MnSi under pressure. We find that Fe doping
increases the THE, indicating an enhancement of the magnitude of the emergent
gauge field. This is consistent with the concurrent reduction in the length
scale of the skyrmion lattice. For both pressurized and doped samples, we
calculate the emergent magnetic field based on the size of the measured THE,
and compare it with a theoretical upper-bound. We find that the ratio of these
two remains more or less constant with pressure or Fe doping, but differs
greatly from that of pure MnSi at ambient pressure. We discuss the implications
of this ratio with respect to trends in the saturated magnetic moment and
helical pitch length as T_C \rightarrow 0 via doping and pressure,
respectively.",1401.3680v1
2014-02-04,Observation of the Meissner effect with ultracold atoms in bosonic ladders,"We report on the observation of the Meissner effect in bosonic flux ladders
of ultracold atoms. Using artificial gauge fields induced by laser-assisted
tunneling, we realize arrays of decoupled ladder systems that are exposed to a
uniform magnetic field. By suddenly decoupling the ladders and projecting into
isolated double wells, we are able to measure the currents on each side of the
ladder. For large coupling strengths along the rungs of the ladder, we find a
saturated maximum chiral current corresponding to a full screening of the
artificial magnetic field. For lower coupling strengths, the chiral current
decreases in good agreement with expectations of a vortex lattice phase. Our
work marks the first realization of a low-dimensional Meissner effect and,
furthermore, it opens the path to exploring interacting particles in low
dimensions exposed to a uniform magnetic field.",1402.0819v1
2014-02-05,Innovation of Superparamagnetism in Lead Nanoparticles,"This work reports, some of the features related to the room temperature
superparamagnetic behaviours of lead nanoparticles. Such behaviours have not
been discussed elaborately, in any literatures, so far. It is obvious from our
studies that the superparamagnetic behaviours of Pb nanoparticles are
surprising behaviours, since bulk Pb has diamagnetic behaviours. Hysteresis
curve from Vibrating Sample Magnetometer study of Pb nanopowder (metal) serves
some new observations. The successful calculations of values like magnetic
size, saturation magnetization, coercive field, and remanent magnetism confirm
its superparamagnetic nature and explore its potential application in various
industries. This work throws some light on and helps further research.",1402.1431v1
2014-04-11,Intense bipolar structures from stratified helical dynamos,"We perform direct numerical simulations of the equations of
magnetohydrodynamics with external random forcing and in the presence of
gravity. The domain is divided into two parts: a lower layer where the forcing
is helical and an upper layer where the helicity of the forcing is zero with a
smooth transition in between. At early times, a large-scale helical dynamo
develops in the bottom layer. At later times the dynamo saturates, but the
vertical magnetic field continues to develop and rises to form dynamic bipolar
structures at the top, which later disappear and reappear. Some of the
structures look similar to $\delta$ spots observed in the Sun. This is the
first example of magnetic flux concentrations, owing to strong density
stratification, from self-consistent dynamo simulations that generate bipolar,
super-equipartition strength, magnetic structures whose energy density can
exceeds the turbulent kinetic energy by even a factor of ten.",1404.3194v2
2014-04-28,Electronic structure and magnetic properties of L1_0 binary alloys,"We present a systematic study of the magnetic properties of L1$_0$ binary
alloys FeNi, CoNi, MnAl and MnGa via two different density functional theory
approaches. Our calculations show large magnetocrystalline anisotropies in the
order $1~\text{MJ/m}^3$ or higher for CoNi, MnAl and MnGa while FeNi shows a
somewhat lower value in the range $0.48 - 0.77 ~\text{MJ/m}^3$. Saturation
magnetization values of $1.3~\text{MA/m}$, $1.0~\text{MA/m}$, $0.8~\text{MA/m}$
and $0.9~\text{MA/m}$ are obtained for FeNi, CoNi, MnAl and MnGa respectively.
Curie temperatures are evaluated via Monte Carlo simulations and show
$T_\text{C}=916~\text{K}$ and $T_\text{C}=1130~\text{K}$ for FeNi and CoNi
respectively. For Mn-based compounds Mn-rich off-stoichiometric compositions
are found to be important for the stability of a ferro or ferrimagnetic ground
state with $T_\text{C}$ greater than $600~\text{K}$. The effect of
substitutional disorder is studied and found to decrease both
magnetocrystalline anisotropies and Curie temperatures in FeNi and CoNi.",1404.7097v2
2014-05-20,Magnetothermodynamics of BPS baby skyrmions,"The magnetothermodynamics of skyrmion type matter described by the gauged BPS
baby Skyrme model at zero temperature is investigated. We prove that the BPS
property of the model is preserved also for boundary conditions corresponding
to an asymptotically constant magnetic field. The BPS bound and the
corresponding BPS equations saturating the bound are found. Further, we show
that one may introduce pressure in the gauged model by a redefinition of the
superpotential. Interestingly, this is related to non-extremal type solutions
in the so-called fake supersymmetry method. Finally, we compute the equation of
state of magnetized BSP baby skyrmions inserted into an external constant
magnetic field $H$ and under external pressure $P$, i.e., $V=V(P,H)$, where $V$
is the ""volume"" (area) occupied by the skyrmions. We show that the BPS baby
skyrmions form a ferromagnetic medium.",1405.5215v2
2014-05-21,Surface twist instabilities and skyrmion states in chiral ferromagnets,"In epitaxial MnSi/Si(111) films, the in-plane magnetization saturation is
never reached due to the formation of specific surface chiral modulations with
the propagation direction perpendicular to the film surfaces [Wilson et al.
Phys. Rev. B 88, 214420 (2013)]. In this paper we show that the occurrence of
such chiral surface twists is a general effect attributed to all bulk and con-
fined magnetic crystals lacking inversion symmetry. We present experimental
investigations of this phenomenon in nanolayers of MnSi/Si(111) supported by
detailed theoretical analysis within the standard phenomenological model. In
magnetic nanolayers with intrinsic or induced chirality, such surface induced
instabilities become sizeable effects and play a crucial role in the formation
of skyrmion lattices and other nontrivial chiral modulations.",1405.5275v1
2014-06-18,QCD sum rules for magnetically induced mixing between $η_c$ and $J/ψ$,"We investigate the properties of charmonia in strong magnetic fields by using
QCD sum rules. We show how to implement the mixing effects between $\eta_c$ and
$J/\psi$ on the basis of field-theoretical approaches, and then show that the
sum rules are saturated by the mixing effects with phenomenologically
determined parameters. Consequently, we find that the mixing effects are the
dominant contribution to the mass shifts of the charmonia in strong magnetic
fields.",1406.4586v2
2014-06-19,Spin-Flop Phenomenon of Two-Dimensional Frustrated Antiferromagnets without Anisotropy in Spin Space,"Motivated by a recent finding of a spin-flop phenomenon in a system without
anisotropy in spin space reported in the S=1/2 Heisenberg antiferromagnet on
the square-kagome lattice, we study the S=1/2 Heisenberg antiferromagnets on
two other lattices composed of vertex-sharing triangles by the numerical
diagonalization method. One is a novel lattice including a shuriken shape with
four teeth; the other is the kagome lattice with
$\sqrt{3}\times\sqrt{3}$-structure distortion, which includes a shuriken shape
with six teeth. We find in the magnetization processes of these systems that a
magnetization jump accompanied by a spin-flop phenomenon occurs at the
higher-field-side edge of the magnetization plateau at one-third the height of
saturation. This finding indicates that the spin-flop phenomenon found in the
isotropic system on the square-kagome lattice is not an exceptional case.",1406.4964v1
2014-06-30,Effect of laser intensity and dynamics of plasma on laser induced breakdown spectroscopy,"Laser-induced breakdown spectroscopy (LIBS) show enhancement in its signal,
when the laser-induced plasma is confined/decelerated under the effect of an
external steady magnetic field or in a small cavity. An enhancement in LIBS
signal has been observed ~2 times in the case of magnetic confinement.
Combination of magnetic and spatial confinement provide enhancement by an order
of magnitude. Theoretical analysis of the decelerated plasma has been found in
agreement with the experimental observations. The enhancement in LIBS signal is
found dependent on the efficiency of plasma confinement as well as on the time
duration of laser. The saturation in LIBS signal at higher laser intensity is
found correlated with electron-ion collision frequency as well as on the
dynamics and instability of plasma plume. Possibility of further enhancement in
emission has also been discussed.",1406.7703v1
2014-07-31,Explaining the Observed Relation Between Stellar Activity and Rotation,"Observations of late-type main-sequence stars have revealed empirical
scalings of coronal activity versus rotation period or Rossby number $Ro$ (a
ratio of rotation period to convective turnover time) which has hitherto lacked
explanation. For $Ro >> 1$, the activity observed as X-ray to bolometric flux
varies as $Ro^{-q}$ with $2\le q \le 3$, whilst $|q| < 0.12$ for $Ro << 1$.
Here we explain the transition between these two regimes and the power law in
the $Ro >> 1$ regime by constructing an expression for the coronal luminosity
based on dynamo magnetic field generation and magnetic buoyancy. We explain the
$Ro<<1$ behavior from the inference that observed rotation is correlated with
internal differential rotation and argue that once the shear time scale is
shorter than the convective turnover time, eddies will be shredded on the shear
time scale and so the eddy correlation time actually becomes the shear time and
the convection time drops out of the equations. We explain the $Ro >> 1$
behavior using a dynamo saturation theory based on magnetic helicity buildup
and buoyant loss.",1407.8500v3
2014-10-18,Magnetoresistance in two-component systems,"Two-component systems with equal concentrations of electrons and holes
exhibit non-saturating, linear magnetoresistance in classically strong magnetic
fields. The effect is predicted to occur in finite-size samples at charge
neutrality in both disorder- and interaction-dominated regimes. The phenomenon
originates in the excess quasiparticle density developing near the edges of the
sample due to the compensated Hall effect. The size of the boundary region is
of the order of the electron-hole recombination length that is inversely
proportional to the magnetic field. In narrow samples and at strong enough
magnetic fields, the boundary region dominates over the bulk leading to linear
magnetoresistance. Our results are relevant for semimetals and narrow-band
semiconductors including most of the topological insulators.",1410.4982v1
2014-10-31,Enhanced ferrimagnetism in auxetic NiFe2O4 in the crossover to the ultrathin film limit,"We investigate the sensitive interplay between magnetic, electronic and
structural properties in the ferrimagnetic oxide NiFe2O4. Emphasis is placed on
the impact of reduced dimensionality in the crossover from bulk-like to
ultrathin films. We observed an enhanced saturation magnetization $M_S$ for
ultrathin NiFe2O4 films on Nb-SrTiO3 (001) substrates that co-occurs with a
reduced out-of-plane lattice constant under compressive in-plane epitaxial
strain. We found a bulk-like cationic coordination of the inverse spinel
lattice independent of the NiFe2O4 film thickness -- thus ruling out a cationic
inversion that nominally could account for an enhanced $M_S$. Our study instead
uncovers a reduction of the unit cell volume, i.e. an auxetic behavior in
ultrathin NiFe2O4 films, which may result in an enhanced magnetic exchange
caused by an increased interatomic electronic localization.",1410.8782v1
2014-11-16,Microscopic Model Calculations for the Magnetization Process of Layered Triangular-Lattice Quantum Antiferromagnets,"Magnetization processes of spin-1/2 layered triangular-lattice
antiferromagnets (TLAFs) under a magnetic field H are studied by means of a
numerical cluster mean-field method with a scaling scheme. We find that small
antiferromagnetic couplings between the layers give rise to several types of
extra quantum phase transitions among different high-field coplanar phases.
Especially, a field-induced first-order transition is found to occur at
H\approx 0.7 H_s, where H_s is the saturation field, as another common quantum
effect of ideal TLAFs in addition to the well-established one-third plateau.
Our microscopic model calculation with appropriate parameters show excellent
agreement with experiments on Ba_3CoSb_2O_9 [T. Susuki et al., Phys. Rev. Lett.
110, 267201 (2013)]. Given this fact, we suggest that the Co^{2+}-based
compounds may allow for quantum simulations of intriguing properties of this
simple frustrated model, such as quantum criticality and supersolid states.",1411.4233v2
2014-12-22,Surface sensitivity of the spin Seebeck effect,"We have investigated the influence of the interface quality on the spin
Seebeck effect (SSE) of the bilayer system yttrium iron garnet (YIG) - platinum
(Pt). The magnitude and shape of the SSE is strongly influenced by mechanical
treatment of the YIG single crystal surface. We observe that the saturation
magnetic field H_{sat} for the SSE signal increases from 55.3 mT to 72.8 mT
with mechanical treatment. The change in the magnitude of H_{sat} can be
attributed to the presence of a perpendicular magnetic anisotropy due to the
treatment induced surface strain or shape anisotropy in the Pt/YIG system. Our
results show that the SSE is a powerful tool to investigate magnetic anisotropy
at the interface.",1412.7712v1
2015-01-06,Neutron Diffraction Studies on Chemical and Magnetic Structure of Multiferroic PbFe0.67W0.33O3,"We report on the single phase synthesis and room temperature structural
characterization of PbFe0.67W0.33O3 (PFW) multiferroic. The PFW was synthesized
by low temperature sintering, Columbite method. Analysis of powder XRD pattern
exhibits single phase formation of PFW with no traces of pyrochlore phase.
Detailed analysis of room temperature neutron diffraction (ND) reveals cubic
phase at room temperature, space group Pm-3m. The ND pattern clearly reveals
magnetic Bragg peak at 2theeta = 18.51 (Q = 1.36{\AA}-1). The refinement of
magnetic structure reveals G-type antiferromagnetic structure in PFW at room
temperature. The dielectric constant and loss tangent decreases with increasing
frequency. The room temperature P-E measurements shows a non-linear slim
hysteresis, typical nature of relaxor multiferroics, with saturation and
remnant polarizations of Ps = 1.50 microC/cm2 and Pr = 0.40 microC/cm2,
respectively.",1501.01103v1
2015-01-14,Suppression of 3D-ordering by defects in the $S=1/2$ frustrated chain magnet LiCuVO$_4$,"We report on a heat capacity study of high quality single crystal samples of
\lcvo\ -- a frustrated spin $S=1/2$ chain system -- in magnetic field amounting
to 3/4 of the saturation field. At low fields up to about 7~T, a linear
temperature dependence of the specific heat, $C_p\propto T$, resulting from 1D
magnetic correlations in the spin chains is followed upon cooling by a sharp
lambda anomaly of the transition into a 3D helical phase with $C_p\propto T^3$
behavior at low temperature. The transition from a spin liquid into a
spin-modulated (SM) phase at higher fields occurs via a hump-like anomaly
which, as the temperature decreases further turns into a $C_p\propto T^2$ law
distinctive for a quasi-2D system. We suggest an explanation for how
nonmagnetic defects in the Cu$^{2+}$ chains can suppress 3D long-range ordering
in the SM phase and leave it undisturbed in a helical phase.",1501.03226v1
2015-02-20,Magnetization patterning induced by electrical spin-polarized current in nanostripes,"The combined action of a transverse spin-polarized current and the
current-induced {\O}rsted field on long ferromagnetic nanostripes is studied
numerically and analytically. The magnetization behavior is analyzed for
stripes with various widths and for all range of the applied current density.
It is established that {\O}rsted field does not destroy periodical
magnetization structures induced by the spin-torque, e.g. vortex-antivortex
crystal and cross-tie domain walls. However, the action of the {\O}rsted field
disables the saturation state for the strong currents: a stationary state with
a single longitudinal domain wall appears instead. Shape of this wall remains
constant with the current increasing. The latter phenomenon is studied both
numerically and analytically.",1502.05885v1
2015-03-05,Feshbach molecule formation through an oscillating magnetic field: subharmonic resonances,"The conversion of ultracold atoms to molecules via a magnetic Feshbach
resonance with a sinusoidal modulation of the field is studied. Different
practical realizations of this method in Bose atomic gases are analyzed. Our
model incorporates many-body effects through an effective reduction of the
complete microscopic dynamics. Moreover, we simulate the experimental
conditions corresponding to the preparation of the system as a thermal gas and
as a condensate. Some of the experimental findings are clarified. The origin of
the observed dependence of the production efficiency on the frequency,
amplitude, and application time of the magnetic modulation is elucidated. Our
results uncover also the role of the atomic density in the dynamics,
specifically, in the observed saturation of the atom-molecule conversion
process.",1503.01700v1
2015-03-11,Evidence for Half-Metallicity in n-type HgCr2Se4,"High quality HgCr$_2$Se$_4$ single crystals have been investigated by
magnetization, electron transport and Andreev reflection spectroscopy. In the
ferromagnetic ground state, the saturation magnetic moment of each unit cell
corresponds to an integer number of electron spins (3 $\mu_B$/Cr$^{3+}$), and
the Hall effect measurements suggest n-type charge carriers. Spin polarizations
as high as $97\%$ were obtained from fits of the differential conductance
spectra of HgCr$_2$Se$_4$/Pb junctions with the modified
Blonder-Tinkham-Klapwijk (BTK) theory. The temperature and bias-voltage
dependencies of the sub-gap conductance are consistent with recent theoretical
calculations based on spin active scatterings at a superconductor/half metal
interface. Our results suggest that n-HgCr$_2$Se$_4$ is a half metal, in
agreement with theoretical calculations that also predict undoped
HgCr$_2$Se$_4$ is a magnetic Weyl semimetal.",1503.03190v3
2015-03-12,"Shubnikov-de Haas oscillations, weak antilocalization effect and large linear magnetoresistance in the putative topological superconductor LuPdBi","We present electronic transport and magnetic properties of single crystals of
semimetallic half-Heusler phase LuPdBi, having theoretically predicted band
inversion requisite for nontrivial topological properties. The compound
exhibits superconductivity below a critical temperature $T_{\rm c}=1.8\,$K,
with a zero-temperature upper critical field $B_{\rm c2}\approx2.3\,$T.
Although superconducting state is clearly reflected in the electrical
resistivity and magnetic susceptibility data, no corresponding anomaly can be
seen in the specific heat. Temperature dependence of the electrical resistivity
suggests existence of two parallel conduction channels: metallic and
semiconducting, with the latter making negligible contribution at low
temperatures. The magnetoresistance is huge and clearly shows a weak
antilocalization effect in small magnetic fields. Above about 1.5 T, the
magnetoresistance becomes linear and does not saturate in fields up to 9 T. The
linear magnetoresistance is observed up to room temperature. Below 10 K, it is
accompanied by Shubnikov-de Haas oscillations. Their analysis reveals charge
carriers with effective mass of $0.06\,m_e$ and a Berry phase very close to
$\pi$, expected for Dirac-fermion surface states, thus corroborating
topological nature of the material.",1503.03697v1
2015-03-19,Anomalous magnetization of $S$=2 ferromagnetic-antiferromagnetic alternating chain with Ising anisotropy,"We present the first experimental realization of an $S=2$
ferromagnetic-antiferromagnetic (F-AF) alternating chain in a new Mn-verdazyl
complex [Mn(hfac)$_2$]$\cdot$($o$-Py-V)
[hfac=1,1,1,5,5,5-hexafluoroacetylacetonate;
$o$-Py-V=3-(2-pyridyl)-1,5-diphenylverdazyl]. Through the $ab$ $initio$
molecular orbital calculation, magnetization, and ESR measurements, this
compound is confirmed to form an $S=2$ F-AF alternating chain with Ising
anisotropy below about 100 K. Furthermore, we find an anomalous change in
magnetization at 1/4 of the saturation value, which is probably a manifestation
of the quantum nature of the system.",1503.05633v1
2015-05-20,Effect of Transverse Magnetic Field on Dynamics of Current Driven Domain Wall Motion in the Presence of Spin-Hall Effect,"Theoretically, we study the dynamics of a current induced domain wall in the
bi-layer structure consists of a ferromagnetic layer and a non-magnetic metal
layer with strong spin-orbit coupling in the presence of spin-Hall effect. The
analytical expressions for the velocity and width of the domain wall interms of
excitation angle are obtained by solving the Landau-Lifshitz-Gilbert equation
with adiabatic, nonadiabatic and spin Hall effect-spin transfer torques using
Schryers and Walker's method. Numerical results show that the occurance of
polarity switching in the domain wall is observed only above the threshold
current density. The presence of transverse magnetic field along with spin Hall
effect-spin transfer torque enchances the value of the threshold current
density, and the corresponding saturated velocity at the threshold current
density is also increased.",1505.05249v1
2015-06-05,Broad universal Feshbach resonances in the chaotic spectrum of Dysprosium atoms,"We report on the observation of weakly-bound dimers of bosonic Dysprosium
with a strong universal s-wave halo character, associated with broad magnetic
Feshbach resonances. These states surprisingly decouple from the chaotic
backgound of narrow resonances, persisting across many such narrow resonances.
In addition they show the highest reported magnetic moment
$\mu\simeq20\,\mu_{\rm B}$ of any ultracold molecule. We analyze our findings
using a coupled-channel theory taking into account the short range van der
Waals interaction and a correction due to the strong dipole moment of
Dysprosium. We are able to extract the scattering length as a function of
magnetic field associated with these resonances and obtain a background
scattering length $a_{\rm bg}=91(16)\,a_0$. These results offer prospects of a
tunability of the interactions in Dysprosium, which we illustrate by observing
the saturation of three-body losses.",1506.01875v2
2015-06-16,Approaching magnetic ordering in graphene materials by FeCl$_3$ intercalation,"We show the successful intercalation of large area (1 cm$^2$) epitaxial
few-layer graphene grown on 4H-SiC with FeCl$_3$. Upon intercalation the
resistivity of this system drops from an average value of $\approx 200 \
\Omega/sq$ to $\approx 16 \ \Omega/sq$ at room temperature. The
magneto-conductance shows a weak localization feature with a temperature
dependence typical of graphene Dirac fermions demonstrating the decoupling into
parallel hole gases of each carbon layer composing the FeCl$_3$ intercalated
structure. The phase coherence length ($\approx 1.2 \mu$m at 280 mK) decreases
rapidly only for temperatures higher than the 2-D magnetic ordering in the
intercalant layer while it tends to saturate for temperatures lower than the
antiferromagnetic ordering between the planes of FeCl$_3$ molecules providing
the first evidence for magnetic ordering in the extreme two-dimensional limit
of graphene.",1506.04959v1
2015-07-23,Theory of nuclear spin dephasing and relaxation by optically illuminated nitrogen-vancy center,"Dephasing and relaxation of the nuclear spins coupled to the nitrogen-vacancy
(NV) center during optical initialization and readout is an important issue for
various applications of this hybrid quantum register. Here we present both an
analytical description and a numerical simulation for this process, which agree
reasonably with the experimental measurements. For the NV center under cyclic
optical transition, our analytical formula not only provide a clear physics
picture, but also allows controlling the nuclear spin dissipation by tuning an
external magnetic field. For more general optical pumping, our analytical
formula reveals significant contribution to the nuclear spin dissipation due to
electron random hopping into/out of the $m=0$ (or $m=\pm1$) subspace. This
contribution is not suppressed even under saturated optical pumping and/or
vanishing magnetic field, thus providing a possible solution to the puzzling
observation of nuclear spin dephasing in zero perpendicular magnetic field [M.
V. G. Dutt \textit{et al}., Science \textbf{316}, 1312 (2007)]. It also implies
that enhancing the degree of spin polarization of the nitrogen-vacancy center
can reduce the effect of optical induced nuclear spin dissipation.",1507.06385v1
2015-07-30,Magnetic Field Amplification via Protostellar Disc Dynamos,"We numerically investigate the generation of a magnetic field in a
protostellar disc via an $\alpha \Omega$-dynamo and the resulting
magnetohydrodynamic (MHD) driven outflows. We find that for small values of the
dimensionless dynamo parameter $\alpha_d$ the poloidal field grows
exponentially at a rate $\sigma \propto \Omega_K \sqrt{\alpha_d}$, before
saturating to a value $\propto \sqrt{\alpha_d}$. The dynamo excites dipole and
octupole modes, but quadrupole modes are suppressed, because of the symmetries
of the seed field. Initial seed fields too weak to launch MHD outflows are
found to grow sufficiently to launch winds with observationally relevant mass
fluxes of order $10^{-9} M_{\odot}/\rm{yr}$ for T Tauri stars. This suggests
$\alpha \Omega$-dynamos may be responsible for generating magnetic fields
strong enough to launch observed outflows.",1507.08702v2
2015-11-05,Size effect on the hysteresis characteristics of a system of interacting core/shell nanoparticles,"We have developed a model for the interacting ore/shell nanoparticles, which
we used to analyze the dependence of the coercive field Hc, the remanent
saturation magnetization Mrs and the satu- ration magnetization Ms on the
interfacial exchange interaction between the core and the shell, the size of
the nanoparticles and their interaction for Fe/Fe3O4 nanoparticles have been
carried out. It has been shown that the hysteresis characteristics increase
together with the size of nanoparticles. Hc and Mrs are changing nonmonotonic
when the constant interfacial exchange interaction changes from negative to
positive values. In the system of core/shell nanoparticles, magnetic
interaction results in Hc and Mrs dropping, which was conformed by experiments.
Usage: Secondary publications and information retrieval purposes.",1511.01617v1
2016-03-15,Highly Sensitive On-Chip Magnetometer with Saturable Absorbers in Two-Color Microcavities,"Interacting resonators can lead to strong non-linearities but the details can
be complicated to predict. In this work, we study the non-linearities
introduced by two nested microcavities that interact with nitrogen vacancy
centers in a diamond waveguide. Each cavity has differently designed resonance;
one in the green and one in the infrared. The magnetic-field dependence of the
nitrogen vacancy center absorption rates on the green and the recently observed
infrared transitions allows us to propose a scalable on-chip magnetometer that
combines high magnetic-field sensitivity and micrometer spatial resolution. By
investigating the system behaviors over several intrinsic and extrinsic
parameters, we explain the main non-linearities induced by the NV centers and
enhanced by the cavities. We finally show that the cavities can improve the
magnetic-field sensitivity by up to two orders of magnitudes.",1603.04529v1
2016-04-06,Numerical simulations of Kelvin-Helmholtz instability: a two-dimensional parametric study,"Using two-dimensional simulations, we numerically explore the dependences of
Kelvin-Helmholtz instability upon various physical parameters, including
viscosity, width of sheared layer, flow speed, and magnetic field strength. In
most cases, a multi-vortex phase exists between the initial growth phase and
final single-vortex phase. The parametric study shows that the evolutionary
properties, such as phase duration and vortex dynamics, are generally sensitive
to these parameters except in certain regimes. An interesting result is that
for supersonic flows, the phase durations and saturation of velocity growth
approach constant values asymptotically as the sonic Mach number increases. We
confirm that the linear coupling between magnetic field and Kelvin-Helmholtz
modes is negligible if the magnetic field is weak enough. The morphological
behaviour suggests that the multi-vortex coalescence might be driven by the
underlying wave-wave interaction. Based on these results, we make a preliminary
discussion about several events observed in the solar corona. The numerical
models need to be further improved to make a practical diagnostic of the
coronal plasma properties.",1604.01546v1
2016-05-01,Numerical study of the Transverse Diffusion coefficient for a one component model of a plasma,"We report the results of MD numerical simulations for a one component model
of a plasma in the weakly coupled regime, at different values of temperature
$T$ and applied magnetic field $\vec B$, in which the diffusion coefficient
$D_{\perp}$ transverse to the field is estimated. We find that there exists a
threshold in temperature, at which an inversion occurs, namely, for $T$ above
the threshold the diffusion coefficient $D_{\perp}$ starts decreasing as $T$
increases. This is at variance with the behavior predicted by the Bohm law
$D_{\perp}\sim T/B$, which actually holds below the threshold. In addition we
find that, for temperatures above such a threshold, another transition occurs,
now with respect to the values of the magnetic field: for weak magnetic fields
the diffusion coefficients scales as $1/B^2$, in agreement with the predictions
of the standard kinetics theory, while it apparently saturates when the field
strength is sufficiently increased.",1605.00235v1
2016-05-03,T/B scaling without quasiparticle mass divergence: YbCo2Ge4,"YbCo$_2$Ge$_4$ is a clean paramagnetic Kondo lattice which displays non-Fermi
liquid behavior. We report a detailed investigation of the specific heat,
magnetic Gr\""uneisen parameter ($\Gamma_{\rm mag}$) and temperature derivative
of the magnetization ($M$) on a high-quality single crystal at temperatures
down to $0.1$~K and magnetic fields up to 7~T. $\Gamma_{\rm mag}$ and $dM/dT$
display a divergence upon cooling and obey $T/B$ scaling. Similar behavior has
previously been found in several other Yb-based Kondo lattices and related to a
zero-field quantum critical point without fine tuning of pressure or
composition. However, in the approach of $B\rightarrow 0$ the electronic heat
capacity coefficient of YbCo$_2$Ge$_4$ saturates at low $T$, excluding
ferromagnetic quantum criticality. This indicates that $T/B$ scaling is
insufficient to prove a zero-field quantum critical point.",1605.00896v2
2016-05-06,"Exchange-mediated, non-linear, out-of-plane magnetic field dependence of the ferromagnetic vortex gyrotropic mode frequency driven by core deformation","We have performed micromagnetic simulations of the vortex gyrotropic mode
resonance in a range of disk geometries subject to spatially uniform
out-of-plane magnetic fields. For disks of small lateral dimensions, we observe
a drop-off in the mode's frequency for field amplitudes approaching the disk
saturation field. This non-linear frequency response is shown to be associated
with an increased vortex core deformation, which results from the demagnetizing
field created when the core is shifted laterally. Such deformation results in
an increase in the average out-of-plane magnetization of the displaced vortex
state, which through an exchange contribution, leads to a sharp decrease in the
vortex stiffness coefficient. It is this decrease in the vortex stiffness
coefficient which leads to the non-linear field dependence of the gyrotropic
mode frequency.",1605.01830v1
2016-06-13,Electronic Transport on the Shastry-Sutherland Lattice in Ising-type Rare Earth Tetraborides,"In the presence of a magnetic field frustrated spin systems may exhibit
plateaus at fractional values of saturation magnetization. Such plateau states
are stabilized by classical and quantum mechanisms including order-by-disorder,
triplon crystallization, and various competing order effects. In the case of
electrically conducting systems, free electrons represent an incisive probe for
the plateau states. Here we study the electrical transport of Ising-type rare
earth tetraborides $R$B$_4$ ($R=$Er, Tm), a metallic Shastry-Sutherland lattice
showing magnetization plateaus. We find that the longitudinal and transverse
resistivities reflect scattering with both the static and dynamic plateau
structure. We model these results consistently with the expected strong
uniaxial anisotropy in a quantitative level, providing a framework for the
study of plateau states in metallic frustrated systems.",1606.04003v2
2016-08-03,An analytical dynamo solution for large-scale magnetic fields of galaxies,"We present an effectively global analytical asymptotic galactic dynamo
solution for the regular magnetic field of an axisymmetric thin disc in the
saturated state. This solution is constructed by combining two well-known types
of local galactic dynamo solution, parameterized by the disc radius. Namely,
the critical (zero growth) solution obtained by treating the dynamo equation as
a perturbed diffusion equation is normalized using a non-linear solution that
makes use of the `no-$z$' approximation and the dynamical $\alpha$-quenching
non-linearity. This overall solution is found to be reasonably accurate when
compared with detailed numerical solutions. It is thus potentially useful as a
tool for predicting observational signatures of magnetic fields of galaxies. In
particular, such solutions could be painted onto galaxies in cosmological
simulations to enable the construction of synthetic polarized synchrotron and
Faraday rotation measure (RM) datasets. Further, we explore the properties of
our numerical solutions, and their dependence on certain parameter values. We
illustrate and assess the degree to which numerical solutions based on various
levels of approximation, common in the dynamo literature, agree with one
another.",1608.01119v3
2016-08-31,Stagnation of electron flow by a nonlinearly generated whistler wave,"Relativistic electron beam transport through a high-density, magnetized
plasma is studied numerically and theoretically. An electron beam injected into
a cold plasma excites Weibel and two-stream instabilities that heat the beam
and saturate. In the absence of an applied magnetic field, the heated beam
continues to propagate. However, when a magnetic field of particular strength
is applied along the direction of beam propagation, a secondary instability of
off-angle whistler modes is excited. These modes then couple nonlinearly
creating a large amplitude parallel propagating whistler that stops the beam.
In this letter, we will show the phenomena in detail and explain the mechanism
of whistler mediated beam stagnation.",1608.08867v1
2016-09-14,Rashba-Edelstein Magnetoresistance in Metallic Heterostructure,"We report the observation of magnetoresistance originating from Rashba
spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein
(RE) magnetoresistance. We show that the simultaneous action of the direct and
inverse RE effects in a Bi/Ag/CoFeB trilayer couples current-induced spin
accumulation to the electric resistance. The electric resistance changes with
the magnetic-field angle, reminiscent of the spin Hall magnetoresistance,
despite the fact that bulk SOC is not responsible for the magnetoresistance. We
further found that, even when the magnetization is saturated, the resistance
increases with increasing the magnetic-field strength, which is attributed to
the Hanle magnetoresistance in this system.",1609.04122v1
2016-10-11,Semiclassical analysis of a magnetization plateau in a 2D frustrated ferrimagnet,"We use a semiclassical large-$S$ expansion to study a plateau at $1/3$
saturation in the magnetization curve of a frustrated ferrimagnet on a
spatially anisotropic kagom\'{e} lattice. The spins have both ferromagnetic and
antiferromagnetic nearest-neighbor Heisenberg couplings, and a frustrating
next-nearest-neighbor coupling in one lattice direction. The magnetization
plateau appears at the classical level for a certain range of couplings, and
quantum fluctuations significantly broaden it at both ends. Near the region of
the phase diagram where the classical plateau destabilizes, we find an exotic
""chiral liquid"" phase that preserves translational and $U(1)$ spin symmetry, in
which bound pairs of magnons with opposite spins are condensed. We show how
this state is obtained naturally from a relativistic field theory formulation.
We comment on the relevance of the model to the material
$\text{Cu}_3\text{V}_2\text{O}_7\text{(OH)}_2 \cdot 2\text{H}_2\text{O}$
(volborthite).",1610.03135v3
2016-11-01,Magnetoelectric Behavior from $S=1/2$ Asymmetric Square Cupolas,"Magnetoelectric properties are studied by a combined experimental and
theoretical study of a quasi-two-dimensional material composed of square
cupolas, Ba(TiO)Cu$_4$(PO$_4$)$_4$. The magnetization is measured up to above
the saturation field, and several anomalies are observed depending on the field
directions. We propose a $S$=1/2 spin model with Dzyaloshinskii-Moriya
interactions, which well reproduces the full magnetization curves. Elaborating
the phase diagram of the model, we show that the anomalies are explained by
magnetoelectric phase transitions. Our theory also accounts for the scaling of
the dielectric anomaly observed in experiments. The results elucidate the
crucial role of the in-plane component of Dzyaloshinskii-Moriya interactions,
which is induced by the noncoplanar buckling of square cupola. We also predict
a `hidden' phase and another magnetoelectric response both of which appear in
nonzero magnetic field.",1611.00086v1
2016-12-13,Gyrofluid computation of magnetic perturbation effects on turbulence and edge localized bursts,"The effects of non-axisymmetric resonant magnetic perturbation fields (RMPs)
on saturated drift-wave turbulence and on ballooning mode bursts in the edge
pedestal of tokamak plasmas are investigated by numerical simulations with a
nonlinear six-moment electromagnetic gyrofluid model including zonal profile
evolution. The vacuum RMP fields are screened by plasma response currents, so
that magnetic transport by perturbed parallel motion is not significantly
changed. Radial transport of both particles and heat is dominated by turbulent
convection even for large RMP amplitudes, where formation of stationary
convective structures leads to edge profile degradation. Modelling of ideal
ballooning mode unstable edge profiles for single bursts including RMP fields
causes resonant mode locking and destabilization.",1612.04121v1
2017-01-26,Frustrated honeycomb-lattice bilayer quantum antiferromagnet in a magnetic field: Unconventional phase transitions in a two-dimensional isotropic Heisenberg model,"We consider the spin-1/2 antiferromagnetic Heisenberg model on a bilayer
honeycomb lattice including interlayer frustration in the presence of an
external magnetic field. In the vicinity of the saturation field, we map the
low-energy states of this quantum system onto the spatial configurations of
hard hexagons on a honeycomb lattice. As a result, we can construct effective
classical models (lattice-gas as well as Ising models) on the honeycomb lattice
to calculate the properties of the frustrated quantum Heisenberg spin system in
the low-temperature regime. We perform classical Monte Carlo simulations for a
hard-hexagon model and adopt known results for an Ising model to discuss the
finite-temperature order-disorder phase transition that is driven by a magnetic
field at low temperatures. We also discuss an effective-model description
around the ideal frustration case and find indications for a spin-flop like
transition in the considered isotropic spin model.",1701.07876v1
2017-01-27,A unified description of collective magnetic excitations,"In this work, we define a set of analytic tools to describe the dynamic
response of the magnetization to small perturbations, which can be used on its
own or in combination with micromagnetic simulations and does not require
saturation. We present a general analytic description of the ferromagnetic high
frequency susceptibility tensor to describe angular as well as frequency
dependent ferromagnetic resonance spectra and account for asymmetries in the
line shape. Furthermore, we expand this model to reciprocal space and show how
it describes the magnon dispersion. Finally we suggest a trajectory dependent
solving tool to describe the equilibrium states of the magnetization.",1701.09078v2
2017-02-21,"Back hopping in spin-transfer-torque devices, possible origin and counter measures","The effect of undesirable high-frequency free-layer switching in magnetic
multilayer systems, referred to as back hopping, is investigated by means of
the spin-diffusion model. A possible origin of the back-hopping effect is found
to be the destabilization of the pinned layer which leads to perpetual
switching of both layers. The influence of different material parameters on the
critical switching currents for the free and pinned layer is obtained by
micromagnetic simulations. It is found that the choice of a free-layer material
with low polarization $\beta$ and saturation magnetization $M_s$, and a
pinned-layer material with high $\beta$ and $M_s$ leads to a low free-layer
critical current and a high pinned-layer critical current and hence reduces the
likelihood of back hopping. While back hopping was observed in various types of
devices, there are only few experiments that exhibit this effect in
perpendicularly magnetized systems. However, our simulations suggest, that this
is likely to change due to loss of pinned-layer anisotropy when decreasing
device sizes.",1702.06604v3
2017-03-16,All-Angle Collimation for Spin Waves,"We studied the effect of collimation for monochromatic beams of spin waves,
resulting from the refraction at the interface separating two magnetic
half-planes. The collimation was observed in broad range of the angles of
ncidence for homogenous Co and Py half-planes, due to significant intrinsic
anisotropy of spin wave propagation in these materials. The effect exists for
the sample saturated by in plane magnetic field tangential to the interface.
The collimation for all possible angles of incidence was found in the system
where the incident spin wave is refracted on the interface between homogeneous
and periodically patterned layers of YIG. The refraction was investigated by
the analysis of isofrequency dispersion contours of both pairs materials, i.e.,
uniform YIG/patterned YIG and Co/Py, which are calculated with the aid of the
plane wave method. Besides, the refraction in Co/Py system was studied using
micromagnetic simulations.",1703.05548v1
2017-03-16,"Magnetic properties, domain wall creep motion and the Dzyaloshinskii-Moriya interaction in Pt/Co/Ir thin films","We study the magnetic properties of perpendicularly magnetised Pt/Co/Ir thin
films and investigate the domain wall creep method of determining the
interfacial Dzyaloshinskii-Moriya (DM) interaction in ultra-thin films.
Measurements of the Co layer thickness dependence of saturation magnetisation,
perpendicular magnetic anisotropy, and symmetric and antisymmetric (i.e. DM)
exchange energies in Pt/Co/Ir thin films have been made to determine the
relationship between these properties. We discuss the measurement of the DM
interaction by the expansion of a reverse domain in the domain wall creep
regime. We show how the creep parameters behave as a function of in-plane bias
field and discuss the effects of domain wall roughness on the measurement of
the DM interaction by domain expansion. Whereas modifications to the creep law
with DM field and in-plane bias fields have taken into account changes in the
energy barrier scaling parameter $\alpha$, we find that both $\alpha$ and the
velocity scaling parameter $v_{0}$ change as a function of in-plane bias field.",1703.05749v2
2017-04-05,The interfacial nature of proximity induced magnetism and the Dzyaloshinskii-Moriya interaction at the Pt/Co interface,"The Dzyaloshinskii-Moriya interaction (DMI) has been shown to stabilise
Ne\'{e}l domain walls in magnetic thin films, allowing high domain wall
velocities driven by spin current effects. DMI occurs at the interface between
ferromagnetic and heavy metal layers with strong spin-orbit coupling, but
details of the interaction remain to be understood and the role of proximity
induced magnetism (PIM) in the heavy metal is unknown. We report interfacial
DMI and PIM in Pt determined as a function of Au and Ir spacer layers in
Pt/Co/Au,Ir/Pt. The length-scale for both interactions is sensitive to
sub-nanometre changes in the spacer thickness, and they correlate over sub
mono-layer spacer thicknesses, but not for thicker spacers. The spacer layer
thickness dependence of the Pt PIM for both Au and Ir shows a rapid monotonic
decay, while the DMI changes rapidly but has a two-step approach to saturation
and continues to change, even after the PIM is lost.",1704.01338v1
2017-04-18,The electronic structure and magnetic phase transition of hexagonal FeSe thin films studied by photoemission spectroscopy,"Hexagonal FeSe thin films were grown on SrTiO3 substrates and the temperature
and thickness dependence of their electronic structures were studied. The
hexagonal FeSe is found to be metallic and electron doped, whose Fermi surface
consists of six elliptical electron pockets. With decreased temperature, parts
of the bands shift downward to high binding energy while some bands shift
upwards to EF. The shifts of these bands begin around 300 K and saturate at low
temperature, indicating a magnetic phase transition temperature of about 300 K.
With increased film thickness, the Fermi surface topology and band structure
show no obvious change except some minor quantum size effect. Our paper reports
the first electronic structure of hexagonal FeSe, and shows that the possible
magnetic transition is driven by large scale electronic structure
reconstruction.",1704.05177v2
2017-04-30,Angular Dependent Magnetization Dynamics of Kagome Artificial Spin Ice Incorporating Topological Defects,"We report angular-dependent spin-wave spectroscopy on kagome artificial spin
ice made of large arrays of interconnected Ni80Fe20 nanobars. Spectra taken in
saturated and disordered states exhibit a series of resonances with
characteristic in-plane angular dependencies. Micromagnetic simulations allow
us to interpret characteristic resonances of a two-step magnetization reversal
of the nanomagnets. The dynamic properties are consistent with topological
defects that are provoked via a magnetic field applied at specific angles.
Simulations that we performed on previously investigated kagome artificial spin
ice consisting of isolated nanobars show characteristic discrepancies in the
spin wave modes which we explain by the absence of vertices.",1705.00270v1
2017-05-02,Strongly interaction-enhanced valley magnetic response in monolayer WSe2,"Coulomb interaction between electrons lies at the heart of magnetism in
solids. In contrast to conventional two-dimensional (2D) systems, electrons in
monolayer transition metal dichalcogenides (TMDs) possess coupled spin and
valley degrees of freedom by the spin-orbit interaction. The electrons are also
strongly interacting even in the high-density regime because of the weak
dielectric screening in two dimensions and a large band mass. The combination
of these properties presents a unique platform for exploring spin and valley
magnetism in 2D electron liquids. Here we report an observation by
magneto-photoluminescence spectroscopy of a nonlinear valley Zeeman effect,
correlated with an over fourfold enhancement in the exciton g-factor in
monolayer WSe2. The effect occurs when the Fermi level crosses the spin-split
upper conduction band, corresponding to a change of the spin-valley degeneracy
from 2 to 4. The enhancement increases, shows no sign of saturation as the
sample temperature decreases. Our result suggests the possibility of rich
many-body ground states in monolayer TMDs with multiple internal degrees of
freedom.",1705.01078v1
2017-05-09,The relation between color spaces and compositional data analysis demonstrated with magnetic resonance image processing applications,"This paper presents a novel application of compositional data analysis
methods in the context of color image processing. A vector decomposition method
is proposed to reveal compositional components of any vector with positive
components followed by compositional data analysis to demonstrate the relation
between color space concepts such as hue and saturation to their compositional
counterparts. The proposed methods are applied to a magnetic resonance imaging
dataset acquired from a living human brain and a digital color photograph to
perform image fusion. Potential future applications in magnetic resonance
imaging are mentioned and the benefits/disadvantages of the proposed methods
are discussed in terms of color image processing.",1705.03457v4
2017-05-11,Itinerant G-type antiferromagnetic order in SrCr$_2$As$_2$,"Neutron diffraction and magnetic susceptibility studies of a polycrystalline
SrCr$_2$As$_2$ sample reveal that this compound is an itinerant G-type
antiferromagnet below the N${\rm \acute{e}}$el temperature $T_{\textrm N}$ =
590(5) K with the Cr magnetic moments aligned along the tetragonal $c$ axis.
The system remains tetragonal to the lowest measured temperature ($\sim$12 K).
The lattice parameter ratio $c/a$ and the magnetic moment saturate at about the
same temperature below $\sim$ 200 K, indicating a possible magnetoelastic
coupling. The ordered moment, $\mu=1.9(1)~\mu_{\rm B}$/Cr, measured at $T = 12$
K, is significantly reduced compared to its localized value ($4~\mu_{\rm
B}$/Cr) due to the itinerant character brought about by the hybridization
between the Cr $3d$ and As $4p$ orbitals.",1705.04246v1
2017-06-19,"Large, nonsaturating thermopower in a quantizing magnetic field","The thermoelectric effect is the generation of an electrical voltage from a
temperature gradient in a solid material due to the diffusion of free charge
carriers from hot to cold. Identifying materials with large thermoelectric
response is crucial for the development of novel electric generators and
coolers. In this paper we consider theoretically the thermopower of Dirac/Weyl
semimetals subjected to a quantizing magnetic field. We contrast their
thermoelectric properties with those of traditional heavily-doped
semiconductors and we show that, under a sufficiently large magnetic field, the
thermopower of Dirac/Weyl semimetals grows linearly with the field without
saturation and can reach extremely high values. Our results suggest an
immediate pathway for achieving record-high thermopower and thermoelectric
figure of merit, and they compare well with a recent experiment on
Pb$_{1-x}$Sn$_x$Se.",1706.06117v2
2017-07-06,Multi-Q mesoscale magnetism in CeAuSb$_2$,"We report the discovery of a field driven transition from a striped to woven
Spin Density Wave (SDW) in the tetragonal heavy fermion compound CeAuSb$_2$.
Polarized along $\bf c$, the sinusoidal SDW amplitude is 1.8(2) $\mu_B$/Ce for
$T \ll T_N$=6.25(10) K with wavevector ${\bf q}_{1}=( \eta, \eta, \frac{1}{2}
)$ ($\eta=0.136(2)$). For ${\bf H}\parallel{\bf c}$, harmonics appearing at
$2{\bf q}_{1}$ evidence a striped magnetic texture below $\mu_\circ
H_{c1}=2.78(1)$ T. Above $H_{c1}$, these are replaced by woven harmonics at
${\bf q}_{1}+{\bf q}_2=(2\eta, 0, 0)+{\bf c}^*$ until $\mu_\circ
H_{c2}=5.42(5)$ T, where satellites vanish and magnetization non-linearly
approaches saturation at 1.64(2) $\mu_B$/Ce for $\mu_\circ H\approx 7$ T.",1707.01611v1
2017-07-25,Linarite - a quasi-critical J$_1$-J$_2$ chain,"The mineral linarite, PbCuSO$_4$(OH)$_2$, is a spin 1/2 chain with
frustrating nearest neighbor ferromagnetic and next-nearest neighbor
antiferromagnetic exchange interactions. Our inelastic neutron scattering
experiments performed above the saturation field establish that the ratio
between these exchanges is such that linarite is extremely close to the quantum
critical point between spin-multipolar phases and the ferromagnetic state.
However, the measured complex magnetic phase diagram depends strongly on the
magnetic field direction. The field-dependent phase sequence is explained by
our classical simulations of a nearly critical model with tiny orthorhombic
exchange anisotropy. The simulations also capture qualitatively the measured
variations of the wave vector as well as the staggered and the uniform
magnetizations in an applied field.",1707.08051v1
2017-08-29,"Structural, magnetic, and electronic properties of GdTiO3 Mott insulator thin films grown by pulsed laser deposition","We report on the optimization process to synthesize epitaxial thin films of
GdTiO3 on SrLaGaO4 substrates by pulsed laser deposition. Optimized films are
free of impurity phases and are fully strained. They possess a magnetic Curie
temperature TC = 31.8 K with a saturation magnetization of 4.2 muB per formula
unit at 10 K. Transport measurements reveal an insulating response, as
expected. Optical spectroscopy indicates a band gap of 0.7 eV, comparable to
the bulk value. Our work adds ferrimagnetic orthotitanates to the palette of
perovskite materials for the design of emergent strongly correlated states at
oxide interfaces using a versatile growth technique such as pulsed laser
deposition.",1708.08785v1
2018-01-17,Hartman effect for spin waves in exchange regime,"Hartman effect for spin waves tunnelling through a barrier in a thin magnetic
film is considered theoretically. The barrier is assumed to be created by a
locally increased magnetic anisotropy field. The considerations are focused on
a nanoscale system operating in the exchange-dominated regime. We derive the
formula for group delay $\tau_{gr}$ of spin wave package and show that
$\tau_{gr}$ saturates with increasing barrier width, which is a signature of
the Hartman effect predicted earlier for photonic and electronic systems. In
our calculations we consider the general boundary exchange conditions which
take into account different strength of exchange coupling between the barrier
and its surrounding. As a system suitable for experimental observation of the
Hartman effect we propose a CoFeB layer with perpendicular magnetic anisotropy
induced by a MgO overlayer.",1801.05876v3
2018-05-24,Disruption of current filaments and isotropization of magnetic field in counter-streaming plasmas,"We study the stability of current filaments produced by the Weibel, or
current filamentation, instability in weakly magnetized counter-streaming
plasmas. It is shown that a resonance exists between the current-carrying ions
and a longitudinal drift-kink mode that strongly deforms and eventually breaks
the current filaments. Analytical estimates of the wavelength, growth rate and
saturation level of the resonant mode are derived and validated by
three-dimensional particle-in-cell simulations. Furthermore, self-consistent
simulations of counter-streaming plasmas indicate that this drift-kink mode is
dominant in the slow down of the flows and in the isotropization of the
magnetic field, playing an important role in the formation of collisionless
shocks.",1805.09814v1
2018-08-17,Director switching dynamics of ferromagnetic nematic liquid crystals,"Successful realization of ferromagnetic nematic liquid crystals has opened up
the possibility to experimentally study a completely new set of fundamental
physical phenomena. In this contribution we present a detailed investigation of
some aspects of the static response and the complex dynamics of ferromagnetic
liquid crystals under the application of an external magnetic field.
Experimental results are then compared with a macroscopic model. Dynamics of
the director were measured by optical methods and analyzed in terms of a
theoretical macroscopic model. A dissipative cross-coupling coefficient
describing the dynamic coupling between the two system order parameters, the
magnetization and the nematic director, is needed to explain the results. In
this contribution we examine the dependency of this coefficient on material
parameters and the saturation magnetization and the liquid crystal host.
Despite the complexity of the system, the theoretical description allows for a
proper interpretation of the results and is connected to several microscopic
aspects of the colloidal suspension.",1808.05843v1
2019-01-28,Magnetotransport properties and giant anomalous Hall angle in half-Heusler compound TbPtBi,"Magnetic lanthanide half-Heuslers ($R$PtBi; $R$ being the lanthanide)
represent an attractive subgroup of the Heusler family and have been identified
as ideal candidates for time reversal symmetry breaking topological Weyl
semimetals. In this paper, we present the detailed analysis of the
magnetotransport properties of frustrated antiferromagnet TbPtBi. This material
shows large, non-saturating magnetoresistance (MR) with unusual magnetic field
dependence. The MR of TbPtBi is significantly anisotropic with respect to the
magnetic field, applied along different crystallographic directions and
indicates the anisotropic nature of the Fermi surface. The chiral anomaly
induced negative longitudinal magnetoresistance confirms the presence of Weyl
fermions. At low temperature, Berry phase driven large anomalous Hall
conductivity has been observed. The calculated anomalous Hall angle is the
largest reported so far.",1901.09534v1
2019-03-04,A Resolution Study of Magnetically Arrested Disks,"We investigate numerical convergence in simulations of magnetically arrested
disks around spinning black holes. Using the general-relativistic
magnetohydrodynamics code Athena++, we study the same system at four
resolutions (up to an effective 512 by 256 by 512 cells) and with two different
spatial reconstruction algorithms. The accretion rate and general large-scale
structure of the flow agree across the simulations. This includes the amount of
magnetic flux accumulated in the saturated state and the ensuing suppression of
the magnetorotational instability from the strong field. The energy of the jet
and the efficiency with which spin energy is extracted via the Blandford-Znajek
process also show convergence. However the spatial structure of the jet shows
variation across the set of grids employed, as do the Lorentz factors.
Small-scale features of the turbulence, as measured by correlation lengths, are
not fully converged. Despite convergence of a number of aspects of the flow,
modeling of synchrotron emission shows that variability is not converged and
decreases with increasing resolution even at our highest resolutions.",1903.01509v1
2019-03-07,Flexible water excitation for fat-free MRI at 3 Tesla using lipid insensitive binomial off-resonant RF excitation (LIBRE) pulses,"Purpose: To develop a robust and flexible low power water excitation pulse
that enables effective fat suppression at high magnetic field strength.
Methods: A water excitation method that uses spatially non-selective pulses was
optimized in numerical simulations, and implemented and tested in phantoms and
healthy volunteers at 3T. The lipid insensitive binomial off-resonant
excitation (LIBRE) pulse comprises two low power rectangular sub-pulses that
have a variable frequency offset, phase offset and duration. The capability and
extent of LIBRE fat suppression was quantitatively compared with conventional
fat saturation (FS) and water excitation (WE) techniques. Results: LIBRE
enables simultaneous water excitation and near complete fat suppression in
large volumes at 3T as demonstrated by numerical simulations, and experiments.
In phantoms and in human subjects, the frequency responses matched well with
those from the numerical simulation. Comparing FS and WE, LIBRE demonstrated an
improved robustness to magnetic field inhomogeneities, and a much more
effectively suppressed fat signal. This applied for a range of pulse durations
and pulses as short as 1.4 ms. Conclusion: A flexible water excitation method
was developed that shows robust, near complete fat suppression at 3T.",1903.02901v1
2019-04-26,Homogenous reduced moment in a gapful scalar chiral kagome antiferromagnet,"We present present a quantitative experimental investigation of the scalar
chiral magnetic order with in $\rm{Nd_3Sb_3Mg_2O_{14}}$. Static magnetization
reveals a net ferromagnetic ground state, and inelastic neutron scattering from
the hyperfine coupled nuclear spin reveals a local ordered moment of 1.76(6)
$\mu_B$, just 61(2)% of the saturated moment size. The experiments exclude
static disorder as the source of the reduced moment. A 38(1) $\mu$eV gap in the
magnetic excitation spectrum inferred from heat capacity rules out thermal
fluctuations and suggests a multipolar explanation for the moment reduction. We
compare $\rm{Nd_3Sb_3Mg_2O_{14}}$ to Nd pyrochlores and show that it is close
to a moment fragmented state.",1904.11779v3
2019-05-03,Field-induced incommensurate ordering in the Heisenberg chains coupled by Ising interaction: Model for the ytterbium aluminum perovskite YbAlO$_3$,"We study isotropic antiferromagnetic Heisenberg chains coupled by
antiferromagnetic Ising interaction as an effective spin model for the
ytterbium aluminum perovskite YbAlO$_3$. Using the density-matrix
renormalization group (DMRG) method we calculate the magnetization curve, local
spin, central charge, and dynamical spin structure factors in the presence of
magnetic field. From the fitting of the experimental magnetization curve, the
effective intrachain and interchain couplings are estimated as $J=2.3$K and
$J_{\rm ic}=0.8$K, respectively. We can quantitatively explain the experimental
observations: (i) phase transition from antiferromagnetic to incommensurate
order at field 0.35T, and (ii) quantum critical behaviors at the saturation
field of 1.21T. Furthermore, the low-energy excitations in the experimental
inelastic neutron scattering spectra can be well described by our DMRG results
of the dynamical structure factors.",1905.01204v1
2019-05-14,Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes,"We report the temperature, magnetic field and time dependences of
magnetization in advanced Ba122 superconducting tapes. The sample exhibits a
peculiar vortex creep behavior. Below 10 K, the normalized magnetization
relaxation rate S=dln(-M)/dln(t) shows a temperature insensitive plateau with a
value comparable to that of the low temperature superconductors, which can be
explained within the framework of the collective creep theory. It then enters
into a second collective creep regime when the temperature increases.
Interestingly, the relaxation rate below 20 K tends to saturate with the
increasing field. However, it changes to a power law dependence on field at a
higher temperature. A vortex phase diagram composed of the collective and the
plastic creep regions is concluded. Benefit from the strong grain boundary
pinning, the advanced Ba122 superconducting tape has promising potential to be
applied not only in liquid helium but also in liquid hydrogen or at the
temperature accessible with cryocoolers.",1905.05372v1
2019-06-22,Observation of two-level critical state in the superconducting FeTe thin films,"FeTe, a non-superconducting parent compound in the iron-chalcogenide family,
becomes superconducting after annealing in oxygen. Under the presence of
magnetism, spin-orbit coupling, inhomogeneity and lattice distortion, the
nature of its superconductivity is not well understood. Here, we combined
mutual inductance technique with magneto transport to study the magnetization
and superconductivity of FeTe thin films. We found that the films with the
highest Tc showed non-saturating superfluid density and a strong magnetic
hysteresis distinct from that in a homogeneous superconductor. Such hysteresis
can be well explained by a two-level critical state model and suggested the
importance of granularity to superconductivity in this compound.",1906.09418v1
2019-07-16,"Magnetic, Structural and cation distribution studies on $FeO \cdot Fe_{(2-x)}Nd_{x}O_{3}$ ($x=0.00, 0.02, 0.04, 0.06 \text{ and } 0.1$) nanoparticles","We synthesized and characterized the colloidal suspensions of $FeO \cdot
Fe_{(2-x)}Nd_{x}O_{3}$ nanoparticles with $x=0.00, 0.02, 0.04, 0.06 \text{ and
}0.1.$ The effect of the $Fe^{3+}$ ion replacement by $Nd^{3+}$ on the crystal
structure is in-depth studied, through X-ray diffraction (XRD) and the obtained
cation distribution. The magnetic properties of the synthesized $FeO \cdot
Fe_{(2-x)}Nd_{x}O_{3}$ nanoparticles also were investigated and corroborated by
other physical methods. A remarkable saturation magnetization of 105
$Am^{2}/kg$ was achieved for $x=0.06$.",1907.07183v1
2019-07-30,Superconducting nanowires as high-rate photon detectors in strong magnetic fields,"Superconducting nanowire single photon detectors are capable of single-photon
detection across a large spectral range, with near unity detection efficiency,
picosecond timing jitter, and sub-10 $\mu$m position resolution at rates as
high as 10$^{9}$ counts/s. In an effort to bring this technology into nuclear
physics experiments, we fabricate Niobium Nitride nanowire detectors using ion
beam assisted sputtering and test their performance in strong magnetic fields.
We demonstrate that these devices are capable of detection of 400 nm wavelength
photons with saturated internal quantum efficiency at temperatures of 3 K and
in magnetic fields potentially up to 5 T at high rates and with nearly zero
dark counts.",1907.13059v2
2019-08-05,Presaturation phase with no dipolar order in a quantum ferro-antiferromagnet,"Magnetization, magnetocaloric, calorimetric, neutron and X-ray diffraction
and inelastic neutron scattering measurements are performed on single crystals
of BaCdVO(PO$_4$)$_2$. The low-temperature crystal structure is found to be of
a lower symmetry than previously assumed. The result is a more complicated
model spin Hamiltonian, which we infer from measurements of the spin wave
dispersion spectrum. The main finding is a novel spin state which emerges in
high magnetic fields after antiferromagnetic order is terminated at
$H_{c1}\simeq 4.0$ T. It is a distinct thermodynamic phase with a well-defined
phase boundary at $H_{c2}\simeq 6.5$ T and is clearly separate from the fully
saturated phase. Yet, it shows no conventional (dipolar) magnetic long range
order. We argue that it is fully consistent with the expectations for a quantum
bond-nematic state.",1908.01734v3
2019-09-13,Hidden spin-orbital order in the Kitaev hyperhoneycomb $β$-Li$_2$IrO$_3$,"We report the existence of a phase transition at high temperature in the 3D
Kitaev candidate material, $\beta$-Li$_2$IrO$_3$. We show that the transition
is bulk, intrinsic and orders a tiny magnetic moment with a spatially
anisotropic saturation moment. We show that even though this transition is
global, it does not freeze the local Ir moments, which order at much lower
temperatures into an incommensurate state. Rather, the ordered moment has an
orbital origin that is coupled to spin correlations, likely of a Kitaev origin.
The separate ordering of spin-correlated orbital moments and of local Ir
moments reveals a novel way in which magnetic frustration in Kitaev systems can
lead to coexisting magnetic states.",1909.06355v1
2019-10-22,Evidence of one-dimensional magnetic heat transport in the triangular-lattice antiferromagnet Cs$_2$CuCl$_4$,"We report on low-temperature heat-transport properties of the spin-1/2
triangular-lattice antiferromagnet Cs$_2$CuCl$_4$. Broad maxima in the thermal
conductivity along the three principal axes, observed at about 5 K, are
interpreted in terms of the Debye model, including the phonon Umklapp
scattering. For thermal transport along the $b$ axis, we observed a pronounced
field-dependent anomaly, close to the transition into the three-dimensional
long-range-ordered state. No such anomalies were found for the transport along
the $a$ and $c$ directions. We argue that this anisotropic behavior is related
to an additional heat-transport channel through magnetic excitations, that can
best propagate along the direction of the largest exchange interaction.
Besides, peculiarities of the heat transport of Cs$_2$CuCl$_4$ in magnetic
fields up to the saturation field and above are discussed.",1910.09833v1
2019-10-22,Disordered quantum spin state in the stripe lattice system consisting of triangular and square tilings,"Quantum fluctuations originating phase competition or geometrical frustration
of spins lead to novel states such as a quantum critical point and a quantum
spin liquid where the strong quantum fluctuations suppress any ordered states
even at 0 K. Utilizing site-selective NMR for a quasi-two dimensional organic
conductor $\lambda$-(STF)$_2$GaCl$_4$, we investigate the non-magnetic
insulating phase of the stripe lattice system consisting of triangular and
square tilings. We found development of AF spin fluctuations with decreasing
temperature. Regardless of large enhancement of spin-lattice relaxation rate
$1/T_1$ owing to critical slowing down below 10 K, no long-range magnetic
ordering was observed down to 1.63 K two orders of magnitude less than the
exchange interaction $J/k_{\rm B} \simeq$ 194 K. Moreover, $1/T_1$ saturated
below 3.5 K. These results are in stark contrast to observed behaviors so far
in other non-magnetic ground states discussed in terms of spin liquids,
demonstrating realization of an exotic quantum state accompanying quantum
criticality.",1910.09963v2
2019-11-19,Magneto-structural correlations in a systematically disordered B2 lattice,"Ferromagnetism in certain B2 ordered alloys such as Fe$_{60}$Al$_{40}$ can be
switched on, and tuned, via antisite disordering of the atomic arrangement. The
disordering is accompanied by a $\sim$1 % increase in the lattice parameter.
Here we performed a systematic disordering of B2 Fe$_{60}$Al$_{40}$ thin films,
and obtained correlations between the order parameter ($S$), lattice parameter
($a_0$), and the induced saturation magnetization ($M_{s}$). As the lattice is
gradually disordered, a critical point occurs at 1-$S$=0.6 and $a_0$=291 pm,
where a sharp increase of the $M_{s}$ is observed. DFT calculations suggest
that below the critical point the system magnetically behaves as it would still
be fully ordered, whereas above, it is largely the increase of $a_0$ in the
disordered state that determines the $M_{s}$. The insights obtained here can be
useful for achieving tailored magnetic properties in alloys through
disordering.",1911.08404v1
2019-12-10,Structural properties and magnetoresistance of La$_{1.952}$Sr$_{0.048}$CuO$_4$ thin films,"The evolution of the structural and transport properties of underdoped
La$_{1.952}$Sr$_{0.048}$CuO$_4$ thin films under compressive epitaxial strain
has been studied. The films of different thicknesses $d$ (from 26 nm to 120 nm)
were deposited using an insulating target. The onset of superconductivity in
the films is observed at temperatures as high as 26 K, while small residual
resistance persists at low temperatures, indicating that superconductivity is
inhomogeneous. The resistance measured under perpendicular magnetic field
saturates below about 0.65 K, suggesting a possible existence of
nonconventional metallic state. The magnetic-field-tuned
superconductor-insulator transition is observed at magnetic field of about 32
T.",1912.04594v2
2019-12-18,Magnetic hysteresis behavior of granular manganite La$_{0.67}$Ca$_{0.33}$MnO$_3$ nanotubes,"A silicon micromechanical torsional oscillator is used to measure the
hysteresis loops of two manganite La_0.67Ca_0.33MnO_3 nanotubes at different
temperatures, applying an external field along its main axes. These structures
are composed of nanograins with a ferromagnetic core surrounded by a dead
layer. Micromagnetic calculations based on the stochastic
Landau-Lifshitz-Gilbert equation, are performed to validate a simple model that
allows for quantitatively describing the ferromagnetic behavior of the system.
Further simulations are used to analyze the experimental data more in depth and
to calculate the coercive field, the saturation and remanent magnetizations,
and the effective magnetic volume for single nanotubes, over a wide temperature
range.",1912.08844v2
2020-01-10,Particle trajectories in Weibel filaments: influence of external field obliquity and chaos,"When two collisionless plasma shells collide, they interpenetrate and the
overlapping region may turn Weibel unstable for some values of the collision
parameters. This instability grows magnetic filaments which, at saturation,
have to block the incoming flow if a Weibel shock is to form. In a recent paper
[J. Plasma Phys. (2016), vol. 82, 905820403], it was found implementing a toy
model for the incoming particles trajectories in the filaments, that a strong
enough external magnetic field $\mathbf{B}_0$ can prevent the filaments to
block the flow if it is aligned with. Denoting $B_f$ the peak value of the
field in the magnetic filaments, all test particles stream through them if
$\alpha=B_0/B_f > 1/2$. Here, this result is extended to the case of an oblique
external field $B_0$ making an angle $\theta$ with the flow. The result,
numerically found, is simply $\alpha > \kappa(\theta)/\cos\theta$, where
$\kappa(\theta)$ is of order unity. Noteworthily, test particles exhibit
chaotic trajectories.",2001.03473v1
2020-02-25,Exceedingly Small Moment Itinerant Ferromagnetism of Single Crystalline La$_{5}$Co$_{2}$Ge$_{3}$,"Single crystals of monoclinic La$_{5}$Co$_{2}$Ge$_{3}$ were grown using a
self-flux method and were characterized by room-temperature powder X-ray
diffraction, anisotropic temperature and field dependent magnetization,
temperature dependent resistivity, specific heat, and muon spin rotation.
La$_{5}$Co$_{2}$Ge$_{3}$ has a Curie temperature ($T_\mathrm{C}$) of 3.8~K and
clear signatures of ferromagnetism in magnetization and $\mu SR$ data, as well
as a clear loss of spin disorder scattering in resistivity data and a sharp
specific heat anomaly. The magnetism associated with La$_{5}$Co$_{2}$Ge$_{3}$
is itinerant, has a change in the entropy at $T_\mathrm {C}$ of $\simeq$0.05 R
ln2 per mol-Co, and has a low-field saturated moment of $\sim 0.1 \mu_\mathrm
B$/Co, making it a rare, itinerant, small moment, low $T_\mathrm C$ compound.",2002.11050v1
2020-03-11,SIMBA: A Skyrmionic In-Memory Binary Neural Network Accelerator,"Magnetic skyrmions are emerging as potential candidates for next generation
non-volatile memories. In this paper, we propose an in-memory binary neural
network (BNN) accelerator based on the non-volatile skyrmionic memory, which we
call as SIMBA. SIMBA consumes 26.7 mJ of energy and 2.7 ms of latency when
running an inference on a VGG-like BNN. Furthermore, we demonstrate
improvements in the performance of SIMBA by optimizing material parameters such
as saturation magnetization, anisotropic energy and damping ratio. Finally, we
show that the inference accuracy of BNNs is robust against the possible
stochastic behavior of SIMBA (88.5% +/- 1%).",2003.05132v1
2020-04-10,Extremely Weakly Interacting $ΔS_z = 0$ and $ΔS_z = 1$ Excitations and Evidence for Fractional Quantization in a Magnetization Plateau: CeSb,"The plateau at 1/3 of the saturation magnetization, $M_s$, in the metamagnet
CeSb is accompanied by a state of ferromagnetic layers of spins in an
up-up-down sequence. We measured $M$ and the specific heat, $C$, in the
plateau, spin wave analyses of which reveal two distinct branches of
excitations. Those with $\Delta S_z = 1$ as measured by $M$, coexist with a
much larger population of $\Delta S_z = 0$ excitations measured by $C$ but
invisible to $M$. The large density of $\Delta S_z = 0$ excitations, their
energy gap, and their seeming lack of interaction with $\Delta S_z = 1$
excitations suggest an analogy with astrophysical dark matter. Additionally, in
the middle of the plateau three sharp jumps in $M(H)$ are seen, the size of
which, $0.15 $%$M_s$, is consistent with fractional quantization of
magnetization-per-site in the down-spin layers.",2004.05236v3
2020-05-10,Linear nonsaturating magnetoresistance in the Nowotny chimney ladder compound Ru$_2$Sn$_3$,"We present magnetoresistivity measurements in high-quality single crystals of
the Nowotny chimney ladder compound Ru$_2$Sn$_3$. We find a linear and
nonsaturating magnetoresistance up to 20 T. The magnetoresistance changes with
the magnetic field orientation at small magnetic fields, from a positive to a
negative curvature. Above 5 T, the magnetoresistance shows no sign of
saturation up to 20 T for any measured angle. The shape of the anisotropy in
the magnetoresistance remains when increasing temperature and Kohler's rule is
obeyed. We associate the linear and nonsaturating magnetoresistance to a small
Fermi surface with hot spots, possibly formed as a consequence of the
structural transition. We discuss the relevance of electron-electron
interactions under magnetic fields and aspects of the topologically nontrivial
properties expected in Ru$_2$Sn$_3$.",2005.04632v1
2020-06-01,Spin-wave spectroscopy of individual ferromagnetic nanodisks,"The increasing demand for ultrahigh data storage densities requires
development of 3D magnetic nanostructures. In this regard, focused electron
beam induced deposition (FEBID) is a technique of choice for direct-writing of
various complex nano-architectures. However, intrinsic properties of
nanomagnets are often poorly known and can hardly be assessed by local optical
probe techniques. Here, we demonstrate spatially resolved spin-wave
spectroscopy of individual circular magnetic elements with radii down to 100
nm. The key component of the setup is a microwave antenna whose microsized
central part is placed over a movable substrate with well-separated CoFe-FEBID
nanodisks. The circular symmetry of the disks gives rise to standing spin-wave
resonances and allows for the deduction of the saturation magnetization and the
exchange stiffness of the material using an analytical theory. The presented
approach is especially valuable for the characterization of direct-write
elements opening new horizons for 3D nanomagnetism and magnonics.",2006.00763v1
2020-06-02,Dynamic magnetization in non-Hermitian quantum spin system,"We report a global effect induced by the local complex field, associated with
the spin-exchange interaction. High-order exceptional point up to ($N+1$)-level
coalescence is created at the critical local complex field applied to the
$N$-size quantum spin chain. The ($N+1$)-order coalescent level is a saturated
ferromagnetic ground state in the isotropic spin system. Remarkably, the final
state always approaches the ground state for an arbitrary initial state with
any number of spin flips; even if the initial state is orthogonal to the ground
state. Furthermore, the switch of macroscopic magnetization is solely driven by
the time and forms a hysteresis loop in the time domain. The retentivity and
coercivity of the hysteresis loop mainly rely on the non-Hermiticity. Our
findings highlight the cooperation of non-Hermiticity and the interaction in
quantum spin system, suggest a dynamical framework to realize magnetization,
and thus pave the way for the non-Hermitian quantum spin system.",2006.01324v1
2020-06-02,The magnetic helicity density patterns from non-axisymmetric solar dynamo,"In the paper we study the helicity density patterns which can result from the
emerging bipolar regions. Using the relevant dynamo model and the magnetic
helicity conservation law we find that the helicity density pattern around the
bipolar regions depends on the configuration of the ambient large-scale
magnetic field, and in general they show the quadrupole distribution. The
position of this pattern relative to the equator can depend on the tilt of the
bipolar region. We compute the time-latitude diagrams of the helicity density
evolution. The longitudinally averaged effect of the bipolar regions show two
bands of sign for the density distribution in each hemisphere. Similar helicity
density patterns are provided by the helicity density flux from the emerging
bipolar regions subjected to the surface differential rotation. Examining
effect of helicity fluxes from the bipolar regions on the large-scale dynamo we
find that its effect to the dynamo saturation is negligible.",2006.01982v3
2020-07-08,Sign-reversal electron magnetization in Mn-doped semiconductor structures,"The diversity of various manganese types and its complexes in the Mn-doped
${\rm A^{III}B^V}$ semiconductor structures leads to a number of intriguing
phenomena. Here we show that the interplay between the ordinary substitutional
Mn acceptors and interstitial Mn donors as well as donor-acceptor dimers could
result in a reversal of electron magnetization. In our all-optical scheme the
impurity-to-band excitation via the Mn dimers results in direct orientation of
the ionized Mn-donor $d$ shell. A photoexcited electron is then captured by the
interstitial Mn and the electron spin becomes parallel to the optically
oriented $d$ shell. That produces, in the low excitation regime, the
spin-reversal electron magnetization. As the excitation intensity increases the
capture by donors is saturated and the polarization of delocalized electrons
restores the normal average spin in accordance with the selection rules. A
possibility of the experimental observation of the electron spin reversal by
means of polarized photoluminescence is discussed.",2007.04098v1
2020-09-17,Investigation of entanglement measures across the magnetization process of a highly frustrated spin-1/2 Heisenberg octahedral chain as a new paradigm of the localized-magnon approach,"The bipartite entanglement across the magnetization process of a highly
frustrated spin-1/2 Heisenberg octahedral chain is examined within the concept
of localized magnons, which enables a simple calculation of the concurrence
measuring a strength of the pairwise entanglement between nearest-neighbor and
next-nearest-neighbor spins from square plaquettes. A full exact
diagonalization of the finite-size Heisenberg octahedral chain with up to 4
unit cells (20 spins) evidences an extraordinary high precision of the
localized-magnon theory in predicting measures of the bipartite entanglement at
sufficiently low temperatures. While the monomer-tetramer phase emergent at low
enough magnetic fields exhibits presence (absence) of the bipartite
entanglement between the nearest-neighbor (next-nearest-neighbor) spins, the
magnon-crystal phase emergent below the saturation field contrarily displays
identical bipartite entanglement between the nearest-neighbor and
next-nearest-neighbor spins. The presented results verify a new paradigm of the
localized-magnon approach concerned with a simple calculation of entanglement
measures.",2009.08504v1
2020-09-25,Universal behavior of the bosonic metallic ground state in a two-dimensional superconductor,"Anomalous metallic behavior, marked by a saturating finite resistivity much
lower than the Drude estimate, has been observed in a wide range of
two-dimensional superconductors. Utilizing the electrostatically gated
LaAlO3/SrTiO3 interface as a versatile platform for superconductor-metal
quantum phase transitions, we probe variations in the gate, magnetic field, and
temperature to construct a phase diagram crossing from superconductor,
anomalous metal, vortex liquid, to Drude metal states, combining longitudinal
and Hall resistivity measurements. We find that the anomalous metal phases
induced by gating and magnetic field, although differing in symmetry, are
connected in the phase diagram and exhibit similar magnetic field response
approaching zero temperature. Namely, within a finite regime of the anomalous
metal state, the longitudinal resistivity linearly depends on field while the
Hall resistivity diminishes, indicating an emergent particle-hole symmetry. The
universal behavior highlights the uniqueness of the quantum bosonic metallic
state, distinct from bosonic insulators and vortex liquids.",2009.12403v2
2020-11-11,Magnetic field decay in young radio pulsars,"The role of magnetic field decay in normal radio pulsars is still debated. In
this paper we present results which demonstrate that an episode of magnetic
field decay in hot young neutron stars can explain anomalous values of braking
indices recently measured for more than a dozen of sources. It is enough to
have few tens of per cent of such hot NSs in the total population to explain
observables. Relatively rapid decay operates at ages
$\lesssim$~few~$\times100$~kyrs with a characteristic timescale of a similar
value. We speculate that this decay can be related to electron scattering off
phonons in neutron star crusts. This type of decay saturates as a neutron star
cools down. Later on, a much slower decay due to crustal impurities dominates.
Finally, we demonstrate that this result is in agreement with our early
studies.",2011.05778v1
2020-11-24,Drive Dependence of the Hall Angle for a Sliding Wigner Crystal in a Magnetic Field,"We numerically examine the depinning and sliding dynamics of a Wigner crystal
in the presence of quenched disorder and a magnetic field. In the disorder-free
limit, the Wigner crystal Hall angle is independent of crystal velocity, but
when disorder is present, we find that Hall angle starts near zero at the
depinning threshold and increases linearly with increasing drive before
reaching a saturation close to the disorder free value at the highest drives.
The drive dependence is the result of a side jump effect produced when the
charges move over pinning sites. The magnitude of the side jump is reduced at
the higher velocities. The drive dependent Hall angle is robust for a wide
range of disorder parameters and should be a generic feature of classical
charges driven in the presence of quenched disorder and a magnetic field.",2011.11802v1
2020-11-24,"Structural, dielectric and magnetic studies of (0-3) type multiferroic (1-x) BaTi0.8Sn0.2O3-(x) La0.5Ca0.5MnO3 (0 <x< 1) composite ceramics","Multiferroic composites with the composition (1-x) BaTi0.8Sn0.2O3 - (x)
La0.5Ca0.5MnO3 (x =0, 0.3, 0.5, 0.7, 0.9 and 1) were prepared by sol-gel
techniques. Rietveld refinements of the composites with 0-3 and 3-0 type
connectivities exhibit the formation of pure phases and confirm the fraction of
the composite samples. It was found that the composites grain size decreases
slightly with increasing the La0.5Ca0.5MnO3 content. Magnetic measurements of
the composite ceramics exhibit a gradual increase in saturation and remanent
magnetization with increasing La0.5Ca0.5MnO3 content. Dielectric data
demonstrate that the composite materials show high values of the dielectric
constant in comparison with the parent compound BaTi0.8Sn0.2O3 (BTSO). In
addition, an attempt is made to measure the magnetoelectric coupling
coefficient and to explain the negative permittivity and losses occurring in
these materials at a certain frequency and temperature conditions.",2011.12270v1
2021-01-22,Quasi-isotropic orbital magnetoresistance in lightly doped SrTiO$_{3}$,"A magnetic field parallel to an electrical current does not produce a Lorentz
force on the charge carriers. Therefore, orbital longitudinal magnetoresistance
is unexpected. Here we report on the observation of a large and non saturating
magnetoresistance in lightly doped SrTiO$_{3-x}$ independent of the relative
orientation of current and magnetic field. We show that this quasi-isotropic
magnetoresistance can be explained if the carrier mobility along all
orientations smoothly decreases with magnetic field. This anomalous regime is
restricted to low concentrations when the dipolar correlation length is longer
than the distance between carriers. We identify cyclotron motion of electrons
in a potential landscape tailored by polar domains as the cradle of
quasi-isotropic orbital magnetoresistance. The result emerges as a challenge to
theory and may be a generic feature of lightly-doped quantum paralectric
materials.",2101.09062v1
2021-01-26,Stabilizing current-driven steady flows of 180$^{\circ}$ domain walls in spin valves by interfacial Dzyaloshinskii-Moriya interaction,"Modulations of interfacial Dzyaloshinskii-Moriya interaction (iDMI) on
current-driven dynamics of 180$^{\circ}$ domain walls (180DWs) in long and
narrow spin valves (LNSVs) with heavy-metal caplayers are systematically
investigated. We focus on LNSVs with in-plane magnetic anisotropy in their free
layers. For planar-transverse polarizers (pinned layers of LNSVs), the Walker
breakdown can be postponed considerably (practical infinity) by iDMI. More
interestingly, the originally unstable traveling mode is also stabilized by
iDMI with high saturation velocity thus serves as fast carrier of information.
For parallel polarizers, the Walker limit is increased and the corresponding
modifications of iDMI to wall velocity in both steady and precessional flows of
180DWs are provided. For perpendicular polarizers, precessional flow of 180DWs
is absent due to the stability of stationary mode beyond the modified Walker
limit. For LNSVs with perpendicular magnetic anisotropy in their free layers,
similar results are obtained. Our findings open new possibilities for
developing magnetic nanodevices based on 180DW propagation with low energy
consumption and high robustness.",2101.10590v1
2021-03-16,A non-local fluid closure for modeling cyclotron resonance in collisionless magnetized plasmas,"A fluid description for collisionless magnetized plasmas that takes into
account the effect of cyclotron resonance has been developed. Following the
same approach as the Landau fluid closure, the heat flux components associated
with transverse electromagnetic fluctuations are approximated by a linear
combination of lower-order moments in wavenumber space. The closure
successfully reproduces the linear cyclotron resonance for electromagnetic
waves propagating parallel to the ambient magnetic field. In the presence of
finite temperature anisotropy, the model gives approximately correct prediction
for an instability destabilized via the cyclotron resonance. A nonlinear
simulation demonstrates the wave growth consistent with the linear theory
followed by the reduction of initial anisotropy, and finally, the saturation of
the instability. The isotropization may be understood in terms of quasi-linear
theory, which is developed within the framework of the fluid model but very
similar to its fully kinetic counterpart. The result indicates that both linear
and nonlinear collisionless plasma responses are approximately incorporated in
the fluid model.",2103.08880v1
2021-04-29,Integral Line-of-Sight Path Following Control of Magnetic Helical Microswimmers Subject to Step-Out Frequencies,"This paper investigates the problem of straight-line path following for
magnetic helical microswimmers. The control objective is to make the helical
microswimmer to converge to a straight line without violating the step-out
frequency constraint. The proposed feedback control solution is based on an
optimal decision strategy (ODS) that is cast as a trust-region subproblem
(TRS), i.e., a quadratic program over a sphere. The ODS-based control strategy
minimizes the difference between the microrobot velocity and an integral
line-of-sight (ILOS)-based reference vector field while respecting the magnetic
saturation constraints and ensuring the absolute continuity of the control
input. Due to the embedded integral action in the reference vector field, the
microswimmer will follow the desired straight line by compensating for the
drift effect of the environmental disturbances as well as the microswimmer
weight.",2104.14241v1
2021-05-10,Role of higher-order effects in spin-misalignment small-angle neutron scattering of high-pressure torsion nickel,"Magnetic-field-dependent unpolarized small-angle neutron scattering (SANS)
experiments demonstrate that high-pressure torsion (HPT) straining induces spin
misalignments in pure Ni, which persist in magnetic fields up to 4 T. The
spin-misalignment scattering patterns are elongated perpendicular to the
applied magnetic field due to an unusual predominant longitudinal
$sin^2(\theta)$-type angular anisotropy. Such a contribution cannot be
explained by the conventional second order (in spin misalignment amplitude)
micromagnetic SANS theory in the approach-to-saturation regime, nor can its
magnitude relative to the other features of the cross sections by the third
order micromagnetic SANS theory. This indicates that the high-density of
crystal defects induced via HPT straining in Ni makes such higher-order effects
in the micromagnetic SANS cross sections observable.",2105.04167v1
2021-06-14,Lepton-driven Non-resonant Streaming Instability,"A strong super-Alfv\'{e}nic drift of energetic particles (or cosmic rays,
CRs) in a magnetized plasma can amplify the magnetic field significantly
through non-resonant streaming instability (NRSI). While the traditional
analysis is done for an ion current, here we use kinetic particle-in-cell
simulations to study how the NRSI behaves when it is driven by electrons or by
a mixture of electrons and positrons. In particular, we characterize growth
rate, spectrum, and helicity of the unstable modes, as well the level of
magnetic field at saturation. Our results are potentially relevant for several
space/astrophysical environments (e.g, electron strahl in the solar wind, at
oblique non-relativistic shocks, around pulsar wind nebulae) and also in
laboratory experiments.",2106.07672v1
2021-09-05,Spin-current amplification by stimulated spin pumping,"Stimulated emission is a process during which an atomic system gives away
energy to create a coherent photon. It is fundamental to the operation of the
optical amplifier. Here we propose two mechanisms for amplifying AC spin
currents in a solid-state magnetic medium by a stimulated spin pumping process.
The first is synchronous and consists of phase-locked pulses that perturb a
precessing magnetic moment. The second is asynchronous and is driven by DC spin
currents. The amplification relies on a non-adiabatic interaction taking place
in a ferromagnetic medium in which the magnetic moment emits spin angular
momentum in the form of spin current before equilibrating with the environment.
The pumped spin current amplifies or absorbs the injected AC spin current
mimicking the operation of the optical gain medium as readily seen from the
gain saturation profiles. The mechanisms we propose are a first step towards a
realistic spin current amplifier.",2109.02078v1
2021-10-05,Experimental study of transport properties of Weyl semimetal LaAlGe thin films grown by molecular beam epitaxy,"Rare earth compounds display diverse electronic, magnetic, and
magneto-transport properties. Recently these compounds of the type RAlGe (R =
La, Ce, Pr) have been shown to exhibit Weyl semimetallic behavior. In this
work, we have investigated the crystal structure, electronic, and
magneto-transport properties of the Weyl semimetal LaAlGe thin films grown by
molecular beam epitaxy. The temperature dependence of longitudinal resistivity
at different magnetic fields is discussed. Observations of magnetoresistances
and Hall effect at different temperatures and their evolution with magnetic
field up to 6 T are also discussed with relevant mechanisms. We have observed
positive unsaturated magnetoresistances, with a small quadratic contribution at
low temperatures, which tends to saturate at higher fields. The Hall
measurements confirm the electron-dominated semimetallic conduction with an
average charge carrier density of ~ 9.68*10^21 cm^(-3) at room temperature.",2110.02322v1
2021-10-25,Spin dependent charge transfer in MoSe2/hBN/Ni hybrid structures,"We present magneto-photoluminescence measurements in a hybrid 2D
semiconductor/ferromagnetic structure consisting of MoSe2/hBN/Ni. When the
Nickel layer is magnetized, we observe circularly polarized photoluminescence
of the trion peak in MoSe2 monolayer under linearly polarized excitation. This
build-up of circular polarization can reach a measured value of about 4% when
the magnetization of Ni is saturated perpendicularly to the sample plane, and
changes its sign when the magnetization is reversed. The circular polarization
decreases when the hBN barrier thickness increases. These results are
interpreted in terms of a spin-dependent charge transfer between the MoSe2
monolayer and the Nickel film. The build-up of circular polarization is
observed up to 120 K, mainly limited by the trion emission that vanishes with
temperature.",2110.13007v1
2022-01-20,Small-angle neutron scattering by spatially inhomogeneous ferromagnets with a nonzero average uniaxial anisotropy,"Micromagnetic small-angle neutron scattering theory is well established for
analyzing spin-misalignment scattering data of bulk ferromagnets. Here, this
theory is extended to allow for a global uniaxial magnetic anisotropy (texture)
of the material, in addition to the already included random zero-average local
anisotropy. Macroscopic cross-sections and spin-misalignment response functions
are computed analytically for several practically relevant mutual anisotropy
and external magnetic field orientations in both parallel and perpendicular
scattering geometries for field magnitudes both above and below the rotational
saturation. Some of these expressions are tested on published experimental data
of magnetic-field-annealed Vitroperm and plastically-deformed Ni, allowing to
determine the corresponding global uniaxial anisotropy quality factors.",2201.08334v1
2022-02-15,Analysis of the robustness and dynamics of spin-locking preparations for the detection of oscillatory magnetic fields,"Extracting quantitative information of neuronal signals by non-invasive
imaging is an outstanding challenge for understanding brain function and
pathology. However, state-of-the-art techniques offer low sensitivity to deep
electrical sources. Stimulus induced rotary saturation (SIRS) is a recently
proposed magnetic resonance imaging (MRI) sequence that detects oscillatory
magnetic fields using a spin-lock preparation. Phantom experiments and
simulations proved its efficiency and sensitivity, but the susceptibility of
the method to field inhomogeneities is still not well understood. In this
study, we simulated and analyzed the dynamic of three spin-lock preparations
and their response to field inhomogeneities in the presence of a resonant
oscillating field. We show that the composite spin-lock preparation is more
robust against field variations within the double resonance effect. In
addition, we tested the capability of the chosen composite spin-lock
preparation to recover information about the spectral components of a composite
signal. This study sets the bases to move one step further towards the clinical
application of MR-based neuronal current imaging.",2202.07705v2
2022-03-04,Simultaneous optical trapping and magnetic micromanipulation of ferromagnetic iron-doped upconversion microparticles in six degrees of freedom,"Optical trapping of magnetic Fe-oxide particles is notoriously difficult due
to their high refractive indices, not to mention high absorptivity at the
trapping infra-red wavelengths. We synthesize Fe co-doped NaYF4:Yb,Er
ferromagnetic upconversion particles that not only have refractive indices
conducive for optical trapping, but also heat less than Haematite particles at
off-resonant wavelengths. These particles are hexagonal shaped with dimensions
of the order of 3 micrometer and also bear high coercivity of 20 mT and
saturation magnetisation of 1 Am^2/kg. This enables simultaneous use of optical
trapping and magnetic forces to generate micro-manipulation in all the six
degrees of freedom of a rigid body. We also show that these particles heat
significantly when illuminated on absorption resonance at 975 nm while emitting
visible light with possible implications for fluorescence microscopy and
photothermal therapy of cancer cells.",2203.02152v2
2022-03-05,Quasi-normal modes of dyonic black holes and magneto-hydrodynamics,"We revisit the magneto-hydrodynamics in (2+1) dimensions and confirm that it
is consistent with the quasi-normal modes of the (3+1) dimensional dyonic black
holes in the most general set-up with finite density, magnetic field and wave
vector. We investigate all possible modes (sound, shear, diffusion, cyclotron
etc.) and their interplay. For the magneto-hydrodynamics we perform a complete
and detailed analysis correcting some prefactors in the literature, which is
important for the comparison with quasi-normal modes. For the quasi-normal mode
computations in holography we identify the independent fluctuation variables of
the dyonic black holes, which is nontrivial at finite density and magnetic
field. As an application of the quasi-normal modes of the dyonic black holes we
investigate a transport property, the diffusion constant. We find that the
diffusion constant at finite density and magnetic field saturates the lower
bound at low temperature. We show that this bound can be understood from the
pole-skipping point.",2203.02642v1
2022-03-16,Quasistatic evolution in magnetoelasticity under subcritical coercivity assumptions,"We study a variational model of magnetoelasticity both in the static and in
the quasistatic setting. The model features a mixed Eulerian-Lagrangian
formulation, as magnetizations are defined on the deformed configuration in the
actual space. The magnetic saturation constraint is formulated in the reference
configuration and involves the Jacobian determinant of deformations. These
belong to the class of possibility discontinuous deformations excluding
cavitation introduced by Barchiesi, Henao and Mora-Corral. We establish a
compactness result which, in particular, yields the convergence of the
compositions of magnetizations with deformations. In the static setting, this
enables us to prove the existence of minimizers by means of classical lower
semicontinuity methods. Our compactness result also allows us to address the
analysis in the quasistatic setting, where we examine rate-independent
evolutions driven by applied loads and boundary conditions. In this case, we
prove the existence of energetic solutions.",2203.08744v2
2022-03-17,Mechanism-based Tuning of Room-temperature Ferromagnetism in Mn-doped \b{eta}-Ga2O3 by Annealing Atmospher,"Mn-doped \b{eta}-Ga2O3 (GMO) films with room-temperature ferromagnetism
(RTFM) are synthesized by polymer-assisted deposition and the effects of
annealing atmosphere (air or pure O2 gas) on their structures and physical
properties are investigated. The characterizations show that the concentrations
of vacancy defects and Mn dopants in various valence states and lattice
constants of the samples are all modulated by the annealing atmosphere.
Notably, the samples annealed in air (GMO-air) exhibit a saturation
magnetization as strong as 170% times that of the samples annealed in pure O2
gas (GMO-O2), which can be quantitatively explained by oxygen vacancy (VO)
controlled ferromagnetism due to bound magnetic polarons established between
delocalized hydrogenic electrons of VOs and local magnetic moments of Mn2+,
Mn3+, and Mn4+ ions in the samples. Our results provide insights into
mechanism-based tuning of RTFM in Ga2O3 and may be useful for design,
fabrication, and application of related spintronic materials.",2203.09331v4
2022-05-27,Nanocriticality in the magnetic phase transition of CoO nanoparticles,"The universal theory of critical phase transitions describes the critical
behavior at second-order phase transitions in infinitely large systems. With
the increased contemporary interest in nanoscale materials, we investigated CoO
nanoparticles by means of neutron scattering and found how the theory of
critical phenomena breaks down in the nanoscale regime. Using CoO as a model
system, we have identified a size-dependent nanocritical temperature region
close to the antiferromagnetic phase transition where the magnetic correlation
length of the nanoparticles converges to a constant value, which is
significantly smaller than that of the saturated state found at low
temperatures. This is in clear contrast to the divergence around $T_{\rm N}$
observed for bulk systems. Our findings of nanocriticality in the magnetic
phase transition is of great importance for the understanding of phase
transitions at the nanoscale.",2205.13975v2
2022-06-05,Evidence of Magnon-Mediated Orbital Magnetism in a Quasi-2D Topological Magnon Insulator,"We explore spin dynamics in Cu(1,3-bdc), a quasi-2D topological magnon
insulator. The results show that the thermal evolution of Land\'e $g$-factor
($g$) is anisotropic: $g_\textrm{in-plane}$ reduces while
$g_\textrm{out-plane}$ increases with increasing temperature $T$. Moreover, the
anisotropy of the $g$-factor ($\Delta g$) and the anisotropy of saturation
magnetization ($\Delta M_\textrm{s}$) are correlated below 4 K, but they
diverge above 4 K. We show that the electronic orbital moment contributes to
the $g$ anisotropy at lower $T$, while the topological orbital moment induced
by thermally excited spin chirality dictates the $g$ anisotropy at higher $T$.
Our work suggests an interplay among topology, spin chirality, and orbital
magnetism in Cu(1,3-bdc).",2206.02191v1
2022-07-13,Microwave-free J-driven DNP (MF-JDNP): A proposal for enhancing the sensitivity of solution-state NMR,"J-driven Dynamic Nuclear Polarization (JDNP) was recently proposed for
enhancing the sensitivity of solution-state nuclear magnetic resonance (NMR),
while bypassing the limitations faced by conventional (Overhauser) DNP at
magnetic fields of interest in analytical applications. Like Overhauser DNP,
JDNP also requires saturating the electronic polarization using high-frequency
microwaves, known to have poor penetration and associated heating effects in
most liquids. The present microwave-free JDNP (MF-JDNP) proposal seeks to
enhance the sensitivity of the solution state NMR by shuttling the sample
between higher and lower magnetic fields, with one of these fields providing an
electron Larmor frequency that matches the inter-electron exchange coupling
Jex. If spins cross this so-called JDNP condition sufficiently fast, we predict
that a sizable nuclear polarization will be created without microwave
irradiation. This MF-JDNP proposal requires radicals whose singlet/triplet
self-relaxation rates are dominated by dipolar hyperfine relaxation, and
shuttling times that can compete with these electron relaxation processes. This
communication discusses the theory behind the MF-JDNP, as well as proposals for
radicals and conditions that could enable this new approach to NMR sensitivity
enhancement.",2207.05996v3
2022-07-18,Study of Thin Iron Films for Polarization Analysis of Ultracold Neutrons,"The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) collaboration aims to search
for the neutron electric dipole moment (nEDM) with unprecedented precision. One
of the essential elements for the nEDM measurement is a polarization analyzer
of ultracold neutrons (UCNs), whose main component is a magnetized thin iron
film. Several thin iron films were deposited on aluminum and silicon ubstrates
and were characterized by vibrating sample magnetometry and cold-neutron
reflectometry. A magnetic field required to saturate the iron film is $\sim$12
kA/m for those on the aluminum substrates and 6.4 kA/m for the silicon
substrates. The magnetic potential of the iron films on the Si substrate was
estimated to be 2 T by the neutron reflectometry, which is sufficient
performance for an UCN polarization analyzer of the nEDM measurement.",2207.08441v1
2022-10-27,A theoretical model for tellurite-sulfates Na$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$(OH)$_4$ and K$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$(OH)$_4$,"A theoretical model for two new tellurite-sulfates, namely
Na$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$(OH)$_4$ and K$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$
(OH)$_4$ is determined to be compatible with ab-initio calculations. The
results obtained in this work show that some previous speculations in the
literature about the couplings are correct, obtaining a model with a mixture of
ferromagnetic and antiferromagnetic couplings. We use a combination of
numerical techniques to study the magnetic properties of the model. Our
numerical calculations based on the density-matrix renormalization group method
reveal that the system presents Ising-like magnetization plateaux at rational
values of the saturation magnetization.",2210.15416v1
2023-01-26,"Magnetic, Optoelectronic, and Rietveld refined structural properties of Al3+ substituted nanocrystalline Ni-Cu spinel ferrites: An experimental and DFT based study","The nanocrystalline Ni0.7Cu0.3AlxFe2-xO4 (x=0.00: 0.02: 0.10) is prepared
through the sol-gel autocombustion route.Both XRD and Rietveld confirm the
single-phase cubic spinel structure of the investigated materials.Other
structural parameters refined by the Rietveld refinement analysis are
corroborated to single-phase cubic spinel formation of the NPs.Leveraging a
vibrating sample magnetometer (VSM) the consequence of Al3+ substitution on the
magnetic parameters is studied.The saturation magnetization (MS) and Bohr
magneton are found to decrease with Al3+ substitution.The Remanence ratio and
coercivity (HC) are observed to be very low suggesting the materials are soft
ferromagnetic.First-principle calculations were carried out using the density
functional theory (DFT) to demonstrate the optoelectronic behavior of the
materials.The electronic bandgap is found low as Eg=2.99eV for the explored
materials with observing defect states at 0.62eV.The optoelectronic properties
of Al3+ substituted Ni-Cu ferrite NPs have been characterized through the DFT
simulation for the first time, demonstrating their potentiality for
optoelectronic device applications.The materials' optical anisotropy is
observed along the x-axis, which manifests their tunability through
light-matter interaction.",2301.11373v1
2023-03-01,Tailed skyrmions -- an obscure branch of magnetic solitons,"We report tailed skyrmions -- a new class of stable soliton solutions of the
2D chiral magnet model. Tailed skyrmions have elongated shapes and emerge in a
narrow range of fields near the transition between the spin spirals and the
saturated state. We analyze the stability range of these solutions in terms of
external magnetic field and magnetocrystalline anisotropy. Minimum energy paths
and the homotopies (continuous transitions) between tailed skyrmions of the
same topological charge have been calculated using the geodesic nudged elastic
bands method. The discovery of tailed skyrmions extends the diversity of
already-known solutions illustrated by complex morphology solitons, such as
tailed skyrmion bags with and without chiral kinks.",2303.00347v1
2023-03-03,Unusual coercivity and zero field stabilization of fully saturated magnetization in single crystals of LaCrGe$_3$,"LaCrGe$_3$ is an itinerant, metallic ferromagnet with a Curie temperature
($T_C$) of $\sim$ 86 K. Whereas LaCrGe$_3$ has been studied extensively as a
function of pressure as an example of avoided ferromagnetic quantum
criticality, questions about its ambient pressure ordered state remain;
specifically, whether there is a change in the nature of the ferromagnetically
ordered state below $T_C$ $\sim$ 86 K. We present anisotropic $M$($H$)
isotherms, coupled with anisotropic AC susceptibility data, and demonstrate
that LaCrGe$_3$ has a remarkable, low temperature coercivity associated with
exceptionally sharp, complete magnetization reversals to and from fully
polarized states. This coercivity is temperature dependent, it drops to zero in
the 40 - 55 K region and reappears in the 70 - 85 K regions. At low
temperatures LaCrGe$_3$ has magnetization loops and behavior that has
previously associated with micromagnetic/nanocrystalline materials, not bulk,
macroscopic samples.",2303.02062v1
2023-03-24,Observation of Colossal Terahertz Magnetoresistance and Magnetocapacitance in a Perovskite Manganite,"We have studied the terahertz response of a bulk single crystal of
La$_{0.875}$Sr$_{0.125}$MnO$_3$ at around its Curie temperature, observing
large changes in the real and imaginary parts of the optical conductivity as a
function of magnetic field. The terahertz resistance and capacitance extracted
from the optical conductivity rapidly increased with increasing magnetic field
and did not show any sign of saturation up to 6 T, reaching 60% and 15%,
respectively, at 180 K. The observed terahertz colossal magnetoresistance and
magnetocapacitance effects can be qualitatively explained by using a
two-component model that assumes the coexistence of two phases with vastly
different conductivities. These results demonstrate the potential use of
perovskite manganites for developing efficient terahertz devices based on
magnetic modulations of the amplitude and phase of terahertz waves.",2303.13820v1
2023-04-06,Magnetic Fields from Compensated Isocurvature Perturbations,"Compensated isocurvature perturbations (CIPs) are perturbations to the
primordial baryon density that are accompanied by dark-matter-density
perturbations so that the total matter density is unperturbed. Such CIPs, which
may arise in some multi-field inflationary models, can be long-lived and only
weakly constrained by current cosmological measurements. Here we show that the
CIP-induced modulation of the electron number density interacts with the
electron-temperature fluctuation associated with primordial adiabatic
perturbations to produce, via the Biermann-battery mechanism, a magnetic field
in the post-recombinaton Universe. Assuming the CIP amplitude saturates the
current BBN bounds, this magnetic field can be stronger than
$10^{-15}\,\mathrm{nG}$ at $z\simeq20$ and stronger by an order of magnitude
than that (produced at second order in the adiabatic-perturbation amplitude) in
the standard cosmological model, and thus can serve as a possible seed for
galactic dynamos.",2304.03299v2
2023-05-10,Double-layer Kagome Metals Pt3Tl2 and Pt3In2,"The connectivity and inherent frustration of the kagome lattice can produce
interesting electronic structures and behaviors in compounds containing this
structural motif. Here we report the properties of Pt3X2 (X = In and Tl) that
adopt a double-layer kagome net structure related to that of the topologically
nontrivial high temperature ferromagnet Fe3Sn2 and the density wave hosting
compound V3Sb2. We examined the structural and physical properties of single
crystal Pt3Tl2 and polycrystalline Pt3In2 using x-ray and neutron diffraction,
magnetic susceptibility, heat capacity, and electrical transport measurements,
along with density functional theory calculations of the electronic structure.
Our calculations show that Fermi levels lie in pseudogaps in the densities of
states with several bands contributing to transport, and this is consistent
with our Hall effect, magnetic susceptibility, and heat capacity measurements.
While electronic dispersions characteristic of simple kagome nets with
nearest-neighbor hopping are not clearly seen, likely due to the extended
nature of the Pt 5d states, we do observe moderately large and non-saturating
magnetoresistance values and quantum oscillations in the magnetoresistance and
magnetization associated with the kagome nets of Pt.",2305.06491v1
2023-05-31,The Ferris ferromagnetic resonance technique: principles and applications,"Measurements of ferromagnetic resonance (FMR) are pivotal to modern magnetism
and spintronics. Recently, we reported on the Ferris FMR technique, which
relies on large-amplitude modulation of the externally applied magnetic field.
It was shown to benefit from high sensitivity while being broadband. The Ferris
FMR also expanded the resonance linewidth such that the sensitivity to spin
currents was enhanced as well. Eventually, the spin Hall angle ({\theta}_SH)
was measurable even in wafer-level measurements that require low current
densities to reduce the Joule heating. Despite the various advantages, analysis
of the Ferris FMR response is limited to numerical modeling where the linewidth
depends on multiple factors such as the field modulation profile and the
magnetization saturation. Here, we describe in detail the basic principles of
operation of the Ferris FMR and discuss its applicability and engineering
considerations. We demonstrated these principles in a measurement of the
orbital Hall effect taking place in Cu, using an Au layer as the orbital to
spin current converter. This illustrates the potential of the Ferris FMR for
the future development of spintronics technology.",2306.01783v1
2023-06-11,Scanning NV magnetometry of focused-electron-beam-deposited cobalt nanomagnets,"Focused-electron-beam-induced deposition is a promising technique for
patterning nanomagnets for spin qubit control in a single step. We fabricate
cobalt nanomagnets in such a process, obtaining cobalt contents and saturation
magnetizations comparable to or higher than those typically obtained using
electron-beam lithography. We characterize the nanomagnets using transmission
electron microscopy and image their stray magnetic field using scanning NV
magnetometry, finding good agreement with micromagnetic simulations. The
magnetometry reveals the presence of magnetic domains and halo side-deposits,
which are common for this fabrication technique. Finally, we estimate dephasing
times for electron spin qubits in the presence of disordered stray fields due
to these side-deposits.",2306.06650v2
2023-07-10,Properties underlying the variation of the magnetic field spectral index in the inner solar wind,"Using data from orbits one to eleven of the Parker Solar Probe (PSP) mission,
the magnetic field spectral index was measured across a range of heliocentric
distances. The previously observed transition between a value of $-5/3$ far
from the Sun and a value of $-3/2$ close to the Sun was recovered, with the
transition occurring at around $50 \, R_{\odot}$ and the index saturating at
$-3/2$ as the Sun is approached. A statistical analysis was performed to
separate the variation of the index on distance from its dependence on other
parameters of the solar wind that are plausibly responsible for the transition;
including the cross helicity, residual energy, turbulence age and the magnitude
of magnetic fluctuations. Of all parameters considered the cross helicity was
found to be by far the strongest candidate for the underlying variable
responsible. The velocity spectral index was also measured and found to be
consistent with $-3/2$ over the range of values of cross helicity measured.
Possible explanations for the behaviour of the indices are discussed, including
the theorised different behaviour of imbalanced, compared to balanced,
turbulence.",2307.04682v1
2023-10-09,Magnetocaloric effect of nanostructured La0.6Sr0.4CoO3,"In this study, we investigate the magnetic and magnetocaloric properties of
nanostructured La0.6Sr0.4CoO3 (LSC) samples synthesized under confinement
conditions within porous templates. Using this method, we obtained
de-agglomerated nanoparticles, which provide us with the feasibility of
applying them in nanoparticle films that can be tailored to intricate
geometries. We specifically explored the impact of pore size of the template on
key parameters including saturation magnetization (MS), Curie temperature (TC),
maximum entropy change ({\Delta}S), and relative cooling power (RCP). Our
findings reveal enhancements in those quantities, that are likely to be related
with the nanostructure of the samples, indicating the potential of
nanostructured LSC as an active material for magnetic refrigeration devices.
Our alternative approach of synthesizing magnetocaloric materials under
confinement conditions presents an exciting prospect for future research and
development in the field.",2310.05722v1
2023-11-03,Massive neutron stars as mass gap candidates: Exploring equation of state and magnetic field,"The densities in the cores of the neutron stars (NSs) can reach several times
that of the nuclear saturation density. The exact nature of matter at these
densities is still virtually unknown. We consider a number of proposed,
phenomenological relativistic mean-field equations of state to construct
theoretical models of NSs. We find that, based on our selected set of models,
the emergence of exotic matter at these high densities restricts the mass of
NSs to $\simeq 2.2 M_\odot$. However, the presence of magnetic fields and a
model anisotropy significantly increases the star's mass, placing it within the
observational mass gap that separates the heaviest NSs from the lightest black
holes. Therefore, we propose that gravitational wave observations, like
GW190814, and other potential candidates within this mass gap, may actually
represent massive, magnetized NSs.",2311.02169v2
2024-01-15,The low-spin ground state of the giant Mn wheels,"The single-molecule magnets (SMMs) {Mn$_{70}$} and {Mn$_{84}$} are
characterized by a 14-site unit cell with $S=2$ spin sites, arranged in a
circular geometry. Experimentally, these SMMs exhibit a magnetic ground state
with a notably low total spin, $S_{\text{tot}}=5-7$. This low-spin ground state
has been up to now difficult to describe theoretically due to the complexity of
the quantum Heisenberg model for this large system. In this work, we are in
fact able to quantitatively reproduce the low-spin energy minimum by employing
large-scale SU(2)-symmetric density-matrix renormalization group (DMRG)
calculations using previously published exchange parameters obtained by
density-functional theory. We do not find a low-spin state for the same
parameters and $S=1$, which leads us to propose that frustrated systems with
$S\geq2$ are inherently prone to weak ferromagnetic interactions. This could
account for the prevalence of similar low-spin Mn-based SMMs. Finally, by
computing the full magnetization curve, we find wide plateaus at 10/14, 11/14,
12/14 and 13/14 of the saturation. This can be explained by independent 3-site
clusters with broken inter-cluster bonds.",2401.07552v1
2024-02-16,Theory of magnetic properties in QED environments: application to molecular aromaticity,"In this work, we present ab initio cavity QED methods which include
interactions with a static magnetic field and nuclear spin degrees of freedom
using different treatments of the quantum electromagnetic field. We derive
explicit expressions for QED-HF magnetizability, nuclear shielding, and
spin-spin coupling tensors. We apply this theory to explore the influence of
the cavity field on the magnetizability of saturated, unsaturated, and aromatic
hydrocarbons, showing the effects of different polarization orientations and
coupling strengths. We also examine how the cavity affects aromaticity
descriptors, such as the nucleus-independent chemical shift and magnetizability
exaltation. We employ these descriptors to study the trimerization reaction of
acetylene to benzene. We show how the optical cavity induces modifications in
the aromatic character of the transition state leading to variations in the
activation energy of the reaction. Our findings shed light on the effects
induced by the cavity on magnetic properties, especially in the context of
aromatic molecules, providing valuable insights into understanding the
interplay between the quantum electromagnetic field and molecules.",2402.10599v1
2001-05-22,"Amplification, Saturation, and Q Thresholds for Runaway: Growth of Self-Gravitating Structures in Models of Magnetized Galactic Gas Disks","We investigate the susceptibility of gaseous, magnetized galactic disks to
formation of self-gravitating condensations using two-dimensional, local
models. We focus on two issues: (1) determining the threshold condition for
gravitational runaway, taking into account nonlinear effects, and (2)
distinguishing the magneto-Jeans instability (MJI) that arises under
inner-galaxy rotation curves from the modified swing amplification (MSA) that
arises under outer-galaxy rotation curves. For axisymmetric density
fluctuations, instability is known to require a Toomre parameter Q<1. For
nonaxisymmetric fluctuations, any nonzero shear $q \equiv -d\ln \Omega /d \ln
R$ winds up wavefronts such that in linear theory amplification saturates. Any
Q threshold for nonaxisymmetric gravitational runaway must originate from
nonlinear effects. We use numerical magnetohydrodynamic simulations to
demonstrate the anticipated threshold phenomenon, to analyze the nonlinear
processes involved, and to evaluate the critical value $Q_c$ for stabilization.
We find $Q_c \sim 1.2-1.4$ for a wide variety of conditions, with the largest
values corresponding to nonzero but subthermal mean magnetic fields. Our
findings for $Q_c$ are similar to those inferred from thresholds for active
star formation in the outer regions of spiral galaxies. MJI is distinct from
MSA in that opposition to Coriolis forces by magnetic tension, rather than
cooperation of epicyclic motion with kinematic shear, enables nonaxisymmetric
density perturbations to grow. We suggest that under low-shear inner-disk
conditions, $Q_c$ will be larger than that in outer disks by a factor $\sim
(v_A/q c_s)^{1/2}$, where $v_A$ and $c_s$ are the respective Alfven and sound
speeds.",0105375v1
2003-09-02,Magnetorotationally-Driven Galactic Turbulence and the Formation of Giant Molecular Clouds,"Using local 3D MHD simulations, we investigate ways in which galactic
turbulence associated with the magnetorotational instability (MRI) may
influence the formation and properties of GMCs. Our disk models are vertically
stratified and subject to uniform shear. Initial magnetic fields are weak and
purely vertical. For simplicity, we adopt an isothermal equation of state. We
find that MRI-driven turbulence develops rapidly, with the saturated-state
Shakura & Sunyaev parameter alpha~(0.15-0.3) dominated by Maxwell stresses.
Many of the dimensionless characteristics of the turbulence (e.g. the ratio of
the Maxwell to Reynolds stresses) are similar to results from previous MRI
studies of accretion disks, hence insensitive to the degree of vertical disk
compression, shear rate, and the presence of self-gravity. The density-weighted
velocity dispersions in non- or weakly self-gravitating disks are sigma_x ~
sigma_y ~ (0.4-0.6)c_s and sigma_z~(0.2-0.3)c_s, suggesting that MRI can
contribute significantly to the observed level of galactic turbulence. The
saturated-state magnetic field strength B ~ 2 \mu G is similar to typical
galactic values. When self-gravity is strong enough, MRI-driven high-amplitude
density perturbations are swing-amplified to form Jeans-mass (~10^7 Msun) bound
clouds. Compared to previous unmagnetized or strongly-magnetized disk models,
the threshold for nonlinear instability in the present models occurs for
surface densities at least 50% lower, corresponding to the Toomre parameter
Q_th~1.6. We present evidence that self-gravitating clouds like GMCs formed
under conditions similar to our models can lose much of their original spin
angular momenta by magnetic braking, preferentially via fields threading
near-perpendicularly to their spin axes.",0309080v1
2002-02-19,Quantum Monte Carlo with Directed Loops,"We introduce the concept of directed loops in stochastic series expansion and
path integral quantum Monte Carlo methods. Using the detailed balance rules for
directed loops, we show that it is possible to smoothly connect generally
applicable simulation schemes (in which it is necessary to include
back-tracking processes in the loop construction) to more restricted loop
algorithms that can be constructed only for a limited range of Hamiltonians
(where back-tracking can be avoided). The ""algorithmic discontinuities"" between
general and special points (or regions) in parameter space can hence be
eliminated. As a specific example, we consider the anisotropic S=1/2 Heisenberg
antiferromagnet in an external magnetic field. We show that directed loop
simulations are very efficient for the full range of magnetic fields (zero to
the saturation point) and anisotropies. In particular for weak fields and
anisotropies, the autocorrelations are significantly reduced relative to those
of previous approaches. The back-tracking probability vanishes continuously as
the isotropic Heisenberg point is approached. For the XY-model, we show that
back-tracking can be avoided for all fields extending up to the saturation
field. The method is hence particularly efficient in this case. We use directed
loop simulations to study the magnetization process in the 2D Heisenberg model
at very low temperatures. For LxL lattices with L up to 64, we utilize the
step-structure in the magnetization curve to extract gaps between different
spin sectors. Finite-size scaling of the gaps gives an accurate estimate of the
transverse susceptibility in the thermodynamic limit: chi_perp = 0.0659 +-
0.0002.",0202316v2
2010-06-24,Dynamics of an Alfven surface in core collapse supernovae,"We investigate the dynamics of an Alfven surface (where the Alfven speed
equals the advection velocity) in the context of core collapse supernovae
during the phase of accretion on the proto-neutron star. Such a surface should
exist even for weak magnetic fields because the advection velocity decreases to
zero at the center of the collapsing core. In this decelerated flow, Alfven
waves created by the standing accretion shock instability (SASI) or convection
accumulate and amplify while approaching the Alfven surface. We study this
amplification using one dimensional MHD simulations with explicit physical
dissipation. In the linear regime, the amplification continues until the Alfven
wavelength becomes as small as the dissipative scale. A pressure feedback that
increases the pressure in the upstream flow is created via a non linear
coupling. We derive analytic formulae for the maximum amplification and the non
linear coupling and check them with numerical simulations to a very good
accuracy. We also characterize the non linear saturation of this amplification
when compression effects become important, leading to either a change of the
velocity gradient, or a steepening of the Alfven wave. Applying these results
to core collapse supernovae shows that the amplification can be fast enough to
affect the dynamics, if the magnetic field is strong enough for the Alfven
surface to lie in the region of strong velocity gradient just above the
neutrinosphere. This requires the presence of a strong magnetic field in the
progenitor star, which would correspond to the formation of a magnetar under
the assumption of magnetic flux conservation. An extrapolation of our analytic
formula (taking into account the nonlinear saturation) suggests that the Alfven
wave could reach an amplitude of B ~ 10^15 G, and that the pressure feedback
could significantly contribute to the pressure below the shock.",1006.4697v2
2013-10-24,Trends in Ultracool Dwarf Magnetism. II. The Inverse Correlation Between X-ray Activity and Rotation as Evidence for a Bimodal Dynamo,"Observations of magnetic activity indicators in solar-type stars exhibit a
relationship with rotation with an increase until a ""saturation"" level and a
moderate decrease in activity in the very fastest rotators (""supersaturation"").
While X-ray data have suggested that this relationship is strongly violated in
ultracool dwarfs (UCDs; spectral type >M7), the limited number of X-ray
detections has prevented firm conclusions. In this paper, we analyze the X-ray
activity-rotation relation in 38 ultracool dwarfs. Our sample represents the
largest catalog of X-ray active ultracool dwarfs to date, including seven new
and four previously-unpublished Chandra observations presented in a companion
paper. We identify a substantial number of rapidly-rotating UCDs with X-ray
activity extending two orders of magnitude below the expected saturation level
and measure a ""supersaturation""-type anticorrelation between rotation and X-ray
activity. The scatter in UCD X-ray activity at a fixed rotation is ~3 times
larger than that in earlier-type stars. We discuss several mechanisms that have
been proposed to explain the data, including centrifugal stripping of the
corona, and find them to be inconsistent with the observed trends. Instead, we
suggest that an additional parameter correlated with both X-ray activity and
rotation is responsible for the observed effects. Building on the results of
Zeeman-Doppler imaging of UCD magnetic fields and our companion study of
radio/X-ray flux ratios, we argue that this parameter is the magnetic field
topology, and that the large scatter in UCD X-ray fluxes reflects the presence
of two dynamo modes that produce distinct topologies.",1310.6758v2
2016-03-09,Local Simulations of Instabilities Driven by Composition Gradients in the ICM,"The distribution of Helium in the intracluster medium (ICM) permeating galaxy
clusters is not well constrained due to the very high plasma temperature.
Therefore, the plasma is often assumed to be homogeneous. A non-uniform Helium
distribution can however lead to biases when measuring key cluster parameters.
This has motivated one-dimensional models that evolve the ICM composition
assuming that the effects of magnetic fields can be parameterized or ignored.
Such models for non-isothermal clusters show that Helium can sediment in the
cluster core leading to a peak in concentration offset from the cluster center.
The resulting profiles have recently been shown to be linearly unstable when
the weakly-collisional character of the magnetized plasma is considered. In
this paper, we present a modified version of the MHD code Athena, which makes
it possible to evolve a weakly-collisional plasma subject to a gravitational
field and stratified in both temperature and composition. We thoroughly test
our implementation and confirm excellent agreement against several analytical
results. In order to isolate the effects of composition, in this initial study
we focus our attention on isothermal plasmas. We show that plasma
instabilities, feeding off gradients in composition, can induce turbulent
mixing and saturate by re-arranging magnetic field lines and alleviating the
composition gradient. Composition profiles that increase with radius lead to
instabilities that saturate by driving the average magnetic field inclination
to roughly $45^{\circ}$. We speculate that this effect may alleviate the core
insulation observed in homogeneous settings, with potential consequences for
the associated cooling flow problem.",1603.05508v2
2017-06-14,Intrinsic suppression of turbulence in linear plasma devices,"Plasma turbulence is the dominant transport mechanism for heat and particles
in magnetized plasmas in linear devices and tokamaks, so the study of
turbulence is important in limiting and controlling this transport. Linear
devices provide an axial magnetic field that serves to confine a plasma in
cylindrical geometry as it travels along the magnetic field from the source to
the strike point. Due to perpendicular transport, the plasma density and
temperature have a roughly Gaussian radial profile with gradients that drive
instabilities, such as resistive drift-waves and Kelvin-Helmholtz. If unstable,
these instabilities cause perturbations to grow resulting in saturated
turbulence, increasing the cross-field transport of heat and particles. When
the plasma emerges from the source, there is a time, $\tau_{\parallel}$, that
describes the lifetime of the plasma based on parallel velocity and length of
the device. As the plasma moves down the device, it also moves azimuthally
according to $E\times B$ and diamagnetic velocities. There is a balance point
in these parallel and perpendicular times that sets the stabilisation
threshold. We simulate plasmas with a variety of parallel lengths and magnetic
fields to vary the parallel and perpendicular lifetimes, respectively, and find
that there is a clear correlation between the saturated RMS density
perturbation level and the balance between these lifetimes. The threshold of
marginal stability is seen to exist where
$\tau_{\parallel}\approx11\tau_{\perp}$. This is also associated with the
product $\tau_{\parallel}\gamma_*$, where $\gamma_*$ is the drift-wave linear
growth rate, indicating that the instability must exist for roughly 100 times
the growth time for the instability to enter the non-linear growth phase. We
explore the root of this correlation and the implications for linear device
design.",1706.04550v1
2019-04-23,Simulating the Diverse Instabilities of Dust in Magnetized Gas,"Recently Squire & Hopkins showed that charged dust grains moving through
magnetized gas under the influence of any external force (e.g. radiation
pressure, gravity) are subject to a spectrum of instabilities. Qualitatively
distinct instability families are associated with different Alfvenic or
magnetosonic waves and drift or gyro motion. We present a suite of simulations
exploring these instabilities, for grains in a homogeneous medium subject to an
external acceleration. We vary parameters such as the ratio of Lorentz-to-drag
forces on dust, plasma $\beta$, size scale, and acceleration. All regimes
studied drive turbulent motions and dust-to-gas fluctuations in the saturated
state, can rapidly amplify magnetic fields into equipartition with velocity
fluctuations, and produce instabilities that persist indefinitely (despite
random grain motions). Different parameters produce diverse morphologies and
qualitatively different features in dust, but the saturated gas state can be
broadly characterized as anisotropic magnetosonic or Alfvenic turbulence.
Quasi-linear theory can qualitatively predict the gas turbulent properties.
Turbulence grows from small to large scales, and larger-scale modes usually
drive more vigorous gas turbulence, but dust velocity and density fluctuations
are more complicated. In many regimes, dust forms structures (clumps,
filaments, sheets) that reach extreme over-densities (up to $\gg 10^{9}$ times
mean), and exhibit substantial sub-structure even in nearly-incompressible gas.
These can be even more prominent at lower dust-to-gas ratios. In other regimes,
dust self-excites scattering via magnetic fluctuations that isotropize and
amplify dust velocities, producing fast, diffusive dust motions.",1904.11494v2
2000-06-13,The inverse cascade and nonlinear alpha-effect in simulations of isotropic helical hydromagnetic turbulence,"A numerical model of isotropic homogeneous turbulence with helical forcing is
investigated. The resulting flow, which is essentially the prototype of the
alpha^2 dynamo of mean-field dynamo theory, produces strong dynamo action with
an additional large scale field on the scale of the box (at wavenumber k=1;
forcing is at k=5). This large scale field is nearly force-free and exceeds the
equipartition value. As the magnetic Reynolds number R_m increases, the
saturation field strength and the growth rate of the dynamo increase. However,
the time it takes to built up the large scale field from equipartition to its
final super-equipartition value increases with magnetic Reynolds number. The
large scale field generation can be identified as being due to nonlocal
interactions originating from the forcing scale, which is characteristic of the
alpha-effect. Both alpha and turbulent magnetic diffusivity eta_t are
determined simultaneously using numerical experiments where the mean-field is
modified artificially. Both quantities are quenched in a R_m-dependent fashion.
The evolution of the energy of the mean field matches that predicted by an
alpha^2 dynamo model with similar alpha and eta_t quenchings. For this model an
analytic solution is given which matches the results of the simulations. The
simulations are numerically robust in that the shape of the spectrum at large
scales is unchanged when changing the resolution from 30^3 to 120^3 meshpoints,
or when increasing the magnetic Prandtl number (viscosity/magnetic diffusivity)
from 1 to 100. Increasing the forcing wavenumber to 30 (i.e. increasing the
scale separation) makes the inverse cascade effect more pronounced, although it
remains otherwise qualitatively unchanged.",0006186v2
2001-04-17,Centaurus A as the Source of ultra-high energy cosmic rays?,"We present numerical simulations for energy spectra and angular distributions
of nucleons above 10^{19} eV injected by the radio-galaxy Centaurus A at a
distance 3.4 Mpc and propagating in extra-galactic magnetic fields in the
sub-micro Gauss range. We show that field strengths B~0.3 micro Gauss, as
proposed by Farrar and Piran, cannot provide sufficient angular deflection to
explain the observational data. A magnetic field of intensity ~1 micro Gauss
could reproduce the observed large-scale isotropy and could marginally explain
the observed energy spectrum. However, it would not readily account for the
E=320 plusminus 93 EeV Fly's Eye event that was detected at an angle 136
degrees away from Cen-A. Such a strong magnetic field also saturates
observational upper limits from Faraday rotation observations and X-ray
bremsstrahlung emission from the ambient gas (assuming equipartition of
energy). This scenario may already be tested by improving magnetic field limits
with existing instruments. We also show that high energy cosmic ray experiments
now under construction will be able to detect the level of anisotropy predicted
by this scenario. We conclude that for magnetic fields B~0.1-0.5 micro Gauss,
considered as more reasonable for the local Supercluster environment, in all
likelihood at least a few sources within ~10 Mpc from the Earth should
contribute to the observed ultra high energy cosmic ray flux.",0104289v1
2003-01-25,Non-normal and Stochastic Amplification in Turbulent Dynamo: Subcritical Case,"Our attention focuses on the stochastic dynamo equation with non-normal
operator that give an insight into the role of stochastics and non-normality in
the galactic magnetic field generation. The main point of this Letter is a
discussion of the generation of a large-scale magnetic field that cannot be
explained by traditional linear eigenvalue analysis. We present a simple
stochastic model for the thin-disk axisymmetric $\alpha \Omega $ dynamo
involving three factors: (a) the non-normality generated by differential
rotation, (b) the nonlinearity reflecting how the magnetic field affects the
turbulent dynamo coefficients, and (c) stochastic perturbations. We show that
even for \textit{subcritical case,} there are three possible mechanisms for the
generation of magnetic field. The first mechanism is a deterministic one that
describes an interplay between transient growth and nonlinear saturation of the
turbulent $\alpha -$effect and diffusivity. It turns out that the trivial state
is nonlinearity unstable to small but finite initial perturbations. The second
and third are the stochastic mechanisms that account for the interaction of
non-normal effect generated by differential rotation and random additive and
multiplicative fluctuations. In particular, we show that in \textit{subcritical
case}the average magnetic energy can grow exponentially with time due to the
multiplicative noise associated with $\alpha -$effect.",0301517v2
2004-03-04,The two-dimensional magnetohydrodynamic Kelvin-Helmholtz instability: compressibility and large-scale coalescence effects,"The Kelvin-Helmholtz (KH) instability occurring in a single shear flow
configuration that is embedded in a uniform flow-aligned magnetic field, is
revisited by means of high resolution two-dimensional (2D) magnetohydrodynamic
(MHD) simulations. First, the calculations extend previous studies of
magnetized shear flows to a higher compressibility regime. The nonlinear
evolution of an isolated KH billow emerging from the fastest growing linear
mode for a convective sonic Mach number $M_{cs}=0.7$ layer is in many respects
similar to its less compressible counterpart (Mach $M_{cs}=0.5$). In
particular, the disruptive regime where locally amplified, initially weak
magnetic fields, control the nonlinear saturation process is found for Alfv\'en
Mach numbers $4\simlt M_A \simlt 30$. The most notable difference between
$M_{cs}=0.7$ versus $M_{cs}=0.5$ layers is that higher density contrasts and
fast magnetosonic shocklet structures are observed. Second, the use of adaptive
mesh refinement allows to parametrically explore much larger computational
domains, including up to 22 wavelengths of the linearly dominant mode. A strong
process of large-scale coalescence is found, whatever the magnetic field
regime. It proceeds through continuous pairing/merging events between adjacent
vortices up to the point where the final large-scale vortical structure reaches
the domain dimensions. This pairing/merging process is attributed to the growth
of subharmonic modes and is mainly controlled by relative phase differences
between them. These grid-adaptive simulations demonstrate that even in very
weak magnetic field regimes ($M_A \simeq 30$), the large-scale KH coalescence
process can trigger tearing-type reconnection events previously identified in
cospatial current-vortex sheets.",0403125v1
2004-07-18,Effects of differential and uniform rotation on nonlinear electromotive force in a turbulent flow,"An effect of the differential rotation on the nonlinear electromotive force
in MHD turbulence is found. It includes a nonhelical $\alpha$ effect which is
caused by a differential rotation, and it is independent of a hydrodynamic
helicity. There is no quenching of this effect contrary to the quenching of the
usual $\alpha$ effect caused by a hydrodynamic helicity. The nonhelical
$\alpha$ effect vanishes when the rotation is constant on the cylinders which
are parallel to the rotation axis. The mean differential rotation creates also
the shear-current effect which changes its sign with the nonlinear growth of
the mean magnetic field. However, there is no quenching of this effect. These
phenomena determine the nonlinear evolution of the mean magnetic field. An
effect of a uniform rotation on the nonlinear electromotive force is also
studied. A nonlinear theory of the ${\bf \Omega} {\bf \times} \bar{\bf J}$
effect is developed, and the quenching of the hydrodynamic part of the usual
$\alpha$ effect which is caused by a uniform rotation and inhomogeneity of
turbulence, is found. Other contributions of a uniform rotation to the
nonlinear electromotive force are also determined. All these effects are
studied using the spectral $\tau$ approximation (the third-order closure
procedure). An axisymmetric mean-field dynamo in the spherical and cylindrical
geometries is considered. The nonlinear saturation mechanism based on the
magnetic helicity evolution is discussed. It is shown that this universal
mechanism is nearly independent of the form of the flux of magnetic helicity,
and it requires only a nonzero flux of magnetic helicity. Astrophysical
applications of these effects are discussed.",0407375v3
2007-03-22,General relativistic simulations of pasive-magneto-rotational core collapse with microphysics,"This paper presents results from axisymmetric simulations of
magneto-rotational stellar core collapse to neutron stars in general relativity
using the passive field approximation for the magnetic field. These simulations
are performed using a new general relativistic numerical code specifically
designed to study this astrophysical scenario. The code is based on the
conformally-flat approximation of Einstein's field equations and conservative
formulations of the magneto-hydrodynamics equations. The code has been recently
upgraded to incorporate a tabulated, microphysical equation of state and an
approximate deleptonization scheme. This allows us to perform the most
realistic simulations of magneto-rotational core collapse to date, which are
compared with simulations employing a simplified (hybrid) equation of state,
widely used in the relativistic core collapse community. Furthermore,
state-of-the-art (unmagnetized) initial models from stellar evolution are used.
In general, stellar evolution models predict weak magnetic fields in the
progenitors, which justifies our simplification of performing the computations
under the approach that we call the passive field approximation for the
magnetic field. Our results show that for the core collapse models with
microphysics the saturation of the magnetic field cannot be reached within
dynamical time scales by winding up the poloidal magnetic field into a toroidal
one. We estimate the effect of other amplification mechanisms including the
magneto-rotational instability (MRI) and several types of dynamos.",0703597v2
1998-09-07,Non-Dissipative Logic Device NOT Based on Two Coupled Quantum Dots,"Non-dissipative dynamics of interacting electrons in two tunnel-coupled
quantum dots is studied theoretically within the framework of the Hubbard
model. Various values of intra-dot Coulomb repulsion energy $U$ and inter-dot
tunneling energy $V$ are considered, which correspond to various size of the
dots and to various distance between them. In the ground state, the average
value of the spin projection (magnetic moment) at each dot is zero. The input
signal (the local external magnetic field $H$) applied to one of the dots at a
time $t=0$ causes the electronic subsystem to evolve in such a way that
magnetic moments of quantum dots become oriented in the opposite directions at
any time $t>0$. For any set of $U$ and $V$, there exist optimal values of $H$
and $t$ which maximize the absolute values of magnetic moments at both dots,
and magnetic moments become almost saturated. Thus, the antiferromagnetic-like
spin ordering can be realized at the stage of coherent temporal evolution, well
before the relaxation to a new ground state at the sacrifice of inelastic
processes. This effect (""dynamical antiferromagnetism"") may be used for
implementation of a logic function NOT in an extremely short time. A
possibility to use the arrays of quantum dots as high-speed single-electron
devices of new generation is discussed.",9809112v1
2003-02-25,Magnetic Phase Diagram of GdNi2B2C: Two-ion Magnetoelasticity and Anisotropic Exchange Couplings,"Extensive magnetization and magnetostriction measurements were carried out on
a single crystal of GdNi2B2C along the main tetragonal axes. Within the
paramagnetic phase, the magnetic and strain susceptibilities revealed a weak
anisotropy in the exchange couplings and two-ion tetragonal-preserving
alpha-strain modes. Within the ordered phase, magnetization and
magnetostriction revealed a relatively strong orthorhombic distortion mode and
rich field-temperature phase diagrams. For H//(100) phase diagram, three
field-induced transformations were observed, namely, at: Hd(T), related to the
domain alignment; Hr(T), associated with reorientation of the moment towards
the c-axis; and Hs(T), defining the saturation process wherein the exchange
field is completely counterbalanced. On the other hand, For H//(001) phase
diagram, only two field-induced transformations were observed, namely at: Hr(T)
and Hs(T). For both phase diagrams, Hs(T) follows the relation
Hs[1-(T/Tn)^2]^(1/2)kOe with Hs(T-->0)=128.5(5) kOe and Tn(H=0)=19.5 K. In
contrast, the thermal evolution of Hr(T) along the c-axis (much simpler than
along the a-axis) follows the relation Hr[1-T/Tr]^(1/3) kOe where
Hr(T-->0)=33.5(5) kOe and Tr(H=0)=13.5 K. It is emphasized that the
magnetoelastic interaction and the anisotropic exchange coupling are important
perturbations and therefore should be explicitly considered if a complete
analysis of the magnetic properties of the borocarbides is desired.",0302521v1
2003-10-14,"Exchange anisotropy, disorder and frustration in diluted, predominantly ferromagnetic, Heisenberg spin systems","Motivated by the recent suggestion of anisotropic effective exchange
interactions between Mn spins in Ga$_{1-x}$Mn$_x$As (arising as a result of
spin-orbit coupling), we study their effects in diluted Heisenberg spin
systems. We perform Monte Carlo simulations on several phenomenological model
spin Hamiltonians, and investigate the extent to which frustration induced by
anisotropic exchanges can reduce the low temperature magnetization in these
models and the interplay of this effect with disorder in the exchange. In a
model with low coordination number and purely ferromagnetic (FM) exchanges, we
find that the low temperature magnetization is gradually reduced as exchange
anisotropy is turned on. However, as the connectivity of the model is
increased, the effect of small-to-moderate anisotropy is suppressed, and the
magnetization regains its maximum saturation value at low temperatures unless
the distribution of exchanges is very wide. To obtain significant suppression
of the low temperature magnetization in a model with high connectivity, as is
found for long-range interactions, we find it necessary to have both
ferromagnetic and antiferromagnetic (AFM) exchanges (e.g. as in the RKKY
interaction). This implies that disorder in the sign of the exchange
interaction is much more effective in suppressing magnetization at low
temperatures than exchange anisotropy.",0310322v1
2006-05-19,Spin-flop transition in antiferromagnetic multilayers,"A comprehensive theoretical investigation on the field-driven reorientation
transitions in uniaxial multilayers with antiferromagnetic coupling is
presented. It is based on a complete survey of the one-dimensional solutions
for the basic phenomenological (micromagnetic) model that describes the
magnetic properties of finite stacks made from ferromagnetic layers coupled
antiferromagnetically through spacer layers. The general structure of the phase
diagrams is analysed. At a high ratio of uniaxial anisotropy to
antiferromagnetic interlayer exchange, only a succession of collinear magnetic
states is possible. With increasing field first-order (metamagnetic)
transitions occur from the antiferromagnetic ground-state to a set of
degenerate ferrimagnetic states and to the saturated ferromagnetic state. At
low anisotropies, a first-order transition from the antiferromagnetic
ground-state to an inhomogeneous spin-flop state occurs. Between these two
regions, transitional magnetic phases occupy the range of intermediate
anisotropies. Detailed and quantitative phase diagrams are given for the basic
model of antiferromagnetic multilayer systems with N = 2 to 16 layers. The
connection of the phase diagrams with the spin-reorientation transitions in
bulk antiferromagnets is discussed. The limits of low anisotropy and large
numbers of layers are analysed by two different representations of the magnetic
energy, namely, in terms of finite chains of staggered vectors and in a general
continuum form. It is shown that the phenomena widely described as ``surface
spin-flop'' are driven only by the cut exchange interactions and the
non-compensated magnetic moment at the surface layers of a stacked
antiferromagnetic system.",0605493v1
2004-09-20,Spontaneous symmetry breaking and response functions,"We study the quantum phase transition occurring in an infinite homogeneous
system of spin 1/2 fermions in a non-relativistic context. As an example we
consider neutrons interacting through a simple spin-spin Heisenberg force. The
two critical values of the coupling strength -- signaling the onset into the
system of a finite magnetization and of the total magnetization, respectively
-- are found and their dependence upon the range of the interaction is
explored. The spin response function of the system in the region where the
spin-rotational symmetry is spontaneously broken is also studied. For a
ferromagnetic interaction the spin response along the direction of the
spontaneous magnetization occurs in the particle-hole continuum and displays,
for not too large momentum transfers, two distinct peaks. The response along
the direction orthogonal to the spontaneous magnetization displays instead,
beyond a softened and depleted particle-hole continuum, a collective mode to be
identified with a Goldstone boson of type II. Notably, the random phase
approximation on a Hartree-Fock basis accounts for it, in particular for its
quadratic -- close to the origin -- dispersion relation. It is shown that the
Goldstone boson contributes to the saturation of the energy-weighted sum rule
for ~25% when the system becomes fully magnetized (that is in correspondence of
the upper critical value of the interaction strength) and continues to grow as
the interaction strength increases.",0409039v1
2009-06-24,Turbulent resistivity driven by the magnetorotational instability,"We measure the turbulent resistivity in the nonlinear regime of the MRI, and
evaluate the turbulent magnetic Prandtl number. We perform a set of numerical
simulations with the Eulerian finite volume codes Athena and Ramses in the
framework of the shearing box model. We consider models including explicit
dissipation coefficients and magnetic field topologies such that the net
magnetic flux threading the box in both the vertical and azimuthal directions
vanishes. We first demonstrate good agreement between the two codes by
comparing the properties of the turbulent states in simulations having
identical microscopic diffusion coefficients (viscosity and resistivity). We
find the properties of the turbulence do not change when the box size is
increased in the radial direction, provided it is elongated in the azimuthal
direction. To measure the turbulent resistivity in the disk, we impose a fixed
electromotive force on the flow and measure the amplitude of the saturated
magnetic field that results. We obtain a turbulent resistivity that is in rough
agreement with mean field theories like the Second Order Smoothing
Approximation. The numerical value translates into a turbulent magnetic Prandtl
number Pm_t of order unity. Pm_t appears to be an increasing function of the
forcing we impose. It also becomes smaller as the box size is increased in the
radial direction, in good agreement with previous results obtained in very
large boxes. Our results are in general agreement with other recently published
papers studying the same problem but using different methodology. Thus, our
conclusion that Pm_t is of order unity appears robust.",0906.4422v2
2009-09-01,Turbulence and Mixing in the Intracluster Medium,"The intracluster medium (ICM) is stably stratified in the hydrodynamic sense
with the entropy $s$ increasing outwards. However, thermal conduction along
magnetic field lines fundamentally changes the stability of the ICM, leading to
the ""heat-flux buoyancy instability"" when $dT/dr>0$ and the ""magnetothermal
instability"" when $dT/dr<0$. The ICM is thus buoyantly unstable regardless of
the signs of $dT/dr$ and $ds/dr$. On the other hand, these
temperature-gradient-driven instabilities saturate by reorienting the magnetic
field (perpendicular to $\hat{\bf r}$ when $dT/dr>0$ and parallel to $\hat{\bf
r}$ when $dT/dr<0$), without generating sustained convection. We show that
after an anisotropically conducting plasma reaches this nonlinearly stable
magnetic configuration, it experiences a buoyant restoring force that resists
further distortions of the magnetic field. This restoring force is analogous to
the buoyant restoring force experienced by a stably stratified adiabatic
plasma. We argue that in order for a driving mechanism (e.g, galaxy motions or
cosmic-ray buoyancy) to overcome this restoring force and generate turbulence
in the ICM, the strength of the driving must exceed a threshold, corresponding
to turbulent velocities $\gtrsim 10 -100 {km/s}$. For weaker driving, the ICM
remains in its nonlinearly stable magnetic configuration, and turbulent mixing
is effectively absent. We discuss the implications of these findings for the
turbulent diffusion of metals and heat in the ICM.",0909.0270v1
2010-06-17,Magnetic helicity flux in the presence of shear,"Magnetic helicity has risen to be a major player in dynamo theory, with the
helicity of the small-scale field being linked to the dynamo saturation process
for the large-scale field. It is a nearly conserved quantity, which allows its
evolution equation to be written in terms of production and flux terms. The
flux term can be decomposed in a variety of fashions. One particular
contribution that has been expected to play a significant role in dynamos in
the presence of mean shear was isolated by Vishniac & Cho (2001, ApJ 550, 752).
Magnetic helicity fluxes are explicitly gauge dependent however, and the
correlations that have come to be called the Vishniac-Cho flux were determined
in the Coulomb gauge, which turns out to be fraught with complications in
shearing systems. While the fluxes of small-scale helicity are explicitly gauge
dependent, their divergences can be gauge independent. We use this property to
investigate magnetic helicity fluxes of small-scale field through direct
numerical simulations in a shearing-box system and find that in a numerically
usable gauge the divergence of the small-scale helicity flux vanishes, while
the divergence of the Vishniac-Cho flux remains finite. We attribute this
seeming contradiction to the existence of horizontal fluxes of small-scale
magnetic helicity with finite divergences even in our shearing-periodic domain.",1006.3549v2
2010-09-03,Magnetic and transport properties of the spin-state disordered oxide La0.8Sr0.2Co_{1-x}Rh_xO_{3-δ},"We report measurements and analysis of magnetization, resistivity and
thermopower of polycrystalline samples of the perovskite-type Co/Rh oxide
La$_{0.8}$Sr$_{0.2}$Co$_{1-x}$Rh$_x$O$_{3-\delta}$. This system constitutes a
solid solution for a full range of $x$,in which the crystal structure changes
from rhombohedral to orthorhombic symmetry with increasing Rh content $x$. The
magnetization data reveal that the magnetic ground state immediately changes
upon Rh substitution from ferromagnetic to paramagnetic with increasing $x$
near 0.25, which is close to the structural phase boundary. We find that one
substituted Rh ion diminishes the saturation moment by 9 $\mu_B$, which implies
that one Rh$^{3+}$ ion makes a few magnetic Co$^{3+}$ ions nonmagnetic (the low
spin state), and causes disorder in the spin state and the highest occupied
orbital. In this disordered composition ($0.05\le x \le 0.75$), we find that
the thermopower is anomalously enhanced below 50 K. In particular, the
thermopower of $x$=0.5 is larger by a factor of 10 than those of $x$=0 and 1,
and the temperature coefficient reaches 4 $\mu$V/K$^2$ which is as large as
that of heavy-fermion materials such as CeRu$_2$Si$_2$.",1009.0728v2
2011-08-09,H2O Maser Polarization of the Water Fountains IRAS 15445-5449 and IRAS 18043-2116,"We present the morphology and linear polarization of the 22-GHz H2O masers in
the high-velocity outflow of two post-AGB sources, d46 (IRAS 15445-5449) and
b292 (IRAS 18043-2116). The observations were performed using The Australia
Telescope Compact Array. Different levels of saturated maser emission have been
detected for both sources. We also present the mid-infrared image of d46
overlaid with the distribution of the maser features that we have observed in
the red-shifted lobe of the bipolar structure. The relative position of the
observed masers and a previous radio continuum observation suggests that the
continnum is produced along the blue-shifted lobe of the jet. It is likely due
to synchrontron radiation, implying the presence of a strong magnetic field in
the jet. The fractional polarization levels measured for the maser features of
d46 indicate that the polarization vectors are tracing the poloidal component
of the magnetic field in the emitting region. For the H2O masers of b292 we
have measured low levels of fractional linear polarization. The linear
polarization in the H2O maser region of this source likely indicates a dominant
toroidal or poloidal magnetic field component. Since circular polarization was
not detected it is not possible to determine the magnetic field strength.
However, we present a 3-sigma evaluation of the upper limit intensity of the
magnetic field in the maser emitting regions of both observed sources.",1108.1911v1
2011-09-28,Numerical Simulations of Driven Supersonic Relativistic MHD Turbulence,"Models for GRB outflows invoke turbulence in relativistically hot magnetized
fluids. In order to investigate these conditions we have performed
high-resolution three-dimensional numerical simulations of relativistic
magneto-hydrodynamical (RMHD) turbulence. We find that magnetic energy is
amplified to several percent of the total energy density by turbulent twisting
and folding of magnetic field lines. Values of epsilon_B near 1% are thus
naturally expected. We study the dependence of saturated magnetic field energy
fraction as a function of Mach number and relativistic temperature. We then
present power spectra of the turbulent kinetic and magnetic energies. We also
present solenoidal (curl-like) and dilatational (divergence-like) power spectra
of kinetic energy. We propose that relativistic effects introduce novel
couplings between these spectral components. The case we explore in most detail
is for equal amounts of thermal and rest mass energy, corresponding to
conditions after collisions of shells with relative Lorentz factors of several.
These conditions are relevant in models for internal shocks, for the late
afterglow phase, for cocoon material along the edge of a relativistic jet as it
propagates through a star, as well neutron stars merging with each other and
with black hole companions. We find that relativistic turbulence decays
extremely quickly, on a sound crossing time of an eddy. Models invoking
sustained relativistic turbulence to explain variability in GRB prompt emission
are thus strongly disfavored unless a persistant driving of the turbulence is
maintained for the duration of the prompt emission.",1109.6294v1
2011-10-19,Current helicity of active regions as a tracer of large-scale solar magnetic helicity,"We demonstrate that the current helicity observed in solar active regions
traces the magnetic helicity of the large-scale dynamo generated field. We use
an advanced 2D mean-field dynamo model with dynamo saturation based on the
evolution of the magnetic helicity and algebraic quenching. For comparison, we
also studied a more basic 2D mean-field dynamo model with simple algebraic
alpha quenching only. Using these numerical models we obtained butterfly
diagrams both for the small-scale current helicity and also for the large-scale
magnetic helicity, and compared them with the butterfly diagram for the current
helicity in active regions obtained from observations. This comparison shows
that the current helicity of active regions, as estimated by $-{\bf A \cdot B}$
evaluated at the depth from which the active region arises, resembles the
observational data much better than the small-scale current helicity calculated
directly from the helicity evolution equation. Here ${\bf B}$ and ${\bf A}$ are
respectively the dynamo generated mean magnetic field and its vector potential.
A theoretical interpretation of these results is given.",1110.4387v2
2011-12-12,Self-similar solutions of viscous and resistive ADAFs with thermal conduction,"We have studied the effects of thermal conduction on the structure of viscous
and resistive advection-dominated accretion flows (ADAFs). The importance of
thermal conduction on hot accretion flow is confirmed by observations of hot
gas that surrounds Sgr A$^*$ and a few other nearby galactic nuclei. In this
research, thermal conduction is studied by a saturated form of it, as is
appropriated for weakly-collisional systems. It is assumed the viscosity and
the magnetic diffusivity are due to turbulence and dissipation in the flow. The
viscosity also is due to angular momentum transport. Here, the magnetic
diffusivity and the kinematic viscosity are not constant and vary by position
and $\alpha$-prescription is used for them. The govern equations on system have
been solved by the steady self-similar method. The solutions show the radial
velocity is highly subsonic and the rotational velocity behaves sub-Keplerian.
The rotational velocity for a specific value of the thermal conduction
coefficient becomes zero. This amount of conductivity strongly depends on
magnetic pressure fraction, magnetic Prandtl number, and viscosity parameter.
Comparison of energy transport by thermal conduction with the other energy
mechanisms implies that thermal conduction can be a significant energy
mechanism in resistive and magnetized ADAFs. This property is confirmed by
non-ideal magnetohydrodynamics (MHD) simulations.",1112.2678v1
2012-09-24,Diffusive shock acceleration with magnetic field amplification and Alfvenic drift,"We explore how wave-particle interactions affect diffusive shock acceleration
(DSA) at astrophysical shocks by performing time-dependent kinetic simulations,
in which phenomenological models for magnetic field amplification (MFA),
Alfvenic drift, thermal leakage injection, Bohm-like diffusion, and a free
escape boundary are implemented. If the injection fraction of cosmic-ray (CR)
particles is greater than 2x10^{-4}, for the shock parameters relevant for
young supernova remnants, DSA is efficient enough to develop a significant
shock precursor due to CR feedback, and magnetic field can be amplified up to a
factor of 20 via CR streaming instability in the upstream region. If scattering
centers drift with Alfven speed in the amplified magnetic field, the CR energy
spectrum can be steepened significantly and the acceleration efficiency is
reduced. Nonlinear DSA with self-consistent MFA and Alfvenic drift predicts
that the postshock CR pressure saturates roughly at 10 % of the shock ram
pressure for strong shocks with a sonic Mach number ranging 20< M_s< 100. Since
the amplified magnetic field follows the flow modification in the precursor,
the low energy end of the particle spectrum is softened much more than the high
energy end. As a result, the concave curvature in the energy spectra does not
disappear entirely even with the help of Alfvenic drift. For shocks with a
moderate Alfven Mach number (M_A<10), the accelerated CR spectrum can become as
steep as E^{-2.1}-E^{-2.3}, which is more consistent with the observed CR
spectrum and gamma-ray photon spectrum of several young supernova remnants.",1209.5203v1
2012-12-05,Columnar antiferromagnetic order and spin supersolid phase on the extended Shastry-Sutherland lattice,"We use large scale quantum Monte Carlo simulations to study an extended
version of the canonical Shastry-Sutherland model -- including additional
interactions and exchange anisotropy -- over a wide range of interaction
parameters and an applied magnetic field. The model is appropriate for
describing the low energy properties of some members of the rare earth
tetraborides. Working in the limit of large Ising-like exchange anisotropy, we
demonstrate the stabilization of columnar antiferromagnetic order in the ground
state at zero field and an extended magnetization plateau at 1/2 the saturation
magnetization in the presence of an applied longitudinal magnetic field --
qualitatively similar to experimentally observed low-temperature phases in
ErB$_4$. Our results show that for an optimal range of exchange parameters, a
spin supersolid ground state is realized over a finite range of applied field
between the columnar antiferromagnetic phase and the magnetization plateau. The
full momentum dependence of the longitudinal and transverse components of the
static structure factor is calculated in the spin supersolid phase to
demonstrate the simultaneous existence of diagonal and off-diagonal long-range
order. Our results will provide crucial guidance in designing further
experiments to search for the interesting spin supersolid phase in ErB$_4$.",1212.0926v2
2013-04-17,Magnetic field amplification by the small-scale dynamo in the early Universe,"In this paper we show that the Universe is already strongly magnetized at
very early epochs during cosmic evolution. Our calculations are based on the
efficient amplification of weak magnetic seed fields, which are unavoidably
present in the early Universe, by the turbulent small-scale dynamo. We identify
two mechanisms for the generation of turbulence in the radiation dominated
epoch where velocity fluctuations are produced by the primordial density
perturbation and by possible first-order phase transitions at the electroweak
or QCD scales. We show that all the necessities for the small-scale dynamo to
work are fulfilled. Hence, this mechanism, operating due to primordial density
perturbations, guarantees fields with comoving field strength
$B_0\sim10^{-6}\varepsilon^{1/2}$ nG on scales up to $\lambda_c\sim0.1$ pc,
where $\varepsilon$ is the saturation efficiency. The amplification of magnetic
seed fields could be even larger if there are first-order phase transitions in
the early Universe. Where, on scales up to $\lambda_c\sim100$ pc, the comoving
field strength due to this mechanism will be $B_0\sim10^{-3}\varepsilon^{1/2}$
nG at the present time. Such fields, albeit on small scales, can play an
important role in structure formation and could provide an explanation to the
apparently observed magnetic fields in the voids of the large-scale structure.",1304.4723v2
2013-06-18,Magnetic anisotropy and lattice dynamics in FeAs studied by Mössbauer spectroscopy,"Iron mono-arsenide in the powder form has been investigated by transmission
57Fe Moessbauer spectroscopy in the temperature range 4.2 - 1000 K. Additional
spectra have been obtained at 20 K and 100 K applying external magnetic field
of 7 T. It was found that the spin spiral propagating along the c-axis leads to
the complex variation of the hyperfine magnetic field amplitude with the spin
orientation varying in the a-b plane. The magnitude of the hyperfine field
pointing in the direction of the local magnetic moment depends on the
orientation of this moment in the a-b plane. Patterns are vastly different for
iron located in the [0 k 0] positions and for iron in the [0 k+1/2 0] positions
within the orthorhombic cell set to the Pnma symmetry. Lattice softens upon
transition to the paramagnetic state at 69.2 K primarily in the a-c plane as
seen by iron atoms. This effect is quite large considering lack of the
structural transition. Two previously mentioned iron sites are discernible in
the paramagnetic region till 300 K by different electron densities on the iron
nuclei. The anisotropy of the iron vibrations developed at the transition to
the paramagnetic state increases with the temperature in accordance with the
harmonic approximation, albeit tends to saturation at high temperatures
indicating gradual onset of the quasi-harmonic conditions. It seems that
neither hyperfine fields nor magnetic moments are correct order parameters in
light of the determined static critical exponents. Sample starts to loose
arsenic at about 1000 K and under vacuum.",1306.4170v3
2013-07-10,Magnetic field generation in a jet-sheath plasma via the kinetic Kelvin-Helmholtz instability,"We have investigated generation of magnetic fields associated with velocity
shear between an unmagnetized relativistic jet and an unmagnetized sheath
plasma. We have examined the strong magnetic fields generated by kinetic shear
(Kelvin-Helmholtz) instabilities. Compared to the previous studies using
counter-streaming performed by Alves et al. (2012), the structure of KKHI of
our jet-sheath configuration is slightly different even for the global
evolution of the strong transverse magnetic field. In our simulations the major
components of growing modes are the electric field $E_{\rm z}$ and the magnetic
field $B_{\rm y}$. After the $B_{\rm y}$ component is excited, an induced
electric field $E_{\rm x}$ becomes significant. However, other field components
remain small. We find that the structure and growth rate of KKHI with mass
ratios $m_{\rm i}/m_{\rm e} = 1836$ and $m_{\rm i}/m_{\rm e} = 20$ are similar.
In our simulations saturation in the nonlinear stage is not as clear as in
counter-streaming cases. The growth rate for a mildly-relativistic jet case
($\gamma_{\rm j} = 1.5$) is larger than for a relativistic jet case
($\gamma_{\rm j} = 15$).",1307.2928v1
2013-09-27,Structural and magnetic properties of Cr-diluted CoFeB,"The crystallization process and the magnetization of Cr diluted CoFeB was
investigated in both ribbon samples and thin film samples with Cr content up to
30 at. %. A primary crystallization of bcc phase from an amorphous precursor in
ribbon samples was observed when the annealing temperature rose to between 421
oC and 456 oC, followed by boron segregation at temperatures between 518 oC and
573 oC. The two onset crystallization temperatures showed strong dependences on
both Cr and B concentrations. The impact of Cr concentration on the magnetic
properties including a reduced saturation magnetization and an enhanced
coercive field was also observed. The magnetizations of both ribbon samples and
thin film samples were well fitted using the generalized Slater-Pauling curve
with modified moments for B (-0.94 {\mu}B) and Cr (-3.6 {\mu}B). Possible
origins of the enhanced coercive field were also discussed. We also achieved a
damping parameter in CoFeCrB thin films at the same level as Co40Fe40B20, much
lower than the value reported for CoFeCrB films previously. The results suggest
a possible advantage of CoFeCrB in reducing the critical switching current
density in Spin Transfer Torque Random Access Memory (STT-RAM).",1309.7331v1
2013-10-14,Magnetic fields during the formation of supermassive black holes,"Observations of quasars at $\rm z> 6$ report the existence of a billion solar
mass black holes. Comprehending their formation in such a short time scale is a
matter of ongoing research. One of the most promising scenarios to assemble
supermassive black holes is a monolithic collapse of protogalactic gas clouds
in atomic cooling halos with $\rm T_{vir} \geq 10^{4} K$. In this article, we
study the amplification and impact of magnetic fields during the formation of
seed black holes in massive primordial halos. We perform high resolution
cosmological magnetohydrodynamics simulations for four distinct halos and
follow their collapse for a few free-fall times until the simulations reach a
peak density of $\rm 7 \times 10^{-10} g/cm^{3}$. Our findings show that
irrespective of the initial seed field, the magnetic field strength reaches a
saturated state in the presence of strong accretion shocks. Under such
conditions, the growth time becomes very short and amplification occurs rapidly
within a small fraction of the free-fall time. We find that the presence of
such strong magnetic fields provides additional support against gravity and
helps in suppressing fragmentation. Massive clumps of a few hundred solar
masses are formed at the end of our simulations and high accretion rates of
$\rm 1 M_{\odot}/yr$ are observed. We expect that in the presence of such
accretion rates, the clumps will grow to form supermassive stars of $\rm \sim
10^{5} M_{\odot}$. Overall, the role of the magnetic fields seems supportive
for the formation of massive black holes.",1310.3680v2
2013-12-11,Distinct magnetic phase transition at the surface of an antiferromagnet,"In the majority of magnetic systems the surface is required to order at the
same temperature as the bulk. In the present study, we report a distinct and
unexpected surface magnetic phase transition, uniquely at a lower temperature
than the N\'eel temperature. Employing grazing incidence X-ray resonant
magnetic scattering we have observed the near surface behavior of uranium
dioxide. UO$_2$ is a non-collinear, triple-q, antiferromagnet with the U ions
on an face-centered-cubic lattice. Theoretical investigations establish that at
the surface the energy increase, due to the lost bonds, reduces when the spins
near the surface rotate, gradually losing their normal to the surface
component. At the surface the lowest-energy spin configuration has a double-q
(planar) structure. With increasing temperature, thermal fluctuations saturate
the in-plane crystal field anisotropy at the surface, leading to soft
excitations that have ferromagnetic $XY$ character and are decoupled from the
bulk. The structure factor of a finite two-dimensional $XY$ model, fits the
experimental data well for several orders of magnitude of the scattered
intensity. Our results support a distinct magnetic transition at the surface in
the Kosterlitz-Thouless universality class.",1312.3136v2
2014-08-07,Magnetic Torque of Microfabricated Elements and Magnetotactic Bacteria,"We present a thorough theoretical analysis of the magnetic torque on
microfabricated elements with dimensions in the range of 100 to 500 {\mu}m and
magneto-somes of magnetotactic bacteria of a few {\mu}m length. We derive
simple equations for field dependent torque and magnetic shape anisotropy that
can be readily used to replace the crude approximations commonly used. We
illustrate and verify the theory on microfabricated elements and magnetotactic
bacteria, by field depedent torque magnetometry and by observing their rotation
in water under application of a rotating magnetic field. The maximum rotation
frequency of the largest microfabricated elements agrees within error
boundaries with theory. For smaller, and especially thinner, elements the
measured frequencies are a factor of three to four too low. We suspect this is
caused by incomplete saturation of the magnetisation in the elements, which is
not incorporated in our model. The maximum rotation frequency of magnetotactic
bacteria agrees with our model within error margins, which are however quite
big due to the large spread in bacteria morphology. The model presented
provides a solid basis for the analysis of experiments with magnetic objects in
liquid, which is for instance the case in the field of medical microrobotics.",1408.1570v1
2015-08-28,Spin-S Kagome quantum antiferromagnets in a field with tensor networks,"Spin-$S$ Heisenberg quantum antiferromagnets on the Kagome lattice offer,
when placed in a magnetic field, a fantastic playground to observe exotic
phases of matter with (magnetic analogs of) superfluid, charge, bond or nematic
orders, or a coexistence of several of the latter. In this context, we have
obtained the (zero temperature) phase diagrams up to $S=2$ directly in the
thermodynamic limit thanks to infinite Projected Entangled Pair States (iPEPS),
a tensor network numerical tool. We find incompressible phases characterized by
a magnetization plateau vs field and stabilized by spontaneous breaking of
point group or lattice translation symmetry(ies). The nature of such phases may
be semi-classical, as the plateaus at $\frac{1}{3}$th, $(1-\frac{2}{9S})$th and
$(1-\frac{1}{9S})$th of the saturated magnetization (the latter followed by a
macroscopic magnetization jump), or fully quantum as the spin-$\frac{1}{2}$
$\frac{1}{9}$-plateau exhibiting coexistence of charge and bond orders. Upon
restoration of the spin rotation $U(1)$ symmetry a finite compressibility
appears, although lattice symmetry breaking persists. For integer spin values
we also identify spin gapped phases at low enough field, such as the $S=2$
(topologically trivial) spin liquid with no symmetry breaking, neither spin nor
lattice.",1508.07189v3
2015-08-31,Growth and Characterization of Ce- Substituted Nd2Fe14B Single Crystals,"Single crystals of (Nd1-xCex)2Fe14B are grown out of Fe-(Nd,Ce) flux.
Chemical and structural analysis of the crystals indicates that
(Nd1-xCex)2Fe14B forms a solid solution until at least x = 0.38 with a
Vegard-like variation of the lattice constants with x. Refinements of single
crystal neutron diffraction data indicate that Ce has a slight site preference
(7:3) for the 4g rare earth site over the 4f site. Magnetization measurements
show that for x = 0.38 the saturation magnetization at 400 K, a temperature
important to applications, falls from 29.8 for the parent Nd2Fe14B to 27.6
(mu)B/f.u., the anisotropy field decreases from 5.5 T to 4.7 T, and the Curie
temperature decreases from 586 to 543 K. First principles calculations carried
out within density functional theory are used to explain the decrease in
magnetic properties due to Ce substitution. Though the presence of the
lower-cost and more abundant Ce slightly affects these important magnetic
characteristics, this decrease is not large enough to affect a multitude of
applications. Ce-substituted Nd2Fe14B is therefore a potential high-performance
permanent magnet material with substantially reduced Nd content.",1508.07792v1
2015-12-10,Investigation of magnetic characteristics of oxygen adsorbed YbFe2As2 single crystals,"Recent discovery of superconductivity in iron pnictides had attracted immense
attention of the scientific community. The parent compounds were spin density
wave (SDW) metals unlike the high-TC superconductors which were Mott
insulators. In this present study, we synthesized single crystal of a new
compound YbFe2As2 by using high temperature solution growth technique without
flux. The YbFe2As2 single crystals had been systematically characterized by
energy dispersive X-ray analysis (EDAX). The presence of oxygen was found by
EDAX on the surfaces of grown YbFe2As2 single crystals which had been kept in
air ambience for few months. The measurement of magnetization (M) versus
temperature (T) using SQUID at constant magnetic field (H = 100 Oe) for
YbFe2As2 had revealed an occurrence of sharp slope change around 140 K which
was the known SDW transition temperature for the parent compound BaFe2As2. An
additional slope change had been observed around 40 K. M vs T data at H= 10000
Oe had exhibited paramagnetic behavior. Result of M versus H measurements for
YbFe2As2 at 2 K had shown that the saturation had not been achieved at H =
80000 Oe. We had carried out magnetization measurements for oxygen adsorbed
YbFe2As2 (YbFe2As2 : O2 ) and BaFe2As2 (BaFe2As2 : O2) for comparative study
also.",1512.03197v1
2016-02-03,"Robust tunability of magnetorestance in Half-Heusler RPtBi (R = Gd, Dy, Tm, and Lu) compounds","We present the magnetic field dependencies of transport properties for
$R$PtBi ($R$ = Gd, Dy, Tm, and Lu) half-Heusler compounds. Temperature and
field dependent resistivity measurements of high quality $R$PtBi single
crystals reveal an unusually large, non-saturating magnetoresistance (MR) up to
300 K under a moderate magnetic field of $H$ = 140 kOe. At 300 K, the large MR
effect decreases as the rare-earth is traversed from Gd to Lu and the magnetic
field dependence of MR shows a deviation from the conventional $H^{2}$
behavior. The Hall coefficient ($R_{H}$) for $R$ = Gd indicates a sign change
around 120 K, whereas $R_{H}$ curves for $R$ = Dy, Tm, and Lu remain positive
for all measured temperatures. At 300 K, the Hall resistivity reveals a
deviation from the linear field dependence for all compounds. Thermoelectric
power measurements on this family show strong temperature and magnetic field
dependencies which are consistent with resistivity measurements. A highly
enhanced thermoelectric power under applied magnetic field is observed as high
as $\sim$100 $\mu$V/K at 140 kOe. Analysis of the transport data in this series
reveals that the rare-earth-based Half-Husler compounds provide opportunities
to tune MR effect through lanthanide contraction and to elucidate the mechanism
of non-trivial MR.",1602.01194v1
2016-07-01,Size dependent magnetic and electrical properties of Ba-doped nanocrystalline BiFeO$_3$,"Improvement in magnetic and electrical properties of multiferroic BiFeO$_3$
in conjunction with their dependence on particle size is crucial due to its
potential applications in multifunctional miniaturized devices. In this
investigation, we report a study on particle size dependent structural,
magnetic and electrical properties of sol-gel derived
Bi$_{0.9}$Ba$_{0.1}$FeO$_3$ nanoparticles of different sizes ranging from
$\sim$ 12 to 49 nm. The substitution of Bi by Ba significantly suppresses
oxygen vacancies, reduces leakage current density and Fe$^{2+}$ state. An
improvement in both magnetic and electrical properties is observed for 10 %
Ba-doped BiFeO$_3$ nanoparticles compared to its undoped counterpart. The
saturation magnetization of Bi$_{0.9}$Ba$_{0.1}$FeO$_3$ nanoparticles increase
with reducing particle size in contrast with a decreasing trend of
ferroelectric polarization. Moreover, a first order metamagnetic transition is
noticed for $\sim$ 49 nm Bi$_{0.9}$Ba$_{0.1}$FeO$_3$ nanoparticles which
disappeared with decreasing particle size. The observed strong size dependent
multiferroic properties are attributed to the complex interaction between
vacancy induced crystallographic defects, multiple valence states of Fe,
uncompensated surface spins, crystallographic distortion and suppression of
spiral spin cycloid of BiFeO$_3$.",1607.00169v1
2016-10-13,Dynamic Domains of DTS: Simulations of a Spherical Magnetized Couette Flow,"The Derviche Tourneur Sodium experiment, a spherical Couette
magnetohydrodynamics experiment with liquid sodium as the medium and a dipole
magnetic field imposed from the inner sphere, recently underwent upgrades to
its diagnostics to better characterize the flow and induced magnetic fields
with global rotation. In tandem with the upgrades, a set of direct numerical
simulations were run with the xshells code to give a more complete view of the
fluid and magnetic dynamics at various rotation rates of the inner and outer
spheres. These simulations reveal several dynamic regimes, determined by the
Rossby number. At positive differential rotation there is a regime of
quasigeostrophic flow, with low levels of fluctuations near the outer sphere.
Negative differential rotation shows a regime of what appear to be saturated
hydrodynamic instabilities at low negative differential rotation, followed by a
regime where filamentary structures develop at low latitudes and persist over
five to ten differential rotation periods as they drift poleward. We emphasize
that all these coherent structures emerge from turbulent flows. At least some
of them seem to be related to linear instabilities of the mean flow. The
simulated flows can produce the same measurements as those that the physical
experiment can take, with signatures akin to those found in the experiment.
This paper discusses the relation between the internal velocity structures of
the flow and their magnetic signatures at the surface.",1610.03964v4
2017-03-27,Estimation of gradients in quantum metrology,"We develop a general theory to estimate magnetic field gradients in quantum
metrology. We consider a system of $N$ particles distributed on a line whose
internal degrees of freedom interact with a magnetic field. Usually gradient
estimation is based on precise measurements of the magnetic field at two
different locations, performed with two independent groups of particles. This
approach, however, is sensitive to fluctuations of the off-set field
determining the level-splitting of the particles and results in collective
dephasing. In this work we use the framework of quantum metrology to assess the
maximal accuracy for gradient estimation. For arbitrary positioning of
particles, we identify optimal entangled and separable states allowing the
estimation of gradients with the maximal accuracy, quantified by the quantum
Fisher information. We also analyze the performance of states from the
decoherence-free subspace (DFS), which are insensitive to the fluctuations of
the magnetic offset field. We find that these states allow to measure a
gradient directly, without the necessity of estimating the magnetic offset
field. Moreover, we show that DFS states attain a precision for gradient
estimation comparable to the optimal entangled states. Finally, for the above
classes of states we find simple and feasible measurements saturating the
quantum Cram\'er-Rao bound.",1703.09123v2
2017-07-21,"Direct Evidence for the Source of Reported Magnetic Behavior in ""CoTe""","In order to unambiguously identify the source of magnetism reported in recent
studies of the Co-Te system, two sets of high-quality, epitaxial CoTe$_x$ films
(thickness $\simeq$ 300 nm) were prepared by pulse laser deposition (PLD).
X-ray diffraction (XRD) shows that all of the films are epitaxial along the
[001] direction and have the hexagonal NiAs structure. There is no indication
of any second phase metallic Co peaks (either $fcc$ or $hcp$) in the XRD
patterns. The two sets of CoTe$_x$ films were grown on various substrates with
PLD targets having Co:Te in the atomic ratio of 50:50 and 35:65. From the
measured lattice parameters $c = 5.396 \AA$ for the former and $c = 5.402\AA$
for the latter, the compositions CoTe$_{1.71}$ (63.1% Te) and CoTe$_{1.76}$
(63.8% Te), respectively, are assigned to the principal phase. Although XRD
shows no trace of metallic Co second phase, the magnetic measurements do show a
ferromagnetic contribution for both sets of films with the saturation
magnetization values for the CoTe$_{1.71}$ films being approximately four times
the values for the CoTe$_{1.76}$ films. $^{59}$Co spin-echo nuclear magnetic
resonance (NMR) clearly shows the existence of metallic Co inclusions in the
films. The source of weak ferromagnetism reported in several recent studies is
due to the presence of metallic Co, since the stoichiometric composition ""CoTe""
does not exist.",1707.06963v2
2017-12-21,Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films,"Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
magnetic damping are relevant for magnon-based spintronics and low-power
wave-like computing. The excitation frequency of spin waves in YIG is rather
low in weak external magnetic fields because of its small saturation
magnetization, which limits the potential of YIG films for high-frequency
applications. Here, we demonstrate how exchange-coupling to a CoFeB film
enables efficient excitation of high-frequency perpendicular standing spin
waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
behavior in broadband spin-wave spectra. A dynamic exchange torque at the
YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
originates from exchange coupling between two dissimilar magnetization
precessions in the YIG and CoFeB layers. As a consequence, spin waves are
emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
matches the perpendicular confinement condition. PSSWs are not excited when the
exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
Micromagnetic simulations confirm the exchange-torque mechanism.",1712.08204v1
2018-01-16,Optical control of carrier wavefunction in magnetic quantum dots,"Spatially indirect Type-II band alignment in magnetically-doped quantum dot
(QD) structures provides unexplored opportunities to control the magnetic
interaction between carrier wavefunction in the QD and magnetic impurities.
Unlike the extensively studied, spatially direct, QDs with Type-I band
alignment where both electrons and holes are confined in the QD, in ZnTe QDs
embedded in a (Zn,Mn)Se matrix only the holes are confined in the QDs.
Photoexcitation with photon energy 3.06 eV (2.54 eV) generates electron-hole
pairs predominantly in the (Zn,Mn)Se matrix (ZnTe QDs). The photoluminescence
(PL) at 7 K in the presence of an external magnetic field exhibits an up to
three-fold increase in the saturation red shift with the 2.54 eV excitation
compared to the shift observed with 3.06 eV excitation. This unexpected result
is attributed to multiple hole occupancy of the QD and the resulting increased
penetration of the hole wavefunction tail further into the (Zn,Mn)Se matrix.
The proposed model is supported by microscopic calculations which accurately
include the role of hole-hole Coulomb interactions as well as the hole-Mn spin
exchange interactions.",1801.05090v1
2018-01-26,Fully kinetic large scale simulations of the collisionless Magnetorotational instability,"We present two-dimensional particle-in-cell (PIC) simulations of the fully
kinetic collisionless magnetorotational instability (MRI) in weakly magnetized
(high $\beta$) pair plasma. The central result of this numerical analysis is
the emergence of a self-induced turbulent regime in the saturation state of the
collisionless MRI, which can only be captured for large enough simulation
domains. One of the underlying mechanisms for the development of this turbulent
state is the drift-kink instability (DKI) of the current sheets resulting from
the nonlinear evolution of the channel modes. The onset of the DKI can only be
observed for simulation domain sizes exceeding several linear MRI wavelengths.
The DKI, together with ensuing magnetic reconnection, activate the turbulent
motion of the plasma in the late stage of the nonlinear evolution of the MRI.
At steady state, the magnetic energy has an MHD-like spectrum with a slope of
$k^{-5/3}$ for $k\rho<1$ and $k^{-3}$ for sub-Larmor scale ($k\rho>1$). We also
examine the role of the collisionless MRI and associated magnetic reconnection
in the development of pressure anisotropy. We study the stability of the system
due to this pressure anisotropy, observing the development of mirror
instability during the early-stage of the MRI. We further discuss the
importance of magnetic reconnection for particle acceleration during the
turbulence regime. In particular, consistent with reconnection studies, we show
that at late times the kinetic energy presents a characteristic slope of
$\epsilon^{-2}$ in the high-energy region.",1801.08657v2
2018-02-22,Correlation of tunnel magnetoresistance with the magnetic properties in perpendicular CoFeB-based junctions with exchange bias,"We investigate the dependence of magnetic properties on the post-annealing
temperature/time, the thickness of soft ferromagnetic electrode and Ta dusting
layer in the pinned electrode as well as their correlation with the tunnel
magnetoresistance ratio, in a series of perpendicular magnetic tunnel junctions
of materials sequence
Ta/Pd/IrMn/CoFe/Ta$(\textit{x})$/CoFeB/MgO$(\textit{y})$/CoFeB$(\textit{z})$/Ta/Pd.
We obtain a large perpendicular exchange bias of 79.6$\,$kA/m for $x=0.3\,$nm.
For stacks with $z=1.05\,$nm, the magnetic properties of the soft electrode
resemble the characteristics of superparamagnetism. For stacks with
$x=0.4\,$nm, $y=2\,$nm, and $z=1.20\,$nm, the exchange bias presents a
significant decrease at post annealing temperature
$T_\textrm{ann}=330\,^{\circ}$C for 60 min, while the interlayer exchange
coupling and the saturation magnetization per unit area sharply decay at
$T_\textrm{ann}=340\,^{\circ}$C for 60 min. Simultaneously, the tunnel
magnetoresistance ratio shows a peak of $65.5\%$ after being annealed at
$T_\textrm{ann}=300\,^{\circ}$C for 60 min, with a significant reduction down
to $10\%$ for higher annealing temperatures
($T_\textrm{ann}\geq330\,^{\circ}$C) and down to $14\%$ for longer annealing
times ($T_\textrm{ann}=300\,^{\circ}$C for 90 min). We attribute the large
decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the
pinned electrode.",1802.08002v2
2018-05-07,Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in Transverse Magnetic Field,"We report on magnetization, sound velocity, and magnetocaloric-effect
measurements of the Ising-like spin-1/2 antiferromagnetic chain system
BaCo$_2$V$_2$O$_8$ as a function of temperature down to 1.3 K and applied
transverse magnetic field up to 60 T. While across the N\'{e}el temperature of
$T_N\sim5$ K anomalies in magnetization and sound velocity confirm the
antiferromagnetic ordering transition, at the lowest temperature the
field-dependent measurements reveal a sharp softening of sound velocity $v(B)$
and a clear minimum of temperature $T(B)$ at $B^{c,3D}_\perp=21.4$ T,
indicating the suppression of the antiferromagnetic order. At higher fields,
the $T(B)$ curve shows a broad minimum at $B^c_\perp = 40$ T, accompanied by a
broad minimum in the sound velocity and a saturation-like magnetization. These
features signal a quantum phase transition which is further characterized by
the divergent behavior of the Gr\""{u}neisen parameter $\Gamma_B \propto
(B-B^{c}_\perp)^{-1}$. By contrast, around the critical field, the
Gr\""{u}neisen parameter converges as temperature decreases, pointing to a
quantum critical point of the one-dimensional transverse-field Ising model.",1805.02392v1
2018-08-07,Magnetoresistance in the in-plane magnetic field induced semi-metallic phase of inverted HgTe quantum wells,"In this study we have measured the magnetoresistance response of inverted
HgTe quantum wells in the presence of a large parallel magnetic field up to 33
T is applied. We show that in quantum wells with inverted band structure a
monotonically decreasing magnetoresistance is observed when a magnetic field up
to order 10 T is applied parallel to the quantum well plane. This feature is
accompanied by a vanishing of non-locality and is consistent with a predicted
modification of the energy spectrum that becomes gapless at a critical in-plane
field $B_{c}$. Magnetic fields in excess of $B_c$ allow us to investigate the
evolution of the magnetoresistance in this field-induced semi-metallic region
beyond the known regime. After an initial saturation phase in the presumably
gapless phase, we observe a strong upturn of the longitudinal resistance. A
small residual Hall signal picked up in non-local measurements suggests that
this feature is likely a bulk phenomenon and caused by the semi-metallicity of
the sample. Theoretical calculations indeed support that the origin of these
features is classical and a power law upturn of the resistance can be expected
due to the specifics of two-carrier transport in thin (semi-)metallic samples
subjected to large magnetic fields.",1808.02268v1
2019-04-25,Correlations far from equilibrium in charged strongly coupled fluids subjected to a strong magnetic field,"Within a holographic model, we calculate the time evolution of 2-point and
1-point correlation functions (of selected operators) within a charged strongly
coupled system of many particles. That system is thermalizing from an
anisotropic initial charged state far from equilibrium towards equilibrium
while subjected to a constant external magnetic field. One main result is that
thermalization times for 2-point functions are significantly (approximately
three times) larger than those of 1-point functions. Magnetic field and charge
amplify this difference, generally increasing thermalization times. However,
there is also a competition of scales between charge density, magnetic field,
and initial anisotropy, which leads to an array of qualitative changes on the
2- and 1-point functions. There appears to be a strong effect of the medium on
2-point functions at early times, but approximately none at later times. At
strong magnetic fields, an apparently universal thermalization time emerges, at
which all 2-point functions appear to thermalize regardless of any other scale
in the system. Hence, this time scale is referred to as saturation time scale.
As extremality is approached in the purely charged case, 2- and 1-point
functions appear to equilibrate at infinitely late time. We also compute
2-point functions of charged operators. Our results can be taken to model
thermalization in heavy ion collisions, or thermalization in selected condensed
matter systems.",1904.11507v2
2019-05-10,Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy,"The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for
spin-gapless semiconductors (SGSs). However, to date, there have been no
experimental attempts at fabricating a junction device. This paper reports a
fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with
CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction
measurements show that the (001) CoFeCrAl electrode films with atomically flat
surfaces have a $B2$-ordered phase. The saturation magnetization is 380
emu/cm$^3$, almost the same as the value given by the Slater--Pauling--like
rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87%
and 165%, respectively. Cross-sectional electron diffraction analysis shows
that the MTJs have MgO interfaces with fewer dislocations. The temperature- and
bias-voltage-dependence of the transport measurements indicates magnon-induced
inelastic electron tunneling overlapping with the coherent electron tunneling.
X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic
arrangement of the Co and Fe magnetic moments of $B2$-ordered CoFeCrAl, in
contrast to the ferrimagnetic arrangement predicted for the $Y$-ordered state
possessing SGS characteristics. Ab-initio calculations taking account of the
Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect
of the Cr-Fe swap disorder on the ability for electronic states to allow
coherent electron tunneling is discussed.",1905.04070v1
2019-06-27,Complex magnetic phase diagram of metamagnetic MnPtSi,"The magnetic, thermal and transport properties as well as electronic band
structure of MnPtSi are reported. MnPtSi is a metal that undergoes a
ferromagnetic transition at $T_{\mathrm{C}}=340$(1) K and a spin-reorientation
transition at $T_{\mathrm{N}}=326$(1) K to an antiferromagnetic phase.
First-principles electronic structure calculations indicate a not-fully
polarized spin state of Mn in a $d^5$ electron configuration with $J=S=3$/2, in
agreement with the saturation magnetization of 3~$\mu_{\mathrm{B}}$ in the
ordered state and the observed paramagnetic effective moment. A sizeable
anomalous Hall effect in the antiferromagnetic phase alongside the
computational study suggests that the antiferromagnetic structure is
non-collinear. Based on thermodynamic and resistivity data we construct a
magnetic phase diagram. Magnetization curves $M$($H$) at low temperatures
reveal a metamagnetic transition of spin-flop type. The spin-flopped phase
terminates at a critical point with $T_{\mathrm{cr}}\approx 300$ K and
$H_{\mathrm{cr}}\approx 10$ kOe, near which a peak of the magnetocaloric
entropy change is observed. Using Arrott plot analysis and magnetoresistivity
data we argue that the metamagnetic transition is of a first-order type,
whereas the strong field dependence of $T_{\mathrm{N}}$ and the linear
relationship of the $T_{\mathrm{N}}$ with $M^2$ hint at its magnetoelastic
nature.",1906.11864v1
2019-09-17,Strong quantum fluctuations due to competition between magnetic phases in a pyrochlore iridate,"We report neutron diffraction measurements of the magnetic structures in two
pyrochlore iridates, Yb2Ir2O7 and Lu2Ir2O7. Both samples exhibit the
all-in-all-out magnetic structure on the Ir4+ sites below TN~ 150,K, with a low
temperature moment of around 0.45 muB/Ir. Below 2\,K, the Yb moments in
Yb2Ir2O7 begin to order ferromagnetically. However, even at 40 mK the ordered
moment is only 0.57(3)muB/Yb, well below the saturated moment of the ground
state doublet of Yb3+ (1.9 muB/Yb), deduced from magnetization measurements and
from a refined model of the crystal field environment, and also significantly
smaller than the ordered moment of Yb in Yb2Ti2O7 (0.9 muB/Yb). A mean-field
analysis shows that the reduced moment on Yb is a consequence of enhanced phase
competition caused by coupling to the all-in-all-out magnetic order on the Ir
sublattice.",1909.07819v3
2019-10-25,Interplay of Bound Magnetic Polaron and p-d exchange interaction in Co-doped 3C-SiC,"Bound Magnetic Polarons (BMP) have been proposed to play an important role in
doped wide band gap semiconductors. We report the experimental evidence
supporting polaronic magnetism and the role of defects on it. Temperature
variation of electron paramagnetic resonance study reveals that the valence
state of cobalt is 2+ and its nearest environment in the system is distorted
tetrahedral in nature. Room temperature ferromagnetism have been found in all
the doped [Co (1, 3, 5) % doped 3C-SiC] samples. The Curie temperature, TC of
the samples have been found to be above 800 K. The isothermal magnetization
plots, to determine the strength of domain wall pinning were analyzed using the
Jiles-Atherton Model. The temperature variation of the anisotropic constant was
determined using Law of Approach to saturation (LAS), which decreases with
increase in temperature. Quantitative analysis of magnetic interaction has been
carried out and the result is explained by using BMP Model, which probably
arises out of the exchange interaction of Co2+ ions with related (Si, C)
defects.",1910.11899v3
2019-10-29,Adiabatic Quantum Estimation: A Numerical Study of the Heisenberg XX Model with Antisymmetric Exchange,"In this paper, we address the adiabatic technique for quantum estimation of
the azimuthal orientation of a magnetic field. Exactly solving a model
consisting of a two-qubit system, where one of which is driven by a static
magnetic field while the other is coupled with the magnetic field rotating
adiabatically, we obtain the analytical expression of the quantum Fisher
information (QFI). We investigate how the two-qubit system can be used to probe
the azimuthal direction of the field and analyze the roles of the intensities
of the magnetic fields, Dzyaloshinskii-Moriya interaction, spin-spin coupling
coefficient, and the polar orientation of the rotating field on the precision
of the estimation. In particular, it is illustrated that the QFI trapping or
saturation may occur if the qubit is subjected to a strong rotating field.
Moreover, we discuss how the azimuthal direction of the rotating field can be
estimated using only the qubit not affected by that field and investigate the
conditions under which this strategy is more efficient than use of the qubit
locally interacting with the adiabatically rotating field. Interestingly, in
the one-qubit scenario, it was found that when the rotating field is weak, the
best estimation is achieved by subjecting the probe to a static magnetic field.",1910.13478v4
2019-11-25,Magnetising the circumgalactic medium of disk galaxies,"The circumgalactic medium (CGM) is one of the frontiers of galaxy formation
and intimately connected to the galaxy via accretion of gas on to the galaxy
and gaseous outflows from the galaxy. Here we analyse the magnetic field in the
CGM of the Milky Way-like galaxies simulated as part of the \textsc{Auriga}
project that constitutes a set of high resolution cosmological
magnetohydrodynamical zoom simulations. We show that before $z=1$ the CGM
becomes magnetised via galactic outflows that transport magnetised gas from the
disk into the halo. At this time the magnetisation of the CGM closely follows
its metal enrichment. We then show that at low redshift an in-situ turbulent
dynamo that operates on a timescale of Gigayears further amplifies the magnetic
field in the CGM and saturates before $z=0$. The magnetic field strength
reaches a typical value of $0.1\,\mu G$ at the virial radius at $z=0$ and
becomes mostly uniform within the virial radius. Its Faraday rotation signal is
in excellent agreement with recent observations. For most of its evolution the
magnetic field in the CGM is an unordered small scale field. Only strong
coherent outflows at low redshift are able to order the magnetic field in parts
of the CGM that are directly displaced by these outflows.",1911.11163v3
2019-12-17,Antiferromagnetic CuMnAs: Ab initio description of finite temperature magnetism and resistivity,"Noncollinear magnetic moments in antiferromagnets (AFM) lead to a complex
behavior of electrical transport, even to a decreasing resistivity due to an
increasing temperature. Proper treatment of such phenomena is required for
understanding AFM systems at finite temperatures; however first-principles
description of these effects is complicated. With ab initio techniques, we
investigate three models of spin fluctuations (magnons) influencing the
transport in AFM CuMnAs; the models are numerically feasible and easily
implementable to other studies. We numerically justified a fully relativistic
collinear disordered local moment approach and we present its uncompensated
generalization. A saturation or a decrease of resistivity caused by magnons,
phonons, and their combination (above approx. 400 K) was observed and explained
by changes in electronic structure. Within the coherent potential
approximation, our finite-temperature approaches may be applied also to systems
with impurities, which are found to have a large impact not only on residual
resistivity, but also on canting of magnetic moments from the AFM to the
ferromagnetic (FM) state.",1912.08025v4
2020-01-23,Global simulations of self-gravitating magnetized protoplanetary disks,"In the early stages of a protoplanetary disk, when its mass is a significant
fraction of its star's, turbulence generated by gravitational instability (GI)
should feature significantly in the disk's evolution. At the same time, the
disk may be sufficiently ionised for magnetic fields to play some role in the
dynamics. Though usually neglected, the impact of magnetism on the GI may be
critical, with consequences for several processes: the efficiency of accretion,
spiral structure formation, fragmentation, and the dynamics of solids. In this
paper, we report on global three-dimensional magnetohydrodynamical simulations
of a self-gravitating protoplanetary disk using the meshless finite mass (MFM)
Lagrangian technique. We confirm that GI spiral waves trigger a dynamo that
amplifies an initial magnetic field to nearly thermal amplitudes (plasma beta <
10), an order of magnitude greater than that generated by the
magneto-rotational instability alone. We also determine the dynamo's nonlinear
back reaction on the gravitoturbulent flow: the saturated state is
substantially hotter, with an associated larger Toomre parameter and weaker,
more 'flocculent' spirals. But perhaps of greater import is the dynamo's
boosting of accretion via a significant Maxwell stress; mass accretion is
enhanced by factors of several relative to either pure GI or pure MRI. Our
simulations use ideal MHD, an admittedly poor approximation in protoplanetary
disks, and thus future studies should explore the full gamut of non-ideal MHD.
In preparation for that, we exhibit a small number of Ohmic runs that reveal
that the dynamo, if anything, is stronger in a non-ideal environment. This work
confirms that magnetic fields are a potentially critical ingredient in
gravitoturbulent young disks, possibly controlling their evolution, especially
via their enhancement of (potentially episodic) accretion.",2001.08693v1
2020-01-31,Measuring stellar magnetic helicity density,"Helicity is a fundamental property of a magnetic field but to date it has
only been possible to observe its evolution in one star - the Sun. In this
paper we provide a simple technique for mapping the large-scale helicity
density across the surface of any star using only observable quantities: the
poloidal and toroidal magnetic field components (which can be determined from
Zeeman-Doppler imaging) and the stellar radius. We use a sample of 51 stars
across a mass range of 0.1-1.34 M$_\odot$ to show how the helicity density
relates to stellar mass, Rossby number, magnetic energy and age. We find that
the large-scale helicity density increases with decreasing Rossby number $R_o$,
peaking at $R_o \simeq 0.1$, with a saturation or decrease below that. For both
fully- and partially-convective stars we find that the mean absolute helicity
density scales with the mean squared toroidal magnetic flux density according
to the power law: $|\langle{h\,}\rangle|$ $\propto$
$\langle{\rm{B_{tor}}^2_{}\,\rangle}^{0.86\,\pm\,0.04}$. The scatter in this
relation is consistent with the variation across a solar cycle, which we
compute using simulations and observations across solar cycles 23 and 24
respectively. We find a significant decrease in helicity density with age.",2001.11749v1
2020-05-23,"Structural, Electronic, and Magnetic Properties of HiPIMS Grown Co-N Thin Films","We studied the growth behavior, structural, electronic, and magnetic
properties of cobalt nitride (Co-N) thin films deposited using direct current
(dc) and high power impulse magnetron sputtering (HiPIMS) processes. The N$_2$
partial gas flow (\pn) was varied in close intervals to achieve the optimum
conditions for the growth of tetra cobalt nitride (\tcn) phase. We found that
Co-N films grown using HiPIMS process adopt (111) orientation as compared to
the growth taking place along the (100) direction in the dcMS process. It was
observed that HiPIMS grown Co-N~films were superior in terms of crystallite
size and uniform surface morphology. The local structure of films was
investigated using x-ray absorption fine structure (XAFS) measurements. We
found that the high energy of adatoms in the HiPIMS technique assisted in the
greater stabilization of fcc-Co and novel \tcn~phase relative to the dcMS
process. Magnetic properties of Co-N thin films were studied using
magneto-optical Kerr effect, vibrating sample magnetometry and polarized
neutron reflectivity. It was found that though the saturation magnetization
remains almost similar in films grown by dcMS or HiPIMS processes, they differ
in terms of their magnetic anisotropy. Such variation can be understood in
terms of differences in the growth mechanisms in dcMS and HiPIMS processes
affecting the local structure of resulting \tcn~phase.",2005.11584v1
2020-05-28,Spin-Pumping-Induced Non-Linear Electric Current on the Surface of a Ferromagnetic Topological Insulator,"We investigate the spin-pumping-induced electric current on the surface of a
three-dimensional topological insulator hybridized with a ferromagnet, namely,
ferromagnetic topological insulator. In order to do this, we establish the
microscopic formalism and construct the perturbation theory using a Keldysh
Green's function approach. We analyze how this electric current is generated by
an exchange interaction and an external ac magnetic field, which is the driving
force of ferromagnetic resonance as well as the spin pumping. The mechanism is
as follows. First, the ferromagnetic resonance is driven and a zero-momentum
magnon emerges. It is the fluctuation from the saturation magnetization
pointing parallel to the precession axis of the ferromagnetic resonance. After
then, the spin pumping is generated with the zero-momentum magnon being the
carrier of spin. The zero-momentum magnon and the topological insulator surface
state couples through the exchange interaction and the spin carried by the
magnon is transferred to it. Owing to the spin-momentum locking, the
transferred spin is converted into the momentum of topological insulator
surface state leading to the generation of electric current flowing
perpendicular to the precession axis of the ferromagnetic resonance. It is
quadratic in the amplitude of external ac magnetic field whereas it is linear
to the strength of the exchange interaction. The associated electric voltage is
described by the spectrum of zero-momentum magnon. The non-linearity of
spin-pumping-induced electric current in the ac magnetic field as well as the
linearity in the exchange-interaction strength reflects that the surface of
ferromagnetic topological insulator has a high-performing functionality of
generating the electric charge current by magnetic controlling.",2005.13850v1
2020-05-28,Spectral signatures of the surface anomalous Hall effect in magnetic axion insulators,"The topological surface states of magnetic topological systems, such as Weyl
semimetals and axion insulators, are associated with unconventional transport
properties such as nonzero or half-quantized surface anomalous Hall effect.
Here we study the surface anomalous Hall effect and its spectral signatures in
different magnetic topological phases using both model Hamiltonian and
first-principles calculations. We demonstrate that by tailoring the
magnetization and interlayer electron hopping, a rich three-dimensional
topological phase diagram can be established, including three types of
topologically distinct insulating phases bridged by Weyl semimetals, and can be
directly mapped to realistic materials such as MnBi2Te4/(Bi2Te3)n systems.
Among them, we find that the surface anomalous Hall conductivity in the
axion-insulator phase is a well-localized quantity either saturated at or
oscillating around e2/2h, depending on the magnetic homogeneity. We also
discuss the resultant chiral hinge modes embedded inside the side surface bands
as the potential experimental signatures for transport measurements. Our study
is a significant step forward towards the direct realization of long-sought
axion insulators in realistic material systems.",2005.13943v4
2020-06-26,Super-Necking Crystal Growth and Structural and Magnetic Properties of SrTb$_2$O$_4$ Single Crystals,"We report on single-crystal growths of the SrTb$_2$O$_4$ compound by a
super-necking technique with a laser-floating-zone furnace and study the
stoichiometry, growth mode, and structural and magnetic properties by scanning
electronic microscopy, neutron Laue, X-ray powder diffraction, and the physical
property measurement system. We optimized the growth parameters, mainly the
growth speed, atmosphere, and the addition of a Tb$_4$O$_7$ raw material.
Neutron Laue diffraction displays the characteristic feature of a single
crystal. Our study reveals an atomic ratio of Sr:Tb $ = 0.97(2){:}2.00(1)$ and
a possible layer by layer crystal growth mode. Our X-ray powder diffraction
study determines the crystal structure, lattice constants and atomic positions.
The paramagnetic (PM) Curie--Weiss (CW) temperature $\theta_{\texttt{CW}} =$
5.00(4) K, and the effective PM moment $M^{\texttt{eff}}_{\texttt{mea}} =$
10.97(1) $\mu_\texttt{B}$ per Tb$^{3+}$ ion. The data of magnetization versus
temperature can be divided into three regimes, showing a coexistence of
antiferromagnetic and ferromagnetic interactions. This probably leads to the
magnetic frustration in the SrTb$_2$O$_4$ compound. The magnetization at 2 K
and 14 T originates from both the Tb1 and Tb2 sites and is strongly frustrated
with an expected saturation field at $\sim$41.5 T, displaying an intricate
phase diagram with three ranges.",2006.14754v2
2020-10-13,Dipolar-stabilized first and second-order antiskyrmions in ferrimagnetic multilayers,"Skyrmions and antiskyrmions are topologically protected spin structures with
opposite topological charge. Particularly in coexisting phases, these two types
of magnetic quasi-particles may show fascinating physics and potential for
spintronic devices. While skyrmions are observed in a wide range of materials,
until now antiskyrmions were exclusive to materials with D2d symmetry. In this
work, we show first and second-order antiskyrmions stabilized by magnetic
dipole-dipole interaction in Fe/Gd-based multilayers. We modify the magnetic
properties of the multilayers by Ir insertion layers. Using Lorentz
transmission electron microscopy imaging, we observe coexisting antiskyrmions,
Bloch skyrmions, and type-2 bubbles and determine the range of material
properties and magnetic fields where the different spin objects form and
dissipate. We perform micromagnetic simulations to obtain more insight into the
studied system and conclude that the reduction of saturation magnetization and
uniaxial anisotropy leads to the existence of this zoo of different spin
objects and that they are primarily stabilized by dipolar interaction.",2010.06555v3
2020-12-04,Anomalous Hall and Nernst effects in ferrimagnetic Mn$_4$N films: possible interpretation and prospect for enhancement,"Ferrimagnetic Mn$_4$N is a promising material for heat flux sensors based on
the anomalous Nernst effect (ANE) because of its sizable uniaxial magnetic
anisotropy ($K_{\rm u}$) and low saturation magnetization ($M_{\rm s}$). We
experimentally and theoretically investigated the ANE and anomalous Hall effect
in sputter-deposited Mn$_4$N films. It was revealed that the observed negative
anomalous Hall conductivity ($\sigma_{xy}$) could be explained by two different
coexisting magnetic structures, that is, a dominant magnetic structure with
high $K_{\rm u}$ contaminated by another structure with negligible $K_{\rm u}$
owing to an imperfect degree of order of nitrogen. The observed transverse
thermoelectric power ($S_{\rm ANE}$) of $+0.5\, \mu{\rm V/K}$ at $300\, {\rm
K}$ gave a transverse thermoelectric coefficient ($\alpha_{xy}$) of $+0.34\,
{\rm A/(m \cdot K)}$, which was smaller than the value predicted from
first-principles calculation. The interpretation for $\alpha_{xy}$ based on the
first-principles calculations led us to conclude that the realization of single
magnetic structure with high $K_{\rm u}$ and optimal adjustment of the Fermi
level are promising approaches to enhance $S_{\rm ANE}$ in Mn$_4$N through the
sign reversal of $\sigma_{xy}$ and the enlargement of $\alpha_{xy}$ up to a
theoretical value of $1.77\, {\rm A/(m \cdot K)}$.",2012.02510v2
2021-04-18,Impact of particle size on the magnetic properties of highly crystalline Yb3+ substituted Ni-Zn nanoferrites,"Yb-substituted Ni-Zn ferrites have been synthesized using sol-gel auto
combustion method. The structural characterization of the compositions has been
performed by X-ray diffraction analysis, field emission scanning electron
microscopy (FESEM), quantum design physical properties measurement system
(PPMS). That ensured the formation of single phase cubic spinel structure.
Crystallite and average grain size are calculated and found to decrease with
increasing Yb3+ contents. Saturation magnetization and Bohr magnetic moment
decrease while the coercivity increases with the increase in Yb3+ contents
successfully explained by the Neels collinear two sub-lattice model and
critical size effect, respectively. Critical particle size has been estimated
at 6.4 nm, the transition point between single domain regime (below the
critical size) and multi-domain regime (beyond the critical size). Curie
temperature reduces due to the weakening of A-O-B super exchange interaction
and redistribution of cations, confirmed by the M-T graph. The compositions
retain ferromagnetic ordered structured below Curie temperature and above Curie
temperature, it becomes paramagnetic, making them plausible candidates for high
temperature magnetic device applications. The relative quality factor peak is
obtained at a very high frequency, indicating the compositions could also be
applicable for high frequency magnetic device applications.",2104.08694v1
2021-06-01,Multiple field-induced phases in the frustrated triangular magnet Cs$_3$Fe$_2$Br$_9$,"The recently discovered material Cs$_3$Fe$_2$Br$_9$ contains Fe$_2$Br$_9$
bi-octahedra forming triangular layers with hexagonal stacking along the $c$
axis. In contrast to isostructural Cr-based compounds, the zero-field ground
state is not a nonmagnetic $S=0$ singlet-dimer state. Instead, the Fe$_2$Br$_9$
bi-octahedra host semiclassical $S=5/2$ Fe$^{3+}$ spins with a pronounced
easy-axis anisotropy along $c$ and interestingly, the intra-dimer spins are
ordered ferromagnetically. The high degree of magnetic frustration due to
(various) competing intra- and inter-dimer couplings leads to a surprisingly
rich magnetic phase diagram. Already the zero-field ground state is reached via
an intermediate phase, and the high-field magnetization and thermal expansion
data for $H\parallel c$ identify ten different ordered phases. Among them are
phases with constant magnetization of 1/3, respectively 1/2 of the saturation
value, and several transitions are strongly hysteretic with pronounced length
changes reflecting strong magnetoelastic coupling.",2106.00440v3
2021-09-08,Picosecond creation of switchable optomagnets with giant photoinduced Kerr rotations in polar antiferromagnetic (Fe$_{1-x}$Zn$_{x}$)$_{2}$Mo$_{3}$O$_{8}$,"On-demand spin orientation with long polarized lifetime and easily detectable
signal is an ultimate goal for spintronics. However, there still exists a
trade-off between controllability and stability of spin polarization, awaiting
a significant breakthrough. Here, we demonstrate switchable optomagnet effects
in (Fe$_{1-x}$Zn$_{x}$)$_{2}$Mo$_{3}$O$_{8}$, from which we can obtain tunable
magnetization, spanning from -40$\%$ to 40$\%$ of a saturated magnetization
that is created from zero magnetization in the antiferromagnetic state without
magnetic fields. It is accomplishable via utilizing circularly-polarized laser
pulses to excite spin-flip transitions in polar antiferromagnets that have no
spin canting, traditionally hard to control without very strong magnetic
fields. The spin controllability in (Fe$_{1-x}$Zn$_{x}$)$_{2}$Mo$_{3}$O$_{8}$
originates from its polar structure that breaks the crystal inversion symmetry,
allowing distinct on-site $d$-$d$ transitions for selective spin flip. By
chemical doping, we exploit the phase competition between antiferromagnetic and
ferrimagnetic states to enhance and stabilize the optomagnet effects, which
result in long-lived photoinduced Kerr rotations. The present study, creating
switchable giant optomagnet effects in polar antiferromagnets, sketches a new
blueprint for the function of antiferromagnetic spintronics.",2109.03498v1
2021-12-21,High-speed imaging of magnetized plasmas: when electron temperature matters,"High speed camera imaging is a powerful tool to probe the spatiotemporal
features of unsteady processes in plasmas, usually assuming light fluctuations
to be a proxy for the plasma density fluctuations. In this article, we
systematically compare high speed camera imaging with simultaneous measurements
of the plasma parameters -- plasma density, electron temperature, floating
potential -- in a modestly magnetized Argon plasma column at low pressure (1
mTorr, magnetic fields ranging from 160 to 640~G). The light emission was
filtered around $488\pm5$~nm, $750\pm5$~nm, $810\pm5$~nm. We show that the
light intensity cannot be interpreted as a proxy for the plasma density and
that the electron temperature cannot be ignored when interpreting high speed
imaging, both for the time-averaged profiles and for the fluctuations. The
features of plasma parameter fluctuations are investigated, with a focus on ion
acoustic waves (at frequency around 70 kHz) at low magnetic field and
low-frequency azimuthal waves (around a few kHz) at larger magnetic fields. An
excellent match is found between the high speed images fluctuations and an
Arrhenius law functional form which incorporates fluctuations of the plasma
density and of the electron temperature. These results explain the
discrepancies between ion saturation current and narrow-band imaging
measurements previously reported in the literature.",2112.11372v1
2022-01-10,Magnetic field amplification by a plasma cavitation instability in relativistic shock precursors,"Plasma streaming instabilities play an important role in magnetic field
amplification and particle acceleration in relativistic shocks and their
environments. However, in the far shock precursor region where accelerated
particles constitute a highly relativistic and dilute beam, streaming
instabilities typically become inefficient and operate at very small scales
when compared to the gyroradii of the beam particles. We report on a plasma
cavitation instability that is driven by dilute relativistic beams and can
increase both the magnetic field strength and coherence scale by orders of
magnitude to reach near-equipartition values with the beam energy density. This
instability grows after the development of the Weibel instability and is
associated with the asymmetric response of background leptons and ions to the
beam current. The resulting net inductive electric field drives a strong energy
asymmetry between positively and negatively charged beam species. Large-scale
particle-in-cell simulations are used to verify analytical predictions for the
growth and saturation level of the instability and indicate that it is robust
over a wide range of conditions, including those associated with pair-loaded
plasmas. These results can have important implications for the magnetization
and structure of shocks in gamma-ray bursts, and more generally for magnetic
field amplification and asymmetric scattering of relativistic charged particles
in plasma astrophysical environments.",2201.03547v1
2022-02-03,Asymptotic behaviour of rotating convection-driven dynamos in the plane layer geometry,"Dynamos driven by rotating convection in the plane layer geometry are
investigated numerically for a range of Ekman number ($E$), magnetic Prandtl
number ($Pm$) and Rayleigh number ($Ra$). The primary purpose of the
investigation is to compare results of the simulations with previously
developed asymptotic theory that is applicable in the limit of rapid rotation.
We find that all of the simulations are in the quasi-geostrophic regime in
which the Coriolis and pressure gradient forces are approximately balanced at
leading order, whereas all other forces, including the Lorentz force, act as
perturbations. Agreement between simulation output and asymptotic scalings for
the energetics, flow speeds, magnetic field amplitude and length scales is
found. The transition from large scale dynamos to small scale dynamos is well
described by the magnetic Reynolds number based on the small convective length
scale, $\widetilde{Rm}$, with large scale dynamos preferred when
$\widetilde{Rm} \lesssim O(1)$. The magnitude of the large scale magnetic field
is observed to saturate and become approximately constant with increasing
Rayleigh number. Energy spectra show that all length scales present in the flow
field and the small-scale magnetic field are consistent with a scaling of
$E^{1/3}$, even in the turbulent regime. For a fixed value of $E$, we find that
the viscous dissipation length scale is approximately constant over a broad
range of $Ra$; the ohmic dissipation length scale is approximately constant
within the large scale dynamo regime, but transitions to a
$\widetilde{Rm}^{-1/2}$ scaling in the small scale dynamo regime.",2202.01382v2
2022-02-05,Cuprates phase diagram deduced from magnetic susceptibility: what is the `true' pseudogap line?,"Two contradictory phase diagrams have dominated the literature of high-$T_c$
cuprate superconductors. Does the pseudogap line cross the superconducting
$T_c$-dome or not? To answer, we have revisited the experimental magnetic
susceptibility and knight shift of four different compounds,
La$_{1-x}$Sr$_x$CuO$_4$, Bi$_2$Sr$_2$Ca$_{1-x}$Y$_x$Cu$_2$O$_8$,
Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$, and YBa$_2$Cu$_3$O$_{6+y}$, as a function of
temperature and doping. The susceptibility can be described by the same
function for all materials, having a magnetic and an electronic contributions.
The former is the 2D antiferromagnetic (AF) square lattice response, with a
characteristic temperature of magnetic correlations $T_{max}$. The latter is
the `Pauli' term, revealing the gap opening in the electronic density of states
at the pseudogap temperature $T^*$.
  From precise fits of the data, we find that $T_{max}(p)$ decreases linearly
as a function of doping ($p$) over a wide range, but saturates abruptly in the
overdoped regime. Concomitantly, $T^*(p)$ is {\it linear and tangent} to the
dome, either crossing or approaching $T_{max}(p)$ at the top of the dome,
indicating a qualitative change of behavior from underdoped to overdoped
regimes.
  Contrary to the idea that the pseudogap terminates just above optimal doping,
our analysis suggests that the gap exists throughout the phase diagram. It is
consistent with a pseudogap due to hole pairs, or `pairons', above $T_c$. We
conclude that $T_{max}$, reflecting the AF magnetic correlations, has often
been misinterpreted as the pseudogap temperature $T^*$.",2202.02589v1
2022-03-05,Dimits transition in three-dimensional ion-temperature-gradient turbulence,"We extend our previous work on the 2D Dimits transition in ion-scale
turbulence (Ivanov et al. 2020) to include variations along the magnetic field.
We consider a three-field fluid model for the perturbations of electrostatic
potential, ion temperature, and ion parallel flow in a
constant-magnetic-curvature geometry without magnetic shear. It is derived in
the cold-ion, long-wavelength asymptotic limit of the gyrokinetic theory. Just
as in the 2D model, a low-transport (Dimits) regime exists and is found to be
dominated by a quasi-static staircase-like arrangement of strong zonal flows
and zonal temperature. This zonal staircase is formed and maintained by a
negative turbulent viscosity for the zonal flows. Unlike the 2D model, the 3D
one does not suffer from an unphysical blow up beyond the Dimits threshold
where the staircase becomes nonlinearly unstable. Instead, a well-defined
finite-amplitude saturated state is established. This qualitative difference
between 2D and 3D is due to the appearance of small-scale `parasitic' modes
that exist only if we allow perturbations to vary along the magnetic field
lines. These modes extract energy from the large-scale perturbations and
provide an effective enhancement of large-scale thermal diffusion, thus aiding
the energy transfer from large injection scales to small dissipative ones. We
show that in our model, the parasitic modes always favour a
zonal-flow-dominated state. In fact, a Dimits state with a zonal staircase is
achieved regardless of the strength of the linear drive provided the system is
sufficiently extended along the magnetic field and sufficient parallel
resolution is provided.",2203.02769v2
2022-04-08,Electron Weibel instability induced magnetic fields in optical-field ionized plasmas,"Generation and amplification of magnetic fields in plasmas is a long-standing
topic that is of great interest to both plasma and space physics. The electron
Weibel instability is a well-known mechanism responsible for self-generating
magnetic fields in plasmas with temperature anisotropy and has been extensively
investigated in both theory and simulations, yet experimental verification of
this instability has been challenging. Recently, we demonstrated a new
experimental platform that enables the controlled initialization of highly
nonthermal and/or anisotropic plasma electron velocity distributions via
optical-field ionization. Using an external electron probe bunch from a linear
accelerator, the onset, saturation and decay of the self-generated magnetic
fields due to electron Weibel instability were measured for the first time to
our knowledge. In this paper, we will first present experimental results on
time-resolved measurements of the Weibel magnetic fields in non-relativistic
plasmas produced by Ti:Sapphire laser pulses (0.8 $\mu m$) and then discuss the
feasibility of extending the study to quasi-relativistic regime by using
intense $\rm CO_2$ (e.g., 9.2 $\mu m$) lasers to produce much hotter plasmas.",2204.04262v1
2022-04-20,Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques,"Spintronics is showing promising results in the search for new materials and
effects to reduce energy consumption in information technology. Among these
materials, ferrimagnets are of special interest, since they can produce large
spin currents that trigger the magnetization dynamics of adjacent layers or
even their own magnetization. Here, we present a study of the generation of
spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice
magnetization is dominant at room temperature. Magnetic properties such as the
saturation magnetization are deduced from magnetometry measurements while
damping constant is estimated from spin-torque ferromagnetic resonance
(ST-FMR). We show that the overall damping-like (DL) and field-like (FL)
effective fields as well as the associated spin Hall angles can be reliably
obtained by performing the dependence of ST-FMR by an added dc current. The sum
of the spin Hall angles for both the spin Hall effect (SHE) and the spin
anomalous Hall effect (SAHE) symmetries are: $\theta_{DL}^{SAHE} +
\theta_{DL}^{SHE}=-0.15 \pm 0.05$ and $\theta_{FL}^{SAHE} +
\theta_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find
that $\theta_{DL}^{SHE}$ is positive and dominated by the negative
$\theta_{DL}^{SAHE}$. The present study paves the way for tuning the different
symmetries in spin conversion in highly efficient ferrimagnetic systems.",2204.09776v1
2022-04-28,"Low-energy spin excitations of the frustrated ferromagnetic $J_1$-$J_2$ chain material linarite, PbCuSO$_4$(OH)$_2$, in applied magnetic fields $\mathbf{H} \parallel b$ axis","We report a study of the spin dynamics of the frustrated ferromagnetic
$J_1$-$J_2$ chain compound linarite, PbCuSO$_4$(OH)$_2$, in applied magnetic
fields up to field polarization. By means of an extreme-environment inelastic
neutron scattering experiment, we have measured the low-energy spin excitations
of linarite in fields up to 8.8 T for $\mathbf{H} \parallel b$ axis. We have
recorded the spin excitation spectra along $h$, $k$ and $l$ for the
field-induced magnetic phases IV, V and the field polarized state close to
saturation. By employing first-principles calculations, we estimate the leading
magnetic exchanges out of the $bc$ plane and model the dispersion relations
using linear spin-wave theory. In this way, we find evidence for a (very weak)
residual magnetic exchange coupling out of the $bc$ plane. Together with the
previously established dominant intrachain couplings $J_1$ and $J_2$ and the
interchain coupling $J_3$, we derive an effective set of exchange couplings for
a microscopic description of linarite. Further, we find that the peculiar
character of phase V manifests itself in the measured spin dynamics.",2204.13482v2
2022-06-03,Engineering the spin-orbit torque efficiency and magnetic properties of Tb/Co ferrimagnetic multilayers by stacking order,"We measured the spin-orbit torques (SOTs), current-induced switching, and
domain wall (DW) motion in synthetic ferrimagnets consisting of Co/Tb layers
with differing stacking order grown on a Pt underlayer. We find that the SOTs,
magnetic anisotropy, compensation temperature and SOT-induced switching are
highly sensitive to the stacking order of Co and Tb and to the element in
contact with Pt. Our study further shows that Tb is an efficient SOT generator
when in contact with Co, such that its position in the stack can be adjusted to
generate torques additive to those generated by Pt. With optimal stacking and
layer thickness, the dampinglike SOT efficiency reaches up to 0.3, which is
more than twice that expected from the Pt/Co bilayer. Moreover, the
magnetization can be easily switched by the injection of pulses with current
density of about 0.5-2*107A/cm2 despite the extremely high perpendicular
magnetic anisotropy barrier (up to 7.8 T). Efficient switching is due to the
combination of large SOTs and low saturation magnetization owing to the
ferrimagnetic character of the multilayers. We observed current-driven DW
motion in the absence of any external field, which is indicative of homochiral
N\'eel-type DWs stabilized by the interfacial Dzyaloshinkii-Moriya interaction.
These results show that the stacking order in transition metal/rare-earth
synthetic ferrimagnets plays a major role in determining the magnetotransport
properties relevant for spintronic applications.",2206.01586v1
2022-09-12,Emergent magnetic states and tunable exchange bias at all 3d nitride heterointerfaces,"Interfacial magnetism stimulates the discovery of giant magnetoresistance and
spin-orbital coupling across the heterointerfaces, facilitating the intimate
correlation between spin transport and complex magnetic structures. Over
decades, functional heterointerfaces composed of nitrides are seldomly explored
due to the difficulty in synthesizing high-quality and correct composition
nitride films. Here we report the fabrication of single-crystalline
ferromagnetic Fe3N thin films with precisely controlled thickness. As film
thickness decreasing, the magnetization deteriorates dramatically, and
electronic state transits from metallic to insulating. Strikingly, the
high-temperature ferromagnetism maintains in a Fe3N layer with a thickness down
to 2 u. c. (~ 8 {\AA}). The magnetoresistance exhibits a strong in-plane
anisotropy and meanwhile the anomalous Hall resistance reserves its sign when
Fe3N layer thickness exceeds 5 u. c. Furthermore, we observe a sizable exchange
bias at the interfaces between a ferromagnetic Fe3N and an antiferromagnetic
CrN. The exchange bias field and saturation moment strongly depend on the
controllable bending curvature using cylinder diameter engineering (CDE)
technique, implying the tunable magnetic states under lattice deformation. This
work provides a guideline for exploring functional nitride films and applying
their interfacial phenomena for innovative perspectives towards the practical
applications.",2209.05209v1
2022-10-07,Role of magnetic fields in the formation of direct collapse black holes,"Direct collapse black holes (DCBHs) are the leading candidates for the origin
of the first supermassive black holes. However, the role of magnetic fields
during their formation is still unclear as none of the previous studies has
been evolved long enough to assess their impact during the accretion phase.
Here, we report the results from a suite of 3D cosmological
magneto-hydrodynamic (MHD) simulations which are evolved for 1.6 Myrs
comparable to the expected lifetime of supermassive stars (SMSs). Our findings
suggest that magnetic fields are rapidly amplified by strong accretion shocks
irrespective of the initial magnetic field strength and reach the saturation
state. They stabilize the accretion disks and significantly reduce
fragmentation by enhancing the Jeans mass in comparison with pure
hydrodynamical runs. Although the initial clump masses are larger in MHD runs,
the rapid coalescence of clumps in non-MHD cases due to the higher degree of
fragmentation results in similar masses. Overall, the central clumps have
masses of $\rm 10^5~M_{\odot}$ and the mean mass accretion rates of $\rm \sim
0.1 ~M_{\odot}/yr$ are similar in both MHD and non-MHD cases. The multiplicity
of SMSs is significantly reduced in MHD simulations. Such strongly amplified
magnetic fields are expected to launch Jets and outflows which may be detected
with upcoming radio telescopes.",2210.05611v2
2023-03-08,Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa,"Spin semimetals are amongst the most recently discovered new class of
spintronic materials, which exhibit a band gap in one spin channel and
semimetallic feature in the other, thus facilitating tunable spin transport.
Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along
with giant coercivity and spin-valve characteristics using a combined
experimental and theoretical study. The alloy crystallizes in an inverse
Heusler structure (without any martensitic transition) with a para- to
ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant
coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient,
relatively low magnitude and weak temperture dependance of electrical
resistivity suggest the semimetallic character of the alloy. This is further
supported by our specific heat measurement. Magnetoresistance (MR) confirms an
irreversible nature (with its magnitude $\sim$1\%) along with a change of sign
across the magnetic transition indicating the potentiality of Mn$_2$IrGa in
magnetic switching applications. In addition, asymmetric nature of MR in the
positive and negative field cycles is indicative of spin-valve characteristics.
Our ab-initio calculations confirm the inverse Heusler structure with
ferrimagnetic ordering to be the lowest energy state, with a saturation
magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic
axis with considerable magneto-crystalline anisotropy energy. A large positive
Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall
conductivity ($\sim$-180 S/cm).",2303.04649v2
2023-06-08,Epitaxial thin films of binary Eu-compounds close to a valence transition,"Intermetallic binary compounds of europium reveal a variety of interesting
phenomena due to the interconnection between two different magnetic and 4f
electronic (valence) states, which are particularly close in energy. The
valence states or magnetic properties are thus particularly sensitive to
strain-tuning in these materials. Consequently, we grew epitaxial EuPd$_2$
(magnetic Eu$^{2+}$) and EuPd$_3$ (nonmagnetic Eu$^{3+}$) thin films on
MgO(001) substrates using molecular beam epitaxy. Ambient X-ray diffraction
confirms an epitaxial relationship of cubic Laves-type (C15) EuPd$_2$ with an
(111)-out-of-plane orientation, whereby eight distinct in-plane
crystallographic domains develop. For simple cubic EuPd$_3$ two different
out-of-plane orientations can be obtained by changing the substrate annealing
temperature under ultra-high vacuum conditions from 600 {\deg}C to 1000 {\deg}C
for one hour. A small resistance minimum evolves for EuPd$_3$ thin films grown
with low temperature substrate annealing, which was previously found even in
single crystals of EuPd$_3$ and might be attributed to a Kondo or weak
localization effect. Absence of influence of an applied magnetic fields and
magnetotransport measurements suggest a nonmagnetic ground state for EuPd$_3$
thin films, i. e., a purely trivalent Eu valence, as found in EuPd$_3$ single
crystals. For EuPd$_2$ magnetic ordering below ~72 K is observed, quite similar
to single crystal behavior. Field dependent measurements of the
magnetoresistance and the Hall effect show hysteresis effects below ~0.4 T and
an anomalous Hall effect below ~70 K, which saturates around 1.4 T, thus
proving a ferromagnetic ground state of the divalent Eu.",2306.05355v2
2023-07-14,Degaussing Procedure and Performance Enhancement by Low-Frequency Shaking of a 3-Layer Magnetically Shielded Room,"We report on the performance of a Magnetically Shielded Room (MSR) intended
for next level $^3$He/$^{129}$Xe co-magnetometer experiments which require
improved magnetic conditions. The MSR consists of three layers of Mu-metal with
a thickness of 3 mm each, and one additional highly conductive copper-coated
aluminum layer with a thickness of 10 mm. It has a cubical shape with an
walk-in interior volume with an edge length of 2560 mm. An optimized degaussing
(magnetic equilibration) procedure using a frequency sweep with constant
amplitude followed by an exponential decay of the amplitude will be presented.
The procedure for the whole MSR takes 21 minutes and measurements of the
residual magnetic field at the center of the MSR show that $|B|<1$ nT can be
reached reliably. The chosen degaussing procedure will be motivated by online
hysteresis measurements of the assembled MSR and by Eddy current simulations
showing that saturation at the center of the Mu-metal layer is reached.
Shielding Factors can be improved by a factor $\approx 4$ in all directions by
low frequency (0.2 Hz), low current (1 A) shaking of the outermost Mu-metal
layer.",2307.07225v1
2023-10-23,Regulating star formation in a magnetized disk galaxy,"We use high-resolution MHD simulations of isolated disk galaxies to
investigate the co-evolution of magnetic fields with a self-regulated,
star-forming interstellar medium (ISM). The simulations are conducted using the
Ramses AMR code on the standard Agora initial condition, with gas cooling, star
formation and feedback. We run galaxies with a variety of initial magnetic
field strengths. The fields grow rapidly and achieve approximate saturation
within 500 Myr, but at different levels. The galaxies reach a quasi-steady
state, with slowly declining star formation due to both gas consumption and
increases in the field strength at intermediate ISM densities. We connect this
behaviour to differences in the gas properties and overall structure of the
galaxies. In particular, strong fields limit feedback bubbles. Different cases
support the ISM using varying combinations of magnetic pressure, turbulence and
thermal energy. Magnetic support is closely linked to stellar feedback in the
case of initially weak fields but not for initially strong fields. The spatial
distribution of these supports is also different in each case, and this is
reflected in the stability of the gas disk. We relate this back to the overall
distribution of star formation in each case. We conclude that a weak initial
field can grow to produce a realistic model of a local disk galaxy, but
starting with typical field strengths will not.",2310.15244v1
2024-01-08,Microwave-assisted synthesis of LaMnO3+d: Tuning physical properties with microwave power,"Synthesis of transition metal oxides by microwave irradiation is a faster and
energy-saving method compared to conventional heating in an electrical furnace
because microwave energy is directly converted into heat within precursors.
However, not much is known about how the physical properties are modified by
the power of microwaves. We synthesized LaMnO3+d by irradiating oxide
precursors with microwaves and studied the impact of microwave power (P = 1000
W, 1200 W, 1400 W and 1600 W) on magnetism, resistivity, magnetoresistance,
thermopower, magnetic entropy change, magnetostriction, and electron spin
resonance. It is found that paramagnetic to ferromagnetic transition becomes
sharper, saturation magnetization increases, and electrical resistivity at low
temperatures dramatically decreases as P increases. While the resistivity of
samples irradiated with MW power of P less than or equal to 1400 W show
insulating-like behavior down to 50 K, an insulator-metal transition occurs in
the sample exposed to P = 1600 W and this sample also shows a maximum
magnetoresistance (= -55%), magneto-thermopower (=-87%), magnetostriction (-180
x10-6) for H = 50 kOe and magnetic entropy change of 4.78 J/kg. K for H = 30
kOe around the Curie temperature. The intensity of electron spin resonance
spectra at 300 K increases with P. We postulate that the much enhanced physical
properties observed for the P = 1600 W sample arise from the creation of higher
hole density, chemical homogeneity, and increased grain size. Our study shows
that microwave power can be used as a knob to tune magnetism and other physical
properties to our advantage.",2401.04087v1
2024-02-21,Field-induced electric polarization and elastic softening caused by parity-mixed $d$-$p$ hybridized states with electric multipoles in Ba$_2$CuGe$_2$O$_7$,"We performed high-magnetic-field magnetization, polarization, and ultrasonic
measurements in Ba$_2$CuGe$_2$O$_7$ to investigate field-induced multiferroic
properties arising from a cross-correlation between electric dipoles and
electric quadrupoles in addition to cross-correlation between magnetic dipoles
and electric dipoles. Magnetization $M$ shows saturation behavior above 20 T
for several magnetic field directions, however, electric polarization $P_c$
exhibits an increase, and elastic constants show a softening above 20 T. Based
on quantum states with a crystalline electric field for the $D_{2d}$ point
group and $d$-$p$ hybridization between Cu-$3d$ and O-$2p$ electrons, we
confirmed that the matrix of an electric dipole $P_z$ was proportional to that
of an electric quadrupole $O_{xy}$. Furthermore, considering the spin-orbit
coupling of $3d$ electrons and the Zeeman effect, we showed that $P_z$ and
$O_{xy}$ simultaneously exhibited field-induced responses. These findings
indicate that the orbital degrees of freedom, in addition to the spin degrees
of freedom, contribute to the high-field multiferroicity in
Ba$_2$CuGe$_2$O$_7$.",2402.13504v1
2024-03-26,"Nanoparticles of NbC produced by laser ablation in liquid: a study of structural, magnetic and superconductivity properties","Niobium carbide (NbC) is a high-field Type II superconductor with a critical
temperature ($T_C$) of 11.1 K, just above that of pure Nb ($T_C = 9$ K).
Downsizing NbC to the nanoparticle scale introduces significant alterations in
its critical field and/or the superconducting temperature. Here we report on
superconducting NbC nanoparticles with $T_C \approx$ 10 K synthesized by laser
ablation in acetone, using the lens-target distance (laser fluence) and
centrifugation as control parameters of the particle size. X-ray diffraction
analyses certified the cubic NbC phase and electron microscopy images revealed
spherical particles with average size near 8 nm, with no apparent size
dependence on fluence. Besides, magnetization curves exhibited magnetic loops
featuring a saturation magnetization around $10^{-3} \mu_B$/molecule along with
a small and typical superconducting loop for all investigated samples. We also
observed a suppression of the diamagnetic behavior below $T_C$ upon decreasing
laser fluence. Moreover, all samples exhibited a weak electron spin resonance
(ESR) Curie-like signal at $g\approx2.0$ probably associated with localized
defects in the particle's surface. The intriguing coexistence of
superconductivity and magnetism in nanoparticles has recently garnered
significant research attention. This complex scenario and unique properties are
due to the substantial increase of surface-to-volume ratio in these
superconducting NbC nanoparticles and further investigation would be crucial to
unveil novel material properties and shed new light on our understanding of the
superconducting phenomenon in this new morphology.",2403.18022v1
2010-08-10,Bridging frustrated-spin-chain and spin-ladder physics: quasi-one-dimensional magnetism of BiCu2PO6,"We derive and investigate the microscopic model of the quantum magnet
BiCu2PO6 using band structure calculations, magnetic susceptibility and
high-field magnetization measurements, as well as ED and DMRG techniques. The
resulting quasi-one-dimensional spin model is a two-leg AFM ladder with
frustrating next-nearest-neighbor couplings along the legs. The individual
couplings are estimated from band structure calculations and by fitting the
magnetic susceptibility with theoretical predictions, obtained using ED. The
nearest-neighbor leg coupling J1, the rung coupling J4, and one of the
next-nearest-neighbor couplings J2 amount to 120-150 K, while the second
next-nearest-neighbor coupling is J2'~J2/2. The spin ladders do not match the
structural chains, and although the next-nearest-neighbor interactions J2 and
J2' have very similar superexchange pathways, they differ substantially in
magnitude due to a tiny difference in the O-O distances and in the arrangement
of non-magnetic PO4 tetrahedra. An extensive ED study of the proposed model
provides the low-energy excitation spectrum and shows that the system is in the
strong rung coupling regime. The strong frustration by the
next-nearest-neighbor couplings leads to a triplon branch with an
incommensurate minimum. This is further corroborated by a strong-coupling
expansion up to second order in the inter-rung coupling. Based on high-field
magnetization measurements, we estimate the spin gap of 32 K and suggest the
likely presence of antisymmetric DM anisotropy and inter-ladder coupling J3. We
also provide a tentative description of the physics of BiCu2PO6 in magnetic
field, in the light of the low-energy excitation spectra and numerical
calculations based on ED and DMRG. In particular, we raise the possibility for
a rich interplay between one- and two-component Luttinger liquid phases and a
magnetization plateau at 1/2 of the saturation value.",1008.1771v2
2011-10-03,Structural and magnetic characterization of the complete delafossite solid solution (CuAlO2){1-x}(CuCrO2){x},"We have prepared the complete delafossite solid solution series between
diamagnetic CuAlO2 and the t2g^3 frustrated antiferromagnet CuCrO2. The
evolution with composition x in CuAl(1-x)Cr(x)O2 of the crystal structure and
magnetic properties has been studied and is reported here. The room-temperature
unit cell parameters follow the Vegard law and increase with x as expected. The
effective moment is equal to the Cr^3+ spin-only S = 3/2 value throughout the
entire solid solution. Theta is negative, indicating that the dominant
interactions are antiferromagnetic, and its magnitude increases with Cr
substitution. For dilute Cr compositions, J_BB was estimated by mean-field
theory to be 2.0 meV. Despite the sizable Theta, long-range antiferromagnetic
order does not develop until very large x, and is preceeded by glassy behavior.
Data presented here, and that on dilute Al-substitution from Okuda et al.,
suggest that the reduction in magnetic frustration due to the presence of
non-magnetic Al does not have as dominant an effect on magnetism as chemical
disorder and dilution of the magnetic exchange. For all samples, the 5 K
isothermal magnetization does not saturate in fields up to 5 T and minimal
hysteresis is observed. The presence of antiferromagnetic interactions is
clearly evident in the sub-Brillouin behavior with a reduced magnetization per
Cr atom. An inspection of the scaled Curie plot reveals that significant
short-range antiferromagnetic interactions occur in CuCrO2 above its Neel
temperature, consistent with its magnetic frustration. Uncompensated
short-range interactions are present in the Al-substituted samples and are
likely a result of chemical disorder.",1110.0250v3
2012-01-19,General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows around Black Holes,"Black hole (BH) accretion flows and jets are qualitatively affected by the
presence of ordered magnetic fields. We study fully three-dimensional global
general relativistic magnetohydrodynamic (MHD) simulations of radially extended
and thick (height $H$ to cylindrical radius $R$ ratio of $|H/R|\sim 0.2--1$)
accretion flows around BHs with various dimensionless spins ($a/M$, with BH
mass $M$) and with initially toroidally-dominated ($\phi$-directed) and
poloidally-dominated ($R-z$ directed) magnetic fields. Firstly, for toroidal
field models and BHs with high enough $|a/M|$, coherent large-scale (i.e. $\gg
H$) dipolar poloidal magnetic flux patches emerge, thread the BH, and generate
transient relativistic jets. Secondly, for poloidal field models, poloidal
magnetic flux readily accretes through the disk from large radii and builds-up
to a natural saturation point near the BH. For sufficiently high $|a/M|$ or low
$|H/R|$ the polar magnetic field compresses the inflow into a geometrically
thin highly non-axisymmetric ""magnetically choked accretion flow"" (MCAF) within
which the standard linear magneto-rotational instability is suppressed. The
condition of a highly-magnetized state over most of the horizon is optimal for
the Blandford-Znajek mechanism that generates persistent relativistic jets with
$\gtrsim 100$% efficiency for $|a/M|\gtrsim 0.9$. A magnetic Rayleigh-Taylor
and Kelvin-Helmholtz unstable magnetospheric interface forms between the
compressed inflow and bulging jet magnetosphere, which drives a new jet-disk
quasi-periodic oscillation (JD-QPO) mechanism. The high-frequency QPO has
spherical harmonic $|m|=1$ mode period of $\tau\sim 70GM/c^3$ for $a/M\sim 0.9$
with coherence quality factors $Q\gtrsim 10$. [abridged]",1201.4163v3
2012-03-17,Electrical transport properties of nanostructured ferromagnetic perovskite oxides La_0.67Ca_0.33MnO_3 and La_0.5Sr_0.5CoO_3 at low temperatures (5 K > T >0.3 K) and high magnetic field,"We report a comprehensive study of the electrical and magneto-transport
properties of nanocrystals of La_0.67Ca_0.33MnO_3 (LCMO) (with size down to 15
nm) and La_0.5Sr_0.5CoO_3 (LSCO) (with size down to 35 nm) in the temperature
range 0.3 K to 5 K and magnetic fields upto 14 T. The transport,
magnetotransport and non-linear conduction (I-V curves) were analysed using the
concept of Spin Polarized Tunnelling in the presence of Coulomb blockade. The
activation energy of transport, \Delta, was used to estimate the tunnelling
distances and the inverse decay length of the tunnelling wave function (\chi)
and the height of the tunnelling barrier (\Phi_B). The magnetotransport data
were used to find out the magnetic field dependences of these tunnelling
parameters. The data taken over a large magnetic field range allowed us to
separate out the MR contributions at low temperatures arising from tunnelling
into two distinct contributions. In LCMO, at low magnetic field, the transport
and the MR are dominated by the spin polarization, while at higher magnetic
field the MR arises from the lowering of the tunnel barrier by the magnetic
field leading to an MR that does not saturate even at 14 T. In contrast, in
LSCO, which does not have substantial spin polarization, the first contribution
at low field is absent, while the second contribution related to the barrier
height persists. The idea of inter-grain tunnelling has been validated by
direct measurements of the non-linear I-V data in this temperature range and
the I-V data was found to be strongly dependent on magnetic field. We made the
important observation that a gap like feature (with magnitude ~ E_C, the
Coulomb charging energy) shows up in the conductance g(V) at low bias for the
systems with smallest nanocrystal size at lowest temperatures (T < 0.7 K). The
gap closes as the magnetic field and the temperature are increased.",1203.3873v1
2013-10-30,Extraction of 3D field maps of magnetic multipoles from 2D surface measurements with applications to the optics calculations of the large-acceptance superconducting fragment separator BigRIPS,"The fringing fields of magnets with large apertures and short lengths greatly
affect ion-optical calculations. In particular, for a high magnetic field where
the iron core becomes saturated, the effective lengths and shapes of the field
distribution must be considered because they change with the excitation
current. Precise measurement of the three-dimensional magnetic fields and the
correct application of parameters in the ion-optical calculations are
necessary. First we present a practical numerical method of extracting full 3D
magnetic field maps of magnetic multipoles from 2D field measurements of the
surface of a cylinder. Using this novel method we extracted the distributions
along the beam axis for the coefficient of the first-order quadrupole
component, which is the leading term of the quadrupole components in the
multipole expansion of magnetic fields and proportional to the distance from
the axis. Higher order components of the 3D magnetic field can be extracted
from the leading term via recursion relations. The measurements were done for
many excitation current values for the large-aperture superconducting triplet
quadrupole magnets (STQs) in the BigRIPS fragment separator at the RIKEN
Nishina Center RI Beam Factory. These distributions were parameterized using
the Enge functions to fit the fringe field shapes at all excitation current
values, so that unmeasured values are interpolated. The extracted distributions
depend only on the position along the beam axis, and thus the measured
three-dimensional field can easily be parameterized for ion-optical
calculations. We implemented these parameters in the ion-optical calculation
code COSY INFINITY and realized a first-order calculation that incorporates the
effect of large and varying fringe fields more accurately. We applied the
calculation to determine the excitation current settings of the STQs...",1310.8336v1
2013-12-09,Strong ferromagnetism at the surface of an antiferromagnet caused by buried magnetic moments,"Carrying a large, pure spin magnetic moment of 7 $\mu$bohr/atom in the
half-filled 4f shell, divalent europium is an outstanding element for
assembling novel magnetic devices in which a two-dimensional electron gas
(2DEG) is polarized due to exchange interaction with an underlying
magnetically-active Eu layer, even in the absence of a magnetic field. A
natural example for such geometry is the intermetallic layered material
EuRh$_2$Si$_2$, in which magnetically active layers of Eu are well separated
from each other by non-magnetic Si-Rh-Si trilayers. Applying angle-resolved
photoelectron spectroscopy (ARPES) to this system, we discovered a large spin
splitting of a Shockley-type surface state formed by itinerant electrons of the
Si-Rh-Si surface related trilayer. ARPES shows that the splitting sets in below
approx. 32.5K and quickly saturates to around 150meV upon cooling.
Interestingly, this temperature is substantially higher than the order
temperature of the Eu 4f moments (approx. 24.5K) in the bulk. Our results
clearly show that the magnetic exchange interaction between the surface state
and the buried 4f moments in the 4th subsurface layer is the driving force for
the formation of itinerant ferromagnetism at the surface. We demonstrate that
the observed spin splitting of the surface state, reflecting properties of
2DEG, is easily controlled by temperature. Such a splitting may also be induced
into states of functional surface layers deposited onto the surface of
EuRh$_2$Si$_2$ or similarly ordered magnetic materials with metallic or
semiconducting properties.",1312.2508v1
2014-03-18,Exploring high temperature magnetic order in CeTi_1-xSc_xGe,"Most of magnetic transitions related to Ce ordering are found below
T_ord~12K. Among the few cases exceeding that temperature, two types of
behaviors can be distinguished. One of them is related to the rare cases of Ce
binary compounds formed in BCC structures, with a quartet ground state, whose
degeneracy is reduced by undergoing different types of transitions mostly
structural. The other group shows evidences of itinerant character with the
outstanding example of CeRh_3B_2 showing the highest T_ord=115K. The second
highest ordering temperature has been reported for CeScGe with T_ord=47K, but
the nature of this magnetic state has not been investigated very deeply. In
order to shed more light into this unusual high temperature ordering we studied
the structural, magnetic, transport and thermal properties of CeTi_1-xSc_xGe
alloys in the stability range of the CeScSi-type structure 0.25<x<1 This system
presents a rich variety of magnetic behaviors along this concentration range,
with the magnetic ordering growing from ferromagnetic (FM) T_C~7K up to an
antiferromagnetic (AFM) transition at T_N=47K. The different regions show the
following characteristics: i) on the Ti rich side (0.25<x<0.50) it exhibits a
FM ground state (GS) with large saturation magnetization values M_sat up to
~1.15 mu_B. ii) Around x=0.60, the first crystal electric field excited doublet
starts to contribute to the GS magnetic properties. Furthermore an AFM
component with a connected metamagnetic transition appears. iii) At x=0.65 a
clear change in the GS nature is associated to a critical point above which the
GS properties can be described like for an itinerant system (with decreasing
M_sat) and an effective GS degeneracy N_eff=4. iv) For x>0.65, the magnetic
phase boundary splits into two transitions, with an intermediate phase
presenting incommensurate spin density waves features.",1403.4490v1
2015-02-20,Magnetic properties of (Fe$_{1-x}$Co$_x$)$_2$B alloys and the effect of doping by 5$d$ elements,"We have explored, computationally and experimentally, the magnetic properties
of \fecob{} alloys. Calculations provide a good agreement with experiment in
terms of the saturation magnetization and the magnetocrystalline anisotropy
energy with some difficulty in describing Co$_2$B, for which it is found that
both full potential effects and electron correlations treated within dynamical
mean field theory are of importance for a correct description. The material
exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations
between $x=0.1$ and $x=0.5$. A simple model for the temperature dependence of
magnetic anisotropy suggests that the complicated non-monotonous temperature
behaviour is mainly due to variations in the band structure as the exchange
splitting is reduced by temperature. Using density functional theory based
calculations we have explored the effect of substitutional doping the
transition metal sublattice by the whole range of 5$d$ transition metals and
found that doping by Re or W elements should significantly enhance the
magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed
in enhancing the magnetic anisotropy due to formation of other phases. On the
other hand, doping by Ir and Re was successful and resulted in magnetic
anisotropies that are in agreement with theoretical predictions. In particular,
doping by 2.5~at.\% of Re on the Fe/Co site shows a magnetocrystalline
anisotropy energy which is increased by 50\% compared to its parent
(Fe$_{0.7}$Co$_{0.3}$)$_2$B compound, making this system interesting, for
example, in the context of permanent magnet replacement materials or in other
areas where a large magnetic anisotropy is of importance.",1502.05916v3
2016-06-07,A moving mesh unstaggered constrained transport scheme for magnetohydrodynamics,"We present a constrained transport (CT) algorithm for solving the 3D ideal
magnetohydrodynamic (MHD) equations on a moving mesh, which maintains the
divergence-free condition on the magnetic field to machine-precision. Our CT
scheme uses an unstructured representation of the magnetic vector potential,
making the numerical method simple and computationally efficient. The scheme is
implemented in the moving mesh code Arepo. We demonstrate the performance of
the approach with simulations of driven MHD turbulence, a magnetized disc
galaxy, and a cosmological volume with primordial magnetic field. We compare
the outcomes of these experiments to those obtained with a previously
implemented Powell divergence-cleaning scheme. While CT and the Powell
technique yield similar results in idealized test problems, some differences
are seen in situations more representative of astrophysical flows. In the
turbulence simulations, the Powell cleaning scheme artificially grows the mean
magnetic field, while CT maintains this conserved quantity of ideal MHD. In the
disc simulation, CT gives slower magnetic field growth rate and saturates to
equipartition between the turbulent kinetic energy and magnetic energy, whereas
Powell cleaning produces a dynamically dominant magnetic field. Such difference
has been observed in adaptive-mesh refinement codes with CT and
smoothed-particle hydrodynamics codes with divergence-cleaning. In the
cosmological simulation, both approaches give similar magnetic amplification,
but Powell exhibits more cell-level noise. CT methods in general are more
accurate than divergence-cleaning techniques, and, when coupled to a moving
mesh can exploit the advantages of automatic spatial/temporal adaptivity and
reduced advection errors, allowing for improved astrophysical MHD simulations.",1606.02310v2
2016-12-12,Hall-effect Mediated Magnetic Flux Transport in Protoplanetary Disks,"The global evolution of protoplanetary disks (PPDs) has recently been shown
to be largely controlled by the amount of poloidal magnetic flux threading the
disk, which is further controlled by the poorly understood process of magnetic
flux transport. In weakly ionized gas as in PPDs, magnetic flux is largely
frozen in the electron fluid, except when resistivity is large. When the disk
is largely laminar, we show that the relative drift between the electrons and
ions (the Hall-drift), and the ions and neutral fluids (ambipolar-drift) can
play a dominant role on the transport of magnetic flux. Using two-dimensional
simulations that incorporate the Hall effect and ambipolar diffusion (AD) with
prescribed diffusivities, we show that when large-scale poloidal field is
aligned with disk rotation, the Hall effect rapidly drags magnetic flux inward
at the midplane region, while it slowly pushes flux outward above/below the
midplane. This leads to a highly radially elongated field configuration as a
global manifestation of the Hall-shear instability. This field configuration
further promotes rapid outward flux transport by AD at the midplane, leading to
instability saturation. In quasi-steady state, magnetic flux is transported
outward at approximately the same rate at all heights, and the rate is
comparable to the Hall-free case. For anti-aligned field polarity, the Hall
effect consistently transports magnetic flux outward, leading to a largely
vertical field configuration in the midplane region. The field lines in the
upper layer first bend radially inward and then outward to launch a disk wind.
Overall, the net rate of outward flux transport is about twice faster than the
aligned case. In addition, the rate of flux transport increases with increasing
disk magnetization. The absolute rate of transport is sensitive to disk
microphysics which remains to be explored in future studies.",1612.03912v1
2019-06-09,Spin dynamics and unconventional magnetism in insulating La$_{(1-2x)}$Sr$_{2x}$Co$_{(1-x)}$Nb$_{x}$O$_3$,"We study the structural, magnetic, transport and electronic properties of
LaCoO$_3$ with Sr/Nb co-substitution, i.e.,
La$_{(1-2x)}$Sr$_{2x}$Co$_{(1-x)}$Nb$_{x}$O$_3$ using x-ray and neutron
diffraction, dc and ac-magnetization, neutron depolarization, dc-resistivity
and photoemission measurements. The powder x-ray and neutron diffraction data
were fitted well with the rhombohedral crystal symmetry (space group
\textit{R$\bar{3}$c}) in Rietveld refinement analysis. The calculated effective
magnetic moment ($\approx$3.85~$\mu_B$) and average spin ($\approx$1.5) of Co
ions from the analysis of magnetic susceptibility data are consistent with 3+
state of Co ions in intermediate-spin (IS) and high-spin (HS) states in the
ratio of $\approx$50:50, i.e., spin-state of Co$^{3+}$ is preserved at least up
to $x=$ 0.1 sample. Interestingly, the magnetization values were significantly
increased with respect to the $x=$ 0 sample, and the M-H curves show
non-saturated behavior up to an applied maximum magnetic field of $\pm$70 kOe.
The ac-susceptibility data show a shift in the freezing temperature with
excitation frequency and the detailed analysis confirm the slower dynamics and
a non-zero value of the Vogel-Fulcher temperature T$_0$, which suggests for the
cluster spin glass. The unusual magnetic behavior indicates the presence of
complex magnetic interactions at low temperatures. The dc-resistivity
measurements show the insulating nature in all the samples. However, relatively
large density of states $\approx$10$^{22}$ eV$^{-1}$cm$^{-3}$ and low
activation energy $\approx$130~meV are found in $x=$ 0.05 sample. Using x-ray
photoemission spectroscopy, we study the core-level spectra of La 3$d$, Co
2$p$, Sr 3$d$, and Nb 3$d$ to confirm the valence state.",1906.03659v1
2019-09-18,Neutron diffraction and magnetic properties of Co$_2$Cr$_{1-x}$Ti$_x$Al Heusler alloys,"We report the structural, magnetic, and magnetocaloric properties of
Co$_2$Cr$_{1-x}$Ti$_x$Al ($x=$ 0--0.5) Heusler alloys for spintronic and
magnetic refrigerator applications. Room temperature X-ray diffraction and
neutron diffraction patterns along with Rietveld refinements confirm that the
samples are of single phase and possess a cubic structure. Interestingly,
magnetic susceptibly measurements indicate a second order phase transition from
paramagnetic to ferromagnetic where the Curie temperature (T$_{\rm C}$) of
Co$_2$CrAl increases from 330~K to 445~K with Ti substitution. Neutron powder
diffraction data of the $x=$ 0 sample across the magnetic phase transition
taken in a large temperature range confirm the structural stability and exclude
the possibility of antiferromagnetic ordering. The saturation magnetization of
the $x=$ 0 sample is found to be 8000~emu/mol (1.45~$\mu_{\rm B}$/{\it f.u.})
at 5~K, which is in good agreement with the value (1.35$\pm$0.05~$\mu_{\rm
B}$/{\it f.u.}) obtained from the Rietveld analysis of the neutron powder
diffraction pattern measured at temperature of 4~K. By analysing the
temperature dependence of the neutron data of the $x=$ 0 sample, we find that
the change in the intensity of the most intense Bragg peak (220) is consistent
with the magnetization behavior with temperature. Furthermore, an enhancement
of change in the magnetic entropy and relative cooling power values has been
observed for the $x=$ 0.25 sample. Interestingly, the critical behavior
analysis across the second order magnetic phase transition and extracted
exponents ($\beta\approx$ 0.496, $\gamma\approx$ 1.348, and $\delta\approx$
3.71 for the $x=$ 0.25 sample) suggest the presence of long-range ordering,
which deviates towards 3D Heisenberg type interactions above T$_{\rm C}$,
consistent with the interaction range value $\sigma$.",1909.08292v1
2020-04-10,Ion beam modification of magnetic tunnel junctions,"The impact of 400 keV $Ar^+$ ion irradiation on the magnetic and electrical
properties of in-plane magnetized magnetic tunnel junction (MTJ) stacks was
investigated by ferromagnetic resonance, vibrating sample magnetometry and
current-in-plane tunneling techniques. The irradiation-induced changes of the
magnetic anisotropy, coupling energies and tunnel magnetoresistance (TMR)
exhibited a correlated dependence on the ion fluence, which allowed us to
distinguish between two irradiation regimes. In the low-fluence regime, ${\Phi}
< 10^{14} cm^{-2}$, the parameters required for having a functioning MTJ were
preserved: the anisotropy of the FeCoB free layer (FL) was weakly modulated
following a small decrease in the saturation magnetization $M_S$; the TMR
decreased continuously; the interlayer exchange coupling (IEC) and the exchange
bias (EB) decreased slightly. In the high-fluence regime, ${\Phi} > 10^{14}
cm^{-2}$, the MTJ was rendered inoperative: the modulation of the FL anisotropy
was strong, caused by a strong decrease in $M_S$, ascribed to a high degree of
interface intermixing between the FL and the Ta capping; the EB and IEC were
also lost, likely due to intermixing of the layers composing the synthetic
antiferromagnet; and the TMR vanished due to the irradiation-induced
deterioration of the MgO barrier and MgO/FeCoB interfaces. We demonstrate that
the layers surrounding the FL play a decisive role in determining the trend of
the magnetic anisotropy evolution resulting from the irradiation, and that an
ion-fluence window exists where such a modulation of magnetic anisotropy can
occur, while not losing the TMR or the magnetic configuration of the MTJ.",2004.05025v1
2020-07-18,Giant magneto-birefringence effect and tuneable colouration of 2D crystals' suspensions,"One of the long sought-after goals in manipulation of light through
light-matter interactions is the realization of magnetic-field-tuneable
colouration, so-called magneto-chromatic effect, which holds great promise for
optical, biochemical and medical applications due to its contactless and
non-invasive nature. This goal can be achieved by magnetic-field controlled
birefringence, where colours are produced by the interference between
phase-retarded components of transmitted polarised light. Thus far
birefringence-tuneable coloration has been demonstrated using electric field,
material chirality and mechanical strain but magnetic field control remained
elusive due to either weak magneto-optical response of transparent media or low
transmittance to visible light of magnetically responsive media, such as
ferrofluids. Here we demonstrate magnetically tuneable colouration of aqueous
suspensions of two-dimensional cobalt-doped titanium oxide which exhibit an
anomalously large magneto-birefringence effect. The colour of the suspensions
can be tuned over more than two wavelength cycles in the visible range by
moderate magnetic fields below 0.8 T. We show that such giant magneto-chromatic
response is due to particularly large phase retardation (>3 pi) of the
polarised light, which in its turn is a combined result of a large
Cotton-Mouton coefficient (three orders of magnitude larger than for known
liquid crystals), relatively high saturation birefringence (delta n = 2 x
10^-4) and high transparency of our suspensions to visible light. The work
opens a new avenue to achieve tuneable colouration through engineered magnetic
birefringence and can readily be extended to other magnetic 2D nanocrystals.
The demonstrated effect can be used in a variety of magneto-optical
applications, including magnetic field sensors, wavelength-tuneable optical
filters and see-through printing.",2007.09388v1
2022-11-28,Entropy engineering and tunable magnetic order in the spinel high entropy oxide,"Spinel oxides are an ideal setting to explore the interplay between
configurational entropy, site selectivity, and magnetism in high entropy
oxides. In this work we characterize the magnetic properties of the spinel
(Cr,Mn,Fe,Co,Ni)$_3$O$_4$ and study the evolution of its magnetism as a
function of non-magnetic gallium substitution. Across the range of compositions
studied here, from 0% to 40% Ga, magnetic susceptibility and powder neutron
diffraction measurements show that ferrimagnetic order is robust in the spinel
HEO. However, we also find that the ferrimagnetic order is highly tunable, with
the ordering temperature, saturated and sublattice moments, and magnetic
hardness all varying significantly as a function of Ga concentration. Through
x-ray absorption and magnetic circular dichroism, we are able to correlate this
magnetic tunability with strong site selectivity between the various cations
and the tetrahedral and octahedral sites in the spinel structure. In
particular, we find that while Ni and Cr are largely unaffected by the
substitution with Ga, the occupancies of Mn, Co, and Fe are each significantly
redistributed. Ga substitution also requires an overall reduction in the
transition metal valence, and this is entirely accommodated by Mn. Finally, we
show that while site selectivity has an overall suppressing effect on the
configurational entropy, over a certain range of compositions, Ga substitution
yields a striking increase in the configurational entropy and may confer
additional stabilization. Spinel oxides can be tuned seamlessly from the
low-entropy to the high-entropy regime, making this an ideal platform for
entropy engineering.",2211.15798v1
2023-03-27,Magnetic properties of cobalt ultrathin film structures controlled by buffer layer roughness,"Growth optimization of multilayers is a topic of interest due to their unique
physical properties. Systems containing magnetic materials, such as
platinum-cobalt, have been studied because of their potential for technological
applications, e.g. spintronics, magnetic storage and magnetic sensors. Since
the magnetic properties of thin layers are strongly related to the growth
parameters, the fine tuning of these parameters is necessary to produce
multilayers with specific properties required in various applications. Here, an
efficient approach to tune the coercive field of Co ultrathin films in the
multilayer by varying the underlayer thickness is demonstrated. Using magnetron
sputtering, we prepared multilayer systems of Au(x)/Pt(5nm)/Co(0.7nm)/Au(5nm)
with various thicknesses of Au underlayer. The surface morphology of
Au(x)/Pt(5nm) stack on which Co layer was deposited was studied by atomic force
microscopy. We show the possibility to control the interfacial roughness by
changing the Au underlayer thickness due to its island-like growth mechanism
(Volmer-Weber mode). As the nominal thickness of Au increases, the islands grow
in larger lateral size, resulting in a higher overall roughness of the layer
surface. Magnetization measurements indicate a direct influence of the
underlayer roughness on the coercivity of the multilayers by promoting
additional magnetic anisotropy. With thickness of the Au layer up to 20 nm, we
can change the coercive field in the range from ~200 Oe to ~1100 Oe, while
remaining a nearly constant saturation magnetization. The use of Cu replacing
Au underlayer in the same multilayers was also investigated, demonstrating the
possibility of coercivity adjustment using different materials. The results are
important for applications where the magnetic properties of multilayer
structures based on Co thin films could be adjusted via buffer layer roughness
engineering.",2303.15141v1
2023-05-04,Influence of high pressure on the remarkable itinerant electron behaviour in Y$_{0.7}$Er$_{0.3}$Fe$_2$D$_{4.2}$ compounds,"Monoclinic Y$_{0.7}$Er$_{0.3}$Fe$_2$D$_{4.2}$ compound exhibits unusual
magnetic properties with different field induced magnetic transitions. The
deuteride is ferrimagnetic at low temperature and the Er and Fe sublattices
present magnetic transitions at different temperatures. The Er moments are
ordered below T$_{Er}$=55 K, whereas the Fe moments remain ferromagnetically
coupled up to T$_{M0}$ = 66 K. At T$_{M0}$ the Fe moments display a sharp
ferromagnetic-antiferromagnetic transition (FM-AFM) through an itinerant
electron metamagnetic (IEM) behaviour very sensitive to any volume change.
Y$_{0.7}$Er$_{0.3}$Fe$_2$D$_{4.2}$ becomes paramagnetic above T$_N$=125 K. The
pressure dependence of T$_{Er}$ and T$_{M0}$ have been extracted from magnetic
measurements under hydrostatic pressure up to 0.49 GPa. Both temperatures
decrease linearly upon applied pressure with dT$_{Er}$/dP=-126 and dTM0/dP=-140
K.GPa$^{-1}$ for a field of B=0.03 T. Both magnetic Er and ferromagnetic Fe
order disappear at P=0.44(4) GPa. However, under a larger applied field B=5 T,
dT$_{M0}$/dP=-156 K.GPa$^{-1}$ whereas dT$_{Er}$/dP=-134 K.GPa$^{-1}$ showing a
weaker sensitivity to pressure and magnetic field. At 2 K the decrease of the
saturation magnetization under pressure can be attributed to a reduction of the
mean Er moment due to canting and/or crystal field effect. Above T$_{M0}$ the
magnetization curves display a metamagnetic behaviour from AFM to FM state,
which is also very sensitive to the applied pressure. The transition field
B$_{trans}$, which increases linearly upon heating, is shifted to lower
temperature upon applied pressure with dT=-17 K between 0 and 0.11 GPa. These
results show a strong decoupling of the Er and Fe magnetic sublattices versus
temperature, applied field and pressure.",2305.02698v1
2023-05-23,Nano-Patterned Magnetic Edges in CrGeTe3 for Quasi 1-D Spintronic Devices,"The synthesis of two-dimensional van der Waals magnets has paved the way for
both technological applications and fundamental research on magnetism confined
to ultra-small length scales. Edge magnetic moments in ferromagnets are
expected to be less magnetized than in the sample interior because of the
reduced amount of neighboring ferromagnetic spins at the sample edge. We
recently demonstrated that CrGeTe3 (CGT) flakes thinner than 10 nm are hard
ferromagnets; i.e., they exhibit an open hysteresis loop. In contrast, thicker
flakes exhibit zero net remnant field in the interior, with hard ferromagnetism
present only at the cleaved edges. This experimental observation suggests that
a nontrivial interaction exists between the sample edge and the interior. Here,
we demonstrate that artificial edges fabricated by focus ion beam etching also
display hard ferromagnetism. This enables us to write magnetic nanowires in CGT
directly and use this method to characterize the magnetic interaction between
the interior and edge. The results indicate that the interior saturation and
depolarization fields depend on the lateral dimensions of the sample. Most
notably, the interior region between the edges of a sample narrower than 300 nm
becomes a hard ferromagnet, suggesting an enhancement of the magnetic exchange
induced by the proximity of the edges. Last, we find that the CGT regions
amorphized by the gallium beam are nonmagnetic, which introduces a novel method
to tune the local magnetic properties of CGT films, potentially enabling
integration into spintronic devices.",2305.14431v1
2024-02-27,Modeling effects of starspots on stellar magnetic cycles,"Observations show that faster-rotating stars tend to have stronger magnetic
activity and shorter magnetic cycles. The cyclical magnetic activity of the Sun
and stars is believed to be driven by the dynamo process. The success of the
Babcock-Leighton (BL) dynamo in understanding the solar cycle suggests an
important role that starspots could play in stellar magnetic cycles. We aim at
extending the BL mechanism to solar-mass stars with various rotation rates and
explore the effects of emergence properties of starspots in latitudes and tilt
angles on stellar magnetic cycles. We adopt a kinematic BL-type dynamo model
operating in the bulk of the convection zone. The profiles of the large-scale
flow fields are from the mean-field hydrodynamical model for various rotators.
The BL source term in the model is constructed based on the rotation dependence
of starspots emergence. That is, faster rotators have starspots at higher
latitudes with larger tilt angles.Faster rotators have poloidal flux appearing
closer to about $\pm55^\circ$ latitudes, where the toroidal field generation
efficiency is the strongest because of the strongest latitudinal differential
rotation there. It takes a shorter time for faster rotators to transport the
surface poloidal field from their emergence latitude to the $\pm 55^\circ$
latitudes of efficient $\Omega$-effect thus shortening their magnetic cycles.
The faster rotators operate in a more supercritical regime due to a stronger BL
$\alpha$-effect relating to the tilt angles, which leads to stronger saturated
magnetic fields and a coupling of the poloidal field between two hemispheres
more difficult. Thus the magnetic field parity shifts from the hemispherically
asymmetric mixed mode to quadrupole, and further to dipole when a star spins
down. The emergence of starspots plays an essential role in the large-scale
stellar dynamo.",2402.17449v1
2001-05-21,Saturation at low $x$,"This talk is an attempt to review all our knowledge on saturation at low $x$
both theoretical and experimental, to stimulate a search for saturation effects
at THERA. The main goals of this presentation are 1. To discuss an intuitive
picture of the deep inelastic scattering that leads to the saturation of the
parton densities;
  2. To show that the saturation hypothesis has solid theoretical proof;
  3. To report on the theoretical progress that has been made over the past two
years in high parton density QCD, and on the property of the saturation phase
that emerges from the theory that has been developed;
  4. To collect all that we know theoretically and experimentally about the
saturation scale $Q_s(x)$ .",0105205v1
2010-03-09,Semiconductor saturable absorbers for ultrafast THz signals,"We demonstrate saturable absorber behavior of n-type semiconductors GaAs, GaP
and Ge in THz frequency range at room temperature using nonlinear THz
spectroscopy. The saturation mechanism is based on a decrease in electron
conductivity of semiconductors at high electron momentum states, due to
conduction band nonparabolicity and scattering into satellite valleys in strong
THz fields. Saturable absorber parameters, such as linear and non-saturable
transmission, and saturation fluence, are extracted by fits to a classic
saturable absorber model. Further, we observe THz pulse shortening, and an
increase of the group refractive index of the samples at higher THz pulse peak
fields.",1003.1942v1
2020-09-17,Exact saturation in pseudo-elementary classes for simple and stable theories,"We study PC-exact saturation for stable and simple theories. Among other
results, we show that PC-exact saturation characterizes the stability cardinals
of size at least continuum of a countable stable theory and, additionally, that
simple unstable theories have PC-exact saturation at singular cardinals,
satisfying mild set-theoretic hypotheses, which had previously been open even
for the random graph. We characterize supersimplicity of countable theories in
terms of having PC-exact saturation at singular cardinals of countable
cofinality. We also consider the local analogue of PC-exact saturation, showing
that local PC-exact saturation for singular cardinals of countable cofinality
characterizes supershort theories.",2009.08365v2
2005-10-07,Size-dependent magnetic properties of Nickel nano-chains,"Magnetic properties with 3 different sizes of Ni nanochains, synthesized by a
technique of wet chemical solution, have been investigated experimentally. The
sample sizes are 50 nm, 75 nm, and 150 nm with a typical length of a few
microns. The characterizations by XRD and TEM reveal that the samples consist
of Ni nano-particles forming one dimensional (1D) chain-like structure. The
magnetic properties have been investigated by FC, ZFC measurements and M-H
measurements. The results can be well explained within the context of
core-shell model. First of all, the freezing of disordered spins in the shell
layer have resulted in a peak-like structure on the ZFC curve. The peak
position occurs around TF ~ 13 K. With the 50 nm sample, the field dependent
behavior of TF(H) has been investigated in detail. It is well described by the
de Almeida-Thouless (AT) equation for the surface spin glass state. Secondly,
the shape anisotropy of 1D structure has caused a wide separation between the
FC and ZFC curves. This is mainly attributed to the blocking of the core
magnetism. Thirdly, by the M-H measurement in the low field region, the open
hysteresis loop measured at 5 K < TF is significantly enlarged in comparison
with that taken at T > TF. This indicates that a significant part of the
contribution to the magnetic irreversibility at T < TF is coming from the
disordered spins in the shell layer. Lastly, with reducing sample size, the
coercivity, HC, increases, whereas the saturation magnetization goes down
dramatically. These imply that, as the sample size reduces, the effect of shape
anisotropy becomes larger in the magnetization reversal process and the
contribution to the magnetism from the ferromagnetically ordered core becomes
smaller.",0510168v2
2012-02-22,Neutron Stars with Hyperons subject to Strong Magnetic Field,"Neutron stars are one of the most exotic objects in the universe and a unique
laboratory to study the nuclear matter above the nuclear saturation density. In
this work, we study the equation of state of the nuclear matter within a
relativistic model subjected to a strong magnetic field. We then apply this EoS
to study and describe some of the physical characteristics of neutron star,
especially the mass-radius relation and chemical compositions. To study the
influence of a the magnetic field and the hyperons in the stellar interior, we
consider altogether four solutions: two different values of magnetic field to
obtain a weak and a strong influence, and two configurations: a family of
neutron stars formed only by protons, electrons and neutrons and a family
formed by protons, electrons, neutrons, muons and hyperons. The limit and the
validity of the results found are discussed with some care. In all cases the
particles that constitute the neutron star are in $\beta$ equilibrium and zero
total net charge. Our work indicates that the effect of a strong magnetic field
has to be taken into account in the description of magnetars, mainly if we
believe that there are hyperons in their interior, in which case, the influence
of the magnetic field can increase the mass by more than 10%. We have also seen
that although a magnetar can reach 2.48$M_{\odot}$, a natural explanation of
why we do not know pulsars with masses above 2.0$M_{\odot}$ arises. We also
discuss how the magnetic field affects the strangeness fraction in some
standard neutron star masses and, to conclude our paper, we revisit the direct
URCA process related to the cooling of the neutron stars and show how it is
affected by the hyperons and the magnetic field.",1202.5016v2
2016-05-23,Dynamical model for spindown of solar-type stars,"Since their formation, stars slow down their rotation rates by the removal of
angular momentum from their surfaces, e.g. via stellar winds. Despite the
complexity of the processes involved, a traditional model, where the removal of
angular momentum loss by magnetic fields is prescribed, has provided a useful
framework to understand observational relations between stellar rotation and
age and magnetic field strength. Here, a spindown model is proposed where loss
of angular momentum by magnetic fields is evolved dynamically, instead of being
kinematically prescribed. To this end, we evolve the stellar rotation and
magnetic field simultaneously over stellar evolution time by extending our
previous work on a dynamo model which incorporates the nonlinear feedback
mechanisms on rotation and magnetic fields. Our extended model reproduces key
observations and explains the presence of the two branches of (fast and slow
rotating) stars which have different relations between rotation rate $\Omega$
vs. time (age), magnetic field strength $|B|$ vs. rotation rate, and frequency
of magnetic field $\omega_{cyc}$ vs. rotation rate. For fast rotating stars we
find: (i) an exponential spindown $\Omega \propto e^{-1.35t}$, with $t$
measured in Gyrs, (ii) $|B|$ saturates for higher rotation rate, (iii)
$\omega_{cyc} \propto \Omega^{0.85}$. For slow rotating stars we obtain: (i) a
power law spindown $\Omega \propto t^{-0.52}$, (ii) $|B|$ scales almost
linearly with rotation rate, (iii) $\omega_{cyc} \propto \Omega^{1.16}$. The
results obtained are in good agreement with observations. The Vaughan-Preston
gap is consistently explained in our model by the shortest spindown timescale
in this transition from fast to slow rotators. Our results highlight the
importance of self-regulation of magnetic fields and rotation by direct and
indirect interactions involving nonlinear feedback in stellar evolution.",1605.07125v2
2019-02-13,"Crystal growth, microstructure and physical properties of SrMnSb$_2$","We report on the crystal and magnetic structures, magnetic, and transport
properties of SrMnSb$_2$ single crystals grown by the self-flux method.
Magnetic susceptibility measurements reveal an antiferromagnetic (AFM)
transition at $T_{\rm N} = 295(3)$ K. Above $T_{\rm N}$, the susceptibility
slightly increases and forms a broad peak at $T \sim 420$ K, which is a typical
feature of two-dimensional magnetic systems. Neutron diffraction measurements
on single crystals confirm the previously reported C-type AFM structure below
$T_{\rm N}$. Both de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects
are observed in SrMnSb$_2$ single crystals. Analysis of the oscillatory
component by a Fourier transform shows that the prominent frequencies obtained
by the two different techniques are practically the same within error
regardless of sample size or saturated magnetic moment. Transmission electron
microscopy (TEM) reveals the existence of stacking faults in the crystals,
which result from a horizontal shift of Sb atomic layers suggesting possible
ordering of Sb vacancies in the crystals. Increase of temperature in
susceptibility measurements leads to the formation of a strong peak at $T \sim
{570}$ K that upon cooling under magnetic field the susceptibility shows a
ferromagnetic transition at $T_{\rm C} \sim 580$ K. Neutron powder diffraction
on crushed single-crystals does not support an FM phase above $T_{\rm N}$.
Furthermore, X-ray magnetic circular dichroism (XMCD) measurements of a single
crystal at the $L_{2,3}$ edge of Mn shows a signal due to induced canting of
AFM moments by the applied magnetic field. All evidence strongly suggests that
a chemical transformation at the surface of single crystals occurs above 500 K
concurrently producing a minute amount of ferromagnetic impurity phase.",1902.04948v1
2019-02-27,Fossil field decay due to nonlinear tides in massive binaries,"Surface magnetic fields have been detected in 5 to 10% of isolated massive
stars, hosting outer radiative envelopes. They are often thought to have a
fossil origin, resulting from the stellar formation phase. Yet, magnetic
massive stars are scarcer in (close) short-period binaries, as reported by the
BinaMIcS (Binarity and Magnetic Interaction in various classes of Stars)
collaboration. Different physical conditions in the molecular clouds giving
birth to isolated stars and binaries are commonly invoked. In addition, we
propose that the observed lower magnetic incidence in close binaries may be due
to nonlinear tides. Indeed, close binaries are probably prone to tidal
instability, a fluid instability growing upon the equilibrium tidal flow via
nonlinear effects. Yet, stratified effects have hitherto been largely
overlooked. We theoretically and numerically investigate tidal instability in
rapidly rotating, stably stratified fluids permeated by magnetic fields. We use
the short-wavelength stability method to propose a comprehensive (local) theory
of tidal instability at the linear onset, discussing damping effects. Then, we
propose a mixing-length theory for the mixing generated by tidal instability in
the nonlinear regime. We successfully assess our theoretical predictions
against proof-of-concept, direct numerical simulations. Finally, we compare our
predictions with the observations of short-period, double-lined spectroscopic
binary systems. Using new analytical results, cross-validated by a direct
integration of the stability equations, we show that tidal instability can be
generated by nonlinear couplings of inertia-gravity waves with the equilibrium
tidal flow in short-period massive binaries, even against the Joule diffusion.
In the nonlinear regime, a fossil magnetic field can be dissipated by the
turbulent magnetic diffusion induced by the saturated tidal flows. We predict
that the turbulent Joule diffusion of fossil fields would occur in a few
million years for several short-period massive binaries. Therefore, turbulent
tidal flows could explain the observed dearth of some short-period magnetic
binaries.",1902.10599v2
2020-04-08,High-order crystal field and rare-earth magnetism in RECo5 intermetallics,"Crystal-field (CF) effects on the rare-earth (RE) ions in ferrimagnetic
intermetallics NdCo$_5$ and TbCo$_5$ are evaluated using an ab initio density
functional + dynamical mean-field theory approach in conjunction with a
quasi-atomic approximation for on-site electronic correlations on the localized
4$f$ shell. The study reveals an important role of the high-order sectoral
harmonic component of the CF in the magnetism of RECo$_5$ intermetallics. An
unexpectedly large value is computed in the both systems for the corresponding
crystal-field parameter (CFP) $A_6^6 \langle r^6 \rangle$, far beyond what one
would expect from only electrostatic contributions. It allows solving the
enigma of the non-saturation of zero-temperature Nd magnetic moments in
NdCo$_5$ along its easy axis in the Co exchange field. This unsaturated state
had been previously found out from magnetization distribution probed by
polarised neutron elastic scattering but had so far remained theoretically
unexplained. The easy plane magnetic anisotropy of Nd in NdCo$_5$ is strongly
enhanced by the large value of $A_6^6\langle r^6 \rangle$. Counter-intuitively,
the polar dependence of anisotropy energy within the easy plane remains rather
small. The easy plane magnetic anisotropy of Nd is reinforced up to high
temperatures, which is explained through $J$-mixing effects. The calculated ab
initio anisotropy constants of NdCo$_5$ and their temperature dependence are in
quantitative agreement with experiment. Unlike NdCo$_5$, the $A_6^6 \langle r^6
\rangle$ CFP has negligible effects on the Tb magnetism in TbCo$_5$ suggesting
that its impact on the RE magnetism is ion-specific across the RECo$_5$ series.
The origin of its large value is the hybridization of RE and Co states in a
hexagonally coordinated local environment of the RE ion in RECo$_5$
intermetallics.",2004.03945v1
2020-04-25,"Effects of Oxidation of Top and Bottom Interfaces on the Electric, Magnetic, and Spin-Orbit Torque Properties of Pt/Co/AlOx Trilayers","Oxidation strongly influences the properties of magnetic layers employed in
spintronic devices. We study the effect of oxidation on the structural,
magnetic, and electrical properties as well as current-induced spin-orbit
torques (SOTs) in Pt/Co/AlOx, Pt/CoOx/Co/AlOx, and PtOx/Co/AlOx layers. We show
how the saturation magnetization, perpendicular magnetic anisotropy, anomalous
Hall resistance, and SOT are systematically affected by the degree of oxidation
of both the Pt/Co and Co/Al interfaces. Oxidation of the Co/Al interface
results in a 21% and 42% variation of the dampinglike and fieldlike SOT
efficiencies, which peak at 0.14 and 0.07, respectively. The insertion of a
paramagnetic CoOx layer between Pt and Co maintains a very strong perpendicular
magnetic anisotropy and improves the dampinglike and fieldlike SOT
efficiencies, up to 0.26 and 0.20, respectively. In contrast with recent
reports, we do not find that the oxidation of Pt leads to a significant
enhancement of the torques. Rather, we find that oxygen migrates from Pt to the
Co and Al layers, leading to a time-dependent oxidation profile and an
effective spin Hall conductivity that decreases with increasing oxygen
concentration. Finally, we study current-induced switching in Pt/Co/AlOx with
different degrees of oxidation and find a linear relationship between the
critical switching current and the effective magnetic anisotropy controlled by
the oxidation of Al. These results highlight the importance of interfaces and
oxidation effects on the SOT and magnetotransport properties of heavy
metal/ferromagnet/oxide trilayers and provide information on how to improve the
SOT efficiency and magnetization-switching characteristics of these systems.",2004.12115v1
2021-05-13,Near-Room-Temperature Ferromagnetic Behavior of Single-Atom-Thick 2D Iron in Nanolaminated Ternary MAX Phases,"Two dimensional (2D) ferromagnetic materials have attracted much attention in
the fields of condensed matter physics and materials science, but their
synthesis is still a challenge given their limitations on structural stability
and susceptibility to oxidization. MAX phases nanolaminated ternary carbides or
nitrides possess a unique crystal structure in which single-atom-thick A
sublayers are interleaved by two dimensional MX slabs, providing nanostructured
templates for designing 2D ferromagnetic materials if the non-magnetic A
sublayers can be substituted replaced by magnetic elements. Here, we report
three new ternary magnetic MAX phases (Ta2FeC, Ti2FeN and Nb2FeC) with A
sublayers of single-atom-thick 2D iron through an isomorphous replacement
reaction of MAX precursors (Ta2AlC, Ti2AlN and Nb2AlC) with a Lewis acid salts
(FeCl2). All these MAX phases exhibit ferromagnetic (FM) behavior. The Curie
temperature (Tc) of Ta2FeC and Nb2FeC MAX phase are 281 K and 291 K,
respectively, i.e. close to room temperature. The saturation magnetization of
these ternary magnetic MAX phases is almost two orders of magnitude higher than
that of V2(Sn,Fe)C MAX phase whose A-site is partial substituted by Fe.
Theoretical calculations on magnetic orderings of spin moments of Fe atoms in
these nanolaminated magnetic MAX phases reveal that the magnetism can be mainly
ascribed to intralayer exchange interaction of the 2D Fe atomic layers. Owning
to the richness in composition of MAX phases, there is a large compositional
space for constructing functional single-atom-thick 2D layers in materials
using these nanolaminated templates.",2105.06139v1
2021-09-02,Phenomenological theory of magnetic 90$^{\circ}$ helical state,"We explore a phenomenological phase diagram for the magnetic helical state
with 90$^{\circ}$ turn angle between neighboring spins in the external magnetic
field. Such state is formed by the Eu spin layers in the superconducting iron
arsenide RbEuFe$_{4}$As$_{4}$. The peculiarity of this spin configuration is
that it is not realized in the standard Heisenberg model with bilinear exchange
interactions. A minimum model allowing for such a state requires the
biquadratic nearest-neighbor interaction term. In addition, in tetragonal
materials the 90$^\circ$ helix state may be stabilized by the in-plane
four-fold anisotropy term, which also fixes helix orientation with respect to
the crystal lattice. Such a system has a very rich behavior in the external
magnetic field. The magnetic field induces the metamagnetic transition to the
double-periodic state with the moment angles ($\alpha$, $\alpha$, $-\alpha$,
$-\alpha$) with respect to the field for the four subsequent spins. The
transition field to this state from the deformed helix is determined by the
strength of biquadratic interaction. The transition is second order for small
biquadratic coupling and becomes first order when this coupling exceeds the
critical value. On the other hand, the aligned state at high magnetic field
becomes unstable with respect to formation of incommensurate fan state which
transforms into the double-periodic state with decreasing magnetic field. The
range of this incommensurate state near the saturation field is proportional to
square of the biquadratic coupling. In addition, when the magnetic field is
applied along one of four the equilibrium moment directions, the deformed helix
state experience the first-order rotation transition at the field determined by
the four-fold anisotropy. rotation transition at the field determined by the
four-fold anisotropy.",2109.01096v2
2022-02-24,Methodology for estimating the magnetic Prandtl number and application to solar surface small-scale dynamo simulations,"Context. A crucial step in the numerical investigation of small-scale dynamos
in the solar atmosphere consists of an accurate determination of the magnetic
Prandtl number, Prm, stemming from radiative magneto-hydrodynamic (MHD)
simulations. Aims. The aims are to provide a reliable methodology for
estimating the effective Reynolds and magnetic Reynolds numbers, Re and Rem,
and their ratio Prm=Rem/Re (the magnetic Prandlt number), that characterise MHD
simulations and to categorise small-scale dynamo simulations in terms of these
dimensionless parameters. Methods. The methodology proposed for computing Re
and Rem is based on the method of projection on proper elements and it relies
on a post-processing step carried out using higher order accurate numerical
operators than the ones in the simulation code. A number of radiative MHD
simulations with different effective viscosities and plasma resistivities were
carried out with the CO5BOLD code, and the resulting growth rate of the
magnetic energy and saturated magnetic field strengths were characterised in
terms of Re and Rem. Results. Overall, the proposed methodology provides a
solid estimate of the dissipation coefficients affecting the momentum and
induction equations of MHD simulation codes, and consequently also a reliable
evaluation of the magnetic Prandtl number characterising the numerical results.
Additionally, it is found that small-scale dynamos are active and can amplify a
small seed magnetic field up to significant values in CO5BOLD simulations with
a grid spacing smaller than h=12 km, even at Prm=0.65. However, it is also
evident that it is difficult to categorise dynamo simulations in terms of Prm
alone, because it is not only important to estimate the amplitude of the
dissipation coefficients, but also at which scales energy dissipation takes
place.",2202.12115v2
2022-08-12,Weyl nodal ring states and Landau quantization with very large magnetoresistance in square-net magnet EuGa$_4$,"Magnetic topological semimetals (TSMs) allow for an effective control of the
topological electronic states by tuning the spin configuration, and therefore
are promising materials for next-generation electronic and spintronic
applications. Of magnetic TSMs, Weyl nodal-line (NL) semimetals likely have the
most tunability, and yet they are the least experimentally studied so far due
to the scarcity of material candidates. Here, using a combination of
angle-resolved photoemission spectroscopy and quantum oscillation measurements,
together with density functional theory calculations, we identify the
square-net compound EuGa4 as a new magnetic Weyl nodal ring (NR) semimetal, in
which the line nodes form closed rings in the vicinity of the Fermi level.
Remarkably, the Weyl NR states show distinct Landau quantization with clear
spin splitting upon application of a magnetic field. At 2 K in a field of 14 T,
the transverse magnetoresistance of EuGa4 exceeds 200,000%, which is more than
two orders of magnitude larger than that of other known magnetic TSMs. High
field magnetoresistance measurements indicate no saturation up to 40 T. Our
theoretical model indicates that the nonsaturating MR naturally arises as a
consequence of the Weyl NR state. Our work thus point to the realization of
Weyl NR states in square-net magnetic materials, and opens new avenues for the
design of magnetic TSMs with very large magnetoresistance.",2208.06407v2
2022-11-18,Global simulations of Tayler instability in stellar interiors: a long-time multi-stage evolution of the magnetic field,"Magnetic fields have been observed in massive Ap/Bp stars and presumably are
also present in the radiative zone of solar-like stars. Yet, to date there is
no clear understanding of the dynamics of the magnetic field in stably
stratified layers. A purely toroidal magnetic field configuration is known to
be unstable, developing mainly non-axisymmetric modes. Rotation and a small
poloidal field component may lead to a stable configuration. Here we perform
global MHD simulations with the EULAG-MHD code to explore the evolution of a
toroidal magnetic field located in a layer whose stratification resembles the
solar tachocline. Our numerical experiments allow us to explore the initial
unstable phase as well as the long-term evolution of the magnetic field. During
the first Alfven cycles, we observe the development of the Tayler instability
with the prominent longitudinal wavenumber, $m=1$. Rotation decreases the
growth rate of the instability, and eventually suppresses it. However, after a
stable phase, sudden energy surges lead to the development of higher order
modes even for fast rotation. These modes extract energy from the initial
toroidal field. Nevertheless, our results show that sufficiently fast rotation
leads to a lower saturation energy of the unstable modes, resulting in a
magnetic topology with only a small fraction of poloidal field which remains
steady for several hundreds of Alfven travel times. At this stage, the system
becomes turbulent and the field is prone to turbulent diffusion. The final
toroidal-poloidal configuration of the magnetic field may represent an
important aspect of the field generation and evolution in stably-stratified
layers.",2211.10536v2
2023-11-01,"Misaligned magnetized accretion flows onto spinning black holes: magneto-spin alignment, outflow power and intermittent jets","Magnetic fields regulate black hole (BH) accretion, governing both the inflow
and outflow dynamics. When a BH becomes saturated with large-scale vertical
magnetic flux, it enters a magnetically-arrested disk (MAD) state. The
dynamically-important BH magnetic flux powers highly efficient relativistic
outflows (or jets) and sporadically erupts from the BH into the disk midplane.
Here we explore the evolution of MADs when the BH and gas angular momentum are
misaligned, which is expected to be more common. Using numerical simulations,
we find that jets from rapidly spinning, prograde BHs force the inner accretion
flow into alignment with the BH spin via the magneto-spin alignment mechanism
for disks initially misaligned at $\mathcal{T}\lesssim 60^{\circ}$. Extremely
misaligned MAD disks, on the other hand, exhibit intermittent jets that blow
out parts of the disk to $\approx 100$ gravitational radii before collapsing,
leaving behind hot cavities and magnetized filaments. These intermittent jet
mechanism forms a mini-feedback cycle and could explain some cases of X-ray and
radio quasi-periodic eruptions observed in dim AGN. Further, we find that (i)
for BHs with low power jets, the BH spin and initial disk tilt angle changes
the amount of horizon magnetic flux, and (ii) geometrically-thick, misaligned
accretion flows do not undergo sustained Lense-Thirring (LT) precession.
Thereby, we suggest that low-luminosity accreting BHs ($\dot{M}\ll 10^{-3}
\dot{M}_{\rm Edd}$) are not likely to exhibit quasi-periodic oscillations in
lightcurves due to LT precession, in agreement with observations of BH X-ray
binaries and AGN in the low-hard/quiescent state. Instead, we suggest that
magnetic flux eruptions can mimic precession-like motion, such as observed in
the M87 jet, by driving large-scale surface waves in the jets.",2311.00432v1
1995-12-06,Solitonic Strings and BPS Saturated Dyonic Black Holes,"We consider a six-dimensional solitonic string solution described by a
conformal chiral null model with non-trivial $N=4$ superconformal transverse
part. It can be interpreted as a five-dimensional dyonic solitonic string wound
around a compact fifth dimension. The conformal model is regular with the
short-distance (`throat') region equivalent to a WZW theory. At distances
larger than the compactification scale the solitonic string reduces to a dyonic
static spherically-symmetric black hole of toroidally compactified heterotic
string. The new four-dimensional solution is parameterised by five charges,
saturates the Bogomol'nyi bound and has nontrivial dilaton-axion field and
moduli fields of two-torus. When acted by combined T- and S-duality
transformations it serves as a generating solution for all the static
spherically-symmetric BPS-saturated configurations of the low-energy heterotic
string theory compactified on six-torus. Solutions with regular horizons have
the global space-time structure of extreme Reissner-Nordstrom black holes with
the non-zero thermodynamic entropy which depends only on conserved (quantised)
charge vectors. The independence of the thermodynamic entropy on moduli and
axion-dilaton couplings strongly suggests that it should have a microscopic
interpretation as counting degeneracy of underlying string configurations. This
interpretation is supported by arguments based on the corresponding
six-dimensional conformal field theory. The expression for the level of the WZW
theory describing the throat region implies a renormalisation of the string
tension by a product of magnetic charges, thus relating the entropy and the
number of oscillations of the solitonic string in compact directions.",9512031v3
2015-06-23,On the dependence of the X-ray continuum variations with luminosity in accreting X-ray pulsars,"Using RXTE/ASM archival data, we investigate the behaviour of the spectral
hardness ratio as a function of X-ray luminosity in a sample of six transient
X-ray pulsars (EXO 2030+375, GX 304-1, 4U 0115+63, V 0332+63, A 0535+26 and MXB
0656-072). In all sources we find that the spectral hardness ratio defined as
$F_{5-12\mathrm{keV}}/ F_{1.33-3\mathrm{keV}}$ increases with the ASM flux
(1.33--12 keV) at low luminosities and then saturates or even slightly
decreases above some critical X-ray luminosity falling into the range
$\sim(3-7)\times10^{37}$~erg~s$^{-1}$. Two-dimensional structure of accretion
columns in the radiation-diffusion limit is calculated for two possible
geometries (filled and hollow cylinder) for mass accretion rates $\dot M$
ranging from $10^{17}$ to 1.2$\times 10^{18}$~g s$^{-1}$. The observed spectral
behaviour in the transient X-ray pulsars with increasing $\dot M$ can be
reproduced by a Compton saturated sidewall emission from optically thick
magnetized accretion columns with taking into account the emission reflected
from the neutron star atmosphere. At $\dot M$ above some critical value $\dot
M_{cr}\sim (6-8)\times 10^{17}$~g~s$^{-1}$, the hight of the column becomes
such that the contribution of the reflected component to the total emission
starts decreasing, which leads to the saturation and even slight decrease of
the spectral hardness. Hollow-cylinder columns have a smaller height than the
filled-cylinder ones, and the contribution of the reflected component in the
total emission does not virtually change with $\dot M$ (and hence the hardness
of the continuum monotonically increases) up to higher mass accretion rates
than $\dot M_{cr}$ for the filled columns.",1506.07082v1
2021-04-01,Improved Accuracy and Precision In Simultaneous Myocardial T1 and T2 mapping with Multi-Parametric SASHA (mSASHA),"Purpose: To develop and validate a multi-parametric SAturation-recovery
single-SHot Acquisition (mSASHA) cardiac T1 and T2 mapping technique with high
accuracy and precision in a single breath-hold.
  Methods: The mSASHA acquisition consists of 9 images in an 11 heartbeat
breath-hold -- the first without preparation, 6 images with saturation recovery
preparation, and 2 images with both saturation recovery and T2-preparation. T1
and T2 values were calculated using a 3-parameter model. mSASHA was validated
in simulations and phantoms on a Siemens 3T Prisma scanner with comparison to a
joint T1-T2 technique with a 4-parameter model. mSASHA values were compared to
reference MOLLI, SASHA and T2p-bSSFP sequences in 10 healthy volunteers.
  Results: mSASHA had high accuracy compared to reference spin-echo
measurements, with an average of -0.7+/-0.4% T1 error and -1.3+/-1.3% T2 error.
mSASHA coefficient of variation (CoV) in phantoms for T1 was lower than MOLLI
(0.7+/-0.1% vs 0.9+/-0.2%, p<0.01) and similar to reference T2p-bSSFP for T2
(1.4+/-0.6% vs 1.5+/-0.5%, p>0.05). In simulations, 3-parameter mSASHA fitting
had higher precision than 4-parameter joint T1-T2 fitting for both T1 and T2.
In-vivo myocardial mSASHA T1 was similar to conventional SASHA (1523+/-18 ms vs
1520+/-18 ms, p>0.05) with similar CoV to both MOLLI and SASHA (3.3+/-0.6% vs
3.1+/-0.6% and 3.3+/-0.5% respectively, p>0.05 for both). Myocardial mSASHA T2
values were 37.1+/-1.1 ms with similar precision to T2p-bSSFP (6.7+/-1.7% vs
6.0+/-1.6%, p>0.05).
  Conclusion: mSASHA provides high accuracy cardiac T1 and T2 quantification in
a single breath-hold, with similar precision to reference MOLLI and linear
T2p-bSSFP reference techniques.",2104.00729v1
2023-05-29,Entanglement entropy analysis of dyonic black holes using doubly holographic theory,"We investigate the entanglement between the eternal black hole and Hawking
radiation. For this purpose, we utilize the doubly holographic theories and
study the entanglement entropy of the radiation to find the Page curve
consistent with the unitarity principle. Doubly holographic theories introduce
two types of boundaries in the AdS bulk, namely the usual AdS boundary and the
Planck brane. In such a setup, we calculate the entanglement entropy by
examining two extremal surfaces: the Hartman-Maldacena (HM) surface and the
island surface. The latter surface emerges when the island appears on the
Planck brane. In this paper, we provide a detailed analysis of dyonic black
holes with regard to the Page curve in the context of the doubly holographic
setup. To begin with, we ascertain that the pertinent topological terms must be
included in the Planck brane to describe the systems at finite density and
magnetic field. Furthermore, we also develop a general numerical method to
compute the time-dependent HM surface and achieve excellent agreement between
the numerical results and analytical expressions. Utilizing numerical
methodology, we find that the entanglement entropy of dyonic black holes
exhibits unitary evolution over time, wherein it grows in early time and
reaches saturation after the Page time. The initial growth can be explained by
the HM surface, while the saturation is attributed to the island surface. In
addition, using the holographic entanglement density, we also show that, for
the first time, the saturated value of the entanglement entropy is twice the
Bekenstein-Hawking entropy with the tensionless brane in double holography.",2305.18122v3
2023-11-07,Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma,"The aim of this study is to analyze the effect of the neutral beam injector
(NBI) operation regime on the saturation phase of the Alfven Eigenmodes (AEs)
in DIII-D plasma. The analysis is done using the linear and nonlinear versions
of the gyro-fluid code FAR3d. A set of parametric analyses are performed
modifying the nonlinear simulation EP \b{eta} (NBI injection power), EP energy
(NBI voltage) and the radial location of the EP density profile gradient (NBI
radial deposition). The analysis indicates a transition from the soft (local
plasma relaxation) to the hard MHD (global plasma relaxation) limit if the
simulation EP \b{eta} >= 0.02, leading to bursting MHD activity caused by
radial AEs overlapping. MHD bursts cause an enhancement of the EP transport
showing ballistic-like features as avalanche-like events. Simulations in the
soft MHD limit show an increment of the EP density gradient as the EP \b{eta}
increases. On the other hand, there is a gradient upper limit in the hard MHD
limit, consistent with the critical-gradient behavior. AEs induce shear flows
and zonal current leading to the deformation of the flux surfaces and the
safety factor profile, respectively, particularly strong for the simulation in
the hard MHD limit. Simulations in the hard MHD regime show a decrease of the
AE frequency in the saturation phase; this is caused by the destabilization of
a transitional mode between a 9/3-10/3 TAE and a 9/3 RSAE that may explain the
AE frequency down-sweeping observed in some DIII-D discharges. Reducing the EP
energy in the nonlinear simulations leads to a weakening of the plasma
perturbation. On the other hand, increasing the EP energy causes the opposite
effect. Nonlinear simulations of off-axis NBI profiles indicate a lower plasma
perturbation as the EP density gradient is located further away from the
magnetic axis.",2311.03729v1
2024-02-27,Ultraviolet and Chromospheric activity and Habitability of M stars,"M-type stars are crucial for stellar activity studies since they cover two
types of magnetic dynamos and particularly intriguing for habitability studies
due to their abundance and long lifespans during the main-sequence stage. In
this paper, we used the LAMOST DR9 catalog and the GALEX UV archive data to
investigate the chromospheric and UV activities of M-type stars. All the
chromospheric and UV activity indices clearly show the saturated and
unsaturated regimes and the well-known activity-rotation relation, consistent
with previous studies. Both the FUV and NUV activity indices exhibit a
single-peaked distribution, while the {\rm H$\alpha$} and \rm {Ca
\scriptsize{\uppercase\expandafter{\romannumeral2}} \normalsize H$\&$K} indices
show a distinct double-peaked distribution. The gap between these peaks
suggests a rapid transition from a saturated population to an unsaturated one.
The smoothly varying distributions of different subtypes suggest a
rotation-dependent dynamo for both early-type (partly convective) to late-type
(fully convective) M stars. We identified a group of stars with high UV
activity above the saturation regime (log$R^{\prime}_{\rm NUV} > -2.5$) but low
chromospheric activity, and the underlying reason is unknown. By calculating
the continuously habitable zone and the UV habitable zone for each star, we
found about 70\% stars in the total sample and 40\% stars within 100 pc are
located in the overlapping region of these two habitable zones, indicating a
number of M stars are potentially habitable. Finally, we examined the
possibility of UV activity studies of M stars using the China Space Station
Telescope.",2402.17384v2
2001-07-31,A Weakly Nonlinear Alfvenic Pulse in a Transversely Inhomogeneous Medium,"The interaction of a weakly nonlinear Alfv\'enic pulse with an Alfv\'en speed
inhomogeneity in the direction perpendicular to the magnetic field is
investigated. Identically to the phase mixing experienced by a harmonic
Alfv\'en wave, sharp transverse gradients are generated in the pulse by the
inhomogeneity. In the initial stage of the evolution of an initially plane
Alfv\'enic pulse, the transverse gradients efficiently generate transversely
propagating fast magnetoacoustic waves. However, high resolution full MHD
numerical simulations of the developed stage of the pulse evolution show that
the generation saturates due to destructive wave interference. It is shown that
the weakly non-linear description of the generated fast magnetoacoustic wave is
well described by the driven wave equation proposed in Nakariakov, Roberts &
Murawski (1997), and a simple numerical code (2D MacCromack), which solves it
with minimal CPU resources produces identical results to those obtained from
the full MHD code ({\it Lare2d}, Arber et al. 2001). A parametric study of the
phenomenon is undertaken, showing that, contrary to one's expectations, steeper
inhomogenities of the Alfv\'en speed do not produce higher saturation levels of
the fast wave generation. There is a certain optimal gradient of the
inhomogeneity that ensures the maximal efficiency of the fast wave generation.",0107580v1
2002-08-06,The Magnetorotational Instability in Core Collapse Supernova Explosions,"We investigate the action of the magnetorotational instability (MRI) in the
context of iron-core collapse. Exponential growth of the field on the rotation
time scale by the MRI will dominate the linear growth process of field line
""wrapping"" with the same characteristic time. We examine a variety of initial
rotation states, with solid body rotation or a gradient in rotational velocity,
that correspond to models in the literature. A relatively modest value of the
initial rotation, a period of ~ 10 s, will give a very rapidly rotating PNS and
hence strong differential rotation with respect to the infalling matter. We
assume conservation of angular momentum on spherical shells. Results are
discussed for two examples of saturation fields, a fiducial field that
corresponds to Alfven velocity = rotational velocity and a field that
corresponds to the maximum growing mode of the MRI. Modest initial rotation
velocities of the iron core result in sub-Keplerian rotation and a
sub-equipartition magnetic field that nevertheless produce substantial MHD
luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G
develop within 300 msec after bounce with an associated MHD luminosity of about
10^{52} erg/s. Bi-polar flows driven by this MHD power can affect or even cause
the explosions associated with core-collapse supernovae.",0208128v2
2004-01-15,High Levels of Circularly Polarized Emission from the Radio Jet in NGC 1275 (3C 84),"We present multi-frequency, high resolution VLBA circular polarization images
of the radio source 3C 84 in the center of NGC 1275. Our images reveal a
complex distribution of circular polarization in the inner parsec of the radio
jet, with local levels exceeding 3% polarization, the highest yet detected with
VLBI techniques. The circular polarization changes sign along the jet, making
3C 84 also the first radio jet to show both signs of circular polarization
simultaneously. The spectrum and changing sign of the circular polarization
indicate that it is unlikely to be purely intrinsic to the emitted synchrotron
radiation. The Faraday conversion process makes a significant and perhaps
dominant contribution to the circular polarization, and the observed spectrum
suggests the conversion process is near saturation. The sign change in the
circular polarization along the jet may result from this saturation or may be
due to a change in magnetic field order after an apparent bend in the jet. From
the small spatial scales probed here, ~ 0.15 pc, and the comparably high levels
of circular polarization inferred for the intra-day variable source PKS
1519-273, we suggest a connection between small spatial scales and efficient
production of circular polarization.",0401319v1
2005-02-16,GEOTAIL observation of the SGR1806-20 Giant Flare: The first 600 ms,"On December 27, 2004, plasma particle detectors on the GEOTAIL spacecraft
detected an extremely strong signal of hard X-ray photons from the giant flare
of SGR1806-20, a magnetar candidate. While practically all gamma-ray detectors
on any satellites were saturated during the first ~500 ms interval after the
onset, one of the particle detectors on GEOTAIL was not saturated and provided
unique measurements of the hard X-ray intensity and the profile for the first
600 ms interval with 5.48 ms time resolution. After ~50 ms from the initial
rapid onset, the peak photon flux (integrated above ~50 keV) reached the order
of 10^7 photons sec^{-1} cm^{-2}. Assuming a blackbody spectrum with kT=175
keV, we estimate the peak energy flux to be 21 erg sec^{-1} cm^{-2} and the
fluence (for 0-600 ms) to be 2.4 erg cm^{-2}. The implied energy release
comparable to the magnetic energy stored in a magnetar (~10^{47} erg) suggests
an extremely efficient energy release mechanism.",0502315v3
2004-03-28,Fully polarized states and decoherence,"The aim of this review is to show how ``ferromagnetic'' states, that is,
states having a fully polarization, can produce intrinsic decoherence by
unitary evolution. This effect can give an understanding of recent experiments
on mesoscopic devices as quantum point contacts showing the 0.7 conductance
anomaly and the wide number of data about saturation of dephasing time observed
at very low temperatures, as a fully polarized two dimensional electron gas.
But similar effects can be seen in different area of physics as for example the
Dicke model describing the interaction of two-level systems with a radiation
mode. In this case one can show that decoherence is intrinsic and remove a
Schr\""odinger cat state leaving a single coherent state, collapsing the wave
function in the thermodynamic limit. So, saturation of dephasing time at low
temperatures in mesoscopic devices can be understood by a fully polarized two
dimensional electron gas that, by an exchange model, can be reduced to a
generalized form of the Dicke Hamiltonian and where the quasiparticles are spin
excitations interacting with magnons. In this way, one can see that several
experiments on nanowires and quantum dots can be satisfactorily explained. The
existence of intrinsic decoherence in the thermodynamic limit could have deep
implications in fundamental problems like quantum measurement and
irreversibility. Recent experiments with cavities with a large number of
photons and with nuclear magnetic resonance in organic molecular crystals give
a first strong support to this view.",0403678v1
2005-05-19,"Impact of Zn substitution on phase formation and superconductivity of Bi1.6Pb0.4 Sr2Ca2Cu3-xZnxO10 with x = 0.0, 0.015, 0.03, 0.06, 0.09 and 0.12","Samples of series Bi1.6Pb0.4Sr2Ca2Cu3-xZnxO10 with x = 0.0, 0.015, 0.03,
0.06, 0.09 and 0.12 are synthesized by solid-state reaction route. All the
samples crystallize in tetragonal structure with majority (> 90%) of Bi-2223
(Bi2Sr2Ca2Cu3O10) phase (c-lattice parameter ~ 36 A0). The proportion of
Bi-2223 phase decreases slightly with an increase in x. The lattice parameters
a and c of main phase (Bi-2223) do not change significantly with increasing x.
Superconducting critical transition temperature (Tc) decreases with x as
evidenced by both resistivity [(T)] and AC magnetic susceptibility [(T)]
measurements. Interestingly the decrement of Tc is not monotonic and the same
saturates at around 96 K for x > 0.06. In fact Tc decreases fast (~10K/at%) for
x = 0.015 and 0.03 samples and later nearly saturates for higher x values.
Present results of Zn doping in Bi-2223 system are compared with Zn doped other
HTSC (High temperature superconducting) systems, namely the RE-123 (REBa2Cu3O7)
and La-214 ((La,Sr)2CuO4).",0505461v1
1995-10-15,General class of BPS saturated dyonic black holes as exact superstring solutions,"We show that a four-parameter generating solution for a general class of
four-dimensional, spherically-symmetric, static, dyonic BPS saturated solutions
of leading-order effective equations of toroidally compactified heterotic or
type II superstring theory are exact string solutions. The corresponding
ten-dimensional background defines a conformal sigma-model which is a
particular case of a `chiral null model' with curved `transverse' part. The
exact conformal invariance is a consequence of the chiral null structure of the
`electric' part of the model and the N=4 world-sheet supersymmetry of its
transverse `magnetic' part. The sigma-model action has a remarkable covariance
under both target space and the electromagnetic $S$-duality transformations,
and it illustrates the relation between string-string duality in six dimensions
and $S$-duality in four dimensions. In general, there exists a large class of
exact six-dimensional superstring solutions described by chiral null models
with four-dimensional transverse parts represented by N=4 supersymmetric
sigma-models with metrics conformal to hyper-Kahler ones.",9510097v4
1998-11-22,Domain Walls in Supersymmetric Yang-Mills Theories,"We study BPS saturated domain walls in the supersymmetric SU(2) gauge theory.
For a theory with a very light adjoint scalar (mass <~ Lambda/400) we use the
perturbed N=2 Seiberg-Witten theory to calculate the actual field configuration
of the domain wall. The wall has a sandwich-like five-layer structure of three
distinct phases -- electric confinement, Coulomb and oblique confinement --
separated by two separate transition regions. For larger scalar masses, the
three-phase structure disappears and the Seiberg-Witten theory becomes
inadequate because of two major problems: First, the higher-derivative
interactions between the light fields become relevant and second, both the
magnetic monopole condensate and the dyon condensate show up in the same region
of space, a phenomenon indescribable in terms of a local field theory.
Nevertheless, we argue that the BPS saturated domain wall continues to exist in
this regime and give a qualitative description of the scalar and gaugino
condensates. Finally, we discuss the domain walls in MQCD and translate the BPS
conditions into coupled non-linear differential equations.",9811195v1
2002-12-23,Domain Walls and Flux Tubes in N=2 SQCD: D-Brane Prototypes,"This paper could have been entitled ""D branes and strings from flesh and
blood."" We study field theoretic prototypes of D branes/strings. To this end we
consider (2+1)-dimensional domain walls in (3+1)-dimensional N=2 SQCD with
SU(2) gauge group and two quark flavors in the fundamental representation. This
theory is perturbed by a small mass term of the adjoint matter which, in the
leading order in the mass parameter, does not break N=2 supersymmetry, and
reduces to a (generalized) Fayet-Iliopoulos term in the effective low-energy
N=2 SQED. We find 1/2 BPS-saturated domain wall solution interpolating between
two quark vacua at weak coupling, and show that this domain wall localizes a
U(1) gauge field. To make contact with the brane/string picture we consider the
Abrikosov-Nielsen-Olesen magnetic flux tube in one of two quark vacua and
demonstrate that it can end on the domain wall. We find an explicit 1/4
BPS-saturated solution for the wall/flux tube junction. We verify that the end
point of the flux tube on the wall plays the role of an electric charge in the
dual (2+1)-dimensional SQED living on the wall. Flow to N=1 theory is
discussed. Our results lead us to a conjecture regarding the notorious ""missing
wall"" in the solution of Kaplunovsky et al.",0212293v2
2006-06-07,Domain Lines as Fractional Strings,"We consider N=2 supersymmetric quantum electrodynamics (SQED) with 2 flavors,
the Fayet--Iliopoulos parameter, and a mass term $\beta$ which breaks the
extended supersymmetry down to N=1. The bulk theory has two vacua; at $\beta=0$
the BPS-saturated domain wall interpolating between them has a moduli space
parameterized by a U(1) phase $\sigma$ which can be promoted to a scalar field
in the effective low-energy theory on the wall world-volume. At small
nonvanishing $\beta$ this field gets a sine-Gordon potential. As a result, only
two discrete degenerate BPS domain walls survive. We find an explicit solitonic
solution for domain lines -- string-like objects living on the surface of the
domain wall which separate wall I from wall II. The domain line is seen as a
BPS kink in the world-volume effective theory. We expect that the wall with the
domain line on it saturates both the $\{1,0\}$ and the $\{{1/2},{1/2}\}$b
central charges of the bulk theory. The domain line carries the magnetic flux
which is exactly 1/2 of the flux carried by the flux tube living in the bulk on
each side of the wall. Thus, the domain lines on the wall confine charges
living on the wall, resembling Polyakov's three-dimensional confinement.",0606060v2
2008-02-09,Spin dynamics near the critical doping in weakly-superconducting underdoped YBa2Cu3O6.35 (Tc=18K),"Using neutron scattering we have determined the magnetic structure and
fluctuations in the YBa2Cu3O6.35 superconductor (Tc=18 K). The long-range
ordered collinear spins of the insulating antiferromagnet are replaced by a
commensurate central mode arising from slow, isotropically polarized,
short-range spin correlations. The inelastic spectrum up to 30 meV is broad in
wave vector and commensurate. In contrast to the the resonance peak of higher
Tc superconductors, the spins exhibit a single overdamped spectrum whose rate
of relaxation decreases on cooling and saturates at 5 meV below 50 K. As the
relaxation rate saturates the quasi-static spin correlations grow and become
resolution limited in energy. The spin susceptibility at high temperatures
illustrates that the dominant energy scale is set by the temperature. At low
temperatures, the scale length is geometric and not linked by velocity to
dynamic widths. There is no observable suppression of the spin fluctuations or
central mode upon the onset of superconductivity. The spins respond not to
coherent charge pairs but to hole doping allowing coexistence of glassy short
range spin order with superconductivity. Since the physics of the weakly
superconducting system YBCO6.35 must connect continuously with that in more
strongly superconducting YBCO6.5, we find that neither incommensurate
stripe-like spin modulations nor a well-defined neutron spin resonance are
essential for the onset with doping of pairing in a high temperature cuprate
superconductor.",0802.1252v1
2009-07-02,The chromospheric emission of solar-type stars in the young open clusters IC 2391 and IC 2602,"In this paper we present chromospheric emission levels of the solar-type
stars in the young open clusters IC 2391 and IC 2602. High resolution
spectroscopic data were obtained for over 50 F, G, and K stars from these
clusters over several observing campaigns using the University College London
Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Unlike older
clusters, the majority (28/52) of the solar-type stars in the two clusters are
rapid-rotators (vsini > 20 km/s) with five of the stars being classified as
ultra-rapid rotators (vsini > 100 km/s). The emission levels in the Calcium
infrared triplet lines were then used as a measure of the chromospheric
activity of the stars. When plotted against Rossby number (NR) the star's
chromospheric emission levels show a plateau in the emission for Log(NR) < -1.1
indicating chromospheric saturation similar to the coronal saturation seen in
previously observed X-ray emission from the same stars. However, unlike the
coronal emission, the chromospheric emission of the stars show little evidence
of a reduction in emission (i.e. supersaturation) for the ultra-rapid rotators
in the clusters. Thus we believe that coronal supersaturation is not the result
of an overall decrease in magnetic dynamo efficiency for ultra-rapid rotators.",0907.0286v1
2010-01-28,A mean-field approach to the propagation of field patterns in stratified magneto rotational turbulence,"Local shearing box simulations of stratified magneto rotational turbulence
invariably exhibit cyclic field patterns which propagate away from the disc
midplane. A common explanation for this is magnetic buoyancy. The recent
analysis by Shi et al. however shows that the flow is buoyantly stable below
one disc scale height H, necessitating an alternative explanation in this
region. We here conduct and analyse direct numerical simulations to explain the
observed behaviour by means of a mean-field description. Apart from the mean
radial and azimuthal field, we monitor the small-scale current helicity, which
we propose as a key indicator for saturation. Reconstructing the horizontally
averaged field, we demonstrate that the problem can be reduced to a
one-dimensional induction equation. By means of the so-called test field
method, we then determine the underlying closure parameters. Our analysis shows
that, apart from a possible direct MRI dynamo, two distinct indirect dynamo
mechanisms operate in the disc. This resolves the issue of the ""wrong"" sign of
the MRI dynamo effect. Finally, we use the obtained closure parameters to run a
dynamically quenched dynamo model. This model approximately recovers the
observed field patterns in the mean fields. Moreover, the model reproduces the
prevailing parity and the distinct phase pattern in the small-scale current
helicity. The latter property might open a potential route to understand the
saturation of MRI induced turbulence.",1001.5250v1
2011-05-05,"Synthesis, magnetization and magneto transport study of RECoPO (RE = La, Nd & Sm)","We report the electrical, magneto transport and specific heat of the layered
polycrystalline RECoPO (RE = La, Nd and Sm) samples. These compounds are
iso-structural to recently discovered superconductor LaFeAs(O/F). Bulk
polycrystalline samples are synthesized by solid state reaction route in an
evacuated sealed quartz tube. All these compounds are crystallized in a
tetragonal structure with space group P4/nmm. The Cobalt in these compounds is
in itinerant state with its paramagnetic moment above 1.4\muB and the same
orders ferromagnetically (FM) with saturation moment of around 0.20\muB below
say 80K. Though, LaCoPO shows single paramagnetic (PM) to ferromagnetic (FM)
transition near 35K, the NdCoPO and SmCoPO exhibit successive PM-FM-AFM
transitions. Both FM and AFM transition temperatures vary with applied field.
Although the itinerant ferromagnetism occurs with small saturation moment,
typical anti-ferromagnetic (AFM) transitions (TN1, TN2) are observed at 69K and
14K for Nd and 57K and 45K for Sm. This FM-AFM transition of Co spins in NdCoPO
and SmCoPO is both field and temperature dependent. The Magneto-transport of
NdCoPO and SmCoPO distinctly follows their successive PM-FM-AFM transitions. It
is clear that Sm/Nd (4f) interacts with the Co (3d) in first time synthesized
Sm/NdCoPO.",1105.0971v2
2012-08-19,$β$ NMR study of Isolated $^8$Li in the enhanced paramagnet Platinum,"We report {\beta} detected nuclear magnetic resonance ({\beta}NMR)
measurements of 8Li+ implanted into high purity Pt. The frequency of the 8Li
{\beta}NMR resonance and the spin-lattice relaxation rates 1/T1 were measured
at temperatures ranging from 3 to 300 K. Remarkably, both the spin-lattice
relaxation rate and the Knight shift K depend linearly on temperature T
although the bulk susceptibility does not. K is found to scale with the
Curie-Weiss dependence of the Pt susceptibility extrapolated to low
temperatures. This is attributed to a defect response of the enhanced
paramagnetism of Pt, i.e. the presence of the interstitial Li+ locally relieves
the tendency for the Curie-Weiss susceptibility to saturate at low T . We
propose that the low temperature saturation in \c{hi} of Pt may be related to
an interband coupling between the s and d bands that is disrupted locally by
the presence of the Li+.",1208.3873v1
2013-05-08,The Fate of Planetesimals in Turbulent Disks with Dead Zones. I. The Turbulent Stirring Recipe,"Turbulence in protoplanetary disks affects planet formation in many ways.
While small dust particles are mainly affected by the aerodynamical coupling
with turbulent gas velocity fields, planetesimals and larger bodies are more
affected by gravitational interaction with gas density fluctuations. For the
latter process, a number of numerical simulations have been performed in recent
years, but a fully parameter-independent understanding has not been yet
established. In this study, we present simple scaling relations for the
planetesimal stirring rate in turbulence driven by magnetorotational
instability (MRI), taking into account the stabilization of MRI due to Ohmic
resistivity. We begin with order-of-magnitude estimates of the
turbulence-induced gravitational force acting on solid bodies and associated
diffusion coefficients for their orbital elements. We then test the predicted
scaling relations using the results of recent Ohmic-resistive MHD simulations
by Gressel et al. We find that these relations successfully explain the
simulation results if we properly fix order-of-unity uncertainties within the
estimates. We also update the saturation predictor for the density fluctuation
amplitude in MRI-driven turbulence originally proposed by Okuzumi & Hirose.
Combination of the scaling relations and saturation predictor allows to know
how the turbulent stirring rate of planetesimals depends on disk parameters
such as the gas column density, distance from the central star, vertical
resistivity distribution, and net vertical magnetic flux. In Paper II, we apply
our recipe to planetesimal accretion to discuss its viability in turbulent
disks.",1305.1889v1
2014-02-20,Synchronization and phase ordering in globally coupled chaotic maps,"We investigate the processes of synchronization and phase ordering in a
system of globally coupled maps possessing bistable, chaotic local dynamics.
The stability boundaries of the synchronized states are determined on the space
of parameters of the system. The collective properties of the system are
characterized by means of the persistence probability of equivalent spin
variables that define two phases, and by a magnetization-like order parameter
that measures the phase-ordering behavior. As a consequence of the global
interaction, the persistence probability saturates for all values of the
coupling parameter, in contrast to the transition observed in the temporal
behavior of the persistence in coupled maps on regular lattices. A
discontinuous transition from a non-ordered state to a collective phase-ordered
state takes place at a critical value of the coupling. On an interval of the
coupling parameter, we find three distinct realizations of the phase-ordered
state, which can be discerned by the corresponding values of the saturation
persistence. Thus, this statistical quantity can provide information about the
transient behaviors that lead to the different phase configurations in the
system. The appearance of disordered and phase-ordered states in the globally
coupled system can be understood by calculating histograms and the time
evolution of local map variables associated to the these collective states.",1402.4870v1
2014-07-17,The Role of the Magnetorotational Instability in the Sun,"We calculate growth rates for nonaxisymmetric instabilities including the
magnetorotational instability (MRI) throughout the Sun. We first derive a
dispersion relation for nonaxisymmetric instability including the effects of
shear, convective buoyancy, and three diffusivities (thermal conductivity,
resistivity, and viscosity). We then use a solar model evolved with the stellar
evolution code MESA and angular velocity profiles determined by Global
Oscillations Network Group (GONG) helioseismology to determine the unstable
modes present at each location in the Sun and the associated growth rates. The
overall instability has unstable modes throughout the convection zone and also
slightly below it at middle and high latitudes. It contains three classes of
modes: large-scale hydrodynamic convective modes, large-scale hydrodynamic
shear modes, and small-scale magnetohydrodynamic (MHD) shear modes, which may
be properly called MRI modes. While large-scale convective modes are the most
rapidly growing modes in most of the convective zone, MRI modes are important
in both stably stratified and convectively unstable locations near the
tachocline at colatitudes theta less than 53 degrees. Nonaxisymmetric MRI modes
grow faster than the corresponding axisymmetric modes; for some poloidal
magnetic fields, the nonaxisymmetric MRI growth rates are similar to the
angular rotation frequency Omega, while axisymmetric modes are stabilized. We
briefly discuss the saturation of the field produced by MRI modes, finding that
the implied field at the base of the convective zone in the Sun is comparable
to that derived based on dynamos active in the tachocline and that the
saturation of field resulting from the MRI may be of importance even in the
upper convection zone.",1407.4654v1
2014-08-22,Composition-spread Growth and the Robust Topological Surface State of Kondo insulator SmB6 Thin Films,"Topological insulators are a class of materials with insulating bulk but
protected conducting surfaces due to the combination of spin-orbit interactions
and time-reversal symmetry. The surface states are topologically non-trivial
and robust against non-magnetic backscattering, leading to interesting physics
and potential quantum computing applications1, 2. Recently there has been a
fast growing interest in samarium hexboride (SmB6), a Kondo insulator predicted
to be the first example of a correlated topological insulator3, 4. Here we
fabricated smooth thin films of nanocrystalline SmB6 films. Their transport
behavior indeed shows that SmB6 is a bulk insulator with topological surface
states. Upon decreasing the temperature, the resistivity \r{ho} of Sm0.14B0.86
(SmB6) films display significant increase below 50 K due to hybridization gap
formation, and it shows a saturation behavior below 10 K. The saturated
resistance of our textured films is similar to that of the single crystals,
suggesting that this conduction is from the surface and robust against grain
boundary scatterings. Point contact spectroscopy (PCS) of the film using a
superconducting tip displays both a Kondo Fano resonance and Andreev
reflection, suggesting the existence of both an insulating Kondo lattice and
metallic surface states.",1408.5413v1
2015-01-16,A Multi-wavelength study of the M dwarf binary YY Geminorum,"We review the results of the 1988 multi-wavelength campaign on the late-type
eclipsing binary YY Geminorum. Observations include: broad-band optical and
near infra-red photometry, simultaneous optical and ultraviolet (IUE)
spectroscopy, X-ray (Ginga) and radio (VLA) data. From models fitted to the
optical light curves, fundamental physical parameters have been determined
together with evidence for transient maculations (spots) located near
quadrature longitudes and intermediate latitudes.
  Eclipses were observed at optical, ultraviolet and radio wavelengths.
Significant drops in 6cm radio emission near the phases of both primary and
secondary eclipse indicate relatively compact radio emitting volumes that may
lie between the binary components. IUE observations during secondary eclipse
are indicative of a uniform chromosphere saturated with MgII plage-type
emission and an extended volume of Ly$\alpha$ emission.
  Profile fitting of high-dispersion H alpha spectra confirms the chromospheric
saturation and indicates significant H$\alpha$ opacity to heights of a few
percent of the photospheric radius. There is evidence for an enhanced H alpha
emission region visible near phase 0.25-0.35 which may be associated with a
large spot on the primary and with two small optical flares which were also
observed at other wavelengths: one in microwave radiation and the other in
X-rays. For both flares, L_X/L_opt is consistent with energy release in closed
magnetic structures.",1501.03930v1
2016-05-17,"Berry phase, entanglement entropy, and algebraic properties of ground states of BCS and BEC superfluids","By using Bogoliubov transformations to construct the ground states of
fermionic Bardeen-Cooper-Schrieffer (BCS) superfluids and weakly-interacting
Bose gases supporting Bose Einstein Condensation (BEC), their algebraic
structures and implications can be analyzed in detail. Both ground states are
generalized squeezed coherent states saturating a generalized Heisenberg
uncertainty relation, and they acquire quantized Berry phases when the
corresponding systems are transported along a closed path in their parameter
spaces. While the Berry phase of the BCS ground state depends on the total
particle number, the Berry phase of the BEC ground state depends only on the
particles outside the BEC. The Berry phases are associated with magnetic
monopoles in the parameter spaces and we found that the Dirac quantization
condition is satisfied. Moreover, both ground states are entangled states of
the fermion or boson quanta and we found the entanglement entropy quantifying
the internal correlations. A fixed particle-number approach of fermionic
superfluids does not saturate the generalized uncertainty relation, exhibits
internal entanglement, and gives corresponding Berry phase. In addition, the
algebraic structures of the ground states can be classified by the $q$-deformed
Hopf algebra, $\bigoplus_{\mathbf{k}}h_{q_{\mathbf{k}}}(1)$ for bosons and
$q$-deformed Hopf superalgebra $\bigoplus_{\mathbf{k}}h_{q_{\mathbf{k}}}(1|1)$
for fermions, respectively.",1605.05213v3
2016-09-07,Ferromagnetic layer thickness dependence of the Dzyaloshinskii-Moriya interaction and spin-orbit torques in Pt\Co\AlOx,"We report the thickness dependence of Dzyaloshinskii-Moriya interaction (DMI)
and spin-orbit torques (SOTs) in Pt\Co(t)\AlOx, studied by current-induced
domain wall (DW) motion and second-harmonic experiments. From the DW motion
study, a monotonous decay of the effective DMI strength with an increasing Co
thickness is observed, in agreement with a DMI originating at the Pt\Co
interface. The study of the ferromagnetic thickness dependence of spin-orbit
torques reveals a more complex behavior. The effective SOT-field driving the DW
motion is found to initially increase and then saturate with an increasing
ferromagnetic thickness, while the effective SOT-fields acting on a saturated
magnetic state exhibit a non-monotonic behavior with increasing Co-thickness.
The observed thickness dependence suggests the spin-Hall effect in Pt as the
main origin of the SOTs, with the measured SOT amplitudes resulting from the
interplay between the varying thickness and the transverse spin diffusion
length of the Co layer.",1609.02078v1
2017-02-13,The Evaporation and Survival of Cluster Galaxies' Coronae Part I: The Effectiveness of Isotropic Thermal Conduction Including Saturation,"We simulate the evolution of cluster galaxies' hot interstellar medium (ISM)
gas due to ram pressure and thermal conduction in the intracluster medium
(ICM). At the density and temperature of the ICM, the mean free paths of ICM
electrons are comparable to the sizes of galaxies, therefore electrons can
efficiently transport heat due to thermal conduction from the hot ICM to the
cooler ISM. Galaxies consisting of dark matter halos and hot gas coronae are
embedded in an ICM-like `wind tunnel' in our simulations. In this paper, we
assume that thermal conduction is isotropic and include the effects of
saturation. We find that as heat is transferred from the ICM to the ISM, the
cooler denser ISM expands and evaporates. This process is significantly faster
than gas loss due to ram pressure stripping; for our standard model galaxy the
evaporation time is $160$ Myr while the ram pressure stripping timescale is
$2.5$ Gyr. Thermal conduction also suppresses the formation of shear
instabilities, and there are no stripped ISM tails since the ISM evaporates
before tails can form. Observations of long-lived X-ray emitting coronae and
ram pressure stripped X-ray tails in galaxies in group and cluster environments
therefore require that thermal conduction is suppressed or offset by some
additional physical process. The most likely process is anisotropic thermal
conduction due to magnetic fields in the ISM and ICM, which we simulate and
study in the next paper in this series.",1702.03971v2
2017-04-02,Extremely large non-saturating magnetoresistance and ultrahigh mobility due to topological surface states in metallic Bi2Te3 topological insulator,"Weak antilocalization (WAL) effects in Bi2Te3 single crystals have been
investigated at high and low bulk charge carrier concentrations. At low charge
carrier density the WAL curves scale with the normal component of the magnetic
field, demonstrating the dominance of topological surface states in
magnetoconductivity. At high charge carrier density the WAL curves scale with
neither the applied field nor its normal component, implying a mixture of bulk
and surface conduction. WAL due to topological surface states shows no
dependence on the nature (electrons or holes) of the bulk charge carriers. The
observations of an extremely large, non-saturating magnetoresistance, and
ultrahigh mobility in the samples with lower carrier density further support
the presence of surface states. The physical parameters characterizing the WAL
effects are calculated using the Hikami-Larkin-Nagaoka formula. At high charge
carrier concentrations, there is a greater number of conduction channels and a
decrease in the phase coherence length compared to low charge carrier
concentrations. The extremely large magnetoresistance and high mobility of
topological insulators have great technological value and can be exploited in
magneto-electric sensors and memory devices.",1704.00339v2
2017-06-05,Dynamics of an $n=1$ explosive instability and its role in high-$β$ disruptions,"Some low-$n$ kink-ballooning modes not far from marginal stability are shown
to exhibit a bifurcation between two very distinct nonlinear paths that depends
sensitively on the background transport levels and linear perturbation
amplitudes. The particular instability studied in this work is an $n=1$ mode
dominated by an $m/n=2/1$ component. It is driven by a large pressure gradient
in weak magnetic shear and can appear in various high-$\beta,$ hybrid/advanced
scenarios. Here it is investigated in reversed shear equilibria where the
region around the safety-factor minimum provides favorable conditions. For a
certain range of parameters, a relatively benign path results in a saturated
""long-lived mode"" (LLM) that causes little confinement degradation. At the
other extreme, the quadrupole geometry of the $2/1$ perturbed pressure field
evolves into a ballooning finger that subsequently transitions from exponential
to explosive growth. The finger eventually leads to a fast disruption with
precursors too short for any mitigation effort. Interestingly, the saturated
LLM state is found to be metastable, it also can be driven explosively unstable
by finite-amplitude perturbations. Similarities to some high-$\beta$
disruptions in reversed-shear discharges are discussed.",1706.01204v1
2017-06-18,"Walls, Anomalies, and (De)Confinement in Quantum Anti-Ferromagnets","We consider the Abelian-Higgs model in 2+1 dimensions with instanton-monopole
defects. This model is closely related to the phases of quantum
anti-ferromagnets. In the presence of $\mathbb{Z}_2$ preserving monopole
operators, there are two confining ground states in the monopole phase,
corresponding to the Valence Bond Solid (VBS) phase of quantum magnets. We show
that the domain-wall carries a 't Hooft anomaly in this case. The anomaly can
be saturated by, e.g., charge-conjugation breaking on the wall or by the domain
wall theory becoming gapless (a gapless model that saturates the anomaly is
$SU(2)_1$ WZW). Either way the fundamental scalar particles (i.e. spinons)
which are confined in the bulk are deconfined on the domain-wall. This
$\mathbb{Z}_2$ phase can be realized either with spin-1/2 on a rectangular
lattice, or spin-1 on a square lattice. In both cases the domain wall contains
spin-1/2 particles (which are absent in the bulk). We discuss the possible
relation to recent lattice simulations of domain walls in VBS. We further
generalize the discussion to Abrikosov-Nielsen-Olsen (ANO) vortices in a dual
superconductor of the Abelian-Higgs model in 3+1 dimensions, and to the
easy-plane limit of anti-ferromagnets. In the latter case the wall can undergo
a variant of the BKT transition (consistent with the anomalies) while the bulk
is still gapped. The same is true for the easy-axis limit of anti-ferromagnets.
We also touch upon some analogies to Yang-Mills theory.",1706.05731v2
2017-07-17,Electrostatic and whistler instabilities excited by an electron beam,"The electron beam-plasma system is ubiquitous in the space plasma
environment. Here, using a Darwin particle-in-cell method, the excitation of
electrostatic and whistler instabilities by a gyrating electron beam is studied
in support of recent laboratory experiments. It is assumed that the total
plasma frequency $\omega_{pe}$ is larger than the electron cyclotron frequency
$\Omega_e$. The fast-growing electrostatic beam-mode waves saturate in a few
plasma oscillations by slowing down and relaxing the electron beam parallel to
the background magnetic field. Upon their saturation, the finite amplitude
electrostatic beam-mode waves can resonate with the tail of the background
thermal electrons and accelerate them to the beam parallel velocity. The
slower-growing whistler waves are excited in primarily two resonance modes: (a)
through Landau resonance due to the inverted slope of the beam electrons in the
parallel velocity; (b) through cyclotron resonance by scattering electrons to
both lower pitch angles and smaller energies. It is demonstrated that, for a
field-aligned beam, the whistler instability can be suppressed by the
electrostatic instability due to a faster energy transfer rate between beam
electrons and the electrostatic waves. Such a competition of growth between
whistler and electrostatic waves depends on the ratio of
$\omega_{pe}/\Omega_e$. In terms of wave propagation, beam-generated
electrostatic waves are confined to the beam region whereas beam-generated
whistler waves transport energy away from the beam.",1707.05346v1
2017-11-13,KOI-256's Magnetic Activity under the Influence of the White Dwarf,"We present the findings about chromospheric activity nature of KOI-256
obtained from the Kepler Mission data. Firstly, it was found that there are
some sinusoidal variations out-of-eclipses due to cool spot activity. The
sinusoidal variations modelled by the SPOTMODEL program indicate that the
active component has two different active regions. Their longitudinal variation
revealed that one of them has a migration period of 3.95 years, while the other
has a migration period of 8.37 years. Secondly, 225 flares were detected from
the short cadence data in total. The parameters, such as increase (Tr) and
decay (Td) times, total flare time (Tt), equivalent durations (P), were
calculated for each flare. The distribution of equivalent durations versus
total flare times in logarithmic scale is modelled to find flare activity
level. The Plateau value known as the saturation level of the active component
was calculated to be 2.3121+-0.0964 s, and the Half-life value, which is
required flare total time to reach the saturation, was computed to be 2233.6 s.
In addition, the frequency of N1, which is the number of flares per an hour in
the system, was found to be 0.05087 1/h, while the flare frequency N2 that the
flare-equivalent duration emitting per an hour was found to be 0.00051.
Contrary to the spot activity, it has been found that the flares are in tends
to appear at specific phases due to the white dwarf component.",1711.04737v1
2017-11-20,Vortices and the saturation of the vertical shear instability in protoplanetary disks,"If sufficiently irradiated by its central star, a protoplanetary disks falls
into an equilibrium state exhibiting vertical shear. This state may be subject
to a hydrodynamical instability, the `vertical shear instability' (VSI), whose
breakdown into turbulence transports a moderate amount of angular momentum
while also facilitating planet formation, possibly via the production of
small-scale vortices. In this paper, we show that VSI modes (a) exhibit
arbitrary spatial profiles and (b) remain nonlinear solutions to the
incompressible local equations, no matter their amplitude. The modes are
themselves subject to parasitic Kelvin-Helmholtz instability, though the disk
rotation significantly impedes the parasites and permits the VSI to attain
large amplitudes (fluid velocities < 10% the sound speed). This `delay' in
saturation probably explains the prominence of the VSI linear modes in global
simulations. More generally, the parasites may set the amplitude of VSI
turbulence in strongly irradiated disks. They are also important in breaking
the axisymmetry of the flow, via the unavoidable formation of vortices. The
vortices, however, are not aligned with the orbital plane and thus express a
pronounced $z$-dependence. We also briefly demonstrate that the vertical shear
has little effect on the magnetorotational instability, whereas magnetic fields
easily quench the VSI, a potential issue in the ionised surface regions of the
disk and also at larger radii.",1711.07436v1
2018-04-24,Fermi Surface and Carriers Compensation of pyrite-type PtBi$_{2}$ Revealed by Quantum Oscillations,"Large non-saturating magnetoresistance has been observed in various materials
and electron-hole compensation has been regarded as one of the main mechanisms.
Here we present a detailed study of the angle-dependent Shubnikov -de Haas
effect on large magnetoresistance material pyrite-type PtBi$_{2}$, which allows
us to experimentally reconstruct its Fermi-surface structure and extract the
physical properties of each pocket. We find its Fermi surface contains four
types of pockets in the Brillouin zone: three ellipsoid-like hole pockets
$\alpha$ with C$_4$ symmetry located on the edges (M points), one intricate
electron pocket $\beta$ merged from four ellipsoids along [111] located on the
corners (R points), two smooth and cambered octahedrons $\gamma$ (electron) and
$\delta$ (hole) on the center ($\Gamma$ point). The deduced carrier densities
of electrons and holes from the volume of pockets prove carrier compensation.
This compensation at low temperatures is also supported by fitting the field
dependence of Hall and magnetoresistance at different temperatures. We conclude
that the compensation is the main mechanism for the large non-saturating
magnetoresistance in pyrite-type PtBi$_{2}$. We found the hole pockets {\alpha}
may contribute major mobility because of their light masses and anisotropy to
relatively avoid large-angle scattering at low temperature. This may be a
common feature of semimetals with large magnetoresistance. The found
sub-quadratic magnetoresistance in high field is probably due to
field-dependent mobilities, another feature of semimetals under high magnetic
fields.",1804.08795v2
2018-10-09,Scrambling dynamics and many-body chaos in a random dipolar spin model,"Is there a quantum many-body system that scrambles information as fast as a
black hole? The Sachev-Ye-Kitaev model can saturate the conjectured bound for
chaos, but it requires random all-to-all couplings of Majorana fermions that
are hard to realize in experiments. Here we examine a quantum spin model of
randomly oriented dipoles where the spin exchange is governed by dipole-dipole
interactions. The model is inspired by recent experiments on dipolar spin
systems of magnetic atoms, dipolar molecules, and nitrogen-vacancy centers. We
map out the phase diagram of this model by computing the energy level
statistics, spectral form factor, and out-of-time-order correlation (OTOC)
functions. We find a broad regime of many-body chaos where the energy levels
obey Wigner-Dyson statistics and the OTOC shows distinctive behaviors at
different times: Its early-time dynamics is characterized by an exponential
growth, while the approach to its saturated value at late times obeys a power
law. The temperature scaling of the Lyapunov exponent $\lambda_L$ shows that
while it is well below the conjectured bound $2\pi T$ at high temperatures,
$\lambda_L$ approaches the bound at low temperatures and for large number of
spins.",1810.03815v2
2018-10-12,Nonlinear dynamics of Shear Alfvén fluctuations in Divertor Tokamak Test facility plasmas,"Following the analysis on linear spectra of shear Alfv\'en fluctuations
excited by energetic particles (EPs) in the Divertor Tokamak Test (DTT)
facility plasmas [T. Wang et al., Phys. Plasmas 25, 062509 (2018)], in this
work, nonlinear dynamics of the corresponding mode saturation and the
fluctuation induced EP transport is studied by hybrid
magnetohydrodynamic-gyrokinetic simulations. For the reversed shear Alfv\'en
eigenmode driven by magnetically trapped EP precession resonance in the central
core region of DTT plasmas, the saturation is mainly due to radial decoupling
of resonant trapped EPs. Consistent with the wave-EP resonance structure, EP
transport occurs in a similar scale to the mode width. On the other hand,
passing EP transport is analyzed in detail for toroidal Alfv\'en eigenmode in
the outer core region, with mode drive from both passing and trapped EPs. It is
shown that passing EPs experience only weak redistributions in the weakly
unstable case; and the transport extends to meso-scale diffusion in the
strongly unstable case, due to orbit stochasticity induced by resonance
overlap. Here, weakly/strongly unstable regime is determined by Chirikov
condition for resonance overlap. This work then further illuminates rich and
diverse nonlinear EP dynamics related to burning plasma studies, and the
capability of DTT to address these key physics.",1810.05327v1
2019-01-08,Quadratic to linear magnetoresistance tuning in TmB4,"The change of a material's electrical resistance (R) in response to an
external magnetic field (B) provides subtle information for the
characterization of its electronic properties and has found applications in
sensor and storage related technologies. In good metals, Boltzmann's theory
predicts a quadratic growth in magnetoresistance (MR) at low B, and saturation
at high fields. On the other hand, a number of nonmagnetic materials with weak
electronic correlation and low carrier concentration for metallicity, such as
inhomogeneous conductors, semimetals, narrow gap semiconductors and topological
insulators, two-dimensional electron gas (2DEG) show positive, non-saturating
linear magnetoresistance (LMR). However, observation of LMR in single crystals
of a good metal is rare. Here we present low-temperature, angle dependent
magnetotransport in single crystals of the antiferromagnetic metal, TmB4. We
observe large, positive and anisotropic MR(B), which can be tuned from
quadratic to linear by changing the direction of the applied field. In view of
the fact that isotropic, single crystalline metals with large Fermi surface
(FS) are not expected to exhibit LMR, we attribute our observations to the
anisotropic FS topology of TmB4. Furthermore, the linear MR is found to be
temperature-independent, suggestive of quantum mechanical origin.",1901.02165v1
2019-03-10,Magnons at low excitations: Observation of incoherent coupling to a bath of two-level-systems,"Collective magnetic excitation modes, magnons, can be coherently coupled to
microwave photons in the single excitation limit. This allows for access to
quantum properties of magnons and opens up a range of applications in quantum
information processing, with the intrinsic magnon linewidth representing the
coherence time of a quantum resonator. Our measurement system consists of a
yttrium iron garnet (YIG) sphere and a three-dimensional (3D) microwave cavity
at temperatures and excitation powers typical for superconducting quantum
circuit experiments. We perform spectroscopic measurements to determine the
limiting factor of magnon coherence at these experimental conditions. Using the
input-output formalism, we extract the magnon linewidth $\kappa_\mathrm{m}$. We
attribute the limitations of the coherence time at lowest temperatures and
excitation powers to incoherent losses into a bath of near-resonance two-level
systems (TLSs), a generic loss mechanism known from superconducting circuits
under these experimental conditions. We find that the TLSs saturate when
increasing the excitation power from quantum excitation to multi-photon
excitation and their contribution to the linewidth vanishes. At higher
temperatures, the TLSs saturate thermally and the magnon linewidth decreases as
well.",1903.03981v3
2019-05-14,Direct evidence for charge compensation induced large magnetoresistance in thin WTe2,"Since the discovery of extremely large non-saturating magnetoresistance (MR)
in WTe2, much effort has been devoted to understanding the underlying
mechanism, which is still under debate. Here, we explicitly identify the
dominant physical origin of the large non-saturating MR through in-situ tuning
of the magneto-transport properties in thin WTe2 film. With an electrostatic
doping approach, we observed a non-monotonic gate dependence of the MR. The MR
reaches a maximum (10600%) in thin WTe2 film at certain gate voltage where
electron and hole concentrations are balanced, indicating that the charge
compensation is the dominant mechanism of the observed large MR. Besides, we
show that the temperature dependent magnetoresistance exhibits similar tendency
with the carrier mobility when the charge compensation is retained, revealing
that distinct scattering mechanisms may be at play for the temperature
dependence of magneto-transport properties. Our work would be helpful for
understanding mechanism of the large MR in other nonmagnetic materials and
offers an avenue for achieving large MR in the non-magnetic materials with
electron-hole pockets.",1905.05364v1
2020-01-06,Highly efficient spin orbit torque in Pt/Co/Ir multilayers with antiferromagnetic interlayer exchange coupling,"We have studied the spin orbit torque (SOT) in Pt/Co/Ir multilayers with 3
repeats of the unit structure. As the system exhibits oscillatory interlayer
exchange coupling (IEC) with varying Ir layer thickness, we compare the SOT of
films when the Co layers are coupled ferromagnetically and
antiferromagnetically. SOT is evaluated using current induced shift of the
anomalous Hall resistance hysteresis loops. A relatively thick Pt layer,
serving as a seed layer to the multilayer, is used to generate spin current via
the spin Hall effect. In the absence of antiferromagnetic coupling, the SOT is
constant against the applied current density and the corresponding spin torque
efficiency (i.e. the effective spin Hall angle) is $\sim$0.09, in agreement
with previous reports. In contrast, for films with antiferromagnetic coupling,
the SOT increases with the applied current density and eventually saturates.
The SOT at saturation is a factor of $\sim$15 larger than that without the
antiferromagnetic coupling. The spin torque efficiency is $\sim$5 times larger
if we assume the net total magnetization is reduced by a factor of 3 due to the
antiferromagnetic coupling. Model calculations based on the Landau Lifshitz
Gilbert equation show that the presence of antiferromagnetic coupling can
increase the SOT but the degree of enhancement is limited, in this case, to a
factor of 1.2-1.4. We thus consider there are other sources of SOT, possibly at
the interfaces, which may account for the highly efficient SOT in the
uncompensated synthetic anti-ferromagnet (SAF) multilayers.",2001.01454v1
2020-06-21,The role of parametric instabilities in turbulence generation and proton heating: Hybrid simulations of parallel propagating Alfvén waves,"Large amplitude Alfv\'en waves tend to be unstable to parametric
instabilities which result in a decay process of the initial wave into
different daughter waves depending upon the amplitude of the fluctuations and
the plasma beta. The propagation angle with respect to the mean magnetic field
of the daughter waves plays an important role in determining the type of decay.
In this paper, we revisit this problem by means of multi-dimensional hybrid
simulations. In particular, we study the decay and the subsequent nonlinear
evolution of large-amplitude Alfv\'en waves by investigating the saturation
mechanism of the instability and its final nonlinear state reached for
different wave amplitudes and plasma beta conditions. As opposed to
one-dimensional simulations where the Decay instability is suppressed for
increasing plasma beta values, we find that the decay process in
multi-dimensions persists at large values of the plasma beta via the
filamentation/magnetosonic decay instabilities. In general, the decay process
acts as a trigger both to develop a perpendicular turbulent cascade and to
enhance mean field-aligned wave-particle interactions. We find indeed that the
saturated state is characterized by a turbulent plasma displaying a
field-aligned beam at the Alfv\'en speed and increased temperatures that we
ascribe to the Landau resonance and pitch angle scattering in phase space.",2006.11839v2
2020-08-24,Joint Design of RF and gradient waveforms via auto-differentiation for 3D tailored excitation in MRI,"This paper proposes a new method for joint design of radiofrequency (RF) and
gradient waveforms in Magnetic Resonance Imaging (MRI), and applies it to the
design of 3D spatially tailored saturation and inversion pulses. The joint
design of both waveforms is characterized by the ODE Bloch equations, to which
there is no known direct solution. Existing approaches therefore typically rely
on simplified problem formulations based on, e.g., the small-tip approximation
or constraining the gradient waveforms to particular shapes, and often apply
only to specific objective functions for a narrow set of design goals (e.g.,
ignoring hardware constraints). This paper develops and exploits an
auto-differentiable Bloch simulator to directly compute Jacobians of the
(Bloch-simulated) excitation pattern with respect to RF and gradient waveforms.
This approach is compatible with \emph{arbitrary} sub-differentiable loss
functions, and optimizes the RF and gradients directly without restricting the
waveform shapes. For computational efficiency, we derive and implement explicit
Bloch simulator Jacobians (approximately halving computation time and memory
usage). To enforce hardware limits (peak RF, gradient, and slew rate), we use a
change of variables that makes the 3D pulse design problem effectively
unconstrained; we then optimize the resulting problem directly using the
proposed auto-differentiation framework. We demonstrate our approach with two
kinds of 3D excitation pulses that cannot be easily designed with conventional
approaches: Outer-volume saturation (90{\deg} flip angle), and inner-volume
inversion.",2008.10594v3
2021-04-03,MR-Contrast-Aware Image-to-Image Translations with Generative Adversarial Networks,"Purpose
  A Magnetic Resonance Imaging (MRI) exam typically consists of several
sequences that yield different image contrasts. Each sequence is parameterized
through multiple acquisition parameters that influence image contrast,
signal-to-noise ratio, acquisition time, and/or resolution. Depending on the
clinical indication, different contrasts are required by the radiologist to
make a diagnosis. As MR sequence acquisition is time consuming and acquired
images may be corrupted due to motion, a method to synthesize MR images with
adjustable contrast properties is required.
  Methods
  Therefore, we trained an image-to-image generative adversarial network
conditioned on the MR acquisition parameters repetition time and echo time. Our
approach is motivated by style transfer networks, whereas the ""style"" for an
image is explicitly given in our case, as it is determined by the MR
acquisition parameters our network is conditioned on.
  Results
  This enables us to synthesize MR images with adjustable image contrast. We
evaluated our approach on the fastMRI dataset, a large set of publicly
available MR knee images, and show that our method outperforms a benchmark
pix2pix approach in the translation of non-fat-saturated MR images to
fat-saturated images. Our approach yields a peak signal-to-noise ratio and
structural similarity of 24.48 and 0.66, surpassing the pix2pix benchmark model
significantly.
  Conclusion
  Our model is the first that enables fine-tuned contrast synthesis, which can
be used to synthesize missing MR contrasts or as a data augmentation technique
for AI training in MRI.",2104.01449v1
2022-01-03,Quantum electrodynamic effects on counter-streaming instabilities in the whole \textbf{k} space,"In a recent work [Bret, EPL \textbf{135} (2021) 35001], quantum
electrodynamic (QED) effects were evaluated for the two-stream instability. It
pertains to the growth of perturbations with a wave vector oriented along the
flow in a collisionless counter-streaming system. Here, the analysis is
extended to every possible orientation of the wave vector. The previous result
for the two-stream instability is recovered, and it is proved that even within
the framework of a 3D analysis, this instability remains fundamentally 1D even
when accounting for QED effects. The filamentation instability, found for wave
vectors normal to the flow, is weakly affected by QED corrections. As in the
classical case, its growth rate saturates at large $k_\perp$. The saturation
value is found independent of QED corrections. Also, the smallest unstable
$k_\perp$ is independent of QED corrections. Surprisingly, unstable modes found
for oblique wave vectors do \emph{not} follow the same pattern. For some, QED
corrections do reduce the growth rate. But for others, the same corrections
increase the growth rate instead. The possibility for QED effects to play a
role in un-magnetized systems is evaluated. Pair production resulting from
gamma emission by particles oscillating in the exponentially growing fields, is
not accounting for.",2201.00499v1
2022-02-04,Measurements of Chromospheric Mg I Emission Lines of Zero-Age Main-Sequence Stars,"The chromosphere is the active atmosphere in which energetic eruption events,
such as flares, occur. Chromospheric activity is driven by the magnetic field
generated by stellar rotation and convection. The relationship between
chromospheric activity and the Rossby number, the ratio of the rotational
period to the convective turnover time, has been extensively examined for many
types of stars, by using narrow chromospheric emission lines, such as the Ca II
lines and the Mg II h and k lines. However, the stars with small Rossby
numbers, i.e., stars with rapid rotations and/or long convective turnover
times, show constant strengths of such lines against the Rossby number. In this
study, we investigate the infrared Mg I emission lines at 8807 A of 47 zero-age
main-sequence (ZAMS) stars in IC 2391 and IC 2602 using the archive data of the
Anglo-Australian Telescope at the University College London Echelle
Spectrograph. After subtracting the photospheric absorption component, the Mg I
line is detected as an emission line for 45 ZAMS stars, whose equivalent widths
are between 0.02 A and 0.52 A. A total of 42 ZAMS stars show the narrower Mg I
emission lines instead of the Ca II infrared triplet emission lines, suggesting
that they are formed at different depths. The ZAMS stars with smaller Rossby
numbers show stronger Mg I emission lines. The Mg I emission line is not
saturated even in ""the saturated regime of the Ca II emission lines,"" i.e.,
Rossby number < 10^(-1.1). The Mg I emission line is considered to be a good
indicator of chromospheric activity, particularly for active objects.",2202.02065v1
2022-04-13,Non-local spin entanglement in a fermionic chain,"An effective two-spin density matrix (TSDM) for a pair of spin-$1/2$ degree
of freedom, residing at a distance of $R$ in a spinful Fermi sea, can be
obtained from the two-electron density matrix following the framework
prescribed in Phys. Rev. A 69, 054305 (2004). We note that the single spin
density matrix (SSDM) obtained from this TSDM for generic spin-degenerate
systems of free fermions is always pinned to the maximally mixed state $i.e.$
$(1/2) \ \mathbb{I}$, independent of the distance $R$ while the TSDM confirms
to the form for the set of maximally entangled mixed state (the so called
""X-state"") at finite $R$. The X-state reduces to a pure state (a singlet) in
the $R\rightarrow 0$ limit while it saturates to an X-state with largest
allowed value of von-Neumann entropy of $2 \ln2$ as $R \rightarrow \infty$
independent of the value of chemical potential. However, once an external
magnetic field is applied to lift the spin-degeneracy, we find that the
von-Neumann entropy of SSDM becomes a function of the distance $R$ between the
two spins. We also show that the von-Neumann entropy of TSDM in the
$R\rightarrow \infty$ limit becomes a function of the chemical potential and it
saturate to $2 \ln2$ only when the band in completely filled unlike the
spin-degenerate case. Finally we extend our study to include spin-orbit
coupling and show that it does effect these asymptotic results. Our findings
are in sharp contrast with previous works which were based on continuum models
owing to physics which stem from the lattice model.",2204.06579v1
2022-09-16,Supergravity and p-brane Ansatz,"This project explores the $D=11$ supergravity model and the properties of its
p-brane ansatz. The initial field content (graviton, gravitino and the
anti-symmetric tensor field) in the action of $D=11$ supergravity is explained
in the context of supersymmetry. The action is then decomposed to the bosonic
sector, which is compared with the $\sigma$-model in string theory at a low
energy limit $\alpha'\xrightarrow{}0$. The dilaton in the $D=10$ string theory
can be realised from the dimensional reduction of $D=11$ supergravity, which
gives the scalar contribution in the action to form the single-charge action.
The field equation of the single-charged action is then derived. An
$SO(D-d)\times Poincare_{d}$ ansatz is introduced to simplify the field
equation. The solution of the field equation bifurcates into the electric
ansatz and the magnetic ansatz. These ansatzes are called p-branes which are
string-like objects that exist in their p-dimensional world volume embedded in
the ambient spacetime. The BPS bounds are saturated for these p-branes, and
upon dimensional reduction, they are similar to extremal Riessner-Nordstrom
black holes up to the scalar. The branic motion is then derived and a special
case of parallel brane orbit is explored. Similar to the Riessner-Nordstrom
black hole, the circular orbit is found to require a specific angular momentum
that increases further from the central brane. The circular orbit always exists
for the extremal case, but the black branes that do not saturate the BPS bound
may not have a circular orbit below a threshold angular momentum.",2209.07730v2
2022-09-21,Starspots and Magnetism: Testing the Activity Paradigm in the Pleiades and M67,"We measure starspot filling fractions for 240 stars in the Pleiades and M67
open star clusters using APOGEE high-resolution H-band spectra. For this work
we developed a modified spectroscopic pipeline which solves for starspot
filling fraction and starspot temperature contrast. We exclude binary stars,
finding that the large majority of binaries in these clusters (80%) can be
identified from Gaia DR3 and APOGEE criteria -- important for field star
applications. Our data agree well with independent activity proxies, indicating
that this technique recovers real starspot signals. In the Pleiades, filling
fractions saturate at a mean level of 0.248$\pm$0.005 for active stars with a
decline at slower rotation; we present fitting functions as a function of
Rossby number. In M67, we recover low mean filling fractions of 0.030$\pm$0.008
and 0.003$\pm$0.002 for main sequence GK stars and evolved red giants
respectively, confirming that the technique does not produce spurious spot
signals in inactive stars. Starspots also modify the derived spectroscopic
effective temperatures and convective overturn timescales. Effective
temperatures for active stars are offset from inactive ones by -109$\pm$11 K,
in agreement with the Pecaut & Mamajek empirical scale. Starspot filling
fractions at the level measured in active stars changes their inferred overturn
timescale, which biases the derived threshold for saturation. Finally, we
identify a population of stars statistically discrepant from mean
activity-Rossby relations and present evidence that these are genuine
departures from a Rossby scaling. Our technique is applicable to the full
APOGEE catalog, with broad applications to stellar, galactic, and exoplanetary
astrophysics.",2209.10549v1
2022-11-08,Quantum metallic state at the titanium sesquioxide heterointerface,"The emergence of the quantum metallic state marked by a saturating finite
electrical resistance in the zero-temperature limit in a variety of
two-dimensional superconductors injects an exciting momentum to the realm of
unconventional superconductivity. Despite much research efforts over last few
decades, there is not yet a general consensus on the nature of this unexpected
quantum metal. Here, we report the observation of a unique quantum metallic
state within the hallmark of Bose-metal characterized by a saturating
resistance and a simultaneously vanishing Hall resistance in the titanium
sesquioxide heterointerface superconductor Ti$_2$O$_3$/GaN. Remarkably, the
quantum bosonic metallic state tuned by a magnetic field in the vicinity of the
two-dimensional superconductivity-metal transition persists in the normal
phase, suggesting the existence of composite bosons, formed by electron Cooper
pairs, even in the normal phase. Our findings indicate the existence of
preformed electron Cooper pairs in the normal phase of heterointerface
superconductors, and shed new light on the pairing mechanism underlying
unconventional superconductivity.",2211.04035v2
2023-02-08,"Data-driven Protection of Transformers, Phase Angle Regulators, and Transmission Lines in Interconnected Power Systems","This dissertation highlights the growing interest in and adoption of machine
learning (ML) approaches for fault detection in modern power grids. Once a
fault has occurred, it must be identified quickly and preventative steps must
be taken to remove or insulate it. As a result, detecting, locating, and
classifying faults early and accurately can improve safety and dependability
while reducing downtime and hardware damage. ML-based solutions and tools to
carry out effective data processing and analysis to aid power system operations
and decision-making are becoming preeminent with better system condition
awareness and data availability. Power transformers, Phase Shift Transformers
or Phase Angle Regulators, and transmission lines are critical components in
power systems, and ensuring their safety is a primary issue. Differential
relays are commonly employed to protect transformers, whereas distance relays
are utilized to protect transmission lines. Magnetizing inrush, overexcitation,
and current transformer saturation make transformer protection a challenge.
Furthermore, non-standard phase shift, series core saturation, low
turn-to-turn, and turn-to-ground fault currents are non-traditional problems
associated with Phase Angle Regulators. Faults during symmetrical power swings
and unstable power swings may cause mal-operation of distance relays and
unintentional and uncontrolled islanding. The distance relays also mal-operate
for transmission lines connected to type-3 wind farms. The conventional
protection techniques would no longer be adequate to address the above
challenges due to limitations in handling and analyzing massive amounts of
data, limited generalizability, incapability to model non-linear systems, etc.
These limitations of differential and distance protection methods bring forward
the motivation of using ML in addressing various protection challenges.",2302.03826v1
2023-10-23,Scaling and Universality at Ramped Quench Dynamical Quantum Phase Transition,"The nonequilibrium dynamics of a periodically driven extended XY model, in
the presence of linear time dependent magnetic filed, is investigated using the
notion of dynamical quantum phase transitions (DQPTs). Along the similar lines
to the equilibrium phase transition, the main purpose of this work is to search
the fundamental concepts such as scaling and universality at the ramped quench
DQPTs. We have shown that the critical points of the model, where the gap
closing occurs, can be moved by tuning the driven frequency and consequently
the presence/absence of DQPTs can be flexibly controlled by adjusting the
driven frequency. %Taking advantage of this property, We have uncovered that,
for a ramp across the single quantum critical point, the critical mode at which
DQPTs occur is classified into three regions: the Kibble-Zurek (KZ) region,
where the critical mode scales linearly with the square root of the sweep
velocity, pre-saturated (PS) region, and the saturated (S) region where the
critical mode makes a plateau versus the sweep velocity. While for a ramp that
crosses two critical points, the critical modes disclose just KZ and PS
regions. On the basis of numerical simulations, we find that the dynamical free
energy scales linerly with time, as approaches to DQPT time, with the exponent
$\nu=1\pm 0.01$ for all sweep velocities and driven frequencies.",2310.15101v2
2020-04-07,"Strong, Temperature-Dependent Spin-Orbit Torques in Heavy Fermion YbAl$_3$","The use of current-generated spin-orbit torques[1] to drive magnetization
dynamics is under investigation to enable a new generation of non-volatile,
low-power magnetic memory. Previous research has focused on spin-orbit torques
generated by heavy metals[2-8], interfaces with strong Rashba
interactions[9,10] and topological insulators [11-14]. These families of
materials can all be well-described using models with noninteracting-electron
bandstructures. Here, we show that electronic interactions within a strongly
correlated heavy fermion material, the Kondo lattice system YbAl$_{3}$, can
provide a large enhancement in spin-orbit torque. The spin-torque conductivity
increases by approximately a factor of 4 as a function of decreasing
temperature from room temperature to the coherence temperature of YbAl$_{3}$
($T^* \approx 37$ K), with a saturation at lower temperatures, achieving a
maximum value greater than any heavy metal element. This temperature dependence
mimics the increase and saturation at $T^*$ of the density of states at the
Fermi level arising from the ytterbium 4$f$-derived heavy bands in the Kondo
regime, as measured by angle-resolved photoemission spectroscopy[15]. We
therefore identify the many-body Kondo resonance as the source of the large
enhancement of spin-orbit torque in YbAl$_{3}$. Our observation reveals new
opportunities in spin-orbit torque manipulation of magnetic memories by
engineering quantum many-body states.",2004.03678v2
2023-05-18,Relaxation behaviours in ferromagnetic monolayers,"In this article, we briefly review the studies on magnetic relaxation
behaviours. The theoretical as well as experimental investigations are reported
briefly. A major part of this article is devoted to the recent Monte Carlo
investigations into the roles of boundary conditions, dynamics and the
Geometrical structures on the relaxation of magnetic monolayers modelled by
two-dimensional Ising ferromagnet. We have studied all these effects for a two
dimensional Ising system with two types of deformations, namely preserving and
area non-preserving.The Glauber protocol and Metropolis dynamical rules are
employed in our simulations and we investigated the systems with both periodic
and open boundary conditions.
  The major findings are the exponential relaxation and the dependence of
relaxation time ($\tau$) on the aspect ratio $R$ (length over breadth). A power
law dependence ($\tau \sim R^{-s}$) has been observed for larger values of
aspect ratio ($R$). The linear thermal ($T$) dependence of exponent ($s$) has
been noticed ($s = aT + b$). The transient behaviours of the spin-flip density
have also been studied here for both surface and bulk/core. Both the saturated
bulk/core and saturated surface spin-flip density are observed to follow the
logarithmic dependence $f_{d} = a + b~\log(L)$ with the system size ($L$).
  For open boundary condition with any kind (Metropolis/Glauber) of dynamical
rule, the faster relaxation has been observed. Similarly, Metropolis algorithm
yields faster relaxation for any kind (open/periodic) of boundary condition. We
appeal to the experimentalists for experimental support which may be applied in
judicious {\it magnetic coating} of the credit cards for quicker response.",2305.10765v3
2023-06-16,Bose-Einstein condensation of a two-magnon bound state in a spin-one triangular lattice,"Interactions of collective excitations often lead to rich emergent phenomena
in many-particle quantum systems. In ordered magnets, the elementary
excitations are spin waves (magnons), which obey Bose-Einstein statistics.
Similar to the Cooper pairs in superconductors, magnons can be paired into
bound states under attractive interactions. Even more interestingly, the Zeeman
coupling to a magnetic field acts as a chemical potential that can tune the
particle density through a quantum critical point (QCP), beyond which a
``hidden order'' is predicted to exist. However, experimental confirmation of
this QCP and the associated new state of matter remain elusive. Here we report
direct observation of the Bose-Einstein condensation (BEC) of the two-magnon
bound state in Na$_2$BaNi(PO$_4$)$_2$. Comprehensive thermodynamic measurements
confirmed the existence of a two-dimensional BEC-QCP at the saturation field.
Inelastic neutron scattering experiments were performed to accurately establish
the magnetic exchange model. An exact solution of the model found stable
2-magnon bound states that were further confirmed by an electron spin resonance
(ESR) experiment, demonstrating that the QCP is due to the pair condensation
and the phase below saturation field is the long-sought-after spin nematic (SN)
phase.",2306.09695v1
1999-11-10,R-Mode Oscillations in Rotating Magnetic Neutron Stars,"We show that r-mode oscillations distort the magnetic fields of neutron stars
and that their occurrence is likely to be limited by this interaction. If the
field is gtrsim 10^{16} (Omega/Omega_B) G, where Omega and Omega_B are the
angular velocities of the star and at which mass shedding occurs, r-mode
oscillations cannot occur. Much weaker fields will prevent gravitational
radiation from exciting r-mode oscillations or damp them on a relatively short
timescale by extracting energy from the modes faster than gravitational wave
emission can pump energy into them. For example, a 10^{10} G poloidal magnetic
field that threads the star's superconducting core is likely to prevent the
ell=2 mode from being excited unless Omega exceeds 0.35 Omega_B. If Omega is
larger than 0.35 Omega_B initially, the ell=2 mode may be excited but is likely
to decay rapidly once Omega falls below 0.35 Omega_B, which happens in lesssim
15^d if the saturation amplitude is gtrsim 0.1. The r-mode oscillations may
play an important role in determining the structure of neutron star magnetic
fields.",9911188v2
2001-10-04,High Resolution Simulations of the Plunging Region in a Pseudo-Newtonian Potential: Dependence on Numerical Resolution and Field Topology,"New three dimensional magnetohydrodynamic simulations of accretion disk
dynamics in a pseudo-Newtonian Paczynski-Wiita potential are presented. These
have finer resolution in the inner disk than any previously reported. Finer
resolution leads to increased magnetic field strength, greater accretion rate,
and greater fluctuations in the accretion rate. One simulation begins with a
purely poloidal magnetic field, the other with a purely toroidal field.
Compared to the poloidal initial field simulation, a purely toroidal initial
field takes longer to reach saturation of the magnetorotational instability and
produces less turbulence and weaker magnetic field energies. For both initial
field configurations, magnetic stresses continue across the marginally stable
orbit; measured in units corresponding to the Shakura-Sunyaev alpha parameter,
the stress grows from ~0.1 in the disk body to as much as ~10 deep in the
plunging region. Matter passing the inner boundary of the simulation has ~10%
greater binding energy and ~10% smaller angular momentum than it did at the
marginally stable orbit. Both the mass accretion rate and the integrated stress
fluctuate widely on a broad range of timescales.",0110118v1
2003-02-05,Beyond the standard accretion disc model: coupled magnetic disc--corona solutions with a physically motivated viscosity law,"We present a systematic, analytical study of geometrically thin, optically
thick accretion disc solutions for magnetized turbulent flows, with an
alpha-like viscosity prescription. Under the only assumptions that (1)
Magneto-Rotational instability (MRI) generates the turbulence that produces the
anomalous viscosity needed for accretion to proceed, and that (2) the magnetic
field amplified by the instability saturates due to buoyant vertical escape, we
are able to self-consistently solve the disc structure equations including the
fraction of power, f, that is carried off by vertical Poynting flux (and likely
dissipated outside the optically thick disc). For low-viscosity discs, we
obtain stable high-f solutions at low accretion rates, when gas pressure
dominates, and unstable, low-f, radiation pressure dominated solutions at high
accretion rates. For high viscosity discs, instead, a new thermally and
viscously stable, radiation pressure dominated solution is found, characterized
by f~1 and appearing only above a critical accretion rate (of the order of few
tenths of the Eddington one). We discuss the regimes of validity of our
assumptions, and the astrophysical relevance of our solutions. We conclude that
our newly discovered thin disc solutions, possibly accompanied by powerful,
magnetically dominated coronae and outflows, should be seriously considered as
models for black holes accreting at super-Eddington rates.",0302074v1
2004-12-06,The Neutrino Bubble Instability: A Mechanism for Generating Pulsar Kicks,"An explanation for the large random velocities of pulsars is presented. Like
many other models, we propose that the momentum imparted to the star is given
at birth. The ultimate source of energy is provided by the intense optically
thick neutrino flux that is responsible for radiating the proto-neutron star's
gravitational binding energy during the Kelvin-Helmholtz phase. The central
feature of the kick mechanism is a radiative-driven magnetoacoustic
instability, which we refer to as ``neutrino bubbles.'' Identical in nature to
the photon bubble instability, the neutrino bubble instability requires the
presence of an equilibrium radiative flux as well as a coherent steady
background magnetic field. Over regions of large magnetic flux densities, the
neutrino bubble instability is allowed to grow on dynamical timescales ~ 1ms,
potentially leading to large luminosity enhancements and density fluctuations.
Local luminosity enhancements, which preferentially occur over regions of
strong magnetic field, lead to a net global asymmetry in the neutrino emission
and the young neutron star is propelled in the direction opposite to these
regions. For favorable values of magnetic field structure, size, and strength
as well as neutrino bubble saturation amplitude, momentum kicks in excess of
1000 km/s can be achieved. Since the neutrino-powered kick is delivered over
the duration of the Kelvin-Helmholtz time ~ a few seconds, one expects
spin-kick alignment from this neutrino bubble powered model.",0412144v1
2005-04-14,Protoneutron star dynamos and pulsar magnetism,"We have investigated the turbulent mean-field dynamo action in protoneutron
stars that are subject to convective and neutron finger instabilities during
the early evolutionary phase. While the first one develops mostly in the inner
regions of the star, the second one is favored in the outer regions, where the
Rossby number is much smaller and a mean-field dynamo action is more efficient.
By solving the mean-field induction equation we have computed the critical spin
period below which no dynamo action is possible and found it to be $\sim 1$ s
for a wide range of stellar models and for both axisymmetric and
non-axisymmetric magnetic fields. Because this critical period is substantially
longer than the characteristic spin period of very young pulsars, we expect
that a mean-field dynamo will be effective for most protoneutron stars. The
saturation dipole field estimated by making use of the model of ``global''
quenching fits well the pulsar magnetic fields inferred from the spin-down
data. Apart from the large scale magnetic field, our model predicts also a
generation of small scale fields which are typically stronger than the poloidal
field and can survive during the lifetime of pulsars. Extremely rapidly
rotating protoneutron stars ($P \sim 1$ ms) may have the dipole field $\sim
(3-6) \times 10^{14}$ G.",0504328v1
2005-08-22,Weibel Filament Decay and Thermalization in Collisionless Shocks and Gamma-Ray Burst Afterglows,"Models for the synchrotron emission of gamma-ray burst afterglows suggest
that the magnetic field is generated in the shock wave that forms as
relativistic ejecta plow through the circum-burst medium. Transverse Weibel
instability efficiently generates magnetic fields near equipartition with the
post-shock energy density. The detailed saturated state of the instability, as
seen in particle-in-cell simulations, consists of magnetically self-pinched
current filaments. The filaments are parallel to the direction of propagation
of the shock and are about a plasma skin depth in radius, forming a
quasi--two-dimensional structure. We use a rudimentary analytical model to
argue that the Weibel filaments are unstable to a kink-like mode, which
destroys their quasi--two-dimensional structure. For wavelengths longer than
than the skin depth, the instability grows at the rate equal to the speed of
light divided by the wavelength. We calculate the transport of collisionless
test particles in the filaments experiencing the instability and show that the
particles diffuse in energy. This diffusion marks the beginning of
thermalization in the shock transition layer, and causes initial magnetic field
decay as particles escape from the filaments. We discuss the implications of
these results for the structure of the shock and the polarization of the
afterglow.",0508464v1
2005-08-31,Simulations of Magnetorotational Instability in a Magnetized Couette Flow,"In preparation for an experimental study of magnetorotational instability
(MRI) in liquid metal, we present non-ideal two-dimensional magnetohydrodynamic
simulations of the nonlinear evolution of MRI in the experimental geometry. The
simulations adopt initially uniform vertical magnetic fields, conducting radial
boundaries, and periodic vertical boundary conditions. No-slip conditions are
imposed at the cylinders. Our linear growth rates compare well with existing
local and global linear analyses. The MRI saturates nonlinearly with horizontal
magnetic fields comparable to the initial axial field. The rate of angular
momentum transport increases modestly but significantly over the initial state.
For modest fluid and magnetic Reynolds numbers Re, Rm between 100 and 1000, the
final state is laminar reduced mean shear except near the radial boundaries,
and with poloidal circulation scaling as the square root of resistivity, in
partial agreement with the analysis of Knobloch and Julien. A sequence of
simulations at Rm=20 and 100 < Re < 25,600 enables extrapolation to the
experimental regime (Rm ~ 20, Re ~ 10^7), albeit with unrealistic boundary
conditions. MRI should increase the experimentally measured torque
substantially over its initial purely hydrodynamic value.",0508665v4
2006-11-06,"A Magnetic Alpha-Omega Dynamo in Active Galactic Nuclei Disks: II. Magnetic Field Generation, Theories and Simulations","It is shown that a dynamo can operate in an Active Galactic Nuclei accretion
disk due to the Keplerian shear and due to the helical motions of expanding and
twisting plumes of plasma heated by many star passages through the disk. Each
plume rotates a fraction of the toroidal flux into poloidal flux, always in the
same direction, through a finite angle, and proportional to its diameter. The
predicted growth rate of poloidal magnetic flux, based upon two analytic
approaches and numerical simulations, leads to a rapid exponentiation of a seed
field, \sim 0.1 to \sim 0.01 per Keplerian period of the inner part of the
disk. The initial value of the seed field may therefore be arbitrarily small
yet reach, through dynamo gain, saturation very early in the disk history.
Because of tidal disruption of stars close to the black hole, the maximum
growth rate occurs at a radius of about 100 gravitational radii from the
central object. The generated mean magnetic field, a quadrupole field, has
predominantly even parity so that the radial component does not reverse sign
across the midplane. The linear growth is predicted to be the same by each of
the following three theoretical analyses: the flux conversion model, the mean
field approach, and numerical modeling. The common feature is the conducting
fluid flow, considered in companion Paper I (Pariev and Colgate 2006) where two
coherent large scale flows occur naturally: the differential winding of
Keplerian motion and differential rotation of expanding plumes.",0611188v1
1998-10-17,Glassy nature of stripe ordering in La(1.6-x)Nd(0.4)Sr(x)CuO(4),"We present the results of neutron-scattering studies on various aspects of
crystalline and magnetic structure in single crystals of
La(1.6-x)Nd(0.4)Sr(x)CuO(4) with x=0.12 and 0.15. In particular, we have
reexamined the degree of stripe order in an x=0.12 sample. Measurements of the
width for an elastic magnetic peak show that it saturates at a finite value
below 30 K, corresponding to a spin-spin correlation length of 200 A. A model
calculation indicates that the differing widths of magnetic and (previously
reported) charge-order peaks, together with the lack of commensurability, can
be consistently explained by disorder in the stripe spacing. Above 30 K, the
width of the nominally elastic signal begins to increase. Interpreting the
signal as critical scattering from slowly fluctuating spins, the temperature
dependence of the width is consistent with renormalized classical behavior of a
2-dimensional anisotropic Heisenberg antiferromagnet. Inelastic scattering
measurements show that incommensurate spin excitations survive at and above 50
K, where the elastic signal is neglible. We also report several results related
to the LTO-to-LTT transition.",9810212v2
2001-10-08,Quantum rotational band model for the Heisenberg molecular magnet Mo72Fe30,"We derive the low temperature properties of the molecular magnet Mo72Fe30,
where 30 Fe(3+) paramagnetic ions occupy the sites of an icosidodecahedron and
interact via isotropic nearest-neighbour antiferromagnetic Heisenberg exchange.
The key idea of our model (J.S. & M.L.) is that the low-lying excitations form
a sequence of rotational bands, i.e., for each such band the excitation
energies depend quadratically on the total spin quantum number. For
temperatures below 50 mK we predict that the magnetisation is described by a
staircase with 75 equidistant steps as the magnetic field is increased up to a
critical value and saturated for higher fields. For higher temperatures thermal
broadening effects wash out the staircase and yield a linear ramp below the
critical field, and this has been confirmed by our measurements (R.M.). We
demonstrate that the lowest two rotational bands are separated by an energy gap
of 0.7 meV, and this could be tested by EPR and inelastic neutron scattering
measurements. We also predict the occurrence of resonances at temperatures
below 0.1 K in the proton NMR spin-lattice relaxation rate associated with
level crossings. As rotational bands characterize the spectra of many magnetic
molecules our method opens a new road towards a description of their
low-temperature behaviour which is not otherwise accessible.",0110149v1
2002-11-24,Coexistence of Superconductivity and Magnetism in R2-xcexrusr2cu 2o10-? (R=Eu and Gd),"R2-xCexRuSr2Cu2O10-d(Ru-2122) is the first Cu-O based system in which
superconductivity (SC) in the CuO2 planes and weak-ferromagnetism (W-FM) in the
Ru sublattice coexists. The hole doping in the CuO2 planes, is controlled by
appropriate variation of the Ce concentration and/or increasing the oxygen
concentration. In Eu2-xCexRuSr2Cu2O10, SC occurs for Ce contents of 0.4-0.8,
with the highest TC=35 K for Ce=0.6. The as-prepared non-SC EuCeRuSr2Cu2O10
sample exhibits magnetic irreversibility below Tirr=125 K and long range o
anti-ferromagnetic (AFM) order at TM =165 K. The saturation moment at 5 K is
Msat=0.89 mB /Ru. Annealing under oxygen pressures, does not affect these
parameters, whereas depletion of oxygen shifts both Tirr and TM up to 169 and
215 K respectively. TM, Tirr and Msat decrease with x, and the Ce dependent
magnetic-SC phase diagram is presented. A simple model for the SC and the
long-range W-FM states is proposed. We argue that: (i) the system becomes AFM
ordered at TM; (b) at Tirr < TM, W-FM is induced by the canting of the Ru
moments, and (c), at lower temperatures the appropriate samples become SC at
TC. The magnetic features are not affected by the SC state, and the two states
coexist.",0211533v1
2003-11-15,A new quantum fluid at high magnetic fields in the marginal charge-density-wave system $α$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ (where $M=$~K and Rb),"Single crystals of the organic charge-transfer salts
$\alpha$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ have been studied using Hall-potential
measurements ($M=$K) and magnetization experiments ($M$ = K, Rb). The data show
that two types of screening currents occur within the high-field,
low-temperature CDW$_x$ phases of these salts in response to time-dependent
magnetic fields. The first, which gives rise to the induced Hall potential, is
a free current (${\bf j}_{\rm free}$), present at the surface of the sample.
The time constant for the decay of these currents is much longer than that
expected from the sample resistivity. The second component of the current
appears to be magnetic (${\bf j}_{\rm mag}$), in that it is a microscopic,
quasi-orbital effect; it is evenly distributed within the bulk of the sample
upon saturation. To explain these data, we propose a simple model invoking a
new type of quantum fluid comprising a CDW coexisting with a two-dimensional
Fermi-surface pocket which describes the two types of current. The model and
data are able to account for the body of previous experimental data which had
generated apparently contradictory interpretations in terms of the quantum Hall
effect or superconductivity.",0311362v1
2004-05-08,Magnetic phases of $t-J$ model on triangular lattice,"We study the magnetic properties of the $t-J$ model on triangular lattice in
light of the recently discovered superconductivity in Na$_{x}$CoO$_{2}$ system.
  We formulate the problem in the Schwinger Boson - slave Fermion scheme and
proposed a sound mean field ansatz(canting ansatz) for the RVB order
parameters. Working with the canting ansatz, we map out the temperature-doping
phase diagram of the model for both sign of the hopping term. We find the
prediction of the $t-J$ model differ drastically from that of earlier LSDA
calculation and there is large doping range in which the system show zero net
magnetization, rather than saturated magnetization as predicted in the LSDA
calculation. We show the result of LSDA is unreliable in the strong coupling
regime due to its neglect of electron correlation. We find the spin Berry phase
play a vital role in this geometrically frustrated system and the various
states in the phases diagram are characterized(and distinguished) by their
respective spin Berry phase, rather than any Landau-like order parameter
related to broken symmetry. We find the spin Berry phase is responsible for the
qualitative difference in the low energy excitation spectrum of the various
states of the phase diagram. We argue the phase boundary in the mean field
phase diagram may serve as the first explicit and realistic example for phase
transition between states with different quantum orders which in our case is
nothing but the spin Berry phase. We also find an exotic state with nonzero
spin chirality but no spin ordering is stable in a large temperature and doping
range and find.......",0405164v1
2004-06-02,Orbital and magnetic transitions in geometrically-frustrated vanadium spinels -- Monte Carlo study of an effective spin-orbital-lattice coupled model --,"We present our theoretical and numerical results on thermodynamic properties
and the microscopic mechanism of two successive transitions in vanadium spinel
oxides $A$V$_2$O$_4$ ($A$=Zn, Mg, or Cd) obtained by Monte Carlo calculations
of an effective spin-orbital-lattice model in the strong correlation limit.
Geometrical frustration in the pyrochlore lattice structure of V cations
suppresses development of spin and orbital correlations, however, we find that
the model exhibits two transitions at low temperatures. First, a discontinuous
transition occurs with an orbital ordering assisted by the tetragonal
Jahn-Teller distortion. The orbital order reduces the frustration in spin
exchange interactions, and induces antiferromagnetic correlations in
one-dimensional chains lying in the perpendicular planes to the tetragonal
distortion. Secondly, at a lower temperature, a three-dimensional
antiferromagnetic order sets in continuously, which is stabilized by the
third-neighbor interaction among the one-dimensional antiferromagnetic chains.
Thermal fluctuations are crucial to stabilize the collinear magnetic state by
the order-by-disorder mechanism. The results well reproduce the experimental
data such as transition temperatures, temperature dependence of the magnetic
susceptibility, changes of the entropy at the transitions, and the magnetic
ordering structure at low temperatures. Quantum fluctuation effect is also
examined by the linear spin wave theory at zero temperature. The staggered
moment in the ground state is found to be considerably reduced from saturated
value, and reasonably agrees with the experimental data.",0406039v1
2004-12-23,Quantum magnetism in two dimensions: From semi-classical Néel order to magnetic disorder,"This is a review of ground-state features of the s=1/2 Heisenberg
antiferromagnet on two-dimensional lattices. A central issue is the interplay
of lattice topology (e.g. coordination number, non-equivalent nearest-neighbor
bonds, geometric frustration) and quantum fluctuations and their impact on
possible long-range order. This article presents a unified summary of all 11
two-dimensional uniform Archimedean lattices which include e.g. the square,
triangular and kagome lattice. We find that the ground state of the spin-1/2
Heisenberg antiferromagnet is likely to be semi-classically ordered in most
cases. However, the interplay of geometric frustration and quantum fluctuations
gives rise to a quantum paramagnetic ground state without semi-classical
long-range order on two lattices which are precisely those among the 11 uniform
Archimedean lattices with a highly degenerate ground state in the classical
limit. The first one is the famous kagome lattice where many low-lying singlet
excitations are known to arise in the spin gap. The second lattice is called
star lattice and has a clear gap to all excitations.
  Modification of certain bonds leads to quantum phase transitions which are
also discussed briefly. Furthermore, we discuss the magnetization process of
the Heisenberg antiferromagnet on the 11 Archimedean lattices, focusing on
anomalies like plateaus and a magnetization jump just below the saturation
field. As an illustration we discuss the two-dimensional Shastry-Sutherland
model which is used to describe SrCu2(BO3)2.",0412662v2
2006-09-15,Magnetic properties of iron nanoparticles prepared by exploding wire technique,"Nanoparticles of iron were prepared in distilled water using very thin iron
wires and sheets, by the electro-exploding wire technique. Transmission
electron microscopy reveals the size of the nanoparticles to be in the range 10
to 50 nm. However, particles of different sizes can be segregated by using
ultrahigh centrifuge. X-ray diffraction studies confirm the presence of the
cubic phase of iron. These iron nanoparticles were found to exhibit
fluorescence in the visible region in contrast to the normal bulk material. The
room temperature hysteresis measurements upto a field of 1.0 tesla were
performed on a suspension of iron particles in the solution as well as in the
powders obtained by filtration. The hysteresis loops indicate that the
particles are superparamagnetic in nature. The saturation magnetizations was ~
60 emu / gm. As these iron particles are very sensitive to oxygen a coating of
non-magnetic iron oxide tends to form around the particles giving it a core -
shell structure. The core particle size is estimated theoretically from the
magnetization measurements. Suspensions of iron nanoparticles in water have
been proposed to be used as an effective decontaminant for ground water.",0609370v1
2007-02-10,Direct measurement of antiferromagnetic domain fluctuations,"Measurements of magnetic noise emanating from ferromagnets due to domain
motion were first carried out nearly 100 years ago and have underpinned much
science and technology. Antiferromagnets, which carry no net external magnetic
dipole moment, yet have a periodic arrangement of the electron spins extending
over macroscopic distances, should also display magnetic noise, but this must
be sampled at spatial wavelengths of order several interatomic spacings, rather
than the macroscopic scales characteristic of ferromagnets. Here we present the
first direct measurement of the fluctuations in the nanometre-scale spin-
(charge-) density wave superstructure associated with antiferromagnetism in
elemental Chromium. The technique used is X-ray Photon Correlation
Spectroscopy, where coherent x-ray diffraction produces a speckle pattern that
serves as a ""fingerprint"" of a particular magnetic domain configuration. The
temporal evolution of the patterns corresponds to domain walls advancing and
retreating over micron distances. While the domain wall motion is thermally
activated at temperatures above 100K, it is not so at lower temperatures, and
indeed has a rate which saturates at a finite value - consistent with quantum
fluctuations - on cooling below 40K. Our work is important because it provides
an important new measurement tool for antiferromagnetic domain engineering as
well as revealing a fundamental new fact about spin dynamics in the simplest
antiferromagnet.",0702265v1
2005-12-12,Multi-monopoles and Magnetic Bags,"By analogy with the multi-vortices, we show that also multi-monopoles become
magnetic bags in the large n limit. This simplification allows us to compute
the spectrum and the profile functions by requiring the minimization of the
energy of the bag. We consider in detail the case of the magnetic bag in the
limit of vanishing potential and we find that it saturates the Bogomol'nyi
bound and there is an infinite set of different shapes of allowed bags. This is
consistent with the existence of a moduli space of solutions for the BPS
multi-monopoles. We discuss the string theory interpretation of our result and
also the relation between the 't Hooft large n limit of certain supersymmetric
gauge theories and the large n limit of multi-monopoles. We then consider
multi-monopoles in the cosmological contest and provide a mechanism that could
lead to their production.",0512133v3
2005-09-14,Why dynamos are prone to reversals,"In a recent paper (Phys. Rev. Lett. 94 (2005), 184506; physics/0411050) it
was shown that a simple mean-field dynamo model with a spherically symmetric
helical turbulence parameter alpha can exhibit a number of features which are
typical for Earth's magnetic field reversals. In particular, the model produces
asymmetric reversals, a positive correlation of field strength and interval
length, and a bimodal field distribution. All these features are attributable
to the magnetic field dynamics in the vicinity of an exceptional point of the
spectrum of the non-selfadjoint dynamo operator. The negative slope of the
growth rate curve between the nearby local maximum and the exceptional point
makes the system unstable and drives it to the exceptional point and beyond
into the oscillatory branch where the sign change happens. A weakness of this
reversal model is the apparent necessity to fine-tune the magnetic Reynolds
number and/or the radial profile of alpha. In the present paper, it is shown
that this fine-tuning is not necessary in the case of higher supercriticality
of the dynamo. Numerical examples and physical arguments are compiled to show
that, with increasing magnetic Reynolds number, there is strong tendency for
the exceptional point and the associated local maximum to move close to the
zero growth rate line. Although exemplified again by the spherically symmetric
alpha^2 dynamo model, the main idea of this ''self-tuning'' mechanism of
saturated dynamos into a reversal-prone state seems well transferable to other
dynamos. As a consequence, reversing dynamos might be much more typical and may
occur much more frequently in nature than what could be expected from a purely
kinematic perspective.",0509118v1
2007-11-04,Torque magnetometry study of metamagnetic transitions in single-crystal HoNi2B2C at T\approx 1.9 K,"Metamagnetic transitions in single-crystal rare-earth nickel borocarbide
HoNi$_2$B$_2$C have been studied at T\approx 1.9 K with a Quantum Design torque
magnetometer. This compound is highly anisotropic with a variety of
metamagnetic states at low temperature which includes antiferromagnetic,
ferrimagnetic, non-collinear and ferromagnetic-like (saturated paramagnet)
states. The critical fields of the transitions depend crucially on the angle
$\theta$ between applied field and the easy axis [110]. Measurements of torque
along the c-axis have been made while changing the angular direction of the
magnetic field (parallel to basal tetragonal $ab$-planes) and with changing
field at fixed angle over a wide angular range. Two new phase boundaries in the
region of the non-collinear phase have been observed, and the direction of the
magnetization in this phase has been precisely determined. At low field the
antiferromagnetic phase is observed to be multidomain. In the angular range
very close to the hard axis [100] ($-6^{\circ} \lesssim\phi \lesssim
6^{\circ}$, where $\phi$ is the angle between field and the hard axis) the
magnetic behavior is found to be ``frustrated'' with a mixture of phases with
different directions of the magnetization.",0711.0533v1
2008-02-13,Magnetoresistance behavior of a ferromagnetic shape memory alloy: Ni_1.75Mn_1.25Ga,"A negative-positive-negative switching behavior of magnetoresistance (MR)
with temperature is observed in a ferromagnetic shape memory alloy
Ni_1.75Mn_1.25Ga. In the austenitic phase between 300 and 120 K, MR is negative
due to s-d scattering. Curiously, below 120K MR is positive, while at still
lower temperatures in the martensitic phase, MR is negative again. The positive
MR cannot be explained by Lorentz contribution and is related to a magnetic
transition. Evidence for this is obtained from ab initio density functional
theory, a decrease in magnetization and resistivity upturn at 120 K. Theory
shows that a ferrimagnetic state with anti-ferromagnetic alignment between the
local magnetic moments of the Mn atoms is the energetically favoured ground
state. In the martensitic phase, there are two competing factors that govern
the MR behavior: a dominant negative trend up to the saturation field due to
the decrease of electron scattering at twin and domain boundaries; and a weaker
positive trend due to the ferrimagnetic nature of the magnetic state. MR
exhibits a hysteresis between heating and cooling that is related to the first
order nature of the martensitic phase transition.",0802.1801v2
2008-04-23,Size induced change-over from first to second order magnetic phase transition in La0.67Ca0.33MnO3 nanoparticles,"In this report we show that in the perovskite manganite La_{1-x}Ca_{x}MnO_3
for a fixed x \approx 0.33, the magnetic transition changes over from first
order to second order on reducing the particle size to nearly few tens of a
nanometer. The change-over is brought about only by reducing the size and with
no change in the stoichiometry. The size reduction to an average size of about
15 nm retains the ferromagnetic state albeit with somewhat smaller saturation
magnetization and the ferromagnetic transition temperature T_{C} is suppressed
by a small amount (4%). The magnetization of the nanoparticles near T_{C}
follow the scaling equation $M/|\epsilon|^\beta =
f_\pm(H/|\epsilon|^{\gamma+\beta})$, where, $\epsilon = |T-T_C|/T_C$. The
critical exponents, associated with the transition have been obtained from
modified Arrott plots and they are found to be $\beta=0.47\pm 0.01$ and
$\gamma=1.06\pm 0.03$. From a plot of M vs H at T_{C} we find the exponent
$\delta=3.10 \pm 0.13$. All the exponents are close to the mean field values.
The change-over of the order of the transition has been attributed to a
lowering of the value of the derivative dT_{C}/dP due to an increased pressure
in the nanoparticles arising due to size reduction. This effect acts in tandem
with the rounding off effect due to random strain in the nanoparticles.",0804.3641v1
2008-04-26,Magnetic phases evolution in the LaMn1-xFexO3+y system,"We have investigated the crystal structure and magnetic properties for
polycrystalline samples of LaMn1-xFexO3+y, in the whole range x=0.0 to x=1.0,
prepared by solid state reaction in air. All samples show the ORT-2
orthorhombic structure that suppresses the Jahn-Teller distortion, thus
favoring a ferromagnetic (FM) superexchange (SE) interaction between
Mn^{3+}-O-Mn^{3+}. For x=0.0 the oxygen excess (y ~ 0.09) produces vacancies in
the La and Mn sites and generates a fraction around 18% of Mn^{4+} ions and 82%
of the usual Mn^{3+} ions, with possible double exchange interaction between
them. The Fe doping in this system is known to produce only stable Fe^{3+}
ions. We find an evolution from a fairly strong FM phase with a Curie
temperature T_{C} ~ 160 K, for x=0.0, to an antiferromagnetic (AFM) phase with
T_{N} = 790 K, for x=1.0, accompanied by clear signatures of a cluster-glass
behavior. For intermediate Fe contents a mixed-phase state occurs, with a
gradual decrease (increase) of the FM (AFM) phase, accompanied by a systematic
transition broadening for 0.2 < x < 0.7. A model based on the expected exchange
interaction among the various magnetic-ion types, accounts very well for the
saturation-magnetization dependence on Fe doping.",0804.4250v1
2008-06-01,3-d resistive MHD simulations of magnetic reconnection and the tearing mode instability in current sheets,"Magnetic reconnection plays a critical role in many astrophysical processes
where high energy emission is observed, e.g. particle acceleration,
relativistic accretion powered outflows, pulsar winds and probably in
dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of
energy and can dissipate its energy to thermal and kinetic energy via the
tearing mode instability. We have performed 3d nonlinear MHD simulations of the
tearing mode instability in a current sheet. Results from a temporal stability
analysis in both the linear regime and weakly nonlinear (Rutherford) regime are
compared to the numerical simulations. We observe magnetic island formation,
island merging and oscillation once the instability has saturated. The growth
in the linear regime is exponential in agreement with linear theory. In the
second, Rutherford regime the island width grows linearly with time. We find
that thermal energy produced in the current sheet strongly dominates the
kinetic energy. Finally preliminary analysis indicates a P(k) 4.8 power law for
the power spectral density which suggests that the tearing mode vortices play a
role in setting up an energy cascade.",0806.0144v1
2008-06-26,Ferromagnetic resonance force spectroscopy of individual sub-micron size samples,"We review how a magnetic resonance force microscope (MRFM) can be applied to
perform ferromagnetic resonance (FMR) spectroscopy of \emph{individual}
sub-micron size samples. We restrict our attention to a thorough study of the
spin-wave eigen-modes excited in permalloy (Py) disks patterned out of the same
43.3 nm thin film. The disks have a diameter of either 1.0 or $0.5 \mu$m and
are quasi-saturated by a perpendicularly applied magnetic field. It is shown
that \emph{quantitative} spectroscopic information can be extracted from the
MRFM measurements. In particular, the data are extensively compared with
complementary approximate models of the dynamical susceptibility: i) a 2D
analytical model, which assumes an homogeneous magnetization dynamics along the
thickness and ii) a full 3D micromagnetic simulation, which assumes an
homogeneous magnetization dynamics below a characteristic length scale $c$ and
which approximates the cylindrical sample volume by a discretized
representation with regular cubic mesh of lateral size $c=3.9$ nm. In our
analysis, the distortions due to a breaking of the axial symmetry are taken
into account, both models incorporating the possibility of a small misalignment
between the applied field and the normal of the disks.",0806.4244v1
2008-07-22,"Microphysical dissipation, turbulence and magnetic fields in hyper-accreting discs","Hyper-accreting discs occur in compact-object mergers and collapsars, and may
power gamma-ray bursts (GRBs). We calculate the microscopic viscosity and
resistivity of plasma in these discs, and discuss the implications for their
global structure and evolution. In the neutrino-cooled innermost regions, the
viscosity is provided mainly by mildly degenerate electrons, while the
resistivity is modified from the Spitzer value due to the effects of both
relativity and degeneracy. The plasma behaves as an almost ideal MHD fluid.
Among the non-ideal MHD effects the Hall term is relatively the most important,
while the magnetic Prandtl number, Pr (the ratio of viscosity to resistivity),
is typically larger than unity: 10 < Pr < 6000. The outer radiatively
inefficient regions also display high Pr. Numerical simulations of the
magneto-rotational instability indicate that the saturation level and angular
momentum transport efficiency may be greatly enhanced at high Pr. If this
behaviour persists in the presence of a strong Hall effect we would expect that
hyper-accreting discs should be strongly magnetised and highly variable. The
expulsion of magnetic field that cannot be dissipated at small scales may also
favour a magnetic outflow. We note the similaries between the Prandtl number in
hyper-accreting discs and X-ray binary discs, which suggests that a comparison
between late-time activity in GRBs and X-ray binary accretion states may be
fruitful. Our results imply that the behavior of high Prandtl number MHD flows
needs to be considered in studies of hyper-accreting discs.",0807.3547v2
2008-11-24,Three-Dimensional Relativistic MHD Simulations of the Kelvin-Helmholtz Instability: Magnetic Field Amplification by a Turbulent Dynamo,"Magnetic field strengths inferred for relativistic outflows including
gamma-ray bursts (GRB) and active galactic nuclei (AGN) are larger than naively
expected by orders of magnitude. We present three-dimensional relativistic
magnetohydrodynamics (MHD) simulations demonstrating amplification and
saturation of magnetic field by a macroscopic turbulent dynamo triggered by the
Kelvin-Helmholtz shear instability. We find rapid growth of electromagnetic
energy due to the stretching and folding of field lines in the turbulent
velocity field resulting from non-linear development of the instability. Using
conditions relevant for GRB internal shocks and late phases of GRB afterglow,
we obtain amplification of the electromagnetic energy fraction to $\epsilon_B
\sim 5 \times 10^{-3}$. This value decays slowly after the shear is dissipated
and appears to be largely independent of the initial field strength. The
conditions required for operation of the dynamo are the presence of velocity
shear and some seed magnetization both of which are expected to be commonplace.
We also find that the turbulent kinetic energy spectrum for the case studied
obeys Kolmogorov's 5/3 law and that the electromagnetic energy spectrum is
essentially flat with the bulk of the electromagnetic energy at small scales.",0811.3638v2
2009-02-17,A Model for Emission from Jets in X-ray Binaries: Consequences of a Single Acceleration Episode,"There are strong evidence for powerful jets in the low/hard state of
black-hole X-ray binaries (BHXRBs). Here, we present a model in which electrons
are accelerated once at the base of the jet, and are cooled by synchrotron
emission and possible adiabatic energy losses. The accelerated electrons assume
a Maxwellian distribution at low energies and possible energetic power law
tail. These assumptions yield to a wealth of spectra, which we study in
details. We identify critical values of the magnetic field, and five transition
frequencies in the spectra. In particular, we show that: (I) the decay of the
magnetic field along the jet enables, for wide jets, production of flat radio
spectra without the need for electrons re-acceleration along the jet. (II) An
increase of the magnetic field above a critical value of ~10^5 G leads to a
sharp decrease in the flux at the radio band, while the flux at higher
frequencies saturates to a constant value. (III) For strong magnetic field, the
flux decays in the optical/UV band as F_nu ~ nu^{-1/2}, irrespective of the
electrons initial distribution. (IV) For B_0 ~ 10^4 G, the X-ray flux gradually
steepens. (V) With adiabatic energy losses, flat spectrum can be obtained only
at a limited frequency range, and under certain conditions (VI) For narrow
jets, r(x) ~ x^{alpha} with alpha < 1/2, flat radio spectrum cannot be
obtained. We provide full description of the spectrum in the different
scenarios, and show that our model is consistent with the key observed
properties of BHXRBs.",0902.2892v2
2009-06-16,"The Meissner Effect and Vortex Expulsion in Color-Superconducting Quark stars, and its Role for Re-heating of Magnetars","Compact stars made of quark matter rather than confined hadronic matter, are
expected to form a color superconductor. This superconductor ought to be
threaded with rotational vortex lines, within which the star's interior
magnetic field is at least partially confined. The vortices (and thus magnetic
flux) would be expelled from the star during stellar spin-down, leading to
magnetic reconnection at the surface of the star and the prolific production of
thermal energy. In this paper, we show that this energy release can re-heat
quark stars to exceptionally high temperatures, such as observed for Soft Gamma
Repeaters (SGRs), Anomalous X-Ray pulsars (AXPs), and X-ray dim isolated
neutron stars (XDINs). Moreover, our numerical investigations of the
temperature evolution, spin-down rate, and magnetic field behavior of such
superconducting quark stars suggest that SGRs, AXPs, and XDINs may be linked
ancestrally. Finally, we discuss the possibility of a time delay before the
star enters the color superconducting phase, which can be used to estimate the
density at which quarks deconfine. From observations, we find this density to
be of the order of five times that of nuclear saturation.",0906.3043v2
2009-06-26,High-field magnetization of a two dimensional spin frustration system Ni$_{5}$(TeO$_{3}$)$_{4}$X$_{2}$ (X = Br and Cl),"High-field magnetization, M($H$), on Ni$_{5}$(TeO$_{3}$)$_{4}$X$_{2}$ (X = Br
and Cl) were measured by using a pulse magnet. These compounds have a two
dimensional crystal structure and a distorted kagome spin frustrated system
which is builded by the Ni$^{2+}$ ions ($\textbf{S}$ = 1). The N\'eel
transition temperatures are $T_{N} \sim$ 28 and 23 K for X = Br and Cl,
respectively. When $T < T_{N}$, we observed a step-like transition at $H_{c}
\sim$ 11 and 10 T for X = Br and Cl, respectively. On the other hand, at $T >
T_{N}$, the field-dependent magnetization curves behaved like a monotonically
increasing straight line up to 55 T. The $H_{c}$ value is close to those
obtained by previous spin resonance studies in which a model of spin-flop
scenario was proposed to explain the field-dependent resonance spectra. Their
model predicts a further transition at around 23 T, however, our observations
did not show any plateau behaviors, saturation or other anomalies up to 55 T,
suggesting that the further transition possibly exists at a much higher field
region.",0906.4856v1
2009-07-12,Odd triplet superconductivity in clean and moderately disordered SFFS junctions,"We study the Josephson effect and pairing correlations in SFFS junctions that
consist of conventional superconductors (S) connected through two metallic
monodomain ferromagnets (F) with transparent and spin inactive interfaces. We
solve the Eilenberger equations for arbitrary relative orientation of
magnetizations of the two F layers in the clean limit and for moderate disorder
in ferromagnets. Spatial variation of pair amplitudes, singlet $f_s$, and odd
in frequency triplet $f_{t0}$ and $f_{t1}$, with 0 and $\pm1$ spin projections,
as well as the Josephson current-phase relations are calculated for different
values of the ferromagnetic layers thickness and angle $\alpha$ between
in-plane magnetizations. In contrast to the dirty limit case, we find that for
$0<\alpha<\pi$ both spin singlet and triplet pair amplitudes in F layers
power-law decay in the same oscillatory manner with distance from the FS
interfaces. This decay gets faster as the impurity-scattering rate in
ferromagnets is increased. The computed triplet amplitude $f_{t1}$ has opposite
signs in the two magnet regions, penetrates into the superconductors and
monotonically decays over the same distance, which is the superconducting
coherence length, as the singlet amplitude $f_s$ saturates to the bulk value.
We point out that influence of misorientation of magnetizations on the
Josephson current can not be attributed directly to the appearance of odd
triplet correlations.",0907.2042v1
2009-12-22,Impurity effects in coupled-ladder BiCu2PO6 studied by NMR and quantum Monte Carlo simulations,"We present a 31P NMR study of the coupled spin 1/2 ladder compound BiCu2PO6.
In the pure material, intrinsic susceptibility and dynamics show a spin gap of
about . Substitution of non magnetic Zn or magnetic Ni impurity at Cu site
induces a staggered magnetization which results in a broadening of the 31P NMR
line, while susceptibility far from the defects is unaffected. The effect of Ni
on the NMR line broadening is twice that of Zn, which is consistent with
Quantum Monte Carlo (QMC) calculations assuming that Ni couples
ferromagnetically to its adjacent Cu. The induced moment follows a 1/T
temperature dependence due to the Curie-like development of the moment
amplitude while its extension saturates and does not depend on impurity content
or nature. This allow us to verify the generically expected scenario for
impurity doping and to extend it to magnetic impurity case: in an
antiferromagnetically correlated low dimensional spin system with
antiferromagnetic correlations, any type of impurity induces a staggered moment
at low temperature, whose extension is not linked to the impurity nature but to
the intrinsic physics at play in the undoped pure system, from 1D to 2D
systems.",0912.4353v3
2010-07-28,Vortex Dynamics in Color-Superconducting Quark stars: The Re-heating of Magnetars,"Compact stars made of quark matter rather than confined hadronic matter, are
expected to form a color superconductor. This superconductor ought to be
threaded with rotational vortex lines within which the star's interior magnetic
field is confined. The vortices (and thus magnetic flux) would be expelled from
the star during stellar spin-down, leading to magnetic reconnection at the
surface of the star and the prolific production of thermal energy. In this
Letter, we show that this energy release can re-heat quark stars to
exceptionally high temperatures, such as observed for Soft Gamma Repeaters
(SGRs), Anomalous X-Ray pulsars (AXPs), and X-ray dim isolated neutron stars
(XDINs). Moreover, our numerical investigations of the temperature evolution,
spin-down rate, and magnetic field behavior of such superconducting quark stars
suggest that SGRs, AXPs, and XDINs may be linked ancestrally. Finally, we
discuss the possibility of a time delay before the star enters the color
superconducting phase, which can be used to estimate the density at which
quarks deconfine. We find this density to be five times that of nuclear
saturation.",1007.4860v1
2010-08-07,T=0 phase diagram and nature of domains in ultrathin ferromagnetic films with perpendicular anisotropy,"We present the complete zero temperature phase diagram of a model for
ultrathin films with perpendicular anisotropy. The whole parameter space of
relevant coupling constants is studied in first order anisotropy approximation.
Because the ground state is known to be formed by perpendicular stripes
separated by Bloch walls, a standard variational approach is used, complemented
with specially designed Monte Carlo simulations. We can distinguish four
regimes according to the different nature of striped domains: a high anisotropy
Ising regime with sharp domain walls, a saturated stripe regime with thicker
walls inside which an in-plane component of the magnetization develops, a
narrow canted-like regime, characterized by a sinusoidal variation of both the
in-plane and the out of plane magnetization components, which upon further
decrease of the anisotropy leads to an in-plane ferromagnetic state via a spin
reorientation transition (SRT). The nature of domains and walls are described
in some detail together with the variation of domain width with anisotropy, for
any value of exchange and dipolar interactions. Our results, although strictly
valid at $T=0$, can be valuable for interpreting data on the evolution of
domain width at finite temperature, a still largely open problem.",1008.1353v1
2010-11-02,Electron transport and anisotropy of the upper critical magnetic field in a Ba0.68K0.32Fe2As2 single crystals,"Early work on the iron-arsenide compounds supported the view, that a reduced
dimensionality might be a necessary prerequisite for high-Tc superconductivity.
Later, however, it was found that the zero-temperature upper critical magnetic
field, Hc2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we
report measurements of the temperature dependence of the electrical
resistivity, \Gamma(T), in Ba0.5K0.5Fe2As2 and Ba0.68K0.32Fe2As2 single
crystals in zero magnetic field and for Ba0.68K0.32Fe2As2 as well in static and
pulsed magnetic fields up to 60 T. We find that the resistivity of both
compounds in zero field is well described by an exponential term due to
inter-sheet umklapp electron-phonon scattering between light electrons around
the M point to heavy hole sheets at the \Gamma point in reciprocal space. From
our data, we construct an H-T phase diagram for the inter-plane (H || c) and
in-plane (H || ab) directions for Ba0.68K0.32Fe2As2. Contrary to published data
for underdoped 122 FeAs compounds, we find that Hc2(T) is in fact anisotropic
in optimally doped samples down to low temperatures. The anisotropy parameter,
{\gamma} = Habc2/Hcc2, is about 2.2 at Tc. For both field orientations we find
a concave curvature of the Hc2 lines with decreasing anisotropy and saturation
towards lower temperature. Taking into account Pauli spin paramagnetism we
perfectly can describe Hc2(T) and its anisotropy.",1011.0698v1
2011-03-11,Optimized fabrication of high quality La0.67Sr0.33MnO3 thin films considering all essential characteristics,"In this article, an overview of the fabrication and properties of high
quality La0.67Sr0.33MnO3 (LSMO) thin films is given. A high quality LSMO film
combines a smooth surface morphology with a large magnetization and a small
residual resistivity, while avoiding precipitates and surface segregation. In
literature, typically only a few of these issues are adressed. We therefore
present a thorough characterization of our films, which were grown by pulsed
laser deposition. The films were characterized with reflection high energy
electron diffraction, atomic force microscopy, x-ray diffraction, magnetization
and transport measurements, x-ray photoelectron spectroscopy and scanning
transmission electron microscopy. The films have a saturation magnetization of
4.0 {\mu}B/Mn, a Curie temperature of 350 K and a residual resistivity of 60
{\mu}{\Omega}cm. These results indicate that high quality films, combining both
large magnetization and small residual resistivity, were realized. A comparison
between different samples presented in literature shows that focussing on a
single property is insufficient for the optimization of the deposition process.
For high quality films, all properties have to be adressed. For LSMO devices,
the thin film quality is crucial for the device performance. Therefore, this
research is important for the application of LSMO in devices.",1103.2267v1
2011-08-09,Numerical Simulations of Driven Relativistic MHD Turbulence,"A wide variety of astrophysical phenomena involve the flow of turbulent
magnetized gas with relativistic velocity or energy density. Examples include
gamma-ray bursts, active galactic nuclei, pulsars, magnetars, micro-quasars,
merging neutron stars, X-ray binaries, some supernovae, and the early universe.
In order to elucidate the basic properties of the relativistic
magnetohydrodynamical (RMHD) turbulence present in these systems, we present
results from numerical simulations of fully developed driven turbulence in a
relativistically warm, weakly magnetized and mildly compressible ideal fluid.
We have evolved the RMHD equations for many dynamical times on a uniform grid
with 1024^3 zones using a high order Godunov code. We observe the growth of
magnetic energy from a seed field through saturation at about 1% of the total
fluid energy. We compute the power spectrum of velocity and density-weighted
velocity and conclude that the inertial scaling is consistent with a slope of
-5/3. We compute the longitudinal and transverse velocity structure functions
of order p up to 11, and discuss their possible deviation from the expected
scaling for non-relativistic media. We also compute the scale-dependent
distortion of coherent velocity structures with respect to the local magnetic
field, finding a weaker scale dependence than is expected for incompressible
non-relativistic flows with a strong mean field.",1108.1991v2
2011-08-19,Structure and magnetic properties of nanostructured Pd-Fe thin films produced by pulse electrodeposition,"Nanostructured Pd-Fe thin films with varied Fe content were prepared by
electrodeposition technique from organic electrolytes on Cu and brass
substrates. The structure and the magnetic properties of the films were
investigated prior to post-deposition annealing. The structure of the Pd1-xFex
thin films with x = 0.14, 0.24, and 0.52 was determined by X-ray diffraction
(XRD) and transmission electron microscopy (TEM) as a solid solution of iron in
palladium face-centered cubic lattice with the (111) orientation of nanograins
relatively to the substrate surface. The films with higher iron concentration,
x = 0.74, 0.91, have structure of a solid solution based on the body-centered
cubic lattice. The average grain size determined by the scanning electron
microscopy (SEM) for the first two alloys is 7-10 nm, and for the latter ones
it is about 120 nm. The saturation magnetization of the films has linear
dependence on the iron content, but coercivity has non-monotonic dependence on
x, i.e. the films with x = 0.68 show highest coercivity. The magnetic
anisotropy of the samples is studied by ferromagnetic resonance (FMR)
spectroscopy.",1108.3888v1
2011-09-15,Surface impedance of superconductors with magnetic impurities,"Motivated by the problem of the residual surface resistance of the
superconducting radio-frequency (SRF) cavities, we develop a microscopic theory
of the surface impedance of s-wave superconductors with magnetic impurities. We
analytically calculate the current response function and surface impedance for
a sample with spatially uniform distribution of impurities, treating magnetic
impurities in the framework of the Shiba theory. The obtained general
expressions hold in a wide range of parameter values, such as temperature,
frequency, mean free path, and exchange coupling strength. This generality, on
the one hand, allows for direct numerical implementation of our results to
describe experimental systems (SRF cavities, superconducting qubits) under
various practically relevant conditions. On the other hand, explicit analytical
expressions can be obtained in a number of limiting cases, which makes possible
further theoretical investigation of certain regimes. As a feature of key
relevance to SRF cavities, we show that in the regime of ""gapless
superconductivity"" the surface resistance exhibits saturation at zero
temperature. Our theory thus explicitly demonstrates that magnetic impurities,
presumably contained in the oxide surface layer of the SRF cavities, provide a
microscopic mechanism for the residual resistance.",1109.3395v2
2011-10-03,Magnetic and density spikes in cosmic ray shock precursors,"In shock precursors populated by accelerated cosmic rays (CR), the CR return
current instability is believed to significantly enhance the pre-shock
perturbations of magnetic field. We have obtained fully-nonlinear exact ideal
MHD solutions supported by the CR return current. The solutions occur as
localized spikes of circularly polarized Alfven envelopes (solitons, or
breathers). As the conventional (undriven) solitons, the obtained magnetic
spikes propagate at a speed $C$ proportional to their amplitude,
$C=C_{A}B_{{\rm max}}/\sqrt{2}B_{0}$. The sufficiently strong solitons run thus
ahead of the main shock and stand in the precursor, being supported by the
return current. This property of the nonlinear solutions is strikingly
different from the linear theory that predicts non-propagating (that is,
convected downstream) circularly polarized waves. The nonlinear solutions may
come either in isolated pulses (solitons) or in soliton-trains (cnoidal waves).
The morphological similarity of such quasi-periodic soliton chains with
recently observed X-ray stripes in Tycho supernova remnant (SNR) is briefly
discussed. The magnetic field amplification determined by the suggested
saturation process is obtained as a function of decreasing SNR blast wave
velocity during its evolution from the ejecta-dominated to the Sedov-Taylor
stage.",1110.0257v1
2011-12-19,Magnetic Fields in Population III Star Formation,"We study the buildup of magnetic fields during the formation of Population
III star-forming regions, by conducting cosmological simulations from realistic
initial conditions and varying the Jeans resolution. To investigate this in
detail, we start simulations from identical initial conditions, mandating 16,
32 and 64 zones per Jeans length, and studied the variation in their magnetic
field amplification. We find that, while compression results in some
amplification, turbulent velocity fluctuations driven by the collapse can
further amplify an initially weak seed field via dynamo action, provided there
is sufficient numerical resolution to capture vortical motions (we find this
requirement to be 64 zones per Jeans length, slightly larger than, but
consistent with previous work run with more idealized collapse scenarios). We
explore saturation of amplification of the magnetic field, which could
potentially become dynamically important in subsequent, fully-resolved
calculations. We have also identified a relatively surprising phenomena that is
purely hydrodynamic: the higher-resolved simulations possess substantially
different characteristics, including higher infall-velocity, increased
temperatures inside 1000 AU, and decreased molecular hydrogen content in the
innermost region. Furthermore, we find that disk formation is suppressed in
higher-resolution calculations, at least at the times that we can follow the
calculation. We discuss the effect this may have on the buildup of disks over
the accretion history of the first clump to form as well as the potential for
gravitational instabilities to develop and induce fragmentation.",1112.4479v1
2012-02-14,Influence of e-e scattering on the temperature dependence of the resistance of a classical ballistic point contact in a two-dimensional electron system,"We experimentally investigate the temperature (T) dependence of the
resistance of a classical ballistic point contact (PC) in a two-dimensional
electron system (2DES). The split-gate PC is realized in a high-quality
AlGaAs/GaAs heterostructure. The PC resistance is found to drop by more than
10% as T is raised from 0.5 K to 4.2 K. In the absence of a magnetic field, the
T dependence is roughly linear below 2 K and tends to saturate at higher T.
Perpendicular magnetic fields on the order of a few 10 mT suppress the
T-dependent contribution dR. This effect is more pronounced at lower
temperatures, causing a crossover to a nearly parabolic T dependence in a
magnetic field. The normalized magnetic field dependencies dR(B) permit an
empiric single parameter scaling in a wide range of PC gate voltages. These
observations give strong evidence for the influence of electron-electron (e-e)
scattering on the resistance of ballistic PCs. Our results are in qualitative
agreement with a recent theory of the e-e scattering based T dependence of the
conductance of classical ballistic PCs [ Phys. Rev. Lett. 101 216807 (2008) and
Phys. Rev. B 81 125316 (2010)].",1202.2952v3
2012-08-21,High temperature structural and magnetic properties of cobalt nanowires,"We present in this paper the structural and magnetic properties of high
aspect ratio Co nanoparticles (~10) at high temperatures (up to 623 K) using in
situ X ray diffraction (XRD) and SQUID characterizations. We show that the
anisotropic shapes, the structural and texture properties are preserved up to
500 K. The coercivity can be modelled by u0Hc=2(Kmc+Kshape)/Ms with Kmc the
magnetocrystalline anisotropy constant, Kshape the shape anisotropy constant
and Ms the saturation magnetization. Hc decreases linearly when the temperature
is increased due to the loss of the Co magnetocrystalline anisotropy
contribution. At 500K, 50% of the room temperature coercivity is preserved
corresponding to the shape anisotropy contribution only. We show that the
coercivity drop is reversible in the range 300 - 500 K in good agreement with
the absence of particle alteration. Above 525 K, the magnetic properties are
irreversibly altered either by sintering or by oxidation.",1208.4403v2
2013-01-25,Magnetic penetration depth in single crystals of SrPd$_2$Ge$_2$ superconductor,"The in-plane magnetic penetration depth, $\lambda_m(T)$, was measured in
single crystals of SrPd$_2$Ge$_2$ superconductor in a dilution refrigerator
down to T=60 mK and in magnetic fields up to $H_{dc} = 1$ T by using a tunnel
diode resonator. The London penetration depth, $\lambda$, saturates
exponentially approaching $T\rightarrow 0$ indicating fully gapped
superconductivity. The thermodynamic Rutgers formula was used to estimate
$\lambda(0) = 426$ nm which was used to calculate the superfluid density,
$\rho_s(T)=\lambda^2(0)/\lambda^2(T)$. Analysis of $\rho_s(T)$ in the full
temperature range shows that it is best described by a single - gap behavior,
perhaps with somewhat stronger coupling. In a magnetic field, the measured
penetration depth is given by the Campbell penetration depth which was used to
calculate the theoretical critical current density $j_c$. For $H \le 0.45$ T,
the strongest pinning is achieved not at the lowest, but at some intermediate
temperature, probably due to matching effect between temperature - dependent
coherence length and relevant pinning lengthscale. Finally, we find a
compelling evidence for surface superconductivity. Combining all measurements,
the entire $H$-$T$ phase diagram of SrPd$_2$Ge$_2$ is constructed with an
estimated $H_{c2}(0)=0.4817$ T.",1301.6054v2
2013-01-28,Surfactant mediated growth of ferromagnetic Mn δ-doped Si,"We present an investigation of Mn {\delta}-doped layers in Si(001) grown by
molecular beam epitaxy. We discovered that a Pb surfactant has significant
effect on the structural and magnetic properties of the submonolayer of Mn,
which depends on the Si capping layer growth temperature, T_Si, and the Mn
coverage, {\theta}_Mn. The results presented in this paper identify three
regions in the growth-phase-diagram characterized by distinct magnetic
behaviors and crystal structures. In one region, X-ray absorption fine
structure (XAFS) and transmission electron microscopy (TEM) experiments
indicate that MnSi nanocrystallites form with B2-like crystal type structures.
At the optimal growth conditions, T_Si = 200 C and {\theta}_Mn = 0.26
monolayer, a ferromagnetic phase develops with a Curie temperature T_C > 400 K
and a saturation moment m_sat = 1.56 {\mu}_B/Mn, whereas T_C drops to zero for
a control sample prepared without Pb. For T_Si > 200 C, MnSi-B20 type
precipitates form with a T_C ~ 170 K. Rutherford backscattering spectroscopy
shows that the increase in the remanent magnetization in these two phases is
possibly correlated with an increase in the Mn substitutional fraction, which
suggests that a Si_{1-x}Mn_x dilute magnetic semiconductor may be forming in
the matrix between the precipitates. Density functional calculations show that
Pb changes the pathway by which the Mn atoms access the Si substitutional
sites, Mn_Si. While the Pb increases the formation energy of Mn_Si at the Si
surface, it enables substitutional incorporation by lowering the formation
energy of Si vacancies by 0.92 eV.",1301.6651v1
2013-07-27,Strain-induced effects on the magnetic and electronic properties of epitaxial Fe$_{1-x}$Co$_{x}$Si thin films,"We have investigated the Co-doping dependence of the structural, transport,
and magnetic properties of \epsilon-FeCoSi epilayers grown by molecular beam
epitaxy on silicon (111) substrates. Low energy electron diffraction, atomic
force microscopy, X-ray diffraction, and high resolution transmission electron
microscopy studies have confirmed the growth of phase-pure, defect-free
\epsilon-FeCoSi epitaxial films with a surface roughness of ~1 nm. These
epilayers are strained due to lattice mismatch with the substrate, deforming
the cubic B20 lattice so that it becomes rhombohedral. The temperature
dependence of the resistivity changes as the Co concentration is increased,
being semiconducting-like for low $x$ and metallic-like for x \gtrsim 0.3. The
films exhibit the positive linear magnetoresistance that is characteristic of
\epsilon-FeCoSi below their magnetic ordering temperatures $T_\mathrm{ord}$, as
well as the huge anomalous Hall effect of order several \mu\Omega cm. The
ordering temperatures are higher than those observed in bulk, up to 77 K for x
= 0.4. The saturation magnetic moment of the films varies as a function of Co
doping, with a contribution of ~1 \mu_{B}/ Co atom for x \lesssim 0.25. When
taken in combination with the carrier density derived from the ordinary Hall
effect, this signifies a highly spin-polarised electron gas in the low x,
semiconducting regime.",1307.7301v1
2013-08-16,Theory of metallic double perovskites with spin orbit coupling and strong correlations; application to ferrimagnetic Ba2FeReO6,"We consider a model of the double perovskite Ba2FeReO6, a room temperature
ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in
the background of Fe moments stabilized by Hund's coupling. We show that for
such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are
essential in driving a half-metallic ground state. Incorporating both strong
spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure
consistent with ab initio calculations. Using our model, we find a large spin
polarization at the Fermi level, and obtain a semi-quantitative understanding
of the saturation magnetization of Ba2FeReO6, as well as X-ray magnetic
circular dichroism data indicating a significant orbital magnetization. Based
on the orbital populations obtained in our theory, we predict a specific doping
dependence to the tetragonal distortion accompanying ferrimagnetic order.
Finally, the combination of a net magnetization and spin-orbit interactions is
shown to induce Weyl nodes in the band structure, and we predict a significant
intrinsic anomalous Hall effect in hole-doped Ba2FeReO6. The uncovered
interplay of strong correlations and spin-orbit coupling lends partial support
to our previous work, which used a local moment description to capture the spin
wave dispersion found in neutron scattering measurements. Our work is of broad
interest for understanding metallic 4d-based and 5d-based double perovskites
which are of fundamental interest and of possible relevance to spintronic
applications.",1308.3701v2
2013-08-30,Spin-polarized electronic structure of the core-shell ZnO/ZnO:Mn nanowires probed by x-ray absorption and emission spectroscopy,"The combination of x-ray spectroscopy methods complemented with theoretical
analysis unravels the coexistence of paramagnetic and antiferromagnetic phases
in the Zn_0.9Mn_0.1O shell deposited onto array of wurtzite ZnO nanowires. The
shell is crystalline with orientation toward the ZnO growth axis, as
demonstrated by X-ray linear dichroism. EXAFS analysis confirmed that more than
90% of Mn atoms substituted Zn in the shell while fraction of secondary phases
was below 10%. The value of manganese spin magnetic moment was estimated from
the Mn K{\beta} X-ray emission spectroscopy to be 4.3{\mu}B which is close to
the theoretical value for substitutional Mn_Zn. However the analysis of L_2,3
x-ray magnetic circular dichroism data showed paramagnetic behaviour with
saturated spin magnetic moment value of 1.95{\mu}B as determined directly from
the spin sum rule. After quantitative analysis employing atomic multiplet
simulations such difference was explained by a coexistence of paramagnetic
phase and local antiferromagnetic coupling of Mn magnetic moments. Finally,
spin-polarized electron density of states was probed by the spin-resolved Mn
K-edge XANES spectroscopy and consequently analyzed by band structure
calculations.",1308.6654v1
2013-10-25,Electronic properties of Co$_{2}$FeSi investigated by x-ray magnetic linear dichroism,"We present experimental XMLD spectra measured on epitaxial (001)-oriented
thin Co$_{2}$FeSi films, which are rich in features and depend sensitively on
the degree of atomic order and interdiffusion from capping layers. Al- and
Cr-capped films with different degrees of atomic order were prepared by DC
magnetron sputtering by varying the deposition temperatures. The local
structural properties of the film samples were additionally investigated by
nuclear magnetic resonance (NMR) measurements. The XMLD spectra of the
different samples show clear and uniform trends at the $L_{3,2}$ edges. The
Al-capped samples show similar behavior as previous measured XMLD spectra of
Co$_2$FeSi$_{0.6}$Al$_{0.4}$. Thus, we assume that during deposition Al atoms
are being implanted into the subsurface of Co$_{2}$FeSi. Such an interdiffusion
is not observed for the corresponding Cr-capped films, which makes Cr the
material of choice for capping Co$_{2}$FeSi films. We report stronger XMLD
intensities at the $L_{3,2}$ Co and Fe egdes for films with a higher saturation
magnetization. Additionally, we compare the spectra with \textit{ab initio}
predictions and obtain a reasonably good agreement. Furthermore, we were able
to detect an XMCD signal at the Si $L$-edge, indicating the presence of a
magnetic moment at the Si atoms.",1310.6910v3
2014-02-11,Spatial Growth of the Current-Driven Instability in Relativistic Jets,"We have investigated the influence of velocity shear and a radial density
profile on the spatial development of the current driven kink instability along
helically magnetized relativistic jets via three-dimensional relativistic
magnetohydrodynamic simulations. In this study, we use a non-periodic
computational box, the jet flow is initially established across the
computational grid, and a precessional perturbation at the inlet triggers
growth of the kink instability. If the velocity shear radius is located inside
the characteristic radius of the helical magnetic field, a static
non-propagating current driven kink is excited as the perturbation propagates
down the jet. Temporal growth disrupts the initial flow across the
computational grid not too far from the inlet. On the other hand, if the
velocity shear radius is outside the characteristic radius of the helical
magnetic field, the kink is advected with the flow and grows spatially down the
jet. In this case flow is maintained to much larger distances from the inlet.
The effect of different radial density profiles is more subtle. When the
density increases with radius, the kink appears to saturate by the end of the
simulation without apparent disruption of the helical twist. This behavior
suggests that relativistic jets consisting of a tenuous spine surrounded by a
denser medium with a velocity shear radius outside the radius of maximum
toroidal magnetic field have a relatively stable configuration.",1402.2370v1
2014-02-26,Mean-field dynamos: the old concept and some recent developments,"This article reproduces the Karl Schwarzschild lecture 2013. Some of the
basic ideas of electrodynamics and magnetohydrodynamics of mean fields in
turbulently moving conducting fluids are explained. It is stressed that the
connection of the mean electromotive force with the mean magnetic field and its
first spatial derivatives is in general neither local nor instantaneous and
that quite a few claims concerning pretended failures of the mean-field concept
result from ignoring this aspect. In addition to the mean-field dynamo
mechanisms of $\alpha^2$ and $\alpha$ $\Omega$ type several others are
considered. Much progress in mean-field electrodynamics and
magnetohydrodynamics results from the test-field method for calculating the
coefficients that determine the connection of the mean electromotive force with
the mean magnetic field. As an important example the memory effect in
homogeneous isotropic turbulence is explained. In magnetohydrodynamic
turbulence there is the possibility of a mean electromotive force that is
primarily independent of the mean magnetic field and labeled as Yoshizawa
effect. Despite of many efforts there is so far no convincing comprehensive
theory of $\alpha$ quenching, that is, the reduction of the $\alpha$ effect
with growing mean magnetic field, and of the saturation of mean-field dynamos.
Steps toward such a theory are explained. Finally, some remarks on laboratory
experiments with dynamos are made.",1402.6557v1
2014-07-08,Linear and nonlinear evolution of current-carrying highly magnetized jets,"We investigate the linear and nonlinear evolution of current-carrying jets in
a periodic configuration by means of high resolution three-dimensional
numerical simulations. The jets under consideration are strongly magnetized
with a variable pitch profile and initially in equilibrium under the action of
a force-free magnetic field. The growth of current-driven (CDI) and
Kelvin-Helmholtz (KHI) instabilities is quantified using three selected cases
corresponding to static, Alfvenic and super-Alfvenic jets.
  During the early stages, we observe large-scale helical deformations of the
jet corresponding to the growth of the initially excited CDI mode. A direct
comparison between our simulation results and the analytical growth rates
obtained from linear theory reveals good agreement on condition that
high-resolution and accurate discretization algorithms are employed.
  After the initial linear phase, the jet structure is significantly altered
and, while slowly-moving jets show increasing helical deformations, larger
velocity shear are violently disrupted on a few Alfven crossing time leaving a
turbulent flow structure. Overall, kinetic and magnetic energies are quickly
dissipated into heat and during the saturated regime the jet momentum is
redistributed on a larger surface area with most of the jet mass travelling at
smaller velocities. The effectiveness of this process is regulated by the onset
of KHI instabilities taking place at the jet/ambient interface and can be held
responsible for vigorous jet braking and entrainment.",1407.1962v1
2014-08-04,Strong evidences for a nonextensive behavior of the rotation period in Open Clusters,"Time-dependent nonextensivity in a stellar astrophysical scenario combines
nonextensive entropic indices $q_{K}$ derived from the modified Kawaler's
parametrization, and $q$, obtained from rotational velocity distribution. These
$q$'s are related through a heuristic single relation given by $q\approx
q_{0}(1-\Delta t/q_{K})$, where $t$ is the cluster age. In a nonextensive
scenario, these indices are quantities that measure the degree of
nonextensivity present in the system. Recent studies reveal that the index $q$
is correlated to the formation rate of high-energy tails present in the
distribution of rotation velocity. On the other hand, the index $q_{K}$ is
determined by the stellar rotation-age relationship. This depends on the
magnetic field configuration through the expression $q_{K}=1+4aN/3$, where $a$
and $N$ denote the saturation level of the star magnetic field and its
topology, respectively. In the present study, we show that the connection
$q-q_{K}$ is also consistent with 548 rotation period data for single
main-sequence stars in 11 Open Clusters aged less than 1 Gyr. The value of
$q_{K}\sim$ 2.5 from our unsaturated model shows that the mean magnetic field
topology of these stars is slightly more complex than a purely radial field.
Our results also suggest that stellar rotational braking behavior affects the
degree of anti-correlation between $q$ and cluster age $t$. Finally, we suggest
that stellar magnetic braking can be scaled by the entropic index $q$.",1408.0657v2
2014-09-20,Large magnetoelectric coupling in nanoscale BiFeO$_3$ from direct electrical measurements,"We report the results of direct measurement of remanent hysteresis loops on
nanochains of BiFeO$_3$ at room temperature under zero and $\sim$20 kOe
magnetic field. We noticed a suppression of remanent polarization by nearly
$\sim$40\% under the magnetic field. The powder neutron diffraction data reveal
significant ion displacements under a magnetic field which seems to be the
origin of the suppression of polarization. The isolated nanoparticles,
comprising the chains, exhibit evolution of ferroelectric domains under dc
electric field and complete 180$^o$ switching in switching-spectroscopy
piezoresponse force microscopy. They also exhibit stronger ferromagnetism with
nearly an order of magnitude higher saturation magnetization than that of the
bulk sample. These results show that the nanoscale BiFeO$_3$ exhibits
coexistence of ferroelectric and ferromagnetic order and a strong
magnetoelectric multiferroic coupling at room temperature comparable to what
some of the type-II multiferroics show at a very low temperature.",1409.5859v1
2014-11-28,Crossover in the magnetic response of single-crystalline Ba$_{1-x}$K$_x$Fe$_2$As$_2$ and Lifshitz critical point evidenced by Hall effect measurements,"We report the doping evolution of magnetic susceptibility $\chi (T)$ and Hall
coefficient $R_H$ in high quality Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($0.13 \leq x
\leq 1$) single crystals. It is found that the normal-state magnetic
susceptibility of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ compounds undergoes a crossover
from linear-$T$ dependence in the undoped and underdoped samples into
KFe$_2$As$_2$-type magnetic response in the overdoped samples with increasing K
content. Hall coefficient $R_H$ of underdoped sample $x$=0.22 shows a rapid
increase above spin-density-wave transition temperature $T_{SDW}$. Below
$T_{SDW}$, it increases slowly. $R_H$ of optimally doped and slightly overdoped
samples ($0.34 \leq x \leq 0.65$) shows relative weak temperature dependence
and saturation tendency below 150 K. However, $R_H$ of K heavily overdoped
samples ($0.80 \leq x \leq 1$) increases rapidly below 150 K. Meanwhile, Hall
angle $cot \theta _H$ displays a concave temperature dependence within the
doping range $0.22 \leq x \leq 0.55$, whereas it changes to a convex
temperature dependence within the doping range $0.65 \leq x \leq 1$. The
dramatic change coincides with Lifshitz transition occurred around the critical
doping $x$=0.80, where ARPES measurements had confirmed that electron pocket
disappears with excess hole doping in Ba$_{1-x}$K$_x$Fe$_2$As$_2$ system. It is
suggested that the characteristic temperature $T$* at around $120 \sim 150$ K
observed in susceptibility and Hall coefficient, as well as previously reported
resistivity data, may indicate an incoherence-coherence crossover in
Ba$_{1-x}$K$_x$Fe$_2$As$_2$ system.",1411.7906v1
2014-12-17,Chromospheric diagnosis with Ca II lines: forward modeling in forward scattering (I),"This paper shows the first synthetic tomography of the quiet solar
chromosphere formed by spatial maps of scattering polarization. It has been
calculated for the CaII 8498, 8542 and 3934 A lines by solving the NLTE
(non-local thermodynamical equilibrium) RT (radiative transfer) problem of the
second kind in a 3D atmosphere model obtained from realistic MHD
(magneto-hydrodynamical) simulations. Maps of circular polarization were
calculated neglecting atomic polarization. Our investigation focuses on the
linear polarization signals induced by kinematics, radiation field anisotropy
and Hanle effect in forward-scattering geometry. Thus, instead of considering
slit profiles at the limb as normally done in the study of the second solar
spectrum, we synthetize and analyze spatial maps of polarization at disk
center. It allows us to understand the spatial signatures of dynamics and
magnetic field in the linear polarization for discriminating them
observationally. Our results suggest new ideas for chromospheric diagnosis that
will be developed throughout a serie of papers. In particular, Hanle Polarity
Inversion Lines and dynamic Hanle diagrams are two concepts introduced in the
present work. We find that chromospheric dynamics and magnetic field topology
create spatial fingerprints in the polarization maps that trace the dynamic
situation of the plasma and the magnetic field. Based on such spatial features
we reconstruct the magnetic field intensity in the middle chromosphere along
grooves of null linear polarization. We finally address the problems of
diagnosing Hanle saturation and kinematic amplification of scattering signals
using Hanle diagrams.",1412.5386v1
2015-11-23,On the Grain-Modified Magnetic Diffusivities in Protoplanetary Disks,"Weakly ionized protoplanetary disks (PPDs) are subject to
non-ideal-magnetohydrodynamic (MHD) effects including Ohmic resistivity, the
Hall effect and ambipolar diffusion (AD), and the resulting magnetic
diffusivities ($\eta_O, \eta_H$ and $\eta_A$) largely control the disk gas
dynamics. The presence of grains not only strongly reduces disk ionization
fraction, but also modify the scalings of $\eta_H$ and $\eta_A$ with magnetic
field strength. We derive analytically asymptotic expressions of $\eta_H$ and
$\eta_A$ in both strong and weak field limits and show that towards strong
field, $\eta_H$ can change sign (at a threshold field strength $B_{\rm th}$),
mimicking a flip of field polarity, and AD is substantially reduced. Applying
to PPDs, we find that when small $\sim0.1$ ($0.01$)$\mu$m grains are
sufficiently abundant [mass ratio $\sim0.01$ ($10^{-4}$)], $\eta_H$ can change
sign up to $\sim2-3$ scale heights above midplane at modest field strength
(plasma $\beta\sim100$) over a wide range of disk radii. Reduction of AD is
also substantial towards the AD dominated outer disk and may activate the
magneto-rotational instability. We further perform local non-ideal MHD
simulations of the inner disk (within 10 AU) and show that with sufficiently
abundant small grains, magnetic field amplification due to the Hall-shear
instability saturates at very low level near the threshold field strength
$B_{\rm th}$. Together with previous studies, we conclude by discussing the
grain-abundance-dependent phenomenology of PPD gas dynamics.",1511.07199v1
2015-12-15,"Half-metallic, Co-based quaternary Heuslers for spintronics: defect- and pressure-induced transitions and properties","Heusler compounds offer potential as spintronic devices due to their
spin-polarization and half-metallicity properties, where electron spin-majority
(minority) manifold exhibits states (band gap) at the electronic chemical
potential, yielding full spin-polarization in a single manifold. Yet, Heuslers
often exhibit intrinsic disorder that degrades its half-metallicity and
spin-polarization. Using density-functional theory, we analyze the electronic
and magnetic properties of equiatomic Heusler ($L$2$_{1}$) CoMnCrAl and
CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder
(thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl
undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained
for a limited range. Antisite disorder between Co-Al pairs in CoMnCrAl and
Co-Ge pairs in CoFeCrGe is energetically the most favored, and retain
half-metallic character in Co-excess samples. However, Co-deficient samples
undergo a transition from half-metallic to metallic, with a discontinuity in
the saturation magnetization. For binary swaps, configurations that compete
with the ground state are identified and show no loss of half-metallicity;
however, the minority-spin bandgap and magnetic moments vary depending on the
atoms swapped. For single binary swaps, there is a significant energy cost in
CoMnCrAl but with no loss of half metallicity. Although a few configurations in
CoFeCrGe energetically compete with the ground statei, however the
minority-spin bandgap and magnetic moments vary depending on the atoms swapped.
These informations should help in controlling these potential spintronic
materials.",1512.04805v2
2016-01-17,Resistivity plateau and extremely large magnetoresistance in NbAs2 and TaAs2,"In topological insulators (TIs), metallic surface conductance saturates the
insulating bulk resistance with de- creasing temperature, resulting in
resistivity plateau at low temperatures as a transport signature originating
from metallic surface modes protected by time reversal symmetry (TRS). Such
characteristic has been found in several materials including Bi2Te2Se, SmB6
etc. Recently, similar behavior has been observed in metallic com- pound LaSb,
accompanying an extremely large magetoresistance (XMR). Shubnikov-de Hass (SdH)
oscillation at low temperatures further confirms the metallic behavior of
plateau region under magnetic fields. LaSb[1] has been proposed by the authors
as a possible topological semimetal (TSM), while negative magnetoresistance is
absent at this moment. Here, high quality single crystals of NbAs2/TaAs2 with
inversion symmetry have been grown and the resistivity under magnetic field is
systematically investigated. Both of them exhibit metallic behavior under zero
magnetic field, and a metal-to-insulator transition occurs when a nonzero
magnetic field is applied, resulting in XMR (1.0*105% for NbAs2 and 7.3*105%
for TaAs2 at 2.5 K & 14 T). With tempera- ture decreased, a resistivity plateau
emerges after the insulator-like regime and SdH oscillation has also been
observed in NbAs2 and TaAs2.",1601.04239v1
2016-07-20,Spatially inhomogeneous electron state deep in the extreme quantum limit of strontium titanate,"When an electronic system is subjected to a sufficiently strong magnetic
field that the cyclotron energy is much larger than the Fermi energy, the
system enters the ""extreme quantum limit"" (EQL) and becomes susceptible to a
number of instabilities. Bringing a three-dimensional electronic system deeply
into the EQL can be difficult, however, since it requires a small Fermi energy,
large magnetic field, and low disorder. Here we present an experimental study
of the EQL in lightly-doped single crystals of strontium titanate, which remain
good bulk conductors down to very low temperatures and high magnetic fields.
Our experiments probe deeply into the regime where theory has long predicted
electron-electron interactions to drive the system into a charge density wave
or Wigner crystal state. A number of interesting features arise in the
transport in this regime, including a striking re-entrant nonlinearity in the
current-voltage characteristics and a saturation of the quantum-limiting field
at low carrier density. We discuss these features in the context of possible
correlated electron states, and present an alternative picture based on
magnetic-field induced puddling of electrons.",1607.06085v1
2016-09-21,Age dependence of wind properties for solar type stars: a 3d study,"Young and rapidly rotating stars are known for intense, dynamo generated
magnetic fields. Spectropolarimetric observations of those stars in precisely
aged clusters are key input for gyrochronology and magnetochronology. We use
ZDI maps of several young K-type stars of similar mass and radius but with
various ages and rotational periods, to perform 3D numerical MHD simulations of
their coronae and follow the evolution of their magnetic properties with age.
Those simulations yield the coronal structure as well as the instant torque
exerted by the magnetized, rotating wind on the star. As stars get older, we
find that the angular momentum loss decreases with $\Omega^3$, which is the
reason for the convergence on the Skumanich law. For the youngest stars of our
sample, the angular momentum loss show signs of saturation around
$8\Omega_{\odot}$, which is a common value used in spin evolution models for
K-type stars. We compare these results to semi-analytical models and existing
braking laws. We observe a complex wind speed distribution for the youngest
stars with slow, intermediate and fast wind components, which are the result of
the interaction with intense and non axisymmetric magnetic fields.
Consequently, in our simulations, the stellar wind structure in the equatorial
plane of young stars varies significantly from a solar configuration,
delivering insight about the past of the solar system interplanetary medium.",1609.06602v2
2016-10-07,On the Fast Magnetic Rotator Regime of Stellar Winds,"Aims: We study the acceleration of the stellar winds of rapidly rotating low
mass stars and the transition between the slow magnetic rotator and fast
magnetic rotator regimes. We aim to understand the properties of stellar winds
in the fast magnetic rotator regime and the effects of magneto-centrifugal
forces on wind speeds and mass loss rates.
  Methods: We extend the solar wind model of Johnstone et al. (2015b) to 1D
magnetohydrodynamic (MHD) simulations of the winds of rotating stars. We test
two assumptions for how to scale the wind temperature to other stars and assume
the mass loss rate scales as Mdot ~ Rstar^2 OmegaStar^1.33 Mstar^-3.36, in the
unsaturated regime, as estimated by Johnstone et al. (2015a).
  Results: For 1.0 Msun stars, the winds can be accelerated to several thousand
km/s, and the effects of magneto-centrifugal forces are much weaker for lower
mass stars. We find that the different assumptions for how to scale the wind
temperature to other stars lead to significantly different mass loss rates for
the rapid rotators. If we assume a constant temperature, the mass loss rates of
solar mass stars do not saturate at rapid rotation, which we show to be
inconsistent with observed rotational evolution. If we assume the wind
temperatures scale positively with rotation, the mass loss rates are only
influenced significantly at rotation rates above 75 OmegaSun. We suggest that
models with increasing wind speed for more rapid rotators are preferable to
those that assume a constant wind speed. If this conclusion is confirmed by
more sophisticated wind modelling. it might provide an interesting
observational constraint on the properties of stellar winds.",1610.02248v1
2017-01-13,Nonmagnetic impurities and roughness effects on the finite temperature magnetic properties of core-shell spherical nanoparticles,"Being inspired by a recent study [V. Dimitriadis et al. Phys. Rev. B
\textbf{92}, 064420 (2015)], we study the finite temperature magnetic
properties of the spherical nanoparticles with core-shell structure including
quenched (i) surface and (ii) interface nonmagnetic impurities (static holes)
as well as (iii) roughened interface effects. The particle core is composed of
ferromagnetic spins, and it is surrounded by a ferromagnetic shell. By means of
Monte Carlo simulation based on an improved Metropolis algorithm, we implement
the nanoparticles using classical Heisenberg Hamiltonians. Particular attention
has also been devoted to elucidate the effects of the particle size on the
thermal and magnetic phase transition features of these systems. For
nanoparticles with imperfect surface layers, it is found that bigger particles
exhibit lower compensation point which decreases gradually with increasing
amount of vacancies, and vanishes at a critical value. In view of nanoparticles
with diluted interface, our Monte Carlo simulation results suggest that there
exists a region in the disorder spectrum where compensation temperature
linearly decreases with decreasing dilution parameter. For nanoparticles with
roughened interface, it is observed that the degree of roughness does not play
any significant role on the variation of both the compensation point and
critical temperature. However, the low temperature saturation magnetizations of
the core and shell interface regions sensitively depend on the roughness
parameter.",1701.03575v1
2017-03-19,"Magnetic properties of Sn-substituted Ni-Zn ferrite:synthesized from nano-sized powders of NiO, ZnO, Fe2O3 and SnO2","A series of Ni0.6-x/2Zn0.4-x/2SnxFe2O4 (x = 0.0, 0.05, 0.1, 0.15, 0.2 and
0.3) (NZSFO) ferrite composites have been synthesized from nano powders using
standard solid state reaction technique. The spinel cubic structure of the
investigated samples has been observed by the X-ray diffraction (XRD). The
magnetic properties such as saturation magnetization (Ms), remanent
magnetization (Mr), coercive field (Hc) and Bohr magneton (B) are calculated
from the hysteresis loops. The value of Ms is found to decrease with increasing
Sn content in the samples. This change has been successfully explained by the
variation of A-B interaction strength due to Sn substitution in different
sites. The compositional stability and quality of the prepared ferrite
composites have also been endorsed by the fairly constant initial permeability
(/) over a wide range of frequency region. The decreasing trend of / with
increasing Sn content has been observed. Curie temperature (TC) has found to
increase with the increase in Sn content. Wide spread frequency utility zone
indicates that the NZSFO can be considered as a good candidate for use in
broadband pulse transformer and wide band read-write heads for video recording.
The abnormal behavior for x = 0.05 has been explained with existing theory.",1703.06385v1
2017-09-20,Electron Heating and Saturation of Self-regulating Magnetorotational Instability in Protoplanetary Disks,"Magnetorotational instability (MRI) has a potential to generate the vigorous
turbulence in protoplanetary disks, although its turbulence strength and
accretion stress remains debatable because of the uncertainty of MRI with low
ionization fraction. We focus on the heating of electrons by strong electric
fields which amplifies nonideal magnetohydrodynamic effects. The heated
electrons frequently collide with and stick to dust grains, which in turn
decreases the ionization fraction and is expected to weaken the turbulent
motion driven by MRI. In order to quantitatively investigate the nonlinear
evolution of MRI including the electron heating, we perform
magnetohydrodynamical simulation with the unstratified shearing box. We
introduce a simple analytic resistivity model depending on the current density
by mimicking resistivity given by the calculation of ionization. Our simulation
confirms that the electron heating suppresses magnetic turbulence when the
electron heating occurs with low current density. We find a clear correlation
between magnetic stress and its current density, which means that the magnetic
stress is proportional to the squared current density. When the turbulent
motion is completely suppressed, laminar accretion flow is caused by ordered
magnetic field. We give an analytical description of the laminar state by using
a solution of linear perturbation equations with resistivity. We also propose a
formula that successfully predicts the accretion stress in the presence of the
electron heating.",1709.07026v1
2017-10-06,Investigation of the interfacial Dzyaloshinskii-Moriya interaction sign in Ir/Co2FeAl systems by Brillouin light scattering,"Co2FeAl (CFA) ultrathin films, of various thicknesses (0.9 nm<tCFA<1.8 nm),
have been grown by sputtering on Si substrates, using Ir as a buffer layer. The
magnetic properties of the structures have been studied by vibrating sample
magnetometry (VSM), miscrostrip ferromagnetic resonance (MS-FMR) and Brillouin
light scattering (BLS) in the Damon-Eshbach geometry. VSM characterizations
show that films are mostly in-plane magnetized and the perpendicular saturating
field increases with decreasing CFA thickness suggesting the existence of
interface anisotropy. The presence of magnetic dead layers of 0.44 nm has been
detected by VSM. The MS-FMR with perpendicular applied magnetic field has been
used to determine the gyromagnetic factor. The BLS measurements reveal a
pronounced nonreciprocal spin waves propagation, due to the interfacial
Dzyaloshinskii-Moriya interaction (DMI) induced by Ir interface with CFA, which
increases with decreasing CFA thickness. The DMI sign has been found to be the
same (negative) as that of Pt/Co, in contrast to the ab-initio calculation on
Ir/Co. The thickness dependence of the effective DMI constant shows the
existence of two regimes similarly to that of the perpendicular anisotropy
constant. The DMI constant Ds was estimated to be -0.37 pJ/m for the thickest
samples where a linear thickness dependence of the effective DMI constant has
been observed.",1710.02433v1
2018-04-26,Large voltage tuning of Dzyaloshinskii-Moriya Interaction: a route towards dynamic control of skyrmion chirality,"Electric control of magnetism is a prerequisite for efficient and low power
spintronic devices. More specifically, in heavy metal/ ferromagnet/ insulator
heterostructures, voltage gating has been shown to locally and dynamically tune
magnetic properties like interface anisotropy and saturation magnetization.
However, its effect on interfacial Dzyaloshinskii-Moriya Interaction (DMI),
which is crucial for the stability of magnetic skyrmions, has been challenging
to achieve and has not been reported yet for ultrathin films. Here, we
demonstrate 130% variation of DMI with electric field in Ta/FeCoB/TaOx
trilayers through Brillouin Light Spectroscopy (BLS). Using polar-
Magneto-Optical-Kerr-Effect microscopy, we further show a monotonic variation
of DMI and skyrmionic bubble size with electric field, with an unprecedented
efficiency. We anticipate through our observations that a sign reversal of DMI
with electric field is possible, leading to a chirality switch. This dynamic
manipulation of DMI establishes an additional degree of control to engineer
programmable skyrmion based memory or logic devices.",1804.09955v2
2018-05-08,Analytical treatment for the development of electromagnetic cascades in intense magnetic fields,"In a strong magnetic field, a high-energy photon can be absorbed and then
produce an electron-positron pair. The produced electron/positron will in turn
radiate a high-energy photon via synchrotron radiation, which then initiates a
cascade. We built a one-dimensional Monte-Carlo code to study the development
of the cascade especially after it reaches the saturated status, when almost
all the energy of the primary particles transfers to the photons. The photon
spectrum in this status has a cut-off due to the absorption by magnetic fields,
which is much sharper than the exponential one. Below the cut-off, the spectral
energy distribution (SED) manifest itself as a broken power-law with a spectral
index of $0.5$ and $0.125$, respectively, below and above the broken energy.
The SED can be fitted by a simple analytical function, which is solely
determined by the product of the cascade scale $R$ and the magnetic field
perpendicular to the motion of the particle B_{\perp}, with an accuracy better
than 96\%. The similarity of the spectrum to that from the cascade in an
isotropic black-body photon field is also studied.",1805.03040v2
2018-07-31,Nature of magnetism and transport in BxCyNz thin films: The intriguing role of nitrogen defects in the electronic structure,"Boron carbonitride (BxCyNz) represents an interesting family of materials
containing all light elements and two dimensional graphene like hybrid layers.
Although rich literature exists on this peculiar material in chemically
processed form, there are relatively fewer reports on device application-worthy
thin film form. This form also offers a natural platform for basic studies on
important aspects such as magnetism and transport, which have attracted
attention in the context of ferromagnetism in doped and defect carbon systems.
Thus, in this work we have grown thin films of this compound using Pulsed Laser
Deposition (PLD) method, and investigated their magnetic and transport
properties in their entirety along with the detailed electronic structure using
various spectroscopic techniques like X-ray photoelectron spectroscopy (XPS),
Valence Band Spectroscopy (VBS) and X-ray absorption near edge spectroscopy
(XANES). In depth analysis of the typical role of dopants and defects,
especially the prevalent nitrogen defects, is elucidated using Density
Functional Theory (DFT) calculations to understand the experimental
observations. A dramatic crossover in the transport mechanism of charge
carriers is observed in this system with the change in doping level of specific
nitrogen defects. A robust and high saturation magnetization is achieved in BCN
films which is higher by almost hundred times as compared to that in similarly
grown undoped carbon film. An anomalous transition and increase in coercive
field is also observed at low temperature. A careful analysis brings out the
intriguing role of specific nitrogen defects in defining the peculiar nature
and concentration dependence of the physical properties of this system.",1807.11667v1
2018-08-02,The Steady Growth of the High-Energy Spectral Cutoff in Relativistic Magnetic Reconnection,"Magnetic reconnection is invoked as an efficient particle accelerator in a
variety of astrophysical sources of non-thermal high-energy radiation. With
large-scale two-dimensional particle-in-cell simulations of relativistic
reconnection (i.e., with magnetization $\sigma\gg1$) in pair plasmas, we study
the long-term evolution of the power-law slope and high-energy cutoff of the
spectrum of accelerated particles. We find that the high-energy spectral cutoff
does not saturate at $\gamma_{\rm cut}\sim 4\sigma$, as claimed by earlier
studies, but it steadily grows with time as long as the reconnection process
stays active. At late times, the cutoff scales approximately as $\gamma_{\rm
cut}\propto \sqrt{t}$, regardless of the flow magnetization and initial
temperature. We show that the particles dominating the high-energy spectral
cutoff reside in plasmoids, and in particular in a strongly magnetised ring
around the plasmoid core. The growth of their energy is driven by the increase
in the local field strength, coupled with the conservation of the first
adiabatic invariant. We also find that the power-law slope of the spectrum
($p=-{\rm d}\log N/{\rm d}\log \gamma$) evolves with time. For
$\sigma\gtrsim10$, the spectrum is hard at early times ($p\lesssim 2$), but it
tends to asymptote to $p\sim 2$; the steepening of the power-law slope allows
the spectral cutoff to extend to higher and higher energies, without violating
the fixed energy budget of the system. Our results demonstrate that
relativistic reconnection is a viable candidate for accelerating the
high-energy particles emitting in relativistic astrophysical sources.",1808.00966v2
2018-08-03,Creation of Magnetic Skyrmion Bubble Lattices by Ultrafast Laser in Ultrathin Films,"Magnetic skyrmions are topologically nontrivial spin textures which hold
great promise as stable information carriers in spintronic devices at the
nanoscale. One of the major challenges for developing novel skyrmion-based
memory and logic devices is fast and controlled creation of magnetic skyrmions
at ambient conditions. Here we demonstrate the single ultrafast (35-fs) laser
pulse-induced generation of skyrmion bubbles and skyrmion bubble lattices from
a ferromagnetic state in sputtered ultrathin magnetic films at room
temperature. The skyrmion bubble density increases with the laser fluence in a
controlled way, and it finally becomes saturated, forming disordered hexagonal
lattices. Moreover, we present that the skyrmion bubble lattice configuration
leads to enhanced topological stability as compared to isolated skyrmions,
suggesting its promising use in data storage. Our findings shed light on the
optical approach to the skyrmion bubble lattice in commonly accessible
materials, paving the road toward the emerging skyrmion-based memory and
synaptic devices.",1808.01385v2
2018-08-17,Temperature Dependence of Magnetic Properties of an 18-nm-thick YIG Film Grown by Liquid Phase Epitaxy: Effect of a Pt Overlayer,"Liquid phase epitaxy of an 18 nm thick Yttrium Iron garnet (YIG) film is
achieved. Its magnetic properties are investigated in the 100 -- 400 K
temperature range, as well as the influence of a 3 nm thick Pt overlayer on
them. The saturation magnetization and the magnetocrystalline cubic anisotropy
of the bare YIG film behave similarly to bulk YIG. A damping parameter of only
a few $10^{-4}$ is measured, together with a low inhomogeneous contribution to
the ferromagnetic resonance linewidth. The magnetic relaxation increases upon
decreasing temperature, which can be partly ascribed to impurity relaxation
mechanisms. While it does not change its cubic anisotropy, the Pt capping
strongly affects the uniaxial perpendicular anisotropy of the YIG film, in
particular at low temperatures. The interfacial coupling in the YIG/Pt
heterostructure is also revealed by an increase of the linewidth, which
substantially grows by lowering the temperature.",1808.05785v2
2018-09-10,The Effect of Nickel Substitution on Magnetism in the Layered van der Waals Ferromagnet Fe$_3$GeTe$_2$,"We have grown a series of nickel substituted single crystals of the layered
ferromagnet (FM) Fe$_3$GeTe$_2$. The large single crystalline samples of
(Fe$_{1-x}$Ni$_x$)$_3$GeTe$_2$ with $x = 0-0.84$ were characterized with single
crystal X-ray diffraction, magnetic susceptibility, electrical resistance and
muon spin spectroscopy. We find Fe can be continuously substituted with Ni with
only minor structural variation. In addition, FM order is suppressed from
$T_\mathrm{C}=212$~K for $x=0$ down to $T_\mathrm{C}=50$~K for $x=0.3$, which
is accompanied with a strong suppression of saturated and effective moment, and
Curie-Weiss temperature. Beyond $x=0.3$, the FM order is continuously smeared
into a FM cluster glass phase, with a nearly full magnetic volume fraction. We
attribute the observed change in the nature of magnetic order to the
intrinsically disordered structure of Fe$_3$GeTe$_2$ and subsequent dilution
effects from the Ni substitution.",1809.03429v2
2018-10-17,"Investigation of the structural, electronic, transport and magnetic properties of Co$_2$FeGa Heusler alloy nanoparticles","We report the structural, transport, electronic, and magnetic properties of
Co$_2$FeGa Heusler alloy nanoparticles. The Rietveld refinements of x-ray
diffraction (XRD) data with the space group Fm$\bar {3}$m clearly demonstrates
that the nanoparticles are of single phase. The particle size (D) decreases
with increasing the SiO$_2$ concentration. The Bragg peak positions and the
inter-planer spacing extracted from high-resolution transmission electron
microscopy image and selected area electron diffraction are in well agreement
with data obtained from XRD. The coercivity initially increases from 127~Oe to
208~Oe between D = 8.5~nm and 12.5~nm, following the D$^{-3/2}$ dependence and
then decreases with further increasing D up to 21.5~nm with a D$^{-1}$
dependence, indicating the transition from single domain to multidomain regime.
The effective magnetic anisotropic constant behaves similarly as coercivity,
which confirms this transition. A complex scattering mechanisms have been
fitted to explain the electronic transport properties of these nanoparticles.
In addition we have studied core-level and valence band spectra using
photoemission spectroscopy, which confirm the hybridization between $d$ states
of Co/Fe. Further nanoparticle samples synthesized by co-precipitation method
show higher saturation magnetization. The presence of Raman active modes can be
associated with the high chemical ordering, which motivates for detailed
temperature dependent structural investigation using synchrotron radiation and
neutron sources.",1810.07660v1
2018-11-02,Electron Strahl and Halo Formation in the Solar Wind,"We propose a kinetic model describing the formation of the strahl and halo
electron populations in the solar wind. We demonstrate that the suprathermal
electrons propagating from the sun along the Parker-spiral magnetic field lines
are progressively focused into a narrow strahl at heliospheric distances
$r\lesssim 1$ AU, while at $r\gtrsim 1$ AU the width of the strahl saturates
due to Coulomb collisions and becomes independent of the distance. Our theory
of the strahl broadening does not contain free parameters and it agrees with
the Wind observations at 1 AU to within $15-20\%$. This indicates that Coulomb
scattering, rather than anomalous turbulent diffusion, plays a dominant role in
strahl formation in these observations. We further propose that the nearly
isotropic halo electron population may be composed of electrons that ran away
from the sun as an electron strahl, but later ended up on magnetic field lines
leading them back to the sun. Through the effects of magnetic defocusing and
Coulomb pitch-angle scattering, a narrow source distribution at large
heliocentric distances appears nearly isotropic at distances $\sim$1 AU. The
halo electrons are, therefore, not produced locally; rather, they are the fast
electrons trapped by magnetic field lines on global heliospheric scales. At the
electron energies $K \lesssim 200\,\, {\rm eV}$, our theory is quite
insensitive to the particular mechanism that produces a population of
sunward-streaming suprathermal particles. At larger energies, however, our
theory indicates that the scattering provided by Coulomb collisions alone is
not sufficient to isotropize a narrow sunward-propagating electron beam.",1811.01098v1
2019-01-07,Maser and other instabilities in a weakly magnetized relativistic plasma: Theory and the astrophysical relevance of the maser,"A sufficient condition for maser instability in a weakly magnetized
relativistic plasma with an isotropic particle distribution function is given.
The maser growth rates and polarizations are computed starting from the exact
dielectric permittivity tensor of a magnetized plasma. For very weak magnetic
fields, our results confirm the approximate validity of the 'standard maser
theory', which is based on the Einstein coefficients method, with one
significant exception. For inclined propagation and realistic (small but
finite) field, the growth rates of the two (nearly circular) polarizations
differ significantly, while the standard theory predicts two (nearly circular)
polarizations with similar growth rates. We show that this deviation is due to
circularly polarized synchrotron emission, which is neglected in the standard
theory.
  The maser is shown to grow slower than Langmuir waves. Nevertheless,
significant generation of EM waves is seen in (highly simplified) direct
numerical simulations. We study the nonlinear saturation of the maser
instability and find that it offers a mechanism for the conversion of a
significant fraction of the plasma energy into radio waves. We briefly discuss
the conditions under which the maser instability may operate in astrophysical
sources, and provide rough estimates that may be used as a guidance when
studying particular astrophysical sources/phenomena.",1901.01700v1
2019-01-08,Ferromagnetic ordering along the hard axis in the Kondo lattice YbIr3Ge7,"Ferromagnetic Kondo lattice compounds are far less common than their
antiferromagnetic analogs. In this work, we report the discovery of a new
ferromagnetic Kondo lattice compound, YbIr3Ge7. Like almost all ferromagnetic
Kondo lattice systems, YbIr3Ge7 shows magnetic order with moments aligned
orthogonal to the crystal electric field (CEF) easy axis. YbIr3Ge7 is unique in
that it is the only member of this class of compounds that crystallizes in a
rhombohedral structure with a trigonal point symmetry of the magnetic site, and
it lacks broken inversion symmetry at the local moment site. AC magnetic
susceptibility, magnetization, and specific heat measurements show that
YbIr3Ge7 has a Kondo temperature TK = 14 K and a Curie temperature TC = 2.4 K.
Ferromagnetic order occurs along the crystallographic [100] hard CEF axis
despite the large CEF anisotropy of the ground state Kramers doublet with a
saturation moment along [001] almost four times larger than the one along
[100]. This implies that a mechanism which considers the anisotropy in the
exchange interaction to explain the hard axis ordering is unlikely. On the
other hand, the broad second-order phase transition at TC favors a
fluctuation-induced mechanism.",1901.02489v1
2019-03-25,Octahedral tilting and emergence of ferrimagnetism in cobalt-ruthenium based double perovskites,"Rare earth based cobalt-ruthenium double perovskites A$_2$CoRuO$_6$ (A = La,
Pr, Nd and Sm) were synthesized and investigated for their structural and
magnetic properties. All the compounds crystallize in the monoclinic $P2_1/n$
structure with the indication of antisite disorder between Co and Ru sites.
While, La compound is already reported to have an antiferromagnetic state below
27 K, the Pr, Nd and Sm systems are found to be ferrimagnetic below $T_c$ = 46,
55 and 78 K respectively. Field dependent magnetization data indicate prominent
hysteresis loop below $T_c$ in the samples containing magnetic rare-earth ions,
however magnetization does not saturate even at the highest applied fields. Our
structural analysis indicates strong distortion in the Co-O-Ru bond angle, as
La$^{3+}$ is replaced by smaller rare-earth ions such as Pr$^{3+}$, Nd$^{3+}$
and Sm$^{3+}$. The observed ferrimagnetism is possibly associated with the
enhanced antiferromagnetic superexchange interaction in the Co-O-Ru pathway due
to bond bending. The Pr, Nd and Sm samples also show small magnetocaloric
effect with Nd sample showing highest value of magnitude $\sim$ 3
Jkg$^{-1}$K$^{-1}$ at 50 kOe. The change in entropy below 20 K is found to be
positive in the Sm sample as compared to the negative value in the Nd
counterpart.",1903.10271v1
2019-07-08,Bloch-to-Néel domain wall transition evinced through morphology of magnetic bubble expansion in Ta/CoFeB/MgO layers,"Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy are often
characterised by vanishing or modest values of interfacial
Dzyaloshinskii-Moriya interaction (DMI), which results in purely Bloch or mixed
Bloch-N\'eel domain walls (DWs). Here we investigate the creep evolution of the
overall magnetic bubble morphology in these systems under the combined presence
of in-plane and out-of-plane magnetic fields and we show that He$^+$ ion
irradiation induces a transition of the internal DW structure towards a fully
N\'eel spin texture. This transition can be correlated to a simultaneous
increase in DMI strength and reduction in saturation magnetisation -- which are
a direct consequence of the effects of ion irradiation on the bottom and top
CoFeB interfaces, respectively. The threshold irradiation dose above which DWs
acquire a pure N\'eel character is experimentally found to be between 12
$\times$ 10$^{18}$ He$^+$/m$^2$ and 16 $\times$ 10$^{18}$ He$^+$/m$^2$,
matching estimations from the one dimensional DW model based on material
parameters. Our results indicate that evaluating the global bubble shape during
its expansion can be an effective tool to sense the internal bubble DW
structure. Furthermore, we show that ion irradiation can be used to achieve
post-growth engineering of a desired DW spin texture.",1907.03708v1
2019-09-05,On the Survival of Cool Clouds in the Circum-Galactic Medium,"We explore the survival of cool clouds in multi-phase circum-galactic media.
We revisit the ""cloud crushing problem"" in a large survey of simulations
including radiative cooling, self-shielding, self-gravity, magnetic fields, and
anisotropic Braginskii conduction and viscosity (with saturation). We explore a
wide range of parameters including cloud size, velocity, ambient temperature
and density, as well as a variety of magnetic field configurations and cloud
turbulence. We find that realistic magnetic fields and turbulence have weaker
effects on cloud survival; the most important physics is radiative cooling and
conduction. Self-gravity and self-shielding are important for clouds which are
initially Jeans-unstable, but largely irrelevant otherwise.
Non-self-gravitating, realistically magnetized clouds separate into four
regimes: (1) At low column densities, clouds evaporate rapidly via conduction.
(2) A ""failed pressure confinement"" regime, where the ambient hot gas cools too
rapidly to provide pressure confinement for the cloud. (3) An ""infinitely
long-lived"" regime, in which the cloud lifetime becomes longer than the cooling
time of gas swept up in the leading bow shock, so the cloud begins to accrete
and grow. (4) A ""classical cloud destruction"" regime, where clouds are
eventually destroyed by instabilities. In the final regime, the cloud lifetime
can exceed the naive cloud-crushing time owing to conduction-induced
compression. However, small and/or slow-moving clouds can also evaporate more
rapidly than the cloud-crushing time. We develop simple analytic models that
explain the simulated cloud destruction times in this regime.",1909.02632v2
2019-09-11,Giant pressure-enhancement of multiferroicity in CuBr2,"Type-II multiferroic materials, in which ferroelectric polarization is
induced by inversion non-symmetric magnetic order, promise new and highly
efficient multifunctional applications based on the mutual control of magnetic
and electric properties. Although this phenomenon has to date been limited to
low temperatures, here we report a giant pressure-dependence of the
multiferroic critical temperature in CuBr$_2$. At 4.5 GPa, $T_\mathrm{C}$ is
enhanced from 73.5 to 162 K, to our knowledge the highest value yet reported
for a non-oxide type-II multiferroic. This growth shows no sign of saturating
and the dielectric loss remains small under these high pressures. We establish
the structure under pressure and demonstrate a 60\% increase in the two-magnon
Raman energy scale up to 3.6 GPa. First-principles structural and magnetic
energy calculations provide a quantitative explanation in terms of dramatically
pressure-enhanced interactions between CuBr$_2$ chains. These large,
pressure-tuned magnetic interactions motivate structural control in cuprous
halides as a route to applied high-temperature multiferroicity.",1909.04989v2
2019-11-19,Efficient Numerical Modeling of the Magnetization Loss on a Helically Wound Superconducting Tape in a Ramped Magnetic Field,"We investigate theoretically the dependence of magnetization loss of a
helically wound superconducting tape on the round core radius $R$ and the
helical conductor pitch in a ramped magnetic field. Using the thin-sheet
approximation, we identify the two-dimensional equation that describes
Faraday's law of induction on a helical tape surface in the steady state. Based
on the obtained basic equation, we simulate numerically the current streamlines
and the power loss $P$ per unit tape length on a helical tape. For $R \gtrsim
w_0$ (where $w_0$ is the tape width), the simulated value of $P$ saturates
close to the loss power $\sim(2/\pi)P_{\rm flat}$ (where $P_{\rm flat}$ is the
loss power of a flat tape) for a loosely twisted tape. This is verified
quantitatively by evaluating power loss analytically in the thin-filament limit
of $w_0/R\rightarrow 0$. For $R \lesssim w_0$, upon thinning the round core,
the helically wound tape behaves more like a cylindrical superconductor as
verified by the formula in the cylinder limit of $w_0/R\rightarrow 2\pi$, and
$P$ decreases further from the value for a loosely twisted tape, reaching $\sim
(2/\pi)^2 P_{\rm flat}$.",1911.08170v1
2019-12-06,Using the Stokes V widths of Fe I lines for diagnostics of the intrinsic solar photospheric magnetic field,"The goal of this study is to explore a novel method for the solar
photospheric magnetic field diagnostics using Stokes V widths of different
magnetosensitive Fe~I spectral lines. We calculate Stokes I and V profiles of
several Fe I lines based on a one-dimensional photospheric model VAL C using
the NICOLE radiative transfer code. These profiles are used to produce
calibration curves linking the intrinsic magnetic field values with the widths
of blue peaks of Stokes V profiles. The obtained calibration curves are then
tested using the Stokes profiles calculated for more realistic photospheric
models based on MHD models of magneto-convection. It is shown that the
developed Stokes V widths (SVW) method can be used with various optical and
near-infrared lines. Out of six lines considered in this study, FeI 6301 line
appears to be the most effective: it is sensitive to fields over ~200G and does
not show any saturation up to ~2kG. Other lines considered can also be used for
the photospheric field diagnostics with this method, however, only in narrower
field value ranges, typically from about 100G to 700-1000G. The developed
method can be a useful alternative to the classical magnetic line ratio method,
particularly when the choice of lines is limited.",1912.03340v1
2019-12-23,Weibel instability drives large magnetic field generation in laser-driven single plume ablation,"First-principles kinetic simulations are used to investigate magnetic field
generation processes in expanding ablated plasmas relevant to laser-driven
foils and hohlraums. In addition to Biermann-battery-generated magnetic fields,
strong filamentary magnetic filaments are found to grow in the corona of single
expanding plasma plumes; such filaments are observed to dominate Biermann
fields at sufficiently large focal radius, reaching saturation values of $\sim$
100 T at National Ignition Facility-like drive conditions. The filamentary
fields result from the ion Weibel instability driven by relative
counterstreaming between the ablated ions and a sparse background population,
which could be the result of a gas prefill in a hohlraum or laser pre-pulse.
The ion-Weibel instability is robust with the inclusion of collisions and grows
on a timescale of 100 ps, with a wavelength on the scale of 100-250 $\mu$m,
over a wide range of background population densities; the instability also
gives rise to coherent density oscillations. These results are of particular
interest to inertial confinement fusion experiments, where such field and
density perturbations can modify heat-transport as well as laser propagation
and absorption.",1912.11120v1
2019-12-27,Localized spin waves at low temperatures in a Cobalt Carbide nanocomposite,"We study magnetic, transport and thermal properties of Cobalt carbide
nanocomposite with a mixture of Co2C and Co3C phases in 1:1 ratio, with an
average particle diameter of 40$\pm 15$ nm. We show that the behavior of the
nanocomposite is completely different from that of either Co3C or Co2C. We
observed that with decreasing temperature the saturation magnetization MS(T)
increases, however, below 100 K, there is a steep rise. A detail analysis shows
the increase in MS(T) down to 100 K is explained via the surface spin freezing
model. However, below 100 K the steep increase in MS(T) is explained by a
finite size effect related to a confinement of spin waves within the nano
particles. The measurement of heat capacity shows broad peak at 100 K along
with presence of another anomaly at a lower temperature 43 K(=Tex). Resistance
measurement in the nanocomposite shows metallic behavior at high T with an
unusual anomaly appearing at Tex, which is near the T regime where MS(T) begins
to increase steeply. A measurement of the temperature gradients across the
sample thickness indicates an abrupt change in thermal conductivity at Tex
which suggests a phase transition at Tex. Our results are explained in terms of
a transformation from a magnetically coupled state with a continuous spectrum
of spin waves into a magnetically decoupled state below 100 K with confined
spin waves.",1912.12085v1
2020-06-17,"Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes","Single-crystalline membranes of functional materials enable the tuning of
properties via extreme strain states; however, conventional routes for
producing membranes require the use of sacrificial layers and chemical
etchants, which can both damage the membrane and limit the ability to make them
ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler
compound GdPtSb on graphene-terminated Al$_2$O$_3$ substrates. Despite the
presence of the graphene interlayer, the Heusler films have epitaxial registry
to the underlying sapphire, as revealed by x-ray diffraction, reflection high
energy electron diffraction, and transmission electron microscopy. The weak Van
der Waals interactions of graphene enable mechanical exfoliation to yield
free-standing GdPtSb membranes, which form ripples when transferred to a
flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic,
measurements on rippled membranes show a spontaneous magnetic moment at room
temperature, with a saturation magnetization of 5.2 bohr magneton per Gd.
First-principles calculations show that the coupling to homogeneous strain is
too small to induce ferromagnetism, suggesting a dominant role for strain
gradients. Our membranes provide a novel platform for tuning the magnetic
properties of intermetallic compounds via strain (piezomagnetixm and
magnetostriction) and strain gradients (flexomagnetism).",2006.10100v3
2020-06-25,Magnetic Fields in the Formation of the First Stars. I. Theory vs. Simulation,"While magnetic fields are important in contemporary star formation, their
role in primordial star formation is unknown. Magnetic fields of order 10^-16 G
are produced by the Biermann battery due to the curved shocks and turbulence
associated with the infall of gas into the dark matter minihalos that are the
sites of formation of the first stars. These fields are rapidly amplified by a
small-scale dynamo until they saturate at or near equipartition with the
turbulence in the central region of the gas. Analytic results are given for the
outcome of the dynamo, including the effect of compression in the collapsing
gas. The mass-to-flux ratio in this gas is 2-3 times the critical value,
comparable to that in contemporary star formation. Predictions of the outcomes
of simulations using smooth particle hydrodynamics (SPH) and grid-based
adaptive mesh refinement (AMR) are given. Because the numerical viscosity and
resistivity for the standard resolution of 64 cells per Jeans length are
several orders of magnitude greater than the physical values, dynamically
significant magnetic fields affect a much smaller fraction of the mass in
simulations than in reality. An appendix gives an analytic treatment of
free-fall collapse, including that in a constant density background. Another
appendix presents a new method of estimating the numerical viscosity; results
are given for both SPH and grid-based codes.",2006.14607v1
2020-07-01,"Impact of V substitution on the physical properties of Ni-Zn-Co ferrites: structural, magnetic, dielectric and electrical properties","We have investigated the Vanadium- (V) substituted Ni-Zn-Co ferrites where
the samples were prepared using solid-state reaction technique. The impact of
V5+ substitution on the structural, magnetic, dielectric and electrical
properties of Ni-Zn-Co ferrites has been studied. XRD analysis confirmed the
formation of a single-phase cubic spinel structure. The lattice constants have
been calculated both theoretically and experimentally along with other
structural parameters such as bulk density, X-ray density and porosity. The
FESEM images are taken to study the surface morphology. FTIR measurement is
also performed which confirms spinel structure formation. The saturation
magnetization (Ms), coercive field (Hc) and Bohr magneton (B) were calculated
from the obtained M-H loops. The temperature dependent permeability is studied
to obtain the Curie temperature. Frequency and composition dependence of
permeability was also analyzed. Dielectric behavior and ac resistivity are also
subjected to investigate the frequency dependency. An inverse relationship was
observed between the composition dependence of dielectric constant and ac
resistivity. The obtained results such as the electrical resistivity,
dielectric constants and magnetic properties suggest the appropriateness of the
studied ferrites in microwave device applications.",2007.00602v1
2020-07-28,Defect Induced Room Temperature Ferromagnetism in High Quality Co-doped ZnO Bulk Samples,"The nature of the often reported room temperature ferromagnetism in
transition metal doped oxides is still a matter of huge debate. Herein we
report on room temperature ferromagnetism in high quality Co-doped ZnO
(Zn1-xCoxO) bulk samples synthesized via standard solid-state reaction route.
Reference paramagnetic Co-doped ZnO samples with low level of structural
defects are subjected to heat treatments in a reductive atmosphere in order to
introduce defects in the samples in a controlled way. A detailed structural
analysis is carried out in order to characterize the induced defects and their
concentration. The magnetometry revealed the coexistence of a paramagnetic and
a ferromagnetic phase at room temperature in straight correlation with the
structural properties. The saturation magnetization is found to increase with
the intensification of the heat treatment, and, therefore, with the increase of
the density of induced defects. The magnetic behavior is fully explained in
terms of the bound magnetic polaron model. Based on the experimental findings,
supported by theoretical calculations, we attribute the origin of the observed
defect-induced-ferromagnetism to the ferromagnetic coupling between the Co ions
mediated by magnetic polarons due to zinc interstitial defects.",2007.14140v1
2020-11-08,Effect of Ti underlayer thickness on the magnetic anisotropy of TbFe thin films,"In this study, we address the impact of Ti underlayer thickness (UL: 0-40 nm)
on the structural, magnetic, and microscopic properties of TbFe thin films. The
structural analysis confirmed the intermixing at interfaces of the Ti and TbFe
layer with the increment of UL thicknesses. Out-of-plane (OOP) coercivity (Hc),
and saturation field (Hs) gradually increased with an increase in UL thickness
regardless of interface mixing. For UL = 10 nm, the domain contrast and OOP
stray field strength were enhanced, which may be due to the extent of d-d
hybridization dominated over the influence of interfacial roughness. While for
UL = 20, and 40 nm, the extent of interfacial roughness dominated the
hybridization effects and as a result, stray fields deteriorated. By placing UL
of 20 nm, Hc increased by nearly 6 times more than the bare TbFe system. So, we
observe a state with high OOP Hc combined with nearly zero OOP stray fields
that are found to co-exist in the sample. The magnetization reversal studies on
a large area reveal domain nucleation followed by domain-wall motion in all the
films. The idea of tuning magnetic properties by varying thicknesses of Ti UL
may useful in spintronics applications.",2011.04068v1
2020-11-17,Non-local magnon-based transport in yttrium iron garnet/platinum heterostructures at high temperatures,"The spin Hall effect in a heavy metal thin film allows to probe the magnetic
properties of an adjacent magnetic insulator via magnetotransport measurements.
Here, we investigate the magnetoresistive response of yttrium iron
garnet/platinum heterostructures from room temperature to beyond the Curie
temperature $T_\mathrm{C, YIG} \approx 560\,\mathrm{K}$ of the ferrimagnetic
insulator. We find that the amplitude of the (local) spin Hall
magnetoresistance decreases monotonically from $300\,\mathrm{K}$ towards
$T_\mathrm{C}$, mimicking the evolution of the saturation magnetization of
yttrium iron garnet. Interestingly, the spin Hall magnetoresistance vanishes
around $500\,\mathrm{K}$, well below $T_\mathrm{C}$, which we attribute to the
formation of a parasitic interface layer by interdiffusion. Around room
temperature the non-local magnon-mediated magnetoresistance exhibits a power
law scaling $T^{\alpha}$ with $\alpha = 3/2$, as already reported. The exponent
decreases gradually to $\alpha \sim 1/2$ at around $420\,\mathrm{K}$, before
the non-local magnetoresistance vanishes rapidly at a similar temperature as
the spin Hall magnetoresistance. We attribute the reduced $\alpha$ at high
temperatures to the increasing thermal magnon population which leads to
enhanced scattering of the non-equilibrium magnon population and a reduced
magnon diffusion length. Finally, we find a magnetic field independent offset
voltage in the non-local signal for $T > 470\,\mathrm{K}$ which we associate
with electronic leakage currents through the normally insulating yttrium iron
garnet film. Indeed, this non-local offset voltage is thermally activated with
an energy close to the band gap.",2011.08589v1
2020-11-27,d0 Ferromagnetism in Li-doped ZnO Compounds,"Recently, d0 ferromagnetic materials have been projected as one of the
promising novel materials for spintronics applications. In this work, we have
studied Li-doped ZnO compounds, i.e. Zn1-xLixO (x=0, 0.02, 0.04, and 0.06)
samples, prepared by the solid-state reaction route method. From the study of
crystal structure using X-ray diffraction (XRD) patterns, it is evident that
the prepared materials have been formed in a single-phase of the hexagonal
wurtzite structure. The refinement of the XRD patterns suggests that there are
very small changes in the lattice parameters upon Li-incorporation in ZnO. The
average crystallite size (SC), estimated from XRD patterns was found to be in
the range of 35-50 nm. The microstructural study by scanning electron
microscope reveals the uniform morphology of the grains of the order of 50-70
nm. The energy dispersive spectrum indicates that no unwanted ferromagnetic
impurities have crept into the final prepared samples. The measurement of the
temperature (T) variation of magnetization (M) with SQUID magnetometer
indicates that undoped ZnO exhibits diamagnetic property but all Li-doped
compounds exhibit room-temperature ferromagnetism and with a magnetic
irreversibility behavior between zero-field cooled and field cooled M-T data.
From the magnetization versus field measurements at 3 and 300 K, it is observed
that Li-doped samples exhibit ferromagnetic loops with ultra-soft coercivity
(~50 Oe) and with a maximum saturation magnetization of 0.10 emu/gm for x= 0.02
sample, which decreases with the increase in Li concentration.",2011.13713v1
2021-04-14,Solar large-scale magnetic field and cycle patterns in solar dynamo,"We compare spectra of the zonal harmonics of the large-scale magnetic field
of the Sun using observation results and solar dynamo models. The main solar
activity cycle as recorded in these tracers is a much more complicated
phenomenon than the eigen solution of solar dynamo equations with the growth
saturated by a back reaction of the dynamo-driven magnetic field on solar
hydrodynamics. The nominal 11(22)-year cycle as recorded in each mode has a
specific phase shift varying from cycle to cycle; the actual length of the
cycle varies from one cycle to another and from tracer to tracer. Both the
observation and the dynamo model show an exceptional role of the axisymmetric
$\ell_{5}$ mode. Its origin seems to be readily connected with the formation
and evolution of sunspots on the solar surface. The results of observations and
dynamo models show a good agreement for the low $\ell_{1}$ and $\ell_{3}$
modes. The results for these modes do not differ significantly for the
axisymmetric and nonaxisymmetric models. Our findings support the idea that the
sources of the solar dynamo arise as a result of both the distributed dynamo
processes in the bulk of the convection zone and the surface magnetic activity.",2104.06808v2
2021-06-04,Structural Monoclinicity and Its Coupling to Layered Magnetism in Few-Layer $\mathrm{CrI_{3}}$,"Using polarization-resolved Raman spectroscopy, we investigate layer number,
temperature, and magnetic field dependence of Raman spectra in one- to
four-layer $\mathrm{CrI_{3}}$. Layer-number-dependent Raman spectra show that
in the paramagnetic phase a doubly degenerated $E_{g}$ mode of monolayer
$\mathrm{CrI_{3}}$ splits into one $A_{g}$ and one $B_{g}$ mode in N-layer (N >
1) $\mathrm{CrI_{3}}$ due to the monoclinic stacking. Their energy separation
increases in thicker samples until an eventual saturation.
Temperature-dependent measurements further show that the split modes tend to
merge upon cooling but remain separated until 10 K, indicating a failed attempt
of the monoclinic-to-rhombohedral structural phase transition that is present
in the bulk crystal. Magnetic-field-dependent measurements reveal an additional
monoclinic distortion across the magnetic-field-induced layered
antiferromagnetism-to-ferromagnetism phase transition. We propose a structural
change that consists of both a lateral sliding toward the rhombohedral stacking
and a decrease in the interlayer distance to explain our experimental
observations.",2106.02657v1
2021-07-08,"Unconventional thermal and magnetic-field-driven changes of a bipartite entanglement of a mixed spin-(1/2,$S$) Heisenberg dimer with an uniaxial single-ion anisotropy","The concept of negativity is adapted in order to explore the quantum and
thermal entanglement of the mixed spin-(1/2,$S$) Heisenberg dimers in presence
of an external magnetic field. The mutual interplay between the spin size $S$,
XXZ exchange and uniaxial single-ion anisotropy is thoroughly examined with a
goal to tune the degree and thermal stability of the pairwise entanglement. It
turns out that the antiferromagnetic spin-(1/2,$S$) Heisenberg dimers exhibit
higher degree of entanglement and higher threshold temperature in comparison
with their ferromagnetic counterparts when assuming the same set of model
parameters. The increasing spin magnitude $S$ accompanied with an easy-plane
uniaxial single-ion anisotropy can enhance not only the thermal stability but
simultaneously the degree of entanglement. It is additionally shown that the
further enhancement of a bipartite entanglement can be achieved in the mixed
spin-(1/2,$S$) Heisenberg dimers, involving half-odd-integer spins $S$. Under
this condition the thermal negativity saturates at low-enough temperatures in
its maximal value regardless of the magnitude of half-odd-integer spin $S$. The
magnetic field induces consecutive discontinuous phase transitions in the mixed
spin-(1/2,$S$) Heisenberg dimers with $S\!>\!1$, which are manifested in a
surprising oscillating magnetic-field dependence of the negativity observed at
low enough temperature.",2107.05628v2
2021-07-21,On the explosive phase of the tearing mode in double current sheet plasmas: effect of the equilibrium magnetic configuration on the onset threshold and growth rate,"Magnetic reconnection associated with the tearing instability occurring in
double-current sheet systems is investigated within the framework of reduced
resistive magnetohydrodynamics (MHD) in a two-dimensional Cartesian geometry.
The explosive non linear phase is particularly explored using the adaptive
finite-element FINMHD code. The critical aspect ratio, that is defined as the
minimum $L/x_s$ ratio (with $L$ and $x_s$ being the periodic system length and
half-distance between the two current layers respectively) necessary for non
linear destabilization after the linear and early non linear saturation phases,
is obtained. The latter threshold is independent of the details of the chosen
initial equilibrium (double Harris-like magnetic profile) and of the
resistivity. Its value is shown to be $4.7$, that is close and slightly smaller
than the value of order $5$ deduced using a more particular equilibrium
configuration in previous studies. The time dependence of the kinetic energy
($E_K$) is shown to follow a double exponential law, $E_K \propto \exp \
[e^{(\gamma^* t)} ]$, with a pseudo-growth rate $\gamma^* \simeq 0.1 \ t_A^
{-1}$ ($t_A$ being the characteristic Alfv\'en time) that is again independent
of the configuration and resistivity. The mechanism offers a possible
explanation for the sudden onset of explosive magnetic energy release occurring
on the fast Alfv\'en time scale in disruptive events of astrophysical plasmas
with pre-existing double current sheets like in the solar corona.",2107.10069v2
2021-08-16,Effects of spin-lattice coupling and a magnetic field in classical Heisenberg antiferromagnets on the breathing pyrochlore lattice,"We theoretically investigate spin-lattice coupling (SLC) effects on the
in-field ordering properties of classical Heisenberg antiferromagnets on the
breathing pyrochlore lattice. Here, we use the two possible simplified models
describing the effect of local lattice distortions on the spin ordering via the
SLC, the bond-phonon and site-phonon models. It is found by means of Monte
Carlo simulations that in both models, the $\frac{1}{2}$ plateau shows up in
the magnetization curve being relatively robust against the breathing
bond-alternation, although magnetic long-range orders (LRO's) are realized only
in the site-phonon model. In the bond-phonon model, additional further neighbor
interactions are necessary to induce a magnetic LRO. In the site-phonon model,
it is also found that in addition to the low-field, middle-field 1/2-plateau,
and high-field phases appearing on both the uniform and breathing pyrochlore
lattices, various types of unconventional phases which can be viewed as LRO's
in units of tetrahedron are induced by the breathing bond-alternation just
below the 1/2 plateau and the saturation field. The occurrence of these
tetrahedron-based orders could be attributed to the nature characteristic of
the breathing pyrochlore lattice, i.e., the existence of the nonequivalent
small and large tetrahedra. Experimental implications of our result are also
discussed.",2108.06961v2
2021-11-07,"Sol-gel synthesized double perovskite Gd$_{2}$FeCrO$_{6}$ nanoparticles: Structural, magnetic and optical properties","Lead-free double perovskites are overtaking single perovskites as solar
harvesting materials due to their superior stability, excellent catalytic
efficiency and minimal toxicity. In this investigation, we have synthesized
double perovskite Gd$_{2}$FeCrO$_{6}$ (GFCO) nanoparticles for the first time
via a facile sol-gel technique to investigate their structural, magnetic and
optical properties. The double perovskite GFCO crystallized in monoclinic
structure with P2$_1$/n space group. The Fe/Cr-O bond length was calculated as
$\sim$1.95 angstrom from the Raman spectrum which was consistent with the
value, $\sim$1.99 angstrom obtained from X-ray diffraction analysis. The
average size of the nanoparticles was determined to be $\sim$70 nm by both
field emission scanning electron microscopy and transmission electron
microscopy. The existence of mixed-valence states of Fe and Cr was confirmed by
X-ray photoelectron spectroscopy. The zero-field cooled (ZFC) and field cooled
(FC) curves largely diverged below 20 K. A downturn was observed in the ZFC
curve at 15 K which corresponds to an antiferromagnetic, N\'eel transition. The
narrow magnetic hysteresis loop recorded at 5 K was nearly saturated and
demonstrated an asymmetric shift along the magnetic field axis indicating the
concurrence of ferromagnetic and antiferromagnetic domains in GFCO
nanoparticles. The UV-visible and photoluminescence spectroscopic analyses
unveiled the semiconducting nature of nanostructured GFCO with an optical band
gap of 2.0 eV. The as-synthesized thermally stable lead-free GFCO semiconductor
might be a potential perovskite material to be employed in photocatalytic and
related solar energy applications due to its ability to absorb the visible
spectrum of the solar light efficiently",2111.04021v1
2021-11-25,Tunable gigahertz dynamics of low-temperature skyrmion lattice in a chiral magnet,"Recently, it has been shown that the chiral magnetic insulator Cu$_2$OSeO$_3$
hosts skyrmions in two separated pockets in temperature and magnetic field
phase space. It has also been shown that the predominant stabilization
mechanism for the low-temperature skyrmion (LTS) phase is via the crystalline
anisotropy, opposed to temperature fluctuations that stabilize the
well-established high-temperature skyrmion (HTS) phase. Here, we report on a
detailed study of LTS generation by field cycling, probed by GHz spin dynamics
in Cu$_2$OSeO$_3$. LTSs are populated via a field cycling protocol with the
static magnetic field applied parallel to the $\langle{100}\rangle$ crystalline
direction of plate and cuboid-shaped bulk crystals. By analyzing
temperature-dependent broadband spectroscopy data, clear evidence of
low-temperature skyrmion excitations with clockwise (CW), counterclockwise
(CCW), and breathing mode (BR) character at temperatures below $T$ = 40 K are
shown. We find that the mode intensities can be tuned with the number of
field-cycles below the saturation field. By tracking the resonance frequencies,
we are able to map out the field-cycle-generated LTS phase diagram, from which
we conclude that the LTS phase is distinctly separated from the
high-temperature counterpart. We also study the mode hybridization between the
dark CW and the BR modes as a function of temperature. By using two
Cu$_2$OSeO$_3$ crystals with different shapes and therefore different
demagnetization factors, together with numerical calculations, we unambiguously
show that the magnetocrystalline anisotropy plays a central role for the mode
hybridization.",2111.13004v1
2022-04-21,Magnetic phase transition induced ferroelectric polarization in BaFeF4 with room temperature weak ferromagnetism,"BaMF4 (M=Fe, Co, Ni and Mn) family are typical multiferroic materials, having
antiferromagnetism at around liquid nitrogen temperature. In this work,
polycrystalline BaFeF4 has been prepared by solid state reaction. The slight
deficiency of Fe leads to the coexistence of valence states of +2 and +3,
facilitating the electrons to hop between the neighboring Fe2+ and Fe3+ ions
through the middle F- ion, leading to the strong double exchange interaction
with weak ferromagnetism above room temperature. A bifurcation at about 170 K
between the zero-field-cooled and field-cooled temperature dependent
magnetization curves indicates the onset of 2-dimensional antiferromagnetism,
which is completed at about 125 K with the sudden drop of magnetization.
Despite the fact of type-I multiferroic, its magnetoelectricity can be
evidenced by the pyroelectric current, which shows a peak starting at about 170
K and finishing at about 125 K. The saturated ferroelectric polarization change
of around 34 {\mu}C/m2 is observed, which is switchable by the reversed poling
electric field and decreases to about 30 {\mu}C/m2 under a magnetic field of 90
kOe. This magnetoelectricity can be qualitatively reproduced by
first-principles calculations. Our results represent substantial progress to
search for high-temperature multiferroics in ferroelectric fluorides.",2204.10052v1
2022-05-17,MRI-driven dynamo at very high magnetic Prandtl numbers,"The dynamo driven by the magnetorotational instability (MRI) is believed to
play an important role in the dynamics of accretion discs and may also explain
the origin of the extreme magnetic fields present in magnetars. Its saturation
level is an important open question known to be particularly sensitive to the
diffusive processes through the magnetic Prandtl number Pm (the ratio of
viscosity to resistivity). Despite its relevance to proto-neutron stars and
neutron star merger remnants, the numerically challenging regime of high Pm is
still largely unknown. Using zero-net flux shearing box simulations in the
incompressible approximation, we studied MRI-driven dynamos at unprecedentedly
high values of Pm reaching 256. The simulations show that the stress and
turbulent energies are proportional to Pm up to moderately high values
($\mathrm{Pm} \sim 50$). At higher Pm, they transition to a new regime
consistent with a plateau independent of Pm for $\rm Pm \gtrsim 100$. This
trend is independent of the Reynolds number, which may suggest an asymptotic
regime where the energy injection and dissipation are independent of the
diffusive processes. Interestingly, large values of Pm not only lead to intense
small-scale magnetic fields but also to a more efficient dynamo at the largest
scales of the box.",2205.08602v2
2022-08-16,Numerical dependencies of the galactic dynamo in isolated galaxies with SPH,"Understanding the numerical dependencies that act on the galactic dynamo is a
crucial step in determining what resolution and what conditions are required to
properly capture the magnetic fields observed in galaxies. Here, we present an
extensive study on the numerical dependencies of the galactic dynamo in
isolated spiral galaxies using smoothed particle magnetohydrodynamics (SPMHD).
We performed 53 isolated spiral galaxy simulations with different initial
setups, feedback, resolution, Jeans floor and dissipation parameters. The
results show a strong mean-field dynamo occurring in the spiral-arm region of
the disk, likely produced by the classical alpha-omega dynamo or the recently
described gravitational instability dynamo. The inclusion of feedback is seen
to work in both a destructive and positive fashion for the amplification
process. Destructive interference for the amplification occurs due to break
down of filament structure in the disk, increase of turbulent diffusion and the
ejection of magnetic flux from the central plane to the circumgalactic medium.
The positive effect of feedback is the increase in vertical motions and the
turbulent fountain flows that develop, showing a high dependence on the
small-scale vertical structure and the numerical dissipation within the galaxy.
Galaxies with an effective dynamo saturate their magnetic energy density at
levels between 10-30% of the thermal energy density. The density averaged
numerical Prandtl number is found to be below unity throughout the galaxy for
all our simulations, with an increasing value with radius. Assuming a turbulent
injection length of 1 kpc, the numerical magnetic Reynolds number are within
the range of $Re_{mag}=10-400$, indicating that some regions are below the
levels required for the small-scale dynamo ($Re_{mag,crit}=30-2700$) to be
active.",2208.07889v1
2022-11-04,Exchange energies in CoFeB/Ru/CoFeB Synthetic Antiferromagnets,"The interlayer exchange coupling confers specific properties to Synthetic
Antiferromagnets that make them suitable for several applications of
spintronics. The efficient use of this magnetic configuration requires an
in-depth understanding of the magnetic properties and their correlation with
the material structure. Here we establish a reliable procedure to quantify the
interlayer exchange coupling and the intralayer exchange stiffness in synthetic
antiferromagnets; we apply it to the ultrasmooth and amorphous
Co$_{40}$Fe$_{40}$B$_{20}$ (5-40 nm)/Ru/ Co$_{40}$Fe$_{40}$B$_{20}$ material
platform. The complex interplay between the two exchange interactions results
in a gradient of the magnetization orientation across the thickness of the
stack which alters the hysteresis and the spin wave eigenmodes of the stack in
a non trivial way. We measured the field-dependence of the frequencies of the
first four spin waves confined within the thickness of the stack. We modeled
these frequencies and the corresponding thickness profiles of these spin waves
using micromagnetic simulations. The comparison with the experimental results
allows to deduce the magnetic parameters that best account for the sample
behavior. The exchange stiffness is established to be 16 $\pm$ 2 pJ/m,
independently of the Co$_{40}$Fe$_{40}$B$_{20}$ thickness. The interlayer
exchange coupling starts from -1.7 mJ/m$^2$ for the thinnest layers and it can
be maintained above -1.3 mJ/m$^2$ for CoFeB layers as thick as 40 nm. The
comparison of our method with earlier characterizations using the sole
saturation fields argues for a need to revisit the tabulated values of
interlayer exchange coupling in thick synthetic antiferromagnets.",2211.02497v1
2022-11-16,Saturation of the magnetorotational instability and the origin of magnetically elevated accretion discs,"We propose that the strength of angular momentum transport in accretion discs
threaded by net vertical magnetic field is determined by a self-regulation
mechanism: the magnetorotational instability (MRI) grows until its own
turbulent resistivity damps the fastest growing mode on the scale of the disc
thickness. Given weak assumptions as to the structure of MRI-derived
turbulence, supported by prior simulation evidence, the proposed mechanism
reproduces the known scaling of the viscous $\alpha$-parameter, $\alpha \propto
\beta_z^{-1/2}$. Here, $\beta_z = 8\pi p_g/B_{z0}^2$ is the initial plasma
$\beta$-parameter on the disc midplane, $B_{z0}$ is the net field, and $p_g $
is the midplane gas pressure. We generalize the argument to discs with strong
suprathermal toroidal magnetic fields, where the MRI growth rate is modified
from the weak-field limit. Additional sources of turbulence are required if
such discs are to become magnetically elevated, with the increased scale
heights near the midplane that are seen in simulations. We speculate that
tearing modes, associated with current sheets broadened by the effective
resistivity, are a possible source of enhanced turbulence in elevated discs.",2211.09261v2
2022-12-30,Boundary Quantum Phase Transitions in the Spin $\frac{1}{2}$ Heisenberg Chain with Boundary Magnetic Fields,"We consider the spin $\frac{1}{2}$ Heisenberg chain with boundary magnetic
fields and analyze it using a combination of Bethe ansatz and density matrix
renormalization group (DMRG) techniques. We show that the system exhibits
several different ground states which depend on the orientation of the boundary
magnetic fields. When both the boundary fields take equal values greater than a
critical field strength, each edge in the ground state accumulates a fractional
spin which saturates to spin $\frac{1}{4}$, which is similar to systems
exhibiting symmetry protected topological phases (SPT). Unlike in SPT systems,
the fractional boundary spin in the Heisenberg spin chain is not a genuine
quantum number since the variance of the associated operator does not vanish,
this is due to the absence of a bulk gap. The system exhibits high energy bound
states when the boundary fields take values greater than the critical field.
All the excitations in the system can be sorted out into towers whose number
depends on the number of bound states exhibited by the system. As the boundary
fields are varied, in addition to the ground state phase transition, we find
that the system may undergo an eigenstate phase transition (EPT) where the
number of towers of the Hilbert space changes. We further inquire how the EPT
reflects itself on local ground state properties by computing the magnetization
profile $\langle S^z_j \rangle$ using DMRG. We identify a clear qualitative
change from low edge fields to high edge fields when crossing the critical
field. We though are unable to conclude on the basis of our data that EPT
corresponds to a genuine phase transition in the ground state.",2212.14832v1
2023-03-22,Enhancing Spin Transfer Torque in Magnetic Tunnel Junction Devices: Exploring the Influence of Capping Layer Materials and Thickness on Device Characteristics,"We have developed and optimized two categories of spin transfer torque
magnetic tunnel junctions (STT-MTJs) that exhibit a high tunnel
magnetoresistance (TMR) ratio, low critical current, high outputpower in the
micro watt range, and auto-oscillation behavior. These characteristics
demonstrate the potential of STT-MTJs for low-power, high-speed, and reliable
spintronic applications, including magnetic memory, logic, and signal
processing. The only distinguishing factor between the two categories, denoted
as A-MTJs and B-MTJs, is the composition of their free layers, 2 CoFeB/0.21
Ta/6 CoFeSiB for A-MTJs and 2 CoFeB/0.21 Ta/7 NiFe for B-MTJs. Our study
reveals that B-MTJs exhibit lower critical currents for auto-oscillation than
A-MTJs. We found that both stacks have comparable saturation magnetization and
anisotropy field, suggesting that the difference in auto-oscillation behavior
is due to the higher damping of A-MTJs compared to B-MTJs. To verify this
hypothesis, we employed the all-optical time-resolved magneto-optical Kerr
effect (TRMOKE) technique, which confirmed that STT-MTJs with lower damping
exhibited auto-oscillation at lower critical current values. Additionally, our
study aimed to optimize the STT-MTJ performance by investigating the impact of
the capping layer on the device's response to electronic and optical stimuli.",2303.12450v2
2023-05-30,Dynamic and Rapid Deep Synthesis of Molecular MRI Signals,"Model-driven analysis of biophysical phenomena is gaining increased attention
and utility for medical imaging applications. In magnetic resonance imaging
(MRI), the availability of well-established models for describing the relations
between the nuclear magnetization, tissue properties, and the externally
applied magnetic fields has enabled the prediction of image contrast and served
as a powerful tool for designing the imaging protocols that are now routinely
used in the clinic. Recently, various advanced imaging techniques have relied
on these models for image reconstruction, quantitative tissue parameter
extraction, and automatic optimization of acquisition protocols. In molecular
MRI, however, the increased complexity of the imaging scenario, where the
signals from various chemical compounds and multiple proton pools must be
accounted for, results in exceedingly long model simulation times, severely
hindering the progress of this approach and its dissemination for various
clinical applications. Here, we show that a deep-learning-based system can
capture the nonlinear relations embedded in the molecular MRI Bloch-McConnell
model, enabling a rapid and accurate generation of biologically realistic
synthetic data. The applicability of this simulated data for in-silico,
in-vitro, and in-vivo imaging applications is then demonstrated for chemical
exchange saturation transfer (CEST) and semisolid macromolecule magnetization
transfer (MT) analysis and quantification. The proposed approach yielded
78%-99% acceleration in data synthesis time while retaining excellent agreement
with the ground truth (Pearson's r$>$0.99, p$<$0.0001, normalized root mean
square error $<$3%).",2305.19413v1
2023-08-31,Flares in the Galactic Centre II: polarisation signatures of flares at mm-wavelengths,"Recent polarimetric mm-observations of the galactic centre by Wielgus et al.
(2022a) showed sinusoidal loops in the Q-U plane with a duration of one hour.
The loops coincide with a quasi-simultaneous X-ray flare. A promising mechanism
to explain the flaring events are magnetic flux eruptions in magnetically
arrested accretion flows (MAD). In our previous work (Porth et al. 2021), we
studied the accretion flow dynamics during flux eruptions. Here, we extend our
previous study by investigating whether polarization loops can be a signature
produced by magnetic flux eruptions. We find that loops in the Q-U plane are
robustly produced in MAD models as they lead to enhanced emissivity of
compressed disk material due to orbiting flux bundles. A timing analysis of the
synthetic polarized lightcurves demonstrate a polarized excess variability at
timescales of ~ 1 hr. The polarization loops are also clearly imprinted on the
cross-correlation of the Stokes parameters which allows to extract a typical
periodicity of 30 min to 1 hr with some evidence for a spin dependence. These
results are intrinsic to the MAD state and should thus hold for a wide range of
astrophysical objects. A subset of GRMHD simulations without saturated magnetic
flux (single temperature SANE models) also produces Q-U loops. However, in
disagreement with the findings of Wielgus et al. (2022a), loops in these
simulations are quasi-continuous with a low polarization excess",2308.16740v1
2023-10-13,"Magnetic structure, excitations and field induced transitions in the honeycomb lattice $\rm{Er_2Si_2O_7}$","We investigate the magnetic properties of the monoclinic D-type
$\rm{Er_2Si_2O_7}$ with a distorted honeycomb lattice using powder and single
crystal neutron scattering techniques, as well as single crystal magnetisation
measurements. The powder neutron diffraction shows that below the ordering
temperature, $T_{\rm N}=1.85$ K, the compound forms a ${\bf q}=0$
antiferromagnetic structure with four sublattices. For $H \! \parallel \! a$,
magnetisation measurements reveal a narrow, but clearly visible plateau at one
third of the magnetisation saturation value. The plateau's stabilisation is
accompanied by a significant increase of the magnetic unit cell, as the
magnetic peaks with fractional indices are observed in single crystal neutron
diffraction experiments. At low-temperatures, the inelastic neutron scattering
measurements reveal the presence of low-energy dispersionless excitations.
Their spectrum is sensitive to the applied field, it significantly softens on
the magnetisation plateau, and demonstrates the behaviour expected for a
non-collinear Ising antiferromagnet away from the plateau.",2310.09268v3
2023-11-13,Robust magnetic proximity induced anomalous Hall effect in a room temperature van der Waals ferromagnetic semiconductor based 2D heterostructure,"Developing novel high-temperature van der Waals ferromagnetic semiconductor
materials and investigating their interface coupling effects with
two-dimensional topological semimetals are pivotal for advancing
next-generation spintronic and quantum devices. However, most van der Waals
ferromagnetic semiconductors exhibit ferromagnetism only at low temperatures,
limiting the proximity research on their interfaces with topological
semimetals. Here, we report an intrinsic, van der Waals layered
room-temperature ferromagnetic semiconductor crystal, FeCr0.5Ga1.5Se4 (FCGS),
with a Curie temperature as high as 370 K, setting a new record for van der
Waals ferromagnetic semiconductors. The saturation magnetization at low
temperature (2 K) and room temperature (300 K) reaches 8.2 emu/g and 2.7 emu/g,
respectively. Furthermore, FCGS possesses a bandgap of approximately 1.2 eV,
which is comparable to the widely used commercial silicon. The FCGS/graphene
heterostructure exhibits an impeccably smooth and gapless interface, thereby
inducing a robust magnetic proximity coupling effect between FCGS and graphene.
After the proximity coupling, graphene undergoes a charge carrier transition
from electrons to holes, accompanied by a transition from non-magnetic to
ferromagnetic transport behavior with robust anomalous Hall effect. Notably,
the anomalous Hall effect remains robust even temperatures up to 400 K.",2311.07183v1
2024-02-11,Probing Magnetic and Triplet Correlations in Spin-Split Superconductors with Magnetic Impurities,"A superconductor (SC) in proximity to a ferromagnetic insulator (FMI) is
predicted to exhibit mixed singlet and triplet pair correlations. The magnetic
proximity effect of FMI spin-splits the energy of Bogoliubov excitations and
leads to a spin polarization at the surface for superconducting films thinner
than the superconducting coherence length. In this work, we study
manifestations of these phenomena in the properties of a magnetic impurity
coupled via Kondo coupling to this FMI/SC system. Using the numerical
renormalization group (NRG) method, we compute the properties of the ground
state and low-lying excited states of a model that incorporates the Kondo
interaction and a Ruderman-Kittel-Kasuya-Yosida (RKKY)-like interaction with
the surface spin polarization. Our main finding is an energy splitting of the
lowest even fermion-parity states caused by the proximity to the FMI. As the
Kondo coupling increases, the splitting grows and saturates to a universal
value equal to twice the exchange field of the FMI. We introduce a two-site
model that can be solved analytically and provides a qualitative understanding
of this and other NRG results. In addition, using perturbation theory we
demonstrate that the mechanism behind the splitting involves the RKKY field and
the triplet correlations of the spin-split superconductor. A scaling analysis
combined with NRG shows that the splitting can be written as a single-parameter
scaling function of the ratio of the Kondo temperature and the superconducting
gap, which is also numerically obtained.",2402.07184v1
2024-02-16,Live magnetic observation of parahydrogen hyperpolarization dynamics,"Nuclear spin hyperpolarization is used in physics, chemistry, and medicine to
produce strong magnetization unachievable by equilibrium polarization
techniques. Hyperpolarization enables magnetic resonance spectroscopy and
imaging with minute samples, and is used to produce MRI spin-tracers and
polarized physics targets. Although widely used, the dynamics of the
hyperpolarization process have never been studied `live' due to the extremely
low (Hz-band) frequencies involved, and/or detector saturation by the driving
fields used. Here, we use an atomic magnetometer with sub-pT sensitivity to
observe, in real time, the complex dynamics of hyperpolarization, without
disturbing or disrupting the process. We start by examining
parahydrogen-induced $^1$H and $^{13}$C magnetization build-up during adiabatic
eigenbasis transformations in the $\mu$T-field avoided state crossings at the
heart of the process; we see live hyperpolarization dynamics including coherent
oscillations, leakage mechanisms and dipolar shifts that would be challenging
or impossible to observe by post hoc measurement. We then extend the methods to
observe the chemical-exchange-driven $^{13}$C hyperpolarization of
[1-$^{13}$C]-pyruvate -- the most important spin tracer for clinical metabolic
imaging. Beyond the interests of hyperpolarization, the observation of
adiabatic transitions in real-time is a fundamentally new approach to NMR,
reveals previously hidden nuclear spin dynamics and enables quantum control and
live process optimization in a variety of chemical scenarios.",2402.10766v1
2024-03-14,Inelastic neutron scattering and muon spin relaxation investigations of the deuterated Kondo lattices CeNiSnD$ _x $,"CeNiSn is a Kondo semimetal where a gap opens at low temperatures due to
hybridization between 4$f$ and conduction electrons, but a full insulating
state fails to develop. Upon the insertion of hydrogen, long range magnetic
order is induced. Here we report zero-field muon-spin relaxation and inelastic
neutron scattering measurements of polycrystalline samples of the deuterides
CeNiSnD$_x$ ($x$=1.0, 1.8). The muon-spin relaxation results confirm magnetic
ordering in the whole sample of CeNiSnD below around 4.7 K, while inelastic
neutron scattering reveals two well-defined crystalline-electric field (CEF)
excitations at around 13 meV and 34 meV in CeNiSnD, and 5 meV and 27 meV for
CeNiSnD$_{1.8}$. These results suggest that hydrogenation leads to the
localization of the Ce-4$f$ electrons, giving rise to long-range magnetic
order. We propose CEF level schemes for both systems, which predict a ground
state moment of 0.96$\mu_{\rm B}$/Ce within the $ab$-plane for CeNiSnD$_{1.8}$
and a saturated moment of 1.26$\mu_{\rm B}$/Ce along the easy $c$ axis for
CeNiSnD, that account for the observed magnetic properties.",2403.09424v1
2019-07-12,On induced saturation for paths,"For a graph $H$, a graph $G$ is $H$-induced-saturated if $G$ does not contain
an induced copy of $H$, but either removing an edge from $G$ or adding a
non-edge to $G$ creates an induced copy of $H$. Depending on the graph $H$, an
$H$-induced-saturated graph does not necessarily exist. In fact, Martin and
Smith (2012) showed that $P_4$-induced-saturated graphs do not exist, where
$P_k$ denotes a path on $k$ vertices. Axenovich and Csik\'{o}s (2019) asked the
existence of $P_k$-induced-saturated graphs for $k \ge 5$; it is easy to
construct such graphs when $k\in\{2, 3\}$. Recently, R\""{a}ty constructed a
graph that is $P_6$-induced-saturated. In this paper, we show that there exists
a $P_{k}$-induced-saturated graph for infinitely many values of $k$. To be
precise, we find a $P_{3n}$-induced-saturated graph for every positive integer
$n$. As a consequence, for each positive integer $n$, we construct infinitely
many $P_{3n}$-induced-saturated graphs. We also show that the Kneser graph
$K(n,2)$ is $P_6$-induced-saturated for every $n\ge 5$.",1907.05546v1
2022-06-01,Defensive Design of Saturating Counters Based on Differential Privacy,"The saturating counter is the basic module of the dynamic branch predictor,
which involves the core technique to improve instruction level parallelism
performance in modern processors. However, most studies focus on the
performance improvement and hardware consumption of saturating counters, while
ignoring the security problems they may cause. In this paper, we creatively
propose to study and design saturating counters from the defense perspective of
differential privacy, so that attackers cannot distinguish the states that
saturating counters are in and further infer sensitive information. To obtain
theoretical guarantees, we use Markov chain to formalize the attack algorithm
applied to the saturating counter, investigate into the optimal attack strategy
and calculate the probability of successful attack. Furthermore, we find that
the attacker is able to accurately guess the branch execution of the victim's
process in the existing saturating counters. To avoid this, we design a new
probabilistic saturating counter, which generalizes the existing conventional
and probabilistic saturating counters. The guarantee of differential privacy is
applied to deduce parameters of the new saturating counters so that the
security requirement can be satisfied. We also theoretically calculate the
misprediction rate when the saturating counter reaches the steady state. The
experimental results on testing programs show that the calculated theoretical
results agree with the experimental performances. Compared with the existing
conventional and probabilistic saturating counters, when the parameters of our
designed models are selected appropriately, the new saturating counters can not
only ensure similar operational performance, but also establish strict security
guarantee.",2206.00279v1
1994-08-04,Gamma-Rays from the Funnels of Thick Accretion Disks Around Active Galactic Nuclei,"We analyse the propagation of particles in the narrow funnel of a thick
accretion disk. It is assumed that: (1) the funnel walls emit black body
radiation with temperature decreasing outwards; (2) the magnetic and electric
fields are longitudinal in the funnel. Such a scenario is consistent with
models in which a large potential drop is induced by a rotating massive black
hole threaded by a magnetic field (Blandford & Znajek 1977, Macdonald & Thorne
1982). The interaction of relativistic protons with thermal photons from the
funnel results in direct production of pairs and/or pions. We discuss the
relative importance of these processes for different conditions in the funnel
(temperature and electric field profiles). Injected pairs interact with thermal
photons in the Thomson or Klein-Nishina regime. Under some conditions, a pair
avalanche results, which we assume saturates in the production of stable
bunches, containing almost equal numbers of electrons and positrons. As a
consequence, highly collimated gamma-ray photons are produced. We obtain
gamma-ray spectra from our model in order to test its applicability to the
gamma-ray emitting AGNs recently reported by EGRET.",9408013v1
1996-09-18,The origin of large scale magnetic fields,"Magnetic fields correlated on several kiloparsec scales are seen in spiral
galaxies. Their origin could be due to the winding up of a primordial
cosmological field or due to amplification of a small seed field by a turbulent
galactic dynamo. Both options have difficulties: There is no known battery
mechanism for producing the required primordial field. Equally the turbulent
dynamo may self destruct before being able to produce the large scale field,
due to excess generation of small scale power. The current status of these
difficulties is discussed. The resolution could depend on the nature of the
saturated field produced by the small scale dynamo. We argue that the small
scale fields do not fill most of the volume of the fluid and instead
concentrate into intermittent ropes, with their peak value of order
equipartition fields, and radii much smaller than their lengths. In this case
these fields neither drain significant energy from the turbulence nor convert
eddy motion of the turbulence on the outer scale to wave like motion. This
preserves the diffusive effects needed for the large scale dynamo operation.",9609123v1
1998-05-07,Angular Momentum Transport in the Central Region of the Galaxy,"We discuss mechanisms for angular momentum transport in the clumpy medium of
the circumnuclear disk at the Galactic center. The viscosity due to clump-clump
collisions is found to be less than some critical viscosity; this meets the
conditions at which a collective mode of nonaxisymmetric shear perturbations in
the disk is able to grow until going into the saturation regime where fully
developed turbulence is established. We find that the angular momentum transfer
due to this turbulent viscosity turns out to comparable to the transport due to
magnetic torques. Taken together, the turbulent and magnetic transfer of
angular momentum are able to provide the inflow of mass into the central parsec
with a rate of about 10^{-2} M_{sun}/yr, consistent with the available data.",9805098v1
1999-04-22,Monopole-antimonopole bound states as a source of ultra-high-energy cosmic rays,"The electromagnetic decay and final annihilation of magnetic
monopole-antimonopole pairs formed in the early universe has been proposed as a
possible mechanism to produce the highest energy cosmic rays. We show that for
a monopole abundance saturating the Parker limit, the density of magnetic
monopolonium formed is many orders of magnitude less than that required to
explain the observed cosmic ray flux. We then propose a different scenario in
which the monopoles and antimonopoles are connected by strings formed at a low
energy phase transition (~ 100 GeV). The bound states decay by gravitational
radiation, with lifetimes comparable with the age of the universe. This
mechanism avoids the problems of the standard monopolonium scenario, since the
binding of monopoles and antimonopoles is perfectly efficient.",9904315v1
1999-08-25,A Unified treatment of small and large- scale dynamos in helical turbulence,"Helical turbulence is thought to provide the key to the generation of
large-scale magnetic fields. Turbulence also generically leads to rapidly
growing small-scale magnetic fields correlated on the turbulence scales. These
two processes are usually studied separately. We give here a unified treatment
of both processes, in the case of random fields, incorporating also a simple
model non-linear drift. In the process we uncover an interesting plausible
saturated state of the small-scale dynamo and a novel analogy between quantum
mechanical (QM) tunneling and the generation of large scale fields. The steady
state problem of the combined small/large scale dynamo, is mapped to a
zero-energy, QM potential problem; but a potential which, for non-zero mean
helicity, allows tunneling of bound states. A field generated by the
small-scale dynamo, can 'tunnel' to produce large-scale correlations, which in
steady state, correspond to a force-free 'mean' field.",9908280v1
2001-06-15,Astrophysical significance of the anisotropic kinetic alpha effect,"The generation of large scale flows by the anisotropic kinetic alpha (AKA)
effect is investigated in simulations with a suitable time-dependent space- and
time-periodic anisotropic forcing lacking parity invariance. The forcing
pattern moves relative to the fluid, which leads to a breaking of the Galilean
invariance as required for the AKA effect to exist. The AKA effect is found to
produce a clear large scale flow pattern when the Reynolds number, R, is small
as only a few modes are excited in linear theory. In this case the
non-vanishing components of the AKA tensor are dynamically independent of the
Reynolds number. For larger values of R, many more modes are excited and the
components of the AKA tensor are found to decrease rapidly with increasing
value of R. However, once there is a magnetic field (imposed and of sufficient
strength, or dynamo-generated and saturated) the field begins to suppress the
AKA effect, regardless of the value of R. It is argued that the AKA effect is
unlikely to be astrophysically significant unless the magnetic field is weak
and R is small.",0106280v1
2002-07-22,A New Dynamical Mean-Field Dynamo Theory and Closure Approach,"We develop a new nonlinear mean field dynamo theory that couples field growth
to the time evolution of the magnetic helicity and the turbulent electromotive
force, $\emfb$. We show that the difference between kinetic and current
helicities emerges naturally as the growth driver when the time derivative of
$\emfb$ is coupled into the theory. The solutions predict significant field
growth in a kinematic phase and a saturation rate/strength that is magnetic
Reynolds number dependent/independent in agreement with numerical simulations.
The amplitude of early time oscillations provides a diagnostic for the closure.",0207435v3
2004-10-27,Magnetic field generation in fully convective rotating spheres,"Magnetohydrodynamic simulations of fully convective, rotating spheres with
volume heating near the center and cooling at the surface are presented. The
dynamo-generated magnetic field saturates at equipartition field strength near
the surface. In the interior, the field is dominated by small-scale structures,
but outside the sphere by the global scale. Azimuthal averages of the field
reveal a large-scale field of smaller amplitude also inside the star. The
internal angular velocity shows some tendency to be constant along cylinders
and is ``anti-solar'' (fastest at the poles and slowest at the equator).",0410645v2
2005-01-21,Diffusion coefficient of a passive contaminant in a local MHD model of a turbulent accretion disc,"We calculate the radial diffusion coefficient for a passive contaminant in an
accretion disc which is turbulent due to the action of the magnetorotational
instability. Numerical MHD simulations are used to follow the evolution of a
local patch of the disc using the shearing box formalism. A separate continuity
equation for the mass fraction of contaminant is integrated along with the MHD
system, and radial profiles of this fraction are obtained as a function of
time. Solutions of a linear diffusion equation are fitted to the numerical
measured profiles of the contaminant, treating the diffusion coefficient D as
the fitting parameter. At early times, the value of D is found to vary, however
once the contaminant is spread over scales comparable to the box size, it
saturates at a steady value. The ratio of D to the transport coefficient of
angular momentum due to shear stress is small. If D can be used as a proxy for
the turbulent magnetic diffusivity, the effective magnetic Prandtl number
P_eff=\nu/D (where \nu is the coefficient of ""efective viscosity"" associated
with shear stress) would be large.",0501474v1
2006-07-06,Empirical relation between angular momentum transport and thermal-to-magnetic pressure ratio in shearing box simulations,"By combining data from different published 3-D simulations of Keplerian
shearing boxes unstable to the magnetorotational instability (MRI), we
highlight tight anti-correlations between the total effective inferred angular
momentum transport parameter, $\alpha_{tot}$, its separate Maxwell and Reynolds
contributions $\alpha_{mag}$ and $\alpha_{kin}$, and the kinetic to magnetic
pressure ratio $\beta$, defined with the initial or saturated (when available)
thermal pressure.
  Plots of $Log (\alpha_{kin}), Log (\alpha_{mag})$, and $Log (\alpha_{tot})$
vs $Log (\beta)$ are well fit by straight lines even as $\alpha_{kin}$,
$\alpha_{mag}$,and $\alpha_{tot}$ vary by four orders of magnitude over the
simulations included. The ratio $\alpha_{kin}/\alpha_{mag}$ and the product
$\alpha_{tot}\beta$ are quite constant and largely independent of the presence
or absence of weak mean fields, the choice of initial and boundary conditions,
and the resolution. In short, simulations have more strongly constrained the
product $\alpha_{tot}\beta$ than $\alpha_{tot}$ itself.",0607119v4
2006-12-27,"Spectral Methods for Time-Dependent Studies of Accretion Flows. III. Three-Dimensional, Self-gravitating, Magnetohydrodynamic Disks","Accretion disks are three-dimensional, turbulent, often self-gravitating,
magnetohydrodynamic flows, which can be modeled in detail with numerical
simulations. In this paper, we present a new algorithm that is based on a
spectral decomposition method to simulate such flows. Because of the high order
of the method, we can solve the induction equation in terms of the magnetic
potential and, therefore, ensure trivially that the magnetic fields in the
numerical solution are divergence free. The spectral method also suffers
minimally from numerical dissipation and allows for an easy implementation of
models for sub-grid physics. Both properties make our method ideal for studying
MHD turbulent flows such as those found in accretion disks around compact
objects. We verify our algorithm with a series of standard tests and use it to
show the development of MHD turbulnce in a simulation of an accretion disk.
Finally, we study the evolution and saturation of the power spectrum of MHD
turbulence driven by the magnetorotational instability.",0612742v1
1994-10-10,Monte Carlo Simulation of Ising Models with Dipole Interaction,"Recently, a new memory effect was found in the metamagnetic domain structure
of the diluted Ising antiferromagnet $Fe_x Mg_{1-x} Cl_2$ by domain imaging
with Faraday contrast. Essential for this effect is the dipole interaction. We
simulate the low temperature behavior of diluted Ising-antiferromagnets by a
Monte Carlo simulation considering long range interaction. The metamagnetic
domain structure occurring due to the dipole interaction is investigated by
graphical representation. In the model considered the antiferromagnetic state
is stable for an external magnetic field smaller than a lower boundary $B_{c1}$
while for fields larger than an upper boundary $B_{c2}$ the system is in the
saturated paramagnetic phase, where the spins are ferromagnetically polarized.
For magnetic fields in between these two boundaries a mixed phase occurs
consisting of ferromagnetic domains in an antiferromagnetic background. The
position of these ferromagnetic domains is stored in the system: after a cycle
in which the field is first removed and afterwards applied again the domains
reappear at their original positions. The reason for this effect can be found
in the frozen antiferromagnetic domain state which occurs after removing the
field.",9410028v1
1998-07-03,Temperature dependence of the normal-state Hall coefficient of a quasi-one-dimensional metal,"We develop a systematic theory of the Hall effect in Q1D conductors in both
weak and strong magnetic fields for a model where the electron relaxation time
varies over the Fermi surface. At high temperatures, the Hall coefficient
saturates at the value $-\beta/ecn$, where the dimensionless coefficient
$\beta$ is determined by the curvature of the longitudinal dispersion law of
electrons, $e$ the electron charge, $c$ is the speed of light, and $n$ is the
hole concentration. At low temperatures, where a strong variation of the
relaxation rate over the Fermi surface develops in the form of ``hot spots'',
the Hall coefficient becomes temperature-dependent and may change sign for a
particular choice of the transverse dispersion law parameters. In our model,
the sign changes in a weak, but not in a strong magnetic field.",9807047v3
1999-03-26,Resistive Transition and Upper Critical Field in Underdoped YBa_2Cu_3O_{6+x} Single Crystals,"A superconducting transition in the temperature dependence of the ab-plane
resistivity of underdoped YBa_2Cu_3O_{6+x} crystals in the range T_c<30 K has
been investigated. Unlike the case of samples with the optimal level of doping,
the transition width increased insignificantly with magnetic field, and in the
range T_c<13 K it decreased with increasing magnetic field. The transition
point T_c(B) was determined by analyzing the fluctuation conductivity. The
curves of B_{c2}(T) measured in the region T/T_c>0.1 did not show a tendency to
saturation and had a positive second derivative everywhere, including the
immediate neighborhood of T_c. The only difference among the curves of
B_{c2}(T) for different crystal states is the scales of T and B, so they can be
described in terms of a universal function, which fairly closely follows
Alexandrov's model of boson superconductivity.",9903397v1
1999-04-22,Magnetotransport in manganites and the role of quantal phases II: Experiment,"As in conventional ferromagnets, the Hall resistivity rho_xy of a
La_{2/3}(Ca,Pb)_{1/3}MnO_3 single crystal exhibits both ordinary and anomalous
contributions at low temperature. However, these contributions, unexpectedly,
have opposite signs. Near Tc, the ordinary contribution is no longer evident
and rho_xy is solely determined by the sample magnetization, reaching an
extremum at approximately 40% of the saturated magnetization. A new model for
the anomalous Hall effect, incorporating the quantal phase accumulated by
double-exchange, three-site hopping reproduces this result. Below Tc, rho_xy
reflects the competition between normal and anomalous Hall effects.",9904332v1
1999-07-22,Charge carrier density collapse in La_0.67Ca_0.33MnO_3 and La_0.67Sr_0.33MnO_3 epitaxial thin films,"We measured the temperature dependence of the linear high field Hall
resistivity of La_0.67Ca_0.33MnO_3 (T_C=232K) and La_0.67Sr_0.33MnO_3
(T_C=345K) thin films in the temperature range from 4K up to 360K in magnetic
fields up to 20T. At low temperatures we find a charge carrier density of 1.3
and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In
this temperature range electron-magnon scattering contributes to the
longitudinal resistivity. At the ferromagnetic transition temperature T_C a
dramatic drop in the number of current carriers $n$ down to 0.6 holes per unit
cell, accompanied by an increase in unit cell volume, is observed. Corrections
of the Hall data due to a non saturated magnetic state will lead a more
pronounced charge carrier density collapse.",9907346v1
1999-09-07,Semiclassical Theory of Integrable and Rough Andreev Billiards,"We study the effect on the density of states in mesoscopic ballistic
billiards to which a superconducting lead is attached. The expression for the
density of states is derived in the semiclassical S-matrix formalism shedding
insight into the origin of the differences between the semiclassical theory and
the corresponding result derived from random matrix models. Applications to a
square billiard geometry and billiards with boundary roughness are discussed.
The saturation of the quasiparticle excitation spectrum is related to the
classical dynamics of the billiard. The influence of weak magnetic fields on
the proximity effect in rough Andreev billiards is discussed and an analytical
formula is derived. The semiclassical theory provides an interpretation for the
suppression of the proximity effect in the presence of magnetic fields as a
coherence effect of time reversed trajectories, similar to the weak
localisation correction of the magneto-resistance in chaotic mesoscopic
systems. The semiclassical theory is shown to be in good agreement with quantum
mechanical calculations.",9909100v2
2000-04-12,Small Angle Shubnikov-de Haas Measurements in Silicon MOSFET's: the Effect of Strong In-Plane Magnetic Field,"Measurements in magnetic fields applied at small angles relative to the
electron plane in silicon MOSFETs indicate a factor of two increase of the
frequency of Shubnikov-de Haas oscillations at H>H_{sat}. This signals the
onset of full spin polarization above H_{sat}, the parallel field above which
the resistivity saturates to a constant value. For H<H_{sat}, the phase of the
second harmonic of the oscillations relative to the first is consistent with
scattering events that depend on the overlap instead of the sum of the spin-up
and spin-down densities of states.",0004201v2
2000-05-16,Magnetic fluctuations in 2D metals close to the Stoner instability,"We consider the effect of potential disorder on magnetic properties of a
two-dimensional metallic system (with conductance $g\gg 1$) when interaction in
the triplet channel is so strong that the system is close to the threshold of
the Stoner instability. We show, that under these conditions there is an
exponentially small probability for the system to form local spin droplets
which are local regions with non zero spin density. Using a non-local version
of the optimal fluctuation method we find analytically the probability
distribution and the typical spin of a local spin droplet (LSD). In particular,
we show that both the probability to form a LSD and its typical spin are
independent of the size of the droplet (within the exponential accuracy). The
LSDs manifest themselves in temperature dependence of observable quantities. We
show, that below certain cross-over temperature the paramagnetic susceptibility
acquires the Curie-like temperature dependence, while the dephasing time
(extracted from magneto-resistance measurements) saturates.",0005267v1
2000-06-30,Off equilibrium properties of vortex creep in superconductors,"We study a model for the dynamics of vortices in type II superconductors. In
particular, we discuss glassy ``off equilibrium'' properties and ``aging'' in
magnetic creep. At low temperatures a crossover point is found, Tg, where
relaxation times seem to diverge a' la Vogel-Tamman-Fulcher. Magnetic creep
changes by crossing Tg: above Tg power law creep is found asymptotically
followed by stretched exponential saturation; below Tg the creep is logarithmic
and vortex motion strongly subdiffusive. In this region violation of time
translation invariance is found along with important dynamical scaling
properties. A thermodynamic glassy transition point can be found at a lower
temperature Tc.",0006491v2
2000-07-14,Cationic ordering control of magnetization in Sr2FeMoO6 double perovskite,"The role of the synthesis conditions on the cationic Fe/Mo ordering in
Sr2FeMoO6 double perovskite is addressed. It is shown that this ordering can be
controlled and varied systematically. The Fe/Mo ordering has a profound impact
on the saturation magnetization of the material. Using the appropriate
synthesis protocol a record value of 3.7muB/f.u. has been obtained. Mossbauer
analysis reveals the existence of two distinguishable Fe sites in agreement
with the P4/mmm symmetry and a charge density at the Fe(m+) ions significantly
larger than (+3) suggesting a Fe contribution to the spin-down conduction band.
The implications of these findings for the synthesis of Sr2FeMoO6 having
optimal magnetoresistance response are discussed.",0007248v1
2001-08-19,Optical Pumping in Ferromagnet-Semiconductor Heterostructures: Magneto-optics and Spin Transport,"Epitaxial ferromagnetic metal - semiconductor heterostructures are
investigated using polarization-dependent electroabsorption measurements on
GaAs p-type and n-type Schottky diodes with embedded In1-xGaxAs quantum wells.
We have conducted studies as a function of photon energy, bias voltage,
magnetic field, and excitation geometry. For optical pumping with circularly
polarized light at energies above the band edge of GaAs, photocurrents with
spin polarizations on the order of 1 % flow from the semiconductor to the
ferromagnet under reverse bias. For optical pumping at normal incidence, this
polarization may be enhanced significantly by resonant excitation at the
quantum well ground-state. Measurements in a side-pumping geometry, in which
the ferromagnet can be saturated in very low magnetic fields, show hysteresis
that is also consistent with spin-dependent transport. Magneto-optical effects
that influence these measurements are discussed.",0108292v1
2001-08-31,Inversion Phenomena of the Anisotropies of the Hamiltonian and the Wave-Function in the Distorted Diamond Type Spin Chain,"We investigate the ground-sate phase diagram of the XXZ version of the S=1/2
distorted diamond chain by use of the degenerate perturbation theory near the
truncation point. In case of the XY-like interaction anisotropy, the phase
diagram consists of the Neel phase and the spin-fluid phase. For the Ising-like
interaction anisotropy case, it consists of three phases: the ferrimagnetic
phase, the Neel phase and the spin-fluid phase. The magnetization in the
ferrimagnetic phase is 1/3 of the saturation magnetization. The remarkable
nature of the phase diagram is the existence of the Neel phase, although the
interaction anisotropy is XY-like. And also, the spin-fluid phase appears in
spite of the Ising-like interaction anisotropy. We call these regions
""inversion regions"".",0108528v1
2001-11-27,Light and electric field control of ferromagnetism in magnetic quantum structures,"A strong influence of illumination and electric bias on the Curie temperature
and saturation value of the magnetization is demonstrated for semiconductor
structures containing a modulation-doped p-type Cd0.96Mn0.04Te quantum well
placed in various built-in electric fields. It is shown that both light beam
and bias voltage generate an isothermal and reversible cross-over between the
paramagnetic and ferromagnetic phases, in the way that is predetermined by the
structure design. The observed behavior is in quantitative agreement with the
expectations for systems, in which ferromagnetic interactions are mediated by
the weakly disordered two-dimensional hole liquid.",0111511v2
2001-12-18,Effects of a Parallel Magnetic Field on the Metal-Insulator Transition in a Dilute Two-Dimensional Electron System,"The temperature dependence of conductivity $\sigma (T)$ of a two-dimensional
electron system in silicon has been studied in parallel magnetic fields B. At
B=0, the system displays a metal-insulator transition at a critical electron
density $n_c(0)$, and $d\sigma/dT >0$ in the metallic phase. At low fields
($B\lesssim 2$ T), $n_c$ increases as $n_c(B) - n_c(0) \propto B^{\beta}$
($\beta\sim 1$), and the zero-temperature conductivity scales as $\sigma
(n_s,B,T=0)/\sigma (n_s,0,0)=f(B^{\beta}/\delta_n)$ (where
$\delta_n=(n_s-n_c(0))/n_c(0)$, and $n_s$ is electron density) as expected for
a quantum phase transition. The metallic phase persists in fields of up to 18
T, consistent with the saturation of $n_c$ at high fields.",0112344v2
2001-12-27,The longitudinal spin relaxation of 2D electrons in Si/SiGe quantum wells in a magnetic field,"The longitudinal spin relaxation time, T1, in a Si/SiGe quantum well is
determined from the saturation of the ESR signal. We find values of a few
microseconds. Investigations of T1 as a function of Fermi energy, concentration
of scattering centers and of the momentum scattering time lead to the
conclusion that for high electron mobility the spin relaxation is ruled by the
Dyakonov-Perel (DP) mechanism while for low mobility the Elliott-Yaffet
mechanism dominates. The DP relaxation is caused by Bychkov-Rashba coupling.
Evaluation of the DP mechanism shows that 1/T1 for high electron mobility can
be effectively reduced by an external magnetic field. The effect of the
degenerate Fermi-Dirac statistics on the DP process is discussed.",0112466v1
2002-01-26,"Unconventional carrier-mediated ferromagnetism above room temperature in ion-implanted (Ga, Mn)P:C","Ion implantation of Mn ions into hole-doped GaP has been used to induce
ferromagnetic behavior above room temperature for optimized Mn concentrations
near 3 at.%. The magnetism is suppressed when the Mn dose is increased or
decreased away from the 3 at.% value, or when n-type GaP substrates are used.
At low temperatures the saturated moment is on the order of one Bohr magneton,
and the spin wave stiffness inferred from the Bloch-law T^3/2 dependence of the
magnetization provides an estimate Tc = 385K of the Curie temperature that
exceeds the experimental value, Tc = 270K. The presence of ferromagnetic
clusters and hysteresis to temperatures of at least 330K is attributed to
disorder and proximity to a metal-insulating transition.",0201492v1
2002-04-08,Phase diagram and critical properties of the frustrated Kondo necklace model in a magnetic field,"The critical properties of the frustrated Kondo necklace model with a half
saturation magnetization ($m=1/2$) have been studied by means of an
exact-diagonalization method. It is shown from bosonization technique that the
model can be effectively expressed as a quantum sine-Gordom model. Thus it may
show three (dimer plateau, N{\'e}el plateau and Tomonaga-Luttinger liquid)
phases due to competitions among the Ising anisotropy $\Delta$, and the
nearest- and next-nearest-neighbor exchange interactions $J_1$ and $J_2$. The
boundary lines on the $\Delta-J_2/J_1$ phase diagram separating the three
phases are determined by the method of level spectroscopy based on the
conformal field theory.",0204174v3
2002-04-11,"Saturated Ferromagnetism and Magnetization Deficit in Optimally Annealed (Ga,Mn)As Epilayers","We examine the Mn concentration dependence of the electronic and magnetic
properties of optimally annealed Ga1-xMnxAs epilayers for 1.35% < x < 8.3%. The
Curie temperature (Tc), conductivity, and exchange energy increase with Mn
concentration up to x ~ 0.05, but are almost constant for larger x, with Tc ~
110 K. The ferromagnetic moment per Mn ion decreases monotonically with
increasing x, implying that an increasing fraction of the Mn spins do not
participate in the ferromagnetism. By contrast, the derived domain wall
thickness, an important parameter for device design, remains surprisingly
constant.",0204250v1
2002-04-16,Magnetic studies of Ca1-xMxRuO3 (M=La and Sr),"CaRuO3 is a perovskite with an orthorhombic distortion and shows the
characteristics of spin-glass behavior below TC=87 K. The La3+ substitution for
Ca2+ in Ca1-xLaxRuO3 samples, induces a disorder in the Ca site (the A site)
and the system becomes antiferromagnetically (AFM) ordered with TN = 58 and 19
K for x=0.1 x=0.5 respectively. In the Ca1-xSrxRuO3 system, the Ca0.8Sr0.2RuO3
sample is canted-AFM ordered at 107 K. The compounds with higher Sr
concentration display ferromagnetic behavior and the saturation moment
increases with Sr. Huge magnetic hysteresis loops are obtained at low
temperatures. The coercive field (HC) decreases with Sr. For x=0.4 HC =9.5 kOe
(at 5 K) whereas for SrRuO3 HC =2.4 kOe. For x=0.4 and 0.6, HC decreases
sharply with temperature and than increases again with a peak at 95 and 115 K,
respectively. On the other hand, for SrRuO3, HC remains practically unchanged
up to 50 K and shows a peak at 90 K and than decrease sharply up to TC =165 K.",0204341v1
2002-05-12,Magnetic field - temperature phase diagram of quasi-two-dimensional organic superconductor lambda-(BETS)_2 GaCl_4 studied via thermal conductivity,"The thermal conductivity kappa of the quasi-two-dimensional (Q2D) organic
superconductor lambda-(BETS)_2 GaCl_4 was studied in the magnetic field H
applied parallel to the Q2D plane. The phase diagram determined from this bulk
measurement shows notable dependence on the sample quality. In dirty samples
the upper critical field H_{c2} is consistent with the Pauli paramagnetic
limiting, and a sharp change is observed in kappa(H) at H_{c2 parallel}. In
contrast in clean samples H_{c2}(T) shows no saturation towards low
temperatures and the feature in kappa(H) is replaced by two slope changes
reminiscent of second-order transitions. The peculiarity was observed below ~
0.33T_c and disappeared on field inclination to the plane when the orbital
suppression of superconductivity became dominant. This behavior is consistent
with the formation of a superconducting state with spatially modulated order
parameter in clean samples.",0205239v2
2002-08-03,Formation of Co nanoclusters in epitaxial Ti_{0.96} Co_{0.04} O_2 thin films and their ferromagnetism,"Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001)
substrates by using plused laser deposition with in-situ reflection high-energy
electron diffraction. The oxygen partial pressure, PO2, during the growth was
systematically varied. As PO2 decreased, the growth behavior was changed from a
2-dimensional layer-by-layer-like growth to a 3-dimensional island-like one,
which resulted in an increase in the saturation magnetization. These structural
and magnetic changes were explained in terms of the formation of cobalt
clusters whose existence was proved by transmission-electron-microscopie
studies. Our work clearly indicates that the cobalt clustering will cause
room-temperature ferromagnetism in the Co-doped TiO2 films.",0208055v1
2002-08-30,Nickel Antidot Arrays on Anodic Alumina Substrates,"Large area nickel antidot arrays with density up to 10^10 /cm^2 have been
fabricated by depositing nickel onto anodic aluminum oxide membranes that
contain lattices of nanopores. Electron microscopy images show a high degree of
order of the antidot arrays. Various sizes and shapes of the antidots were
observed with increasing thickness of the deposited nickel. New features appear
in the antidot arrays in both magnetization and transport measurements when the
external magnetic field is parallel to the current direction, including an
enhancement and a nonmonotonous field dependence of the magnetoresistance,
larger values of the coercive field and remanence moment, and smaller
saturation field.",0208608v2
2002-11-14,"Preparation and structural properties of thin films and multilayers of the Heusler compounds Cu2MnAl, Co2MnSn, Co2MnSi and Co2MnGe","We report on the preparation of thin films and multilayers of the
intermetallic Heusler compound CuMnAl, Co2MnSn, Co2MnSi and Co2MnGe by
rf-sputtering on MgO and Al2O3 substrates. Cu2MnAl can be grown epitaxially
with (100)-orientation on MgO (100) and in (110)-orientation on Al2O3 a-plane.
The Co based Heusler alloys need metallic seedlayers to induce high quality
textured growth. We also have prepared multilayers with smooth interfaces by
combining the Heusler compounds with Au and V. An analysis of the ferromagnetic
saturation magnetization of the films indicates that the Cu2MnAl-compound tends
to grow in the disordered B2-type structure whereas the Co-based Heusler alloy
thin films grow in the ordered L21 structure. All multilayers with thin layers
of the Heusler compounds exhibit a definitely reduced ferromagnetic
magnetization indicating substantial disorder and intermixing at the
interfaces.",0211271v1
2003-02-21,Field-induced XY behavior in the S=1/2 antiferromagnet on the square lattice,"Making use of the quantum Monte Carlo method based on the worm algorithm, we
study the thermodynamic behavior of the S=1/2 isotropic Heisenberg
antiferromagnet on the square lattice in a uniform magnetic field varying from
very small values up to the saturation value. The field is found to induce a
Berezinskii-Kosterlitz-Thouless transition at a finite temperature, above which
a genuine XY behavior in an extended temperature range is observed. The phase
diagram of the system is drawn, and the thermodynamic behavior of the specific
heat and of the uniform and staggered magnetization is discussed in sight of an
experimental investigation of the field-induced XY behavior.",0302440v1
2003-06-04,Impurity Effects on the A_1-A_2 Splitting of Superfluid 3He in Aerogel,"When liquid 3He is impregnated into silica aerogel a solid-like layer of 3He
atoms coats the silica structure. The surface 3He is in fast exchange with the
liquid on NMR timescales. The exchange coupling of liquid 3He quasiparticles
with the localized 3He spins modifies the scattering of 3He quasiparticles by
the aerogel structure. In a magnetic field the polarization of the solid spins
gives rise to a splitting of the scattering cross-section of for `up' vs.
`down' spin quasiparticles, relative to the polarization of the solid 3He. We
discuss this effect, as well as the effects of non-magnetic scattering, in the
context of a possible splitting of the superfluid transition for
$\uparrow\uparrow$ vs. $\downarrow\downarrow$ Cooper pairs for superfluid 3He
in aerogel, analogous to the A_1-A_2 splitting in bulk 3He. Comparison with the
existing measurements of T_c for B< 5 kG, which show no evidence of an A_1-A_2
splitting, suggests a liquid-solid exchange coupling of order J = 0.1 mK.
Measurements at higher fields, B > 20 kG, should saturate the polarization of
the solid 3He and reveal the A_1-A_2 splitting.",0306099v1
2003-07-21,Study of an Antiferromagnetic Sawtooth Chain with Spin-1/2 and Spin-1 sites,"We study the low-energy properties of a sawtooth chain with spin-1's at the
bases of the triangles and spin-1/2's at the vertices of the triangles. The
spins have Heisenberg antiferromagnetic interactions between nearest neighbors,
with a coupling J_2 between a spin-1 and a spin-1/2, and a coupling J_1 = 1
between two spin-1's. Analysis of the exact diagonalization data for periodic
chains containing up to N=12 unit cells shows that the ground state is a
singlet for exchange couplings up to approximately J_2 = 3.8, whereas for
larger J_2, the system exhibits a ferrimagnetic ground state characterized by a
net ferromagnetic moment per unit cell of 1/2. In the region of small
interactions J_2, the mixed spin sawtooth chain maps on to an effective
isotropic spin model representing two weakly interacting and frustrated
spin-1/2 Heisenberg chains composed of spin-1/2 sites at odd and even vertices
respectively. Finally, we study the phenomenon of a macroscopic magnetization
jump which occurs if a magnetic field is applied with a value close to the
saturation field for J_2 = 2.",0307492v1
2004-01-03,History-Induced Critical Behavior in Disordered Systems,"Barkhausen noise as found in magnets is studied both with and without the
presence of long-range (LR) demagnetizing fields using the non-equilibrium,
zero-temperature random-field Ising model. Two distinct subloop behaviors arise
and are shown to be in qualitative agreement with experiments on thin film
magnets and soft ferromagnets. With LR fields present subloops resemble a
self-organized critical system, while their absence results in subloops that
reflect the critical point seen in the saturation loop as the system disorder
is changed. In the former case, power law distributions of noise are found in
subloops, while in the latter case history-induced critical scaling is studied
in avalanche size distributions, spin-flip correlation functions, and
finite-size scaling of the second moments of the size distributions. Results
are presented for simulations of over 10^8 spins.",0401023v1
2004-07-22,Levitation of the quantum Hall extended states in the $B\to$ 0 limit,"We investigate the fate of the quantum Hall extended states within a
continuum model with spatially correlated disorder potentials. The model can be
projected onto a couple of the lowest Landau bands. Levitation of the $n=0$
critical states is observed if at least the two lowest Landau bands are
considered. The dependence on the magnetic length $l_B=(\hbar/(eB))^{1/2}$ and
on the correlation length of the disorder potential $\eta$ is combined into a
single dimensionless parameter $\hat\eta=\eta/l_B$. This enables us to study
the behavior of the critical states for vanishing magnetic field. In the two
Landau band limit, we find a disorder dependent saturation of the critical
states' levitation which is in contrast to earlier propositions, but in accord
with some experiments.",0407584v2
2004-11-26,Room-temperature ferromagnetism in Sr_(1-x)Y_xCoO_(3-delta) (0.2 < x < 0.25),"We have measured magnetic susceptibility and resistivity of
Sr$_{1-x}$Y$_x$CoO$_{3-\delta}$ ($x=$ 0.1, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3,
and 0.4), and have found that Sr$_{1-x}$Y$_x$CoO$_{3-\delta}$ is a room
temperature ferromagnet with a Curie temperature of 335 K in a narrow
compositional range of 0.2 $\leq x\leq$ 0.25. This is the highest transition
temperature among perovskite Co oxides. The saturation magnetization for $x=$
0.225 is 0.25 $\mu_B$/Co at 10 K, which implies that the observed
ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar
Sr/Y ordering.",0411671v3
2004-11-28,Disorder-induced microscopic magnetic memory,"Using coherent x-ray speckle metrology, we have measured the influence of
disorder on major loop return point memory (RPM) and complementary point memory
(CPM) for a series of perpendicular anisotropy Co/Pt multilayer films. In the
low disorder limit, the domain structures show no memory with field cycling--no
RPM and no CPM. With increasing disorder, we observe the onset and the
saturation of both the RPM and the CPM. These results provide the first direct
ensemble-sensitive experimental study of the effects of varying disorder on
microscopic magnetic memory and are compared against the predictions of
existing theories.",0411698v1
2004-12-13,Quantum interference of electrons in Nb_{5-δ}Te_4 single crystals,"The compound $Nb_{5-\delta}Te_4$ ($\delta=0.23$) with quasi-one-dimensional
crystal structure undergoes a transition to superconductivity at $T_c$=0.6--0.9
K. Its electronic transport properties in the normal state are studied in the
temperature range 1.3--270 K and in magnetic fields up to 11 T. The temperature
variation of the resistivity is weak ($<2%$) in the investigated temperature
range. Nonmonotonic behavior of the resistivity is observed which is
characterized by two local maxima at $T\sim$2 K and $\sim$30 K. The temperature
dependence of the resistivity is interpreted as an interplay of weak
localization, weak antilocalization, and electron-electron interaction effects
in the diffusion and the Cooper channel. The temperature dependence of the
dephasing time $\tau_\phi$ extracted from the magnetoresistance data is
determined by the electron-phonon interaction. The saturation of $\tau_\phi$ in
the low-temperature limit correlates with $T_c$ of the individual crystal and
is ascribed to the scattering on magnetic impurities.",0412315v1
2005-04-22,Possible Localization Behavior of the Inherent Conducting Polymer (CH$_3$)$_{0.9}$ReO$_3$,"Polymeric methyltrioxorhenium (poly-MTO) represents the first example of an
inherent conducting organometallic oxide. It adopts the structural motives and
transport properties of some classical perovskites in two dimensions. In this
study we present resistivity data down to 30 mK which exhibit a crossover from
a metallic (d$\rho$/d$T >$ 0) to an insulating (d$\rho$/d$T <$ 0) behavior at
about 30 K. Below 30 K an unusual resistivity behavior, similar to that of some
doped cuprate systems, is observed: initially the resistivity increases
approximately as $\rho \sim$ log$(1/T$) before it starts to saturate below 2 K.
Furthermore, a linear positive magnetoresistance is found (up to 7 T).
Temperature dependent magnetization and specific heat measurements in various
magnetic fields indicate that the unusual resistivity behavior may be driven by
spatial localization of the d$^1$ moments at the Re atoms.",0504585v1
2005-04-27,Effect of toroidal moment on a macroscopic self-organization of electrons in the quantum Hall regime,"We have studied CR lineshape of terahertz-light-induced current in InAs
quantum wells in tilted quantizing magnetic fields. We have observed dramatic
modification of the lineshape with increasing of in-plane component of magnetic
field as well as with increasing of transverse built-in electric field in the
well. Scenario of the modification shows that the energy spectrum asymmetry is
determined by so-called toroidal moment of the system and is a function of
Landau quantum number. Macroscopic self-organization of electrons under the
conditions of quantum Hall effect has also been directly demonstrated in both
linear and saturation regimes of the light absorption.",0504720v1
2005-07-30,Specific Heat Study on a Novel Spin-Gapped System : (CH_3)_2NH_2CuCl_3,"Specific heat measurements down to 120mK have been performed on a
quasi-one-dimensional $S=1/2$ spin-gapped system (CH$_3$)$_2$NH$_2$CuCl$_3$ in
a magnetic field up to 8 T. This compound has a characteristic magnetization
curve which shows a gapless ground state and a plateau at 1/2 of the saturation
value. We have observed a spontaneous antiferromagnetic ordering and a
field-induced one below and above the 1/2 plateau field range, respectively.
The field versus temperature phase diagram is quite unusual and completely
different from those of the other quantum spin systems investigated so far. In
the plateau field range, a double-structure in the specific heat is observed,
reflecting the coexistence of ferromagnetic and antiferromagnetic excitations.
These behaviors are discussed on the basis of a recently proposed novel quantum
spin chain model consisting of weakly coupled ferromagnetic and
antiferromagnetic dimers.",0508007v1
2005-09-27,Antiferromagnetic ordering in heavy fermion system Ce2Au2Cd,"La2Au2Cd and Ce2Au2Cd were prepared from the elements by reactions in sealed
tantalum tubes in a water-cooled sample chamber of an induction furnace. These
intermetallics crystallize with the tetragonal Mo2FeB2 type, space group
P4/mbm. While La2Au2Cd is Pauli paramagnetic, Ce2Au2Cd shows Curie-Weiss
behaviour above 100 K with an experimental magnetic moment of 2.41(2) muB/Ce
atom, indicating trivalent cerium. Antiferromagnetic ordering is detected for
Ce2Au2Cd at 5.01(2) K and magnetization measurements reveal a metamagnetic
transition at 3 K at a critical field of around 20 kOe with a saturation moment
of 1.50(2)muB/Ce atom at 80 kOe. The low-temperature heat capacity properties
characterize Ce2Au2Cd as a heavy fermion material with an electronic specific
heat coefficient (gamma) = 807(5) mJ/mol K2 as compared to La2Au2Cd with gamma
= 6(5) mJ/mol K2.",0509703v2
2005-10-07,Quantum effects in a half-polarized pyrochlore antiferromagnet,"We study quantum effects in a spin-3/2 antiferromagnet on the pyrochlore
lattice in an external magnetic field, focusing on the vicinity of a plateau in
the magnetization at half the saturation value, observed in CdCr$_2$O$_4$, and
HgCr$_2$O$_4$. Our theory, based on quantum fluctuations, predicts the
existence of a symmetry-broken state on the plateau, even with only
nearest-neighbor microscopic exchange. This symmetry broken state consists of a
particular arrangement of spins polarized parallel and antiparallel to the
field in a 3:1 ratio on each tetrahedron. It quadruples the lattice unit cell,
and reduces the space group from $Fd\bar{3}m$ to $P4_332$. We also predict that
for fields just above the plateau, the low temperature phase has transverse
spin order, describable as a Bose-Einstein condensate of magnons. Other
comparisons to and suggestions for experiments are discussed.",0510202v1
2005-12-15,Nematic order in square lattice frustrated ferromagnets,"We present a new scenario for the breakdown of ferromagnetic order in a
two-dimensional quantum magnet with competing ferromagnetic and
antiferromagnetic interactions. In this, dynamical effects lead to the
formation of two-magnon bound states, which undergo Bose-Einstein condensation,
giving rise to bond-centered nematic order. This scenario is explored in some
detail for an extended Heisenberg model on a square lattice. In particular, we
present numerical evidence confirming the existence of a state with d-wave
nematic correlations but no long range magnetic order, lying between the
saturated ferromagnetic and collinear antiferromagnetic phases of the
ferromagnetic J1-J2 model. We argue by continuity of spectra that this phase is
also present in a model with 4-spin cyclic exchange.",0512349v1
2006-01-16,"Selective dilution and magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}M'_xO_3 (M' = Al, Ti)","The magnetic lattice of mixed-valence Mn ions in La$_{0.7}$Sr$_{0.3}$MnO$_3$
is selectively diluted by partial substitution of Mn by Al or Ti. The
ferromagnetic transition temperature and the saturation moment decreases with
substitution in both series. The volume fraction of the non-ferromagnetic
phases evolves non-linearly with the substitution concentration and faster than
theoretically expected. By presenting the data in terms of selective dilutions,
the reduction of $T_\mathrm{c}$ is found to be scaled by the relative ionic
concentrations and is consistent with a prediction derived from molecular-field
theory.",0601308v1
2006-02-04,Compensation of Effective Field in the Field-Induced Superconductor k-(BETS)2FeBr4 Observed by 77Se NMR,"We report results of 77Se NMR frequency shift in the normal state of the
organic charge-transfer-salt k-(BETS)2FeBr4 which shows magnetic field-induced
superconductivity (FISC). From a simple mean field analysis, we determined the
field and the temperature dependences of the magnetization m_{pi} of the \pi
conduction electrons on BETS molecules. We found that the Fe spins are
antiferromagnetically coupled to the pi electrons and determined the exchange
field to be J = -2.3T/mu_B. The exchange field from the fully saturated Fe
moments (5 mu_B) is compensated by an external field of 12T. This is close to
the central field of the FISC phase, consistent with the Jaccarino-Peter local
field-compensation mechanism for FISC (Phys. Rev. Lett. 9, 290 (1962)).",0602099v1
2006-02-07,Field-Induced Ferromagnetic Order and Colossal Magnetoresistance in La_{1.2}Sr_{1.8}Mn_2O_7: a ^{139}La NMR study,"In order to gain insights into the origin of colossal magneto-resistance
(CMR) in manganese oxides, we performed a ^{139}La NMR study in the
double-layered compound La_{1.2}Sr_{1.8}Mn_2O_7. We find that above the Curie
temperature T_C=126 K, applying a magnetic field induces a long-range
ferromagnetic order that persists up to T=330 K. The critical field at which
the induced magnetic moment is saturated coincides with the field at which the
CMR effect reaches to a maximum. Our results therefore indicate that the CMR
observed above T_C in this compound is due to the field-induced ferromagnetism
that produces a metallic state via the double exchange interaction.",0602161v1
2006-02-09,Anisotropic magnetoresistance and anisotropic tunneling magnetoresistance due to quantum interference in ferromagnetic metal break junctions,"We measure the low-temperature resistance of permalloy break junctions as a
function of contact size and the magnetic field angle, in applied fields large
enough to saturate the magnetization. For both nanometer-scale metallic
contacts and tunneling devices we observe large changes in resistance with
angle, as large as 25% in the tunneling regime. The pattern of
magnetoresistance is sensitive to changes in bias on a scale of a few mV. We
interpret the effect as a consequence of conductance fluctuations due to
quantum interference.",0602251v2
2006-04-07,Possibility of field-induced incommensurate order in quasi-one-dimensional frustrated spin system,"We study an incommensurate long-range order induced by an external magnetic
field in a quasi-one-dimensional bond-alternating spin system, F5PNN, focusing
on the role of the frustrating interaction which can be enhanced by a
high-pressure effect. On the basis of the density matrix renormalization group
analysis of a microscopic model for F5PNN, we present several H-T phase
diagrams for typical parameters of the frustrating next-nearest-neighbour
coupling and the interchain interaction, and then discuss how the field-induced
incommensurate order develops by the frustration effect in such phase diagrams.
A magnetization plateau at half the saturation moment is also mentioned.",0604194v1
2006-05-21,High-temperature ferromagnetism of $sp$ electrons in narrow impurity bands: Application to CaB$_6$,"Ferromagnetism with high Curie temperature $T_c$, well above room
temperature, and very small saturation moment has been reported in various
carbon and boron systems. It is argued that the magnetization must be very
inhomogeneous with only a small fraction of the sample ferromagnetically
ordered. It is shown that a possible source of high $T_c$ within the
ferromagnetic regions is itinerant electrons occupying a narrow impurity band.
Correlation effects do not reduce the effective interaction which enters the
Stoner criterion in the same way as in a bulk band. It is also shown how, in
the impurity band case, spin wave excitations may not be effective in lowering
$T_c$ below its value given by Stoner theory. These ideas are applied to
CaB$_6$ and a thorough review of the experimental situation in this material is
given. It is suggested that the intrinsic magnetism of the B$_2$ and O$_2$
dimers might be exploited in suitable structures containing these elements.",0605495v1
2006-06-13,Electron-Dephasing Time in A Two-Dimensional Spin-Polarized System with Rashba Spin-Orbit Interaction,"We calculate the dephasing time $\tau_{\phi}(B)$ of an electron in a
two-dimensional quantum well with a Rashba spin-orbit interaction,
spin-polarized by an arbitrarily large magnetic field parallel to the layer.
$\tau_\phi (B)$ is estimated from the logarithmic corrections to the
conductivity, within a perturbative approach, that assumes weak isotropic
disorder scattering. Our result indicates that for any value of the magnetic
field, the dephasing rate changes with respect to its unpolarized state value
by a universal function whose parameter is the ratio of the Zeeman splitting
energy $(E_Z)$ to the spin-orbit interaction $(E_{SOI})$, confirming the
experimental report published in Phys. Rev. Lett. {\bf 94}, 186805 (2005) . In
the high field limit, when $E_Z>>E_{SOI}$, the dephasing rate saturates and
reaches asymptotically to a value equal to twice the spin relaxation rate.",0606328v2
2006-06-21,Evidence of s-Wave Subdominant Order Parameter in YBCO from Break Junction Tunneling Spectra,"The tunneling spectra of YBa2Cu3O7 break-junctions have been investigated for
the tunneling direction close to the node one. The zero-bias conductance peak
(ZBCP) and Josephson current have been studied with temperature and magnetic
field. The observed deep splitting of ZBCP which starts at Ts<20-30K is in
agreement with the theory for the dx2-y2+-is order parameter [Y. Tanuma, Y.
Tanaka, and S. Kashiwaya, Phys. Rev. B 64, 214519 (2001)]. The low (0.04T)
magnetic field depresses significantly such splitting. The 1/T temperature
dependence of maximum Josephson current goes to saturation at T<Ts also
confirming the mixed order parameter formation.",0606552v2
2006-08-07,"Growth, Structure and Properties of Epitaxial Thin Films of First Principles Predicted Multiferroic Bi2FeCrO6","We report the structural and physical properties of epitaxial Bi2FeCrO6 thin
films on epitaxial SrRuO3 grown on (100)-oriented SrTiO3 substrates by pulsed
laser ablation. The 300 nm thick films exhibit both ferroelectricity and
magnetism at room temperature with a maximum dielectric polarization of 2.8
microC/cm2 at Emax = 82 kV/cm and a saturated magnetization of 20 emu/cc
(corresponding to ~ 0.26 Bohr magneton per rhombohedral unit cell), with
coercive fields below 100 Oe. Our results confirm the predictions made using
ab-initio calculations about the existence of multiferroic properties in
Bi2FeCrO6.",0608178v1
2006-08-14,Electronic and Magnetic Properties of Mn doped Ge Nanowires,"Using {\it ab initio} total energy density-functional theory calculations, we
investigate the electronic, structural and magnetic properties of Manganese
doped Germanium nanowires. The nanowires have been constructed along the [110]
direction and the dangling bonds on the surface have been saturated by hydrogen
atoms. We observed that the Mn has lower formation energy at the center of the
wire when compared to regions close to the surface. The Mn-Mn coupling has
lower energy for a high-spin configuration except when they are first nearest
neighbors. These results show that Ge:Mn nanowires are potential candidates for
ferromagnetic quasi-one dimentional systems.",0608315v2
2006-11-09,New ultrasmall iron-oxide nanoparticles with high magnetisation as potential T1-MRI contrast agents for Molecular Imaging,"Here we report on the synthesis of very small gamma-Fe2O3 nanoparticles (5
nm) presenting very narrow particle size distribution and exceptionally high
saturation magnetisation. The synthesis has been carried out in an organic
medium with subsequent transfer to an aqueous solution at physiological pH. The
structural and magnetic properties were kept unaltered after the solvent
exchange. NMR relaxometric measurements show the potential of these particles
as specific reporters for magnetic resonance molecular imaging.",0611243v1
2006-12-24,Structural and magnetic properties of Mn-implanted Si,"Structural and ferromagnetic properties in Mn implanted, p-type Si were
investigated. High resolution structural analysis techniques like synchrotron
X-ray diffraction revealed the formation of MnSi1.7 nanoparticles already in
the as implanted samples. Depending on the Mn-fluence, the size increases from
5 nm to 20 nm upon rapid thermal annealing. No significant evidence is found
for Mn substituting Si sites either in the as-implanted or annealed samples.
The observed ferromagnetism yields a saturation moment of 0.21 mu_B per
implanted Mn at 10 K, which could be assigned to MnSi1.7 nanoparticles as
revealed by a temperature dependent magnetization measurement.",0612612v1
2007-03-19,Enhanced magnetocaloric effect in frustrated magnetic molecules with icosahedral symmetry,"We investigate the magnetocaloric properties of certain antiferromagnetic
spin systems that have already been or very likely can be synthesized as
magnetic molecules. It turns out that the special geometric frustration which
is present in antiferromagnets that consist of corner-sharing triangles leads
to an enhanced magnetocaloric effect with high cooling rates in the vicinity of
the saturation field. These findings are compared with the behavior of a simple
unfrustrated spin ring as well as with the properties of the icosahedron. To
our surprise, also for the icosahedron large cooling rates can be achieved but
due to a different kind of geometric frustration.",0703480v1
2001-11-23,Dimming Supernovae without Cosmic Acceleration,"We present a simple model where photons propagating in extra-galactic
magnetic fields can oscillate into very light axions. The oscillations may
convert some of the photons departing a distant supernova into axions, making
the supernova appear dimmer and hence more distant than it really is. Averaging
over different configurations of the magnetic field we find that the dimming
saturates at about 1/3 of the light from the supernovae at very large
redshifts. This results in a luminosity-distance vs. redshift curve almost
indistinguishable from that produced by the accelerating Universe, if the axion
mass and coupling scale are m ~ 10^-16 eV, M ~ 4 10^11 GeV. This phenomenon may
be an alternative to the accelerating Universe for explaining supernova
observations.",0111311v2
1995-02-16,STATIC FOUR-DIMENSIONAL ABELIAN BLACK HOLES IN KALUZA-KLEIN THEORY,"Static, four-dimensional (4-d) black holes (BH's) in ($4+n$)-d Kaluza-Klein
(KK) theory with Abelian isometry and diagonal internal metric have at most one
electric ($Q$) and one magnetic ($P$) charges, which can either come from the
same $U(1)$-gauge field (corresponding to BH's in effective 5-d KK theory) or
from different ones (corresponding to BH's with $U(1)_M\times U(1)_E$ isometry
of an effective 6-d KK theory). In the latter case, explicit non-extreme
solutions have the global space-time of Schwarzschild BH's, finite temperature,
and non-zero entropy. In the extreme (supersymmetric) limit the singularity
becomes null, the temperature saturates the upper bound
$T_H=1/4\pi\sqrt{|QP|}$, and entropy is zero. A class of KK BH's with
constrained charge configurations, exhibiting a continuous electric-magnetic
duality, are generated by global $SO(n)$ transformations on the above classes
of the solutions.",9502099v1
1995-07-18,Dyonic BPS Saturated Black Holes of Heterotic String on a Six-Torus,"Within effective heterotic superstring theory compactified on a six-torus we
derive minimum energy (supersymmetric), static, spherically symmetric
solutions, which are manifestly invariant under the target space $O(6,22)$ and
the strong-weak coupling $SL(2)$ duality symmetries with 28 electric and 28
magnetic charges subject to one constraint. The class of solutions with a
constant axion corresponds to dyonic configurations subject to two charge
constraints, with purely electric [or purely magnetic] and dyonic
configurations preserving ${1\over 2}$ and ${1\over 4}$ of $N=4$ supersymmetry,
respectively. General dyonic configurations in this class have a space-time of
extreme Reissner-Nordstr\"" om black holes while configurations with more
constrained charges have a null or a naked singularity.",9507090v2
1996-02-20,Macroscopic Entropy of $N=2$ Extremal Black Holes,"Extremal BPS-saturated black holes in $N=2$, $d=4$ supergravity can carry
electric and magnetic charges $(q^\Lambda_{(m)},q_\Lambda^{(e)})$. It is shown
that in smooth cases the moduli fields at the horizon take a fixed ""rational""
value $X^\Lambda(q_{(m)},q^{(e)})$ which is determined by the charges and is
independent of the asymptotic values of the moduli fields. A universal formula
for the Bekenstein-Hawking entropy is derived in terms of the charges and the
moduli space geometry at $X^\Lambda(q_{(m)},q^{(e)})$. This work extends
previous results of Ferrara, Kallosh and the author for the pure magnetic case.",9602111v3
1998-08-12,On Phases of Gauge Theories and the Role of Non-BPS Solitons in Field Theory,"As shown in hep-th/9709081, non-BPS saturated solitons play an important role
in the duality transformations of N=1 supersymmetric gauge theories. In
particular, a massive spinor in an SO(N) gauge theory with massless matter in
the vector representation appears in the dual description as a magnetic
monopole with a Z_2 charge. This claim is supported by numerous tests,
including detailed matching of flavor quantum numbers. This fact makes it
possible to test the phase of an SO(N) gauge theory using massive spinors as a
probe. It is thereby shown explicitly that the free magnetic phase which
appears in supersymmetric theories is a non-confining phase. A fully
non-abelian version of the Dual Meissner effect is also exhibited, in which the
monopoles are confined by non-BPS string solitons with Z_2 charges.",9808073v1
2001-04-04,Wave particle duality: Merging de Broglie's ''double solution'' waves into (3+0)D electromagnetic solitons,"The well known light filaments, are obtained in various media whose index of
refraction increases before a saturation with the electric field; adding a
small perturbation which increases the index with the magnetic field, and
neglecting the absorption, a filament curves and closes into a torus. This
transformation of a (2+1)D soliton into a (3+0)D soliton shows the existence of
those solitons, while a complete study, with a larger magnetic effect, would
require numerical computations, the starting point being, possibly, the
perturbed, curved filament.
  The flux of energy in the regular filaments is nearly a ''critical flux'',
depending slightly on the external fields, so that the energy of the (3+0)D
soliton is quantified, but may be slightly changed by external interactions.
  The creation of electron positron pairs in the vacuum by purely
electromagnetic fields shows a nonlinearity of vacuum at high energies;
supposing this nonlinearity convenient, elementary particles may be (3+0)D
solitons.
  Set that the nearly linear part of the soliton is the $\Psi$ wave while the
remainder, (the torus) is the $u$ wave; if the torus is not absorbed by Young
slits, it is guided by the transmitted, interfering remainder of the $\Psi$
wave.",0104007v1
2001-05-31,Description of collective magnetic states within a spherical single particle basis,"A many body Hamiltonian comprising pairing, quadrupole-quadrupole and
spin-spin interaction is treated within a projected spherical basis with the
aim of describing the detailed structure of the magnetic states of orbital and
spin-flip nature in $^{144, 148-154}$Sm. The mean field for the single particle
motion takes care of the volume conservation of a phenomenological core which
results in having a complex dependence on deformation for single particle
energies. Several experimental features like the total orbital and total spin
strengths, the shape of the orbital strength distribution, the hump structure
of the spin strength distribution, the quadratic dependence of the orbital
strength on nuclear deformation, the saturation effect of the orbital strength
with respect to the Casten's factor P are very well described within a
quasiparticle random phase approximation formalism. Comparison of present
results with those obtained in some previous treatments are also given.",0105078v1
2003-09-29,An equilibrium model for RFP plasmas in the presence of resonant tearing modes with an application to particle and heat transport,"The equilibrium of a finite-beta cylindrical RFP plasma in the presence of
saturated-amplitude tearing modes is investigated. The singularities arising
from the perturbative analysis of the MHD force balance equation JxB=grad(p)
are resolved through a proper regularization of the cylindrical symmetric
component of the pressure and parallel current density profiles, by setting to
zero their gradient at the modes rational surfaces. An equilibrium model, which
satisfies the regularization rule at the various rational surfaces, is
developed. The comparison with the experimental data from the Reversed Field
eXperiment (RFX) gives encouraging results. The model provides an easy tool to
extrapolate the magnetic data, ordinarily measured only at the plasma edge,
inside the plasma. As an application, we present the computation of the
particle and heat stochastic diffusion coefficient from the reconstructed
magnetic field profile.",0309114v1
2006-09-14,Comparison between resistive and collisionless double tearing modes for nearby resonant surfaces,"The linear instability and nonlinear dynamics of collisional (resistive) and
collisionless (due to electron inertia) double tearing modes (DTMs) are
compared with the use of a reduced cylindrical model of a tokamak plasma. We
focus on cases where two q = 2 resonant surfaces are located a small distance
apart. It is found that regardless of the magnetic reconnection mechanism,
resistivity or electron inertia, the fastest growing linear eigenmodes may have
high poloidal mode numbers m ~ 10. The spectrum of unstable modes tends to be
broader in the collisionless case. In the nonlinear regime, it is shown that in
both cases fast growing high-m DTMs lead to an annular collapse involving small
magnetic island structures. In addition, collisionless DTMs exhibit multiple
reconnection cycles due to reversibility of collisionless reconnection and
strong ExB flows. Collisionless reconnection leads to a saturated stable state,
while in the collisional case resistive decay keeps the system weakly dynamic
by driving it back towards the unstable equilibrium maintained by a source
term.",0609115v4
2003-10-05,Local entanglement and quantum phase transition in the Hubbard model,"The local entanglement $E_v$ of the one-dimensional Hubbard model is studied
on the basis of its Bethe-ansatz solution. The relationship between the local
entanglement and the on-site Coulomb interaction $U$ is obtained. Our results
show that $E_v$ is an even analytic function of $U$ at half-filling and it
reaches a maximum at the critical point U=0. The variation of the local
entanglement with the filling factor shows that the ground state with maximal
symmetry possesses maximal entanglement. The magnetic field makes the local
entanglement to decrease and approach to zero at saturated magnetization. The
on-site Coulomb interaction always suppresses the local entanglement.",0310030v1
2007-05-02,Effect of temperature-dependent shape anisotropy on coercivity with aligned Stoner-Wohlfarth soft ferromagnets,"The temperature variation effect of shape anisotropy on the coercivity,
HC(T), for the aligned Stoner-Wohlfarth (SW) soft ferromagnets, such as fcc Ni,
fcc Co and bcc Fe, are investigated within the framework of Neel-Brown (N-B)
analysis. An extended N-B equation is thus proposed,by introducing a single
dimensionless correction function, the reduced magnetization, m(\tao) =
MS(T)/MS(0), in which \tao = T/TC is the reduced temperature, MS(T) is the
saturation magnetization, and TC is the Curie temperature. The factor, m(\tao),
accounts for the temperature-dependent effect of the shape anisotropy. The
constants, H0 and E0, are for the switching field at zero temperature and the
potential barrier at zero field, respectively. According to this newly derived
equation, the blocking temperature above which the properties of
superparamagnetism show up is described by the expression, TB =
E0m^2(\tao)/[kBln(t/t0)], with the extra correction factor m^2(\tao). The
possible effect on HC(T) and the blocking temperature, TB, attributed to the
downshift of TC resulting from the finite size effect has been discussed also.",0705.0195v1
2007-05-22,Effect of Mo doping for the Mn site in the ferromagnetic manganite La0.7Ca0.3MnO3,"The structure, electronic, and magnetic properties of the Mo-doped perovskite
La0.7Ca0.3Mn1-xMoxO3 (x < 0.1) have been studied. A significant increase in
resistivity and lattice parameters were observed with Mo doping. A marginal
decrease in the Curie temperature Tc and the associated metal-insulator
transition Tp were observed. Magnetization data reveal that long-range
ferromagnetic ordering persists in all samples studied and the saturation
moment decreases linearly as x increases. Enhancement in magnetoresistance at
near Tc in the Mo-doped compounds with an optimum doping value x = 0.05 was
observed. The overall experimental results can be explained by considering the
induced Mn2+ ions with Mo6+ in the Mo-doped systems, with the strong FM
coupling between Mn4+/2+- O - Mn3+.",0705.3080v1
2007-05-22,Charge Transport and Inhomogeneity near the Charge Neutrality Point in Graphene,"The magnetic field-dependent longitudinal and Hall components of the
resistivity rho_xx(H) and rho_xy(H) are measured in graphene on silicon dioxide
substrates at temperatures from 1.6 K to room temperature. At charge densities
near the charge-neutrality point rho_xx(H) is strongly enhanced and rho_xy(H)
is suppressed, indicating nearly equal electron and hole contributions to the
transport current. The data are inconsistent with uniformly distributed
electron and hole concentrations (two-fluid model) but in excellent agreement
with the recent theoretical prediction for inhomogeneously distributed electron
and hole regions of equal mobility. At low temperatures and high magnetic
fields rho_xx(H) saturates to a value ~h/e^2, with Hall conductivity << e^2/h,
which may indicate a regime of localized v = 2 and v = -2 quantum Hall puddles.",0705.3239v2
2007-07-24,Power Dependence of the Photocurrent Lineshape in a Semiconductor Quantum Dot,"We propose a kinetic theory to describe the power dependence, $I_{PC}(P)$, of
the photocurrent (PC) lineshape in optically pumped quantum dots at low
temperatures, in both zero and finite magnetic fields. We show that there is a
crossover power $P_c$, determined by the electron and hole tunneling rates, at
which the photocurrent spectra become strongly influenced by the dot kinetics,
and no longer reflect the exciton lifetime in the dot. For $P>P_c$, we show
that the photocurrent saturates due to the slow hole escape rate (in e.g.,
InGaAs/GaAs dots), whereas the line-width increases with power: $\Gamma \propto
\sqrt{P}$. We also analyze to what measure the spin-doublet lineshape of the
photocurrent studied in a high magnetic field reflects the degree of circular
polarization of the incident light.",0707.3555v1
2007-08-03,Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles,"The shape of ferromagnetic resonance spectra of highly dispersed, chemically
disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
to the particle magnetic moments determined from the Langevin analysis of the
magnetization isotherms. These novel features are explained by the scattering
of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
spin-orbit coupling, while the sd-exchange can be ruled out. The large
saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
dominance of an overdamped 1 meV e/h-pair which seems to originate from the
discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.",0708.0463v1
2007-08-14,The zero-energy state in graphene in a high magnetic field,"The fate of the charge-neutral Dirac point in graphene in a high magnetic
field $H$ has been investigated at low temperatures ($T\sim$ 0.3 K). In samples
with small $V_0$ (the gate voltage needed to access the Dirac point), the
resistance $R_0$ at the Dirac point diverges steeply with $H$, signalling a
crossover to an insulating state in intense field. The approach to the
insulating state is highly unusual. Despite the steep divergence in $R_0$, the
profile of $R_0$ vs. $T$ in fixed $H$ saturates to a $T$-independent value
below 2 K, consistent with charge carrying gapless excitations.",0708.1959v2
2007-09-07,What is Minimal Model of 3He Adsorbed on Graphite? -Importance of Density Fluctuations in 4/7 Registered Solid -,"We show theoretically that the second layer of 3He adsorbed on graphite and
solidified at 4/7 of the first-layer density is close to the fluid-solid
boundary with substantial density fluctuations on the third layer. The solid
shows a translational symmetry breaking as in charge-ordered insulators of
electronic systems. We construct a minimal model beyond the multiple-exchange
Heisenberg model. An unexpectedly large magnetic field required for the
measured saturation of magnetization is well explained by the density
fluctuations. The emergence of quantum spin liquid is understood from the same
mechanism as in the Hubbard model and in \kappa-(ET)_2Cu_2(CN)_3 near the Mott
transitions.",0709.1040v2
2007-09-10,"Exact shering box solutions of MHD flows with resistivity, viscosity and cooling","Axisymmetric incompressible modes of the magneto-rotational instability (MRI)
with a vertical wavenumber are exact solutions of the non-linear local
equations of motion for a disk (shearing box). They are referred to as ""channel
solutions"". Here, we generalize a class of these solutions to include energy
losses, viscous, and resistive effects. In the limit of zero shear, we recover
the result that torsional Alfv\'en waves are exact solutions of the non-linear
equations. Our method allows the extension of these solutions into the
dissipative regime.
  These new solutions serve as benchmarks for simulations including dissipation
and energy loss, and to calibrate numerical viscosity and resistivity in the
Zeus3D code. We quantify the anisotropy of numerical dissipation and compute
its scaling with time and space resolution. We find a strong dependence of the
dissipation on the mean magnetic field that may affect the saturation state of
the MRI as computed with Zeus3D. It is also shown that elongated grid cells
generally preclude isotropic dissipation and that a Courant time step smaller
than that which is commonly used should be taken to avoid spurious
anti-diffusion of magnetic field.",0709.1388v1
2007-10-19,"Disorder, Metal-Insulator crossover and Phase diagram in high-Tc cuprates","We have studied the influence of disorder induced by electron irradiation on
the normal state resistivities $\rho(T)$ of optimally and underdoped YBa2CuOx
single crystals, using pulsed magnetic fields up to 60T to completely restore
the normal state. We evidence that point defect disorder induces low T upturns
of rho(T) which saturate in some cases at low T in large applied fields as
would be expected for a Kondo-like magnetic response. Moreover the magnitude of
the upturns is related to the residual resistivity, that is to the
concentration of defects and/or their nanoscale morphology. These upturns are
found quantitatively identical to those reported in lower Tc cuprates, which
establishes the importance of disorder in these supposedly pure compounds. We
therefore propose a realistic phase diagram of the cuprates, including
disorder, in which the superconducting state might reach the antiferromagnetic
phase in the clean limit.",0710.3737v2
2007-11-15,Enhancement in spin-torque efficiency by nonuniform spin current generated within a tapered nanopillar spin valve,"We examine the effect a spatially non-uniform spin current with a component
polarized partially out of the plane has on a low saturation magnetization
nanomagnet free layer. Micromagnetic simulations indicate that the spin torque
efficiency acting upon the reversing nanomagnet can be enhanced through this
process, resulting in faster switching with smaller currents. In doing so, we
determine that micromagnetic structure within the nanomagnets can be beneficial
for reversal processes. We verify this enhancement experimentally in devices
with a tapered nanopillar geometry that generates a spin current polarized
partly out of plane. Finally, to take even better advantage of these effects,
we examine micromagnetically the benefits of a tapered three-magnetic-layer
structure that further reduces reversal times while maintaining the thermal
stability of the free layer.",0711.2479v1
2008-03-07,Photoassociation of a Bose-Einstein Condensate near a Feshbach Resonance,"We measure the effect of a magnetic Feshbach resonance (FR) on the rate and
light-induced frequency shift of a photoassociation resonance in ultracold
$^7$Li. The photoassociation-induced loss rate coefficient, $K_p$, depends
strongly on magnetic field, varying by more than a factor of 10$^4$ for fields
near the FR. At sufficiently high laser intensities, $K_p$ for a thermal gas
decreases with increasing intensity, while saturation is observed for the first
time in a Bose-Einstein condensate. The frequency shift is also strongly
field-dependent and exhibits an anomalous blue-shift for fields just below the
FR.",0803.1167v2
2008-04-29,Wang-Landau study of the random bond square Ising model with nearest- and next-nearest-neighbor interactions,"We report results of a Wang-Landau study of the random bond square Ising
model with nearest- ($J_{nn}$) and next-nearest-neighbor ($J_{nnn}$)
antiferromagnetic interactions. We consider the case $R=J_{nn}/J_{nnn}=1$ for
which the competitive nature of interactions produces a sublattice ordering
known as superantiferromagnetism and the pure system undergoes a second-order
transition with a positive specific heat exponent $\alpha$. For a particular
disorder strength we study the effects of bond randomness and we find that,
while the critical exponents of the correlation length $\nu$, magnetization
$\beta$, and magnetic susceptibility $\gamma$ increase when compared to the
pure model, the ratios $\beta/\nu$ and $\gamma/\nu$ remain unchanged. Thus, the
disordered system obeys weak universality and hyperscaling similarly to other
two-dimensional disordered systems. However, the specific heat exhibits an
unusually strong saturating behavior which distinguishes the present case of
competing interactions from other two-dimensional random bond systems studied
previously.",0804.4545v2
2008-05-03,The Effects of Thermal Conduction on the ADAF with a Toroidal Magnetic Field,"The observation of the hot gas surrounding Sgr $A^*$ and a few other nearby
galactic nuclei imply that electron and proton mean free paths are comparable
to the gas capture radius. So, the hot accretion flows is likely to proceed
under week-collision conditions. Hence, thermal conduction has been suggested
as a possible mechanism by which the sufficient extra heating is provided in
hot ADAF accretion disks. We consider the effects of thermal conduction in the
presence of a toroidal magnetic field in an advection-dominated accretion flow
around a compact object. For a steady-state structure of such accretion flows a
set of self-similar solutions are presented. We find two types solutions which
represent high and slow accretion rate. They have different behaviors with
saturated thermal conduction parameter, $\phi$.",0805.0344v1
2008-06-30,Novel Regime of Operation for Superconducting Quantum Interference Filters,"A new operating regime of the Superconducting Quantum Interference Filter
(SQIF) is investigated. The voltage to magnetic field response function, V(H),
is determined by a Fraunhofer dependence of the critical current and magnetic
flux focusing effect in Josephson junctions (F-mode). For SQIF-arrays made of
high-Tc superconducting bicrystal Josephson junctions the F-mode plays a
predominant role in the voltage-field response V(H). The relatively large
superconducting loops of the SQIF are used for inductive coupling to the
external input circuit. It is shown that the output noise of a SQIF-array
measured with a cooled amplifier in the 1-2 GHz range is determined by the
slope of the V(H) characteristic. Power gain and saturation power were
evaluated using low frequency SQIF parameters. Finally, we consider the
influence of the spread in the parameters of Josephson junctions in the
SQIF-array on the V(H) characteristic of the whole structure.",0806.4839v1
2008-08-15,Collective excitations in two-dimensional antiferromagnet in strong magnetic field,"We discuss spin-$\frac12$ two-dimensional (2D) Heisenberg antiferromagnet
(AF) on a square lattice at T=0 in strong magnetic field H near its saturation
value $H_c$. A perturbation approach is proposed to obtain spectrum of magnons
with momenta not very close to AF vector in the leading order in small
parameter $(H_c-H)/H_c$. We find that magnons are well-defined quasi-particles
at $H>0.9H_c$ although the damping is quite large near the zone boundary. A
characteristic rotonlike local minimum in the spectrum is observed at ${\bf
k}=(\pi,0)$ accompanied by decrease of the damping near $(\pi,0)$. The
suggested approach can be used in discussion of short-wavelength excitations in
other 2D Bose gases of particles or quasi-particles.",0808.2127v3
2008-08-16,All Oxide Ferromagnet/Semiconductor Epitaxial Heterostructures,"Oxide based ferromagnet/semiconductor heterostructures offer substantial
advantages for spin electronics. We have grown (111) oriented Fe3O4 thin films
and Fe3O4/ZnO heterostructures on ZnO(0001) and Al2O3(0001) substrates by
pulsed laser deposition. High quality crystalline films with mosaic spread as
small as 0.03 degree, sharp interfaces, and rms surface roughness of 0.3 nm
were achieved. Magnetization measurements show clear ferromagnetic behavior of
the magnetite layers with a saturation magnetization of 3.2 muB/f.u. at 300 K.
Our results demonstrate that the Fe3O4/ZnO system is an intriguing and
promising candidate for the realization of multi-functional heterostructures.",0808.2245v1
2008-08-21,Masses and Magnetic moments of Triply Heavy Flavour Baryons in Hypercentral Model,"Triply heavy flavour baryons are studied using the hyper central description
of the three-body system. The confinement potential is assumed as hyper central
coulomb plus power potential with power index $p$. The ground state
($J^P={1/2}^+$ and ${3/2}^+$) masses of heavy flavour baryons are computed for
different power index, $ p$ starting from 0.5 to 2.0. The predicted masses are
found to attain a saturated value with respect to variation in $p$ beyond the
power index $p>1.0$. Using the spin-flavour structure of the constituting
quarks and by defining effective mass of the confined quarks within the
baryons, the magnetic moments are computed with no additional free parameters.",0808.2880v1
2008-09-10,Radiation-Dominated Disks Are Thermally Stable,"When the accretion rate is more than a small fraction of Eddington, the inner
regions of accretion disks around black holes are expected to be
radiation-dominated. However, in the alpha-model, these regions are also
expected to be thermally unstable. In this paper, we report two 3-d radiation
MHD simulations of a vertically-stratified shearing box in which the ratio of
radiation to gas pressure is ~ 10, and yet no thermal runaway occurs over a
timespan ~ 40 cooling times. Where the time-averaged dissipation rate is
greater than the critical dissipation rate that creates hydrostatic equilibrium
by diffusive radiation flux, the time-averaged radiation flux is held to the
critical value, with the excess dissipated energy transported by radiative
advection. Although the stress and total pressure are well-correlated as
predicted by the alpha-model, we show that stress fluctuations precede pressure
fluctuations, contrary to the usual supposition that the pressure controls the
saturation level of the magnetic energy. This fact explains the thermal
stability. Using a simple toy-model, we show that independently-generated
magnetic fluctuations can drive radiation pressure fluctuations, creating a
correlation between the two while maintaining thermal stability.",0809.1708v1
2008-10-02,Renormalized theory of the ion cyclotron turbulence in magnetic field--aligned plasma shear flow,"The analytical treatment of nonlinear evolution of the shear-flow-modified
current driven ion cyclotron instability and shear-flow-driven ion cyclotron
kinetic instabilities of magnetic field--aligned plasma shear flow is
presented. Analysis is performed on the base of the nonlinear dispersion
equation, which accounts for a new combined effect of plasma turbulence and
shear flow. It consists in turbulent scattering of ions across the shear flow
with their convection by shear flow and results in enhanced nonlinear
broadening of ion cyclotron resonances. This effect is found to lead to the
saturation of ion cyclotron instabilities as well as to the development of
nonlinear shear flow driven ion cyclotron instability. 52.35.Ra",0810.0362v1
2008-10-07,Interface Ferromagnetism in (110)-Oriented La0.7Sr0.3MnO3/SrTiO3 Ultrathin Superlattices,"We explore manganite interface magnetism in epitaxially grown
La0.7Sr0.3MnO3(LSMO)/SrTiO3 ultrathin superlattices (SL) along (110)
orientation. we show that robust ferromagnetism persists down to four
monolayers LSMO(MLs) (~1.1 nm in thickness), of which 50% Mn is at the
interface state. Above eight MLs, the magnetic moment is nearly saturated to
the theoretical value of 3.7u_B, with an estimated interface moment of 3.2u_B.
In comparison to (100)-oriented SLs which were previously shown to have a spin
canted ground state, (110)-oriented SLs exhibit stronger low-dimensional
ferromagnetism and better metallicity, suggesting a ferromagnetic interface
spin state well suited for all-oxide spintronic devices. The underlining
mechanism is qualitatively discussed.",0810.1309v2
2008-11-16,Evidence for Local Moment by Electron Spin Resonance Study on Polycrystalline LaFeAsO$_{1-x}$F$_x$ (x=0 and 0.13),"The temperature dependence of electron spin resonance (ESR) was studied in
the oxypnictide superconductors LaFeAsO$_{1-x}$F$_x$ (x = 0.0 and 0.13). In the
samples, the ESR signal indicates that the g factor and peak-to-peak linewidth
strongly depend on temperature, especially at low temperatures. It indicates a
strong coupling picture with existence of local moment. The dependence
mentioned above gradually attenuates, and tends to saturation around
room-temperature. This behavior could be ascribed to ""bottleneck"" effect due to
coupling of local moment and itinerant electron. In addition, a Curie-Weiss
like behavior is also observed in temperature dependent integral intensity for
the two samples. Our results strongly support the existence of local moments in
these materials while its origin is still unclear. The results also indicate
strong magnetic frustration in this system, and magnetic fluctuation mechanism
for superconductivity is suggested.",0811.2567v1
2008-12-05,A First Look at Rotation in Inactive Late-Type M Dwarfs,"We have examined the relationship between rotation and activity in 14
late-type (M6-M7) M dwarfs, using high resolution spectra taken at the W.M.
Keck Observatory and flux-calibrated spectra from the Sloan Digital Sky Survey.
Most were selected to be inactive at a spectral type where strong H-alpha
emission is quite common. We used the cross-correlation technique to quantify
the rotational broadening; six of the stars in our sample have vsini > 3.5
km/s. Our most significant and perplexing result is that three of these stars
do not exhibit H-alpha emission, despite rotating at velocities where previous
work has observed strong levels of magnetic field and stellar activity. Our
results suggest that rotation and activity in late-type M dwarfs may not always
be linked, and open several additional possibilities including a
rotationally-dependent activity threshold, or a possible dependence on stellar
parameters of the Rossby number at which magnetic/activity ""saturation"" takes
place in fully convective stars.",0812.1220v1
2008-12-19,Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder,"We measure by inelastic neutron scattering the spin excitation spectra as a
function of applied magnetic field in the quantum spin-ladder material
(C5H12N)2CuBr4. Discrete magnon modes at low fields in the quantum disordered
phase and at high fields in the saturated phase contrast sharply with a spinon
continuum at intermediate fields characteristic of the Luttinger-liquid phase.
By tuning the magnetic field, we drive the fractionalization of magnons into
spinons and, in this deconfined regime, observe both commensurate and
incommensurate continua.",0812.3880v1
2008-12-23,Two and One-dimensional Honeycomb Structure of Boron Nitride,"This paper presents a systematic study of two and one dimensional honeycomb
structure of boron nitride (BN) using first-principles plane wave method.
Two-dimensional (2D) graphene like BN is a wide band gap semiconductor with
ionic bonding. Phonon dispersion curves demonstrate the stability of 2D BN
flakes. Quasi 1D armchair BN nanoribbon are nonmagnetic semiconductors with
edge states. Upon passivation of B and N with hydrogen atoms these edge states
disappear and band gap increases. Bare zigzag BN nanoribbons are metallic, but
become a ferromagnetic semiconductor when their both edges are passivated with
hydrogen. However, their magnetic ground state, electronic band structure and
band gap are found to be strongly dependent on whether B- or N-edge of the
ribbon is saturated with hydrogen. Vacancy defects in armchair and zigzag
nanoribbons affects also magnetic state and electronic structure. In order to
reveal dimensionality effects these properties are contrasted with those of
various 3D BN crystals and 1D BN atomic chain.",0812.4454v1
2009-03-26,Simulations of the dynamic switching of vortex chirality in magnetic nanodisks by a uniform field pulse,"We present a possibility to switch the chirality of a spin vortex occurring
in a magnetic nanodisk by applying a uniform in-plane field pulse, based on
optimizing its strength and duration. The related spin-dynamical process,
investigated by micromagnetic simulations, consists of several stages. After
applying the field, the original vortex is expelled from the disk, after which
two C-shaped states oscillate between each other. The essence of the method is
based on turning the field off at a suitably chosen moment for which the
orientation of the C-state will evolve into the nucleation of a vortex with the
desirable chirality. This idea simply uses the information about the original
chirality present inside the nanodisk during the dynamic process before losing
it in saturation, and can thus be regarded as analogous to the recent studies
on the polarity switching.",0903.4653v5
2009-05-04,Magnon BEC and various phases of 3D quantum helimagnets under high magnetic field,"We study high-field phase diagram and low-energy excitations of
three-dimensional quantum helimagnets. Slightly below the saturation field, the
emergence of magnetic order may be viewed as Bose-Einstein condensation (BEC)
of magnons. The method of dilute Bose gas enables a quantitative analysis of
quantum effects in these helimagnets and thereby three phases are found: cone,
coplanar fan and a phase-separated one. As an application, we map out the phase
diagram of a 3D helimagnet which consists of frustrated J1-J2 chains as a
function of frustration and an interchain coupling. Moreover, we also calculate
the stability of the 2-magnon bound state to investigate the possibility of the
bound-magnon BEC.",0905.0249v2
2009-06-01,Non-Abelian Chern-Simons vortices with generic gauge groups,"We study non-Abelian Chern-Simon BPS-saturated vortices enjoying N=2
supersymmetry in d=2+1 dimensions, with generic gauge groups of the form U(1) x
G', with G' being a simple group, allowing for orientational modes in the
solutions. We will keep the group as general as possible and utilizing the
powerful moduli matrix formalism to provide the moduli spaces of vortices and
derive the corresponding master equations. Furthermore, we study numerically
the vortices applying a radial Ansatz to solve the obtained master equations
and we find especially a splitting of the magnetic fields, when the coupling
constants for the trace-part and the traceless part of the Chern-Simons term
are varied, such that the Abelian magnetic field density can become negative
near the origin of the vortex while the non-Abelian part stays positive, and
vice versa.",0906.0021v1
2009-06-08,Anomalous Pressure Dependence of the Superconducting Transition Temperature in FeSe1-x Studied by DC Magnetic Measurements,"The pressure dependence of superconducting transition temperature $T_{\rm c}$
has been investigated through the DC magnetic measurements for FeSe$_{0.8}$ and
FeSe$_{1.0}$. For both samples, with increasing pressure $P$, the $T_{\rm
c}$$-$$P$ curve exhibits a two-step increase, showing a local maximum of
$\sim$11 K at $P$$\sim$1.0 GPa and a rapid increase with an extremely large
pressure coefficient for $P$$>$1.5 GPa. $T_{\rm c}$ saturates at $\sim$25 K (21
K) in FeSe$_{1.0}$ (FeSe$_{0.8}$) for $P$$>$3 GPa. A rapid decrease in
superconducting volume fraction is observed with an increase in $T_{\rm c}$
above 1.5 GPa, suggesting the presence of electronic inhomogeneity.",0906.1534v3
2009-08-04,Suppression of secondary phase formation in Fe implanted ZnO single crystals,"Unwanted secondary phases are one of the major problems in diluted magnetic
semiconductor creation. Here, the authors show possibilities to avoid such
phases in Fe implanted and postannealed ZnO(0001) single crystals. While -Fe
nanoparticles are formed after such doping in as-polished crystals, high
temperature (1273 K) annealing in O2 or high vacuum before implantation
suppresses these phases. Thus, the residual saturation magnetization in the
preannealed ZnO single crystals is about 20 times lower than for the
as-polished ones and assigned to indirect coupling between isolated Fe ions
rather than to clusters.",0908.0396v1
2009-08-31,Pair Creation in Electric Flux Tube and Chiral Anomaly,"Using chiral anomaly, we discuss the pair creation of massless fermions under
the effect of magnetic field $\vec{B}$ when an electric flux tube $\vec{E}$
parallel to $\vec{B}$ is switched on. The tube is axial symmetric and
infinitely long. In the limit $B\gg E$, we can analytically obtain the spatial
and temporal behaviors of the number density of the fermions, the azimuthal
magnetic field generated by the fermions etc.. We find that the life time $t_c$
of the electric field is shorter as the width of the tube is narrower. Applying
it to the glasma in high-energy heavy-ion collisions, we find that color
electric field decays fast such as $t_c\simeq Q_s^{-1}$ with saturation
momentum $Q_s$.",0908.4466v1
2009-09-23,Quantum Hall effect of the surface states in topological insulator,"We study the quantum Hall effect in the surface states of topological
insulator in the presence of a perpendicular magnetic field in the framework of
edge states. Motion of Dirac fermions will form descrete Landau levels, among
which a fully saturated zero mode will have different behaviors near the
boundary according to the sign of the effective mass for Dirac fermions. The
Hall conductance is quantized to be n (n is an integer) in the unit of e^2/h
for a positive mass, n+1 for a negative mass, and n+1/2 for massless fermions.
In topological insulator the massive term to the Dirac fermions can be the
Zeeman coupling in a magnetic field or be induced by the finite-size effect in
an ultrathin film. For example the g-factor of Bi_2Se_3 is positive and give
rise to a positive mass term for Dirac fermions. We address experimental
realization of the quantum Hall effect in topological insulators.",0909.4125v1
2009-11-02,Giant anomalous Hall resistivity of the room temperature ferromagnet Fe3Sn2 - a frustrated metal with the kagome-bilayer structure,"We have investigated magnetic and transport properties of the {\it
kagom\'{e}-bilayer} ferromagnet Fe$_{3}$Sn$_{2}$. A soft ferromagnetism and a
large anomalous Hall effect are observed. The saturated Hall resistivity of
Fe$_{3}$Sn$_{2}$ is 3.2 $\mu\Omega$cm at 300 K, which is almost 20 times higher
than that of typical itinerant-ferromagnets such as Fe and Ni. The anomalous
Hall coefficient $R_{{\rm s}}$ is 6.7$\times10^{-9}$ $\Omega$cm/G at 300 K,
which is three orders of magnitude larger than that of pure Fe. $R_{{\rm s}}$
obeys an unconventional scaling to the longitudinal resistivity, $\rho_{xx}$,
of $R_{{\rm s}} \propto \rho_{xx}^{3.3}$. Such a relationship cannot be
explained by the skew and/or side-jump mechanisms and indicates that the origin
of the anomalous Hall effect in the frustrated magnet Fe$_{3}$Sn$_{2}$ is
indeed extraordinary.",0911.0289v1
2009-11-09,Electric field generation by the electron beam filamentation instability: Filament size effects,"The filamentation instability (FI) of counter-propagating beams of electrons
is modelled with a particle-in-cell simulation in one spatial dimension and
with a high statistical plasma representation. The simulation direction is
orthogonal to the beam velocity vector. Both electron beams have initially
equal densities, temperatures and moduli of their nonrelativistic mean
velocities. The FI is electromagnetic in this case. A previous study of a small
filament demonstrated, that the magnetic pressure gradient force (MPGF) results
in a nonlinearly driven electrostatic field. The probably small contribution of
the thermal pressure gradient to the force balance implied, that the
electrostatic field performed undamped oscillations around a background
electric field. Here we consider larger filaments, which reach a stronger
electrostatic potential when they saturate. The electron heating is enhanced
and electrostatic electron phase space holes form. The competition of several
smaller filaments, which grow simultaneously with the large filament, also
perturbs the balance between the electrostatic and magnetic fields. The
oscillations are damped but the final electric field amplitude is still
determined by the MPGF.",0911.1727v1
2009-11-21,Comparison of Fluid Attenuated Inversion Recovery Sequence with Spin Echo T2-Weighted MRI for Characterization of Brain Pathology,"Twenty cases of different brain pathology have been studied via MRI using an
open resistive magnet with magnetic field strength of 0.2 Tesla. The relative
signal intensity with respect to the repetition time (TR) at fixed echo time
(TE) 0.117 sec. has been studied. It was found that the signal intensity
saturates for most lesions beyond a certain TR~6 sec in the T2 - weighted
image. The signal intensity differs with respect to the inversion time (TI) for
fat and cerebrospinal fluid (CSF). It was found that the intensity is nulled
for CSF at TI ~1.5 sec. and for Fat at TI~0.10 sec in the FLAIR imaging
sequence. Thus the intensity of the lesions is qualitatively different for the
two sequences. From the radiological diagnostic point of view, it was concluded
that the FLAIR sequence is more useful for the detection of lesions compared to
T2 sequences.",0911.4159v2
2009-12-15,Dimer mean-field model for the Ising spin glass,"A dimer mean-field model for the Ising spin-glass is presented. Despite its
simplicity it captures some of the essential features of the spin-glass
physics. The distribution of the single-spin magnetization is determined from a
self-consistent integral equation. By solving the self-consistency condition
numerically, we find that there are two temperature scales characterizing the
glass transition. At the first, higher temperature, the glass order parameter
becomes non-vanishing, and at the second, freezing temperature, it saturates to
its maximal value. The effect of magnetic field and the existence of the
Almeida-Thouless line are discussed. Finally, it is shown that the information
compressibility, defined as the derivative of entropy with respect to energy,
diverges at the freezing temperature. This indicates a zero internal
temperature and true glassy dynamics with diverging relaxation times.",0912.2959v1
2010-01-12,The magnetohydrodynamic instability of current-carrying jets,"Magnetohydrodynamic instabilities can be responsible for the formation of
structures with various scales in astrophysical jets. We consider the stability
properties of jets containing both the azimuthal and axial field of subthermal
strength. A magnetic field with complex topology in jets is suggested by
theoretical models and is consistent with recent observations. Stability is
discussed by means of a linear analysis of the ideal magnetohydrodynamic
equations. We argue that in azimuthal and axial magnetic fields the jet is
always unstable to non-axisymmetric perturbations. Stabilization does not occur
even if the strengths of these field components are comparable. If the axial
field is weaker than the azimuthal one, instability occurs for perturbations
with any azimuthal wave number $m$, and the growth rate reaches a saturation
value for low values of $m$. If the axial field is stronger than the toroidal
one, the instability shows for perturbations with relatively high $m$.",1001.1987v2
2010-02-08,Processing and Characterization of Multiferroic Bi-relaxors,"We compare chemical solution deposition (CSD), and pulsed-laser-deposition
(PLD), specimens of the new room-temperature, single-phase, multiferroic
magnetoelectric, [PbFe2/3W1/3O3]x[PbZr0.53Ti0.47O3]1-x (PZTFWx ~ 0.40<x<0.20)
with polarization, loss (<1%), and resistivity (typically 108 ohm.cm) equal to
or superior to BiFeO3. Single phase polycrystalline multiferroics PZTFWx thin
films were fabricated on platinized silicon substrate by CSD and as epitaxial
single-crystal films on MgO substrate by PLD. High dielectric constants (1200-
3000), high polarization (30 - 60 micro C/cm2), weak saturation magnetization
(0.48 - 4.53 emu/cm3), a broad dielectric temperature peak, high-frequency
dispersion, low dielectric loss and low leakage current were observed in these
materials, suggesting the family as candidates for room-temperature
multiferroic devices. The ferroelectric switching in these materials can be
suppressed or quenched with applied magnetic field.",1002.1637v1
2010-02-12,Instability of Magnons in Two-dimensional Antiferromagnet at High Magnetic Fields,"Spin dynamics of the square lattice Heisenberg antiferromagnet, \BaMnGeO, is
studied by a combination of bulk measurements, neutron diffraction, and
inelastic neutron scattering techniques. Easy plane type antiferromagnetic
order is identified at $T \le 4.0$ K. The exchange interactions are estimated
as $J_1$ = 27.8(3)${\mu}$eV and $J_2$ = 1.0(1) ${\mu}$eV, and the saturation
field $H_{\rm C}$ is 9.75 T. Magnetic excitation measurements with high
experimental resolution setup by triple axis neutron spectrometer reveals the
instability of one magnon excitation in the field range of $0.7H_{\rm C}
\lesssim H \lesssim 0.85H_{\rm C}$.",1002.2470v1
2010-02-19,Resistive double-diffusive instability in the dead-zones of protostellar disks,"We outline a novel linear instability that may arise in the dead-zones of
protostellar disks, and possibly the fluid interiors of planets and
protoplanets. In essence it is an axisymmetric buoyancy instability, but one
that would not be present in a purely hydrodynamical gas. The necessary
ingredients for growth include a negative radial entropy gradient (of any
magnitude), weak magnetic fields, and efficient resistive diffusion (in
comparison with thermal diffusion). The character of the instability is local,
axisymmetric, and double-diffusive, and it attacks lengths much shorter than
the resistive scale. Like the axisymmetric convective instability, it draws its
energy from the negative radial entropy gradient; but by utilising the
diffusing magnetic field, it can negate the stabilising influence of rotation.
Its nonlinear saturated state, while not transporting appreciable angular
momentum, could drive radial and vertical mixing, which may influence the
temperature structure of the disk, dust dynamics and, potentially, planet
formation.",1002.3750v2
2010-08-03,Transverse Thermoelectric Conductivity of Bilayer Graphene in Quantum Hall Regime,"We performed electric and thermoelectric transport measurements of bilayer
graphene in a magnetic field up to 15 Tesla. The transverse thermoelectric
conductivity $\rm\alpha_{xy}$, determined from four transport coefficients,
attains a peak value of $\rm\alpha_{xy, peak}$ whenever chemical potential lies
in the center of a Landau level. The temperature dependence of $\rm\alpha_{xy,
peak}$ is dictated by the disorder width $\rm W_L$. For $\rm k_BT/W_L\leq$0.2,
$\rm\alpha_{xy, peak}$ is nominally linear in temperature, which gives
$\rm\alpha_{xy,peak}/T=0.19 \pm 0.03 n A/K^2$ independent of the magnetic
field, temperature and Landau Level index. At $\rm k_BT/W_L\geq$0.5,
$\rm\alpha_{xy, peak}$ saturates to a value close to the predicted universal
value of $\rm 4\times(ln2)k_Be/h$ according to the theory of Girvin and Jonson.
We remark that an anomaly is found in $\rm\alpha_{xy}$ near the charge neutral
point, similar to that in single-layer graphene",1008.0442v2
2010-09-13,Theromelectricity in Graphene: Effects of a gap and magnetic fields,"We calculate the thermopower of monolayer graphene in various circumstances.
First we show that experiments on the thermopower of graphene can be understood
quantitatively with a very simple model of screening in the semiclassical
limit. We can calculate the energy dependent scattering time for this model
exactly. We then consider acoustic phonon scattering which might be the
operative scattering mechanism in free standing films, and predict that the
thermopower will be linear in any induced gap in the system. Further, the
thermopower peaks at the same value of chemical potential (tunable by gate
voltage) independent of the gap. Finally, we show that in the semiclassical
approximation, the thermopower in a magnetic field saturates at high field to a
value which can be calculated exactly and is independent of the details of the
scattering. This effect might be observable experimentally.",1009.2343v1
2010-10-09,Temperature dependence of Magnetic properties in Nanocrystalline copper ferrite thin films,"The copper ferrite thin films have been deposited by RF sputtering at a 50W
rf power. The As-deposited films are annealed in air at $800^{\circ}$C and then
slow cooled. The As-deposited (AD) as well as slow cooled (SC) films are
studied using a SQUID Magnetometer. The M Vs H curves have been recorded at
various temperatures between 5K to 300K. The coercivities obtained from the MH
curves are then plotted against temperature (T). The magnetization in the films
does not saturate, even at the highest field of 7T. The high field part of the
M Vs H curves is fitted using the H1/2 term of Chikazumi expression M(H)= Q*(1-
a /Hn), with n=1/2. The variation of coefficient 'a' of H1/2 term has been
observed with temperature (T). An attempt has been made to correlate this with
the coercivity (Hc) in the case of annealed films.",1010.1882v1
2010-10-15,Post-flare evolution of AR 10923 with Hinode/XRT,"Flares are dynamic events which involve rapid changes in coronal magnetic
topology end energy release. Even if they may be localized phenomena, the
magnetic disturbance at their origin may propagate and be effective in a larger
part of the active region. We investigate the temporal evolution of a flaring
active region with respect to the loops morphology, the temperature, and
emission measure distributions. We consider $Hinode/XRT$ data of a the 2006
November 12th C1.1 flare. We inspect the evolution of the morphology of the
flaring region also with the aid of TRACE data. XRT filter ratios are used to
derive temperature and emission measure maps and evolution. The analyzed flare
includes several brightenings. We identify a coherent sequence of tangled and
relaxed loop structures before, during, and after the brightenings. Although
the thermal information is incomplete because of pixel saturation at the flare
peak, thermal maps show fine, evolving spatial structuring. Temperature and
emission measure variations show up in great detail, and we are able to detect
a secondary heating of larger loops close to the proper flaring region. Finally
we estimate the amount of energy released in these flaring loops during the
flare decay.",1010.3124v1
2010-10-29,Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field,"Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2
antiferromagnetic chain with alternating $g$-tensor and Dzyaloshinskii-Moriya
interactions that exhibits a field-induced spin gap, are probed by means of
pulsed-field electron spin resonance spectroscopy. In particular, we report on
a minimum of the gap in the vicinity of the saturation field $H_{sat}=48.5$ T
associated with a transition from the sine-Gordon region (with soliton-breather
elementary excitations) to a spin-polarized state (with magnon excitations).
This interpretation is fully confirmed by the quantitative agreement over the
entire field range of the experimental data with the DMRG investigation of the
spin-1/2 Heisenberg chain with a staggered transverse field.",1010.6141v1
2010-12-20,Particle size dependence of magnetization and non-centrosymmetry in nanoscale BiFeO3,"The saturation magnetization (M_s), antiferromagnetic transition point (T_N),
and the off-center displacements of Bi and Fe ions have been measured as a
function of particle size in nanoscale BiFeO3. T_N decreases down to ~550 K for
particles of size ~5 nm from ~653 K in bulk while M_s rises by more than an
order of magnitude. Analysis of crystallographic structure from Rietveld
refinement of x-ray diffraction patterns shows significant rise in off-center
displacements of Bi (del_Bi) and Fe (del_Fe) ions within a unit cell with the
decrease in particle size. The net unit-cell polarization P_S too, is found to
be larger in nanoscale regime.",1012.4288v1
2011-01-14,Investigation of phonon behavior in Pr2NiMnO6 by micro-Raman spectroscopy,"The temperature dependence of phonon excitations and the presence of spin
phonon coupling in polycrystalline Pr2NiMnO6 samples were studied using
micro-Raman spectroscopy and magnetometry. Magnetic properties show a single
ferromagnetic-to-paramagnetic transition at 228 K and a saturation
magnetization close to 4.95 \muB/f.u.. Three distinct Raman modes at 657, 642,
and 511 cm-1 are observed. The phonon excitations show a clear hardening due to
anharmonicity from 300 K down to 10 K. Further, temperature dependence of the
657 cm-1 mode shows only a small softening. This reflects the presence of a
relatively weak spin-phonon coupling in Pr2NiMnO6 contrary to other double
perovskites previously studied.",1101.2805v1
2011-01-27,Asymmetric graphene model applied to graphite-like carbon-based ferromagnetism,"Several experiments have recently found room-temperature ferromagnetism in
graphite-like carbon based materials. This paper offers a model explaining such
ferromagnetism by using an asymmetric nano-graphene. Our first typical model is
C48H24 graphene molecule, which has three dihydrogenated (-CH2) zigzag edges.
There are several multiple spin states competing for stable minimum energy in
the same atomic topology. Both molecular orbital and density function theory
methods indicate that the quartet state(S=3/2) is more stable than that of
doublet (S=1/2), which means that larger saturation magnetization will be
achieved. We also enhanced this molecule to an infinite length ribbon having
many (-CH2) edges. Similar results were obtained where the highest spin state
was more stable than lower spin state. In contrast, a nitrogen substituted
(-NH) molecule C45N3H21 demonstrated opposite results. that is, the lowest spin
state(S=1/2) is more stable than that of highest one(S=3/2), which arises from
the slight change in atom position.",1101.5209v1
2011-02-19,Manganese valence and magnetotransport in ultrathin films of La$_{0.67}$Ca$_{0.33}$MnO$_3$,"We report a comparative study of the properties of very thin films of
La$_{0.67}$Ca$_{0.33}$MnO$_3$ grown epitaxially under strain on flat SrTiO$_3$
(STO), lattice matched on NdGaO$_3$ (NGO), and strained on $1^{\circ}$-miscut
STO. We use transmission electron microscopy and electron energy loss
spectroscopy to study the microstructure, composition, and Mn valence state.
Near the interface we find no significant segregation, but a charge
compensation layer where the valence is enhanced over the nominal value of
3.3+, and a relaxation to this value over several nanometer. The transport
properties show well-known behavior for the films on flat STO and NGO, namely
values of the metal-insulator transition temperature which are strongly (STO)
or only little (NGO) reduced with respect to the bulk value. The reduction in
films on miscut STO however is less strong than in films on flat STO, even
though they appear similar as to strain state and interface layer.
Magnetically, we find reduced values of the saturation magnetization for the
strained films with respect to the bulk value, which cannot only be ascribed to
the interface layer.",1102.4004v1
2011-05-05,Antiferromagnet with two coupled antiferromagnetic sublattices in a magnetic field,"We discuss the magnon spectrum of an antiferromagnet (AF) in a magnetic field
$h$ consisting of two interpenetrating AF sublattices coupled by the exchange
interaction at T=0. One-ion easy-plane anisotropy is also taken into account.
We calculate using the 1/S expansion the gap in the spectrum which is a
manifestation of the order-by-disorder effect in this system and the optical
magnon mode splitting. Both of these phenomena originate from the
inter-sublattice interaction. We calculate also the gap value at $h\approx h_c$
in the leading order of the small parameter $(h_c-h)/h_c$ using the magnon
Bose-Einstein condensation treatment, where $h_c$ is the saturation field. By
comparing results obtained within these two approaches we conclude that the 1/S
expansion gives a qualitatively correct result at $h\sim h_c$ even at large
one-ion anisotropy but it overestimates the gap value. The application is
discussed of these results to the actively studied AF of the considered type
$\rm NiCl_2$-$\rm 4SC(NH_2)_2$ (DTN).",1105.1044v1
2011-05-26,Schwinger Mechanism with Energy Dissipation in Glasma,"Initial states of glasma in high energy heavy ion collisions are longitudinal
classical color electric and magnetic fields. Assuming finite color electric
conductivity, we show that the color electric field decays by quark pair
production with the life time of the order of $Q_s^{-1}$, i.e. the inverse of
the saturation momentum. Quarks and anti-quarks created in the pair production
are immediately thermalized as far as their temperature $\beta^{-1}$ is lower
than $Q_s$. Namely, a relaxation time of the quarks to be thermalized is much
shorter than $Q_s^{-1}$ when $\beta^{-1} \ll Q_s$. We also show that the quarks
acquire longitudinal momentum of the order of $Q_s$ by the acceleration of the
electric field. To discuss the quark pair production, we use chiral anomaly
which has been shown to be very powerful tool in the presence of strong
magnetic field.",1105.5188v2
2011-06-07,Magnetoelastic effects in Jahn-Teller distorted CrF$_2$ and CuF$_2$ studied by neutron powder diffraction,"We have studied the temperature dependence of crystal and magnetic structures
of the Jahn-Teller distorted transition metal difluorides CrF$_2$ and CuF$_2$
by neutron powder diffraction in the temperature range 2-280 K. The lattice
parameters and the unit cell volume show magnetoelastic effects below the
N\'eel temperature. The lattice strain due to the magnetostriction effect
couples with the square of the order parameter of the antiferromagnetic phase
transition. We also investigated the temperature dependence of the Jahn-Teller
distortion which does not show any significant effect at the antiferromagnetic
phase transition but increases linearly with increasing temperature for CrF$_2$
and remains almost independent of temperature in CuF$_2$. The magnitude of
magnetovolume effect seems to increase with the low temperature saturated
magnetic moment of the transition metal ions but the correlation is not at all
perfect.",1106.1349v1
2011-07-21,The Kelvin-Helmholtz instability in weakly ionised plasmas: Ambipolar dominated and Hall dominated flows,"The Kelvin-Helmholtz instability is well known to be capable of converting
well-ordered flows into more disordered, even turbulent, flows. As such it
could represent a path by which the energy in, for example, bowshocks from
stellar jets could be converted into turbulent energy thereby driving molecular
cloud turbulence. We present the results of a suite of fully multifluid
magnetohydrodynamic simulations of this instability using the HYDRA code. We
investigate the behaviour of the instability in a Hall dominated and an
ambipolar diffusion dominated plasma as might be expected in certain regions of
accretion disks and molecular clouds respectively.
  We find that, while the linear growth rates of the instability are unaffected
by multifluid effects, the non-linear behaviour is remarkably different with
ambipolar diffusion removing large quantities of magnetic energy while the Hall
effect, if strong enough, introduces a dynamo effect which leads to continuing
strong growth of the magnetic field well into the non-linear regime and a lack
of true saturation of the instability.",1107.4241v1
2011-07-21,Approaching Quantum Criticality in ferromagnetic Ce_2 (Pd_1-x Rh_x)_2 In alloys,"Low temperature magnetic and thermal (C_m) properties of the ferromagnetic
(FM) alloys Ce_2.15 (Pd_1-x Rh_x)_1.95 In_0.9 were investigated in order to
explore the possibility for tuning a quantum critical point (QCP) by doping Pd
with Rh. As expected, the magnetic transition observed at T = 4.1K in the
parent alloy decreases with increasing Rh concentration. Nevertheless it splits
into two transitions, the upper being antiferromagnetic (AF) whereas the lower
FM. The AF phase boundary extrapolates to T_N = 0 for x_cr ~ 0.65 whereas the
first order FM transition vanishes at x ~ 0.3. The QC character of the T_N => 0
point arises from the divergent T dependence of the tail of C_m/T observed in
the x = 0.5 and 0.55 alloys, and the tendency to saturation of the maximum of
C_m(T_N)/T as observed in exemplary Ce compounds for T_N => 0. Beyond the
critical concentration the unit cell volume deviates from the Vegard's law in
coincidence with a strong increase of the Kondo temperature.",1107.4308v1
2011-09-09,"Magnetisation Studies of Geometrically Frustrated Antiferromagnets SrLn2O4, with Ln = Er, Dy and Ho","We present the results of susceptibility \chi(T) and magnetisation M(H)
measurements performed on single crystal samples of the rare-earth oxides
SrLn2O4 (Ln = Er, Dy and Ho). The measurements reveal the presence of magnetic
ordering transition in SrHo2O4 at 0.62 K and confirm that SrEr2O4 orders
magnetically at 0.73 K, while in SrDy2O4 such a transition is absent down to at
least 0.5 K. The observed ordering temperatures are significantly lower than
the Curie-Weiss temperatures, \theta_{CW}, obtained from the high-temperature
linear fits to the 1/\chi(T) curves, which implies that these materials are
subject to geometric frustration. Strong anisotropy found in the \chi(T) curves
for a field applied along the different crystallographic directions is also
evident in the M(H) curves measured both above and below the ordering
temperatures. For all three compounds the magnetisation plateaux at
approximately one third of the magnetisation saturation values can be seen for
certain directions of applied field, which is indicative of field-induced
stabilisation of a collinear {\it two-up one-down} structure.",1109.2094v1
2011-09-27,Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films,"A systematic study of the temperature and magnetic field dependence of the
longitudinal and transverse resistivities of epitaxial thin films of magnetite
(Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar
Hall effect (PHE) are sensitive to the in-plane orientation of current and
magnetization with respect to crystal axes in a way consistent with the cubic
symmetry of the system. We also show that the AMR exhibit sign reversal as a
function of temperature, and that it shows significant field dependence without
saturation up to 9 T. Our results provide a unified description of the
anisotropic magnetoresistance effects in epitaxial magnetite films and
illustrate the need for a full determination of the resistivity tensor in
crystalline systems.",1109.5828v1
2011-10-24,CoB/Ni-Based Multilayer Nanowire with High-Speed Domain Wall Motion under Low Current Control,"The spin-transfer torque motion of magnetic domain walls (DWs) in a
CoB/Ni-based nanowire driven by a low current density of
(1.12\pm0.8)\times10^{11} A m^{-2} has been observed indirectly by
magnetotransport measurements. A high DW velocity of 85\pm4 m/s at zero field
was measured at the threshold current density. Upon increasing the current
density to 2.6\times10^{11} A m^{-2}, the DW velocity increases to 197\pm16 m/s
before decreasing quickly in the high-current-density regime attributed to
nonadiabatic spin-transfer torque at a low damping factor and weak pinning. The
addition of B atoms to the Co layers decreased the magnitude of saturation
magnetization, Gilbert damping factor, and density of pinning sites, making the
CoB/Ni multilayer nanowire favorable for practical applications.",1110.5112v3
2011-11-28,Investigation of weak itinerant ferromagnetism and critical behavior of Y$_2$Ni$_7$,"The weak itinerant ferromagnetic behavior of Y$_2$Ni$_7$ is investigated
through magnetic, transport and calorimetric measurements. The low value of
saturation moment, large Rhodes-Wohlfarth ratio, large value of the linear term
in heat capacity and Fermi liquid like resistivity behavior with enhanced
electron-electron scattering contribution establish firmly the weak itinerant
ferromagetic nature of the sample. The critical exponents associated with the
paramagnetic to ferromagnetic transition are also investigated from
magnetization isotherms using modified Arrott plot, Kouvel-Fisher plot and
critical isotherm technique. The more accurate Kouvel-Fisher plot provides the
critical exponents to be $\beta$ = 0.306, $\gamma$ = 1.401 and $\delta$ =
5.578. These values are markedly different from the mean field values and
correspond closely to the two dimensional Ising spin system with long range
spin spin interaction.",1111.6343v1
2012-01-27,Deconfinement in the presence of a strong magnetic background: an exercise within the MIT bag model,"We study the effect of a very strong homogeneous magnetic field B on the
thermal deconfinement transition within the simplest phenomenological approach:
the MIT bag pressure for the quark- gluon plasma and a gas of pions for the
hadronic sector. Even though the model is known to be crude in numerical
precision and misses the correct nature of the (crossover) transition, it
provides a simple setup for the discussion of some subtleties of vacuum and
thermal contributions in each phase, and should provide a reasonable
qualitative description of the critical temperature in the presence of B. We
find that the critical temperature decreases, saturating for very large fields.",1201.5881v3
2012-03-01,Edge superconducting state in Nb thin film with rectangular arrays of antidots,"Superconducting Nb thin films with rectangular arrays of submicron antidots
have been systemically investigated by transport measurements. In low fields,
the magnetoresistance curves demonstrate well-defined dips at integral and
rational numbers of flux quanta per unit cell, which corresponds to a
superconducting wire network-like regime. When the magnetic field is higher
than a saturation field, interstitial vortices interrupt the collective
oscillation in low fields and form vortex sublattice, where a larger magnetic
field interval is observed. In higher fields, a crossover behavior from the
interstitial sublattice state to a single-loop-like state is observed,
characterized by oscillations with a period of $\Phi_0/\pi r_{eff}^2$,
originating from the existence of edge superconducting states with a size
$r_{eff}$ around the antidots.",1203.0269v2
2012-05-15,GaMnN epitaxial films with high magnetization,"We report on the fabrication of pseudomorphic wurtzite GaMnN grown on GaN
with Mn concentrations up to 10% using molecular beam epitaxy. According to
Rutherford backscattering the Mn ions are mainly at the Ga-substitutional
positions, and they are homogeneously distributed according to depth-resolved
Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A
random Mn distribution is indicated by transmission electron microscopy, no
Mn-rich clusters are present for optimized growth conditions. A linear increase
of the c-lattice parameter with increasing Mn concentration is found using
x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting
quantum-interference measurements showing saturation magnetizations of up to
150 emu/cm^3.",1205.3475v2
2012-05-30,Planetesimal Formation in Magnetorotationally Dead Zones: Critical Dependence on the Net Vertical Magnetic Flux,"Turbulence driven by magnetorotational instability (MRI) affects planetesimal
formation by inducing diffusion and collisional fragmentation of dust
particles. We examine conditions preferred for planetesimal formation in
MRI-inactive ""dead zones"" using an analytic dead-zone model based on our recent
resistive MHD simulations. We argue that successful planetesimal formation
requires not only a sufficiently large dead zone (which can be produced by tiny
dust grains) but also a sufficiently small net vertical magnetic flux (NVF).
Although often ignored, the latter condition is indeed important since the NVF
strength determines the saturation level of turbulence in MRI-active layers. We
show that direct collisional formation of icy planetesimal across the
fragmentation barrier is possible when the NVF strength is lower than 10 mG
(for the minimum-mass solar nebula model). Formation of rocky planetesimals via
the secular gravitational instability is also possible within a similar range
of the NVF strength. Our results indicate that the fate of planet formation
largely depends on how the NVF is radially transported in the initial disk
formation and subsequent disk accretion processes.",1205.6754v1
2012-06-04,The role of stepped surfaces on the magnetotransport in strained thin films of La0.67Ca0.33MnO3,"We report a comparative study of the properties of very thin films of
La0.67Ca0.33MnO3 grown epitaxially under strain on flat SrTiO3 (STO) and on 1
deg miscut STO. For the films on flat STO the transport properties show
well-known behavior, namely values of the metal-insulator transition
temperature which are strongly reduced with respect to the bulk value. The
reduction in films on miscut STO is significantly less strong than in films on
flat STO, even though they appear similar as to strain state. Moreover, the
residual resistance at low temperatures is lower than for the case of flat
films. Magnetically, we find reduced values of the saturation magnetization
with respect to the bulk value, indicating the presence of a dead layer in both
cases. We argue that the higher density of the step edges on the miscut
substrates lead to strain relaxation in the form of point defects and an
increased electronic bandwidth, which actually make the electronic properties
more robust.",1206.0767v1
2012-06-19,Magnetic vortex-antivortex crystals generated by spin-polarized current,"We study vortex pattern formation in thin ferromagnetic films under the
action of strong spin-polarized currents. Considering the currents which are
polarized along the normal of the film plane, we determine the critical current
above which the film goes to a saturated state with all magnetic moments being
perpendicular to the film plane. We show that stable square vortex-antivortex
superlattices (\emph{vortex crystals}) appears slightly below the critical
current. The melting of the vortex crystal occurs with current further
decreasing. A mechanism of current-induced periodic vortex-antivortex lattice
formation is proposed. Micromagnetic simulations confirm our analytical results
with a high accuracy.",1206.4125v2
2012-07-17,Friedel oscillations and horizon charge in 1D holographic liquids,"In many-body fermionic systems at finite density correlation functions of the
density operator exhibit Friedel oscillations at a wavevector that is twice the
Fermi momentum. We demonstrate the existence of such Friedel oscillations in a
3d gravity dual to a compressible finite-density state in a (1+1) dimensional
field theory. The bulk dynamics is provided by a Maxwell U(1) gauge theory and
all the charge is behind a bulk horizon. The bulk gauge theory is compact and
so there exist magnetic monopole tunneling events. We compute the effect of
these monopoles on holographic density-density correlation functions and
demonstrate that they cause Friedel oscillations at a wavevector that directly
counts the charge behind the bulk horizon. If the magnetic monopoles are taken
to saturate the bulk Dirac quantization condition then the observed Fermi
momentum exactly agrees with that predicted by Luttinger's theorem, suggesting
some Fermi surface structure associated with the charged horizon. The mechanism
is generic and will apply to any charged horizon in three dimensions. Along the
way we clarify some aspects of the holographic interpretation of Maxwell
electromagnetism in three bulk dimensions and show that perturbations about the
charged BTZ black hole exhibit a hydrodynamic sound mode at low temperature.",1207.4208v1
2012-08-10,"Electronic structure, optical and magnetic properties of Co$_{2}$FeGe Heusler alloy films","Optical properties of ferromagnetic half-metallic full-Heusler Co$_{2}$FeGe
alloy are investigated experimentally and theoretically. Co$_{2}$FeGe thin
films were obtained by DC magnetron sputtering and show the saturation
magnetization at $T$=10 K of $m\approx$5.6 $\mu_{B}$/f.u., close to the value
predicted by the Slater-Pauling rule. First-principles calculations of the
electronic structure and the dielectric tensor are performed using the
full-potential linearized-augmented-plane-wave method in the generalized
gradient (GGA) and GGA+U approximations. The measured interband optical
conductivity spectrum for the alloy exhibits a strong absorption band in the 1
- 4 eV energy range with pronounced fine structure, which agrees well with the
calculated half-metallic spectrum of the system, suggesting a near perfect
spin-polarization in the material.",1208.2193v1
2012-08-31,Ordering in weakly coupled random singlet spin chains,"The influence of bond randomness on long range magnetic ordering in the
weakly coupled S = 1/2 antiferromagnetic spin chain materials
Cu(py)2(Cl1-xBrx)2 is studied by muon spin rotation and bulk measurements.
Disorder is found to have a strong effect on the ordering temperature TN, and
an even stronger one on the saturation magnetization m0, but considerably more
so in the effectively lower-dimensional Br-rich materials. The observed
behavior is attributed to Random Singlet ground states of individual spin
chains, but remains in contradiction with chain mean field theory predictions.
In this context, we discuss the possibility of a universal distribution of
ordered moments in the weakly coupled Random Singlet chains model.",1208.6479v2
2012-09-27,"Insulating behavior at the neutrality point in dual-gated, single-layer graphene","The fate of the low-temperature conductance at the charge-neutrality (Dirac)
point in a single sheet of graphene is investigated down to 20 mK. As the
temperature is lowered, the peak resistivity diverges with a power-law behavior
and becomes as high as several Megohms per square at the lowest temperature, in
contrast with the commonly observed saturation of the conductivity. As a
perpendicular magnetic field is applied, our device remains insulating and
directly transitions to the broken-valley-symmetry, nu=0 quantum Hall state,
indicating that the insulating behavior we observe at zero magnetic field is a
result of broken valley symmetry. Finally we discuss the possible origins of
this effect.",1209.6364v2
2012-10-12,Shearing box simulations of accretion disk winds,"The launching process of a magnetically driven outflow from an accretion disk
is investigated in a local, shearing box model which allows a study of the
feedback between accretion and angular momentum loss. The mass-flux instability
found in previous linear analyses of this problem is recovered in a series of
2D (axisymmetric) simulations in the MRI-stable (high magnetic field strength)
regime. At low field strengths that are still sufficient to suppress MRI, the
instability develops on a short radial length scale and saturates at a modest
amplitude. At high field strengths, a long-wavelength ""clump"" instability of
large amplitude is observed, with growth times of a few orbits. As speculated
before, the unstable connection between disk and outflow may be relevant for
the time dependence observed in jet-producing disks. The success of the
simulations is due in a large part to the implementation of an effective
wave-transmitting upper boundary condition.",1210.3574v1
2012-10-26,Spin injection from a half-metal at finite temperatures,"Spin injection from a half-metallic electrode in the presence of thermal spin
disorder is analyzed using a combination of random matrix theory,
spin-diffusion theory, and explicit simulations for the tight-binding s-d
model. It is shown that efficient spin injection from a half-metal is possible
as long as the effective resistance of the normal metal does not exceed a
characteristic value, which does not depend on the resistance of the
half-metallic electrode, but is rather controlled by spin-flip scattering at
the interface. This condition can be formulated as \alpha<(l/L)/T, where \alpha
is the relative deviation of the magnetization from saturation, l and L the
mean-free path and the spin-diffusion length in the non-magnetic channel, and T
the transparency of the tunnel barrier at the interface (if present). The
general conclusions are confirmed by tight-binding s-d model calculations. A
rough estimate suggests that efficient spin injection from true half-metallic
ferromagnets into silicon or copper may be possible at room temperature across
a transparent interface.",1210.7194v2
2012-12-23,Classical Model Predictive Control of a Permanent Magnet Synchronous Motor,"A model predictive control (MPC) scheme for a permanent-magnet synchronous
motor (PMSM) is presented. The torque controller optimizes a quadratic cost
consisting of control error and machine losses repeatedly, accounting the
voltage and current limitations. The scheme extensively relies on optimization,
to meet the runtime limitation, a suboptimal algorithm based on differential
flatness, continuous parameterization and linear programming is introduced.
  The multivariable controller exploits cross-coupling effects in the
long-range constrained predictive control strategy. The optimization results in
fast and smooth torque dynamics while inherently using field-weakening to
improve the power efficiency and the current dynamics in high speed operation.
As distinctive MPC feature, constraint handling is improved, instead of just
saturating the control input, field weakening is applied dynamically to bypass
the voltage limitation. The performance of the scheme is demonstrated by
experimental and numerical results.",1212.5815v2
2013-01-25,Upper critical field of isoelectron substituted SrFe$_2$(As$_{1-x}$P$_x$)$_2$,"The upper critical field $H_{c2}$ of optimally doped iron-based
superconductor SrFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ ($x$ = 0.35, $T_c$ = 25 K)
was measured as a function of temperature down to 1.6 K for two principal
directions of magnetic field $H \parallel c$ and $H \parallel a$. Measurements
were performed in pulsed magnetic fields up to 65 T using a tunnel-diode
resonator technique on as-grown and heavy-ion irradiated single crystals, with
columnar defect density corresponding to a matching field $B\phi$ = 25 T. The
$H_{c2,c}(T)$ is close to $T$-linear, while clear saturation is observed for
$H_{c2,a}(T)$, leading to a strongly temperature dependent anisotropy parameter
$\gamma$. The linear shape of $H_{c2,c}(T)$ is very similar to that observed in
nodal KFe$_2$As$_2$ but very different from full-gap LiFeAs. Irradiation does
not introduce any additional features on $H_{c2}(T)$ line corresponding to the
matching field. Instead, it suppresses uniformly both $T_c$ and $H_{c2}$,
keeping their ratio constant.",1301.6142v1
2013-02-24,Superparamagnetic Transition and Local Disorder in CuFe2O4 Nanoparticles,"We present X-ray diffraction (XRD), M\""ossbauer spectroscopy (MS) and d.c.
magnetization measurements performed on ball-milled CuFe2O4 samples. The
average particle size <d> was found to decrease to the nanometer range after
t=15 min of milling. Room temperature M\""ossbauer data showed that the fraction
of particles above the blocking temperature TB increases with milling time, and
almost complete superparamagnetic samples are obtained for <d> = 7(2) nm.
Magnetization measurements below TB suggest spin canting in milled samples. The
values of saturation moment mu_S reveal that site populations are slightly
affected by milling. M\""ossbauer resonant intensities are accounted for on the
basis of local disorder of Fe3+ environments, and the development of sample
inhomogeneities of CuxFe3-xO4 composition.",1302.5876v1
2013-04-07,Critical Temperature Studies of the Anisotropic Bi- and Multilayer Heisenberg Ferromagnets in Pair Approximation,"The Pair Approximation method is applied to studies of the bilayer and
multilayer magnetic systems with simple cubic structure. The method allows to
take into account quantum effects related with non-Ising couplings. The paper
adopts the anisotropic Heisenberg model for spin $S=1/2$ and considers the
phase transition temperatures as a function of the exchange integrals strength
in line with the role of intra- and interplanar anisotropic interactions in the
onset of low-dimensional magnetism. The compensation effect for the Curie
temperature is found for asymmetric interactions within the neighbouring planes
of the bilayer system. The paper predicts the saturation of the Curie
temperature for strong interplanar interactions. However, such an effect for
the multilayer system occurs only when the interplanar interactions are of
purely isotropic character.",1304.2029v1
2013-05-15,Roles of oxygen vacancies on ferromagnetism in Ni doped In2O3: A hybrid functional study,"The roles of oxygen vacancies on the electronic and magnetic properties of Ni
doped In$_2$O$_3$ have been studied by first-principles calculations based on
hybrid functional theory. Our results predict that the Ni-doped In$_2$O$_3$
system displays a ferromagnetic semiconducting character. However, the presence
of oxygen vacancies results in antiferromagnetic coupling between the
neighboring Ni pair bridged by an oxygen vacancy. The antiferromagnetic
coupling is found to arise from the predominant role of superexchange due to
the strong Ni 3d-O 2p hybridization. Consequently, the oxygen vacancies play a
key role in the lower saturation magnetization of Ni:In$_2$O$_3$
polycrystalline sample, as observed in experiments.",1305.3391v2
2013-06-29,Strain-induced enhancement of coercivity in amorphous TbFeCo films,"We report a strong size dependence of coercivity in amorphous ferrimagnetic
TbFeCo films. The as-deposited film exhibited a low saturation magnetization
(Ms=100 emu/cc) and a high perpendicular anisotropy (Ku=10^6 erg/cc). Hall-bar
devices were fabricated for characterizing the magneto-transport behaviors. A
significant increase in coercivity (up to 300 %) was observed at room
temperature as the width of Hall bar was reduced. The large coercivity
enhancement was attributed to the relaxation of film stress. The effect of
strain and dimensionality on the coercivity in TbFeCo makes it attractive for
tunable coercivity and the magnetization reversal in future nanoscale devices.",1307.0057v1
2013-07-07,Inverse effect of magnetostriction in magnetoelectric laminates,"We introduce the notion of inverse effect of magnetostriction for
magnetostrictive/piezoelectric heterostructures and study this effect
theoretically and experimentally. It is shown that the inverse effect of
magnetostriction may crucially contribute to the mechanism of magnetoelectric
coupling. It is shown that the studied effect essentially modifies the
saturation magnetostriction of the whole structure as compared to its magnetic
phase bulk and also induces an additional magnetic anisotropy. Our
consideration provides useful insight into the fundamental issue of
strain-mediated magnetoelectric coupling. Understanding this effect may lead to
its utilization in original experimental concepts and the improvement of the ME
coupling.",1307.1868v2
2013-07-08,Spin thermopower in the overscreened Kondo model,"We study the spin thermopower in the two-channel spin-1/2 Kondo model which
exhibits the phenomenon of impurity spin overscreening and non-Fermi-liquid
properties. While magnetic field lower than the Kondo temperature does not
strongly polarize the impurity spin, we show that it nevertheless strongly
affects the low-energy part of the spectral function. In turn, this leads to
characteristic saturation of the spin Seebeck coefficient at the value of
0.388kB/|e| at T ~ T*, where T* ~ B^2/TK is the scale of the crossover between
the intermediate-temperature non-Fermi-liquid regime and the low-temperature
Fermi-liquid regime. We show that measuring the spin thermopower at low
magnetic fields would provide a sensitive test for distinguishing regular Fermi
liquid, singular Fermi liguid, and non-Fermi liquid behaviour in nanodevices.",1307.2273v1
2013-07-15,Weak Antilocalization and Linear Magnetoresistance in The Surface State of SmB6,"Strongly correlated Kondo insulator SmB6 is known for its peculiar low
temperature residual conduction, which has recently been demonstrated to arise
from a robust metallic surface state, as predicted by the theory of topological
Kondo insulator (TKI). Photoemission, quantum oscillation and magnetic doping
experiments have provided evidence for the Dirac-like dispersion and
topological protection. Questions arise as whether signatures of spin-momentum
locking and electron interaction could be resolved in transport measurements.
Here we report metallic conduction of surface state down to mK temperatures
with saturation behaviors suggestive of Kondo effect. We observe in the surface
state the weak-antilocalization (WAL) effect that is in agreement with a
spin-momentum locked metallic surface. At larger perpendicular magnetic fields,
the surface state exhibits an unusual linear magnetoresistance similar to those
found in Bi-based topological insulators and in graphene. (Correspondence to:
xia.jing@uci.edu)",1307.4133v1
2013-08-30,Energy dissipation of moved magnetic vortices,"A two-dimensional easy-plane ferromagnetic substrate, interacting with a
dipolar tip which is magnetised perpendicular with respect to the easy plane is
studied numerically by solving the Landau-Lifshitz Gilbert equation. The
dipolar tip stabilises a vortex structure which is dragged through the system
and dissipates energy. An analytical expression for the friction force in the
v$\rightarrow$0-limit based on the Thiele equation is presented. The
limitations of this result which predicts a diverging friction force in the
thermodynamic limit, are demonstrated by a study of the size dependence of the
friction force. While for small system sizes the dissipation depends
logarithmically on the system size, it saturates at a specific velocity
dependent value. This size can be regarded as an effective vortex size and it
is shown how this effective vortex size agrees with the infinite extension of a
vortex in the thermodynamic limit. A magnetic friction number is defined which
represents a general criterion for the validity of the Thiele equation and
quantifies the degree of nonlinearity in the response of a driven spin
configuration.",1308.6714v1
2013-09-10,Magnetoresistance evidence on surface state and field-dependent bulk gap in Kondo insulator SmB6,"Recently, the resistance saturation at low temperature in Kondo insulator
SmB6, a long-standing puzzle in condensed matter physics, was proposed to
originate from topological surface state. Here,we systematically studied the
magnetoresistance of SmB6 at low temperature up to 55 Tesla. Both temperature-
and angular-dependent magnetoresistances show a similar crossover behavior
below 5 K. Furthermore, the angular-dependent magnetoresistance on different
crystal face confirms a two-dimensional surface state as the origin of
magnetoresistances crossover below 5K. Based on two-channels model consisting
of both surface and bulk states, the field-dependence of bulk gap with critical
magnetic field (Hc) of 196 T is extracted from our temperature-dependent
resistance under different magnetic fields. Our results give a consistent
picture to understand the low-temperature transport behavior in SmB6,
consistent with topological Kondo insulator scenario.",1309.2378v3
2013-09-16,Epitaxial Growth of Spinel Cobalt Ferrite Films on MgAl$_2$O$_4$ Substrates by Direct Liquid Injection Chemical Vapor Deposition,"The direct liquid injection chemical vapor deposition (DLI-CVD) technique has
been used for the growth of cobalt ferrite (CFO) films on (100)-oriented
MgAl$_2$O$_4$ (MAO) substrates. Smooth and highly epitaxial cobalt ferrite thin
films, with the epitaxial relationship $\mathrm{MAO} (100)\:[001] \parallel
\mathrm{CFO} (100)\:[001]$, are obtained under optimized deposition conditions.
The films exhibit bulk-like structural and magnetic properties with an
out-of-plane lattice constant of $8.370\;\mathrm{\AA}$ and a saturation
magnetization of $420\;\mathrm{kA/m}$ at room temperature. The Raman spectra of
films on MgAl$_2$O$_4$ support the fact that the Fe$^{3+}$- and the
Co$^{2+}$-ions are distributed in an ordered fashion on the B-site of the
inverse spinel structure. The DLI-CVD technique has been extended for the
growth of smooth and highly oriented cobalt ferrite thin films on a variety of
other substrates, including MgO, and piezoelectric lead magnesium niobate-lead
titanate and lead zinc niobate-lead titanate substrates.",1309.4031v1
2013-10-18,Transverse Demagnetization Dynamics of a Unitary Fermi Gas,"Understanding the quantum dynamics of strongly interacting fermions is a
problem relevant to diverse forms of matter, including high-temperature
superconductors, neutron stars, and quark-gluon plasma. An appealing benchmark
is offered by cold atomic gases in the unitary limit of strong interactions.
Here we study the dynamics of a transversely magnetized unitary Fermi gas in an
inhomogeneous magnetic field. We observe the demagnetization of the gas, caused
by diffusive spin transport. At low temperatures, the diffusion constant
saturates to the conjectured quantum-mechanical lower bound $\simeq \hbar/m$,
where $m$ is the particle mass. The development of pair correlations,
indicating the transformation of the initially non-interacting gas towards a
unitary spin mixture, is observed by measuring Tan's contact parameter.",1310.5140v2
2013-11-06,"The synthesis and characterization of 1111-type diluted magnetic semiconductors (La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co)","The doping effect of Sr and transition metals Mn, Fe, Co into the direct-gap
semiconductor LaZnAsO has been investigated. Our results indicate that the
single phase ZrCuSiAs-type tetragonal crystal structure is preserved in
(La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co) with the doping level up to x = 0.1.
While the system remains semiconducting, doping with Sr and Mn results in
ferromagnetic order with TC ~ 30K, and doping with Sr and Fe results in a spin
glass like state below ~6K with a saturation moment of ~0.02 muB/Fe, an order
of magnitude smaller than the ~0.4 muB/Mn of Sr and Mn doped samples. The same
type of magnetic state is observed neither for (Zn,Fe) substitution without
carrier doping, nor for Sr and Co doped specimens.",1311.1304v1
2013-11-12,Growth of (CH$_3$)$_2$NH$_2$CuCl$_3$ single crystals using evaporation method with different temperatures and solvents,"The bulk single crystals of of low-dimensional magnet
(CH$_3$)$_2$NH$_2$CuCl$_3$ (DMACuCl$_3$ or MCCL) are grown by a slow
evaporation method with different kinds of solvents, different degrees of
super-saturation of solution and different temperatures of solution,
respectively. Among three kinds of solvent, methanol, alcohol and water,
alcohol is found to be the best one for growing MCCL crystals because of its
structural similarity to the raw materials and suitable evaporation rate. The
best growth temperature is in the vicinity of 35 $^{\circ}$C. The problem of
the crystals deliquescing in air has been solved through recrystallization
process. The crystals are characterized by means of x-ray diffraction, specific
heat and magnetic susceptibility.",1311.2680v1
2013-12-05,Vortex-crystal pattern in an anti-artificial spin ice system,"We have proposed in this work an original system composed by anti-dots
nanopatterned in a ferromagnetic thin film, mimicking negatively the structure
of an articial spin ice. In the hysteresis loop we notice the emergency of an
anisotropy in the magnetization saturation and in the micromagnetic
simulations, in the beginning of the hysteresis loop (relaxation), the
formation of a vortex crystal array with vortices in diferent positions
possessing random polarization and chirality. The crystal of vortices in this
electrically connected sample could be most eficient than those observed in
non-connected nanodiscs for current-driven or magnetic vortices switching by
electric currents.",1312.1646v1
2014-03-10,Microwave saturation spectroscopy of nitrogen-vacancy ensembles in diamond,"Negatively-charged nitrogen-vacancy (NV$^-$) centers in diamond have
generated much recent interest for their use in sensing. The sensitivity
improves when the NV ground-state microwave transitions are narrow, but these
transitions suffer from inhomogeneous broadening, especially in high-density NV
ensembles. To better understand and remove the sources of broadening, we
demonstrate room-temperature spectral ""hole burning"" of the NV ground-state
transitions. We find that hole burning removes the broadening caused by
magnetic fields from $^{13}$C nuclei and demonstrate that it can be used for
magnetic-field-insensitive thermometry.",1403.2119v1
2014-03-25,The deceiving delta: on the equilibrium dependent dynamics of nonlinear magnetic islands,"The linear stability parameter delta is commonly used as a figure of merit
for the nonlinear dynamics of the tearing mode. It is shown, through state of
the art numerical simulations, that factors other than delta can play a very
important role in determining the evolution of nonlinear magnetic islands. In
particular, two different equilibria are analysed and it is shown that, once
perturbed, they have a qualitatively and quantitatively different response
despite the fact that they are characterised by the same delta. The different
behaviour can still be associated with linear properties of the equilibrium. It
is also studied how the nonlinear and saturation phase are affected by an
increasing delta in the two equilibria. As the instability drive is increased,
the systems move from a dynamics characterised by a ""universal"" generalised
Rutherford equation to a Y-point configuration and then to a plasmoid unstable
Y-point. Finally, for even larger delta the second harmonic overcomes the
fundamental,leading to an interesting double island structure.",1403.6376v1
2014-05-07,Anisotropic giant magnetoresistance in NbSb2,"The extremely large transverse magnetoreistance (the magnetoresistant ratio
$\sim 1.3\times10^5\%$ in 2 K and 9 T field, and $4.3\times 10^6\%$ in 0.4 K
and 32 T field, without saturation), and the metal-semiconductor crossover
induced by magnetic field, are reported in NbSb$_2$ single crystal with
electric current parallel to the $b$-axis. The metal-semiconductor crossover is
preserved when the current is along the $ac$-plane but the magnetoresistant
ratio is significantly suppressed. The sign reversal of the Hall resistivity in
the field close to the crossover point, and the electronic structure
calculation reveals the coexistence of a small number of holes with very high
mobility and a large number of electrons with low mobility. These effects are
attributed to the change of the Fermi surface induced by the magnetic field.",1405.1719v2
2014-05-12,Characterization of spin-orbit interactions of GaAs heavy holes using a quantum point contact,"We present transport experiments performed in high quality quantum point
contacts embedded in a GaAs two-dimensional hole gas. The strong spin-orbit
interaction results in peculiar transport phenomena, including the previously
observed anisotropic Zeeman splitting and level-dependent effective g-factors.
Here we find additional effects, namely the crossing and the anti-crossing of
spin-split levels depending on subband index and magnetic field direction. Our
experimental observations are reconciled in an heavy hole effective spin-orbit
Hamiltonian where cubic- and quadratic-in-momentum terms appear. The spin-orbit
components, being of great importance for quantum computing applications, are
characterized in terms of magnitude and spin structure. In the light of our
results, we explain the level dependent effective g-factor in an in-plane
field. Through a tilted magnetic field analysis, we show that the QPC
out-of-plane g-factor saturates around the predicted 7.2 bulk value.",1405.2981v2
2014-05-16,Quantum Otto heat engine based on a multiferroic chain working substance,"We study a quantum Otto engine operating on the basis of a helical spin- 1/2
multiferroic chain with strongly coupled magnetic and ferroelectric order
parameters. The presence of a finite spin chirality in the working substance
enables steering of the cycle by an external electric field that couples to the
electric polarization. We observe a direct connection between the chirality,
the entanglement and the efficiency of the engine. An electric-field dependent
threshold temperature is identified above which the pair correlations in the
system, as quantified by the thermal entanglement, diminish. In contrast to the
pair correlations, the collective many-body thermal entanglement is less
sensitive to the electric field, and in the high temperature limit converges to
a constant value. We also discuss the correlations between the threshold
temperature of the pair entanglement, the spin chirality and the minimum of the
fidelities in relation to the electric and magnetic fields. The efficiency of
the quantum Otto cycle shows a saturation plateau with increasing electric
field amplitude.",1405.4162v2
2014-10-26,Dynamics of single-domain magnetic particles at elevated temperatures,"A stochastic differential equation that describes the dynamics of
single-domain magnetic particles at any temperature is derived using a
classical formalism. The deterministic terms recover existing theory and the
stochastic process takes the form of a mean-reverting random walk. In the
ferromagnetic state diffusion is predominantly angular and the relevant
diffusion coefficient increases linearly with temperature before saturating at
the Curie point ($T_c$). Diffusion in the macrospin magnitude, while
vanishingly small at room temperature, increases sharply as the system
approaches $T_c$. Beyond $T_c$, in the paramagnetic state, diffusion becomes
isotropic and independent of temperature. The stochastic macrospin model agrees
well with atomistic simulations.",1410.6980v4
2014-11-14,Parametric instability of classical Yang-Mills fields in a color magnetic background,"We investigate instabilities of classical Yang-Mills fields in a
time-dependent spatially homogeneous color magnetic background field in a
non-expanding geometry for elucidating the earliest stage dynamics of
ultra-relativistic heavy-ion collisions. The background gauge field
configuration considered in this article is spatially homogeneous and
temporally periodic, and is alluded by Berges-Scheffler-Schlichting-Sexty
(BSSS). We discuss the whole structure of instability bands of fluctuations
around the BSSS background gauge field on the basis of Floquet theory, which
enables us to discuss the stability in a systematic way. We find various
instability bands on the $(p_z, p_T)$-plane. These instability bands are caused
by parametric resonance despite the fact that the momentum dependence of the
growth rate for $|\mathbf{p}| \leq \sqrt{B}$ is similar to a Nielsen-Olesen
instability. Moreover, some of instability bands are found to emerge not only
in the low momentum but also in the high momentum region; typically of the
order of the saturation momentum as $|\mathbf{p}| \sim \sqrt{B} \sim Q_{\rm
s}$.",1411.3809v3
2015-01-12,Nonlinear spin diffusion and spin rotation in a trapped Fermi gas,"Transverse spin diffusion in a polarized, interacting Fermi gas leads to the
Leggett-Rice effect, where the spin current precesses around the local
magnetization. With a spin-echo sequence both the transverse diffusivity and
the spin-rotation parameter $\gamma$ are obtained; the sign of $\gamma$ reveals
the repulsive or attractive character of the effective interaction. In a
trapped Fermi gas the spin diffusion equations become nonlinear, and their
numerical solution exhibits an inhomogeneous spin state even at the spin echo
time. While the microscopic diffusivity and $\gamma$ increase at weak coupling,
their apparent values inferred from the trap-averaged magnetization saturate in
agreement with a recent experiment for a dilute ultracold Fermi gas.",1501.02677v2
2015-01-13,Doping control of realization of an extended Nagaoka ferromagnetic state from the Mott state,"Inspired by the Nagaoka ferromagnetism, we propose an itinerant model to
study the transition between the Mott singlet state and a ferromagnetic state
by emulating a doping process in finite lattices. In the Nagaoka
ferromagnetism, the total spin of the system takes the maximum value when an
electron is removed from the half-filled system. To incorporate a procedure of
the electron removal, our model contains extra sites as a reservoir of
electrons, and the chemical potential of the reservoir controls the
distribution of electrons. As a function of the chemical potential, the system
exhibits ground-state phase transitions among various values of the total spin,
including a saturated ferromagnetic state due to the Nagaoka mechanism at
finite hole density. We discuss the nature of the ferromagnetism by measuring
various physical quantities, such as the distribution of electrons, the spin
correlation functions, the magnetization process in the magnetic field, and
also the entanglement entropy.",1501.02899v1
2015-02-09,Angular Momentum Transport and Particle Acceleration during Magnetorotational Instability in a Kinetic Accretion Disk,"Angular momentum transport and particle acceleration during the
magnetorotational instability (MRI) in a collisionless accretion disk are
investigated using three-dimensional particle-in-cell (PIC) simulation. We show
that the kinetic MRI can provide not only high energy particle acceleration but
also enhancement of angular momentum transport. We find that the plasma
pressure anisotropy inside the channel flow with $p_{\|} > p_{\perp}$ induced
by active magnetic reconnection suppresses the onset of subsequent
reconnection, which in turn leads to high magnetic field saturation and
enhancement of Maxwell stress tensor of angular momentum transport. Meanwhile,
during the quiescent stage of reconnection the plasma isotropization progresses
in the channel flow, and the anisotropic plasma with $p_{\perp} > p_{\|}$ due
to the dynamo action of MRI outside the channel flow contributes to rapid
reconnection and strong particle acceleration. This efficient particle
acceleration and enhanced angular momentum transport in a collisionless
accretion disk may explain the origin of high energy particles observed around
massive black holes.",1502.02452v1
2015-04-13,Spin-entropy contribution to thermopower in the [Ca$_2$CoO$_{3-t}$]$_{0.62}$(CoO$_2$) misfits,"Two samples of the [Ca$_2$CoO$_{3-t}$]$_{0.62}$(CoO$_2$) misfit cobaltate,
often denoted as the Ca$_{3}$Co$_{3.93}$O$_{9}$ phase, were prepared from the
same ceramic material by the oxygen and argon annealing, resulting in different
carrier concentrations in the conducting CoO$_{2}$ layers, n=0.31 and 0.19
hole/Co, respectively. Electrical and thermal transport properties were studied
in dependence of magnetic field up to 140 kOe. The magnetothermopower data
reveal an extra spin-entropy contribution to Seebeck coefficient that is not
expected for carriers of Fermi liquid character. Its magnitude is
unprecedentedly large and makes at zero field up to 50$\%$ of the theoretical
limit k$_B$/$e$ ln2$ = 59 \mu VK^{-1}$. This spin-entropy contribution is
gradually suppressed with increasing magnetic field, and the saturation is even
observed when temperatures are low enough. To understand the results, the
thermopower is treated in terms of purely thermodynamic Kelvin formula, and
so-called Spin liquid model is evoked, providing a reason for the spin-entropy
manifestation in the [Ca$_2$CoO$_{3-t}$]$_{0.62}$(CoO$_2$) misfits.",1504.03104v2
2015-04-21,New memory devices based on the proton transfer process,"Memory devices operating due to the fast proton transfer (PT) process are
proposed by means of the first-principles calculations. Writing an information
is performed using the electrostatic potential of the scanning tunneling
microscopy (STM). Reading an information is based on the effect of the local
magnetization induced at the zigzag graphene nanoribbon (Z-GNR) edge -
saturated with oxygen or the hydroxy group - and can be realized with the use
of the giant magnetoresistance (GMR), magnetic tunnel junction (MTJ) or
spin-transfer torque (STT) devices. The energetic barriers for the hop-forward
and -backward processes can be tuned by the distance and potential of the STM
tip. Thus, enabling to tailor the non-volatile logic states. The proposed
system enables very dense packing of the logic cells and could be used in the
random access and flash memory devices.",1504.05607v2
2015-04-23,Three-Dimensional Crystallization of Vortex Strings in Frustrated Quantum Magnets,"We demonstrate that frustrated exchange interactions can produce exotic 3D
crystals of vortex strings near the saturation field (H=Hsat) of body- and
face-centered cubic Mott insulators. The combination of cubic symmetry and
frustration leads to a magnon spectrum of the fully polarized spin state
(H>Hsat) with degenerate minima at multiple noncoplanar Q vectors. This
spectrum becomes gapless at the quantum critical point H=Hsat and the magnetic
ordering below Hsat can be formally described as a condensate of a dilute gas
of bosons. By expanding in the lattice gas parameter, we find that different
vortex crystals span sizable regions of the phase diagrams for isotropic
exchange and are further stabilized by symmetric exchange anisotropy.",1504.06270v2
2015-06-23,Spin polarization studies in half-metallic Co2TiX (X = Ge and Sn) Heusler alloys,"In this paper, we investigated the Co2TiX (X = Ge, Sn) Heusler alloys by
structural, magnetic and spin polarization measurements to probe the
half-metallic nature. Alloys are synthesized using the arc melting technique,
and found to exist in L21 crystal structure with Fm-3m space group. Curie
temperature (TC) is found to be 384 and 371 K for Co2TiGe and Co2TiSn
respectively. The saturation magnetization (MS) value of 1.8 and 2.0 Bohr
magneton/f.u. are obtained at 5 K for for Co2TiGe and Co2TiSn respectively,
compared to 2.0 Bohr magneton/f.u. calculated by Slater-Pauling rule. To obtain
the spin polarization value, differential conductance curves are recorded at
the ferromagnetic/superconducting point contact at 4.2 K. The current spin
polarization (P) value of 0.63 and 0.64 are deduced for Co2TiGe and Co2TiSn
respectively. Considering the high current spin polarization and TC, these
materials appear to be promising for spintronic devices.",1506.07109v1
2015-07-13,Majorana Fermi Sea in Insulating SmB6: A proposal and a Theory of Quantum Oscillations in Kondo Insulators,"In an exciting development, SmB6, a Kondo insulator has been shown to exhibit
bulk quantum oscillations. We propose that SmB6 is a bulk scalar Majorana Fermi
Liquid} (MFL) with a finite gap for charge and spin excitations. In their study
of Kondo insulators in 1993, Coleman, Miranda and Tsvelik (CMT) envisaged such
a remarkable possibility, using a mean field ansatz. We generalize CMT theory
to non-zero magnetic fields and show a counter intuitive result that the scalar
Majorana fermi liquid, while remaining electrically insulating, responds to
external magnetic field and exhibits Landau diamagnetism and quantum
oscillations. Physics of an emergent compactified 2-channel Kondo lattice
physics that is behind formation of the novel scalar Majorana fermi liquid
phase is discussed. It is also suggested that a known resistivity saturation in
SmB6 as well as a new strong deviation of quantum oscillation amplitude from
Lifshitz-Kosevich formula in SmB6 at low temperatures are due to a coherent
fluctuation of charge of a neutral scalar Majorana fermion. Possible presence
of 2-dimensional Majorana fermion excitations in surfaces of SmB6, and other
Topological Kondo Insulators (TKI) is pointed out.",1507.03477v1
2015-07-22,Magnetic field decay in normal radio pulsars,"We analyse the origin of the magnetic field decay in normal radio pulsars
found by us in a recent study. This decay has a typical time scale $\sim 4
\times 10^5$~yrs, and operates in the range $\sim 10^5$~--~few$\times
10^5$~yrs. We demonstrate that this field evolution may be either due to the
Ohmic decay related to the scattering from phonons, or due to the Hall cascade
which reaches the Hall attractor. According to our analysis the first
possibility seems to be more reliable. So, we attribute the discovered field
decay mainly to the Ohmic decay on phonons which is saturated at the age
few$\times 10^5$~yrs, when a NS cools down to the critical temperature below
which the phonon scattering does not contribute much to the resistivity of the
crust. Some role of the Hall effect and attractor is not excluded, and will be
analysed in our further studies.",1507.07962v1
2015-09-04,Spin frustration and fermionic entanglement in an exactly solved hybrid diamond chain with the localized Ising spins and mobile electrons,"The strongly correlated spin-electron system on a diamond chain containing
localized Ising spins on its nodal lattice sites and mobile electrons on its
interstitial sites is exactly solved in a magnetic field using the
transfer-matrix method. We have investigated in detail all available ground
states, the magnetization processes, the spin-spin correlation functions around
an elementary plaquette, fermionic quantum concurrence and spin frustration. It
is shown that the fermionic entanglement between mobile electrons hopping on
interstitial sites and the kinetically-induced spin frustration are closely
related yet independent phenomena. In the ground state, quantum entanglement
only appears within a frustrated unsaturated paramagnetic phase, while thermal
fluctuations can promote some degree of quantum entanglement above the
non-frustrated ground states with saturated paramagnetic or classical
ferrimagnetic spin arrangements.",1509.01639v1
2015-09-07,Successively Thresholded Domain Boundary Roughening Driven by Pinning Centers and Missing Bonds: Hard-Spin Mean-Field Theory Applied to d=3 Ising Magnets,"Hard-spin mean-field theory has recently been applied to Ising magnets,
correctly yielding the absence and presence of an interface roughening
transition respectively in $d=2$ and $d=3$ dimensions and producing the
ordering-roughening phase diagram for isotropic and anisotropic systems. The
approach has now been extended to the effects of quenched random pinning
centers and missing bonds on the interface of isotropic and anisotropic Ising
models in $d=3$. We find that these frozen impurities cause domain boundary
roughening that exhibits consecutive thresholding transitions as a function
interaction of anisotropy. For both missing-bond and pinning-center impurities,
for moderately large values the anisotropy, the systems saturate to the
""solid-on-solid"" limit, exhibiting a single universal curve for the domain
boundary width as a function of impurity concentration.",1509.01910v2
2015-10-13,Nematic magnetoelastic effect contrasted between Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ and FeSe,"To elucidate the origin of nematic order in Fe-based superconductors, we
report a Raman scattering study of lattice dynamics, which quantify the extent
of $C_4$-symmetry breaking, in BaFe$_2$As$_2$ and FeSe. FeSe possesses a
nematic ordering temperature $T_\mathrm{s}$ and orbital-related band-energy
split below $T_\mathrm{s}$ that are similar to those in BaFe$_2$As$_2$, but
unlike BaFe$_2$As$_2$ it has no long-range magnetic order. We find that the
$E_g$ phonon-energy split in FeSe sets in only well below $T_\mathrm{s}$, and
its saturated value is substantially smaller than that in BaFe$_2$As$_2$.
Together with reported results for the Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ family,
the data suggest that magnetism exerts a major influence on the lattice.",1510.03526v1
2015-11-07,Production of Semi Quark Gluon Monopole Plasma by Glasma Decay,"Using the standard Lagrangian of gluons and a model of dual superconductor
for magnetic monopoles, we calculate the number densities of the gluons and
monopoles produced by the decay of background color electric $E$ and magnetic
$B$ fields ( glasma ). We find that gluons are dominant decay products when the
initial values of the gauge fields are large such that
$gE=gB>(0.5\mbox{GeV})^2$, while they are suppressed and monopoles are dominant
decay products when the initial values are small such that
$gE=gB<(0.4\mbox{GeV})^2$. The feature of the gluon dominance at large $gE=gB$
and the monopole dominance at small $gE=gB$ is similar to the one of
thermalized quark gluon monopole plasmas proposed recently, if we identify
$\sqrt{gE}=\sqrt{gB}$ as temperatures of the plasmas. Although the model of the
monopoles is phenomenological, our analysis suggests that the monopoles play
important roles in the decay of the glasmas with small saturation momenta, to
which classical statistical field theories are not applicable.",1511.02271v2
2015-11-15,Exotic Superconducting Properties in Topological Nodal Semimetal PbTaSe$_2$,"We report the electronic properties of superconductivity in the topological
nodal-line semimetal PbTaSe$_2$. Angle-resolved photoemission measurements
accompanied by band calculations confirmed the nodal-line band structure in the
normal state of single crystalline PbTaSe$_2$. Resistivity,
magnetic-susceptibility and specific heat measurements have also been performed
on high-quality single crystals. We observed upward features and large
anisotropy in upper critical field ($H_{c2}$) measured in-plane
(H//\textbf{ab}) and out-plane (H//\textbf{c}), respectively. Especially,
$H_{c2}$ measured in H//\textbf{ab} shows sudden upward features rather than a
signal of saturation in ultralow temperatures. The specific heat measurements
under magnetic field reveal a full superconducting gap with no gapless nodes.
These behaviors in this clean noncentrosymmetric superconductor is possibly
related to the underlying exotic physics, providing important clue for
realization of topological superconductivity.",1511.04673v2
2015-12-30,D mesons in a magnetic field,"We investigate the mass spectra of open heavy flavor mesons in an external
constant magnetic field within QCD sum rules. Spectral ans\""atze on the
phenomenological side are proposed in order to properly take into account
mixing effects between the pseudoscalar and vector channels, and the Landau
levels of charged mesons. The operator product expansion is implemented up to
dimension-5 operators. As a result, we find for neutral D mesons a significant
positive mass shift that goes beyond simple mixing effects. In contrast,
charged D mesons are further subject to Landau level effects, which together
with the mixing effects almost completely saturate the mass shifts obtained in
our sum rule analysis.",1512.08864v2
2016-01-10,"Interfacial Dzyaloshinskii-Moriya interaction, surface anisotropy energy,and spin pumping at spin orbit coupled Ir/Co interface","The interfacial Dzyaloshinskii-Moriya interaction (iDMI), surface anisotropy
energy, and spin pumping at the Ir/Co interface are experimentally investigated
by performing Brillouin light scattering. Contrary to previous reports, we
suggest that the sign of the iDMI at the Ir/Co interface is the same as in the
case of the Pt/Co interface. We also find that the magnitude of the iDMI energy
density is relatively smaller than in the case of the Pt/Co interface, despite
the large strong spin-orbit coupling (SOC) of Ir. The saturation magnetization
and the perpendicular magnetic anisotropy (PMA) energy are significantly
improved due to a strong SOC. Our findings suggest that an SOC in an Ir/Co
system behaves in different ways for iDMI and PMA. Finally, we determine the
spin pumping effect at the Ir/Co interface, and it increases the Gilbert
damping constant from 0.012 to 0.024 for 1.5 nmthick Co.",1601.02210v3
2016-01-14,P-shell carriers assisted dynamic nuclear spin polarization in single quantum dots at zero external magnetic field,"Repeated injection of spin polarized carriers in a quantum dot leads to the
polarization of nuclear spins, a process known as dynamic nuclear spin
polarization (DNP). Here, we report the first observation of p-shell carrier
assisted DNP in single QDs at zero external magnetic field. The nuclear field -
measured by using the Overhauser shift of the singly charged exciton state of
the QDs - continues to increase, even after the carrier population in the
s-shell saturates. This is also accompanied by an abrupt increase in nuclear
spin buildup time as p-shell emission overtakes that of the s-shell. We
attribute the observation to p-shell electrons strongly altering the nuclear
spin dynamics in the QD, supported by numerical simulation results based on a
rate equation model of coupling between electron and nuclear spin system. DNP
with p-shell carriers could open up avenues for further control to increase the
degree of nuclear spin polarization in QDs.",1601.03480v2
2016-01-18,Large and exact quantum degeneracy in a Skyrmion magnet,"We identify a large family of ground states of a topological Skyrmion magnet
whose classical degeneracy persists to all orders in a semiclassical expansion.
This goes along with an exceptional robustness of the concomitant ground state
configurations, which are not at all dressed by quantum fluctuations. We trace
these twin observations back to a common root: this class of topological ground
states saturates a Bogomolny inequality. A similar phenomenology occurs in
high-energy physics for some field theories exhibiting supersymmetry. We
propose quantum Hall ferromagnets, where these Skyrmions configurations arise
naturally as ground states away from integer filling, as the best available
laboratory realisations.",1601.04645v1
2016-02-17,Fractional Spin Fluctuation as a Precursor of Quantum Spin Liquids: Majorana Dynamical Mean-Field Study for the Kitaev Model,"Experimental identification of quantum spin liquids remains a challenge, as
the pristine nature is to be seen in asymptotically low temperatures. We here
theoretically show that the precursor of quantum spin liquids appears in the
spin dynamics in the paramagnetic state over a wide temperature range. Using
the cluster dynamical mean-field theory and the continuous-time quantum Monte
Carlo method, which are newly developed in the Majorana fermion representation,
we calculate the dynamical spin structure factor, relaxation rate in nuclear
magnetic resonance, and magnetic susceptibility for the honeycomb Kitaev model
whose ground state is a canonical example of the quantum spin liquid. We find
that dynamical spin correlations show peculiar temperature and frequency
dependence even below the temperature where static correlations saturate. The
results provide the experimentally-accessible symptoms of the fluctuating
fractionalized spins evincing the quantum spin liquids.",1602.05253v2
2016-03-15,"Footprints of hyperfine, spin-orbit, and decoherence effects in Pauli spin blockade","We detect in real time inter-dot tunneling events in a weakly coupled two
electron double quantum dot in GaAs. At finite magnetic fields, we observe two
characteristic tunneling times, T_d and T_b, belonging to, respectively, a
direct and a blocked (spin-flip-assisted) tunneling. The latter corresponds to
lifting of a Pauli spin blockade and the tunneling times ratio eta=T_b/T_d
characterizes the blockade efficiency. We find pronounced changes in the
behavior of eta upon increasing the magnetic field, with eta increasing,
saturating and increasing again. We explain this behavior as due to the
crossover of the dominant blockade lifting mechanism from the hyperfine to
spin-orbit interactions and due to a change in the contribution of the charge
decoherence.",1603.04861v1
2016-03-17,Linear and nonlinear magneto-optical rotation on the narrow strontium intercombination line,"In the presence of an external static magnetic field, an atomic gas becomes
optically active, showing magneto-optical rotation. In the saturated regime,
the coherences among the excited substates give a nonlinear contribution to the
rotation of the light polarization. In contrast with the linear magneto-optical
rotation, the nonlinear counterpart is insensitive to Doppler broadening. By
varying the temperature of a cold strontium gas, we observe both regimes by
driving the $J=0\rightarrow J=1$ transition on the intercombination line. For
this narrow transition, the sensitivity to the static magnetic field is
typically three orders of magnitude larger than for a standard broad alkali
transition.",1603.05425v1
2016-04-29,Hydrostatic pressure tuned magneto-structural transition and occurrence of pressure induced exchange bias effect in Mn$_{0.85}$Fe$_{0.15}$NiGe alloy,"Magnetic and magneto-functional behavior of a Fe-doped MnNiGe alloy with
nominal composition Mn$_{0.85}$Fe$_{0.15}$NiGe have been investigated in
ambient as well as in high pressure condition. The alloy undergoes first order
martensitic phase transition (MPT) around 200 K and also shows large
conventional magnetocaloric effect (MCE) ($\Delta S$ $\sim$ -21 J/kg-K for
magnetic field ($H$) changing from 0-50 kOe) around the transition in ambient
condition. Application of external hydrostatic pressure ($P$) results a shift
in MPT towards the lower temperature and a clear decrease in the saturation
moment of the alloy at 5 K. The peak value of MCE is also found to decrease
with increasing external $P$ ($\sim$ 18 J/kg-K decrease in $\Delta S$ has been
observed for $P$ = 12.5 kbar). The most interesting observation is the
occurance of exchange bias effect (EBE) on application of external $P$. The
competing ferromagnetic and antiferromagnetic interaction in presence of
external $P$ plays the pivotal role towards the observation of $P$ induced EBE.",1604.08761v1
2016-05-20,High-frequency behavior of FeN thin films fabricated by reactive sputtering,"We investigated high-frequency behavior of FeN thin films prepared by
reactive sputtering through ferromagnetic resonance (FMR) and its relationship
with the static magnetic properties. The FMR was observed in the frequency
range from 2 to 18 GHz in the FeN films fabricated at proper nitrogen flow rate
(NFR). In those FeN thin films, a decrease of the saturation magnetization and
the corresponding decrease of the FMR frequency were observed as NFR was
increased during the deposition. The external field dependences of the FMR
frequencies were well fit to the Kittel formula and the Land\'e g-factors
determined from the fit were found to be very close to the free electron value.
The high-field damping parameters were almost insensitive to the growth
condition of NFR. However, the low-field damping parameters exhibited high
sensitivity to NFR very similar to the dependence of the hard-axis coercivity
on NFR, suggesting that extrinsic material properties such as impurities and
defect structures could be important in deciding the low-field damping
behavior.",1605.06179v1
2016-06-08,A method to decrease the harmonic distortion in Mn-Zn ferrite/PZT and Ni-Zn ferrite/PZT layered composite rings exhibiting high magnetoelectric effects,"We have investigated the magnetoelectric (ME) effect in layered composite
rings subjected to circumferential AC magnetic fields and DC magnetic fields in
radial, axial or circumferential directions. Bilayer samples were obtained
combining different grades of commercial Mn-Zn ferrites or Ni-Zn ferrites with
commercial lead zirconate titanate (PZT). Mn-Zn ferrites with low
magnetostriction saturation () and low magneto-crystalline anisotropy constants
show high ME capabilities when associated with PZT in ring structures. In
certain conditions, these ME effects are higher than those obtained with
Terfenol-D/PZT composites in the same layered ring structure. Magnetostrictive
and mechanical characterizations have given results that explain these high ME
performances. Nevertheless, Mn-Zn ferrite/PZT composites exhibit voltages
responses with low linearity especially at high signal level. Based on the
particular structure of the ME device, a method to decrease the nonlinear
harmonic distortion of the ME voltages is proposed. Harmonic distortion
analysis of ME voltages measured in different configurations allows us to
explain the phenomenon.",1606.02469v1
2016-07-20,Landau quantization and neutron emissions by nuclei in the crust of a magnetar,"Magnetars are neutron stars endowed with surface magnetic fields of the order
of $10^{14}-10^{15}$~G, and with presumably much stronger fields in their
interior. As a result of Landau quantization of electron motion, the
neutron-drip transition in the crust of a magnetar is shifted to either higher
or lower densities depending on the magnetic field strength. The impact of
nuclear uncertainties is explored considering the recent series of
Brussels-Montreal microscopic nuclear mass models. All these models are based
on the Hartree-Fock-Bogoliubov method with generalized Skyrme functionals. They
differ in their predictions for the symmetry energy coefficient at saturation,
and for the stiffness of the neutron-matter equation of state. For comparison,
we have also considered the very accurate but more phenomenological model of
Duflo and Zuker. Although the equilibrium composition of the crust of a
magnetar and the onset of neutron emission are found to be model dependent, the
quantum oscillations of the threshold density are essentially universal.",1607.05934v1
2016-07-28,Study of CPO resonances on the intercombination line in $^{173}$Yb,"We study coherent population oscillations (CPO) in an odd isotope of the
two-electron atom Yb. The experiments are done using magnetic sublevels of the
$ F_g = 5/2 \rightarrow F_e = 3/2 $ hyperfine transition in $^{173}$Yb of the $
{\rm {^1S_0} \rightarrow {^3P_1}} $ intercombination line. The experiments are
done both with and without an appied magnetic field. In the absence of an
applied field, the complicated sublevel structure along with the saturated
fluorescence effect causes the linewidth to be larger than the 190 kHz natural
linewidth of the transition. In the presence of a field (of magnitude 330 mG),
a well-defined quantization axis is present which results in the formation of
two M-type systems. The total fluorescence is then limited by spin coherence
among the ground sublevels. In addition, the pump beam gets detuned from
resonance which results in a reduced scattering rate from the $ {\rm ^3P_1} $
state. Both of these effects result in a reduction of the linewidth to a
subnatural value of about 100 kHz.",1607.08331v3
2016-07-28,Fractional magnetization plateaux of the spin-1/2 Heisenberg orthogonal-dimer chain revisited: strong-coupling approach developed from the exactly solved Ising-Heisenberg model,"The spin-1/2 Heisenberg orthogonal-dimer chain is considered within the
perturbative strong-coupling approach, which is developed from the exactly
solved spin-1/2 Ising-Heisenberg orthogonal-dimer chain with the Heisenberg
intradimer and the Ising interdimer couplings. Although the spin-1/2
Ising-Heisenberg orthogonal-dimer chain exhibits just intermediate plateaux at
zero, one-quarter and one-half of the saturation magnetization, the
perturbative treatment up to second order stemming from this exactly solvable
model additionally corroborates the fractional one-third plateau as well as the
gapless Luttinger spin-liquid phase. It is evidenced that the approximate
results obtained from the strong-coupling approach are in an excellent
agreement with the state-of-the-art numerical data obtained for the spin-1/2
Heisenberg orthogonal-dimer chain within the exact diagonalization and
density-matrix renormalization group method. The nature of individual quantum
ground states is comprehensively studied within the developed perturbation
theory.",1607.08457v2
2016-09-15,Magnetoelectric Response in Multiferroic SrFe12O19 Ceramics,"We report here the realization of ferroelectricity, ferromagnetism and
magnetocapacitance effect in SrFe12O19 ceramics at room temperature. The
ceramics demonstrate a saturated polarization hysteresis loop, two I-V peaks
and large anomaly of dielectric constant near Curie temperature. These
evidences confirmed the ferroelectricity of SrFe12O19 ceramics after annealing
in O2 atmosphere. The remnant polarization of the SrFe12O19 ceramic is 103
{\mu}C/cm2. The material also exhibits strong ferromagnetic characterization,
the coercive field and remnant magnetic moment are 6192Oe and 35.8emu/g,
respectively. Subsequent annealing SrFe12O19 ceramics in O2 not only reveals
its innate ferroelectricity but also improves the ferromagnetic properties
through transforming Fe2+ into Fe3+. By applying a magnetic field, the
capacitance demonstrates remarkable change along with B field, the maximum
relative change of dielectric constant is 1174%, which reflects a giant
magnetocapacitance effect in SrFe12O19. These combined functional responses in
SrFe12O19 ceramics opens substantial possibilities for applications in novel
electric devices.",1609.04483v1
2016-09-15,Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy,"We analyze the structural and magnetic characteristics of (111)-oriented
lutetium iron garnet (Lu$_3$Fe$_5$O$_{12}$) films grown by molecular-beam
epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the
in- and out-of-plane ferromagnetic resonance allow us to quantify the effects
of two-magnon scattering, along with the surface anisotropy and the saturation
magnetization. We achieve effective damping coefficients of $11.1(9) \times
10^{-4}$ for 5.3 nm films and $32(3) \times 10^{-4}$ for 2.8 nm films, among
the lowest values reported to date for any insulating ferrimagnetic sample of
comparable thickness.",1609.04753v1
2016-09-30,Pair entanglement in dimerized spin-s chains,"We examine the pair entanglement in the ground state of finite dimerized
spin-$s$ chains interacting through anisotropic $XY$ couplings immersed in a
transverse magnetic field, by means of a self-consistent pair mean field
approximation. The approach, which makes no a priori assumptions on the pair
states, predicts, for sufficiently low coupling between pairs, $2s$ distinct
dimerized phases for increasing fields below the pair factorizing field,
separated by spin parity breaking phases. The dimerized phases lead to
approximate magnetization and pair entanglement plateaus, while the parity
breaking phases are characterized by weak pair entanglement but non-negligible
entanglement of the pair with the rest of the system. These predictions are
confirmed by the exact results obtained in finite $s=1$ and $s=3/2$ chains. It
is also shown that for increasing values of the spin $s$, the entanglement of
an isolated pair, as measured by the negativity, rapidly saturates in the
anisotropic $XY$ case but increases as $s^{1/2}$ in the $XX$ case, reflecting a
distinct single spin entanglement spectrum.",1610.00056v2
2016-10-05,Universal front propagation in the quantum Ising chain with domain-wall initial states,"We study the melting of domain walls in the ferromagnetic phase of the
transverse Ising chain, created by flipping the order-parameter spins along
one-half of the chain. If the initial state is excited by a local operator in
terms of Jordan-Wigner fermions, the resulting longitudinal magnetization
profiles have a universal character. Namely, after proper rescalings, the
profiles in the noncritical Ising chain become identical to those obtained for
a critical free-fermion chain starting from a step-like initial state. The
relation holds exactly in the entire ferromagnetic phase of the Ising chain and
can even be extended to the zero-field XY model by a duality argument. In
contrast, for domain-wall excitations that are highly non-local in the
fermionic variables, the universality of the magnetization profiles is lost.
Nevertheless, for both cases we observe that the entanglement entropy
asymptotically saturates at the ground-state value, suggesting a simple form of
the steady state.",1610.01540v3
2016-10-06,Quantum Size Effect Exponential Heat Capacity in 4 nm Natural Nickel Nanolattice,"Quantum size effect-induced heat capacity of metal nanoparticles at low
temperatures was predicted 79 years ago to be exponential. This, however, has
not been reported until date. In defiance, we demonstrate here observation of
exponentially decaying heat capacity, below 45.2 K, associated with quantum
jumps, exceptionally in 4 nm naturally assembled hexagonal closed packed (hcp)
lattice of nickel nanoparticles; high magnetic fields have negligible effect on
these features. Magnetic susceptibilities in contrast reveal evolution of
quantum size effects with decrease in particle size. They exhibit sharp rise
below about 30 K and vestiges of saturations below 5 K. The former is explained
by Curie-like characteristics of odd electrons while the latter tend towards
the orthogonal even-like case. These characteristics, ascribed to the ensembles
of Ni nanoparticles, will give a new direction in understanding this crucial
thermodynamic phenome-non.",1610.01756v1
2016-10-27,Giant variation of the perpendicular magnetic anisotropy at Fe/MgO interfaces by oxygen migration: a first-principles study,"A characteristic dependence of voltage control of perpendicular magnetic
anisotropy (VCMA) on oxygen migration at Fe/MgO interfaces was revealed by
performing systematic {\it ab initio} study of the energetics of the oxygen
path around the interface. We find that the surface anisotropy energy exhibits
a Boltzmann sigmoidal behavior as a function of the migrated O-atoms
concentration. The obtained variation of the VCMA efficiency factor $\beta$
reveals a saturation limit beyond a critical concentration of migrated O, about
$54\%$, at which the anisotropy switches from perpendicular to in plane.
Furthermore, depending on the range of variation of the applied voltage, two
regimes associated with reversible or irreversible ions displacement are
predicted to occur, yielding different VCMA response. According to our
findings, one can distinguish from the order of magnitude of $\beta$ the VCMA
driving mechanism: an effect of several tens of fJ/(V.m) is likely associated
to charge-mediated effect combined with slight reversible oxygen displacements
whereas an effect of the order of thousands of fJ/(V.m) is more likely
associated with irreversible oxygen ionic migration.",1610.08859v2
2016-11-07,Giant coronal loops dominate the quiescent X-ray emission in rapidly rotating M stars,"Observations indicate that magnetic fields in rapidly rotating stars are very
strong, on both small and large scales. What is the nature of the resulting
corona? Here we seek to shed some light on this question. We use the results of
an anelastic dynamo simulation of a rapidly rotating fully-convective M-star to
drive a physics-based model for the stellar corona. We find that due to the
several kilo Gauss large-scale magnetic fields at high latitudes, the corona
and its X-ray emission are dominated by star-size large hot loops, while the
smaller, underlying colder loops are not visible much in the X-ray. Based on
this result we propose that, in rapidly rotating stars, emission from such
coronal structures dominates the quiescent, cooler but saturated X-ray
emission.",1611.02141v1
2017-01-03,Universal Absence of Walker Breakdown and Linear Current-Velocity Relation via Spin-Orbit Torques in Coupled and Single Domain Wall Motion,"We consider theoretically domain wall motion driven by spin-orbit and spin
Hall torques. We find that it is possible to achieve universal absence of
Walker breakdown for all spin-orbit torques using experimentally relevant
spin-orbit coupling strengths. For spin-orbit torques other than the pure
Rashba spin-orbit torque, this gives a linear current-velocity relation instead
of a saturation of the velocity at high current densities. The effect is very
robust and is found in both soft and hard magnetic materials, as well as in the
presence of the Dzyaloshinskii-Moriya interaction and in coupled domain walls
in synthetic antiferromagnets, where it leads to very high domain wall
velocities. Moreover, recent experiments have demonstrated that the switching
of a synthetic antiferromagnet does not obey the usual spin Hall
angle-dependence, but that domain expansion and contraction can be selectively
controlled toggling only the applied in-plane magnetic field magnitude and not
its sign. We show for the first time that the combination of spin Hall torques
and interlayer exchange coupling produces the necessary relative velocities for
this switching to occur.",1701.00786v2
2017-02-23,Diffusionless hydromagnetic modes in rotating ellipsoids: a road to weakly nonlinear models?,"We investigate free hydromagnetic eigenmodes of an incompressible, inviscid
and ideal electrically conducting fluid in rotating triaxial ellipsoids. The
container rotates with an angular velocity tilted from its figure. The magnetic
base state is a uniform current density also tilted. Three-dimensional
perturbations upon the base state are expanded onto a finite-dimensional
polynomial basis. By combining symbolic and numerical computations, we are able
to get the eigenmodes of high spatial complexity. Hydromagnetic modes of the
sphere still exist in triaxial geometry. A plane-wave analysis is also carried
on, explaining the dispersion relation observed in our model. Without magnetic
field, the modes reduce to the inertial modes of the ellipsoids, which form a
complete basis. We propose to use these modes to study the weakly nonlinear
saturation of inertial instabilities, especially the elliptical one.",1702.07198v1
2017-04-23,Direct Observation of Attractive Skyrmions and Skyrmion Clusters in the Cubic Helimagnet Cu$_2$OSeO$_3$,"We report the discovery of attractive magnetic skyrmions and their clusters
in non-centrosymmetric ferromagnets. These three-dimensional solitons have been
predicted to exist in the cone phase of chiral ferromagnets (J. Phys: Condens.
Matter 28 (2016) 35LT01) and are fundamentally different from the more common
repulsive axisymmetric skyrmions that occur in the magnetically saturated
state. We present real-space images of these skyrmion clusters in thin (~70 nm)
single-crystal samples of Cu$_2$OSeO$_3$ taken using transmission electron
microscopy and develop a phenomenological theory describing this type of
skyrmion.",1704.06876v2
2017-06-04,Field- and temperature-modulated spin-diode effect in a GMR nanowire with dipolar coupling,"An analytical model of the spin-diode effect induced by resonant
spin-transfer torque in a ferromagnetic bilayer with strong dipolar coupling
provides the resonance frequencies and the lineshapes of the magnetic field
spectra obtained under field or laser-light modulation. The effect of laser
irradiation is accounted for by introducing the temperature dependence of the
saturation magnetization and anisotropy, as well as thermal spin-transfer
torques. The predictions of the model are compared with experimental data
obtained with single Co/Cu/Co spin valves, embedded in nanowires and produced
by electrodeposition. Temperature modulation provides excellent signal-to-noise
ratio. High temperature-modulation frequency is possible because these
nanostructures have a very small heat capacity and are only weakly heat-sunk.
The two forms of modulation give rise to qualitative differences in the spectra
that are accounted for by the model.",1706.01036v1
2017-06-20,Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations,"A self-regulating magnetic flux pumping mechanism in tokamaks that maintains
the core safety factor at $q\approx 1$, thus preventing sawteeth, is analyzed
in nonlinear 3D magnetohydrodynamic simulations using the M3D-C$^1$ code. In
these simulations, the most important mechanism responsible for the flux
pumping is that a saturated $(m=1,n=1)$ quasi-interchange instability generates
an effective negative loop voltage in the plasma center via a dynamo effect. It
is shown that sawtoothing is prevented in the simulations if $\beta$ is
sufficiently high to provide the necessary drive for the $(m=1,n=1)$
instability that generates the dynamo loop voltage. The necessary amount of
dynamo loop voltage is determined by the tendency of the current density
profile to centrally peak which, in our simulations, is controlled by the
peakedness of the applied heat source profile.",1706.06672v1
2017-07-19,Single-atom transistor as a precise magnetic field sensor,"Feshbach resonances, which allow for tuning the interactions of ultracold
atoms with an external magnetic field, have been widely used to control the
properties of quantum gases. We propose a~scheme for using scattering
resonances as a probe for external fields, showing that by carefully tuning the
parameters it is possible to reach a $10^{-5}$G (or nT) level of precision with
a single pair of atoms. We show that for our collisional setup it is possible
to saturate the quantum precision bound with a simple measurement protocol.",1707.06018v2
2017-07-21,Mn$_2$VAl Heusler alloy thin films: Appearance of antiferromagnetism and an exchange bias in a layered structure with Fe,"Mn$_2$VAl Heusler alloy films were epitaxially grown on MgO(100) single
crystal substrates by means of ultra-high-vacuum magnetron sputtering. A2 and
L2$_1$ type Mn$_2$VAl order was controlled by the deposition temperatures.
A2-type Mn$_2$VAl films showed no spontaneous magnetization and L2$_1$-type
Mn$_2$VAl films showed ferrimagnetic behavior with a maximum saturation
magnetization of 220 emu/cm$^3$ at room temperature. An antiferromagnetic
reflection was observed with neutron diffraction at room temperature for an
A2-type Mn$_2$VAl film deposited at 400$^\circ$C. A bilayer sample of the
antiferromagnetic A2 Mn$_2$VAl and Fe showed an exchange bias of 120 Oe at 10
K.",1707.06731v1
2017-08-09,Enormous sample scale-up from nanoliter to microliter in high field liquid state dynamic nuclear polarization,"Dynamic nuclear polarization (DNP) enhances nuclear magnetic resonance (NMR)
signals by transferring electron spin polarization to nuclei. As DNP requires
microwave magnetic fields B1 strong enough to saturate electron spins,
microwave resonators are generally used to achieve a sufficient B1, at the
expense of restricting the sample size. Higher fields improve NMR sensitivity
and resolution. However, resonators at 9 T for example can only hold
nano-liters (nL). Larger volumes are possible by avoiding resonators, but the
higher power needed to reach B1 is likely to evaporate the sample. Here, we
demonstrate a breakthrough in liquid state DNP at 9 T, boosting the sample size
to the microliter range. We could use high-power (70 W) microwaves thanks to a
planar probe designed to alleviate dielectric heating. We enhanced the 1H NMR
signal intensity of 2 uL of liquid water by a factor of 14, while maintaining
the water temperature below 40 degree Celsius.",1708.02800v1
2017-11-24,Faraday rotation signatures of fluctuation dynamos in young galaxies,"Observations of Faraday rotation through high-redshift galaxies have revealed
that they host coherent magnetic fields that are of comparable strengths to
those observed in nearby galaxies. These fields could be generated by
fluctuation dynamos. We use idealized numerical simulations of such dynamos in
forced compressible turbulence up to rms Mach number of 2.4 to probe the
resulting rotation measure (RM) and the degree of coherence of the magnetic
field. We obtain rms values of RM at dynamo saturation of the order of 45 - 55
per cent of the value expected in a model where fields are assumed to be
coherent on the forcing scale of turbulence. We show that the dominant
contribution to the RM in subsonic and transonic cases comes from the general
sea of volume filling fields, rather than from the rarer structures. However,
in the supersonic case, strong field regions as well as moderately overdense
regions contribute significantly. Our results can account for the observed RMs
in young galaxies.",1711.08865v2
2018-01-10,Skyrmion states in thin confined polygonal nanostructures,"Recent studies have demonstrated that skyrmionic states can be the ground
state in thin-film FeGe disk nanostructures in the absence of a stabilising
applied magnetic field. In this work, we advance this understanding by
investigating to what extent this stabilisation of skyrmionic structures
through confinement exists in geometries that do not match the cylindrical
symmetry of the skyrmion -- such as as squares and triangles. Using simulation,
we show that skyrmionic states can form the ground state for a range of system
sizes in both triangular and square-shaped FeGe nanostructures of
$10\,\text{nm}$ thickness in the absence of an applied field. We further
provide data to assist in the experimental verification of our prediction; to
imitate an experiment where the system is saturated with a strong applied field
before the field is removed, we compute the time evolution and show the final
equilibrium configuration of magnetization fields, starting from a uniform
alignment.",1801.03275v1
2018-01-16,Conformal Mapping Approach to Dipole Shim Design,"Passive shims are often used to reduce the size and cost of room-temperature
magnetic dipoles. In this paper we revisit an analytic approach to the problem
of optimum shim design, and we extend it by taking into consideration the
effect of magnetic saturation. We derive an abacus curve to determine optimum
shim dimensions as a function of the desired dipole nominal field. We show
that, for nominal fields below 1.2 T, a pole with such shims can be made at
least one half gap height narrower than a pole without. We discuss the range of
validity of this approach and verify its predictions using 2 and 3-dimensional
finite-element calculations.",1801.05470v2
2018-01-24,Quantization of magnetoelectric fields,"The effect of quantum coherence involving macroscopic degree of freedom, and
occurring in systems far larger than individual atoms are one of the topical
fields in modern physics. Because of material dispersion, a phenomenological
approach to macroscopic quantum electrodynamics, where no canonical formulation
is attempted, is used. The problem becomes more complicated when geometrical
forms of a material structure have to be taken into consideration. Magnetic
dipolar mode (MDM) oscillations in a magnetically saturated quasi 2D ferrite
disk are macroscopically quantized states. In this ferrimagnetic structure,
long range dipole dipole correlation in positions of electron spins can be
treated in terms of collective excitations of a system as a whole. The near
fields in the proximity of a MDM ferrite disk have space and time symmetry
breakings. Such MDM-originated fields, called magnetoelectric (ME) fields,carry
both spin and orbital angular momentums. By virtue of unique topology, ME
fields are different from free space electromagnetic (EM) fields. The ME fields
are quantum fluctuations in vacuum. We call these quantized states ME photons.
There are not virtual EM photons. We show that energy, spin and orbital angular
momenta of MDM oscillations constitute the key physical quantities that
characterize the ME field configurations. We show that vacuum can induce a
Casimir torque between a MDM ferrite disk, metal walls, and dielectric samples.",1801.08042v1
2018-04-23,Magnetic field-induced resistivity upturn and exceptional magneto-resistance in Weyl semimetal TaSb2,"We study magneto-transport properties in single crystals of TaSb_2, which is
a recently discovered topological semimetal. In the presence of magnetic field,
the electrical resistivity shows onset of insulating behaviour followed by
plateau at low temperature. Such resistivity plateau is generally assigned to
topological surface states. TaSb2 exhibits extremely high magneto-resistance
with non-saturating field dependence. We find that aspects of extremely large
magneto resistance and resistivity plateau are well accounted by classical
Kohler scaling. Unambiguous evidence for anomalous Chiral transport is provided
with observation of negative longitudinal magneto-resistance. Shubnikov-de Haas
oscillations reveal two dominating frequencies, 201 T and 455 T. These aspects
categorize TaSb2 as a Type-II Weyl semimetal. At low temperature, the field
dependence of Hall resistivity shows non-linear behaviour that indicates the
presence of two types of charge carriers in consonance with reported electronic
band structure. Analysis of Hall resistivity imply very high electron
mobilities.",1804.08434v1
2018-05-14,Homogeneous and heterogeneous nucleation of skyrmions in thin layers of cubic helimagnets,"Formation of isolated chiral skyrmions by homogeneous and heterogeneous
nucleation has been studied in thin layers of cubic helimagnets via elongation
of torons and chiral bobbers, correspondingly. Both torons and bobbers are
localized in three dimensions, contain singularities, and according to the
theoretical analysis within the standard phenomenological models can exist as
metastable states in saturated and modulated phases of noncentrosymmetric
ferromagnets. Their elongation into the defect-free skyrmion filament is
facilitated by small anisotropic contributions making skyrmion cores negative
with respect to the surrounding parental state. We show that isolated magnetic
torons pose the same problem of compatibility with a surrounding phase as the
torons in confinement-frustrated chiral nematics [I. Smalyukh et al., Nature
Mater 9, 139-145 (2010)]. We underline the distinct features of magnetic and
liquid-crystals torons and calculate phase diagrams indicating their stability
regions.",1805.04990v1
2018-06-27,Photocatalytic activity enhancement by addition of lanthanum into the BiFeO3 structure and the effect of synthesis method,"In this paper, the photocatalytic activity of multiferroics BiFeO3 (BFO) and
Bi0.8La0.2FeO3 (BLFO) nanocrystals with two different morphologies which were
synthesized by two different sol-gel (SG) and hydrothermal (HT) methods have
been studied. All the obtained samples were characterized using X-ray
diffractometer, Fourier transform infrared spectroscopy, transmission electron
microscopy, UV-vis spectroscopy and vibrating sample magnetometer. Differential
thermal analysis (DTA) measurements were probed ferroelectric- paraelectric
first-order phase transition (TC) for all samples. Addition of lanthanum
decreases the electric phase transition. For photocatalyst application of
bismuth ferrite, adsorption potential of nanoparticles for methylene blue (MB)
organic dye was evaluated. The doping of La in the BFO structure enhanced the
photocatalytic activity and about 71% degradation of MB dye was obtained under
visible irradiation. The magnetic and ferroelectric properties of BLFO
nanoparticles improve compared to the undoped BiFeO3 nanoparticles. The
non-saturation at high applied magnetic field for as-prepared samples by HT is
related to the size and shape of products. This work not only presents an
effect of lanthanum substitution into the bismuth ferrite structure on the
physical properties of BFO, but also compares the synthesis method and its
influence on the photocatalytic activity and multiferroics properties of all
nanopowders.",1807.03127v1
2018-07-31,New room-temperature ferromagnet: B-added Pd0.75Mn0.25 alloy,"Mn-based room-temperature ferromagnets attract considerable attention due to
their high ordered Mn moment. We have found that a Pd0.75Mn0.25 alloy with
added B (Pd0.75Mn0.25Bx) shows room-temperature soft ferromagnetism, whereas
the parent Pd0.75Mn0.25 alloy is a spin-glass system. The saturated Mn moment
at room temperature systematically increases to 2.68\muB/Mn as x increases to
0.125. The maximum Curie temperature of 390 K is also realized at an x of
0.125. The experimental results suggest a tunable soft ferromagnetism, which is
governed only by the boron concentration. Our results will pave the way in
chemical control of room-temperature bulk ferromagnetism in Mn compounds based
on the addition of an atom with a small atomic radius.",1807.11640v1
2018-08-07,"Development of Ferromagnetic Fluctuations in Heavily Overdoped (Bi,Pb)_2_Sr_2_CuO_6+delta_ Copper Oxides","We demonstrate the presence of ferromagnetic (FM) fluctuations in the
superconducting and non-superconducting heavily overdoped regimes of
high-temperature superconducting copper oxides, using
(Bi,Pb)_2_Sr_2_CuO_6+delta_ (Bi-2201) single crystals. Magnetization curves
exhibit a tendency to be saturated in high magnetic fields at low temperatures
in the heavily overdoped crystals, which is probably a precursor phenomenon of
a FM transition at a lower temperature. Muon spin relaxation detects the
enhancement of spin fluctuations at high temperatures below 200 K.
Correspondingly, the ab-plane resistivity follows a 4/3 power law in a wide
temperature range, which is characteristic of metals with two-dimensional FM
fluctuations due to itinerant electrons. As the Wilson ratio evidences the
enhancement of spin fluctuations with hole doping in the heavily overdoped
regime, it is concluded that two-dimensional FM fluctuations reside in the
heavily overdoped Bi-2201 cuprates, which is probably related to the decrease
in the superconducting transition temperature in the heavily overdoped
cuprates.",1808.02317v1
2018-08-13,Nonlinear firehose relaxation and constant-B field fluctuations,"The nonlinear evolution of Alfv\'enic fluctuations in the firehose unstable
regime is investigated numerically and theoretically for an anisotropic plasma
described by the one-fluid double adiabatic equations. We revisit the
traditional theory of the instability and examine the nonlinear saturation
mechanism, showing that it corresponds to evolution towards states that
minimize an appropriate energy functional. We demonstrate that such states
correspond to broadband magnetic and velocity field fluctuations with an
overall constant magnitude of the magnetic field. These nonlinear states
provide a basin of attraction for the long-term nonlinear evolution of the
instability, a self-organization process that may play a role in maintaining
the constant-$B$ Alfv\'enic states seen in the solar wind in the high-$\beta$
regime.",1808.04453v2
2018-08-20,Electronic transport properties of Co cluster-decorated graphene,"Interactions of magnetic elements with graphene may lead to various
electronic states that have potential applications. We report an in-situ
experiment in which the quantum transport properties of graphene are measured
with increasing cobalt coverage in continuous ultra-high vacuum environment.
The results show that e-beam deposited cobalt forms clusters on the surface of
graphene, even at low sample temperatures. Scattering of charge carriers by the
absorbed cobalt clusters results in the disappearance of the Shubnikov-de Haas
(SdH) oscillations and the appearance of negative magnetoresistance (MR) which
shows no sign of saturation up to an applied magnetic field of 9 T. We propose
that these observations could originate from quantum interference driven by
cobalt disorder and can be explained by the weak localization theory.",1808.06331v1
2018-12-12,Emergent prethermalization signatures in out-of-time ordered correlations,"How a many-body quantum system thermalizes --or fails to do so-- under its
own interaction is a fundamental yet elusive concept. Here we demonstrate
nuclear magnetic resonance observation of the emergence of prethermalization by
measuring out-of-time ordered correlations. We exploit Hamiltonian engineering
techniques to tune the strength of spin-spin interactions and of a transverse
magnetic field in a spin chain system, as well as to invert the Hamiltonian
sign to reveal out-of-time ordered correlations. At large fields, we observe an
emergent conserved quantity due to prethermalization, which can be revealed by
an early saturation of correlations. Our experiment not only demonstrates a new
protocol to measure out-of-time ordered correlations, but also provides new
insights in the study of quantum thermodynamics.",1812.04776v1
2018-12-30,Dynamics of Magnetoelectric Reversal of Antiferromagnetic Domain,"When electric and magnetic fields are applied together on a magnetoelectric
antiferromagnet, the domain state is subject to reversal. Although the initial
and final conditions are saturated single-domain states, the process of
reversal may decompose into local multi-domain switching events. In thin films
of Cr2O3, the magnetoelectric coercivity and the switching speed found from
experiments are considerably lower than expected from magnetic anisotropy,
similar to Brown's paradox in ferromagnetic materials. Multi-domain effects
originate because antiferromagnetic domain walls are metastably pinned by
lattice defects, not due to reduction of magnetostatic energy, which is
negligible. This paper theoretically analyzes domain reversal in thin-film
magnetoelectric antiferromagnets in the form of nucleation, domain wall
propagation, and coherent rotation. The timescales of reversal mechanisms are
modeled as a function of applied magnetoelectric pressure. The theory is
assessed with reference to latest experimental works on magnetoelectric
switching of thin-film Cr2O3: domain wall propagation is found to be dominant
and responsible for switching in the experiments. The results bear implications
in the energy-delay performance of ME memory devices utilizing
antiferromagnetic insulators, which are prospective for nonvolatile technology.",1812.11579v3
2019-02-01,Non-linear modeling of the threshold between ELM mitigation and ELM suppression by Resonant Magnetic Perturbations in ASDEX Upgrade,"The interaction between Edge Localized Modes (ELMs) and Resonant Magnetic
Perturbations (RMPs) is modeled with the magnetohydrodynamic code JOREK using
experimental parameters from ASDEX Upgrade discharges. The ELM mitigation or
suppression is optimal when the amplification of both tearing and peeling-kink
responses result in a better RMP penetration. The ELM mitigation or suppression
is not only due to the reduction of the pressure gradient, but predominantly
arises from the toroidal coupling between the ELMs and the RMP-induced mode at
the plasma edge, forcing the edge modes to saturate at a low level. The
bifurcation from ELM mitigation to ELM suppression is observed when the RMP
amplitude is increased. ELM mitigation is characterized by rotating modes at
the edge, while the mode locking to RMPs is induced by the resonant braking of
the electron perpendicular flow in the ELM suppression regime.",1902.00398v2
2019-02-27,From kagome strip to kagome lattice: Realizations of frustrated S=1/2 antiferromagnets in Ti(III) fluorides,"We investigate the connection between highly frustrated kagome based
Hamiltonians and a recently synthesized family of materials containing Ti3+
S=1/2 ions. Employing a combination of all electron density functional theory
and numerical diagonalization techniques, we establish the Heisenberg
Hamiltonians for the distorted kagome antiferromagnets Rb2NaTi3F12, Cs2NaTi3F12
and Cs2KTi3F12. We determine magnetization curves in excellent agreement with
experimental observations. Our calculations successfully clarify the
relationship between the experimental observations and the
magnetization-plateau behavior at 1/3 height of the saturation and predict
characteristic behaviors under fields that are higher than the experimentally
measured region. We demonstrate that the studied Ti(III) family of materials
interpolates between kagome strip and kagome lattice.",1902.10309v1
2019-03-20,Electronic Structure Calculations of CeRh$_{3}$B$_{2}$,"The electronic structure of the ferromagnetic material CeRh$_{3}$B$_{2}$ is
studied by means of first-principles calculations with an emphasis on the
treatment of localized $4f$ states around Ce. Via the construction of an
effective spin model from electronic structure calculations, we estimated the
Curie temperature $T_{\rm C}$ of CeRh$_{3}$B$_{2}$ and found a specific
configuration of the electronic structure which explains the exceptionally high
measured value of $T_{\rm C} \sim 120$ K as well as the small saturation
magnetization and the topology of the Fermi surface. Present advance in the
understanding of the subtle nature of the $4f$-electron state in
CeRh$_{3}$B$_{2}$ that brings about the exceptionally high $T_{\rm C}$ should
be also of technological relevance to exploit the utility of Ce in rare-earth
permanent magnets.",1903.08480v1
2019-03-27,Nonlinear Evolution of Ion Kinetic Instabilities in the Solar Wind,"In-situ observations of the solar wind (SW) plasma from 0.29 to 1AU show that
the protons and alpha particles are often non-Maxwellian, with evidence of
kinetic instabilities, temperature anisotropies, differential ion streaming,
and associated magnetic fluctuations spectra. The kinetic instabilities in the
SW multi-ion plasma can lead to preferential heating of alpha particles and the
dissipation of magnetic fluctuation energy, affecting the kinetic and global
properties of the SW. Using for the first time a three-dimensional hybrid
model, where ions are modeled as particle using the Particle-In-Cell (PIC)
method and electrons are treated as fluid, we study the onset, nonlinear
evolution and dissipation of ion kinetic instabilities. The
Alfven/ion-cyclotron, and the ion drift instabilities are modeled in the region
close to the Sun (~10R_s). Solar wind expansion is incorporated in the model.
The model produces self-consistent non-Maxwellian velocity distribution
functions (VDFs) of unstable ion populations, the associated temperature
anisotropies, and wave spectra for several typical SW instability cases in the
nonlinear growth and saturation stage of the instabilities. The 3D hybrid
modeling of the multi-ion SW plasma could be used to study the SW acceleration
region close to the Sun that will be explored by the Parker Solar Probe
mission.",1903.11343v1
2019-04-10,On the properties of a newborn magnetar powering the X-ray transient CDF-S XT2,"Very recently \citet{XueYQ2019} reported an important detection of the X-ray
transient, CDF-S XT2, whose light curve is analogous to X-ray plateau features
of gamma-ray burst afterglows. They suggested that this transient is powered by
a remnant stable magnetar from a binary neutron star merger since several
pieces of evidence (host galaxy, location, and event rate) all point toward
such an assumption. In this paper, we revisit this scenario and confirm that
this X-ray emission can be well explained by the internal gradual magnetic
dissipation process in an ultra-relativistic wind of the newborn magnetar. We
show that both the light curve and spectral evolution of CDF-S XT2 can be well
fitted by such a model. Furthermore, we can probe some key properties of the
central magnetar, such as its initial spin period, surface magnetic field
strength and wind saturation Lorentz factor.",1904.05480v2
2019-04-11,Study of soft/hard bimagnetic CoFe2/CoFe2O4 nanocomposite,"We report an experimental study of the bimagnetic nanocomposites
CoFe2/CoFe2O4.The precursor material, CoFe2O4 was prepared using the
conventional stoichiometric combustion method. The nanocomposite CoFe2/CoFe2O4
was obtained by total reduction of CoFe2O4 using a thermal treatment at 350oC
in H2 atmospheres following a partial oxidation in O2 atmospheres at 380oC
during 120; 30; 15, 10, and 5 min. The X-ray diffraction and Mossbauer
spectroscopy confirmed the formation the material CoFe2/CoFe2O4 The magnetic
hysteresis with different saturation magnetization confirms the formation of
the CoFe2/CoFe2O4 with different content of CoFe2O4. The high energy milling to
the precursor material increase the coercivity from 1.0 to 3.3 kOe, however the
same effect was not observed to the CoFe2/CoFe2O4 material.",1904.05984v1
2019-04-23,Tailored tunnel magnetoresistance response in three ultrathin chromium trihalides,"Materials that demonstrate large magnetoresistance have attracted significant
interest for many decades. Recently, extremely large tunnel magnetoresistance
(TMR) has been reported by several groups across ultrathin CrI$_3$ by
exploiting the weak antiferromagnetic coupling between adjacent layers. Here,
we report a comparative study of TMR in all three chromium trihalides (CrX$_3$,
X= Cl, Br, or I) in the two-dimensional limit. As the materials exhibit
different transition temperatures and interlayer magnetic ordering in the
ground state, tunneling measurements allow for an easy determination of the
field-temperature phase diagram for the three systems. By changing sample
thickness and biasing conditions, we then demonstrate how to maximize and
further tailor the TMR response at different temperatures for each material. In
particular, near the magnetic transition temperature, TMR is non-saturating up
to the highest fields measured for all three compounds owing to the large,
field-induced exchange coupling.",1904.10476v2
2019-05-04,Identification and time-resolved study of YIG spin wave modes in a MW cavity in strong coupling regime,"Recently, the hybridization of microwave-frequency cavity modes with
collective spin excitations attracted large interest for the implementation of
quantum computation protocols, which exploit the transfer of information among
these two physical systems. Here, we investigate the interaction among the
magnetization precession modes of a small YIG sphere and the MW electromagnetic
modes, resonating in a tridimensional aluminum cavity. In the strong coupling
regime, anti-crossing features were observed in correspondence of various
magnetostatic modes, which were excited in a magnetically saturated sample.
Time-resolved studies show evidence of Rabi oscillations, demonstrating
coherent exchange of energy among photons and magnons modes. To facilitate the
analysis of the standing spin-wave patterns, we propose here a new procedure,
based on the introduction of a novel functional variable. The resulting easier
identification of magnetostatic modes can be exploited to investigate, control
and compare many-levels hybrid systems in cavity- and opto-magnonics research.",1905.01522v2
2019-07-03,"Rotational dynamics of planetary cores: instabilities driven by precession, libration and tides","In this chapter, we explore how gravitational interactions drive turbulent
flows inside planetary cores and provide an interesting alternative to
convection to explain dynamo action and magnetic fields around terrestrial
bodies. In the first section, we introduce tidal interactions and their effects
on the shape and rotation of astrophysical bodies. A method is given to derive
the primary response of liquid interiors to these tidally-driven perturbations.
In the second section, we detail the stability of this primary response and
demonstrate that it is able to drive resonance of inertial waves. As the
instability mechanism is introduced, we draw an analogy with the parametric
amplification of a pendulum whose length is periodically varied. Lastly, we
present recent results regarding this instability, in particular its non-linear
saturation and its ability to drive dynamo action. We present how it has proved
helpful to explain the magnetic field of the early Moon.",1907.02001v1
2019-07-17,Multiple phase transitions and high-field quadrupolar order in a model for $β$-TeVO$_4$,"Motivated by the complex behavior of the frustrated magnet $\beta$-TeVO$_4$,
we study an anisotropic Heisenberg model for coupled spin-$1/2$ zigzag chains.
Using cluster mean field approach to capture quantum correlations we find, upon
reducing temperature in the absence of applied field, (i) a partially ordered
state, (ii) a collinear antiferromagnetic phase, and (iii) an elliptical spiral
state characterized by finite vector chirality. For finite fields, we find
metamagnetic response close to saturation magnetization. We show via explicit
calculations that the quadrupolar order parameter is finite in the metamagnetic
regime. The exchange parameters reported in the ab-initio study of
$\beta$-TeVO$_4$ are used in our study. We compare our results with those
reported in recent experiments on $\beta$-TeVO$_4$ and highlight similarities
as well as differences between experimental results and our cluster mean field
calculations.",1907.07354v2
2019-07-31,Large spin Hall magnetoresistance in antiferromagnetic α-Fe2O3/Pt heterostructures,"We investigate the spin Hall magnetoresistance (SMR) at room temperature in
thin film heterostructures of antiferromagnetic, insulating, (0001)-oriented
alpha-Fe2O3 (hematite) and Pt. We measure their longitudinal and transverse
resistivities while rotating an applied magnetic field of up to 17T in three
orthogonal planes. For out-of-plane magnetotransport measurements, we find
indications for a multidomain antiferromagnetic configuration whenever the
field is aligned along the film normal. For in-plane field rotations, we
clearly observe a sinusoidal resistivity oscillation characteristic for the SMR
due to a coherent rotation of the Neel vector. The maximum SMR amplitude of
0.25% is, surprisingly, twice as high as for prototypical ferrimagnetic
Y3Fe5O12/Pt heterostructures. The SMR effect saturates at much smaller magnetic
fields than in comparable antiferromagnets, making the alpha-Fe2O3/Pt system
particularly interesting for room-temperature antiferromagnetic spintronic
applications.",1907.13393v4
2019-08-16,Emergent Snake Magnetic Domains in Canted Kagome Ice,"We study the two-dimensional kagome-ice model derived from a pyrochlore
lattice with second- and third-neighbor interactions. The canted moments align
along the local $\langle 111 \rangle$ axes of the pyrochlore and respond to
both in-plane and out-of-plane external fields. We find that the combination of
further-neighbor interactions together with the external fields introduces a
rich phase diagram with different spin textures. Close to the phase boundaries,
metastable $\textit{""snake""}$ domains emerge with extremely long relaxation
time. Our kinetic Monte Carlo analysis of the magnetic-field quench process
from saturated state shows unusually slow dynamics. Despite that the interior
spins are almost frozen in snake domains, the spins on the edge are free to
fluctuate locally, leading to frequent creation and annihilation of
monopole-anti-monopole bound states. Once the domains are formed, these
excitations are localized and can hardly propagate due to the energy barrier of
snakes. The emergence of such snake domains may shed light on the experimental
observation of dipolar spin ice under tilted fields, and provide a new strategy
to manipulate both spin and charge textures in artificial spin ice.",1908.05872v1
2019-08-22,Phase diagram and quantum criticality of Heisenberg spin chains with Ising-like interchain couplings -- Implication to YbAlO$_3$,"Motivated by recent progress on field-induced phase transitions in
quasi-one-dimensional quantum antiferromagnets, we study the phase diagram of
$S=1/2$ antiferromagnetic Heisenberg chains with Ising anisotropic interchain
couplings under a longitudinal magnetic field via large-scale quantum Monte
Carlo simulations. The interchain interactions is shown to enhance longitudinal
spin correlations to stabilize an incommensurate longitudinal spin density wave
order at low temperatures. With increasing field the ground state changes to a
canted antiferromagnetic order until the magnetization fully saturates above a
quantum critical point controlled by the $(3+2)$D XY universality. Increasing
temperature in the quantum critical regime the system experiences a fascinating
dimension crossover to a universal Tomonaga-Luttinger liquid. The calculated
NMR relaxation rate $1/T_1$ indicates this Luttinger liquid behavior survives a
broad field and temperature regime. Our results determine the global phase
diagram and quantitative features of quantum criticality of a general model for
quasi-one-dimensional spin chain compounds, and thus lay down a concrete ground
to the study on these materials.",1908.08467v1
2019-08-24,Emergent critical phenomenon in spin-1/2 ferromagnetic-leg ladders: Quasi-one-dimensional Bose--Einstein condensate,"We examine the magnetic-field-induced criticality of phase boundary near
saturation field $H_{\mathrm{c}}$ in the spin-1/2 ferromagnetic (FM)-leg ladder
3-Cl-4-F-V [=3-(3-chloro-4-fluorophenyl)-1,5-diphenylverdazyl], the predominant
interactions of which arise from FM chains (strong-leg type). Critical
temperatures were precisely determined through dc magnetization, specific heat,
and magnetocaloric effect measurements. The criticality of 3-Cl-4-F-V is
characterized by a linear phase boundary with respect to $H_{\mathrm{c}}-H$
near $H\,=\,H_{\mathrm{c}}$. This behavior is similar to that of another
strong-leg-type FM-leg ladder. The universal critical behavior in these
strong-leg-type FM-leg ladders is expected to demonstrate the theoretically
predicted quasi-one-dimensional Bose--Einstein condensation.",1908.09076v1
2019-09-06,The interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films,"We report on broadband ferromagnetic resonance linewidth measurements
performed on epitaxial Heusler thin films. A large and anisotropic two-magnon
scattering linewidth broadening is observed for measurements with the
magnetization lying in the film plane, while linewidth measurements with the
magnetization saturated perpendicular to the sample plane reveal low Gilbert
damping constants of $(1.5\pm0.1)\times 10^{-3}$, $(1.8\pm0.2)\times 10^{-3}$,
and $<8\times 10^{-4}$ for Co$_2$MnSi/MgO, Co$_2$MnAl/MgO, and Co$_2$FeAl/MgO,
respectively. The in-plane measurements are fit to a model combining Gilbert
and two-magnon scattering contributions to the linewidth, revealing a
characteristic disorder lengthscale of 10-100 nm.",1909.02738v2
2019-10-17,Magneto-dielectric Effect in Relaxor Dipolar Glassy Tb2CoMnO6 Film,"We report magneto-dielectric properties of partially B-site ordered
monoclinic Tb2CoMnO6 double perovskite thin film epitaxially grown by
metalorganic aerosol deposition technique. Transmission electron microscopy and
electron energy loss spectroscopy mapping shows the presence and distribution
of both Co2+ and Co3+ ions in the film, evidencing a partial B-site disorder,
which was further confirmed by the observation of reduced saturation
magnetization at low temperatures. The ferromagnetic Curie temperature, TC=110
K, is slightly higher as compared to the bulk value (100 K) probably due to an
in plane tensile strain. Remarkably, a short range ordering of spins at T*~190
K>>TC was established and assigned to the B-site disorder in the film. Two
different dielectric relaxation peaks have been observed; they merge at the
same temperature T* of short range spin correlations. Moreover, an unexpected
high temperature dipolar relaxor-glass-like transition at T~T* was observed, at
which a coupling to short range magnetic correlations results in a 4%
magneto-dielectric coupling.",1910.07991v1
2019-11-06,High spin mixing conductance and spin interface transparency at $Co_2Fe_{0.4}Mn_{0.6}Si$ Heusler alloy and Pt interface,"Ferromagnetic materials exhibiting low magnetic damping ($\alpha$) and
moderately high saturation magnetization are required from the viewpoints of
generation, transmission and detection of spin wave. Since spin-to-charge
conversion efficiency is another important parameter, high spin mixing
conductance ($g_{r}^{\uparrow \downarrow}$) is the key for efficient
spin-to-charge conversion. Full Heusler alloys e.g. $Co_2Fe_{0.4}Mn_{0.6}Si$
(CFMS), which are predicted to be 100$\%$ spin polarized, possess low $\alpha$.
However, the $g_{r}^{\uparrow \downarrow}$ at the interface between CFMS and a
paramagnet has not fully been understood. Here, we report the investigations of
spin pumping and inverse spin Hall effect in $CFMS/Pt$ bilayers. Damping
analysis indicates the presence of significant spin pumping at the interface of
CFMS and Pt, which is also confirmed by the detection of inverse spin Hall
voltage. We show that in CFMS/Pt the $g_{r}^{\uparrow \downarrow}$
(1.77$\times$10$^{20}$m$^{-2}$) and interface transparency (84$\%$) are higher
compared to values reported for other ferromagnet/heavy metal systems.",1911.02230v1
2019-12-19,Gyrokinetic investigation of Alfvén instabilities in the presence of turbulence,"The global and electromagnetic gyrokinetic particle-in-cell code ORB5 is
employed to investigate the self-consistent interactions between Alfv\'en modes
(AM) and ion temperature gradient (ITG) turbulence in a magnetically confined
plasma. Here, an axisymmetric magnetic equilibrium with reversed shear and
large aspect ratio is considered. An AM with toroidal mode number n=5 is driven
unstable by introducing a population of suprathermal ions. Once the AM
saturates in the presence of the fully developed turbulence, the ion heat flux
is dominated by the AM and its main harmonics. ITG-induced transport is found
to also be enhanced in the presence of the unstable AM.",1912.09409v1
2020-01-23,In-vivo Magnetic Resonance Imaging of GABA and Glutamate,"Chemical Exchange Saturation Transfer (CEST) Magnetic Resonance Imaging (MRI)
is a molecular imaging methodology capable of mapping brain metabolites with
relatively high spatial resolution. Specificity is the main goal of such
experiments; yet CEST is confounded by spectral overlap between different
molecular species. Here, we overcome this major limitation using a general
framework termed overlap-resolved CEST (orCEST) - a kind of spectrally-edited
experiment restoring specificity. First, we present evidence revealing that
CEST experiments targeting the central nervous system's primary excitatory
neurotransmitter, Glutamate (GluCEST) - is significantly contaminated by
gamma-aminobutyric acid (GABA) - the primary inhibitory neurotransmitter in the
CNS. Then, we harness the novel orCEST methodology to separate Glutamate and -
for the first time - GABA signals, thus delivering the desired specificity.
In-vivo orCEST experiments resolved the rat brain's primary neurotransmitters
and revealed changes in Glutamate and GABA levels upon water deprivation in
thirst-related areas. orCEST's features bode well for many applications in
neuroscience and biomedicine.",2001.08515v1
2020-01-30,An anomalous refraction of spin waves as a way to guide signals in curved magnonic multimode waveguides,"We present a method for efficient spin wave guiding within the magnonic
nanostructures. Our technique is based on the anomalous refraction in the
metamaterial flat slab. The gradual change of the material parameters
(saturation magnetization or magnetic anisotropy) across the slab allows
tilting the wavefronts of the transmitted spin waves and controlling the
refraction. Numerical studies of the spin wave refraction are preceded by the
analytical calculations of the phase shift acquired by the spin wave due to the
change of material parameters in a confined area. We demonstrate that our
findings can be used to guide the spin waves smoothly in curved waveguides,
even through sharp bends, without reflection and scattering between different
waveguide's modes, preserving the phase -- the quantity essential for wave
computing.",2001.11356v1
2020-02-26,Singlet state encoded magnetic resonance (SISTEM) spectroscopy,"Magnetic resonance spectroscopy (MRS) allows the analysis of biochemical
processes non invasively and in vivo. Still, its application in clinical
diagnostics is rare. Routine MRS is limited to spatial, chemical and temporal
resolutions of cubic centimetres, mM and minutes. In fact, the signal of many
metabolites is strong enough for detection, but the resonances significantly
overlap, exacerbating identification and quantification. In addition, the
signals of water and lipids are much stronger and dominate the entire spectrum.
To suppress the background and isolate selected signals, usually, relaxation
times, J-coupling and chemical shifts are used. Here, we propose methods to
isolate the signals of selected molecular groups within endogenous metabolites
by using long-lived spin states (LLS). We exemplify the method by preparing the
LLSs of coupled protons in the endogenous molecules N-acetyl-L-aspartic acid
(NAA). First, we store polarization in long-lived, double spin states and then
apply saturation pulses and double quantum filters to suppress background
signals. We show that LLS can be used to selectively prepare and measure the
signals of chosen metabolites or drugs in the presence of water, inhomogeneous
field and highly concentrated fatty solutions. The pH measurement presented
here is one of the possible applications.",2002.11350v1
2020-03-06,Epitaxial growth and orientation-dependent anomalous Hall effect of noncollinear antiferromagnetic Mn$_3$Ni$_{0.35}$Cu$_{0.65}$N films,"We report the growth of noncollinear antiferromagnetic (AFM)
Mn$_3$Ni$_{0.35}$Cu$_{0.65}$N films and the orientation-dependent anomalous
Hall effect (AHE) of (001) and (111) films due to nonzero Berry curvature. We
found that post-annealing at 500$^\circ$C can significantly improve the AHE
signals, though using the appropriate post-annealing conditions is important.
The AHE and magnetization loops show sharp flipping at the coercive field in
(111) films, while (001) films are hard to saturate by a magnetic field. The
anomalous Hall conductivity of (111) films is an order of magnitude larger than
that of (001) films. The present results provide not only a better
understanding of the AHE in Mn$_3X$N systems but also further opportunities to
study the unique phenomena related to noncollinear AFM.",2003.03031v1
2020-03-09,The self-similar structure of advection-dominated discs with outflow and radial viscosity,"Observational evidence and theoretical arguments postulate that outflows may
play a significant role in the advection-dominated accretion discs (ADAFs).
While the azimuthal viscosity is the main focus of most previous studies in
this context, recent studies indicated that disc structure can also be affected
by the radial viscosity. In this work, we incorporate these physical
ingredients and the toroidal component of the magnetic field to explore their
roles in the steady-state structure of ADAFs. We thereby present a set of
similarity solutions where outflows contribute to the mass loss, angular
momentum removal, and the energy extraction. Our solutions indicate that the
radial viscosity causes the disc to rotate with a slower rate, whereas the
radial gas velocity increases. For strong winds, the infall velocity may be of
order the Keplerian speed if the radial viscosity is considered and the
saturated conduction parameter is high enough. We show that the strength of
magnetic field and of wind can affect the effectiveness of radial viscosity.",2003.04752v1
2020-03-14,Magnetar formation through a convective dynamo in protoneutron stars,"The release of spin-down energy by a magnetar is a promising scenario to
power several classes of extreme explosive transients. However, it lacks a firm
basis because magnetar formation still represents a theoretical challenge.
Using the first three-dimensional simulations of a convective dynamo based on a
protoneutron star interior model, we demonstrate that the required dipolar
magnetic field can be consistently generated for sufficiently fast rotation
rates. The dynamo instability saturates in the magnetostrophic regime with the
magnetic energy exceeding the kinetic energy by a factor of up to 10. Our
results are compatible with the observational constraints on galactic magnetar
field strength and provide strong theoretical support for millisecond
protomagnetar models of gamma-ray burst and superluminous supernova central
engines.",2003.06662v1
2020-03-18,A firehose-like aperiodic instability of the counter-beaming electron plasmas,"Depending on the physical conditions involved the beam plasma systems may
reveal new unstable regimes triggered by the wave instabilities of different
nature. We show through linear theory and numerical simulations the existence
of an aperiodic electromagnetic instability which solely develops and control
the stability of two symmetric plasma populations counter-moving along the
regular magnetic field with a relative drift, $v_d$, small enough to not exceed
the particle thermal speed, $\alpha_e$. Emerging at highly oblique angles this
mode resembles properties of the aperiodic firehose instability driven by
temperature anisotropy. The high growth rates achieved with increasing the
relative drift or/and decreasing the plasma beta parameter lead to significant
saturation levels of the fluctuating magnetic field power, which explain the
relative fast relaxation of electrons. For $v_d>\alpha_e$ this instability can
coexist with the electrostatic two-stream instability, dominating the long-term
dynamics of the plasma as soon as $v_d$ has relaxed to values smaller than the
thermal speed.",2003.08245v1
2020-05-05,Study of single crystalline SrAgSb and SrAuSb semimetals,"Given renewed interest in the electronic properties of semimetallic compounds
with varying degrees of spin orbit coupling we have grown single crystals of
SrAgSb and SrAuSb, measured their temperature and field dependent electrical
resistivity and magnetization and performed density functional theory (DFT)
band structure calculations. Magnetization measurements are consistent with a
diamagnetic host with a small amount of local moment bearing impurities.
Although the residual resistivity ratio (RRR) for all samples studied was
relatively low, ranging between 2.4 and 3.4, the compounds had non-saturating
magnetoresistance (MR), reaching values of $\sim$ 17% and $\sim$ 70% at 4 K and
9 T for SrAgSb and SrAuSb respectively. Band structure calculations, using the
experimentally determined Wyckoff positions for the Sr, Ag/Au, and Sb atoms,
show that whereas SrAgSb is a topologically trivial, but compensated,
semimetal; SrAuSb is a topologically non-trivial, Dirac semimetal.",2005.02323v1
2020-05-25,Dynamical signatures of quasiparticle interactions in quantum spin chains,"We study the transverse dynamical susceptibility of an antiferromagnetic
spin$-1/2$ chain in presence of a longitudinal Zeeman field. In the low
magnetization regime in the gapless phase, we show that the marginally
irrelevant backscattering interaction between the spinons creates a non-zero
gap between two branches of excitations at small momentum. We further
demonstrate how this gap varies upon introducing a second neighbor
antiferromagnetic interaction, vanishing in the limit of a non-interacting
""spinon gas"". In the high magnetization regime, as the Zeeman field approaches
the saturation value, we uncover the appearance of two-magnon bound states in
the transverse susceptibility. This bound state feature generalizes the one
arising from string states in the Bethe ansatz solution of the integrable case.
Our results are based on numerically accurate, unbiased matrix-product-state
techniques as well as analytic approximations.",2005.12399v1
2020-06-17,Scaling the electrical current switching of exchange bias in fully-epitaxial antiferromagnet/ferromagnet bilayers,"While the electrical current manipulation of antiferromagnets (AFMs) has been
demonstrated, the extent of the studied AFM materials has been limited with few
systematic experiments and a poor understanding. We compare the electrical
current switching of the exchange-bias field ($H_{ex}$) in
AFM-Mn$_3A$N/ferromagnet-Co$_3$FeN bilayers. An applied pulse current can
manipulate $H_{ex}$ with respect to the current density and FM layer
magnetization, which shifts exponentially as a function of the current density.
We found that the saturation current density and exponential decay constant
$\tau$ increase with the local moment of AFM Mn atoms. Our results highlight
the effect of the AFM local moment to electrical current switching of $H_{ex}$,
although it has a near-zero net magnetization, and may provide a facile way to
explore the electrical current manipulation of AFM materials.",2007.01070v1
2020-07-21,New $τ$-based evaluation of the hadronic contribution to the vacuum polarization piece of the muon anomalous magnetic moment,"We revisit the isospin-breaking and electromagnetic corrections to the decay
$\tau^-\to\pi^-\pi^0\nu_\tau$, which allow its use as input in the two-pion
contribution to the (leading order) hadronic vacuum polarization part of the
muon anomalous magnetic moment. We extend a previous resonance chiral
Lagrangian analysis, which included those operators saturating the
next-to-leading order chiral low energy constants, by including the
contributions of the next subleading terms. As a result, we improve agreement
between the two-pion tau decay and $e^+e^-$ data and reduce the discrepancy
between experiment and the SM prediction of $a_\mu$ (using $\tau$ input).",2007.11019v3
2020-08-04,Quantum correlations in the spin-1/2 Heisenberg XXZ chain with modulated Dzyaloshinskii-Moriya interaction,"We study a one-dimensional spin-1/2 XXZ Heisenberg model with alternating
Dzyaloshinskii- Moriya interaction, using the numerical Lanczos method.
Recently, the ground state (GS) phase diagram of this model has been
established using the bosonization approach and extensive density matrix
renormalization group computations. Four quantum phases - saturated
ferromagnetic (FM), Luttinger liquid (LL), and two (C1 and C2) gapped phases
with composite structure of GS order, characterized by the coexistence of
long-range alternating dimer, chirality and antiferromagnetic order have been
identified. Here we reexamine the same problem using the exact diagonalization
Lanczos method for chains up to N = 26 sites and explicitly detect positions of
quantum critical points (QCP) by investigating the quantum correlations as the
entanglement and the quantum discord (QD). It is shown that the entanglement
quantified by concurrence and the first derivative of the QD are able to reveal
besides the standard FM QCP also the Berezinskii-Kosterlitz-Thouless (BKT)
phase transition point between the LL and the gapped C1 phase and the Ising
type critical point separating the C1 and C2 phases.",2008.01443v1
2020-09-02,Giant inverse Faraday effect in Dirac semimetals,"We have studied helicity dependent photocurrent (HDP) in Bi-based Dirac
semimetal thin films. HDP increases with film thickness before it saturates,
changes its sign when the majority carrier type is changed from electrons to
holes and takes a sharp peak when the Fermi level lies near the charge
neutrality point. These results suggest that irradiation of circularly
polarized light to Dirac semimetals induces an effective magnetic field that
aligns the carrier spin along the light spin angular momentum and generates a
spin current along the film normal. The effective magnetic field is estimated
to be orders of magnitude larger than that caused by the inverse Faraday effect
(IFE) in typical transition metals. We consider the small effective mass and
the large $g$-factor, characteristics of Dirac semimetals with strong spin
orbit coupling, are responsible for the giant IFE, opening pathways to develop
systems with strong light-spin coupling.",2009.01388v1
2020-09-07,Graded Index Confined Spin Waves in an Intermediate Domain Wall,"We propose a mathematical model for describing propagating confined modes in
domain walls of intermediate angle between domains. The proposed model is
derived from the linearised Bloch equations of motion and after reasonable
assumptions, in the scenario of a thick enough magnetic patch, are accounted.
The model shows that there is a clear dependence of the local wavenumber of the
confined spin wave on the local angle of the wall and excitation frequency
used, which leads to the definition of a local index of refraction in the wall
as a function of such angle and frequency. Therefore, the model applies to 1-D
propagating modes, although it also has physical implications for 2-D scenarios
where a domain wall merges with a saturated magnetic region. Micromagnetic
simulations are in good agreement with the predictions of the model and also
give insight on the effects of curved finite structures may have on the
propagating characteristics of spin waves in domain walls.",2009.03195v2
2020-11-27,d0 Ferromagnetism in Ag-doped Monoclinic ZrO2 Compounds,"Recently d0 or intrinsic ferromagnetism was believed to provide an
alternative pathway to transition metal induced ferromagnetism in oxide. In
pursuit of augmenting the area of d0 ferromagnetism; we have undertaken to
study the crystal structure and magnetic properties of Ag-doped ZrO2 compounds.
Polycrystalline samples of Zr1-xAgxO2 (with x=0, 0.02, 0.04, 0.06 and 0.08)
were prepared by solid-state reaction route. All the prepared compounds are
found to crystallize in monoclinic symmetry of ZrO2. In our study, pure ZrO2
compound exhibits paramagnetic behavior. However, the Ag-doped ZrO2 compounds
exhibit ferromagnetic to paramagnetic transition. The Curie temperature was
found to increase from 28.7 K for x=0.02 to 173.2 K for x= 0.08 doped ZrO2.
Thus, the introduction of Ag in ZrO2 induces ferromagnetism with a large
ThetaC. The measurements of hysteresis curves indicate that Ag doped ZrO2
compounds exhibit hysteresis loops with a coercivity of around 1350 Oe.
Moreover, increase in Ag concentration resulted increase in the value of
saturation magnetization (MS); the maximum value of MS was recorded as 0.01
{\mu}B/Ag ion for x= 0.06 sample. The sintering of sample at high temperature
(13500C) diminishes the ferromagnetism and it leads to paramagnetic behaviour.",2011.13727v1
2020-12-17,Electromagnetic ion cyclotron instability stimulated by the suprathermal ions in space plasmas: A quasi-linear approach,"In collision-poor space plasmas protons with an excess of kinetic energy or
temperature in direction perpendicular to background magnetic field can excite
the electromagnetic ion cyclotron (EMIC) instability. This instability is
expected to be highly sensitive to suprathermal protons, which enhance the
high-energy tails of the observed velocity distributions and are well
reproduced by the (bi-)Kappa distribution functions. In this paper we present
the results of a refined quasilinear (QL) approach, able to describe the
effects of suprathermal protons on the extended temporal evolution of EMIC
instability. It is thus shown that suprathermals have a systematic stimulating
effect on the EMIC instability, enhancing not only the growth rates and the
range of unstable wave-numbers, but also the magnetic fluctuating energy
density reached at the saturation. In effect, the relaxation of anisotropic
temperature becomes also more efficient, i.e., faster in time and closer to
isotropy.",2012.09899v1
2021-03-10,Crystal Growth of a New 8H Perovskite Sr8Os6.3O24 Exhibiting High TC Ferromagnetism,"Single crystals of a new twinned hexagonal perovskite compound Sr8Os6.3O24
have been synthesized, and structural and magnetic properties have been
determined. The compound crystallizes in a hexagonal cell with lattice
parameters a = 9.6988(3) {\AA} and c = 18.1657(5) {\AA}. The structure is an
eight-layered hexagonal B-site deficient perovskite with the layer sequence
(ccch)2 and represents the first example of a hexagonal structure among 5d
oxides adopting a twin option. The sample shows spontaneous ferromagnetic
magnetization below 430 K with a small saturation moment of 0.11 {\mu}B/Os ion.
This is the highest Curie temperature (TC) reported for any bulk perovskite
containing only 5d ions at the B site.",2103.06305v1
2021-04-30,Spin polarization and magnetotransport properties of systematically disordered $\mathrm{Fe}_{60}\mathrm{Al}_{40}$ thin films,"We investigate the evolution of spin polarization, spontaneous Hall angle
(SHA), saturation magnetization and Curie temperature of $B2$-ordered
Fe$_{60}$Al$_{40}$ thin films under varying antisite disorder, induced by
Ne$^{+}$-ion irradiation. The spin polarization increases monotonically as a
function of ion fluence. A relatively high polarization of 46 % and the SHA of
3.1 % are achieved on 40 nm thick films irradiated with 2 $\cdot$ 10$^{16}$
ions/cm$^2$ at 30 keV. An interesting divergence in the trends of the
magnetization and SHA is observed for low disorder concentrations. The high
spin polarization and its broad tunability range make ion-irradiated
Fe$_{60}$Al$_{40}$ a promising material for application in spin electronic
devices.",2104.14792v1
2021-05-11,First-principles calculations and experimental studies on Co2FeGe Heusler alloy nanoparticles for spintronics applications,"Here, we report the synthesis and physical properties of Co2FeGe (CFG)
Heusler alloy (HA) nanoparticles (NPs). The NPs of size 23 nm are prepared
using the co-precipitation method. X-ray and selected area electron diffraction
patterns have confirmed the cubic Heusler phase of the NPs with the
A2-disorder. These NPs are soft ferromagnetic, and exhibit a high saturation
magnetization (Ms) along with a very high Curie temperature (Tc) of 1060 K. The
observed Tc value matches closely with the theoretically calculated one
following a model provided by Wurmehl et al. [1]. The high Ms and Tc make the
present system a potential candidate for magnetically activated nano-devices
working at high temperatures. The near-integral value 5.9 mehoB/f.u. of Ms at
low temperatures indicates that the half-metallic ferromagnetism is preserved
even in the particles even on the 20 nm length scale. Additionally, we have
facilitated the existing HA-NP preparation method, which can be used in
synthesizing other HA-NPs. The first-principles density functional theory
computations complement the experimental results.",2105.05200v1
2021-06-14,Linear unsaturated magnetoresistance in YSi single crystal,"Linear magnetoresistance is a phenomenon that has been observed in a few
topological compounds that originate from classical and quantum phenomena.
Here, we performed electrical transport measurements, in zero and applied
magnetic fields, on the YSi single crystal along all three principal
crystallographic directions of the orthorhombic crystal structure. For
$I~\parallel~[001]$ and $H~\parallel~[100]$ direction above $\approx 10$~T,
mobility fluctuation driven linear magnetoresistance is observed without any
sign of saturation up to $14$~T magnetic field. Anisotropy in the Fermi surface
is immanent from the angular dependence of the magnetoresistance. Kohler rule
violation is observed in this system and Hall data signifies multiple charge
carriers in YSi.",2106.07264v1
2021-06-16,"Unusual dynamic susceptibility arising from soft ferromagnetic domains in MnBi8Te13 and Sb-doped MnBi2nTe3n+1 (n=2, 3)","MnBi2nTe3n+1(MBT) is the first intrinsic magnetic topological insulator and
is promising to hostemergent phenomena such as quantum anomalous Hall effect.
They can be made ferromagnetic by having n >= 4 or with Sb doping. We studied
the magnetic dynamics in a few selected ferromag-netic (FM) MBT compounds,
including MnBi8Te13and Sb doped MnBi2nTe3n+1(n= 2,3) usingAC susceptibility and
magneto-optical imaging. Slow relaxation behavior is observed in all
threecompounds, suggesting its universality among FM MBT. We attribute the
origin of the relaxationbehavior to the irreversible domain movements since
they only appear below the saturation fieldswhen ferromagnetic domains form.
The very soft ferromagnetic domain nature is revealed by thelow-field
fine-structured domains and high-field sea-urchin-shaped remanent-state domains
imagedvia our magneto-optical measurements. Finally, we ascribe the rare
""double-peak"" behavior ob-served in the AC susceptibility under small DC bias
fields to the very soft ferromagnetic domainformations.",2106.08969v1
2021-07-13,Phase diagram and spin waves in the frustrated ferro-antiferromagnet SrZnVO(PO4)2,"Single crystals of the frustrated S=1/2 ferro-antiferromagnetic proximate
square lattice material SrZnZnVO(PO$_4$)$_2$ are studied in magnetometric,
calorimetric, neutron diffraction and inelastic neutron scattering experiments.
The measured spin wave spectrum reveals a substantial degree of magnetic
frustration and a large quantum renormalization of the exchange constants. The
H-T magnetic phase diagram is established. It features a novel pre-saturation
phase, which appears for only one particular field orientation. The results are
discussed noting the similarities and differences with the previously studied
and similarly structured Pb$_2$VO(PO$_4$)$_2$ compound.",2107.06114v1
2021-09-04,"Anomalous Hall effect in ferrimagnetic metal RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice","Kagome lattice, made of corner-sharing triangles, provides an excellent
platform for hosting exotic topological quantum states. Here we systematically
studied the magnetic and transport properties of RMn6Sn6 (R = Tb, Dy, Ho) with
clean Mn kagome lattice. All the compounds have a collinear ferrimagnetic
structure with different easy axis at low temperature. The low-temperature
magnetoresistance (MR) is positive and has no tendency to saturate below 7 T,
while the MR gradually declines and becomes negative with the increasing
temperature. A large intrinsic anomalous Hall conductivity about 250
{\Omega}-1cm-1, 40 {\Omega}-1cm-1, 95 {\Omega}-1cm-1 is observed for TbMn6Sn6,
DyMn6Sn6, HoMn6Sn6, respectively. Our results imply that RMn6Sn6 system is an
excellent platform to discover other intimately related topological or quantum
phenomena and also tune the electronic and magnetic properties in future
studies.",2109.01866v1
2021-09-12,Modeling of A Realistic DC Source in A CVSR,"Continuously Variable Series Reactor (CVSR) can adjust the total reactance in
an ac circuit using the saturation characteristic of the ferromagnetic core,
shared by an ac and a dc winding. The bias magnetic flux produced by the dc
winding can regulate the equivalent ac inductance in order to control power
flow, damp oscillations, or limit fault currents. Gyrator-Capacitor approach is
used to model the interface between the magnetic and the electric circuits. Two
different dc control source models are considered: the usual ideal dc source
and a realistic dc source composed of a power electronics-based converter and
an ac voltage source. This paper investigates CVSR's behaviour in terms of
induced voltage across ac winding, flux densities (B) throughout the CVSR core,
and power interchange with the dc control circuit during normal conditions in
both cases.",2109.05568v1
2021-09-16,Large Magnetoresistance and Weak Antilocalization in V1-delta Sb2 Single Crystal,"The binary pnictide semimetals have attracted considerable attention due to
their fantastic physical properties that include topological effects, negative
magnetoresistance, Weyl fermions and large non-saturation magnetoresistance. In
this paper, we have successfully grown the high-quality V1-deltaSb2 single
crystals by Sb flux method and investigated their electronic transport
properties. A large positive magnetoresistance that reaches 477% under a
magnetic field of 12 T at T = 1.8 K was observed. Notably, the
magnetoresistance showed a cusp-like feature at the low magnetic fields and
such feature weakened gradually as the temperature increased, which indicated
the presence of weak antilocalization effect (WAL). The angle-dependent
magnetoconductance and the ultra-large prefactor alpha extracted from the
Hikami-Larkin-Nagaoka equation revealed that the WAL effect is a 3D bulk effect
originated from the three-dimensional bulk spin-orbital coupling.",2109.07736v1
2021-10-09,Enhancement of spin-orbit coupling and magnetic scattering in hydrogenated graphene,"Spin-orbit coupling (SOC) can provide essential tools to manipulate electron
spins in two-dimensional materials like graphene, which is of great interest
for both fundamental physics and spintronics application. In this paper, we
report the low-field magnetotransport of in situ hydrogenated graphene where
hydrogen atoms are attached to the graphene surface in continuous low
temperature and vacuum environment. Transition from weak localization to weak
antilocalization with increasing hydrogen adatom density is observed,
indicating enhancing Bychkov-Rashba-type SOC in a mirror symmetry broken
system. From the low-temperature saturation of phase breaking scattering rate,
the existence of spin-flip scattering is identified, which corroborates the
existence of magnetic moments in hydrogenated graphene.",2110.04477v1
2021-10-12,Large positive magnetoresistance in photocarrier doping potassium tantalites in the extreme quantum limit,"We report on a high-field magnetotransport study of KTaO3 single crystals.
This material is a promising candidate to study in the extreme quantum limit
(EQL). By photocarrier doping with 360 nm light, we have observed a significant
positive, non-saturating, and linear magnetoresistance at low temperatures
accompanied by a vanishing Hall coefficient. When cooled down to 10 K and
subjected to a magnetic field of 12 T, the value of magnetoresistance of KTaO3
(100) is increased by as much as 433%. Such behavior can be attributed to all
electrons occupying only the lowest Landau level in the EQL. In this state, a
quantum magnetoresistance is produced. This result provides novel insights into
the next generation of magnetic devices based on complex materials and adds a
new family of materials with positive magnetoresistance.",2110.05791v1
2021-10-27,SN 2008iy circumstellar interaction: Bright and lesser light effect,"Optical photometry and spectra of the luminous type IIn supernova SN~2008iy
are analysed in detail with implications for cosmic ray acceleration and the
radio emission. The light curve and expansion velocities indicate ejecta with
the kinetic energy of $3\times10^{51}$ erg to collide with the $\sim10$ Msun
circumstellar envelope. The luminous Ha is explained as originated primarily
from circumstellar clouds interacting with the forward shock. For the first
time the fluorescent OI 8446A emission is used to demonstrate that the cloud
fragmentation cascade spans a scale range > 2.3 dex. The narrow circumstellar
Ha permitted us to estimate the acceleration efficiency of cosmic rays. The
found value is close to the efficiency inferred in the same way for other two
SNe~IIn, SN~1997eg and SN~2002ic. The efficiency of cosmic ray acceleration is
utilized to reproduce the radio flux from SN~2008iy for the amplified magnetic
field consistent with the saturated turbulent magnetic field in the diffusive
shock acceleration mechanism.",2110.14409v1
2021-11-12,The QCD Adler function and the muon $g-2$ anomaly from renormalons,"We describe the Adler function in Quantum Chromodynamics using a transseries
representation within a resurgent framework. The approach is based on a
Borel-Ecalle resummation of the infrared renormalons combined with an effective
running for the strong coupling. The new approach is flexible enough to give
values in agreement with the current Adler function determinations. We then
apply our finding to the muon's anomalous magnetic moment studying the
possibility of saturating, solely in terms of the vacuum polarization function,
the current discrepancy between the best Standard Model value for the muon's
anomalous magnetic moment and the experimental value obtained by the most
recent muon g-2 collaboration. The latter shows that the Adler function's new
representation can also be consistent with recent lattice determinations.",2111.06792v3
2021-12-23,NMR evidence against a spin-nematic nature of the presaturation phase in the frustrated magnet SrZnVO(PO4)2,"Using $^{31}$P nuclear magnetic resonance (NMR) we investigate the recently
discovered presaturation phase in the highly frustrated two-dimensional spin
system SrZnVO(PO$_4$)$_2$ [F. Landolt et al., Phys. Rev. B 104, 224435 (2021)].
Our data provide two pieces of evidence against the presumed spin-nematic
character of this phase: i) NMR spectra reveal that it hosts a dipolar spin
order and ii) the 1/$T_1$ relaxation rate data recorded above the saturation
field can be fitted by the sum of a single-magnon term, exponential in the gap,
and a critical second-order term, exponential in the triple gap, leaving no
space for a nematic spin dynamics, characterized by a double-gap exponential.
We explain the unexpectedly broad validity of the simple fit and the related
critical spin dynamics.",2112.12603v2
2022-02-01,Numerical Model Of Harmonic Hall Voltage Detection For Spintronic Devices,"We present a numerical macrospin model for harmonic voltage detection in
multilayer spintronic devices. The core of the computational backend is based
on the Landau-Lifshitz-Gilbert-Slonczewski equation, which combines high
performance with satisfactory, for large-scale applications, agreement with the
experimental results. We compare the simulations with the experimental findings
in Ta/CoFeB bilayer system for angular- and magnetic field-dependent resistance
measurements, electrically detected magnetisation dynamics, and harmonic Hall
voltage detection. Using simulated scans of the selected system parameters such
as the polar angle $\theta$, magnetisation saturation
($\mu_\textrm{0}M_\textrm{s}$) or uniaxial magnetic anisotropy ($K_\textrm{u}$)
we show the resultant changes in the harmonic Hall voltage, demonstrating the
dominating influence of the $\mu_\textrm{0}M_\textrm{s}$ on the first and
second harmonics. In the spin-diode ferromagnetic resonance (SD-FMR) technique
resonance method the ($\mu_\textrm{0}M_\textrm{s}$, $K_\textrm{u}$) parameter
space may be optimised numerically to obtain a set of viable curves that fit
the experimental data.",2202.00364v1
2022-02-17,The role of slow magnetostrophic waves in the formation of the axial dipole in planetary dynamos,"The preference for the axial dipole in planetary dynamos is investigated
through the analysis of wave motions in spherical dynamo models. Our study
focuses on the role of slow magnetostrophic waves, which are generated from
localized balances between the Lorentz, Coriolis and buoyancy (MAC) forces.
Since the slow waves are known to intensify with increasing field strength,
simulations in which the field grows from a small seed towards saturation are
useful in understanding the role of these waves in dynamo action. Axial group
velocity measurements in the energy-containing scales show that fast inertial
waves slightly modified by the magnetic field and buoyancy are dominant under
weak fields. However, the dominance of the slow waves is evident for strong
fields satisfying $|\omega_M/\omega_C| \sim $ 0.1, where $\omega_M$ and
$\omega_C$ are the frequencies of the Alfv\'en and inertial waves respectively.
A MAC wave window of azimuthal wavenumbers is identified wherein helicity
generation by the slow waves strongly correlates with dipole generation.
Analysis of the magnetic induction equation suggests a poloidal--poloidal field
conversion in the formation of the dipole. Finally, the attenuation of slow
waves may result in polarity reversals in a strongly driven Earth's core.",2202.08784v1
2022-03-09,Exchange spin waves in thin films with gradient composition,"We report investigation of ferromagnetic resonance phenomenon in
ferromagnetic thin films with essentially non-uniform composition. Epitaxial
Pd-Fe thin film with linear distribution of Fe content across the thickness is
used as the model material. Anomalous perpendicular standing spin waves are
observed and quantified using the collective dynamic equation. Numerical
analysis yields the exchange stiffness constant for diluted Pd-Fe alloy
$D=2A/\mu_0M_s=15$~T$\cdot$nm$^2$ and the ratio of the effective magnetization
to the saturation magnetization $M_{eff}/M_s=1.16$. It is demonstrated that,
overall, engineering of thin films with non-uniform composition across the
thickness can be used for high-frequency or low-field magnonic operations using
exchange spin waves.",2203.05014v1
2022-03-22,Nonlinear magnetoconductivity in Weyl and multi-Weyl semimetal in quantizing magnetic field,"Magnetotransport and magneto-optics experiments offer a very powerful probe
for studying the physical properties of materials. Here, we investigate the
second-order nonlinear magnetoconductivity of tilted type-I Weyl and multi-Weyl
semimetal. In contrast to the presence of chiral anomaly in the linear response
regime, we show that Weyl semimetal do not host chiral charge pumping in the
nonlinear transport regime. We predict that an inversion symmetry broken and
tilted Weyl semimetal can support finite longitudinal nonlinear
magnetoconductivity, which is otherwise absent in untilted Weyl semimetal. The
nonlinear magnetoconductivity vanishes in the ultra-quantum limit, oscillates
in the intermediate magnetic field regime and saturates in the semiclassical
limit. The nonlinear magnetoconductivity depends intricately on the tilt
orientation, and it can be used to determine the tilt orientation in Weyl and
multi-Weyl semimetals, via nonlinear magnetoresistivity or second harmonic
generation experiments.",2203.11980v2
2022-03-23,Topological Hybrids of Magnons and Magnon Bound Pairs,"We consider quantum condensed matter systems without particle-number
conservation. Since the particle number is not a good quantum number, states
belonging to different particle-number sectors can hybridize, which causes
topological anticrossings in the spectrum. The resulting spectral gaps support
chiral edge excitations whose wavefunction is a superposition of states in the
two hybridized sectors. This situation is realized in fully saturated
spin-anisotropic quantum magnets without spin conservation, in which single
magnons hybridize with magnon bound pairs, i.e., two-magnon bound states. The
resulting chiral edge excitations are exotic composites that carry mixed
spin-multipolar character, inheriting spin-dipolar and spin-quadrupolar
character from their single-particleness and two-particleness, respectively. In
contrast to established topological magnons, the topological effects discussed
here are of genuine quantum mechanical origin and vanish in the classical
limit. We discuss implications for both intrinsic anomalous Hall-type transport
and beyond-spintronics computation paradigms. We conclude that fully polarized
quantum magnets are a promising platform for topology caused by hybridizations
between particle-number sectors, complementing the field of ultracold atoms
working with a conserved number of particles.",2203.12374v1
2022-05-23,Linear Flavor-Wave Analysis of SU(4)-Symmetric Tetramer Model with Population Imbalance,"We study the quantum magnetism of the SU(4) Mott insulator in a square
optical superlattice, in which atoms with four nuclear-spin components strongly
interact with each other, in the presence of an external field that controls
the imbalance between the population of two components and that of the other
two. This is a natural extension of the physics of spin-dimer materials under
strong magnetic field. We apply an extended linear flavor-wave theory based on
four-site plaquettes and unveil the ground-state phase diagram and excitation
spectra. When the population of the four components is balanced and the
plaquesttes are weakly coupled, the ground state is approximately given by the
direct product of local SU(4)-singlet states. In high-field, the system reaches
a ""saturated state"" where only two components are present. Our main finding is
a nontrivial intermediate phase, which has a checkerboard-like arrangement of
the SU(4)-singlet and four-site resonating-valence-bond states.",2205.11155v1
2022-06-14,Locked mode disruptions in DIII-D and application to ITER,"Disruptions are a serious problem in tokamaks, in which thermal and magnetic
energy confinement is lost. This paper uses data from the DIII-D experiment,
theory, and simulations to demonstrate that resistive wall tearing modes (RWTM)
produce the thermal quench (TQ) in a typical locked mode shot. Analysis of the
linear RWTM dispersion relation shows the parameter dependence of the growth
rate, particularly on the resistive wall time. Linear simulations of the locked
mode equilibrium show that it is unstable with a resistive wall, and stable
with an ideally conducting wall. Nonlinear simulations demonstrate that the
RWTM grows to sufficient amplitude to cause a complete thermal quench. The RWTM
growth time is proportional to the thermal quench time. The nonlinearly
saturated RWTM magnetic perturbation amplitude agrees with experimental
measurements. The onset condition is that the q = 2 rational surface is
sufficiently close to the resistive wall. Collectively, this identifies the
RWTM as the cause of the TQ. In ITER, RWTMs will produce long TQ times compared
to present-day experiments. ITER disruptions may be significantly more benign
than previously predicted.",2206.06773v2
2022-07-12,Photonic heat transport from weak to strong coupling,"Superconducting circuits provide a favorable platform for quantum
thermodynamic experiments. An important component for such experiments is a
heat valve, i.e. a device which allows one to control the heat power flowing
through the system. Here we theoretically study the heat valve based on a
superconducting quantum interference device (SQUID) coupled to two heat baths
via two resonators. The heat current in such system can be tuned by magnetic
flux. We investigate how does the heat current modulation depend on the
coupling strength g between the SQUID and the resonators. In the weak coupling
regime the heat current modulation grows as g2, but, surprisingly, at the
intermediate coupling it can be strongly suppressed. This effect is linked to
the resonant nature of the heat transport at weak coupling, where the heat
current dependence on the magnetic flux is a periodic set of narrow peaks. At
the intermediate coupling, the peaks become broader and overlap, thus reducing
the heat modulation. At very strong coupling the heat modulation grows again
and finally saturates at a constant value.",2207.05586v1
2022-07-29,Three-Dimensional Neutron Far-Field Tomography of a Bulk Skyrmion Lattice,"Skyrmions are topologically-protected spin textures thought to nucleate and
annihilate on points of vanishing magnetization, called Bloch points. However,
owing to a lack of bulk techniques, experimental visualizations of skyrmion
lattices and their stabilization through defects in three-dimensions remain
elusive. Here, we present a tomographic algorithm applied to a
Co$_8$Zn$_8$Mn$_4$ skyrmion lattice host, processing multi-projection small
angle neutron scattering measurements to generate mean scattering feature
reconstructions (MSFR) of the bulk spin textures. Digital phantoms validated
the algorithm; reconstructions of the sample show a disordered skyrmion lattice
with a topological saturation of 63~\%, exhibiting three-dimensional
topological transitions through two different emergent (anti)monopole defect
pathways with densities of 147~$\mu$m$^{-3}$ and 21~$\mu \mathrm{m}^{-3}$ for
branching and segmentation events, respectively. Our techniques produce
experimentally-informed visualizations of bulk skyrmion lattice structures and
defects, enabling future bulk studies over a wide variety of sample shapes and
chemistries, magnetic phases, and external parameters.",2208.00023v1
2022-08-31,Possible origin of extremely large magnetoresistance in the topological insulator CaBi2 single crystal,"CaBi2 has been experimentally found to be a superconductor with a transition
temperature of 2 K and identified as a topological insulator via spin- and
angle-resolved photoemission spectroscopy, which makes it a possible platform
to study the interplay between superconductivity and topology. But the detailed
transport properties for CaBi2 single crystal remain unexplored in experiments.
Here, we systematically studied the magneto-transport properties of CaBi2
single crystal grown by a flux method. CaBi2 shows a magnetic-field-induced
upturn behavior with a plateau in resistivity at low temperature. An extremely
large and non-saturating magnetoresistance up to ~15000% at 3 K and 12 T was
achieved. The possible reason for the magnetic field and temperature dependence
of resistivity and extremely large magnetoresistance at low temperature was
discussed by adopting the Kohler's scaling law, which can be understood by the
compensation effect confirmed by the Hall Effect measurement.",2208.14595v1
2022-11-08,Short-distance constraints on the hadronic light-by-light,"The muon anomalous magnetic moment continues to attract interest due to the
potential tension between experimental measurement [1,2] and the Standard Model
prediction [3]. The hadronic light-by-light contribution to the magnetic moment
is one of the two diagrammatic topologies currently saturating the theoretical
uncertainty. With the aim of improving precision on the hadronic light-by-light
in a data-driven approach founded on dispersion theory [4,5], we derive various
short-distance constraints of the underlying correlation function of four
electromagnetic currents. Here, we present our previous progress in the purely
short-distance regime and current efforts in the so-called Melnikov-Vainshtein
limit.",2211.04068v1
2022-11-20,Spin-wave spectra in antidot lattice with inhomogeneous perpendicular magnetocrystalline anisotropy,"Magnonic crystals are structures with periodically varied magnetic properties
that are used to control collective spin-wave excitations. With micromagnetic
simulations, we study spin-wave spectra in a 2D antidot lattice based on a
multilayered thin film with perpendicular magnetic anisotropy (PMA). We show
that the modification of the PMA near the antidot edges introduces interesting
modifications to the spin-wave spectra, even in a fully saturated state. In
particular, the spectra split in two types of excitations, bulk modes with
amplitude concentrated in a homogeneous part of antidot lattice, and edge modes
with an amplitude localized in the rims of reduced PMA at the antidot edges.
Their dependence on the geometrical or material parameters is distinct but at
resonance conditions fulfilled, we found strong hybridization between bulk and
radial edge modes. Interestingly, the hybridization between the fundamental
modes in bulk and rim is of magnetostatic origin but the exchange interactions
determine the coupling between higher-order radial rim modes and the
fundamental bulk mode of the antidot lattice.",2211.11002v1
2022-12-05,Probing Accretion Turbulence in the Galactic Center with EHT Polarimetry,"Magnetic fields grown by instabilities driven by differential rotation are
believed to be essential to accretion onto black holes. These instabilities
saturate in a turbulent state; therefore, the spatial and temporal variability
in the horizon-resolving images of Sagittarius A* (Sgr A*) will be able to
empirically assess this critical aspect of accretion theory. However,
interstellar scattering blurs high-frequency radio images from the Galactic
center and introduces spurious small-scale structures, complicating the
interpretation of spatial fluctuations in the image. We explore the impact of
interstellar scattering on the polarized images of Sgr A* and demonstrate that
for credible physical parameters, the intervening scattering is
non-birefringent. Therefore, we construct a scattering mitigation scheme that
exploits horizon-resolving polarized millimeter/submillimeter VLBI observations
to generate statistical measures of the intrinsic spatial fluctuations and
therefore the underlying accretion flow turbulence. An optimal polarization
basis is identified, corresponding to measurements of the fluctuations in
magnetic field orientation in three dimensions. We validate our mitigation
scheme using simulated data sets and find that current and future ground-based
experiments will readily be able to accurately measure the image-fluctuation
power spectrum.",2212.02544v1
2022-12-19,Towards an effective action for chiral magnetohydrodynamics,"We consider chiral magnetohydrodynamics, i.e. a finite-temperature system
where an axial $U(1)$ current is not conserved due to an Adler-Bell-Jackiw
anomaly saturated by the dynamical operator $F_{\mu\nu} \tilde{F}^{\mu\nu}$. We
express this anomaly in terms of the 1-form symmetry associated with magnetic
flux conservation and study its realization at finite temperature. We present
Euclidean generating functional and dissipative action approaches to the
dynamics and reproduce some aspects of chiral MHD phenomenology from an
effective theory viewpoint, including the chiral separation and magnetic
effects. We also discuss the construction of non-invertible axial symmetry
defect operators in our formalism.",2212.09787v1
2023-02-06,Interaction-induced Metal to Topological Insulator Transition,"By means of exact diagonalizations, the Bernevig-Hughes-Zhang model at
quarter-filling in the limit of strong Hubbard on-site repulsion is
investigated. We find that the non-interacting metallic state will be turned
into a Chern insulator with saturated magnetization under strong correlations.
That is, at such a metal-insulator transition, both the topological and the
magnetic properties of the system are changed due to spontaneous breaking of
time reversal symmetry in the ground states. According to our findings, this
topological phase transition seems to be of first order. Our results illustrate
the interesting physics in topological Mott transitions and provide guidance to
the search of more interaction-induced topological phases in similar systems.",2302.02771v1
2023-04-18,A Positive Energy Theorem for AdS Solitons,"The uncharged AdS$_4$ soliton has been recently shown to be continuously
connected to a magnetic, supersymmetric AdS$_4$ soliton within $\mathcal{N}=8$
gauged supergravity. By constructing the asymptotic superalgebra, we establish
a positive energy theorem for the magnetic AdS$_4$ solitons admitting
well-defined asymptotic Killing spinors, antiperiodic on a contractible $S^1$.
We show that there exists only one discrete solution endowed with these
boundary conditions satisfying the bound, the latter being saturated by the
null energy supersymmetric configuration. Despite having negative energy, the
uncharged AdS$_4$ soliton does not contradict the positive energy theorem, as
it does not admit well-defined asymptotic Killing spinors.",2304.09201v2
2023-05-06,Giant magnetostriction in La2CoMnO6 synthesized by microwave irradiation,"Polycrystalline insulating ferromagnetic double perovskite La2CoMnO6
possessing monoclinic structure and a high ferromagnetic Curie temperature (TC
= 222 K) was rapidly synthesized ( 30 min) by irradiating stoichiometric
mixture of oxides with the microwave. The sample exhibits negative
magnetostriction, i.e., contraction of length along the magnetic field
direction in the ferromagnetic state. At 10 K, the parallel magnetostriction
does not show saturation up to a magnetic field of 50 kOe where it reaches 610
ppm which is one of the highest values of magnetostriction found so far among
perovskite oxides with 3d ions. The magnitude of magnetostriction decreases
monotonically as the temperature increases and becomes negligible above TC. The
giant magnetostriction in this double perovskite is suggested to originate from
large spin-orbit coupling associated with Co2+ (d7) cation. The obtained
magnetostriction value is comparable to 630 ppm in an identical composition
obtained through solid-state reaction over several days in a conventional
furnace which indicates the advantages of microwave-assisted synthesis in
saving reaction time and electric power without deteriorating physical
properties.",2305.03886v1
2023-05-22,Singlet quantum phases and magnetization of the frustrated spin-1/2 ladder with ferromagnetic (F) exchange in legs and alternating F-AF exchange in rungs,"The magnetization $M(h)$ is used to identify three singlet quantum phases of
the ladder with isotropic exchange interactions. The Dimer phase with
frustrated F exchanges in rungs and legs has a first-order $M(h)$ transition at
$0$ K from singlet to ferromagnetic at the saturation field $h_s$. The
Haldane-DAF phase with strong F exchange in rungs and net AF exchange between
rungs has continuous $M(h)$ and is adiabatically connected to the $S = 1$
Heisenberg AF chain. The AF phase with strong F exchange in legs and net AF
exchange between legs has continuous $M(h)$ and is adiabatically connected to
the spin-1/2 $J_1-J_2$ model with $J_1 > 0$ and $J_2 < 0$. All three singlet
phases have finite gaps to the lowest triplet state.",2305.12884v1
2023-06-20,Tayler-Spruit dynamos in simulated radiative stellar layers,"The Tayler-Spruit dynamo mechanism has been proposed two decades ago as a
plausible mechanism to transport angular momentum in radiative stellar layers.
Direct numerical simulations are still needed to understand its trigger
conditions and the saturation mechanisms. The present study follows up on
(Petitdemange et al. 2023), where we reported the first numerical simulations
of a Tayler-Spruit dynamo cycle. Here we extend the explored parameter space to
assess in particular the influence of stratification on the dynamo solutions.
We also present numerical verification of theoretical assumptions made in
(Spruit 2002), which are instrumental in deriving the classical prescription
for angular momentum transport implemented in stellar evolution codes. A
simplified radiative layer is modeled numerically by considering the dynamics
of a stably-stratified, differentially rotating, magnetized fluid in a
spherical shell. Our simulations display a diversity of magnetic field
topologies and amplitudes depending on the flow parameters, including
hemispherical solutions. The Tayler-Spruit dynamos reported here are found to
satisfy magnetostrophic equilibrium and achieve efficient turbulent transport
of angular momentum, following Spruit's heuristic prediction.",2306.11711v3
2023-06-29,Zeeman field-induced two-dimensional Weyl semimetal phase in cadmium arsenide,"We report a topological phase transition in quantum-confined cadmium arsenide
(Cd3As2) thin films under an in-plane Zeeman field when the Fermi level is
tuned into the topological gap via an electric field. Symmetry considerations
in this case predict the appearance of a two-dimensional Weyl semimetal (2D
WSM), with a pair of Weyl nodes of opposite chirality at charge neutrality that
are protected by space-time inversion (C2T) symmetry. We show that the 2D WSM
phase displays unique transport signatures, including saturated resistivities
on the order of h/e^2 that persist over a range of in-plane magnetic fields.
Moreover, applying a small out-of-plane magnetic field, while keeping the
in-plane field within the stability range of the 2D WSM phase, gives rise to a
well-developed odd integer quantum Hall effect, characteristic of degenerate,
massive Weyl fermions. A minimal four-band k.p model of Cd3As2, which
incorporates first-principles effective g factors, qualitatively explains our
findings.",2306.16794v1
2023-07-04,Normal state magneto transport properties of FeSe$_{0.5}$Te$_{0.5}$ superconductor: The role of topological surface states,"Doped Iron Chalcogenide (FeCh) superconductors are extensively studied in the
context of topological superconductivity. However, the evidence of topological
surface states in electrical transport measurements of the doped FeCh system is
yet warranted. In the present letter, we performed angle-dependent magneto
transport measurements on a single crystal of a doped FeCh system, i.e.,
FeSe$_{0.5}$Te$_{0.5}$. A non-saturating linear magnetoresistance (MR) has been
observed under the magnetic field up to 14 T in the normal state of
FeSe$_{0.5}$Te$_{0.5}$. The MR is shown to possess anisotropy, which indicates
the presence of topological surface states in FeSe$_{0.5}$Te$_{0.5}$.
Angle-dependent Magneto-conductivity (MC) at low magnetic fields has been
modelled by Hikami Larkin Nagaoka (HLN) formalism, which shows the presence of
weak antilocalization (WAL) effect in FeSe$_{0.5}$Te$_{0.5}$. The observed WAL
effect is found to be 2D in nature through angle-dependent magneto transport
measurements. Theoretical calculations based on Density Functional Theory (DFT)
are also performed to get more confidence on the presence of topological
surface states in FeSe$_{0.5}$Te$_{0.5}$.",2307.01476v1
2023-09-06,Charge-transfer-driven enhanced room-temperature ferromagnetism in BiFeO$_3$/Ag nanocomposite,"We report observation of more than an order of magnitude jump in saturation
magnetization in BiFeO$_3$/Ag nanocomposite at room temperature compared to
what is observed in bare BiFeO$_3$ nanoparticles. Using transmission electron
microscopy together with energy dispersive x-ray spectra (which maps the
element concentration across the BiFeO$_3$/Ag interface) and x-ray
photoelectron spectroscopy, we show that both the observed specific
self-assembly pattern of BiFeO$_3$ and Ag nanoparticles and the charge transfer
between Ag and O are responsible for such an enormous rise in room-temperature
magnetization. The BiFeO$_3$/Ag nanocomposites, therefore, could prove to be
extremely useful for a variety of applications including biomedical.",2309.02845v1
2023-09-18,Large Nonreciprocity of Shear-Horizontal Surface Acoustic Waves induced by Magnetoelastic Bilayers,"We report large nonreciprocity in the transmission of shear-horizontal
surface acoustic waves (SAWs) on LiTaO3 substrate coated with a FeCoSiB/NiFeCu
magnetoelastic bilayer. The large difference in saturation magnetization of the
two layers not only brings nonreciprocal spin waves (SWs), but also ensures the
phonon-magnon (SAWs-SWs) coupling at relatively low wavenumbers. It is found
that the angle between the magnetization and the wavevector play important
roles in determining the strength of magnetoelastic coupling and
nonreciprocity, simultaneously. A large nonreciprocal transmission of SAWs
about 30 dB (i.e. 60 dB/mm) is demonstrated at 2.33 GHz. In addition, the
dispersion relation between coupled SH-SAWs and nonreciprocal SWs is developed,
which provide a good insight into the observed phenomena. Our results offer a
convenient approach to implement nonreciprocal SAW isolators or circulators.",2309.09521v1
2023-09-21,High-Field Optical Cesium Magnetometer for Magnetic Resonance Imaging,"We present a novel high-field optical quantum magnetometer based on saturated
absorption spectroscopy on the extreme angular-momentum states of the cesium D2
line. With key features including continuous readout, high sampling rate, and
sensitivity and accuracy in the ppm-range, it represents a competitive
alternative to conventional techniques for measuring magnetic fields of several
teslas. The prototype has four small separate field probes, and all support
electronics and optics are fitted into a single 19-inch rack to make it
compact, mobile, and robust. The field probes are fiber coupled and made from
non-metallic components, allowing them to be easily and safely positioned
inside a 7 T MRI scanner. We demonstrate the capabilities of this magnetometer
by measuring two different MRI sequences, and we show how it can be used to
reveal imperfections in the gradient coil system, to highlight the potential
applications in medical MRI. We propose the term EXAAQ (EXtreme
Angular-momentum Absorption-spectroscopy Quantum) magnetometry, for this novel
method.",2309.12006v2
2023-10-09,Spatial asymmetry of optically excited spin waves in anisotropic ferromagnetic film,"We analytically discuss and micromagnetically prove the ways to tune the
spatial asymmetry of the initial phase, amplitude, and wavevectors of
magnetostatic waves driven by ultrafast laser excitation. We consider that the
optical pulse heats a thin ferromagnetic metallic film and abruptly decreases
the saturation magnetization and the parameter of uniaxial anisotropy. The two
corresponding terms of laser-induced torque have different azimuthal
symmetries, with the 4-fold symmetry of the demagnetization-related term, and
the isotropic distribution of the anisotropy-related term. As a result, the
initial phase and amplitude of excited magnetostatic waves have a non-trivial
azimuthal distribution tunable with the angle between the external magnetic
field and anisotropy axis, and the laser spot diameter. Moreover, the variation
of these parameters tunes the distribution of wavevectors, resulting in
additional asymmetry between the spectral components of the waves propagating
in different directions.",2310.05895v1
2023-10-10,Helically-trapped electron mode in optimized stellarator,"Global gyrokinetic simulations find a strong helically-trapped electron mode
(HTEM) driven by density gradients in the optimized stellarator W7-X fusion
experiment. The eigenmode structure localizes in the inner side of the torus
with an unfavorable magnetic curvature and weak magnetic field, where there is
a large fraction of helically-trapped electrons. The mode is excited mostly by
the ion free energy and propagates in the ion direction with a linear frequency
much smaller than the diamagnetic frequency. The instability saturates by
nonlinear processes of turbulence spreading in the real space and spectral
transfer from unstable to damped regions. The steady state HTEM turbulence
drives a large particle flux that may have significant implications for the
confinement of fusion fuel and removal of fusion ash in the stellarator
reactor.",2310.06988v1
2023-11-09,Squeezing Bose-Bose liquid drops,"We explore ultradilute Bose-Bose liquid droplets squeezed by an external
harmonic potential in one spatial direction. Our theoretical study is based on
a functional that is built using quantum Monte Carlo results of the bulk phase
and incorporates finite-range effects. A characteristic feature of these drops
is the existence of a critical atom number, that is the minimum number of
particles to have a many-body bound state. We report results on the critical
atom numbers for different magnetic fields and applying confinement strengths
towards a quasi-two-dimensional setup. In the regime where the local density
approximation is expected to be valid, we find that the critical atom number
decreases linearly with the harmonic oscillator length of the confining
potential. With the largest squeezing explored in our work, we predict stable
drops at the level of one thousand atoms. Our functional reduces the critical
numbers for any confinement and applied magnetic field with respect to the
estimations based on the Lee-Huang-Yang model. We observe saturated drops when
the number of atoms in the drop is much larger than the critical value, their
central density being higher for the quantum Monte Carlo functional than for
the Lee-Huang-Yang one.",2311.05244v1
2023-11-23,Exciting high-frequency short-wavelength spin waves using high harmonics of a magnonic cavity mode,"Confined spin-wave modes are a promising object for studying nonlinear
effects and future quantum technologies. Here, using micromagnetic simulations,
we use a microwave magnetic field from a coplanar waveguide (CPW) to pump a
standing spin-wave confined in the cavity of magnonic crystal. We find that the
frequency of the fundamental cavity mode is equal to the ferromagnetic
resonance frequency of the plane film and overlaps with the magnonic bandgap,
allowing high magnetic field tunability. Multi-frequency harmonics of the
cavity mode are generated once the microwave amplitude surpasses a certain
threshold. Specifically, the second and third harmonics at 0.5 T equate to 48.6
and 72.9 GHz with wavelengths of 44 and 22 nm respectively, which propagate
into the crystal. This effect reaches saturation when the CPW covers the entire
cavity, making the system feasible for realization. These processes show
potential for the advancement of magnonics at high-frequencies and very
short-wavelengths.",2311.14143v1
2023-12-05,Miniaturized Double-Wing Delta-E Effect Sensors,"Magnetoelastic composites are integral elements of sensors and actuators
utilizing magnetostriction for their functionality. Their sensitivity typically
scales with the saturation magnetostriction and inversely with magnetic
anisotropy. However, this makes the devices prone to minuscule residual
anisotropic stress from the fabrication process, impairing their performance
and reproducibility, hence limiting their suitability for arrays. This study
presents a shadow mask deposition technology combined with a free-free
magnetoelectric microresonator design intended to minimize residual stress and
inhomogeneity in the magnetoelastic layer. Resonators are experimentally and
theoretically analyzed regarding local stress anisotropy, magnetic anisotropy,
and the {\Delta}E effect in several resonance modes. Further, the sensitivity
is analyzed in the example of {\Delta}E-effect sensors. The results demonstrate
a device-to-device variation of the resonance frequency < 0.2 % with
sensitivities comparable with macroscopic {\Delta}E-effect sensors. The
reproducibility is drastically improved over previous magnetoelastic device
arrays. This development marks a step forward in the reproducibility and
homogeneity of magnetoelastic resonators and contributes to the feasibility of
large-scale, integrated sensor arrays.",2312.02903v1
2024-01-26,Rotational evolution of young-to-old stars with data-driven three-dimensional wind models,"Solar-type stars form with a wide range of rotation rates. A wide range
persists until a stellar age of 0.6 Gyr, after which solar-type stars exhibit
Skumanich spin-down. Rotational evolution models incorporating polytropic
stellar winds struggle to simultaneously reproduce these two regimes, namely
the initially wide range and the Skumanich spin-down without imposing an
a-priori cap on the wind mass-loss rate. We show that a three-dimensional wind
model driven by Alfv\'en waves and observational data yields wind torques that
agree with the observed age distribution of rotation rates. In our models of
the Sun and twenty-seven open cluster stars aged from 0.04 to 0.6 Gyr that have
observationally derived surface magnetic maps and rotation rates, we find
evidence of exponential spin-down in young stars that are rapid rotators and
Skumanich spin-down for slow rotators. The two spin-down regimes emerge
naturally from our data-driven models. Our modelling suggests that the observed
age distribution of stellar rotation rates arises as a consequence of magnetic
field strength saturation in rapid rotators.",2401.14747v1
2024-03-24,Axion-Polaritons in quark stars: a possible solution to the missing pulsar problem,"This paper proposes an alternative mechanism to solve the so-called missing
pulsar problem, a standing paradox between the theoretical expectations about
the number of pulsars that should exist in the galaxy center of the Milky Way
and their absence in the observations. The mechanism is based on the
transformation of incident $\gamma$ rays into hybridized modes, known as
axion-polaritons, which can exist inside highly magnetized quark stars with a
quark matter phase known as the magnetic dual chiral density wave phase. This
phase, which is favored over several other dense matter phases candidates at
densities a few times nuclear saturation density, has already passed several
important astrophysical tests. In the proposed mechanism, the absence of young
magnetars occurs because as electromagnetic waves inside the star can only
propagate through the hybridized modes, incident photons coming from a
$\gamma$-ray burst get transformed into massless and massive axion polaritons
by the Primakoff effect. Once thermalized, the massive axion-polaritons can
self-gravitate up to a situation where their total mass overpasses the
Chandrasekhar limit for these bosons, producing a mini blackhole that collapses
the star.",2403.17035v1
2000-12-22,The Origin of the Magnetic Fields of the Universe: The Plasma Astrophysics of the Free Energy of the Universe,"(abridged) The interpretation of Faraday rotation measure maps of AGNs within
galaxy clusters has revealed regions, $\sim 50-100$ kpc, that are populated
with large, $\sim 30 \mu$ G magnetic fields. The magnetic energy of these
coherent regions is $\sim 10^{59-60}$ ergs, and the total magnetic energy over
the whole cluster ($\sim 1$ Mpc across) is expected to be even larger. A
sequence of physical processes that are responsible for the production,
redistribution and dissipation of these magnetic fields is proposed. These
fields are associated with single AGNs within the cluster and therefore with
all galaxies during their AGN phase, simply because only the central
supermassive black holes ($\sim 10^8 M_{\odot}$) have an accessible energy,
$\sim 10^{61}$ ergs. We propose an $\alpha-\Omega$ dynamo process in an
accretion disk. The disk rotation naturally provides a large winding number,
$\sim 10^{11}$ turns, sufficient to make both large gain and large flux. The
helicity of the dynamo can be generated by the differential plume rotation
derived from star-disk collisions. This helicity generation process has been
demonstrated in the laboratory and the dynamo gain was simulated numerically. A
liquid sodium analog of the dynamo is being built. Speculations are that the
back reaction of the saturated dynamo will lead to the formation of a
force-free magnetic helix, which will carry the energy and flux of the dynamo
away from the accretion disk and redistribute the field within the clusters and
galaxy walls. The magnetic reconnection of a small fraction of this energy
logically is the source of the AGN luminosity, and the remainder of the field
energy should then dominate the free energy of the present-day universe.",0012484v1
2009-03-13,$^{63/65}$Cu- and $^{35/37}$Cl-NMR Studies of Triplet Localization in the Quantum Spin System NH$_4$CuCl$_3$,"$^{63/65}$Cu- and $^{35/37}$Cl-NMR experiments were performed to investigate
triplet localization in the $S=1/2$ dimer compound NH$_4$CuCl$_3$, which shows
magnetization plateaus at one-quarter and three-quarters of the saturation
magnetization. In $^{63/65}$Cu-NMR experiments, signal from only the singlet Cu
site was observed, because that from the triplet Cu site was invisible due to
the strong spin fluctuation of onsite 3$d$-spins. We found that the temperature
dependence of the shift of $^{63/65}$Cu-NMR spectra at the singlet Cu site
deviated from that of macroscopic magnetization below T=6 K. This deviation is
interpreted as the triplet localization in this system. From the
$^{35/37}$Cl-NMR experiments at the 1/4-plateau phase, we found the two
different temperature dependences of Cl-shift, namely the temperature
dependence of one deviates below T=6 K from that of the macroscopic
magnetization as observed in the $^{63/65}$Cu-NMR experiments, whereas the
other corresponds well with that of the macroscopic magnetization in the entire
experimental temperature region. We interpreted these dependences as reflecting
the transferred hyperfine field at the Cl site located at a singlet site and at
a triplet site, respectively. This result also indicates that the triplets are
localized at low temperatures. $^{63/65}$Cu-NMR experiments performed at high
magnetic fields between the one-quarter and three-quarters magnetization
plateaus have revealed that the two differently oriented dimers in the unit
cell are equally occupied by triplets, the fact of which limits the theoretical
model on the periodic structure of the localized triplets.",0903.2312v2
2010-12-21,Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films,"We present an investigation of the magnetic behavior of epitaxial MnAs films
grown on GaAs(100). We address the dependence of the magnetic moment,
ferromagnetic transition temperature ($T_c$) and magnetocrystalline anisotropy
constants on epitaxial conditions. From thorough structural and magnetic
investigations, our findings indicate a more complex relationship between
strain and magnetic properties in MnAs films than a simple stretch/compression
of the unit cell axes. While a small increase is seen in the anisotropy
constants the enhancement of the magnetic moment at saturation is significant.
X-ray magnetic circular dichroism results show a behavior of the spin- and
orbital-moment which is consistent with a structural transition at $T_c$. In
particular, we find that the ratio of the orbital to spin moment shows a marked
increase in the coexistence region of the ferromagnetic $\alpha$- and
paramagnetic $\beta$-phases, a result that is well in accord with the observed
increase of the $c/a$-ratio in the same temperature region. The \textit{ab
initio} density functional calculations reveal that the magnetic properties are
more sensitive towards change in in-plane axis as compared to a change of the
out-of-plane axis, which is explained by the analysis of band structures. The
effects of electron correlation in MnAs using \textit{ab initio} dynamical mean
field theory are also presented.",1012.4717v1
2012-02-03,Dead zones as safe-havens for planetesimals: influence of disc mass and external magnetic field,"(Abridged) Planetesimals embedded in a protoplanetary disc are stirred by
gravitational torques exerted by density fluctuations in the surrounding
turbulence. In particular, planetesimals in a disc supporting fully developed
magneto-rotational turbulence are readily excited to velocity dispersions above
the threshold for catastrophic disruption, halting planet formation. We aim to
examine the stirring of planetesimals lying instead in a magnetically-decoupled
midplane dead zone, stirred only by spiral density waves propagating out of the
disc's magnetically-coupled turbulent surface layers. We extend previous
studies to include a wider range of disc models, and explore the effects of
varying the disc column density and external magnetic field strength. [...] The
strength of the stirring is found to be independent of the gas surface density,
which is contrary to the increase with disc mass expected from a simple linear
wave picture. The discrepancy arises from the shearing out of density waves as
they propagate into the dead zone, resulting in density structures near the
midplane that exert weaker stochastic torques on average. We provide a simple
analytic fit to our numerically obtained torque amplitudes that accounts for
this effect. The stirring on the other hand depends sensitively on the net
vertical magnetic flux, up to a saturation level above which magnetic forces
dominate in the turbulent layers. For the majority of our models, the
equilibrium planetesimal velocity dispersions lie between the thresholds for
disrupting strong and weak aggregates, suggesting that collision outcomes will
depend on material properties. However, discs with relatively weak magnetic
fields yield reduced stirring, and their dead zones provide safe-havens even
for the weakest planetesimals against collisional destruction.",1202.0771v1
2016-02-04,Magnetic anisotropy in the frustrated spin chain compound $β$-TeVO$_4$,"Isotropic and anisotropic magnetic behavior of the frustrated spin chain
compound $\beta$-TeVO$_4$ is reported. Three magnetic transitions observed in
zero magnetic field are tracked in fields applied along different
crystallographic directions using magnetization, heat capacity, and
magnetostriction measurements. Qualitatively different temperature-field
diagrams are obtained below 10 T for the field applied along $a$ or $b$ and
along $c$, respectively. In contrast, a nearly isotropic high-field phase
emerges above 18 T and persists up to the saturation that occurs around 22.5 T.
Upon cooling in low fields, the transitions at $T_{\rm N1}$ and $T_{\rm N2}$
toward the spin-density-wave and stripe phases are of the second order, whereas
the transition at $T_{\rm N3}$ toward the helical state is of the first order
and entails a lattice component. Our microscopic analysis identifies frustrated
$J_1-J_2$ spin chains with a sizable antiferromagnetic interchain coupling in
the $bc$ plane and ferromagnetic couplings along the $a$ direction. The
competition between these ferromagnetic interchain couplings and the helical
order within the chain underlies the incommensurate order along the
$a$-direction, as observed experimentally. Although a helical state is
triggered by the competition between $J_1$ and $J_2$ within the chain, the
plane of the helix is not uniquely defined because of competing magnetic
anisotropies. Using high-resolution synchrotron diffraction and $^{125}$Te
nuclear magnetic resonance, we also demonstrate that the crystal structure of
$\beta$-TeVO$_4$ does not change down to 10 K, and the orbital state of
V$^{4+}$ is preserved.",1602.01632v2
2017-05-12,Spectral variability of photospheric radiation due to faculae I: The Sun and Sun-like stars,"Context. Stellar spectral variability on timescales of a day and longer,
arising from magnetic surface features such as dark spots and bright faculae,
is an important noise source when characterising extra-solar planets. Current
1D models of faculae do not capture the geometric properties and fail to
reproduce observed solar facular contrasts. Magnetoconvection simulations
provide facular contrasts accounting for geometry. Aims. We calculate facular
contrast spectra from magnetoconvection models of the solar photosphere with a
view to improve (a) future parameter determinations for planets with early G
type host stars and (b) reconstructions of solar spectral variability. Methods.
Regions of a solar twin (G2, log g=4.44) atmosphere with a range of initial
average vertical magnetic fields (100 to 500~G) were simulated using a 3D
radiation-magnetohydrodynamics code, MURaM, and synthetic intensity spectra
were calculated from the ultraviolet (149.5~nm) to the far infrared (160000~nm)
with the ATLAS9 radiative transfer code. Nine viewing angles were investigated
to account for facular positions across most of the stellar disc. Results.
Contrasts of the radiation from simulation boxes with different levels of
magnetic flux relative to an atmosphere with no magnetic field are a
complicated function of position, wavelength and magnetic field strength that
is not reproduced by 1D facular models. Generally, contrasts increase towards
the limb, but at UV wavelengths a saturation and decrease are observed close to
the limb. Contrasts also increase strongly from the visible to the UV; there is
a rich spectral dependence, with marked peaks in molecular bands and strong
spectral lines. At disc centre, a complex relationship with magnetic field was
found and areas of strong magnetic field can appear either dark or bright,
depending on wavelength...",1705.04455v1
2017-11-14,"Growth, electrical, structural, and magnetic properties of half-Heusler CoTi$_{1-x}$Fe$_x$Sb","Epitaxial thin films of the substitutionally alloyed half-Heusler series
CoTi$_{1-x}$Fe$_x$Sb were grown by molecular beam epitaxy on InAlAs/InP(001)
substrates for concentrations 0.0$\leq$x$\leq$1.0. The influence of Fe on the
structural, electronic, and magnetic properties was studied and compared to
that expected from density functional theory. The films are epitaxial and
single crystalline, as measured by reflection high-energy electron diffraction
and X-ray diffraction. Using in-situ X-ray photoelectron spectroscopy, only
small changes in the valence band are detected for x$\leq$0.5. For films with
x$\geq$0.05, ferromagnetism is observed in SQUID magnetometry with a saturation
magnetization that scales linearly with Fe content. A dramatic decrease in the
magnetic moment per formula unit occurs when the Fe is substitutionally alloyed
on the Co site indicating a strong dependence on the magnetic moment with site
occupancy. A crossover from both in-plane and out-of-plane magnetic moments to
only in-plane moment occurs for higher concentrations of Fe. Ferromagnetic
resonance indicates a transition from weak to strong interaction with a
reduction in inhomogeneous broadening as Fe content is increased.
Temperature-dependent transport reveals a semiconductor to metal transition
with thermally activated behavior for x$\leq$0.5. Anomalous Hall effect and
large negative magnetoresistance (up to -18.5% at 100 kOe for x=0.3) are
observed for higher Fe content films. Evidence of superparamagnetism for x=0.3
and x=0.2 suggests for moderate levels of Fe, demixing of the
CoTi$_{1-x}$Fe$_x$Sb films into Fe rich and Fe deficient regions may be
present. Atom probe tomography is used to examine the Fe distribution in a
x=0.3 film. Statistical analysis reveals a nonhomogeneous distribution of Fe
atoms throughout the film, which is used to explain the observed magnetic and
electrical behavior.",1711.05320v1
2017-11-16,Pure phase BiFeO$_3$ thin films sputtered over Si: A new route towards high magnetization,"We have investigated the structural and magnetic properties of BiFeO$_3$
(BFO) thin films grown over (100)-oriented Si substrates by rf magnetron
sputtering in a new route under O$_2$ free low pressure Ar atmosphere.
Single-phase BFO films were deposited in a heated substrate and post-annealed
in situ. The new routed allows high deposition rate and produce polycrystalline
BFO pure phase, confirmed by high resolution X-ray diffraction. Scanning
electron and atomic force microscopy reveal very low surface roughness and mean
particle size of 33 nm. The BFO phase and composition were confirmed by
transmission electron microscopy and line scanning energy-dispersive X-ray
spectroscopy in transmission electron microscopy mode. The surface chemistry of
the thin film, analyzed by X-ray photoelectron spectroscopy, reveals the
presence of Fe$^{3+}$ and Fe$^{2+}$ in a 2:1 ratio, a strong indication that
the film contains oxygen vacancies. An hysteretic ferromagnetic behavior with
room temperature high saturation magnetization $\sim 165 \times 10^3$ A/m was
measured along the film perpendicular and parallel directions. Such high
magnetization, deriving from this new route, is explained in the scope of
oxygen vacancies, the break of the antiferromagnetic cycloidal order and the
increase of spin canting by change in the surface/volume ratio. Understanding
the magnetic behavior of a multiferroic thin films is a key for the development
of heterogeneous layered structures and multilayered devices and the production
of multiferroic materials over Si substrates opens new possibilities in the
development of materials that can be directly integrated into the existent
semiconductor and spintronic technologies.",1711.05873v3
2018-02-22,Room Temperature Intrinsic Ferromagnetism in Epitaxial Manganese Selenide Films in the Monolayer Limit,"Monolayer van der Waals (vdW) magnets provide an exciting opportunity for
exploring two-dimensional (2D) magnetism for scientific and technological
advances, but the intrinsic ferromagnetism has only been observed at low
temperatures. Here, we report the observation of room temperature
ferromagnetism in manganese selenide (MnSe$_x$) films grown by molecular beam
epitaxy (MBE). Magnetic and structural characterization provides strong
evidence that in the monolayer limit, the ferromagnetism originates from a vdW
manganese diselenide (MnSe$_2$) monolayer, while for thicker films it could
originate from a combination of vdW MnSe$_2$ and/or interfacial magnetism of
$\alpha$-MnSe(111). Magnetization measurements of monolayer MnSe$_x$ films on
GaSe and SnSe$_2$ epilayers show ferromagnetic ordering with large saturation
magnetization of ~ 4 Bohr magnetons per Mn, which is consistent with density
functional theory calculations predicting ferromagnetism in monolayer
1T-MnSe$_2$. Growing MnSe$_x$ films on GaSe up to high thickness (~ 40 nm)
produces $\alpha$-MnSe(111), and an enhanced magnetic moment (~ 2x) compared to
the monolayer MnSe$_x$ samples. Detailed structural characterization by
scanning transmission electron microscopy (STEM), scanning tunneling microscopy
(STM), and reflection high energy electron diffraction (RHEED) reveal an abrupt
and clean interface between GaSe(0001) and $\alpha$-MnSe(111). In particular,
the structure measured by STEM is consistent with the presence of a MnSe$_2$
monolayer at the interface. These results hold promise for potential
applications in energy efficient information storage and processing.",1802.08152v1
2018-09-07,EPR measurements of Eu{+2} spins in metallic EuCo{2-y}As2 single crystals,"The Eu{+2} spins S = 7/2 in the metallic compound EuCo{2-y}As2 order into an
antiferromagnetic helical structure below a Neel temperature TN = 40 to 45 K.
The effective magnetic moment mu_eff of the Eu spins in the paramagnetic state
from 100 to 300 K is found from static magnetic susceptibility measurements to
be enhanced by about 7% compared to the value expected for spectroscopic
splitting factor g = 2, and the saturation moment at high applied fields H and
low temperatures T is also sometimes enhanced. Here
electron-paramagnetic-resonance (CW EPR) measurements versus applied magnetic
field H at fixed X-band rf (microwave) angular frequency omega were carried out
using a linearly-polarized rf magnetic field oriented perpendicular to H to
study the microscopic magnetic properties of the Eu spins. In order to analyze
the data, the complex magnetic susceptibility chi(omega) at fixed H was used
that was derived for linearly-polarized rf fields from the modified Bloch
equations [M. A. Garstens and J. I. Kaplan, Phys. Rev. 99, 459 (1955)] (GK). It
is shown that their formulation when applied to calculate the Dysonian
absorptive susceptibility chi_D''(H) of local magnetic moments in metals yields
a prediction that can be very different from the traditionally-used form of
chi_D''(H). By fitting the derivative of the field-swept CW EPR data for
EuCo{2-y}As2 by chi_D''(H) at fixed omega derived from the GK chi_D''(omega) at
fixed H, the Eu spin spectroscopic splitting factor (g-factor) is found to be
approximately 2.00 from 300 to ~125 K, and then to continuously increase to
approximately 2.16 on further cooling to 50 K. We speculate that the
enhancement of the Eu g-factor on cooling from 125 to 50 K arises from
continuously-increasing local short-range ferromagnetic correlations between
the Co 3d-band electrons and the Eu spins.",1809.02653v4
2018-11-10,Non-Coplanar Model States in Quantum Magnetism Applications of the High-Order Coupled Cluster Method,"Coplanar model states for applications of the coupled cluster method (CCM) to
problems in quantum magnetism are those in which all spins lie in a plane,
whereas three-dimensional (3D) model states are, by contrast, non-coplanar ones
in which all the spins do not lie in any single plane. Here we extend the CCM
to non-coplanar / 3D model states and we present results for three cases: (a)
the spin-half one-dimensional Ising ferromagnet in an applied transverse
magnetic field (as an exactly solvable test model to use as a yardstick for the
viability and accuracy of our new methodology); (b) the spin-half
triangular-lattice Heisenberg antiferromagnet in the presence of an external
magnetic field; and (c) the spin-$S$ triangular-lattice {\it XXZ}
antiferromagnet in the presence of an external magnetic field, for the cases
$\frac{1}{2} \leq S \leq5 $. For 3D model states the sets of algebraic CCM
equations for the ket- and bra-state correlation coefficients become
complex-valued, but ground-state expectation values of all physical observables
are manifestly real numbers, as required. Excellent correspondence is seen with
the results of other methods, where they exist, for these systems. CCM results
demonstrate explicitly that coplanar ordering is favoured over non-coplanar
ordering for the triangular-lattice spin-half Heisenberg antiferromagnet at all
values of the applied external magnetic field, whereas for the anisotropic {\it
XXZ} model non-coplanar ordering can be favoured in some regions of the
parameter space. Specifically, we present a precise determination of the
boundary (i.e., the critical value of the {\it XXZ} anisotropy parameter
$\Delta$) between a 3D ground state and a coplanar ground state for the {\it
XXZ} model for values for the external magnetic field near to saturation, for
values of the spin quantum number $S \leq 5$.",1811.04228v1
2019-03-13,Estimating magnetic filling factors from Zeeman-Doppler magnetograms,"Low-mass stars are known to have magnetic fields that are believed to be of
dynamo origin. Two complementary techniques are principally used to
characterise them. Zeeman-Doppler imaging (ZDI) can determine the geometry of
the large-scale magnetic field while Zeeman broadening can assess the total
unsigned flux including that associated with small-scale structures such as
spots. In this work, we study a sample of stars that have been previously
mapped with ZDI. We show that the average unsigned magnetic flux follows an
activity-rotation relation separating into saturated and unsaturated regimes.
We also compare the average photospheric magnetic flux recovered by ZDI,
$\langle B_V\rangle$, with that recovered by Zeeman broadening studies,
$\langle B_I\rangle$. In line with previous studies, $\langle B_V\rangle$
ranges from a few % to $\sim$20% of $\langle B_I\rangle$. We show that a power
law relationship between $\langle B_V\rangle$ and $\langle B_I\rangle$ exists
and that ZDI recovers a larger fraction of the magnetic flux in more active
stars. Using this relation, we improve on previous attempts to estimate filling
factors, i.e. the fraction of the stellar surface covered with magnetic field,
for stars mapped only with ZDI. Our estimated filling factors follow the
well-known activity-rotation relation which is in agreement with filling
factors obtained directly from Zeeman broadening studies. We discuss the
possible implications of these results for flux tube expansion above the
stellar surface and stellar wind models.",1903.05595v1
2020-01-21,"Mechanical behavior, enhanced dc resistivity, energy band gap and high temperature magnetic properties of Y-substituted Mg-Zn ferrites","We report the synthesis of Y-substituted Mg-Zn ferrites using conventional
standard ceramic technique. XRD patterns confirm the single phase cubic spinel
structure up to x = 0.03 and appearance of a secondary phase of YFeO3for higher
Y contents. FESEM images depict the distribution of grains and EDS spectra
confirmed the absence of any unwanted element. Completion of solid state
reaction and formation of spinel structure has been revealed from FTIR spectra.
The FTIR data along with lattice constant, bulk density and porosity were
further used to calculate the stiffness constant (Cij), elastic constant and
Debye temperatures. Mechanical stability of all studied compositions is
confirmed from Cij using Born stability conditions. Brittleness and isotropic
nature are also confirmed using Poisson ratio and anisotropy constants,
respectively. The enhancement of dc electrical resistivity with Y content is
observed. The energy band gap (increased with Y contents) is found in good
agreement with dc electrical resistivity. Ferrimagnetic to paramagnetic phase
change has been observed from the field dependent high temperature
magnetization curves. The magnetic moments and saturation magnetization were
found to be decreased with increasing temperature. The Curie temperature (Tc)
has been measured from temperature dependent magnetic moment (M-T) and initial
permeability and found to be in good agreement with each other. Decrease in Tc
with Y content is due to redistribution of cations and weakening of the
exchange coupling constant. The magnetic phase transition has been analyzed by
Arrott plot and found to have second order phase transition. The dc resistivity
endorses the prepared ferrites are suitable for high frequency and high
temperature magnetic device applications as well.",2001.07313v1
2020-09-13,Mapping the magnetic state as a function of anti-site disorder in Sm$ _{2} $NiMnO$ _{6} $ double perovskite thin films,"The predictability of any characteristic functional aspect in a double
perovskite system has always been compromised by its strong dependence over the
inevitably present anti-site disorders (ASD). Here, we aim to precisely map the
quantitative and qualitative nature of ASD with the corresponding modifications
in observables describing the magnetic and electronic state in epitaxial Sm$
_{2} $NiMnO$ _{6} $ (SNMO) double perovskite thin films. The concentration and
distribution patterns of ASD are effectively controlled by optimizing growth
conditions and estimated on both local and global scales utilizing extended
X-ray absorption fine structure and bulk magnetometry. Depending upon the
defect densities, the nature of disorder distribution can vary from homogeneous
to partially segregated patches. Primarily, the effect of varying B-site
cationic arrangement in SNMO is reflected as the competition of long range
ferromagnetic (FM) and short scale antiferromagnetic (AFM) interactions
originated from ordered Ni-O-Mn and disordered Ni-O-Ni or Mn-O-Mn bonds,
respectively, which leads to systematic shift in magnetic transition
temperature and drastic drop in saturation magnetization. In addition, we have
observed that the gradual increment in density of ASD leads to significant
deviation from uniaxial anisotropy character, reduction in anisotropy energy
and enhancement of moment pinning efficiency. However, the observed signatures
of $ Ni^{2+}+Mn^{4+} \longrightarrow Ni^{3+}+Mn^{3+} $ charge
disproportionation is found to be independent of cation disorder densities.
This work serves as a basic route-map to tune the characteristic magnetic
anisotropy, magnetic phase transitions, and magnetization reversal mechanism by
controlling ASD in a general double perovskite system.",2009.06020v3
2021-03-14,Perpendicular magnetic anisotropy in ultra-thin Cu$_2$Sb-type (Mn-Cr)AlGe films onto thermally oxidized silicon substrates,"Perpendicularly magnetized films showing small saturation magnetization,
$M_\mathrm{s}$, are essential for spin-transfer-torque writing type
magnetoresistive random access memories, STT-MRAMs. An intermetallic compound,
{(Mn-Cr)AlGe} of the Cu$_2$Sb-type crystal structure was investigated, in this
study, as a material showing the low $M_\mathrm{s}$ ($\sim 300$ kA/m) and
high-perpendicular magnetic anisotropy, $K_\mathrm{u}$. The layer thickness
dependence of $K_\mathrm{u}$ and effects of Mg-insertion layers at top and
bottom (Mn-Cr)AlGe$|$MgO interfaces were studied in film samples fabricated
onto thermally oxidized silicon substrates to realize high-$K_\mathrm{u}$ in
the thickness range of a few nanometer. Optimum Mg-insertion thicknesses were
1.4 and 3.0 nm for the bottom and the top interfaces, respectively, which were
relatively thick compared to results in similar insertion effect investigations
on magnetic tunnel junctions reported in previous studies. The cross-sectional
transmission electron microscope images revealed that the Mg-insertion layers
acted as barriers to interdiffusion of Al-atoms as well as oxidization from the
MgO layers. The values of $K_\mathrm{u}$ were about $7 \times 10^5$ and $2
\times 10^5$ J/m$^3$ at room temperature for 5 and 3 nm-thick (Mn-Cr)AlGe
films, respectively, with the optimum Mg-insertion thicknesses. The
$K_\mathrm{u}$ at a few nanometer thicknesses is comparable or higher than
those reported in perpendicularly magnetized CoFeB films which are
conventionally used in MRAMs, while the $M_\mathrm{s}$ value is one third or
less smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are
promising from the viewpoint of not only the magnetic properties, but also the
compatibility to the silicon process in the film fabrication.",2103.07847v2
2021-06-18,Magnetic field-induced non-trivial electronic topology in Fe3GeTe2,"The anomalous Hall, Nernst and thermal Hall coefficients of
Fe$_{3-x}$GeTe$_2$ display several features upon cooling, like a reversal in
the Nernst signal below $T = 50$ K pointing to a topological transition (TT)
associated to the development of magnetic spin textures. Since the anomalous
transport variables are related to the Berry curvature, a possible TT might
imply deviations from the Wiedemann-Franz (WF) law. However, the anomalous Hall
and thermal Hall coefficients of Fe$_{3-x}$GeTe$_2$ are found, within our
experimental accuracy, to satisfy the WF law for magnetic-fields $\mu_0H$
applied along its inter-layer direction. Surprisingly, large anomalous
transport coefficients are also observed for $\mu_0H$ applied along the planar
\emph{a}-axis as well as along the gradient of the chemical potential, a
configuration that should not lead to their observation due to the absence of
Lorentz force. However, as $\mu_0H$ $\|$ \emph{a}-axis is increased,
magnetization and neutron scattering indicate just the progressive canting of
the magnetic moments towards the planes followed by their saturation. These
anomalous planar quantities are found to not scale with the component of the
planar magnetization ($M_{\|}$), showing instead a sharp decrease beyond $\sim
\mu_0 H_{\|} = $ 4 T which is the field required to align the magnetic moments
along $\mu_0 H_{\|}$. We argue that locally chiral spin structures, such as
skyrmions, and possibly skyrmion tubes, lead to a field dependent
spin-chirality and hence to a novel type of topological anomalous transport.
Locally chiral spin-structures are captured by our Monte-Carlo simulations
incorporating small Dzyaloshinskii-Moriya and biquadratic exchange
interactions.",2106.09861v2
2021-12-15,Turbulent magnetic field amplification in binary neutron star mergers,"Magnetic fields are expected to play a key role in the dynamics and the
ejection mechanisms that accompany the merger of two neutron stars. General
relativistic magnetohydrodynamic (MHD) simulations offer a unique opportunity
to unravel the details of the ongoing physical processes. Nevertheless, current
numerical studies are severely limited by the fact that any affordable
resolution remains insufficient to fully capture the small-scale dynamo,
initially triggered by the Kelvin-Helmholtz instability, and later sourced by
several MHD processes involving differential rotation. Here, we alleviate this
limitation by using explicit large-eddy simulations, a technique where the
unresolved dynamics occurring at the sub-grid scales (SGS) is modeled by extra
terms, which are functions of the resolved fields and their derivatives. The
combination of high-order numerical schemes, high resolutions, and the gradient
SGS model allow us to capture the small-scale dynamos produced during the
binary neutron star mergers. Here we follow the first 50 milliseconds after the
merger and, for the first time, we find numerical convergence on the magnetic
field amplification, in terms of integrated energy and spectral distribution
over spatial scales. We also find that the average intensity of the magnetic
field in the remnant saturates at $\sim 10^{16}$~G around $5$~ms after the
merger. After $20-30$~ms, both toroidal and poloidal magnetic field components
grow continuously, fed by the winding mechanism that provides a slow inverse
cascade. We find no clear hints for magneto-rotational instabilities, and no
significant impact of the magnetic field on the redistribution of angular
momentum in the remnant in our simulations, probably due to the very turbulent
and dynamical topology of the magnetic field at all stages, with small-scale
components largely dominating over the large-scale ones.",2112.08413v2
2022-02-16,"Spin Seebeck effect in iron oxide thin films: Effects of phase transition, phase coexistence, and surface magnetism","Understanding impacts of phase transition, phase coexistence, and surface
magnetism on the longitudinal spin Seebeck effect (LSSE) in a magnetic system
is essential to manipulate the spin to charge current conversion efficiency for
spincaloritronic applications. We aim to elucidate these effects by performing
a comprehensive study of the temperature dependence of LSSE in biphase iron
oxide (BPIO = alpha-Fe2O3 + Fe3O4) thin films grown on Si (100) and Al2O3 (111)
substrates. A combination of temperature-dependent anomalous Nernst effect
(ANE) and electrical resistivity measurements show that the contribution of ANE
from the BPIO layer is negligible compared to the intrinsic LSSE in the
Si/BPIO/Pt heterostructure even at room temperature. Below the Verwey
transition of the Fe3O4 phase, the total signal across BPIO/Pt is dominated by
the LSSE. Noticeable changes in the intrinsic LSSE signal for both Si/BPIO/Pt
and Al2O3/BPIO/Pt heterostructures around the Verwey transition of the Fe3O4
phase and the antiferromagnetic (AFM) Morin transition of the alpha-Fe2O3 phase
are observed. The LSSE signal for Si/BPIO/Pt is found to be almost two times
greater than that for Al2O3/BPIO/Pt, an opposite trend is observed for the
saturation magnetization though. Magnetic force microscopy reveals the higher
density of surface magnetic moments of the Si/BPIO film compared to the
Al2O3/BPIO film, which underscores a dominant role of interfacial magnetism on
the LSSE signal and thereby explains the larger LSSE for Si/BPIO/Pt.",2202.07910v1
2022-06-02,Magnetic dilution effect and topological phase transitions in (Mn$_{1-x}$Pb$_x$)Bi$_2$Te$_4$,"As the first intrinsic antiferromagnetic (AFM) topological insulator (TI),
MnBi$_2$Te$_4$ has provided a material platform to realize various emergent
phenomena arising from the interplay of magnetism and band topology. Here by
investigating (Mn$_{1-x}$Pb$_x$)Bi$_2$Te$_4$ $(0\leq x \leq 0.82)$ single
crystals via the x-ray, electrical transport, magnetometry and neutron
measurements, chemical analysis, external pressure, and first-principles
calculations, we reveal the magnetic dilution effect on the magnetism and band
topology in MnBi$_2$Te$_4$. With increasing $x$, both lattice parameters $a$
and $c$ expand linearly by around 2\%. All samples undergo the paramagnetic to
A-type antiferromagnetic transition with the N$\acute{e}$el temperature
decreasing lineally from 24 K at $x=0$ to 2 K at $x=0.82$. Our neutron data
refinement of the $x=0.37$ sample indicates that the ordered moment is
4.3(1)$\mu_B$/Mn at 4.85 K and the amount of the Mn$_{\rm{Bi}}$ antisites is
negligible within the error bars. Isothermal magnetization data reveal a slight
decrease of the interlayer plane-plane antiferromagnetic exchange interaction
and a monotonic decrease of the magnetic anisotropy, due to diluting magnetic
ions and enlarging the unit cell. For $x=0.37$, the application of external
pressures enhances the interlayer antiferromagnetic coupling, boosting the
N$\acute{e}$el temperature at a rate of 1.4 K/GPa and the saturation field at a
rate of 1.8 T/GPa. Furthermore, our first-principles calculations reveal that
the band inversion in the two end materials, MnBi$_2$Te$_4$ and PbBi$_2$Te$_4$,
occurs at the $\Gamma$ and $Z$ point, respectively, while two gapless points
appear at $x = $ 0.44 and $x = $ 0.66, suggesting possible topological phase
transitions with doping.",2206.01324v1
2022-10-07,"Magnetic induction processes in Hot Jupiters, application to KELT-9b","The small semi-major axes of Hot Jupiters lead to high atmospheric
temperatures of up to several thousand Kelvin. Under these conditions,
thermally ionised metals provide a rich source of charged particles and thus
build up a sizeable electrical conductivity. Subsequent electromagnetic
effects, such as the induction of electric currents, Ohmic heating, magnetic
drag, or the weakening of zonal winds have thus far been considered mainly in
the framework of a linear, steady-state model of induction. For Hot Jupiters
with an equilibrium temperature $T_{eq} > 1500$ K, the induction of atmospheric
magnetic fields is a runaway process that can only be stopped by non-linear
feedback. For example, the back-reaction of the magnetic field onto the flow
via the Lorentz force or the occurrence of magnetic instabilities. Moreover, we
discuss the possibility of self-excited atmospheric dynamos. Our results
suggest that the induced atmospheric magnetic fields and electric currents
become independent of the electrical conductivity and the internal field, but
instead are limited by the planetary rotation rate and wind speed. As an
explicit example, we characterise the induction process for the hottest
exoplanet, KELT-9b by calculating the electrical conductivity along atmospheric
$P-T$-profiles for the day- and nightside. Despite the temperature varying
between 3000 K and 4500 K, the resulting electrical conductivity attains an
elevated value of roughly 1 S/m throughout the atmosphere. The induced magnetic
fields are predominately horizontal and might reach up to a saturation field
strength of 400 mT, exceeding the internal field by two orders of magnitude.",2210.03351v1
2023-12-01,Magneto-transport in the monolayer MoS2 material system for high-performance field-effect transistor applications,"Electronic transport in monolayer MoS2 is significantly constrained by
several extrinsic factors despite showing good prospects as a transistor
channel material. Our paper aims to unveil the underlying mechanisms of the
electrical and magneto-transport in monolayer MoS2. In order to quantitatively
interpret the magneto-transport behavior of monolayer MoS2 on different
substrate materials, identify the underlying bottlenecks, and provide
guidelines for subsequent improvements, we present a deep analysis of the
magneto-transport properties in the diffusive limit. Our calculations are
performed on suspended monolayer MoS2 and MoS2 on different substrate materials
taking into account remote impurity and the intrinsic and extrinsic phonon
scattering mechanisms. We calculate the crucial transport parameters such as
the Hall mobility, the conductivity tensor elements, the Hall factor, and the
magnetoresistance over a wide range of temperatures, carrier concentrations,
and magnetic fields. The Hall factor being a key quantity for calculating the
carrier concentration and drift mobility, we show that for suspended monolayer
MoS2 at room temperature, the Hall factor value is around 1.43 for magnetic
fields ranging from 0.001 to 1 Tesla, which deviates significantly from the
usual value of unity. In contrast, the Hall factor for various substrates
approaches the ideal value of unity and remains stable in response to the
magnetic field and temperature. We also show that the MoS2 over an Al2O3
substrate is a good choice for the Hall effect detector. Moreover, the
magnetoresistance increases with an increase in magnetic field strength for
smaller magnetic fields before reaching saturation at higher magnetic fields.
The presented theoretical model quantitatively captures the scaling of mobility
and various magnetoresistance coefficients with temperature, carrier densities
and magnetic fields.",2312.00378v1
2011-07-15,The Expected Order of Saturated RNA Secondary Structures,"We show the expected order of RNA saturated secondary structures of size $n$
is $\log_4n(1+O(\frac{\log_2n}{n}))$, if we select the saturated secondary
structure uniformly at random. Furthermore, the order of saturated secondary
structures is sharply concentrated around its mean. As a consequence saturated
structures and structures in the traditional model behave the same with respect
to the expected order. Thus we may conclude that the traditional model has
already drawn the right picture and conclusions inferred from it with respect
to the order (the overall shape) of a structure remain valid even if enforcing
saturation (at least in expectation).",1107.3033v1
2014-03-14,The Effect of Saturation on Belief Propagation Decoding of LDPC Codes,"We consider the effect of LLR saturation on belief propagation decoding of
low-density parity-check codes. Saturation occurs universally in practice and
is known to have a significant effect on error floor performance. Our focus is
on threshold analysis and stability of density evolution.
  We analyze the decoder for certain low-density parity-check code ensembles
and show that belief propagation decoding generally degrades gracefully with
saturation. Stability of density evolution is, on the other hand, rather
strongly affected by saturation and the asymptotic qualitative effect of
saturation is similar to reduction of variable node degree by one.",1403.3678v1
2015-10-16,Looking for quark saturation in proton and nuclei,"The quark saturation behavior at low $Q^2$ is shown in a numeric solution of
the DGLAP equation with parton recombination corrections, which resembles the
widely discussed JIMWLK saturation of gluons. Our calculation suggests that the
partonic saturation can be interpreted as a dynamical balance between the
splitting and the fusion processes of partons, without any other condensation
mechanisms added. The nuclear shadowing saturation at small $x$ resulted from
the proposed quark saturation is also discussed.",1510.04787v2
2023-12-22,Lipschitz saturation of complex algebraic varieties,"This paper is devoted to the study of Lipschitz Saturation of complex
algebraic varieties. More precisely, we adapt classical results concerning the
Lipschitz Saturation of analytic varieties to algebraic varieties using recent
works about seminormalization and continuous rational functions. We investigate
the concept of Lipschitz Saturation of a variety in another and we focus on the
case where there is no finite morphism between the two varieties. This
investigation leads us to answer, in the case of algebraic varieties, to an
open question of Pham and Teissier concerning the finiteness of the Lipschitz
Saturation of general algebras. Finally, we use the Lipschitz saturation to
provide algebraic criteria for two algebraic varieties to be linked by a
birational and locally biLipschitz homeomorphism.",2312.14517v1
1999-08-29,Rigid aleph_epsilon-saturated models of superstable theories,"In a countable superstable NDOP theory, the existence of a rigid
aleph_epsilon-saturated model implies the existence of 2^lambda rigid
aleph_epsilon-saturated models of power lambda for every lambda>2^{aleph_0}.",9908158v1
2009-04-30,Benchmark tests of slow light in saturable absorbers,"A series of benchmark tests of slow light in saturable absorbers is proposed.
Stage I concerns experimental tests of saturable absorption, which can mimic
slow light in saturable media. Stage II outlines the more demanding
requirements for practical observation of spectral hole-burning in the
absorption line, which is responsible for the reduction in group velocity.",0904.4780v1
2011-08-19,On the existence of global saturation for spectral regularization methods with optimal qualification,"A family of real functions {g_\alpha} defining a spectral regularization
method with optimal qualification is considered. Sufficient condition on the
family and on the optimal qualification guaranteeing the existence of
saturation are established. Appropriate characterizations of both the
saturation function and the saturation set are found and some examples are
provided.",1108.4072v1
2014-09-30,Saturated free algebras revisited,"We give an exposition of results of Baldwin-Shelah on saturated free
algebras, at the level of generality of complete first order theories $T$ with
a saturated model $M$ which is in the algebraic closure of an indiscernible
set. We then make some new observations when $M$ is a saturated free algebra,
analogous to (more difficult) results for the free group, such as a description
of forking.",1409.8604v1
2015-10-09,Exact saturation in simple and NIP theories,"A theory $T$ is said to have exact saturation at a singular cardinal $\kappa$
if it has a $\kappa$-saturated model which is not $\kappa^{+}$-saturated. We
show, under some set-theoretic assumptions, that any simple theory has exact
saturation. Also, an NIP theory has exact saturation if and only if it is not
distal. This gives a new characterization of distality.",1510.02741v1
2018-07-30,The saturation number of carbon nanocones and nanotubes,"The saturation number of a graph is the cardinality of a smallest maximal
matching. This paper presents bounds for the saturation number of carbon
nanocones which are asymptotically equal. The same techniques are applied for
the saturation number of certain families of carbon nanotubes, which improve
previous results and in one case, yields the exact value.",1807.11355v1
2020-12-06,Saturation Numbers for Minors,"The saturation number $\text{sat}(n,\mathcal{F})$ is the minimum number of
edges in any graph which does not contain a member of $\mathcal{F}$ as a
subgraph, but will if any edge is added. We give a few upper and lower bounds
for saturation numbers for minors. In particular, we shall show that certain
Generalized Petersen Graphs are $K^r$-minor saturated for $6\le r\le 8$.",2012.03155v1
2021-02-08,Reconstruction of Sparse Signals under Gaussian Noise and Saturation,"Most compressed sensing algorithms do not account for the effect of
saturation in noisy compressed measurements, though saturation is an important
consequence of the limited dynamic range of existing sensors. The few
algorithms that handle saturation effects either simply discard saturated
measurements, or impose additional constraints to ensure consistency of the
estimated signal with the saturated measurements (based on a known saturation
threshold) given uniform-bounded noise. In this paper, we instead propose a new
data fidelity function which is directly based on ensuring a certain form of
consistency between the signal and the saturated measurements, and can be
expressed as the negative logarithm of a certain carefully designed likelihood
function. Our estimator works even in the case of Gaussian noise (which is
unbounded) in the measurements. We prove that our data fidelity function is
convex. We moreover, show that it satisfies the condition of Restricted Strong
Convexity and thereby derive an upper bound on the performance of the
estimator. We also show that our technique experimentally yields results
superior to the state of the art under a wide variety of experimental settings,
for compressive signal recovery from noisy and saturated measurements.",2102.03975v1
2021-05-17,Induction and Skolemization in saturation theorem proving,"We consider a typical integration of induction in saturation-based theorem
provers and investigate the effects of Skolem symbols occurring in the
induction formulas. In a practically relevant setting we establish a
Skolem-free characterization of refutation in saturation-based proof systems
with induction. Finally, we use this characterization to obtain unprovability
results for a concrete saturation-based induction prover.",2105.07734v2
2003-10-01,General Relativistic Magnetohydrodynamic Simulations of Collapsars,"We have performed 2.5-dimensional general relativistic magnetohydrodynamic
(MHD) simulations of the gravitational collapse of a magnetized rotating
massive star as a model of gamma ray bursts (GRBs). The current calculation
focuses on general relativistic MHD with simplified microphysics (we ignore
neutrino cooling, physical equation of state, and photodisintegration).
Initially, we assume that the core collapse has failed in this star. A few
$M_{\odot}$ black hole is inserted by hand into the calculation. The
simulations presented in the paper follow the accretion of gas into a black
hole that is assumed to have formed before the calculation begins.The
simulation results show the formation of a disk-like structure and the
generation of a jetlike outflow inside the shock wave launched at the core
bounce. We have found that the jet is accelerated by the magnetic pressure and
the centrifugal force and is collimated by the pinching force of the toroidal
magnetic field amplified by the rotation and the effect of geometry of the
poloidal magnetic field. The maximum velocity of the jet is mildly relativistic
(0.3c). The velocity of the jet becomes larger as the initial rotational
velocity of stellar matter gets faster. On the other hand, the dependence on
the initial magnetic field strength is a bit more complicated: the velocity of
the jet increases with the initial field strength in the weak field regime,
then is saturated at some intermediate field strength, and decreases beyond the
critical field strength. These results are related to the stored magnetic
energy determined by the balance between the propagation time of the Alfven
wave and the rotation time of the disk (or twisting time).",0310017v2
2005-02-18,"The Magnetic Properties of an L Dwarf Derived from Simultaneous Radio, X-ray, and H-alpha Observations","We present the first simultaneous, multi-wavelength observations of an L
dwarf, the L3.5 candidate brown dwarf 2MASS J00361617+1821104, conducted with
the Very Large Array, the Chandra X-ray Observatory, and the Kitt Peak 4-m
telescope. We detect strongly variable and periodic radio emission (P=3 hr)
with a fraction of about 60% circular polarization. No X-ray emission is
detected to a limit of L_X/L_{bol}<2e-5, several hundred times below the
saturation level observed in early M dwarfs. Similarly, we do not detect
H-alpha emission to a limit of L_{H-alpha}/L_{bol}<2e-7, the deepest for any L
dwarf observed to date. The ratio of radio to X-ray luminosity is at least four
orders of magnitude in excess of that observed in a wide range of active stars
(including M dwarfs) providing the first direct confirmation that late-M and L
dwarfs violate the radio/X-ray correlation. The radio emission is due to
gyrosynchrotron radiation in a large-scale magnetic field of about 175 G, which
is maintained on timescales longer than three years. The detected 3-hour period
may be due to (i) the orbital motion of a companion at a separation of about
five stellar radii, similar to the configuration of RS CVn systems, (ii) an
equatorial rotation velocity of about 37 km/s and an anchored, long-lived
magnetic field, or (iii) periodic release of magnetic stresses in the form of
weak flares. In the case of orbital motion, the magnetic activity may be
induced by the companion, possibly explaining the unusual pattern of activity
and the long-lived signal. We conclude that fully convective stars can maintain
a large-scale and stable magnetic field, but the lack of X-ray and H-alpha
emission indicates that the atmospheric conditions are markedly different than
in early-type stars and even M dwarfs. [abridged]",0502384v1
2007-11-09,Magnetic field amplification in proto-neutron stars -- The role of the neutron-finger instability for dynamo excitation,"During the first 40 s after their birth, proto-neutron stars are expected to
be subject to at least two types of instability: the convective instability and
the neutron-finger one. Both instabilities involve convective motions and hence
can trigger dynamo actions which may be responsible for the large magnetic
fields in neutron stars and magnetars. We have solved the mean-field induction
equation in a simplified one-dimensional model of both the convective and the
neutron-finger instability zones. Although very idealized, the model includes
the nonlinearities introduced by the feedback processes which tend to saturate
the growth of the magnetic field (alpha-quenching) and suppress its turbulent
diffusion (eta-quenching). The possibility of a dynamo action is studied within
a dynamical model of turbulent diffusivity where the boundary of the unstable
zone is allowed to move. We show that the dynamo action can be operative and
that the amplification of the magnetic field can still be very effective.
Furthermore, we confirm the existence of a critical spin-period, below which
the dynamo is always excited independently of the degree of differential
rotation, and whose value is related to the size of the neutron-finger
instability zone. Finally we provide a relation for the intensity of the final
field as a function of the spin of the star and of its differential rotation.
Although they were obtained by using a toy model, we expect that our results
are able to capture the qualitative and asymptotic behaviour of a mean-field
dynamo action developing in the neutron-finger instability zone. Overall, we
find that such a dynamo is very efficient in producing magnetic fields well
above equipartition and thus that it could represent a possible explanation for
the large surface magnetic fields observed in neutron stars.",0711.1498v3
2011-11-23,Statistical analysis of the mass-to-flux ratio in turbulent cores: effects of magnetic field reversals and dynamo amplification,"We study the mass-to-flux ratio (M/\Phi) of clumps and cores in simulations
of supersonic, magnetohydrodynamical turbulence for different initial magnetic
field strengths. We investigate whether the (M/\Phi)-ratio of core and
envelope, R = (M/\Phi)_{core}/(M/\Phi)_{envelope} can be used to distinguish
between theories of ambipolar diffusion and turbulence-regulated star
formation. We analyse R for different Lines-of-Sight (LoS) in various sub-cubes
of our simulation box. We find that, 1) the average and median values of |R|
for different times and initial magnetic field strengths are typically greater,
but close to unity, 2) the average and median values of |R| saturate at average
values of |R| ~ 1 for smaller magnetic fields, 3) values of |R| < 1 for small
magnetic fields in the envelope are caused by field reversals when turbulence
twists the field lines such that field components in different directions
average out. Finally, we propose two mechanisms for generating values |R| ~< 1
for the weak and strong magnetic field limit in the context of a turbulent
model. First, in the weak field limit, the small-scale turbulent dynamo leads
to a significantly increased flux in the core and we find |R| ~< 1. Second, in
the strong field limit, field reversals in the envelope also lead to values |R|
~< 1. These reversals are less likely to occur in the core region where the
velocity field is more coherent and the internal velocity dispersion is
typically subsonic.",1111.5539v2
2014-05-09,Magnetic effects on the low-T/|W| instability in differentially rotating neutron stars,"Dynamical instabilities in protoneutron stars may produce gravitational waves
whose observation could shed light on the physics of core-collapse supernovae.
When born with sufficient differential rotation, these stars are susceptible to
a shear instability (the ""low-T/|W| instability""), but such rotation can also
amplify magnetic fields to strengths where they have a considerable impact on
the dynamics of the stellar matter. Using a new magnetohydrodynamics module for
the Spectral Einstein Code, we have simulated a differentially-rotating neutron
star in full 3D to study the effects of magnetic fields on this instability.
Though strong toroidal fields were predicted to suppress the low-T/|W|
instability, we find that they do so only in a small range of field strengths.
Below 4e13 G, poloidal seed fields do not wind up fast enough to have an effect
before the instability saturates, while above 5e14 G, magnetic instabilities
can actually amplify a global quadrupole mode (this threshold may be even lower
in reality, as small-scale magnetic instabilities remain difficult to resolve
numerically). Thus, the prospects for observing gravitational waves from such
systems are not in fact diminished over most of the magnetic parameter space.
  Additionally, we report that the detailed development of the low-T/|W|
instability, including its growth rate, depends strongly on the particular
numerical methods used. The high-order methods we employ suggest that growth
might be considerably slower than found in some previous simulations.",1405.2144v1
2014-06-18,Non-thermal Gamma-ray Emission from Delayed Pair Breakdown in a Magnetized and Photon-rich Outflow,"We consider delayed, volumetric heating in a magnetized outflow that has
broken out of a confining medium and expanded to a high Lorentz factor ($\Gamma
\sim 10^2-10^3$) and low optical depth to scattering ($\tau_{\rm T} \sim
10^{-3}-10^{-2}$). The energy flux at breakout is dominated by the magnetic
field, with a modest contribution from quasi-thermal gamma rays whose spectrum
was calculated in Paper I. We focus on the case of extreme baryon depletion in
the magnetized material, but allow for a separate baryonic component that is
entrained from a confining medium. Dissipation is driven by relativistic motion
between these two components, which develops once the photon compactness drops
below $ 4\times 10^3(Y_e/0.5)^{-1}$. We first calculate the acceleration of the
magnetized component following breakout, showing that embedded MHD turbulence
provides significant inertia, the neglect of which leads to unrealistically
high estimates of flow Lorentz factor. After re-heating begins, the pair and
photon distributions are evolved self-consistently using a one-zone kinetic
code that incorporates an exact treatment of Compton scattering, pair
production and annihilation, and Coulomb scattering. Heating leads to a surge
in pair creation, and the scattering depth saturates at $\tau_{\rm T} \sim$
1-4. The plasma maintains a very low ratio of particle to magnetic pressure,
and can support strong anisotropy in the charged particle distribution, with
cooling dominated by Compton scattering. High-energy power-law spectra with
photon indices in the range observed in GRBs ($-3 < \beta < -3/2$) are obtained
by varying the ratio of heat input to the seed energy in quasi-thermal photons.
We contrast our results with those for continuous heating across an expanding
photosphere, and show that the latter model produces soft-hard evolution that
is inconsistent with observations of GRBs.",1406.4774v1
2015-08-03,Structural and ferromagnetic properties of an orthorhombic phase of MnBi stabilized with Rh additions,"The article addresses the possibility of alloy elements in MnBi which may
modify the thermodynamic stability of the NiAs-type structure without
significantly degrading the magnetic properties. The addition of small amounts
of Rh and Mn provides an improvement in the thermal stability with some
degradation of the magnetic properties. The small amounts of Rh and Mn
additions in MnBi stabilize an orthorhombic phase whose structural and magnetic
properties are closely related to the ones of the previously reported
high-temperature phase of MnBi (HT~MnBi). To date, the properties of the
HT~MnBi, which is stable between $613$ and $719$~K, have not been studied in
detail because of its transformation to the stable low-temperature MnBi
(LT~MnBi), making measurements near and below its Curie temperature difficult.
The Rh-stabilized MnBi with chemical formula Mn$_{1.0625-x}$Rh$_{x}$Bi
[$x=0.02(1)$] adopts a new superstructure of the NiAs/Ni$_2$In structure
family. It is ferromagnetic below a Curie temperature of $416$~K. The critical
exponents of the ferromagnetic transition are not of the mean-field type but
are closer to those associated with the Ising model in three dimensions. The
magnetic anisotropy is uniaxial; the anisotropy energy is rather large, and it
does not increase when raising the temperature, contrary to what happens in
LT~MnBi. The saturation magnetization is approximately $3$~$\mu_B$/f.u. at low
temperatures. While this exact composition may not be application ready, it
does show that alloying is a viable route to modifying the stability of this
class of rare-earth-free magnet alloys.",1508.00473v1
2015-09-09,The monoclinic crystal structure of $α$-RuCl$_3$ and the zigzag antiferromagnetic ground state,"The layered honeycomb magnet alpha-RuCl3 has been proposed as a candidate to
realize a Kitaev spin model with strongly frustrated, bond-dependent,
anisotropic interactions between spin-orbit entangled jeff=1/2 Ru4+ magnetic
moments. Here we report a detailed study of the three-dimensional crystal
structure using x-ray diffraction on untwinned crystals combined with
structural relaxation calculations. We consider several models for the stacking
of honeycomb layers and find evidence for a crystal structure with a monoclinic
unit cell corresponding to a stacking of layers with a unidirectional in-plane
offset, with occasional in-plane sliding stacking faults, in contrast with the
currently-assumed trigonal 3-layer stacking periodicity. We report electronic
band structure calculations for the monoclinic structure, which find support
for the applicability of the jeff=1/2 picture once spin orbit coupling and
electron correlations are included. We propose that differences in the
magnitude of anisotropic exchange along symmetry inequivalent bonds in the
monoclinic cell could provide a natural mechanism to explain the spin gap
observed in powder inelastic neutron scattering, in contrast to spin models
based on the three-fold symmetric trigonal structure, which predict a gapless
spectrum within linear spin wave theory. Our susceptibility measurements on
both powders and stacked crystals, as well as neutron powder diffraction show a
single magnetic transition at TN ~ 13K. The analysis of the neutron data
provides evidence for zigzag magnetic order in the honeycomb layers with an
antiferromagnetic stacking between layers. Magnetization measurements on
stacked single crystals in pulsed field up to 60T show a single transition
around 8T for in-plane fields followed by a gradual, asymptotic approach to
magnetization saturation, as characteristic of strongly anisotropic exchange
interactions.",1509.02670v2
2016-03-21,Magnetic Field Evolution in Giant Radio Relics using the example of CIZA J2242.8+5301,"Giant radio relics are the arc-shaped diffuse radio emission regions observed
in the outskirts of some merging galaxy clusters. They are believed to trace
shock-waves in the intra-cluster medium. Recent observations demonstrated that
some prominent radio relics exhibit a steepening above 2 GHz in their radio
spectrum. This challenges standard theoretical models because shock
acceleration is expected to accelerate electrons to very high energies with a
power-law distribution in momentum. In this work we attempt to reconcile these
data with the shock-acceleration scenario. We propose that the spectral
steepening may be caused by the highest energy electrons emitting
preferentially in lower magnetic fields than the bulk of synchrotron bright
electrons in relics. Here, we focus on a model with an increasing mag- netic
field behind the shock front, which quickly saturates and then declines. We
derive the time-evolution of cosmic-ray electron spectra in time variable
magnetic fields and an expanding medium. We then apply the formalism on the
large radio relic in the cluster CIZA J2242.8+5301 (the Sausage relic). We show
that under favourable circumstances of magnetic field amplification downstream,
our model can explain the observed radio spectrum, the brightness profile and
the spectral index profile of the relic. A possible interpretation for the
required amplification of the magnetic field downstream is a dynamo acting
behind the shock with an injection scale of magnetic turbulence of about 10
kpc. Our models require injection efficiencies of CRe - which are in tension
with simple diffusive shock acceleration from the thermal pool. We show that
this problem can likely be alleviated considering pre-existing CRe.",1603.06570v1
2016-06-15,Modulated magnetism and anomalous electronic transport in $\rm Ce_3Cu_4As_4O_2$,"The complex magnetism and transport properties of tetragonal
Ce$_3$Cu$_4$As$_4$O$_2$ were examined through neutron scattering and physical
properties measurements on polycrystalline samples. The lamellar structure
consists of alternating layers of $\rm CeCu_4As_4$ with a single square Ce
lattice and oxygen-linked Ce bi-layer $\rm Ce_2O_2$. Extending along $\bf c$, a
tube-like Fermi surface from DFT calculations points to a quasi-two-dimensional
electronic system. Peaks in the specific heat at the Ne\'{e}l temperature
$T_{N}=24$ $\rm K$, $T_{2}~=~16 $ $\rm K$ and $T_{3}~=~1.9$ $ \rm K$ indicate
three magnetic phase transitions or distinct cross-over phenomena. For
$T<T_{N}$ neutron diffraction indicates the development of ferromagnetic ab
sheets for both Ce sites, with alternating polarization along $\bf{c}$, a wave
vector ${\bf k}_{1}={\bf c}^*$. For $T<T_{2}$, quasi-two-dimensional low-energy
spin fluctuations with ${\bf k}_{2}=\frac{1}{2}{\bf a}^*$ and polarized
perpendicular to ${\bf k}_{2}$ are suppressed. The data are consistent with
quasi-two-dimensional antiferromagnetic order in the $\rm CeCu_4As_4$ planes
polarized along the ${\bf k}_{2}$ wave vector. $T_{3}$ marks a spin-flop
transition where the ${\bf k}_{1}$ staggered magnetization switches to in-plane
polarization. While the narrow 4f bands lie deep below the Fermi surface, there
are significant transport anomalies associated with the transitions; in
particular a substantial reduction in resistivity for $T<T_{N}$. At $T=100$ $
\rm mK$ the ${\bf k}_1$ modulated staggered moment is $0.85~\mu_B$, which
matches the $0.8~\mu_B$ saturation magnetization achieved for H $~=~7$ $ \rm T$
at $T~=~2$ $ \rm K$. From low T Lorentzian fits the correlation length is in
excess of 75 \AA. We argue the unusual sequence of magnetic transitions results
from competing interactions and anisotropies for the two Ce sites.",1606.04937v1
2016-11-02,The impact of magnetic fields on the chemical evolution of the supernova-driven ISM,"We present three-dimensional magneto-hydrodynamical simulations of the
self-gravitating interstellar medium (ISM) in a periodic (256 pc)$^3$ box with
a mean number density of 0.5 cm$^{-3}$. At a fixed supernova rate we
investigate the multi-phase ISM structure, H$_{2}$ molecule formation and
density-magnetic field scaling for varying initial magnetic field strengths (0,
$6\times 10^{-3}$, 0.3, 3 $\mu$G). All magnetic runs saturate at mass weighted
field strengths of $\sim$ 1 $-$ 3 $\mu$G but the ISM structure is notably
different. With increasing initial field strengths (from $6\times 10^{-3}$ to 3
$\mu$G) the simulations develop an ISM with a more homogeneous density and
temperature structure, with increasing mass (from 5% to 85%) and volume filling
fractions (from 4% to 85%) of warm (300 K $<$ T $<$ 8000 K) gas, with
decreasing volume filling fractions (VFF) from $\sim$ 35% to $\sim$ 12% of hot
gas (T $> 10^5$ K) and with a decreasing H$_{2}$ mass fraction (from 70% to $<$
1%). Meanwhile the mass fraction of gas in which the magnetic pressure
dominates over the thermal pressure increases by a factor of 10, from 0.07 for
an initial field of $6\times 10^{-3}$ $\mu$G to 0.7 for a 3 $\mu$G initial
field. In all but the simulations with the highest initial field strength
self-gravity promotes the formation of dense gas and H$_{2}$, but does not
change any other trends. We conclude that magnetic fields have a significant
impact on the multi-phase, chemical and thermal structure of the ISM and
discuss potential implications and limitations of the model.",1611.00585v1
2017-05-31,The Evaporation and Survival of Cluster Galaxies' Coronae Part II: The Effectiveness of Anisotropic Thermal Conduction and Survival of Stripped Galactic Tails,"We simulate anisotropic thermal conduction between the intracluster medium
(ICM) and the hot coronal interstellar medium (ISM) gas in cluster galaxies. In
the earlier Paper I (Vijayaraghavan & Sarazin 2017a), we simulated the
evaporation of the hot ISM due to isotropic (possibly saturated) conduction
between the ISM and ICM. We found that hot coronae evaporate on $\sim 10^2$ Myr
timescales, significantly shorter than the $\sim 10^3$ Myr gas loss times due
to ram pressure stripping. No tails of stripped gas are formed. This is in
tension with the observed ubiquity and implied longevity of compact X-ray
coronae and stripped ISM tails, and requires the suppression of evaporation,
possibly due to magnetic fields and anisotropic conduction. We perform a series
of wind tunnel simulations similar to Paper I, now including ISM and ICM
magnetic fields. We simulate the effect of anisotropic conduction for a range
of extreme magnetic field configurations: parallel and perpendicular to the ICM
wind, and continuous and completely disjoint between the ISM and ICM. We find
that when conduction is anisotropic, gas loss due to evaporation is severely
reduced; the overall gas loss rates with and without anisotropic conduction do
not differ by more than $10 - 20\%$. Magnetic fields also prevent stripped
tails from evaporating in the ICM by shielding, and providing few pathways for
heat transport between the ICM and ISM. The morphology of stripped tails and
magnetic fields in the tails and wakes of galaxies are sensitive to the initial
magnetic field configuration.",1706.00021v2
2017-08-21,Comment on `Oxygen vacancy-induced magnetic moment in edge-sharing CuO$_{2}$ chains of Li$_{2}$CuO$_{2}$',"In a recent work devoted to the magnetism of Li$_{2}$CuO$_{2}$, Shu et al.
[New J. Phys. 19 (2017) 023026] have proposed a ""simplified"" unfrustrated
microscopic model that differs considerably from the models refined through
decades of prior work. We show that the proposed model is at odds with known
experimental data, including the reported magnetic susceptibility $\chi(T)$
data up to 550~K. Using an 8$^{\rm th}$ order high-temperature expansion for
$\chi(T)$, we show that the experimental data for Li$_{2}$CuO$_{2}$ are
consistent with the prior model derived from inelastic neutron scattering (INS)
studies. We also establish the $T$-range of validity for a Curie-Weiss law for
the real frustrated magnetic system. We argue that the knowledge of the
long-range ordered magnetic structure for $T<T_N$ and of $\chi(T)$ in a
restricted $T$-range provides insufficient information to extract all of the
relevant couplings in frustrated magnets; the saturation field and INS data
must also be used to determine several exchange couplings, including the weak
but decisive frustrating antiferromagnetic (AFM) interchain couplings.",1708.06335v2
2018-05-12,Coexistence of magnetic fluctuations and long-range orders in the one-dimensional $J_1-J_2$ zigzag chains materials BaDy$_2$O$_4$ and BaHo$_2$O$_4$,"The compounds BaDy$_2$O$_4$ and BaHo$_2$O$_4$ are part of a family of
frustrated systems exhibiting interesting properties, including spin
liquid-type ground states, magnetic field-induced phases, and the coexistence
of short- and long-range magnetic orders, with dominant one-dimensional
correlations, which can be described as Ising $J_1-J_2$ zigzag chains along the
$c$-axis. We have investigated polycrystalline samples of BaDy$_2$O$_4$ and
BaHo$_2$O$_4$ with both neutron diffraction and neutron spectroscopy, coupled
to detailed crystalline electric field calculations. The latter points to
site-dependent anisotropic magnetism in both materials, which is corroborated
by the magnetic structures we determined. The two systems show the coexistence
of two different long-range orders --- two double N\'eel
$\uparrow\uparrow\downarrow\downarrow$ orders in the $ab$-plane with
propagation vectors $\mathbf{k}_1$ = ($\frac{1}{2}$,0,$\frac{1}{2}$) and
$\mathbf{k}_2$ = ($\frac{1}{2}$,$\frac{1}{2}$,$\frac{1}{2}$) for BaDy$_2$O$_4$,
and two distinct arrangements of simple N\'eel
$\uparrow\downarrow\uparrow\downarrow$ orders along the $c$-axis, both with the
propagation vector $\mathbf{k}_0$ = (0,0,0) for BaHo$_2$O$_4$. The order for
both wave vectors in BaDy$_2$O$_4$ occurs at $T_\mathrm{N}$ = 0.48 K, while in
BaHo$_2$O$_4$, the first order sets in at $T_\mathrm{N}\sim$ 1.3 K and the
second one has a lower ordering temperature of 0.84 K. Both compounds show
extensive diffuse scattering which we successfully modeled with a
one-dimensional axial next-nearest neighbor Ising (ANNNI) model. In both
materials, strong diffusive scattering persists to temperatures well below
where the magnetic order is fully saturated. The ANNNI model fits indicate the
presence of sites which do not order with moments in the $ab$-plane.",1805.04694v1
2019-03-19,Magnetic properties and domain structure of ultrathin yttrium iron garnet/Pt bilayers,"We report on the structure, magnetization, magnetic anisotropy, and domain
morphology of ultrathin yttrium iron garnet (YIG)/Pt films with thickness
ranging from 3 to 90 nm. We find that the saturation magnetization is close to
the bulk value in the thickest films and decreases towards low thickness with a
strong reduction below 10 nm. We characterize the magnetic anisotropy by
measuring the transverse spin Hall magnetoresistance as a function of applied
field. Our results reveal strong easy plane anisotropy fields of the order of
50-100 mT, which add to the demagnetizing field, as well as weaker in-plane
uniaxial anisotropy ranging from 10 to 100 $\mu$T. The in-plane easy axis
direction changes with thickness, but presents also significant fluctuations
among samples with the same thickness grown on the same substrate. X-ray
photoelectron emission microscopy reveals the formation of zigzag magnetic
domains in YIG films thicker than 10 nm, which have dimensions larger than
several 100 $\mu$m and are separated by achiral N\'{e}el-type domain walls.
Smaller domains characterized by interspersed elongated features are found in
YIG films thinner than 10 nm.",1903.08285v1
2019-04-23,First 100 ms of a long-lived magnetized neutron star formed in a binary neutron star merger,"The recent multimessenger observation of the short gamma-ray burst (SGRB) GRB
170817A together with the gravitational wave (GW) event GW170817 provides
evidence for the long-standing hypothesis associating SGRBs with binary neutron
star (BNS) mergers. The nature of the remnant object powering the SGRB, which
could have been either an accreting black hole (BH) or a long-lived magnetized
neutron star (NS), is, however, still uncertain. General relativistic
magnetohydrodynamic (GRMHD) simulations of the merger process represent a
powerful tool to unravel the jet launching mechanism, but so far most
simulations focused the attention on a BH as the central engine, while the
long-lived NS scenario remains poorly investigated. Here, we explore the latter
by performing a GRMHD BNS merger simulation extending up to ~100 ms after
merger, much longer than any previous simulation of this kind. This allows us
to (i) study the emerging structure and amplification of the magnetic field and
observe a clear saturation at magnetic energy $E_\mathrm{mag} \sim 10^{51}$
erg, (ii) follow the magnetically supported expansion of the outer layers of
the remnant NS and its evolution into an ellipsoidal shape without any
surrounding torus, and (iii) monitor density, magnetization, and velocity along
the axis, observing no signs of jet formation. We also argue that the
conditions at the end of the simulation disfavor later jet formation on
subsecond timescales if no BH is formed. Furthermore, we examine the rotation
profile of the remnant, the conversion of rotational energy associated with
differential rotation, the overall energy budget of the system, and the
evolution of the GW frequency spectrum. Finally, we perform an additional
simulation where we induce the collapse to a BH ~70 ms after merger, in order
to gain insights on the prospects for massive accretion tori in case of a late
collapse. We find that...",1904.10222v2
2019-06-27,The low-frequency break observed in the slow solar wind magnetic spectra,"Fluctuations of solar wind magnetic field and plasma parameters exhibit a
typical turbulence power spectrum with a spectral index ranging between $\sim
-5/3$ and $\sim -3/2$. In particular, at $1$ AU, the magnetic field spectrum,
observed within fast corotating streams, also shows a clear steepening for
frequencies higher than the typical proton scales, of the order of $\sim
3\times10^{-1}$ Hz, and a flattening towards $1/f$ at frequencies lower than
$\sim 10^{-3}$ Hz. However, the current literature reports observations of the
low-frequency break only for fast streams. Slow streams, as observed to date,
have not shown a clear break, and this has commonly been attributed to slow
wind intervals not being long enough. Actually, because of the longer transit
time from the Sun, slow wind turbulence would be older and the frequency break
would be shifted to lower frequencies with respect to fast wind. Based on this
hypothesis, we performed a careful search for long-lasting slow wind intervals
throughout $12$ years of Wind satellite measurements. Our search, based on
stringent requirements not only on wind speed but also on the level of magnetic
compressibility and Alfv\'enicity of the turbulent fluctuations, yielded $48$
slow wind streams lasting longer than $7$ days. This result allowed us to
extend our study to frequencies sufficiently low and, for the first time in the
literature, we are able to show that the $1/f$ magnetic spectral scaling is
also present in the slow solar wind, provided the interval is long enough.
However, this is not the case for the slow wind velocity spectrum, which keeps
the typical Kolmogorov scaling throughout the analysed frequency range. After
ruling out the possible role of compressibility and Alfv\'enicity for the 1/f
scaling, a possible explanation in terms of magnetic amplitude saturation, as
recently proposed in the literature, is suggested.",1906.11767v1
2019-06-29,Terahertz Faraday and Kerr rotation spectroscopy of Bi$_{1-x}$Sb$_x$ films in high magnetic fields up to 30 Tesla,"We report results of terahertz Faraday and Kerr rotation spectroscopy
measurements on thin films of $\text{Bi}_{1-x}\text{Sb}_{x}$, an alloy system
that exhibits a semimetal-to-topological-insulator transition as the Sb
composition $x$ increases. By using a single-shot time-domain terahertz
spectroscopy setup combined with a table-top pulsed mini-coil magnet, we
conducted measurements in magnetic fields up to 30~T, observing distinctly
different behaviors between semimetallic ($x < 0.07$) and topological insulator
($x > 0.07$) samples. Faraday and Kerr rotation spectra for the semimetallic
films showed a pronounced dip that blue-shifted with the magnetic field,
whereas spectra for the topological insulator films were positive and
featureless, increasing in amplitude with increasing magnetic field and
eventually saturating at high fields ($>$20~T). Ellipticity spectra for the
semimetallic films showed resonances, whereas the topological insulator films
showed no detectable ellipticity. To explain these observations, we developed a
theoretical model based on realistic band parameters and the Kubo formula for
calculating the optical conductivity of Landau-quantized charge carriers. Our
calculations quantitatively reproduced all experimental features, establishing
that the Faraday and Kerr signals in the semimetallic films predominantly arise
from bulk hole cyclotron resonances while the signals in the topological
insulator films represent combined effects of surface carriers originating from
multiple electron and hole pockets. These results demonstrate that the use of
high magnetic fields in terahertz magnetopolarimetry, combined with detailed
electronic structure and conductivity calculations, allows us to unambiguously
identify and quantitatively determine unique contributions from different
species of carriers of topological and nontopological nature in
Bi$_{1-x}$Sb$_x$.",1907.00137v1
2020-05-19,The benefits of a Bayesian analysis for the characterization of magnetic nanoparticles,"Magnetic nanoparticles offer a unique potential for various biomedical
applications, but prior to commercial usage a standardized characterization of
their structural and magnetic properties is required. For a thorough
characterization, the combination of conventional magnetometry and advanced
scattering techniques has shown great potential. In the present work, we
characterize a powder sample of high-quality iron oxide nanoparticles that are
surrounded with a homogeneous thick silica shell by DC magnetometry and
magnetic small-angle neutron scattering (SANS). To retrieve the particle
parameters such as their size distribution and saturation magnetization from
the data, we apply standard model fits of individual data sets as well as
global fits of multiple curves, including a combination of the magnetometry and
SANS measurements. We show that by combining a standard least-squares fit with
a subsequent Bayesian approach for the data refinement, the probability
distributions of the model parameters and their cross correlations can be
readily extracted, which enables a direct visual feedback regarding the quality
of the fit. This prevents an overfitting of data in case of highly correlated
parameters and renders the Bayesian method as an ideal component for a
standardized data analysis of magnetic nanoparticle samples.",2005.09325v3
2020-08-02,Chiral properties of (2+1)-flavor QCD in strong magnetic fields at zero temperature,"We present lattice QCD results for masses and magnetic polarizabilities of
light and strange pseudoscalar mesons, chiral condensates, decay constants of
neutral pion, and neutral kaon in the presence of background magnetic fields
with $eB$ ranging up to around 3.35 GeV$^2$ ($\sim70~M_\pi^2$) in the vacuum.
The computations were carried out in (2+1)-flavor QCD mostly on $32^3 \times
96$ lattices using the highly improved staggered quark action with $M_{\pi}
\approx $ 220 MeV at zero temperature. We find that the masses of neutral
pseudoscalar mesons monotonously decrease as the magnetic field strength grows
and then saturate at a nonzero value, while there exists a nonmonotonous
behavior of charged pion and kaon masses in the magnetic field. We observe a
$qB$ scaling of the up and down quark flavor components of neutral pion mass,
neutral pion decay constant as well as the quark chiral condensates at 0.05
$\lesssim eB\lesssim$ 3.35 GeV$^2$. We show that the correction to the
Gell-Mann-Oakes-Renner relation involving the neutral pion is less than 6% and
the correction for the relation involving neutral kaon is less than 30% at
$eB\lesssim$ 3.35 GeV$^2$. We also derive the Ward-Takahashi identities for QCD
in the magnetic field in the continuum formulation including the relation
between integrated neutral pseudoscalar meson correlators and chiral
condensates.",2008.00493v4
2021-05-24,Spin Canting in Exchange Coupled Bi-Magnetic Nanoparticles: Interfacial Effects and Hard / Soft Layer Ordering,"We investigate the spatial distribution of spin orientation in magnetic
nanoparticles consisting of hard and soft magnetic layers. The nanoparticles
are synthesized in a core / shell spherical morphology where the magnetically
hard, high anisotropy layer is CoFe$_2$O$_4$ (CFO) while the lower anisotropy
material is Fe$_3$O$_4$ (FO). The nanoparticles have a mean diameter of
$\sim$9.2 - 9.6 nm and are synthesized as two variants: a conventional hard /
soft core / shell structure with a CFO core / FO shell (CFO@FO) and the
inverted structure FO core / CFO shell (FO@CFO). High resolution electron
microscopy confirms the coherent spinel structure across the core / shell
boundary in both variants while magnetometry indicates the nanoparticles are
superparamagnetic at 300 K and develop a considerable anisotropy at reduced
temperatures. Low temperature \textit{M vs. H} loops suggest a multi-step
reversal process. Temperature dependent small angle neutron scattering (SANS)
with full polarization analysis reveals a strong perpendicular plane alignment
of the spins near zero field, indicative of spin canting, but the perpendicular
alignment quickly disappears upon application of a weak field and little spin
ordering parallel to the field until the coercive field is reached. Above the
coercive field of the sample, spins orient predominantly along the field
direction. At both zero field and near saturation, the parallel magnetic SANS
peak coincides with the structural peak, indicating the magnetization is
uniform throughout the nanoparticle volume, while near the coercive field the
parallel scattering peak shifts to higher momentum transfer (Q), suggesting
that the coherent scattering volume is smaller and likely originates in the
softer Fe$_3$O$_4$ portion of the nanoparticle.",2105.11501v1
2022-01-10,Formation of Magnetically Truncated Accretion Disks in 3D Radiation-Transport Two-Temperature GRMHD Simulations,"Multi-wavelength observations suggest that the accretion disk in the hard and
intermediate states of X-ray binaries (XRBs) and active galactic nuclei (AGN)
transitions from a cold, thin disk at large distances into a hot, thick flow
close to the black hole. However, the formation, structure and dynamics of such
truncated disks are poorly constrained due to the complexity of the
thermodynamic, magnetic, and radiative processes involved. We present the first
radiation-transport two-temperature general relativistic magnetohydrodynamic
(GRMHD) simulations of truncated disks radiating at ~35% of the Eddington
luminosity with and without large-scale poloidal magnetic flux. We demonstrate
that when a geometrically-thin accretion disk is threaded by large-scale net
poloidal magnetic flux, it self-consistently transitions at small radii into a
two-phase medium of cold gas clumps floating through a hot, magnetically
dominated corona. This transition occurs at a well-defined truncation radius
determined by the distance out to which the disk is saturated with magnetic
flux. The average ion and electron temperatures in the semi-opaque corona
reach, respectively, T_i ~ 10^10K and T_e ~ 5 10^8K. The system produces
radiation, powerful collimated jets and broader winds at the total energy
efficiency exceeding ~90%, the highest ever energy extraction efficiency from a
spinning black hole by a radiatively efficient flow in a GRMHD simulation. This
is consistent with jetted ejections observed during XRB outbursts. The
two-phase medium may naturally lead to broadened iron line emission observed in
the hard state.",2201.03526v3
2022-06-08,Gravitoturbulent dynamo in global simulations of gaseous disks,"The turbulence driven by gravitational instabilities (GIs) can amplify
magnetic fields in massive gaseous disks. This GI dynamo may appear in young
circumstellar disks, whose weak ionization challenges other amplification
routes, as well as in active galactic nuclei. Although regarded as a
large-scale dynamo, only local simulations have so far described its kinematic
regime. We study the GI dynamo in global magnetohydrodynamic (MHD) models of
accretion disks, focusing on its kinematic phase. We perform resistive MHD
simulations with the Pluto code for different radiative cooling times and
electrical resistivities. A weak magnetic field seeds the dynamo, and we adopt
mean-field and heuristic models to capture its essence. We recover the same
induction process leading to magnetic field amplification as previously
identified in local simulations. The dynamo is, however, global in nature,
connecting distant annuli of the disk via a large-scale dynamo mode of a fixed
growth rate. This large-scale amplification can be described by a mean-field
model that does not rely on conventional alpha-Omega effects. When varying the
disk parameters we find an optimal resistivity that facilitates magnetic
amplification, whose magnetic Reynolds number, Rm < 10, is substantially
smaller than in local simulations. Unlike local simulations, we find an optimal
cooling rate and the existence of global oscillating dynamo modes. The
nonlinear saturation of the dynamo puts the disk in a strongly magnetized
turbulent state on the margins of the effective range of GI. In our
simulations, the accretion power eventually exceeds the threshold required by
local thermal balance against cooling, leaving the long-term nonlinear outcome
of the GI dynamo uncertain.",2206.03917v2
2008-11-11,Semi-global simulations of the magneto-rotational instability in core collapse supernovae,"Possible effects of magnetic fields in core collapse supernovae rely on an
efficient amplification of the weak pre-collapse fields. It has been suggested
that the magneto-rotational instability (MRI) leads to rapid field growth.
Although MRI studies exist for accretion discs, the application of their
results to core collapse supernovae is inhibited as the physics of supernova
cores is substantially different from that of accretion discs. We address the
problem of growth and saturation of the MRI by means of semi-global
simulations, which combine elements of global and local simulations by taking
the presence of global background gradients into account and using a local
computational grid. We analyze the dispersion relation of the MRI to identify
different regimes of the instability. This analysis is complemented by
simulations, where we consider a local computational box rotating at
sub-Keplerian velocity, and where we allow for a radial entropy gradient. We
identify six regimes of the MRI depending on the ratio of the entropy and
angular velocity gradient. Our numerical models confirm the instability
criteria and growth rates for all relevant regimes. The MRI grows exponentially
within milliseconds the flow and magnetic field geometries being dominated by
channel flows. The MRI growth ceases once the channels are disrupted by
resistive instabilities (due to finite numerical conductivity), and MHD
turbulence sets in. From an analysis of the growth rates of the resistive
instabilities, we deduce scaling laws for the termination amplitude of the MRI
which agree well with our numerical models. We determine the dependence of the
development of coherent flow structures in the saturated state on the aspect
ratio of the simulation boxes. [abridged]",0811.1652v2
2011-11-29,Oscillatory large-scale dynamos from Cartesian convection simulations,"We present results from compressible Cartesian convection simulations with
and without imposed shear. In the former case the dynamo is expected to be of
$\alpha^2\varOmega$ type which is generally expected to be relevant for the
Sun, whereas the latter case refers to $\alpha^2$ dynamos which are more likely
to occur in more rapidly rotating stars whose differential rotation is small.
We perform a parameter study where the shear flow and the rotational influence
are varied to probe the relative importance of both types of dynamos.
Oscillatory solutions are preferred both in the kinematic and saturated regimes
when the negative ratio of shear to rotation rates, $q\equiv -S/\varOmega$, is
between 1.5 and 2, i.e., when shear and rotation are of comparable strengths.
Other regions of oscillatory solutions are found with small values of $q$,
i.e., when shear is weak in comparison to rotation, and in the regime of large
negative $q$s, when shear is very strong in comparison to rotation. However,
exceptions to these rules also appear so that for a given ratio of shear to
rotation, solutions are non-oscillatory for small and large shear, but
oscillatory in the intermediate range. Changing the boundary conditions from
vertical field to perfect conductor ones changes the dynamo mode from
oscillatory to quasi-steady. Furthermore, in many cases an oscillatory solution
exists only in the kinematic regime whereas in the nonlinear stage the mean
fields are stationary. However, the cases with rotation and no shear are always
oscillatory in the parameter range studied here and the dynamo mode does not
depend on the magnetic boundary conditions. The strengths of total and
large-scale components of the magnetic field in the saturated state, however,
are sensitive to the chosen boundary conditions.",1111.6894v2
2013-02-26,Inverse Z-spectrum analysis for MT- and spillover-corrected and T1-compensated steady-state pulsed CEST-MRI - application to pH-weighted MRI of acute stroke,"Endogenous chemical exchange saturation transfer (CEST) effects are always
diluted by competing effects such as direct water proton saturation (spillover)
and macromolecular magnetization transfer (MT). This leads to T2-and
MT-shine-through effects in the actual biochemical contrast of CEST. Therefore,
a simple evaluation algorithm which corrects the CEST signal was searched for.
By employing a recent eigenspace theory valid for spinlock and continuous wave
(cw) CEST we predict that the inverse Z-spectrum is beneficial to Z-spectrum
itself. Based on this we propose a new spillover- and MT-corrected
magnetization transfer ratio (MTRRex) yielding Rex, the exchange dependent
relaxation rate in the rotating frame. For verification, the amine proton
exchange of creatine in solutions with different agar concentration was studied
experimentally at clinical field strength of 3T. In contrast to the compared
standard evaluation for pulsed CEST experiments, MTRasym, our approach shows no
T2 or MT shine through effect. We demonstrate that spillover can be corrected
properly and also quantitative evaluation of pH and creatine concentration is
possible which proves MTRRex as quantitative CEST-MRI method. A spillover
correction is of special interest for clinical static field strengths and
protons resonating near the water peak. This is the case for -OH-CEST effects
like gagCEST or glucoCEST, but also amine exchange of creatine or glutamate
which require high B1. Although, only showed for amine exchange, we propose our
normalization to work generally for DIACEST, PARACEST in slow- and fast
exchange regime not just as a correction, but also for quantitative CEST-MRI.
Applied to acute stroke induced in rat brain, the corrected CEST signal shows
significantly higher contrast between stroke area and normal tissue as well as
less B1 dependency compared to conventional approaches.",1302.6605v2
2014-01-13,Influence of La and Mn vacancies on the electronic and magnetic properties of LaMnO$_{3}$ thin films grown by pulsed laser deposition,"With pulsed laser deposition we have grown c-axis oriented thin films of the
nominal composition LaMnO$_{3}$ (LMO) on LSAT(001) substrates. We find that,
depending on the oxygen background pressure during growth, the LMO films
contain sizeable amounts of La and/or Mn vacancies that strongly influence
their electronic and magnetic properties. Specifically, we show that the Mn/La
ratio can be systematically varied from 0.92 at 0.11 mbar to 1.09 at 0.30 mbar
of oxygen. These cationic vacancies lead to markedly different disorder effects
that become most pronounced once the samples are fully oxygenated and thus
strongly hole doped. All as-grown and thus slightly oxygen deficient LMO films
are ferromagnetic insulators with saturation moments in excess of 2.5 \mu
$_{B}$ per Mn ion, their transport and optical properties that can be
understood in terms of trapped ferromagnetic polarons. Upon oxygen annealing,
the most La-deficient films develop a metallic response with an even larger
ferromagnetic saturation moment of 3.8 \mu $_{B}$ per Mn ion. In contrast, in
the oxygenated Mn-deficient films the ferromagnetic order is almost completely
suppressed to less than 0.5 \mu $_{B}$ per Mn ion and the transport remains
insulator-like. We compare our results with the ones that were previously
obtained on bulk samples and present an interpretation in terms of the much
stronger disorder potential of the Mn vacancies as compared to the La
vacancies. We also discuss the implications for the growth of LMO thin films
with well-defined physical properties that, for example, are a prerequisite for
the study of interface effects in multilayers.",1401.2820v2
2017-04-13,Exact diagonalization and cluster mean-field study of triangular-lattice XXZ antiferromagnets near saturation,"Quantum magnetic phases near the magnetic saturation of triangular-lattice
antiferromagnets with XXZ anisotropy have been attracting renewed interest
since it has been suggested that a nontrivial coplanar phase, called the
$\pi$-coplanar or $\Psi$ phase, could be stabilized by quantum effects in a
certain range of anisotropy parameter $J/J_z$ besides the well-known 0-coplanar
(known also as $V$) and umbrella phases. Recently, Sellmann $et$ $al$. [Phys.
Rev. B {\bf 91}, 081104(R) (2015)] claimed that the $\pi$-coplanar phase is
absent for $S=1/2$ from an exact-diagonalization analysis in the sector of the
Hilbert space with only three down-spins (three magnons). We first reconsider
and improve this analysis by taking into account several low-lying eigenvalues
and the associated eigenstates as a function of $J/J_z$ and by sensibly
increasing the system sizes (up to 1296 spins). A careful identification
analysis shows that the lowest eigenstate is a chirally antisymmetric
combination of finite-size umbrella states for $J/J_z\gtrsim 2.218$ while it
corresponds to a coplanar phase for $J/J_z\lesssim 2.218$. However, we
demonstrate that the distinction between 0-coplanar and $\pi$-coplanar phases
in the latter region is fundamentally impossible from the symmetry-preserving
finite-size calculations with fixed magnon number.} Therefore, we also perform
a cluster mean-field plus scaling analysis for small spins $S\leq 3/2$. The
obtained results, together with the previous large-$S$ analysis, indicate that
the $\pi$-coplanar phase exists for any $S$ except for the classical limit
($S\rightarrow \infty$) and the existence range in $J/J_z$ is largest in the
most quantum case of $S=1/2$.",1704.04024v2
2018-12-18,Electronic properties of type-II Weyl semimetal WTe$_2$. A review perspective,"Currently, there is a flurry of research interest on materials with an
unconventional electronic structure, and we have already seen significant
progress in their understanding and engineering towards real-life applications.
The interest erupted with the discovery of graphene and topological insulators
in the previous decade. The electrons in graphene simulate massless Dirac
Fermions with a linearly dispersing Dirac cone in their band structure, while
in topological insulators, the electronic bands wind non-trivially in momentum
space giving rise to gapless surface states and bulk bandgap. Weyl semimetals
in condensed matter systems are the latest addition to this growing family of
topological materials. Weyl Fermions are known in the context of high energy
physics since almost the beginning of quantum mechanics. They apparently
violate charge conservation rules, displaying the ""chiral anomaly"", with such
remarkable properties recently theoretically predicted and experimentally
verified to exist as low energy quasiparticle states in certain condensed
matter systems. Not only are these new materials extremely important for our
fundamental understanding of quantum phenomena, but also they exhibit
completely different transport phenomena. For example, massless Fermions are
susceptible to scattering from non-magnetic impurities. Dirac semimetals
exhibit non-saturating extremely large magnetoresistance as a consequence of
their robust electronic bands being protected by time reversal symmetry. These
open up whole new possibilities for materials engineering and applications
including quantum computing. In this review, we recapitulate some of the
outstanding properties of WTe$_2$, namely, its non-saturating titanic
magnetoresistance due to perfect electron and hole carrier balance up to a very
high magnetic field observed for the very first time. (Continued. Please see
the main article).",1812.07215v1
2020-10-24,The Evolution of the Solar-Stellar Activity,"We present a brief review of observational results contributing to modern
ideas on the evolution of stellar activity. Basic laws, derived for both
rotation-age and activity-rotation relationships, allow us to trace how the
activity of low-mass stars changes with age during their stay on the main
sequence. We focus on the evaluation of the activity properties of stars that
could be analogs of the young Sun. Our study includes joint consideration of
different tracers of activity, rotation and magnetic fields of Sun-like stars
of various ages. We identify rotation periods, when the saturated regime of
activity changes to the unsaturated mode, when the solar-type activity is
formed: for G- and K-type stars, they are 1.1 and 3.3 days, respectively. This
corresponds to an age interval of about 0.2-0.6 Gyr, when regular sunspot cycle
began to be established on the early Sun. We discuss properties of the coronal
and chromospheric activity in young Suns. Our evaluation of the EUV-fluxes in
the spectral range of 1350-1750 A shows that the far-UV radiation of the early
Sun was a factor of 7 times more intense than that of the present-day Sun, and
twice higher when the regular sunspot cycle was established. For the young Sun,
we can estimate the possible mass loss rate associated with quasi-steady
outflow as $10^{-12} M_\odot$/yr. The results of observations of the largest
flares on solar-type stars are also discussed, leading to conclusion that the
most powerful phenomena occur on the fast-rotating stars in the saturated
activity regime. Our estimate of the stellar magnetic fields makes it possible
to evaluate the maximal possible flare energy. This could help us better
understand the origin of extreme events on the Sun in the past.",2010.12922v1
2020-11-25,Supergap and subgap enhanced currents in asymmetric {S_1FS_2} Josephson junctions,"We have theoretically studied the supercurrent profiles in three-dimensional
normal metal and ferromagnetic Josephson configurations, where the magnitude of
the superconducting gaps in the superconducting leads are unequal, i.e.,
$\Delta_1\neq \Delta_2$, creating asymmetric $S_1NS_2$ and $S_1FS_2$ systems.
Our results reveal that by increasing the ratio of the superconducting gaps
$\Delta_2/\Delta_1$, the critical supercurrent in a ballistic $S_1NS_2$ system
can be enhanced by more than $100\%$, and reaches a saturation point, or decays
away, depending on the junction thickness, magnetization strength, and chemical
potential. The total critical current in a diffusive $S_1NS_2$ system was found
to be enhanced by more than $50\%$ parabolically, and reaches saturation by
increasing one of the superconducting gaps. In a uniform ferromagnetic
junction, the supercurrent undergoes reversal by increasing
$\Delta_2/\Delta_1>1$. Through decomposing the total supercurrent into its
supergap and subgap components, our results illustrate their crucial relative
contributions to the Josephson current flow. It was found that the competition
of subgap and supergap currents in a $S_1FS_2$ junction results in the
emergence of second harmonics in the current-phase relation. In contrast to a
diffusive asymmetric Josephson configuration, the behavior of the supercurrent
in a ballistic system with $\Delta_2/\Delta_1=1$ can be properly described by
the subgap current component only, in a wide range of parameter sets, including
Fermi level mismatch, magnetization strength, and junction thickness.
Interestingly, when $\Delta_2/\Delta_1>1$, our results have found multiple
parameter sets where the total supercurrent is driven by the supergap
component. Therefore, our comprehensive study highlights the importance of
subgap and supergap supercurrent components in both the ballistic and diffusive
regimes.",2011.12967v2
2023-09-26,Tensor-valued and frequency-dependent diffusion MRI and magnetization transfer saturation MRI evolution during adult mouse brain maturation,"Although rodent models are a predominant study model in neuroscience
research, research investigating healthy rodent brain maturation remains
limited. This motivates further study of normal brain maturation in rodents to
exclude confounds of developmental changes from interpretations of disease
mechanisms. 11 C57Bl/6 mice (6 males) were scanned longitudinally at 3, 4, 5,
and 8 months of age using frequency-dependent and tensor-valued diffusion MRI
(dMRI), and Magnetization Transfer saturation (MTsat) MRI. Total kurtosis
showed significant increases over time in all regions, which was driven by
increases in isotropic kurtosis while anisotropic kurtosis remained stable.
Increases in total and isotropic kurtosis with age were matched with increases
in MTsat. Quadratic fits revealed that most metrics show a maximum/minimum
around 5-6 months of age. Most dMRI metrics revealed significantly different
trajectories between males and females, while the MT metrics did not. Linear
fits between kurtosis and MT metrics highlighted that changes in total kurtosis
found throughout normal brain development are driven by isotropic kurtosis,
while differences in total kurtosis between brain regions are driven by
anisotropic kurtosis. Overall, the trends observed in conventional dMRI and MT
metrics are comparable to previous studies on normal brain development, while
the trajectories of our more advanced dMRI metrics provide novel insight. Based
on the developmental trajectories of tensor-valued dMRI and MT metrics, our
results suggest myelination during brain maturation is not a main contributor
to microscopic diffusion anisotropy and anisotropic kurtosis in axons. For
studies that only calculate total kurtosis, we suggest caution in attributing
neurobiological changes to changes in total kurtosis as we show here constant
anisotropic kurtosis in the presence of increasing myelin content.",2309.15202v1
2024-01-08,Maser polarization through anisotropic pumping,"(Abridged) Polarized emission from masers is an excellent tool to study
magnetic fields in maser sources. The linear polarization of most masers is
understood as an interplay of maser saturation and anisotropic pumping.
However, for the latter mechanism, no quantitative modeling has been presented
yet. We present a comprehensive model of maser polarization, including
quantitative modeling of both anisotropic pumping and the effects of maser
saturation on the polarization of masers. We extend regular maser excitation
modeling with a dimension that describes the molecular population alignments,
as well as including the linear polarization dimension to the radiative
transfer. The results of the excitation analysis yield the anisotropic pumping
and decay parameters, that are subsequently used in one-dimensional proper
maser polarization radiative transfer modeling. We present the anisotropic
pumping parameters for a variety of transitions from class I CH$_3$OH masers,
H$_2$O masers and SiO masers. SiO masers are highly anisotropically pumped due
to them occurring in the vicinity of a late-type star, that irradiates the
maser region with a strong directional radiation field. Class I CH$_3$OH masers
and H$_2$O masers occur in association with shocks, and they are modestly
anisotropically pumped due to the anisotropy of the excitation region. Our
modeling constitutes the first quantitative constraints on the anisotropic
pumping of masers. We find that anisotropic pumping can explain the high
polarization yields of SiO masers, as well as the modest polarization of
unsaturated class I CH$_3$OH masers. We predict that the $183$ GHz H$_2$O maser
is strongly anisotropically pumped. Finally, we outline a mechanism through
which non-Zeeman circular polarization is produced, when the magnetic field
changes direction along the propagation through an anisotropically pumped
maser.",2401.04185v1
1998-02-17,Nonlinear Evolution of the Magnetorotational Instability in Ion-Neutral Disks,"We carry out three-dimensional magnetohydrodynamical simulations of the
magnetorotational (Balbus-Hawley) instability in weakly-ionized plasmas. We
adopt a formulation in which the ions and neutrals each are treated as separate
fluids coupled only through a collisional drag term. Ionization and
recombination processes are not considered. The linear stability of the
ion-neutral system has been previously considered by Blaes and Balbus (1994).
Here we extend their results into the nonlinear regime by computing the
evolution of Keplerian angular momentum distribution in the local shearing box
approximation. We find significant turbulence and angular momentum transport
when the collisional frequency is on order 100 times the orbital frequency. At
higher collision rates, the two-fluid system studied here behaves much like the
fully ionized systems studied previously. At lower collision rates the
evolution of the instability is determined primarily by the properties of the
ions, with the neutrals acting as a sink for the turbulence. Since in this
regime saturation occurs when the magnetic field is superthermal with respect
to the ion pressure, we find the amplitude of the magnetic energy and the
corresponding angular momentum transport rate is proportional to the ion
density. Our calculations show the ions and neutrals are essentially decoupled
when the collision frequency is less than 0.01 times the orbital frequency; in
this case the ion fluid behaves as in the single fluid simulations and the
neutrals remain quiescent. We find that purely toroidal initial magnetic field
configurations are unstable to the magnetorotational instability across the
range of coupling frequencies.",9802227v1
1998-08-22,Three-Dimensional Evolution of the Parker Instability under a Uniform Gravity,"Using an isothermal MHD code, we have performed three-dimensional,
high-resolution simulations of the Parker instability. The initial equilibrium
system is composed of exponentially-decreasing isothermal gas and magnetic
field (along the azimuthal direction) under a uniform gravity. The evolution of
the instability can be divided into three phases: linear, nonlinear, and
relaxed. During the linear phase, the perturbations grow exponentially with a
preferred scale along the azimuthal direction but with smallest possible scale
along the radial direction, as predicted from linear analyses. During the
nonlinear phase, the growth of the instability is saturated and flow motion
becomes chaotic. Magnetic reconnection occurs, which allows gas to cross field
lines. This, in turn, results in the redistribution of gas and magnetic field.
The system approaches a new equilibrium in the relaxed phase, which is
different from the one seen in two-dimensional works. The structures formed
during the evolution are sheet-like or filamentary, whose shortest dimension is
radial. Their maximum density enhancement factor relative to the initial value
is less than 2. Since the radial dimension is too small and the density
enhancement is too low, it is difficult to regard the Parker instability alone
as a viable mechanism for the formation of giant molecular clouds.",9808244v1
1999-04-16,Battery and Dynamo theory in the Kerr metric,"The generation and evolution of magnetic fields in the plasma accreting into
a rotating black hole is studied in the 3+1 split of the Kerr metric. Attention
is focused on effects of the gravitomagnetic potential. The gravitomagnetic
force appears as battery term in the generalized Ohm's law. The gravitomagnetic
battery is likely to saturate at higher field strength than the classical
Biermann battery.
  The coupling of the gravitomagnetic potential with electric fields appears as
gravitomagnetic current in Maxwell's equations. In the magnetohydrodynamic
induction equation, this current re-appears as source term for the poloidal
magnetic field, which can produce closed magnetic structures around an
accreting black hole. In principle, even self-excited axisymmetric dynamo
action is possible, which means that Cowling's anti-dynamo theorem does not
hold in the Kerr metric.
  Finally, simulations of the alpha-Omega dynamo in accretion flows into the
hole are presented. I assume a simple expression of alpha in this relativistic
context. The modes of the dynamo are oscillating for dynamo numbers which are
typical for accretion disks. In a zero angular momentum flow into a Kerr black
hole there is still shear, i.e. the angular velocity, Omega, of the plasma
equals the angular velocity of space, omega, and it has been speculated (Meier
1998) that even then a dynamo could operate. This is shown to be unlikely due
to the rapid accretion.",9904215v1
2000-06-07,The Effect of Expansion on Mass Entrainment and Stability of Super-Alfvénic Jets,"We extend investigations of mass entrainment by jets, which previously have
focused on cylindrical supermagnetosonic jets and expanding trans-Alfv\'enic
jets, to a set of expanding supermagnetosonic jets. We precess these jets at
the origin to excite the helical mode of the Kelvin-Helmholtz (or KH)
instability, in order to compare the results with predictions from linear
stability analysis. We analyze this simulation set for the spatial development
of magnetized mass, which we interpret as jet plus entrained, initially
unmagnetized external mass. As with the previous simulation sets, we find that
the growth of magnetized mass is associated with the growth of the KH
instability through linear, nonlinear, and saturated stages and with the
expansion of magnetized material in simulated observations of the jet. From
comparison of measured wavelengths and wave speeds with the predictions from
linear stability analysis, we see evidence that the KH instability is the
primary cause for mass entrainment in these simulations, and that the expansion
reduces the rate of mass entrainment. This reduced rate can be observed as a
somewhat greater distance between the two transition points separating the
three stages of expansion.",0006102v1
2004-08-24,The polarization of mm methanol masers,"We present a survey of the polarization properties of mm-wavelength methanol
masers, comprising both classes, and transitions from 84.5 to 157.0 GHz. Linear
polarization is found in more than half of the observed objects, and circular
polarization is tentatively detected in two sources. Class I and Class II
CH_3OH masers show similar polarization properties.The largest linear
polarization is found in the 133 GHz Class I maser towards L379 (39.5 %), and
in the 157 GHz Class II maser towards G9.62+0.19 (36.7 %). The spectral
profiles of the polarization angle of Class I masers are mostly flat, except
for two sources showing a linear slope. Since the mm-line methanol masers are
expected to be weakly (or not) saturated, we suggest that the stronger
fractional polarizations found by us are enhanced by anisotropic pumping and
radiative losses. In NGC 7538, we find, for both maser classes, a good
agreement between our polarization angles, and those measured for the
submillimeter dust continuum. This can be taken as evidence for magnetic
alignment of dust grains. It is also possible that an unsaturated maser with
equally populated magnetic substates simply amplifies polarized continuum seed
radiation. For Class II masers, the polarization properties of the various
velocity components towards a given source with detectable polarization are
quite homogeneous. A possible explanation is discussed. Since methanol is
non-paramagnetic, the circular polarization of the unsaturated maser emission
can only be due to variations of the angle between the magnetic field and the
line of sight along the maser propagation path.",0408446v1
2005-10-31,A Qualitative Interpretation of the Second Solar Spectrum of Ce ll,"This is a theoretical investigation on the formation of the linearly
polarized line spectrum of ionized cerium in the sun. We calculate the
scattering line polarization pattern emergent from a plane-parallel layer of Ce
{\sc ii} atoms illuminated from below by the photospheric radiation field,
taking into account the differential pumping induced in the various magnetic
sublevels by the anisotropic radiation field. We find that the line
polarization pattern calculated with this simple model is in good qualitative
agreement with reported observations. Interestingly, the agreement improves
when some amount of atomic level depolarization is considered. We find that the
best fit to the observations corresponds to the situation where the ground and
metastable levels are depolarized to about one fifth of the corresponding value
obtained in the absence of any depolarizing mechanism. One possibility to have
this situation is that the depolarizing rate value of elastic collisions is
exactly $D=10^6{\rm s}^{-1}$, which is rather unlikely. Therefore, we interpret
that fact as} due to the presence of a turbulent magnetic field in the limit of
saturated Hanle effect for the lower-levels. For this turbulent magnetic field
we obtain a lower limit of 0.8 gauss and an upper limit of 200-300 gauss.",0511011v1
1999-03-26,Surface effects in nanoparticles: application to maghemite $γ$-Fe_{2}O_{3},"We present a microscopic model for nanoparticles, of the maghemite ($\gamma
$% -Fe$_{2}$O$_{3}$) type, and perform classical Monte Carlo simulations of
their magnetic properties. On account of M\""{o}ssbauer spectroscopy and
high-field magnetisation results, we consider a particle as composed of a core
and a surface shell of constant thickness. The magnetic state in the particle
is described by the anisotropic classical Dirac-Heisenberg model including
exchange and dipolar interactions and bulk and surface anisotropy. We consider
the case of ellipsoidal (or spherical) particles with free boundaries at the
surface. Using a surface shell of constant thickness ($\sim 0.35$ nm) we vary
the particle size and study the effect of surface magnetic disorder on the
thermal and spatial behaviors of the net magnetisation of the particle. We
study the shift in the surface ``critical region'' for different
surface-to-core ratios of the exchange coupling constants. It is also shown
that the profile of the local magnetisation exhibits strong temperature
dependence, and that surface anisotropy is reponsible for the non saturation of
the magnetisation at low temperatures.",9903398v5
2001-05-16,"Correlation functions, free energies and magnetizations in the two-dimensional random-field Ising model","Transfer-matrix methods are used to calculate spin-spin correlation functions
($G$), Helmholtz free energies ($f$) and magnetizations ($m$) in the
two-dimensional random-field Ising model close to the zero-field bulk critical
temperature $T_{c 0}$, on long strips of width $L = 3 - 18$ sites, for binary
field distributions. Analysis of the probability distributions of $G$ for
varying spin-spin distances $R$ shows that describing the decay of their
averaged values by effective correlation lengths is a valid procedure only for
not very large $R$. Connections between field-- and correlation function
distributions at high temperatures are established, yielding approximate
analytical expressions for the latter, which are used for computation of the
corresponding structure factor. It is shown that, for fixed $R/L$, the
fractional widths of correlation-function distributions saturate asymptotically
with $L^{-2.2}$. Considering an added uniform applied field $h$, a connection
between $f(h)$, $m(h)$, the Gibbs free energy $g(m)$ and the distribution
function for the uniform magnetization in zero uniform field, $P_0(m)$, is
derived and first illustrated for pure systems, and then applied for non-zero
random field. From finite-size scaling and crossover arguments, coupled with
numerical data, it is found that the width of $P_0(m)$ varies against
(non-vanishing, but small) random-field intensity $H_0$ as $H_0^{-3/7}$.",0105326v1
2002-03-04,Order to disorder transition in the XY-like quantum magnet Cs2CoCl4 induced by noncommuting applied fields,"We explore the effects of noncommuting applied fields on the ground-state
ordering of the quasi-one-dimensional spin-1/2 XY-like antiferromagnet Cs2CoCl4
using single-crystal neutron diffraction. In zero field interchain couplings
cause long-range order below T_N=217(5) mK with chains ordered
antiferromagnetically along their length and moments confined to the (b,c)
plane. Magnetic fields applied at an angle to the XY planes are found to
initially stabilize the order by promoting a spin-flop phase with an increased
perpendicular antiferromagnetic moment. In higher fields the antiferromagnetic
order becomes unstable and a transition occurs to a phase with no long-range
order in the (b,c) plane, proposed to be a spin liquid phase that arises when
the quantum fluctuations induced by the noncommuting field become strong enough
to overcome ordering tendencies. Magnetization measurements confirm that
saturation occurs at much higher fields and that the proposed spin-liquid state
exists in the region 2.10 < H_SL < 2.52 T || a. The observed phase diagram is
discussed in terms of known results on XY-like chains in coexisting
longitudinal and transverse fields.",0203070v1
2004-02-03,Observation of ferromagnetism above 900 K in Cr-GaN and Cr-AlN,"We report the observation of ferromagnetism at over 900K in Cr-GaN and Cr-AlN
thin films. The saturation magnetization moments in our best films of Cr-GaN
and Cr-AlN at low temperatures are 0.42 and 0.6 u_B/Cr atom, respectively,
indicating that 14% and 20%, of the Cr atoms, respectively, are magnetically
active. While Cr-AlN is highly resistive, Cr-GaN exhibits thermally activated
conduction that follows the exponential law expected for variable range hopping
between localized states. Hall measurements on a Cr-GaN sample indicate a
mobility of 0.06 cm^2/V.s, which falls in the range characteristic of hopping
conduction, and a free carrier density (1.4E20/cm^3), which is similar in
magnitude to the measured magnetically-active Cr concentration (4.9E19/cm^3). A
large negative magnetoresistance is attributed to scattering from loose spins
associated with non-ferromagnetic impurities. The results indicate that
ferromagnetism in Cr-GaN and Cr-AlN can be attributed to the double exchange
mechanism as a result of hopping between near-midgap substitutional Cr impurity
bands.",0402103v2
2004-04-16,Non-Markovian Effects on the Two-Dimensional Magnetotransport: Low-field Anomaly in Magnetoresistance,"We discuss classical magnetotransport in a two-dimensional system with strong
scatterers. Even in the limit of very low field, when $\omega_c \tau \ll 1$
($\omega_c$ is the cyclotron frequency, $\tau$ is the scattering time) such a
system demonstrates strong negative magnetoresistance caused by non-Markovian
memory effects. A regular method for the calculation of non-Markovian
corrections to the Drude conductivity is presented. A quantitative theory of
the recently discovered anomalous low-field magnetoresistance is developed for
the system of two-dimensional electrons scattered by hard disks of radius $a,$
randomly distributed with concentration $n.$ For small magnetic fields the
magentoresistance is found to be parabolic and inversely proportional to the
gas parameter, $ \delta \rho_{xx}/\rho \sim - (\omega_c \tau)^2 / n a^2.$ In
some interval of magnetic fields the magnetoresistance is shown to be linear
$\delta \rho_{xx}/\rho \sim - \omega_c \tau $ in a good agreement with the
experiment and numerical simulations. Magnetoresistance saturates for $\omega_c
\tau \gg na^2$, when the anomalous memory effects are totally destroyed by the
magnetic field. We also discuss magnetotransport at very low fields and show
that at such fields magnetoresistance is determined by the trajectories having
a long Lyapunov region.",0404397v2
2004-07-28,Paramagnetic reentrance of the ac-screening: Evidence of vortex avalanches in Pb thin films,"We have studied the influence of a square array of pinning centers on the
dynamics of vortex avalanches in Pb thin films by means of ac- and dc-
magnetization measurements. Close to the superconducting transition Tc the
commensurability between the vortex lattice and the pinning array leads to the
well known local increments of the critical current. As temperature T
decreases, matching features progressively fade out and eventually disappear.
Further down in temperature vortex avalanches develop and dominate the magnetic
response. These avalanches manifest themselves as jumps in the dc-magnetization
and produce a lower ac-shielding giving rise to a paramagnetic reentrance in
the ac-screening x'(T). Within the flux jump regime two subregimes can be
identified. Close to the boundary where vortex avalanches develope, the field
separation between consecutive jumps follow the periodicity of the pinning
array and a field and temperature dependent screening is observed. In this
regime, the response also depends on frequency f in agreement with theoretical
models for magnetothermal instabilities. At low enough temperatures and fields,
the screening saturates to a constant value independent of T, H, and f, where
jumps are randomly distributed. We have also found that vortex instabilities
occupy a larger portion of the H-T diagram in patterned samples than in films
without nanoengineered pinning sites. Finally, we discuss the possible origin
of the vortex avalanches and compare our results with previous experimental and
theoretical studies.",0407737v1
2005-01-21,The isotropic XY model on the inhomogeneous periodic chain,"The static and dynamic properties of the isotropic XY-model $(s=1/2)$ on the
inhomogeneous periodic chain, composed of \emph{N} segments with \emph{n}
different exchange interactions and magnetic moments, in a transverse field
\emph{h} are obtained exactly at arbitrary temperatures. The properties are
determined by introducing the generalized Jordan-Wigner transformation and by
reducing the problem to a diagonalization of a finite matrix of \emph{n-th}
order. The diagonalization procedure is discussed in detail and the critical
behaviour induced by the transverse field, at T=0, is presented. The quantum
transitions are determined by analyzing the behaviour of the induced
magnetization, defined as $(1/n)\sum_{m=1}^{n}\mu_{m}<S_{j,m}^{z}>$ where
$\mu_{m}$ is the magnetic moment at site \emph{m} within the segment \emph{j},
as a function of the field, and the critical fields determined exactly. The
dynamic correlations, $<S_{j,m}^{z}(t)S_{j^{'},m^{'}}^{z}(0)>$, and the dynamic
susceptibility $\chi_{q}^{zz}(\omega)$ are also obtained at arbitrary
temperatures. Explicit results are also presented in the limit T=0, where the
critical behaviour occurs, for the static susceptibility $\chi_{q}^{zz}(0)$ as
a function of the transverse field \emph{h}, and for the frequency dependency
of dynamic susceptibility $\chi_{q}^{zz}(\omega)$. Also in this limit, the
transverse time-correlation $<S_{j,m}^{x}(t)S_{j^{'},m^{'}}^{x}(0)>$, the
dynamic and isothermal susceptibilities, $\chi_{q}^{xx}(\omega)$ and
$\chi_{T}^{xx}$, are obtained for the transverse field greater or equal than
the saturation field.",0501525v1
2005-11-29,Lower critical field and intragrain critical current density in the ruthenate-cuprate RuSr$_{2}$Gd$_{1.5}$Ce$_{0.5}$Cu$_{2}$O$_{10}$,"The lower critical field of the grains, $H_{c1}$, and the intragrain critical
current density, $J_{c}$, were determined for the superconducting
ruthenate-cuprate RuSr$_{2}$Gd$_{1.5}$Ce$_{0.5}$Cu$_{2}$O$_{10-\delta}$
[Ru-1222(Gd)] through a systematic study of the hysteresis in magnetoresistance
loops. A reliable method, based on the effects of the magnetization of the
grains on the net local field at the intergranular junctions is provided,
circumventing the problem of the strong masking of the superconducting
diamagnetic signal by the ferromagnetic background. The temperature dependency
of $H_{c1}$ and $J_{c}$ both exhibit a smooth increase on cooling without
saturation down to $T/T_{SC}$ $\cong $ 0.2. The obtained $H_{c1}$ values vary
between 150 and 1500 Oe in the 0.2 $\leq $ $% T/T_{SC}$ $\leq $ 0.4 interval,
for samples annealed in an oxygen flow; oxygenation under high pressure (50
atm) leads to a further increase. These values are much larger than the
previously reported rough assessments (25-50 Oe), using conventional
magnetization measurements. High $J_{c}$ values of $% \sim $ 10$^{7}$
A/cm$^{2}$, comparable to the high-T$_{c}$ cuprates, were obtained. The
$H_{c1}(T)$ and $J_{c}(T)$ dependencies are explained in the context of a
magnetic phase separation scenario.",0511718v1
2006-04-11,A single layer of Mn in a GaAs quantum well: a ferromagnet with quantum fluctuations,"Some of the highest transition temperatures achieved for Mn-doped GaAs have
been in delta-doped heterostructures with well-separated planes of Mn. But in
the absence of magnetic anisotropy, the Mermin-Wagner theorem implies that a
single plane of magnetic ions cannot be ferromagnetic. Using a Heisenberg
model, we show that the same mechanism that produces magnetic frustration and
suppresses the transition temperature in bulk Mn-doped GaAs, due to the
difference between the light and heavy band masses, can stabilize ferromagnetic
order for a single layer of Mn in a GaAs quantum well. This comes at the price
of quantum fluctuations that suppress the ordered moment from that of a fully
saturated ferromagnet. By comparing the predictions of Heisenberg and
Kohn-Luttinger models, we conclude that the Heisenberg description of a
Mn-doped GaAs quantum well breaks down when the Mn concentration becomes large,
but works quite well in the weak-coupling limit of small Mn concentrations.
This comparison allows us to estimate the size of the quantum fluctuations in
the quantum well.",0604288v4
2007-08-19,Incommensurate Spin Ordering and Fluctuations in underdoped La_{2-x}Ba_{x}CuO_{4},"Using neutron scattering techniques, we have studied incommensurate spin
ordering as well as low energy spin dynamics in single crystal underdoped \LBCO
with x$\sim$0.095 and 0.08; high temperature superconductors with T$_C \sim$ 27
K and 29 K respectively. Static two dimensional incommensurate magnetic order
appears below T$_N$=39.5 $\pm$ 0.3 K in \LBCO (x=0.095) and a similar
temperature for x=0.08 within the low temperature tetragonal phase. The spin
order is unaffected by either the onset of superconductivity or the application
of magnetic fields of up to 7 Tesla applied along the c-axis in the x=0.095
sample. Such magnetic field {\it independent} behaviour is in marked contrast
with the field induced enhancement of the staggered magnetisation observed in
the related \LSCO system, indicating this phenomenon is not a universal
property of cuprate superconductors. Surprisingly, we find that
incommensurability $\delta $ is only weakly dependent on doping relative to
\LSCO. Dispersive excitations in \LBCO (x=0.095) at the same incommensurate
wavevector persist up to at least 60 K. The dynamical spin susceptibility of
the low energy spin excitations saturates below \tc, in a similar manner to
that seen in the superconducting state of La$_2$CuO$_{4+y}$.",0708.2519v3
2008-09-17,"Late stage, non-equilibrium dynamics in the dipolar Ising model","Magnetic domain structures are a fascinating area of study with interest
deriving both from technological applications and fundamental scientific
questions. The nature of the striped magnetic phases observed in ultra-thin
films is one such intriguing system. The non-equilibrium dynamics of such
systems as they evolve toward equilibrium has only recently become an area of
interest and previous work on model systems showed evidence of complex, slow
dynamics with glass-like properties as the stripes order mesoscopically. To aid
in the characterization of the observed phases and the nature of the
transitions observed in model systems we have developed an efficient method for
identifying clusters or domains in the spin system, where the clusters are
based on the stripe orientation. Thus we are able to track the growth and decay
of such clusters of stripes in a Monte Carlo simulation and observe directly
the nature of the slow dynamics. We have applied this method to consider the
growth and decay of ordered domains after a quench from a saturated magnetic
state to temperatures near and well below the critical temperature in the two
dimensional dipolar Ising model. We discuss our method of identifying stripe
domains or clusters of stripes within this model and present the results of our
investigations.",0809.2808v1
2009-01-21,Instability of the collinear phase in two-dimensional ferromagnet in strong in-plane magnetic field,"It is well-known that in thin ferromagnetic film with a net magnetization
perpendicular to the film the collinear arrangement of spins is unstable in an
in-plane field $H$ smaller than its saturation value $H_c$. Existence of a
stripe phase was proposed with elongated domains of alternating direction of
magnetization component perpendicular to the film. We consider in the present
paper the strong-field regime $H<H_c$ and discuss the minimal microscopic model
describing this phenomenon, two-dimensional Heisenberg ferromagnet with strong
easy-axis anisotropy and dipolar forces. The noncollinear (stripe) phase is
discussed using the technique of the Bose-Einstein condensation of magnons.
Some previously unknown results are observed concerning the stripe phase.
Evolution is established of the spin arrangement in the noncollinear phase upon
the field rotation within the plane. We find a rapid decreasing of the period
of the stripe structure as the field decreases. We demonstrate that spins
components perpendicular to the film form a sinusoid in the noncollinear phase
at $H\approx H_c$ that transforms to a step-like profile upon the field
decreasing so that the domain wall density decreases from unity to a value much
smaller than unity. The spin-wave spectrum in the noncollinear phase is
discussed.",0901.3259v2
2009-03-05,Altair - the 'hottest' magnetically active star in X-rays,"The A7 star Altair is one of the hottest magnetically active stars. Its
proximity to the Sun allows a detailed investigation of a corona in X-rays for
a star with a shallow convection zone. We used a deep XMM-Newton observation of
Altair and analyzed X-ray light curves, spectra, and emission lines,
investigated the temporal behavior and properties of the X-ray emitting plasma
and studied the global coronal structure. We find that Altair's corona with an
X-ray luminosity of L_X =1.4 x 10^27 erg/s and a very low activity level of log
L_X/L_bol = -7.4, is located predominantly at low latitude regions. The X-ray
emission is dominated by cool plasma (1-4 MK) at low density, and elemental
abundances exhibit a solar-like FIP effect and Ne/O ratio. The X-ray brightness
varies by 30 % over the observation, most likely due to rotational modulation
and minor activity; in contrast, no strong flares or significant amounts of hot
plasma were detected. The X-ray activity level of Altair is apparently close to
the saturation level, which is reduced by roughly four orders of magnitude when
compared to late-type stars. With its fast rotation, Altair provides an
inefficient, but very stable dynamo that mainly operates in convective layers
below its 'cooler' surface areas around the equator. This dynamo mechanism
results in magnetic activity and leads to X-ray properties that are overall
very similar to those of the quiescent Sun, despite very different underlying
stars.",0903.0966v1
2009-03-13,2D XY Behavior observed in quasi-2D quantum Heisenberg antiferromagnets,"The magnetic properties of a new family of molecular-based quasi-two
dimension $S=1/2$ Heisenberg antiferromagnets are reported. Three compounds,
($Cu(pz)_2(ClO_4)_2$, $Cu(pz)_2(BF_4)_2$, and $[Cu(pz)_2(NO_3)](PF_6)$) contain
similar planes of Cu$^{2+}$ ions linked into magnetically square lattices by
bridging pyrazine molecules (pz = $C_4H_4N_2$). The anions provide charge
balance as well as isolation between the layers. Single crystal measurements of
susceptibility and magnetization, as well as muon spin relaxation studies,
reveal low ratios of N\'{e}el temperatures to exchange strengths ($4.25 / 17.5
= 0.243$, $3.80/15.3=0.248$, and $3.05/10.8=0.282$, respectively) while the
ratio of the anisotropy fields $H_A$ (kOe) to the saturation field
$H_\mathrm{SAT}$ (kOe) are small ($2.6/490 = 5.3\times10^{-3}$,
$2.4/430=5.5\times10^{-3}$, and $0.07/300=2.3\times10^{-4}$, respectively),
demonstrating close approximations to a 2D Heisenberg model. The
susceptibilities of ClO$_4$ and BF$_4$ show evidence of an exchange anisotropy
crossover (Heisenberg to $XY$) at low temperatures; their ordering transitions
are primarily driven by the $XY$ behavior with the ultimate 3D transition
appearing parasitically. The PF$_6$ compound remains Heisenberg-like at all
temperatures, with its transition to the N\'{e}el state due to the interlayer
interactions. Effects of field-induced anisotropy have been observed.",0903.2470v1
2009-04-08,Anisotropy of the upper critical field in a Co-doped BaFe2As2 single crystal,"The temperature dependence of the upper critical magnetic field (Hc2) in a
BaFe1.84Co0.16As2 single crystal was determined via resistivity, for the
inter-plane (H^ab) and in-plane (H//ab) directions in pulsed and static
magnetic fields of up to 60 T. Suppressing superconductivity in a pulsed
magnetic field at 3He temperatures permits us to construct an H-T phase diagram
from quantitative Hc2(0) values and determine its behavior in low temperatures.
Hc2(0) with H//ab (Hc2//(0)) and H^ab (Hc2^(0)) are ~ 55 T and 50 T
respectively. These values are ~ 1.2 - 1.4 times larger than the weak-coupling
Pauli paramagnetic limit (Hp = 1.84 Tc), indicating that enhanced paramagnetic
limiting is essential and this superconductor is unconventional. While Hc2//ab
is saturated at low temperature, Hc2 with H^ab (Hc2^) exhibits almost linear
temperature dependence towards T = 0 K which results in reduced anisotropy of
Hc2 in low temperature. The anisotropy of Hc2 was ~ 3.4 near Tc, and decreases
rapidly with lower temperatures reaching ~ 1.1 at T = 0.7 K.",0904.1418v3
2009-05-08,Magnetotransport in polycrystalline La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ thin films of controlled granularity,"Polycrystalline La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO) thin films were
synthesized by pulsed laser ablation on single crystal (100) yttria-stabilized
zirconia (YSZ) substrates to investigate the mechanism of magneto-transport in
a granular manganite. Different degrees of granularity is achieved by using the
deposition temperature (T$_{D}$) of 700 and 800 $^{0}$C. Although no
significant change in magnetic order temperature (T$_C$) and saturation
magnetization is seen for these two types of films, the temperature and
magnetic field dependence of their resistivity ($\rho$(T, H)) is strikingly
dissimilar. While the $\rho$(T,H) of the 800 $^{0}$C film is comparable to that
of epitaxial samples, the lower growth temperature leads to a material which
undergoes insulator-to-metal transition at a temperature (T$_{P}$ $\approx$ 170
K) much lower than T$_C$. At T $\ll$ T$_P$, the resistivity is characterized by
a minimum followed by ln $\emph{T}$ divergence at still lower temperatures. The
high negative magnetoresistance ($\approx$ 20$%$) and ln $\emph{T}$ dependence
below the minimum are explained on the basis of Kondo-type scattering from
blocked Mn-spins in the intergranular material. Further, a striking feature of
the T$_D$ = 700 $^{0}$C film is its two orders of magnitude larger anisotropic
magnetoresistance (AMR) as compared to the AMR of epitaxial films. We attribute
it to unquenching of the orbital angular momentum of 3d electrons of Mn ions in
the intergranular region where crystal field is poorly defined.",0905.1306v1
2009-07-29,"Domain walls, canted states and stripe width variation in ultrathin magnetic films with perpendicular anisotropy","Stripe width variation in ultrathin magnetic films is a well known phenomenon
still not well understood. We analyze this problem considering a 2D Heisenberg
model with ferromagnetic exchange interactions, dipolar interactions and
perpendicular anisotropy, relevant e.g. in Fe/Cu(001) films. By extending a
classic result of Yafet & Gyorgy (YG) and using Monte Carlo simulations we
calculate the complete zero temperature phase diagram of the model. Through
this calculation we analyze the correlation between domain walls structure and
stripe width variation, as the perpendicular anisotropy changes. In particular,
we found evidences that the recently detected canted state becomes the ground
state of the system close to the Spin Reorientation Transition (SRT) for any
value of the exchange to dipolar couplings ratio. Far away of the SRT the
canted ground state is replaced by a saturated stripes state, in which
in--plane magnetization components are only present inside the walls. We find
that the domain wall structure strongly depends on the perpendicular
anisotropy: close to SRT it is well described by YG approximation, but a strong
departure is observed in the large anisotropy limit. Moreover, we show that
stripe width variation is directly related to domain wall width variation with
the anisotropy.",0907.5153v1
2009-12-08,"Anisotropy of upper critical field in one-dimensional organic system, (TMTTF)$_2$PF$_6$ under extremely high pressure","We have measured the temperature dependent resistivity of (TMTTF)$_2$PF$_6$
to 7 GPa using a turnbuckle DAC (diamond anvil cell) and in magnetic field up
to 5 T. Unlike many other organic conductors, a zero resistance was observed in
the superconducting state even under high pressures. Superconductivity was
observed over a range of $P$ = 4.18 GPa to 6.03 GPa and showed a peak $T_c$ of
2.25 K at 4.58 GPa. The temperature dependence of the upper critical magnetic
field $H_{c2}(T)$ was determined via resistivity at $P$ = 4.58 GPa, for the
intrachain ($a$), interchain ($b'$), and interlayer ($c^*$) configurations and
the $H_{c2}(T)$ displays positive curvature without saturation, which may be
originated by a FFLO state, for magnetic field along a-axis and $b'$-axis in T
$\ge$ 0.5 K for $P$ = 4.48 GPa. This feature is suppressed with increasing
pressure and the orbital pair breaking mechanism becomes dominant. The values
of the Ginzberg-Landau coherence length for three different axes obtained from
this work shows that (TMTTF)$_2$PF$_6$ is an anisotropic three - dimensional
superconductor.",0912.1391v1
2009-12-09,X-ray emitting MHD accretion shocks in classical T Tauri stars. Case for moderate to high plasma-beta values,"AIMS. We investigate the stability and dynamics of accretion shocks in CTTSs,
considering the case of beta >= 1 in the post-shock region. In these cases the
1D approximation is not valid and a multi-dimensional MHD approach is
necessary.
  METHODS. We model an accretion stream propagating through the atmosphere of a
CTTS and impacting onto its chromosphere, by performing 2D axisymmetric MHD
simulations. The model takes into account the stellar magnetic field, the
gravity, the radiative cooling, and the thermal conduction (including the
effects of heat flux saturation).
  RESULTS. The dynamics and stability of the accretion shock strongly depends
on the plasma beta. In the case of shocks with beta > 10, violent outflows of
shock-heated material (and possibly MHD waves) are generated at the base of the
accretion column and strongly perturb the surrounding stellar atmosphere and
the accretion column itself (modifying, therefore, the dynamics of the shock).
In shocks with beta ~ 1, the post-shock region is efficiently confined by the
magnetic field. The shock oscillations induced by cooling instability are
strongly influenced by beta: for beta > 10, the oscillations may be rapidly
dumped by the magnetic field, approaching a quasi-stationary state, or may be
chaotic with no obvious periodicity due to perturbation of the stream induced
by the post-shock plasma itself; for beta ~ 1 the oscillations are
quasi-periodic, although their amplitude is smaller and the frequency higher
than those predicted by 1D models.",0912.1799v1
2010-03-01,"Optical initialization, readout and dynamics of a Mn spin in a quantum dot","We have investigated the spin preparation efficiency by optical pumping of
individual Mn atoms embedded in CdTe/ZnTe quantum dots. Monitoring the time
dependence of the intensity of the fluorescence during the resonant optical
pumping process in individual quantum dots allows to directly probe the
dynamics of the initialization of the Mn spin. This technique presents the
convenience of including preparation and read-out of the Mn spin in the same
step. Our measurements demonstrate that Mn spin initialization, at zero
magnetic field, can reach an efficiency of 75% and occurs in the tens of
\emph{ns} range when a laser resonantly drives at saturation one of the quantum
dot transition. We observe that the efficiency of optical pumping changes from
dot to dot and is affected by a magnetic field of a few tens of mT applied in
Voigt or Faraday configuration. This is attributed to the local strain
distribution at the Mn location which predominantly determines the dynamics of
the Mn spin under weak magnetic field. The spectral distribution of the
spin-flip scattered photons from quantum dots presenting a weak optical pumping
efficiency reveals a significant spin relaxation for the exciton split in the
exchange field of the Mn spin.",1003.0370v2
2010-04-01,MRI channel flows in vertically-stratified models of accretion disks,"Simulations of the magnetorotational instability (MRI) in 'unstratified'
shearing boxes exhibit powerful coherent flows, whereby the fluid vertically
splits into countermoving planar jets or `channels'. Channel flows correspond
to certain axisymmetric linear MRI modes, and their preponderance follows from
the remarkable fact that they are approximate nonlinear solutions of the MHD
equations in the limit of weak magnetic fields. We show in this paper,
analytically and with one-dimensional numerical simulations, that this property
is also shared by certain axisymmetric MRI modes in vertically-stratified
shearing boxes. These channel flows rapidly capture significant amounts of
magnetic and kinetic energy, and thus are vulnerable to secondary shear
instabilities. We examine these parasites in the vertically stratified context,
and estimate the maximum amplitudes that channels attain before they are
destroyed. These estimates suggest that a dominant channel flow will usually
drive the disk's magnetic field to thermal strengths. The prominence of these
flows and their destruction place enormous demands on simulations, but channels
in their initial stages also offer a useful check on numerical codes. These
benchmarks are especially valuable given the increasing interest in the
saturation of the stratified MRI. Lastly we speculate on the potential
connection between 'run-away' channel flows and outburst behaviour in
protostellar and dwarf nova disks.",1004.0109v1
2010-05-09,Different response of the crystal structure to isoelectronic doping in BaFe2[As(1-x)P(x)]2 and [Ba(1-x)Sr(x)]Fe2As2,"Superconductivity up to 30 K in charge neutrally doped BaFe2[As(1-x)P(x)]2
has been ascribed to chemical pressure, caused by the shrinking unit cell. But
the latter induces no superconductivity in [Ba(1-x)Sr(x)]Fe2As2 in spite of the
same volume range. We show that the spin-density-wave (SDW) state of BaFe2As2
becomes suppressed in BaFe2[As(1-x)P(x)]2 by a subtle reorganization of the
crystal structure, where arsenic and phosphorus are located at different
coordinates z(As), z(P). High-resolution X-ray diffraction experiments with
BaFe2[As(1-x)P(x)]2 single crystals reveal almost unchanged Fe-P bonds, but a
contraction of the Fe-As bonds, which remain nearly unchanged in
[Ba(1-x)Sr(x)]Fe2As2. Since the Fe-As bond length is a gauge for the magnetic
moment, our results show why the SDW is suppressed by P-, but not by Sr-doping.
Only the Fe-P interaction increases the width of the iron 3d bands, which
destabilizes the magnetic SDW ground state. The simultaneous contraction of the
Fe{As bonds is rather a consequence of the vanishing magnetism. Ordered
structure models of BaFe2[As(1-x)P(x)]2 obtained by DFT calculations agree
perfectly with the single-crystal X-ray structure determinations. The
contraction of the Fe-As bonds saturates at doping levels above x = 0.3, which
corrects the unreasonable linear decrease of the so-called pnictide height.",1005.1411v2
2010-07-01,Exactly solvable mixed-spin Ising-Heisenberg diamond chain with the biquadratic interactions and single-ion anisotropy,"An exactly solvable variant of mixed spin-(1/2,1) Ising-Heisenberg diamond
chain is considered. Vertical spin-1 dimers are taken as quantum ones with
Heisenberg bilinear and biquadratic interactions and with single-ion
anisotropy, while all interactions between spin-1 and spin-1/2 residing on the
intermediate sites are taken in the Ising form. The detailed analysis of the
$T=0$ ground state phase diagram is presented. The phase diagrams have shown to
be rather rich, demonstrating large variety of ground states: saturated one,
three ferrimagnetic with magnetization equal to 3/5 and another four
ferrimagnetic ground states with magnetization equal to 1/5. There are also two
frustrated macroscopically degenerated ground states which could exist at zero
magnetic filed.
  Solving the model exactly within classical transfer-matrix formalism we
obtain an exact expressions for all thermodynamic function of the system. The
thermodynamic properties of the model have been described exactly by exact
calculation of partition function within the direct classical transfer-matrix
formalism, the entries of transfer matrix, in their turn, contain the
information about quantum states of vertical spin-1 XXZ dimer (eigenvalues of
local hamiltonian for vertical link).",1007.0098v2
2011-05-03,Universality of the Small-Scale Dynamo Mechanism,"We quantify possible differences between turbulent dynamo action in the Sun
and the dynamo action studied in idealized simulations. For this purpose we
compare Fourier-space shell-to-shell energy transfer rates of three
incrementally more complex dynamo simulations: an incompressible, periodic
simulation driven by random flow, a simulation of Boussinesq convection, and a
simulation of fully compressible convection that includes physics relevant to
the near-surface layers of the Sun. For each of the simulations studied, we
find that the dynamo mechanism is universal in the kinematic regime because
energy is transferred from the turbulent flow to the magnetic field from
wavenumbers in the inertial range of the energy spectrum. The addition of
physical effects relevant to the solar near-surface layers, including
stratification, compressibility, partial ionization, and radiative energy
transport, does not appear to affect the nature of the dynamo mechanism. The
role of inertial-range shear stresses in magnetic field amplification is
independent from outer-scale circumstances, including forcing and
stratification. Although the shell-to-shell energy transfer functions have
similar properties to those seen in mean-flow driven dynamos in each simulation
studied, the saturated states of these simulations are not universal because
the flow at the driving wavenumbers is a significant source of energy for the
magnetic field.",1105.0546v1
2011-06-17,Scaling the effect of the dipolar interactions on the ZFC/FC curves of random nanoparticle assemblies,"Zero Field Cooling (ZFC) and Field Cooling (FC) protocols are commonly used
to investigate the properties of magnetic nanoparticle systems. For
non-interacting conditions the particle properties are fairly well correlated
with the shape of the ZFC/FC curves. However, that is not the case when
significant dipolar interparticle interactions (DII) are present, what
frequently occurs in experimental samples (e.g. aggregates in biological
systems; or the dried powder often used for the ZFC/FC measurements). The
purpose of this work is to show how the influence of the DII on the ZFC/FC
curves, computed by the volume sample concentration c, can be described in a
general way if scaled by the dimensionless parameter c_0 = 2K/M_S^2; where K
and M_S are the anisotropy and saturation magnetization constants of the
particles, respectively. This scaling parameter, which is straightforwardly
derived from the energy equation governing the system, has an analogous meaning
to the normalization of the external magnetic field H by the anisotropy field
of the particles, H_A = 2K/M_S. We use a Monte Carlo technique to show how
apparently different T_B vs. c curves of various particles types (where T_B is
the blocking temperature), follow the same trend if scaling c/c_0.",1106.3403v2
2011-07-13,Coils and transformers - often used but seldomly explained correctly,"The devices coil and transformer are subjects of interest in numerous
schoolbooks, in introductory scientific textbooks of physics and engineering,
and in laboratory courses at universities. Many descriptions, however, draw a
somewhat distorted picture of the underlying physical mechanisms and provide
half-knowledge or even clear misconceptions that should not be left uncommented
and are therefore studied in detail:
  (1) Primary and secondary voltage at a transformer have a different sign.
  (2) Electromagnetic induction is the only mechanism of importance for coils
and transformers.
  (3) The terminal voltage at coils and transformers is compensated by the
so-called ""induced voltage"" (emf), which explains why Kirchhoff's voltage law
also applies to coils and transformers.
  (4) The cores of coils and transformers are used for their ability to store
energy. Energy is transported from the primary to the secondary coil within the
magnetic core.
  (5) The stray magnetic and electric fields are sencondary effects not having
a major effect on energy transport.
  (6) The higher the load current, the easier a transformer goes into
saturation.
  (7) The higher the number of turns at the primary coil, the larger the
magnetic flux in the core.
  (8) Transformers with cores having an air gap have a lower coupling factor,
because the stray inductivity increases.
  In the paper, the most important characteristics of coil and transformers are
derived directly from Maxwell's equation for idealised conditions, and
subsequently, the different misconceptions are discussed and corrected.",1107.2684v2
2012-01-31,Local 2D Particle-in-cell simulations of the collisionless MRI,"The magnetorotational instability (MRI) is a crucial mechanism of angular
momentum transport in a variety of astrophysical accretion disks. In systems
accreting at well below the Eddington rate, such as the central black hole in
the Milky Way (Sgr A*), the rate of Coulomb collisions between particles is
very small, making the disk evolve essentially as a collisionless plasma. We
present a nonlinear study of the collisionless MRI using first-principles
particle-in-cell (PIC) plasma simulations. In this initial study we focus on
local two-dimensional (axisymmetric) simulations, deferring more realistic
three-dimensional simulations to future work. For simulations with net vertical
magnetic flux, the MRI continuously amplifies the magnetic field until the
Alfv\'en velocity, v_A, is comparable to the speed of light, c (independent of
the initial value of v_A/c). This is consistent with the lack of saturation of
MRI channel modes in analogous axisymmetric MHD simulations. The amplification
of the magnetic field by the MRI generates a significant pressure anisotropy in
the plasma (with the perpendicular pressure being larger than the parallel
pressure). We find that this pressure anisotropy in turn excites mirror modes
and that the volume averaged pressure anisotropy remains near the threshold for
mirror mode excitation. Particle energization is due to both reconnection and
viscous heating associated with the pressure anisotropy. Reconnection produces
a distinctive power-law component in the energy distribution function of the
particles, indicating the likelihood of non-thermal ion and electron
acceleration in collisionless accretion disks. This has important implications
for interpreting the observed emission -- from the radio to the gamma-rays --
of systems such as Sgr A*.",1201.6407v1
2012-11-15,Alignment of Magnetized Accretion Disks and Relativistic Jets with Spinning Black Holes,"Accreting black holes (BHs) produce intense radiation and powerful
relativistic jets, which are affected by the BH's spin magnitude and direction.
While thin disks might align with the BH spin axis via the Bardeen-Petterson
effect, this does not apply to jet systems with thick disks. We used fully
three-dimensional general relativistic magnetohydrodynamical simulations to
study accreting BHs with various BH spin vectors and disk thicknesses with
magnetic flux reaching saturation. Our simulations reveal a ""magneto-spin
alignment"" mechanism that causes magnetized disks and jets to align with the BH
spin near BHs and further away to reorient with the outer disk. This mechanism
has implications for the evolution of BH mass and spin, BH feedback on host
galaxies, and resolved BH images for SgrA* and M87.",1211.3651v1
2012-12-13,Diffusive Shock Acceleration at Cosmological Shock Waves,"We reexamine nonlinear diffusive shock acceleration (DSA) at cosmological
shocks in the large scale structure of the Universe, incorporating
wave-particle interactions that are expected to operate in collisionless
shocks. Adopting simple phenomenological models for magnetic field
amplification (MFA) by cosmic-ray (CR) streaming instabilities and Alfv'enic
drift, we perform kinetic DSA simulations for a wide range of sonic and
Alfv'enic Mach numbers and evaluate the CR injection fraction and acceleration
efficiency. In our DSA model the CR acceleration efficiency is determined
mainly by the sonic Mach number Ms, while the MFA factor depends on the
Alfv'enic Mach number and the degree of shock modification by CRs. We show that
at strong CR modified shocks, if scattering centers drift with an effective
Alfv'en speed in the amplified magnetic field, the CR energy spectrum is
steepened and the acceleration efficiency is reduced significantly, compared to
the cases without such effects. As a result, the postshock CR pressure
saturates roughly at ~ 20 % of the shock ram pressure for strong shocks with
Ms>~ 10. In the test-particle regime (Ms<~ 3), it is expected that the magnetic
field is not amplified and the Alfv'enic drift effects are insignificant,
although relevant plasma physical processes at low Mach number shocks remain
largely uncertain.",1212.3246v1
2013-02-06,Magnetic irreversibility in ultrafine ZnFe2O4 partices,"Pure ultrafine ZnFe2O4 particles have been obtained from mechanosynthesis of
the ZnO and Fe2O3 oxides. The average grain diameter was estimated from x-ray
diffraction to be <d> = 36(6) nm. Refinement of neutron diffraction (ND) data
showed that the resulting cubic spinel structure is oxygen-deficient, with ~7%
of Fe3+ ions occupying the tetrahedral A sites. Magnetization curves taken at
4.2 K showed absence of saturation up to fields H = 9 Tesla, associated to a
spin-canted produced by the milling process. Field-cooled (FC) and
zero-field-cooled (ZFC) curves showed irreversible behavior extending well
above room temperature, which is associated to spin disorder. Annealing samples
at 300 {\deg}C yields an average grain size <d> = 50(6) nm, and ~16% of Fe3+
ions at A sites. Partial oxygen recovery is also deduced from neutron data
refinement in annealed samples. Concurrently, decrease of magnetic
irreversibility is noticed, assigned to partial recovery of the collinear spin
structure. Complex M\""ossbauer spectra were observed at room temperature and 80
K, with broad hyperfine field distributions spanning from ~10 T to ~40 T. At T
= 4.2 K, hyperfine field distributions indicate high disorder in Fe local
environments. The above data suggest the existence of Fe-rich clusters,
yielding strong superexchange interactions between Fe ions at A and B sites of
the spinel structure.",1302.1276v1
2013-06-25,Magnetic self-organisation in Hall-dominated magnetorotational turbulence,"The magnetorotational instability (MRI) is the most promising mechanism by
which angular momentum is efficiently transported outwards in astrophysical
discs. However, its application to protoplanetary discs remains problematic.
These discs are so poorly ionised that they may not support magnetorotational
turbulence in regions referred to as `dead zones'. It has recently been
suggested that the Hall effect, a non-ideal magnetohydrodynamic (MHD) effect,
could revive these dead zones by enhancing the magnetically active column
density by an order of magnitude or more. We investigate this idea by
performing local, three-dimensional, resistive Hall-MHD simulations of the MRI
in situations where the Hall effect dominates over Ohmic dissipation. As
expected from linear stability analysis, we find an exponentially growing
instability in regimes otherwise linearly stable in resistive MHD. However,
instead of vigorous and sustained magnetorotational turbulence, we find that
the MRI saturates by producing large-scale, long-lived, axisymmetric structures
in the magnetic and velocity fields. We refer to these structures as zonal
fields and zonal flows, respectively. Their emergence causes a steep reduction
in turbulent transport by at least two orders of magnitude from extrapolations
based upon resistive MHD, a result that calls into question contemporary models
of layered accretion. We construct a rigorous mean-field theory to explain this
new behaviour and to predict when it should occur. Implications for
protoplanetary disc structure and evolution, as well as for theories of planet
formation, are briefly discussed.",1306.5887v1
2013-07-05,The influence of Strong Magnetic Field in Hyperonic Neutron Stars,"The physics of neutron stars leads historically towards Landau's speculation.
Even before the discovery of the neutron, he postulated the possible existence
of stars more compact than white dwarfs, containing matter of the order of
nuclear density. From a modern point of view neutron stars are compact objects
maintained by the equilibrium between gravity and the degeneracy pressure of
the fermions together with a strong nuclear repulsion force due to the high
density reached in their interior. While the physics in the vicinity of nuclear
saturation density is well know from phenomenology, the physics of ultra-dense
nuclear matter is still an open puzzle. In this work we study dense nuclear
matter within a relativistic model, allowing hyperons to be present through
beta equilibrium. The presence of hyperons is justifiable since the
constituents of neutron stars are fermions. So, according to the Pauli
principle, as the baryon density increases, so do the Fermi momentum and the
Fermi energy. On the other hand, this hyperonic matter softens the equation of
state (EoS) and a recent measurement of pulsar PSR J1614-2230 implies that the
EoS has to be stiff enough to produce a 2.0 $M_{\odot}$ pulsar. We also
consider Duncan's magnetar ideas and study the influence of strong magnetic
fields on the EoS. We see that a strong magnetic field produces very massive
neutron stars, in agreement with the astronomical observations.",1307.1691v1
2013-08-06,Electronic structure and magnetic properties of Gd-doped and Eu-rich EuO,"The effects of Gd doping and O vacancies on the magnetic interaction and
Curie temperature of EuO are studied using first-principles calculations.
Linear response calculations in the virtual crystal approximation show a broad
maximum in the Curie temperature as a function of doping, which results from
the combination of the saturating contribution from indirect exchange and a
decreasing contribution from the f-d hopping mechanism. Non-Heisenberg
interaction at low doping levels and its effect on the Curie temperature are
examined. The electronic structure of a substitutional Gd and of an O vacancy
in EuO are evaluated. When the 4f spins are disordered, the impurity state goes
from single to double occupation, but correlated bound magnetic polarons are
not ruled out. At higher vacancy concentrations typical for Eu-rich EuO films,
the impurity states broaden into bands and remain partially filled. To go
beyond the homogeneous doping picture, magnetostructural cluster expansions are
constructed, which describe the modified exchange parameters near Gd dopants or
O vacancies. Thermodynamic properties are studied using Monte Carlo
simulations. The Curie temperature for Gd-doped EuO agrees with the results of
the virtual crystal approximation and shows a maximum of about 150 K. At 3.125%
vacancy concentration the Curie temperature increases to 120 K, consistent with
experimental data for Eu-rich film samples.",1308.1223v1
2013-11-27,"Hall Effect in Neutron Star Crusts: Evolution, Endpoint and Dependence on Initial Conditions","We present new simulations of the evolution of axially symmetric magnetic
fields in neutron star crusts under the influence of the Hall effect and
subdominant Ohmic dissipation. In the Hall effect, differential rotation of the
electron fluid generates toroidal field by winding of the poloidal field. For
this reason, we focus on the influence of the initial choice of the electron
angular velocity profile on the subsequent and long term magnetic evolution.
Whereas previous simulations have generally chosen angular velocities
increasing outwards, corresponding to the lowest order Ohmic mode in the crust,
a more realistic choice is an angular velocity decreasing outwards,
corresponding to the MHD equilibrium field that is likely present at the time
of crust formation. We find that the evolution passes through three basic
phases. The early evolution is a response to the initial conditions. During the
second phase the field consists of poloidal and toroidal components which
eventually relax to an isorotation state in which the angular velocity of the
electrons becomes constant along poloidal magnetic field lines, causing Hall
evolution to saturate. In the third phase the field dissipates slowly while
maintaining isorotation. We discuss the implications for the long term field
structure and observable properties of isolated neutron stars.",1311.7004v1
2013-11-28,Predictive Scaling Laws for Spherical Rotating Dynamos,"State of the art numerical models of the Geodynamo are still performed in a
parameter regime extremely remote from the values relevant to the physics of
the Earth's core. In order to establish a connection between dynamo modeling
and the geophysical motivation, {it is necessary to use} scaling laws. Such
scaling laws establish the dependence of essential quantities (such as the
magnetic field strength) on measured or controlled quantities. They allow for a
direct confrontation of advanced models with geophysical {constraints}.
  (...)
  We show that previous empirical scaling laws for the magnetic field strength
essentially reflect the statistical balance between energy production and
dissipation for saturated dynamos. Such power based scaling laws are thus
necessarily valid for any dynamo in statistical equilibrium and applicable to
any numerical model, irrespectively of the dynamo mechanism.
  We show that direct numerical fits can provide contradictory results owing to
biases in the parameters space covered in the numerics and to the role of a
priori hypothesis on the fraction of ohmic dissipation.
  We introduce predictive scaling laws, i.e. relations involving input
parameters of the governing equations only. We guide our reasoning on physical
considerations. We show that our predictive scaling laws can properly describe
the numerical database and reflect the dominant forces balance at work in these
numerical simulations. We highlight the dependence of the magnetic field
strength on the rotation rate. Finally, our results stress that available
numerical models operate in a viscous dynamical regime, which is not relevant
to the Earth's core.",1311.7395v2
2014-07-03,Hyperfine coupling and spin polarization in the bulk of the topological insulator Bi$_2$Se$_3$,"Nuclear magnetic resonance (NMR) and transport measurements have been
performed at high magnetic fields and low temperatures in a series of $n$-type
Bi$_{2}$Se$_{3}$ crystals. In low density samples, a complete spin polarization
of the electronic system is achieved, as observed from the saturation of the
isotropic component of the $^{209}$Bi NMR shift above a certain magnetic field.
The corresponding spin splitting, defined in the phenomenological approach of a
3D electron gas with a large (spin-orbit-induced) effective $g$-factor, scales
as expected with the Fermi energy independently determined by simultaneous
transport measurements. Both the effective electronic $g$-factor and the
""contact"" hyperfine coupling constant are precisely determined. The magnitude
of this latter reveals a non negligible $s$-character of the electronic wave
function at the bottom of the conduction band. Our results show that the bulk
electronic spin polarization can be directly probed via NMR and pave the way
for future NMR investigations of the electronic states in Bi-based topological
insulators.",1407.1040v2
2014-07-30,Exact ground states of a spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice in a magnetic field,"Exact ground states of a spin-1/2 Ising-Heisenberg model on the
Shastry-Sutherland lattice with Heisenberg intra-dimer and Ising inter-dimer
couplings are found by two independent rigorous procedures. The first method
uses a unitary transformation to establish a mapping correspondence with an
effective classical spin model, while the second method relies on the
derivation of an effective hard-core boson model by continuous unitary
transformations. Both methods lead to equivalent effective Hamiltonians
providing a convincing proof that the spin-1/2 Ising-Heisenberg model on the
Shastry-Sutherland lattice exhibits a zero-temperature magnetization curve with
just two intermediate plateaus at one-third and one-half of the saturation
magnetization, which correspond to stripe and checkerboard orderings of
singlets and polarized triplets, respectively. The nature of the remarkable
stripe order relevant to the one-third plateau is thoroughly investigated with
the help of the corresponding exact eigenvector. The rigorous results for the
spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice are compared
with the analogous results for the purely classical Ising and fully quantum
Heisenberg models. Finally, we discuss to what extent the critical fields of
SrCu2(BO3)2 and (CuCl)Ca2Nb3O10 can be described within the suggested
Ising-Heisenberg model.",1407.8229v2
2014-08-20,Spontaneous chiral symmetry breaking and the Chiral Magnetic Effect for interacting Dirac fermions with chiral imbalance,"We report on a mean-field study of spontaneous breaking of chiral symmetry
for Dirac fermions with contact interactions in the presence of chiral
imbalance, which is modelled by nonzero chiral chemical potential. We point out
that chiral imbalance lowers the vacuum energy of Dirac fermions, which leads
to the increase of the renormalized chiral chemical potential upon chiral
symmetry breaking. The critical coupling strength for the transition to the
broken phase is slightly lowered as the chiral chemical potential is increased,
and the transition itself becomes milder. Furthermore, we study the chiral
magnetic conductivity in different phases and find that it grows both in the
perturbative weak-coupling regime and in the strongly coupled phase with broken
chiral symmetry. In the strong coupling regime the chiral magnetic effect is
saturated by vector-like bound states (vector mesons) with mixed transverse
polarizations. General pattern of meson mixing in the presence of chiral
imbalance is also considered. We discuss the relevance of our study for Weyl
semimetals and strongly interacting QCD matter. Finally, we comment on the
ambiguity of the regularization of the vacuum energy of Dirac fermions in the
presence of chirality imbalance.",1408.4573v2
2014-08-27,Dynamics of a mesoscopic nuclear spin ensemble interacting with an optically driven electron spin,"The ability to discriminate between simultaneously occurring noise sources in
the local environment of semiconductor InGaAs quantum dots, such as electric
and magnetic field fluctuations, is key to understanding their respective
dynamics and their effect on quantum dot coherence properties. We present a
discriminatory approach to all-optical sensing based on two-color resonance
fluorescence of a quantum dot charged with a single electron. Our measurements
show that local magnetic field fluctuations due to nuclear spins in the absence
of an external magnetic field are described by two correlation times, both in
the microsecond regime. The nuclear spin bath dynamics show a strong dependence
on the strength of resonant probing, with correlation times increasing by a
factor of four as the optical transition is saturated. We interpret the
behavior as motional averaging of both the Knight field of the resident
electron spin and the hyperfine-mediated nuclear spin-spin interaction due to
optically-induced electron spin flips.",1408.6437v2
2014-11-11,Relaxation mechanisms affecting magneto-optical resonances in an extremely thin cell: experiment and theory for the cesium D$_1$ line,"We have measured magneto-optical signals obtained by exciting the $D_1$ line
of cesium atoms confined to an extremely thin cell (ETC), whose walls are
separated by less than one micrometer, and developed an improved theoretical
model to describe these signals with experimental precision. The theoretical
model was based on the optical Bloch equations and included all neighboring
hyperfine transitions, the mixing of the magnetic sublevels in an external
magnetic field, and the Doppler effect, as in previous studies. However, in
order to model the extreme conditions in the ETC more realistically, the model
was extended to include a unified treatment of transit relaxation and wall
collisions with relaxation rates that were obtained directly from the thermal
velocities of the atoms and the length scales involved. Furthermore, the
interaction of the atoms with different regions of the laser beam were modeled
separately to account for the varying laser beam intensity over the beam
profile as well as saturation effects that become important near the center of
the beam at the relatively high laser intensities used during the experiments
in order to obtain measurable signals. The model described the experimentally
measured signals for laser intensities for magnetic fields up to 55~G and laser
intensities up to 1~W/cm$^2$ with excellent agreement.",1411.2750v1
2014-12-04,Acoustomagnetoelectric Effect in Graphene Nanoribbon in the Presence of External Electric and Magnetic Field,"The Acoustomagnetoelectric Effect (AME) in Graphene Nanoribbon (GNR) was
theoretically studied using the Boltzmann kinetic equation. On open circuit,
the general formular for Surface Acoustomagnetoelectric field
($\vec{E}_{SAME}$) in GNR with energy dispersion $\varepsilon(p)$ near the
Fermi point was calculated. The $E_{SAME}$ was found to depend on the magnetic
strength ($\eta$), $\alpha$ = ${\hbar \omega_q}/{E_g}$ and the energy gap
($E_g$). The expression for $\vec{E}_{SAME}$ was analyzed numerically for
varying width of GNR, magnetic strength ($\eta$) and $\alpha$ at different
sub-bands indices ($p_i$). It was noted that the dependence of $\vec{E}_{SAME}$
on the width of GNR increased to a saturation point of approximately
$15$Vcm$^{-1}$ and remained constant. For $E_{SAME}$ versus $\eta$, the
$E_{SAME}$ increases rapidly to a maximum point and then decayed to a constant
minimum value. The graph was modulated either by varying the width of GNR or
the sub-band index $p_i$ with an inversion occurring at $p_i = 6$. The
dependence of $E_{SAME}$ versus $\alpha$ was analyzed. The $E_{SAME}$ was
constant up to a point and sharply increased asymptotically at approximately
$\alpha = 1$. A $3$D graph of $\vec{E}_{SAME}$ with $\eta$ and width is also
presented. This study is relevant for investigating the properties of GNR.",1412.1678v5
2014-12-15,The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars,"To better understand the observed distributions of rotation rate and magnetic
activity of sun-like and low-mass stars, we derive a physically motivated
scaling for the dependence of the stellar-wind torque on Rossby number. The
torque also contains an empirically-derived scaling with stellar mass (and
radius), which provides new insight into the mass-dependence of stellar
magnetic and wind properties. We demonstrate that this new formulation explains
why the lowest mass stars are observed to maintain rapid rotation for much
longer than solar-mass stars, and simultaneously, why older populations exhibit
a sequence of slowly rotating stars, in which the low-mass stars rotate more
slowly than solar-mass stars. The model also reproduces some previously
unexplained features in the period-mass diagram for the Kepler field, notably:
the particular shape of the ""upper envelope"" of the distribution, suggesting
that ~95% of Kepler field stars with measured rotation periods are younger than
~4 Gyr; and the shape of the ""lower envelope,"" corresponding to the location
where stars transition between magnetically saturated and unsaturated regimes.",1412.4786v1
2015-01-22,High spin polarization and large spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy,"In this paper, we investigate CoFeCrAl alloy by means of various experimental
techniques and ab-initio calculations to look for half-metallic nature. The
alloy is found to exist in the cubic Heusler structure, with presence of B2
ordering. Saturation magnetization (MS) value of about 2 Bohr magneton/f.u. is
observed at 8 K under ambient pressure, which is in good agreement with the
Slater-Pauling rule. MS values are found to be independent of pressure, which
is a prerequisite for half-metals. The ab-initio electronic structure
calculations predict half-metallic nature for the alloy with a spin slitting
energy of 0.31 eV. Importantly, this system shows a high current spin
polarization value of 0.67 [with error of 0.02], as deduced from the point
contact Andreev reflection (PCAR) measurements. Linear dependence of electrical
resistivity with temperature indicates the possibility of reasonably high spin
polarization at elevated temperatures (~150 K) as well. All these suggest that
CoFeCrAl is a promising material for the spintronic devices.",1501.05599v1
2015-02-08,Tuning the scattering mechanism in three-dimensional Dirac semimetal Cd$_{3}$As$_{2}$,"To probe the charge scattering mechanism in Cd$_{3}$As$_{2}$ single crystal,
we have analyzed the temperature and magnetic field dependence of the Seebeck
coefficient ($S$). The large saturation value of $S$ at high field clearly
demonstrates the linear energy dispersion of three-dimensional Dirac fermion. A
wide tunability of the charge scattering mechanism has been realized by varying
the strength of the magnetic field and carrier density via In doping. With the
increase in magnetic field, the scattering time crosses over from being nearly
energy independent to a regime of linear dependence. On the other hand, the
scattering time enters into the inverse energy-dependent regime and the Fermi
surface strongly modifies with 2\% In doping at Cd site. With further increase
in In content from 2 to 4\%, we did not observe any Shubnikov-de Haas
oscillation up to 9 T field, but the magnetoresistance is found to be quite
large as in the case of undoped sample.",1502.02264v5
2015-02-24,$S$ = 1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain in a zinc-verdazyl complex,"We successfully synthesized the zinc-verdazyl complex
[Zn(hfac)$_2$]$\cdot$($o$-Py-V) [hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate;
$o$-Py-V = 3-(2-pyridyl)-1,5-diphenylverdazyl], which is an ideal model
compound with an $S$ = 1/2 ferromagnetic-antiferromagnetic alternating
Heisenberg chain (F-AF AHC). $Ab$ $initio$ molecular orbital (MO) calculations
indicate that two dominant interactions $J_{\rm{F}}$ and $J_{\rm{AF}}$ form the
$S=1/2$ F-AF AHC in this compound. The magnetic susceptibility and magnetic
specific heat of the compound exhibit thermally activated behavior below
approximately 1 K. Furthermore, its magnetization curve is observed up to the
saturation field and directly indicates a zero-field excitation gap of 0.5 T.
These experimental results provide evidence for the existence of a Haldane gap.
We successfully explain the results in terms of the $S=1/2$ F-AF AHC through
quantum Monte Carlo calculations with $|J_{\rm{AF}}/J_{\rm{F}}|$ = 0.22. The
$ab$ $initio$ MO calculations also indicate a weak AF interchain interaction
$J'$ and that the coupled F-AF AHCs form a honeycomb lattice. The $J'$
dependence of the Haldane gap is calculated, and the actual value of $J'$ is
determined to be less than 0.01$|J_{\rm{F}}|$.",1502.06804v1
2015-05-07,Spin and charge density waves in the Lieb lattice,"We study the mean-field phase diagram of the two-dimensional (2D) Hubbard
model in the Lieb lattice allowing for spin and charge density waves. Previous
studies of this diagram have shown that the mean-field magnetization
surprisingly deviates from the value predicted by Lieb's theorem
\cite{Lieb1989} as the on-site repulsive Coulomb interaction ($U$) becomes
smaller \cite{Gouveia2015}. Here, we show that in order for Lieb's theorem to
be satisfied, a more complex mean-field approach should be followed in the case
of bipartite lattices or other lattices whose unit cells contain more than two
types of atoms. In the case of the Lieb lattice, we show that, by allowing the
system to modulate the magnetization and charge density between sublattices,
the difference in the absolute values of the magnetization of the sublattices,
$m_{\text{Lieb}}$, at half-filling, saturates at the exact value $1/2$ for any
value of $U$, as predicted by Lieb. Additionally, Lieb's relation,
$m_{\text{Lieb}}=1/2$, is verified approximately for large $U$, in the $n \in
[2/3,4/3]$ range. This range includes not only the ferromagnetic region of the
phase diagram of the Lieb lattice (see Ref.~\onlinecite{Gouveia2015}), but also
the adjacent spiral regions. In fact, in this lattice, below or at
half-filling, $m_{\text{Lieb}}$ is simply the filling of the quasi-flat bands
in the mean-field energy dispersion both for large and small $U$.",1505.01656v1
2015-06-04,Manipulation of the spin helix in FeGe thin films and FeGe/Fe multilayers,"Magnetic materials without structural inversion symmetry can display the
Dzyaloshinskii-Moriya interaction, which manifests itself as chiral magnetic
ground states. These chiral states can interact in complex ways with applied
fields and boundary conditions provided by finite sample sizes that are of the
order of the lengthscale of the chiral states. Here we study epitaxial thin
films of FeGe with a thickness close to the helix pitch of the helimagnetic
ground state, which is about 70 nm, by conventional magnetometry and polarized
neutron reflectometry. We show that the helix in an FeGe film reverses under
the application of a field by deforming into a helicoidal form, with twists in
the helicoid being forced out of the film surfaces on the way to saturation. An
additional boundary condition was imposed by exchange coupling a ferromagnetic
Fe layer to one of the interfaces of an FeGe layer. This forces the FeGe spins
at the interface to point in the same direction as the Fe, preventing node
expulsion and giving a handle by which the reversal of the helical magnet may
be controlled.",1506.01575v1
2015-08-04,An Extended Magnetohydrodynamics Model for Relativistic Weakly Collisional Plasmas,"Black holes that accrete far below the Eddington limit are believed to
accrete through a geometrically thick, optically thin, rotationally supported
plasma that we will refer to as a radiatively inefficient accretion flow
(RIAF). RIAFs are typically collisionless in the sense that the Coulomb mean
free path is large compared to $GM/c^2$, and relativistically hot near the
event horizon. In this paper we develop a phenomenological model for the plasma
in RIAFs, motivated by the application to sources such as Sgr A* and M87. The
model is derived using Israel-Stewart theory, which considers deviations up to
second order from thermal equilibrium, but modified for a magnetized plasma.
This leads to thermal conduction along magnetic field lines and a difference in
pressure, parallel and perpendicular to the field lines (which is equivalent to
anisotrotropic viscosity). In the non-relativistic limit, our model reduces to
the widely used Braginskii theory of magnetized, weakly collisional plasmas. We
compare our model to the existing literature on dissipative relativistic
fluids, describe the linear theory of the plasma, and elucidate the physical
meaning of the free parameters in the model. We also describe limits of the
model when the conduction is saturated and when the viscosity implies a large
pressure anisotropy. In future work, the formalism developed in this paper will
be used in numerical models of RIAFs to assess the importance of non-ideal
processes for the dynamics and radiative properties of slowly accreting black
holes.",1508.00878v1
2015-08-06,The energy budget of stellar magnetic fields,"Spectropolarimetric observations have been used to map stellar magnetic
fields, many of which display strong bands of azimuthal fields that are
toroidal. A number of explanations have been proposed to explain how such
fields might be generated though none are definitive. In this paper, we examine
the toroidal fields of a sample of 55 stars with magnetic maps, with masses in
the range 0.1-1.5$\,{\rm M}_\odot$. We find that the energy contained in
toroidal fields has a power law dependence on the energy contained in poloidal
fields. However the power index is not constant across our sample, with stars
less and more massive than 0.5$\,{\rm M}_\odot$ having power indices of
0.72$\pm$0.08 and 1.25$\pm$0.06 respectively. There is some evidence that these
two power laws correspond to stars in the saturated and unsaturated regimes of
the rotation-activity relation. Additionally, our sample shows that strong
toroidal fields must be generated axisymmetrically. The latitudes at which
these bands appear depend on the stellar rotation period with fast rotators
displaying higher latitude bands than slow rotators. The results in this paper
present new constraints for future dynamo studies.",1508.01403v1
2015-10-30,"Feedback Regulated Turbulence, Magnetic Fields, and Star Formation Rates in Galactic Disks","We use three-dimensional magnetohydrodynamic (MHD) simulations to investigate
the quasi-equilibrium states of galactic disks regulated by star formation
feedback. We incorporate effects from massive-star feedback via time-varying
heating rates and supernova (SN) explosions. We find that the disks in our
simulations rapidly approach a quasi-steady state that satisfies vertical
dynamical equilibrium. The star formation rate (SFR) surface density
self-adjusts to provide the total momentum flux (pressure) in the vertical
direction that matches the weight of the gas. We quantify feedback efficiency
by measuring feedback yields, \eta_c\equiv P_c/\Sigma_SFR (in suitable units),
for each pressure component. The turbulent and thermal feedback yields are the
same for HD and MHD simulations, \eta_th~1 and \eta_ turb~4, consistent with
the theoretical expectations. In MHD simulations, turbulent magnetic fields are
rapidly generated by turbulence, and saturate at a level corresponding to
\eta_mag,t~1. The presence of magnetic fields enhances the total feedback yield
and therefore reduces the SFR, since the same vertical support can be supplied
at a smaller SFR. We suggest further numerical calibrations and observational
tests in terms of the feedback yields.",1511.00018v1
2016-03-03,Classical impurities and boundary Majorana zero modes in quantum chains,"We study the response of classical impurities in quantum Ising chains. The Z2
degeneracy they entail renders the existence of two decoupled Majorana modes at
zero energy an exact property of a finite system at arbitrary values of its
bulk parameters. We trace the evolution of these modes across the transition
from the disordered phase to the ordered one and analyze the concomitant
qualitative changes of local magnetic properties of an isolated impurity. In
the disordered phase, the two ground states differ only close to the impurity,
and they are related by the action of an explicitly constructed quasi-local
operator. In this phase the local transverse spin susceptibility follows a
Curie law. The critical response of a boundary impurity is logarithmically
divergent and maps to the two-channel Kondo problem, while it saturates for
critical bulk impurities, as well as in the ordered phase. The results for the
Ising chain translate to the related problem of a resonant level coupled to a
1d p-wave superconductor or a Peierls chain, whereby the magnetic order is
mapped to topological order. We find that the topological phase always exhibits
a continuous impurity response to local fields as a result of the level
repulsion of local levels from the boundary Majorana zero mode. In contrast,
the disordered phase generically features a discontinuous magnetization or
charging response. This difference constitutes a general thermodynamic
fingerprint of topological order in phases with a bulk gap.",1603.01037v1
2016-06-23,Resistive properties and phase diagram of the organic antiferromagnetic metal $κ$-(BETS)$_2$FeCl$_4$,"The low-temperature electronic state of the layered organic charge-transfer
salt $\kappa$-(BETS)$_2$FeCl$_4$ was probed by interlayer electrical resistance
measurements under magnetic field. Both above and below
$T_{\mathrm{N}}=0.47\,$K, the temperature of antiferromagnetic ordering of
$3d$-electron spins of Fe$^{3+}$ localized in the insulating anion layers, a
non-saturating linear $R(T)$ dependence has been observed. A weak
superconducting signal has been detected in the antiferromagnetic state, at
temperatures $\leq 0.2\,$K. Despite the very high crystal quality, only a tiny
fraction of the sample appears to be superconducting. Besides a small kink
feature in the resistivity, the impact of the antiferromagnetic ordering of
localized Fe$^{3+}$ spins on the conduction $\pi$-electron system is clearly
manifested in the Fermi surface reconstruction, as evidenced by Shubnikov-de
Haas oscillations. The ""magnetic field -- temperature"" phase diagrams for the
field directions parallel to each of the three principal crystal axes have been
determined. For magnetic field along the easy axis a spin-flop transition has
been found. Similarities and differences between the present material and the
sister compound $\kappa$-(BETS)$_2$FeBr$_4$ are discussed.",1606.07331v3
2016-06-23,A coupled $2\times2$D Babcock-Leighton solar dynamo model. II. Reference dynamo solutions,"In this paper we complete the presentation of a new hybrid $2\times2$D flux
transport dynamo (FTD) model of the solar cycle based on the Babcock-Leighton
mechanism of poloidal magnetic field regeneration via the surface decay of
bipolar magnetic regions (BMRs). This hybrid model is constructed by allowing
the surface flux transport (SFT) simulation described in Lemerle et al. 2015 to
provide the poloidal source term to an axisymmetric FTD simulation defined in a
meridional plane, which in turn generates the BMRs required by the SFT. A key
aspect of this coupling is the definition of an emergence function describing
the probability of BMR emergence as a function of the spatial distribution of
the internal axisymmetric magnetic field. We use a genetic algorithm to
calibrate this function, together with other model parameters, against observed
cycle 21 emergence data. We present a reference dynamo solution reproducing
many solar cycle characteristics, including good hemispheric coupling, phase
relationship between the surface dipole and the BMR-generating internal field,
and correlation between dipole strength at cycle maximum and peak amplitude of
the next cycle. The saturation of the cycle amplitude takes place through the
quenching of the BMR tilt as a function of the internal field. The observed
statistical scatter about the mean BMR tilt, built into the model, acts as a
source of stochasticity which dominates amplitude fluctuations. The model thus
can produce Dalton-like epochs of strongly suppressed cycle amplitude lasting a
few cycles and can even shut off entirely following an unfavorable sequence of
emergence events.",1606.07375v3
2016-09-15,Ferromagnetism and the Effect of Free Charge Carriers on Electric Polarization in Y_2NiMnO_6 Double Perovskite,"The double perovskite Y_2NiMnO_6 displays ferromagnetic transition at Tc = 81
K. The ferromagnetic order at low temperature is confirmed by the saturation
value of magnetization (M_s) and also, validated by the refined ordered
magnetic moment values extracted from neutron powder diffraction data at 10 K.
This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The
cation-ordered P 21/n nuclear structure is revealed by neutron powder
diffraction studies at 300 and 10 K. Analysis of frequency dependent dielectric
constant and equivalent circuit analysis of impedance data takes into account
the bulk contribution to total dielectric constant. This reveals an anomaly
which coincides with the ferromagnetic transition temperature (T_c).
Pyrocurrent measurements register a current flow with onset near Tc and a peak
at 57 K that shifts with temperature ramp rate. The extrinsic nature of the
observed pyrocurrent is established by employing a special protocol
measurement. It is realized that the origin is due to re-orientation of
electric dipoles created by the free charge carriers and not by spontaneous
electric polarization at variance with recently reported magnetism-driven
ferroelectricity in this material",1609.04511v1
2016-12-20,Magnons in a two dimensional transverse field XXZ model,"The XXZ model on a square lattice in the presence of a transverse magnetic
field is studied within the spin wave theory to investigate the resulting
canted antiferromagnet. The small and large field regimes are probed separately
both for easy-axis and easy-plane scenarios which reveal an unentangled
factorized ground state at an intermediate value of the field. Goldstone modes
are obtained for the field-free $XY$ antiferromagnet as well as for the
isotropic antiferromagnet with field up to its saturation value. Moreover, for
an easy-plane anisotropy, we find that there exists a non-zero field, where
magnon degeneracy appears as a result of restoration of an U(1) sublattice
symmetry and that, across that field, there occurs a magnon band crossing. For
completeness, we then obtain the system phase diagram for $S=1/2$ via large
scale quantum Monte Carlo simulations using the stochastic series expansion
technique. Our numerical method is based on a quantization of spin along the
direction of the applied magnetic field and does not suffer from a
sign-problem, unlike comparable algorithms based on a spin quantization along
the axis of anisotropy. With this formalism, we are also able to obtain powder
averages of the transverse and longitudinal magnetizations, which may be useful
for understanding experimental measurements on polycrystalline samples.",1612.06608v3
2016-12-20,Magnetocrystalline anisotropy of Laves phase Fe$_2$Ta$_{1-x}$W$_x$ from first principles - the effect of 3d-5d hybridisation,"The magnetic properties of Fe$_2$Ta and Fe$_2$W in the hexagonal Laves phase
are computed using density functional theory in the generalised gradient
approximation, with the full potential linearised augmented plane wave method.
The alloy Fe$_2$Ta$_{1-x}$W$_x$ is studied using the virtual crystal
approximation to treat disorder. Fe$_2$Ta is found to be ferromagnetic with a
saturation magnetization of $\mu_0 M_\text{s} = 0.66~\mathrm{T}$ while, in
contrast to earlier computational work, Fe$_2$W is found to be ferrimagnetic
with $\mu_0 M_\text{s} = 0.35~\mathrm{T}$. The transition from the ferri- to
the ferromagnetic state occurs for $x \leq 0.1$. The magnetocrystalline
anisotropy energy (MAE) is calculated to $1.25~\mathrm{MJ/m^3}$ for Fe$_2$Ta
and $0.87~\mathrm{MJ/m^3}$ for Fe$_2$W. The MAE is found to be smaller for all
values $x$ in Fe$_2$Ta$_{1-x}$W$_x$ than for the end compounds and it is
negative (in-plane anisotropy) for $0.1 \leq x \leq 0.9$. The MAE is carefully
analysed in terms of the electronic structure. Even though there are weak 5d
contributions to the density of states at the Fermi energy in both end
compounds, a reciprocal space analysis, using the magnetic force theorem,
reveals that the MAE originates mainly from regions of the Brillouin zone with
strong 3d-5d hybridisation near the Fermi energy. Perturbation theory and its
applicability in relation to the MAE is discussed.",1612.06802v1
2016-12-30,"Topological phase in $1D$ topological Kondo insulator: $Z_{2}$ topological insulator, Haldane-like phase and Kondo breakdown","We have simulated a half-filled $1D$ $p$-wave periodic Anderson model with
numerically exact projector quantum Monte Carlo technique, and the system is
indeed located in the Haldane-like state as detected in previous works on the
$p$-wave Kondo lattice model, though the soluble non-interacting limit
corresponds to the conventional $Z_{2}$ topological insulator. The
site-resolved magnetization in an open boundary system and strange correlator
for the periodic boundary have been used to identify the mentioned topological
states. Interestingly, the edge magnetization in the Haldane-like state is not
saturated to unit magnetic moment due to the intrinsic charge fluctuation in
our periodic Anderson-like model, which is beyond the description of the Kondo
lattice-like model in existing literature. The finding here underlies the
correlation driven topological state in this prototypical interacting
topological state of matter and naive use of non-interacting picture should be
taken care. Moreover, no trace of the surface Kondo breakdown at zero
temperature is observed and it is suspected that frustration-like interaction
may be crucial in inducing such radical destruction of Kondo screening. The
findings here may be relevant to our understanding of interacting topological
materials like topological Kondo insulator candidate SmB$_{6}$.",1612.09376v3
2017-02-12,Some consequences of shear on galactic dynamos with helicity fluxes,"Galactic dynamo models sustained by supernova (SN) driven turbulence and
differential rotation have revealed that the sustenance of large scale fields
requires a flux of small scale magnetic helicity to be viable. Here we
generalize a minimalist analytic version of such galactic dynamos to explore
some heretofore unincluded contributions from shear on the total turbulent
energy and turbulent correlation time, with the helicity fluxes maintained by
either winds, diffusion, or magnetic buoyancy. We construct an analytic
framework for modeling the turbulent energy and correlation time as functions
of SN rate and shear. We compare our prescription with previous approaches that
only include rotation. The solutions depend separately on the rotation period
and the eddy turnover time and not just on their ratio (the Rossby number). We
consider models in which these two time scales are allowed to be independent
and also a case in which they are mutually dependent on radius when a radial
dependent SN rate model is invoked. For the case of a fixed rotation period (or
fixed radius) we show that the influence of shear is dramatic for low Rossby
numbers, reducing the correlation time of the turbulence, which in turn,
strongly reduces the saturation value of the dynamo compared to the case when
the shear is ignored. We also show that even in the absence of winds or
diffusive fluxes, magnetic buoyancy may be able to sustain sufficient helicity
fluxes to avoid quenching.",1702.03560v2
2017-03-02,Diversity of quantum ground states and quantum phase transitions of a spin-1/2 Heisenberg octahedral chain,"The spin-1/2 Heisenberg octahedral chain with regularly alternating monomeric
and square-plaquette sites is investigated using various analytical and
numerical methods: variational technique, localized-magnon approach, exact
diagonalization (ED) and density-matrix renormalization group (DMRG) method.
The model belongs to the class of flat-band systems and it has a rich
ground-state phase diagram including phases with spontaneously broken
translational symmetry. Moreover, it exhibits an anomalous low-temperature
thermodynamics close to continuous or discontinuous field-driven quantum phase
transitions between three quantum ferrimagnetic phases, tetramer-hexamer phase,
monomer-tetramer phase, localized-magnon phase and two different spin-liquid
phases. If the intra-plaquette coupling is at least twice as strong as the
monomer-plaquette coupling, the variational method furnishes a rigorous proof
of the monomer-tetramer ground state in a low-field region and the
localized-magnon approach provides an exact evidence of a single magnon trapped
at each square plaquette in a high-field region. In the rest of parameter space
we have numerically studied the ground-state phase diagram and magnetization
process using DMRG and ED methods. It is shown that the zero-temperature
magnetization curve may involve up to four intermediate plateaus at zero,
one-fifth, two-fifth and three-fifth of the saturation magnetization, while the
specific heat exhibits a striking low-temperature peak in a vicinity of
discontinuous quantum phase transitions.",1703.00715v2
2017-03-31,Gigantic negative magnetoresistance in a disordered topological insulator,"With the recent discovery of Weyl semimetals, the phenomenon of negative
magnetoresistance (MR) is attracting renewed interest. While small negative MR
can occur due to the suppression of spin scattering or weak localization, large
negative MR is rare in materials, and when it happens, it is usually related to
magnetism. The large negative MR in Weyl semimetals is peculiar in that it is
unrelated to magnetism and comes from chiral anomaly. Here we report that there
is a new mechanism for large negative MR which is not related to magnetism but
is related to disorder. In the newly-synthesized bulk-insulating topological
insulator TlBi$_{0.15}$Sb$_{0.85}$Te$_2$, we observed gigantic negative MR
reaching 98% in 14 T at 10 K, which is unprecedented in a nonmagnetic system.
Supported by numerical simulations, we argue that this phenomenon is likely due
to the Zeeman effect on a barely percolating current path formed in the
disordered bulk. Since disorder can also lead to non-saturating linear MR in
Ag$_{2+\delta}$Se, the present finding suggests that disorder engineering in
narrow-gap systems is useful for realizing gigantic MR in both positive and
negative directions.",1703.10784v2
2017-04-10,Large magnetoresistance and Fermi surface study of Sb$_2$Se$_2$Te single crystal,"We have studied the magnetotransport properties of a Sb$_2$Se$_2$Te single
crystal. Magnetoresistance (MR) is maximum when the magnetic field is
perpendicular to the sample surface and reaches to a value of 1100\% at $B$=31
T with no sign of saturation. MR shows Shubnikov de Haas (SdH) oscillations
above $B$=15 T. The frequency spectrum of SdH oscillations consists of three
distinct peaks at $\alpha$=32 T, $\beta$=80 T and $\gamma$=117 T indicating the
presence of three Fermi surface pockets. Among these frequencies, $\beta$ is
the prominent peak in the frequency spectrum of SdH oscillations measured at
different tilt angles of the sample with respect to the magnetic field. From
the angle dependence $\beta$ and Berry phase calculations, we have confirmed
the trivial topology of the $\beta$-pocket. The cyclotron masses of charge
carriers, obtained by using the Lifshitz-Kosevich formula, are found to be
$m^{*}_{\beta}=0.16m_o$ and $m^{*}_{\gamma}=0.63m_o$ for the $\beta$ and
$\gamma$ bands respectively. Large MR of Sb$_2$Se$_2$Te is suitable for
utilization in electronic instruments such as a computer hard disc, high field
magnetic sensors, and memory devices.",1704.02682v3
2017-04-23,Anomalous Transport Properties of Dense QCD in a Magnetic Field,"Despite recent advancements in the study and understanding of the phase
diagram of strongly interacting matter, the region of high baryonic densities
and low temperatures has remained difficult to reach in the lab. Things are
expected to change with the planned HIC experiments at FAIR in Germany and NICA
in Russia, which will open a window to the high-density-low-temperature segment
of the QCD phase map, providing a unique opportunity to test the validity of
model calculations that have predicted the formation of spatially inhomogeneous
phases with broken chiral symmetry at intermediate-to-high densities. Such a
density region is also especially relevant for the physics of neutron stars, as
they have cores that can have several times the nuclear saturation density. On
the other hand, strong magnetic fields, whose presence is fairly common in HIC
and in neutron stars, can affect the properties of these exotic phases and lead
to signatures potentially observable in these two settings. In this paper, I
examine the anomalous transport properties produced by the spectral asymmetry
of the lowest Landau level (LLL) in a QCD-inspired NJL model with a background
magnetic field that exhibits chiral symmetry breaking at high density via the
formation of a Dual Chiral Density Wave (DCDW) condensate. It turns out that in
this model the electromagnetic interactions are described by the axion
electrodynamics equations and there is a dissipationless Hall current.",1704.06991v1
2017-05-18,Stratified Simulations of Collisionless Accretion Disks,"This paper presents a series of stratified shearing-box simulations of
collisionless accretion disks in the recently developed framework of kinetic
magnetohydrodynamics (MHD), which can handle finite non-gyrotropy of a pressure
tensor. Although a fully kinetic simulation predicted a more efficient
angular-momentum transport in collisionless disks than in the standard MHD
regime, the enhanced transport has not been observed in past kinetic MHD
approaches to gyrotropic pressure anisotropy. For the purpose of investigating
this missing link between the fully kinetic and MHD treatments, this paper pays
attention to the role of non-gyrotropic pressure, and makes a first attempt to
incorporate certain collisionless effects into disk-scale, stratified disk
simulations. When the timescale of gyrotropization was longer than, or
comparable to, the disk rotation frequency of the orbit, we found that the
finite non-gyrotropy selectively remaining in the vicinity of current sheets
contributes to suppressing magnetic reconnection in the shearing-box system.
This leads to increases both in the saturated amplitude of the MHD turbulence
driven by magnetorotational instabilities and in the resultant efficiency of
angular-momentum transport. Our results seem favorable for fast advection of
magnetic fields toward the rotation axis of a central object, which is required
to launch an ultra-relativistic jet from a black-hole accretion system in, for
example, a magnetically arrested disk state.",1705.06507v1
2017-05-23,Half-magnetization plateau in a Heisenberg antiferromagnet on a triangular lattice,"We present the phase diagram in a magnetic field of a 2D isotropic Heisenberg
antiferromagnet on a triangular lattice. We consider spin-$S$ model with
nearest-neighbor ($J_1$) and next-nearest-neighbor ($J_2$) interactions. We
focus on the range of $1/8<J_2/J_1<1$, where the ordered states are different
from those in the model with only nearest neighbor exchange. A classical ground
state in this range has four sublattices and is infinitely degenerate in any
field. The actual order is then determined by quantum fluctuations via ""order
from disorder"" phenomenon. We argue that the phase diagram is rich due to
competition between competing four-sublattice quantum states which break either
$\mathbb{Z}_3$ orientational symmetry or $\mathbb{Z}_4$ sublattice symmetry. At
small and high fields, the ground state is a $\mathbb{Z}_3$-breaking canted
stripe state, but at intermediate fields the ordered states break
$\mathbb{Z}_4$ sublattice symmetry. The most noticeable of such states is
""three up, one down"" state in which spins in three sublattices are directed
along the field and in one sublattice opposite to the field. Such a state
breaks no continuous symmetry and has gapped excitations. As the consequence,
magnetization has a plateau at exactly one half of the saturation value. We
identify gapless states, which border the ""three up, one down"" state and
discuss the transitions between these states and the canted stripe state.",1705.08515v1
2017-06-13,Structural ordering of laser-processed FePdCu thin alloy films,"The Cu/Fe/Pd multilayers were transformed into L10-ordered FePdCu alloy by
pulsed laser annealing. The initial multilayers were irradiated with 1, 10,
100, and 1000 laser pulses with duration time of 10 ns and energy density of
235 mJ/cm2. The gradual change of the number of laser pulses allowed to
investigate the structural and magnetic properties at early stages of the
transformation and L10-ordering processes. The measurements were carried out
using X-Ray Diffraction, SQUID magnetometry, and Magnetic Force Microscopy. We
found that L10 FePdCu (111)-oriented nanograins are formed by ordering of the
coherent domains present in the as-deposited multilayer. The irradiation does
not change the vertical size of the (111) crystallites. The L10 (002)-oriented
grains appear at the later stages of the transformation and their size
increases with the number of applied laser pulses. Additionally, the laser
annealing induces the magnetic ordering of the irradiated material, which was
observed as an increase of the saturation magnetisation and the Curie
temperature with the rising number of pulses. We also observed, that
irradiation with 1000 pulses leads to the loss of order, which is reflected in
the drop of the Curie temperature.",1706.03918v1
2017-06-24,Weak antilocalization effect due to topological surface states in Bi$_2$Se$_{2.1}$Te$_{0.9}$,"We have investigated the weak antilocalization (WAL) effect in the p-type
Bi$_2$Se$_{2.1}$Te$_{0.9}$ topological system. The magnetoconductance shows a
cusp-like feature at low magnetic fields, indicating the presence of the WAL
effect. The WAL curves measured at different tilt angles merge together when
they are plotted as a function of the normal field components, showing that
surface states dominate the magnetoconductance in the
Bi$_2$Se$_{2.1}$Te$_{0.9}$ crystal. We have calculated magnetoconductance per
conduction channel and applied the Hikami-Larkin-Nagaoka formula to determine
the physical parameters that characterize the WAL effect. The number of
conduction channels and the phase coherence length do not change with
temperature up to T=5 K. In addition, the sample shows a large positive
magnetoresistance that reaches 1900% under a magnetic field of 35 T at T=0.33K
with no sign of saturation. The magnetoresistance value decreases with both
increasing temperature and tilt angle of the sample surface with respect to the
magnetic field. The large magnetoresistance of topological insulators can be
utilized in future technology such as sensors and memory devices.",1706.08006v2
2017-07-11,Interface Dzyaloshinskii-Moriya interaction in the interlayer exchange antiferromagnetic coupled Pt/CoFeB/Ru/CoFeB systems,"Interfacial Dzyaloshinskii-Moriya interaction (iDMI) in interlayer exchange
coupled (IEC) Pt/Co$_{20}$Fe$_{60}$B$_{20}$(1.12
nm)/Ru/Co$_{20}$Fe$_{60}$B$_{20}$(1.12 nm) systems have been studied
theoretically and experimentally. Vibrating sample magnetometer has been used
to measure their magnetization at saturation and their interlayer exchange
coupling constants. These latter are found to be of an antiferromagnetic nature
for the investigated Ru range thickness (0.5-1 nm). Their dynamic magnetic
properties were studied using Brillouin light scattering (BLS) technique. The
BLS measurements reveal pronounced non-reciprocal spin waves propagation. In
contrast to the calculations for symmetrical IEC CoFeB layers, this
experimental nonreciprocity is Ru thickness and thus coupling strength
dependent. Therefore, to explain the experimental behaviour, a theoretical
model based on the perpendicular interface anisotropy difference between the
bottom and top CoFeB layers has been developed. We show that the Ru thickness
dependence of the spin wave non-reciprocity is well reproduced by considering a
constant iDMI and different perpendicular interfacial anisotropy fields between
the top and bottom CoFeB layers. This anisotropy difference has been confirmed
by the investigation of the CoFeB thickness dependence of effective
magnetization of Pt/CoFeB/Ru and Ru/CoFeB/MgO individual layers, where a linear
behaviour has been observed.",1707.03427v1
2017-09-18,Magnetic and magnetotransport properties of Bi$_2$Se$_3$ thin films doped by Eu,"Structural, magnetic and magnetotransport properties of
(Bi$_{1-x}$Eu$_x$)$_2$Se$_3$ thin films have been studied experimentally as a
function of Eu content. The films were synthesized by MBE. It is demonstrated
that Eu distribution is not uniform, it enter quint-layers forming inside them
plain (pancake-like) areas containing Eu atoms, which sizes and concentration
increase with the growth of Eu content. Positive magnetoresistance related to
the weak antilocalization was observed up to 15K. The antilocalization was not
followed by weak localization as theory predicts for nontrivial topological
states. Surprisingly, the features of antilocalization were seen even at Eu
content $x$ $=$ 0.21. With the increase of Eu content the transition to
ferromagnetic state occurs at $x$ about 0.1 and with the Curie temperature
$\approx$ 8K, that rises up to 64K for $x$ $=$ 0.21. At temperatures above 1-2
K, the dephasing length is proportional to $T^{-1/2}$ indicating the dominant
contribution of inelastic $e-e$ scattering into electron phase breaking.
However, at low temperatures the dephasing length saturates, that could be due
to the scattering on magnetic ions.",1709.06200v1
2017-10-01,Theory of ground states for classical Heisenberg spin systems IV,"We extend the theory of ground states of classical Heisenberg spin systems
previously published to the case where the interaction with an external
magnetic field is described by a Zeeman term. The ground state problem for the
Heisenberg-Zeeman Hamiltonian can be reduced first to the relative ground state
problem, and, in a second step, to the absolute ground state problem for pure
Heisenberg Hamiltonians depending on an additional Lagrange parameter. We
distinguish between continuous and discontinuous reduction. Moreover, there are
various general statements about Heisenberg-Zeeman systems that will be proven
under most general assumptions. One topic is the connection between the minimal
energy functions $E_{min}$ for the Heisenberg energy and $H_{min}$ for the
Heisenberg-Zeeman energy which turn out to be essentially mutual
Legendre-Fenchel transforms. This generalization of the traditional Legendre
transform is especially suited to cope with situations where the function
$E_{min}$ is not convex and consequently there is a magnetization jump at a
critical field. Another topic is magnetization and the occurrence of threshold
fields $B_{thr}$ and saturation fields $B_{sat}$, where we provide a general
formula for the latter. We suggest a distinction between ferromagnetic and
anti-ferromagnetic systems based on the vanishing of $B_{sat}$ for the former
ones. Parabolic systems are defined in such a way that $E_{min}$ and $H_{min}$
have a particularly simple form and studied in detail. For a large class of
parabolic systems the relative ground states can be constructed from the
absolute ground state by means of a so-called umbrella family. Finally we
provide a counter-example of a parabolic system where this construction is not
possible.",1710.00318v1
2018-04-03,"Electron mirror branch: Observational evidence from ""historical"" AMPTE-IRM and Equator-S measurements","Based on now historical magnetic and plasma data and available wave spectra
from the AMPTE-IRM spacecraft, and on as well historical Equator-S high-cadence
magnetic field observations of mirror modes in the magnetosheath near the
dayside magnetopause, we present some observational evidence for a recent
theoretical evaluation by Noreen et al. (2017) of the contribution of a global
electron temperature anisotropy to the evolution of mirror modes in the
high-temperature anisotropic collisionless plasma of the magnetosheath causing
a separate electron mirror branch. These old data most probably indicate that
signatures of this electron effect on mirror modes had indeed been observed
already long ago in magnetic and wave data though had not been recognised as
such. Unfortunately either poor time resolution or complete lack of plasma data
would have inhibited the confirmation of the notoriously required pressure
balance in the electron branch for unambiguous confirmation of a separate
electron mirror mode. If confirmed by future high-resolution observations, in
both cases the large mirror mode amplitudes suggest that mirror modes escape
quasilinear saturation being in a state of weak kinetic plasma turbulence.",1804.01131v2
2018-04-06,"Low mass planet migration in magnetically torqued dead zones - II. Flow-locked and runaway migration, and a torque prescription","We examine the migration of low mass planets in laminar protoplanetary discs,
threaded by large scale magnetic fields in the dead zone that drive radial gas
flows. As shown in Paper I, a dynamical corotation torque arises due to the
flow-induced asymmetric distortion of the corotation region and the evolving
vortensity contrast between the librating horseshoe material and background
disc flow. Using simulations of laminar torqued discs containing migrating
planets, we demonstrate the existence of the four distinct migration regimes
predicted in Paper I. In two regimes, the migration is approximately locked to
the inward or outward radial gas flow, and in the other regimes the planet
undergoes outward runaway migration that eventually settles to fast steady
migration. In addition, we demonstrate torque and migration reversals induced
by midplane magnetic stresses, with a bifurcation dependent on the disc surface
density. We develop a model for fast migration, and show why the outward
runaway saturates to a steady speed, and examine phenomenologically its
termination due to changing local disc conditions. We also develop an
analytical model for the corotation torque at late times that includes
viscosity, for application to discs that sustain modest turbulence. Finally, we
use the simulation results to develop torque prescriptions for inclusion in
population synthesis models of planet formation.",1804.02290v1
2018-04-15,$\mathrm{Co_2Fe_{1-x}Cr_xSi}$ Heusler Alloys : A promising material for spintronics application,"In this article, we investigated the effect of Cr substitution in place of Fe
on the structural, magnetic and transport properties of $\mathrm{Co_2FeSi}$
alloy. A comprehensive structural analysis is done using X-ray diffraction
(XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
Quaternary Heusler compounds $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ with Cr content (x =
0.1, 0.3, 0.5) were found to crystallize in cubic structure. The synchrotron
based EXAFS studies reveal that the anti-site disorder increases with the
increase in Cr concentration. The saturation magnetization values in all the
alloys are found to be less than those expected from the Slater-Pauling rule,
which may be due to the some inherent disorder. A detailed resistivity analysis
in the temperature range of 5-300 K is done, taking into account different
scattering mechanisms. The residual resistivity ratio is found to decrease with
increasing Cr concentration. A disorder induced resistivity minimum due to weak
localization effect is seen for x = 0.5. The resistivity measurements also
indicate that the half-metallic character survives upto 100 K for x = 0.1,
whereas the alloys with x= 0.3 and 0.5 show signature of half- metallic nature
even at higher temperatures. First principles calculation done with a more
robust exchange correlation functional (namely HSE-06) confirms the half
metallicity in the entire concentration range. Theoretically simulated band gap
and magnetic moments compliment the experimental findings and are compared
wherever possible. All these properties make $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ a
promising material for spintronics application.",1804.05321v1
2018-06-07,High Performance Metallic Amorphous Magnetic Flake-based Magnetodielectric Inductors,"Flake-shaped FeSi-based metallic amorphous alloy particles, having an aspect
ratio as high as 175 to 1, were prepared by ball milling gas atomized amorphous
powders of an effective diameter of 20 micrometers. The starting powder had a
saturation magnetic flux density, Bs, of 1.5 T and a coercivity, Hc, of 94 A/m.
The aspect ratio of the flakes, as well as their magnetic properties, were
controlled by milling process parameters, such as duration, speed, and the
type, mass and diameter of the milling balls. To minimize the oxidation of the
charge, the powders were handled in an argon gas-purged glove box, milled in
toluene, and subsequently dried in vacuo. Subsequently, soft magnetodielectric
composites were prepared by suspending and aligning the FeSi-based powders in
paraffin wax or epoxy resin. The composites were then pressed into toroids for
measurements of their high frequency complex permeability by a vector network
analyzer. The influence of the flake aspect ratio and volume loading fraction
on the permeability of the composites were investigated. Results indicate that
the composite permeability increases with the flake aspect ratio. For example,
for a given loading factor of 30 vol.%, the composite permeability at 0.1 GHz
nearly tripled and approached the value of 10 by increasing the aspect ratio of
the FeSi-based inclusions from 1 (spheres) to greater than 175 to 1 (flakes).",1806.02486v2
2018-06-21,Unconventional critical state in YBa$_{2}$Cu$_{3}$O$_{7-δ}$ thin films with a vortex-pin lattice fabricated by masked He$^+$ ion beam irradiation,"Thin superconducting YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ films are patterned with
a vortex-pin lattice consisting of columnar defect regions (CDs) with 180 nm
diameter and 300 nm spacing. They are fabricated by irradiation with 75 keV
He$^+$ ions through a stencil mask. Peaks of the critical current reveal the
commensurate trapping of vortices in domains near the edges of the sample. Upon
ramping an external magnetic field, the positions of the critical current peaks
are shifted from their equilibrium values to lower magnetic fields in virgin
and to higher fields in field-saturated down-sweep curves, respectively. Based
on previous theoretical predictions, this irreversibility is interpreted as a
nonuniform, terrace-like critical state, in which individual domains are
occupied by a constant number of vortices per pinning site. The
magnetoresistance, probed at low current densities, is hysteretic and angle
dependent and exhibits minima that correspond to the peaks of the critical
current. The minima's positions scale with the component of the magnetic field
parallel to the axes of the CDs, as long as the tilted vortices can be
accommodated within the CDs. This behavior, different from unirradiated films,
confirms that the CDs dominate the pinning.",1806.08164v1
2018-06-25,"3D global simulations of RIAFs: convergence, effects of azimuthal extent and dynamo","We study the long-term evolution of non-radiative geometrically thick
($H/R\approx 0.5$) accretion flows using 3D global ideal MHD simulations and a
pseudo-Newtonian gravity. We find that resolving the scale height with 42 grid
points is adequate to obtain convergence with the product of quality factors
$\langle \langle Q_{\theta} \rangle \rangle \langle \langle Q_{\phi} \rangle
\rangle \geq 300$ and magnetic tilt angle $\theta_B \sim
13^{\circ}-14^{\circ}$. Like previous global isothermal thin disk simulations,
we find stronger mean magnetic fields for the restricted azimuthal domains.
Imposing periodic boundary conditions with the azimuthal extent smaller than
$2\pi$ make the turbulent field at low $m$ appear as a mean field in the runs
with smaller azimuthal extent. But unlike previous works, we do not find a
monotonic trend in turbulence with the azimuthal extent. We conclude that the
minimum azimuthal extent should be $\geq \pi/2$ to capture the flow structure,
but a full $2 \pi$ extent is necessary to study the dynamo. We find an
intermittent dynamo cycle, with $\alpha$-quenching playing an important role in
the nonlinear saturated state. Unlike previous local studies, we find almost
similar values of kinetic and magnetic $\alpha$-s, giving rise to an irregular
distribution of dynamo-$\alpha$. The effects of dynamical quenching are shown
explicitly for the first time in global simulations of accretion flows.",1806.09629v3
2018-08-03,Collapse of Kondo state and ferromagnetic quantum phase transition in YbFe$_2$Zn$_{20}$,"We present the electrical resistivity data under application of pressures up
to $\sim$ 26 GPa and down to 50 mK temperatures on YbFe$_2$Zn$_{20}$. We find a
pressure induced magnetic phase transition with an onset at $p_c$=18.2$\pm$0.8
GPa. At ambient pressure, YbFe$_2$Zn$_{20}$ manifests a heavy fermion,
nonmagnetic ground state and the Fermi liquid behavior at low temperatures. As
pressure is increased, the power law exponent in resistivity, $n$, deviates
significantly from Fermi liquid behavior and tends to saturate with $n$ = 1
near $p_c$. A pronounced resistivity maximum, $T_\text{max}$, which scales with
Kondo temperature is observed. $T_\text{max}$ decreases with increasing
pressure and flattened out near $p_c$ indicating the suppression of Kondo
exchange interaction. For $p>p_c$, $T_\text{max}$ shows a sudden upward shift,
most likely becoming associated with crystal electric field scattering.
Application of magnetic field for $p>p_c$ broadens the transition and shifts it
toward the higher temperature, which is a typical behavior of the ferromagnetic
transition. The magnetic transition appears to abruptly develop above $p_c$,
suggesting probable first-order (with changing pressure) nature of the
transition; once stabilized, the ordering temperature does not depend on
pressure up to $\sim$ 26 GPa. Taken as a whole, these data suggest that
YbFe$_2$Zn$_{20}$ has a quantum phase transition at $p_c$ = 18.2 GPa associated
with the avoided quantum criticality in metallic ferromagnets.",1808.01367v1
2018-11-12,Evidence for unconventional superconductivity in Half-Heusler YPdBi and TbPdBi compounds revealed by London penetration depth measurements,"The half-Heusler compounds YPdBi and TbPdBi, while having similar band
structure, exhibit different magnetic properties. YPdBi is a diamagnet, while
TbPdBi shows antiferromagnetic order below 5.5 K. Both are superconductors with
T${_c}\approx$1 K for YPdBi and T${_c}\approx$1.75 K for TbPdBi. Such a
contrast in properties between these two compounds opens a question about the
effects of band structure or magnetic correlations on superconductivity. Using
the combination of a tunnel diode oscillator (TDO) and a commercial dilution
refrigerator, we measured temperature dependent magnetic penetration depth
$\Delta\lambda(T)$ in single crystals of YPdBi and TbPdBi, down to temperatures
as low as 0.1K. We found that penetration depths of both compounds do not show
exponential temperature dependence and saturation at low temperatures, as
expected for conventional BCS superconductors. Instead, in both compounds, the
penetration depth can be described by a power law $\Delta\lambda(T) = A\times
T^{n}$. The coefficient A was found to be about 50$\%$ smaller in TbPdBi, but
the exponents are very similar, $n = 2.76\pm 0.04$ in YPdBi and $n = 2.6\pm
0.3$ in TbPdBi, respectively. Our results suggest unconventional
superconductivity in both YPdBi and TbPdBi.",1811.05045v1
2019-03-26,Engineering of spin mixing conductance in Ru/FeCo/Ru interfaces: Effect of Re Doping,"We have deposited polycrystalline Re doped $(Fe_{65}Co_{35})_{100-x}Re_{x}$
(0 $\leq$ x $\leq$ 12.6 at\%) thin films grown under identical conditions and
sandwiched between thin layers of Ru in order to study the phenomenon of spin
pumping as a function of Re concentration. In-plane and out-of-plane
ferromagnetic resonance spectroscopy results show an enhancement of the Gilbert
damping with an increase in Re doping. We found evidence of an increase in the
real part of effective spin mixing conductance
[Re($g^{\uparrow\downarrow}_{eff}$)] with the increase in Re doping of 6.6
at\%, while a decrease is evident at higher Re doping. The increase in
Re($g^{\uparrow\downarrow}_{eff}$) can be linked to the Re doping induced
change of the interface electronic structure in the non-magnetic Ru layer and
the effect interfacial spin-orbit coupling has on the effective spin-mixing
conductance. The lowest and highest values of
Re($g^{\uparrow\downarrow}_{eff}$) are found to be 9.883(02) $nm^{-2}$ and
19.697(02) $nm^{-2}$ for 0 at\% and 6.6 at\% Re doping, respectively. The
saturation magnetization decreases with increasing Re doping, from 2.362(13) T
for the undoped film to 1.740(03) T for 12.6 at\% Re doping. This study opens a
new direction of tuning the spin-mixing conductance in magnetic
heterostructures by doping of the ferromagnetic layerr, which is essential for
the realization of energy efficient operation of spintronic devices.",1903.10966v2
2019-04-03,Study of the Effect of Annealing on the Properties of Mn2RuxGa Thin Films,"The effect of vacuum annealing thin films of the compensated ferrimagnetic
half-metal Mn2RuxGa at temperatures from 250 to 400 degree Celsius is
investigated. The 39.3 nm films deposited on (100) MgO substrates exhibit
perpendicular magnetic anisotropy due to a small 1% tetragonal elongation
induced by substrate strain. The main change on annealing is a modification in
the compensation temperature, which first increases from 50 K for the
as-deposited film to 185 K after annealing at 250 degree Celsius, and then
falls to 140 K after annealing at 400 degree Celsius. There are minor changes
in the atomic order, coercivity, resistivity and anomalous Hall effect (AHE),
but the net magnetization measured by SQUID magnetometry with the field applied
in-plane or perpendicular-to-the-plane changes more significantly. It saturates
at 20 to 30 kA/m at room temperature, and a small soft component is seen in the
perpendicular SQUID loops which is absent in the square AHE hysteresis loops.
This is explained by the half-metallic nature of the compound; the AHE probes
only the 4c Mn sublattice that provides the spin-polarized electrons at the
Fermi level, whereas the SQUID measures the sum of the oppositely-aligned 4c
and 4a sublattice magnetisations.",1904.01993v1
2019-04-05,"Stoichiometry, Phase, and Texture Evolution in PLD-Grown Hexagonal Barium Ferrite Films as a Function of Laser Process Parameters","Barium hexaferrite (BaFe12O19 or BaM) films were grown on c-plane sapphire
(0001) substrates by pulsed laser deposition (PLD) to evaluate the effects of
the laser fluence on their composition, structure, and magnetic properties.
Continuum's Surelite pulsed 266nm Nd:YAG laser was employed, and the laser
fluence varied systemically between 1 and 5.7 [J/cm2]. Deviations from the
stoichiometric transfer between the BaM targets and deposited thin films
occurred as the laser fluence changed. The Fe to Ba ratio in the films
increased with the laser fluence. The films deposited at the laser fluences
below 4 J/cm2 showed undesirable 3-dimensional islands on the surface.
Moreover, insufficient laser energy resulted in the deposition of some
secondary phases, for example, barium monoferrite (BaFe2O4) and Magnetite
(Fe3O4). On the other hand, laser fluences above 5 J/cm2 promoted resputtering
and degraded the film quality, structure, and magnetic properties. BaM films
deposited at 4.8 J/cm2 - the optimal laser fluence - showed excellent c-axis
orientation perpendicular to the film plane with the anisotropy field of 16 kOe
and saturation magnetization of 4.39 kOe. These results clearly demonstrate a
strong influence of the laser parameters on the PLD-grown hexaferrite films and
pave the path for the high-yield production using PLD systems.",1904.03157v2
2019-07-10,Electronic Transport Evidence for Topological Nodal-Line Semimetals of ZrGeSe single crystals,"Although the band topology of ZrGeSe has been studied via magnetic torque
technique, the electronic transport behaviors related to the relativistic
Fermions in ZrGeSe are still unknown. Here, we first report systematic
electronic transport properties of high-quality ZrGeSe single crystals under
magnetic fields up to 14 T. Resistivity plateaus of temperature dependent
resistivity curves both in the presence and absence of magnetic fields as well
as large, non-saturating magnetoresistance in low-temperature region were
observed. By analyzing the temperature- and angular-dependent Shubnikov-de Haas
oscillations and fitting it via the Lifshitz-Kosevich (LK) formula with the
Berry phase being taken into account, we proved that Dirac fermions dominate
the electronic transport behaviors of ZrGeSe and the presence of non-trivial
Berry phase. First principles calculations demonstrate that ZrGeSe possesses
Dirac bands and normal bands near Fermi surface, resulting in the observed
magnetotransport phenomena. These results demonstrate that ZrGeSe is a
topological nodal-line semimetal, which provides a fundamentally important
platform to study the quantum physics of topological semimetals.",1907.04762v1
2019-08-05,Spin inertia and polarization recovery in quantum dots: Role of pumping strength and resonant spin amplification,"Spin inertia measurements are a novel experimental tool to study long-time
spin relaxation processes in semiconductor nanostructures. We develop a theory
of the spin inertia effect for resident electrons and holes localized in
quantum dots. We consider the spin orientation by short optical pulses with
arbitrary pulse area and detuning from the trion resonance. The interaction
with an external longitudinal magnetic field and the hyperfine interaction with
the nuclear spin bath is considered in both the ground and excited (trion)
states of the quantum dots. We analyze how the spin inertia signal depends on
the magnetic field (polarization recovery) and on the modulation frequency of
the helicity of the pump pulses as well as on their power and detuning. In
particular, we elaborate how approaching the saturation limit of the spin
polarization influences the measurements. The quantitative description of spin
inertia measurements will enable the determination of the parameters of spin
dynamics such as the spin relaxation times in the ground and excited states and
the parameters of the hyperfine interaction. Finally, we predict the emergence
of resonant spin amplification due to the transverse components of the nuclear
spin fluctuations, which manifests itself as oscillations of the spin
polarization as a function of the longitudinal magnetic field.",1908.01531v3
2019-09-04,Formation of Power-law Electron Energy Spectra in Three-dimensional Low-$β$ Magnetic Reconnection,"While observations have suggested that power-law electron energy spectra are
a common outcome of strong energy release during magnetic reconnection, e.g.,
in solar flares, kinetic simulations have not been able to provide definite
evidence of power-laws in energy spectra of non-relativistic reconnection. By
means of 3D large-scale fully kinetic simulations, we study the formation of
power-law electron energy spectra in non-relativistic low-$\beta$ reconnection.
We find that both the global spectrum integrated over the entire domain and
local spectra within individual regions of the reconnection layer have
power-law tails with a spectral index $p \sim 4$ in the 3D simulation, which
persist throughout the non-linear reconnection phase until saturation. In
contrast, the spectrum in the 2D simulation rapidly evolves and quickly becomes
soft. We show that 3D effects such as self-generated turbulence and chaotic
magnetic field lines enable the transport of high-energy electrons across the
reconnection layer and allow them to access several main acceleration regions.
This leads to a sustained and nearly constant acceleration rate for electrons
at different energies. We construct a model that explains the observed
power-law spectral index in terms of the dynamical balance between particle
acceleration and escape from main acceleration regions, which are defined based
upon a threshold for the curvature drift acceleration term. This result could
be important for explaining the formation of power-law energy spectrum in solar
flares.",1909.01911v1
2019-09-21,Tailoring the optical and physical properties of La doped ZnO nanostructured thin films,"The modification and tailoring the characteristics of nanostructured
materials are of great interest due to controllable and unusual inherent
properties in such materials. A simple spray pyrolysis technique is used to
prepare pure and La-doped ZnO films. The influence of La concentration (0,
0.33, 0.45, 0.66, 0.92 and 1.04 at. %) on the structural, optical, and magnetic
properties of ZnO was investigated. The exact nominal compositions of the
prepared films were determined from the field emission scanning electron
microscope occupied with EDX. X-ray diffraction confirmed that the samples
possessed single-phase hexagonal wurtzite structure. The main crystal size was
decreased from 315.50 {\AA} to 229.04 {\AA} depending on La dopant
concentration. This decrease is due to the small ionic radius of Zn ions in
compared to La ions. The band gap values were found to be depend strongly on
La3+ ion content. Introducing La into ZnO induces a clear magnetic moment
without any distortion in the geometrical symmetry, it also reveals the
ferromagnetic coupling. The saturation magnetic moment of 1.04 at% La-doped ZnO
shows the highest value of 0.014 emu, which is ~23 times higher than pure ZnO
sample. The obtained results were discussed and compared with other literature
data and showed an acceptable agreement.",1909.09869v1
2019-09-23,Electron pairing in mirror modes: Surpassing the quasilinear limit,"The mirror mode evolving in collisionless magnetised high-temperature
thermally anisotropic plasmas is shown to develop an interesting macro-state.
Starting as a classical zero frequency ion fluid instability it saturates
quasi-linearly at very low magnetic level, while forming elongated magnetic
bubbles which trap the electron component to perform an adiabatic bounce motion
along the magnetic field. {Further evolution of the mirror mode towards a
stationary state is determined by the bouncing trapped electrons which interact
with the thermal level of ion sound waves, generate attractive wake potentials
which give rise to formation of electron pairs in the lowest-energy singlet
state of two combined electrons. Pairing takes preferentially place near the
bounce-mirror points where the pairs become spatially locked with all their
energy in the gyration. The resulting large anisotropy of pairs enters the
mirror growth rate in the quasi-linearly stable mirror mode. It breaks the
quasilinear stability and causes further growth. Pressure balance is either
restored by dissipation of the pairs and their anisotropy or inflow of plasma
from the environment. In the first case new pairs will continuously form until
equilibrium is reached. In the final state the fraction of pairs can be
estimated. This process is open to experimental verification. To our knowledge
it is the only process where in high temperature plasma pairing may occur and
has an important observable macroscopic effect: breaking the quasilinear limit
and generation of localised diamagnetism.}",1909.10163v1
2019-10-11,Observation of Fano resonance in photoluminescence of a two-dimensional magnetic semiconductor,"Quantum interference gives rise to the asymmetric Fano resonance line shape
when the final states of an electronic transition follows within a continuum of
states and a discrete state, which has significant applications in optical
switching and sensing. The resonant optical phenomena associated with Fano
resonance have been observed by absorption spectra, Raman spectra, transmission
spectra, etc., but have rarely been reported in photoluminescence (PL)
spectroscopy. In this work, we performed spectroscopic studies on layered
chromium thiophosphate (CrPS4), a promising ternary antiferromagnetic
semiconductor with PL in near-infrared wavelength region and observed Fano
resonance when CrPS4 experiences phase transition into the antiferromagnetic
state below N\'eel temperature (38 K). The photoluminescence of the continuum
states results from the d band transitions localized at Cr3+ ions, while the
discrete state reaches saturation at high excitation power and can be enhanced
by the external magnetic field, suggesting it is formed by an impurity level
from extra atomic phosphorus. Our findings provide insights into the electronic
transitions of CrPS4 and their connection to its intrinsic magnetic properties.",1910.05164v1
2019-10-22,Magnetic topological insulator MnBi6Te10 with zero-field ferromagnetic state and gapped Dirac surface states,"Magnetic topological insulators (TIs) with nontrivial topological electronic
structure and broken time-reversal symmetry exhibit various exotic topological
quantum phenomena. The realization of such exotic phenomena at high temperature
is one of central topics in this area. We reveal that MnBi6Te10 is a magnetic
TI with an antiferromagnetic ground state below 10.8 K whose nontrivial
topology is manifested by Dirac-like surface states. The ferromagnetic axion
insulator state with Z4 = 2 emerges once spins polarized at field as low as 0.1
T, accompanied with saturated anomalous Hall resistivity up to 10 K. Such a
ferromagnetic state is preserved even external field down to zero at 2 K.
Theoretical calculations indicate that the few-layer ferromagnetic MnBi6Te10 is
also topologically nontrivial with a non-zero Chern number. Angle-resolved
photoemission spectroscopy experiments further reveal three types of Dirac
surface states arising from different terminations on the cleavage surfaces,
one of which has insulating behavior with an energy gap of ~ 28 meV at the
Dirac point. These outstanding features suggest that MnBi6Te10 is a promising
system to realize various topological quantum effects at zero field and high
temperature.",1910.10101v2
2019-11-17,A Monte Carlo Study on the Variation of Residual Magnetisation with the Ratio of Coupling Strengths and Non-magnetic Impurities in an Ising Trilayer,"We have studied a spin-1/2, ABA, Ising trilayer system with two different
types of interactions, in-plane ferromagnetic and out-of-plane
anti-ferromagnetic, among the lattice sites, on different layers. In the pure
case, devoid of any impurity, we employed Monte-Carlo method with single
spin-flip Metropolis algorithm to find out the anti-ferromagnetic critical
temperature (N\'eel temperature) and another lower temperature, called the
compensation temperature, both with total magnetisation zero, in accordance
with already established results for square lattice. Then non-magnetic
impurities, (spin value= 0) were implanted on each layer at randomly picked
sites and their concentration was increased in steps from 5% to 20%. The ratio
of inter-planar anti-ferromagnetic to mid-layer ferromagnetic coupling strength
as well as the ratio of top and bottom layer ferromagnetic to mid layer
ferromagnetic coupling strength were also varied and N\'eel and compensation
temperatures, both were observed shifting towards lower temperature values with
increase in concentration of impurities in the lattice for any fixed ratio of
different coupling strengths, in absence of any external magnetic field. In
addition, the magnitude of the residual magnetisation i.e. the ratio of the
peak value of the magnetisation in between N\'eel and compensation points and
the saturated value of magnetisation, was also observed to vary with different
values of controlling parameters.",1911.07261v2
2019-11-19,Superconductivity below 2.5K in Nb0.25Bi2Se3 topological insulator single crystal,"We report crystal growth and below 2.5K superconductivity of Nb0.25Bi2Se3.
These crystals are grown by self flux method. The X-ray diffraction (XRD)
pattern of as grown crystal flake shows (00l) plane (c-orientation) growth. The
Rietveld refinement of crushed crystal powder XRD (PXRD) pattern confirms the
phase purity of the studied sample having R-3m space group of rhombohedral
crystalline structure. The Raman spectrum of the studied Nb0.25Bi2Se3 crystal
distinctly shows three well defined vibrational modes in terms of A11g, Eg2,
A21g at around 72, 129 and 173cm-1, which are slightly shifted in comparison to
pure Bi2Se3. Magnetization studies in terms of field cooled (FC) and Zero field
cooled (ZFC) magnetic susceptibility measurements show the diamagnetic
transition (Tconset) of the compound at around 2.5K and near saturation of the
same below around 2.1K. The isothernal magnetization (MH) being taken at 2K,
revealed the lower critical field (Hc1) of around 50Oe and the upper critical
field (Hc2) of 900Oe. It is clear the studied Nb0.25Bi2Se3 is a bulk
superconductor. The superconducting critical parameters thus calculated viz.
the coherence length, upper and lower critical fields and superconducting
transition temperature for as grown Nb0.25Bi2Se3 single crystal are reported
here.",1911.08108v1
2020-03-24,Anisotropic Physical Properties of the Kondo Semimetal CeCu$_{1.11}$As$_2$,"The recently proposed novel materials class called Weyl-Kondo semimetal
(WKSM) is a time reversal invariant but inversion symmetry broken Kondo
semimetal in which Weyl nodes are pushed to the Fermi level by the Kondo
interaction. Here we explore whether CeCu$_{1+x}$As$_2$ may be a new WKSM
candidate. We report on its single-crystal growth, structure determination and
physical properties investigation. Previously published studies on
polycrystalline samples suggest that it is indeed a Kondo semimetal, which is
confirmed by our investigations on single crystals. X-ray diffraction reveals
that CeCu$_{1+x}$As$_2$ crystallizes in a tetragonal centrosymmetric structure,
although the inversion symmetry could still be broken locally due to partially
occupied Cu sites. Chemical analysis results in an average occupation $x$ =
0.11(1). The electrical resistivity increases logarithmically with decreasing
temperature, and saturates below 10 K. A Kondo temperature $T_{\mathrm{K}}$
$\approx$ 4 K is extracted from entropy, estimated from the specific heat
measurements. From Hall effect experiments, a charge carrier density of $8.8
\times 10^{20}$ cm$^{-3}$ is extracted, a value characteristic of a semimetal.
The magnetization shows pronounced anisotropy, with no evidence of magnetic
ordering down to 0.4 K. We thus classify CeCu$_{1.11}$As$_2$ as a tetragonal
Kondo semimetal with anisotropic magnetic properties, with a possibly broken
inversion symmetry, thus fulfilling the necessary conditions for a WKSM state.",2003.10794v1
2020-03-30,Electric heating and angular momentum transport in laminar models of protoplanetary disks,"The vertical temperature structure of a protoplanetary disk bears on several
processes relevant to planet formation, such as gas and dust grain chemistry,
ice lines and convection. The temperature profile is controlled by irradiation
from the central star and by any internal source of heat such as might arise
from gas accretion. We investigate the heat and angular momentum transport
generated by the resistive dissipation of magnetic fields in laminar disks. We
use local one-dimensional simulations to obtain vertical temperature profiles
for typical conditions in the inner disk (0.5 to 4 au). Using simple
assumptions for the gas ionization and opacity, the heating and cooling rates
are computed self-consistently in the framework of radiative non-ideal
magnetohydrodynamics. We characterize steady solutions that are symmetric about
the midplane and which may be associated with saturated Hall-shear unstable
modes. We also examine the dissipation of electric currents driven by global
accretion-ejection structures. In both cases we obtain significant heating for
a sufficiently high opacity. Strong magnetic fields can induce an order-unity
temperature increase in the disk midplane, a convectively unstable entropy
profile, and a surface emissivity equivalent to a viscous heating of $\alpha
\sim 10^{-2}$. These results show how magnetic fields may drive efficient
accretion and heating in weakly ionized disks where turbulence might be
inefficient, at least for a range of radii and ages of the disk.",2003.13263v2
2020-07-09,Results of search for magnetized quark-nugget dark matter from radial impacts on Earth,"Magnetized Quark Nuggets (MQNs) are a recently proposed dark-matter candidate
consistent with the Standard Model and with Tatsumi's theory of quark-nugget
cores in magnetars. Previous publications have covered their formation in the
early universe, aggregation into a broad mass distribution before they can
decay by the weak force, interaction with normal matter through their
magnetopause, and first observation consistent MQNs, i.e. a nearly tangential
impact limiting their surface-magnetic-field parameter B_o from Tatsumi's
values of 0.1 to 10.0 TT to new value of 1.65 TT +/- 21%. The MQN mass
distribution and interaction cross section depend strongly on B_o. Their
magnetopause is much larger than their geometric dimensions and can cause
sufficient energy deposition to form non-meteorite craters, which are reported
approximately annually. We report computer simulations of the MQN energy
deposition in water-saturated peat, soft sediments, and granite and report
results from excavating such a crater. Five points of agreement between
observations and hydrodynamic simulations of an MQN impact support this second
observation consistent with MQN dark matter and suggest a method for qualifying
additional MQN events. The results also redundantly constrain B_o to greater
than 0.4 TT.",2007.04826v3
2020-07-14,Microtearing modes as the source of magnetic fluctuations in the JET pedestal,"We report on a detailed study of magnetic fluctuations in the JET pedestal,
employing basic theoretical considerations, gyrokinetic simulations, and
experimental fluctuation data, to establish the physical basis for their
origin, role, and distinctive characteristics. We demonstrate quantitative
agreement between gyrokinetic simulations of microtearing modes (MTMs) and two
magnetic frequency bands with corresponding toroidal mode numbers n=4 and 8.
Such disparate fluctuation scales, with substantial gaps between toroidal mode
numbers, are commonly observed in pedestal fluctuations. Here we provide a
clear explanation, namely the alignment of the relevant rational surfaces (and
not others) with the peak in the omega star profile, which is localized in the
steep gradient region of the pedestal. We demonstrate that a global treatment
is required to capture this effect. Nonlinear simulations suggest that the MTM
fluctuations produce experimentally-relevant transport levels and saturate by
relaxing the background electron temperature gradient, slightly downshifting
the fluctuation frequencies from the linear predictions. Scans in
collisionality are compared with simple MTM dispersion relations. At the
experimental points considered, MTM growth rates can either increase or
decrease with collision frequency depending on the parameters thus defying any
simple characterization of collisionality dependence.",2007.07332v1
2020-08-04,Ultrathin perpendicular free layers for lowering the switching current in STT-MRAM,"The critical current density $J_{c0}$ required for switching the
magnetization of the free layer (FL) in a spin-transfer torque magnetic random
access memory (STT-MRAM) cell is proportional to the product of the damping
parameter, saturation magnetization and thickness of the free layer, $\alpha
M_S t_F$. Conventional FLs have the structure CoFeB/nonmagnetic spacer/CoFeB.
By reducing the spacer thickness, W in our case, and also splitting the single
W layer into two layers of sub-monolayer thickness, we have reduced $t_F$ while
minimizing $\alpha$ and maximizing $M_S$, ultimately leading to lower $J_{c0}$
while maintaining high thermal stability. Bottom-pinned MRAM cells with device
diameter in the range of 55-130 nm were fabricated, and $J_{c0}$ is lowest for
the thinnest (1.2 nm) FLs, down to 4 MA/cm$^2$ for 65 nm devices, $\sim$30%
lower than 1.7 nm FLs. The thermal stability factor $\Delta_{\mathrm{dw}}$, as
high as 150 for the smallest device size, was determined using a domain wall
reversal model from field switching probability measurements. With high
$\Delta_{\mathrm{dw}}$ and lowest $J_{c0}$, the thinnest FLs have the highest
spin-transfer torque efficiency.",2008.01343v1
2020-09-13,Topologically-Driven Linear Magnetoresistance in Helimagnetic FeP,"The helimagnet FeP is part of a family of binary pnictide materials with the
MnP-type structure which share a nonsymmorphic crystal symmetry that preserves
generic band structure characteristics through changes in elemental
composition. It shows many similarities, including in its magnetic order, to
isostructural CrAs and MnP, two compounds that are driven to superconductivity
under applied pressure. Here we present a series of high magnetic field
experiments on high quality single crystals of FeP, showing that the resistance
not only increases without saturation by up to several hundred times its zero
field value by 35 T, but that it also exhibits an anomalously linear field
dependence over the entire field range when the field is aligned precisely
along the crystallographic c-axis. A close comparison of quantum oscillation
frequencies to electronic structure calculations links this orientation to a
semi-Dirac point in the band structure which disperses linearly in a single
direction in the plane perpendicular to field, a symmetry-protected feature of
this entire material family. We show that the two striking features of MR-large
amplitude and linear field dependence-arise separately in this system, with the
latter likely due to a combination of ordered magnetism and topological band
structure.",2009.05984v2
2020-10-10,Collisionless Rayleigh-Taylor-like instability of the boundary between a hot pair plasma and an electron-proton plasma: the undular mode,"We study with a two-dimensional particle-in-cell simulation the stability of
a discontinuity or piston, which separates an electron-positron cloud from a
cooler electron-proton plasma. Such a piston might be present in the
relativistic jets of accreting black holes separating the jet material from the
surrounding ambient plasma and when pair clouds form during an X-ray flare and
expand into the plasma of the accretion disk corona. We inject a pair plasma at
a simulation boundary with a mildly relativistic temperature and mean speed. It
flows across a spatially uniform electron-proton plasma, which is permeated by
a background magnetic field. The magnetic field is aligned with one simulation
direction and oriented orthogonally to the mean velocity vector of the pair
cloud. The expanding pair cloud expels the magnetic field and piles it up at
its front. It is amplified to a value large enough to trap ambient electrons.
The current of the trapped electrons, which are carried with the expanding
cloud front, drives an electric field that accelerates protons. A solitary wave
grows and changes into a piston after it saturated. Our simulations show that
this piston undergoes a collision-less instability similar to a Rayleigh-Taylor
instability. The undular mode grows and we observe fingers in the proton
density distribution. The effect of the instability is to deform the piston but
it cannot destroy it.",2010.04981v1
2020-10-17,Multiscale modelling of magnetostatic effects on magnetic nanoparticles with application to hyperthermia,"We extend a renormalization group-based course-graining method for
micromagnetic simulations to include properly scaled magnetostatic
interactions. We apply the method in simulations of dynamic hysteresis loops at
clinically relevant sweep rates and at 310 K of iron oxide nanoparticles (NPs)
of the kind that have been used in preclinical studies of magnetic
hyperthermia. The coarse-graining method, along with a time scaling involving
sweep rate and Gilbert damping parameter, allow us to span length scales from
the unit cell to NPs approximately 50 nm in diameter with reasonable simulation
times. For both NPs and the nanorods composing them, we report effective
uniaxial anisotropy strengths and saturation magnetizations, which differ from
those of the bulk materials magnetite and maghemite of which they are made, on
account of the combined non-trivial effects of temperature, inter-rod exchange,
magnetostatic interactions and the degree of orientational order within the
nanorod composites. The effective parameters allow treating the NPs as single
macrospins, and we find for the test case of calculating loops for two aligned
NPs that using the dipole approximation is sufficient for distances beyond 1.5
times the NP diameter. We also present a study on relating integration time
step to micromagnetic cell size, finding that the optimal time step size scales
approximately linearly with cell volume.",2010.08848v1
2020-11-12,Topological Hall effect arising from the mesoscopic and microscopic non-coplanar magnetic structure in MnBi,"The topological Hall effect (THE), induced by the Berry curvature, which
originates from non-zero scalar spin chirality, is an important feature for
mesoscopic topological structures, such as skyrmions. However, the THE might
also arise from other microscopic non-coplanar spin structures in the lattice.
Thus, the origin of the THE inevitably needs to be determined to fully
understand skyrmions and find new host materials. Here, we examine the Hall
effect in both bulk- and micron-sized lamellar samples of MnBi. The sample size
affects the temperature and field range in which the THE is detectable.
Although bulk sample exhibits the THE only upon exposure to weak fields in the
easy-cone state, in thin lamella the THE exists across a wide temperature range
and occurs at fields near saturation. Our results show that both the
non-coplanar spin structure in the lattice and topologically non-trivial
skyrmion bubbles are responsible for the THE, and that the dominant mechanism
depends on the sample size. Hence, the magnetic phase diagram for MnBi is
strongly size-dependent. Our study provides an example in which the THE is
simultaneously induced by two mechanisms, and builds a bridge between
mesoscopic and microscopic magnetic structures.",2011.06340v1
2021-02-26,Non-Uniform Hysteresis in Small Clusters of Magnetic Nanoparticles,"Using first-principle calculations and kinetic Monte Carlo simulation, we
study the local and averaged hysteresis in tiny clusters of k magnetic
nanoparticles (MNPs) or k-mers. We also analyze the variation of local dipolar
field acting on the constituent nanoparticles as a function of the external
magnetic field. The dipolar interaction is found to promote chain-like
arrangement in such a cluster. Irrespective of cluster size, the local
hysteresis response depends strongly on the corresponding dipolar field acted
on a nanoparticle. In a small k-mer, there is a wide variation in local
hysteresis as a function of nanoparticle position. On the other hand, the local
hysteresis is more uniform for larger k-mer, except for MNPs at the boundary.
In the case of superparamagnetic nanoparticle and weak dipolar interaction, the
local hysteresis loop area Ai is minimal and depends weakly on the k-mer size.
While for ferromagnetic counterpart, Ai is considerably large even for weakly
interacting MNPs. The value of Ai is found to be directly proportional to the
dipolar field acting on the nanoparticle. The dipolar interaction and k-mer
size also enhances the coercivity and remanence. There is always an increase in
Ai with clutser size and dipolar interaction strength. Similarly, the averaged
hysteresis loop area A also depends strongly on the k-mer size, particle size
and dipolar interaction strength. A and Ai always increase with k-mer size and
dipolar interaction strength. Interestingly, the value of A saturates for k>=20
and considerable dipolar interaction irrespective of particle size. We believe
that the present work would help understand the intricate role of dipolar
interaction on hysteresis and organizational structure of MNPs and their usage
in drug delivery and hyperthermia applications.",2102.13440v1
2021-03-03,Cosmic ray protons and electrons from supernova remnants,"The spectrum of cosmic ray protons and electrons released by supernova
remnants throughout their evolution is poorly known, because of the difficulty
in accounting for particle escape and confinement in the downstream of a shock
front, where both adiabatic and radiative losses are present. Here we calculate
the spectrum of cosmic ray protons released during the evolution of supernovae
of different types, accounting for the escape from upstream and for adiabatic
losses of particles advected downstream of the shock and liberated at later
times. The same calculation is carried out for electrons. The magnetic field in
the post-shock region is calculated by using an analytic treatment of the
magnetic field amplification due to non--resonant and resonant streaming
instability and their saturation. We find that when the field is the result of
the growth of the cosmic-ray--driven non--resonant instability alone, the
spectrum of electrons and protons released by a supernova remnant are indeed
different, but such a difference becomes appreciable only at energies $\gtrsim
100-1000$ GeV, while observations of the electron spectrum require such a
difference to be present at energies as low as $\sim 10$ GeV. An effect at such
low energies requires substantial magnetic field amplification in the late
stages of the supernova remnant evolution (shock velocity $\ll 1000$ km/s),
perhaps not due to streaming instability but hydrodynamical processes. We
comment on the feasibility of such conditions and speculate on the possibility
that the difference in spectral shape between electrons and protons may reflect
either some unknown acceleration effect, or additional energy losses in cocoons
around the sources.",2103.02375v1
2021-05-05,Phenomenological model for the third-harmonic magnetic response of superconductors: application to Sr$_{2}$RuO$_{4}$,"We employ the phenomenological Lawrence-Doniach model to compute the
contributions of the superconducting fluctuations to the third-harmonic
magnetic response, denoted here by $\overline{M_{3}}$, which can be measured in
a precise way using ac magnetic fields and lock-in techniques. We show that, in
an intermediate temperature regime, this quantity behaves as the third-order
nonlinear susceptibility, which shows a power-law dependence with the reduced
temperature $\epsilon=\frac{T-T_{c}}{T_{c}}$ as $\epsilon^{-5/2}$. Very close
to $T_{c}$, however, $\overline{M_{3}}$ saturates due to the nonzero amplitude
of the ac field. We compare our theoretical results with experimental data for
three conventional superconductors -- lead, niobium, and vanadium -- and for
the unconventional superconductor Sr$_{2}$RuO$_{4}$ (SRO). We find good
agreement between theory and experiment for the elemental superconductors,
although the theoretical values for the critical field systematically deviate
from the experimental ones. In the case of SRO, however, the phenomenological
model completely fails to describe the data, as the third-harmonic response
remains sizable over a much wider reduced temperature range compared to Pb, Nb,
and V. We show that an inhomogeneous distribution of $T_{c}$ can partially
account for this discrepancy, since regions with a locally higher $T_{c}$
contribute to the fluctuation $\overline{M_{3}}$ significantly more than
regions with the ""nominal"" $T_{c}$ of the clean system. However, the
exponential temperature dependence of $\overline{M_{3}}$ first reported in Ref.
[3] is not captured by the model with inhomogeneity. We conclude that, while
inhomogeneity is an important ingredient to understand the superconducting
fluctuations of SRO and other perovskite superconductors, additional effects
may be at play, such as non-Gaussian fluctuations or rare-region effects.",2105.01813v1
2021-08-02,Large-amplitude longitudinal oscillations in solar prominences simulated with different resolutions,"Large-amplitude longitudinal oscillations (LALOs) in solar prominences have
been widely studied in the last decades. However, their damping and
amplification mechanisms are not well understood. In this study, we investigate
the attenuation and amplification of LALOs using high-resolution numerical
simulations with progressively increasing spatial resolutions. We performed
time-dependent numerical simulations of LALOs using the 2D magnetic
configuration that contains a dipped region. After the prominence mass loading
in the magnetic dips, we triggered LALOs by perturbing the prominence mass
along the magnetic field. We performed the experiments with four values of
spatial resolution. In the simulations with the highest resolution, the period
shows a good agreement with the pendulum model. The convergence experiment
revealed that the damping time saturates at the bottom prominence region with
improving the resolution, indicating the existence of a physical reason for the
damping of oscillations. At the prominence top, the oscillations are amplified
during the first minutes and then are slowly attenuated. The characteristic
time suggests more significant amplification in the experiments with the
highest spatial resolution. The analysis revealed that the energy exchange
between the bottom and top prominence regions is responsible for the
attenuation and amplification of LALOs. The high-resolution experiments are
crucial for the study of the periods and the damping mechanism of LALOs. The
period agrees with the pendulum model only when using high enough spatial
resolution. The results suggest that numerical diffusion in simulations with
insufficient spatial resolution can hide important physical mechanisms, such as
amplification of oscillations.",2108.01143v1
2021-08-20,Spectropolarimeter on-board the Aditya-L1: Polarization Modulation and Demodulation,"One of the major science goals of the Visible Emission Line Coronagraph
(VELC) payload aboard the Aditya-L1 mission is to map the coronal magnetic
field topology and the quantitative estimation of longitudinal magnetic field
on routine basis. The infrared (IR) channel of VELC is equipped with a
polarimeter to carry out full Stokes spectropolarimetric observations in the Fe
XIII line at 1074.7~nm. The polarimeter is in dual-beam setup with continuously
rotating waveplate as the polarization modulator. Detection of circular
polarization due to Zeeman effect and depolarization of linear polarization in
the presence of magnetic field due to saturated Hanle effect in the Fe~{\sc
xiii} line require high signal-to-noise ratio (SNR). Due to limited number of
photons, long integration times are expected to build the required SNR. In
other words signal from a large number of modulation cycles are to be averaged
to achieve the required SNR. This poses several difficulties. One of them is
the increase in data volume and the other one is the change in modulation
matrix in successive modulation cycles. The latter effect arises due to a
mismatch between the retarder's rotation period and the length of the signal
detection time in the case of VELC spectropolarimeter (VELC/SP). It is shown in
this paper that by appropriately choosing the number of samples per half
rotation the data volume can be optimized. A potential solution is suggested to
account for modulation matrix variation from one cycle to the other.",2108.08997v1
2021-09-13,Evolution of switchbacks in the inner Heliosphere,"We analyze magnetic field data from the first six encounters of PSP, three
Helios fast streams and two Ulysses south polar passes covering heliocentric
distances $0.1\lesssim R\lesssim 3$ au. We use this data set to statistically
determine the evolution of switchbacks of different periods and amplitudes with
distance from the Sun. We compare the radial evolution of magnetic field
variances with that of the mean square amplitudes of switchbacks, and quantify
the radial evolution of the cumulative counts of switchbacks per km. We find
that the amplitudes of switchbacks decrease faster than the overall turbulent
fluctuations, in a way consistent with the radial decrease of the mean magnetic
field. This could be the result of a saturation of amplitudes and may be a
signature of decay processes of large amplitude Alfv\'enic fluctuations in the
solar wind. We find that the evolution of switchback occurrence in the solar
wind is scale-dependent: the fraction of longer duration switchbacks increases
with radial distance whereas it decreases for shorter switchbacks. This implies
that switchback dynamics is a complex process involving both decay and in-situ
generation in the inner heliosphere. We confirm that switchbacks can be
generated by the expansion although other type of switchbacks generated closer
to the sun cannot be ruled out.",2109.06341v1
2021-10-01,Gate-tunable Intrinsic Anomalous Hall Effect in Epitaxial MnBi2Te4 Films,"Anomalous Hall effect (AHE) is an important transport signature revealing
topological properties of magnetic materials and their spin textures. Recently,
antiferromagnetic MnBi2Te4 has been demonstrated to be an intrinsic magnetic
topological insulator that exhibits quantum AHE in exfoliated nanoflakes.
However, its complicated AHE behaviors may offer an opportunity for the
unexplored correlation between magnetism and band structure. Here, we show the
Berry curvature dominated intrinsic AHE in wafer-scale MnBi2Te4 thin films. By
utilizing a high-dielectric SrTiO3 as the back-gate, we unveil an ambipolar
conduction and electron-hole carrier (n-p) transition in ~7 septuple layer
MnBi2Te4. A quadratic relation between the saturated AHE resistance and
longitudinal resistance suggests its intrinsic AHE mechanism. For ~3 septuple
layer MnBi2Te4, however, the AHE reverses its sign from pristine negative to
positive under the electric-gating. The first-principles calculations
demonstrate that such behavior is due to the competing Berry curvature between
polarized spin-minority-dominated surface states and spin-majority-dominated
inner-bands. Our results shed light on the physical mechanism of the
gate-tunable intrinsic AHE in MnBi2Te4 thin films and provide a feasible
approach to engineering its AHE.",2110.00540v1
2021-10-03,Chiral transport of hot carriers in graphene in the quantum Hall regime,"Photocurrent (PC) measurements can reveal the relaxation dynamics of
photo-excited hot carriers beyond the linear response of conventional transport
experiments, a regime important for carrier multiplication. In graphene subject
to a magnetic field, PC measurements are able to probe the existence of Landau
levels with different edge chiralities which is exclusive to relativistic
electron systems. Here, we report the accurate measurement of PC in graphene in
the quantum Hall regime. Prominent PC oscillations as a function of gate
voltage on samples' edges are observed. These oscillation amplitudes form an
envelope which depends on the strength of the magnetic field, as does the PCs'
power dependence and their saturation behavior. We explain these experimental
observations through a model using optical Bloch equations, incorporating
relaxations through acoustic-, optical- phonons and Coulomb interactions. The
simulated PC agrees with our experimental results, leading to a unified
understanding of the chiral PC in graphene at various magnetic field strengths,
and providing hints for the occurrence of a sizable carrier multiplication.",2110.01079v1
2021-10-20,"Manifestations of Spinodal Decomposition into Dilute Pd$_{1-x}$Fe$_{x}$ ""Phases"" in Iron-Implanted Palladium Films: FMR Study","Palladium-iron alloys produced by high-dose implantation of iron ions into
epitaxial palladium films were investigated with the ferromagnetic resonance
(FMR) and vibrating sample magnetometry (VSM) techniques. The samples reveal
distinct multiple FMR responses depending on the dose of iron ion implantation.
The post-implantation annealing at 770 K does not bring the implanted films to
a homogeneous solid solution state, as might be expected from the Pd-Fe phase
diagram. On the contrary, the system approaches a stable state composed of
several magnetic phases. FMR spectra exhibit an angular behavior specific for a
stack of interacting magnetic layers. This observation, correlated with the
magnetometry data, indicates that the palladium-iron binary alloy has a
previously unknown tendency towards spinodal decomposition into isostructural
phases with well-defined iron concentrations and, accordingly, with different
temperatures of ferromagnetic ordering and saturation magnetizations.",2110.10397v1
2021-11-25,Colossal Anomalous Hall Conductivity and Topological Hall Effect in Ferromagnetic Kagome Metal Nd$_3$Al,"Historically, the genesis of anomalous Hall effect (AHE) in magnetic
materials has always been a fascinating yet controversial topic in the solid
state physics community. Recent progress on the understanding of this topic has
revealed an intimate connection between the Berry curvature of occupied
electronic states and the intrinsic AHE. Magnetic Weyl semimetals with broken
time reversal symmetry is a classic example, which is expected to show large
contributions to Berry curvature around the topological nodes and hence to the
AHE. Here, we report a kagome metallic ferromagnet Nd$_3$Al, with a large
unconventional positive magnetoresistance (~ 80 %) and colossal anomalous Hall
conductivity of 1.8x10^5 S/cm (largest ever reported to the best of our
knowledge). We also show that the magnetic state of this compound is quite
different from its analogues in many respects. While the compound is
predominantly an itinerant ferromagnet, its low temperature phase exhibits
topological band structure, enhanced skew scattering as well as topological
spin texture arising in the spin frustrated kagome lattice. Various
experimental findings such as topological Hall effect, non-saturating positive
magnetoresistance etc. give strong indication to this scenario. Ab-initio
calculations broadly confirm the experimental findings by revealing the
presence of flat bands and Weyl points originating from the itinerant Nd
moments. The non-trivial band structure, enhanced skew scattering and the spin
texture in a clean polycrystalline sample are found be responsible for the
colossal Hall conductivity and topological Hall effect.",2111.12944v1
2021-11-26,Optical Stabilization of Fluctuating High Temperature Ferromagnetism in YTiO$_3$,"In quantum materials, degeneracies and frustrated interactions can have a
profound impact on the emergence of long-range order, often driving strong
fluctuations that suppress functionally relevant electronic or magnetic phases.
Engineering the atomic structure in the bulk or at heterointerfaces has been an
important research strategy to lift these degeneracies, but these equilibrium
methods are limited by thermodynamic, elastic, and chemical constraints. Here,
we show that all-optical, mode-selective manipulation of the crystal lattice
can be used to enhance and stabilize high-temperature ferromagnetism in
YTiO$_3$, a material that exhibits only partial orbital polarization, an
unsaturated low-temperature magnetic moment, and a suppressed Curie
temperature, $T_c$ = 27 K. The enhancement is largest when exciting a 9 THz
oxygen rotation mode, for which complete magnetic saturation is achieved at low
temperatures and transient ferromagnetism is realized up to $T_{neq} >$ 80 K,
nearly three times the thermodynamic transition temperature. First-principles
and model calculations of the nonlinear phonon-orbital-spin coupling reveal
that these effects originate from dynamical changes to the orbital polarization
and the makeup of the lowest quasi-degenerate Ti $t_{2g}$ levels. Notably,
light-induced high temperature ferromagnetism in YTiO$_3$ is found to be
metastable over many nanoseconds, underscoring the ability to dynamically
engineer practically useful non-equilibrium functionalities.",2111.13622v1
2021-11-28,CoFeVSb: A Promising Candidate for Spin Valve and Thermoelectric Applications,"We report a combined theoretical and experimental study of a novel quaternary
Heusler system CoFeVSb from the view point of room temperature spintronics and
thermoelectric applications. It crystallizes in cubic structure with small
DO$_3$-type disorder. The presence of disorder is confirmed by room temperature
synchrotron X-ray diffraction(XRD) and extended X-ray absorption fine structure
(EXAFS) measurements. Magnetization data reveal high ordering temperature with
a saturation magnetization of 2.2 $\mu_B$/f.u. Resistivity measurements reflect
half-metallic nature. Double hysteresis loop along with asymmetry in the
magnetoresistance(MR) data reveals room temperature spin-valve feature, which
remains stable even at 300 K. Hall measurements show anomalous behavior with
significant contribution from intrinsic Berry phase. This compound also large
room temperature power factor ($\sim0.62$ mWatt/m/K$^{2}$) and ultra low
lattice thermal conductivity ($\sim0.4$ W/m/K), making it a promising candidate
for thermoelectric application. Ab-initio calculations suggest weak
half-metallic behavior and reduced magnetization (in agreement with experiment)
in presence of DO$_3$ disorder. We have also found an energetically competing
ferromagnetic FM)/antiferromagnetic (AFM) interface structure within an
otherwise FM matrix: one of the prerequisites for spin valve behavior.
Coexistence of so many promising features in a single system is rare, and hence
CoFeVSb gives a fertile platform to explore numerous applications in future.",2111.14081v1
2022-02-02,Universal Scaling Laws for Solar and Stellar Atmospheric Heating,"The Sun and sun-like stars commonly host the multi-million-Kelvin coronae and
the 10,000-Kelvin chromospheres. These extremely hot gases generate X-ray and
Extreme Ultraviolet emissions that may impact the erosion and chemistry of
(exo)planetary atmospheres, influencing the climate and conditions of
habitability. However, the mechanism of coronal and chromospheric heating is
still poorly understood. While the magnetic field most probably plays a key
role in driving and transporting energy from the stellar surface upwards, it is
not clear if the atmospheric heating mechanisms of the Sun and active sun-like
stars can be described in a unified manner. To this end, we report on a
systematic survey of the responses of solar and stellar atmospheres to surface
magnetic flux over a wide range of temperatures. By analyzing 10 years of
multi-wavelength synoptic observations of the Sun, we reveal that the
irradiance and magnetic flux show power-law relations with an exponent
decreasing from above- to sub-unity as the temperature decreases from the
corona to the chromosphere. Moreover, this trend indicating the efficiency of
atmospheric heating can be extended to sun-like stars. We also discover that
the power-law exponent has a solar cycle dependence, where it becomes smallest
at activity maximum, probably due to the saturation of atmospheric heating. Our
study provides observational evidence that the mechanism of atmospheric heating
is universal among the Sun and sun-like stars, regardless of age or activity.",2202.01232v2
2022-02-10,Landau parameters and entrainment matrix of cold stellar matter: effect of the symmetry energy and strong magnetic fields,"Nuclear matter properties based on a relativistic approach suitable for the
description of multi-component systems are calculated. We use a set of nuclear
relativistic mean-field models that satisfy acceptable nuclear matter
properties and neutron star observations. The effects of the density dependence
of the symmetry energy and of the Landau quantization due to the presence of a
strong external magnetic field are discussed. Properties such as the proton
fraction, the Landau mass, Landau parameters and entrainment matrix, the
adiabatic index and speed of sound are calculated for cold $\beta$-equilibrium
matter. A large dispersion on the calculated properties is obtained at two to
three times saturation density $\rho_0 $. The proton Landau mass can be as low
as one third of the vacuum nucleon mass at 2-3$~\rho_0 $. Similar effects are
obtained for the Landau parameters, in particular, the ones involving protons,
where the relative dispersion of $F^0_{pp}$ and $F^1_{pp}$ is as high as 30\%
to 50\% at 2-3$~\rho_0 $. These parameters are particularly sensitive to the
symmetry energy. The effect of the magnetic field on the nuclear properties is
small for fields as high as 10$^{18}$G except for a small range of densities
just above the crust-core transition. Tables with the EoS, and the parameters,
are provided in the Supplementary Material section.",2202.05231v1
2022-04-04,"Magnetocaloric properties of $R_3$Ga$_5$O$_{12}$ ($R$ = Tb,Gd,Nd,Dy)","We report the characteristic magnetic properties of several members of the
rare-earth garnet family, Gd$_3$Ga$_5$O$_{12}$ (GGG), Dy$_3$Ga$_5$O$_{12}$
(DGG), Tb$_3$Ga$_5$O$_{12}$ (TGG), and Nd$_3$Ga$_5$O$_{12}$ (NGG), and compare
their relative potential utility for magnetocaloric cooling, including their
minimal adiabatic demagnetization refrigeration (ADR) temperatures and relative
cooling parameters. A main objective of this work concerns the identification
of potential improvements over the magnetocaloric properties of GGG for use in
low temperature ADR cryostats. Using Tb$^{+3}$ and Dy$^{+3}$ in the rare-earth
site offers, in principle, a higher saturation magnetization and Nd$^{+3}$
gives a lower de Gennes factor and therefore potentially reduced magnetic
transition temperatures, limiting the useful temperature range. Our results
show that Dy$_3$Ga$_5$O$_{12}$ yields an optimal relative cooling parameter
($RCP$) at low applied fields and low limiting temperatures, which would allow
for the design of more efficient ADR cryostats.",2204.01752v2
2022-07-29,Precision Measurement of the Excited State Landé g-factor and Diamagnetic Shift of the Cesium D$_{2}$ Line,"We have performed saturated absorption spectroscopy on the cesium D$_{2}$
line in 3 T and 7 T magnetic fields. By means of sideband spectroscopy on the
extreme angular momentum states we have measured the linear magnetic frequency
shift of the transition to be $\gamma_1 = 13.994\:301(11)$ GHz/T. This
corresponds to an optical magnetic field measurement of better than 1 ppm
accuracy. From this value we can calculate the fine structure Land\'e g-factor
$g_J\left(6^2P_{3/2}\right) = 1.334\:087\:49(52)$. This is consistent with the
previous best measurement, and improves the accuracy by more than two orders of
magnitude. We have also measured, for the first time ever, the quadratic
diamagnetic shift as $\gamma_2 = 0.4644(35)\:\mathrm{MHz/T^2}$. Our work opens
up the field of accurate high field optical magnetometry using atomic cesium.
These high accuracy measurements also allow for testing of advanced atomic
structure models, as our results are incompatible with the Russel-Saunders
coupling value, and the hydrogen-constant-core-model value, by 31 and 7
standard deviations respectively.",2208.00077v1
2022-12-20,Efficient and all-carbon electrical readout of a NV based quantum sensor,"The spin readout of an ensemble of nitrogen-vacancy (NV) centers in diamond
can be realized by a photoconductive detection that is a complementary method
to the optical detection of the NV electron spin magnetic resonance. Here, we
implement the photoconductive detection through graphitic planar electrodes
that collect the photocurrent. Graphitic electrodes are patterned using a xenon
Focused-Ion Beam on an Optical-Grade quality diamond crystal containing a
nitrogen concentration of ~1 ppm and a NV concentration of a few ppb.
Resistance and current-voltage characteristics of the NV-doped diamond junction
are investigated tuning the 532 nm pump beam intensity. The junction has an
ohmic behavior and under a strong bias field, we observe velocity saturation of
the optically-induced carriers in the diamond junction. We perform the
photoconductive detection in continuous-wave regime of the magnetic resonance
of the NV centers ensemble for a magnetic field applied along the <100> and the
<111> direction with a magnitude above 100 mT. This technique enables the
realization of all-carbon diamond quantum sensors integrating graphitic
microstructures for the electrical readout.",2212.10349v1
2023-04-26,Assessment of sol-gel derived iron oxide substituted 45S5 bioglass-ceramics for biomedical applications,"Magnetic bioactive glass ceramic (MGC) powders have been synthesized by sol
gel route by systematically substituting silicon dioxide with iron oxide in the
45S5 glass composition. Powder x-ray diffraction studies revealed a variation
in the percentage of combeite (Ca$_2$Na$_2$Si$_3$O$_9$), magnetite
(Fe$_3$O$_4$), and hematite (Fe$_2$O$_3$) nanocrystalline phases in MGC powders
as a function of composition. Zeta potential measurements showed that MGC
containing up to 10 wt.% iron oxide formed stable suspensions. Saturation
magnetization and heat generation capacity of MGC fluids increased with
increase in iron oxide content. Degradation of MGC powders was investigated in
phosphate buffer saline (PBS). In vitro bioactivity of the MGC powders taken in
pellet form was confirmed by observing the pH variation as well as
hydroxyapatite layer (HAp) formation upon soaking in modified simulated body
fluid. These studies showed a decrement in overall bioactivity in samples with
high iron oxide content due to the proportional decrease in silanol group.
Monitoring the proliferation of MG-63 osteoblast cell in Dulbecco's Modified
Eagle Medium (DMEM) revealed that MGC with up to 10 wt.% iron oxide exhibited
acceptable viability. The systematic study revealed that the MGC with 10 wt.%
iron oxide exhibited optimal cell viability, magnetic properties and induction
heating capacity which were better than those of FluidMag-CT, which is used for
hyperthermia treatment.",2304.13437v1
2023-06-28,Emergent criticality in fully frustrated quantum magnets,"Phase transitions in condensed matter are often linked to exotic emergent
properties. We study the fully frustrated bilayer Heisenberg antiferromagnet to
demonstrate that an applied magnetic field creates a novel emergent
criticality. The quantum phase diagram contains four states, the DS (singlets
on every interlayer dimer bond), DTAF (all triplets with antiferromagnetic
order), TC (a singlet-triplet checkerboard) and FM (saturated ferromagnet). The
thermal phase diagram is dominated by a wall of discontinuities extending from
the zero-field DTAF-DS transition to a quantum critical endpoint where the
field drives the DTAF and TC into the FM. This first-order wall is terminated
at finite temperatures by a line of critical points, where the
Berezinskii-Kosterlitz-Thouless (BKT) transition of the DTAF and the thermal
Ising transition of the TC also terminate. We demonstrate by quantum Monte
Carlo simulations that the BKT transition does not change the Ising nature of
the DTAF-DS critical line. By contrast, the combination of symmetries merging
on the multicritical DTAF-TC line leads to a 4-state Potts universality not
contained in the microscopic Hamiltonian, which we associate with the
Ashkin-Teller model. Our results represent a systematic step in understanding
emergent phenomena in quantum magnetic materials including the
``Shastry-Sutherland compound'' SrCu$_2$(BO$_3$)$_2$.",2306.16288v1
2023-07-10,3D Simulations of Magnetoconvection in a Rapidly Rotating Supernova Progenitor,"We present a first 3D magnetohydrodynamic (MHD) simulation of oxygen, neon
and carbon shell burning in a rapidly rotating 16 M_sun core-collapse supernova
progenitor. We also run a purely hydrodynamic simulation for comparison. After
180s (15 and 7 convective turnovers respectively), the magnetic fields in the
oxygen and neon shells achieve saturation at 10^{11}G and 5 x 10^{10}G. The
strong Maxwell stresses become comparable to the radial Reynolds stresses and
eventually suppress convection. The suppression of mixing by convection and
shear instabilities results in the depletion of fuel at the base of the burning
regions, so that the burning shell eventually move outward to cooler regions,
thus reducing the energy generation rate. The strong magnetic fields
efficiently transport angular momentum outwards, quickly spinning down the
rapidly rotating convective oxygen and neon shells and forcing them into rigid
rotation. The hydrodynamic model shows complicated redistribution of angular
momentum and develops regions of retrograde rotation at the base of the
convective shells. We discuss implications of our results for stellar evolution
and for the subsequent core-collapse supernova. The rapid redistribution of
angular momentum in the MHD model casts some doubt on the possibility of
retaining significant core angular momentum for explosions driven by
millisecond magnetars. However, findings from multi-D models remain tentative
until stellar evolution calculations can provide more consistent rotation
profiles and estimates of magnetic field strengths to initialise multi-D
simulations without substantial numerical transients. We also stress the need
for longer simulations, resolution studies, and an investigation of non-ideal
effects.",2307.04833v2
2023-07-12,BMS$_{3}$ (Carrollian) field theories from a bound in the coupling of current-current deformations of CFT$_{2}$,"Two types of Carrollian field theories are shown to emerge from finite
current-current deformations of toroidal CFT$_{2}$'s when the deformation
coupling is precisely fixed, up to a sign. In both cases the energy and
momentum densities fulfill the BMS$_{3}$ algebra. Applying these results to the
bosonic string, one finds that the electric-like deformation (positive
coupling) reduces to the standard tensionless string. The magnetic-like
deformation (negative coupling) yields to a new theory, still being
relativistic, devoid of tension and endowed with an ""inner Carrollian
structure"". Classical solutions describe a sort of ""self-interacting null
particle"" moving along generic null curves of the original background metric,
not necessarily geodesics. This magnetic-like theory is also shown to be
recovered from inequivalent limits in the tension of the bosonic string.
Electric- and magnetic-like deformations of toroidal CFT$_{2}$'s can be seen to
correspond to limiting cases of continuous exactly marginal (trivial)
deformations spanned by an SO(1,1) automorphism of the current algebra. Thus,
the absolute value of the current-current deformation coupling is shown to be
bounded. When the bound saturates, the deformation ceases to be exactly
marginal, but still retains the full conformal symmetry in two alternative
ultrarelativistic regimes.",2307.06367v2
2023-08-08,Ionically-Driven Synthesis and Exchange Bias in Mn$_{4}$N/MnN$_{x}$ Heterostructures,"Ferrimagnets have received renewed attention as a promising platform for
spintronic applications. Of particular interest is the Mn4N from the
${\epsilon}$-phase of the manganese nitride as an emergent rare-earth-free
spintronic material due to its perpendicular magnetic anisotropy, small
saturation magnetization, high thermal stability, and large domain wall
velocity. We have achieved high-quality (001)-ordered Mn$_{4}$N thin film by
sputtering Mn onto ${\eta}$-phase Mn$_{3}$N$_{2}$ seed layers on Si substrates.
As the deposited Mn thickness varies, nitrogen ion migration across the
Mn$_{3}$N$_{2}$/Mn layers leads to a continuous evolution of the layers to
Mn$_{3}$N$_{2}$/Mn$_{2}$N/Mn$_{4}$N, Mn$_{2}$N/Mn$_{4}$N, and eventually
Mn$_{4}$N alone. The ferrimagnetic Mn$_{4}$N indeed exhibits perpendicular
magnetic anisotropy, and forms via a nucleation-and-growth mechanism. The
nitrogen ion migration is also manifested in a significant exchange bias, up to
0.3 T at 5 K, due to the interactions between ferrimagnetic Mn$_{4}$N and
antiferromagnetic Mn$_{3}$N$_{2}$ and Mn$_{2}$N. These results demonstrate a
promising all-nitride magneto-ionic platform with remarkable tunability for
device applications.",2308.04274v2
2023-08-25,Evidence of the Coulomb gap in the density of states of MoS$_2$,"$\mathrm{MoS_2}$ is an emergent van der Waals material that shows promising
prospects in semiconductor industry and optoelectronic applications. However,
its electronic properties are not yet fully understood. In particular, the
nature of the insulating state at low carrier density deserves further
investigation, as it is important for fundamental research and applications. In
this study, we investigate the insulating state of a dual-gated exfoliated
bilayer $\mathrm{MoS_2}$ field-effect transistor by performing magnetotransport
experiments. We observe positive and non-saturating magnetoresistance, in a
regime where only one band contributes to electron transport. At low electron
density ($\sim 1.4\times 10^{12}~\mathrm{cm^{-2}}$) and a perpendicular
magnetic field of 7 Tesla, the resistance exceeds by more than one order of
magnitude the zero field resistance and exponentially drops with increasing
temperature. We attribute this observation to strong electron localization.
Both temperature and magnetic field dependence can, at least qualitatively, be
described by the Efros-Shklovskii law, predicting the formation of a Coulomb
gap in the density of states due to Coulomb interactions. However, the
localization length obtained from fitting the temperature dependence exceeds by
more than one order of magnitude the one obtained from the magnetic field
dependence. We attribute this discrepancy to the presence of a nearby metallic
gate, which provides electrostatic screening and thus reduces long-range
Coulomb interactions. The result of our study suggests that the insulating
state of $\mathrm{MoS_2}$ originates from a combination of disorder-driven
electron localization and Coulomb interactions.",2308.13337v2
2023-09-24,Novel one-pot sol-gel synthesis route of Fe3C/few-layered graphene core/shell nanoparticles embedded in a carbon matrix,"Fe3C/few-layered graphene core/shell nanoparticles embedded in a carbon
matrix are synthesized by a novel two-step surfactant sol-gel strategy, where
the processes of hydrolysis, polycondensation and drying take place in a
one-pot. The present approach is based on the combined action of oleic acid and
oleylamine, which act sterically on the precursor micelles when a densification
temperature is performed in a reducing atmosphere. The structural and magnetic
evolution of the formed compounds is investigated, ranging from iron oxides
such as Fe3O4 and FeO, to the formation of pure Fe3C/C samples from 700 {\deg}C
onwards. Interestingly, Fe3C nanoparticles with a size of ~20 nm crystallize
immersed in the carbon matrix and the surrounding environment forms an oriented
encapsulation built by few-layered graphene. The nanostructures show a
saturation magnetization of ~43 emu/g and a moderate coercivity of ~500 Oe.
Thereby, an innovative chemical route to produce single phase Fe3C
nanoparticles is described, and an effective method of few-layered graphene
passivation is proposed, yielding a product with a high magnetic response and
high chemical stability against environmental corrosion.",2309.15858v1
2023-11-10,Enhancement of optical absorption in multiferroic (1-x)PZT-xPFN thin films: Experiments and first-principles analysis,"Multiferroic compounds have gained research attention in the field of
ferroelectric photovoltaics due to the presence of transition-metal d states
from magnetic ions, which tend to reduce the bandgap value. In this work,
0.5Pb(Zr0.52Ti0.48)O3 - 0.5Pb(Fe0.5Nb0.5)O3 PZTFN0.5 thin films were
synthesized using a sol-gel route to investigate the effect of iron doping on
optical and multiferroic properties. For comparative analysis, the end-member
compositions, Pb(Zr0.52Ti0.48)O3 (PZT) and Pb(Fe0.5Nb0.5)O3 (PFN), were also
synthesized under identical conditions. Our results revealed that the presence
of Fe ions, besides inducing multiferroic behavior, effectively enhances the
optical absorption of the material in the visible light region. Optical
transitions at 3.0 eV (2.4 eV) and 2.7 eV (2.2 eV) for the direct (indirect)
bandgap were determined for PZTFN0.5 and PFN, respectively, indicating that the
absorption edges of the iron-containing films result more promising than PZT
(Eg 3.6eV) for photovoltaic applications. Both PZTFN0.5 and PFN thin films
exhibit multiferroic behavior at room temperature, with different electric and
magnetic properties. While PZTFN0.5 presents saturated hysteresis loops with
remanent polarization values around 10 uC/cm2 and magnetization of 1.6 emu/cm2,
PFN displays significantly larger remanence (31 emu/cm2) but poorer
ferroelectric properties due to the presence of leakage. Microscopic insights
into the structural and electronic properties of the PZTFN0.5 solid solution
were provided from first-principles calculations.",2311.05855v1
2023-11-15,Growth and Characterization of $β$-Mn Structured CoZn Thin Films,"Thin films of polycrystalline $\beta$-Mn structure CoZn have been grown on
thermally oxidized Si substrates by co-sputtering from elemental targets
followed by annealing. A range of films grown with variable Co deposition power
and fixed Zn deposition power were produced, so as to vary the proportions of
the two elements reaching the substrate, which were annealed post-growth.
Whilst all films exhibited a (211) $\beta$-Mn structure CoZn texture in X-ray
diffraction, transmission electron microscopy showed that the composition with
the highest integrated intensity for that Bragg peak contained large vacancies
and was covered by a thick ZnO cap owing to being Co-deficient overall. CoZn
films deposited at ratios tuned to give the optimal volume fraction of
$\beta$-Mn were continuous, with crystallites up to 200~nm in size, with a much
thinner ZnO cap layer. Magnetic measurements show that such optimal CoZn films
have a Curie temperature $T_\mathrm{C} \sim 420$~K and saturation magnetization
of 120~emu/cm$^3$, properties close to those reported for bulk crystals. The
$\beta$-Mn structure is chiral (P4$_{1}$32/P4$_{3}$32 space group) and is known
to give rise to a Dzyaloshinkii-Moriya interaction (DMI) that stabilizes
room-temperature skyrmions in the bulk. Our thin films are thus a potential
materials platform, compatible with planar processing technology, for magnetic
skyrmions arising from a bulk DMI.",2311.08824v2
2023-12-03,Experimental apparatus for non-contact resistivity measurements of the rock core plug based on magnetic induction,"A new apparatus has been developed to measure the conductivity of rock
samples. The probe, which consists of multi-coil transmitters and receivers
doesn't require physical contact with the samples. The measurement is based on
the induction principle. The measurement system is validated by using saline
solutions and water-saturated sands of known conductivity. This work presents
details of the development of a system of magnetic resistivity measurements by
magnetic induction for petrophysical applications. The first application
consists of measuring the resistivity of the core plug which is 0.038 m in
diameter. Currently the system is operating properly at a frequency of 50 kHz
with a current of up to 500 mA at 20 {\deg}C. During the study two types of
samples were investigated: aqueous solutions with conductivities between 1 to
100 mS/cm and rocks. Several tests were carried out with the objective of
investigating the performance of the instrument, such as the experiment to
obtain sensitivity for the measurement system as a function of the current
applied to the transmitter coil.",2312.01375v1
2024-02-01,Quasi-perpendicular shocks of galaxy clusters in hybrid kinetic simulations: The structure of the shocks,"Context: Cosmic ray acceleration in galaxy clusters is still an ongoing
puzzle, with relativistic electrons forming radio relics at merger shocks and
emitting synchrotron radiation. In the present work we perform hybrid-kinetic
simulations in a range of various quasi-perpendicular foreshock conditions,
including plasma beta, magnetic obliquity, and the shock Mach number. Aims: We
study the ion kinetic physics, responsible for the shock structure and wave
turbulence, that in turn affects the particle acceleration processes. Methods:
We apply a recently developed generalized fluid-particle hybrid numerical code
that can combine fluid modeling for both kinetic ions and fluid electrons. The
model utilizes the exact form of the generalized Ohm's law, allowing for
arbitrary choice of mass and energy densities, as well as the charge-to-mass
ratio of the kinetic species. Results: We show that the properties of
ion-driven multi-scale magnetic turbulence in merger shocks are in agreement
with the ion structures observed in PIC simulations. In typical shocks with the
sonic Mach number $M_s=3$, the magnetic structures and shock front density
ripples grow and saturate at wavelengths reaching approximately four ion Larmor
radii. Finally, we note that the steady-state structure of $M_s=3$ shocks in
high-beta plasmas shows evidence that there is little difference between 2D and
3D simulations. The turbulence near the shock front seems to be a 2D-like
structure in 3D simulations.",2402.00571v1
2024-02-22,Revisiting thermoelectric effects in the crust of neutron stars,"Context. Large thermal variations have been observed in neutron stars that
typically are not aligned with density gradients. Such terms may activate the
Biermann battery effect, leading to thermo-electric interactions and the
generation of electromotive force. Aims. We aim to identify the impact a
temperature anisotropy on a neutron star's crust can have in the evolution of
its magnetic field, through the thermo-electric terms. Methods. We consider a
neutron star crust with large temperature gradients, associated with long-lived
hot spots, described by a Gaussian-type function localized. We simulate the
interplay between the battery term and the Hall and Ohmic evolution
numerically, for axisymmetric systems. Results. The results indicate that for
crust temperatures of $\sim$$10^9$ K the toroidal field can be amplified up to
$\sim$$10^{14}$ - $10^{15}$ G near the points of maximum temperature gradients,
and it locally changes the architecture of the poloidal field lines. For
internal crustal temperatures around $\sim$$10^8$ K, the temperature gradient
generates fields of about two orders of magnitude lower. In such cases,
saturation is achieved after some hundred thousand years, after which the
battery and Ohmic dissipation balance each other. Conclusions. We conclude that
the thermoelectric effect can impact the overall magnetic field evolution,
provided that the thermal gradient is maintained for a sufficiently long time.
Neutron stars endowned with moderate strength magnetic fields may be affected
by the thermoelectric effect if the hotspots survive for timescales of a few
kiloyears.",2402.14911v1
2020-10-16,Saturation problems about forbidden $0$-$1$ submatrices,"A $0$-$1$ matrix $M$ is saturating for a $0$-$1$ matrix $P$ if $M$ does not
contain a submatrix that can be turned into $P$ by changing some $1$ entries to
$0$ entries, and changing an arbitrary $0$ to $1$ in $M$ introduces such a
submatrix in $M$. In saturation problems for $0$-$1$ matrices we are interested
in estimating the minimum number of $1$ entries in an $m \times n$ matrix that
is saturating for $P$, in terms of $m$ and $n$.
  In other words, we wish to give good estimates for the saturation function of
$P$. Recently, Brualdi and Cao initiated the study of saturation problems in
the context of $0$-$1$ matrices.
  We extend their work in several directions. We prove that every $0$-$1$
forbidden matrix has its saturation function either in $\Theta(1)$ or
$\Theta(n)$ in the case when we restrict ourselves to square saturating
matrices. Then we give a partial answer to a question posed by Brualdi and Cao
about the saturation function of $J_k$, which is obtained from the identity
matrix $I_k$ by putting the first row after the last row. Furthermore, we
exhibit a $5\times 5$ permutation matrix with the saturation function bounded
from the above by a fixed constant. We complement this result by identifying
large classes of $0$-$1$ matrices with linear saturation function. Finally, we
completely resolve the related semisaturation problem as far as the constant
vs. linear dichotomy is concerned.",2010.08256v2
2002-11-04,X-rays in the Orion Nebula Cluster: Constraints on the origins of magnetic activity in pre-main sequence stars,"A recent Chandra/ACIS observation of the Orion Nebula Cluster detected 1075
sources (Feigelson et al. 2002), providing a uniquely large and well-defined
sample to study the dependence of magnetic activity on bulk properties for
stars descending the Hayashi tracks. The following results are obtained: (1)
X-ray luminosities L_t in the 0.5-8 keV band are strongly correlated with
bolometric luminosity with <log L_t/L_bol> = -3.8 for stars with masses 0.7<M<2
Mo, an order of magnitude below the main sequence saturation level; (2) the
X-ray emission drops rapidly below this level in some or all stars with 2<M<3
Mo; (3) the presence or absence of infrared circumstellar disks has no apparent
relation to X-ray levels; and (4) X-ray luminosities exhibit a slight rise as
rotational periods increase from 0.4 to 20 days. This last finding stands in
dramatic contrast to the strong anticorrelation between X-rays and period seen
in main sequence stars.
  The absence of a strong X-ray/rotation relationship in PMS stars, and
particularly the high X-ray values seen in some very slowly rotating stars, is
a clear indication that the mechanisms of magnetic field generation differ from
those operating in main sequence stars. The most promising possibility is a
turbulent dynamo distributed throughout the deep convection zone, but other
models such as alpha-Omega dynamo with `supersaturation' or relic core fields
are not immediately excluded. The drop in magnetic activity in
intermediate-mass stars may reflect the presence of a significant radiative
core. The evidence does not support X-ray production in large-scale star-disk
magnetic fields.",0211049v1
2002-11-27,Asymmetric Explosions of Thermonuclear Supernovae,"A type Ia supernova explosion starts in a white dwarf as a laminar
deflagration at the center of the star and soon several hydrodynamic
instabilities (in particular, the Rayleigh-Taylor (R-T) instability) begin to
act. In previous work (Ghezzi, de Gouveia Dal Pino, & Horvath 2001), we
addressed the propagation of an initially laminar thermonuclear flame in
presence of a magnetic field assumed to be dipolar. We were able to show that,
within the framework of a fractal model for the flame velocity, the front is
affected by the field through the quenching of the R-T instability growth in
the direction perpendicular to the field lines. As a consequence, an asymmetry
develops between the magnetic polar and the equatorial axis that gives a
prolate shape to the burning front. We have here computed numerically the total
integrated asymmetry as the flame front propagates outward through the
expanding shells of decreasing density of the magnetized white dwarf
progenitor, for several chemical compositions, and found that a total asymmetry
of about 50 % is produced between the polar and equatorial directions for
progenitors with a surface magnetic field B ~ 5 x 10^{7} G, and a composition
C12 = 0.2 and O16 = 0.8 (in this case, the R-T instability saturates at scales
\~ 20 times the width of the flame front). This asymmetry is in good agreement
with the inferred asymmetries from spectropolarimetric observations of very
young supernova remnants, which have recently revealed intrinsic linear
polarization interpreted as evidence of an asymmetric explosion in several
objects,such as SN1999by, SN1996X, and SN1997dt. Larger magnetic field
strengths will produce even larger asymmetries. We have also found that for
lighter progenitors the total asymmetry is larger.",0211605v2
2007-06-13,Simulations of the Poynting--Robertson Cosmic Battery in Resistive Accretion Disks,"We describe the results of numerical ""2.5--dimensional"" MHD simulations of an
initially unmagnetized disk model orbiting a central point--mass and responding
to the continual generation of poloidal magnetic field due to a secular source
that emulates the Poynting--Robertson (PR) drag on electrons in the vicinity of
a luminous stellar or compact accreting object. The fluid in the disk and in
the surrounding hotter atmosphere has finite electrical conductivity and allows
for the magnetic field to diffuse freely out of the areas where it is
generated, while at the same time, the differential rotation of the disk twists
the poloidal field and quickly induces a substantial toroidal--field component.
The secular PR term has dual purpose in these simulations as the source of the
magnetic field and the trigger of a magnetorotational instability (MRI) in the
disk. The MRI is especially mild and does not destroy the disk because a small
amount of resistivity dampens the instability efficiently. In simulations with
moderate resistivities (diffusion timescales up to $\sim$16 local dynamical
times) and after $\sim$100 orbits, the MRI has managed to transfer outward
substantial amounts of angular momentum and the inner edge of the disk, along
with azimuthal magnetic flux, has flowed toward the central point--mass where a
new, magnetized, nuclear disk has formed. The toroidal field in this nuclear
disk is amplified by differential rotation and it cannot be contained; when it
approaches equipartition, it unwinds vertically and produces episodic jet--like
outflows. The poloidal field in the inner region cannot diffuse back out if the
characteristic diffusion time is of the order of or larger than the dynamical
time; it continues to grow linearly in time undisturbed and without saturation,
as the outer sections of many poloidal loops are being drawn radially outward.",0706.3187v1
2009-10-02,"On the room temperature multiferroic BiFeO3: Magnetic, dielectric and thermal properties","Magnetic dc susceptibility between 1.5 and 800 K, ac susceptibility and
magnetization, thermodynamic properties, temperature dependence of radio and
audio-wave dielectric constants and conductivity, contact-free dielectric
constants at mm-wavelengths, as well as ferroelectric polarization are reported
for single crystalline BiFeO3. A well developed anomaly in the magnetic
susceptibility signals the onset of antiferromagnetic order close to 635 K.
Beside this anomaly no further indications of phase or glass transitions are
indicated in the magnetic dc and ac susceptibilities down to the lowest
temperatures. The heat capacity has been measured from 2 K up to room
temperature and significant contributions from magnon excitations have been
detected. From the low-temperature heat capacity an anisotropy gap of the
magnon modes of the order of 6 meV has been determined. The dielectric
constants measured in standard two-point configuration are dominated by
Maxwell-Wagner like effects for temperatures T > 300 K and frequencies below 1
MHz. At lower temperatures the temperature dependence of the dielectric
constant and loss reveals no anomalies outside the experimental errors,
indicating neither phase transitions nor strong spin phonon coupling. The
temperature dependence of the dielectric constant was measured contact free at
microwave frequencies. At room temperature the dielectric constant has an
intrinsic value of 53. The loss is substantial and strongly frequency dependent
indicating the predominance of hopping conductivity. Finally, in small thin
samples we were able to measure the ferroelectric polarization between 10 and
200 K. The saturation polarization is of the order of 40 microC/cm^2,
comparable to reports in literature.",0910.0385v2
2011-05-09,Turbulence in Global Simulations of Magnetized Thin Accretion Disks,"We use a global magnetohydrodynamic simulation of a geometrically thin
accretion disk to investigate the locality and detailed structure of turbulence
driven by the magnetorotational instability (MRI). The model disk has an aspect
ratio $H / R \simeq 0.07$, and is computed using a higher-order Godunov MHD
scheme with accurate fluxes. We focus the analysis on late times after the
system has lost direct memory of its initial magnetic flux state. The disk
enters a saturated turbulent state in which the fastest growing modes of the
MRI are well-resolved, with a relatively high efficiency of angular momentum
transport $< < \alpha > > \approx 2.5 \times 10^{-2}$. The accretion stress
peaks at the disk midplane, above and below which exists a moderately
magnetized corona with patches of superthermal field. By analyzing the spatial
and temporal correlations of the turbulent fields, we find that the spatial
structure of the magnetic and kinetic energy is moderately well-localized (with
correlation lengths along the major axis of $2.5H$ and $1.5H$ respectively),
and generally consistent with that expected from homogenous incompressible
turbulence. The density field, conversely, exhibits both a longer correlation
length and a long correlation time, results which we ascribe to the importance
of spiral density waves within the flow. Consistent with prior results, we show
that the mean local stress displays a well-defined correlation with the local
vertical flux, and that this relation is apparently causal (in the sense of the
flux stimulating the stress) during portions of a global dynamo cycle. We argue
that the observed flux-stress relation supports dynamo models in which the
structure of coronal magnetic fields plays a central role in determining the
dynamics of thin-disk accretion.",1105.1789v1
2012-10-24,Local outflows from turbulent accretion disks,"The aim of this paper is to investigate the properties of accretion disks
threaded by a weak vertical magnetic field, with a particular focus on the
interplay between MHD turbulence driven by the magnetorotational instability
(MRI) and outflows that might be launched from the disk. For that purpose, we
use a set of numerical simulations performed with the MHD code RAMSES in the
framework of the shearing box model. We concentrate on the case of a rather
weak vertical magnetic field such that the initial ratio beta0 of the thermal
and magnetic pressures in the disk midplane equals 10^4. As reported recently,
we find that MHD turbulence drives an efficient outflow out of the
computational box. We demonstrate a strong sensitivity of that result to the
box size: enlargements in the radial and vertical directions lead to a
reduction of up to an order of magnitude in the mass-loss rate. Such a
dependence prevents any realistic estimates of disk mass-loss rates being
derived using shearing-box simulations. We find however that the flow
morphology is robust and independent of the numerical details of the
simulations. Its properties display some features and approximate invariants
that are reminiscent of the Blandford & Payne launching mechanism, but
differences exist. For the magnetic field strength considered in this paper, we
also find that angular momentum transport is most likely dominated by MHD
turbulence, the saturation of which scales with the magnetic Prandtl number,
the ratio of viscosity and resistivity, in a way that is in good agreement with
expectations based on unstratified simulations. This paper thus demonstrates
for the first time that accretion disks can simultaneously exhibit MRI-driven
MHD turbulence along with magneto-centrifugally accelerated outflows.",1210.6664v2
2012-11-07,Ground States of Spin-1/2 Triangular Antiferromagnets in a Magnetic Field,"We use a combination of density matrix renormalization group calculations and
analytical approaches to study a simplified model for a spatially anisotropic
spin-1/2 triangular lattice Heisenberg antiferromagnet: the three-leg
triangular spin tube (TST). The model is described by three Heisenberg chains,
with exchange constant J, coupled antiferromagnetically with exchange constant
J' along the diagonals of the ladder system, with periodic boundary conditions
in the shorter direction. We determine the full phase diagram of this model as
a function of spatial anisotropy, J'/J, and magnetic field. We find a rich
phase diagram, which is dominated by quantum states - phases corresponding to
the classical ground state appears only in a small region. Among the dominant
phases generated by quantum effects are commensurate and incommensurate
coplanar quasi-ordered states, which appear in the vicinity of the isotropic
region for most fields, and in the high field region for most anisotropies. The
coplanar states, while not classical ground states, can be understood
semiclassically. Even more strikingly, the largest region of phase space is
occupied by a spin density wave phase, which has incommensurate collinear
correlations along the field. This phase has no semiclassical analog, and may
be ascribed to enhanced one-dimensional (1d) fluctuations due to frustration.
Cutting across the phase diagram is a magnetization plateau, with a gap to all
excitations and up up down spin order, with a quantized magnetization equal to
1/3 of the saturation value. In the TST, this plateau extends almost but not
quite to the decoupled chains limit. Most of the above features are expected to
carry over to the two dimensional system, which we also discuss. At low field,
a dimerized phase appears, which is particular to the 1d nature of the TST, and
which can be understood from quantum Berry phase arguments.",1211.1676v2
2015-02-24,Temperature- and Field Dependent Characterization of a Twisted Stacked-Tape Cable,"The Twisted Stacked-Tape Cable (TSTC) is one of the major high temperature
superconductor cable concepts combining scalability, ease of fabrication and
high current density making it a possible candidate as conductor for large
scale magnets. To simulate the boundary conditions of such a magnets as well as
the temperature dependence of Twisted Stacked-Tape Cables a 1.16 m long sample
consisting of 40, 4 mm wide SuperPower REBCO tapes is characterized using the
""FBI"" (force - field - current) superconductor test facility of the Institute
for Technical Physics (ITEP) of the Karlsruhe Institute of Technology (KIT). In
a first step, the magnetic background field is cycled while measuring the
current carrying capabilities to determine the impact of Lorentz forces on the
TSTC sample performance. In the first field cycle, the critical current of the
TSTC sample is tested up to 12 T. A significant Lorentz force of up to 65.6
kN/m at the maximal magnetic background field of 12 T result in a 11.8 %
irreversible degradation of the current carrying capabilities. The degradation
saturates (critical cable current of 5.46 kA at 4.2 K and 12 T background
field) and does not increase in following field cycles. In a second step, the
sample is characterized at different background fields (4-12 T) and surface
temperatures (4.2-37.8 K) utilizing the variable temperature insert of the
""FBI"" test facility. In a third step, the performance along the length of the
sample is determined at 77 K, self-field. A 15 % degradation is obtained for
the central part of the sample which was within the high field region of the
magnet during the in-field measurements.",1502.06728v1
2015-07-31,"Vorticity, Shocks and Magnetic Fields in Subsonic, ICM-like Turbulence","We analyze high resolution simulations of compressible, MHD turbulence with
properties resembling conditions in galaxy clusters. The flow is driven to
turbulence Mach number $\mathcal{M}_t \sim 1/2$ in an isothermal medium with an
initially very weak, uniform seed magnetic field ($\beta = P_g/P_B = 10^6$).
Since cluster turbulence is likely to result from a mix of sheared (solenoidal)
and compressive forcing processes, we examine the distinct turbulence
properties for both cases. In one set of simulations velocity forcing is
entirely solenoidal ($\nabla\cdot \delta {\vec u} = 0$), while in the other it
is entirely compressive ($\nabla\times \delta {\vec u} = 0$). Both cases
develop a mixture of solenoidal and compressive turbulent motions, since each
generates the other. The development of compressive turbulent motions leads to
shocks, even when the turbulence is solenoidally forced and subsonic. Shocks,
in turn, produce and amplify vorticity, which is especially important in
compressively forced turbulence. To clarify those processes we include a pair
of appendices that look in detail at vorticity evolution in association with
shocks. From our simulation analyses we find that magnetic fields amplified to
near saturation levels in predominantly solenoidal turbulence can actually
enhance vorticity on small scales by concentrating and stabilizing shear. The
properties, evolution rates and relative contributions of the kinetic and
magnetic turbulent elements depend strongly on the character of the forcing.
Specifically, shocks are stronger, but vorticity evolution and magnetic field
amplification are slower and weaker when the turbulence is compressively
forced. We identify a simple relation to estimate characteristic shock
strengths in terms of the turbulence Mach number and the character of the
forcing. Our results will be helpful in understanding flow motions in galaxy
clusters.",1507.08737v1
2016-02-11,Supersaturation and activity-rotation relation in PMS stars: the young Cluster h Per,"The magnetic activity of late-type MS stars is characterized by different
regimes, and their activity levels are well described by Ro, the ratio between
P_rot and the convective turnover time. Very young PMS stars show, similarly to
MS stars, intense magnetic activity. However they do not show clear
activity-rotation trends, and it still debated which stellar parameters
determine their magnetic activity levels. To bridge the gap between MS and PMS
stars, we studied the activity-rotation relation in the young cluster h Per, a
~13 Myr old cluster, that contains both fast and slow rotators, whose members
have ended their accretion phase and have already developed a radiative core.
It offers us the opportunity to study the activity level of intermediate-age
PMS stars with different rotational velocities, excluding any interactions with
the circumstellar environment. We constrained the magnetic activity levels of h
Per members measuring their X-ray emission from a Chandra observation, while
P_rot were obtained by Moraux et al. (2013). We collected a final catalog of
414 h Per members with known P_rot, T_eff, M_star, with 169 of them having also
detected X-ray emission. We found that h Per members, with 1.0 M_sun < M_star <
1.4 M_sun, display different activity regimes: fast rotators show
supersaturation, while slower rotators have activity levels compatible to the
non-saturated regime. At 13 Myr h Per is therefore the youngest cluster showing
activity-rotation regimes analogous to that of MS stars, indicating that, at
this age, magnetic field production is likely regulated by the alpha-Omega type
dynamo. Moreover we observed that supersaturation is better described by P_rot
than Ro, and that the observed patterns are compatible with the hypothesis of
centrifugal stripping. In this scenario we inferred that coronae can produce
structures as large as ~2 R_star above the stellar surface.",1602.03696v2
2016-04-28,Temperature evolution of magnetic structure of HoFeO$_3$ by single crystal neutron diffraction,"We have investigated the temperature evolution of the magnetic structures of
HoFeO$_3$ by single crystal neutron diffraction. The three different magnetic
structures found as a function of temperature for \hfo\ are described by the
magnetic groups Pb$'$n$'2_1$, Pbn$2_1$ and Pbn$'2_1'$ and are stable in the
temperature ranges $\approx$ 600-55~K, 55-37~K and 35$>T>2$~K respectively. In
all three the fundamental coupling between the Fe sub-lattices remains the same
and only their orientation and the degree of canting away from the ideal axial
direction varies. The magnetic polarisation of the Ho sub-lattices in these two
higher temperature regions, in which the major components of the Fe moment lie
along $x$ and $y$, is very small. The canting of the moments from the axial
directions is attributed to the antisymmetric interactions allowed by the
crystal symmetry. They include contributions from single ion anisotropy as well
as the Dzyaloshinski antisymmetric exchange. In the low temperature phase two
further structural transitions are apparent in which the spontaneous
magnetisation changes sign with respect to the underlying antiferromagnetic
configuration. In this temperature range the antisymmetric exchange energy
varies rapidly as the the Ho sub-lattices begin to order. So long as the
ordered Ho moments are small the antisymmetric exchange is due only to Fe-Fe
interactions, but as the degree of Ho order increases the Fe-Ho interactions
take over whilst at the lowest temperatures, when the Ho moments approach
saturation the Ho-Ho interactions dominate. The reversals of the spontaneous
magnetisation found in this study suggest that in \hfo\ the sums of the Fe-Fe
and Ho-Ho antisymmetric interactions have the same sign as one another, but
that of the Ho-Fe terms is opposite.",1604.08349v1
2017-08-18,Low mass planet migration in magnetically torqued dead zones - I. Static migration torque,"Motivated by models suggesting that the inner planet forming regions of
protoplanetary discs are predominantly lacking in viscosity-inducing
turbulence, and are possibly threaded by Hall-effect generated large-scale
horizontal magnetic fields, we examine the dynamics of the corotation region of
a low-mass planet in such an environment. The corotation torque in an inviscid,
isothermal, dead zone ought to saturate, with the libration region becoming
both symmetrical and of a uniform vortensity, leading to fast inward migration
driven by the Lindblad torques alone. However, in such a low viscosity
situation, the material on librating streamlines essentially preserves its
vortensity. If there is relative radial motion between the disc gas and the
planet, the librating streamlines will no longer be symmetrical. Hence, if the
gas is torqued by a large scale magnetic field so that it undergoes a net
inflow or outflow past the planet, driving evolution of the vortensity and
inducing asymmetry of the corotation region, the corotation torque can grow,
leading to a positive torque. In this paper we treat this effect by applying a
symmetry argument to the previously studied case of a migrating planet in an
inviscid disc. Our results show that the corotation torque due to a laminar
Hall-induced magnetic field in a dead zone behaves quite differently from that
studied previously for a viscous disc. Furthermore, the magnetic field induced
corotation torque and the dynamical corotation torque in a low viscosity disc
can be regarded as one unified effect.",1708.05721v2
2018-08-01,"Rare earth size dependence on structural, electronic and magnetic properties of R2NiMnO6 double perovskites","Rare earth Manganite Nickelite double perovskites are prepared by solgel
assisted combustion route, where, R varies from La, Pr, Nd, Sm, Gd, Tb, Dy, Y,
and Ho. The samples have been systematically investigated using powder xray
diffraction, Raman spectroscopy, ultraviolet visible spectroscopy,
magnetization, and synchrotron based xray absorption spectroscopy measurements.
All compounds in the family crystallize in the monoclinic structure and the
monoclinic distortion enhances with decreasing trivalent rare earth radii. The
magnetic ordering temperature, Tc, decreases from 270 K for La to 80 K for Ho
samples as the rare earth radii decrease from 0.116nm for La to 0.102nm in case
of Ho. An additional anomaly is observed in samples containing Nd, Sm, Tb, and
Dy at lower temperatures, which originates from the 3d to 4f coupling between
Mn and Ni and Nd, Sm, Tb and Dy magnetic moments. Further, high saturation
magnetization is achieved for all samples indicating that they are atomically
ordered and have less anti site disorders. Upon decreasing the size of rare
earth ions, the local structure shows an expansion of NiO6 octahedra and almost
unchanged MnO6 octahedra. Xray absorption near edge spectroscopy reveals that
majority of Ni and Mn ions are in positive 2 and positive 4 valence states in
all the samples. Raman spectra of RNMO show a softening of phonon modes
resulting in the elongation of Ni to O and Mn to O bond lengths. Finally, a
correlation between lattice parameters, structural distortion, octahedral
tilting, superexchange angle, and electronic band gap, Curie temperature, and
the rare earth ionic radius is established.",1808.00170v1
2019-03-04,Noncontrast free-breathing respiratory self-navigated coronary artery cardiovascular magnetic resonance angiography at 3 T using lipid insensitive binomial off-resonant excitation (LIBRE),"Robust and homogeneous lipid suppression is mandatory for coronary magnetic
resonance angiography (MRA) since coronary arteries are commonly embedded in
fat. However, effective large volume lipid suppression becomes challenging when
performing radial whole-heart coronary MRA and the problem may even be
exacerbated at increasing magnetic field strengths. Incomplete fat suppression
also generates artifacts, and may affect advanced motion correction methods.
The aim was to evaluate a recently reported lipid insensitive MRI method for
self-navigated coronary MRA at 3T. Lipid insensitive binomial off resonant
excitation (LIBRE) radiofrequency (RF) excitation pulses were included into a
self-navigated 3D radial GRE coronary MRA sequence at 3T. LIBRE was compared
against conventional fat saturation (FS) and binomial 1-180{\deg}-1 water
excitation (WE). First, fat suppression of all techniques was numerically
characterized using Matlab and experimentally validated in phantoms and in legs
of human volunteers. Subsequently, free-breathing self-navigated coronary MRA
was performed using the LIBRE pulse as well as FS and WE in ten volunteers.
Results obtained in the simulations were confirmed by the experimental
validations as LIBRE enabled near complete fat suppression for 3D radial
imaging in vitro and in vivo. For self-navigated whole-heart coronary MRA at
3T, fat SNR was significantly attenuated using LIBRE compared with conventional
FS. LIBRE increased the RCA vessel sharpness significantly (37 +/- 9% (LIBRE)
vs. 29 +/- 8% (FS) and 30 +/- 8% (WE), both p<0.05) and led to a significant
increase in the measured RCA vessel length to (83 +/- 31 mm (LIBRE) vs. 56 +/-
12 mm (FS) and 59 +/- 27 (WE) p<0.05). LIBRE enables robust large volume fat
suppression and significantly improves coronary artery image quality at 3T
compared to the use of conventional fat suppression and water excitation.",1903.01325v2
2019-10-01,"Oxygen deficiency and migration mediated electric polarization in Fe,Co-substituted SrTiO$_{3-δ}$","We use density functional theory (DFT) calculations to show that oxygen
vacancies ($v_\mathrm{O}$) and mobility induce noncentrosymmetric polar
structures in SrTi$_{1-x-y}$Fe$_{x}$Co$_{y}$O$_{3-\delta}$ ($x=y=0.125$) with
$\delta = \{0.125, 0.25\}$, enhance the saturation magnetization and give rise
to large changes in the electric polarization $\vert\Delta P\vert$. We present
an intuitive set of rules for SrTiFeCoO$_{3-\delta}$ (STFC), which are based on
the interplay between (Co/Fe)-$v_\mathrm{O}$ defects, magnetic cations
coordination and topological vacancy disorder. STFC structures convey layered
crystals with sheets of linear organized O$_{4,5,6}$-coordinated Fe-Co pairs,
sandwiched with layers of O$_{5}$-coordinated Ti. Co,Fe-$v_\mathrm{O}$ defects
are the source of the crystal distortions, cations off-centering and bending of
the oxygen octahedra, which added to the charge redistribution mediated by
$v_\mathrm{O}$, the cations electronegativity and valence states trigger an
effective electric polarization. Oxygen migrations for $\delta=0.125$ provides
us with $\vert\Delta \mathbf{P}\vert$ $>\sim10 \mu$C/cm$^2$ due to a
quantum-of-polarization differences between $\delta=0.125$ structures.
Increasing the deficiency to $\delta=0.25$ yields $\vert\Delta \mathbf{P}\vert$
whose O-migration resolved polarization for $\delta=0.25$ is $>\sim3
\mu$C/cm$^2$ in the worst case scenario. Magnetism is dominated by the Fe,Co
spin states for $\delta=0.125$ while there is a raid of Ti magnetic moments
($\sim1\mu_{B}$) for $\delta=0.25$. Magnetic and electric order parameters
change for variations of $\delta$ or oxygen migrations for a given deficiency.
Our results capture characteristics observed in the end-members of the series
SrTi(Co,Fe)O$_{3}$, and suggest the existence of a broader set of rules for
oxygen deficient multiferroic oxides.",1910.00176v2
2020-07-25,Time-resolved fast turbulent dynamo in a laser plasma,"Understanding magnetic-field generation and amplification in turbulent plasma
is essential to account for observations of magnetic fields in the universe. A
theoretical framework attributing the origin and sustainment of these fields to
the so-called fluctuation dynamo was recently validated by experiments on laser
facilities in low-magnetic-Prandtl-number plasmas ($\mathrm{Pm} < 1$). However,
the same framework proposes that the fluctuation dynamo should operate
differently when $\mathrm{Pm} \gtrsim 1$, the regime relevant to many
astrophysical environments such as the intracluster medium of galaxy clusters.
This paper reports a new experiment that creates a laboratory $\mathrm{Pm}
\gtrsim 1$ plasma dynamo for the first time. We provide a time-resolved
characterization of the plasma's evolution, measuring temperatures, densities,
flow velocities and magnetic fields, which allows us to explore various stages
of the fluctuation dynamo's operation. The magnetic energy in structures with
characteristic scales close to the driving scale of the stochastic motions is
found to increase by almost three orders of magnitude from its initial value
and saturate dynamically. It is shown that the growth of these fields occurs
exponentially at a rate that is much greater than the turnover rate of the
driving-scale stochastic motions. Our results point to the possibility that
plasma turbulence produced by strong shear can generate fields more efficiently
at the driving scale than anticipated by idealized MHD simulations of the
nonhelical fluctuation dynamo; this finding could help explain the large-scale
fields inferred from observations of astrophysical systems.",2007.12837v1
2020-09-08,Disorder and magnetic field induced Bose-metal state in two-dimensional Ta$_x$(SiO$_2$)$_{1-x}$ granular films,"The origin of the intermediate anomalous metallic state in two-dimensional
superconductor materials remains enigmatic. In the present paper, we observe
such a state in a series of $\sim$9.0 nm thick Ta$_x$(SiO$_2$)$_{1-x}$ ($x$
being the volume fraction of Ta) nanogranular films. At zero field, the $x$
$\gtrsim$ 0.75 films undergo a Berezinskii-Kosterlitz-Thouless transition as
transform from normal to superconducing states upon cooling. For the $x$
$\lesssim$ 0.71 films, the resistance increases with decreasing temperature
from 2 K down to 40 mK. A normal state to anomalous metallic state transition
is observed in the $x$ $\simeq$ 0.73 film, i.e., near the transition
temperature, the resistance of the film decreases sharply upon cooling as if
the system would cross over to superconducting state, but then saturates to a
value far less than that in normal state. When a small magnetic field
perpendicular to the film plane is applied, the anomalous metallic state occurs
in the $x$ $\gtrsim$ 0.75 films. It is found that both disorder and magnetic
field can induce the transition from superconductor to anomalous metal and
their influences on the transition are similar. For the the magnetic field
induced case, we find the sheet resistance $R_{\square}(T,H)$ ($T$ and $H$
being the temperature and the magnitude of magnetic field) data near the
crossover from the anomalous metal to superconductor and in the vicinity of the
anomalous metal to insulator transition, respectively, obey unique scaling laws
deduced from the Bose-metal model. Our results strongly suggest that the
anomalous metallic state in the Ta$_x$(SiO$_2$)$_{1-x}$ granular films is
bosonic and dynamical gauge field fluctuation resulting from superconducting
quantum fluctuations plays a key role in its formation.",2009.03511v1
2020-09-17,Particle acceleration by relativistic magnetic reconnection driven by kink instability turbulence in Poynting flux dominated jets,"Particle acceleration in magnetized relativistic jets still puzzles
theorists, specially when one tries to explain the highly variable emission
observed in blazar jets or gamma-ray bursts putting severe constraints on
current models. In this work we investigate the acceleration of particles
injected in a three-dimensional relativistic magnetohydrodynamical jet subject
to current driven kink instability (CDKI), which drives turbulence and fast
magnetic reconnection. Test protons injected in the nearly stationary snapshots
of the jet, experience an exponential acceleration up to a maximum energy. For
a background magnetic field of $B \sim 0.1$ G, this saturation energy is $\sim
10^{16}$ eV, while for $B \sim 10$ G it is $\sim 10^{18}$ eV. The simulations
also reveal a clear association of the accelerated particles with the regions
of fast reconnection. In the early stages of the development of the non-linear
growth of CDKI in the jet, when there are still no sites of fast reconnection,
injected particles are also efficiently accelerated, but by magnetic curvature
drift in the wiggling jet spine. However, they have to be injected with an
initial energy much larger than that required for particles to accelerate in
reconnection sites. Finally, we have also obtained from the simulations an
acceleration time due to reconnection with a weak dependence on the particles
energy $E$, $t_A \propto E^{0.1}$. The energy spectrum of the accelerated
particles develops a high energy tail with a power law index $p \sim$ -1.2 in
the beginning of the acceleration, in agreement with earlier works. Our results
provide an appropriate multi-dimensional framework for exploring this process
in real systems and explain their complex emission patterns, specially in the
very high energy bands and the associated neutrino emission recently detected
in some blazars.",2009.08516v5
2020-10-21,The impact of magnetic fields on momentum transport and saturation of shear-flow instability by stable modes,"The Kelvin-Helmholtz (KH) instability of a shear layer with an
initially-uniform magnetic field in the direction of flow is studied in the
framework of 2D incompressible magnetohydrodynamics with finite resistivity and
viscosity using direct numerical simulations. The shear layer evolves freely,
with no external forcing, and thus broadens in time as turbulent stresses
transport momentum across it. As with KH-unstable flows in hydrodynamics, the
instability here features a conjugate stable mode for every unstable mode in
the absence of dissipation. Stable modes are shown to transport momentum up its
gradient, shrinking the layer width whenever they exceed unstable modes in
amplitude. In simulations with weak magnetic fields, the linear instability is
minimally affected by the magnetic field, but enhanced small-scale fluctuations
relative to the hydrodynamic case are observed. These enhanced fluctuations
coincide with increased energy dissipation and faster layer broadening, with
these features more pronounced in simulations with stronger fields. These
trends result from the magnetic field reducing the effects of stable modes
relative to the transfer of energy to small scales. As field strength
increases, stable modes become less excited and thus transport less momentum
against its gradient. Furthermore, the energy that would otherwise transfer
back to the driving shear due to stable modes is instead allowed to cascade to
small scales, where it is lost to dissipation. Approximations of the turbulent
state in terms of a reduced set of modes are explored. While the Reynolds
stress is well-described using just two modes per wavenumber at large scales,
the Maxwell stress is not.",2010.11198v1
2020-12-09,Pressure control of the magnetic anisotropy of the quasi-two-dimensional van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$,"We report the results of the pressure-dependent measurements of the static
magnetization and of the ferromagnetic resonance (FMR) of Cr$_2$Ge$_2$Te$_6$ to
address the properties of the ferromagnetic phase of this quasi-two-dimensional
van der Waals magnet. The static magnetic data at hydrostatic pressures up to
3.4 GPa reveal a gradual suppression of ferromagnetism in terms of a reduction
of the critical transition temperature, a broadening of the transition width
and an increase of the field necessary to fully saturate the magnetization
$M_{\rm s}$. The value of $M_{\rm s} \simeq 3\mu_{\rm B}$/Cr remains constant
within the error bars up to a pressure of 2.8 GPa. The anisotropy of the FMR
signal continuously diminishes in the studied hydrostatic pressure range up to
2.39 GPa suggesting a reduction of the easy-axis type magnetocrystalline
anisotropy energy (MAE). A quantitative analysis of the FMR data gives evidence
that up to this pressure the MAE constant $K_{\rm U}$, although getting
significantly smaller, still remains finite and positive, i.e. of the easy-axis
type. Therefore, a recently discussed possibility of switching the sign of the
magnetocrystalline anisotropy in Cr$_2$Ge$_2$Te$_6$ could only be expected at
still higher pressures, if possible at all due to the observed weakening of the
ferromagnetism under pressure. This circumstance may be of relevance for the
design of strain-engineered functional heterostructures containing layers of
Cr$_2$Ge$_2$Te$_6$.",2012.05193v2
2021-04-28,Structural transformation and magnetic properties of (Fe$_{0.7}$Co$_{0.3}$)$_2$B alloys doped with 5$d$ elements: A combined first-principles and experimental study,"(Fe,Co)$_2$B-based compounds with specified 5$d$ substitutions are considered
as promising materials for permanent magnets without rare-earth elements. We
conducted a combined first-principles and experimental study focused on
(Fe$_{0.7}$Co$_{0.3}$)$_2$B alloys doped with W and Re. First, we used
full-potential local-orbital scheme to systematically investigate (Fe,Co)$_2$B
alloys with 3$d$, 4$d$, and 5$d$ substitutions. Computational analyses showed a
significant increase in magnetocrystalline anisotropy only for the Re doped
sample. Simultaneously, the structural and magnetic properties of the
(Fe$_{0.7-x}$Co$_{0.3-x}$M$_{2x}$)$_2$B ($M$ = W, Re; $x$ = 0, 0.025) alloys
were investigated experimentally. The desired (Fe,Co)$_2$B tetragonal phase was
synthesized by heat treatment of amorphous precursors. We observed that
isothermal annealing increases the coercive field of all samples. However, the
obtained values, without further optimization, are well below the threshold for
permanent magnet applications. Nevertheless, annealing of substituted samples
at 750$^o$C significantly improves saturation magnetization values.
Furthermore, M\""{o}ssbauer spectroscopy revealed a reduction of the hyperfine
field due to the presence of Co atoms in the (Fe,Co)$_2$B phase, where
additional defect positions are formed by Re and W. Radio-frequency
M\""{o}ssbauer studies showed that (Fe$_{0.7}$Co$_{0.3}$)$_2$B and the
W-substituted sample began to crystallize when exposed to an radio frequency
field of 12 Oe, indicating that the amorphous phase is stabilized by Re
substitution. Improvement of thermal stability of
(Fe$_{0.675}$Co$_{0.275}$Re$_{0.05}$)$_2$B alloy is consistent with the results
of differential scanning calorimetry and thermomagnetic measurements.",2104.13724v2
2021-10-27,A Subgrid Turbulent Mean Field Dynamo Model for Cosmological Galaxy Formation Simulations,"Magnetic fields have been included in cosmological simulations of galaxy
formation only recently, due to advances in numerical techniques and a better
understanding of the galaxy formation physics. In this paper, we develop a new
subgrid model for the turbulent dynamo that takes place in the supersonic
interstellar medium in star-forming galaxies. It is based on a mean-field
approach that computes the turbulent kinetic energy at unresolved scales (the
so-called subgrid scales) and modifies the induction equation to account for
the corresponding $\alpha$ dynamo. Our subgrid model depends on one free
parameter, the quenching parameter, that controls the saturation of the subgrid
dynamo. Thanks to this mean-field approach, we can now model the fast
amplification of the magnetic field inside turbulent star-forming galaxies,
without relying on artificially strong initial fields or without using
prohibitively expensive high-resolution simulations. We show that the evolution
of the magnetic field in our zoom-in Milky Way-like galaxy is consistent with a
simple picture, in which the field is in equipartition with the turbulent
kinetic energy inside the star-forming disc, with a field strength around 10
$\mu$G at low redshift, while at the same time strong galactic outflows fill
the halo with a slightly weaker magnetic field, whose strength (10 nG) is
consistent will the ideal MHD dilution factor. Our results are in good
agreement with recent theoretical and numerical predictions. We also compare
our simulation with Faraday depth observations at both low and high redshift,
seeing overall good agreement with some caveats. Our model naturally predicts
stronger magnetic fields at high redshift (around 100 $\mu$G in the galaxy and
1 $\mu$G in the halo), but also stronger depolarisation effects due to stronger
turbulence at early time.",2110.14246v2
2022-06-24,Exploring the disk-jet connection in NGC 315,"Aims. Hot accretion flows are thought to be able to power the relativistic
jets observed in Active Galactic Nuclei. They can present themselves as SANE
(Standard And Normal Evolution) disks or MAD (Magnetically Arrested Disks), two
states implying profound differences in the physical properties of the disks
themselves and of the outflows they produce. Methods. In this paper we use a
multi-frequency and multi-epoch data set to study the giant radio galaxy NGC
315, with the goal to explore the properties of its accretion disk and
sub-parsec jet. We analyze the source maps with a pixel-based analysis and we
use theoretical models to link the observational properties of the jet to the
physical state of the accretion disk. Results. We propose that the bulk flow in
NGC 315 accelerates on sub-pc scales, concurrently with the parabolic
expansion. We show that this fast acceleration can be theoretically reconciled
with a magnetically driven acceleration. Along the acceleration and collimation
zone, we observe an unexpected spectral behavior, with very steep spectral
index values $\alpha \sim -1.5$ ($S_\nu \propto \nu^\alpha$) between 22 GHz and
43 GHz. Based on the properties of this region, we predict the black hole of
NGC 315 to be fast rotating and the magnetic flux threading the accretion disk
to be in excellent agreement with that expected in the case of a MAD. Using a
new formalism based on the core-shift effect, we model the magnetic field
downstream a quasi-parabolic accelerating jet and we reconstruct it up to the
event horizon radius. In the MAD scenario, we compare it with the expected
magnetic saturation strengths in the disk, finding a good agreement.",2206.12193v1
2022-11-25,Two-band conduction as a pathway to non-linear Hall effect and unsaturated negative magnetoresistance in the martensitic compound GdPd2Bi,"The present work aims to address the electronic and magnetic properties of
the intermetallic compound GdPd$_2$Bi through a comprehensive study of the
structural, magnetic, electrical and thermal transport on a polycrystalline
sample, followed by theoretical calculations. Our findings indicate that the
magnetic ground state is antiferromagnetic in nature. Magnetotransport data
present prominent hysteresis loop hinting a structural transition with further
support from specific heat and thermopower measurements, but no such signature
is observed in the magnetization study. Temperature dependent powder x-ray
diffraction measurements confirm martensitic transition from the
high-temperature (HT) cubic Heusler $L2_1$ structure to the low-temperature
(LT) orthorhombic $Pmma$ structure similar to many previously reported shape
memory alloys. The HT to LT phase transition is characterized by a sharp
increase in resistivity associated with prominent thermal hysteresis. Further,
we observe robust Bain distortion between cubic and orthorhombic lattice
parameters related by $a_{orth} = \sqrt{2}a_{cub}$, $b_{orth} = a_{cub}$ and
$c_{orth} = a_{cub}/\sqrt{2}$, that occurs by contraction along $c$-axis and
elongation along $a$-axis respectively. The sample shows an unusual
`non-saturating' $H^2$-dependent negative magnetoresistance for magnetic field
as high as 150 kOe. In addition, non-linear field dependence of Hall
resistivity is observed below about 30 K, which coincides with the sign change
of the Seebeck coefficient. The electronic structure calculations confirm
robust metallic states both in the LT and HT phases. It indicates complex
nature of the Fermi surface along with the existence of both electron and hole
charge carriers. The anomalous transport behaviors can be related to the
presence of both electron and hole pockets.",2211.13982v1
2023-04-05,Understanding the Relationship between Solar Coronal Abundances and F10.7 cm Radio Emission,"Sun-as-a-star coronal plasma composition, derived from full-Sun spectra, and
the F10.7 radio flux (2.8 GHz) have been shown to be highly correlated (r =
0.88) during solar cycle 24. However, this correlation becomes nonlinear during
increased solar magnetic activity. Here, we use co-temporal, high spatial
resolution, multi-wavelength images of the Sun to investigate the underlying
causes of the non-linearity between coronal composition (FIP bias) and F10.7
solar index correlation. Using the Karl G. Jansky Very Large Array (JVLA),
Hinode/EIS (EUV Imaging Spectrometer), and the Solar Dynamic Observatory (SDO),
we observed a small active region, AR 12759, throughout the solar atmosphere
from the photosphere to the corona. Results of this study show that the
magnetic field strength (flux density) in active regions plays an important
role in the variability of coronal abundances, and it is likely the main
contributing factor to this non-linearity during increased solar activity.
Coronal abundances above cool sunspots are lower than in dispersed magnetic
plage regions. Strong magnetic concentrations are associated with stronger
F10.7 cm gyroresonance emission. Considering that as the solar cycle moves from
minimum to maximum, the size of sunspots and their field strength increase with
gyroresonance component, the distinctly different tendencies of radio emission
and coronal abundances in the vicinity of sunspots is the likely cause of
saturation of Sun-as-a-star coronal abundances during solar maximum, while the
F10.7 index remains well correlated with the sunspot number and other magnetic
field proxies.",2304.02552v1
2023-09-29,Turbulent dynamo action and its effects on the mixing at the convective boundary of an idealized oxygen-burning shell,"Convection is one of the most important mixing processes in stellar
interiors. Hydrodynamic mass entrainment can bring fresh fuel from neighboring
stable layers into a convection zone, modifying the structure and evolution of
the star. Under some conditions, strong magnetic fields can be sustained by the
action of a turbulent dynamo, adding another layer of complexity and possibly
altering the dynamics in the convection zone and at its boundaries. In this
study, we used our fully compressible Seven-League Hydro code to run detailed
and highly resolved three-dimensional magnetohydrodynamic simulations of
turbulent convection, dynamo amplification, and convective boundary mixing in a
simplified setup whose stratification is similar to that of an oxygen-burning
shell in a star with an initial mass of $25\ M_\odot$. We find that the random
stretching of magnetic field lines by fluid motions in the inertial range of
the turbulent spectrum (i.e., a small-scale dynamo) naturally amplifies the
seed field by several orders of magnitude in a few convective turnover
timescales. During the subsequent saturated regime, the magnetic-to-kinetic
energy ratio inside the convective shell reaches values as high as $0.33$, and
the average magnetic field strength is ${\sim}10^{10}\,\mathrm{G}$. Such strong
fields efficiently suppress shear instabilities, which feed the turbulent
cascade of kinetic energy, on a wide range of spatial scales. The resulting
convective flows are characterized by thread-like structures that extend over a
large fraction of the convective shell. The reduced flow speeds and the
presence of magnetic fields with strengths up to $60\%$ of the equipartition
value at the upper convective boundary diminish the rate of mass entrainment
from the stable layer by ${\approx}\,20\%$ as compared to the purely
hydrodynamic case.",2309.17225v1
2024-02-19,Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures,"Quantum magnonics investigates the quantum-mechanical properties of magnons
such as quantum coherence or entanglement for solid-state quantum information
technologies at the nanoscale. The most promising material for quantum
magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons
with the longest lifetimes. YIG films of the highest quality are grown on a
paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has
reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at
temperatures below 50 K despite the increase in YIG magnetization. We
investigated a 97 nm-thick YIG film grown on 500 $\mathrm{\mu}$m-thick GGG
substrate through a series of experiments conducted at temperatures as low as
30 mK, and using both analytical and numerical methods. Our findings suggest
that the primary factor contributing to the FMR frequency shift is the stray
magnetic field created by the partially magnetized GGG substrate. This stray
field is antiparallel to the applied external field and is highly
inhomogeneous, reaching up to 40 mT in the center of the sample. At
temperatures below 500 mK, the GGG field exhibits a saturation that cannot be
described by the standard Brillouin function for a paramagnet. Including the
calculated GGG field in the analysis of the FMR frequency versus temperature
dependence allowed the determination of the cubic and uniaxial anisotropies. We
find that the total anisotropy increases more than three times with the
decrease in temperature down to 2 K. Our findings enable accurate predictions
of the YIG/GGG magnetic systems behavior at low and ultra-low millikelvin
temperatures, crucial for developing quantum magnonic devices.",2402.12112v1
2024-02-22,Shubnikov-de Haas oscillations of biaxial-strain-tuned superconductors in pulsed magnetic field up to 60 T,"Two-dimensional (2D) materials have gained increasing prominence not only in
fundamental research but also in daily applications. However, to fully harness
their potential, it is crucial to optimize their properties with an external
parameter and track the electronic structure simultaneously. Magnetotransport
over a wide magnetic field range is a powerful method to probe the electronic
structure and, for metallic 2D materials, quantum oscillations superimposed on
the transport signals encode Fermi surface parameters. In this manuscript, we
utilize biaxial strain as an external tuning parameter and investigate the
effects of strain on the electronic properties of two quasi-2D superconductors,
MoTe$_2$ and RbV$_3$Sb$_5$, by measuring their magnetoresistance in pulsed
magnetic fields up to 60 T. With a careful selection of insulating substrates,
we demonstrate the possibility of both the compressive and tensile biaxial
strain, imposed on MoTe$_2$ and RbV$_3$Sb$_5$, respectively. For both systems,
the applied strain has led to superconducting critical temperature enhancement
compared to their free-standing counterparts, proving the effectiveness of this
biaxial strain method at cryogenic temperatures. Clear quantum oscillations in
the magnetoresistance -- the Shubnikov-de Haas (SdH) effect -- are obtained in
both samples. In strained MoTe$_2$, the magnetoresistance exhibits a nearly
quadratic dependence on the magnetic field and remains non-saturating even at
the highest field. Whereas in strained RbV$_3$Sb$_5$, two SdH frequencies
showed a substantial enhancement in effective mass values, hinting at a
possible enhancement of charge fluctuations. Our results demonstrate that
combining biaxial strain and pulsed magnetic field paves the way for studying
2D materials under unprecedented conditions.",2402.14534v1
2003-04-10,Ground Canonicity,"We explore how different proof orderings induce different notions of
saturation. We relate completion, paramodulation, saturation, redundancy
elimination, and rewrite system reduction to proof orderings.",0304017v1
2004-12-14,Saturation in DIS at low x,"Saturation at low x appears as an almost unaboidable consequence of the
two-gluon excange generic structure.",0412174v1
2010-03-02,More (\ell_r) saturated (\mathcal{L}_\infty) spaces,"We present some new examples of separable (\mathcal_\infty) spaces which are
(\ell_r) saturated for some (1 < r < \infty).",1003.0579v1
2018-01-12,Graph cover-saturation,"Graph $G$ is $F$-saturated if $G$ contains no copy of graph $F$ but any edge
added to $G$ produces at least one copy of $F$. One common variant of
saturation is to remove the former restriction: $G$ is $F$-semi-saturated if
any edge added to $G$ produces at least one new copy of $F$. In this paper we
take this idea one step further. Rather than just allowing edges of $G$ to be
in a copy of $F$, we require it: $G$ is $F$-covered if every edge of $G$ is in
a copy of $F$. It turns out that there is smooth interaction between coverage
and semi-saturation, which opens for investigation a natural analogue to
saturation numbers. Therefore we present preliminary cover-saturation theory
and structural bounds for the cover-saturation numbers of graphs. We also
establish asymptotic cover-saturation densities for cliques and paths, and
upper and lower bounds (with small gaps) for cycles and stars.",1801.04250v2
2019-10-07,Investigating saturation effects in ultraperipheral collisions at the LHC with the color dipole model,"We investigate saturation effects in $ep$ scattering as well as in
ultraperipheral $p$A and AA collisions at small $x$ with four variants of the
impact parameter dependent color dipole model: with and without gluon
saturation and with and without a novel mechanism that suppresses unphysical
dipole radii above the confinement scale, a problem not addressed by most
implementations. We show that $ep$ scattering at HERA can be very well
described by any of the four variants. When going from $ep$ to $e$A scattering,
saturation effects are expected to increase as $\sim$A$^{1/3}$. In lieu of an
electron-ion collider, we confront the different versions of the dipole model
with data recorded in ultraperipheral collisions at the LHC in order to
estimate the sensitivity of the data to gluon saturation in the target nuclei.
We find that ultraperipheral PbPb collisions indicate strong saturation effects
while $p$Pb collisions turn out to not have any discriminating power to
distinguish saturation from non-saturation scenarios.",1910.02899v2
2021-07-27,Saturation of Rota's basis conjecture,"We prove an asymptotic saturation-type version of Rota's basis conjecture. It
relies on the connection of Tao's slice rank with unstable tensors from
geometric invariant theory.",2107.12926v1
2023-01-02,On the saturation stress of deformed metals,"Crystalline materials exhibit an hysteresis behaviour when deformed
cyclically. The origins of this tension-compression asymmetry have been fully
understood only recently as being caused by an asymmetry in the junction
strength and a reduced mean free path of dislocations inherited from previous
deformation stage. Here, we investigate the saturation stress in fcc single-
and poly-crystals using a Crystal Plasticity framework derived from dislocation
dynamics simulations. In the absence of plastic localization and damage
mechanism, the single-crystal mechanical response eventually saturates. We show
that the cyclic saturation stress converges asymptotically to the monotonic
saturation stress as the cycle plastic increment increases, and this
convergence can be observed for some experimental conditions. The analysis of
the experimental literature suggests that the mechanisms controlling the
saturation in single crystals are the same controlling the cyclic response of
polycrystals with large grains. We propose also analytical and approximated
models to predict the saturation stress over the considered loading conditions.
The saturation stress appears as a fundamental property of dislocations,
explaining the consistency observed in the experimental literature. This work
provides a unified view on the monotonous and cyclic responses of fcc single
and poly-crystals, which may help in interpreting experimental data.",2301.00625v1
2023-01-11,Pragmatic Estimation of Sample Size for Number of Interviews for PRO development in the 2009 FDA PRO guidance,"PROs developed de novo, using the FDA guidance may involve structured patient
interviews or focus groups. Qualitative Research is a methodology for eliciting
and coding interviews and produces concepts or themes. These concepts are used
to develop items in a PRO for use as an endpoint in Clinical trials. A
convention in the field is that interviews and code/concept elicitation are
considered complete when subsequent interviews produces ""no new concepts""
-termed ""saturation"". FDA reviewers frequently challenge PRO developers whether
there are sufficient patient interviews to confirm that saturation is achieved
after occurrence of zero new concepts. Several authors have reported that
concrete criteria are need for confirming that saturation is achieved (Francis
2010, Mason 2010, Marshall 2013). I provide statistical methodology for
confirming saturation, suitable for review by a regulatory authority. Type I
error for saturation, may occur if further interviews elicited more concepts
after first occurrence of saturation. I use published data set on code
elicitation (Guest, 2006) to demonstrate that saturation may occur more than
once in a sequence of interviews. I provide a statistical definition for
saturation in qualitative research, that addresses regulatory concerns for
PRO's developed for use as a clinical trial endpoint in a regulatory
submission.",2301.04760v1
2024-02-01,Saturated ideals from Laver collapses,"Addressing a question of Shioya, we show that two-step iterations of the
Laver collapse can force saturated ideals and Chang conjectures.",2402.00527v1
1997-09-18,Supersaturation in X-ray emission of clusters stars,"A population of cool dwarfs with extreme rotational velocities (v sini > 100
km/sec) is present in young open clusters. ROSAT observations have shown that
these very fast rotators exhibit a level of X-ray activity a factor of 3-5
below the saturated level which is usually observed (both in X-rays and other
magnetic activity indicators) for `normally' fast rotators. This phenomenon has
been denominated ""Supersaturation"". W UMa contact binaries seem to be
supersaturated as well, while the scatter in the rotation-activity relation for
RS CVn and BY Dra binaries does not allow us to clearly discern whether they
exhibit supersaturation or not. Supersaturation is not seen in Halpha for Alpha
Per supersaturated stars. Two alternative lines of interpretation are
discussed.",9709177v1
2001-10-20,Chandra Observations of High Mass Young Stellar Objects in the Monoceros R2 molecular cloud,"We observed the Monoceros R2 molecular cloud with the ACIS-I array onboard
the Chandra X-ray Observatory. From the central 3.2' x 3.2' region, we detect
154 sources above the detection limit of ~5x10^-16 ergs s^-1 cm^-2 with a 100
ks-exposure. About 85% of the X-ray sources are identified with an infrared
counterpart, including four high mass stars in zero age main sequence (ZAMS)
and/or pre main sequence (PMS) phase. The X-ray spectra of the high mass ZAMS
and PMS stars are represented with a thin thermal plasma model of a temperature
above 2 keV. The X-rays are time-variable and exhibit rapid flares. These high
temperature plasma and flaring activity are similar to those seen in low mass
PMS stars and contrary to the behavior observed in high mass main sequence
stars. The X-ray luminosity increases as the intrinsic K-band flux increases.
However, the X-ray luminosity saturates at a level of ~10^31 ergs s^-1. We
conclude that high mass ZAMS and PMS emit X-rays, possibly due to the magnetic
activity like those of low mass stars.",0110462v1
2001-11-29,Numerical study of the magnetorotational instability in weakly magnetised accretion disks: Resolution dependence of the Shakura-Sunyaev alpha,"In this letter, we present numerical calculations made to investigate the
possible resolution dependence of the Shakura & Sunyaev (1973) viscosity
parameter alpha from local magnetohydrodynamic simulations of the
magnetorotational instability (MRI). We find that the values of alpha do indeed
depend significantly on the numerical resolution but also that when the highest
resolutions attainable by the computational resources available are used, the
growth of the alpha-parameter seems to saturate. The values of alpha are at
most of the order of 10^(-3), which indicates that the sole presence of
turbulence due to dynamo generated magnetic field in the disk is not enough to
reproduce alphas of the order unity which could explain some observational
results (e.g. Cannizzo 1993).",0111554v1
2004-01-15,Conference Summary: Three Dimensional Explosions,"This is the text of a summary of the workshop on asymmetric explosions held
in Austin in June, 2003. A brief review is given of the author's own interests
in dynamo theory as it may apply in the core collapse ambience. Of particular
interest are saturation fields for the cases with central neutron stars and
black holes and the possibility of driving MHD jets with the resulting fields.
Interesting physics that may arise with large fields such as effects on the
equation of state to produce anisotropic pressure and effects on neutrino cross
sections and transport are briefly outlined. A brief summary of the
contributions to the workshop is then given with special credit to Scratchy
Serapkin. Of special note were the summaries of the advances due to
spectropolarimetry in revealing the asymmetric nature of supernovae. Major
progress in understanding the binary progenitors and explosion physics of Type
Ia was presented. Other talks entwined the nature of asymmetric core collapse,
gamma-ray bursts and ""hypernovae."" My final charge to the attendees was ""Go
thee forth and think about rotation and magnetic fields!""",0401323v1
2005-01-25,"A New Godunov Scheme for MHD, with Application to the MRI in disks","We describe a new numerical scheme for MHD which combines a higher order
Godunov method (PPM) with Constrained Transport. The results from a selection
of multidimensional test problems are presented. The complete test suite used
to validate the method, as well as implementations of the algorithm in both F90
and C, are available from the web. A fully three-dimensional version of the
algorithm has been developed, and is being applied to a variety of
astrophysical problems including the decay of supersonic MHD turbulence, the
nonlinear evolution of the MHD Rayleigh-Taylor instability, and the saturation
of the magnetorotational instability in the shearing box. Our new simulations
of the MRI represent the first time that a higher-order Godunov scheme has been
applied to this problem, providing a quantitative check on the accuracy of
previous results computed with ZEUS; the latter are found to be reliable.",0501547v1
2005-06-07,Self-Sustained Ionization and Vanishing Dead Zones in Protoplanetary Disks,"We analyze the ionization state of the magnetohydrodynamically turbulent
protoplanetary disks and propose a new mechanism of sustaining ionization.
First, we show that in the quasi-steady state of turbulence driven by
magnetorotational instability in a typical protoplanetary disk with dust
grains, the amount of energy dissipation should be sufficient for providing the
ionization energy that is required for activating magnetorotational
instability. Second, we show that in the disk with dust grains the energetic
electrons that compose electric currents in weakly ionized gas can provide
collisional ionization, depending on the actual saturation state of
magnetorotational turbulence. On the other hand, we show that in the
protoplanetary disks with the reduced effect of dust grains, the turbulent
motion can homogenize the ionization degree, leading to the activation of
magnetorotational instability even in the absence of other ionization
processes. The results in this Letter indicate that most of the regions in
protoplanetary disks remain magnetically active, and we thus require a change
in the theoretical modeling of planet formation.",0506131v2
2006-02-13,Properties of localized protons in neutron star matter for realistic nuclear models,"We study the localization of protons in the core of neutron stars for ten
realistic nuclear models that share a common behaviour of nuclear symmetry
energy which saturates and eventually decreases at high densities. This results
in the low proton fraction of beta-stable neutron star matter. Protons form a
small admixture in the neutron star core, which is localized at sufficiently
high densities. For every model we calculate the density $n_{loc}$ above which
the localization effect is present. Our results indicate that localization
occurs at densities above $0.5-1.0 fm^{-3}$. The phase with localized protons
occupies a spherical shell or a core region inside neutron stars which contains
significant fraction of all nucleons. Proton localization is of great
importance for astrophysical properties of neutron stars as it strongly affects
transport coefficients of neutron star matter and can produce spontaneous
magnetization in neutron stars.",0602281v1
2006-02-15,Phase speed of electrostatic waves: The critical parameter for efficient electron surfing acceleration,"Particle acceleration by means of non-linear plasma wave interactions is of
great topical interest. Accordingly, in this paper we focus on the electron
surfing process. Self-consistent kinetic simulations, using both relativistic
Vlasov and PIC (Particle In Cell) approaches, show here that electrons can be
accelerated to highly relativistic energies (up to 100 m_e c^2) if the phase
speed of the electrostatic wave is mildly relativistic (0.6c to 0.9c for the
magnetic field strengths considered). The acceleration is strong because of
relativistic stabilisation of the nonlinearly saturated electrostatic wave,
seen in both relativistic Vlasov and PIC simulations. An inverse power law
momentum distribution can arise for the most strongly accelerated electrons.
These results are of relevance to observed rapid changes in the radio
synchrotron emission intensities from microquasars, gamma ray bursts and other
astrophysical objects that require rapid acceleration mechanisms for electrons.",0602337v1
2006-08-17,A weakly nonlinear analysis of the magnetorotational instability in a model channel flow,"We show by means of a perturbative weakly nonlinear analysis that the
axisymmetric magnetorotational instability (MRI) of a viscous, resistive,
incompressible rotating shear flow in a thin channel gives rise to a real
Ginzburg-Landau equation for the disturbance amplitude. For small magnetic
Prandtl number (${\cal P}_{\rm m}$), the saturation amplitude is $\propto
\sqrt{{\cal P}_{\rm m}}$ and the resulting momentum transport scales as ${\cal
R}^{-1}$, where $\cal R$ is the {\em hydrodynamic} Reynolds number. Simplifying
assumptions, such as linear shear base flow, mathematically expedient boundary
conditions and continuous spectrum of the vertical linear modes, are used to
facilitate this analysis. The asymptotic results are shown to comply with
numerical calculations using a spectral code. They suggest that the transport
due to the nonlinearly developed MRI may be very small in experimental setups
with ${\cal P}_{\rm m} \ll 1$.",0608374v3
2006-11-24,An in-depth study of the pre-polar candidate WX LMi,"Optical photometry, spectroscopy and XMM-Newton ultraviolet and X-ray
observations with full phase coverage are used for an in-depth study of WXLMi,
a system formerly termed as a low-accretion rate polar. We find a constant low
mass accretion rate, M_dot ~ 1.5e-13 M_sun/yr, a peculiar accretion geometry
with one spot not being accessible via Roche-lobe overflow, a low temperature
of the white dwarf, Teff < 8000 K and the secondary likely being Roche-lobe
underfilling. All this lends further support to the changed view on WXLMi and
related systems as detached binaries, i.e. magnetic post-common envelope
binaries without significant Roche-lobe overflow in the past. The transfer rate
determined here is compatible with accretion from a stellar wind. We use
cyclotron spectroscopy to determine the accretion geometry and to constrain the
plasma temperatures. Both, cyclotron spectroscopy and X-ray plasma diagnostics
reveal low plasma temperatures below 3 keV on both accretion spots. For the low
m_dot, high B plasma at the accretion spots in WXLMi, cyclotron cooling is
dominating thermal plasma radiation in the optical. Optical spectroscopy and
X-ray timing reveal atmospheric, chromospheric and coronal activity at the
saturation level on the dM4.5 secondary star.",0611758v1
2006-12-20,Hardness-Intensity Correlations in Magnetar Afterglows,"We explore the hardness-intensity correlations observed in several AXPs and
SGRs within the framework of a thermally emitting magnetar model. Using our
detailed atmosphere models and taking into account reprocessing of the surface
emission by the magnetosphere, we show that the hardness of the surface spectra
increases with increasing temperature and hence the changes in the effective
temperatures of the outer layers of the star alone can account for the observed
correlations. We conclude that the slow release of the heat deposited in the
deep crust during a magnetar burst naturally accounts for the spectral changes
during the afterglow. The correlations are further enhanced by changes in the
structures of the magnetic currents during or following a burst. However, the
additional hardening produced by scattering of the surface photons off the
magnetospheric charges saturates at moderate values of the scattering optical
depth.",0612561v1
1993-04-16,Conductance statistics in small insulating GaAs:Si wires at low temperature. II. Experimental study,"We have observed reproducible conductance fluctuations at low temperature in
a small GaAs:Si wire driven across the Anderson transition by the application
of a gate voltage. We analyse quantitatively the log-normal conductance
statistics in terms of truncated quantum fluctuations. Quantum fluctuations due
to small changes of the electron energy (controlled by the gate voltage) cannot
develop fully due to identified geometrical fluctuations of the resistor
network describing the hopping through the sample.
  The evolution of the fluctuations versus electron energy and magnetic field
shows that the fluctuations are non-ergodic, except in the critical insulating
region of the Anderson transition, where the localization length is larger than
the distance between Si impurities.
  The mean magnetoconductance is in good accordance with simulations based on
the Forward-Directed-Paths analysis, i.e. it saturates to $ {\rm ln} (\sigma
(H>1)/\sigma (0))\simeq 1, $ as $ \sigma (0) $ decreases over orders of
magnitude in the strongly localized regime.",9304029v1
1995-12-13,Quantum transport in a multiwalled carbon nanotube,"We report on electrical resistance measurements of an individual carbon
nanotube down to a temperature T=20 mK. The conductance exhibits a ln T
dependence and saturates at low temperature. A magnetic field applied
perpendicular to the tube axis, increases the conductance and produces
aperiodic fluctuations. The data find a global and coherent interpretation in
terms of two-dimensional weak localization and universal conductance
fluctuations in mesoscopic conductors. The dimensionality of the electronic
system is discussed in terms of the peculiar structure of carbon nanotubes.",9512106v2
1997-05-26,Tunneling into Current-Carrying Surface States of High T$_c$ Superconductors,"Theoretical results for the ab-plane tunneling conductance in the d-wave
model for high Tc superconductors are presented. The d-wave model predicts
surface bound states below the maximum gap. A sub-dominant order parameter,
stabilized by the surface, leads to a splitting of the zero-bias conductance
peak (ZBCP) in zero external field and to spontaneous surface currents. In a
magnetic field screening currents shift the quasiparticle bound state spectrum
and lead to a voltage splitting of the ZBCP that is linear in H at low fields,
and saturates at a pairbreaking critical field of order 3 Tesla. Comparisons
with recent experimental results on Cu/YBCO junctions are presented.",9705260v1
1997-07-16,New Far Infrared Vibrational Mode in Zn Doped CuGeO3,"We report on far infrared measurements on Zn and Si doped crystals of the
spin-Peierls compound CuGeO3. Zn doping has the effect of introducing several
new absorption lines, polarized in the ab-plane, between 5 and 55 cm-1. The
intensity of the absorption grows with Zn concentration but saturates above 2%
Zn. One line at 10 cm-1 loses intensity above 4K, and a second line at 20 cm-1
is absent at low temperatures but grows to peak at about 40K in agreement with
a three level model with two excited states 10 and 30 cm-1 above the ground
state. As the doping is increased these lines broaden, and a temperature
independent absorption developes over the entire range from 5 to 55 cm-1. These
features are magnetic field independent up to 16T and are absent in Si doped
samples. We suggest the new absorption is due to localized lattice modes of the
zinc ion and the surrounding GeO4 tetrahedra.",9707163v1
1999-07-10,Universal conductance fluctuations in three dimensional metallic single crystals of Si,"In this paper we report the measurement of conductance fluctuations in single
crystals of Si made metallic by heavy doping (n \approx 2-2.5n_c, n_c being
critical composition at Metal-Insulator transition). Since all dimensions (L)
of the samples are much larger than the electron phase coherent length L_\phi
(L/L_\phi \sim 10^3), our system is truly three dimensional. Temperature and
magnetic field dependence of noise strongly indicate the universal conductance
fluctuations (UCF) as predominant source of the observed magnitude of noise.
Conductance fluctuations within a single phase coherent region of L_\phi^3 was
found to be saturated at <(\delta G_\phi)^2> \approx (e^2/h)^2. An accurate
knowledge of the level of disorder, enables us to calculate the change in
conductance \delta G_1 due to movement of a single scatterer as \delta G_1 \sim
e^2/h, which is \sim 2 orders of magnitude higher than its theoretically
expected value in 3D systems.",9907158v2
1999-08-13,Resistive upper critical fields and irreversibility lines of optimally-doped high-T_c cuprates,"We present the resistively-determined upper critical field H^{\rho}_{c2}(T)
and the irreversibility lines H^{\rho}_{irr}(T) of various high-T_c cuprates,
deduced from measurements in 61-T pulsed magnetic fields applied parallel to
the c-axis. The SHAPE of both H^{\rho}_{c2}(T) and H^{\rho}_{irr}(T) depends
monotonically on the anisotropy of the material and none of the samples show
saturation of H^{\rho}(T) at low temperatures. The anomalous positive
curvature, d^2 H^{\rho}/dT^2 > 0, is the strongest in materials with the
largest normal-state anisotropy, regardless of whether anisotropy is varied by
changing the carrier concentration or by comparing a variety of optimally-doped
compounds.",9908190v1
1999-12-10,High-Field Quasiparticle Tunneling in Bi_2Sr_2CaCu_2O_8+delta: Negative Magnetoresistance in the Superconducting State,"We report on the c-axis resistivity rho_c(H) in Bi_2Sr_2CaCu_2O_{8+\delta}
that peaks in quasi-static magnetic fields up to 60 T. By suppressing the
Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity
\sigma_c (H), we find that the negative slope of \rho_c(H) above the peak is
due to quasiparticle tunneling conductivity \sigma_q(H) across the CuO_2 layers
below H_{c2}. At high fields (a) \sigma_q(H) grows linearly with H, and (b)
\rho_c(T) tends to saturate (sigma_c \neq 0) as T->0, consistent with the
scattering at the nodes of the d-gap. A superlinear sigma_q(H) marks the normal
state above T_c.",9912194v1
2000-09-08,Ferromagnetism in the Two-Dimensional Periodic Anderson Model,"Using the constrained-path Monte Carlo method, we studied the magnetic
properties of the two-dimensional periodic Anderson model for electron fillings
between 1/4 and 1/2. We also derived two effective low energy theories to
assist in interpreting the numerical results. For 1/4 filling we found that the
system can be a Mott or a charge transfer insulator, depending on the relative
values of the Coulomb interaction and the charge transfer gap between the two
non-interacting bands. The insulator may be a paramagnet or antiferromagnet. We
concentrated on the effect of electron doping on these insulating phases. Upon
doping we obtained a partially saturated ferromagnetic phase for low
concentrations of conduction electrons. If the system were a charge transfer
insulator, we would find that the ferromagnetism is induced by the well-known
RKKY interaction. However, we found a novel correlated hopping mechanism
inducing the ferromagnetism in the region where the non-doped system is a Mott
insulator. Our regions of ferromagnetism spanned a much smaller doping range
than suggested by recent slave boson and dynamical mean field theory
calculations, but they were consistent with that obtained by density matrix
renormalization group calculations of the one-dimensional periodic Anderson
model.",0009128v1
2000-11-06,Quantum Hall Ferromagnetism in a Two-Dimensional Electron System,"Experiments on a nearly spin degenerate two-dimensional electron system
reveals unusual hysteretic and relaxational transport in the fractional quantum
Hall effect regime. The transition between the spin-polarized (with fill
fraction $\nu = 1/3$) and spin-unpolarized ($\nu = 2/5$) states is accompanied
by a complicated series of hysteresis loops reminiscent of a classical
ferromagnet. In correlation with the hysteresis, magnetoresistance can either
grow or decay logarithmically in time with remarkable persistence and does not
saturate. In contrast to the established models of relaxation, the relaxation
rate exhibits an anomalous divergence as temperature is reduced. These results
indicate the presence of novel two-dimensional ferromagnetism with a
complicated magnetic domain dynamic.",0011081v1
2000-11-29,Level and Eigenfunction Statistics in Billiards with Surface Scattering,"Statistical properties of billiards with diffusive boundary scattering are
investigated by means of the supersymmetric sigma-model in a formulation
appropriate for chaotic ballistic systems. We study level statistics,
parametric level statistics, and properties of electron wavefunctions. In the
universal regime, our results reproduce conclusions of the random matrix
theory, while beyond this regime we obtain a variety of system-specific results
determined by the classical dynamics in the billiard. Most notably, we find
that level correlations do not vanish at arbitrary separation between energy
levels, or if measured at arbitrarily large difference of magnetic fields.
Saturation of the level number variance indicates strong rigidity of the
spectrum. To study spatial correlations of wavefunction amplitudes, we
reanalyze and refine derivation of the ballistic version of the sigma-model.
This allows us to obtain a proper matching of universal short-scale
correlations with system-specific ones.",0011498v2
2001-06-28,Field-Induced gap due to four-spin exchange in a spin ladder,"The effect of the four-spin cyclic exchange interaction at each plaquette in
the $S=1/2$ two-leg spin ladder is investigated at T=0, especially focusing on
the field-induced gap. The strong rung coupling approximation suggests that it
yields a plateau at half of the saturation moment ($m=1/2$) in the
magnetization curve, which corresponds to a field-induced spin gap with a
spontaneous breaking of the translational symmetry. A precise phase diagram at
$m=1/2$ is also presented based on the level spectroscopy analysis of the
numerical data obtained by Lanczos method. The boundary between the gapless and
plateau phases is confirmed to be of the Kosterlitz-Thouless (KT) universality
class.",0106584v1
2001-12-07,Proton Spin Relaxation Induced by Quantum Tunneling in Fe8 Molecular Nanomagnet,"The spin-lattice relaxation rate $T_{1}^{-1}$ and NMR spectra of $^1$H in
single crystal molecular magnets of Fe8 have been measured down to 15 mK. The
relaxation rate $T_1^{-1}$ shows a strong temperature dependence down to 400
mK. The relaxation is well explained in terms of the thermal transition of the
iron state between the discreet energy levels of the total spin S=10. The
relaxation time $T_1$ becomes temperature independent below 300 mK and is
longer than 100 s. In this temperature region stepwise recovery of the
$^1$H-NMR signal after saturation was observed depending on the return field of
the sweep field. This phenomenon is attributed to resonant quantum tunneling at
the fields where levels cross and is discussed in terms of the Landau-Zener
transition.",0112111v1
2002-02-07,Ferromagnetism in the Kondo-lattice model,"We propose a modified RKKY-technique to evaluate the magnetic properties of
the ferromagnetic Kondo-lattice model. Together with a previously developed
selfenergy approach to the conduction electron part of the model we get a
closed system of equations which can be solved self-consistently.
Ferromagnetism appears for relatively low electron (hole) densities, while it
is excluded around half-filling ($n=1$). For small $J$ conventional RKKY ($\sim
J^2$) is reproduced; however, with strong deviations already for very moderate
exchange couplings. For not too small $n$ a critical $J_c$ is needed to produce
ferromagnetism with a finite Curie temperature $T_{\textrm{C}}$, which
increases with $J$, then running into a kind of saturation, in order to fall
off again and disappearing above an upper critical exchange $J$.",0202114v3
2003-01-08,Kondo effect in underdoped n-type superconductors,"We present high-field magnetotransport properties of high-quality
single-crystalline thin films of heavily underdoped nonsuperconducting
(La,Ce)2CuO4, (Pr,Ce)2CuO4, and (Nd,Ce)2CuO4. All three materials show
identical behavior. They are metallic at high temperatures and show an
insulating upturn at low temperatures. The insulating upturn has a log T
dependence, but saturates toward the lowest temperatures. Notably, the
insulating upturn tends to be suppressed by applying magnetic fields. This
negative magnetoresistance has a log B dependence, and its anisotropy shows non
simple behavior. We discuss these findings from the viewpoints of Kondo
scattering and also two-dimensional weak localization, and demonstrate Kondo
scattering as a more plausible explanation. The Kondo scatters are identified
as Cu2+ spins in the CuO2 planes.",0301090v1
2003-02-12,Measurement of positive and negative scattering lengths in a Fermi gas of atoms,"An exotic superfluid phase has been predicted for an ultracold gas of
fermionic atoms. This phase requires strong attractive interactions in the gas,
or correspondingly atoms with a large, negative s-wave scattering length. Here
we report on progress toward realizing this predicted superfluid phase. We
present measurements of both large positive and large negative scattering
lengths in a quantum degenerate Fermi gas of atoms. Starting with a
two-component gas that has been evaporatively cooled to quantum degeneracy, we
create controllable, strong interactions between the atoms using a
magnetic-field Feshbach resonance. We then employ a novel rf spectroscopy
technique to directly measure the mean-field interaction energy, which is
proportional to the s-wave scattering length. Near the peak of the resonance we
observe a saturation of the interaction energy; it is in this strongly
interacting regime that superfluidity is predicted to occur. We have also
observed anisotropic expansion of the gas, which has recently been suggested as
a signature of superfluidity. However, we find that this can be attributed to a
purely collisional effect.",0302246v1
2003-03-12,Fundamental Curie temperature limit in ferromagnetic GaMnAs,"We provide experimental evidence that the upper limit of ~110 K commonly
observed for the Curie temperature T_C of Ga(1-x)Mn(x)As is caused by the
Fermi-level-induced hole saturation. Ion channeling, electrical and
magnetization measurements on a series of Ga(1-x-y)Mn(x)Be(y)As layers show a
dramatic increase of the concentration of Mn interstitials accompanied by a
reduction of T_C with increasing Be concentration, while the free hole
concentration remains relatively constant at ~5x10^20 cm^-3. These results
indicate that the concentrations of free holes and ferromagnetically active Mn
spins are governed by the position of the Fermi level, which controls the
formation energy of compensating interstitial Mn donors.",0303217v1
2003-04-29,Investigation of the Jahn-Teller Transition in TiF3 using Density Functional Theory,"We use first principles density functional theory to calculate electronic and
magnetic properties of TiF3 using the full potential linearized augmented plane
wave method. The LDA approximation predicts a fully saturated ferromagnetic
metal and finds degenerate energy minima for high and low symmetry structures.
The experimentally observed Jahn-Teller phase transition at Tc=370K can not be
driven by the electron-phonon interaction alone, which is usually described
accurately by LDA.
  Electron correlations beyond LDA are essential to lift the degeneracy of the
singly occupied Ti t2g orbital. Although the on-site Coulomb correlations are
important, the direction of the t2g-level splitting is determined by the
dipole-dipole interactions. The LDA+U functional predicts an aniferromagnetic
insulator with an orbitally ordered ground state. The input parameters U=8.1 eV
and J=0.9 eV for the Ti 3d orbital were found by varying the total charge on
the TiF$_6^{2-}$ ion using the molecular NRLMOL code. We estimate the
Heisenberg exchange constant for spin-1/2 on a cubic lattice to be
approximately 24 K. The symmetry lowering energy in LDA+U is about 900 K per
TiF3 formula unit.",0304667v2
2003-05-29,Stripes and the (Cu)13-BEC model,"The (Cu)13-BEC model of high-temperature superconductivity was previously
shown to account for many of the principal thermodynamic and electronic
properties of the superconducting cuprates. Here I show that this model is also
able to account for many of the key characteristics of the coupled CDW and SDW
orders in these compounds. These include the general coexistence of metallic
parallel stripes with superconductivity, the well-known linear relationship
between the incommensurability of the SDW-induced IC magnetic peaks and the
dopant concentration, as well as the saturation of this incommensurabilty at a
value of about 1/8 for doping greater than 1/8. The model also provides a
natural explanation for the celebrated 1/8-anomaly in LSCO and LBCO. It is also
able to account for the severe suppression of the superconductivity in LNSCO at
all doping levels and for the variations in the properties of LBSCO, at a fixed
hole doping of 1/8, as its crystal structure is changed. Furthermore, the
(Cu)13-BEC model is also consistent with many of the characteristics of the SDW
orders in Y123. Most importantly, scanning tunneling microscopy results on
Bi2212 appear to provide a direct validation of the CDW order predicted by the
model.",0305672v1
2003-07-01,Effect of two bands on critical fields in MgB2 thin films with various resistivity values,"Upper critical fields of four MgB2 thin films were measured up to 28 Tesla at
Grenoble High Magnetic Field Laboratory. The films were grown by Pulsed Laser
Deposition and showed critical temperatures ranging between 29.5 and 38.8 K and
resistivities at 40 K varying from 5 to 50 mWcm. The critical fields in the
perpendicular direction turned out to be in the 13-24 T range while they were
estimated to be in 42-57 T the range in ab-planes. In contrast to the
prediction of the BCS theory, we did not observe any saturation at low
temperatures: a linear temperature dependence is exhibited even at lowest
temperatures at which we made the measurements. Moreover, the critical field
values seemed not to depend on the normal state resistivity value. In this
paper, we analyze these data considering the multiband nature of
superconductivity in MgB2 We will show how the scattering mechanisms that
determine critical fields and resistivity can be different.",0307013v2
2004-01-07,Large positive magneto-resistance in high mobility 2D electron gas : interplay of short and long range disorder,"We have observed a large positive quasi-classical magneto-resistance (MR) in
a high mobility 2D electron gas in AlGaAs/GaAs heterostructure. The
magneto-resistance is non-saturating and increases with magnetic field as
$\rho_{xx}\sim B^{\alpha} (\alpha=0.9-1.2)$. In antidot lattices a
non-monotonic MR is observed. We show that in both cases this MR can be
qualitatively described in terms of the theory recently advanced by Polyakov et
al (PRB, 64, 205306 (2001)). Their prediction is that such behavior as we
observe may be the consequence of a concurrent existence of short and long
range scattering potentials.",0401085v2
2004-04-08,"""Spin-Flop"" Transition and Anisotropic Magnetoresistance in Pr_{1.3-x}La_{0.7}Ce_{x}CuO_{4}: Unexpectedly Strong Spin-Charge Coupling in Electron-Doped Cuprates","We use transport and neutron-scattering measurements to show that a
magnetic-field-induced transition from noncollinear to collinear spin
arrangement in adjacent CuO_{2} planes of lightly electron-doped
Pr_{1.3-x}La_{0.7}Ce_{x}CuO_{4} (x=0.01) crystals affects significantly both
the in-plane and out-of-plane resistivity. In the high-field collinear state,
the magnetoresistance (MR) does not saturate, but exhibits an intriguing
four-fold-symmetric angular dependence, oscillating from being positive at
B//[100] to being negative at B//[110]. The observed MR of more than 30% at low
temperatures induced by a modest modification of the spin structure indicates
an unexpectedly strong spin-charge coupling in electron-doped cuprates.",0404196v1
2004-04-30,Metal-Insulator-Like Behavior in Semimetallic Bismuth and Graphite,"When high quality bismuth or graphite crystals are placed in a magnetic field
directed along the c-axis (trigonal axis for bismuth) and the temperature is
lowered, the resistance increases as it does in an insulator but then
saturates. We show that the combination of unusual features specific to
semimetals, i.e., low carrier density, small effective mass, high purity, and
an equal number of electrons and holes (compensation), gives rise to a unique
ordering and spacing of three characteristic energy scales, which not only is
specific to semimetals but which concomitantly provides a wide window for the
observation of apparent field induced metal-insulator behavior. Using
magnetotransport and Hall measurements, the details of this unusual behavior
are captured with a conventional multi-band model, thus confirming the
occupation by semimetals of a unique niche between conventional metals and
semiconductors.",0404725v2
2004-05-26,Vortex in Maxwell-Chern-Simons models coupled to external backgrounds,"We consider Maxwell-Chern-Simons models involving different non-minimal
coupling terms to a non relativistic massive scalar and further coupled to an
external uniform background charge. We study how these models can be
constrained to support static radially symmetric vortex configurations
saturating the lower bound for the energy. Models involving Zeeman-type
coupling support such vortices provided the potential has a ""symmetry breaking""
form and a relation between parameters holds. In models where minimal coupling
is supplemented by magnetic and electric field dependant coupling terms, non
trivial vortex configurations minimizing the energy occur only when a non
linear potential is introduced. The corresponding vortices are studied
numerically",0405605v1
2004-07-02,Spin Polarization Dependence of the Coulomb Drag at Large $r_{s}$,"We find that the temperature dependence of the drag resistivity ($\rho_{D}$)
between two dilute two-dimensional hole systems exhibits an unusual dependence
upon spin polarization. Near the apparent metal-insulator transition, the
temperature dependence of the drag, given by $T^{\alpha}$, weakens with the
application of a parallel magnetic field ($B_{||}$), with $\alpha$ saturating
at half its zero field value for $B_{||} > B^{*}$, where $B^{*}$ is the
polarization field. Furthermore, we find that $\alpha$ is roughly 2 at the
parallel field induced metal-insulator transition, and that the temperature
dependence of $\rho_{D}/T^{2}$ at different $B_{||}$ looks strikingly similar
to that found in the single layer resistivity. In contrast, at higher
densities, far from the zero field transition, the temperature dependence of
the drag is roughly independent of spin polarization, with $\alpha$ remaining
close to 2, as expected from a simple Fermi liquid picture.",0407049v1
2004-11-08,Hysteresis in an Ising model with mobile bonds,"Hysteresis is studied in a disordered Ising model in which diffusion of
antiferromagnetic bonds is allowed in addition to spin flips. Saturation
behavior changes to a figure-eight loop when diffusion is introduced. The upper
and lower fields delimiting the figure-eight are determined by the Hamiltonian,
while its surface and the crossing point depend on the temperature and details
of the dynamics. The main avalanche is associated with the disappearance of
hidden order. Some experimental observations of figure-eight anomalies are
discussed. It is argued they are a signal of a transient rearrangement of
domain couplings, characteristic of amorphous and/or magnetically soft samples,
and similar to evolution of kinetic glasses.",0411187v1
2004-11-12,Hysteresis and avalanches in the T=0 random-field Ising model with 2-spin-flip dynamics,"We study the non-equilibrium behavior of the three-dimensional Gaussian
random-field Ising model at T=0 in the presence of a uniform external field
using a 2-spin-flip dynamics. The deterministic, history-dependent evolution of
the system is compared with the one obtained with the standard 1-spin-flip
dynamics used in previous studies of the model. The change in the dynamics
yields a significant suppression of coercivity, but the distribution of
avalanches (in number and size) stays remarkably similar, except for the
largest ones that are responsible for the jump in the saturation magnetization
curve at low disorder in the thermodynamic limit. By performing a finite-size
scaling study, we find strong evidence that the change in the dynamics does not
modify the universality class of the disorder-induced phase transition.",0411330v1
2005-04-21,"Quantitative analysis of proximity effect in $Nb/Co_{60}Fe_{40}$, Nb/Ni, and $Nb/Cu_{40}Ni_{60}$ bilayers","We have studied the behavior of the superconducting critical temperature Tc
in $Nb/Co_{60}Fe_{40}$, Nb/Ni, and $Nb/Cu_{40}Ni_{60}$ bilayers as a function
of the thickness of each ferromagnetic metal layer. The Tc s of three sets of
bilayers exhibit non-monotonic behavior as a function of each ferromagnetic
metal thickness. Employing the quantitative analysis based on Usadel formalism
of the effect of the exchange energy, we observed that the Tc behavior of
$Nb/Co_{60}Fe_{40}$ bilayers is in good agreement with the theoretical values
over the entire range of the data. On the other hand, the Tc s of Nb/Ni and
$Nb/Cu_{40}Ni_{60}$ bilayers show a higher value in the small thickness regime
than the theoretical prediction obtained from the calculation, which matches
the dip position and the saturation value of Tc in the large thickness limit.
This discrepancy is probably due to the weakened magnetic properties of Ni and
$Cu_{40}Ni_{60}$ when they are thin. We discuss the values of our fitting
parameters and its implication on the validity of the current Usadel formalism
of the effect of the exchange energy.",0504543v1
2005-05-02,"Influence of annealing parameters on the ferromagnetic properties of optimally passivated (Ga,Mn)As epilayers","The influence of annealing parameters - temperature and time - on the
magnetic properties of As-capped (Ga,Mn)As epitaxial thin films have been
investigated. The dependence of the transition temperature (Tc) on annealing
time marks out two regions. The Tc peak behavior, characteristic of the first
region, is more pronounced for thick samples, while for the second
(`saturated') region the effect of the annealing time is more pronounced for
thin samples. A right choice of the passivation medium, growth conditions along
with optimal annealing parameters routinely yield Tc-values of ~ 150 K and
above, regardless of the thickness of the epilayers.",0505040v1
2005-06-03,Singlet-triplet decoherence due to nuclear spins in a double quantum dot,"We have evaluated hyperfine-induced electron spin dynamics for two electrons
confined to a double quantum dot. Our quantum solution accounts for decay of a
singlet-triplet correlator even in the presence of a fully static nuclear spin
system, with no ensemble averaging over initial conditions. In contrast to an
earlier semiclassical calculation, which neglects the exchange interaction, we
find that the singlet-triplet correlator shows a long-time saturation value
that differs from 1/2, even in the presence of a strong magnetic field.
Furthermore, we find that the form of the long-time decay undergoes a
transition from a rapid Gaussian to a slow power law ($\sim 1/t^{3/2}$) when
the exchange interaction becomes nonzero and the singlet-triplet correlator
acquires a phase shift given by a universal (parameter independent) value of
$3\pi/4$ at long times. The oscillation frequency and time-dependent phase
shift of the singlet-triplet correlator can be used to perform a precision
measurement of the exchange interaction and Overhauser field fluctuations in an
experimentally accessible system. We also address the effect of orbital
dephasing on singlet-triplet decoherence, and find that there is an optimal
operating point where orbital dephasing becomes negligible.",0506090v1
2005-06-15,Sign change of the Grueneisen parameter and magnetocaloric effect near quantum critical points,"We consider the Grueneisen parameter and the magnetocaloric effect near a
pressure and magnetic field controlled quantum critical point, respectively.
Generically, the Grueneisen parameter (and the thermal expansion) displays a
characteristic sign change close to the quantum-critical point signaling an
accumulation of entropy. If the quantum critical point is the endpoint of a
line of finite temperature phase transitions, T_c \propto (p_c-p)^Psi, then we
obtain for p<p_c, (1) a characteristic increase \Gamma \sim T^{-1/(\nu z)} of
the Grueneisen parameter Gamma for T>T_c, (2) a sign change in the Ginzburg
regime of the classical transition, (3) possibly a peak at T_c, (4) a second
increase Gamma \sim -T^{-1/(nu z)} below T_c for systems above the upper
critical dimension and (5) a saturation of Gamma \propto 1/(p_c-p). We argue
that due to the characteristic divergencies and sign changes the thermal
expansion, the Grueneisen parameter and magnetocaloric effect are excellent
tools to detect and identify putative quantum critical points.",0506336v2
2005-06-27,Ferromagnetism of the Hubbard Model at Strong Coupling in the Hartree-Fock Approximation,"As a contribution to the study of Hartree-Fock theory we prove rigorously
that the Hartree-Fock approximation to the ground state of the d-dimensional
Hubbard model leads to saturated ferromagnetism when the particle density (more
precisely, the chemical potential mu) is small and the coupling constant U is
large, but finite. This ferromagnetism contradicts the known fact that there is
no magnetization at low density, for any U, and thus shows that HF theory is
wrong in this case. As in the usual Hartree-Fock theory we restrict attention
to Slater determinants that are eigenvectors of the z-component of the total
spin, {S}_z = sum_x n_{x,\uparrow} - n_{x,\downarrow}, and we find that the
choice 2{S}_z = N = particle number gives the lowest energy at fixed 0 < mu <
4d.",0506695v2
2006-01-09,Muon-spin-rotation measurements of the penetration depth in Li_2Pd_3B,"Measurements of the magnetic field penetration depth $\lambda$ in the ternary
boride superconductor Li$_2$Pd$_3$B ($T_c\simeq7.3$ K) have been carried out by
means of muon-spin rotation ($\mu$SR). The absolute values of $\lambda$, the
Ginzburg-Landau parameter $\kappa$, and the first $H_{c1}$ and the second
$H_{c2}$ critical fields at T=0 obtained from $\mu$SR were found to be
$\lambda(0)=252(2)$ nm, $\kappa(0)=27(1)$, $\mu_0H_{c1}(0)=9.5(1)$ mT, and
$\mu_0H_{c2}(0)=3.66(8)$ T, respectively. The zero-temperature value of the
superconducting gap $\Delta_0=$1.31(3) meV was found, corresponding to the
ratio $2\Delta_0/k_BT_c=4.0(1)$. At low temperatures $\lambda(T)$ saturates and
becomes constant below $T\simeq 0.2T_c$, in agreement with what is expected for
s-wave BCS superconductors. Our results suggest that Li$_2$Pd$_3$B is a s-wave
BCS superconductor with the only one isotropic energy gap.",0601156v2
2006-04-28,Linear independence of localized magnon states,"At the magnetic saturation field, certain frustrated lattices have a class of
states known as ""localized multi-magnon states"" as exact ground states. The
number of these states scales exponentially with the number $N$ of spins and
hence they have a finite entropy also in the thermodynamic limit $N\to \infty$
provided they are sufficiently linearly independent. In this article we present
rigorous results concerning the linear dependence or independence of localized
magnon states and investigate special examples. For large classes of spin
lattices including what we called the orthogonal type and the isolated type as
well as the kagom\'{e}, the checkerboard and the star lattice we have proven
linear independence of all localized multi-magnon states. On the other hand the
pyrochlore lattice provides an example of a spin lattice having localized
multi-magnon states with considerable linear dependence.",0604649v1
2006-04-29,Electron and boson clusters in confined geometries: symmetry breaking in quantum dots and harmonic traps,"We discuss the formation of crystalline electron clusters in semiconductor
quantum dots and of crystalline patterns of neutral bosons in harmonic traps.
In a first example, we use calculations for two electrons in an elliptic
quantum dot to show that the electrons can localize and form a molecular dimer.
The calculated singlet-triplet splitting (J) as a function of the magnetic
field (B) agrees with cotunneling measurements, with its behavior reflecting
the effective dissociation of the dimer for large B. Knowledge of the dot shape
and of J(B) allows determination of the degree of entanglement. In a second
example, we study strongly repelling neutral bosons in two-dimensional harmonic
traps. Going beyond the Gross-Pitaevskii (GP) mean-field approximation, we show
that bosons can localize and form polygonal-ring-like crystalline patterns. The
total energy of the crystalline phase saturates in contrast to the GP solution,
and its spatial extent becomes smaller than that of the GP condensate.",0605012v1
2006-05-17,Noninvasive measurements of gas exchange in a three-dimensional fluidized bed using hyperpolarized 129Xe NMR,"We present a novel NMR technique that provides a non-invasive, direct
measurement of gas exchange in a three-dimensional gas-fluidized bed of solid
particles. The NMR spectrum of hyperpolarized 129Xe gas in an Al2O3 particle
bed displays three resolved peaks corresponding to xenon in bubbles, the
interstitial spaces (emulsion), and adsorbed on particles. Modified NMR
exchange and saturation-recovery sequences, together with data analysis based
on an exchange-coupled set of Bloch equations, yield gas exchange rate
constants between the emulsion and adsorbed phases, and between the bubble and
emulsion phases. The results are in approximate agreement previously unverified
predictions from well-known models of fluidized bed behavior. Incorporation of
NMR imaging methodologies would straightforwardly allow similar measurements on
a spatially-resolved basis.",0605436v1
2006-06-18,In-plane hole density in Ca(0.1)La(0.9)Ba(1.65)La(0.35)Cu(3)O(y) ; nuclear resonance study over the full doping range,"We report in-plane Cu(63) Nuclear Magnetic Resonance measurements for a
series of fully enriched Ca(0.1)La(0.9)Ba(1.65)La(0.35)Cu(3)O(y) powder
samples, which belong to the YBCO family, but the doping could vary from very
underdoped to extremely overdoped. From these measurements we determine the
average nuclear quadrupole resonance frequency \nu_Q, and its second moment
\Delta(\nu_Q), both set by the in-plane hole density, n, as a function of
oxygen level, y. We find that in the overdoped side n is saturated, but
\Delta(\nu_Q) rapidly increases with increasing y. The relevance of these
results to the increasing penetration depth in overdoped cuprates is discussed.",0606475v1
2006-10-23,Dynamical polarization of graphene at finite doping,"The polarization of graphene is calculated exactly within the random phase
approximation for arbitrary frequency, wave vector, and doping. At finite
doping, the static susceptibility saturates to a constant value for low
momenta. At $q=2 k_{F}$ it has a discontinuity only in the second derivative.
In the presence of a charged impurity this results in Friedel oscillations
which decay with the same power law as the Thomas Fermi contribution, the
latter being always dominant. The spin density oscillations in the presence of
a magnetic impurity are also calculated. The dynamical polarization for low $q$
and arbitrary $\omega $ is employed to calculate the dispersion relation and
the decay rate of plasmons and acoustic phonons as a function of doping. The
low screening of graphene, combined with the absence of a gap, leads to a
significant stiffening of the longitudinal acoustic lattice vibrations.",0610630v2
2006-12-19,Magnetothermal transport in the spin-1/2 chains of copper pyrazine dinitrate,"We present experiments on the thermal transport in the spin-1/2 chain
compound copper pyrazine dinitrate Cu(C_4 H_4 N_2)(NO_3)_2. The heat
conductivity shows a surprisingly strong dependence on the applied magnetic
field B, characterized at low temperatures by two main features. The first one
appearing at low B is a characteristic dip located at mu_B B ~ k_B T, that may
arise from Umklapp scattering. The second one is a plateau-like feature in the
quantum critical regime, mu_B |B-B_c| < k_B T, where B_c is the saturation
field at T=0. The latter feature clearly points towards a momentum and field
independent mean free path of the spin excitations, contrary to theoretical
expectations.",0612486v2
2007-01-01,Exact Thermodynamics of Pairing and Charge-spin Separation Crossovers in Small Hubbard Nanoclusters,"The exact numerical diagonalization and thermodynamics in an ensemble of
small Hubbard clusters in the ground state and finite temperatures reveal
intriguing insights into the nascent charge and spin pairings, Bose
condensation and ferromagnetism in nanoclusters. The phase diagram off half
filling strongly suggests the existence of subsequent transitions from electron
pairing into unsaturated and saturated ferromagnetic Mott-Hubbard like
insulators, driven by electron repulsion. Rigorous criteria for the existence
of quantum critical points in the ground state and corresponding crossovers at
finite temperatures are formulated. The phase diagram for 2x4-site clusters
illustrates how these features are scaled with cluster size. The phase
separation and electron pairing, monitored by a magnetic field and electron
doping, surprisingly resemble phase diagrams in the family of doped high Tc
cuprates.",0701022v1
2001-02-28,Implications of the r-mode instability of rotating relativistic stars,"Several recent surprises appear dramatically to have improved the likelihood
that the spin of rapidly rotating, newly formed neutron stars (and, possibly,
of old stars spun up by accretion) is limited by a nonaxisymmetric instability
driven by gravitational waves. Except for the earliest part of the spin-down,
the axial l=m=2 mode (an r-mode) dominates the instability, and the emitted
waves may be observable by detectors with the sensitivity of LIGO II. A review
of these hopeful results is followed by a discussion of constraints on the
instability set by dissipative mechanisms, including viscosity, nonlinear
saturation, and energy loss to a magnetic field driven by differential
rotation.",0102114v2
1995-04-06,Static Quantities of the W bosons in the MSSM,"I discuss the static quantities of the W boson, magnetic dipole and electric
quadrupole moments, in the context of the minimal supersymmetric standard
model, in which supersymmetry is broken by soft terms $A_o,\, m_o,\, M_{1/2}$.
Following a renormalization group analysis it is found that the supersymmetric
values of $\Delta k_{\gamma}$ and $\Delta Q_{\gamma}$ can be largely different,
in some cases, from the standard model predictions but of the same order of
magnitude for values of \quad $A_0,m_0,M_{1/2} \leq {\cal O}(1 TeV) $.
Therefore possible supersymmetric structure can be probed provided the accuracy
of measurements for $\Delta k_{\gamma}$, $\Delta Q_{\gamma}$ reaches
$10^{-2}-10^{-3}$ and hence hard to be detected at LEP2. In cases where
$M_{1/2} \ll A_0,m_0 $, the charginos and neutralinos may give substantial
contributions saturating the LEP2 sensitivity limits. This occurs when their
masses $m_{\tilde C},m_{\tilde Z}$ turn out to be both light satisfying
$m_{\tilde C}+m_{\tilde Z} \simeq M_W $. However these extreme cases are
perturbatively untrustworthy and besides unnatural for they occupy a small
region in the parameter space.",9504240v1
2000-06-15,Deconfining by Winding: The Magnetic Monopole Vacua at High Temperatures,"Characterizing the vacuum of a thermalized SU(3) Yang-Mills theory in the
dual Ginzburg-Landau description, the possibility of topologically nontrivial,
classical monopole fields in the deconfining phase is explored. These fields
are assumed to be Bogomoln'yi-Prasad-Sommerfield (BPS) saturated solutions
along the compact, euclidean time dimension. A corresponding, gauge invariant
monopole interaction is constructed. The model passes first tests. In
particular, a reasonable value for the critical temperature is obtained, and
the partial persistence of nonperturbative features in the deconfining phase of
SU(3) Yang-Mills theory, as it is measured on the lattice, follows naturally.",0006163v3
2001-04-19,Deconfining by Winding,"A model for the quantum effective description of the vacuum structure of
thermalized SU(3) Yang-Mills theory is proposed. The model is based on Abelian
projection leading to a Ginzburg-Landau theory for the magnetic sector. The
possibility of topologically non-trivial, effective monopole fields in the
deconfining phase is explored. These fields are assumed to be
Bogomol'nyi-Prasad-Sommerfield saturated solutions along the compact, euclidean
time dimension. Accordingly, a gauge invariant interaction for the monopole
fields is constructed.
  Motivated by the corresponding lattice results the vacuum dynamics is assumed
to be dominated by the monopole fields. A reasonable value for the critical
temperature is obtained, and the partial persistence of non-perturbative
features in the deconfining phase of SU(3) Yang-Mills theory, as it is measured
on the lattice, follows naturally.",0104188v2
2005-05-02,VA\tilde V correlator within the instanton vacuum model,"The correlator of vector and nonsinglet axial-vector currents in the external
electromagnetic field is calculated within the instanton liquid model of QCD
vacuum. In general the correlator has two Lorentz structures: longitudinal w_L
and transversal w_T with respect to axial-vector index. Within the instanton
model the saturation of the anomalous w_L structure is demonstrated. It is
known that in the chiral limit the transversal structure w_T is free from
perturbative corrections. In this limit within the instanton model we calculate
the transversal invariant function w_T at arbitrary momentum transfer, q, and
show the absence of power corrections to this structure at large q^2. Instead
there arise the exponential corrections to w_T at large q^2 reflecting nonlocal
properties of QCD vacuum. The slope of w_T at zero virtuality, the QCD vacuum
magnetic susceptibility of the quark condensate and its momentum dependence are
estimated.",0505007v2
2006-02-23,Implication of the B -> rho rho data on the B -> pi pi puzzle,"We point out that the B -> rho rho data have seriously constrained the
possibility of resolving the B -> pi pi puzzle from the large observed B^0 ->
pi^0 pi^0 branching ratio in the available theoretical approaches. The
next-to-leading-order (NLO) contributions from the vertex corrections, the
quark loops, and the magnetic penguin evaluated in the perturbative QCD (PQCD)
approach have saturated the experimental upper bound of the B^0 -> rho^0 rho^0
branching ratio, and do not help. The NLO PQCD predictions for the B^0 ->
rho^\mp rho^\pm and B^\pm -> rho^\pm rho^0 branching ratios are consistent with
the data. The inclusion of the NLO jet function from the soft-collinear
effective theory into the QCD-improved factorization approach, though enhancing
the B^0 -> pi^0 pi^0 branching ratio sufficiently, overshoots the bound of the
B^0 -> rho^0 rho^0 branching ratio, and deteriorates the predictions for the
B^\pm -> pi^0 K^\pm and B^0 -> pi^\mp K^\pm direct CP asymmetries.",0602214v3
2006-05-05,Upper Bound on the Hadronic Light-by-Light Contribution to the Muon g-2,"There are indications that hadronic loops in some electroweak observables are
almost saturated by parton level effects. Taking this as the hypothesis for
this work, we propose a genuine parton level estimate of the hadronic
light-by-light contribution to the anomalous magnetic moment of the muon, a_mu
(LBL,had). Our quark mass definitions and values are motivated in detail, and
the simplicity of our approach allows for a transparent error estimate. For
infinitely heavy quarks our treatment is exact, while for asymptotically small
quark masses a_mu (LBL,had) is overestimated. Interpolating, this suggests
quoting an upper bound. We obtain a_mu (LBL,had) < 1.59 10^-9 (95% CL).",0605052v2
1993-03-10,"Magnetic Monopoles, Bogomol'nyi Bound and SL(2,Z) Invariance in String Theory","We show that in heterotic string theory compactified on a six dimensional
torus, the lower bound (Bogomol'nyi bound) on the dyon mass is invariant under
the SL(2,Z) transformation that interchanges strong and weak coupling limits of
the theory. Elementary string excitations are also shown to satisfy this lower
bound. Finally, we identify specific monopole solutions that are related via
the strong-weak coupling duality transformation to some of the elementary
particles saturating the Bogomol'nyi bound, and these monopoles are shown to
have the same mass and degeneracy of states as the corresponding elementary
particles.",9303057v2
1995-01-12,SEMILOCAL NONTOPOLOGICAL SOLITONS IN A CHERN-SIMONS THEORY.,"We show the existence of self-dual semilocal nontopological vortices in a
$\Phi^2$ Chern-Simons (C-S) theory. The model of scalar and gauge fields with a
$SU(2)_{global} \times U(1)_{local}$ symmetry includes both the C-S term and an
anomalous magnetic contribution. It is demonstrated here, that the vortices are
stable or unstable according to whether the vector topological mass $\kappa$ is
less than or greater than the mass $m$ of the scalar field. At the boundary,
$\kappa = m$, there is a two-parameter family of solutions all saturating the
self-dual limit. The vortex solutions continuously interpolates between a ring
shaped structure and a flux tube configuration.",9501041v1
1995-12-20,Dyonic Black Hole in Heterotic String Theory,"We study some features of dyonic Black hole solution in heterotic string
theory on a six torus. This solution has 58 parameters. Of these, 28 parameters
denote the electric charge of the black hole, another 28 correspond to the
magnetic charge, and the other two parameters being the mass and the angular
momentum of the black hole. We discuss the extremal limit and show that in
various limits, it reduces to the known black hole solutions. The solutions
saturating the Bogomolnyi bound are identified. Explicit solution is presented
for the non-rotating dyonic black hole.",9512157v3
1996-02-01,Extreme dyonic black holes in string theory,"Supersymmetric extreme dyonic black holes of toroidally compactified
heterotic or type II string theory can be viewed as lower-dimensional images of
solitonic strings wound around a compact dimension. We consider conformal sigma
models which describe string configurations corresponding to various extreme
dyonic black holes in four and five dimensions. These conformal models have
regular short-distance region equivalent to a WZW theory with level
proportional to magnetic charges. Arguments are presented suggesting a
universal relation between the black hole entropy (area) and the statistical
entropy of BPS-saturated oscillation states of solitonic string.[Extended
version of a talk at the Workshop ""Frontiers in Quantum Field Theory"", in honor
of the 60th birthday of K. Kikkawa (Osaka, Japan, 14-17 December 1995)]",9601177v4
1996-10-18,On the weak coupling spectrum of N=2 supersymmetric SU(n) gauge theory,"The weak coupling spectrum of BPS saturated states of pure $N=2$
supersymmetric SU$(n)$ gauge theory is investigated. The method uses known
results on the dyon spectrum of the analogous theory with $N=4$ supersymmetry,
along with the action on these states of the semi-classical monodromy
transformations. For dyons whose magnetic charge is not a simple root of the
Lie algebra, it is found that the weak coupling region is divided into a series
of domains, for which the dyons have different electric charge, separated by
walls on which the dyons decay. The proposed spectrum is shown to be consistent
with the exact solution of the theory at strong coupling in the sense that the
states at weak coupling can account for the singularities at strong coupling.",9610142v1
1997-01-26,Solitons in 1+1 Dimensional Gauged Sigma Models,"We study soliton solutions in 1+1 dimensional gauged sigma models, obtained
by dimensional reduction from its 2+1 dimensional counterparts. We show that
the Bogomol'nyi bound of these models can be expressed in terms of two
conserved charges in a similar way to that of the BPS dyons in 3+1 dimensions.
Purely magnetic vortices of the 2+1 dimensional completely gauged sigma model
appear as charged solitons in the corresponding 1+1 dimensional theory. The
scale invariance of these solitons is also broken because of the dimensional
reduction. We obtain exact static soliton solutions of these models saturating
the Bogomol'nyi bound.",9701132v2
1997-08-27,Brane Dynamics From the Born-Infeld Action,"We use the abelian Born-Infeld action for the worldvolume gauge field and
transverse displacement scalars to explore new aspects of D-brane structure and
dynamics. We study several classic gauge field configurations, including point
charges in any worldvolume dimension and vortices in two worldvolume
dimensions, and show that, with an appropriate excitation of the transverse
coordinate field, they are BPS-saturated solutions. The Coulomb point charge
solutions turn out to represent, with considerable fidelity, fundamental
strings attached to the brane (their magnetic counterparts describe D1-branes
attached to D3-branes). We also show that S-matrix for small excitations
propagating on the point charge solution is consistent with (and gives further
illuminating information about) Polchinski's effective open string boundary
condition.",9708147v3
1999-06-02,Super 0-brane and GS Superstring Actions on AdS_2 \times S^2,"The super 0-brane and GS superstring actions on AdS$_2 \times S^2$ background
with 2-form flux are constructed by supercoset approach. We find the super
0-brane action contains two parameters which are interpreted as the electric
and magnetic charges of the super 0-brane. The obtained super 0-brane action
describes the BPS saturated dyonic superparticle moving on AdS$_2 \times S^2$
background. The WZ action contains the required coupling with 2-form flux. For
GS superstring, we find the string action on AdS$_2 \times S^2$ takes the same
form as those in AdS$_3 \times S^3$ and AdS$_5 \times S^5$ with RR field
background.",9906013v2
2000-08-28,Exact Solutions of Multi-Vortices and False Vacuum Bubbles in Noncommutative Abelian-Higgs Theories,"We consider the noncommutative Abelian-Higgs theory and construct new types
of exact multi-vortex solutions that solve the static equations of motion. They
in general do not follow from the BPS equations; only for some specific values
of parameters, they satisfy the BPS equations saturating the Bogomol'nyi bound.
We further consider the Abelian-Higgs theory with more complicated scalar
potential allowing unstable minima and construct exact solutions of
noncommutative false vacuum bubble with integer magnetic flux. The classical
stability of the solutions is discussed.",0008204v4
2003-10-13,"S-Duality, Deconstruction and Confinement for a Marginal Deformation of N=4 SUSY Yang-Mills","We study an exactly marginal deformation of N=4 SUSY Yang-Mills with gauge
group U(N) using field theory and string theory methods. The classical theory
has a Higgs branch for rational values of the deformation parameter. We argue
that the quantum theory also has an S-dual confining branch which cannot be
seen classically. The low-energy effective theory on these branches is a
six-dimensional non-commutative gauge theory with sixteen supercharges.
Confinement of magnetic and electric charges, on the Higgs and confining
branches respectively, occurs due to the formation of BPS-saturated strings in
the low energy theory. The results also suggest a new way of deconstructing
Little String Theory as a large-N limit of a confining gauge theory in four
dimensions.",0310117v2
2004-08-31,Non-Abelian Vortices in N=1* Gauge Theory,"We consider the N=1* supersymmetric SU(2) gauge theory and demonstrate that
the Z_2 vortices in this theory acquire orientational zero modes, associated
with the rotation of magnetic flux inside SU(2) group, and turn into the
non-Abelian strings, when the masses of all chiral fields become equal. These
non-Abelian strings are not BPS-saturated. We study the effective theory on the
string world sheet and show that it is given by two-dimensional
non-supersymmetric O(3) sigma model. The confined 't Hooft-Polyakov monopole is
seen as a junction of the Z_2-string and anti-string, and as a kink in the
effective world sheet sigma model. We calculate its mass and show that besides
the four-dimensional confinement of monopoles, they are also confined in the
two-dimensional theory: the monopoles stick to anti-monopoles to form the
meson-like configurations on the strings they are attached to.",0408235v2
2006-11-02,Integrable Vortex Dynamics in Anisotropic Planar Spin Liquid Model,"The problem of magnetic vortex dynamics in an anisotropic spin liquid model
is considered. For incompressible flow the model admits reduction to saturating
Bogomolny inequality analytic projections of spin variables, subject the linear
holomorphic Schr\""odinger equation. It allows us to construct N vortex
configurations in terms of the complex Hermite polynomials. Using complex
Galilean boost transformations, the interaction of the vortices and the vortex
chain lattices (vortex crystals) are studied. By the complexified Cole-Hopf
transformation, integrable N vortex dynamics is described by the holomorphic
Burgers equation. Mapping of the point vortex problem to N-particle problem,
the complexified Calogero-Moser system, showing its integrability and the
Hamiltonian structure, is given.",0611002v1
2005-08-19,Quarks and Antiquarks in Nuclei,"The Chiral Quark-Soliton model provides the quark and antiquark substructure
of the nucleon, which is embedded in nuclear matter. This provides a new way to
asses the effects of the nuclear medium on the nucleon. We calculate nuclear
binding and saturation, describe the European Muon Collaboration (EMC) effect
consistently with Drell-Yan experiments, and predict modifications to the
polarized parton distributions. We also calculate the electromagnetic form
factors of a bound proton, and find significant modifications of the
electromagnetic form factors in the nuclear environment. In every case, the
properties of the sea of quark-antiquark pairs in the nucleon are very
important, and serve to mitigate the valence quark effect. The changes in the
sea quarks when the nucleon is immersed in the nuclear medium are the primary
mode by which consistency is maintained with experimental constraints
(Drell-Yan data, magnetic moment), while still maintaining a significant effect
needed to explain the deep inelastic scattering and polarization transfer data.",0508036v1
2001-03-26,An Atom Faucet,"We have constructed and modeled a simple and efficient source of slow atoms.
  From a background vapour loaded magneto-optical trap, a thin laser beam
extracts a continuous jet of cold rubidium atoms. In this setup, the extraction
column that is typical to leaking MOT systems is created without any optical
parts placed inside the vacuum chamber. For detailed analysis, we present a
simple 3D numerical simulation of the atomic motion in the presence of multiple
saturating laser fields combined with an inhomogeneous magnetic field. At a
pressure of $P_{\rm Rb87}=1 \times 10^{-8}$ mbar, the moderate laser power of
10 mW per beam generates a jet of flux $\Phi =1.3\times 10^8$ atoms/s with a
mean velocity of 14 m/s and a divergence of $<20$ mrad.",0103085v1
2002-06-03,An equilibrium model for RFP plasmas in the presence of resonant tearing modes,"The equilibrium of a finite-beta RFP plasma in the presence of
saturated-amplitude tearing modes is investigated. The singularities of the MHD
force balance equation JXB=grad(p) at the modes rational surfaces are resolved
through a proper regularization of the zeroth-order (equilibrium) profiles, by
setting to zero there the gradient of the pressure and parallel current
density. An equilibrium model, which satisfies the regularization rule at the
various rational surfaces, is developed. The comparison with the experimental
data from the Reversed Field eXperiment (RFX) gives encouraging results. The
model provides an easy tool for magnetic analysis: many aspects of the
perturbations can be analyzed and reconstructed.",0206006v3
2005-11-14,Nonlinear evolution of the m=1 internal kink mode in the presence of magnetohydrodynamic turbulence,"The nonlinear evolution of the m=1 internal kink mode is studied numerically
in a setting where the tokamak core plasma is surrounded by a turbulent region
with low magnetic shear. As a starting point we choose configurations with
three nearby q=1 surfaces where triple tearing modes (TTMs) with high poloidal
mode numbers m are unstable. While the amplitudes are still small, the fast
growing high-m TTMs enhance the growth of the m=1 instability. This is
interpreted as a fast sawtooth trigger mechanism. The TTMs lead to a partial
collapse, leaving behind a turbulent belt with q ~= 1 around the unreconnected
core plasma. Although, full reconnection can occur if the core displacement
grows large enough, it is shown that the turbulence may actively prevent
further reconnection. This is qualitatively similar to experimentally observed
partial sawtooth crashes with post-cursor oscillations due to a saturated
internal kink.",0511126v2
2003-12-19,"Galilean Satellites as Sites for Incipient Life, and the Earth as its Shelter","Numerous problems connected with an assumption of the life origin on the
Earth do not arise on Galilean satellites. Here, in presence of a practically
non-salt water and of a great deal (~5-10%) of abiogenic organics, a great
diversity of conditions, which are unthinkable for the Earth, were realized
more than once. They were caused by global electrochemical processes in the
magnetic field presence what could entail an absolute enantiomeric synthesis.
The subsequent explosions of the satellites' icy envelopes saturated by the
electrolysis products resulted in appearance of hot massive atmospheres and
warm deep oceans and ejection of the dirty ice fragments (=comet nuclei), what
led to the material exchange with other bodies, etc.",0312031v2
2001-07-02,Comparative study of the transient evolution of Hanle EIT/EIA resonances,"The temporal evolutions of coherent resonances corresponding to
electromagnetically induced transparency (EIT) and absorption (EIA) were
observed in a Hanle absorption experiment carried on the $D_{2}$ lines of $%
^{87}$Rb vapor by suddenly turning the magnetic field on or off. The main
features of the experimental observations are well reproduced by a theoretical
model based on Bloch equation where the atomic level degeneracy has been fully
accounted for. Similar (opposite phase) evolutions were observed at low optical
field intensities for Hanle/EIT or Hanle/EIA resonances. Unlike the Hanle/EIA\
transients which are increasingly shorter for driving field intensities
approaching saturation, the $B\neq 0$ transient of the Hanle/EIT signal at
large driving field intensities present a long decay time approaching the
atomic transit time. Such counterintuitive behavior is interpreted as a
consequence of the Zeno effect.",0107007v1
2007-04-14,Terahertz Time-Domain Magnetospectroscopy of a High-Mobility Two-Dimensional Electron Gas,"We have observed cyclotron resonance in a high-mobility GaAs/AlGaAs
two-dimensional electron gas by using the techniques of terahertz time-domain
spectroscopy combined with magnetic fields. From this, we calculate the real
and imaginary parts of the diagonal elements of the magnetoconductivity tensor,
which in turn allows us to extract the concentration, effective mass, and
scattering time of the electrons in the sample. We demonstrate the utility of
ultrafast terahertz spectroscopy, which can recover the true linewidth of
cyclotron resonance in a high-mobility ($>{10}^{6} \mathrm{cm^{2} V^{-1}
s^{-1}}$) sample without being affected by the saturation effect.",0704.1883v1
2007-06-11,Absence of long-range Ni/Mn ordering in ferromagnetic La2NiMnO6 thin films,"Epitaxial La2NiMnO6 thin films have been grown on (001)-oriented SrTiO3 using
the PLD technique. The thin films are semiconducting and FM with a TC close to
270K, a coercive field of 920Oe, and a saturation magnetization of 5muB per
f.u. TEM, conducted at RT, reveals a majority phase having ""I-centered""
structure with a=c=1.4asub and b=2asub along with a minority phase-domains
having ""P-type"" structure (asub being the lattice parameter of the perovskite
structure). A discusion on the presence of Ni/Mn long-range ordering, in light
of recent literature on double perovskites La2NiMnO6 is presented.",0706.1414v1
2007-06-25,Calorimetric Evidence for a Fulde-Ferrell-Larkin-Ovchinnikov Superconducting State in the Layered Organic Superconductor κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$,"The specific heat of the layered organic superconductor $\kappa$-%
(BEDT-TTF)$_2$Cu(NCS)$_2$, where BEDT-TTF is bisethylenedithio-%
tetrathiafulvalene, has been studied in magnetic fields up to 28 T applied
perpendicular and parallel to the superconducting layers. In parallel fields
above 21 T, the superconducting transition becomes first order, which signals
that the Pauli-limiting field is reached. Instead of saturating at this field
value, the upper critical field increases sharply and a second first-order
transition line appears within the superconducting phase. Our results give
strong evidence that the phase, which separates the homogeneous superconducting
state from the normal state is a realization of a
Fulde-Ferrell-Larkin-Ovchinnikov state.",0706.3584v2
2007-07-24,Quantisation of Hopping Magnetoresistance Prefactor in Strongly Correlated Two-Dimensional Electron Systems,"We report an universal behaviour of hopping transport in strongly interacting
mesoscopic two-dimensional electron systems (2DES). In a certain window of
background disorder, the resistivity at low perpendicular magnetic fields
follows the expected relation $\rho(B_\perp) = \rho_{\rm{B}}\exp(\alpha
B_\perp^2)$. The prefactor $\rho_{\rm{B}}$ decreases exponentially with
increasing electron density but saturates to a finite value at higher
densities. Strikingly, this value is found to be universal when expressed in
terms of absolute resistance and and shows quantisation at $R_{\rm{B}}\approx
h/e^2$ and $R_{\rm{B}}\approx 1/2$ $ h/e^2$. We suggest a strongly correlated
electronic phase as a possible explanation.",0707.3543v2
2007-08-07,Spin-exchange relaxation free magnetometry with Cs vapor,"We describe a Cs atomic magnetometer operating in the spin-exchange
relaxation-free (SERF) regime. With a vapor cell temperature of
$103^\circ\rm{C}$ we achieve intrinsic magnetic resonance widths $\Delta B=17
{\rm \mu G}$ corresponding to an electron spin-relaxation rate of $300 {\rm
s^{-1}}$ when the spin-exchange rate is $\Gamma_{SE}=14000 {\rm s^{-1}}$. We
also observe an interesting narrowing effect due to diffusion. Signal-to-noise
measurements yield a sensitivity of about $400\thinspace{\rm pG/\sqrt{Hz}}$.
Based on photon shot noise, we project a sensitivity of $40 {\rm
pG/\sqrt{Hz}}$. A theoretical optimization of the magnetometer indicates
sensitivities on the order of $2 {\rm pG/\sqrt{Hz}}$ should be achievable in a
$1 {\rm cm^3}$ volume. Because Cs has a higher saturated vapor pressure than
other alkali metals, SERF magnetometers using Cs atoms are particularly
attractive in applications requiring lower temperatures.",0708.1012v1
2007-08-16,On the possibility of a bimodal solar dynamo,"A simple way to couple an interface dynamo model to a fast tachocline model
is presented, under the assumption that the dynamo saturation is due to a
quadratic process and that the effect of finite shear layer thickness on the
dynamo wave frequency is analoguous to the effect of finite water depth on
surface gravity waves. The model contains one free parameter which is fixed by
the requirement that a solution should reproduce the helioseismically
determined thickness of the tachocline. In this case it is found that, in
addition to this solution, another steady solution exists, characterized by a
four times thicker tachocline and 4-5 times weaker magnetic fields. It is
tempting to relate the existence of this second solution to the occurrence of
grand minima in solar activity.",0708.2131v1
2007-10-04,A Three Dimensional Kasteleyn Transition: Spin Ice in a [100] Field,"We examine the statistical mechanics of spin-ice materials with a [100]
magnetic field. We show that the approach to saturated magnetisation is, in the
low-temperature limit, an example of a 3D Kasteleyn transition, which is
topological in the sense that magnetisation is changed only by excitations that
span the entire system. We study the transition analytically and using a Monte
Carlo cluster algorithm, and compare our results with recent data from
experiments on Dy2Ti2O7.",0710.0976v3
2007-10-25,Nucleon Form Factors and Hidden Symmetry in Holographic QCD,"The vector dominance of the electromagnetic form factors both for mesons and
baryons arises naturally in holographic QCD, where both the number of colors
and the 't Hooft coupling are taken to be very large, offering a bona-fide
derivation of the notion of vector dominance. The crucial ingredient for this
is the infinite tower of vector mesons in the approximations made which share
features that are characteristic of the quenched approximation in lattice QCD.
We approximate the infinite sum by contributions from the lowest four vector
mesons of the tower which turn out to saturate the charge and magnetic moment
sum rules within a few percent and compute them totally free of unknown
parameters for momentum transfers Q^2 less than 1GeV^2. We identify certain
observables that can be reliably computed within the approximations and others
that are not, and discuss how the improvement of the latter can enable one to
bring holographic QCD closer to QCD proper.",0710.4615v2
2007-12-10,Quantum well states in Fe/Nb(001) multilayers: First principles study,"We present a first-principles study to understand the phenomena of interlayer
exchange coupling in Fe/Nb multilayers using the linearized-muffin-tin-orbitals
method within the generalized gradient approximation. We find that the exchange
coupling oscillates with both short and long periodicities, which have been
examined in terms of the Ruderman-Kittel-Kasuya-Yosida (RKKY) model as well as
the quantum well (QW) model. We have investigated the behavior of the exchange
coupling by artificially varying moments of Fe atoms in ferromagnetic layers.
For a small moment of Fe, the coupling shows bilinearity in the magnetic
moments, implying its RKKY character. However, at higher moments close to that
of bulk Fe, the saturation of long-period oscillations is in accordance with
the QW model. Quantum well dispersions around the Fermi level demonstrate that
the majority-spin bands contribute largely to the formation of quantum well
states, which we analyze quantitatively by making use of the phase accumulation
model. Our analysis indicates that the quantum well model gives a better
description of the oscillatory behavior of the exchange coupling in Fe/Nb
multilayers.",0712.1432v1
2008-01-14,A note on the extensivity of the holographic entanglement entropy,"We consider situations where the renormalized geometric entropy, as defined
by the AdS/CFT ansatz of Ryu and Takayanagi, shows extensive behavior in the
volume of the entangled region. In general, any holographic geometry that is
`capped' in the infrared region is a candidate for extensivity provided the
growth of minimal surfaces saturates at the capping region, and the induced
metric at the `cap' is non-degenerate. Extensivity is well-known to occur for
highly thermalized states. In this note, we show that the holographic ansatz
predicts the persistence of the extensivity down to vanishing temperature, for
the particular case of conformal field theories in 2+1 dimensions with a
magnetic field and/or electric charge condensates.",0801.2153v3
2008-02-08,"Superconducting Transition in the $β$-Pyrochlore AOs$_2$O$_6$ (A=Cs, Rb, K) under Pressure","Pressure dependence of superconducting transition temperature $T_{\rm c}$ has
been determined through the DC magnetic measurements under pressure up to
$P$=10 GPa for $\beta$-pyrochlore oxides AOs$_2$O$_6$ with A=Cs ($T_{\rm
c}$=3.3 K), Rb (6.3 K) and K (9.6 K). Both for A=Rb and Cs, $T_{\rm c}$
increases with increasing $P$ and shows a saturation at $T_{\rm cm}$$\sim$8.8
K, which is considered as the upper limit of $T_{\rm c}$ inherent in
AOs$_2$O$_6$. In contrast, the $T_{\rm c}-P$ curve for KOs$_2$O$_6$ shows a
sharp maximum of $\sim$10 K at $P$$\sim$0.5 GPa, and $T_{\rm c}$ is higher than
$T_{\rm cm}$ for 0$\leq$$P$$\leq$1.5GPa, suggesting the enhanced
superconductivity due to the rattling of K ions.",0802.1179v1
2008-05-22,Non-equilibrium of Ionization and the Detection of Hot Plasma in Nanoflare-heated Coronal Loops,"Impulsive nanoflares are expected to transiently heat the plasma confined in
coronal loops to temperatures of the order of 10 MK. Such hot plasma is hardly
detected in quiet and active regions, outside flares. During rapid and short
heat pulses in rarified loops the plasma can be highly out of equilibrium of
ionization. Here we investigate the effects of the non-equilibrium of
ionization (NEI) on the detection of hot plasma in coronal loops.
Time-dependent loop hydrodynamic simulations are specifically devoted to this
task, including saturated thermal conduction, and coupled to the detailed
solution of the equations of ionization rate for several abundant elements. In
our simulations, initially cool and rarified magnetic flux tubes are heated to
10 MK by nanoflares deposited either at the footpoints or at the loop apex. We
test for different pulse durations, and find that, due to NEI effects, the loop
plasma may never be detected at temperatures above ~5 MK for heat pulses
shorter than about 1 min. We discuss some implications in the framework of
multi-stranded nanoflare-heated coronal loops.",0805.3512v1
2008-09-10,Investigating the high energy QCD approaches for prompt photon production at the LHC,"We investigate the rapidity and transverse momentum distributions of the
prompt photon production at the CERN LHC energies considering the current
perturbative QCD approaches for this scattering process. Namely, we compare the
predictions from the usual NLO pQCD calculations to the the color dipole
formalism, using distinct dipole cross sections. Special attention is paid to
parton saturation models at high energies, which are expected to be important
at the forward rapidities in pp collisions at the LHC.",0809.1884v1
2008-09-24,Effect of Pt doping on the critical temperature and upper critical field in YNi2-xPtxB2C (x=0-0.2),"We investigate the evolution of superconducting properties by doping
non-magnetic impurity in single crystals of YNi2-xPtxB2C (x=0-0.2). With
increasing Pt doping the critical temperature (Tc) monotonically decreases from
15.85K and saturates to a value ~13K for x>0.14. However, unlike conventional
s-wave superconductors, the upper critical field (HC2) along both
crystallographic directions a and c decreases with increasing Pt doping.
Specific heat measurements show that the density of states (N(EF)) at the Fermi
level (EF) and the Debye temperatures (Theta_D) in this series remains constant
within the error bars of our measurement. We explain our results based on the
increase in intraband scattering in the multiband superconductor YNi2B2C.",0809.4274v1
2008-12-05,Generic susceptibilities of the half-filled Hubbard model in infinite dimensions,"Around a metal-to-insulator transition driven by repulsive interaction (Mott
transition) the single particle excitations and the collective excitations are
equally important. Here we present results for the generic susceptibilities at
zero temperature in the half-filled Hubbard model in infinite dimensions.
Profiting from the high resolution of dynamic density-matrix renormalization at
all energies, results for the charge, spin and Cooper-pair susceptibilities in
the metallic and the insulating phase are computed. In the insulating phase, an
almost saturated local magnetic moment appears. In the metallic phase a
pronounced low-energy peak is found in the spin response.",0812.1071v2
2009-01-09,Electron-electron interaction effects in quantum point contacts,"We consider electron-electron interaction effects in quantum point contacts
on the first quantization plateau, taking into account all scattering
processes. We compute the low-temperature linear and nonlinear conductance,
shot noise, and thermopower, by perturbation theory and a self-consistent
nonperturbative method. On the conductance plateau, the low-temperature
corrections are solely due to momentum-nonconserving processes that change the
relative number of left- and right-moving electrons. This leads to a
suppression of the conductance for increasing temperature or voltage. The size
of the suppression is estimated for a realistic saddle-point potential, and is
largest in the beginning of the conductance plateau. For large magnetic field,
interaction effects are strongly suppressed by the Pauli principle, and hence
the first spin-split conductance plateau has a much weaker interaction
correction. For the nonperturbative calculations, we use a self-consistent
nonequilibrium Green's function approach, which suggests that the conductance
saturates at elevated temperatures. These results are consistent with many
experimental observations related to the so-called 0.7 anomaly.",0901.1183v1
2009-01-30,Line-of-sight statistical methods for turbulent medium: VCS for emission and absorption lines,"We present an overview of the Velocity Coordinate Spectrum (VCS), a new
technique for studying astrophysical turbulence that utilizes the line-of-sight
statistics of Doppler-broadened spectral lines. We consider the retrieval of
turbulence spectra from emission intensity observations of both high and low
spatial resolution and find that the VCS allows one to study turbulence even
when the emitting turbulent volume is not spatially resolved. This opens
interesting prospects for using the technique for extragalactic research. VCS
developed for spectral emission lines is applicable to absorption lines as well
if the optical depth is used instead of intensity. VCS for absorption lines in
point-source spectra benefit from effectively narrow beam and does not require
dense sky coverage by sampling directions. Even strongly saturated absorption
lines still carry the information about the small scale turbulence, albeit
limited to the wings of a line. Combining different absorption lines one can
develop tomography of the turbulence in the interstellar gas in all its
complexity.",0902.0011v1
2009-02-05,Temperature dependence of antiferromagnetic susceptibility in ferritin,"We show that antiferromagnetic susceptibility in ferritin increases with
temperature between 4.2 K and 180 K (i. e. below the N\'{e}el temperature) when
taken as the derivative of the magnetization at high fields ($30\times10^4$
Oe). This behavior contrasts with the decrease in temperature previously found,
where the susceptibility was determined at lower fields ($5\times10^4$ Oe). At
high fields (up to $50 \times10^4$ Oe) the temperature dependence of the
antiferromagnetic susceptibility in ferritin nanoparticles approaches the
normal behavior of bulk antiferromagnets and nanoparticles considering
superantiferromagnetism, this latter leading to a better agreement at high
field and low temperature. The contrast with the previous results is due to the
insufficient field range used ($< 5 \times10^4$ Oe), not enough to saturate the
ferritin uncompensated moment.",0902.0929v1
2009-02-10,Constraints on Neutron Star Crusts From Oscillations in Giant Flares,"We show that the fundamental seismic shear mode, observed as a quasi-periodic
oscillation in giant flares emitted by highly-magnetized neutron stars, is
particularly sensitive to the nuclear physics of the crust. The identification
of an oscillation at ~ 30 Hz as the fundamental crustal shear mode requires a
nuclear symmetry energy that depends very weakly on density near saturation. If
the nuclear symmetry energy varies more strongly with density, then lower
frequency oscillations, previously identified as torsional Alfven modes of the
fluid core, could instead be associated with the crust. If this is the case,
then future observations of giant flares should detect oscillations at around
18 Hz. An accurate measurement of the neutron skin thickness of lead will also
constrain the frequencies predicted by the model.",0902.1683v2
2009-02-18,Non-linear spectroscopy of rubidium: An undergraduate experiment,"In this paper, we describe two complementary non-linear spectroscopy methods
which both allow to achieve Doppler-free spectra of atomic gases. First,
saturated absorption spectroscopy is used to investigate the structure of the
$5{\rm S}_{1/2}\to 5{\rm P}_{3/2}$ transition in rubidium. Using a slightly
modified experimental setup, Doppler-free two-photon absorption spectroscopy is
then performed on the $5{\rm S}_{1/2}\to 5{\rm D}_{5/2}$ transition in
rubidium, leading to accurate measurements of the hyperfine structure of the
$5{\rm D}_{5/2}$ energy level. In addition, electric dipole selection rules of
the two-photon transition are investigated, first by modifying the polarization
of the excitation laser, and then by measuring two-photon absorption spectra
when a magnetic field is applied close to the rubidium vapor. All experiments
are performed with the same grating-feedback laser diode, providing an
opportunity to compare different high resolution spectroscopy methods using a
single experimental setup. Such experiments may acquaint students with quantum
mechanics selection rules, atomic spectra and Zeeman effect.",0902.3115v1
2009-03-13,Operator Space Entanglement Entropy in XY Spin Chains,"The complexity of representation of operators in quantum mechanics can be
characterized by the operator space entanglement entropy (OSEE). We show that
in the homogeneous Heisenberg XY spin 1/2 chains the OSEE for initial local
operators grows at most logarithmically with time. The prefactor in front of
the logarithm generally depends only on the number of stationary points of the
quasi-particle dispersion relation and for the XY model changes from 1/3 to 2/3
exactly at the point of quantum phase transition to long-range magnetic
correlations in the non-equilibrium steady state. In addition, we show that the
presence of a small disorder triggers a saturation of the OSEE.",0903.2432v3
2009-03-23,Entanglement entropy with localized and extended interface defects,"The quantum Ising chain of length, L, which is separated into two parts by
localized or extended defects is considered at the critical point where scaling
of the interface magnetization is non-universal. We measure the entanglement
entropy between the two halves of the system in equilibrium, as well as after a
quench, when the interaction at the interface is changed for time t>0. For the
localized defect the increase of the entropy with log(L) or with log(t)
involves the same effective central charge, which is a continuous function of
the strength of the defect. On the contrary for the extended defect the
equilibrium entropy is saturated, but the non-equilibrium entropy has a
logarithmic time-dependence the prefactor of which depends on the strength of
the defect.",0903.3740v1
2009-05-12,Reconstructing the Neutron-Star Equation of State from Astrophysical Measurements,"The properties of matter at ultra-high densities, low temperatures, and with
a significant asymmetry between protons and neutrons can be studied exclusively
through astrophysical observations of neutron stars. We show that measurements
of the masses and radii of neutron stars can lead to tight constraints on the
pressure of matter at three fiducial densities, from 1.85 to 7.4 times the
density of nuclear saturation, in a manner that is largely model-independent
and that captures the key characteristics of the equation of state. We
demonstrate that observations with 10% uncertainties of at least three neutron
stars can lead to measurements of the pressure at these fiducial densities with
an accuracy of 0.11 dex or ~ 30%. Observations of three neutron stars with 5%
uncertainties are sufficient to distinguish at a better than 3-sigma confidence
level between currently proposed equations of state. In the electromagnetic
spectrum, such accurate measurements will become possible for weakly-magnetic
neutron stars during thermonuclear flashes and in quiescence with future
missions such as the International X-ray Observatory (IXO).",0905.1959v2
2009-05-24,Muon-spin rotation measurements of the penetration depth of the Mo_3Sb_7 superconductor,"Measurements of the magnetic field penetration depth \lambda in
superconductor Mo_3Sb_7 (T_c~2.1 K) were carried out by means of
muon-spin-rotation. The absolute values of \lambda, the Ginzburg-Landau
parameter \kappa, the first H_{c1} and the second H_{c2} critical fields at T=0
are \lambda(0)=720(100)nm, \kappa(0)=55(9), \mu_0H_{c1}(0)=1.8(3)mT, and
\mu_0H_{c2}(0)=1.9(2)T. The zero temperature value of the superconducting
energy gap \Delta(0) was found to be 0.35(1)meV corresponding to the ratio
2\Delta(0)/k_BT_c=3.83(10). At low temperatures \lambda^{-2}(T) saturates and
becomes constant below T~0.3T_c, in agreement with what is expected for s-wave
BCS superconductors. Our results suggest that Mo_3Sb_7 is a BCS superconductor
with the isotropic energy gap",0905.3906v1
2009-05-24,Frequency and temperature dependence of the anomalous Hall conductivity in a chiral px+ipy superconductor with impurities,"We calculate frequency and temperature dependence of the anomalous ac Hall
conductivity induced by impurity scattering in a chiral px+ipy superconductor,
such as Sr2RuO4, with spontaneous time-reversal-symmetry breaking in the
absence of an external magnetic field. We consider two models of disorder,
Gaussian and non-Gaussian, characterized by the second and third moments of the
random impurity potential, respectively. Within both models, we find that the
anomalous Hall conductivity has a finite real value at zero frequency, exhibits
singularities at the threshold of photon absorption across the superconducting
gap, and decays as some power of the high frequency \Omega. The Hall
conductivity increases linearly with the decrease of temperature below the
superconducting transition and saturates at zero temperature. Using our results
for the high-frequency Hall conductivity, we estimate the polar Kerr angle for
light reflection from the material and compare it with the experimental
measurements in Sr2RuO4 by Xia et al., Phys. Rev. Lett. 97, 167002 (2006).",0905.3918v3
2009-06-27,Negative and Positive Magnetoresistance in Bilayer Graphene: Effects of Weak Localization and Charge Inhomogeneity,"We report measurements of magnetoresistance in bilayer graphene as a function
of gate voltage (carrier density) and temperature. We examine multiple
contributions to the magnetoresistance, including those of weak localization
(WL), universal conductance fluctuations (UCF), and inhomogeneous charge
transport. A clear WL signal is evident at all measured gate voltages (in the
hole doped regime) and temperature ranges (from 0.25 K to 4.3 K), and the phase
coherence length extracted from WL data does not saturate at low temperatures.
The WL data is fit to demonstrate that electron-electron Nyquist scattering is
the major source of phase decoherence. A decrease in UCF amplitude with
increasing gate voltage and temperature is shown to be consistent with a
corresponding decrease in the phase coherence length. In addition, a weak
positive magnetoresistance at higher magnetic fields is observed, and
attributed to inhomogeneous charge transport.",0906.5090v2
2009-07-07,On a stochastic model for the spin-down of solar type stars,"Modeling the rotation history of solar-type stars is still an unsolved
problem in modern astrophysics. One of the main challenges is to explain the
dispersion in the distribution of stellar rotation rate for young stars.
Previous works have advocated dynamo saturation or magnetic field localization
to explain the presence of fast rotators and star-disk coupling in pre-main
sequence to account for the existence of slow rotators. Here, we present a new
model that can account for the presence of both types of rotators by
incorporating fluctuations in the solar wind. This renders the spin-down
problem probabilistic in nature, some stars experiencing more braking on
average than others. We show that random fluctuations in the loss of angular
momentum enhance the population of both fast and slow rotators compared to the
deterministic case. Furthermore, the distribution of rotational speed is
severely skewed towards large values in agreement with observations.",0907.1226v1
2009-07-21,Confinement of electrons in size modulated silicon nanowires,"Based on first-principles calculations we showed that superlattices of
periodically repeated junctions of hydrogen saturated silicon nanowire segments
having different lengths and diameters form multiple quantum well structures.
The band gap of the superlattice is modulated in real space as its diameter
does and results in a band gap in momentum space which is different from
constituent nanowires. Specific electronic states can be confined in either
narrow or wide regions of superlattice. The type of the band lineup and hence
the offsets of valence and conduction bands depend on the orientation of the
superlattice as well as on the diameters of the constituent segments. Effects
of the SiH vacancy and substitutional impurities on the electronic and magnetic
properties have been investigated by carrying out spin-polarized calculations.
Substitutional impurities with localized states near band edges can make
modulation doping possible. Stability of the superlattice structure was
examined by ab initio molecular dynamics calculations at high temperatures.",0907.3591v1
2009-09-30,Doppler-free laser spectroscopy of buffer gas cooled molecular radicals,"We demonstrate Doppler-free saturated absorption spectroscopy of cold
molecular radicals formed by laser ablation inside a cryogenic buffer gas cell.
By lowering the temperature, congested regions of the spectrum can be
simplified, and by using different temperatures for different regions of the
spectrum a wide range of rotational states can be studied optimally. We use the
technique to study the optical spectrum of YbF radicals with a resolution of 30
MHz, measuring the magnetic hyperfine parameters of the electronic ground
state. The method is suitable for high resolution spectroscopy of a great
variety of molecules at controlled temperature and pressure, and is
particularly well-suited to those that are difficult to produce in the gas
phase.",0909.5534v2
2009-10-05,Isotope shifts and hyperfine structure of the Fe I 372 nm resonance line,"We report measurements of the isotope shifts of the $3d^64s^2 a ^5D_4 -
3d^64s4p z ^5F_5^o$ Fe I resonance line at 372 nm between all four stable
isotopes $^{54}$Fe, $^{56}$Fe, $^{57}$Fe, and $^{58}$Fe, as well as the
complete hyperfine structure of that line for $^{57}$Fe, the only stable
isotope having a non-zero nuclear spin. The field and specific mass shift
coefficients of the transition have been derived from the data, as well as the
experimental value for the hyperfine structure magnetic dipole coupling
constant $A$ of the excited state of the transition in $^{57}$Fe: $A(3d^64s4p z
^5F_5^o) = 81.69(86)$ MHz. The measurements were done by means of Doppler-free
laser saturated-absorption spectroscopy in a Fe-Ar hollow cathode using both
natural and enriched iron samples. The measured isotope shifts and hyperfine
constants are reported with uncertainties at the percent level.",0910.0479v1
2009-10-07,Entanglement in a spin system with inverse square statistical interaction,"We investigate the entanglement content of the ground state of a system
characterized by effective elementary degrees of freedom with fractional
statistics. To this end, we explicitly construct the ground state for a chain
of $N$ spins with inverse square interaction (the Haldane-Shastry model) in the
presence of an external uniform magnetic field. For such a system at zero
temperature, we evaluate the entanglement in the ground state both at finite
size and in the thermodynamic limit. We relate the behavior of the quantum
correlations with the spinon condensation phenomenon occurring at the
saturation field.",0910.1227v2
2009-10-09,Dynamics of Fully Nonlinear Drift Wave-Zonal Flow Turbulence System in Plasmas,"We present numerical simulations of fully nonlinear drift wave-zonal flow
(DW-ZF) turbulence systems in a nonuniform magnetoplasma. In our model, the
drift wave (DW) dynamics is pseudo-three-dimensional (pseudo-3D) and accounts
for self-interactions among finite amplitude DWs and their coupling to the
two-dimensional (2D) large amplitude zonal flows (ZFs). The dynamics of the 2D
ZFs in the presence of the Reynolds stress of the pseudo-3D DWs is governed by
the driven Euler equation. Numerical simulations of the fully nonlinear coupled
DW-ZF equations reveal that shortscale DW turbulence leads to nonlinear
saturated dipolar vortices, whereas the ZF sets in spontaneously and is
dominated by a monopolar vortex structure. The ZFs are found to suppress the
cross-field turbulent particle transport. The present results provide a better
model for understanding the coexistence of short- and large-scale coherent
structures, as well as associated subdued cross-field particle transport in
magnetically confined fusion plasmas.",0910.1635v2
2009-12-08,Coupling Photosphere and Corona: Linear and Turbulent Regimes,"In a recent work Grappin et al. [1] have shown that low- frequency movements
can be transmitted from one footpoint to the other along a magnetic loop, thus
mimicking a friction effect of the corona on the photosphere, and invalidating
the line-tying approximation. We consider here successively the effect of high
frequencies and turbulent damping on the process. We use a very simple
atmospheric model which allows to study analytically the laminar case, and to
study the turbulent case both using simple phenomenological arguments and a
more sophisticated turbulence model [2]. We find that, except when turbulent
damping is such that all turbulence is damped during loop traversal, coupling
still occurs between distant footpoints, and moreover the coronal field induced
by photospheric movements saturates at finite values.",0912.1497v1
2009-12-11,Direct observation of electronic inhomogeneities induced by point defect disorder in manganite films,"We have investigated the influence of point defect disorder in the electronic
properties of manganite films. Real-time mapping of ion irradiated samples
conductivity was performed though conductive atomic force microscopy (CAFM).
CAFM images show electronic inhomogeneities in the samples with different
physical properties due to spatial fluctuations in the point defect
distribution. As disorder increases, the distance between conducting regions
increases and the metal-insulator transition shifts to lower temperatures.
Transport properties in these systems can be interpreted in terms of a
percolative model. The samples saturation magnetization decreases as the
irradiation dose increases whereas the Curie temperature remains unchanged.",0912.2233v1
2010-01-11,Pauli-limited upper critical field in Fe1+yTe1-xSex,"In this work we investigated the temperature dependence of the upper critical
field u0Hc2(T) of Fe1.02(3)Te0.61(4)Se0.39(4) and Fe1.05(3)Te0.89(2)Se0.11(2)
single crystals by measuring the magnetotransport properties in stable dc
magnetic fields up to 35 T. Both crystals show that u0Hc2(T) in the ab-plane
and along the c-axis exhibit saturation at low temperatures. The anisotropy of
u0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic when
the temperature T->0. Furthermore, u0Hc2(0) deviates from the conventional
Werthamer-Helfand-Hohenberg (WHH) theoretical prediction values for both field
directions. Our analysis indicates that the spin-paramagnetic pair-breaking
effect is responsible for the temperature-dependent behavior of u0Hc2(T) in
both field directions.",1001.1751v3
2010-01-18,Density Effects on the Negative Refractive Index of a Split Ring Resonator Metamaterial,"Perfect lensing and cloaking based on complementary media are possible
applications of negative refractive index materials. Metamaterials represent
the natural candidates to realize such property by tailoring the effective
dielectric permittiviy and magnetic permeability. The fine tuning of $n<0$ of
metamaterials is limited by coarse grained inclusions which give discreteness
to the electromagnetic parameters as a function of their density. We study the
negative refractive index of a metamaterial as a function of the linear density
of the lattice period at microwave frequency. The negative refractive index is
obtained by a waveguide filled with a split ring resonator array in a frequency
band below the cut off frequency of the waveguide. The special value of $n=-1$
typical of perfect lensing is maintained by tuning the density on a bandwidth
of 1 GHz. A cut-off density above which the metamaterial operates is observed.
A second critical density above which the transmission saturates is found close
to the Pendry limit. Such results on the density of negative refractive index
metamaterials open new paths towards the fine tuning of constitutive parameters
at wanted values by means of transformation optics.",1001.2976v2
2010-03-10,Effects of excess Fe on upper critical field and magnetotransport in Fe1+y(Te1-xSx)z,"We have investigated the upper critical field anisotropy and magnetotransport
properties of Fe1.14(1)Te0.91(2)S0.09(2) single crystals in stable magnetic
fields up to 35 T. The results show that u0Hc2(T) along the c axis and in the
ab-plane exhibit saturation at low temperatures. The anisotropy of u0Hc2(T)
decreases with decreasing temperature, becoming nearly isotropic for T->0. Our
analysis indicates that the spin-paramagnetic pair-breaking with spin-orbital
scattering is responsible for the behavior of u0Hc2(T). Furthermore, from
analysis of the normal state properties, we show evidence that the excess Fe
acting as Kondo-type impurities is a key factor determining the normal and
superconducting state physical properties.",1003.2209v1
2010-05-28,Growth and characterization of multiferroic BiMnO$_3$ thin films,"We have grown epitaxial thin films of multiferroic BiMnO$_3$ using pulsed
laser deposition. The films were grown on SrTiO$_3$ (001) substrates by
ablating a Bi-rich target. Using x-ray diffraction we confirmed that the films
were epitaxial and the stoichiometry of the films was confirmed using Auger
electron spectroscopy. The films have a ferromagnetic Curie temperature ($T_C$)
of 85$\pm$5 K and a saturation magnetization of 1 $\mu_B$/Mn. The electric
polarization as a function of electric field ($P-E$) was measured using an
interdigital capacitance geometry. The $P-E$ plot shows a clear hysteresis that
confirms the multiferroic nature of the thin films.",1005.5404v1
2010-05-30,Quasi-1d quantum helimagnets: The fate of multipolar phases,"Coupled frustrated spin-1/2 chains in high magnetic fields described within
the ferro- antiferromagnetic J1-J2 Heisenberg model are studied by the DMRG,
the hard core boson, and the spin wave theory approaches. Multipolar phases
related to magnon bound states are destroyed (supported) by weak
antiferromagnetic (ferromagnetic) interchain couplings Jic. We show that
quantum spin nematics might be found for LiVCuO4 whereas for Li(Na)Cu2O2 it is
prevented by a sizeable antiferromagnetic Jic. Also for Li2ZrCuO4 with a small
antiferromagnetic Jic expected triatic or quartic phases are unlikely, too. The
saturation field is found to be strongly affected even by a relatively small
Jic.",1005.5500v2
2010-07-13,Exact results on the quench dynamics of the entanglement entropy in the toric code,"We study quantum quenches in the two-dimensional Kitaev toric code model and
compute exactly the time-dependent entanglement entropy of the non-equilibrium
wave-function evolving from a paramagnetic initial state with the toric code
Hamiltonian. We find that the area law survives at all times. Adding disorder
to the toric code couplings makes the entanglement entropy per unit boundary
length saturate to disorder-independent values at long times and in the
thermodynamic limit. There are order-one corrections to the area law from the
corners in the subsystem boundary but the topological entropy remains zero at
all times. We argue that breaking the integrability with a small magnetic field
could change the area law to a volume scaling as expected of thermalized states
but is not sufficient for forming topological entanglement due to the presence
of an excess energy and a finite density of defects.",1007.2014v3
2010-08-06,Long ranged interactions in carbon atomic chains,"Based on first-principles calculations we revealed fundamental properties of
infinite and finite size monatomic chains of carbon atoms in equilibrium and
under an applied strain. Distributions of bond lengths and magnetic moments at
atomic sites exhibit interesting even-odd disparity depending on the number of
carbon atoms in the chain and on the type of saturation of carbon atoms at both
ends. It was shown that, the $\pi$-bands of carbon atomic chains behave as a
one dimensional free electron system. A local perturbation created by a small
displacement of the single carbon atom at the center of a long chain induces
oscillations of atomic forces and charge density, which are carried to long
distances over the chain. These long ranged oscillations are identified as
Friedel oscillations showing $1/r$ decay rate in one dimensional systems.",1008.1126v2
2010-08-31,Quantitative atomic spectroscopy for primary thermometry,"Quantitative spectroscopy has been used to measure accurately the
Doppler-broadening of atomic transitions in $^{85}$Rb vapor. By using a
conventional platinum resistance thermometer and the Doppler thermometry
technique, we were able to determine $k_B$ with a relative uncertainty of
$4.1\times 10^{-4}$, and with a deviation of $2.7\times 10^{-4}$ from the
expected value. Our experiment, using an effusive vapour, departs significantly
from other Doppler-broadened thermometry (DBT) techniques, which rely on weakly
absorbing molecules in a diffusive regime. In these circumstances, very
different systematic effects such as magnetic sensitivity and optical pumping
are dominant. Using the model developed recently by Stace and Luiten, we
estimate the perturbation due to optical pumping of the measured $k_B$ value
was less than $4\times 10^{-6}$. The effects of optical pumping on atomic and
molecular DBT experiments is mapped over a wide range of beam size and
saturation intensity, indicating possible avenues for improvement. We also
compare the line-broadening mechanisms, windows of operation and detection
limits of some recent DBT experiments.",1008.5229v3
2010-09-02,Phase-space characterization of complexity in quantum many-body dynamics,"We propose a phase-space Wigner harmonics entropy measure for many-body
quantum dynamical complexity. This measure, which reduces to the well known
measure of complexity in classical systems and which is valid for both pure and
mixed states in single-particle and many-body systems, takes into account the
combined role of chaos and entanglement in the realm of quantum mechanics. The
effectiveness of the measure is illustrated in the example of the Ising chain
in a homogeneous tilted magnetic field. We provide numerical evidence that the
multipartite entanglement generation leads to a linear increase of entropy
until saturation in both integrable and chaotic regimes, so that in both cases
the number of harmonics of the Wigner function grows exponentially with time.
The entropy growth rate can be used to detect quantum phase transitions. The
proposed entropy measure can also distinguish between integrable and chaotic
many-body dynamics by means of the size of long term fluctuations which become
smaller when quantum chaos sets in.",1009.0560v1
2010-09-07,Mesoscopic transport in ultrathin films of La$_{0.67}$Ca$_{0.33}$MnO$_3$,"We investigate the electrical transport in mesoscopic structures of
La$_{0.67}$Ca$_{0.33}$MnO$_3$ in the regime of the metal-insulator transition
by fabricating microbridges from strained and unstrained thin films. We measure
current-voltage characteristics as function of temperature and in high magnetic
fields and with varying film thickness. For strained films, in warming from the
metallic to the insulating state, we find non-linear effects in the steep part
of the transition characterized by a differential resistance with a strong peak
around zero applied current, and saturating at higher currents after resistance
drops up to 60 %. We propose that this nonlinear behavior is associated with
melting of the insulating state by injecting charge carriers, signalling the
occurrence of an intervening phase which involves the formation of short range
polaron correlations.",1009.1386v1
2010-09-09,"Structure and stability of graphene nanoribbons in oxygen, carbon dioxide, water, and ammonia","We determine, by means of density functional theory, the stability and the
structure of graphene nanoribbon (GNR) edges in presence of molecules such as
oxygen, water, ammonia, and carbon dioxide. As in the case of
hydrogen-terminated nanoribbons, we find that the most stable armchair and
zigzag configurations are characterized by a non-metallic/non-magnetic nature,
and are compatible with Clar's sextet rules, well known in organic chemistry.
In particular, we predict that, at thermodynamic equilibrium, neutral GNRs in
oxygen-rich atmosphere should preferentially be along the armchair direction,
while water-saturated GNRs should present zigzag edges. Our results promise to
be particularly useful to GNRs synthesis, since the most recent and advanced
experimental routes are most effective in water and/or ammonia-containing
solutions.",1009.1808v1
2010-09-09,(Ir-)Reversibility and thermal equilibrium in magnetic domain pattern formation in ultra-thin ferromagnetic films,"We investigate the details of pattern formation and transitions between
different modulated phases in ultra-thin Fe films on Cu(001). At high
temperature, the transitions between the uniform saturated state, the bubble
state and the striped state are completely reversible, while at low temperature
the bubble phase is avoided. The observed non-equilibrium behavior can be
qualitatively explained by considering the intrinsic energy barriers appearing
in the system due to the competition between the short-ranged exchange and the
long-ranged dipolar interactions. Our experiments suggest that the height of
these energy barriers is related to the domain size and is therefore strongly
temperature dependent.",1009.1815v1
2010-09-20,Ultra-high energy nuclei source in the direction to Virgo cluster,"The significant anisotropy in the arrival directions of the 69 events with
energy E> 55 EeV detected by Pierre Auger collaboration is located in the
20-degree region centered near Cen A. Not only the 2-point, but also the
3-point and 4-point autocorrelation functions are completely saturated by this
region. Besides there is an deficit of events in the direction of Virgo
cluster. If one assumes that the excess around Cen A is due to heavy nuclei
shifted from Virgo, one can explain 20-degree scale of this anomaly. Also
location of the highest energy event between the Cen A region and the Virgo
cluster supports this idea. Magnitude and direction of the magnetic field is
similar in this case to those expected for Galactic models. The existence of
nuclei sources in the sky opens the road for a self-consistent description of
Auger data.",1009.3879v1
2010-11-01,On the Bogomol'nyi bound in Einstein-Maxwell-dilaton gravity,"It has been shown that the 4-dimensional Einstein-Maxwell-dilaton theory
allows a Bogomol'nyi-type inequality for an arbitrary dilaton coupling constant
$\alpha $, and that the bound is saturated if and only if the (asymptotically
flat) spacetime admits a nontrivial spinor satisfying the gravitino and the
dilatino Killing spinor equations. The present paper revisits this issue and
argues that the dilatino equation fails to ensure the dilaton field equation
unless the solution is purely electric/magnetic, or the dilaton coupling
constant is given by $\alpha=0, \sqrt 3$, corresponding to the
Brans-Dicke-Maxwell theory and the Kaluza-Klein reduction of 5-dimensional
vacuum gravity, respectively. A systematic classification of the supersymmetric
solutions reveals that the solution can be rotating if and only if the solution
is dyonic or the coupling constant is given by $\alpha=0, \sqrt 3$. This
implies that the theory with $\alpha \ne 0, \sqrt 3$ cannot be embedded into
supergravity except for the static truncation. Physical properties of
supersymmetric solutions are explored from various points of view.",1011.0261v2
2011-01-05,Alfvén waves and ideal two-dimensional Galerkin truncated magnetohydrodynamics,"We investigate numerically the dynamics of two-dimensional Euler and ideal
magnetohydrodynamics (MHD) flows in systems with a finite number of modes, up
to $4096^2$, for which several quadratic invariants are preserved by the
truncation and the statistical equilibria are known. Initial conditions are the
Orszag-Tang vortex with a neutral X-point centered on a stagnation point of the
velocity field in the large scales. In MHD, we observe that the total energy
spectra at intermediate times and intermediate scales correspond to the
interactions of eddies and waves, $E_T(k)\sim k^{-3/2}$. Moreover, no
dissipative range is visible neither for Euler nor for MHD in two dimensions;
in the former case, this may be linked to the existence of a vanishing
turbulent viscosity whereas in MHD, the numerical resolution employed may be
insufficient. When imposing a uniform magnetic field to the flow, we observe a
lack of saturation of the formation of small scales together with a significant
slowing-down of their equilibration, with however a cut-off independent partial
thermalization being reached at intermediate scales.",1101.1078v1
2011-03-31,High Q-factor Sapphire Whispering Gallery Mode Microwave Resonator at Single Photon Energies and milli-Kelvin Temperatures,"The microwave properties of a crystalline sapphire dielectric whispering
gallery mode resonator have been measured at very low excitation strength
(E/hf=1) and low temperatures (T = 30 mK). The measurements were sensitive
enough to observe saturation due to a highly detuned electron spin resonance,
which limited the loss tangent of the material to about 2e-8 measured at 13.868
and 13.259 GHz. Small power dependent frequency shifts were also measured which
correspond to an added magnetic susceptibility of order 1e-9. This work shows
that quantum limited microwave resonators with Q-factors > 1e8 are possible
with the implementation of a sapphire whispering gallery mode system.",1103.6094v2
2011-04-13,Current induced vortex superlattices in nanomagnets,"Influence of the spin-transfer torque on the vortex state magnetic nanodisk
is studied numerically via Slonczewski-Berger mechanism. The existence of a
critical current is determined for the case of same-directed electrical
current, its spin polarization and polarity of the vortex. The critical current
separates two regimes: (i) deformed but static vortex state and (ii)
essentially dynamic state under which the spatio-temporal periodic structures
can appear. The structure is a stable vortex-antivortex lattice. Symmetry of
the lattice depends on the applied current value and for high currents (close
to saturation) only square lattices are observed. General relations for sizes
of the stable lattice is obtained analytically.",1104.2483v1
2011-05-04,"Diffusion of Mn interstitials in (Ga,Mn)As epitaxial layers","Magnetic properties of thin (Ga,Mn)As layers improve during annealing by
out-diffusion of interstitial Mn ions to a free surface. Out-diffused Mn atoms
participate in the growth of a Mn-rich surface layer and a saturation of this
layer causes an inhibition of the out-diffusion. We combine high-resolution
x-ray diffraction with x-ray absorption spectroscopy and a numerical solution
of the diffusion problem for the study of the out-diffusion of Mn interstitials
during a sequence of annealing steps. Our data demonstrate that the
out-diffusion of the interstitials is substantially affected by the internal
electric field caused by an inhomogeneous distribution of charges in the
(Ga,Mn)As layer.",1105.0849v1
2011-05-17,Superconductivity and ferromagnetism in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$,"Superconductivity and ferromagnetism are two antagonistic cooperative
phenomena, which makes it difficult for them to coexist. Here we demonstrate
experimentally that they do coexist in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ with
$0.2\leq x\leq0.4$, in which superconductivity is associated with Fe-3$d$
electrons and ferromagnetism comes from the long-range ordering of Eu-4$f$
moments via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. The coexistence
is featured by large saturated ferromagnetic moments, high and comparable
superconducting and magnetic transition temperatures, and broad coexistence
ranges in temperature and field. We ascribe this unusual phenomenon to the
robustness of superconductivity as well as the multi-orbital characters of iron
pnictides.",1105.3255v1
2011-07-20,The Capabilities of a Perturbed Toric Code as a Quantum Memory,"We analyze the effect of typical, unknown perturbations on the 2D toric code
when acting as a quantum memory, incorporating the effects of error correction
on read-out. By transforming the system into a 1D transverse Ising model
undergoing an instantaneous quench, and making extensive use of Lieb-Robinson
bounds, we prove that for a large class of perturbations, the survival time of
stored information grows at least logarithmically with the system size. A
uniform magnetic field saturates this scaling behavior. We show that
randomizing the stabilizer strengths gives a polynomial survival time with a
degree that depends on the strength of the perturbation.",1107.3940v3
2011-09-19,Quantum spin liquid in frustrated one dimensional LiCuSbO4,"A quantum magnet, LiCuSbO4, with chains of edge-sharing S = 1/2 CuO6
octahedra is reported. While the Curie-Weiss constant is ferromagnetic, \theta
= 30 K, no phase transition or spin freezing occurs down to 100 mK. Specific
heat indicates a distinct high field phase near the 12 T saturation field.
Neutron scattering shows incommensurate spin correlations with q =
0.47\pm0.01{\pi}/a and places an upper limit of 70 \mueV on a potential spin
gap. Exact diagonalization of easy plane S = 1/2 chains with competing ferro-
and antiferromagnetic interactions (J1 = - 75 K, J2 = 34 K) accounts for the T
> 2 K data.",1109.4061v4
2011-11-08,"A mechanism giving a finite value to the speed of light, and some experimental consequences","We admit that the vacuum is not empty but is filled with continuously
appearing and disappearing virtual fermion pairs. We show that if we simply
model the propagation of the photon in vacuum as a series of transient captures
within the virtual pairs, we can derive the finite light velocity $c$ as the
average delay on the photon propagation. We then show that the vacuum
permittivity $\epsilon_0$ and permeability $\mu_0$ originate from the
polarization and the magnetization of the virtual fermions pairs. Since the
transit time of a photon is a statistical process within this model, we expect
it to be fluctuating. We discuss experimental tests of this prediction. We also
study vacuum saturation effects under high photon density conditions.",1111.1847v1
2011-12-06,Entanglement of two harmonic modes coupled by angular momentum,"We examine the entanglement induced by an angular momentum coupling between
two harmonic systems. The Hamiltonian corresponds to that of a charged particle
in a uniform magnetic field in an anisotropic quadratic potential, or
equivalently, to that of a particle in a rotating quadratic potential. We
analyze both the vacuum and thermal entanglement, obtaining analytic
expressions for the entanglement entropy and negativity through the gaussian
state formalism. It is shown that vacuum entanglement diverges at the edges of
the dynamically stable sectors, increasing with the angular momentum and
saturating for strong fields, whereas at finite temperature, entanglement is
non-zero just within a finite field or frequency window and no longer diverges.
Moreover, the limit temperature for entanglement is finite in the whole stable
domain. The thermal behavior of the gaussian quantum discord and its difference
with the negativity is also discussed.",1112.1441v1
2011-12-27,Absorbing states of zero-temperature Glauber dynamics in random networks,"We study zero-temperature Glauber dynamics for Ising-like spin variable
models in quenched random networks with random zero-magnetization initial
conditions. In particular, we focus on the absorbing states of finite systems.
While it has quite often been observed that Glauber dynamics lets the system be
stuck into an absorbing state distinct from its ground state in the
thermodynamic limit, very little is known about the likelihood of each
absorbing state. In order to explore the variety of absorbing states, we
investigate the probability distribution profile of the active link density
after saturation as the system size $N$ and $<k >$ vary. As a result, we find
that the distribution of absorbing states can be split into two self-averaging
peaks whose positions are determined by $<k>$, one slightly above the ground
state and the other farther away. Moreover, we suggest that the latter peak
accounts for a non-vanishing portion of samples when $N$ goes to infinity while
$<k >$ stays fixed. Finally, we discuss the possible implications of our
results on opinion dynamics models.",1112.5927v2
2012-01-09,The role of boundaries in the MagnetoRotational Instability,"In this paper, we investigate numerically the flow of an electrically
conducting fluid in a cylindrical Taylor-Couette flow when an axial magnetic
field is applied. To minimize Ekman recirculation due to vertical no-slip
boundaries, two independently rotating rings are used at the vertical endcaps.
This configuration reproduces setup used in laboratory experiments aiming to
observe the MagnetoRotational Instability (MRI). Our 3D global simulations show
that the nature of the bifurcation, the non-linear saturation, and the
structure of axisymmetric MRI modes are significantly affected by the presence
of boundaries. In addition, large scale non-axisymmetric modes are obtained
when the applied field is sufficiently strong. We show that these modes are
related to Kelvin-Helmoltz destabilization of a free Shercliff shear layer
created by the combined action of the applied field and the rotating rings at
the endcaps. Finally, we compare our numerical simulations to recent
experimental results obtained in the Princeton MRI experiment.",1201.1853v1
2012-01-13,Linear and Weakly Nonlinear Analysis of the Magneto-Rotational-Instability in Thin Keplerian Discs,"The linear instability of thin, vertically-isothermal Keplerian discs, under
the influence of axial magnetic field is investigated. Solutions of the
stability problem are found explicitly by asymptotic expansions in the small
aspect ratio of the disc. It is shown that the perturbations are decoupled into
in-plane and vertical modes. Exact expressions for the growth rates as well as
the number of unstable modes are derived. Those are the discrete counterpart of
the continuous infinite homogeneous cylinder magnetorotational (MRI) spectrum.
In addition, a weakly nonlinear analysis of the MRI is performed. It is shown
that near the instability threshold the latter is saturated by the stable
magnetoacoustic modes.",1201.2847v1
2012-01-27,Giant negative magnetoresistance in high-mobility 2D electron systems,"We report on a giant negative magnetoresistance in very high mobility
GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at
$B \simeq 1$ kG, where the magnetoresistivity develops a minimum emerging at $T
\lesssim 2$ K. Unlike the zero-field resistivity which saturates at $T \simeq 2
$ K, the resistivity at this minimum continues to drop at an accelerated rate
to much lower temperatures and becomes several times smaller than the
zero-field resistivity. Unexpectedly, we also find that the effect is destroyed
not only by increasing temperature but also by modest in-plane magnetic fields.
The analysis shows that giant negative magnetoresistance cannot be explained by
existing theories considering interaction-induced or disorder-induced
corrections.",1201.5679v1
2012-04-27,Observation of a Free-Shercliff-Layer Instability in Cylindrical Geometry,"We report on observations of a free-Shercliff-layer instability in a
Taylor-Couette experiment using a liquid metal over a wide range of Reynolds
numbers, $Re\sim 10^3-10^6$. The free Shercliff layer is formed by imposing a
sufficiently strong axial magnetic field across a pair of differentially
rotating axial endcap rings. This layer is destabilized by a hydrodynamic
Kelvin-Helmholtz-type instability, characterized by velocity fluctuations in
the $r-\theta$ plane. The instability appears with an Elsasser number above
unity, and saturates with an azimuthal mode number $m$ which increases with the
Elsasser number. Measurements of the structure agree well with 2D global linear
mode analyses and 3D global nonlinear simulations. These observations have
implications for a range of rotating MHD systems in which similar shear layers
may be produced.",1204.6339v1
2012-05-14,Isotope shifts and hyperfine structure of the Fe I 373.7 nm resonance line,"We report measurements of the isotope shifts of the 3d6 4s2 a 5D3 - 3d6 4s4p
z 5F4o FeI resonance line at 373.7 nm between all four stable isotopes 54Fe,
56Fe, 57Fe and 58Fe, as well as the complete hyperfine structure of that line
for 57Fe, the only stable isotope having a non-zero nuclear spin. The field and
specific mass shift coefficients of the transition have been derived from the
data, as well as the experimental value for the hyperfine structure magnetic
dipole coupling constant A of the excited state of the transition in 57Fe :
A(3d6 4s4p z 5F4o) = 68.21(69) MHz. The measurements were carried out by means
of high-resolution Doppler-free laser saturated absorption spectroscopy in a
Fe-Ar hollow cathode discharge cell using both natural and enriched iron
samples. The measured isotope shifts and hyperfine constants are reported with
uncertainties at the percent level.",1205.3146v1
2012-06-01,Deep Spin-Glass Hysteresis Area Collapse and Scaling in the $d=3$ $\pm J$ Ising Model,"We investigate the dissipative loss in the $\pm J$ Ising spin glass in three
dimensions through the scaling of the hysteresis area, for a maximum magnetic
field that is equal to the saturation field. We perform a systematic analysis
for the whole range of the bond randomness as a function of the sweep rate, by
means of frustration-preserving hard-spin mean field theory. Data collapse
within the entirety of the spin-glass phase driven adiabatically (i.e.,
infinitely-slow field variation) is found, revealing a power-law scaling of the
hysteresis area as a function of the antiferromagnetic bond fraction and the
temperature. Two dynamic regimes separated by a threshold frequency $\omega_c$
characterize the dependence on the sweep rate of the oscillating field. For
$\omega < \omega_c$, the hysteresis area is equal to its value in the adiabatic
limit $\omega = 0$, while for $\omega > \omega_c$ it increases with the
frequency through another randomness-dependent power law.",1206.0230v2
2012-06-04,Coarse-grained spin density-functional theory: infinite-volume limit via the hyperfinite,"Coarse-grained spin density functional theory (SDFT) is a version of SDFT
which works with number/spin densities specified to a limited resolution ---
averages over cells of a regular spatial partition --- and external potentials
constant on the cells. This coarse-grained setting facilitates a rigorous
investigation of the mathematical foundations which goes well beyond what is
currently possible in the conventional formualation. Problems of existence,
uniqueness and regularity of representing potentials in the coarse-grained SDFT
setting are here studied using techniques of (Robinsonian) nonstandard
analysis. Every density which is nowhere spin-saturated is V-representable, and
the set of representing potentials is the functional derivative, in an
appropriate generalized sense, of the Lieb interal energy functional.
Quasi-continuity and closure properties of the set-valued representing
potentials map are also established. The extent of possible non-uniqueness is
similar to that found in non-rigorous studies of the conventional theory,
namely non-uniqueness can occur for states of collinear magnetization which are
eigenstates of $S_z$.",1206.0769v2
2012-07-19,Dipolar order by disorder in the classical Heisenberg antiferromagnet on the kagome lattice,"Ever since the experiments which founded the field of highly frustrated
magnetism, the kagome Heisenberg antiferromagnet has been the archetypical
setting for the study of fluctuation induced exotic ordering. To this day the
nature of its classical low-temperature state has remained a mystery: the
non-linear nature of the fluctuations around the exponentially numerous
harmonically degenerate ground states has not permitted a controlled theory,
while its complex energy landscape has precluded numerical simulations at low
temperature. Here we present an efficient Monte Carlo algorithm which removes
the latter obstacle. Our simulations detect a low-temperature regime in which
correlations saturate at a remarkably small value. Feeding these results into
an effective model and analyzing the results in the framework of an appropriate
field theory implies the presence of long-range dipolar spin order with a
tripled unit cell.",1207.4752v2
2012-08-08,Evidence for two-gap superconductivity in the non-centrosymmetric compound LaNiC$_2$,"We study the superconducting properties of the non-centrosymmetric compound
LaNiC$_2$ by measuring the London penetration depth $\Delta \lambda (T)$, the
specific heat $C(T,B)$ and the electrical resistivity $\rho (T,B)$. Both
$\Delta\lambda (T)$ and the electronic specific heat $C_e(T)$ exhibit
exponential behavior at low temperatures and can be described in terms of a
phenomenological two-gap BCS model. The residual Sommerfeld coefficient in the
superconducting state, $\gamma_0(B)$, shows a fast increase at low fields and
then an eventual saturation with increasing magnetic field. A pronounced upturn
curvature is observed in the upper critical field $B_{c2}(T)$ near $T_{c}$. All
the experimental observations support the existence of two-gap
superconductivity in LaNiC$_2$.",1208.1596v1
2012-09-29,Nonsaturating Dephasing Time at Low Temperature in an Open Quantum Dot,"We report measurements of the electron dephasing time extracted from the weak
localization (WL) correction to the average conductance in an open AlGaAs/GaAs
quantum dot from 1 K to 13 mK. In agreement with theoretical predictions but in
contrast with previous measurements in quantum dots, the extracted dephasing
time does not saturate at the lowest temperatures. We find that the dephasing
time follows an inverse linear power law with temperature. We determine that
the extraction of the dephasing time from WL is applicable down to our lowest
temperatures, but extraction from finite magnetic field conductance
fluctuations is complicated by charging effects below 13 mK.",1210.0087v1
2012-10-02,Graphene as a reversible spin manipulator of molecular magnets,"One of the primary objectives in molecular nano-spintronics is to manipulate
the spin states of organic molecules with a d-electron center, by suitable
external means. In this letter, we demonstrate by first principles density
functional calculations, as well as second order perturbation thoery, that a
strain induced change of the spin state, from S=1 $\to$ S=2, takes place for an
iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene
lattice. The process is reversible in a sense that the application of tensile
or compressive strains in the graphene lattice can stabilize FeP in different
spin states, each with a unique saturation moment and easy axis orientation.
The effect is brought about by a change in Fe-N bond length in FeP, which
influences the molecular level diagram as well as the interaction between the C
atoms of the graphene layer and the molecular orbitals of FeP.",1210.0666v1
2012-11-20,Bond Randomness Induced Magnon Decoherence in a Spin-1/2 Ladder Compound,"We have used a combination of neutron resonant spin-echo and triple-axis
spectroscopies to determine the energy and linewidth of the magnon resonance in
IPA-Cu(Cl$_{0.95}$Br$_{0.05}$)$_3$, a model spin-1/2 ladder antiferromagnet
where Br substitution induces bond randomness. We find that the bond defects
induce a blueshift, $\delta \Delta$, and broadening, $\delta \Gamma$, of the
magnon gap excitation compared to the pure compound. At temperatures exceeding
the energy scale of the inter-ladder exchange interactions, $\delta \Delta$ and
$\delta \Gamma$ are temperature independent within the experimental error, in
agreement with Matthiessen's rule according to which magnon-defect scattering
yields a temperature independent contribution to the magnon mean free path.
Upon cooling, $\delta \Delta$ and $\delta \Gamma$ become temperature dependent
and saturate at values lower than those observed at higher temperature,
consistent with the crossover from one-dimensional to two-dimensional spin
correlations with decreasing temperature previously observed in pure
IPA-CuCl$_3$. These results indicate limitations in the applicability of
Matthiessen's rule for magnon scattering in low-dimensional magnets.",1211.4741v1
2012-12-04,Three Dimensional Structure of Relativistic Jet Formation,"Using high resolution adaptive mesh refinement simulations in 3D, we
investigate the formation of relativistic jets from rotating magnetospheres.
Here, we focus on the development of non-axisymmetric modes due to internal and
external perturbations to the jet. These originate either from injection of
perturbations with the flow or from a clumpy external medium. In the helical
field geometry of the accelerating jet, the m=1 to m=5 modes are analyzed and
found to saturate at a height of \sim 20 inner disk radii. We also discuss a
means to control artificial amplification of m = 4 noise in the cartesian
simulation geometry. Strong perturbations due to an in-homogeneous ambient
medium lead to flow configurations with increased magnetic pitch and thus
indicate a self-stabilization of the jet formation mechanism.",1212.0676v1
2012-12-18,Photoluminescence studies of Zeeman effect in type-II InSb/InAs nanostructures,"Electron spin polarization up to 100% has been observed in type-II narrow-gap
heterostructures with ultrathin InSb insertions in an InAs matrix via
investigation of circularly polarized photoluminescence in an external magnetic
field applied in Faraday geometry. The polarization degree decreases
drastically, changes its sign, and saturates finally at the value of 10% in the
limit of either high temperature or strong excitation. The observed effect is
explained in terms of strong Zeeman splitting of the electron conduction band
in the InAs matrix and a heavy-hole state confined in the InSb insertion, due
to a large intrinsic g-factor of both types of carriers. The hole ground state
in a monolayer scale InSb/InAs quantum well, calculated using a tight-binding
approach, fits well the observed emission wavelength. Temperature dependence of
the emission polarization degree is in good agreement with its theoretical
estimation performed in the framework of a proposed phenomenological model.",1212.4341v1
2012-12-28,Magneto-resistance up to 60 Tesla in Topological Insulator Bi2Te3 Thin Films,"We report magneto-transport studies of topological insulator Bi_{2}Te_{3}
thin films grown by pulsed laser deposition. A non-saturating linear-like
magneto-resistance (MR) is observed at low temperatures in the magnetic field
range from a few Tesla up to 60 Tesla. We demonstrate that the strong
linear-like MR at high field can be well understood as the weak
antilocalization phenomena described by Hikami-Larkin-Nagaoka theory. Our
analysis suggests that in our system, a topological insulator, the elastic
scattering time can be longer than the spin-orbit scattering time. We briefly
discuss our results in the context of Dirac Fermion physics and 'quantum linear
magnetoresistance'.",1212.6464v1
2013-01-10,Evolution of solar-type stellar wind,"By extending our self-consistent MHD simulations for the solar wind, we study
the evolution of stellar winds of solar-type stars from early main sequence
stage to red giant phase. Young solar-type stars are active and the mass loss
rates are larger by up to ~ 100 times than that of the present-day sun. We
investigate how the stellar wind is affected when the magnetic field strength
and fluctuation amplitude at the photosphere increase. While the mass loss rate
sensitively depends on the input energy from the surface because of the global
instability related to the reflection and nonlinear dissipation of Alfven
waves, it saturates at ~ 100 times because most of the energy is used up for
the radiative losses rather than the kinetic energy of the wind. After the end
of the main sequence phase when the stellar radius expands by ~ 10 times, the
steady hot corona with temperature $10^6$ K, suddenly disappears. Chromospheric
materials, with hot bubbles embedded owing to thermal instability, directly
stream out; the red giant wind is not a steady stream but structured outflow.",1301.2359v1
2013-04-25,Universal corrections to the entanglement entropy in gapped quantum spin chains: a numerical study,"We carry out a numerical study of the bi-partite entanglement entropy in the
gapped regime of two paradigmatic quantum spin chain models: the Ising chain in
an external magnetic field and the anti-ferromagnetic XXZ model. The universal
scaling limit of these models is described by the massive Ising field theory
and the SU(2)-Thirring (sine-Gordon) model, respectively. We may therefore
exploit quantum field theoretical results to predict the behaviour of the
entropy. We numerically confirm that, in the scaling limit, corrections to the
saturation of the entropy at large region size are proportional to the Bessel
function K0(2mr) where m is a mass scale (the inverse correlation length) and r
the length of the region under consideration. The proportionality constant is
simply related to the number of particle types in the universal spectrum. This
was originally predicted in publications involving two of the current authors
for two-dimensional quantum field theories. Away from the universal region our
numerics suggest an entropic behaviour following quite closely the quantum
field theory prediction, except for extra dependencies on the correlation
length.",1304.6874v1
2013-05-07,Micromagnetic modelling of anisotropic damping in ferromagnet,"We report a numerical implementation of the Landau-Lifshitz-Baryakhtar
theory, which dictates that the micromagnetic relaxation term obeys the
symmetry of the magnetic crystal, i. e. replacing the single intrinsic damping
constant with a tensor of corresponding symmetry. The effect of anisotropic
relaxation is studied in thin saturated ferromagnetic disk and ellipse with and
without uniaxial magneto-crystalline anisotropy. We investigate the angular
dependency of the linewidth of magnonic resonances with respect to the given
structure of the relaxation tensor. The simulations suggest that the anisotropy
of the magnonic linewidth is determined by only two factors: the projection of
the relaxation tensor onto the plane of precession and the ellipticity of the
later.",1305.1641v2
2013-05-15,Competing orders in the 2D half-filled SU(2N) Hubbard model through the pinning field quantum Monte-Carlo simulations,"We non-perturbatively investigate the ground state magnetic properties of the
2D half-filled SU($2N$) Hubbard model in the square lattice by using the
projector determinant quantum Monte Carlo simulations combined with the method
of local pinning fields. Long-range Neel orders are found for both the SU(4)
and SU(6) cases at small and intermediate values of $U$. In both cases, the
long-range Neel moments exhibit non-monotonic behavior with respect to $U$,
which first grow and then drop as $U$ increases. This result is fundamentally
different from the SU(2) case in which the Neel moments increase monotonically
and saturate. In the SU(6) case, a transition to the columnar dimer phase is
found in the strong interaction regime.",1305.3571v3
2013-05-25,On the definition and interpretation of a static quark anti-quark potential in the colour-adjoint channel,"We study possibilities to define a static quark anti-quark pair in a
colour-adjoint orientation based on Wilson loops with generator insertions,
using both lattice QCD and leading order perturbation theory in various gauges.
Non-perturbatively, the only way to obtain non-zero results while maintaining
positivity of the Hamiltonian is by some form of temporal gauge. In this case
the correlator is equivalent to a gauge invariant correlation function of a
static quark anti-quark pair and a static adjoint quark, the resulting
three-point potential is attractive. Saturating open colour indices with colour
magnetic fields instead also leads to a gauge invariant correlator. However
this object is found to couple to the singlet sector only. There appears to be
no lattice observable that reproduces the repulsive adjoint potential predicted
by perturbation theory in Lorenz or Coulomb gauges.",1305.5957v1
2013-06-18,Interaction of Ultra Relativistic e- e+ Fireball Beam with Plasma,"Ab initio simulations of the propagation in a plasma of a soon to be
available relativistic electron-positron beam or fireball beam provide an
effective mean for the study of microphysics relevant to astrophysical
scenarios. We show that the current filamentation instability associated with
some of these scenarios reaches saturation after only 10 cm of propagation in a
typical laboratory plasma with a density 10^17/cc. The different regimes of the
instability, from the purely transverse to the mixed mode filamentation, can be
accessed by varying the background plasma density. The instability generates
large local plasma gradients, intense transverse magnetic fields, and enhanced
emission of radiation. We suggest that these effects may be observed
experimentally for the first time.",1306.4380v2
2013-07-11,Large Linear Magnetoresistance and Shubnikov-de Hass Oscillations in Single Crystals of YPdBi Heusler Topological Insulators,"We report the observation of a large linear magnetoresistance (MR) and
Shubnikov-de Hass (SdH) quantum oscillations in single crystals of YPdBi
Heusler topological insulators. Owning to the successfully obtained the
high-quality YPdBi single crystals, large non-saturating linear MR of as high
as 350% at 5K and over 120% at 300 K under a moderate magnetic field of 7 T is
observed. In addition to the large, field-linear MR, the samples exhibit
pronounced SdH quantum oscillations at low temperature. Analysis of the SdH
data manifests that the high-mobility bulk electron carriers dominate the
magnetotransport and are responsible for the observed large linear MR in YPdBi
crystals. These findings imply that the Heusler-based topological insulators
have superiorities for investigating the novel quantum transport properties and
developing the potential applications.",1307.3022v1
2013-07-23,Honeycomb Heisenberg Spin Ladder: Unusual Ground State and Thermodynamic Properties,"The unusual ground state and thermodynamic properties of spin-1/2 two-leg
honeycomb (HC) spin ladder are systematically studied by jointly utilizing
various analytical and numerical methods. The HC spin ladder is found to
exhibit behaviors dramatically different from those of the conventional square
spin ladder. A strong relevant term nJ and a half saturation magnetization
plateau that can be attributed to the formation of diluted dimer states are
observed in the HC ladder, both of which are absent in the square ladder. The
ground state phase diagram of the HC spin ladder is identified, and the
thermodynamic properties of the specific heat and susceptibility for different
couplings are thoroughly explored, where two kinds of excitations are unveiled.
The distinct Wilson ratios for both spin ladders at the lower critical fields
are also obtained. Our calculated result is well fitted to the experimental
data of the two-leg HC spin ladder compound [Cu2L1(N3)4]n.",1307.5945v1
2013-09-03,Criticality and quenched disorder: rare regions vs. Harris criterion,"We employ scaling arguments and optimal fluctuation theory to establish a
general relation between quantum Griffiths singularities and the Harris
criterion for quantum phase transitions in disordered systems. If a clean
critical point violates the Harris criterion, it is destabilized by weak
disorder. At the same time, the Griffiths dynamical exponent $z'$ diverges upon
approaching the transition, suggesting unconventional critical behavior. In
contrast, if the Harris criterion is fulfilled, power-law Griffiths
singularities can coexist with clean critical behavior but $z'$ saturates at a
finite value. We present applications of our theory to a variety of systems
including quantum spin chains, classical reaction-diffusion systems and
metallic magnets; and we discuss modifications for transitions above the upper
critical dimension. Based on these results we propose a unified classification
of phase transitions in disordered systems.",1309.0753v2
2013-09-17,Heteroepitaxial Growth and Multiferroic Properties of Mn-doped BiFeO3 films on SrTiO3 buffered III-V Semiconductor GaAs,"Epitaxial Mn-doped BiFeO3 (MBFO) thin films were grown on GaAs (001)
substrate with SrTiO3 (STO) buffer layer by pulsed laser deposition. X-ray
diffraction results demonstrate that the films show pure (00l) orientation, and
MBFO(100)//STO(100), whereas STO (100)//GaAs (110). Piezoresponse force
microscopy images and polarization versus electric field loops indicate that
the MBFO films grown on GaAs have an effective ferroelectric switching. The
MBFO films exhibit good ferroelectric behavior (2Pr ~ 92 {\mu}C/cm2 and 2EC ~
372 kV/cm). Ferromagnetic property with saturated magnetization of 6.5 emu/cm3
and coercive field of about 123 Oe is also found in the heterostructure at room
temperature.",1309.4222v1
2013-10-03,Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy,"The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure
the free neutrons and heavy charged particles from the radioactive ion beam
induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the
Constrained Molecular Dynamics model(CoMD), which demonstrated that the <N/Z>
of the heavy fragments and free neutron multiplicities were observables
sensitive to the density dependence of the symmetry energy at sub-saturation
densities. Through comparison of these simulations with the experimental data
constraints on the density dependence of the symmetry energy were extracted.
The advantage of radioactive ion beams as a probe of the symmetry energy is
demonstrated through examination of CoMD calculations for stable and
radioactive beam induced reactions.",1310.0990v1
2013-10-24,Uncertainty relation for focal spots in light beams,"Uncertainty relations for light pulses found in [Phys. Rev. A {\bf 86},
022118 (2012)] were derived in the three-dimensional case which emphasized the
localization in a volume. Here we derive the uncertainty relation for light
beams in the two-dimensional plane perpendicular to the direction of the beam
propagation which is more interesting for realistic beams. This uncertainty
relation connects the area of the focal spot with the spectrum of transverse
photon momenta. The shape of the beam that saturates the uncertainty relation
is very close to a Gaussian. The directions of the electric and magnetic field
vectors are those of the circularly polarized plane wave. Our uncertainty
relation for the focal spot is quite general but we were able to determine the
value of the lower bound only for beams made of many photons.",1310.6570v1
2013-11-18,Vortical field amplification and particle acceleration at rippled shocks,"Supernova Remnants (SNRs) shocks are believed to accelerate charged particles
and to generate strong turbulence in the post-shock flow. From high-energy
observations in the past decade, a magnetic field at SNR shocks largely
exceeding the shock-compressed interstellar field has been inferred. We outline
how such a field amplification results from a small-scale dynamo process
downstream of the shock, providing an explicit expression for the turbulence
back-reaction to the fluid whirling. The spatial scale of the $X-$ray rims and
the short time-variability can be obtained by using reasonable parameters for
the interstellar turbulence. We show that such a vortical field saturation is
faster than the acceleration time of the synchrotron emitting energetic
electrons.",1311.5207v1
2013-11-25,Anomalous Viscosity of the Quark-Gluon Plasma,"The shear viscosity of the quark-gluon plasma is predicted to be lower than
the collisional viscosity for weak coupling. The estimated ratio of the shear
viscosity to entropy density is rather close to the ratio calculated by N = 4
super Yang-Mills theory for strong coupling, which indicates that the
quark-gluon plasma might be strongly coupled. However, in presence of momentum
anisotropy, the Weibel instability can arise and drive the turbulent transport.
Shear viscosity can be lowered by enhanced collisionality due to turbulence,
but the decorrelation time and its relation to underlying dynamics and
color-magnetic fields have not been calculated self-consistently. In this
paper, we use resonance broadening theory for strong turbulence to calculate
the anomalous viscosity of the quark-gluon plasma for nonequilibrium. For
saturated Weibel instability, we estimate the scalings of the decorrelation
rate and viscosity and compare these with collisional transport. This
calculation yields an explicit connection between the underlying momentum space
anisotropy and the viscosity anomaly.",1311.6347v2
2014-01-16,Structure of longitudinal chromomagnetic fields in high energy collisions,"We compute expectation values of spatial Wilson loops in the forward light
cone of high-energy collisions. We consider ensembles of gauge field
configurations generated from a classical Gaussian effective action as well as
solutions of high-energy renormalization group evolution with fixed and running
coupling. The initial fields correspond to a color field condensate exhibiting
domain-like structure over distance scales of order the saturation scale. At
later times universal scaling emerges at large distances for all ensembles,
with a nontrivial critical exponent. Finally, we compare the results for the
Wilson loop to the two-point correlator of magnetic fields.",1401.4124v2
2014-03-19,Low anisotropy of the upper critical field in a strongly anisotropic layered cuprate: Evidence for paramagnetically limited superconductivity,"We study angular-dependent magnetoresistance in a low $T_c$ layered cuprate
Bi$_{2.15}$Sr$_{1.9}$CuO$_{6+\delta}$. The low $T_c$ ~ 4 K allows complete
suppression of superconductivity by modest magnetic fields and facilitate
accurate analysis of the upper critical field $H_{c2}$. We observe an universal
exponential decay of fluctuation conductivity in a broad range of temperatures
above $T_c$ and propose a new method for extraction of $H_{c2}(T)$ from the
scaling analysis of the fluctuation conductivity at $T>T_c$. Our main result is
observation of a surprisingly low $H_{c2}$ anisotropy ~ 2, which is much
smaller than the effective mass anisotropy of the material ~ 300. We show that
the anisotropy is decreasing with increasing field and saturates at a small
value when the field reaches the paramagnetic limit. We argue that the dramatic
discrepancy of high field and low field anisotropies is a clear evidence for
paramagnetically limited superconductivity.",1403.4817v2
2014-06-03,Muon spin rotation and relaxation in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$: Paramagnetic states,"Positive-muon ($\mu^+$) Knight shifts have been measured in the paramagnetic
states of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloys, where $x =$ 0, 0.25, 0.45,
0.50, 0.55, 0.75, and 1.00. In Pr-substituted NdOs$_4$Sb$_{12}$ ($x \le$ 0.75),
but not in NdOs$_4$Sb$_{12}$, Clogston-Jaccarino plots of $\mu^+$ Knight
shift~$K$ versus magnetic susceptibility~$\chi$ exhibit an anomalous saturation
of $K(\chi)$ at $\sim-$0.5% for large susceptibilities (low temperatures),
indicating a reduction of the coupling strength between $\mu^+$ spins and $4f$
paramagnetism for temperatures $\lesssim$ 15~K. We speculate that itinerant
Pr$^{3+}$ quadrupolar excitations, invoked to mediate the superconducting
Cooper-pair interaction, might modify the $\mu^+$-$4f$ ion indirect spin-spin
interaction.",1406.0903v1
2014-08-28,Statistical simulation of the magnetorotational dynamo,"Turbulence and dynamo induced by the magnetorotational instability (MRI) are
analyzed using quasi-linear statistical simulation methods. It is found that
homogenous turbulence is unstable to a large scale dynamo instability, which
saturates to an inhomogenous equilibrium with a strong dependence on the
magnetic Prandtl number (Pm). Despite its enormously reduced nonlinearity, the
dependence of the angular momentum transport on Pm in the quasi-linear model is
qualitatively similar to that of nonlinear MRI turbulence. This indicates that
recent convergence problems may be related to large scale dynamo and suggests
how dramatically simplified models may be used to gain insight into the
astrophysically relevant regimes of very low or high Pm.",1408.6793v2
2014-09-06,Crossover between Fermi liquid and non-Fermi liquid behavior in the non-centrosymmetric compound Yb$_2$Ni$_{12}$P$_7$,"A crossover from a non-Fermi liquid to a Fermi liquid phase in
Yb$_2$Ni$_{12}$P$_7$ is observed by analyzing electrical resistivity $\rho(T)$,
magnetic susceptibility $\chi(T)$, specific heat $C(T)$, and thermoelectric
power $S(T)$ measurements. The electronic contribution to specific heat,
$C_{e}(T)$, behaves as $C_{e}(T)/T \sim -\ln(T)$ for 5 K $< T <$ 15 K, which is
consistent with non-Fermi liquid behavior. Below $T \sim$ 4 K, the upturn in
$C_{e}(T)/T$ begins to saturate, suggesting that the system crosses over into a
Fermi-liquid ground state. This is consistent with robust $\rho(T) - \rho_0 =
AT^2$ behavior below $T \sim$ 4 K, with the power-law exponent becoming
sub-quadratic for $T >$ 4 K. A crossover between Fermi-liquid and non-Fermi
liquid behavior suggests that Yb$_2$Ni$_{12}$P$_7$ is in close proximity to a
quantum critical point, in agreement with results from recent measurements of
this compound under applied pressure.",1409.2066v1
2014-10-15,Beam-beam effects in BEPCII,"We first introduce the design parameters of the Beijing Electron-Positron
Collider II (BEPCII) and the simulation study of beam-beam effects during the
design process of the machine. The main advances since 2007 are briefly
introduced and reviewed. The longitudinal feedback system was installed to
suppress the coupled bunch instability in January 2010. The horizontal tune
decreased from 6.53 to 6.508 during the course of data taken in December, 2010.
The saturation of the beam-beam parameter was found in 2011, and the vacuum
chambers and magnets near the north crossing point were moved 15 cm in order to
mitigate the long range beam-beam interaction. At the beginning of 2013, the
beam-beam parameter achieved 0.04 with the new lower $\alpha_{p}$ lattice and
the peak luminosity achieved 7 x 10$^{32}$ cm$^{-2}$ s$^{-1}$.",1410.4057v1
2014-10-28,Universal Braess paradox in open quantum dots,"We present analytical and numerical results that demonstrate the presence of
the Braess paradox in chaotic quantum dots. The paradox that we identify,
originally perceived in classical networks, shows that the addition of more
capacity to the network can suppress the current flow in the universal regime.
We investigate the weak localization term, showing that it presents the paradox
encoded in a saturation minimum of the conductance, under the presence of
hyperflow in the external leads. In addition, we demonstrate that the weak
localization suffers a transition signal depending on the overcapacity lead and
presents an echo on the magnetic crossover before going to zero due to the full
time-reversal symmetry breaking.We also show that the quantum interference
contribution can dominate the Ohm term in the presence of constrictions and
that the corresponding Fano factor engenders an anomalous behavior",1410.7750v1
2014-10-31,Dissociative Adsorption of Molecules on Graphene and Silicene,"We study the interaction of H$_2$, O$_2$, CO, H$_2$O and OH molecules with
the vacancy defects of graphene and silicene. Atoms around the bare vacancy
reconstruct and specific chemically active sites are created. While H$_2$,
O$_2$ and CO remain intact on both pristine graphene and silicene, these
molecules can dissociate when they are placed at the close proximity of these
chemically active sites and nucleate centers for the hydrogenation and
oxygenation. Saturation of the dangling bonds at the defect sites by
constituent atoms of dissociated molecules gives rise to significant
modification of electronic and magnetic properties. We analyzed the mechanism
of the dissociation and revealed a concerted action of surrounding host atoms
together with dissociated molecules to lower the energy barrier needed for
dissociation. The dissociations of H$_2$O and OH are hindered by high energy
barriers. Our study suggests that graphene and silicene can be functionalized
by creating meshes of single vacancy, where specific molecules can dissociate,
while some other molecules can be pinned.",1410.8730v1
2014-12-02,Dynamical quenching with non-local alpha and downward pumping,"In light of new results, the one-dimensional mean-field dynamo model of
Brandenburg & Kapyla (2007) with dynamical quenching and a nonlocal
Babcock-Leighton alpha effect is re-examined for the solar dynamo. We extend
the one-dimensional model to include the effects of turbulent downward pumping
(Kitchatinov & Olemskoy 2011), and to combine dynamical quenching with shear.
We use both the conventional dynamical quenching model of Kleeorin & Ruzmaikin
(1982) and the alternate one of Hubbard & Brandenburg (2011), and confirm that
with varying levels of non-locality in the alpha effect, and possibly shear as
well, the saturation field strength can be independent of the magnetic Reynolds
number.",1412.0997v1
2014-12-29,Perfect charge compensation in WTe2 for the extraordinary magnetoresistance: From bulk to monolayer,"The electronic structure of WTe2 bulk and layers are investigated by using
the first principles calculations. The perfect electron-hole (n-p) charge
compensation and high carrier mobilities are found in WTe2 bulk, which may
result in the large and non-saturating magnetoresistance (MR) observed very
recently in the experiment [Ali et al., Nature 514, 205 (2014)]. The monolayer
and bilayer of WTe2 preserve the semimetallic property, with the equal hole and
electron carrier concentrations. Moreover, the very high carrier mobilities are
also found in WTe2 monolayer, indicating that the WTe2 monolayer would have the
same extraordinary MR effect as the bulk, which could have promising
applications in nanostructured magnetic devices.",1412.8335v1
2015-01-29,Resolution of hyperfine transitions in metastable 83Kr using Electromagnetically Induced Transparency,"Narrow linewidth signals of Electromagnetically Induced Transparency (EIT) in
the metastable 83Kr have been observed for the first time. Various hyperfine
transitions in 4p55s[3/2]2 to 4p55p[5/2]3 manifolds of 83Kr have been
identified through the experimentally observed EIT signals. Some unresolved or
poorly resolved hyperfine transitions in saturated absorption spectroscopy
(SAS) are clearly resolved in the present work. Using the spectral separation
of these EIT identified hyperfine transitions, the magnetic hyperfine constant
(A) and the electric quadrupole hyperfine constant (B) are determined with
improved accuracy for 4p55s[3/2]2 and 4p55p[5/2]3 manifolds.",1501.07381v2
2015-02-11,High Field Ultrasound Measurements in UPt3 and the Single Energy Scale Model of Metamagnetism,"We report longitudinal ultrasound velocity measurements for magnetic fields
up to 33 T applied parallel to the a-axis of the heavy electron compound
UPt$_{3}$. A characteristic dip in the sound velocity at the metamagnetic
critical field, $H_{c}=20$ T, reported in earlier work is reproduced and shown
to be independent of temperature at very low temperatures. We show that the
single energy scale model (B.S. Shivaram et al., Phys. Rev. B89, 241107(R),
2014) captures the observed key features of the field dependence in the sound
velocity shift, $\delta v_{s}$. The shift $\delta v_{s}$ at $H_{c}$ is found to
be inversely dependent on temperature above 3\thinspace K and assumes a fixed
value at low T. This saturation in $\delta v_{s}$ below 3 K is accounted for by
level broadening of the Uranium spin states.",1502.03412v1
2015-02-16,Anisotropic Magnetotransport and Exotic Longitudinal Linear Magnetoresistance in WTe2 Crystals,"WTe2 semimetal, as a typical layered transition-metal dichalcogenide, has
recently attracted much attention due to the extremely large, non-saturating
parabolic magnetoresistance in perpendicular field. Here, we report a
systematic study of the angular dependence of the magnetoresistance in WTe2
single crystal. The violation of the Kohler rule and a significant anisotropic
magnetotransport behavior in different magnetic field directions are observed.
Surprisingly, when the applied field is parallel to the tungsten chains of
WTe2, an exotic large longitudinal linear magnetoresistance as high as 1200% at
15 T and 2 K is identified. Violation of the Kohler rule in transverse
magnetoresistance can be understood based on a dual effect of the excitons
formation and thermal activation, while large longitudinal linear
magnetoresistance reflects perfectly the scattering and nesting of quasi-1D
nature of this balanced hole-electron system. Our work will stimulate studies
of such double-carrier correlated material and corresponding quantum physics.",1502.04465v1
2015-03-25,Magnetotransport of single crystalline NbAs,"We report transport measurement in zero and applied magnetic field on a
single crystal of NbAs. Transverse and longitudinal magnetoresistance in the
plane of this tetragonal structure does not saturate up to 9 T. In the
transverse configuration ($H \parallel c$, $I \perp c$) it is 230,000 \% at 2
K. The Hall coefficient changes sign from hole-like at room temperature to
electron-like below $\sim$ 150 K. The electron carrier density and mobility
calculated at 2 K based on a single band approximation are 1.8 x 10$^{19}$
cm$^{-3}$ and 3.5 x 10$^{5}$ cm$^2$/Vs, respectively. These values are similar
to reported values for TaAs and NbP, and further emphasize that this class of
noncentrosymmetric, transition-metal monopnictides is a promising family to
explore the properties of Weyl semimetals and the consequences of their novel
electronic structure.",1503.07571v1
2015-03-27,Dynamic nuclear polarization and the paradox of Quantum Thermalization,"Dynamic Nuclear Polarization (DNP) is to date the most effective technique to
increase the nuclear polarization up to a factor $100,000$ opening disruptive
perspectives for medical applications. In DNP, the nuclear spins are driven to
an - out of equilibrium - hyperpolarized state by microwave saturation of the
electron spins in interaction with them. Here we show that the electron dipolar
interactions compete with the local magnetic fields resulting in two distinct
dynamical phases: for strong interactions the electron spins equilibrate to an
extremely low effective temperature that boosts DNP efficiency. For weak
interaction this spin temperature is not defined and the polarization profile
has an 'hole burning' shape characteristic of the non interacting case. The
study of the many-body eigenstates reveals that these two phases are intimately
related to the problem of thermalization in closed quantum systems where
breaking of ergodicity is expected varying the strength of the interactions.",1503.08181v2
2015-04-07,Multiple Fermi pockets revealed by Shubnikov-de Haas oscillations in WTe2,"We use magneto-transport measurements to investigate the electronic structure
of WTe2 single crystals. A non-saturating and parabolic magnetoresistance is
observed in the temperature range between 2.5 to 200 K and magnetic fields up
to 8 T. Shubnikov - de Haas oscillations with beating patterns are observed.
The fast Fourier transform of the SdH oscillations reveals three oscillation
frequencies, corresponding to three pairs of Fermi pockets with comparable
effective masses , m* ~ 0.31 me. By fitting the Hall resistivity, we infer the
presence of one pair of electron pockets and two pairs of hole pockets,
together with nearly perfect compensation of the electron-hole carrier
concentration. These magnetotransport measurements reveal the complex
electronic structure in WTe2, explaining the nonsaturating magnetoresistance.",1504.01460v1
2015-04-27,Fricke S-duality in CHL models,"We consider four dimensional CHL models with sixteen spacetime
supersymmetries obtained from orbifolds of type IIA superstring on K3 x T^2 by
a Z_N symmetry acting (possibly) non-geometrically on K3. We show that most of
these models (in particular, for geometric symmetries) are self-dual under a
weak-strong duality acting on the heterotic axio-dilaton modulus S by a ""Fricke
involution"" S --> -1/NS. This is a novel symmetry of CHL models that lies
outside of the standard SL(2,Z)-symmetry of the parent theory, heterotic
strings on T^6. For self-dual models this implies that the lattice of purely
electric charges is N-modular, i.e. isometric to its dual up to a rescaling of
its quadratic form by N. We verify this prediction by determining the lattices
of electric and magnetic charges in all relevant examples. We also calculate
certain BPS-saturated couplings and verify that they are invariant under the
Fricke S-duality. For CHL models that are not self-dual, the strong coupling
limit is dual to type IIA compactified on T^6/Z_N, for some Z_N-symmetry
preserving half of the spacetime supersymmetries.",1504.07260v3
2015-06-18,Short-period stellar activity cycles with Kepler photometry,"We study the short-periodic component of stellar activity with a cycle
periods Pcyc up to 1000 days using the Kepler mission photometry of
fast-rotating (rotational periods from 1 to 4 days) stars with spectra of M4V
to F3V. Applying the originally developed two non-spectral methods, we measured
the effective period of stellar cycles in 462 objects. The obtained results are
in accordance with previous measurements by Vida et al. (2014), do not seem to
result from a beating effect. The performed measurements of Pcyc cluster in a
specific branch which covers the previously unstudied region in the
Saar-Brandenburg (1999) diagram, and connects the branch of inactive stars with
the area populated by super-active objects. It is shown that the formation of
the discovered branch is due to the alpha-quenching effect, which saturates the
magnetic dynamo and decreases the cycle periods with the increase of inverted
Rossby number. This finding is important in the context of the discussion on
catastrophic quenching and other heuristic approximations of the non-linear
alpha-effect.",1506.05725v1
2015-07-16,Radiation Reaction Effect on Laser Driven Auto-Resonant Particle Acceleration,"The effects of radiation reaction force on laser driven auto-resonant
particle acceleration scheme are studied using Landau-Lifshitz equation of
motion. These studies are carried out for both linear as well as circularly
polarized laser fields in the presence of static axial magnetic field. From the
parametric study, a radiation reaction dominated region has been identified in
which the particle dynamics is greatly effected by this force. In the radiation
reaction dominated region the two significant effects on particle dynamics are
seen viz., (1) saturation in energy gain by the initially resonant particle,
(2) net energy gain by a initially non-resonant particle which is caused due to
resonance broadening. It has been further shown that with the optimum choice of
parameters this scheme can be efficiently used to produce electrons with
energies in the range of hundreds of TeV. The quantum corrections to the
Landu-Lifshitz equation of motion have also been taken into account. The
difference in the energy gain estimates of the particle by the quantum
corrected and classical Landu-Lifshitz equation are found to be insignificant
for the present day as well as upcoming laser facilities.",1507.04446v1
2015-07-16,Linear magnetoresistance in metals: guiding center diffusion in a smooth random potential,"We predict that guiding center (GC) diffusion yields a linear and
non-saturating (transverse) magnetoresistance in 3D metals. Our theory is
semi-classical and applies in the regime where the transport time is much
greater than the cyclotron period, and for weak disorder potentials which are
slowly varying on a length scale much greater than the cyclotron radius. Under
these conditions, orbits with small momenta along magnetic field $B$ are
squeezed and dominate the transverse conductivity. When disorder potentials are
stronger than the Debye frequency, linear magnetoresistance is predicted to
survive up to room temperature and beyond. We argue that magnetoresistance from
GC diffusion explains the recently observed giant linear magnetoresistance in
3D Dirac materials.",1507.04730v2
2015-08-08,Effect of electron diamagnetic drifts on cylindrical double-tearing modes,"Double-tearing modes (DTMs) have been proposed as a driver of `off-axis
sawtooth' crashes in reverse magnetic shear tokamak configurations. Recently
differential rotation provided by equilibrium sheared flows has been shown
capable of decoupling the two DTM resonant layers, slowing the growth the
instability. In this work we instead supply this differential rotation using an
electron diamagnetic drift, which emerges in the presence of an equilibrium
pressure gradient and finite Larmor radius physics. Diamagnetic drifts have the
additional benefit of stabilizing reconnection local to the two tearing layers.
Conducting linear and nonlinear simulations with the extended MHD code MRC-3d,
we consider an m=2, n=1 cylindrical double-tearing mode. We show that
asymmetries between the resonant layers and the emergence of an ideal MHD
instability cause the DTM evolution to be highly dependent on the location of
the pressure gradient. By locating a strong drift near the outer, dominant
resonant surface are we able to saturate the mode and preserve the annular
current ring, suggesting that the appearance of DTM activity in advanced
tokamaks depends strongly on the details of the plasma pressure profile.",1508.01959v1
2015-09-14,Ground-state phases of rung-alternated spin-1/2 Heisenberg ladder,"The ground-state phase diagram of Heisenberg spin-1/2 system on a two-leg
ladder with rung alternation is studied by combining analytical approaches with
numerical simulations. For the case of ferromagnetic leg exchanges a unique
ferrimagnetic ground state emerges, whereas for the case of antiferromagnetic
leg exchanges several different ground states are stabilized depending on the
ratio between exchanges along legs and rungs. For the more general case of a
honeycomb-ladder model for the case of ferromagnetic leg exchanges besides
usual rung-singlet and saturated ferromagnetic states we obtain a ferrimagnetic
Luttinger liquid phase with both linear and quadratic low energy dispersions
and ground state magnetization continuously changing with system parameters.
For the case of antiferromagnetic exchanges along legs, different dimerized
states including states with additional topological order are suggested to be
realized.",1509.04062v1
2015-09-15,Traveling Wave Parametric Amplifier based on a chain of Coupled Asymmetric SQUIDs,"A traveling wave parametric amplifier (TWPA) composed of a transmission line
made up of a chain of coupled asymmetric superconducting quantum interference
devices (SQUIDs) is proposed. The unique nature of this transmission line is
that its nonlinearity can be tuned with an external magnetic flux and can even
change sign. This feature of the transmission line can be used to perform phase
matching in a degenerate four-wave mixing process which can be utilized for
parametric amplification of a weak signal in the presence of a strong pump.
Numerical simulations of the TWPA design have shown that with tuning, phase
matching can be achieved and an exponential gain as a function of the
transmission line length can be realized. The flexibility of the proposed
design can realize: compact TWPAs with less than 211 unit cells, signal gains
greater than 20 dB, 3 dB bandwidth greater than 5.4 GHz, and saturation powers
up to -98 dBm. This amplifier design is well suited for multiplexed readout of
quantum circuits or astronomical detectors in a compact configuration which can
foster on-chip implementations.",1509.04573v1
2015-09-25,Turbulent Reconnection in Relativistic Plasmas And Effects of Compressibility,"We report turbulence effects on magnetic reconnection in relativistic plasmas
using 3-dimensional relativistic resistive magnetohydrodynamics simulations. We
found reconnection rate became independent of the plasma resistivity due to
turbulence effects similarly to non-relativistic cases. We also found
compressible turbulence effects modified the turbulent reconnection rate
predicted in non-relativistic incompressible plasmas; The reconnection rate
saturates and even decays as the injected velocity approaches to the Alfv\'en
velocity. Our results indicate the compressibility cannot be neglected when
compressible component becomes about half of incompressible mode occurring when
the Alfv\'en Mach number reaches about $0.3$. The obtained maximum reconnection
rate is around $0.05$ to $0.1$, which will be able to reach around $0.1$ to
$0.2$ if injection scales are comparable to the sheet length.",1509.07703v2
2015-11-12,Adiabatic Mach-Zehnder interferometer in dipolar spin-1 condensate,"Mach-Zehnder interferometer, a powerful tool for a wide variety of
measurements, has been realized with Bose-Einstein condensates in recent
experiments. In this report, we propose and analyze a realizable scheme for
performing a Heisenberg-limited Mach-Zehnder interferometry with dipolar spin-1
condensate. Based upon adiabatic processes of sweeping the transverse magnetic
field, we demonstrate a perfect phase transition, which accomplishes the beam
splitter, phase shifter and recombiner as for a Mach-Zehnder interferometer.
The attractive dipolar interaction ensures the existence of a path-entangled
state which enhances the phase measurement precision to the Heisenberg limit.
We also discuss the spin-$1$ squeezing induced in the adiabatic passage and
show that the squeezing parameter attains its minimal value near the point of
saturation field.",1511.03893v1
2015-11-13,Cosmic ray transport and anisotropies to high energies,"A model is introduced, in which the irregularity spectrum of the Galactic
magnetic field beyond the dissipation length scale is first a Kolmogorov
spectrum $k^{-5/3}$ at small scales $\lambda \, = \, 2 \pi/k$ with $k$ the
wave-number, then a saturation spectrum $k^{-1}$, and finally a shock-dominated
spectrum $k^{-2}$ mostly in the halo/wind outside the Cosmic Ray disk. In an
isotropic approximation such a model is consistent with the Interstellar Medium
(ISM) data. With this model we discuss the Galactic Cosmic Ray (GCR) spectrum,
as well as the extragalactic Ultra High Energy Cosmic Rays (UHECRs), their
chemical abundances and anisotropies. UHECRs may include a proton component
from many radio galaxies integrated over vast distances, visible already below
3 EeV.",1511.04229v1
2015-11-19,Nonlinear convection stagnation point heat transfer and MHD fluid flow in porous medium towards a permeable shrinking sheet,"This investigation deals with the analysis of stagnation point heat transfer
and corresponding flow features of hydromagnetic viscous incompressible fluid
over a vertical shrinking sheet. The considered sheet is assumed to be
permeable and subject to addition of stagnation point to control the generated
vorticity in the boundary layer. The sheet is placed on the right side of the
fluid saturated porous medium which is having permeability of specified form.
Nonlinear convection waves in the flow field are realized due to the envisaged
nonlinear relation between density and temperature. The equations governing the
nonlinear convection boundary layer flow are modeled and simplified using
similarity transformations. The economized equations are solved for numerical
solutions by employing the implicit finite difference scheme also known as
Keller-box method. The influence of the associated parameters of the problem on
velocity and temperature distributions, skin friction and rate of heat transfer
are presented through graphs and tables, and qualitatively discussed. The study
reveals that interaction among magnetic field, porous medium permeability and
nonlinear convection parameters substantially enhance the solution range and
thus endorse their control to sustain the boundary layer flow.",1511.06109v1
2015-12-14,Influence of dephasing on many-body localization,"We study the effects of dephasing noise on a prototypical many-body localized
system -- the XXZ spin 1/2 chain with a disordered magnetic field. At times
longer than the inverse dephasing strength the dynamics of the system is
described by a probabilistic Markov process on the space of diagonal density
matrices, while all off-diagonal elements of the density matrix decay to zero.
The generator of the Markovian process is a bond-disordered spin chain. The
scaling variable is identified, and independence of relaxation on the
interaction strength is demonstrated. We show that purity and von Neumann
entropy are extensive, showing no signatures of localization, while the
operator space entanglement entropy exhibits a logarithmic growth with time
until the final saturation corresponding to localization breakdown, suggesting
a many-body localized dynamics of the effective Markov process.",1512.04408v2
2015-12-16,Observationally constraining gravitational wave emission from short gamma-ray burst remnants,"Observations of short gamma-ray bursts indicate ongoing energy injection
following the prompt emission, with the most likely candidate being the birth
of a rapidly rotating, highly magnetised neutron star. We utilise X-ray
observations of the burst remnant to constrain properties of the nascent
neutron star, including its magnetic field-induced ellipticity and the
saturation amplitude of various oscillation modes. Moreover, we derive strict
upper limits on the gravitational wave emission from these objects by looking
only at the X-ray light curve, showing the burst remnants are unlikely to be
detected in the near future using ground-based gravitational wave
interferometers such as Advanced LIGO.",1512.05368v2
2015-12-22,Spin torque study of the spin Hall conductivity and spin diffusion length in platinum thin films with varying resistivity,"We report measurements of the spin torque efficiencies in
perpendicularly-magnetized Pt/Co bilayers where the Pt resistivity $\rho_{Pt}$
is strongly dependent on thickness $t_{Pt}$ . The damping-like spin Hall torque
efficiency per unit current density, $\xi^j_{DL}$ , varies significantly with
$t_{Pt}$, exhibiting a peak value $\xi^j_{DL}=0.12$ at $t_{Pt} = 2.8 - 3.9$ nm.
In contrast, $\xi^j_{DL}/\rho_{Pt}$ increases monotonically with $t_{Pt}$ and
saturates for $t_{Pt} > 5$ nm, consistent with an intrinsic spin Hall effect
mechanism, in which $\xi^j_{DL}$ is enhanced by an increase in $\rho_{Pt}$ .
Assuming the Elliott-Yafet spin scattering mechanism dominates we estimate that
the spin diffusion length $\lambda_s = (0.77 \pm 0.08) \times 10^{-15} \Omega
m^2 /\rho_{Pt}$.",1512.06931v1
2016-01-24,Inelastic electron scattering off a quantum dot in the cotunneling regime: the signature of mesoscopic Stoner instability,"We explore the inelastic electron scattering cross section off a quantum dot
close to the Stoner instability. We focus on the regime of strong Coulomb
blockade in which the scattering cross section is dominated by the cotunneling
processes. For large enough exchange interaction the quantum dot acquires a
finite total spin in the ground state. In this, so-called mesoscopic Stoner
instability, regime we find that at low enough temperatures the inelastic
scattering cross section (including the contribution due to an elastic electron
spin-flip) for an electron with a low energy with respect to the chemical
potential is different from the case of a magnetic impurity with the same spin.
This difference stems from (i) presence of a low-lying many-body states of a
quantum dot and (ii) the correlations of the tunneling amplitudes. Our results
provide a possible explanation for absence of the dephasing rate saturation at
low temperatures in recent experiment [N. Teneh, A. Yu. Kuntsevich, V. M.
Pudalov, and M. Reznikov, Phys. Rev. Lett. 109, 226403 (2012)] in which
existence of local spin droplets in disordered electron liquid has been
unraveled.",1601.06381v1
2016-01-25,Large Magnetoresistance in Compensated Semimetals TaAs$_2$ and NbAs$_2$,"We report large magnetoresistance (MR) at low temperatures in
single-crystalline nonmagnetic compounds TaAs$_2$ and NbAs$_2$. Both compounds
exhibit parabolic-field-dependent MR larger than $5\times10^3$ in a magnetic
field of 9 Tesla at 2 K. The MR starts to deviate from parabolic dependence
above 10 T and intends to be saturated in 45 T for TaAs$_2$ at 4.2 K. The Hall
resistance measurements and band structural calculations reveal their
compensated semimetal characteristics. The large MR at low temperatures is
ascribed to a resonance effect of the balanced electrons and holes with large
mobilities. We also discuss the relation of the MR and samples' quality for
TaAs$_2$ and other semimetals. We found that the magnitudes of MR are strongly
dependent on the samples' quality for different compounds.",1601.06482v1
2016-02-16,Perfect charge compensation in extremely large magnetoresistance materials LaSb and LaBi revealed by the first-principles calculations,"By the first-principles electronic structure calculations, we have
systematically studied the electronic structures of recently discovered
extremely large magnetoresistance (XMR) materials LaSb and LaBi. We find that
both LaSb and LaBi are semimetals with the electron and hole carriers in
perfect balance. The calculated carrier densities in the order of $10^{20}$
cm$^{-3}$ are in good agreement with the experimental values, implying long
mean free time of carriers and thus high carrier mobilities. With a
semiclassical two-band model, the perfect charge compensation and high carrier
mobilities naturally explain (i) the XMR observed in LaSb and LaBi; (ii) the
non-saturating quadratic dependence of XMR on external magnetic field; and
(iii) the resistivity plateau in the turn-on temperature behavior at very low
temperatures. The explanation of these features without resorting to the
topological effect indicates that they should be the common characteristics of
all perfectly electron-hole compensated semimetals.",1602.05061v1
2016-02-28,Goldilocks Probes for Noisy Interferometry via Quantum Annealing to Criticality,"Quantum annealing is explored as a resource for quantum information beyond
solution of classical combinatorial problems. Envisaged as a generator of
robust interferometric probes, we examine a Hamiltonian of $N>> 1$
uniformly-coupled spins subject to a transverse magnetic field. The discrete
many-body problem is mapped onto dynamics of a single one-dimensional particle
in a continuous potential. This reveals all the qualitative features of the
ground state beyond typical mean-field or large classical spin models. It
illustrates explicitly a graceful warping from an entangled unimodal to
bi-modal ground state in the phase transition region. The transitional
`Goldilocks' probe has a component distribution of width $N^{2/3}$ and exhibits
characteristics for enhanced phase estimation in a decoherent environment. In
the presence of realistic local noise and collective dephasing, we find this
probe state asymptotically saturates ultimate precision bounds calculated
previously. By reducing the transverse field adiabatically, the Goldilocks
probe is prepared in advance of the minimum gap bottleneck, allowing the
annealing schedule to be terminated `early'. Adiabatic time complexity of probe
preparation is shown to be linear in $N$",1602.08752v1
2016-05-11,Magnetotransport and de Haas-van Alphen measurements in the type-II Weyl semimetal TaIrTe$_4$,"The layered ternary compound TaIrTe$_4$ has been predicted to be a type-II
Weyl semimetal with only four Weyl points just above the Fermi energy.
Performing magnetotransport measurements on this material we find that the
resistivity does not saturate for fields up to 70 T and follows a $ \rho \sim
B^{1.5}$ dependence. Angular-dependent de Haas-van Alphen (dHvA) measurements
reveal four distinct frequencies. Analyzing these magnetic quantum oscillations
by use of density functional theory (DFT) calculations we establish that in
TaIrTe$_4$ the Weyl points are located merely $\sim$ 40-50 meV above the
chemical potential, suggesting that the chemical potential can be tuned into
the four Weyl nodes by moderate chemistry or external pressure, maximizing
their chiral effects on electronic and magnetotransport properties.",1605.03380v1
2016-07-05,Inverse participation ratios in the XXZ spin chain,"We investigate numerically the inverse participation ratios in a spin-1/2 XXZ
chain, computed in the ""Ising"" basis (i.e., eigenstates of $\sigma^z_i$). We
consider in particular a quantity $T$, defined by summing the inverse
participation ratios of all the eigenstates in the zero magnetization sector of
a finite chain of length $N$, with open boundary conditions. From a dynamical
point of view, $T$ is proportional to the stationary return probability to an
initial basis state, averaged over all the basis states (initial conditions).
We find that $T$ exhibits an exponential growth, $T\sim\exp(aN)$, in the gapped
phase of the model and a linear scaling, $T\sim N$, in the gapless phase. These
two different behaviors are analyzed in terms of the distribution of the
participation ratios of individual eigenstates. We also investigate the effect
of next-nearest-neighbor interactions, which break the integrability of the
model. Although the massive phase of the non-integrable model also has
$T\sim\exp(aN)$, in the gapless phase $T$ appears to saturate to a constant
value.",1607.01300v2
2016-07-10,Robust Topological Terahertz Circuits using Semiconductors,"Topological Insulator-based devices can transport electrons/photons at the
surfaces of materials without any back reflections, even in the presence of
obstacles. Topological properties have recently been studied using
non-reciprocal materials such as gyromagnetics or using bianisotropy. However,
these effects usually saturate at optical frequencies and limit our ability to
scale down devices. In order to implement topological devices that we introduce
in this paper for the terahertz range, we show that semiconductors can be
utilized via their cyclotron resonance in combination with small magnetic
fields. We propose novel terahertz operating devices such as the topological
tunable power splitter and the topological circulator. This work opens new
perspectives in the design of terahertz integrated devices and circuits with
high functionality.",1607.02697v2
2016-07-19,Interaction-Induced Weakening of Localization in Few-Particle Disordered Heisenberg Chains,"We investigate real-space localization in the few-particle regime of the XXZ
spin-$1/2$ chain with a random magnetic field. Our investigation focuses on the
time evolution of the spatial variance of non-equilibrium densities, as
resulting for a specific class of initial states, namely, pure product states
of densely packed particles. Varying the strength of both particle-particle
interactions and disorder, we numerically calculate the long-time evolution of
the spatial variance $\sigma(t)$. For the two-particle case, the saturation of
this variance yields an increased but finite localization length, with a
parameter scaling different to known results for bosons. We find that this
interaction-induced increase is the stronger the more particles are taken into
account in the initial condition. We further find that our non-equilibrium
dynamics are clearly inconsistent with normal diffusion and instead point to
subdiffusive dynamics with $\sigma(t) \propto t^{1/4}$.",1607.05664v3
2016-08-26,Mass enhancement in multiple bands approaching optimal doping in a high-temperature superconductor,"Pnictides provide an opportunity to study the effects of quantum criticality
in a multi-band high temperature superconductor. Quasiparticle mass divergence
near optimal doping, observed in two major classes of high-temperature
superconductors, pnictides and cuprates, is a direct experimental indicator of
enhanced electronic interactions that accompany quantum criticality. Whether
quasiparticles on all Fermi surface pockets in BaFe2(As1-xPx)2 are affected by
quantum criticality is an open question, which specific heat measurements at
high magnetic fields can directly address. Here we report specific heat
measurements up to 35T in BaFe2(As1-xPx)2 over a broad doping range, 0.44 <= x
<= 0.6. We observe saturation of C/T in the normal state at all dopings where
superconductivity is fully suppressed. Our measurements demonstrate that
quasiparticle mass increases towards optimal doping in multiple pockets, some
of which exhibit even stronger mass enhancement than previously reported from
quantum oscillations of a single pocket.",1608.07510v2
2016-10-05,"The weakly nonlinear magnetorotational instability in a global, cylindrical Taylor-Couette flow","We conduct a global, weakly nonlinear analysis of the magnetorotational
instability (MRI) in a Taylor-Couette flow. This is a multiscale perturbative
treatment of the nonideal, axisymmetric MRI near threshold, subject to
realistic radial boundary conditions and cylindrical geometry. We analyze both
the standard MRI, initialized by a constant vertical background magnetic field,
and the helical MRI, with an azimuthal background field component. This is the
first weakly nonlinear analysis of the MRI in a global Taylor-Couette geometry,
as well as the first weakly nonlinear analysis of the helical MRI. We find that
the evolution of the amplitude of the standard MRI is described by a real
Ginzburg-Landau equation (GLE), while the amplitude of the helical MRI takes
the form of a complex GLE. This suggests that the saturated state of the
helical MRI may itself be unstable on long spatial and temporal scales.",1610.01603v2
2016-10-28,Dynamo-driven plasmoid formation from a current-sheet instability,"Axisymmetric current-carrying plasmoids are formed in the presence of
nonaxisymmetric fluctuations during nonlinear three-dimensional resistive MHD
simulations in a global toroidal geometry. We utilize the helicity injection
technique to form an initial poloidal flux in the presence of a toroidal guide
field. As helicity is injected, two types of current sheets are formed from 1)
the oppositely directed field lines in the injector region (primary
reconnecting current sheet), and 2) the poloidal flux compression near the
plasma edge (edge current sheet). We first find that nonaxisymmetic
fluctuations arising from the current-sheet instability isolated near the
plasma edge have tearing parity but can nevertheless grow fast (on the poloidal
Alfven time scale). These modes saturate by breaking up the current sheet.
Second, for the first time a dynamo poloidal flux amplification is observed at
the reconnetion site (in the region of the oppositely directed magnetic field).
This fluctuation-induced flux amplification increases the local Lundquist
number, which then triggers a plasmoid instability and breaks the primary
current sheet at the reconnection site. The plasmoids formation driven by
large-scale flux amplification, i.e. a large-scale dynamo, observed here has
strong implications for astrophysical reconnection as well as fast reconnection
events in laboratory plasmas.",1610.09050v1
2016-10-28,FORC+: A method for separating reversible from irreversible behavior using first order reversal curves,"First Order Reversal Curves (FORCs) have been used for a number of years for
the extraction of information from magnetization measurements. The results are
most unambiguous for irreversible processes -- for a collection of Preisach
hysterons, one gets a ""FORC distribution"" $\rho(H_{down},H_{up})$, the number
of hysterons with given downward \& upward reversal fields. There have been
many proposals for dealing with reversible behavior, usually involving
inserting it somehow into the irreversible FORC distribution. Here we will try
to do the opposite, to separate them into another function which we will call
the (reversible) ""saturation field distribution"", which is identically zero for
a completely irreversible system of hysterons, while the irreversible FORC
distribution is identically zero for a reversible system. Thus in a system with
both purely reversible and purely irreversible components, such as
single-domain Stoner-Wohlfarth particles with hard or easy axis along the
field, this approach cleanly separates them. For more complicated systems, as
with conventional FORC distributions, it at least provides a ""signature"" making
it possible to identify microscopic models that might give a particular pair of
irreversible and reversible distributions.",1610.09199v1
2016-11-14,Light-by-light scattering sum rules in light of new data,"We evaluate the light-quark meson contributions to three exact light-by-light
scattering sum rules in light of new data by the Belle Collaboration, which
recently has extracted the transition form factors of the tensor meson
$f_2(1270)$ as well as of the scalar meson $f_0(980)$. We confirm a previous
finding that the $\eta, \eta^\prime$ and helicity-2 $f_2(1270)$ contributions
saturate one of these sum rules up to photon virtualities around 1 GeV$^2$. At
larger virtualities, our sum rule analysis shows an important contribution of
the $f_2(1565)$ meson and provides a first empirical extraction of its
helicity-2 transition form factor. Two further sum rules allow us to predict
the helicity-0 and helicity-1 transition form factors of the $f_2(1270)$ meson.
Furthermore, our analysis also provides an update for the scalar and tensor
meson hadronic light-by-light contributions to the muon's anomalous magnetic
moment.",1611.04646v2
2016-11-18,Temporal evolution of auto-oscillations in a YIG/Pt microdisc driven by pulsed spin Hall effect-induced spin-transfer torque,"The temporal evolution of pulsed Spin Hall Effect - Spin Transfer Torque
(SHE-STT) driven auto-oscillations in a Yttrium Iron Garnet (YIG) / platinum
(Pt) microdisc is studied experimentally using time-resolved Brillouin Light
Scattering (BLS) spectroscopy. It is demonstrated that the frequency of the
auto-oscillations is different in the center and at the edge of the
investigated disc that is related to the simultaneous STT excitation of a
bullet and a non-localized spin-wave mode. Furthermore, the magnetization
precession intensity is found to saturate on a time scale of 20 ns or longer,
depending on the current density. For this reason, our findings suggest that a
proper ratio between the current and the pulse duration is of crucial
importance for future STT-based devices.",1611.06054v1
2016-11-26,Specific Heat of Spin Excitations Measured by FerromagneticResonance,"Using ferromagnetic-resonance spectroscopy (FMR), we investigate the
anisotropic properties of epitaxial 3 nmPt/2 nmAg/10 nmFe/10 nmAg/GaAs(001)
films in fully saturated meta-stable states at temperatures ranging from 70 K
to 280 K. By comparison to spin-wave theory calculations, we identify the role
of thermal fluctuation of magnons in overcoming the energy barrier associated
with these meta-stable states. We show that the energy associated with the size
of the barrier that bounds the meta-stable regime is proportional to the heat
stored in the magnonic bath. Our findings offer the possibility to measure the
magnonic contribution to the heat capacity by FMR, independent of other
contributions at temperatures ranging from 0 K to ambient temperature and
above. The only requirement being that the selected sample exhibits magnetic
anisotropy, here, magnetocrystalline anisotropy.",1611.08713v2
2016-12-15,Exploring Localization in Nuclear Spin Chains,"Characterizing out-of-equilibrium many-body dynamics is a complex but crucial
task for quantum applications and the understanding of fundamental phenomena. A
central question is the role of localization in quenching quantum
thermalization, and whether localization survives in the presence of
interactions. The localized phase of interacting systems (many-body
localization, MBL) exhibits a long-time logarithmic growth in entanglement
entropy that distinguishes it from the noninteracting Anderson localization
(AL), but entanglement is difficult to measure experimentally. Here, we present
a novel correlation metric, capable of distinguishing MBL from AL in
high-temperature spin systems. We demonstrate the use of this metric to detect
localization in a natural solidstate spin system using nuclear magnetic
resonance (NMR). We engineer the natural Hamiltonian to controllably introduce
disorder and interactions and observe the emergence of localization. In
particular, while our correlation metric saturates for AL, it keeps increasing
logarithmically for MBL, a behavior reminiscent of entanglement entropy, as we
confirm by simulations. Our results show that our NMR techniques, akin to
measuring out-of-time correlations, are well suited for studying localization
in spin systems.",1612.05249v1
2016-12-15,Giant Hall photoconductivity in narrow-gapped Dirac materials,"Carrier dynamics acquire a new character in the presence of Bloch-band Berry
curvature, which naturally arises in gapped Dirac materials (GDMs). Here we
argue that photoresponse in GDMs with small band gaps is dramatically enhanced
by Berry curvature. This manifests in a giant and saturable Hall
photoconductivity when illuminated by circularly polarized light. Unlike Hall
motion arising from a Lorentz force in a magnetic field, which impedes
longitudinal carrier motion, Hall photoconductivity arising from Berry
curvature can boost longitudinal carrier transport. In GDMs, this results in a
helicity-dependent photoresponse in the Hall regime, where photoconductivity is
dominated by its Hall component. We find that the induced Hall conductivity per
incident irradiance is enhanced by up to six orders of magnitude when moving
from the visible regime (with corresponding band gaps) to the far infrared.
These results suggest that narrow-gap GDMs are an ideal test-bed for the unique
physics that arise in the presence of Berry curvature, and open a new avenue
for infrared and terahertz optoelectronics.",1612.05269v1
2017-02-03,Linear magnetoresistance and surface to bulk coupling in topological insulator thin films,"We explore the temperature dependent magnetoresistance of bulk insulating
topological insulator thin films. Thin films of Bi2Se2Te and BiSbTeSe1.6 were
grown using Pulsed Laser Deposition technique and subjected to transport
measurements. Magnetotransport measurements indicate a non-saturating linear
magnetoresistance (LMR) behavior at high magnetic field values. We present a
careful analysis to explain the origin of LMR taking into consideration all the
existing models of LMR. Here we consider that the bulk insulating states and
the metallic surface states constitute two parallel conduction channels.
Invoking this, we were able to explain linear magnetoresistance behavior as a
competition between these parallel channels. We observe that the crossover
field, where LMR sets in, decreases with increasing temperature. We propose
that this cross over field can be used phenomenologically to estimate the
strength of surface to bulk coupling.",1702.00950v1
2017-02-26,Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering,"We report the enhancement of spin-orbit torques in MnAl/Ta films with
improving chemical ordering through annealing. The switching current density is
increased due to enhanced saturation magnetization MS and effective anisotropy
field HK after annealing. Both damplinglike effective field HD and fieldlike
effective field HF have been increased in the temperature range of 50 to 300 K.
HD varies inversely with MS in both of the films, while the HF becomes liner
dependent on 1/MS in the annealed film. We infer that the improved chemical
ordering has enhanced the interfacial spin transparency and the transmitting of
the spin current in MnAl layer.",1702.07990v1
2017-04-05,Robust odd-parity superconductivity in the doped topological insulator Nb$_x$Bi$_2$Se$_3$,"We present resistivity and magnetization measurements on proton-irradiated
crystals demonstrating that the superconducting state in the doped topological
superconductor Nb$_x$Bi$_2$Se$_3$ (x = 0.25) is surprisingly robust against
disorder-induced electron scattering. The superconducting transition
temperature $T_c$ decreases without indication of saturation with increasing
defect concentration, and the corresponding scattering rates far surpass
expectations based on conventional theory. The low-temperature variation of the
London penetration depth $\Delta\lambda(T)$ follows a power law
($\Delta\lambda(T)\sim T^2$) indicating the presence of symmetry-protected
point nodes. Our results are consistent with the proposed robust nematic $E_u$
pairing state in this material.",1704.01225v1
2017-04-20,Ferrimagnetism in the Spin-1/2 Heisenberg Antiferromagnet on a Distorted Triangular Lattice,"The ground state of the spin-$1/2$ Heisenberg antiferromagnet on a distorted
triangular lattice is studied using a numerical-diagonalization method. The
network of interactions is the $\sqrt{3}\times\sqrt{3}$ type; the interactions
are continuously controlled between the undistorted triangular lattice and the
dice lattice. We find new states between the nonmagnetic 120-degree-structured
state of the undistorted triangular case and the up-up-down state of the dice
case. The intermediate states show spontaneous magnetizations that are smaller
than one third of the saturated magntization corresponding to the up-up-down
state.",1704.06013v2
2017-04-28,The design and the performance of stratospheric mission in the search for the Schumann resonances,"The technical details of a balloon stratospheric mission that is aimed at
measuring the Schumann resonances are described. The gondola is designed
specifically for the measuring of faint effects of ELF (Extremely Low Frequency
electromagnetic waves) phenomena. The prototype met the design requirements.
The ELF measuring system worked properly for entire mission; however, the level
of signal amplification that was chosen taking into account ground-level
measurements was too high. Movement of the gondola in the Earth magnetic field
induced the signal in the antenna that saturated the measuring system. This
effect will be taken into account in the planning of future missions. A large
telemetry dataset was gathered during the experiment and is currently under
processing. The payload consists also of biological material as well as
electronic equipment that was tested under extreme conditions.",1704.08930v2
2017-06-21,Scaling of Majorana Zero-Bias Conductance Peaks,"We report an experimental study of the scaling of zero-bias conductance peaks
compatible with Majorana zero modes as a function of magnetic field, tunnel
coupling, and temperature in one-dimensional structures fabricated from an
epitaxial semiconductor-superconductor heterostructure. Results are consistent
with theory, including a peak conductance that is proportional to tunnel
coupling, saturates at $2e^2/h$, decreases as expected with field-dependent
gap, and collapses onto a simple scaling function in the dimensionless ratio of
temperature and tunnel coupling.",1706.07033v2
2017-06-29,Magnetotransport properties of MoP$_2$,"We report magnetotransport and de Haas-van Alphen (dHvA) effect studies on
MoP$_2$ single crystals, predicted to be type-2 Weyl semimetal with four pairs
of robust Weyl points located below the Fermi level and long Fermi arcs. The
temperature dependence of resistivity shows a peak before saturation, which
does not move with magnetic field. Large nonsaturating magnetoresistance (MR)
was observed, and the field dependence of MR exhibits a crossover from
semicalssical weak-field $B^2$ dependence to the high-field linear-field
dependence, indicating the presence of Dirac linear energy dispersion. In
addition, systematic violation of Kohler's rule was observed, consistent with
multiband electronic transport. Strong spin-orbit coupling (SOC) splitting has
an effect on dHvA measurements whereas the angular-dependent dHvA orbit
frequencies agree well with the calculated Fermi surface. The cyclotron
effective mass $\sim$ 1.6$m_e$ indicates the bands might be trivial, possibly
since the Weyl points are located below the Fermi level. Interestingly,
quasi-two dimensional(2D) band structure is observed even though the crystal
structure of MoP$_2$ is not layered.",1706.09830v1
2017-07-21,Modeling alignment enhancement for solid polarized targets,"A model of dynamic orientation using optimized radiofrequency (RF)
irradiation produced perpendicular to the holding field is developed for the
spin-1 system required for tensor-polarized fixed-target experiments. The
derivation applies to RF produced close to the Larmor frequency of the nucleus
and requires the electron spin-resonance linewidth to be much smaller than the
nuclear magnetic resonance frequency. The rate equations are solved numerically
to study a semi-saturated steady-state resulting from the two sources of
irradiation: microwave from the DNP process and the additional RF used to
manipulate the tensor polarization. The steady-state condition and
continuous-wave NMR lineshape are found that optimize the spin-1 alignment in
the polycrystalline materials used as solid polarized targets in charged-beam
nuclear and particle physics experiments.",1707.07065v1
2017-07-30,Incommensurate magnetism near quantum criticality in CeNiAsO,"Two phase transitions in the tetragonal strongly correlated electron system
CeNiAsO were probed by neutron scattering and zero field muon spin rotation.
For $T <T_{N1}$ = 8.7(3) K, a second order phase transition yields an
incommensurate spin density wave with wave vector $\textbf{k} = (0.44(4), 0,
0)$. For $T < T_{N2}$ = 7.6(3) K, we find co-planar commensurate order with a
moment of $0.37(5)~\mu_B$, reduced to $30 \%$ of the saturation moment of the
$|\pm\frac{1}{2}\rangle$ Kramers doublet ground state, which we establish by
inelastic neutron scattering. Muon spin rotation in $\rm CeNiAs_{1-x}P_xO$
shows the commensurate order only exists for x $\le$ 0.1 so the transition at
$x_c$ = 0.4(1) is from an incommensurate longitudinal spin density wave to a
paramagnetic Fermi liquid.",1707.09645v2
2017-08-18,Strongly-coupled anisotropic gauge theories and holography,"We initiate a non-perturbative study of anisotropic, non-conformal and
confining gauge theories that are holographically realized in gravity by
generic Einstein-Axion-Dilaton systems. In the vacuum our solutions describe RG
flows from a conformal field theory in the UV to generic scaling solutions in
the IR with generic hyperscaling violation and dynamical exponents $\theta$ and
$z$. We formulate a generalization of the holographic c-theorem to the
anisotropic case. At finite temperature, we discover that the anisotropic
deformation reduces the confinement-deconfinement phase transition temperature
suggesting a possible alternative explanation of inverse magnetic catalysis
solely based on anisotropy. We also study transport and diffusion properties in
anisotropic theories and observe in particular that the butterfly velocity that
characterizes both diffusion and growth of chaos transverse to the anisotropic
direction, saturates a constant value in the IR which can exceed the bound
given by the conformal value.",1708.05691v2
2017-08-28,Dependence of Dzyaloshinskii-Moriya interaction on the oxygen coverage in Pt/Co/MOx trilayers,"We have studied the interfacial Dzyaloshinskii-Moriya interaction (DMI) in a
series of Pt/Co/MOx (M=Al, Gd) trilayers in which the degree of oxidation of
the top Co interface is varied. To access to reliable values of the DMI
strength, we have used a method based on the measurement of the saturation
velocity of field driven chiral N\'eel domain walls. We show that the effective
DMI strength in the Pt/Co/MOx trilayers varies with the oxidation degree of the
Co/MOx interface. This strongly suggests that the Co/MOx interface gives a
distinct contribution to the total DMI, adding to that of the Pt/Co interface.
The DMI presents a maximum for the oxygen coverage maximizing also the
interface magnetic anisotropy energy Ks. This calls for common microscopic
origins for the contributions of the Co/MOx interface to DMI and Ks.",1708.08516v1
2017-09-14,Proximity Effect in Superconducting-Ferromagnetic Granular Structures,"We examined the proximity effect in granular films made of Pb, a
superconductor, and Ni, a ferromagnet, with various compositions. Slow decay of
the critical temperature as a function of the relative volume concentration of
Ni per sample was demonstrated by our measurements, followed by a saturation of
T$_c$. Using an approximate theoretical description of our granular system in
terms of a layered one, we show that our data can only be reasonably fitted by
a multilayer model. This indicates the importance of the interplay between
different ferromagnetic grains; when non-collinearly magnetized they should
lead to triplet Cooper pairing.",1709.04760v2
2017-09-15,Impact and mitigation strategy for future solar flares,"It is widely established that extreme space weather events associated with
solar flares are capable of causing widespread technological damage. We develop
a simple mathematical model to assess the economic losses arising from these
phenomena over time. We demonstrate that the economic damage is characterized
by an initial period of power-law growth, followed by exponential amplification
and eventual saturation. We outline a mitigation strategy to protect our planet
by setting up a magnetic shield to deflect charged particles at the Lagrange
point L$_1$, and demonstrate that this approach appears to be realizable in
terms of its basic physical parameters. We conclude our analysis by arguing
that shielding strategies adopted by advanced civilizations will lead to
technosignatures that are detectable by upcoming missions.",1709.05348v2
2017-10-30,Nontopological first-order vortices in a gauged $CP(2)$ model with a dielectric function,"We consider nontopological first-order solitons arising from a gauged $CP(2)$
model in the presence of the Maxwell term multiplied by a nontrivial dielectric
function. We implement the corresponding first-order scenario by proceeding the
minimization of the total energy, this way introducing the corresponding energy
lower-bound, such a construction being only possible due to a differential
constraint including the dielectric function itself and the self-interacting
potential defining the model. We saturate the aforementioned bound by focusing
our attention on those solutions fulfilling a particular set of two coupled
first-order differential equations. In the sequel, in order to solve these
equations, we choose the dielectric function explicitly, also calculating the
corresponding self-interacting potential. We impose appropriate boundary
conditions supporting nontopological solitons, from which we verify that the
energy of final structures is proportional to the magnetic flux they engender,
both quantities being not quantized, as expected. We depict the new numerical
solutions, whilst commenting on the main properties they present.",1710.11215v1
2017-11-04,"Superconducting, Insulating, and Anomalous Metallic Regimes in a Gated Two-Dimensional Semiconductor-Superconductor Array","The superconductor-insulator transition in two dimensions has been widely
investigated as a paradigmatic quantum phase transition. The topic remains
controversial, however, because many experiments exhibit a metallic regime with
saturating low-temperature resistance, at odds with conventional theory. Here,
we explore this transition in a novel, highly controllable system, a
semiconductor heterostructure with epitaxial Al, patterned to form a regular
array of superconducting islands connected by a gateable quantum well. Spanning
nine orders of magnitude in resistance, the system exhibits regimes of
superconducting, metallic, and insulating behavior, along with signatures of
flux commensurability and vortex penetration. An in-plane magnetic field
eliminates the metallic regime, restoring the direct superconductor-insulator
transition, and improves scaling, while strongly altering the scaling exponent.",1711.01451v2
2017-12-05,The Weak Gravity Conjecture and Emergence from an Ultraviolet Cutoff,"We study ultraviolet cutoffs associated with the Weak Gravity Conjecture
(WGC) and Sublattice Weak Gravity Conjecture (sLWGC). There is a magnetic WGC
cutoff at the energy scale $e G_N^{-1/2}$ with an associated sLWGC tower of
charged particles. A more fundamental cutoff is the scale at which gravity
becomes strong and field theory breaks down entirely. By clarifying the nature
of the sLWGC for nonabelian gauge groups we derive a parametric upper bound on
this strong gravity scale for arbitrary gauge theories. Intriguingly, we show
that in theories approximately saturating the sLWGC, the scales at which loop
corrections from the tower of charged particles to the gauge boson and graviton
propagators become important are parametrically identical. This suggests a
picture in which gauge fields emerge from the quantum gravity scale by
integrating out a tower of charged matter fields. We derive a converse
statement: if a gauge theory becomes strongly coupled at or below the quantum
gravity scale, the WGC follows. We sketch some phenomenological consequences of
the UV cutoffs we derive.",1712.01868v2
2017-12-05,Two-dimensional semimetal in HgTe quantum well under hydrostatic pressure,"We report results of systematic measurements of charge transport properties
of the 20.5nm wide HgTe-based quantum well in perpendicular magnetic field,
performed under hydrostatic pressures up to 15.1 kbar. At ambient pressure
transport is well described by the two-band semiclassical model.In contrast, at
elevated pressure, we observed non-monotonic pressure dependence of resistivity
at CNP. For pressures lower than $\approx9$ kbar, resistivity grows with
pressure, in accord with expectations from the band structure calculations and
the model incorporating effects of disorder on transport in 2D semimetals with
indirect band overlap. For higher pressures, the resistivity saturates and
starts decreasing upon further increase of pressure. Above $\approx14$ kbar the
resistance and hopping transport character sharply change, which may indicate
formation of the excitonic insulator state. The data also reveals strong
influence of disorder on transport in 2D electron-hole system with a small band
overlap.",1712.01879v2
2018-01-05,Self-excitation in a helical liquid metal flow: The Riga dynamo experiments,"The homogeneous dynamo effect is at the root of magnetic field generation in
cosmic bodies, including planets, stars and galaxies. While the underlying
theory had increasingly flourished since the middle of the 20th century,
hydromagnetic dynamos were not realized in laboratory until 1999. On 11
November 1999, this situation changed with the first observation of a kinematic
dynamo in the Riga experiment. Since that time, a series of experimental
campaigns has provided a wealth of data on the kinematic and the saturated
regime. This paper is intended to give a comprehensive survey about these
experiments, to summarize their main results and to compare them with numerical
simulations.",1801.01749v1
2018-01-22,Bootstrapping hypercubic and hypertetrahedral theories in three dimensions,"There are three generalizations of the Platonic solids that exist in all
dimensions, namely the hypertetrahedron, the hypercube, and the
hyperoctahedron, with the latter two being dual. Conformal field theories with
the associated symmetry groups as global symmetries can be argued to exist in
$d=3$ spacetime dimensions if the $\varepsilon=4-d$ expansion is valid when
$\varepsilon\to1$. In this paper hypercubic and hypertetrahedral theories are
studied with the non-perturbative numerical conformal bootstrap. In the $N=3$
cubic case it is found that a bound with a kink is saturated by a solution with
properties that cannot be reconciled with the $\varepsilon$ expansion of the
cubic theory. Possible implications for cubic magnets and structural phase
transitions are discussed. For the hypertetrahedral theory evidence is found
that the non-conformal window that is seen with the $\varepsilon$ expansion
exists in $d=3$ as well, and a rough estimate of its extent is given.",1801.07127v4
2018-02-08,Ultraviolet laser spectroscopy of aluminum atoms in hollow-cathode lamp,"We report precision measurement of aluminum atoms
${^{2}P_{1/2}}-{^{2}S_{1/2}}$ transition at 394 nm and
${^{2}P_{3/2}}-{^{2}S_{1/2}}$ transition at 396 nm in a hollow-cathode lamp
(HCL). Both absorption spectroscopy and saturated absorption spectroscopy (SAS)
are performed. From the absorption spectroscopy the Doppler linewidth is
estimated to be 2.6 GHz. The SAS spectroscopy is analyzed based on the
velocity-changing-effect model. With a frequency comb calibrated wavemeter, the
frequencies of ${^{2}P_{1/2}},{F=3}-{^{2}S_{1/2}},{F=2}$ transition and
${^{2}P_{3/2}},{F=4}-{^{2}S_{1/2}},{F=3}$ transition are measured to be
759.905401(10) THz and 756.547403(10) THz, respectively. The hyperfine
structure constants of aluminum atoms are determined and compared with
previously reported measurement results and theoretical calculation. Reasonable
agreement is found for the magnetic dipole constant (A constant), while the
electric quadrupole constant (B constant) has a large deviation.",1802.02749v1
2018-03-08,Quantum Interactions of Topological Solitons from Electrodynamics,"The Casimir energy for the classically stable configurations of the
topological solitons in 2D quantum antiferromagnets is studied by performing
the path-integral over quantum fluctuations. The magnon fluctuation around the
solitons saturating the Bogomol'nyi inequality may be viewed as a charged
scalar field coupled with an effective magnetic field induced by the solitons.
The magnon-soliton couping is closely related to the Pauli Hamiltonian, with
which the effective action is calculated by adapting the worldline formulation
of the derivative expansion for the 2+1d quantum electrodynamics in an external
field. The resulting framework is more flexible than the conventional
scattering analysis based on the Dashen-Hasslacher-Neveu formula. We obtain a
short-range attractive well and a universal long-range $1/r$-type repulsive
potential between two solitons.",1803.03181v5
2018-04-18,Comparison of Sensitivity and Low Frequency Noise Contributions in GMR and TMR Spin Valve Sensors with a Vortex State Free Layer,"Magnetoresistive spin valve sensors based on the giant- (GMR) and tunnelling-
(TMR) magnetoresisitve effect with a flux-closed vortex state free layer design
are compared by means of sensitivity and low frequency noise. The vortex state
free layer enables high saturation fields with negligible hysteresis, making it
attractive for applications with a high dynamic range. The measured GMR devices
comprise lower pink noise and better linearity in resistance but are less
sensitive to external magnetic fields than TMR sensors. The results show a
comparable detectivity at low frequencies and a better performance of the TMR
minimum detectable field at frequencies in the white noise limit.",1804.06940v1
2018-05-01,On The Design of a Novel Finite-Time Nonlinear Extended State Observer for Class of Nonlinear Systems with Mismatch Disturbances and Uncertainties,"In this paper, a novel finite - time Nonlinear Extended State Observer
(NLESO) is proposed and employed in Active Disturbance Rejection Control (ADRC)
to stabilize a nonlinear system against system's uncertainties and
discontinuous disturbances using output feedback technique. The first task was
to aggregate the uncertainties, disturbances, and any other undesired
nonlinearities in the system into a single term called the ""generalized
disturbance"". Consequently, the ESO estimates the generalized disturbance and
cancel it from the input channel in an online fashion. A peaking phenomenon
that existed in Linear ESO (LESO) has been reduced significantly by adopting a
saturation - like nonlinear function in the proposed Nonlinear ESO (NLESO).
Stability analysis of the NLEO is studied using finite - time Lyapunov theory,
and the comparisons are presented over simulations on Permanent Magnet DC
(PMDC) motor to confirm the effectiveness of the proposed observer concerning
LESO.",1805.00257v4
2018-05-25,Extreme magnetoresistance and Shubnikov-de Haas oscillations in ferromagnetic DySb,"The electronic structures of a representative rare earth monopnictide (i.e.,
DySb) under high magnetic field (i.e., in the ferromagnetic state) are studied
from both experimental and theoretical aspects. A non-saturated extremely large
positive magnetoresistance (XMR) is observed (as large as 3.7*10^4% at 1.8 K
and 38.7 T), along with the Shubnikov-de Haas oscillations that are well
reproduced by our first principles calculations. Three possible origins of XMR
are examined. Although a band inversion is found theoretically, suggesting that
DySb might be topologically nontrivial, it is deeply underneath the Fermi
level, which rules out a topological nature of the XMR. The total densities of
electron-like and hole-like carriers are not fully compensated, showing that
compensation is unlikely to account for the XMR. The XMR is eventually
understood in terms of high mobility that is associated with the steep linear
bands. This discovery is important to the intensive studies on the XMR of rare
earth monopnictides.",1805.09998v2
2018-06-08,Quantum dynamics of disordered spin chains with power-law interactions,"We use extensive numerical simulations based on matrix product state methods
to study the quantum dynamics of spin chains with strong on-site disorder and
power-law decaying ($1/r^\alpha$) interactions. We focus on two spin-$1/2$
Hamiltonians featuring power-law interactions: Heisenberg and XY and
characterize their corresponding long-time dynamics using three distinct
diagnostics: decay of a staggered magnetization pattern $I(t)$, growth of
entanglement entropy $S(t)$, and growth of quantum Fisher information $F_Q(t).$
For sufficiently rapidly decaying interactions $\alpha>\alpha_c$ we find a
many-body localized phase, in which $I(t)$ saturates to a non-zero value,
entanglement entropy grows as $S(t)\propto t^{1/\alpha}$, and Fisher
information grows logarithmically. Importantly, entanglement entropy and Fisher
information do not scale the same way (unlike short range interacting models).
The critical power $\alpha_c$ is smaller for the XY model than for the
Heisenberg model.",1806.03339v1
2018-06-21,Detection and characterization of Many-Body Localization in Central Spin Models,"We analyze a disordered central spin model, where a central spin interacts
equally with each spin in a periodic one dimensional random-field Heisenberg
chain. If the Heisenberg chain is initially in the many-body localized (MBL)
phase, we find that the coupling to the central spin suffices to delocalize the
chain for a substantial range of coupling strengths. We calculate the phase
diagram of the model and identify the phase boundary between the MBL and
ergodic phase. Within the localized phase, the central spin significantly
enhances the rate of the logarithmic entanglement growth and its saturation
value. We attribute the increase in entanglement entropy to a non-extensive
enhancement of magnetization fluctuations induced by the central spin. Finally,
we demonstrate that correlation functions of the central spin can be utilized
to distinguish between MBL and ergodic phases of the 1D chain. Hence, we
propose the use of a central spin as a possible experimental probe to identify
the MBL phase.",1806.08316v1
2018-06-22,Half moons are pinch points with dispersion,"""Pinch points,"" singular features observed in (quasi-)elastic neutron
scattering, are a widely discussed hallmark of spin liquids with an emergent
gauge symmetry. Much less attention has been paid to ""half moons,"" distinctive
crescent patterns at finite energy, which have been observed in experiments on
a number of pyrochlore magnets, and in a wide range of model calculations. Here
we unify these two phenomena within a single framework, paying particular
attention to the case of ordered, or field-saturated states, where pinch points
and half moons can be found in bands of excitations above a gap. We find that
half moons are nothing other than pinch points inscribed on a dispersing band.
Molecular dynamics simulations of the kagome lattice antiferromagnet are used
to explore how these bands evolve into the ground state and excitations of a
classical spin liquid. We explicitly demonstrate that this theory can reproduce
the pinch points and half moons observed in Nd$_2$Zr$_2$O$_7$.",1806.08520v2
2018-07-30,Ultralow-temperature thermal conductivity of Pr2Ir2O7: a metallic spin-liquid candidate with quantum criticality,"The frustrated pyrochlore iridate Pr$_2$Ir$_2$O$_7$ was proposed as a
metallic quantum spin liquid located at a zero-field quantum critical point.
Here we present the ultralow-temperature thermal conductivity measurements on
the Pr$_2$Ir$_2$O$_7$ single crystals to detect possible exotic excitations. In
zero field, the thermal conductivity shows a dramatic suppression above a
characteristic temperature $T_s \approx$ 0.12 K. With increasing field, $T_s$
increases and the thermal conductivity tends to saturate above $H$ = 5 T. The
Wiedemann-Franz law is verified at high fields and inferred at zero field. It
suggests the normal behavior of electrons at the quantum critical point, and
the absence of mobile fermionic magnetic excitations. The strong suppression of
thermal conductivity is attributed to the scattering of phonons by the spin
system, likely the fluctuating spins. These results shed new light on the
microscopic description on this novel compound.",1807.11185v1
2018-10-10,First-principles investigation of the effect of substitution and surface adsorption on magnetostrictive properties of Fe-Ga alloys,"Materials with large magnetostriction are widely used in sensors, actuators,
micro electromechanical systems, and energy-harvesters. Binary Fe-Ga alloys
(Galfenol) are the most promising rare-earth-free candidates combining numerous
advantages such as low saturation magnetic field (~200 Oe), excellent ductility
and low cost, while further improving their performance is imperative for
practical applications. Using density functional theory calculation, we report
results of the effect of substituting small amount of additional elements X
(eg. X = Ag, Pd and Cu) on magnetostriction of Fe-Ga alloys, and find that it
may double the magnetostriction with a substitutional percentage of only 1.6%.
Moreover, adsorbents with high chemical activity (eg. O or Os atoms) may affect
the surface energy of different face-orientations of Fe-Ga alloys, indicating
proper surface treatments are necessary to tune the alignment of Fe-Ga grains
to achieve better performance. These results may be helpful to further optimize
the magnetostrictive properties of Fe-Ga alloys for device applications.",1810.04708v1
2018-10-13,Noise in the helical edge channel anisotropically coupled to a local spin,"We calculate the frequency-dependent shot noise in the edge states of a
two-dimensional topological insulator coupled to a magnetic impurity with spin
$S=1/2$ of arbitrary anisotropy. If the anisotropy is absent, the noise is
purely thermal at low frequencies, but tends to the Poissonian noise of the
full current $I$ at high frequencies. If the interaction only flips the
impurity spin but conserves those of electrons, the noise at high voltages
$eV\gg T$ is frequency-independent. Both the noise and the backscattering
current $I_{bs}$ saturate at voltage-independent values. Finally, if the
Hamiltonian contains all types of non-spin-conserving scattering, the noise at
high voltages becomes frequency-dependent again. At low frequencies, its ratio
to $2eI_{bs}$ is larger than 1 and may reach 2 in the limit $I_{bs}\to 0$. At
high frequencies it tends to 1.",1810.05831v1
2018-12-03,The Landau-Lifshitz-Bloch equation for domain wall motion in antiferromagnets,"In this work, we derive the Landau-Lifshitz-Bloch equation accounting for the
multi-domain antiferromagnetic (AFM) lattice at finite temperature, in order to
investigate the domain wall (DW) motion, the core issue for AFM spintronics.
The continuity equation of the staggered magnetization is obtained using the
continuum approximation, allowing an analytical calculation on the domain wall
dynamics. The influence of temperature on the static domain wall profile is
investigated, and the analytical calculations reproduce well earlier numerical
results on temperature gradient driven saturation velocity of the AFM domain
wall, confirming the validity of this theory. Moreover, it is worth noting that
this theory could be also applied to dynamics of various wall motions in an AFM
system. The present theory represents a comprehensive approach to the domain
wall dynamics in AFM materials, a crucial step toward the development of AFM
spintronics.",1812.00759v2
2018-12-06,Generic machine identification and maximum efficiency operation of induction machines,"This paper proposes an advanced machine identification method for inverter
fed squirrel-cage induction machines, based on steady-state measurements in the
rotor flux oriented dq-reference frame. The measured machine maps are used to
extract maximum efficiency per torque (MEPT) look-up tables, which guarantee
the maximum achievable efficiency in every operating point. Furthermore, it is
shown, that comparable results can be achieved, even without a torque sensor.
The main advantage of the described method is its generality, which implicitly
covers magnetic saturation, iron losses and other nonlinear effects that are
typically neglected or approximated by complex models. Finally, the
efficiencies of V/Hz and field-oriented control (FOC) are calculated for
different speeds and load torques, allowing for quantitative assessment and
comparison of both methods.",1812.02431v1
2018-12-10,Electromagnetic turbulence suppression by energetic particle driven modes,"In recent years, a strong reduction of plasma turbulence in the presence of
energetic particles has been reported in a number of magnetic confinement
experiments and corresponding gyrokinetic simulations. While highly relevant to
performance predictions for burning plasmas, an explanation for this primarily
nonlinear effect has remained elusive so far. A thorough analysis finds that
linearly marginally stable energetic particle driven modes are excited
nonlinearly, depleting the energy content of the turbulence and acting as an
additional catalyst for energy transfer to zonal modes (the dominant turbulence
saturation channel). Respective signatures are found in a number of simulations
for different JET and ASDEX Upgrade discharges with reduced transport levels
attributed to energetic ion effects.",1812.03755v1
2018-12-12,Room-temperature ferromagnetic insulating state in highly cation-ordered epitaxial oxide double perovskite,"Ferromagnetic insulators (FMIs) are one of the most important components in
developing dissipationless electronic and spintronic devices. However, since
ferromagnetism generally accompanies metallicity, FMIs are innately rare to
find in nature. Here, novel room-temperature FMI films are epitaxially
synthesized by deliberate control of the ratio of two B-site cations in the
double perovskite Sr2FeReO6. In contrast to the known ferromagnetic metallic
phase in stoichiometric Sr2FeReO6, a FMI state with a high Curie temperature
(Tc~400 K) and a large saturation magnetization (MS~1.8 {\mu}B/f.u.) is found
in highly cation-ordered Fe-rich phases. The stabilization of the FMI state is
attributed to the formation of extra Fe3+-Fe3+ and Fe3+-Re6+ bonding states,
which originate from the excess Fe. The emerging FMI state by controlling
cations in the epitaxial oxide perovskites opens the door to developing novel
oxide quantum materials & heterostructures.",1812.04953v1
2019-01-05,Nonlinear excitation of geodesic acoustic mode by toroidal Alfvén eigenmodes and impact on plasma performance,"Spontaneous nonlinear excitation of geodesic acoustic mode (GAM) by toroidal
Alfv\'en eigenmode (TAE) is investigated using nonlinear gyrokinetic theory. It
is found that, the nonlinear decay process depends on thermal ion \beta value.
Here, \beta is the plasma thermal to magnetic pressure ratio. In the low-\beta
limit, TAE decays into a GAM and a lower TAE sideband in the toroidicity
induced shear Alfv\'en wave continuous spectrum gap; while in the high-\beta
limit, TAE decays into a GAM and a propagating kinetic TAE in the continuum.
Both cases are investigated for the spontaneous decay conditions. The nonlinear
saturation levels of both GAM and daughter wave are derived. The corresponding
power balance and wave particle power transfer to thermal plasma are computed.
Implications on thermal plasma heating are also discussed.",1901.01366v1
2019-01-08,Fabrication of yttrium-iron-garnet/Pt multilayers for the longitudinal spin Seebeck effect,"For longitudinal spin Seebeck effect (LSSE) devices, a multilayer structure
comprising ferromagnetic and nonmagnetic layers is expected to improve their
thermoelectric power. In this study, we developed the fabrication method for
alternately stacked yttrium-iron-garnet (YIG)/Pt multilayer films on a
gadolinium gallium garnet (GGG) (110) substrate, GGG/[YIG(49 nm)/Pt(4 nm)]$_n$
($n =$ 1 - 5) based on room-temperature sputtering and $ex$-$situ$
post-annealing method and we evaluated their structural and LSSE properties.
The fabricated [YIG/Pt]$_n$ samples show flat YIG/Pt interfaces and almost
identical saturation magnetization $M_{\rm s}$, although they contain
polycrystalline YIG layers on Pt layers as well as single-crystalline YIG
layers on GGG. In the samples, we observed clear LSSE signals and found that
the LSSE thermoelectric power factor (PF) increases monotonically with
increasing $n$; the PF of the [YIG/Pt]$_5$ sample is enhanced by a factor of
$\sim 28$ compared to that of [YIG/Pt]$_1$. This work may provide a guideline
for developing future multilayerbased LSSE devices.",1901.02129v1
2019-02-20,Surface-induced positive planar Hall effect in topological Kondo insulator SmB6 microribbons,"Whether the surface states in SmB6 are topological is still a critical issue
in the field of topological Kondo insulators. In the magneto-transport study of
single crystalline SmB6 microribbons, we have revealed a positive planar Hall
effect (PHE), the amplitude of which increases dramatically with decreasing
temperatures but saturates below 5 K. This positive PHE is ascribed to the
surface states of SmB6 and expected to arise from the anisotropy in lifting the
topological protection from back-scattering by the in-plane magnetic field,
thus suggesting the topological nature of surface states in SmB6. On the
contrary, a negative PHE is observed for the bulk states at high temperatures,
which is almost three orders of magnitudes weaker than the surface-induced
positive PHE.",1902.07364v1
2019-04-15,Evolution of three-dimensional Relativistic Ion Weibel Instability: Competition with Kink Instability,"In this paper, we report our recent findings on the relativistic Weibel
instability and its nonlinear saturation by performing numerical simulations of
collisionless plasmas. Analysis of the obtained numerical results revealed that
the nonlinear phase of the Weibel instability can be described by
characteristic phases based on the Weibel filaments' current density in terms
of particle and Alfv\'en limit currents. We also analyzed the relativistic kink
instability based on the energy principle in the magnetohydrodynamic (MHD)
regime, and found that the Weibel filaments do not suffer from the kink-type
instability in the MHD regime up to 1000 $\omega_{p,i}^{-1}$. This finding
allowed a magnetic field to be sustained by relativistic Weibel instability
that was stable enough to be a seed for MHD dynamos.",1904.07008v1
2019-05-08,Charge density wave and large non-saturating magnetoresistance in YNiC$_2$ and LuNiC$_2$,"We report a study of physical properties of two quasi-low dimensional metals
YNiC$_2$ and LuNiC$_2$ including the investigation of transport,
magnetotransport, galvanomagnetic and specific heat properties. In YNiC$_2$ we
reveal two subsequent transitions associated with the formation of weakly
coupled charge density wave at $T_{CDW}$ = 318 K, and its locking in with the
lattice at $T_1$ = 275 K. These characteristic temperatures follow the
previously proposed linear scaling with the unit cell volume, demonstrating its
validity extended beyond the lanthanide-based $R$NiC$_2$. We also find that, in
the absence of magnetic ordering able to interrupt the development of charge
density wave, the Fermi surface nesting leads to opening of small pockets,
containing high mobility carriers. This effect gives rise to substantial
enhancement of magnetoresistance, reaching 470 % for YNiC$_2$ and 50 % for
LuNiC$_2$ at $T$ = 1.9 K and $B$ = 9 T.",1905.02919v1
2019-05-27,Magnetohydrodynamics in graphene: shear and Hall viscosities,"Viscous phenomena are the hallmark of the hydrodynamic flow exhibited by
Dirac fermions in clean graphene at high enough temperatures. We report a
quantitative calculation of the electronic shear and Hall viscosities in
graphene based on the kinetic theory combined with the renormalization group
providing a unified description at arbitrary doping levels and non-quantizing
magnetic fields. At charge neutrality, the Hall viscosity vanishes, while the
field-dependent shear viscosity decays from its zero-field value saturating to
a nonzero value in classically strong fields. Away from charge neutrality, the
field-dependent viscosity coefficients tend to agree with the semiclassical
expectation.",1905.11424v2
2019-05-30,Possibility of $ρ$ Meson Condensation in Neutron Star: Unified Approach of Chiral SU(3) Model and QCD Sum Rules,"In the present work the conjunction of chiral SU(3) model with QCD sum rules
is employed to explore the possibility of $\rho$ meson condensation in neutron
stars. The quark and gluon condensates in terms of which the in-medium masses
of $\rho$ mesons can be expressed are calculated using the chiral SU(3) model
in the charge neutral matter which is relevant for neutron stars. It is
observed that condition of $\rho$ meson condensation is satisfied for the
density of about 7$\rho_{0}$, where $\rho_{0}$ is the nuclear saturation
density. In the end, a brief qualitative discussion of the magnetic field is
also involved to check out for the further possibility of $\rho$ meson
condensation.",1905.13184v1
2019-06-19,Bosonic topological insulator intermediate state in the superconductor-insulator transition,"A low-temperature intervening metallic regime arising in the two-dimensional
superconductor-insulator transition challenges our understanding of electronic
fluids. Here we develop a gauge theory revealing that this emergent anomalous
metal is a bosonic topological insulator where bulk transport is suppressed by
mutual statistics interactions between out-of-condensate Cooper pairs and
vortices and the longitudinal conductivity is mediated by symmetry-protected
gapless edge modes. We explore the magnetic-field-driven
superconductor-insulator transition in a niobium titanium nitride device and
find marked signatures of a bosonic topological insulator behavior of the
intervening regime with the saturating resistance. The observed
superconductor-anomalous metal and insulator-anomalous metal dual phase
transitions exhibit quantum Berezinskii-Kosterlitz-Thouless criticality in
accord with the gauge theory.",1906.07969v2
2019-07-08,Knot spectrum of turbulence,"Streamlines, vortex lines and magnetic flux tubes in turbulent fluids and
plasmas display a great amount of coiling, twisting and linking, raising the
question as to whether their topological complexity (continually created and
destroyed by reconnections) can be quantified. In superfluid helium, the
discrete (quantized) nature of vorticity can be exploited to associate to each
vortex loop a knot invariant called the Alexander polynomial whose degree
characterizes the topology of that vortex loop. By numerically simulating the
dynamics of a tangle of quantum vortex lines, we find that this quantum
turbulence always contains vortex knots of very large degree which keep
forming, vanishing and reforming, creating a distribution of topologies which
we quantify in terms of a knot spectrum and its scaling law. We also find
results analogous to those in the wider literature, demonstrating that the
knotting probability of the vortex tangle grows with the vortex length, as for
macromolecules, and saturates above a characteristic length, as found for
tumbled strings.",1907.03420v1
2019-08-03,Coherent control of Optical limiting in atomic systems,"Generation and control of the reverse saturable absorption (RSA) and optical
limiting (OL) are investigated in a four-level Y-type quantum system. It is
demonstrated that the applied laser fields induce the RSA and it can be
coherently controlled by either intensity or frequency of the applied laser
fields. The effect of the static magnetic field on the induced RSA is studied
and we obtain that it has a constructive role in determining the intensity
range in which the OL is established in the system. In addition, we find that
the OL threshold can be decreased either by increasing the length of the medium
or by getting the atomic system denser. Finally, Z-scan technique is presented
to confirm our theoretical results. The proposed scheme can be used in
designing the coherent optical limiters with controllable threshold and
intensity range of OL.",1908.01186v1
2019-08-21,Lyapunov growth in quantum spin chains,"The Ising spin chain with longitudinal and transverse magnetic fields is
often used in studies of quantum chaos, displaying both chaotic and integrable
regions in its parameter space. However, even at a strongly chaotic point this
model does not exhibit Lyapunov growth of the commutator squared of spin
operators, as this observable saturates before exponential growth can manifest
itself (even in situations where a spatial suppression factor makes the initial
commutator small). We extend this model from the spin 1/2 Ising model to higher
spins, demonstrate numerically that a window of exponential growth opens up for
sufficiently large spin, and extract a quantity which corresponds to a notion
of a Lyapunov exponent. In the classical infinite-spin limit, we identify and
compute the appropriate classical analogue of the commutator squared, and show
that the corresponding exponent agrees with the infinite-spin limit extracted
from the quantum spin chain.",1908.08059v3
2019-09-10,Highly Mobile Carriers in a Candidate of Quasi-Two-Dimensional Topological Semimetal AuTe$_2$Br,"We report the crystal and electronic structures of a non-centrosymmetric
quasi-two-dimensional (2D), candidate of topological semimetal AuTe2Br. The
Fermi surface of this layered compound consists of 2D-like, topological trivial
electron and non-trivial hole pockets which host a Dirac cone along the kz
direction. Our transport measurements on the single crystals show highly
anisotropic, compensated low-density electrons and holes, both of which exhibit
ultrahigh mobility at a level of 10^5cm^2V^-1s^-1 at low temperature. The
highly mobile, compensated carriers lead a non-saturated, parabolic
magnetoresistance as large as 3*10^5 in single-crystalline AuTe2Br in a
magnetic field up to 58 T.",1909.04296v1
2019-10-01,Unique Dirac and Triple point fermiology in simple transition metals and their binary alloys,"Noble metal surfaces (Au, Ag and Cu etc.) have been extensively studied for
the Shockley type surface states (SSs). Very recently, some of these Shockley
SSs have been understood from the topological consideration, with the knowledge
of global properties of electronic structure. In this letter, we show the
existence of Dirac like excitations in the elemental noble metal Ru, Re and Os
based on symmetry analysis and first principle calculations. The unique SSs
driven Fermi arcs have been investigated in details for these metals. Our
calculated SSs and Fermi arcs are consistent with the previous transport and
photo-emission results. We attribute these Dirac excitation mediated Fermi arc
topology to be the possible reasons behind several existing transport
anomalies, such as large non-saturating magneto resistance, anomalous Nernst
electromotive force and its giant oscillations, magnetic breakdown etc. We
further show that the Dirac like excitations in these elemental metal can
further be tuned to three component Fermionic excitations, using symmetry
allowed alloy mechanism.",1910.00196v2
2019-10-23,Magnon crystallization in the kagome lattice antiferromagnet,"We present numerical evidence for the crystallization of magnons below the
saturation field at non-zero temperatures for the highly frustrated spin-half
kagome Heisenberg antiferromagnet. This phenomenon can be traced back to the
existence of independent localized magnons or equivalently flat-band
multi-magnon states. We present a loop-gas description of these localized
magnons and a phase diagram of this transition, thus providing information for
which magnetic fields and temperatures magnon crystallization can be observed
experimentally. The emergence of a finite-temperature continuous transition to
a magnon-crystal is expected to be generic for spin models in dimension $D>1$
where flat-band multi-magnon ground states break translational symmetry.",1910.10448v3
2019-11-26,Pressure effect on multiferroic CuBr2,"The quasi-1D spin chain compound CuBr2 has been found to be multiferroic
below TN (73.5K) under ambient pressure, in which the spontaneous electric
polarization is induced by emerging spin spiral ordering propagating along
b-axis. Herein we studied the hydrostatic pressure effect on the magnetic,
dielectric and structural properties of CuBr2. The multiferroic transition
temperature is greatly enhanced under hydrostatic pressure. From ambient to
about 1 GPa (the limit of our homemade apparatus), TN increases unprecedentedly
by more than 20K, and no sign of saturation is observed in our experiments.
Meanwhile the corresponding dielectric loss keeps rather low (<<0.1). Further
synchrotron-based high pressure X-ray diffraction measurements reveal that
there is no pressure-induced structural phase transition in CuBr2 up to 10.2
GPa. Upon increasing pressure, the b-axis (along the spin chain) just changes
slowly while transverse a- and c- axis parameters shrink much more greatly.
Pressure greatly reduces the separation between spin chains and enhance the
inter-chain coupling interactions in CuBr2, which results in the giant increase
of multiferroic critical temperate. Our finding suggests a new effective way to
improve the known multiferroic systems towards practical high temperature
multiferroicity.",1911.11453v1
2020-01-03,Extremely large linear magnetoresistance in Antimony crystal,"In this letter we report the observation of extremely large non-saturating
linear magnetoresistance (MR) in Antimony(Sb) crystal. An extremely large
magnetoresistance (XMR) of 43000% at 2K and large unsaturating MR$\sim\ $70% at
room temperature is observed at the magnetic field of 9T. Hall measurements
reveal a very high mobility $\sim\ $3.8 x 10$^{4}$ cm$^{2}$/Vs of charge
carriers and strong temperature dependence of carrier concentration and
mobility. The respective scaling of MR and crossover field (B$_{c}$) from
quadratic to linear MR with mobility and inverse of mobility describes the
classical origin of large linear MR in this crystal as suggested by Parish and
Littlewood (PL) model for disordered systems.",2001.00778v1
2020-01-13,Spin-1/2 $XX$ chain in a transverse field with regularly alternating $g$-factors: Static and dynamic properties,"We consider the spin-1/2 isotropic $XY$ chain in an external magnetic field
directed along $z$ axis with periodically varying $g$-factors. To reveal the
effects of regularly alternating $g$-factors, we calculate various static and
dynamic equilibrium quantities in the ground state and at finite temperatures.
We demonstrate that because of the regularly alternating $g$-factors the
saturation field may disappear and the field dependence of the susceptibility
in the ground state has additional logarithmic singularity at zero field.
Moreover, the zero-field susceptibility has a logarithmic singularity as $T\to
0$. Furthermore, the dynamic structure factors exhibit much more structure in
the ""wave vector -- frequency"" plane that can be traced out to modifications of
the two-fermion excitation continua which exclusively determine
$S_{zz}(\kappa,\omega)$ and dominate the properties of $S_{xx}(\kappa,\omega)$.
We discuss what changes can be observed in dynamic experiments on the
corresponding substances.",2001.04159v3
2020-02-10,Structural and magneto-transport studies of iron intercalated Bi2Se3 single crystals,"A detailed investigation on the structural and magneto-transport properties
of iron intercalated Bi2Se3 single crystals have been presented. The x-ray
diffraction and Raman studies confirm the intercalation of Fe in the van der
Waals gaps between the layers. The electrical resistivity of the compounds
decreases upon intercalation, and Hall resistivity shows the enhancement of the
charge carriers upon intercalation. The magnetoresistance shows the
non-saturating linear behavior at higher magnetic field and low temperature.
Intercalation of Fe increases the onset of the linear magnetoresistance
behavior, indicating the reduction in quantum effects. The Kohler scaling
employed on the magnetoresistance data indicates single scattering process for
all these compounds in the measured temperature range of 3- 300 K.",2002.03609v2
2020-03-30,Reduction of the sign problem near $T=0$ in quantum Monte Carlo simulations,"Building on a recent investigation of the Shastry-Sutherland model [S. Wessel
et al., Phys. Rev. B 98, 174432 (2018)], we develop a general strategy to
eliminate the Monte Carlo sign problem near the zero temperature limit in
frustrated quantum spin models. If the Hamiltonian of interest and the
sign-problem-free Hamiltonian---obtained by making all off-diagonal elements
negative in a given basis---have the same ground state and this state is a
member of the computational basis, then the average sign returns to one as the
temperature goes to zero. We illustrate this technique by studying the
triangular and kagome lattice Heisenberg antiferrromagnet in a magnetic field
above saturation, as well as the Heisenberg antiferromagnet on a modified
Husimi cactus in the dimer basis. We also provide detailed appendices on using
linear programming techniques to automatically generate efficient directed loop
updates in quantum Monte Carlo simulations.",2003.13356v1
2020-04-02,Soft x-ray absorption of thin films detected using substrate luminescence: A performance analysis,"X-ray absorption spectroscopy of thin films is central to a broad range of
scientific fields, and is typically detected using indirect techniques. X-ray
excited optical luminescence (XEOL) from the sample's substrate is one such
detection method, in which the luminescence signal acts as an effective
transmission measurement through the film. This detection method has several
advantages that make it versatile compared to others, in particular for
insulating samples or when a probing depth larger than 10nm is required. In
this work we present a systematic performance analysis of this method with the
aim of providing guidelines for its advantages and pitfalls, enabling a wider
use of this method by the thin film community. We compare and quantify the
efficiency of XEOL from a range of commonly used substrates. Our measurements
demonstrate the equivalence between XEOL and x-ray transmission measurements
for thin films. Moreover, we show the applicability of XEOL to magnetic studies
by employing XMCD sum rules with XEOL-generated data. Lastly, we demonstrate
that above a certain thickness XEOL shows a saturation-like effect, which can
be modelled and corrected for.",2004.01047v1
2020-07-14,Nonlinear mechanisms that regulate the solar cycle amplitude,"The solar magnetic activity cycle has an amplitude that varies within a wide
but limited range of values. This implies that there are nonlinear mechanisms
that prevent runaway solutions. The purpose of this paper is to propose
observable nonlinear mechanisms in the framework of the Babcock-Leighton-type
dynamo. Sunspot emergences show systematic properties that strong cycles tend
to have higher mean latitudes and lower tilt angle coefficients. We use the
surface flux transport model to investigate the effect of these systematic
properties on the expected final total dipolar moment, i.e. cancellation plus
generation of dipole moment by a whole solar cycle. We demonstrate that the
systematic change in latitude has similar nonlinear feedback on the solar cycle
(latitudinal quenching) as tilt does (tilt quenching). Both forms of quenching
lead to the expected final total dipolar moment being enhanced for weak cycles
and being saturated to a nearly constant value for normal and strong cycles.
This explains observed long-term solar cycle variability, e.g., the
Gnevyshev-Ohl rule, which, in turn, justifies the nonlinear mechanisms inherent
in the Babcock-Leighton-type dynamo.",2007.07069v2
2020-07-29,Shape of solar cycles and mid-term solar activity oscillations,"The evolution of the solar activity comprises, apart from the well-known
11-year cycle, various temporal scales ranging from months up to the secondary
cycles known as mid-term oscillations. Its nature deserves a physical
explanation. In this work, we consider the 5-to-6 year oscillations as derived
both from sunspot and from solar magnetic dipole time series. Using the solar
dynamo model, we deduced that these variations may be a manifestation of the
dynamo nonlinearities and non-harmonic shape of the solar activity cycles. We
conclude that the observed mid-term oscillations are related to the nonlinear
saturation of the dynamo processes in the solar interior.",2007.14779v2
2020-08-13,On the mechanism of polarised metrewave stellar emission,"Two coherent radio emission mechanisms operate in stellar coronae: plasma
emission and cyclotron emission. They directly probe the electron density and
magnetic field strength respectively. Most stellar radio detections have been
made at cm-wavelengths where it is often not possible to uniquely identify the
emission mechanism, hindering the utility of radio observations in probing
coronal conditions. In anticipation of stellar observations from a suite of
sensitive low-frequency ($\nu\sim 10^2\,{\rm MHz}$) radio telescopes, here I
apply the general theory of coherent emission in non-relativistic plasma to the
low-frequency case. I consider the recently reported low-frequency emission
from dMe flare stars AD Leo and UV Ceti and the quiescent star GJ 1151 as test
cases. My main conclusion is that unlike the cm-wave regime, for reasonable
turbulence saturation regimes, the emission mechanism in metre-wave
observations ($\nu\sim 10^2\,{\rm MHz}$) can often be identified based on the
observed brightness temperature, emission duration and polarisation fraction. I
arrive at the following heuristic: M-dwarf emission that is $\gtrsim
\,$hour-long with $\gtrsim 50\%$ circular polarised fraction at brightness
temperatures of $\gtrsim 10^{12}\,$K at $\sim 100\,{\rm MHz}$ in canonical
M-dwarfs strongly favours a cyclotron maser interpretation.",2008.05707v1
2020-09-13,Electric field control of disorder-tunable superconductivity and the emergence of quantum metal at an oxide interface,"We report on an extraordinary field effect of the superconducting
LaAlO3/KTaO3(111) interface with Tc ~2 K. By applying a gate voltage (VG)
across KTaO3, the interface can be continuously tuned from superconducting into
insulating states, yielding a dome-shaped Tc-VG dependence. The electric gating
has only a minor effect on carrier density as evidenced in the Hall-effect
measurement, while it changes spatial profile of the carriers in the interface,
hence the carrier's disorder level significantly. As temperature is decreased,
the resistance saturates at lowest temperature in both superconducting and
insulating sides, despite an initial dramatic dropping or increasing, which
suggests an emergence of quantum metallic state associated with failed
superconductor and/or fragile insulator. A VG-modulation of the
magnetic-field-driven superconductor to insulator quantum phase transition
reveals a non-universal criticality.",2009.05896v1
2020-10-19,Gyrokinetic investigation of Alfvén instabilities in the presence of turbulence,"The nonlinear dynamics of beta-induced Alfv\'en Eigenmodes (BAE) driven by
energetic particles (EP) in the presence of ion-temperature-gradient (ITG)
turbulence is investigated, by means of selfconsistent global gyrokinetic
simulations and analytical theory. A tokamak magnetic equilibrium with large
aspect ratio and reversed shear is considered. A previous study of this
configuration has shown that the electron species plays an important role in
determining the nonlinear saturation level of a BAE in the absence of
turbulence [A. Biancalani, et al., J. Plasma Phys. (2020)]. Here, we extend the
study to a turbulent plasma. The EPs are found modify the heat fluxes by
introducing energy at the large spatial scales, mainly at the toroidal mode
number of the dominant BAE and its harmonics. In this regime, BAEs are found to
carry a strong electron heat flux. The feed-back of the global relaxation of
the temperature profiles induced by the BAE, and on the turbulence dynamics, is
also discussed.",2010.09516v1
2020-10-25,Criticality-enhanced quantum sensing in ferromagnetic Bose-Einstein condensates: role of readout measurement and detection noise,"We theoretically investigate estimation of the control parameter in a
ferromagnetic Bose-Einstein condensate near second order quantum phase
transitions. We quantify sensitivity by quantum and classical Fisher
information and using the error-propagation formula. For these different
metrics, we find the same, beyond-standard-quantum-limit (SQL) scaling with
atom number near critical points, and SQL scaling away from critical points. We
find that both depletion of the $m_f=0$ Zeeman sub-level and transverse
magnetization provide signals of sufficient quality to saturate the sensitivity
scaling. To explore the effect of experimental imperfections, we study the
scaling around criticality at nonzero temperature and with nonzero detection
noise. Our results suggest the feasibility of sub-SQL sensing in ferromagnetic
condensates with current experimental capabilities.",2010.13133v1
2020-11-12,Anomalous Hall effect and negative longitudinal magnetoresistance in half-Heusler topological semimetal candidates TbPtBi and HoPtBi,"Half-Heusler compounds have attracted significant attention because of their
topologically non-trivial electronic structure, which leads to unusual electron
transport properties. We thoroughly investigated the magnetotransport
properties of high-quality single crystals of two half-Heusler phases, TbPtBi
and HoPtBi, in pursuit of the characteristic features of topologically
non-trivial electronic states. Both studied compounds are characterized by the
giant values of transverse magnetoresistance with no sign of saturation in
magnetic field up to 14 T. HoPtBi demonstrates the Shubnikov-de Haas effect
with two principal frequencies, indicating a complex Fermi surface; the
extracted values of carrier effective masses are rather small, $0.18\,m_e$ and
$0.27\,m_e$. The investigated compounds exhibit negative longitudinal
magnetoresistance and anomalous Hall effect, which likely arise from a nonzero
Berry curvature. Both compounds show strongly anisotropic magnetoresistance,
that in HoPtBi exhibits a butterfly-like behavior.",2011.06290v1
2020-11-13,Interaction-induced topological superconductivity in antiferromagnet-superconductor junctions,"We predict that junctions between an antiferromagnetic insulator and a
superconductor provide a robust platform to create a one-dimensional
topological superconducting state. Its emergence does not require the presence
of intrinsic spin-orbit coupling nor non-collinear magnetism, but arises solely
from repulsive electronic interactions on interfacial solitonic states. We
demonstrate that a topological superconducting state is generated by repulsive
interactions at arbitrarily small coupling strength, and that the size of the
topological gap rapidly saturates to the one of the parent trivial
superconductor. Our results put forward antiferromagnetic insulators as a new
platform for interaction-driven topological superconductivity.",2011.06990v3
2020-11-27,Experimental Detection of the Correlation Rényi Entropy in the Central Spin Model,"We propose and experimentally measure an entropy that quantifies the volume
of correlations among qubits. The experiment is carried out on a nearly
isolated quantum system composed of a central spin coupled and initially
uncorrelated with 15 other spins. Due to the spin-spin interactions,
information flows from the central spin to the surrounding ones forming
clusters of multi-spin correlations that grow in time. We design a nuclear
magnetic resonance experiment that directly measures the amplitudes of the
multi-spin correlations and use them to compute the evolution of what we call
correlation R\'enyi entropy. This entropy keeps growing even after the
equilibration of the entanglement entropy. We also analyze how the saturation
point and the timescale for the equilibration of the correlation R\'enyi
entropy depend on the system size.",2011.13948v1
2020-12-11,Compositional effect on auto-oscillation behavior of Ni100-xFex/Pt spin Hall nano-oscillators,"We demonstrate the compositional effect on the magnetodynamic and
auto-oscillations properties of Ni100-xFex/Pt (x= 10 to 40) nanoconstriction
based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance
(ST-FMR) performed on microstrips, we measure a significant reduction in both
damping and spin Hall efficiency with increasing Fe content, which lowers the
spin pumping contribution. The strong compositional effect on spin Hall
efficiency is primarily attributed to the increased saturation magnetization in
Fe-rich devices. As a direct consequence, higher current densities are required
to drive spin-wave auto-oscillations at higher microwave frequencies in Fe-rich
nano-constriction devices. Our results establish the critical role of the
compositional effect in engineering the magnetodynamic and auto-oscillation
properties of spin Hall devices for microwav eand magnonic applications.",2012.06121v2
2021-01-11,Magnetotransport in overdoped La$_{2-x}$Sr$_x$CuO$_4$: a Fermi liquid approach,"Recently, several experiments on La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) challenged
the Fermi liquid picture for overdoped cuprates, and stimulated intensive
debates [1]. In this work, we study the magnetotransport phenomena in such
systems based on the Fermi liquid assumption. The Hall coefficient $R_H$ and
magnetoresistivity $\rho_{xx}$ are investigated near the van Hove singularity
$x_{\tiny\text{VHS}}\approx0.2$ across which the Fermi surface topology changes
from hole- to electron-like. Our main findings are: (1) $R_H$ depends on the
magnetic field $B$ and drops from positive to negative values with increasing
$B$ in the doping regime $x_{\tiny\text{VHS}}<x\lesssim0.3$; (2) $\rho_{xx}$
grows up as $B^2$ at small $B$ and saturates at large $B$, while in the
transition regime a ""nearly linear"" behavior shows up. Our results can be
further tested by future magnetotransport experiments in the overdoped LSCO.",2101.03741v1
2021-03-03,Near-Room Temperature Ferromagnetic Insulating State in Highly Distorted LaCoO2.5 with CoO5 Square Pyramids,"Dedicated control of oxygen vacancies is an important route to
functionalizing complex oxide films. It is well-known that tensile strain
significantly lowers the oxygen vacancy formation energy, whereas compressive
strain plays a minor role. Thus, atomically reconstruction by extracting oxygen
from a compressive-strained film is challenging. Here we report an unexpected
LaCoO2.5 phase with a zigzag-like oxygen vacancy ordering through annealing a
compressive-strained LaCoO3 in vacuum. The synergetic tilt and distortion of
CoO5 square pyramids with large La and Co shifts are quantified using scanning
transmission electron microscopy. The large in-plane expansion of CoO5 square
pyramids weaken the crystal-field splitting and facilitated the ordered
high-spin state of Co2+, which produces an insulating ferromagnetic state with
a Curie temperature of ~284 K and a saturation magnetization of ~0.25
{\mu}B/Co. These results demonstrate that extracting targeted oxygen from a
compressive-strained oxide provides an opportunity for creating unexpected
crystal structures and novel functionalities.",2103.02100v1
2021-03-11,Spin Nernst Effect of Antiferromagnetic Magnons in the Presence of Spin Diffusion,"Magnon spin Nernst effect was recently proposed as an intrinsic effect in
antiferromagnets, where spin diffusion and boundary spin transmission have been
ignored. However, diffusion processes are essential to convert a bulk spin
current into boundary spin accumulation, which determines the spin injection
rate into detectors through imperfect transmission. We formulate a diffusive
theory to describe the detection of magnon spin Nernst effect with boundary
conditions reflecting real device geometry. Thanks to the spin diffusion
effect, the output signals in both electronic and optical detection grow
rapidly with an increasing system size in the transverse dimension, which
eventually saturate. Counterintuitively, the measurable signals are even
functions of magnetic field, yielding optical detection more favorable than
electronic detection.",2103.06870v3
2021-04-26,Insensitivity of the complexity rate of change to the conformal anomaly and Lloyd's bound as a possible renormalization condition,"We determine the effect on the computational complexity of a conformal
anomaly using the Complexity=Action prescription of the gauge/gravity
correspondence. To allow the involvement of said anomaly, we extend previous
studies to include arbitrary values for the anisotropic parameter and the
magnetic field respectively on the Mateos-Trancanelli and the D'Hoker-Kraus
holographic models. Our main result is that the rate of change of the
computational complexity is independent of the conformal anomaly in both cases.
In addition, this allows us to also show that, if so desired, the saturation of
Lloyd's bound at infinite time can be used as a renormalization condition.",2104.12796v2
2021-05-14,An energy harvesting technology controlled by ferromagnetic resonance,"We have successfully demonstrated electrical charging using the electromotive
force (EMF) generated in a ferromagnetic metal (FM) film under ferromagnetic
resonance (FMR). In the case of Ni80Fe20 films, electrical charge due to the
EMF generated under FMR can be accumulated in a capacitor; however, the amount
of charge is saturated well below the charging limit of the capacitor.
Meanwhile in the case of Co50Fe50, electrical charge generated under FMR can be
accumulated in a capacitor and the amount of charge increases linearly with the
FMR duration time. The difference between the Ni80Fe20 and Co50Fe50 films is
due to the respective magnetic field ranges for the FMR excitation. When the FM
films were in equivalent thermal states during FMR experiments, Co50Fe50 films
could maintain FMR in a detuned condition, while Ni80Fe20 films were outside
the FMR excitation range. The EMF generation phenomenon in an FM film under FMR
can be used an energy harvesting technology by appropriately controlling the
thermal conditions of the FM film.",2105.06606v1
2021-05-24,A non-perturbative study of bulk photovoltaic effect enhanced by an optically induced phase transition,"Solid systems with strong correlations and interactions under light
illumination have the potential for exhibiting interesting bulk photovoltaic
behavior in the non-perturbative regime, which has remained largely unexplored
in the past theoretical studies. We investigate the bulk photovoltaic response
of a perovskite manganite with strongly coupled electron-spin-lattice dynamics,
using real-time simulations performed with a tight-binding model. The transient
changes in the band structure and the photoinduced phase transitions, emerging
from spin and phonon dynamics, result in a nonlinear current versus intensity
behavior beyond the perturbative limit. The current rises sharply across a
photoinduced magnetic phase transition, which later saturates at higher light
intensities due to excited phonon and spin modes. The predicted peak
photoresponsivity is orders of magnitude higher than other known ferroelectric
oxides such as BiFeO$_3$. We disentangle phonon-and spin-assisted components to
the ballistic photocurrent, showing that they are comparable in magnitude. Our
results illustrate a promising alternative way for controlling and optimizing
the bulk photovoltaic response through the photoinduced phase transitions in
strongly-correlated systems.",2105.11310v1
2021-05-27,Integrable quantum many-body sensors for AC field sensing,"Quantum sensing is inevitably an elegant example of the supremacy of quantum
technologies over their classical counterparts. One of the desired endeavors of
quantum metrology is AC field sensing. Here, by means of analytical and
numerical analysis, we show that integrable many-body systems can be exploited
efficiently for detecting the amplitude of an AC field. Unlike the conventional
strategies in using the ground states in critical many-body probes for
parameter estimation, we only consider partial access to a subsystem. Due to
the periodicity of the dynamics, any local block of the system saturates to a
steady state which allows achieving sensing precision well beyond the classical
limit, almost reaching the Heisenberg bound. We associate the enhanced quantum
precision to closing of the Floquet gap, resembling the features of quantum
sensing in the ground state of critical systems. We show that the proposed
protocol can also be realized in near-term quantum simulators, e.g. ion-traps,
with a limited number of qubits. We show that in such systems a simple block
magnetization measurement and a Bayesian inference estimator can achieve very
high precision AC field sensing.",2105.13507v2
2021-06-16,Self-dual solitons in a Born-Infeld baby Skyrme model,"We show the existence of self-dual (topological) solitons in a gauged version
of the baby Skyrme model in which the Born-Infeld term governs the gauge field
dynamics. The successful implementation of the Bogomol'nyi-Prasad-Sommerfield
formalism provides a lower bound for the energy and the respective self-dual
equations whose solutions are the solitons saturating such a limit. The energy
lower bound (Bogomol'nyi bound) is proportional to the topological charge of
the Skyrme field and therefore quantized. In contrast, the total magnetic flux
is a nonquantized quantity. Furthermore, the model supports three types of
self-dual solitons profiles: the first describes compacton solitons, the second
follows a Gaussian decay law, and the third portrays a power-law decay.
Finally, we perform numerical solutions of the self-dual equations and depicted
the soliton profiles for different values of the parameters controlling the
nonlinearity of the model.",2106.08546v1
2021-08-31,Slowdown of interpenetration of two counterpropagating plasma slab due to collective effects,"The nonlinear evolution of electromagnetic instabilities driven by the
interpenetration of two $e^-\,e^+$ plasma clouds is explored using {\it ab
initio} kinetic plasma simulations. We show that the plasma clouds slow down
due to both oblique and Weibel generated electromagnetic fields, which deflect
the particle trajectories, transferring bulk forward momentum into transverse
momentum and thermal velocity spread. This process causes the flow velocity
$v_{inst}$ to decrease approximately by a factor of $\sqrt{1/3}$ in a time
interval $\Delta t_{\alpha B} \omega_p \sim c/(v_{fl}\sqrt{\alpha_B})$, where
$\alpha_B$ is the magnetic equipartition parameter determined by the non-linear
saturation of the instabilities, $v_{fl}$ is the initial flow speed, and
$\omega_p$ is the plasma frequency. For the $\alpha_B$ measured in our
simulations, $\Delta t_{\alpha B}$ is close to $10 \times$ the instability
growth time. We show that as long as the plasma slab length $L > v_{fl} \Delta
t_{\alpha B}$, the plasma flow is expected to slow down by a factor close to
$1/\sqrt{3}$.",2109.00023v1
2021-09-02,Force Correlations in Disordered Magnets,"We present a proof of principle for the validity of the functional
renormalization group, by measuring the force correlations in Barkhausen-noise
experiments. Our samples are soft ferromagnets in two distinct universality
classes, differing in the range of spin interactions, and the effects of eddy
currents. We show that the force correlations have a universal form predicted
by the functional renormalization group, distinct for short-range and
long-range elasticity, and mostly independent of eddy currents. In all cases
correlations grow linearly at small distances, as in mean-field models, but in
contrast to the latter are bounded at large distances. As a consequence,
avalanches are anti-correlated. We derive bounds for these anti-correlations,
which are saturated in the experiments, showing that the multiple domain walls
in our samples effectively behave as a single wall.",2109.01197v3
2021-10-26,Topological phase transitions in strongly correlated systems: application to Co$_3$Sn$_2$S$_2$,"The topological transition in the strongly correlated half-metallic
ferromagnetic compound Co$_3$Sn$_2$S$_2$ from Weyl semimetal (including chiral
massless fermions) to a non-magnetic state is treated. This transition goes
with a change in topological invariant, and is accompanied by a non-topological
transition from saturated ferromagnetic to paramagnetic state, the minority
Fermi surface being transformed from ghost (hidden) to real. A corresponding
description is given in terms of slave fermion representation for the effective
narrow-band Hubbard model. The system Co$_3$Sn$_2$S$_2$ provides a bright
example of coexistence of non-trivial topology and strong low-dimensional
ferromagnetism. A comparison is performed with other compounds where
frustrations result in formation of a correlated paramagnetic state.",2110.13709v1
2021-11-05,Transverse momentum broadening in real-time lattice simulations of the glasma,"The study of jets in heavy-ion collisions provides important information
about the interaction of partons with the medium that they traverse. The seeds
of jets are highly energetic partons, which are produced from hard scatterings
during the collision event. As such, they are affected by all different stages
of the medium's time evolution, including the glasma, which is the
pre-equilibrium precursor state of the quark-gluon plasma. Here we report on
our numerical lattice simulations of partons traversing the boost-invariant,
non-perturbative glasma as created at the early stages of collisions at RHIC
and LHC. We find that partons quickly accumulate transverse momentum up to the
saturation momentum during the glasma stage. Furthermore, we observe an
interesting anisotropy in transverse momentum broadening of partons with larger
broadening in the rapidity than in the azimuthal direction. Its origin can be
related to correlations among the longitudinal color-electric and
color-magnetic flux tubes in the initial state of the glasma. We compare these
observations to the semi-analytic results obtained by a weak-field
approximation, where we also find such an anisotropy in a parton's transverse
momentum broadening.",2111.03400v1
2021-11-26,Damping of Pseudo-Goldstone Fields,"Approximate symmetries abound in Nature. If these symmetries are also
spontaneously broken, the would-be Goldstone modes acquire a small mass, or
inverse correlation length, and are referred to as pseudo-Goldstones. At
nonzero temperature, the effects of dissipation can be captured by
hydrodynamics at sufficiently long scales compared to the local equilibrium.
Here we show that in the limit of weak explicit breaking, locality of
hydrodynamics implies that the damping of pseudo-Goldstones is completely
determined by their mass and diffusive transport coefficients. We present many
applications: superfluids, QCD in the chiral limit, Wigner crystal and density
wave phases in the presence of an external magnetic field or not, nematic
phases and (anti-)ferromagnets. For electronic density wave phases,
pseudo-Goldstone damping generates a contribution to the resistivity
independent of the strength of disorder, which can have a linear temperature
dependence provided the associated diffusivity saturates a bound. This is
reminiscent of the phenomenology of strange metal high $T_c$ superconductors,
where charge density waves are observed across the phase diagram.",2111.13459v2
2021-12-07,On transverse momentum broadening in real-time lattice simulations of the glasma and in the weak-field limit,"In these proceedings, we report on our numerical lattice simulations of
partons traversing the boost-invariant, non-perturbative glasma as created at
the early stages of collisions at RHIC and LHC. Since these highly energetic
partons are produced from hard scatterings during heavy-ion collisions, they
are already affected by the first stage of the medium's time evolution, the
glasma, which is the pre-equilibrium precursor state of the quark-gluon plasma.
We find that partons quickly accumulate transverse momentum up to the
saturation momentum during the glasma stage. Moreover, we observe an
interesting anisotropy in transverse momentum broadening of partons with larger
broadening in the rapidity than in the azimuthal direction. Its origin can be
related to correlations among the longitudinal color-electric and
color-magnetic flux tubes in the initial state of the glasma. We compare these
observations to the semi-analytic results obtained by a weak-field
approximation, where we also find such an anisotropy in a parton's transverse
momentum broadening.",2112.03883v1
2021-12-30,Digital Rock Typing DRT Algorithm Formulation with Optimal Supervised Semantic Segmentation,"Each grid block in a 3D geological model requires a rock type that represents
all physical and chemical properties of that block. The properties that
classify rock types are lithology, permeability, and capillary pressure.
Scientists and engineers determined these properties using conventional
laboratory measurements, which embedded destructive methods to the sample or
altered some of its properties (i.e., wettability, permeability, and porosity)
because the measurements process includes sample crushing, fluid flow, or fluid
saturation. Lately, Digital Rock Physics (DRT) has emerged to quantify these
properties from micro-Computerized Tomography (uCT) and Magnetic Resonance
Imaging (MRI) images. However, the literature did not attempt rock typing in a
wholly digital context. We propose performing Digital Rock Typing (DRT) by: (1)
integrating the latest DRP advances in a novel process that honors digital rock
properties determination, while; (2) digitalizing the latest rock typing
approaches in carbonate, and (3) introducing a novel carbonate rock typing
process that utilizes computer vision capabilities to provide more insight
about the heterogeneous carbonate rock texture.",2112.15068v2
2022-01-21,"Anomalous metals: from ""failed superconductor"" to ""failed insulator""","Resistivity saturation is found on both superconducting and insulating sides
of an ""avoided"" magnetic-field-tuned superconductor-to-insulator transition
(H-SIT) in a two-dimensional In/InO$_x$ composite, where the anomalous metallic
behaviors cut off conductivity or resistivity divergence in the
zero-temperature limit. The granular morphology of the material implies a
system of Josephson junctions (JJ) with a broad distribution of Josephson
coupling E$_J$ and charging energy E$_C$ , with a H-SIT determined by the
competition between E$_J$ and E$_C$ . By virtue of self-duality across the true
H-SIT, we invoke macroscopic quantum tunneling effects to explain the
temperature-independent resistance where the ""failed superconductor"" side is a
consequence of phase fluctuations and the ""failed insulator"" side results from
charge fluctuations. While true self-duality is lost in the avoided transition,
its vestiges are argued to persist, owing to the incipient duality of the
percolative nature of the dissipative path in the underlying random JJ system.",2201.08801v1
2022-01-23,Differential configurational complexity and phase transitions of the BPS solutions in the O(3)-sigma model,"Using a spherically symmetric ansatz, we show that the Chern-Simons
O(3)-sigma model with a logarithmic potential admits topological solutions.
This result is quite interesting since the Gausson-type logarithmic potential
only predicted topological solutions in $(1+1)$D models. To accomplish our
goal, the Bogomol'nyi-Prasad-Sommerfield (BPS) method is used, to saturate the
energy and obtain the BPS equations. Next, we show by the numerical method is
the graphical results of the topological fields, as well as, the magnetic field
behavior that generates a flux given by $\Phi_{flux}=-\mathcal{Q}/\kappa$ and
the energy density of the structures of vortices. On the other hand, we
evaluate the measure of the differential configurational complexity (DCC) of
the topological structures, by considering the energy density of the vortex.
This analysis is important because it will provide us with information about
the possible phase transitions associated with the localized structures and it
shows that our model only supports the one-phase transition.",2201.09303v2
2022-01-26,Nonlinear magnon polaritons,"We experimentally and theoretically demonstrate that nonlinear spin-wave
interactions suppress the hybrid magnon-photon quasiparticle or ""magnon
polariton"" in microwave spectra of an yttrium iron garnet film detected by an
on-chip split-ring resonator. We observe a strong coupling between the Kittel
and microwave cavity modes in terms of an avoided crossing as a function of
magnetic fields at low microwave input powers, but a complete closing of the
gap at high powers. The experimental results are well explained by a
theoretical model including the three-magnon decay of the Kittel magnon into
spin waves. The gap closure originates from the saturation of the ferromagnetic
resonance above the Suhl instability threshold by a coherent back reaction from
the spin waves.",2201.10889v2
2022-02-07,Wall Ion Loss Reduction by Acceleration Zone Shifting in Anode-Layer Hall Thruster,"In this study, wall ion loss and erosion rate are evaluated in the RAIJIN
thruster. The novelty of this work is the detailed analysis of measured
guard-ring (metallic channel wall) current, which enables a fast evaluation of
the wall ion loss and erosion rate. The current-voltage characteristics of the
guard-ring current indicate that the sheath on the guard rings is in the ion
saturation regime and that the guard-ring current can be used as a wall ion
flux indicator. The experimental results demonstrate that the wall ion loss can
be significantly reduced in the magnetic configuration of RAIJIN thrusters with
the acceleration zone shifting.",2202.02921v1
2022-03-08,Interplay between nonlinear spectral shift and nonlinear damping of spin waves in ultrathin YIG waveguides,"We use the phase-resolved imaging to directly study the nonlinear
modification of the wavelength of spin waves propagating in 100-nm thick,
in-plane magnetized YIG waveguides. We show that, by using moderate microwave
powers, one can realize spin waves with large amplitudes corresponding to
precession angles in excess of 10 degrees and nonlinear wavelength variation of
up to 18 percent in this system. We also find that, at large precession angles,
the propagation of spin waves is strongly affected by the onset of nonlinear
damping, which results in a strong spatial dependence of the wavelength. This
effect leads to a spatially dependent controllability of the wavelength by the
microwave power. Furthermore, it leads to the saturation of nonlinear spectral
shift's effects several micrometers away from the excitation point. These
findings are important for the development of nonlinear, integrated spin-wave
signal processing devices and can be used to optimize their characteristics.",2203.04018v1
2022-03-17,Multiparameter quantum metrology in the Heisenberg Limit regime: many repetition scenario vs. full optimization,"We discuss the Heisenberg limit in the multiparameter metrology within two
different paradigms -- the one, where the measurement is repeated many times
(so the Cram\'er-Rao bound is guaranteed to be asymptotically saturable) and
the second one, where all the resources are allocated into one experimental
realization (analyzed with the mimimax approach). We investigate the potential
advantage of measuring all the parameter simultaneously compared to estimating
them individually, while spending the same total amount of resources. We show
that in general the existence of such an advantage, its magnitude and
conditions under which it occurs depends on which of the two paradigms has been
chosen. In particular, for the problem of magnetic field sensing using $N$
entangled spin-$1/2$, we show that the predictions based purely on the
Cram\'er-Rao formalism may be overly pessimistic in this matter -- the minimax
approach reveals the superiority of measuring all the parameters jointly
whereas the Cram\'er-Rao approach indicates lack of such an advantage.",2203.09541v3
2022-04-06,Critical quantum thermometry and its feasibility in spin systems,"In this work, we study temperature sensing with finite-sized strongly
correlated systems exhibiting quantum phase transitions. We use the quantum
Fisher information (QFI) approach to quantify the sensitivity in the
temperature estimation, and apply a finite-size scaling framework to link this
sensitivity to critical exponents of the system around critical points. We
numerically calculate the QFI around the critical points for two
experimentally-realizable systems: the spin-1 Bose-Einstein condensate and the
spin-chain Heisenberg XX model in the presence of an external magnetic field.
Our results confirm finite-size scaling properties of the QFI. Furthermore, we
discuss experimentally-accessible observables that (nearly) saturate the QFI at
the critical points for these two systems.",2204.02734v2
2022-04-13,Core localized alpha-channeling via low frequency Alfven mode generation in reversed shear scenarios,"A novel channel for fuel ions heating in tokamak core plasma is proposed and
analyzed using nonlinear gyrokinetic theory. The channel is achieved via
spontaneous decay of reversed shear Alfven eigenmode (RSAE) into low frequency
Alfven modes (LFAM), which then heat fuel ions via collisionless ion Landau
damping. The conditions for RSAE spontaneous decay are investigated, and the
saturation level and the consequent fuel ion heating rate are also derived. The
channel is expected to be crucial for future reactors operating under reversed
shear configurations, where fusion alpha particles are generated in the tokamak
core where the magnetic shear is typically reversed, and there is a dense RSAE
spectrum due to the small alpha particle characteristic dimensionless orbits.",2204.06169v1
2022-07-01,Pulse Frequency Fluctuations of Persistent Accretion Powered Pulsars,"In this study, we examine the long term torque noise fluctuations of
persistent Xray binaries Her X-1, Vela X-1, GX 301-2, CEN X-3, 4U 1538-53, OAO
1657-415 and 4U 1626-67 using the historical pulse frequency measurements
provided by CGRO/BATSE and Fermi/GBM. We find that known disk-fed sources
exhibit $1/\omega^{2}$ red noise component in their power density spectra which
is saturated over long timescales. On the other hand, wind-fed sources form a
clear white noise component and the wind-fed sources with occasional transient
disk formation imprint $1/\omega$ type flicker noise. We discuss their
long-term timing noise properties based on the models to describe the power
density spectrum of pulse frequency derivative fluctuations in terms of
monochromatic and colored noise processes. Furthermore, we investigate the
relation between measured timing noise strengths and other independently
measured physical parameters. Despite the low number of sample sources, we
suggest that noise strengths of these sources are correlated with their
luminosities and uncorrelated with their magnetic fields strengths, implying
that the dominant noise generating mechanism is accretion",2207.00248v2
2022-08-19,Triggering of tearing instability by impurity radiation through resistive interchange reversal in a tokamak,"Recent MHD simulations find that the reversal of the local resistive
interchange parameter $D_R$ from negative to positive due to impurity radiation
cooling is able to trigger the resistive tearing mode growth in a tokamak above
a threshold in impurity level. A layer of perturbed Pfirsch-Schl\""{u}ter
current density and resistivity are also induced by the impurity radiation,
which further govern the tearing mode growth and saturation in the nonlinear
stage. The impurity threshold and the tearing mode growth strongly depend on
the parallel thermal conductivity, and such a dependence derives from the
impact on $D_R$ of the fast parallel thermal equilibration along the helical
magnetic field lines.",2208.09161v1
2022-09-08,Dominance of Electron-Magnon Scattering in Itinerant Ferromagnet Fe3GeTe2,"Fe3GeTe2 is a 2-dimensional van der Waals material exhibiting itinerant
ferromagnetism upto 230 K. Here, we study aspects of scattering mechanism in
Fe3Ge2Te2 single crystals via resistivity, magneto-transport and Hall effect
measurements. The quadratic temperature dependence of electrical resistivity
below the Curie temperature hints towards the dominance of electron-magnon
scattering. A non-saturating positive magnetoresistance (MR) is observed at low
temperatures when the magnetic field is applied parallel to the sample plane.
The linear negative MR at high fields for T < TC corroborates to the
suppression in magnon population due to the damping of spin waves. In the high
temperature regime T > TC,MR can be described by the scattering from spin
fluctuations using the model described by Khosla and Fischer. Isothermal Hall
resistivity curves unveil the presence of anomalous Hall resistivity.
Correlation between MR and side jump mechanism further reveals that the
electron-magnon scattering is responsible for the side jump contribution to the
anomalous Hall effect. Our results provide a clear understanding of the role of
electron-magnon scattering on anomalous Hall effect that rules out its origin
to be the topological band structure.",2209.03555v1
2022-09-13,Self-dual compact gauged baby skyrmions in a continuous medium,"We investigate the existence of self-dual configurations in the restricted
gauged baby Skyrme model enlarged with a $Z_2$--symmetry, which introduces a
real scalar field. For such a purpose, we implement the Bogomol'nyi procedure
that provides a lower bound for the energy and the respective self-dual
equations whose solutions saturate such a bound. Aiming to solve the self-dual
equations, we specifically focused on a class of topological structures called
compacton. We obtain the corresponding numerical solutions within two distinct
scenarios, each defined by a scalar field, allowing us to describe different
magnetic media. Finally, we analyze how the compacton profiles change when
immersed in each medium.",2209.06309v2
2022-10-24,Amorphous and polycrystalline routes towards a chiral spin liquid,"We show that a chiral spin liquid spontaneously emerges in partially
amorphous, polycrystalline, or ion-irradiated Kitaev materials. In these
systems, time-reversal symmetry is broken spontaneously due to a non-zero
density of plaquettes with an odd number of edges, $n_{odd}$. This mechanism
opens a sizeable gap, at small $n_{odd}$ compatible with that of typical
amorphous materials and polycrystals, and which can alternatively be induced by
ion-irradiation. We find that the gap is proportional to $n_{odd}$, saturating
at $n_{odd}\sim 40\%$. Using exact diagonalization, we find that the chiral
spin liquid is approximately as stable to Heisenberg interactions as Kitaev's
honeycomb spin liquid model. Our results open up a significant number of
non-crystalline systems where chiral spin liquids can emerge without external
magnetic fields.",2210.13548v2
2022-12-22,Magnetoelasticity-driven phase inversion of ultrafast spin precession in NixFe100-x thin films,"We present strong evidences for the deterministic role of magnetoelasticity
in ultrafast spin dynamics of ferromagnetic NixFe100-x alloy films. Without a
change in the crystal structure, we observed sudden Pi-phase inversion of the
spin precession in the range of x = 87.0 - 97.5. In addition, it was found that
the phase was continuously changed and reversed its sign by varying the pump
fluence. These cannot be explained simply by temperature dependence of
magnetocrystalline, demagnetizing, and Zeeman fields which have been
conventionally considered so far in describing the spin dynamics. Through the
temperature- and composition-dependent simulations adding the magnetoelastic
field generated from the lattice thermal strain, we revealed that the
conventional and magnetoelastic fields were competing around x = 95.3, where
the spin dynamics showed the largest phase shift. For analytic understanding,
we further show that the temperature-dependent interplay of the Curie
temperature, saturation magnetization, and magnetostriction, which are
demonstrated to be the most important macroscopic parameters, determines the
ultrafast spin dynamics. Our extensive study emphasizes that magnetoelasticity
is the key ingredient for fully understanding the driving mechanism of
ultrafast spin dynamics.",2212.11852v1
2022-12-25,Quantum Geometric Oscillations in Two-Dimensional Flat-Band Solids,"Two-dimensional van der Waals heterostructures can be engineered into
artificial superlattices that host flat bands with significant Berry curvature
and provide a favorable environment for the emergence of novel electron
dynamics. In particular, the Berry curvature can induce an oscillating
trajectory of an electron wave packet transverse to an applied static electric
field. Though analogous to Bloch oscillations, this novel oscillatory behavior
is driven entirely by quantum geometry in momentum space instead of band
dispersion. While the orbits of Bloch oscillations can be localized by
increasing field strength, the size of the geometric orbits saturates to a
nonzero plateau in the strong-field limit. In non-magnetic materials, the
geometric oscillations are even under inversion of the applied field, whereas
the Bloch oscillations are odd, a property that can be used to distinguish
these two co-existing effects.",2212.12852v2
2023-01-24,Validation and traceability of miniaturized multi-parameter cluster of radiosondes used for atmospheric observations,"In this work we designed and developed a cluster of light expendable
radiosondes that can float passively inside warm clouds to study their
micro-physical processes. This involves the tracking of both saturated and
unsaturated turbulent air parcels. The aim of this new kind of observation
system is to obtain Lagrangian statistics of the intense turbulence inside warm
clouds and of the lower intensity turbulence that is typical of the air
surrounding such clouds. Each radiosonde in a cluster includes an electronic
board, which is mounted onto a small, biodegradable balloon filled with a
mixture of helium and air. The cluster is able to float inside clouds for a few
hours and to measure air temperature, pressure, humidity and the associated
position, velocity, acceleration and magnetic field readings of each radiosonde
along their trajectory.",2301.09928v3
2023-02-06,The out-of-plane magnetoresistance in a Van der Waals thin film of WTe2,"We report the magneto-transport measurements of thin film devices of the
topological Weyl semimetal WTe2 with the applied current along and vertical to
the in-plane directions. The device is composed of a Van der Waals thin film of
WTe2 sandwiched between top and bottom Au electrodes.At low temperatures, we
found a large unsaturated in-plane magnetoresistance and a saturated
out-of-plane magnetoresistance when the external magnetic fields are applied
perpendicular to the plane. By analysis of Shubnikov-de Haas oscillations, one
oscillation peak is found in the out-of-plane magnetoresistance, in contrast to
four oscillation peaks in the in-plane magnetoresistance.Our work provides new
insight into the origin of the unsaturated magnetoresistance in WTe2 and may
inspire non-planar engineering to reach higher integration in spintronics.",2302.02645v1
2023-03-15,Rare observation of spin-gapless semiconducting characteristics and related band topology of quaternary Heusler alloy CoFeMnSn,"In this paper, we report the theoretical investigation and experimental
realization of a new spin-gapless semiconductor (SGSs) compound CoFeMnSn
belonging to the family of quaternary Heusler alloys. Through the use of
several ground-state energy calculations, the most stable structure has been
identified. Calculations of the spin-polarized band structure in optimized
structure's reveals the SGS nature of the compound. The compound form in an
ordered crystal structure and exhibit a high ferromagnetic transition
temperature (T$_{\rm C}$ = 560 K), making the material excellent for room
temperature applications. Adherence of saturation magnetization to the
Slater-Pauling rule, together with the nearly temperature-independent
resistivity, conductivity, and carrier concentration of the compound in the
temperature regime 5$-$300 K along with the low value of anomalous Hall
conductivity (AHC) further confirms the SGS nature. Theoretical calculations
also reveal the robustness of the SGS state due to lattice contraction and one
can obtain a high value of intrinsic AHC using hole doping. Combined SGS and
topological properties of the compound make CoFeMnSn suitable for spintronics
and magneto-electronics devices.",2303.08589v2
2023-04-28,A numerical study of bounds in the correlations of fractional quantum Hall states,"We numerically compute the guiding center static structure factor $\bar S(\bf
k)$ of various fractional quantum Hall (FQH) states to
$\mathcal{O}\left((k\ell)^6\right)$ where $k$ is the wavenumber and $\ell$ is
the magnetic length. Employing density matrix renormalization group on an
infinite cylinder of circumference $L_y$, we study the two-dimensional limit
using $L_y/\xi \gg 1$, where $\xi$ is the correlation length. The main findings
of our work are: 1) the ground states that deviate away from the ideal
conformal block wavefunctions, do not saturate the Haldane bound, and 2) the
coefficient of $O\left((k\ell)^6\right)$ term appears to be bounded above by a
value predicted by field theories proposed in the literature. The first finding
implies that the graviton mode is not maximally chiral for experimentally
relevant FQH states.",2304.14991v4
2023-06-25,Photon echo and fractional excitation lensing of $S=1/2$ XY spin chain,"We study numerically the two-dimensional coherent spectrum (2DCS) of the
Tomonaga-Luttinger liquid hosted by the $S=1/2$ XY spin chain. The 2DCS
characterizes the system's third order nonlinear magnetic response triggered by
three pulses, separated successively by the delay time and the waiting time. It
exhibits a photon echo signal resulting from a lensing process of the
fractional excitations: A pair of photon-excited fractional excitations,
initially moving apart, reverse their direction of motion, and annihilate each
other. In the XY chain, the nonlinearity in the dispersion relation of the
Jordan-Wigner fermions leads to the dispersion of the fractional excitation
wave packets and thereby suppresses lensing. The magnitude of the echo signal
decreases exponentially with increasing delay time. The decay rate scales with
the temperature $T$ as $T^n$ at low temperature, where $n$ is the leading order
of the Jordan-Wigner fermion dispersion, and as $T$ at high temperature. By
contrast, as the waiting time increases, the magnitude of the echo signal
saturates, reflecting the integrability of the system. Our results illustrate
the effectiveness of the 2DCS in detecting subtle dynamical properties of
optical excitations in spin chains.",2306.14220v1
2023-07-08,Superconducting Gap Structure of Filled Skutterudite LaOs$_4$As$_{12}$ Compound through $μ$SR Investigations,"Filled skutterudite compounds have gained attention recently as an innovative
platforms for studying intriguing low-temperature superconducting properties.
Regarding the symmetry of the superconducting gap, contradicting findings from
several experiments have been made for LaRu$_{4}$As$_{12}$ and its
isoelectronic counterpart, LaOs$_{4}$As$_{12}$. In this vein, we report
comprehensive bulk and microscopic results on LaOs$_{4}$As$_{12}$ utilizing
specific heat analysis and muon-spin rotation/relaxation ($\mu$SR)
measurements. Bulk superconductivity with $T_C$ = 3.2 K was confirmed by heat
capacity. The superconducting ground state of the filled-skutterudite
LaOs$_{4}$As$_{12}$ compound is found to have two key characteristics:
superfluid density exhibits saturation type behavior at low temperature, which
points to a fully gapped superconductivity with gap value of $2\Delta/k_BT_C$ =
3.26; additionally, the superconducting state does not show any sign of
spontaneous magnetic field, supporting the preservation of time-reversal
symmetry. These results open the door for the development of La-based
skutterudites as special probes for examining the interplay of single- and
multiband superconductivity in classical electron-phonon systems.",2307.03946v1
2023-07-10,Core localized alpha-channeling via low frequency Alfven mode generation in reversed shear scenarios,"A novel channel for fuel ions heating in tokamak core plasma is proposed and
analyzed using nonlinear gyrokinetic theory. The channel is achieved via
spontaneous decay of reversed shear Alfv\'en eigenmode (RSAE) into low
frequency Alfv\'en modes (LFAM), which then heat fuel ions via collisionless
ion Landau damping. The conditions for RSAE spontaneous decay are investigated,
and the saturation level and the consequent fuel ion heating rate are also
derived. The channel is expected to be crucial for future reactors operating
under reversed shear configurations, where fusion alpha particles are generated
in the tokamak core where the magnetic shear is typically reversed, and there
is a dense RSAE spectrum due to the small alpha particle characteristic
dimensionless orbits.",2307.04388v1
2023-07-21,Evidence for Pseudogap Phase in Cerium Superhydrides: CeH$_{10}$ and CeH$_9$,"Polyhydride superconductors have been shown to possess metallic properties
with a Bardeen-Cooper-Schrieffer-type superconducting ground state. Here, we
provide evidence for unconventional transport associated with a pseudogap phase
in cubic cerium superhydride CeH$_{10}$ ($\textit{T}$$_C$ = 116 K) at pressure
of 115-125 GPa. A large negative magnetoresistance in the non-superconducting
state below 90 K, quasi $\textit{T}$-linear electrical resistance, and a
sign-change of its temperature dependence mark the emergence of this phase. We
studied the magnetic phase diagrams and the upper critical fields
$\textit{B}$$_{C2}$(T) of CeH$_{10}$, CeH$_9$, and CeD$_9$ in pulsed fields up
to 70 T. $\textit{B}$$_{C2}$(T) of CeH$_9$ and CeD$_9$ exhibits pronounced
saturation at low temperatures in accordance with the
Werthamer-Helfand-Hohenberg model, whereas CeH$_{10}$ stands out in particular,
as it does not obey this model. Our observations, therefore, reveal the
unconventional nature of non-superconducting state of cerium superhydride
CeH$_{10}$.",2307.11742v2
2023-08-21,Proximity-induced sequence of field transitions in Kitaev candidate BaCo$_2$(AsO$_4$)$_2$,"We study field-induced phase transitions of the minimal exchange model
proposed earlier for BaCo$_2$(AsO$_4$)$_2$, a candidate for Kitaev honeycomb
model, using numerical minimization of classical spin clusters. We show that
experimentally observed sequence of step-like transitions in magnetic field is
realized in the phase diagram of the minimal model. Surprisingly, intermediate
up-up-down plateau phase is stabilized only in the proximity of a
double-zigzag$-$zigzag phase boundary. We systematically map out the region of
stability of experimentally observed cascade of transitions and argue that
BaCo$_2$(AsO$_4$)$_2$ exchange parameters are close to a region of strong phase
competition, which can explain suppressed saturation field.",2308.10672v2
2023-08-30,Impact of epitaxial strain relaxation on ferromagnetism in a freestanding La2/3Sr1/3MnO3 membrane,"Manganite perovskites host emerging physical properties of
strongly-correlated electrons with charge, spin, and lattice degrees of
freedom. Using epitaxial lift-off technique, we report enhancement of
saturation magnetization and ferromagnetic transition temperature of the
freestanding La2/3Sr1/3MnO3 membrane compared with the as-grown film on SrTiO3
substrate involving lateral tensile strain. Structural analysis reveals
shrinkage of unit-cell volume by tensile strain relaxation in the freestanding
membrane, which causes enhancement of the ferromagnetic interaction. The impact
of the microscopic lattice deformation on the ferromagnetism of La2/3Sr1/3MnO3
indicates a high potential of this material for flexible electronics
application with intriguing functionalities in strongly-correlated electron
systems.",2308.16045v1
2023-09-05,Post disruption reconnection event driven by a runaway current,"The role of a runaway current in a post disruption plasma is investigated
through numerical simulations in an asymmetric magnetic reconnection event.
While the runaways do not alter the linear growth of the island, they lead to a
rotation of the island in the poloidal direction as found in [C. Liu et al.
Physics of Plasmas 27, 092507 (2020)]. The role of a microlayer smaller than
the resistive one is thoroughly investigated. While the resistive layer
controls the transition of the island from the linear to the nonlinear stage,
the microlayer width causes the runaways to become nonlinear as soon as the
size of the island exceeds it. Moreover, this transition of the runways
electrons to the nonlinear phase is accompanied by a drastic redistribution of
runaways within the island with respect to the symmetric case. The influence of
the electron skin depth on the linear evolution is also taken into account.
Finally, nonlinear simulations show that the rotation frequency tends toward
zero when the island saturates.",2309.02549v1
2023-10-09,Estimation theory of photon-magnon coupling strength in a driven-dissipative double-cavity-magnon system,"Cavity-magnon systems are emerging as a fruitful architecture for the
integration of quantum technologies and spintronic technologies, where magnons
are coupled to microwave photons via the magnetic-dipole interaction.
Controllable the photon-magnon (P-M) couplings provide a powerful means of
accessing and manipulating quantum states in such hybrid systems. Thus
determining the relevant P-M couplings is a fundamental task. Here we address
the quantum estimation problem for the P-M coupling strength in a
double-cavity-magnon system with drive and dissipation. The effects of various
physical factors on the estimation precision are investigated and the
underlying physical mechanisms are discussed in detail. Considering that in
practical experiments it is almost infeasible to perform measurements on the
global quantum state of this composite system, we identify the optimal
subsystem for performing measurements and estimations. Further, we evaluate the
performance of different Gaussian measurements, indicating that optimal
Gaussian measurement almost saturates the ultimate theoretical bound on the
estimation precision given by the quantum Fisher information.",2310.05412v1
2023-10-19,Quantum Octets in Air Stable High Mobility Two-Dimensional PdSe2,"Two-dimensional (2D) materials have drawn immense interest in scientific and
technological communities, owing to their extraordinary properties that are
profoundly altered from their bulk counterparts and their enriched tunability
by gating, proximity, strain, and external fields. For digital applications, an
ideal 2D material would have high mobility, air stability, sizable band gap,
and be compatible with large-scale synthesis. Here we demonstrate air-stable
field-effect transistors using atomically thin few-layer PdSe2 sheets that are
sandwiched between hexagonal BN (hBN), with record high saturation current
>350{\mu}A/{\mu}m, and field effect mobilities 700 and 10,000 cm2/Vs at 300K
and 2K, respectively. At low temperatures, magnetotransport studies reveal
unique octets in quantum oscillations, arising from 2-fold spin and 4-fold
valley degeneracies, which can be broken by in-plane and out-of-plane magnetic
fields toward quantum Hall spin and orbital ferromagnetism.",2310.13154v1
2024-01-03,Light thermal dark matter via type-I seesaw portal,"We propose a minimal scenario for light thermal dark matter (DM) in sub-GeV
to GeV ballpark by incorporating a scalar singlet DM in a type-I seesaw
scenario extended by an additional Higgs doublet $\phi_2$. The latter permits
efficient annihilation of light scalar DM into leptonic final states including
right-handed neutrinos (RHN). While DM annihilation into charged lepton final
states is kept either suppressed or in a kinematically forbidden ballpark to
avoid cosmic microwave background (CMB) bounds, the RHN, active neutrino final
states remain safe from such bounds even if they are allowed kinematically. We
discuss the interplay of forbidden and non-forbidden channels in generating
light thermal DM relic while incorporating constraints from cosmology as well
as laboratory experiments. The model can also explain the anomalous magnetic
moment of muon, W-mass anomaly and saturate experimental bounds on charged
lepton flavour violation and DM direct detection while offering tantalising
detection prospects of the lightest RHN, the mass of which is kept in the same
ballpark as DM.",2401.01639v1
2024-01-05,Resonant Decay of Kinetic Alfvén Waves and Implication on Spectral Cascading,"A general equation describing the resonant nonlinear mode-coupling among
kinetic Alfv\'en waves (KAWs) is derived using nonlinear gyrokinetic theory,
which can be applied to study the potentially strong spectral energy transfer
of KAWs. As a first application, the parametric decay of a pump KAW into two
sideband KAWs are studied, with particular emphasis on the cascading in
perpendicular wavenumber. It is found that, for the ""co-propagating"" cases with
all three KAWs propagating in the same direction along the equilibrium magnetic
field line, it exhibits a dual cascading character in the perpendicular
wavenumber space; while for the ""counter-propagating"" cases with one sideband
propagating in the opposite direction with respect to the pump wave, it
instead, can exhibit both dual and inverse cascading behaviors. The
implications on SAW instability nonlinear saturation and charged particle
transport in fusion plasmas is also discussed.",2401.02711v1
2024-01-20,A review on the Vortex and Coherent Structures in Dusty Plasma Medium,"Dusty plasma which is nothing but an admixture of electrons, ions and massive
charged solid particles of sub-micron to micron sized in the background of
neutrals. The dust grain medium exhibits fluid as well as solid-like
characteristics depending on the background medium conditions. It supports
various self-sustained non-linear dynamical structures as a result of the
saturation of instabilities. The vortical or vortex structure in the dusty
plasma medium is one of self-sustained dynamical structures that are formed
either by internal instabilities or external perturbation. In this review
report, the author discusses the theoretical, experimental, and computational
research works on vortical and coherent structures in unmagnetized as well as
in magnetized dusty plasma. The sources of vortex formation such as obstacle,
ion drag shear, dust charge gradient, RT and K-H instabilities are pointed out
in detail. The studies on the evolution of vortices by researchers are also
discussed.",2401.11209v1
2024-02-12,Experimental roadmap for optimal state transfer and entanglement generation in power-law systems,"Experimental systems with power-law interactions have recently garnered
interest as promising platforms for quantum information processing. Such
systems are capable of spreading entanglement superballistically and achieving
an asymptotic speed-up over locally interacting systems. Recently, protocols
developed by Eldredge et al. [Phys. Rev. Lett. 119, 170503 (2017)] and Tran et
al. [Phys. Rev. X 11, 031016 (2021)] for the task of transferring a quantum
state between distant particles quickly were shown to be optimal and saturate
theoretical bounds. However, the implementation of these protocols in physical
systems with long-range interactions remains to be fully realized. In this
work, we provide an experimental roadmap towards realizing fast state-transfer
protocols in three classes of atomic and molecular systems with dipolar
interactions: polar molecules composed of alkali-metal dimers, neutral atoms in
excited Rydberg states, and atoms with strong magnetic moments (e.g.
dysprosium). As a guide to near-term experimental implementation, we
numerically evaluate the tradeoffs between the two protocols for small system
sizes and develop methods to address potential crosstalk errors that may arise
during the execution of the protocols.",2402.07974v1
2024-03-28,Infrared Vertical External Cavity Surface Emitting Laser Threshold Magnetometer,"Nitrogen-vacancy (NV) centers have considerable promise as high sensitivity
magnetometers, however are commonly limited by inefficient collection and low
contrasts. Laser threshold magnetometry (LTM) enables efficient collection and
high contrasts, providing a path towards higher sensitivity magnetometry. We
demonstrate an infrared LTM using an ensemble of NV centers in a single crystal
diamond plate integrated into a vertical external cavity surface emitting
laser. The laser was tuned to the spin dependent absorption line of the NV
centers, allowing for optical readout by monitoring the laser output power. We
demonstrate a magnetic sensitivity of 7.5~nT/$\sqrt{\textit{Hz}}$ in the
frequency range between 10 and 50 Hz. Furthermore, the contrast and the
projected PSNL sensitivity are shown to improve significantly by operating
close to the lasing threshold, achieving 18.4\% and
26.6~pT/$\sqrt{\textit{Hz}}$ near threshold. What's more, an unexpected
saturable absorption phenomenon was observed near threshold, which enhanced the
contrast and projected PSNL sensitivity.",2403.19751v1
2024-04-02,Robustness of high-$β$ W7-X plasmas against ideal ballooning instability,"To examine the robustness of the designed 5% $\beta$-limit for
high-performance operation in the W7-X stellarator, we undertake nonlinear
magnetohydrodynamic (MHD) simulations of pressure-driven instabilities using
the M3D-$C^1$ code. Consistent with linear analyses, ideal ballooning
instabilities occur as $\beta$ exceeds 5% in the standard configuration.
Nonetheless, the modes saturate nonlinearly at relatively low levels without
triggering large-scale crashes, even though confinement degradation worsens as
$\beta$ increases. In contrast, in an alternative configuration with nearly
zero magnetic shear, ideal interchange modes induce a pressure crash at $\beta=
1\%$. These results suggest that the standard W7-X configuration might have a
soft $\beta$-limit that is fairly immune to major MHD events, and that
interchange instabilities tend to be more detrimental than ideal ballooning in
stellarators.",2404.01966v1
2001-06-20,Saturation of electrical resistivity in metals at large temperatures,"We present a microscopic model for systems showing resistivity saturation. An
essentially exact quantum Monte-Carlo calculation demonstrates that the model
describes saturation. We give a simple explanation for saturation, using charge
conservation and considering the limit where thermally excited phonons have
destroyed the periodicity. Crucial model features are phonons coupling to the
hopping matrix elements and a unit cell with several atoms. We demonstrate the
difference to a model of alkali-doped C60 with coupling to the level positions,
for which there is no saturation.",0106397v2
2005-10-15,Observation of Interband Two-Photon Absorption Saturation in CdS Nanocrystals,"We report the observation of interband two-photon absorption (TPA) saturation
in cadmium sulfide nanocrystals (CdS NCs) under intense femtosecond laser
excitation with 1.6-eV photon energy. The observation has been compared to
interband TPA saturation in bulk CdS under the same experimental conditions. By
using both Z-scan technique and transient absorption measurement, the
saturation intensity has been determined to be 190 GW/cm^2 for CdS NCs of 4-nm
diameter, which shows two orders of magnitude greater than that for CdS bulk
crystal. The results are in agreement with an inhomogeneously-broadened,
saturated TPA model.",0510402v1
2002-12-23,Strangeness Saturation: Energy- and System-Size Dependence,"Relativistic heavy-ion collisions lead to a final state which has a higher
degree of strangeness saturation than those of elementary collisions. A
systematic analysis of this phenomenon, based on the strangeness saturation
factor, is made for C+C, Si+Si and Pb+Pb collisions at the CERN SPS collider
and for Au+Au collisions at RHIC energies. Strangeness saturation is shown to
increase with the number of participants within a colliding system, at both
CERN SPS and RHIC energies. The saturation observed in central collisions of
lighter nuclei deviates from that seen in peripheral collisions of heavier
nuclei with an equivalent participant number, which could be due to the
difference in nuclear density.",0212335v1
2003-08-31,Contributions of gluon recombination to saturation phenomena,"Parton distributions in the small $x$ region are numerically predicted by
using a modified DGLAP equation with the GRV-like input distributions. We find
that gluon recombination at twist-4 level obviously suppresses the rapid growth
of parton densities with $x$ decrease. We show that before the saturation scale
$Q^2_s$ is reached, saturation and partial saturation appear in the small $x$
behavior of parton distributions in nucleus and free proton, respectively. The
antishadowing contributions to the saturation phenomena are also discussed.",0309003v1
2003-12-18,Saturation at Hadron Colliders,"We extend the saturation models a la Golec-Biernat and Wusthoff to
cross-sections of hard processes initiated by virtual-gluon probes separated by
large rapidity intervals at hadron colliders. We derive their analytic
expressions and apply them to physical examples, such as saturation effects for
Mueller-Navelet forward jets. By comparison to gamma*-gamma* cross-sections we
find a more abrupt transition to saturation. We propose to study observables
with a potentially clear saturation signal and to use heavy vector and flavored
mesons as alternative hard probes to forward jets.",0312261v2
2004-06-09,Saturation in two-hard-scale processes at hadron colliders,"A study of saturation effects in two-hard-scale hadronic processes such as
Mueller-Navelet jets is presented. The cross-sections are expressed in the
dipole framework while saturation is implemented via an extention of the
Golec-Biernat and Wusthoff model. The transition to saturation is found to be
more abrupt than in gamma*-gamma* cross-sections. Observables with a
potentially clear saturation signal are proposed.",0406111v1
1992-10-12,Saturation in the Nuclear Matter Problem,"Once density-dependent meson masses are introduced into the nuclear many-body
problem, conventional mechanisms for saturation no longer operate. We suggest
that a loop correction, essentially the introduction of the axial vector
coupling $g_A(\rho,k)$ as function of density $\rho$ and momentum $k$, can
bring about saturation, and present schematic calculations to illustrate this.
We find that a very small density-dependence in $g_A$ gives rise to a very
large saturating effect on nuclear matter. In fact, this new saturation
mechanism turns out to be more powerful than any of the conventional
mechanisms.",9210010v1
2012-06-18,Saturated fractions of two-factor designs,"In this paper we study saturated fractions of a two-factor design under the
simple effect model. In particular, we define a criterion to check whether a
given fraction is saturated or not, and we compute the number of saturated
fractions. All proofs are constructive and can be used as actual methods to
build saturated fractions. Moreover, we show how the theory of Markov bases for
contingency tables can be applied to two-factor designs for moving between the
designs with given margins.",1206.3911v2
2013-01-16,Saturating Auto-Encoders,"We introduce a simple new regularizer for auto-encoders whose hidden-unit
activation functions contain at least one zero-gradient (saturated) region.
This regularizer explicitly encourages activations in the saturated region(s)
of the corresponding activation function. We call these Saturating
Auto-Encoders (SATAE). We show that the saturation regularizer explicitly
limits the SATAE's ability to reconstruct inputs which are not near the data
manifold. Furthermore, we show that a wide variety of features can be learned
when different activation functions are used. Finally, connections are
established with the Contractive and Sparse Auto-Encoders.",1301.3577v3
2015-05-11,Saturation and Geometrical Scaling: from Deep Inelastic ep Scattering to Heavy Ion Collisions,"Saturation of gluon distribution is a consequence of the non-linear evolution
equations of QCD. Saturation implies the existence of so called saturation
momentum which is defined as a gluon density per unit rapidity per transverse
area. At large energies for certain kinematical domains saturation momentum is
the only scale for physical processes. As a consequence different observables
exhibit geometrical scaling (GS). We discuss a number of examples of GS in
different reactions.",1505.02458v1
2016-02-07,Phonon lasing as a likely mechanism for density-dependent velocity saturation in GaN transistors,"We show that density-dependent velocity saturation in a GaN High Electron
Mobility Transistor (HEMT) can be related to the stimulated emission of
longitudinal optical (LO) phonons. As the drift velocity of electrons
increases, the drift of the Fermi distribution in reciprocal space produces
population inversion and gain for the LO phonons. Once this gain reaches a
threshold value, the avalanche-like increase of LO emission causes a rapid loss
of electron energy and momentum and leads to drift velocity saturation. Our
simple model correctly predicts both the general trend of the saturation
velocity decreasing with increasing electron density and the values of
saturation velocity measured in our experiments.",1602.02417v1
2016-07-04,Unconventional double-bended saturation of optical transmission in graphene due to many-particle interactions,"We present a joint theory-experiment study on the transmission/absorption
saturation after ultrafast pulse excitation in graphene. We reveal an
unconventional double-bended saturation behavior: Both bendings separately
follow the standard saturation model exhibiting two saturation fluences,
however, the corresponding fluences differ by three orders of magnitude and
have different physical origin. Our results reveal that this new and unexpected
behavior can be ascribed to an interplay between fluence- and time-dependent
many-particle scattering processes and phase-space filling effects.",1607.00870v1
2016-10-07,"Transitively-Saturated Property, Banach Recurrence and Lyapunov Regularity","The topological entropy of various gap-sets on periodic-like recurrence and
Birkhoff regularity were considered in [69] but some Banach recurrence and
Lyapunov regularity are not considered.
  In this paper we introduce five new levels on Banach recurrence and show they
all carry full topological entropy, and simultaneously combine with Lyapunov
regularity to get some refined theory on mixed multifractal analysis of [8,29].
  In this process, we strengthen Pfister and Sullivan's result of [58] from
saturated property to transitively-saturated property (and from
single-saturated property to transitively-convex-saturated property).",1610.02166v2
2018-06-18,Detour-saturated graphs of small girths,"A detour of a graph G is a longest path in G. The detour order of G is the
number of vertices in a detour of G. A graph is said to be detour-saturated if
the addition of any edge increases strictly the detour order. L.W. Beineke,
J.E. Dunbar and M. Frick asked the following three questions in 2005. (1) What
is the smallest order of a detour-saturated graph of girth 4? (2) Let Pr be the
graph obtained from the Petersen graph by splitting one of its vertices into
three leaves. Is Pr the smallest triangle-free detour-saturated graph? (3) Does
there exist a detour-saturated graph with finite girth bigger than 5? We answer
these questions.",1806.06564v1
2019-01-28,Induced Saturation of $P_{6}$,"A graph $G$ is called $H$-induced-saturated if $G$ does not contain an
induced copy of $H$, but removing any edge from $G$ creates an induced copy of
$H$ and adding any edge of $G^{c}$ to $G$ creates an induced copy of $H$.
Martin and Smith showed that there does not exist a $P_{4}$-induced-saturated
graph, where $P_{4}$ is the path on 4 vertices. Axenovich and Csik\'os studied
related questions, and asked if there exists a $P_{n}$-induced-saturated graph
for any $n\geq5$. Our aim in this short note is to show that there exists a
$P_{6}$-induced-saturated graph.",1901.09801v1
2023-11-28,Finite-Time Computation of Polyhedral Input-Saturated Output-Admissible Sets,"The paper introduces a novel algorithm for computing the output admissible
set of linear discrete-time systems subject to input saturation. The proposed
method takes advantage of the piecewise-affine dynamics to propagate the output
constraints within the non-saturated and saturated regions. The constraints are
then shared between regions to ensure a proper transition from one region to
another. The resulting algorithm generates a set that is proven to be
polyhedral, safe, positively invariant, and finitely determined. Moreover, the
set is also proven to be strictly larger than the maximal output admissible set
that would be obtained by treating input saturation as a constraint.",2311.16427v1
2024-01-29,Bandwidth-induced saturation in multimode fiber-based absorbers,"Multimode fiber-based saturable absorbers enable mode-locking in lasers,
generating ultrafast pulses and providing an exceptional platform for
investigating nonlinear phenomena. Previous analyses in the continuous wave
(CW) limit showed that saturable absorption can be obtained due to nonlinear
interactions between transverse modes. We find experimentally that saturable
absorption can be achieved thanks to the interplay of single-mode fiber
nonlinearity and the wavelength-dependent linear transmission of the multimode
fiber, even with negligible intermodal nonlinearities. We further show that
even when intermodal nonlinearities are significant, the CW analysis may not be
sufficient for long multimode fibers. Understanding the underlying mechanisms
of multimode fiber-based saturable absorbers opens new possibilities for
developing programmable devices for ultrafast control.",2401.16121v1
2020-03-09,Localized magnetic field structures and their boundaries in the near-Sun solar wind from Parker Solar Probe measurements,"One of the discoveries made by Parker Solar Probe during first encounters
with the Sun is the ubiquitous presence of relatively small-scale structures
standing out as sudden deflections of the magnetic field. They were called
switchbacks as some of them show up the full reversal of the radial component
of the magnetic field and then return to regular conditions. Analyzing the
magnetic field and plasma perturbations associated with switchbacks we identify
three types of structures with slightly different characteristics: 1. Alfvenic
structures, where the variations of the magnetic field components take place
while the magnitude of the field remains constant; 2. Compressional, the field
magnitude varies together with changes of the components; 3. Structures
manifesting full reversal of the magnetic field (extremal class of Alfvenic
structures). Processing of structures boundaries and plasma bulk velocity
perturbations lead to the conclusion that they represent localized magnetic
field tubes with enhanced parallel plasma velocity and ion beta moving together
with respect to surrounding plasma. The magnetic field deflections before and
after the switchbacks reveal the existence of total axial current. The electric
currents are concentrated on the relatively narrow boundary layers on the
surface of the tubes and determine the magnetic field perturbations inside the
tube. These currents are closed on the structure surface, and typically have
comparable azimuthal and the axial components. The surface of the structure may
also accommodate an electromagnetic wave, that assists to particles in carrying
currents. We suggest that the two types of structures we analyzed here may
represent the local manifestations of the tube deformations corresponding to a
saturated stage of the Firehose instability development.",2003.05409v1
2002-09-04,Electrical resistivity at large temperatures: Saturation and lack thereof,"Many transition metal compounds show saturation of the resistivity at high
temperatures, T, while the alkali-doped fullerenes and the high-Tc cuprates are
usually considered to show no saturation. We present a model of transition
metal compounds, showing saturation, and a model of alkali-doped fullerenes,
showing no saturation. To analyze the results we use the f-sum rule, which
leads to an approximate upper limit for the resistivity at large T. For some
systems and at low T, the resistivity increases so rapidly that this upper
limit is approached for experimental T. The resistivity then saturates. For a
model of transition metal compounds with weakly interacting electrons, the
upper limit corresponds to a mean free path consistent with the Ioffe-Regel
condition. For a model of the high Tc cuprates with strongly interacting
electrons, however, the upper limit is much larger than the Ioffe-Regel
condition suggests. Since this limit is not exceeded by experimental data, the
data are consistent with saturation also for the cuprates. After ""saturation""
the resistivity usually grows slowly. For the alkali-doped fullerenes,
""saturation"" can be considered to have happened already for T=0, due to
orientational disorder. For these systems, however, the resistivity grows so
rapidly after ""saturation"" that this concept is meaningless. This is due to the
small band width and to the coupling to the level energies of the important
phonons.",0209099v1
2010-06-22,Sustainable Throughput of Wireless LANs with Multi-Packet Reception Capability under Bounded Delay-Moment Requirements,"With the rapid proliferation of broadband wireless services, it is of
paramount importance to understand how fast data can be sent through a wireless
local area network (WLAN). Thanks to a large body of research following the
seminal work of Bianchi, WLAN throughput under saturated traffic condition has
been well understood. By contrast, prior investigations on throughput
performance under unsaturated traffic condition was largely based on
phenomenological observations, which lead to a common misconception that WLAN
can support a traffic load as high as saturation throughput, if not higher,
under non-saturation condition. In this paper, we show through rigorous
analysis that this misconception may result in unacceptable quality of service:
mean packet delay and delay jitter may approach infinity even when the traffic
load is far below the saturation throughput. Hence, saturation throughput is
not a sound measure of WLAN capacity under non-saturation condition. To bridge
the gap, we define safe-bounded-mean-delay (SBMD) throughput and
safe-bounded-delay-jitter (SBDJ) throughput that reflect the actual network
capacity users can enjoy when they require finite mean delay and delay jitter,
respectively.
  Our earlier work proved that in a WLAN with multi-packet reception (MPR)
capability, saturation throughput scales super-linearly with the MPR capability
of the network. This paper extends the investigation to the non-saturation case
and shows that super-linear scaling also holds for SBMD and SBDJ throughputs.
Our results here complete the demonstration of MPR as a powerful
capacity-enhancement technique for WLAN under both saturation and
non-saturation conditions.",1006.4228v1
2022-10-10,A hyperbolic-elliptic PDE model and conservative numerical method for gravity-dominated variably-saturated groundwater flow,"Richards equation is often used to represent two-phase fluid flow in an
unsaturated porous medium when one phase is much heavier and more viscous than
the other. However, it cannot describe the fully saturated flow due to
degeneracy in the capillary pressure term. Mathematically, gravity-driven
variably saturated flows are interesting because their governing partial
differential equation switches from hyperbolic in the unsaturated region to
elliptic in the saturated region. Moreover, the presence of wetting fronts
introduces strong spatial gradients often leading to numerical instability. In
this work, we develop a robust, multidimensional mathematical and computational
model for such variably saturated flow in the limit of negligible capillary
forces. The elliptic problem for saturated regions is built-in efficiently into
our framework for a reduced system corresponding to the saturated cells, with
the boundary condition of the fixed head at the unsaturated cells. In summary,
this coupled hyperbolic-elliptic PDE framework provides an efficient,
physics-based extension of the hyperbolic Richards equation to simulate fully
saturated regions. Finally, we provide a suite of easy-to-implement yet
challenging benchmark test problems involving saturated flows in one and two
dimensions. These simple problems, accompanied by their corresponding
analytical solutions, can prove to be pivotal for the code verification, model
validation (V&V) and performance comparison of such simulators. Our numerical
solutions show an excellent comparison with the analytical results for the
proposed problems. The last test problem on two-dimensional infiltration in a
stratified, heterogeneous soil shows the formation and evolution of multiple
disconnected saturated regions.",2210.04724v1
1998-10-21,Nonlinear Alpha Effect in Dynamo Theory,"We extend the standard two-scale theory of the turbulent dynamo coefficient
$\alpha$ to include the nonlinear back reaction of the mean field $\bar B$ on
the turbulence. We calculate the turbulent emf as a power series in $\bar B$,
assuming that the base state of the turbulence ($\bar B=0$) is isotropic, and,
for simplicity, that the magnetic diffusivity equals the kinematic viscosity.
The power series converges for all $\bar B$, and for the special case that the
spectrum of the turbulence is sharply peaked in $k$, our result is proportional
to a tabulated function of the magnetic Reynolds number $R_M$ and the ratio
$\beta$ of $\bar B$ (in velocity units) to the rms turbulent velocity $v_0$.
For $\beta\to 0$ (linear regime) we recover the results of Steenbeck et al.
(1966) as modified by Pouquet et al. (1976). For $R_M\gg 1$, the usual
astrophysical case, $\alpha$ starts to decrease at $\beta \sim 1$, dropping
like $\beta^{-2}$ as $\beta \to \infty$. Hence for large $R_M$, $\alpha$
saturates at $\bar B\sim v_0$, as estimated by Kraichnan (1979), rather than at
$\bar B\sim R^{-1/2}_Mv_0$, as inferred by Cattaneo and Hughes (1996) from
their numerical simulations at $R_M$=100. We plan to carry out simulations with
various values of $R_M$ to investigate the discrepency.",9810345v1
2001-01-26,Global accretion disk simulations of magneto-rotational instability,"We perform global three-dimensional simulations of accretion disks
integrating the compressible, non-viscous, but diffusive MHD equations. The
disk is supposed to be isothermal. We make use of the ZEUS-3D code integrating
the MHD equations and added magnetic diffusivity. We measure the efficiency of
the angular-momentum transport. Various model simulations delivered transport
parameters of alpha_SS=0.01 to 0.05 which are consistent with several local
numerical investigations. Two of the models reach a highly turbulent state at
which alpha_SS is of the order of 0.1. After a certain stage of saturating of
the turbulence, Reynolds stress is found to be negative (inward transport) in
many of the models, whereas Maxwell stresses dominate and deliver a positive
(outward) total transport. Several of the models yield strongly fluctuating
Reynolds stresses, while Maxwell stresses are smooth and always transport
outwards.
  Dynamo action is found in the accretion disk simulations. A positive
dynamo-alpha is indicated in the northern hemisphere of the most prominent run,
coming along with negative kinetic and current helicities (all having the
opposite sign on the southern side). The dipolar structure of the magnetic
field is maintained throughout the simulations, although indication for a decay
of antisymmetry is found. The simulations covered relatively thick disks, and
results of thin-disk dynamo models showing quadrupolar fields may not be
compatible with the results presented here.",0101470v1
2001-10-01,A variable efficiency for thin disk black hole accretion,"We explore the presence of torques at the inner edges of geometrically-thin
black hole accretion disks using 3-dimensional magnetohydrodynamic (MHD)
simulations in a pseudo-Newtonian potential. By varying the saturation level of
the magnetorotational instability that leads to angular momentum transport, we
show that the dynamics of gas inside the radius of marginal stability varies
depending upon the magnetic field strength just outside that radius. Weak
fields are unable to causally connect material within the plunging region to
the rest of the disk, and zero torque is an approximately correct boundary
condition at the radius of marginal stability. Stronger fields, which we obtain
artificially but which may occur physically within more complete disk models,
are able to couple at least some parts of the plunging region to the rest of
the disk. In this case, angular momentum (and implicitly energy) is extracted
from the material in the plunging region. Furthermore, the magnetic coupling to
the plunging region can be highly time dependent with large fluctuations in the
torque at the radius of marginal stability. This implies varying accretion
efficiencies, both across systems and within a given system at different times.
The results suggest a possible link between changes in X-ray and outflow
activity, with both being driven by transitions between weak and strong field
states.",0110028v1
2002-03-02,The Magnetohydrodynamics of Convection-Dominated Accretion Flows,"Radiatively inefficient accretion flows onto black holes are unstable due to
both an outwardly decreasing entropy (`convection') and an outwardly decreasing
rotation rate (the `magnetorotational instability'; MRI). Using a linear
magnetohydrodynamic stability analysis, we show that long-wavelength modes are
primarily destabilized by the entropy gradient and that such `convective' modes
transport angular momentum inwards. Moreover, the stability criteria for the
convective modes are the standard Hoiland criteria of hydrodynamics. By
contrast, shorter wavelength modes are primarily destabilized by magnetic
tension and differential rotation. These `MRI' modes transport angular momentum
outwards. The convection-dominated accretion flow (CDAF) model, which has been
proposed for radiatively inefficient accretion onto a black hole, posits that
inward angular momentum transport and outward energy transport by
long-wavelength convective fluctuations are crucial for determining the
structure of the accretion flow. Our analysis suggests that the CDAF model is
applicable to a magnetohydrodynamic accretion flow provided the magnetic field
saturates at a sufficiently sub-equipartition value (plasma beta >> 1), so that
long-wavelength convective fluctuations can fit inside the accretion disk.
Numerical magnetohydrodynamic simulations are required to determine whether
such a sub-equipartition field is in fact obtained.",0203026v2
2002-07-06,The nonlinear small-scale dynamo and isotropic MHD turbulence,"This is a brief review of the main results of our recent studies of the
nonlinear evolution of the small-scale MHD dynamo in the high-Prandtl-number
regime and of the structure of the resulting saturated state of the isotropic
homogeneous MHD turbulence. It is emphasized that the MHD regime without a
uniform mean field (as is the case in our studies) is fundamentally different
from the one in which such a field is externally imposed. The ability of the
turbulence to bend and fold the magnetic-field lines leads to the emergence of
a distinctive small-scale structure. The fields are organized in folds of
characteristic length comparable to the size of the largest turbulent eddies
with spatial-direction reversals at the resistive scale. These folds are very
hard to destroy. In the nonlinear regime, the folding structure coexists with
Alfven waves propagating along the folds. The turbulent energy injected by the
forcing is dissipated in part resistively via the small-scale magnetic fields,
and in part viscously via the Alfven waves.",0207151v1
2002-08-30,Compton Heated Outflow from CDAFs,"Convection-dominated accretion flows (CDAF) are expected to have a shallower
density profile and a higher radiation efficiency as compared to
advection-dominated accretion flows (ADAF). Both solutions have been developed
to account for the observed properties of the low luminosity, high temperature
X-ray sources believed to involve accretion onto massive black holes.
Self-similar CDAFs also have steeper poloidal density gradients and
temperatures close to the virial temperature. All these characteristics make
CDAFs more capable of producing polar outflows driven by Compton heating as
compared to other classical accretion disks. We investigate the conditions for
producing such outflows in CDAFs and look for the mass accretion rate, or,
equally, the luminosity of CDAFs for which such outflows will exist. When the
electron temperature saturates around 10^11 K at the inner region, polar
outflows are probable for 8x10^-7 <~ L/L_E <~ 4x10^-5, where L_E is the
Eddington luminosity. Outflows are well collimated with small opening angles.
The luminosity range for which outflow solutions exist is narrower for lower
electron temperature flows and disappears completely for electron temperature
<~ 6x10^9 K. When the magnetic field is present, we find that outflows are
possible if the magnetic field is less than from 10% to 1% of the equipartition
field. We also find that outflows are more likely to be produced when the
viscosity parameter alpha is small. The tendency for jet-like collimated
outflows for these solutions is presumably astrophysically relevant given the
high frequency of jets from AGNs.",0208555v2
2002-10-24,Local Magnetohydrodynamical Models of Layered Accretion Disks,"Using numerical MHD simulations, we have studied the evolution of the
magnetorotational instability in stratified accretion disks in which the
ionization fraction (and therefore resistivity) varies substantially with
height. This model is appropriate to dense, cold disks around protostars or
dwarf nova systems which are ionized by external irradiation of cosmic rays or
high-energy photons. We find the growth and saturation of the MRI occurs only
in the upper layers of the disk where the magnetic Reynolds number exceeds a
critical value; in the midplane the disk remains queiscent. The vertical
Poynting flux into the ""dead"", central zone is small, however velocity
fluctuations in the dead zone driven by the turbulence in the active layers
generate a significant Reynolds stress in the midplane. When normalized by the
thermal pressure, the Reynolds stress in the midplane never drops below about
10% of the value of the Maxwell stress in the active layers, even though the
Maxwell stress in the dead zone may be orders of magnitude smaller than this.
Significant mass mixing occurs between the dead zone and active layers.
Fluctuations in the magnetic energy in the active layers can drive vertical
oscillations of the disk in models where the ratio of the column density in the
dead zone to that in the active layers is <10. These results have important
implications for the global evolution of a layered disk, in particular there
may be residual mass inflow in the dead layer. We discuss the effects that dust
in the disk may have on our results.",0210541v1
2002-11-20,Magnetic Field in Supernovae,"A relatively modest value of the initial rotation of the iron core, a period
of ~ 6-31 s, will give a very rapidly rotating protoneutron star and hence
strong differential rotation with respect to the infalling matter. Under these
conditions, a seed field is expected to be amplified by the MRI and to grow
exponentially. Exponential growth of the field on the time scale Omega^{-1} by
the magnetorotational instability (MRI) will dominate the linear growth process
of field line ""wrapping"" with the same characteristic time. The shear is
strongest at the boundary of the newly formed protoneutron star. Modest initial
rotation velocities of the iron core result in sub-Keplerian rotation and a
sub-equipartition magnetic field that nevertheless produce substantial MHD
luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G
develop ~ 300 msec after bounce with an associated MHD luminosity of ~ 10^{49}
- 10^{53} erg s^{-1}. Bi-polar flows driven by this MHD power can affect or
even cause the explosions associated with core-collapse supernovae. If the
initial rotation is too slow, then there will not be enough rotational energy
to power the supernova despite the high luminosities. The MRI should be active
and may qualitatively alter the flow if a black hole forms directly or after a
fall-back delay.",0211458v1
2003-05-26,Transition from collisionless to collisional MRI,"Recent calculations by Quataert et al. (2002) found that the growth rates of
the magnetorotational instability (MRI) in a collisionless plasma can differ
significantly from those calculated using MHD. This can be important in hot
accretion flows around compact objects. In this paper we study the transition
from the collisionless kinetic regime to the collisional MHD regime, mapping
out the dependence of the MRI growth rate on collisionality. A kinetic closure
scheme for a magnetized plasma is used that includes the effect of collisions
via a BGK operator. The transition to MHD occurs as the mean free path becomes
short compared to the parallel wavelength $2\pi/k_{\Par}$. In the weak magnetic
field regime where the Alfv\'en and MRI frequencies $\omega$ are small compared
to the sound wave frequency $k_{\Par} c_0$, the dynamics are still effectively
collisionless even if $\omega \ll \nu$, so long as the collision frequency $\nu
\ll k_{\Par} c_{0}$; for an accretion flow this requires $\nu \lsim \Omega
\sqrt{\beta}$. The low collisionality regime not only modifies the MRI growth
rate, but also introduces collisionless Landau or Barnes damping of long
wavelength modes, which may be important for the nonlinear saturation of the
MRI.",0305486v2
2005-07-25,Steady-State Electrostatic Layers from Weibel Instability in Relativistic Collisionless Shocks,"It is generally accepted that magnetic fields generated in the nonlinear
development of the transverse Weibel instability provide effective
collisionality in unmagnetized collisionless shocks. Recently, extensive two
and three dimensional simulations improved our understanding of the growth and
saturation of the instability in colliding plasma shells. However, the
steady-state structure of the shock wave transition layers remains poorly
understood. We use basic physical considerations and order-of-magnitude
arguments to study the steady state structure in relativistic unmagnetized
collisionless shocks in pair plasmas. The shock contains an electrostatic layer
resulting from the formation of stationary, magnetically-focused current
filaments. The filaments form where the cold upstream plasma and the
counterstreaming thermal plasma interpenetrate. The filaments are not entirely
neutral and strong electrostatic fields are present. Most of the downstream
particles cannot cross this layer into the upstream because they are trapped by
the electrostatic field. We identify the critical location in the shock
transition layer where the electromagnetic field ceases to be static. At this
location, the degree of charge separation in the filaments reaches a maximum
value, the current inside the filaments comes close to the Alfv\'en limit, and
the phase space distribution function starts to isotropize. We argue that the
radius of the current filaments upstream of the critical location is about
twice the upstream plasma skin depth. Finally, we show that some downstream
particles cross the electrostatic layer and run ahead of the shock into the
preshock medium without causing instability. These particles may play an
important role in particle acceleration.",0507553v1
2006-03-28,Quark deconfinement in neutron star cores: The effects of spin-down,"We study the role of spin-down in driving quark deconfinement in the high
density core of isolated neutron stars. Assuming spin-down to be solely due to
magnetic braking, we obtain typical timescales to quark deconfinement for
neutron stars that are born with Keplerian frequencies. Employing different
equations of state (EOS), we determine the minimum and maximum neutron star
masses that will allow for deconfinement via spin-down only. We find that the
time to reach deconfinement is strongly dependent on the magnetic field and
that this time is least for EOS that support the largest minimum mass at zero
spin, unless rotational effects on stellar structure are large. For a fiducial
critical density of $5\rho_0$ for the transition to the quark phase
($\rho_0=2.5\times10^{14}$g/cm$^3$ is the saturation density of nuclear
matter), we find that neutron stars lighter than $1.5M_{\odot}$ cannot reach a
deconfined phase. Depending on the EOS, neutron stars of more than
$1.5M_{\odot}$ can enter a quark phase only if they are spinning faster than
about 3 milliseconds as observed now, whereas larger spin periods imply that
they are either already quark stars or will never become one.",0603743v1
1998-01-22,Density-matrix renormalization study of the Hubbard model on a Bethe lattice,"The half-filled Hubbard model on the Bethe lattice with coordination number
$z=3$ is studied using the density-matrix renormalization group (DMRG) method.
Ground-state properties such as the energy $E$, average local magnetization
$<\hat S_z>$, its fluctuations $<\hat S_z^2 > - < \hat S_z>^2$ and various spin
correlation functions $<\hat S_z(i) \hat S_z(j) > - < S_z(i)> < S_z(j)>$ are
determined as a function of the Coulomb interaction strength $U/t$. The
calculated local magnetic moments $<\hat S_z(i)>$ increase monotonically with
increasing Coulomb repulsion $U/t$ forming an antiferromagnetic
spin-density-wave state which matches the two sublattices of the bipartite
Bethe lattice. At large $U/t$, $<\hat S_z(i)>$ is strongly reduced with respect
to the saturation value 1/2 due to exchange fluctuations between nearest
neighbors (NN) spins ($|< S_z(i)>|\simeq 0.35$ for $U/t\to +\infty$).
$<S_z(i)^2> - < S_z(i)>^2$ shows a maximum for $U/t=2.4$--2.9 which results
from the interplay between the usual increase of $<S_z(i)^2>$ with increasing
$U/t$ and the formation of important permanent moments $<S_z(i)>$ at large
$U/t$. NN sites show antiferromagnetic spin correlations which increase with
increasing Coulomb repulsion. In contrast next NN sites are very weakly
correlated over the whole range of $U/t$. The accuracy of the DMRG results is
discussed by comparison with tight-binding exact results, independent DMRG
calculations for the Heisenberg model and simple first-order perturbation
estimates.",9801228v2
1999-02-17,Quantum Monte Carlo Study of Weakly Coupled Spin Ladders,"We report a quantum Monte Carlo study of the thermodynamic properties of
arrays of spin ladders with various widths ($n$), coupled via a weak
inter-ladder exchange coupling $\alpha J$, where $J$ is the intra-ladder
coupling both along and between the chains. This coupled ladder system serves
as a simplified model for the magnetism of presumed ordered spin and charge
stripes in the two-dimensional CuO$_2$ planes of hole-doped copper oxides. Our
results for $n=3$ with weak inter-ladder coupling $\alpha=0.05$, estimated from
the $t-t'-t''-J$ model, show good agreement with the ordering temperature of
the recently observed spin density wave condensation in La$_2$CuO$_{4+y}$. We
show that there exists a quantum critical point at $\alpha_c \simeq 0.07$ for
$n=4$, and determine the phase diagram. Our data at this quantum critical point
agree quantitatively with the universal scaling predicted by the quantum
nonlinear $\sigma$ model. We also report results on random mixtures of $n=2$
and $n=3$ ladders, which correspond to the doping region near but above 1/8.
Our study on the magnetic static structure factor reveals a saturation of the
incommensurability of the spin correlations around 1/8, while the
incommensurability of the charge stripes grows linearly with hole
concentration. The implications of this result for the interpretation of
neutron scattering experiments on the dynamic spin fluctuations in
La$_{2-x}$Sr$_x$CuO$_4$ are discussed.",9902248v1
2000-08-24,Precursory Metal-Insulator transition in a small cluster of the `t-J' model: Exact analytic results,"We study the effect of hole hopping in a doped antiferromagnet described by
the `t-J' model, using exact analytic solutions for small clusters. In spite of
the small size, they reveal interesting details about the magnetic order, which
are not apparent in Mean Field treatments or in numerical calculations. The
4-site cluster with one hole yields the most interesting physics, displaying
different behaviors for the ground state: i) an antiferromagnetic phase for
t<<J, where the hole seems to be localized, not affecting the order of the
Heisenberg spins; ii)another regime for t~J that presents mixed ferro and
antiferro correlations and coexistence of metallic and insulating behaviors,
with the presence of charge and spin density waves, in what may be the analog
of the spiral phase obtained in Mean Field solutions; and finally iii)for t>>J,
we obtain strong ferromagnetic correlations (maximum spin) and no density
waves, with quantum fluctuations precluding the saturation of the magnetic
moment. This behavior shows traces of a metal-insulator transition as the hole
kinetic energy competes with the antiferromagnetic interactions.",0008373v1
2001-11-06,Spin-dependent electrical transport in ion-beam sputter deposited Fe-Cr multilayers,"The temperature dependence of the electrical resistivity and
magnetoresistance of Xe-ion beam sputtered Fe-Cr multilayers has been
investigated. The electrical resistivity between 5 and 300 K in the fully
ferromagnetic state, obtained by applying a field beyond the saturation field
(H_sat) necessary for the antiferromagnetic(AF)-ferromagnetic(FM) field-induced
transition, shows evidence of spin-disorder resistivity as in crystalline Fe
and an s-d scattering contribution (as in 3d metals and alloys). The sublattice
magnetization m(T) in these multilayers has been calculated in terms of the
planar and interlayer exchange energies. The additional spin-dependent
scattering \Delta \rho (T) = \rho(T,H=0)_AF - \rho(T,H=H_sat)_FM in the AF
state over a wide range of temperature is found to be proportional to the
sublattice magnetization, both \Delta \rho(T) and m(T) reducing along with the
antiferromagnetic fraction. At intermediate fields, the spin-dependent part of
the electrical resistivity (\rho_s (T)) fits well to the power law \rho_s (T) =
b - cT^\alpha where c is a constant and b and \alpha are functions of H. At low
fields \alpha \approx 2 and the intercept b decreases with H much the same way
as the decrease of \Delta \rho (T) with T. A phase diagram (T vs. H_sat) is
obtained for the field- induced AF to FM transition. Comparisons are made
between the present investigation and similar studies using dc magnetron
sputtered and molecular beam epitaxy (MBE) grown Fe-Cr multilayers.",0111084v1
2001-11-20,The longitudinal dynamic correlation and dynamic susceptibility of the isotropic XY-model on the 1d alternating superlattice,"The dynamic susceptibility $\chi_{Q}^{zz}(\omega)$ of the isotropic XY-model
(s=1/2) on the alternating superlattice (closed chain) in a transverse field
$h$ is obtained exactly at arbitrary temperatures. It is determined from the
results obtained for the dynamic correlations $<S_{jn}^{z}(t)S_{lm}^{z}(0)>$,
which have been calculated by introducing the generalized Jordan-Wigner
transformation, by using Wick's theorem and by reducing the problem to a
diagonalization of a finite matrix. The static properties are also reobtained
within this new formalism and all exact results are determined for arbitrary
temperatures. Explicit results are obtained numerically in the limit T=0, where
the critical behaviour occurs. A detailed analysis is presented for the
behaviour of the static susceptibility $\chi_{Q}^{zz}(0)$, as a function of the
transverse field h, and for the frequency dependency of the dynamic
susceptibility $\chi_{Q}^{zz}(\omega)$. It is also shown, in this temperature
limit, that within the magnetization plateaus which correspond to the different
phases, even when the induced magnetization is not saturated, the effective
dynamic correlation, $<\sum\limits_{n;m\in
cell:\text{}j;l}S_{jn}^{z}(t)S_{lm}^{z}(0)>$, is time independent, which
constitutes an unexpected result.",0111372v1
2005-08-31,Spinel ferrites: old materials bring new opportunities for spintronics,"Over the past few years, intensive studies of ultrathin epitaxial films of
perovskite oxides have often revealed exciting properties like giant
magnetoresistive tunnelling and electric field effects. Spinel oxides appear as
even more versatile due to their more complex structure and the resulting many
degrees of freedom. Here we show that the epitaxial growth of nanometric
NiFe2O4 films onto perovskite substrates allows the stabilization of novel
ferrite phases with properties dramatically differing from bulk ones. Indeed,
NiFe2O4 films few nanometres thick have a saturation magnetization at least
twice that of the bulk compound and their resistivity can be tuned by orders of
magnitude, depending on the growth conditions. By integrating such thin NiFe2O4
layers into spin-dependent tunnelling heterostructures, we demonstrate that
this versatile material can be useful for spintronics, either as a conductive
electrode in magnetic tunnel junctions or as a spin-filtering insulating
barrier in the little explored type of tunnel junction called spin-filter. Our
findings are thus opening the way for the realisation of monolithic spintronics
architectures integrating several layers of a single material, where the layers
are functionalised in a controlled manner.",0508764v1
2005-09-20,Formation of Mn2+ in La2/3Ca1/3MnO3 Thin Films due to Air Exposure,"We report on the chemical stability of La2/3Ca1/3MnO3 thin films. X-ray
absorption spectroscopy at the Mn L-edge and O K-edge makes evident deviations
from the nominally expected (2/3-1/3) Mn3+/Mn4+ ratio after the growth of thin
films on LaAlO3 substrates. As-grown thin films, exhibiting Curie temperature,
TC, well below that of the LCMO bulk material, develop an unexpected Mn2+
contribution after a few days of air exposure which increases with time.
Moreover, a reduction of the saturation magnetization, MS, is also detected.
The similarity of the results obtained by electron yield and fluorescence yield
demonstrates that the location of the Mn valence anomalies are not confined to
a narrow surface region of the film but can extend throughout the film
thickness in case of granular films. High temperature annealing not only
improves the magnetic and transport properties of such as-grown films but also
recovers the expected 2/3-1/3 Mn3+/Mn4+ ratio, which thereafter is stable to
air exposure. Similar results on La2/3Ca1/3MnO3 films grown on SrTiO3 and
NdGaO3 substrates demonstrate that there is no direct relation between the
observed Mn valence instability and the strain state of the films due to their
lattice mismatch with the substrate. A mechanism for the formation of Mn2+ ions
formation is discussed.",0509513v1
2006-09-29,Vortex configurations and critical parameters in superconducting thin films containing antidot arrays: Nonlinear Ginzburg-Landau theory,"Using the non-linear Ginzburg-Landau (GL) theory, we obtain the possible
vortex configurations in superconducting thin films containing a square lattice
of antidots. The equilibrium structural phase diagram is constructed which
gives the different ground-state vortex configurations as function of the size
and periodicity of the antidots for a given effective GL parameter
$\kappa^{*}$. Giant-vortex states, combination of giant- and multi-vortex
states, as well as symmetry imposed vortex-antivortex states are found to be
the ground state for particular geometrical parameters of the sample. The
antidot occupation number $n_o$ is calculated as a function of related
parameters and comparison with existing expressions for the saturation number
$n_s$ and with experimental results is given. For a small radius of antidots a
triangular vortex lattice is obtained, where some of the vortices are pinned by
the antidots and some of them are located between them. Transition between the
square pinned and triangular vortex lattices is given for different values of
the applied field. The enhanced critical current at integer and rational
matching fields is found, where the level of enhancement at given magnetic
field directly depends on the vortex-occupation number of the antidots. For
certain parameters of the antidot lattice and/or temperature the critical
current is found to be larger for higher magnetic fields.
Superconducting/normal $H-T$ phase boundary exhibits different regimes as
antidots are made larger, and we transit from a plain superconducting film to a
thin-wire superconducting network. Presented results are in good agreement with
available experiments and suggest possible new experiments.",0609772v1
2006-10-24,"Synthesis, Structure, and Ferromagnetism of a New Oxygen Defect Pyrochlore System Lu2V2O_{7-x} (x = 0.40-0.65)","A new fcc oxygen defect pyrochlore structure system Lu2V2O_{7-x} with x =
0.40 to 0.65 was synthesized from the known fcc ferromagnetic semiconductor
pyrochlore compound Lu2V2O7 which can be written as Lu2V2O6O' with two
inequivalent oxygen sites O and O'. Rietveld x-ray diffraction refinements
showed significant Lu-V antisite disorder for x >= 0.5. The lattice parameter
versus x (including x = 0) shows a distinct maximum at x ~ 0.4. We propose that
these observations can be explained if the oxygen defects are on the O'
sublattice of the structure. The magnetic susceptibility versus temperature
exhibits Curie-Weiss behavior above 150 K for all x, with a Curie constant C
that increases with x as expected in an ionic model. However, the magnetization
measurements also show that the (ferromagnetic) Weiss temperature theta and the
ferromagnetic ordering temperature T_C both strongly decrease with increasing x
instead of increasing as expected from C(x). The T_C decreases from 73 K for x
= 0 to 21 K for x = 0.65. Furthermore, the saturation moment at a field of 5.5
T at 5 K is nearly independent of x, with the value expected for a fixed spin
1/2 per V. The latter three observations suggest that Lu2V2O_{7-x} may contain
localized spin 1/2 vanadium moments in a metallic background that is induced by
oxygen defect doping, instead of being a semiconductor as suggested by the C(x)
dependence.",0610680v1
1994-09-20,Supersymmetric Dyonic Black Holes in Kaluza-Klein Theory,"We study supersymmetric, four-dimensional (4-d), Abelian charged black holes
(BH's) arising in (4+n)-d (1 \le n \le 7) Kaluza-Klein (KK) theories. Such
solutions, which satisfy supersymmetric Killing spinor equations (formally
satisfied for any n) and saturate the corresponding Bogomol'nyi bounds, can be
obtained if and only if the isometry group of the internal space is broken down
to the U(1)_E \times U(1)_M gauge group; they correspond to dyonic BH's with
electric Q and magnetic P charges associated with {\it different} U(1) factors.
The internal metric of such configurations is diagonal with (n-2) internal
radii constant, while the remaining two radii (associated with the respective
electric and magnetic U(1) gauge fields) and the 4-d part of the metric turn
out to be independent of n, i.e., solutions are effectively those of
supersymmetric 4-d BH's of 6-d KK theory. For Q \ne 0 and P \ne 0, 4-d
space-time has a null singularity, finite temperature (T_H \propto 1 /
\sqrt{|QP|}) and zero entropy. Special cases with either Q=0 or P=0 correspond
to the supersymmetric 4-d BH's of 5-d KK theory, first derived by Gibbons and
Perry, which have a naked singularity and infinite temperature.",9409119v1
2002-01-02,(3+0)D electromagnetic solitons and de Broglie's ''double solution'',"The well known light filaments are obtained in various media whose index of
refraction increases before a saturation with the electric field; adding a
small perturbation which increases the index with the magnetic field, and
neglecting the absorption, a filament curves and closes into a torus. This
transformation of a (2+1)D soliton into a (3+0)D soliton shows the existence of
those solitons, while a complete study, with a larger magnetic effect, would
require numerical computations, the starting point being, possibly, the
perturbed, curved filament.
  The flux of energy in the regular filaments is nearly a ''critical flux'',
depending slightly on the external fields, so that the energy of the (3+0)D
soliton is quantified, but may be slightly changed by external interactions.
  The nearly linear part of the soliton, an evanescent wave, is partly
transmitted by Young holes, making transmitted and reflected interference
patterns, thus index variations which guide the remainder of the soliton, just
as de Broglie's pilot waves.
  The creation of electron positron pairs in the vacuum by purely
electromagnetic fields shows a nonlinearity of vacuum at high energies;
supposing this nonlinearity convenient, elementary particles may be (3+0)D
solitons or light bullets, so that it may be a connection with the superstrings
theory.",0201002v1
2007-09-10,Hysteretic response of electron-nuclear spin system in single InAlAs quantum dots:Excitation power and polarization dependences,"We report the hysteresis of optically-pumped nuclear spin polarization and
the degree of circular polarization of photoluminescence on the excitation
power and electron spin polarization in single InAlAs quantum dots. By
increasing (or decreasing) the excitation power at a particular excitation
polarization, an abrupt rise (or drop) and a clear hysteretic behavior were
observed in the Overhauser shift of the photoluminescence of the exciton and
exciton complexes from the same single quantum dot under an external magnetic
field of 5 T. However, the degree of circular polarization shows different
behaviors between a positively charged exciton and a neutral exciton or
biexciton; further, only positively charged exciton exhibits the precisely
synchronized change and hysteretic behavior. It is suggested that the electron
spin distribution is affected by the flip-flop of electron-nuclear spins.
Further, the hysteresis is observed as a function of the degree of circular
polarization of the excitation light and its dependence on the excitation power
is studied. The saturation of the Overhauser shift after the abrupt rise
indicates the almost complete cancellation of the external magnetic field by
the nuclear field created within the width that is decided by the correlation
time between the electron and the nuclei spin system.",0709.1382v1
2007-10-04,A Defective Graphene Phase Predicted to be a Room Temperature Ferromagnetic Semiconductor,"Theoretical calculations, based on hybrid exchange density functional theory,
are used to show that in graphene a periodic array of defects generates a
ferromagnetic ground state at room temperature for unexpectedly large defect
separations. This is demonstrated for defects that consist of a carbon vacancy
in which two of the dangling bonds are saturated with H atoms. The magnetic
coupling mechanism is analysed and found to be due to an instability in the
$\pi$ electron system with respect to a long-range spin polarisation
characterised by alternation in the spin direction between adjacent carbon
atoms. The disruption of the $\pi$-bonding opens a semiconducting gap at the
Fermi edge. The size of the energy gap and the magnetic coupling strength are
strong functions of the defect separation and can thus be controlled by varying
the defect concentration. The position of the semiconducting energy gap and the
electron effective mass are strongly spin-dependent and this is expected to
result in a spin asymmetry in the transport properties of the system. A
defective graphene sheet is therefore a very promising material with an
in-built mechanism for tailoring the properties of the spintronic devices of
the future.",0710.0957v3
2008-07-10,Modeling of Spin Metal-Oxide-Semiconductor Field-Effect-Transistor: A Non-Equilibrium Green's Function Approach with Spin Relaxation,"A spin metal-oxide-semiconductor field-effect-transistor (spin MOSFET), which
combines a Schottky-barrier MOSFET with ferromagnetic source and drain
contacts, is a promising device for spintronic logic. Previous simulation
studies predict that this device should display a very high magnetoresistance
(MR) ratio (between the cases of parallel and anti-parallel magnetizations) for
the case of half-metal ferromagnets (HMF). We use the non-equilibrium Green's
function (NEGF) formalism to describe tunneling and carrier transport in this
device and to incorporate spin relaxation at the HMF-semiconductor interfaces.
Spin relaxation at interfaces results in non-ideal spin injection. Minority
spin currents arise and dominate the leakage current for anti-parallel
magnetizations. This reduces the MR ratio and sets a practical limit for spin
MOSFET performance. We found that MR saturates at a lower value for smaller
source-to-drain bias. In addition, spin relaxation at the detector side is
found to be more detrimental to MR than that at the injector side, for drain
bias less than the energy difference of the minority spin edge and the Fermi
level.",0807.1709v2
2009-03-05,The theory of gyrokinetic turbulence: A multiple-scales approach,"Gyrokinetics is a rich and rewarding playground to study some of the
mysteries of modern physics. In this thesis I present work, motivated by the
quest for fusion energy, which seeks to uncover some of the inner workings of
turbulence in magnetized plasmas.
  I begin with the fundamental theory of gyrokinetics, and a novel formulation
of its extension to the equations for mean-scale transport -- the equations
which must be solved to determine the performance of magnetically confined
fusion devices. The second project presents gyrokinetic secondary instability
theory as a mechanism to bring about saturation of the basic instabilities that
drive gyrokinetic turbulence. Emphasis is put on the ability for this analytic
theory to predict basic properties of the nonlinear state, which can be applied
to a mixing length phenomenology of transport. The final project is an
application of the methods from inertial range understanding of fluid
turbulence, to describe the stationary state of fully developed two-dimensional
gyrokinetic turbulence. This work explores the relatively new idea of a
phase-space cascade, whereby fine scales are nonlinearly generated in both
position space and velocity space, and ultimately smoothed by collisional
entropy production. This process constitutes the thermodynamic balance which
occurs in the true steady state of a turbulent plasma, including those found in
fusion devices.",0903.1091v2
2009-03-13,"Epitaxial thin films of the multiferroic double perovskite Bi2FeCrO6 grown on (100)-oriented SrTiO3 substrates: Growth, characterization, and optimization","The influence of the deposition pressure PO2 and substrate temperature TS
during the growth of Bi2FeCrO6 thin films grown by pulsed laser deposition has
been investigated. It is found that the high volatility of Bi makes the
deposition very difficult and that the growth of pure Bi2FeCrO6 thin films on
SrTiO3 substrates is possible only in a narrow deposition parameter window. We
find that the pure Bi2FeCrO6 phase is formed within a narrow window around an
oxygen pressure PO2 =1.210-2 mbar and around a substrate temperature TS=680
degC. At lower temperature or higher pressure, Bi7.38Cr0.62O12+x_also called
(b*Bi2O3)and Bi2Fe4O9 /Bi2(Fe,Cr)4O9+x phases are detected, while at lower
pressure or higher temperature a (Fe,Cr)3O4 phase forms. Some of these
secondary phases are not well known and have not been previously studied. We
previously reported Fe/Cr cation ordering as the probable origin of the tenfold
improvement in magnetization at saturation of our Bi2FeCrO6 film, compared to
BiFeO3. Here, we address the effect of the degree of cationic ordering on the
magnetic properties of the Bi2FeCrO6 single phase. Polarization measurements at
room temperature reveal that our Bi2FeCrO6 films have excellent ferroelectric
properties with ferroelectric hysteresis loops exhibiting a remanent
polarization as high as 55-60 miroC/cm2 along the pseudocubic (001) direction.",0903.2402v1
2009-03-18,Superconductor-ferromagnet nanocomposites created by co-deposition of niobium and dysprosium,"We have created superconductor-ferromagnet composite films in order to test
the enhancement of critical current density, Jc, due to magnetic pinning. We
co-sputter the type-II superconductor niobium (Nb) and the low-temperature
ferromagnet dysprosium (Dy) onto a heated substrate; the immiscibility of the
two materials leads to a phase-separated composite of magnetic regions within a
superconducting matrix. Over a range of compositions and substrate
temperatures, we achieve phase separation on scales from 5 nm to 1 micron. The
composite films exhibit simultaneous superconductivity and ferromagnetism.
Transport measurements show that while the self-field Jc is reduced in the
composites, the in-field Jc is greatly enhanced up to the 3 T saturation field
of Dy. In one instance, the phase separation orders into stripes, leading to
in-plane anisotropy in Jc.",0903.3142v2
2009-04-07,Heat and Dust in Active Layers of Protostellar Disks,"Requirements for magnetic coupling and accretion in the active layer of a
protostellar disk are re-examined, and some implications for thermal emission
from the layer are discussed. The ionization and electrical conductivity are
calculated following the general scheme of Ilgner and Nelson but with an
updated UMIST database of chemical reactions and some improvements in the grain
physics, and for the minimum-mass solar nebula rather than an alpha disk. The
new limits on grain abundance are slightly more severe than theirs. Even for
optimally sized grains, the layer should be at least marginally optically thin
to its own thermal radiation, so that narrow, highly saturated emission lines
of water and other molecular species would be expected if accretion is driven
by turbulence and standard rates of ionization prevail. If the grain size
distribution extends broadly from well below a micron to a millimeter or more,
as suggested by observations, then the layer may be so optically thin that its
cooling is dominated by molecular emission. Even under such conditions, it is
difficult to have active layers of more than 10g/cm^2 near 1AU unless dust is
entirely eliminated or greatly enhanced ionization rates are assumed.
Equipartition-strength magnetic fields are then required in these regions of
the disk if observed accretion rates are driven by magnetorotational
turbulence. Wind-driven accretion might allow weaker fields and less massive
active layers but would not heat the layer as much as turbulence and therefore
might not produce emission lines.",0904.1240v2
2009-08-26,On the strong impact of doping in the triangular antiferromagnet CuCrO2,"Electronic band structure calculations using the augmented spherical wave
method have been performed for CuCrO2. For this antiferromagnetic (T_N = 24 K)
semiconductor crystallizing in the delafossite structure, it is found that the
valence band maximum is mainly due to the t_2g orbitals of Cr^3+ and that spin
polarization is predicted with 3 mu_B per Cr^3+. The structural
characterizations of CuCr1-xMgxO2 reveal a very limited range of Mg^2+
substitution for Cr^3+ in this series. As soon as x = 0.02, a maximum of 1% Cr
ions substituted by Mg site is measured in the sample. This result is also
consistent with the detection of Mg spinel impurities from X-ray diffraction
for x = 0.01. This explains the saturation of the Mg^2+ effect upon the
electrical resistivity and thermoelectric power observed for x > 0.01. Such a
very weak solubility limit could also be responsible for the discrepancies
found in the literature. Furthermore, the measurements made under magnetic
field (magnetic susceptibility, electrical resistivity and Seebeck coefficient)
support that the Cr^4+ ""holes"", created by the Mg^2+ substitution, in the
matrix of high spin Cr^3+ (S = 3/2) are responsible for the transport
properties of these compounds.",0908.3828v1
2009-09-16,Mn valence instability in La2/3Ca1/3MnO3 thin films,"A Mn valence instability on La2/3Ca1/3MnO3 thin films, grown on LaAlO3
(001)substrates is observed by x-ray absorption spectroscopy at the Mn L-edge
and O K-edge. As-grown samples, in situ annealed at 800 C in oxygen, exhibit a
Curie temperature well below that of the bulk material. Upon air exposure a
reduction of the saturation magnetization, MS, of the films is detected.
Simultaneously a Mn2+ spectral signature develops, in addition to the expected
Mn3+ and Mn4+ contributions, which increases with time. The similarity of the
spectral results obtained by total electron yield and fluorescence yield
spectroscopy indicates that the location of the Mn valence anomalies is not
confined to a narrow surface region of the film, but can extend throughout the
whole thickness of the sample. High temperature annealing at 1000 C in air,
immediately after growth, improves the magnetic and transport properties of
such films towards the bulk values and the Mn2+ signature in the spectra does
not appear. The Mn valence is then stable even to prolonged air exposure. We
propose a mechanism for the Mn2+ ions formation and discuss the importance of
these observations with respect to previous findings and production of thin
films devices.",0909.3037v1
2010-01-12,Higher Winding Strings and Confined Monopoles in N=2 SQCD,"We consider composite string solutions in N=2 SQCD with the gauge group U(N),
the Fayet--Iliopoulos term \xi \neq 0 and N (s)quark flavors. These bulk
theories support non-Abelian strings and confined monopoles identified with
kinks in the two-dimensional world-sheet theory. Similar and more complicated
kinks (corresponding to composite confined monopoles) must exist in the
world-sheet theories on composite strings. In a bid to detect them we analyze
the Hanany--Tong (HT) model, focusing on a particular example of N=2. Unequal
quark mass terms in the bulk theory result in the twisted masses in the N=(2,2)
HT model. For spatially coinciding 2-strings, we find three distinct minima of
potential energy, corresponding to three different 2-strings. Then we find
BPS-saturated kinks interpolating between each pair of vacua. Two kinks can be
called elementary. They emanate one unit of the magnetic flux and have the same
mass as the conventional 't Hooft--Polyakov monopole on the Coulomb branch of
the bulk theory (\xi =0). The third kink represents a composite bimonopole,
with twice the minimal magnetic flux. Its mass is twice the mass of the
elementary confined monopole. We find instantons in the HT model, and discuss
quantum effects in composite strings at strong coupling. In addition, we study
the renormalization group flow in this model.",1001.1903v1
2010-04-23,Anisotropy of the in-plane angular magnetoresistance of electron-doed Sr1-xLaxCuO2 thin films,"Signatures of antiferromagnetism (AF) in the underdoped Ln2-xCexCuO4 (Ln =
Nd, Pr,...) family are observed even for doping levels for which
superconductivity exists. We have looked for a similar property in a different
electron-doped cuprate family, Sr1-xLaxCuO2, which consists of CuO2 planes
separated by Sr/La atoms, and is exempt of the possible influence of magnetic
rare earth ions. We report in-plane magnetoresistance measurements in the
normal state of underdoped, superconducting, c-axis oriented, epitaxial
Sr1-xLaxCuO2 thin films. This probe is sensitive to spin arrangement and we
find that the in-plane magnetoresistance, which is negative and does not
saturate for T, exhibits an angular dependence when measured upon rotating a
magnetic field within the CuO2 planes. The analysis reveals a superposition of
fourfold and twofold angular oscillations. Both of these increase in amplitude
with increasing field and decreasing and appear below a temperature, which gets
higher with decreasing doping levels. Our results demonstrate that these
magnetoresistance oscillations, also observed for the Ln2-xCexCuO4 (Ln = Nd,
Pr,...) family and attributed to an AF signature, are, without ambiguity, a
property of CuO2 planes. Besides, these oscillations vary with doping in an
unusual way compared to previous results: fourfold oscillations are essentially
present in the more underdoped samples while only twofold oscillations are
visible in the less underdoped ones. This intriguing observation appears to be
a consequence of spin dilution with increasing doping level.",1004.4163v1
2010-09-03,Imaging Spectropolarimetry with IBIS II: on the fine structure of G-band bright features,"We present new results from first observations of the quiet solar photosphere
performed through the Interferometric BIdimensional Spectrometer (IBIS) in
spectropolarimetric mode. IBIS allowed us to measure the four Stokes parameters
in the FeI 630.15 nm and FeI 630.25 nm lines with high spatial and spectral
resolutions for 53 minutes; the polarimetric sensitivity achieved by the
instrument is 0.003 the continuum intensity level. We focus on the correlation
which emerges between G-band bright feature brightness and magnetic filling
factor of ~ 1000 G (kG) fields derived by inverting Stokes I and V profiles.
More in detail, we present the correlation first in a pixel-by-pixel study of
an approximatively 3 arcsec wide bright feature (a small network patch) and
then we show that such a result can be extended to all the bright features
found in the dataset at any instant of the time sequence. The higher the kG
filling factor associated to a feature the higher the brightness of the feature
itself. Filling factors up to about 35 % are obtained for the brightest
features. Considering the values of the filling factors derived from the
inversion analysis of spectropolarimetric data and the brightness variation
observed in G-band data we put forward an upper limit for the smallest scale
over which magnetic flux concentrations in intergranular lanes produce a G-band
brightness enhancement (~ 0.1''). Moreover, the brightness saturation observed
for feature sizes comparable to the resolution of the observations is
compatible with large G-band bright features being clusters of sub-arcsecond
bright points. This conclusion deserves to be confirmed by forthcoming
spectropolarimetric observations at higher spatial resolution.",1009.0721v1
2011-02-16,Numerical Simulation of Current Sheet Formation in a Quasi-Separatrix Layer using Adaptive Mesh Refinement,"The formation of a thin current sheet in a magnetic quasi-separatrix layer
(QSL) is investigated by means of numerical simulation using a simplified
ideal, low-$\beta$, MHD model. The initial configuration and driving boundary
conditions are relevant to phenomena observed in the solar corona and were
studied earlier by Aulanier et al., A&A 444, 961 (2005). In extension to that
work, we use the technique of adaptive mesh refinement (AMR) to significantly
enhance the local spatial resolution of the current sheet during its formation,
which enables us to follow the evolution into a later stage. Our simulations
are in good agreement with the results of Aulanier et al. up to the calculated
time in that work. In a later phase, we observe a basically unarrested collapse
of the sheet to length scales that are more than one order of magnitude smaller
than those reported earlier. The current density attains correspondingly larger
maximum values within the sheet. During this thinning process, which is finally
limited by lack of resolution even in the AMR studies, the current sheet moves
upward, following a global expansion of the magnetic structure during the
quasi-static evolution. The sheet is locally one-dimensional and the plasma
flow in its vicinity, when transformed into a co-moving frame, qualitatively
resembles a stagnation point flow. In conclusion, our simulations support the
idea that extremely high current densities are generated in the vicinities of
QSLs as a response to external perturbations, with no sign of saturation.",1102.3291v1
2012-02-20,The contribution from blazar cascade emission to the extragalactic gamma-ray background: What a role does the extragalactic magnetic field play?,"We estimate the contribution to the extragalactic gamma-ray background (EGRB)
from both intrinsic and cascade emissions produced by blazars using a simple
semi- analysis method for two models of the blazar gamma-ray luminosity
function (GLF). For the cascade emission, we consider two possible
contributions: one is due to that the flux of the cascade emission is lower
than the Fermi LAT sensitivity (case I), which is independent on the
extragalactic magnetic field (EGMF), another is due to the fact that the flux
of the cascade emission is larger than the Fermi LAT sensitivity but the
emission angle is larger than LAT point-spread-function (PSF) angle (case II),
which depends on the EGMF. Our results indicate that (1) blazar contribution to
the EGRB is dominant although it depends on the GLF model and the EGMF; (2) the
EGMF plays an important role in estimating the contribution from the cascade
emission produced by blazars, the contribution from the cascade emission will
significantly alter the EGRB spectrum when the strength of the EGMF is large
enough (say BEGMF > 10-12 G); and (3) since the cascade emission in case II
reaches a saturation when the strength of the EGMF is ? 10-11 G, it is very
possible that the contribution from the cascade emission produced by blazars
can be considered as another method to probe the upper limit of the strength of
the EGMF.",1202.4250v1
2012-04-04,Quantum phase transitions in the exactly solved spin-1/2 Heisenberg-Ising ladder,"Ground-state behaviour of the frustrated quantum spin-1/2 two-leg ladder with
the Heisenberg intra-rung and Ising inter-rung interactions is examined in
detail. The investigated model is transformed to the quantum Ising chain with
composite spins in an effective transverse and longitudinal field by employing
either the bond-state representation or the unitary transformation. It is shown
that the ground state of the Heisenberg-Ising ladder can be descended from
three exactly solvable models: the quantum Ising chain in a transverse field,
the 'classical' Ising chain in a longitudinal field or the spin-chain model in
a staggered longitudinal-transverse field. The last model serves in evidence of
the staggered bond phase with alternating singlet and triplet bonds on the
rungs of two-leg ladder, which appears at moderate values of the external
magnetic field and consequently leads to a fractional plateau at a half of the
saturation magnetization. The ground-state phase diagram totally consists of
five ordered and one quantum disordered phase, which are separated from each
other either by the lines of discontinuous or continuous quantum phase
transitions. The order parameters are exactly calculated for all five ordered
phases and the quantum disordered phase is characterized through different
short-range spin-spin correlations.",1204.1008v2
2012-05-01,A quasi-analytical model for energy-delay-reliability tradeoff studies during write operations in perpendicular STT-RAM cell,"One of the biggest challenges the current STT-RAM industry faces is
maintaining a high thermal stability while trying to switch within a given
voltage pulse and energy cost. In this paper, we present a physics based
analytical model that uses a modified Simmons' tunneling expression to capture
the spin dependent tunneling in a magnetic tunnel junction(MTJ). Coupled with
an analytical derivation of the critical switching current based on the
Landau-Lifshitz-Gilbert equation, and the write error rate derived from a
solution to the Fokker-Planck equation, this model provides us a quick estimate
of the energydelay- reliability tradeoffs in perpendicular STTRAMs due to
thermal fluctuations. In other words, the model provides a simple way to
calculate the energy consumed during a write operation that ensures a certain
error rate and delay time, while being numerically far less intensive than a
full-fledged stochastic calculation. We calculate the worst case energy
consumption during anti-parallel (AP) to parallel (P) and P to AP switchings
and quantify how increasing the anisotropy field HK and lowering the saturation
magnetization MS, can significantly reduce the energy consumption. A case study
on how manufacturing variations of the MTJ cell can affect the energy
consumption and delay is also reported.",1205.0183v1
2012-06-06,Cosmic-ray acceleration in supernova remnants: non-linear theory revised,"A rapidly growing amount of evidences, mostly coming from the recent
gamma-ray observations of Galactic supernova remnants (SNRs), is seriously
challenging our understanding of how particles are accelerated at fast shocks.
The cosmic-ray (CR) spectra required to account for the observed phenomenology
are in fact as steep as $E^{-2.2}--E^{-2.4}$, i.e., steeper than the
test-particle prediction of first-order Fermi acceleration, and significantly
steeper than what expected in a more refined non-linear theory of diffusive
shock acceleration. By accounting for the dynamical back-reaction of the
non-thermal particles, such a theory in fact predicts that the more efficient
the particle acceleration, the flatter the CR spectrum. In this work we put
forward a self-consistent scenario in which the account for the magnetic field
amplification induced by CR streaming produces the conditions for reversing
such a trend, allowing --- at the same time --- for rather steep spectra and CR
acceleration efficiencies (about 20%) consistent with the hypothesis that SNRs
are the sources of Galactic CRs. In particular, we quantitatively work out the
details of instantaneous and cumulative CR spectra during the evolution of a
typical SNR, also stressing the implications of the observed levels of
magnetization on both the expected maximum energy and the predicted CR
acceleration efficiency. The latter naturally turns out to saturate around
10-30%, almost independently of the fraction of particles injected into the
acceleration process as long as this fraction is larger than about $10^{-4}$.",1206.1360v1
2012-06-07,Anisotropic magnetothermoelectric power of ferromagnetic thin films,"We compare the behavior of the magnetothermoelectric power (MTEP)in metallic
ferromagnetic thin films of Ni80Fe20 (Permalloy; Py), Co and CrO2 at
temperatures in the range of 100 K to 400 K. In 25 nm thick Py films and 50 nm
thick Co films both the anisotropic magnetoresistance (AMR) and MTEP show a
relative change in resistance and thermoelectric power (TEP) of the order of
0.2% when the magnetic field is reversed, and in both cases there is no
significant change in AMR or MTEP any more after the saturation field has been
reached. Surprisingly, both Py and Co films have opposite MTEP behavior
although both have the same sign for AMR and TEP. The data on 100 nm films of
fully spin-polarized CrO2, grown both on TiO2 and on sapphire, show a different
picture. The MTEP behavior at low fields shows peaks similar to the AMR in
these films, with variations up to 1%. With increasing field both the MR and
the MTEP variations keeps growing, with MTEP showing relative changes of 1.5%
with the thermal gradient along the b-axis and even 20% with the gradient along
the c-axis, with an intermediate value of 3% for the film on sapphire. It
appears that the low-field effects are due to magnetic domain switching, while
the high-field effects are intrinsic to the electronic structure of CrO2.",1206.1527v2
2012-10-16,Interaction-induced charge and spin pumping through a quantum dot at finite bias,"We investigate charge and spin transport through an adiabatically driven,
strongly interacting quantum dot weakly coupled to two metallic contacts with
finite bias voltage. Within a kinetic equation approach, we identify
coefficients of response to the time-dependent external driving and relate
these to the concepts of charge and spin emissivities previously discussed
within the time-dependent scattering matrix approach. Expressed in terms of
auxiliary vector fields, the response coefficients allow for a straightforward
analysis of recently predicted interaction-induced pumping under periodic
modulation of the gate and bias voltage [Phys. Rev. Lett. 104, 226803 (2010)].
We perform a detailed study of this effect and the related adiabatic Coulomb
blockade spectroscopy, and, in particular, extend it to spin pumping. Analytic
formulas for the pumped charge and spin in the regimes of small and large
driving amplitude are provided for arbitrary bias. In the absence of a magnetic
field, we obtain a striking, simple relation between the pumped charge at zero
bias and at bias equal to the Coulomb charging energy. At finite magnetic
field, there is a possibility to have interaction-induced pure spin pumping at
this finite bias value, and generally, additional features appear in the pumped
charge. For large-amplitude adiabatic driving, the magnitude of both the pumped
charge and spin at the various resonances saturate at values which are
independent of the specific shape of the pumping cycle. Each of these values
provide an independent, quantitative measurement of the junction asymmetry.",1210.4452v1
2012-12-10,Proton temperature anisotropy and magnetic reconnection in the solar wind: effects of kinetic instabilities on current sheet stability,"We investigate the role of kinetic instabilities driven by a proton
anisotropy on the onset of magnetic reconnection by means of 2-D hybrid
simulations. The collisionless tearing of a current sheet is studied in the
presence of a proton temperature anisotropy in the surrounding plasma. Our
results confirm that anisotropic protons within the current sheet region can
significantly enhance/stabilize the tearing instability of the current.
Moreover, fluctuations associated to linear instabilities excited by large
proton temperature anisotropies can significantly influence the stability of
the plasma and perturb the current sheets, triggering the tearing instability.
We find that such a complex coupling leads to a faster tearing evolution in a
regime with larger perpendicular temperature when an ion-cyclotron instability
is generated by the anisotropic proton distribution functions. On the contrary,
in the presence of the opposite anisotropy, fire hose fluctuations excited by
the unstable background protons with larger parallel temperature are not able
to efficiently destabilize the current sheets, which remain stable for a long
time after fire hose saturation. We discuss possible influences of this novel
coupling on the solar wind and heliospheric plasma dynamics.",1212.2101v1
2013-04-18,"Magnetostructural transition, metamagnetism, and magnetic phase coexistence in Co10Ge3O16","Co10Ge3O16 crystallizes in an intergrowth structure featuring alternating
layers of spinel and rock salt. Variable-temperature powder synchrotron X-ray
and neutron diffraction, magnetometry, and heat capacity experiments reveal a
magnetostructural transition at T_N = 203 K. This rhombohedral-to-monoclinic
transition involves a slight elongation of the CoO6 octahedra along the apical
axis. Below T_N, the application of a large magnetic field causes a
reorientation of the Co^2+ Ising spins. This metamagnetic transition is
first-order as evidenced by a latent heat observed in temperature-dependent
measurements. This transition is initially seen at T = 180 K as a broad upturn
in the M-H near H_C = 3.9 T. The upturn sharpens into a kink at T = 120 K and a
""butterfly"" shape emerges, with the transition causing hysteresis at high
fields while linear and reversible behavior persists at low fields. H_C
decreases as temperature is lowered and the loops at positive and negative
fields merge beneath T = 20 K. The antiferromagnetism is described by k_M = (00
1/2) and below T = 20 K a small uncompensated component with k_M = (000)
spontaneously emerges. Despite the Curie-Weiss analysis and ionic radius
indicating the Co2+ is in its high-spin state, the low-temperature M-H trends
toward saturation at M_S = 1.0 uB/Co. We conclude that the field-induced state
is a ferrimagnet, rather than a S = 1/2 ferromagnet. The unusual H-T phase
diagram is discussed with reference to other metamagnets and Co(II) systems.",1304.5000v3
2013-05-14,Effects of local dissipation profiles on magnetized accretion disk spectra,"We present spectral calculations of non-LTE accretion disk models appropriate
for high luminosity stellar mass black hole X-ray binary systems. We first use
a dissipation profile based on scaling the results of shearing box simulations
of Hirose et al. (2009) to a range of annuli parameters. We simultaneously
scale the effective temperature, orbital frequency and surface density with
luminosity and radius according to the standard \alpha-model (Shakura &
Sunyaev, 1973). This naturally brings increased dissipation to the disk surface
layers (around the photospheres) at small radii and high luminosities. We find
that the local spectrum transitions directly from a modified black body to a
saturated Compton scattering spectrum as we increase the effective temperature
and orbital frequency while decreasing midplane surface density. Next, we
construct annuli models based on the parameters of a L/L_Edd=0.8 disk orbiting
a 6.62 solar mass black hole using two modified dissipation profiles that
explicitly put more dissipation per unit mass near the disk surface. The new
dissipation profiles are qualitatively similar to the one found by Hirose et
al. (2009), but produce strong near power-law spectral tails. Our models also
include physically motivated magnetic acceleration support based once again on
scaling the Hirose et al. (2009) results. We present three full-disk spectra
each based on one of the dissipation prescriptions. Our most aggressive
dissipation profile results in a disk spectrum that is in approximate
quantitative agreement with certain observations of the steep power law (SPL)
spectral states from some black hole X-ray binaries.",1305.3320v1
2013-07-23,Resistance asymmetry of a two-dimensional electron gas caused by an effective spin injection,"We have performed conductivity measurements on a Si-MOSFET sample with a slot
in the upper gate, allowing for different electron densities n_1 and n_2 across
the slot. Dynamic longitudinal resistance was measured by a standard lock-in
technique, while maintaining a large DC current through the source-drain
channel. We find that in a parallel magnetic field, the resistance of the
sample, R(I_DC), is asymmetric with respect to the direction of the DC current.
The asymmetry becomes stronger with an increase of either the magnetic field or
the difference between n_1 and n_2. These observations are interpreted in terms
of the effective spin injection: the degree of spin polarisation is different
in the two parts of the sample, implying different magnitudes of spin current
away from the slot. The carriers thus leave the excess spin (of the appropriate
sign) in the region around the slot, leading to spin accumulation (or
depletion) and to the spin drift-diffusion phenomena. Due to the positive
magnetoresistance of the two-dimensional electron gas, this change in a local
magnetisation affects the resistivity near the slot and the measured net
resistance, giving rise to an asymmetric contribution. We further observe that
the value of R(I_DC) saturates at large I_DC; we suggest that this is due to
electron tunnelling from the two-dimensional n-type layer into the p-type
silicon (or into another ""spin reservoir"") at the slot.",1307.6260v2
2013-12-20,Magnon condensation with finite degeneracy on the triangular lattice,"We study the spin 1/2 triangular-lattice $J_1$-$J_2$-$J_3$ antiferromagnet
close to the saturation field using the dilute Bose gas theory, where the
magnetic structure is determined by the condensation of magnons. We focus on
the case of ferromagnetic $J_1$ and antiferromagnetic $J_2,J_3$, that is
particularly rich because frustration effects allow the single-magnon energy
dispersion to have six-fold degenerate minima at incommensurate momenta. Our
calculation also includes an interlayer coupling $J_0$, which covers both
antiferromagnetic and ferromagnetic cases including negligibly small regime
(two-dimensional case). Besides the spiral and fan phases, we find a new
double-$q$ phase (superposition of two modes), dubbed ""${\bf Q}_0$-${\bf Q}_1$""
(or simply ""01"") phase, that enjoys a new type of multiferroic character.
Certain phase boundaries have a singular $J_0$ dependence for $J_0\to 0$,
implying that even a very small interlayer coupling drastically changes the
ground state. A mechanism for this singularity is presented. Moreover, in some
regions of the parameter space, we show that a dilute gas of magnons can not be
stable, and phase separation (corresponding to a magnetization jump) is
expected. In the $J_1$-$J_2$ model ($J_3=0$), formation of two-magnon bound
states is observed, which can lead to a quadrupolar (spin-nematic) ordered
phase. Exact diagonalization analysis is also applied to the search of bound
states.",1312.5935v2
2014-02-06,Scattering mechanisms in textured FeGe thin films: magnetoresistance and the anomalous Hall effect,"A textured thin film of FeGe was grown by magnetron sputtering with a
helimagnetic ordering temperature of TN = 276 +/- 2 K. From 5 K to room
temperature a variety of scattering processes contribute towards the overall
longitudinal and Hall resistivities. These were studied by combining
magnetometry and magnetotransport measurements. The high-field
magnetoresistance (MR) displays three clear temperature regimes: Lorentz force
MR dominates at low temperatures, above T ~ 80 K scattering from spin-waves
predominates, whilst finally for T > 200 K scattering from fluctuating local
moments describes the MR. At low fields, where the magnetisation is no longer
technically saturated, we find a scaling of magnetoresistance with the square
of the magnetisation, indicating that the MR due to the unwinding of spins in
the conical phase arises from a similar mechanism to that in magnetic domain
walls. This MR is only visible up to a temperature of about 200 K. No features
can be found in the temperature or field dependence of the longitudinal
resistivity that belie the presence of the underlying magnetic phase transition
at TN: the marked changes in behavior are at much lower temperatures. The
anomalous Hall effect has a dramatic temperature dependence in which the
anomalous Hall resistivity scales quadratically with the longitudinal
resistivity: comparison with anomalous Hall scaling theory shows that our
system is in the intrinsic 'moderately dirty' regime. Lastly, we find evidence
of a topological Hall effect of size 100 ~Ohm cm.",1402.1276v2
2014-06-14,MuSR Investigation and Suppression of TC by overdoped Li in Diluted Ferromagnetic Semiconductor Li1+y(Zn1-xMnx)P,"We use muon spin relaxation (muSR) to investigate the magnetic properties of
a bulk form diluted ferromagnetic semiconductor (DFS) Li1.15(Zn0.9Mn0.1)P with
T_C ~ 22 K. MuSR results confirm the gradual development of ferromagnetic
ordering below T_C with a nearly 100% magnetic ordered volume. Despite its low
carrier density, the relation between static internal field and Curie
temperature observed for Li(Zn,Mn)P is consistent with the trend found in
(Ga,Mn)As and other bulk DFSs, indicating these systems share a common
mechanism for the ferromagnetic exchange interaction. Li1+y(Zn1-xMnx)P has the
advantage of decoupled carrier and spin doping, where Mn2+ substitution for
Zn2+ introduces spins and Li+ off-stoichiometry provides carriers. This
advantage enables us to investigate the influence of overdoped Li on the
ferromagnetic ordered state. Overdoping Li suppresses both T_C and saturation
moments for a certain amount of spins, which indicates that more carriers are
detrimental to the ferromagnetic exchange interaction, and that a delicate
balance between charge and spin densities is required to achieve highest T_C.",1406.3744v1
2014-08-26,Generalized investigation of the rotation-activity relation: Favouring rotation period instead of Rossby number,"Magnetic activity in Sun-like and low-mass stars causes X-ray coronal
emission, which is stronger for more rapidly rotating stars. This relation is
often interpreted in terms of the Rossby number, i.e., the ratio of rotation
period to convective overturn time. We reconsider this interpretation on the
basis of the observed X-ray emission and rotation periods of 821 stars with
masses below 1.4 Msun. A generalized analysis of the relation between X-ray
luminosity normalized by bolometric luminosity, L_X/L_bol, and combinations of
rotational period, P, and stellar radius, R, shows that the Rossby formulation
does not provide the solution with minimal scatter. Instead, we find that the
relation L_X/L_bol ~ P^{-2}R^{-4} optimally describes the non-saturated
fraction of the stars. This relation is equivalent to L_X ~ P^{-2}, indicating
that the rotation period alone determines the total X-ray emission. Since L_X
is directly related to the magnetic flux at the stellar surface, this means
that the surface flux is determined solely by the star's rotation and is
independent of other stellar parameters. While a formulation in terms of a
Rossby number would be consistent with these results if the convective overturn
time scales exactly as L_bol^{-1/2}, our generalized approach emphasizes the
need to test a broader range of mechanisms for dynamo action in cool stars.",1408.6175v1
2014-09-16,Interacting tilt and kink instabilities in repelling current channels,"We present a numerical study in resistive magnetohydrodynamics where the
initial equilibrium configuration contains adjacent, oppositely directed,
parallel current channels. Since oppositely directed current channels repel,
the equilibrium is liable to an ideal magnetohydrodynamic tilt instability.
This tilt evolution, previously studied in planar settings, involves two
magnetic islands or fluxropes, which on Alfvenic timescales undergo a combined
rotation and separation. This in turn leads to the creation of (near) singular
current layers, posing severe challenges to numerical approaches. Using our
open-source grid-adaptive MPI-AMRVAC software, we revisit the planar evolution
case in compressible MHD, as well as its extension to 2.5D and full 3D
scenarios. As long as the third dimension remains ignorable, pure tilt
evolutions result which are hardly affected by out of plane magnetic field
components. In all 2.5D runs, our simulations do show secondary tearing type
disruptions throughout the near singular current sheets in the far nonlinear
saturation regime. In full 3D, both current channels can be liable to
additional ideal kink deformations. We discuss the effects of having both tilt
and kink instabilities acting simultaneously in the violent, reconnection
dominated evolution. In 3D, both the tilt and the kink instabilities can be
stabilized by tension forces. As a concrete space plasma application, we argue
that interacting tilt-kink instabilities in repelling current channels provide
a novel route to initiate solar coronal mass ejections, distinctly different
from currently favored pure kink or torus instability routes.",1409.4543v1
2014-09-18,Permutation Entropy and Statistical Complexity Analysis of Turbulence in Laboratory Plasmas and the Solar Wind,"The Bandt-Pompe permutation entropy and the Jensen-Shannon statistical
complexity are used to analyze fluctuating time series of three different
plasmas: the magnetohydrodynamic (MHD) turbulence in the plasma wind tunnel of
the Swarthmore Spheromak Experiment (SSX), drift-wave turbulence of ion
saturation current fluctuations in the edge of the Large Plasma Device (LAPD)
and fully-developed turbulent magnetic fluctuations of the solar wind taken
from the WIND spacecraft. The entropy and complexity values are presented as
coordinates on the CH plane for comparison among the different plasma
environments and other fluctuation models. The solar wind is found to have the
highest permutation entropy and lowest statistical complexity of the three data
sets analyzed. Both laboratory data sets have larger values of statistical
complexity, suggesting these systems have fewer degrees of freedom in their
fluctuations, with SSX magnetic fluctuations having slightly less complexity
than the LAPD edge fluctuations. The CH plane coordinates are compared to the
shape and distribution of a spectral decomposition of the waveforms. These
results suggest that fully developed turbulence (solar wind) occupies the
lower-right region of the CH plane, and that other plasma systems considered to
be turbulent have less permutation entropy and more statistical complexity.
This paper presents the first use of this statistical analysis tool on solar
wind plasma, as well as on an MHD turbulent experimental plasma.",1409.5455v1
2014-11-21,A new spin gapless semiconductor: quaternary Heusler CoFeCrGa alloy,"Despite a plethora of materials suggested for spintronic applications, a new
class of materials has emerged, namely spin gapless semiconductors (SGS), that
offers potentially more advantageous properties than existing ones. These
magnetic semiconductors exhibit a finite band gap for one spin channel and a
closed gap for the other. Here, supported by the first-principles,
electronic-structure calculations, we report the first experimental evidence of
SGS behavior in equiatomic quaternary CoFeCrGa, having a cubic Heusler (L21)
structure but exhibiting chemical disorder (DO3 structure). CoFeCrGa is found
to transform from SGS to half-metallic phase under pressure, which is
attributed to unique electronic-structure features. The saturation
magnetization (MS) obtained at 8 K agrees with the Slater-Pauling rule and the
Curie temperature (TC) is found to exceed 400 K. Carrier concentration (up to
250 K) and electrical conductivity are observed to be nearly temperature
independent, prerequisites for SGS. The anomalous Hall coefficient is estimated
to be 185 S/cm at 5 K. Considering the SGS properties and high TC, this
material appears to be promising for spintronic applications.",1411.5772v2
2015-02-15,Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal NbP,"Recent experiments have revealed spectacular transport properties of
conceptually simple semimetals. For example, normal semimetals (e.g. WTe$_2$)
have started a new trend to realize a large magnetoresistance, which is the
change of electrical resistance by an external magnetic field. Weyl semimetal
(WSM) is a topological semimetal with massless relativistic electrons as the
three-dimensional analogue of graphene and promises exotic transport properties
and surface states, which are different from those of the famous topological
insulators (TIs). In this letter, we choose to utilize NbP in magneto-transport
experiments because its band structure is on assembly of a WSM and a normal
semimetal. Such a combination in NbP indeed leads to the observation of
remarkable transport properties, an extremely large magnetoresistance of
850,000 % at 1.85 K (250 % at room temperature) in a magnetic field of 9 T
without any signs of saturation, and ultrahigh carrier mobility of
5$\times$10$^6$ cm$^2$ V$^{-1}$ s$^{-1}$ accompanied by strong Shubnikov-de
Hass (SdH) oscillations. NbP presents a unique example to consequent design the
functionality of materials by combining the topological and conventional
phases.",1502.04361v2
2015-05-06,Role of spin-orbit coupling and evolution of the electronic structure of WTe$_2$ under an external magnetic field,"Here, we present a detailed study on the temperature and angular dependence
of the Shubnikov-de-Haas (SdH) effect in the semi-metal WTe$_2$. This compound
was recently shown to display a very large non-saturating magnetoresistance
which was attributed to nearly perfectly compensated densities of electrons and
holes. We observe four fundamental SdH frequencies and attribute them to
spin-orbit split, electron- and hole-like, Fermi surface (FS) cross-sectional
areas. Their angular dependence seems consistent with ellipsoidal FSs with
volumes suggesting a modest excess in the density of electrons with respect to
that of the holes. We show that density functional theory (DFT) calculations
fail to correctly describe the FSs of WTe$_2$. When their cross-sectional areas
are adjusted to reflect the experimental data, the resulting volumes of the
electron/hole FSs obtained from the DFT calculations would imply a pronounced
imbalance between the densities of electrons and holes. We find evidence for
field-dependent Fermi surface cross-sectional areas by fitting the oscillatory
component superimposed onto the magnetoresistivity signal to several
Lifshitz-Kosevich components. We also observe a pronounced field-induced
renormalization of the effective masses. Taken together, our observations
suggest that the electronic structure of WTe$_2$ evolves with the magnetic
field. This evolution might be a factor contributing to its pronounced
magnetoresistivity.",1505.01242v2
2016-03-01,Suppression of thermal conduction in a mirror-unstable plasma,"The ICM plasma is subject to firehose and mirror instabilities at scales of
order the ion Larmor radius. The mirror instability generates fluctuations of
magnetic-field strength $\delta B / B \sim 1$. These fluctuations act as
magnetic traps for the heat-conducting electrons, suppressing their transport.
We calculate the effective parallel thermal conductivity in the ICM in the
presence of the mirror fluctuations for different stages of the evolution of
the instability. The mirror fluctuations are limited in amplitude by the
maximum and minimum values of the field strength, with no large deviations from
the mean value. This key property leads to a finite suppression of thermal
conduction at large scales. We find suppression down to $\approx 0.2$ of the
Spitzer value for the secular phase of the perturbations' growth, and $\approx
0.3$ for their saturated phase. The effect operates in addition to other
suppression mechanisms and independently of them. Globally, fluctuations
$\delta B / B \sim 1$ can be present on much larger scales, of the order of the
scale of turbulent motions. However, we do not expect large suppression of
thermal conduction by these, because their scale is considerably larger than
the collisional mean free path of the ICM electrons. The obtained suppression
of thermal conduction by a factor of $\sim 5$ appears to be characteristic and
potentially universal for a weakly collisional mirror-unstable plasma.",1603.00524v3
2016-03-23,Multi-photon transitions and Rabi resonance in continuous wave EPR,"The study of microwave and radiofrequency multi-photon transitions in
continuous wave (CW) EPR spectroscopy is extended to a Rabi resonance
condition, when the radio frequency of the magnetic-field modulation matches
the Rabi frequency of a spin system in the microwave field. Using the
non-secular perturbation theory based on the Bogoliubov averaging method, the
analytical description of the response of the spin system is derived for all
modulation frequency harmonics. When the modulation frequency exceeds the EPR
linewidth, multi-photon transitions result in sidebands in absorption EPR
spectra measured with phase-sensitive detection at any harmonic. The saturation
of different-order multi-photon transitions is shown to be significantly
different and to be sensitive to the Rabi resonance. The noticeable frequency
shifts of sidebands are found to be the signatures of this resonance. The
inversion of two-photon lines in some spectral intervals of the out-of-phase
first-harmonic signal is predicted under passage through the Rabi resonance.
The inversion indicates the transition from absorption to stimulated emission
or vice versa, depending on the sideband. The manifestation of the primary and
secondary Rabi resonance is also demonstrated in time-resolved steady-state EPR
signals formed by all harmonics of the modulation frequency. Our results
provide a theoretical framework for future developments in multi-photon CW EPR
spectroscopy, which can be useful for samples with long spin relaxation times
and extremely narrow EPR lines",1603.07228v1
2016-05-11,Percolation via combined electrostatic and chemical doping in complex oxide films,"Stimulated by experimental advances in electrolyte gating methods, we
investigate theoretically percolation in thin films of inhomogenous complex
oxides, such as La$_{1-x}$Sr$_{x}$CoO$_{3}$ (LSCO), induced by a combination of
bulk chemical and surface electrostatic doping. Using numerical and analytical
methods, we identify two mechanisms that describe how bulk dopants reduce the
amount of electrostatic surface charge required to reach percolation: (i)
bulk-assisted surface percolation, and (ii) surface-assisted bulk percolation.
We show that the critical surface charge strongly depends on the film thickness
when the film is close to the chemical percolation threshold. In particular,
thin films can be driven across the percolation transition by modest surface
charge densities \emph{via} surface-assisted bulk percolation. If percolation
is associated with the onset of ferromagnetism, as in LSCO, we further
demonstrate that the presence of critical magnetic clusters extending from the
film surface into the bulk results in considerable volume enhancement of the
saturation magnetization, with pronounced experimental consequences. These
results should significantly guide experimental work seeking to verify
gate-induced percolation transitions in such materials.",1605.03463v1
2016-05-12,Intertwined Lattice Deformation and Magnetism in Monovacancy Graphene,"Using density functional calculations we have investigated the local spin
moment formation and lattice deformation in graphene when an isolated vacancy
is created. We predict two competing equilibrium structures: a ground state
planar configuration with a saturated local moment of 1.5 $\mu_B$, and a
metastable non-planar configuration with a vanishing magnetic moment, at a
modest energy expense of ~50 meV. Though non-planarity relieves the lattice of
vacancy-induced strain, the planar state is energetically favored due to
maximally localized defect states (v$\sigma$, v$\pi$). In the planar
configuration, charge transfer from itinerant (Dirac) states weakens the
spin-polarization of v$\pi$ yielding a fractional moment, which is aligned
parallel to the unpaired v$\sigma$ electron through Hund's coupling. In the
non-planar configuration, the absence of orthogonal symmetry allows interaction
between v$\sigma$ and local d$\pi$ states, to form a hybridized
v$\sigma^\prime$ state. The non-orthogonality also destabilizes the Hund's
coupling, and an antiparallel alignment between v$\sigma$ and v$\pi$ lowers the
energy. The gradual spin reversal of v$\pi$ with increasing non-planarity opens
up the possibility of an intermediate structure with balanced v$\pi$ spin
population. If such a structure is realized under external perturbations,
diluted vacancy concentration may lead to v$\sigma$ based spin-1/2
paramagnetism.",1605.03921v1
2016-06-11,"Conetronics in 2D Metal-Organic Frameworks: Double Dirac Cones, Magnetic Half Dirac Cones and Quantum Anomalous Hall Effect","Based on recently synthesized Ni3C12S12 class 2D metal-organic frameworks, we
predict electronic properties of M3C12S12 and M3C12O12, where M is Zn, Cd, Hg,
Be, or Mg with no M orbital contributions to bands near Fermi level. For
M3C12S12, their band structures exhibit double Dirac cones with different Fermi
velocities that are n and p type, respectively, which are switchable by
few-percent strain. The crossing of two cones are symmetry-protected to be
non-hybridizing, leading to two independent channels in 2D node-line semimetals
at the same k-point akin to spin-channels in spintronics, rendering conetronics
device possible. The node line rings right at their crossing, which are both
electron and hole pockets at the Fermi level, can give rise to
magnetoresistance that will not saturate when the magnetic field is infinitely
large, due to perfect n-p compensation. For M3C12O12, together with conjugated
metal-tricatecholate polymers M3(HHTP)2, the spin-polarized slow Dirac cone
center is pinned precisely at the Fermi level, making the systems conducting in
only one spin or cone channel. Quantum anomalous Hall effect can arise in MOFs
with non-negligible spin-orbit coupling like Cu3C12O12. Compounds of M3C12S12
and M3C12O12 with different M, can be used to build spintronic and
cone-selecting heterostructure devices, tunable by strain or electrostatic
gating.",1606.04094v1
2016-08-24,The Weak Gravity Conjecture and Effective Field Theory,"The Weak Gravity Conjecture (WGC) is a proposed constraint on theories with
gauge fields and gravity, requiring the existence of light charged particles
and/or imposing an upper bound on the field theory cutoff $\Lambda$. If taken
as a consistency requirement for effective field theories (EFTs), it rules out
possibilities for model-building including some models of inflation. I
demonstrate simple models which satisfy all forms of the WGC, but which through
Higgsing of the original gauge fields produce low-energy EFTs with gauge forces
that badly violate the WGC. These models illustrate specific loopholes in
arguments that motivate the WGC from a bottom-up perspective; for example the
arguments based on magnetic monopoles are evaded when the magnetic confinement
that occurs in a Higgs phase is accounted for. This indicates that the WGC
should not be taken as a veto on EFTs, even if it turns out to be a robust
property of UV quantum gravity theories. However, if the latter is true then
parametric violation of the WGC at low energy comes at the cost of non-minimal
field content in the UV. I propose that only a very weak constraint is
applicable to EFTs, $\Lambda \lesssim \left(-\log g \right)^{-1/2} M_\text{pl}$
where $g$ is the gauge coupling, motivated by entropy bounds. Remarkably, EFTs
produced by Higgsing a theory that satisfies the WGC can saturate but not
violate this bound.",1608.06951v2
2016-09-30,Superconductivity mediated by quantum critical antiferromagnetic fluctuations: The rise and fall of hot spots,"In several unconventional superconductors, the highest superconducting
transition temperature $T_{c}$ is found in a region of the phase diagram where
the antiferromagnetic transition temperature extrapolates to zero, signaling a
putative quantum critical point. The elucidation of the interplay between these
two phenomena - high-$T_{c}$ superconductivity and magnetic quantum criticality
- remains an important piece of the complex puzzle of unconventional
superconductivity. In this paper, we combine sign-problem-free Quantum Monte
Carlo simulations and field-theoretical analytical calculations to unveil the
microscopic mechanism responsible for the superconducting instability of a
general low-energy model, called spin-fermion model. In this approach,
low-energy electronic states interact with each other via the exchange of
quantum critical magnetic fluctuations. We find that even in the regime of
moderately strong interactions, both the superconducting transition temperature
and the pairing susceptibility are governed not by the properties of the entire
Fermi surface, but instead by the properties of small portions of the Fermi
surface called hot spots. Moreover, $T_{c}$ increases with increasing
interaction strength, until it starts to saturate at the crossover from
hot-spots dominated to Fermi-surface dominated pairing. Our work provides not
only invaluable insights into the system parameters that most strongly affect
$T_{c}$, but also important benchmarks to assess the origin of
superconductivity in both microscopic models and actual materials.",1609.09568v2
2016-10-04,Equation of State for Nucleonic and Hyperonic Neutron Stars with Mass and Radius Constraints,"We obtain a new equation of state for the nucleonic and hyperonic inner core
of neutron stars that fulfills the 2$M_{\odot}$ observations as well as the
recent determinations of stellar radii below 13 km. The nucleonic equation of
state is obtained from a new parametrization of the FSU2 relativistic
mean-field functional that satisfies these latest astrophysical constraints
and, at the same time, reproduces the properties of nuclear matter and finite
nuclei while fulfilling the restrictions on high-density matter deduced from
heavy-ion collisions. On the one hand, the equation of state of neutron star
matter is softened around saturation density, which increases the compactness
of canonical neutron stars leading to stellar radii below 13 km. On the other
hand, the equation of state is stiff enough at higher densities to fulfill the
2$M_{\odot}$ limit. By a slight modification of the parametrization, we also
find that the constraints of 2$M_{\odot}$ neutron stars with radii around 13 km
are satisfied when hyperons are considered. The inclusion of the high magnetic
fields present in magnetars further stiffens the equation of state. Hyperonic
magnetars with magnetic fields in the surface of $ \sim 10^{15}$ G and with
values of $\sim 10^{18}$ G in the interior can reach maximum masses of
2$M_{\odot}$ with radii in the 12-13 km range.",1610.00919v2
2016-12-17,"Upper critical field, pressure-dependent superconductivity and electronic anisotropy of Sm$_4$Fe$_2$As$_2$Te$_{1-x}$O$_{4-y}$F$y$","We present a detailed study of the electrical transport properties of a
recently discovered iron-based superconductor:
Sm$_4$Fe$_2$As$_2$Te$_{0.72}$O$_{2.8}$F$_{1.2}$. We followed the temperature
dependence of the upper critical field by resistivity measurement of single
crystals in magnetic fields up to 16 T, oriented along the two main
crystallographic directions. This material exhibits a zero-temperature upper
critical field of 90 T and 65 T parallel and perpendicular to the Fe$_2$As$_2$
planes, respectively. An unprecedented superconducting magnetic anisotropy
$\gamma_H=H_{c2}^{ab}/H_{c2}^c \sim 14$ is observed near Tc, and it decreases
at lower temperatures as expected in multiband superconductors. Direct
measurement of the electronic anisotropy was performed on microfabricated
samples, showing a value of $\rho_c/\rho_{ab}(300K) \sim 5$ that raises up to
19 near Tc. Finally, we have studied the pressure and temperature dependence of
the in-plane resistivity. The critical temperature decreases linearly upon
application of hydrostatic pressure (up to 2 GPa) similarly to overdoped
cuprate superconductors. The resistivity shows saturation at high temperatures,
suggesting that the material approaches the Mott-Ioffe-Regel limit for metallic
conduction. Indeed, we have successfully modelled the resistivity in the normal
state with a parallel resistor model that is widely accepted for this state.
All the measured quantities suggest strong pressure dependence of the density
of states.",1612.05792v1
2016-12-20,Indirect Searches of the Degenerate MSSM,"A degenerate sfermionic particle spectrum can escape constraints from flavor
physics, and at the same time evade the limits from the direct searches if the
degeneracy extends to the gaugino-higgsino sector. Inspired by this, we
consider a scenario where all the soft terms have an approximately common mass
scale at $M_{\text{SUSY}}$, with splittings $\lesssim \mathcal{O}(10\%)$. As a
result, the third generation sfermions have large to maximal (left-right)
mixing, the same being the case with charginos and some sectors of the
neutralino mass matrix. We study this scenario in the light of discovery of the
Higgs boson with mass $\sim$ 125 GeV. We consider constraints from $B$-physics,
the anomalous magnetic moment of the muon and the dark matter relic density. We
find that a supersymmetric spectrum as light as 600 GeV could be consistent
with all current data and also account for the observed anomalous magnetic
moment of the muon within $2\sigma$. The neutralino relic density is generally
too small to saturate the measured cold dark matter relic density. Direct
detection limits from XENON100 and LUX put severe constraints on this scenario
which will be conclusively probed by XENONnT experiment.",1612.06471v1
2017-01-23,Crystal Growth and Magneto-transport of Bi2Se3 Single crystals,"In this letter, we report growth and characterization of bulk Bi2Se3 single
crystals. The studied Bi2Se3 crystals are grown by self flux method through
solid state reaction from high temperature (950C) melt of constituent elements
and slow cooling (2C/hour). The resultant crystals are shiny and grown in [00l]
direction, as evidenced from surface XRD. Detailed Reitveld analysis of PXRD
(powder x-ray diffraction) of the crystals showed that these are crystallized
in rhombohedral crystal structure with space group of R3m (D5) and the lattice
parameters are a = 4.14(2)A, b = 4.14 (2) A and c = 28.7010(7) A. Temperature
versus resistivity (R-T) plots revealed metallic conduction down to 2K, with
typical room temperature resistivity (R300K) of around 0.53 mohm-cm and
residual resistivity of 0.12 mohm-cm. Resistivity under magnetic field ]
measurements exhibited large +Ve magneto resistance right from 2K to 200K.
Isothermal magneto resistance [RH] measurements at 2K, 100K and 200K exhibited
magneto resistance (MR) of up to 240, 130 and 60 percent respectively at 14
Tesla. Further the MR plots are non saturating and linear with field at all
temperature. At 2K the MR plots showed clear quantum oscillations at above say
10 Tesla applied field. Also the Kohler plots i.e., were seen consolidating on
one plot. Interestingly, the studied Bi2Se3 single crystal exhibited the
Shubnikov-de Haas oscillations (SdH) at 2K under different applied magnetic
fields ranging from 4Tesla to 14 Tesla",1701.06280v2
2017-02-10,Mesoscopic transport in electrostatically-defined spin-full channels in quantum Hall ferromagnets,"In this work we use electrostatic control of quantum Hall ferromagnetic
transitions in CdMnTe quantum wells to study electron transport through
individual domain walls (DWs) induced at a specific location. These DWs are
formed due to hybridization of two counter-propagating edge states with
opposite spin polarization. Conduction through DWs is found to be symmetric
under magnetic field direction reversal, consistent with the helical nature of
these DWs. We observe that long domain walls are in the insulating regime with
localization length 4 - 6~$\mu$m. In shorter DWs the resistance saturates to a
non-zero value at low temperatures. Mesoscopic resistance fluctuations in a
magnetic field are investigated. The theoretical model of transport through
impurity states within the gap induced by spin-orbit interactions agrees well
with the experimental data. Helical DWs have required symmetry for the
formation of synthetic p-wave superconductors. Achieved electrostatic control
of a single helical domain wall is a milestone on the path to their
reconfigurable network and ultimately to a demonstration of braiding of
non-Abelian excitations.",1702.03279v2
2017-06-30,Dy doped BiFeO$_3$ : A Bulk Ceramic with Improved Multiferroic Properties Compared to Nano Counterparts,"The synthesis as well as structural, multiferroic and optical
characterization of Dy doped BiFeO$_3$ multiferroic ceramic are presented. Bulk
polycrystalline Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ sample is synthesized by solid
state reaction, while their nano counterparts are prepared using ultrasonic
probe sonication technique. Significant improvement of phase purity in the as
synthesized samples is observed after the doping of Dy both in bulk
Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ sample and corresponding nanoparticles as evidenced
from Rietveld refinement. Magnetization measurements using SQUID magnetometer
exhibit enhanced magnetic properties for Dy doped bulk
Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ ceramic compared to their nanostructured
counterparts as well as undoped BiFeO$_3$. Within the applied field range,
saturation polarization is observed for Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ bulk
ceramic only. As a result, intrinsic ferroelectric behavior is obtained just
for this sample. Optical bandgap measurements reveal lower bandgap for Dy doped
bulk Bi$_{0.9}$Dy$_{0.1}$FeO$_3$ ceramic compared to that of corresponding
nanoparticles and undoped BiFeO$_3$. The outcome of this investigation
demonstrates the potential of Dy as a doping element in BiFeO$_3$ that provides
a bulk ceramic material with improved multiferroic and optical properties
compared to those of corresponding nanoparticles which involve rigorous
synthesis procedure.",1706.10226v1
2017-07-07,Solar plasma radio emission in the presence of imbalanced turbulence of kinetic-scale Alfvén waves,"We study the influence of kinetic-scale Alfv\'enic turbulence on the
generation of plasma radio emission in the solar coronal regions where the
plasma/magnetic pressure ratio $\beta $ is smaller than the electron/ion mass
ratio $m_{e}/m_{i}$. The present study is motivated by the phenomenon of solar
type I radio storms associated with the strong magnetic field of active
regions. The measured brightness temperature of the type I storms can be up to
$10^{10}$ K for continuum emission, and can exceed $10^{11}$ K for type I
bursts. At present, there is no generally accepted theory explaining such high
brightness temperatures and some other properties of the type I storms. We
propose the model with the imbalanced turbulence of kinetic-scale Alfv\'en
waves producing an asymmetric quasilinear plateau on the upward half of the
electron velocity distribution. The Landau damping of resonant Langmuir waves
is suppressed and their amplitudes grow spontaneously above the thermal level.
The estimated saturation level of Langmuir waves is high enough to generate
observed type I radio emission at the fundamental plasma frequency. Harmonic
emission does not appear in our model because the backward-propagating Langmuir
waves undergo a strong Landau damping. Our model predicts $100\%$ polarization
in the sense of the ordinary (o-) mode of type I emission.",1707.02295v1
2017-07-27,Electron spin resonance for the detection of long-range spin nematic order,"In this paper we propose that electron spin resonance (ESR) measurements
enable us to detect the long-range spin nematic order. We show that the
frequency of the paramagnetic resonance peak in the ESR spectrum is shifted by
the ferroquadrupolar order parameter together with other quantities. The
ferroquadrupolar order parameter is extractable from the angular dependence of
the frequency shift. In contrast, the antiferroquadrupolar order parameter is
usually invisible in the frequency shift. Instead, the long-range
antiferroquadrupolar order yields a characteristic resonance peak in the ESR
spectrum, which we call a magnon-pair resonance peak. This resonance
corresponds to the excitation of the bound magnon pair at the wave vector $\bm
k={\bm 0}$. Reflecting the condensation of bound magnon pairs, the field
dependence of the magnon-pair resonance frequency shows a singular upturn at
the saturation field. Moreover, the intensity of the magnon-pair resonance peak
shows a characteristic angular dependence and it vanishes when the magnetic
field is parallel to one of the axes that diagonalize the weak anisotropic
interactions. We confirm these general properties of the magnon-pair resonance
peak in the spin nematic phase by studying an $S=1$ bilinear-biquadratic model
on the square lattice in the linear flavor-wave approximation. In addition, we
argue applications to the $S=1/2$ frustrated ferromagnets and also the $S=1/2$
orthogonal dimer spin system SrCu$_2$(BO$_3$)$_2$, both of which are candidate
materials of spin nematics. Our theory for the antiferroquadrupolar ordered
phase is consistent with many features of the magnon-pair resonance peak
experimentally observed in the low-magnetization regime of
SrCu$_2$(BO$_3$)$_2$.",1707.08784v2
2017-08-16,"Role of pinning mechanism in co-precipitation derived cobalt rich, cobalt ferrite nanoparticles","Cobalt ferrite nanoparticles have been synthesized using a co-precipitation
approach. Co:Fe precursor ratio is varied over a certain window (1.05 to 1.2).
It is observed that the 1.15:2 precursor ratio gives better phase control but
poor coercivity. On the other hand, 1.05:2 precursor ratio results in
substantially better coercivity values (274kA/m; almost 300% the value reported
for co-precipitated cobalt ferrite by Praveena et al.), but moderate BH product
maximum (2.25 kJ/m3; ~ comparable to many reports on cobalt ferrite
nanoparticles so far). The nanoparticles with best coercivity are annealed at
873K for varying durations (2, 4, 6, 12 hrs). It is observed that the
coercivity drops drastically (almost by 80%) after annealing for 2 hours.
However thereafter coercivity and saturation magnetization improves marginally
with increasing duration of annealing. These studies, along with
thermogravimetric analysis, and infrared spectroscopic results indicate that a
hydroxide nanophase based flux pinning mechanism at the grain boundary plays an
important role in explaining the observed magnetic property trends. It is
believed that this result will be generically helpful in developing soft
chemically derived ferrites with higher coercivity and moderate (BH)max.
However to develop plausible applications using the reported ferrites that use
nanophase flux pinning, soft materials and device processing methods will need
to be explored.",1708.04839v1
2017-09-04,Extended Phase Graph formalism for systems with Magnetization Transfer and Chemical Exchange,"An Extended Phase Graph framework for modelling systems with exchange or
magnetization transfer (MT) is proposed. The framework, referred to as EPG-X,
models coupled two-compartment systems by describing each compartment with
separate phase graphs that exchange during evolution periods. There are two
variants: EPG-X(BM) for systems governed by the Bloch-McConnell equations; and
EPG-X(MT) for the pulsed MT formalism. For the MT case the ""bound"" protons have
no transverse components so their phase graph consists only longitudinal
states. EPG-X was used to model steady-state gradient echo imaging, MT effects
in multislice Turbo Spin Echo imaging, multiecho CPMG for multicomponent T2
relaxometry and transient variable flip angle gradient echo imaging of the type
used for MR Fingerprinting. Experimental data were also collected for the final
case. Steady-state predictions from EPG-X closely match directly derived
steady-state solutions which differ substantially from classic ""single pool""
EPG predictions. EPG-X(MT) predicts similar MT related levels of signal
attenuation in white matter as have been reported elsewhere in the literature.
Modelling of CPMG echo trains with EPG-X(BM) suggests that exchange processes
can lead to an underestimate of the fraction of short T2 species. Modelling of
transient gradient echo sequences with EPG-X(MT) suggests that measurable MT
effects result from variable saturation of bound protons, particularly after
inversion pulses. In conclusion, EPG-X can be used for modelling of the
transient signal response of systems exhibiting chemical exchange or MT. This
may be particularly beneficial for relaxometry approaches that rely on
characterising transient rather than steady-state sequences.",1709.00832v1
2017-09-30,Dimensional crossover and incipient quantum size effects in superconducting niobium nanofilms,"Superconducting and normal state properties of sputtered Niobium nanofilms
have been systematically investigated, as a function of film thickness in a
d=9-90 nm range, on different substrates. The width of the
superconducting-to-normal transition for all films remained in few tens of mK,
thus remarkably narrow, confirming their high quality. We found that the
superconducting critical current density exhibits a pronounced maximum, three
times larger than its bulk value, for film thickness around 25 nm, marking the
3D-to-2D crossover. The extracted magnetic penetration depth shows a sizeable
enhancement for the thinnest films, aside the usual demagnetization effects.
Additional amplification effects of the superconducting properties have been
obtained in the case of sapphire substrates or squeezing the lateral size of
the nanofilms. For thickness close to 20 nm we also measured a doubled
perpendicular critical magnetic field compared to its saturation value for d>33
nm, indicating shortening of the correlation length and the formation of small
Cooper pairs in the condensate. Our data analysis evidences an exciting
interplay between quantum-size and proximity effects together with
strong-coupling effects and importance of disorder in the thinnest films,
locating the ones with optimally enhanced critical properties close to the
BCS-BEC crossover regime.",1710.00265v1
2017-10-06,3d Transition Metals and Oxides within Carbon Nanotubes by Co-Pyrolysis of Metallocene & Camphor: High Filling Efficiency and Self-Organized Structures,"We demonstrate that a single zone furnace with a modified synthesis chamber
design is sufficient to obtain metal (Fe, Co or Ni) filled carbon nanotubes
(CNT) with high filling efficiency and controlled morphology. Samples are
formed by pyrolysis of metallocenes, a synthesis technique that otherwise
requires a dual zone furnace. Respective metallocene in all three cases are
sublimed in powder form, a crucial factor for obtaining high filling
efficiency. While Fe@CNT is routinely produced using this technique,
well-formed Ni@CNT or Co@CNT samples are reported for the first time. This is
achieved by sublimation of nickelocene (or cobaltocene) in combination with
'camphor'. These samples exhibit some of the highest saturation magnetization
(Ms) values, at least an order of magnitude higher than that reported for Ni or
Co filled CNT, by aerosol assisted pyrolysis. The results also elucidate on why
Ni or Co@CNT are relatively difficult to obtain by pyrolyzing powder
metallocene alone. Overall, a systematic variation of synthesis parameters
provides insights for obtaining narrow length and diameter distribution and
reduced residue particles outside filled CNT - factors which are important for
device related applications. Finally, the utility of this technique is
demonstrated by obtaining highly aligned forest of Fe2O3@CNT, wherein Fe2O3 is
a functional magnetic oxide relevant to spintronics and battery applications.",1710.02413v1
2017-12-24,The screening effects on field enhancement factor of zigzag graphene nanoribbon arrays: A first-principles study,"The field screening effect on the electronic and field-emission properties of
zigzag graphene nanoribbons (ZGNRs) has been studied using first-principles
calculations. We have systematically investigated the effect of inter-ribbon
distance and ribbon width on the work function, field enhancement factor, band
gap and edge magnetism of zigzag graphene nanoribbons (ZGNRs). It is found that
the work function of ZGNRs increases rapidly as the inter-ribbon distance Dx
increases, which is caused by the positive dipole at the edge of the ribbon.
For a given Dx, the work function of ZGNRs decreases as the ribbon width W
increases. The wider the width of ribbon, the stronger the effect of
inter-ribbon distance on the work function. Using a simple linear interpolation
model, we can obtain the work function of ZGNR of any ribbon-width. For the
case of Dx < W, the field enhancement factor increases rapidly as the
inter-ribbon distance increases. As we further increase Dx, the enhancement
factor increases slowly and then tends toward saturation. The inter-ribbon
distance of ZGNRs can modulate the magnitude of the band gap and edge
magnetism. These observations above can all be explained by the screening
effect.",1712.08935v1
2018-02-02,Full- & Reduced-Order State-Space Modeling of Wind Turbine Systems with Permanent-Magnet Synchronous Generator,"Wind energy is an integral part of nowadays energy supply and one of the
fastest growing sources of electricity in the world today. Accurate models for
wind energy conversion systems (WECSs) are of key interest for the analysis and
control design of present and future energy systems. Existing control-oriented
WECSs models are subject to unstructured simplifications, which have not been
discussed in literature so far. Thus, this technical note presents are thorough
derivation of a physical state-space model for permanent magnet synchronous
generator WECSs. The physical model considers all dynamic effects that
significantly influence the system's power output, including the switching of
the power electronics. Alternatively, the model is formulated in the $(a,b,c)$-
and $(d,q)$-reference frame. Secondly, a complete control and operation
management system for the wind regimes II and III and the transition between
the regimes is presented. The control takes practical effects such as input
saturation and integral windup into account. Thirdly, by a structured model
reduction procedure, two state-space models of WECS with reduced complexity are
derived: a non-switching model and a non-switching reduced-order model. The
validity of the models is illustrated and compared through a numerical
simulation study.",1802.00799v1
2018-03-23,Dissipative structures in magnetorotational turbulence,"Via the process of accretion, magnetorotational turbulence removes energy
from a disk's orbital motion and transforms it into heat. Turbulent heating is
far from uniform and is usually concentrated in small regions of intense
dissipation, characterised by abrupt magnetic reconnection and higher
temperatures. These regions are of interest because they might generate
non-thermal emission, in the form of flares and energetic particles, or
thermally process solids in protoplanetary disks. Moreover, the nature of the
dissipation bears on the fundamental dynamics of the magnetorotational
instability (MRI) itself: local simulations indicate that the large-scale
properties of the turbulence (e.g. saturation levels, the stress-pressure
relationship) depend on the short dissipative scales. In this paper we
undertake a numerical study of how the MRI dissipates and the small-scale
dissipative structures it employs to do so. We use the Godunov code RAMSES and
unstratified compressible shearing boxes. Our simulations reveal that
dissipation is concentrated in ribbons of strong magnetic reconnection that are
significantly elongated in azimuth, up to a scale height. Dissipative
structures are hence meso-scale objects, and potentially provide a route by
which large scales and small scales interact. We go on to show how these
ribbons evolve over time --- forming, merging, breaking apart, and
disappearing. Finally, we reveal important couplings between the large-scale
density waves generated by the MRI and the small-scale structures, which may
illuminate the stress-pressure relationship in MRI turbulence.",1803.08757v1
2018-04-13,Tuning Spin Dynamics and Localization Near the Metal-Insulator Transition in Fe/GaAs heterostructures,"We present a simultaneous investigation of coherent spin dynamics in both
localized and itinerant carriers in Fe/GaAs heterostructures using ultrafast
and spin-resolved pump-probe spectroscopy. We find that for excitation
densities that push the transient Fermi energy of photocarriers above the
mobility edge there exist two distinct precession frequencies in the ob-served
spin dynamics, allowing us to simultaneously monitor both localized and
itinerant states. For low magnetic fields (below 3 T) the beat frequency
between these two excitations evolves linearly, indicating that the nuclear
polarization is saturated almost immediately and that the hyperfine coupling to
these two states is comparable, despite the 100x enhancement in nuclear
polarization provided by the presence of the Fe layer. At higher magnetic
fields (above 3 T) the Zeeman energy drives reentrant localization of the
photocarriers. Subtracting the constant hyperfine contribution from both sets
of data allows us to extract the Lande g-factor for each state and estimate
their energy relative to the bottom of the conduction band, yielding -2.16 meV
and 17 meV for localized and itinerant states, respectively. This work advances
our fundamental understanding of spin-spin interactions between electron and
nuclear spin species, as well as between localized and itinerant electronics
states, and therefore has implications for future work in both spintronics and
quantum information/computation.",1804.04761v1
2018-06-11,Electric-field quenching of optically detected magnetic resonance in a $π$-conjugated polymer,"Electric fields are central to the operation of optoelectronic devices based
on conjugated polymers since they drive the recombination of electrons and
holes to excitons in organic light-emitting diodes but are also responsible for
the dissociation of excitons in solar cells. One way to track the microscopic
effect of electric fields on charge carriers formed under illumination of a
polymer film is to exploit the fluorescence arising from delayed recombination
of carrier pairs, a process which is fundamentally spin dependent. Such
spin-dependent recombination can be probed directly in fluorescence, by
optically detected magnetic resonance (ODMR). Depending on the relative
orientation, an electric field may either dissociate or stabilize an
electron-hole carrier pair. We find that the ODMR signal in a polymer film is
quenched in an electric field, but that, at fields exceeding 1 MV/cm, this
quenching saturates. This finding contrasts the complete ODMR suppression that
was previously observed in polymeric photodiodes, indicating that
exciton-charge interactions---analogous to Auger recombination in crystalline
semiconductors---may constitute the dominant carrier-pair dissociation process
in organic electronics.",1806.03805v1
2018-09-24,Simulations of radiative turbulent mixing layers,"Radiative turbulent mixing layers should be ubiquitous in multi-phase gas
with shear flow. They are a potentially attractive explanation for the high
ions such as OVI seen in high velocity clouds and the circumgalactic medium
(CGM) of galaxies. We perform 3D MHD simulations with non-equilibrium (NEI) and
photoionization modeling, with an eye towards testing simple analytic models.
Even purely hydrodynamic collisional ionization equilibrium (CIE) calculations
have column densities much lower than observations. Characteristic inflow and
turbulent velocities are much less than the shear velocity, and the layer width
$h \propto t_\mathrm{cool}^{1/2}$ rather than $h \propto t_\mathrm{cool}$.
Column densities are not independent of density or metallicity as analytic
scalings predict, and show surprisingly weak dependence on shear velocity and
density contrast. Radiative cooling, rather than Kelvin-Helmholtz instability,
appears paramount in determining the saturated state. Low pressure due to fast
cooling both seeds turbulence and sets the entrainment rate of hot gas, whose
enthalpy flux, along with turbulent dissipation, energizes the layer.
Regardless of initial geometry, magnetic fields are amplified and stabilize the
mixing layer via magnetic tension, producing almost laminar flow and depressing
column densities. NEI effects can boost column densities by factors of a few.
Suppression of cooling by NEI or photoionization can in principle also increase
OVI column densities, but in practice is unimportant for CGM conditions. To
explain observations, sightlines must pierce hundreds or thousands of mixing
layers, which may be plausible if the CGM exists as a `fog' of tiny cloudlets.",1809.09101v2
2018-09-24,"The failure of stellar feedback, magnetic fields, conduction, and morphological quenching in maintaining red galaxies","The quenching ""maintenance'"" and related ""cooling flow"" problems are
important in galaxies from Milky Way mass through clusters. We investigate this
in halos with masses $\sim 10^{12}-10^{14}\,{\rm M}_{\odot}$, using
non-cosmological high-resolution hydrodynamic simulations with the FIRE-2
(Feedback In Realistic Environments) stellar feedback model. We specifically
focus on physics present without AGN, and show that various proposed ""non-AGN""
solution mechanisms in the literature, including Type Ia supernovae, shocked
AGB winds, other forms of stellar feedback (e.g. cosmic rays), magnetic fields,
Spitzer-Braginskii conduction, or ""morphological quenching"" do not halt or
substantially reduce cooling flows nor maintain ""quenched"" galaxies in this
mass range. We show that stellar feedback (including cosmic rays from SNe)
alters the balance of cold/warm gas and the rate at which the cooled gas within
the galaxy turns into stars, but not the net baryonic inflow. If anything,
outflowing metals and dense gas promote additional cooling. Conduction is
important only in the most massive halos, as expected, but even at $\sim
10^{14}\,{\rm M}_{\odot}$ reduces inflow only by a factor $\sim 2$ (owing to
saturation effects and anisotropic suppression). Changing the morphology of the
galaxies only slightly alters their Toomre-$Q$ parameter, and has no effect on
cooling (as expected), so has essentially no effect on cooling flows or
maintaining quenching. This all supports the idea that additional physics,
e.g., AGN feedback, must be important in massive galaxies.",1809.09120v1
2018-10-21,String orders in the Luttinger liquid phase of one-dimensional spin-1/2 systems,"Luttinger liquid (LL) phase refers to a quantum phase which emerges in the
ground state phase diagram of quite often low-dimensional quantum magnets as
spin-1/2 XX, XYY and frustrated chains. It is believed that the quasi
long-range order exists between particles forming the system in the LL phase.
Here, at the first step we concentrate on the study of correlated spin
particles in the one-dimensional (1D) spin-1/2 XX model which is exactly
solvable. We show that the spin-1/2 particles form string orders with an even
number of spins in the LL phase of the 1D spin-1/2 XX model. As soon as the
transverse magnetic field is applied to the system, string orders with an odd
number of spins induce in the LL phase. All ordered strings of spin-1/2
particles will be destroyed at the quantum critical transverse field, $h_c$. No
strings exist in the saturated ferromagnetic phase. At the second step we focus
on the LL phase in the ground state phase diagram of the 1D spin-1/2 XYY and
frustrated ferromagnetic models. We show that the even-string orders exist in
the LL phase of the 1D spin-1/2 XYY model but in the LL phase of the 1D
spin-1/2 frustrated ferromagnetic model we found all kind of strings. In
addition, the existence of a clear relation between the long-distance
entanglement and string orders in the LL phase is shown. Also, the effect of
the thermal fluctuations on the behavior of the string orders is studied.",1810.08903v1
2018-11-05,"Avoiding the $H_c=0$ anomaly using FORC+ (expanded version of paper GG-05, MMM-Intermag 2019)","In conventional FORC (First Order Reversal Curve) analysis of a magnetic
system, reversible and low-coercivity irreversible materials are treated as
being qualitatively different: the FORC distribution shows low-coercivity
materials but completely hides reversible (zero-coercivity) ones. This
distinction is artificial -- as the coercivity approaches zero, the physical
properties of an irreversible material change smoothly into those of a
reversible material. We have developed a method (called FORC+, implemented in
free software at http://MagVis.org) for displaying the reversible properties of
a system (a reversible switching-field distribution, R-SFD) together with the
irreversible ones (the usual FORC distribution), so that there is no sudden
discontinuity in the display when the coercivity becomes zero. We will define a
""FORC+ dataset"" to include the usual FORC distribution, the R-SFD, the
saturation magnetization, and what we will call the ""lost hysteron
distribution"" (LHD) such that no information is lost -- the original FORC
curves can be exactly recovered from the FORC+ dataset. We also give some
examples of the application of FORC+ to real data -- it uses a novel
complementary-color display that minimizes the need for smoothing. In systems
which switch suddenly (thus having sharp structures in the FORC distribution)
direct display of un-smoothed raw data allows visualization of sharp structures
that would be washed out in a conventional smoothed FORC display. This is an
expanded version of paper GG-05, MMM-Intermag 2019, with a discrete derivation
of the FORC distribution (Eq. 1) and an additional example (Fig. 7).",1811.02080v1
2018-11-21,The Rotationally Modulated Polarization of $ξ$ Boo A,"We have observed the active star $\xi$ Boo A (HD 131156A) with high precision
broadband linear polarimetry contemporaneously with circular
spectropolarimetry. We find both signals are modulated by the 6.43 day rotation
period of $\xi$ Boo A. The signals from the two techniques are 0.25 out of
phase, consistent with the broadband linear polarization resulting from
differential saturation of spectral lines in the global transverse magnetic
field. The mean magnitude of the linear polarization signal is ~4 ppm/G but its
structure is complex and the amplitude of the variations suppressed relative to
the longitudinal magnetic field. The result has important implications for
current attempts to detect polarized light from hot Jupiters orbiting active
stars in the combined light of the star and planet. In such work stellar
activity will manifest as noise, both on the time scale of stellar rotation,
and on longer time scales - where changes in activity level will manifest as a
baseline shift between observing runs.",1811.08534v2
2018-12-16,Magnetic field effects on one-dimensional Anderson localization of light,"Transport of coherent waves in multiple-scattering media may exhibit
fundamental, non intuitive phenomena such as halt of diffusion by disorder
called Anderson localization. For electromagnetic waves, this phenomenon was
observed only in one and two dimensions so far. However, none of these
experiments studied the contribution of reciprocal paths nor their manipulation
by external fields. In order to weaken the effect of reciprocity of coherent
wave transport on Anderson localization in one dimension (1D), we studied light
propagation through stacks of parallel Faraday-active glass slides exposed to
magnetic fields up to 18 Tesla. Measurements of light transmission statistics
are presented and compared to 1D transfer-matrix simulations. The latter
reveals a self-organization of the polarization states in this system leading
to a saturation of the Faraday rotation-induced reciprocity breaking, an
increase of the localization length, and a decrease of transmission
fluctuations when reciprocity is broken. This is confirmed experimentally for
samples containing small numbers of slides while for larger samples a crossover
from a 1D to a quasi-1D transport regime is found.",1812.06447v3
2019-01-03,Self-dual solitons in a generalized Chern-Simons baby Skyrme model,"We have shown the existence of self-dual solitons in a type of generalized
Chern-Simons baby Skyrme model where the generalized function (depending only
in the Skyrme field) is coupled to the sigma-model term. The consistent
implementation of the Bogomol'nyi-Prasad-Sommerfield (BPS) formalism requires
the generalizing function becomes the superpotential defining properly the
self-dual potential. Thus, we have obtained a topological energy lower-bound
(Bogomol'nyi bound) and the self-dual equations satisfied by the fields
saturating such a bound. The Bogomol'nyi bound being proportional to the
topological charge of the Skyrme field is quantized whereas the total magnetic
flux is not. Such as expected in a Chern-Simons model the total magnetic flux
and the total electrical charge are proportional to each other. Thus, by
considering the superpotential a well-behaved function in the whole target
space we have shown the existence of three types of self-dual solutions:
compacton solitons, soliton solutions whose tail decays following an
exponential-law $e^{-\alpha r^{2}}$ ($\alpha>0$), and solitons having a
power-law decay $r^{-\beta}$ ($\beta>0$). The profiles of the two last solitons
can exhibit a compactonlike behavior. The self-dual equations have been solved
numerically and we have depicted the soliton profiles, commenting on the main
characteristics exhibited by them.",1901.00655v2
2019-01-21,Dust Polarization Maps from TIGRESS: E/B power asymmetry and TE correlation,"We present the first large set of all-sky synthetic dust polarization maps
derived directly from a self-consistent magnetohydrodynamics simulation using
the TIGRESS framework. Turbulence in this simulation is predominantly driven by
supernova explosions, with rates that are self-consistently regulated by
feedback loops. The simulation covers both the outer scale and inertial range
of turbulence with uniformly high resolution. The shearing-box utilized in the
simulation in concert with resolved supernova-driven turbulence enables to
capture the generation, growth, and saturation of both turbulent and mean
magnetic fields. We construct polarization maps at 353 GHz as seen by observers
inside a model of the multiphase, turbulent, magnetized interstellar medium
(ISM). To fully sample the simulated ISM state, we use 350 snapshots spanning
over ~350Myr (more than six feedback loops) and nine representative observers.
The synthetic skies show a prevalent E/B power asymmetry (EE>BB) and positive
TE correlation in broad agreement with observations by the Planck satellite.
However, the ranges of EE/BB~1.4-1.7 and TE/(TT*EE)^{1/2}~0.2-0.3 are generally
lower. We find large fluctuations of E/B asymmetry and TE correlation depending
on the observer's position, and temporal fluctuations of interstellar medium
properties due to bursts of star formation. The synthetic maps are made
publicly available to provide novel models of the microwave sky.",1901.07079v2
2019-03-05,Cubic symmetry and magnetic frustration on the $fcc$ spin lattice in K$_2$IrCl$_6$,"Cubic crystal structure and regular octahedral environment of Ir$^{4+}$
render antifluorite-type K$_2$IrCl$_6$ a model fcc antiferromagnet with a
combination of Heisenberg and Kitaev exchange interactions. High-resolution
synchrotron powder diffraction confirms cubic symmetry down to at least 20 K,
with a low-energy rotary mode gradually suppressed upon cooling. Using
thermodynamic and transport measurements, we estimate the activation energy of
$\Delta\simeq 0.7$ eV for charge transport, the antiferromagnetic Curie-Weiss
temperature of $\theta_{\rm CW}\simeq -43$ K, and the extrapolated saturation
field of $H_s\simeq 87$ T. All these parameters are well reproduced \textit{ab
initio} using $U_{\rm eff}=2.2$ eV as the effective Coulomb repulsion
parameter. The antiferromagnetic Kitaev exchange term of $K\simeq 5$ K is about
one half of the Heisenberg term $J\simeq 13$ K. While this combination removes
a large part of the classical ground-state degeneracy, the selection of the
unique magnetic ground state additionally requires a weak second-neighbor
exchange coupling $J_2\simeq 0.2$ K. Our results suggest that K$_2$IrCl$_6$ may
offer the best possible cubic conditions for Ir$^{4+}$ and demonstrates the
interplay of geometrical and exchange frustration in a high-symmetry setting.",1903.01660v2
2019-03-22,Effects of post-deposition annealing on the structure and magnetization of PLD grown Yttrium Iron Garnet films,"We report on the recrystallization of 200 nm thick as-grown Yttrium Iron
Garnet (Y_3.4 Fe_4.6 O_12) films on (111) face of Gadolinium Gallium Garnet
(GGG) single crystals by post-deposition annealing. Epitaxial conversion of the
as-grown microcrystalline YIG films was seen after annealing at 800oC for more
than 30 minutes both in ambient oxygen as well as in air. The as-grown oxygen
annealed samples at 800oC for 60 minutes crystallize epitaxially and show
excellent figure-of-merit for saturation magnetization (MS = 3.3 {\mu}B/f.u.,
comparable to bulk value) and coercivity (HC ~ 1.1 Oe). The ambient air
annealing at 800oC with a very slow rate of cooling (2oC/min) results in a
double layer structure with a thicker unstrained epitaxial top layer having the
MS and HC of 2.9 {\mu}B/f.u. and 0.12 Oe respectively. The symmetric and
asymmetric Reciprocal space maps of both the samples reveal a locking of the
in-plane lattice of the film to the in-plane lattice of substrate, indicating a
pseudomorphic growth. The residual stress calculated by sin^2 {\psi} technique
is compressive in nature. The lower layer in air annealed sample is highly
strained, whereas, the top layer has negligible compressive stress.",1903.09457v1
2019-03-19,Two-dimensional Magnetization-Transfer - CPMG MRI reveals tract- specific signatures in fixed rat spinal cord,"Multiexponential T2 (MET2) Relaxometry and Magnetization Transfer (MT) are
among the most promising MRI-derived techniques for white matter (WM)
characterization. Both techniques are shown to have histologically correlated
sensitivity to myelin, but these correlations are not fully understood.
Furthermore, MET2 and MT reports on different features of WM, thus being
specific to different (patho)physiological states. Two-dimensional studies,
such as those commonly used in NMR, have been rarely performed in this context.
Here, off-resonance irradiation effects on MET2 components were evaluated in
fixed rat spinal cord white matter at 16.4T. These 2D MT-MET2 experiments
reveal that MT affects both short and long T2 in a tract-specific fashion. The
spatially distinct modulations enhanced contrast between
microstructurally-distinct spinal cord tracts. Two hypotheses to explain these
findings were proposed: either selective elimination of a short T2 component
through pre-saturation is combined with intercompartmental water exchange
effects that occur on the timescale of irradiation; or other macromolecular
species that exist within the tissue - other than myelin - such as
neurofilaments, may be involved in the apparent microstructural segregation of
the spinal cord (SC) from MET2. Though further investigation is required to
elucidate the underlying mechanism, this phenomenon adds a new dimension for WM
characterization.",1903.10376v1
2019-04-10,Magnetohydrodynamics in a Cylindrical Shearing Box,"We develop a framework for magnetohydrodynamical (MHD) simulations in a local
cylindrical shearing box by extending the formulation of the Cartesian shearing
box. We construct shearing-periodic conditions at the radial boundaries of a
simulation box from the conservation relations of the basic MHD equations,
taking into account the explicit radial dependence of physical quantities. We
demonstrate quasi-steady mass accretion, which cannot be handled by the
standard Cartesian shearing box model, with an ideal MHD simulation in a
vertically unstratified cylindrical shearing box up to 200 rotations. In this
demonstrative run we set up (i) net vertical magnetic flux, (ii) a locally
isothermal equation of state, and (iii) a sub-Keplerian equilibrium rotation,
whereas the sound velocity and the initial Alfven velocity have the same radial
dependence as that of the Keplerian velocity. Inward mass accretion is induced
to balance with the outward angular momentum flux of the MHD turbulence
triggered by the magnetorotational instability in a self-consistent manner. We
discuss detailed physical properties of the saturated magnetic field, in
comparison to the results of a Cartesian shearing box simulation.",1904.05032v3
2019-08-20,"Peculiarities in pseudo-transitions of a mixed spin-$(1/2,1)$ Ising-Heisenberg double-tetrahedral chain in an external magnetic field","Recently, it has been rigorously verified that several one-dimensional (1D)
spin models may exhibit a peculiar pseudo-transition accompanied with anomalous
response of thermodynamic quantities in a close vicinity of pseudo-critical
temperature. In the present work we will introduce and exactly solve a mixed
spin-(1/2,1) Ising-Heisenberg double-tetrahedral chain in an external magnetic
field as another particular example of 1D lattice-statistical model with
short-range interactions that displays a pseudo-transition of this type. The
investigated model exhibits at zero temperature three ferrimagnetic phases,
three frustrated phases, and one saturated paramagnetic phase. The ground-state
phase diagram involves five unusual interfaces (phase boundaries), at which the
residual entropy per site equals to a larger entropy of one of two coexisting
phases. Four such interfaces are between a non-degenerate ferrimagnetic phase
and a macroscopically degenerate frustrated phase, while one interface is
between two non-degenerate ferrimagnetic phases. Though thermal excitations
typically destroy all fingerprints of zero-temperature phase transitions of 1D
lattice-statistical models with short-range forces, the mixed spin-(1/2,1)
Ising-Heisenberg double-tetrahedral chain is quite robust with respect to
thermal excitations and it displays peculiar pseudo-transitions close to all
five aforementioned interfaces.",1908.07286v2
2019-10-06,Self-dual solitons in a Maxwell-Chern-Simons baby Skyrme model,"We have studied the existence de self-dual solitons in a gauged version of
the baby Skyrme model in which the gauge field dynamics is governed by the
Maxwell-Chern-Simons action. For such a purpose, we have developed a detailed
implementation of the Bogomol'nyi-Prasad-Sommerfield formalism providing the
self-dual equations whose solutions saturate the energy lower bound. Such a
bound related to the topological charge of the Skyrme field becomes quantized
whereas both the total magnetic flux and the total electrical charge are not.
We have found two types of self-dual Skyrme field profiles: the first is
described by a solution which decays following an exponential-law ($e^{-\alpha
r^2}$, $\alpha>0$); the second is portrayed by a solution having a power-law
decay ($r^{-\beta}$, $\beta>0$). On other hand, in both cases the asymptotic
behavior of the gauge field is similar to the one presented in the context of
the Abelian Higgs models describing Abrikosov-Nielsen-Olesen charged vortices.
Other interesting feature we highlight is the localized magnetic flux
inversion, a property does not observed in others gauged baby Skyrme models
already studied in literature. Numerical results are presented for rotationally
symmetrical field configurations by remarking some of its essential features.",1910.02362v1
2019-10-18,A substantial increase of Curie temperature in a new type of diluted magnetic semiconductors via effects of chemical pressure,"Chemical pressure is an effective method to tune physical properties,
particularly for diluted magnetic semiconductors (DMS) of which ferromagnetic
ordering is mediated by charge carriers. Via substitution of smaller Ca for
larger Sr, we introduce chemical pressure on (Sr,Na)(Cd,Mn)2As2 to fabricate a
new DMS material (Ca,Na)(Cd,Mn)2As2. Carriers and spins are introduced by
substitutions of (Ca,Na) and (Cd,Mn) respectively. The unit cell volume reduces
by 6.2% after complete substitution of Ca for Sr, suggesting a subsistent
chemical pressure. Importantly the local geometry of [Cd/MnAs4] tetrahedron is
optimized via chemical compression that increases the Mn-As hybridization
leading to enhanced ferromagnetic interactions. As a result, the maximum Curie
temperature (TC) is increased by about 50% while the the maximum saturation
moment increases by over 100% from (Sr,Na)(Cd,Mn)2As2 to (Ca,Na)(Cd,Mn)2As2.
The chemical pressure estimated from the equation of state is equal to an
external physical pressure of 3.6 GPa.",1910.08305v2
2019-11-27,Data-Driven Recursive Least Squares Estimation for Model Predictive Current Control of Permanent Magnet Synchronous Motors,"The performance of model predictive controllers (MPC) strongly depends on the
model quality. In the field of electric drive control, white-box (WB) modeling
approaches derived from first-order physical principles are most common. This
procedure typically does not cover parasitic effects and parameter deviations
are frequent. These issues are particularly crucial in the domain of
self-commissioning drives when a hand-tailored, accurate WB plant model is not
available. In order to compensate for such modeling errors and, therefore, to
improve the control performance during transients and steady-state, this paper
proposes a data-driven, real-time capable recursive least squares (RLS)
estimation method for the current control of a permanent magnet synchronous
motor (PMSM). The effect of the flux linkage and voltage harmonics due to the
winding scheme can also be taken into account. Moreover, a compensating scheme
for the interlocking time of the inverter is proposed. The proposed
identification algorithm is investigated using the well-known
finite-control-set MPC (FCS-MPC) in the rotor-oriented coordinate system. The
extensive experimental results show the superior performance of the presented
scheme compared to a FCS-MPC-based on a state-of-the-art WB motor model using
look-up tables for adressing (cross-)saturation.",1911.12065v1
2019-12-02,The Magnetorotational Instability Prefers Three Dimensions,"The magnetorotational instability (MRI) occurs when a weak magnetic field
destabilises a rotating, electrically conducting fluid with inwardly increasing
angular velocity. The MRI is essential to astrophysical disk theory where the
shear is typically Keplerian. Internal shear layers in stars may also be MRI
unstable, and they take a wide range of profiles, including near-critical. We
show that the fastest growing modes of an ideal magnetofluid are
three-dimensional provided the shear rate, $S$, is near the two-dimensional
onset value, $S_c$. For a Keplerian shear, three-dimensional modes are unstable
above $S\approx0.10S_c$, and dominate the two-dimensional modes until
$S\approx2.05S_{c}$. These three-dimensional modes dominate for shear profiles
relevant to stars and at magnetic Prandtl numbers relevant to liquid-metal
laboratory experiments. Significant numbers of rapidly growing
three-dimensional modes remain well past $2.05S_{c}$. These finding are
significant in three ways. First, weakly nonlinear theory suggests that the MRI
saturates by pushing the shear rate to its critical value. This can happen for
systems, like stars and laboratory experiments, that can rearrange their
angular velocity profiles. Second, the non-normal character and large transient
growth of MRI modes should be important whenever three-dimensionality exists.
Finally, three-dimensional growth suggests direct dynamo action driven from the
linear instability.",1912.00972v1
2019-12-10,F+ Center Exchange Mechanism and Magneto Crystalline Anisotropy in Ni doped 3C-SiC,"We report the experimental evidence in support of room temperature
ferromagnetism in Ni doped 3C-SiC. Curie temperature is found to be > 350 K.
Temperature dependent Electron paramagnetic resonance (EPR) study reveals that
the valence state of Ni is 2+ and its environmental symmetry. A clear shift in
both XRD and Raman peak confirms the incorporation of Ni in the host lattice.
The variation in number of vacancies $V_{\mathrm{Si}}$, $V_{\mathrm{C}}$ and
the number of free electron due to doping is consistent with the change in
magnetization of the system. A direct correlation of ferromagnetic order (FM)
with F+ centers exchange mechanism is established. The temperature variation of
the anisotropic constant was determined using Law of Approach to Saturation
(LAS). It was found that effective magnetic anisotropic constant decreases with
increase in temperature. The EPR line width of the annealed sample increases
with decrease in temperature, whereas the integrated intensity decreases with
decrease in temperature. This could be due to incomplete quenching of orbital
angular momentum in Si$_{x}$Ni$_{1-x}$C. In addition to this, the orbital
degeneracy of fast relaxing impurity such as Ni in the cubic crystal field is
not completely removed. This results in the line width decrease with increase
in temperature.",1912.05921v2
2020-01-03,Synthesis and characterization of Zn doped Mn ferrites nanostructures,"Zn doped Mn ferrites nanoparticles were fabricated by using Co-precipitation.
Variation in structure, magnetic and optical properties of MnZn ferrites has
been discussed. First of all, samples were synthesized, annealed at different
temperatures and then characterized. The as-synthesized and annealed samples
were investigated by X-ray diffraction (XRD), Scanning electron microscopy
(SEM), Energy Dispersive spectroscopy (EDX), Ultra Violet visible spectrometry
(Uv-Vis spectrometry) and Vibrating sample magnetometer (VSM). The average
crystallite size of MnZn ferrites nanoparticles determined from XRD were in the
range of 42 to 60 nm. These nanoparticles possess normal spinel structure. The
SEM images showed the physical shape of the samples, which showed that the as
prepared samples are more agglomerated and having flake like shape rather than
annealed at 700C while the samples have longitudinal or rod like shape on
annealing at 700C. The coercivity (Hc), saturation magnetization (Ms), and
remanence (Mr) of Nps were also calculated. The (Ms) value is increasing from
26 to 65 emu/g, the coercivity (Hc) is varying from 13 to 193 Oe and remanence
(Mr) has also showing increasing trend although very less, from 0.031 to 0.798
emu/g which are a little part of their bulk counter parts. The band gap energy
of the samples was showing decreasing trend as with the increase of particle
size which is of the order of 3.5 to 2.9 eV.",2001.00741v1
2020-03-03,Parabolic diamond scanning probes for single spin magnetic field imaging,"Enhancing the measurement signal from solid state quantum sensors such as the
nitrogen-vacancy (NV) center in diamond is an important problem for sensing and
imaging of condensed matter systems. Here we engineer diamond scanning probes
with a truncated parabolic profile that optimizes the photonic signal from
single embedded NV centers, forming a high-sensitivity probe for nanoscale
magnetic field imaging. We develop a scalable fabrication procedure based on
dry etching with a flowable oxide mask to reliably produce a controlled tip
curvature. The resulting parabolic tip shape yields a median saturation count
rate of 2.1 $\pm$ 0.2 MHz, the highest reported for single NVs in scanning
probes to date. Furthermore, the structures operate across the full NV
photoluminescence spectrum, emitting into a numerical aperture of 0.46 and the
end-facet of the truncated tip, located near the focus of the parabola, allows
for small NV-sample spacings and nanoscale imaging. We demonstrate the
excellent properties of these diamond scanning probes by imaging ferromagnetic
stripes with a spatial resolution better than 50 nm. Our results mark a 5-fold
improvement in measurement signal over the state-of-the art in scanning-probe
based NV sensors.",2003.01733v1
2020-03-19,Common dynamo scaling in slowly rotating young and evolved stars,"One interpretation of the activity and magnetism of late-type stars is that
these both intensify with decreasing Rossby number up to a saturation level,
suggesting that stellar dynamos depend on both rotation and convective
turbulence. Some studies have claimed, however, that rotation alone suffices to
parametrise this scaling adequately. Here, we tackle the question of the
relevance of turbulence to stellar dynamos by including evolved, post main
sequence stars in the analysis of the rotation-activity relation. These stars
rotate very slowly compared with main sequence stars, but exhibit similar
activity levels. We show that the two evolutionary stages fall together in the
rotation-activity diagram and form a single sequence in the unsaturated regime
in relation only to Rossby numbers derived from stellar models, confirming
earlier preliminary results that relied on a more simplistic parametrisation of
the convective turnover time. This mirrors recent results of fully convective M
dwarfs, which likewise fall on the same rotation-activity sequence as partially
convective solar-type stars. Our results demonstrate that turbulence plays a
crucial role in driving stellar dynamos and suggest that there is a common
turbulence-related dynamo mechanism explaining the magnetic activity of all
late-type stars.",2003.08997v1
2020-03-22,Magnetohydrodynamic modelling of star-planet interaction and associated auroral radio emission,"We present calculations of auroral radio powers of magnetised hot Jupiters
orbiting Sun-like stars, computed using global magnetohydrodynamic (MHD)
modelling of the magnetospheric and ionospheric convection arising from the
interaction between the magnetosphere and the stellar wind. Exoplanetary
auroral radio powers are traditionally estimated using empirical or
analytically-derived relations, such as the Radiometric Bode's Law (RBL), which
relates radio power to the magnetic or kinetic energy dissipated in the stellar
wind-planet interaction. Such methods risk an oversimplification of the
magnetospheric electrodynamics giving rise to radio emission. As the next step
toward a self-consistent picture, we model the stellar
wind-magnetosphere-ionosphere coupling currents using a 3D MHD model. We
compute electron-cyclotron maser instability-driven emission from the
calculated ionospheric field-aligned current density. We show that the auroral
radio power is highly sensitive to interplanetary magnetic field (IMF)
strength, and that the emission is saturated for plausible hot Jupiter Pedersen
conductances, indicating that radio power may be largely independent of
ionospheric conductance. We estimate peak radio powers of $10^{14}$ W from a
planet exposed to an IMF strength of $10^3$ nT, implying flux densities at a
distance of 15 pc from Earth potentially detectable with current and future
radio telescopes. We also find a relation between radio power and planetary
orbital distance that is broadly consistent with results from previous analytic
models of magnetosphere-ionosphere coupling at hot Jupiters, and indicates that
the RBL likely overestimates the radio powers by up to two orders of magnitude
in the hot Jupiter regime",2003.09991v1
2020-04-22,Simultaneous Nodal Superconductivity and Time-Reversal Symmetry Breaking in the Noncentrosymmetric Superconductor CaPtAs,"By employing a series of experimental techniques, we provide clear evidence
that CaPtAs represents a rare example of a noncentrosymmetric superconductor
which simultaneously exhibits nodes in the superconducting gap and broken
time-reversal symmetry (TRS) in its superconducting state (below $T_c$
$\approx$ 1.5 K). Unlike in fully-gapped superconductors, the magnetic
penetration depth $\lambda(T)$ does not saturate at low temperatures, but
instead it shows a $T^2$-dependence, characteristic of gap nodes. Both the
superfluid density and the electronic specific heat are best described by a
two-gap model comprising of a nodeless gap and a gap with nodes, rather than by
single-band models. At the same time, zero-field muon-spin spectra exhibit
increased relaxation rates below the onset of superconductivity, implying that
TRS is broken in the superconducting state of CaPtAs, hence indicating its
unconventional nature. Our observations suggest CaPtAs to be a new remarkable
material which links two apparently disparate classes, that of TRS-breaking
correlated magnetic superconductors with nodal gaps and the weakly-correlated
noncentrosymmetric superconductors with broken TRS, normally exhibiting only a
fully-gapped behavior.",2004.10425v1
2020-05-27,Thermodynamic behaviour of magnetocaloric quantities in spin-1/2 Ising square trilayer,"A spin-1/2, Ising trilayered ferrimagnetic system on square Bravais lattice
is studied, employing Monte-Carlo simulation with the single spin-flip
Metropolis algorithm. The bulk of such a system is formed by three layers, each
of which is composed entirely either by A or B type of atoms, resulting in two
distinct compositions: ABA and AAB and two different types of magnetic
interactions: ferromagnetic between like atoms and antiferromagnetic between
unlike atoms. For such systems, Inverse Absolute of Reduced Residual
Magnetisation is the absolute value of the ratio of the extremum of the
magnetisation in between compensation and critical points and the saturation
magnetisation. Variation of relative interaction strengths in the Hamiltonian,
for a range of values, leads to the shift of compensation point and critical
point and changes in the magnitude of Inverse absolute of Reduced Residual
magnetisation. Probable mathematical forms of dependences of the Inverse
absolute of Reduced Residual magnetisation and temperature interval between the
compensation and critical points on controlling parameters were proposed in the
absence of applied magnetic field and have obtained phase diagrams for both
types of configurations from these relations. This alternative description of
the simulated systems may help technologists design magnetocaloric materials
according to desired characteristics.",2005.13509v6
2020-06-25,Dynamics of reversed shear Alfvén eigenmode and energetic particles during current ramp-up,"Hybrid MHD-gyrokinetic code simulations are used to investigate the dynamics
of frequency sweeping reversed shear Alfv\'en eigenmode (RSAE) strongly driven
by energetic particles (EPs) during plasma current ramp-up in a conventional
tokamak configuration. A series of weakly reversed shear equilibria
representing time slices of long timescale MHD equilibrium evolution is
considered, where the self-consistent RSAE-EP resonant interactions on the
short timescale are analyzed in detail. Both linear and nonlinear RSAE dynamics
are shown to be subject to the non-perturbative effect of EPs by maximizing
wave-EP power transfer. In linear stage, EPs induce evident mode structure and
frequency shifts; meanwhile, RSAE saturates by radial decoupling with resonant
EPs due to weak magnetic shear, and gives rise to global EP convective
transport and non-adiabatic frequency chirping. The spatiotemporal scales of
phase space wave-EP interactions are characterized by the perpendicular
wavelength and wave-particle trapping time. The simulations provide insights
into general as well as specific features of RSAE spectra and EP transport from
experimental observations, and illustrate the fundamental physics of wave-EP
resonant interaction with the interplay of magnetic geometry, plasma
non-uniformity and non-perturbative EPs.",2006.14242v1
2020-07-14,Can we trust MHD jump conditions for collisionless shocks?,"When applied to compute the density jump of a shock, the standard
magnetohydrodynamic (MHD) formalism assumes, 1) that all the upstream material
passes downstream, together with the momentum and energy it carries, and 2)
that pressures are isotropic. In a collisionless shock, shock accelerated
particles going back and forth around the front can invalid the first
assumption. In addition, an external magnetic field can sustain stable pressure
anisotropies, invaliding the second assumption. It is therefore unclear whether
the density jump of a collisionless shock fulfils the MHD jump or not.
  Here we try to clarify this issue. A literature review is conducted on 68
articles dealing with Particle-In-Cell simulations of collisionless shocks. We
analyze the factors triggering departure from the MHD density jump and quantify
their influence on $\Delta_{RH}$, the relative departure from the
Rankine-Hugoniot jump. For small departures we propose $\Delta_{RH} = +
\mathcal{O}(10^{-1-3.7\kappa})t^\kappa - \sigma \mathcal{O}(1)$ where $t$ is
the timescale of the simulation, $\sigma$ the magnetization parameter and
$\kappa$ a constant of order unity. The first term stems from the energy
leakage into accelerated particle. The second term stems from the downstream
anisotropy triggered by the field (assuming an isotropic upstream). This
relation allows to assess to which extent a collisionless shock fulfils the RH
density jump.
  In the strong field limit and for parallel shocks, the departure caused by
the field saturates at a finite, negative, value. For perpendicular shocks, the
departure goes to zero at small and high $\sigma$'s so that we find here a
departure window. The results obtained have to be checked against full 3D
simulations.",2007.06906v1
2020-08-03,Wind-MRI interactions in local models of protoplanetary discs: I. Ohmic resistivity,"A magnetic disc wind is an important mechanism that may be responsible for
driving accretion and structure formation in protoplanetary discs. Recent
numerical simulations have shown that these winds can take either the
traditional `hourglass' symmetry about the mid-plane, or a `slanted' symmetry
dominated by a mid-plane toroidal field of a single sign. The formation of this
slanted symmetry state has not previously been explained. We use radially local
1D vertical shearing box simulations to assess the importance of large-scale
MRI channel modes in influencing the formation and morphologies of these wind
solutions. We consider only Ohmic resistivity and explore the effect of
different magnetisations, with the mid-plane $\beta$ parameter ranging from
$10^5$ to $10^2$. We find that our magnetic winds go through three stages of
development: cyclic, transitive and steady, with the steady wind taking a
slanted symmetry profile similar to those observed in local and global
simulations. We show that the cycles are driven by periodic excitation of the
$n=2$ or $3$ MRI channel mode coupled with advective eviction, and that the
transition to the steady wind is caused by a much more slowly growing $n=1$
mode altering the wind structure. Saturation is achieved through a combination
of advective damping from the strong wind, and suppression of the instability
due to a strong toroidal field. A higher disc magnetisation leads to a greater
tendency towards, and more rapid settling into the slanted symmetry steady
wind, which may have important implications for mass and flux transport
processes in protoplanetary discs.",2008.00906v1
2020-10-08,The effects of rotation on the lithium depletion of G- and K-dwarfs in Messier 35,"New fibre spectroscopy and radial velocities from the WIYN telescope are used
to measure photospheric lithium in 242 high-probability, zero-age-main-sequence
(ZAMS) F- to K-type members of the rich cluster M35. Combining these with
published rotation periods, the connection between lithium depletion and
rotation is studied in unprecedented detail. At $T_{\rm eff}<5500$ K there is a
strong relationship between faster rotation and less Li depletion, although
with a dispersion larger than measurement uncertainties. Components of
photometrically identified binary systems follow the same relationship. A
correlation is also established between faster rotation rate (or smaller Rossby
number), decreased Li depletion and larger stellar radius at a given $T_{\rm
eff}$. These results support models where starspots and interior magnetic
fields lead to inflated radii and reduced Li depletion during the pre main
sequence (PMS) phase for the fastest rotators. However, the data are also
consistent with the idea that all stars suffered lower levels of Li depletion
than predicted by standard PMS models, perhaps because of deficiencies in those
models or because saturated levels of magnetic activity suppress Li depletion
equally in PMS stars of similar $T_{\rm eff}$ regardless of rotation rate, and
that slower rotators subsequently experience more mixing and post-PMS Li
depletion.",2010.04217v1
2020-12-05,Levy noise-induced self-induced stochastic resonance in a memristive neuron,"Self-induced stochastic resonance (SISR) is a subtle resonance mechanism
requiring a nontrivial scaling limit between the stochastic and the
deterministic timescales of an excitable system, leading to the emergence of a
limit cycle behavior which is absent without noise. All previous studies on
SISR in neural systems have only considered the idealized Gaussian white noise.
Moreover, these studies have ignored one electrophysiological aspect of the
nerve cell: its memristive properties. In this paper, first, we show that in
the excitable regime, the asymptotic matching of the Levy timescale (that
follows a power law, unlike Gaussian noise that follows Kramers law) and the
deterministic timescale (controlled by the singular parameter) can also induce
a strong SISR. In addition, it is shown that the degree of SISR induced by Levy
noise is not always higher than that of Gaussian noise. Second, we show that,
for both types of noises, the two memristive properties of the neuron have
opposite effects on the degree of SISR: the stronger the feedback gain
parameter that controls the modulation of the membrane potential with the
magnetic flux and the weaker the feedback gain parameter that controls the
saturation of the magnetic flux, the higher the degree of SISR. Finally, we
show that, for both types of noises, the degree of SISR in the memristive
neuron is always higher than in the non-memristive neuron. Our results could
find applications in designing neuromorphic circuits operating in noisy
regimes.",2012.03032v3
2021-01-18,Magnetoelastic properties of a spin-1/2 Ising-Heisenberg diamond chain in vicinity of a triple coexistence point,"We study magnetoelastic properties of a spin-1/2 Ising-Heisenberg diamond
chain, whose elementary unit cell consists of two decorating Heisenberg spins
and one nodal Ising spin. It is assumed that each couple of the decorating
atoms including the Heisenberg spins harmonically vibrates perpendicularly to
the chain axis, while the nodal atoms involving the Ising spins are placed at
rigid positions when ignoring their lattice vibrations. An effect of the
magnetoelastic coupling on a ground state and finite-temperature properties is
particularly investigated close to a triple coexistence point depending on a
spring-stiffness constant ascribed to the Heisenberg interaction. The
magnetoelastic nature of the Heisenberg dimers is reflected through a non-null
plateau of the entropy emergent in a low-temperature region, whereas the
specific heat displays an anomalous peak slightly below the temperature region
corresponding to the entropy plateau. The magnetization also exhibits a plateau
in the same temperature region at almost saturated value before it gradually
tends to zero upon increasing of temperature. The magnetic susceptibility
displays within the plateau region an inverse temperature dependence, which
slightly drops above this plateau, whereas an inverse temperature dependence is
repeatedly recovered at high enough temperatures.",2101.07044v1
2021-03-12,Data-driven low-fidelity models for multi-fidelity Monte Carlo sampling in plasma micro-turbulence analysis,"The linear micro-instabilities driving turbulent transport in magnetized
fusion plasmas (as well as the respective nonlinear saturation mechanisms) are
known to be sensitive with respect to various physical parameters
characterizing the background plasma and the magnetic equilibrium. Therefore,
uncertainty quantification is essential for achieving predictive numerical
simulations of plasma turbulence. However, the high computational costs of the
required gyrokinetic simulations and the large number of parameters render
standard Monte Carlo techniques intractable. To address this problem, we
propose a multi-fidelity Monte Carlo approach in which we employ data-driven
low-fidelity models that exploit the structure of the underlying problem such
as low intrinsic dimension and anisotropic coupling of the stochastic inputs.
The low-fidelity models are efficiently constructed via sensitivity-driven
dimension-adaptive sparse grid interpolation using both the full set of
uncertain inputs and subsets comprising only selected, important parameters. We
illustrate the power of this method by applying it to two plasma turbulence
problems with up to $14$ stochastic parameters, demonstrating that it is up to
four orders of magnitude more efficient than standard Monte Carlo methods
measured in single-core performance, which translates into a runtime reduction
from around eight days to one hour on 240 cores on parallel machines.",2103.07539v2
2021-04-10,ODMR on Single TR12 Centers in Diamond,"Point defects in insulators are considered promising candidates for quantum
technologies. In keeping with this, we present an extensive optically-detected
magnetic resonance (ODMR) study at room-temperature on individual TR12 centers
(ZPL at 471nm), which are known in the literature since 1956. In this work we
found TR12 centers to show a strong ODMR signal under optical saturation. These
observed defects were created in high-purity epitaxial layers of diamond by
standard irradiation and annealing processes. From the analysis of the ODMR
spectra along with antibunching measurements and coherent population trapping,
we proposed the energy level structure of TR12 center, consisting of ground
state and excited state singlets complemented by a metastable triplet in
between. Mapping the fluorescence dependence of the center on an external
magnetic field and on the polarization of laser excitation, allows us to
identify twelve inequivalent orientations for TR12 centers. This includes the
exact orientations of the dipole transition and the triplet axes in the diamond
lattice in full agreement with the results of modeling based on the proposed
level structure. Furthermore, a static Jahn-Teller effect was detected through
fluorescence switching between two levels at low optical excitation power,
directly observable in the real-time fluorescence signal for various
polarization of laser excitation. Based on these results we discuss the
prospects of the TR12 center in diamond for quantum sensing and quantum
information processing.",2104.04746v1
2021-05-06,Investigating lack of accretion disk eccentricity growth in a global 3D MHD simulation of a superhump system,"We present the results of a 3D global magnetohydrodynamic (MHD) simulation of
an AM CVn system that was aimed at exploring eccentricity growth in the
accretion disc self-consistently from a first principles treatment of the MHD
turbulence. No significant eccentricity growth occurs in the simulation. In
order to investigate the reasons why, we ran 2D alpha disc simulations with
alpha values of 0.01, 0.1, and 0.2, and found that only the latter two exhibit
significant eccentricity growth. We present an equation expressing global
eccentricity evolution in terms of contributing forces and use it to analyze
the simulations. As expected, we find that the dominant term contributing to
the growth of eccentricity is the tidal gravity of the companion star. In the
2D simulations, the alpha viscosity directly contributes to eccentricity
growth. In contrast, the overall magnetic forces in the 3D simulation damp
eccentricity. We also analyzed the mode-coupling mechanism of Lubow, and
confirmed that the spiral wave excited by the 3:1 resonance was the dominant
contributor to eccentricity growth in the 2D $\alpha=0.1$ simulations, but
other waves also contribute significantly. We found that the $\alpha=0.1$ and
0.2 simulations had more relative mass at larger radii compared to the
$\alpha=0.01$ and 3D MHD simulation, which also had an effective $\alpha$ of
0.01. This suggests that in 3D MHD simulations without sufficient poloidal
magnetic flux, MRI turbulence does not saturate at a high enough $\alpha$ to
spread the disc to large enough radii to reproduce the superhumps observed in
real systems.",2105.02392v1
2021-06-06,Particle Diffusion and Acceleration in Magnetorotational Instability Turbulence,"Hot accretion flows contain collisionless plasmas that are believed to be
capable of accelerating particles to very high energies, as a result of
turbulence generated by the magnetorotational instability (MRI). We conduct
unstratified shearing-box simulations of the MRI turbulence in ideal
magnetohydrodynamic (MHD), and inject energetic (relativistic) test particles
in simulation snapshots to conduct a detailed investigation on particle
diffusion and stochastic acceleration. We consider different amount of net
vertical magnetic flux to achieve different disk magnetizations levels at
saturated states, with sufficiently high resolution to resolve the gyro-radii
($R_g$) of most particles. Particles with large $R_g$ ($\gtrsim0.03$ disk scale
height $H$) show spatial diffusion coefficients of $\sim30$ and $\sim5$ times
Bohm values in the azimuthal and poloidal directions, respectively. We further
measure particle momentum diffusion coefficient $D(p)$ by applying the
Fokker-Planck equation to particle momentum evolution. For these particles,
contribution from turbulent fluctuations scales as $D(p)\propto p$, and shear
acceleration takes over when $R_g\gtrsim0.1H$, characterized by $D(p)\propto
p^3$. For particles with smaller $R_g$ ($\lesssim0.03H$), their spatial
diffusion coefficients roughly scale as $\sim p^{-1}$, and show evidence of
$D(p)\propto p^2$ scaling in momentum diffusion but with large uncertainties.
We find that multiple effects contribute to stochastic
acceleration/deceleration, and the process is also likely affected by
intermittency in the MRI turbulence. We also discuss the potential of
accelerating PeV cosmic-rays in hot accretion flows around supermassive black
holes.",2106.03098v1
2021-06-27,A new low-beta regime for unstable proton firehose modes in bi-Kappa distributed plasmas,"In the solar wind plasma an excess of kinetic temperature along the
background magnetic field stimulates proton firehose modes to grow if the
parallel plasma beta parameter is sufficiently high, i.e., $\beta_{p
\parallel}\gtrsim 1$. This instability can prevent the expansion-driven
anisotropy from increasing indefinitely, and explain the observations.
Moreover, such kinetic instabilities are expected to be even more effective in
the presence of suprathermal Kappa-distributed populations, which are
ubiquitous in the solar wind, are less affected by collisions than the core
population, but contribute with an additional free energy. In this work we use
both linear and extended quasi-linear (QL) frameworks to characterize the
unstable periodic proton firehose modes (propagating parallel to the magnetic
field) under the influence of suprathermal protons. Linear theory predicts a
systematic stimulation of the instability, suprathermals amplifying the growth
rates and decreasing the instability thresholds to lower anisotropies and lower
plasma betas ($\beta_{p \parallel}<1$). In perfect agreement with these
results, the QL approach reveals a significant enhancement of the resulting
electromagnetic fluctuations up to the saturation with a stronger back reaction
on protons, leading also to a faster and more efficient relaxation of the
temperature anisotropy.",2106.14291v1
2021-06-27,Ferromagnetic Cr4PtGa17: A Novel Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice,"We describe the crystal structure and elementary magnetic properties of a
previously unreported ternary intermetallic compound, Cr4PtGa17, which
crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group
R3m. The crystal structure is closely related to those of XYZ half-Heusler
compounds, where X, Y and Z are reported to be single elements only, occupying
three different face-centered cubic sublattices. The new material, Cr4PtGa17,
can be most straightforwardly illustrated by writing the formula as
(PtGa2)(Cr4Ga14)Ga (X=PtGa2, Y = Cr4Ga14, Z = Ga), that is, the X and Y sites
are occupied by clusters instead of single elements. The magnetic Cr occupies a
breathing pyrochlore lattice. Ferromagnetic ordering is found below TC ~61 K,
by both neutron diffraction and magnetometer studies, with a small, saturated
moment of ~0.25 muB/Cr observed at 2 K, making Cr4PtGa17 the first
ferromagnetically ordered material with a breathing pyrochlore lattice. A
magnetoresistance of ~140% was observed at 2 K. DFT calculations suggest that
the material has a nearly-half-metallic electronic structure. The new material,
Cr4PtGa17, the first realization of both a half-Heusler-type structure and a
breathing pyrochlore lattice, might pave a new way to achieve novel types of
half-Heusler compounds.",2106.14296v2
2021-10-27,Magneto-Thermal Instability In Galaxy Clusters II: Three-Dimensional Simulations,"In the intracluster medium (ICM) of galaxies, exchanges of heat across
magnetic field lines are strongly suppressed. This anisotropic heat conduction,
in the presence of a large-scale temperature gradient, destabilizes the
outskirts of galaxy clusters via the magneto-thermal instability (MTI), and
thus supplies a source of observed ICM turbulence. In this paper we continue
our investigation of the MTI with 3D simulations using the Boussinesq code
SNOOPY. We redress two issues intrinsic to our previous 2D study: an inverse
energy cascade and the impossibility of dynamo action. Contrary to 2D
simulations, we find inconsequential transport of energy across scales (most
energy is dissipated at the same scale as its injection), and that turbulent
eddies are vertically elongated at or below the thermal conduction length, but
relatively isotropic on larger scales. Similar to 2D, however, the saturated
turbulent energy levels and the integral scale follow clear power-laws that
depend on the thermal diffusivity, temperature gradient, and buoyancy
frequency. We also show that the MTI amplifies magnetic fields, through a
fluctuation dynamo, to equipartition strengths provided that the integral scale
of MTI turbulence is larger than the viscous dissipation scale. Finally, we
show that our scaling laws are consistent with extant observations of ICM
turbulence if the thermal conductivity is reduced by a factor of $\sim 10$ from
its Spitzer value, and that on global cluster scales the stable stratification
significantly reduces the vertical elongation of MTI motions.",2110.14696v1
2022-03-02,The Hardness-intensity Correlation of Photospheric Emission from a Structured Jet for Gamma-Ray Bursts,"For many gamma-ray bursts (GRBs), hardness-intensity correlation (HIC) can be
described by a power-law function, $E_{\rm p}\propto F^{\kappa}$, where $E_{\rm
p}$ is the peak energy of $\nu F_{\nu}$ spectrum, and $F$ is the instantaneous
energy flux. In this paper, HIC of the non-dissipative photospheric emission
from a structured jet is studied in different regimes. An intermediate
photosphere, which contains both of unsaturated and saturated emissions is
introduced, and we find positive $\kappa<1/4$ in this case. The same conclusion
could be generalized to the photospheric emission from a hybrid jet without
magnetic dissipations, or that with sub-photospheric magnetic dissipations and
fully thermalized. This may imply that the contribution peaking at $\sim1/2$ in
the distribution of observed $\kappa$ are mainly from the prompt emission of
GRBs with synchrotron origin. Besides, emissions of the intermediate
photosphere could give a smaller low-energy photon index $\alpha$ than that in
the unsaturated regime, and naturally reproduce anti-correlation in
$\alpha-E_{\rm p}$ in a GRB pulse.",2203.00882v6
2022-05-20,Band Structure Driven Thermoelectric Response of Topological Semiconductor ZrTe$_5$,"We report a transport, thermodynamic, and spectroscopic study of the recently
identified topological semiconductor ZrTe$_5$ with a focus on elucidating the
connections between its band structure and unusual thermoelectric properties.
Using time and angle resolved photoemission spectroscopy (tr-ARPES) we observe
a small electronic band gap and temperature dependent Fermi level which
traverses from a single valence to conduction band with lowering temperature,
consistent with previous reports. This low temperature Fermi surface closely
matches that derived from quantum oscillations, suggesting it is reflective of
the bulk electronic structure. The Seebeck and low field Nernst response is
characterized by an unusually large and non-monotonic temperature evolution. We
find this can be quantitatively explained using a semiclassical model based on
the observed band character and a linear temperature shifting of the Fermi
level. Additionally, we observe a large, non-saturating enhancement of both
thermoelectric coefficients in magnetic field. We show this can be captured by
the Zeeman energy associated with a large effective $g$-factor of 25.8
consistent with that derived from Lifshitz-Kosevich analysis of the quantum
oscillations. Together these observations provide a comprehensive picture of
ZrTe$_{5}$ as a model high mobility semiconductor and potential platform for
significant magnetic field driven thermoelectricity.",2205.10394v1
2022-06-17,Thermal conductivity of triangular-lattice antiferromagnet Na2BaCo(PO4)2: Absence of itinerant fermionic excitations,"We present the ultralow-temperature specific heat and thermal conductivity
measurements on single crystals of triangular-lattice antiferromagnet
Na$_2$BaCo(PO$_4$)$_2$, which was recently argued to host itinerant fermionic
excitations, like a quantum spin liquid, above its antiferromagnetic phase
transition temperature $T_{\rm N}$ = 0.148 K. In specific heat measurements, we
confirm the peaks due to antiferromagnetic ordering when magnetic field $\mu_0
H \leq$ 1 T, roughly consistent with previous work [N. Li $et$ $al.$, Nat.
Commun. 11, 4216 (2020)]. However, in thermal conductivity measurements, we
observe negligible residual linear term in zero and finite magnetic fields, in
sharp contrast to previous report [N. Li $et$ $al.$, Nat. Commun. 11, 4216
(2020)]. At 0.35 K, the thermal conductivity increases with field up to 3 T
then saturates, similar to that of another triangular-lattice compound
YbMgGaO$_4$, which further shows that the heat is conducted only by phonons
with scattering from spins and boundary. Our results clearly demonstrate the
absence of itinerant fermionic excitations in the disordered state above
$T_{\rm N}$ in this frustrated antiferromagnet Na$_2$BaCo(PO$_4$)$_2$, thus
such a state is not as exotic as previously reported.",2206.08866v1
2022-08-01,Effect of magnetism and phonons on localized carriers in the ferrimagnetic kagome metals GdMn$_6$Sn$_6$ and TbMn$_6$Sn$_6$,"Kagome metals possess peculiar optical spectra consisting of contributions
from free charge carriers in a Drude-type response, localized carriers seen as
a strongly temperature-dependent localization peak, and, in some cases, phonons
displaying strong anomalies. The rare-earth kagome metal series,
$R$Mn$_6$Sn$_6$, provides a marvelous playground to study the electronic
properties of kagome metals in the presence of variable magnetic order. Here,
we report temperature-dependent reflectivity studies on two members of the
$R$Mn$_6$Sn$_6$ family, GdMn$_6$Sn$_6$ (in-plane ferrimagnet) and
TbMn$_6$Sn$_6$ (out-of-plane ferrimagnet), in a broad energy range (50 - 18000
cm$^{-1}$, equivalent to 6.2 meV - 2.23 eV) down to 10 K. At high temperatures,
a phonon mode at approximately 160 cm$^{-1}$ is observed, which becomes
screened out in TbMn$_6$Sn$_6$ below $\sim$ 150 K as the localization peak
linearly passes through the mode. In GdMn$_6$Sn$_6$, the disappearance of the
phonon is accompanied by the onset of saturation of the peak position,
suggesting an unusual interplay between the two features.",2208.00756v2
2022-08-15,Valley-coherent quantum anomalous Hall state in AB-stacked MoTe2/WSe2 bilayers,"Moir\'e materials provide fertile ground for the correlated and topological
quantum phenomena. Among them, the quantum anomalous Hall (QAH) effect, in
which the Hall resistance is quantized even under zero magnetic field, is a
direct manifestation of the intrinsic topological properties of a material and
an appealing attribute for low-power electronics applications. The QAH effect
has been observed in both graphene and transition metal dichalcogenide (TMD)
moir\'e materials. It is thought to arise from the interaction-driven valley
polarization of the narrow moir\'e bands. Here, we show surprisingly that the
newly discovered QAH state in AB-stacked MoTe2/WSe2 moir\'e bilayers is not
valley-polarized but valley-coherent. The layer- and helicity-resolved optical
spectroscopy measurement reveals that the QAH ground state possesses
spontaneous spin (valley) polarization aligned (anti-aligned) in two TMD
layers. In addition, saturation of the out-of-plane spin polarization in both
layers occurs only under high magnetic fields, supporting a canted spin
texture. Our results call for a new mechanism for the QAH effect and highlight
the potential of TMD moir\'e materials with strong electronic correlations and
spin-orbit interactions for exotic topological states.",2208.07452v1
2022-09-12,Recursive Prediction Error Gradient-Based Algorithms and Framework to Identify PMSM Parameters Online,"Real-time acquisition of accurate machine parameters is of significance to
achieving high performance in electric drives, particularly targeted for
mission-critical applications. Unlike the saturation effects, the temperature
variations are difficult to predict, thus it is essential to track
temperature-dependent parameters online. In this paper, a unified framework is
developed for online parameter identification of rotating electric machines,
premised on the Recursive Prediction Error Method (RPEM). Secondly, the
prediction gradient ($\mathbf{\Psi}^T$)-based RPEM is adopted for
identification of the temperature-sensitive parameters, i.e., the permanent
magnet flux linkage ($\Psi_m$) and stator-winding resistance ($R_s$) of the
Interior Permanent Magnet Synchronous Machine (IPMSM). Three algorithms,
namely, Stochastic Gradient (SGA), Gauss-Newton (GNA), and physically
interpretative method (PhyInt) are investigated for the estimation gains
computation. A speed-dependent gain-scheduling scheme is used to decouple the
inter-dependency of $\Psi_m$ and $R_s$. With the aid of offline simulation
methods, the main elements of RPEM such as $\mathbf{\Psi}^T$ are analyzed. The
concept validation and the choice of the optimal algorithm is made with the use
of System-on-Chip (SoC) based Embedded Real-Time Simulator (ERTS).
Subsequently, the selected algorithms are validated with the aid of a 3-kW,
IPMSM drive where the control and estimation routines are implemented in the
SoC-based industrial embedded control system. The experimental results reveal
that $\mathbf{\Psi}^T$-based RPEM, in general, can be a versatile technique in
temperature-sensitive parameter adaptation both online and offline.",2209.05094v1
2022-10-10,Complete field-induced spectral response of the spin-1/2 triangular-lattice antiferromagnet CsYbSe$_2$,"Fifty years after Anderson's resonating valence-bond proposal, the spin-1/2
triangular-lattice Heisenberg antiferromagnet (TLHAF) remains the ultimate
platform to explore highly entangled quantum spin states in proximity to
magnetic order. Yb-based delafossites are ideal candidate TLHAF materials,
which allow experimental access to the full range of applied in-plane magnetic
fields. We perform a systematic neutron scattering study of CsYbSe$_2$, first
proving the Heisenberg character of the interactions and quantifying the
second-neighbour coupling. We then measure the complex evolution of the
excitation spectrum, finding extensive continuum features near the
120$^{\circ}$-ordered state, throughout the 1/3-magnetization plateau and
beyond this up to saturation. We perform cylinder matrix-product-state (MPS)
calculations to obtain an unbiased numerical benchmark for the TLHAF and
spectacular agreement with the experimental spectra. The measured and
calculated longitudinal spectral functions reflect the role of multi-magnon
bound and scattering states. These results provide valuable insight into
unconventional field-induced spin excitations in frustrated quantum materials.",2210.04928v3
2022-11-08,The Impact of Cosmic Ray Injection on Magnetic Flux Tubes in a Galactic Disk,"In galactic disks, the Parker instability results when non-thermal pressure
support exceeds a certain threshold. The non-thermal pressures considered in
the Parker instability are cosmic ray pressure and magnetic pressure. This
instability takes a long time to saturate $(>500 \, \mathrm{Myr})$ and assumes
a background with fixed cosmic ray pressure to gas pressure ratio. In reality,
galactic cosmic rays are injected into localized regions $(< 100
\,\mathrm{pc})$ by events like supernovae, increasing the cosmic ray pressure
to gas pressure ratio. In this work, we examine the effect of such cosmic ray
injection on large scales $ (\sim 1\,\mathrm{kpc})$ in cosmic ray
magnetohydrodynamic simulations using the \texttt{Athena++} code. We vary the
background properties, dominant cosmic ray transport mechanism, and injection
characteristics between our simulation runs. We find the injection will disrupt
the interstellar medium on shorter timescales than the Parker instability. If
cosmic ray transport by advection is dominant, cosmic ray injection disrupts
the disk on short time scales $(<100\,\mathrm{Myr})$. If cosmic ray transport
by the streaming instability is dominant, the injection creates a buoyant flux
tube long after the initial injection $(>150\,\mathrm{Myr})$. Finally, when
cosmic ray transport by diffusion dominates, the injected cosmic rays make an
entire flux tube over pressured in a short time $(\sim 10 \, \mathrm{Myr})$.
This over pressure pushes gas off the tube and drives buoyant rise on time
scales similar to the advection dominated case.",2211.04503v2
2022-12-02,Polarized Maser Emission with In-Source Faraday Rotation,"We discuss studies of polarization in astrophysical masers with particular
emphasis on the case where the Zeeman splitting is small compared to the
Doppler profile, resulting in a blend of the transitions between magnetic
substates. A semi-classical theory of the molecular response is derived, and
coupled to radiative transfer solutions for 1 and 2-beam linear masers,
resulting in a set of non-linear, algebraic equations for elements of the
molecular density matrix. The new code, PRISM, implements numerical methods to
compute these solutions. Using PRISM, we demonstrate a smooth transfer between
this case and that of wider splitting. For a J=1-0 system, with parameters
based on the $v=1, J=1-0$ transition of SiO, we investigate the behaviour of
linear and circular polarization as a function of the angle between the
propagation axis and the magnetic field, and with the optical depth, or
saturation state, of the model. We demonstrate how solutions are modified by
the presence of Faraday rotation, generated by various abundances of free
electrons, and that strong Faraday rotation leads to additional angles where
Stokes-Q changes sign. We compare our results to a number of previous models,
from the analytical limits derived by Goldreich, Keeley and Kwan in 1973,
through computational results by W. Watson and co-authors, to the recent work
by Lankhaar and Vlemmings in 2019. We find that our results are generally
consistent with those of other authors given the differences of approach and
the approximations made.",2212.01410v1
2023-04-06,How baryons appear in low-energy QCD: Domain-wall Skyrmion phase in strong magnetic fields,"Low-energy dynamics of QCD can be described by pion degrees of freedom in
terms of the chiral perturbation theory(ChPT). A chiral soliton lattice(CSL),
an array of solitons, is the ground state due to the chiral anomaly in the
presence of a magnetic field larger than a certain critical value at finite
density. Here, we show in a model-independent and fully analytic manner (at the
leading order of ChPT) that the CSL phase transits to a {\it domain-wall
Skyrmion phase} when the chemical potential is larger than the critical value
$\mu_{\rm c} = 16\pi f_{\pi}^2/3m_{\pi} \sim 1.03 \;\; {\rm GeV}$ with the
pion's decay constant $f_{\pi}$ and mass $m_{\pi}$, which can be regarded as
the nuclear saturation density. There spontaneously appear stable
two-dimensional Skyrmions or lumps on a soliton surface, which can be viewed as
three-dimensional Skyrmions carrying even baryon numbers from the bulk despite
no Skyrme term. They behave as superconducting rings with persistent currents
due to a charged pion condensation, and areas of the rings' interiors are
quantized. This phase is in scope of future heavy-ion collider experiments.",2304.02940v1
2023-07-17,Slonczewski-spin-current driven dynamics of 180$^{\circ}$ domain walls in spin valves with interfacial Dzyaloshinskii-Moriya interaction,"Steady-flow dynamics of ferromagnetic 180$^{\circ}$ domain walls (180DWs) in
long and narrow spin valves (LNSVs) with interfacial Dzyaloshinskii-Moriya
interaction (IDMI) under spin currents with Slonczewski $g-$factor are
examined. Depending on the magnetization orientation of polarizers (pinned
layers of LNSVs), dynamics of 180DWs in free layers of LNSVs are subtly
manipulated: (i) For parallel polarizers, stronger spin polarization leads to
higher Walker limit thus ensures the longevity of faster steady flows.
Meantime, IDMI induces both the stable-region flapping and its width
enlargement. (ii) For perpendicular polarizers, a wandering of 180DWs between
bi- and tri-stability persists with the criticality adjusted by the IDMI. (iii)
For planar-transverse polarizers, IDMI makes the stable region of steady flows
completely asymmetric and further imparts a high saturation wall velocity under
large current density. Under the last two polarizers, the ultrahigh
differential mobility of 180DWs survives. The combination of Slonczewski spin
current and IDMI provides rich possibilities of fine controlling on 180DW
dynamics, hence opens avenues for magnetic nanodevices with rich functionality
and high robustness.",2307.08419v1
2023-08-21,Unravelling the Period Gap using LAMOST Chromospheric Activity Indices,"In our recent catalogue of BY Draconis (BY Dra) variables based on Zwicky
Transient Facility data, we found traces of a period gap in the period-colour
diagram. We combined our BY Dra database with catalogues from the {\sl Kepler}
and K2 surveys, revealing a prominent period gap. Here, we use this combined
ZTF-{\sl Kepler}-K2 data set to investigate the origin of the period gap
observed for BY Dra stars using chromospheric activity indices. We use low- and
medium-resolution spectra from the LAMOST Data Release 7 to derive magnetic
activity indices for the Ca {\sc ii} H and K and H$\alpha$ emission lines. We
find a strong dependence of chromospheric activity on both stellar mass and
rotation period. For partially convective K-M-type stars, the activity
decreases steeply up to an age of $\sim$700-1000 Myr, subsequently evolving to
the type of low-level saturation associated with spin-down stallation. In
contrast, F-G-type stars with thinner convective envelopes exhibit constant
activity with increasing age. We suspect that the observed steep decrease for
partially convective stars is driven by core-envelope coupling. This mechanism
reduces differential rotation at the core-envelope transition, hence leading to
decreased magnetic activity. Moreover, we derive activity indices for
previously known star clusters and find similar trends as regards their
activity levels as a function of age. In particular, very low-level activity is
observed around the location of the period gap. Therefore, we conclude that the
period gap, defined by the non-detection of variable sources, is driven by a
minimum in chromospheric activity.",2308.10539v1
2023-09-14,Microscopic study of the impurity effect in the kagome superconductor La(Ru$_{1-x}$Fe$_{x}$)$_{3}$Si$_{2}$,"We report on the effect of magnetic impurities on the microscopic
superconducting (SC) properties of the kagome-lattice superconductor
La(Ru$_{1-x}$Fe$_{x}$)$_{3}$Si$_{2}$ using muon spin relaxation/rotation. A
strong suppression of the superconducting critical temperature $T_{\rm c}$, the
SC volume fraction, and the superfluid density was observed. We further find a
correlation between the superfluid density and $T_{\rm c}$ which is considered
a hallmark feature of unconventional superconductivity. Most remarkably,
measurements of the temperature-dependent magnetic penetration depth
${\lambda}$ reveal a change in the low-temperature behavior from exponential
saturation to a linear increase, which indicates that Fe doping introduces
nodes in the superconducting gap structure at concentrations as low as
$x=$~0.015. Our results point to a rare example of unconventional
superconductivity in the correlated kagome lattice and accessible tunability of
the superconducting gap structure, offering new insights into the microscopic
mechanisms involved in superconducting order.",2309.07827v2
2023-11-14,"A cool, magnetic white dwarf accreting planetary debris","We present an analysis of spectroscopic data of the cool, highly magnetic and
polluted white dwarf 2MASS J0916-4215. The atmosphere of the white dwarf is
dominated by hydrogen, but numerous spectral lines of magnesium, calcium,
titanium, chromium, iron, strontium, along with Li I, Na I, Al I, and K I
lines, are found in the incomplete Paschen-Back regime, most visibly, in the
case of Ca II lines. Extensive new calculations of the Paschen-Back effect in
several spectral lines are presented and results of the calculations are
tabulated for the Ca II H&K doublet. The abundance pattern shows a large
lithium and strontium excess, which may be viewed as a signature of planetary
debris akin to Earth's continental crust accreted onto the star, although the
scarcity of silicon indicates possible dilution in bulk Earth material.
Accurate abundance measurements proved sensitive to the value of the broadening
parameter due to collisions with neutral hydrogen (Gamma_HI), particularly in
saturated lines such as the resonance lines of Ca I and Ca II. We found that
Gamma_HI if formulated with values from the literature could be overestimated
by a factor of 10 in most resonance lines.",2311.07937v1
2024-03-13,Chiral spin state and nematic ferromagnet in the spin-1 Kitaev-$Γ$ model,"The higher-spin Kitaev magnets, in which the Kitaev interaction and
off-diagonal exchange couplings are overwhelmingly large, have emerged as a
fertile avenue to explore exotic phases and unusual excitations. In this work,
we study the quantum phase diagram of the spin-1 Kitaev-$\Gamma$ model on the
honeycomb lattice using density-matrix renormalization group. It harbours six
distinct phases and the intriguing findings are three magnetically ordered
phases in which both time-reversal symmetry and lattice symmetry albeit of
different sort are broken spontaneously. The chiral spin state originates from
the order-by-disorder effect and exhibits an almost saturated scalar spin
chirality at the quantum level. Depending on the relative strength of the two
interactions, it also features columnar or plaquette valence-bond-solid-like
pattern as a consequence of the translational symmetry breaking. In parallel,
the nematic ferromagnets are situated at ferromagnetic Kitaev side and possess
small but finite ferromagnetic ordering. The lattice-rotational symmetry
breaking enforces nonequivalent bond energy along one of the three bonds.
Although the intrinsic difference between the two nematic ferromagnets remains
elusive, the discontinuities in the von Neumann entropy, hexagonal plaquette
operator, and Wilson loop operator convincingly suggest that they are separated
via a first-order phase transition.",2403.08382v1
2004-09-27,Bunching instability of rotating relativistic electron layers and coherent synchrotron radiation,"We study the stability of a collisionless, relativistic, finite-strength,
cylindrical layer of charged particles in free space by solving the linearized
Vlasov-Maxwell equations and compute the power of the emitted electromagnetic
waves. The layer is rotating in an external magnetic field parallel to the
layer. This system is of interest to understanding the high brightness
temperature of pulsars which cannot be explained by an incoherent radiation
mechanism. Coherent synchrotron radiation has also been observed recently in
bunch compressors used in particle accelerators. We consider equilibrium layers
with a `thermal' energy spread and therefore a non-zero radial thickness. The
particles interact with their retarded electromagnetic self-fields. The effect
of the betatron oscillations is retained. A short azimuthal wavelength
instability is found which causes a modulation of the charge and current
densities. The growth rate is found to be an increasing function of the
azimuthal wavenumber, a decreasing function of the Lorentz factor, and
proportional to the square root of the total number of electrons. We argue that
the growth of the unstable perturbation saturates when the trapping frequency
of electrons in the wave becomes comparable to the growth rate. Owing to this
saturation we can predict the radiation spectrum for a given set of parameters.
Our predicted brightness temperatures are proportional to the square of the
number of particles and scale by the inverse five-third power of the azimuthal
wavenumber which is in rough accord with the observed spectra of radio pulsars.",0409645v2
2005-06-22,The Origin of T Tauri X-ray Emission: New Insights from the Chandra Orion Ultradeep Project,"We use the data of the Chandra Orion Ultradeep Project (COUP) to study the
nearly 600 X-ray sources that can be reliably identified with optically well
characterized T Tauri stars (TTS) in the Orion Nebula Cluster. We detect X-ray
emission from more than 97% of the optically visible late-type (spectral types
F to M) cluster stars. This proofs that there is no ``X-ray quiet'' population
of late-type stars with suppressed magnetic activity. All TTS with known
rotation periods lie in the saturated or super-saturated regime of the relation
between activity and Rossby numbers seen for main-sequence (MS) stars, but the
TTS show a much larger scatter in X-ray activity than seen for the MS stars.
Strong near-linear relations between X-ray luminosities, bolometric
luminosities and mass are present. We also find that the fractional X-ray
luminosity rises slowly with mass over the 0.1 - 2 M_sun range. The plasma
temperatures determined from the X-ray spectra of the TTS are much hotter than
in MS stars, but seem to follow a general solar-stellar correlation between
plasma temperature and activity level. The large scatter about the relations
between X-ray activity and stellar parameters seems to be related to the
influence of accretion on the X-ray emission. While the X-ray activity of the
non-accreting TTS is consistent with that of rapidly rotating MS stars, the
accreting stars are less X-ray active (by a factor of ~2-3 on average) and
produce much less well defined correlations than the non-accretors. We discuss
possible reasons for the suppression of X-ray emission by accretion and the
implications of our findings on long-standing questions related to the origin
of the X-ray emission from young stars.",0506526v1
2010-11-02,Discovery of a QPO in the X-ray pulsar 1A 1118-615: correlated spectral and aperiodic variability,"Our goal is to investigate the X-ray timing and spectral variability of the
high-mass X-ray binary 1A 1118-615 during a type-II outburst. We performed a
detailed color, spectral and timing analysis of a giant outburst from 1A
1118-615, using RXTE data. Results. We report the discovery of a variable
quasi-periodic oscillation (QPO) in the power spectral density of 1A 1118-615,
with a centroid frequency of ~0.08 Hz. The centroid frequency of the QPO
correlates with the X-ray flux, as expected according to the most accredited
models for QPO production. For energies above ~4 keV, the QPO rms variability
decreases as the energy increases. Pulse profiles display energy dependence,
with a two-peak profile at lower energies, and a single peak at higher
energies. From spectral analysis, we confirm the presence of a cyclotron
absorption feature at ~60 keV, the highest value measured for an X-ray pulsar.
We find that the spectral parameters (photon index, cutoff energy, iron
fluorescence line strength) display a marked dependence with flux. We detect
two different levels of neutral hydrogen column density, possibly due to the Be
companion activity. We report for the first time a correlation between the
timing and spectral parameters in an X-ray pulsar. All the correlations found
between spectral/timing parameters and X-ray flux are present up to a flux of
~6x10^-9 erg cm^-2 s^-1, when a saturation level is reached. We propose that
the saturation observed corresponds to the minimum extent of the neutron star
magnetosphere. We estimate the magnetic field of the neutron star from two
independent ways, using results from spectral (cyclotron line energy) and
timing (QPO frequency) analysis, obtaining consistent values, of ~7-8x10^12 G.
Results from the comprehensive spectral and timing analysis are discussed in
comparison with other X-ray pulsars.",1011.0564v2
2011-09-29,Geosynchronous magnetopause crossings: necessary conditions,"The experimental data on GOES magnetic measurements and plasma measurements
on LANL geosynchronous satellites is used for selection of 169 case events
containing 638 geosynchronous magnetopause crossings (GMCs) in 1995 to 2001. We
study the necessary conditions for the geosynchronous magnetopause crossings
using scatter plot of the GMCs in the coordinate space of Psw versus Bz. In
such representation the upstream solar wind conditions demonstrate sharp
envelope boundary under which no GMCs are occurred. The boundary has two strait
horizontal branches where Bz does not influence on the magnetopause location.
The first branch is located in the range of Psw=21 nPa for large positive Bz
and is associated with an asymptotic regime of the pressure balance. The second
branch asymptotically approaches to the range of Psw=4.8 nPa under very strong
negative Bz and it is associated with a regime of the Bz influence saturation.
We suggest that the saturation is caused by relatively high contribution of the
magnetosphere thermal pressure into the pressure balance on the magnetopause.
The intermediate region of the boundary for the moderate negative and small
positive IMF Bz can be well approximated by a hyperbolic tangent function. We
interpret the envelope boundary as a range of necessary upstream solar wind
conditions required for GMC in the point on the magnetopause located mostly
close to the Earth (""perigee"" point). We obtain that the dipole tilt angle and
dawn-dusk asymmetry influence on the ""perigee"" point location. We find that the
aGSM latitude of this point depends linearly on the dipole tilt angle with the
slope about -0.5. The aGSM longitude of the ""perigee"" point decreases with IMF
Bz with a rate of about 2 angular minutes per 1 nT. An empirical model
predicting the magnetopause crossing of the geosynchronous orbit in the
""perigee"" point is proposed.",1109.6513v2
2014-02-24,Time resolved spectroscopy of SGR J1550-5418 bursts detected with Fermi/GBM,"We report on time-resolved spectroscopy of the 63 brightest bursts of SGR
J1550-5418, detected with Fermi/Gamma-ray Burst Monitor during its 2008-2009
intense bursting episode. We performed spectral analysis down to 4 ms
time-scales, to characterize the spectral evolution of the bursts. Using a
Comptonized model, we find that the peak energy, E_peak, anti-correlates with
flux, while the low-energy photon index remains constant at -0.8 up to a flux
limit F~10^-5 erg s-1 cm-2. Above this flux value the E_peak-flux correlation
changes sign, and the index positively correlates with flux reaching 1 at the
highest fluxes. Using a two black-body model, we find that the areas and fluxes
of the two emitting regions correlate positively. Further, we study here for
the first time, the evolution of the temperatures and areas as a function of
flux. We find that the area-kT relation follows lines of constant luminosity at
the lowest fluxes, R^2 \propto kT^-4, with a break at higher fluxes ($F>10^-5.5
erg s-1 cm-2). The area of the high-kT component increases with flux while its
temperature decreases, which we interpret as due to an adiabatic cooling
process. The area of the low-kT component, on the other hand, appears to
saturate at the highest fluxes, towards R_max~30 km. Assuming that crust quakes
are responsible for SGR bursts and considering R_max as the maximum radius of
the emitting photon-pair plasma fireball, we relate this saturation radius to a
minimum excitation radius of the magnetosphere, and put a lower limit on the
internal magnetic field of SGR J1550-5418, B_int>~4.5x10^15 G.",1402.6015v1
2014-07-07,Rossby and Drift Wave Turbulence and Zonal Flows: the Charney-Hasegawa-Mima model and its extensions,"A detailed study of the Charney-Hasegawa-Mima model and its extensions is
presented. These simple nonlinear partial differential equations suggested for
both Rossby waves in the atmosphere and also drift waves in a
magnetically-confined plasma exhibit some remarkable and nontrivial properties,
which in their qualitative form survive in more realistic and complicated
models, and as such form a conceptual basis for understanding the turbulence
and zonal flow dynamics in real plasma and geophysical systems. Two idealised
scenarios of generation of zonal flows by small-scale turbulence are explored:
a modulational instability and turbulent cascades.
  A detailed study of the generation of zonal flows by the modulational
instability reveals that the dynamics of this zonal flow generation mechanism
differ widely depending on the initial degree of nonlinearity. A numerical
proof is provided for the extra invariant in Rossby and drift wave turbulence
-zonostrophy and the invariant cascades are shown to be characterised by the
zonostrophy pushing the energy to the zonal scales.
  A small scale instability forcing applied to the model demonstrates the
well-known drift wave - zonal flow feedback loop in which the turbulence which
initially leads to the zonal flow creation, is completely suppressed and the
zonal flows saturate. The turbulence spectrum is shown to diffuse in a manner
which has been mathematically predicted.
  The insights gained from this simple model could provide a basis for
equivalent studies in more sophisticated plasma and geophysical fluid dynamics
models in an effort to fully understand the zonal flow generation, the
turbulent transport suppression and the zonal flow saturation processes in both
the plasma and geophysical contexts as well as other wave and turbulence
systems where order evolves from chaos.",1407.1896v1
2017-04-07,Simultaneous 183 GHz H2O Maser and SiO Observations Towards Evolved Stars Using APEX SEPIA Band 5,"We investigate the use of 183 GHz H2O masers for characterization of the
physical conditions and mass loss process in the circumstellar envelopes of
evolved stars. We used APEX SEPIA Band 5 to observe the 183 GHz H2O line
towards 2 Red Supergiant and 3 Asymptotic Giant Branch stars. Simultaneously,
we observed lines in 28SiO v0, 1, 2 and 3, and for 29SiO v0 and 1. We detected
the 183 GHz H2O line towards all the stars with peak flux densities greater
than 100 Jy, including a new detection from VY CMa. Towards all 5 targets, the
water line had indications of being due to maser emission and had higher peak
flux densities than for the SiO lines. The SiO lines appear to originate from
both thermal and maser processes. Comparison with simulations and models
indicate that 183 GHz maser emission is likely to extend to greater radii in
the circumstellar envelopes than SiO maser emission and to similar or greater
radii than water masers at 22, 321 and 325 GHz. We speculate that a prominent
blue-shifted feature in the W Hya 183 GHz spectrum is amplifying the stellar
continuum, and is located at a similar distance from the star as mainline OH
maser emission. From a comparison of the individual polarizations, we find that
the SiO maser linear polarization fraction of several features exceeds the
maximum fraction allowed under standard maser assumptions and requires strong
anisotropic pumping of the maser transition and strongly saturated maser
emission. The low polarization fraction of the H2O maser however, fits with the
expectation for a non-saturated maser. 183 GHz H2O masers can provide strong
probes of the mass loss process of evolved stars. Higher angular resolution
observations of this line using ALMA Band 5 will enable detailed investigation
of the emission location in circumstellar envelopes and can also provide
information on magnetic field strength and structure.",1704.02133v1
2017-09-15,Pressure-anisotropy-induced nonlinearities in the kinetic magnetorotational instability,"In collisionless and weakly collisional plasmas, such as hot accretion flows
onto compact objects, the magnetorotational instability (MRI) can differ
significantly from the standard (collisional) MRI. In particular, pressure
anisotropy with respect to the local magnetic-field direction can both change
the linear MRI dispersion relation and cause nonlinear modifications to the
mode structure and growth rate, even when the field and flow perturbations are
small. This work studies these pressure-anisotropy-induced nonlinearities in
the weakly nonlinear, high-ion-beta regime, before the MRI saturates into
strong turbulence. Our goal is to better understand how the saturation of the
MRI in a low collisionality plasma might differ from that in the collisional
regime. We focus on two key effects: (i) the direct impact of self-induced
pressure-anisotropy nonlinearities on the evolution of an MRI mode, and (ii)
the influence of pressure anisotropy on the ""parasitic instabilities"" that are
suspected to cause the mode to break up into turbulence. Our main conclusions
are: (i) The mirror instability regulates the pressure anisotropy in such a way
that the linear MRI in a collisionless plasma is an approximate nonlinear
solution once the mode amplitude becomes larger than the background field (just
as in MHD). This implies that differences between the collisionless and
collisional MRI become unimportant at large amplitudes. (ii) The break up of
large amplitude MRI modes into turbulence via parasitic instabilities is
similar in collisionless and collisional plasmas. Together, these conclusions
suggest that the route to magnetorotational turbulence in a collisionless
plasma may well be similar to that in a collisional plasma, as suggested by
recent kinetic simulations. As a supplement to these findings, we offer
guidance for the design of future kinetic simulations of magnetorotational
turbulence.",1709.05428v2
2018-03-10,Quantum Dimensional Transition in Spin-$\frac{1}{2}$ Antiferromagnetic Heisenberg Model on A Square Lattice and Space Reduction in Matrix Product State,"We study the spin-$\frac{1}{2}$ antiferromagnetic Heisenberg model on an
infinity-by-$N$ square lattice for even $N$'s up to $14$. Previously, the
nonlinear sigma model perturbatively predicts that its spin rotational symmetry
asymptotically breaks when $N\rightarrow \infty$, i.e., when it is
two-dimensional (2D). However, we identified a critical width $N_c = 10$ for
which this symmetry breaks spontaneously. It defines a dimensional transition
from one-dimension (1D) including quasi-1D to 2D. The finite-size effect
differs from that of the $N$-by-$N$ lattice. The ground state (GS) energy per
site approaches the thermodynamic limit value, in agreement with the previously
accepted value, by one order of $1/N$ faster than when using $N$-by-$N$
lattices in the literature. We build and variationally solve a matrix product
state (MPS) on a chain, converting the $N$ sites in the rung into an effective
site. We show that the area law of entanglement entropy does not apply when $N$
increases in our method, and show that the reduced density matrix of each
effective site will have a saturating number of dominant diagonal elements with
increasing $N$. These two characteristics make the MPS rank needed to obtain a
demanded energy accuracy quickly saturate when $N$ is large, making our
algorithm efficient for large $N$'s. And, the latter enables space reduction in
MPS. Within the framework of MPS, we prove a theorem that the spin-spin
correlation at infinite separation is the square of staggered magnetization and
demonstrate that the eigenvalue structure of a building MPS unit of $\langle
g\mid g\rangle$, $\mid g\rangle$ being the GS, is responsible for order,
disorder and quasi-long-range order.",1803.03779v2
2018-12-18,Two-dimensional Ca-Cl crystals under ambient conditions observed directly by cryo-electron microscopy,"Recently, we report the direct observation, under ambient conditions, of
Na2Cl and Na3Cl as two-dimensional (2D) Na-Cl crystals, together with regular
NaCl, on reduced graphene oxide membranes and on the surfaces of natural
graphite powders from salt solutions far below the saturated concentration.
However, what are these abnormal stoichiometries for high valence ions, such as
calcium ions and copper ions still remain unknown. Here, using cryo-electron
microscopy, we report the direct observation of two-dimensional (2D) Ca-Cl
crystals on reduced graphene oxide (rGO) membranes, in which the calcium ions
are only monovalent (i.e. +1). Remarkably, metallic properties rather than
insulating are displayed by those CaCl crystals. We note that such CaCl
crystals are obtained by simply incubating rGO membranes in salt solutions
below the saturated concentration, under ambient conditions. Theoretical
studies show that the formation of those abnormal crystals is attributed to the
strong cation-pi interactions of the Ca2+ ions with the aromatic rings in the
graphitic surfaces. Since strong cation-pi interactions also exist between
other metal ions (such as Mg2+, Fe2+, Co2+, Cu2+, Cd2+, Cr2+ and Pb2+) and
graphitic surfaces, similar 2D crystals with abnormal valence state of the
metal cations and corresponding abnormal properties are highly expected. The 2D
crystals with monovalent calcium ions show unusual electronic properties, and
can be applicated in catalyzer, hydrogen storage, high-performance conducting
electrodes and sensors. These findings also produce functionalized graphene
including compact ""graphene-metallic CaCl-insulating CaCl2"" junction that can
serve as transistors down to the atomic scale, and other devices for magnetic,
optical and mechanical applications.",1812.07195v1
2019-01-29,Higher superconducting transition temperature by breaking the universal pressure relation,"By investigating the bulk superconducting state via dc magnetization
measurements, we have discovered a common resurgence of the superconductive
transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+{\delta} (Bi2201) and
bilayer Bi2Sr2CaCu2O8+{\delta} (Bi2212) to beyond the maximum Tcs (Tc-maxs)
predicted by the universal relation between Tc and doping (p) or pressure (P)
at higher pressures. The Tc of under-doped Bi2201 initially increases from 9.6
K at ambient to a peak at ~ 23 K at ~ 26 GPa and then drops as expected from
the universal Tc-P relation. However, at pressures above ~ 40 GPa, Tc rises
rapidly without any sign of saturation up to ~ 30 K at ~ 51 GPa. Similarly, the
Tc for the slightly overdoped Bi2212 increases after passing a broad valley
between 20-36 GPa and reaches ~ 90 K without any sign of saturation at ~ 56
GPa. We have therefore attributed this Tc-resurgence to a possible
pressure-induced electronic transition in the cuprate compounds due to a charge
transfer between the Cu 3d_(x^2-y^2 ) and the O 2p bands projected from a
hybrid bonding state, leading to an increase of the density of states at the
Fermi level, in agreement with our density functional theory calculations.
Similar Tc-P behavior has also been reported in the trilayer
Br2Sr2Ca2Cu3O10+{\delta} (Bi2223). These observations suggest that higher Tcs
than those previously reported for the layered cuprate high temperature
superconductors can be achieved by breaking away from the universal Tc-P
relation through the application of higher pressures.",1901.10404v1
2020-04-13,Discrimination of Internal Faults and Other Transients in an Interconnected System with Power Transformers and Phase Angle Regulators,"This study solves the problem of accurate detection of internal faults and
classification of transients in a 5-bus interconnected system for Phase Angle
Regulators (PAR) and Power Transformers. The analysis prevents mal-operation of
differential relays in case of transients other than faults which include
magnetizing inrush, sympathetic inrush, external faults with CT saturation,
capacitor switching, non-linear load switching, and ferroresonance. A gradient
boosting classifier (GBC) is used to distinguish the internal faults from the
transient disturbances based on 1.5 cycles of 3-phase differential currents
registered by a change detector. After the detection of an internal fault, GBCs
are used to locate the faulty unit (Power Transformer, PAR series, or exciting
unit) and identify the type of fault. In case a transient disturbance is
detected, another GBC classifies them into the six transient disturbances. Five
most relevant frequency and time domain features obtained using Information
Gain are used to train and test the classifiers. The proposed algorithm
distinguishes the internal faults from the other transients with a balanced
accuracy of 99.95%. The faulty transformer unit is located with a balanced
accuracy of 99.5% and the different transient disturbances are identified with
a balanced accuracy of 99.3%. Moreover, the reliability of the scheme is
verified for different rating and connection of the transformers involved, CT
saturation, and noise levels in the signals. These GBC classifiers can work
together with a conventional differential relay and offer a supervisory control
over its operation. PSCAD/EMTDC software is used for simulation of the
transients and to develop the two and three-winding transformer models for
creating the internal faults including inter-turn and inter-winding faults.",2004.06003v2
2020-07-31,Magnetohydrodynamics of protoplanetary discs,"Protoplanetary discs are made of gas and dust orbiting a young star. They are
also the birth place of planetary systems, which motivates a large amount of
observational and theoretical research.
  In these lecture notes, I present a review of the magnetic mechanisms applied
to the outer regions R>1 AU of these discs, which are the planet-formation
regions. In contrast to usual astrophysical plasmas, the gas in these regions
is noticeably cold (T<300 K) and dense, which implies a very low ionisation
fraction close to the disc midplane. In these notes, I deliberately ignore the
innermost R~0.1 AU region which is influenced by the star-disk interaction and
various radiative effects.
  I start by presenting a short overview of the observational evidence for the
dynamics of these objects. I then introduce the methods and approximations used
to model these plasmas, including non-ideal MHD, and the uncertainties
associated with this approach. In this framework, I explain how the global
dynamics of these discs is modelled, and I present a stability analysis of this
plasma in the local approximation, introducing the non-ideal magneto-rotational
instability. Following this mostly analytical part, I discuss numerical models
which have been used to describe the saturation mechanisms of this instability,
and the formation of large-scale structures by various saturation mechanisms.
Finally, I show that local numerical models are insufficient since magnetised
winds are also emitted from the surface of these objects. After a short
introduction on winds physics, I present global models of protoplanetary discs,
including both a large-scale wind and the non-ideal dynamics of the disc.",2007.15967v1
2020-10-13,Hydrodynamical simulations of protoplanetary disks including irradiation of stellar photons. I. Resolution study for Vertical Shear Instability (VSI),"In recent years hydrodynamical (HD) models have become important to describe
the gas kinematics in protoplanetary disks, especially in combination with
models of photoevaporation and/or magnetic-driven winds. We focus on diagnosing
the the vertical extent of the VSI at 203 cells per scale height and allude at
what resolution per scale height we obtain convergence. Finally, we determine
the regions where EUV, FUV and X-Rays are dominant in the disk. We perform
global HD simulations using the PLUTO code. We adopt a global isothermal
accretion disk setup, 2.5D (2 dimensions, 3 components) which covers a radial
domain from 0.5 to 5.0 and an approximately full meridional extension. We
determine the 50 cells per scale height to be the lower limit to resolve the
VSI. For higher resolutions, greater than 50 cells per scale height, we observe
the convergence for the saturation level of the kinetic energy. We are also
able to identify the growth of the `body' modes, with higher growth rate for
higher resolution. Full energy saturation and a turbulent steady state is
reached after 70 local orbits. We determine the location of the EUV-heated
region defined by the radial column density to be 10$^{19}$ cm$^{-2}$ located
at $H_\mathrm{R}\sim9.7$, and the FUV/X-Rays-heated boundary layer defined by
10$^{22}$ cm$^{-2}$ located at $H_\mathrm{R}\sim6.2$, making it necessary to
introduce the need of a hot atmosphere. For the first time, we report the
presence of small scale vortices in the r-Z plane, between the characteristic
layers of large scale vertical velocity motions. Such vortices could lead to
dust concentration, promoting grain growth. Our results highlight the
importance to combine photoevaporation processes in the future high-resolution
studies of the turbulence and accretion processes in disks.",2010.06711v1
2021-04-11,"The effects of non-helical component of hypermagnetic field on the evolution of the matter-antimatter asymmetry, vorticity, and hypermagnetic field","We study the evolution of the matter-antimatter asymmetry ({\eta}), the
vorticity, and the hypermagnetic field in the symmetric phase of the early
Universe, and in the temperature range 100 GeV < T < 10 TeV. We assume a
configuration for the hypermagnetic field which includes both helical and
non-helical (Bz) components. Consequently, the hypermagnetic field and the
fluid vorticity can directly affect each other, the manifestations of which we
explore in three scenarios. In the first scenario, we show that in the presence
of a small vorticity and a large {\eta}eR, helicity can be generated and
amplified for an initially strong Bz. The generation of the helical seed is due
to the chiral vortical effect (CVE) and/or the advection term, while its growth
is mainly due to the chiral magnetic effect (CME) which leads to the production
of the baryon asymmetry, as well. The vorticity saturates to a nonzero value
which depends on Bz, even in the presence of the viscosity, due to the
back-reaction of Bz on the plasma. Increasing the initial vorticity, makes the
values of the helicity, {\eta}s, and vorticity reach their saturation curves
sooner, but does not change their final values at the onset of the electroweak
phase transition. The second scenario is similar to the first except we assume
that all initial {\eta}s are zero. We find that much higher initial vorticity
is required for the generation process. In the third scenario, we show that in
the presence of only a strong hypermagnetic field, {\eta}s and vorticity can be
generated and amplified. Increasing the initial helicity, increases the final
{\eta}s and vorticity. We find that although the presence of a nonzero initial
Bz is necessary in all three scenarios, its increase only increases the final
values of vorticity.",2104.05013v1
2022-08-10,"Starspots, chromospheric emission lines, and flares of zero-age main-sequence stars","Zero-age main-sequence (ZAMS) stars are considered to have enormous starspots
and show strong chromospheric emission lines because of their strong surface
magnetic field. We discuss the dynamo activities of ZAMS stars with respect to
their periodic light variation caused by a starspot and with respect to the
strength of the chromospheric emission lines. The light curves of $33$ ZAMS
stars in IC 2391 and IC 2602 were obtained from \textit{TESS} photometric data.
The light curves can be grouped into the following four categories: single
frequency, possible shape changer, beater, and complex variability. The
amplitudes of the light curves are $0.001-0.145\,\mathrm{mag}$, similar to
those of ZAMS stars in Pleiades. The starspot coverages are $0.1-21\%$. We
found that the light variations and Ca\,\emissiontype{II} emission line
strength of ZAMS stars in IC 2391, IC 2602, and the Pleiades cluster are as
large as those of the most active superflare stars and two orders larger than
those of the Sun, and are located on the extensions of the superflare stars.
These results suggest that superflare stars link the properties of the Sun to
those of the ZAMS stars of ages between $30$ and $120\,\mathrm{Myr}$. ZAMS
stars with a single frequency or possible shape change in the light curve tend
to have both large light variation, indicating large spot coverage, and
saturated Ca\,\emissiontype{II} emission line strength. ZAMS stars with beat or
complex variability have small spot coverage and a faint Ca\,\emissiontype{II}
emission line. We also detected $21$ flares in the \textit{TESS} light curves
of $12$ ZAMS stars in IC 2391 and IC 2602, where most of these stars have
saturated chromospheric Ca\,\emissiontype{II} emission lines. The energies of
the flares are estimated to be $\sim 10^{33}-10^{35}\,\mathrm{erg}$, which is
comparable with the energy of a superflare.",2208.05175v2
2023-04-27,Heisenberg Limit beyond Quantum Fisher Information,"The Heisenberg limit provides a fundamental bound on the achievable
estimation precision with a limited number of $N$ resources used (e.g., atoms,
photons, etc.). Using entangled quantum states makes it possible to scale the
precision with $N$ better than when resources would be used independently.
Consequently, the optimal use of all resources involves accumulating them in a
single execution of the experiment. Unfortunately, that implies that the most
common theoretical tool used to analyze metrological protocols - quantum Fisher
information (QFI) - does not allow for a reliable description of this problem,
as it becomes operationally meaningful only with multiple repetitions of the
experiment. In this thesis, using the formalism of Bayesian estimation and the
minimax estimator, I derive asymptotically saturable bounds on the precision of
the estimation for the case of noiseless unitary evolution. For the case where
the number of resources $N$ is strictly constrained, I show that the final
measurement uncertainty is $\pi$ times larger than would be implied by a naive
use of QFI. I also analyze the case where a constraint is imposed only on the
average amount of resources, the exact value of which may fluctuate (in which
case QFI does not provide any universal bound for precision). In both cases, I
study the asymptotic saturability and the rate of convergence of these bounds.
In the following part, I analyze the problem of the Heisenberg limit when
multiple parameters are measured simultaneously on the same physical system. In
particular, I investigate the existence of a gain from measuring all parameters
simultaneously compared to distributing the same amount of resources to measure
them independently. I focus on two examples - the measurement of multiple phase
shifts in a multi-arm interferometer and the measurement of three magnetic
field components.",2304.14370v1
2005-12-20,Integrable models and quantum spin ladders: comparison between theory and experiment for the strong coupling ladder compounds,"(abbreviated) This article considers recent advances in the investigation of
the thermal and magnetic properties of integrable spin ladder models and their
applicability to the physics of real compounds. The ground state properties of
the integrable two-leg spin-1/2 and the mixed spin-(1/2,1) ladder models at
zero temperature are analyzed by means of the Thermodynamic Bethe Ansatz.
Solving the TBA equations yields exact results for the critical fields and
critical behaviour. The thermal and magnetic properties of the models are
investigated in terms of the recently introduced High Temperature Expansion
method, which is discussed in detail. It is shown that in the strong coupling
limit the integrable spin-1/2 ladder model exhibits three quantum phases: (i) a
gapped phase in the regime $H<H_{c1}$, (ii) a fully polarised phase for
$H>H_{c2}$, and (iii) a Luttinger liquid magnetic phase in the regime
$H_{c1}<H<H_{c2}$. The critical behaviour in the vicinity of the critical
points is of the Pokrovsky-Talapov type. The temperature-dependent thermal and
magnetic properties are directly evaluated from the exact free energy
expression and compared to known experimental results for a range of strong
coupling ladder compounds. Similar analysis of the mixed spin-(1/2,1) ladder
model reveals a rich phase diagram, with a 1/3 and a full saturation
magnetisation plateau within the strong antiferromagnetic rung coupling regime.
For weak rung coupling, the fractional magnetisation plateau is diminished and
a new quantum phase transition occurs. The phase diagram can be directly
deduced from the magnetisation curve obtained from the exact result derived
from the HTE. The thermodynamics of the spin-orbital model with different
single-ion anisotropies is also investigated.",0512489v3
2006-05-19,"Magnetic state dynamics in itinerant paramagnet UM3B2 (M= Co, Ir) probed by 11B NMR","We have carried out the $^{11}$B NMR measurement on the itinerant
paramagnetic systems U$M_{3}$B$_{2}$ ($M =$ Co, Ir) to investigate the
low-dimensional characteristics of the $5f$-electrons due to the structural
anisotropy. The recent X-ray analysis suggests that UIr$_3$B$_2$ has a
different structure modulated from the ever-known superlattice. The azimuth
angle variation of NMR spectrum within the $ab$-plane clarified that B atoms
occupy the single site, and a certain ligands arrangement surrounding B atom
turns to the same orientation as the another one through the three- or six-fold
rotation around the c-axis. These results have been consistent with the X-ray
proposition. To evaluate the temperature ($T$) development of general
susceptibility ($\chi_{q,\omega}$), Knight shift and nuclear spin-lattice
relaxation rates measurements were performed and the similar variations of
$\chi_{q,\omega}$ were identified in both UCo$_{3}$B$_{2}$ and
UIr$_{3}$B$_{2}$. Above a crossover point defined as $T^{*}\simeq50$ K, the
evolution of $\chi_{q,\omega}$ is dominant at $q=0$, suggesting that
ferromagnetic correlations develop in high-$T$ regimes; meanwhile, below
$T^{*}$, the $q=0$ part in $\chi_{q,\omega}$ shows the saturation tendency, and
a different class of dispersion at finite-$q$ suddenly emerges. This particular
magnetic correlations are interpreted as the antiferromagnetic correlations,
and notable feature of the magnetic state dynamics in low-$T$ regimes is that
the antiferromagnetic correlations arise together with the ferromagnetic
component at the same time. The unique magnetic correlations obtained from NMR
experiment will be discussed by the possible low-dimensionality of
U$M_{3}$B$_{2}$ lattice.",0605483v1
2006-10-05,Fundamental Magnetic Properties and Structural Implications for Nanocrystalline Fe-Ti-N Thin Films,"The magnetization (M) as a function of temperature (T) from 2 to 300 K and
in-plane field (H) up to 1 kOe, room temperature easy and hard direction
in-plane field hysteresis loops for fields between -100 and +100 Oe, and 10 GHz
ferromagnetic resonance (FMR) profiles have been measured for a series of
soft-magnetic nano-crystalline 50 nm thick Fe-Ti-N films made by magnetron
sputtering in an in-plane field. The nominal titanium concentration was 3 at. %
and the nitrogen concentrations (xN) ranged from zero to 12.7 at. %. The
saturation magnetization (Ms) vs. T data and the extracted exchange parameters
as a function of xN are consistent with a lattice expansion due to the addition
of interstitial nitrogen in the body-centered-cubic (bcc) lattice and a
structural transition to body-centered-tetragonal (bct) in the 6-8 at. %
nitrogen range. The hysteresis loop and FMR data show a consistent picture of
the changes in both the uniaxial and cubic anisotropy as a function of xN.
Films with xN > 1.9 at. % show an overall uniaxial anisotropy, with an
anisotropy field parameter Hu that increases with xN. The corresponding
dispersion averaged uniaxial anisotropy energy density parameter <Ku> = HuMs/2
is a linear function of xN, with a rate of increase of 950 erg/cm3 per at. %
nitrogen. The estimated uniaxial anisotropy energy per nitrogen atom is 30
J/mol, a value consistent with other systems. For xN below 6 at. %, the scaling
of coercive force Hc data with the sixth power of the grain size D indicate a
grain averaged effective cubic anisotropy energy density parameter <K1> that is
about an order of magnitude smaller that the nominal K1 values for iron, and
give a quantitative <K1> vs. D response that matches predictions for exchange
coupled random grains with cubic anisotropy.",0610160v1
2002-06-01,The r-modes in accreting neutron stars with magneto-viscous boundary layers,"We explore the dynamics of the r-modes in accreting neutron stars in two
ways. First, we explore how dissipation in the magneto-viscous boundary layer
(MVBL) at the crust-core interface governs the damping of r-mode perturbations
in the fluid interior. Two models are considered: one assuming an
ordinary-fluid interior, the other taking the core to consist of superfluid
neutrons, type II superconducting protons, and normal electrons. We show,
within our approximations, that no solution to the magnetohydrodynamic
equations exists in the superfluid model when both the neutron and proton
vortices are pinned. However, if just one species of vortex is pinned, we can
find solutions. When the neutron vortices are pinned and the proton vortices
are unpinned there is much more dissipation than in the ordinary-fluid model,
unless the pinning is weak. When the proton vortices are pinned and the neutron
vortices are unpinned the dissipation is comparable or slightly less than that
for the ordinary-fluid model, even when the pinning is strong. We also find in
the superfluid model that relatively weak radial magnetic fields ~ 10^9 G (10^8
K / T)^2 greatly affect the MVBL, though the effects of mutual friction tend to
counteract the magnetic effects. Second, we evolve our two models in time,
accounting for accretion, and explore how the magnetic field strength, the
r-mode saturation amplitude, and the accretion rate affect the cyclic evolution
of these stars. If the r-modes control the spin cycles of accreting neutron
stars we find that magnetic fields can affect the clustering of the spin
frequencies of low mass x-ray binaries (LMXBs) and the fraction of these that
are currently emitting gravitational waves.",0206001v2
1994-12-22,String Solitons,"We review the status of solitons in superstring theory, with a view to
understanding the strong coupling regime. These {\it solitonic} solutions are
non-singular field configurations which solve the empty-space low-energy field
equations (generalized, whenever possible, to all orders in $\alpha'$), carry a
non-vanishing topological ""magnetic"" charge and are stabilized by a topological
conservation law. They are compared and contrasted with the {\it elementary}
solutions which are singular solutions of the field equations with a
$\sigma$-model source term and carry a non-vanishing Noether ""electric"" charge.
In both cases, the solutions of most interest are those which preserve half the
spacetime supersymmetries and saturate a Bogomol'nyi bound. They typically
arise as the extreme mass=charge limit of more general two-parameter solutions
with event horizons. We also describe the theory {\it dual} to the fundamental
string for which the roles of elementary and soliton solutions are
interchanged. In ten spacetime dimensions, this dual theory is a superfivebrane
and this gives rise to a string/fivebrane duality conjecture according to which
the fivebrane may be regarded as fundamental in its own right, with the
strongly coupled string corresponding to the weakly coupled fivebrane and
vice-versa. After compactification to four spacetime dimensions, the fivebrane
appears as a magnetic monopole or a dual string according as it wraps around
five or four of the compactified dimensions. This gives rise to a
four-dimensional string/string duality conjecture which subsumes a
Montonen-Olive type duality in that the magnetic monopoles of the fundamental
string correspond to the electric winding states of the dual string. This leads
to a {\it duality of dualities} whereby under string/string duality the the
strong/weak coupling $S$-duality trades places with the minimum/maximum length
$T$-duality. Since these magnetic monopoles are extreme black holes, a
prediction of $S$-duality is that the corresponding electric massive states of
the fundamental string are also extreme black holes.",9412184v1
2007-05-24,MHD simulations of the magnetorotational instability in a shearing box with zero net flux. II. The effect of transport coefficients,"We study the influence of the choice of transport coefficients (viscosity and
resistivity) on MHD turbulence driven by the magnetorotational instability
(MRI) in accretion disks. We follow the methodology described in paper I: we
adopt an unstratified shearing box model and focus on the case where the net
vertical magnetic flux threading the box vanishes. For the most part we use the
finite difference code ZEUS, including explicit transport coefficients in the
calculations. However, we also compare our results with those obtained using
other algorithms (NIRVANA, the PENCIL code and a spectral code) to demonstrate
both the convergence of our results and their independence of the numerical
scheme. We find that small scale dissipation affects the saturated state of MHD
turbulence. In agreement with recent similar numerical simulations done in the
presence of a net vertical magnetic flux, we find that turbulent activity
(measured by the rate of angular momentum transport) is an increasing function
of the magnetic Prandtl number Pm for all values of the Reynolds number Re that
we investigated. We also found that turbulence disappears when the Prandtl
number falls below a critical value Pm_c that is apparently a decreasing
function of Re. For the limited region of parameter space that can be probed
with current computational resources, we always obtained Pm_c>1. We conclude
that the magnitudes of the transport coefficients are important in determining
the properties of MHD turbulence in numerical simulations in the shearing box
with zero net flux, at least for Reynolds numbers and magnetic Prandtl numbers
that are such that transport is not dominated by numerical effects and thus can
be probed using current computational resources.",0705.3622v2
2007-09-24,Nonlinear Dynamics of the Parker Scenario for Coronal Heating,"The Parker or field line tangling model of coronal heating is studied
comprehensively via long-time high-resolution simulations of the dynamics of a
coronal loop in cartesian geometry within the framework of reduced
magnetohydrodynamics (RMHD). Slow photospheric motions induce a Poynting flux
which saturates by driving an anisotropic turbulent cascade dominated by
magnetic energy. In physical space this corresponds to a magnetic topology
where magnetic field lines are barely entangled, nevertheless current sheets
(corresponding to the original tangential discontinuities hypothesized by
Parker) are continuously formed and dissipated.
  Current sheets are the result of the nonlinear cascade that transfers energy
from the scale of convective motions ($\sim 1,000 km$) down to the dissipative
scales, where it is finally converted to heat and/or particle acceleration.
Current sheets constitute the dissipative structure of the system, and the
associated magnetic reconnection gives rise to impulsive ``bursty'' heating
events at the small scales. This picture is consistent with the slender loops
observed by state-of-the-art (E)UV and X-ray imagers which, although apparently
quiescent, shine bright in these wavelengths with little evidence of entangled
features.
  The different regimes of weak and strong MHD turbulence that develop, and
their influence on coronal heating scalings, are shown to depend on the loop
parameters, and this dependence is quantitatively characterized: weak
turbulence regimes and steeper spectra occur in {\it stronger loop fields} and
lead to {\it larger heating rates} than in weak field regions.",0709.3687v2
2009-08-16,"Evolution of the bulk properties, structure, magnetic order, and superconductivity with Ni doping in CaFe2-xNixAs2","Magnetization, susceptibility, specific heat, resistivity, neutron and x-ray
diffraction have been used to characterize the properties of single crystalline
CaFe2-xNixAs2 as a function of Ni doping for x varying from 0 to 0.1. The
combined first-order structural and magnetic phase transitions occur together
in the undoped system at 172 K, with a small decrease in the area of the a-b
plane along with an abrupt increase in the length of the c-axis in the
orthorhombic phase. With increasing x the ordered moment and transition
temperature decrease, but the transition remains sharp at modest doping while
the area of the a-b plane quickly decreases and then saturates. Warming and
cooling data in the resistivity and neutron diffraction indicate hysteresis of
~2 K. At larger doping the transition is more rounded, and decreases to zero
for x=0.06. The susceptibility is anisotropic for all values of x. Electrical
resistivity for x = 0.053 and 0.06 shows a superconducting transition with an
onset of nearly 15 K which is further corroborated by substantial diamagnetic
susceptibility. For the fully superconducting sample there is no long range
magnetic order and the structure remains tetragonal at all temperature, but
there is an anomalous increase in the area of the a-b plane in going to low T.
Heat capacity data show that the density of states at the Fermi level increases
for x > 0.053 as inferred from the value of Sommerfeld coefficient. The regime
of superconductivity is quite restrictive, with a maximum TC of 15 K and an
upper critical field Hc2=14 T. Superconductivity disappears in the overdoped
region.",0908.2255v2
2010-11-02,The baroclinic instability in the context of layered accretion. Self-sustained vortices and their magnetic stability in local compressible unstratified models of protoplanetary disks,"Turbulence and angular momentum transport in accretion disks remains a topic
of debate. With the realization that dead zones are robust features of
protoplanetary disks, the search for hydrodynamical sources of turbulence
continues. A possible source is the baroclinic instability (BI), which has been
shown to exist in unmagnetized non-barotropic disks. We present shearing box
simulations of baroclinicly unstable, magnetized, 3D disks, in order to assess
the interplay between the BI and other instabilities, namely the
magneto-rotational instability (MRI) and the magneto-elliptical instability. We
find that the vortices generated and sustained by the baroclinic instability in
the purely hydrodynamical regime do not survive when magnetic fields are
included. The MRI by far supersedes the BI in growth rate and strength at
saturation. The resulting turbulence is virtually identical to an MRI-only
scenario. We measured the intrinsic vorticity profile of the vortex, finding
little radial variation in the vortex core. Nevertheless, the core is disrupted
by an MHD instability, which we identify with the magneto-elliptic instability.
This instability has nearly the same range of unstable wavelengths as the MRI,
but has higher growth rates. In fact, we identify the MRI as a limiting case of
the magneto-elliptic instability, when the vortex aspect ratio tends to
infinity (pure shear flow). We conclude that vortex excitation and
self-sustenance by the baroclinic instability in protoplanetary disks is viable
only in low ionization, i.e., the dead zone. Our results are thus in accordance
with the layered accretion paradigm. A baroclinicly unstable dead zone should
be characterized by the presence of large-scale vortices whose cores are
elliptically unstable, yet sustained by the baroclinic feedback. As magnetic
fields destroy the vortices and the MRI outweighs the BI, the active layers are
unmodified.",1011.0497v3
2011-04-27,Mass accretion to young stars triggered by flaring activity in circumstellar disks,"Young low-mass stars are characterized by ejection of collimated outflows and
by circumstellar disks which they interact with through accretion of mass. The
accretion builds up the star to its final mass and is also believed to power
the mass outflows, which may in turn remove the excess angular momentum from
the star-disk system. However, although the process of mass accretion is a
critical aspect of star formation, some of its mechanisms are still to be fully
understood. A point not considered to date and relevant for the accretion
process is the evidence of very energetic and frequent flaring events in these
stars. Flares may easily perturb the stability of the disks, thus influencing
the transport of mass and angular momentum. Here we report on three-dimensional
magnetohydrodynamic modeling of the evolution of a flare with an idealized
non--equilibrium initial condition occurring near the disk around a rotating
magnetized star. The model takes into account the stellar magnetic field, the
gravitational force, the viscosity of the disk, the magnetic-field-oriented
thermal conduction (including the effects of heat flux saturation), the
radiative losses from optically thin plasma, and the coronal heating. We show
that, during its first stage of evolution, the flare gives rise to a hot
magnetic loop linking the disk to the star. The disk is strongly perturbed by
the flare: disk material evaporates under the effect of the thermal conduction
and an overpressure wave propagates through the disk. When the overpressure
reaches the opposite side of the disk, a funnel flow starts to develop there,
accreting substantial disk material onto the young star from the side of the
disk opposite to the flare.",1104.5107v1
2011-08-31,Gyrokinetic Equations for Strong-Gradient Regions,"A gyrokinetic theory is developed under a set of orderings applicable to the
edge region of tokamaks and other magnetic confinement devices, as well as to
internal transport barriers. The result is a practical set equations that is
valid for large perturbation amplitudes [q{\delta}{\psi}/T = O(1), where
{\delta}{\psi} = {\delta}{\phi} - v_par {\delta}A_par/c], which is
straightforward to implement numerically, and which has straightforward
expressions for its conservation properties. Here, q is the particle charge,
{\delta}{\phi} and {\delta}A_par are the perturbed electrostatic and parallel
magnetic potentials, v_par is the parallel velocity, c is the speed of light,
and T is the temperature. The derivation is based on the quantity
{\epsilon}:=({\rho}/{\lambda})q{\delta}{\psi}/T << 1 as the small expansion
parameter, where {\rho} is the gyroradius and {\lambda} is the perpendicular
wavelength. Physically, this ordering requires that the E\times B velocity and
the component of the parallel velocity perpendicular to the equilibrium
magnetic field are small compared to the thermal velocity. For nonlinear
fluctuations saturated at ""mixing-length"" levels (i.e., at a level such that
driving gradients in profile quantities are locally flattened), {\epsilon} is
of order {\rho}/L, where L is the equilibrium profile scale length, for all
scales {\lambda} ranging from {\rho} to L. This is true even though
q{\delta}{\psi}/T = O(1) for {\lambda} ~ L. Significant additional
simplifications result from ordering L/R =O({\epsilon}), where R is the spatial
scale of variation of the magnetic field. We argue that these orderings are
well satisfied in strong-gradient regions, such as edge and screapeoff layer
regions and internal transport barriers in tokamaks, and anticipate that our
equations will be useful as a basis for simulation models for these regions.",1108.6327v2
2011-09-01,The Elemental Shear Dynamo,"A quasi-linear theory is presented for how randomly forced, barotropic
velocity fluctuations cause an exponentially-growing, large-scale (mean)
magnetic dynamo in the presence of a uniform shear flow, $\vec{U} = S x
\vec{e}_y$. It is a ""kinematic"" theory for the growth of the mean magnetic
energy from a small initial seed, neglecting the saturation effects of the
Lorentz force. The quasi-linear approximation is most broadly justifiable by
its correspondence with computational solutions of nonlinear
magneto-hydrodynamics, and it is rigorously derived in the limit of large
resistivity, $\eta \rightarrow \infty$. Dynamo action occurs even without mean
helicity in the forcing or flow, but random helicity variance is then
essential. In a sufficiently large domain and with small wavenumber $k_z$ in
the direction perpendicular to the mean shearing plane, a positive exponential
growth rate $\gamma$ can occur for arbitrary values of $\eta$, the viscosity
$\nu$, and the random-forcing correlation time $t_f$ and phase angle $\theta_f$
in the shearing plane. The value of $\gamma$ is independent of the domain size.
The shear dynamo is ""fast"", with finite $\gamma > 0$ in the limit of $\eta
\rightarrow 0$. Averaged over the random forcing ensemble, the mean magnetic
field grows more slowly, if at all, compared to the r.m.s. field (or magnetic
energy). In the limit of small Reynolds numbers ($\eta, \ \nu \rightarrow
\infty$), the dynamo behavior is related to the well-known alpha--omega {\it
ansatz} when the forcing is steady ($t_f \rightarrow \infty$) and to the
""incoherent"" alpha--omega {\it ansatz} when the forcing is purely fluctuating.",1109.0289v2
2011-09-29,Developing the Technique of Measurements of Magnetic Field in the CMS Steel Yoke Elements With Flux-Loops and Hall Probes,"Compact muon solenoid (CMS) is a general-purpose detector designed to run at
the highest luminosity at the CERN large hadron collider (LHC). Its distinctive
features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m
long free bore, enclosed inside a 10000-ton return yoke made of construction
steel. Accurate characterization of the magnetic field everywhere in
theCMSdetector, including the large ferromagnetic parts of the yoke, is
required. To measure the field in and around ferromagnetic parts, a set of
flux-loops and Hall probe sensors will be installed on several of the steel
pieces. Fast discharges of the solenoid during system commissioning tests will
be used to induce voltages in the flux-loops that can be integrated to measure
the flux in the steel at full excitation of the solenoid. The Hall sensors will
give supplementary information on the axial magnetic field and permit
estimation of the remanent field in the steel after the fast discharge. An
experimental R&D program has been undertaken, using a test flux-loop, two Hall
sensors, and sample disks made from the same construction steel used for the
CMS magnet yoke. A sample disc, assembled with the test flux-loop and the Hall
sensors, was inserted between the pole tips of a dipole electromagnet equipped
with a computer-controlled power supply to measure the excitation of the steel
from full saturation to zero field. The results of the measurements are
presented and discussed.",1109.6465v1
2011-10-21,Magnetic properties and revisited exchange integrals of the frustrated chain cuprate PbCuSO$_4$(OH)$_2$ - linarite,"We present a detailed study in the paramagnetic regime of the frustrated $s$
= 1/2 spin-compound linarite, PbCuSO$_4$(OH)$_2$, with competing ferromagnetic
nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange
interactions. Our data reveal highly anisotropic values for the saturation
field along the crystallographic main directions, with $\sim$ 7.6, $\sim$ 10.5
and $\sim$ 8.5\,T for the $a$, $b$, and $c$ axes, respectively. In the
paramagnetic regime, this behavior is explained mainly by the anisotropy of the
\textit{g}-factor but leaving room for an easy-axis exchange anisotropy. Within
the isotropic $J_1$-$J_2$ spin model our experimental data are described by
various theoretical approaches yielding values for the exchange interactions
$J_1$ $\sim$ -100\,K and $J_2$ $\sim$ 36\,K. These main intrachain exchange
integrals are significantly larger as compared to the values derived in two
previous studies in the literature and shift the frustration ratio $\alpha =
J_2/|J_1|$ $\approx$ 0.36 of linarite closer to the 1D critical point at 0.25.
Electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements
further prove that the static susceptibility is dominated by the intrinsic spin
susceptibility. The Knight shift as well as the broadening of the linewidth in
ESR and NMR at elevated temperatures indicate a highly frustrated system with
the onset of magnetic correlations far above the magnetic ordering temperature
$T_\mathrm{N}$ = 2.75(5)\,K, in agreement with the calculated exchange
constants.",1110.4729v1
2012-02-14,Dephasing and Hyperfine Interaction in Carbon Nanotubes Double Quantum Dots: Disordered Case,"We study theoretically the \emph{return probability experiment}, used to
measure the dephasing time $T_2^*$, in a double quantum dot (DQD) in
semiconducting carbon nanotubes (CNTs) with spin-orbit coupling and disorder
induced valley mixing. Dephasing is due to hyperfine interaction with the spins
of the ${}^{13}$C nuclei. Due to the valley and spin degrees of freedom four
bounded states exist for any given longitudinal mode in the quantum dot. At
zero magnetic field the spin-orbit coupling and the valley mixing split those
four states into two Kramers doublets. The valley mixing term for a given dot
is determined by the intra-dot disorder and therefore the states in the Kramers
doublets belonging to different dots are different. We show how nonzero
single-particle interdot tunneling amplitudes between states belonging to
different doublets give rise to new avoided crossings, as a function of
detuning, in the relevant two particle spectrum, crossing over from the two
electrons in one dot states configuration, $(0,2)$, to the one electron in each
dot configuration, $(1,1)$. In contrast to the clean system, multiple
Landau-Zener processes affect the separation and the joining stages of each
single-shot measurement and they affect the outcome of the measurement in a way
that strongly depends on the initial state. We find that a well-defined return
probability experiment is realized when, at each single-shot cycle, the (0,2)
ground state is prepared. In this case, valley mixing increases the saturation
value of the measured return probability, whereas the probability to return to
the (0,2) ground state remains unchanged. Finally, we study the effect of the
valley mixing in the high magnetic field limit; for a parallel magnetic field
the predictions coincide with a clean nanotube, while the disorder effect is
always relevant with a magnetic field perpendicular to the nanotube axis.",1202.2929v2
2012-02-16,Solitary magnetic perturbations at the ELM onset,"Edge localised modes (ELMs) allow maintaining sufficient purity of tokamak
H-mode plasmas and thus enable stationary H-mode. On the other hand in a future
device ELMs may cause divertor power flux densities far in excess of tolerable
material limits. The size of the energy loss per ELM is determined by
saturation effects in the non-linear phase of the ELM, which at present is
hardly understood. Solitary magnetic perturbations (SMPs) are identified as
dominant features in the radial magnetic fluctuations below 100kHz. They are
typically observed close (+-0.1ms) to the onset of pedestal erosion. SMPs are
field aligned structures rotating in the electron diamagnetic drift direction
with perpendicular velocities of about 10km/s. A comparison of perpendicular
velocities suggests that the perturbation evoking SMPs is located at or inside
the separatrix. Analysis of very pronounced examples showed that the number of
peaks per toroidal turn is 1 or 2, which is clearly lower than corresponding
numbers in linear stability calculations. In combination with strong peaking of
the magnetic signals this results in a solitary appearance resembling modes
like palm tree modes, edge snakes or outer modes. This behavior has been
quantified as solitariness and correlated to main plasma parameters. SMPs may
be considered as a signature of the non-linear ELM-phase originating at the
separatrix or further inside. Thus they provide a handle to investigate the
transition from linear to non-linear ELM phase. By comparison with data from
gas puff imaging processes in the non-linear phase at or inside the separatrix
and in the scrape-off-layer (SOL) can be correlated. A connection between the
passing of an SMP and the onset of radial filament propagation has been found.
Eventually the findings related to SMPs may contribute to a future quantitative
understanding of the non-linear ELM evolution.",1202.3603v1
2012-03-01,Emergent Mesoscale Phenomena in Magnetized Accretion Disc Turbulence,"We study how the structure and variability of magnetohydrodynamic (MHD)
turbulence in accretion discs converge with domain size. Our results are based
on a series of vertically stratified local simulations, computed using the
Athena code, that have fixed spatial resolution, but varying radial and
azimuthal extent (from \Delta R = 0.5H to 16H, where H is the vertical scale
height). We show that elementary local diagnostics of the turbulence, including
the Shakura-Sunyaev {\alpha} parameter, the ratio of Maxwell stress to magnetic
energy, and the ratio of magnetic to fluid stresses, converge to within the
precision of our measurements for spatial domains of radial size Lx \geq 2H. We
obtain {\alpha} = 0.02-0.03, consistent with recent results. Very small domains
(Lx = 0.5H) return anomalous results, independent of spatial resolution. The
convergence with domain size is only valid for a limited set of diagnostics:
larger spatial domains admit the emergence of dynamically important mesoscale
structures. In our largest simulations, the Maxwell stress shows a significant
large scale non-local component, while the density develops long-lived
axisymmetric perturbations (zonal flows) at the 20% level. Most strikingly, the
variability of the disc in fixed-sized patches decreases strongly as the
simulation volume increases. We find generally good agreement between our
largest local simulations and global simulations with comparable spatial
resolution. There is no direct evidence that the presence of curvature terms or
radial gradients in global calculations materially affect the turbulence,
except to perhaps introduce an outer radial scale for mesoscale structures. The
demonstrated importance of mean magnetic fields, seen in both large local and
global simulations implies that the growth and saturation of these fields is
likely of critical importance for the evolution of accretion discs. (abridged)",1203.0314v1
2013-10-24,Trends in Ultracool Dwarf Magnetism. I. X-Ray Suppression and Radio Enhancement,"Although ultracool dwarfs (UCDs) are now known to generate and dissipate
strong magnetic fields, a clear understanding of the underlying dynamo is still
lacking. We have performed X-ray and radio observations of seven UCDs in a
narrow range of spectral type (M6.5-M9.5) but spanning a wide range of
projected rotational velocities (v sin i ~ 3-40 km/s). We have also analyzed
unpublished archival Chandra observations of four additional objects. All of
the newly-observed targets are detected in the X-ray, while only one is
detected in the radio, with the remainder having sensitive upper limits. We
present a database of UCDs with both radio and X-ray measurements and consider
the data in light of the so-called G\""udel-Benz relation (GBR) between magnetic
activity in these bands. Some UCDs have very bright radio emission and faint
X-ray emission compared to what would be expected for rapid rotators, while
others show opposite behavior. We show that UCDs would still be
radio-over-luminous relative to the GBR even if their X-ray emission were at
standard rapid-rotator ""saturation"" levels. Recent results from Zeeman-Doppler
imaging and geodynamo simulations suggest that rapidly-rotating UCDs may harbor
a bistable dynamo that supports either a stronger, axisymmetric magnetic field
or a weaker, non-axisymmetric field. We suggest that the data can be explained
in a scenario in which strong-field objects obey the GBR while weak-field
objects are radio-over-luminous and X-ray-under-luminous, possibly because of a
population of gyrosynchrotron-emitting coronal electrons that is continuously
replenished by low-energy reconnection events.",1310.6757v2
2014-01-05,Soft X-ray emission in kink-unstable coronal loops,"Solar flares are associated with intense soft X-ray emission generated by the
hot flaring plasma. Kink unstable twisted flux-ropes provide a source of
magnetic energy which can be released impulsively and account for the flare
plasma heating. We compute the temporal evolution of the thermal X-ray emission
in kink-unstable coronal loops using MHD simulations and discuss the results of
with respect to solar flare observations. The model consists of a highly
twisted loop embedded in a region of uniform and untwisted coronal magnetic
field. We let the kink instability develop, compute the evolution of the plasma
properties in the loop (density, temperature) without accounting for mass
exchange with the chromosphere. We then deduce the X-ray emission properties of
the plasma during the whole flaring episode. During the initial phase of the
instability plasma heating is mostly adiabatic. Ohmic diffusion takes over as
the instability saturates, leading to strong and impulsive heating (> 20 MK),
to a quick enhancement of X-ray emission and to the hardening of the thermal
X-ray spectrum. The temperature distribution of the plasma becomes broad, with
the emission measure depending strongly on temperature. Significant emission
measures arise for plasma at temperatures T > 9 MK. The magnetic flux-rope then
relaxes progressively towards a lower energy state as it reconnects with the
background flux. The loop plasma suffers smaller sporadic heating events but
cools down conductively. The total thermal X-ray emission slowly fades away
during this phase, and the high temperature component of emission measure
distribution converges to the power-law distribution $EM\propto T^{-4.2}$. The
amount of twist deduced directly from the X-ray emission patterns is
considerably lower than the maximum magnetic twist in the simulated flux-ropes.",1401.0916v2
2014-02-25,"Structural, magnetic and superconducting properties of pulsed-laser-deposition-grown $\rm{La_{1.85}Sr_{0.15}CuO_{4}/La_{2/3}Ca_{1/3}MnO_{3}}$ superlattices on $\rm{(001)}$-oriented $\rm{LaSrAlO_{4}}$ substrates","Epitaxial La1.85Sr0.15CuO4/La2/3Ca1/3MnO3 superlattices on (001)-oriented
LaSrAlO4 substrates have been grown with pulsed laser deposition technique.
Their structural, magnetic and superconducting properties have been determined
with in-situ reflection high energy electron diffraction, x-ray diffraction,
specular neutron reflectometry, scanning transmission electron microscopy,
electric transport, and magnetization measurements. We find that despite the
large mismatch between the in-plane lattice parameters of LSCO and LCMO these
superlattices can be grown epitaxially and with a high crystalline quality.
While the first LSCO layer remains clamped to the LSAO substrate, a sizeable
strain relaxation occurs already in the first LCMO layer. The following LSCO
and LCMO layers adopt a nearly balanced state in which the tensile and
compressive strain effects yield alternating in-plane lattice parameters with
an almost constant average value. No major defects are observed in the LSCO
layers, while a significant number of vertical antiphase boundaries are found
in the LCMO layers. The LSCO layers remain superconducting with a relatively
high superconducting onset temperature of about 36 K. The macroscopic
superconducting response is also evident in the magnetization data due to a
weak diamagnetic signal below 10 K for H || ab and a sizeable paramagnetic
shift for H || c that can be explained in terms of a vortex-pinning-induced
flux compression. The LCMO layers maintain a strongly ferromagnetic state with
a Curie temperature of about 190 K and a large low-temperature saturation
moment of about 3.5(1) muB. These results suggest that the LSCO/LCMO
superlattices can be used to study the interaction between the antagonistic
ferromagnetic and superconducting orders and, in combination with previous
studies on YBCO/LCMO superlattices, may allow one to identify the relevant
mechanisms.",1402.6258v1
2014-06-09,Competition between superconductivity and magnetic/nematic order as a source of anisotropic superconducting gap in underdoped Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$,"The in-plane London penetration depth, $\Delta\lambda(T)$, was measured using
a tunnel diode resonator technique in single crystals of
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ with doping levels $x$ ranging from heavily
underdoped, $x$=0.16 ($T_{c}$=7~K) to nearly optimally doped, $x$= 0.34
($T_{c}=$39 K). Exponential saturation of $\Delta\lambda(T)$ in the $T\to0$
limit is found in optimally doped samples, with the superfluid density
$\rho_{s}(T)\equiv(\lambda(0)/\lambda(T))^{2}$ quantitatively described by a
self-consistent $\gamma$-model with two nodeless isotropic superconducting
gaps. As the doping level is decreased towards the extreme end of the
superconducting dome at $x$=0.16, the low-temperature behavior of
$\Delta\lambda(T)$ becomes non-exponential and best described by the power-law
$\Delta\lambda(T)\propto T^{2}$, characteristic of strongly anisotropic gaps.
The change between the two regimes happens within the range of coexisting
magnetic/nematic order and superconductivity, $x<0.25$, and is accompanied by a
rapid rise in the absolute value of $\Delta\lambda(T)$ with underdoping. This
effect, characteristic of the competition between superconductivity and other
ordered states, is very similar to but of significantly smaller magnitude than
what is observed in the electron-doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$
compounds. Our study suggests that the competition between superconductivity
and magnetic/nematic order in hole-doped compounds is weaker than in
electron-doped compounds, and that the anisotropy of the superconducting state
in the underdoped iron pnictides is a consequence of the anisotropic changes in
the pairing interaction and in the gap function promoted by both magnetic and
nematic long-range order.",1406.2369v1
2014-09-29,Magnetotransport Measurements of the Surface States of Samarium Hexaboride using Corbino Structures,"The recent conjecture of a topologically-protected surface state in SmB$_6$
and the verification of robust surface conduction below 4 K have prompted a
large effort to understand the surface states. Conventional Hall transport
measurements allow current to flow on all surfaces of a topological insulator,
so such measurements are influenced by contributions from multiple surfaces of
varying transport character. Instead, we study magnetotransport of SmB$_6$
using a Corbino geometry, which can directly measure the conductivity of a
single, independent surface. Both (011) and (001) crystal surfaces show a
strong negative magnetoresistance at all magnetic field angles measured. The
(011) surface has a carrier mobility of $122\text{
cm}^2/\text{V}\cdot\text{sec}$ with a carrier density of $2.5\times10^{13}
\text{ cm}^{-2}$, which are significantly smaller than indicated by Hall
transport studies. This mobility value can explain a failure so far to observe
Shubnikov-de Haas oscillations. Analysis of the angle-dependence of
conductivity on the (011) surface suggests a combination of a field-dependent
enhancement of the carrier density and a suppression of Kondo scattering from
native oxide layer magnetic moments as the likely origin of the negative
magnetoresistance. Our results also reveal a hysteretic behavior whose
magnitude depends on the magnetic field sweep rate and temperature. Although
this feature becomes smaller when the field sweep is slower, does not disappear
or saturate during our slowest sweep-rate measurements, which is much slower
than a typical magnetotransport trace. These observations cannot be explained
by quantum interference corrections such as weak anti-localization, but are
more likely due to an extrinsic magnetic effect such as the magnetocaloric
effect or glassy ordering.",1409.8199v2
2015-01-30,Steady mirror structures in a plasma with pressure anisotropy,"In the first part we present a review of our results concerning the weakly
nonlinear regime of the mirror instability in the framework of an asymptotic
model. This model belongs to the class of gradient type systems for which the
free energy can only decrease in time. It reveals a behavior typical for
subcritical bifurcations: below the mirror instability threshold, all localized
stationary structures are unstable, while above threshold, the system displays
a blow-up behavior. It is shown that taking the electrons into account
(non-zero temperature) does not change the structure of the asymptotic model.
For bi-Maxwellian distribution functions for both electrons and ions, the model
predicts the formation of magnetic holes. The second part contains original
results concerning two-dimensional steady mirror structures which can form in
the saturated regime. Based on Grad-Shafranov-like equations, a gyrotropic
plasma, where the pressures in the static regime are only functions of the
amplitude of the local magnetic field, is shown to be amenable to a variational
principle with a free energy density given by the parallel tension. This
approach is used to demonstrate that small-amplitude static holes constructed
slightly below the mirror instability threshold identify with lump solitons of
KPII equation and turn out to be unstable. It is also shown that regularizing
effects such as finite Larmor radius corrections cannot be ignored in the
description of large-amplitude mirror structures. Using the gradient method,
which is based on a variational principle for anisotropic MHD taking into
account ion finite Larmor radius effects, we found both one-dimensional
magnetic structures in the form of stripes and two-dimensional bubbles when the
magnetic field component transverse to the plane is increased. These structures
realize minimum of the free energy.",1501.07702v1
2015-05-21,Angular momentum transport and large eddy simulations in magnetorotational turbulence: the small Pm limit,"Angular momentum transport in accretion discs is often believed to be due to
magnetohydrodynamic turbulence mediated by the magnetorotational instability.
Despite an abundant literature on the MRI, the parameters governing the
saturation amplitude of the turbulence are poorly understood and the existence
of an asymptotic behavior in the Ohmic diffusion regime is not clearly
established. We investigate the properties of the turbulent state in the small
magnetic Prandtl number limit. Since this is extremely computationally
expensive, we also study the relevance and range of applicability of the most
common subgrid scale models for this problem. Unstratified shearing boxes
simulations are performed both in the compressible and incompressible limits,
with a resolution up to 800 cells per disc scale height. The latter constitutes
the largest resolution ever attained for a simulation of MRI turbulence. In the
presence of a mean magnetic field threading the domain, angular momentum
transport converges to a finite value in the small Pm limit. When the mean
vertical field amplitude is such that {\beta}, the ratio between the thermal
and magnetic pressure, equals 1000, we find {\alpha}~0.032 when Pm approaches
zero. In the case of a mean toroidal field for which {\beta}=100, we find
{\alpha}~0.018 in the same limit. Both implicit LES and Chollet-Lesieur closure
model reproduces these results for the {\alpha} parameter and the power
spectra. A reduction in computational cost of a factor at least 16 (and up to
256) is achieved when using such methods. MRI turbulence operates efficiently
in the small Pm limit provided there is a mean magnetic field. Implicit LES
offers a practical and efficient mean of investigation of this regime but
should be used with care, particularly in the case of a vertical field.
Chollet-Lesieur closure model is perfectly suited for simulations done with a
spectral code.",1505.05661v1
2015-11-16,Electric quadrupole interaction in cubic BCC alpha-Fe,"Moessbauer transmission spectra for the 14.41-keV resonant line in 57Fe have
been collected at room temperature by using 57Co(Rh) commercial source and
alpha-Fe strain-free single crystal as an absorber. The absorber was magnetized
to saturation in the absorber plane perpendicular to the gamma-ray beam axis
applying small external magnetic field. Spectra were collected for various
orientations of the magnetizing field, the latter lying close to the [110]
crystal plane. A positive electric quadrupole coupling constant was found
practically independent on the field orientation. One obtains the following
value Vzz=+1.61(4)x10^19 V/m^2 for the (average) principal component of the
electric field gradient (EFG) tensor under assumption that the EFG tensor is
axially symmetric and the principal axis is aligned with the magnetic hyperfine
field acting on the 57Fe nucleus. The nuclear spectroscopic electric quadrupole
moment for the first excited state of the 57Fe nucleus was adopted as +0.17 b.
Similar measurement was performed at room temperature using as-rolled
polycrystalline alpha-Fe foil of high purity in the zero external field.
Corresponding value for the principal component of the EFG was found as
Vzz=+1.92(4)x10^19 V/m^2. Hence, it seems that the origin of the EFG is
primarily due to the local (atomic) electronic wave function distortion caused
by the spin-orbit interaction between effective electronic spin S and
incompletely quenched electronic angular momentum L. It seems as well that the
lowest order term proportional to the product L.LAMBDA.S dominates, as no
direction dependence of the EFG principal component is seen. The lowest order
term is isotropic for a cubic symmetry as one has LAMBDA=lambda.1 for cubic
systems with the symbol 1 denoting unit operator and lambda being the coupling
parameter.",1511.04933v4
2015-11-18,On the electron dynamics during island coalescence in asymmetric magnetic reconnection,"We present an analysis of the electron dynamics during rapid island merging
in asymmetric magnetic reconnection. We consider a doubly periodic system with
two asymmetric transitions. The upper layer is an asymmetric Harris sheet
initially perturbed to promote a single reconnection site. The lower layer is a
tangential discontinuity that promotes the formation of many X-points,
separated by rapidly merging islands. Across both layers the magnetic field and
the density have a strong jump, but the pressure is held constant. Our analysis
focuses on the consequences of electron energization during island coalescence.
We focus first on the parallel and perpendicular components of the electron
temperature to establish the presence of possible anisotropies and
non-gyrotropies. Thanks to the direct comparison between the two different
layers simulated, we can distinguish three main types of behavior
characteristic of three different regions of interest. The first type
represents the regions where traditional asymmetric reconnections take place
without involving island merging. The second type of regions instead show
reconnection events between two merging islands. Finally, the third regions
identifies the regions between two diverging island and where typical signature
of reconnection is not observed. Electrons in these latter regions additionally
show a flat-top distribution resulting from the saturation of a two-stream
instability generated by the two interacting electron beams from the two
nearest reconnection points. Finally, the analysis of agyrotropy shows the
presence of a distinct double structure laying all over the lower side facing
the higher magnetic field region. The distinguishing features found for the
three types of regions investigated provide clear indicators to the recently
launched MMS NASA mission for investigating magnetopause reconnection involving
multiple islands.",1511.05693v1
2016-02-08,PIC Simulations of the Effect of Velocity Space Instabilities on Electron Viscosity and Thermal Conduction,"In low-collisionality plasmas, velocity-space instabilities are a key
mechanism providing an effective collisionality for the plasma. We use
particle-in-cell (PIC) simulations to study the interplay between electron and
ion-scale velocity-space instabilities and their effect on electron pressure
anisotropy, viscous heating, and thermal conduction. The adiabatic invariance
of the magnetic moment in low-collisionality plasmas leads to pressure
anisotropy, $p_{\perp,j} > p_{||,j}$, if the magnetic field $\vec{B}$ is
amplified ($p_{\perp,j}$ and $p_{||,j}$ denote the pressure of species $j$
[electron, ion] perpendicular and parallel to $\vec{B}$). If the resulting
anisotropy is large enough, it can in turn trigger small-scale plasma
instabilities. Our PIC simulations explore the nonlinear regime of the mirror,
ion-cyclotron, and electron whistler instabilities, through continuous
amplification of the magnetic field $|\vec{B}|$ by an imposed shear in the
plasma. In the regime $1 \lesssim \beta_j \lesssim 20$ ($\beta_j \equiv 8\pi
p_j/|\vec{B}|^2$), the saturated electron pressure anisotropy, $\Delta
p_e/p_{||,e}$, is determined mainly by the (electron-lengthscale) whistler
marginal stability condition, with a modest factor of $\sim 1.5-2$ decrease due
to the trapping of electrons by the mirrors. We explicitly calculate the mean
free path of the electrons and ions along the mean magnetic field and provide a
simple physical prescription for the mean free path and thermal conductivity in
low-collisionality $\beta_j \gtrsim 1$ plasmas. Our results imply that
velocity-space instabilities likely decrease the thermal conductivity of plasma
in the outer parts of massive, hot, galaxy clusters. We also discuss the
implications of our results for electron heating and thermal conduction in
low-collisionality accretion flows onto black holes, including Sgr A* in the
Galactic Center.",1602.03126v2
2016-08-10,Non-Maxwellian electron distribution functions due to self-generated turbulence in collisionless guide-field reconnection,"Non-Maxwellian electron velocity space distribution functions (EVDF) are
useful signatures of plasma conditions and non-local consequences of
collisionless magnetic reconnection. In the past, EVDFs were obtained mainly
for antiparallel reconnection and under the influence of weak guide-fields in
the direction perpendicular to the reconnection plane. EVDFs are, however, not
well known, yet, for oblique (or component-) reconnection in dependence on
stronger guide-magnetic fields and for the exhaust (outflow) region of
reconnection away from the diffusion region. In view of the multi-spacecraft
Magnetospheric Multiscale Mission (MMS), we derived the non-Maxwellian EVDFs of
collisionless magnetic reconnection in dependence on the guide-field strength
$b_g$ from small ($b_g\approx0$) to very strong ($b_g=8$) guide-fields, taking
into account the feedback of the self-generated turbulence. For this sake, we
carried out 2.5D fully-kinetic Particle-in-Cell simulations using the ACRONYM
code. We obtained anisotropic EVDFs and electron beams propagating along the
separatrices as well as in the exhaust region of reconnection. The beams are
anisotropic with a higher temperature in the direction perpendicular rather
than parallel to the local magnetic field. The beams propagate in the direction
opposite to the background electrons and cause instabilities. We also obtained
the guide-field dependence of the relative electron-beam drift speed, threshold
and properties of the resulting streaming instabilities including the strongly
non-linear saturation of the self-generated plasma turbulence. This turbulence
and its non-linear feedback cause non-adiabatic parallel electron acceleration
and EVDFs well beyond the limits of the quasi-linear approximation, producing
phase space holes and an isotropizing pitch-angle scattering.",1608.03110v2
2016-12-22,Disruption of sheetlike structures in Alfvénic turbulence by magnetic reconnection,"We propose a mechanism whereby the intense, sheet-like structures naturally
formed by dynamically aligning Alfv\'enic turbulence are destroyed by magnetic
reconnection at a scale $\hat{\lambda}_{\rm D}$, larger than the dissipation
scale predicted by models of intermittent, dynamically aligning turbulence. The
reconnection process proceeds in several stages: first, a linear tearing mode
with $N$ magnetic islands grows and saturates, and then the $X$-points between
these islands collapse into secondary current sheets, which then reconnect
until the original structure is destroyed. This effectively imposes an upper
limit on the anisotropy of the structures within the perpendicular plane, which
means that at scale $\hat{\lambda}_{\rm D}$ the turbulent dynamics change: at
scales larger than $\hat{\lambda}_{\rm D}$, the turbulence exhibits
scale-dependent dynamic alignment and a spectral index approximately equal to
$-3/2$, while at scales smaller than $\hat{\lambda}_{\rm D}$, the turbulent
structures undergo a succession of disruptions due to reconnection, limiting
dynamic alignment, steepening the effective spectral index and changing the
final dissipation scale. The scaling of $\hat{\lambda}_{\rm D}$ with the
Lundquist (magnetic Reynolds) number $S_{L_\perp}$ depends on the order of the
statistics being considered, and on the specific model of intermittency; the
transition between the two regimes in the energy spectrum is predicted at
approximately $\hat{\lambda}_{\rm D} \sim S_{L_\perp}^{-0.6}$. The spectral
index below $\hat{\lambda}_{\rm D}$ is bounded between $-5/3$ and $-2.3$. The
final dissipation scale is at $\hat{\lambda}_{\eta,\infty}\sim
S_{L_\perp}^{-3/4}$, the same as the Kolmogorov scale arising in theories of
turbulence that do not involve scale-dependent dynamic alignment.",1612.07604v3
2017-01-11,Spontaneous flux concentrations from the negative effective magnetic pressure instability beneath a radiative stellar surface,"The formation of sunspots requires the concentration of magnetic flux near
the surface. The negative magnetic pressure instability (NEMPI) might be a
possible mechanism for accomplishing this, but it has mainly been studied in
simple systems using an isothermal equation of state without a natural free
surface. We study NEMPI in a stratified Cartesian mean-field model where
turbulence effects are parameterized. We use an ideal equation of state and
include radiation transport, which establishes selfconsistently a free surface.
We use a Kramers-type opacity with adjustable exponents chosen such that the
deeper layers are approximately isentropic. No convection is therefore possible
in this model, allowing us to study NEMPI with radiation in isolation. We
restrict ourselves to two-dimensional models. We use artificially enhanced
mean-field coefficients to allow NEMPI to develop, making it therefore possible
to study the reason why it is much harder to excite in the presence of
radiation. NEMPI yields moderately strong magnetic flux concentrations a
certain distance beneath the surface where optical depth is unity. The
instability is oscillatory and in the form of upward travelling waves. This
seems to be a new effect that has not been found in earlier models without
radiative transport. The horizontal wavelength is about ten times smaller than
what has been found previously in more idealized isothermal models. In our
models, NEMPI saturates at field strengths too low to explain sunspots.
Furthermore, the structures appear too narrow and too far beneath the surface
to cause significant brightness variations at the radiative surface. We
speculate that the failure to reproduce effects resembling sunspots may be
related to the neglect of convection.",1701.03018v2
2017-02-03,Giant magnetoresistance and structure of electrodeposited Co/Cu multilayers: the influence of layer thicknesses and Cu deposition potential,"The giant magnetoresistance (GMR) and structure was investigated for
electrodeposited Co/Cu multilayers prepared by a conventional
galvanostatic/potentiostatic pulse combination from a pure sulfate electrolyte
with various layer thicknesses, total multilayer thickness and Cu deposition
potential. X-ray diffraction (XRD) measurements revealed superlattice satellite
reflections for many of the multilayers having sufficiently large thickness (at
least 2 nm) of both constituent layers. The bilayer repeats derived from the
positions of the visible superlattice reflections were typically 10-20% higher
than the nominal values.The observed GMR was found to be dominated by the
multilayer-like ferromagnetic (FM) contribution even for multilayers without
visible superlattice satellites. There was always also a modest
superparamagnetic (SPM) contribution to the GMR and this term was the largest
for multilayers with very thin (0.5 nm) magnetic layers containg apparently a
small amount of magnetically decoupled SPM regions. No oscillatory GMR behavior
with spacer thickness was observed at any magnetic layer thickness. The
saturation of the coercivity as measured by the peak position of the MR(H)
curves indicated a complete decoupling of magnetic layers for large spacer
thicknesses. The GMR increased with total multilayer thickness which could be
ascribed to an increasing SPM contribution to the GMR due to an increasing
surface roughness, also indicated by the increasing coercivity. For multilayers
with Cu layers deposited at more and more positive potentials, the GMRFM term
increased and the GMRSPM term decreased. At the same time, a corresponding
reduction of surface roughness measured with atomic force microscopy indicated
an improvement of the multilayer structural quality which was, however, not
accompanied by an increase of the superlattice reflection intensities.",1702.01065v1
2017-06-27,Solar Cycle Variability Induced by Tilt Angle Scatter in a Babcock--Leighton Solar Dynamo Model,"We present results from a three-dimensional Babcock--Leighton dynamo model
that is sustained by the explicit emergence and dispersal of bipolar magnetic
regions (BMRs). On average, each BMR has a systematic tilt given by Joy's law.
Randomness and nonlinearity in the BMR emergence of our model produce variable
magnetic cycles. However, when we allow for a random scatter in the tilt angle
to mimic the observed departures from Joy's law, we find more variability in
the magnetic cycles. We find that the observed standard deviation in Joy's law
of $\sigma_\delta = 15^\circ$ produces a variability comparable to observed
solar cycle variability of $\sim $ 32%, as quantified by the sunspot number
maxima between 1755--2008. We also find that tilt angle scatter can promote
grand minima and grand maxima. The time spent in grand minima for
$\sigma_\delta = 15^\circ$ is somewhat less than that inferred for the Sun from
cosmogenic isotopes (about 9% compared to 17%). However, when we double the
tilt scatter to $\sigma_\delta = 30^\circ$, the simulation statistics are
comparable to the Sun ($\sim $18% of the time in grand minima and $\sim 10$% in
grand maxima). Though the Babcock--Leighton mechanism is the only source of
poloidal field, we find that our simulations always maintain magnetic cycles
even at large fluctuations in the tilt angle. We also demonstrate that tilt
quenching is a viable and efficient mechanism for dynamo saturation; a
suppression of the tilt by only 1-2$^\circ$ is sufficient to limit the dynamo
growth. Thus, any potential observational signatures of tilt quenching in the
Sun may be subtle.",1706.08933v2
2017-09-06,Dispersion of the solar magnetic flux in undisturbed photosphere as derived from SDO/HMI data,"To explore the magnetic flux dispersion in the undisturbed solar photosphere,
magnetograms acquired by Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamic Observatory (SDO) were utilized. Two areas, a coronal hole area
(CH) and an area of super-granulation pattern, SG, were analyzed. We explored
the displacement and separation spectra and the behavior of the turbulent
diffusion coefficient, $K$. The displacement and separation spectra are very
similar to each other. Small magnetic elements (of size 3-100 squared pixels
and the detection threshold of 20 Mx sm$^{-2}$) in both CH and SG areas
disperse in the same way and they are more mobile than the large elements (of
size 20-400 squared pixels and the detection threshold of 130 Mx sm$^{-2}$).
The regime of super-diffusivity is found for small elements ($\gamma \approx
1.3 $ and $K$ growing from $\sim$100 to $\sim$ 300 km$^2$ s$^{-1}$). Large
elements in the CH area are scanty and show super-diffusion with $\gamma
\approx 1.2$ and $K$ = (62-96) km$^2$ s$^{-1}$ on rather narrow range of
500-2200 km. Large elements in the SG area demonstrate two ranges of linearity
and two diffusivity regimes: sub-diffusivity on scales (900-2500) km with
$\gamma=0.88$ and $K$ decreasing from $\sim$130 to $\sim$100 km$^2$ s$^{-1}$,
and super-diffusivity on scales (2500-4800) km with $\gamma \approx 1.3$ and
$K$ growing from $\sim$140 to $\sim$200 km$^2$ s$^{-1}$. Comparison of our
results with the previously published shows that there is a tendency of
saturation of the diffusion coefficient on large scales, i.e., the turbulent
regime of super-diffusivity is gradually replaced by normal diffusion.",1709.01724v1
2017-11-21,Thickness-dependence of the Dzyaloshinskii-Moriya interaction in Co2FeAl ultrathin films: effects of the annealing temperature and the heavy metal material,"Interfacial Dzyaloshinskii-Moriya interaction (iDMI) has been investigated in
Co2FeAl (CFA) ultrathin films of various thicknesses (0.8 nm<tCFA<2 nm) grown
on Si substrates, using Pt, W, Ir and MgO buffer or/and capping layers.
Vibrating sample magnetometry revealed that magnetization at saturation (Ms)
for the Pt and Ir buffered films is higher than the usual Ms of CFA due to the
proximity induced magnetization (PIM) in Ir and Pt, estimated to be 19% and
27%, respectively. The presence of PIM in these materials is confirmed using
x-ray resonant magnetic reflectivity. Moreover, while no PIM is induced in W,
higher PIM is obtained with Pt when it is used as buffer layer rather than
capping layer. Brillouin light scattering (BLS) in the Damon-Eshbach geometry
has been used to investigate iDMI constants and the perpendicular anisotropy
field versus the annealing temperature. The DMI sign has been found to be
negative for Pt/CFA and Ir/CFA while it is positive for W/CFA. The thickness
dependence of the effective iDMI constant for stacks involving Pt and W shows
the existence of two regimes similarly to that of the perpendicular anisotropy
constant due to the degradation of the interfaces as the CFA thickness
approaches the nanometer. The surface iDMI and anisotropy constants of each
stack have been determined for the thickest samples where a linear thickness
dependence of the effective iDMI constant and the effective magnetization has
been observed. The interface anisotropy and iDMI constants, investigated for
Pt/CFA/MgO system, showed different trends with the annealing temperature. The
decrease of iDMI constant with increasing annealing temperature is probably due
to the electronic structure changes at the interfaces, while the increase of
the interface anisotropy constant is coherent the interface quality and
disorder enhancement.",1711.07776v1
2018-05-17,Modification of Spin Ice Physics in Ho$_2$Ti$_2$O$_7$ Thin Films,"We present an extensive study on the effect of substrate orientation, strain,
stoichiometry and defects on spin ice physics in Ho$_2$Ti$_2$O$_7$ thin films
grown onto yttria-stabilized-zirconia substrates. We find that growth in
different orientations produces different strain states in the films. All films
exhibit similar c-axis lattice parameters for their relaxed portions, which are
consistently larger than the bulk value of 10.10 \AA. Transmission electron
microscopy reveals anti-site disorder and growth defects to be present in the
films, but stuffing is not observed. The amount of disorder depends on the
growth orientation, with the (110) film showing the least. Magnetization
measurements at 1.8 K show the expected magnetic anisotropy and saturation
magnetization values associated with a spin ice for all orientations; shape
anisotropy is apparent when comparing in and out-of-plane directions.
Significantly, only the (110) oriented films display the hallmark spin ice
plateau state in magnetization, albeit less well-defined compared to the
plateau observed in a single crystal. Neutron scattering maps on the more
disordered (111) oriented films show the Q=0 phase previously observed in bulk
materials, but the Q=X phase giving the plateau state remains elusive. We
conclude that the spin ice physics in thin films is modified by defects and
strain, leading to a reduction in the temperature at which correlations drive
the system into the spin ice state.",1805.06565v2
2018-07-31,High Resolution Imaging of the Magnetic Field in the central parsec of the Galaxy,"We discuss a high resolution (FWHM~ 0.45 arcsec) image of the emissive
polarization from warm dust in the minispiral in the Galactic Centre and
discuss the implications for the magnetic field in the dusty filaments. The
image was obtained at a wavelength of 12.5 microns with the CanariCam multimode
mid-infrared imager on the Gran Telescopio Canarias. It confirms the results
obtained from previous observations but also reveals new details of the
polarization structures. In particular, we identify regions of coherent
magnetic field emission at position angles of ~45 deg to the predominantly
north--south run of field lines in the Northern Arm which may be related to
orbital motions inclined to the general flow of the Northern Arm. The luminous
stars that have been identified as bow-shock sources in the Northern Arm do not
disrupt or dilute the field but are linked by a coherent field structure,
implying that the winds from these objects may push and compress the field but
do not overwhelm it. The magnetic field in the the low surface brightness
regions in the East-West Bar to the south of SgrA* lies along the Bar, but the
brighter regions generally have different polarization position angles,
suggesting that they are distinct structures. In the region of the Northern Arm
sampled here, there is only a weak correlation between the intensity of the
emission and the degree of polarization. This is consistent with saturated
grain alignment where the degree of polarization depends on geometric effects,
including the angle of inclination of the field to the line of sight and
superposition of filaments with different field directions, rather than the
alignment efficiency.",1807.11744v1
2018-09-10,Magnetic properties and field-driven dynamics of chiral domain walls in epitaxial Pt/Co/Au$_x$Pt$_{1-x}$ trilayers,"Chiral domain walls in ultrathin perpendicularly magnetised layers have a
N\'{e}el structure stabilised by a Dzyaloshinskii-Moriya interaction (DMI) that
is generated at the interface between the ferromagnet and a heavy metal.
Different heavy metals are required above and below a ferromagnetic film in
order to generate the structural inversion asymmetry needed to ensure that the
DMI arising at the two interfaces does not cancel. Here we report on the
magnetic properties of epitaxial Pt/Co/Au$_x$Pt$_{1-x}$ trilayers grown by
sputtering onto sapphire substrates with 0.6 nm thick Co. As $x$ rises from 0
to 1 a structural inversion asymmetry is generated. We characterise the
epilayer structure with x-ray diffraction and cross-sectional transmission
electron microscopy, revealing (111) stacking. The saturation magnetization
falls as the proximity magnetisation in Pt is reduced, whilst the perpendicular
magnetic anisotropy $K_\mathrm{u}$ rises. The micromagnetic DMI strength $D$
was determined using the bubble expansion technique and also rises from a
negligible value when $x=0$ to $\sim 1$ mJ/m$^2$ for $x = 1$. The depinning
field at which field-driven domain wall motion crosses from the creep to the
depinning regime rises from $\sim 40$ to $\sim 70$ mT, attributed to greater
spatial fluctuations of the domain wall energy with increasing Au
concentration. Meanwhile, the increase in DMI causes the Walker field to rise
from $\sim 10$ to $\sim 280$ mT, meaning that only in the $x = 1$ sample is the
steady flow regime accessible. The full dependence of domain wall velocity on
driving field bears little resemblance to the prediction of a simple
one-dimensional model, but can be described very well using micromagnetic
simulations with a realistic model of disorder. These reveal a rise in Gilbert
damping as $x$ increases.",1809.03217v2
2019-01-14,Finding pathways for stoichiometric Co4N thin films,"In this work, we studied the pathways for formation of stoichiometric
\tcn~thin films. Polycrystalline and epitaxial \tcn~films were prepared using
reactive direct current magnetron (dcMS) sputtering technique. A systematic
variation in the substrate temperature (\Ts) during the dcMS process reveals
that the lattice parameter (LP) decreases as \Ts~increases. We found that
nearly stoichiometric \tcn~films can be obtained when \Ts~= 300\,K. However,
they emerge from the transient state of Co target ($\phi$3\,inch). By reducing
the target size to $\phi$1\,inch, now the \tcn~phase formation takes place from
the metallic state of Co target. In this case, LP of \tcn~film comes out to be
$\sim$99\p~of the value expected for \tcn. This is the largest value of LP
found so far for \tcn. The pathways achieved for formation of polycrystalline
\tcn~were adopted to grow an epitaxial \tcn~film, which shows four fold
magnetic anisotropy in magneto-optic Kerr effect measurements. Detailed
characterization using secondary ion mass spectroscopy indicates that N
diffuses out when \Ts~is raised even to 400\,K. Measurement of electronic
structure using x-ray photoelectron spectroscopy and x-ray absorption
spectroscopy further confirms it. Magnetization measurements using bulk
magnetization and polarized neutron reflectivity show that the saturation
magnetization of stoichiometric \tcn~film is even larger than pure Co. Since
all our measurements indicated that N could be diffusing out, when \tcn~films
are grown at high \Ts, we did actual N self-diffusion measurements in a CoN
sample and found that N self-diffusion was indeed substantially higher. The
outcome of this work clearly shows that the \tcn~films grown prior to this work
were always N deficient and the pathways for formation of a stoichiometric
\tcn~have been achieved.",1901.04139v1
2019-04-16,Numerical study of tearing mode seeding in tokamak X-point plasma,"A detailed understanding of island seeding is crucial to avoid (N)TMs and
their negative consequences like confinement degradation and disruptions. In
the present work, we investigate the growth of 2/1 islands in response to
magnetic perturbations. Although we use externally applied perturbations
produced by resonant magnetic perturbation (RMP) coils for this study, results
are directly transferable to island seeding by other MHD instabilities creating
a resonant magnetic field component at the rational surface. Experimental
results for 2/1 island penetration from ASDEX Upgrade are presented extending
previous studies. Simulations are based on an ASDEX Upgrade L-mode discharge
with low collisionality and active RMP coils. Our numerical studies are
performed with the 3D, two fluid, non-linear MHD code JOREK. All three phases
of mode seeding observed in the experiment are also seen in the simulations:
first a weak response phase characterized by large perpendicular electron flow
velocities followed by a fast growth of the magnetic island size accompanied by
a reduction of the perpendicular electron velocity, and finally the saturation
to a fully formed island state with perpendicular electron velocity close to
zero. Thresholds for mode penetration are observed in the plasma rotation as
well as in the RMP coil current. A hysteresis of the island size and electron
perpendicular velocity is observed between the ramping up and down of the RMP
amplitude consistent with an analytically predicted bifurcation. The transition
from dominant kink/bending to tearing parity during the penetration is
investigated.",1904.07542v1
2019-09-10,Contributions of magnetic structure and nitrogen to perpendicular magnetocrystalline anisotropy in antiperovskite $ε$-Mn$_4$N,"To study how nitrogen contributes to perpendicular magnetocrystalline
anisotropy (PMA) in the ferrimagnetic antiperovskite Mn$_4$N, we examined both
the fabrication of epitaxial Mn$_4$N films with various nitrogen contents and
first-principles density-functional calculations. Saturation magnetization
($M_{\rm s}$) peaks of 110 mT and uniaxial PMA energy densities ($K_{\rm u}$)
of 0.1 MJ/m$^3$ were obtained for a N$_2$ gas flow ratio ($Q$) of $\sim 10 \%$
during sputtering deposition, suggesting nearly single-phase crystalline
$\epsilon$-Mn$_4$N. Segregation of $\alpha$-Mn and nitrogen-deficient Mn$_4$N
grains was observed for $Q \approx 6\%$, which was responsible for a decrease
in the $M_{\rm s}$ and $K_{\rm u}$. The first-principles calculations revealed
that the magnetic structure of Mn$_4$N showing PMA was ""type-B"" having a
collinear structure, whose magnetic moments couple parallel within the c-plane
and alternating along the c-direction. In addition, the $K_{\rm u}$ calculated
using Mn$_{32}$N$_x$ supercells showed a strong dependence on nitrogen
deficiency, in qualitative agreement with the experimental results. The
second-order perturbation analysis of $K_{\rm u}$ with respect to the
spin-orbit interaction revealed that not only spin-conserving but also
spin-flip processes contribute significantly to the PMA in Mn$_4$N. We also
found that both contributions decreased with increasing nitrogen deficiency,
resulting in the reduction of $K_{\rm u}$. It was noted that the decrease in
the spin-flip contribution occurred at the Mn atoms in face-centered sites.
This is one of the specific PMA characteristics we found for
antiperovskite-type Mn$_4$N.",1909.04308v3
2020-04-27,"Hadamard magnetization transfers achieve dramatic sensitivity enhancements in homonuclear multidimensional NMR correlations of labile sites in proteins, polysaccharides and nucleic acids","EXSY, TOCSY and NOESY lie at the foundation of homonuclear NMR experiments in
organic and pharmaceutical chemistry, as well as in structural biology. Limited
magnetization transfer efficiency is an intrinsic downside of these methods,
particularly when targeting rapidly exchanging species such as labile protons
ubiquitous in polysaccharides, sidechains and backbones of proteins, and in
bases and sugars of nucleic acids: the fast decoherence imparted on these
protons through solvent exchanges, greatly reduces their involvement in
homonuclear correlation experiments. We have recently discussed how these
decoherences can be visualized as an Anti-Zeno Effect, that can be harnessed to
enhance the efficiency of homonuclear transfers within Looped PROjected
SpectroscopY (L-PROSY) leading to 200-300% enhancements in NOESY and TOCSY
cross-peaks for amide groups in biomolecules. This study demonstrates that even
larger sensitivity gains per unit time, equivalent to reductions by several
hundred-folds in the duration of experiments, can be achieved by looping
inversion or using saturation procedures. In the ensuing experiments a priori
selected frequencies are encoded according to Hadamard recipes, and
subsequently resolved along the indirect dimension via linear combinations.
Magnetization-transfer (MT) processes reminiscent of those occurring in CEST
provide significant enhancements in the resulting cross-peaks, in only a
fraction of acquisition time of a normal 2D experiment. The effectiveness of
the ensuing three-way polarization transfer interplay between water, labile and
non-labile protons was corroborated experimentally for proteins,
homo-oligosaccharides and nucleic acids. In all cases, cross-peaks barely
detectable in conventional 2D NMR counterparts, were measured ca. 10-fold
faster and with 200-600% signal enhancements by the Hadamard MT counterparts.",2004.13063v1
2020-05-20,Alfvén-wave driven magnetic rotator winds from low-mass stars I: rotation dependences of magnetic braking and mass-loss rate,"Observations of stellar rotation show that low-mass stars lose angular
momentum during the main sequence. We simulate the winds of Sun-like stars with
a range of rotation rates, covering the fast and slow magneto-rotator regimes,
including the transition between the two. We generalize an Alfv\'en-wave driven
solar wind model that builds on previous works by including the
magneto-centrifugal force explicitly. In this model, the surface-averaged open
magnetic flux is assumed to scale as $B_\ast f^{\rm open}_\ast \propto {\rm
Ro}^{-1.2}$, where $f^{\rm open}_\ast$ and ${\rm Ro}$ are the surface open-flux
filling factor and Rossby number, respectively. We find that, 1. the angular
momentum loss rate (torque) of the wind is described as $\tau_w \approx 2.59
\times 10^{30} {\rm \ erg} \ \left( \Omega_\ast / \Omega_\odot \right)^{2.82}$,
yielding a spin-down law $\Omega_\ast \propto t^{-0.55}$. 2. the mass-loss rate
saturates at $\dot{M}_w \sim 3.4 \times 10^{-14} M_\odot {\rm \ yr^{-1}}$, due
to the strong reflection and dissipation of Alfv\'en waves in the chromosphere.
This indicates that the chromosphere has a strong impact in connecting the
stellar surface and stellar wind. Meanwhile, the wind ram pressure scales as
$P_w \propto \Omega_\ast^{0.57}$, which is able to explain the lower-envelope
of the observed stellar winds by Wood et al. 3. the location of the Alfv\'en
radius is shown to scale in a way that is consistent with 1D analytic theory.
Additionally, the precise scaling of the Alfv\'en radius matches previous works
which used thermally-driven winds. Our results suggest that the Alfv\'en-wave
driven magnetic rotator wind plays a dominant role in the stellar spin-down
during the main-sequence.",2005.09817v2
2020-08-13,On the detection of surface spin freezing in iron oxide nanoparticles and its long-term evolution under ambient oxidation,"Exchange bias effects linked to surface spin freezing (SSF) are commonly
found in iron oxide nanoparticles, while signatures of SSF in low-field
temperature-dependent magnetization curves have been much less frequently
reported. Here, we present magnetic properties of dense assemblies of
similar-sized (~ 8 nm diameter) particles synthesized by a magnetite (sample
S1) and a maghemite (sample S2) method, and the influence of long-term (4-year)
sample aging under ambient conditions on these properties. The size of the
exchange bias field of the different sample (fresh or aged) states is found to
correlate with (a) whether a low-temperature hump feature signaling the SSF
transition is detected in out-of-phase ac susceptibility or zero-field-cooled
(ZFC) dc magnetization recorded at low field and with (b) the prominence of
irreversibility between FC and ZFC curves recorded at high field. Sample S1
displays a lower magnetization than S2, and it is in S1 where the largest SSF
effects are found. These effects are significantly weakened by aging but remain
larger than the SSF effects in S2, where the influence of aging is considerably
smaller. A non-saturating component due to spin disorder in S1 also weakens
with aging, accompanied by, we infer, an increase in the superspin and the
radius of the ordered nanoparticle cores. X-ray diffraction and M\""ossbauer
spectroscopy provide indication of maghemite-like stoichiometry in both aged
samples as well as thicker disordered particle shells in aged-S1 relative to
aged-S2 (crystallographically-disordered and spin-disordered according to
diffraction and M\""ossbauer, respectively). The pronounced diminution in SSF
effects with aging in S1 is attributed to a (long-term) transition, caused by
ambient oxidation, from magnetite-like to maghemite-like stoichiometry, and a
concomitant softening of the spin-disordered shell anisotropy...",2008.05874v1
2020-09-14,Shear-Driven Transition to Isotropically Turbulent Solar Wind Outside the Alfven Critical Zone,"Motivated by prior remote observations of a transition from striated solar
coronal structures to more isotropic ``flocculated'' fluctuations, we propose
that the dynamics of the inner solar wind just outside the Alfv\'en critical
zone, and in the vicinity of the first $\beta=1$ surface, is powered by the
relative velocities of adjacent coronal magnetic flux tubes. We suggest that
large amplitude flow contrasts are magnetically constrained at lower altitude
but shear-driven dynamics are triggered as such constraints are released above
the Alfv\'en critical zone, as suggested by global magnetohydrodynamic (MHD)
simulations that include self-consistent turbulence transport. We argue that
this dynamical evolution accounts for features observed by {\it Parker Solar
Probe} ({\it PSP}) near initial perihelia, including magnetic ``switchbacks'',
and large transverse velocities that are partially corotational and saturate
near the local Alfv\'en speed. Large-scale magnetic increments are more
longitudinal than latitudinal, a state unlikely to originate in or below the
lower corona. We attribute this to preferentially longitudinal velocity shear
from varying degrees of corotation. Supporting evidence includes comparison
with a high Mach number three-dimensional compressible MHD simulation of
nonlinear shear-driven turbulence, reproducing several observed diagnostics,
including characteristic distributions of fluctuations that are qualitatively
similar to {\it PSP} observations near the first perihelion. The concurrence of
evidence from remote sensing observations, {\it in situ} measurements, and both
global and local simulations supports the idea that the dynamics just above the
Alfv\'en critical zone boost low-frequency plasma turbulence to the level
routinely observed throughout the explored solar system.",2009.06537v1
2020-11-05,Polarized emission of CdSe nanocrystals in magnetic field: the role of phonon-assisted recombination of the dark exciton,"The recombination dynamics and spin polarization of excitons in CdSe
nanocrystals synthesized in a glass matrix are investigated using polarized
photoluminescence in high magnetic fields up to 30 Tesla. The dynamics are
accelerated by increasing temperature and magnetic field, confirming the dark
exciton nature of the low-temperature photoluminescence (PL). The circularly
polarized PL in magnetic fields reveals several unusual appearances: (i) a
spectral dependence of the polarization degree, (ii) its low saturation value,
and (iii) a stronger intensity of the Zeeman component which is higher in
energy. The latter feature is the most surprising being in contradiction with
the thermal population of the exciton spin sublevels. The same contradiction
was previously observed in the ensemble of wet-chemically synthesized CdSe
nanocrystals, but was not understood. We present a theory which explains all
the observed features and shows that the inverted ordering of the circular
polarized PL maxima from the ensemble of nanocrystals is a result of
competition between the zero phonon (ZPL) and one optical phonon (1PL) assisted
emission of the dark excitons. The essential aspects of the theoretical model
are different polarization properties of the dark exciton emission via ZPL and
1PL recombination channels and the inhomogeneous broadening of the PL spectrum
from the ensemble of nanocrystals exceeding the optical phonon energy.",2011.02786v1
2021-11-14,"Structure, optical and magnetic properties of Fe doped, Fe+Cr co-doped ZnO nanoparticles","The study particularly focuses on the effect of the Cr co-doping on the
structural, optical and magnetic properties of Zn0.99Fe0.01O.
Zn0.99-xFe0.01CrxO (x =0, 0.01, 0.03 and 0.05) nanoparticles. Powder x-ray
diffraction (XRD) analysis confirms all the samples have hexagonal wurtzite
structures. The average crystallite size (D) and microstrain of the samples
were calculated using the Williamson-Hall relation and D was found to be 13 +-
1 nm for Zn0.99Fe0.01O. In Cr co-doped samples, D increase slightly with Cr
content and are given by 9 +- 1, 10 +- 1, and 11 +- 1 nm for the samples with x
= 0.01, 0.03 and 0.05, respectively; while the strain decreased with increase
in Cr co-doping. Transmission electron microscopy (TEM) images of the samples
indicate that particles are in the nano-regime and agglomerated. Particle sizes
are found to be 14 +- 1, 11 +- 1 and 12 +- 1 nm for Zn0.99-xFe0.01CrxO with x =
0, 0.03 and 0.05, respectively. The substitution of Fe3+ and Cr3+ at Zn2+ sites
has an impact on the optical properties. The band-gap decreases from 3.296 +-
0.002 eV to 3.258 +- 0.002 eV with increase of Cr concentration.
Photoluminescence (PL) of Zn0.96Fe0.01Cr0.03O revealed the presence of defects,
the emission peaks at 410 nm and 513 nm are attributed to Zn vacancies (VZn)
and singly ionized oxygen vacancies, respectively. The M(-H) curves of
Zn0.99-xFe0.01CrxO (x = 0.03 and 0.05) measured at room temperature using a
vibrating sample magnetometer (VSM) are found to be hysteretic, signifying room
temperature ferromagnetism (RTFM). Maximum saturation magnetization, 0.67 +-
0.01 emu.g-1, is observed in Zn0.94Fe0.01Cr0.05O. The observed RTFM in Fe+Cr
co-doped ZnO is explained by of bound magnetic polaron (BMP) mechanism, the
BMPs are formed by VZn and Vo^+ defects. This paper enhances the understanding
of the origin of RTFM in Fe+Cr co-doped ZnO nanoparticles.",2111.07266v1
2022-04-23,3D Simulations of Strongly Magnetised Non-Rotating Supernovae: Explosion Dynamics and Remnant Properties,"We investigate the impact of strong initial magnetic fields in core-collapse
supernovae of non-rotating progenitors by simulating the collapse and explosion
of a 16.9 Msun star for a strong- and weak-field case assuming a twisted-torus
field with initial central field strengths of ~1012 G and ~106 G. The
strong-field model has been set up with a view to the fossil-field scenario for
magnetar formation and emulates a pre-collapse field configuration that may
occur in massive stars formed by a merger. This model undergoes shock revival
already 100 s after bounce and reaches an explosion energy of 9.3 x 10^50 erg
at 310 ms, in contrast to a more delayed and less energetic explosion in the
weak-field model. The strong magnetic fields help trigger a neutrino-driven
explosion early on, which results in a rapid rise and saturation of the
explosion energy. Dynamically, the strong initial field leads to a fast
build-up of magnetic fields in the gain region to 40% of kinetic equipartition
and also creates sizable pre-shock ram pressure perturbations that are known to
be conducive to asymmetric shock expansion. For the strong-field model, we find
an extrapolated neutron star kick of ~350 km/s, a spin period of ~70 ms, and no
spin-kick alignment. The dipole field strength of the proto-neutron star is 2 x
10^14 G by the end of the simulation with a declining trend. Surprisingly, the
surface dipole field in the weak-field model is stronger, which argues against
a straightforward connection between pre-collapse fields and the birth magnetic
fields of neutron stars.",2204.11009v3
2022-05-11,Effect of magnetic phase coexistence on spin-phonon coupling and magnetoelectric effect in polycrystalline Sm0.5Y0.5Fe0.58Mn0.42O3,"The polycrystalline co-doped samples of Sm0.5Y0.5Fe0.58Mn0.42O3 were prepared
by solid-state reaction route and its various physical properties with their
correlations have been investigated. The dc magnetization measurements on the
sample revealed a weak ferromagnetic (WFM) transition at TN=361 K that is
followed by an incomplete spin reorientation (SR) transition at TSR1= 348 K. A
first order magnetic transition (FOMT) around 292 K completes the spin
reorientation transition and the material enters into a nearly collinear
antiferromagnetic (AFM) state for T < 260 K. The compound exhibited
magnetization reversal below the compensation temperature (Tcomp) = 92 K at low
measured field of 100 Oe. At further low temperature below 71 K, the compound
also exhibited Zero-field cooled memory effects confirming a reentrant
spinglass state formation. Robust magnetodielectric (MD) magnetoelectric
coupling has been established in the present material through field dependent
dielectric and resistivity measurements. True ferroelectric transition with a
considerable value of saturation polarization (= 0.06 micro C/cm2 at 15 K) have
been found in the specimen below TFE= 108 K. We observed an intense spin-phonon
coupling (SPC) across TSR and TN from the temperature dependent Raman
spectroscopy and is responsible for the intrinsic magnetoelectric effect. This
SPC also stabilizes the ferroelectric state below TFE in the material. The
delicate interplay of the lattice (Phonons), charge and spins governs the
observed features in the investigated physical properties of the material that
makes the specimen a promising multifunctional material.",2205.05291v2
2022-07-19,"Batchelor, Saffman, and Kazantsev spectra in galactic small-scale dynamos","The magnetic fields in galaxy clusters and probably also in the interstellar
medium are believed to be generated by a small-scale dynamo. Theoretically,
during its kinematic stage, it is characterized by a Kazantsev spectrum, which
peaks at the resistive scale. It is only slightly shallower than the Saffman
spectrum that is expected for random and causally connected magnetic fields.
Causally disconnected fields have the even steeper Batchelor spectrum. Here we
show that all three spectra are present in the small-scale dynamo. During the
kinematic stage, the Batchelor spectrum occurs on scales larger than the
energy-carrying scale of the turbulence, and the Kazantsev spectrum on smaller
scales within the inertial range of the turbulence -- even for a magnetic
Prandtl number of unity. In the saturated state, the dynamo develops a Saffman
spectrum on large scales, suggestive of the build-up of long-range
correlations. At large magnetic Prandtl numbers, elongated structures are seen
in synthetic synchrotron emission maps showing the parity-even E polarization.
We also observe a significant excess in the E polarization over the parity-odd
B polarization at subresistive scales, and a deficiency at larger scales. This
finding is at odds with the observed excess in the Galactic microwave
foreground emission, which is believed to be associated with larger scales. The
E and B polarizations may be highly non-Gaussian and skewed in the kinematic
regime of the dynamo. For dust emission, however, the polarized emission is
always nearly Gaussian, and the excess in the E polarization is much weaker.",2207.09414v2
2023-03-03,Comparative study of magnetocaloric properties for Gd$^{3+}$ compounds with different frustrated lattice geometries,"As materials with suppressed ordering temperatures and enhanced ground state
entropies, frustrated magnetic oxides are ideal candidates for cryogenic
magnetocaloric refrigeration. While previous materials design has focused on
tuning the magnetic moments, their interactions, and density of moments on the
lattice, there has been relatively little attention to frustrated lattices.
Prior theoretical work has shown that the magnetocaloric cooling rate at the
saturation field is proportional to a macroscopic number of soft mode
excitations that arise due to the classical ground state degeneracy. The number
of these modes is directly determined by the geometry of the frustrating
lattice. For corner-sharing geometries, the pyrochlore has 50\% more modes than
the garnet and kagome lattices, whereas the edge-sharing \emph{fcc} has only a
subextensive number of soft modes. Here, we study the role of soft modes in the
magnetocaloric effect of four large-spin Gd$^{3+}$ ($L=0$, $J=S=7/2$)
Heisenberg antiferromagnets on a kagome, garnet, pyrochlore, and \emph{fcc}
lattice. By comparing measurements of the magnetic entropy change $\Delta S_m$
of these materials at fields up to $9$~T with predictions using mean-field
theory and Monte Carlo simulations, we are able to understand the relative
importance of spin correlations and quantization effects. We observe that
tuning the value of the nearest neighbor coupling has a more dominant
contribution to the magnetocaloric entropy change in the liquid-He cooling
regime ($2$-$20$~K), rather than tuning the number of soft mode excitations.
Our results inform future materials design in terms of dimensionality, degree
of magnetic frustration, and lattice geometry.",2303.01773v1
2023-08-22,"Structural, morphological, and magnetic characterizations of (Fe0.25Mn0.75)2O3 nanocrystals: a comprehensive stoichiometric determination","Iron manganese trioxide (Fe0.25Mn0.75)2O3 nanocrystals were synthesized by
the sol-gel method. The 80 K Mossbauer spectrum was well-fitted using two
doublets representing the 8b and 24d crystallographic sites of the
(FexMn1-x)2O3 phase and two weak extra sextets which were attributed to
crystalline and amorphous hematite. Our findings showed formation of a bixbyite
primary phase. The Raman spectrum exhibits six Raman active modes, typical of
(Fe,Mn)2O3, and two extra Raman modes associated with the secondary hematite
phase. X-ray photoelectron spectroscopy analysis confirmed the presence of
oxygen vacancy onto the (FexMn1-x)2O3 particle surface, with varying oxidation
states. X-band magnetic resonance data revealed a single broad resonance line
in the whole temperature range (3.8 K - 300 K). The temperature dependence of
both resonance field and resonance linewidth shows a remarkable change in the
range of 40 - 50 K, herein credited to surface spin glass behavior. The model
picture used assumes (FexMn1-x)2O3 nanoparticles with a core-shell structure.
Results indicate that below about 50 K the spin system of shell reveals a
paramagnetic to spin glass-like transition upon cooling, with a critical
temperature estimated at 43 K. In the higher temperature range, the
superparamagnetic hematite (secondary) phase contributes remarkably to the
temperature dependence of the resonance linewidth. Zero-field-cooled (ZFC) and
fieldcooled (FC) data show strong irreversibility and a peak in the ZFC curve
at 33 K, attributed to a paramagnetic-ferrimagnetic transition of the main
phase. Hysteresis curve at 5 K shows a low coercive field of 4 kOe, with the
magnetization not reaching saturation at 70 kOe, suggesting the occurrence of a
ferrimagnetic core with a magnetic disorder at surface, characteristic of
core-shell spin-glass-like behavior.",2308.11128v2
2023-09-30,MRI turbulence in vertically stratified accretion discs at large magnetic Prandtl numbers,"The discovery of the first binary neutron star merger, GW170817, has spawned
a plethora of global numerical relativity simulations. These simulations are
often ideal (with dissipation determined by the grid) and/or axisymmetric
(invoking ad hoc mean-field dynamos). However, binary neutron star mergers
(similar to X-ray binaries and active galactic nuclei inner discs) are
characterised by large magnetic Prandtl numbers, $\rm Pm$, (the ratio of
viscosity to resistivity). $\rm Pm$ is a key parameter determining dynamo
action and dissipation but it is ill-defined (and likely of order unity) in
ideal simulations. To bridge this gap, we investigate the magnetorotational
instability (MRI) and associated dynamo at large magnetic Prandtl numbers using
fully compressible, three-dimensional, vertically stratified, isothermal
simulations of a local patch of a disc. We find that, within the bulk of the
disc ($z\lesssim2H$, where $H$ is the scale-height), the turbulent intensity
(parameterized by the stress-to-thermal-pressure ratio $\alpha$), and the
saturated magnetic field energy density, $E_\text{mag}$, produced by the MRI
dynamo, both scale as a power with Pm at moderate Pm ($4\lesssim \text{Pm}
\lesssim 32$): $E_\text{mag} \sim \text{Pm}^{0.74}$ and $\alpha \sim
\text{Pm}^{0.71}$, respectively. At larger Pm ($\gtrsim 32$) we find deviations
from power-law scaling and the onset of a plateau. Compared to our recent
unstratified study, this scaling with Pm becomes weaker further away from the
disc mid-plane, where the Parker instability dominates. We perform a thorough
spectral analysis to understand the underlying dynamics of small-scale
MRI-driven turbulence in the mid-plane and of large-scale Parker-unstable
structures in the atmosphere.",2310.00453v1
2022-01-11,"Single-crystal epitaxial europium iron garnet films with strain-induced perpendicular magnetic anisotropy: structural, strain, magnetic, and spin transport properties","Single-crystal europium iron garnet (EuIG) thin films epitaxially
strain-grown on gadolinium gallium garnet (GGG)(100) substrates using off-axis
sputtering have strain-induced perpendicular magnetic anisotropy (PMA). By
varying the sputtering conditions, we have tuned the europium/iron (Eu/Fe)
composition ratios in the films to tailor the film strains. The films exhibited
an extremely smooth, particle-free surface with roughness as low as 0.1 nm as
observed using atomic force microscopy. High-resolution x-ray diffraction
analysis and reciprocal space maps showed in-plane epitaxial film growth, very
smooth film/substrate interface, excellent film crystallinity with a small full
width at half maximum of 0.012$^{\circ}$ in the rocking curve scans, and an
in-plane compressive strain without relaxation. In addition, spherical
aberration-corrected scanning transmission electron microscopy showed an
atomically abrupt interface between the EuIG film and GGG. The measured
squarish out-of-plane magnetization-field hysteresis loops by vibrating sample
magnetometry in conjunction with the measurements from angle-dependent x-ray
magnetic dichroism demonstrated the PMA in the films. We have tailored the
magnetic properties of the EuIG thin films, including saturation magnetization
ranging from 71.91 to 124.51 emu/c.c. (increase with the (Eu/Fe) ratios),
coercive field from 27 to 157.64 Oe, and the strength of PMA field ($H_\bot$)
increasing from 4.21 to 18.87 kOe with the in-plane compressive strain from
-0.774 to -1.044%. We have also investigated spin transport in Pt/EuIG bi-layer
structure and evaluated the real part of spin mixing conductance to be
$3.48\times10^{14} {\Omega}^{-1}m^{-2}$. We demonstrated the current-induced
magnetization switching with a low critical switching current density of
$3.5\times10^6 A/cm^2$, showing excellent potential for low-dissipation
spintronic devices.",2201.03843v1
2021-07-10,An End-to-End AI-Based Framework for Automated Discovery of CEST/MT MR Fingerprinting Acquisition Protocols and Quantitative Deep Reconstruction (AutoCEST),"Purpose: To develop an automated machine-learning-based method for the
discovery of rapid and quantitative chemical exchange saturation transfer
(CEST) MR fingerprinting acquisition and reconstruction protocols.
  Methods: An MR physics governed AI system was trained to generate optimized
acquisition schedules and the corresponding quantitative reconstruction
neural-network. The system (termed AutoCEST) is composed of a CEST saturation
block, a spin dynamics module, and a deep reconstruction network, all
differentiable and jointly connected. The method was validated using a variety
of chemical exchange phantoms and an in-vivo mouse brain at 9.4T.
  Results: The acquisition times for AutoCEST optimized schedules ranged from
35-71s, with a quantitative image reconstruction time of only 29 ms. The
resulting exchangeable proton concentration maps for the phantoms were in good
agreement with the known solute concentrations for AutoCEST sequences (mean
absolute error = 2.42 mM; Pearson's r=0.992 , p$<$0.0001), but not for an
unoptimized sequence (mean absolute error = 65.19 mM; Pearson's r=-0.161,
p=0.522). Similarly, improved exchange rate agreement was observed between
AutoCEST and quantification of exchange using saturation power (QUESP) methods
(mean absolute error: 35.8 Hz, Pearson's r=0.971, p$<$0.0001) compared to an
unoptimized schedule and QUESP (mean absolute error = 58.2 Hz; Pearson's
r=0.959, p$<$0.0001). The AutoCEST in-vivo mouse brain semi-solid proton
volume-fractions were lower in the cortex (12.21$\pm$1.37%) compared to the
white-matter (19.73 $\pm$ 3.30%), as expected, and the amide proton
volume-fraction and exchange rates agreed with previous reports.
  Conclusion: AutoCEST can automatically generate optimized CEST/MT acquisition
protocols that can be rapidly reconstructed into quantitative exchange
parameter maps.",2107.04737v1
2006-04-28,Observation of Saturable and Reverse Saturable Absorption at Longitudinal Surface Plasmon Resonance in Gold Nanorods,"Saturable and reverse saturable absorption at longitudinal surface plasmon
resonance (SPR) in gold nanorods (Au NRs) have been observed using Z-scan and
transient absorption techniques with femtosecond laser pulses. At lower
excitation irradiances, the wavelength dispersion of saturable absorption has
been determined near the longitudinal mode of SPR with a recovery time
determined to be a few ten picoseconds on the SPR resonance. With higher
excitation irradiances, reverse saturable absorption occurs and becomes
dominant. The underlying mechanisms are discussed. Such reversible saturable
absorption makes Au NRs an ideal candidate for optical limiting applications.",0604651v1
2008-06-04,Phenomenological Model and Phase Behavior of Saturated and Unsaturated Lipids and Cholesterol,"We present a phenomenological theory for the phase behavior of ternary
mixtures of cholesterol and saturated and unsaturated lipids, one which
describes both liquid and gel phases, and illuminates the mechanism of the
behavior. In a binary system of the lipids, the two phase separate when the
saturated chains are well ordered, as in the gel phase, simply due to packing
effects. In the liquid phase the saturated ones are not sufficiently well
ordered for separation to occur. The addition of cholesterol, however,
increases the saturated lipid order to the point that phase separation is once
again favorable. For the system above the main chain transition of the
saturated lipid, we can obtain phase diagrams in which there is liquid-liquid
phase separation in the ternary system but not in any of the binary ones, while
below that temperature we obtain the more common phase diagram in which a gel
phase, rich in saturated lipid, appears in addition to the two liquid phases.",0806.0675v1
2008-06-24,Measurements of the aeolian sand transport saturation length,"The wavelength at which a dune pattern emerges from a flat sand bed is
controlled by the sediment transport saturation length, which is the length
needed for the sand flux to adapt to a change of wind strength. The influence
of the wind shear velocity on this saturation length and on the subsequent dune
initial wavelength has remained controversial. In this letter, we present
direct measurements of the saturation length performed in a wind tunnel
experiment. In complement, initial dune wavelengths are measured under
different wind conditions -- in particular after storms. Using the linear
stability analysis of dune formation, it is then possible to deduce the
saturation length from field data. Both direct and indirect measurements agree
that the saturation length is almost independent of the wind strength. This
demonstrates that, in contrast with erosion, grain inertia is the dominant
dynamical mechanism limiting sediment transport saturation.",0806.3931v1
2008-12-16,Saturable absorption or slow light?,"Quantitative analysis of slow light experiments utilising coherent population
oscillation (CPO) in a range of saturably absorbing media, including ruby and
alexandrite, Er3+:Y2SiO5, bacteriorhodopsin, semi-conductor quantum devices and
erbium doped optical fibres, shows that the observations may be more simply
interpreted as saturable absorption phenomena. A basic two-level model of a
saturable absorber displays all the effects normally associated with slow
light, namely phase shift and modulation gain of the transmitted signal, hole
burning in the modulation frequency spectrum and power broadening of the
spectral hole, arising from the finite response time of the non-linear
absorption. Only where hole-burning in the optical spectrum is observed (using
independent pump and probe beams), or pulse delays exceeding the limits set by
saturable absorption are obtained, can reasonable confidence be placed in the
observation of slow light in such experiments. Superluminal ('fast light')
phenomena in media with reverse saturable absorption (RSA) may be similarly
explained.",0812.3076v1
2009-01-19,BFKL and CCFM evolutions with saturation boundary,"We perform numerical studies of the BFKL and CCFM equations for the
unintegrated gluon distribution supplemented with an absorptive boundary which
mimics saturation. For the BFKL equation, this procedure yields the same
results for the saturation momentum and the gluon distribution above saturation
as the non-linear BK equation, for both fixed and running coupling, and for all
the considered energies. This similarity goes beyond expectations based on the
correspondence with statistical physics, which hold only for fixed coupling and
asymptotically high energies. For the CCFM equation, whose non-linear
generalization is not known, our method provides the first study of the
approach towards saturation. We find that, in the running-coupling case, the
CCFM and BFKL predictions for the energy dependence of the saturation momentum
are identical within our numerical accuracy. A similar saturation boundary
could be easily implemented in the CCFM-based Monte Carlo event generators, so
like CASCADE.",0901.2873v1
2010-07-28,Global Saturation of Regularization Methods for Inverse Ill-Posed Problems,"In this article the concept of saturation of an arbitrary regularization
method is formalized based upon the original idea of saturation for spectral
regularization methods introduced by A. Neubauer in 1994. Necessary and
sufficient conditions for a regularization method to have global saturation are
provided. It is shown that for a method to have global saturation the total
error must be optimal in two senses, namely as optimal order of convergence
over a certain set which at the same time, must be optimal (in a very precise
sense) with respect to the error. Finally, two converse results are proved and
the theory is applied to find sufficient conditions which ensure the existence
of global saturation for spectral methods with classical qualification of
finite positive order and for methods with maximal qualification. Finally,
several examples of regularization methods possessing global saturation are
shown.",1008.0108v1
2011-05-10,"Gluon saturation and baryon stopping in the SPS, RHIC and LHC energy regions","A new geometrical scaling method with gluon saturation rapidity limit is
proposed to study the gluon saturation feature of the central rapidity region
of relativistic nuclear collisions. The net-baryon number is essentially
transported by valence quarks that probe the saturation regime in the target by
multiple scattering. We take advantage of the gluon saturation model with
geometric scaling of the rapidity limit to investigate the net baryon
distributions, nuclear stopping power and gluon saturation features in the SPS
and RHIC energy regions. Predictions for net-baryon rapidity distributions, the
mean rapidity loss and gluon saturation feature in central Pb + Pb collisions
at LHC are made in this paper.",1105.1835v4
2011-07-06,Next-to-leading and resummed BFKL evolution with saturation boundary,"We investigate the effects of the saturation boundary on small-x evolution at
the next-to-leading order accuracy and beyond. We demonstrate that the
instabilities of the next-to-leading order BFKL evolution are not cured by the
presence of the nonlinear saturation effects, and a resummation of the higher
order corrections is therefore needed for the nonlinear evolution. The
renormalization group improved resummed equation in the presence of the
saturation boundary is investigated, and the corresponding saturation scale is
extracted. A significant reduction of the saturation scale is found, and we
observe that the onset of the saturation corrections is delayed to higher
rapidities. This seems to be related to the characteristic feature of the
resummed splitting function which at moderately small values of x possesses a
minimum.",1107.1252v1
2012-10-16,Saturation-Dependence of Dispersion in Porous Media,"In this study, we develop a saturation-dependent treatment of dispersion in
porous media using concepts from critical path analysis, cluster statistics of
percolation, and fractal scaling of percolation clusters. We calculate spatial
solute distributions as a function of time and calculate arrival time
distributions as a function of system size. Our previous results correctly
predict the range of observed dispersivity values over ten orders of magnitude
in experimental length scale, but that theory contains no explicit dependence
on porosity or relative saturation. This omission complicates comparisons with
experimental results for dispersion, which are often conducted at saturation
less than 1. We now make specific comparisons of our predictions for the
arrival time distribution with experiments on a single column over a range of
saturations. This comparison suggests that the most important predictor of such
distributions as a function of saturation is not the value of the saturation
per se, but the applicability of either random or invasion percolation models,
depending on experimental conditions.",1210.4581v1
2014-01-21,Impact of Dispersive and Saturable Gain/Loss on Bistability of Nonlinear Parity-Time Bragg Gratings,"We report on the impact of realistic gain and loss models on the bistable
operation of nonlinear parity-time Bragg gratings. In our model we include both
dispersive and saturable gain and show that levels of gain/loss saturation can
have significant impact on the bistable operation of a nonlinear PT Bragg
grating based on GaAs material. The hysteresis of the nonlinear PT Bragg
grating is analyzed for different levels of gain and loss and different
saturation levels. We show that high saturation levels can improve the
nonlinear operation by reducing the intensity at which the bistability occurs.
However when the saturation intensity is low, saturation inhibits the PT
characteristics of the grating.",1401.5233v2
2014-12-27,Analysis of Saturated Belief Propagation Decoding of Low-Density Parity-Check Codes,"We consider the effect of log-likelihood ratio saturation on belief
propagation decoder low-density parity-check codes. Saturation is commonly done
in practice and is known to have a significant effect on error floor
performance. Our focus is on threshold analysis and stability of density
evolution.
  We analyze the decoder for standard low-density parity-check code ensembles
and show that belief propagation decoding generally degrades gracefully with
saturation. Stability of density evolution is, on the other hand, rather
strongly effected by saturation and the asymptotic qualitative effect of
saturation is similar to reduction by one of variable node degree.
  We also show under what conditions the block threshold for the saturated
belief propagation corresponds with the bit threshold.",1412.8090v1
2017-05-27,Power System Supplementary Damping Controllers in the Presence of Saturation,"This paper presents the analysis and a method to design supplementary damping
controllers (SDCs) for synchronous generators considering the effects of
saturation limits. Usually such saturations of control signals are imposed in
order to enforce practical limitations such as component ratings. However, to
guarantee the stability in the presence of saturation limits, the state
trajectories must remain inside the domain of attraction (DA). In this paper,
the domain of attraction of a single-machine infinite-bus (SMIB) power system
with saturation nonlinearity is estimated and compared with the exact
description of the null controllable region. Then, state-feedback controllers
are designed to enlarge the DA. Our analysis shows that nonlinear effects of
saturation should be considered to guarantee stability and satisfactory
performance. Simulation results on a detailed nonlinear model of a synchronous
generator indicate that the DA enlarges with the proposed controller. The
results also indicate that Critical Clearing Time (CCT) and damping of the
system with saturation can be improved by the proposed method.",1705.09849v1
2019-06-30,On countably saturated linear orders and certain class of countably saturated graphs,"The idea of this paper is to explore the existence of canonical countably
saturated models for different classes of structures. It is well-known that,
under CH, there exists a unique countably saturated linear order of cardinality
$\mathfrak{c}$. We provide some examples of pairwise non-isomorphic countably
saturated linear orders of cardinality $\mathfrak{c}$, under different
set-theoretic assumptions. We give a new proof of the old theorem of Harzheim,
that the class of countably saturated linear orders has a uniquely determined
one-element basis. From our proof it follows that this minimal linear order is
a Fra\""isse limit of certain Fra\""isse class. In particular, it is homogeneous
with respect to countable subsets. Next, we prove the existence and uniqueness
of the uncountable version of the random graph. This graph is isomorphic to
$(H(\omega_1),\in \cup \ni)$, where $H(\omega_1)$ is the set of hereditarily
countable sets, and two sets are connected if one of them is an element of the
other. In the last section, an example of a prime countably saturated Boolean
algebra is presented.",1907.00432v4
2020-03-30,Rainbow Saturation,"We introduce a notion of rainbow saturation and the corresponding rainbow
saturation number. This is the saturation version of the rainbow Tur\'an
numbers whose systematic study was initiated by Keevash, Mubayi, Sudakov, and
Verstra\""ete. We give examples of graphs for which the rainbow saturation
number is bounded away from the ordinary saturation number. This includes all
complete graphs $K_n$ for $n\geq 4$, and several bipartite graphs. It is
notable that there are non-bipartite graphs for which this is the case, as this
does not happen when it comes to the rainbow extremal number versus the
traditional extremal number. We also show that saturation numbers are linear
for a large class of graphs, providing a partial rainbow analogue of a well
known theorem of K\'asonyi and Tuza. We conclude this paper with related open
questions and conjectures.",2003.13200v2
2020-12-31,Unified description of saturation and bistability of intersubband transitions in the weak and strong light-matter coupling regimes,"We propose a unified description of intersubband absorption saturation for
quantum wells inserted in a resonator, both in the weak and strong light-matter
coupling regimes. We demonstrate how absorption saturation can be engineered.
In particular we show that the saturation intensity increases linearly with the
doping in the strong coupling regime, while it remains doping independent in
weak coupling. Hence, countering intuition, the most suitable region to exploit
low saturation intensities is not the ultra-strong coupling regime, but is
instead at the onset of the strong light-matter coupling. We further derive
explicit conditions for the emergence of bistability. This work sets the path
towards yet unexisting ultrafast mid-infrared semiconductor saturable
absorption mirrors (SESAMs) and bistable systems. As an example, we show how to
design a mid-infrared SESAM with a three orders of magnitude reduction in
saturation intensity, down to about 5 kW/cm2.",2012.15633v3
2022-03-09,Gym-saturation: an OpenAI Gym environment for saturation provers,"`gym-saturation` is an OpenAI Gym environment for reinforcement learning (RL)
agents capable of proving theorems. Currently, only theorems written in a
formal language of the Thousands of Problems for Theorem Provers (TPTP) library
in clausal normal form (CNF) are supported. `gym-saturation` implements the
'given clause' algorithm (similar to the one used in Vampire and E Prover).
Being written in Python, `gym-saturation` was inspired by PyRes. In contrast to
the monolithic architecture of a typical Automated Theorem Prover (ATP),
`gym-saturation` gives different agents opportunities to select clauses
themselves and train from their experience. Combined with a particular agent,
`gym-saturation` can work as an ATP. Even with a non trained agent based on
heuristics, `gym-saturation` can find refutations for 688 (of 8257) CNF
problems from TPTP v7.5.0.",2203.04699v1
2022-03-18,Optimizing Randomized and Deterministic Saturation Designs under Interference,"Randomized saturation designs are a family of designs which assign a possibly
different treatment proportion to each cluster of a population at random. As a
result, they generalize the well-known (stratified) completely randomized
designs and the cluster-based randomized designs, which are included as special
cases. We show that, under the stable unit treatment value assumption, either
the cluster-based or the stratified completely randomized design are in fact
optimal for the bias and variance of the difference-in-means estimator among
randomized saturation designs. However, this is no longer the case when
interference is present. We provide the closed form of the bias and variance of
the difference-in-means estimator under a linear model of interference and
investigate the optimization of each of these objectives. In addition to the
randomized saturation designs, we propose a deterministic saturation design,
where the treatment proportion for clusters are fixed, rather than randomized,
in order to further improve the estimator under correct model specification.
Through simulations, we illustrate the merits of optimizing randomized
saturation designs to the graph and potential outcome structure, as well as
showcasing the additional improvements yielded by well-chosen deterministic
saturation designs.",2203.09682v1
2023-06-17,Projective and external saturation problem for posets,"We introduce two variants of the poset saturation problem. For a poset $P$
and the Boolean lattice $\mathcal{B}_n$, a family $\mathcal{F}$ of sets, not
necessarily from $\mathcal{B}_n$, is \textit{projective $P$-saturated} if (i)
it does not contain any strong copies of $P$, (ii) for any $G\in
\mathcal{B}_n\setminus \mathcal{F}$, the family $\mathcal{F}\cup \{G\}$
contains a strong copy of $P$, and (iii) for any two different
$F,F'\in\mathcal{F}$ we have $F\cap[n]\neq F'\cap [n]$. Ordinary strongly
$P$-saturated families, i.e., subfamilies $\mathcal{F}$ required to be from
$\mathcal{B}_n$ satisfying (i) and (ii), automatically satisfy (iii) as they
lie within $\mathcal{B}_n$. We study what phenomena are valid both for the
ordinary saturation number $\mathrm{sat}^*(n,P)$ and the projective saturation
number, the size of the smallest projective $P$-saturated family.
  Note that the projective saturation number might differ for a poset and its
dual. We also introduce an even more relaxed and symmetric version of poset
saturation, \textit{external saturation}. We conjecture that all finite posets
have bounded external saturation number, and prove this in some special cases.",2306.10387v1
2023-06-29,Saturating linear sets of minimal rank,"Saturating sets are combinatorial objects in projective spaces over finite
fields that have been intensively investigated in the last three decades. They
are related to the so-called covering problem of codes in the Hamming metric.
In this paper, we consider the recently introduced linear version of such sets,
which is, in turn, related to the covering problem in the rank metric. The main
questions in this context are how small the rank of a saturating linear set can
be and how to construct saturating linear sets of small rank. Recently, Bonini,
Borello, and Byrne provided a lower bound on the rank of saturating linear sets
in a given projective space, which is shown to be tight in some cases. In this
paper, we provide construction of saturating linear sets meeting the lower
bound and we develop a link between the saturating property and the
scatteredness of linear sets. The last part of the paper is devoted to show
some parameters for which the bound is not tight.",2306.17081v2
2023-12-02,Saturation results around the Erdős--Szekeres problem,"In this paper, we consider saturation problems related to the celebrated
Erd\H{o}s--Szekeres convex polygon problem. For each $n \ge 7$, we construct a
planar point set of size $(7/8) \cdot 2^{n-2}$ which is saturated for convex
$n$-gons. That is, the set contains no $n$ points in convex position while the
addition of any new point creates such a configuration. This demonstrates that
the saturation number is smaller than the Ramsey number for the
Erd\H{o}s--Szekeres problem. The proof also shows that the original
Erd\H{o}s--Szekeres construction is indeed saturated.
  Our construction is based on a similar improvement for the saturation version
of the cups-versus-caps theorem. Moreover, we consider the generalization of
the cups-versus-caps theorem to monotone paths in ordered hypergraphs. In
contrast to the geometric setting, we show that this abstract saturation number
is always equal to the corresponding Ramsey number.",2312.01223v1
2010-10-11,Investigating coronal saturation and super-saturation in fast-rotating M-dwarf stars,"At fast rotation rates the coronal activity of G- and K-type stars has been
observed to ""saturate"" and then decline again at even faster rotation rates --
a phenomenon dubbed ""super-saturation"". In this paper we investigate coronal
activity in fast-rotating M-dwarfs using deep XMM-Newton observations of 97
low-mass stars of known rotation period in the young open cluster NGC 2547, and
combine these with published X-ray surveys of low-mass field and cluster stars
of known rotation period. Like G- and K-dwarfs, we find that M-dwarfs exhibit
increasing coronal activity with decreasing Rossby number N_R, the ratio of
period to convective turnover time, and that activity saturates at L_x/L_bol ~
10^-3 for log N_R < -0.8. However, super-saturation is not convincingly
displayed by M-dwarfs, despite the presence of many objects in our sample with
log N_R < -1.8, where super-saturation is observed to occur in higher mass
stars. Instead, it appears that a short rotation period is the primary
predictor of super-saturation; P <=0.3d for K-dwarfs and perhaps P <=0.2d for
M-dwarfs. These observations favour the ""centrifugal stripping"" model for
super-saturation, where coronal structures are forced open or become
radiatively unstable as the Keplerian co-rotation radius moves inside the X-ray
emitting coronal volume.",1010.2152v1
2017-03-20,A barotropic model of eddy saturation,"""Eddy saturation"" refers to a regime in which the total volume transport of
an oceanic current is insensitive to the wind stress strength. Baroclinicity is
currently believed to be key to the development of an eddy-saturated state. In
this paper, it is shown that eddy saturation can also occur in a purely
barotropic flow over topography, without baroclinicity. Thus, eddy saturation
is a fundamental property of barotropic dynamics above topography. It is
demonstrated that the main factor controlling the appearance or not of
eddy-saturated states in the barotropic setting is the structure of geostrophic
contours, that is the contours of $f/H$ of the ratio of the Coriolis parameter
to the ocean's depth. Eddy-saturated states occur when the geostrophic contours
are open, that is when the geostrophic contours span the whole zonal extent of
the domain. This minimal requirement for eddy-saturated states is demonstrated
using numerical integrations of a single-layer quasi-geostrophic flow over two
different topographies characterized by either open or closed geostrophic
contours with parameter values loosely inspired by the Southern Ocean. In this
setting, transient eddies are produced through a barotropic-topographic
instability that occurs due tot the interaction of the large-scale zonal flow
with the topography. Through the study of this barotropic-topographic
instability insight is gained on how eddy-saturated states are established.",1703.06594v4
2018-03-16,Induced Saturation of Graphs,"A graph $G$ is $H$-saturated for a graph $H$, if $G$ does not contain a copy
of $H$ but adding any new edge to $G$ results in such a copy. An $H$-saturated
graph on a given number of vertices always exists and the properties of such
graphs, for example their highest density, have been studied intensively. A
graph $G$ is $H$-induced-saturated if $G$ does not have an induced subgraph
isomorphic to $H$, but adding an edge to $G$ from its complement or deleting an
edge from $G$ results in an induced copy of $H$. It is not immediate anymore
that $H$-induced-saturated graphs exist. In fact, Martin and Smith (2012)
showed that there is no $P_4$-induced-saturated graph. Behrens et.al. (2016)
proved that if $H$ belongs to a few simple classes of graphs such as a class of
odd cycles of length at least $5$, stars of size at least $2$, or matchings of
size at least $2$, then there is an $H$-induced-saturated graph. This paper
addresses the existence question for $H$-induced-saturated graphs. It is shown
that Cartesian products of cliques are $H$-induced-saturated graphs for $H$ in
several infinite families, including large families of trees. A complete
characterization of all connected graphs $H$ for which a Cartesian product of
two cliques is an $H$-induced-saturated graph is given. Finally, several
results on induced saturation for prime graphs and families of graphs are
provided.",1803.06244v1
2023-07-17,"Varying quench dynamics in the transverse Ising chain: the Kibble-Zurek, saturated, and pre-saturated regimes","According to the Kibble-Zurek mechanism, there is a universal power-law
relationship between the defect density and the quench rate during a slow
linear quench through a critical point. It is generally accepted that a fast
quench results in a deviation from the Kibble-Zurek scaling law and leads to
the formation of a saturated plateau in the defect density. By adjusting the
quench rate from slow to very fast limits, we observe the varying quench
dynamics and identify a pre-saturated regime that lies between the saturated
and Kibble-Zurek regimes. This significant result is elucidated through the
adiabatic-impulse approximation first, then verified by a rigorous analysis on
the transverse Ising chain as well. As we approach the turning point from the
saturated to pre-saturated regimes, we notice a change in scaling laws and,
with an increase in the initial transverse field, a shrinking of the saturated
regime until it disappears. During another turning point from the Kibble-Zurek
to pre-saturated regimes, we observe an attenuation of the dephasing effect and
a change in the behavior of the kink-kink correlation function from a Gaussian
decay to an exponential decay. Finally, the coherent many-body oscillation
after quench exhibits different behaviors in the three regimes and shows a
significant change of scaling behavior between the S and PS regimes.",2307.08599v3
2005-04-26,The independent scattering approximation in the saturated regime,"We show that a saturable single-frequency elastic T-matrix approach to
scattering of light by atoms agrees remarkably well with a master equation
description in the regime of unsaturated atoms, or for large separation between
the atoms. If the atoms are in each other's near-field and the saturation of
the atoms is high enough, the two approaches yield different results.",0504673v1
2000-10-05,Comments on parton saturation at small x in large nuclei,"It is argued that the gluon density introduced by A.Mueller in relation to
the saturation phenomenon is different from the standardly defined one, which
turned out to have a soliton-like form in the numerical calculations. It is
shown that A.Mueller's densities obtained from the latter possess the same
saturation properties as originally predicted.",0010041v1
2003-09-17,Saturation regimes at LHC energies,"The effects of saturation and unitarization for hadron-hadron scattering at
LHC energies are explored in several models. It is shown that different choices
of saturation parameters lead to sizable differences in the energy dependence
of total cross sections, and to dramatic changes in elastic differential cross
sections.",0309194v1
2004-01-19,Instanton-Driven Saturation at Small x,"We report on the interesting possibility of instanton-driven gluon saturation
in lepton-nucleon scattering at small Bjorken-x. Our results crucially involve
non-perturbative information from high-quality lattice simulations. The
conspicuous, intrinsic instanton size scale < rho > ~ 0.5 fm, as known from the
lattice, turns out to determine the saturation scale. A central result is the
identification of the ``colour glass condensate'' with the QCD-sphaleron state.",0401137v1
2006-07-11,"Color strings, pomeron shadowing and Color Glass Condensate","I review the problem of parton saturation and its implications through three
in principal different approaches, but somewhat related: saturation in a
geometrical approach, QCD saturation through the Color Glass Condensate and
shadowing in a Pomeron approach.",0607120v1
2000-01-28,Stabilization of Spatial Solitons by Gain Diffusion,"It is shown, that diffusion of saturated gain (e.g. diffusion of population
inversion in lasers) causes, and/or enhances a modulational instability of
generated light field. In case of a subcritical system (e.g. a laser with
saturable absorber) the enhancement of the modulational instability stabilizes
spatial solitons. These predictions are made for general nonlinear optical
systems, and are illustrated by numerical simulation of lasers with saturable
absorber.",0001064v1
2005-10-07,From percolation to the Color Glass Condensate,"I review the problem of parton saturation and its implications through three
in principal different approaches, but somewhat related: saturation in a
geometrical approach, QCD saturation through the Color Glass Condensate and
perturbative Pomeron approach with initial conditions. I also make some
comments about how that could be related to a Quark Gluon Plasma formation.",0510026v1
2007-06-15,Heavy Flavor Production in DGLAP improved Saturation Model,"The saturation model with DGLAP evolution is shown to give good description
of the production of the charm and beauty quarks in deep inelastic scattering.
The modifications of saturation properties caused by the presence of heavy
quarks are also discussed.",0706.2276v1
2008-07-07,Chirped-pulse oscillators: an impact of the dynamic gain saturation,"An effect of the dynamic gain saturation on chirped-pulse oscillator was
investigated. It was found, that the dynamic gain saturation causes strong
perturbations of the pulse front that destabilizes an oscillator. As a result,
the chirped-pulse exists only within some limited range of dispersions and
there is a limit of energy growth for a given resonator period.",0807.1050v1
2009-03-20,Saturation and linear transport equation,"We show that the GBW saturation model provides an exact solution to the one
dimensional linear transport equation. We also show that it is motivated by the
BK equation considered in the saturated regime when the diffusion and the
splitting term in the diffusive approximation are balanced by the nonlinear
term.",0903.3521v2
2010-07-28,Introduction to the Physics of Saturation,"We present a brief introduction to the physics of parton saturation/Color
Glass Condensate (CGC).",1007.5021v1
2010-09-09,Saturation effects in QCD from linear transport equation,"We show that the GBW saturation model provides an exact solution to the
one-dimensional linear transport equation. We also show that it is motivated by
the BK equation considered in the saturated regime when the diffusion and the
splitting term in the diffusive approximation are balanced by the nonlinear
term.",1009.1757v1
2012-08-25,Remark on the coherent information saturating its upper bound,"Coherent information is a useful concept in quantum information theory. It
connects with other notions in data processing. In this short remark, we
discuss the coherent information saturating its upper bound. A necessary and
sufficient condition for this saturation is derived.",1208.5101v2
2012-12-31,A valuation theoretic characterization of recursively saturated real closed fields,"We give a valuation theoretic characterization for a real closed field to be
recursively saturated. Our result extends the characterization of Harnik and
Ressayre \cite{hr} for a divisible ordered abelian group to be recursively
saturated.",1212.6842v1
2014-05-09,Sandwiching saturation number of fullerene graphs,"The saturation number of a graph $G$ is the cardinality of any smallest
maximal matching of $G$, and it is denoted by $s(G)$. Fullerene graphs are
cubic planar graphs with exactly twelve 5-faces; all the other faces are
hexagons. They are used to capture the structure of carbon molecules. Here we
show that the saturation number of fullerenes on $n$ vertices is essentially
$n/3$.",1405.2197v1
2016-04-19,Black Hole Spindown by Light Bosons,"The saturation mechanism for the fastest-growing instability of massive
scalar field in Kerr metric is identified, assuming saturation by cubic or
quartic nonlinearities of the field potential. The resulting spindown rate of
the black hole is calculated. The (rather involved) saturation scenario is
confirmed by numerical simulations.",1604.06422v1
2016-07-14,Saturation and geometrical scaling in small systems,"Saturation and geometrical scaling (GS) of gluon distributions are a
consequence of the non-linear evolution equations of QCD. We argue that in pp
GS holds for the inelastic cross-section rather than for the multiplicity
distributions. We also discuss possible fluctuations of the proton saturation
scale in pA collisions at the LHC.",1607.04235v1
2016-10-01,On cohomology of saturated fusion systems and support varieties,"In this short note we study the cohomology algebra of saturated fusion
systems using finite groups which realize saturated fusion systems and
Hochschild cohomology of group algebras. A similar result to a theorem of
Alperin is proved for varieties of cohomology algebras of fusions systems
associated to block algebras of finite groups.",1610.00095v2
2017-01-11,Saturation rank for finite group schemes: Finite groups and Infinitesimal group schemes,"We investigate the saturation rank of a finite group scheme, defined over an
algebraically closed field $\Bk$ of positive characteristic $p$. We begin by
exploring the saturation rank for finite groups and infinitesimal group
schemes. Special attention is given to reductive Lie algebras and the second
Frobenius kernel of the algebraic group $\SL_{n}$.",1701.02951v1
2017-08-09,Weak saturation and weak amalgamation property,"The two model-theoretic concepts of weak saturation and weak amalgamation
property are studied in the context of accessible categories. We relate these
two concepts providing sufficient conditions for existence and uniqueness of
weakly saturated objects of an accessible category K. We discuss the
implications of this fact in classical model theory.",1708.02738v2
2017-08-28,Periodic groups saturated with finite simple groups of lie type rank 1,"In the Kourovka notebook the following question is posed 14.101:
  Is it true that a periodic group saturated with finite simple groups of Lie
type whose ranks are bounded in the aggregate, is itself a simple group of Lie
type?
  In this paper we give a partial answer to this question for periodic groups
saturated by finite simple groups of Lie type rank 1.",1708.08181v1
2017-12-10,"Asymptotics of Chebyshev Polynomials, III. Sets Saturating SzegŐ, Schiefermayr, and Totik--Widom Bounds","We determine which sets saturate the Szeg}o and Schiefermayr lower bounds on
the norms of Chebyshev Polynomials. We also discuss sets that saturate the
Totik--Widom upper bound.",1712.03482v1
2019-03-08,"Decomposability, Convexity and Continuous Linear Operators in $L^1(μ,E)$: The Case for Saturated Measure Spaces","Motivated by the Lyapunov convexity theorem in infinite dimensions, we extend
the convexity of the integral of a decomposable set to separable Banach spaces
under the strengthened notion of nonatomicity of measure spaces, called
""saturation"", and provide a complete characterization of decomposability in
terms of saturation.",1903.04301v1
2021-04-02,Saturation bounds for smooth varieties,"We prove bounds on the saturation degrees of homogeneous ideals (and their
powers) defining smooth complex projective varieties. For example, we show that
a classical statement due to Macualay for zero-dimensional complete
intersection ideals holds for any smooth variety. For curves, we bound the
saturation degree of powers in terms of the regularity.",2104.01218v1
2022-03-17,Obstructions to countable saturation in corona algebras,"We study the extent of countable saturation for coronas of abelian
C*-algebras. In particular, we show that the corona algebra of $C_0(\bbR^n)$ is
countably saturated if and only if $n=1$.",2203.09351v2
2007-10-17,Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. II. Mixed Trends in VB10 and LSR1835+32 and the Possible Role of Rotation,"[Abridged] As part of our on-going investigation of magnetic activity in
ultracool dwarfs we present simultaneous radio, X-ray, UV, and optical
observations of LSR1835+32 (M8.5), and simultaneous X-ray and UV observations
of VB10 (M8), both with a duration of about 9 hours. LSR1835+32 exhibits
persistent radio emission and H-alpha variability on timescales of ~0.5-2 hr.
The detected UV flux is consistent with photospheric emission, and no X-ray
emission is detected to a deep limit of L_X/L_bol<10^-5.7. The H-alpha and
radio emission are temporally uncorrelated, and the ratio of radio to X-ray
luminosity exceeds the correlation seen in F-M6 stars by >2x10^4. Similarly,
L_Halpha/L_X>10 is at least 30 times larger than in early M dwarfs, and
eliminates coronal emission as the source of chromospheric heating. The lack of
radio variability during four rotations of LSR1835+32 requires a uniform
stellar-scale field of ~10 G, and indicates that the H-alpha variability is
dominated by much smaller scales, <10% of the chromospheric volume. VB10, on
the other hand, shows correlated flaring and quiescent X-ray and UV emission,
similar to the behavior of early M dwarfs. Delayed and densely-sampled optical
spectra exhibit a similar range of variability amplitudes and timescales to
those seen in the X-rays and UV, with L_Halpha/L_X~1. Along with our previous
observations of the M8.5 dwarf TVLM513-46546 we conclude that late M dwarfs
exhibit a mix of activity patterns, which points to a transition in the
structure and heating of the outer atmosphere by large-scale magnetic fields.
We find that rotation may play a role in generating the fields as evidenced by
a tentative correlation between radio activity and rotation velocity. The X-ray
emission, however, shows evidence for super-saturation at vsini>25 km/s.",0710.3383v1
2009-08-19,Long-term monitoring in IC4665: Fast rotation and weak variability in very low mass objects,"We present the combined results of three photometric monitoring campaigns
targeting very low mass (VLM) stars and brown dwarfs in the young open cluster
IC4665 (age ~40 Myr). In all three runs, we observe ~100 cluster members,
allowing us for the first time to put limits on the evolution of spots and
magnetic activity in fully convective objects on timescales of a few years. For
20 objects covering masses from 0.05 to 0.5 Msol we detect a periodic flux
modulation, indicating the presence of magnetic spots co-rotating with the
objects. The detection rate of photometric periods (~20%) is significantly
lower than in solar-mass stars at the same age, which points to a mass
dependence in the spot properties. With two exceptions, none of the objects
exhibit variability and thus spot activity in more than one season. This is
contrary to what is seen in solar-mass stars and indicates that spot
configurations capable of producing photometric modulations occur relatively
rarely and are transient in VLM objects. The rotation periods derived in this
paper range from 3 to 30h, arguing for a lack of slow rotators among VLM
objects. The periods fit into a rotational evolution scenario with pre-main
sequence contraction and moderate (40-50%) angular momentum losses due to wind
braking. By combining our findings with literature results, we identify two
regimes of rotational and magnetic properties, called C- and I-sequence. Main
properties on the C-sequence are fast rotation, weak wind braking, Halpha
emission, and saturated activity levels, while the I-sequence is characterised
by slow rotation, strong wind braking, no Halpha emission, and linear
activity-rotation relationship. Rotation rate and stellar mass are the primary
parameters that determine in which regime an object is found. (abridged)",0908.2811v1
2009-11-27,Shaken and stirred: conduction and turbulence in clusters of galaxies,"(abridged) Uninhibited radiative cooling in clusters of galaxies would lead
to excessive mass accretion rates contrary to observations. One of the key
proposals to offset radiative energy losses is thermal conduction from outer,
hotter layers of cool core clusters to their centers. However, conduction is
sensitive to magnetic field topology. In cool-core clusters the heat buoyancy
instability (HBI) leads to B-fields ordered preferentially in the direction
perpendicular to that of gravity, which significantly reduces the level of
conduction below the classical Spitzer-Braginskii value. However, the cluster
cool cores are rarely in perfect hydrostatic equilibrium. Sloshing motions due
to minor mergers, galaxy motions or AGN can significantly perturb the gas and
affect the level of thermal conduction. We perform 3D AMR MHD simulations of
the effect of turbulence on the properties of the anisotropic thermal
conduction in cool core clusters. We show that very weak subsonic motions, well
within observational constraints, can randomize the magnetic field and
significantly boost effective thermal conduction beyond the saturated values
expected in the pure unperturbed HBI case. We find that the turbulent motions
can essentially restore the conductive heat flow to the cool core to level
comparable to the theoretical maximum of 1/3 Spitzer for a highly tangled
field. Runs with radiative cooling show that the cooling catastrophe can be
averted and the cluster core stabilized. Above a critical Froude number, these
same turbulent motions also eliminate the tangential bias in the velocity and
magnetic field that is otherwise induced by the trapped g-modes. Our results
can be tested with future radio polarization measurements, and have
implications for efficient metal dispersal in clusters.",0911.5198v2
2010-05-26,CeRu$_4$Sn$_6$: heavy fermions emerging from a Kondo-insulating state,"The combination of low-temperature specific-heat and
nuclear-magnetic-resonance (NMR) measurements reveals important information of
the ground-state properties of CeRu$_4$Sn$_6$, which has been proposed as a
rare example of a tetragonal Kondo-insulator (KI). The NMR
spin-latticerelaxation rate $1/T_1$ deviates from the Korringa law below 100 K
signaling the onset of an energy gap $\Delta E_g1/k_B \simeq 30$K. This gap is
stable against magnetic fields up to 10 T. Below 10 K, however, unusual
low-energy excitations of in-gap states are observed, which depend strongly on
the field H. The specific heat C detects these excitations in the form of an
enhanced Sommerfeld coefficient $\gamma = C(T)/T$ : In zero field, $\gamma$
increases steeply below 5 K, reaching a maximum at 0.1 K, and then saturates at
$\gamma = 0.6$ J/molK$^2$. This maximum is shifted to higher temperatures with
increasing field suggesting a residual density of states at the Fermi level
developing a spin gap $\Delta E_g2$. A simple model, based on two narrow
quasiparticle bands located at the Fermi level - which cross the Fermi level in
zero field at 0.022 states/meV f.u. - can account qualitatively as well as
quantitatively for the measured observables. In particular, it is demonstrated
that fitting our data of both specific heat and NMR to the model, incorporating
a Ce magnetic moment of $\mu = \Delta E_g1/\mu_{0H} \simeq 1 \mu_B$, leads to
the prediction of the field dependence of the gap. Our measurements rule out
the presence of a quantum critical point as the origin for the enhanced
$\gamma$ in CeRu$_4$Sn$_6$ and suggest that this arises rather from correlated,
residual in-gap states at the Fermi level. This work provides a fundamental
route for future investigations into the phenomenon of narrow-gap formation in
the strongly correlated class of system",1005.4912v1
2011-03-18,Hall diffusion and the magnetorotational instability in protoplanetary discs,"The destabilising effect of Hall diffusion in a Keplerian disc allows the MRI
to occur for much lower ionisation levels than would otherwise be possible.
However, simulations suggest that the consequences for the saturated state are
not as significant as suggested by the linear instability. Close inspection
reveals that that the simulations have not yet probed the Hall-dominated
regime. Here we revisit the effect of Hall diffusion on the MRI and the
implications for the extent of MHD turbulence in protoplanetary discs.
  We conduct a local stability analysis for a vertical, weak magnetic field
subject to axisymmetric perturbations with a vertical wave vector. The
diffusivity dependence is presented using analytic expressions and contours in
the eta_H - eta_P plane for the maximum growth rate and corresponding wave
number, the upper cut-off for unstable wave numbers, and the loci that divide
the plane into regions of different characteristic behaviour. In the
highly-diffusive limit the magnetic field decouples from the fluid
perturbations and the diffusive MRI reduces to a diffusive plane-parallel shear
instability with effective shear rate 1.5 Omega. We give analytic expressions
for the growth rate and wave number of the most unstable mode.
  Finally, we illustrate the critical effect of Hall diffusion on the extent of
dead zones in protoplanetary discs by applying a local stability criterion to a
simple model of the minimum-mass solar nebula at 1 au, including x-ray and
cosmic-ray ionisation and a population of 1 micron grains. Hall diffusion
increases or decreases the MRI-active column density by an order of magnitude
or more, depending on whether B is parallel or antiparallel to the rotation
axis, respectively. Existing estimates of the depth of magnetically active
layers in protoplanetary discs are likely to be wildly inaccurate.
  [Abridged]",1103.3562v2
2011-06-14,Disorder-dependent superconducting phase-diagram at high magnetic fields in Fe$_{1 + y}$Se$_{x}$Te$_{1-x}$ ($x \sim 0.4$),"We compare the superconducting phase-diagram under high magnetic fields (up
to $H = 45$ T) of Fe$_{1+y}$Se$_{0.4}$Te$_{0.6}$ single crystals originally
grown by the Bridgman-Stockbarger (BRST) technique, which were annealed to
display narrow superconducting transitions and the optimal transition
temperature $T_c \gtrsim 14$ K, with the diagram for samples of similar
stoichiometry grown by the traveling-solvent floating-zone technique as well as
with the phase-diagram reported for crystals grown by a self-flux method. We
find that the so-annealed samples tend to display higher ratios $H_{c2}/T_c$,
particularly for fields applied along the inter-planar direction, where the
upper critical field $H_{c2}(T)$ exhibits a pronounced downward curvature
followed by saturation at lower temperatures $T$. This last observation is
consistent with previous studies indicating that this system is Pauli limited.
An analysis of our $H_{c2}(T)$ data using a multiband theory suggests the
emergence of the Farrel-Fulde-Larkin-Ovchnikov state at low temperatures. A
detailed structural x-ray analysis, reveals no impurity phases but an
appreciable degree of mosaicity in as-grown BRST single-crystals which remains
unaffected by the annealing process. Energy-dispersive x-ray analysis showed
that the annealed samples have a more homogeneous stoichiometric distribution
of both Fe and Se with virtually the same content of interstitial Fe as the
non-annealed ones. Thus, we conclude that stoichiometric disorder, in contrast
to structural disorder, is detrimental to the superconducting phase diagram of
this series under high magnetic fields. Finally, a scaling analysis of the
fluctuation conductivity in the superconducting critical regime, suggests that
the superconducting fluctuations have a two-dimensional character in this
system.",1106.2818v2
2012-12-21,Nuclei in Strongly Magnetised Neutron Star Crusts,"We discuss the ground state properties of matter in outer and inner crusts of
neutron stars under the influence of strong magnetic fields. In particular, we
demonstrate the effects of Landau quantization of electrons on compositions of
neutron star crusts. First we revisit the sequence of nuclei and the equation
of state of the outer crust adopting the Baym, Pethick and Sutherland (BPS)
model in the presence of strong magnetic fields and most recent versions of the
theoretical and experimental nuclear mass tables. Next we deal with nuclei in
the inner crust. Nuclei which are arranged in a lattice, are immersed in a
nucleonic gas as well as a uniform background of electrons in the inner crust.
The Wigner-Seitz approximation is adopted in this calculation and each lattice
volume is replaced by a spherical cell. The coexistence of two phases of
nuclear matter - liquid and gas, is considered in this case. We obtain the
equilibrium nucleus corresponding to each baryon density by minimizing the free
energy of the cell. We perform this calculation using Skyrme nucleon-nucleon
interaction with different parameter sets. We find nuclei with larger mass and
charge numbers in the inner crust in the presence of strong magnetic fields
than those of the zero field case for all nucleon-nucleon interactions
considered here. However, SLy4 interaction has dramatic effects on the proton
fraction as well as masses and charges of nuclei. This may be attributed to the
behaviour of symmetry energy with density in the sub-saturation density regime.
Further we discuss the implications of our results to shear mode oscillations
of magnetars.",1212.5348v1
2013-02-28,Rayleigh-Taylor Instability in a Relativistic Fireball on a Moving Computational Grid,"We numerically calculate the growth and saturation of the Rayleigh-Taylor
instability caused by the deceleration of relativistic outflows with Lorentz
factor {\Gamma} = 10, 30, and 100. The instability generates turbulence whose
scale exhibits strong dependence on Lorentz factor, as only modes with angular
size smaller than 1/{\Gamma} can grow. We develop a simple diagnostic to
measure the kinetic energy in turbulent fluctuations, and calculate a ratio of
turbulent kinetic energy to thermal energy of .03 in the region affected by the
instability. Although our numerical calculation does not include magnetic
fields, we argue that small scale turbulent dynamo amplifies magnetic fields to
nearly this same fraction, giving a ratio of magnetic to thermal energy of ~
.01, to within a factor of two. The instability completely disrupts the contact
discontinuity between the ejecta and the swept up circumburst medium. The
reverse shock is stable, but is impacted by the Rayleigh-Taylor instability,
which strengthens the reverse shock and pushes it away from the forward shock.
The forward shock front is unaffected by the instability, but Rayleigh-Taylor
fingers can penetrate of order 10% of the way into the energetic region behind
the shock during the two-shock phase of the explosion. We calculate afterglow
emission from the explosion and find the reverse shock emission peaks at a
later time due to its reduced Lorentz factor and modified density and pressure
at the shock front. These calculations are performed using a novel numerical
technique that includes a moving computational grid. The moving grid is
essential as it maintains contact discontinuities to high precision and can
easily evolve flows with extremely large Lorentz factors.",1302.7306v3
2014-05-01,Theory of Bosons in two-leg ladders with large magnetic fields,"We calculate the ground state of a Bose gas trapped on a two-leg ladder where
Raman-induced hopping mimics the effect of a large magnetic field. In the
mean-field limit, where there are large numbers of particles per site, this
maps onto a uniformly frustrated two-leg ladder classical spin model. The net
particle current always vanishes in the ground state, but generically there is
a finite ""chiral current"", corresponding to equal and opposite flow on the two
legs. We vary the strength of the hopping across the rungs of the ladder and
the interaction between the bosons. We find three phases: (1) A ""saturated
chiral current phase"" (SCCP), where the density is uniform and the chiral
current is simply related to the strength of the magnetic field. In this state
the only broken symmetry is the $U(1)$ condensate phase. (2) A ""biased ladder
phase"" (BLP), where the density is higher on one leg than the other. The fluid
velocity is higher on the lower density leg, so the net current is zero. In
addition to the $U(1)$ condensate phase, this has a broken $Z_2$ reflection
symmetry. (3) A ""modulated density phase"" (MDP), where the atomic density is
modulated along the ladder. In addition to the $U(1)$ condensate phase, this
has a second broken $U(1)$ symmetry corresponding to translations of the
density wave. We further study the fluctuations of the condensate in the BLP,
finding a roton-maxon like excitation spectrum. Decreasing the hopping along
the rungs softens the spectrum. As the energy of the ""roton"" reaches to zero,
the BLP becomes unstable. We describe the experimental signatures of these
phases, including the response to changing the frequency of the Raman
transition.",1405.0230v1
2014-08-21,On the radiation driven alignment of dust grains: Detection of the polarization hole in a starless core,"We aim to investigate the polarization properties of a starless core in a
very early evolutionary stage. Linear polarization data reveal the properties
of the dust grains in the distinct phases of the interstellar medium. Our goal
is to investigate how the polarization degree and angle correlate with the
cloud and core gas. We use optical, near infrared and submillimeter
polarization observations toward the starless object Pipe-109 in the Pipe
nebula. Our data cover a physical scale range of 0.08 to 0.4 pc, comprising the
dense gas, envelope and the surrounding cloud. The cloud polarization is well
traced by the optical data. The near infrared polarization is produced by a
mixed population of grains from the core border and the cloud gas. The optical
and near infrared polarization toward the cloud reach the maximum possible
value and saturate with respect to the visual extinction. The core polarization
is predominantly traced by the submillimeter data and have a steep decrease
with respect to the visual extinction. Modeling of the submillimeter
polarization indicates a magnetic field main direction projected onto the
plane-of-sky and loss of grain alignment for densities higher than
$6\times10^4$ cm$^{-3}$ (or $A_V > 30$ mag). Pipe-109 is immersed in a
magnetized medium, with a very ordered magnetic field. The absence of internal
source of radiation significantly affects the polarization efficiencies in the
core, creating a polarization hole at the center of the starless core. This
result supports the theory of dust grain alignment via radiative torques.",1408.5133v1
2015-07-16,On the role of tachoclines in solar and stellar dynamos,"Rotational shear layers at the boundary between radiative and convective
zones, tachoclines, play a key role in the process of magnetic field generation
in solar-like stars. We present two sets of global simulations of rotating
turbulent convection and dynamo. The first set considers a stellar convective
envelope only; the second one, aiming at the formation of a tachocline,
considers also the upper part of the radiative zone. Our results indicate that
the resulting mean-flows and dynamo properties like the growth rate, saturation
energy and mode depend on the Rossby (Ro) number. For the first set of models
either oscillatory (with ~2 yr period) or steady dynamo solutions are obtained.
The models in the second set naturally develop a tachocline which, in turn,
leads to the generation of strong mean magnetic field. Since the field is also
deposited into the stable deeper layer, its evolutionary time-scale is much
longer than in the models without a tachocline. Surprisingly, the magnetic
field in the upper turbulent convection zone evolves in the same time scale as
the deep field. These models result in either an oscillatory dynamo with ~30 yr
period or in a steady dynamo depending on Ro. In terms of the mean-field dynamo
coefficients computed using FOSA, the field evolution in the oscillatory models
without a tachocline seems to be consistent with dynamo waves propagating
according to the Parker-Yoshimura sign rule. In the models with tachoclines the
dynamics is more complex involving other transport mechanisms as well as
tachocline instabilities.",1507.04434v3
2015-08-08,Direct comparison of domain wall behavior in Permalloy nanowires patterned by electron beam lithography and focused ion beam milling,"Nominally identical permalloy nanowires, with widths down to 150 nm, were
fabricated onto a single electron transparent Si$_{3}$N$_{4}$ membrane using
electron beam lithography (EBL) and focused ion beam (FIB) milling.
Transmission electron microscopy (TEM) experiments were performed to compare
the nanostructures produced by these two techniques in what we believe is the
first direct comparison of fabrication techniques for nominally identical
nanowires. Both EBL and FIB methods produced high quality structures with edge
roughness being of the order of the mean grain size 5 -10 nm observed in the
continuous films. However, significant grain growth was observed along the
edges of the FIB patterned nanowires. Lorentz TEM \emph{in situ} imaging was
carried out to compare the magnetic behavior of the domain walls in the
patterned nanowires with anti-notches present to pin domain walls. The overall
process of domain wall pinning and depinning at the anti-notches showed
consistent behaviour between nanowires fabricated by the two methods with the
FIB structures having slightly lower characteristic fields compared to the EBL
wires. However, a significant difference was observed in the formation of a
vortex structure inside the anti-notches of the EBL nanowires after depinning
of the domain walls. No vortex structure was seen inside the anti-notches of
the FIB patterned nanowires. Results from micromagnetic simulations suggest
that the vortex structure inside the anti-notch can be suppressed if the
saturation magnetization (M$_{s}$) is reduced along the nanowires edges. Whilst
the two fabrication methods show that well defined structures can be produced
for the dimensions considered here, the differences in the magnetic behavior
for nominally identical structures may be an issue if such structures are to be
used as conduits for domain walls in potential memory and logic applications.",1508.01910v1
2015-12-09,"Standard model of the rare-earths, analyzed from the Hubbard I approximation","In this work we examine critically the electronic structure of the rare-earth
elements by use of the so-called Hubbard I approximation. From the theoretical
side all measured features of both occupied and unoccupied states are
reproduced, without significant deviations between observations and theory. We
also examine cohesive properties like the equilibrium volume and bulk modulus,
where we find, in general, a good agreement between theory and measurements. In
addition we have reproduced the spin and orbital moments of these elements, as
they are reflected from measurements of the saturation moment. We have also
employed the Hubbard I approximation to extract the interatomic exchange
parameters of an effective spin Hamiltonian for the heavy rare earths. We show
that the Hubbard I approximation gives results which are consistent with
calculations where $4f$ electrons are treated as core states for Gd. The latter
approach was also used to address the series of the heavy/late rare-earths. Via
Monte Carlo simulations we obtained ordering temperatures which reproduce
measurements within about $20\%$. We have further illustrated the accuracy of
these exchange parameters by comparing measured and calculated magnetic
configurations for the heavy rare earths and the magnon dispersion for Gd. The
Hubbard I approximation is compared to other theories of the electronic
structure, and we argue that it is superior. We discuss the relevance of our
results in general, and how this makes it possible to treat the electronic
structure of materials containing rare-earth elements, such as permanent
magnets, magnetostrictive compounds, photovoltaics, optical fibers, topological
insulators, and molecular magnets.",1512.02848v2
2017-02-18,At the limits of criticality-based quantum metrology: apparent super-Heisenberg scaling revisited,"We address the question whether the super-Heisenberg scaling for quantum
estimation is realizable. We unify the results of two approaches. In the first
one, the original system is compared with its copy rotated by the parameter
dependent dynamics. If the parameter is coupled to the one-body part of the
Hamiltonian the precision of its estimation is known to scale at most as
$N^{-1}$ (Heisenberg scaling) in terms of the number of elementary subsystems
used, $N$. The second approach considers fidelity at criticality often leading
to an apparent super-Heisenberg scaling. However, scaling of time needed to
ensure adiabaticity of the evolution brings back the the Heisenberg limit. We
illustrate the general theory on a ferromagnetic Heisenberg spin chain which
exhibits such super-Heisenberg scaling of fidelity around the critical value of
the magnetic field. Even an elementary estimator represented by a single-site
magnetization already outperforms the Heisenberg behavior providing the
$N^{-1.5}$ scaling. In this case Fisher information sets the ultimate scaling
as $N^{-1.75}$ which can be saturated by measuring magnetization on all sites
simultaneously. We discuss universal scaling predictions of the estimation
precision offered by such observables, both at zero and finite temperatures,
and support them with numerical simulations in the model. We provide an
experimental proposal of realization of the considered model via mapping the
system to ultra-cold bosons in periodically shaken optical lattice. We
explicitly derive that the Heisenberg limit is recovered when time needed for
preparation of quantum states involved is taken into acocunt.",1702.05660v3
2017-06-05,Robust techniques for polarization and detection of nuclear spin ensembles,"Highly sensitive nuclear spin detection is crucial in many scientific areas
including nuclear magnetic resonance spectroscopy (NMR), imaging (MRI) and
quantum computing. The tiny thermal nuclear spin polarization represents a
major obstacle towards this goal which may be overcome by Dynamic Nuclear Spin
Polarization (DNP) methods. The latter often rely on the transfer of the
thermally polarized electron spins to nearby nuclear spins, which is limited by
the Boltzmann distribution of the former. Here we demonstrate the polarization
and read out of a nuclear spin bath consisting of $^{13}$C nuclear spins in
diamond by using a single nitrogen-vacancy (NV) center. Our method utilizes
microwave dressed states to transfer the NV's high ($>$~92~\%) non-equilibrium
electron spin polarization induced by short laser pulses to the surrounding
carbon nuclear spins, where the NV is repeatedly repolarized optically, thus
providing an effectively infinite polarization reservoir. A saturation of the
polarization in the nuclear ""frozen core"" is achieved, which is confirmed by
the decay of the polarization transfer signal and shows an excellent agreement
with theoretical simulations. Hereby we introduce the Polarization Read Out by
Polarization Inversion (PROPI) method as a quantitative magnetization measure
of the nuclear spin bath. Moreover, we show that using the integrated solid
effect both for single and double quantum transitions a nuclear spin
polarization can be achieved even when the static magnetic field is not aligned
along the NV's crystal axis. This opens a path for the application of our DNP
technique to spins in and outside of nanodiamonds, enabling their application
as MRI tracers.",1706.01315v2
2017-08-06,Comparative analysis of magnetic resonance in the polaron pair recombination and the triplet exciton-polaron quenching models,"We present a comparative theoretical study of magnetic resonance within the
polaron pair recombination (PPR) and the triplet exciton-polaron quenching
(TPQ) models. Both models have been invoked to interpret the photoluminescence
detected magnetic resonance (PLDMR) in $\pi$-conjugated materials. We show that
resonance lineshapes calculated within the two models differ dramatically in
several regards. First, in the PPR model, the lineshape exhibits unusual
behavior upon increasing the microwave power: it evolves from fully positive at
weak power to fully negative at strong power. In contrast, in the TPQ model,
the PLDMR is completely positive, showing a monotonic saturation. Second, the
two models predict different dependencies of the resonance signal on the
photoexcitation power, $P_L$. At low $P_L$, the resonance amplitude $\Delta
I/I$ is $\propto P_L$ in the PPR model, while it is $\propto P_L^2$ crossing
over to $P_L^3$ in the TPQ model. On the physical level, the differences stem
from different underlying spin dynamics. Most prominently, a negative resonance
within the PPR model has its origin in the microwave-induced spin-Dicke effect,
leading to the resonant quenching of photoluminescence. The spin-Dicke effect
results from the spin-selective recombination, resulting in a highly correlated
precession of the on-resonance pair-partners under the strong microwave power.
This effect is not relevant to TPQ, where the majority of triplets are
off-resonance due to the strong zero-field splitting. The analytical evaluation
of lineshapes for the two models is enabled by expressing these shapes via the
eigenvalues of a complex Hamiltonian. This bypasses the necessity of solving
the much larger complex system of stochastic Liouville equations. Our findings
pave the way towards a reliable discrimination between the two mechanisms via
cw PLDMR.",1708.01917v1
2017-11-21,Quantum correlations in periodically driven spin chains: Revivals and steady-state properties,"We study the dynamics of microscopic quantum correlations, viz., bipartite
entanglement and quantum discord between nearest neighbor sites, in Ising spin
chain with a periodically varying external magnetic field along the transverse
direction. Quantum correlations exhibit periodic revivals with the driving
cycles in the finite-size chain. The time of first revival is proportional to
the system size and is inversely proportional to the maximum group velocity of
Floquet quasi-particles. On the other hand, the local quantum correlations in
the infinite chain may get saturated to non-zero values after a sufficiently
large number of driving cycles. Moreover, we investigate the convergence of
local density matrices, from which the quantum correlations under study
originate, towards the final steady-state density matrices as a function of
driving cycles. We find that the geometric distance, $d$, between the reduced
density matrices of non-equilibrium state and steady-state obeys a power-law
scaling of the form $d \sim n^{-B}$, where $n$ is the number of driving cycles
and $B$ is the scaling exponent. The steady-state quantum correlations are
studied as a function of time period of the driving field and are marked by the
presence of prominent peaks in frequency domain. The steady-state features can
be further understood by probing band structures of Floquet Hamiltonian and
purity of the bipartite state between nearest neighbor sites. Finally, we
compare the steady-state values of the local quantum correlations with that of
the canonical Gibbs ensemble and infer about their canonical ergodic
properties. Moreover, we identify generic features in the ergodic properties
depending upon the quantum phases of the initial state and the pathway of
repeated driving that may be within the same quantum phase or across two
different equilibrium phases.",1711.07769v3
2018-09-24,Ionic Tuning of Cobaltites at the Nanoscale,"Control of materials through custom design of ionic distributions represents
a powerful new approach to develop future technologies ranging from spintronic
logic and memory devices to energy storage. Perovskites have shown particular
promise for ionic devices due to their high ion mobility and sensitivity to
chemical stoichiometry. In this work, we demonstrate a solid-state approach to
control of ionic distributions in (La,Sr)CoO$_{3}$ thin films. Depositing a Gd
capping layer on the perovskite film, oxygen is controllably extracted from the
structure, up-to 0.5 O/u.c. throughout the entire 36 nm thickness. Commensurate
with the oxygen extraction, the Co valence state and saturation magnetization
show a smooth continuous variation. In contrast, magnetoresistance measurements
show no-change in the magnetic anisotropy and a rapid increase in the
resistivity over the same range of oxygen stoichiometry. These results suggest
significant phase separation, with metallic ferromagnetic regions and
oxygen-deficient, insulating, non-ferromagnetic regions, forming percolated
networks. Indeed, X-ray diffraction identifies oxygen-vacancy ordering,
including transformation to a brownmillerite crystal structure. The unexpected
transformation to the brownmillerite phase at ambient temperature is further
confirmed by high-resolution scanning transmission electron microscopy which
shows significant structural - and correspondingly chemical - phase separation.
This work demonstrates room-temperature ionic control of magnetism, electrical
resistivity, and crystalline structure in a 36 nm thick film, presenting new
opportunities for ionic devices that leverage multiple material
functionalities.",1809.08728v1
2018-12-13,On the 1/f spectrum in the solar wind and its connection with magnetic compressibility,"We discuss properties of Alfv\'enic fluctuations with large amplitude in
plasmas characterised by low magnetic field compression. We note that in such
systems power laws can not develop with arbitrarily steep slopes at large
scales, i.e. when $|\delta \bf{B}|$ becomes of the order of the background
field $|\bf{B}|$. In such systems there is a scale $l_0$ at which the spectrum
has to break due to the condition of weak compressibility. A very good example
of this dynamics is offered by solar wind fluctuations in Alfv\'enic fast
streams, characterised by the property of constant field magnitude. We show
here that the distribution of $\delta B=|\delta \bf{B}|$ in the fast wind
displays a strong cut-off at $\delta B/|{\bf B}|\lesssim2$, as expected for
fluctuations bounded on a sphere of radius $B=|{\bf B}|$. This is also
associated with a saturation of the rms of the fluctuations at large scales and
introduces a specific length $l_0$ above which the amplitude of the
fluctuations becomes independent on the scale $l$. Consistent with that, the
power spectrum at $l>l_0$ is characterised by a -1 spectral slope, as expected
for fluctuations that are scale-independent. Moreover, we show that the
spectral break between the 1/f and inertial range in solar wind spectra indeed
corresponds to the scale $l_0$ at which $\left<\delta B/B\right>\sim1$. Such a
simple model provides a possible alternative explanation of magnetic spectra
observed in interplanetary space, also pointing out the inconsistency for a
plasma to simultaneously maintain $|\bf{B}|\sim$const. at arbitrarily large
scales and satisfy a Kolmogorov scaling.",1812.05716v1
2019-06-23,A Quark-Nova in the wake of a core-collapse Supernova: a unifying model for long duration Gamma-Ray Bursts and Fast Radio Bursts,"[Abridged] By appealing to a Quark-Nova (QN; the explosive transition of a
neutron star to a quark star) in the wake of a core-collapse Supernova
explosion of a massive star, we develop a unified model for long duration
Gamma-ray Bursts (LGRBs) and Fast Radio Bursts (FRBs). The time delay (years to
decades) between the SN and the QN and, the fragmented nature (i.e. millions of
chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine.
In our model, a LGRB light-curve exhibits the interaction of the fragmented QN
ejecta with a turbulent (i.e. filamentary and magnetically saturated) SN ejecta
which is shaped by its interaction with an underlying pulsar wind nebula (PWN).
The afterglow is due to the interaction of the QN chunks, exiting the SN
ejecta, with the surrounding medium. Our model can fit BAT/XRT prompt and
afterglow light-curves, simultaneously with their spectra, thus yielding the
observed properties of LGRBs (e.g. the Band function and the X-ray flares). We
find that the Yonetoku law and the Amati law are not fundamental but
phenomenological. FRBs result from coherent synchrotron emission when the QN
chunks interact with non-turbulent weakly magnetized PWN-SN ejecta, where
conditions are prone to the Weibel instability. Magnetic field amplification
induced by the Weibel instability sets the bunching length for electrons and
pairs to radiate coherently. The resulting emission frequency, luminosity,
duration and dispersion measure in our model are consistent with FRB data. We
find a natural unification of high-energy burst phenomena from FRBs to LGRBs
including X-ray Flashes and X-ray rich GRBs as well as Super-Luminous SNe. We
find a possible connection between Ultra-High Energy Cosmic Rays and FRBs and
propose that a QN following a binary neutron star merger can yield a short GRB
(SGRB) with fits to BAT/XRT light-curves.",1906.09559v2
2019-12-17,Nonlinear dynamics of energetic-particle driven geodesic acoustic modes in ASDEX Upgrade,"Turbulence in tokamaks generates radially sheared zonal flows. Their
oscillatory counterparts, geodesic acoustic modes (GAMs), appear due to the
action of the magnetic field curvature. The GAMs can be driven unstable by an
anisotropic energetic particle (EP) population leading to the formation of
global radial structures, called EGAMs. The EGAMs can redistribute EP energy to
the bulk plasma through collisionless wave-particle interaction. In such a way,
the EGAMs might contribute to the plasma heating. Thus, investigation of EGAM
properties, especially in the velocity space, is necessary for precise
understanding of the transport phenomena in tokamak plasmas.
  In this work, the nonlinear dynamics of EGAMs without considering the mode
interaction with the turbulence is investigated with the help of a
Mode-Particle-Resonance (MPR) diagnostic implemented in the global gyrokinetic
particle-in-cell code ORB5. An ASDEX Upgrade discharge is chosen as a reference
case for this investigation due to its rich EP nonlinear dynamics. An
experimentally relevant magnetic field configuration, thermal species profiles
and an EP density profile are taken for EGAM chirping modelling and its
comparison with available empirical data. The same magnetic configuration is
used to explore energy transfer by the mode from the energetic particles to the
thermal plasma including kinetic electron effects. For a given EGAM level the
plasma heating by the mode can be significantly enhanced by varying the EP
parameters. Electron dynamics decreases the EGAM saturation amplitude and
consequently reduces the plasma heating, even though the mode transfers its
energy to thermal ions much more than to electrons.",1912.07950v2
2020-07-17,"Crystalline and magnetic structures, magnetization, heat capacity and anisotropic magnetostriction effect in a yttrium-chromium oxide","We have studied a nearly stoichiometric insulating
Y$_{0.97(2)}$Cr$_{0.98(2)}$O$_{3.00(2)}$ single crystal by performing
measurements of magnetization, heat capacity, and neutron diffraction. Albeit
that the YCrO$_3$ compound behaviors like a soft ferromagnet with a coersive
force of $\sim$ 0.05 T, there exist strong antiferromagnetic (AFM) interactions
between Cr$^{3+}$ spins due to a strongly negative paramagnetic Curie-Weiss
temperature, i.e., -433.2(6) K. The coexistence of ferromagnetism and
antiferromagnetism may indicate a canted AFM structure. The AFM phase
transition occurs at $T_\textrm{N} =$ 141.5(1) K, which increases to
$T_\textrm{N}$(5T) = 144.5(1) K at 5 T. Within the accuracy of the present
neuron-diffraction studies, we determine a G-type AFM structure with a
propagation vector \textbf{k} = (1 1 0) and Cr$^{3+}$ spin directions along the
crystallographic \emph{c} axis of the orthorhombic structure with space group
\emph{Pnma} below $T_\textrm{N}$. At 12 K, the refined moment size is 2.45(6)
$\mu_\textrm{B}$, $\sim$ 82\% of the theoretical saturation value 3
$\mu_\textrm{B}$. The Cr$^{3+}$ spin interactions are probably two-dimensional
Ising like within the reciprocal (1 1 0) scattering plane. Below
$T_\textrm{N}$, the lattice configuration (\emph{a}, \emph{b}, \emph{c}, and
\emph{V}) deviates largely downward from the Gr$\ddot{\textrm{u}}$neisen law,
displaying an anisotropic magnetostriction effect and a magnetoelastic effect.
Especially, the sample contraction upon cooling is enhanced below the AFM
transition temperature. There is evidence to suggest that the actual
crystalline symmetry of YCrO$_3$ compound is probably lower than the currently
assumed one. Additionally, we compared the $t_{2\textrm{g}}$ YCrO$_3$ and the
$e_\textrm{g}$ La$_{7/8}$Sr$_{1/8}$MnO$_3$ single crystals for a further
understanding of the reason for the possible symmetry lowering.",2007.08985v2
2020-10-05,Small-Scale Dynamo in Supernova-Driven Interstellar Turbulence,"Magnetic fields grow quickly even at early cosmological times, suggesting the
action of a small-scale dynamo (SSD) in the interstellar medium of galaxies.
Many studies have focused on idealized turbulent driving of the SSD. Here we
simulate more realistic supernova-driven turbulence to determine whether it can
drive an SSD. Magnetic field growth occurring in our models appears
inconsistent with simple tangling of magnetic fields, but consistent with SSD
action, reproducing and confirming models by Balsara et al. (2004) that did not
include physical resistivity $\eta$. We vary $\eta$, as well as the numerical
resolution and supernova rate, $\dot\sigma$, to delineate the regime in which
an SSD occurs. For a given $\dot\sigma$ we find convergence for SSD growth rate
with resolution of a parsec. For $\dot\sigma\simeq\dot\sigma_{\rm sn}$, with
$\dot\sigma_{\rm sn}$ the solar neighbourhood rate, the critical resistivity
below which an SSD occurs is $0.005>\eta_{\rm crit}>0.001\,\rm kpc^{-1}\,\rm km
s^{-1}$, and this increases with the supernova rate. Across the modelled range
of 0.5--4 pc resolution we find that for $\eta<\eta_{\rm crit}$, the SSD
saturates at about 5% of kinetic energy equipartition, independent of growth
rate. In the range $0.2\dot\sigma_{\rm sn}\leq \dot\sigma\leq8\dot\sigma_{\rm
sn}$ growth rate increases with $\dot\sigma$. SSDs in the supernova-driven
interstellar medium commonly exhibit erratic growth.",2010.01833v6
2020-12-23,Transition to turbulence in quasi-two-dimensional MHD flow driven by lateral walls,"This manuscript has been accepted for publication in Physical Review Fluids,
see
https://journals.aps.org/prfluids/accepted/d5074S28J6b11905012b7cb06505e8f2149dd5f20.
  This work investigates the mechanisms that underlie transitions to turbulence
in a three-dimensional domain in which the variation of flow quantities in the
out-of-plane direction is much weaker than any in-plane variation. This is
achieved using a model for the quasi-two-dimensional magnetohydrodynamic flow
in a duct with moving lateral walls and an orthogonal magnetic field. In this
environment, conventional subcritical routes to turbulence, which are highly
three-dimensional, are prohibited. To elucidate the remaining mechanisms
involved in quasi-two-dimensional turbulent transitions, the magnetic field
strength and degree of antisymmetry in the base flow are varied, the latter via
the relative motion of the lateral duct walls. Introduction of any amount of
antisymmetry to the base flow drives the critical Reynolds number infinite, as
the TS instabilities take on opposite signs of rotation, and destructively
interfere. However, an increasing magnetic field strength limits interaction
between the instabilities, permitting finite critical Reynolds numbers. The
transient growth only mildly depends on the base flow, with negligible
differences for friction parameters $H \gtrsim 30$. Direct numerical
simulations, initiated with random noise, indicate that for $H \leq 1$,
supercritical exponential growth leads to saturation, but not turbulence. For
higher $3 \leq H \leq 10$, a turbulent transition occurs, and is maintained at
$H=10$. For $H \geq 30$, the turbulent transition still occurs, but is short
lived, as the turbulent state quickly collapses. In addition, for $H \geq 3$,
an inertial subrange is identified, with the perturbation energy exhibiting a
$-5/3$ power law dependence on wave number.",2012.12497v1
2021-02-22,Stochastic fluctuation and transport of tokamak edge plasmas with the resonant magnetic perturbation field,"We present that a statistical method known as the Complexity-Entropy analysis
is useful to characterize a state of plasma turbulence and flux in the resonant
magnetic perturbation (RMP) edge localized mode (ELM) control experiment. The
RMP ELM suppression phase with the stochastic pedestal top temperature
fluctuation can be distinguished from the natural ELM free phase with the
chaotic fluctuation. It is discussed that the stochastic temperature
fluctuation localized near the pedestal top can be originated from the narrow
layer of the field penetration near the pedestal top. The forced magnetic
island can emit the resonant drift wave of comparable sizes (relatively low-k)
in the RMP ELM suppression phase, and it can results in the generation of
stochastic higher wavenumber fluctuations coupled to tangled fields around the
island. The analysis of the ion saturation current measurement around the main
outer striking point on the divertor shows that it also becomes more stochastic
as the stronger plasma response to the RMP field is expected.",2102.10733v7
2021-02-24,"Gamma irradiated nanostructured NiFe2O4: Effect of gamma-photon on morphological, structural, optical and magnetic properties","The current manuscript highlights the preparation of NiFe2O4 nanoparticles by
adopting sol-gel auto combustion route. The prime focus of this study is to
investigate the impact of gamma irradiation on the microstructural,
morphological, functional, optical and magnetic characteristics. The resulted
NiFe2O4 products have been characterized employing numerous instrumental
equipments such as FESEM, XRD, UV visible spectroscopy, FTIR and PPMS for a
variety of gamma ray doses (0 kGy, 25 kGy and 100 kGy). FESEM micrographs
illustrate the aggregation of ferrite nanoparticles in pristine NiFe2O4 product
having an average particle size of 168 nm and the surface morphology is altered
after exposure to gamma-irradiation. XRD spectra have been analyzed employing
Rietveld method and the results of the XRD investigation reveal the desired
phases (cubic spinel phases) of NiFe2O4 with observing other transitional
phases. Several microstructural parameters such as bond length, bond angle,
hopping length etc. have been determined from the analysis of Rietveld method.
This study reports that the gamma irradiations demonstrate a great influence on
optical bandgap energy and it varies from 1.80 and 1.89 eV evaluated via K M
function. FTIR measurement depicts a proof for the persistence of Ni-O and Fe-O
stretching vibrations within the respective products and thus indicating the
successful development of NiFe2O4. The saturation magnetization (MS) of
pristine Ni ferrite product is noticed to be 28.08 emug-1. A considerable
increase in MS is observed in case of low gamma-dose (25 kGy) and a decrement
nature is disclosed after the result of high dose of gamma irradiation
(100kGy).",2102.12385v1
2021-10-12,Small moment antiferromagnetic ordering in single crystalline La2Ni7,"Single crystals of La2Ni7 have been grown out of a binary, La-Ni melt.
Temperature dependent, zero magnetic field, specific heat, electrical
resistivity, and low field magnetization measurements indicate that there is a
series of antiferromagnetic phase transitions at T1 = 61.0 \pm 0.2 K, T2 = 56.5
\pm 0.2 K and T3 = 42.2 \pm 0.2 K. The three specific heat anomalies found at
these temperatures qualitatively have very small entropy changes associated
with them and the anisotropic M(H) data saturate at ~ 0.12 {\mu}B/Ni; both
observations strongly suggesting the AFM order is associated with very small,
itinerant, moments. Anisotropic, H||c and H{\perp}c, {\rho}(H) and M(H)
isotherms as well as constant field, {\rho}(T) and M(T) sweeps manifest
signatures of multiple phase lines and result in H-T phase diagrams that are
clearly anisotropic. Analysis of M(T) and M(H) data allow for the
identification of the two lower temperature magnetically ordered states as
antiferromagnetically ordered, with the moments aligned along the
crystallographic c-axis, and the higher temperature, T2 < T < T1, state as
having a finite ferromagnetic component. In addition, the metamagnetic
transition at low temperatures, for H applied along the crystallographic c-axis
(H||c) appears to be a near classic example of a spin-flop transition,
resulting in a field stabilized antiferromagnetic state with the moments
ordered perpendicular to the c-axis. Although the small moment ordering, and
existence of multiple phase transitions in field and temperature, suggesting an
energetic proximity of these states, could foretell a degree of pressure
sensitivity, our measurements of R(T) for applied pressures up to 2.0 GPa
indicate that there is very little pressure dependence of T1, T2 and T3.",2110.06349v1
2021-12-15,Wide ferromagnetic domain walls can host both adiabatic reflectionless spin transport and finite nonadiabatic spin torque: A time-dependent quantum transport picture,"The key concept in spintronics of current-driven noncollinear magnetic
textures, such as magnetic domain walls (DWs), is adiabaticity, i.e., how
closely electronic spins track classical localized magnetic moments (LMMs) of
the texture. When mistracking occurs nonadiabatic effects arise, the salient of
which is nonadiabatic spin transfer torque (STT) where spin angular momentum is
exchanged between electrons and LMMs to cause their dynamics and enable DW
motion without any current threshold. The microscopic mechanisms behind
nonadiabatic STT have been debated theoretically for nearly two decades, but
with unanimous conclusion that they should be significant only in narrow DWs.
However, this contradicts sharply experiments [O. Boulle {\em et al.}, Phys.
Rev. Lett. {\bf 101}, 216601 (2008); C. Burrowes {\em et al.}, Nat. Phys. {\bf
6}, 17 (2010)] observing nonadiabatic STT in DWs much wider than putatively
relevant $\sim 1$ nm scale, as well as largely insensitive to further
increasing the DW width $w$. Here we employ time-dependent quantum transport
for electrons to obtain both nonadiabatic and adiabatic STT from the exact
nonequilibrium density matrix and its lowest order as adiabatic density matrix
defined by assuming that LMMs are infinitely slow. This allows us to
demonstrate that our microscopically, and without any simplifications of prior
derivations like effectively static DW, extracted nonadiabatic STT: (i) does
not decay, but instead saturates at a finite value, with increasing $w$ of a
moving DW ensuring entry into the adiabatic limit, which we characterize by
showing that electronic spins do not reflect from the static DW in this limit;
and (ii) it has both out-of-DW-plane, as is the case of phenomenological
expression widely used in the LLG equation, and in-plane components, where the
former remains finite with increasing $w$.",2112.08356v2
2022-04-10,Activity and Rotation of Nearby Field M Dwarfs in the TESS Southern Continuous Viewing Zone,"The evolution of magnetism in late-type dwarfs remains murky, as we can only
weakly predict levels of activity for M dwarfs of a given mass and age. We
report results from our spectroscopic survey of M dwarfs in the Southern
Continuous Viewing Zone (CVZ) of the Transiting Exoplanet Survey Satellite
(TESS). As the TESS CVZs overlap with those of the James Webb Space Telescope,
our targets constitute a legacy sample for studies of nearby M dwarfs. For 122
stars, we obtained at least one $R\approx 2000$ optical spectrum with which we
measure chromospheric $\mathrm{H}\alpha$ emission, a proxy for magnetic field
strength. The fraction of active stars is consistent with what is expected for
field M dwarfs; as in previous studies, we find that late-type M dwarfs remain
active for longer than their early type counterparts. While the TESS light
curves for $\approx$20% of our targets show modulations consistent with
rotation, TESS systematics are not well enough understood for confident
measurements of rotation periods ($P_{\mathrm{rot}}$) longer than half the
length of an observing sector. We report periods for 12 stars for which we
measure $P_{\mathrm{rot}} {\lower0.8ex\hbox{$\buildrel <\over\sim$}}$ 15 d or
find confirmation for the TESS-derived $P_{\mathrm{rot}}$ in the literature.
Our sample of 21 $P_{\mathrm{rot}}$, which includes periods from the
literature, is consistent with our targets being spun-down field stars.
Finally, we examine the $\mathrm{H}\alpha$-to-bolometric luminosity
distribution for our sample. Two stars are rotating fast enough to be
magnetically saturated, but are not, hinting at the possibility that fast
rotators may appear inactive in $\mathrm{H}\alpha$.",2204.04700v1
2022-05-13,The Factory and the Beehive. IV. A Comprehensive Study of the Rotation X-ray Activity Relation in Praesepe and the Hyades,"X-ray observations of low-mass stars in open clusters are critical to
understanding the dependence of magnetic activity on stellar properties and
their evolution. Praesepe and the Hyades, two of the nearest, most-studied open
clusters, are among the best available laboratories for examining the
dependence of magnetic activity on rotation for stars with masses lower than
$\approx 1\ M_{\odot}$. We present an updated study of the rotation X-ray
activity relation in the two clusters. We updated membership catalogs that
combine pre-Gaia catalogs with new catalogs based on Gaia Data Release 2. The
resulting catalogs are the most inclusive ones for both clusters: 1739 Praesepe
and 1315 Hyades stars. We collected X-ray detections for cluster members, for
which we analyzed, re-analyzed, or collated data from ROSAT, the Chandra X-ray
Observatory, the Neil Gehrels Swift Observatory, and XMM-Newton. We have
detections for 326 Praesepe and 462 Hyades members, of which 273 and 164,
respectively, have rotation periods, an increase of 6$\times$ relative to what
was previously available. We find that at $\approx$700 Myr, only M dwarfs
remain saturated in X-rays, with only tentative evidence for supersaturation.
We also find a tight relation between the Rossby number and fractional X-ray
luminosity $L_\mathrm{X}/L_\mathrm{bol}$ in unsaturated single members,
suggesting a power-law index between $-3.2$ and $-3.9$. Lastly, we find no
difference in the coronal parameters between binary and single members. These
results provide essential insight into the relative efficiency of magnetic
heating of the stars' atmospheres, thereby informing the development of robust
age-rotation-activity relations.",2205.06461v1
2023-01-11,Coupling multi-fluid dynamics equipped with Landau closures to the particle-in-cell method,"The particle-in-cell (PIC) method is successfully used to study magnetized
plasmas. However, this requires large computational costs and limits
simulations to short physical run-times and often to setups in less than three
spatial dimensions. Traditionally, this is circumvented either via hybrid-PIC
methods (adopting massless electrons) or via magneto-hydrodynamic-PIC methods
(modelling the background plasma as a single charge-neutral
magneto-hydrodynamical fluid). Because both methods preclude modelling
important plasma-kinetic effects, we introduce a new fluid-PIC code that
couples a fully explicit and charge-conservative multi-fluid solver to the PIC
code SHARP through a current-coupling scheme and solve the full set of
Maxwell's equations. This avoids simplifications typically adopted for Ohm's
Law and enables us to fully resolve the electron temporal and spatial scales
while retaining the versatility of initializing any number of ion, electron, or
neutral species with arbitrary velocity distributions. The fluid solver
includes closures emulating Landau damping so that we can account for this
important kinetic process in our fluid species. Our fluid-PIC code is
second-order accurate in space and time. The code is successfully validated
against several test problems, including the stability and accuracy of shocks
and the dispersion relation and damping rates of waves in unmagnetized and
magnetized plasmas. It also matches growth rates and saturation levels of the
gyro-scale and intermediate-scale instabilities driven by drifting charged
particles in magnetized thermal background plasmas in comparison to linear
theory and PIC simulations. This new fluid-SHARP code is specially designed for
studying high-energy cosmic rays interacting with thermal plasmas over
macroscopic timescales.",2301.04679v2
2023-03-04,Nonlinear microtearing modes in MAST and their stochastic layer formation,"First nonlinear gyrokinetic simulations of microtearing modes in the core of
a MAST case are performed on two surfaces of the high-collisionality discharge
used in Valovi\v{c} et al. Nucl. Fusion 51.7 (2011) to obtain the favorable
energy confinement scaling with collisionality, $\tau_E\propto\,\nu_*^{-1}$. On
the considered surfaces microtearing modes dominate linearly at binormal length
scales of the order of the ion Larmor radius. While the effect of electron
collision frequency is moderate in linear simulations, a strong dependence on
this parameter is found in nonlinear simulations at $r/a=0.5$, where $r$ and
$a$ are the surface and tokamak minor radius, respectively. The dynamics of
magnetic islands generated by microtearing modes is analysed, showing that the
radial extent of the stochastic region caused by islands overlapping plays an
important role in determining the saturation level of the microtearing mode
driven heat flux. Local nonlinear gyrokinetic simulations show that the
microtearing mode driven heat flux, $Q_e^\mathrm{MTM}$, is largely dominated by
magnetic flutter and depends strongly on the magnetic shear, $\hat{s}$.
Comparing two surfaces, $r/a=0.5$ and $r/a=0.6$, reveals that
$Q_e^\mathrm{MTM}$ is negligible at $r/a=0.5$ ($\hat{s}=0.34$), with the
electron temperature gradient driven heat flux, $Q_e^\mathrm{ETG}$, comparable
to the experimental electron heat flux, $Q_e^\mathrm{exp}$, while
$Q_e^\mathrm{MTM}$ is significantly larger and comparable to $Q_e^\mathrm{ETG}$
and $Q_e^\mathrm{exp}$ at $r/a=0.6$ ($\hat{s}=1.1$). Microtearing modes cause
more experimentally significant transport in higher $\hat{s}$ regions and may
influence (together with electron temperature gradient modes) the observed
scaling of energy confinement time with collisionality (Valovi\v{c} et al.
Nucl. Fusion 51.7 (2011)).",2303.02379v3
2023-03-15,High spin-polarization in a disordered novel quaternary Heusler alloy FeMnVGa,"In this work, we report the successful synthesis of a Fe-based novel
half-metallic quaternary Heusler alloy FeMnVGa and its structural, magnetic and
transport properties probed through different experimental methods and
theoretical technique. Density functional theory (DFT) calculations performed
on different types of structure reveal that Type-2 ordered structure (space
group: F-43m, Ga at 4a, V at 4b, Mn at 4c and Fe at 4d) possess minimum energy
among all the ordered variants. Ab-initio simulations in Type 2 ordered
structure further reveal that the compound is half-metallic ferromagnet (HMF)
having a large spin-polarization (89.9 %). Neutron diffraction reveal that the
compound crystalizes in disordered Type-2 structure (space group: Fm-3m) in
which Ga occupy at 4a, V at 4b and Fe/Mn occupy 4c/4d sites with 50:50
proportions. The structural disorder is further confirmed by X-ray diffraction
(XRD), extended X-ray absorption fine structure (EXAFS),57Fe Mossbauer
spectrometry results and DFT calculations. Magnetisation studies suggest that
the compound orders ferromagnetically below TC ~ 293 K and the saturation
magnetization follows Slater-Pauling rule. Mossbauer spectrometry, along with
neutron diffraction suggest that Mn is the major contributor to the total
magnetism in the compound consistent with the theoretical calculations. First
principle calculations indicate that spin-polarization remain high (81.3 %)
even in the presence of such large atomic disorder. The robustness of the HMF
property in presence of disorder is a quite unique characteristic over other
reported HMF in literature and make this compound quiet promising for
spintronics applications.",2303.08579v1
2023-06-28,Degenerate and non-degenerate parametric excitation in YIG nanostructures,"We study experimentally the processes of parametric excitation in microscopic
magnetically saturated disks of nanometer-thick Yttrium Iron Garnet. We show
that, depending on the relative orientation between the parametric pumping
field and the static magnetization, excitation of either degenerate or
non-degenerate magnon pairs is possible. In the latter case, which is
particularly important for applications associated with the realization of
computation in the reciprocal space, a single-frequency pumping can generate
pairs of magnons whose frequencies correspond to different eigenmodes of the
disk. We show that, depending on the size of the disk and the modes involved,
the frequency difference in a pair can vary in the range 0.1-0.8 GHz. We
demonstrate that in this system, one can easily realize a practically important
situation where several magnon pairs share the same mode. We also observe the
simultaneous generation of up to six different modes using a fixed-frequency
monochromatic pumping. Our experimental findings are supported by numerical
calculations that allow us to unambiguously identify the excited modes. Our
results open new possibilities for the implementation of reciprocal-space
computing making use of low damping magnetic insulators.",2306.16094v1
2023-08-18,"Magnon Diffusion Length and Longitudinal Spin Seebeck Effect in Vanadium Tetracyanoethylene (V[TCNE]$_x$, $x \sim 2$)","Spintronic, spin caloritronic, and magnonic phenomena arise from complex
interactions between charge, spin, and structural degrees of freedom that are
challenging to model and even more difficult to predict. This situation is
compounded by the relative scarcity of magnetically-ordered materials with
relevant functionality, leaving the field strongly constrained to work with a
handful of well-studied systems that do not encompass the full phase space of
phenomenology predicted by fundamental theory. Here we present an important
advance in this coupled theory-experiment challenge, wherein we extend existing
theories of the spin Seebeck effect (SSE) to explicitly include the
temperature-dependence of magnon non-conserving processes. This expanded theory
quantitatively describes the low-temperature behavior of SSE signals previously
measured in the mainstay material yttrium iron garnet (YIG) and predicts a new
regime for magnonic and spintronic materials that have low saturation
magnetization, $M_S$, and ultra-low damping. Finally, we validate this
prediction by directly observing the spin Seebeck resistance (SSR) in the
molecule-based ferrimagnetic semiconductor vanadium tetracyanoethylene
(V[TCNE]$_x$, $x \sim 2$). These results validate the expanded theory, yielding
SSR signals comparable in magnitude to YIG and extracted magnon diffusion
length ($\lambda_m>1$ $\mu$ m) and magnon lifetime for V[TCNE]$_x$
($\tau_{th}\approx 1-10$ $\mu$ s) exceeding YIG ($\tau_{th}\sim 10$ ns).
Surprisingly, these properties persist to room temperature despite relatively
low spin wave stiffness (exchange). This identification of a new regime for
highly efficient SSE-active materials opens the door to a new class of magnetic
materials for spintronic and magnonic applications.",2308.09752v1
2023-12-26,Observation of a 1/3 Magnetisation Plateau Phase as Evidence for the Kitaev Interaction in a Honeycomb-Lattice Antiferromagnet,"Fractional magnetisation plateaus, in which the magnetisation is pinned at a
fraction of its saturated value within a range of external magnetic field, are
spectacular macroscopic manifestations of the collective quantum behaviours.
One prominent example of the plateau phase is found in spin-1/2
triangular-lattice antiferromagnets featuring strong geometrical frustration,
and is often interpreted as quantum-fluctuation-stabilised state in magnetic
field via the ""order-by-disorder"" mechanism. Here, we observe an unprecedented
1/3 magnetisation plateau between 5.2 and 7.4 T at 2 K in a spin-1
antiferromagnet Na$_3$Ni$_2$BiO$_6$ with a honeycomb lattice, where
conventionally no geometrical frustration is anticipated. By carrying out
elastic neutron scattering measurements, we propose the spin structure of the
plateau phase to be an unusual partial spin-flop ferrimagnetic order,
transitioning from the zigzag antiferromagnetic order in zero field. Our
theoretical calculations show that the plateau phase is stabilised by the
bond-anisotropic Kitaev interaction. These results provide a new paradigm for
the exploration of rich quantum phases in frustrated magnets and exotic Kitaev
physics in high-spin systems.",2312.15932v1
2006-12-18,Amplitude Saturation in Beta Cephei Models - Preliminary Results,"Using nonlinear hydrocodes we have calculated single mode saturation
amplitudes for beta Cephei models. Predicted saturation amplitudes are
systematically higher than amplitudes observed in beta Cephei variables, even
in monoperiodic ones. We argue that collective saturation of the pulsation
instability by a dozen or so acoustic modes brings the theoretical amplitudes
to the observed level.",0612489v1
1997-06-10,Analysis of the Interplay of Quantum Phases and Nonlinearity Applied to Dimers with Anharmonic Interactions,"We extend our analysis of the effects of the interplay of quantum phases and
nonlinearity to address saturation effects in small quantum systems.
  We find that initial phases dramatically control the dependence of
self-trapping on initial asymmetry of quasiparticle population and can compete
or act with nonlinearity as well as saturation effects. We find that there is a
minimum finite saturation value in order to obtain self-trapping that crucially
depends on the initial quasiparticle phases and present a detailed
phase-diagram in terms of the control parameters of the system: nonlinearity
and saturation.",9706093v1
2002-10-24,Violation of Ioffe-Regel condition but saturation of resistivity of the high Tc cuprates,"We demonstrate that the resistivity data of a number of high Tc cuprates, in
particular La(2-x)SrxCuO4, are consistent with resistivity saturation, although
the Ioffe-Regel condition is strongly violated. By using the f-sum rule
together with calculations of the kinetic energy in the t-J model, we show that
the saturation resistivity is unusually large. This is related to the strong
reduction of the kinetic energy due to strong correlation effects. The
fulfilment of the Ioffe-Regel condition for conventional transition metal
compounds is found to be somewhat accidental.",0210543v1
2003-08-01,A density functional theory study of electric potential saturation: planar geometry,"We investigate the possibility of electrostatic potential saturation, which
may lead to the phenomenon of effective charge saturation. The system under
study is a uniformly charged infinite plane immersed in an arbitrary
electrolyte made up of several micro-species. To describe the electric double
layer, we use a generic density functional theory in which the local
micro-ionic density profiles are arbitrary functions of the local electrostatic
potential. A necessary and sufficient condition is obtained for saturation,
whereby the electrostatic potential created by the plane becomes independent of
its bare charge, provided the latter is large enough.",0308015v1
2005-10-07,Electric Field-Dependent Charge-Carrier Velocity in Semiconducting Carbon Nanotubes,"Charge transport in semiconducting single-walled nanotubes (SWNTs) with
Schottky-barrier contacts has been studied at high bias. We observe nearly
symmetric ambipolar transport with electron and hole currents significantly
exceeding 25 micron-ampere, the reported current limit in metallic SWNTs due to
optical phonon emission. Four simple models for the field-dependent velocity
(ballistic, current saturation, velocity saturation, and constant mobility) are
studied in the unipolar regime; the high-bias behavior is best explained by a
velocity saturation model with a saturation velocity of 2 x 10^7 cm/s.",0510158v1
1999-11-09,"Small-x Physics, High Parton Densities and Parton Saturation in QCD","Partons are defined as the quanta in a Fock space description of a hadron.
Gluon saturation is described in the Weizs\""{a}cker-Williams approximation for
a large nucleus. The elements of DGLAP and BFKL evolution are given with the
BFKL equation derived in a large-$N_c$ dipole formalism. A more general
discussion of saturation is given in terms of a dipole scattering on a nucleon
or nucleus. Possible evidence for saturation at HERA is discussed.",9911289v1
2001-12-10,Nonlinear QCD Evolution: Saturation without Unitarization,"We consider the perturbative description of saturation based on the nonlinear
QCD evolution equation of Balitsky and Kovchegov (BK). Although the nonlinear
corrections lead to saturation of the scattering amplitude locally in impact
parameter space, we show that they do not unitarize the total cross section.
The total cross section for the scattering of a strongly interacting probe on a
hadronic target is found to grow exponentially with rapidity. The origin of
this violation of unitarity is the presence of long range Coulomb fields away
from the saturation region. The growth of these fields with rapidity is not
tempered by the nonlinearity of the BK equation.",0112140v1
2002-09-11,The Energy Dependence of the Saturation Momentum from RG Improved BFKL Evolution,"We study the energy dependence of the saturation momentum in the context of
the collinearly improved Leading and Next to Leading BFKL evolution, and in the
presence of saturation boundaries. We find that the logarithmic derivative of
the saturation momentum is varying very slowly with Bjorken-x, and its value is
in agreement with the Golec-Biernat and Wusthoff model in the relevant x
region. The scaling form of the amplitude for dipole-dipole or dipole-hadron
scattering in the perturbative side of the boundary is given.",0209121v1
2003-11-07,Energy dependence of Cronin momentum in saturation model for $p+A$ and $A+A$ collisions,"We calculate $\sqrt{s}$ dependence of Cronin momentum for $p+A$ and $A+A$
collisions in saturation model. We show that this dependence is consistent with
expectation from formula which was obtained using simple dimentional
consideration. This can be used to test validity of saturation model (and
distinguish among its variants) and measure $x$ dependence of saturation
momentum from experimental data.",0311099v1
2003-11-14,Introduction to Low x Physics and Saturation,"The idea of saturation of parton densities in small x physics is briefly
introduced. Some aspects of saturation are described, mainly focusing on the
status of our knowledge on the non-linear equations describing the high parton
density regime. Implications of saturation ideas on the description of nuclear
collisions at the Relativistic Heavy Ion Collider are discussed.",0311182v1
2004-07-01,Saturation and forward jets at HERA,"We analyse forward-jet production at HERA in the framework of the
Golec-Biernat and Wusthoff saturation models. We obtain a good description of
the forward jet cross sections measured by the H1 and ZEUS collaborations in
the two-hard-scale region kT ~ Q >> Lambda_QCD with two different
parametrisations with either significant or weak saturation effects. The weak
saturation parametrization gives a scale compatible with the one found for the
proton structure function F_2. We argue that Mueller-Navelet jets at the
Tevatron and the LHC could help distinguishing between both options.",0407011v2
2004-07-13,Instanton-driven Gluon Saturation,"We report on the interesting possibility of instanton-driven gluon saturation
in lepton-nucleon scattering at small Bjorken-x. The explicitly known instanton
gauge field serves as a concrete realization of an underlying non-perturbative
saturation mechanism associated with strong classical fields. The conspicuous,
intrinsic instanton size scale known from lattice simulations, turns out to
determine the saturation scale. The ``colour glass condensate'' can be
identified in our approach with the QCD-sphaleron state, dominating
instanton-induced processes in the softer regime.",0407146v1
2006-10-18,Saturation effects in diffractive scattering at LHC energies,"Unitarization schemes can be reduced to non-linear equations which saturate
at small $b$ the evolution of the elastic amplitude with $s$, and which mimic
parton saturation in the non-perturbative regime. These equations enable us to
study the effect of saturation on total and elastic cross sections for various
models, and to evaluate the uncertainties on $\sigma_{tot}$ and $\rho(s,t)$ at
the LHC in the presence of a hard pomeron.",0610222v2
2003-03-28,Lattice packings with gap defects are not completely saturated,"We show that a honeycomb circle packing in $\R^2$ with a linear gap defect
cannot be completely saturated, no matter how narrow the gap is. The result is
motivated by an open problem of G. Fejes T\'oth, G. Kuperberg, and W.
Kuperberg, which asks whether of a honeycomb circle packing with a linear shift
defect is completely saturated. We also show that an fcc sphere packing in
$\R^3$ with a planar gap defect is also not completely saturated.",0303366v1
2005-01-28,Discrete soliton collisions in a waveguide array with saturable nonlinearity,"We study the symmetric collisions of two mobile breathers/solitons in a model
for coupled wave guides with a saturable nonlinearity. The saturability allows
the existence of breathers with high power. Three main regimes are observed:
breather fusion, breather reflection and breather creation. The last regime
seems to be exclusive of systems with a saturable nonlinearity, and has been
previously observed in continuous models. In some cases a ``symmetry breaking''
can be observed, which we show to be an numerical artifact.",0501050v2
2002-11-22,Saturation in heteronuclear photoassociation of 6Li7Li,"We report heteronuclear photoassociation spectroscopy in a mixture of
magneto-optically trapped 6Li and 7Li. Hyperfine resolved spectra of the
vibrational level v=83 of the singlet state have been taken up to intensities
of 1000 W/cm^2. Saturation of the photoassociation rate has been observed for
two hyperfine transitions, which can be shown to be due to saturation of the
rate coefficient near the unitarity limit. Saturation intensities on the order
of 40 W/cm^2 can be determined.",0211098v1
2007-06-18,A unified description of diffractive deep inelastic scattering with saturation,"We propose a new description of inclusive diffraction in deep inelastic
scattering (DIS). The diffractive structure functions are expressed in the
dipole picture and contain heavy-quark contributions. The dipole scattering
amplitude, a saturation model fitted on inclusive DIS data, features a
saturation scale Q_s(x) larger than 1 GeV for x=10^{-5}. The q\bar{q}g
contribution to the diffractive final state is modeled in such a way that both
the large-Q^2 and small-beta limits are implemented. In the regime xpom<0.01 in
which saturation is expected to be relevant, we obtain a parameter-free
description of the HERA data with chi^2/points=1.2.",0706.2682v1
2008-05-14,On unconditionally saturated Banach spaces,"We prove a structural property of the class of unconditionally saturated
separable Banach spaces. We show, in particular, that for every analytic set
$\aaa$, in the Effros-Borel space of subspaces of $C[0,1]$, of unconditionally
saturated separable Banach spaces, there exists an unconditionally saturated
Banach space $Y$, with a Schauder basis, that contains isomorphic copies of
every space $X$ in the class $\aaa$.",0805.2046v1
2009-04-17,Nuclear Saturation with Low Momentum Interactions,"Relativistic effects are investigated in nuclear matter calculations
employing renormalized low-momentum nucleon-nucleon ($NN$) interactions. It is
demonstrated that the relativistic effects cure a problem of non-relativistic
low-momentum interactions, which fail to reproduce saturation of nuclear
matter. Including relativistic effects, one already obtains saturation in a
Hartree-Fock calculation. Brueckner-Hartree-Fock calculations lead to a further
improvement of the saturation properties. The results are rather insensitive to
the realistic $NN$ interaction on which they are based.",0904.2663v1
2010-07-15,The effect of gain saturation in a gain compensated perfect lens,"The transmission of evanescent waves in a gain-compensated perfect lens is
discussed. In particular, the impact of gain saturation is included in the
analysis, and a method for calculating the fields of such nonlinear systems is
developed. Gain compensation clearly improves the resolution; however, a number
of nonideal effects arise as a result of gain saturation. The resolution
associated with the lens is strongly dependent on the saturation constant of
the active medium.",1007.2486v1
2010-10-12,Saturation of interband absorption in graphene,"The transient response of an intrinsic graphene, which is caused by the
ultrafast interband transitions, is studied theoretically for the range of
pumping correspondent to the saturated absorption regime. Spectral and temporal
dependencies of the photoexcited concentration as well as the transmission and
relitive absotption coefficients are considered for mid-IR and visible (or
near-IR) spectral regions at different durations of pulse and broadening
energies. The characteristic intencities of saturation are calculated and the
results are compared with the experimental data measured for the near-IR lasers
with a saturable absorber. The negative absorption of a probe radiation during
cascade emission of optical phonons is obtained.",1010.2392v1
2010-12-31,The Status of Parton Saturation and the CGC,"This is a personal summary of the meeting ""Saturation, the Color Glass
Condensate and Glasma: What Have we Learned from RHIC?"" that took place at BNL
in May 2010. The purpose of the meeting was to discuss the status of high
density QCD and parton saturation, and to review the progress that RHIC has
allowed in the field.",1101.0260v1
2011-05-23,Saturating Sperner families,"A family $\cF \subseteq 2^{[n]}$ saturates the monotone decreasing property
$\cP$ if $\cF$ satisfies $\cP$ and one cannot add any set to $\cF$ such that
property $\cP$ is still satisfied by the resulting family. We address the
problem of finding the minimum size of a family saturating the $k$-Sperner
property and the minimum size of a family that saturates the Sperner property
and that consists only of $l$-sets and $(l+1)$-sets.",1105.4453v1
2011-12-09,Saturated Domino Coverings,"A domino covering of a board is saturated if no domino is redundant. We
introduce the concept of a fragment tiling and show that a minimal fragment
tiling always corresponds to a maximal saturated domino covering. The size of a
minimal fragment tiling is the domination number of the board. We define a
class of regular boards and show that for these boards the domination number
gives the size of a minimal X-pentomino covering. Natural sequences that count
maximal saturated domino coverings of square and rectangular boards are
obtained. These include the new sequences A193764, A193765, A193766, A193767,
and A193768 of OEIS.",1112.2115v1
2012-02-10,Gluon saturation and pseudo-rapidity distributions of charged hadrons at RHIC energy regions,"We modified the gluon saturation model by rescaling the momentum fraction
according to saturation momentum and introduced the Cooper-Frye hydrodynamic
evolution to systematically study the pseudo-rapidity distributions of final
charged hadrons at different energies and different centralities for Au-Au
collisions in relativistic heavy-ion collisions at BNL Relativistic Heavy Ion
Collider (RHIC). The features of both gluon saturation and hydrodynamic
evolution at different energies and different centralities for Au-Au collisions
are investigated in this paper.",1202.2174v3
2012-03-06,Uniquely K_r-Saturated Graphs,"A graph G is uniquely K_r-saturated if it contains no clique with r vertices
and if for all edges e in the complement, G + e has a unique clique with r
vertices. Previously, few examples of uniquely K_r-saturated graphs were known,
and little was known about their properties. We search for these graphs by
adapting orbital branching, a technique originally developed for symmetric
integer linear programs. We find several new uniquely K_r-saturated graphs with
4 \leq r \leq 7, as well as two new infinite families based on Cayley graphs
for Z_n with a small number of generators.",1203.1084v1
2012-03-30,Enumeration of saturated chains in Dyck lattices,"We determine a general formula to compute the number of saturated chains in
Dyck lattices, and we apply it to find the number of saturated chains of length
2 and 3. We also compute what we call the Hasse index (of order 2 and 3) of
Dyck lattices, which is the ratio between the total number of saturated chains
(of length 2 and 3) and the cardinality of the underlying poset.",1203.6807v1
2013-04-30,A Characterization of Saturated Designs for Factorial Experiments,"In this paper we study saturated fractions of factorial designs under the
perspective of Algebraic Statistics. We define a criterion to check whether a
fraction is saturated or not with respect to a given model. The proposed
criterion is based purely on combinatorial objects. Our technique is
particularly useful when several fractions are needed. We also show how to
generate random saturated fractions with given projections, by applying the
theory of Markov bases for contingency tables.",1304.7914v1
2013-05-01,Unitarity Saturation In P-P Scattering,"The properties of soft p-p scattering amplitudes at the TeV-scale are studied
so as to identify the impact of s and t channel unitarity screenings on their
behavior at exceedingly high energies and determine the rate at which they
approach the bounds implied by unitarity saturation. I shall examine the
relevant high energy soft cross section features, as well as, the corresponding
behavior of the coupled phenomenological models aiming to reproduce this
data.\\ My conclusion is that p-p black body saturation is not attained up to
100 TeV. More over, I do not expect that saturation will be attained at
energies that can be investigated experimentally.",1305.0299v1
2013-07-28,Saturable absorption in multi-core fiber couplers,"The saturable absorption characteristics of two-, three-, and five-core
one-dimensional fiber coupler arrays and the seven-core hexagonal fiber coupler
array are investigated. It is shown that the performance of all these saturable
absorbers are comparable and not much is gained, if anything, by going from a
two-core nonlinear coupler geometry to a higher number of cores. This
observation is supported by the similarity of the saturable absorption curves,
as well as comparable pulse characteristics obtained from the simulation of a
generic mode-locked fiber laser cavity.",1307.7338v1
2014-05-14,Saturation of the morphisms in the database category,"In this paper we present the problem of saturation of a given morphism in the
database category DB, which is the base category for the functiorial semantics
of the database schema mapping systems used in Data Integration theory. This
phenomena appears in the case when we are using the Second-Order
tuple-generating dependencies (SOtgd) with existentially quantified
non-built-in functions, for the database schema mappings. We provide the
algorithm of the saturation for a given morphism, which represents a mapping
between two relational databases, and show that the original morphism in DB can
be equivalently substituted by its more powerful saturated version in any
commutative diagram in DB.",1405.3955v1
2015-03-09,Combinatorial characterizations of the saturation and the associated primes of the fourth power of edge ideals,"To compute the local cohomology of powers of edge ideals one needs to know
their saturations. The saturation of the second and third powers has been
described in terms of the graph in [13] and [10]. In this article, we give a
combinatorial description of the generators of the saturation of the fourth
power. As a consequence, we are able to give a complete classification of the
associated primes of the fourth power of edge ideals in terms of the graph.",1503.02396v1
2015-10-19,Random Nonlinear Infinite-Level-System Model for Amorphous Solid Phonon Echo and Saturation Phenomena,"The first two successful predictions for amorphous solid experiments by
tunneling-two-level-system (TTLS) was phonon echo and saturation phenomena. In
this paper by generalizing TTLS to infinite-level-system model with certain
randomness and nonlinearity, we prove that phonon echo is a stimulated emission
process. The classical infinite-level-system (taking $\hbar\to 0$ limit) cannot
find saturation effect, while quantum infinite-level-system can find it with
certain nonlinearity assumed. We also prove that without randomness or
nonlinearity neither phonon echo nor saturation exists in arbitrary
infinite-level-system.",1510.05538v2
2015-10-28,Saturation and geometrical scaling -- from small $x$ deep inelastic ep scattering to high energy proton-proton and heavy ion collisions,"Gluon distributions of colliding hadrons saturate as a result of the
non-linear evolution equations of QCD. As a consequence there exists the so
called saturation momentum, which is related to the gluon density per unit
rapidity per transverse area. When saturation momentum is the only scale for
physical processes, different observables exhibit geometrical scaling (GS). We
show a number of examples of GS and its violation in different reactions.",1510.08475v2
2015-11-02,Saturation Physics on the Energy Frontier,"Saturation physics is expected to be relevant at sufficiently small parton
momentum fractions $x$ in high-energy proton- (or deuteron-)ion collisions at
RHIC and the LHC. Accordingly, these collisions provide the best available
testing ground for the saturation model. However, producing precise numerical
predictions from the model is a complicated task; the state of the art in this
area involves next-to-leading order QCD calculations, which are difficult to do
numerically. Here I'll review recent progress in extracting numerical
predictions from saturation models and matching them to experimental results.",1511.00386v1
2015-12-21,Dynamics of viscous coalescing droplets in a saturated vapor phase,"The dynamics of two liquid droplets coalescing in their saturated vapor phase
are investigated by Lattice Boltzmann numerical simulations. Attention is paid
to the effect of the vapor phase on the formation and growth dynamics of the
liquid bridge in the viscous regime. We observe that the onset of the
coalescence occurs earlier and the expansion of the bridge initially proceeds
faster when the coalescence takes place in a saturated vapor compared to the
coalescence in a non-condensable gas. We argue that the initially faster
evolution of the coalescence in the saturated vapor is caused by the vapor
transport through condensation during the early stages of the coalescence.",1512.06814v1
2016-12-20,Imbibition triggered by capillary condensation in nanopores,"We study the spatio-temporal dynamics of water uptake by capillary
condensation from unsaturated vapor in mesoporous silicon layers (pore radius
$r_\mathrm{p} \simeq 2$ nm), taking advantage of the local changes in optical
reflectance as a function of water saturation. Our experiments elucidate two
qualitatively different regimes as a function of the imposed external vapor
pressure: for low saturations, equilibration occurs via a diffusion-like
process; for high saturations, an imbibition-like wetting front results in fast
equilibration towards a fully saturated sample. We show that the imbibition
dynamics can be described by a modified Lucas-Washburn equation that takes into
account the liquid stresses implied by Kelvin equation.",1612.06684v1
2017-10-10,Saturation of Berge Hypergraphs,"Given a graph $F$, a hypergraph is a Berge-$F$ if it can be obtained by
expanding each edge in $F$ to a hyperedge containing it. A hypergraph $H$ is
Berge-$F$-saturated if $H$ does not contain a subgraph that is a Berge-$F$, but
for any edge $e\in E(\overline{H})$, $H+e$ does. The $k$-uniform saturation
number of Berge-$F$ is the minimum number of edges in a $k$-uniform
Berge-$F$-saturated hypergraph on $n$ vertices. For $k=2$ this definition
coincides with the classical definition of saturation for graphs. In this paper
we study the saturation numbers for Berge triangles, paths, cycles, stars and
matchings in $k$-uniform hypergraphs.",1710.03735v1
2017-11-14,On ISS-Lyapunov functions for infinite-dimensional linear control systems subject to saturations,"- This article deals with the derivation of ISS-Lyapunov functions for
infinite-dimensional linear systems subject to saturations. Two cases are
considered: 1) the saturation acts in the same space as the control space; 2)
the saturation acts in another space, especially a Banach space. For the first
case, an explicit ISS-Lyapunov function can be derived. For the second case, we
can only ensure the existence of an ISS-Lyapunov function.",1711.05024v1
2017-12-09,On the saturation number of graphs,"Let $G=(V,E)$ be a simple connected graph. A matching $M$ in a graph $G$ is a
collection of edges of $G$ such that no two edges from $M$ share a vertex. A
matching $M$ is maximal if it cannot be extended to a larger matching in $G$.
The cardinality of any smallest maximal matching in $G$ is the saturation
number of $G$ and is denoted by $s(G)$. In this paper we study the saturation
number of the corona product of two specific graphs. We also consider some
graphs with certain constructions that are of importance in chemistry and study
their saturation number.",1712.03422v1
2018-01-03,Saturation of the hosing instability in quasi-linear plasma accelerators,"The beam hosing instability is analyzed theoretically for a witness beam in
the quasi-linear regime of plasma accelerators. In this regime, the hosing
instability saturates, even for a monoenergetic bunch, at a level much less
than standard scalings predict. Analytic expressions are derived for the
saturation distance and amplitude and are in agreement with numerical results.
Saturation is due to the natural head-to-tail variations in the focusing force,
including the self-consistent transverse beam loading.",1801.01104v1
2018-02-27,Nonlinear absorption study in four and five energy level systems,"Nonlinear absorption in four and five energy level systems have been studied
with the aid of steady-state rate equation approach. We report on the
tunability of saturable and reverse saturable absorption as a function of
spectroscopic parameters (lifetimes and absorption cross-sections). Detailed
information is given on the estimation of spectroscopic parameters in the
nonlinear absorption spectroscopy. The exhaustive graphical analysis of this
article can provide the brief idea about transmittance curves of the nonlinear
absorption to the experimentalists. In four and five level cascade models,
simultaneously saturable and reverse saturable absorption can be generated.",1802.09907v1
2019-07-19,Spectral Analysis of Latent Representations,"We propose a metric, Layer Saturation, defined as the proportion of the
number of eigenvalues needed to explain 99% of the variance of the latent
representations, for analyzing the learned representations of neural network
layers. Saturation is based on spectral analysis and can be computed
efficiently, making live analysis of the representations practical during
training. We provide an outlook for future applications of this metric by
outlining the behaviour of layer saturation in different neural architectures
and problems. We further show that saturation is related to the generalization
and predictive performance of neural networks.",1907.08589v1
2019-11-02,"On The Study Of D-Optimal Saturated Designs For Mean, Main Effects and $F_1$-Two-Factor Interactions For $2^k$-Factorial Experiments","The goal of this paper is to develop methods for the construction of
saturated designs that include the mean, main effects and the two-factor
interactions of one factor with a subset of the remaining factors. If one
factor is interacting with all the remaining factors give a method for the
construction of a d-optimal saturated design. If one factor is interacting with
a proper subset of the remaining factor we discuss the saturated d-optimal
design for specific cases.",1911.00794v1
2020-12-29,Matrix patterns with bounded saturation function,"A 0-1 matrix $M$ contains a 0-1 matrix pattern $P$ if we can obtain $P$ from
$M$ by deleting rows and/or columns and turning arbitrary 1-entries into 0s.
The saturation function $\mathrm{sat}(P,n)$ for a 0-1 matrix pattern $P$
indicates the minimum number of 1s in a $n \times n$ 0-1 matrix that does not
contain $P$, but changing any 0-entry into a 1-entry creates an occurrence of
$P$. Fulek and Keszegh recently showed that the saturation function is either
bounded or in $\Theta(n)$. Building on their results, we find a large class of
patterns with bounded saturation function, including both infinitely many
permutation matrices and infinitely many non-permutation matrices.",2012.14717v1
2021-05-05,An exact characterization of saturation for permutation matrices,"A 0-1 matrix $M$ contains a 0-1 matrix pattern $P$ if we can obtain $P$ from
$M$ by deleting rows and/or columns and turning arbitrary 1-entries into 0s.
The saturation function $\mathrm{sat}(P,n)$ for a 0-1 matrix pattern $P$
indicates the minimum number of 1s in an $n \times n$ 0-1 matrix that does not
contain $P$, but changing any 0-entry into a 1-entry creates an occurrence of
$P$. Fulek and Keszegh recently showed that each pattern has a saturation
function either in $O(1)$ or in $\Theta(n)$. We fully classify the saturation
functions of permutation matrices.",2105.02210v2
2021-07-07,Nonlinear reversed shear Alfven eigenmode saturation due to spontaneous zonal current generation,"General nonlinear equations describing reversed shear Alfven eigenmode (RSAE)
self-modulation via zero frequency zonal structure (ZFZS) generation are
derived using nonlinear gyrokinetic theory, which are then applied to study the
spontaneous ZFZS excitation as well as RSAE nonlinear saturation. It is found
that both electrostatic zonal flow (ZF) and electromagnetic zonal current (ZC)
can be preferentially excited by finite amplitude RSAE, depending on specific
plasma parameters. The modification to local shear Alfven wave continuum is
evaluated using the derived saturation level of ZC, which is shown to play a
comparable role in saturating RSAE with the ZFZS scattering.",2107.02996v1
2021-09-21,Saturation Problems in Convex Geometric Hypergraphs,"A convex geometric hypergraph (abbreviated cgh) consists of a collection of
subsets of a strictly convex set of points in the plane. Extremal problems for
cgh's have been extensively studied in the literature, and in this paper we
consider their corresponding saturation problems. We asymptotically determine
the saturation number of two geometrically disjoint $r$-tuples. Further,
amongst the eight nonisomorphic $3$-uniform cgh's on two edges, we determine
the saturation number for seven of these up to order of magnitude and the
eighth up to a log factor.",2109.09931v1
2021-11-29,Stability Analysis of a Feedback-linearization-based Controller with Saturation: A Tilt Vehicle with the Penguin-inspired Gait Plan,"Saturations in control signal can challenge the stability proof of a
feedback-linearization-based controller, even leading the system unstable [1].
Thus, several approaches are established to avoid reaching the saturation bound
[2,3]. Meanwhile, to help design the controller for a quad-tilt-rotor, [1]
modeled a tilt vehicle with implementing the feedback-linearization-based
controllers. In this article, we provide a gait plan for this tilt vehicle and
control it utilizing the feedback linearization. Since saturations exist in the
control signals, we study the stability based on Lyapunov theory.",2111.14456v1
2022-02-23,Speaker recognition improvement using blind inversion of distortions,"In this paper we propose the inversion of nonlinear distortions in order to
improve the recognition rates of a speaker recognizer system. We study the
effect of saturations on the test signals, trying to take into account real
situations where the training material has been recorded in a controlled
situation but the testing signals present some mismatch with the input signal
level (saturations). The experimental results shows that a combination of data
fusion with and without nonlinear distortion compensation can improve the
recognition rates with saturated test sentences from 80% to 88.57%, while the
results with clean speech (without saturation) is 87.76% for one microphone.",2203.01164v1
2022-05-27,Saturation Correction to Projectile -- some ${\cal{O}}(g^5)$ results within LCPT,"We revisited the first saturation correction to projectile in nucleus-nucleus
collisions \cite{Chirilli:2015tea} within diagrammatic light cone perturbation
theory (LCPT). To get an analytic expression for the saturation correction in
projectile authors in \cite{Chirilli:2015tea} calculated complete
${\cal{O}}(g^3)$ amplitudes, where the main results are given in transverse
coordinate space. However to find the complete first saturation correction in
the projectile, one needs to calculate both ${\cal{O}}(g^3)$ and
${\cal{O}}(g^5)$ gluon production amplitudes. We here present a detailed
calculation of a sample graph at ${\cal{O}}(g^5)$ in diagrammatic light cone
perturbation theory.",2205.13960v1
2023-01-07,Measuring Power with a Saturated Photodiode,"Accurate measurement of optical power is pivotal in many applications and
scientific research. However, traditional power meters are unable to measure
power levels beyond a certain saturation point, limiting their usefulness in
high-power applications. In this technical note, I discuss how optical power
can be measured using a saturated photodiode. I demonstrate that by monitoring
both the dc photocurrent and ac noise, it is possible to accurately measure
power levels beyond its saturation point.",2301.02658v1
2023-03-21,Some results on the saturation number for unions of cliques,"Graph $G$ is $H$-saturated if $H$ is not a subgraph of $G$ and $H$ is a
subgraph of $G+e$ for any edge $e$ not in $G$. The saturation number for a
graph $H$ is the minimal number of edges in any $H$-saturated graph of order
$n$. In this paper, the saturation number for $K_p\cup (t-1)K_q$ ($t\geqslant
3$ and $2\leqslant p<q$) is determined, and the extremal graph for $K_p\cup
2K_q$ is determined. Moreover, the saturation number and the extremal graph for
$K_p\cup K_q\cup K_r$ ($ r\geqslant p+q$) are completely determined.",2303.11893v2
2023-10-05,On the Lipschitz saturation of toric singularities,"We begin the study of Lipschitz saturation for germs of toric singularities.
By looking at their associated analytic algebras, we prove that if (X,0) is a
germ of toric singularity with smooth normalization then its Lipschitz
saturation is again toric. Finally we show how to calculate the Lipschitz
saturation for some families of toric singularities starting from the semigroup
that defines them.",2310.03216v1
2024-02-21,Saturation of $k$-chains in the Boolean lattice,"Given a set $X$, a collection $\mathcal{F} \subset \mathcal{P}(X)$ is said to
be $k$-Sperner if it does not contain a chain of length $k+1$ under set
inclusion and it is saturated if it is maximal with respect to this
probability. Gerbner et al. proved that the smallest saturated $k$-Sperner
system contains at least $2^{k/2-1}$ elements, and later, Morrison, Noel, and
Scott showed that the smallest such set contains no more than $2^{0.976723k}$
elements. We improve both the upper and lower bounds, showing that the size of
the smallest saturated $k$-Sperner system lies between $\sqrt{k}2^{k/2}$ and
$2^{0.950978k}$.",2402.14113v2
2024-02-24,Adjusting exceptional points using saturable nonlinearities,"We study the impact of saturable nonlinearity on the presence and location of
exceptional points in a non-Hermitian dimer system. The inclusion of the
saturable nonlinearity leads to the emergence of multiple eigenvalues,
exceeding the typical two found in the linear counterpart. To identify the
exceptional points, we calculate the nonlinear eigenvalues both from a
polynomial equation for the defined population imbalance and through a fully
numerical method. Our results reveal that exceptional points can be precisely
located by adjusting the non-equal saturable nonlinearities in the detuning
space.",2402.15792v1
2024-04-03,Quotient-saturated groups,"We introduce the new notion of quotient-saturation as a measure of the
immensity of the quotient structure of a group. We present a sufficient
condition for a finitely presented group to be quotient-saturated, and use it
to deduce that non-elementary finitely presented subgroups of a hyperbolic
group (in particular, non-elementary hyperbolic groups themselves) are
quotient-saturated. Finally, we elaborate on the previous results to extend the
scope of this property to finitely presented acylindrically hyperbolic groups.",2404.03104v1
2022-12-09,Rainbow saturation for complete graphs,"We call an edge-colored graph rainbow if all of its edges receive distinct
colors. An edge-colored graph $\Gamma$ is called $H$-rainbow saturated if
$\Gamma$ does not contain a rainbow copy of $H$ and adding an edge of any color
to $\Gamma$ creates a rainbow copy of $H$. The rainbow saturation number
$sat(n,{R}(H))$ is the minimum number of edges in an $n$-vertex $H$-rainbow
saturated graph. Gir\~{a}o, Lewis, and Popielarz conjectured that
$sat(n,{R}(K_r))=2(r-2)n+O(1)$ for fixed $r\geq 3$. Disproving this conjecture,
we establish that for every $r\geq 3$, there exists a constant $\alpha_r$ such
that $$r + \Omega\left(r^{1/3}\right) \le \alpha_r \le r + r^{1/2} \qquad
\text{and} \qquad sat(n,{R}(K_r)) = \alpha_r n + O(1).$$ Recently, Behague,
Johnston, Letzter, Morrison, and Ogden independently gave a slightly weaker
upper bound which was sufficient to disprove the conjecture. They also
introduced the weak rainbow saturation number, and asked whether this is equal
to the rainbow saturation number of $K_r$, since the standard weak saturation
number of complete graphs equals the standard saturation number. Surprisingly,
our lower bound separates the rainbow saturation number from the weak rainbow
saturation number, answering this question in the negative. The existence of
the constant $\alpha_r$ resolves another of their questions in the affirmative
for complete graphs. Furthermore, we show that the conjecture of Gir\~{a}o,
Lewis, and Popielarz is true if we have an additional assumption that the
edge-colored $K_r$-rainbow saturated graph must be rainbow. As an ingredient of
the proof, we study graphs which are $K_r$-saturated with respect to the
operation of deleting one edge and adding two edges.",2212.04640v2
1992-05-07,On $c_0$-saturated Banach spaces,"A Banach space E is c_0-saturated if every closed infinite dimensional
subspace of E contains an isomorph of c_0. A c_0-saturated Banach space with an
unconditional basis which has a quotient space isomorphic to l^2 is
constructed.",9205205v1
2004-04-20,An Invitation to the Generalized Saturation Conjecture,"We report about some results, interesting examples, problems and conjectures
revolving around the parabolic Kostant partition functions, the parabolic
Kostka polynomials and ``saturation'' properties of several generalizations of
the Littlewood--Richardson numbers.",0404353v2
2004-10-25,"Expansions, omitting types, and standard systems","Recursive saturation and resplendence are two important notions in models of
arithmetic. Kaye, Kossak, and Kotlarski introduced the notion of arithmetic
saturation and argued that recursive saturation might not be as rigid as first
assumed.
  In this thesis we give further examples of variations of recursive
saturation, all of which are connected with expandability properties similar to
resplendence. However, the expandability properties are stronger than
resplendence and implies, in one way or another, that the expansion not only
satisfies a theory, but also omits a type. We conjecture that a special version
of this expandability is in fact equivalent to arithmetic saturation. We prove
that another of these properties is equivalent to \beta-saturation. We also
introduce a variant on recursive saturation which makes sense in the context of
a standard predicate, and which is equivalent to a certain amount of ordinary
saturation.
  The theory of all models which omit a certain type p(x) is also investigated.
We define a proof system, which proves a sentence if and only if it is true in
all models omitting the type p(x). The complexity of such proof systems are
discussed and some explicit examples of theories and types with high
complexity, in a special sense, are given.
  We end the thesis by a small comment on Scott's problem. We prove that, under
the assumption of Martin's axiom, every Scott set of cardinality <2^{\aleph_0}
closed under arithmetic comprehension which has the countable chain condition
is the standard system of some model of PA. However, we do not know if there
exists any such uncountable Scott sets.",0410523v1
2007-08-02,"Eigencone, saturation and Horn problems for symplectic and odd orthogonal groups","We consider the eigenvalue problem and the associated intersection theory of
homogenous spaces for the symplectic and odd orthogonal groups. We solve the
Horn and saturation problems for these classical groups.",0708.0398v1
2008-12-08,Theoretical concepts of parton saturation - from HERA to LHC,"We present a short summary of parton saturation concepts as seen in deep
inelastic scattering.",0812.1523v1
2009-01-19,Application of the quadratures method to the NLS with saturation,"The solution of nonlinear Schroedinger equation with saturation was found by
means the quadratures method in terms of degeneracy theory. It was shown the
existence conditions for soliton solutions.",0901.2796v1
2009-08-27,Asymptotics of Canonical and Saturated RNA Secondary Structures,"It is a classical result of Stein and Waterman that the asymptotic number of
RNA secondary structures is $1.104366 n^{-3/2} 2.618034^n$. In this paper, we
study combinatorial asymptotics for two special subclasses of RNA secondary
structures - canonical and saturated structures. Canonical secondary structures
were introduced by Bompf\""unewerer et al., who noted that the run time of
Vienna RNA Package is substantially reduced when restricting computations to
canonical structures. Here we provide an explanation for the speed-up.
Saturated secondary structures have the property that no base pairs can be
added without violating the definition of secondary structure (i.e. introducing
a pseudoknot or base triple). Here we compute the asymptotic number of
saturated structures, we show that the asymptotic expected number of base pairs
is $0.337361 n$, and the asymptotic number of saturated stem-loop structures is
$0.323954 1.69562^n$, in contrast to the number $2^{n-2}$ of (arbitrary)
stem-loop structures as classically computed by Stein and Waterman. Finally, we
show that the density of states for [all resp. canonical resp. saturated]
secondary structures is asymptotically Gaussian. We introduce a stochastic
greedy method to sample random saturated structures, called quasi-random
saturated structures, and show that the expected number of base pairs of is
$0.340633 n$.",0908.4003v1
2010-10-04,Sharp upper bounds of the Betti numbers for a given Hilbert polynomial,"We show that there exists a saturated graded ideal in a standard graded
polynomial ring which has the largest total Betti numbers among all saturated
graded ideals for a fixed Hilbert polynomial.",1010.0457v1
2011-09-07,Saturation of uncertainty relations for twisted acceleration-enlarged Newton-Hooke space-times,"Using Fock representation we construct states saturating uncertainty
relations for twist-deformed acceleration-enlarged Newton-Hooke space-times.",1109.1428v1
2011-11-18,Gluon Saturation in QCD at High Energy: Beyond Leading Logarithms,"Progresses towards the calculation and the understanding of NLO/NLL
contributions to Deep Inelastic Scattering at low x with gluon saturation are
being reviewed.",1111.4440v1
2012-09-17,The saturation property for branching rules -- Examples,"For a few pairs $G\subset \hat G$ of reductive groups, we study the
decomposition of irreducible $\hait G$-modules into $G$-modules. In particular,
we observe the saturation property for all of these pairs.",1209.3589v1
2014-05-22,Saturation algorithms for model-checking pushdown systems,"We present a survey of the saturation method for model-checking pushdown
systems.",1405.5593v1
2015-12-05,Sets of Completely Decomposed Primes in Extensions of Number Fields,"We introduce the notion of saturated sets of primes of an algebraic number
field and prove an analogue of Riemann's existence theorem for the
decomposition groups of infinite stably saturated sets of primes.",1512.01694v1
2016-10-08,Anderson localization and saturable nonlinearity in one-dimensional disordered lattices,"We investigate numerically the propagation and the Anderson localization of
plane waves in a one-dimensional lattice chain, where disorder and saturable
nonlinearity are simultaneously present. Using a calculation scheme for solving
the stationary discrete nonlinear Schr\""{o}dinger equation in the fixed input
case, the disorder-averaged logarithmic transmittance and the localization
length are calculated in a numerically precise manner. The localization length
is found to be a nonmonotonic function of the incident wave intensity,
acquiring a minimum value at a certain finite intensity, due to saturation
effects. For low incident intensities where the saturation effect is
ineffective, the enhancement of localization due to Kerr-type nonlinearity
occurs in a way similar to the case without saturation. For sufficiently high
incident intensities, we find that the localization length is an increasing
function of the incident wave intensity, which implies that localization is
suppressed for stronger input intensities, and ultimately approaches a
saturation value. This feature is associated with the fact that the nonlinear
system is reduced to an effectively linear one, when either the incident wave
intensity or the saturation parameter is sufficiently large. We also find that
the nonlinear saturation effect is stronger and more pronounced when the energy
of the incident wave is larger.",1610.02521v1
2017-09-21,Particle-in-cell simulation of Buneman instability beyond quasilinear saturation,"Spatio-temporal evolution of Buneman instability has been followed
numerically till its quasilinear quenching and beyond, using an in-house
developed electrostatic 1D particle-in-cell simulation code. For different
initial drift velocities $k_{L}v_{0}/\omega_{pe} \approx 0.1 \, - \, 1$ and for
a wide range of electron to ion mass ratios (m/M), growth rate obtained from
simulation agrees well with the numerical solution of the fourth order
dispersion relation. Quasi-linear saturation of Buneman instability occurs when
ratio of electrostatic field energy density ($\sum\limits_{k}
|E_{k}|^{2}/8{\pi}$) to initial electron drift kinetic energy density ($W_{0} =
\frac{1}{2} n_{0}m v^{2}_{0}$) reaches up to a constant value, which as
predicted by Hirose [Plasma Physics 20, 481(1978)], is independent of initial
electron drift velocity but depends on electron to ion mass ratio m/M as
$\sum\limits_{k} |E_{k}|^{2}/16{\pi}W_{0} \approx (m/M)^{1/3}$. This result
stands verified in our simulations. Growth of the instability beyond the first
saturation (quasilinear saturation ) till its final saturation [Ishihara et.
al., PRL 44, 1404(1980)] follows an algebraic scaling with time. In contrast to
the quasilinear saturation, the ratio of final saturated electrostatic field
energy density to initial kinetic energy density, is relatively independent of
electron to ion mass ratio and is found to depend only on the initial drift
velocity. Beyond the final saturation, electron phase space holes coupled to
large amplitude ion solitary waves, a state known as coupled hole-soliton , are
seen in our simulations. The propagation characteristics ( amplitude - speed
relation ) of these coherent modes is found to be consistent with the theory of
Saeki et. al. [PRL 80, 1224(1998)].",1709.07478v1
2017-10-13,Finite saturation for unirational varieties,"We import ideas from geometry to settle Sarnak's saturation problem for a
large class of algebraic varieties.",1710.04962v3
2018-02-21,Dynamics of Viscous Entrapped Saturated Zones in Partially Wetted Porous Media,"As a typical multiphase fluid flow process, drainage in porous media is of
fundamental interest in nature and industrial applications. During drainage
processes in unsaturated soils and porous media in general, saturated clusters,
in which a liquid phase fully occupies the pore space between solid grains,
affect the relative permeability and effective stress of the system. In this
study, we experimentally studied drainage processes in unsaturated granular
media as a model porous system. The distribution of saturated clusters is
analysed by an optical imaging method under different drainage conditions, in
which pore-scale information from Voronoi and Delaunay tessellation was used to
characterise the topology of saturated cluster distributions. By employing
statistical analyses, the observed spatial and temporal information of
multiphase flow and fluid entrapment in porous media are described. The results
indicate that the distributions of both the crystallised cell size and pore
size are positively correlated to the spatial and temporal distribution of
saturated cluster sizes. The saturated cluster size is found to follow a
lognormal distribution, in which the generalised Bond number correlates
negatively to the scale parameter and positively to the shape parameter. These
findings can be used to connect pore-scale behaviour with overall
hydro-mechanical characteristics in partially saturated porous media, using
both the degree of saturation and generalised Bond number.",1802.07387v1
2019-06-08,Splitting-based domain decomposition methods for two-phase flow with different rock types,"In this paper, we are concerned with the global pressure formulation of
immiscible incompressible two-phase flow between different rock types. We
develop for this problem two robust schemes based on domain decomposition (DD)
methods and operator-splitting techniques. The first scheme follows a
sequential procedure in which the (global) pressure, the saturation-advection
and the saturation-diffusion problems are fully decoupled. In this scheme, each
problem is treated individually using various DD approaches and specialized
numerical methods. The coupling between the different problems is explicit and
the time-marching is with no iterations. To adapt to different time scales of
problem components and different rock types, the novel scheme uses a multirate
time stepping strategy, by taking multiple finer time steps for
saturation-advection within one coarse time step for saturation-diffusion and
pressure, and permits independent time steps for the advection step in the
different rocks. In the second scheme, we review the classical Implicit
Pressure--Explicit Saturation (IMPES) method (by decoupling only pressure and
saturation) in the context of multirate coupling schemes and
nonconforming-in-time DD approaches. For the discretization, the
saturation-advection problem is approximated with the explicit Euler method in
time, and in space with the cell-centered finite volume method of first order
of Godunov type. The saturation-diffusion problem is approximated in time with
the implicit Euler method and in space with the mixed finite element method, as
in the pressure problem. Finally, in a series of numerical experiments, we
investigate the practicality of the proposed schemes, the accuracy-in-time of
the multirate and nonconforming time strategies, and compare the convergence of
various DD methods within each approach.",1906.03470v2
2021-05-10,Examining and Mitigating Kernel Saturation in Convolutional Neural Networks using Negative Images,"Neural saturation in Deep Neural Networks (DNNs) has been studied
extensively, but remains relatively unexplored in Convolutional Neural Networks
(CNNs). Understanding and alleviating the effects of convolutional kernel
saturation is critical for enhancing CNN models classification accuracies. In
this paper, we analyze the effect of convolutional kernel saturation in CNNs
and propose a simple data augmentation technique to mitigate saturation and
increase classification accuracy, by supplementing negative images to the
training dataset. We hypothesize that greater semantic feature information can
be extracted using negative images since they have the same structural
information as standard images but differ in their data representations. Varied
data representations decrease the probability of kernel saturation and thus
increase the effectiveness of kernel weight updates. The two datasets selected
to evaluate our hypothesis were CIFAR- 10 and STL-10 as they have similar image
classes but differ in image resolutions thus making for a better understanding
of the saturation phenomenon. MNIST dataset was used to highlight the
ineffectiveness of the technique for linearly separable data. The ResNet CNN
architecture was chosen since the skip connections in the network ensure the
most important features contributing the most to classification accuracy are
retained. Our results show that CNNs are indeed susceptible to convolutional
kernel saturation and that supplementing negative images to the training
dataset can offer a statistically significant increase in classification
accuracies when compared against models trained on the original datasets. Our
results present accuracy increases of 6.98% and 3.16% on the STL-10 and
CIFAR-10 datasets respectively.",2105.04128v1
2021-09-08,Weak saturation of multipartite hypergraphs,"Given $q$-uniform hypergraphs ($q$-graphs) $F,G$ and $H$, where $G$ is a
spanning subgraph of $F$, $G$ is called weakly $H$-saturated in $F$ if the
edges in $E(F)\setminus E(G)$ admit an ordering $e_1,\dots, e_k$ so that for
all $i\in [k]$ the hypergraph $G\cup \{e_1,\dots,e_i\}$ contains an isomorphic
copy of $H$ which in turn contains the edge $e_i$. The weak saturation number
of $H$ in $F$ is the smallest size of an $H$-weakly saturated subgraph of $F$.
Weak saturation was introduced by Bollob\'as in 1968, but despite decades of
study our understanding of it is still limited. The main difficulty lies in
proving lower bounds on weak saturation numbers, which typically withstands
combinatorial methods and requires arguments of algebraic or geometrical
nature.
  In our main contribution in this paper we determine exactly the weak
saturation number of complete multipartite $q$-graphs in the directed setting,
for any choice of parameters. This generalizes a theorem of Alon from 1985. Our
proof combines the exterior algebra approach from the works of Kalai with the
use of the colorful exterior algebra motivated by the recent work of Bulavka,
Goodarzi and Tancer on the colorful fractional Helly theorem. In our second
contribution answering a question of Kronenberg, Martins and Morrison, we
establish a link between weak saturation numbers of bipartite graphs in the
clique versus in a complete bipartite host graph. In a similar fashion we
asymptotically determine the weak saturation number of any complete $q$-partite
$q$-graph in the clique, generalizing another result of Kronenberg et al.",2109.03703v2
2021-11-25,Sketch-Guided Equality Saturation: Scaling Equality Saturation to Complex Optimizations of Functional Programs,"Generating high-performance code for diverse hardware and application domains
is challenging. Functional array programming languages with patterns like map
and reduce have been successfully combined with term rewriting to define and
explore optimization spaces. However, deciding what sequence of rewrites to
apply is hard and has a huge impact on the performance of the rewritten
program. Equality saturation avoids the issue by exploring many possible ways
to apply rewrites, efficiently representing many equivalent programs in an
e-graph data structure.
  Equality saturation has some limitations when rewriting functional language
terms, as currently naive encodings of the lambda calculus are used. We present
new techniques for encoding polymorphically typed lambda calculi, and show that
the efficient encoding reduces the runtime and memory consumption of equality
saturation by orders of magnitude.
  Moreover, equality saturation does not yet scale to complex compiler
optimizations. These emerge from long rewrite sequences of thousands of rewrite
steps, and may use pathological combinations of rewrite rules that cause the
e-graph to quickly grow too large. This paper introduces \emph{sketch-guided
equality saturation}, a semi-automatic technique that allows programmers to
provide program sketches to guide rewriting. Sketch-guided equality saturation
is evaluated for seven complex matrix multiplication optimizations, including
loop blocking, vectorization, and multi-threading. Even with efficient lambda
calculus encoding, unguided equality saturation can locate only the two
simplest of these optimizations, the remaining five are undiscovered even with
an hour of compilation time and 60GB of RAM. By specifying three or fewer
sketch guides all seven optimizations are found in seconds of compilation time,
using under 1GB of RAM, and generating high performance code.",2111.13040v2
2021-12-06,Saturated Models for the Working Model Theorist,"We put in print a classical result that states that for most purposes, there
is no harm in assuming the existence of saturated models in model theory. The
presentation is aimed for model theorists with only basic knowledge of
axiomatic set theory.",2112.02774v1
2023-05-20,Ultra-fast Graphene-Plasmonic Hybrid Metasurface Saturable Absorber with Low Saturation Fluence,"Exploring novel materials with enhanced optical nonlinearities at low power
levels with ultrafast response and small footprints is of great interests for
information processing, communication, sensing and quantum systems. Recent
progress on nonlinear metamaterials and metasurfaces suggests promising
solutions to overcome the limitations of nonlinear materials in nature. Here we
present a design concept for highly enhanced saturable absorption effect based
on subwavelength-thick (<1/5$\lambda$0) hybrid graphene-plasmonic metasurface
structures in infrared wavelengths. Our theoretical and experimental results
demonstrated that, by exciting nonequilibrium carriers inside nanoscale
hotspots, one could not only enhance the saturable absorption in graphene, but
also reduce the saturation fluence by over 3 orders of magnitude (from ~ 1
mJ/cm2 to ~100 nJ/cm2). Our pump-probe measurement results suggested an
ultrashort saturable absorption recovery time (<60 fs), which is ultimately
determined by the relaxation dynamics of photoexcited carriers in graphene. We
also observed pulse narrowing effects in our devices based on the
autocorrelation measurement results. Such design concepts can be tailored via
structure engineering to operate in broader wavelength ranges up to mid- and
far- infrared spectral regions. These ultrafast low-saturation fluence
saturable absorber designs can enable low-threshold, compact, self-starting
mode-locked lasers, laser pulse shaping, and high-speed optical information
processing.",2305.12136v1
2023-07-13,On stepwise advancement of fractures and pressure oscillations in saturated porous media,"Comments to K.M. Pervaiz Fathima, Ren\'e de Borst, Implications of single or
multiple pressure degrees of freedom at fracture in fluid saturated porous
media, Engineering Fracture Mechanics, 213 (2019), 1-20.",2307.06960v1
2023-10-16,A saturated 1-system of curves on the surface of genus 3,"We construct a saturated system of 33 essential simple closed curves that are
pairwise non-homotopic and intersect at most once on the oriented, closed
surface of genus 3.",2310.10814v2
1999-11-16,Nonlinear r-modes in a spherical shell: issues of principle,"We use a simple physical model to study the nonlinear behaviour of the r-mode
instability. We assume that r-modes (Rossby waves) are excited in a thin
spherical shell of rotating incompressible fluid. For this case, exact Rossby
wave solutions of arbitrary amplitude are known. We find that:
  (a) These nonlinear Rossby waves carry ZERO physical angular momentum and
positive physical energy, which is contrary to the folklore belief that the
r-mode angular momentum and energy are negative.
  (b) Within our model, we confirm the differential drift reported by Rezzolla,
Lamb and Shapiro (1999).
  Radiation reaction is introduced into the model by assuming that the fluid is
electrically charged; r-modes are coupled to electromagnetic radiation through
current (magnetic) multipole moments. We find that:
  (c) To linear order in the mode amplitude, r-modes are subject to the CFS
instability, as expected.
  (d) Radiation reaction decreases the angular velocity of the shell and causes
differential rotation (which is distinct from but similar in magnitude to the
differential drift reported by Rezzolla et al.) prior to saturation of the
r-mode growth. This is contrary to the phenomenological treatments to date,
which assume that the loss of stellar angular momentum is accounted for by the
r-mode growth. We demonstrate, for the first time, that r-mode radiation
reaction leads to differential rotation.
  (e) We show that for l=2 r-mode electromagnetic radiation reaction is
equivalent to gravitational radiation reaction in the lowest post-Newtonian
order.",9911295v1
2002-01-11,The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability: I. Local Axisymmetric Simulations,"The effect of the Hall term on the evolution of the magnetorotational
instability (MRI) in weakly ionized accretion disks is investigated using local
axisymmetric simulations. First, we show that the Hall term has important
effects on the MRI when the temperature and density in the disk is below a few
thousand K and between 10^13 and 10^18 cm^{-3} respectively. Such conditions
can occur in the quiescent phase of dwarf nova disks, or in the inner part
(inside 10 - 100 AU) of protoplanetary disks. When the Hall term is important,
the properties of the MRI are dependent on the direction of the magnetic field
with respect to the angular velocity vector \Omega. If the disk is threaded by
a uniform vertical field oriented in the same sense as \Omega, the axisymmetric
evolution of the MRI is an exponentially growing two-channel flow without
saturation. When the field is oppositely directed to \Omega, however, small
scale fluctuations prevent the nonlinear growth of the channel flow and the MRI
evolves into MHD turbulence. These results are anticipated from the
characteristics of the linear dispersion relation. In axisymmetry on a field
with zero-net flux, the evolution of the MRI is independent of the size of the
Hall term relative to the inductive term. The evolution in this case is
determined mostly by the effect of ohmic dissipation.",0201179v1
2002-03-18,Activity at the Deuterium-Burning Mass Limit in Orion,"We report very intense and variable Halpha emission (pseudo-equivalent widths
of ~180, 410 A) of S Ori 55, a probable free-floating, M9-type substellar
member of the young sigma Orionis open star cluster. After comparison with
state-of-the-art evolutionary models, we infer that S Ori 55 is near or below
the cluster deuterium-burning mass borderline, which separates brown dwarfs and
planetary-mass objects. We find its mass to be 0.008-0.015 Msun for ages
between 1 Myr and 8 Myr, with ~0.012 Msun the most likely value at the cluster
age of 3 Myr. The largest Halpha intensity reached the saturation level of log
L(Halpha)/L(bol) = -3. We discuss several possible scenarios for such a strong
emission. We also show that sigma Orionis M and L dwarfs have in general more
Halpha emission than their older field spectral counterparts. This could be due
to a decline in the strength of the magnetic field with age in brown dwarfs and
isolated planetary-mass objects, or to a likely mass accretion from disks in
the very young sigma Orionis substellar members.",0203283v1
2003-11-09,Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop,"We study dynamical consequences of the kink instability of a twisted coronal
flux rope, using the force-free coronal loop model by Titov & D\'emoulin (1999)
as the initial condition in ideal-MHD simulations. When a critical value of the
twist is exceeded, the long-wavelength ($m=1$) kink mode develops. Analogous to
the well-known cylindrical approximation, a helical current sheet is then
formed at the interface with the surrounding medium. In contrast to the
cylindrical case, upward-kinking loops form a second, vertical current sheet
below the loop apex at the position of the hyperbolic flux tube (generalized X
line) in the model. The current density is steepened in both sheets and
eventually exceeds the current density in the loop (although the kink
perturbation starts to saturate in our simulations without leading to a global
eruption). The projection of the field lines that pass through the vertical
current sheet shows an S shape whose sense agrees with the typical sense of
transient sigmoidal (forward or reverse S-shaped) structures that brighten in
soft X rays prior to coronal eruptions. The upward-kinked loop has the opposite
S shape, leading to the conclusion that such sigmoids do not generally show the
erupting loops themselves but indicate the formation of the vertical current
sheet below them that is the central element of the standard flare model.",0311199v1
2004-01-15,On the deep minimum state in the Seyfert galaxy MCG-6-30-15,"(abridged) We present a detailed spectral analysis of the first observation
of the Seyfert 1 galaxy MCG-6-30-15 by the European Photon Imaging Camera on
board the XMM-Newton observatory, together with contemporaneous data from the
Proportional Counter Array on the Rossi X-ray Timing Explorer. Confirming our
previously published result, we find that the presence of extremely broadened
reflection features from an ionized relativistic accretion disk is required
even when one employs the latest X-ray reflection models and includes the
effect of complex absorption. The extremely broadened reflection features are
also present if the primary continuum is modeled with a thermal Comptonisation
spectrum rather than a simple power-law continuum. With this fact established,
we examine these data using a relativistic smearing function corresponding to a
``generalized thin accretion disk'' model. We find strong evidence for torquing
of the central parts of the accretion disk (presumably through magnetic
interactions with the plunging region of the disk and/or the rotating black
hole itself). We also perform a study of spectral variability within our
observation. We find that the disk reflection features maintain roughly a
constant equivalent width with respect to the observed continuum, as predicted
by simple reflection models. Taken together with other studies of MCG-6-30-15
that find disk features to possess constant intensity at higher flux states, we
suggest that the flux of disk features undergoes a saturation once the source
emerges from a Deep Minimum state.",0401305v1
2004-01-22,Thermal conduction in cosmological SPH simulations,"Thermal conduction in the intracluster medium has been proposed as a possible
heating mechanism for offsetting central cooling losses in rich clusters of
galaxies. In this study, we introduce a new formalism to model conduction in a
diffuse ionised plasma using smoothed particle hydrodynamics (SPH), and we
implement it in the parallel TreePM/SPH-code GADGET-2. We consider only
isotropic conduction and assume that magnetic suppression can be described in
terms of an effective conductivity, taken as a fixed fraction of the
temperature-dependent Spitzer rate. We also account for saturation effects in
low-density gas. Our formulation manifestly conserves thermal energy even for
individual and adaptive timesteps, and is stable in the presence of small-scale
temperature noise. This allows us to evolve the thermal diffusion equation with
an explicit time integration scheme along with the ordinary hydrodynamics. We
use a series of simple test problems to demonstrate the robustness and accuracy
of our method. We then apply our code to spherically symmetric realizations of
clusters, constructed under the assumptions of hydrostatic equilibrium and a
local balance between conduction and radiative cooling. While we confirm that
conduction can efficiently suppress cooling flows for an extended period of
time in these isolated systems, we do not find a similarly strong effect in a
first set of clusters formed in self-consistent cosmological simulations.
However, their temperature profiles are significantly altered by conduction, as
is the X-ray luminosity.",0401456v3
2004-12-15,Magnetospheric eclipses in the double pulsar system J0737-3039,"We argue that eclipses of radio emission from the millisecond pulsar A in the
double pulsar system J0737-3039 are due to synchrotron absorption by plasma in
the closed field line region of the magnetosphere of its normal pulsar
companion B. A's radio beam only illuminates B's magnetosphere for about 10
minutes surrounding the time of eclipse. During this time it heats particles at
r\gtrsim 10^9 cm to relativistic energies and enables extra plasma to be
trapped by magnetic mirroring. An enhancement of the plasma density by a factor
\sim 10^2 is required to match the duration and optical depth of the observed
eclipses. The extra plasma might be supplied by a source near B through B\gamma
pair creation by energetic photons produced in B's outer gap. Excitation of
pairs' gyrational motions by cyclotron absorption of A's radio beam can result
in their becoming trapped between conjugate mirror points in B's magnetosphere.
Because the trapping efficiency decreases with increasing optical depth, the
plasma density enhancement saturates even under steady state illumination. The
result is an eclipse with finite, frequency dependent, optical depth. After
illumination by A's radio beam ceases, the trapped particles cool and are lost.
The entire cycle repeats every orbital period. We speculate that the
asymmetries between eclipse ingress and egress result in part from the
magnetosphere's evolution toward a steady state when illuminated by A's radio
beam. We predict that A's linear polarization will vary with both eclipse phase
and B's rotational phase.",0412355v3
2005-09-13,Nonlinear Photon Bubbles Driven by Buoyancy,"We derive an analytic model for nonlinear ""photon bubble"" wave trains driven
by buoyancy forces in magnetized, radiation pressure-dominated atmospheres.
Continuous, periodic wave solutions exist when radiative diffusion is slow
compared to the dynamical timescale of the atmosphere. We identify these waves
with the saturation of a linear instability discovered by Arons - therefore,
these wave trains should develop spontaneously. The buoyancy-driven waves are
physically distinct from photon bubbles in the presence of rapid diffusion,
which evolve into trains of gas pressure-dominated shocks as they become
nonlinear.
  Like the gas pressure-driven shock trains, buoyancy-driven photon bubbles can
exhibit very large density contrasts, which greatly enhance the flow of
radiation through the atmosphere. However, steady-state solutions for
buoyancy-driven photon bubbles exist only when an extra source of radiation is
added to the energy equation, in the form of a flux divergence. We argue that
this term is required to compensate for the radiation flux lost via the
bubbles, which increases with height. We speculate that an atmosphere subject
to buoyancy-driven photon bubbles, but lacking this compensating energy source,
would lose pressure support and collapse on a timescale much shorter than the
radiative diffusion time in the equivalent homogeneous atmosphere.",0509357v1
2006-03-08,The signature of the magnetorotational instability in the Reynolds and Maxwell stress tensors in accretion discs,"The magnetorotational instability is thought to be responsible for the
generation of magnetohydrodynamic turbulence that leads to enhanced outward
angular momentum transport in accretion discs. Here, we present the first
formal analytical proof showing that, during the exponential growth of the
instability, the mean (averaged over the disc scale-height) Reynolds stress is
always positive, the mean Maxwell stress is always negative, and hence the mean
total stress is positive and leads to a net outward flux of angular momentum.
More importantly, we show that the ratio of the Maxwell to the Reynolds
stresses during the late times of the exponential growth of the instability is
determined only by the local shear and does not depend on the initial spectrum
of perturbations or the strength of the seed magnetic. Even though we derived
these properties of the stress tensors for the exponential growth of the
instability in incompressible flows, numerical simulations of shearing boxes
show that this characteristic is qualitatively preserved under more general
conditions, even during the saturated turbulent state generated by the
instability.",0603178v2
2007-02-26,Modeling time delays in the X-ray spectrum of the Seyfert galaxy MCG-6-30-15,"We propose a reflection model of the time delays detected during an
exceptionally bright, single flare in MCG-6-30-15. We consider a scenario in
which the delays of the hard X-rays with respect to the soft X-rays are caused
by the presence of the delayed reflection component. We employ a model of the
flare, which is accompanied by reprocessed emission. We consider two
geometries/thermal states of the reprocessing medium: a partially ionized
accretion disk surface and a distribution of magnetically confined, cold blobs.
The reprocessing by cold blobs predicts positive time delays and a saturation
in the time delay -- energy relation, which is likely present in the data. The
model requires a strong reflection component and relies on the apparent
pivoting of the combined primary and reflected spectrum. The reflection by the
ionized disk surface does not reproduce the observed delays. We discuss the
relation between the two reflection scenarios and argue that they are both
present in MCG-6-30-15.",0702685v1
1999-12-07,Quantum Resonances and Regularity Islands in Quantum Maps,"We study analytically as well as numerically the dynamics of a quantum map
near a quantum resonance of an order q. The map is embedded into a continuous
unitary transformation generated by a time-independent quasi-Hamiltonian. Such
a Hamiltonian generates at the very point of the resonance a local gauge
transformation described the unitary unimodular group SU(q). The resonant
energy growth of is attributed to the zero Liouville eigenmodes of the
generator in the adjoint representation of the group while the non-zero modes
yield saturating with time contribution. In a vicinity of a given resonance,
the quasi-Hamiltonian is then found in the form of power expansion with respect
to the detuning from the resonance. The problem is related in this way to the
motion along a circle in a (q^2-1)-component inhomogeneous ""magnetic"" field of
a quantum particle with $q$ intrinsic degrees of freedom described by the SU(q)
group. This motion is in parallel with the classical phase oscillations near a
non-linear resonance. The most important role is played by the resonances with
the orders much smaller than the typical localization length, q << l. Such
resonances master for exponentially long though finite times the motion in some
domains around them. Explicit analytical solution is possible for a few lowest
and strongest resonances.",9912009v1
1995-12-26,The Hubbard Model: Introduction and Selected Rigorous Results,"The Hubbard model is a ""highly oversimplified model"" for electrons in a solid
which interact with each other through extremely short ranged repulsive
(Coulomb) interaction. The Hamiltonian of the Hubbard model consists of two
pieces; H_hop which describes quantum mechanical hopping of electrons, and Hint
which describes nonlinear repulsive interaction. Either H_hop or H_int alone is
easy to analyze, and does not favor any specific order. But their sum
H=H_hop+H_int is believed to exhibit various nontrivial phenomena including
metal-insulator transition, antiferromagnetism, ferrimagnetism, ferromagnetism,
Tomonaga-Luttinger liquid, and superconductivity. It is believed that we can
find various interesting ""universality classes"" of strongly interacting
electron systems by studying the idealized Hubbard model.
  In the present article we review some mathematically rigorous results on the
Hubbard model which shed light on ""physics"" of this fascinating model. We
mainly concentrate on magnetic properties of the model at its ground states. We
discuss Lieb-Mattis theorem on the absence of ferromagnetism in one dimension,
Koma-Tasaki bounds on decay of correlations at finite temperatures in
two-dimensions, Yamanaka-Oshikawa-Affleck theorem on low-lying excitations in
one-dimension, Lieb's important theorem for half-filled model on a bipartite
lattice, Kubo-Kishi bounds on the charge and superconducting susceptibilities
of half-filled models at finite temperatures, and three rigorous examples of
saturated ferromagnetism due to Nagaoka, Mielke, and Tasaki. We have tried to
make the article accessible to nonexperts by describing basic definitions and
elementary materials in detail.",9512169v4
1998-07-18,Delta-Function Bose Gas Picture of S=1 Antiferromagnetic Quantum Spin Chains Near Critical Fields,"We study the zero-temperature magnetization curve (M-H curve) of the S=1
bilinear-biquadratic spin chain, whose Hamiltonian is given by $H=\sum_{i} S_i
S_{i+1}+\beta (S_iS_{i+1})^2 with $0 \leq \beta <1$. We focus on validity of
the delta-function bose-gas picture near the two critical fields: the
saturation field $H_s$ and the lower critical field $H_c$ associated with the
Haldane gap. Near $H_s$, we take ``low-energy effective S-matrix'' approach,
which gives correct effective bose-gas coupling constant $c$, different from
the spin-wave value. Comparing the M-H curve of the bose gas with the
product-wavefunction renormalization group (PWFRG) calculation, excellent
agreement is seen. Near $H_c$, comparing the PWFRG result with the bose-gas
prediction, we find that there are two distinct regions of $\beta$ separated by
a critical value $\beta_c(\approx 0.41)$. In the region $0<\beta<\beta_c$, the
effective coupling $c$ is positive but rather small. The small value of $c$
makes the ``critical region'' of the square-root behavior $M\sim \sqrt{H-H_c}$
very narrow. Further, we find that in the $\beta \to \beta_c-0$, the
square-root behavior transmutes to a different one, $M\sim (H-H_c)^{1/4}$. In
the region $\beta_c<\beta <1$, the square-root behavior is rather distinct, but
the effective coupling $c$ becomes negative.",9807266v1
1999-08-16,Structural instability associated with the tilting of CuO6 octahedra in La2-xSrxCuO4,"Comprehensive inelastic neutron-scattering measurements were performed to
study the soft optical phonons in La2-xSrxCuO4 at x=0.10, 0.12 and 0.18. We
found at x=0.18 that the softening of Z-point phonon, suggesting incipient
structural transition from the low-temperature orthorhombic (LTO) to
low-temperature tetragonal (LTT) phase, breaks at Tc, which is consistent with
the previous report by Lee et al. for the optimally doped x=0.15 sample. As for
x=0.10 and 0.12, on the other hand, the softening continues even below Tc. It
is thus clarified that the breaking of soft phonon is characteristic of
La2-xSrxCuO4 in the optimally and overdoped regions. In the course of studying
the soft phonons, we discovered that a central peak remains above the LTO to
high-temperature tetragonal (HTT) phase transition at Ts1 and splits into
incommensurate components along the (1 1 0)HTT direction at higher
temperatures. This is a common feature for both x=0.12 and 0.18 and their
temperature dependences of the splitting 2d can be scaled by using a
renormalized temperature T/Ts1. In the high temperature limit, d saturates
around d ~ 0.12 r.l.u., which value is close to the splitting of incommensurate
magnetic signals. This implies that the incipient lattice modulation starts
appearing at very high temperature. Details of this modulation and its
relations with other properties are, however, not yet clarified.",9908217v1
2001-10-31,Electrodynamic response of MgB2 sintered pellets and thin films,"We present a study of the electrodynamic response of MgB2 pellets and thin
film samples exhibiting critical temperatures ranging between 26 and 38 K. We
have performed accurate measurements of the surface impedance ZS =RS+iXS as a
function of the temperature and of the magnitude of the electromagnetic field.
The temperature variation and the field dependence of ZS was measured by a
dielectric resonator cavity technique in the microwave region. In particular,
the temperature variation of the magnetic penetration depth was also determined
in the RF region by a single coil mutual inductance method. In the case of the
films, for T<TC/2 a clear exponential behavior of the penetration depth is
observed, which can be explained by a simple BCS s-wave model with a reduced
value of the energy gap. On the contrary, pellets show no evidence of
saturation, and the experimental results strictly follow a quadratic dependence
down to the lowest temperatures. This behavior can be induced by the presence
of metallic Mg inclusions that may locally depress the gap. The analysis of the
field dependence of the surface impedance in the microwave region confirms that
the electrodynamic response of MgB2 is dominated by different sources of
dissipation, depending on the sample history, likely to be ascribed to the
predominance of grain boundaries or normal regions on its surface.",0110640v1
2004-03-11,Magnetoresistance and dephasing in a two-dimensional electron gas at intermediate conductances,"We study, both theoretically and experimentally, the negative
magnetoresistance (MR) of a two-dimensional (2D) electron gas in a weak
transverse magnetic field $B$. The analysis is carried out in a wide range of
zero-$B$ conductances $g$ (measured in units of $e^2/h$), including the range
of intermediate conductances, $g\sim 1$. Interpretation of the experimental
results obtained for a 2D electron gas in GaAs/In$_x$Ga$_{1-x}$As/GaAs single
quantum well structures is based on the theory which takes into account terms
of higher orders in $1/g$, stemming from both the interference contribution and
the mutual effect of weak localization (WL) and Coulomb interaction. We
demonstrate that at intermediate conductances the negative MR is described by
the standard WL ""digamma-functions"" expression, but with a reduced prefactor
$\alpha$. We also show that at not very high $g$ the second-loop corrections
dominate over the contribution of the interaction in the Cooper channel, and
therefore appear to be the main source of the lowering of the prefactor,
$\alpha\simeq 1-2/\pi g$. We further analyze the regime of a ""weak insulator"",
when the zero-$B$ conductance is low $g(B=0)<1$ due to the localization at low
$T$, whereas the Drude conductance is high, $g_0>>1.$ In this regime, while the
MR still can be fitted by the digamma-functions formula, the experimentally
obtained value of the dephasing rate has nothing to do with the true one. The
corresponding fitting parameter in the low-$T$ limit is determined by the
localization length and may therefore saturate at $T\to 0$, even though the
true dephasing rate vanishes.",0403289v1
2004-04-06,Anomalous scaling behavior of the dynamical spin susceptibility of Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$,"Inelastic neutron scattering measurements have been performed on single
crystals of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$
in broad energy [0.1, 9.5 meV] and temperature [40 mK, 294 K] ranges in order
to address the question of scaling behavior of the dynamical spin
susceptibility at the quantum critical point of an itinerant magnetic system.
For two wavevectors $\mathbf{Q}$ corresponding to uncorrelated and
antiferromagnetically correlated spin fluctuations, it is found that the
dynamical spin susceptibility $\chi''(\mathbf{Q},E,T)$ is independent of
temperature below a cut-off temperature $T_{\mathbf{Q}}$: the spin fluctuation
amplitude saturates at low temperatures contrarily to its expected divergence
at a quantum critical point. Above $T_{\mathbf{Q}}$, a $\mathbf{Q}$-dependent
scaling behavior of the form $T\chi''(\mathbf{Q},E,T) =
C_{\mathbf{Q}}f[E/(a_{\mathbf{Q}}T^{\beta_{\mathbf{Q}}})]$ with
$\beta_{\mathbf{Q}}<1$ is obtained. This scaling does not enter the general
framework of quantum phase transition theories, since it is obtained in a high
temperature range, where Kondo spin fluctuations depend strongly on
temperature.",0404124v2
2004-07-20,Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films,"We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots
and the preparation of room-temperature ferromagnetic nanocrystalline thin
films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation
reaction in DMSO under atmospheric conditions. Synthesis was monitored by
electronic absorption and electron paramagnetic resonance (EPR) spectroscopies.
Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the
synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from
the surfaces of as-prepared nanocrystals using dodecylamine to yield
high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and
uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and
Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic
susceptibilities, confirmed that the manganese is substitutionally incorporated
into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing
from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was
observed in spin-coated thin films of the nanocrystals, with 300 K saturation
moments as large as 1.35 Bohr magneton/Mn2+ and TC > 350 K. A distinct
ferromagnetic resonance signal was observed in the EPR spectra of the
ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its
dependence on synthetic variables are discussed in the context of these and
previous theoretical and experimental results.",0407500v1
2004-11-16,Upper Critical Fields up to 60T in Dirty Magnesium Diboride Thin Films,"Upper critical fields of several magnesium diboride thin films were measured
up to 28 T at the Grenoble High Magnetic Field Laboratory (GHMFL) in Grenoble
and up to 60 T at the Laboratoire National des Champs Magnetiques Pulses
(LNCMP) in Toulouse. The samples were prepared both by pulsed laser deposition
(PLD) and hybrid physical chemical vapour deposition (HPCVD) technique; they
have critical temperatures between 29 and 39 K and normal state resistivities
between 5 and 250 &#956;ohmcm; one of them has been intentionally doped with
carbon. The measured critical fields were exceptionally high; we obtained the
record value of 52 T at 4.2 K in the parallel orientation. In contrast with the
BCS predictions, no saturation in Hc2 at low temperature was observed.
Furthermore, films with a wide range of resistivity values showed similar
critical fields, suggesting that in a two band system resistivity and Hc2 are
not trivially linked. The high Hc2 values seem to be related with the expanded
c-axis. The structure of one of the samples was carefully investigated with
X-ray diffraction at European Synchrotron Radiation Facility (ESRF) in
Grenoble.",0411404v1
2005-01-12,Current induced magnetization switching in exchange biased spin-valves for CPP-GMR heads,"In contrast to earlier studies performed on simple Co/Cu/Co sandwiches, we
have investigated spin transfer effects in complex spin-valve pillars with a
diameter of 130nm developed for current-perpendicular to the plane (CPP)
magneto-resistive heads. The structure of the samples included an exchange
biased synthetic pinned layer and a free layer both laminated by insertion of
several ultrathin Cu layers. Despite the small thickness of the polarizing
layer, our results show that the free layer can be switched between the
parallel (P) and the antiparallel (AP) states by applying current densities of
the order of 10^7 A/cm^2. A strong asymmetry is observed between the two
critical currents IcAP-P and IcP-AP, as predicted by the model of Slonczewski
model. Thanks to the use of exchange biased structures, the stability phase
diagrams could be obtained in the four quadrants of the (H, I) plan. The
critical lines derived from the magnetoresistance curves measured with
different sense currents, and from the resistance versus current curves
measured for different applied fields, match each other very well. The main
features of the phase diagrams can be reproduced by investigating the stability
of the solutions of the Landau Lifshitz Gilbert equation including spin torque
term within a macrospin model. A spin-transfer saturation effect was observed
in the positive currents range. We attribute it to a de-depolarization effect
which appears as a consequence of the asymmetric heating of the pillars, whose
top and the bottom leads are made of different materials.",0501281v1
2005-05-09,"Prospects of high temperature ferromagnetism in (Ga,Mn)As semiconductors","We report on a comprehensive combined experimental and theoretical study of
Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad
agreement between theoretical expectations and measured data allows us to
conclude that T_c in high-quality metallic samples increases linearly with the
number of uncompensated local moments on Mn_Ga acceptors, with no sign of
saturation. Room temperature ferromagnetism is expected for a 10% concentration
of these local moments. Our magnetotransport and magnetization data are
consistnent with the picture in which Mn impurities incorporated during growth
at interstitial Mn_I positions act as double-donors and compensate neighboring
Mn_Ga local moments because of strong near-neighbor Mn_Ga-Mn_I
antiferromagnetic coupling. These defects can be efficiently removed by
post-growth annealing. Our analysis suggests that there is no fundamental
obstacle to substitutional Mn_Ga doping in high-quality materials beyond our
current maximum level of 6.2%, although this achievement will require further
advances in growth condition control. Modest charge compensation does not limit
the maximum Curie temperature possible in ferromagnetic semiconductors based on
(Ga,Mn)As.",0505215v1
2006-08-30,Spin-quadrupole ordering of spin-3/2 ultracold fermionic atoms in optical lattices in the one-band Hubbard model,"Based on a generalized one-band Hubbard model, we study magnetic properties
of Mott insulating states for ultracold spin-3/2 fermionic atoms in optical
lattices. When the \textit{s}-wave scattering lengths for the total spin
$S=2,0$ satisfy conditions $a_{2}>a_{0}>0$, we apply a functional integral
approach to the half filled case, where the spin-quadrupole fluctuations
dominate. On a 2D square lattice, the saddle point solution yields a staggered
spin-quadrupole ordering at zero temperature with symmetry breaking from SO(5)
to SO(4). Both spin and spin-quadrupole static structure factors are
calculated, displaying highly anisotropic spin antiferromagnetic fluctuations
and antiferroquadrupole long-range correlations, respectively. When Gaussian
fluctuations around the saddle point are taken into account, spin-quadrupole
density waves with a linear dispersion are derived. Compared with the spin
density waves in the half filled spin-1/2 Hubbard model, the quadrupole density
wave velocity is saturated in the strong-coupling limit, and there are no
transverse spin-quadrupole mode couplings, as required by the SO(4) invariance
of the effective action. Finally, in the strong-coupling limit of the model
Hamiltonian, we derive the effective hyperfine spin-exchange interactions for
the Mott insulating phases in the quarter filled and half filled cases,
respectively.",0608673v3
2006-04-04,Deconfinement in dense 2-color QCD,"We study SU(2) lattice gauge theory with two flavors of Wilson fermion at
non-zero chemical potential mu and low temperature on a 8^3x16 system. We
identify three regimes along the mu-axis. For mu<~m_pi/2 the system remains in
the vacuum phase, and all physical observables considered remain essentially
unchanged. The intermediate regime is characterised by a non-zero diquark
condensate and an associated increase in the baryon density, consistent with
what is expected for Bose-Einstein condensation of tightly bound diquarks. We
also observe screening of the static quark potential here. In the high-density
deconfined regime we find a non-zero Polyakov loop and a strong modification of
the gluon propagator, including significant screening in the magnetic sector in
the static limit, which must have a non-perturbative origin. The behaviour of
thermodynamic observables and the superfluid order parameter are consistent
with a Fermi surface disrupted by a BCS diquark condensate. The energy per
baryon as a function of mu exhibits a minimum in the deconfined regime,
implying that macroscopic objects such as stars formed in this theory are
largely composed of quark matter.",0604004v2
1995-07-09,"Long Distance Contribution to $s \to dγ$ and Implications for $Ω^-\to Ξ^-γ, B_s \to B_d^*γ$ and $b \to sγ$","We estimate the long distance (LD) contribution to the magnetic part of the
$s \to d\gamma$ transition using the Vector Meson Dominance approximation
$(V=\rho,\omega,\psi_i)$. We find that this contribution may be significantly
larger than the short distance (SD) contribution to $s \to d\gamma$ and could
possibly saturate the present experimental upper bound on the $\Omega^-\to
\Xi^-\gamma$ decay rate, $\Gamma^{\rm MAX}_{\Omega^-\to \Xi^-\gamma} \simeq
3.7\times10^{-9}$eV. For the decay $B_s \to B^*_d\gamma$, which is driven by $s
\to d\gamma$ as well, we obtain an upper bound on the branching ratio $BR(B_s
\to B_d^*\gamma)<3\times10^{-8}$ from $\Gamma^{\rm MAX}_{\Omega^-\to
\Xi^-\gamma}$. Barring the possibility that the Quantum Chromodynamics
coefficient $a_2(m_s)$ be much smaller than 1, $\Gamma^{\rm MAX}_{\Omega^-\to
\Xi^-\gamma}$ also implies the approximate relation $\frac{2}{3} \sum_i
\frac{g^2_{\psi_i}(0)}{m^2_{\psi_i}} \simeq \frac{1}{2}
\frac{g^2_\rho(0)}{m^2_\rho} + \frac{1}{6}\frac{g^2_\omega(0)}{m^2_\omega}$.
This relation agrees quantitatively with a recent independent estimate of the
l.h.s. by Deshpande et al., confirming that the LD contributions to $b \to
s\gamma$ are small. We find that these amount to an increase of $(4\pm2)\%$ in
the magnitude of the $b \to s \gamma$ transition amplitude, relative to the SD
contribution alone.",9507267v1
1992-05-13,Supersymmetry as a Cosmic Censor,"In supersymmetric theories the mass of any state is bounded below by the
values of some of its charges. The corresponding bounds in case of
Schwarzschild and Reissner-Nordstr\""om black holes are known to coincide with
the requirement that naked singularities be absent. Here we investigate charged
dilaton black holes in this context. We show that the extreme solutions
saturate the supersymmetry bound of $N=4\ d=4$ supergravity, or dimensionally
reduced superstring theory. Specifically, we have shown that extreme dilaton
black holes, with electric and magnetic charges, admit super-covariantly
constant spinors. The supersymmetric positivity bound for dilaton black holes,
$M \geq \frac{1}{\sqrt 2}(|Q|+|P|)$, takes care of the absence of naked
singularities of the dilaton black holes and is, in this sense, equivalent to
the cosmic censorship condition. The temperature, entropy and singularity are
discussed. The Euclidean action (entropy) of the extreme black hole is given by
$2\pi |PQ|$. We argue that this result, as well as the one for Lorentzian
signature, is not altered by higher order corrections in the supersymmetric
theory. When a black hole reaches its extreme limit, it cannot continue to
evaporate by emitting elementary particles, since this would violate the
supersymmetric positivity bound. We speculate on the possibility that an
extreme black hole may ``evaporate"" by emitting smaller extreme black holes.",9205027v1
2003-12-01,D-term strings,"We study the embedding of cosmic strings, related to the
Abrikosov-Nielsen-Olesen vortex solution, into d=4, N=1 supergravity. We find
that the local cosmic string solution which saturates the BPS bound of
supergravity with $D$-term potential for the Higgs field and with constant
Fayet--Iliopoulos term, has 1/2 of supersymmetry unbroken. We observe an
interesting relation between the gravitino supersymmetry transformation,
positive energy condition and the deficit angle of the cosmic string. We argue
that the string solutions with magnetic flux with F-term potential cannot be
supersymmetric, which leads us to a conjecture that D1-strings (wrapped
D(1+q)-branes) of string theory in the effective 4d supergravity are described
by the D-term strings that we study in this paper. We give various consistency
checks of this conjecture, and show that it highlights some generic properties
of non-BPS string theory backgrounds, such as brane-anti-brane systems.
Supersymmetry breaking by such systems can be viewed as FI D-term breaking,
which implies, under certain conditions, the presence of gauged R-symmetry on
such backgrounds. The D-term nature of the brane-anti-brane energy can also
provide information on the superpotential for the tachyon, which Higgses the
R-symmetry. In this picture, the inter-brane force can be viewed as a result of
the world-volume gauge coupling renormalization by the open string loops.",0312005v3
2000-03-23,Enhanced dielectronic recombination of lithium-like Ti19+ ions in external ExB fields,"Dielectronic recombination(DR) of lithium-like Ti19+(1s2 2s) ions via 2s->2p
core excitations has been measured at the Heidelberg heavy ion storage ring
TSR. We find that not only external electric fields (0 <= Ey <= 280 V/cm) but
also crossed magnetic fields (30 mT <= Bz <= 80 mT) influence the DR via high-n
(2p_j nl)-Rydberg resonances. This result confirms our previous finding for
isoelectronic Cl14+ ions [Bartsch T et al, PRL 82, 3779 (1999)] that
experimentally established the sensitivity of DR to ExB fields. In the present
investigation the larger 2p_{1/2}-2p_{3/2} fine structure splitting of Ti19+
allowed us to study separately the influence of external fields via the two
series of Rydberg DR resonances attached to the 2s -> 2p_{1/2} and 2s ->
2p_{3/2} excitations of the Li-like core, extracting initial slopes and
saturation fields of the enhancement. We find that for Ey > 80 V/cm the field
induced enhancement is about 1.8 times stronger for the 2p_{3/2} series than
for the 2p_{1/2} series.",0003055v2
2003-12-11,"Start-to-End Simulations of SASE FEL at the TESLA Test Facility, Phase 1","Phase 1 of the vacuum ultra-violet (VUV) free-electron laser (FEL) at the
TESLA Test Facility (TTF) recently concluded operation. It successfully
demonstrated the saturation of a SASE FEL in the in the wavelength range of
80-120 nm. We present a posteriori start-to-end numerical simulations of this
FEL. These simulations are based on the programs Astra and elegant for the
generation and transport of the electron distribution. An independent
simulation of the intricate beam dynamics in the magnetic bunch compressor is
performed with the program CSRtrack. The SASE FEL process is simulated with the
code FAST. From our detailed simulations and the resulting phase space
distribution at the undulator entrance, we found that the FEL was driven only
by a small fraction (slice) of the electron bunch. This ""lasing slice"" is
located in the head of the bunch, and has a peak current of approximately 3 kA.
A strong energy chirp (due to the space charge field after compression) within
this slice had a significant influence on the FEL operation. Our study shows
that the radiation pulse duration is about 40 fs (FWHM) with a corresponding
peak power of 1.5 GW. The simulated FEL properties are compared with various
experimental data and found to be in excellent agreement.",0312074v1
2007-07-16,Blue laser cooling transitions in Tm I,"We have studied possible candidates for laser cooling transitions in
$^{169}$Tm in the spectral region 410 -- 420 nm. By means of saturation
absorption spectroscopy we have measured the hyperfine structure and rates of
two nearly closed cycling transitions from the ground state
$4\textrm{f}^{13}6\textrm{s}^2(^2\textrm{F}_0)(J_g=7/2)$ to upper states
$4\textrm{f}^{12}(^3\textrm{H}_5)5\textrm{d}_{3/2}6\textrm{s}^2(J_e=9/2)$ at
410.6 nm and
$4\textrm{f}^{12}(^3\textrm{F}_4)5\textrm{d}_{5/2}6\textrm{s}^2(J_e=9/2)$ at
420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and
48(6) ns respectively. Decay rates from these levels to neighboring
opposite-parity levels are evaluated by means of Hartree-Fock calculations. We
conclude, that the strong transition at 410.6 nm has an optical leak rate of
less then $2\cdot10^{-5}$ and can be used for efficient laser cooling of
$^{169}$Tm from a thermal atomic beam. The hyperfine structure of two other
even-parity levels which can be excited from the ground state at 409.5 nm and
418.9 nm is also measured by the same technique. In addition we give a
calculated value of $7(2)$ s$^{-1}$ for the rate of magnetic-dipole transition
at 1.14 $\mu$m between the fine structure levels
$(J_g=7/2)\leftrightarrow(J'_g=5/2)$ of the ground state which can be
considered as a candidate for applications in atomic clocks.",0707.2280v2
2007-10-01,Highly Efficient Modeling of Dynamic Coronal Loops,"Observational and theoretical evidence suggests that coronal heating is
impulsive and occurs on very small cross-field spatial scales. A single coronal
loop could contain a hundred or more individual strands that are heated
quasi-independently by nanoflares. It is therefore an enormous undertaking to
model an entire active region or the global corona. Three-dimensional MHD codes
have inadequate spatial resolution, and 1D hydro codes are too slow to simulate
the many thousands of elemental strands that must be treated in a reasonable
representation. Fortunately, thermal conduction and flows tend to smooth out
plasma gradients along the magnetic field, so ""0D models"" are an acceptable
alternative. We have developed a highly efficient model called Enthalpy-Based
Thermal Evolution of Loops (EBTEL) that accurately describes the evolution of
the average temperature, pressure, and density along a coronal strand. It
improves significantly upon earlier models of this type--in accuracy,
flexibility, and capability. It treats both slowly varying and highly impulsive
coronal heating; it provides the differential emission measure distribution,
DEM(T), at the transition region footpoints; and there are options for heat
flux saturation and nonthermal electron beam heating. EBTEL gives excellent
agreement with far more sophisticated 1D hydro simulations despite using four
orders of magnitude less computing time. It promises to be a powerful new tool
for solar and stellar studies.",0710.0185v2
2007-12-07,Locality and low-dimensions in the prediction of natural experience from fMRI,"Functional Magnetic Resonance Imaging (fMRI) provides dynamical access into
the complex functioning of the human brain, detailing the hemodynamic activity
of thousands of voxels during hundreds of sequential time points. One approach
towards illuminating the connection between fMRI and cognitive function is
through decoding; how do the time series of voxel activities combine to provide
information about internal and external experience? Here we seek models of fMRI
decoding which are balanced between the simplicity of their interpretation and
the effectiveness of their prediction. We use signals from a subject immersed
in virtual reality to compare global and local methods of prediction applying
both linear and nonlinear techniques of dimensionality reduction. We find that
the prediction of complex stimuli is remarkably low-dimensional, saturating
with less than 100 features. In particular, we build effective models based on
the decorrelated components of cognitive activity in the classically-defined
Brodmann areas. For some of the stimuli, the top predictive areas were
surprisingly transparent, including Wernicke's area for verbal instructions,
visual cortex for facial and body features, and visual-temporal regions for
velocity. Direct sensory experience resulted in the most robust predictions,
with the highest correlation ($c \sim 0.8$) between the predicted and
experienced time series of verbal instructions. Techniques based on non-linear
dimensionality reduction (Laplacian eigenmaps) performed similarly. The
interpretability and relative simplicity of our approach provides a conceptual
basis upon which to build more sophisticated techniques for fMRI decoding and
offers a window into cognitive function during dynamic, natural experience.",0712.1219v2
2008-04-29,Phase Diagram and Entanglement of Ising Model With Dzyaloshinskii-Moriya Interaction,"We have studied the phase diagram and entanglement of the one dimensional
Ising model with Dzyaloshinskii-Moriya (DM) interaction. We have applied the
quantum renormalization group (QRG) approach to get the stable fixed points,
critical point and the scaling of coupling constants. This model has two
phases, antiferromagnetic and saturated chiral ones. We have shown that the
staggered magnetization is the order parameter of the system and DM interaction
produces the chiral order in both phases. We have also implemented the exact
diagonalization (Lanczos) method to calculate the static structure factors. The
divergence of structure factor at the ordering momentum as the size of systems
goes to infinity defines the critical point of the model. Moreover, we have
analyzed the relevance of the entanglement in the model which allows us to shed
insight on how the critical point is touched as the size of the system becomes
large. Nonanalytic behavior of entanglement and finite size scaling have been
analyzed which is tightly connected to the critical properties of the model. It
is also suggested that a spin-fluid phase has a chiral order in terms of new
spin operators which are defined by a nonlocal transformation.",0804.4579v3
2008-06-05,The sawtooth chain: From Heisenberg spins to Hubbard electrons,"We report on recent studies of the spin-half Heisenberg and the Hubbard model
on the sawtooth chain. For both models we construct a class of exact
eigenstates which are localized due to the frustrating geometry of the lattice
for a certain relation of the exchange (hopping) integrals. Although these
eigenstates differ in details for the two models because of the different
statistics, they share some characteristic features. The localized eigenstates
are highly degenerate and become ground states in high magnetic fields
(Heisenberg model) or at certain electron fillings (Hubbard model),
respectively. They may dominate the low-temperature thermodynamics and lead to
an extra low-temperature maximum in the specific heat. The ground-state
degeneracy can be calculated exactly by a mapping of the manifold of localized
ground states onto a classical hard-dimer problem, and explicit expressions for
thermodynamic quantities can be derived which are valid at low temperatures
near the saturation field for the Heisenberg model or around a certain value of
the chemical potential for the Hubbard model, respectively.",0806.0922v2
2008-06-28,Spin-dependent scattering in a silicon transistor,"The scattering of conduction electrons off neutral donors depends sensitively
on the relative orientation of their spin states. We present a theory of
spin-dependent scattering in the two dimensional electron gas (2DEG) of field
effect transistors. Our theory shows that the scattering mechanism is dominated
by virtual transitions to negatively ionized donor levels. This effect
translates into a source-drain current that always gets reduced when donor
spins are at resonance with a strong microwave field. We propose a model for
donor impurities interacting with conduction electrons in a silicon transistor,
and compare our explicit numerical calculations to electrically detected
magnetic resonance (EDMR) experiments. Remarkably, we show that EDMR is optimal
for donors placed into a sweet spot located at a narrow depth window quite far
from the 2DEG interface. This allows significant optimization of spin signal
intensity for the minimal number of donors placed into the sweet spot, enabling
the development of single spin readout devices. Our theory reveals an
interesting dependence on conduction electron spin polarization p_c. As p_c
increases upon spin injection, the EDMR amplitude first increases as p_{c}^{2},
and then saturates when a polarization threshold p_T is reached. These results
show that it is possible to use EDMR as an in-situ probe of carrier spin
polarization in silicon and other materials with weak spin-orbit coupling.",0806.4638v3
2008-09-23,Dissipation and Heating in Supersonic Hydrodynamic and MHD Turbulence,"We study energy dissipation and heating by supersonic MHD turbulence in
molecular clouds using Athena, a new higher-order Godunov code. We analyze the
dependence of the saturation amplitude, energy dissipation characteristics,
power spectra, sonic scaling, and indicators of intermittency in the turbulence
on factors such as the magnetic field strength, driving scale, energy injection
rate, and numerical resolution. While convergence in the energies is reached at
moderate resolutions, we find that the power spectra require much higher
resolutions that are difficult to obtain. In a 1024^3 hydro run, we find a
power law relationship between the velocity dispersion and the spatial scale on
which it is measured, while for an MHD run at the same resolution we find no
such power law. The time-variability and temperature intermittency in the
turbulence both show a dependence on the driving scale, indicating that
numerically driving turbulence by an arbitrary mechanism may not allow a
realistic representation of these properties. We also note similar features in
the power spectrum of the compressive component of velocity for supersonic MHD
turbulence as in the velocity spectrum of an initially-spherical MHD blast
wave, implying that the power law form does not rule out shocks, rather than a
turbulent cascade, playing a significant role in the regulation of energy
transfer between spatial scales.",0809.4005v1
2008-09-24,Discovery of X-ray emission from the eclipsing brown-dwarf binary 2MASS J05352184-0546085,"The eclipsing brown-dwarf binary system 2MASS J05352184-0546085 is a case sui
generis. For the first time, it allows a detailed analysis of the individual
properties of young brown dwarfs, in particular, masses, and radii, and the
temperature ratio of the system components can be determined accurately. The
system shows a ""temperature reversal"" with the more massive component being the
cooler one, and both components are found to be active. We analyze X-ray images
obtained by Chandra and XMM-Newton containing 2MASS J05352184-0546085 in their
respective field of view. The Chandra observatory data show a clear X-ray
source at the position of 2MASS J05352184-0546085, whereas the XMM-Newton data
suffer from contamination from other nearby sources, but are consistent with
the Chandra detection. No indications of flaring activity are found in either
of the observations (together about 70 ks), and we thus attribute the observed
flux to quiescent emission. With an X-ray luminosity of 3*10^{28} erg/s we find
an L_X/L_{bol}-ratio close to the saturation limit of 10^{-3} and an
L_{X}/L_{H\alpha}-ratio consistent with values obtained from low-mass stars.
The X-ray detection of 2MASS J05352184-0546085 reported here provides
additional support for the interpretation of the temperature reversal in terms
of magnetically suppressed convection, and suggests that the activity phenomena
of young brown dwarfs resemble those of their more massive counterparts.",0809.4129v1
2008-11-14,Reduction of the field-dependent microwave surface resistance in YBa_2Cu_3O_7 with sub-micrometric BaZrO_3 inclusions as a function of BaZrO_3 concentration,"In order to study the vortex pinning determined by artificially introduced
pinning centers in the small-vortex displacement regime, we measured the
microwave surface impedance at 47.7 GHz in the mixed state of
YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ thin films, where sub-micrometric BaZrO$_3$
particles have been incorporated. As a function of the BaZrO$_3$ content, we
observe that the absolute losses slightly decrease up to a BaZrO$_3$ content of
5%, and then increase. We found that the magnetic-field-induced losses behave
differently, in that they are not monotonic with increasing BaZrO$_3$
concentration: at small concentration (2.5%) the field-induced losses increase,
but large reduction of the losses themselves, by factors up to 3, is observed
upon further increasing the BaZrO$_3$ concentration in the target up to 7%.
Using measurements of both surface resistance and surface reactance we estimate
vortex pinning-related parameters. We find that BaZrO$_3$ inclusions introduce
deep and steep pinning wells. In particular, the minimum height of the energy
barrier for single vortices is raised. At larger BaZrO$_3$ content (5% and 7%)
the phenomenon is at its maximum, but it is unclear whether it shows a
saturation or not, thus leaving room for further improvements.",0811.2351v1
2008-12-26,Flux quanta driven by high-density currents in low-impurity V3Si and LuNi2B2C: free flux flow and flux-core size effect,"High density direct currents (DC) are used to drive flux quanta via the
Lorentz force towards a highly ordered ""free flux flow"" (FFF) dynamic state,
made possible by the weak-pinning environment of high-quality, single-crystal
samples of two low-Tc superconducting compounds, V3Si and LuNi2B2C. We report
the effect of the magnetic field-dependent fluxon core size on flux flow
resistivity rho_f. Much progress has been made in minimizing the technical
challenges associated with the use of high currents. Attainment of a FFF phase
is indicated by the saturation at highest currents of flux-flow dissipation
levels that are well below the normal state resistance and have field-dependent
values. The field dependence of the corresponding rho_f is shown to be
consistent with a prediction based on a model for the decrease of flux core
size at higher fields in weak-coupling BCS s-wave materials.",0812.4715v4
2009-02-11,Non-exponential London penetration depth in Ba$_{1-}$K$_{x}$Fe$_{2}$As$_{2}$ single crystals,"We have studied the in- and out-of-plane magnetic penetration depths in the
hole- doped iron based superconductor Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$
($T_{c}\approx$ 30K). The study was performed on single crystals grown from
different fluxes and we find that the results are nearly the same. The in-plane
London penetration depth $\lambda_{ab}$ does not show exponential saturation at
low temperature, as would be expected from a fully gapped superconductor.
Instead, $\lambda_{ab}(T)$ shows a power-law behavior, $\lambda\propto T^{n}$
($n\approx 2$), down to $T\approx 0.02 T_{c}$, similar to the electron doped
Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$. The penetration depth anisotropy
$\gamma_{\lambda}=\lambda_{c}(T)/\lambda_{ab}(T)$ increases upon cooling,
opposite to the trend observed in the anisotropy of the upper critical field,
$\gamma_{\xi}=H_{c2}^{\perp c}(0)/H_{c2}^{\parallel c}(0)$. These are universal
characteristics of both the electron and hole doped 122 systems, suggesting
unconventional superconductivity. The behavior of the in-plane superfluid
density $\rho_{ab}(T)$ is discussed in light of existing theoretical models
proposed for the iron pnictides superconductors.",0902.1804v1
2009-02-12,"Manganite charge and orbitally ordered and disordered states probed by Fe substitution into Mn site in LnBaMn1.96Fe0.04O5, LnBaMn1.96Fe0.04O6 and LnBaMn1.96Fe0.04O5.5 (Ln=Y, Gd, Sm, Nd, Pr, La)","The layered manganese oxides LnBaMn1.96Fe0.04Oy (Ln=Y, Gd, Sm, Nd, Pr, La)
have been synthesized for y=5, 5.5 and 6. In the oxygen-saturated state (y=6)
they exhibit the charge and orbital order at ambient temperature for Ln=Y, Gd,
Sm, but unordered eg-electronic system for Ln=La,Pr,Nd. Fourfold increase of
quadrupole splitting was observed owing to the charge and orbital ordering.
This is in agreement with the jumplike increase in distortion of the reduced
perovskite-like cell for the charge and orbitally ordered manganites compared
to the unordered ones. Substitution of 2 percents of Mn by Fe suppresses the
temperatures of structural and magnetic transitions by 20 to 50 K. Parameters
of the crystal lattices and the room-temperature M\""{o}ssbauer spectra were
studied on forty samples whose structures were refined within five symmetry
groups: P4/mmm, P4/nmm, Pm-3m, Icma and P2/m. Overwhelming majority of the Fe
species are undifferentiated in the M\""{o}ssbauer spectra for most of the
samples. Such the single-component spectra in the two-site structures are
explained by the preference of Fe towards the site of Mn(III) and by the
segmentation of the charge and orbitally ordered domains.",0902.2027v2
2009-02-15,Sudden Critical Current Drops Induced in S/F Structures,"In the search for new physical properties of S/F structures, we have found
that the superconductor critical current can be controlled by the domain state
of the neighboring ferromagnet. The superconductor is a thin wire of thickness
d_{s} ~ 2 xi_{S}. Nb/Co and Nb/Py (Permalloy Ni_{80}Fe_{20}) bilayer structures
were grown with a significant magnetic anisotropy. Critical current
measurements of Nb/Co structures with ferromagnet thickness d_{F} > 30nm show
sudden drops in two very defined steps when the measurements are made along the
hard axes direction (i.e. current track parallel to hard anisotropy axes
direction). These drops disappear when they are made along the easy axis
direction or when the ferromagnet thickness is below 30nm. The drops are
accompanied by vortex flux flow. In addition magnetorestistance measurements
close to Tc show a sharp increase near saturation fields of the ferromagnet.
Similar results are reproduced in Nb/Py bilayer structure with the ferromagnet
thickness d_{F} ~ 50nm along the easy anisotropy axes. These results are
explained as being due to spontaneous vortex formation and flow induced by
Bloch domain walls of the ferromagnet underneath. We argue these Bloch domain
walls produce a 2D vortex-antivortex lattice structure.",0902.2572v2
2009-08-17,Criticality in the randomness-induced second-order phase transition of the triangular Ising antiferromagnet with nearest- and next-nearest-neighbor interactions,"Using a Wang-Landau entropic sampling scheme, we investigate the effects of
quenched bond randomness on a particular case of a triangular Ising model with
nearest- ($J_{nn}$) and next-nearest-neighbor ($J_{nnn}$) antiferromagnetic
interactions. We consider the case $R=J_{nnn}/J_{nn}=1$, for which the pure
model is known to have a columnar ground state where rows of nearest-neighbor
spins up and down alternate and undergoes a weak first-order phase transition
from the ordered to the paramagnetic state. With the introduction of quenched
bond randomness we observe the effects signaling the expected conversion of the
first-order phase transition to a second-order phase transition and using the
Lee-Kosterlitz method, we quantitatively verify this conversion. The emerging,
under random bonds, continuous transition shows a strongly saturating specific
heat behavior, corresponding to a negative exponent $\alpha$, and belongs to a
new distinctive universality class with $\nu=1.135(11)$, $\gamma/\nu=1.744(9)$,
and $\beta/\nu=0.124(8)$. Thus, our results for the critical exponents support
an extensive but weak universality and the emerged continuous transition has
the same magnetic critical exponent (but a different thermal critical exponent)
as a wide variety of two-dimensional (2d) systems without and with quenched
disorder.",0908.2298v1
2009-09-15,Quantum machine using cold atoms,"For a machine to be useful in practice, it preferably has to meet two
requirements: namely, (i) to be able to perform work under a load and (ii) its
operational regime should ideally not depend on the time at which the machine
is switched-on. We devise a minimal setup, consisting of two atoms only, for an
ac-driven quantum motor which fulfills both these conditions. Explicitly, the
motor consists of two different interacting atoms placed into a ring-shaped
periodic optical potential -- an optical ""bracelet"" --, resulting from the
interference of two counter-propagating Laguerre-Gauss laser beams. This
bracelet is additionally threaded by a pulsating magnetic flux. While the first
atom plays a role of a quantum ""carrier"", the second serves as a quantum
""starter"", which sets off the ""carrier"" into a steady rotational motion. For
fixed zero-momentum initial conditions the asymptotic carrier velocity
saturates to a unique, nonzero value which becomes increasingly independent on
the starting time with increasing ""bracelet""-size. We identify the quantum
mechanisms of rectification and demonstrate that our quantum motor is able to
perform useful work.",0909.2813v2
2009-11-12,Comparisons and Connections between Mean Field Dynamo Theory and Accretion Disc Theory,"The origin of large scale magnetic fields in astrophysical rotators, and the
conversion of gravitational energy into radiation near stars and compact
objects via accretion have been subjects of active research for a half century.
Magnetohydrodynamic turbulence makes both problems highly nonlinear, so both
subjects have benefitted from numerical simulations.However, understanding the
key principles and practical modeling of observations warrants testable
semi-analytic mean field theories that distill the essential physics. Mean
field dynamo (MFD) theory and alpha-viscosity accretion disc theory exemplify
this pursuit. That the latter is a mean field theory is not always made
explicit but the combination of turbulence and global symmetry imply such. The
more commonly explicit presentation of assumptions in 20th century textbook
MFDT has exposed it to arguably more widespread criticism than incurred by 20th
century alpha-accretion theory despite complementary weaknesses. In the 21st
century however, MFDT has experienced a breakthrough with a dynamical
saturation theory that consistently agrees with simulations. Such has not yet
occurred in accretion disc theory, though progress is emerging. Ironically
however, for accretion engines, MFDT and accretion theory are presently two
artificially uncoupled pieces of what should be a single coupled theory. Large
scale fields and accretion flows are dynamically intertwined because large
scale fields likely play a key role in angular momentum transport. I discuss
and synthesize aspects of recent progress in MFDT and accretion disc theory to
suggest why the two likely conspire in a unified theory.",0911.2315v2
2010-05-11,Spin susceptibility of interacting two-dimensional electrons in the presence of spin-orbit coupling,"A long-range interaction via virtual particle-hole pairs between Fermi-liquid
quasiparticles leads to a nonanalytic behavior of the spin susceptibility
$\chi$ as a function of the temperature ($T$), magnetic field ($\mathbf{B}$),
and wavenumber. In this paper, we study the effect of the Rashba spin-orbit
interaction (SOI) on the nonanalytic behavior of $\chi$ for a two-dimensional
electron liquid. Although the SOI breaks the SU(2) symmetry, it does not
eliminate nonanalyticity but rather makes it anisotropic: while the linear
scaling of $\chi_{zz}$ with $T$ and $|\mathbf{B}|$ saturates at the energy
scale set by the SOI, that of $\chi_{xx}$ ($=\chi_{yy}$) continues through this
energy scale, until renormalization of the electron-electron interaction in the
Cooper channel becomes important. We show that the Renormalization Group flow
in the Cooper channel has a non-trivial fixed point, and study the consequences
of this fixed point for the nonanalytic behavior of $\chi$. An immediate
consequence of SOI-induced anisotropy in the nonanalytic behavior of $\chi$ is
a possible instability of a second-order ferromagnetic quantum phase transition
with respect to a first-order transition to an XY ferromagnetic state.",1005.1913v2
2011-02-13,The fratricide of alpha-Omega dynamos by their alpha-squared siblings,"Context. Helically forced magneto-hydrodynamic shearing-sheet turbulence can
support different large-scale dynamo modes, although the {\alpha} - {\Omega}
mode is generally expected to dominate because it is the fastest growing. In an
{\alpha} - {\Omega} dynamo, most of the field amplification is produced by the
shear. As differential rotation is an ubiquitous source of shear in
astrophysics, such dynamos are believed to be the source of most astrophysical
large-scale magnetic fields. Aims. We study the stability of oscillatory
migratory {\alpha} - {\Omega} type dynamos in turbulence simulations. Methods.
We use shearing-sheet simulations of hydromagnetic turbulence that is helically
forced at a wavenumber that is about three times larger than the lowest
wavenumber in the domain so that both {\alpha} - {\Omega} and {\alpha}2 dynamo
action is possible. Results. After initial dominance and saturation, the
{\alpha} - {\Omega} mode is found to be destroyed by an orthogonal {\alpha}2
mode sustained by the helical turbulence alone. We show that there are at least
two processes through which this transition can occur. Conclusions. The
fratricide of {\alpha} - {\Omega} dynamos by its {\alpha}2 sibling is discussed
in the context of grand minima of solar and stellar activity. However, the
genesis of {\alpha} - {\Omega} dynamos from an {\alpha}2 dynamo has not yet
been found.",1102.2617v1
2011-03-23,Galactic centre star formation writ large in gamma-rays,"We have modelled the high-energy astrophysics of the inner 200 pc of the
Galaxy with a view to explaining the diffuse, broad-band (radio continuum to
TeV gamma-ray), non-thermal signal detected from this region. Our modelling
pins down the ISM parameters for the environment wherein cosmic ray (CR)
electrons and ions reside in the Galactic centre (GC). We find that the
magnetic field in this region is 100-300 microG, the gas density < 60 cm^-3,
and that a powerful (> 200 km/s) 'super'-wind acts to remove > 95% of the
cosmic rays accelerated in the region before they have time to lose their
energy in situ. The ~ 10^39 erg/s carried away by the GC cosmic ray protons is
precisely enough to energise the ~GeV gamma-ray emission from the Fermi
'bubbles' recently found to extend north and south of the GC out to distances
of ~10 kpc, provided that the bubbles constitute thick targets to the GC
protons and that the situation has reached steady state. In such a situation of
'saturation' the hard, uniform spectrum of the bubbles are explained and
secondary electron synchrotron explains the non-thermal microwave emission
found in WMAP data mirroring the bubbles. Given the very low density of the
bubble plasma (<0.01 cm^-3), the pp loss time in the Bubbles is > 5 Gyr. Our
scenario thus has the startling implication that a GC source of nonthermal
particles of time-averaged power 10^39 erg/s has persisted since the youth of
the Galaxy.",1103.4523v2
2012-01-12,Detection of accretion X-rays from QS Vir: cataclysmic or a lot of hot air?,"An XMM-Newton observation of the nearby ""pre-cataclysmic"" short-period (P_orb
= 3.62 hr) binary QS Vir (EC 13471-1258) revealed regular narrow X-ray eclipses
when the white dwarf passed behind its M2-4 dwarf companion. The X-ray emission
provides a clear signature of mass transfer and accretion onto the white dwarf.
The low-resolution XMM-Newton EPIC spectra are consistent with a cooling flow
model and indicate an accretion rate of Mdot= 1.7\times10^-13M\odot/yr. At 48
pc distant, QS Vir is then the second nearest accreting cataclysmic variable
known, with one of the lowest accretion rates found to date for a non-magnetic
system. To feed this accretion through a wind would require a wind mass loss
rate of Mdot ~ 2 \times 10^-12M\odot/yr if the accretion efficiency is of the
order of 10%. Consideration of likely mass loss rates for M dwarfs suggests
this is improbably high and pure wind accretion unlikely. A lack of accretion
disk signatures also presents some difficulties for direct Roche lobe overflow.
We speculate that QS Vir is on the verge of Roche lobe overflow, and that the
observed mass transfer could be supplemented by upward chromospheric flows on
the M dwarf, analogous to spicules and mottles on the Sun, that escape the
Roche surface to be subsequently swept up into the white dwarf Roche lobe. If
so, QS Vir would be in a rare evolutionary phase lasting only a million years.
The X-ray luminosity of the M dwarf estimated during primary eclipse is L_X = 3
\times 10^28 erg/s, which is consistent with that of rapidly rotating
""saturated"" K and M dwarfs.",1201.2682v1
2012-01-14,Stabilization of the high-spin state of Co$^{3+}$ in LaCo$_{1-x}$Rh$_{x}$O$_3$,"The rhodium doping in the LaCo$_{1-x}$Rh$_{x}$O$_3$ perovskite series
($x=0.02-0.5$) has been studied by X-ray diffraction, electric transport and
magnetization measurements, complemented by electronic structure GGA+U
calculations in supercell for different concentration regimes. No charge
transfer between Co$^{3+}$ and Rh$^{3+}$ is evidenced. The diamagnetic ground
state of LaCoO$_3$, based on Co$^{3+}$ in low-spin (LS) state, is disturbed
even by a small doping of Rh. The driving force is the elastic energy connected
with incorporation of a large Rh$^{3+}$ cation into the matrix of small LS
Co$^{3+}$ cations, which is relaxed by formation of large Co$^{3+}$ in
high-spin (HS) state in the next-nearest sites to the inserted Rh atom. With
increasing temperature, the population of Co$^{3+}$ in HS state increases
through thermal excitation, and a saturated phase is obtained close to room
temperature, consisting of a nearest-neighbor correlation of small (LS
Co$^{3+}$) and large (HS Co$^{3+}$ and LS Rh$^{3+}$) cations in a kind of
double perovskite structure. The stabilizing role of elastic and electronic
energy contributions is demonstrated in supercell calculations for dilute Rh
concentration compared to other dopants with various trivalent ionic radius.",1201.3050v1
2012-02-15,The HBI in a quasi-global model of the intracluster medium,"In this paper we investigate how convective instabilities influence heat
conduction in the intracluster medium (ICM) of cool-core galaxy clusters. The
ICM is a high-beta, weakly collisional plasma in which the transport of
momentum and heat is aligned with the magnetic field. The anisotropy of heat
conduction, in particular, gives rise to instabilities that can access energy
stored in a temperature gradient of either sign. We focus on the heat-flux
buoyancy-driven instability (HBI), which feeds on the outwardly increasing
temperature profile of cluster cool cores. Our aim is to elucidate how the
global structure of a cluster impacts on the growth and morphology of the
linear HBI modes when in the presence of Braginskii viscosity, and ultimately
on the ability of the HBI to thermally insulate cores. We employ an idealised
quasi-global model, the plane-parallel atmosphere, which captures the essential
physics -- e.g. the global radial profile of the cluster -- while letting the
problem remain analytically tractable. Our main result is that the dominant HBI
modes are localised to the the innermost (~<20%) regions of cool cores. It is
then probable that, in the nonlinear regime, appreciable field-line insulation
will be similarly localised. Thus, while radio-mode feedback appears necessary
in the central few tens of kpc, heat conduction may be capable of offsetting
radiative losses throughout most of a cool core over a significant fraction of
the Hubble time. Finally, our linear solutions provide a convenient numerical
test for the nonlinear codes that tackle the saturation of such convective
instabilities in the presence of anisotropic transport.",1202.3440v2
2012-05-22,On the origin of sub-TeV gamma-ray pulsed emission from rotating neutron stars,"Intriguing sub-TeV tails in the pulsed $\gamma$-ray emission from the Crab
pulsar have been recently discovered by the MAGIC and VERITAS Collaborations.
They were not clearly predicted by any pulsar model. It is at present argued
that this emission is produced by electrons in the Inverse Compton process
occurring either in the outer gap of the pulsar magnetosphere or in the pulsar
wind region at some distance from the light cylinder. We analyse another
scenario which is consistent with the basic features of this enigmatic
emission. It is proposed that this emission is caused by electrons accelerated
very close to the light cylinder where the $e^\pm$ plasma can not saturate
induced huge electric fields. Electrons reach energies sufficient for
production of hard $\gamma$-ray spectra in the curvature radiation process. Due
to different curvature radii of the leading and trailing magnetic field lines,
the $\gamma$-ray spectra from separate pulses should extend to different
maximum energies. The scenario can also explain the lower level $\gamma$-ray
emission from the interpulse region (between P1 and P2) observed in the Crab
pulsar light curve. Moreover, we argue that pulsars with parameters close to
the Vela pulsar should also show pulsed emission with the cut-off at clearly
lower energies ($\sim$50 GeV) than that observed in the case of the Crab
pulsar. On the other hand, such tail emission is not expected in pulsars with
parameters close to the Geminga pulsar. The model also predicts the tail
$\gamma$-ray emission extending up to $\sim$50 GeV from some millisecond
pulsars with extreme parameters such as PSR J0218+4243 and PSR J1823-3021A.",1205.4855v1
2012-06-04,Edge excitations of the canted antiferromagnetic phase of the $ν=0$ quantum Hall state in graphene: a simplified analysis,"We perform a simplified analysis of the edge excitations of the canted
antiferromagnetic (CAF) phase of the $\nu=0$ quantum Hall state in both
monolayer and bilayer graphene. Namely, we calculate, within the framework of
quantum Hall ferromagnetism, the mean-field quasiparticle spectrum of the CAF
phase neglecting the modification of the order parameter at the edge. We
demonstrate that, at a fixed perpendicular component $B_\perp$ of the magnetic
field, the gap $\Delta_\text{edge}$ in the edge excitation spectrum gradually
decreases upon increasing the parallel component $B_\parallel$, as the CAF
phase continuously transforms to the fully spin-polarized ferromagnetic (F)
phase. The edge gap closes completely ($\Delta_\text{edge}=0$) once the F
phase, characterized by gapless counter-propagating edge excitations, is
reached at some finite $B_\perp$-dependent value $B_\parallel^*$ and remains
closed upon further increase of $B_\parallel$. This results in an gradual
insulator-metal transition, in which the conductance $G \sim (e^2/h)
\exp(-\Delta_\text{edge}/T)$ grows exponentially with $B_\parallel$ in the
range $0<B_\parallel<B_\parallel^*$, while in the gapped CAF phase, and
saturates to a metallic value $G \sim e^2/h$ in the F phase at
$B_\parallel>B_\parallel^*$. This unique transport feature of the CAF phase
provides a way to identify and distinguish it from other competing phases of
the $\nu=0$ quantum Hall state in a tilted-field experiment.",1206.0724v1
2012-06-20,Stacking-order dependence in thermoelectric transport of biased trilayer graphene,"We numerically study the thermoelectric and thermal transport in trilayer
graphene with different stacking orders in the presence of interlayer bias
under a strong perpendicular magnetic field. In biased ABA-stacked case, we
find that the thermoelectric conductivity displays different asymptotic
behaviors with the varying of the temperature, similar to that of monolayer
graphene. In the high temperature regime, the transverse thermoelectric
conductivity $\alpha_{xy}$ saturates to a universal value $2.77 k_B e/h$ at the
center of each LL, while it displays a linear temperature dependence at low
temperatures limit. The calculated transverse thermal conductivity
$\kappa_{xy}$ exhibits two plateaus away from the band center. The transition
between the two plateaus is continuous, which is accompanied by a pronounced
peak in the longitudinal thermal conductivity $\kappa_{xx}$. In biased
ABC-stacked case, it is found that both the thermoelectric conductivity and
thermal conductivity have similar properties to the biased bilayer graphene,
which is consistent with the behavior of a band insulator. The obtained results
demonstrate the sensitivity of the thermoelectric conductivity to the band gap
near the Dirac point. We also verify the validity of the Mott-relation and the
generalized Wiedemann-Franz law.",1206.4387v1
2012-06-24,The Patterns of High-Level Magnetic Activity Occurring on the Surface of V1285 Aql: The OPEA Model of Flares and DFT Models of Stellar Spots,"Statistically analyzing Johnson UBVR observations of V1285 Aql during the
three observing seasons, both activity level and behavior of the star are
discussed in respect to obtained results. We also discuss the out-of-flare
variation due to rotational modulation. Eighty-three flares were detected in
the U-band observations of season 2006 . First, depending on statistical
analyses using the independent samples t-test, the flares were divided into two
classes as the fast and the slow flares. According to the results of the test,
there is a difference of about 73 s between the flare-equivalent durations of
slow and fast flares. The difference should be the difference mentioned in the
theoretical models. Second, using the one-phase exponential association
function, the distribution of the flare-equivalent durations versus the flare
total durations was modeled. Analyzing the model, some parameters such as
plateau, half-life values, mean average of the flare-equivalent durations,
maximum flare rise, and total duration times are derived. The plateau value,
which is an indicator of the saturation level of white-light flares, was
derived as 2.421{\pm}0.058 s in this model, while half-life is computed as 201
s. Analyses showed that observed maximum value of flare total duration is 4641
s, while observed maximum flare rise time is 1817 s. According to these
results, although computed energies of the flares occurring on the surface of
V1285 Aql are generally lower than those of other stars, the length of its
flaring loop can be higher than those of more active stars.",1206.5794v1
2012-10-20,The Kelvin-Helmholtz instability in Orion: a source of turbulence and chemical mixing,"Hydrodynamical instabilities are believed to power some of the small scale
(0.1-10 pc) turbulence and chemical mixing in the interstellar medium.
Identifying such instabilities has always been difficult but recent
observations of a wavelike structure (the Ripples) in the Orion nebula have
been interpreted as a signature of the Kelvin-Helmholtz instability (KHI),
occurring at the interface between the HII region and the molecular cloud.
However, this has not been verified theoretically. In this letter, we
investigate theoretically the stability of this interface using observational
constraints for the local physical conditions. A linear analysis shows that the
HII/molecular cloud interface is indeed KH unstable for a certain range of
magnetic field orientation. We find that the maximal growth-rates correspond to
typical timescales of a few 1e4 years and instability wavelengths of 0.06 to
0.6 pc. We predict that after 2e5 years the KHI saturates and forms a turbulent
layer of thickness ~0.5 pc. The KHI can remain in linear phase over a maximum
distance of 0.75 pc. These spatial and time scales are compatible with the
Ripples representing the linear phase of the KHI. These results suggest that
the KHI may be crucial to generate turbulence and to bring heavy elements
injected by the winds of massive stars in HII regions to colder regions where
planetary systems around low mass stars are being formed. This could apply to
the transport of 26Al injected by a massive star in an HII region to the
nascent solar-system.",1210.5596v2
2013-04-09,Dynamo effects in magnetorotational turbulence with finite thermal diffusivity,"We investigate the saturation level of hydromagnetic turbulence driven by the
magnetorotational instability in the case of vanishing net flux. Motivated by a
recent paper of Bodo, Cattaneo, Mignone, & Rossi, we here focus on the case of
a non-isothermal equation of state with constant thermal diffusivity. The
central aim of the paper is to complement the previous result with closure
parameters for mean-field dynamo models, and to test the hypothesis that the
dynamo is affected by the mode of heat transport. We perform computer
simulations of local shearing-box models of stratified accretion disks with
approximate treatment of radiative heat transport, which is modeled via thermal
conduction. We study the effect of varying the (constant) thermal diffusivity,
and apply different vertical boundary conditions. In the case of impenetrable
vertical boundaries, we confirm the transition from mainly conductive to mainly
convective vertical heat transport below a critical thermal diffusivity. This
transition is however much less dramatic when more natural outflow boundary
conditions are applied. Similarly, the enhancement of magnetic activity in this
case is less pronounced. Nevertheless, heating via turbulent dissipation
determines the thermodynamic structure of accretion disks, and clearly affects
the properties of the related dynamo. This effect may however have been
overestimated in previous work, and a careful study of the role played by
boundaries will be required.",1304.2587v1
2013-12-04,Pulsar wind model for the spin-down behavior of intermittent pulsars,"Intermittent pulsars are part-time radio pulsars. They have higher slow down
rate in the on state (radio-loud) than in the off state (radio-quiet). This
gives the evidence that particle wind may play an important role in pulsar
spindown. The effect of particle acceleration is included in modeling the
rotational energy loss rate of the neutron star. Applying the pulsar wind model
to the three intermittent pulsars (PSR B1931+24, PSR J1841-0500, and PSR
J1832+0029), their magnetic field and inclination angle are calculated
simultaneously. The theoretical braking indices of intermittent pulsars are
also given. In the pulsar wind model, the density of the particle wind can
always be the Goldreich-Julian density. This may ensure that different on
states of intermittent pulsars are stable. The duty cycle of particle wind can
be determined from timing observations. It is consistent with the duty cycle of
the on state. Inclination angle and braking index observations of intermittent
pulsars may help to test different models of particle acceleration. At present,
the inverse Compton scattering induced space charge limited flow with field
saturation model can be ruled out.",1312.1016v3
2014-03-06,The Evolution of Writhe in Kink-Unstable Flux Ropes and Erupting Filaments,"The helical kink instability of a twisted magnetic flux tube has been
suggested as a trigger mechanism for solar filament eruptions and coronal mass
ejections (CMEs). In order to investigate if estimations of the pre-eruptive
twist can be obtained from observations of writhe in such events, we
quantitatively analyze the conversion of twist into writhe in the course of the
instability, using numerical simulations. We consider the line tied,
cylindrically symmetric Gold-Hoyle flux rope model and measure the writhe using
the formulae by Berger and Prior which express the quantity as a single
integral in space. We find that the amount of twist converted into writhe does
not simply scale with the initial flux rope twist, but depends mainly on the
growth rates of the instability eigenmodes of higher longitudinal order than
the basic mode. The saturation levels of the writhe, as well as the shapes of
the kinked flux ropes, are very similar for considerable ranges of initial flux
rope twists, which essentially precludes estimations of pre-eruptive twist from
measurements of writhe. However, our simulations suggest an upper twist limit
of $\sim 6\pi$ for the majority of filaments prior to their eruption.",1403.1565v1
2014-05-15,Radial Stresses and Energy Transport in Accretion Disks,"Early in the study of viscous accretion disks it was realized that energy
transfers from distant sources must be important, not least because the flow at
the disk midplane in the bulk of the disk is likely outwards, out of the
gravitational potential well. If the source of the viscosity is powered by
accretion, such as in the case of the magneto-rotational instability, such
distant energy sources must lie in the innermost regions of the disk, where
accretion occurs even at the midplane. We argue here that modulations in this
energy supply can alter the accretion rate on dynamical, rather than far longer
viscous, time scales. This means that both the steady state value of and
fluctuations in the inner disk's accretion rate, depending on the details of
the inner boundary condition and occurring on the inner disk's rapid evolution
time, can affect the outer disk. This is particularly interesting because
observations have shown that disk accretion is not steady (e.g.~EX Lupi type
objects). We also note that the power supplied to shearing boxes is set by the
boxes themselves rather than the physical energy fluxes in a global disk. That
is, their saturated magnetic field is not subject to the full set of energy
constraints present in an actual disk. Our analysis suggests that large scale
radial transport of energy has a critical impact on the evolution and
variability of accretion disks.",1405.3991v2
2014-09-02,On seed island generation and the non-linear self-consistent interaction of the tearing mode with electromagnetic gyro-kinetic turbulence,"The multi-scale interaction of self-consistently driven magnetic islands with
electromagnetic turbulence is studied within the three dimensional, toroidal
gyro-kinetic framework. It can be seen that, even in the presence of
electromagnetic turbulence the linear structure of the mode is retained.
Turbulent fluctuations do not destroy the growing island early in its
development, which then maintains a coherent form as it grows.
  The island is seeded by the electromagnetic turbulence fluctuations, which
provide an initial island structure through nonlinear interactions and which
grows at a rate significantly faster than the linear tearing growth rate. These
island structures saturate at a width that is approximately $\rho_{i}$ in size.
In the presence of turbulence the island then grows at the linear rate even
though the island is significantly wider than the resonant layer width, a
regime where the island is expected to grow at a significantly reduced
non-linear rate.
  A large degree of stochastisation around the separatrix, and an almost
complete break down of the X-point is seen. This significantly reduces the
effective island width.",1409.0648v2
2014-11-12,Cross-calibration of the Transition Radiation Detector of AMS-02 for an Energy Measurement of Cosmic-Ray Ions,"Since May 2011 the AMS-02 experiment is installed on the International Space
Station and is observing cosmic radiation. It consists of several
state-of-the-art sub-detectors, which redundantly measure charge and energy of
traversing particles. Due to the long exposure time of AMS-02 of many years the
measurement of momentum for protons and ions is limited systematically by the
spatial resolution and magnetic field strength of the silicon tracker. The
maximum detectable rigidity for protons is about 1.8~TV, for helium about
3.6~TV. We investigate the possibility to extend the range of the energy
measurement for heavy nuclei ($Z\geq2$) with the transition radiation detector
(TRD). The response function of the TRD shows a steep increase in signal from
the level of ionization at a Lorentz factor $\gamma$ of about 500 to
$\gamma\approx20000$, where the transition radiation signal saturates. For
heavy ions the signal fluctuations in the TRD are sufficiently small to allow
an energy measurement with the TRD beyond the limitations of the tracker. The
energy resolution of the TRD is determined and reaches a level of about 20\%
for boron ($Z=5$). After adjusting the operational parameters of the TRD a
measurement of boron and carbon could be possible up to 5~TeV/nucleon.",1411.3329v1
2015-02-01,"Enhanced conduction band density of states in intermetallic EuTSi$_3$ (T=Rh, Ir)","We report on the physical properties of single crystalline EuRhSi$_3$ and
polycrystalline EuIrSi$_3$, inferred from magnetisation, electrical transport,
heat capacity and $^{151}$Eu M\""ossbauer spectroscopy. These previously known
compounds crystallise in the tetragonal BaNiSn$_3$-type structure. The single
crystal magnetisation in EuRhSi$_3$ has a strongly anisotropic behaviour at 2 K
with a spin-flop field of 13 T, and we present a model of these magnetic
properties which allows the exchange constants to be determined. In both
compounds, specific heat shows the presence of a cascade of two close
transitions near 50 K, and the $^{151}$Eu M\""ossbauer spectra demonstrate that
the intermediate phase has an incommensurate amplitude modulated structure. We
find anomalously large values, with respect to other members of the series, for
the RKKY N\'eel temperature, for the spin-flop field (13 T), for the spin-wave
gap ($\simeq$ 20-25 K) inferred from both resistivity and specific heat data,
for the spin-disorder resistivity in EuRhSi$_3$ ($\simeq 35$ $\mu$Ohm.cm) and
for the saturated hyperfine field (52 T). We show that all these quantities
depend on the electronic density of states at the Fermi level, implying that
the latter must be strongly enhanced in these two materials. EuIrSi$_3$
exhibits a giant magnetoresistance ratio, with values exceeding 600 % at 2 K in
a field of 14 T.",1502.00285v1
2015-02-02,Superconductivity emerging from suppressed large magnetoresistant state in WTe2,"The recent discovery of large and non-saturating magnetoresistance (LMR) in
WTe2 provides a unique playground to find new phenomena and significant
perspective for potential applications. Here we report the first observation of
superconductivity near the proximity of suppressed LMR state in pressurized
WTe2 through high-pressure synchrotron X-ray diffraction, electrical
resistance, magnetoresistance, and ac magnetic susceptibility measurements. It
is found that the positive magnetoresistance effect can be turned off at a
critical pressure of 10.5 GPa without crystal structure change and
superconductivity emerges simultaneously. The maximum superconducting
transition temperature can be reached to 6.5 K at ~15 GPa and it decreases down
to 2.6 K at ~25 GPa. In-situ high pressure Hall coefficient measurements at 10
K demonstrate that elevating pressure decreases hole carrier's population but
increases electron carrier's population. Significantly, at the critical
pressure, we observed a sign change in the Hall coefficient, indicating a
possible Lifshitz-type quantum phase transition in WTe2.",1502.00493v2
2015-02-03,Transitions to valence-bond solid order in a honeycomb lattice antiferromagnet,"We use Quantum Monte-Carlo methods to study the ground state phase diagram of
a S=1/2 honeycomb lattice magnet in which a nearest-neighbor antiferromagnetic
exchange J (favoring N\'eel order) competes with two different multi-spin
interaction terms: a six-spin interaction Q_3 that favors columnar valence-bond
solid (VBS) order, and a four-spin interaction Q_2 that favors staggered VBS
order. For Q_3 ~ Q_2 >> J, we establish that the competition between the two
different VBS orders stabilizes N\'eel order in a large swathe of the phase
diagram even when J is the smallest energy-scale in the Hamiltonian. When Q_3
>> (Q_2,J) (Q_2 >> (Q_3,J)), this model exhibits at zero temperature phase
transition from the N\'eel state to a columnar (staggered) VBS state. We
establish that the N\'eel-columnar VBS transition is continuous for all values
of Q_2, and that critical properties along the entire phase boundary are
well-characterized by critical exponents and amplitudes of the non-compact CP^1
(NCCP^1) theory of deconfined criticality, similar to what is observed on a
square lattice. However, a surprising three-fold anisotropy of the phase of the
VBS order parameter at criticality, whose presence was recently noted at the
Q_2=0 deconfined critical point, is seen to persist all along this phase
boundary. We use a classical analogy to explore this by studying the critical
point of a three-dimensional XY model with a four-fold anisotropy field which
is known to be weakly irrelevant at the three-dimensional XY critical point. In
this case, we again find that the critical anisotropy appears to saturate to a
nonzero value over the range of sizes accessible to our simulations.",1502.01035v1
2015-02-09,Mutual independence of critical temperature and superfluid density under pressure in optimally electron-doped superconducting LaFeAsO$_{1-x}$F$_{x}$,"The superconducting properties of LaFeAsO$_{1-x}$F$_{x}$ in conditions of
optimal electron-doping are investigated upon the application of external
pressure up to $\sim 23$ kbar. Measurements of muon-spin spectroscopy and dc
magnetometry evidence a clear mutual independence between the critical
temperature $T_{c}$ and the low-temperature saturation value for the ratio
$n_{s}/m^{*}$ (superfluid density over effective band mass of Cooper pairs).
Remarkably, a dramatic increase of $\sim 30$ % is reported for $n_{s}/m^{*}$ at
the maximum pressure value while $T_{c}$ is substantially unaffected in the
whole accessed experimental window. We argue and demonstrate that the
explanation for the observed results must take the effect of non-magnetic
impurities on multi-band superconductivity into account. In particular, the
unique possibility to modify the ratio between intra-band and inter-bands
scattering rates by acting on structural parameters while keeping the amount of
chemical disorder constant is a striking result of our proposed model.",1502.02713v1
2015-03-20,Finite-temperature superconducting correlations of the Hubbard model,"We utilize numerical linked-cluster expansions (NLCEs) and the determinantal
quantum Monte Carlo algorithm to study pairing correlations in the square
lattice Hubbard model. To benchmark the NLCE, we first locate the
finite-temperature phase transition of the attractive model to a
superconducting state away from half filling. We then explore the
superconducting properties of the repulsive model for the d-wave and extended
s-wave pairing symmetries. The pairing structure factor shows a strong tendency
to d-wave pairing and peaks at an interaction strength comparable to the
bandwidth. The extended s-wave structure factor and correlation length are
larger at higher temperatures but clearly saturate as temperature is lowered,
whereas the d-wave counterparts, which start off lower at high temperatures,
continue to rise near half filling. This rise is even more dramatic in the
d-wave susceptibility. The convergence of NLCEs breaks down as the
susceptibilities and correlation lengths become large, so we are unable to
determine the onset of long-range order. However, our results extend the
conclusion, previously restricted to only magnetic and charge correlations,
that NLCEs offer unique window into pairing in the Hubbard model at strong
coupling.",1503.06213v2
2015-05-05,Direct evidence for the emergence of a pressure induced nodal superconducting gap in the iron-based superconductor Ba_0.65Rb_0.35Fe_2As_2,"Identifying the superconducting (SC) gap structure of the iron-based
high-temperature superconductors (Fe-HTS's) remains a key issue for the
understanding of superconductivity in these materials. In contrast to other
unconventional superconductors, in the Fe-HTS's both $d$-wave and extended
s-wave pairing symmetries are close in energy, with the latter believed to be
generally favored over the former. Probing the proximity between these very
different SC states and identifying experimental parameters that can tune them,
are of central interest. Here we report high-pressure muon spin rotation
experiments on the temperature-dependent magnetic penetration depth (lambda) in
the optimally doped Fe-HTS Ba_0.65Rb_0.35Fe_2As_2. At ambient pressure this
material is known to be a nodeless s-wave superconductor. Upon pressure a
strong decrease of (lambda) is observed, while the SC transition temperature
remains nearly constant. More importantly, the low-temperature behavior of
(1/lambda^{2}) changes from exponential saturation at zero pressure to a
power-law with increasing pressure, providing unambiguous evidence that
hydrostatic pressure promotes nodal SC gaps. Comparison to microscopic models
favors a d-wave over a nodal s^{+-}-wave pairing as the origin of the nodes.
Our results provide a new route of understanding the complex topology of the SC
gap in Fe-HTS's.",1505.01223v1
2015-05-07,A Simple Way to Estimate the Soft X-ray Class of Far-Side Solar Flares Observed with STEREO/EUVI,"Around the peaks of substantial flares, bright artifact nearly horizontal
saturation streaks (B-streaks) corresponding to the brightest parts of the
flare sources appear in the STEREO/EUVI 195 A images. We show that the length
of such B-streaks can be used for the solution of an actual problem of
evaluating the soft X-ray flux and class of far-side flares registered with
double STEREO spacecraft but invisible from Earth. For this purpose from data
on about 350 flares observed from January 2007 to July 2014 (mainly exceeding
the GOES M1.0 level) both with GOES and STEREO, an empirical relation is
established correlating the GOES 1-8 A peak flux and the B-streak length. This
allowed us for the same years to estimate the soft X-ray classes for
approximately 65 strong far-side flares observed by STEREO. The results of this
simple and prompt method are consistent with the estimations of Nitta et al.
(Solar Phys., 288, 241, 2013) based on the calculations of the EUVI full-disk
digital number output. In addition, we studied some features of the B-streaks
in impulsive and long-duration flares and demonstrated that B-streaks in
several consecutive EUVI images can be used to reconstruct a probable time
history of strong far-side flares.",1505.01649v2
2015-05-20,Scaling properties of a ferromagnetic thin film model at the depinning transition,"In this paper, we perform a detailed study of the scaling properties of a
ferromagnetic thin film model. Recently, interest has increased in the scaling
properties of the magnetic domain wall (MDW) motion in disordered media when an
external driving field is present. We consider a (1+1)-dimensional model, based
on evolution rules, able to describe the MDW avalanches. The global interface
width of this model shows Family-Vicsek scaling with roughness exponent
$\zeta\simeq 1.585$ and growth exponent $\beta\simeq 0.975$. In contrast, this
model shows scaling anomalies in the interface local properties characteristic
of other systems with depinning transition of the MDW, e.g. quenched
Edwards-Wilkinson (QEW) equation and random-field Ising model (RFIM) with
driving. We show that, at the depinning transition, the saturated average
velocity $v_\mathrm{sat}\sim f^\theta$ vanished very slowly (with $\theta\simeq
0.037$) when the reduced force $f=p/p_\mathrm{c}-1\to 0^{+}$. The simulation
results show that this model verifies all accepted scaling relations which
relate the global exponents and the correlation length (or time) exponents,
valid in systems with depinning transition. Using the interface tilting method,
we show that the model, close to the depinning transition, exhibits a
nonlinearity similar to the one included in the Kardar-Parisi-Zhang (KPZ)
equation. The nonlinear coefficient $\lambda\sim f^{-\phi}$ with $\phi\simeq
-1.118$, which implies that $\lambda\to 0$ as the depinning transition is
approached, a similar qualitatively behaviour to the driven RFIM. We conclude
this work by discussing the main features of the model and the prospects opened
by it.",1505.05223v2
2015-07-13,Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions,"Nuclei colliding at very high energy create a strong, quasi-classical gluon
field during the initial phase of their interaction. We present an analytic
calculation of the initial space-time evolution of this field in the limit of
very high energies using a formal recursive solution of the Yang-Mills
equations. We provide analytic expressions for the initial chromo-electric and
chromo-magnetic fields and for their energy-momentum tensor. In particular, we
discuss event-averaged results for energy density and energy flow as well as
for longitudinal and transverse pressure of this system. For example, we find
that the ratio of longitudinal to transverse pressure very early in the system
behaves as $p_L/p_T =
-[1-\frac{3}{2a}(Q\tau)^2]/[1-\frac{1}{a}(Q\tau)^2]+\mathcal{O}(Q\tau)^4$ where
$\tau$ is the longitudinal proper time, $Q$ is related to the saturation scales
$Q_s$ of the two nuclei, and $a = \ln (Q^2/\hat{m}^2)$ with $\hat m$ a scale to
be defined later. Our results are generally applicable if $\tau \lesssim 1/Q$.
As already discussed in a previous paper, the transverse energy flow $S^i$ of
the gluon field exhibits hydrodynamic-like contributions that follow transverse
gradients of the energy density $\nabla^i \varepsilon$. In addition, a
rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law
and generates non-vanishing angular momentum of the field. We will discuss the
space-time picture that emerges from our analysis and its implications for
observables in heavy ion collisions.",1507.03524v1
2015-08-23,Fire Hose instability driven by alpha particle temperature anisotropy,"We investigate properties of a solar wind-like plasma including a secondary
alpha particle population exhibiting a parallel temperature anisotropy with
respect to the background magnetic field, using linear and quasi-linear
predictions and by means of one-dimensional hybrid simulations. We show that
anisotropic alpha particles can drive a parallel fire hose instability
analogous to that generated by protons, but that, remarkably, the instability
can be triggered also when the parallel plasma beta of alpha particles is below
unity. The wave activity generated by the alpha anisotropy affects the
evolution of the more abundant protons, leading to their anisotropic heating.
When both ion species have sufficient parallel anisotropies both of them can
drive the instability, and we observe generation of two distinct peaks in the
spectra of the fluctuations, with longer wavelengths associated to alphas and
shorter ones to protons. If a non-zero relative drift is present, the unstable
modes propagate preferentially in the direction of the drift associated with
the unstable species. The generated waves scatter particles and reduce their
temperature anisotropy to marginally stable state, and, moreover, they
significantly reduce the relative drift between the two ion populations. The
coexistence of modes excited by both species leads to saturation of the plasma
in distinct regions of the beta/anisotropy parameter space for protons and
alpha particles, in good agreement with in situ solar wind observations. Our
results confirm that fire hose instabilities are likely at work in the solar
wind and limit the anisotropy of different ion species in the plasma.",1508.05638v1
2015-09-15,Novel valley depolarization dynamics and valley Hall effect of exciton in mono- and bilayer MoS$_2$,"We investigate the valley depolarization dynamics and valley Hall effect of
exciton due to the electron-hole exchange interaction in mono- and bilayer
MoS$_2$ by solving the kinetic spin Bloch equations. The effect of the exciton
energy spectra by the electron-hole exchange interaction is explicitly
considered. For the valley depolarization dynamics, in the monolayer MoS$_2$,
it is found that in the strong scattering regime, the conventional motional
narrowing picture is no longer valid, and a novel valley depolarization channel
is opened. For the valley Hall effect of exciton, in both the mono- and bilayer
MoS$_2$, with the exciton equally pumped in the K and K' valleys, the system
can evolve into the equilibrium state where the valley polarization is parallel
to the effective magnetic field due to the exchange interaction. With the drift
of this equilibrium state by applied uniaxial strain, the exchange interaction
can induce the {\it momentum-dependent} valley/photoluminesence polarization,
which leads to the valley/photoluminesence Hall current. Specifically, the
disorder strength dependence of the valley Hall conductivity is revealed. In
the strong scattering regime, the valley Hall conductivity decreases with the
increase of the disorder strength; whereas in the weak scattering regime, it
saturates to a constant, which can be much larger than the one in Fermi system
due to the absence of the Pauli blocking.",1509.04404v1
2015-10-05,Depinning of disordered bosonic chains,"We consider one-dimensional bosonic chains with a repulsive boson-boson
interaction that decays exponentially on large length-scales. This model
describes transport of Cooper-pairs in a Josepshon junction array, or transport
of magnetic flux quanta in quantum-phase-slip ladders, i.e. arrays of
superconducting wires in a ladder-configuration that allow for the coherent
tunnelling of flux quanta. In the low-frequency, long wave-length regime these
chains can be mapped to an effective model of a one-dimensional elastic field
in a disordered potential. The onset of transport in these systems, when biased
by external voltage, is described by the standard depinning theory of elastic
media in disordered pinning potentials. We numerically study the regimes that
are of relevance for quantum-phase-slip ladders. These are (i) very short
chains and (ii) the regime of weak disorder. For chains shorter than the
typical pinning length, i.e., the Larkin length, the chains reach a saturation
regime where the depinning voltage does not depend on the decay length of the
repulsive interaction. In the regime of weak disorder we find an emergent
correlation length-scale that depends on the disorder strength. For arrays
shorter than this length the onset of transport is similar to the clean arrays,
i.e., is due to the penetration of solitons into the array. We discuss the
depinning scenarios for longer arrays in this regime.",1510.01383v1
2016-02-05,Large nonsaturating magnetoresistance and signature of non-degenerate Dirac nodes in ZrSiS,"While the discovery of Dirac and Weyl type excitations in electronic systems
is a major breakthrough in recent condensed matter physics, finding appropriate
materials for fundamental physics and technological applications, is an
experimental challenge. In all the reported materials, linear dispersion
survives only up to a few hundred meV from the Dirac or Weyl nodes. On the
other hand, real materials are subject to uncontrolled doping during
preparation and thermal effect near room temperature can hinder the rich
physics. In ZrSiS, ARPES measurements have shown an unusually robust linear
dispersion (up to $\sim$2 eV) with multiple non-degenerate Dirac nodes. In this
context, we present the magnetotransport study on ZrSiS crystal, which
represents a large family of materials (\textit{WHM} with \textit{W} = Zr, Hf;
\textit{H} = Si, Ge, Sn; \textit{M} = O, S, Se, Te) with identical band
topology. Along with extremely large and non-saturating magnetoresistance (MR),
$\sim$ 1.4 $\times$ 10$^{5}$ \% at 2 K and 9 T, it shows strong anisotropy
depending on the direction of the magnetic field. Quantum oscillation and Hall
effect measurements have revealed large hole and small electron Fermi pockets.
Non-trivial $\pi$ Berry phase confirms the Dirac fermionic nature for both
types of charge carriers. The long-sought relativistic phenomenon of massless
Dirac fermions, known as Adler-Bell-Jackiw chiral anomaly, has also been
observed.",1602.01993v3
2016-03-05,Topological phase transition induced extreme magnetoresistance in TaSb$_{2}$,"We report extremely large positive magnetoresistance of 1.72 million percent
in single crystal TaSb$_{2}$ at moderate conditions of 1.5 K and 15 T. The
quadratic growth of magnetoresistance (MR $\propto\,B^{1.96}$) is not
saturating up to 15 T, a manifestation of nearly perfect compensation with
$<0.1\%$ mismatch between electron and hole pockets in this semimetal. The
compensation mechanism is confirmed by temperature-dependent MR, Hall and
thermoelectric coefficients of Nernst and Seebeck, revealing two pronounced
Fermi surface reconstruction processes without spontaneous symmetry breaking,
\textit{i.e.} Lifshitz transitions, at around 20 K and 60 K, respectively.
Using quantum oscillations of magnetoresistance and magnetic susceptibility,
supported by density-functional theory calculations, we determined that the
main hole Fermi surface of TaSb$_{2}$ forms a unique shoulder structure along
the $F-L$ line. The flat band top of this shoulder pocket is just a few meV
above the Fermi level, leading to the observed topological phase transition at
20 K when the shoulder pocket disappears. Further increase in temperature
pushes the Fermi level to the band top of the main hole pocket, induced the
second Lifshitz transition at 60 K when hole pocket vanishes completely.",1603.01717v1
2016-03-15,Gyrokinetic simulations of fusion plasmas using a spectral velocity space representation,"Magnetic confinement fusion reactors suffer severely from heat and particle
losses through turbulent transport, which has inspired the construction of ever
larger and more expensive reactors. Numerical simulations are vital to their
design and operation, but particle collisions are too infrequent for fluid
descriptions to be valid. Instead, strongly magnetised fusion plasmas are
described by the gyrokinetic equations, a nonlinear integro-differential system
for evolving the particle distribution functions in a five-dimensional position
and velocity space, and the consequent electromagnetic field. Due to the high
dimensionality, simulations of small reactor sections require hundreds of
thousands of CPU hours on High Performance Computing platforms.
  We develop a Hankel-Hermite spectral representation for velocity space that
exploits structural features of the gyrokinetic system. The representation
exactly conserves discrete free energy in the absence of explicit dissipation,
while our Hermite hypercollision operator captures Landau damping with few
variables. Calculation of the electromagnetic fields becomes purely local,
eliminating inter-processor communication in, and vastly accelerating, searches
for linear instabilities. We implement these ideas in SpectroGK, an efficient
parallel code.
  Turbulent fusion plasmas may dissipate free energy through linear phase
mixing to fine scales in velocity space, as in Landau damping, or through a
nonlinear cascade to fine scales in physical space, as in hydrodynamic
turbulence. Using SpectroGK to study saturated electrostatic drift-kinetic
turbulence, we find that the nonlinear cascade suppresses linear phase mixing
at energetically-dominant scales, so the turbulence is fluid-like. We use this
observation to derive Fourier-Hermite spectra for the electrostatic potential
and distribution function, and confirm these spectra with simulations.",1603.04727v1
2016-04-27,Compensated semimetal LaSb with unsaturated magnetoresistance,"By combining angle-resolved photoemission spectroscopy and quantum
oscillation measurements, we performed a comprehensive investigation on the
electronic structure of LaSb, which exhibits near-quadratic extremely large
magnetoresistance (XMR) without any sign of saturation at magnetic fields as
high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal
hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center $\Gamma$ and one
ellipsoidal electron FS at the BZ boundary $X$. The hole and electron carriers
calculated from the enclosed FS volumes are perfectly compensated, and the
carrier compensation is unaffected by temperature. We further reveal that LaSb
is topologically trivial but share many similarities with the Weyl semimetal
TaAs family in the bulk electronic structure. Based on these results, we have
examined the mechanisms that have been proposed so far to explain the
near-quadratic XMR in semimetals.",1604.08142v2
2016-07-06,Quadrupole Splittings in the near-infrared spectrum of $^{14}$NH$_3$,"Sub-Doppler, saturation dip, spectra of lines in the $v_1 + v_3$, $v_1 +
2v_4$ and $v_3 + 2v_4$ bands of $^{14}$NH$_3$ have been measured by frequency
comb-referenced diode laser absorption spectroscopy. The observed spectral line
widths are dominated by transit time broadening, but show resolved or
partially-resolved hyperfine splittings that are primarily determined by the
$^{14}$N quadrupole coupling. Modeling of the observed line shapes based on the
known hyperfine level structure of the ground state of the molecule shows that,
in nearly all cases, the excited state level has hyperfine splittings similar
to the same rotational level in the ground state. The data provide accurate
frequencies for the line positions and easily separate lines overlapped in
Doppler-limited spectra. The observed hyperfine splittings can be used to make
and confirm rotational assignments and ground state combination differences
obtained from the measured frequencies are comparable in accuracy to those
obtained from conventional microwave spectroscopy. One upper state level shows
very clear differences from the expected splittings. Examination of the known
vibration-rotation level structure shows there is a near degeneracy between
this level in $v_1+v_3$ and a rotational level in the $v_1 + 2v_4$ manifold
which is of the appropriate symmetry to be mixed by magnetic hyperfine terms
that couple ortho- and para- forms of the molecule.",1607.01646v2
2016-08-02,"A path towards understanding the rotation-activity relation of M dwarfs with K2 mission, X-ray and UV data","We study the relation between stellar rotation and magnetic activity for a
sample of 134 bright, nearby M dwarfs observed in the Kepler Two-Wheel (K2)
mission during campaigns C0 to C4. The K2 lightcurves yield photometrically
derived rotation periods for 97 stars (79 of which without previous period
measurement), as well as various measures for activity related to cool spots
and flares. We find a clear difference between fast and slow rotators with a
dividing line at a period of ~10d at which the activity level changes abruptly.
All photometric diagnostics of activity (spot cycle amplitude, flare peak
amplitude and residual variability after subtraction of spot and flare
variations) display the same dichotomy, pointing to a quick transition between
a high-activity mode for fast rotators and a low-activity mode for slow
rotators. This unexplained behavior is reminiscent of a dynamo mode-change seen
in numerical simulations that separates a dipolar from a multipolar regime. A
substantial number of the fast rotators are visual binaries. A tentative
explanation is accelerated disk evolution in binaries leading to higher initial
rotation rates on the main-sequence and associated longer spin-down and
activity lifetimes. We combine the K2 rotation periods with archival X-ray and
UV data. X-ray, FUV and NUV detections are found for 26, 41, and 11 stars from
our sample, respectively. Separating the fast from the slow rotators, we
determine for the first time the X-ray saturation level separately for early-
and for mid-M stars.",1608.00772v1
2016-10-18,"Preparation, structure and giant magnetoresistance of electrodeposited Fe Co/Cu multilayers","No systematic studies have been carried out on the giant magnetoresistance
(GMR) of electrodeposited (ED) Fe-Co/Cu multilayers since the elaboration of a
method for the optimization of the Cu layer deposition potential. In this
paper, we present results on the electrochemical optimization of the Cu layer
deposition potential which was found to depend on the relative iron
concentration in the bath. An X-ray diffraction study of ED Fe5Co95(1.5
nm)/Cu(dCu) multilayers with dCu ranging from 0.8 nm to 10 nm revealed an fcc
structure. For most of the multilayers, a weak superlattice satellite
reflection could be identified. The room-temperature magnetoresistance was
studied in detail as a function of the individual layer thicknesses.
Multilayers with Cu layer thicknesses above about 1.5 nm were found to exhibit
a GMR behavior with a maximum GMR of about 5 % and a typical saturation field
of 1 kOe. The GMR magnitude decreased with increasing Fe-content in the
magnetic layer. The spacer layer thickness evolution of the MR data was
established in detail after separating the ferromagnetic and superparamagnetic
GMR contributions and no oscillatory GMR was found. A comparison with
literature data on both physically deposited and ED Fe-Co/Cu multilayers is
also made.",1610.05631v1
2016-11-17,On the measurements of numerical viscosity and resistivity in Eulerian MHD codes,"We propose a simple ansatz for estimating the value of the numerical
resistivity and the numerical viscosity of any Eulerian MHD code. We test this
ansatz with the help of simulations of the propagation of (magneto)sonic waves,
Alfven waves, and the tearing mode instability using the MHD code Aenus. By
comparing the simu- lation results with analytical solutions of the
resistive-viscous MHD equations and an empirical ansatz for the growth rate of
tearing modes we measure the numerical viscosity and resistivity of Aenus. The
comparison shows that the fast-magnetosonic speed and wavelength are the
characteristic velocity and length, respectively, of the aforementioned
(relatively simple) systems. We also determine the dependance of the numerical
viscosity and resistivity on the time integration method, the spatial
reconstruction scheme and (to a lesser extent) the Riemann solver employed in
the simulations. From the measured results we infer the numerical resolution
(as a function of the spatial reconstruction method) required to properly
resolve the growth and saturation level of the magnetic field amplified by the
magnetorotational instability in the post-collapsed core of massive stars. Our
results show that it is to the best advantage to resort to ultra-high order
methods (e.g., 9th-order Monotonicity Preserving method) to tackle this problem
properly, in particular in three dimensional simulations.",1611.05858v2
2017-01-07,Spectrum of the Nuclear Environment for GaAs Spin Qubits,"Using a singlet-triplet spin qubit as a sensitive spectrometer of the GaAs
nuclear spin bath, we demonstrate that the spectrum of Overhauser noise agrees
with a classical spin diffusion model over six orders of magnitude in
frequency, from 1 mHz to 1 kHz, is flat below 10 mHz, and falls as $1/f^2$ for
frequency $f \! \gtrsim \! 1$ Hz. Increasing the applied magnetic field from
0.1 T to 0.75 T suppresses electron-mediated spin diffusion, which decreases
spectral content in the $1/f^2$ region and lowers the saturation frequency,
each by an order of magnitude, consistent with a numerical model. Spectral
content at megahertz frequencies is accessed using dynamical decoupling, which
shows a crossover from the few-pulse regime ($\lesssim \! 16$ $\pi$-pulses),
where transverse Overhauser fluctuations dominate dephasing, to the many-pulse
regime ($\gtrsim \! 32$ $\pi$-pulses), where longitudinal Overhauser
fluctuations with a $1/f$ spectrum dominate.",1701.01855v2
2017-01-09,Gyrokinetic theory for particle transport in fusion plasmas,"Predicting the dynamics of a thermonuclear plasma during a magnetic
confinement experiment is fundamental in order to make nuclear fusion a
reliable source of energy. The development of a set of equations describing the
plasma evolution on a given time scale is the main requirement to reach this
goal. A limited amount of works have studied in a self-consistent way
collisional transport and fluctuation induced transport. The motivation of this
work stems from the fundamental importance of the self-consistency of the
adopted description in order to understand transport processes on the energy
confinement (transport) time scale because of the mutual interaction between
collisions and turbulence. In turn, this is crucial in order to predict fluxes
of particle and energy and, ultimately, the overall plasma evolution. Using
flux coordinates and the drift ordering we derive a set of evolutions equations
for the number of particles and the energy density on the transport time scale.
These equations show the interplay between collisions and fluctuations and, in
particular, show that fluctuations may enhance collisional transport while the
collisions can damp long lived structures formed by saturated instabilities,
i.e zonal structures. Fluctuation induced fluxes are described using
gyrokinetic field theory, which makes a comparison with the theory of phase
space zonal structures possible, revealing that the fluctuations induced part
of the transport equations can be obtained by taking the proper moment of the
long length scale limit of the equation governing the evolution of phase space
zonal structures. Finally, we show that plasma nonlinear evolution can yield to
structures formation that are characterized by mesoscales, intermediate between
the typical ones of plasma turbulence and those of the reference plasma
equilibrium.",1701.02202v1
2017-01-11,The intrinsic and interstellar broadband linear polarization of nearby FGK dwarfs,"We present linear polarization measurements of nearby FGK dwarfs to
parts-per-million (ppm) precision. Before making any allowance for interstellar
polarization, we found that the active stars within the sample have a mean
polarization of 28.5 +/- 2.2 ppm while the inactive stars have a mean of 9.6
+/- 1.5 ppm. Amongst inactive stars we initially found no difference between
debris disk host stars (9.1 +/- 2.5 ppm) and the other FGK dwarfs (9.9 +/- 1.9
ppm). We develop a model for the magnitude and direction of interstellar
polarization for nearby stars. When we correct the observations for the
estimated interstellar polarization we obtain 23.0 +/-2.2 ppm for the active
stars, 7.8 +/- 2.9 ppm for the inactive debris disk host stars and 2.9 +/- 1.9
ppm for the other inactive stars. The data indicates that whilst some debris
disk host stars are intrinsically polarized most inactive FGK dwarfs have
negligible intrinsic polarization, but that active dwarfs have intrinsic
polarization at levels ranging up to ~45 ppm. We briefly consider a number of
mechanisms, and suggest differential saturation of spectral lines in the
presence of magnetic fields is the best able to explain the polarization seen
in active dwarfs. The results have implications for current attempts to detect
polarized reflected light from hot Jupiters by looking at the combined light of
the star and planet.",1701.02890v1
2017-02-17,Scalable explicit implementation of anisotropic diffusion with Runge-Kutta-Legendre super-time-stepping,"An important ingredient in numerical modelling of high temperature magnetised
astrophysical plasmas is the anisotropic transport of heat along magnetic field
lines from higher to lower temperatures.Magnetohydrodynamics (MHD) typically
involves solving the hyperbolic set of conservation equations along with the
induction equation. Incorporating anisotropic thermal conduction requires to
also treat parabolic terms arising from the diffusion operator. An explicit
treatment of parabolic terms will considerably reduce the simulation time step
due to its dependence on the square of the grid resolution ($\Delta x$) for
stability. Although an implicit scheme relaxes the constraint on stability, it
is difficult to distribute efficiently on a parallel architecture. Treating
parabolic terms with accelerated super-time stepping (STS) methods has been
discussed in literature but these methods suffer from poor accuracy (first
order in time) and also have difficult-to-choose tuneable stability parameters.
In this work we highlight a second order (in time) Runge Kutta Legendre (RKL)
scheme (first described by Meyer et. al. 2012) that is robust, fast and
accurate in treating parabolic terms alongside the hyperbolic conversation
laws. We demonstrate its superiority over the first order super time stepping
schemes with standard tests and astrophysical applications. We also show that
explicit conduction is particularly robust in handling saturated thermal
conduction. Parallel scaling of explicit conduction using RKL scheme is
demonstrated up to more than $10^4$ processors.",1702.05487v2
2017-04-18,Possible topologically non-trivial superconducting order parameter in type-II Weyl semimetal T_d-MoTe_2,"MoTe_2, with the orthorhombic T_d phase, is a new type (type-II) of Weyl
semimetal, where the Weyl Fermions emerge at the boundary between electron and
hole pockets. Non-saturating magnetoresistance (MR), and superconductivity were
also observed in T_d-MoTe_2. Understanding the superconductivity in T_d-MoTe_2,
which was proposed to be topologically non-trivial, is of eminent interest.
Here, we report high-pressure (p_max = 1.3 GPa) muon spin rotation experiments
on the temperature-dependent magnetic penetration depth in T_d-MoTe_2. A
substantial increase of the superfluid density n_s/m^* and a linear scaling
with T_c is observed under pressure. Moreover, the superconducting order
parameter in T_d-MoTe_2 is determined to be two gap (s+s)-wave symmetric. We
also excluded time reversal symmetry breaking in the SC state with sensitive
zero-field ${\mu}$SR experiments. Considering the previous report
\cite{Balicas1} on the strong suppression of T_c in T_d-MoTe_2 by disorder, we
suggest that s^{+-} (topological order parameter) state is more likely to be
realized in MoTe_2 than the s^{++} (trivial) state. Should s^{+-} be the SC gap
symmetry, the T_d-MoTe_2 is, to our knowledge, the first known example of a
time reversal invariant topological (Weyl) superconductor.",1704.05185v1
2017-04-24,Mass-Imbalanced Ionic Hubbard Chain,"A repulsive Hubbard model with both spin-asymmetric hopping (${t_\uparrow\neq
t_\downarrow}$) and a staggered potential (of strength $\Delta$) is studied in
one dimension. The model is a compound of the mass-imbalanced (${t_\uparrow\neq
t_\downarrow}$, ${\Delta=0}$) and ionic (${t_\uparrow = t_\downarrow}$,
${\Delta>0}$) Hubbard models, and may be realized by cold atoms in engineered
optical lattices. We use mostly mean-field theory to determine the phases and
phase transitions in the ground state for a half-filled band (one particle per
site). We find that a period-two modulation of the particle (or charge) density
and an alternating spin density coexist for arbitrary Hubbard interaction
strength, ${U\geqslant 0}$. The amplitude of the charge modulation is largest
at ${U=0}$, decreases with increasing $U$ and tends to zero for
${U\rightarrow\infty}$. The amplitude for spin alternation increases with $U$
and tends to saturation for ${U\rightarrow\infty}$. Charge order dominates
below a critical value $U_c$, whereas magnetic order dominates above. The
mean-field Hamiltonian has two gap parameters, $\Delta_\uparrow$ and
$\Delta_\downarrow$, which have to be determined self-consistently. For
${U<U_c}$ both parameters are positive, for ${U>U_c}$ they have different
signs, and for ${U=U_c}$ one gap parameter jumps from a positive to a negative
value. The weakly first-order phase transition at $U_c$ can be interpreted in
terms of an avoided criticality (or metallicity). The system is reluctant to
restore a symmetry that has been broken explicitly.",1704.07459v2
2017-05-23,Temperature independent band structure of WTe2 as observed from ARPES,"Extremely large magnetoresistance (XMR), observed in transition metal
dichalcogendies, WTe$_2$, has attracted recently a great deal of research
interests as it shows no sign of saturation up to the magnetic field as high as
60 T, in addition to the presence of type-II Weyl fermions. Currently, there
has been a lot of discussion on the role of band structure changes on the
temperature dependent XMR in this compound. In this contribution, we study the
band structure of WTe$_2$ using angle-resolved photoemission spectroscopy
(ARPES) and first-principle calculations to demonstrate that the temperature
dependent band structure has no substantial effect on the temperature dependent
XMR as our measurements do not show band structure changes on increasing the
sample temperature between 20 and 130 K. We further observe an electronlike
surface state, dispersing in such a way that it connects the top of bulk
holelike band to the bottom of bulk electronlike band. Interestingly, similar
to bulk states, the surface state is also mostly intact with the sample
temperature. Our results provide invaluable information in shaping the
mechanism of temperature dependent XMR in WTe$_2$.",1705.09146v2
2017-06-28,Instabilities of a U(1) quantum spin liquid in disordered non-Kramers pyrochlores,"Quantum spin liquids (QSLs) are exotic phases of matter exhibiting long-range
entanglement and supporting emergent gauge fields. A vigorous search for
experimental realizations of these states has identified several materials with
properties hinting at QSL physics. A key issue in understanding these QSL
candidates is often the interplay of weak disorder of the crystal structure
with the spin liquid state. It has recently been pointed out that in at least
one important class of candidate QSLs - pyrochlore magnets based on non-Kramers
ions such as Pr$^{3+}$ or Tb$^{3+}$- structural disorder can actually promote a
$U(1)$ QSL ground state. Here we set this proposal on a quantitative footing by
analyzing the stability of the QSL state in the minimal model for these
systems: a random transverse field Ising model. We consider two kinds of
instability, which are relevant in different limits of the phase diagram:
condensation of spinons and confinement of the $U(1)$ gauge fields. Having
obtained stability bounds on the QSL state we apply our results directly to the
disordered candidate QSL Pr$_2$Zr$_2$O$_7$. We find that the available data for
currently studied samples of Pr$_2$Zr$_2$O$_7$ is most consistent with it a
ground state outside the spin liquid regime, in a paramagnetic phase with
quadrupole moments near saturation due to the influence of structural disorder.",1706.09238v2
2017-07-10,Two-temperature momentum distribution in a Thulium magneto-optical trap,"Second-stage laser cooling of thulium atoms at the 530.7 nm transition with a
natural linewidth of 350 kHz offers an interesting possibility to study
different regimes of a magneto-optical trap (MOT). The intermediate value of
the spectral linewidth of the cooling transition allows the observation of
three distinct regimes depending on intensity and detuning of the cooling
beams. Namely, the ""bowl-shaped"" regime when light pressure force competes with
gravity, the ""double structure"" regime with interplay between Doppler and
polarization-gradient (sub-Doppler) cooling, and the ""symmetric"" regime when
Doppler cooling dominates over sub-Doppler cooling and gravity. The
polarization-gradient cooling manifests itself by a two-temperature momentum
distribution of atoms resulting in a double-structure of the spatial MOT
profile consisting of a cold central fraction surrounded by a hot halo. We
studied the ""double structure"" regime at different saturation parameters and
compared observations with calculations based on semiclassical and quantum
approaches. The quantum treatment adequately reproduces experimental results if
the MOT magnetic field is properly taken into account.",1707.02947v3
2017-10-09,"Finite temperature physics of $1D$ topological Kondo insulator: Stable Haldane phase, Emergent energy scale and Beyond","We have studied the one-dimensional $p$-wave periodic Anderson model at
finite temperature with the help of the numerically exact determinant quantum
Monte Carlo simulation. It is found that the topological Haldane phase
established for ground-state is still stable against small thermal fluctuation
and its characteristic edge magnetization develops at low temperature.
Moreover, the saturated low-$T$ spin structure factor and the $\frac{1}{T}$-law
of susceptibility are useful to detect the free edge spin moment, which may be
relevant for experimental explorations. We have also comparatively studied the
conventional $s$-wave periodic Anderson model, which helps us identify an
emergent energy scale $T_{cr}$. $T_{cr}$ signals a crossover into interesting
low-$T$ regime and seems to be the expected Ruderman-Kittel-Kasuya-Yosida
(RKKY) coupling. Finally, the collective Kondo screening effect has been
examined and it is heavily reduced at boundary, which may give a fruitful
playground for novel physics beyond the well-established Haldane state and
topological band insulators.",1710.02978v3
2017-10-31,Spin susceptibility of charge ordered YBa2Cu3Oy across the upper critical field,"The value of the upper critical field Hc2, a fundamental characteristic of
the superconducting state, has been subject to strong controversy in high-Tc
copper-oxides. Since the issue has been tackled almost exclusively by
macroscopic techniques so far, there is a clear need for local-probe
measurements. Here, we use 17O NMR to measure the spin susceptibility
$\chi_{spin}$ of the CuO2 planes at low temperature in charge ordered
YBa2Cu3Oy. We find that $\chi_{spin}$ increases (most likely linearly) with
magnetic field H and saturates above field values ranging from 20 to 40 T. This
result is consistent with Hc2 values claimed by G. Grissonnanche et al. [Nat.
Commun. 5, 3280 (2014)] and with the interpretation that the
charge-density-wave (CDW) reduces Hc2 in underdoped YBa2Cu3Oy. Furthermore, the
absence of marked deviation in $\chi_{spin}(H)$ at the onset of long-range CDW
order indicates that this Hc2 reduction and the Fermi-surface reconstruction
are primarily rooted in the short-range CDW order already present in zero
field, not in the field-induced long-range CDWorder. Above Hc2, the relatively
low values of $\chi_{spin}$ at T=2 K show that the pseudogap is a ground-state
property, independent of the superconducting gap.",1711.00109v1
2017-11-28,Nodal multigap superconductivity in KCa$_2$Fe$_4$As$_4$F$_2$,"We find evidence that the newly discovered Fe-based superconductor
KCa$_2$Fe$_4$As$_4$F$_2$ ($T_c~=~33.36(7)$~K) displays multigap
superconductivity with line nodes. Transverse field muon spin rotation
($\mu$SR) measurements show that the temperature dependence of the superfluid
density does not have the expected behavior of a fully-gapped superconductor,
due to the lack of saturation at low temperatures. Moreover, the data cannot be
well fitted using either single band models or a multiband $s$-wave model, yet
are well described by two-gap models with line nodes on either one or both of
the gaps. Meanwhile the zero-field $\mu$SR results indicate a lack of time
reversal symmetry breaking in the superconducting state, but suggest the
presence of magnetic fluctuations. These results demonstrate a different route
for realizing nodal superconductivity in iron-based superconductors. Here the
gap structure is drastically altered upon replacing one of the spacer layers,
indicating the need to understand how the pairing state is tuned by changes of
the asymmetry between the pnictogens located either side of the Fe planes.",1711.10139v2
2017-12-19,Li doping kagome spin liquid compounds,"Herbertsmithite and Zn-doped barlowite are two compounds for experimental
realization of twodimensional gapped kagome spin liquid. Theoretically, it has
been proposed that charge doping a quantum spin liquid gives rise to exotic
metallic states, such as high-temperature superconductivity. However, one
recent experiment about herbertsmithite with successful Li-doping shows
surprisingly the insulating state even under the heavy doped scenario, which
can hardly be explained by many-body physics. Using first-principles
calculation, we performed a comprehensive study about the Li intercalated
doping effect of these two compounds. For the Li-doped herbertsmithite, we
identified the optimized Li position at the Cl-(OH)$_3$-Cl pentahedron site
instead of previously speculated Cl-(OH)$_3$ tetrahedral site. With the
increase of Li doping concentration, the saturation magnetization decreases
linearly due to the charge transfer from Li to Cu ions. Moreover, we found that
Li forms chemical bonds with the nearby (OH)$^-$ and Cl$^-$ ions, which lowers
the surrounding chemical potential and traps the electron, as evidenced by the
localized charge distribution, explaining the insulating behavior measured
experimentally. Though with different structure from herbertsmithite, Zn-doped
Barlowite shows the same features upon Li doping. We conclude that Li doping
this family of kagome spin liquid cannot realize exotic metallic states, other
methods should be further explored, such as element substitution with different
valence electrons.",1712.06791v2
2017-12-19,Anomalous metals -- failed superconductors,"The observation of metallic ground states in a variety of two-dimensional
electronic systems poses a fundamental challenge for the theory of electron
fluids. Here, we analyze evidence for the existence of a regime, which we call
the ""anomalous metal regime,"" in diverse 2D superconducting systems driven
through a quantum superconductor to metal transition (QSMT) by tuning physical
parameters such as the magnetic field, the gate voltage in the case of systems
with a MOSFET geometry, or the degree of disorder. The principal
phenomenological observation is that in the anomalous metal, as a function of
decreasing temperature, the resistivity first drops as if the system were
approaching a superconducting ground state, but then saturates at low
temperatures to a value that can be orders of magnitude smaller than the Drude
value. The anomalous metal also shows a giant positive magneto-resistance.
Thus, it behaves as if it were a ""failed superconductor."" This behavior is
observed in a broad range of parameters. We moreover exhibit, by theoretical
solution of a model of superconducting grains embedded in a metallic matrix,
that as a matter of principle such anomalous metallic behavior can occur in the
neighborhood of a QSMT. However, we also argue that the robustness and
ubiquitous nature of the observed phenomena are difficult to reconcile with any
existing theoretical treatment, and speculate about the character of a more
fundamental theoretical framework.",1712.07215v1
2018-01-07,Graphene $n$-$p$ junctions in the Quantum Hall regime: numerical study of incoherent scattering effects,"We investigate electronic transport through a graphene $n$-$p$ junction in
the quantum Hall effect regime at high perpendicular magnetic field, when the
filling factors in the $n$-doped and $p$-doped regions are fixed to 2 and -2
respectively. We compute numerically the conductance $G$, the noise $Q$ and the
Fano factor $F$ of the junction when inelastic effects are included along the
interface in a phenomenological way, by means of fictitious voltage probes.
Using a scaling approach, we extract the system coherence length $L_\phi$ and
describe the full crossover between the coherent limit ($W\ll L_\phi$) and the
incoherent limit ($W\gg L_\phi$), $W$ being the interface length. While $G$
saturates at the value $e^2/h$ in the incoherent regime, $Q$ and $F$ are found
to vanish exponentially for large length $W$. Corrections due to disorder are
also investigated. Our results are finally compared to available experimental
data.",1801.02235v2
2018-01-09,Superfluid drag in the two-component Bose-Hubbard model,"In multicomponent superfluids and superconductors, co- and counter-flows of
components have in general different properties. It was discussed in 1975 by
Andreev and Bashkin, in the context of He$^3$/He$^4$ superfluid mixtures, that
inter-particle interactions produce a dissipationless drag. The drag can be
understood as a superflow of one component induced by phase gradients of the
other component. Importantly the drag can be both positive (entrainment) and
negative (counter-flow). The effect is known to be of crucial importance for
many properties of diverse physical systems ranging from the dynamics of
neutron stars, rotational responses of Bose mixtures of ultra-cold atoms to
magnetic responses of multicomponent superconductors. Although there exists a
substantial literature that includes the drag interaction phenomenologically,
much fewer regimes are covered by quantitative studies of the microscopic
origin of the drag and its dependence on microscopic parameters. Here we study
the microscopic origin and strength of the drag interaction in a quantum system
of two-component bosons on a lattice with short-range interaction. By
performing quantum Monte-Carlo simulations of a two-component Bose-Hubbard
model we obtain dependencies of the drag strength on the boson-boson
interactions and properties of the optical lattice. Of particular interest are
the strongly-correlated regimes where the ratio of co-flow and counter-flow
superfluid stiffnesses can diverge, corresponding to the case of saturated
drag.",1801.03052v1
2018-03-01,Turbulence Closure for Mixing Length Theories,"We present an approach to turbulence closure based on mixing length theory
with three-dimensional fluctuations against a two-dimensional background. This
model is intended to be rapidly computable for implementation in stellar
evolution software and to capture a wide range of relevant phenomena with just
a single free parameter, namely the mixing length. We incorporate magnetic,
rotational, baroclinic and buoyancy effects exactly within the formalism of
linear growth theories with nonlinear decay. We treat differential rotation
effects perturbatively in the corotating frame using a novel controlled
approximation which matches the time evolution of the reference frame to
arbitrary order. We then implement this model in an efficient open source code
and discuss the resulting turbulent stresses and transport coefficients. We
demonstrate that this model exhibits convective, baroclinic and shear
instabilities as well as the magnetorotational instability (MRI). It also
exhibits non-linear saturation behaviour, and we use this to extract the
asymptotic scaling of various transport coefficients in physically interesting
limits.",1803.00579v3
2018-03-10,Observation of Chiral character deep in the topological insulating regime in Bi$_{1-x}$Sb$_x$,"Bi$_{1-x}$Sb$_x$ is a topological insulator (TI) for $x \approx 0.03
$--$0.20$. Close to the Topological phase transition at $x = 0.03$, a magnetic
field induced Weyl semi-metal (WSM) state is stabilized due to the splitting of
the Dirac cone into two Weyl cones of opposite chirality. A signature of the
Weyl state is the observation of a Chiral anomaly [negative longitudnal
magnetoresistance (LMR)] and a violation of the Ohm's law (non-linear $I-V$).
We report the unexpected discovery of a Chiral anomaly in the whole range ($x =
0.032, 0.072, 0.16$) of the TI state. This points to a field induced WSM state
in an extended $x$ range and not just near the topological transition at $x =
0.03$. Surprisingly, the strongest Weyl phase is found at $x = 0.16$ with a
non-saturating negative LMR much larger than observed for $x = 0.03$. The
negative LMR vanishes rapidly with increasing angle between $B$ and $I$.
Additionally, non-linear $I$--$V$ is found for $x = 0.16$ indicating a
violation of Ohm's law. This unexpected observation of a strong Weyl state in
the whole TI regime in Bi$_{1-x}$Sb$_x$ points to a gap in our understanding of
the detailed electronic structure evolution in this alloy system.",1803.03825v1
2018-04-09,Boiling crisis dynamics: low gravity experiments at high pressure,"To understand the boiling crisis mechanism, one can take advantage of the
slowing down of boiling at high pressures, in the close vicinity of the
liquid-vapor critical point of the given fluid. To preserve conventional bubble
geometry, such experiments need to be carried out in low gravity. We report
here two kinds of saturated boiling experiments. First we discuss the spatial
experiments with SF$_6$ at 46$^\circ$ C. Next we address two ground-based
experiments under magnetic gravity compensation with H$_2$ at 33 K. We compare
both kinds of experiments and show their complementarity. The dry spots under
vapor bubbles are visualized by using transparent heaters made with metal oxide
films. We evidence two regimes of the dry spots growth: the regime of circular
dry spots and the regime of chain coalescence of dry spots that immediately
precedes the heater dryout. A recent H$_2$ experiment is shown to bridge the
gap between the near-critical and low pressure boiling experiments.",1804.03050v1
2018-04-18,Equation of state and optical properties of shock-compressed C:H:N:O molecular mixtures,"Water, ethanol, and ammonia are the key components of the mantles of Uranus
and Neptune. To improve structure and evolution models and give an explanation
of the magnetic fields and luminosities of the icy giants, those components
need to be characterised at planetary conditions (some Mbar and a few $10^3$
K). Those conditions are typical of the Warm Dense Matter regime, which
exhibits a rich phase diagram, with the coexistence of many states of matter
and a large variety of chemical processes. H$_2$O, C:H:O, and C:H:N:O mixtures
have been compressed up to 2.8 Mbar along the principal Hugoniot using
laser-driven decaying shocks. The experiments were performed at the GEKKO XII
and LULI 2000 laser facilities using standard optical diagnostics (Doppler
velocimetry and pyrometry) to characterise equation of state and optical
reflectivity of the shocked states. The results show that H$_2$O and the
C:H:N:O mixture share the same equation of state with a density scaling, while
the reflectivity behaves differently by what concerns both the onset pressures
and the saturation values. The reflectivity measurement at two frequencies
allows to estimate the conductivity and the complex refractive index using a
Drude model.",1804.06595v1
2018-04-21,Experimental Signatures of Spin Superfluid Ground State in Canted Antiferromagnet Cr2O3 via Nonlocal Spin Transport,"Spin superfluid is a novel emerging quantum matter arising from the
Bose-Einstein condensate (BEC) of spin-1 bosons. We demonstrate the spin
superfluid ground state in canted antiferromagnetic Cr2O3 thin film at low
temperatures via nonlocal spin transport. A large enhancement of the nonlocal
spin signal is observed below ~ 20 K, and it saturates from ~ 5 K down to 2 K.
We show that the spins can propagate over very long distances (~ 20 micro
meters) in such spin superfluid ground state and the nonlocal spin signal
decreases very slowly as the spacing increases with an inverse relationship,
which is consistent with theoretical prediction. Furthermore, spin
superfluidity has been investigated in the canted antiferromagnetic phase of
the (11-20)-oriented Cr2O3 film, where the magnetic field dependence of the
associated critical temperature follows a two-thirds power law near the
critical point. The experimental demonstration of the spin superfluid ground
state in canted antiferromagnet will be extremely important for the fundamental
physics on the BEC of spin-1 bosons and paves the way for future spin
supercurrent devices, such as spin-Josephson junctions.",1804.07966v1
2018-05-09,Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs,"We use inelastic neutron scattering to study acoustic phonons and spin
excitations in single crystals of NaFeAs, a parent compound of iron pnictide
superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural
transition at $T_s\approx 58$ K and a collinear antiferromagnetic (AF) order at
$T_N\approx 45$ K. While longitudinal and out-of-plane transverse acoustic
phonons behave as expected, the in-plane transverse acoustic phonons reveal
considerable softening on cooling to $T_s$, and then harden on approaching
$T_N$ before saturating below $T_N$. In addition, we find that spin-spin
correlation lengths of low-energy magnetic excitations within the FeAs layer
and along the $c$-axis increase dramatically below $T_s$, and show weak anomaly
across $T_N$. These results suggest that the electronic nematic phase present
in the paramagnetic tetragonal phase is closely associated with dynamic
spin-lattice coupling, possibly arising from the one-phonon-two-magnon
mechanism.",1805.03493v1
2018-06-18,Renormalization of quantum dot $g$-factor in superconducting Rashba nanowires,"We study analytically and numerically the renormalization of the $g$-factor
in semiconducting Rashba nanowires (NWs), consisting of a normal and
superconducting section. If the potential barrier between the sections is high,
a quantum dot (QD) is formed in the normal section. For harmonic (hard-wall)
confinement, the effective $g$-factor of all QD levels is suppressed
exponentially (power-law) in the product of the spin-orbit interaction (SOI)
wavevector and the QD length. If the barrier between the two sections is
removed, the $g$-factor of the emerging Andreev bound states is suppressed less
strongly. In the strong SOI regime and if the chemical potential is tuned to
the SOI energy in both sections, the $g$-factor saturates to a universal
constant. Remarkably, the effective $g$-factor shows a pronounced peak at the
SOI energy as function of the chemical potentials. In addition, if the SOI is
uniform, the $g$-factor renormalization as a function of the chemical potential
is given by a universal dependence which is independent of the QD size. This
prediction provides a powerful tool to determine experimentally whether the SOI
in the whole NW is uniform and, moreover, gives direct access to the SOI
strengths of the NW via $g$-factor measurements. In addition, it allows one to
find the optimum position of the chemical potential for bringing the NW into
the topological phase at large magnetic fields.",1806.06842v1
2018-11-08,Light-induced anomalous Hall effect in graphene,"Many striking non-equilibrium phenomena have been discovered or predicted in
optically-driven quantum solids, ranging from light-induced superconductivity
to Floquet-engineered topological phases. These effects are expected to lead to
dramatic changes in electrical transport, but can only be comprehensively
characterized or functionalized with a direct interface to electrical devices
that operate at ultrafast speeds. Here, we make use of laser-triggered
photoconductive switches to measure the ultrafast transport properties of
monolayer graphene, driven by a mid-infrared femtosecond pulse of circularly
polarized light. The goal of this experiment is to probe the transport
signatures of a predicted light-induced topological band structure in graphene,
similar to the one originally proposed by Haldane. We report the observation of
an anomalous Hall effect in the absence of an applied magnetic field. We also
extract quantitative properties of the non-equilibrium state. The dependence of
the effect on a gate potential used to tune the Fermi level reveals multiple
features that reflect the effective band structure expected from Floquet
theory. This includes a ~60 meV wide conductance plateau centered at the Dirac
point, where a gap of approximately equal magnitude is expected to open. We
also find that when the Fermi level lies within this plateau, the estimated
anomalous Hall conductance saturates around ~1.8$\pm$0.4 e$^2$/h.",1811.03522v2
2018-11-29,Application of an extended van der Pauw method to anisotropic magnetoresistance measurements of ferromagnetic films,"We demonstrate anisotropic resistivity measurements using the extended van
der Pauw (vdP) method in ferromagnetic Ni80Fe20 (Py) films. We apply it to
measure anisotropic magnetoresistance (AMR) and compare the results of the vdP
method with the more conventional Hall-bar method along the hard and easy axis
of the film and show that the vdP method gives more reliable AMR result. For
instance, the AMR result along the hard and easy axis of the film are in close
agreement. Further, we applied the vdP method to study AMR in a series of Py
films with thicknesses ranging between 10-250 nm. The films were grown by
sputtering deposition at an angle with respect to the substrate normal and with
an in-situ magnetic field, both conditions assisting in the definition of
in-plane uniaxial anisotropy. The microstructure of Py films was characterized
using X-ray reflectivity, diffraction and polar mapping of (111) planes. We
detected no off-normal texture and negligible surface roughness, which
indicates that self-shadowing is not dominating in our growth. Yet the films
have well defined uniaxial anisotropy. Abrupt changes in the average
resistivity vs. film thickness were observed, which cannot be explained by the
models accounting for the thickness and grain size but strongly correlate with
the changes in (111) texture in the films. We compared our results with the
literature and show that independent of growth method, substrate and deposition
temperature, the AMR value presents a saturation behavior with thickness at
about 100 nm.",1811.12029v1
2018-12-23,Constraining Theories of Polarized SiO Maser Transport: Multi-Epoch Analysis of a $π/2$ Electric Vector Rotation Feature,"The detailed polarization mechanisms of SiO masers originating from the near
circum\-stellar environment of Asymptotic Giant Branch stars are not yet
definitively known. Prevailing theories are broadly classified as either Zeeman
or non-Zeeman in origin, the latter including effects such as anisotropic
pumping or anisotropic resonant scattering. The predicted behavior of the
linear and circular polarization fractions and electric vector position angle
vary by theory. In particular, individual maser features that exhibit a
rotation in linear polarization of $\sim \pi/2$ as a function of frequency over
their extent can be utilized as a test of several maser polarization transport
theories. In this paper, we analyze one SiO ($\nu=1$, $J=1-0$) maser feature
toward the Mira variable, TX Cam that exhibits this internal polarization
rotation and persists across five epochs (spanning $\sim3$ months). We compare
our results to the predictions by several maser polarization theories and find
that the linear polarization across the feature is consistent with a geometric
effect for a saturated maser originating when the angle between the projected
magnetic field and the line of sight ($\theta$) crosses the Van Vleck angle
$\theta_F \sim 55^{\circ}$. However, the electric vector position angle (EVPA)
exhibits a smooth rotation across the spatial extent of the feature rather than
the expected abrupt $\pi/2$ flip. We discuss possible explanations for this
discrepancy and alternative theories. Circular polarization across the feature
is also analyzed and it is the most accurately described by Zeeman effects
giving rise to a circular polarization fraction of the form $m_c$ is
approximately proportional to $\cos \theta$.",1812.09631v1
2018-12-29,Single-layer tensor network study of the Heisenberg model with chiral interactions on a kagome lattice,"We study the antiferromagnetic kagome Heisenberg model with additional
scalar-chiral interaction by using the infinite projected entangled-pair state
(iPEPS) ansatz. We discuss in detail the implementation of optimization
algorithm in the framework of the single-layer tensor network based on the
corner-transfer matrix technique. Our benchmark based on the full-update
algorithm shows that the single-layer algorithm is stable, which leads to the
same level of accuracy as the double-layer ansatz but with much less
computation time. We further apply this algorithm to study the nature of the
kagome Heisenberg model with a scalar-chiral interaction by computing the bond
dimension scaling of magnetization, bond energy difference, chiral order
parameter and correlation length. In particular, we find that for strong chiral
coupling the correlation length, which is extracted from the transfer matrix,
saturates to a finite value for large bond dimension, representing a gapped
spin-liquid state. Further comparison with density matrix renormalization group
results supports that our iPEPS faithfully represents the time-reversal
symmetry breaking chiral state. Our iPEPS simulation results shed new light on
constructing PEPS for describing gapped chiral topological states.",1812.11436v3
2019-01-28,Super-Eddington accretion onto the Galactic ultraluminous X-ray pulsar Swift J0243.6+6124,"We report on the spectral behavior of the first Galactic ultraluminous X-ray
pulsar Swift J0243.6+6124 with NuSTAR observations during its 2017-2018
outburst. At sub-Eddington levels, the source spectrum is characterized by
three emission components, respectively from the accretion column, the hot
spot, and a broad iron line emission region. When the source is above the
Eddington limit, the hot spot temperature increases and the spectrum features
two more blackbody components. One blackbody component has a radius of 10-20 km
and is likely originated from the top of the accretion column. The other one
saturates at a blackbody luminosity of (1 - 2)*10^38 erg/s, coincident with the
Eddington limit of a neutron star. This is well consistent with the scenario
that super-Eddington accretion onto compact objects will power optically-thick
outflows and indicates an accretion rate 60-80 times the critical value. This
suggests that super-Eddington accretion onto magnetized systems can also power
massive winds. At super-Eddington levels, the iron line becomes more
significant and blueshifted, and is argued to be associated with the ultrafast
wind in the central funnel or jets. This source, if located in external
galaxies, will appear like other ultraluminous pulsars.",1901.09485v1
2019-02-16,Bulk Fermi surface of the type-II Weyl semimetal candidate NbIrTe$_{4}$,"Recently, a new group of layered transition-metal tetra-chalcogenides were
proposed, via first principles calculations, to correspond to a new family of
Weyl type-II semimetals with promising topological properties in the bulk as
well as in the monolayer limit. In this article, we present measurements of the
Shubnikov-de Haas (SdH) and de Haas-van Alphen effects under high magnetic
fields for the type-II Weyl semimetallic candidate NbIrTe$_{4}$. We find that
the angular dependence of the observed Fermi surface extremal cross-sectional
areas agree well with our DFT calculations supporting the existence of Weyl
type-II points in this material. Although we observe a large and non-saturating
magnetoresistivity in NbIrTe$_{4}$ under fields all the way up to 35 T,
Hall-effect measurements indicate that NbIrTe$_{4}$ is not a compensated
semimetal. The transverse magnetoresistivity displays a four-fold angular
dependence akin to the so-called butterfly magnetoresistivity observed in nodal
line semimetals. However, we conclude that its field and this unconventional
angular-dependence are governed by the topography of the Fermi-surface and the
resulting anisotropy in effective masses and in carrier mobilities.",1902.06159v3
2019-03-08,Josephson Field-Effect Transistors Based on All-Metallic Al/Cu/Al Proximity Nanojunctions,"We demonstrate the first \textit{all-metallic} mesoscopic
superconductor-normal metal-superconductor (SNS) field-effect controlled
Josephson transistors (SNS-FETs) and show their full characterization from the
critical temperature $T_c$ down to 50 mK in the presence of both electric and
magnetic field. The ability of a static electric field -applied by mean of a
lateral gate electrode- to suppress the critical current $I_s$ in a
proximity-induced superconductor is proven for both positive and negative gate
voltage values. $I_s$ suppression reached typically about one third of its
initial value, saturating at high gate voltages. The transconductance of our
SNS-FETs obtains values as high as 100 nA/V at 100 mK. On the fundamental
physics side, our results suggest that the mechanism at the basis of the
observed phenomenon is quite general and does not rely on the existence of a
true pairing potential, but rather the presence of superconducting correlations
is enough for the effect to occur. On the technological side, our findings
widen the family of materials available for the implementation of all-metallic
field-effect transistors to \textit{synthetic} proximity-induced
superconductors.",1903.03435v2
2019-04-22,Highly anisotropic interlayer magnetoresistance in ZrSiS nodal-line Dirac semimetal,"We instigate the angle-dependent magnetoresistance (AMR) of the layered
nodal-line Dirac semimetal ZrSiS for the in-plane and out-of-plane current
directions. This material has recently revealed an intriguing butterfly-shaped
in-plane AMR that is not well understood. Our measurements of the polar
out-of-plane AMR show a surprisingly different response with a pronounced
cusp-like feature. The maximum of the cusp-like anisotropy is reached when the
magnetic field is oriented in the $a$-$b$ plane. Moreover, the AMR for the
azimuthal out-of-plane current direction exhibits a very strong four-fold
$a$-$b$ plane anisotropy. Combining the Fermi surfaces calculated from first
principles with the Boltzmann's semiclassical transport theory we reproduce and
explain all the prominent features of the unusual behavior of the in-plane and
out-of-plane AMR. We are also able to clarify the origin of the strong
non-saturating transverse magnetoresistance as an effect of imperfect
charge-carrier compensation and open orbits. Finally, by combining our
theoretical model and experimental data we estimate the average relaxation time
of $2.6\times10^{-14}$~s and the mean free path of $15$~nm at 1.8~K in our
samples of ZrSiS.",1904.09933v2
2019-04-29,Type-II Ising superconductivity and anomalous metallic state in macro-size ambient-stable ultrathin crystalline films,"Recent emergence of two-dimensional (2D) crystalline superconductors has
provided a promising platform to investigate novel quantum physics and
potential applications. To reveal essential quantum phenomena therein, ultralow
temperature transport investigation on high quality ultrathin superconducting
films is critically required, although it has been quite challenging
experimentally. Here we report a systematic transport study on the ultrathin
crystalline PdTe2 films grown by molecular beam epitaxy (MBE). Interestingly, a
new type of Ising superconductivity in 2D centrosymmetric materials is revealed
by the detection of large in-plane critical field more than 7 times Pauli
limit. Remarkably, in perpendicular magnetic field, we provide solid evidence
of anomalous metallic state characterized by the resistance saturation at low
temperatures with high quality filters. The robust superconductivity with
intriguing quantum phenomena in the macro-size ambient-stable ultrathin PdTe2
films remains almost the same for 20 months, showing great potentials in
electronic and spintronic applications.",1904.12719v2
2019-05-03,Evidence of quantum vortex fluid in the mixed state of a very weakly pinned a-MoGe thin film,"Quantum fluids refer to a class of systems that remain in fluid state down to
absolute zero temperature. In this letter, using a combination of
magnetotransport and scanning tunneling spectroscopy down to 300 mK, we show
that vortices in a very weakly pinned a-MoGe thin film can form a quantum
vortex fluid. Under the application of a magnetic field perpendicular to the
plane of the film, the vortex state transforms from a vortex solid to a hexatic
vortex fluid and eventually to an isotropic vortex liquid. The fact that the
two latter states remain fluid down to absolute zero temperature is evidenced
from the electrical resistance which saturates to a finite value at low
temperatures. Furthermore, scanning tunneling spectroscopy measurements reveal
a soft gap at the center of each vortex, which arises from large zero point
fluctuation of vortices.",1905.01045v4
2019-08-27,Contribution of the chiral vortical effect to the evolution of the hypermagnetic field and the matter-antimatter asymmetry in the early Universe,"In this paper, we study the contribution of the chiral vortical effect, in
addition to that of the chiral magnetic effect, to the evolution of the
hypermagnetic field and the matter-antimatter asymmetry in the symmetric phase
of the early Universe in the temperature range 100GeV < T < 10TeV. We choose a
fully helical Chern-Simons wave configuration for the velocity and the
hypermagnetic vector potential fields. The latter makes the plasma force-free
in the absence of viscosity. We show that the most pronounced effect of the
chiral vorticity is the production and initial growth of the hypermagnetic
field. In particular, we show that in the presence of a non-zero matter
asymmetry, the hypermagnetic field can grow from zero initial value only in the
presence of a non-zero vorticity field. Moreover, we show that larger initial
growths not only result in larger maximum values of the hypermagnetic field,
but also cause the saturation of the hypermagnetic field and the conversion of
the lepton-baryon asymmetry to occur more quickly, i.e., at a higher
temperature. We show that the damping of the vorticity due to the presence of
viscosity, which typically occurs extremely rapidly, does not significantly
affect the evolution.",1908.10105v2
2019-10-23,"HFQPOs and discoseismic mode excitation in eccentric, relativistic discs. I. Hydrodynamic simulations","High-frequency quasi-periodic oscillations (HFQPOs) observed in the emission
of black-hole X-ray binary systems promise insight into strongly curved
spacetime. `Discoseismic' oscillations with frequencies set by the intrinsic
properties of the central black hole, in particular `trapped inertial waves'
(r-modes), offer an attractive explanation for HFQPOs. To produce an observable
signature, however, such oscillations must be excited to sufficiently large
amplitudes. Turbulence driven by the magnetorotational instability (MRI) fails
to provide the necessary amplification, but r-modes may still be excited via
interaction with accretion disc warps or eccentricities. We present 3D global
hydrodynamic simulations of relativistic accretion discs, which demonstrate for
the first time the excitation of trapped inertial waves by an imposed
eccentricity in the flow. While the r-modes' saturated state depends on the
vertical boundary conditions used in our unstratified, cylindrical framework,
their excitation is unambiguous in all runs with eccentricity >0.005 near the
ISCO. These simulations provide a proof of concept, demonstrating the
robustness of trapped inertial wave excitation in a non-magnetized context. In
a companion paper, we explore the competition between this excitation, and
damping by magnetohydrodynamic turbulence.",1910.10696v3
2019-10-30,A note on the experiment parameters for the non-resonant streaming instability: competition between left and right circularly polarized modes,"A non-resonant streaming instability driven by cosmic-ray currents, also
called Bell's instability, is proposed as a candidate for providing the
required magnetic turbulence of efficient diffusive shock accelerations. To
demonstrate the saturation level and mechanism of the non-resonant streaming
instability in a laboratory environment, we attempt to develop an experiment at
the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). As an electron
beam is used to replace the proton beam to carry the cosmic-ray current in our
experiment, the polarization of the non-resonant streaming instability will be
modified from the left-handed (LH) mode to the right-handed (RH) mode. The
theoretical instability analysis shows that the growth rate of this RH
non-resonant mode may be smaller than it of the LH resonant mode. However the
LH resonant mode can be ignored in our experiment while the expected wavelength
is longer than the used plasma cell. The results of PIC simulations will also
support this contention and the occurrence of non-resonant streaming
instability in our experiment.",1910.13756v1
2020-01-14,Spectrum variability of the active solar-type star Xi Bootis A,"An extensive spectroscopic study on \xi Boo A (chromospherically active
solar-type star) was conducted based on the spectra obtained in 2008 December
though 2010 May, with an aim to detect any spectrum variability and to
understand its physical origin. For each spectrum, the atmospheric parameters
were spectroscopically determined based on Fe lines, and the equivalent widths
(along with the line-broadening parameters) of selected 99 lines were measured.
We could detect meaningful small fluctuations in the equivalent widths of
medium-strength lines. This variation was found to correlate with the effective
temperature (T_eff) consistently with the T-sensitivity of each line, which
indicates that the difference in the mean temperature averaged over the disk of
inhomogeneous condition is mainly responsible for this variability. It was also
found that the macrobroadening widths of medium-strength lines and the
equivalent widths dispersion of saturated lines tend to increase with the
effective Lande factor, suggesting an influence of magnetic field. Our power
spectrum analysis applied to the time-sequence data of V I/Fe II line-strength
ratio and T_eff could not confirm the 6.4 d period reported by previous
studies. We suspect that surface inhomogeneities of \xi Boo A at the time of
our observations were not so much simple (such as single star patch) as rather
complex (e.g., intricate aggregate of spots and faculae).",2001.04590v1
2020-01-23,The theory of direct laser excitation of nuclear transitions,"A comprehensive theoretical study of direct laser excitation of a nuclear
state based on the density matrix formalism is presented. The nuclear clock
isomer $^{229\text{m}}$Th is discussed in detail, as it could allow for direct
laser excitation using existing technology and provides the motivation for this
work. The optical Bloch equations are derived for the simplest case of a pure
nuclear two-level system and for the more complex cases taking into account the
presence of magnetic sub-states, hyperfine-structure and Zeeman splitting in
external fields. Nuclear level splitting for free atoms and ions as well as for
nuclei in a solid-state environment is discussed individually. Based on the
obtained equations, nuclear population transfer in the low-saturation limit is
reviewed. Further, nuclear Rabi oscillations, power broadening and nuclear
two-photon excitation are considered. Finally, the theory is applied to the
special cases of $^{229\text{m}}$Th and $^{235\text{m}}$U, being the nuclear
excited states of lowest known excitation energies. The paper aims to be a
didactic review with many calculations given explicitly.",2001.08320v2
2020-02-18,Signatures of dephasing by mirror-symmetry breaking in weak-antilocalization magnetoresistance across the topological transition in Pb$_{1-x}$Sn$_{x}$Se,"Many conductors, including recently studied Dirac materials, show saturation
of coherence length on decreasing temperature. This surprising phenomenon is
assigned to external noise, residual magnetic impurities or two-level systems
specific to non-crystalline solids. Here, by considering the SnTe-class of
compounds as an example, we show theoretically that breaking of mirror symmetry
deteriorates Berry's phase quantization, leading to additional dephasing in
weak-antilocalization magnetoresistance (WAL-MR). Our experimental studies of
WAL-MR corroborate these theoretical expectations in (111) Pb$_{1-x}$Sn$_x$Se
thin film with Sn contents $x$ corresponding to both topological crystalline
insulator and topologically trivial phases. In particular, we find the
shortening of the phase coherence length in samples with intentionally broken
mirror symmetry. Our results indicate that the classification of quantum
transport phenomena into universality classes should encompass, in addition to
time-reversal and spin-rotation invariances, spatial symmetries in specific
systems.",2002.07622v5
2020-04-27,Anisotropy driven reversal of magnetisation in Blume-Capel ferromagnet: A Monte Carlo study,"The two dimensional Spin-1 Blume-Capel ferromagnet is studied by Monte Carlo
simulation with Metropolis algorithm. Starting from initial ordered spin
configuration the reversal of magnetisation is investigated in presence of a
magnetic field ($h$) applied in the opposite direction. The variations of the
reversal time with the strength of single site anisotropy are investigated in
details. The exponential dependence was observed. The systematic variations of
the mean reversal time with positive and negative anisotropy was found. The
mean macroscopic reversal time was observed to be linearly dependent on a
suitably defined microscopic reversal time. The saturated magnetisation $M_f$
after the reversal was noticed to be dependent of the strength of anisotropy
$D$. An interesting scaling relation was obtained, $|M_f| \sim
|h|^{\beta}f(D|h|^{-\alpha})$ with the scaling function of the form $f(x)=
\frac{1}{1+e^{(x-a)/b}}$. The temporal evolution of density of $S_i^z=0$
(surrounded by all $S_i^z=+1$) is observed to be exponentially decaying. The
growth of mean density of $S_i^z=-1$ has been fitted in a function
$\rho_{-1}(t) \sim \frac{1}{a+e^{(t_c-t)/c}}$. The characteristic time shows
$t_c \sim e^{-rD}$ and a crossover in the rate of exponential falling is
observed at $D=1.5$. The metastable volume fraction has been found to obey the
Avrami's law.",2004.12586v4
2020-05-20,Sub-grid-scale effects in magnetised plasma turbulence,"In the present paper, we use a coarse-graining approach to investigate the
nonlinear redistribution of free energy in both position and scale space for
weakly collisional magnetised plasma turbulence. For this purpose, we use
high-resolution numerical simulations of gyrokinetic (GK) turbulence that span
the proton-electron range of scales, in a straight magnetic guide field
geometry. Accounting for the averaged effect of the particles' fast gyro-motion
on the slow plasma fluctuations, the GK approximation captures the dominant
energy redistribution mechanisms in strongly magnetised plasma turbulence.
Here, the GK system is coarse-grained with respect to a cut-off scale,
separating in real space the contributions to the nonlinear interactions from
the coarse-grid-scales and the sub-grid-scales (SGS). We concentrate on the
analysis of nonlinear SGS effects. Not only that this allows us to investigate
the flux of free energy across the scales, but also to now analyse its spatial
density. We find that the net value of scale flux is an order of magnitude
smaller than both the positive and negative flux density contributions. The
dependence of the results on the filter type is also analysed. Moreover, we
investigate the advection of energy in position space. This rather novel
approach for GK turbulence can help in the development of SGS models that
account for advective unstable structures for space and fusion plasmas, and
with the analysis of the turbulent transport saturation.",2005.10166v2
2020-05-26,On quasi-parallel whistler waves in the solar wind,"The recent simulations showed that the whistler heat flux instability, which
presumably produces the most of quasi-parallel coherent whistler waves in the
solar wind, is not efficient in regulating the electron heat conduction. In
addition, recent spacecraft measurements indicated that some fraction of
coherent whistler waves in the solar wind may propagate anti-parallel to the
electron heat flux, being produced due to a perpendicular temperature
anisotropy of suprathermal electrons. We present analysis of properties of
parallel and anti-parallel whistler waves unstable at electron heat fluxes and
temperature anisotropies of suprathermal electrons typical of the pristine
solar wind. Assuming the electron population consisting of counter-streaming
dense thermal core and tenuous suprathermal halo populations, we perform a
linear stability analysis to demonstrate that anti-parallel whistler waves are
expected to have smaller frequencies, wave numbers and growth rates compared to
parallel whistler waves. The stability analysis is performed over a wide range
of parameters of core and halo electron populations. Using the quasi-linear
scaling relation we show that anti-parallel whistler waves saturate at
amplitudes of one order of magnitude smaller than parallel whistler waves,
which is at about $10^{-3}\;B_0$ in the pristine solar wind. The analysis shows
that the presence of anti-parallel whistler waves in the pristine solar wind is
more likely to be obscured by turbulent magnetic field fluctuations, because of
lower frequencies and smaller amplitudes compared to parallel whistler waves.
The presented results will be also valuable for numerical simulations of the
electron heat flux regulation in the solar wind.",2005.12606v1
2020-05-28,Joint Total Variation ESTATICS for Robust Multi-Parameter Mapping,"Quantitative magnetic resonance imaging (qMRI) derives tissue-specific
parameters -- such as the apparent transverse relaxation rate R2*, the
longitudinal relaxation rate R1 and the magnetisation transfer saturation --
that can be compared across sites and scanners and carry important information
about the underlying microstructure. The multi-parameter mapping (MPM) protocol
takes advantage of multi-echo acquisitions with variable flip angles to extract
these parameters in a clinically acceptable scan time. In this context,
ESTATICS performs a joint loglinear fit of multiple echo series to extract R2*
and multiple extrapolated intercepts, thereby improving robustness to motion
and decreasing the variance of the estimators. In this paper, we extend this
model in two ways: (1) by introducing a joint total variation (JTV) prior on
the intercepts and decay, and (2) by deriving a nonlinear maximum \emph{a
posteriori} estimate. We evaluated the proposed algorithm by predicting
left-out echoes in a rich single-subject dataset. In this validation, we
outperformed other state-of-the-art methods and additionally showed that the
proposed approach greatly reduces the variance of the estimated maps, without
introducing bias.",2005.14247v1
2020-05-29,Effects of Longitudinal Short-Distance Constraints on the Hadronic Light-by-Light Contribution to the Muon $g-2$,"We present a model-independent method to estimate the effects of
short-distance constraints (SDCs) on the hadronic light-by-light contribution
to the muon anomalous magnetic moment $a_\mu^\text{HLbL}$. The relevant loop
integral is evaluated using multi-parameter families of interpolation
functions, which satisfy by construction all constraints derived from general
principles and smoothly connect the low-energy region with those where either
two or all three independent photon virtualities become large. In agreement
with other recent model-based analyses, we find that the SDCs and thus the
infinite towers of heavy intermediate states that are responsible for
saturating them have a rather small effect on $a_\mu^\text{HLbL}$. Taking as
input the known ground-state pseudoscalar pole contributions, we obtain that
the longitudinal SDCs increase $a_\mu^\text{HLbL}$ by $(9.1\pm 5.0) \times
10^{-11}$, where the isovector channel is responsible for $(2.6\pm 1.5) \times
10^{-11}$. More precise estimates can be obtained with our method as soon as
further accurate, model-independent information about important low-energy
contributions from hadronic states with masses up to 1-2 GeV become available.",2006.00007v2
2020-06-12,Horizontal shear instabilities at low Prandtl number,"Turbulent mixing in the radiative regions of stars is usually either ignored
or crudely accounted for in most stellar evolution models. However, there is
growing theoretical and observational evidence that such mixing is present and
can affect various aspects of a star's life. In this work, we present a first
attempt at quantifying mixing by horizontal shear instabilities in stars using
Direct Numerical Simulations. The shear is driven by a body force, and rapidly
becomes unstable. At saturation, we find that several distinct dynamical
regimes exist, depending on the relative importance of stratification and
thermal diffusion (viscosity can in principle also matter, but is usually
negligible in most stellar applications). In each of the regimes identified, we
put forward a certain number of theoretically motivated scaling laws for the
turbulent vertical eddy scale, the typical turbulent diffusion coefficient, and
the typical amplitude of temperature fluctuations (among other quantities).
Based on our findings, we predict that the majority of stars should fall into
one of two categories: high P\'eclet number stratified turbulence, and low
P\'eclet number stratified turbulence. The latter is presented in detail in a
related paper by Cope et al. (2020), while the former is discussed here.
Applying our results to the best-known stellar shear layer, namely the solar
tachocline, we find that it should lie in the high P\'eclet number stratified
turbulence regime, and predict a substantial amount of vertical mixing for
temperature, momentum and composition. Taken as is, the new turbulence model
predictions are incompatible with the Spiegel & Zahn (1992) model of the solar
tachocline. However, we also show that rotation and magnetic fields are likely
to affect the turbulence, and need to be taken into account in future studies.",2006.07436v1
2020-06-17,Intelligent Protection & Classification of Transients in Two-Core Symmetric Phase Angle Regulating Transformers,"This paper investigates the applicability of time and time-frequency features
based classifiers to distinguish internal faults and other transients -
magnetizing inrush, sympathetic inrush, external faults with current
transformer saturation, and overexcitation - for Indirect Symmetrical Phase
Angle Regulating Transformers (ISPAR). Then the faulty transformer unit
(series/exciting) of the ISPAR is located, or else the transient disturbance is
identified. An event detector detects variation in differential currents and
registers one-cycle of 3-phase post transient samples which are used to extract
the time and time-frequency features for training seven classifiers. Three
different sets of features - wavelet coefficients, time-domain features, and
combination of time and wavelet energy - obtained from exhaustive search using
Decision Tree, random forest feature selection, and maximum Relevance Minimum
Redundancy are used. The internal fault is detected with a balanced accuracy of
99.9%, the faulty unit is localized with balanced accuracy of 98.7% and the
no-fault transients are classified with balanced accuracy of 99.5%. The results
show potential for accurate internal fault detection and localization, and
transient identification. The proposed scheme can supervise the operation of
existing microprocessor-based differential relays resulting in higher stability
and dependability. The ISPAR is modeled and the transients are simulated in
PSCAD/EMTDC by varying several parameters.",2006.09865v1
2020-07-19,Anisotropic Neutron Stars Modelling: Constraints in Krori-Barua Spacetime,"Dense nuclear matter is expected to be anisotropic due to effects such as
solidification, superfluidity, strong magnetic fields, hyperons,
pion-condesation. Therefore an anisotropic neutron star core seems more
realistic than an ideally isotropic one. We model anisotropic neutron stars
working in the Krori-Barua (KB) ansatz without preassuming an equation of
state. We show that the physics of general KB solutions is encapsulated in the
compactness. Imposing physical and stability requirements yields a maximum
allowed compactness $2GM/Rc^2 < 0.71$ for a KB-spacetime. We further input
observational data from numerous pulsars and calculate the boundary density. We
focus especially on data from the LIGO/Virgo collaboration as well as recent
independent measurements of mass and radius of miilisecond pulsars with white
dwarf companions by the Neutron Star Interior Composition Explorer (NICER). For
these data the KB-spacetime gives the same boundary density which surprisingly
equals the nuclear saturation density within the data precision. Since this
value designates the boundary of a neutron core, the KB-spacetime applies
naturally to neutron stars. For this boundary condition we calculate a maximum
mass of 4.1 solar masses.",2007.09797v2
2020-07-24,Bumblebee field in a Topological Framework,"A vector field coming from spontaneous Lorentz violation mechanism, namely
Bumblebee model is analysed in a topological framework in a $(1+2)D$ Minkowski
space-time. Taking a $(1+2)D$ nonlinear Bumblebee vector matter field dynamics
where we include topological like Chern-Simons type terms, a vector version of
a soliton state, or vortex was found. The Nielsen-Olesen procedure was used in
order to derive a Lorentz-violation vector parameter which characterizes, via
Spontaneous Symmetry Breaking mechanism, the non-trivial vacuum. We verify the
stability of the model as much as the magnetic vortex, and noticed that the
soliton modes with polarized direction generated can be associated with local
anisotropy of vacuum energy. The vortex equations of motion and the asymptotic
behaviour is presented. We have obtained that the effect of the Lorentz
symmetry violation expressed by the a time-like Bumblebee vector field vacuum
could be shown as kind of pulse at a fixed point $r_0$ in a limitless universe,
or as a barrier at $r_0$ which can represent a boundary in the universe, if the
Bumblebee vector field vacuum has space-like characteristic. We also analyse
the spectrum via propagators where we note that the topological mass
contributes as well to the dynamical mass poles. We obtain that the
Chern-Simons type terms, in fact, indicates the ""speed"" of the field to
saturate the asymptotic limit and that the vortex core can not be dimension
zero.",2007.12675v1
2020-07-29,The thermal-radiative wind in the neutron star low mass X-ray binary GX 13+1,"We fit the observed high ionisation X-ray absorption lines in the neutron
star binary GX13+1 with a full simulation of a thermal-radiative wind. This
uses a radiation hydrodynamic code coupled to Monte Carlo radiation transfer to
compute the observed line profiles from Hydrogen and Helium-like iron and
Nickel, including all strong K{\alpha} and K{\beta} transitions. The wind is
very strong as this object has a very large disc and is very luminous. The
absorption lines from Fe K{\alpha} are strongly saturated as the ion columns
are large, so the line equivalent widths (EWs) depend sensitively on the
velocity structure. We additionally simulate the lines including isotropic
turbulence at the level of the azimuthal and radial velocities. We fit these
models to the Fe xxv and xxvi absorption lines seen in the highest resolution
Chandra third order HETGS data. These data already rule out the addition of
turbulence at the level of the radial velocity of ~500 km/s. The velocity
structure predicted by the thermal-radiative wind alone is a fairly good match
to the observed profile, with an upper limit to additional turbulence at the
level of the azimuthal velocity of ~100 km/s. This gives stringent constraints
on any remaining contribution from magnetic acceleration.",2007.14607v1
2020-07-30,Model-driven reconstruction with phase-constrained highly-oversampled MRI,"The Nyquist-Shannon theorem states that the information accessible by
discrete Fourier protocols saturates when the sampling rate reaches twice the
bandwidth of the detected continuous time signal. This maximum rate (the
NS-limit) plays a prominent role in Magnetic Resonance Imaging (MRI).
Nevertheless, reconstruction methods other than Fourier analysis can extract
useful information from data oversampled with respect to the NS-limit, given
that relevant prior knowledge is available. Here we present PhasE-Constrained
OverSampled MRI (PECOS), a method that exploits data oversampling in
combination with prior knowledge of the physical interactions between
electromagnetic fields and spins in MRI systems. In PECOS, highly
oversampled-in-time k-space data are fed into a phase-constrained variant of
Kaczmarz's algebraic reconstruction algorithm, where prior knowledge of the
expected spin contributions to the signal is codified into an encoding matrix.
PECOS can be used for scan acceleration in relevant scenarios by oversampling
along frequency-encoded directions, which is innocuous in MRI systems under
reasonable conditions. We find situations in which the reconstruction quality
can be higher than with NS-limited acquisitions and traditional Fourier
reconstruction. Besides, we compare the performance of a variety of encoding
pulse sequences as well as image reconstruction protocols, and find that
accelerated spiral trajectories in k-space combined with algebraic
reconstruction techniques are particularly advantageous. The proposed sampling
and reconstruction method is able to improve image quality for fully-sampled
k-space trajectories, while allowing accelerated or undersampled acquisitions
without regularization or signal extrapolation to unmeasured regions.",2007.15674v2
2021-01-17,Metallization of Shock-Compressed Liquid Ammonia,"Ammonia is predicted to be one of the major components in the depths of the
ice giant planets Uranus and Neptune. Their dynamics, evolution, and interior
structure are insufficiently understood and models rely imperatively on data
for equation of state and transport properties. Despite its great significance,
the experimentally accessed region of the ammonia phase diagram today is still
very limited in pressure and temperature. Here we push the probed regime to
unprecedented conditions, up to $\sim$350 GPa and $\sim$40000 K. Along the
Hugoniot, the temperature measured as a function of pressure shows a subtle
change in slope at $\sim$7000 K and $\sim$90 GPa, in agreement with ab initio
simulations we have performed. This feature coincides with the gradual
transition from a molecular liquid to a plasma state. Additionally, we
performed reflectivity measurements, providing the first experimental evidence
of electronic conduction in high-pressure ammonia. Shock reflectance
continuously rises with pressure above 50 GPa and reaches saturation values
above 120 GPa. Corresponding electrical conductivity values are up to 1 order
of magnitude higher than in water in the 100 GPa regime, with possible
significant contributions of the predicted ammonia-rich layers to the
generation of magnetic dynamos in ice giant interiors.",2101.06692v1
2021-02-10,"Screening, Friedel oscillations, RKKY interaction, and Drude transport in anisotropic two-dimensional systems","We investigate the effect of the mass anisotropy on Friedel Oscillations,
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, screening properties, and
Boltzmann transport in two dimensional (2D) metallic and doped semiconductor
systems. We calculate the static polarizability and the dielectric function
within the random phase approximation with the mass anisotropy fully taken into
account without making any effective isotropic approximation in the theory. We
find that carrier screening exhibits an isotropic behavior for small momenta
despite the anisotropy of the system, and becomes strongly anisotropic above a
certain threshold momentum. Such an anisotropy of screening leads to
anisotropic Friedel oscillations, and an anisotropic RKKY interaction
characterized by a periodicity dependent on the direction between the localized
magnetic moments. We also explore the disorder limited dc transport properties
in the presence of mass anisotropy based on the Boltzmann transport theory.
Interestingly, we find that the anisotropy ratio of the short range disorder
limited resistivity along the heavy- and light-mass directions is always the
same as the mass anisotropy ratio whereas for the long range disorder limited
resistivity the anisotropy ratio is the same as the mass ratio only in the low
density limit, and saturates to the square root of the mass ratio in the high
density limit. Our theoretical work should apply to many existing and
to-be-discovered anisotropic 2D systems.",2102.05659v2
2021-02-22,High T$_C$ ferromagnetic inverse Heusler alloys: A comparative study of Fe$_2$RhSi and Fe$_2$RhGe,"We report the results of experimental investigations on structural, magnetic,
resistivity, caloric properties of Fe$_2$RhZ (Z=Si,Ge) along with
\textit{ab-initio} band structure calculations using first principle
simulations. Both these alloys are found to crystallize in inverse Heusler
structure but with disorder in tetrahedral sites between Fe and Rh. Fe$_2$RhSi
has saturation moment of 5.00 $\mu_B$ and while its counterpart has 5.19
$\mu_B$. Resistivity measurement reveals metallic nature in both of them.
Theoretical simulations using generalized gradient approximation(GGA) predict
inverse Heusler structure with ferromagnetic ordering as ground state for both
the alloys. However it underestimates the experimentally observed moments.
GGA+$U$ approach, with Hubbard $U$ values estimated from density functional
perturbation theory helps to improve the comparison of the experimental
results. Fe$_2$RhSi is found to be half metallic ferromagnet while Fe$_2$RhGe
is not. Varying $U$ values on Fe and Rh sites does not change the net moment
much in Fe$_2$RhSi, unlike in Fe$_2$RhGe. Relatively small exchange splitting
of orbitals in Fe$_2$RhGe compared to that of Fe$_2$RhSi is the reason for not
opening the band gap in the minority spin channel in the former. High ordering
temperature and moment make Fe$_2$RhSi useful for spintronics applications.",2102.10967v1
2021-03-10,Role of the symmetry energy on the neutron-drip transition in accreting and nonaccreting neutron stars,"In this paper, we study the role of the symmetry energy on the neutron-drip
transition in both nonaccreting and accreting neutron stars, allowing for the
presence of a strong magnetic field as in magnetars. The density, pressure, and
composition at the neutron-drip threshold are determined using the recent set
of the Brussels-Montreal microscopic nuclear mass models, which mainly differ
in their predictions for the value of the symmetry energy $J$ and its slope $L$
in infinite homogeneous nuclear matter at saturation. Although some
correlations between on the one hand the neutron-drip density, the pressure,
the proton fraction and on the other hand $J$ (or equivalently $L$) are found,
these correlations are radically different in nonaccreting and accreting
neutron stars. In particular, the neutron-drip density is found to increase
with $L$ in the former case, but decreases in the latter case depending on the
composition of ashes from x-ray bursts and superbursts. We have qualitatively
explained these different behaviors using a simple mass formula. We have also
shown that the details of the nuclear structure may play a more important role
than the symmetry energy in accreting neutron-star crusts.",2103.05926v1
2021-03-22,Many-body localization in tilted and harmonic potentials,"We discuss nonergodic dynamics of interacting spinless fermions in a tilted
optical lattice as modeled by XXZ spin chain in magnetic (or electric) field
changing linearly across the chain. The time dynamics is studied using exact
propagation for small chains and matrix product states techniques for larger
system sizes. We consider both the initial N\'eel separable state as well as
the quantum quench scenario in which the initial state may be significantly
entangled. We show that the entanglement dynamics is significantly different in
both cases. In the former a rapid initial growth is followed by a saturation
for sufficiently large tilt, $F$. In the latter case the dynamics seems to be
dominated by pair tunneling and the effective tunneling rate scales as $1/F^2$.
In the presence of an additional harmonic potential the imbalance is found to
be entirely determined by a local effective tilt, $F_{\text{loc}}$, the
entanglement entropy growth is modulated with frequency that follows
$1/F_{loc}^2$ scaling first but at long time the dynamics is determined rather
by the curvature of the harmonic potential. Only for large tilts or
sufficiently large curvatures, corresponding to the deeply localized regime, we
find the logarithmic entanglement growth for N\'eel initial state. The same
curvature determines long-time imbalance for large $F$ which reveals strong
revival phenomena associated with the manifold of equally spaced states,
degenerate in the absence of the harmonic potential.",2103.11699v2
2021-03-30,Positive magnetoresistance and chiral anomaly in exfoliated type-II Weyl semimetal $T_\mathrm{d}$-WTe$_{2}$,"Layered van der Waals semimetallic $T_\mathrm{d}$-WTe$_{2}$, exhibiting
intriguing properties which include non-saturating extreme positive
magnetoresistance (MR) and tunable chiral anomaly, has emerged as model
topological type-II Weyl semimetal system. Here, $\sim$45 nm thick mechanically
exfoliated flakes of $T_\mathrm{d}$-WTe$_{2}$ are studied $via$ atomic force
microscopy, Raman spectroscopy, low-$T$/high-$\mu_{0}H$ magnetotransport
measurements and optical reflectivity. The contribution of anisotropy of the
Fermi liquid state to the origin of the large positive transverse
$\mathrm{MR}_\perp$ and the signature of chiral anomaly of the type-II Weyl
fermions are reported. The samples are found to be stable in air and no
oxidation or degradation of the electronic properties are observed. A
transverse $\mathrm{MR}_\perp$ $\sim$1200\,\% and an average carrier mobility
of $5000$\, cm$^{2}$V$^{-1}$s$^{-1}$ at $T=5\,\mathrm{K}$ for an applied
perpendicular field $\mu_{0}H_{\perp} = 7\,\mathrm{T}$ are established. The
system follows a Fermi liquid model for $T\leq50\,\mathrm{K}$ and the
anisotropy of the Fermi surface is concluded to be at the origin of the
observed positive MR. The anisotropy of the electronic behaviour is also
confirmed by optical reflectivity measurements. The relative orientation of the
crystal axes and of the applied electric and magnetic fields is proven to give
rise to the observed chiral anomaly in the in-plane magnetotransport.",2103.16326v1
2021-04-22,Dynamic Spin Fluctuations in the Frustrated Spin Chain Compound Li$_3$Cu$_2$SbO$_6$,"We report the signatures of dynamic spin fluctuations in the layered
honeycomb Li$_3$Cu$_2$SbO$_6$ compound, with a 3$d$ S = 1/2 $d^9$ Cu$^{2+}$
configuration, through muon spin rotation and relaxation ($\mu$SR) and neutron
scattering studies. Our zero-field (ZF) and longitudinal-field (LF)-$\mu$SR
results demonstrate the slowing down of the Cu$^{2+}$ spin fluctuations below
4.0 K. The saturation of the ZF relaxation rate at low temperature, together
with its weak dependence on the longitudinal field between 0 and 3.2 kG,
indicates the presence of dynamic spin fluctuations persisting even at 80 mK
without static order. Neutron scattering study reveals the gaped magnetic
excitations with three modes at 7.7, 13.5 and 33 meV. Our DFT calculations
reveal that the next nearest neighbors (NNN) AFM exchange ($J_{AFM}$ = 31 meV)
is stronger than the NN FM exchange ($J_{FM}$ = -21 meV) indicating the
importance of the orbital degrees of freedom. Our results suggest that the
physics of Li$_3$Cu$_2$SbO$_6$ can be explained by an alternating AFM chain
rather than the honeycomb lattice.",2104.10859v1
2021-05-03,Magnetorotational instability with smoothed particle hydrodynamics,"We present a thorough numerical study on the MRI using the smoothed particle
magnetohydrodynamics method (SPMHD) with the geometric density average force
expression (GDSPH). We perform shearing box simulations with different initial
setups and a wide range of resolution and dissipation parameters. We show, for
the first time, that MRI with sustained turbulence can be simulated
successfully with SPH, with results consistent with prior work with grid-based
codes. In particular, for the stratified boxes, our simulations reproduce the
characteristic butterfly diagram of the MRI dynamo with saturated turbulence
for at least 100 orbits. On the contrary, traditional SPH simulations suffer
from runaway growth and develop unphysically large azimuthal fields, similar to
the results from a recent study with mesh-less methods. We investigated the
dependency of MRI turbulence on the numerical Prandtl number in SPH, focusing
on the unstratified, zero net-flux case. We found that turbulence can only be
sustained with a Prandtl number larger than $\sim$2.5, similar to the critical
values of physical Prandtl number found in grid-code simulations. However,
unlike grid-based codes, the numerical Prandtl number in SPH increases with
resolution, and for a fixed Prandtl number, the resulting magnetic energy and
stresses are independent of resolution. Mean-field analyses were performed on
all simulations, and the resulting transport coefficients indicate no
$\alpha$-effect in the unstratified cases, but an active $\alpha\Omega$ dynamo
and a diamagnetic pumping effect in the stratified medium, which are generally
in agreement with previous studies. There is no clear indication of a
shear-current dynamo in our simulation, which is likely to be responsible for a
weaker mean-field growth in the tall, unstratified, zero net-flux simulation.",2105.01091v1
2021-06-05,"Single-file dynamics of colloids in circular channels: time scales, scaling laws and their universality","In colloidal systems, Brownian motion emerges from the massive separation of
time and length scales associated to characteristic dynamics of the solute and
solvent constituents. This separation of scales produces several temporal
regimes in the colloidal dynamics when combined with the effects of the
interaction between the particles, confinement conditions, and state variables,
such as density and temperature. Some examples are the short- and long-time
regimes in two- and three-dimensional open systems and the diffusive and
sub-diffusive regimes observed in the single-file dynamics along a straight
line. This work studies the way in which a confining geometry induces new time
scales. We report on the dynamics of interacting colloidal particles moving
along a circle by combining a heuristic theoretical analysis of the involved
scales, Brownian Dynamics computer simulations, and video-microscopy
experiments with paramagnetic colloids confined to lithographic circular
channels subjected to an external magnetic field. The systems display four
temporal regimes in this order: one-dimensional free diffusion, single-file
sub-diffusion, free-cluster rotational diffusion, and the expected saturation
due to the confinement. We also report analytical expressions for the
mean-square angular displacement and crossover times obtained from scaling
arguments, which accurately reproduce both experiments and simulations. Our
generic approach can be used to predict the long-time dynamics of many other
confined physical systems.",2106.02908v2
2021-06-28,Exact solutions of few-magnon problems in the spin-$S$ periodic XXZ chain,"We solve few-magnon problems for a finite-size spin-$S$ periodic Heisenberg
XXZ chain with single-ion anisotropy through constructing sets of exact Bloch
states achieving block diagonalization of the system. Concretely, the
two-magnon (three-magnon) problem is converted to a single-particle one on a
one-dimensional (two-dimensional) effective lattice whose size depends linearly
(quadratically) on the total number of sites. For parameters lying within
certain ranges, various types of multimagnon bound states are manifested and
shown to correspond to edge states on the effective lattices. In the absence of
the single-ion anisotropy, we reveal the condition under which exact
zero-energy states emerge. As applications of the formalism, we calculate the
transverse dynamic structure factor for a higher-spin chain near saturation
magnetization and find signatures of the multimagnon bound states. We also
calculate the real-time three-magnon dynamics from certain localized states,
which are relevant to cold-atom quantum simulations, by simulating
single-particle quantum walks on the effective lattices. This provides a
physically transparent interpretation of the observed dynamics in terms of
propagation of bound state excitations. Our method can be directly applied to
more general spin or itinerant particle systems possessing translational
symmetry.",2106.14809v4
2021-07-14,Visualizing the strongly reshaped skyrmion Hall effect in multilayer wire devices,"Magnetic skyrmions are nanoscale spin textures touted as next-generation
computing elements. When subjected to lateral currents, skyrmions move at
considerable speeds. Their topological charge results in an additional
transverse deflection known as the skyrmion Hall effect (SkHE). While
promising, their dynamic phenomenology with current, skyrmion size, geometric
effects and disorder remain to be established. Here we report on the ensemble
dynamics of individual skyrmions forming dense arrays in Pt/Co/MgO wires by
examining over 20,000 instances of motion across currents and fields. The
skyrmion speed reaches 24 m/s in the plastic flow regime and is surprisingly
robust to positional and size variations. Meanwhile, the SkHE saturates at
$\sim 22^\circ$, is substantially reshaped by the wire edge, and crucially
increases weakly with skyrmion size. Particle model simulations suggest that
the SkHE size dependence - contrary to analytical predictions - arises from the
interplay of intrinsic and pinning-driven effects. These results establish a
robust framework to harness SkHE and achieve high-throughput skyrmion motion in
wire devices.",2107.07022v1
2021-08-30,Twenty-Five Years of Dissipative Solitons,"In 1995, C. I. Christov and M. G. Velarde introduced the concept of a
dissipative soliton in a long-wave thin-film equation [Physica D 86, 323--347].
In the 25 years since, the subject has blossomed to include many related
phenomena. The focus of this short note is to survey the conceptual influence
of the concept of a ""production-dissipation (input-output) energy balance"" that
they identified. Our recent results on nonlinear periodic waves as dissipative
solitons (in a model equation for a ferrofluid interface in a parallel-flow
rectangular geometry subject to an inhomogeneous magnetic field) have shown
that the classical concept also applies to nonlocalized (specifically,
spatially periodic) nonlinear coherent structures. Thus, we revisit the
so-called KdV-KSV equation studied by C. I. Christov and M. G. Velarde to
demonstrate that it also possesses spatially periodic dissipative soliton
solutions. These coherent structures arise when the linearly unstable flat film
state evolves to sufficiently large amplitude. The linear instability is then
arrested when the nonlinearity saturates, leading to permanent traveling waves.
Although the two model equations considered in this short note feature the same
prototypical linear long-wave instability mechanism, along with similar linear
dispersion, their nonlinearities are fundamentally different. These nonlinear
terms set the shape and eventual dynamics of the nonlinear periodic waves.
Intriguingly, the nonintegrable equations discussed in this note also exhibit
multiperiodic nonlinear wave solutions, akin to the polycnoidal waves discussed
by J. P. Boyd in the context of the completely integrable KdV equation.",2108.13351v1
2021-09-18,Breaking the Computational Bottleneck: Design of Near-Optimal High-Memory Spatially-Coupled Codes,"Spatially-coupled (SC) codes, known for their threshold saturation phenomenon
and low-latency windowed decoding algorithms, are ideal for streaming
applications and data storage systems. SC codes are constructed by partitioning
an underlying block code, followed by rearranging and concatenating the
partitioned components in a convolutional manner. The number of partitioned
components determines the memory of SC codes. In this paper, we investigate the
relation between the performance of SC codes and the density distribution of
partitioning matrices. While adopting higher memories results in improved SC
code performance, obtaining finite-length, high-performance SC codes with high
memory is known to be computationally challenging. We break this computational
bottleneck by developing a novel probabilistic framework that obtains (locally)
optimal density distributions via gradient descent. Starting from random
partitioning matrices abiding by the obtained distribution, we perform
low-complexity optimization algorithms that minimize the number of detrimental
objects to construct high-memory, high-performance quasi-cyclic SC codes. We
apply our framework to various objects of interests, from the simplest short
cycles, to more sophisticated objects such as concatenated cycles aiming at
finer-grained optimization. Simulation results show that codes obtained through
our proposed method notably outperform state-of-the-art SC codes with the same
constraint length and optimized SC codes with uniform partitioning. The
performance gain is shown to be universal over a variety of channels, from
canonical channels such as additive white Gaussian noise and binary symmetric
channels, to practical channels underlying flash memory and magnetic recording
systems.",2109.08978v1
2021-10-06,Entropic order parameters in weakly coupled gauge theories,"The entropic order parameters measure in a universal geometric way the
statistics of non-local operators responsible for generalized symmetries. In
this article, we compute entropic order parameters in weakly coupled gauge
theories. To perform this computation, the natural route of evaluating
expectation values of physical (smeared) non-local operators is prevented by
known difficulties in constructing suitable smeared Wilson loops. We circumvent
this problem by studying the smeared non-local class operators in the enlarged
non-gauge invariant Hilbert space. This provides a generic approach for smeared
operators in gauge theories and explicit formulas at weak coupling. In this
approach, the Wilson and 't Hooft loops are labeled by the full weight and
co-weight lattices respectively. We study generic Lie groups and discuss
couplings with matter fields. Smeared magnetic operators, as opposed to the
usual infinitely thin ones, have expectation values that approach one at weak
coupling. The corresponding entropic order parameter saturates to its maximum
topological value, except for an exponentially small correction, which we
compute. On the other hand, smeared 't Hooft loops and their entropic disorder
parameter are exponentially small. We verify that both behaviors match the
certainty relation for the relative entropies. In particular, we find upper and
lower bounds (that differ by a factor of 2) for the exact coefficient of the
linear perimeter law for thin loops at weak coupling. This coefficient is
unphysical/non-universal for line operators. We end with some comments
regarding the RG flows of entropic parameters through perturbative beta
functions.",2110.02980v2
2021-11-10,"Very-High Dynamic Range, 10,000 frames/second Pixel Array Detector for Electron Microscopy","Precision and accuracy of quantitative scanning transmission electron
microscopy (STEM) methods such as ptychography, and the mapping of electric,
magnetic and strain fields depend on the dose. Reasonable acquisition time
requires high beam current and the ability to quantitatively detect both large
and minute changes in signal. A new hybrid pixel array detector (PAD), the
second-generation Electron Microscope Pixel Array Detector (EMPAD-G2),
addresses this challenge by advancing the technology of a previous generation
PAD, the EMPAD. The EMPAD-G2 images continuously at a frame-rates up to 10 kHz
with a dynamic range that spans from low-noise detection of single electrons to
electron beam currents exceeding 180 pA per pixel, even at electron energies of
300 keV. The EMPAD-G2 enables rapid collection of high-quality STEM data that
simultaneously contain full diffraction information from unsaturated bright
field disks to usable Kikuchi bands and higher-order Laue zones. Test results
from 80 to 300 keV are presented, as are first experimental results
demonstrating ptychographic reconstructions, strain and polarization maps. We
introduce a new information metric, the Maximum Usable Imaging Speed (MUIS), to
identify when a detector becomes electron-starved, saturated or its pixel count
is mismatched with the beam current.",2111.05889v1
2021-12-06,Mechanism of spin ordering in Fe$_{3}$O$_{4}$ nanoparticles by surface coating with organic acids,"Saturation magnetization values close to the bulk have been reported for
coated magnetite nanoparticles with organic acids. The mechanism of this effect
is not yet understood. Here we show that a previously proposed rationalization
in Nano Letters 12 (2021) 2499-2503 was based on electronic structure
properties that are not consistent with several existing density functional
theory studies. Our study is based on a wide set of Hubbard-corrected density
functional tight binding (DTFB+U) and hybrid density functional theory (HSE06)
calculations on Fe$_{3}$O$_{4}$ nanocubes of more than 400 atoms. We provide a
new explanation for the spin ordering in coated nanoparticles, through the
investigation of spin-flipping phenomena. In particular, we show that the
spin-flip of d electrons at octahedral Fe$^{3+}$ sites, which is confirmed to
be more favorable near the surface, especially where atomic reorganization can
take place such as at corner sites, can be hampered by the presence of adsorbed
organic acids because they do not only limit the surface reconstruction but
also allow for additional ferromagnetic superexchange interaction between
octahedral Fe sites as a consequence of the carboxylates bridging binding mode.
The proof-of-concept of this mechanism is given by a simplified model of the
Fe(III) tert-butoxide dimer.",2112.02966v2
2021-12-21,Fast long-wavelength exchange spin waves in partially-compensated Ga:YIG,"Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing
attention from the perspective of novel magnon-based data processing
applications. For short wavelengths needed in small-scale devices, the group
velocity is directly proportional to the spin-wave exchange stiffness constant
$\lambda_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering
(BLS) spectroscopy, we directly measure $\lambda_\mathrm{ex}$ in Ga-substituted
YIG thin films and show that it is about three times larger than for pure YIG.
Consequently, the spin-wave group velocity overcomes the one in pure YIG for
wavenumbers $k > 4$ rad/$\mu$m, and the ratio between the velocities reaches a
constant value of around 3.4 for all $k > 20$ rad/$\mu$m. As revealed by
vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR)
spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert
damping ($\alpha < 10^{-3}$), a decreased saturation magnetization $\mu_0
M_\mathrm{S}~\approx~20~$mT and a pronounced out-of-plane uniaxial anisotropy
of about $\mu_0 H_{\textrm{u1}} \approx 95 $ mT which leads to an out-of-plane
easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport
for all wavelengths in nano-scale systems independently of dipolar effects.",2112.11348v1
2021-12-31,Ferromagnetic Enhancement in LaMnO3 Films with Release and Flexure,"A variety of novel phenomena and functionalities emerge from lowering the
dimensionality of materials and enriching the degrees of freedom in modulation.
In this work, it is found that the saturation magnetization of LaMnO3 (LMO)
films is largely enhanced by 56% after releasing from a brand-new phase of
tetragonal strontium aluminate buffer layer, and is significantly increased by
92% with bending films to a curvature of 1 mm-1 using a water-assisted
direct-transferring method. Meanwhile, the Curie temperature of LMO films has
been improved by 13 K. High-resolution spherical aberration-corrected scanning
transmission electron microscopy and first-principles calculations
unambiguously demonstrate that the enhanced ferromagnetism is attributed to the
strengthened Mn-O-Mn super-exchange interactions from the augmented
characteristics of the unconventional P21/n structure caused by the
out-of-plane lattice shrinking after strain releasing and increased flexure
degree of freestanding LMO films. This work paves a way to achieve large-scale
and crack-and-wrinkle-free freestanding films of oxides with largely improved
functionalities.",2112.15307v1
2022-01-10,$B^2$ to $B$-linear magnetoresistance due to impeded orbital motion,"Strange metals exhibit a variety of anomalous magnetotransport properties,
the most striking of which is a resistivity that increases linearly with
magnetic field $B$ over a broad temperature and field range. The ubiquity of
this behavior across a spectrum of correlated metals - both single- and
multi-band, with either dominant spin and/or charge fluctuations, of varying
levels of disorder or inhomogeneity and in proximity to a quantum critical
point or phase - obligates the search for a fundamental underlying principle
that is independent of the specifics of any material. Strongly anisotropic
(momentum-dependent) scattering can generate $B$-linear magnetoresistance but
only at intermediate field strengths. At high enough fields, the
magnetoresistance must eventually saturate. Here, we consider the ultimate
limit of such anisotropy, a region or regions on the Fermi surface that impede
all orbital (cyclotron) motion through them, but whose imposition can be
modelled nonetheless through a modified Boltzmann theoretical treatment.
Application of the proposed theorem suggests that the realization of
quadratic-to-linear magnetoresistance requires the presence of a bounded sector
on the Fermi surface possibly separating two distinct types of carriers. While
this bounded sector may have different origins or manifestations, we expect its
existence to account for the anomalous magnetotransport found in a wide range
of correlated materials.",2201.03292v1
2022-01-20,Quantum Dipolar Coupling Thermal Correction for NMR Signal during Natural Rock Flooding by Melding Experimentation and Numerical Simulation (Th-CENS),"Researchers have used NMR to measure multi-phase fluid saturation and
distribution inside porous media of natural rock. However, the NMR signal
amplitude suffers reduction with the increase of temperature. The main reason
is the Transverse Overhauser Effect, where heating increases the freedom for
ionic motion, affecting spinning behavior by having two spins go in two
opposite directions to form the Dipolar Coupling. We approach solving NMR
thermal effects correction by melding experimentation and numerical simulation
method. We use NMR for Cretaceous carbonate rock multi-phase flow research. We
conduct time step in-situ temperature measurement for four different sections
of the flooding system at the inlet, center, and outlet along the flooding
path. In addition, we conduct a temperature measurement at the NMR device
radial axis, representing the permanent magnet temperature. We build a 3D
cylindrical heat transfer model for the numerical simulator that simulates
thermal effect distribution on the NMR for optimally generating the correction
model. The insight provided by the simulator improved the understanding of the
thermal distribution at the natural rock core plug to produce a better thermal
correction model that meld experimentation and simulation, a method we call
Th-CENS.",2201.08834v1
2022-02-09,Giant transverse and longitudinal magneto-thermoelectric effect in polycrystalline nodal-line semimetal Mg3Bi2,"Topological semimetals provide new opportunities for exploring new
thermoelectric phenomena, because of their exotic and nontrivial electronic
structure topology around the Fermi surface. In this study, we report on the
discovery of giant transverse and longitudinal magneto-thermoelectric (MTE)
effects in Mg3Bi2, which is predicted to be a type-II nodal-line semimetal in
the absence of spin-orbit coupling (SOC). The maximum transverse power factor
is 2182 {\mu}Wm^{-1}K^{-2} at 13.5 K and 6 Tesla. The longitudinal power factor
reaches up to 3043{\mu}Wm^{-1}K^{-2} at 15 K and 13 Tesla, which is 20 times
higher than in a zero-strength magnetic field and is also comparable to
state-of-the-art MTE materials. By compensating Mg loss in the Mg-rich
conditions for turning carrier concentration, the sample obtained in this work
shows a large linear non-saturating magnetoresistance of 940% under a field of
14 Tesla. This is a two-orders-of-magnitude increase with respect to the normal
Mg-deficiency Mg3Bi2 sample. Using density functional calculations, we
attribute the underlying mechanism to the parent nodal-line electronic
structure without SOC and the anisotropic Fermi surface shape with SOC,
highlighting the essential role of high carrier mobility and open electron
orbits in moment space. Our work offers a new avenue toward highly efficient
thermoelectric materials through the design of Fermi surfaces with special
topological electronic structures in novel quantum materials.",2202.04293v1
2022-04-26,AGN jets do not prevent the suppression of conduction by the heat buoyancy instability in simulated galaxy clusters,"Centres of galaxy clusters must be efficiently reheated to avoid a cooling
catastrophe. One potential reheating mechanism is anisotropic thermal
conduction, which could transport thermal energy from intermediate radii to the
cluster center. However, if fields are not re-randomised, anisotropic thermal
conduction drives the heat buoyancy instability (HBI) which reorients magnetic
field lines and shuts off radial heat fluxes. We revisit the efficiency of
thermal conduction under the influence of spin-driven AGN jets in idealised
magneto-hydrodynamical simulations with anisotropic thermal conduction. Despite
the black hole spin's ability to regularly re-orientate the jet so that the
jet-induced turbulence is driven in a quasi-isotropic fashion, the HBI remains
efficient outside the central 50 kpc of the cluster, where the reservoir of
heat is the largest. As a result, conduction plays no significant role in
regulating the cooling of the intra-cluster medium if central active galactic
nuclei are the sole source of turbulence. Whistler-wave driven saturation of
thermal conduction reduces the magnitude of the HBI but does not prevent it.",2204.12514v2
2022-04-26,Band Flattening and Landau Level Merging in Strongly-Correlated Two-Dimensional Electron Systems,"We review recent experimental results indicating the band flattening and
Landau level merging at the chemical potential in strongly-correlated
two-dimensional (2D) electron systems. In ultra-clean, strongly interacting 2D
electron system in SiGe/Si/SiGe quantum wells, the effective electron mass at
the Fermi level monotonically increases in the entire range of electron
densities, while the energy-averaged mass saturates at low densities. The
qualitatively different behavior of the two masses reveals a precursor to the
interaction-induced single-particle spectrum flattening at the chemical
potential in this electron system, in which case the fermion ""condensation"" at
the Fermi level occurs in a range of momenta, unlike the condensation of
bosons. In strong magnetic fields, perpendicular to the 2D electron layer, a
similar effect of different fillings of quantum levels at the chemical
potential -- the merging of the spin- and valley-split Landau levels at the
chemical potential -- is observed in Si inversion layers and bilayer 2D
electron system in GaAs. Indication of merging of the quantum levels of
composite fermions with different valley indices is also reported in
ultra-clean SiGe/Si/SiGe quantum wells.",2204.12565v3
2022-04-27,"Prospects for a flavour violating $Z^\prime$ explanation of $Δ a_{μ,e}$","The apparent tensions emerging from the comparison of experimental data of
the anomalous magnetic moments of the muon and electron to the Standard Model
predictions ($\Delta a_{\mu,e}$) could be interpreted as a potential signal of
New Physics. Models encompassing a light vector boson have been known to offer
a satisfactory explanation to $\Delta a_{\mu}$, albeit subject to stringent
experimental constraints. Here we explore a minimal extension of the Standard
Model via a leptophilic vector boson $Z^\prime$, under the hypothesis of
strictly flavour-violating couplings of the latter to leptons. The most
constraining observables to this ad-hoc construction emerge from lepton flavour
universality violation (in $Z$ and $\tau$ decays) and from rare charged lepton
flavour violating transitions. Once these are accommodated, one can saturate
the tensions in $\Delta a_{\mu}$, but $\Delta a_{e}$ is predicted to be
Standard Model-like. We infer prospects for several observables, including
leptonic $Z$ decays and several charged lepton flavour violating processes. We
also discuss potential signatures of the considered $Z^\prime$ at a future muon
collider, emphasising the role of the $\mu^+\mu^- \to\tau^+\tau^- $
forward-backward asymmetry as a key probe of the model.",2204.13134v3
2022-05-04,Surface states induced weak anti-localization effect in Bi0.85Sb0.15 topological single crystal,"We report, an experimental evidence of surface states (SS) driven
magneto-transport in a Bi0.85Sb0.15 single crystal. Detailed high field (up to
12T) and low temperature (down to 2K) magneto-transport measurements are been
carried out on the studied Bi0.85Sb0.15 single crystal. The phase, composition
and Raman modes are studied through X-ray diffraction, Energy dispersive X-ray,
and Raman spectroscopy. The obtained crystal shows non-saturating
magnetoresistance (4250%) at 2K and 12T, along with the existence of weak-anti
localization (WAL) effect at around zero magnetic field. Further, the
Hikami-Larkin-Nagaoka (HLN) analysis is performed to analyse the WAL effect.
The prefactor and phase coherence length are deduced at various temperatures,
which signified the presence of more than one conduction channel in the studied
Bi0.85Sb0.15 single crystal. The effect of quantum scattering, bulk
contribution from underneath the surface states and defects are been studied by
adding various field dependent quadratic, linear and constant terms to the SS
driven HLN equation. Various possible scattering mechanism are studied by
analysing the temperature dependence of the phase coherence length. Angle
dependent magneto-conductivity of the studied Bi0.85Sb0.15 single crystal
clearly confirmed the surface states dominated transport in present crystal.",2205.01880v2
2022-05-04,Mixing the solar wind proton and electron scales. Theory and 2D-PIC simulations of firehose instability,"Firehose-like instabilities (FIs) are cited in multiple astrophysical
applications. Of particular interest are the kinetic manifestations in
weakly-collisional or even collisionless plasmas, where these instabilities are
expected to contribute to the evolution of macroscopic parameters. Relatively
recent studies have initiated a realistic description of FIs, as induced by the
interplay of both species, electrons and protons, dominant in the solar wind
plasma. This work complements the current knowledge with new insights from
linear theory and the first disclosures from 2D PIC simulations, identifying
the fastest growing modes near the instability thresholds and their long-run
consequences on the anisotropic distributions. Thus, unlike previous setups,
these conditions are favorable to those aperiodic branches that propagate
obliquely to the uniform magnetic field, with (maximum) growth rates higher
than periodic, quasi-parallel modes. Theoretical predictions are, in general,
confirmed by the simulations. The aperiodic electron FI (a-EFI) remains
unaffected by the proton anisotropy, and saturates rapidly at low-level
fluctuations. Regarding the firehose instability at proton scales, we see a
stronger competition between the periodic and aperiodic branches. For the
parameters chosen in our analysis, the a-PFI is excited before than the p-PFI,
with the latter reaching a significantly higher fluctuation power. However,
both branches are significantly enhanced by the presence of anisotropic
electrons. The interplay between EFIs and PFIs also produces a more pronounced
proton isotropization.",2205.02338v1
2022-07-18,Josephson Diode Effect in High Mobility InSb Nanoflags,"We report evidence of non-reciprocal dissipation-less transport in single
ballistic InSb nanoflag Josephson junctions, owing to a strong spin-orbit
coupling. Applying an in-plane magnetic field, we observe an inequality in
supercurrent for the two opposite current propagation directions. This
demonstrates that these devices can work as Josephson diodes, with
dissipation-less current flowing in only one direction. For small fields, the
supercurrent asymmetry increases linearly with the external field, then it
saturates as the Zeeman energy becomes relevant, before it finally decreases to
zero at higher fields. We show that the effect is maximum when the in-plane
field is perpendicular to the current vector, which identifies Rashba
spin-orbit coupling as the main symmetry-breaking mechanism. While a variation
in carrier concentration in these high-quality InSb nanoflags does not
significantly influence the diode effect, it is instead strongly suppressed by
an increase in temperature. Our experimental findings are consistent with a
model for ballistic short junctions and show that the diode effect is intrinsic
to this material. Our results establish InSb Josephson diodes as a useful
element in superconducting electronics.",2207.08772v1
2022-08-10,A Feshbach resonance in collisions between ultracold ground state molecules,"Collisional resonances are an important tool which has been used to modify
interactions in ultracold gases, for realizing novel Hamiltonians in quantum
simulations, for creating molecules from atomic gases and for controlling
chemical reactions. So far, such resonances have been observed for atom-atom
collisions, atom-molecule collisions and collisions between Feshbach molecules
which are very weakly bound. Whether such resonances exist for ultracold ground
state molecules has been debated due to the possibly high density of states
and/or rapid decay of the resonant complex. Here we report a very pronounced
and narrow (25 mG) Feshbach resonance in collisions between two ground state
NaLi molecules. This molecular Feshbach resonance has two special
characteristics. First, the collisional loss rate is enhanced by more than two
orders of magnitude above the background loss rate which is saturated at the
$p$-wave universal value, due to strong chemical reactivity. Second, the
resonance is located at a magnetic field where two open channels become nearly
degenerate. This implies the intermediate complex predominantly decays to the
second open channel. We describe the resonant loss feature using a model with
coupled modes which is analogous to a Fabry-P\'erot cavity. Our observations
prove the existence of long-lived coherent intermediate complexes even in
systems without reaction barriers and open up the possibility of coherent
control of chemical reactions.",2208.05557v1
2022-09-13,The influence of host star activity evolution on the population of super-Earths and mini-Neptunes,"The detected exoplanet population displays a dearth of planets with sizes of
about two Earth radii, the so-called radius gap. This is interpreted as an
evolutionary effect driven by a variety of possible atmospheric mass loss
processes of exoplanets. For mass loss driven by an exoplanet's irradiation by
stellar X-ray and extreme-UV photons, the time evolution of the stellar
magnetic activity is important. It is known from observations of open stellar
clusters that stars of the same age and mass do not all follow the same time
evolution of activity-induced X-ray and extreme-UV luminosities. Here we
explore how a realistic spread of different stellar activity tracks influences
the mass loss and radius evolution of a simulated population of small
exoplanets and the observable properties of the radius gap. Our results show
qualitatively that different saturation time scales, i.e. the young age at
which stellar high-energy emission starts to decline, and different activity
decay tracks over moderate stellar ages can cause changes in the population
density of planets in the gap, as well as in the observable width of the gap.
We also find that while the first 100 million years of mass loss are highly
important to shape the radius gap, significant evolution of the gap properties
is expected to take place for at least the first 500-600 million years, i.e.
the age of the Hyades cluster. Observations of exoplanet populations with
defined ages will be able to shed more light on the radius gap evolution.",2209.05860v1
2022-09-27,Spatially Dependent Photometric Activity of M dwarfs in the Solar Cylinder,"We study the relationship between Galactic location ($R, Z$) and photometric
activity for 3.6 million M dwarf stars within 1 kpc of the Sun. For this
purpose, we identify 906 unique flare events as a proxy for magnetic activity
from the SkyMapper Southern Survey DR3. We adopt vertical distance $|Z|$ from
the Galactic disc as a proxy for age and confirm a strong trend of flaring
fraction decreasing with growing stellar age. Among M dwarfs within 50 pc of
the Sun, we find a flaring fraction of 1-in-1,500, independent of spectral type
from M2 to M7, suggesting that these stars are all in a flare-saturated young
evolutionary stage. We find a hint of a kink in the slope of the overall flare
fraction near 100 pc from the plane, where a steep decline begins; this slope
change is visible for mid-type M dwarfs (M3--M5), suggesting it is not an
artefact of mixing spectral type. Together with SDSS H$\alpha$ emission, this
trend is additional evidence that the activity fraction of M dwarfs depends on
Galactic height and activity lifetime. While there is a hint of flattening of
the overall activity fraction above $|Z|\approx$ 500 pc, our data do not
constrain this further. Within $\sim$500 pc distance from the Sun, we find no
sign of radial disk gradients in flare activity, which may only be revealed by
samples covering a larger radial range.",2209.13107v1
2022-10-17,Saturation of the filamentation instability and dispersion measure of Fast Radio Bursts,"Nonlinear effects are crucial for the propagation of Fast Radio Bursts (FRBs)
near the source. We study the filamentation of FRBs in the relativistic winds
of magnetars, which are commonly invoked as the most natural FRB progenitors.
As a result of filamentation, the particle number density and the radiation
intensity develop strong gradients along the direction of the wind magnetic
field. A steady state is reached when the plasma pressure balances the
ponderomotive force. In such a steady state, particles are confined into
periodically spaced thin sheets, and electromagnetic waves propagate between
them as in a waveguide. We show that: (i) The dispersion relation resembles
that in the initial homogeneous plasma, but the effective plasma frequency is
determined by the separation of the sheets, not directly by the mean particle
density. (ii) The contribution of relativistic magnetar winds to the dispersion
measure of FRBs could be several orders of magnitude larger than previously
thought. The dispersion measure of the wind depends on the properties of
individual bursts (e.g. the luminosity), and therefore can change significantly
among different bursts from repeating FRBs. (iii) Induced Compton scattering is
suppressed because most of the radiation propagates in near vacuum regions.",2210.08754v2
2022-12-05,Propagating spin-wave spectroscopy in nanometer-thick YIG films at millikelvin temperatures,"Performing propagating spin-wave spectroscopy of thin films at millikelvin
temperatures is the next step towards the realisation of large-scale integrated
magnonic circuits for quantum applications. Here we demonstrate spin-wave
propagation in a $100\,\mathrm{nm}$-thick yttrium-iron-garnet film at the
temperatures down to $45 \,\mathrm{mK}$, using stripline nanoantennas deposited
on YIG surface for the electrical excitation and detection. The clear
transmission characteristics over the distance of $10\,\mu \mathrm{m}$ are
measured and the subtracted spin-wave group velocity and the YIG saturation
magnetisation agree well with the theoretical values. We show that the
gadolinium-gallium-garnet substrate influences the spin-wave propagation
characteristics only for the applied magnetic fields beyond $75\,\mathrm{mT}$,
originating from a GGG magnetisation up to $47 \,\mathrm{kA/m}$ at $45
\,\mathrm{mK}$. Our results show that the developed fabrication and measurement
methodologies enable the realisation of integrated magnonic quantum
nanotechnologies at millikelvin temperatures.",2212.02257v3
2023-03-09,The strong effect of electron thermal conduction on the global structure of the heliosphere,"Voyager 1 and 2 crossed the heliopause at $\sim$122 AU in 2012 and $\sim$119
AU in 2018, respectively. It was quite a surprise because the thickness of the
inner heliosheath obtained by the existing at that time models of the global
heliosphere was significantly larger (by 20-40 AU). Until now, the problem of
the heliosheath thickness has not been fully resolved. Earlier in the frame of
an oversimplified toy model of nearly isothermal solar wind plasma it has been
shown that the effect of electron thermal conduction may significantly reduce
the thickness of the inner heliosheath.
  In this paper, we present the first results of our 3D kinetic-MHD model of
the global heliosphere, where the effect of thermal electron conduction has
been considered rigorously. The thermal conduction acts mainly along the
magnetic field lines. Classical and saturated thermal fluxes are employed when
appropriate.
  It is shown the effects of thermal conduction are significant. The thickness
of the inner heliospheric is reduced. It is desired effect since it helps to
reconcile the thickness obtained in the model with Voyager data. The other
effects are the strong depletion of the heliosheath plasma temperature toward
the heliopause and the increase of the plasma temperature in the supersonic
solar wind upstream of the termination shock.",2303.05547v1
2023-03-27,Turbulence in the Tail of a Jellyfish Galaxy,"When galaxies move through the intracluster medium (ICM) inside galaxy
clusters, the ram pressure of the ICM can strip the gas from galaxies. The
stripped gas forms tails on the trailing side. These galaxies are hence dubbed
``jellyfish galaxies''. ESO 137-001 is a quintessential jellyfish galaxy
located in the nearest rich cluster, the Norma cluster. Its spectacular
multiphase tail has complex morphology and kinematics both from the imprinted
galaxy's interstellar medium (ISM) and as a result of the interactions between
the stripped gas and the surrounding hot plasma, mediated by radiative cooling
and magnetic fields. We study the kinematics of the multiphase tail using
high-resolution observations of the ionized and the molecular gas in the entire
structure. We calculate the velocity structure functions (VSFs) in moving
frames along the tail and find that turbulence driven by Kelvin-Helmholtz (KH)
instability quickly overwhelms the original ISM turbulence and saturates at
$\sim 30$ kpc. There is also a hint that the far end of the tail has possibly
started to inherit pre-existing large-scale ICM turbulence likely caused by
structure formation. Turbulence measured by the molecular gas is generally
consistent with that measured by the ionized gas in the tail but has a slightly
lower amplitude. Most of the measured turbulence is below the mean free path of
the hot ICM ($\sim 11$ kpc). Using warm/cool gas as a tracer of the hot ICM, we
find that the isotropic viscosity of the hot plasma must be suppressed below
0.01 percent Spitzer level.",2303.15500v1
2023-05-29,Deciphering the physical basis of the intermediate-scale instability,"We study the underlying physics of cosmic-ray (CR) driven instabilities that
play a crucial role for CR transport across a wide range of scales, from
interstellar to galaxy cluster environments. By examining the linear dispersion
relation of CR-driven instabilities in a magnetised electron-ion background
plasma, we establish that both, the intermediate and gyroscale instabilities
have a resonant origin and show that these resonances can be understood via a
simple graphical interpretation. These instabilities destabilise wave modes
parallel to the large-scale background magnetic field at significantly distinct
scales and with very different phase speeds. Furthermore, we show that
approximating the electron-ion background plasma with either
magnetohydrodynamics (MHD) or Hall-MHD fails to capture the fastest growing
instability in the linear regime, namely the intermediate-scale instability.
This finding highlights the importance of accurately characterising the
background plasma for resolving the most unstable wave modes. Finally, we
discuss the implications of the different phase speeds of unstable modes on
particle-wave scattering. Further work is needed to investigate the relative
importance of these two instabilities in the non-linear, saturated regime and
to develop a physical understanding of the effective CR transport coefficients
in large-scale CR hydrodynamics theories.",2305.18050v2
2023-08-14,Gate-tunable kinetic inductance parametric amplifier,"Superconducting parametric amplifiers play a crucial role in the preparation
and readout of quantum states at microwave frequencies, enabling high-fidelity
measurements of superconducting qubits. Most existing implementations of these
amplifiers rely on the nonlinearity from Josephson junctions, superconducting
quantum interference devices or disordered superconductors. Additionally,
frequency tunability arises typically from either flux or current biasing. In
contrast, semiconductor-based parametric amplifiers are tunable by local
electric fields, which impose a smaller thermal load on the cryogenic setup
than current and flux biasing and lead to vanishing crosstalk to other on-chip
quantum systems. In this work, we present a gate-tunable parametric amplifier
that operates without Josephson junctions, utilizing a proximitized
semiconducting nanowire. This design achieves near-quantum-limited performance,
featuring more than 20 dB gain and a 30 MHz gain-bandwidth product. The absence
of Josephson junctions allows for advantages, including substantial saturation
powers of -120dBm, magnetic field compatibility up to 500 mT and frequency
tunability over a range of 15 MHz. Our realization of a parametric amplifier
supplements efforts towards gate-controlled superconducting electronics,
further advancing the abilities for high-performing quantum measurements of
semiconductor-based and superconducting quantum devices.",2308.06989v2
2023-08-23,Detecting Magnetar Giant Flares with MoonBEAM,"Magnetars are slowly-rotating neutron stars with extremely strong magnetic
fields that rarely produce extremely bright, energetic giant flares. Magnetar
Giant Flares (MGFs) begin with a short (200 ms) intense flash, followed by
fainter emission lasting several minutes that is modulated by the magnetar spin
period (typically 2-12 s). Over the last 40 years, only three MGFs have been
observed within our Galaxy and the Magellanic Clouds, which all suffered from
instrumental saturation due to their extreme intensity. It has been proposed,
that extragalactic MGFs masquerade as a small subset of short Gamma-ray Bursts
(GRBs), noting that the sensitivity of current instrumentation prevents us from
detecting the pulsating tail to distances slightly beyond the Magellanic
Clouds. However, their initial bright flash is readily observable out to
distances of < 25 Mpc. In this presentation, we will evaluate the spectral and
temporal behaviors of MGFs using recent observations from events such as
GRB200415A, to differentiate them from other progenitors, such as short GRBs.
We then present an overview of the Moon Burst Energetics All-sky Monitor
(MoonBEAM), which will attempt to discover more of these events, providing
highly sensitive data that will help unravel the nature of these phenomena
further in an attempt to better understand their emission mechanisms
comparatively with GRBs. In doing so, MoonBEAM will help provide a
comprehensive picture of energetic astrophysical phenomena, a key goal of the
Astro2020 decadal survey.",2308.12396v1
2023-09-01,Naked forward shock seen in the TeV afterglow data of GRB221009A,"We explore the implications of the light curve of the early TeV gamma-ray
afterglow of GRB221009A reported by the LHAASO collaboration. We show that the
reported offset of the reference time, $T_*$, allows the determination of the
relativistic jet activation time, which occurs approximately $200\,\mathrm{s}$
after the GBM trigger time and closely precedes the moment at which GBM was
saturated. We find that while the LHAASO data do not exclude the homogeneous
circumburst medium scenario, the progenitor wind scenario looks preferable,
finding excellent agreement with the expected size of the stellar bubble. We
conclude that the initial growth of the light curve is dominated by processes
internal to the jet or by gamma-gamma attenuation on the photons emitted during
the prompt phase. Namely, either the activation of the acceleration process or
the decrease of internal gamma-gamma absorption can naturally explain the
initial rapid flux increase. The subsequent slow flux growth phase observed up
to $T_*+18\,\mathrm{s}$ is explained by the build-up of the synchrotron
radiation -- the target for inverse Compton scattering, which is also supported
by a softer TeV spectrum measured during this period. The duration of this
phase allows an almost parameter-independent determination of the jet's initial
Lorentz factor, $\Gamma_0\approx600$, and magnetic field strength,
$B'\sim0.3\,\mathrm{G}$. These values appear to match well those previously
revealed through spectral modeling of the GRB emission.",2309.00673v1
2023-10-12,Positronium laser cooling via the $1^3S$-$2^3P$ transition with a broadband laser pulse,"We report on laser cooling of a large fraction of positronium (Ps) in
free-flight by strongly saturating the $1^3S$-$2^3P$ transition with a
broadband, long-pulsed 243 nm alexandrite laser. The ground state Ps cloud is
produced in a magnetic and electric field-free environment. We observe two
different laser-induced effects. The first effect is an increase in the number
of atoms in the ground state after the time Ps has spent in the long-lived
$3^3P$ states. The second effect is the one-dimensional Doppler cooling of Ps,
reducing the cloud's temperature from 380(20) K to 170(20) K. We demonstrate a
58(9) % increase in the coldest fraction of the Ps ensemble.",2310.08760v1
2023-10-23,Scrambling in Ising spin systems with constant and periodic transverse magnetic fields,"Scrambling of quantum information in both integrable and nonintegrable
systems, including the transverse field Ising model (TFIM) and Floquet spin
systems are studied. Our study employs tripartite mutual information (TMI),
with negative TMI serving as an indicator of scrambling, where a more negative
value suggests a higher degree of scrambling. In the integrable and
nonintegrable TFIM, we observe pronounced scrambling behavior, with the initial
growth following a power-law pattern. However, nonintegrable TFIM exhibits a
higher degree of scrambling compared to the integrable version. In the Floquet
system, TMI is studied across periods from $0$ to $\pi/2$. Both integrable and
nonintegrable Floquet systems display scrambling behavior across all periods,
except at $\tau=\pi/4$, featuring power-law growth for small periods and abrupt
jumps for larger ones. Nonintegrable Floquet systems exhibit more pronounced
scrambling compared to integrable ones across all periods. The degree of
scrambling increases as we move towards $\tau = \pi/4$, reaching its peak near
$\tau = \pi/4$ (but not at $\tau = \pi/4$), regardless of the initial states.
TMI saturation fluctuates less in the Floquet system in comparison to the TFIM.
The growth of scrambling in the Floquet system mirrors TFIM for small periods
but exhibits notably faster growth for larger periods. For a small period, the
degree of scrambling in a Floquet system is comparable to that in the TFIM, but
it becomes significantly greater for larger periods.",2310.14620v1
2023-12-14,Revisiting RXTE observations of MXB 0656-072 during the type I outbursts in 2007-2008,"We report on the timing characteristics of MXB 0656-072 throughout its
2007-2008 type I outbursts utilising RXTE/PCA and Fermi/GBM data. Using pulse
timing technique, we explore the spin frequency evolution of the source during
this interval. Subsequently, by examining the torque-luminosity relation, we
show that the overall frequency evolution is substantially in line with the
Ghosh-Lamb model. Furthermore, the residuals of the spin frequencies do not
exhibit clear orbital modulations, which possibly indicate that the system is
observed on a relatively top view. In the RXTE/PCA observations, the pulsed
emission is found to be disappearing below $\sim$$5 \times 10^{36}$ erg
s$^{-1}$, whereas the profiles maintain stability above this value within our
analysis timeframe. In addition, we incorporate two novel methods along with
the conventional Deeter method in order to generate higher-resolution power
density spectra (PDS). A red noise pattern in the PDSs is also verified in
these new methods, common in disk-fed sources, with a steepness of $\Gamma \sim
-2$, reaching saturation at a time-scale of $\sim$150 d. Considering the models
for spectral transitions, we discuss the possible scenarios for the dipolar
magnetic field strength of MXB 0656-072 and its coherence with deductions from
the cyclotron resonance scattering feature (CRSF).",2312.08943v1
2024-01-25,Thermal and Magnetoelastic Properties of the van der Waals Ferromagnet Fe$_{3-δ}$GeTe$_2$: Anisotropic Spontaneous Magnetostriction and Ferromagnetic Magnon Excitations,"By determining the lattice parameters as a function of temperature of the
hexagonal van der Waals ferromagnet Fe$_{2.92(1)}$Ge$_{1.02(3)}$Te$_2$ we
obtain the temperature dependence of the spontaneous in-plane magnetostriction
in the ferromagnetic and the linear thermal expansion coefficients in the
paramagnetic state. The spontaneous magnetostriction is clearly seen in the
temperature dependence of the in-plane lattice parameter $a(T)$, but less well
pronounced perpendicular to the planes along $c$. Below $T_{\rm C}$ the
spontaneous magnetostriction follows the square of the magnetization and leads
to an expansion of the hexagonal layers. Extrapolating to $T\rightarrow$ 0~K we
obtain a spontaneous in-plane saturation magnetostriction of $\lambda_{{\rm
sp},a}(T \rightarrow 0) \approx-220 ~\times~10^{-6}$. In the paramagnetic state
the linear thermal expansion coefficients amount to
13.9(1)$\times$10$^{-6}$~K$^{-1}$ and to 23.2(2)$\times$10$^{-6}$~K$^{-1}$ for
the in-plane and out-of-plane direction, respectively, indicating a linear
volume thermal expansion coefficient of 50.8(4)$\times$10$^{-6}$K$^{-1}$ which
we use to estimate the volume thermal expansion contribution to the heat
capacity determined at constant pressure. A Sommerfeld-type linear term in the
low-temperature heat capacities can be quantitatively ascribed to 2dim
ferromagnetic magnon excitations.",2401.14050v1
2024-01-26,First-principles methodology for studying magnetotransport in narrow-gap semiconductors: an application to Zirconium Pentatelluride ZrTe5,"The origin of anomalous resistivity peak and accompanied sign reversal of
Hall resistivity of ZrTe$_5$ has been under debate for a long time. Although
various theoretical models have been proposed to account for these intriguing
transport properties, a systematic study from first principles view is still
lacking. In this work, we present a first principles calculation combined with
Boltzmann transport theory to investigate the transport properties in
narrow-gap semiconductors at different temperatures and doping densities within
the relaxation time approximation. Regarding the sensitive
temperature-dependent chemical potential and relaxation time of semiconductors,
we take proper approximation to simulate these two variables, and then
comprehensively study the transport properties of ZrTe$_5$ both in the absence
and presence of an applied magnetic field. Without introducing topological
phases and correlation interactions, we qualitatively reproduced crucial
features observed in experiments, including zero-field resistivity anomaly,
nonlinear Hall resistivity with sign reversal, and non-saturating
magnetoresistance at high temperatures. Our calculation allows a systematic
interpretation of the observed properties in terms of multi-carrier and Fermi
surface geometry. Our method can be extended to other narrow-gap semiconductors
and further pave the way to explore interesting and novel transport properties
of this field.",2401.15151v1
2024-02-16,Spectral variations within solar flare ribbons,"Solar flare ribbons are intense brightenings of principally chromospheric
material that are responsible for a large fraction of the chromospheric
emission in solar and stellar flares. We present an on-disc observation of
flare ribbon substructures in an X9.3-class flare observed by the Swedish 1-m
Solar Telescope. We identify categories of ribbon substructures seen in the Ca
II 8542 \AA, H$\alpha$, and Ca II K lines, focusing on their spatial locations
and their (spectro-)polarimetric properties. Color Collapsed Plotting
(COCOPLOT) software is used to assist in identifying areas of interest. We
present five categories of spectral profiles within the general body of the
flare ribbon: (1) Extremely broadened spectral line profiles, where the
standard Fabry-Perot interferometer wavelength windows ($\approx 70$ km
s$^{-1}$) are insufficiently wide to allow for a complete analysis of the
dynamics and atmospheric conditions. The mechanisms causing this degree of this
broadening are not yet clearly understood. (2) Long-lived, dense kernels that
manifest as more saturated chromospheric line profiles with lower signal in
both Stokes parameters. They are interpreted as footpoints of bunched magnetic
field loops, whose chromospheric lines form at greater heights than the nearby
areas. (3) Doppler-shifted leading edges of the flare ribbon in regions that
transiently display lower Stokes signals due to the emission dominating at
greater heights in the atmosphere. (4) Condensed coronal rain overlapping the
flare ribbons in the line of sight, producing exceptionally high Doppler shifts
near the footpoints...",2402.10611v2
2024-03-20,Towards Learning Contrast Kinetics with Multi-Condition Latent Diffusion Models,"Contrast agents in dynamic contrast enhanced magnetic resonance imaging allow
to localize tumors and observe their contrast kinetics, which is essential for
cancer characterization and respective treatment decision-making. However,
contrast agent administration is not only associated with adverse health risks,
but also restricted for patients during pregnancy, and for those with kidney
malfunction, or other adverse reactions. With contrast uptake as key biomarker
for lesion malignancy, cancer recurrence risk, and treatment response, it
becomes pivotal to reduce the dependency on intravenous contrast agent
administration. To this end, we propose a multi-conditional latent diffusion
model capable of acquisition time-conditioned image synthesis of DCE-MRI
temporal sequences. To evaluate medical image synthesis, we additionally
propose and validate the Fr\'echet radiomics distance as an image quality
measure based on biomarker variability between synthetic and real imaging data.
Our results demonstrate our method's ability to generate realistic
multi-sequence fat-saturated breast DCE-MRI and uncover the emerging potential
of deep learning based contrast kinetics simulation. We publicly share our
accessible codebase at https://github.com/RichardObi/ccnet.",2403.13890v1
2002-03-14,Geometric Scaling above the Saturation Scale,"We show that the evolution equations in QCD predict geometric scaling for
quark and gluon distribution functions in a large kinematical window, which
extends above the saturation scale up to momenta $Q^2$ of order $100 {\rm
GeV}^2$. For $Q^2 < Q^2_s$, with $Q_s$ the saturation momentum, this is the
scaling predicted by the Colour Glass Condensate and by phenomenological
saturation models. For $1 \simle \ln(Q^2/Q_s^2) \ll \ln(Q_s^2/\Lambda^2_{\rm
QCD})$, we show that the solution to the BFKL equation shows approximate
scaling, with the scale set by $Q_s$. At larger $Q^2$, this solution does not
scale any longer. We argue that for the intermediate values of $Q^2$ where we
find scaling, the BFKL rather than the double logarithmic approximation to the
DGLAP equation properly describes the dynamics. We consider both fixed and
running couplings, with the scale for running set by the saturation momentum.
The anomalous dimension which characterizes the approach of the gluon
distribution function towards saturation is found to be close to, but lower
than, one half.",0203137v1
2003-10-30,Saturation and BFKL dynamics in the HERA data at small x,"We show that the HERA data for the inclusive structure function F_2(x,Q^2)
for x < 0.01 and 0.045 < Q^2 < 45 GeV^2 can be well described within the color
dipole picture, with a simple analytic expression for the dipole-proton
scattering amplitude, which is an approximate solution to the non-linear
evolution equations in QCD. For dipole sizes less than the inverse saturation
momentum 1/Q_s(x), the scattering amplitude is the solution to the BFKL
equation in the vicinity of the saturation line. It exhibits geometric scaling
and scaling violations by the diffusion term. For dipole sizes larger than
1/Q_s(x), the scattering amplitude saturates to one. The fit involves three
parameters: the proton radius R, the value x_0 of x at which the saturation
scale Q_s equals 1GeV, and the logarithmic derivative of the saturation
momentum \lambda. The value of \lambda extracted from the fit turns out to be
consistent with a recent calculation using the next-to-leading order BFKL
formalism.",0310338v1
2005-03-18,Energy Conservation and Saturation in Small-x Evolution,"Important corrections to BFKL evolution are obtained from non-leading
contributions and from non-linear effects due to unitarisation or saturation.
It has been difficult to estimate the relative importance of these effects, as
NLO effects are most easily accounted for in momentum space while unitarisation
and saturation are easier in transverse coordinate space. An essential
component of the NLO contributions is due to energy conservation effects, and
in this paper we present a model for implementing such effects together with
saturation in Mueller's dipole evolution formalism. We find that energy
conservation severely dampens the small-x rise of the gluon density and, as a
consequence, the onset of saturation is delayed. Using a simple model for the
proton we obtain a reasonable qualitative description of the x-dependence of F2
at low Q^2 as measured at HERA even without saturation effects. We also give
qualitative descriptions of the energy dependence of the cross section for
gamma*-gamma* and gamma*-nucleus scattering.",0503181v2
1995-11-30,"Transferring saturation, the finite cover property, and stability","Saturation is (mu,kappa)-transferable in T if and only if there is an
expansion T_1 of T with |T_1| = |T| such that if M is a mu-saturated model of
T_1 and |M| \geq kappa then the reduct M|L(T) is kappa-saturated. We
characterize theories which are superstable without the finite cover property
(f.c.p.), or without f.c.p. as, respectively those where saturation is
(aleph_0,lambda)-transferable or (kappa(T),lambda)-transferable for all lambda.
Further if for some mu \geq |T|, 2^mu > mu^+, stability is equivalent to: or
all mu \geq |T|, saturation is (\mu,2^mu)-transferable.",9511205v3
2006-05-17,Saturation points on faces of a rational polyhedral cone,"Different commutative semigroups may have a common saturation. We consider
distinguishing semigroups with a common saturation based on their ``sparsity''.
We propose to qualitatively describe sparsity of a semigroup by considering
which faces of the corresponding rational polyhedral cone have saturation
points. For a commutative semigroup we give a necessary and sufficient
condition for determining which faces have saturation points. We also show that
we can construct a commutative semigroup with arbitrary consistent patterns of
faces with saturation points.",0605479v4
2010-05-27,Non-linear evolution in CCFM: The interplay between coherence and saturation,"We solve the CCFM equation numerically in the presence of a boundary
condition which effectively incorporates the non-linear dynamics. We retain the
full dependence of the unintegrated gluon distribution on the coherence scale,
and extract the saturation momentum. The resulting saturation scale is a
function of both rapidity and the coherence momentum. In Deep Inelastic
Scattering this will lead to a dependence of the saturation scale on the photon
virtuality in addition to the usual x-Bjorken dependence. At asymptotic
energies the interplay between the perturbative non-linear physics, and that of
the QCD coherence, leads to an interesting and novel dynamics where the
saturation momentum itself eventually saturates. We also investigate various
implementations of the ""non-Sudakov"" form factor. It is shown that the
non-linear dynamics leads to almost identical results for different form
factors. Finally, different choices of the scale of the running coupling are
analyzed and implications for the phenomenology are discussed.",1005.5153v1
2011-07-09,The Search for Super-saturation in Chromospheric Emission,"We investigate if the super-saturation phenomenon observed at X-ray
wavelengths for the corona, exists in the chromosphere for rapidly rotating
late-type stars. Moderate resolution optical spectra of fast rotating EUV- and
X-ray- selected late-type stars were obtained. Stars in alpha Per were observed
in the northern hemisphere with the Isaac Newton 2.5 m telescope and IDS
spectrograph. Selected objects from IC 2391 and IC 2602 were observe in the
southern hemisphere with the Blanco 4m telescope and R-C spectrograph at CTIO.
Ca II H & K fluxes were measured for all stars in our sample. We find the
saturation level for Ca II K at log(L_CaK/L_bol) = -4.08. The Ca II K flux does
not show a decrease as a function of increased rotational velocity or smaller
Rossby number as observed in the X-ray. This lack of ""super-saturation""
supports the idea of coronal-stripping as the cause of saturation and
super-saturation in stellar chromospheres and corona, but the detailed
underlying mechanism is still under investigation.",1107.1786v1
2011-09-30,Dynamics of Saturated Energy Condensation in Two-Dimensional Turbulence,"In two-dimensional forced Navier-Stokes turbulence, energy cascades to the
largest scales in the system to form a pair of coherent vortices known as the
Bose condensate. We show, both numerically and analytically, that the energy
condensation saturates and the system reaches a statistically stationary state.
The time scale of saturation is inversely proportional to the viscosity and the
saturation energy level is determined by both the viscosity and the force. We
further show that, without sufficient resolution to resolve the small-scale
enstrophy spectrum, numerical simulations can give a spurious result for the
saturation energy level. We also find that the movement of the condensate is
similar to the motion of an inertial particle with an effective drag force.
Furthermore, we show that the profile of the saturated coherent vortices can be
described by a Gaussian core with exponential wings.",1109.6937v2
2012-08-20,A Simple Proof of Threshold Saturation for Coupled Vector Recursions,"Convolutional low-density parity-check (LDPC) codes (or spatially-coupled
codes) have now been shown to achieve capacity on binary-input memoryless
symmetric channels. The principle behind this surprising result is the
threshold-saturation phenomenon, which is defined by the belief-propagation
threshold of the spatially-coupled ensemble saturating to a fundamental
threshold defined by the uncoupled system.
  Previously, the authors demonstrated that potential functions can be used to
provide a simple proof of threshold saturation for coupled scalar recursions.
In this paper, we present a simple proof of threshold saturation that applies
to a wide class of coupled vector recursions. The conditions of the theorem are
verified for the density-evolution equations of: (i) joint decoding of
irregular LDPC codes for a Slepian-Wolf problem with erasures, (ii) joint
decoding of irregular LDPC codes on an erasure multiple-access channel, and
(iii) general protograph codes on the BEC. This proves threshold saturation for
these systems.",1208.4080v3
2014-06-18,Saturation and elementary equivalence of C*-algebras,"We study the saturation properties of several classes of $C^*$-algebras.
Saturation has been shown by Farah and Hart to unify the proofs of several
properties of coronas of $\sigma$-unital $C^*$-algebras; we extend their
results by showing that some coronas of non-$\sigma$-unital $C^*$-algebras are
countably degree-$1$ saturated. We then relate saturation of the abelian
$C^*$-algebra $C(X)$, where $X$ is $0$-dimensional, to topological properties
of $X$, particularly the saturation of $CL(X)$.",1406.4875v4
2016-06-20,Consensus with Output Saturations,"This paper consider a standard consensus algorithm under output saturations.
In the presence of output saturations, global consensus can not be realized due
to the existence of stable, unachievable equilibrium points for the consensus.
Therefore, this paper investigates necessary and sufficient initial conditions
for the achievement of consensus, that is an exact domain of attraction.
Specifically, this paper considers singe-integrator agents with both fixed and
time-varying undirected graphs, as well as double-integrator agents with fixed
undirected graph. Then, we derive that the consensus will be achieved if and
only if the average of the initial states (only velocities for
double-integrator agents with homogeneous saturation levels for the outputs) is
within the minimum saturation level. An extension to the case of fixed directed
graph is also provided in which an weighted average is required to be within
the minimum saturation limit.",1606.05980v1
2016-12-13,Weak Value Amplification Can Outperform Conventional Measurement in the Presence of Detector Saturation,"Weak value amplification (WVA) is a technique in which one can magnify the
apparent strength of a measurement signal. Some have claimed that WVA can
outperform more conventional measurement schemes in parameter estimation.
Nonetheless, a significant body of theoretical work has challenged this
perspective, suggesting WVA to be fundamentally sub-optimal. Optimal
measurements may not be practical, however. Two practical considerations that
have been conjectured to afford a benefit to WVA over conventional measurement
are certain types of noise and detector saturation. Here, we report a
theoretical study of the role of saturation and pixel noise in WVA-based
measurement, in which we carry out a Bayesian analysis of the Fisher
information available using a saturable, pixelated, digitized, and/or noisy
detector. We draw two conclusions: first, that saturation alone does not confer
an advantage to the WVA approach over conventional measurement, and second,
that WVA can outperform conventional measurement when saturation is combined
with intrinsic pixel noise and/or digitization.",1612.04327v1
2017-01-11,The Saturation Number of Induced Subposets of the Boolean Lattice,"Given a poset $P$, a family $F$ of elements in the Boolean lattice is said to
be $P$-saturated if (1) $F$ contains no copy of $P$ as a subposet and (2) every
proper superset of $F$ contains a copy of $P$ as a subposet. The maximum size
of a $P$-saturated family is denoted by $La(n,P)$, which has been studied for a
number of choices of $P$. The minimum size of a $P$-saturated family,
$sat(n,P)$, was introduced by Gerbner et al. (2013), and parallels the deep
literature on the saturation function for graphs.
  We introduce and study the concept of saturation for induced subposets. As
opposed to induced saturation in graphs, the above definition of saturation for
posets extends naturally to the induced setting. We give several exact results
and a number of bounds on the induced saturation number for several small
posets. We also use a transformation to the biclique cover problem to prove a
logarithmic lower bound for a rich infinite family of target posets.",1701.03010v2
2018-02-18,CGC/saturation approach: an impact-parameter dependent model for diffraction production in DIS,"In the paper we discussed the evolution equations for diffractive production
in the framework of CGC/saturation approach, and found the analytical solutions
for several kinematic regions. The most impressive features of these solutions
are, that diffractive production does not exibit geometric scaling behaviour
i.e. being a function of one variable.
  Based on these solutions, we suggest an impact parameter dependent saturation
model, which is suitable for describing diffraction production both deep in the
saturation region, and in the vicinity of the saturation scale. Using the model
we attempted to fit the combined data on diffraction production from H1 and
ZEUS collaborations. We found that we are able describe both
  $x_\pom$ and $\beta$ dependence, as well as $Q$ behavior of the measured
cross sections. In spite of the sufficiently large $\chi^2/d.o.f.$ we believe
that our description provides an initial impetus to find a fit of the
experimental data, based on the solution of the CGC/saturation equation, rather
than on describing the diffraction system in simplistic manner, assuming that
only quark-antiquark pair and one extra gluons, are produced.",1802.06344v1
2018-02-19,Bulk hydrodynamic stability and turbulent saturation in compressing hot spots,"For hot spots compressed at constant velocity, we give a hydrodynamic
stability criterion that describes the expected energy behavior of non-radial
hydrodynamic motion for different classes of trajectories (in $\rho R$ --- $T$
space). For a given compression velocity, this criterion depends on $\rho R$,
$T$, and $\mathrm{d}T/\mathrm{d}(\rho R)$ (the trajectory slope), and applies
point-wise, so that the expected behavior can be determined instantaneously
along the trajectory. Among the classes of trajectories are those where the
hydromotion is guaranteed to decrease, and those where the hydromotion is
bounded by a saturated value. We calculate this saturated value, and find the
compression velocities for which hydromotion may be a substantial fraction of
hot-spot energy at burn time. The Lindl ""attractor"" trajectory (Lindl, 1995) is
shown to experience non-radial hydrodynamic energy that grows towards this
saturated state. Comparing the saturation value to available detailed 3D
simulation results, we find that the fluctuating velocities in these
simulations reach substantial fractions of the saturated value.",1802.06817v1
2018-05-15,On the Dihadron Angular Correlations in Forward $pA$ collisions,"Dihadron angular correlations in forward $pA$ collisions have been considered
as one of the most sensitive observables to the gluon saturation effects. In
general, both parton shower effects and saturation effects are responsible for
the back-to-back dihadron angular de-correlations. With the recent progress in
the saturation formalism, we can incorporate the parton shower effect by adding
the corresponding Sudakov factor in the saturation framework. In this paper, we
carry out the first detailed numerical study in this regard, and find a very
good agreement with previous RHIC $pp$ and $dAu$ data. This study can help us
to establish a baseline in $pp$ collisions which contains little saturation
effects, and further make predictions for dihadron angular correlations in
$pAu$ collisions, which will allow to search for the signal of parton
saturation.",1805.05712v1
2018-09-19,Direct Reconstruction of Saturated Samples in Band-Limited OFDM Signals,"Given a set of samples, a few of them being possibly saturated, we propose an
efficient algorithm in order to cancel saturation while reconstructing
band-limited signals. Our method satisfies a minimum-loss constraint and relies
on sinc-related bases. It involves matrix inversion and is a direct,
non-iterative approach. It consists of two main steps: (i) regression, to
estimate the expansion coefficients of the signal model; (ii) interpolation, to
restore an estimated value for those samples that are saturated. Because the
proposed method is free from tuning parameters, it is hardware-friendly and we
expect that it will be particularly useful in the context of orthogonal
frequency-division multiplexing. There, the high peak-to-average power ratio of
the transmitted signal results in a challenging decoding stage in the presence
of saturation, which causes significant decoding errors due to the nonlinearity
of amplifiers and receivers, ultimately resulting in band distortion and
information loss. Our experiments on realistic simulations confirm that our
proposed reconstruction of the saturated samples can significantly reduce
transmission errors in modern high-throughput digital-communication receivers.",1809.07188v1
2019-05-18,On greedy heuristics for computing D-efficient saturated subsets,"Let $\mathcal{F}$ be a set consisting of $n$ real vectors of dimension $m
\leq n$. For any saturated, i.e., $m$-element, subset $\mathcal{S}$ of
$\mathcal{F}$, let $\mathrm{vol}(\mathcal{S})$ be the volume of the
parallelotope formed by the vectors of $\mathcal{S}$. A set $\mathcal{S}^*$ is
called a $D$-optimal saturated subset of $\mathcal{F}$, if it maximizes
$\mathrm{vol}(\mathcal{S})$ among all saturated subsets of $\mathcal{F}$. In
this paper, we propose two greedy heuristics for the construction of saturated
subsets performing well with respect to the criterion of $D$-optimality: an
improvement of the method suggested by Galil and Kiefer for the initiation of
$D$-optimal experimental design algorithms, and a modification of the
Kumar-Yildirim method, the original version of which was proposed for the
initiation of the minimum-volume enclosing ellipsoid algorithms. We provide
geometric and analytic insights into the two methods, and compare them to the
commonly used random and regularized greedy heuristics. We also suggest
variants of the greedy methods for a large set $\mathcal{F}$, for the
construction of $D$-efficient non-saturated subsets, and for alternative
optimality criteria.",1905.07647v1
2020-04-07,egg: Fast and Extensible Equality Saturation,"An e-graph efficiently represents a congruence relation over many
expressions. Although they were originally developed in the late 1970s for use
in automated theorem provers, a more recent technique known as equality
saturation repurposes e-graphs to implement state-of-the-art, rewrite-driven
compiler optimizations and program synthesizers. However, e-graphs remain
unspecialized for this newer use case. Equality saturation workloads exhibit
distinct characteristics and often require ad-hoc e-graph extensions to
incorporate transformations beyond purely syntactic rewrites.
  This work contributes two techniques that make e-graphs fast and extensible,
specializing them to equality saturation. A new amortized invariant restoration
technique called rebuilding takes advantage of equality saturation's distinct
workload, providing asymptotic speedups over current techniques in practice. A
general mechanism called e-class analyses integrates domain-specific analyses
into the e-graph, reducing the need for ad hoc manipulation.
  We implemented these techniques in a new open-source library called egg. Our
case studies on three previously published applications of equality saturation
highlight how egg's performance and flexibility enable state-of-the-art results
across diverse domains.",2004.03082v3
2020-05-11,$P_{n}$-induced-saturated graphs exist for all $n \geq 6$,"Let $P_{n}$ be a path graph on $n$ vertices. We say that a graph $G$ is
$P_{n}$-induced-saturated if $G$ contains no induced copy of $P_{n}$, but
deleting any edge of $G$ as well as adding to $G$ any edge of $G^{c}$ creates
such a copy. Martin and Smith (2012) showed that there is no
$P_{4}$-induced-saturated graph. On the other hand, there trivially exist
$P_{n}$-induced-saturated graphs for $n=2,3$. Axenovich and Csik\'{o}s (2019)
ask for which integers $n \geq 5$ do there exist $P_{n}$-induced-saturated
graphs. R\""{a}ty (2019) constructed such a graph for $n=6$, and Cho, Choi and
Park (2019) later constructed such graphs for all $n=3k$ for $k \geq 2$. We
show by a different construction that $P_{n}$-induced-saturated graphs exist
for all $n \geq 6$, leaving only the case $n=5$ open.",2005.05033v2
2021-03-11,Two-phase hyperbolic model for porous media saturated with a viscous fluid and its application to wavefields simulation,"We derive and study a new hyperbolic two-phase model of a porous deformable
medium saturated by a viscous fluid. The governing equations of the model are
derived in the framework of Symmetric Hyperbolic Thermodynamically Compatible
(SHTC) systems and by generalizing the unified hyperbolic model of continuum
fluid and solid mechanics. Similarly to the unified model, the presented model
takes into account the viscosity of the saturating fluid through a hyperbolic
reformulation. The model accounts for such dissipative mechanisms as
interfacial friction and viscous dissipation of the saturated fluid. Using the
presented nonlinear finite-strain SHTC model, the governing equations for the
propagation of small-amplitude waves in a porous medium saturated with a
viscous fluid are derived. As in the conventional Biot theory of porous media,
three types of waves can be found: fast and slow compression waves and shear
waves. It turns out that the shear wave attenuates rapidly due to the viscosity
of the saturating fluid, and this wave is difficult to see in typical test
cases. However, some test cases are presented in which shear waves can be
observed in the vicinity of interfaces between regions with different porosity.",2103.06969v1
2021-05-14,Defect Saturation in a Rapidly Quenched Bose Gas,"We investigate the saturation of defect density in an atomic Bose gas rapidly
cooled into a superfluid phase. The number of quantum vortices, which are
spontaneously created in the quenched gas, exhibits a Poissonian distribution
not only for a slow quench in the Kibble-Zurek (KZ) scaling regime but also for
a fast quench in which case the mean vortex number is saturated. This shows
that the saturation is not caused by destructive vortex collisions, but by the
early-time coarsening in an emerging condensate, which is further supported by
the observation that the condensate growth lags the quenching in the saturation
regime. Our results demonstrate that the defect saturation is an effect beyond
the KZ mechanism, opening a path for studying critical phase transition
dynamics using the defect number distribution.",2105.06601v2
2021-06-03,Predicting water flow in fully and partially saturated porous media: a new fractal-based permeability model,"Predicting the permeability of porous media in saturated and partially
saturated conditions is of crucial importance in many geo-engineering areas,
from water resources to vadose zone hydrology or contaminant transport
predictions. Many models have been proposed in the literature to estimate the
permeability from properties of the porous media such as porosity, grain size
or pore size. In this study, we develop a model of the permeability for porous
media saturated by one or two fluid phases with all physically-based parameters
using a fractal upscaling technique. The model is related to microstructural
properties of porous media such as fractal dimension for pore space, fractal
dimension for tortuosity, porosity, maximum radius, ratio of minimum pore
radius and maximum pore radius, water saturation and irreducible water
saturation. The model is favorably compared to existing and widely used models
from the literature. Then, comparison with published experimental data for both
unconsolidated and consolidated samples, we show that the proposed model
estimate the permeability from the medium properties very well.",2106.01670v1
2021-09-16,Saturated and linear isometric transfer systems for cyclic groups of order $p^mq^n$,"Transfer systems are combinatorial objects which classify $N_\infty$ operads
up to homotopy. By results of A. Blumberg and M. Hill, every transfer system
associated to a linear isometries operad is also saturated (closed under a
particular two-out-of-three property). We investigate saturated and linear
isometric transfer systems with equivariance group $C_{p^mq^n}$, the cyclic
group of order $p^mq^n$ for $p,q$ distinct primes and $m,n\ge 0$. We give a
complete enumeration of saturated transfer systems for $C_{p^mq^n}$. We also
prove J. Rubin's saturation conjecture for $C_{pq^n}$; this says that every
saturated transfer system is realized by a linear isometries operad for $p,q$
sufficiently large (greater than $3$ in this case).",2109.08210v1
2021-09-27,Recent advances of MXene saturable absorber for near-infrared mode-locked fiber laser,"To date, MXene has been discovered for its viability as alternatives to
conventional saturable absorber such as carbon nanotube and graphene. The
characteristics of high nonlinear saturable absorption, astounding modulation
depth, flexible bandgap tunability, and high electron density near Fermi level
are the fundamentals of the MXene as an excellent saturable absorber candidate.
In particular, the research effort contributed to MXene in nonlinear ul-trafast
optics are extensively growing because MXene comprises one of the largest
families in 2D nanomaterials that provides huge combination possibilities by
forming a class of metal carbide or metal nitride with 2D layered structure.
Herein, this review summarizes the recent development on synthesis and material
characterization of the MXene, the studies on its nonlinear saturable
absorption and the application of the MXene saturable absorber in near-infrared
mode-locked fiber laser. Finally, some issues and challenges as well as future
perspectives of this novel material are discussed.",2109.13011v1
2021-11-09,First saturation correction in high energy proton-nucleus collisions: Part III. Ensemble averaging,"In high energy proton-nucleus collisions, the gluon saturation effects from
the nucleus are fully incorporated into the light-like Wilson lines. The gluon
saturation effects from the proton, which are anticipated to be important
either in the extreme high energy limit or towards the dense-dense
(nucleus-nucleus) collision regimes, have been studied perturbatively within
the Color Glass Condensate effective theory in previous papers of this series.
A configuration-by-configuration expression for the single inclusive semi-hard
gluon production including the first saturation correction was obtained. In
this paper, we perform ensemble averaging in the McLerran-Venugopalan model and
the Dipole Approximation. We find that, in the saturation correction, the
effects of the initial state interactions are negligible while the final state
interactions play most important role and give a positive-valued contribution
to the semi-hard gluon spectrum. Furthermore, we show that the single gluon
spectrum scales approximately $1/k_{\perp}^{4}$ at small $k_{\perp}$,
suggesting that a resummation of higher order saturation corrections is
required to regulate the infrared region of the gluon spectrum.",2111.05304v2
2021-12-13,Bistable soliton switching dynamics in a $\mathcal{PT}$-symmetric coupler with saturable nonlinearity,"We investigate the switching dynamics in a $\mathcal{PT}$-symmetric fiber
coupler composed of a saturable nonlinear material as the core. In such a
saturable nonlinear medium, bistable solitons may evolve due to the balance
between dispersion and saturable nonlinearity, which we extend in the context
of the $\mathcal{PT}$-symmetric coupler. Our investigations of power-controlled
and phase-sensitive switching show richer soliton switching dynamics than the
currently existing conventional counterparts, which may lead to ultrafast and
efficient all-optical switching dynamics at very low power owing to the
combined effects of $\mathcal{PT}$ symmetry and saturable nonlinearity. In
addition to the input power, the relative phase of the input solitons and
saturable coefficient are additional controlling parameters that efficiently
tailor the switching dynamics. Also, we provide a suitable range of system and
pulse parameters that would be helpful for the practical realization of the
coupler to use in all-optical switching devices and photonic circuits. Finally,
we develop a variational approach to analytically investigate the switching
dynamics in such $\mathcal{PT}$-symmetric couplers that excellently predicts
the numerical findings.",2112.06684v2
2022-03-10,Saturation of Ordered Graphs,"Recently, the saturation problem of $0$-$1$ matrices gained a lot of
attention. This problem can be regarded as a saturation problem of ordered
bipartite graphs. Motivated by this, we initiate the study of the saturation
problem of ordered and cyclically ordered graphs.
  We prove that dichotomy holds also in these two cases, i.e., for a
(cyclically) ordered graph its saturation function is either bounded or linear.
We also determine the order of magnitude for large classes of (cyclically)
ordered graphs, giving infinite many examples exhibiting both possible
behaviours, answering a problem of P\'alv\""olgyi. In particular, in the ordered
case we define a natural subclass of ordered matchings, the class of linked
matchings, and we start their systematic study, concentrating on linked
matchings with at most three links and prove that many of them have bounded
saturation function.
  In both the ordered and cyclically ordered case we also consider the
semisaturation problem, where dichotomy holds as well and we can even fully
characterize the graphs that have bounded semisaturation function.",2203.05307v1
2022-11-03,Harmonics of Parton Saturation in Lepton-Jet Correlations at the EIC,"Parton saturation is one of the most intriguing phenomena in the high energy
nuclear physics research frontier, especially in the upcoming era of the
Electron-Ion Collider (EIC). The lepton-jet correlation in deep inelastic
scattering provides us with a new gateway to the parton saturation at the EIC.
In particular, we demonstrate that azimuthal angle anisotropies of the
lepton-jet correlation are sensitive to the strength of the saturation momentum
in the EIC kinematic region. In contrast to the predictions based on the
collinear framework calculation, significant nuclear modification of the
anisotropies is observed when we compare the saturation physics results in e +
p and e + Au scatterings. By measuring these harmonic coefficients at the EIC,
one can conduct quantitative analysis in different collisional systems and
unveil compelling evidence for saturation effects.",2211.01647v4
2022-11-16,The rainbow saturation number is linear,"Given a graph $H$, we say that an edge-coloured graph $G$ is $H$-rainbow
saturated if it does not contain a rainbow copy of $H$, but the addition of any
non-edge in any colour creates a rainbow copy of $H$. The rainbow saturation
number $\text{rsat}(n,H)$ is the minimum number of edges among all $H$-rainbow
saturated edge-coloured graphs on $n$ vertices. We prove that for any non-empty
graph $H$, the rainbow saturation number is linear in $n$, thus proving a
conjecture of Gir\~{a}o, Lewis, and Popielarz. In addition, we also give an
improved upper bound on the rainbow saturation number of the complete graph,
disproving a second conjecture of Gir\~{a}o, Lewis, and Popielarz.",2211.08589v1
2022-12-07,A Decision Diagram Operation for Reachability,"Saturation is considered the state-of-the-art method for computing fixpoints
with decision diagrams. We present a relatively simple decision diagram
operation called REACH that also computes fixpoints. In contrast to saturation,
it does not require a partitioning of the transition relation. We give
sequential algorithms implementing the new operation for both binary and
multi-valued decision diagrams, and moreover provide parallel counterparts. We
implement these algorithms and experimentally compare their performance against
saturation on 692 model checking benchmarks in different languages. The results
show that the REACH operation often outperforms saturation, especially on
transition relations with low locality. In a comparison between parallelized
versions of REACH and saturation we find that REACH obtains comparable speedups
up to 16 cores, although falls behind saturation at 64 cores. Finally, in a
comparison with the state-of-the-art model checking tool ITS-tools we find that
REACH outperforms ITS-tools on 29% of models, suggesting that REACH can be
useful as a complementary method in an ensemble tool.",2212.03684v1
2023-02-13,Restoring the saturation response of a PMT using pulse-shape and artificial-neural-networks,"The linear response of a photomultiplier tube (PMT) is a required property
for photon counting and reconstruction of the neutrino energy. The linearity
valid region and the saturation response of PMT were investigated using a
linear-alkyl-benzene (LAB)-based liquid scintillator. A correlation was
observed between the two different saturation responses, with pulse-shape
distortion and pulse-area decrease. The observed pulse-shape provides useful
information for the estimation of the linearity region relative to the
pulse-area. This correlation-based diagnosis allows an ${in}$-${situ}$
estimation of the linearity range, which was previously challenging. The
measured correlation between the two saturation responses was employed to train
an artificial-neural-network (ANN) to predict the decrease in pulse-area from
the observed pulse-shape. The ANN-predicted pulse-area decrease enables the
prediction of the ideal number of photoelectrons irrelevant to the saturation
behavior. This pulse-shape-based machine learning technique offers a novel
method for restoring the saturation response of PMTs.",2302.06170v3
2023-02-13,Saturation of spiral instabilities in disk galaxies,"Spiral density waves can arise in galactic disks as linear instabilities of
the underlying stellar distribution function. Such an instability grows
exponentially in amplitude at some fixed growth rate $\beta$ before saturating
nonlinearly. However, the mechanisms behind saturation, and the resulting
saturated spiral amplitude, have received little attention. Here we argue that
one important saturation mechanism is the nonlinear trapping of stars near the
spiral's corotation resonance. Under this mechanism, we show analytically that
an $m$-armed spiral instability will saturate when the libration frequency of
resonantly trapped orbits reaches $\omega_\mathrm{lib} \sim \mathrm{a\,\,
few}\times m^{1/2} \beta$. For a galaxy with a flat rotation curve this implies
a maximum relative spiral surface density $\vert \delta\Sigma/\Sigma_0\vert
\sim \mathrm{a\,\,few} \times (\beta/\Omega_\mathrm{p})^2 \cot \alpha$, where
$\Omega_\mathrm{p}$ is the spiral pattern speed and $\alpha$ is its pitch
angle. This result is in reasonable agreement with recent $N$-body simulations,
and suggests that spirals driven by internally-generated instabilities reach
relative amplitudes of at most a few tens of percent; higher amplitude spirals,
like in M51 and NGC 1300, are likely caused by very strong bars and/or tidal
perturbations.",2302.06602v2
2023-04-04,Route to stabilize cubic gauche polynitrogen to ambient conditions via surface-saturation by hydrogen,"Cubic gauche polynitrogen (cg-N) is an attractive high-energy density
material. However, high-pressure synthesized cg-N will decompose at
low-pressure and cannot exist at ambient conditions. Here, the stabilities of
cg-N surfaces with and without saturations at different pressures and
temperatures are investigated systematically. Pristine surfaces at 0 GPa are
very brittle and will decompose at 300 K, especially (1 1 0) surface will
collapse completely just after structural relaxation, whereas the
decompositions of surfaces can be suppressed by applying pressure, indicating
that surface instability causes the cg-N decomposition at low-pressure. Due to
the saturation of dangling bonds and transferring electrons to the surfaces,
saturation with H can stabilize surfaces at ambient conditions, while OH
saturation cannot because of getting electrons from the surfaces. An acidic
environment or surface saturation with less electronegative adsorbates is more
favorable for the stability of polymerized nitrogen.",2304.01755v1
2023-05-18,Weak saturation in graphs: a combinatorial approach,"The weak saturation number $\mathrm{wsat}(n,F)$ is the minimum number of
edges in a graph on $n$ vertices such that all the missing edges can be
activated sequentially so that each new edge creates a copy of $F$. A usual
approach to prove a lower bound for the weak saturation number is algebraic: if
it is possible to embed edges of $K_n$ in a vector space in a certain way
(depending on $F$), then the dimension of the subspace spanned by the images of
the edges of $K_n$ is a lower bound for the weak saturation number. In this
paper, we present a new combinatorial approach to prove lower bounds for weak
saturation numbers that allows to establish worst-case tight (up to constant
additive terms) general lower bounds as well as to get exact values of the weak
saturation numbers for certain graph families. It is known (Alon, 1985) that,
for every $F$, there exists $c_F$ such that $\mathrm{wsat}(n,F)=c_Fn(1+o(1))$.
Our lower bounds imply that all values in the interval
$\left[\frac{\delta}{2}-\frac{1}{\delta+1},\delta-1\right]$ with step size
$\frac{1}{\delta+1}$ are achievable by $c_F$ (while any value outside this
interval is not achievable).",2305.11043v2
2023-05-27,Super resolution computational saturated absorption microscopy,"Imaging beyond the diffraction limit barrier has attracted wide attention due
to the ability to resolve image features that were previously hidden. Of the
various super-resolution microscopy techniques available, a particularly simple
method called saturated excitation microscopy (SAX) requires only a simple
modification of a laser scanning microscope where the illumination beam power
is sinusoidally modulated and driven into saturation. SAX images are extracted
from harmonics of the modulation frequency and exhibit improved spatial
resolution. Unfortunately, this elegant strategy is hindered by the incursion
of shot noise that prevents high resolution imaging in many realistic
scenarios. Here, we demonstrate a new technique for super resolution imaging
that we call computational saturated absorption (CSA) in which a joint
deconvolution is applied to a set of images with diversity in spatial frequency
support among the point spread functions used in the image formation with
saturated laser scanning fluorescence microscope. CSA microscopy allows access
to the high spatial frequency diversity in a set of saturated effective point
spread functions, while avoiding image degradation from shot noise.",2305.17348v1
2023-07-23,Saturating automata for game semantics,"Saturation is a fundamental game-semantic property satisfied by strategies
that interpret higher-order concurrent programs. It states that the strategy
must be closed under certain rearrangements of moves, and corresponds to the
intuition that program moves (P-moves) may depend only on moves made by the
environment (O-moves).
  We propose an automata model over an infinite alphabet, called saturating
automata, for which all accepted languages are guaranteed to satisfy a closure
property mimicking saturation.
  We show how to translate the finitary fragment of Idealized Concurrent Algol
(FICA) into saturating automata, confirming their suitability for modelling
higher-order concurrency. Moreover, we find that, for terms in normal form, the
resultant automaton has linearly many transitions and states with respect to
term size, and can be constructed in polynomial time. This is in contrast to
earlier attempts at finding automata-theoretic models of FICA, which did not
guarantee saturation and involved an exponential blow-up during translation,
even for normal forms.",2307.12302v2
2023-08-02,Injection-Limited and Space-Charge-Limited Conduction in Wide Bandgap Semiconductors with Velocity Saturation Effect,"Carrier conduction in wide bandgap semiconductors (WBS) often exhibits
velocity saturation at the high-electric field regime. How such effect
influences the transition between contact-limited and space-charge-limited
current in a two-terminal device remains largely unexplored thus far. Here, we
develop a generalized carrier transport model that includes contact-limited
field-induced carrier injection, space charge, carrier scattering and velocity
saturation effect. The model reveals various transitional behaviors in the
current-voltage characteristics, encompassing Fowler-Nordheim emission,
trap-free Mott-Gurney (MG) SCLC and \emph{velocity-saturated SCLC}. Using GaN,
6H-SiC and 4H-SiC WBS as examples, we show that the velocity-saturated SCLC
completely dominates the high-voltage ($10^2 \sim 10^4$ V) transport for
typical sub-$\mu$m GaN and SiC diodes, thus unravelling velocity-saturated SCLC
as a central transport mechanism in WBG electronics.",2308.00955v1
2024-01-30,$G$-complete reducibility and saturation,"Let $H \subseteq G$ be connected reductive linear algebraic groups defined
over an algebraically closed field of characteristic $p> 0$. In our first
principal theorem we show that if a closed subgroup $K$ of $H$ is
$H$-completely reducible, then it is also $G$-completely reducible in the sense
of Serre, under some restrictions on $p$, generalising the known case for $G =
GL(V)$. Our second main theorem shows that if $K$ is $H$-completely reducible,
then the saturation of $K$ in $G$ is completely reducible in the saturation of
$H$ in $G$ (which is again a connected reductive subgroup of $G$), under
suitable restrictions on $p$, again generalising the known instance for $G =
GL(V)$. We also study saturation of finite subgroups of Lie type in $G$. We
show that saturation is compatible with standard Frobenius endomorphisms, and
we use this to generalise a result due to Nori from 1987 in case $G = GL(V)$.",2401.16927v3
2024-03-19,Magnetic field morphology and evolution in the Central Molecular Zone and its effect on gas dynamics,"The interstellar medium in the Milky Way's Central Molecular Zone (CMZ) is
known to be strongly magnetised, but its large-scale morphology and impact on
the gas dynamics are not well understood. We explore the impact and properties
of magnetic fields in the CMZ using three-dimensional non-self gravitating
magnetohydrodynamical simulations of gas flow in an external Milky Way barred
potential. We find that: (1) The magnetic field is conveniently decomposed into
a regular time-averaged component and an irregular turbulent component. The
regular component aligns well with the velocity vectors of the gas everywhere,
including within the bar lanes. (2) The field geometry transitions from
parallel to the Galactic plane near $z=0$ to poloidal away from the plane. (3)
The magneto-rotational instability (MRI) causes an in-plane inflow of matter
from the CMZ gas ring towards the central few parsecs of $0.01-0.1$ M$_\odot$
yr$^{-1}$ that is absent in the unmagnetised simulations. However, the magnetic
fields have no significant effect on the larger-scale bar-driven inflow that
brings the gas from the Galactic disc into the CMZ. (4) A combination of bar
inflow and MRI-driven turbulence can sustain a turbulent vertical velocity
dispersion of $\sigma_z \simeq 5$ km s$^{-1}$ on scales of $20$ pc in the CMZ
ring. The MRI alone sustains a velocity dispersion of $\sigma_z \simeq 3$ km
s$^{-1}$. Both these numbers are lower than the observed velocity dispersion of
gas in the CMZ, suggesting that other processes such as stellar feedback are
necessary to explain the observations. (5) Dynamo action driven by differential
rotation and the MRI amplifies the magnetic fields in the CMZ ring until they
saturate at a value that scales with the average local density as $B \simeq 102
(n/10^3 cm^{-3})^{0.33}$ $\mu$G. Finally, we discuss the implications of our
results within the observational context in the CMZ.",2403.13048v1
2003-05-09,Numerical Study of Compressible Magnetohydrodynamic Turbulence in Two Dimensions,"We have studied forced turbulence of compressible magnetohydrodynamic (MHD)
flows through two-dimensional simulations with different numerical resolutions.
First, hydrodynamic turbulence with Mach number $<M_s >_{\rm init} \equiv < v
>_{\rm rms}/ c_s = 1$ and density compression ${< \delta\rho / \rho >}_{\rm
rms} \simeq 0.45$ was generated by enforcing a random force. Then, initial,
uniform magnetic fields of various strengths were added with Alfv\'enic Mach
number $<M_A >_{\rm init} \equiv < v >_{\rm rms} / c_{A, {\rm init}} \gg 1$. An
isothermal equation of state was employed, and no explicit dissipation was
included. After the MHD turbulence is saturated, the resulting flows are
categorized as very weak field (VWF), weak field (WF), and strong field (SF)
classes, which have $<M_A > \equiv < v >_{\rm rms} / < c_A >_{\rm rms} \gg 1$,
$<M_A > > 1$, and $<M_A > \sim 1$, respectively. Not only in the SF regime but
also in the WF regime, turbulent transport is suppressed by the magnetic field.
In the SF cases, the energy power spectra in the inertial range, although no
longer power-law, exhibit a range with slopes close to $\sim1.5$, hinting the
Iroshnikov-Kraichnan spectrum. Our simulations were able to produce the SF
class behaviors only with high resolution of at least $1024^2$ grid cells. The
specific requirements for the simulation of the SF class should depend on the
code (and the numerical scheme) as well as the initial setup, but our results
do indicate that very high resolution would be required for converged results
in simulation studies of MHD turbulence.",0305165v1
2006-03-01,Chandra X-Ray Observations of Young Clusters. III. NGC 2264 and the Orion Flanking Fields,"Chandra observations of solar-like pre-main sequence (PMS) stars in the Orion
Flanking Fields (age ~1 Myr) and NGC 2264 (~3 Myr) are compared with the
results of the COUP survey of similar objects in the ONC (~0.5 Myr). The
correlations between log Lx and mass found for PMS stars on convective tracks
in these clusters are consistent with the relationships found for the ONC,
indicating little change in the median values of either log Lx or log Lx/Lbol
during the first ~3-5 Myr of evolution down convective tracks. The fraction of
stars with extreme values of Lx, more than 10 times higher than the average for
a given Lbol or with log Lx/Lbol greater than the canonical saturation value of
-2.9, is however larger by a factor of two in the younger ONC when compared
with the Orion FF and NGC 2264.
  PMS stars in NGC 2264 on radiative tracks have Lx/Lbol values that are
systematically lower by a factor of ~10 times than those found for stars of
similar mass on convective tracks. The dramatic decrease in flux from
convective to radiative phases of PMS evolution is likely related to major
structural changes which influence the efficiency of magnetic field generation
and thus the level of magnetic activity.
  As in the ONC, we find that stars with measured periods have, on average,
higher X-ray luminosities. However, there is a wide range in Lx and Lx/Lbol for
both periodic and non-periodic stars of similar mass. Among stars with measured
periods, the level of X-ray emission does not correlate with the rotation rate.
  For this data set, we find no statistically significant correlation between
X-ray flux and (a) the presence or absence of circumstellar accretion disks, or
(b) disk accretion rates as assessed from ultraviolet excesses.",0603027v1
2001-09-10,"Novel features of Josephson flux-flow in Bi-2212: contribution of in-plane dissipation, coherent response to mm-wave radiation, size effect","We studied Josephson flux-flow (JFF) in Bi-2212 stacks fabricated from single
crystal whiskers by focused ion beam technique. For long junctions with the
in-plane sizes 30 x 2 (mu)m^2, we found considerable contribution of the
in-plane dissipation to the JFF resistivity, (rho)_(Jff), at low temperatures.
According to recent theory [A. Koshelev, Phys. Rev. B62, R3616 (2000)] that
results in quadratic type dependence of (rho)_(Jff)(B) with the following
saturation. The I-V characteristics in JFF regime also can be described
consistently by that theory. In JFF regime we found Shapiro-step response to
the external mm-wave radiation. The step position is proportional to the
frequency of applied microwaves and corresponds to the Josephson emission from
all the 60 intrinsic junctions of the stack being synchronized. That implies
the coherence of the JFF over the whole thickness of the stack and demonstrates
possibility of synchronization of intrinsic junctions by magnetic field. We
also found a threshold character of an appearance of the JFF branch on the I-V
characteristic with the increase of magnetic field, the threshold field B_t
being scaled with the junction size perpendicular to the field L (L = 30-1.4
(mu)m), as B_t = (Phi)_0/Ls, where (Phi)_0 is flux quantum, s is the interlayer
spacing. On the I-V characteristics of small stacks in the JFF regime we found
Fiske-step features associated with resonance of Josephson radiation with the
main resonance cavity mode in transmission line formed by stack.",0109181v1
2004-10-22,Formation of convective cells in the scrape-off layer of the CASTOR tokamak,"Understanding of the scrape-off layer (SOL) physics in tokamaks requires
diagnostics with sufficient temporal and spatial resolution. This contribution
describes results of experiments performed in the SOL of the CASTOR tokamak
(R=40 cm, a = 6 cm) by means of a ring of 124 Langmuir probes surrounding the
whole poloidal cross section. The individual probes measure either the ion
saturation current of the floating potential with the spatial resolution up to
3 mm. Experiments are performed in a particular magnetic configuration,
characterized by a long parallel connection length in the SOL, L_par ~q2piR. We
report on measurements in discharges, where the edge electric field is modified
by inserting a biased electrode into the edge plasma. In particular, a complex
picture is observed, if the biased electrode is located inside the SOL. The
poloidal distribution of the floating potential appears to be strongly
non-uniform at biasing. The peaks of potential are observed at particular
poloidal angles. This is interpreted as formation of a biased flux tube, which
emanates from the electrode along the magnetic field lines and snakes q times
around the torus. The resulting electric field in the SOL is 2-dimensional,
having the radial as well as the poloidal component. It is demonstrated that
the poloidal electric field E_pol convects the edge plasma radially due to the
E_pol x B_T drift either inward or outward depending on its sign. The
convective particle flux is by two orders of magnitude larger than the
fluctuation-induced one and consequently dominates.",0410208v1
2007-05-24,MHD simulations of the magnetorotational instability in a shearing box with zero net flux. I. The issue of convergence,"We study the properties of MHD turbulence driven by the magnetorotational
instability (MRI) in accretion disks. We adopt the local shearing box model and
focus on the special case for which the initial magnetic flux threading the
disk vanishes. We employ the finite difference code ZEUS to evolve the ideal
MHD equations. Performing a set of numerical simulations in a fixed
computational domain with increasing resolution, we demonstrate that turbulent
activity decreases as resolution increases. We quantify the turbulent activity
by measuring the rate of angular momentum transport through evaluating the
standard alpha parameter. We find alpha=0.004 when (N_x,N_y,N_z)=(64,100,64),
alpha=0.002 when (N_x,N_y,N_z)=(128,200,128) and alpha=0.001 when
(N_x,N_y,N_z)=(256,400,256). This steady decline is an indication that
numerical dissipation, occurring at the grid scale is an important determinant
of the saturated form of the MHD turbulence. Analysing the results in Fourier
space, we demonstrate that this is due to the MRI forcing significant flow
energy all the way down to the grid dissipation scale. We also use our results
to study the properties of the numerical dissipation in ZEUS. Its amplitude is
characterised by the magnitude of an effective magnetic Reynolds number Re_M
which increases from 10^4 to 10^5 as the number of grid points is increased
from 64 to 256 per scale height. The simulations we have carried out do not
produce results that are independent of the numerical dissipation scale, even
at the highest resolution studied. Thus it is important to use physical
dissipation, both viscous and resistive, and to quantify contributions from
numerical effects, when performing numerical simulations of MHD turbulence with
zero net flux in accretion disks at the resolutions normally considered.",0705.3621v2
2007-11-20,Highly Frustrated Magnetic Clusters: The kagome on a sphere,"We present a detailed study of the low-energy excitations of two existing
finite-size realizations of the planar kagome Heisenberg antiferromagnet on the
sphere, the cuboctahedron and the icosidodecahedron. After highlighting a
number of special spectral features (such as the presence of low-lying singlets
below the first triplet and the existence of localized magnons) we focus on two
major issues. The first concerns the nature of the excitations above the
plateau phase at 1/3 of the saturation magnetization Ms. Our exact
diagonalizations for the s=1/2 icosidodecahedron reveal that the low-lying
plateau states are adiabatically connected to the degenerate collinear
``up-up-down'' ground states of the Ising point, at the same time being well
isolated from higher excitations. A complementary physical picture emerges from
the derivation of an effective quantum dimer model which reveals the central
role of the topology and the intrinsic spin s. We also give a prediction for
the low energy excitations and thermodynamic properties of the spin s=5/2
icosidodecahedron Mo72Fe30. In the second part we focus on the low-energy
spectra of the s>1/2 Heisenberg model in view of interpreting the broad
inelastic neutron scattering response reported for Mo72Fe30. To this end we
demonstrate the simultaneous presence of several broadened low-energy ``towers
of states'' or ``rotational bands'' which arise from the large discrete spatial
degeneracy of the classical ground states, a generic feature of highly
frustrated clusters. This semiclassical interpretation is further corroborated
by their striking symmetry pattern which is shown, by an independent group
theoretical analysis, to be a characteristic fingerprint of the classical
coplanar ground states.",0711.3231v2
2008-05-26,A Swift gaze into the 2006 March 29th burst forest of SGR 1900+14,"We report on the intense burst ``forest'' recorded on 2006 March 29 which
lasted for ~30s. More than 40 bursts were detected both by BAT and by XRT,
seven of which are rare intermediate flares (IFs): several times 10^{42} ergs
were released. The BAT data were used to carry out time-resolved spectroscopy
in the 14-100keV range down to 8ms timescales.
  This unique dataset allowed us to test the magnetar model predictions such as
the magnetically trapped fireball and the twisted magnetosphere over an
unprecedented range of fluxes and with large statistics (in terms of both
photons and IFs). We confirmed that a two blackbody component fits adequately
the time-resolved and integrated spectra of IFs. However, Comptonization models
give comparable good reduced chi^2. Moreover, we found: i) a change of
behavior, around ~10^{41} erg/s, above which the softer blackbody shows a sort
of saturation while the harder one still grows to a few times 10^{41} erg/s;
ii) a rather sharp correlation between temperature and radii of the blackbodies
(R^2 prop kT^{-3}), which holds for the most luminous parts of the flares
(approximately for L_{tot} > 10^{41} erg/s). Within the magnetar model, the
majority of these findings can be accounted for in terms of thermalised
emission from the E-mode and O-mode photospheres. Interestingly, the maximum
observed luminosity coming from a region of ~15km matches the magnetic
Eddington luminosity at the same radius, for a surface dipole field of ~8 x
10^{14} G (virtually equal to the one deduced from the spindown of SGR
1900+14).",0805.3919v1
2008-11-28,"Transport, magnetic, and structural properties of La$_{0.7}$Ce$_{0.3}$MnO$_3$ thin films. Evidence for hole-doping","Cerium-doped manganite thin films were grown epitaxially by pulsed laser
deposition at $720 ^\circ$C and oxygen pressure $p_{O_2}=1-25 $Pa and were
subjected to different annealing steps. According to x-ray diffraction (XRD)
data, the formation of CeO$_2$ as a secondary phase could be avoided for
$p_{O_2}\ge 8 $Pa. However, transmission electron microscopy shows the presence
of CeO$_2$ nanoclusters, even in those films which appear to be single phase in
XRD. With O$_2$ annealing, the metal-to-insulator transition temperature
increases, while the saturation magnetization decreases and stays well below
the theoretical value for electron-doped La$_{0.7}$Ce$_{0.3}$MnO$_3$ with mixed
Mn$^{3+}$/Mn$^{2+}$ valences. The same trend is observed with decreasing film
thickness from 100 to 20 nm, indicating a higher oxygen content for thinner
films. Hall measurements on a film which shows a metal-to-insulator transition
clearly reveal holes as dominating charge carriers. Combining data from x-ray
photoemission spectroscopy, for determination of the oxygen content, and x-ray
absorption spectroscopy (XAS), for determination of the hole concentration and
cation valences, we find that with increasing oxygen content the hole
concentration increases and Mn valences are shifted from 2+ to 4+. The
dominating Mn valences in the films are Mn$^{3+}$ and Mn$^{4+}$, and only a
small amount of Mn$^{2+}$ ions can be observed by XAS. Mn$^{2+}$ and Ce$^{4+}$
XAS signals obtained in surface-sensitive total electron yield mode are
strongly reduced in the bulk-sensitive fluorescence mode, which indicates
hole-doping in the bulk for those films which do show a metal-to-insulator
transition.",0811.4710v1
2010-04-08,"MRI-driven turbulent transport: the role of dissipation, channel modes and their parasites","In the recent years, MRI-driven turbulent transport has been found to depend
in a significant way on fluid viscosity $\nu$ and resistivity $\eta$ through
the magnetic Prandtl number $Pm=\nu/\eta$. In particular, the transport
decreases with decreasing $Pm$; if persistent at very large Reynolds numbers,
this trend may lead to question the role of MRI-turbulence in YSO disks, whose
Prandtl number is usually very small. In this context, the principle objective
of the present investigation is to characterize in a refined way the role of
dissipation. Another objective is to characterize the effect of linear (channel
modes) and quasi-linear (parasitic modes) physics in the behavior of the
transport. These objectives are addressed with the help of a number of
incompressible numerical simulations. The horizontal extent of the box size has
been increased in order to capture all relevant (fastest growing) linear and
secondary parasitic unstable modes. The major results are the following: i- The
increased accuracy in the computation of transport averages shows that the
dependence of transport on physical dissipation exhibits two different regimes:
for $Pm \lesssim 1$, the transport has a power-law dependence on the magnetic
Reynolds number rather than on the Prandtl number; for $Pm > 1$, the data are
consistent with a primary dependence on $Pm$ for large enough ($\sim 10^3$)
Reynolds numbers. ii- The transport-dissipation correlation is not clearly or
simply related to variations of the linear modes growth rates. iii- The
existence of the transport-dissipation correlation depends neither on the
number of linear modes captured in the simulations, nor on the effect of the
parasitic modes on the saturation of the linear modes growth. iv- The transport
is usually not dominated by axisymmetric (channel) modes",1004.1384v1
2010-04-26,Chromospheric activity among fast rotating M-dwarfs in the open cluster NGC 2516,"We report radial velocities (RVs), projected equatorial velocities (v sin i)
and CaII triplet (CaT) chromospheric activity indices for 237 late-K to mid-M
candidate members of the young open cluster NGC 2516. These stars have rotation
periods between 0.1 and 15 days. Intermediate resolution spectra were obtained
using the Giraffe spectrograph at the Very Large Telescope. Membership was
confirmed on the basis of RVs for 210 targets. We see a marked increase in the
fraction of rapidly rotators as we move to cooler spectral types. About 20 per
cent of M0-M1 stars have v sin i >15km/s, increasing to 90 per cent of M4
stars. Activity indices derived from the first two lines of the CaT (8498A and
8542A) show differing dependencies on rotation period and mass for stars lying
above and below the fully convective boundary. Higher mass stars, of spectral
type K3-M2.5, show chromospheric activity which increases with decreasing
Rossby number (the ratio of period to convective turnover time), saturating for
Rossby numbers <0.1. For cooler stars, which are probably fully convective and
almost all of which have Rossby numbers <0.1, there is a clear decrease in
chromospheric activity as (V-I)_0 increases, amounting to a fall of about a
factor of 2-3 between spectral types M2.5 and M4. This decrease in activity
levels at low Rossby numbers is not seen in X-ray observations of the coronae
of cluster M-dwarfs or of active field M-dwarfs. There is no evidence for
supersaturation of chromospheric activity for stars of any spectral type at
Rossby numbers <0.01. We suggest that the fall in the limiting level of
chromospheric emission beyond spectral type M3 in NGC~2516 is, like the
simultaneous increase in rotation rates in field stars, associated with a
change in the global magnetic topology as stars approach the fully convective
boundary and not due to any decrease in dynamo-generated magnetic flux.",1004.4557v1
2010-10-04,Way to increase the user access at the LCLS baseline,"The LCLS beam is meant for a single user, but the baseline undulator is long
enough to serve two users simultaneously. To this end, we propose a setup
composed of two elements: an X-ray mirrors pair for X-ray beam deflection, and
a 4 m-long magnetic chicane, which creates an offset for mirrors pair
installation in the middle of the baseline undulator. The insertable mirrors
pair can separate spatially the X-ray beams generated in the first and in the
second half of the baseline undulator. Rapid switching of the FEL amplification
process allows deactivating one half and activating another half of the
undulator. As proposed elsewhere, using a kicker installed upstream of the LCLS
baseline undulator and an already existing corrector in the first half of the
undulator, it is possible to rapidly switch the X-ray beam from one user to
another. We present simulation results for the LCLS baseline, and show that it
is possible to generate two saturated SASE X-ray beams in the whole 0.8-8 keV
photon energy range in the same baseline undulator. These can serve two users.
Our technique does not perturb the baseline mode of operation of the LCLS
undulator. Also, the magnetic chicane setup is very flexible, and can be used
as a self-seeding setup too. We present simulation results for the LCLS
baseline undulator with SHAB. One can produce monochromatic radiation at the
2nd harmonic as well as at the 1st. We describe an efficient way for obtaining
multi-user operation at the LCLS hard X-ray FEL. To this end, a photon beam
distribution system based on the use of crystals in the Bragg reflection
geometry is proposed. The reflectivity of crystal deflectors can be switched
fast enough by flipping the crystals with piezoelectric devices. Monochromatic
hard X-rays can then be distributed among 6 independent experiments, thereby
enabling 6 users to work in parallel in the near and far experimental halls.",1010.0489v1
2011-05-12,Thermal Instability in Gravitationally-Stratified Plasmas: Implications for Multi-Phase Structure in Clusters and Galaxy Halos,"We study the interplay among cooling, heating, conduction, and magnetic
fields in gravitationally stratified plasmas using simplified, plane-parallel
numerical simulations. Since the physical heating mechanism remains uncertain
in massive halos such as groups or clusters, we adopt a simple,
observationally-motivated prescription which enforces global thermal
equilibrium when averaged over large scales. The plasma remains susceptible to
local thermal instability, however, and cooling drives an inward flow of
material. In contrast to previous results, we argue that the thermal stability
of the plasma is independent of its convective stability. We find that the
ratio of the cooling timescale to the dynamical timescale t_cool/t_ff controls
the saturation of the thermal instability: when t_cool/t_ff < 1, the plasma
develops extended multi-phase structure, whereas when t_cool / t_ff > 1 it does
not. (In a companion paper, we show that the criterion for thermal instability
in a spherical potential is somewhat less stringent, t_cool / t_ff < 10.) When
thermal conduction is anisotropic with respect to the magnetic field, the
criterion for multi-phase structure is essentially independent of the thermal
conductivity of the plasma. Our criterion for local thermal instability to
produce multi-phase structure is an extension of the cold vs. hot accretion
modes in galaxy formation that applies at all radii in hot halos, not just to
the virial shock. We show that this criterion is consistent with data on
multi-phase gas in the ACCEPT sample of clusters; in addition, when t_cool /
t_ff > 1, the net cooling rate to low temperatures and the mass flux to small
radii are suppressed enough relative to models without heating to be
qualitatively consistent with star formation rates and x-ray line emission in
groups and clusters.",1105.2563v2
2013-04-04,On the origin of the radio emission of Sw 1644+57,"We apply relativistic equipartition synchrotron arguments to the radio data
of the tidal disruption event candidate Sw 1644+57. We find that, regardless of
the details of the equipartition scenario considered, the energy required to
produce the observed radio (i.e., energy in magnetic field and radio emitting
electrons) must increase by a factor of ~20 during the first 200 days. It then
saturates. This energy increase cannot be alleviated by a varying geometry of
the system. The radio data can be explained by: (i) An afterglow like emission
of the X-ray emitting narrow relativistic jet. The additional energy can arise
here from a slower moving material ejected in the first few days that gradually
catches up with the slowing down blast wave (Berger et al. 2012). However, this
requires at least ~4x10^{53} erg in the slower moving outflow. This is much
more than the energy of the fast moving outflow that produced the early X-rays
and it severely constrains the overall energy budget. (ii) Alternatively, the
radio may arise from a mildly relativistic quasi-spherical outflow. Here, the
energy for the radio emission increases with time to at least ~10^{51} erg
after 200 days. This scenario requires, however, a second X-ray emitting
collimated relativistic component. Given these results, it is worthwhile to
consider models in which the energy of the magnetic field and/or of the radio
emitting electrons increases with time without a continuous energy supply to
the blast wave. This can happen, for example, if the energy is injected
initially mostly in one form (Poynting flux or baryonic) and it is gradually
converted to the other form, leading to a deviation from equipartition. Another
intriguing possibility is that a gradually decreasing Inverse Compton cooling
modifies the synchrotron emission and leads to an increase of the available
energy in the radio emitting electrons (Kumar et al. 2013).",1304.1542v2
2013-05-08,Surface tension of the core-crust interface of neutron stars with global charge neutrality,"It has been shown recently that taking into account strong, weak,
electromagnetic, and gravitational interactions, and fulfilling the global
charge neutrality of the system, a transition layer will happen between the
core and crust of neutron stars, at the nuclear saturation density. We use
relativistic mean field theory together with the Thomas-Fermi approximation to
study the detailed structure of this transition layer and calculate its surface
and Coulomb energy. We find that the surface tension is proportional to a
power-law function of the baryon number density in the core bulk region. We
also analyze the influence of the electron component and the gravitational
field on the structure of the transition layer and the value of the surface
tension to compare and contrast with known phenomenological results in nuclear
physics. Based on the above results we study the instability against
Bohr-Wheeler surface deformations in the case of neutron stars obeying global
charge neutrality. Assuming the core-crust transition at nuclear density
$\rho_{core}\approx 2.7 * 10^{14}$ g cm$^{-3}$, we find that the instability
sets the upper limit to the crust density, $\rho_{crust}^{crit}\approx 1.2 *
10^{14}$ g cm$^{-3}$. This result implies a nonzero lower limit to the maximum
electric field of the core-crust transition surface and makes inaccessible a
limit of quasilocal charge neutrality in the limit $\rho_{crust}=\rho_{core}$.
The general framework presented here can be also applied to study the stability
of sharp phase transitions in hybrid stars as well as in strange stars, both
bare and with outer crust. The results of this work open the way to a more
general analysis of the stability of these transition surfaces, accounting for
other effects such as gravitational binding, centrifugal repulsion, magnetic
field induced by rotating electric field, and therefore magnetic dipole-dipole
interactions.",1305.1974v2
2013-08-16,Area inequalities for stable marginally outer trapped surfaces in Einstein-Maxwell-dilaton theory,"We prove area inequalities for stable marginally outer trapped surfaces in
Einstein-Maxwell-dilaton theory. Our inspiration comes on the one hand from a
corresponding upper bound for the area in terms of the charges obtained
recently by Dain, Jaramillo and Reiris [1] in the pure Einstein-Maxwell case
without symmetries, and on the other hand from Yazadjiev's inequality [2] in
the axially symmetric Einstein-Maxwell-dilaton case. The common issue in these
proofs and in the present one is a functional ${\mathscr W}$ of the matter
fields for which the stability condition readily yields an {\it upper} bound.
On the other hand, the step which crucially depends on whether or not a dilaton
field is present is to obtain a {\it lower} bound for ${\mathscr W}$ as well.
We obtain the latter by first setting up a variational principle for ${\mathscr
W}$ with respect to the dilaton field $\phi$, then by proving existence of a
minimizer $\psi$ as solution of the corresponding Euler-Lagrange equations and
finally by estimating ${\mathscr W}(\psi)$. In the special case that the normal
components of the electric and magnetic fields are proportional we obtain the
area bound $A \ge 8\pi P Q$ in terms of the electric and magnetic charges. In
the generic case our results are less explicit but imply rigorous
`perturbation' results for the above inequality. All our inequalities are
saturated for a 2-parameter family of static, extreme solutions found by
Gibbons [3]. Via the Bekenstein-Hawking relation $A = 4S$ our results give
positive lower bounds for the entropy $S$ which are particularly interesting in
the Einstein-Maxwell-dilaton case.",1308.3659v3
2014-02-01,Gate-tunable Kondo resistivity and dephasing rate in graphene studied by numerical renormalization group calculations,"We investigate the resistivity and dephasing rate in the Kondo regime due to
magnetic impurities in graphene with different chemial potentials ($\mu$). The
Kondo effect due to either carbon vacancies or magnetic adatoms in graphene is
described by the single-orbital pseudo-gap asymmetric Anderson impurity model.
We find that although the Anderson impurity model considered here is a mixed
valence system, it can be drived into either the Kondo [$\mu > \mu_c$ (critical
value) $>0$] or mixed valency ($\mu \approx \mu_c$) or empty orbital ($\mu <
\mu_c$) regime by a gate voltage, giving rise to characteristic features in
resistivity and dephasing rate in each regime. Specifically, in the case of
$\mu < \mu_c$, the shapes of the resistivity (dephasing rate) curves for
different $\mu$ are nearly identical. However, as temperature decreases, they
start to increase to their maxima at a lower $T/T_K$ but more rapidly [as
$(T_K/T)^{3/2}$] than in normal metals [here $T$ ($T_K$) denotes the (Kondo)
temperature]. As $T$ further decreases, after reaching the maximum, the
dephasing rate drops more quickly than in normal metals, behaving as
$(T/T_K)^3$ instead of $(T/T_K)^2$. Furthermore, the resistivity has a distinct
peak above the saturation value near $T_K$. In the case of $\mu > \mu_c$, in
contrast, the resistivity curve has an additional broad shoulder above 10$T_K$
and the dephasing rate exhibits an interesting shoulder-peak shape. In the
narrow boundary region ($\mu \approx \mu_c$), both the resistivity and
dephasing rate curves are similar to the corresponding ones in normal metals.
This explains the conventional Kondo like resistivity from recent experiments
on graphene with defects. The resistivity and dephasing rate are analysized in
terms of the calculated $T$-dependent spectral function, correlation
self-energy and renormalized impurity level.",1402.0040v1
2015-08-10,A nonextensive view of the stellar braking indices,"The present work is based on a description for the angular mometum loss rate
due to magnetic braking for main-sequence stars on the relationship between
stellar rotation and age. In general, this loss rate denoted by $\mathrm
dJ/\mathrm dt$ depends on angular velocity $\Omega$ in the form $\mathrm
dJ/\mathrm dt\propto\Omega^{q}$, where $q$ is a parameter extracted from
nonextensive statistical mechanics. Already, in context of stellar rotation,
this parameter is greater than unity and it is directly related to the braking
index. For $q$ equal to unity, the scenario of saturation of the magnetic field
is recovered, otherwise $q$ indicates an unsaturated field. This new approach
have been proposed and investigated by de Freitas \& De Medeiros for
unsaturated field stars. In present work, we propose a nonextensive approach
for the stellar rotational evolution based on the Reiners \& Mohanthy model. In
this sense, we developed a nonextensive version of Reiners \& Mohanthy torque
and also compare this generalized version with the model proposed in de Freitas
\& De Medeiros based on the spin-down Kawaler torque for the main-sequence
stars with F and G spectral types. We use the same sample of $\sim16 000$ field
stars with rotational velocity $v \sin i$ limited in age and mass. As a result,
we show that the Kawaler and Reiners \& Mohanthy models exhibit strong
discrepancies, mainly in relation to the domain of validity of the entropic
index $q$. These discrepancies are mainly due to sensitivity on the stellar
radius. Finally, our results showed that modified Kawaler prescription is
compatible with a wider mass range, while the Reiners \& Mohanty model is
restricted to masses less than G6 stars.",1508.02237v1
2015-11-13,Evolution of Accretion Discs around a Kerr Black Hole using Extended Magnetohydrodynamics,"Black holes accreting well below the Eddington rate are believed to have
geometrically thick, optically thin, rotationally supported accretion discs in
which the Coulomb mean free path is large compared to $GM/c^2$. In such an
environment, the disc evolution may differ significantly from ideal
magnetohydrodynamic predictions. We present non-ideal global axisymmetric
simulations of geometrically thick discs around a rotating black hole. The
simulations are carried out using a new code ${\rm\it grim}$, which evolves a
covariant extended magnetohydrodynamics model derived by treating non-ideal
effects as a perturbation of ideal magnetohydrodynamics. Non-ideal effects are
modeled through heat conduction along magnetic field lines, and a difference
between the pressure parallel and perpendicular to the field lines. The model
relies on an effective collisionality in the disc from wave-particle scattering
and velocity-space (mirror and firehose) instabilities. We find that the
pressure anisotropy grows to match the magnetic pressure, at which point it
saturates due to the mirror instability. The pressure anisotropy produces
outward angular momentum transport with a magnitude comparable to that of MHD
turbulence in the disc, and a significant increase in the temperature in the
wall of the jet. We also find that, at least in our axisymmetric simulations,
conduction has a small effect on the disc evolution because (1) the heat flux
is constrained to be parallel to the field and the field is close to
perpendicular to temperature gradients, and (2) the heat flux is choked by an
increase in effective collisionality associated with the mirror instability.",1511.04445v1
2016-01-09,Field-induced resistivity plateau and unsaturated negative magnetoresistance in topological semimetal TaSb2,"Several prominent transport properties have been identified as key signatures
of topologicalmaterials. One is the resistivity plateau at low temperatures as
observed in several topological insulators (TIs), another is the negative
magnetoresistance (MR) when the applied magnetic field is parallel to the
current direction as observed in several topological semimetals (TSMs)
including Dirac semimetals (DSMs) and Weyl semimetals (WSMs). Usually, these
two exotic phenomena emerge in distinct materials with or without time reversal
symmetry (TRS), respectively. Here we report the discovery of a new member in
TSMs, TaSb2, which clearly exhibits both of these phenomena in a single
material. This compound crystallizes in a base-centered monoclinic,
centrosymmetric structure, and is metallic with a low carrier density in the
zero field. While applying magnetic field it exhibits insulating behavior
before appearance of a resistivity plateau below Tc =13 K. In the plateau
regime, the ultrahigh carrier mobility and extreme magnetoresistance (XMR) for
the field perpendicular to the current are observed as in DSMs and WSMs, in
addition to a quantum oscillation behavior with non-trivial Berry phases. In
contrast to the most known DSMs and WSMs, the negative MR in TaSb2 does not
saturate up to 9 T, which, together with the almost linear Hall resistivity,
manifests itself an electron-hole non-compensated TMS. These findings indicate
that the resistivity plateau could be a generic feature of topology-protected
metallic states even in the absence of TRS and compatible with the negative MR
depending on the field direction. Our experiment extends a materials basis
represented by TaSb2 as a new platform for future theoretical investigations
and device applications of topological materials.",1601.02062v1
2016-05-29,Bulk Fermi-surface of the Weyl type-II semi-metallic candidate MoTe2,"The electronic structure of WTe$_2$ and orthorhombic $\gamma-$MoTe$_2$, are
claimed to contain pairs of Weyl type-II points. A series of ARPES experiments
claim a broad agreement with these predictions. We synthesized single-crystals
of MoTe$_2$ through a Te flux method to validate these predictions through
measurements of its bulk Fermi surface (FS) \emph{via} quantum oscillatory
phenomena. We find that the superconducting transition temperature of
$\gamma-$MoTe$_2$ depends on disorder as quantified by the ratio between the
room- and low-temperature resistivities, suggesting the possibility of an
unconventional superconducting pairing symmetry. Similarly to WTe$_2$, the
magnetoresistivity of $\gamma-$MoTe$_2$ does not saturate at high magnetic
fields and can easily surpass $10^{6}$ \%. Remarkably, the analysis of the de
Haas-van Alphen (dHvA) signal superimposed onto the magnetic torque, indicates
that the geometry of its FS is markedly distinct from the calculated one. The
dHvA signal also reveals that the FS is affected by the Zeeman-effect
precluding the extraction of the Berry-phase. A direct comparison between the
previous ARPES studies and density-functional-theory (DFT) calculations reveals
a disagreement in the position of the valence bands relative to the Fermi level
$\varepsilon_F$. Here, we show that a shift of the DFT valence bands relative
to $\varepsilon_F$, in order to match the ARPES observations, and of the DFT
electron bands to explain some of the observed dHvA frequencies, leads to a
good agreement between the calculations and the angular dependence of the FS
cross-sectional areas observed experimentally. However, this relative
displacement between electron- and hole-bands eliminates their crossings and,
therefore, the Weyl type-II points predicted for $\gamma-$MoTe$_2$.",1605.09065v5
2016-11-10,The H$α$ emission of nearby M dwarfs and its relation to stellar rotation,"The high-energy emission from low-mass stars is mediated by the magnetic
dynamo. Although the mechanisms by which fully convective stars generate
large-scale magnetic fields are not well understood, it is clear that, as for
solar-type stars, stellar rotation plays a pivotal role. We present 270 new
optical spectra of low-mass stars in the Solar Neighborhood. Combining our
observations with those from the literature, our sample comprises 2202
measurements or non-detections of H$\alpha$ emission in nearby M dwarfs. This
includes 466 with photometric rotation periods. Stars with masses between 0.1
and 0.6 solar masses are well-represented in our sample, with fast and slow
rotators of all masses. We observe a threshold in the mass-period plane that
separates active and inactive M dwarfs. The threshold coincides with the
fast-period edge of the slowly rotating population, at approximately the
rotation period at which an era of rapid rotational evolution appears to cease.
The well- defined active/inactive boundary indicates that H$\alpha$ activity is
a useful diagnostic for stellar rotation period, e.g. for target selection for
exoplanet surveys, and we present a mass-period relation for inactive M dwarfs.
We also find a significant, moderate correlation between
$L_{\mathrm{H}\alpha}/L_{\mathrm{bol}}$ and variability amplitude: more active
stars display higher levels of photometric variability. Consistent with
previous work, our data show that rapid rotators maintain a saturated value of
$L_{\mathrm{H}\alpha}/L_{\mathrm{bol}}$. Our data also show a clear power-law
decay in $L_{\mathrm{H}\alpha}/L_{\mathrm{bol}}$ with Rossby number for slow
rotators, with an index of $-1.7 \pm 0.1$.",1611.03509v1
2017-02-10,Structure and variability in the corona of the ultrafast rotator LO Peg,"Low-mass ultrafast rotators show the typical signatures of magnetic activity
and are known to produce flares, probably as a result of magnetic reconnection.
As a consequence, the coronae of these stars exhibit very large X-ray
luminosities and high plasma temperatures, as well as a pronounced inverse FIP
effect. To probe the relationship between the coronal properties with a
spectral type of ultra-fast rotators with rotation period P < 1d, we analyse
the K3 rapid-rotator LO Peg observed with XMM-Newton and compare it with other
low-mass rapid rotators of spectral types G9-M1. We investigate the temporal
evolution of coronal properties like the temperatures, emission measures,
abundances, densities and the morphology of the involved coronal structures. We
find two distinguishable levels of activity in the XMM-Newton observation of
LO~Peg, which shows significant X-ray variability both in phase and amplitude,
implying the presence of an evolving active region on the surface. The X-ray
flux varies by 28%, possibly due to rotational modulation. During our
observation, a large X-ray flare with a peak X-ray luminosity of 2E30 erg/s and
an energy of 7.3E33 erg was observed. At the flare onset we obtain clear
signatures for the occurrence of the Neupert effect. The flare plasma also
shows an enhancement of iron by a factor of 2 during the rise and peak phase of
the flare. Our modeling analysis suggests that the scale size of the flaring
X-ray plasma is smaller than 0.5 R_star. Further, the flare loop length appears
to be smaller than the pressure scale height of the flaring plasma. Our studies
show that the X-ray properties of the LO~Peg are very similar to those of other
low-mass ultrafast rotators, i.e., the X-ray luminosity is very close to
saturation, its coronal abundances follow a trend of increasing abundance with
increasing first ionisation potential, the so-called inverse FIP effect.",1702.03158v1
2017-02-20,Quantum critical phase with infinite projected entangled paired states,"A classification of SU(2)-invariant Projected Entangled Paired States (PEPS)
on the square lattice, based on a unique site tensor, has been recently
introduced by Mambrini et al.~\cite{Mambrini2016}. It is not clear whether such
SU(2)-invariant PEPS can either i) exhibit long-range magnetic order (like in
the N\'eel phase) or ii) describe a genuine quantum critical point (QCP) or
quantum critical phase (QCPh) separating two ordered phases. Here, we identify
a specific family of SU(2)-invariant PEPS of the classification which provides
excellent variational energies for the $J_1-J_2$ frustrated Heisenberg model,
especially at $J_2=0.5$, corresponding to the approximate location of the QCP
or QCPh separating the N\'eel phase from a dimerized phase. The PEPS are build
from virtual states belonging to the $\frac{1}{2}^{\otimes N} \oplus 0$
SU(2)-representation, i.e. with $N$ ""colors"" of virtual
\hbox{spin-$\frac{1}{2}$}. Using a full update infinite-PEPS approach directly
in the thermodynamic limit, based on the Corner Transfer Matrix renormalization
algorithm supplemented by a Conjugate Gradient optimization scheme, we provide
evidence of i) the absence of magnetic order and of ii) diverging correlation
lengths (i.e. showing no sign of saturation with increasing environment
dimension) in both the singlet and triplet channels, when the number of colors
$N\ge 3$. We argue that such a PEPS gives a qualitative description of the QCP
or QCPh of the $J_1-J_2$ model.",1702.05950v5
2017-09-04,Full angular dependence of the spin Hall and ordinary magnetoresistance in epitaxial antiferromagnetic NiO(001)/Pt thin films,"We report the observation of the three-dimensional angular dependence of the
spin Hall magnetoresistance (SMR) in a bilayer of the epitaxial
antiferromagnetic insulator NiO(001) and the heavy metal Pt, without any
ferromagnetic element. The detected angular-dependent longitudinal and
transverse magnetoresistances are measured by rotating the sample in magnetic
fields up to 11 T, along three orthogonal planes (xy-, yz- and xz-rotation
planes, where the z-axis is orthogonal to the sample plane). The total
magnetoresistance has contributions arising from both the SMR and ordinary
magnetoresistance. The onset of the SMR signal occurs between 1 and 3 T and no
saturation is visible up to 11 T. The three-dimensional angular dependence of
the SMR can be explained by a model considering the reversible field-induced
redistribution of magnetostrictive antiferromagnetic S- and T-domains in the
NiO(001), stemming from the competition between the Zeeman energy and the
elastic clamping effect of the non-magnetic MgO substrate. From the observed
SMR ratio, we estimate the spin mixing conductance at the NiO/Pt interface to
be greater than $2\times10^{14}$ ${\Omega}^{-1}$ $m^{-2}$. Our results
demonstrate the possibility to electrically detect the N\'eel vector direction
in stable NiO(001) thin films, for rotations in the xy- and xz- planes.
Moreover, we show that a careful subtraction of the ordinary magnetoresistance
contribution is crucial to correctly estimate the amplitude of the SMR.",1709.00910v5
2017-12-10,The role of fast ions in stabilising the ion temperature gradient mode,"Turbulence driven by small scale instabilities causes large heat and particle
transport and is a major limiting factor of current fusion devices. Above a
critical value, the ion temperature gradient leads to the growth of a
microinstability -- the ion temperature gradient mode -- that often dominates
the ion energy transport. It has recently been discovered that energetic ions
generated by auxiliary heating may reduce the growth of this instability. By
applying the gyrokinetic formalism and performing linear simulations using the
local continuum gyrokinetic code GS2, we explore the linear physics of this
stabilising effect. In order to isolate important effects due to the presence
of fast ions, we make use of the flexibility of GS2 to change the plasma and
magnetic geometry parameters independently. We assess the possibility to
neglect magnetic geometry changes to simplify the analysis, by investigating
its contribution to the stabilising effect. For the cases studied we find that
the Shafranov shift and safety factor profile might have to be taken into
account. For fixed fast ion density and temperature a destabilising influence
of their density gradient is found, while the high fast ion temperature
gradient is stabilising, both as predicted by theoretical models. A large part
of the observed stabilisation comes from the fast ion contribution to the
plasma $\beta$. In addition, the effect of $\beta$ is enhanced because of the
large density and temperature gradients of the fast ions. We investigate the
role of hot ion mass and charge in order to evaluate the stabilisation of
different types of hot ions. Also the possibility of adjusting the electron and
ion profiles to account for the presence of fast ions without including them as
a kinetic species, is considered. Finally, quasi-linear theory is invoked for
linking linear results to saturated values of the nonlinear heat fluxes.",1712.03587v1
2018-11-14,"Anisotropic-Exchange Magnets on a Triangular Lattice: Spin Waves, Accidental Degeneracies, and Dual Spin Liquids","We present an extensive overview of the phase diagram, spin-wave excitations,
and finite-temperature transitions of the anisotropic-exchange magnets on an
ideal nearest-neighbor triangular lattice. We investigate transitions between
five principal classical phases of the corresponding model: ferromagnetic,
N\'{e}el, its dual, and the two stripe phases. Transitions are identified by
the spin-wave instabilities and by the Luttinger-Tisza approach. Some of the
transitions are direct and others occur via intermediate phases with more
complicated forms of ordering. In a portion of the N\'{e}el phase, we find
spin-wave instabilities to a long-range spiral-like state. In the stripe
phases, quantum fluctuations are mostly negligible, leaving the ordered moment
nearly saturated even for the $S=1/2$ case. However, for a two-dimensional
surface of the full 3D parameter space, the spin-wave spectrum in one of the
stripe phases exhibits an enigmatic accidental degeneracy manifested by
pseudo-Goldstone modes. As a result, despite the nearly classical ground state,
the ordering transition temperature in a wide region of the phase diagram is
significantly suppressed from the mean-field expectation. We identify this
accidental degeneracy as due to an exact correspondence to an extended
Kitaev-Heisenberg model with emergent symmetries that naturally lead to the
pseudo-Goldstone modes. There are previously studied dualities within the
Kitaev-Heisenberg model on the triangular lattice that are exposed here in a
wider parameter space. One important implication of this correspondence for the
$S=1/2$ case is the existence of a region of the spin-liquid phase that is dual
to the spin-liquid phase discovered recently by us. We complement our studies
by the density-matrix renormalization group of the $S=1/2$ model to confirm
some of the duality relations and to verify the existence of the dual
spin-liquid phase.",1811.05983v4
2019-05-26,Imaging viscous flow of the Dirac fluid in graphene,"The electron-hole plasma in charge-neutral graphene is predicted to realize a
quantum critical system whose transport features a universal hydrodynamic
description, even at room temperature. This quantum critical ""Dirac fluid"" is
expected to have a shear viscosity close to a minimum bound, with an
inter-particle scattering rate saturating at the Planckian time $\hbar/(k_B
T)$. While electrical transport measurements at finite carrier density are
consistent with hydrodynamic electron flow in graphene, a ""smoking gun"" of
viscous behavior remains elusive. In this work, we directly image viscous Dirac
fluid flow in graphene at room temperature via measurement of the associated
stray magnetic field. Nanoscale magnetic imaging is performed using quantum
spin magnetometers realized with nitrogen vacancy (NV) centers in diamond.
Scanning single-spin and wide-field magnetometry reveals a parabolic Poiseuille
profile for electron flow in a graphene channel near the charge neutrality
point, establishing the viscous transport of the Dirac fluid. This measurement
is in contrast to the conventional uniform flow profile imaged in an Ohmic
conductor. Via combined imaging-transport measurements, we obtain viscosity and
scattering rates, and observe that these quantities are comparable to the
universal values expected at quantum criticality. This finding establishes a
nearly-ideal electron fluid in neutral graphene at room temperature. Our
results pave the way to study hydrodynamic transport in quantum critical fluids
relevant to strongly-correlated electrons in high-$T_c$ superconductors. This
work also highlights the capability of quantum spin magnetometers to probe
correlated-electronic phenomena at the nanoscale.",1905.10791v3
2019-08-14,NuSTAR and XMM-Newton observations of SXP 59 during its 2017 giant outburst,"The Be X-ray pulsar (BeXRP) SXP 59 underwent a giant outburst in 2017 with a
peak X-ray luminosity of $1.1\times10^{38}$ erg~s$^{-1}$. We report on the
X-ray behaviour of SXP 59 with the XMM--Newton and NuSTAR observations
collected at the outburst peak, decay, and the low luminosity states. The pulse
profiles are energy dependent, the pulse fraction increases with the photon
energy and saturates at $\sim$ 65% above 10 keV. It is difficult to constrain
the change in the geometry of emitting region with the limited data.
Nevertheless, because the pulse shape generally has a double-peaked profile at
high luminosity and a single peak profile at low luminosity, we prefer the
scenario that the source transited from the super-critical state to the
sub-critical regime. This result would further imply that the neutron star (NS)
in SXP 59 has a typical magnetic field. We confirm that the soft excess
revealed below 2 keV is dominated by a cool thermal component. On the other
hand, the NuSTAR spectra can be described as a combination of the non-thermal
component from the accretion column, a hot blackbody emission, and an iron
emission line. The temperature of the hot thermal component decreases with
time, while its size remains constant ($R \sim 0.6$ km). The existence of the
hot blackbody at high luminosity cannot be explained with the present accretion
theories for BeXRPs. It means that either more sophisticated spectral models
are required to describe the X-ray spectra of luminous BeXRPs, or there is
non-dipole magnetic field close to the NS surface.",1908.04908v2
2020-06-16,Topological Dirac states in a layered telluride TaPdTe$_5$ with quasi-one-dimensional PdTe$_2$ chains,"We report the synthesis and systematic studies of a new layered ternary
telluride TaPdTe5 with quasi-one-dimensional PdTe2 chains. This compound
crystalizes in a layered orthorhombic structure with space group Cmcm. Analysis
of its curved field-dependent Hall resistivity, using the two-band model,
indicates the hole-dominated transport with a high mobility ${\mu}_h$ = 2.38
$\times$ 10$^3$ cm$^2$ V$^{-1}$ s$^{-1}$ at low temperatures. The in-plane
magnetoresistance (MR) displays significant anisotropy with field applied along
the crystallographic $b$ axis. The MR with the current applied along the
$c$-axis is also measured in high magnetic fields up to 51.7 T. Remarkably, it
follows a power-law dependence and reaches (9.5 $\times$ 10$^3$)% at 2.1 K
without any signature of saturation. The De Haas-van Alphen oscillations show a
small Fermi-surface pocket with a nontrivial Berry phase. The Shubnikov-de Haas
(SdH) oscillations are detected at low temperatures and under magnetic fields
above 28.5 T. Two effective masses $m^*$ (0.26$m_e$ and 0.41$m_e$) are
extracted from the oscillatory SdH data. Our first-principles calculations
unveil a topological Dirac cone in its surface states, and, in particular, the
topological index indicates that TaPdTe$_5$ is a topologically nontrivial
material.",2006.09070v2
2020-08-24,Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun. I. Dissipation and generation of waves,"The partial ionization of the solar plasma causes several nonideal effects
such as the ambipolar diffusion, the Hall effect, and the Biermann battery
effect. Here we report on the first three-dimensional realistic simulations of
solar local dynamo where all three effects were taken into account. The
simulations started with a snapshot of already saturated battery-seeded dynamo,
where two new series were developed: one with solely ambipolar diffusion and
another one also taking into account the Hall term in the generalized Ohm's
law. The simulations were then run for about 4 hours of solar time to reach the
stationary regime and improve the statistics. In parallel, a purely MHD dynamo
simulation was also run for the same amount of time. The simulations are
compared in a statistical way. The results show that, with the inclusion of the
ambipolar diffusion, the amplitudes of the incompressible perturbations related
to Alfven waves are reduced, and the Poynting flux is absorbed, with a
frequency dependence. The Hall effect causes the opposite action: significant
excess of incompressible perturbations is generated and an excess of the
Poynting flux is observed in the chromospheric layers. The model with ambipolar
diffusion shows, on average, sharper current sheets and slightly more abundant
fast magneto-acoustic shocks in the chromosphere. The model with the Hall
effect has higher temperatures at the lower chromosphere and stronger and more
vertical magnetic field concentrations all over the chromosphere. The study of
high-frequency waves reveals that significant power of incompressible
perturbations is associated with areas with intense and more vertical magnetic
fields and larger temperatures. We find a positive correlation between the
magnitude of the ambipolar heating and the temperature increase at the same
location after a characteristic time of 10^2 sec.",2008.10429v1
2020-09-10,Parallel Spin Stripes and Their Coexistance with Superconducting Ground States at Optimal and High Doping in La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$,"Quasi-two dimensional quantum magnetism is clearly highly correlated with
superconducting ground states in cuprate-based High T$_c$ superconductivity.
Three dimensional, commensurate long range magnetic order in La$_2$CuO$_4$
quickly evolves to quasi-two dimensional, incommensurate correlations on doping
with mobile holes, and superconducting ground states follow for x as small as
0.05 in the La$_{2-x}$Sr$_x$/Ba$_x$CuO$_4$ family of superconductors. It has
long been known that the onset of superconducting ground states in these
systems is coincident with a remarkable rotation of the incommensurate spin
order from ""diagonal stripes"" below x = 0.05, to ""parallel stripes"" above.
However, little is known about the spin correlations at optimal and high doping
levels, where the dome of superconductivity draws to an end. Here we present
new elastic and inelastic neutron scattering measurements on single crystals of
La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ with x = 0.125, 0.19, 0.24 and 0.26, and
show that two dimensional, quasi-static, parallel spin stripes are observed to
onset at temperatures such that the parallel spin stripe phase envelopes all
superconducting ground states in this system. Parallel spin stripes stretch
across 0.05 < < 0.26, with rapidly decreasing moment size and onset
temperatures for x > 0.125. We also show that the low energy, parallel spin
stripe fluctuations for optimally doped x = 0.19 display dynamic spectral
weight which grows with decreasing temperature and saturates below its
superconducting T$_c$. The elastic order parameter for x = 0.19 also shows
plateau behavior coincident with the onset of superconductivity. This set of
observations assert the foundational role played by two dimensional parallel
spin stripe order and fluctuations in High T$_c$ cuprate superconductivity.",2009.04627v1
2020-10-21,A new cosmic ray-driven instability,"Cosmic ray (CR)-driven instabilities play a decisive role during particle
acceleration at shocks and CR propagation in galaxies and galaxy clusters.
These instabilities amplify magnetic fields and modulate CR transport so that
the intrinsically collisionless CR population is tightly coupled to the thermal
plasma and provides dynamical feedback. Here, we show that CRs with a finite
pitch angle drive electromagnetic waves (along the background magnetic field)
unstable on intermediate scales between the gyro-radii of CR ions and electrons
as long as CRs are drifting with a velocity less than half of the Alfv\'en
speed of electrons. By solving the linear dispersion relation, we show that
this new instability typically grows faster by more than an order of magnitude
in comparison to the commonly discussed resonant instability at the ion
gyroscale. We find the growth rate for this intermediate-scale instability and
identify the growing modes as background ion-cyclotron modes in the frame that
is comoving with the CRs. We confirm the theoretical growth rate with a
particle-in-cell (PIC) simulation and study the non-linear saturation of this
instability. We identify three important astro-physical applications of this
intermediate-scale instability, which is expected to 1. modulate CR transport
and strengthen CR feedback in galaxies and galaxy clusters, 2. enable electron
injection into the diffusive shock acceleration process, and 3. decelerate CR
escape from the sites of particle acceleration which would generate gamma-ray
halos surrounding CR sources such as supernova remnants.",2010.11197v2
2020-11-20,Activity-rotation in the dM4 star Gl 729. A possible chromospheric cycle,"Recently, new debates about the role of layers of strong shear have emerged
in stellar dynamo theory. Further information on the long-term magnetic
activity of fully convective stars could help determine whether their
underlying dynamo could sustain activity cycles similar to the solar one.
  We performed a thorough study of the short- and long-term magnetic activity
of the young active dM4 star Gl 729. First, we analyzed long-cadence $K2$
photometry to characterize its transient events (e.g., flares) and global and
surface differential rotation. Then, from the Mount Wilson $S$-indexes derived
from CASLEO spectra and other public observations, we analyzed its long-term
activity between 1998 and 2020 with four different time-domain techniques to
detect cyclic patterns. Finally, we explored the chromospheric activity at
different heights with simultaneous measurements of the H$\alpha$ and the Na I
D indexes, and we analyzed their relations with the $S$-Index.
  We found that the cumulative flare frequency follows a power-law distribution
with slope $\sim- 0.73$ for the range $10^{32}$ to $10^{34}$ erg. We obtained
$P_{rot} = (2.848 \pm 0.001)$ days, and we found no evidence of differential
rotation. We also found that this young active star presents a long-term
activity cycle with a length of $\text{about four}$ years; there is less
significant evidence of a shorter cycle of $0.8$ year. The star also shows a
broad activity minimum between 1998 and 2004. We found a correlation between
the S index, on the one hand, and the H$\alpha$ the Na I D indexes, on the
other hand, although the saturation level of these last two indexes is not
observed in the Ca lines.
  Because the maximum-entropy spot model does not reflect migration between
active longitudes, this activity cycle cannot be explained by a solar-type
dynamo. It is probably caused by an $\alpha^2$-dynamo.",2011.10391v1
2020-12-28,"Structural, optical and magnetic properties of nanostructured Cr-substituted Ni-Zn spinel ferrites synthesized by a microwave combustion method","Nanoparticles of Cr3+-substituted Ni-Zn ferrites with a general formula
Ni0.4Zn0.6-xCrxFe2O4 (x = 0.0 - 0.6) have been synthesized via a facile
microwave combustion route. The crystalline phase has been characterized by
XRD, TEM, FT-I and XPS revealing the spinel ferrite structure without extra
phases. Crystallite sizes of 23 - 32 nm as estimated by XRD analyses, after
corrections for crystal stains by Williamson-Hall method, are comparable to the
average particle sizes observed by TEM which indicates successfully synthesized
nanocrystals. Rietveld refinement analyses of the XRD patterns have inferred a
monotonic decrease behavior of the lattice parameter with Cr doping in
agreement with Vegard's law of solid solution series. Furthermore, cations
distribution with an increased inversion factor indicate the B-site preference
of Cr3+ ions. The oxidation states and cations distribution indicated by XPS
results imply the Cr3+ doping on the account of Zn2+ ions and a partial
reduction of Fe3+ to Fe2+ to keep the charge balance in a composition series of
(Ni2+)0.4(Zn2+, Cr3+)0.6(Fe2+, Fe3+)2(O2-)4. The optical properties were
explored by optical UV-Vis spectroscopy indicating allowed direct transitions
with band gap energy that decreases from 3.9 eV to 3.7 eV with Cr doping.
Furthermore, the photocatalytic activity for the degradation of methyl orange
(MO) dye was investigated showing largely enhanced photodecomposition up to 30%
of MO dye over Ni0.4Cr0.6Fe2O4 for 6 hours. A vibrating sample magnetometry
(VSM) measurements at room temperature show further enhancement in the
saturation magnetization of Ni0.4Zn0.6Fe2O4 , the highest in Ni-Zn ferrites,
from about 60 to 70 emu/g with the increase of Cr concentration up to x = 0.1,
while the coercivity shows a general increase in the whole range of Cr doping.",2012.14232v1
2021-03-17,Distinguishing two-component anomalous Hall effect from topological Hall effect,"In transport, the topological Hall effect (THE) presents itself as
non-monotonic features (or humps and dips) in the Hall signal and is widely
interpreted as a sign of chiral spin textures, like magnetic skyrmions.
However, when anomalous Hall effect (AHE) is also present, the co-existence of
two AHEs could give rise to similar artifacts, making it difficult to
distinguish between genuine THE with AHE and two-component AHE. Here we confirm
genuine THE with AHE by means of transport and magneto-optical Kerr effect
(MOKE) microscopy, in which magnetic skyrmions are directly observed, and find
that genuine THE occurs in the transition region of the AHE. In sharp contrast,
the artifact ""THE"", or two-component AHE occurs well beyond the saturation of
the ""AHE component"" (under the false assumption of THE+AHE). Furthermore, we
distinguish artifact ""THE"" from genuine THE by three methods: 1. Minor loops,
2. Temperature dependence, 3. Gate dependence. Minor loops of genuine THE with
AHE are always within the full loop, while minor loops of the artifact ""THE""
may reveal a single loop that cannot fit into the ""AHE component"". Besides, the
temperature or gate dependence of the artifact ""THE"" may also be accompanied by
a polarity change of the ""AHE component"", as the non-monotonic features vanish,
while the temperature dependence of genuine THE with AHE reveals no such
change. Our work may help future researchers to exercise cautions and use these
methods to examine carefully in order to ascertain genuine THE.",2103.09878v3
2021-08-13,Criticality-Enhanced Quantum Sensing via Continuous Measurement,"Present protocols of criticality-enhanced sensing with open quantum sensors
assume direct measurement of the sensor and omit the radiation quanta emitted
to the environment, thereby potentially missing valuable information. Here we
propose a protocol for criticality-enhanced sensing via continuous observation
of the emitted radiation quanta. Under general assumptions, we establish a
scaling theory for the global quantum Fisher information of the joint system
and environment state at dissipative critical points. We derive universal
scaling laws featuring transient and long-time behavior governed by the
underlying critical exponents. Importantly, such scaling laws exceed the
standard quantum limit and can in principle saturate the Heisenberg limit. To
harness such advantageous scaling, we propose a practical sensing scheme based
on continuous detection of the emitted quanta as realized experimentally in
various quantum-optical setups. In such a scheme a single interrogation
corresponds to a (stochastic) quantum trajectory of the open system evolving
under the nonunitary dynamics dependent on the parameter to be sensed and the
backaction of the continuous measurement. Remarkably, we demonstrate that the
associated precision scaling significantly exceeds that based on direct
measurement of the critical steady state, thereby establishing the metrological
value of the continuous detection of the emitted quanta at dissipative
criticality. We illustrate our protocol via counting the photons emitted by the
open Rabi model, a paradigmatic model for the study of dissipative phase
transition with finite components. Our protocol is applicable to generic
quantum-optical open sensors permitting continuous readout, and may find
applications at the frontier of quantum sensing, such as the human-machine
interface, magnetic diagnosis of heart disease, and zero-field nuclear magnetic
resonance.",2108.06349v2
2021-12-01,Numerical Study of Cosmic Ray Confinement through Dust Resonant Drag Instabilities,"We investigate the possibility of cosmic ray (CR) confinement by charged dust
grains through resonant drag instabilities (RDIs). We perform
magnetohydrodynamic particle-in-cell simulations of magnetized gas mixed with
charged dust and cosmic rays, with the gyro-radii of dust and GeV CRs on
$\sim\mathrm{AU}$ scales fully resolved. As a first study, we focus on one type
of RDI wherein charged grains drift super-Alfv{\'e}nically, with Lorentz forces
strongly dominating over drag forces. Dust grains are unstable to the RDIs and
form concentrated columns and sheets, whose scale grows until saturating at the
simulation box size. Initially perfectly-streaming CRs are strongly scattered
by RDI-excited Alfv{\'e}n waves, with the growth rate of the CR perpendicular
velocity components equaling the growth rate of magnetic field perturbations.
These rates are well-predicted by analytic linear theory. CRs finally become
isotropized and drift at least at $\sim v_\mathrm{A}$ by unidirectional
Alfv\'{e}n waves excited by the RDIs, with a uniform distribution of the pitch
angle cosine $\mu$ and a flat profile of the CR pitch angle diffusion
coefficient $D_{\mu\mu}$ around $\mu = 0$, without the ""$90$ degree pitch angle
problem."" With CR feedback on the gas included, $D_{\mu\mu}$ decreases by a
factor of a few, indicating a lower CR scattering rate, because the
backreaction on the RDI from the CR pressure adds extra wave damping, leading
to lower quasi-steady-state scattering rates. Our study demonstrates that the
dust-induced CR confinement can be very important under certain conditions,
e.g., the dusty circumgalactic medium around quasars or superluminous galaxies.",2112.00752v2
2022-02-15,Thermodynamics of the spin-half square-kagome lattice antiferromagnet,"Over the last decade, the interest in the spin-$1/2$ Heisenberg
antiferromagnet (HAF) on the square-kagome (also called shuriken) lattice has
been growing as a model system of quantum magnetism with a quantum paramagnetic
ground state, flat-band physics near the saturation field, and quantum scars.
Here, we present large-scale numerical investigations of the specific heat
$C(T)$, the entropy $S(T)$ as well as the susceptibility $\chi(T)$ by means of
the finite-temperature Lanczos method for system sizes of
$N=18,24,30,36,42,48$, and $N=54$. We find that the specific heat exhibits a
low-temperature shoulder below the major maximum which can be attributed to
low-lying singlet excitations filling the singlet-triplet gap, which is
significantly larger than the singlet-singlet gap. This observation is further
supported by the behavior of the entropy $S(T)$, where a change in the
curvature is present just at about $T/J=0.2$, the same temperature where the
shoulder in $C$ sets in. For the susceptibility the low-lying singlet
excitations are irrelevant, and the singlet-triplet gap leads to an
exponentially activated low-temperature behavior. The maximum in $\chi(T)$ is
found at a pretty low temperature $T_{\rm max}/J=0.146$ (for $N=42$) compared
to $T_{\rm max}/J=0.935$ for the unfrustrated square-lattice HAF signaling the
crucial role of frustration also for the susceptibility. We find a striking
similarity of our square-kagome data with the corresponding ones for the kagome
HAF down to very low $T$. The magnetization process featuring plateaus and
jumps and the field dependence of the specific heat that exhibits
characteristic peculiarities attributed to the existence of a flat one-magnon
band are as well discussed.",2202.07357v2
2022-02-16,Giant oscillatory tunnel magnetoresistance in CoFe/MgO/CoFe(001) junctions,"The tunnel magnetoresistance (TMR) effect observed in magnetic tunnel
junctions (MTJs) is commonly used in many spintronic applications because the
effect can easily convert from local magnetic states to electric signals in a
wide range of device resistances. In this study, we demonstrated TMR ratios of
up to 631% at room temperature (RT), which is two or more times larger than
those used currently for magnetoresistive random access memory (MRAM) devices,
using CoFe/MgO/CoFe(001) epitaxial MTJs. The TMR ratio increased up to 1143% at
10 K, which corresponds to an effective tunneling spin polarization of 0.923.
The observed large TMR ratios resulted from the fine-tuning of atomic-scale
structures of the MTJs, such as crystallographic orientations and MgO interface
oxidation, in which the well-known Delta1 coherent tunneling mechanism for the
giant TMR effect is expected to be pronounced. However, behavior that is not
covered by the standard coherent tunneling theory was unexpectedly manifested;
i.e., (i) TMR saturation at a thick MgO barrier region and (ii) enhanced TMR
oscillation with a 0.32 nm period in MgO thickness. Particularly, the TMR
oscillatory behavior dominates the transport in a wide range of MgO
thicknesses; the peak-to-valley difference of the TMR oscillation exceeded 140%
at RT, attributable to the appearance of large oscillatory components in
resistance area product (RA). Further, we found that the oscillatory behaviors
of the TMR ratio and RA survive, even under a +-1 V bias voltage application,
indicating the robustness of the oscillation. Our demonstration of the giant
RT-TMR ratio will be an essential step for establishing spintronic
architectures, such as large-capacity MRAMs and spintronic artificial neural
networks. More essentially, the present observations can trigger us to revisit
the true TMR mechanism in crystalline MTJs.",2202.07847v1
2022-02-25,Astrophysical Plasma Instabilities induced by Long-Range Interacting Dark Matter,"If dark matter (DM) is millicharged or darkly charged, collective plasma
processes may dominate momentum exchange over direct particle collisions.
Plasma streaming instabilities can couple the momentum of the DM to
counter-streaming baryons or other DM and result in the counter-streaming
fluids coming to rest with each other, just as happens for baryonic
collisionless shocks in astrophysical systems. While electrostatic plasma
instabilities are highly suppressed by Landau damping when DM is millicharged,
in the cosmological situations of interest, electromagnetic instabilities such
as the Weibel can couple momenta, assuming that the linear instability
saturates in the manner typically found for baryonic plasmas. We find that the
streaming of DM in the pre-Recombination universe is affected more strongly by
direct collisions than collective processes, validating previous constraints.
However, when considering magnetized Weibel and Firehose instabilities, the
properties of the Bullet Cluster merger are likely to be substantially altered
if $[q_\chi/m_\chi] \gtrsim 10^{-12}-10^{-11}$, where $[q_\chi/m_\chi]$ is the
charge-to-mass ratio of the DM relative to that of the proton. The Weibel
growth rates are even faster in the case of a dark-$U(1)$ charge, potentially
ruling out $[q_\chi/m_\chi] \gtrsim 10^{-14}$ in the Bullet Cluster system, in
agreement with previous work. The strongest previous limits on millicharged DM
(mDM) arise from considering the spin-down of galactic disks. We show that
plasma instabilities or tangled background magnetic fields could lead to
diffusive propagation of the DM, weakening these spin-down limits. Thus, plasma
instabilities may place some of the most stringent constraints over much of the
millicharged, and our results corroborate previous extremely stringent
potential constraints on the dark-charged parameter space.",2202.12464v2
2022-04-17,MRXCAT-CDTI: A Numerical Cardiac Diffusion Tensor Imaging Phantom,"Magnetic Resonance cardiac diffusion tensor imaging (cDTI) and cardiac
intravoxel incoherent motion imaging enables probing of in vivo myofiber
architecture and myocardial perfusion surrogates. To study the impact of
experimental parameters such as resolution, off-resonances and heart-rate
variations, we propose a numerical open-source framework called MRXCAT-CDTI. It
allows simulating diffusion and perfusion contrast for spin-echo (SE) and
stimulated echo acquisition mode (STEAM) cDTI sequences. The Fourier encoder
supports in-plane and/or through-slice off-resonance effects, as well as T2*
effects during single-shot image encoding. Optional lesions are included to
mimic ischemic and infarcted myocardial regions. MRXCAT-CDTI allows assessing
realistic influences on data acquisition, and how these affect the data
encoding process and subsequent data processing. As an example, heart-rate
variations lead to differences in partial saturation and relaxation of
magnetization that end up in errors of 9 to 30% for cDTI angle metrics if not
accounted for. For SE echo-planar cDTI, in-plane off-resonance effects more
adversely affect cDTI metrics compared to through-slice off-resonances. With
this work we propose an open-source MRXCAT-CDTI numerical simulation framework
that offers realistic image encoding effects found in cardiac diffusion and
perfusion data to systematically study influences of data encoding,
reconstruction, and post-processing to promote reproducible research.",2204.07966v1
2022-12-28,Rossby numbers of fully and partially convective stars,"We investigate stellar magnetic activity from the theoretical point of view,
by using stellar evolution models to calculate theoretical convective turnover
times ($\tau_{\rm c}$) and Rossby numbers (${\rm Ro}$) for pre-main-sequence
and main-sequence stars. The problem is that the canonical place where
$\tau_{\rm c}$ is usually determined (half a mixing length above the base of
the convective zone) fails for fully convective stars and there is no agreement
on this in the literature. Our calculations were performed with the ATON
stellar evolution code. We concentrated our analysis on fully and partially
convective stars motivated by recent observations of slowly rotating fully
convective stars, whose X-ray emissions correlate with their Rossby numbers in
the same way as in solar-like stars, suggesting that the presence of a
tachocline is not required for magnetic field generation. We investigate the
behaviour of $\tau_{\rm c}$ over the stellar radius for stars of different
masses and ages. As ${\rm Ro}$ depends on $\tau_{\rm c}$, which varies strongly
with the stellar radius, we use our theoretical results to determine a better
radial position at which to calculate it for fully convective stars. Using our
alternative locations, we fit a sample of 847 stars in the rotation-activity
diagram ($L_{\rm X}/L_{\rm bol}$ versus ${\rm Ro}$) with a two-part power-law
function. Our fit parameters are consistent with previous work, showing that
stars with ${\rm Ro}$$\leq$${\rm Ro_{sat}}$ are distributed around a saturation
level in $L_{\rm X}/L_{\rm bol}$ and, for stars with ${\rm Ro}$$>$${\rm
Ro_{sat}}$, $L_{\rm X}/L_{\rm bol}$ clearly decays with ${\rm Ro}$ with an
exponent of $-2.4\!\pm\!0.1$.",2212.13958v1
2023-01-14,CoRuVSi: A potential candidate for spin semimetal with promising spintronic and thermoelectric properties,"Based on our experimental and theoretical studies, we report the
identification of the quaternary Heusler alloy, CoRuVSi as a new member of the
recently discovered spin semimetals class. Spin polarised semimetals possess a
unique band structure in which one of the spin bands shows semimetallic nature,
while the other shows semiconducting/insulating nature. Our findings show that
CoRuVSi possesses interesting spintronic and thermoelectric properties.
Magnetization data reveal a weak ferri-/antiferro magnetic ordering at low
temperatures, with only a very small moment $\sim$ 0.13 $\mu_B$/f.u.,
attributed to the disorder. Transport results provide strong evidence of
semimetallicity dominated by two-band conduction, while magnetoresistance data
show a non-saturating, linear, positive, magnetoresistance. Spin polarization
measurements using point-contact Andreev reflection spectra reveal a reasonably
high spin polarization of $\sim$ 50\%, which matches fairly well with the
simulated result. Furthermore, CoRuVSi shows a high thermopower value of $0.7$
$m Watt/ m-K^{2}$ at room temperature with the dominant contribution from the
semimetallic bands, rendering it as a promising thermoelectric material as
well. Our ab-initio simulation not only confirms a unique semimetallic feature,
but also reveals that the band structure hosts a linear band crossing at $\sim$
-0.4 eV below the Fermi level incorporated by a band-inversion. In addition,
the observed topological non-trivial features of the band structure is
corroborated with the simulated Berry curvature, intrinsic anomalous Hall
conductivity and the Fermi surface. The coexistence of many interesting
properties relevant for spintronic, topological and thermoelectric applications
in a single material is extremely rare and hence this study could promote a
similar strategy to identify other potential materials belonging to same class.",2301.05854v1
2023-02-14,Collapsar Black Holes are Likely Born Slowly Spinning,"Collapsing stars constitute the main black hole (BH) formation channel, and
are occasionally associated with the launch of relativistic jets that power $
\gamma $-ray bursts (GRBs). Thus, collapsars offer an opportunity to infer the
natal (before spin-up/down by accretion) BH spin directly from observations. We
show that once the BH saturates with large-scale magnetic flux, the jet power
is dictated by the BH spin and mass accretion rate. Core-collapse simulations
by Halevi et al. 2023 and GRB observations favor stellar density profiles that
yield an accretion rate $ \dot{m} \approx 10^{-2} M_\odot~{\rm s^{-1}} $,
weakly dependent on time. This leaves the spin as the main factor that governs
the jet power. By comparing the jet power to characteristic GRB luminosities,
we find that the majority of BHs associated with jets are likely born slowly
spinning with a dimensionless spin $ a \simeq 0.2 $, or $ a \lesssim 0.5 $ for
wobbling jets, with the main uncertainty originating in the unknown $ \gamma
$-ray radiative efficiency. This result could be applied to the entire
core-collapse BH population, unless an anti-correlation between the stellar
magnetic field and angular momentum is present. In a companion paper,
Jacquemin-Ide et al. 2023, we show that regardless of the natal spin, the
extraction of BH rotational energy leads to spin-down to $ a \lesssim 0.2 $,
consistent with gravitational-wave observations. We verify our results by
performing the first 3D general relativistic magnetohydrodynamic simulations of
collapsar jets with characteristic GRB energies, powered by slowly spinning
BHs. We find that jets of typical GRB power struggle to escape from the star,
providing the first numerical indication that many jets fail to generate a GRB.",2302.07271v2
2023-07-04,Critical dynamical behavior of the Ising model,"We investigate the dynamical critical behavior of the two- and
three-dimensional Ising model with Glauber dynamics in equilibrium. In contrast
to the usual standing, we focus on the mean-squared deviation of the
magnetization $M$, MSD$_M$, as a function of time, as well as on the
autocorrelation function of $M$. These two functions are distinct but closely
related. We find that MSD$_M$ features a first crossover at time $\tau_1 \sim
L^{z_{1}}$, from ordinary diffusion with MSD$_M$ $\sim t$, to anomalous
diffusion with MSD$_M$ $\sim t^\alpha$. Purely on numerical grounds, we obtain
the values $z_1=0.45(5)$ and $\alpha=0.752(5)$ for the two-dimensional Ising
ferromagnet. Related to this, the magnetization autocorrelation function
crosses over from an exponential decay to a stretched-exponential decay. At
later times, we find a second crossover at time $\tau_2 \sim L^{z_{2}}$. Here,
MSD$_M$ saturates to its late-time value $\sim L^{2+\gamma/\nu}$, while the
autocorrelation function crosses over from stretched-exponential decay to
simple exponential one. We also confirm numerically the value
$z_{2}=2.1665(12)$, earlier reported as the single dynamic exponent. Continuity
of MSD$_M$ requires that $\alpha(z_{2}-z_{1})=\gamma/\nu-z_1$. We speculate
that $z_{1} = 1/2$ and $\alpha = 3/4$, values that indeed lead to the expected
$z_{2} = 13/6$ result. A complementary analysis for the three-dimensional Ising
model provides the estimates $z_{1} = 1.35(2)$, $\alpha=0.90(2)$, and $z_{2} =
2.032(3)$. While $z_{2}$ has attracted significant attention in the literature,
we argue that for all practical purposes $z_{1}$ is more important, as it
determines the number of statistically independent measurements during a long
simulation.",2307.01837v2
2023-11-30,The Factory and the Beehive. V. Chromospheric and Coronal Activity and Its Dependence on Rotation in Praesepe and the Hyades,"Low-mass (< 1.2 Solar mass) main-sequence stars lose angular momentum over
time, leading to a decrease in their magnetic activity. The details of this
rotation-activity relation remain poorly understood. Using observations of
members of the $\approx$700 Myr-old Praesepe and Hyades open clusters, we aim
to characterize the rotation-activity relation for different tracers of
activity at this age. To complement published data, we obtained new optical
spectra for 250 Praesepe stars, new X-ray detections for ten, and new rotation
periods for 28. These numbers for Hyads are 131, 23, and 137, respectively. The
latter increases the number of Hyads with periods by 50%. We used these data to
measure the fractional H$\alpha$ and X-ray luminosities,
$\mathit{L}_{H\alpha}/\mathit{L}_{bol}$ and $\mathit{L}_X/\mathit{L}_{bol}$,
and to calculate Rossby numbers $\mathit{R}_o$. We found that at $\approx$700
Myr almost all M dwarfs exhibit H$\alpha$ emission, with binaries having the
same overall color-H$\alpha$ equivalent width distribution as single stars. In
the $\mathit{R}_o-\mathit{L}_{H\alpha}/\mathit{L}_{bol}$ plane, unsaturated
single stars follow a power-law with index $\beta = -5.9 \pm 0.8$ for
$\mathit{R}_o > 0.3$. In the $\mathit{R}_o-\mathit{L}_X/\mathit{L}_{bol}$
plane, we see evidence for supersaturation for single stars with $\mathit{R}_o
\lesssim 0.01$, following a power-law with index $\beta_{sup} =
0.5^{+0.2}_{-0.1}$, supporting the hypothesis that stellar coronae are being
centrifugally stripped. We found that the critical $\mathit{R}_o$ value at
which activity saturates is smaller for $\mathit{L}_X/\mathit{L}_{bol}$ than
for $\mathit{L}_{H\alpha}/\mathit{L}_{bol}$. Finally, we observed an almost 1:1
relation between $\mathit{L}_{H\alpha}/\mathit{L}_{bol}$ and
$\mathit{L}_X/\mathit{L}_{bol}$, suggesting that both the corona and the
chromosphere experience similar magnetic heating.",2311.18690v2
2023-12-29,Inverse Gertsenshtein effect as a probe of high-frequency gravitational waves,"We apply the inverse Gertsenshtein effect, i.e., the graviton-photon
conversion in the presence of a magnetic field, to constrain high-frequency
gravitational waves (HFGWs). Using existing astrophysical measurements, we
compute upper limits on the GW energy densities $\Omega_{\rm GW}$ at 16
different frequency bands. Given the observed magnetisation of galaxy clusters
with field strength $B\sim\mu{\rm G}$ correlated on $\mathcal{O}(10)\,{\rm
kpc}$ scales, we estimate HFGW constraints in the $\mathcal{O}(10^2)\,{\rm
GHz}$ regime to be $\Omega_{\rm GW}\lesssim10^{16}$ with the temperature
measurements of the Atacama Cosmology Telescope (ACT). Similarly, we
conservatively obtain $\Omega_{\rm GW}\lesssim10^{13} (10^{11})$ in the
$\mathcal{O}(10^2)\,{\rm MHz}$ ($\mathcal{O}(10)\,{\rm GHz}$) regime by
assuming uniform magnetic field with strength $B\sim0.1\,{\rm nG}$ and
saturating the excess signal over the Cosmic Microwave Background (CMB)
reported by radio telescopes such as the Experiment to Detect the Global EoR
Signature (EDGES), LOw Frequency ARray (LOFAR), and Murchison Widefield Array
(MWA), and the balloon-borne second generation Absolute Radiometer for
Cosmology, Astrophysics, and Diffuse Emission (ARCADE2) with graviton-induced
photons. Although none of these existing constraints fall below the critical
value of $\Omega_{\rm GW} = 1$ or reaches the Big Bang Nucleosynthesis (BBN)
bound of $\Omega_{\rm GW}\simeq1.2\times10^{-6}$, the upcoming Square Kilometer
Array (SKA) can improve the sensitivities by roughly 10 orders of magnitude and
potentially become realistic probes of HFGWs. We also explore several
next-generation CMB surveys, including Primordial Inflation Explorer (PIXIE),
Polarized Radiation Interferometer for Spectral disTortions and INflation
Exploration (PRISTINE) and Voyage 2050, that could potentially provide
constraints competitive to the current BBN bound.",2312.17636v1
2007-03-28,Nuclear Saturation and Correlations,"The relation between nuclear saturation and NN-correlations is examined.
Nucleons bound in a nucleus have a reduced effective mass due to the mean
field. This results in off-energy-shell scatterings modifying the free-space
NN-interaction by a dispersion correction. This is a major contribution to the
density-dependence of the effective in-medium force and to saturation.
Low-momentum effective interactions have been derived by renormalisation
methods whereby correlations may be reduced by effectively cutting off high
momentum components of the interaction. The effect of these cut-offs on
dispersive corrections and on saturation is the main focus of this paper. The
role of the tensor-force, its strength and its effect on correlations is of
particular interest. The importance of the definition of the mean field in
determining saturation as well as compressibility is also pointed out.
  With a cut-off below $\sim 2.6 fm^{-1}$ there is no saturation but at lower
density the binding energy is still well approximated suggesting that such a
force may be useful in nuclear structure calculations of (small) finite nuclei
if saturation is not an issue.
  A separable interaction that fits experimental phase-shifts exactly by
inverse scattering methods is used. Recent experiments measure short ranged
correlations (SRC's) to be 0.23 for $^{56}Fe$. Other experiments have obtained
a depletion of occupation-numbers in $^{208}Pb$ to be $\sim 0.2$. For nuclear
matter with the separable interaction and a continuous spectrum we obtain the
related quantity $\kappa$ to be 0.175 with the Bonn-B deuteron parameters,
while Machleidt's gets $\kappa= 0.125$ for the Bonn-B potential and a
continuous spectrum.",0703093v1
2008-11-06,The saturation scale and its x-dependence from Lambda polarization studies,"The transverse polarization of forward Lambda hyperons produced in
high-energy p-A collisions is expected to display an extremum at a transverse
momentum around the saturation scale. This was first observed within the
context of the McLerran-Venugopalan model which has an x-independent saturation
scale. The extremum arises due to the k_t-odd nature of the polarization
dependent fragmentation function, which probes approximately the derivative of
the dipole scattering amplitude. The amplitude changes most strongly around the
saturation scale, resulting in a peak in the polarization. We find that the
observation also extends to the more realistic case in which the saturation
scale Q_s is x dependent. Since a range of x and therefore Q_s values is probed
at a given transverse momentum and rapidity, this result is a priori not
expected. Moreover, the measurement of Lambda polarization over a range of x_F
values actually provides a direct probe of the x dependence of the saturation
scale. This novel feature is demonstrated for typical LHC kinematics and for
several phenomenological models of the dipole scattering amplitude. We show
that although the measurement will be challenging, it may be feasible at LHC.
The situation at RHIC is not favorable, because the peak will likely be at too
low transverse momentum of the Lambda to be a trustworthy measure of the
saturation scale.",0811.0998v1
2014-02-19,Exclusive vector meson production at high energies and gluon saturation,"We systematically study exclusive diffractive (photo) production of vector
mesons ($J/\psi$, $\psi(2s)$, $\phi$ and $\rho$) off protons in high-energy
collisions and investigate whether the production is a sensitive probe of gluon
saturation. We confront saturation-based results for diffractive $\psi(2s)$ and
$\rho$ production at HERA and $J/\psi$ photoproduction with all available data
including recent ones from HERA, ALICE and LHCb, finding good agreement. In
particular, we show that the $t$-distribution of differential cross sections of
photoproduction of vector mesons offers a unique opportunity to discriminate
among saturation and non-saturation models. This is due to the emergence of a
pronounced dip (or multiple dips) in the $t$-distribution of diffractive
photoproduction of vector mesons at relatively large, but potentially
accessible $|t|$ that can be traced back to the unitarity features of colour
dipole amplitude in the saturation regime. We show that in saturation models
the dips in $t$-distribution recede towards lower $|t|$ with decreasing mass of
the vector meson, increasing energy or decreasing Bjorken-$x$, and decreasing
virtuality $Q$. We provide various predictions for exclusive (photo) production
of different vector mesons including the ratio of $\psi(2s)/J/\psi$ at HERA,
the LHC, and future colliders.",1402.4831v3
2015-03-06,Graphs with induced-saturation number zero,"Given graphs $G$ and $H$, $G$ is $H$-saturated if $H$ is not a subgraph of
$G$, but for all $e \notin E(G)$, $H$ appears as a subgraph of $G + e$. While
for every $n \ge |V(H)|$, there exists an $n$-vertex graph that is
$H$-saturated, the same does not hold for induced subgraphs. That is, there
exist graphs $H$ and values of $n \ge |V(H)|$ for which every $n$-vertex graph
$G$ either contains $H$ as an induced subgraph, or there exists $e \notin E(G)$
such that $G + e$ does not contain $H$ as an induced subgraph. To circumvent
this, Martin and Smith make use of trigraphs when introducing the concept of
induced saturation and the induced saturation number of graphs. This allows for
edges that can be included or excluded when searching for an induced copy of H,
and the induced saturation number is the minimum number of such edges that are
required.
  In this paper, we show that the induced saturation number of many common
graphs is zero. Consequently, this yields graphs, instead of trigraphs, that
are H-induced-saturated. We introduce a new parameter for such graphs,
indsat*(n;H), which is the minimum number of edges in an H-induced-saturated
graph on n vertices. We provide bounds on indsat*(n;H) for many graphs. In
particular, we determine indsat*(n;paw) completely, and indsat*(n;$K_{1,3}$)
for infinitely many n.",1503.02105v1
2015-07-03,Over Saturation in SiPMs: The Difference Between Signal Charge and Signal Amplitude,"A recent report on the over saturation in SiPMs is puzzling. The
measurements, using a variety of SiPMs, show an excess in signal far beyond the
physical limit of the number of SiPM microcells without indication of an
ultimate saturation. In this work I propose a solution to this problem.
Different measurements and theoretical models of avalanche propagation indicate
that multiple simultaneous primary avalanches produce an ever narrower and
faster signal. This is because of a speed-up of effective avalanche propagation
processes. It means that SiPMs, operated at their saturation regime, should
become faster the more light they detect. Therefore, signal extraction methods
that use the amplitude of the signal should see an over saturation effect.
Measurements with a commercial SiPM illuminated with bright picosecond pulses
in the saturation regime demonstrate that indeed the rising edge of the SiPM
signal gets faster as the light pulses get brighter. A signal extractor based
on the amplitude shows a nonlinear behavior in comparison to an integrating
charge extractor. This supports the proposed solution for the over saturation
effect. Furthermore I show that this effect can already be seen with a
bandwidth of 300MHz, which means that it should be taken into account for fast
sampling experiments.",1507.00863v1
2015-11-02,Saturation Power based Simple Energy Efficiency Maximization Schemes for MU-MISO Systems,"In this paper, we investigate an energy efficiency (EE) maximization problem
in multi-user multiple input single output downlink channels. The optimization
problem in this system model is difficult to solve in general, since it is in
non-convex fractional form. Hence, conventional algorithms have addressed the
problem in an iterative manner for each channel realization, which leads to
high computational complexity. To tackle this complexity issue, we propose a
new simple method by utilizing the fact that the EE maximization is identical
to the spectral efficiency (SE) maximization for the region of the power below
a certain transmit power referred to as saturation power. In order to calculate
the saturation power, we first introduce upper and lower bounds of the EE
performance by adopting a maximal ratio transmission beamforming strategy.
Then, we propose an efficient way to compute the saturation power for the EE
maximization problem. Once we determine the saturation power corresponding to
the maximum EE in advance, we can solve the EE maximization problem with SE
maximization schemes with low complexity. The derived saturation power is
parameterized by employing random matrix theory, which relies only on the
second order channel statistics. Hence, this approach requires much lower
computational complexity compared to a conventional scheme which exploits
instantaneous channel state information, and provides insight on the saturation
power. Numerical results validate that the proposed algorithm achieves near
optimal EE performance with significantly reduced complexity.",1511.00446v2
2015-11-03,Quantum hacking: saturation attack on practical continuous-variable quantum key distribution,"We identify and study a new security loophole in continuous-variable quantum
key distribution (CV-QKD) implementations, related to the imperfect linearity
of the homodyne detector. By exploiting this loophole, we propose an active
side-channel attack on the Gaussian-modulated coherent state CV-QKD protocol
combining an intercept-resend attack with an induced saturation of the homodyne
detection on the receiver side (Bob). We show that an attacker can bias the
excess noise estimation by displacing the quadratures of the coherent states
received by Bob. We propose a saturation model that matches experimental
measurements on the homodyne detection and use this model to study the impact
of the saturation attack on parameter estimation in CV-QKD.We demonstrate that
this attack can bias the excess noise estimation beyond the null key threshold
for any system parameter, thus leading to a full security break. If we consider
an additional criteria imposing that the channel transmission estimation should
not be affected by the attack, then the saturation attack can only be launched
if the attenuation on the quantum channel is sufficient, corresponding to
attenuations larger than approximately 6 dB. We moreover discuss the possible
counter-measures against the saturation attack and propose a new counter-
measure based on Gaussian post-selection that can be implemented by classical
post-processing and may allow to distill secret key when the raw measurement
data is partly saturated.",1511.01007v1
2016-07-04,CGC/saturation approach: a new impact-parameter dependent model in the next-to-leading order of perturbative QCD,"This paper is the first attempt to build CGC/saturation model based on the
next-to-leading order corrections to linear and non-linear evolution in QCD. We
assume that the renormalization scale is the saturation momentum and found that
the scattering amplitude has geometric scaling behaviour deep in the saturation
domain with the explicit formula of this behaviour at large $\tau = r^2 Q^2_s$.
We built a model that include this behaviour, as well as the ingredients that
has been known: (i) the behaviour of the scattering amplitude in the vicinity
of the saturation momentum, using the NLO BFKL kernel, (ii) the pre-asymptotic
behaviour of $\ln\Lb Q^2_s\Lb Y \Rb\Rb$, as function of $Y$ and (iii) the
impact parameter behaviour of the saturation momentum, which has exponential
behaviour $\propto \exp\Lb -\, m\, b\Rb$ at large $b$.We demonstrated that the
model is able to describe the experimental data for the deep inelastic
structure function. Despite this, our model has difficulties that are related
to the small value of the QCD coupling at $Q_s\Lb Y_0\Rb$ and the large values
of the saturation momentum, which indicate the theoretical inconsistency of our
description.",1607.00832v2
2017-10-10,Experimental investigation of water distribution in two-phase zone during gravity-dominated evaporation,"We characterize the water repartition within the partially saturated
(two-phase) zone (PSZ) during evaporation out of mixed wettable porous media by
controlling the wettability of glass beads, their sizes, and as well the
surrounding relative humidity. Here, Capillary numbers are low and under these
conditions, the percolating front is stabilized by gravity. Using experimental
and numerical analyses, we find that the PSZ saturation decreases with the Bond
number, where packing of smaller particles have higher saturation values than
packing made of larger particles. Results also reveal that the extent (height)
of the PSZ, as well as water saturation in the PSZ, both increase with
wettability. We also numerically calculate the saturation exclusively contained
in connected liquid films and results show that values are less than the
expected PSZ saturation. These results strongly reflect that the two-phase zone
is not solely made up of connected capillary networks, but also made of
disconnected water clusters or pockets. Moreover, we also find that global
saturation (PSZ + full wet zone) decreases with wettability, confirming that
greater quantity of water is lost via evaporation with increasing
hydrophilicity. These results show that connected liquid films are favored in
more hydrophilic systems while disconnected water pockets are favored in less
hydrophilic systems.",1710.03831v1
2019-07-25,Experimental study of the non-linear saturation of the elliptical instability: inertial wave turbulence versus geostrophic turbulence,"In this paper, we present an experimental investigation of the turbulent
saturation of the flow driven by parametric resonance of inertial waves in a
rotating fluid. In our set-up, a half-meter wide ellipsoid filled with water is
brought to solid body rotation, and then undergoes sustained harmonic
modulation of its rotation rate. This triggers the exponential growth of a pair
of inertial waves via a mechanism called the libration-driven elliptical
instability. Once the saturation of this instability is reached, we observe a
turbulent state for which energy is injected into the resonant inertial waves
only. Depending on the amplitude of the rotation rate modulation, two different
saturation states are observed. At large forcing amplitudes, the saturation
flow mainly consists of a steady, geostrophic anticyclone. Its amplitude
vanishes as the forcing amplitude is decreased while remaining above the
threshold of the elliptical instability. Below this secondary transition, the
saturation flow is a superposition of inertial waves which are in weakly
non-linear resonant interaction, a state that could asymptotically lead to
inertial wave turbulence. In addition to being a first experimental observation
of a wave-dominated saturation in unstable rotating flows, the present study is
also an experimental confirmation of the model of Le Reun et al, PRL (2017) who
introduced the possibility of these two turbulent regimes. The transition
between these two regimes and their relevance to geophysical applications are
finally discussed.",1907.10907v3
2020-11-01,Multiplicity-dependent saturation momentum in $p$-Pb collisions at 5.02 TeV,"Semi-inclusive transverse momentum spectra observed in proton-proton and
proton-lead nuclear collisions at LHC energies obey a geometric scaling with a
scaling variable using multiplicity-dependent saturation momentum. The
saturation momentum extracted from the experimental data is proportional to the
1/6 power of the hadron multiplicity in the final state. On the other hand, the
system's transverse size is proportional to the 1/3 power of the multiplicity,
and the saturation momentum and the transverse size of the system are strongly
correlated with the hadron multiplicity in the final state. Since the
saturation momentum is proportional to the average transverse momentum of
hadrons, one predicts average transverse momentum is also proportional to the
1/6 power of the multiplicity, which is consistent with experimental results at
the LHC energy. We found that a nuclear modification factor $R_{\rm pPb}$
calculated by the multiplicity-dependent saturation momentum decreases at
$p_{\rm T} \lesssim$ 1GeV/$c$ and that our model can partially explain the
$R_{\rm pPb}$'s behavior thought to be caused by nuclear shadowing. On the
other hand, Cronin enhancement experimentally observed at $2 \lesssim p_{\rm T}
\lesssim $ 6 GeV/$c$ is not reproduced. However, the experimental result,
including the Cronin effect, can be reproduced well by introducing $p_{\rm T}$
dependence as a 4$\sim$5\% correction to the multiplicity-dependent saturation
momentum.We also discuss a relation between the geometric scaling in the
semi-inclusive distributions and the string percolation model.",2011.00456v2
2022-01-24,Methane-saturated layers limit the observability of impact craters on Titan,"As the only icy satellite with a thick atmosphere and liquids on its surface,
Titan represents a unique end-member to study the impact cratering process.
Unlike craters on other Saturnian satellites, Titan's craters are
preferentially located in high-elevation regions near the equator. This led to
the hypothesis that the presence of liquid methane in Titan's lowlands affects
crater morphology, making them difficult to identify. This is because surfaces
covered by weak fluid-saturated sediment limit the topographic expression of
impact craters, as sediment moves into the crater cavity shortly after
formation. Here we simulate crater-forming impacts on Titan's surface,
exploring how a methane-saturated layer overlying a methane-clathrate layer
affects crater formation. Our numerical results show that impacts form smaller
craters in a methane-clathrate basement than a water-ice basement, due to the
differences in strength. We find that the addition of a methane-saturated layer
atop this basement reduces crater depths and influences crater morphology. The
morphology of impact craters formed in a thin methane-saturated layer are
similar to those in a ""dry"" target, but a thick saturated layer produces an
impact structure with little to no topography. A thick methane-saturated layer
(thicker than 40% of the impactor diameter) could explain the dearth of craters
in the low-elevation regions on Titan.",2201.09587v1
2022-11-02,How to minimize the environmental contamination caused by hydrocarbon releases by onshore pipelines: The key role of a three-dimensional three-phase fluid flow numerical model,"The contamination impact and the migration of the contaminant into the
surrounding environment due to the presence of a spilled oil pipeline will
cause significant damage to the natural ecosystem. For this reason, it is
decisive to develop a rapid response strategy that might include accurate
predictions of oil migration trajectories from numerical simulation modeling.
In this paper, a three-dimensional model based on a high-resolution
shock-capturing conservative method to resolve the nonlinear governing partial
differential equations of the migration of a spilled light nonaqueous liquid
oil contaminant in a variably saturated zone is employed to investigate the
migration of the oil pipeline leakage with great accuracy. The effects on the
oil type density, gasoline and diesel oil, the unsaturated zone depth, its
saturation, the hydraulic gradient, and the pressure oil pipeline are
investigated through the temporal evolution of the contaminant migration
following the saturation profiles of the three-phase fluids flow in the
variably saturated zone. The calculation results indicate that the leaking
oil's pressure is the parameter that significantly affects the contaminants'
arrival time to the groundwater table. Also, the water saturation of the
unsaturated zone influences the arrival time as the water saturation increases
for a fixed depth. The unsaturated zone depth significantly influences the
contaminant migration unsaturated zone. At the same time, the oil density and
the hydraulic gradient have limited effects on the contaminant migration in the
variably saturated zone.",2211.01279v1
2022-07-22,Accelerated and Quantitative 3D Semisolid MT/CEST Imaging using a Generative Adversarial Network (GAN-CEST),"Purpose: To substantially shorten the acquisition time required for
quantitative 3D chemical exchange saturation transfer (CEST) and semisolid
magnetization transfer (MT) imaging and allow for rapid chemical exchange
parameter map reconstruction. Methods: Three-dimensional CEST and MT magnetic
resonance fingerprinting (MRF) datasets of L-arginine phantoms, whole-brains,
and calf muscles from healthy volunteers, cancer patients, and cardiac patients
were acquired using 3T clinical scanners at 3 different sites, using 3
different scanner models and coils. A generative adversarial network supervised
framework (GAN-CEST) was then designed and trained to learn the mapping from a
reduced input data space to the quantitative exchange parameter space, while
preserving perceptual and quantitative content. Results: The GAN-CEST 3D
acquisition time was 42-52 seconds, 70% shorter than CEST-MRF. The quantitative
reconstruction of the entire brain took 0.8 seconds. An excellent agreement was
observed between the ground truth and GAN-based L-arginine concentration and pH
values (Pearson's r > 0.97, NRMSE < 1.5%). GAN-CEST images from a brain-tumor
subject yielded a semi-solid volume fraction and exchange rate NRMSE of
3.8$\pm$1.3% and 4.6$\pm$1.3%, respectively, and SSIM of 96.3$\pm$1.6% and
95.0$\pm$2.4%, respectively. The mapping of the calf-muscle exchange parameters
in a cardiac patient, yielded NRMSE < 7% and SSIM > 94% for the semi-solid
exchange parameters. In regions with large susceptibility artifacts, GAN-CEST
has demonstrated improved performance and reduced noise compared to MRF.
Conclusion: GAN-CEST can substantially reduce the acquisition time for
quantitative semisolid MT/CEST mapping, while retaining performance even when
facing pathologies and scanner models that were not available during training.",2207.11297v2
2005-02-21,Aperture Photometry of Saturated Star Images from Digitised Photographic Plates,"Saturated stellar images on digitised photographic plates are many times
greater in area than the `seeing disk' seen in unsaturated CCD images. Indeed
the flux profile of a bright star can be traced out for several degrees from
the star's centre. The radius of the saturated stellar image can often be
directly related to the magnitude of the star, a fact well known and exploited
in iris photometry. In this work we compare the radial flux profile of stars in
the approximate range B ~9 to ~13 mag, obtained from scans of plates from the
Bamberg Sky Patrol archive, with a profile of the form measured by King. We
show that simple aperture photometry of saturated stellar images, obtained from
photo-positives of scanned photographic plates, yield data that are in
agreement with simulations using a (saturated) synthetic stellar radius
profile. Raw plate magnitudes from this aperture photometry can be easily and
satisfactorily transformed to standard magnitudes, as demonstrated in a recent
study carried out by the current authors.",0502411v1
1999-06-29,Enhanced Saturation Coverages in Adsorption-Desorption Processes,"Many experimental studies of protein deposition on solid surfaces involve
alternating adsorption/desorption steps. In this paper, we investigate the
effect of a desorption step (separating two adsorption steps) on the kinetics,
the adsorbed-layer structure, and the saturation density. Our theoretical
approach involves a density expansion of the pair distribution function and an
application of an interpolation formula to estimate the saturation density as a
function of the density at which the desorption process commences, $\rho_1$,
and the density of the depleted configuration, $\rho_2$. The theory predicts an
enhancement of the saturation density compared with that of a simple,
uninterrupted RSA process and a maximum in the saturation density when
$\rho_2={2/3}\rho_1$. The theoretical results are in qualitative and in
semi-quantitative agreement with the results of numerical simulations.",9906429v1
2002-04-22,Dynamic scaling and universality in evolution of fluctuating random networks,"We found that models of evolving random networks exhibit dynamic scaling
similar to scaling of growing surfaces. It is demonstrated by numerical
simulations of two variants of the model in which nodes are added as well as
removed [Phys. Rev. Lett. 83, 5587 (1999)]. The averaged size and connectivity
of the network increase as power-laws in early times but later saturate.
Saturated values and times of saturation change with paramaters controlling the
local evolution of the network topology. Both saturated values and times of
saturation obey also power-law dependences on controlling parameters. Scaling
exponents are calculated and universal features are discussed.",0204476v2
1996-05-14,Large multiplicity fluctuations and saturation effects in onium collisions,"This paper studies two related questions in high energy onium-onium
scattering: the probability of producing an unusually large number of particles
in a collision, where it is found that the cross section for producing a
central multiplicity proportional to $k$ should decrease exponentially in
$\sqrt{k}$. Secondly, the nature of gluon (dipole) evolution when dipole
densities become so high that saturation effects due to dipole-dipole
interactions become important: measures of saturation are developed to help
understand when saturation becomes important, and further information is
obtained by exploiting changes of frame, which interchange unitarity and
saturation corrections.",9605302v1
2001-06-21,Quarkonium suppression as a probe of a saturated gluon plasma ?,"A dense parton system is expected to be formed in the early stage of
relativistic heavy-ion collisions at RHIC energies and above. The probability
of a quark gluon plasma production and the resulting strength of its signatures
depends strongly on the initial conditions associated to the distributions of
partons in the nuclear wave functions. At very high energies, the growth of
parton distributions should saturate, possibly forming a Color Glass
Condensate, which is characterized by a bulk momentum scale $Q_s$. As a direct
consequence, the possible signatures of the QGP should be $Q_s$-dependent if
the saturation scenario is valid for RHIC and LHC. In this Letter we assume the
saturation scenario for the QGP formation and estimate the saturation scale
dependence of quarkonium suppression. We conclude that, if this scenario is
valid, the $\Upsilon$ suppression only occurs at large values of $Q_s$.",0106244v1
2002-01-30,Conformal invariant saturation,"We show that, in onium-onium scattering at (very) high energy, a transition
to saturation happens due to quantum fluctuations of QCD dipoles. This
transition starts when the order $\alpha^2$ correction of the dipole loop is
compensated by its faster energy evolution, leading to a negative interference
with the tree level amplitude. After a derivation of the the one-loop dipole
contribution using conformal invariance of the elastic 4-gluon amplitude in
high energy QCD, we obtain an exact expression of the saturation line in the
plane (Y,L) where Y is the total rapidity and L, the logarithm of the onium
scale ratio. It shows universal features implying the Balitskyi - Fadin -
Kuraev - Lipatov (BFKL) evolution kernel and the square of the QCD triple
Pomeron vertex. For large L, only the higher BFKL Eigenvalue contributes,
leading to a saturation depending on leading log perturbative QCD
characteristics. For initial onium scales of same order, however, it involves
an unlimited summation over all conformal BFKL Eigenstates. In all cases,
conformal invariance is preserved for the saturation mechanism based on dipole
loops.",0201285v2
2002-12-04,Saturation Effects in Hadronic Cross Sections,"We compute total and differential elastic cross sections of high-energy
hadronic collisions in the loop-loop correlation model that provides a unified
description of hadron-hadron, photon-hadron, and photon-photon reactions. The
impact parameter profiles of pp and gamma*p collisions are calculated. For
ultra-high energies the hadron opacity saturates at the black disc limit which
tames the growth of the hadronic cross sections in agreement with the Froissart
bound. We compute the impact parameter dependent gluon distribution of the
proton xG(x,Q^2,b) and find gluon saturation at small Bjorken x. These
saturation effects manifest S-matrix unitarity in hadronic collisions and
should be observable in future cosmic ray and accelerator experiments at
ultra-high energies. The c.m. energies and Bjorken x at which saturation sets
in are determined and LHC and THERA predictions are given.",0212070v1
2003-03-04,Nonlinear kT factorization for Forward Dijets in DIS off Nuclei in the Saturation Regime,"We develop the QCD description of the breakup of photons into forward dijets
in small-x deep inelastic scattering off nuclei in the saturation regime. Based
on the color dipole approach, we derive a multiple scattering expansion for
intranuclear distortions of the jet-jet transverse momentum spectrum. A special
attention is paid to the non-Abelian aspects of the propagation of color
dipoles in a nuclear medium. We report a nonlinear $k_{\perp}$-factorization
formula for the breakup of photons into dijets in terms of the collective
Weizs\""acker-Williams (WW) glue of nuclei as defined in ref.
\cite{Saturation,NSSdijet}. For hard dijets with the transverse momenta above
the saturation scale the azimuthal decorrelation (acoplanarity) momentum is of
the order of the nuclear saturation momentum QA. For minijets with the
transverse momentum below the saturation scale the nonlinear kT-factorization
predicts a complete disappearance of the jet-jet correlation. We comment on a
possible relevance of the nuclear decorrelation of jets to the experimental
data from the STAR-RHIC Collaboration.",0303024v1
2003-03-19,Saturation of nuclear matter and short-range correlations,"A fully self-consistent treatment of short-range correlations in nuclear
matter is presented. Different implementations of the determination of the
nucleon spectral functions for different interactions are shown to be
consistent with each other. The resulting saturation densities are closer to
the empirical result when compared with (continuous-choice)
Brueckner-Hartree-Fock values. Arguments for the dominance of short-range
correlations in determining the nuclear-matter saturation density are
presented. A further survey of the role of long-range correlations suggests
that the inclusion of pionic contributions to ring diagrams in nuclear matter
leads to higher saturation densities than empirically observed. A possible
resolution of the nuclear-matter saturation problem is suggested.",0303047v1
2007-04-12,Saturated actions by finite dimensional Hopf *-algebras on C*-algebras,"If a finite group action $\alpha$ on a unital $C^*$-algebra $M$ is saturated,
the canonical conditional expectation $E:M\to M^\alpha$ onto the fixed point
algebra is known to be of index finite type with $Index(E)=|G|$ in the sense of
Watatani. More generally if a finite dimensional Hopf $*$-algebra $A$ acts on
$M$ and the action is saturated, the same is true with $Index (E)=\dim(A)$. In
this paper we prove that the converse is true. Especially in case $M$ is a
commutative $C^*$-algebra $C(X)$ and $\alpha$ is a finite group action, we give
an equivalent condition in order that the expectation $E:C(X)\to C(X)^\alpha$
is of index finite type, from which we obtain that $\alpha$ is saturated if and
only if $G$ acts freely on $X$.
  Actions by compact groups are also considered to show that the gauge action
$\gamma$ on a graph $C^*$-algebra $C^*(E)$ associated with a locally finite
directed graph $E$ is saturated.",0704.1549v1
2007-10-21,On the Behavior of the Distributed Coordination Function of IEEE 802.11 with Multirate Capability under General Transmission Conditions,"The aim of this paper is threefold. First, it presents a multi-dimensional
Markovian state transition model characterizing the behavior of the IEEE 802.11
protocol at the Medium Access Control layer which accounts for packet
transmission failures due to channel errors modeling both saturated and
non-saturated traffic conditions. Second, it provides a throughput analysis of
the IEEE 802.11 protocol at the data link layer in both saturated and
non-saturated traffic conditions taking into account the impact of both the
physical propagation channel and multirate transmission in Rayleigh fading
environment. The general traffic model assumed is M/M/1/K. Finally, it shows
that the behavior of the throughput in non-saturated traffic conditions is a
linear combination of two system parameters; the payload size and the packet
rates, $\lambda^{(s)}$, of each contending station. The validity interval of
the proposed model is also derived.
  Simulation results closely match the theoretical derivations, confirming the
effectiveness of the proposed models.",0710.3955v1
2009-04-01,Long-time saturation of the Loschmidt echo in quantum chaotic billiards,"The Loschmidt echo (LE) (or fidelity) quantifies the sensitivity of the time
evolution of a quantum system with respect to a perturbation of the
Hamiltonian. In a typical chaotic system the LE has been previously argued to
exhibit a long-time saturation at a value inversely proportional to the
effective size of the Hilbert space of the system. However, until now no
quantitative results have been known and, in particular, no explicit expression
for the proportionality constant has been proposed. In this paper we perform a
quantitative analysis of the phenomenon of the LE saturation and provide the
analytical expression for its long-time saturation value for a semiclassical
particle in a two-dimensional chaotic billiard. We further perform extensive
(fully quantum mechanical) numerical calculations of the LE saturation value
and find the numerical results to support the semiclassical theory.",0904.0172v1
2009-09-14,Nuclear modification factor in p+pb collisions at LHC and saturation,"We provide predictions for the nuclear modification factor R_{pA} for pions
and direct photon production in p+A collisions at LHC energy at midrapidity
within different saturation models fitted to HERA data. In our approach we have
no free parameters to adjust and all model parameters are fitted to other
reactions. Our approach gives a rather good description of PHENIX data for
R_{pA} for pions. We show that, in various saturation models, the pion Cronin
enhancement is replaced by a moderate suppression at LHC energy at midrapidity
due to gluon shadowing effects. However, Cronin enhancement of direct photons
can survive at LHC energy in models with a larger saturation scale. We show
that both shadowing and saturation effects are important at LHC in p+A
collisions and give rise to a rather sizable effect in the nuclear modification
factor R_{pA}. Therefore, a precise measurement of p+A collisions at LHC is
crucial in order to understand the underlying dynamics of heavy ion collisions.",0909.2664v2
2010-03-12,Inelastic Scattering and Current Saturation in Graphene,"We present a study of transport in graphene devices on polar insulating
substrates by solving the Bolzmann transport equation in the presence of
graphene phonon, surface polar phonon, and Coulomb charged impurity scattering.
The value of the saturated velocity shows very weak dependence on the carrier
density, the nature of the insulating substrate, and the low-field mobility,
varied by the charged impurity concentration. The saturated velocity of 4 - 8 x
10^7 cm/s calculated at room temperature is significantly larger than reported
experimental values. The discrepancy is due to the self-heating effect which
lowers substantially the value of the saturated velocity. We predict that by
reducing the insulator oxide thickness, which limits the thermal conductance,
the saturated currents can be significantly enhanced. We also calculate the
surface polar phonon contribution to the low-field mobility as a function of
carrier density, temperature, and distance from the substrate.",1003.2455v1
2010-05-06,Can the nuclear symmetry potential at supra-saturation densities be negative?,"In the framework of an Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU)
transport model, for the central $^{197}$Au+$^{197}$Au reaction at an incident
beam energy of 400 MeV/nucleon, effect of nuclear symmetry potential at
supra-saturation densities on the pre-equilibrium clusters emission is studied.
It is found that for the positive symmetry potential at supra-saturation
densities the neutron to proton ratio of lighter clusters with mass number
$A\leq3$ ($(n/p)_{A\leq3}$) is larger than that of the weighter clusters with
mass number $A>3$ ($(n/p)_{A>3}$), whereas for the negative symmetry potential
at supra-saturation densities the $(n/p)_{A\leq3}$ is \emph{smaller} than that
of the $(n/p)_{A>3}$. This may be considered as a probe of the negative
symmetry potential at supra-saturation densities.",1005.0962v1
2010-05-15,Mobility and Saturation Velocity in Graphene on SiO2,"We examine mobility and saturation velocity in graphene on SiO2 above room
temperature (300-500 K) and at high fields (~1 V/um). Data are analyzed with
practical models including gated carriers, thermal generation, ""puddle"" charge,
and Joule heating. Both mobility and saturation velocity decrease with rising
temperature above 300 K, and with rising carrier density above 2x10^12 cm^-2.
Saturation velocity is >3x10^7 cm/s at low carrier density, and remains greater
than in Si up to 1.2x10^13 cm^-2. Transport appears primarily limited by the
SiO2 substrate, but results suggest intrinsic graphene saturation velocity
could be more than twice that observed here.",1005.2711v2
2010-07-13,A variational approach for the deformation of a saturated porous solid. A second-gradient theory extending Terzaghi's effective stress principle,"The principle of virtual power is used to derive the equilibrium field
equations of a porous solid saturated with a fluid, including second
density-gradient effects; the intention is the elucidation and extension of the
effective stress principle of Terzaghi and Fillunger. In the context of a first
density-gradient theory for a saturated solid we interpret the porewater
pressure as a Lagrange multiplier in the expression for the deformation energy,
assuring that the saturation constraint is verified. We prove that this
saturation pressure is distributed among the constituents according their
respective volume fraction (Delesse law) only if they are both true
density-preserving.",1007.2084v1
2011-01-18,Saturation of Hadron Production in Proton-(anti)Proton Collisions at Low Pt,"Experimental data on inclusive cross sections of the hadrons produced in high
energy proton-(anti)proton collisions are analyzed in the z-scaling approach.
Saturation of the scaling function PSI(z) for z<0.1 (low transverse momenta)
was found. The first results on charged hadron spectra in pp collisions
obtained by the CMS Collaboration at the LHC have confirmed the saturation down
to the value of z=0.05. The CMS data on neutral K-meson production at s^{1/2}=7
TeV extend the saturation region even to a lower value of z=0.002 in the new
energy domain. A microscopic scenario of hadron production at a constituent
level based on the z-scaling is discussed in the saturation regime.",1101.3439v1
2011-02-03,"A Model of Electrowetting, Reversed Electrowetting and Contact Angle Saturation","While electrowetting has many applications, it is limited at large voltages
by contact angle saturation - a phenomenon that is still not well understood.
We propose a generalized approach for electrowetting that, among other results,
can shed new light on contact angle saturation. The model assumes the existence
of a minimum (with respect to the contact angle) in the electric energy and
accounts for a quadratic voltage dependence ~U^2 in the low-voltage limit,
compatible with the Young-Lippmann formula, and a ~1/U^2 saturation at the
high-voltage limit. Another prediction is the surprising possibility of a
reversed electrowetting regime, in which the contact angle increases with
applied voltage. By explicitly taking into account the effect of the
counter-electrode, our model is shown to be applicable to several AC and DC
experimental electrowetting-on-dielectric (EWOD) setups. Several features seen
in experiments compare favorably with our results. Furthermore, the AC
frequency dependence of EWOD agrees quantitatively with our predictions. Our
numerical results are complemented with simple analytical expressions for the
saturation angle in two practical limits.",1102.0791v3
2011-08-11,Effects of MAC Approaches on Non-Monotonic Saturation with COPE - A Simple Case Study,"We construct a simple network model to provide insight into network design
strategies. We show that the model can be used to address various approaches to
network coding, MAC, and multi-packet reception so that their effects on
network throughput can be evaluated. We consider several topology components
which exhibit the same non-monotonic saturation behavior found within the Katti
et. al. COPE experiments. We further show that fairness allocation by the MAC
can seriously impact performance and cause this non-monotonic saturation. Using
our model, we develop a MAC that provides monotonic saturation, higher
saturation throughput gains and fairness among flows rather than nodes. The
proposed model provides an estimate of the achievable gains for the cross-layer
design of network coding, multi-packet reception, and MAC showing that
super-additive throughput gains on the order of six times that of routing are
possible.",1108.2514v1
2011-12-18,Maximal determinants and saturated D-optimal designs of orders 19 and 37,"A saturated D-optimal design is a {+1,-1} square matrix of given order with
maximal determinant. We search for saturated D-optimal designs of orders 19 and
37, and find that known matrices due to Smith, Cohn, Orrick and Solomon are
optimal. For order 19 we find all inequivalent saturated D-optimal designs with
maximal determinant, 2^30 x 7^2 x 17, and confirm that the three known designs
comprise a complete set. For order 37 we prove that the maximal determinant is
2^39 x 3^36, and find a sample of inequivalent saturated D-optimal designs. Our
method is an extension of that used by Orrick to resolve the previously
smallest unknown order of 15; and by Chadjipantelis, Kounias and Moyssiadis to
resolve orders 17 and 21. The method is a two-step computation which first
searches for candidate Gram matrices and then attempts to decompose them. Using
a similar method, we also find the complete spectrum of determinant values for
{+1,-1} matrices of order 13.",1112.4160v1
2012-03-11,Automated Synthesis of a Finite Complexity Ordering for Saturation,"We present in this paper a new procedure to saturate a set of clauses with
respect to a well-founded ordering on ground atoms such that A < B implies
Var(A) {\subseteq} Var(B) for every atoms A and B. This condition is satisfied
by any atom ordering compatible with a lexicographic, recursive, or multiset
path ordering on terms. Our saturation procedure is based on a priori ordered
resolution and its main novelty is the on-the-fly construction of a finite
complexity atom ordering. In contrast with the usual redundancy, we give a new
redundancy notion and we prove that during the saturation a non-redundant
inference by a priori ordered resolution is also an inference by a posteriori
ordered resolution. We also prove that if a set S of clauses is saturated with
respect to an atom ordering as described above then the problem of whether a
clause C is entailed from S is decidable.",1203.2809v1
2012-11-14,Multi-stable regime and intermediate solutions in a nonlinear saturable coupler,"We show, theoretically and experimentally, the existence of a multi-stable
regime in a nonlinear saturable coupler. In spite of its simplicity, we found
that this model shows generic and fundamental properties of extended saturable
lattices. The study of this basic unit becomes crucial to understand
localization mechanisms and dynamical properties of extended discrete nonlinear
saturable systems. We theoretically predict the regions of existence of
intermediate solutions, and experimentally confirm it by observing a
multi-stable propagation regime in a LiNbO3 saturable coupler. This constitutes
the first experimental evidence of the existence of these unstable
symmetry-broken stationary solutions.",1211.3379v3
2012-12-05,Saturating directed spaces,"Directed topology is a refinement of standard topology, where spaces may have
non-reversible paths. It has been put forward as a candidate approach to the
analysis of concurrent processes. Recently, a wealth of different frameworks
for, i.e., categories of, directed spaces have been proposed. In the present
work, starting from Grandis's notion of directed space, we propose an
additional condition of saturation for distinguished sets of paths and show how
it allows to rule out exotic examples without any serious collateral damage.
Our saturation condition is local in a natural sense, and is satisfied by the
directed interval (and the directed circle). Furthermore we show in which sense
it is the strongest condition fulfilling these two basic requirements. Our
saturation condition selects a full, reflective subcategory of Grandis's
category of d-spaces, which is closed under arbitrary limits of d-spaces, has
arbitrary colimits (obtained by saturating the corresponding colimits of
d-spaces), and has nice cylinder and cocylinder constructions. Finally, the
forgetful functor to plain topological spaces has both a right and a left
adjoint.",1212.1074v1
2013-01-24,Pricing Using a Homogeneously Saturated Equation,"A homogeneously saturated equation for the time development of the price of a
financial asset is presented and investigated for the pricing of European call
options using noise that is distributed as a Student's t-distribution. In the
limit that the saturation parameter of the equation equals zero, the standard
model of geometric motion for the price of an asset is obtained. The
homogeneously saturated equation for the price of an asset is similar to a
simple equation for the output of a homogeneously broadened laser. The
homogeneously saturated equation tends to limit the range of returns and thus
seems to be realistic.
  Fits to linear returns obtained from the adjusted closing values for the S&P
500 index were used to obtain best-fit parameters for Student's t-distributions
and for normal distributions, and these fits were used to price options, and to
compare approaches to modelling prices.
  This work has value in understanding the pricing of assets and of European
call options.",1301.5877v1
2013-06-07,Saturated hydraulic conductivity determined by on ground mono-offset Ground-Penetrating Radar inside a single ring infiltrometer,"In this study we show how to use GPR data acquired along the infiltration of
water inside a single ring infiltrometer to inverse the saturated hydraulic
conductivity. We used Hydrus-1D to simulate the water infiltration. We
generated water content profiles at each time step of infiltration, based on a
particular value of the saturated hydraulic conductivity, knowing the other van
Genuchten parameters. Water content profiles were converted to dielectric
permittivity profiles using the Complex Refractive Index Method relation. We
then used the GprMax suite of programs to generate radargrams and to follow the
wetting front using arrival time of electromagnetic waves recorded by a
Ground-Penetrating Radar (GPR). Theoretically, the 1D time convolution between
reflectivity and GPR signal at any infiltration time step is related to the
peak of the reflected amplitude recorded in the corresponding trace in the
radargram. We used this relation ship to invert the saturated hydraulic
conductivity for constant and falling head infiltrations. We present our method
on synthetic examples and on two experiments carried out on sand soil. We
further discuss on the uncertainties on the retrieved saturated hydraulic
conductivity computed by our algorithm from the van Genuchten parameters.",1306.1627v1
2013-06-14,Gluon saturation scale from the KGBJS equation,"The CCFM equation and its extended form with a quadratic term (KGBJS
equation) are solved with fixed and running coupling constant. The solution of
the KGBJS equation is compared to gluon densities resulting from the CCFM and
BK equations. As the saturation scale $Q_s$ now becomes available as a function
of the hard scale $p$ we observe that low values of $p$ impede its growth with
$\frac 1 x$. Also, at values much larger than partons transversal momentum the
saturation effects become independent on the hard scale what we call liberation
of saturation scale. We also introduce the hard-scale-related saturation scale
$P_s$ and investigate its energy dependence. We observe that the new scale as a
function of $x$ decreases starting from the value of transversal momentum of
gluon.",1306.3369v1
2013-12-11,Density of Saturated Nuclear Matter at Large $N_{c}$ and Heavy Quark Mass Limits,"We exhibit the existence of stable, saturated nuclear matter in the large
$N_{c}$ and heavy quark mass limits of QCD. In this limit, baryons (with the
same spin flavor structure) interact at leading order in $N_{c}$ via a
repulsive interaction due to the Pauli exclusion principle and at subleading
order in $1/N_c$ via the exchange of glueballs. Assuming that the lightest
glueball is a scalar, which implies that the subleading baryon interaction is
attractive, we find that nuclear matter saturates since the subleading
attractive interaction is longer ranged than the leading order repulsive one.
We find that the saturated matter is in the form of a crystal with either a
face-centered cubic or a hexagonal-close-packed symmetry with baryon densities
of $\mathcal{O}((\, \tilde{\alpha}_{s} m_q (\ln
(N_{c}m_{q}\Lambda_{\textrm{QCD}}^{-1}))^{-1})^3 )$. Remarkably, the leading
order expression for the density of saturated nuclear matter is independent of
the lighest glueball mass and scalar-glueball-baryon coupling in the extreme
large $N_{c}$ limit or heavy quark limit (or both), which we define precisely
in this work.",1312.3339v1
2014-02-02,High intensity study of THz detectors based on field effect transistors,"Terahertz power dependence of the photoresponse of field effect transistors,
operating at frequencies from 0.1 to 3 THz for incident radiation power density
up to 100 kW/cm^2 was studied for Si metal-oxide-semiconductor field-effect
transistors and InGaAs high electron mobility transistors. The photoresponse
increased linearly with increasing radiation power up to kW/cm^2 range. The
saturation of the photoresponse was observed for all investigated field effect
transistors for intensities above several kW/cm^2. The observed signal
saturation is explained by drain photocurrent saturation similar to saturation
in direct currents output characteristics. The theoretical model of terahertz
field effect transistor photoresponse at high intensity was developed. The
model explains quantitatively experimental data both in linear and nonlinear
(saturation) range. Our results show that dynamic range of field effect
transistors is very high and can extend over more than six orderd of magnitudes
of power densities (from 0.5 mW/cm^2 to 5 kW/cm^2).",1402.0259v1
2014-07-15,Transverse Spin and Classical Gluon Fields: Combining Two Perspectives on Hadronic Structure,"In recent decades, the spin and transverse momentum of quarks and gluons were
found to play integral roles in the structure of the nucleon. Simultaneously,
the onset of gluon saturation in hadrons and nuclei at high energies was
predicted to result in a new state of matter dominated by classical gluon
fields. Understanding both of these contributions to hadronic structure is
essential for current and future collider phenomenology. In this Dissertation,
we study the combined effects of transverse spin and gluon saturation using the
Glauber-Gribov-Mueller / McLerran-Venugopalan model of a heavy nucleus in the
quasi-classical approximation. We investigate the use of a
transversely-polarized projectile as a probe of the saturated gluon fields in
the nucleus, finding that the transverse spin asymmetry of produced particles
couples to the component of the gluon fields which is antisymmetric under both
time reversal and charge conjugation. We also analyze the effects of saturation
on the transverse spin asymmetry (Sivers function) of quarks within the wave
function of the nucleus, finding that gluon saturation preferentially generates
the asymmetry through the orbital angular momentum of the nucleons, together
with nuclear shadowing.",1407.4047v1
2014-09-18,The Saturation Number for the length of Degree Monotone Paths,"A degree monotone path in a graph $G$ is a path $P$ such that the sequence of
degrees of the vertices in the order in which they appear on $P$ is monotonic.
The length of the longest degree monotone path in $G$ is denoted by $mp(G)$.
This parameter, inspired by the well-known Erdos-Szekeres theorem, has been
studied by the authors in two earlier papers. Here we consider a saturation
problem for the parameter $mp(G)$. We call $G$ saturated if, for every edge $e$
added to $G$, $mp(G+e) >mp(G)$, and we define $h(n,k)$ to be the least possible
number of edges in a saturated graph $G$ on $n$ vertices with $mp(G) < k$,
while $mp(G+e) \geq k$ for every new edge $e$.
  We obtain linear lower and upper bounds for $h(n,k)$, we determine exactly
the values of $h(n,k)$ for $k=3$ and $4$, and we present constructions of
saturated graphs.",1409.5213v1
2014-11-10,Smoothing of Limit Linear Series of Rank One on Saturated Metrized Complexes of Algebraic Curves,"We investigate the smoothing problem of limit linear series of rank one on an
enrichment of the notions of nodal curves and metrized complexes called
saturated metrized complexes. We give a finitely verifiable full criterion for
smoothability of a limit linear series of rank one on saturared metrized
complexes, characterize the space of all such smoothings, and extend the
criterion to metrized complexes. As applications, we prove that all limit
linear series of rank one are smoothable on saturated metrized complexes
corresponding to curves of compact-type, and prove an analogue for saturated
metrized complexes of a theorem of Harris and Mumford on the characterization
of nodal curves contained in a given gonality stratum. In addition, we give a
full combinatorial criterion for smoothable limit linear series of rank one on
saturated metrized complexes corresponding to nodal curves whose dual graphs
are made of separate loops.",1411.2325v4
2015-01-13,Classical Gluon Production Amplitude for Nucleus-Nucleus Collisions: First Saturation Correction in the Projectile,"We calculate the classical single-gluon production amplitude in
nucleus-nucleus collisions including the first saturation correction in one of
the nuclei (the projectile) while keeping multiple-rescattering (saturation)
corrections to all orders in the other nucleus (the target). In our
approximation only two nucleons interact in the projectile nucleus: the
single-gluon production amplitude we calculate is order-g^3 and is
leading-order in the atomic number of the projectile, while resumming all
order-one saturation corrections in the target nucleus. Our result is the first
step towards obtaining an analytic expression for the first projectile
saturation correction to the gluon production cross section in nucleus-nucleus
collisions.",1501.03106v1
2015-03-04,Saturated simple and 2-simple topological graphs with few edges,"A simple topological graph is a topological graph in which any two edges have
at most one common point, which is either their common endpoint or a proper
crossing. More generally, in a k-simple topological graph, every pair of edges
has at most k common points of this kind. We construct saturated simple and
2-simple graphs with few edges. These are k-simple graphs in which no further
edge can be added. We improve the previous upper bounds of Kyn\v{c}l, Pach,
Radoi\v{c}i\'c, and T\'oth and show that there are saturated simple graphs on n
vertices with only 7n edges and saturated 2-simple graphs on n vertices with
14.5n edges. As a consequence, 14.5n edges is also a new upper bound for
k-simple graphs (considering all values of k). We also construct saturated
simple and 2-simple graphs that have some vertices with low degree.",1503.01386v2
2015-08-12,Black phosphorus as saturable absorber for the Q-switched Er:ZBLAN fiber laser at 2.8 μm,"Black phosphorus, a newly emerged two-dimensional material, has attracted
wide attention as novel photonic material. Here, multi-layer black phosphorus
is successfully fabricated by liquid phase exfoliation method. By employing
black phosphorus as saturable absorber, we demonstrate a passively Q-switched
Er-doped ZBLAN fiber laser at the wavelength of 2.8 {\mu}m. The modulation
depth and saturation fluence of the black phosphorus saturable absorber are
measured to be 15% and 9 {\mu}J/cm2, respectively. The Q-switched fiber laser
delivers a maximum average power of 485 mW with corresponding pulse energy of
7.7 {\mu}J and pulse width of 1.18 {\mu}s at repetition rate of 63 kHz. To the
best of our knowledge, this is the first time to demonstrate that black
phosphorus can realize Q-switching of 2.8-{\mu}m fiber laser. Our research
results show that black phosphorus is a promising saturable absorber for
mid-infrared pulsed lasers.",1508.02850v1
2015-08-19,Multilayer black phosphorus as broadband saturable absorber for pulsed lasers from 1 to 2.7 μm wavelength,"It attracts wide interest to seek universe saturable absorber covering
wavelengths from near infrared to mid-infrared band. Multilayer black
phosphorus, with variable direct bandgap (0.3-2 eV) depending on the layer
number, becomes a good alternative as a universe saturable absorber for pulsed
lasers. In this contribution, we first experimentally demonstrated broadband
saturable absorption of multilayer black phosphorus from 1 {\mu}m to 2.7 {\mu}m
wavelength. With the as-fabricated black phosphorus nanoflakes as saturable
absorber, stable Q-switching operation of bulk lasers at 1.03 {\mu}m, 1.93
{\mu}m, 2.72 {\mu}m were realized, respectively. In contrast with large-bandgap
semiconducting transition metal dichalcogenides, such as MoS2, MoSe2,
multilayer black phosphorus shows particular advantage at the long wavelength
regime thanks to its narrow direct bandgap. This work will open promising
optoelectronic applications of black phosphorus in mid-infrared spectral region
and further demonstrate that BP may fill the gap of between zero-bandgap
graphene and large-bandgap TMDs.",1508.04510v1
2016-05-20,Theory of graphene saturable absorption,"Saturable absorption is a non-perturbative nonlinear optical phenomenon that
plays a pivotal role in the generation of ultrafast light pulses. Here we show
that this effect emerges in graphene at unprecedentedly low light intensities,
thus opening avenues to new nonlinear physics and applications in optical
technology. Specifically, we theoretically investigate saturable absorption in
extended graphene by developing a non-perturbative single-particle approach,
describing conduction-electron dynamics in the atomically-thin material using
the two-dimensional Dirac equation for massless Dirac fermions, which is recast
in the form of generalized Bloch equations. By solving the electron dynamics
non-perturbatively, we account for both interband and intraband contributions
to the intensity-dependent saturated conductivity and conclude that the former
dominates regardless of the intrinsic doping state of the material. The results
are in excellent agreement with atomistic quantum-mechanical simulations
including higher-band effects. Additionally, we find that the modulation depth
of saturable absorption in graphene can be electrically manipulated through an
externally applied gate voltage. Our results are relevant for the development
of graphene-based optoelectronic devices, as well as for applications in
mode-locking and random lasers.",1605.06499v1
2016-07-11,Saturation of the f-mode instability in neutron stars: II. Applications and results,"We present the first results on the saturation of the f-mode instability in
neutron stars, due to nonlinear mode coupling. Emission of gravitational waves
drives the f-mode (fundamental mode) unstable in fast-rotating, newborn neutron
stars. The initial growth phase of the mode is followed by its saturation,
because of energy leaking to other modes of the star. The saturation point
determines the strain of the generated gravitational-wave signal, which can
then be used to extract information about the neutron star equation of state.
The parent (unstable) mode couples via parametric resonances with pairs of
daughter modes, with the triplets' evolution exhibiting a rich variety of
behaviors. We study both supernova- and merger-derived neutron stars, simply
modeled as polytropes in a Newtonian context, and show that the parent may
couple to many different daughter pairs during the star's evolution through the
instability window, with the saturation amplitude changing by orders of
magnitude.",1607.03059v1
2016-07-11,Nonlinear Stabilization of High-Energy and Ultrashort Pulses in Passively Modelocked Lasers with Fast Saturable Absorption,"The two most commonly used models for passively modelocked lasers with fast
saturable absorbers are the Haus modelocking equation (HME) and the
cubic-quintic modelocking equation (CQME). The HME corresponds to a special
limit of the CQME in which only a cubic nonlinearity in the fast saturable
absorber is kept in the model. Here, we use singular perturbation theory to
demonstrate that the CQME has a stable high-energy solution for an arbitrarily
small but non-zero quintic contribution to the fast saturable absorber. As a
consequence, we find that the CQME predicts the existence of stable modelocked
pulses when the cubic nonlinearity is orders of magnitude larger than the value
at which the HME predicts that modelocked pulses become unstable. This
intrinsically larger stability range is consistent with experiments. Our
results suggest a possible path to obtain high-energy and ultrashort pulses by
fine tuning the higher-order nonlinear terms in the fast saturable absorber.",1607.03162v1
2016-09-21,Saturating Splines and Feature Selection,"We extend the adaptive regression spline model by incorporating saturation,
the natural requirement that a function extend as a constant outside a certain
range. We fit saturating splines to data using a convex optimization problem
over a space of measures, which we solve using an efficient algorithm based on
the conditional gradient method. Unlike many existing approaches, our algorithm
solves the original infinite-dimensional (for splines of degree at least two)
optimization problem without pre-specified knot locations. We then adapt our
algorithm to fit generalized additive models with saturating splines as
coordinate functions and show that the saturation requirement allows our model
to simultaneously perform feature selection and nonlinear function fitting.
Finally, we briefly sketch how the method can be extended to higher order
splines and to different requirements on the extension outside the data range.",1609.06764v3
2016-11-02,Optimal Heavy-Traffic Queue Length Scaling in an Incompletely Saturated Switch,"We consider an input queued switch operating under the MaxWeight scheduling
algorithm. This system is interesting to study because it is a model for
Internet routers and data center networks. Recently, it was shown that the
MaxWeight algorithm has optimal heavy-traffic queue length scaling when all
ports are uniformly saturated. Here we consider the case when an arbitrary
number of ports are saturated (which we call the incompletely saturated case),
and each port is allowed to saturate at a different rate. We use a recently
developed drift technique to show that the heavy-traffic queue length under the
MaxWeight scheduling algorithm has optimal scaling with respect to the switch
size even in these cases.",1611.00745v1
2017-06-27,Effect of saturable nonlinearity on cw stability in passively mode-locked lasers with fast saturable absorbers,"The self-starting dynamics of a model for passively mode-locked lasers with
saturable absorber, in which the optical amplifier has a saturable
nonlinearity, is examined. The basic assumption is that the laser will operate
in the mode-locked regime when the continuous-wave regime becomes unstable.
Within the framework of the modulational-instability analysis, a global map for
the laser self-starting criteria is constructed. According to this map, the
saturable nonlinearity enhances the input-field intensity required for laser
self-starting. Analytical expression of the zero modulation-frequency regime of
this threshold input field is derived, which turns out to be valid in the
normal as well as in the anomalous dispersion regime, where evidence of
self-starting is also given.",1706.09028v1
2017-06-30,Saturation of entropy production in quantum many-body systems,"Bridging the second law of thermodynamics and microscopic reversible dynamics
has been a longstanding problem in statistical physics. We here address this
problem on the basis of quantum many-body physics, and discuss how the entropy
production saturates in isolated quantum systems under unitary dynamics. First,
we rigorously prove the saturation of the entropy production in the long time
regime, where a total system can be in a pure state. Second, we discuss the
non-negativity of the entropy production at saturation, implying the second law
of thermodynamics. This is based on the eigenstate thermalization hypothesis
(ETH), which states that even a single energy eigenstate is thermal. We also
numerically demonstrate that the entropy production saturates at a non-negative
value even when the initial state of a heat bath is a single energy eigenstate.
Our results reveal fundamental properties of the entropy production in isolated
quantum systems at late times.",1706.10112v2
2017-08-12,Noisy Softmax: Improving the Generalization Ability of DCNN via Postponing the Early Softmax Saturation,"Over the past few years, softmax and SGD have become a commonly used
component and the default training strategy in CNN frameworks, respectively.
However, when optimizing CNNs with SGD, the saturation behavior behind softmax
always gives us an illusion of training well and then is omitted. In this
paper, we first emphasize that the early saturation behavior of softmax will
impede the exploration of SGD, which sometimes is a reason for model converging
at a bad local-minima, then propose Noisy Softmax to mitigating this early
saturation issue by injecting annealed noise in softmax during each iteration.
This operation based on noise injection aims at postponing the early saturation
and further bringing continuous gradients propagation so as to significantly
encourage SGD solver to be more exploratory and help to find a better
local-minima. This paper empirically verifies the superiority of the early
softmax desaturation, and our method indeed improves the generalization ability
of CNN model by regularization. We experimentally find that this early
desaturation helps optimization in many tasks, yielding state-of-the-art or
competitive results on several popular benchmark datasets.",1708.03769v1
2017-10-05,Current Saturation in Nonmetallic Field Emitters,"It has been known for a long time that traditional semiconductor (e.g.
intrinsic and doped Si and Ge or binary SiC and GaN) field emitters
significantly deviate from Fowler-Nordheim (FN) law and saturate when a large
current, on the order of microamperes or more, is attempted to be drawn from
them. Many experiments established that the field emission current from
carbonic materials, such as carbon nanotubes, amorphous carbon and
polycrystalline diamond films, also deviate from FN law and saturate. These
findings suggested that the saturation and departure from FN law is a broad and
general phenomenon that applies to the class of nonmetallic field emitters. In
this letter, we report a universal formula that describes the current
saturation effect in nonmetallic field emitters. The formula accounts for
material's bulk properties and field emitter geometry.",1710.03692v2
2017-12-01,On Edge-Colored Saturation Problems,"Let $\mathcal{C}$ be a family of edge-colored graphs. A $t$-edge colored
graph $G$ is $(\mathcal{C}, t)$-saturated if $G$ does not contain any graph in
$\mathcal{C}$ but the addition of any edge in any color in $[t]$ creates a copy
of some graph in $\mathcal{C}$. Similarly to classical saturation functions,
define $\mathrm{sat}_t(n, \mathcal{C})$ to be the minimum number of edges in a
$(\mathcal{C},t)$ saturated graph. Let $\mathcal{C}_r(H)$ be the family
consisting of every edge-colored copy of $H$ which uses exactly $r$ colors.
  In this paper we consider a variety of colored saturation problems. We
determine the order of magnitude for $\mathrm{sat}_t(n, \mathcal{C}_r(K_k))$
for all $r$, showing a sharp change in behavior when $r\geq \binom{k-1}{2}+2$.
A particular case of this theorem proves a conjecture of Barrus, Ferrara,
Vandenbussche, and Wenger. We determine $\mathrm{sat}_t(n, \mathcal{C}_2(K_3))$
exactly and determine the extremal graphs. Additionally, we document some
interesting irregularities in the colored saturation function.",1712.00163v1
2018-03-22,Precise algorithm to generate random sequential adsorption of hard polygons at saturation,"Random sequential adsorption (RSA) is a time-dependent packing process, in
which particles of certain shapes are randomly and sequentially placed into an
empty space without overlap. In the infinite-time limit, the density approaches
a ""saturation"" limit. Although this limit has attracted particular research
interest, the majority of past studies could only probe this limit by
extrapolation. We have previously found an algorithm to reach this limit using
finite computational time for spherical particles, and could thus determine the
saturation density of spheres with high accuracy. In this paper, we generalize
this algorithm to generate saturated RSA packings of two-dimensional polygons.
We also calculate the saturation density for regular polygons of three to ten
sides, and obtain results that are consistent with previous,
extrapolation-based studies.",1803.08348v2
2018-06-19,Optimal measurements for quantum multiparameter estimation with general states,"We generalize the approach by Braunstein and Caves [Phys. Rev. Lett. 72, 3439
(1994)] to quantum multi-parameter estimation with general states. We derive a
matrix bound of the classical Fisher information matrix due to each measurement
operator. The saturation of all these bounds results in the saturation of the
matrix Helstrom Cram\'er-Rao bound. Remarkably, the saturation of the matrix
bound is equivalent to the saturation of the scalar bound with respect to any
given positive definite weight matrix. Necessary and sufficient conditions are
obtained for the optimal measurements that give rise to the Helstrom
Cram\'er-Rao bound associated with a general quantum state. To saturate the
Helstrom bound with separable measurements or collective measurement entangling
only a small number of identical states, we find it is necessary for the
symmetric logarithmic derivatives to commute on the support of the state. As an
important application of our results, we construct several local optimal
measurements for the problem of estimating the three-dimensional separation of
two incoherent optical point sources.",1806.07337v3
2018-06-28,Band-edge quasiparticles from electron phonon coupling and resistivity saturation,"We address the problem of resistivity saturation observed in materials such
as the A-15 compounds. To do so, we calculate the resistivity for the
Hubbard-Holstein model in infinite spatial dimensions to second order in
on-site repulsion $U\leq D$ and to first order in (dimensionless)
electron-phonon coupling strength $\lambda\leq0.5$, where $D$ is the
half-bandwidth. We identify a unique mechanism to obtain two parallel quantum
conducting channels: low-energy and band-edge high-energy quasi-particles. We
identify the source of the hitherto unremarked high-energy quasi-particles as a
positive slope in the frequency-dependence of the real part of the electron
self-energy. In the presence of phonons, the self-energy grows linearly with
the temperature at high-$T$, causing the resistivity to saturate. As $U$ is
increased, the saturation temperature is pushed to higher values, offering a
mechanism by which electron-correlations destroy saturation.",1806.11227v2
2018-09-17,Saturating the quantum Cramér-Rao bound using LOCC,"The quantum Cram\'er-Rao bound (QCRB) provides an ultimate precision limit
allowed by quantum mechanics in parameter estimation. Given any quantum state
dependent on a single parameter, there is always a positive-operator valued
measurement (POVM) saturating the QCRB. However, the QCRB-saturating POVM
cannot always be implemented efficiently, especially in multipartite systems.
In this paper, we show that the POVM based on local operations and classical
communication (LOCC) is QCRB-saturating for arbitrary pure states or rank-two
mixed states with varying probability distributions over fixed eigenbasis.
Local measurements without classical communication, however, is not
QCRB-saturating in general.",1809.06017v3
2018-10-30,A note on saturation for Berge-G hypergraphs,"For a graph G, a hypergraph H is called Berge-G if there is a hypergraph H',
isomorphic to H, containing all vertices of G, so that e is contained in f(e)
for each edge e of G, where f is a bijection between E(G) and E(H'). The set of
all Berge-G hypergraphs is denoted B(G). A hypergraph H is called Berge-G
saturated if it does not contain any subhypergraph from B(G), but adding any
new hyperedge of size at least 2 to H creates such a subhypergraph. Each
Berge-G saturated hypergraph has at least |E(G)|-1 hyperedges. We show that for
each graph G that is not a certain star and for any n at least |V(G)|, there is
a Berge-G saturated hypergraph on n vertices and exactly |E(G)|-1 hyperedges.
This solves a problem of finding a saturated hypergraph on n vertices with the
smallest number of edges exactly.",1810.12734v1
2019-02-21,Low $x$ physics as an infinite twist (G)TMD framework: unravelling the origins of saturation,"We show how the formulations of low $x$ physics involving Wilson line
operators can be fully rewritten into an infinite twist TMD or GTMD framework,
respectively for inclusive and exclusive observables. This leads to a perfect
match between low $x$ physics and moderate $x$ formulations of QCD in terms of
GTMDs, TMDs, GPDs or PDFs. We derive the BFKL limit as a kinematic limit and
argue that beyond the Wandzura-Wilczek approximation, 3-body and 4-body
unintegrated PDFs should be taken into account even in this regime. Finally, we
analyze how saturation should be understood as three distinct effects:
saturation through non-linearities in the evolution equations at small $x$,
saturation through multiple interactions with slow gluons as TMD gauge links,
and saturation as the enhancement of genuine twist corrections.",1902.07930v1
2019-03-17,System Level Synthesis with State and Input Constraints,"This paper addresses the problem of designing distributed controllers with
state and input constraints in the System Level Synthesis (SLS) framework.
Using robust optimization, we show how state and actuation constraints can be
incorporated into the SLS structure. Moreover, we show that the dual variable
associated with the constraint has the same sparsity pattern as the SLS
parametrization, and therefore the computation distributes using a simple
primal-dual algorithm. We provide a stability analysis for SLS design with
input saturation under the Internal Model Control (IMC) framework. We show that
the closed-loop system with saturation is stable if the controller has a gain
less than one. In addition, a saturation compensation scheme that incorporates
the saturation information is proposed which improves the naive SLS design
under saturation.",1903.07174v3
2019-03-26,Bottom stresses of static packing of granular chains,"We experimentally measure the static stress at the bottom of a granular
chains column with a precise and reproducible method. The relation, between the
filling mass and the apparent mass converted from the bottom stress, is
investigated on various chain lengths. Our measurements reconfirm that the
scaling behavior of the stress saturation curves is in accord with the
theoretical expectation of the Janssen model. Additionally, the saturation mass
is displayed as a nonmonotonic function of the chain length, where a
distinguishing transition of the saturation mass is found at the persistence
length of the granular chain. We repeat the measurement with another measuring
methodology and a silo with different size, respectively, the position of the
peak maintains robust. In order to understand the transition of the saturation
mass, the friction coefficient and the volume fraction of granular chains are
also measured, from which Janssen parameter can be calculated. Finally, we
preliminarily measure the bottom stress for two distinct packing structures of
long chains, find the effect of the entanglements on the bottom stress, and
argue that the entanglements might be responsible for the transition of the
saturation mass.",1903.10664v1
2019-09-12,Ecological communities from random generalised Lotka-Volterra dynamics with non-linear feedback,"We investigate the outcome of generalised Lotka-Volterra dynamics of
ecological communities with random interaction coefficients and non-linear
feedback. We show in simulations that the saturation of non-linear feedback
stabilises the dynamics. This is confirmed in an analytical
generating-functional approach to generalised Lotka-Volterra equations with
piecewise linear saturating response. For such systems we are able to derive
self-consistent relations governing the stable fixed-point phase, and to carry
out a linear stability analysis to predict the onset of unstable behaviour. We
investigate in detail the combined effects of the mean, variance and
co-variance of the random interaction coefficients, and the saturation value of
the non-linear response. We find that stability and diversity increases with
the introduction of non-linear feedback, where decreasing the saturation value
has a similar effect to decreasing the co-variance. We also find co-operation
to no longer have a detrimental effect on stability with non-linear feedback,
and the order parameters mean abundance and diversity to be less dependent on
the symmetry of interactions with stronger saturation.",1909.05802v2
2019-10-19,A Novel Scheme of Digital Instantaneous Automatic Gain Control (DIAGC) for Pulse Radars,"Several schemes for gain control are used for preventing saturation of
receiver, and overloading of data processor, tracker or display in pulse
radars. The use of digital processing techniques open the door to a variety of
digital automatic gain control schemes for analyzing digitized return signals
and controlling receiver gain only at saturating clutter zones without
affecting the detection at other zones. In this paper, we present a novel
scheme of Digital Instantaneous Automatic Gain Control (DIAGC) which is based
on storing digitally the dwell based clutter returns and deriving the gain
control. The returns corresponding to the first two PRTs in a dwell are used to
analyze the presence of saturating clutter zones and the depth of saturation.
Third PRT onwards proper gain control is applied at the IF stage to prevent
saturation of the following stages. FPGA based scheme is used for digital data
processing, storing, threshold calculation and gain control generation. The
effect of DIAGC on pulse compression is also addressed in this paper.",1910.08861v1
2019-11-28,Saturated random packing built of arbitrary polygons under random sequential adsorption protocol,"Random packings and their properties are a popular and active field of
research. Numerical algorithms that can efficiently generate them are useful
tools in their study. This paper focuses on random packings produced according
to the random sequential adsorption (RSA) protocol. Developing the idea
presented in [G. Zhang, Phys. Rev. E {\bf 97}, 043311 (2018)], where saturated
random packings built of regular polygons were studied, we create an algorithm
that generates strictly saturated packings built of any polygons. Then, the
algorithm was used to determine the packing fractions for arbitrary triangles.
The highest mean packing density, $0.552814 \pm 0.000063$, was observed for
triangles of side lengths $0.63:1:1$. Additionally, microstructural properties
of such packings, kinetics of their growth as well as distributions of
saturated packing fractions and the number of RSA iterations needed to reach
saturation were analyzed.",1911.12626v1
2020-01-09,Black holes often saturate entanglement entropy the fastest,"There is a simple bound on how fast the entanglement entropy of a subregion
of a many-body quantum system can saturate in a quench: $t_\text{sat}\geq
R/v_B$, where $t_\text{sat}$ is the saturation time, $R$ the radius of the
largest inscribed sphere, and $v_B$ the butterfly velocity characterizing
operator growth. By combining analytic and numerical approaches, we show that
in systems with a holographic dual, the saturation time is equal to this lower
bound for a variety of differently shaped entangling surfaces, implying that
the dual black holes saturate the entanglement entropy as fast as possible.
This finding adds to the growing list of tasks that black holes are the fastest
at. We furthermore analyze the complete time evolution of entanglement entropy
for large regions with a variety of shapes, yielding more detailed information
about the process of thermalization in these systems.",2001.03172v3
2020-11-12,Hamiltonian Dynamics of Saturated Elongation in Amyloid Fiber Formation,"Elongation is a fundament process in amyloid fiber growth, which is normally
characterized by a linear relationship between the fiber elongation rate and
the monomer concentration. However, in high concentration regions, a sub-linear
dependence was often observed, which could be explained by a universal
saturation mechanism. In this paper, we modeled the saturated elongation
process through a Michaelis-Menten like mechanism, which is constituted by two
sub-steps -- unspecific association and dissociation of a monomer with the
fibril end, and subsequent conformational change of the associated monomer to
fit itself to the fibrillar structure. Typical saturation concentrations were
found to be $7-70\mu M$ for A$\beta$40, $\alpha$-synuclein and etc.
Furthermore, by using a novel Hamiltonian formulation, analytical solutions
valid for both weak and strong saturated conditions were constructed and
applied to the fibrillation kinetics of $\alpha$-synuclein and silk fibroin.",2011.06222v1
2021-07-06,Saturation-Aware Model Predictive Energy Management for Droop-Controlled Islanded Microgrids,"In this paper, we propose a minimax model predictive control (MPC)-based
energy management system that is robust with respect to uncertainties in
renewable infeed and load. The MPC formulation includes a model of low-level
droop control with saturation at the power and energy limits of the units.
Robust MPC-based energy management systems tend to under-utilize the renewable
energy sources to guarantee safe operation. In order to mitigate this effect,
we further consider droop control of renewable energy sources. For a microgrid
with droop-controlled units, we show that enhancing droop feedback with
saturation enlarges the space of feasible control actions. However, the
resulting controller requires to solve a mixed-integer problem with additional
variables and equations representing saturation. We derive a computationally
tractable formulation for this problem. Furthermore, we investigate the
performance gained by using droop with saturation, renewable droop and
combination of both in a case study.",2107.02719v1
2021-07-16,Maximising Precision in Saturation-Limited Absorption Measurements,"Quantum fluctuations in the intensity of an optical probe is noise which
limits measurement precision in absorption spectroscopy. Increased probe power
can offer greater precision, however, this strategy is often constrained by
sample saturation. Here, we analyse measurement precision for a generalised
absorption model in which we account for saturation and explore its effect on
both classical and quantum probe performance. We present a classical
probe-sample optimisation strategy to maximise precision and find that optimal
probe powers always fall within the saturation regime. We apply our
optimisation strategy to two examples, high-precision Doppler broadened
thermometry and an absorption spectroscopy measurement of Chlorophyll A. We
derive a limit on the maximum precision gained from using a non-classical probe
and find a strategy capable of saturating this bound. We evaluate
amplitude-squeezed light as a viable experimental probe state and find it
capable of providing precision that reaches to within > 85% of the ultimate
quantum limit with currently available technology.",2107.07888v1
2021-09-27,Mono-elemental saturable absorber in mode-locked fiber laser: A review,"Two-dimensional mono-elemental material is an excellent saturable absorber
candidate with low saturation intensity, large modulation depth, high
nonlinearities, and fast recovery time of excited carriers. Typically, these
mono-elemental material with two-dimensional structure possesses tunable
bandgap from metallic to semiconducting according to different number of
layers. The successful application of these materials as the saturable absorber
has exploited the development of mode-locked fiber lasers. Therefore, this
review is intended to provide an up-to-date information to the development of
mono-elemental saturable absorber for the advances in mode-locked fiber laser,
with emphasis on their material properties, synthesis process and material
characterization. Meanwhile, issues and challenges of the review research topic
will be highlighted and addressed with several concrete recommendations.",2109.13024v1
2021-10-25,Saturated $2$-planar drawings with few edges,"A drawing of a graph is $k$-plane if every edge contains at most $k$
crossings. A $k$-plane drawing is saturated if we cannot add any edge so that
the drawing remains $k$-plane. It is well-known that saturated $0$-plane
drawings, that is, maximal plane graphs, of $n$ vertices have exactly $3n-6$
edges. For $k>0$, the number of edges of saturated $n$-vertex $k$-plane graphs
can take many different values. In this note, we establish some bounds on the
minimum number of edges of saturated $2$-plane graphs under different
conditions. If two edges can cross at most once, then such a graph has at least
$n-1$ edges. If two edges can cross many times, then we show the tight bound of
$\lfloor2n/3\rfloor$ for the number of edges.",2110.12781v3
2021-12-22,An Alternate Policy Gradient Estimator for Softmax Policies,"Policy gradient (PG) estimators are ineffective in dealing with softmax
policies that are sub-optimally saturated, which refers to the situation when
the policy concentrates its probability mass on sub-optimal actions.
Sub-optimal policy saturation may arise from bad policy initialization or
sudden changes in the environment that occur after the policy has already
converged. Current softmax PG estimators require a large number of updates to
overcome policy saturation, which causes low sample efficiency and poor
adaptability to new situations. To mitigate this problem, we propose a novel PG
estimator for softmax policies that utilizes the bias in the critic estimate
and the noise present in the reward signal to escape the saturated regions of
the policy parameter space. Our theoretical analysis and experiments, conducted
on bandits and various reinforcement learning environments, show that this new
estimator is significantly more robust to policy saturation.",2112.11622v2
2021-12-24,A semi-bijective algorithm for saturated extended 2-regular simple stacks,"Combinatorics of biopolymer structures, especially enumeration of various RNA
secondary structures and protein contact maps, is of significant interest for
communities of both combinatorics and computational biology. However, most of
the previous combinatorial enumeration results for these structures are
presented in terms of generating functions, and few are explicit formulas. This
paper is mainly concerned with finding explicit enumeration formulas for a
particular class of biologically relevant structures, say, saturated 2-regular
simple stacks, whose configuration is related to protein folds in the 2D
honeycomb lattice. We establish a semi-bijective algorithm that converts
saturated 2-regular simple stacks into forests of small trees, which produces a
uniform formula for saturated extended 2-regular simple stacks with any of the
six primary component types. Summarizing the six different primary component
types, we obtain a bivariate explicit formula for saturated extended 2-regular
simple stacks with $n$ vertices and $k$ arcs. As consequences, the uniform
formula can be reduced to Clote's results on $k$-saturated 2-regular simple
stacks and the optimal 2-regular simple stacks, and Guo et al.'s result on the
optimal extended 2-regular simple stacks.",2112.13087v2
2022-01-25,Exclusive processes in $ep$ collisions at the EIC and LHeC: A closer look on the predictions of saturation models,"The exclusive production of vector mesons and photons in $ep$ collisions is
investigated considering three phenomenological saturation models based on
distinct assumptions for the treatment of the dipole - hadron scattering
amplitude. The latest high precision HERA data for the reduced and vector meson
cross sections are used to update the saturation model proposed by Marquet -
Peschanski - Soyez (MPS), which predicts that the saturation model is dependent
of the squared momentum transfer $t$. The MPS predictions for the photon
virtuality, energy and $t$ - dependencies of the exclusive $\rho$, $J/\Psi$ and
DVCS cross sections are presented and a detailed comparison with the results
derived using the impact parameter saturation models is performed. Our results
indicate that a future experimental analysis of the $t$ - distribution
$d\sigma/dt$ for exclusive processes in the kinematical range that will covered
by the EIC and LHeC, considering the distinct photon polarizations and large
values of $t$, will be able to discriminate between the distinct approaches for
the QCD dynamics at high energies.",2201.10499v1
2022-03-17,Neutron star mass formula with nuclear saturation parameters,"We derive the empirical formulas for the neutron star mass and gravitational
redshift as a function of the central density and specific combination of the
nuclear saturation parameters, which are applicable to the stellar models
constructed with the central density up to threefold nuclear saturation
density. Combining the both empirical formulas, one also estimates the neutron
star radius. In practice, we find that the neutron star mass (radius) can be
estimated within $\sim 10\%$ (a few percent) accuracy by comparing the mass and
radius evaluated with our empirical formulas to those determined with the
specific equation of state. Since our empirical formulas directly connect the
neutron star mass and radius to the nuclear saturation parameters, one can
discuss the neutron star properties with the specific values of nuclear
saturation parameters constrained via nuclear experiments.",2203.09004v1
2022-06-08,Wavelike nature of the vertical shear instability in global protoplanetary disks,"The vertical shear instability (VSI) is a robust phenomenon in irradiated
protoplanetary disks (PPDs). The majority of previous numerical simulations
have focused on the turbulent properties of its saturated state. However, the
saturation of the VSI manifests as large-scale coherent radially travelling
inertial waves. In this paper, we study inertial-wave-disk interactions and
their impact on VSI saturation. Inertial-wave linear theory is developed and
applied to a representative global 2D simulation using the Athena++ code. It is
found that the VSI saturates by separating the disk into several radial wave
zones roughly demarcated by corotation resonances (turning points); this
structure also manifests in modest radial variations in the vertical turbulence
strength. Future numerical work should employ large radial domains to
accommodate this radial structure of the VSI, while concurrently adopting
sufficiently fine resolutions to resolve the parametric instability that
attacks the saturated VSI inertial waves.",2206.03840v2
2022-08-10,Saturation-based Boolean conjunctive query answering and rewriting for the guarded quantification fragments,"Query answering is an important problem in AI, database and knowledge
representation. In this paper, we develop saturation-based Boolean conjunctive
query answering and rewriting procedures for the guarded, the loosely guarded
and the clique-guarded fragments. Our query answering procedure improves
existing resolution-based decision procedures for the guarded and the loosely
guarded fragments and this procedure solves Boolean conjunctive query answering
problems for the guarded, the loosely guarded and the clique-guarded fragments.
Based on this query answering procedure, we also introduce a novel
saturation-based query rewriting procedure for these guarded fragments. Unlike
mainstream query answering and rewriting methods, our procedures derive a
compact and reusable saturation, namely a closure of formulas, to handle the
challenge of querying for distributed datasets. This paper lays the theoretical
foundations for the first automated deduction decision procedures for Boolean
conjunctive query answering and the first saturation-based Boolean conjunctive
query rewriting in the guarded, the loosely guarded and the clique-guarded
fragments.",2208.05365v2
2022-08-19,The saturation of exponents and the asymptotic fourth state of turbulence,"A recent discovery about the inertial range of homogeneous and isotropic
turbulence is the saturation of the scaling exponents $\zeta_n$ for large $n$,
defined via structure functions of order $n$ as $S_{n}(r)=\overline{(\delta_r
u)^{n}}=A(n)r^{\zeta_{n}}$. We focus on longitudinal structure functions for
$\delta_r u$ between two positions that are $r$ apart in the same direction. In
a previous paper (Phys.\ Rev.\ Fluids 6, 104604, 2021), we developed a theory
for $\zeta_n$, which agrees with measurements for all $n$ for which reliable
data are available, and shows saturation for large $n$. Here, we derive
expressions for the probability density functions of $\delta_r u$ for four
different states of turbulence, including the asymptotic fourth state
corresponding to the saturation of exponents for large $n$. This saturation
means that the scale separation is violated in favor of a strongly-coupled
quasi-ordered flow structures, which take the form of long and thin (worm-like)
structures of length $L$ and thickness $l=O(L/Re)$.",2208.09561v1
2022-10-17,"Decoherence, Entanglement Negativity and Circuit Complexity for Open Quantum System","In this paper, we compare the saturation time scales for complexity, linear
entropy and entanglement negativity for two open quantum systems. Our first
model is a coupled harmonic oscillator, where we treat one of the oscillators
as the bath. The second one is a type of Caldeira Leggett model, where we
consider a one-dimensional free scalar field as the bath. Using these open
quantum systems, we discovered that both the complexity of purification and the
complexity from operator state mapping is always saturated for a completely
mixed state. More explicitly, the saturation time scale for both types of
complexity is smaller than the saturation time scale for linear entropy. On top
of this, we found that the saturation time scale for linear entropy and
entanglement negativity is of the same order for the Caldeira Leggett model.",2210.09268v1
2022-11-20,The saturation number of monomial ideals,"Let $S=\mathbb{K}[x_1,\ldots, x_n]$ be the polynomial ring over a field
$\mathbb{K}$ and $\mathfrak{m}= (x_1, \ldots, x_n)$ be the irredundant maximal
ideal of $S$. For an ideal $I \subset S$, let $\mathrm{sat}(I)$ be the minimum
number $k$ for which $I \colon \mathfrak{m}^k = I \colon \mathfrak{m}^{k+1}$.
In this paper, we compute the saturation number of irreducible monomial ideals
and their powers. We apply this result to find the saturation number of the
ordinary powers and symbolic powers of some families of monomial ideals in
terms of the saturation number of irreducible components appearing in an
irreducible decomposition of these ideals. Moreover, we give an explicit
formula for the saturation number of monomial ideals in two variables.",2211.10982v2
2023-03-11,Rate-Distortion Optimization With Alternative References For UGC Video Compression,"User generated content (UGC) refers to videos that are uploaded by users and
shared over the Internet. UGC may have low quality due to noise and previous
compression. When re-encoding UGC for streaming or downloading, a traditional
video coding pipeline will perform rate-distortion (RD) optimization to choose
coding parameters. However, in the UGC video coding case, since the input is
not pristine, quality ``saturation'' (or even degradation) can be observed,
i.e., increased bitrate only leads to improved representation of coding
artifacts and noise present in the UGC input. In this paper, we study the
saturation problem in UGC compression, where the goal is to identify and avoid
during encoding, the coding parameters and rates that lead to quality
saturation. We proposed a geometric criterion for saturation detection that
works with rate-distortion optimization, and only requires a few frames from
the UGC video. In addition, we show how to combine the proposed saturation
detection method with existing video coding systems that implement
rate-distortion optimization for efficient compression of UGC videos.",2303.06254v1
2023-05-01,Inference of relative permeability curves in reservoir rocks with ensemble Kalman method,"Multiphase flows through reservoir rocks are a universal and complex
phenomenon. Relative permeability is one of the primary determinants in
reservoir performance calculations. Accurate estimation of the relative
permeability is crucial for reservoir management and future production. In this
paper, we propose inferring relative permeability curves from sparse saturation
data with an ensemble Kalman method. We represent these curves through a series
of positive increments of relative permeability at specified saturation values,
which guarantees monotonicity within, and boundedness between, 0 and 1. The
proposed method is validated by the inference performances in two synthetic
benchmarks designed by SPE and a field-scale model developed by Equinor that
includes certain real-field features. The results indicate that the relative
permeability curves can be accurately estimated within the saturation intervals
having available observations and appropriately extrapolated to the remaining
saturations by virtue of the embedded constraints. The predicted well responses
are comparable to the ground truths, even though they are not included as the
observation. The study demonstrates the feasibility of using ensemble Kalman
method to infer relative permeability curves from saturation data, which can
aid in the predictions of multiphase flow and reservoir production.",2305.01029v1
2023-07-10,Saturation and multifractality of Lagrangian and Eulerian scaling exponents in 3D isotropic turbulence,"Inertial range scaling exponents for both Lagrangian and Eulerian structure
functions are obtained from direct numerical simulations of isotropic
turbulence in triply periodic domains at Taylor-scale Reynolds number up to
1300. We reaffirm that transverse Eulerian scaling exponents saturate at
$\approx 2.1$ for moment orders $p \ge 10$, significantly differing from the
longitudinal exponents (which are predicted to saturate at $\approx 7.3$ for $p
\ge 30$ from a recent theory). The Lagrangian scaling exponents likewise
saturate at $\approx 2$ for $p \ge 8$. The saturation of Lagrangian exponents
and transverse Eulerian exponents is related by the same multifractal spectrum
by utilizing the well known frozen hypothesis to relate spatial and temporal
scales. Furthermore, this spectrum is different from the known spectra for
Eulerian longitudinal exponents, suggesting that that Lagrangian intermittency
is characterized solely by transverse Eulerian intermittency. We discuss
possible implication of this outlook when extending multifractal predictions to
the dissipation range, especially for Lagrangian acceleration.",2307.04846v2
2023-11-28,On the saturation spectrum of the unions of disjoint cycles,"Let $G$ be a graph and $\mathcal{H}$ be a family of graphs. We say $G$ is
$\mathcal{H}$-saturated if $G$ does not contain a copy of $H$ with
$H\in\mathcal{H}$, but the addition of any edge $e\notin E(G)$ creates at least
one copy of some $H\in\mathcal{H}$ within $G+e$. The saturation number of
$\mathcal{H}$ is the minimum size of an $\mathcal{H}$-saturated graph on $n$
vertices, and the saturation spectrum of $\mathcal{H}$ is the set of all
possible sizes of an $\mathcal{H}$-saturated graph on $n$ vertices. Let
$k\mathcal{C}_{\ge 3}$ be the family of the unions of $k$ vertex-disjoint
cycles. In this note, we completely determine the saturation number and the
saturation spectrum of $k\mathcal{C}_{\ge 3}$ for $k=2$ and give some results
for $k\ge 3$.",2311.16899v1
2023-12-15,Intersection-saturated groups without free subgroups,"A group $G$ is said to be intersection-saturated if for every strictly
positive integer $n$ and every map $c\colon \mathcal{P}(\{1,\dots,
n\})\setminus \emptyset \rightarrow \{0,1\}$, one can find subgroups
$H_1,\dots, H_n\leq G$ such that for every non-empty subset $I\subseteq
\{1,\dots, n\}$, the intersection $\bigcap_{i\in I}H_i$ is finitely generated
if and only if $c(I)=0$. We obtain a new criterion for a group to be
intersection-saturated based on the existence of arbitrarily high direct powers
of a subgroup admitting an automorphism with a non-finitely generated set of
fixed points. We use this criterion to find new examples of
intersection-saturated groups, including Thompson's groups and the Grigorchuk
group. In particular, this proves the existence of finitely presented
intersection-saturated groups without non-abelian free subgroups, thus
answering a question of Delgado, Roy and Ventura.",2312.09954v2
2023-12-25,Saturation of nuclear matter in the relativistic Brueckner Hatree-Fock approach with a leading order covariant chiral nuclear force,"Nuclear saturation is a crucial feature in nuclear physics that plays a
fundamental role in understanding various nuclear phenomena, ranging from
properties of finite nuclei to those of neutron stars. However, a proper
description of nuclear saturation is highly nontrivial in modern
nonrelativistic~\textit{ab initio}~studies because of the elusive three-body
forces. In this letter, we calculate the equation of state for nuclear matter
in the relativistic Brueckner-Hartree-Fock framework with the leading order
covariant chiral nuclear force. We show that a simultaneous description of the
nucleon-nucleon scattering data and the saturation of the symmetric nuclear
matter can be achieved. In this regard, the relativistic effects nicely explain
the saturation of nuclear matter. As a result, the present study provides a new
perspective on one of the most salient features in nuclear physics.",2312.15672v1
2024-02-05,Declipping and the recovery of vectors from saturated measurements,"A frame $(x_j)_{j\in J}$ for a Hilbert space $H$ allows for a linear and
stable reconstruction of any vector $x\in H$ from the linear measurements
$(\langle x,x_j\rangle)_{j\in J}$. However, there are many situations where
some information in the frame coefficients is lost. In applications where one
is using sensors with a fixed dynamic range, any measurement above that range
is registered as the maximum, and any measurement below that range is
registered as the minimum. Depending on the context, recovering a vector from
such measurements is called either declipping or saturation recovery. We
initiate a frame theoretic approach to saturation recovery in a similar way to
what [BCE06] did for phase retrieval. We characterize when saturation recovery
is possible, show optimal frames for use with saturation recovery correspond to
minimal multi-fold packings in projective space, and prove that the classical
frame algorithm may be adapted to this non-linear problem to provide a
reconstruction algorithm.",2402.03237v1
2024-02-17,A lower bound on the saturation number and a strengthening for triangle-free graphs,"The saturation number $\operatorname{sat}(n, H)$ of a graph $H$ and positive
integer $n$ is the minimum size of an $n$-vertex graph which does not contain a
subgraph isomorphic to $H$ but to which the addition of any edge creates such a
subgraph. Erd\H{o}s, Hajnal, and Moon first studied saturation numbers of
complete graphs, and Cameron and Puleo introduced a general lower bound on
$\operatorname{sat}(n,H)$. In this paper, we present another lower bound on
$\operatorname{sat}(n, H)$ with a strengthening when $H$ is triangle-free.
Demonstrating its effectiveness, we determine the saturation numbers of
diameter-$3$ trees up to an additive constant; these are double stars $S_{s,t}$
on $s + t$ vertices whose centers have degrees $s$ and $t$. Faudree, Faudree,
Gould, and Jacobson determined that $\operatorname{sat}(n, S_{t,t}) = (t-1)n/2
+ O(1)$. We show that $\operatorname{sat}(n,S_{s,t}) = (st+s)n/(2t+4) + O(1)$
when $s < t$. We also determine lower and upper bounds on the saturation
numbers of certain diameter-$4$ caterpillars.",2402.11387v2
2024-03-08,Fault Recovery and Transient Stability of Grid-Forming Converters Equipped with Current Saturation,"When grid-forming (GFM) inverter-based resources (IBRs) experience large grid
disturbances (e.g., short-circuit faults), the current limiter may be triggered
and GFM IBRs enter the current saturation mode, inducing nonlinear dynamical
behaviors and imposing great challenges to the post-disturbance transient angle
stability. This paper presents a systematic study to reveal the fault recovery
behaviors of a GFM IBR and identify the risk of instability. The impact of the
angle of the magnitude-saturated current on the post-fault recovery and
transient stability is also investigated. The selection of the angle of
magnitude-saturated current significantly influences the post-fault behaviors
while a few additional dynamical conditions that have a substantial impact are
also identified. It is found that the system may follow multiple post-fault
recovery trajectories depending on those conditions: 1) Convergence to the
normal stable equilibrium point (SEP), 2) convergence to the saturated stable
equilibrium point (SSEP), and 3) divergence (instability). To examine the
models' accuracy, several cases are simulated.",2403.05236v1
2024-01-07,Haze Removal via Regional Saturation-Value Translation and Soft Segmentation,"This paper proposes a single image dehazing prior, called Regional
Saturation-Value Translation (RSVT), to tackle the color distortion problems
caused by conventional dehazing approaches in bright regions. The RSVT prior is
developed based on two key observations regarding the relationship between hazy
and haze-free points in the HSV color space. First, the hue component shows
marginal variation between corresponding hazy and haze-free points,
consolidating a hypothesis that the pixel value variability induced by haze
primarily occurs in the saturation and value spaces. Second, in the 2D
saturation-value coordinate system, most lines passing through hazy-clean point
pairs are likely to intersect near the atmospheric light coordinates.
Accordingly, haze removal for the bright regions can be performed by properly
translating saturation-value coordinates. In addition, an effective soft
segmentation method based on a morphological min-max channel is introduced. By
combining the soft segmentation mask with the RSVT prior, a comprehensive
single image dehazing framework is devised. Experimental results on various
synthetic and realistic hazy image datasets demonstrate that the proposed
scheme successfully addresses color distortion issues and restores visually
appealing images. The code of this work is available at
https://github.com/tranleanh/rsvt.",2403.12054v1
1996-09-19,Nonequilibrium Critical Dynamics of a Three Species Monomer-Monomer Model,"We study a three species monomer-monomer catalytic surface reaction model
with a reactive steady state bordered by three equivalent unreactive phases
where the surface is saturated with one species. The transition from the
reactive to a saturated phase shows directed percolation critical behavior.
Each pair of these reactive-saturated phase boundaries join at a bicritical
point where the universal behavior is in the even branching annihilating random
walk class. We find the crossover exponent from bicritical to critical behavior
and a new exponent associated with the bicritical interface dynamics.",9609191v1
1997-02-06,Boltzmann Collision Kernels and Velocity Saturation in Semiconductors,"For different models of the electron-phonon interaction, the asymptotic
behaviour of the moments of the stationary homogeneous solution of the linear
Boltzmann equation is determined in the limit of a high external field. For
Hilbert-Schmidt kernels of a finite rank, a result recently proven for kernels
of rank one is found generally valid; as a consequence velocity saturation is
excluded for these collision models. For a class of singular collision kernels
in contrast, velocity saturation is generally obtained.",9702062v1
1998-08-18,Resistivity saturation revisited: results from a dynamical mean field theory,"We use the dynamical mean field method to study the high-temperature
resistivity of electrons strongly coupled to phonons. The results reproduce the
qualtiative behavior of the temperature and disorder dependence of the
resistivity of the 'A-15' materials, which is commonly described in terms of
saturation, but imply that the resistivity does not saturate. Rather, a change
in temperature dependence occurs when the scattering becomes strong enough to
cause a breakdown of the Migdal approximation.",9808188v2
1999-03-18,Force fluctuations in granular materials,"Force fluctuations in granular materials are investigated. A continuum
equation is derived starting from a discrete model proposed in the literature.
The influence of boundary conditions is investigated. For periodic boundary
conditions the average weight is found to increase linearly with depth while it
saturates to a constant value for absorbing boundary conditions, which models
the existence of walls. The scale dependencies of the saturation weight, the
saturation depth and the average squared fluctuations are obtained. The
analytical results are compared with previous works and with numerical
simulations in one dimension.",9903282v2
2001-08-21,Metals with Small Electron Mean-Free Path: Saturation versus Escalation of Resistivity,"Resistivity of metals is commonly observed either to 'escalate' beyond the
Ioffe-Regel limit (mean free path l equal to lattice constant a) or to
'saturate' at this point. It is argued that neither behavior is
well-understood, and that 'escalation' is not necessarily more mysterious than
'saturation.'",0108343v2
2002-08-14,Can one hear the shape of a saturation patch?,"The theory of the acoustics of patchy-saturation in porous media is used to
analyze experimental data on wave velocity and attenuation in partially water
saturated limestones. It is demonstrated that the theory can be used to deduce
the value of V/A, the ratio of the volume to area of the water patch, and l_f,
the Poisson size of the water patch. One can ``hear'' the shape of a patch if
the properties of the rock and the measurement frequencies are such as to
satisfy the specific requirements for the validity of the theory.",0208290v1
2002-10-17,Size effects on generation recombination noise,"We carry out an analytical theory of generation-recombination noise for a two
level resistor model which goes beyond those presently available by including
the effects of both space charge fluctuations and diffusion current. Finite
size effects are found responsible for the saturation of the low frequency
current spectral density at high enough applied voltages. The saturation
behaviour is controlled essentially by the correlations coming from the long
range Coulomb interaction. It is suggested that the saturation of the current
fluctuations for high voltage bias constitutes a general feature of
generation-recombination noise.",0210365v1
2003-07-17,Photoassociation of a Quantum Degenerate Gas,"We have measured the intensity dependent rate and frequency shift of a
photoassociation transition in a quantum degenerate gas of 7Li. The rate
increases linearly with photoassociation laser intensity for low intensities,
whereas saturation is observed at higher intensities. The measured rates and
shifts agree reasonably well with theory within the estimated systematic
uncertainties. Several theoretically predicted saturation mechanisms are
discussed, but a theory in which saturation arises because of quantum
mechanical unitarity agrees well with the data.",0307447v1
2005-07-01,Pattern reconstruction and sequence processing in feed-forward layered neural networks near saturation,"The dynamics and the stationary states for the competition between pattern
reconstruction and asymmetric sequence processing are studied here in an
exactly solvable feed-forward layered neural network model of binary units and
patterns near saturation. Earlier work by Coolen and Sherrington on a parallel
dynamics far from saturation is extended here to account for finite stochastic
noise due to a Hebbian and a sequential learning rule. Phase diagrams are
obtained with stationary states and quasi-periodic non-stationary solutions.
The relevant dependence of these diagrams and of the quasi-periodic solutions
on the stochastic noise and on initial inputs for the overlaps is explicitly
discussed.",0507039v1
2004-06-17,Abstract Canonical Inference,"An abstract framework of canonical inference is used to explore how different
proof orderings induce different variants of saturation and completeness.
Notions like completion, paramodulation, saturation, redundancy elimination,
and rewrite-system reduction are connected to proof orderings. Fairness of
deductive mechanisms is defined in terms of proof orderings, distinguishing
between (ordinary) ""fairness,"" which yields completeness, and ""uniform
fairness,"" which yields saturation.",0406030v2
2001-01-23,Asymptotic Freedom in Curvature-Satured Gravity,"For a spatially flat Friedmann model with line element $ds^2=a^2 [
da^2/B(a)-dx^2-dy^2-dz^2 ] $, the 00-component of the Einstein field equation
reads $8\pi G T_{00}=3/a^2$ containing no derivative. For a nonlinear
Lagrangian ${\cal L}(R)$, we obtain a second--order differential equation for
$B$ instead of the expected fourth-order equation. We discuss this equation for
the curvature-saturated model proposed by Kleinert and Schmidt. Finally, we
argue that asymptotic freedom $G_{{\rm eff}}^{-1}\to 0$ is fulfilled in
curvature-saturated gravity.",0101090v2
1996-08-07,Unitarity and Saturation in the Dipole Formulation,"This talk reviews briefly some of the main results of the small-x dipole
formulation with regards to unitarity corrections. It illustrates the
correspondence between unitarity and saturation corrections in the dipole
approach and multiple t-channel pomeron exchange in the traditional BFKL view,
and discusses how one can estimate and understand the effects of saturation.",9608250v1
1999-03-15,Saturation in Diffractive Deep Inelastic Scattering,"We successfully describe the HERA-data on diffractive deep inelastic
scattering using a saturation model which has been applied in our earlier
analysis of the inclusive $ep$-scattering data. No further parameters are
needed. Saturation already turned out to be essential in describing the
transition from large to small values of $Q^2$ in inclusive scattering. It is
even more important for diffractive processes and naturally leads to a constant
ratio of the diffractive versus inclusive cross sections. We present an
extensive discussion of our results as well as detailed comparison with data.",9903358v2
2001-01-24,Nonlinear evolution and saturation for heavy nuclei in DIS,"The nonlinear evolution equation for the scattering amplitude of colour
dipole off the heavy nucleus is solved in the double logarithmic approximation.
It is found that if the initial parton density in a nucleus is smaller then
some critical value, then the scattering amplitude is a function of one scaling
variable inside the saturation region, whereas if it is greater then the
critical value, then the scaling behaviour breaks down. Dependence of the
saturation scale on the number of nucleons is discussed as well.",0101275v2
2001-09-03,Saturation and geometric scaling in DIS at small x,"We present various aspects of the saturation model which provides good
description of inclusive and diffractive DIS at small x. The model uses parton
saturation ideas to take into account unitarity requirements. A new scaling
predicted by the model in the small x domain is successfully confronted with
the data.",0109010v2
2001-11-19,Initial state of the QGP from perturbative QCD + saturation,"The production of the initial state of the QGP in very high-energy $AA$
collisions is discussed within the framework of perturbative QCD and
saturation. The next-to-leading order computation of the transverse energy of
minijets is reviewed. Saturation of parton production, conjectured to occur at
a dynamically determinable perturbative scale, leads to estimates of the
initial densities. The final state multiplicities are predicted by assuming an
isentropic hydrodynamical further evolution. Comparison with RHIC data is
shown.",0111223v1
2002-05-15,The Energy Dependence of the Saturation Momentum,"We study BFKL evolution and, in particular, the energy dependence of the
saturation momentum in the presence of saturation boundaries limiting the
region of linear BFKL evolution. In the case of fixed coupling evolution we
confirm the previously found exponential term in $Q_s(Y)$ and determine the
prefactor $Y$ and $\alpha$ dependences. In the running coupling case we find
$Y^{1/6}$ corrections to the $Y^{1/2}$exponential behavior previously known.
Geometrical scaling of the scattering amplitude is valid in a wide-range of
momenta for fixed coupling evolution and in a more restricted region for
running coupling evolution.",0205167v1
2002-05-30,Gluon Saturation and S-Matrix Unitarity,"The impact parameter dependent gluon distribution of the proton xG(x,Q^2,b)
is investigated in a loop-loop correlation model that respects the S-matrix
unitarity condition in impact parameter space. We find low-x saturation of
G(x,Q^2,b) as a manifestation of S-matrix unitarity. The integrated gluon
distribution xG(x,Q^2) does not saturate because of the growth of the effective
proton radius with decreasing x.",0205343v1
2002-06-14,Saturation model for 2-gamma physics,"We introduce a saturation model for photon-photon interactions, based on a
QCD dipole picture of high energy scattering. The two-dipole cross-section is
assumed to satisfy the saturation property. This pomeron-like contribution is
supplemented with QPM and non-pomeron reggeon contributions. The model gives a
very good description of the data on the gamma-gamma total cross-section, on
the photon structure function F_2^gamma(x,Q^2) at low x and on the
gamma*-gamma* cross-section.",0206130v1
2002-08-01,Saturation and Pion Production in Proton-Nucleus Collisions,"We study the effects of gluon saturation on pion production in high energy
proton-nucleus collisions using the color glass condensate model. At high
p_perp, we show that the p_perp-distribution of gluons behaves as ~
1/(p_perp^7) in accordance with both conventional perturbative QCD calculations
and experiment. Fragmentation of gluons into pions leads to a rapidity
dependent depletion of pions relative to the conventional perturbative QCD
predictions. We argue that these clear and systematic differences provide a
signal for the onset of gluon saturation which is accessible in upcoming
experiments.",0208007v1
2002-10-16,The Colour Glass Condensate,"I review the physical and mathematical foundations for the theoretical
description of the hadron wavefunction at small $x$ as a Colour Glass
Condensate. In this context, I discuss the phenomenon of gluon saturation and
some of its remarkable consequences: a new ``geometric scaling'' for $F_2$,
which has been recently identified at HERA, and the unitarization of the
hadronic cross-sections at high energy. I show that by combining saturation and
confinement one obtains cross-sections which saturate the Froissart bound.",0210236v2
2002-12-09,A Gaussian effective theory for gluon saturation,"We construct a Gaussian approximation to the effective theory for the Colour
Glass Condensate which describes correctly the gluon distribution both in the
low density regime at high transverse momenta (above the saturation scale
$Q_s$), and in the high density regime below $Q_s$, and provides a simple
interpolation between these two regimes. At high momenta, the effective theory
reproduces the BFKL dynamics, while at low momenta, it exhibits gluon
saturation and, related to it, colour neutrality over the short distance scale
$1/Q_s \ll 1/\Lambda_{QCD}$. Gauge--invariant quantities computed within this
approximation are automatically infrared finite.",0212123v1
2003-05-05,Nuclear Heavy Quark Photoproduction in a Saturation Model,"We calculate the nuclear inclusive and diffractive cross sections for heavy
quark photoproduction within a phenomenological saturation approach. The
nuclear cross section is obtained by the extension of the saturation model
through Glauber-Gribov formalism. We predict large nuclear heavy quark cross
section at LHC energies.",0305045v2
2003-12-01,Diffractive photon dissociation in the saturation regime from the Good and Walker picture,"Combining the QCD dipole model with the Good and Walker picture, we formulate
diffractive dissociation of a photon of virtuality Q^2 off a hadronic target,
in the kinematical regime in which Q is close to the saturation scale and much
smaller than the invariant mass of the diffracted system. We show how the
obtained formula compares to the HERA data and discuss what can be learnt from
such a phenomenology. In particular, we argue that diffractive observables in
these kinematics provide useful pieces of information on the saturation regime
of QCD.",0312022v1
2004-07-01,QCD Saturation Equations including Dipole-Dipole Correlation,"We derive two coupled non-linear evolution equations corresponding to the
truncation of the Balitsky infinite hierarchy of saturation equations after
inclusion of dipole-dipole correlations, i.e. one step beyond the
Balitsky-Kovchegov (BK) equation. We exhibit an exact solution for maximal
correlation which still satisfies the same asymptotic geometric scaling as BK
but with the S-matrix going to 1/2 (instead of 0) in the full saturation
region.",0407007v2
2004-07-22,Low x saturation at HERA ?,"We compare the predictions of two distinct dipole models for inclusive and
exclusive diffractive processes. While only one of these dipole models contains
perturbative saturation dynamics, we show that the predictions of both models
are fully consistent with the available HERA data, indicating no compelling
evidence for saturation at present HERA energies.",0407261v1
2004-10-01,Parton Saturation Approach in Heavy Quark Production at High Energies,"The high parton density regime of the Quantum Chromodynamics (QCD), where the
physics of parton saturation is expected to be dominant, is briefly discussed.
Some phenomenological aspects of saturation are described, mainly focusing on
possible signatures of the non-linear QCD dynamics in the heavy quark
production in electron-proton/nucleus collisions. Implications of these effects
in the heavy quark production in ultraperipheral heavy-ion collisions are also
presented.",0410012v2
2004-11-25,Gluon Saturation in the Colour Dipole Model?,"We use data on the deep inelastic structure function F_2 in order to
constrain the cross-section for scattering a colour dipole off a proton. The
data seem to prefer parameterisations which include saturation effects. That is
they indicate that the strong rise with energy of the dipole cross-section,
which holds for small dipoles, pertains only for r < r_s(x) where r_s(x)
decreases monotonically as x decreases. Subsequent predicitions for the
diffractive structure function F_2^{D(3)} also hint at saturation, although the
data are not really sufficiently accurate.",0411337v1
2004-12-06,Nonlinear evolution equations in QCD,"The following lectures are an introduction to the phenomena of partonic
saturation and nonlinear evolution equations in Quantum Chromodynamics. After a
short introduction to the linear evolution, the problems of unitarity bound and
parton saturation are discussed. The nonlinear Balitsky-Kovchegov evolution
equation in the high energy limit is introduced, and the progress towards the
understanding of the properties of its solution is reviewed. We discuss the
concepts of the saturation scale, geometrical scaling and the lack of the
infrared diffusion. Finally, we give a brief summary of current theoretical
developments which extend beyond the Balitsky-Kovchegov equation.",0412084v1
2005-10-13,Particle production and saturation at HERA,"Perturbative QCD in the high-energy limit describes the evolution of
scattering amplitudes with increasing energy towards and into the so-called
saturation regime. Comparisons of the predictions with experimental data for a
number of observables led to significant progress and understanding. We discuss
the case of particle-production cross-sections measured at HERA and argue that
these measurements have the potential to provide evidence for the saturation
regime of QCD.",0510176v1
2007-01-22,Has saturation physics been observed in deuteron-gold collisions at RHIC?,"We have addressed the question of whether saturation (CGC) has been observed
in deuteron-gold collisions at RHIC. We have made a detailed analysis of the
Cronin peak characteristic of the nuclear modification factor measured for d-Au
collisions at mid-rapidity. The Cronin peak which is obtained around $p_t\simeq
3$ GeV may be reproduced at the proper height only by boosting the saturation
momentum by a huge non-perturbative additional component. At forward rapidity,
we get a quantitative agreement with data, reproducing hadron production
spectra and the $R_{CP}$ ratio using a recently developed description of the
small-x physics.",0701184v1
2007-01-29,Reflective scattering from unitarity saturation,"Proceeding from optical analogy we propose a new physical interpretation of
unitarity saturation leading to antishadowing as a reflective scattering. This
interpretation of antishadowing is related to the non-perturbative aspects of
strong interactions and follows from the specific property of the unitarity
saturation when elastic $S$-matrix $S(s,b)|_{b=0}\to -1$ at $s\to \infty$. The
analogy with Berry phase and experimental consequences of the proposed
interpretation as reflective scattering at the LHC and in the cosmic rays
studies are discussed.",0701241v4
1997-12-23,The entropy of near-extreme N=2 black holes,"We give an explicit form of the classical entropy for four-dimensional static
near-BPS-saturated black holes of generic N=2 superstring vacua. The expression
is obtained by determining the leading corrections in the non-extremality
parameter to the corresponding BPS-saturated black hole solutions. These
classical results are quantitatively compared with the microscopic leading
order corrections to the microscopic result of Maldacena Strominger and Witten
for N=2 BPS-saturated black holes.",9712221v1
2000-05-12,Abrikosov String in N=2 Supersymmetric QED,"We study the Abrikosov-Nielsen-Olesen string in N=2 supersymmetric QED with
N=2-preserving superpotential, in which case the Abrikosov string is found to
be 1/2-BPS saturated. Adding a quadratic small perturbation in the
superpotential breaks N=2 supersymmetry to N=1 supersymmetry. Then the
Abrikosov string is no longer BPS saturated. The difference between the string
tensions for the non-BPS and BPS saturated situation is found to be negative to
the first order of the perturbation parameter.",0005119v2
1998-10-30,The saturation conjecture (after A. Knutson and T. Tao),"In this exposition we give a simple and complete treatment of A. Knutson and
T. Tao's recent proof (http://front.math.ucdavis.edu/math.RT/9807160) of the
saturation conjecture, which asserts that the Littlewood-Richardson semigroup
is saturated. The main tool is Knutson and Tao's hive model for
Berenstein-Zelevinsky polytopes. In an appendix of W. Fulton it is shown that
the hive model is equivalent to the original Littlewood-Richardson rule.",9810180v1
2002-04-17,Generators and representability of functors in commutative and noncommutative geometry,"We give a sufficient condition for an Ext-finite triangulated category to be
saturated. Saturatedness means that every contravariant cohomological functor
of finite type to vector spaces is representable. The condition consists in
existence of a strong generator. We prove that the bounded derived categories
of coherent sheaves on smooth proper commutative and noncommutative varieties
have strong generators, hence saturated. In contrast the similar category for a
smooth compact analytic surface with no curves is not saturated.",0204218v2
2002-08-13,Geometric Proofs of Horn and Saturation Conjectures,"We provide a geometric proof of the Schubert calculus interpretation of the
Horn conjecture, and show how the saturation conjecture follows from it. The
geometric proof gives a strengthening of Horn and saturation conjectures. We
also establish transversality theorems for Schubert calculus in non-zero
characteristic.
  Some parts of the version posted in Nov 2002 (concerning explicit invariants
constructed from Schubert calculus) have been removed from this version. They
have appeared separately in IMRN 2004, no. 69, pages 3709--3721 "" Invariant
theory of GL(n) and Intersection theory of Grassmannians""",0208107v3
2003-03-06,Paracategories I: internal parategories and saturated partial algebras,"Based on the monoid classifier, we give an alternative axiomatization of
Freyd's paracategories, which can be interpreted in any bicategory of partial
maps. Assuming furthermore a free-monoid monad T in our ambient category, and
coequalisers satisfying some exactness conditions, we give an abstract envelope
construction, putting paramonoids (and paracategories) in the more general
context of partial algebras. We introduce for the latter the crucial notion of
saturation, which characterises those partial algebras which are isomorphic to
the ones obtained from their enveloping algebras. We also set up a
factorisation system for partial algebras, via epimorphisms and (monic) Kleene
morphisms and relate the latter to saturation.",0303083v1
2006-01-10,Steady free convection in a bounded and saturated porous medium,"In this paper we are interested with a strongly coupled system of partial
differential equations that modelizes free convection in a two-dimensional
bounded domain filled with a fluid saturated porous medium. This model is
inspired by the one of free convection near a semi-infinite impermeable
vertical flat plate embedded in a fluid saturated porous medium. We establish
the existence and uniqueness of the solution for small data in some unusual
spaces.",0601219v1
2000-08-18,Periodically kicked turbulence,"Periodically kicked turbulence is theoretically analyzed within a mean field
theory. For large enough kicking strength A and kicking frequency f the
Reynolds number grows exponentially and then runs into some saturation. The
saturation level can be calculated analytically; different regimes can be
observed. For large enough Re we find the saturation level to be proportional
to A*f, but intermittency can modify this scaling law. We suggest an
experimental realization of periodically kicked turbulence to study the
different regimes we theoretically predict and thus to better understand the
effect of forcing on fully developed turbulence.",0008025v1
2006-02-20,Spatial synchronization and extinction of species under external forcing,"We study the interplay between synchronization and extinction of a species.
Using a general model we show that under a common external forcing, the species
with a quadratic saturation term in the population dynamics first undergoes
spatial synchronization and then extinction, thereby avoiding the rescue
effect. This is because the saturation term reduces the synchronization time
scale but not the extinction time scale. The effect can be observed even when
the external forcing acts only on some locations provided there is a
synchronizing term in the dynamics. Absence of the quadratic saturation term
can help the species to avoid extinction.",0602041v1
1999-01-08,Saturation of product's exoticity in compound nuclear reactions and its role in the production of new n-deficient nuclei with radioactive projectiles,"Representation in terms of a new parameter, exoticity, a measure of
n-deficiency or p-richness, clearly brings out the saturation tendency of the
product's maximum exoticity in a compound nuclear reaction as the compound
nucleus is made more and more exotic using radioactive projectile (RIBs). The
effect of this saturation on the production of new proton-rich species with
RIBs over a wide Z-range has been discussed.",9901015v1
1999-06-15,Effective field theory for nuclear matter,"We apply the relativistic chiral Lagrangian to the nuclear equation of state.
An effective chiral power expansion scheme, which is constructed to work around
nuclear saturation density, is presented. The leading and subleading terms are
evaluated and are shown to provide an equation of state with excellent
saturation properties. Our saturation mechanism is found to probe details of
the nuclear pion dynamics.",9906045v1
2001-02-15,Nuclear Matter EOS with a Three-body Force,"The effect of a microscopic three-body force on the saturation properties of
nuclear matter is studied within the Brueckner-Hartree-Fock approach. The
calculations show a decisive improvement of the saturation density along with
an overall agreement with the empirical saturation point. With the three-body
force the symmetry energy turns more rapidly increasing with density, which
allows for the direct URCA process to occur in $\beta$-stable neutron star
matter. The influence of the three-body force on the nuclear mean field does
not diminish the role of the ground state correlations.",0102038v1
2004-12-26,"Cronin momentum behavior in saturation model for $p+A$, $d+A$, $A+A$ collisions","In this paper we consider Cronin momentum behaviour for $p+A$, $d+A$ and
$A+A$ collisions in saturation model. Our analysis shows that Cronin momentum
behavior at different rapidities and energies, can be related with scaling law
using simple dimensional consideration. Using exact numerical solution of
Balitsky-Kovchegov equation we show that although this dependence is slightly
different for McLerran-Venugopalan and Balitsky-Kovchegov definition of gluon
distribution function in simple model in this case dependencies is almost the
same (i.e ratio of Cronin momentum calculated using these gluon distribution
functions is big constant). This can be used to experimentally distinguish this
two variant of gluon distribution function definition in saturation model and
choose the right one.",0412098v1
2004-11-25,220 fs Er-Yb:glass laser mode-locked by a broadband low-loss Si/Ge saturable absorber,"We demonstrate femtosecond performance of an ultra-broadband
high-index-contrast saturable Bragg reflector consisting of a
silicon/silicon-dioxide/germanium structure that is fully compatible with CMOS
processing. This device offers a reflectivity bandwidth of over 700 nm and
sub-picosecond recovery time of the saturable loss. It is used to achieve
mode-locking of an Er-Yb:glass laser centered at 1540 nm, generating 220 fs
pulses, with the broadest output spectrum to date.",0411232v1
2005-08-01,Phase diagram of a ternary mixture of cholesterol and saturated and unsaturated lipids calculated from a microscopic model,"We employ a molecular model to study a ternary mixture of saturated lipid,
with tails of sixteen carbons, a mono unsaturated lipid with tails of eighteen
carbons, and cholesterol. The model, solved within mean-field theory, produces
several forms of phase diagrams depending upon the relative strengths of
interactions, but only one that shows the coexistence of two liquid phases
observed in experiment. The lipids in the phase rich in cholesterol are more
ordered than those in the other. The binary cholesterol, saturated lipid system
also exhibits liquid, liquid coexistence.",0508011v1
2005-12-16,Saturable absorption and 'slow light',"Quantitative evaluation of some recent 'slow light' experiments based on
coherent population oscillations (CPO) shows that they can be more simply
interpreted as saturable absorption phenomena. Therefore they do not provide an
unambiguous demonstration of 'slow light'. Indeed a limiting condition on the
spectral bandwidth is not generally satisfied, such that the requirements for
burning a narrow spectral hole in the homogeneously broadened absorption line
are not met. Some definitive tests of 'slow light' phenomena are suggested,
derived from analysis of phase shift and pulse delay for a saturable absorber",0512149v2
2002-10-09,Fidelity Decay Saturation Level for Initial Eigenstates,"We show that the fidelity decay between an initial eigenstate state evolved
under a unitary chaotic operator and the same eigenstate evolved under a
perturbed operator saturates well before the 1/N limit, where $N$ is the size
of the Hilbert space, expected for a generic initial state. We provide a
theoretical argument and numerical evidence that, for intermediate perturbation
strengths, the saturation level depends quadratically on the perturbation
strength.",0210063v1
2006-03-10,Saturation of fidelity in the atom-optics kicked rotor,"We show that the quantum fidelity is accessible to cold atom experiments for
a large class of evolutions in periodical potentials, properly taking into
account the experimental initial conditions of the atomic ensemble. We prove
analytically that, at the fundamental quantum resonances of the atom-optics
kicked rotor, the fidelity saturates at a constant, time-independent value
after a small number of kicks. The latter saturation arises from the bulk of
the atomic ensemble, whilst for the resonantly accelerated atoms the fidelity
is predicted to decay slowly according to a power law.",0603095v1
2007-05-01,Non-abelian plasma instabilities for strong anisotropy,"We numerically investigate gauge field instabilities in anisotropic SU(2)
plasmas using weak field initial conditions. The growth of unstable modes is
stopped by non-abelian effects for moderate anisotropy. If we increase the
anisotropy the growth continues beyond the non-abelian saturation bound. We
find strong indications that the continued growth is not due to over-saturation
of infrared field modes, but instead due to very rapid growth of high momentum
modes which are not unstable in the weak field limit. The saturation amplitude
strongly depends on the initial conditions. For strong initial fields we do not
observe the sustained growth.",0705.0180v1
2008-03-05,Ultimate field-free molecular alignment by combined adiabatic-impulsive field design,"We show that a laser pulse designed as an adiabatic ramp followed by a kick
allows one to reach a perfect postpulse molecular alignment, free of
saturation. The mechanism is based on an optimized distribution of the energy
between a weakly efficient but non saturating adiabatic ramp and an efficient
but saturating impulsive field. Unprecedent degrees of alignment are predicted
using state-of-the-art pulse shaping techniques and non-destructive field
intensities. The scheme can be extended to reach high degrees of orientation of
polar molecules using designed half-cycle pulses.",0803.0711v1
2008-04-03,Polarization Saturation in Strained Ferroelectrics,"Using density-functional calculations we study the structure and polarization
response of tetragonal PbTiO3, BaTiO3 and SrTiO3 in a strain regime that is
previously overlooked. Different from common expectations, we find that the
polarizations in all three substances saturate at large strains, demonstrating
a universal phenomenon. The saturation is shown to originate from an unusual
and strong electron-ion correlation that leads to cancellation between
electronic and ionic polarizations. Our results shed new insight on the
polarization properties, and reveal the existence of a fundamental limit to the
strain-induced polarization enhancement.",0804.0630v1
2008-04-11,Running Coupling Effects in Small-x QCD,"We study effects of the running of the coupling in QCD at small Bjorken-x and
in particular the ones related to gluon saturation. After introducing the steps
taken to the derivation of the next to leading order nonlinear evolution
equation, we discuss the infrared sensitivity of the Pomeron intercept, the
energy dependence of the saturation momentum and the appearance of geometrical
scaling, and the dominance of the running coupling effects over the ones
introduced by loops of Pomerons.",0804.1918v1
2008-06-30,The dipole picture in DIS: saturation and heavy quarks,"We discuss the description of the proton structure function within the dipole
factorisation framework. We parametrise the forward dipole amplitude to account
for saturation as predicted by the small-x QCD evolution equations. Contrarily
to previous models, the saturation scale does not decrease when taking heavy
quarks into account. We show that the same dipole amplitude also allows to
reproduce diffractive data and exclusive vector meson production.",0807.0020v1
2008-09-02,Interaction Grammars,"Interaction Grammar (IG) is a grammatical formalism based on the notion of
polarity. Polarities express the resource sensitivity of natural languages by
modelling the distinction between saturated and unsaturated syntactic
structures. Syntactic composition is represented as a chemical reaction guided
by the saturation of polarities. It is expressed in a model-theoretic framework
where grammars are constraint systems using the notion of tree description and
parsing appears as a process of building tree description models satisfying
criteria of saturation and minimality.",0809.0494v1
2008-09-16,High energy scattering in the saturation regime including running coupling and rare fluctuation effects,"The analytic result for the $S$-matrix in the saturation regime including the
running coupling is obtained. To get this result we solve the Balitsky and
Kovchegov-Weigert evolution equations in the saturation regime, which include
running coupling corrections. We study also the effect of rare fluctuations on
top of the running coupling. We find that the rare fluctuations are less
important in the running coupling case as compared to the fixed coupling case.",0809.2666v1
2008-09-24,Dipole models and parton saturation in ep scattering,"In this contribution we briefly review the current status of the dipole
models and parton saturation on the basis of results presented at the HERA-LHC
workshops in the years 2006-2008. The problem of foundations of the dipole
models is addressed within the QCD formalism. Some limitations of the models
and open problems are pointed out. Furthermore, we review and compare the
currently used dipole models and summarise the applications to describe various
sets of HERA data. Finally we outline some of the theoretical approaches to the
problem of multiple scattering and saturation.",0809.4191v1
2008-11-21,Influence of higher-order harmonics on the saturation of the tearing mode,"The nonlinear saturation of the tearing mode is revisited in slab geometry by
taking into account higher-order harmonics in the outer solution. The general
formalism for tackling this problem in the case of a vanishing current gradient
at the resonant surface is derived. It is shown that, although the higher-order
harmonics lead to corrections in the final saturation equation, they are of
higher order in the perturbation parameter, which provides a formal proof that
the standard one-harmonic approach is asymptotically correct.",0811.3651v1
2008-12-09,Heavy ions and parton saturation from RHIC to LHC,"The phenomenology of gluon saturation at small parton momentum fraction,
Bjorken-x, in the proton and in the nucleus is introduced. The
experimentally-accessible kinematic domains at the nucleus-nucleus colliders
RHIC and LHC are discussed. Finally, the saturation hints emerging from
measurements at RHIC and the perspectives for LHC are described.",0812.1607v3
2008-12-22,Saturation effects in final states due to CCFM with absorptive boundary,"We apply the absorptive boundary prescription to include saturation effects
in CCFM evolution equation. We are in particular interested in saturation
effects in exclusive processes which can be studied using Monte Carlo event
generator CASCADE. We calculate cross section for three-jet production and
distribution of charged hadrons.",0812.4082v2
2009-05-15,"Multiple Interactions, Saturation, and Final States in pp Collisions and DIS","In high energy collisions saturation and multiple collisions are most easily
accounted for in transverse coordinate space, while analyses in momentum space
have been more suitable for calculating properties of exclusive final states.
In this talk I describe an extension of Mueller's dipole cascade model, which
attempts to combine the good features of both these descriptions. Besides
saturation it also includes effects of correlations and fluctuations, which
have been difficult to account for in previous approaches. The model reproduces
successfully total, elastic, and diffractive cross sections in pp collisions
and DIS, and a description of final states will be ready soon.",0905.2492v1
2009-05-31,Transport properties of graphene in the high-current limit,"We present a detailed study of the high-current transport properties of
graphene devices patterned in a four-point configuration. The current tends to
saturate as the voltage across graphene is increased but never reaches the
complete saturation as in metallic nanotubes. Measurements are compared to a
model based on the Boltzmann equation, which includes electron scattering
processes due to charged and neutral impurities, and graphene optical-phonons.
The saturation is incomplete because of the competition between disorder and
optical-phonon scattering.",0906.0188v1
2009-06-16,Hydrodynamic theory of transport in doped graphene,"We study non-linear dc transport in graphene using a hydrodynamic approach
and conclude that in clean samples the drift velocity saturates at a weakly
density-dependent value v_{sat} ~ 10^7 cm/s. We show that saturation results
from the interactions between graphene's Dirac quasi-particles and both
acoustic and optical phonons. Saturation is accompanied by substantial electron
heating and is not reached at realistic driving fields in moderately or
strongly disordered samples. We find that it is essential to account for
interactions among graphene's Dirac quasi-particles, which increase the linear
response resistivity at high temperatures or low densities.",0906.2992v1
2009-08-12,The complexity of classification problems for models of arithmetic,"We observe that the classification problem for countable models of arithmetic
is Borel complete. On the other hand, the classification problems for finitely
generated models of arithmetic and for recursively saturated models of
arithmetic are Borel; we investigate the precise complexity of each of these.
Finally, we show that the classification problem for pairs of recursively
saturated models and for automorphisms of a fixed recursively saturated model
are Borel complete.",0908.1718v2
2010-01-24,Measuring the saturation scale in nuclei,"The saturation momentum seeing in the nuclear infinite momentum frame is
directly related to transverse momentum broadening of partons propagating
through the medium in the nuclear rest frame. Calculation of broadening within
the color dipole approach including the effects of saturation in the nucleus,
gives rise to an equation which describes well data on broadening in Drell-Yan
reaction and heavy quarkonium production.",1001.4281v1
2010-04-21,Terahertz Response of Field-Effect Transistors in Saturation Regime,"We report on the broadband THz response of InGaAs/GaAs HEMTs operating at
1.63 THz and room temperature deep in the saturation regime. We demonstrate
that responses show linear increase with drain-to-source voltage (or drain bias
current) and reach very high values up to 170V/W. We also develop a
phenomenological theory valid both in the ohmic and in the saturation regimes.",1004.3740v1
2010-04-27,Stabilization of two-dimensional solitons in cubic-saturable nonlinear lattices,"We consider soliton dynamics and stability in a nonlinear lattice formed by
alternating domains with focusing cubic and saturable nonlinearities. We find
that in such lattices solitons centered on cubic domains may be stabilized even
in two-dimensional geometries, in spite of their intrinsic catastrophic
instability in the absence of the lattice. Solitons centered on saturable
domains are always unstable.",1004.4771v1
2010-05-31,Saturation of the Raman amplification by self-phase modulation in silicon nanowaveguides,"We experimentally show that the self-phase modulation of picosecond pump
pulses, induced by both the optical Kerr effect and free-carrier refraction,
has a detrimental effect on the maximum on-off Raman gain achievable in silicon
on insulator nanowaveguides, causing it to saturate. A simple calculation of
the Raman gain coefficient from the measured broadened output pump spectra
perfectly matches the saturated behavior of the amplified Raman signal observed
experimentally at different input pump powers.",1005.5599v1
2010-07-09,Fusion systems on small p-groups,"In this article we study several classes of `small' 2-groups: we complete the
classification, started in [Stancu, 2006], of all saturated fusion systems on
metacyclic p-groups for all primes p. We consider Suzuki 2-groups, and classify
all center-free saturated fusion systems on 2-groups of 2-rank 2. We end by
classifying all possible F-centric, F-radical subgroups in saturated fusion
systems on 2-groups of 2-rank 2.",1007.1639v1
2010-07-20,High-field Carrier Velocity and Current Saturation in Graphene Field-Effect Transistors,"We obtain the output characteristics of graphene field-effect transistors by
using the charge-control model for the current, based on the solution of the
Boltzmann equation in the field-dependent relaxation time approximation. Closed
expressions for the conductance, transconductance and saturation voltage are
derived. We found good agreement with the experimental data of Meric et al.
[1], without assuming a carrier density-dependent velocity saturation.",1007.3504v1
2010-09-07,Parton saturation at strong coupling from AdS/CFT,"I describe the parton picture at strong coupling emerging from the
gauge/gravity duality, with emphasis on the universality of the phenomenon of
parton saturation. I discuss several consequences of this picture for the
phenomenology of a strongly coupled quark-gluon plasma, which are potentially
relevant for heavy ion collisions at RHIC and LHC.",1009.1278v1
2010-09-21,Low scale saturation of Effective NN Interactions and their Symmetries,"The Skyrme force parameters can be uniquely determined by coarse graining the
NN interactions at a characteristic momentum scale. We show how exact Vlowk
potentials to second order in momenta are accurately and universally saturated
with physical NN scattering threshold parameters at CM momentum scales of about
Lambda=250 MeV for the S-waves and Lambda=100 MeV for the P-waves. The pattern
of Wigner and Serber symmetries unveiled previously is also saturated at these
scales.",1009.4161v2
2010-12-06,Dark solitons in mode-locked lasers,"Dark soliton formation in mode-locked lasers is investigated by means of a
power-energy saturation model which incorporates gain and filtering saturated
with energy, and loss saturated with power. It is found that general initial
conditions evolve into dark solitons under appropriate requirements also met in
the experimental observations. The resulting pulses are well approximated by
dark solitons of the unperturbed nonlinear Schr\""{o}dinger equation. Notably,
the same framework also describes bright pulses in anomalous and normally
dispersive lasers.",1012.1366v1
2011-01-26,Azimuthal correlations of forward di-hadrons in d+Au collisions suppressed by saturation,"RHIC experiments have recently measured the azimuthal correlation function of
forward di-hadrons. The data show a disappearance of the away-side peak in
central d+Au collisions, compared to p+p collisions, as was predicted by
saturation physics. Indeed, we argue that this effect, absent at mid-rapidity,
is a consequence of the small-x evolution into the saturation regime of the
Gold nucleus wave function. We show that the data are well described in the
Color Glass Condensate framework.",1101.5109v1
2011-01-31,Inclusive hadron distributions in p+p collisions from saturation models of HERA DIS data,"Dipole models based on various saturation scenarios provide reasonable fits
to small-x DIS inclusive, diffractive and exclusive data from HERA. Proton
un-integrated gluon distributions extracted from such fits are employed in a
$k_\bot$-factorization framework to calculate inclusive gluon distributions at
various energies. The n-particle multiplicity distribution predicted in the
Glasma flux tube approach shows good agreement with data over a wide range of
energies. Hadron inclusive transverse momentum distributions expressed in terms
of the saturation scale demonstrate universal behavior over a wider kinematic
range systematically with increasing center of mass energies.",1101.5922v1
2011-02-25,On the composition product of saturated fusion systems,"We say that a fusion system is the composition product of two subsystems if
every morphism can be factored as a morphism in one fusion system followed by a
morphism in the other. We establish a relationship between the characteristic
idempotent of a saturated fusion system that is the composition product of
saturated subsystems and the characteristic idempotents of the component
systems. Consequently we obtain a compatibility result for transfer through the
composition product and transfer through the component systems.",1102.5280v1
2011-06-27,Extended maximum concurrent flow problem with saturated capacity,"The present work studies a kind of Maximum Concurrent Flow Problem, called as
Extended Maximum Concurrent Flow Problem with Saturated Capacity. Our major
contributions are as follows: (A) Propose the definition of Extensive Maximum
Concurrent Flow Problem with Saturated Capacity and prove its solutions exist.
(B) Design a approximation algorithm to solve the problem. (C) Propose and
prove the complexity and the approximation measures of the algorithm we design.",1106.5421v2
2011-10-18,Algorithms for strongly stable ideals,"Strongly stable monomial ideals are important in algebraic geometry,
commutative algebra, and combinatorics. Prompted, for example, by combinatorial
approaches for studying Hilbert schemes and the existence of maximal total
Betti numbers among saturated ideals with a given Hilbert polynomial, in this
note we present three algorithms to produce all strongly stable ideals with
certain prescribed properties: the saturated strongly stable ideals with a
given Hilbert polynomial, the almost lexsegment ideals with a given Hilbert
polynomial, and the saturated strongly stable ideals with a given Hilbert
function. We also establish results for estimating the complexity of our
algorithms.",1110.4080v2
2011-10-23,On locally defined formations of soluble Lie and Leibniz algebras,"It is well-known that all saturated formations of finite soluble groups are
locally defined and, except for the trivial formation, have many different
local definitions. I show that for Lie and Leibniz algebras over a field of
characteristic 0, the formations of all nilpotent algebras and of all soluble
algebras are the only locally defined formations and that the latter has many
local definitions. Over a field of non-zero characteristic, a saturated
formation of soluble Lie algebras has at most one local definition but a
locally defined saturated formation of soluble Leibniz algebras other than that
of nilpotent algebras has more than one local definition.",1110.5009v1
2011-11-25,Low-loss flake-graphene saturable absorber mirror for laser mode-locking at sub-200-fs pulse duration,"Saturable absorbers are a key component for mode-locking femtosecond lasers.
Polymer films containing graphene flakes have recently been used in
transmission as laser mode-lockers, but suffer from high nonsaturable loss,
limiting their application in low-gain lasers. Here we present a saturable
absorber mirror based on a film of pure graphene flakes. The device is used to
mode lock an erbium-doped fiber laser, generating pulses with state-of-the-art,
sub-200-fs duration. The laser characteristic indicate that the film exhibits
low nonsaturable loss (13% per pass) and large absorption modulation depth (45%
of low-power absorption).",1111.6011v1
2012-01-02,Quantum uncertainty relation saturated by the eigenstates of the harmonic oscillator,"We re-derive the Schr\""{o}dinger-Robertson uncertainty principle for the
position and momentum of a quantum particle. Our derivation does not directly
employ commutation relations, but works by reduction to an eigenvalue problem
related to the harmonic oscillator, which can then be further exploited to find
a larger class of constrained uncertainty relations. We derive an uncertainty
relation under the constraint of a fixed degree of Gaussianity and prove that,
remarkably, it is saturated by all eigenstates of the harmonic oscillator. This
goes beyond the common knowledge that the (Gaussian) ground state of the
harmonic oscillator saturates the uncertainty relation.",1201.0453v2
2012-03-16,Nonlinear dynamics of beta induced Alfvén eigenmode driven by energetic particles,"Nonlinear saturation of beta induced Alfv\'en eigenmode, driven by slowing
down energetic particles via transit resonance, is investigated by the
nonlinear hybrid magnetohyrodynamic gyro-kinetic code (XHMGC). Saturation is
characterized by frequency chirping and symmetry breaking between co- and
counter-passing particles, which can be understood as the the evidence of
resonance-detuning. The scaling of the saturation amplitude with the growth
rate is also demonstrated to be consistent with radial resonance detuning due
to the radial non-uniformity and mode structure.",1203.3769v1
2012-09-07,Higher-order Kerr effect and harmonic cascading in gases,"The higher-order Kerr effect (HOKE) has been recently advocated to explain
measurements of the saturation of the nonlinear refractive index in gases. Here
we show that cascaded third-harmonic generation results in an effective fifth
order nonlinearity that is negative and significant. Higher-order harmonic
cascading will also occur from the HOKE, and the cascading contributions may
significantly modify the observed nonlinear index change. At lower wavelengths
cascading increases the HOKE saturation intensity, while for longer wavelengths
cascading will decrease the HOKE saturation intensity.",1209.1487v3
2013-01-14,Multipacting Analysis in Micro-pulse Electron Gun Design,"Modeling multipacting to steady state saturation is of interest in
determining the performance of micro-pulse electron gun. In this paper, a novel
method is proposed to calculate the multipacting resonance parameters for the
gun. This method works well, and the 2-D simulation results suggest that steady
state saturation can be achieved in the gun. After saturation the transition
from two-surface multipacting to single-surface multipacting is occurred, and
an extensive range of electrons emission time is a suggested way to avoid this
kind of transition.",1301.2854v1
2013-01-22,Saturation of gluon density and soft p-p collisions at LHC,"We calculate the unintegrated gluon distribution at low intrinsic transverse
momenta and its parameters are found from the best description of the SPS and
LHC data on the $pp$ collision in the soft kinematical region. It allows us to
study the saturation of the gluon density at low $Q^2$ more carefully and find
the saturation scale.",1301.5156v1
2013-03-15,Nuclear symmetry energy from the Fermi-energy difference in nuclei,"The neutron-proton Fermi-energy difference and the correlation to nucleon
separation energies for some magic nuclei are investigated with the Skyrme
energy density functionals and nuclear masses, with which the nuclear symmetry
energy at sub-saturation densities is constrained from 54 Skyrme parameter
sets. The extracted nuclear symmetry energy at sub-saturation density of 0.11
fm$^{-3}$ is 26.2 $\pm$ 1.0 MeV with 1.5 $\sigma$ uncertainty. By further
combining the neutron-skin thickness of 208Pb, ten Skyrme forces with slope
parameter of 28<L<65 are selected for the description of the symmetry energy
around saturation densities.",1303.3659v1
2013-04-03,Increased mode instability thresholds of fiber amplifiers by gain saturation,"We show by numerical modeling that saturation of the population inversion
reduces the stimulated thermal Rayleigh gain relative to the laser gain in
large mode area fiber amplifiers. We show how to exploit this effect to raise
mode instability thresholds by a substantial factor. We also demonstrate that
when suppression of stimulated Brillouin scattering and the population
saturation effect are both taken into account, counter-pumped amplifiers have
higher mode instability thresholds than co-pumped amplifiers for fully
Yb$^{3+}$ doped cores, and confined doping can further raise the thresholds.",1304.1064v1
2014-01-20,Gluon saturation and initial conditions for relativistic heavy ion collisions,"We present an overview of theoretical aspects of the phenomenon of gluon
saturation in high energy scattering in Quantum Chromo Dynamics. Then we review
the state-of-the-art of saturation-based phenomenological approaches to the
study and characterisation of the initial state of ultra-relativistic heavy ion
collisions performed at RHIC and the LHC. Our review focuses mostly in the
Color Glass Condensate effective theory, although we shall also discuss other
approaches in parallel.",1401.4866v1
2014-01-26,Hadron Multiplicities in p+p and p+Pb Collisions,"Experiments at the Large Hadron Collider (LHC) have measured multiplicity
distributions in p+p and p+Pb collisions at a new domain of collision energy.
Based on considering an energy-dependent broadening of the nucleon's density
distribution, charged hadron multiplicities are studied with the
phenomenological saturation model and the evolution equation dependent
saturation model. By assuming the saturation scale have a small dependence on
the 3-dimensional root mean square (rms) radius at different energy, the
theoretical results are in good agreement with the experimental data from CMS
and ALICE collaboration. Then, the predictive results in p+p collisions at
$\sqrt{s}=$ 14 TeV of the LHC are also given.",1401.6625v1
2014-02-20,Cluster-liquid transition in finite saturated fermionic systems,"The role of saturation for cluster formation in finite systems such as atomic
nuclei is analyzed by considering three length-scale ratios, and performing
deformation-constrained self-consistent mean-field calculations. The effect of
clusterisation in deformed light systems is related to the saturation property
of the inter-nucleon interaction. The formation of clusters at low nucleon
density is illustrated by expanding the radius of $^{16}$O. A phase diagram
shows that the formation of clusters can be interpreted as a hybrid state
between the crystal and the liquid phases. In the hybrid cluster phase the
confining potential attenuates the delocalization generated by the effective
nuclear interaction.",1402.5080v2
2014-07-28,A Systematic Approach to the Reconstruction of Saturated SDO/AIA Images,"EUV images of solar flares provided by the Atmospheric Imaging Assembly
onboard the Solar Dynamics Observatory (SDO/AIA) are often affected by
saturation effects in their core, physically most interesting region. We
introduce an image reconstruction procedure that allows recovering information
in the primary saturation domain using the secondary images produced by the
diffraction fringes as input data. Such a procedure is based on standard
image-processing tools like correlation, convolution, and back-projection. Its
effectiveness is tested in the case of SDO/AIA observations of the July 8 2013
flaring event.",1407.7343v1
2014-09-18,Saturation of the leading spike growth in backward Raman amplifiers,"Backward Raman amplification of laser pulses in plasmas can produce nearly
relativistic unfocused output intensities and multi-exawatt powers in compact
devices. The largest achievable intensity depends on which of major competitive
processes sets this limit. It is shown here that the relativistic electron
nonlinearity can cause saturation of the leading amplified spike intensity
before filamentation instabilities develop. A simple analytical model for the
saturation, which supports numerical simulations, is suggested. The upper limit
for the leading output spike unfocused intensity is calculated.",1409.5195v1
2014-09-18,Exceeding the leading spike intensity and fluence limits in backward Raman amplifiers,"The leading amplified spike in backward Raman amplifiers can reach nearly
relativistic intensities before the saturation by the relativistic electron
nonlinearity, which sets an upper limit to the largest achievable leading spike
intensity. It is shown here that this limit can be substantially exceeded by
the initially sub-dominant spikes, which surprisingly outgrow the leading spike
after its nonlinear saturation. Furthermore, an initially negligible group
velocity of the amplified pulse in strongly under-critical plasma appears to be
capable of delaying the filamentation instability in the nonlinear saturation
regime. This enables further amplification of the pulse to even larger output
fluences.",1409.5407v1
2014-10-28,Brief Review of Saturation Physics,"We present a short overview of saturation physics followed by a summary of
the recent progress in our understanding of nonlinear small-$x$ evolution.
Topics include McLerran-Venugopalan model, Glauber-Mueller approximation,
nonlinear BK/JIMWLK evolution equations, along with the running-coupling and
NLO corrections to these equations. We conclude with selected topics in
saturation phenomenology.",1410.7722v1
2014-11-06,Domain of attraction of saturated switched systems under dwell-time switching,"This paper considers discrete-time switched systems under dwell-time
switching and in the presence of saturation nonlinearity. Based on Multiple
Lyapunov Functions and using polytopic representation of nested saturation
functions, a sufficient condition for asymptotic stability of such systems is
derived. It is shown that this condition is equivalent to linear matrix
inequalities (LMIs) and as a result, the estimation of domain of attraction is
formulated into a convex optimization problem with LMI constraints. Through
numerical examples, it is shown that the proposed approach is less conservative
than the others in terms of both minimal dwell-time needed for stability and
the size of the obtained domain of attraction.",1411.1486v1
2015-01-05,Statistical properties of the radiation from SASE FEL operating in a post-saturation regime with and without undulator tapering,"We describe statistical and coherence properties of the radiation from x-ray
free electron lasers (XFEL) operating in the post-saturation regime. We
consider practical case of the SASE3 FEL at the European XFEL. We perform
comparison of the main characteristics of the X-ray FEL operating in the
post-saturation regime with and without undulator tapering: efficiency,
coherence time and degree of transverse coherence.",1501.00899v1
2015-03-08,DESAT: an SSW tool for SDO/AIA image de-saturation,"Saturation affects a significant rate of images recorded by the Atmospheric
Imaging Assembly on the Solar Dynamics Observatory. This paper describes a
computational method and a technological pipeline for the de-saturation of such
images, based on several mathematical ingredients like Expectation
Maximization, image correlation and interpolation. An analysis of the
computational properties and demands of the pipeline, together with an
assessment of its reliability are performed against a set of data recorded from
the Feburary 25 2014 flaring event.",1503.02302v1
2015-03-19,Terahertz nonlinear conduction and absorption saturation in silicon waveguides,"We employ a silicon dielectric waveguide to confine and concentrate terahertz
pulses, and observe that the absorption saturates under strong terahertz
fields. By comparing the response between lightly-doped and intrinsic silicon
waveguides, we confirm the role of hot carriers in this saturable absorption.
We introduce a nonlinear dynamical model of Drude conductivity that, when
incorporated into a wave propagation equation, accurately reproduces the
observations and elucidates the physical mechanisms underlying this nonlinear
effect. The results are numerically confirmed by Monte Carlo simulations of the
Boltzmann transport equation, coupled with split-step nonlinear wave
propagation.",1503.05639v1
2015-05-18,Model Independent Description of Amplification and Saturation Using Green's Function,"High-gain Free Electron Laser (FEL) is one of the many electron-beam
instabilities that have a number of common features linking the shot noise, the
amplification and the saturation. In this paper, we present a new,
model-independent description of the interplay between these effects. We derive
a simple formula for a maximum attainable gain before instability saturates.
Application of this model-independent formula to FELs is compared with FEL
theory and simulations. We apply the limitations resulting from these findings
to FEL amplifiers used for seeded FELs and for Coherent electron Cooling.",1505.04735v1
2015-09-04,Stabilization of a linear Korteweg-de Vries equation with a saturated internal control,"This article deals with the design of saturated controls in the context of
partial differential equations. It is focused on a linear Korteweg-de Vries
equation, which is a mathematical model of waves on shallow water surfaces. In
this article, we close the loop with a saturating input that renders the
equation nonlinear. The well-posedness is proven thanks to the nonlinear
semigroup theory. The proof of the asymptotic stability of the closed-loop
system uses a Lyapunov function.",1509.01471v1
2015-10-05,Describing the response of saturated SiPMs,"We have developed a function which describes SiPM response in both small
signal and highly saturated regimes. The function includes the reactivation of
SiPM pixels during a single input light pulse, and results in an approximately
linear increase of SiPM response in the highly saturated regime, as observed in
real SiPMs. This article shows that the function can accurately describe the
measured response of real SiPM devices over a wide range of signal intensities.",1510.01102v4
2016-01-19,Atomic saturation of reduced powers,"Our aim was to generalize some theorems about the saturation of ultra-powers
to reduced powers. Naturally, we deal via saturation for types consisting of
atomic formulas. We succeed to generalize the theory of dense linear is maximal
and so is any pair (T, Delta) which is SOP_3 (Delta consists of atomic or
conjunction of atomic formulas). However, SOP_2 is not enough, so the p equals
t theorem cannot be generalized in this case. Similarly the unique dual of
cofinality.",1601.04824v3
2016-01-21,Beyond nonlinear saturation of backward Raman amplifiers,"Backward Raman amplification is limited by relativistic nonlinear dephasing
resulting in saturation of the leading spike of the amplified pulse. Pump
detuning is employed to mitigate the relativistic phase mismatch and to
overcome the associated saturation. The amplified pulse can then be reshaped
into a mono-spike pulse with little precursory power ahead of it, with the
maximum intensity increasing by a factor of two. This detuning can be employed
advantageously both in regimes where the group velocity dispersion is
unimportant and where the dispersion is important but small.",1601.05832v1
2016-04-14,Effects of flake size on mode-locking behavior for flake-graphene saturable absorber mirrors,"After advent of graphene as a saturable absorber many experiments have been
conducted to produce short pulse duration pulses. Here, we have measured the
properties of flake-graphene saturable absorber mirrors of various flake sizes
dependent on fabrication technique. These mirrors enabled us to obtain a large
mode-locking bandwidth of 16nm in an erbium-doped fiber laser. Mirrors with
large flake size and multi-layered thickness induce strong pulse shaping and
reflect mode-locked train of pulses with very large bandwidths.",1604.04113v1
2016-07-05,Optimal waiting time bounds for some flux-saturated diffusion equations,"We consider the Cauchy problem for two prototypes of flux-saturated diffusion
equations. In arbitrary space dimension, we give an optimal condition on the
growth of the initial datum which discriminates between occurrence or
nonoccurrence of a waiting time phenomenon. We also prove optimal upper bounds
on the waiting time. Our argument is based on the introduction of suitable
families of subsolutions and on a comparison result for a general class of
flux-saturated diffusion equations.",1607.01245v3
2016-07-22,Scaling properties of the number of random sequential adsorption iterations needed to generate saturated random packing,"The properties of the number of iterations in random sequential adsorption
protocol needed to generate finite saturated random packing of spherically
symmetric shapes were studied. Numerical results obtained for one, two, and
three dimensional packings were supported by analytical calculations valid for
any dimension $d$. It has been shown that the number of iterations needed to
generate finite saturated packing is subject to Pareto distribution with
exponent $-1-1/d$ and the median of this distribution scales with packing size
according to the power-law characterized by exponent $d$. Obtained resultscan
be used in designing effective RSA simulations.",1607.06668v2
2016-08-08,Saturation in inclusive production beyond leading logarithm accuracy,"We review recent progress on the calculations on the inclusive forward hadron
production within the saturation formalism. After introducing the concept of
perturbative parton saturation and nonlinear evolution we discuss the formalism
for the forward hadron production at high energy in the leading and
next-to-leading order. Numerical results are presented and compared with the
experimental data on forward hadron production in $dA$ and $pA$. We discuss the
problem of the negativity of the NLO cross section at high transverse momenta,
study its origin in detail and present possible improvements which include the
corrected kinematics and the suitable choice of the rapidity cutoff.",1608.02285v1
2016-09-19,Global stabilization of a Korteweg-de Vries equation with saturating distributed control,"This article deals with the design of saturated controls in the context of
partial differential equations. It focuses on a Korteweg-de Vries equation,
which is a nonlinear mathematical model of waves on shallow water surfaces. Two
different types of saturated controls are considered. The well-posedness is
proven applying a Banach fixed point theorem, using some estimates of this
equation and some properties of the saturation function. The proof of the
asymptotic stability of the closed-loop system is separated in two cases: i)
when the control acts on all the domain, a Lyapunov function together with a
sector condition describing the saturating input is used to conclude on the
stability, ii) when the control is localized, we argue by contradiction. Some
numerical simulations illustrate the stability of the closed-loop nonlinear
partial differential equation. 1. Introduction. In recent decades, a great
effort has been made to take into account input saturations in control designs
(see e.g [39], [15] or more recently [17]). In most applications, actuators are
limited due to some physical constraints and the control input has to be
bounded. Neglecting the amplitude actuator limitation can be source of
undesirable and catastrophic behaviors for the closed-loop system. The standard
method to analyze the stability with such nonlinear controls follows a two
steps design. First the design is carried out without taking into account the
saturation. In a second step, a nonlinear analysis of the closed-loop system is
made when adding the saturation. In this way, we often get local stabilization
results. Tackling this particular nonlinearity in the case of finite
dimensional systems is already a difficult problem. However, nowadays, numerous
techniques are available (see e.g. [39, 41, 37]) and such systems can be
analyzed with an appropriate Lyapunov function and a sector condition of the
saturation map, as introduced in [39]. In the literature, there are few papers
studying this topic in the infinite dimensional case. Among them, we can cite
[18], [29], where a wave equation equipped with a saturated distributed
actuator is studied, and [12], where a coupled PDE/ODE system modeling a
switched power converter with a transmission line is considered. Due to some
restrictions on the system, a saturated feedback has to be designed in the
latter paper. There exist also some papers using the nonlinear semigroup theory
and focusing on abstract systems ([20],[34],[36]). Let us note that in [36],
[34] and [20], the study of a priori bounded controller is tackled using
abstract nonlinear theory. To be more specific, for bounded ([36],[34]) and
unbounded ([34]) control operators, some conditions are derived to deduce, from
the asymptotic stability of an infinite-dimensional linear system in abstract
form, the asymptotic stability when closing the loop with saturating
controller. These articles use the nonlinear semigroup theory (see e.g. [24] or
[1]). The Korteweg-de Vries equation (KdV for short)",1609.05728v1
2016-11-08,Saturation and geometrical scaling,"We discuss emergence of geometrical scaling as a consequence of the nonlinear
evolution equations of QCD, which generate a new dynamical scale, known as the
saturation momentum: Qs. In the kinematical region where no other energy scales
exist, particle spectra exhibit geometrical scaling (GS), i.e. they depend on
the ratio pT=Qs, and the energy dependence enters solely through the energy
dependence of the saturation momentum. We confront the hypothesis of GS in
different systems with experimental data.",1611.02436v1
2016-12-09,Compact foliations with finite transverse LS category,"We prove that if F is a foliation of a compact manifold M with all leaves
compact submanifolds, and the transverse saturated category of F is finite,
then the leaf space M/F is compact Hausdorff. The proof is surprisingly
delicate, and is based on some new observations about the geometry of compact
foliations. Colman proved in her 1998 doctoral thesis that the transverse
saturated category of a compact Hausdorff foliation is always finite, so we
obtain a new characterization of the compact Hausdorff foliations among the
compact foliations as those with finite transverse saturated category.",1612.03022v1
2017-01-05,Saturating sets in projective planes and hypergraph covers,"Let $\Pi_q$ be an arbitrary finite projective plane of order $q$. A subset
$S$ of its points is called saturating if any point outside $S$ is collinear
with a pair of points from $S$. Applying probabilistic tools we improve the
upper bound on the smallest possible size of the saturating set to
$\lceil\sqrt{3q\ln{q}}\rceil+ \lceil(\sqrt{q}+1)/2\rceil$. The same result is
presented using an algorithmic approach as well, which points out the
connection with the transversal number of uniform multiple intersecting
hypergraphs.",1701.01379v2
2017-04-05,"Comment on ""Biologically inspired protection of deep networks from adversarial attacks""","A recent paper suggests that Deep Neural Networks can be protected from
gradient-based adversarial perturbations by driving the network activations
into a highly saturated regime. Here we analyse such saturated networks and
show that the attacks fail due to numerical limitations in the gradient
computations. A simple stabilisation of the gradient estimates enables
successful and efficient attacks. Thus, it has yet to be shown that the
robustness observed in highly saturated networks is not simply due to numerical
limitations.",1704.01547v1
2017-07-04,Elimination via saturation,"This short paper presents saturation-based algorithms for homogenization and
elimination. This algorithm can compute elimination ideals by using syzygies
and ideal membership test, hence it works with any} monomial order, in
particular without the use of block-elimination orders. The used saturation is
a translation of the geometric fact that the projective closure of an affine
scheme has no components in the hyperplane at infinity.",1707.00925v3
2017-08-22,Multi-TeV Energy Resolution Studies with VERITAS,"This work aims to investigate the systematic uncertainty in gamma-ray spectra
arising from saturation effects from bright images reconstructed by VERITAS.
The goal of the work is to improve or validate the energy resolution used for
deriving gamma-ray spectra in the sub-TeV to multi-TeV energy regime with
VERITAS. Saturation from multi-TeV gamma-ray events affects the image
brightness used to reconstruct the energy of the primary gamma ray, and
potentially biases the energy estimate. We discuss a method for investigating
the energy resolution bias in these multi-TeV gamma-ray events by looking at
showers with large core distances that do not saturate the cameras.",1708.06728v1
2017-09-06,Enriched Galerkin methods for two-phase flow in porous media with capillary pressure,"In this paper, we propose an enriched Galerkin (EG) approximation for a
two-phase pressure saturation system with capillary pressure in heterogeneous
porous media. The EG methods are locally conservative, have fewer degrees of
freedom compared to discontinuous Galerkin (DG), and have an efficient pressure
solver. To avoid non-physical oscillations, an entropy viscosity stabilization
method is employed for high order saturation approximations. Entropy residuals
are applied for dynamic mesh adaptivity to reduce the computational cost for
larger computational domains. The iterative and sequential IMplicit Pressure
and Explicit Saturation (IMPES) algorithms are treated in time. Numerical
examples with different relative permeabilities and capillary pressures are
included to verify and to demonstrate the capabilities of EG.",1709.01644v1
2017-09-12,Decomposition method related to saturated hyperball packings,"In this paper we study the problem of hyperball (hypersphere) packings in
$3$-dimensional hyperbolic space. We introduce a new definition of the
non-compact saturated ball packings and describe to each saturated hyperball
packing, a new procedure to get a decomposition of 3-dimensional hyperbolic
space $\HYP$ into truncated tetrahedra. Therefore, in order to get a density
upper bound for hyperball packings, it is sufficient to determine the density
upper bound of hyperball packings in truncated simplices.",1709.04369v1
2017-09-22,Superconducting single-photon detectors with saturated dependence of quantum efficiency vs. bias current,"It was investigated the possibility of creating NbN superconducting
single-photon detectors with saturated dependence of quantum efficiency versus
normalized bias current. It was shown that the saturation increases for the
detectors based on finer films with a lower value of Rs300/Rs20. The decreasing
of Rs300/Rs20 related to increasing influence of quantum corrections to
conductivity of superconductors and, in its turn, to decreasing electron
diffusion coefficient. The best samples has constant value of system quantum
effi-ciency 94% at Ib/Ic~0.8 and wavelength 1.31 mkm.",1709.07686v2
2017-11-03,Rainbow saturation and graph capacities,"The $t$-colored rainbow saturation number $rsat_t(n,F)$ is the minimum size
of a $t$-edge-colored graph on $n$ vertices that contains no rainbow copy of
$F$, but the addition of any missing edge in any color creates such a rainbow
copy. Barrus, Ferrara, Vandenbussche and Wenger conjectured that $rsat_t(n,K_s)
= \Theta(n\log n)$ for every $s\ge 3$ and $t\ge \binom{s}{2}$. In this short
note we prove the conjecture in a strong sense, asymptotically determining the
rainbow saturation number for triangles. Our lower bound is probabilistic in
spirit, the upper bound is based on the Shannon capacity of a certain family of
cliques.",1711.01047v2
2017-11-07,"Saturation of Jacobian ideals: some applications to nearly free curves, line arrangements and rational cuspidal plane curves","In this note we describe the minimal resolution of the ideal $I_f$, the
saturation of the Jacobian ideal of a nearly free plane curve $C:f=0$. In
particular, it follows that this ideal $I_f$ can be generated by at most 4
polynomials. Related general results by Hassanzadeh and Simis on the saturation
of codimension 2 ideals are discussed in detail. Some applications to rational
cuspidal plane curves and to line arrangements are also given.",1711.02595v3
2017-11-30,Saturation model of DIS : an update,"We present the results of new fits to the recently extracted data on $F_2$ at
low $x$ with the GBW saturation model and its modification to cover high values
of $Q^2$. We find that the model stands the test of time and gives a good
description of the data with slightly modified parameters. All the essential
elements of the model, especially the saturation scale, are retained.",1711.11360v3
2017-12-17,CGC/saturation approach: soft interaction at the LHC energies,"In this paper we demonstrate that our model which is based on the
CGC/saturation approach, is able to describe the soft interaction collisions
including the new TOTEM prelimenary data at 13 TeV. We believe that this
strengthens the argument that the CGC/saturation approach is the only viable
candidate for an effective theory for high energy QCD.",1712.06992v1
2018-04-11,"Saturation in regular, exotic and random pore networks","Porcolation simulations were carried out on various networks; both regular
and irregular. The saturation curve was obtained for cubic networks, localized
and completely random 3D networks and networks based on exotic graphs like
Sierpi\'nski triangle and carpet. For the random graph generation a
modification of the cell list algorithm was introduced, which is capable of
generating local random graphs efficiently. With the help of this graph
generation method, the effect of locality was investigated, and it was proven
to be an important property of random networks from the viewpoint of liquid
propagation. The saturation curves of local random networks with different
prescribed pore degree distributions were also obtained.",1804.03944v1
2018-07-02,Resumming subleading Sudakov logarithms in saturation regime,"We investigate the scale dependence of transverse momentum dependent(TMD)
gluon distribution in saturation regime. We found that in the Collins-2011
scheme, the scale dependence of small x gluon TMD is governed by the same
renormalization group(RG) equation that holds at moderate or large $x$.
Following the standard procedure, one then can resum both double leading
logarithm and single leading logarithm in saturation regime by jointly solving
the Collins-Soper equation and the RG equation.",1807.00506v1
2018-10-10,Approximate controllability for Navier--Stokes equations in {\rm 3D} Cylinders under Lions boundary conditions by an explicit saturating set,"An explicit saturating set consisting of eigenfunctions of Stokes operator in
general 3D Cylinders is proposed. The existence of saturating sets implies the
approximate controllability for Navier--Stokes equations in $\rm 3D$ Cylinders
under Lions boundary conditions.",1810.04799v3
2018-10-12,Nonlinear saturation of toroidal Alfven eigenmodes via nonlinear mode couplings,"Gyrokinetic theory of nonlinear mode coupling as a mechanism for toroidal
Alfven eigenmode (TAE) saturation in the fusion plasma related parameter regime
is presented, including 1) para- metric decay of TAE into lower kinetic TAE
(LKTAE) and geodesic acoustic mode (GAM), and 2) enhanced TAE coupling to shear
Alfven wave (SAW) continuum via ion induced scattering. Our theory shows that,
for TAE saturation in the parameter range of practical interest, several
processes with comparable scattering cross sections can be equally important.",1810.05300v1
2018-10-23,Saturated Models in Mathematical Fuzzy Logic,"This paper considers the problem of building saturated models for first-order
graded logics. We define types as pairs of sets of formulas in one free
variable which express properties that an element is expected, respectively, to
satisfy and to falsify. We show, by means of an elementary chains construction,
that each model can be elementarily extended to a saturated model where as many
types as possible are realized. In order to prove this theorem we obtain, as
by-products, some results on tableaux (understood as pairs of sets of formulas)
and their consistency and satisfiability, and a generalization of the
Tarski--Vaught theorem on unions of elementary chains.",1810.09742v1
2018-11-12,Effect of saturated absorption on sub-Poissonian lasing,"This paper discusses the effect of saturated absorption on the quantum
features of a sub-Poissonian laser. It is shown that when both media (laser and
absorbing) are saturated, the appearance of an additional element in the cavity
does not lead to the demolition of the quantum properties (regular statistics
of photons and quadrature squeezing) of laser radiation.",1811.04672v1
2018-12-11,Saturation and alternate pathways in four-wave mixing in rubidium,"We have examined the frequency spectrum of the blue light generated via
four-wave mixing in a rubidium vapor cell inside a ring cavity. At high atomic
density and input laser power, two distinct frequency components separated by
$116 \pm 4$ MHz are observed, indicating alternate four-wave mixing channels
through the $6p_{3/2}$ hyperfine states. The dependence of the generated light
on excitation intensity and atomic density are explored, and indicate the
primary process has saturated. This saturation results when the excitation rate
through the 6p state becomes equal to the rate through the 5p state, giving no
further gain with atomic density while a quadratic intensity dependence
remains.",1812.04465v1
2019-01-16,Enhanced nonreciprocal transmission through a saturable cubic-quintic nonlinear dimer defect,"The transmission properties through a saturable cubic-quintic nonlinear
defect attached to lateral linear chains is investigated. Particular attention
is directed to the possible non-reciprocal diode-like transmission when the
parity-symmetry of the defect is broken. Distinct cases of parity breaking are
considered including asymmetric linear and nonlinear responses. The spectrum of
the transmission coefficient is analytically computed and the influence of the
degree of saturation analyzed in detail. The transmission of Gaussian
wave-packets is also numerically investigated. Our results unveil that spectral
regions with high transmission and enhanced diode-like operation can be
achieved.",1901.05224v1
2019-03-07,Left saturation closure for Ore localizations,"In this paper, we introduce the notion of LSat, the left saturation closure
of a subset of a module at a subset of the base ring, which generalizes
multiple important concepts related to Ore localization. We show its
significance in finding a saturated normal form for left Ore sets as well as in
characterizing the units of a localized ring.
  Furthermore, LSat encompasses the notion of local closure of submodules and
ideals from the realm of algebraic analysis, where it describes the result of
extending a submodule or ideal from a ring to its localization and contracting
it back again.",1903.03172v1
2019-07-26,Local stabilization of an unstable parabolic equation via saturated controls,"We derive a saturated feedback control, which locally stabilizes a linear
reaction-diffusion equation. In contrast to most other works on this topic, we
do not assume the Lyapunov stability of the uncontrolled system and consider
general unstable systems. Using Lyapunov methods, we provide estimates for the
region of attraction for the closed-loop system, given in terms of linear and
bilinear matrix inequalities. We show that our results can be used with
distributed as well as scalar boundary control, and with different types of
saturations. The efficiency of the proposed method is demonstrated by means of
numerical simulations.",1907.11473v2
2019-08-05,Nonlinear transmission of laser light through coronal plasma due to self-induced incoherence,"The success of direct laser-driven inertial confinement fusion (ICF) relies
critically on the efficient coupling of laser light to plasma. At ignition
scale, the absolute stimulated Raman scattering (SRS) instability can severely
inhibit this coupling by redirecting and strongly depleting laser light. This
Letter describes a new dynamic saturation regime of the absolute SRS
instability. The saturation occurs when spatiotemporal fluctuations in the
ion-acoustic density detune the instability resonance. The dynamic saturation
mitigates the strong depletion of laser light and enhances its transmission
through the instability region, explaining the coupling of laser light to ICF
targets at higher plasma densities.",1908.01684v1
2019-09-24,The saturation number of $\cb$-bounded stable monomial ideals and their powers,"Let $S=K[x_1,\ldots,x_n]$ be the polynomial ring in $n$ variables over a
field $K$. In this paper, we compute the socle of $\cb$-bounded strongly stable
ideals and determine that the saturation number of strongly stable ideals and
of equigenerated $\cb$-bounded strongly stable ideals. We also provide explicit
formulas for the saturation number $\sat(I)$ of Veronese type ideals $I$. Using
this formula, we show that $\sat(I^k)$ is quasi-linear from the beginning and
we determine the quasi-linear function explicitly.",1909.10663v1
2019-10-02,Exploring origin of small x saturation in collinear approach,"A modification of the collinear evolution equations as an appropriate
approach to improve the behavior of parton distribution functions in the region
of small longitudinal momentum fractions, and to find more theoretical
arguments to clarify the possible appearence of saturation regime is suggested.
It is argued that parton diffusion in the rapidity space at large parton
densities along the space-time evolution could result in the emergence of a
natural saturation scale on which freezing actually occurs.",1910.00819v1
2020-01-06,Remarks on input-to-state stability of collocated systems with saturated feedback,"We investigate input-to-state stability (ISS) of infinite-dimensional
collocated control systems subject to saturated feedback. Here, the unsaturated
closed loop is dissipative and uniformly globally asymptotically stable. Under
an additional assumption on the linear system, we show ISS for the saturated
one. We discuss the sharpness of the conditions in light of existing results in
the literature.",2001.01636v3
2020-01-13,Approximation smooth and sparse functions by deep neural networks without saturation,"Constructing neural networks for function approximation is a classical and
longstanding topic in approximation theory. In this paper, we aim at
constructing deep neural networks (deep nets for short) with three hidden
layers to approximate smooth and sparse functions. In particular, we prove that
the constructed deep nets can reach the optimal approximation rate in
approximating both smooth and sparse functions with controllable magnitude of
free parameters. Since the saturation that describes the bottleneck of
approximate is an insurmountable problem of constructive neural networks, we
also prove that deepening the neural network with only one more hidden layer
can avoid the saturation. The obtained results underlie advantages of deep nets
and provide theoretical explanations for deep learning.",2001.04114v1
2020-03-12,Optimal nonlinear damping control of second-order systems,"Novel nonlinear damping control is proposed for the second-order systems. The
proportional output feedback is combined with the damping term which is
quadratic to the output derivative and inverse to the set-point distance. The
global stability, passivity property, and convergence time and accuracy are
demonstrated. Also the control saturation case is explicitly analyzed. The
suggested nonlinear damping is denoted as optimal since requiring no design
additional parameters and ensuring a fast convergence, without transient
overshoots for a non-saturated and one transient overshoot for a saturated
control configuration.",2003.05670v3
2020-03-19,The saturated prefilter monad,"This paper considers some extensions of the notion of filter to the
quantale-valued context, including saturated prefilter, $\top$-filter and
bounded saturated prefilter. The question is whether these constructions give
rise to monads on the category of sets. It is shown that the answer depends on
the structure of the quantale. Specifically, if the quantale is the unit
interval equipped with a continuous t-norm, then these constructions give rise
to monads if and only if the implication operator corresponding to that t-norm
is continuous at each point off the diagonal.",2003.08610v2
2020-03-20,Well-posedness of dispersion managed nonlinear Schrödinger equations,"We prove local and global well-posedness results for the Gabitov-Turitsyn or
dispersion managed nonlinear Schr\""odinger equation with a large class of
nonlinearities and arbitrary average dispersion on $L^2(\mathbb{R})$ and
$H^1(\mathbb{R})$. Moreover, when the average dispersion is non-negative, we
show that the set of ground states is orbitally stable. This covers the case of
non-saturated and saturated nonlinear polarizations and yields, for saturated
nonlinearities, the first proof of orbital stability.",2003.09076v3
2020-07-07,Resistivity saturation in an electron-doped cuprate,"We report the observation of resistivity saturation in lightly doped ($x\sim
0.10)$ as-grown samples of the electron-doped cuprate La$_{2-x}$Ce$_x$CuO$_4$
(LCCO). The saturation occurs at resistivity values roughly consistent with the
phenomenological Mott-Ioffe-Regel criterion once the low effective carrier
density of these materials is included in the analysis. These results imply
that, at least for light doping, the high-temperature metallic phase of these
materials is not necessarily strange and may be understood as simply a
low-density metal.",2007.03685v1
2020-10-28,Self-sweeping ytterbium-doped fiber laser based on a fiber saturable absorber,"Generally speaking, the self-sweeping effect relies on the dynamical grating
formed in a gain fiber. Here, the normal self-sweeping was generated in a
pump-free ytterbium-doped fiber which serves as a fiber saturable absorber and
is introduced to the laser cavity by a circulator in this experiment. The
sweeping rate and the sweeping range alter as usual, both of which can be
controlled by the pump power. Further, a new self-pulse signal is observed and
discussed in this work, which shows the difference of the self-sweeping effects
between active fiber and fiber saturable absorber.",2010.14818v1
2021-04-13,Stabilisation of the complex double integrator by means of a saturated linear feedback,"Consider the saturated complex double integrator, i.e., the linear control
system $\dot x=Ax+B\sigma(u)$, where $x\in\R^4$, $u\in\R$, $B\in\R^4$, the
$4\times 4$ matrix $A$ is not diagolizable and admits a non zero purely
imaginary eigenvalue of multiplicity two, the pair $(A,B)$ is controllable and
$\sigma:\R\to\R$ is a saturation function. We prove that there exists a linear
feedback $u=K^Tx$ such that the resulting closed loop system given by $\dot
x=Ax+B\sigma(K^Tx)$ is globally asymptotically stable with respect to the
origin.",2104.06302v1
2021-06-11,Saturation Numbers for Linear Forests $P_6$ + $tP_2$,"A graph $G$ is $H$-saturated if it contains no $H$ as a subgraph, but does
contain $H$ after the addition of any edge in the complement of $G$. The
saturation number, $sat (n, H)$, is the minimum number of edges of a graph in
the set of all $H$-saturated graphs with order $n$. In this paper, we determine
the saturation number $sat (n, P_6 + tP_2)$ for $n \geq 10t/3 + 10$ and
characterize the extremal graphs for $n >10t/3 + 20$.",2106.06466v2
2021-07-06,Symbol Elimination for Parametric Second-Order Entailment Problems (with Applications to Problems in Wireless Network Theory),"We analyze possibilities of second-order quantifier elimination for formulae
containing parameters -- constants or functions. For this, we use a constraint
resolution calculus obtained from specializing the hierarchical superposition
calculus. If saturation terminates, we analyze possibilities of obtaining
weakest constraints on parameters which guarantee satisfiability. If the
saturation does not terminate, we identify situations in which finite
representations of infinite saturated sets exist. We identify situations in
which entailment between formulae expressed using second-order quantification
can be effectively checked. We illustrate the ideas on a series of examples
from wireless network research.",2107.02333v1
2021-08-09,The saturation number of $C_6$,"A graph $G$ is called $C_k$-saturated if $G$ is $C_k$-free but $G+e$ not for
any $e\in E(\overline{G})$. The saturation number of $C_k$, denoted
$sat(n,C_k)$, is the minimum number of edges in a $C_k$-saturated graph on $n$
vertices. Finding the exact values of $sat(n,C_k)$ has been one of the most
intriguing open problems in extremal graph theory. In this paper, we study the
saturation number of $C_6$. We prove that ${4n}/{3}-2 \le sat(n,C_6) \le
{(4n+1)}/{3}$ for $n\ge9$, which significantly improves the existing lower and
upper bounds for $sat(n,C_6)$.",2108.03910v3
2022-02-15,Saturation for the $3$-uniform loose $3$-cycle,"Let $F$ and $H$ be $k$-uniform hypergraphs. We say $H$ is $F$-saturated if
$H$ does not contain a subgraph isomorphic to $F$, but $H+e$ does for any
hyperedge $e\not\in E(H)$. The saturation number of $F$, denoted
$\mathrm{sat}_k(n,F)$, is the minimum number of edges in a $F$-saturated
$k$-uniform hypergraph $H$ on $n$ vertices. Let $C_3^{(3)}$ denote the
$3$-uniform loose cycle on $3$ edges. In this work, we prove that
  \[
  \left(\frac{4}3+o(1)\right)n\leq \mathrm{sat}_3(n,C_3^{(3)})\leq
\frac{3}2n+O(1).
  \]
  This is the first non-trivial result on the saturation number for a fixed
short hypergraph cycle.",2202.07149v1
2022-03-19,Sub-additive unstable topological pressure on saturated subsets,"In this paper, we continue our investigation on sub-additive pressures for
$C^1$-smooth partially hyperbolic diffeomorphisms. Under the assumption of
unstable almost product property, we show that the unstable Bowen topological
pressure on the saturated set of a given non-empty compact connected set of
invariant measures equals the infimum of the summation of unstable metric
entropy and the corresponding \emph{Lyapunov exponent}, where the infimum is
taken over all invariant measures inside the compact connected set above.
Moreover, we also show that the unstable topological capacity pressure on the
saturated sets above coincide with the unstable topological pressure of the
whole system.",2203.10279v1
2022-06-06,Every Finite Poset is Isomorphic to a Saturated Subset of the Spectrum of a Noetherian UFD,"We show that every finite poset is isomorphic to a saturated subset of the
spectrum of a Noetherian unique factorization domain. In addition, we show that
every finite poset is isomorphic to a saturated subset of the spectrum of a
quasi-excellent domain.",2206.02867v2
2022-12-26,Emergence of nuclear saturation within $Δ$--full chiral effective field theory,"Nuclear saturation is a key property of low-energy nuclear physics that
depends on fine details of the nuclear interaction. Here we develop a unified
statistical framework that uses realistic nuclear forces to link the
theoretical modeling of finite nuclei and infinite nuclear matter. We construct
fast and accurate emulators for nuclear-matter observables and employ an
iterative history-matching approach to explore and reduce the enormous
parameter domain of $\Delta$-full chiral interactions. We find that model
calibration including \nuc{16}{O} observables gives saturation predictions that
are more accurate and have a smaller variance than those that only use few-body
data.",2212.13203v1
2023-01-10,Supersolvable saturated matroids and chordal graphs,"A matroid is supersolvable if it has a maximal chain of flats each of which
is modular. A matroid is saturated if every round flat is modular. In this
article we present supersolvable saturated matroids as analogues to chordal
graphs, and we show that several results for chordal graphs hold in this
matroid context. In particular, we consider matroid analogues of the reduced
clique graph and clique trees for chordal graphs. The latter is a
maximum-weight spanning tree of the former. We also show that the matroid
analogue of a clique tree is an optimal decomposition for the matroid parameter
of tree-width.",2301.03776v2
2023-02-02,Nonlinear Regge trajectories and saturation of the Hagedorn spectrum,"We argue that two seemingly different phenomena, namely the well-known
saturation of the Hagedorn exponential distribution and the less familiar
saturation of Regge trajectories at resonance masses $m\approx$ 2-2.5 GeV are
related and have the same origin: quark deconfinement. We show that the slope
of the real part of non-linear Regge trajectories determines the prefactor
$f(m)$ in Hagedorn's resonance mass density distribution $\rho(m)$. While the
Hagedorn distribution comes from statistics, Regge trajectories contain
dynamics.",2302.00838v1
2023-05-08,Symbolic Model Construction for Saturated Constrained Horn Clauses,"Clause sets saturated by hierarchic ordered resolution do not offer a model
representation that can be effectively queried, in general. They only offer the
guarantee of the existence of a model. We present an effective symbolic model
construction for saturated constrained Horn clauses. Constraints are in linear
arithmetic, the first-order part is restricted to a function-free language. The
model is constructed in finite time, and non-ground clauses can be effectively
evaluated with respect to the model. Furthermore, we prove that our model
construction produces the least model.",2305.05064v2
2023-05-15,Criteria for supersolvability of saturated fusion systems,"Let $p$ be a prime number. A saturated fusion system $\mathcal{F}$ on a
finite $p$-group $S$ is said to be supersolvable if there is a series $1 = S_0
\le S_1 \le \dots \le S_m = S$ of subgroups of $S$ such that $S_i$ is strongly
$\mathcal{F}$-closed for all $0 \le i \le m$ and such that $S_{i+1}/S_i$ is
cyclic for all $0 \le i < m$. We prove some criteria that ensure that a
saturated fusion system $\mathcal{F}$ on a finite $p$-group $S$ is
supersolvable provided that certain subgroups of $S$ are abelian and weakly
$\mathcal{F}$-closed. Our results can be regarded as generalizations of purely
group-theoretic results of Asaad.",2305.09008v1
2023-05-25,Power Counting to Saturation,"We present a description of saturation in small x deep inelastic scattering
from power counting in a top-down effective theory derived from QCD. A
factorization formula isolates the universal physics of the nucleus at leading
power in x. The onset of saturation is then understood as a breakdown in the
expansion in an emergent power counting parameter, which is defined by the
matrix element of a gauge invariant operator. We demonstrate the presence of a
novel collinear-soft radiation mode, which clarifies the role played by the
medium size in deciding linear/non-linear evolution of the cross section in
$\ln x$.",2305.16393v1
2023-05-26,Nonlinear saturation of resistive tearing modes in a cylindrical tokamak with and without solving the dynamics,"We show that the saturation of resistive tearing modes in a cylindrical
tokamak, as well as the corresponding island width, can be directly calculated
with an MHD equilibrium code without solving the dynamics and without
considering resistivity. The results are compared to initial value resistive
MHD simulations and to an analytical nonlinear theory. For small enough
islands, the agreement is remarkable. For sufficiently large islands, the
equilibrium calculations, which assume a flat current profile inside the
island, overestimate the saturation amplitude. On the other hand, excellent
agreement between nonlinear resistive MHD simulations and nonlinear theory is
observed for all the considered tearing unstable equilibria.",2305.16785v2
2024-01-23,A new mathematical model for cell motility with nonlocal repulsion from saturated areas,"The main purpose of this work is the modelling of large populations of cells
under different interactions among themselves, in balance with natural random
diffusion. We focus on cell-cell adhesion mechanisms for one single population
confined in isolated domains. Our most relevant contribution is the proposal of
a mathematical model, that includes a nonlocal saturation coefficient
multiplying an appropriate nonlocal drift term, that can even induce repulsion
effects from saturated areas.",2401.13117v1
2024-01-27,Effects of non-condensable gas on laser-induced cavitation bubbles,"This study presents experimental observations of single laser-induced
cavitation bubbles collapsing in water with different levels of air saturation.
The average trends of the bubble size reveal a clear yet little dependence of
the energy dissipation at collapse on the water gas content. Similarly, the
observed trend of luminescence energy at collapse varies within the
investigated range of air saturation levels, in agreement with findings in
similar works. We argue that perturbations in bubble shape may amplify with
decreasing air saturation, consequently affecting light emission.",2401.15421v1
2024-02-21,Overcoming Saturation in Density Ratio Estimation by Iterated Regularization,"Estimating the ratio of two probability densities from finitely many samples,
is a central task in machine learning and statistics. In this work, we show
that a large class of kernel methods for density ratio estimation suffers from
error saturation, which prevents algorithms from achieving fast error
convergence rates on highly regular learning problems. To resolve saturation,
we introduce iterated regularization in density ratio estimation to achieve
fast error rates. Our methods outperform its non-iteratively regularized
versions on benchmarks for density ratio estimation as well as on large-scale
evaluations for importance-weighted ensembling of deep unsupervised domain
adaptation models.",2402.13891v1
2007-05-20,Dependence of hillslope moisture content on downhill saturation,"We derive steady equilibria for lateral downslope moisture flow in an
idealized thin closed layer as a solution to the 1D Richards' Equation. The
equilibria are determined by two free parameters: the downslope flux and a
boundary condition. Solutions exhibit a constant downslope flow speed and
moisture content for the constant equilibrium flux, which is the product of the
two. However where an isolated zone of fixed saturation degree exists
representing a boundary condition, the flow speed immediately upslope is
reduced and the moisture content correspondingly increased to preserve the
constant equilibrium flux. The capillary head jump at the saturated zone
produces a blockage that gives a high moisture content back upslope through a
pooling distance determined by the equilibrium condition that the downslope
flux is constant. In our numerical integrations, the vertically projected
pooling height is more than 10 km for a fully saturated zone in mixed silty or
clay soils, but decreases by about an order of magnitude with every 10%
decrease in the boundary-zone saturation degree. The drying of downhill
saturated zones with the increased speed of mountain moisture outflow and
corresponding decreased mountain moisture content gives a viable explanation
for the mysterious ~69% unaccounted drop seen in the spring outflow in the La
Luz / Fresnal Watershed at Alamogordo's upstream spring-box diversions in the
semiarid southeastern New Mexico USA.",0705.2840v2
2009-01-02,Existence of an upper limit on the density of excitons in carbon nanotubes by diffusion-limited exciton-exciton annihilation: Experiment and theory,"Through an investigation of photoemission properties of highly-photoexcited
single-walled carbon nanotubes, we demonstrate that there is an upper limit on
the achievable excitonic density. As the intensity of optical excitation
increases, all photoluminescence emission peaks arising from different
chirality single-walled carbon nanotubes showed clear saturation in intensity.
Each peak exhibited a saturation value that was independent of the excitation
wavelength, indicating that there is an upper limit on the excitonic density
for each nanotube species. We propose that this saturation behavior is a result
of efficient exciton-exciton annihilation through which excitons decay
non-radiatively. In order to explain the experimental results and obtain
excitonic densities in the saturation regime, we have developed a model, taking
into account the generation, diffusion-limited exciton-exciton annihilation,
and spontaneous decays of one-dimensional excitons. Using the model, we were
able to reproduce the experimentally obtained saturation curves under certain
approximations, from which the excitonic densities were estimated. The validity
of the model was confirmed through comparison with Monte Carlo simulations.
Finally, we show that the conventional rate equation for exciton-exciton
annihilation without taking into account exciton diffusion fails to fit the
experimentally observed saturation behavior, especially at high excitonic
densities.",0901.0211v1
2009-03-31,Stroke saturation on a MEMS deformable mirror for woofer-tweeter adaptive optics,"High-contrast imaging of extrasolar planet candidates around a main-sequence
star has recently been realized from the ground using current adaptive optics
(AO) systems. Advancing such observations will be a task for the Gemini Planet
Imager, an upcoming ""extreme"" AO instrument. High-order ""tweeter"" and low-order
""woofer"" deformable mirrors (DMs) will supply a >90%-Strehl correction, a
specialized coronagraph will suppress the stellar flux, and any planets can
then be imaged in the ""dark hole"" region. Residual wavefront error scatters
light into the DM-controlled dark hole, making planets difficult to image above
the noise. It is crucial in this regard that the high-density tweeter, a
micro-electrical mechanical systems (MEMS) DM, have sufficient stroke to deform
to the shapes required by atmospheric turbulence. Laboratory experiments were
conducted to determine the rate and circumstance of saturation, i.e. stroke
insufficiency. A 1024-actuator 1.5-um-stroke MEMS device was empirically tested
with software Kolmogorov-turbulence screens of r_0=10-15cm. The MEMS when
solitary suffered saturation ~4% of the time. Simulating a woofer DM with ~5-10
actuators across a 5-m primary mitigated MEMS saturation occurrence to a
fraction of a percent. While no adjacent actuators were saturated at opposing
positions, mid-to-high-spatial-frequency stroke did saturate more frequently
than expected, implying that correlations through the influence functions are
important. Analytical models underpredict the stroke requirements, so empirical
studies are important.",0903.5355v1
2009-08-25,Hadrons and direct photon in pp and pA collisions at LHC and saturation effects,"We investigate hadrons and direct photon production in pp and pA collisions
at the energies of RHIC and LHC within the color-dipole approach employing
various saturation models. We show that greatest sensitivity to saturation
effects is reached at very forward rapidities for pp collisions at LHC
(\sqrt{s}=14 TeV). The ratio of direct-photon to pion production can be about
20-10 (at \eta=7-8). Therefore, direct photon production at forward rapidities
should provide a rather clean probe. We calculate the rapidity dependence of
the invariant cross-section and find some peculiar enhancement at forward
rapidities which is more pronounced for direct photon production. We show that
this peak is further enhanced by saturation effects. We provide predictions for
the nuclear modification factor R_{pA} for pions and direct photon production
in pA collisions at LHC energy at midrapidity. We show within various
saturation models that the pion Cronin enhancement at RHIC is replaced by a
moderate suppression at LHC energy at midrapidity due to gluon shadowing
effects. Cronin enhancement of direct photons can survive at LHC energy within
models with a larger saturation scale.",0908.3695v2
2012-12-13,Analytical model for flux saturation in sediment transport,"The transport of sediment by a fluid along the surface is responsible for
dune formation, dust entrainment and for a rich diversity of patterns on the
bottom of oceans, rivers, and planetary surfaces. Most previous models of
sediment transport have focused on the equilibrium (or saturated) particle
flux. However, the morphodynamics of sediment landscapes emerging due to
surface transport of sediment is controlled by situations out-of-equilibrium.
In particular, it is controlled by the saturation length characterizing the
distance it takes for the particle flux to reach a new equilibrium after a
change in flow conditions. The saturation of mass density of particles
entrained into transport and the relaxation of particle and fluid velocities
constitute the main relevant relaxation mechanisms leading to saturation of the
sediment flux. Here we present a theoretical model for sediment transport
which, for the first time, accounts for both these relaxation mechanisms and
for the different types of sediment entrainment prevailing under different
environmental conditions. Our analytical treatment allows us to derive a closed
expression for the saturation length of sediment flux, which is general and can
thus be applied under different physical conditions.",1212.3052v5
2014-02-20,Precise Algorithm to Generate Random Sequential Addition of Hard Hyperspheres at Saturation,"Random sequential addition (RSA) time-dependent packing process, in which
congruent hard hyperspheres are randomly and sequentially placed into a system
without interparticle overlap, is a useful packing model to study disorder in
high dimensions. Of particular interest is the infinite-time {\it saturation}
limit in which the available space for another sphere tends to zero. However,
the associated saturation density has been determined in all previous
investigations by extrapolating the density results for near-saturation
configurations to the saturation limit, which necessarily introduces numerical
uncertainties. We have refined an algorithm devised by us [S. Torquato, O.
Uche, and F.~H. Stillinger, Phys. Rev. E {\bf 74}, 061308 (2006)] to generate
RSA packings of identical hyperspheres. The improved algorithm produce such
packings that are guaranteed to contain no available space using finite
computational time with heretofore unattained precision and across the widest
range of dimensions ($2 \le d \le 8$). We have also calculated the packing and
covering densities, pair correlation function $g_2(r)$ and structure factor
$S(k)$ of the saturated RSA configurations. As the space dimension increases,
we find that pair correlations markedly diminish, consistent with a recently
proposed ""decorrelation"" principle, and the degree of ""hyperuniformity""
(suppression of infinite-wavelength density fluctuations) increases. We have
also calculated the void exclusion probability in order to compute the
so-called quantizer error of the RSA packings, which is related to the second
moment of inertia of the average Voronoi cell. Our algorithm is easily
generalizable to generate saturated RSA packings of nonspherical particles.",1402.4883v1
2015-05-25,Modulation instability in high-order coupled nonlinear Schrödinger equations with saturable nonlinearities,"The influence of a saturable nonlinearity on the modulation instability in
oppositely directed coupler in the presence of high-order effects is
investigated. By using the standard linear stability analysis, we obtain the
instability gain that exhibits a significant change in the bands of instability
due to the effects of a saturable nonlinearity. We also show that even in the
presence of saturation there is no change in instability gain when we compare
the results obtained for both channels not influenced by self-steepening effect
or for both channels influenced by self-steepening effect but opposite in sign.
Regarding the Raman effect, there is reflection symmetry (asymmetry) to the
gain at zero perturbation frequency when the values of the Raman coefficients
in each directional coupler are equal and with same (opposite) sign. For the
anomalous group velocity dispersion regime we observe that the growth of the
saturation parameter is followed by an increase in the null gain region near
{\Omega} = 0, enlarging the separation of the instability bands close to this
point. Finally, we show that an efficient control of the modulation instability
can be realized by adjusting self-steepening effect and intrapulse Raman
scattering, even in the presence of a saturable nonlinearity.",1505.06719v1
2015-12-21,A further update on possible crises in nuclear-matter theory,"The ancient problem of the saturation of symmetric nuclear matter is reviewed
with an update on the status of the crises that were identified at an early
stage by John Clark. We discuss how the initial problem with variational
calculations providing more binding than the two hole-line contribution for the
same interaction was overcome by calculations including three hole-line
contributions without however reproducing the empirical nuclear saturation
properties. It is argued that this remaining problem is still open because many
solutions have been proposed or ad hoc adjustments implemented without
generating universal agreement on the proper interpretation of the physics. The
problem of nuclear saturation therefore persists leading to the necessity of an
analysis of the way the nuclear saturation properties are obtained from
experimental data. We clarify the role of short-range correlations and review
results for nuclear saturation when such ingredients are completely taken into
account using the Green's function method. The role of long-range correlations
is then analyzed with special emphasis on the importance of attractive
pion-dominated excitation modes which inevitably lead to higher saturation
densities than observed. Because such modes have no counterpart in finite
nuclear systems, it is therefore argued that they should not be considered when
calculating nuclear matter properties. The remaining open question is then
whether long-range correlations in finite nuclei which in turn have no
counterpart in infinite matter, represent the remaining missing ingredient in
this analysis.",1512.06793v1
2019-05-13,Velocity Saturation in La-doped BaSnO3 Thin Films,"BaSnO_{3}, a high mobility perovskite oxide, is an attractive material for
oxide-based electronic devices. However, in addition to low-field mobility,
high-field transport properties such as the saturation velocity of carriers
play a major role in determining device performance. We report on the
experimental measurement of electron saturation velocity in La-doped BaSnO_{3}
thin films for a range of doping densities. Predicted saturation velocities
based on a simple LO-phonon emission model using an effective LO phonon energy
of 120 meV show good agreement with measurements of velocity saturation in
La-doped BaSnO_{3} films.. Density-dependent saturation velocity in the range
of 1.6x10^{7} cm/s reducing to 2x10^{6} cm/s is predicted for {\delta}-doped
BaSnO3 channels with carrier densities ranging from 10^{13} cm^{-2} to
2x10^{14} cm^{-2} respectively. These results are expected to aid the informed
design of BaSnO3 as the active material for high-charge density electronic
transistors.",1905.05112v2
2020-03-19,Gas relative permeability in unconventional reservoir rocks,"Accurate modeling of gas relative permeability has practical applications in
oil and gas exploration, production and recovery of unconventional reservoirs.
In this study, we apply concepts from the effective-medium approximation (EMA)
and universal power-law scaling from percolation theory. Although the EMA has
been successfully used to estimate relative permeability in conventional porous
media, to the best of our knowledge, its applications to unconventional
reservoir rocks have not been addressed yet. The main objective of this study,
therefore, is to evaluate the efficiency of EMA, in combination with universal
power-law scaling from percolation theory, in estimating gas relative
permeability from pore size distribution and pore connectivity. We presume that
gas flow is mainly controlled by two main mechanisms contributing in parallel
(1) hydraulic flow and (2) molecular flow. We then apply the EMA to determine
effective conductances and, consequently, gas relative permeability at higher
gas saturations, and the universal scaling from percolation theory at lower gas
saturation values. Comparisons with two pore-network simulations and six
experimental measurements from the literature show that, in the absence of
microfractures, the proposed model estimates gas relative permeability
reasonably well in shales and tight porous rocks. More specifically, we found
that the crossover point, gas saturation at which transport crosses from
percolation theory to the EMA, is non-universal. The value of crossover gas
saturation is a function of pore space characteristics such as pore size
distribution broadness and critical gas saturation. This means that one should
expect the crossover gas saturation to vary from one rock sample to another.",2003.08988v1
2020-12-28,Almost all permutation matrices have bounded saturation functions,"Saturation problems for forbidden graphs have been a popular area of research
for many decades, and recently Brualdi and Cao initiated the study of a
saturation problem for 0-1 matrices. We say that 0-1 matrix $A$ is saturating
for the forbidden 0-1 matrix $P$ if $A$ avoids $P$ but changing any zero to a
one in $A$ creates a copy of $P$. Define $sat(n, P)$ to be the minimum possible
number of ones in an $n \times n$ 0-1 matrix that is saturating for $P$. Fulek
and Keszegh proved that for every 0-1 matrix $P$, either $sat(n, P) = O(1)$ or
$sat(n, P) = \Theta(n)$. They found two 0-1 matrices $P$ for which $sat(n, P) =
O(1)$, as well as infinite families of 0-1 matrices $P$ for which $sat(n, P) =
\Theta(n)$. Their results imply that $sat(n, P) = \Theta(n)$ for almost all $k
\times k$ 0-1 matrices $P$.
  Fulek and Keszegh conjectured that there are many more 0-1 matrices $P$ such
that $sat(n, P) = O(1)$ besides the ones they found, and they asked for a
characterization of all permutation matrices $P$ such that $sat(n, P) = O(1)$.
We affirm their conjecture by proving that almost all $k \times k$ permutation
matrices $P$ have $sat(n, P) = O(1)$. We also make progress on the
characterization problem, since our proof of the main result exhibits a family
of permutation matrices with bounded saturation functions.",2012.14150v1
2021-12-28,Investigating the migration of immiscible contaminant fluid flow in homogeneous and heterogeneous aquifers with high-precision numerical simulations,"Numerical modeling of the migration of three-phase immiscible fluid flow in
variably saturated zones is challenging due to the different behavior of the
system between unsaturated and saturated zones. This behavior results in the
use of different numerical methods for the numerical simulation of the fluid
flow depending on whether it is in the unsaturated or saturated zones. This
paper shows that using a high-resolution shock-capturing conservative method to
resolve the nonlinear governing coupled partial differential equations of a
three-phase immiscible fluid flow allows the numerical simulation of the system
through both zones providing a unitary vision (and resolution) of the migration
of an immiscible contaminant problem within a porous medium. In particular,
using different initial scenarios (including impermeable 'lenses' in
heterogeneous aquifers), three-dimensional numerical simulation results are
presented on the temporal evolution of the contaminant migration following the
saturation profiles of the three-phases fluids flow in variably saturated
zones. It is considered either light nonaqueous phase liquid with a density
less than the water, or dense nonaqueous phase liquid, which has densities
greater than the water initially released in unsaturated dry soil. Our study
shows that the fate of the migration of immiscible contaminants in variably
saturated zones can be accurately described, using a unique mathematical
conservative model, with different evolution depending on the value of the
system's physical parameters, including the contaminant density, and accurately
tracking the evolution of the sharp (shock) contaminant front.",2112.14229v2
2024-03-20,Saturation and fluctuations in the proton wavefunction at large momentum transfers in exclusive diffraction at HERA,"We present a model of proton geometry where the number and size of gluon
density hotspots in the proton's thickness function evolves with the resolution
scale of the event given by the Mandelstam $t$ variable in exclusive
diffractive $ep$ collisions. We use the impact-parameter dependent saturation
dipole model bSat/IPSat, as well as its linearised (non-saturated) version
bNonSat. In the latter the proton thickness has a clear interpretation as a
thickness and in the former it is directly related to the saturation scale. The
resulting phenomenological model for the splitting of hotspots, making full use
of earlier experimental and phenomenological studies, is able to describe the
entire incoherent $t$-spectrum for $|t|>1.1~$GeV$^2$ with a single
phenomenological parameter. We use the previously suggested hotspot model as an
initial condition for our evolution. The resulting model is a resolution
scale-evolution in the same vein as a parton shower.The incoherent cross
section is directly proportional to geometrical fluctuations in the proton's
inital state. The hotspot evolution give rise to several kinds of
event-by-event fluctuations such as in the hotspot number, width and
normalization, and saturation scale fluctuations is a direct effect of these. A
natural consequence of our resolution based evolution is that the hotspots
obtain an effective repulsion. We use our hotspot evolution model to
investigate saturation scale effects in the $t$-spectrum, and found that HERA
data is not sensitive to this physics.",2403.13631v1
1999-06-01,Error-Correcting Codes That Nearly Saturate Shannon's Bound,"Gallager-type error-correcting codes that nearly saturate Shannon's bound are
constructed using insight gained from mapping the problem onto that of an Ising
spin system. The performance of the suggested codes is evaluated for different
code rates in both finite and infinite message length.",9906011v1
2001-09-21,Illumination of quantum Hall effect,"We show that illumination by continuous white radiation saturates the
population of levels so that some of the transitions are not observed. This
reduces the number of observable transitions so that the resolution of
transitions is improved. In the case of \nu = 11/2 the improved resolution
leads to clear observation of zero in the transverse resistivity which appears
as a finite resistivity in absence of saturating radiation.",0109407v1
1999-07-01,"Parton saturation, production, and equilibration in high energy nuclear collisions","Deeply inelastic scattering of electrons off nuclei can determine whether
parton distributions saturate at HERA energies. If so, this phenomenon will
also tell us a great deal about how particles are produced, and whether they
equilibrate, in high energy nuclear collisions.",9907209v1
1999-09-13,The Logarithmic Derivative of the F_{2} Structure Function and Saturation,"We show that when screening corrections are included $\frac{\partial
F_{2}(x,Q^{2})}{\partial ln(Q^{2}/Q_{0}^{2})}$ is consistent with the behaviour
that one expects in pQCD. Screening corrections explain the enigma of the
Caldwell plot. Saturation has not been reached at present HERA energies.",9909343v1
2001-11-20,Parton Saturation-An Overview,"The idea of partons and the utility of using light-cone gauge in QCD are
introduced. Saturation of quark and gluon distributions are discussed using
simple models and in a more general context. The Golec-Biernat W\usthoff model
and some simple phenomenology are described. A simple, but realistic, equation
for unitary, the Kovchegov equation, is discussed, and an elementary derivation
of the JIMWLK equation is given.",0111244v1
2002-03-27,A Modification of the Saturation Model: DGLAP evolution,"We propose to modify the saturation model of Golec-Biernat and Wusthoff by
including DGLAP evolution. We find considerable improvement for the total deep
inelastic cross section, in particular in the large Q^2 region. The successful
description of DIS diffraction is preserved.",0203258v2
2002-05-22,Saturation at low x and nonlinear evolution,"In this talk the results of the analytical and numerical analysis of the
nonlinear Balitsky-Kovchegov equation are presented. The characteristic BFKL
diffusion into infrared regime is suppressed by the generation of the
saturation scale. We identify the scaling and linear regimes for the solution.
We also study the impact of subleading corrections onto the nonlinear
evolution.",0205249v1
2002-06-13,Saturation and Vector Mesons,"Through an analysis of diffractive vector meson production, we show that the
proton appears quite dense to a small size probe at present HERA energies. This
means that saturation effects are already important.",0206117v1
2002-07-02,DGLAP evolution in the saturation model,"A modification of the saturation model of deep inelastic scattering at small
x which includes the Altarelli-Parisi (DGLAP) evolution is presented.
Significant improvement of the description of the structure function F_2 at
large Q^2 is achieved and a good description of diffractive data is preserved.",0207031v1
2002-08-27,Towards strangeness saturation in central heavy-ion collisions at high energies,"Analyses of the centrality binned identified hadron multiplicities at SPS and
RHIC within the statistical-thermal model point to strangeness saturation with
increasing centrality and energy.",0208247v1
2003-04-29,"Strangeness Saturation: Dependence on System-Size, Centrality and Energy","The dependence of the strangeness saturation factor on the system size,
centrality and energy is studied in relativistic heavy-ion collisions.",0304269v1
2003-05-02,Is Quark Saturation Related to the Pauli Principle?,"Below the saturation momentum the sea quark occupation number reaches a pure
number, independent of any parameters in QCD, reminiscent of a Pauli Principle
result. We argue, however, that the Pauli Principle plays no role in the
result.",0305023v2
2003-07-14,Hard-soft Pomeron transition from QCD saturation in the dipole picture,"We pose the question: how far can we push the QCD dipole model and the idea
of QCD saturation to the kinematical regions traditionally associated with soft
nonperturbative physics? The answer is that it works sufficiently well allowing
a smooth transition from hard (BFKL) pomeron to the soft one.",0307174v1
2003-11-21,Saturation and Diffractive DIS,"We review QCD based descriptions of diffractive deep inelastic scattering
emphasizing the role of models with parton saturation. These models provide
natural explanation of such experimentally observed facts as the constant ratio
of diffractive and total DIS cross sections as a function of the Bjorken
variable x and Regge factorization of diffractive parton distributions.",0311278v2
2004-08-24,Saturation scale from the Balitsky-Kovchegov equation,"Recently Munier and Peschanski presented an analysis of the
Balitsky--Kovchegov (BK) equation concerning the extraction of the saturation
scale, using a simpler equation. We numerically analyze the full BK equation
confirming the universality of their analysis.",0408255v1
2004-12-22,"DIS at low x, phenomenological aspects","Saturation at low x appears as an almost unavoidable consequence of the
two-gluon exchange generic structure. Consistency of the ansatz for the vector
part of the color dipole cross section with conventional evolution determines
the energy dependence of the saturation scale.",0412334v1
2005-01-03,Saturation and High Density QCD,"Recent progress in understanding general properties of high energy scattering
near the unitarity limit, where high density gluon components of the
wavefunction are dominant, is reviewed. The similarity of the QCD problem and
that of reaction-diffusion processes in statistical physics is emphasized. The
energy dependence of the saturation momentum and the status of geometric
scaling are discussed.",0501012v1
2005-04-06,Saturation effects at LHC energies,"Within the framework of a modified Balitsky-Kovchegov equation, we calculated
and provide estimates of non-linear saturation effects expected in the LHC
range of energies.",0504040v3
2005-10-30,Possible saturation effects at HERA and LHC in the $k_T$-factorization approach,"We consider possible saturation effects in the structure function $F_L$ at
fixed W in HERA energy range and in $b\bar b-$production at LHC energies in the
framework of $k_T-$facrorization approach.",0510403v1
2005-11-03,Recent results on saturation and CGC,"I discuss recent results on the Color Glass Condensate which is a dense
saturated gluonic state and appears as the universal picture of hadrons or
nuclei at very high energies.",0511031v1
2000-04-26,BPS Saturated Vacua Interpolation along One Compact Dimension,"A class of generalized Wess-Zumino models with distinct vacua is
investigated. These models allow for BPS saturated vacua interpolation along
one compact spatial dimension. The properties of these interpolations are
studied.",0004178v2
1993-04-12,The automorphism group of a saturated model has a large dense free subgroup,"We prove that for a stable theory $T,$ if $M$ is a saturated model of $T$ of
cardinality $\lambda$ where $\lambda > \big|T\big|,$ then $Aut(M)$ has a dense
free subgroup on $2^{\lambda}$ generators. This affirms a conjecture of Hodges.",9304201v1
2003-04-15,Automorphism groups of saturated structures; a review,"We will review the main results concerning the automorphism groups of
saturated structures which were obtained during the two last decades. The main
themes are: the small index property in the countable and uncountable cases;
the possibility of recovering a structure or a significant part of it from its
automorphism group; the subgroup of strong automorphisms.",0304205v1
2006-06-28,Reidemeister numbers of saturated weakly branch groups,"We prove for a wide class of saturated weakly branch group (including the
(first) Grigorchuk group and the Gupta-Sidki group) that the Reidemeister
number of any automorphism is infinite.",0606725v1
2004-02-04,Nuclear matter saturation in a relativistic chiral theory and QCD susceptibilities,"We study a chiral relativistic theory of nuclear matter aimed at the
desciption of both the binding and saturation properties and the QCD
properties, quark condensate and QCD susceptibilities. For this purpose the
nucleon scalar response of the quark-meson coupling model is introduced in the
linear sigma model. The consequences for the nuclear and the QCD scalar
susceptibilities are discussed.",0402018v1
2000-09-03,Soliton Generation and Picosecond Collapse in Solid-State Lasers with Semiconductor Saturable Absorber,"Based on self - consistent field theory we study a soliton generation in cw
solid-state lasers with semiconductor saturable absorber. Various soliton
destabilizations, i.e. the switch from femtosecond to picosecond generation
(''picosecond collapse''), an automodulation regime, breakdown of soliton
generation and hysteresis behavior, are predicted.",0009009v1
2000-09-21,Nonlinear Effects in CW Mode-Locked Solid-State Lasers with Semiconductor Saturable Absorbers,"The influence of nonlinear properties of semiconductor saturable absorbers on
ultrashort pulse generation was investigated. It was shown, that linewidth
enhancement, quadratic and linear ac Stark effect contribute essentially to the
mode locking in cw solid-state lasers, that can increase the pulse stability,
decrease pulse duration and reduce the mode locking threshold",0009067v1
2007-08-30,Broadening of band-gap in photonic crystals with optically saturated media,"Due to strong absorption of the incident light, the media with high
refractive index are considered restrictive for applications in photonic
crystals (PhCs). The possibility to resolve this problem by optical saturation
effectively minimizing the absorption of the PhC medium is discussed. Such
approach might be promising for the significant broadening of the photonic
band-gap.",0708.4043v1
2007-11-30,Coherent backscattering of light from saturated atoms,"We survey recent progress achieved in understanding the impact of inelastic
processes on coherent backscattering of light from cold atoms that are
saturated by a powerful laser field.",0711.4960v1
2008-07-15,"Saturated extensions, the attractors method and Hereditarily James Tree Space","In the present work we provide a variety of examples of HI Banach spaces
containing no reflexive subspace and we study the structure of their duals as
well as the spaces of their linear bounded operators. Our approach is based on
saturated extensions of ground sets and the method of attractors.",0807.2392v1
2009-03-24,Note on inconsistency of unitarity saturation and maximal odderon,"It is shown that regime of elastic scattering with maximal odderon
contribution is not compatible with unitarity and black disk limits saturation.",0903.4042v2
2009-07-09,Gluon saturation effects on J/Psi production in heavy ion collisions,"We discuss a novel mechanism for J/Psi$ production in nuclear collisions
arising due to the high density of gluons. We demonstrate that gluon saturation
in the colliding nuclei is a dominant source of J/Psi suppression and can
explain its experimentally observed rapidity and centrality dependence.",0907.1604v2
2009-10-21,On the different regimes of subaqueous transport,"We review different aspects of subaqueous sediment transport. We discuss the
static threshold and its dependency with longitudinal and transverse slopes, as
well as cohesion. We describe the different regimes of transport: erosion and
momentum limited bed load, and suspended load. In all these cases, we derive
the expressions of the saturation flux $q_{\rm sat}$ and the saturation length
$L_{\rm sat}$ and discuss their dependencies.",0910.4119v1
2010-03-03,The cofinal property of the Reflexive Indecomposable Banach spaces,"It is shown that every separable reflexive Banach space is a quotient of a
reflexive Hereditarily Indecomposable space, which yields that every separable
reflexive Banach is isomorphic to a subspace of a reflexive Indecomposable
space. Furthermore, every separable reflexive Banach space is a quotient of a
reflexive complementably $\ell_p$ saturated space with $1<p<\infty$ and of a
$c_0$ saturated space.",1003.0870v1
2010-03-24,"Wideband tunable, graphene-mode locked, ultrafast laser","We report a tunable ultrafast fiber laser mode-locked with a graphene
saturable absorber. The linear dispersions of the Dirac electrons in graphene
enable wideband tunability. We get ~1ps pulses, tunable between 1525 and
1559nm, demonstrating graphene as a broadband saturable absorber.",1003.4714v1
2010-05-30,Sparse fusion systems,"We define sparse saturated fusion systems and show that, for odd primes,
sparse systems are constrained. This simplifies the proof of the
Glauberman-Thompson p-nilpotency theorem for fusion systems and a related
theorem of Stellmacher. We then define a more restrictive class of saturated
fusion systems, called extremely sparse, that are constrained for all primes.",1005.5503v1
2010-06-30,A Saturation Method for the Modal Mu-Calculus with Backwards Modalities over Pushdown Systems,"We present an extension of an algorithm for computing directly the denotation
of a mu-calculus formula X over the configuration graph of a pushdown system to
allow backwards modalities. Our method gives the first extension of the
saturation technique to the full mu-calculus with backwards modalities.",1006.5906v1
2010-09-01,Color Glass Condensate and Glasma,"In this talk, I review the Color Glass Condensate theory of gluon saturation,
and its application to the early stages of heavy ion collisions.",1009.0093v2
2010-10-11,Infinite saturated orders,"We generalize the notion of saturated order to infinite partial orders and
give both a set-theoretic and an algebraic characterization of such orders. We
then study the proof theoretic strength of the equivalence of these
characterizations in the context of reverse mathematics, showing that depending
on one's choice of definitions it is either provable in $\mathsf{RCA}_0$ or
equivalent to $\mathsf{ACA}_0$.",1010.2219v1
2011-06-08,Saturation of Coulomb sum rules in the 6^Li case,"The Coulomb sums S_L(q) of the 6^Li nucleus have been obtained from electron
scattering measurements at 3-momentum transfers q = 1.125 - 1.625 fm^{-1}. It
is found that at q > 1.35 fm^{-1} the Coulomb sum of the nucleus becomes
saturated: S_L(q) = 1.",1106.1538v1
2011-09-21,The stellar activity-rotation relationship and the evolution of stellar dynamos,"We present a sample of 824 solar and late-type stars with X-ray luminosities
and rotation periods. This is used to study the relationship between rotation
and stellar activity and derive a new estimate of the convective turnover time.
From an unbiased subset of this sample the power law slope of the unsaturated
regime, L_X / L_bol = Ro^\beta, is fit as \beta = -2.70 +/- 0.13. This is
inconsistent with the canonical \beta=-2 slope to a confidence of 5 sigma, and
argues for an additional term in the dynamo number equation. From a simple
scaling analysis this implies \Delta\Omega / \Omega = \Omega^0.7, i.e. the
differential rotation of solar-type stars gradually declines as they spin down.
Super-saturation is observed for the fastest rotators in our sample and its
parametric dependencies are explored. Significant correlations are found with
both the corotation radius and the excess polar updraft, the latter theory
providing a stronger dependence and being supported by other observations. We
estimate mass-dependent empirical thresholds for saturation and
super-saturation and map out three regimes of coronal emission. Late F-type
stars are shown never to pass through the saturated regime, passing straight
from super-saturated to unsaturated X-ray emission. The theoretical threshold
for coronal stripping is shown to be significantly different from the empirical
saturation threshold (Ro < 0.13), suggesting it is not responsible. Instead we
suggest that a different dynamo configuration is at work in stars with
saturated coronal emission. This is supported by a correlation between the
empirical saturation threshold and the time when stars transition between
convective and interface sequences in rotational spin-down models.",1109.4634v1
2011-09-29,Affine Sieve,"We establish the main saturation conjecture in [BGS10] connected with
executing a Brun sieve in the setting of an orbit of a group of affine linear
transformations. This is carried out under the condition that the Zariski
closure of the group is Levi-semisimple. It is likely that this condition is
also necessary for such saturation to hold.",1109.6432v1
2011-11-21,"Comment on ""Saturation of the All-Optical Kerr Effect""","Br\'ee, Demircan, and Steinmeyer [Phys. Rev. Lett. 106, 183902 (2011)]
recently calculated higher-order Kerr effect (HOKE) coefficients using the
nonlinear Kramers-Kronig relations. We show that the saturated and negative
nonlinear index of refraction obtained by Br\'ee et al. is an artifact of their
use of a perturbative theory of ionization in an intensity region where it
breaks down.",1111.4932v1
2012-12-17,"Small x, Saturation, and Diffraction in Collisions with electrons, protons, and nuclei","The Lund dipole model DIPSY is based on BFKL evolution and saturation. It can
be applied to collisions between electrons, protons, and nuclei. In this talk I
present some recent results for exclusive final states in inelastic collisions,
a method to generate final states in diffractive excitation, and some results
for collisions with nuclei.",1212.3977v1
2013-01-07,On saturated uniformly A-convex algebras,"Following ideas of A.C.Cochran, we give a suitable definition of a saturated
uniformly A-convex algebra. In the m-convex case, such algebra is a uniform
topological one.",1301.1207v3
2013-04-19,On Thompson's $p$-complement theorems for saturated fusion systems,"In this short note we prove that a saturated fusion system admitting some
special type of automorphism is nilpotent. This generalizes classical results
by J.G. Thompson.",1304.5352v2
2013-11-04,Automorphism Groups of Countable Arithmetically Saturated Models of Peano Arithmetic,"If M,N are countable, arithmetically saturated models of Peano Arithmetic and
Aut(M) is isomorphic to Aut(N), then the Turing-jumps of Th(M) and Th(N) are
recursively equivalent.",1311.0772v3
2014-03-13,Properties of random sequential adsorption of generalized dimers,"Saturated random packing of particles built of two identical, relatively
shifted spheres in two and three dimensional flat and homogeneous space was
studied numerically using random sequential adsorption algorithm. The shift
between centers of spheres varied from 0.0 to 8.0 sphere diameters. Numerical
simulations allowed determine random sequential adsorption kinetics, saturated
random coverage ratio as well as available surface function and density
autocorrelation function.",1403.3200v1
2014-05-28,Singularly perturbed elliptic problems with nonautonomous asymptotically linear nonlinearities,"We consider a class of singularly perturbed elliptic problems with
nonautonomous asymptotically linear nonlinearities. The dependence on the
spatial coordinates comes from the presence of a potential and of a function
representing a saturation effect. We investigate the existence of nontrivial
nonnegative solutions concentrating around local minima of both the potential
and of the saturation function. Necessary conditions to locate the possible
concentration points are also given.",1405.7166v1
2014-06-16,Saturation of a large scale instability and non linear stuctures in a rotating stratified flow,"In this letter, we present non linear structures resulting from the
saturation of a large scale instability in rotating stratified fluids with
small scale forced turbulence which we found in \cite{[1]}. These structures
are of helical kinks type. The different solutions that we plotted correspond
to solutions linking two different stationnary points for different values of
the Rayleigh and the Taylor numbers.",1406.3962v1
2014-12-01,Neutrosophic information in the framework of multi-valued representation,"The paper presents some steps for multi-valued representation of neutrosophic
information. These steps are provided in the framework of multi-valued logics
using the following logical value: true, false, neutral, unknown and saturated.
Also, this approach provides some calculus formulae for the following
neutrosophic features: truth, falsity, neutrality, ignorance,
under-definedness, over-definedness, saturation and entropy. In addition, it
was defined net truth, definedness and neutrosophic score.",1412.4802v1
2015-03-14,CGC/saturation approach for soft interactions at high energy: inclusive production,"In this letter we demonstrate that our dipole model is successful in
describing the inclusive production within the same framework as diffractive
physics. We believe that this achievement stems from the fact that our approach
incorporates the positive features of the Reggeon approach and CGC/saturation
effective theory, for high energy QC",1503.04294v1
2014-12-19,Kinematics of Electrons in The Volume of a Planar Vacuum Diode in Regime of Saturation. Parameters of Hysteresis,"The kinematics laws of electrons motion in the volume of a planar vacuum
diode running in regime of current saturation are used. The characteristics of
diode hysteresis in the conditions of S-figurative instability are got and
analyzed.",1503.06646v1
2015-05-22,Approximations of superstability in concrete accessible categories,"We generalize the constructions and results of Chapter 10 in Baldwin's
""Categoricity"" to coherent accessible categories with concrete directed
colimits and concrete monomorphisms. In particular, we prove that if any
category of this form is categorical in a successor, directed colimits of
saturated objects are themselves saturated.",1505.06047v1
2015-12-06,Good ultrafilters and highly saturated models: a friendly explanation,"Highly saturated models are a fundamental part of the model-theoretic
machinery of nonstandard analysis. Of the two methods for producing them,
ultrapowers constructed with the aid of $\kappa^+$-good ultrafilters seems by
far the less popular. Motivated by the hypothesis that this is partly due to
the standard exposition being somewhat dense, a presentation is given which is
designed to be easier to digest.",1512.01827v1
2016-05-09,The strength of countable saturation,"We determine the proof-theoretic strength of the principle of countable
saturation in the context of the systems for nonstandard arithmetic introduced
in our earlier work.",1605.02534v2
2016-05-25,On the topological pressure of the saturated set with non-uniform structure,"We derive a conditional variational principle of the saturated set for
systems with the non-uniform structure. Our result applies to a broad class of
systems including beta-shifts, S-gap shifts and their factors.",1605.07845v1
2016-07-17,"Converse results, saturation and quasi-optimality for Lavrentiev regularization of accretive problems","This paper deals with Lavrentiev regularization for solving linear ill-posed
problems, mostly with respect to accretive operators on Hilbert spaces. We
present converse and saturation results which are an important part in
regularization theory. As a byproduct we obtain a new result on the
quasi-optimality of a posteriori parameter choices. Results in this paper are
formulated in Banach spaces whenever possible.",1607.04879v1
2016-09-21,Unconditionally saturated Banach space with the scalar-plus-compact property,"We construct a Bourgain-Delbaen $\mathscr{L}_\infty$-space
$\mathfrak{X}_{Kus}$ with strongly heterogenous structure: any bounded operator
on $\mathfrak{X}_{Kus}$ is a compact perturbation of a multiple of the
identity, whereas the space $\mathfrak{X}_{Kus}$ is saturated with
unconditional basic sequences.",1609.06506v2
2016-11-04,Unique Prediction for High-Energy J/ψPhotoproduction: Color Transparency and Saturation,"Based on the color-dipole picture, we present a successful parameter-free
prediction for the recent high-energy $J/\psi$ photoproduction data from the
Large Hadron Collider. The experimental data provide empirical evidence for the
transition from color transparency to saturation.",1611.01382v1
2017-10-22,Coupled complex Ginzburg-Landau systems with saturable nonlinearity and asymmetric cross-phase modulation,"We formulate and study dynamics from a complex Ginzburg-Landau system with
saturable nonlinearity, including asymmetric cross-phase modulation (XPM)
parameters. Such equations can model phenomena described by complex
Ginzburg-Landau systems under the added assumption of saturable media. When the
saturation parameter is set to zero, we recover a general complex cubic
Ginzburg-Landau system with XPM. We first derive conditions for the existence
of bounded dynamics, approximating the absorbing set for solutions. We use this
to then determine conditions for amplitude death of a single wavefunction. We
also construct exact plane wave solutions, and determine conditions for their
modulational instability. In a degenerate limit where dispersion and
nonlinearity balance, we reduce our system to a saturable nonlinear
Schr\""odinger system with XPM parameters, and we demonstrate the existence and
behavior of spatially heterogeneous stationary solutions in this limit. Using
numerical simulations we verify the aforementioned analytical results, while
also demonstrating other interesting emergent features of the dynamics, such as
spatiotemporal chaos in the presence of modulational instability. In other
regimes, coherent patterns including uniform states or banded structures arise,
corresponding to certain stable stationary states. For sufficiently large yet
equal XPM parameters, we observe a segregation of wavefunctions into different
regions of the spatial domain, while when XPM parameters are large and take
different values, one wavefunction may decay to zero in finite time over the
spatial domain (in agreement with the amplitude death predicted analytically).
While saturation will often regularize the dynamics, such transient dynamics
can still be observed - and in some cases even prolonged - as the saturability
of the media is increased, as the saturation may act to slow the timescale.",1710.07968v2
2017-12-13,Approximate controllability for Navier--Stokes equations in $\mathrm{3D}$ rectangles under Lions boundary conditions,"The $\mathrm{3D}$ Navier--Stokes system, under Lions boundary conditions, is
proven to be approximately controllable provided a suitable saturating set does
exist. An explicit saturating set for $\mathrm{3D}$ rectangles is given.",1712.04900v1
2018-02-13,Selfinjective algebras having a generalized standard family of quasi-tubes maximally saturated by simple and projective modules,"We give a complete description of finite dimensional selfinjective algebras
over an algebraically closed field whose Auslander-Reiten quiver admits a
generalized standard family of quasi-tubes maximally saturated by simple and
projective modules. In particular, we show that these algebras are
selfinjective algebras of strictly canonical type.",1802.04577v1
2018-11-20,Elementary Equivalence Theorem for PAC structures,"We generalize a well-known theorem binding the elementary equivalence
relation on the level of PAC fields and the isomorphism class of their absolute
Galois groups. Our results concern two cases: saturated PAC structures and
non-saturated PAC structures.",1811.08510v3
2018-11-26,Localized chaos of elliptically polarized cavity solitons in broad-area VCSEL with saturable absorber,"We introduce a spin-flip model for a broad-area Vertical-Cavity
Surface-Emitting Laser (VCSEL) with a saturable absorber. We demonstrate
simultaneous existence of orthogonally linearly polarized and elliptically
polarized cavity solitons. We show that polarization degree of freedom leads to
period doubling route to spatially localized chaos of the elliptically
polarized cavity solitons.",1811.10350v1
2018-12-28,Estimating Some General Molecular Descriptors of Saturated Hydrocarbons,"Three general molecular descriptors, namely the general sum-connectivity
index, general Platt index and ordinary generalized geometric-arithmetic index,
are studied here. Best possible bounds for the aforementioned descriptors of
arbitrary saturated hydrocarbons are derived. These bounds are expressed in
terms of number of carbon atoms and number of carbon-carbon bonds of the
considered hydrocarbons.",1812.11115v1
2019-01-04,More rigid ideals,"We extend prior results of Cody-Eskew, showing the consistency of GCH with
the statement that for all regular cardinals $\kappa \leq \lambda$, where
$\kappa$ is the successor of a regular cardinal, there is a rigid saturated
ideal on $\mathcal{P}_\kappa\lambda$. We also show the consistency of some
instances of rigid saturated ideals on $\mathcal{P}_\kappa\lambda$ where
$\kappa$ is the successor of a singular cardinal.",1901.02075v1
2019-07-24,"The norm of the saturation of a binomial ideal, and applications to Markov bases","Given a pure binomial ideal I in variables x_i, we define a new measure of
the complexity of the saturation of I with respect to the product of the
variables x_i, which we call the norm. We give a bound on the norm in terms of
easily-computed invariants of the ideal. We discuss statistical applications
both practical and theoretical.",1907.10268v1
2019-12-20,Miniaturized saturated absorption spectrometer,"We describe a saturated absorption setup that is robust, compact and require
minimum alignment. These properties are attained using a diffuse probe beam
generated by a retro-reflecting film. This concept was studied and applied to
built a miniaturized setup that had shown the same performance than an
optimized table-top experiment.",1912.10060v1
2019-12-20,Hadron multiplicity calculation: a configurational entropy approach to the saturation scale in QCD,"This paper investigates the configurational entropic content of
hadron-nucleus collisions. Hadron multiplicities and Au nuclei are employed to
compute the critical points of the configurational entropy as a function of the
saturation scale in deep inelastic scatterings, in QCD. The results match
phenomenological data to the precision of 0.39%.",1912.10071v1
2020-01-06,Non-Stationary Saturation of Inhomogeneously Broadened Spin Systems with Effective Cross-Relaxation,"Non-stationary saturation of inhomogeneously broadened EPR lines is
investigated under effective cross-relaxation. The generalized kinetic
equations are solved and the complex susceptibility is calculated. All
quantities change in time exponentially.",2001.01362v2
2020-01-17,Non-Stationary Saturation of Inhomogeneously Broadened EPR Lines,"Non-stationary saturation of inhomogeneously broadened EPR lines is studied
when cross-relaxation has the characteristics of spectral diffusion. A system
of generalized kinetic equations is solved in quadratures in this
approximation. The result is valid not only when the contribution of the
spectral diffusion is negligible or dominant, but also in the intermediate
case.",2001.06461v1
2020-03-01,Criteria for exact saturation and singular compactness,"We introduce the class of unshreddable theories, which contains the simple
and NIP theories, and prove that such theories have exactly saturated models in
singular cardinals, satisfying certain set-theoretic hypotheses. We also give
criteria for a theory to have singular compactness.",2003.00597v2
2020-05-12,Fundamental pushouts of n-complicial sets,"The paper focuses on investigating how certain relations between strict
$n$-categories are preserved in a particular implementation of
$(\infty,n)$-categories, given by saturated $n$-complicial sets. In this model,
we show that the $(\infty,n)$-categorical nerve of $n$-categories is
homotopically compatible with $1$-categorical suspension and wedge. As an
application, we show that certain pushouts encoding composition in
$n$-categories are homotopy pushouts of saturated $n$-complicial sets.",2005.05844v1
2020-05-26,VC-saturated set systems,"The well-known Sauer lemma states that a family $\mathcal{F}\subseteq
2^{[n]}$ of VC-dimension at most $d$ has size at most
$\sum_{i=0}^d\binom{n}{i}$. We obtain both random and explicit constructions to
prove that the corresponding saturation number, i.e., the size of the smallest
maximal family with VC-dimension $d\ge 2$, is at most $4^{d+1}$, and thus is
independent of $n$.",2005.12545v2
2020-07-02,Gray tensor product and saturated $N$-complicial sets,"We show that the pretensor and tensor products of simplicial sets with
marking are compatible with the homotopy theory of saturated $N$-complicial
sets (which are a proposed model of $(\infty,N)$-categories), in the form of a
Quillen bifunctor and a homotopical bifunctor, respectively.",2007.01235v1
2020-11-10,The continuation of finite $E_\mathfrak{F}$-groups theory,"We describe the structure of finite groups with $\mathfrak{F}$-subnormal or
self-normalizing primary cyclic subgroups when $\mathfrak{F}$ is a
subgroup-closed saturate superradical formation containing all nilpotent
groups. We prove that groups with absolutely $\mathfrak{F}$-subnormal or
self-normalizing primary cyclic subgroups are soluble when $\mathfrak{F}$ is a
subgroup-closed saturate formation containing all nilpotent groups.",2011.05291v1
2020-11-17,The catenary degree of the saturated numerical semigroups with prime multiplicity,"In this paper we present the set of saturated numerical semigroups with prime
multiplicity. We also characterize the catenary degree of these semigroups that
we acquire. The catenary degree of a numerical semigroup is the variant which
measures the distance between factorizations of elements within that numerical
semigroup.",2011.08929v1
2020-12-22,The Lipschitz Saturation of a Module,"In this work we extend the concept of the Lipschitz saturation of an ideal
defined in [5] to the context of modules in some different ways, and we prove
they are generically equivalent.",2012.12239v1
2021-01-19,Indices of equilibrium points of linear control systems with saturated state feedback,"In this paper we investigate some properties of equilibrium points in
n-dimensional linear control systems with saturated state feedback. We provide
an index formula for equilibrium points and discuss its relation to boundaries
of attraction basins in feedback systems with single input. In addition, we
also touch upon convexity of attraction basin.",2101.07474v1
2021-12-01,A further generalization of the Glauberman-Thompson $p$-nilpotency criterion in fusion systems,"Let $p$ be a prime and $\mathcal{F}$ be a saturated fusion system over a
finite $p$-group $P$. The fusion system $\mathcal{F}$ is said to be nilpotent
if $\mathcal{F}=\mathcal{F}_{P}(P)$. We provide new criteria for a saturated
fusion system $\mathcal{F}$ to be nilpotent, which may be viewed as extending
the Glauberman-Thompson $p$-nilpotency criterion to fusion systems.",2112.00341v2
2021-12-14,Upper capacity entropy and packing entropy of saturated sets for amenable group actions,"Let $(X,G)$ be a $G$-action topological system, where $G$ is a countable
infinite discrete amenable group and $X$ a compact metric space. In this paper
we study the upper capacity entropy and packing entropy for systems with weaker
version of specification. We prove that the upper capacity always carries full
entropy while there is a variational principle for packing entropy of saturated
sets.",2112.07425v1
2022-02-15,Saturated Kripke Structures as Vietoris Coalgebras,"We show that the category of coalgebras for the compact Vietoris endofunctor
$\mathbb{V}$ on the category Top of topological spaces and continuous mappings
is isomorphic to the category of all modally saturated Kripke structures.
Extending a result of Bezhanishvili, Fontaine and Venema, we also show that
Vietoris subcoalgebras as well as bisimulations admit topological closure and
that the category of Vietoris coalgebras has a terminal object.",2202.07786v1
2022-03-18,Optimal Dose-Limited Phase Estimation without Entanglement,"Phase estimation is one of the most important facets of quantum metrology,
with applications in sensing, microscopy, and quantum computation. When
estimating a phase shift in a lossy medium, there is an upper bound on the
attainable information per particle sent through the phase shift. Previously,
only entanglement-enhanced measurements have been shown to saturate this bound.
We introduce a measurement scheme which can saturate the bound without relying
on entanglement.",2203.10137v1
2022-04-07,"Fixed Sets of Automorphisms of Countable, Arithmetically Saturated Structures","If an automorphism f of a structure M is such that fix(f^k) = fix(f) for all
positive k, then M|fix(f) is a substructure of M. The possible isomorphism
types of such M|fix(f) are characterized when M is countable and arithmetically
saturated.",2204.03557v2
2022-07-20,Prime ideals of the Burnside ring of a saturated fusion system,"In a 1969 article, A. Dress described the prime ideals of the Burnside ring
of a finite group G and the inclusion relations between them. One may ask
whether similar results exist for the Burnside ring of a saturated fusion
system F on a finite p-group S. The present paper answers positively, providing
a typology for the prime ideals of A(F) and for those of A(F) (p) as a
consequence.",2207.09722v1
2022-09-15,Sharpness of saturated fusion systems on a Sylow $p$-subgroup of ${\rm G}_2(p)$,"We prove that the D\'iaz-Park's sharpness conjecture holds for saturated
fusion systems defined on a Sylow $p$-subgroup of the group ${\rm G}_2(p)$, for
$p\geq 5$.",2209.07388v2
2022-10-24,Limits of saturated ideals,"We investigate the question whether a given homogeneous ideal is a limit of
saturated ones. We provide cohomological necessary criteria for this to hold
and apply them to a range of examples. Our motivation comes from the theory of
border apolarity and varieties of sums of powers, where the question above is
tightly connected to proving new lower bounds for border ranks of tensors.",2210.13579v1
2023-02-04,Saturated Fusion Systems on Sylow $p$-subgroups of Rank $2$ Simple Groups of Lie Type,"For any prime $p$ and $S$ a $p$-group isomorphic to a Sylow $p$-subgroup of a
rank $2$ simple group of Lie type in characteristic $p$, we determine all
saturated fusion systems supported on $S$ up to isomorphism.",2302.02222v1
2023-02-12,Unified Derivation of Uncertainty Relations and Their Saturation Conditions,"We analyze uncertainty relations due to Kennard, Robertson, Schr\""odinger,
Maccone and Pati in a unified way from matrix theory point of view. Short
proofs are given to these uncertainty relations and characterizations of the
saturation conditions are given.",2302.06002v2
2023-02-16,Iterative density matrix revisited: Excitonic phenomena to InAs quantum well as a saturable absorber,"By solving the Liouville equation, third-order nonlinear terms is found via
iterative density matrix. Regarding the improved modeling, all frequency range
is taken instead of weak absorptive limit. Considered process can be compared
with saturation fitting for heavy-hole excitons in the InAs quantum well.",2302.08349v1
2023-05-09,Saturation for Flagged Skew Littlewood-Richardson Coefficients,"We define and study a generalization of the Littlewood-Richardson (LR)
coefficients, which we call the flagged skew LR coefficients. These subsume
several previously studied extensions of the LR coefficients. We establish the
saturation property for these coefficients, generalizing work of Knutson-Tao
and Kushwaha-Raghavan-Viswanath.",2305.05195v2
2023-08-24,The generic equivalence among the Lipschitz saturation of a sheaf of modules,"In this work, we extend the concept of the Lipschitz saturation of an ideal
to the context of modules in some different ways, and we prove they are
generically equivalent.",2308.13119v1
2023-08-28,Universally injective and integral contractions on relative Lipschitz saturation of algebras,"In this work, we obtain contraction results for a class of diagrams of ring
morphisms which strictly includes the ones obtained by Lipman. Further, we
present some applications on quotient and in the changing of the base ring in
the saturation.",2308.14624v1
2023-09-14,A survey on relative Lipschitz saturation of algebras and its relation with radicial algebras,"In this work, we introduce the concept of relative Lipschitz saturation,
along with its key categorical and algebraic properties, and demonstrate how
such a structure always gives rise to a radicial algebra.",2309.07965v1
2023-11-02,Realization of saturated transfer systems on cyclic groups of order $p^nq^m$ by linear isometries $N_\infty$-operads,"We prove a new case of Rubin's saturation conjecture about the realization of
$G$-transfer systems, for $G$ a finite cyclic group, by linear isometries
$N_\infty$-operads, namely the case of cyclic groups of order $p^nq^m$ for
$p,q$ distinct primes and $n,m\in \mathbb{N}$.",2311.01608v1
2024-02-06,Comment on the paper 'Saturation and Multifractality of Lagrangian and Eulerian Scaling Exponents in Three-Dimensional Turbulence',"We comment on the paper 'Saturation and Multifractality of Lagrangian and
Eulerian Scaling Exponents in Three-Dimensional Turbulence' by D. Buaria and
K.R. Sreenivasan. We point out some physical interpretation of the results
discussed in the paper.",2402.04189v1
2002-01-07,X-ray Spectra and Pulse Frequency Changes in SAX J2103.5+4545,"The November 1999 outburst of the transient pulsar SAX J2103.5+4545 was
monitored with the large area detectors of the Rossi X-Ray Timing Explorer
until the pulsar faded after a year. The 358 s pulsar was spun up for 150 days,
at which point the flux dropped quickly by a factor of 7, the frequency
saturated and, as the flux continued to decline, a weak spin-down began. The
pulses remained strong during the decay and the spin-up/flux correlation can be
fit to the Ghosh and Lamb derivations for the spin-up caused by accretion from
a thin, pressure-dominated disk, for a distance 3.2 kpc and a surface magnetic
field 1.2 10^{13} Gauss. During the bright spin-up part of the outburst, the
flux was subject to strong orbital modulation, peaking 3 days after periastron
of the eccentric 12.68 day orbit, while during the faint part, there was little
orbital modulation. The X-ray spectra were typical of accreting pulsars,
describable by a cut-off power-law, with an emission line near the 6.4 keV of K
alpha fluorescence from cool iron. The equivalent width of this emission did
not share the orbital modulation, but nearly doubled during the faint phase,
despite little change in the column density. The outburst could have been
caused by an episode of increased wind from a Be star, such that a small
accretion disk is formed during each periastron passage. A change in the wind
and disk structure apparently occurred after 5 months such that the accretion
rate was no longer modulated or the diffusion time was longer. The distance
estimate implies the X-ray luminosity observed was between 1 10^{36} ergs
s^{-1} and 6 \times 10^{34} ergs s^{-1}, with a small but definite correlation
of the intrinsic power-law spectral index.",0201080v1
2002-03-19,X-ray emitting young stars in the Orion Nebula,"The Orion Nebula Cluster and the molecular cloud in its vicinity have been
observed with the ACIS-I detector on board the Chandra X-ray Observatory with
23 hours exposure. We detect 1075 X-ray sources: 91% are spatially associated
with known stellar members of the cluster, and 7% are newly identified deeply
embedded cloud members. This provides the largest X-ray study of a pre-main
sequence stellar population. We examine here the X-ray properties of Orion
young stars as a function of mass. Results include: (a) the discovery of rapid
variability in the O9.5 31 M_o star \theta^2A Ori, and several early B stars,
inconsistent with the standard model of X-ray production in small wind shocks;
(b) support for the hypothesis that intermediate-mass mid-B through A type
stars do not themselves produce significant X-ray emission; (c) confirmation
that low-mass G- through M-type T Tauri stars exhibit powerful flaring but
typically at luminosities considerably below the `saturation' level; (d)
confirmation that the presence or absence of a circumstellar disk has no
discernable effect on X-ray emission; (e) evidence that T Tauri plasma
temperatures are often very high with T >= 100 MK, even when luminosities are
modest and flaring is not evident; and (f) detection of the largest sample of
pre-main sequence very low mass objects showing high flaring levels and a
decline in magnetic activity as they evolve into L- and T-type brown dwarfs.",0203316v1
2002-08-22,"Three-Dimensional Simulations of Parker, Magneto-Jeans, and Swing Instabilities in Shearing Galactic Gas Disks","We use 3D MHD simulations to investigate nonlinear development of the Parker,
magneto-Jeans (MJI), and swing mechanisms in galactic disks. The model disks
are local, isothermal, and begin from a vertically-stratified equilibrium. We
first construct axisymmetric equilibria and examine their stability. Finite
disk thickness reduces the critical Toomre Q parameter below unity; we find Q_c
\~ 0.75, 0.72, and 0.57 for \beta=\infty, 10, and 1 cases, respectively. We
then pursue fully 3D models. In non-self-gravitating cases, the peak density
enhancement from the `pure' Parker instability is less a factor of two. The
dominant growing modes have radial wavelengths comparable to the disk scale
height H, much shorter than the azimuthal wavelength (~10-20 H). Shearing
disks, being more favorable to midplane-symmetric modes, have somewhat
different late-time magnetic field profiles from nonshearing disks, but
otherwise saturated states are similar. Late-time velocity fluctuations at 10%
of the sound speed persist, but no characteristic structural signatures of
Parker modes remain in the new equilibria. In self-gravitating cases, the
development of density structure is qualitatively similar to our previous
results from thin-disk simulations. The Parker instability, although it may
help seed structure or tip the balance under marginal conditions, appears to
play a secondary role. In shearing disks with Q less than a threshold level ~
1, swing amplification can produce bound clouds of a few times the local Jeans
mass. The most powerful cloud-condensing mechanism appears to be the MJI. Our
simulations show that condensations of a local Jeans mass (~3\times 10^7 M_sun)
grow very rapidly, supporting the idea that MJI is at least partly responsible
for the formation of bound cloud complexes in spiral galaxies.",0208414v1
2004-02-27,Chandra observation of an unusually long and intense X-ray flare from a young solar-like star in M78,"LkHA312 has been observed serendipitously with the ACIS-I detector on board
Chandra with 26h continuous exposure. This H_alpha emission line star belongs
to the star-forming region M78 (NGC2068). From the optical and NIR data, we
show that it is a pre-main sequence (PMS) low-mass star with a weak NIR excess.
This genuine T Tauri star displayed an X-ray flare with an unusual long rise
phase (~8h). The X-ray emission was nearly constant during the first 18h of the
observation, and then increased by a factor of 13 during a fast rise phase
(~2h), and reached a factor of 16 above the quiescent X-ray level at the end of
a gradual phase (~6h) showing a slower rise. To our knowledge this flare, with
\~0.4-~0.5 cts/s, has the highest count rate observed so far with Chandra from
a PMS low-mass star. By chance, the source position, 8.2' off-axis, protected
this observation from pile-up. We make a spectral analysis of the X-ray
emission versus time, showing that the plasma temperature of the quiescent
phase and the flare peak reaches 29MK and 88MK, respectively. The quiescent and
flare luminosities in the energy range 0.5--8keV corrected from absorption
(N_H~1.7E21 cm^{-2}) are 6E30erg/s and ~1E32erg/s, respectively. The ratio of
the quiescent X-ray luminosity on the LkHA312 bolometric luminosity is very
high with log(L_X/L_bol)= -2.9, implying that the corona of LkHA312 reached the
`saturation' level. The X-ray luminosity of the flare peak reaches ~2% of the
stellar bolometric luminosity. The different phases of this flare are finally
discussed in the framework of solar flares, which leads to the magnetic loop
height from 3.1E10 to 1E11 cm (0.2-0.5 R*, i.e., 0.5-1.3 R_sun).",0402672v1
2001-09-25,Single Spin Dynamics and Decoherence in a Quantum Dot via Charge Transport,"We investigate the spin dynamics of a quantum dot with a spin-1/2 ground
state in the Coulomb blockade regime and in the presence of a magnetic rf field
leading to electron spin resonances (ESR). We show that by coupling the dot to
leads, spin properties on the dot can be accessed via the charge current in the
stationary and non-stationary limit. We present a microscopic derivation of the
current and the master equation of the dot using superoperators, including
contributions to decoherence and energy shifts due to the tunnel coupling. We
give a detailed analysis of sequential and co-tunneling currents, for linearly
and circularly oscillating ESR fields, applied in cw and pulsed mode. We show
that the sequential tunneling current exhibits a spin satellite peak whose
linewidth gives a lower bound on the decoherence time T_2 of the dot-spin.
Similarly, the spin decoherence can be accessed also in the cotunneling regime
via ESR induced spin flips. We show that the conductance ratio of the spin
satellite peak and the conventional peak due to sequential tunneling saturates
at the universal conductance ratio of 0.71 for strong ESR fields. We describe a
double-dot setup which generates spin dependent tunneling and acts as a current
pump (at zero bias), and as a spin inverter which inverts the spin-polarization
of the current. We show that Rabi oscillations of the dot-spin induce coherent
oscillations in the time-dependent current. These oscillations are observable
in the time-averaged current as function of ESR pulse-duration, and they allow
one to access the spin coherence directly in the time domain. We analyze the
measurement and read-out process of the dot-spin via currents in spin-polarized
leads and identify measurement time and efficiency by calculating the counting
statistics, noise, and the Fano factor.",0109470v1
2002-11-10,Tortuosity Measurement and the Effects of Finite Pulse Widths on Xenon Gas Diffusion NMR Studies of Porous Media,"We have extended the utility of NMR as a technique to probe porous media
structure over length scales of ~ 100 - 2000 micron by using the spin 1/2 noble
gas 129Xe imbibed into the system's pore space. Such length scales are much
greater than can be probed with NMR diffusion studies of water-saturated porous
media. We utilized Pulsed Gradient Spin Echo NMR measurements of the
time-dependent diffusion coefficient, D(t) of the xenon gas filling the pore
space to study further the measurements of both the surface area-pore volume
ratio, S/Vp, and the tortuosity (pore connectivity) of the medium. In
uniform-size glass bead packs, we observed D(t) decreasing with increasing t,
reaching an observed asymptote of ~ 0.62 - 0.65D0, that could be measured over
diffusion distances extending over multiple bead diameters. Measurements of
D(t)/D0 at differing gas pressures showed this tortuosity limit was not
affected by changing the characteristic diffusion length of the spins during
the diffusion encoding gradient pulse. This was not the case at the short time
limit, where D(t)/D0 was noticeably affected by the gas pressure in the sample.
Increasing the gas pressure, and hence reducing D0 and the diffusion during the
gradient pulse served to reduce the previously observed deviation of D(t)/D0
from the S/Vp relation. The Pade approximation is used to interpolate between
the long and short time limits in D(t). While the short time D(t) point lay
above the interpolation line in the case of small beads, due to diffusion
during the gradient pulse on the order of the pore size, it was also noted that
the experimental D(t) data fell below the Pade line in the case of large beads,
most likely due to finite size effects.",0211184v1
2005-06-30,AC Conductance in Dense Array of the Ge$_{0.7}$Si$_{0.3}$ Quantum Dots in Si,"Complex AC-conductance, $\sigma^{AC}$, in the systems with dense
Ge$_{0.7}$Si$_{0.3}$ quantum dot (QD) arrays in Si has been determined from
simultaneous measurements of attenuation, $\Delta\Gamma=\Gamma(H)-\Gamma(0)$,
and velocity, $\Delta V /V=(V(H)-V(0)) / V(0)$, of surface acoustic waves (SAW)
with frequencies $f$ = 30-300 MHz as functions of transverse magnetic field $H
\leq$ 18 T in the temperature range $T$ = 1-20 K. It has been shown that in the
sample with dopant (B) concentration 8.2$ \times 10^{11}$ cm$^{-2}$ at
temperatures $T \leq$4 K the AC conductivity is dominated by hopping between
states localized in different QDs. The observed power-law temperature
dependence, $\sigma_1(H=0)\propto T^{2.4}$, and weak frequency dependence,
$\sigma_1(H=0)\propto \omega^0$, of the AC conductivity are consistent with
predictions of the two-site model for AC hopping conductivity for the case of
$\omega \tau_0 \gg $1, where $\omega=2\pi f$ is the SAW angular frequency and
$\tau_0$ is the typical population relaxation time. At $T >$ 7 K the AC
conductivity is due to thermal activation of the carriers (holes) to the
mobility edge. In intermediate temperature region 4$ < T<$ 7 K, where AC
conductivity is due to a combination of hops between QDs and diffusion on the
mobility edge, one succeeded to separate both contributions. Temperature
dependence of hopping contribution to the conductivity above $T^*\sim$ 4.5 K
saturates, evidencing crossover to the regime where $\omega \tau_0 < $1. From
crossover condition, $\omega \tau_0(T^*)$ = 1, the typical value, $\tau_0$, of
the relaxation time has been determined.",0506800v1
2007-04-24,Rotation and activity of pre-main-sequence stars,"We present a study of rotation (vsini) and chromospheric activity (Halpha EW)
based on an extensive set of high-resolution optical spectra obtained with MIKE
on the 6.5m Magellan Clay telescope. Our targets are 74 F-M dwarfs in the young
stellar associations Eta Cha, TW Hydrae, Beta Pic, and Tuc-Hor, spanning ages
from 6 to 30 Myr. While the Halpha EW for most F and G stars are consistent
with pure photospheric absorption, most K and M stars show chromospheric
emission. By comparing Halpha EW in our sample to results in the literature, we
see a clear evolutionary sequence: Chromospheric activity declines steadily
from the T Tauri phase to the main sequence. Using activity as an age
indicator, we find a plausible age range for the Tuc-Hor association of 10-40
Myr. Between 5 and 30 Myr, we do not see evidence for rotational braking in the
total sample, thus angular momentum is conserved, in contrast to younger stars.
This difference indicates a change in the rotational regulation at 5-10 Myr,
possibly because disk braking cannot operate longer than typical disk
lifetimes, allowing the objects to spin up. The rotation-activity relation is
flat in our sample; in contrast to main-sequence stars, there is no linear
correlation for slow rotators. We argue that this is because young stars
generate their magnetic fields in a fundamentally different way from
main-sequence stars, and not just the result of a saturated solar-type dynamo.
By comparing our rotational velocities with published rotation periods for a
subset of stars, we determine ages of 13 (7-20) Myr and 9 (7-17} Myr for the
Eta Cha and TWA associations, respectively, consistent with previous estimates.
Thus we conclude that stellar radii from evolutionary models by Baraffe et al.
(1998) are in agreement with the observed radii within +-15%. (abridged)",0704.3266v1
2009-01-07,Synthesis and characterization of single phase Mn doped ZnO,"Different samples of Zn1-xMnxO series have been prepared by conventional
solid state sintering method. It has been identified, up to what extent of
doping enable us to synthesize single-phase polycrystalline Mn doped ZnO
samples which is one of the prerequisite for dilute magnetic semiconductor and
we have analyzed its certain other physical aspects. In synthesizing the
samples proportion of Mn varies from 1 at% to 5 at%. However the milling times
have been varied (6, 12, 24, 48 & 96 hours) for only 2 at% Mn doped samples
while for other samples (1, 3, 4 & 5 at% Mn doped) the milling time has been
kept fixed at 96 hours. Room temperature X-Ray diffraction (XRD) data reveal
that all of the prepared samples up to 3 at% of Mn doping exhibit wurtzite-type
structure, no segregation of Mn and/or its oxides has been found. The 4 at% Mn
doped samples show a weak peak of ZnMn2O4 apart from usual other peaks of ZnO
and the intensity of this impurity peak has been further increased for 5 at% of
Mn doping. So beyond 3 at% doping single-phase behavior is destroyed. Band gap
for all the 2 at% Mn doped samples have been estimated as between 3.21 to 3.19
eV and reason for this low band gap values has been explained through the grain
boundary trapping model. The room temperature resistivity measurement shows
increase of resistivity up to 48 hours of milling and with further milling it
saturates. The defect state of these samples has been investigated by using
positron annihilation lifetime (PAL) spectroscopy technique. Here all the
relevant lifetime parameters of positron i.e. free annihilation (tau 1), at
defect site (tau 2) and average (tau av) increases with milling time.",0901.0807v1
2009-01-12,Planet formation bursts at the borders of the dead zone in 2D numerical simulations of circumstellar disks,"As accretion in protoplanetary disks is enabled by turbulent viscosity, the
border between active and inactive (dead) zones constitutes a location where
there is an abrupt change in the accretion flow. The gas accumulation that
ensues triggers the Rossby wave instability, that in turn saturates into
anticyclonic vortices. It was suggested that the trapping of solids within them
leads to a burst of planet formation on very short timescales. We perform
two-dimensional global simulations of the dynamics of gas and solids in a
non-magnetized thin protoplanetary disk with the Pencil Code. We use multiple
particle species of radius 1, 10, 30, and 100 cm, solving for the particles'
gravitational interaction by a particle-mesh method. The dead zone is modeled
as a region of low viscosity. Adiabatic and locally isothermal equations of
state are used. We find that the Rossby wave instability is triggered under a
variety of conditions, thus making vortex formation a robust process. Inside
the vortices, fast accumulation of solids occurs and the particles collapse
into objects of planetary mass in timescales as short as five orbits. Because
the drag force is size-dependent, aerodynamical sorting ensues within the
vortical motion, and the first bound structures formed are composed primarily
of similarly-sized particles. In addition to erosion due to ram pressure, we
identify gas tides from the massive vortices as a disrupting agent of formed
protoplanetary embryos. We also estimate the collisional velocity history of
the particles that compose the most massive embryo by the end of the
simulation, finding that the vast majority of them never experienced a
collision with another particle at speeds faster than 1 m/s.",0901.1638v4
2011-03-03,Chromospheric Activities and Kinematics for Solar Type Dwarfs and Subgiants: Analysis of the Activity Distribution and the AVR,"In this work we present chromospheric activity indices, kinematics,
radial-velocities and rotational velocities for more than 850 FGK-type dwarfs
and subgiant stars in the southern hemisphere and test how best to calibrate
and measure S-indices from echelle spectra. We confirm the bimodal distribution
of chromospheric activities for such stars and highlight the role that the more
active K-dwarfs play in biasing the number of active stars. We show that the
age-activity relationship does appear to continue to ages older than the Sun if
we simply compare main sequence stars and subgiant stars, with an offset of
around 2.5 Gyrs between the peaks of both distributions. Also we show evidence
for an increased spin-down timescale for cool K dwarfs compared with earlier F
and G type stars. In addition, we show how kinematics can be used to preselect
inactive stars for future planet search projects. We see the well known trend
between projected rotational velocity and activity, however we also find a
correlation between kinematic space velocity and chromospheric activity. It
appears that after the Vaughan-Preston gap there is a quick step function in
the kinematic space motion towards a significantly larger spread in velocities.
We speculate on reasons for this correlation and provide some model scenarios
to describe the bimodal activity distribution through magnetic saturation,
residual low level gas accretion or accretion by the star of planets or
planetesimals. Finally, we provide a new empirical measurement for the disk
heating law, using the latest age-activity relationships to reconstruct the
age-velocity distribution for local disk stars. We find a value of
0.337+/-0.045 for the exponent of this power law (i.e. sigma_tot proportional
to t^0.337), in excellent agreement with those found using isochrone fitting
methods and with theoretical disk heating models. [Abridged]",1103.0584v1
2011-07-21,Glueballs in large-N YM by localization on critical points,"By exploiting in large-N YM the change of variables from the gauge connection
to the ASD part of its curvature by a non-SUSY version of the Nicolai map, we
show that certain twistor Wilson loops supported on a Lagrangian submanifold of
twistor space are localized on lattices of surface operators of Z(N) holonomy
that form translational invariant sectors labelled by the magnetic charge
k=1,2,...,N-1 at a point. The localization is obtained reducing the loop
equation in the ASD variables in the holomorphic gauge, regularized by analytic
continuation to Minkowski space-time, to a critical equation, by exploiting the
invariance of the twistor Wilson loops by deformations for the addition of
backtracking arcs ending with cusps on the singular divisor of surface
operators. Alternatively localization is obtained contracting the YM measure in
the ASD variables on the fixed points of a semigroup that acts on the fiber of
the Lagrangian twistor fibration which twistor Wilson loops are supported on
and leaves invariant their v.e.v.. The masses squared of the fluctuations of
surface operators in the sectors labelled by k, supported on the Lagrangian
submanifold analytically continued to Minkowski space-time, form a trajectory
linear in k that does not include any massless state. The glueballs propagators
in the holomorphic/antiholomorphic sector defined by correlators of a complex
combination of the ASD curvature and its adjoint saturate at short distances
the logarithms of perturbation theory by a sum of pure poles. In this framework
Regge trajectories of higher spins are related to fluctuations of surface
operators with pole singularities of any order.",1107.4320v4
2012-05-10,Mid-Infrared Extinction Mapping of Infrared Dark Clouds II. The Structure of Massive Starless Cores and Clumps,"(abridged) We develop the mid-infrared extinction (MIREX) mapping technique
of Butler & Tan (2009, Paper I), presenting a new method to correct for the
Galactic foreground emission based on observed saturation in independent cores.
Using Spitzer GLIMPSE 8 micron images, this allows us to accurately probe mass
surface densities, Sigma, up to ~0.5g/cm^2 with 2"" resolution. We then
characterize the structure of 42 massive starless and early-stage IRDC cores
and their surrounding clumps, measuring Sigma_cl(r) from the core/clump
centers. We first assess the properties of the core/clump at a scale where the
total enclosed mass as projected on the sky is M_cl=60Msun. We find these
objects have a mean radius of R_cl~0.1pc, mean Sigma_cl=0.3g/cm^2 and, if fit
by a power law density profile rho_cl ~ r^{-k_{rho,cl}}, a mean value of
k_{rho,cl}=1.1. If we assume a core is embedded in each clump and subtract the
surrounding clump envelope to derive the core properties, we find a mean core
density power law index of k_{rho,c} = 1.6. We repeat this analysis as a
function of radius and derive the best-fitting power law plus uniform clump
envelope model for each of the 42 core/clumps. The cores have typical masses of
M_c~100Msun and mean Sigma_c~0.1g/cm^2, and are embedded in clumps with
comparable mass surface densities. We conclude massive starless cores exist and
are well-described by singular polytropic spheres. Their relatively low values
of Sigma and the fact that they are IR dark may imply that their fragmentation
is inhibited by magnetic fields rather than radiative heating. Comparing to
massive star-forming cores, there is tentative evidence for an evolution
towards higher densities and steeper density profiles as star formation
proceeds.",1205.2391v1
2013-02-05,The UV and X-ray activity of the M dwarfs within 10pc of the Sun,"We systematically study the X-ray and ultraviolet emission of a subsample of
M dwarfs from a recent proper-motion survey, selecting all M dwarfs within 10pc
to obtain a nearly volume-limited sample (~90% completeness). Archival ROSAT,
XMM-Newton and GALEX data are combined with published spectroscopic studies of
Halpha emission and rotation to obtain a broad picture of stellar activity on M
dwarfs. We make use of synthetic model spectra to determine the relative
contributions of photospheric and chromospheric emission to the ultraviolet
flux. We also analyse the same diagnostics for a comparison sample of young M
dwarfs in the TWHya association (~10Myrs). We find that generally the emission
in the GALEX bands is dominated by the chromosphere but the photospheric
component is not negligible in early-M field dwarfs. The surface fluxes for the
Halpha, near-ultraviolet, far-ultraviolet and X-ray emission are connected via
a power law dependence. We present here for the first time such flux-flux
relations involving broad-band ultraviolet emission for M dwarfs. For given
spectral type the activity indices, defined as flux ratio between the activity
diagnostic and the bolometric flux of the star, display a spread of 2-3 dex
which is largest for M4 stars. The mean activity index for fast rotators,
likely representing the saturation level, decreases from X-rays over the FUV to
the NUV band and Halpha, i.e. the fractional radiation output increases with
atmospheric height. The comparison to the ultraviolet and X-ray properties of
TWHya members shows a drop of nearly three orders of magnitude for the
luminosity in these bands between ~10Myr and few Gyrs age. A few young field
dwarfs (< 1Gyr) in the 10pc sample bridge the gap indicating that the drop in
magnetic activity with age is a continuous process. The slope of the age decay
is steeper for the X-ray than for the UV luminosity.",1302.1061v1
2014-03-05,Bond disorder and spinon heat transport in the $S=\tfrac{1}{2}$ Heisenberg spin chain compound Sr$_2$CuO$_3$: from clean to dirty limits,"We investigate the effect of disorder on the heat transport properties of the
$S=\tfrac{1}{2}$ Heisenberg chain compound Sr$_2$CuO$_3$ upon chemically
substituting Sr by increasing concentrations of Ca. As Ca occupies sites
outside but near the Cu-O-Cu spin chains, bond disorder, i.e. a spatial
variation of the exchange interaction $J$, is expected to be realized in these
chains. We observe that the magnetic heat conductivity
($\kappa_{\mathrm{mag}}$) due to spinons propagating in the chains is gradually
but strongly suppressed with increasing amount of Ca, where the doping
dependence can be understood in terms of increased scattering of spinons due to
Ca-induced disorder. This is also reflected in the spinon mean free path which
can be separated in a doping independent but temperature dependent scattering
length due to spinon-phonon scattering, and a temperature independent but
doping dependent spinon-defect scattering length. The latter spans from very
large ($>$ 1300 lattice spacings) to very short ($\sim$ 12 lattice spacings)
and scales with the average distance between two neighboring Ca atoms. Thus,
the Ca-induced disorder acts as an effective defect within the spin chain, and
the doping scheme allows to cover the whole doping regime between the clean and
the dirty limits. Interestingly, at maximum impurity level we observe, in
Ca-doped Sr$_2$CuO$_3$, an almost linear increase of $\kappa_{\mathrm{mag}}$ at
temperatures above 100 K which reflects the intrinsic low temperature behavior
of heat transport in a Heisenberg spin chain. These findings are quite
different from that observed for the Ca-doped double spin chain compound,
SrCuO$_2$, where the effect of Ca seems to saturate already at intermediate
doping levels.",1403.1145v2
2014-09-26,The Factory and The Beehive II. Activity and Rotation in Praesepe and the Hyades,"Open clusters are collections of stars with a single, well-determined age,
and can be used to investigate the connections between angular-momentum
evolution and magnetic activity over a star's lifetime. We present the results
of a comparative study of the relationship between stellar rotation and
activity in two benchmark open clusters: Praesepe and the Hyades. As they have
the same age and roughly solar metallicity, these clusters serve as an ideal
laboratory for testing the agreement between theoretical and empirical
rotation-activity relations at $\approx$600 Myr. We have compiled a sample of
720 spectra --- more than half of which are new observations --- for 516
high-confidence members of Praesepe; we have also obtained 139 new spectra for
130 high-confidence Hyads. We have collected rotation periods ($P_{rot}$) for
135 Praesepe members and 87 Hyads. To compare $H\alpha$ emission, an indicator
of chromospheric activity, as a function of color, mass, and Rossby number
$R_o$, we first calculate an expanded set of $\chi$ values, with which we can
obtain the $H\alpha$ to bolometric luminosity ratio, $L_{H\alpha}/L_{bol}$,
even when spectra are not flux-calibrated and/or stars lack reliable distances.
Our $\chi$ values cover a broader range of stellar masses and colors (roughly
equivalent to spectral types from K0 to M9), and exhibit better agreement
between independent calculations, than existing values. We find no difference
between the two clusters in their $H\alpha$ equivalent width or
$L_{H\alpha}/L_{bol}$ distributions, and therefore take the merged $H\alpha$
and $P_{rot}$ data to be representative of 600-Myr-old stars. Our analysis
shows that $H\alpha$ activity in these stars is saturated for
$R_o\leq0.11^{+0.02}_{-0.03}$. Above that value activity declines as a
power-law with slope $\beta=-0.73^{+0.16}_{-0.12}$, before dropping off rapidly
at $R_o\approx0.4$...",1409.7603v1
2015-01-01,Motivation and challenge to capture both large scale and local transport in next generation accretion theory,"Accretion disc theory is less developed than stellar evolution theory
although a similarly mature phenomenological picture is ultimately desired.
While the interplay of theory and numerical simulations has amplified community
awareness of the role of magnetic fields in angular momentum transport, there
remains a long term challenge to incorporate insight gained from simulations
back into improving practical models for comparison with observations. Here we
emphasize the need to incorporate the role of non-local transport more
precisely. To show where large scale transport would fit into the theoretical
framework and how it is currently missing, we review why the wonderfully
practical approach of Shakura-Sunyaev (1973,SS73) is necessarily a mean field
theory, and one which does not include large scale transport. Observations of
coronae and jets combined with the interpretation of results even from shearing
box simulations of the magnetorotational instability (MRI) suggest that a
significant fraction of disc transport is indeed non-local. We show that the
Maxwell stresses in saturation are dominated by large scale contributions and
the physics of MRI transport is not fully captured by a viscosity. We also
clarify the standard physical interpretation of the MRi as it applies to
shearing boxes. Computational limitations have so far focused most attention
toward local simulations but the next generation of global simulations should
help to inform improved mean field theories. Mean field accretion theory and
mean field dynamo theory should in fact be unified into a single theory that
predicts the time evolution of spectra and luminosity from separate disc,
corona, and outflow contributions. Finally, we note that any mean field theory
has a finite predictive precision that needs to be quantified when comparing
the predictions to observations.",1501.00291v4
2015-06-27,Theory of the nonlinear Rashba-Edelstein effect,"It is well known that a current driven through a two-dimensional electron gas
with Rashba spin-orbit coupling induces a spin polarization in the
perpendicular direction (Edelstein effect). This phenomenon has been
extensively studied in the linear response regime, i.e., when the average drift
velocity of the electrons is a small fraction of the Fermi velocity. Here we
investigate the phenomenon in the nonlinear regime, meaning that the average
drift velocity is comparable to, or exceeds the Fermi velocity. This regime is
realized when the electric field is very large, or when electron-impurity
scattering is very weak. The quantum kinetic equation for the density matrix of
noninteracting electrons is exactly and analytically solvable, reducing to a
problem of spin dynamics for ""unpaired"" electrons near the Fermi surface. The
crucial parameter is $\gamma=eEL_s/E_F$, where $E$ is the electric field, $e$
is the absolute value of the electron charge, $E_F$ is the Fermi energy, and
$L_s = \hbar/(2m\alpha)$ is the spin-precession length in the Rashba spin-orbit
field with coupling strength $\alpha$. If $\gamma\ll1$ the evolution of the
spin is adiabatic, resulting in a spin polarization that grows monotonically in
time and eventually saturates at the maximum value $n(\alpha/v_F)$, where $n$
is the electron density and $v_F$ is the Fermi velocity. If $\gamma \gg 1$ the
evolution of the spin becomes strongly non-adiabatic and the spin polarization
is progressively reduced, and eventually suppressed for $\gamma\to \infty$. We
also predict an inverse nonlinear Edelstein effect, in which an electric
current is driven by a magnetic field that grows linearly in time. The
""conductivities"" for the direct and the inverse effect satisfy generalized
Onsager reciprocity relations, which reduce to the standard ones in the linear
response regime.",1506.08330v1
2015-09-04,Standing Sausage Modes In Nonuniform Magnetic Tubes: An Inversion Scheme For Inferring Flare Loop Parameters,"Standing sausage modes in flare loops are important for interpreting
quasi-periodic pulsations (QPPs) in solar flare lightcurves. We propose an
inversion scheme that consistently uses their periods $P$ and damping times
$\tau$ to diagnose flare loop parameters. We derive a generic dispersion
relation governing linear sausage waves in pressure-less straight tubes, for
which the transverse density inhomogeneity takes place in a layer of arbitrary
width $l$ and is of arbitrary form. We find that $P$ and $\tau$ depend on the
combination of $[R/v_{\rm Ai}, L/R, l/R, \rho_{\rm i}/\rho_{\rm e}]$, where $R$
is the loop radius, $L$ is the looplength, $v_{\rm Ai}$ is the internal
Alfv\'en speed, and $\rho_{\rm i}/\rho_{\rm e}$ is the density contrast. For
all the density profiles examined, $P$ and $\tau$ experience saturation when
$L/R \gg 1$, yielding an inversion curve in the $[R/v_{\rm Ai}, l/R, \rho_{\rm
i}/\rho_{\rm e}]$ space with a specific density profile when $L/R$ is
sufficiently large. When applied to a spatially unresolved QPP event, the
scheme yields that $R/v_{\rm Ai}$ is the best constrained, whereas $l/R$
corresponds to the other extreme. For spatially resolved QPPs, while $L/R \gg
1$ cannot be assumed beforehand, an inversion curve remains possible due to
additional geometrical constraints. When a spatially resolved QPP event
involves another mode, as is the case for a recent event, the full set of
$[v_{\rm Ai}, l, \rho_{\rm i}/\rho_{\rm e}]$ can be inferred. We conclude that
the proposed scheme provides a useful tool for magneto-seismologically
exploiting QPPs.",1509.01442v1
2015-09-22,Quantum Simulations of Nuclei and Nuclear Pasta with the Multi-resolution Adaptive Numerical Environment for Scientific Simulations,"Neutron star and supernova matter at densities just below the nuclear matter
saturation density is expected to form a lattice of exotic shapes. These
so-called nuclear pasta phases are caused by Coulomb frustration. Their elastic
and transport properties are believed to play an important role for thermal and
magnetic field evolution, rotation and oscillation of neutron stars.
Furthermore, they can impact neutrino opacities in core-collapse supernovae. In
this work, we present proof-of-principle 3D Skyrme Hartree-Fock (SHF)
simulations of nuclear pasta with the Multi-resolution ADaptive Numerical
Environment for Scientific Simulations (MADNESS). We perform benchmark studies
of $^{16} \mathrm{O}$, $^{208} \mathrm{Pb}$ and $^{238} \mathrm{U}$ nuclear
ground states and calculate binding energies via 3D SHF simulations. Results
are compared with experimentally measured binding energies as well as with
theoretically predicted values from an established SHF code. The nuclear pasta
simulation is initialized in the so-called waffle geometry as obtained by the
Indiana University Molecular Dynamics (IUMD) code. The size of the unit cell is
24\:fm with an average density of about $\rho = 0.05 \:\mathrm{fm}^{-3}$,
proton fraction of $Y_p = 0.3$ and temperature of $T=0\:$MeV. Our calculations
reproduce the binding energies and shapes of light and heavy nuclei with
different geometries. For the pasta simulation, we find that the final geometry
is very similar to the initial waffle state. In the present pasta calculations
spin-orbit forces are not included but will be added in the future. Within the
MADNESS framework, we can successfully perform calculations of inhomogeneous
nuclear matter. By using pasta configurations from IUMD it is possible to
explore different geometries and test the impact of self-consistent
calculations on the latter.",1509.06671v2
2015-12-08,The nature of the electrical conduction in ferromagnetic atomic-size contacts: insights from shot noise measurements and theoretical simulations,"With the goal to elucidate the nature of spin-dependent electronic transport
in ferromagnetic atomic contacts, we present here a combined experimental and
theoretical study of the conductance and shot noise of metallic atomic contacts
made of the 3d ferromagnetic materials Fe, Co, and Ni. For comparison, we also
present the corresponding results for the noble metal Cu. Conductance and shot
noise measurements, performed using a low-temperature break junction setup,
show that in these ferromagnetic nanowires: (i) there is no conductance
quantization of any kind, (ii) transport is dominated by several partially-open
conduction channels, even in the case of single-atom contacts, and (iii) the
Fano factor of large contacts saturates to values that clearly differs from
those of monovalent (nonmagnetic) metals. We rationalize these observations
with the help of a theoretical approach that combines molecular dynamics
simulations to describe the junction formation with nonequilibrium Green's
function techniques to compute the transport properties within the
Landauer-Buettiker framework. Our theoretical approach successfully reproduces
all the basic experimental results and it shows that all the observations can
be traced back to the fact that the d bands of the minority-spin electrons play
a fundamental role in the transport through ferromagnetic atomic-size contacts.
These d bands give rise to partially open conduction channels for any contact
size, which in turn lead naturally to the different observations described
above. Thus, the transport picture for these nanoscale ferromagnetic wires that
emerges from the ensemble of our results is clearly at variance with the well
established conduction mechanism that governs the transport in macroscopic
ferromagnetic wires, where the d bands are responsible for the magnetism but do
not take part in the charge flow.",1512.02601v1
2016-03-28,The Efficiency of Magnetic Field Amplification at Shocks by Turbulence,"Turbulent dynamo field amplification has often been invoked to explain the
strong field strengths in thin rims in supernova shocks ($\sim 100 \, \mu$G)
and in radio relics in galaxy clusters ($\sim \mu$G). We present high
resolution MHD simulations of the interaction between pre-shock turbulence,
clumping and shocks, to quantify the conditions under which turbulent dynamo
amplification can be significant. We demonstrate numerically converged field
amplification which scales with Alfv\'en Mach number, $B/B_0 \propto {\mathcal
M}_{\rm A}$, up to ${\mathcal M}_{\rm A} \sim 150$. This implies that the
post-shock field strength is relatively independent of the seed field.
Amplification is dominated by compression at low ${\mathcal M}_{\rm A}$, and
stretching (turbulent amplification) at high ${\mathcal M}_{\rm A}$. For high
$\mathcal{M}_{\rm A}$, the $B$-field grows exponentially and saturates at
equipartition with turbulence, while the vorticity jumps sharply at the shock
and subsequently decays; the resulting field is orientated predominately along
the shock normal (an effect only apparent in 3D and not 2D). This agrees with
the radial field bias seen in supernova remnants. By contrast, for low
$\mathcal{M}_{\rm A}$, field amplification is mostly compressional, relatively
modest, and results in a predominantly perpendicular field. The latter is
consistent with the polarization seen in radio relics. Our results are
relatively robust to the assumed level of gas clumping. Our results imply that
the turbulent dynamo may be important for supernovae, but is only consistent
with the field strength, and not geometry, for cluster radio relics. For the
latter, this implies strong pre-existing $B$-fields in the ambient cluster
outskirts.",1603.08518v2
2016-04-04,Ferro-deformation and shape phase transitions over the nuclear chart: 50 < protons (Z) < 82 and 50 < neutrons (N) < 126,"We study a global nuclear structure in the framework of experimental
observables. With the aid of large nuclear structure data at the national
nuclear data center, NNDC, we present the distinctive systematic patterns
emerged in the first 2+ excited energies, E(2+) and their energy ratios to the
first 4+ levels, R = E(4+)/E(2+), in the even-even nuclei, over 50 < Z < 82 for
protons, and 50 < N < 126 for neutrons. We introduce the so-called pseudo-shell
configurations from the subshells mixture in order to explain a semi-double
shell closure, a shape phase transition, and a reinforced deformation. It is
found that the reinforced deformation arises when Z = 64 or 66 correlates with
N = 90 and reaches its maximum, indicating R = 3.3. Such a saturated reinforced
deformation spans over Z = 58 to 72 and N = 100 to 106 as showing its center at
Z = 64 or 66 and at N = 102 or 104. We define this reinforced deformation 'a
ferro-deformation' like a ferro-magnetism in condensed matter physics. The
shape coexistence would be expected to occur, such as a ferro-deformation, with
a strong rotational mode, and a near spherical shape, with a vibrational mode,
at the critical points of Z = 64 or 66, with N = 88 and 90; 150Sm and 152Sm,
152Gd and 154Gd, and 154Dy and 156Dy. We suggest that a super-deformation,
which can be formed at high-lying excited states in a moderate deformed
nucleus, would correspond to the ferro-deformation at N = 88 for the nuclei;
Sm, Gd, and Dy. We argue that the ferro-deformation can be closely associated
with a strong spin-orbital interaction between neutrons and protons in the
spin-orbit doublet, h9/2-h11/2, leading to the critical points at Z, N = 64,
104.",1604.01017v1
2016-04-19,Evidence for Cluster to Cluster Variations in Low-Mass Stellar Rotational Evolution,"A concordance model for angular momentum evolution has been developed by
multiple investigators. This approach postulates that star forming regions and
clusters are an evolutionary sequence which can be modeled with assumptions
about the coupling between protostars and accretion disks, angular momentum
loss from magnetized winds that saturates in a mass-dependent fashion at high
rotation rates, and core-envelope decoupling for solar analogs. We test this
approach by combining established data with the large h Per dataset from the
MONITOR project and new low-mass Pleiades data. We confirm prior results that
young low-mass stars can be used to test star-disk coupling and angular
momentum loss independent of the treatment of internal angular momentum
transport. For slow rotators, we confirm the need for star-disk interactions to
evolve the ONC to older systems, using h Per (age 13~Myr) as our natural
post-disk case. Further interactions are not required to evolve slow rotators
from h Per to older systems, implying no justification for extremely long-lived
disks as an alternative to core-envelope decoupling. However, our wind models
cannot evolve rapid rotators from h Per to older systems consistently; this
appears to be a general problem for any wind model that becomes ineffective in
low-mass young stars. We outline two possible solutions: either there is cosmic
variance in the distribution of stellar rotation rates in different clusters or
there are substantially enhanced torques in low-mass rapid rotators. We favor
the former explanation and discuss observational tests that could be used to
distinguish them. If the distribution of initial conditions depends on
environment, models which test parameters by assuming a universal underlying
distribution of initial conditions will need to be re-evaluated.",1604.05729v1
2016-07-15,The Aerogel Cherenkov Detector for the SHMS magnetic spectrometer in Hall C at Jefferson Lab,"Hadronic reactions producing strange quarks such as exclusive or
semi-inclusive kaon production, play an important role in studies of hadron
structure and the dynamics that bind the most basic elements of nuclear
physics. The small-angle capability of the new Super High Momentum Spectrometer
(SHMS) in Hall C, coupled with its high momentum reach - up to the anticipated
11-GeV beam energy in Hall C - and coincidence capability with the
well-understood High Momentum Spectrometer, will allow for probes of such
hadron structure involving strangeness down to the smallest distance scales to
date. To cleanly select the kaons, a threshold aerogel Cerenkov detector has
been constructed for the SHMS. The detector consists of an aerogel tray
followed by a diffusion box. Four trays for aerogel of nominal refractive
indices of n=1.030, 1.020, 1.015 and 1.011 were constructed. The tray
combination will allow for identification of kaons from 1 GeV/c up to 7.2
GeV/c, reaching 10^-2 proton and 10^-3 pion rejection, with kaon detection
efficiency better than 95%. The diffusion box of the detector is equipped with
14 five-inch diameter photomultiplier tubes. Its interior walls are covered
with Gore diffusive reflector, which is superior to the commonly used Millipore
paper and improved the detector performance by 35%. The inner surface of the
two aerogel trays with higher refractive index is covered with Millipore paper,
however, those two trays with lower aerogel refractive index are again covered
with Gore diffusive reflector for higher performance. The measured mean number
of photoelectrons in saturation is ~12 for n=1.030, ~sim8 for n=1.020, ~10 for
n=1.015, and ~5.5 for n=1.011. The design details, the results of component
characterization, and initial performance tests and optimization of the
detector are presented.",1607.05264v1
2016-08-17,Kinematics of the jet in M87 on scales of 100 -- 1000 Schwarzschild radii,"Very long baseline interferometry (VLBI) imaging of radio emission from
extragalactic jets provides a unique probe of physical mechanisms governing the
launching, acceleration, and collimation of relativistic outflows. The
two-dimensional structure and kinematics of the jet in M\,87 (NGC\,4486) have
been studied by applying the Wavelet-based Image Segmentation and Evaluation
(WISE) method to 11 images obtained from multi-epoch Very Long Baseline Array
(VLBA) observations made in January-August 2007 at 43 GHz ($\lambda = 7$ mm).
The WISE analysis recovers a detailed two-dimensional velocity field in the jet
in M\,87 at sub-parsec scales. The observed evolution of the flow velocity with
distance from the jet base can be explained in the framework of MHD jet
acceleration and Poynting flux conversion. A linear acceleration regime is
observed up to $z_{obs} \sim 2$\,mas. The acceleration is reduced at larger
scales, which is consistent with saturation of Poynting flux conversion.
Stacked cross correlation analysis of the images reveals a pronounced
stratification of the flow. The flow consists of a slow, mildly relativistic
layer (moving at $\beta \sim 0.5\,c$), associated either with instability
pattern speed or an outer wind, and a fast, accelerating stream line (with
$\beta \sim 0.92$, corresponding to a bulk Lorentz factor $\gamma \sim 2.5$). A
systematic difference of the apparent speeds in the northern and southern limbs
of the jet is detected, providing evidence for jet rotation. The angular
velocity of the magnetic field line associated with this rotation suggests that
the jet in M87 is launched in the inner part of the disk, at a distance $r_0
\sim 5\, R_\mathrm{s}$ from the central engine. The combined results of the
analysis imply that MHD acceleration and conversion of Poynting flux to kinetic
energy play the dominant roles in collimation and acceleration of the flow in
M\,87.",1608.05063v1
2017-03-02,Analysis of the flux growth rate in emerging active regions on the Sun,"We studied the emergence process of 42 active region (ARs) by analyzing the
time derivative, R(t), of the total unsigned flux. Line-of-sight magnetograms
acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar
Dynamics Observatory (SDO) were used. A continuous piecewise linear fitting to
the R(t)-profile was applied to detect an interval, dt_2, of nearly-constant
R(t) covering one or several local maxima. The averaged over dt_2 magnitude of
R(t) was accepted as an estimate of the maximal value of the flux growth rate,
R_MAX, which varies in a range of (0.5-5)x10^20 Mx hour^-1 for active regions
with the maximal total unsigned flux of (0.5-3)x10^22 Mx. The normalized flux
growth rate, R_N, was defined under an assumption that the saturated total
unsigned flux, F_MAX, equals unity. Out of 42 ARs in our initial list, 36 event
were successfully fitted and they form two subsets (with a small overlap of 8
events): the ARs with a short (<13 hours) interval dt_2 and a high (>0.024
hour^-1) normalized flux emergence rate, R_N, form the ""rapid"" emergence event
subset. The second subset consists of ""gradual"" emergence events and it is
characterized by a long (>13 hours) interval dt_2 and a low R_N (<0.024
hour^-1). In diagrams of R_MAX plotted versus F_MAX, the events from different
subsets are not overlapped and each subset displays an individual power law.
The power law index derived from the entire ensemble of 36 events is
0.69+-0.10. The ""rapid"" emergence is consistent with a ""two-step"" emergence
process of a single twisted flux tube. The ""gradual"" emergence is possibly
related to a consecutive rising of several flux tubes emerging at nearly the
same location in the photosphere.",1703.00739v1
2017-03-22,Verification of Gyrokinetic codes: theoretical background and applications,"In fusion plasmas the strong magnetic field allows the fast gyro-motion to be
systematically removed from the description of the dynamics, resulting in a
considerable model simplification and gain of computational time. Nowadays, the
gyrokinetic (GK) codes play a major role in the understanding of the
development and the saturation of turbulence and in the prediction of the
subsequent transport. Naturally, these codes require thorough verification and
validation.
  Here we present a new and generic theoretical framework and specific
numerical applications to test the faithfulness of the implemented models to
theory and to verify the domain of applicability of existing GK codes. For a
sound verification process, the underlying theoretical GK model and the
numerical scheme must be considered at the same time, which has rarely been
done and therefore makes this approach pioneering. At the analytical level, the
main novelty consists in using advanced mathematical tools such as variational
formulation of dynamics for systematization of basic GK code's equations to
access the limits of their applicability. The verification of numerical scheme
is proposed via the benchmark effort.
  In this work, specific examples of code verification are presented for two GK
codes: the multi-species electromagnetic ORB5 (PIC) and the radially global
version of GENE (Eulerian). The proposed methodology can be applied to any
existing GK code. We establish a hierarchy of reduced GK Vlasov-Maxwell
equations implemented in the ORB5 and GENE codes using the Lagrangian
variational formulation. At the computational level, detailed verifications of
global electromagnetic test cases developed from the CYCLONE Base Case are
considered, including a parametric $\beta$-scan covering the transition from
ITG to KBM and the spectral properties at the nominal $\beta$ value.",1703.07582v2
2017-06-23,Asymptotic structure of $\mathcal{N}=2$ supergravity in 3D: extended super-BMS$_3$ and nonlinear energy bounds,"The asymptotically flat structure of $\mathcal{N}=(2,0)$ supergravity in
three spacetime dimensions is explored. The asymptotic symmetries are spanned
by an extension of the super-BMS$_3$ algebra, with two independent $\hat{u}(1)$
currents of electric and magnetic type. These currents are associated to $U(1)$
fields being even and odd under parity, respectively. Remarkably, although the
$U(1)$ fields do not generate a backreaction on the metric, they provide
nontrivial Sugawara-like contributions to the BMS$_3$ generators, and hence to
the energy and the angular momentum. The entropy of flat cosmological
spacetimes with $U(1)$ fields then acquires a nontrivial dependence on the
$\hat{u}(1)$ charges. If the spin structure is odd, the ground state
corresponds to Minkowski spacetime, and although the anticommutator of the
canonical supercharges is linear in the energy and in the electric-like
$\hat{u}(1)$ charge, the energy becomes bounded from below by the energy of the
ground state shifted by the square of the electric-like $\hat{u}(1)$ charge. If
the spin structure is even, the same bound for the energy generically holds,
unless the absolute value of the electric-like charge is less than minus the
mass of Minkowski spacetime in vacuum, so that the energy has to be
nonnegative. The explicit form of the Killing spinors is found for a wide class
of configurations that fulfills our boundary conditions, and they exist
precisely when the corresponding bounds are saturated. It is also shown that
the spectra with periodic or antiperiodic boundary conditions for the fermionic
fields are related by spectral flow, in a similar way as it occurs for the
$\mathcal{N}=2$ super-Virasoro algebra. Indeed, our super-BMS$_3$ algebra can
be recovered from the flat limit of the superconformal algebra with
$\mathcal{N}=(2,2)$, truncating the fermionic generators of the right copy.",1706.07542v3
2017-11-30,Anomalous and regular transport in spin 1/2 chains: AC conductivity,"We study magnetization transport in anisotropic spin-$1/2$ chains governed by
the integrable XXZ model with and without integrability-breaking perturbations
at high temperatures ($T\to \infty$) using a hybrid approach that combines
exact sum-rules with judiciously chosen Ans\""atze. In the integrable XXZ model
we find (i) super-diffusion at the isotropic (Heisenberg) point, with frequency
dependent conductivity $ \sigma'(\omega\to 0) \sim |\omega|^{\alpha}$, where
$\alpha=-3/7$ in close numerical agreement with recent $t$-DMRG computations;
(ii) a continuously drifting exponent from $\alpha=-1^+$ in the XY limit of the
model to $\alpha>0$ within the Ising regime; and (iii) a diffusion constant
saturating in the XY coupling deep in the Ising limit. We consider two kinds of
integrability breaking perturbations --- a simple next-nearest-neighbor
spin-flip term ($J_2$) and a three-spin assisted variant ($t_2$), natural in
the fermion particle representation of the spin chain. In the first case we
discover a remarkable sensitivity of $\sigma'(\omega)$ to the sign of $J_2$,
with enhanced low frequency spectral weight and a pronounced upward shift in
the magnitude of $\alpha$ for $J_2>0$. Perhaps even more surprising, we find
sub-diffusion ($\alpha>0$) over a range of $J_2<0$. By contrast, the effects of
the \enquote{fermionic} three-spin perturbation are sign symmetric; this
perturbation produces a clearly observable hydrodynamic relaxation. At large
strength of the integrability breaking term $J_2\to \pm \infty$ the problem is
effectively non-interacting (fermions hopping on odd and even sublattices) and
we find $\alpha\to -1$ behavior reminiscent of the XY limit of the XXZ chain.
Exact diagonalization studies largely corroborate these findings at
mid-frequencies.",1711.11214v2
2017-12-13,Magnetotransport in a model of a disordered strange metal,"Despite much theoretical effort, there is no complete theory of the 'strange'
metal state of the high temperature superconductors, and its
linear-in-temperature, $T$, resistivity. Recent experiments showing an
unexpected linear-in-field, $B$, magnetoresistivity have deepened the puzzle.
We propose a simple model of itinerant electrons, interacting via random
couplings with electrons localized on a lattice of quantum 'dots' or 'islands'.
This model is solvable in a large-$N$ limit, and can reproduce observed
behavior. The key feature of our model is that the electrons in each quantum
dot are described by a Sachdev-Ye-Kitaev model describing electrons without
quasiparticle excitations. For a particular choice of the interaction between
the itinerant and localized electrons, this model realizes a controlled
description of a diffusive marginal-Fermi liquid (MFL) without momentum
conservation, which has a linear-in-$T$ resistivity and a $T \ln T$ specific
heat as $T\rightarrow 0$. By tuning the strength of this interaction relative
to the bandwidth of the itinerant electrons, we can additionally obtain a
finite-$T$ crossover to a fully incoherent regime that also has a linear-in-$T$
resistivity. We show that the MFL regime has conductivities which scale as a
function of $B/T$; however, its magnetoresistance saturates at large $B$. We
then consider a macroscopically disordered sample with domains of MFLs with
varying densities of electrons. Using an effective-medium approximation, we
obtain a macroscopic electrical resistance that scales linearly in the magnetic
field $B$ applied perpendicular to the plane of the sample, at large $B$. The
resistance also scales linearly in $T$ at small $B$, and as $T f(B/T)$ at
intermediate $B$. We consider implications for recent experiments reporting
linear transverse magnetoresistance in the strange metal phases of the
pnictides and cuprates.",1712.05026v3
2017-12-19,"Convective blueshifts in the solar atmosphere, I. Absolute measurements with LARS of the spectral lines at 6302 Å","The solar convection manifests as granulation and intergranulation at the
solar surface. In the photosphere, convective motions induce differential
Doppler shifts to spectral lines. The observed convective blueshift varies
across the solar disk. We focus on the impact of solar convection on the
atmosphere and aim to resolve its velocity stratification in the photosphere.
We performed high-resolution spectroscopic observations of the solar spectrum
in the 6302\,\AA\ range with the Laser Absolute Reference Spectrograph (LARS)
at the Vacuum Tower Telescope. A laser frequency comb enabled the calibration
of the spectra to an absolute wavelength scale with an accuracy of ${\rm
1\,m\,s^{-1}}$. We systematically scanned the Quiet Sun from disk center to the
limb at ten selected heliocentric positions. The analysis included 99 time
sequences of up to 20\,min in length. By means of ephemeris and reference
corrections, we translated wavelength shifts into absolute line-of-sight
velocities. A bisector analysis on the line profiles yielded the shapes and
convective shifts of seven photospheric lines. At disk center, the bisector
profiles of the iron lines feature a pronounced C-shape with maximum convective
blueshifts of up to ${\rm -450\,m\,s^{-1}}$ in the spectral line wings. Toward
the solar limb, the bisectors change into a \textbackslash-shape with a
saturation in the line core at a redshift of ${\rm +100\,m\,s^{-1}}$. The
center-to-limb variation of the line core velocities shows a slight increase in
blueshift when departing the disk center for larger heliocentric angles. This
increase in blueshift is more pronounced for the magnetically less active
meridian than for the equator. Toward the solar limb, the blueshift decreases
and can turn into a redshift. Best spectroscopic measurements enabled the
accurate determination of absolute convective shifts in the solar photosphere.",1712.07059v1
2018-01-04,Complex temperature dependence of coupling and dissipation of cavity-magnon polaritons from milliKelvin to room temperature,"Hybridized magnonic-photonic systems are key components for future
information processing technologies such as storage, manipulation or conversion
of data both in the classical (mostly at room temperature) and quantum
(cryogenic) regime. In this work, we investigate a YIG sphere coupled strongly
to a microwave cavity over the full temperature range from $290\,\mathrm{K}$
down to $30\,\mathrm{mK}$. The cavity-magnon polaritons are studied from the
classical to the quantum regime where the thermal energy is less than one
resonant microwave quanta, i.e. at temperatures below $1\,\mathrm{K}$. We
compare the temperature dependence of the coupling strength $g_{\rm{eff}}(T)$,
describing the strength of coherent energy exchange between spin ensemble and
cavity photon, to the temperature behavior of the saturation magnetization
evolution $M_{\rm{s}}(T)$ and find strong deviations at low temperatures. The
temperature dependence of magnonic disspation is governed at intermediate
temperatures by rare earth impurity scattering leading to a strong peak at
$40\,$K. The linewidth $\kappa_{\rm{m}}$ decreases to $1.2\,$MHz at $30\,$mK,
making this system suitable as a building block for quantum electrodynamics
experiments. We achieve an electromagnonic cooperativity in excess of $20$ over
the entire temperature range, with values beyond $100$ in the milliKelvin
regime as well as at room temperature. With our measurements, spectroscopy on
strongly coupled magnon-photon systems is demonstrated as versatile tool for
spin material studies over large temperature ranges. Key parameters are
provided in a single measurement, thus simplifying investigations
significantly.",1801.01439v1
2018-03-17,Is Quintessence an Indication of a Time-Varying Gravitational Constant?,"A model is presented where the quintessence parameter, w, is related to a
time-varying gravitational constant. Assuming a present value of w equals -.98,
we predict a current variation of G dot/G = -.06 H0. H0 is Hubbles parameter, G
is Newtons constant and G dot is the derivative of G with respect to time.
Thus, G has a cosmic origin, is decreasing with respect to cosmological time,
and is proportional to H0, as originally proposed by the Dirac-Jordan
hypothesis. Within our model, we can explain the cosmological constant
fine-tuning problem, the discrepancy between the present very weak value of the
cosmological constant, and the much greater vacuum energy found in earlier
epochs. To formalize and solidify our model, we give two distinct functions of
G(a), the cosmic scale parameter. We treat inverse G as an order parameter,
which vanishes at high energies; at low temperatures, it reaches a saturation
value, a value we are close to today. Our first function for inverse G is
motivated by a charging capacitor; the second treats inverse G by analogy to a
magnetic response. Both functions, even though very distinct, give a remarkably
similar tracking behavior for w(a). Interestingly, both functions indicate the
onset of G formation at a temperature of approximately 7 *1021 degrees Kelvin,
in contrast to the concordance model. At the temperature of formation, we find
that G has increased to roughly 4*1020 times its present value. For most of
cosmic evolution, however, our variable G model gives results similar to the
predictions of the concordance model, except in the very early universe, as we
shall demonstrate. Within our framework, the weakening of G to its current
value G0 is speculated as the true cause for the observed unanticipated
acceleration of the universe.",1803.06431v1
2018-04-30,Detailed study on the Fermi surfaces of the type-II Dirac semimetallic candidates PdTe2 and PtTe2,"We present a detailed quantum oscillatory study on the Dirac type-II
semimetallic candidates PdTe$_{2}$ and PtTe$_{2}$ \emph{via} the temperature
and the angular dependence of the de Haas-van Alphen (dHvA) and Shubnikov-de
Haas (SdH) effects. In high quality single crystals of both compounds, i.e.
displaying carrier mobilities between $10^3$ and $10^4$ cm$^2$/Vs, we observed
a large non-saturating magnetoresistivity (MR) which in PtTe$_2$ at a
temperature $T = 1.3$ K, leads to an increase in the resistivity up to $5
\times 10^{4}$ % under a magnetic field $\mu_0 H = 62$ T. These high mobilities
correlate with their light effective masses in the range of 0.04 to 1 bare
electron mass according to our measurements. For PdTe$_{2}$ the experimentally
determined Fermi surface cross-sectional areas show an excellent agreement with
those resulting from band-structure calculations. Surprisingly, this is not the
case for PtTe$_{2}$ whose agreement between calculations and experiments is
relatively poor even when electronic correlations are included in the
calculations. Therefore, our study provides a strong support for the existence
of a Dirac type-II node in PdTe$_2$ and probably also for PtTe$_2$. Band
structure calculations indicate that the topologically non-trivial bands of
PtTe$_2$ do not cross the Fermi-level ($\varepsilon_F$). In contrast, for
PdTe$_2$ the Dirac type-II cone does intersect $\varepsilon_F$, although our
calculations also indicate that the associated cyclotron orbit on the Fermi
surface is located in a distinct $k_z$ plane with respect to the one of the
Dirac type-II node. Therefore it should yield a trivial Berry-phase.",1805.00087v1
2018-05-07,Surface superconductivity in the Weyl semimetal MoTe2 detected by point contact spectroscopy,"MoTe2 is a Weyl semimetal, which exhibits unique non-saturating
magnetoresistance and strongly reinforced superconductivity under pressure.
Here, we demonstrate that a novel mesoscopic superconductivity at ambient
pressure arises on the surface of MoTe2 with a critical temperature up to 5 K
significantly exceeding the bulk Tc=0.1K. We measured the derivatives of I-V
curves for metallic hetero-contacts of MoTe2 with Ag or Cu, homo-contacts of
MoTe2 as well as ""soft"" point contacts (PCs). Large number of these
hetero-contacts exhibit a dV/dI dependence, which is characteristic for Andreev
reflection. It allows to determine the superconducting gap \Delta. The average
gap values are 2\Delta=1.30+/-0.15 meV with a 2\Delta/kBTc ratio of 3.7+/-0.4,
which slightly exceeds the standard BCS value of 3.52. Furthermore, the
temperature dependence of the gap follows a BCS-like behavior, which points to
a nodeless superconducting order parameter with some strong-coupling
renormalization. Remarkably, the observation of a ""gapless-like"" single minimum
in the dV/dI of ""soft"" PCs may indicate a topological superconducting state of
the MoTe2 surface as these contacts probe mainly the interface and avoid
additional pressure effect. Therefore, MoTe2 might be a suitable material to
study new forms of topological superconductivity.",1805.02470v2
2018-07-13,Many-body localization and delocalization in large quantum chains,"We theoretically study the quench dynamics for an isolated Heisenberg spin
chain with a random on-site magnetic field, which is one of the paradigmatic
models of a many-body localization transition. We use the time-dependent
variational principle as applied to matrix product states, which allows us to
controllably study chains of a length up to $L=100$ spins, i.e., much larger
than $L \simeq 20$ that can be treated via exact diagonalization. For the
analysis of the data, three complementary approaches are used: (i)
determination of the exponent $\beta$ which characterizes the power-law decay
of the antiferromagnetic imbalance with time; (ii) similar determination of the
exponent $\beta_\Lambda$ which characterizes the decay of a Schmidt gap in the
entanglement spectrum, (iii) machine learning with the use, as an input, of the
time dependence of the spin densities in the whole chain. We find that the
consideration of the larger system sizes substantially increases the estimate
for the critical disorder $W_c$ that separates the ergodic and many-body
localized regimes, compared to the values of $W_c$ in the literature. On the
ergodic side of the transition, there is a broad interval of the strength of
disorder with slow subdiffusive transport. In this regime, the exponents
$\beta$ and $\beta_\Lambda$ increase, with increasing $L$, for relatively small
$L$ but saturate for $L \simeq 50$, indicating that these slow power laws
survive in the thermodynamic limit. From a technical perspective, we develop an
adaptation of the ""learning by confusion"" machine learning approach that can
determine $W_c$.",1807.05051v4
2018-09-24,Site-specific spin crossover in Fe$_{2}$TiO$_{4}$ post-spinel under high pressures to near a megabar,"X-ray diffraction studies to ~90 GPa at room temperature show that
Fe$_{2}$TiO$_{4}$ ferrous inverse spinel undergoes the following sequence of
structural transitions : cubic (Fd3m) to tetragonal (I41/amd)to
orthorhombic(Cmcm) to orthorhombic(Pmma),at the indicated onset transition
pressures. Within the Cmcm phase, site-specific spin crossover is initiated and
involves only highly distorted octahedral sites constituting ~25% of all Fe
locations. This is manifest as a steeper volume decrease of dV/V0 ~ 3.5% beyond
~40 GPa and an emergent diamagnetic component discerned in 57Fe M\""ossbauer
spectroscopy at variable cryogenic temperatures. A subsequent Cmcm to Pmma
Fe/Ti disorder-order reconfiguration is facilitated at 6-fold coordinated
(octahedral) sites. The rest of the high-spin Fe in 6-fold and 8-fold
coordinated sites (~75% abundance) in the Pmma phase exhibit average saturation
internal magnetic fields of H$_{hf}$ ~ 42 T to ~90 GPa, typical of spin-only
(orbitally quenched) Fermi-contact values. By contrast average H$_{hf}$ ~ 20 T
values, signifying unquenched orbital moments, occur below the 40-45 GPa
spin-crossover initiation regime in the Cmcm phase. Therefore site-specific
spin crossover invokes a cooperative lattice response and polyhedral
distortions at the rest of the high-spin Fe sites, translating to 3d level
(sub-band) changes and consequential orbital moment quenching. Near ~90 GPa
Fe$_{2}$TiO$_{4}$ is a partially spin-converted chemically ordered Pmma
post-spinel structure having a persistent charge gap of ~100 meV. Despite
structural symmetry changes, partial spin crossover and lattice compressibility
resulting in a ~33% total reduction in unit-cell volume and corresponding 3d
bandwidth broadening, strong electron correlations persist at high
densification.",1809.09056v1
2019-01-16,Strong suppression of near-field radiative heat transfer by superconductivity in NbN,"Near-field (NF) radiative heat transfer (RHT) over vacuum space between
closely spaced bodies can exceed the Planck far-field (FF) values by orders of
magnitude. Strong effect of superconductivity on NF RHT between plane-parallel
thin-film surfaces of niobium (Nb) was recently discovered and discussed in a
short paper [Kr\'al\'ik et al., Phys. Rev. B 95, 060503 (2017)]. We present
here an extensive set of experimental results on NF as well as FF RHT for
geometrically identical samples made of niobium nitride (NbN), including a
detailed discussion of the experimental setup and errors. The results with NbN
show more precise agreement with theory than the original experiments with Nb.
We observed a steep decrease of the heat flux at the transition to
superconductivity when the colder sample (absorber) passed from normal to
superconducting (SC) state ($T_c \approx 15.2$ K), corresponding to up to an
8-fold contrast between the normal and SC states. This differs dramatically
from the situation in the FF regime, where only a weak effect of
superconductivity was observed. Surprisingly, the contrast remains sizeable
even at high temperatures of the hot sample (radiator) with the characteristic
energy of radiation far above the SC energy gap. We explain the maximum of
contrast in heat flux between the normal and SC states, found at a distance
about ten times shorter than the crossover distance between NF and FF heat
flux, being $d \approx 1000/T$ [${\mu}$m]. We analyze in detail the roles of
transversal electric (TE) and magnetic (TM) modes in the steep decrease of heat
flux below the SC critical temperature and the subsequent flux saturation at
low temperatures. Interestingly, we expose experimentally for the first time
the effect of destructive interference of FF thermal radiation in the vacuum
gap, which was observable at temperatures below the absorber superconducting
transition.",1901.05538v2
2019-04-12,Quasilinear approach of the cumulative whistler instability in fast solar winds: Constraints of electron temperature anisotropy,"Context. Solar outflows are a considerable source of free energy which
accumulates in multiple forms like beaming (or drifting) components and/or
temperature anisotropies. However, kinetic anisotropies of plasma particles do
not grow indefinitely and particle-particle collisions are not efficient enough
to explain the observed limits of these anisotropies. Instead, the
self-generated wave instabilities can efficiently act to constrain kinetic
anisotropies, but the existing approaches are simplified and do not provide
satisfactory explanations. Thus, small deviations from isotropy shown by the
electron temperature ($T$) in fast solar winds are not explained yet.
  Aims. This paper provides an advanced quasilinear description of the whistler
instability driven by the anisotropic electrons in conditions typical for the
fast solar winds. The enhanced whistler-like fluctuations may constrain the
upper limits of temperature anisotropy $A \equiv T_\perp /T_\parallel > 1$,
where $\perp, \parallel$ are defined with respect to the magnetic field
direction.
  Methods. Studied are the self-generated whistler instabilities, cumulatively
driven by the temperature anisotropy and the relative (counter)drift of the
electron populations, e.g., core and halo electrons. Recent studies have shown
that quasi-stable states are not bounded by the linear instability thresholds
but an extended quasilinear approach is necessary to describe them in this
case.
  Results. Marginal conditions of stability are obtained from a quasilinear
theory of the cumulative whistler instability, and approach the quasi-stable
states of electron populations reported by the observations.The instability
saturation is determined by the relaxation of both the temperature anisotropy
and the relative drift of electron populations.",1904.06202v2
2019-06-13,Activity and rotation of the X-ray emitting Kepler stars,"The relation between magnetic activity and rotation in late-type stars
provides fundamental information on stellar dynamos and angular momentum
evolution. Rotation/activity studies found in the literature suffer from
inhomogeneity in the measure of activity indexes and rotation periods. We
overcome this limitation with a study of the X-ray emitting late-type
main-sequence stars observed by XMM-Newton and Kepler. We measure rotation
periods from photometric variability in Kepler light curves. As activity
indicators, we adopt the X-ray luminosity, the number frequency of white-light
flares, the amplitude of the rotational photometric modulation, and the
standard deviation in the Kepler light curves. The search for X-ray flares in
the light curves provided by the EXTraS (Exploring the X-ray Transient and
variable Sky) FP-7 project allows us to identify simultaneous X-ray and
white-light flares. A careful selection of the X-ray sources in the Kepler
field yields 102 main-sequence stars with spectral types from A to M. We find
rotation periods for 74 X-ray emitting main-sequence stars, 22 of which without
period reported in the previous literature. In the X-ray activity/rotation
relation, we see evidence for the traditional distinction of a saturated and a
correlated part, the latter presenting a continuous decrease in activity
towards slower rotators. For the optical activity indicators the transition is
abrupt and located at a period of ~ 10 d but it can be probed only marginally
with this sample which is biased towards fast rotators due to the X-ray
selection. We observe 7 bona-fide X-ray flares with evidence for a white-light
counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of
~ 0.15 d^{-1} , consistent with the optical flare frequency obtained from the
much longer Kepler time-series.",1906.05587v2
2019-08-19,Erosion of an exoplanetary atmosphere caused by stellar winds,"We present a formalism for a first-order estimation of the magnetosphere
radius of exoplanets orbiting stars in the range from 0.08 to 1.3 Mo. With this
radius, we estimate the atmospheric surface that is not protected from stellar
winds. We have analyzed this unprotected surface for the most extreme
environment for exoplanets: GKM-type and very low-mass stars at the two limits
of the habitable zone. The estimated unprotected surface makes it possible to
define a likelihood for an exoplanet to retain its atmosphere. This function
can be incorporated into the new habitability index SEPHI. Using different
formulations in the literature in addition to stellar and exoplanet physical
characteristics, we estimated the stellar magnetic induction, the main
characteristics of the stellar wind, and the different star-planet interaction
regions (sub- and super-Alfv\'enic, sub- and supersonic). With this
information, we can estimate the radius of the exoplanet magnetopause and thus
the exoplanet unprotected surface. We have conducted a study of the auroral
aperture angles for Earth-like exoplanets orbiting the habitable zone of its
star, and found different behaviors depending on whether the star is in
rotational saturated or unsaturated regimes, with angles of aperture of the
auroral ring above or below 36^\circ, respectively, and with different slopes
for the linear relation between the auroral aperture angle at the inner edge of
the habitable zone versus the difference between auroral aperture angles at the
two boundaries of the habitable zone. When the planet is tidally locked, the
unprotected angle increases dramatically to values higher than 40^\circ with a
low likelihood of keeping its atmosphere. When the impact of stellar wind is
produced in the sub-Alfv\'enic regime, the likelihood of keeping the atmosphere
is almost zero for exoplanets orbiting very close to their star.",1908.06695v1
2019-09-06,"Flux Free Single Crystal Growth and Detailed Physical Property Characterization of Bi1-xSbx (x = 0.05, 0.1 and 0.15) Topological Insulator","Here, we report the crystal growth, physical and transport properties of
Bi1-xSbx (x = 0.05, 0.1 and 0.15) topological insulator. Single crystals of
Bi1-xSbx (x = 0.05, 0.1 and 0.15) were grown by melting bismuth and antimony
together using the facile self flux method. The XRD measurements displayed
highly indexed 00l lines and confirmed the crystalline nature as well as the
rhombohedral structure of the Bi1-xSbx (x = 0.05, 0.1 and 0.15) crystals. Raman
spectroscopy measurements for Bi1-xSbx system revealed four peaks within the
spectral range of 10 to 250 cm-1 namely A1g and Eg modes corresponding to Bi-Bi
and Sb-Sb vibrations. Scanning electron microscopy (SEM) and energy dispersive
Temperature dependent electrical resistivity curves with and without applied
magnetic field exhibited a metallic behaviour and linear non-saturating
magneto-resistance (MR) respectively for all the antimony (Sb) concentrations
of x = 0.05, 0.1 and 0.15. The lowest Sb concentration sample with x = 0.05
(Bi0.95Sb0.05) exhibited the highest MR value of about 1400%, followed by x =
0.1 and 0.15 samples (Bi0.9Sb0.1 and Bi0.85Sb0.05) with MR values reaching up
to 500% and 110% respectively at 2K and 6Tesla applied field. The
magneto-conductivity (MC) is fitted to the HLN (Hikami Larkin Nagaoka) equation
and it is found that the charge conduction mechanism is mainly dominated by WAL
(weak anti-localization) along with a small contribution from WL (weak
localization) effect. Summarily, the short letter discusses the synthesis,
interesting transport and magneto-transport properties of Bi1-xSbx (x = 0.05,
0.1 and 0.15), which could be useful in understanding the fascinating
properties of topological insulators and their technological applications.",1909.02711v1
2019-10-15,The Fast Radio Burst Luminosity Function and Death Line in the Low-Twist Magnetar Model,"We explore the burst energy distribution of fast radio bursts (FRBs) in the
low-twist magnetar model of Wadiasingh and Timokhin (2019). Motivated by the
power-law fluence distributions of FRB 121102, we propose an elementary model
for the FRB luminosity function of individual repeaters with an inversion
protocol which directly relates the power-law distribution index of magnetar
short burst fluences to that for FRBs. The protocol indicates the FRB energy
scales virtually linearly with crust/field dislocation amplitude, if magnetar
short bursts prevail in the magnetoelastic regime. Charge starvation in the
magnetosphere during bursts (required in WT19) for individual repeaters implies
the predicted burst fluence distribution is narrow, $\lesssim 3$ decades for
yielding strains and oscillation frequencies feasible in magnetar crusts.
Requiring magnetic confinement and charge starvation, we obtain a death line
for FRBs which segregates magnetars from the normal pulsar population,
suggesting only the former will host recurrent FRBs. We convolve the burst
energy distribution for individual magnetars to define the distribution of
luminosities in evolved magnetar populations. The broken power-law luminosity
function's low energy character depends on the population model, while the high
energy index traces that of individual repeaters. Independent of the evolved
population, the broken power-law isotropic-equivalent energy/luminosity
function peaks at $\sim10^{37}-10^{40}$ erg with a low-energy cutoff at $\sim
10^{37}$ erg. Lastly, we consider the local fluence distribution of FRBs, and
find that it can constrain the subset of FRB-producing magnetar progenitors.
Our model suggests that improvements in sensitivity may reveal flattening of
the global FRB fluence distribution and saturation in FRB rates.",1910.06979v2
2019-11-04,On the Jet Production Efficiency in a Sample of the Youngest Radio Galaxies,"Here we discuss the jet production efficiency in a sample of 17 young radio
galaxies with measured redshifts, kinematic ages, and nuclear X-ray fluxes, for
which the observed luminosities of compact jets/lobes and accretion disks
correspond to the same episode of the AGN activity. For the targets, we analyze
the available optical data, estimating the bolometric luminosities of the
accretion disks $L_{\rm bol}$, and the black hole masses; we also derive the
minimum jet kinetic luminosities, $P_{\rm j}$. With such, we investigate the
distribution of our sample in the three-dimensional space of the accretion rate
$\lambda_{\rm Edd} \equiv L_{\rm bol}/L_{\rm Edd}$, the nuclear X-ray
luminosity $L_{\rm X}$ considered here as a limit for the emission of the disk
coronae, and $P_{\rm j}$, expressing the latter two parameters either in the
Eddington units, or in the units of the disk luminosity. We find that (i) the
accretion rate $\lambda_{\rm Edd}$ in our sample is distributed within a narrow
range $\lambda_{\rm Edd} \sim 0.01 - 0.2$; (ii) the normalized jet power
$P_{\rm j}/L_{\rm Edd}$ formally correlates with the accretion rate
$\lambda_{\rm Edd}$, with some saturation at the largest values $\lambda_{\rm
Edd}> 0.05$; (iii) the jet production efficiency $\eta_{\rm jet} \equiv P_{\rm
j}/\dot{M}_{\rm acc} c^2$ spans a range from $\eta_{\rm jet} \lesssim 10^{-3}$
up to $\sim 0.2$ at maximum, which is below the level expected for magnetically
arrested disks around maximally spinning black holes; and (iv) there is a
diversification in $\eta_{\rm jet}$ on the hardness--intensity diagram $L_{\rm
X}/L_{\rm bol} - \lambda_{\rm Edd}$, with the jets being produced most
efficiently during the high/hard states, and suppressed during the soft states.",1911.01197v2
2020-04-17,Explicit Structure-Preserving Geometric Particle-in-Cell Algorithm in Curvilinear Orthogonal Coordinate Systems and Its Applications to Whole-Device 6D Kinetic Simulations of Tokamak Physics,"Explicit structure-preserving geometric Particle-in-Cell (PIC) algorithm in
curvilinear orthogonal coordinate systems is developed. The work reported
represents a further development of the structure-preserving geometric PIC
algorithm [1-12], achieving the goal of practical applications in magnetic
fusion research. The algorithm is constructed by discretizing the field theory
for the system of charged particles and electromagnetic field using Whitney
forms, discrete exterior calculus, and explicit non-canonical symplectic
integration. In addition to the truncated infinitely dimensional symplectic
structure, the algorithm preserves exactly many important physical symmetries
and conservation laws, such as local energy conservation, gauge symmetry and
the corresponding local charge conservation. As a result, the algorithm
possesses the long-term accuracy and fidelity required for
first-principles-based simulations of the multiscale tokamak physics. The
algorithm has been implemented in the SymPIC code, which is designed for
high-efficiency massively-parallel PIC simulations in modern clusters. The code
has been applied to carry out whole-device 6D kinetic simulation studies of
tokamak physics. A self-consistent kinetic steady state for fusion plasma in
the tokamak geometry is numerically found with a predominately diagonal and
anisotropic pressure tensor. The state also admits a steady-state sub-sonic ion
flow in the range of 10 km/s, agreeing with experimental observations [13, 14]
and analytical calculations [15, 16]. Kinetic ballooning instability in the
self-consistent kinetic steady state is simulated. It shows that high-n
ballooning modes have larger growth rates than low-n global modes, and in the
nonlinear phase the modes saturate approximately in 5 ion transit times ...",2004.08150v4
2020-05-25,Gas and dust dynamics in starlight-heated protoplanetary disks,"Theoretical models of the ionization state in protoplanetary disks suggest
the existence of large areas with low ionization and weak coupling between the
gas and magnetic fields. In this regime hydrodynamical instabilities may become
important. In this work we investigate the gas and dust structure and dynamics
for a typical T Tauri system under the influence of the vertical shear
instability (VSI). We use global 3D radiation hydrodynamics simulations
covering all $360^\circ$ of azimuth with embedded particles of 0.1 and 1mm
size, evolved for 400 orbits. Stellar irradiation heating is included with
opacities for 0.1- to 10-$\mu$m-sized dust. Saturated VSI turbulence produces a
stress-to-pressure ratio of $\alpha \simeq 10^{-4}$. The value of $\alpha$ is
lowest within 30~au of the star, where thermal relaxation is slower relative to
the orbital period and approaches the rate below which VSI is cut off. The rise
in $\alpha$ from 20 to 30~au causes a dip in the surface density near 35~au,
leading to Rossby wave instability and the generation of a stationary,
long-lived vortex spanning about 4~au in radius and 40~au in azimuth. Our
results confirm previous findings that mm size grains are strongly vertically
mixed by the VSI. The scale height aspect ratio for 1mm grains is determined to
be 0.037, much higher than the value $H/r=0.007$ obtained from millimeter-wave
observations of the HL~Tau system. The measured aspect ratio is better fit by
non-ideal MHD models. In our VSI turbulence model, the mm grains drift radially
inwards and many are trapped and concentrated inside the vortex. The turbulence
induces a velocity dispersion of $\sim 12$~m/s for the mm grains, indicating
that grain-grain collisions could lead to fragmentation.",2005.11974v1
2020-06-01,Fluctuations of topological charge and chiral density in the early stage of high energy nuclear collisions,"We study systematically the topological charge density and the chiral density
correlations in the early stage of high energy nuclear collisions: the intial
condition is given by the McLerran-Venugopalan model and the evolution of the
gluon fields is studied via the Classical Yang-Mills equations up to proper
time $\tau\approx 1$ fm/c for an $SU(2)$ evolving Glasma. Topological charge is
related to the gauge invariant $\bm E \cdot \bm B$ where $\bm E$ and $\bm B$
denote the color-electric and color-magnetic fields, while the chiral density
is produced via the chiral anomaly of Quantum Chromodynamics. We study how the
correlation lengths are related to the collision energy, and how the correlated
domains grow up with proper time in the transverse plane for a boost invariant
longitudinal expansion. We estimate the correlation lengths of both quantities,
that after a short transient results of the order of the typical energy scale
of the model, namely the inverse of the saturation scale. We estimate the
proper time for the formation of a steady state in which the production of the
chiral density in the transverse plane per unit rapidity slows down, as well as
the amount of chiral density that would be present at the switch time between
the Classical Yang-Mills evolution and the relativistic transport or hydro for
the quark-gluon plasma phase.",2006.01090v3
2020-08-26,Spectroscopic Monitoring of Blazar S5 0716+714: Brightness-Dependent Spectral Behavior,"In this paper, we report the new results of spectroscopic observations of
$\gamma$-ray blazar S5 0716+714 from 2019 September to 2020 March with the 2.4
m optical telescope at Lijiang Observatory of Yunnan Observatories. The median
cadence of observations is $\sim$ 1 day. During the second observation period
(Epoch2), the observational data reveal an extremely bright state and a
bluer-when-brighter (BWB) chromatism. The BWB trend of Epoch2 differs
significantly from that of the first observation period (Epoch1). A
significantly brightness-dependent BWB chromatism emerges in the total data of
Epoch1 and Epoch2. The BWB trend becomes weaker towards the brighter states,
and likely becomes saturated at the highest state. Based on a log-parabolic
function, a power-law of synchrotron peak flux and frequency $\nu_{\rm{p}}$,
and a power-law of the curvature of synchrotron spectrum and its
$\nu_{\rm{p}}$, simulation well reproduces the brightness-dependent BWB trend
of S5 0716+714. The BWB trend is seemingly controlled by the shift of
$\nu_{\rm{p}}$ with respect to the observational window, and effectively may be
dominated by the variations of electron average energy and magnetic field in
emitting region.",2008.11341v1
2020-10-12,"Flares in Open Clusters with K2. II. Pleiades, Hyades, Praesepe, Ruprecht 147, and M67","Flares, energetic eruptions on the surfaces of stars, are an unmistakable
manifestation of magnetically driven emission. Their occurrence rates and
energy distributions trace stellar characteristics such as mass and age. But
before flares can be used to constrain stellar properties, the flaring-age-mass
relation requires proper calibration. This work sets out to quantify flaring
activity of independently age-dated main sequence stars for a broad range of
spectral types using optical light curves obtained by the Kepler satellite.
Drawing from the complete K2 archive, we searched 3435 $\sim 80$ day long light
curves of 2111 open cluster members for flares using the open-source software
packages K2SC to remove instrumental and astrophysical variability from K2
light curves, and AltaiPony to search and characterize the flare candidates. We
confirmed a total of 3844 flares on high probability open cluster members with
ages from zero age main sequence (Pleiades) to 3.6 Gyr (M67). We extended the
mass range probed in the first study of this series to span from Sun-like stars
to mid-M dwarfs. We added the Hyades (690 Myr) to the sample as a comparison
cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several
hundred light curves from the late K2 Campaigns in the remaining clusters. The
flare energy distribution was similar in the entire parameter space, following
a power law relation with exponent $\alpha\approx 1.84-2.39$. The flaring rates
declined with age, and declined faster for higher mass stars. We found evidence
that a rapid decline in flaring activity occurred in M1-M2 dwarfs around
Hyades/Praesepe age, when these stars spun down to rotation periods of about 10
days, while higher mass stars had already transitioned to lower flaring rates,
and lower mass stars still resided in the saturated activity regime. (abridged)",2010.05576v1
2020-11-17,Properties of polarized synchrotron emission from fluctuation-dynamo action -- I. Application to galaxy clusters,"Using magnetohydrodynamic simulations of fluctuation dynamos, we perform
broad-bandwidth synthetic observations to investigate the properties of
polarized synchrotron emission and the role that Faraday rotation plays in
inferring the polarized structures in the intracluster medium (ICM) of galaxy
clusters. In the saturated state of the dynamo, we find a Faraday depth (FD)
dispersion $\sigma_{\rm FD} \approx 100$ rad m$^{-2}$, in agreement with
observed values in the ICM. Remarkably, the FD power spectrum is qualitatively
similar to $M(k)/k$, where $M(k)$ is the magnetic spectrum and $k$ the
wavenumber. However, this similarity is broken at high $k$ when FD is obtained
by applying RM synthesis to polarized emission from the ICM due to poor
resolution and complexities of spectrum in FD space. Unlike the Gaussian
probability distribution function (PDF) obtained for FD, the PDF of the
synchrotron intensity is lognormal. A relatively large $\sigma_{\rm FD}$ in the
ICM gives rise to strong frequency-dependent variations of the pixel-wise mean
and peak polarized intensities at low frequencies ($\lesssim 1.5\,{\rm GHz}$).
The mean fractional polarization $\langle p \rangle$ obtained at the resolution
of the simulations increases from $<0.1$ at 0.5 GHz to its intrinsic value of
$\sim0.3$ at 6 GHz. Beam smoothing significantly affects the polarization
properties below $\lesssim 1.5\,{\rm GHz}$, reducing $\langle p \rangle$ to
$\lesssim 0.01$ at 0.5 GHz. At frequencies $\gtrsim 5\,{\rm GHz}$, polarization
remains largely unaffected, even when recovered using RM synthesis. Thus, our
results underline the need for high-frequency ($\gtrsim 5\,{\rm GHz}$)
observations with future radio telescopes to effectively probe the properties
of polarized emission in the ICM.",2011.08499v2
2021-01-13,Rapid Spectral Variability of a Giant Flare from a Magnetar in NGC 253,"Magnetars are slowly-rotating neutron stars with extremely strong magnetic
fields ($10^{13-15}$ G), episodically emitting $\sim100$ ms long X-ray bursts
with energies of $\sim10^{40-41}$ erg. Rarely, they produce extremely bright,
energetic giant flares that begin with a short ($\sim0.2$ s), intense flash,
followed by fainter, longer lasting emission modulated by the magnetar spin
period (typically 2-12 s), thus confirming their origin. Over the last 40
years, only three such flares have been observed in our local group; they all
suffered from instrumental saturation due to their extreme intensity. It has
been proposed that extra-galactic giant flares likely constitute a subset of
short gamma-ray bursts, noting that the sensitivity of current instrumentation
prevents us from detecting the pulsating tail, while the initial bright flash
is readily observable out to distances $\sim 10-20$ Mpc. Here, we report X- and
gamma-ray observations of GRB 200415A, which exhibits a rapid onset, very fast
time variability, flat spectra and significant sub-millisecond spectral
evolution. These attributes match well with those expected for a giant flare
from an extra-galactic magnetar, noting that GRB 200415A is directionally
associated with the galaxy NGC 253 ($\sim$3.5 Mpc away). The detection of
$\sim3$ MeV photons provides definitive evidence for relativistic motion of the
emitting plasma. The observed rapid spectral evolution can naturally be
generated by radiation emanating from such rapidly-moving gas in a rotating
magnetar.",2101.05146v1
2021-03-23,Exact one- and two-site reduced dynamics in a finite-size quantum Ising ring after a quench: A semi-analytical approach,"We study the non-equilibrium dynamics of a homogeneous quantum Ising ring
after a quench, in which the transverse field $g$ suddenly changes from zero to
a nonzero value. The long-timescale reduced dynamics of a single spin and of
two nearest-neighbor spins, which involves the evaluation of expectation values
of odd operators that break the fermion parity, is exactly obtained for
finite-size but large rings through the use of a recently developed Pfaffian
method [N. Wu, Phys. Rev. E 101, 042108 (2020)]. Time dependence of the
transverse and longitudinal magnetizations, single-spin purity, expectation
value of the string operator $X_j=\prod^{j-1}_{l=1}\sigma^z_l\sigma^x_j$,
several equal-time two-site correlators, and pairwise concurrence after
quenches to different phases are numerically studied. Our main findings are
that (i) The expectation value of a generic odd operator approaches zero in the
long-time limit; (ii) $\langle X_j\rangle_t$ exhibits $j$-independent
exponential decay for a quench to $g=1$ and the time at which $\langle
X_j\rangle_t$ reaches its first maximum scales linearly with $j$; (iii) The
single-spin purity dynamics is mainly controlled by
$\langle\sigma^x_j\rangle_t$ ($\langle\sigma^z_j\rangle_t$) for a quench to
$g<1$ ($g\geq 1$). For quenches to the disordered phase with $g\gg1$, the
single-spin tends to be in the maximally mixed state and the transverse and
longitudinal correlators $\langle\sigma^z_j\sigma^z_{j+1}\rangle_t$ and
$\langle\sigma^x_j\sigma^x_{j+1}\rangle_t$ respectively approaches $-0.25$ and
$0.5$ in the thermodynamic limit; (iv) The nearest-neighbor entanglement
acquires a finite plateau value that increases with increasing $g$, and
approaches a saturated value $\sim0.125$ for $g\gg1$.",2103.12509v2
2021-05-26,Mott-Anderson Metal-Insulator Transitions from Entanglement,"A metal can be driven to an insulating phase through distinct mechanisms. A
possible way is via the Coulomb interaction, which then defines the Mott
metal-insulator transition (MIT). Another possibility is the MIT driven by
disorder, the so-called Anderson MIT. Here we analyze interacting particles in
disordered Hubbard chains $-$ thus comprising the Mott-Anderson physics $-$ by
investigating the ground-state entanglement with density functional theory. The
localization signature on entanglement is found to be a local minimum at a
certain critical density. Individually, the Mott (Anderson) MIT has a single
critical density whose minimum entanglement decreases as the interaction
(disorder) enhances. While in the Mott MIT entanglement saturates at finite
values, characterizing partial localization, in the Anderson MIT the system
reaches full localization, with zero entanglement, for sufficiently strong
disorder. In the combined Mott-Anderson MIT, we find three critical densities
referring to local minima on entanglement. One of them is the same as for the
Anderson MIT, but now the presence of interaction requires a stronger disorder
potential to induce localization. A second critical density is related to the
Mott MIT, but due to disorder it is displaced by a factor proportional to the
concentration of impurities. The third local minimum on entanglement is unique
to the concomitant presence of disorder and interaction, found to be related to
an effective density phenomenon, thus referred to as a Mott-like MIT. Since
entanglement has been intrinsically connected to the magnetic susceptibility
$-$ a quantity promptly available in cold atoms experiments $-$ our detailed
numerical description might be useful for the experimental investigation of
Mott-Anderson MIT.",2105.12529v2
2021-06-28,The eROSITA Final Equatorial-Depth Survey (eFEDS). The stellar counterparts of eROSITA sources identified by machine learning and Bayesian algorithms,"Stars are ubiquitous X-ray emitters and will be a substantial fraction of the
X-ray sources detected in the on-going all-sky survey performed by the eROSITA
instrument aboard the Spectrum Roentgen Gamma (SRG) observatory. We use the
X-ray sources in the eROSITA Final Equatorial-Depth Survey (eFEDS) field
observed during the SRG performance verification phase to investigate different
strategies to identify the stars among other source categories. We focus here
on Support Vector Machine (SVM) and Bayesian approaches, and our approaches are
based on a cross-match with the Gaia catalog, which will eventually contain
counterparts to virtually all stellar eROSITA sources. We estimate that 2060
stars are among the eFEDS sources based on the geometric match distance
distribution, and we identify the 2060 most likely stellar sources with the SVM
and Bayesian methods, the latter being named HamStars in the eROSITA context.
Both methods reach completeness and reliability percentages of almost 90%, and
the agreement between both methods is, incidentally, also about 90%. Knowing
the true number of stellar sources allowed us to derive association
probabilities $p_{ij}$ for the SVM method similar to the Bayesian method so
that one can construct samples with defined completeness and reliability
properties using appropriate cuts in $p_{ij}$. The thus identified stellar
sources show the typical characteristics known for magnetically active stars,
specifically, they are generally compatible with the saturation level, show a
large spread in activity for stars of spectral F to G, and have comparatively
high fractional X-ray luminosities for later spectral types.",2106.14521v1
2021-07-05,"Surface rotation and photometric activity for Kepler targets. II. G and F main-sequence stars, and cool subgiant stars","Dark magnetic spots crossing the stellar disc lead to quasi-periodic
brightness variations, which allow us to constrain stellar surface rotation and
photometric activity. The current work is the second of this series (Santos et
al. 2019; Paper I), where we analyze the Kepler long-cadence data of 132,921
main-sequence F and G stars and late subgiant stars. Rotation-period candidates
are obtained by combining wavelet analysis with autocorrelation function.
Reliable rotation periods are then selected via a machine learning (ML)
algorithm (Breton et al. 2021), automatic selection, and complementary visual
inspection. The ML training data set comprises 26,521 main-sequence K and M
stars from Paper I. To supplement the training, we analyze in the same way as
Paper I, i.e. automatic selection and visual inspection, 34,100 additional
stars. We finally provide rotation periods Prot and associated photometric
activity proxy Sph for 39,592 targets. Hotter stars are generally faster
rotators than cooler stars. For main-sequence G stars, Sph spans a wider range
of values with increasing effective temperature, while F stars tend to have
smaller Sph values in comparison with cooler stars. Overall for G stars, fast
rotators are photometrically more active than slow rotators, with Sph
saturating at short periods. The combined outcome of the two papers accounts
for average Prot and Sph values for 55,232 main-sequence and subgiant FGKM
stars (out of 159,442 targets), with 24,182 new Prot detections in comparison
with McQuillan et al. (2014). The upper edge of the Prot distribution is
located at longer Prot than found previously.",2107.02217v2
2021-07-01,Cooling flows around cold clouds in the circumgalactic medium: steady-state models & comparison with TNG50,"Cold, non-self-gravitating clumps occur in various astrophysical systems,
ranging from the interstellar and circumgalactic medium (CGM), to AGN outflows
and solar coronal loops. Cold gas has diverse origins such as turbulent mixing
or precipitation from hotter phases. We obtain the analytic solution for a
steady pressure-driven 1-D cooling flow around cold, local over-densities,
irrespective of their origin. Our solutions describe the slow and steady
radiative cooling-driven gas inflow in the saturated regime of nonlinear
thermal instability in clouds, sheets and filaments. Such a cooling flow
develops when the gas around small clumps undergoes radiative cooling. These
small-scale, cold `seeds' are embedded in a large volume-filling hot CGM
maintained by feedback. We use a simple two-fluid treatment to include magnetic
fields as an additional polytropic fluid. To test the limits of applicability
of these analytic solutions, we compare with the gas structure found in and
around small-scale cold clouds in the CGM of massive halos in the TNG50
cosmological MHD simulation from the IllustrisTNG suite. Despite qualitative
resemblance of the gas structure, we find deviations from steady state profiles
generated by our model. Complex geometries and turbulence all add complexity
beyond our analytic solutions. We derive an exact relation between the mass
cooling rate ($\dot{\rm M}_{\rm cool}$) and the radiative cooling rate
($\dot{\rm E}_{\rm cool}$) for a steady cooling flow. A comparison with the
TNG50 clouds shows that this cooling flow relation only applies in a narrow
temperature range around $\rm \sim 10^{4.5}$ K where the isobaric cooling time
is the shortest. In general, turbulence and mixing, instead of radiative
cooling, may dominate the transition of gas between different temperature
phases.",2107.02722v2
2021-09-30,Electron Heat Flux in the Solar Wind: Generalized Approaches to Fluid Transport with a Variety of Skewed Velocity Distributions,"In the solar corona and solar wind, electron heat conduction is an important
process that transports energy over large distances and helps determine the
spatial variation of temperature. High-density regions undergoing rapid
particle-particle collisions exhibit a heat flux described well by classical
Spitzer-Harm theory. However, much of the heliosphere is closer to a more
collisionless state, and there is no standard description of heat conduction
for fluid-based (e.g., magnetohydrodynamic) models that applies generally. Some
proposed models rely on electron velocity distributions that exhibit negative
values of the phase-space density. In this paper, we explore how
positive-definite velocity distributions can be used in fluid-based
conservation equations for the electron heat flux along magnetic-field lines in
the corona and solar wind. We study both analytic forms of skewed distributions
(e.g., skew-normal distributions, two-sided bi-Maxwellians, and
constant-collision-time electrostatic solutions) and empirical fits to
measurements of core, halo, and strahl electrons in interplanetary space. We
also present example solutions to a generalized conservation equation for the
heat flux in the solar wind, with some limiting cases found to resemble known
free-streaming approximations. The resulting values of the electron heat flux
vary as a function of radial distance and Knudsen number in ways that resemble
observed data. We note that this model does not include the effects of kinetic
instabilities (which may impose saturation limits when active), so for now its
regime of applicability is limited to collisionless heat-flux evolution away
from the known instability boundaries in parameter space.",2109.15267v1
2021-10-05,"Possible unconventional pairing in $(\text{Ca,Sr})_{3}(\text{Ir,Rh})_{4}\text{Sn}_{13}$ superconductors revealed by controlling disorder","We study the evolution of temperature-dependent resistivity with controlled
point-like disorder induced by 2.5 MeV electron irradiation in stoichiometric
compositions of the ""3-4-13"" stannides,
$(\text{Ca,Sr})_{3}(\text{Ir,Rh})_{4}\text{Sn}_{13}$.Three of these cubic
compounds exhibit a microscopic coexistence of charge-density wave (CDW) order
and superconductivity (SC), while $\text{Ca}_{3}\text{Rh}_{4}\text{Sn}_{13}$
does not develop CDW order. As expected, the CDW transition temperature,
$T_{\text{CDW}}$, is universally suppressed by irradiation in all three
compositions. The superconducting transition temperature, $T_{c}$, behaves in a
more complex manner. In $\text{Sr}_{3}\text{Rh}_{4}\text{Sn}_{13}$, it
increases initially in a way consistent with a direct competition of CDW and
SC, but quickly saturates at higher irradiation doses. In the other three
compounds, $T_{c}$ is monotonically suppressed by irradiation. The strongest
suppression is found in $\text{Ca}_{3}\text{Rh}_{4}\text{Sn}_{13}$, which does
not have CDW order. We further examine this composition by measuring the London
penetration depth, $\lambda(T)$, from which we derive the superfluid density.
The result unambiguously points to a weak-coupling, full single gap, isotropic
superconducting state. Therefore, we must explain two seemingly incompatible
experimental observations: a single isotropic superconducting gap and a
significant suppression of $T_{c}$ by non-magnetic disorder. We conduct a
quantitative theoretical analysis based on a generalized Anderson theorem which
points to an unconventional multiband $s^{+-}$-pairing state where the sign of
the order parameter is different on one (or a small subset) of the smaller
Fermi surface sheets, but remains overall fully-gapped.",2110.02025v3
2022-04-05,Quantum noise limited microwave amplification using a graphene Josephson junction,"Josephson junctions (JJ) and their tunable properties, including their
nonlinearities, form the core of superconducting circuit quantum
electrodynamics (cQED). In quantum circuits, low-noise amplification of feeble
microwave signals is essential and the Josephson parametric amplifiers (JPA)
are the widely used devices. The existing JPAs are based on Al-AlOx-Al tunnel
junctions realized in a superconducting quantum interference device geometry,
where magnetic flux is the knob for tuning the frequency. Recent experimental
realizations of 2D van der Waals JJs provide an opportunity to implement
various cQED devices with the added advantage of tuning the junction properties
and the operating point using a gate potential. While other components of a
possible 2D van der Waals cQED architecture have been demonstrated -- quantum
noise limited amplifier, an essential component, has not been realized. Here we
implement a quantum noise limited JPA, using a graphene JJ, that has linear
resonance gate tunability of 3.5 GHz. We report 24 dB amplification with 10 MHz
bandwidth and -130 dBm saturation power; performance on par with the best
single-junction JPAs. Importantly, our gate tunable JPA works in the
quantum-limited noise regime which makes it an attractive option for highly
sensitive signal processing. Our work has implications for novel bolometers --
the low heat capacity of graphene together with JJ nonlinearity can result in
an extremely sensitive microwave bolometer embedded inside a quantum
noise-limited amplifier. In general, our work will open up exploration of
scalable device architecture of 2D van der Waals materials by integrating a
sensor with the quantum amplifier.",2204.02103v1
2022-08-06,Theoretical studies on switching of magnetisation in thin film,"In the present chapter, we focus on the switching of magnetisation, or the
metastable lifetime of a ferromagnetic system. In this regard, particularly the
Ising model and the Blume-Capel model, have been simulated in the presence of
an externally applied magnetic field by the Monte-Carlo simulation technique
based on the Metropolis algorithm. Magnetisation switching is found to be
faster in the presence of disorder, modelled here by a quenched random field.
The strength of the random field is observed to play a similar role to that
played by temperature. Becker-D\""oring theory of classical nucleation
(originally proposed for the spin-1/2 Ising system) has been verified in the
random field Ising model. However, a stronger random field affects the
nucleation regime. In a cubic Ising lattice, surface reversal time is found to
be different from the bulk reversal time. That distinct behaviour of the
surface in contrast to the bulk has been studied here by introducing a relative
interfacial interaction strength ($R$). Depending on $R$, temperature, and
applied field, a competitive switching of magnetisation of surface and bulk is
noticed. The effect of anisotropy ($D$) on the metastable lifetime has been
investigated. We report a linear dependency of the mean macroscopic reversal
time on a suitably defined microscopic reversal time. The saturated
magnetisation $M_f$, after the reversal, is noticed to be strongly dependent on
$D$. $M_f$, $D$, and $h$ (field) are found to follow a proposed scaling
relation. Finally, Becker-D\""oring theory as well as Avrami's law are verified
in spin-$s$ Ising and Blume-Capel models. The switching time depends on the
number of accessible spin states.",2208.03480v3
2022-10-06,Exploring the limits of MEG spatial resolution with multipolar expansions,"The advent of scalp magnetoencephalography (MEG) based on optically pumped
magnetometers (OPMs) may represent a step change in the field of human
electrophysiology. Compared to cryogenic MEG based on superconducting quantum
interference devices, scalp MEG promises significantly higher spatial
resolution imaging but it also comes with numerous challenges regarding how to
optimally design OPM arrays. In this context, we sought to provide a systematic
description of MEG spatial resolution as a function of the number of sensors,
sensor-to-brain distance, sensor type, and signal-to-noise ratio. To that aim,
we present an analytical theory based on MEG multipolar expansions that
enables, once supplemented with experimental input and simulations,
quantitative assessment of the limits of MEG spatial resolution in terms of two
qualitatively distinct regimes. In the regime of asymptotically high-density
MEG, we provide a mathematically rigorous description of how magnetic field
smoothness constraints spatial resolution to a slow, logarithmic divergence. In
the opposite regime of low-density MEG, it is sensor density that constraints
spatial resolution to a faster increase following a square-root law. The
transition between these two regimes controls how MEG spatial resolution
saturates as sensors approach sources of neural activity. This two-regime model
of MEG spatial resolution integrates known observations (e.g., the difficulty
of improving spatial resolution by increasing sensor density, the gain brought
by moving sensors on scalp, or the usefulness of multi-component sensors) and
gathers them under a unifying theoretical framework that highlights the
underlying physics and reveals properties inaccessible to simulations. We
propose that this framework may find useful applications to benchmark the
design of future OPM-based scalp MEG systems.",2210.02863v2
2022-10-15,Non-local magnon transconductance in extended magnetic insulating films.\\ Part I: spin diode effect,"This review provides a comprehensive study of the nonlinear transport
properties of magnons, which are electrically emitted or absorbed inside
extended YIG films by spin transfer effects via a YIG$\vert$Pt interface. Our
purpose is to experimentally elucidate the pertinent picture behind the
asymmetric electrical variation of the magnon transconductance analogous to an
electric diode. The feature is rooted in the variation of the density of
low-lying spin excitations via an electrical shift of the magnon chemical
potential. As the intensity of the spin transfer increases in the forward
direction (regime of magnon emission), the transport properties of low-energy
magnon go through 3 distinct regimes: \textit{i)} at low currents, where the
spin current is a linear function of the electrical current, the spin transport
is ballistic and set by the film thickness; \textit{ii)} for amplitudes of the
order of the damping compensation threshold, it switches to a highly correlated
regime limited by magnon-magnon relaxation process and marked by a saturation
of the magnon transconductance. Here the main bias, that controls the magnon
density, are thermal fluctuations beneath the emitter. \textit{iii)} As the
temperature under the emitter approaches the Curie temperature, scattering with
high-energy magnons dominates, leading to diffusive transport. We note that
such sequence of transport regimes bears analogy with electron hydrodynamic
transport in ultra-pure media predicted by Radii Gurzhi. This study restricted
to low energy part of the magnon manifold complements part II of this
review\cite{kohno_2F}, which concentrates instead on the whole spectrum of
propagating magnons.",2210.08304v2
2022-11-02,High Temperature Ferromagnetism in Cr$_{1+x}$Pt$_{5-x}$P,"We present the growth and basic magnetic and transport properties of
Cr$_{1+x}$Pt$_{5-x}$P. We show that single crystals can readily be grown from a
high-temperature solution created by adding dilute quantities of Cr to Pt-P
based melts. Like other 1-5-1 compounds, Cr$_{1+x}$Pt$_{5-x}$P adopts a
tetragonal P4/mmm structure composed face-sharing CrPt$_3$ like slabs that are
broken up along the c-axis by sheets of P atoms. EDS and X-ray diffraction
measurements both suggest Cr$_{1+x}$Pt$_{5-x}$P has mixed occupancy between Cr
and Pt atoms, similar to what is found in the closely related compound
CrPt$_3$, giving real compositions of Cr$_{1.5}$Pt$_{4.5}$P (x = 0.5). We
report that Cr$_{1.5}$Pt$_{4.5}$P orders ferromagnetically at T$_C$ = 464.5 K
with a saturated moment of $\approx$ 2.1 $\mu_{\textit{B}}$/Cr at 1.8 K. Likely
owing to the strong spin-orbit coupling associated with the large quantity of
high Z Pt atoms, Cr$_{1.5}$Pt$_{4.5}$P has exceptionally strong planar
anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and
300 K respectively. The resistance of Cr$_{1.5}$Pt$_{4.5}$P has a metallic
temperature dependence with relatively weak magnetoresistance. Electronic band
structure calculations show that CrPt$_5$P has a large peak in the density of
states near the Fermi level which is split into spin majority and minority
bands in the ferromagnetic state. Furthermore, the calculations suggest
substantial hybridization between Cr-3d and Pt-5d states near the Fermi level,
in agreement with the experimentally measured anisotropy.",2211.01491v1
2022-11-11,"The unaltered pulsar: GRO J1750-27, a super-critical X-ray neutron star that does not blink an eye","When accreting X-ray pulsars (XRPs) undergo bright X-ray outbursts, their
luminosity-dependent spectral and timing features can be analysed in detail.
The XRP GRO J1750-27 recently underwent one of such episodes, during which it
was observed with $NuSTAR$ and monitored with $NICER$. Such a data set is
rarely available, as it samples the outburst over more than a month at a
luminosity that is always exceeding ${\sim}5\times10^{37}\,$erg/s. This value
is larger than the typical critical luminosity value, where a radiative shock
is formed above the neutron star's surface. Our data analysis of the joint
spectra returns a highly ($N_H\sim(5-8)\times10^{22}\,$cm$^{-2}$) absorbed
spectrum showing a K$\alpha$ iron line, a soft blackbody component likely
originating from the inner edge of the accretion disk, and confirms the
discovery of one of the deepest cyclotron lines, at a centroid energy of
${\sim}44\,$keV corresponding to a magnetic field strength of
$4.7\times10^{12}\,$G. This value is independently supported by the best-fit
physical model for spectral formation in accreting XRPs which, in agreement
with recent findings, favours a distance of $14$ kpc and also reflects a
bulk-Comptonization dominated accretion flow. Contrary to theoretical
expectations and observational evidence from other similar sources, the pulse
profiles as observed by $NICER$ through the outburst raise, peak and decay
remain remarkably steady. The $NICER$ spectrum, including the iron K$\alpha$
line best-fit parameters, also remain almost unchanged at all probed outburst
stages, similar to the pulsed fraction behaviour. We argue that all these
phenomena are linked and interpret them as resulting from a saturation effect
of the accretion column's emission, which occurs in the high-luminosity regime.",2211.06367v2
2022-11-21,Magnetic activities and parameters of 43 flare stars in the GWAC archive,"In the archive of the Ground Wide Angle Camera (GWAC), we found 43 white
light flares from 43 stars, among which, three are sympathetic or homologous
flares, and one of them also has a quasi-periodic pulsation with a period of
$13.0\pm1.5$ minutes. Among these 43 flare stars, there are 19 new active stars
and 41 stars that have available TESS and/or K2 light curves, from which we
found 931 stellar flares. We also obtained rotational or orbital periods of 34
GWAC flare stars, of which 33 are less than 5.4 days, and ephemerides of three
eclipsing binaries from these light curves. Combining with low resolution
spectra from LAMOST and the Xinglong 2.16m telescope, we found that $L_{\rm
H\alpha}/L_{\rm bol}$ are in the saturation region in the rotation-activity
diagram. From the LAMOST medium-resolution spectrum, we found that Star \#3
(HAT 178-02667) has double H$\alpha$ emissions which imply it is a binary, and
two components are both active stars. Thirteen stars have flare frequency
distributions (FFDs) from TESS and/or K2 light curves. These FFDs show that the
flares detected by GWAC can occur at a frequency of 0.5 to 9.5 yr$^{-1}$. The
impact of flares on habitable planets was also studied based on these FFDs, and
flares from some GWAC flare stars may produce enough energetic flares to
destroy ozone layers, but none can trigger prebiotic chemistry on their
habitable planets.",2211.11240v1
2023-01-10,Cosmic Ray Drag and Damping of Compressive Turbulence,"While it is well-known that cosmic rays (CRs) can gain energy from turbulence
via second order Fermi acceleration, how this energy transfer affects the
turbulent cascade remains largely unexplored. Here, we show that damping and
steepening of the compressive turbulent power spectrum are expected once the
damping time $t_{\rm damp} \sim \rho v^{2}/\dot{E}_{\rm CR} \propto E_{\rm
CR}^{-1}$ becomes comparable to the turbulent cascade time. Magnetohydrodynamic
(MHD) simulations of stirred compressive turbulence in a gas-CR fluid with
diffusive CR transport show clear imprints of CR-induced damping, saturating at
$\dot{E}_{\rm CR} \sim \tilde{\epsilon}$, where $\tilde{\epsilon}$ is the
turbulent energy input rate. In that case, almost all the energy in large scale
motions is absorbed by CRs and does not cascade down to grid scale. Through a
Hodge-Helmholtz decomposition, we confirm that purely compressive forcing can
generate significant solenoidal motions, and we find preferential CR damping of
the compressive component in simulations with diffusion and streaming,
rendering small-scale turbulence largely solenoidal, with implications for
thermal instability and proposed resonant scattering of $E > 300$ GeV CRs by
fast modes. When CR transport is streaming dominated, CRs also damp large scale
motions, with kinetic energy reduced by up to to an order of magnitude in
realistic $E_{\rm CR} \sim E_{\rm g}$ scenarios, but turbulence (with a reduced
amplitude) still cascades down to small scales with the same power spectrum.
Such large scale damping implies that turbulent velocities obtained from the
observed velocity dispersion may significantly underestimate turbulent forcing
rates, i.e. $\tilde{\epsilon} \gg \rho v^{3}/L$.",2301.04156v2
2023-01-11,Heat transport and convective velocities in compositionally-driven convection in neutron star and white dwarf interiors,"We investigate heat transport associated with compositionally-driven
convection driven by crystallization at the ocean-crust interface in accreting
neutron stars, or growth of the solid core in cooling white dwarfs. We study
the effect of thermal diffusion and rapid rotation on the convective heat
transport, using both mixing length theory and numerical simulations of
Boussinesq convection. We determine the heat flux, composition gradient and
P\'eclet number, $\mathrm{Pe}$ (the ratio of thermal diffusion time to
convective turnover time) as a function of the composition flux. We find two
regimes of convection with a rapid transition between them as the composition
flux increases. At small Pe, the ratio between the heat flux and composition
flux is independent of Pe,, because the loss of heat from convecting fluid
elements due to thermal diffusion is offset by the smaller composition gradient
needed to overcome the reduced thermal buoyancy. At large Pe, the temperature
gradient approaches the adiabatic gradient, saturating the heat flux. We
discuss the implications for neutron star and white dwarf cooling. Convection
in neutron stars spans both regimes. We find rapid mixing of neutron star
oceans, with a convective turnover time of order weeks to minutes depending on
rotation. Except during the early stages of core crystallization, white dwarf
convection is in the thermal-diffusion-dominated fingering regime. We find
convective velocities much smaller than recent estimates for
crystallization-driven dynamos. The small fraction of energy carried as kinetic
energy calls into question the effectiveness of crystallization-driven dynamos
as an explanation for observed white dwarf magnetic fields.",2301.04273v3
2023-01-14,On the Generation and Evolution of Switchbacks and the Morphology of Alfvénic Transition: Low Mach-number Boundary Layers,"We investigate the generation and evolution of switchbacks (SBs), the nature
of the sub-Alfv\'enic wind observed by Parker Solar Probe (PSP), and the
morphology of the Alfv\'enic transition, all of which are key issues in solar
wind research. First we highlight a special structure in the pristine solar
wind, termed a low Mach-number boundary layer (LMBL). An increased Alfv\'en
radius and suppressed SBs are observed within an LMBL. A probable source on the
Sun for an LMBL is the peripheral region inside a coronal hole with rapidly
diverging open fields. The sub-Alfv\'enic wind detected by PSP is an LMBL flow
by nature. The similar origin and similar properties of the sub-Alfv\'enic
intervals favor a wrinkled surface for the morphology of the Alfv\'enic
transition. We find that a larger deflection angle tends to be associated with
a higher Alfv\'en Mach number. The magnetic deflections have an origin well
below the Alfv\'en critical point, and deflection angles larger than
$90^{\circ}$ seem to occur only when $M_{\rm A} \gtrsim 2$. The velocity
enhancement in units of the local Alfv\'en speed generally increases with the
deflection angle, which is explained by a simple model. A nonlinearly evolved,
saturated state is revealed for SBs, where the local Alfv\'en speed is roughly
an upper bound for the velocity enhancement. In the context of these results,
the most promising theory on the origin of SBs is the model of expanding waves
and turbulence, and the patchy distribution of SBs is attributed to modulation
by reductions in the Alfv\'en Mach number. Finally, a picture on the generation
and evolution of SBs is created based on the results.",2301.05829v1
2023-03-02,Synchrotron Radiation Dominates the Extremely Bright GRB 221009A,"The brightest Gamma-ray burst, GRB 221009A, has spurred numerous theoretical
investigations, with particular attention paid to the origins of ultra-high
energy TeV photons during the prompt phase. However, analyzing the mechanism of
radiation of photons in the $\sim$MeV range has been difficult because the high
flux causes pile-up and saturation effects in most GRB detectors. In this
letter, we present systematic modeling of the time-resolved spectra of the GRB
using unsaturated data obtained from Fermi/GBM (precursor) and
SATech-01/GECAM-C (main emission and flare). Our approach incorporates the
synchrotron radiation model, which assumes an expanding emission region with
relativistic speed and a global magnetic field that decays with radius, and
successfully fits such a model to the observational data. Our results indicate
that the spectra of the burst are fully in accordance with a synchrotron origin
from relativistic electrons accelerated at a large emission radius. The lack of
thermal emission in the prompt emission spectra supports a
Poynting-flux-dominated jet composition.",2303.00898v2
2023-07-04,On electromagnetic turbulence and transport in STEP,"In this work, we present first-of-their-kind nonlinear local gyrokinetic
simulations of electromagnetic turbulence at mid-radius in the burning plasma
phase of the conceptual high-$\beta$, reactor-scale, tight-aspect-ratio tokamak
STEP (Spherical Tokamak for Energy Production). A prior linear analysis in D.
Kennedy et al. 2023 Nucl. Fusion 63 126061 reveals the presence of unstable
hybrid kinetic ballooning modes, where inclusion of the compressional magnetic
field fluctuation, $\delta B_{\parallel}$, is crucial, and subdominant
microtearing modes are found at binormal scales approaching the ion-Larmor
radius. Local nonlinear gyrokinetic simulations on the selected surface in the
central core region suggest that hybrid kinetic ballooning modes can drive
large turbulent transport, and that there is negligible turbulent transport
from subdominant microtearing modes when hybrid kinetic ballooning modes are
artificially suppressed (through the omission of $\delta B_{\parallel}$).
Nonlinear simulations that include perpendicular equilibrium flow shear can
saturate at lower fluxes that are more consistent with the available sources in
STEP. This analysis suggests that hybrid kinetic ballooning modes could play an
important role in setting the turbulent transport in STEP, and possible
mechanisms to mitigate turbulent transport are discussed. Increasing the safety
factor or the pressure gradient strongly reduces turbulent transport from
hybrid kinetic ballooning modes in the cases considered here. Challenges of
simulating electromagnetic turbulence in this high-$\beta$ regime are
highlighted. In particular the observation of radially extended turbulent
structures in the absence of equilibrium flow shear motivates future advanced
global gyrokinetic simulations that include $\delta B_\parallel$.",2307.01669v3
2023-11-12,"Three young planets around the K-dwarf K2-198: High-energy environment, evaporation history and expected future","Planets orbiting young stars are thought to experience atmospheric
evaporation as a result of the host stars' high magnetic activity. We study the
evaporation history and expected future of the three known transiting
exoplanets in the young multiplanet system K2-198. Based on spectroscopic and
photometric measurements, we estimate an age of the K-dwarf host star between
200 and 500 Myr, and calculate the high-energy environment of these planets
using eROSITA X-ray measurements. We find that the innermost planet K2-198c has
likely lost its primordial envelope within the first few tens of Myr regardless
of the age at which the star drops out of the saturated X-ray regime. For the
two outer planets, a range of initial envelope mass fractions is possible,
depending on the not-yet-measured planetary mass and the stars' spin-down
history. Regarding the future of the system, we find that the outermost planet
K2-198b is stable against photoevaporation for a wide range of planetary
masses, while the middle planet K2-198d is only able to retain an atmosphere
for a mass range between ~7 and 18 Earth-masses. Lower-mass planets are too
susceptible to mass loss, and a very thin present-day envelope for higher-mass
planets is easily lost with the estimated mass-loss rates. Our results support
the idea that all three planets started out above the radius valley in the
(sub-)Neptune regime and were then transformed into their current states by
atmospheric evaporation, but also stress the importance of measuring planetary
masses for (young) multiplanet systems before conducting more detailed
photoevaporation simulations.",2311.06897v1
1996-05-02,A Procedure for Correcting the Apparent Optical Depths of Moderately Saturated Interstellar Absorption Lines,"Most observations of absorption lines from interstellar and intergalactic
matter have sufficient resolution to show most of the structure at differing
radial velocities of the absorber. In analyzing the lines, however, it is
important to sense and correct for the fact that some parts of a profile may
have some very narrow structures that are saturated and then degraded by the
convolution of the true spectrum by the instrumental profile. This can be done
by comparing at each velocity the apparent optical depths of two lines that
have significantly different transition probabilities. If their ratio is
smaller than the ratio of the lines' values of f(lambda), the actual saturation
is more severe than that indicated by the raw optical depths. This paper
describes a simple procedure for selectively boosting apparent optical depth of
the weaker of the two lines at each velocity value, so that unresolved
saturated structure is accounted for, thus yielding a very nearly correct
answer for the column density per unit velocity. Some test examples that
demonstrate the use of the correction method are given, along with a simple
recipe for invoking it.",9605010v1
2002-02-19,Saturation of the R-mode Instability,"Rossby waves (r-modes) in rapidly rotating neutron stars are unstable because
of the emission of gravitational radiation. We study saturation of this
instability by nonlinear transfer of energy to stellar ""inertial"" oscillation
modes. We present detailed calculations of stellar inertial modes in the WKB
limit, their linear damping by bulk and shear viscosity, and the nonlinear
coupling forces among these modes. The saturation amplitude is derived in the
extreme limits of strong or weak driving by radiation reaction, as compared to
the damping rate of low order inertial modes. We find the saturation energy is
{\it extremely small}, at least four orders of magnitude smaller than that
found by previous investigators. We discuss the consequences of this result for
spin evolution of young neutron stars, and neutron stars being spun up by
accretion in Low Mass X-ray Binaries.We also discuss the detection of these
gravitational waves by LIGO.",0202345v2
2000-07-26,Universal saturation of electron dephasing in three-dimensional disordered metals,"We have systematically investigated the low-temperature electron dephasing
times $\tau_\phi$ in more than 40 three-dimensional polycrystalline impure
metals with distinct material characteristics. In all cases, a saturation of
the dephasing time is observed below about a (few) degree(s) Kelvin, depending
on samples. The value of the saturated dephasing time $\tau_0$ [$\equiv
\tau_\phi (T \to 0 {\rm K})$] falls basically in the range 0.005 to 0.5 ns for
all samples. Particularly, we find that $\tau_0$ scales with the electron
diffusion constant $D$ as $\tau_0 \sim D^{- \alpha}$, with $\alpha$ close to or
slightly larger than 1, for over two decades of $D$ from about 0.1 to 10
cm$^2$/s. Our observation suggests that the saturation behavior of $\tau_\phi$
is universal and intrinsic in three-dimensional polycrystalline impure metals.
A complete theoretical explanation is not yet available.",0007417v2
2002-12-24,Density-of-states picture and stability of ferromagnetism in the highly-correlated Hubbard model,"The problem of stability of saturated and non-saturated ferromagnetism in the
Hubbard model is considered in terms of the one-particle Green's functions.
Approximations by Edwards and Hertz and some versions of the self-consistent
approximations based on the 1/z-expansion are considered. The account of
longitudinal fluctuations turns out to be essential for description of the
non-saturated state. The corresponding pictures of density of states are
obtained. ""Kondo"" density-of-states singularities owing to spin-flip processes
are analyzed. The critical electron concentrations for instabilities of
saturated ferromagnetism and paramagnetic state are calculated for various
lattices. Drawbacks of various approximations are discussed. A comparison with
the results of previous works is performed.",0212586v2
2003-02-03,Scattering of signal in vertical granular chain with impurities,"We investigate the scattering process of impulse from impurities in vertical
granular chain system under gravity. Most of the studies are focused on the
case of light impurities. The reflection rates follow power laws with the
impuity depth. There is a valley in the curve of reflection rate versus the
initial perturbation strength and the curve is not symmetric. Some results on
the scattering process from heavy impurities are also presented. There is a
transition region in the initial velocity space. Through this region the
exponent for leading peak changes smoothly from its saturant value in small $
v_i$ side to its saturant value in large $v_i$ side; the exponent for signal
speed changes smoothly from its saturant value in small $v_i$ side to its
saturant value in large $v_i$ side. Both the peak of the exponent for
reflection rate and the valley for the reflection rate versus $v_i$ also locate
within this transition region.",0302055v2
2003-03-04,Spin-sensitive Bleaching and Spin-Relaxation in QW's,"Spin-sensitive saturation of absorption of infrared radiation has been
investigated in p-type GaAs QWs. It is shown that the absorption saturation of
circularly polarized radiation is mostly controlled by the spin relaxation time
of the holes. The saturation behavior has been investigated for different QW
widths and in dependence on the temperature with the result that the saturation
intensity substantially decreases with narrowing of QWs. Spin relaxation times
were experimentally obtained by making use of calculated (linear) absorption
coefficients for inter-subband transitions.",0303056v1
2003-05-17,Saturation of electrical resistivity,"Resistivity saturation is observed in many metallic systems with a large
resistivity, i.e., when the resistivity has reached a critical value, its
further increase with temperature is substantially reduced. This typically
happens when the apparent mean free path is comparable to the interatomic
separations - the Ioffe-Regel condition. Recently, several exceptions to this
rule have been found. Here, we review experimental results and early theories
of resistivity saturation. We then describe more recent theoretical work,
addressing cases both where the Ioffe-Regel condition is satisfied and where it
is violated. In particular we show how the (semiclassical) Ioffe-Regel
condition can be derived quantum-mechanically under certain assumptions about
the system and why these assumptions are violated for high-Tc cuprates and
alkali-doped fullerides.",0305412v1
2004-02-24,Spin relaxation times of 2D holes from spin sensitive bleaching of inter-subband absorption,"We present spin relaxation times of 2D holes obtained by means of spin
sensitive bleaching of the absorption of infrared radiation in p-type
GaAs/AlGaAs quantum wells (QWs). It is shown that the saturation of
inter-subband absorption of circularly polarized radiation is mainly controlled
by the spin relaxation time of the holes. The saturation behavior has been
determined for different QW widths and in a wide temperature range with the
result that the saturation intensity substantially decreases with narrowing of
the QWs. Spin relaxation times are derived from the measured saturation
intensities by making use of calculated (linear) absorption coefficients for
direct inter-subband transitions. It is shown that spin relaxation is due to
the D'yakonov-Perel' mechanism governed by hole-hole scattering. The problem of
selection rules is addressed.",0402572v1
2006-03-13,The quantum paraelectric behavior of SrTiO_{3} revisited: relevance of the structural phase transition temperature,"It has been known for a long time that the low temperature behavior shown by
the dielectric constant of quantum paraelectric $SrTiO_{3}$ can not be fitted
properly by Barrett's formula using a single zero point energy or saturation
temperature ($T_{1}$). As it was originally shown [K. A. M\""{u}ller and H.
Burkard, Phys. Rev. B {\bf 19}, 3593 (1979)] a crossover between two different
saturation temperatures ($T_{1l}$=77.8K and $T_{1h}$=80K) at $T\sim10K$ is
needed to explain the low and high temperature behavior of the dielectric
constant. However, the physical reason for the crossover between these two
particular values of the saturation temperature at $T\sim10K$ is unknown. In
this work we show that the crossover between these two values of the saturation
temperature at $T\sim10K$ can be taken as a direct consequence of (i) the
quantum distribution of frequencies $g(\Omega)\propto\Omega^{2}$ associated
with the complete set of low-lying modes and (ii) the existence of a definite
maximum phonon frequency given by the structural transition critical
temperature $T_{tr}$.",0603354v1
2006-04-02,Universal low-temperature behavior of frustrated quantum antiferromagnets in the vicinity of the saturation field,"We study the low-temperature thermodynamic properties of a number of
frustrated quantum antiferromagnets which support localized magnon states in
the vicinity of the saturation field. For this purpose we use 1) a mapping of
the low-energy degrees of freedom of spin systems onto the hard-core object
lattice gases and 2) an exact diagonalization of finite spin systems of up to
N=30 sites. The considered spin systems exhibit universal behavior which is
determined by a specific hard-core object lattice gas representing the
independent localized magnon states. We test the lattice gas description by
comparing its predictions with the numerical results for low-lying energy
states of finite spin systems. For all frustrated spin systems considered we
find a strong variation of the low-temperature specific heat passing the
saturation field and a maximum in the isothermal entropy at saturation field
resulting in an enhanced magnetocaloric effect.",0604023v1
2006-08-17,Random Sequential Addition of Hard Spheres in High Euclidean Dimensions,"Employing numerical and theoretical methods, we investigate the structural
characteristics of random sequential addition (RSA) of congruent spheres in
$d$-dimensional Euclidean space $\mathbb{R}^d$ in the infinite-time or
saturation limit for the first six space dimensions ($1 \le d \le 6$).
Specifically, we determine the saturation density, pair correlation function,
cumulative coordination number and the structure factor in each =of these
dimensions. We find that for $2 \le d \le 6$, the saturation density $\phi_s$
scales with dimension as $\phi_s= c_1/2^d+c_2 d/2^d$, where $c_1=0.202048$ and
$c_2=0.973872$. We also show analytically that the same density scaling
persists in the high-dimensional limit, albeit with different coefficients. A
byproduct of this high-dimensional analysis is a relatively sharp lower bound
on the saturation density for any $d$ given by $\phi_s \ge
(d+2)(1-S_0)/2^{d+1}$, where $S_0\in [0,1]$ is the structure factor at $k=0$
(i.e., infinite-wavelength number variance) in the high-dimensional limit.
Consistent with the recent ""decorrelation principle,"" we find that pair
correlations markedly diminish as the space dimension increases up to six. Our
work has implications for the possible existence of disordered classical ground
states for some continuous potentials in sufficiently high dimensions.",0608402v1
2000-07-18,Geometric scaling for the total gamma^* p cross section in the low x region,"We observe that the saturation model of deep inelastic scattering, which
successfully describes inclusive and diffractive data at small x, predicts a
geometric scaling of the total gamma^* p cross section in the region of small
Bjorken variable x. The geometric scaling in this case means that the cross
section is a function of only one dimensionless variable tau = Q^2 R_0^2(x),
where the function R_0(x) (called saturation radius) decreases with decreasing
x. We show that the experimental data from HERA in the region x<0.01 confirm
the expectations of this scaling over a very broad region of Q^2. We suggest
that the geometric scaling is more general than the saturation model.",0007192v2
2001-03-02,Saturation and Universality in QCD at small x,"We find approximate solutions to the renormalization group equation which
governs the quantum evolution of the effective theory for the Color Glass
Condensate. This is a functional Fokker-Planck equation which generates in
particular the non-linear evolution equations previously derived by Balitsky
and Kovchegov within perturbative QCD. In the limit where the transverse
momentum of the external probe is large compared to the saturation momentum,
our approximations yield the Gaussian Ansatz for the effective action of the
McLerran-Venugopalan model. In the opposite limit, of a small external
momentum, we find that the effective theory is governed by a scale-invariant
universal action which has the correct properties to describe gluon saturation.",0103032v2
2001-03-27,The Transverse Energy as a Barometer of a Saturated Plasma,"The evolution of the gluon plasma produced with saturation initial conditions
is calculated via Boltzmann transport theory for nuclear collisions at high
energy. The saturation scale increases with the nuclear size and the beam
energy, and thus we find that the perturbative rescattering rate decreases
relative to the initial longitudinal expansion rate of the plasma. The
effective longitudinal pressure remains significantly below the lattice QCD
pressure until the plasma cools to near the confinement scale. Therefore, the
transverse energy per unit of rapidity and its dependence on beam energy
provides a sensitive test of gluon saturation models: the fractional transverse
energy loss due to final state interactions is smaller and exhibits a weaker
energy dependence than if ideal (nondissipative) hydrodynamics applied
throughout the evolution.",0103291v1
2001-08-29,Diffractive dissociation and saturation scale from non-linear evolution in high energy DIS,"This paper presents the first numerical solution to the non-linear evolution
equation for diffractive dissociation processes in deep inelastic scattering.
It is shown that the solution depends on one scaling variable $\tau = Q^2/Q^{D
2}_s(x,x_0)$, where $Q^D_s(x,x_0)$ is the saturation scale for the diffraction
processes. The dependence of the saturation scale $Q^D_s(x,x_0)$ on both $x$
and $x_0$ is investigated, ($Y_0 = \ln(1/x_0)$ is a minimal rapidity gap for
the diffraction process). The $x$ - dependence of $Q^D_s$ turns out to be the
same as of the saturation scale in the total inclusive DIS cross section. In
our calculations $Q^D_s(x,x_0)$ reveals only mild dependence on $x_0$. The
scaling is shown to hold for $x \ll x_0$ but is violated at $ x \sim x_0$.",0108239v1
2001-10-31,Saturation model for two-photon interactions at high energies,"We formulate and analyse a saturation model for the total gamma gamma and
gamma* gamma* cross-sections and for the real photon structure function
F_2^gamma(x,Q^2). The model is based on a picture in which the gamma* gamma*
total cross-section for arbitrary photon virtualities is driven by the
interaction of colour dipoles, into which the virtual photons fluctuate. The
cross-section describing this interaction is assumed to satisfy the saturation
property with the saturation radius taken from the Golec-Biernat and Wusthoff
analysis of the gamma* p interaction at HERA. The model is supplemented by the
QPM and non-pomeron reggeon contributions. The model gives a very good
description of the data on the gamma gamma total cross-section, on the photon
structure function F_2^gamma(x,Q^2) at low x and on the gamma* gamma*
cross-section extracted from LEP double tagged events. Production of heavy
flavours in gamma gamma collisions is also studied. Predictions of the model
for the very high energy range which will be probed at future linear colliders
are given.",0110409v1
2002-05-18,Understanding Geometric Scaling at Small x,"Geometric scaling is a novel scaling phenomenon observed in deep inelastic
scattering at small x: the total virtual photon-proton cross section depends
upon the two kinematical variables Q^2 and x only via their combination Q^2
R_0^2(x), with R_0^2(x) \propto x^{\lambda}. At sufficiently low Q^2, below the
saturation scale Q_s^2(x) (a few GeV^2), this phenomenon finds a natural
explanation as a property of the Color Glass Condensate, the high-density
matter made of saturated gluons. To explain the experimental observation of
geometric scaling up to much higher values of Q^2, of the order of 100 GeV^2,
we study the solution to the BFKL equation subjected to a saturation boundary
condition at Q^2\sim Q_s^2(x). We find that the scaling extends indeed above
the saturation scale, within a window 1 < \ln(Q^2/Q_s^2) <<
\ln(Q_s^2/\Lambda^2_{\rm QCD}), which is consistent with phenomenology.",0205198v1
2002-06-14,Two-photon cross-sections from the saturation model,"A saturation model for the total gamma-gamma and gamma*-gamma* cross-sections
and for the real photon structure function F_2^gamma(x,Q^2) is described. The
model is based on a QCD dipole picture of high energy scattering. The
two-dipole cross-section is assumed to satisfy the saturation property with the
saturation radius taken from the GBW analysis of the gamma*-p interaction at
HERA. The model is combined with the QPM and non-pomeron reggeon contributions
an it gives a very good description of the data on the gamma-gamma total
cross-section, on the photon structure function F_2^gamma(x,Q^2) at low x and
on the gamma*-gamma* cross-section. Production of heavy quarks in gamma-gamma
collisions is also studied.",0206129v1
2003-01-21,QCD-Instantons and Saturation at Small x,"We briefly report on the contribution of QCD-instantons to the phenomenon of
saturation in deep-inelastic scattering (DIS) at small Bjorken-x. The
explicitly known instanton gauge field serves as a concrete realization of an
underlying non-perturbative saturation mechanism associated with strong
classical fields. Two independent strategies were pursued, with consistent
results: On the one hand, an approach starting from instanton-perturbation
theory was considered and on the other hand, the scattering of a Wilson loop in
an instanton gauge field background. In both cases, the conspicuous, intrinsic
instanton size scale <rho> ~ 0.5 fm, as known from the lattice, turns out to
determine the saturation scale.",0301177v1
2003-02-20,Anatomy of QCD Strings and Saturation Effects in High-Energy Scattering,"We develop a model to compute high-energy reactions of hadrons and photons.
The perturbative interaction is described by gluon exchange and the
non-perturbative interaction by the stochastic vacuum model which leads to
quark-confinement in dipoles via a string of color fields. We study the QCD
structure of the dipole-dipole scattering in momentum space focussing
especially on interactions between strings. We represent the string as a
collection of stringless dipoles, show confinement effects in high-energy
scattering and calculate unintegrated gluon distributions of hadrons and
photons. In the impact parameter space of the scattering process we investigate
the unitarity limit of the S-matrix. We calculate the impact parameter profiles
for proton-proton and photon-proton scattering, determine the energy values at
which the profiles saturate at the black disc limit, estimate the impact
parameter dependent gluon distribution of the proton and discuss gluon
saturation. We compare the model results for p p, pi p, K p, gamma p and gamma
gamma reactions with experimental data and identify saturation effects in
experimental observables.",0302179v1
2003-04-21,An Impact Parameter Dipole Saturation Model,"We develop a dipole model for HERA DIS data which incorporates the impact
parameter distribution of the proton. The model describes the inclusive total
$\gamma^*p$ cross-sections as well as the diffractive $J/\psi$ differential
cross-sections. We compare the model with previous approaches and show that the
$t$-distributions are sensitive to saturation phenomena. We estimate the
boundary of the saturation region and show that it dominates the data in the
low-$Q^2$ region where the total $\gamma^*p$ cross-section exhibits the same
universal rise as hadronic cross-sections. The model is then extended to nuclei
and shows good agreement with the nuclear shadowing data at small-$x$. Finally,
we estimate the saturation scale in nuclei.",0304189v3
2003-08-06,Saturation Physics in Heavy Ion Collisions,"We discuss expectations of saturation physics for various observables in
heavy ion collisions. We show how simple saturation-inspired assumptions about
particle production in heavy ion collisions lead to Kharzeev-Levin-Nardi model.
Comparing this model to RHIC data on particle multiplicities we conclude that
saturation effects may play an important role in particle production and
dynamics at the early stages of Au-Au collisions already at RHIC energies. We
then estimate the contribution of the initial state two-particle azimuthal
correlations to elliptic flow observable v_2 in Au-Au collisions by
constructing a lower bound on these non-flow effects based on v_2 obtained from
the analysis of proton-proton (pp) collisions.",0308076v1
2004-03-26,Jet Azimuthal Correlations and Parton Saturation in the Color Glass Condensate,"We consider the influence of parton saturation in the Color Glass Condensate
on the back-to-back azimuthal correlations of high $p_T$ hadrons in $pA$ (or
$dA$) collisions. When both near--side and away--side hadrons are detected at
mid-rapidity at RHIC energy, the effects of parton saturation are constrained
to transverse momenta below the saturation scale $p_T \leq Q_s$; in this case
the back-to-back correlations do not disappear but exhibit broadening. However
when near-side and away-side hadrons are separated by several units of
rapidity, quantum evolution effects lead to the depletion of back-to-back
correlations as a function of rapidity interval between the detected hadrons
(at fixed $p_T$). This applies to both $pp$ and $pA$ (or $dA$) collisions;
however, due to the initial conditions provided by the Color Glass Condensate,
the depletion of the back-to-back correlations is significantly stronger in the
$pA$ case. An experimental study of this effect would thus help to clarify the
origin of the high $p_T$ hadron suppression at forward rapidities observed
recently at RHIC.",0403271v1
2004-05-21,Small-x physics near the saturation regime,"We consider the T-matrix near the unitarity limit and the energy dependence
of the saturation momentum. We discuss the solution to the Kovchegov equation,
or equivalently, to the BFKL evolution in the presence of a single saturation
boundary. We include some of the correlations missed in the Kovchegov equation
by solving the BFKL equation in the presence of two boundaries. The T-matrix
now turns out to be frame-independent, which was not the case for the solution
in the case of a single boundary, and it doesn't show the scaling behavior of
the solution to the Kovchegov equation. We find for the saturation momentum an
energy dependence which differs from the one following from the Kovchegov
equation.",0405205v1
2005-04-18,Solution to the Balitsky-Kovchegov equation in the saturation domain,"The solution to the Balitsky-Kovchegov equation is found in the deep
saturation domain. The controversy between different approaches regarding the
asymptotic behaviour of the scattering amplitude is solved. It is shown that
the dipole amplitude behaves as $ 1 - \exp (- z + \ln z)$ with $ z = \ln (r^2
Q^2_s)$ ($ r$ -size of the dipole, $Q_s$ is the saturation scale) in the deep
saturation region. This solution is developed from the scaling solution to the
homogeneous Balitsky-Kovchegov equation. The dangers associated with making
simplifications in the BFKL kernel, to investigate the asymptotic behaviour of
the scattering amplitude, is pointed out . In particular, the fact that the
Balitsky-Kovchegov equation belongs to the
Fisher-Kolmogorov-Petrovsky-Piscounov -type of equation, needs further careful
investigation.",0504146v1
2005-04-23,Testing saturation with diffractive jet production in deep inelastic scattering,"We analyse the dissociation of a photon in diffractive deep inelastic
scattering in the kinematic regime where the diffractive mass is much bigger
than the photon virtuality. We consider the dominant q\bar{q}g component
keeping track of the transverse momentum of the gluon which can be measured as
a final-state jet. We show that the diffractive gluon-jet production
cross-section is strongly sensitive to unitarity constraints. In particular, in
a model with parton saturation, this cross-section is sensitive to the scale at
which unitarity effects become important, the saturation scale. We argue that
the measurement of diffractive jets at HERA in the limit of high diffractive
mass can provide useful information on the saturation regime of QCD.",0504214v2
2005-08-01,Has saturation physics been observed in deuteron-gold collisions at RHIC?,"In the framework of the recently proposed saturation picture, we examine in a
systematic way whether the nuclear modification factor measured for d-Au
collisions at RHIC may be simply explained. The Cronin peak which is obtained
at mid-rapidity around $k_{\bot}\simeq 3$ GeV may be reproduced at the proper
height only by boosting the saturation momentum by an additional nuclear
component as already shown in the literature. In this respect, mid-rapidity
RHIC data cannot necessarily be seen as a probe of the saturation picture. The
large rapidity ($\eta\simeq 3$) region allows us to test the shape of the
unintegrated gluon distribution in the nucleus, investigating various
parameterizations inspired by large rapidity solutions (of the BFKL and) of the
Balitsky-Kovchegov (BK) equation. A satisfactory description of $R_{CP}$ at
RHIC is obtained in the BK picture.",0508026v2
2005-11-17,Traveling waves in high energy QCD,"Saturation is expected to occur when a high density of partons (mainly
gluons)- or equivalently strong fields in Quantum Chromodynamics (QCD) - is
realized in the weak coupling regime. A way to reach saturation is through the
high-energy evolution of an extended target probed at a fixed hard scale. In
this case, the transition to saturation is expected to occur from nonlinear
perturbative QCD dynamics. We discuss this approach to saturation, which is
mathematically characterized by the appearance of traveling wave patterns in a
suitable kinematical representation. A short review on traveling waves in high
energy QCD and a first evidence of this phenomenon in deep-inelastic proton
scattering are presented.",0511214v1
1999-10-07,BPS Saturated Solitons in N=2 Two-Dimensional Theories on RxS (Domain Walls in Theories with Compactified Dimensions),"We discuss topologically stable solitons in two-dimensional theories with the
extended supersymmetry assuming that the spatial coordinate is compact. This
problem arises in the consideration of the domain walls in the popular theories
with compactified extra dimensions. Contrary to naive expectations, it is shown
that the solitons on the cylinder can be BPS saturated. In the case of one
chiral superfield, a complete theory of the BPS saturated solitons is worked
out. We describe the classical solutions of the BPS equations. Depending on the
choice of the Kahler metric, the number of such solutions can be arbitrarily
large. Although the property of the BPS saturation is preserved order by order
in perturbation theory, nonperturbative effects eliminate the majority of the
classical BPS states upon passing to the quantum level. The number of the
quantum BPS states is found. It is shown that the N=2 field theory includes an
auxiliary N=1 quantum mechanics, Witten's index of which counts the number of
the BPS particles.",9910071v1
2000-06-04,Leaving the BPS bound: Tunneling of classically saturated solitons,"We discuss quantum tunneling between classically BPS saturated solitons in
two-dimensional theories with N=2 supersymmetry and a compact space dimension.
Genuine BPS states form shortened multiplets of dimension two. In the models we
consider there are two degenerate shortened multiplets at the classical level,
but there is no obstruction to pairing up through quantum tunneling. The
tunneling amplitude in the imaginary time is described by instantons. We find
that the instanton is nothing but the 1/4 BPS saturated ``wall junction,''
considered previously in the literature in other contexts. Two central charges
of the superalgebra allow us to calculate the instanton action without finding
the explicit solution (it is checked, though, numerically, that the saturated
solution does exist). We present a quantum-mechanical interpretation of the
soliton tunneling.",0006026v1
2005-01-06,Heisenberg saturation of the Froissart bound from AdS-CFT,"In a previous paper, we have analyzed high energy QCD from AdS-CFT and proved
the saturation of the Froissart bound (a purely QCD proof of which is still
lacking). In this paper we describe the calculation in more physical terms and
map it to QCD language. We find a remarkable agreement with the 1952 Heisenberg
description of the saturation (pre-QCD!) in terms of shockwave collisions of
pion field distributions. It provides a direct map between gauge theory physics
and the gravitational physics on the IR brane of the Randall-Sundrum model.
Saturation occurs through black hole production on the IR brane, which is in
QCD production of a nonlinear pion field soliton of a Born-Infeld action in the
hadron collision, that decays into free pions.",0501038v2
1999-08-01,Notions of denseness,"The notion of a completely saturated packing [Fejes Toth, Kuperberg and
Kuperberg, Highly saturated packings and reduced coverings, Monats. Math. 125
(1998) 127-145] is a sharper version of maximum density, and the analogous
notion of a completely reduced covering is a sharper version of minimum
density. We define two related notions: uniformly recurrent and weakly
recurrent dense packings, and diffusively dominant packings. Every compact
domain in Euclidean space has a uniformly recurrent dense packing. If the
domain self-nests, such a packing is limit-equivalent to a completely saturated
one. Diffusive dominance is yet sharper than complete saturation and leads to a
better understanding of n-saturation.",9908003v3
2001-06-04,Subsymmetric sequences and minimal spaces,"We show that every Banach space saturated with subsymmetric sequences
contains a minimal subspace.",0106023v2
2003-02-19,Topologische und algebraische Filter,"We provide the set of filters (saturated submonoids) in a commutative monoid
with a topology (like the spectrum of a ring) and study the resulting spaces.",0302235v1
2004-04-06,Determinantal processes with number variance saturation,"Consider Dyson's Hermitian Brownian motion model after a finite time S, where
the process is started at N equidistant points on the real line. These N points
after time S form a determinantal process and has a limit as N tends to
infinity. This limting determinantal proceess has the interesting feature that
it shows number variance saturation. The variance of the number of particles in
an interval converges to a limiting value as the length of the interval goes to
infinity. Number variance saturation is also seen for example in the zeros of
the Riemann zeta function (Odlyzko, Berry). The process can also be constructed
using non-intersecting paths and we consider several variants of this
construction. One construction leads to a model which shows a transition from a
non-universal behaviour with number variance saturation to a universal
sine-kernel behaviour as we go up the line.",0404133v1
2007-03-19,Algebraization of complex analytic varieties and derived categories,"We prove that a compact complex analytic variety is algebraizable if and only
if its bounded derived dg-category of coherent sheaves is saturated.",0703555v1
1998-05-15,Resonance trapping and saturation of decay widths,"Resonance trapping appears in open many-particle quantum systems at high
level density when the coupling to the continuum of decay channels reaches a
critical strength. Here a reorganization of the system takes place and a
separation of different time scales appears. We investigate it under the
influence of additional weakly coupled channels as well as by taking into
account the real part of the coupling term between system and continuum. We
observe a saturation of the mean width of the trapped states. Also the decay
rates saturate as a function of the coupling strength. The mechanism of the
saturation is studied in detail. In any case, the critical region of
reorganization is enlarged. When the transmission coefficients for the
different channels are different, the width distribution is broadened as
compared to a chi_K^2 distribution where K is the number of channels. Resonance
trapping takes place before the broad state overlaps regions beyond the
extension of the spectrum of the closed system.",9805029v1
1999-07-20,Saturation from nuclear pion dynamics,"We construct an equation-of-state for nuclear matter based on the chiral
Lagrangian. The relevant scales are discussed and an effective chiral power
expansion scheme, which is constructed to work around the nuclear saturation
density, is presented. A realistic equation-of-state is obtained by adjusting
one free parameter, when the leading and subleading terms in the expansion are
included. The saturation mechanism is due to correlations induced by the
one-pion-exchange interaction. Furthermore, we find a substantial deviation
from the Fermi-gas estimate of the quark condensate in nuclear matter already
at the saturation density.",9907078v2
2001-08-13,Nuclear equation of state and spectral functions,"An overview is given of the theoretical work on nucleon spectral functions in
finite nuclei. The consequences of the observed spectral strength distribution
are then considered in the context of the nuclear-matter saturation problem.
Arguments are presented suggesting that short-range correlations are mainly
responsible for the actual value of the observed charge density in 208Pb and by
extension for the empirical value of the saturation density of nuclear matter.
This observation combined with the general understanding of the spectroscopic
strength suggests that a renewed study of nuclear matter, emphasizing the
self-consistent determination of the spectral strength due to short-range and
tensor correlations, may shed light on the perennial nuclear saturation
problem. First results using such a scheme are presented. Arguments are
discussed that clarify the role of long-range correlations and their relevance
for nuclear saturation.",0108030v1
2002-04-12,Saturation of nuclear matter and radii of unstable nuclei,"We examine relations among the parameters characterizing the phenomenological
equation of state (EOS) of nearly symmetric, uniform nuclear matter near the
saturation density by comparing macroscopic calculations of radii and masses of
stable nuclei with the experimental data. The EOS parameters of interest here
are the symmetry energy S_0, the symmetry energy density-derivative coefficient
L and the incompressibility K_0 at the normal nuclear density. We find a
constraint on the relation between K_0 and L from the empirically allowed
values of the slope of the saturation line (the line joining the saturation
points of nuclear matter at finite neutron excess), together with a strong
correlation between S_0 and L. In the light of the uncertainties in the values
of K_0 and L, we macroscopically calculate radii of unstable nuclei as expected
to be produced in future facilities. We find that the matter radii depend
strongly on L while being almost independent of K_0, a feature that will help
to determine the L value via systematic measurements of nuclear size.",0204033v1
2005-07-04,Non-locality in the nucleon-nucleon interaction and nuclear matter saturation,"We study the possible relationship between the saturation properties of
nuclear matter and the inclusion of non-locality in the nucleon-nucleon
interaction. To this purpose we compute the saturation curve of nuclear matter
within the Bethe-Brueckner-Goldstone theory using a recently proposed realistic
non-local potential, and compare it with the corresponding curves obtained with
a purely local realistic interaction (Argonne v$_{18}$) and the most recent
version of the one-boson exchange potential (CD Bonn). We find that the
inclusion of non-locality in the two-nucleon bare interaction strongly affects
saturation, but it is unable to provide a consistent description of few-body
nuclear systems and nuclear matter.",0507009v2
2006-09-11,Universality of the saturation scale and the initial eccentricity in heavy ion collisions,"Recent estimates that Color Glass Condensate initial conditions may generate
a larger initial eccentricity for noncentral relativistic heavy ion collisions
(relative to the initial eccentricity assumed in earlier hydrodynamic
calculations) have raised the possibility of a higher bound on the viscosity of
the Quark Gluon Plasma. We show that this large initial eccentricity results in
part from a definition of the saturation scale as proportional to the number of
nucleons participating in the collision. A saturation scale proportional to the
nuclear thickness function (and therefore independent of the probe) leads to a
smaller eccentricity, albeit still larger than the value used in hydrodynamic
models. Our results suggest that the early elliptic flow in heavy ion
collisions (unlike multiplicity distributions) is sensitive to the universality
of the saturation scale in high energy QCD.",0609021v1
2004-10-19,A novel approach for the temperature dependency of saturated signal power in EDFAs,"The temperature dependency of the saturated signal power for the transition
in erbium-doped fiber amplifiers (EDFAs) pumped at 980 nm and 1480 nm pump
wavelengths within a temperature range from 20 to 60 oC are investigated by a
novel approach. For 1480 nm pumping regime, it is seen that the saturated
signal power increases more quickly than that of 980 nm pumping regime, with
the increasing temperature. The variation in the saturated signal power with
temperature is nearly constant at 980 nm pumping regime. In addition, the
population inversion with respect to the increasing normalized signal power is
examined and it is seen that it is independent of temperature for 980 nm but it
strongly depends on temperature for 1480 nm especially at lower normalized
signal powers.",0410132v2
2005-07-28,X-point collapse and saturation in the nonlinear tearing mode reconnection,"We study the nonlinear evolution of the resistive tearing mode in slab
geometry in two dimensions. We show that, in the strongly driven regime (large
Delta'), a collapse of the X-point occurs once the island width exceeds a
certain critical value ~1/Delta'. A current sheet is formed and the
reconnection is exponential in time with a growth rate ~eta^1/2, where eta is
the resistivity. If the aspect ratio of the current sheet is sufficiently
large, the sheet can itself become tearing-mode unstable, giving rise to
secondary islands, which then coalesce with the original island. The saturated
state depends on the value of Delta'. For small Delta', the saturation
amplitude is ~Delta' and quantitatively agrees with the theoretical prediction.
If Delta' is large enough for the X-point collapse to have occured, the
saturation amplitude increases noticeably and becomes independent of Delta'.",0507206v1
2007-05-13,Gluon saturation and the Froissart bound: a simple approach,"At very high energies we expect that the hadronic cross sections satisfy the
Froissart bound, which is a well-established property of the strong
interactions. In this energy regime we also expect the formation of the Color
Glass Condensate, characterized by gluon saturation and a typical momentum
scale: the saturation scale $Q_s$. In this paper we show that if a saturation
window exists between the nonperturbative and perturbative regimes of Quantum
Chromodynamics (QCD), the total cross sections satisfy the Froissart bound.
Furthermore, we show that our approach allows us to describe the high energy
experimental data on $pp/p\bar{p}$ total cross sections.",0705.1842v2
2007-05-24,Saturation QCD predictions with heavy quarks at HERA,"The measurement of the proton structure function at HERA is often seen as a
hint for the observation of saturation in high-energy QCD e.g. through the
observation of geometric scaling. Accordingly, the dipole picture provides a
powerful framework in which the QCD-based saturation models can be confronted
to the data. In this paper, we give a parametrisation of proton structure
function which is directly constrained by the dynamics of QCD in its
high-energy limit and fully includes the heavy quark effects. We obtain a good
agreement with the available data. Furthermore, to the contrary of various
models in the literature, we do not observe a significant decrease of the
saturation momentum due to the heavy quark inclusion.",0705.3672v1
2007-06-06,Saturation effects in the sub-Doppler spectroscopy of Cesium vapor confined in an Extremely Thin Cell,"Saturation effects affecting absorption and fluorescence spectra of an atomic
vapor confined in an Extremely Thin Cell (cell thickness $L < 1 \mu m$) are
investigated experimentally and theoretically. The study is performed on the
$D_{2}$ line ($\lambda ~= ~852 nm)$ of $Cs$ and concentrates on the two
situations $L = \lambda /2$ and $L =\lambda$, the most contrasted ones with
respect to the length dependence of the coherent Dicke narrowing. For $L =
\lambda /2$, the Dicke-narrowed absorption profile simply broadens and
saturates in amplitude when increasing the light intensity, while for $L
=\lambda$, sub-Doppler dips of reduced absorption at line-center appear on the
broad absorption profile. For a fluorescence detection at $L =\lambda$,
saturation induces narrow dips, but only for hyperfine components undergoing a
population loss through optical pumping. These experimental results are
interpreted with the help of the various existing models, and are compared with
numerical calculations based upon a two-level modelling that considers both a
closed and an open system.",0706.0837v1
2007-10-30,AgInSe2 Nanorods: A semiconducting material for saturable absorber,"AgInSe2 nanorods (NRs) with diameter of 15 nm have been investigated for
their nonlinear optical responses by using Z-scan and transient absorption
techniques with femtosecond laser pulses of photon energy greater than the
bandgap. At excitation irradiance of 20 GW/cm2, AgInSe2 NRs reveal saturation
in the nonlinear absorption and optical Kerr nonlinearity with a recovery time
determined to be a few ten picoseconds. Such large saturable absorption and
Kerr nonlinearity exhibit a third-order susceptibility of 1.2 x 10-8 esu and a
figure of merit of 0.04 esu.cm.s-1, making AgInSe2 NRs a promising candidate
for saturable absorption devices.",0710.5573v1
2007-12-20,Lie algebra F-normalisers are intravariant,"Let F be a saturated formation of soluble Lie algebras and let U be an
F-normaliser of the soluble Lie algebra L. Then U is intravariant in L.",0712.3306v1
2008-01-03,Observation of coherence revival and fidelity saturation in a delta-kicked rotor potential,"We experimentally investigate the effect of atomic $\delta$-kicked rotor
potentials on the mutual coherence between wavepackets in an atom
interferometer. The differential action of the kicked rotor degrades the mutual
coherence, leading to a reduction of the interferometry fringe visibility;
however, when the repetition rate of the kicked rotor is at or near the quantum
resonance, we observe revival of matter-wave coherence as the number of kicks
increases, resulting in non-vanishing coherence in the large kick number limit.
This coherence saturation effect reflects a saturation of fidelity decay due to
momentum displacements in deep quantum regime. The saturation effect is
accompanied with an invariant distribution of matter-wave coherence under the
kicked rotor perturbations.",0801.0475v3
2008-02-12,Resummation of projectile-target multiple scatterings and parton saturation,"In the framework of a toy model which possesses the main features of QCD in
the high energy limit, we conduct a numerical study of scattering amplitudes
constructed from parton splittings and projectile-target multiple interactions,
in a way that unitarizes the amplitudes without however explicit saturation in
the wavefunction of the incoming states. This calculation is performed in two
different ways. One of these formulations, the closest to field theory,
involves the numerical resummation of a factorially divergent series, for which
we develop appropriate numerical tools. We accurately compare the properties of
the resulting amplitudes with what would be expected if saturation were
explicitly included in the evolution of the states. We observe that the
amplitudes have similar properties in a small but finite range of rapidity in
the beginning of the evolution, as expected. Some of the features of
reaction-diffusion processes are already present in that range, even when
saturation is left out of the model.",0802.1656v1
2008-04-09,Saturation in Deep Inelastic Scattering from AdS/CFT,"We analyze deep inelastic scattering at small Bjorken x, using the
approximate conformal invariance of QCD at high energies. Hard pomeron
exchanges are resummed eikonally, restoring unitarity at large values of the
phase shift in the dual AdS geometry. At weak coupling this phase is imaginary,
corresponding to a black disk in AdS. In this saturated regime, cross sections
exhibit geometric scaling and have a simple universal form, which we test
against available experimental data for the proton structure function
F_2(x,Q^2). We predict, in particular, the dependence of the cross section on
the scaling variable (Q/Q_s)^2 in the deeply saturated region, where Q_s is the
usual saturation scale. We find agreement with current data on F_2 in the
kinematical region 0.5 < Q^2 < 10 GeV^2, x < 10^-2, with an average 6%
accuracy. We conclude by discussing the relation of our approach with the
commonly used dipole formalism.",0804.1562v3
2008-04-20,Nonlinear Photoluminescence Excitation Spectroscopy of Carbon Nanotubes: Exploring the Upper Density Limit of One-Dimensional Excitons,"We have studied emission properties of high-density excitons in single-walled
carbon nanotubes through nonlinear photoluminescence excitation spectroscopy.
As the excitation intensity was increased, all emission peaks arising from
different chiralities showed clear saturation in intensity. Each peak exhibited
a saturation value that was independent of the excitation wavelength,
indicating that there is an upper limit on the exciton density for each
nanotube species. We developed a theoretical model based on exciton diffusion
and exciton-exciton annihilation that successfully reproduced the saturation
behavior, allowing us to estimate exciton densities. These estimated densities
were found to be still substantially smaller than the expected Mott density
even in the saturation regime, in contrast to conventional semiconductor
quantum wires.",0804.3190v1
2008-06-18,Analytic pro-p groups of small dimensions,"According to Lazard, every p-adic Lie group contains an open pro-p subgroup
which is saturable. This can be regarded as the starting point of p-adic Lie
theory, as one can naturally associate to every saturable pro-p group G a Lie
lattice L(G) over the p-adic integers.
  Essential features of saturable pro-p groups include that they are
torsion-free and p-adic analytic. In the present paper we prove a converse
result in small dimensions: every torsion-free p-adic analytic pro-p group of
dimension less than p is saturable.
  This leads to useful consequences and interesting questions. For instance, we
give an effective classification of 3-dimensional soluble torsion-free p-adic
analytic pro-p groups for p > 3. Our approach via Lie theory is comparable with
the use of Lazard's correspondence in the classification of finite p-groups of
small order.",0806.2968v1
2008-09-05,New properties of z-scaling: flavor independence and saturation at low z,"Experimental data on inclusive cross sections of particles produced in high
energy proton-(anti)proton collisions at ISR, RHIC, and Tevatron are analyzed
in the framework of $z$-scaling. New features of the scaling function $\psi(z)$
are established. These are flavor independence of $\psi(z)$ including particles
with heavy flavor content and saturation at low $z$. The flavor independence
means that the shape of the scaling function $\psi(z)$ is the same for
different hadron species. The saturation corresponds to flattening of $\psi(z)$
for $z<0.1$. Relations of model parameters used in data $z$-presentation with
some thermodynamical quantities (entropy, specific heat, temperature) are
discussed. It is shown that behavior of the particle spectra at low $z$ is
controlled by a parameter $c$ interpreted as a specific heat of the created
medium associated with production of the inclusive particle. The saturation
regime of $\psi(z)$ observed at low $z$ is assumed to be preferable in
searching for phase transitions of hadron matter and for study of
non-perturbative QCD in high energy proton-(anti)proton collisions at U70,
RHIC, Tevatron, and LHC.",0809.1033v1
2008-10-08,Saturation of Two Level Systems and Charge Noise in Josephson Junction Qubits,"We study the charge noise $S_Q$ in Josephson qubits produced by fluctuating
two level systems (TLS) with electric dipole moments in the substrate. The TLS
are driven by an alternating electric field of angular frequency $\Omega$ and
electric field intensity $I$. It is not widely appreciated that TLS in small
qubits can easily be strongly saturated if $I\gg I_c$, where $I_c$ is the
critical electric field intensity. To investigate the effect of saturation on
the charge noise, we express the noise spectral density in terms of density
matrix elements. To determine the dependence of the density matrix elements on
the ratio $I/I_c$, we find the steady state solution for the density matrix
using the Bloch-Redfield differential equations. We then obtain an expression
for the spectral density of charge fluctuations as a function of frequency $f$
and the ratio $I/I_c$. We find $1/f$ charge noise at low frequencies, and that
the charge noise is white (constant) at high frequencies. Using a flat density
of states, we find that TLS saturation has no effect on the charge noise at
either high or low frequencies.",0810.1334v2
2008-12-11,Mixed scenario of the charged liquid surface reconstruction,"Discussed in the paper is a mixed scenario of the charged liquid surface
reconstruction in the situation where the 2D surface charge density is close to
its saturation value.",0812.2157v1
2009-02-11,Asymptotic behavior of two-phase flows in heterogeneous porous media for capillarity depending only on space. I. Convergence to the optimal entropy solution,"We consider an immiscible two-phase flow in a heterogeneous one-dimensional
porous medium. We suppose particularly that the capillary pressure field is
discontinuous with respect to the space variable. The dependence of the
capillary pressure with respect to the oil saturation is supposed to be weak,
at least for saturations which are not too close to 0 or 1. We study the
asymptotic behavior when the capillary pressure tends to a function which does
not depend on the saturation. In this paper, we show that if the capillary
forces at the spacial discontinuities are oriented in the same direction that
the gravity forces, or if the two phases move in the same direction, then the
saturation profile with capillary diffusion converges toward the unique optimal
entropy solution to the hyperbolic scalar conservation law with discontinuous
flux functions.",0902.1877v3
2009-06-15,CCFM Evolution with Unitarity Corrections,"We considerably extend our previous analysis of the implementation of an
absorptive boundary condition, which mimics saturation effects, on the linear
CCFM evolution. We present detailed results for the evolution of the
unintegrated gluon density in the presence of saturation and extract the energy
dependence of the emerging saturation momentum. We show that CCFM and BFKL
evolution lead to almost identical predictions after including the effects of
gluon saturation and of the running of the coupling. We moreover elucidate
several important and subtle aspects of the CCFM formalism, such as its
relation to BFKL, the structure of the angular ordered cascade, and the
derivation of more inclusive versions of CCFM. We also propose non--leading
modifications of the standard CCFM evolution which may play an important role
for phenomenological studies.",0906.2683v2
2009-07-30,Baryon stopping and saturation physics in relativistic collisions,"We investigate baryon transport in relativistic heavy-ion collisions at
energies reached at the CERN Super Proton Synchrotron, BNL Relativistic
Heavy-Ion Collider (RHIC), and CERN LHC in the model of saturation. An
analytical scaling law is derived within the color glass condensate framework
based on small-coupling QCD. Transverse momentum spectra, net-baryon rapidity
distributions and their energy, mass and centrality dependences are well
described. In a comparison with RHIC data in Au + Au collisions at sqrt (s_NN)
= 62.4 GeV and 200 GeV, the gradual approach to the gluon saturation regime is
investigated, and limits for the saturation-scale exponent are determined.
Predictions for net-baryon rapidity spectra and the mean rapidity loss in
central Pb + Pb collisions at LHC energies of sqrt (s_NN) = 5.52 TeV are made.",0907.5444v2
2009-10-30,Atomic layer graphene as saturable absorber for ultrafast pulsed lasers,"The optical conductance of monolayer graphene is defined solely by the fine
structure constant. The absorbance has been predicted to be independent of
frequency. In principle, the interband optical absorption in zero-gap graphene
could be saturated readily under strong excitation due to Pauli blocking. Here,
we demonstrate the use of atomic layer graphene as saturable absorber in a
mode-locked fiber laser for the generation of ultrashort soliton pulses (756
fs) at the telecommunication band. The modulation depth can be tuned in a wide
range from 66.5% to 6.2% by varying the thickness of graphene. Our results
suggest that ultrathin graphene films are potentially useful as optical
elements in fiber lasers. Graphene as a laser mode locker can have many merits
such as lower saturation intensity, ultrafast recovery time, tunable modulation
depth and wideband tuneability.",0910.5820v1
2010-01-07,Numerical modelling of unsaturated-saturated flow under centrifugation with no outflow,"A novel centrifuge set-up for the study of unsaturated flow characteristics
in porous media is examined. In this set-up, simple boundary conditions can be
used, but a free moving boundary between unsaturated-saturated flow arises. A
precise and numerically efficient approximation is presented for the
mathematical model based on Richards' nonlinear and degenerate equation
expressed in terms of effective saturation using the Van Genuchten-Mualem
ansatz for the soil parameters in the unsaturated zone. Sensitivity of the
measurable quantities (rotational moment, center of gravity and time period to
achieve quasi steady state) on the soil parameters is investigated in several
numerical experiments. They show that the set-up is suitable for the
determination of the soil parameters via the solution of an inverse problem in
an iterative way, excluding the saturated hydraulic conductivity. For this
parameter, an existing simple centrifuge set-up is repeated and augmented with
transient measurements.",1001.1070v1
2010-02-24,Correlations in impact-parameter space in a hierarchical saturation model for QCD at high energy,"In order to get an estimate of the homogeneity of the distribution of matter
in a fast hadron or nucleus, we compute the correlations of the saturation
scales Q_s between different points in impact-parameter space, in some specific
saturation models. We find that these correlations are quite strong: The
saturation scale is nearly uniform in domains whose sizes scale like
exp[const*ln^2(1/\alpha_s^2)]/Q_s, which means that the density of gluons
should not fluctuate significantly over regions of that typical size. We expect
these conclusions as well as the explicit analytical expressions we obtain for
the correlations to be true also for full QCD in appropriate limits.",1002.4575v1
2010-03-09,On saturation of charged hadron production in pp collisions at LHC,"First results on charged hadron transverse momentum spectra in pp collisions
obtained by the CMS Collaboration at LHC were analyzed in z-scaling approach.
The first LHC data confirm z-scaling. The saturation regime of the scaling
function psi(z) observed in pp and antp-pp interactions at lower energy sqrt s
= 19-1960 GeV is verified. The saturation of psi(z) for charged hadrons is
found down to z=0.05 at the highest energy sqrt s = 2360 GeV reached till now
at colliders. A microscopic scenario of hadron production is discussed in
connection with search for new signatures of phase transitions in hadron
matter. Constituent energy loss and its dependencies on the transverse momentum
of charged hadrons and collision energy are estimated. The beam energy scan at
LHC in the saturation region is suggested.",1003.1913v1
2010-03-15,Saturating the holographic entropy bound,"The covariant entropy bound states that the entropy, S, of matter on a
light-sheet cannot exceed a quarter of its initial area, A, in Planck units.
The gravitational entropy of black holes saturates this inequality. The entropy
of matter systems, however, falls short of saturating the bound in known
examples. This puzzling gap has led to speculation that a much stronger bound,
S< A^{3/4}, may hold true. In this note, we exhibit light-sheets whose entropy
exceeds A^{3/4} by arbitrarily large factors. In open FRW universes, such
light-sheets contain the entropy visible in the sky; in the limit of early
curvature domination, the covariant bound can be saturated but not violated. As
a corollary, we find that the maximum observable matter and radiation entropy
in universes with positive (negative) cosmological constant is of order
Lambda^{-1} (Lambda^{-2}), and not |Lambda|^{-3/4} as had hitherto been
believed. Our results strengthen the evidence for the covariant entropy bound,
while showing that the stronger bound S< A^{3/4} is not universally valid. We
conjecture that the stronger bound does hold for static, weakly gravitating
systems.",1003.3012v1
2010-06-02,Correlations in impact-parameter space in saturation models,"In order to get an estimate of the homogeneity of the distribution of matter
in a fast hadron, we compute the correlation of the saturation scales between
different impact parameters. We find that these correlations are quite strong:
The saturation scale is nearly uniform in a wide domain around each point in
impact-parameter space. We provide analytical expressions for the correlations,
which are supported by numerical simulations. Although the numerical
calculations are done for specific saturation models which are obtained from
QCD after drastic simplifications, we expect our analytical formulas to be
correct for full QCD in asymptotic limits, since their derivation requires only
a few general assumptions.",1006.0425v1
2010-07-12,Mutual boosting of the saturation scales in colliding nuclei,"Saturation of small-x gluons in a nucleus, which has the form of transverse
momentum broadening of projectile gluons in pA collisions in the nuclear rest
frame, leads to a modification of the parton distribution functions in the beam
compared with pp collisions. The DGLAP driven gluon distribution turns out to
be suppressed at large x, but significantly enhanced at x<<1. This is a high
twist effect. In the case of nucleus-nucleus collisions all participating
nucleons on both sides get enriched in gluon density at small x, which leads to
a further boosting of the saturation scale. We derive reciprocity equations for
the saturation scales corresponding to a collision of two nuclei. The solution
of these equations for central collisions of two heavy nuclei demonstrate a
significant, up to several times, enhancement of Q_{sA}^2, in AA compared with
pA collisions.",1007.1913v2
2010-07-14,Monolayer Graphene as Saturable Absorber in Mode-locked Laser,"We demonstrate that the intrinsic properties of monolayer graphene allow it
to act as a more effective saturable absorber for mode-locking fiber lasers
compared to multilayer graphene. The absorption of monolayer graphene can be
saturated at lower excitation intensity compared to multilayer graphene,
graphene with wrinkle-like defects, and functionalized graphene. Monolayer
graphene has a remarkable large modulation depth of 95.3%, whereas the
modulation depth of multilayer graphene is greatly reduced due to nonsaturable
absorption and scattering loss. Picoseconds ultrafast laser pulse (1.23 ps) can
be generated using monolayer graphene as saturable absorber. Due to the
ultrafast relaxation time, larger modulation depth and lower scattering loss of
monolayer graphene, it performs better than multilayer graphene in terms of
pulse shaping ability, pulse stability and output energy.",1007.2243v2
2010-11-12,Piezoresistance in silicon at uniaxial compressive stresses up to 3 GPa,"The room-temperature longitudinal piezoresistance of n-type and p-type
crystalline silicon along selected crystal axes is investigated under uniaxial
compressive stresses up to 3 GPa. While the conductance ($G$) of n-type silicon
eventually saturates at $\approx 45%$ of its zero-stress value ($G_0$) in
accordance with the charge transfer model, in p-type material $G/G_0$ increases
above a predicted limit of $\approx 4.5$ without any significant saturation,
even at 3 GPa. Calculation of $G/G_0$ using \textit{ab-initio} density
functional theory reveals that neither $G$ nor the mobility, when properly
averaged over the hole distribution, saturate at stresses lower than 3 GPa. The
lack of saturation has important consequences for strained silicon
technologies.",1011.3008v3
2010-12-21,Non-linear viscous saturation of r-modes,"Pulsar spin frequencies and their time evolution are an important source of
information on compact stars and their internal composition. Oscillations of
the star can reduce the rotational energy via the emission of gravitational
waves. In particular unstable oscillation modes, like r-modes, are relevant
since their amplitude becomes large and can lead to a fast spin-down of young
stars if they are saturated by a non-linear saturation mechanism. We present a
novel mechanism based on the pronounced large-amplitude enhancement of the bulk
viscosity of dense matter. We show that the enhanced damping due to non-linear
bulk viscosity can saturate r-modes of neutron stars at amplitudes appropriate
for an efficient spin-down.",1012.4834v2
2011-03-18,Gluon saturation and entropy production in proton proton collisions,"We study properties of high energy factorisable gluon densities focusing on
saturation effects. In particular we show that the property of saturation of
unintegrated gluon density allows for introduction of thermodynamical entropy
associated with production of gluons. This is due to the observation that
saturation scale acts like a mass of a gluon which related with temperature via
thermodynamical relations allows for calculations of entropy. We also show that
obtained entropy behaves like multiplicity of produced gluons.",1103.3654v4
2011-04-19,Energy dependence of the saturation scale and the charged multiplicity in pp and AA collisions,"A natural framework to understand the energy dependence of bulk observables
from lower energy experiments to the LHC is provided by the Color Glass
Condensate, which leads to a ""geometrical scaling"" in terms of an energy
dependent saturation scale Q_s. The measured charged multiplicity, however,
seems to grow faster (~\sqrt{s}^0.3) in nucleus-nucleus collisions than it does
for protons (~\sqrt{s}^0.2), violating the expectation from geometric scaling.
We argue that this difference between pp and AA collisions can be understood
from the effect of DGLAP evolution on the value of the saturation scale, and is
consistent with gluon saturation observations at HERA.",1104.3725v2
2011-04-22,A natural model of the multiverse axioms,"If ZFC is consistent, then the collection of countable computably saturated
models of ZFC satisfies all of the Multiverse Axioms introduced by Hamkins.",1104.4450v1
2011-08-12,A Minimax Linear Quadratic Gaussian Method for Antiwindup Control Synthesis,"In this paper, a dynamic antiwindup compensator design is proposed which
augments the main controller and guarantees robust performance in the event of
input saturation. This is a two stage process in which first a robust optimal
controller is designed for an uncertain linear system which guarantees the
internal stability of the closed loop system and provides robust performance in
the absence of input saturation. Then a minimax linear quadratic Gaussian (LQG)
compensator is designed to guarantee the performance in certain domain of
attraction, in the presence of input saturation. This antiwindup augmentation
only comes into action when plant is subject to input saturation. In order to
illustrate the effectiveness of this approach, the proposed method is applied
to a tracking control problem for an air-breathing hypersonic flight vehicle
(AHFV).",1108.2568v1
2011-10-05,Boosted saturation bound in colliding nuclei,"Interaction with a nucleus in pA collisions enhances the higher Fock
components in the projectile proton. Effectively, this corresponds to an
increase of the hard scale of the process by the saturation momentum Q^2 ->
Q^2+Q_{sA}^2, which leads to an increased gluon distribution function at small
x (but suppressed at x -> 1) compared to that in pp collisions. In the case of
AA collisions the gluon distributions of bound nucleons in both nuclei turn out
to be enhanced, i.e. to be boosted to higher saturation scales compared to pA
collisions. A set of bootstrap equations relating the saturation scales in the
colliding nuclei is derived and solved. The boosting effect has a moderate
magnitude at the energies of RHIC, but becomes significant at LHC.",1110.0964v1
2011-10-25,Growth saturation of unstable thin films on transverse-striped hydrophilic-hydrophobic micropatterns,"Using three-dimensional numerical simulations, we demonstrate the growth
saturation of an unstable thin liquid film on micropatterned
hydrophilic-hydrophobic substrates. We consider different transverse-striped
micropatterns, characterized by the total fraction of hydrophilic coverage and
the width of the hydrophilic stripes. We compare the growth of the film on the
micropatterns to the steady states observed on homogeneous substrates, which
correspond to a saturated sawtooth and growing finger configurations for
hydrophilic and hydrophobic substrates, respectively. The proposed
micropatterns trigger an alternating fingering-spreading dynamics of the film,
which leads to a complete suppression of the contact line growth above a
critical fraction of hydrophilic stripes. Furthermore, we find that increasing
the width of the hydrophilic stripes slows down the advancing front, giving
smaller critical fractions the wider the hydrophilic stripes are. Using
analytical approximations, we quantitatively predict the growth rate of the
contact line as a function of the covering fraction, and predict the threshold
fraction for saturation as a function of the stripe width.",1110.5496v1
2011-12-08,Induced Saturation Number,"In this paper, we discuss a generalization of the notion of saturation in
graphs in order to deal with induced structures. In particular, we define ${\rm
indsat}(n,H)$, which is the fewest number of gray edges in a trigraph so that
no realization of that trigraph has an induced copy of $H$, but changing any
white or black edge to gray results in some realization that does have an
induced copy of $H$.
  We give some general and basic results and then prove that ${\rm
indsat}(n,P_4)=\lceil (n+1)/3\rceil$ for $n\geq 4$ where $P_4$ is the path on 4
vertices. We also show how induced saturation in this setting extends to a
natural notion of saturation in the context of general Boolean formulas.",1112.1923v2
2012-04-02,Constraining the nuclear equation of state at subsaturation densities,"Only one third of the nucleons in $^{208}$Pb occupy the saturation density
area. Consequently nuclear observables related to average properties of nuclei,
such as masses or radii, constrain the equation of state (EOS) not at
saturation density but rather around the so-called crossing density, localised
close to the mean value of the density of nuclei: $\rho\simeq$0.11 fm$^{-3}$.
This provides an explanation for the empirical fact that several EOS quantities
calculated with various functionals cross at a density significantly lower than
the saturation one. The third derivative M of the energy at the crossing
density is constrained by the giant monopole resonance (GMR) measurements in an
isotopic chain rather than the incompressibility at saturation density. The GMR
measurements provide M=1110 $\pm$ 70 MeV (6% uncertainty), whose extrapolation
gives K$_\infty$=230 $\pm$ 40 MeV (17% uncertainty).",1204.0399v3
2012-06-05,Electric field induced saturation effects in photoassociation of a pair of heteronuclear atoms,"We theoretically study saturation effects induced by an external static
electric field on photoassociation (PA) of a heteronuclear atom pair. A static
electric field influences scattering wave-function of two heteronuclear atoms
as described in [D. Chakraborty, J. Hazra and B. Deb, J. Phys. B. {\bf 44}
095201 (2011)]. For certain values of electric field strengths there exist
anisotropic resonances in ground state scattering leading to a large
modification of scattering wave-function at short and intermediate separations
where photoassociative Franck-Condon overlap is significant. Photoassociation
rate as a function of collision energy shows a splitting near resonant electric
field in the mili Kelvin energy regime. This splitting with a prominent dip
occurs due to resonant enhancement of free-bound stimulated linewidth leading
to saturation in free-bound transitions. We study electric field induced
saturation effects on both one- and two-colour PA. Our results suggest that a
static electric field may influence the formation of ground state polar
molecules in two-colour PA.",1206.0859v1
2012-06-28,Simulation of grains in a vibrated U-tube without interstitial fluid,"We present a computational study using Molecular Dynamics of the development
of an accumulation of grains in one side of a two dimensional U-tube under
vertical vibrations. Studying the evolution of the height difference between
the centers of mass of the branches of the tube, we found that it reaches a
saturation value after vibrating for some time. We obtain that this saturation
value is the same if the simulation start with the arms leveled or with a large
initial height difference. We explore the effect of the width of the tube, the
density of the grains and the coefficient of restitution between the grains and
the wall on the value of the saturation. We obtain a value of the width of the
tube for which the saturation value reaches a maximum, and show that the
transport of grains between arms is favored for low grain densities and high
grain-wall restitution coefficient.",1206.6546v1
2012-10-04,Graphene Oxide vs. Reduced Graphene Oxide as saturable absorbers for Er-doped passively mode-locked fiber laser,"In this work we demonstrate comprehensive studies on graphene oxide (GO) and
reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of
Er-doped fiber lasers. The paper describes the fabrication process of both
saturable absorbers and detailed comparison of their parameters. Our results
show, that there is no significant difference in the laser performance between
the investigated SA. Both provided stable, mode-locked operation with sub-400
fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center
wavelength. It has been shown that GO might be successfully used as an
efficient SA without the need of its reduction to rGO. Taking into account
simpler manufacturing technology and the possibility of mass production, GO
seems to be a good candidate as a cost-effective material for saturable
absorbers for Er-doped fiber lasers.",1210.1469v1
2013-01-18,Homogeneously Saturated Model for Development in Time of the Price of an Asset,"The time development of the price of a financial asset is considered by
constructing and solving Langevin equations for a homogeneously saturated
model, and for comparison, for a standard model and for a logistic model. The
homogeneously saturated model uses coupled rate equations for the money supply
and for the price of the asset, similar to the coupled rate equations for
population inversion and power density in a simple model of a homogeneously
broadened laser.
  Predictions of the models are compared for random numbers drawn from a
Student's t-distribution. It is known that daily returns of the DJIA and S&P
500 indices are fat tailed and are described well by Student's t-distributions
over the range of observed values. The homogeneously saturated model shows
returns that are consistent with daily returns for the indices (in the range of
-30% to +30%) whereas the standard model and the logistic model show returns
that are far from consistent with observed daily returns for the indices.",1301.4519v1
2013-02-28,Torque Saturation in Bipedal Robotic Walking through Control Lyapunov Function Based Quadratic Programs,"This paper presents a novel method for directly incorporating user-defined
control input saturations into the calculation of a control Lyapunov function
(CLF)-based walking controller for a biped robot. Previous work by the authors
has demonstrated the effectiveness of CLF controllers for stabilizing periodic
gaits for biped walkers, and the current work expands on those results by
providing a more effective means for handling control saturations. The new
approach, based on a convex optimization routine running at a 1 kHz control
update rate, is useful not only for handling torque saturations but also for
incorporating a whole family of user-defined constraints into the online
computation of a CLF controller. The paper concludes with an experimental
implementation of the main results on the bipedal robot MABEL.",1302.7314v1
2013-04-07,Statistical Mechanics of a Discrete Schrödinger Equation with Saturable Nonlinearity,"We study the statistical mechanics of the one-dimensional discrete nonlinear
Schr\""odinger (DNLS) equation with saturable nonlinearity. Our study represents
an extension of earlier work [Phys. Rev. Lett. {\bf 84}, 3740 (2000)] regarding
the statistical mechanics of the one-dimensional DNLS equation with a cubic
nonlinearity. As in this earlier study we identify the spontaneous creation of
localized excitations with a discontinuity in the partition function. The fact
that this phenomenon is retained in the saturable DNLS is non-trivial, since in
contrast to the cubic DNLS whose nonlinear character is enhanced as the
excitation amplitude increases, the saturable DNLS in fact becomes increasingly
linear as the excitation amplitude increases. We explore the nonlinear dynamics
of this phenomenon by direct numerical simulations.",1304.2065v1
2013-05-23,Half-Saturation Constants in Functional Responses,"Our aim is to provide an overview of half-saturation constants reported in
literature and to explore their consistency with body size. In many ecological
models, intake of nutrients by plants and consumption of food by animals is
considered to be a hyperbolic function of the nutrient concentration and the
food density, respectively. However, data on the concentration (or density) at
which half of the maximum intake rate is reached are scarce, limiting the
applicability of the computational models. The meta-analysis was conducted on
literature published worldwide. Most studies focused on algae and
invertebrates, whereas some included fish, birds and mammals. The
half-saturation constants obtained were linked to body size using ordinary
regression analysis. The observed trends were compared to those noted in
reviews on other density parameters. Half-saturation constants for different
clades range within one or two orders of magnitude. Although these constants
are inherently variable, exploring allometric relationships across different
taxa helps to improve consistent parameterization of ecological models.",1305.5533v1
2013-06-01,A study of saturated tensor cone for symmetrizable Kac-Moody algebras,"Let $\fg$ be a symmetrizable Kac-Moody Lie algebra with the standard Cartan
subalgebra $\fh$ and the Weyl group $W$. Let $P_+$ be the set of dominant
integral weights. For $\lambda \in P_+$, let $L(\lambda)$ be the irreducible,
integrable, highest weight representation of $\fg$ with highest weight
$\lambda$. For a positive integer $s$, define the {\em saturated tensor
semigroup} as \begin{align*} \Gamma_s:= \{(\lambda_1, \dots, \lambda_s,\mu)\in
P_+^{s+1}: \exists\, N>1 \,\,\text{with}\,\, L(N\mu)\subset
L(N\lambda_1)\otimes \dots \otimes L(N\lambda_s)\}. \end{align*} The aim of
this paper is to begin a systematic study of $\Gamma_s$ in the infinite
dimensional symmetrizable Kac-Moody case. In this paper, we produce a set of
necessary inequalities satisfied by $\Gamma_s$. We further prove that any
integer $d>0$ is a saturation factor for $A^{(1)}_1$ and 4 is a saturation
factor for $A^{(2)}_2$.",1306.0073v1
2013-06-07,Estimating Saturated Hydraulic Conductivity from Surface Ground-Penetrating Radar Monitoring of Infiltration,"In this study we used Hydrus-1D to simulate water infiltration from a ring
infiltrometer. We generated water content profiles at each time step of
infiltration, based on a particular value of the saturated hydraulic
conductivity while knowing the other van Genuchten parameters. Water content
profiles were converted to dielectric permittivity profiles using the Complex
Refractive Index Method relation. We then used the GprMax suite of programs to
generate radargrams and to follow the wetting front using arrival time of
electromagnetic waves recorded by a Ground-Penetrating Radar (GPR).
Theoretically, the depth of the inflection point of the water content profile
simulated at any infiltration time step is related to the peak of the reflected
amplitude recorded in the corresponding trace in the radargram. We used this
relationship to invert the saturated hydraulic conductivity for constant and
falling head infiltrations. We present our method on synthetic examples and on
two experiments carried out on sand. We further discuss the possibility of
estimating two other van Genuchten parameters, n and \alpha, in addition to the
saturated hydraulic conductivity.",1306.1823v1
2013-07-15,Towards the Test of Saturation Physics Beyond Leading Logarithm,"We present results from the first next-to-leading order (NLO) numerical
analysis of forward hadron production in pA collisions in the small-x
saturation formalism. Using parton distributions and fragmentation functions at
NLO, as well as the dipole amplitude from the solution to the
Balitsky-Kovchegov equation with running coupling, together with the NLO
corrections to the hard coefficients, we obtain a good description of the
available RHIC data in dAu collisions. We also comment on the results in the
large p_T region beyond the saturation scale. Furthermore, we make predictions
for forward hadron production in pPb collisions at the LHC. This analysis not
only incorporates the important NLO corrections for all partonic channels, but
also reduces the renormalization scale dependence and therefore helps to
significantly reduce the theoretical uncertainties. It therefore provides a
precise test of saturation physics beyond the leading logarithmic
approximation.",1307.4057v1
2013-07-30,Intrinsic Localized Modes in a Nonlinear Electrical Lattice with Saturable Nonlinearity,"This experimental study of driven intrinsic localized modes (ILMs) in an
electronic circuit lattice with saturable nonlinearity follows the theoretical
work of Hadzievski and coworkers. They proposed that a saturable nonlinearity
could introduce transition points where localized excitations in nonintegrable
lattices would move freely. In our experiments MOS capacitors provide the
saturable nonlinearity in an electric lattice. Because of the soft nonlinearity
driver locked, auto-resonance stationary ILMs are observed below the bottom of
a linear frequency band of the lattice. With decreasing driver frequency the
width of the ILM changes in a step-wise manner as does the softening of the
barrier between site-centered and bond-centered ILM locations in agreement with
theoretical expectations. However, the steps show hysteresis between up and
down frequency scans and such hysteresis inhibits the free motion of ILMs.",1307.7801v1
2013-10-14,Waves statistics for generalized one-dimensional Nonlinear Schrodinger Equation with saturated nonlinearity,"We measure spectra, spatial correlation functions and probability density
functions (PDFs) for waves amplitudes for generalized one-dimensional nonlinear
Schrodinger (NLS) equation of focusing type with saturated nonlinearity. All
additional terms beyond the classical NLS equation are small. As initial
conditions we use perturbed by weak noise modulationally unstable condensate.
On the PDFs we observe power-law region for small and medium amplitudes
followed by intermediate region and then Rayleigh far tail. Power-law region
appears starting from some critical levels of average amplitude and coefficient
related to saturated nonlinearity, and then becomes more pronounced with
average amplitude and saturation coefficient. Correlation of phases becomes
significant for large wave events and contributes about one order of magnitude
to the frequencies of their occurrence. Waves statistics for the considered
systems turns out to be exceptionally stable against additional stochastic
forces.",1310.3618v2
2014-01-10,Moist-entropic vertical adiabatic lapse rates: the standard cases and some lead towards inhomogeneous conditions,"This note is a companion of Marquet and Geleyn (2013, {arXiv:1401.2379
[ao-ph]}), where adiabatic lapse rates $\Gamma_{ns}$ and $\Gamma_{sw}$ are
derived for non-saturated ($\Gamma_{ns}$) or saturated ($\Gamma_{sw}$) parcel
of moist-air. They are computed in terms of the vertical derivative of the
moist-air entropy potential temperature $\theta_s$ defined in Marquet (2011,
{arXiv:1401.1097 [ao-ph]}). The saturated value $\Gamma_{sw}$ is rewritten in
this note so that a more compact formulation is obtained. The new formulation
for $\Gamma_{sw}$ is expressed in term of a weighting factor $C$. This factor
may represent the proportion of an air parcel being in saturated conditions.",1401.2383v2
2014-02-23,On Saturated $k$-Sperner Systems,"Given a set $X$, a collection $\mathcal{F}\subseteq\mathcal{P}(X)$ is said to
be $k$-Sperner if it does not contain a chain of length $k+1$ under set
inclusion and it is saturated if it is maximal with respect to this property.
Gerbner et al. conjectured that, if $|X|$ is sufficiently large with respect to
$k$, then the minimum size of a saturated $k$-Sperner system
$\mathcal{F}\subseteq\mathcal{P}(X)$ is $2^{k-1}$. We disprove this conjecture
by showing that there exists $\varepsilon>0$ such that for every $k$ and $|X|
\geq n_0(k)$ there exists a saturated $k$-Sperner system
$\mathcal{F}\subseteq\mathcal{P}(X)$ with cardinality at most
$2^{(1-\varepsilon)k}$.
  A collection $\mathcal{F}\subseteq \mathcal{P}(X)$ is said to be an
oversaturated $k$-Sperner system if, for every
$S\in\mathcal{P}(X)\setminus\mathcal{F}$, $\mathcal{F}\cup\{S\}$ contains more
chains of length $k+1$ than $\mathcal{F}$. Gerbner et al. proved that, if
$|X|\geq k$, then the smallest such collection contains between $2^{k/2-1}$ and
$O\left(\frac{\log{k}}{k}2^k\right)$ elements. We show that if $|X|\geq k^2+k$,
then the lower bound is best possible, up to a polynomial factor.",1402.5646v2
2014-02-25,On coalgebras with internal moves,"In the first part of the paper we recall the coalgebraic approach to handling
the so-called invisible transitions that appear in different state-based
systems semantics. We claim that these transitions are always part of the unit
of a certain monad. Hence, coalgebras with internal moves are exactly
coalgebras over a monadic type. The rest of the paper is devoted to supporting
our claim by studying two important behavioural equivalences for state-based
systems with internal moves, namely: weak bisimulation and trace semantics.
  We continue our research on weak bisimulations for coalgebras over order
enriched monads. The key notions used in this paper and proposed by us in our
previous work are the notions of an order saturation monad and a saturator. A
saturator operator can be intuitively understood as a reflexive, transitive
closure operator. There are two approaches towards defining saturators for
coalgebras with internal moves. Here, we give necessary conditions for them to
yield the same notion of weak bisimulation.
  Finally, we propose a definition of trace semantics for coalgebras with
silent moves via a uniform fixed point operator. We compare strong and weak
bisimilation together with trace semantics for coalgebras with internal steps.",1402.6281v1
2014-03-10,Probing Gluon Saturation through Dihadron Correlations at an Electron-Ion Collider,"Two-particle azimuthal angle correlations have been proposed to be one of the
most direct and sensitive probes to access the underlying gluon dynamics
involved in hard scatterings. In anticipation of an Electron-Ion Collider
(EIC), detailed studies of dihadron correlation measurements in electron-proton
and electron-ion collisions at an EIC have been performed. The impact of such
measurements on the understanding of the different gluon distribution
functions, as a clean signature for gluon saturation and to constrain
saturation models further, has been explored. It is shown that dihadron
correlation measurements will be one of the key methods to probe gluon
saturation phenomena at a future EIC.",1403.2413v3
2014-03-27,Saturation of atomic transitions using sub-wavelength diameter tapered optical fibers in rubidium vapor,"We experimentally investigate ultralow-power saturation of the rubidium D2
transitions using a tapered optical fiber (TOF) suspended in a warm Rb vapor. A
direct comparison of power-dependent absorption measurements for the TOF system
with those obtained in a standard free-space vapor cell system highlights the
differences in saturation behavior for the two systems. The effects of
hyperfine pumping in the TOF system are found to be minimized due to the short
atomic transit times through the highly confined evanescent optical mode guided
by the TOF. The TOF system data is well-fit by a relatively simple empirical
absorption model that indicates nanoWatt-level saturation powers.",1403.7141v2
2014-05-14,Convective overstability in accretion disks: 3D linear analysis and nonlinear saturation,"Recently, Klahr & Hubbard (2014) claimed that a hydrodynamical linear
overstability exists in protoplanetary disks, powered by buoyancy in the
presence of thermal relaxation. We analyse this claim, confirming it through
rigorous compressible linear analysis. We model the system numerically,
reproducing the linear growth rate for all cases studied. We also study the
saturated properties of the overstability in the shearing box, finding that the
saturated state produces finite amplitude fluctuations strong enough to trigger
the subcritical baroclinic instability. Saturation leads to a fast burst of
enstrophy in the box, and a large-scale vortex develops in the course of the
next $\approx$100 orbits. The amount of angular momentum transport achieved is
of the order of $\alpha \approx 10^{-3}$, as in compressible SBI models. For
the first time, a self-sustained 3D vortex is produced from linear amplitude
perturbation of a quiescent base state.",1405.3437v2
2014-06-26,The saturation number for Cayley's cubic surface,"We investigate the density of rational points on Cayley's cubic surface whose
coordinates have few prime factors. The key tools used are the circle method
and universal torsors.",1406.6963v1
2014-07-24,Diffractive photoproduction of vector mesons at the LHC,"We confront saturation-based results for diffractive $\psi(2s)$ and $\rho$
production at HERA and $J/\psi$ photoproduction with all available data
including recent ones from HERA, ALICE and LHCb, finding a good agreement. We
show that the $t$-distribution of differential cross-section of photoproduction
of vector mesons offers a unique opportunity to discriminate among saturation
and non-saturation models. This is due to emergence of a pronounced dip (or
multiple dips) in the $t$-distribution of diffractive photoproduction of vector
mesons at relatively large, but potentially accessible $|t|$ that can be traced
back to the unitarity features of colour dipole amplitude in the saturation
regime. We provide various predictions for exclusive (photo)-production of
different vector mesons including the ratio of $\psi(2s)/J/\psi$ at HERA, the
LHC and at future colliders.",1407.6703v1
2014-08-17,A model for strong interactions at high energy based on the CGC/saturation approach,"We present our first attempt to develop a model for soft interactions at high
energy, based on the BFKL Pomeron and the CGC/saturation approach. We construct
an eikonal-type model, whose opacity is determined by the exchange of the
dressed BFKL Pomeron. The Green's function of the Pomeron is calculated in the
framework of the CGC/saturation approach. Using five parameters we achieve a
good description of the experimental data at high energies (
$W\,\geq\,0.546\,TeV$). The model results in different behaviour for the single
and double diffraction cross sections at high energies. The single diffraction
cross section reaches a saturated value (about 10 mb) at high energies, while
the double diffraction cross section continues growing slowly",1408.3811v3
2014-09-23,Preconditioning the prior to overcome saturation in Bayesian inverse problems,"We study Bayesian inference in statistical linear inverse problems with
Gaussian noise and priors in Hilbert space. We focus our interest on the
posterior contraction rate in the small noise limit. Existing results suffer
from a certain saturation phenomenon, when the data generating element is too
smooth compared to the smoothness inherent in the prior. We show how to
overcome this saturation in an empirical Bayesian framework by using a
non-centered data-dependent prior. The center is obtained from a
preconditioning regularization step, which provides us with additional
information to be used in the Bayesian framework. We use general techniques
known from regularization theory. To highlight the significance of the findings
we provide several examples. In particular, our approach allows to obtain and,
using preconditioning improve after saturation, minimax rates of contraction
established in previous studies. We also establish minimax contraction rates in
cases which have not been considered so far.",1409.6496v1
2014-09-29,Saturation Number of Trees in the Hypercube,"A graph $H^{\prime}$ is $(H, G)$-saturated if it is $G$-free and the addition
of any edge of $H$ not in $H^{\prime}$ creates a copy of $G$. The saturation
number $sat(H, G)$ is the minimum number of edges in a $(H, G)$-saturated
graph. We investigate bounds on the saturation number of trees $T$ in the
$n$-dimensional hypercube $Q_n$. We first present a general lower bound on the
saturation number based on the minimum degree of non-leaves. From there, we
suggest two general methods for constructing $T$-saturated subgraphs of $Q_n$,
and prove nontrivial upper bounds for specific types of trees, including paths,
generalized stars, and certain caterpillars under a restriction on minimum
degree with respect to diameter.",1409.7983v2
2014-12-14,Dielectric anisotropy in polar solvents under external fields,"We investigate dielectric saturation and increment in polar liquids under
external fields. We couple a previously introduced dipolar solvent model to a
uniform electric field and derive the electrostatic kernel of interacting
dipoles. This procedure allows an unambiguous definition of the liquid
dielectric permittivity embodying non-linear dielectric response and
correlation effects.We find that the presence of the external field results in
a dielectric anisotropy characterized by a two-component dielectric
permittivity tensor. The increase of the electric field amplifies the
permittivity component parallel to the field direction, i.e. dielectric
increment is observed along the field. However, the perpendicular component is
lowered below the physiological permittivity, indicating dielectric saturation
perpendicular to the field. By comparison with Molecular Dynamics simulations
from the literature, we show that the mean-field level dielectric response
theory underestimates dielectric saturation. The inclusion of dipolar
correlations at the weak-coupling level intensify the mean-field level
dielectric saturation and improves the agreement with simulation data at weak
electric fields. The correlation-corrected theory predicts as well the presence
of a metastable configuration corresponding to the antiparallel alignment of
dipoles with the field. This prediction can be verified by solvent-explicit
simulations where solvent molecules are expected to be trapped transiently in
this metastable state.",1412.4425v2
2015-01-07,CSMA/CA Bottleneck Remediation in Saturation Mode with New Backoff Strategy,"Many modern wireless networks integrate carrier sense mul-tiple
access/collision avoidance (CSMA/CA) with exponential backoff as medium access
control (MAC) technique. In order to decrease the MAC overhead and the
collision probability, we propose in this paper a new backoff strategy leading
to better saturation throughput and access de-lay performance comparing to the
classical protocol. We investigate the CSMA/CA with RTS/CTS technique, and we
show that our strategy reaches better saturation throughput and access delay
especially in dense networks. This proposed strategy distributes users over all
the backoff stages to solve the bottleneck problem present in the first backoff
stage. Finally, we analyze our strategy and we compare it to the classical one
modeled by Markov chain. Analytical and simulation results show the improvment
in term of saturation throughput. Cumulative density func-tion (CDF) of the
access delay illustrates the important gain obtained by the proposed strategy.",1501.01422v1
2015-03-13,Discrete Element Method simulations of the saturation of aeolian sand transport,"The saturation length of aeolian sand transport ($L_s$), characterizing the
distance needed by wind-blown sand to adapt to changes in the wind shear, is
essential for accurate modeling of the morphodynamics of Earth's sandy
landscapes and for explaining the formation and shape of sand dunes. In the
last decade, it has become a widely-accepted hypothesis that $L_s$ is
proportional to the characteristic distance needed by transported particles to
reach the wind speed (the ``drag length''). Here we challenge this hypothesis.
From extensive numerical Discrete Element Method simulations, we find that, for
medium and strong winds, $L_s\propto V_s^2/g$, where $V_s$ is the saturated
value of the average speed of sand particles traveling above the surface and
$g$ the gravitational constant. We show that this proportionality is consistent
with a recent analytical model, in which the drag length is just one of four
similarly important length scales relevant for sand transport saturation.",1503.03946v1
2015-03-25,Grain Scale Modeling of Arbitrary Fluid Saturation in Random Packings,"We propose a model for increasing liquid saturation in a granular packing
which can account for liquid redistribution at saturation levels beyond the
well-studied capillary bridge regime. The model is capable of resolving and
combining capillary bridges, menisci and fully saturated pores to form local
liquid clusters of any shape. They can exchange volume due to the local Laplace
pressure gradient via a liquid film on the surfaces of grains. Local
instabilities like Haines jumps trigger the discontinuous evolution of the
liquid front. The applicability of the model is demonstrated and compared to
benchmark experiments on the level of individual liquid structures as well as
on larger systems.",1503.07470v1
2015-03-26,Holographic Thermalization in Charged Dilaton Anti-de Sitter Spacetime,"We study holographic thermalization in spacetimes with a chemical potential
and a non-trivial dilaton field. Three non-local observables are used to probe
the whole process and investigate the effect of the ratio of the chemical
potential over temperature $\chi$ and the dilaton-Maxwell coupling constant
$\alpha$. It is found that the saturation time is not always a monotonically
increasing function of $\chi$, the situation depends on $\alpha$. When $0
\leq\alpha \leq 1$, larger $\chi$ yields longer saturation time, while for
$\alpha>1$, the situation becomes more complex. More interesting, we found that
although $\alpha$ indeed has influence on the whole thermalization process, it
nearly does not affect the saturation time, which indicates the universality of
the saturation time for the dual one-parameter field theories.",1503.07700v1
2015-03-27,"Wideband saturable absorption in few-layer molybdenum diselenide (MoSe2) for Q-switching Yb-, Er- and Tm-doped fiber lasers","We fabricate a free-standing molybdenum diselenide (MoSe2) saturable absorber
by embedding liquid-phase exfoliated few-layer MoSe2 flakes into a polymer
film. The MoSe2-polymer composite is used to Q-switch fiber lasers based on
ytterbium (Yb), erbium (Er) and thulium (Tm) gain fiber, producing trains of
microsecond-duration pulses with kilohertz repetition rates at 1060 nm, 1566 nm
and 1924 nm, respectively. Such operating wavelengths correspond to sub-bandgap
saturable absorption in MoSe2, which is explained in the context of
edge-states, building upon studies of other semiconducting transition metal
dichalcogenide (TMD)-based saturable absorbers. Our work adds few-layer MoSe2
to the growing catalog of TMDs with remarkable optical properties, which offer
new opportunities for photonic devices.",1503.08003v2
2015-03-30,Chains of saturated models in AECs,"We study when a union of saturated models is saturated in the framework of
tame abstract elementary classes (AECs) with amalgamation. We prove:
  $\mathbf{Theorem}$
  If $K$ is a tame AEC with amalgamation satisfying a natural definition of
superstability (which follows from categoricity in a high-enough cardinal),
then for all high-enough $\lambda$:
  * The union of an increasing chain of $\lambda$-saturated models is
$\lambda$-saturated.
  * There exists a type-full good $\lambda$-frame with underlying class the
saturated models of size $\lambda$.
  * There exists a unique limit model of size $\lambda$.
  Our proofs use independence calculus and a generalization of averages to this
non first-order context.",1503.08781v4
2015-04-28,Black phosphorus as a new broadband saturable absorber for infrared passively Q-switched fiber lasers,"Black phosphorus (BP) with its enticing electric and optical properties is
intensely researched in the field of optoelectronics. In this paper, Q-switched
pulses at 1550 nm and 2 um wavelengths are obtained by inserting
bulk-structured BP based saturable absorber (SA) into an erbium-doped fiber
laser (EDFL) and an thulium/holmium-doped fiber laser (THDFL), respectively.
The BP-SA was prepared by depositing powered BP material on to the flat side of
a side-polished single mode fiber. Q-switched 1550 nm pulses with width tuned
from 9.35 to 31 us were obtained for the EDFL. For the THDFL, over 100 nm
wavelength range could be achieved from 1832 to 1935 nm by adjusting the pump
power. To the best of our knowledge, these results demonstrated the broadband
saturable absorption property of BP and for the first time verified that BP as
a new two-dimensional material for applications in saturable absorption
devices.",1504.07341v1
2015-05-19,Implementing the exact kinematical constraint in the saturation formalism,"We revisit the issue of the large negative next-to-leading order (NLO) cross
section for single inclusive hadron production in $pA$ collisions in the
saturation formalism. By implementing the exact kinematical constraint in the
modified dipole splitting functions, two additional positive NLO correction
terms are obtained. In the asymptotic large $k_\perp$ limit, we analytically
show that these two terms become as large as the negative NLO contributions
found in our previous calculation. Furthermore, the numerical results
demonstrate that the applicable regime of the saturation formalism can be
extended to a larger $k_\perp$ window, where the exact matching between the
saturation formalism (in the asymptotic $k_\perp$ regime) and the collinear
factorization calculations will have to be performed separately. In addition,
after significantly improving the numerical accuracy of the NLO correction, we
obtain excellent agreement with the LHC and RHIC data for forward hadron
productions.",1505.05183v2
2015-07-12,"Yb- and Er-doped fiber laser Q-switched with an optically uniform, broadband WS2 saturable absorber","We demonstrate a ytterbium (Yb) and an erbium (Er)-doped fiber laser
Q-switched by a solution processed, optically uniform, few-layer tungsten
disulfide saturable absorber (WS2-SA). Nonlinear optical absorption of the
WS2-SA in the sub-bandgap region, attributed to the edge-induced states, is
characterized by 3.1% and 4.9% modulation depths with 1.38 and 3.83 MW/cm2
saturation intensities at 1030 and 1558 nm, respectively. By integrating the
optically uniform WS2-SA in the Yb- and Er-doped laser cavities, we obtain
self-starting Q-switched pulses with microsecond duration and kilohertz
repetition rates at 1030 and 1558 nm. Our work demonstrates broadband
sub-bandgap saturable absorption of a single, solution processed WS2-SA,
providing new potential efficacy for WS2 in ultrafast photonic applications.",1507.03188v1
2015-08-11,CGC/saturation approach: a new impact-parameter dependent model,"{In this paper we propose a new impact-parameter dependent CGC/saturation
model. We introduce two new features in the model that make it consistent with
what we know theoretically about the deep inelastic scattering. They are: the
use of the exact form of the solution to the non-linear (BK) equation, whereas
in all previous attempts only the form of $r^2Q^2_s$ dependence, has been taken
into account; and the large impact parameter dependence, through the
$b$-dependence of the saturation momentum which reproduce the correct behaviour
of the amplitude at large impact parameters $b$ ($A \propto \exp\Lb - \mu
b\Rb$) as well as at large momentum transferred $Q_T$ ($A $ decreases as a
power of $Q_T$ as it follows from perturbative QCD). These improvement compared
to all previous attempts to build such models, allows us to claim, that the
experimental data are in accord with the prediction of CGC/saturation approach
while previously, based on similar models, we could only conclude that the DIS
data, perhaps, can be described by introducing the shadowing corrections at
small photon virtualities.",1508.02544v2
2015-08-13,Intrinsic Fluctuations of the Proton Saturation Momentum Scale in High Multiplicity p+p Collisions,"High multiplicity events in p+p collisions are studied using the theory of
the Color Glass Condensate. We show that intrinsic fluctuations of the proton
saturation momentum scale are needed in addition to the sub-nucleonic color
charge fluctuations to explain the very high multiplicity tail of distributions
in p+p collisions. The origin of such intrinsic fluctuations are presumably
non-perturbative in nature. Classical Yang Mills simulations using the
IP-Glasma model are performed to make quantitative estimations. We find that
fluctuations as large as $\cal O$(1) of the average values of the saturation
momentum scale can lead to rare high multiplicity events seen in p+p data at
RHIC and LHC energies. Using the available data on multiplicity distributions
we try to constrain the distribution of the proton saturation momentum scale
and make predictions for the multiplicity distribution in 13 TeV p+p
collisions.",1508.03292v2
2015-09-14,Correcting for accidental correlations in saturated avalanche photodiodes,"In this paper we present a general method for estimating rates of accidental
coincidence between a pair of single photon detectors operated within their
saturation regimes. By folding the effects of recovery time of both detectors
and the detection circuit into an ""effective duty cycle"" we are able to
accomodate complex recovery behaviour at high event rates. As an example, we
provide a detailed high-level model for the behaviour of passively quenched
avalanche photodiodes, and demonstrate effective background subtraction at
rates commonly associated with detector saturation. We show that by
post-processing using the updated model, we observe an improvement in
polarization correlation visibility from 88.7% to 96.9% in our experimental
dataset. This technique will be useful in improving the signal-to-noise ratio
in applications which depend on coincidence measurements, especially in
situations where rapid changes in flux may cause detector saturation.",1509.03959v3
2015-10-02,Contact angle saturation in electrowetting: Injection of ions into the surrounding media,"We use the Poisson-Boltzmann theory to predict contact angle saturation of
aqueous droplets in electrowetting. Our theory predicts that injection of ions
from the droplet into its surrounding medium is responsible for the deviation
of the apparent contact angle from the Young-Lippmann equation for large
applied voltages. The ion injection substantially decreases the Maxwell stress
and increases the osmotic pressure at the interface between the two media,
leading to saturation of the apparent contact angle. Moreover, we find that the
contact angle does not saturate, but only has a broad minimum that increases
again upon further increase of the applied voltage, in agreement with
experiments.",1510.00613v1
2015-10-08,Formation of bubbly horizon in liquid-saturated porous medium by surface temperature oscillation,"We study non-isothermal diffusion transport of a weakly-soluble substance in
a liquid-saturated porous medium being in contact with the reservoir of this
substance. The surface temperature of the porous medium half-space oscillates
in time, which results in a decaying solubility wave propagating deep into the
porous medium. In such a system, the zones of saturated solution and
non-dissolved phase coexist with the zones of undersaturated solution. The
effect is firstly considered for the case of annual oscillation of the surface
temperature of water-saturated ground being in contact with atmosphere. We
reveal the phenomenon of formation of a near-surface bubbly horizon due to the
temperature oscillation. An analytical theory of the phenomenon is developed.
Further, the treatment is extended to the case of higher frequency oscillations
and case of weakly-soluble solids and liquids.",1510.02459v2
2015-10-26,Nuclear saturation in lowest-order Brueckner theory with two- and three-nucleon forces in view of chiral effective field theory,"The nuclear saturation mechanism is discussed in terms of two-nucleon and
three-nucleon interactions in chiral effective field theory (Ch-EFT), using the
framework of lowest-order Brueckner theory. After the Coester band, which is
observed in calculating saturation points with various nucleon-nucleon (NN)
forces, is revisited using modern NN potentials and their low-momentum
equivalent interactions, detailed account of the saturation curve of the Ch-EFT
interaction is presented. The three-nucleon force (3NF) is treated by reducing
it to an effective two-body interaction by folding the third nucleon degrees of
freedom. Uncertainties due to the choice of the 3NF low-energy constants $c_D$
and $c_E$ are discussed. The reduction of the cutoff-energy dependence of the
NN potential is explained by demonstrating the effect of the 3NF in the
$^1$S$_0$ and $^3$S$_1$ states.",1510.07469v1
2016-02-18,Revise Saturated Activation Functions,"In this paper, we revise two commonly used saturated functions, the logistic
sigmoid and the hyperbolic tangent (tanh).
  We point out that, besides the well-known non-zero centered property, slope
of the activation function near the origin is another possible reason making
training deep networks with the logistic function difficult to train. We
demonstrate that, with proper rescaling, the logistic sigmoid achieves
comparable results with tanh.
  Then following the same argument, we improve tahn by penalizing in the
negative part. We show that ""penalized tanh"" is comparable and even outperforms
the state-of-the-art non-saturated functions including ReLU and leaky ReLU on
deep convolution neural networks.
  Our results contradict to the conclusion of previous works that the
saturation property causes the slow convergence. It suggests further
investigation is necessary to better understand activation functions in deep
architectures.",1602.05980v2
2016-02-26,Investigating the Temperature Effects on Resistive Random Access Memory (RRAM) Devices,"In this paper, we report the effect of filament radius and filament
resistivity on the saturated temperature of ZnO, TiO2, WO3 and HfO2 Resistive
Random Access Memory (RRAM) devices. We resort to the thermal reaction model of
RRAM for the present analysis. The results substantiate decrease in saturated
temperature with increase in the radius and resistivity of filament for the
investigated RRAM devices. Moreover, a sudden change in the saturated
temperature at a lower value of filament radius and resistivity is observed as
against the steady change at the medium and higher value of the filament radius
and resistivity. Results confirm the dependence of saturated temperature on the
filament size and resistivity in RRAM.",1602.08262v1
2016-03-03,Medium-induced gluon radiation in hard forward parton scattering in the saturation formalism,"We derive the medium-induced, coherent gluon radiation spectrum associated
with the hard forward scattering of an energetic parton off a nucleus, in the
saturation formalism and within the Gaussian approximation for the relevant
correlators of Wilson lines. The calculation reproduces the simple expression
for the spectrum previously obtained in the opacity expansion formalism, and
rigorously specifies its validity range. The connection between the
calculations in the opacity expansion and saturation formalisms is made
apparent. This study may serve as a first step in order to implement
consistently induced coherent energy loss and gluon shadowing in
`saturation-based models' of hadron nuclear suppression in proton-nucleus
collisions.",1603.01028v1
2016-03-07,CGC/saturation approach for high energy soft interactions: $\mathbf{v_2}$ in proton-proton collisions,"In this paper we continue our program to construct a model for high energy
soft interactions, based on the CGC/saturation approach. We demonstrate that in
our model which describes diffractive physics as well as multi-particle
production at high energy, the density variation mechanism leads to the value
of $v_2$ which is about $60\% \div 70\%$ of the measured $v_2$. Bearing in mind
that in CGC/saturation approach there are two other mechanisms present: Bose
enhancement in the wave function and local anisotropy, we believe that the
azimuthal long range rapidity correlations in proton-proton collisions stem
from the CGC/saturation physics, and not from quark-gluon plasma production.",1603.02143v1
2016-04-23,Determination of Oxygen Saturation and Photoplethysmogram from Near Infrared Scattering Images,"The near infrared scattering images of human muscle include some information
on bloodstream and hemoglobin concentration according to skin depth and time.
This paper addressed a method of determining oxygen saturation and
photoplethysmogram from the near infrared (NIR) scattering images of muscle.
Depending on the modified Beer-Lambert Law and the diffuse scattering model of
muscular tissue, we determined an extinction coefficient matrix of hemoglobin
from the near infrared scattering images and analyzed distribution of oxygen
saturation of muscle with a depth from the extinction coefficient matrix. And
we determined a dynamic attenuation variation curve with respect to fragmentary
image frames sensitive to bloodstream from scattering image frames of muscle
with time and then obtained the photoplethysmogram and heart rate by Fourier
transformation and inverse transformation. This method based on the NIR
scattering images can be applied in measurement of an average oxygen saturation
and photoplethysmogram even in local region of optically heterogeneous muscle
and skin.",1604.06855v1
2016-04-24,Saturation of Nuclear Matter and Roles of Many-Body Forces: nuclear matter in neutron stars probed by nucleus-nucleus scattering,"Yoichiro Nambu put a great foot print in nuclear physics in the era of its
fundamental developments including his pioneering insight into essential
ingredients of repulsive core of nuclear force and its relation to the
saturation of nuclear matter. The present review article focuses onto recent
developments of the interaction models between colliding nuclei in terms of
Brueckner's G-matrix theory staring from realistic nuclear forces and the
saturation property of symmetric nuclear matter as well as neutron-star matter.
A recently proposed unique scenario of extracting the saturation property of
nuclear matter and stiffness of neutron stars through the analysis of
nucleus-nucleus elastic scattering in laboratories is presented in some detail.",1604.07632v1
2015-12-11,Scrape-off layer turbulence in TCV: evidence in support of stochastic modelling,"Intermittent fluctuations in the TCV scrape-off layer have been investigated
by analysing long Langmuir probe data time series under stationary conditions,
allowing calculation of fluctuation statistics with high accuracy. The ion
saturation current signal is dominated by the frequent occurrence of
large-amplitude bursts attributed to filament structures moving through the
scrape-off layer. The average burst shape is well described by a
double-exponential wave-form with constant duration, while the waiting times
and peak amplitudes of the bursts both have an exponential distribution.
Associated with bursts in the ion saturation current is a dipole shaped
floating potential structure and radially outwards directed electric drift
velocity and particle flux, with average peak values increasing with the
saturation current burst amplitude. The floating potential fluctuations have a
normal probability density function while the distributions for the ion
saturation current and estimated radial velocity have exponential tails for
large fluctuations. These findings are discussed in the light of prevailing
theories for filament motion and a stochastic model for intermittent scrape-off
layer plasma fluctuations.",1604.08163v1
2016-07-12,Saturation scale fluctuations and multi-particle rapidity correlations,"We study the effect of intrinsic fluctuations of the proton saturation
momentum scale on event-by-event rapidity distributions. Saturation scale
fluctuations generate an asymmetry in the single particle rapidity distribution
in each event resulting in genuine n-particle correlations having a component
linear in the rapidities of the produced particles, $y_1\cdots y_n$. We
introduce a color domain model that naturally explains the centrality
dependence of the two-particle rapidity correlations recently measured by ATLAS
while constraining the probability distribution of saturation scale
fluctuations in the proton. Predictions for n = 4, 6 and 8 particle
correlations find that the four and eight-particle cumulant change sign at an
intermediate multiplicity, a signature which could be tested experimentally.",1607.03219v1
2016-07-15,High Gluon Densities in Heavy Ions Collisions,"The early stages of heavy ion collisions are dominated by high density
systems of gluons that carry each a small fraction $x$ of the momenta of the
colliding nucleons. A distinguishing feature of such systems is the phenomenon
of ""saturation"" which tames the expected growth of the gluon density as the
energy of the collision increases. The onset of saturation occurs at a
particular transverse momentum scale, the ""saturation momentum"", that emerges
dynamically and that marks the onset of non-linear gluon interactions. At high
energy, and for large nuclei, the saturation momentum is large compared to the
typical hadronic scale, making high density gluons amenable to a description
with weak coupling techniques. This paper reviews some of the challenges faced
in the study of such dense systems of small $x$ gluons, and of the progress
made in addressing them. The focus is on conceptual issues, and the
presentation is both pedagogical, and critical. Examples where high gluon
density could play a visible role in heavy ion collisions are briefly discussed
at the end, for illustration purpose.",1607.04448v1
2016-07-19,Non-quasiparticle transport and resistivity saturation: A view from the large-N limit,"The electron dynamics in metals are usually well described by the
semiclassical approximation for long-lived quasiparticles. However, in some
metals, the scattering rate of the electrons at elevated temperatures becomes
comparable to the Fermi energy; then, this approximation breaks down, and the
full quantum-mechanical nature of the electrons must be considered. In this
work, we study a solvable, large-$N$ electron-phonon model, which at high
temperatures enters the non-quasiparticle regime. In this regime, the model
exhibits ""resistivity saturation"" to a temperature-independent value of the
order of the quantum of resistivity - the first analytically tractable model to
do so. The saturation is not due to a fundamental limit on the electron
lifetime, but rather to the appearance of a second conductivity channel. This
is suggestive of the phenomenological ""parallel resistor formula"", known to
describe the resistivity of a variety of saturating metals.",1607.05725v1
2016-09-06,Global stabilization of a Korteweg-de Vries equation with a distributed control saturated in L 2 -norm,"This article deals with the design of saturated controls in the context of
partial differential equations. It is focused on a Korteweg-de Vries equation,
which is a nonlinear mathematical model of waves on shallow water surfaces. The
aim of this article is to study the influence of a saturating in L 2-norm
distributed control on the well-posedness and the stability of this equation.
The well-posedness is proven applying a Banach fixed point theorem. The proof
of the asymptotic stability of the closed-loop system is tackled with a
Lyapunov function together with a sector condition describing the saturating
input. Some numerical simulations illustrate the stability of the closed-loop
nonlinear partial differential equation.",1609.01447v1
2016-12-02,A Novel Framework based on SVDD to Classify Water Saturation from Seismic Attributes,"Water saturation is an important property in reservoir engineering domain.
Thus, satisfactory classification of water saturation from seismic attributes
is beneficial for reservoir characterization. However, diverse and non-linear
nature of subsurface attributes makes the classification task difficult. In
this context, this paper proposes a generalized Support Vector Data Description
(SVDD) based novel classification framework to classify water saturation into
two classes (Class high and Class low) from three seismic attributes seismic
impedance, amplitude envelop, and seismic sweetness. G-metric means and program
execution time are used to quantify the performance of the proposed framework
along with established supervised classifiers. The documented results imply
that the proposed framework is superior to existing classifiers. The present
study is envisioned to contribute in further reservoir modeling.",1612.00841v1
2017-01-25,Solution to the evolution equation at NLL for high parton density QCD,"We analytically solve the full next-to-leading logarithmic Balitsky-Kovchegov
equation in the saturation regime, which includes corrections from quark and
gluon loops, and large double transverse logarithms. The analytic result for
the $S$-matrix in the saturation regime shows that the linear rapidity decrease
with rapidity of the exponent in running coupling case is replaced by rapidity
raised to power of 3/2 decreasing. The collinearly-improved Balitsky-Kovchegov
equation are also analytically solved in the saturation regime. It shows that
the double collinear logarithms do not contribute to the $S$-matrix and the
solution is the same as the one obtained from the leading order
Balitsky-Kovchegov equation. The numerical solutions to the leading order and
full next-to-leading logarithmic Balitsky-Kovchegov equations are performed in
order to test the analytic results derived in the saturation regime.",1701.07378v1
2017-02-02,Unveiling saturation effects from nuclear structure function measurements at the EIC,"We analyze the possibility of extracting a clear signal of non-linear parton
saturation effects from future measurements of nuclear structure functions at
the Electron-Ion Collider (EIC), in the small-x region. Our approach consists
in generating pseudodata for electron-gold collisions, using the
running-coupling Balitsky-Kovchegov evolution equation, and in assessing the
compatibility of these saturate pseudodata with existing sets of nuclear parton
distribution functions (nPDFs), extrapolated if necessary. The level of
disagreement between the two is quantified by applying a Bayesian reweighting
technique. This allows to infer the parton distributions needed in order to
describe the pseudodata, which we find quite different from the actual
distributions, especially for sea quarks and gluons. This tension suggests
that, should saturation effects impact the future nuclear structure function
data as predicted, a successful refitting of the nPDFs may not be achievable,
which would unambiguously signal the presence of non-linear effects.",1702.00839v4
2017-02-21,Mixed-gap vector solitons in PT-symmetric lattices with saturable nonlinearity,"We have investigated mixed-gap vector solitons involving incoherently coupled
fundamental and dipole components in a parity-time (PT) symmetric lattice with
saturable nonlinearity. For the focusing case, vector solitons emerge from the
semi-infinite and the first finite gaps, while for the defocusing case, vector
solitons emerge from the first finite and the second finite gaps. For both
cases, we find that stronger saturable nonlinearity is relative to sharper
increase/decrease of soliton power with propagation constant and to narrower
existence domain of vector solitons. This finding is helpful for realizing
high-power solitons with limited range of propagation constant. Additionally,
our numerical calculations show that increasing the weight of dipole component
results in destabilization of vector solitons, while stronger saturable
nonlinearity to certain extent suppresses the instability of vector solitons.",1702.06232v1
2017-02-25,Upper bounds on the smallest size of a saturating set in projective planes and spaces of even dimension,"In a projective plane $\Pi_{q}$ (not necessarily Desarguesian) of order $q$,
a point subset $\mathcal{S}$ is saturating (or dense) if any point of
$\Pi_{q}\setminus \mathcal{S}$ is collinear with two points in $\mathcal{S}$.
Modifying an approach of [31], we proved the following upper bound on the
smallest size $s(2,q)$ of a saturating set in $\Pi_{q}$: \begin{equation*}
s(2,q)\leq \sqrt{(q+1)\left(3\ln q+\ln\ln q
+\ln\frac{3}{4}\right)}+\sqrt{\frac{q}{3\ln q}}+3. \end{equation*} The bound
holds for all q, not necessarily large.
  By using inductive constructions, upper bounds on the smallest size of a
saturating set in the projective space $\mathrm{PG}(N,q)$ with even dimension
$N$ are obtained.
  All the results are also stated in terms of linear covering codes.",1702.07939v1
2017-03-01,Multistability and Switching in Oppositely Directed Saturable Coupler,"We report a novel optical multistability in two core oppositely directed
saturable coupler (ODSC) with negative index material (NIM) channel. The
dynamics are studied using the Langrangian variational method and Jacobi
elliptic functions are used to construct the analytical solutions. The ODSC
exhibits a bandgap as a consequence of the effective feedback mechanism due to
the opposite directionality of the phase velocity and Poynting vector in the
NIM channel. We observe that the system admits multiple stable states for some
control parameter, which is a result of the combination of nonlinear saturation
and the unique backward-coupling mechanism in the NIM channel. The number of
multiple stable states increase with the strength of the nonlinear saturation.
Taking the advantage of multiple stable states, one can construct ultrafast
switching devices with a flexible switching operation. The studies on the
transmission characteristics of the ODSC implies the existence of multiple
transmission resonance windows, which could help in the realization of gap
soliton in homogeneous systems like coupler. With more degrees of design
freedom and controllability, the ODSC could be the choice for a future
generation of all-optical switching.",1703.00486v1
2017-03-30,The unsaturated flow in porous media with dynamic capillary pressure,"In this paper we consider a degenerate pseudoparabolic equation for the
wetting saturation of an unsaturated two-phase flow in porous media with
dynamic capillary pressure-saturation relationship where the relaxation
parameter depends on the saturation. Following the approach given in [12] the
existence of a weak solution is proved using Galerkin approximation and
regularization techniques. A priori estimates needed for passing to the limit
when the regularization parameter goes to zero are obtained by using
appropriate test-functions, motivated by the fact that considered PDE allows a
natural generalization of the classical Kullback entropy. Finally, a special
care was given in obtaining an estimate of the mixed derivative term by
combining the information from the capillary pressure with obtained a priori
estimates on the saturation.",1703.10662v2
2017-04-18,Distributed Event-Triggered Control for Global Consensus of Multi-Agent Systems with Input Saturation,"We consider the global consensus problem for multi-agent systems with input
saturation over digraphs. Under a mild connectivity condition that the
underlying digraph has a directed spanning tree, we use Lyapunov methods to
show that the widely used distributed consensus protocol, which solves the
consensus problem for the case without input saturation constraints, also
solves the global consensus problem for the case with input saturation
constraints. In order to reduce the overall need of communication and system
updates, we then propose a distributed event-triggered control law. Global
consensus is still realized and Zeno behavior is excluded. Numerical
simulations are provided to illustrate the effectiveness of the theoretical
results.",1704.05429v1
2017-05-15,Doppler-free resolution near-infrared spectroscopy at 1.28~$μ$m with the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy method,"We report on the Doppler-free saturation spectroscopy of the nitrous oxide
(N$_2$O) overtone transition at 1.28~$\mu$m. This measurement is performed by
the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy
(NICE-OHMS) technique based on the quantum-dot (QD) laser. A high intra-cavity
power, up to 10~W, reaches the saturation limit of the overtone line using an
optical cavity with a high finesse of 113,500. At a pressure of several mTorr,
the saturation dip is observed with a full width at half-maximum of about 2~MHz
and a signal-to-noise ratio of 71. To the best of our knowledge, this is the
first saturation spectroscopy of molecular overtone transitions in 1.3~$\mu$m
region. The QD laser is then locked to this dispersion signal with a stability
of 15 kHz at 1 sec integration time. We demonstrate the potential of the N$_2$O
as markers because of its particularly rich spectrum at the vicinity of
1.28-1.30 $\mu$m where lies several important forbidden transitions of atomic
parity violation measurements and the 1.3 $\mu$m O-band of optical
communication.",1705.05208v1
2017-07-22,Dynamical phase diagram of parity-time symmetry with competing saturable channels,"Nonlinear channels play a critical role in realizing dynamical functions.
Neural ionic channels and non-volatile memristors each derive representative
biological and electrical functionalities, such as repetitive firing or pinched
hysteresis. In electromagnetics, saturable channels of amplification or
absorption provide a large nonlinearity for nonequilibrium wave dynamics, from
conventional lasing to mode locking to recent achievements of the
non-reciprocity in complex potentials. Here, we investigate the dynamical phase
diagram of parity-time symmetric systems, governed by competing nonlinear
channels of saturable amplification and absorption. Determined by the relative
strength and saturation level of the channels, three distinctive phases of
fast- and slow-response equilibriums, and an oscillating nonequilibrium are
demonstrated. On phase boundaries, we also reveal the chaotic existence of the
strong oscillation state, which allows the non-reciprocal realization of
repetitive resonator firing with fully tunable time delays. This work will
promote the wave-based realization of nonlinear and chaotic temporal functions,
toward light-based neural systems.",1707.07096v1
2017-08-11,"Nonreciprocal Atomic Scattering: A saturable, quantum Yagi-Uda antenna","Recent theoretical studies of a pair of atoms in a 1D waveguide find that the
system responds asymmetrically to incident fields from opposing directions at
low powers. Since there is no explicit time-reversal symmetry breaking elements
in the device, this has caused some debate. Here we show that the asymmetry
arises from the formation of a quasi-dark-state of the two atoms, which
saturates at extremely low power. In this case the nonlinear saturability
explicitly breaks the assumptions of the Lorentz reciprocity theorem. Moreover,
we show that the statistics of the output field from the driven system can be
explained by a very simple stochastic mirror model and that at steady state,
the two atoms and the local field are driven to an entangled, tripartite
$\left| W \right\rangle$ state. Because of this, we argue that the device is
better understood as a saturable Yagi-Uda antenna, a distributed system of
differentially-tuned dipoles that couples asymmetrically to external fields.",1708.03450v2
2017-08-19,An efficient distribution method for nonlinear two-phase flow in highly heterogeneous multidimensional stochastic porous media,"In the context of stochastic two-phase flow in porous media, we introduce a
novel and efficient method to estimate the probability distribution of the
wetting saturation field under uncertain rock properties in highly
heterogeneous porous systems, where streamline patterns are dominated by
permeability heterogeneity, and for slow displacement processes (viscosity
ratio close to unity). Our method, referred to as the frozen streamline
distribution method (FROST), is based on a physical understanding of the
stochastic problem. Indeed, we identify key random fields that guide the
wetting saturation variability, namely fluid particle times of flight and
injection times. By comparing saturation statistics against full-physics Monte
Carlo simulations, we illustrate how this simple, yet accurate FROST method
performs under the preliminary approximation of frozen streamlines. Further, we
inspect the performance of an accelerated FROST variant that relies on a
simplification about injection time statistics. Finally, we introduce how
quantiles of saturation can be efficiently computed within the FROST framework,
hence leading to robust uncertainty assessment.",1708.05888v1
2017-10-13,Compressive three-dimensional super-resolution microscopy with speckle-saturated fluorescence excitation,"Nonlinear structured illumination microscopy (nSIM) is an effective approach
for super-resolution wide-field fluorescence microscopy with a theoretically
unlimited resolution. In nSIM, carefully designed, highly-contrasted
illumination patterns are combined with the saturation of an optical transition
to enable sub-diffraction imaging. While the technique proved useful for
two-dimensional imaging, extending it to three-dimensions (3D) is challenging
due to the fading/fatigue of organic fluorophores under intense cycling
conditions. Here, we present a compressed sensing approach that allows for the
first time 3D sub-diffraction nSIM of cultured cells by saturating fluorescence
excitation. Exploiting the natural orthogonality of transverse speckle
illumination planes, 3D probing of the sample is achieved by a single
two-dimensional scan. Fluorescence contrast under saturated excitation is
ensured by the inherent high density of intensity minima associated with
optical vortices in polarized speckle patterns. Compressed speckle microscopy
is thus a simple approach that enables 3D super-resolved nSIM imaging with
potentially considerably reduced acquisition time and photobleaching.les fast
3D super-resolved imaging with considerably minimized photo-bleaching.",1710.05056v2
2017-10-31,High Saturation Power Josephson Parametric Amplifier with GHz Bandwidth,"We present design and simulation of a Josephson parametric amplifier with
bandwidth exceeding 1.6 GHz, and with high saturation power approaching -90 dBm
at a gain of 22.8 dB. An improvement by a factor of roughly 50 in bandwidth
over the state of the art is achieved by using well-established impedance
matching techniques. An improvement by a factor of roughly 100 in saturation
power over the state of the art is achieved by implementing the Josephson
nonlinear element as an array of rf-SQUIDs with a total of 40 junctions.
WRSpice simulations of the circuit are in excellent agreement with the
calculated gain and saturation characteristics.",1711.07549v1
2017-12-29,Chaotic Dynamics and Optical Power Saturation in Parity-Time (PT) Symmetric Double Ring Resonator,"We report emergence of saturation and chaotic spiking of optical power in a
double ring resonator with balanced loss and gain, obeying the so-called
parity-time symmetry. We have modeled the system using a discrete-time
iterative equation known as the Ikeda Map. In the linear regime, evolution of
optical power in the system shows power saturation behavior below the PT
threshold and exponential blow-up above the PT threshold. We found that in the
unbroken PT regime, optical power saturation occurs owing to the existence of
stable stationary states, which lies on the surface of 4-dimensional
hypersphere. Inclusion of Kerr nonlinearity into our model leads to the
emergence of a stable, chaotic and divergent region in the parameter basin for
period-1 cycle. A closer inspection into the system shows us that the largest
Lyapunov exponent blows up in the divergent region. It is found that the
existence of high non-negative largest Lyapunov exponent causes chaotic spiking
of optical power in the resonators.",1712.10196v2
2018-01-01,Note on lower estimates of multiplicities,"In this note we would like to give an explicit lower bound by using a lower
saturated subset of \mathbb{R}_{\geq 0}^n.",1801.00525v1
2018-03-19,Model theory and ultraproducts,"The article motivates recent work on saturation of ultrapowers from a general
mathematical point of view.",1803.07118v1
2018-04-10,Optical solitons in media with focusing and defocusing saturable nonlinearity and a parity-time-symmetric external potential,"We report results for solitons in models of waveguides with focusing or
defocusing saturable nonlinearity and a parity-time(PT )-symmetric
complex-valued external potential of the Scarf-II type. The model applies to
the nonlinear wave propagation in graded-index optical waveguides with balanced
gain and loss. We find both fundamental and multipole solitons for both
focusing and defocusing signs of the saturable nonlinearity in such PT
-symmetric waveguides. The dependence of the propagation constant on the
soliton's power is presented for different strengths of the nonlinearity
saturation, S. The stability of fundamental, dipole, tripole, and quadrupole
solitons is investigated by means of the linear-stability analysis and direct
numerical simulations of the corresponding (1+1)-dimensional nonlinear
Schrodinger-type equation. The results show that the instability of the
stationary solutions can be mitigated or completely suppressed, increasing the
value of S.",1804.03314v1
2018-04-24,On the saturation conjecture for $\operatorname{Spin}(2n)$,"In this paper we examine the saturation conjecture on decompositions of
tensor products of irreducible representations for complex semisimple algebraic
groups of type $D$ (the even \emph{spin} groups: Spin$(2n)$ for $n\ge 4$ an
integer), extending work done by Kumar-Kapovich-Millson on Spin(8). Our main
theorem asserts that the saturation conjecture holds for Spin(10) and Spin(12):
for all triples of dominants weights $\lambda,\mu,\nu$ such that
$\lambda+\mu+\nu$ is in the root lattice, and for any $N>0$, $$
\left(V(\lambda)\otimes V(\mu)\otimes V(\nu)\right)^G \ne 0 $$ if and only if
$$ \left(V(N\lambda)\otimes V(N\mu)\otimes V(N\nu)\right)^G\ne 0, $$ for $G=$
Spin(10) or Spin(12). Some related results for groups of other types are listed
as well.",1804.09229v3
2018-06-09,Saturable impurity in an optical array: Green function approach,"We examine a one-dimensional linear waveguide array containing a single
saturable waveguide. By using the formalism of lattice Green functions, we
compute in closed form the localized mode and the transmission across the
impurity in closed form. For the single saturable impurity in the bulk, we find
that an impurity state is always possible, independent of the impurity
strength. For the surface saturable impurity case, a minimum nonlinearity
strength is necessary to create a bound state. The transmission coefficient
across the impurity shows a sub-linear behavior with an absence of any
resonance. The dynamical selftrapping at the bulk impurity site shows no
selftrapping transition, and it resembles the behavior of a weak linear
impurity. For the surface impurity however, there is a selftrapping transition
at a critical nonlinearity value. The asymptotic propagation of the optical
power shows a ballistic character in both cases, with a speed that decreases
with an increase in nonlinearity strength.",1806.03491v1
2018-06-26,Understanding Dropout as an Optimization Trick,"As one of standard approaches to train deep neural networks, dropout has been
applied to regularize large models to avoid overfitting, and the improvement in
performance by dropout has been explained as avoiding co-adaptation between
nodes. However, when correlations between nodes are compared after training the
networks with or without dropout, one question arises if co-adaptation
avoidance explains the dropout effect completely. In this paper, we propose an
additional explanation of why dropout works and propose a new technique to
design better activation functions. First, we show that dropout can be
explained as an optimization technique to push the input towards the saturation
area of nonlinear activation function by accelerating gradient information
flowing even in the saturation area in backpropagation. Based on this
explanation, we propose a new technique for activation functions, {\em gradient
acceleration in activation function (GAAF)}, that accelerates gradients to flow
even in the saturation area. Then, input to the activation function can climb
onto the saturation area which makes the network more robust because the model
converges on a flat region. Experiment results support our explanation of
dropout and confirm that the proposed GAAF technique improves image
classification performance with expected properties.",1806.09783v3
2018-06-26,Anomalous optical saturation of low-energy Dirac states in graphene and its implication for nonlinear optics,"We reveal that optical saturation of the low-energy states takes place in
graphene for arbitrarily weak electromagnetic fields. This effect originates
from the diverging field-induced interband coupling at the Dirac point. Using
semiconductor Bloch equations to model the electronic dynamics of graphene, we
argue that the charge carriers undergo ultrafast Rabi oscillations leading to
the anomalous saturation effect. The theory is complemented by a many-body
study of the carrier relaxations dynamics in graphene. It will be demonstrated
that the carrier relaxation dynamics is slow around the Dirac point, which in
turn leads to a more pronounced saturation. The implications of this effect to
the nonlinear optics of graphene is then discussed. Our analysis show that the
conventional perturbative treatment of the nonlinear optics, i.e., expanding
the polarization field in a Taylor series of the electric field, is problematic
for graphene, in particular at small Fermi levels and large field amplitudes.",1806.10123v2
2018-11-18,STOAViz: Visualizing Saturated Thickness of Ogallala Aquifer,"In this paper, we introduce STOAViz, a visual analytics tool for analyzing
the saturated thickness of the Ogallala aquifer. The saturated thicknesses are
monitored by sensors integrated on wells distributed on a vast geographic area.
Our analytics application also captures the trends and patterns (such as
average/standard deviation over time, sudden increase/decrease of saturated
thicknesses) of water on an individual well and a group of wells based on their
geographic locations. To highlight the usefulness and effectiveness of STOAViz,
we demonstrate it on the Southern High Plains Aquifer of Texas. The work was
developed using feedback from experts at the water resource center at a
university. Moreover, our technique can be applied on any geographic areas
where wells and their measurements are available.",1811.07385v1
2018-11-22,Exclusive $ρ$ and $J/Ψ$ photoproduction in ultraperipheral $pA$ collisions: Predictions of the gluon saturation models for the momentum transfer distributions,"In this letter we complement previous studies on exclusive vector meson
photoproduction in hadronic collisions presenting a comprehensive analysis of
the $t$ - spectrum measured in exclusive $\rho$ and $J/\Psi$ photoproduction in
$pA$ collisions at the LHC. We compute the differential cross sections
considering two phenomenological models for the gluon saturation effects and
present predictions for $pPb$ and $pCa$ collisions. Moreover, we compare our
predictions with the recent preliminary CMS data for the exclusive $\rho$
photoproduction. We demonstrate that the gluon saturation models are able to
describe the CMS data at small - $t$. On the other hand, the models
underestimate the few data point at large -- $t$. Our results indicate that
future measurements of the large -- $t$ region can be useful to probe the
presence or absence of a dip in the $t$ -- spectrum and discriminate between
the different approaches to the gluon saturation effects.",1811.09124v1
2018-11-28,Entanglement Evolution in Lifshitz-type Scalar Theories,"We study propagation of entanglement after a mass quench in free scalar
Lifshitz theories. We show that entanglement entropy goes across three distinct
growth regimes before relaxing to a generalized Gibbs ensemble, namely 'initial
rapid growth', 'main linear growth' and 'tortoise saturation'. We show that
although a wide spectrum of quasi-particles are responsible for entanglement
propagation, as long as the occupation number of the zero mode is not
divergent, the linear main growth regime is dominated by the fastest
quasi-particle propagating on the edges of a widen light-cone. We present
strong evidences in support of effective causality and therefore define an
effective notion of saturation time in these theories. The larger the dynamical
exponent is, the shorter the linear main growth regime becomes. Due to a pile
of tortoise modes which become dominant after saturation of fast modes, exact
saturation time is postponed to infinity.",1811.11470v2
2019-01-17,Adaptive backstepping control for FOS with nonsmooth nonlinearities,"This paper proposes an original solution to input saturation and dead zone of
fractional order system. To overcome these nonsmooth nonlinearities, the
control input is decomposed into two independent parts by introducing an
intermediate variable, and thus the problem of dead zone and saturation
transforms into the problem of disturbance and saturation afterwards. With the
procedure of fractional order adaptive backstepping controller design, the
bound of disturbance is estimated, and saturation is compensated by the virtual
signal of an auxiliary system as well. In spite of the existence of nonsmooth
nonlinearities, the output is guaranteed to track the reference signal
asymptotically on the basis of our proposed method. Some simulation studies are
carried out in order to demonstrate the effectiveness of method at last.",1901.05588v1
2019-01-22,Towards Non-saturating Recurrent Units for Modelling Long-term Dependencies,"Modelling long-term dependencies is a challenge for recurrent neural
networks. This is primarily due to the fact that gradients vanish during
training, as the sequence length increases. Gradients can be attenuated by
transition operators and are attenuated or dropped by activation functions.
Canonical architectures like LSTM alleviate this issue by skipping information
through a memory mechanism. We propose a new recurrent architecture
(Non-saturating Recurrent Unit; NRU) that relies on a memory mechanism but
forgoes both saturating activation functions and saturating gates, in order to
further alleviate vanishing gradients. In a series of synthetic and real world
tasks, we demonstrate that the proposed model is the only model that performs
among the top 2 models across all tasks with and without long-term
dependencies, when compared against a range of other architectures.",1902.06704v1
2019-03-31,Robust Extended Kalman Filtering for Systems with Measurement Outliers,"Outliers can contaminate the measurement process of many nonlinear systems,
which can be caused by sensor errors, model uncertainties, change in ambient
environment, data loss or malicious cyber attacks. When the extended Kalman
filter (EKF) is applied to such systems for state estimation, the outliers can
seriously reduce the estimation accuracy. This paper proposes an innovation
saturation mechanism to modify the EKF toward building robustness against
outliers. This mechanism applies a saturation function to the innovation
process that the EKF leverages to correct the state estimation. As such, when
an outlier occurs, the distorting innovation is saturated and thus prevented
from damaging the state estimation. The mechanism features an adaptive
adjustment of the saturation bound. The design leads to the development robust
EKF approaches for continuous- and discrete-time systems. They are proven to be
capable of generating bounded-error estimation in the presence of bounded
outlier disturbances. An application study about mobile robot localization is
presented, with the numerical simulation showing the efficacy of the proposed
design. Compared to existing methods, the proposed approaches can effectively
reject outliers of various magnitudes, types and durations, at significant
computational efficiency and without requiring measurement redundancy.",1904.00335v1
2019-04-06,On the saturation of acoustic mode frequencies at high solar activity,"Acoustic mode frequencies obtained by applying spherical harmonic
decomposition to HMI, MDI and GONG observations were analysed throughout the
solar cycle. Evidence of a deviation from a linear relation with solar radio
flux was found indicating a saturation effect at high solar activity. The
Gompertz model, which is one of the most frequently used sigmoid functions to
fit growth data, is used. It is shown that its fitting to MDI and GONG data are
statistically significant and a median saturation of four-hundred sfu is
estimated. This saturation level is 50% larger than any obtained in the last
century, hence the small effect observed in the minimum-to-maximum frequency
shift. However, as shown here, it should not be disregarded.",1904.03452v1
2019-05-09,Diffractive dijet production in impact parameter dependent saturation models,"We study coherent diffractive dijet production in electron-hadron and
electron-nucleus collisions within the dipole picture. We provide semi-analytic
results for the differential cross section and elliptic anisotropy in the angle
between dijet transverse momentum and hadron recoil momentum. We demonstrate
the direct relation between angular moments of the dipole amplitude in
coordinate space and angular moments of the diffractive dijet cross sections.
To perform explicit calculations we employ two different saturation models,
extended to include the target geometry. In the limit of large photon
virtuality or quark masses, we find fully analytic results that allow direct
insight into how the differential cross section and elliptic anisotropy depend
on the saturation scale, target geometry, and kinematic variables. We further
provide numerical results for more general kinematics in collisions at a future
electron-ion collider, and study the effects of approaching the saturated
regime on diffractive dijet observables.",1905.03763v2
2019-06-17,Charging of quantum batteries with general harmonic power,"We analyse the charging process of quantum batteries with general harmonic
power. To describe the charge efficiency, we introduce the charge saturation
and the charging power, and divide the charging mode into the saturated
charging mode and the unsaturated charging mode. The relationships between the
time-dependent charge saturation and the parameters of general driving field
are discussed both analytically and numerically. And according to the Floquet
theorem, we give the expressions of time-dependent charge saturation with the
quasiengery and the Floquet states of the system. With both the analytical and
numerical results, we find the optimal parameters to reach the best charging
efficiency.",1906.06880v2
2019-06-20,Eddy saturation of the Southern Ocean: a baroclinic versus barotropic perspective,"""Eddy saturation"" is the regime in which the total time-mean volume transport
of an oceanic current is relatively insensitive to the wind stress forcing and
is often invoked as a dynamical description of Southern Ocean circulation. We
revisit the problem of eddy saturation using a primitive-equations model in an
idealized channel setup with bathymetry. We apply only mechanical wind stress
forcing; there is no diapycnal mixing or surface buoyancy forcing. Our main aim
is to assess the relative importance of two mechanisms for producing eddy
saturated states: (i) the commonly invoked baroclinic mechanism that involves
the competition of sloping isopycnals and restratification by production of
baroclinic eddies, and (ii) the barotropic mechanism, that involves production
of eddies through lateral shear instabilities or through the interaction of the
barotropic current with bathymetric features. Our results suggest that the
barotropic flow-component plays a crucial role in determining the total volume
transport.",1906.08442v3
2019-07-10,A positivity preserving iterative method for finding the ground states of saturable nonlinear Schrödinger equations,"In this paper, we propose an iterative method to compute the positive ground
states of saturable nonlinear Schr\""odinger equations. A discretization of the
saturable nonlinear Schr\""odinger equation leads to a nonlinear algebraic
eigenvalue problem (NAEP). For any initial positive vector, we prove that this
method converges globally with a locally quadratic convergence rate to a
positive solution of NAEP. During the iteration process, the method requires
the selection of a positive parameter $\theta_k$ in the $k$th iteration, and
generates a positive vector sequence approximating the eigenvector of NAEP and
a scalar sequence approximating the corresponding eigenvalue. We also present a
halving procedure to determine the parameters $\theta_k$, starting with
$\theta_k=1$ for each iteration, such that the scalar sequence is strictly
monotonic increasing. This method can thus be used to illustrate the existence
of positive ground states of saturable nonlinear Schr\""odinger equations.
Numerical experiments are provided to support the theoretical results.",1907.04644v1
2019-10-08,Optimal L-Infinity Frequency Control in Microgrids Considering Actuator Saturation,"Inverter-connected resources can improve transient stability in low-inertia
grids by injecting active power to minimize system frequency deviations
following disturbances. In practice, most generation and load disturbances are
step changes and the engineering figure-of-merit is often the peak overshoot in
frequency resulting from these step disturbances. In addition, the
inverter-connected resources tend to saturate much more easily than
conventional synchronous machines. However, despite these challenges, standard
controller designs must deal with averaged quantities through $H_2$ or
$H_\infty$ norms and must account for saturation in ad hoc manners. In this
paper, we address these challenges by explicitly considering $L_\infty$ control
with saturation using a linear matrix inequality-based approach. We show that
this approach leads to significant improvements in stability performance.",1910.03720v1
2019-10-11,"The saturation number of $K_{3,3}$","A graph $G$ is called $F$-saturated if $G$ does not contain $F$ as a subgraph
(not necessarily induced) but the addition of any missing edge to $G$ creates a
copy of $F$. The saturation number of $F$, denoted by $sat(n,F)$, is the
minimum number of edges in an $n$-vertex $F$-saturated graph. Determining the
saturation number of complete partite graphs is one of the most important
problems in the study of saturation number. The value of $sat(n,K_{2,2})$ was
shown to be $\lfloor\frac{3n-5}{2}\rfloor$ by Ollmann, and a shorter proof was
later given by Tuza. For $K_{2,3}$, there has been a series of study aiming to
determine $sat(n,K_{2,3})$ over the years. This was finally achieved by Chen
who confirmed a conjecture of Bohman, Fonoberova, and Pikhurko that $sat(n,
K_{2,3})= 2n-3$ for all $n\geq 5$. In this paper, we prove a conjecture of
Pikhurko and Schmitt that $sat(n, K_{3,3})=3n-9$ when $n \geq 9$.",1910.04967v2
2019-10-28,Saturation corrections to dilute-dense particle production and azimuthal correlations in the Color Glass Condensate,"We perform a numerical study of higher order saturation corrections to the
dilute-dense approximation for multi-particle production in high-energy
hadronic collisions in the framework of the Color Glass Condensate. We compare
semi-analytical results obtained by performing a leading order expansion in the
dilute field of the projectile with numerical simulations of the full Classical
Yang-Mills dynamics for a number of phenomenologically relevant observables. By
varying the saturation momentum of the target and the projectile, we establish
the regime of validity of the dilute-dense approximation and assess the
magnitude and basic features of higher order saturation corrections. In
particular, we find that dilute-dense approximation faithfully reproduces
dense-dense results if restricted to the range of its validity.",1910.12496v1
2019-11-20,Flexural Fatigue Life of Woven Carbon/Vinyl Ester Composites under Sea Water Saturation,"The adverse effects of sea water environment on the fatigue life of woven
carbon fiber/vinyl ester composites are established at room temperature in view
of long-term survivability of offshore structures. It is observed that the
influence of sea water saturation on the fatigue life is more pronounced when
the maximum cyclic displacement approaches maximum quasi-static deflection,
that is, the reduction in the number of cycles to failure are comparable
between dry and sea water saturated samples at lower strain ranges (~37% at
0.46% strain), but are drastically different at higher strain ranges (~90% at
0.62% strain). Key damage modes that manifest during the fatigue loading is
also identified, and a non-linear model is established for predicting low cycle
fatigue life of these composites in dry and sea water saturated conditions.",1911.08665v2
2019-11-20,Drift velocity saturation and large current density in an intrinsic three-dimensional Dirac semimetal cadmium arsenide,"Transport of electrons at high electric fields is investigated in an
intrinsic three-dimensional Dirac semimetal cadmium arsenide, considering the
scattering of electrons from acoustic and optical phonons. Screening and hot
phonon effect are taken in to account. Expressions for the hot electron
mobility $\mu$ and power loss $P$ are obtained as a function of electron
temperature $T_e$. The dependence of drift velocity $v_d$ on electric field $E$
and electron density $n_e$ has been studied. Hot phonon effect is found to set
in the saturation of $v_d$ at relatively low $E$ and significantly degrades its
magnitude. The drift velocity is found to saturate at a value $v_{ds} \sim
10^7$ cm/s and it is weakly dependent on $n_e$. A large saturation current
density $\sim 10^6$ A/cm$^2$ is predicted.",1911.08965v1
2019-11-25,Optimizing Josephson-Ring-Modulator-based Josephson Parametric Amplifiers via full Hamiltonian control,"Josephson Parametric Amplifiers (JPA) are nonlinear devices that are used for
quantum sensing and qubit readout in the microwave regime. While JPAs regularly
operate in the quantum limit, their gain saturates for very small (few photons)
input power. In a previous work, we showed that the saturation power of JPAs is
not limited by pump depletion, but instead by the high-order nonlinearity of
Josephson junctions, the nonlinear circuit elements that enable amplification
in JPAs. Here, we present a systematic study of the nonlinearities in JPAs, we
show which nonlinearities limit the saturation power, and present a strategy
for optimizing the circuit parameters for achieving the best possible JPA. For
concreteness, we focus on JPAs that are constructed around a Josephson Ring
Modulator (JRM). We show that by tuning the external and shunt inductors, we
should be able to take the best experimentally available JPAs and improve their
saturation power by $\sim 15$ dB. Finally, we argue that our methods and
qualitative results are applicable to a broad range of cavity based JPAs.",1911.11176v3
2019-11-26,On grouops with formational subnormal or self-normalizing subgroups,"We establish the structure of finite groups with $\mathfrak{F}$-subnormal or
self-normalizing primary cyclic subgroups in case $\mathfrak{F}$ is a
subgroup-closed saturated superradical formation containing all nilpotent
groups.",1911.11648v1
2019-12-18,Saturation of radiative heat transfer due to many-body thermalization,"Radiative heat transfer between two bodies saturates at very short separation
distances due to the nonlocal optical response of the materials. In this work,
we show that the presence of radiative interactions with a third body or
external bath can also induce a saturation of the heat transfer, even at
separation distances for which the optical response of the materials is purely
local. We demonstrate that this saturation mechanism is a direct consequence of
a thermalization process resulting from many-body interactions in the system.
This effect could have an important impact in the field of nanoscale thermal
management of complex systems and in the interpretation of measured signals in
thermal metrology at the nanoscale.",1912.08515v1
2020-03-03,Algorithms for fusion systems with applications to $p$-groups of small order,"For a prime $p$, we describe a protocol for handling a specific type of
fusion system on a $p$-group by computer. These fusion systems contain all
saturated fusion systems. This framework allows us to computationally determine
whether or not two subgroups are conjugate in the fusion system for example. We
describe a generation procedure for automizers of every subgroup of the
$p$-group. This allows a computational check of saturation. These procedures
have been implemented using MAGMA. We describe a program to search for
saturated fusion systems $\mathcal{F}$ on $p$-groups with $O_p(\mathcal{F})=1$
and $O^p(\mathcal{F})=\mathcal{F}$. Employing these computational methods we
determine all such fusion system on groups of order $p^n$ where $(p,n) \in
\{(3,4),(3,5),(3,6),(3,7),(5,4),(5,5),(5,6),(7,4),(7,5)\}$. This gives the
first complete picture of which groups can support saturated fusion systems on
small $p$-groups of odd order.",2003.01600v4
2020-03-11,Entropy Bound and Unitarity of Scattering Amplitudes,"We establish that unitarity of scattering amplitudes imposes universal
entropy bounds. The maximal entropy of a self-sustained quantum field object of
radius R is equal to its surface area and at the same time to the inverse
running coupling evaluated at the scale R. The saturation of these entropy
bounds is in one-to-one correspondence with the non-perturbative saturation of
unitarity by 2-to-N particle scattering amplitudes at the point of optimal
truncation. These bounds are more stringent than Bekenstein's bound and in a
consistent theory all three get saturated simultaneously. This is true for all
known entropy-saturating objects such as solitons, instantons, baryons,
oscillons, black holes or simply lumps of classical fields. We refer to these
collectively as ""saturons"" and show that in renormalizable theories they behave
in all other respects like black holes. Finally, it is argued that the
confinement in SU(N) gauge theory can be understood as a direct consequence of
the entropy bounds and unitarity.",2003.05546v1
2020-04-11,"A lower bound on the saturation number, and graphs for which it is sharp","Let $H$ be a fixed graph. We say that a graph $G$ is $H$-saturated if it has
no subgraph isomorphic to $H$, but the addition of any edge to $G$ results in
an $H$-subgraph. The saturation number $\mathrm{sat}(H,n)$ is the minimum
number of edges in an $H$-saturated graph on $n$ vertices. K\'aszonyi and Tuza,
in 1986, gave a general upper bound on the saturation number of a graph $H$,
but a nontrivial lower bound has remained elusive. In this paper we give a
general lower bound on $\mathrm{sat}(H,n)$ and prove that it is asymptotically
sharp (up to an additive constant) on a large class of graphs. This class
includes all threshold graphs and many graphs for which the saturation number
was previously determined exactly. Our work thus gives an asymptotic common
generalization of several earlier results. The class also includes disjoint
unions of cliques, allowing us to address an open problem of Faudree, Ferrara,
Gould, and Jacobson.",2004.05410v2
2020-04-13,"Saturation problems in the Ramsey theory of graphs, posets and point sets","In 1964, Erd\H{o}s, Hajnal and Moon introduced a saturation version of
Tur\'an's classical theorem in extremal graph theory. In particular, they
determined the minimum number of edges in a $K_r$-free, $n$-vertex graph with
the property that the addition of any further edge yields a copy of $K_r$. We
consider analogues of this problem in other settings. We prove a saturation
version of the Erd\H{o}s-Szekeres theorem about monotone subsequences and
saturation versions of some Ramsey-type theorems on graphs and Dilworth-type
theorems on posets.
  We also consider semisaturation problems, wherein we allow the family to have
the forbidden configuration, but insist that any addition to the family yields
a new copy of the forbidden configuration. In this setting, we prove a
semisaturation version of the Erd\H{o}s-Szekeres theorem on convex $k$-gons, as
well as multiple semisaturation theorems for sequences and posets.",2004.06097v2
2020-07-21,Narrow bandwidth Q-switched Erbium-doped fiber laser based on dynamic saturable absorption filtering effect,"We proposed a narrow spectral bandwidth Erbium-doped fiber (EDF) laser
Q-switched by a homemade saturable dynamic induced grating (SDIG) which is
introduced via reforming the structure of a fiber saturable absorbers FSA with
a piece of EDF and a fiber Bragg grating. The SDIG integrates both saturable
absorption and spectral filtering effect simultaneously, which was confirmed
through theoretical analysis and experimental results for the first time, to
the best of our knowledge. Further study verified that the spectral width of
the Q-switched emissions is decided by the length of the SDIG and the input
power of the pump source. The Q-switched pulse with the narrowest spectral
width of about 29.1 pm achieved in this work is the narrowest bandwidth pulse
in the domain of the FSA Q-switched fiber lasers when the length of SDIG and
pump power are 20 cm and 250 mW, respectively. Our method provides a simple way
to obtain the Q-switched pulses with narrow bandwidths, which have promising
applications for nonlinear frequency conversion, Doppler LIDAR and coherent
beam combinations.",2007.10583v1
2020-07-21,Models of Jacobians of curves,"We show that the Jacobians of prestable curves over toroidal varieties always
admit N\'eron models. These models are rarely quasi-compact or separated, but
we also give a complete classification of quasi-compact separated group-models
of such Jacobians. In particular we show the existence of a maximal
quasi-compact separated group model, which we call the saturated model, which
has the extension property for all torsion sections. The N\'eron model and the
saturated model coincide over a Dedekind base, so the saturated model gives an
alternative generalisation of the classical notion of N\'eron models to
higher-dimensional bases; in the general case we give necessary and sufficient
conditions for the N\'eron model and saturated model to coincide. The key
result, from which most others descend, is that the logarithmic Jacobian of
\cite{Molcho2018The-logarithmic} is a log Neron model of the Jacobian.",2007.10792v1
2020-09-14,Accelerated Nonlinear Model Predictive Control by Exploiting Saturation,"We present an approach for accelerating nonlinear model predictive control.
If the current optimal input signal is saturated, also the optimal signals in
subsequent time steps often are. We propose to use the open-loop optimal input
signals whenever the first and some subsequent input signals are saturated. We
only solve the next optimal control problem, when a non-saturated signal is
encountered, or the end of the horizon is reached. In this way, we can save a
significant number of NLPs to be solved while on the other hand keep the
performance loss small. Furthermore, the NMPC is reactivated in time when it
comes to controlling the system safely to its reference.",2009.06347v1
2020-09-20,Correction Method for the Readout Saturation of the DAMPE Calorimeter,"The DArk Matter Particle Explorer (DAMPE) is a space-borne high energy
cosmic-ray and $\gamma$-ray detector which operates smoothly since the launch
on December 17, 2015. The bismuth germanium oxide (BGO) calorimeter is one of
the key sub-detectors of DAMPE used for energy measurement and electron proton
identification. For events with total energy deposit higher than decades of
TeV, the readouts of PMTs coupled on the BGO crystals would become saturated,
which results in an underestimation of the energy measurement. Based on
detailed simulations, we develop a correction method for the saturation effect
according to the shower development topologies and energies measured by
neighbouring BGO crystals. The verification with simulated and on-orbit events
shows that this method can well reconstruct the energy deposit in the saturated
BGO crystal.",2009.09438v1
2020-10-05,Sample weighting as an explanation for mode collapse in generative adversarial networks,"Generative adversarial networks were introduced with a logistic MiniMax cost
formulation, which normally fails to train due to saturation, and a
Non-Saturating reformulation. While addressing the saturation problem, NS-GAN
also inverts the generator's sample weighting, implicitly shifting emphasis
from higher-scoring to lower-scoring samples when updating parameters. We
present both theory and empirical results suggesting that this makes NS-GAN
prone to mode dropping. We design MM-nsat, which preserves MM-GAN sample
weighting while avoiding saturation by rescaling the MM-GAN minibatch gradient
such that its magnitude approximates NS-GAN's gradient magnitude. MM-nsat has
qualitatively different training dynamics, and on MNIST and CIFAR-10 it is
stronger in terms of mode coverage, stability and FID. While the empirical
results for MM-nsat are promising and favorable also in comparison with the
LS-GAN and Hinge-GAN formulations, our main contribution is to show how and why
NS-GAN's sample weighting causes mode dropping and training collapse.",2010.02035v1
2020-10-06,Multi-Rees algebras on principal ideal rings,"When $R$ is a Noetherian ring and we have a family of ideals in which every
ideal contains at least one nonzero divisor, then it is already known that the
defining ideal of the multi-Rees algebra of these ideals is equal to a
saturated ideal. In such a case to get the defining ideal of the multi-Rees
algebra we only need to saturate the first syzygies of direct sum of this
family of ideals. However, this fact is not true, when at least one of these
ideals does not contain any nonzero divisor. In this paper we show that the
defining ideal of the multi-Rees algebra of a family of ideals of a polynomial
ring over a principal ideal ring, is equal to another kind of saturated ideal,
where we saturate more explicit polynomials other than just first syzygies.
Please notice that in general some of these ideals may not contain nonzero
divisors. Given this explicit formula, we can compute Gr\""{o}bner basis of the
defining ideal using an elimination order, which we talk about in the present
paper.",2010.02899v2
2020-10-28,Receptor Saturation Modeling for Synaptic DMC,"Synaptic communication is a natural Molecular Communication (MC) system which
may serve as a blueprint for the design of synthetic MC systems. In particular,
it features highly specialized mechanisms to enable inter-symbol interference
(ISI)-free and energy efficient communication. The understanding of synaptic MC
is furthermore critical for disruptive innovations in the context of
brain-machine interfaces. However, the physical modeling of synaptic MC is
complicated by the possible saturation of the molecular receiver arising from
the competition of postsynaptic receptors for neurotransmitters. Saturation
renders the system behavior nonlinear and is commonly neglected in existing
analytical models. In this work, we propose a novel model for receptor
saturation in terms of a nonlinear, state-dependent boundary condition for
Fick's diffusion equation. We solve the resulting boundary-value problem using
an eigenfunction expansion of the Laplace operator and the incorporation of the
receiver memory as feedback system into the corresponding state-space
description. The presented solution is numerically stable and computationally
efficient. Furthermore, the proposed model is validated with particle-based
stochastic computer simulations.",2010.14828v2
2020-11-06,Geometric conditions for saturating the data processing inequality,"The data processing inequality (DPI) is a scalar inequality satisfied by
distinguishability measures on density matrices. For some distinguishability
measures, saturation of the scalar DPI implies an operator equation relating
the arguments of the measure. These results are typically derived using
functional analytic techniques. In a complementary approach, we use geometric
techniques to derive a formula that gives an operator equation from DPI
saturation for any distinguishability measure; moreover, for a broad class of
distinguishability measures, the derived operator equation is sufficient to
imply saturation as well. Our operator equation coincides with known results
for the sandwiched R\'{e}nyi relative entropies, and gives new results for
$\alpha$-$z$ R\'{e}nyi relative entropies and a family of of quantum
$f$-divergences, which we compute explicitly.",2011.03473v2
2020-11-09,A type of shadowing and distributional chaos,"For any continuous self-map of a compact metric space, we prove a saturation
of distributionally scrambled Mycielski sets under a type of shadowing and the
chain transitivity.",2011.04248v1
2020-11-20,Deep unfolding-based output feedback control design for linear systems with input saturation,"In this paper, we propose a deep unfolding-based framework for the output
feedback control of systems with input saturation. Although saturation commonly
arises in several practical control systems, there is still a scarce of
effective design methodologies that can directly deal with the severe
non-linearity of the saturation operator. In this paper, we aim to design an
anti-windup controller for enlarging the region of stability of the closed-loop
system by learning from the numerical simulations of the closed-loop system.
The data-driven framework we propose in this paper is based on a deep-learning
technique called Neural Ordinary Differential Equations. Within our framework,
we first obtain a candidate controller by using the deep-learning technique,
which is then tested by the existing theoretical results already established in
the literature, thereby avoiding the computational challenge in the
conventional design methodologies as well as theoretically guaranteeing the
performance of the system. Our numerical simulation shows that the proposed
framework can significantly outperform a conventional design methodology based
on linear matrix inequalities.",2011.10196v2
2020-12-03,Saturated $k$-Plane Drawings with Few Edges,"A drawing of a graph is $k$-plane if no edge is crossed more than $k$ times.
In this paper we study saturated $k$-plane drawings with few edges. This are
$k$-plane drawings in which no edge can be added without violating
$k$-planarity. For every number of vertices $n>k+1$, we present a tight
construction with $\frac{n-1}{k+1}$ edges for the case in which the edges can
self-intersect. If we restrict the drawings to be $\ell$-simple we show that
the number of edges in saturated $k$-plane drawings must be higher. We present
constructions with few edges for different values of $k$ and $\ell$. Finally,
we investigate saturated straight-line $k$-plane drawings.",2012.02281v4
2020-12-20,Robust Alignment of Multi-Exposed Images with Saturated Regions,"It is challenging to align multi-exposed images due to large illumination
variations, especially in presence of saturated regions. In this paper, a novel
image alignment algorithm is proposed to cope with the multi-exposed images
with saturated regions. Specifically, the multi-exposed images are first
normalized by using intensity mapping functions (IMFs) in consideration of
saturated pixels. Then, the normalized images are coded by using the local
binary pattern (LBP). Finally, the coded images are aligned by formulating an
optimization problem by using a differentiable Hamming distance. Experimental
results show that the proposed algorithm outperforms state-of-the-art alignment
methods for multi-exposed images in terms of alignment accuracy and robustness
to exposure values.",2012.10872v1
2021-03-14,Sharp transition to strongly anomalous transport in unsaturated porous media,"The simultaneous presence of liquid and gas in porous media increases flow
heterogeneity compared to saturated flows. However, so far the impact of
saturation on flow statistics and transport dynamics remained unclear. Here, we
develop a theoretical framework that captures the impact of flow reorganization
on the statistics of pore-scale fluid velocities, due to the presence of gas in
the pore space, which leads to the development of a highly-structured flow
field. Preferential flow is distributed spatially through the denoted backbone
and flow recirculation occurs in dead-end regions branching from it. This
induces a marked change in the scaling of the velocity PDF compared to the
saturated case, and a sharp transition to strongly anomalous transport. We
develop a transport model based on the continuous time random walk theory that
successfully predicts advective transport dynamics for all saturation degrees.
Our results provide a new modelling framework linking phase heterogeneity to
flow heterogeneity and to transport in unsaturated media.",2103.08016v1
2021-03-23,A stabilized computational nonlocal poromechanics model for dynamic analysis of saturated porous media,"In this article we formulate a stable computational nonlocal poromechanics
model for dynamic analysis of saturated porous media. As a novelty, the
stabilization formulation eliminates zero-energy modes associated with the
original multiphase correspondence constitutive models in the coupled nonlocal
poromechanics model. The two-phase stabilization scheme is formulated based on
an energy method that incorporates inhomogeneous solid deformation and fluid
flow. In this method, the nonlocal formulations of skeleton strain energy and
fluid flow dissipation energy equate to their local formulations. The stable
coupled nonlocal poromechanics model is solved for dynamic analysis by an
implicit time integration scheme. As a new contribution, we validate the
coupled stabilization formulation by comparing numerical results with
analytical and finite element solutions for one-dimensional and two-dimensional
dynamic problems in saturated porous media. Numerical examples of dynamic
strain localization in saturated porous media are presented to demonstrate the
efficacy of the stable coupled poromechanics framework for localized failure
under dynamic loads.",2103.12259v1
2021-03-30,Local output feedback stabilization of a Reaction-Diffusion equation with saturated actuation,"This paper is concerned with the output feedback stabilization of a
reaction-diffusion equation by means of bounded control inputs in the presence
of saturations. Using a finite-dimensional controller composed of an observer
coupled with a finite-dimensional state-feedback, we derive a set of conditions
ensuring the stability of the closed-loop plant while estimating the associated
domain of attraction in the presence of saturations. This set of conditions is
shown to be always feasible for an order of the observer selected large enough.
The stability analysis relies on Lyapunov functionals along with a generalized
sector condition classically used to study the stability of linear
finite-dimensional plants in the presence of saturations.",2103.16523v2
2021-06-25,Training Saturation in Layerwise Quantum Approximate Optimisation,"Quantum Approximate Optimisation (QAOA) is the most studied gate based
variational quantum algorithm today. We train QAOA one layer at a time to
maximize overlap with an $n$ qubit target state. Doing so we discovered that
such training always saturates -- called \textit{training saturation} -- at
some depth $p^*$, meaning that past a certain depth, overlap can not be
improved by adding subsequent layers. We formulate necessary conditions for
saturation. Numerically, we find layerwise QAOA reaches its maximum overlap at
depth $p^*=n$. The addition of coherent dephasing errors to training removes
saturation, recovering robustness to layerwise training. This study sheds new
light on the performance limitations and prospects of QAOA.",2106.13814v1
2021-06-30,Saturated Transformers are Constant-Depth Threshold Circuits,"Transformers have become a standard neural network architecture for many NLP
problems, motivating theoretical analysis of their power in terms of formal
languages. Recent work has shown that transformers with hard attention are
quite limited in power (Hahn, 2020), as they can be simulated by constant-depth
AND/OR circuits (Hao et al. 2021). However, hard attention is a strong
assumption, which may complicate the relevance of these results in practice. In
this work, we analyze the circuit complexity of transformers with saturated
attention: a generalization of hard attention that more closely captures the
attention patterns learnable in practical transformers. We first show that
saturated transformers transcend the known limitations of hard-attention
transformers. We then prove saturated transformers with floating-point values
can be simulated by constant-depth threshold circuits, giving the class
$\mathsf{TC}^0$ as an upper bound on the formal languages they recognize.",2106.16213v3
2021-07-20,Does vacuum saturation work for the higher dimensional vacuum condensates in the QCD sum rules?,"In the QCD sum rules for the tetraquark (molecular) states, the higher
dimensional vacuum condensates play an important role in extracting the
tetraquark masses. We carry out the operator product expansion up to the vacuum
condensates of dimension-10 and observe that the vacuum condensates of
dimensions $6$, $8$ and $10$ have the same expressions but opposite signs for
the $C\gamma_5\otimes \gamma_\mu C$-type and $C\otimes \gamma_\mu C$ type
four-quark currents, which make their influences distinguishable, and they are
excellent channels to examine the vacuum saturation approximation. We introduce
a parameter $\kappa$ to parameterize the derivation from the vacuum saturation
or factorization approximation, and choose two sets parameters to examine the
influences on the predicted tetraquark masses, which can be confronted to the
experimental data in the future. In all the channels, smaller value of the
$\kappa$ leads to better convergent behavior in the operator product expansion,
which favors the vacuum saturation approximation.",2107.09328v2
2021-07-20,Fourth-order moment of the light field in atmosphere for moderate and strong turbulence,"Collisionless Boltzmann equation is used to describe the intensity
correlations in partially saturated and fully saturated regimes in terms of
photon distribution function in the phase space. Explicit expression for fourth
moment of the light fields is obtained for the case of moderate and strong
turbulence. Such expression consists of two terms accounting for two regions in
the phase space that independently contribute to the correlation function. It
is shown that present solution agrees with previous results for fully saturated
regime. Additionally it embodies the effect of partially saturated radiation
where the correlations of photon trajectories are important and the magnitude
of the scintillation index is well above the unity. Fourth moment is used to
study the fluctuations of transmittance which consider the effect of finite
detector aperture.",2107.09358v1
2021-08-06,Sub-barrier quantum tunneling: eliminating the MacColl-Hartman paradox,"I show that the MacColl-Hartman effect, namely, the saturation of the group
delay time of sub-barrier quantum tunneling as a function of the barrier width,
comes from the saturating behavior of a more fundamental concept - the phase of
the stationary wave function. The explanation of saturation is given based on
the decomposition of the stationary wave function into the spectrum of wave
numbers and formulation of the initial condition for the direction of
propagation of the incident matter wave. It is also shown that the saturation
plateau of MacColl and Hartman actually doesn't continue indefinitely, but has
a finite length. After the plateau, the sub-barrier tunneling time
monotonically increases with increasing width of the potential, and this
applies both to the maximum's of the wave packet and to the average tunneling
time.",2108.03054v1
2021-10-26,Event-triggered Consensus of Matrix-weighted Networks Subject to Actuator Saturation,"The ubiquitous interdependencies among higher-dimensional states of
neighboring agents can be characterized by matrix-weighted networks. This paper
examines event-triggered global consensus of matrix-weighted networks subject
to actuator saturation. Specifically, a distributed dynamic event-triggered
coordination strategy, whose design involves sampled state of agents,
saturation constraint and auxiliary systems, is proposed for this category of
generalized network to guarantee its global consensus. Under the proposed
event-triggered coordination strategy, sufficient conditions are derived to
guarantee the leaderless and leader-follower global consensus of the
multi-agent systems on matrix-weighted networks, respectively. The Zeno
phenomenon can be excluded for both cases under the proposed coordination
strategy. It turns out that the spectral properties of matrix-valued weights
are crucial in event-triggered mechanism design for matrix-weighted networks
with actuator saturation constraint. Finally, simulations are provided to
demonstrate the effectiveness of proposed event-triggered coordination
strategy. This work provides a more general design framework compared with
existing results that are only applicable to scalar-weighted networks.",2110.13356v1
2021-11-09,Generation and dynamics of soliton and soliton molecules from a VSe2/GO-based fiber laser,"Recently, in addition to exploring the application of new saturable absorber
devices in fiber lasers, soliton dynamics has also become a focus of current
research. In this article, we report an ultrashort pulse fiber laser based on
VSe2/GO nanocomposite and verify the formation process of soliton and soliton
molecules by the numerical simulation. The prepared VSe2/GO-based device shows
excellent saturable absorption characteristics with a modulation depth of 14.3%
and a saturation absorption intensity of 0.93MW/cm2. The conventional soliton
is obtained with pulse width of 573fs, which is currently the narrowest pulse
width based on VSe2-related material, and has a signal-to-noise ratio of 60.4
dB. In addition, the soliton molecules are realized based on the VSe2/GO for
the first time and have a pulse interval of ~2.2ps. We study the soliton
dynamics through numerical simulation and reveal that before the formation of
the soliton, it undergoes multiple nonlinear stages, such as soliton
mode-locking, soliton splitting, and soliton oscillation. Furthermore, the
results of numerical simulation are agreed well with the experimental data.
These results indicate that the VSe2/GO might be another promising saturable
absorber material for ultrafast photonics, and deepen the understanding of
soliton dynamics in ultrafast fiber lasers.",2111.05138v1
2021-11-11,Hybrid Saturation Restoration for LDR Images of HDR Scenes,"There are shadow and highlight regions in a low dynamic range (LDR) image
which is captured from a high dynamic range (HDR) scene. It is an ill-posed
problem to restore the saturated regions of the LDR image. In this paper, the
saturated regions of the LDR image are restored by fusing model-based and
data-driven approaches. With such a neural augmentation, two synthetic LDR
images are first generated from the underlying LDR image via the model-based
approach. One is brighter than the input image to restore the shadow regions
and the other is darker than the input image to restore the high-light regions.
Both synthetic images are then refined via a novel exposedness aware saturation
restoration network (EASRN). Finally, the two synthetic images and the input
image are combined together via an HDR synthesis algorithm or a multi-scale
exposure fusion algorithm. The proposed algorithm can be embedded in any smart
phones or digital cameras to produce an information-enriched LDR image.",2111.06038v2
2021-12-12,Probing parton saturation and the gluon dipole via diffractive jet production at the Electron-Ion Collider,"We demonstrate that hard dijet production via coherent inelastic diffraction
is a promising channel for probing gluon saturation at the Electron-Ion
Collider. By $inelastic$ diffraction we mean a process in which the two hard
jets - a quark-antiquark pair generated by the decay of the virtual photon -
are accompanied by a softer gluon jet, emitted by the quark or the antiquark.
This process can be described as the elastic scattering of an effective
gluon-gluon dipole. The cross section takes a factorised form, between a hard
factor and a unintegrated (""Pomeron"") gluon distribution describing the
transverse momentum imbalance between the hard dijets. The dominant
contribution comes from the black disk limit and leads to a dijet imbalance of
the order of the target saturation momentum $Q_s$ evaluated at the rapidity
gap. Integrating out the dijet imbalance, we obtain a collinear factorization
where the initial condition for the DGLAP evolution is set by gluon saturation.",2112.06353v2
2021-12-29,Finitely generated saturated multi-Rees algebras,"We study the question of finite generation of saturated multi-Rees algebras
and investigate the asymptotic behaviour of related length functions. In the
setup of excellent local domains, we show that the saturated multi-Rees algebra
of a finite collection of ideals is finitely generated when the analytic spread
is not maximal and the associated length function eventually agrees with a
polynomial. Similar results are obtained when we restrict to two-dimensional
local UFDs with no restrictions on the analytic spread. We further prove that
the saturated multi-Rees algebra of finitely many monomial ideals in a
polynomial ring modulo an irreducible monomial ideal, is always finitely
generated. In this case, the corresponding length function is shown to exhibit
piecewise quasi-polynomial behaviour. We also produce multi-ideal versions of a
theorem of Amao.",2112.14587v2
2022-01-05,Nuclei in the toy world: beyond the Pomeron in zero transverse dimensions,"We explore possible extensions of the $t$-channel and $s$-channel unitary
model of high energy evolution in zero transverse dimensions appropriate to
very high energy/atomic number where the dipole density in a toy hadron is
parametrically high.We suggest that the appropriate generalization is to allow
emission of more than one dipole in a single step of energy evolution. We
construct explicitly such a model that preserves the $t$-channel and s-channel
unitarity and have the correct low density limit, and study the particle
multiplicity distribution resulting from this evolution. We consider initial
conditions of a single dipole and many dipoles at initial rapidity. We observe
that the saturation regime in this model is preceded by a parametric range of
rapidities
$\frac{1}{\alpha_s}\ln\frac{1}{\alpha_s}<Y<\frac{1}{\alpha_s}\ln\frac{1}{\alpha_s^2}$,
where the saturation effects are still unimportant, but multiple emissions
determine the properties of the evolution. We also discuss the influence of the
saturation on the parton cascade and, in particular, find that in the
saturation regime the entropy of partons becomes $S \approx \h \ln N$ where $N$
is the mean multiplicity.",2201.01551v2
2022-03-09,Mapping global dynamics of benchmark creation and saturation in artificial intelligence,"Benchmarks are crucial to measuring and steering progress in artificial
intelligence (AI). However, recent studies raised concerns over the state of AI
benchmarking, reporting issues such as benchmark overfitting, benchmark
saturation and increasing centralization of benchmark dataset creation. To
facilitate monitoring of the health of the AI benchmarking ecosystem, we
introduce methodologies for creating condensed maps of the global dynamics of
benchmark creation and saturation. We curated data for 3765 benchmarks covering
the entire domains of computer vision and natural language processing, and show
that a large fraction of benchmarks quickly trended towards near-saturation,
that many benchmarks fail to find widespread utilization, and that benchmark
performance gains for different AI tasks were prone to unforeseen bursts. We
analyze attributes associated with benchmark popularity, and conclude that
future benchmarks should emphasize versatility, breadth and real-world utility.",2203.04592v4
2022-05-10,Balanced control between performance and saturation for constrained nonlinear systems,"This paper addresses the balanced control between performance and saturation
for a class of constrained nonlinear systems, including the branches: balanced
command filtered backstepping (BCFB) and balanced performance control (BPC). To
balance the interconnection and conflict between performance and saturation
constraints, define a performance safety evaluation (PSE) function, which
evaluates the system safety under the destabilizing effect variables (DEVs)
like saturation quantity and filter errors, then the cumulative effects of DEVs
are fully utilized and compensated for the performance recovery. Specifically,
there exists some degree of tolerance for the DEVs in the safety region, and
the compensation operation works when the evaluation of the system goes
dangerous. The advantages of the proposed methodology are illustrated in the
numerical simulation.",2205.04674v1
2022-06-10,The Z3RO Family of Precoders Cancelling Nonlinear Power Amplification Distortion in Large Array Systems,"Large array systems use a massive number of antenna elements and clever
precoder designs to achieve an array gain at the user location. These precoders
require linear front-ends, and more specifically linear power amplifiers (PAs),
to avoid distortion. This reduces the energy efficiency since PAs are most
efficient close to saturation, where they generate most nonlinear distortion.
Moreover, the use of conventional precoders can induce a coherent combining of
distortion at the user locations, degrading the signal quality. In this work,
novel linear precoders, simple to compute and to implement, are proposed that
allow working close to saturation, while cancelling the third-order
nonlinearity of the PA without prior knowledge of the signal statistics and PA
model. Their design consists in saturating a single or a few antennas on
purpose together with an negative gain with respect to all other antennas to
compensate for the overall nonlinear distortion at the user location. The
performance gains of the designs are significant for PAs working close to
saturation, as compared to maximum ratio transmission (MRT) precoding and
perfect per-antenna digital pre-distortion (DPD) compensation.",2206.05112v1
2022-07-08,Nuclear geometry at high energy from exclusive vector meson production,"We show that when saturation effects are included one obtains a good
description of the exclusive $\mathrm{J}/\psi$ production spectra in ultra
peripheral lead-lead collisions as recently measured by the ALICE Collaboration
at the LHC. As exclusive spectra are sensitive to the spatial distribution of
nuclear matter at small Bjorken-$x$, this implies that gluon saturation effects
modify the impact parameter profile of the target as we move towards small $x$.
In addition to saturation effects, we find a preference for larger nuclear
strong-interaction radii compared to the typical charge radius. We demonstrate
the role of finite photon transverse momentum and the interference between the
cases for which the role of photon emitter and target are switched between the
nuclei. We show that these effects are comparable to the experimental precision
for $p_T$-differential cross sections and as such need to be included when
comparing to LHC data. Finally, the integrated $\mathrm{J}/\psi$ production
cross sections from the LHC and preliminary transverse momentum spectra from
RHIC are shown to prefer calculations with fluctuating nucleon substructure,
although these datasets would require even stronger saturation effects than
predicted from our framework.",2207.03712v1
2022-07-27,The onset and saturation of the Faraday instability in miscible fluids in a rotating environment,"We investigate the influence of rotation on the onset and saturation of the
Faraday instability in a vertically oscillating two-layer miscible fluid using
a theoretical model and direct numerical simulations (DNS). Our analytical
approach utilizes the Floquet analysis to solve a set of the Mathieu equations
obtained from the linear stability analysis. The solution of the Mathieu
equations comprises stable and harmonic, and sub-harmonic unstable regions in a
three-dimensional stability diagram. We find that the Coriolis force stabilizes
the flow and delays the onset of the sub-harmonic instability responsible for
turbulent mixing at lower forcing amplitudes. However, at higher forcing
amplitudes, the flow is energetic enough to mitigate the stabilizing effect of
rotation, and the evolution of the turbulent mixing zone is similar in both
rotating and non-rotating environments. These results are corroborated by DNS
at different Coriolis frequencies and forcing amplitudes. We also observe that
for $\left(f/\omega\right)^2<0.25$, where $f$ is the Coriolis frequency, and
$\omega$ is the forcing frequency, the instability, and the turbulent mixing
zone size-$L$ saturates. When $\left(f/\omega\right)^2\geq0.25$, the turbulent
mixing zone size-$L$ never saturates and continues to grow.",2207.13739v1
2022-08-04,Estimating relative diffusion from 3D micro-CT images using CNNs,"In the past several years, convolutional neural networks (CNNs) have proven
their capability to predict characteristic quantities in porous media research
directly from pore-space geometries. Due to the frequently observed significant
reduction in computation time in comparison to classical computational methods,
bulk parameter prediction via CNNs is especially compelling, e.g. for effective
diffusion. While the current literature is mainly focused on fully saturated
porous media, the partially saturated case is also of high interest. Due to the
qualitatively different and more complex geometries of the domain available for
diffusive transport present in this case, standard CNNs tend to lose robustness
and accuracy with lower saturation rates. In this paper, we demonstrate the
ability of CNNs to perform predictions of relative diffusion directly from full
pore-space geometries. As such, our CNN conveniently fuses diffusion prediction
and a well-established morphological model which describes phase distributions
in partially saturated porous media.",2208.03337v1
2022-10-04,Fast Saturating Gate for Learning Long Time Scales with Recurrent Neural Networks,"Gate functions in recurrent models, such as an LSTM and GRU, play a central
role in learning various time scales in modeling time series data by using a
bounded activation function. However, it is difficult to train gates to capture
extremely long time scales due to gradient vanishing of the bounded function
for large inputs, which is known as the saturation problem. We closely analyze
the relation between saturation of the gate function and efficiency of the
training. We prove that the gradient vanishing of the gate function can be
mitigated by accelerating the convergence of the saturating function, i.e.,
making the output of the function converge to 0 or 1 faster. Based on the
analysis results, we propose a gate function called fast gate that has a doubly
exponential convergence rate with respect to inputs by simple function
composition. We empirically show that our method outperforms previous methods
in accuracy and computational efficiency on benchmark tasks involving extremely
long time scales.",2210.01348v1
2023-03-23,Intra-Pulse Intensity Noise Shaping by Saturable Absorbers,"In this work, we identify and characterize intra-pulse intensity noise
shaping by saturable absorbers applied in mode-locked lasers and ultra-low
noise nonlinear fiber amplifiers. Reshaped intra-pulse intensity noise
distributions are shown to be inevitably interconnected with self-amplitude
modulation, the fundamental physical mechanism for initiation and stabilization
of ultra-short pulses in the steady-state of a mode-locked laser. A theoretical
model is used to describe the ultrafast saturation dynamics by an intra-pulse
noise transfer function for widely-applied slow and fast saturable absorbers.
For experimental verification of the theoretical results, spectrally-resolved
relative intensity noise measurements are applied on chirped input pulses to
enable the direct measurement of intra-pulse noise transfer functions using a
versatile experimental platform. It is further demonstrated, how the
characterized intra-pulse intensity noise distribution of ultrafast laser
systems can be utilized for quantum-limited intensity noise suppression via
tailored optical bandpass filtering.",2303.13420v2
2023-04-24,Adaptive-saturated RNN: Remember more with less instability,"Orthogonal parameterization is a compelling solution to the vanishing
gradient problem (VGP) in recurrent neural networks (RNNs). With orthogonal
parameters and non-saturated activation functions, gradients in such models are
constrained to unit norms. On the other hand, although the traditional vanilla
RNNs are seen to have higher memory capacity, they suffer from the VGP and
perform badly in many applications. This work proposes Adaptive-Saturated RNNs
(asRNN), a variant that dynamically adjusts its saturation level between the
two mentioned approaches. Consequently, asRNN enjoys both the capacity of a
vanilla RNN and the training stability of orthogonal RNNs. Our experiments show
encouraging results of asRNN on challenging sequence learning benchmarks
compared to several strong competitors. The research code is accessible at
https://github.com/ndminhkhoi46/asRNN/.",2304.11790v1
2023-04-24,Probing gluon saturation via diffractive jets in ultra-peripheral nucleus-nucleus collisions,"We argue that semi-inclusive photo-production of a pair of hard jets via
coherent diffraction in nucleus-nucleus ultra-peripheral collisions at high
energy is a golden channel to study gluon saturation. The dominant contribution
is the diffractive production of three jets in an asymmetric configuration. Two
of the jets are hard and propagate at nearly central pseudo-rapidities. The
third jet is semi-hard, with transverse momentum comparable to the nuclear
saturation momentum, and is well separated in pseudo-rapidity from the hard
dijets. The emission of the semi-hard jet allows for strong scattering, thus
avoiding the ""higher-twist"" suppression of the exclusive dijet production due
to colour transparency. We compute the trijet cross-section using the
diffractive TMD factorisation which emerges from the CGC effective theory at
high energy. The cross-section is controlled by gluon saturation, which leaves
its imprints on the structure of the final state, notably on the rapidity
distribution.",2304.12401v1
2023-06-10,Linear saturation numbers of Berge-$C_3$ and Berge-$C_4$,"The linear saturation number $sat^{lin}_k(n,\mathcal{F})$ (linear extremal
number $ex^{lin}_k(n,\mathcal{F})$) of $\mathcal{F}$ is the minimum (maximum)
number of hyperedges of an $n$-vertex linear $k$-uniform hypergraph containing
no member of $\mathcal{F}$ as a subgraph, but the addition of any new hyperedge
such that the result hypergraph is still a linear $k$-uniform hypergraph
creates a copy of some hypergraph in $\mathcal{F}$. Determining $ex_3^{lin}(n$,
Berge-$C_3$) is equivalent to the famous (6,3)-problem, which has been settled
in 1976. Since then, determining the linear extremal numbers of Berge cycles
was extensively studied. As the counterpart of this problem in saturation
problems, the problem of determining the linear saturation numbers of Berge
cycles is considered. In this paper, we prove that $sat^{lin}_k$($n$,
Berge-$C_t)\ge \big\lfloor\frac{n-1}{k-1}\big\rfloor$ for any integers $k\ge3$,
$t\ge 3$, and the equality holds if $t=3$. In addition, we provide an upper
bound for $sat^{lin}_3(n,$ Berge-$C_4)$ and for any disconnected
Berge-$C_4$-saturated linear 3-uniform hypergraph, we give a lower bound for
the number of hyperedges of it.",2306.06435v1
2023-07-05,A $p$-step-ahead sequential adaptive algorithm for D-optimal nonlinear regression design,"Under a nonlinear regression model with univariate response an algorithm for
the generation of sequential adaptive designs is studied. At each stage, the
current design is augmented by adding $p$ design points where $p$ is the
dimension of the parameter of the model. The augmenting $p$ points are such
that, at the current parameter estimate, they constitute the locally D-optimal
design within the set of all saturated designs. Two relevant subclasses of
nonlinear regression models are focused on, which were considered in previous
work of the authors on the adaptive Wynn algorithm: firstly, regression models
satisfying the `saturated identifiability condition' and, secondly, generalized
linear models. Adaptive least squares estimators and adaptive maximum
likelihood estimators in the algorithm are shown to be strongly consistent and
asymptotically normal, under appropriate assumptions. For both model classes,
if a condition of `saturated D-optimality' is satisfied, the almost sure
asymptotic D-optimality of the generated design sequence is implied by the
strong consistency of the adaptive estimators employed by the algorithm. The
condition states that there is a saturated design which is locally D-optimal at
the true parameter point (in the class of all designs).",2307.02086v1
2023-08-02,A Model Predictive Approach for Enhancing Transient Stability of Grid-Forming Converters,"A model predictive control (MPC) method for enhancing post-fault transient
stability of a grid-forming (GFM) inverter based resources (IBRs) is developed
in this paper. This proposed controller is activated as soon as the converter
enters into the post-fault current-saturation mode. It aims at mitigating the
instability arising from insufficient deceleration due to current saturation
and thus improving the transient stability of a GFM-IBR. The MPC approach
optimises the post-fault trajectory of GFM IBRs by introducing appropriate
corrective phase angle jumps and active power references where the post-fault
dynamics of GFM IBRs are addressed. These two signals provide controllability
over GFM IBR's post-fault trajectory. This paper addresses the mitigation of
oscillations between current-saturation mode and normal mode by forced
saturation if conditions for remaining in the normal mode do not hold. The
performance of the proposal is tested via dynamic simulations under various
grid conditions and compared with other existing strategies. The results
demonstrate significant improvement in transient stability.",2308.01020v2
2023-08-22,High Dynamic Range Imaging of Dynamic Scenes with Saturation Compensation but without Explicit Motion Compensation,"High dynamic range (HDR) imaging is a highly challenging task since a large
amount of information is lost due to the limitations of camera sensors. For HDR
imaging, some methods capture multiple low dynamic range (LDR) images with
altering exposures to aggregate more information. However, these approaches
introduce ghosting artifacts when significant inter-frame motions are present.
Moreover, although multi-exposure images are given, we have little information
in severely over-exposed areas. Most existing methods focus on motion
compensation, i.e., alignment of multiple LDR shots to reduce the ghosting
artifacts, but they still produce unsatisfying results. These methods also
rather overlook the need to restore the saturated areas. In this paper, we
generate well-aligned multi-exposure features by reformulating a motion
alignment problem into a simple brightness adjustment problem. In addition, we
propose a coarse-to-fine merging strategy with explicit saturation
compensation. The saturated areas are reconstructed with similar well-exposed
content using adaptive contextual attention. We demonstrate that our method
outperforms the state-of-the-art methods regarding qualitative and quantitative
evaluations.",2308.11140v1
2023-11-20,Novel Cross Section Ratios as Possible Signals of Saturation in UPCs,"We propose new cross section ratios in ultra-peripheral A$+$A and $p+$A
collisions (UPCs) as a potential experimental signal of saturation physics. We
consider the ratio $R_1$ of elastic vector meson photoproduction cross section
to the inclusive hadron or jet photoproduction cross section. The ratio can be
measured in the $\gamma +$A and $\gamma + p$ collisions taking place in the
UPCs. We label the ratios $R_1 ({\rm A})$ and $R_1 (p)$, respectively.
Constructing the double ratio $R_{\rm{UPC}} ({\rm A}) = R_1 ({\rm A})/R_1 (p)$,
and performing a small-$x$ calculation both in the quasi-classical
approximation and by including small-$x$ evolution, we observe that
$R_{\rm{UPC}} ({\rm A})$ exhibits a markedly different dependence on the
nuclear atomic number inside and outside the saturation region. This result
indicates that $R_{\rm{UPC}} ({\rm A})$ and $R_1 ({\rm A})$ measurements in
UPCs may help in the experimental searches for the evidence of saturation
physics.",2311.12208v1
2023-12-25,A variational principle for the Bowen metric mean dimension of saturated set,"This paper investigates a variational principle for the Bowen metric mean
dimension of saturated sets $G_K$, where $K$ is a compact connected subset of
the convex combination of finite invariant measures for the systems with
g-almost product property. In fact, we prove the variational principle of a
saturated set with more information, that is $G_K\cap \{x\in X: C_f(X) \subset
\omega_f(x)\}$, which reveals that the limit point set of a saturated set
contains all structure of the orbits. As an application, we obtain a more
general version of multifractal analysis, which is derived independently and
can imply partial results of Backes and Rodrigues (2023 IEEE Trans. Inform.
Theory. 69 5485-5496).",2312.15647v2
2024-01-06,Reflections on Inductive Thematic Saturation as a potential metric for measuring the validity of an inductive Thematic Analysis with LLMs,"This paper presents a set of reflections on saturation and the use of Large
Language Models (LLMs) for performing Thematic Analysis (TA). The paper
suggests that initial thematic saturation (ITS) could be used as a metric to
assess part of the transactional validity of TA with LLM, focusing on the
initial coding. The paper presents the initial coding of two datasets of
different sizes, and it reflects on how the LLM reaches some form of analytical
saturation during the coding. The procedure proposed in this work leads to the
creation of two codebooks, one comprising the total cumulative initial codes
and the other the total unique codes. The paper proposes a metric to
synthetically measure ITS using a simple mathematical calculation employing the
ratio between slopes of cumulative codes and unique codes. The paper
contributes to the initial body of work exploring how to perform qualitative
analysis with LLMs.",2401.03239v1
2024-02-11,Quantum geometric bound for saturated ferromagnetism,"Despite its abundance in nature, predicting the occurrence of ferromagnetism
in the ground state is possible only under very limited conditions such as in a
flat band system with repulsive interaction or in a band with a single hole
under infinitely large Coulomb repulsion, etc. Here, we propose a general
condition to achieve saturated ferromagnetism based on the quantum geometry of
electronic wave functions in itinerant electron systems. By analyzing
multi-band repulsive Hubbard models with an integer band filling, relevant to
either ferromagnetic insulators or semimetals, we propose a rigorous quantum
geometric upper bound on the spin stiffness. By employing this geometric bound,
we establish that saturated ferromagnetism is prohibited in the absence of
interband coupling, even when the local Hubbard repulsion is infinitely large.
As a corollary, this shows that saturated ferromagnetism is forbidden in any
half-filled Hubbard model. We also derive the condition that the upper bound of
the spin stiffness can be completely characterized by the Abelian quantum
metric. We believe that our findings reveal a profound connection between
quantum geometry and ferromagnetism, which can be extended to various
symmetry-broken ground states in itinerant electronic systems.",2402.07171v1
2024-02-20,Inference on LATEs with covariates,"In theory, two-stage least squares (TSLS) identifies a weighted average of
covariate-specific local average treatment effects (LATEs) from a saturated
specification without making parametric assumptions on how available covariates
enter the model. In practice, TSLS is severely biased when saturation leads to
a number of control dummies that is of the same order of magnitude as the
sample size, and the use of many, arguably weak, instruments. This paper
derives asymptotically valid tests and confidence intervals for an estimand
that identifies the weighted average of LATEs targeted by saturated TSLS, even
when the number of control dummies and instrument interactions is large. The
proposed inference procedure is robust against four key features of saturated
economic data: treatment effect heterogeneity, covariates with rich support,
weak identification strength, and conditional heteroskedasticity.",2402.12607v1
2024-03-04,Saturated Partial Embeddings of Planar Graphs,"In this work, we study how far one can deviate from optimal behavior when
embedding a planar graph. For a planar graph $G$, we say that a plane subgraph
$H\subseteq G$ is a \textit{plane-saturated subgraph} if adding any edge
(possibly with new vertices) to $H$ would either violate planarity or make the
resulting graph no longer a subgraph of $G$. For a planar graph $G$, we define
the \textit{plane-saturation ratio}, $\psr(G)$, as the minimum value of
$\frac{e(H)}{e(G)}$ for a plane-saturated subgraph $H$ of $G$ and investigate
how small $\psr(G)$ can be. While there exist planar graphs where $\psr(G)$ is
arbitrarily close to $0$, we show that for all twin-free planar graphs,
$\psr(G)>1/16$, and that there exist twin-free planar graphs where $\psr(G)$ is
arbitrarily close to $1/16$. In fact, we study a broader category of planar
graphs, focusing on classes characterized by a bounded number of degree $1$ and
degree $2$ twin vertices. We offer solutions for some instances of bounds while
positing conjectures for the remaining ones.",2403.02458v1
2024-03-06,Saturating Sorting without Sorts,"We present a first-order theorem proving framework for establishing the
correctness of functional programs implementing sorting algorithms with
recursive data structures.
  We formalize the semantics of recursive programs in many-sorted first-order
logic and integrate sortedness/permutation properties within our first-order
formalization. Rather than focusing on sorting lists of elements of specific
first-order theories, such as integer arithmetic, our list formalization relies
on a sort parameter abstracting (arithmetic) theories and hence concrete sorts.
We formalize the permutation property of lists in first-order logic so that we
automatically prove verification conditions of such algorithms purely by
superpositon-based first-order reasoning. Doing so, we adjust recent efforts
for automating inducion in saturation. We advocate a compositional approach for
automating proofs by induction required to verify functional programs
implementing and preserving sorting and permutation properties over
parameterized list structures. Our work turns saturation-based first-order
theorem proving into an automated verification engine by (i) guiding automated
inductive reasoning with manual proof splits and (ii) fully automating
inductive reasoning in saturation. We showcase the applicability of our
framework over recursive sorting algorithms, including Mergesort and Quicksort.",2403.03712v1
2024-03-30,Saturation effect in confined quantum systems with energy-dependent potentials,"In this paper, we study the saturation effect in the energy or mass spectra
of three quantum models with energy-dependent potentials: the harmonic
oscillator, the hydrogen atom, and the heavy quarkonia. We used the method
proposed in \cite{garcia2009exactly}, which is based on studying various
canonical point and gauge transformations applied to a function, $g(x)$,
multiplied by a given differential equation of known solutions as special
orthogonal functions, that convert it into a Schr{{\""o}}dinger-like equation.
The first two models stem from implementing the method on the confluent
hypergeometric differential of the well-known solutions ${}_1 F_1$, while the
third model (heavy quarkonia) stems possibly from the hypergeometric
differential of the well-known solutions ${}_2 F_1$. In particular, the heavy
quarkonia mass spectra for both $c\bar c$ and $b\bar b$ are produced at
different values of the saturation parameter $\lambda$ and compared with the
available experimental data. It is found that these systems may exhibit
saturation effect when the energy-dependent effect is included.",2404.00302v1
2002-12-11,Lectures on Diffraction and Saturation of Nuclear Partons in DIS off Heavy Nuclei,"The Lorentz contraction of ultrarelativistic nuclei entails a spatial overlap
and fusion (recombination, saturation) of partons belonging to different
nucleons at the same impact parameter. In these lectures we present a
consistent description of the fusion of partons in terms of nuclear attenuation
of color dipole states of the photon and collective Weizs\""acker-Williams (WW)
gluon structure function of a nucleus. The point that all observables for DIS
off nuclei are uniquely calculable in terms of the nuclear WW glue amounts to a
new form of factorization in the saturation regime.
  We start with the theory of multichannel propagation of color dipoles in a
nuclear medium including the color-singlet to color-octet to color-octet
transitions. We show how the Glauber-Gribov formulas are recovered from the
multichannel formalism. Then we derive the two-plateau momentum distribution of
final state (FS) quarks produced in deep inelastic scattering (DIS) off nuclei
in the saturation regime. Then we comment on the signatures of saturation in
exclusive diffractive DIS. A large body of these lectures is on the recent
theory of jet-jet inclusive cross sections. We show that for hard dijets the
decorrelation momentum is of the order of the nuclear saturation momentum
$Q_A$. For minijets with the transverse momentum below the saturation scale we
predict a complete disappearance of the azimuthal jet-jet correlation. We
conclude with comment on a possible relevance of the decorrelation of jets to
the experimental data from the STAR-RHIC Collaboration.",0212161v2
2016-12-07,"Field emission: the theoretical link between voltage loss, reduction in field enhancement factor, and Fowler-Nordheim-plot saturation","With a large-area field electron emitter, when an individual post-like
emitter is sufficiently resistive, and current through it sufficiently large,
then voltage loss occurs along it. This Letter provides a simple analytical and
conceptual demonstration that this voltage loss is directly and inextricably
linked to a reduction in the field enhancement factor (FEF) at the post apex. A
formula relating apex-FEF reduction to this voltage loss was obtained in the
paper by E. Minoux, O. Groening, K. B. K. Teo, S. H. Dalal, L. Gangloff, J.-P.
Schnell, L. Hudanski, I. Y. Y. Bu., P. Vincent, P. Legagneux, G. A. J.
Amaratunga, and W. I. Milne [Nano Lett. 5, 2135 (2005)], by fitting to
numerical results from a Laplace solver. This Letter derives the same formula
analytically, by using a ""floating sphere"" model. The analytical proof brings
out the underlying physics more clearly, and shows that the effect is a general
phenomenon, related to reduction in the magnitude of the surface charge in the
most protruding parts of an emitter. Voltage-dependent FEF-reduction is one
cause of ""saturation"" in Fowler-Nordheim plots. Another is a voltage-divider
effect, due to measurement-circuit resistance. An integrated theory of both
effects is presented. Both together, or either by itself, can cause saturation.
Experimentally, if saturation occurs but voltage loss is small (< 20 V, say),
then saturation is more probably due to FEF-reduction than voltage division. In
this case, existing treatments of electrostatic interaction (""shielding"")
between closely spaced emitters may need modification. Other putative causes of
saturation exist, so the present theory is a partial story. Its extension seems
possible, and could lead to a more general physical understanding of the causes
of FN-plot saturation.",1612.02187v2
2019-10-18,Does carrier velocity saturation help to enhance fmax in graphene field-effect transistors?,"It has been argued that current saturation in graphene field-effect
transistors (GFETs) is needed to get the highest possible maximum oscillation
frequency (fmax). This paper numerically investigates whether velocity
saturation can help to get better current saturation and if that correlates
with enhanced fmax. For such a purpose, we used a drift-diffusion simulator
that includes several factors that influence output conductance, especially at
short channel lengths and-or large drain bias: short-channel electrostatics,
saturation velocity, graphene-dielectric interface traps, and self-heating
effects. As a testbed for our investigation, we analyzed fabricated GFETs with
high extrinsin cutoff frequency fT,x (34 GHz) and fmax (37 GHz). Our
simulations allow for a microscopic (local) analysis of the channel parameteres
such as carrier concentration, drift and saturation velocities. For biases far
away from the Dirac voltage, where the channel behaves as unipolar, we
confirmed that the higher is the drift velocity, as close as possible to the
saturation velocity, the greater fmax is. However, the largest fmax is recorded
at biases near the crossover between unipolar and bipolar behavior, where it
does not hold that the highest drift velocity maximizes fmax. In fact, the
position and magnitude of the largest fmax depend on the complex interplay
between the carrier concentration and total velocity which, in turn, are
impacted by the self-heating. Importantly, this effect was found to severely
limit radio-frequency performance, reducing the maximum fmax from around 60 to
40 GHz.",1910.08304v1
2020-12-15,Saturation effects in SIDIS at very forward rapidities,"Using the dipole picture for electron-nucleus deep inelastic scattering at
small Bjorken $x$, we study the effects of gluon saturation in the nuclear
target on the cross-section for SIDIS (single inclusive hadron, or jet,
production). We argue that the sensitivity of this process to gluon saturation
can be enhanced by tagging on a hadron (or jet) which carries a large fraction
$z \simeq 1$ of the longitudinal momentum of the virtual photon. This opens the
possibility to study gluon saturation in relatively hard processes, where the
virtuality $Q^2$ is (much) larger than the target saturation momentum $Q_s^2$,
but such that $z(1-z)Q^2\lesssim Q_s^2$. Working in the limit $z(1-z)Q^2\ll
Q_s^2$, we predict new phenomena which would signal saturation in the SIDIS
cross-section. For sufficiently low transverse momenta $k_\perp\ll Q_s$ of the
produced particle, the dominant contribution comes from elastic scattering in
the black disk limit, which exposes the unintegrated quark distribution in the
virtual photon. For larger momenta $k_\perp\gtrsim Q_s$, inelastic collisions
take the leading role. They explore gluon saturation via multiple scattering,
leading to a Gaussian distribution in $k_\perp$ centred around $Q_s$. When
$z(1-z)Q^2\ll Q^2$, this results in a Cronin peak in the nuclear modification
factor (the $R_{pA}$ ratio) at moderate values of $x$. With decreasing $x$,
this peak is washed out by the high-energy evolution and replaced by nuclear
suppression ($R_{pA}<1$) up to large momenta $k_\perp\gg Q_s$. Still for
$z(1-z)Q^2\ll Q_s^2$, we also compute SIDIS cross-sections integrated over
$k_\perp$. We find that both elastic and inelastic scattering are controlled by
the black disk limit, so they yield similar contributions, of zeroth order in
the QCD coupling.",2012.08562v2
2000-07-12,X-ray Emission From Nearby M-dwarfs: the Super-saturation Phenomenon,"A rotation rate and X-ray luminosity analysis is presented for rapidly
rotating single and binary M-dwarf systems. X-ray luminosities for the majority
of both single & binary M-dwarf systems with periods below $\simeq 5-6$ days
(equatorial velocities, V$_{eq}>$ 6 km~s$^{-1}$) are consistent with the
current rotation-activity paradigm, and appear to saturate at about $10^{-3}$
of the stellar bolometric luminosity. The single M-dwarf data show tentative
evidence for the super-saturation phenomenon observed in some ultra-fast
rotating ($>$ 100 km~s$^{-1}$) G & K-dwarfs in the IC 2391, IC 2602 and Alpha
Persei clusters. The IC 2391 M star VXR60b is the least X-ray active and most
rapidly rotating of the short period (P$_{rot}<$ 2 days) stars considered
herein, with a period of 0.212 days and an X-ray activity level about 1.5 sigma
below the mean X-ray emission level for most of the single M-dwarf sample. For
this star, and possibly one other, we cautiously believe that we have
identified the first evidence of super-saturation in M-dwarfs. If we are wrong,
we demonstrate that only M-dwarfs rotating close to their break up velocities
are likely to exhibit the super-saturation effect at X-ray wavelengths.",0007159v1
2006-06-26,Identification of New M Dwarfs in the Solar Neighborhood,"We present the results from a spectroscopic study of 1080 nearby active M
dwarfs, selected by correlating the 2MASS and ROSAT catalogs. We have derived
the spectral types and estimated distances for all of our stars. The spectral
types range between K5 and M6. Nearly half of our stars lie within 50 pc. We
have measured the equivalent width of the H alpha emission line. Our targets
show an increase in chromospheric activity from early to mid-spectral types,
with a peak in activity around M5. Using the count rate and hardness ratios
obtained from the ROSAT catalog, we have derived the X-ray luminosities. Our
stars display a ""saturation-type"" relation between the chromospheric and
coronal activity. The relation is such that log (Lx/Lbol) remains ""saturated""
at a value of about -3 for varying H alpha equivalent width. We have found 568
matches in the USNO-B catalog, and have derived the tangential velocities for
these stars. There is a slight trend of decreasing chromospheric activity with
age, such that the stars with higher Vtan have lower H alpha equivalent widths.
The coronal emission, however, remains saturated at a value of log (Lx/Lbol) -3
for varying tangential velocities, suggesting that the coronal activity remains
saturated with age. We do not find any break in the saturation-type relation at
the spectral type where stars become fully convective (~M3.5). Most of the
stars in our sample show more coronal emission than the dMe stars in the Hyades
and Praesepe clusters, and have Vtan< 40km/s, suggesting a young population.",0606617v1
2002-04-24,Perturbative Saturation and the Soft Pomeron,"We show that perturbation theory provides two distinct mechanisms for the
power like growth of hadronic cross sections at high energy. One, the leading
BFKL effect is due to the growth of the parton density, and is characterized by
the leading BFKL exponent. The other mechanism is due to the infrared
diffusion, or the long range nature of the Coulomb field of perturbatively
massless gluons. When perturbative saturation effects are taken into account,
the first mechanism is rendered ineffective but the second one persists. We
suggest that these two distinct mechanisms are responsible for the appearance
of two pomerons. The density growth effects are responsible for the hard
pomeron and manifest themselves in small systems (e.g. gamma^* or small size
fluctuations in the proton wave function) where saturation effects are not
important. The soft pomeron is the manifestation of the exponential growth of
the black saturated regions which appear in typical hadronic systems. We point
out that the nonlinear generalization of the BFKL equation which takes into
account wave function saturation effects (""pomeron loops"") provides a well
defined perturbative framework for the calculation of the soft pomeron
intercept. The conjecture of a perturbative soft pomeron is consistent with
picturing the proton as a loosely bound system of several small black regions
corresponding e.g. to constituent quarks of size about 0.3 fm. Phenomenological
implications of this picture are compatible with the main qualitative features
of data on p-p scattering.",0204277v1
2006-08-04,Saturation physics at HERA and RHIC: An unified description,"One of the frontiers of QCD which are intensely investigated in high energy
experiments is the high energy (small $x$) regime, where we expect to observe
the non-linear behavior of the theory. In this regime, the growth of the parton
distribution should saturate, forming a Color Glass Condensate (CGC). In fact,
signals of parton saturation have already been observed both in $ep$ deep
inelastic scattering at HERA and in deuteron-gold collisions at RHIC.
Currently, the description of the experimental data of these experiments is
possible considering different phenomenological saturation models for the two
processes within the CGC formalism. In this letter we analyze the universality
of these dipole cross section parameterizations and verify that they are not
able to describe the HERA and RHIC data simultaneously. We analyze possible
improvements in the parameterizations and propose a new parametrization for the
forward dipole amplitude which allows us to describe quite well the small-$x$
$ep$ HERA data on $F_2$ structure function as well as the $dAu$ RHIC data on
charged hadron spectra. It is an important signature of the universality of the
saturation physics.",0608063v2
2006-03-04,A generalization of the integer linear infeasibility problem,"Does a given system of linear equations with nonnegative constraints have an
integer solution? This is a fundamental question in many areas. In statistics
this problem arises in data security problems for contingency table data and
also is closely related to non-squarefree elements of Markov bases for sampling
contingency tables with given marginals. To study a family of systems with no
integer solution, we focus on a commutative semigroup generated by a finite
subset of $\Z^d$ and its saturation. An element in the difference of the
semigroup and its saturation is called a ``hole''. We show the necessary and
sufficient conditions for the finiteness of the set of holes. Also we define
fundamental holes and saturation points of a commutative semigroup. Then, we
show the simultaneous finiteness of the set of holes, the set of non-saturation
points, and the set of generators for saturation points. We apply our results
to some three- and four-way contingency tables. Then we will discuss the time
complexities of our algorithms.",0603108v5
1996-12-02,Nuclear Matter Studies with Density-dependent Meson-Nucleon Coupling Constants,"Due to the internal structure of the nucleon, we should expect, in general,
that the effective meson nucleon parameters may change in nuclear medium. We
study such changes by using a chiral confining model of the nucleon. We use
density-dependent masses for all mesons except the pion. Within a
Dirac-Brueckner analysis, based on the relativistic covariant structure of the
NN amplitude, we show that the effect of such a density dependence in the NN
interaction on the saturation properties of nuclear matter, while not large, is
quite significant. Due to the density dependence of the $g_{\sigma NN}$, as
predicted by the chiral confining model, we find, in particular, a looping
behavior of the binding energy at saturation as a function of the saturation
density. A simple model is described, which exhibits looping and which is shown
to be mainly caused by the presence of a peak in the density dependence of the
medium modified $\sigma N$ coupling constant at low density.
  The effect of density dependence of the coupling constants and the meson
masses tends to improve the results for $E/A$ and density of nuclear matter at
saturation. From the present study we see that the relationship between binding
energy and saturation density may not be as universal as found in
nonrelativistic studies and that more model dependence is exhibited once medium
modifications of the basic nuclear interactions are considered.",9612007v2
2008-01-04,Single-contact pressure solution creep on calcite monocrystals,"Pressure solution creep rates and interface structures have been measured by
two methods on calcite single crystals. In the first kind of experiments,
calcite monocrystals were indented at 40 degrees C for six weeks using ceramic
indenters under stresses in the 50-200 MPa range in a saturated solution of
calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation
(depth of the hole below the indenter) is measured ex-situ at the end of the
experiment. In the second type of experiment, calcite monocrystals were
indented by spherical glass indenters for 200 hours under stresses in the 0-100
MPa range at room temperature in a saturated aqueous solution of calcite. The
displacement of the indenter was continuously recorded using a specially
constructed differential dilatometer. The experiments conducted in a
calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate
owing to the fairly high solubility of calcite in this solution. In contrast,
the experiments conducted in a calcite-saturated aqueous solution show moderate
indentation rate and the dry control experiments did not show any measurable
deformation. The rate of calcite indentation is found to be inversely
proportional to the indenter diameter, thus indicating that the process is
diffusion-controlled. The microcracks in the dissolution region under the
indenter dramatically enhance the rate of calcite indentation by a significant
reduction of the distance of solute transport in the trapped fluid phase. This
result indicates that care should be taken in extrapolating the kinetic data of
pressure solution creep from one mineral to another.",0801.0725v1
2008-02-15,New Implementation Framework for Saturation-Based Reasoning,"The saturation-based reasoning methods are among the most theoretically
developed ones and are used by most of the state-of-the-art first-order logic
reasoners. In the last decade there was a sharp increase in performance of such
systems, which I attribute to the use of advanced calculi and the intensified
research in implementation techniques. However, nowadays we are witnessing a
slowdown in performance progress, which may be considered as a sign that the
saturation-based technology is reaching its inherent limits. The position I am
trying to put forward in this paper is that such scepticism is premature and a
sharp improvement in performance may potentially be reached by adopting new
architectural principles for saturation. The top-level algorithms and
corresponding designs used in the state-of-the-art saturation-based theorem
provers have (at least) two inherent drawbacks: the insufficient flexibility of
the used inference selection mechanisms and the lack of means for intelligent
prioritising of search directions. In this position paper I analyse these
drawbacks and present two ideas on how they could be overcome. In particular, I
propose a flexible low-cost high-precision mechanism for inference selection,
intended to overcome problems associated with the currently used instances of
clause selection-based procedures. I also outline a method for intelligent
prioritising of search directions, based on probing the search space by
exploring generalised search directions. I discuss some technical issues
related to implementation of the proposed architectural principles and outline
possible solutions.",0802.2127v1
2008-05-08,Could saturation effects be visible in a future electron-ion collider?,"We expect to observe parton saturation in a future electron - ion collider.
In this letter we discuss this expectation in more detail considering two
different models which are in good agreement with the existing experimental
data on nuclear structure functions. In particular, we study the predictions of
saturation effects in electron - ion collisions at high energies, using a
generalization for nuclear targets of the b-CGC model, which describes the $ep$
HERA quite well. We estimate the total, longitudinal and charm structure
functions in the dipole picture and compare them with the predictions obtained
using collinear factorization and modern sets of nuclear parton distributions.
Our results show that inclusive observables are not very useful in the search
for saturation effects. In the small $x$ region they are very difficult to
disentangle from the predictions of the collinear approaches . This happens
mainly because of the large uncertainties in the latter. On the other hand, our
results indicate that the contribution of diffractive processes to the total
cross section is about 20 % at large A and small Q^2, allowing for a detailed
study of diffractive observables. The study of diffractive processes becomes
essential to observe parton saturation.",0805.1255v1
2009-04-16,Bounds on M/R for static objects with a positive cosmological constant,"We consider spherically symmetric static solutions of the Einstein equations
with a positive cosmological constant $\Lambda,$ which are regular at the
centre, and we investigate the influence of $\Lambda$ on the bound of M/R,
where M is the ADM mass and R is the area radius of the boundary of the static
object. We find that for any solution which satisfies the energy condition
$p+2p_{\perp}\leq\rho,$ where $p\geq 0$ and $p_{\perp}$ are the radial and
tangential pressures respectively, and $\rho\geq 0$ is the energy density, and
for which $0\leq \Lambda R^2\leq 1,$ the inequality
  \frac{M}{R}\leq\frac29-\frac{\Lambda R^2}{3}+\frac29 \sqrt{1+3\Lambda R^2},
holds. If $\Lambda=0$ it is known that infinitely thin shell solutions uniquely
saturate the inequality, i.e. the inequality is sharp in that case. The
situation is quite different if $\Lambda>0.$ Indeed, we show that infinitely
thin shell solutions do not generally saturate the inequality except in the two
degenerate situations $\Lambda R^2=0$ and $\Lambda R^2=1$. In the latter
situation there is also a constant density solution, where the exterior
spacetime is the Nariai solution, which saturates the inequality, hence, the
saturating solution is non-unique. In this case the cosmological horizon and
the black hole horizon coincide. This is analogous to the charged situation
where there is numerical evidence that uniqueness of the saturating solution is
lost when the inner and outer horizons of the Reissner-Nordstr\""{o}m solution
coincide.",0904.2497v3
2010-08-25,Heavy quarkonium production: Nontrivial transition from pA to AA collisions,"Two novel QCD effects, double color filtering and mutual boosting of the
saturation scales in colliding nuclei, affect the transparency of the nuclei
for quark dipoles in comparison with proton-nucleus collisions. The former
effect increases the survival probability of the dipoles, since color filtering
in one nucleus makes the other one more transparent. The second effect acts in
the opposite direction and is stronger, it makes the colliding nuclei more
opaque than in the case of pA collisions. As a result of parton saturation in
nuclei the effective scale is shifted upwards, what leads to an increase of the
gluon density at small x. This in turn leads to a stronger transverse momentum
broadening in AA compared with pA collisions, i.e. to an additional growth of
the saturation momentum. Such a mutual boosting leads to a system of
reciprocity equations, which result in a saturation scale, a few times higher
in AA than in pA collisions at the energies of LHC. Since the dipole cross
section is proportional to the saturation momentum squared, the nuclei become
much more opaque for dipoles in AA than in pA collisions. For the same reason
gluon shadowing turns out to be boosted to a larger magnitude compared with the
product of the gluon shadowing factors in each of the colliding nuclei. All
these effects make it more difficult to establish a baseline for anomalous
J/Psi suppression in heavy ion collisions at high energies.",1008.4272v2
2011-08-31,Two-dimensional Moist Stratified Turbulence and the Emergence of Vertically Sheared Horizontal Flows,"Moist stratified turbulence is studied in a two-dimensional Boussinesq system
influenced by condensation and evaporation. The problem is set in a periodic
domain and employs simple evaporation and condensation schemes, wherein both
the processes push parcels towards saturation. Numerical simulations
demonstrate the emergence of a moist turbulent state consisting of ordered
structures with a clear power-law type spectral scaling from initially
spatially uncorrelated conditions. An asymptotic analysis in the limit of rapid
condensation and strong stratification shows that, for initial conditions with
enough water substance to saturate the domain, the equations support a
straightforward state of moist balance characterized by a hydrostatic,
saturated, vertically sheared horizontal flow (VSHF). For such initial
conditions, by means of long time numerical simulations, the emergence of moist
balance is verified. Specifically, starting from uncorrelated data, subsequent
to the development of a moist turbulent state, the system experiences a rather
abrupt transition to a regime which is close to saturation and dominated by a
strong VSHF. On the other hand, initial conditions which do not have enough
water substance to saturate the domain, do not attain moist balance. Rather,
the system remains in a turbulent state and oscillates about moist balance.
Even though balance is not achieved with these general initial conditions, the
time scale of oscillation about moist balance is much larger than the imposed
time scale of condensation and evaporation, thus indicating a distinct dominant
slow component in the moist stratified two-dimensional turbulent system.",1108.6192v1
2012-04-06,Constructing regular ultrafilters from a model-theoretic point of view,"This paper contributes to the set-theoretic side of understanding Keisler's
order. We consider properties of ultrafilters which affect saturation of
unstable theories: the lower cofinality $\lcf(\aleph_0, \de)$ of $\aleph_0$
modulo $\de$, saturation of the minimum unstable theory (the random graph),
flexibility, goodness, goodness for equality, and realization of symmetric
cuts. We work in ZFC except when noted, as several constructions appeal to
complete ultrafilters thus assume a measurable cardinal. The main results are
as follows. First, we investigate the strength of flexibility, detected by
non-low theories. Assuming $\kappa > \aleph_0$ is measurable, we construct a
regular ultrafilter on $\lambda \geq 2^\kappa$ which is flexible (thus: ok) but
not good, and which moreover has large $\lcf(\aleph_0)$ but does not even
saturate models of the random graph. We prove that there is a loss of
saturation in regular ultrapowers of unstable theories, and give a new proof
that there is a loss of saturation in ultrapowers of non-simple theories.
Finally, we investigate realization and omission of symmetric cuts, significant
both because of the maximality of the strict order property in Keisler's order,
and by recent work of the authors on $SOP_2$. We prove that for any $n <
\omega$, assuming the existence of $n$ measurable cardinals below $\lambda$,
there is a regular ultrafilter $D$ on $\lambda$ such that any $D$-ultrapower of
a model of linear order will have $n$ alternations of cuts, as defined below.
Moreover, $D$ will $\lambda^+$-saturate all stable theories but will not
$(2^{\kappa})^+$-saturate any unstable theory, where $\kappa$ is the smallest
measurable cardinal used in the construction.",1204.1481v1
2012-06-24,Saturation Levels for White-light Flares of Flare Stars: Variation of Minimum Flare Duration for Saturation,"Taking into account results obtained from models and from statistical
analyses of obtained parameters, we discuss flare activity levels and flare
characteristics of five UV Ceti stars. We present the parameters of unpublished
flares detected over two years of observations of V1005 Ori. We compare
parameters of the U-band flares detected over several seasons of observations
of AD Leo, EV Lac, EQ Peg, V1054 Oph, and V1005 Ori. Flare frequencies
calculated for all program stars and maximum energy levels of the flares are
compared, and we consider which is the most correct parameter as an indicator
of flare activity levels. Using the One Phase Exponential Association function,
the distributions of flare equivalent duration versus flare total duration are
modeled for each program star. We use the Independent Samples t-Test in the
statistical analyses of the parameters obtained from the models. The results
reveal some properties of flare processes occurring on the surfaces of UV Ceti
type stars. (1) Flare energies cannot be higher than a specific value
regardless of the length of the flare total duration. This must be a saturation
level for white-light flares occurring in flare processes observed in the U
band. Thus, for the first time it is shown that white-light flares have a
saturation in a specific energy range. (2) The span values, which are the
difference between the equivalent durations of flares with the shortest and
longest total durations, are almost equal for each star. (3) The half-life
values, minimum flare durations for saturation, increase toward the later
spectral types.",1206.5793v1
2012-08-10,A Dividing Line Within Simple Unstable Theories,"We give the first (ZFC) dividing line in Keisler's order among the unstable
theories, specifically among the simple unstable theories. That is, for any
infinite cardinal $\lambda$ for which there is $\mu < \lambda \leq 2^\mu$, we
construct a regular ultrafilter D on $\lambda$ such that (i) for any model $M$
of a stable theory or of the random graph, $M^\lambda/D$ is
$\lambda^+$-saturated but (ii) if $Th(N)$ is not simple or not low then
$N^\lambda/D$ is not $\lambda^+$-saturated. The non-saturation result relies on
the notion of flexible ultrafilters. To prove the saturation result we develop
a property of a class of simple theories, called Qr1, generalizing the fact
that whenever $B$ is a set of parameters in some sufficiently saturated model
of the random graph, $|B| = \lambda$ and $\mu < \lambda \leq 2^\mu$, then there
is a set $A$ with $|A| = \mu$ such that any non-algebraic $p \in S(B)$ is
finitely realized in $A$. In addition to giving information about simple
unstable theories, our proof reframes the problem of saturation of ultrapowers
in several key ways. We give a new characterization of good filters in terms of
""excellence,"" a measure of the accuracy of the quotient Boolean algebra. We
introduce and develop the notion of {moral} ultrafilters on Boolean algebras.
We prove a so-called ""separation of variables"" result which shows how the
problem of constructing ultrafilters to have a precise degree of saturation may
be profitably separated into a more set-theoretic stage, building an excellent
filter, followed by a more model-theoretic stage: building moral ultrafilters
on the quotient Boolean algebra, a process which highlights the complexity of
certain patterns, arising from first-order formulas, in certain Boolean
algebras.",1208.2140v1
2012-11-02,Multiplicities and $p_T$ spectra in ultrarelativistic heavy ion collisions from a next-to-leading order improved perturbative QCD + saturation + hydrodynamics model,"We bring the EKRT framework, which combines perturbative QCD (pQCD) minijet
production with gluon saturation and hydrodynamics, to next-to-leading order
(NLO) in pQCD as rigorously as possible. We chart the model uncertainties, and
study the viability and predictive power of the model in the light of the RHIC
and LHC measurements in central $A+A$ collisions. In particular, we introduce a
new set of measurement functions to define the infrared- and collinear-safe
minijet transverse energy, $E_T$, in terms of which we formulate the
saturation. We update the framework with the EPS09 NLO nuclear parton
distributions (nPDFs), and study the propagation of the nPDF uncertainties into
the computed $E_T$, saturation scales and the final-state multiplicities. The
key parameters, which need to be fixed using the measurements, are identified,
and their correlation is discussed. We convert the saturated minijet $E_T$ into
QCD-matter initial conditions for longitudinally boost-invariant ideal
hydrodynamics. We compute the charged-particle multiplicities and identified
bulk hadron $p_T$ spectra in 5% most central Au+Au collisions at RHIC and Pb+Pb
at the LHC. We obtain an encouragingly good agreement with the experimental
data, simultaneously at RHIC and LHC, showing that the approach has a definite
predictive power.",1211.0461v1
2012-12-12,Analysis of combined HERA data in the Impact-Parameter dependent Saturation model,"The Impact-Parameter dependent Saturation Model (IP-Sat) is a simple dipole
model that incorporates key features of the physics of gluon saturation and
matches smoothly to the perturbative QCD dipole expression at large Q^2 for a
given x. It was previously shown that the model gives a good description of
HERA data suggesting evidence for gluon saturation effects at small x. The
model has also been applied to proton-proton and proton-nucleus collisions and
provides the basis for the IP-Glasma model of initial conditions in heavy ion
collisions. Here we present a reanalysis of available data in electron-proton
collisions at small Bjorken-x, including the recently released combined data
from the ZEUS and H1 collaborations. We first confront the model to the high
precision combined data for the reduced cross-section and obtain its
parameters. With these parameters fixed, we compare model results to data for
the structure function F_2, the longitudinal structure function F_L, the charm
structure function F_2^{c\bar{c}}, exclusive vector meson (J/\psi, \phi and
\rho) production and Deeply Virtual Compton Scattering (DVCS). Excellent
agreement is obtained for the processes considered at small x in a wide range
of Q^2. Our results strongly hint at universality of the IP-Sat dipole
amplitude and the extracted impact-parameter distribution of the proton. They
also provide a benchmark for further refinements in studies of QCD saturation
at colliders.",1212.2974v1
2013-01-04,On the role of electron-nucleus contact and microwave saturation in Thermal Mixing DNP,"We have explored the manifold physical scenario emerging from a model of
Dynamic Nuclear Polarization (DNP) via thermal mixing under the hypothesis of
highly effective electron-electron interaction. When the electron and nuclear
reservoirs are also assumed to be in strong thermal contact and the microwave
irradiation saturates the target electron transition, the enhancement of the
nuclear polarization is expected to be considerably high even if the
irradiation frequency is set far away from the centre of the ESR line (as
already observed by Borghini) and the typical polarization time is reduced on
moving towards the boundaries of said line. More reasonable behaviours are
obtained by reducing the level of microwave saturation or the contact between
electrons and nuclei in presence of nuclear leakage. In both cases the function
describing the dependency of the steady state nuclear polarization on the
frequency of irradiation becomes sharper at the edges and the build up rate
decreases on moving off-resonance. If qualitatively similar in terms of the
effects produced on nuclear polarization, the degree of microwave saturation
and of electron-nucleus contact has a totally different impact on electron
polarization, which is of course strongly correlated to the effectiveness of
saturation and almost insensitive, at the steady state, to the magnitude of the
interactions between the two spin reservoirs. The likelihood of the different
scenario is discussed in the light of the experimental data currently available
in literature, to point out which aspects are suitably accounted and which are
not by the declinations of thermal mixing DNP considered here.",1301.0798v2
2014-08-14,"Tameness, Uniqueness and amalgamation","We combine two approaches to the study of classification theory of AECs: 1.
that of Shelah: studying non-forking frames without assuming the amalgamation
property but assuming the existence of uniqueness triples and 2. that of
Grossberg and VanDieren: (studying non-splitting) assuming the amalgamation
property and tameness. In [JrSh875], we derive a good non-forking
$\lambda^+$-frame from a semi-good non-forking $\lambda$-frame. But the classes
$K_{\lambda^+}$ and $\preceq \restriction K_{\lambda^+}$ are replaced:
$K_{\lambda^+}$ is restricted to the saturated models and the partial order
$\preceq \restriction K_{\lambda^+}$ is restricted to the partial order
$\preceq^{NF}_{\lambda^+}$. Here, we avoid the restriction of the partial order
$\preceq \restriction K_{\lambda^+}$, assuming that every saturated model (in
$\lambda^+$ over $\lambda$) is an amalgamation base and
$(\lambda,\lambda^+)$-tameness for non-forking types over saturated models, (in
addition to the hypotheses of [JrSh875]): We prove that $M \preceq M^+$ if and
only if $M \preceq^{NF}_{\lambda^+}M^+$, provided that $M$ and $M^+$ are
saturated models. We present sufficient conditions for three good non-forking
$\lambda^+$-frames: one relates to all the models of cardinality $\lambda^+$
and the two others relate to the saturated models only. By an `unproven claim'
of Shelah, if we can repeat this procedure $\omega$ times, namely, `derive'
good non-forking $\lambda^{+n}$ frame for each $n<\omega$ then the categoricity
conjecture holds. Vasey applies one of our main theorems in a proof of the
categoricity conjecture under the above `unproven claim' of Shelah and more
assumptions. In [Jrprime], we apply the main theorem in a proof of the
existence of primeness triples.",1408.3383v3
2014-11-03,Core-crust transition properties of neutron stars within systematically varied extended relativistic mean-field model,"The model dependence and the symmetry energy dependence of the core-crust
transition properties for the neutron stars are studied using three different
families of systematically varied extended relativistic mean field model.
Several forces within each of the families are so considered that they yield
wide variations in the values of the nuclear symmetry energy $a_{\rm sym}$ and
its slope parameter $L$ at the saturation density. The core-crust transition
density is calculated using a method based on random-phase-approximation. The
core-crust transition density is strongly correlated, in a model independent
manner, with the symmetry energy slope parameter evaluated at the saturation
density. The pressure at the transition point dose not show any meaningful
correlations with the symmetry energy parameters at the saturation density. At
best, pressure at the transition point is correlated with the symmetry energy
parameters and their linear combination evaluated at the some sub-saturation
density. Yet, such correlations might not be model independent. The
correlations of core-crust transition properties with the symmetry energy
parameter are also studied by varying the symmetry energy within a single
model. The pressure at the transition point is correlated once again with the
symmetry energy parameter at the sub-saturation density.",1411.0427v1
2015-02-16,Color Image Enhancement Using the lrgb Coordinates in the Context of Support Fuzzification,"Image enhancement is an important stage in the image-processing domain. The
most known image enhancement method is the histogram equalization. This method
is an automated one, and realizes a simultaneous modification for brightness
and contrast in the case of monochrome images and for brightness, contrast,
saturation and hue in the case of color images. Simple and efficient methods
can be obtained if affine transforms within logarithmic models are used. A very
important thing in the affine transform determination for color images is the
coordinate system that is used for color space representation. Thus, the using
of the RGB coordinates leads to a simultaneous modification of luminosity and
saturation. In this paper using the lrgb perceptual coordinates one can define
affine transforms, which allow a separated modification of luminosity l and
saturation s (saturation being calculated with the component rgb in the
chromatic plane). Better results can be obtained if partitions are defined on
the image support and then the pixels are separately processed in each window
belonging to the defined partition. Classical partitions frequently lead to the
appearance of some discontinuities at the boundaries between these windows. In
order to avoid all these drawbacks the classical partitions may be replaced by
fuzzy partitions. Their elements will be fuzzy windows and in each of them
there will be defined an affine transform induced by parameters using the fuzzy
mean, fuzzy variance and fuzzy saturation computed for the pixels that belong
to the analyzed window. The final image is obtained by summing up in a weight
way the images of every fuzzy window.",1502.04499v1
2015-12-23,Impact of sample geometry on the measurement of pressure-saturation curves: experiments and simulations,"In this paper we study the influence of sample geometry on the measurement of
pressure-saturation relationships, by analyzing the drainage of a two-phase
flow from a quasi-2D random porous medium. The medium is transparent, which
allows for the direct visualization of the invasion pattern during flow, and is
initially saturated with a viscous liquid (a dyed glycerol-water mix). As the
pressure in the liquid is gradually reduced, air penetrates from an open inlet,
displacing the liquid which leaves the system from an outlet on the opposite
side. Pressure measurements and images of the flow are recorded and the
pressure-saturation relationship is computed. We show that this relationship
depends on the system size and aspect ratio. The effects of the system's
boundaries on this relationship are measured experimentally and compared with
simulations produced using an invasion percolation algorithm. The pressure
build up at the beginning and end of the invasion process are particularly
affected by the boundaries of the system whereas at the central part of the
model (when the air front progresses far from these boundaries), the invasion
happens at a statistically constant capillary pressure. These observations have
led us to propose a much simplified pressure-saturation relationship, valid for
systems that are large enough such that the invasion is not influenced by
boundary effects. The properties of this relationship depend on the capillary
pressure thresholds distribution, sample dimensions and average pore
connectivity and its applications may be of particular interest for simulations
of two-phase flow in large porous media.",1512.07415v1
2016-03-17,Phase field modeling of partially saturated deformable porous media,"A poromechanical model of partially saturated deformable porous media is
proposed based on a phase field approach at modeling the behavior of the
mixture of liquid water and wet air, which saturates the pore space, the phase
field being the saturation (ratio). While the standard retention curve is
expected still to provide the intrinsic retention properties of the porous
skeleton, depending on the porous texture, an enhanced description of surface
tension between the wetting (liquid water) and the non-wetting (wet air) fluid,
occupying the pore space, is stated considering a regularization of the phase
field model based on an additional contribution to the overall free energy
depending on the saturation gradient. The aim is to provide a more refined
description of surface tension interactions.
  An enhanced constitutive relation for the capillary pressure is established
together with a suitable generalization of Darcy's law, in which the gradient
of the capillary pressure is replaced by the gradient of the so-called
generalized chemical potential, which also accounts for the \lq\lq
force\rq\rq\, associated to the local free energy of the phase field model. A
micro-scale heuristic interpretation of the novel constitutive law of capillary
pressure is proposed, in order to compare the envisaged model with that one
endowed with the concept of average interfacial area.
  The considered poromechanical model is formulated within the framework of
strain gradient theory in order to account for possible effects, at laboratory
scale, of the micro-scale hydro-mechanical couplings between highly-localized
flows (fingering) and localized deformations of the skeleton (fracturing).",1603.05564v1
2017-01-03,Mixed one-bit compressive sensing with applications to overexposure correction for CT reconstruction,"When a measurement falls outside the quantization or measurable range, it
becomes saturated and cannot be used in classical reconstruction methods. For
example, in C-arm angiography systems, which provide projection radiography,
fluoroscopy, digital subtraction angiography, and are widely used for medical
diagnoses and interventions, the limited dynamic range of C-arm flat detectors
leads to overexposure in some projections during an acquisition, such as
imaging relatively thin body parts (e.g., the knee). Aiming at overexposure
correction for computed tomography (CT) reconstruction, we in this paper
propose a mixed one-bit compressive sensing (M1bit-CS) to acquire information
from both regular and saturated measurements. This method is inspired by the
recent progress on one-bit compressive sensing, which deals with only sign
observations. Its successful applications imply that information carried by
saturated measurements is useful to improve recovery quality. For the proposed
M1bit-CS model, alternating direction methods of multipliers is developed and
an iterative saturation detection scheme is established. Then we evaluate
M1bit-CS on one-dimensional signal recovery tasks. In some experiments, the
performance of the proposed algorithms on mixed measurements is almost the same
as recovery on unsaturated ones with the same amount of measurements. Finally,
we apply the proposed method to overexposure correction for CT reconstruction
on a phantom and a simulated clinical image. The results are promising, as the
typical streaking artifacts and capping artifacts introduced by saturated
projection data are effectively reduced, yielding significant error reduction
compared with existing algorithms based on extrapolation.",1701.00694v1
2017-04-10,Saturation with chiral interactions and consequences for finite nuclei,"We explore the impact of nuclear matter saturation on the properties and
systematics of finite nuclei across the nuclear chart. Using the ab initio
in-medium similarity renormalization group (IM-SRG), we study ground-state
energies and charge radii of closed-shell nuclei from $^4$He to $^{78}$Ni,
based on a set of low-resolution two- and three-nucleon interactions that
predict realistic saturation properties. We first investigate in detail the
convergence properties of these Hamiltonians with respect to model-space
truncations for both two- and three-body interactions. We find one particular
interaction that reproduces well the ground-state energies of all closed-shell
nuclei studied. As expected from their saturation points relative to this
interaction, the other Hamiltonians underbind nuclei, but lead to a remarkably
similar systematics of ground-state energies. Extending our calculations to
complete isotopic chains in the $sd$ and $pf$ shells with the valence-space
IM-SRG, the same interaction reproduces not only experimental ground states but
two-neutron-separation energies and first excited $2^+$ states. We also
calculate radii with the valence-space IM-SRG for the first time. Since this
particular interaction saturates at too high density, charge radii are still
too small compared with experiment. Except for this underprediction, the radii
systematics is, however, well reproduced. Our results highlight the importance
of nuclear matter as a theoretical benchmark for the development of
next-generation chiral interactions.",1704.02915v1
2018-09-15,"Equiangular lines, Incoherent sets and Quasi-symmetric designs","The absolute upper bound on the number of equiangular lines that can be found
in $\mathbf{R}^d$ is $d(d+1)/2$. Examples of sets of lines that saturate this
bound are only known to exist in dimensions $d=2,3,7$ or $23$. By considering
the additional property of incoherence, we prove that there exists a set of
equiangular lines that saturates the absolute bound and the incoherence bound
if and only if $d=2,3,7$ or $23$. This allows us classify all tight spherical
$5$-designs $X$ in $\mathbf{S}^{d-1}$, the unit sphere, with the property that
there exists a set of $d$ points in $X$ whose pairwise inner products are
positive.
  For a given angle $\kappa$, there exists a relative upper bound on the number
of equiangular lines in $\mathbf{R}^d$ with common angle $\kappa$. We prove
that classifying sets of lines that saturate this bound along with the
incoherence bound is equivalent to classifying certain quasi-symmetric designs,
which are combinatorial designs with two block intersection numbers. Given a
further natural assumption, we classify the known sets of lines that saturate
these two bounds. This family comprises of the lines mentioned above and the
maximal set of $16$ equiangular lines found in $\mathbf{R}^6$. There are
infinitely many known sets of lines that saturate the relative bound, so this
result is surprising. To shed some light on this, we identify the $E_8$ lattice
with the projection onto an $8$-dimensional subspace of a sublattice of the
Leech lattice defined by $276$ equiangular lines in $\mathbf{R}^{23}$. This
identification leads us to observe a correspondence between sets of equiangular
lines in small dimensions and the exceptional curves of del Pezzo surfaces.",1809.05739v3
2019-01-14,Quantum Null Energy Condition and its (non)saturation in 2d CFTs,"We consider the Quantum Null Energy Condition (QNEC) for holographic
conformal field theories in two spacetime dimensions (CFT$_2$). We show that
QNEC saturates for all states dual to vacuum solutions of AdS$_3$ Einstein
gravity, including systems that are far from thermal equilibrium. If the
Ryu-Takayanagi surface encounters bulk matter QNEC does not need to be
saturated, whereby we give both analytical and numerical examples. In
particular, for CFT$_2$ with a global quench dual to AdS$_3$-Vaidya geometries
we find a curious half-saturation of QNEC for large entangling regions. We also
address order one corrections from quantum backreactions of a scalar field in
AdS$_3$ dual to a primary operator of dimension $h$ in a large central charge
expansion and explicitly compute both, the backreacted Ryu--Takayanagi surface
part and the bulk entanglement contribution to EE and QNEC. At leading order
for small entangling regions the contribution from bulk EE exactly cancels the
contribution from the back-reacted Ryu-Takayanagi surface, but at higher orders
in the size of the region the contributions are almost equal while QNEC is not
saturated. For a half-space entangling region we find that QNEC is gapped by
$h/4$ in the large $h$ expansion.",1901.04499v2
2019-01-31,Scully-Lamb quantum laser model for parity-time-symmetric whispering-gallery microcavities: Gain saturation effects and non-reciprocity,"We use a non-Lindbladian master equation of the Scully-Lamb laser model for
the analysis of light propagation in a parity-time symmetric photonic system
composed of coupled active and passive whispering-gallery microresonators.
Performing the semiclassical approximation, we obtain a set of two nonlinear
coupled differential equations describing the time evolution of intracavity
fields. These coupled equations are able to explain the experimentally-observed
light non-reciprocity [Peng {\em et al.}, Nature Physics {\bf 10}, 394 (2014),
Chang {\em et al.}, Nature Photonics {\bf 8}, 524 (2014)]. We show that this
effect arises from the interplay between gain saturation in the active
microcavity, intercavity coupling, and losses in the cavities. Additionally,
using this approach, we study the effect of the gain saturation on exceptional
points, i.e., exotic degeneracies in non-Hermitian systems. Namely, we
demonstrate that the inclusion of gain saturation leads to a modification of
the exceptional points in the presence of intense intracavity fields. The
Scully-Lamb master equation for systems of coupled optical structures, as
proposed and applied here, constitutes a promising tool for the study of
quantum optical effects in coupled systems with losses, gain, and gain
saturation.",1901.11421v3
2019-04-24,Saturation momentum scale extracted from semi-inclusive transverse spectra in high-energy pp collisions,"Geometric scaling is well confirmed for transverse momentum distributions
observed in proton-proton collisions at LHC energies. We introduced
multiplicity dependence on a saturation momentum of the geometrical scaling,
assuming the scaling holds for semi-inclusive distributions as well as for
inclusive distributions. The saturation momentum is usually given by Bjorken's
$x$ variable, but redefinition of the scaling variable can make the saturation
momentum a function of collision energy $W$. We treat the energy as a free
parameter (denoted $W^*$ to distinguish it from $W$) and associate the
energy-dependent saturation momentum $Q_{\rm sat}(W^*)$ with particle number
density. By using $Q_{\rm sat}(W^*)$ for a scaling variable $\tau$, we show
semi-inclusive distributions can be geometrically scaled. i.e., all
semi-inclusive spectra observed at $W$=0.90, 2.76 and 7.00 TeV overlap one
universal function. The particle density dependences of mean transverse
momentum $\langle p_{\rm T} \rangle$ for LHC energies scales in terms of
$Q_{\rm sat}(W^*)$. Furthermore, our model explains a scaling property of
event-by-event $p_{\rm T}$ fluctuation measure $\sqrt{C_m}/\langle p_{\rm
T}\rangle$ at LHC energies for pp collisions, where $C_m$ is two-particle
transverse momentum correlator. Our analysis of the $p_{\rm T}$ fluctuation
makes possible to evaluate a non-perturbative coefficient of the gluon
correlation function.",1904.10823v2
2020-01-13,Interactive Visualization of Saturation Attempts in Vampire,"Many applications of formal methods require automated reasoning about system
properties, such as system safety and security. To improve the performance of
automated reasoning engines, such as SAT/SMT solvers and first-order theorem
prover, it is necessary to understand both the successful and failing attempts
of these engines towards producing formal certificates, such as logical proofs
and/or models. Such an analysis is challenging due to the large number of
logical formulas generated during proof/model search. In this paper we focus on
saturation-based first-order theorem proving and introduce the SATVIS tool for
interactively visualizing saturation-based proof attempts in first-order
theorem proving. We build SATVIS on top of the world-leading theorem prover
VAMPIRE, by interactively visualizing the saturation attempts of VAMPIRE in
SATVIS. Our work combines the automatic layout and visualization of the
derivation graph induced by the saturation attempt with interactive
transformations and search functionality. As a result, we are able to analyze
and debug (failed) proof attempts of VAMPIRE. Thanks to its interactive
visualisation, we believe SATVIS helps both experts and non-experts in theorem
proving to understand first-order proofs and analyze/refine failing proof
attempts of first-order provers.",2001.04100v1
2020-05-15,Single Image HDR Reconstruction Using a CNN with Masked Features and Perceptual Loss,"Digital cameras can only capture a limited range of real-world scenes'
luminance, producing images with saturated pixels. Existing single image high
dynamic range (HDR) reconstruction methods attempt to expand the range of
luminance, but are not able to hallucinate plausible textures, producing
results with artifacts in the saturated areas. In this paper, we present a
novel learning-based approach to reconstruct an HDR image by recovering the
saturated pixels of an input LDR image in a visually pleasing way. Previous
deep learning-based methods apply the same convolutional filters on
well-exposed and saturated pixels, creating ambiguity during training and
leading to checkerboard and halo artifacts. To overcome this problem, we
propose a feature masking mechanism that reduces the contribution of the
features from the saturated areas. Moreover, we adapt the VGG-based perceptual
loss function to our application to be able to synthesize visually pleasing
textures. Since the number of HDR images for training is limited, we propose to
train our system in two stages. Specifically, we first train our system on a
large number of images for image inpainting task and then fine-tune it on HDR
reconstruction. Since most of the HDR examples contain smooth regions that are
simple to reconstruct, we propose a sampling strategy to select challenging
training patches during the HDR fine-tuning stage. We demonstrate through
experimental results that our approach can reconstruct visually pleasing HDR
results, better than the current state of the art on a wide range of scenes.",2005.07335v1
2020-06-15,Feature Space Saturation during Training,"We propose layer saturation - a simple, online-computable method for
analyzing the information processing in neural networks. First, we show that a
layer's output can be restricted to the eigenspace of its variance matrix
without performance loss. We propose a computationally lightweight method for
approximating the variance matrix during training. From the dimension of its
lossless eigenspace we derive layer saturation - the ratio between the
eigenspace dimension and layer width. We show that saturation seems to indicate
which layers contribute to network performance. We demonstrate how to alter
layer saturation in a neural network by changing network depth, filter sizes
and input resolution. Furthermore, we show that well-chosen input resolution
increases network performance by distributing the inference process more evenly
across the network.",2006.08679v5
2020-12-15,Edge-Minimum Saturated k-Planar Drawings,"For a class $\mathcal{D}$ of drawings of loopless (multi-)graphs in the
plane, a drawing $D \in \mathcal{D}$ is \emph{saturated} when the addition of
any edge to $D$ results in $D' \notin \mathcal{D}$ - this is analogous to
saturated graphs in a graph class as introduced by Tur\'an (1941) and
Erd\H{o}s, Hajnal, and Moon (1964). We focus on $k$-planar drawings, that is,
graphs drawn in the plane where each edge is crossed at most $k$ times, and the
classes $\mathcal{D}$ of all $k$-planar drawings obeying a number of
restrictions, such as having no crossing incident edges, no pair of edges
crossing more than once, or no edge crossing itself. While saturated $k$-planar
drawings are the focus of several prior works, tight bounds on how sparse these
can be are not well understood. We establish a generic framework to determine
the minimum number of edges among all $n$-vertex saturated $k$-planar drawings
in many natural classes. For example, when incident crossings, multicrossings
and selfcrossings are all allowed, the sparsest $n$-vertex saturated $k$-planar
drawings have $\frac{2}{k - (k \bmod 2)} (n-1)$ edges for any $k \geq 4$, while
if all that is forbidden, the sparsest such drawings have
$\frac{2(k+1)}{k(k-1)}(n-1)$ edges for any $k \geq 6$.",2012.08631v3
2021-07-13,Attention-Guided Progressive Neural Texture Fusion for High Dynamic Range Image Restoration,"High Dynamic Range (HDR) imaging via multi-exposure fusion is an important
task for most modern imaging platforms. In spite of recent developments in both
hardware and algorithm innovations, challenges remain over content association
ambiguities caused by saturation, motion, and various artifacts introduced
during multi-exposure fusion such as ghosting, noise, and blur. In this work,
we propose an Attention-guided Progressive Neural Texture Fusion (APNT-Fusion)
HDR restoration model which aims to address these issues within one framework.
An efficient two-stream structure is proposed which separately focuses on
texture feature transfer over saturated regions and multi-exposure tonal and
texture feature fusion. A neural feature transfer mechanism is proposed which
establishes spatial correspondence between different exposures based on
multi-scale VGG features in the masked saturated HDR domain for discriminative
contextual clues over the ambiguous image areas. A progressive texture blending
module is designed to blend the encoded two-stream features in a multi-scale
and progressive manner. In addition, we introduce several novel attention
mechanisms, i.e., the motion attention module detects and suppresses the
content discrepancies among the reference images; the saturation attention
module facilitates differentiating the misalignment caused by saturation from
those caused by motion; and the scale attention module ensures texture blending
consistency between different coder/decoder scales. We carry out comprehensive
qualitative and quantitative evaluations and ablation studies, which validate
that these novel modules work coherently under the same framework and
outperform state-of-the-art methods.",2107.06211v1
2021-11-30,AutoDrop: Training Deep Learning Models with Automatic Learning Rate Drop,"Modern deep learning (DL) architectures are trained using variants of the SGD
algorithm that is run with a $\textit{manually}$ defined learning rate
schedule, i.e., the learning rate is dropped at the pre-defined epochs,
typically when the training loss is expected to saturate. In this paper we
develop an algorithm that realizes the learning rate drop
$\textit{automatically}$. The proposed method, that we refer to as AutoDrop, is
motivated by the observation that the angular velocity of the model parameters,
i.e., the velocity of the changes of the convergence direction, for a fixed
learning rate initially increases rapidly and then progresses towards soft
saturation. At saturation the optimizer slows down thus the angular velocity
saturation is a good indicator for dropping the learning rate. After the drop,
the angular velocity ""resets"" and follows the previously described pattern - it
increases again until saturation. We show that our method improves over SOTA
training approaches: it accelerates the training of DL models and leads to a
better generalization. We also show that our method does not require any extra
hyperparameter tuning. AutoDrop is furthermore extremely simple to implement
and computationally cheap. Finally, we develop a theoretical framework for
analyzing our algorithm and provide convergence guarantees.",2111.15317v2
2022-03-24,Investigating saturation effects and the virtual pion in leading neutron events at HERA with the dipole model,"We investigate events with very forward neutrons in $ep$ collisions at HERA
using impact parameter dependent colour dipole models with and without
saturation. This is the first study of the leading neutron process deploying
these models. The model predictions are compared with the available HERA
measurements for $6<Q^2<100$~GeV$^2$, $70<W<245$~GeV. Our analysis shows that
the models exhibit Feynman scaling, independent of $Q^2$. Our results
demonstrate that the $W$ and $Q^2$ dependence of the cross section is
independent of the presence of a forward neutron as predicted by the limiting
fragmentation hypothesis, which is a consequence of Feynman scaling itself. We
infer that the HERA leading neutron production inclusive data is insensitive to
saturation physics and these cross sections may not be able to distinguish
gluon saturation effects in future $ep$ colliders. We provide a good
description of the leading neutron structure function $F_2^{LN}$ at small $x$
using an assumption that the small-$x$ structure of protons and pions is
universal up to a normalisation. We also show that the observables in the
exclusive diffractive measurements with a vector meson in the final state are
more sensitive to saturation physics at small $x$ than inclusive measurements.
At last, we provide a prediction for the $\hat t$ spectrum in exclusive vector
meson production in the dipole model using Yukawa theory to model the virtual
pion's spatial wave function.",2203.13314v3
2022-07-11,Computational coupled large-deformation periporomechanics for dynamic failure and fracturing in variably saturated porous media,"The large-deformation mechanics and multiphysics of continuous or fracturing
partially saturated porous media under static and dynamic loads are significant
in engineering and science. This article is devoted to a computational coupled
large-deformation periporomechanics paradigm assuming passive air pressure for
modeling dynamic failure and fracturing in variably saturated porous media. The
coupled governing equations for bulk and fracture material points are
formulated in the current/deformed configuration through the updated
Lagrangian-Eulerian framework. It is hypothesized that the horizon of a mixed
material point remains spherical, and its neighbor points are determined in the
current configuration. As a significant contribution, the mixed
interface/phreatic material points near the phreatic line are explicitly
considered for modeling the transition from partial to full saturation (vice
versa) through the mixed peridynamic state concept. We have formulated the
coupled constitutive correspondence principle and stabilization scheme in the
updated Lagrangian-Eulerian framework for bulk and interface points. We
numerically implement the coupled large deformation periporomechanics through a
fully implicit fractional-step algorithm in time and a hybrid updated
Lagrangian-Eulerian meshfree method in space. Numerical examples are presented
to validate the implemented stabilized computational coupled large deformation
periporomechanics and demonstrate its efficacy and robustness in modeling
dynamic failure and fracturing in variably saturated porous media.",2207.04580v1
2022-08-27,Beyond DGLAP improved saturation model,"We present a modification of the DGLAP improved saturation model with respect
to the nonlinear correction (NLC). The GLR-MQ improved saturation model is
considered by employing the parametrization of proton structure function due to
the Laplace transforms method, which preserves its behavior success in the low
and high $Q^{2}$ regions. We show that the geometric scaling holds for the
GLR-MQ improved model in a wide kinematic region $rQ_{s}$. These results are
comparable with other models in a wide kinematic region $rQ_{s}$. The behavior
of the dipole cross sections, with respect to the GLR-MQ improved saturation
model, are comparable with the Color Glass Condensate (CGC) model. The model
describes the dipole cross sections in the inclusive and diffractive processes.
We also compare the nonlinear corrections to the impact-parameter dependent
saturation (IP-Sat) model with the impact-parameter dependent color glass
condensate (b-CGC) dipole model. Finally, we consider the linear and nonlinear
corrections to the IP Non-Sat model. These results provide a benchmark for
further investigation of QCD at small $x$ in future experiments such as the
Large Hadron Collider and Future Circular Collider projects.",2208.13037v4
2023-04-14,SMAE: Few-shot Learning for HDR Deghosting with Saturation-Aware Masked Autoencoders,"Generating a high-quality High Dynamic Range (HDR) image from dynamic scenes
has recently been extensively studied by exploiting Deep Neural Networks
(DNNs). Most DNNs-based methods require a large amount of training data with
ground truth, requiring tedious and time-consuming work. Few-shot HDR imaging
aims to generate satisfactory images with limited data. However, it is
difficult for modern DNNs to avoid overfitting when trained on only a few
images. In this work, we propose a novel semi-supervised approach to realize
few-shot HDR imaging via two stages of training, called SSHDR. Unlikely
previous methods, directly recovering content and removing ghosts
simultaneously, which is hard to achieve optimum, we first generate content of
saturated regions with a self-supervised mechanism and then address ghosts via
an iterative semi-supervised learning framework. Concretely, considering that
saturated regions can be regarded as masking Low Dynamic Range (LDR) input
regions, we design a Saturated Mask AutoEncoder (SMAE) to learn a robust
feature representation and reconstruct a non-saturated HDR image. We also
propose an adaptive pseudo-label selection strategy to pick high-quality HDR
pseudo-labels in the second stage to avoid the effect of mislabeled samples.
Experiments demonstrate that SSHDR outperforms state-of-the-art methods
quantitatively and qualitatively within and across different datasets,
achieving appealing HDR visualization with few labeled samples.",2304.06914v1
2023-08-28,Effect of fiber curvature on gas diffusion layer two-phase dynamics of a proton exchange membrane fuel cell,"The dynamics of two-phase flow within the cathode of a proton exchange
membrane fuel cell, particularly in Gas Diffusion Layers (GDLs) with varying
fiber curvatures, remain underexplored. Using a periodic surface model, we
stochastically reconstruct three GDL types with different fiber curvatures,
incorporating vital parameters derived from a physical GDL. Considering the
randomness in reconstruction, the structure generation process is iterated four
times for each GDL type, enabling an ensemble average analysis. Pore network
models are adopted to reveal disparities in these GDL porous structures. The
subsequent two-phase simulations are conducted to explore liquid transport
through these GDLs and interfaces to assembled gas channels. Time-varying GDL
total, local water saturation, and capillary pressure are investigated. Results
show stochastic reconstructions exhibit similar frequency peak ranges in pore
and throat diameters, and coordination numbers, but diverge from the physical
GDL. Bigger fiber curvature tends to enhance pore network connectivity by
increasing smaller pores, leading to heightened water saturation and capillary
pressure. Straight-fiber GDLs, compared to curved-fiber GDLs, show greater
potential proximity to the physical GDL in terms of overall water saturation
and capillary pressure but are also accompanied by increased uncertainty.
Despite similar layer porosity, water saturation in the same layer of all
samples differs increasingly from the inlet to the outlet. Water breakthrough
and detachment near the GDL can induce significant water saturation instability
at the GDL and gas channel interface. Detached droplets in gas channels
connected with straight-fiber GDLs exhibit larger sizes and slower movement
than those in channels assembled with curved-fiber GDLs. These findings can be
utilized in future GDL design and optimization.",2308.14539v2
2023-12-18,Incoherent ${\rm J}/ψ$ production at large $|t|$ identifies the onset of saturation at the LHC,"We predict that the onset of gluon saturation can be uniquely identified
using incoherent ${\rm J}/\psi$ production in Pb$\unicode{x2013}$Pb collisions
at currently accessible energies of the LHC. The diffractive incoherent
photo-production of a ${\rm J}/\psi$ vector meson off a hadron provides
information on the partonic structure of the hadron. Within the Good-Walker
approach it specifically measures the variance over possible target
configurations of the hadronic colour field. For this process then, gluon
saturation sets in when the cross section reaches a maximum, as a function of
the centre-of-mass energy of the photon-hadron system ($W$), and then
decreases. We benchmark the energy-dependent hot-spot model against data from
HERA and the LHC and demonstrate a good description of the available data. We
show that the study of the energy dependence of the incoherent production of
${\rm J}/\psi$ allows us to pinpoint the onset of saturation effects by
selecting the region of Mandelstam-$t$ around 1 GeV$^2$ where the contribution
of hot spots is dominant. We predict the onset of saturation in a Pb target to
occur for $W$ around a few hundred GeV. This can be measured with current data
in ultra-peripheral Pb$\unicode{x2013}$Pb collisions at the LHC.",2312.11320v2
2024-02-16,Superradiant pulse saturation in a Free Electron Laser,"A study is made of the saturation mechanism of a single superradiant spike of
radiation in a Free Electron Laser. A one-dimensional (1D) computer model is
developed using the Puffin, un-averaged FEL simulation code, which allows
sub-radiation wavelength evolution of both the spike radiation field and the
electron dynamics to be modelled until the highly non-linear saturation process
of the spike is observed. Animations of the process from the start to the end
of the interaction are available. The resultant saturated spike duration is at
the sub-wavelength scale and has a broad spectrum. The electrons passing
through the spike can both lose and gain energy many times greater than that of
the normal non-pulsed FEL interaction. A saturation mechanism is proposed and
tested via a simple analysis of the 1D FEL equations. The scaling results of
the analysis are seen to be in good agreement with the numerical results. A
simple model of three dimensional diffraction effects of the radiation is
applied to the results of the 1D simulations. This greatly reduces longer
wavelengths of the power spectrum, which are seen to be emitted mainly after
the electrons have propagated through the spike, and is seen to be in
qualitative agreement with recent experimental results.",2402.11026v1
2024-02-18,Saturability of the Quantum Cramér-Rao Bound in Multiparameter Quantum Estimation at the Single-Copy Level,"The quantum Cram\'{e}r-Rao bound (QCRB) as the ultimate lower bound for
precision in quantum parameter estimation is only known to be saturable in the
multiparameter setting in special cases and under conditions such as full or
average commutavity of the symmetric logarithmic derivatives (SLDs) associated
with the parameters. Moreover, for general mixed states, collective
measurements over infinitely many identical copies of the quantum state are
generally required to attain the QCRB. In the important and experimentally
relevant single-copy scenario, a necessary condition for saturating the QCRB in
the multiparameter setting for general mixed states is the so-called partial
commutativity condition on the SLDs. However, it is not known if this condition
is also sufficient. This paper establishes necessary and sufficient conditions
for saturability of the multiparameter QCRB in the single-copy setting in terms
of the commutativity of a set of projected SLDs and the existence of a unitary
solution to a system of nonlinear partial differential equations. New necessary
conditions that imply partial commutativity are also obtained, which together
with another condition become sufficient. Moreover, when the sufficient
conditions are satisfied an optimal measurement saturating the QCRB can be
chosen to be projective and explicitly characterized. An example is developed
to illustrate the case of a multiparameter quantum state where the conditions
derived herein are satisfied and can be explicitly verified.",2402.11567v3
2022-09-09,Magnetically confined mountains on accreting neutron stars with multipole magnetic fields,"Magnetically confined mountains on accreting neutron stars are candidates for
producing continuous gravitational waves. We formulate a magnetically confined
mountain on a neutron star with strong multipole magnetic fields and obtain
some sequences of numerical solutions. We find that the mass ellipticity of the
mountain increases by one order of magnitude if the neutron star has strong
multipole magnetic fields. As matter accretes on to the magnetic pole, the size
of the mountain increases and the magnetic fields are buried. If the neutron
star has a dipole magnetic field, the dipole magnetic field is buried and
transformed into multipole components. By contrast, if the neutron star has
both dipole and strong multipole magnetic fields, the multipole magnetic fields
are buried and transformed into a negative dipole component. We also calculate
magnetically confined mountains with toroidal magnetic fields and find that the
ellipticity becomes slightly smaller when the mountain has toroidal magnetic
fields. If the multipole magnetic fields are buried, they sustain the intense
toroidal magnetic field near the stellar surface, and the ratio of the toroidal
magnetic field to the poloidal magnetic field is close to 100. The hidden
strong toroidal magnetic fields are sustained by the buried multipole magnetic
fields.",2209.04352v1
2001-06-21,Instantons in the Saturation Environment,"We show that instanton calculations in QCD become theoretically well defined
in the gluon saturation environment which suppresses large size instantons. The
effective cutoff scale is determined by the inverse of the saturation scale. We
concentrate on two most important cases: the small-x tail of a gluon
distribution of a high energy hadron or a large nucleus and the central
rapidity region in a high energy hadronic or heavy ion collision. In the
saturation regime the gluon density in a single large ultrarelativistic nucleus
is high and gluonic fields are given by the classical solutions of the
equations of motion. We show that these strong classical fields do not affect
the density of instantons in the nuclear wave function compared to the
instanton density in the vacuum. A classical solution with non-trivial
topological charge is found for the gluon field of a single nucleus at the
lowest order in the instanton perturbation theory. In the case of
ultrarelativistic heavy ion collisions a strong classical gluonic field is
produced in the central rapidity region. We demonstrate that this field
introduces a suppression factor of exp{-c \rho^4 Q_s^4 / [8 \alpha^2 N_c (Q_s
\tau)^2]} in the instanton size distribution, where Q_s is the saturation scale
of both (identical) nuclei, \tau is the proper time and c = 1 is the gluon
liberation coefficient. This factor suggests that gluonic saturation effects at
the early stages of nuclear collisions regulate the instanton size distribution
in the infrared region and make the instanton density finite by suppressing
large size instantons.",0106248v2
2006-01-17,On correlations and discreteness in non-linear QCD evolution,"We consider modifications of the standard non-linear QCD evolution in an
attempt to account for some of the missing ingredients discussed recently, such
as correlations, discreteness in gluon emission and Pomeron loops. The
evolution is numerically performed using the Balitsky-Kovchegov equation on
individual configurations defined by a given initial value of the saturation
scale, for reduced rapidities $y=(\alpha_s N_c/\pi) Y<10$. We consider the
effects of averaging over configurations as a way to implement correlations,
using three types of Gaussian averaging around a mean saturation scale.
Further, we heuristically mimic discreteness in gluon emission by considering a
modified evolution in which the tails of the gluon distributions are cut-off.
The approach to scaling and the behavior of the saturation scale with rapidity
in these modified evolutions are studied and compared with the standard
mean-field results. For the large but finite values of rapidity explored, no
strong quantitative difference in scaling for transverse momenta around the
saturation scale is observed. At larger transverse momenta, the influence of
the modifications in the evolution seems most noticeable in the first steps of
the evolution. No influence on the rapidity behavior of the saturation scale
due to the averaging procedure is found. In the cut-off evolution the rapidity
evolution of the saturation scale is slowed down and strongly depends on the
value of the cut-off. Our results stress the need to go beyond simple
modifications of evolution by developing proper theoretical tools that
implement such recently discussed ingredients.",0601132v3
2015-05-06,On upper bounds on the smallest size of a saturating set in a projective plane,"In a projective plane $\Pi _{q}$ (not necessarily Desarguesian) of order $q,$
a point subset $S$ is saturating (or dense) if any point of $\Pi _{q}\setminus
S$ is collinear with two points in$~S$. Using probabilistic methods, the
following upper bound on the smallest size $ s(2,q)$ of a saturating set in
$\Pi _{q}$ is proved: \begin{equation*} s(2,q)\leq 2\sqrt{(q+1)\ln
(q+1)}+2\thicksim 2\sqrt{q\ln q}. \end{equation*} We also show that for any
constant $c\ge 1$ a random point set of size $k$ in $\Pi _{q}$ with $
2c\sqrt{(q+1)\ln(q+1)}+2\le k<\frac{q^{2}-1}{q+2}\thicksim q$ is a saturating
set with probability greater than $1-1/(q+1)^{2c^{2}-2}.$ Our probabilistic
approach is also applied to multiple saturating sets. A point set $S\subset
\Pi_{q}$ is $(1,\mu)$-saturating if for every point $Q$ of $\Pi _{q}\setminus
S$ the number of secants of $S$ through $Q$ is at least $\mu $, counted with
multiplicity. The multiplicity of a secant $ \ell $ is computed as
${\binom{{\#(\ell \,\cap S)}}{{2}}}.$ The following upper bound on the smallest
size $s_{\mu }(2,q)$ of a $(1,\mu)$-saturating set in $\Pi_{q}$ is proved:
\begin{equation*} s_{\mu }(2,q)\leq 2(\mu +1)\sqrt{(q+1)\ln (q+1)}+2\thicksim
2(\mu +1)\sqrt{ q\ln q}\,\text{ for }\,2\leq \mu \leq \sqrt{q}. \end{equation*}
  By using inductive constructions, upper bounds on the smallest size of a
saturating set (as well as on a $(1,\mu)$-saturating set) in the projective
space $PG(N,q)$ are obtained.
  All the results are also stated in terms of linear covering codes.",1505.01426v3
2019-04-22,CEST MR-Fingerprinting: practical considerations and insights for acquisition schedule design and improved reconstruction,"Purpose: To understand the influence of various acquisition parameters on the
ability of CEST MR-Fingerprinting (MRF) to discriminate different chemical
exchange parameters and to provide tools for optimal acquisition schedule
design and parameter map reconstruction. Methods: Numerical simulations were
conducted using a parallel-computing implementation of the Bloch-McConnell
equations, examining the effect of TR, TE, flip-angle, water T$_{1}$ and
T$_{2}$, saturation-pulse duration, power, and frequency on the discrimination
ability of CEST-MRF. A modified Euclidean-distance matching metric was
evaluated and compared to traditional dot-product matching. L-Arginine phantoms
of various concentrations and pH were scanned at 4.7T and the results compared
to numerical findings. Results: Simulations for dot-product matching
demonstrated that the optimal flip-angle and saturation times are 30$^{\circ}$
and 1100 ms, respectively. The optimal maximal saturation power was 3.4 $\mu$T
for concentrated solutes with a slow exchange-rate, and 5.2 $\mu$T for dilute
solutes with medium-to-fast exchange-rates. Using the Euclidean-distance
matching metric, much lower maximum saturation powers were required (1.6 and
2.4 $\mu$T, respectively), with a slightly longer saturation time (1500 ms) and
90$^{\circ}$ flip-angle. For both matching metrics, the discrimination ability
increased with the repetition time. The experimental results were in agreement
with simulations, demonstrating that more than a 50% reduction in scan-time can
be achieved by Euclidean-distance-based matching. Conclusion: Optimization of
the CEST-MRF acquisition schedule is critical for obtaining the best exchange
parameter accuracy. The use of Euclidean-distance-based matching of signal
trajectories simultaneously improved the discrimination ability and reduced the
scan time and maximal saturation power required.",1904.09732v1
2019-11-20,Moist Shallow Water Response to Tropical Forcing: Initial Value Problems,"The response of a spherical moist shallow water system to tropical imbalances
in the presence of inhomogeneous saturation fields is examined. While the
initial moist response is similar to the dry reference run, albeit with a
reduced equivalent depth, the long time solution depends quite strikingly on
the nature of the saturation field. For a saturation field that only depends on
latitude, specifically, one with a peak at the equator and falls off
meridionally in both hemispheres, height imbalances adjust to large-scale,
low-frequency westward propagating modes. When the background saturation
environment is also allowed to vary with longitude, in addition to a westward
quadrupole, there is a distinct eastward propagating response at long times.
The nature of this eastward propagating mode is well described by moist
potential vorticity conservation and it consists of wave packets that arc out
to midlatitudes and return to the tropics and are predominantly rotational in
character. In all moist cases, initially formed Kelvin waves decay, and this
appears to be tied to the off-equatorial organization of moisture anomalies by
rotational modes. Many of these basic features carry over to the response in
the presence of realistic saturation fields derived from reanalysis based
precipitable water. In boreal summer, long time eastward response is restricted
to northern hemisphere and takes the form of a wavetrain that passes over
Indian landmass into the subtropics, reaching across the Pacific to North
America. In boreal winter, the eastward mode consists of a subtropically
confined rotational quadrupole along with midlatitudinal disturbances. Thus, in
addition to circumnavigating westward Rossby waves, slow eastward propagating
modes appear to be a robust feature of the shallow water system with
interactive moisture in the presence of saturation fields that vary with
latitude and longitude.",1911.08811v3
2020-11-10,Saturated fusion systems on $p$-groups of maximal class,"For a prime number $p$, a finite $p$-group of order $p^n$ has maximal class
if it has nilpotency class $n-1$. Here we examine saturated fusion systems on
maximal class $p$-groups and, in particular, we describe all the reduFor a
prime number $p$, a finite $p$-group of order $p^n$ has maximal class if and
only if it has nilpotency class $n-1$. Here we examine saturated fusion systems
$\mathcal F$ on maximal class $p$-groups $S$ of order at least $p^4$. The
Alperin-Goldschmidt Theorem for saturated fusion systems yields that $\mathcal
F$ is entirely determined by the $\mathcal F$-automorphisms of its $\mathcal
F$-essential subgroups and of $S$ itself. If an $\mathcal F$-essential subgroup
either has order $p^2$ or is non-abelian of order $p^3$, then it is called an
$\mathcal F$-pearl. The facilitating and technical theorem in this work shows
that an $\mathcal F$-essential subgroup is either an $\mathcal F$-pearl, or one
of two explicitly determined maximal subgroups of $S$. This result is easy to
prove if $S$ is a $2$-group and can be read from the work of D'\iaz, Ruiz, and
Viruel together with that of Parker and Semeraro when $p=3$. The main
contribution is for $p \ge 5$ as in this case there is no classification of the
maximal class $p$-groups.
  The main Theorem describes all the reduced saturated fusion systems on a
maximal class $p$-group of order at least $p^4$ and follows from two more
extensive theorems. These two theorems describe all saturated fusion systems,
not restricting to the reduced ones for example, on exceptional and
non-exceptional maximal class $p$-groups respectively. As a corollary, we have
the easy to remember result that states that, if $O_p(\mathcal F)=1$, then
either $\mathcal F$ has $\mathcal F$-pearls or $S$ is isomorphic to a Sylow
$p$-subgroup of $\mathrm G_2(p)$ with $p\ge 5$ and the fusion systems are
explicitly described.",2011.05011v2
2023-03-06,Monitoring Fluid Saturation in Reservoirs Using Time-Lapse Full-Waveform Inversion,"Monitoring the rock-physics properties of the subsurface is of great
importance for reservoir management. For either oil and gas applications or CO2
storage, seismic data are a valuable source of information for tracking changes
in elastic properties which can be related to fluids saturation and pressure
changes within the reservoir. Changes in elastic properties can be estimated
with time-lapse full-waveform inversion. Monitoring rock-physics properties,
such as saturation, with time-lapse full-waveform inversion is usually a
two-step process: first, elastic properties are estimated with full-waveform
inversion, then, the rock-physics properties are estimated with rock-physics
inversion. However, multiparameter time-lapse full-waveform inversion is prone
to crosstalk between parameter classes across different vintages. This leads to
leakage from one parameter class to another, which, in turn, can introduce
large errors in the estimated rock-physics parameters. To avoid inaccuracies
caused by crosstalk and the two-step inversion strategy, we reformulate
time-lapse full-waveform inversion to estimate directly the changes in the
rock-physics properties. Using Gassmann's model, we adopt a new
parameterization containing porosity, clay content, and water saturation. In
the context of reservoir monitoring, changes are assumed to be induced by fluid
substitution only. The porosity and clay content can thus be kept constant
during time-lapse inversion. We compare this parameterization with the usual
density-velocity parameterization for different benchmark models. Results
indicate that the proposed parameterization eliminates crosstalk between
parameters of different vintages, leading to more accurate estimation of
saturation changes. We also show that using the parameterization based on
porosity, clay content, and water saturation, the elastic changes can be
monitored more accurately.",2303.03136v3
2023-04-04,Modulational instability in $\cal{PT}$-symmetric Bragg grating structures with saturable nonlinearity,"We investigate the nontrivial characteristics of modulational instability
(MI) in a system of Bragg gratings with saturable nonlinearity. We also
introduce an equal amount of gain and loss into the existing system which gives
rise to an additional degree of freedom, thanks to the concept of $\cal PT$-
symmetry. We obtain the nonlinear dispersion relation of the saturable model
and discover that such dispersion relations for both the conventional and $\cal
PT$- symmetric cases contradict with the conventional Kerr and saturable
systems by not displaying the typical signature of loop formation in either the
upper branch or lower branch of the curve drawn against the wavenumber and
detuning parameter. We then employ a standard linear stability analysis in
order to study the MI dynamics of the continuous waves perturbed by an
infinitesimal perturbation. The main objective of this paper is twofold. We
first investigate the dynamics of the MI gain spectrum at the top and bottom of
the photonic bandgap followed by a comprehensive analysis carried out in the
anomalous and normal dispersion regimes. As a result, this perturbed system
driven by the saturable nonlinearity and gain/loss yields a variety of
instability spectra, which include the conventional side bands, monotonically
increasing gain, the emergence of a single spectrum in either of the Stokes
wavenumber region, and so on. In particular, we observe a remarkably peculiar
spectrum, which is caused predominantly by the system parameter though the
perturbation wavenumber boosts the former. We also address the impact of all
the physical parameters considered in the proposed model which include coupling
coefficient, dispersion parameter, and saturable nonlinearity on the phenomenon
of MI for different $\cal PT$- symmetric regimes ranging from unbroken to
broken one in greater detail.",2304.01927v1
2022-10-31,Superconducting Magnet System Concept with a Mechanical Energy Transfer in the Magnetic Field,"There is an interest to design superconducting magnet systems working in a
persistent current mode. These systems continuously generate magnetic field
with disconnected power source working like permanent magnet devices. In this
paper proposed a magnet system concept based on the direct mechanical energy
transfer in the magnetic field. Short circuited superconducting coils do not
have current leads and power source. To pump the mechanical energy in the
superconducting coil used a magnetizer which magnetically coupled with the
coil. The mechanical removing the magnetizer from the magnet induces a
persistent current in the superconducting coil which generates the magnetic
field. Iron dominated magnet system concept was investigated using OPERA3d code
which confirmed a visibility of proposed approach.",2211.00102v1
2014-06-25,Transforming magnets,"Based on the form-invariant of Maxwell's equations under coordinate
transformations, we extend the theory of transformation optics to
transformation magneto-statics, which can design magnets through coordinate
transformations. Some novel DC magnetic field illusions created by magnets
(e.g. shirking magnets, cancelling magnets and overlapping magnets) are
designed and verified by numerical simulations. Our research will open a new
door to designing magnets and controlling DC magnetic fields.",1406.6512v1
1995-05-23,"Isotropy, homogeneity and dipole saturation","A distribution of points that satisfies the property of local isotropy is not
necessarily homogeneous: homogeneity is implied by the condition of local
isotropy together with the assumption of analyticity or regularity. Here we
show that the evidence of dipole saturation in galaxies (and clusters)
catalogues, together with a monotone growth of the monopole, is an evidence of
isotropy but not of homogeneity. This is fully compatible with a fractal
structure which has the property of local isotropy, but it is non-analytic and
non-homogeneous.",9505106v1
1998-04-03,Polarization of Astronomical Maser Radiation. IV. Circular Polarization Profiles,"Profile comparison of the Stokes parameters $V$ and $I$ is a powerful tool
for maser data analysis, providing the first direct methods for unambiguous
determination of (1) the maser saturation stage, (2) the amplification optical
depth and intrinsic Doppler width of unsaturated masers, and (3) the
comparative magnitudes of Zeeman splitting and Doppler linewidth. Circular
polarization recently detected in OH 1720 MHz emission from the Galactic center
appears to provide the first direct evidence for maser saturation.",9804040v1
2000-05-31,Consequences of parton's saturation and string's percolation on the developments of cosmic ray showers,"At high gluon or string densities, gluons' saturation or the strong
interaction among strings, either forming colour ropes or giving rise to
string's percolation, induces a strong suppression in the particle
multiplicities produced at high energy. This suppression implies important
modifications on cosmic ray shower development. In particular, it is shown that
it affects the depth of maximum, the elongation rate, and the behaviour of the
number of muons at energies around 10^{17}-10^{18} eV. The existing cosmic ray
data point out in the same direction.",0005588v1
2004-11-05,The QCD Black Disk Limit in Cosmic Ray Air Showers,"We discuss particle production in the high energy limit of QCD. Due to a
large gluon density, the interaction reaches the black disk limit and the
projectile is resolved into its partonic structure at the saturation scale.
This leads to suppression of forward particle production and hereby to a faster
absorption of cosmic ray air showers. This property is most suitable for the
distinction of evolution scenarios for the saturation scale, e.g. fixed and
running coupling BFKL, the latter of which is favored by air shower
measurements.",0411143v1
2005-11-16,The role of differential rotation in the evolution of the r-mode instability,"We discuss the role of differential rotation in the evolution of the l=2
r-mode instability of a newly born, hot, rapidly-rotating neutron star. It is
shown that the amplitude of the r-mode saturates in a natural way at a value
that depends on the amount of differential rotation at the time the instability
becomes active. It is also shown that, independently of the saturation
amplitude of the mode, the star spins down to a rotation rate that is
comparable to the inferred initial rotation rates of the fastest pulsars
associated with supernova remnants.",0511485v1
1997-10-10,Intrinsic Decoherence in Mesoscopic Systems,"We present measurements of the phase coherence time $\tau_\phi$ in six
quasi-1D Au wires and clearly show that $\tau_\phi$ is temperature independent
at low temperatures. We suggest that zero-point fluctuations of the intrinsic
electromagnetic environment are responsible for the observed saturation of
$\tau_\phi$. We introduce a new functional form for the temperature dependence
and present the results of a calculation for the saturation value of
$\tau_\phi$. This explains the observed temperature dependence of our samples
as well as many 1D and 2D systems reported to date.",9710095v1
1997-12-05,Influence of Hydrodynamic Interactions on the Kinetics of Colloidal Particle's Adsorption,"The kinetics of irreversible adsorption of spherical particles onto a flat
surface is theoretically studied. Previous models, in which hydrodynamic
interactions were disregarded, predicted a power-law behavior $t^{-2/3}$ for
the time dependence of the coverage of the surface near saturation.
Experiments, however, are in agreement with a power-law behavior of the form
$t^{-1/2}$. We outline that, when hydrodynamic interactions are considered, the
assymptotic behavior is found to be compatible with the experimental results in
a wide region near saturation.",9712076v1
2001-01-11,Mutual Information of Population Codes and Distance Measures in Probability Space,"We studied the mutual information between a stimulus and a large system
consisting of stochastic, statistically independent elements that respond to a
stimulus. The Mutual Information (MI) of the system saturates exponentially
with system size. A theory of the rate of saturation of the MI is developed. We
show that this rate is controlled by a distance function between the response
probabilities induced by different stimuli. This function, which we term the
{\it Confusion Distance} between two probabilities, is related to the Renyi
$\alpha$-Information.",0101161v3
2002-04-19,Using NMR to Measure Fractal Dimensions,"A comment is made on the recent PFG NMR measurements by Stallmach, et al. on
water-saturated sands [Phys. Rev. Lett. 88, 105505 (2002)]. It is pointed out
that the usual law for the time-dependent diffusion coefficient D(t) used by
these authors is not valid for a fractal surface. It is shown that (1-D(t)/D0)
\~ t^[(3-Ds)/2] at short times for a surface of fractal dimension Ds, where D0
is the bulk diffusion coefficient. Preliminary PFG NMR data on water saturated
limestone and plastic beads are presented to illustrate this analysis.",0204431v1
2002-05-09,"Saturation of Spontaneous Polarization Charge in Pyroelectric Crystals of LiNbO3, LiTaO3 and CsNO3 at Low Temperature Above 4.2 K","Experimental observations of the change in the polarization charge of
pyroelectric crystals of LiNbO3, LiTaO3 and CsNO3, as the temperature of the
crystal is changed from about 300K to a lower limit of 4.2K, are described. It
was found that the rate of change of the polarization charge slowed down
considerably and, perhaps, reached a zero rate of change. The onset of this
saturation of the polarization charge occurred at low temperatures, above the
temperature of liquid helium, which were different for each of the three types
of crystal.",0205189v2
2002-05-23,Bistable Gradient Networks II: Storage Capacity and Behaviour Near Saturation,"We examine numerically the storage capacity and the behaviour near saturation
of an attractor neural network consisting of bistable elements with an
adjustable coupling strength, the Bistable Gradient Network (BGN). For strong
coupling, we find evidence of a first-order ""memory blackout"" phase transition
as in the Hopfield network. For weak coupling, on the other hand, there is no
evidence of such a transition and memorized patterns can be stable even at high
levels of loading. The enhanced storage capacity comes, however, at the cost of
imperfect retrieval of the patterns from corrupted versions.",0205465v1
2002-07-31,Microwave saturation of the Rydberg states of electrons on helium,"We present measurements of the resonant microwave excitation of the Rydberg
energy levels of surface state electrons on superfluid helium. The temperature
dependent linewidth agrees well with theoretical predictions and is very small
below 300 mK. Absorption saturation and power broadening were observed as the
fraction of electrons in the first excited state was increased to 0.49, close
to the thermal excitation limit of 0.5. The Rabi frequency was determined as a
function of microwave power. The high values of the ratio of the Rabi frequency
to linewidth confirm this system as an excellent candidate for creating qubits.",0208001v1
2002-08-20,Calculations on Electronic States in QDs woth Saturated Shapes,"Electronic States of Si and Ge QDs of 5 to 3127 atoms with saturated shapes
in a size range of 0.57 to 4.92 nm for Si and 0.60 to 5.13 nm for Ge are
calculated by using an empirical tight binding model combined with the
irreducible representations of the group theory. The results are compared with
those of Si and Ge quantum dots with spherical shape. The effects of the shapes
on electronic states in QDs are discussed.",0208395v1
2002-09-12,Electron dephasing near zero temperature: an experimental review,"The behavior of the electron dephasing time near zero temperature,
$\tau_\phi^0$, has recently attracted vigorous attention. This renewed interest
is primarily concerned with whether $\tau_\phi^0$ should reach a finite or an
infinite value as $T \to$ 0. While it is accepted that $\tau_\phi^0$ should
diverge if there exists only electron-electron (electron-phonon) scattering,
several recent measurements have found that $\tau_\phi^0$ depends only very
weakly on temperature, if at all, when $T$ is sufficiently low. This article
discusses the current experimental status of ""the saturation problem"", and
concludes that the origin(s) for this widely observed saturation are still
unresolved.",0209275v1
2002-12-10,A giant overshoot effect in the Janssen granular column,"We present new experimental results on the mechanical behavior of static
granular assemblies confined in a vertical column. Our measurements confirm,
for the first time, the universal Janssen's scaling for the stress saturation
curve. We show consequently, in the context of isotropic elasticity, a relation
between the Poisson ratio and granular packing fraction. Moreover, using a
systematic study of the overshoot effect created by a top mass equal to the
saturation mass, we show behaviors reproduced qualitatively by isotropic
elastic materials but in the case of a granular assembly of a spectacular
amplitude. These experimental results are strong tests for any theory of
granular matter.",0212228v1
2003-08-22,Controlling a mesoscopic spin environment by quantum bit manipulation,"We present a unified description of cooling and manipulation of a mesoscopic
bath of nuclear spins via coupling to a single quantum system of electronic
spin (quantum bit). We show that a bath cooled by the quantum bit rapidly
saturates. Although the resulting saturated states of the spin bath (``dark
states'') generally have low degrees of polarization and purity, their symmetry
properties make them a valuable resource for the coherent manipulation of
quantum bits. Specifically, we demonstrate that the dark states of nuclear
ensembles can be used to coherently control the system-bath interaction and to
provide a robust, long-lived quantum memory for qubit states.",0308459v1
2005-04-05,Cs adsorption on Si(001) surface: ab initio study,"First-principles calculations using density functional theory based on
norm-conserving pseudopotentials have been performed to investigate the Cs
adsorption on the Si(001) surface for 0.5 and 1 ML coverages. We found that the
saturation coverage corresponds to 1 ML adsorption with two Cs atoms occupying
the double layer model sites. While the 0.5 ML covered surface is of metallic
nature, we found that 1 ML of Cs adsorption corresponds to saturation coverage
and leads to a semiconducting surface. The results for the electronic behavior
and surface work function suggest that adsorption of Cs takes place via
polarized covalent bonding.",0504088v2
2005-08-09,Classical magnetotransport of inhomogeneous conductors,"We present a model of magnetotransport of inhomogeneous conductors based on
an array of coupled four-terminal elements. We show that this model generically
yields non-saturating magnetoresistance at large fields. We also discuss how
this approach simplifies finite-element analysis of bulk inhomogeneous
semiconductors in complex geometries. We argue that this is an explanation of
the observed non-saturating magnetoresistance in silver chalcogenides and
potentially in other disordered conductors. Our method may be used to design
the magnetoresistive response of a microfabricated array.",0508229v2
2005-10-24,Universality in edge-source diffusion dynamics,"We show that in edge-source diffusion dynamics the integrated concentration
N(t) has a universal dependence with a characteristic time-scale tau=(A/P)^2
pi/(4D), where D is the diffusion constant while A and P are the
cross-sectional area and perimeter of the domain, respectively. For the
short-time dynamics we find a universal square-root asymptotic dependence
N(t)=N0 sqrt(t/tau) while in the long-time dynamics N(t) saturates
exponentially at N0. The exponential saturation is a general feature while the
associated coefficients are weakly geometry dependent.",0510627v2
2005-12-09,Stacking of oligo and polythiophenes cations in solution: surface tension and dielectric saturation,"The stacking of positively charged (or doped) terthiophene oligomers and
quaterthiophene polymers in solution is investigated applying a recently
developed unified electrostatic and cavitation model for first-principles
calculations in a continuum solvent. The thermodynamic and structural patterns
of the dimerization are explored in different solvents, and the distinctive
roles of polarity and surface tension are characterized and analyzed.
Interestingly, we discover a saturation in the stabilization effect of the
dielectric screening that takes place at rather small values of $\epsilon_0$.
Moreover, we address the interactions in trimers of terthiophene cations, with
the aim of generalizing the results obtained for the dimers to the case of
higher-order stacks and nanoaggregates.",0512203v1
2005-12-14,Terahertz plasma wave generation in ultra-short-channel Field Effect Transistors: theory vs experiment,"Taking into account both the scattering and the velocity saturation of
carriers, we examine the ""shallow-water"" instability of the two-dimensional
electron gas in a field effect transistor. It is shown that both the scattering
(which is analogous to friction in a shallow-water channel) and the carrier
velocity saturation lead to damping of the plasma wave instability. Threshold
diagram of instability is calculated. The actual device parameters required for
observation of plasma wave generation are compared with those reported in
recent sub-terahertz emission experiments.",0512322v1
1994-11-24,Meson Correlators in QCD Vacuum - is Saturation the Right Approach ?,"Equal time, point to point correlation functions for spatially separated
meson currents are calculated with respect to a variational construct for the
ground state of QCD. With exact calculations, vector, axial vector and scalar
channels show qualitative agreement with the phenomenological predictions,
where as pseudoscalar channel does not. However, the pseudoscalar correlator,
when approximated by saturating with intermediate one pion states agrees with
results obtained from spectral density functions parametrised by pion decay
constant and $<\bar \psi \psi>$ value obtained from chiral perturbation theory.",9411402v1
1996-09-13,Saturation of Gluon Density at Small x,"Gluon distribution function at small x is computed using the extended
McLerran-Venugopalan model. A lipatov like enhancement is seen as well as a
non-trivial transverse momentum dependence which is estimated. It is shown that
gluon density saturates at small x which would lead to unitarization of cross
sections computed with this distribution function.",9609350v1
1997-09-04,A modified BFKL equation with unitarity,"We propose a modified Balitskii-Fadin-Kuraev-Lipatov equation from the
viewpoint of the resummation technique, which satisfies the unitarity bound.
The idea is to relax the strong rapidity ordering and to restrict phase space
for real gluon emissions in the evaluation of the BFKL kernel. It is found that
the gluon distribution function rises as a power of the Bjorken variable $x$,
and then saturates at $x\to 0$. We estimate that the saturation begins to occur
for $x< 10^{-4}$.",9709236v2
1998-02-19,Higgs mass saturation effect and the LHC discovery potential,"In view of recent perturbative and nonperturbative evidence that the peak of
the Higgs resonance saturates as the coupling increases, we examine the
potential of the future Large Hadron Collider to discover a heavy Higgs
resonance by gluon fusion.",9802367v1
1998-07-27,Saturation Effects in Deep Inelastic Scattering at low $Q^2$ and its Implications on Diffraction,"We present a model based on the concept of saturation for small $Q^2$ and
small $x$. With only three parameters we achieve a good description of all Deep
Inelastic Scattering data below $x=0.01$. This includes a consistent treatment
of charm and a successful extrapolation into the photoproduction regime. The
same model leads to a roughly constant ratio of diffractive and inclusive cross
section.",9807513v1
1999-04-20,Parton Saturation at Small x and in Large Nuclei,"Quark and gluon distributions in the light-cone wavefunction of a high energy
hadron or nucleus are calculated in the saturation regime. One loop
calculations are performed explicitly using the equivalence between the parton
distribution in the light-cone wavefunction and the production distribution of
that parton in a current-nucleon (nucleus) scattering. We argue that, except
for some overall numerical factors, the Weizsacker- Williams wavefunction
correctly gives the physics of the gluon distribution in a light-cone
wavefunction.",9904404v1
1999-07-29,From QCD to heavy ion collisions,"This talk will discuss how heavy ion experiments, when moving from SPS (10 +
10 GeV) to RHIC (100+100 GeV) and to LHC (2750+2750 GeV), will enter a new
domain of QCD in which the production of even large pT gluons is so abundant
that it is simultaneously perturbative but such that the phase space density of
gluons is saturated. The saturation scale is estimated, quantitative numbers
for the initial production of gluons at the LHC are given and options for their
subsequent evolution are outlined. For parametrically large nuclei and
energies, classical field methods will be applicable.",9907544v1
1999-10-27,Low Energy Constants from High Energy Theorems,"New constraints on resonance saturation in chiral perturbation theory are
investigated. These constraints arise because each consistent saturation scheme
must map to a representation of the full QCD chiral symmetry group. The
low-energy constants of chiral perturbation theory are then related by a set of
mixing angles. It is shown that vector meson dominance is a consequence of the
fact that nature has chosen the lowest-dimensional nontrivial chiral
representation. It is further shown that chiral symmetry places an upper bound
on the mass of the lightest scalar in the hadron spectrum.",9910525v1
2000-02-29,Non-saturation of the J/psi suppression at large transverse energy in the comovers approach,"We show that, contrary to recent claims, the $J/\psi$ suppression resulting
from its interaction with comovers does not saturate at large transverse energy
$E_T$. On the contrary, it shows a characteristic structure - change of
curvature near the knee of the $E_T$ distribution - which is due to the $E_T$
(or multiplicity) fluctuation, and agrees with recent experimental results.",0002300v1
2000-05-30,Loops and legs beyond perturbation theory,"Within the non-perturbative 1/N expansion, we discuss numerical methods for
calculating multi-loop Feynman graph needed to derive physical scattering
amplitudes. We apply higher order 1/N methods to the scalar sector of the
standard model, and show the existence of a mass saturation effect. The mass
saturation has direct implications for future searches at the LHC and at
possible muon colliders.",0005307v1
2000-07-24,Colour Dipoles and Saturation,"We employ values of the colour dipole cross section extracted from
electroproduction and photoproduction data to show that gluon saturation
effects are not required by the current HERA data but will become important in
the THERA energy region.",0007257v1
2000-09-19,A manifestation of a gluon saturation in e-A DIS,"This is a short presentation of our talks given at eRHIC Workshop at the BNL.
We give here a status report of our attempts to understand how gluon saturation
will manifest itself in deep inelastic scattering with nuclei. This summary
reflects our current understanding and shows directions of our research rather
then a final answer to the question. Nevertheless, we are able to share with
our reader our tentative answer to the question:``Why do we need to measure DIS
with nuclei and why these data will be complementary to the information
obtained from proton DIS"".",0009217v1
2000-09-25,Particle Rapidity Density Saturation in Heavy Ion Collisions and the Dual String Model,"We show that the Dual String Model with fusion leads, in heavy ion
collisions, to strict saturation of the particle (pseudo-)rapidity density,
normalised to the number of participant nucleons, as that number increases.
Asymptotically, as the centre-of-mass energy goes to infinity with the number
of participants fixed, this density approaches the nucleon-nucleon density.
  A comparison with recent WA98 data is presented.",0009288v1
2000-10-06,Searching Saturation in eA Processes,"The high density effects should be manifest at small x and/or large nuclei.
In this letter we consider the behavior of nuclear structure function $F_2^A$
slope in the kinematic region which could be explored in the future eA
colliders as a search of these effects. We verify that the high density implies
that the maximum value of the slope occurs at large values of the photon
virtuality, i.e. in a perturbative regime, and is dependent of the number of
nucleons A and energy. Our conclusion is that the measurement of this
observable will allow to explicit the saturation.",0010060v1
2001-02-06,QCD sum rules for rho mesons in nuclear matter,"We investigate QCD sum rules for vector currents in the rho meson channel in
the nuclear medium. For increased sensitivity, we subtract out the vacuum
contributions. With a saturation scheme often considered in the literature, we
find these subtracted sum rules to be unstable. It indicates the importance of
other contributions neglected in the saturation scheme. These include more
Landau singularities at low energy, additional operators in the medium, and
possibly the in-medium width of the rho meson.",0102062v2
2001-05-10,Vacuum Saturation Hypothesis and QCD Sum Rules,"The accuracy of the vacuum saturation hypothesis is discussed using the
examples of vacuum expectation values of four-quark operators and the parameter
$B$, which determines the short-distance contribution to the $K^0 - \bar K^0$
mixing. Note added: The approach based on sum rules in position (x-)space as
elaborated in the paper is relevant and useful tool for the current
phenomenology. In particular, it provides the unique possibility of direct
non-perturbative estimation of the VEV's of four-quark operators renormalized
in any scheme, including the MSbar one.",0105093v1
2001-05-31,Diffractive parton distributions and the saturation model,"We construct diffractive parton distributions in the model of DIS diffraction
in which the diffractive state is formed by the $q\bar{q}$ and $q\bar{q}g$
components. The interaction of such systems with the proton is described by the
dipole cross section given by the saturation model. We find Regge factorization
property with the measured at HERA depenedence on energy. The found parton
distributions are evolved with the DGLAP evolution equations to make a
comparison with the data.",0105333v1
2001-06-11,Scaling phenomena from non-linear evolution in high energy DIS,"The numerical solutions of the non-linear evolution equation are shown to
display the ``geometric'' scaling recently discovered in the experimental data.
The phenomena hold both for proton and nucleus targets for all $x$ below
$10^{-2}$ and $0.25 {\rm GeV^{2}}\le Q^2 \le 2.5\times10^3 {\rm GeV^{2}}$. The
scaling is practically exact (few percent error) in the saturation region. In
addition, an approximate scaling is found in the validity domain of the linear
evolution where it holds with about 10% accuracy.
  Basing on the scaling phenomena we determine the saturation scale $Q_s(x)$
and study both its $x$-dependence and the atomic number dependence for the
nuclei.",0106112v1
2001-06-28,Heavy ion collision multiplicities and gluon distribution functions,"Atomic number ($A$) and energy ($\roots$) scaling exponents of multiplicity
and transverse energy in heavy ion collisions are analytically derived in the
perturbative QCD + saturation model. The exponents depend on the small-$x$
behaviour of gluon distribution functions at an $x$-dependent scale. The
relation between initial state and final state saturation is also discussed.",0106330v1
2001-07-06,An example of resonance saturation at one loop,"We argue that the large-Nc expansion of QCD can be used to treat a Lagrangian
of resonances in a perturbative way. As an illustration of this we compute the
L_10 coupling of the Chiral Lagrangian by integrating out resonance fields at
one loop. Given a Lagrangian and a renormalization scheme, this is how in
principle one can answer in a concrete and unambiguous manner questions such as
at what scale resonance saturation takes place.",0107062v2
2001-11-29,Gluon Saturation at small x,"At very high energies, the relevant component of the hadron wavefunction can
be described as a Color Glass Condensate, i.e., a state of high density gluonic
matter whose distribution is random, but frozen over the relevant time scales.
The weight function for this distribution obeys a renormalization group
equation in the form of a functional Fokker-Planck equation. Its solution leads
to an effective theory which predicts gluon saturation at sufficiently high
energy, or small Bjorken's $x$.",0111400v1
2001-11-30,The Diffractive Logarithmic Slope and the Saturation Phenomena,"The logarithmic slope of the diffractive structure function is a potential
observable scanning the hard and soft contributions in diffraction, allowing to
disentangle the QCD dynamics. We report our calculations concerning this
quantity, in particular the estimates emerging from the saturation model
applied to diffraction dissociation.",0111444v1
2001-11-30,Saturation in DIS processes,"We examine HERA data with a view of determining whether unique signs of
saturation can be identified. Concentrating on two channels the logarithmic
slope of $F_{2}$, and the production of $J/\Psi$, which are sensitive to the
behaviour of $xG(x,Q^{2})$ the gluon density distribution in the proton, we
show that our model incorporating screening corrections and alternative models
comprising a sum of a ""soft"" and ""hard"" component provide good fits to the
data.",0111449v1
2001-11-30,Dipole-proton $S$-matrix derived from diffractive meson electroproduction,"Through a determination of the $S$-matrix element for the scattering of a
localized colour dipole on a proton, we show that saturation effects can
already be sizable at HERA. The saturation scale is found to be around 1-1.5
$GeV^2$ for the highest available energies and for central collisions, and is a
decreasing function of the impact parameter.",0111454v1
2002-04-18,Does parton saturation at high density explain hadron multiplicities at RHIC ?,"We discuss the recent claim that hadron multiplicities measured at RHIC
energies are directly described in terms of gluon degrees of freedom fixed from
the initial conditions of central heavy ion collisions. The argument is based
on the parton saturation scenario expected to be valid at high parton densities
and on the assumption of conserved gluon number. Alternatively we conjecture
that ""bottom-up"" equilibration before hadronization modifies this picture, due
to nonconservation of the number of gluons.",0204211v1
2002-05-03,Photon production in high energy proton-nucleus collisions,"We calculate the photon production cross-section in $pA$ collisions under the
assumption that the nucleus has reached the saturation regime, while the proton
can be described by the standard parton distribution functions. We show that
due to the strong classical field $O(1/g)$ of the nucleus, bremsstrahlung
diagrams become dominant over the direct photon diagrams. In particular, we
show that $\gamma-$jet transverse momentum spectrum and correlations are very
sensitive to gluon saturation effects in the nucleus.",0205037v1
2002-05-17,Thermal QCD sum rules for mesons,"A recently proposed scheme is used to saturate the spectral side of the QCD
sum rules derived from the thermal, two-point correlation functions of the
vector and the axial-vector currents. At low temperature, it constructs the
spectral representation from all the one-loop Feynman diagrams for the
two-point functions. The old saturation scheme treats incorrectly some of these
contributions. We end up with the familiar QCD sum rules obtained from the
difference of the two corresponding vacuum correlation functions. The
possibility of obtaining new sum rules in other media is discussed.",0205186v1
2002-05-29,Geometric Scaling in a Symmetric Saturation Model,"We illustrate geometric scaling for the photon-proton cross section with a
very simple saturation model. We describe the proton structure function F2 at
small x in a wide kinematical range with an elementary functional form and a
small number of free parameters. We speculate that the symmetry between low and
high Q2 recently discovered in the data could be related to a well-known
symmetry of the two-gluon- exchange dipole-dipole cross section.",0205319v1
2002-06-21,Gluon Distributions and Color Charge Correlations in a Saturated Light-cone Wavefunction,"We describe the light-cone wavefunction in the saturation regime in terms of
the density of gluons per unit of transverse phase space, the occupation
number, and in terms of the color charge correlator. The simple McLerran-
Venugopalan model gives what are claimed to be general results for the phase
space gluon density, but it does not well describe the general case for the
charge correlator. We derive the general momentum dependence and rapidity
dependence of the color charge correlator which exhibits strong color
shielding. A simplel physical picture which leads to these general results is
described.",0206216v1
2002-06-21,Parton saturation effects to the Drell-Yan process in the color dipole picture,"We report on the results obtained in the study of the parton saturation
effects, taken into account through the multiscattering Glauber-Mueller
approach, applied to the Drell-Yan (DY) process described in the color dipole
picture. As a main result, one shows that those effects play an important role
in the estimates of the DY differential cross section atRHIC energies.",0206218v1
2002-07-15,Saturation effects in DIS at low x,"We review basic ideas related to saturation of parton densities at small
value of the Bjorken variable x. A special emphasis is put on interpreting the
results from the ep deep inelastic scattering experiments at HERA.",0207188v3
2002-08-15,Heavy Quark Photoproduction in k_T Factorization Approach,"We investigate the heavy quark photoproduction based on the k_T factorization
approach, focusing on the results from the saturation model. The deviations in
the results using the unintegrated gluon distribution considering the
saturation model and the derivative of the collinear gluon distribution are
analysed. Total cross sections and p_T distributions are analysed in detail,
setting the deviations between the color dipole approximation and the complete
semihard approach.",0208155v2
2002-12-20,QCD Saturation and Deuteron-Nucleus Collisions,"We make quantitative predictions for the rapidity and centrality dependencies
of hadron multiplicities in dA collisions at RHIC basing on the ideas of parton
saturation in the Color Glass Condensate.",0212316v4
2003-02-04,Saturation of optimality limits in hadron-hadron scatterings,"In this paper the optimal unitarity lower bound on logarithmic slope of the
diffraction peak is investigated. It is shown that the unitarity lower bound is
just the optimal logarithmic slopes predicted by the principle of least
distance in space of states. A systematic tendency towards the saturation of
the most forward-peaked limit is observed from all the available experimental
data of all principal hadron-hadron (e.g., antiproton-proton, proton-proton,
kaon-proton, pion-proton) scatterings practically at all laboratory momenta.",0302018v2
2003-02-11,Deeply Virtual Compton Scattering and Saturation Approach,"We investigate the deeply virtual Compton scattering (DVCS) in the color
dipole approach, implementing the dipole cross section through the saturation
model, which interpolates successfully between soft and hard regimes. The
imaginary and real part of the DVCS amplitude are obtained and the results are
compared to the available data.",0302079v2
2003-02-20,Nonlinear corrections to the DGLAP equations; looking for the saturation limits,"The effects of the first nonlinear corrections to the DGLAP equations are
studied in light of the HERA data. Saturation limits are determined in the
DGLAP+GLRMQ approach for the free proton and for the Pb nucleus.",0302185v1
2003-03-14,Gamma^* - Gamma^* Scattering: Saturation and Unitarization in the BFKL approach,"In this paper $\gamma^* - \gamma^*$ scattering with large, but more or less
equal virtualities of two photons is discussed using BFKL dynamics, emphasizing
the large impact parameter behavior ($b_t$) of the dipole-dipole amplitude. It
is shown that the non-perturbative contribution is essential to fulfill the
unitarity constraints in the region of $b_t > 1/2 m_\pi$, where $m_{\pi}$ is
pion mass. The saturation and the unitarization of the dipole-dipole amplitude
is considered in the framework of the Glauber-Mueller approach. The main result
is that we can satisfy the unitarity constraints introducing the
non-perturbative corrections only in initial conditions (Born amplitude).",0303118v1
2003-05-06,Nuclear Structure Functions at Small x in Multiple Scattering Approaches,"A simple model for nuclear structure functions in the region of small $x$ and
small and moderate $Q^2$, is presented. It is a parameter-free extension, in
the Glauber-Gribov approach to nuclear collisions, of a saturation model for
the nucleon. A reasonable agreement with experimental data on ratios of nuclear
structure functions is obtained. The unintegrated gluon distribution and the
behavior of the saturation scale which result from this model are discussed.",0305057v1
2003-06-04,Decorrelation of forward dijets in DIS off nuclei,"Based on the color dipole QCD approach we discuss the multiple scattering
mechanism (MSM) of suppression of back-to-back azimuthal correlations of high
$p_{T}$ forward dijets in DIS off nuclei. We quantify the effect in terms of
acoplanarity/decorrelation momentum of jets. For hard dijets the decorrelation
momentum is found to be of the order of the nuclear saturation momentum $Q_A$.
Minijets with the transverse momentum below the saturation scale are proved to
be completely decorrelated. The analysis of DIS indicates that in heavy ion
collisions the contribution of MSM to the reactions dynamics can be of the
order of magnitude of the decorrelation effect observed at RHIC.",0306038v1
2003-08-28,Dilepton Transverse Momentum in the Color Dipole Approach,"We investigate the Drell-Yan transverse momentum distribution in the
framework of the color dipole approach. Special attention is paid to parton
saturation effects at high energies. Predictions at LHC energies ($\sqrt{s}=14$
TeV) are given and extrapolated down to ISR energies ($\sqrt{s}=62$ GeV).
Unitarity corrections are implemented through the multiple scattering
Glauber-Mueller approach and are compared with predictions of the BGBK
saturation model.",0308304v1
2003-11-03,System-size dependence,"The final state in The final state in heavy-ion collisions has a higher
degree of strangeness saturation than the one produced in collisions between
elementary particles like p-p or p-$\bar{p}$. A systematic analysis of this
phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider
and for $Au-Au$ collisions at RHIC and at AGS energies. Strangeness saturation
is shown to increase smoothly with the number of participants at AGS, CERN and
RHIC energies.",0311020v1
2004-07-09,Saturation and Traveling waves,"High parton density effects with energy obey non-linear QCD evolution
equations for which exact solutions are not known. The mathematical class to
which the non-linear Balitsky-Kovchegov equation belongs is identified, proving
the existence of asymptotic in energy traveling wave solutions which are
``universal'' i.e. independent of the initial conditions and of the precise
form of the non-linearities. This has an direct impact on geometrical scaling
and the diffusive transition to saturation, which is shown to be ``normal'' for
constant QCD coupling and ``abnormal'' for running coupling.",0407115v1
2004-08-02,Deeply Virtual Compton Scattering in the Saturation Approach,"We summarize here our investigations on the deeply virtual Compton scattering
(DVCS) in the color dipole approach, implementing the dipole cross section
through the saturation model. The role played by its QCD evolution and the
skewedness effects in the DVCS cross section are discussed. The
phenomenological results are compared to the recent H1 and ZEUS experimental
data.",0408019v1
2004-08-03,"CGC, QCD Saturation and RHIC data (Kharzeev-Levin-McLerran-Nardi point of view)","This is the talk given at the Workshop:""Focus on Multiplicitioes"", Bari,
Italy, 17-19 June,2004.. In this talk, we are going to discuss ion-ion and
deuteron - nucleus RHIC data and show that they support, if not more, the idea
of the new QCD phase: colour glass condensate with saturated parton density. .",0408039v2
2004-08-10,Saturation and non-linear effects in diffractive processes,"Through a direct implementation of the saturation regime resulting from the
unitarity limit in the impact parameter representation, we explore various
possibilities for the energy dependence of hadronic scattering. We show that it
is possible to obtain a good description of the scattering amplitude from a
hard pomeron provided one includes non-linear effects.",0408129v2
2004-09-22,QCD saturation in the dipole sector with correlations,"In this paper we study the description of saturation in Balitsky,
Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov and Kovner (B-JIMWLK)
picture when restricted to observables made up only from dipole operators. We
derive a functional form of the evolution equation for the dipole probability
distribution and find a one-parameter family of exact solutions to the dipole
evolution equations.",0409256v3
2004-12-22,Impact of saturation on spin effects in proton-proton scattering,"For pomerons described by a sum of two simple-pole terms, a soft and a hard
pomeron, the unitarity bounds from saturation in impact-parameter space are
examined. We consider the effect of these bounds on observables linked with
polarisation, such as the analyzing power in elastic proton-proton scattering,
for LHC energies. We obtain the s and t dependence of the Coulomb-nuclear
interference at small momentum transfer, and show that the effect of the hard
pomeron may be observed at the LHC.",0412341v1
2005-03-03,Neutrino texture saturating the CP asymmetry,"We study a neutrino mass texture which can explain the neutrino oscillation
data and also saturate the upper bound of the CP asymmetry $\epsilon_1$ in the
leptogenesis. We consider the thermal and non-thermal leptogenesis based on the
right-handed neutrino decay in this model. A lower bound of the reheating
temperature required for the explanation of the baryon number asymmetry is
estimated as $O(10^8)$GeV for the thermal leptogenesis and $O(10^{6})$GeV for
the non-thermal one.It can be lower than the upper bound of the reheating
temperature imposed by the cosmological gravitino problem. An example of the
construction of the discussed texture is also presented.",0503031v1
2005-03-24,The energy dependence of the saturation scale in DIS at low x,"Consistency of the previously suggested color-dipole representation of
deep-inelastic scattering (DIS_) and vector-meson production at low x with
DGLAP evolution allows one to predict the exponent of the W^2 dependence of the
saturation scale Lambda_sat^2(W^2) ~ (W^2)^C-2. One finds C_2^theory = 0.27 in
agreement with the model-independent analysis of the experimental data from
HERA on deep-inelastic electron scattering.",0503251v3
2005-04-11,The Balitsky-Kovchegov equation in full momentum space,"We analyse the Balitsky-Kovchegov (BK) saturation equation in momentum space
and solve it numerically. We confirm that, in the limit where the transverse
momentum of the incident particle k is much bigger than the momentum transfer
q, the equation admits travelling-wave solutions. We extract the q dependence
of the saturation scale Q_s(Y) and verify that Q_s(Y=cste) scales as
max(q,Q_T), where Q_T is the scale caracterizing the target.",0504080v2
2005-04-15,Open and hidden charm production in pA collisions,"We discuss production of charmed mesons and J/Psi in p(d)A collisions at high
energies. We argue that when the saturation scale Qs characterizing the parton
density in a nucleus exceeds the quark mass m, the naive perturbation theory
breaks down. Consequently, we calculate a process of heavy quark production in
both open and hidden channels in the framework of the parton saturation model
(Color Glass Condensate). We demonstrate that at RHIC such description is in
agreement with experimental data on charm production.",0504133v1
2005-07-08,"J/Psi photo- and electroproduction, the saturation scale and the gluon structure function","Our approach to low-x deep inelastic scattering based on the ell-perp
factorization of perturbative QCD (the color-dipole picture) yields
parameter-free absolute predictions for J/Psi production. The connection of
J/Psi production to the low-x saturation scale and to the gluon structure
function is clarified.",0507098v3
2005-09-05,Testing saturation with large-mass diffraction in DIS,"In large-mass diffraction in deep inelastic scattering, we study the gluon
jet close to the rapidity gap and show that its transverse momentum spectrum is
peaked around a value which caracterizes the onset of S-matrix unitarity. We
argue that such a measurement of diffractive jets could help understanding if
at the present energies, unitarity comes as a consequence of saturation.",0509034v1
2005-12-20,Asymptotic neutrino-nucleon cross section and saturation effects,"In this paper we present a simple analytic expression for the (spin-averaged)
neutrino-nucleon cross section for ultra-high energies at twist-2, obtained as
the asymptotic limit of our previous findings. This expression gives values for
the cross section in remarkable numerical agreement with the previous numerical
evaluation in the energy region relevant for forthcoming neutrino experiments.
Moreover, we discuss the role and the relevance of saturation and recombination
effects in our approach, in comparison with other recent suggestions.",0512259v1
2005-12-27,Dipole amplitude correlation in saturation model beyond mean field approximation,"In this paper we calculate dipole amplitude and dipole amplitude correlations
using first and second equation from Balitsky-Kovchegov hierarchy. Our analysis
shows that even in presence of weak dipole correlation in initial condition
mean field approximation breaks down through evolution. This difference
asymptotically grows not only by absolute value but also by relative difference
of dipole correlation from mean field value. This could affect physical values
related to dipole correlation such as elliptic flow $v_2$ and 'back-forward'
asymmetry in saturation model.",0512343v1
2006-05-13,DGLAP improved saturation model with heavy flavours,"The DGLAP improved saturation model of Bartels, Golec and Kowalski is
supplemented by the contribution from the heavy quarks: charm and beauty. It is
shown to give good description of both the total proton structure function F2
and, as a prediction, the heavy quarks contribution F2c and F2b. The reasonable
agreement for the longitudinal and diffractive structure functions is also
found.",0605154v1
2006-06-07,Geometric scaling in diffractive deep inelastic scattering,"The geometric scaling property observed in the HERA data at small x, that the
deep inelastic scattering (DIS) total cross-section is a function of only the
variable Q^2*x^\lambda, has been argued to be a manifestation of the saturation
regime of QCD and of the saturation scale Q^2_s(x) x^{-\lambda}. We show that
this implies a similar scaling in the context of diffractive DIS and we
observe, for several diffractive observables, that the experimental data from
HERA confirm the expectations of this scaling.",0606079v2
2006-07-25,Heavy flavour production in DGLAP improved saturation model,"The charm and beauty quark production in deep inelastic scattering at low
values of the Bjorken variable x is considered in the DGLAP improved saturation
model. After fitting parameters of the model to the structure function F_2, the
heavy quark contributions Fc_2 and Fb_2 are predicted. A good description of
the data is found. Predictions for the longitudinal structure function F_L and
the diffractive structure function FD_2 are also presented.",0607276v3
2006-08-04,A geometrical scaling solution to the BFKL Pomeron Calculus in the saturation domain,"In this paper the exact analytical solution is found for the BFKL Pomeron
calculus in QCD, in which all Pomeron loops have been included. This solution
manifests the geometrical scaling behaviour and matches with the solution to
the linear evolution equation on the line $r^2= 1/Q^2_s(x)$, where $r$ is the
dipole size and $Q_s$ is the saturation momentum.",0608043v2
2006-10-23,Mini review on saturation and recent developments,"I discuss the saturation regime of QCD: the weak-coupling regime that
describes large parton densities inside hadrons and the resulting high-energy
behavior of scattering amplitudes. I briefly review past successes in the
context of deep inelastic scattering at HERA and forward particle production at
RHIC, and I present some recent progresses that significantly improved our
understanding of high-energy scattering in QCD.",0610300v1
2006-12-01,Traveling waves and the renormalization group improved Balitsky-Kovchegov equation,"I study the incorporation of renormalization group (RG) improved BFKL kernels
in the Balitsky-Kovchegov (BK) equation which describes parton saturation. The
RG improvement takes into account important parts of the next-to-leading and
higher order logarithmic corrections to the kernel. The traveling wave front
method for analyzing the BK equation is generalized to deal with RG-resummed
kernels, restricting to the interesting case of fixed QCD coupling. The results
show that the higher order corrections suppress the rapid increase of the
saturation scale with increasing rapidity. I also perform a ""diffusive""
differential equation approximation, which illustrates that some important
qualitative properties of the kernel change when including RG corrections.",0612005v1
2006-12-11,Search for new physics from $B\toπφ$,"We investigate the pure penguin process $B^-\to \pi^-\phi$ using QCD
factorization approach to calculate hadronic matrix elements to the $\alpha_s$
order in some well-known NP models. It is shown that the NP contributions in
R-parity conserved SUSY models and 2HDMs are not enough to saturate the
experimental upper bounds for $B\to \phi \pi$. We have shown that the flavor
changing $Z^\prime$ models can make the branching ratios of $B\to \phi \pi$ to
saturate the bound under all relevant experimental constraints.",0612116v1
2007-01-26,QCD at small x and nucleus-nucleus collisions,"At large collision energy sqrt(s) and relatively low momentum transfer Q, one
expects a new regime of Quantum Chromo-Dynamics (QCD) known as ""saturation"".
This kinematical range is characterized by a very large occupation number for
gluons inside hadrons and nuclei; this is the region where higher twist
contributions are as large as the leading twist contributions incorporated in
collinear factorization. In this talk, I discuss the onset of and dynamics in
the saturation regime, some of its experimental signatures, and its
implications for the early stages of Heavy Ion Collisions.",0701225v1
2007-02-03,Nuclear Modification to Parton Distribution Functions and Parton Saturation,"We introduce a generalized definition of parton distribution functions (PDFs)
for a more consistent all-order treatment of power corrections. We present a
new set of modified DGLAP evolution equations for nuclear PDFs, and show that
the resummed $\alpha_s A^{1/3}/Q^2$-type of leading nuclear size enhanced power
corrections significantly slow down the growth of gluon density at small-$x$.
We discuss the relation between the calculated power corrections and the
saturation phenomena.",0702040v1
1995-11-17,Particle Growth and BPS Saturated States,"Consistency of the Bekenstein bound on entropy requires the physical
dimensions of particles to grow with momentum as the particle is boosted to
transplanckian energies. In this paper the problem of particle growth in
heterotic string theory is mapped into a problem involving the properties of
BPS saturated black holes as the charge is increased. Explicit calculation
based on the black hole solutions of Sen are shown to lead to a growth pattern
consistent with the holographic speculation described in earlier work.",9511116v2
1997-06-30,Complex BPS domain walls and phase transition in mass in supersymmetric QCD,"We study the domain walls connecting different chirally asymmetric vacua in
supersymmetric QCD. We show that BPS - saturated solutions exist only in the
limited range of mass. When m exceeds some critical value, the domain wall
either ceases to be BPS - saturated or disappears altogether. In any case, the
properties of the system are qualitatively changed.",9706217v2
1997-12-08,BPS Saturation from Null Reduction,"We show that any $d$-dimensional strictly stationary, asymptotically
Minkowskian solution $(d\ge 4)$ of a null reduction of $d+1$-dimensional pure
gravity must saturate the BPS bound provided that the KK vector field can be
identified appropriately. We also argue that it is consistent with the field
equations.",9712078v1
1998-11-10,Non-Perturbative States in Superstring Theories,"Massless BPS-saturated states in toroidally compactified heterotic string
were discussed first. Then, I constructed a large class of BPS-saturated states
of toroidally compactified type II string theories. They were parametrized by
four independent parameters. Both orthogonal and non-orthogonal intersections
of non-perturbative states in the corresponding ten dimensional theories were
discussed. Phenomenologically, I considered the string effect in the form of
threshold corrections on dilatonic charged black holes, and the superpotential
of N=1 supergravity theory",9811093v1
1999-09-14,BPS States with Extra Supersymmetry,"A state saturating a BPS bound derived from a supersymmetry algebra preserves
some fraction of the supersymmetry. This fraction of supersymmetry depends on
the charges carried by the system, and we show that in general there are
configurations of charges for which a BPS state would preserve more than half
the original supersymmetry. We investigate configurations that could preserve
3/4 supersymmetry in string theory, M-theory and supersymmetric field theories
and discuss whether states saturating these bounds actually occur in these
theories.",9909098v3
1999-12-10,Domain wall junctions in a generalized Wess-Zumino model,"We investigate domain wall junctions in a generalized Wess-Zumino model with
a Z(N) symmetry. We present a method to identify the junctions which are
potentially BPS saturated. We then use a numerical simulation to show that
those junctions indeed saturate the BPS bound for N=4. In addition, we study
the decay of unstable non-BPS junctions.",9912081v3
2001-07-05,Deformed Boost Transformations That Saturate at the Planck Scale,"We derive finite boost transformations based on the Lorentz sector of the
bicross-product-basis $\kappa$-Poincare' Hopf albegra. We emphasize the role of
these boost transformations in a recently-proposed new relativistic theory. We
find that when the (dimensionful) deformation parameter is identified with the
Planck length, which together with the speed-of-light constant has the status
of observer-independent scale in the new relativistic theory, the deformed
boosts saturate at the value of momentum that corresponds to the inverse of the
Planck length.",0107039v1
2002-04-06,Supercurves,"The TST-dual of the general 1/4-supersymmetric D2-brane supertube is
identified as a 1/4-supersymmetric IIA `supercurve': a string with arbitrary
transverse displacement travelling at the speed of light. A simple proof is
given of the classical upper bound on the angular momentum, which is also
recovered as the semi-classical limit of a quantum bound. The classical bound
is saturated by a `superhelix', while the quantum bound is saturated by a
bosonic oscillator state in a unique SO(8) representation.",0204062v1
2005-05-02,"Scattering amplitudes for particles and strings in six-dimensional (2,0) theory","We study the scattering of low-energy tensor multiplet particles against a
BPS saturated cosmic string. We show that the corresponding S-matrix is largely
determined by symmetry considerations. We then apply a specific supersymmetric
model of (2,0) theory and calculate the scattering amplitudes to lowest
non-trivial order in perturbation theory. Our results are valid as long as the
energy of the incoming particle is much lower than the square root of the
string tension. The calculation involves the quantization of a (2,0) tensor
multiplet and the derivation of an effective action describing the low-energy
particles in the presence of a nearly BPS saturated string.",0505015v2
1993-08-15,A saturated model of an unsuperstable theory of cardinality greater than its theory has the small index property,"A model M of cardinality lambda is said to have the small index property if
for every G subseteq Aut(M) such that [Aut(M):G] <= lambda there is an A
subseteq M with |A|< lambda such that Aut_A(M) subseteq G. We show that if M^*
is a saturated model of an unsuperstable theory of cardinality > Th(M), then
M^* has the small index property.",9308216v1
2000-07-11,Passive scalar intermittency in low temperature helium flows,"We report new measurements of turbulent mixing of temperature fluctuations in
a low temperature helium gas experiment, spanning a range of microscale
Reynolds number, $R_{\lambda}$, from 100 to 650. The exponents $\xi_{n}$ of the
temperature structure functions $<|\theta(x+r)-\theta(x)|^n > \sim r^{\xi_{n}}$
are shown to saturate to $\xi_{\infty} \simeq 1.45 \pm 0.1$ for the highest
orders, $n \sim 10$. This saturation is a signature of statistics dominated by
front-like structures, the cliffs. Statistics of the cliff characteristics are
performed, particularly their width are shown to scale as the Kolmogorov length
scale.",0007011v1
2003-03-21,Bifurcations and Averages in the Homoclinic Chaos of a Laser with a Saturable Absorber,"The dynamical bifurcations of a laser with a saturable absorber were
calculated, with the 3-2 level model, as function of the gain parameter. The
average power of the laser is shown to have specific behavior at bifurcations.
The succession of periodic-chaotic windows, known to occur in the homoclinic
chaos, was studied numerically. A critical exponent of 1/2 is found on the
tangent bifurcations from chaotic into periodic pulsations.",0303047v1
2003-05-02,Phase separation in coupled chaotic maps on fractal networks,"The phase ordering dynamics of coupled chaotic maps on fractal networks are
investigated. The statistical properties of the systems are characterized by
means of the persistence probability of equivalent spin variables that define
the phases. The persistence saturates and phase domains freeze for all values
of the coupling parameter as a consequence of the fractal structure of the
networks, in contrast to the phase transition behavior previously observed in
regular Euclidean lattices. Several discontinuities and other features found in
the saturation persistence curve as a function of the coupling are explained in
terms of changes of stability of local phase configurations on the fractals.",0305004v1
2004-09-27,Exact Solutions of the Saturable Discrete Nonlinear Schrodinger Equation,"Exact solutions to a nonlinear Schr{\""o}dinger lattice with a saturable
nonlinearity are reported. For finite lattices we find two different
standing-wave-like solutions, and for an infinite lattice we find a localized
soliton-like solution. The existence requirements and stability of these
solutions are discussed, and we find that our solutions are linearly stable in
most cases. We also show that the effective Peierls-Nabarro barrier potential
is nonzero thereby indicating that this discrete model is quite likely
nonintegrable.",0409057v1
2005-06-17,Instabilities of multi-hump vector solitons in coupled nonlinear Schroedinger equations,"Spectral stability of multi-hump vector solitons in the Hamiltonian system of
coupled nonlinear Schr\""{o}dinger (NLS) equations is investigated both
analytically and numerically. Using the closure theorem for the negative index
of the linearized Hamiltonian, we classify all possible bifurcations of
unstable eigenvalues in the systems of coupled NLS equations with cubic and
saturable nonlinearities. We also determine the eigenvalue spectrum numerically
by the shooting method. In case of cubic nonlinearities, all multi-hump vector
solitons in the non-integrable model are found to be linearly unstable. In case
of saturable nonlinearities, stable multi-hump vector solitons are found in
certain parameter regions, and some errors in the literature are corrected.",0506034v1
2006-03-30,Radiationless Travelling Waves In Saturable Nonlinear Schrödinger Lattices,"The longstanding problem of moving discrete solitary waves in nonlinear
Schr{\""o}dinger lattices is revisited. The context is photorefractive crystal
lattices with saturable nonlinearity whose grand-canonical energy barrier
vanishes for isolated coupling strength values. {\em Genuinely localised
travelling waves} are computed as a function of the system parameters {\it for
the first time}. The relevant solutions exist only for finite velocities.",0603071v2
2006-08-10,Dark Solitons in Discrete Lattices: Saturable versus Cubic Nonlinearities,"In the present work, we study dark solitons in dynamical lattices with the
saturable nonlinearity and compare them with those in lattices with the cubic
nonlinearity. This comparison has become especially relevant in light of recent
experimental developments in the former context. The stability properties of
the fundamental waves, for both on-site and inter-site modes, are examined
analytically and corroborated by numerical results. Furthermore, their
dynamical evolution when they are found to be unstable is obtained through
appropriately crafted numerical experiments.",0608023v1
2002-01-28,Systematics of mid-rapidity K-/pi ratio in heavy-ion collisions,"It is observed that K-/pi in A+A and possibly p+p and pbar+p collisions
follows an interesting systematic in omega, the pion transverse energy per unit
of rapidity and transverse overlap area. The systematics show a linear increase
of K-/pi with omega in the AGS and SPS energy regime and a saturation at RHIC
energy. The systematics indicate that omega might be the relevant variable
underlying K-/pi. At high energy, the omega variable is related to the gluon
saturation scale in high density QCD, and perhaps to the initial energy density
in the Bjorken picture.",0201018v2
1997-06-02,Nuclear Saturation with in-Medium Meson Exchange Interactions,"We show that the assumption of dropping meson masses together with
conventional many-body effects, implemented in the relativistic Dirac-Brueckner
formalism, explains nuclear saturation. We use a microscopic model for
correlated $2\pi$ exchange and include the standard many-body effects on the
in-medium pion propagation, which initially increase the attractive
nucleon-nucleon ($NN$) potential with density. For the vector meson exchanges
in both the $\pi\pi$ and $NN$ sector, we assume Brown-Rho scaling which---in
concert with `chiral' $\pi\pi$ contact interactions---reduces the attraction at
higher densities.",9706006v1
1998-07-14,Chiral dynamics of the nuclear equation of state,"We present a new chiral power expansion scheme for the nuclear equation of
state. The scheme is effective in the sense that it is constructed to work
around nuclear saturation density. The leading and subleading terms are
evaluated and are shown to provide an excellent equation of state. As a further
application we considered the chiral quark condensate in nuclear matter.
Already at nuclear saturation density we predict a substantially smaller
reduction of the condensate as compared to conventional approaches.",9807040v1
2003-08-19,"Chiral solitons in nuclei: Saturation, EMC effect and Drell-Yan experiments","The Chiral Quark-Soliton model of the nucleon contains a mechanism for an
attractive interaction between nucleons. This, along with the exchange of
vector mesons between nucleons, is used to compute the saturation properties of
infinite nuclear matter. This provides a new way to asses the effects of the
nuclear medium on a nucleon that includes valence and sea quarks. We show that
the model simultaneously describes the nuclear EMC effect and the related
Drell-Yan experiments.",0308048v2
2003-12-01,Equation of state for nuclear matter based on density dependent effective interaction,"An interesting method of obtaining equation of state for nuclear matter, from
a density dependent M3Y interaction, by minimizing the energy per nucleon is
described. The density dependence parameters of the interaction are obtained by
reproducing the saturation energy per nucleon and the saturation density of
spin and isospin symmetric cold infinite nuclear matter. The nuclear matter
equation of state thus obtained is then used to calculate the pressure, the
energy density, the nuclear incompressibility and the velocity of sound in
nuclear medium. The results obtained are in good agreement with experimental
data and provide a unified description of radioactivity, scattering and nuclear
matter.",0312002v2
2006-07-18,The High-Density Symmetry Energy and Direct Urca,"The symmetry energy of nucleonic matter is usually assumed to be quadratic in
the isospin density. While this may be justified at sub-saturation densities,
there is no need to enforce this restriction at super-saturation densities. The
presence of a quartic term can strongly modify the critical density for the
direct Urca process which leads to faster cooling of neutron stars. Neutron
star cooling predictions which lie below the observational data can, for some
equations of state, be repaired with a quartic term which effectively turns off
the direct Urca process.",0607040v1
1994-04-20,Whitham deformations partially saturating the modulational instability in the nonlinear Schrodinger equation,"In the framework of Gurevich and Pitaevskii approach [1] we construct
modulated by Whitham [2] solution of nonlinear Shrodinger (NS) equation
partially saturating the modulational instability. This solution describes new
scenario of monochromatic wave evolution in NS equation which leads to
generation of new phase and oscillation region.",9404003v1
2003-07-18,Saturated-absorption spectroscopy: Eliminating crossover resonances using co-propagating beams,"We demonstrate a new technique for saturated-absorption spectroscopy using
co-propagating beams that does not have the problem of crossover resonances.
The pump beam is locked to a transition and its absorption signal is monitored
while the probe beam is scanned. As the probe comes into resonance with another
transition, the pump absorption is reduced and the signal shows a Doppler-free
dip. We use this technique to measure hyperfine intervals in the $D_2$ line of
$^{85}$Rb with a precision of 70 kHz, and to resolve hyperfine levels in the
$D_2$ line of $^{39}$K that are less than 10 MHz apart.",0307095v1
2003-09-23,Saturation induced coherence loss in coherent backscattering of light,"We use coherent backscattering (CBS) of light by cold Strontium atoms to
study the mutual coherence of light waves in the multiple scattering regime. As
the probe light intensity is increased, the atomic optical transition starts to
be saturated. Nonlinearities and inelastic scattering then occur. In our
experiment, we observe a strongly reduced enhancement factor of the coherent
backscattering cone when the intensity of the probe laser is increased,
indicating a partial loss of coherence in multiple scattering.",0309095v1
2006-07-04,Beam interactions in one-dimensional saturable waveguide arrays,"The interaction between two parallel beams in one-dimensional discrete
saturable systems has been investigated using lithium niobate nonlinear
waveguide arrays. When the beams are separated by one channel and in-phase it
is possible to observe soliton fusion at low power levels. This new result is
confirmed numerically. By increasing the power, soliton-like propagation of
weakly-coupled beams occurs. When the beams are out-of-phase the most
interesting result is the existence of oscillations which resemble the recently
discovered Tamm oscillations.",0607028v1
1996-04-29,A Class of Quantum Error-Correcting Codes Saturating the Quantum Hamming Bound,"I develop methods for analyzing quantum error-correcting codes, and use these
methods to construct an infinite class of codes saturating the quantum Hamming
bound. These codes encode $k=n-j-2$ qubits in $n=2^j$ qubits and correct $t=1$
error.",9604038v2
1998-11-13,Stationary States in Saturated Two-Photon Processes and Generation of Phase-Averaged Mixtures of Even and Odd Quantum States,"We consider a relaxation of a single mode of the quantized field in a
presence of one- and two-photon absorption and emission processes. Exact
stationary solutions of the master equation for the diagonal elements of the
density matrix in the Fock basis are found in the case of completely saturated
two-photon emission. If two-photon processes dominate over single-photon ones,
the stationary state is a mixture of phase averaged even and odd coherent
states.",9811031v1
2003-07-30,Sub and Super-Luminal Propagation of Intense Pulses in Media with Saturated and Reverse Absorption,"We develop models for the propagation of intense pulses in solid state media
which can have either saturated absorption or exhibit reverse absorption . We
show that the experiments of Bigelow {\it et al.}[Phys. Rev. Lett. {\bf 90},
113903 (2003); Science {\bf 301}, 200 (2003).] on subluminal propagation in
Ruby and superluminal propagation in Alexandrite are well explained by
modelling them as three level and four level systems coupled to Maxwell
equations. We present results well beyond the traditional pump-probe approach.",0307224v1
2004-03-08,Coherent backscattering of light by atoms in the saturated regime,"We present the first calculation of coherent backscattering with inelastic
scattering by saturated atoms. We consider the scattering of a
quasi-monochromatic laser pulse by two distant atoms in free space. By
restricting ourselves to scattering of two photons, we employ a perturbative
approach, valid up to second order in the incident laser intensity. The
backscattering enhancement factor is found to be smaller than two (after
excluding single scattering), indicating a loss of coherence between the doubly
scattered light emitted by both atoms. Since the undetected photon carries
information about the path of the detected photon, the coherence loss can be
explained by a which-path argument, in analogy with a double-slit experiment.",0403057v1
2004-11-22,Phase delay time and superluminal propagation in barrier tunneling,"In this work we study the behaviour of Wigner phase delay time for tunneling
in the reflection mode. Our system consists of a circular loop connected to a
single wire of semi-infinite length in the presence of Aharonov-Bohm flux. We
calculate the analytical expression for the saturated delay time. This
saturated delay time is independent of Aharonov- Bohm flux and the width of the
opaque barrier thereby generalizing the Hartman effect. This effect implies
superluminal group velocities as a consequence. We also briefly discuss the
concept called ""space collapse or space destroyer"".",0411161v1
2005-10-20,Lyapunov Generation of Entanglement and the Correspondence Principle,"We show how a classically vanishing interaction generates entanglement
between two initially nonentangled particles, without affecting their classical
dynamics. For chaotic dynamics, the rate of entanglement is shown to saturate
at the Lyapunov exponent of the classical dynamics as the interaction strength
increases. In the saturation regime, the one-particle Wigner function follows
classical dynamics better and better as one goes deeper and deeper in the
semiclassical limit. This demonstrates that quantum-classical correspondence at
the microscopic level requires neither high temperatures, nor coupling to a
large number of external degrees of freedom.",0510157v1
2007-05-11,Observation of higher-order solitons in defocusing waveguide arrays,"We observe experimentally higher-order solitons in waveguide arrays with
defocusing saturable nonlinearity. Such solitons can comprise several in-phase
bright spots and are stable above a critical power threshold. We elucidate the
impact of the nonlinearity saturation on the domains of existence and stability
of the observed complex soliton states.",0705.1704v1
2007-05-11,Kerr quasinormal modes and Hod's time-temperature bound,"We give an explicit expression for the frequencies of slowly damped
quasinormal modes of near-extreme Kerr black holes. It follows from this
expression that the near-extreme Kerr holes obey the Hod's bound: in the limit
of maximal rotation, $\lim \sup \omega_{IS}/T\leq \pi / \hbar$, where $\omega
_{IS}$ is the decay rate of the slowest decaying quasinormal mode, $T$ is the
black hole temperature. On the other hand, the bound is not saturated in the
sense that $\lim \inf \omega_{IS}/T< \pi /\hbar$ is a strict inequality. {\it
It remains unclear} whether the bound is saturated in the sense that $\lim \sup
\omega_{IS}/T= \pi /\hbar$.",0705.1725v1
2007-05-15,Elliptic flow from pQCD + saturation + hydro model,"We have previously predicted multiplicities and transverse momentum spectra
of hadrons for the most central LHC Pb+Pb collisions at $\sqrt{s_{NN}}=5.5$ TeV
using initial state for hydrodynamic evolution from pQCD + final state
saturation model. By considering binary collision and wounded nucleon profiles
we extend these studies to non-central collisions, and predict the $p_{T}$
dependence of minimum bias $v_{2}$ for pions at the LHC. For protons we also
show how the $p_{T}$ dependence of $v_2$ changes from RHIC to the LHC.",0705.2114v1
2007-05-23,Soliton emission in amplifying optical lattice surfaces,"We address surface solitons supported by the interface of optical lattices
imprinted in saturable media with surface-localized gain. The nonlinearity
saturation puts restrictions on the maximal energy flow carried by surface
solitons. As a consequence, the presence of thin amplifying layer near the
surface results in the controllable emission of solitons towards the lattice at
angles depending on the amplification rate and on lattice depth.",0705.3461v1
2007-06-11,Non-forward Balitsky-Kovchegov equation and Vector Mesons,"Considering the Balitsky-Kovchegov QCD evolution equation in full momentum
space, we derive the travelling wave solutions expressing the nonlinear
saturation constraints on the dipole scattering amplitude at non-zero momentum
transfer. A phenomenological application to elastic vector meson production
shows the compatibility of data with the QCD prediction: an enhanced saturation
scale at intermediate momentum transfer.",0706.1446v1
2007-06-12,x-Evolution of Phenomenological Dipole Cross Sections,"Deep inelastic scattering at small x can be described very effectively using
saturation inspired dipole models. We investigate whether such models are
compatible with the numerical solutions of the Balitsky-Kovchegov (BK) equation
which is expected to describe the nonlinear evolution in x of the dipole cross
section. We find that the BK equation yields results that are qualitatively
different from those of phenomenological studies. Geometric scaling is
recovered only towards asymptotic rapidities. In this limit the value of the
anomalous dimension gamma(r,x) at the saturation scale approaches approximately
0.44, in contrast to the value 0.63 commonly used in the models.",0706.1666v1
2007-07-10,Effect of Two Level System Saturation on Charge Noise in Josephson Junction Qubits,"We show that charge noise $S_Q$ in Josephson qubits can be produced by
fluctuating two level systems (TLS) with electric dipole moments in the
substrate using a flat density of states. At high frequencies the frequency and
temperature dependence of the charge noise depends on the ratio $J/J_c$ of the
electromagnetic flux $J$ to the critical flux $J_c$. It is not widely
appreciated that TLS in small qubits can easily be strongly saturated with
$J/J_c\gg 1$. Our results are consistent with experimental conclusions that
$S_Q\sim 1/f$ at low frequencies and $S_Q\sim f$ at high frequencies.",0707.1514v1
2007-07-15,Saturation model in the non-Glauber approach,"In this paper a new saturation model is presented. This model is based on the
theoretical solution for the generating functional, and it is quite different
and not more complicated than the Glauber-like approach used before. The model
describes the structure function F_{2} of the proton, as well as the
diffractive structure function F_{2}^{D}. We show the difference between our
model, and the eikonal approach by calculating the multiplicity distribution,
using the AGK cutting rules strategy.",0707.2202v4
2007-07-19,Strong saturation absorption imaging of dense clouds of ultracold atoms,"We report on a far above saturation absorption imaging technique to
investigate the characteristics of dense packets of ultracold atoms. The
transparency of the cloud is controlled by the incident light intensity as a
result of the non-linear response of the atoms to the probe beam. We detail our
experimental procedure to calibrate the imaging system for reliable
quantitative measurements, and demonstrate the use of this technique to extract
the profile and its spatial extent of an optically thick atomic cloud.",0707.2930v1
2007-08-06,Step-up simultaneous tests for identifying active effects in orthogonal saturated designs,"A sequence of null hypotheses regarding the number of negligible effects
(zero effects) in orthogonal saturated designs is formulated. Two step-up
simultaneous testing procedures are proposed to identify active effects
(nonzero effects) under the commonly used assumption of effect sparsity. It is
shown that each procedure controls the experimentwise error rate at a given
$\alpha$ level in the strong sense.",0708.0715v1
2007-08-09,Saturation of elliptic flow and shear viscosity,"Effect of shear viscosity on elliptic flow is studied in causal dissipative
hydrodynamics in 2+1 dimensions. Elliptic flow is reduced in viscous dynamics.
Causal evolution of minimally viscous fluid ($\eta/s$=0.08), can explain the
PHENIX data on elliptic flow in 16-23% Au+Au collisions up to $p_T\approx$3.6
GeV. In contrast, ideal hydrodynamics, can explain the same data only up to
$p_T\approx$1.5 GeV. $p_T$ spectra of identified particles are also better
explained in minimally viscous fluid than in ideal dynamics. However,
saturation of elliptic flow at large $p_T$ is not reproduced.",0708.1252v2
2007-10-10,Optical saturation driven by exciton confinement in molecular-chains: a TDDFT study,"We have identified excitonic confinement in one-dimensional molecular chains
(i.e. polyacetylene and H$_2$) as the main driving force for the saturation of
the chain polarizability as a function of the number of molecular units. This
conclusion is based on first principles time--dependent density functional
theory calculations performed with a new derived exchange--correlation kernel.
The failure of simple local and semi--local functionals is shown to be related
to the lack of memory effects, spatial ultranonlocality, and self--interaction
corrections. These effects get smaller as the gap of the system reduces, in
which case such simple approximations do perform better.",0710.2057v1
2007-10-25,Robust control of uncertain multi-inventory systems via Linear Matrix Inequality,"We consider a continuous time linear multi inventory system with unknown
demands bounded within ellipsoids and controls bounded within ellipsoids or
polytopes. We address the problem of ""-stabilizing the inventory since this
implies some reduction of the inventory costs. The main results are certain
conditions under which ""-stabilizability is possible through a saturated linear
state feedback control. All the results are based on a Linear Matrix
Inequalities (LMIs) approach and on some recent techniques for the modeling and
analysis of polytopic systems with saturations.",0710.4765v1
2007-11-16,Electromagnetically induced transparency at high optical power,"We observe electromagnetically induced transparency (EIT) in Rb vapor at
various optical intensities, starting from below saturation to several times
the saturation intensity. The observed Lorentzian width of the EIT signal is
very small. Solving the time dependant density matrix equation of motion with a
phenomenological decay constant, we find an expression suitable in explaining
the EIT signal. In this experimental observation and theoretical analysis
intensity of EIT signal and its Lorentzian width increases with Rabi frequency
of optical field.",0711.2662v2
2007-12-11,Saturation of Transverse Energy per Charged Hadron and Freeze-Out Criteria in Heavy-Ion Collisions,"For beam energies from SPS to RHIC, the transverse energy per charged
particle, $E_T/N_{\textrm{ch}}$, saturates at a value of approximately 0.8 GeV.
A direct connection between this value and the freeze-out criterium $E/N
\approx 1$ GeV for the primordial energy and particle number in the hadronic
resonance gas model is established.",0712.1671v1
2007-12-19,An essentially saturated surface not of Kaehler-type,"It is shown that if $X$ is an Inoue surface of type $S_M$ then the
irreducible components of the Douady space of $X^n$ are compact, for all $n>0$.
This gives an example of an essentially saturated compact complex manifold (in
the sense of model theory) that is not of Kaehler-type. Among the known compact
complex surfaces without curves, it is shown that these are the only examples.",0712.3234v1
2008-01-31,Towards the saturation of the Froissart bound,"It is the aim of this paper to summarize results about the construction of
amplitudes, which rigorously satisfy Mandelstam analyticity, crossing symmetry,
and (at least partly) the constraints imposed by elastic and inelastic
unitarity. The results are discussed under particular emphasis of a strong
increase of the absorptive part of the forward amplitude and the saturation of
the Froissart bound.",0801.4871v3
2008-02-04,Geometric Scaling in Mueller-Navelet Jets,"We argue that the production of Mueller-Navelet jets at the LHC represents a
convenient environment to study gluon saturation and high energy scattering in
the presence of unitarity corrections. We show that, in a suitable range of
transverse momenta for the produced jets, the cross section for the partonic
subprocess should exhibit geometric scaling. We point out that, in the presence
of a running coupling, the cross section for producing hard jets cannot be
fully computed in perturbation theory, not even after taking into account the
saturation effects: the non-perturbative physics affects the overall
normalization of the cross section, but not also its geometric scaling
behavior.",0802.0343v1
2008-02-05,Slow light in saturable absorbers,"In connection with the experiments recently achieved on doped crystals,
biological samples, doped optical fibers and semiconductor heterostructures, we
revisit the theory of the propagation of a pulse-modulated light in a saturable
absorber. Explicit analytical expressions of the transmitted pulse are
obtained, enabling us to determine the parameters optimizing the time-delay of
the transmitted pulse with respect to the incident pulse. We finally compare
the maximum fractional delay or figure of merit so attainable to those which
have been actually demonstrated in the experiments.",0802.0636v2
2008-02-26,Saturation of nuclear matter in effective field theory,"The two- and three-nucleon interaction derived in chiral effective field
theory at next-to-next-to-leading order is used to obtain the binding energy of
nuclear matter. Saturation is found at a binding energy per particle E/A =
-16.2 \pm 0.3 MeV and a Fermi momentum k_F = 1.30 \pm 0.03 fm^{-1}, where the
uncertainty is due to the cut-off dependence of the two-nucleon interaction.
The sensitivity of these values to the three-nucleon force is also studied.",0802.3782v2
2008-04-11,Exact Bright and Dark Spatial Soliton Solutions in Saturable Nonlinear Media,"We present exact analytical bright and dark (black and grey) solitary wave
solutions of a nonlinear Schrodinger-type equation describing the propagation
of spatial beams in media exhibiting a saturable nonlinearity (such as
centrosymmetric photorefractive materials). A qualitative study of the
stationary equation is carried out together with a discussion of the stability
of the solutions.",0804.1852v1
2008-04-22,Dynamics of saturated Bragg diffraction in a stored light grating in cold atoms,"We report on a detailed investigation of the dynamics and the saturation of a
light grating stored in a sample of cold cesium atoms. We employ Bragg
diffraction to retrieve the stored optical information impressed into the
atomic coherence by the incident light fields. The diffracted efficiency is
studied as a function of the intensities of both writing and reading laser
beams. A theoretical model is developed to predict the temporal pulse shape of
the retrieved signal and compares reasonably well with the observed results.",0804.3523v1
2008-04-24,High-field Current-carrying Capacity of Semiconducting Carbon Nanotubes,"It is shown that current saturation in semiconducting carbon nanotubes is
indistinguishable from metallic nanotubes if the carrier density is above a
critical value determined by the bandgap and the LO phonon energy. This feature
stems from the higher number of current-carrying states in the semiconducting
tubes due to the van-Hove singularity at the band-edge. Above this critical
carrier density, the ensemble saturation velocity at high-fields is found to be
independent of the bandgap, but strongly dependent on the carrier density,
explaining recent observations.",0804.3997v2
2008-06-03,Prompt neutrino fluxes from atmospheric charm,"We calculate the prompt neutrino flux from atmospheric charm production by
cosmic rays, using the dipole picture in a perturbative QCD framework, which
incorporates the parton saturation effects present at high energies. We compare
our results with the next-to-leading order perturbative QCD result and find
that saturation effects are large for neutrino energies above 10^6 GeV, leading
to a substantial suppression of the prompt neutrino flux. We comment on the
range of prompt neutrino fluxes due to theoretical uncertainties.",0806.0418v2
2008-08-20,Saturation physics and angular correlations at RHIC and LHC,"We investigate the angular correlation between pions and photons produced in
deuteron-gold collisions at RHIC and proton-lead collisions at LHC using the
Color Glass Condensate formalism and make predictions for the dependence of the
production cross section on the angle between the pion and photon at different
rapidities and transverse momenta. Measuring this dependence would shed further
light on the role of high gluon density and saturation dynamics at RHIC and
LHC.",0808.2769v1
2008-08-20,Distinct pseudogap and superconducting state quasiparticle relaxation dynamics in near-optimally doped SmFeAsO0.8F0.2 single crystals,"We use femtosecond spectroscopy to investigate the quasiparticle relaxation
and low-energy electronic structure in a near-optimally doped pnictide
superconductor with T_c=49.5 K. Multiple relaxation processes are evident, with
distinct superconducting state quasiparticle (QP) recombination dynamics
exhibiting a T-dependent superconducting (SC) gap, and a clear ""pseudogap"" (PG)
-like feature with an onset around 200K indicating the existence of a
temperature-independent gap of magnitude \Delta_PG= 61 +- 9 meV above T_c. Both
the SC and PG components show saturation as a function of fluence with distinct
saturation thresholds ~0.15 \muJ/cm^2 and 1.5 \muJ/cm^2, respectively.",0808.2772v2
2008-09-19,Polarization proximity effect in isolator crystal pairs,"We experimentally studied the polarization dynamics (orientation and
ellipticity) of near infrared light transmitted through magnetooptic Yttrium
Iron Garnet crystal pairs using a modified balanced detection scheme. When the
pair separation is in the sub-millimeter range, we observed a proximity effect
in which the saturation field is reduced by up to 20%. 1D magnetostatic
calculations suggest that the proximity effect originates from magnetostatic
interactions between the dipole moments of the isolator crystals. This
substantial reduction of the saturation field is potentially useful for the
realization of low-power integrated magneto-optical devices.",0809.3292v1
2008-10-31,The exact probability distribution of saturating states in random sequential adsorption,"We consider the non-overlapping irreversible random sequential adsorption
(RSA) process on one-dimensional finite line, which is known also as the car
parking process. The probability of each coverage in saturating states is
analytically and exactly obtained. In the derivation, a new representation of
states in RSA process is introduced, which effectively works to make the
calculation clear and simple.",0810.5632v2
2008-12-05,Doubly periodic waves of a discrete nonlinear Schrödinger system with saturable nonlinearity,"A system of two discrete nonlinear Schr\""odinger equations of the
Ablowitz-Ladik type with a saturable nonlinearity is shown to admit a doubly
periodic wave, whose long wave limit is also derived. As a by-product, several
new solutions of the elliptic type are provided for NLS-type discrete and
continuous systems.",0812.1196v1
2008-12-19,Multipomeron Cuts and Hard Processes on Nuclei,"With nuclear targets comes a new scale into the pQCD description of hard
processes - the saturation scale. In the saturation regime, the familiar linear
k_\perp-factorization breaks down and must be replaced by a nonlinear
k_\perp-factorization, which accounts for absorptive and multiple scattering
corrections to the hard process. Predictions for partial cross sections
corresponding to a fixed number of cut Pomerons (the topological cross
sections) can be obtained in a surprisingly straightforward manner. We discuss
some applications to deep inelastic scattering.",0812.3802v1
2009-01-05,Probing the Symmetry Energy with Heavy Ions,"Constraints on the EoS for symmetric matter (equal neutron and proton
numbers) at supra-saturation densities have been extracted from energetic
collisions of heavy ions. Collisions of neutron-deficient and neutron-rich
heavy ions now provide initial constraints on the EoS of neutron-rich matter at
sub-saturation densities. Comparisons are made to other available constraints.",0901.0412v1
2009-01-08,Color Glass Condensate and its relation to HERA physics,"I give a brief overview of the effective theory for the Color Glass
Condensate, which is the high-density gluonic matter which controls high-energy
scattering in QCD in the vicinity of the unitarity limit. I concentrate on
fundamental phenomena, like gluon saturation, unitarization, and geometric
scaling, and the way how these are encoded in the formalism. I emphasize the
importance of the next-to-leading order corrections, especially the running of
the coupling, for both conceptual and phenomenological issues. I survey the
implications of the CGC theory for the HERA physics and its phenomenological
applications based on saturation models.",0901.0986v1
2009-02-07,Scaling Laws for Spreading of a Liquid Under Pressure,"We study squeeze flow of two different fluids (castor oil and ethylene
glycol) between a pair of glass plates and a pair of perspex plates, under an
applied load. The film thickness is found to vary with time as a power-law,
where the exponent increases with load. After a certain time interval the area
of fluid-solid contact saturates to a constant value. This saturation area,
increases with load at different rates for different fluid-solid combinations.",0902.1222v1
2009-02-27,Freeness of actions of finite groups on C*-algebras,"We describe some of the forms of freeness of group actions on noncommutative
C*-algebras that have been used, with emphasis on actions of finite groups. We
give some indications of their strengths, weaknesses, applications, and
relationships to each other. The properties discussed include the Rokhlin
property, K-theoretic freeness, the tracial Rokhlin property, pointwise
outerness, saturation, hereditary saturation, and the requirement that the
strong Connes spectrum be the entire dual.",0902.4891v1
2009-03-16,'Hausdorff distance' via conical cocompletion,"In the context of quantaloid-enriched categories, we explain how each
saturated class of weights defines, and is defined by, an essentially unique
full sub-KZ-doctrine of the free cocompletion KZ-doctrine. The KZ-doctrines
which arise as full sub-KZ-doctrines of the free cocompletion, are
characterised by two simple ""fully faithfulness"" conditions. Conical weights
form a saturated class, and the corresponding KZ-doctrine is precisely (the
generalisation to quantaloid-enriched categories of) the Hausdorff doctrine of
[Akhvlediani et al., 2009].",0903.2722v2
2009-03-18,Prediction for unintegrated parton distributions,"Unintegrated parton distributions in the proton and nucleus are predicted by
a modified DGLAP equation incorporating the shadowing corrections, which
include exact energy-momentum conservation in each splitting and fusion
vertices. We find that the nuclear shadowing effects are obvious, although they
are far from the saturation limit. On the other hand, we point out that the
suppression of the unintegrated gluon distribution toward lower $k_t^2$ may
arise from the valence-like input rather than the saturation effects.",0903.3073v2
2009-04-14,Multiwavelength Passively Mode Locked Fiber Laser: all normal dispersion,"We report on the generation of multiwavelength gain-guided soliton (GGS) in
an all normal dispersion birefringent fiber laser passively mode-locked with a
semiconductor saturable absorber mirror (SESAM). Determined by the cavity
birefringence, we observe the stable single-, dual- and triple- wavelength mode
locked GGSs, which is a natural consequence of the mutual nonlinear interaction
among the normal cavity dispersion, cavity fiber nonlinear Kerr effect, laser
gain saturation and bandwidth limitation resulting from the intra-cavity
birefringent filter.",0904.2066v2
2009-04-22,Dispersion and Dispersivity Tensors in Saturated Porous Media with Uniaxial Symmetry,"The coefficients of dispersion, D_{ij}, and the dispersivity, a_{ijkl},
appear in the expression for the flux of a solute in saturated flow through
porous media. We present a detailed analysis of these tensors in an axially
symmetric porous medium and show that in such a medium, the dispersivity is
governed by 6 independent moduli. We present also the constraints that have to
be satisfied by these moduli. We also show that at least two independent
experiments are required in order to obtain the values of these coefficients
for any three-dimensional porous medium domain.",0904.3447v1
2009-05-12,Extended Skyrme interaction (I): spin fluctuations in dense matter,"Most of the Skyrme interactions are known to predict spin or isospin
instabilities beyond the saturation density of nuclear matter which contradict
predictions based on realistic interactions. A modification of the standard
Skyrme interaction is proposed so that the ferromagnetic instability is
removed. The new terms are density dependent and modify only the spin p-h
interaction in the case of spin-saturated system. Consequences for the nuclear
response function and neutrino mean free path are shown. The overall effect of
the RPA correlations makes dense matter more transparent for neutrino
propagation by a factor of 2 to 10 depending of the density.",0905.1931v2
2009-06-05,Fano resonances in saturable waveguide arrays,"We study a waveguide array with an embedded nonlinear saturable impurity. We
solve the impurity problem in closed form and find the nonlinear localized
modes. Next, we consider the scattering of a small-amplitude plane wave by a
nonlinear impurity mode, and discover regions in parameter space where
transmission is fully suppressed. We relate these findings with Fano resonances
and propose this setup as a mean to control the transport of light across the
array.",0906.1160v2
2009-06-16,Rapidity and energy dependence of average transverse momentum and particle density in saturation models,"Saturation models -- colour glass condensate and string percolation -- impose
a strict relation between the average transverse momentum, <P_T>, and the
rapidity particle densities, dn/dy. By combining this relation with an
appropriate evolution equation for dn/dy, and imposing energy-momentum
conservation, we obtain a fair description of data, for generic AB collisions
(hadron-hadron, hadron-nucleus and nucleus-nucleus) at all rapidities and
(high) energies. Predictions are given for the LHC.",0906.2976v1
2009-10-02,On the saturation sequence of the rational normal curve,"Let $C \subseteq \P^d$ denote the rational normal curve of order $d$. Its
homogeneous defining ideal $I_C \subseteq \QQ[a_0,...,a_d]$ admits an
$SL_2$-stable filtration $J_2 \subseteq J_4 \subseteq ... \subseteq I_C$ by
sub-ideals such that the saturation of each $J_{2q}$ equals $I_C$. Hence, one
can associate to $d$ a sequence of integers $(\alpha_1,\alpha_2,...)$ which
encodes the degrees in which the successive inclusions in this filtration
become trivial. In this paper we establish several lower and upper bounds on
the $\alpha_q$, using \emph{inter alia} the methods of classical invariant
theory.",0910.0298v1
2009-10-02,Saturation in nuclei,"This talk discusses some recent studies of gluon saturation in nuclei. We
stress the connection between the initial condition in heavy ion collisions and
observables in deep inelastic scattering (DIS). The dominant degree of freedom
in the small x nuclear wavefunction is a nonperturbatively strong classical
gluon field, which determines the initial condition for the glasma fields in
the initial stages of a heavy ion collision. A correlator of Wilson lines from
the same classical fields, known as the dipole cross section, can be used to
compute many inclusive and exclusive observables in DIS.",0910.0402v1
2009-10-05,Saturation and Critical Phenomena in DIS,"It is argued that the expected turn-down in $x- Q^2$ of the cross sections
(structure functions $F_2(x,Q^2)$), assumed to result from the saturation of
parton densities in the nucleon, is related to a phase transition from the
(almost) ideal partonic gas, obeying Bjorken scaling, to a partonic ""liquid"".
This can be quantified in the framework of statistical models, percolation and
other approaches to collective phenomena of the strongly interacting matter.
Similarities and differences between the case of lepton-hadron, hadron-hadron
and nuclear collisions are discussed.",0910.0796v1
2009-10-19,Gluon Saturation Effects at the Nuclear Surface: Inelastic Cross Section of Proton-Nucleus at Ultra High Energy Cosmic Ray domain,"Considering the high-energy limit of the QCD gluon distribution inside a
nucleus, we calculate the proton-nucleus total inelastic cross section using a
simplified dipole model. We show that, if gluon saturation occurs in the
nuclear surface region, the total cross section of proton-nucleus collisions
increases more rapidly as a function of the incident energy compared to that of
a Glauber-type estimate. We discuss the implications of this with respect to
recent ultra-high-energy cosmic ray experiments.",0910.3701v2
2009-10-21,"Dynamic saturation in semiconductor optical amplifiers: accurate model, role of carrier density, and slow light","We developed an improved model in order to predict the RF behavior and the
slow light properties of the SOA valid for any experimental conditions. It
takes into account the dynamic saturation of the SOA, which can be fully
characterized by a simple measurement, and only relies on material fitting
parameters, independent of the optical intensity and the injected current. The
present model is validated by showing a good agreement with experiments for
small and large modulation indices.",0910.4064v2
2009-10-26,Current Saturation and Surface Polar Phonon Scattering in Graphene,"We present a study of transport in graphene devices on polar insulating
substrates using a tight-binding model. The mobility is computed using a
multiband Boltzmann treatment. We provide the scaling of the surface polar
phonon contribution to the low-field mobility with carrier density,
temperature, and distance from the substrate. At high bias, we find that
graphene self-heating effect is essential to account for the observed saturated
current behavior. We predict that by optimizing the device cooling, the high
bias currents can be significantly enhanced.",0910.4665v1
2009-10-26,Why is the nuclear symmetry energy so uncertain at supra-saturation densities?,"Within the interacting Fermi gas model for isospin asymmetric nuclear matter,
effects of the in-medium three-body interaction and the two-body short-range
tensor force due to the $\rho$ meson exchange as well as the short-range
nucleon correlation on the high-density behavior of the nuclear symmetry energy
are demonstrated respectively in a transparent way. Possible physics origins of
the extremely uncertain nuclear symmetry energy at supra-saturation densities
are discussed.",0910.4803v2
2009-12-04,Saturated-absorption cavity ring-down spectroscopy,"We report on a novel approach to cavity-ring-down spectroscopy with the
sample gas in saturated-absorption regime. This technique allows to decouple
and simultaneously retrieve empty-cavity background and absorption signal, by
means of a theoretical model that we developed and tested. The high sensitivity
and frequency precision for spectroscopic applications are exploited to
measure, for the first time, the hyperfine structure of an excited vibrational
state of $^{17}$O$^{12}$C$^{16}$O in natural abundance with an accuracy of a
few parts in $10^{-11}$.",0912.0831v2
2010-02-28,"Graphene mode locked, wavelength-tunable, dissipative soliton fiber laser","Atomic layer graphene possesses wavelength-insensitive ultrafast saturable
absorption, which can be exploited as a full-band mode locker. Taking advantage
of the wide band saturable absorption of the graphene, we demonstrate
experimentally that wide range (1570 nm - 1600nm) continuous wavelength tunable
dissipative solitons could be formed in an erbium doped fiber laser mode locked
with few layer graphene.",1003.0154v1
2010-03-17,Method for characterizing single photon detectors in saturation regime by cw laser,"We derive an analytical expression for the count probability of a single
photon detector for a wide range of input optical power that includes
afterpulsing effects. We confirm the validity of the expression by fitting it
to the data obtained from a saturated commercial Single Photon Detector by
illuminating it with a cw laser. Detector efficiency and afterpulsing
probability extracted from the fits agree with the manufacture specs for low
repetition frequencies.",1003.3485v1
2010-05-08,Multi-convex sets in real projective spaces and their duality,"We study intersections of projective convex sets in the sense of Steinitz. In
a projective space, an intersection of a nonempty family of convex sets splits
into multiple connected components each of which is a convex set. Hence, such
an intersection is called a multi-convex set. We derive a duality for saturated
multi-convex sets: there exists an order anti-isomorphism between nonempty
saturated multi-convex sets in a real projective space and those in the dual
projective space. In discrete geometry and computational geometry, these
results allow to transform a given problem into a dual problem which sometimes
is easier to solve. This will be pursued in a later paper.",1005.1852v1
2010-08-16,Drell-Yan process at forward rapidity at the LHC,"We analyze the Drell-Yan lepton pair production at forward rapidity at the
Large Hadron Collider. Using the dipole framework for the computation of the
cross section we find a significant suppression in comparison to the collinear
factorization formula due to saturation effects in the dipole cross section. We
develop a twist expansion in powers of Q_s^2/M^2 where Q_s is the saturation
scale and M the invariant mass of the produced lepton pair. For the nominal LHC
energy the leading twist description is sufficient down to masses of 6 GeV.
Below that value the higher twist terms give a significant contribution.",1008.2652v1
2010-08-19,Multiplicity distributions and long range rapidity correlations,"The physics of the initial conditions of heavy ion collisions is dominated by
the nonlinear gluonic interactions of QCD. These lead to the concepts of parton
saturation and the Color Glass Condensate (CGC). We discuss recent progress in
calculating multi-gluon correlations in this framework, prompted by the
observation that these correlations are in fact easier to compute in a dense
system (nucleus-nucleus) than a dilute one (proton-proton).",1008.3226v1
2010-08-26,Exact Solutions of the Two-Dimensional Discrete Nonlinear Schrödinger Equation with Saturable Nonlinearity,"We show that the two-dimensional, nonlinear Schr\""odinger lattice with a
saturable nonlinearity admits periodic and pulse-like exact solutions. We
establish the general formalism for the stability considerations of these
solutions and give examples of stability diagrams. Finally, we show that the
effective Peierls-Nabarro barrier for the pulse-like soliton solution is zero.",1008.4592v1
2010-08-26,Staggered and short period solutions of the Saturable Discrete Nonlinear Schrödinger Equation,"We point out that the nonlinear Schr{\""o}dinger lattice with a saturable
nonlinearity also admits staggered periodic as well as localized pulse-like
solutions. Further, the same model also admits solutions with a short period.
We examine the stability of these solutions and find that the staggered as well
as the short period solutions are stable in most cases. We also show that the
effective Peierls-Nabarro barrier for the pulse-like soliton solutions is zero.",1008.4594v1
2010-09-03,"Reduced, tame and exotic fusion systems","We define here two new classes of saturated fusion systems, reduced fusion
systems and tame fusion systems. These are motivated by our attempts to better
understand and search for exotic fusion systems: fusion systems which are not
the fusion systems of any finite group. Our main theorems say that every
saturated fusion system reduces to a reduced fusion system which is tame only
if the original one is realizable, and that every reduced fusion system which
is not tame is the reduction of some exotic (nonrealizable) fusion system.",1009.0622v1
2010-09-16,"Single and double inclusive particle production in d+Au collisions at RHIC, leading twist and beyond","We discuss the evidence for the presence of QCD saturation effects in the
data collected in d+Au collisions at RHIC. In particular we focus our analysis
on forward hadron yields and azimuthal correlations. Approaches alternative to
the CGC description of these two observables are discussed in parallel.",1009.3215v1
2010-10-19,Modeling of the Output and Transfer Characteristics of Graphene Field-Effect Transistors,"We obtain the output and transfer characteristics of graphene field-effect
transistors by using the charge-control model for the current, based on the
solution of the Boltzmann equation in the field-dependent relaxation time
approximation. Closed expressions for the conductance, transconductance and
saturation voltage are derived. We found good agreement with the experimental
data of Meric et al. [Nature Nanotechnology 3, 684 (2008)] without assuming
carrier density-dependent velocity saturation.",1010.4037v1
2010-11-14,Gluon Evolution and Saturation Proceedings,"Almost 40 years ago, Gribov and colleagues at the Leningrad Nuclear Physics
Institute developed the ideas that led to the
Dokhsitzer-Gribov-Altarelli-Parisi the Baltisky-Fadin-Kuraev-Lipatov equations.
These equations describe the evolution of the distributions for quarks and
gluon inside a hadron to increased resolution scale of a probe or to smaller
values of the fractional momentum of a hadronic constituent. I motivate and
discuss the generalization required of these equations needed for high energy
processes when the density of constituents is large. This leads to a theory of
saturation realized by the Color Glass Condensate",1011.3202v1
2010-12-13,A $c_0$ saturated Banach space with tight structure,"It is shown that variants of the HI methods could yield objects closely
connected to the classical Banach spaces. Thus we present a new $c_0$ saturated
space, denoted as $\mathfrak{X}_0$, with rather tight structure. The space
$\mathfrak{X}_0$ is not embedded into a space with an unconditional basis and
its complemented subspaces have the following structure. Everyone is either of
type I, namely, contains an isomorph of $\mathfrak{X}_0$ itself or else is
isomorphic to a subspace of $c_0$ (type II). Furthermore for any analytic
decomposition of $\mathfrak{X}_0$ into two subspaces one is of type I and the
other is of type II. The operators of $\mathfrak{X}_0$ share common features
with those of HI spaces.",1012.2758v1
2011-01-07,"Fluctuations, Saturation, and Diffractive Excitation at low x","Diffractive excitation is usually described by the Good--Walker formalism for
low masses, and by the triple-Regge formalism for high masses. In the
Good-Walker formalism the cross section is determined by the fluctuations in
the interaction. By taking the fluctuations in the BFKL ladder into account, it
is possible to describe both low and high mass excitation in the Good-Walker
formalism. In high energy pp collisions the fluctuations are strongly
suppressed by saturation, which implies that pomeron exchange does not
factorise between DIS and pp collisions. The Dipole Cascade Model reproduces
the expected triple-Regge form for the bare pomeron, and the triple-pomeron
coupling is estimated.",1101.1404v1
2011-01-27,Mobility of high-power solitons in saturable nonlinear photonic lattices,"We theoretically study the properties of one-dimensional nonlinear saturable
photonic lattices exhibiting multiple mobility windows for stationary
solutions. The effective energy barrier decreases to a minimum in those power
regions where a new intermediate stationary solution appears. As an
application, we investigate the dynamics of high-power gaussian-like beams
finding several regions where the light transport is enhanced.",1101.5354v2
2011-02-18,Extended Longitudinal Scaling: direct evidence of saturation,"Multiparticle production of charged particles at high energies exhibit the
phenomenon of Limiting Fragmentation. Furthermore, the region in rapidity over
which the production of particles appears to be independent of energy,
increases with energy. It is argued that this phenomenon, known as Extended
Longitudinal Scaling, is a direct manifestation of some kind of saturation,
akin to that in the Color Glass Condensate picture of particle production.",1102.3921v1
2011-03-01,Cycle-saturated graphs with minimum number of edges,"A graph $G$ is called $H$-saturated if it does not contain any copy of $H$,
but for any edge $e$ in the complement of $G$ the graph $G+e$ contains some
$H$. The minimum size of an $n$-vertex $H$-saturated graph is denoted by
$\sat(n,H)$. We prove $$\sat(n,C_k) = n + n/k + O((n/k^2) + k^2)$$ holds for
all $n\geq k\geq 3$, where $C_k$ is a cycle with length $k$. We have a similar
result for semi-saturated graphs $$\ssat(n,C_k) = n + n/(2k) + O((n/k^2) +
k).$$ We conjecture that our three constructions are optimal.",1103.0067v1
2011-04-14,Jump at the onset of saltation,"We reveal a discontinuous transition in the saturated flux for aeolian
saltation by simulating explicitly particle motion in turbulent flow. The
discontinuity is followed by a coexistence interval with two metastable
solutions. The modification of the wind profile due to momentum exchange
exhibits a second maximum at high shear strength. The saturated flux depends on
the strength of the wind as $q_s=q_0+A(u_*-u_t)(u_*^2+u_t^2)$.",1104.2767v2
2011-04-27,Isomorph-free generation of 2-connected graphs with applications,"Many interesting graph families contain only 2-connected graphs, which have
ear decompositions. We develop a technique to generate families of unlabeled
2-connected graphs using ear augmentations and apply this technique to two
problems. In the first application, we search for uniquely K_r-saturated graphs
and find the list of uniquely K_4-saturated graphs on at most 12 vertices,
supporting current conjectures for this problem. In the second application, we
verifying the Edge Reconstruction Conjecture for all 2-connected graphs on at
most 12 vertices. This technique can be easily extended to more problems
concerning 2-connected graphs.",1104.5261v1
2011-04-28,Inhomogeneous Gain Saturation in EDF: Experiment and Modeling,"Erbium-Doped Fiber Amplifiers can present holes in spectral gain in
Wavelength Division Multiplexing operation. The origin of this inhomogeneous
saturation behavior is still a subject of controversy. In this paper we present
both an experimental methods and a gain's model. Our experimental method allow
us to measure the first homogeneous linewidth of the 1.5 $\mu$m erbium emission
with gain spectral hole burning consistently with the other measurement in the
literature and the model explains the differences observed in literature
between GSHB and other measurement methods.",1104.5302v1
2011-05-10,Distribution of linearly polarized gluons inside a large nucleus,"The distribution of linearly polarized gluons inside a large nucleus is
studied in the framework of the color glass condensate. We find that the
Weizs\""acker-Williams distribution saturates the positivity bound at large
transverse momenta and is suppressed at small transverse momenta, whereas the
dipole distribution saturates the bound for any value of the transverse
momentum. We also discuss processes in which both distributions of linearly
polarized gluons can be probed.",1105.1991v2
2011-05-27,Gluon spectrum in the glasma from JIMWLK evolution,"The JIMWLK equation with a ""daughter dipole"" running coupling is solved
numerically starting from an initial condition given by the
McLerran-Venugopalan model. The resulting Wilson line configurations are then
used to compute the spectrum of gluons comprising the glasma inital state of a
high energy heavy ion collision. The development of a geometrical scaling
region makes the spectrum of produced gluons harder. Thus the ratio of the mean
gluon transverse momentum to the saturation scale grows with energy. Also the
total gluon multiplicity increases with energy slightly faster than the
saturation scale squared.",1105.5511v2
2011-07-05,Proton-proton cross-sections: the interplay between density and radius,"We argue that there are two mechanisms responsable for the growth of high
energy cross-sections - \sigma_{tot} and \sigma_{el}, say - in pp collisions.
One is by the increase of matter \emph{density}, resulting in the black disk
saturation. The other is by exclusively radial expansion affecting the
periphery of the overlap area. Within this simple model we can reproduce all
available data in pp from ISR to LHC. In order to achieve a fast growth in the
very high energy cosmic ray energies, we propose a fast black disk saturation
followed by the dominance of geometric scaling (GS).",1107.0912v2
2011-08-03,Open Saturated Sets Without Holonomy,"Open, connected, saturated sets W without holonomy in codimension one
foliations play key roles as fundamental building blocks. Here, for the case of
foliated 3-manifolds, we produce a finite system of closed, convex,
non-overlapping polyhedral cones in the first cohomology of W with real
coefficients such that the isotopy classes of possible foliations of W without
holonomy, either dense leaved in W or proper, correspond one-to-one to the rays
in the interiors of these cones. This generalizes our classification of depth
one foliations to foliations of finite depth and more general foliations.",1108.0714v3
2011-09-02,High-energy factorization and evolution with improved kinematics,"The high-energy factorization and the associated B-JIMWLK or BK evolution
equations are presented, using the example of DIS structure functions. The
necessity of taking gluon saturation into account is discussed, and also the
various approximations underlying high-energy factorization. The appearance of
large NLL corrections in such a framework with or without gluon saturation is
recalled, and their physical origin is explained. Finally, old and new results
are presented about the resummation of some of those large corrections, related
to kinematical approximations.",1109.0547v1
2011-09-15,Not All Saturated 3-Forests Are Tight,"A basic statement in graph theory is that every inclusion-maximal forest is
connected, i.e. a tree. Using a definiton for higher dimensional forests by
Graham and Lovasz and the connectivity-related notion of tightness for
hypergraphs introduced by Arocha, Bracho and Neumann-Lara in, we provide an
example of a saturated, i.e. inclusion-maximal 3-forest that is not tight. This
resolves an open problem posed by Strausz.",1109.3390v1
2011-10-11,Steady State Solutions of a Mass-Conserving Bistable Equation with a Saturating Flux,"We consider a mass-conserving bistable equation with a saturating flux on an
interval. This is the quasilinear analogue of the Rubinstein-Steinberg
equation, suitable for description of order parameter conserving solid-solid
phase transitions in the case of large spatial gradients in the order
parameter. We discuss stationary solutions and investigate the change in
bifurcation diagrams as the mass constraint and the length of the interval are
varied.",1110.2323v1
2011-10-28,Physics-Based Compact Modeling of Double-Gate Graphene Field-Effect Transistor Operation Including Description of Two Saturation Modes,"Based on diffusion-drift approximation a version of analytic compact model
for large-area double-gate graphene field-effect transistor is presented. As
parts of the model, the electrostatics of double-gate structure is described
and a unified phenomenological approach for modeling of the two drain current
saturation modes is proposed.",1110.6319v2
2011-12-13,High-frequency performance of graphene field effect transistors with saturating IV-characteristics,"High-frequency performance of graphene field-effect transistors (GFETs) with
boron-nitride gate dielectrics is investigated. Devices show saturating IV
characteristics and fmax values as high as 34 GHz at 600-nm channel length.
Bias dependence of fT and fmax and the effect of the ambipolar channel on
transconductance and output resistance are also examined.",1112.2777v1
2011-12-16,Countable saturation of corona algebras,"We present unified proofs of several properties of the corona of
$\sigma$-unital C*-algebras such as AA-CRISP, SAW*, being sub-$\sigma$-Stonean
in the sense of Kirchberg, and the conclusion of Kasparov's Technical Theorem.
Although our results were obtained by considering C*-algebras as models of the
logic for metric structures, the reader is not required to have any knowledge
of model theory of metric structures (or model theory, or logic in general).
The proofs involve analysis of the extent of model-theoretic saturation of
corona algebras.",1112.3898v2
2012-01-10,Stable nonlinear amplification of solitons without gain saturation,"We demonstrate that the cubic gain applied in a localized region, which is
embedded into a bulk waveguide with the cubic-quintic nonlinearity and uniform
linear losses, supports stable spatial solitons in the absence of the quintic
dissipation. The system, featuring the bistability between the solitons and
zero state (which are separated by a family of unstable solitons), may be used
as a nonlinear amplifier for optical and plasmonic solitons, which, on the
contrary to previously known settings, does not require gain saturation. The
results are obtained in an analytical form and corroborated by the numerical
analysis.",1201.2095v1
2012-02-23,Study of full implicit petroleum engineering finite volume scheme for compressible two phase flow in porous media,"An industrial scheme, to simulate the two compressible phase flow in porous
media, consists in a finite volume method together with a phase-by-phase
upstream scheme. The implicit finite volume scheme satisfies industrial
constraints of robustness. We show that the proposed scheme satisfy the maximum
principle for the saturation, a discrete energy estimate on the pressures and a
function of the saturation that denote capillary terms. These stabilities
results allow us to derive the convergence of a subsequence to a weak solution
of the continuous equations as the size of the discretization tends to zero.
The proof is given for the complete system when the density of the each phase
depends on the own pressure.",1202.5274v1
2012-03-06,High Frequency Geodesic Acoustic Modes in Electron Temperature Gradient Mode Turbulence,"In this work the first demonstration of a high frequency branch of the
geodesic acoustic mode (GAM) driven by electron temperature gradient (ETG)
modes is presented. The work is based on a fluid description of the ETG mode
retaining non-adiabatic ions and the dispersion relation for high frequency
GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for
ETG turbulence through the interaction with high frequency GAMs is found,
resulting in a significantly enhanced ETG turbulence saturation level compared
to the mixing length estimate.",1203.1174v2
2012-03-15,Saturation Spectroscopy of Iodine in Hollow-core Optical Fibre,"We present high-resolution spectroscopy of Iodine vapour that is loaded and
trapped within the core of a hollow-core photonic crystal fibre (HC-PCF). We
compare the observed spectroscopic features to those seen in a conventional
iodine cell and show that the saturation characteristics differ significantly.
Despite the confined geometry it was still possible to obtain sub-Doppler
features with a spectral width of ~6 MHz with very high contrast. We provide a
simple theory which closely reproduces all the key observations of the
experiment.",1203.3346v1
2012-05-11,Elliptic flow and the symmetry energy at supra-saturation density,"The elliptic flow in collisions of neutron-rich heavy-ion systems at
intermediate energies emerges as an observable sensitive to the strength of the
symmetry energy at supra-saturation densities. First results obtained by
comparing ratios or differences of neutron and hydrogen flows with predictions
of transport models favor a moderately soft to linear density dependence,
consistent with ab-initio nuclear-matter theories. Comprehensive data sets of
high accuracy can be expected to improve our knowledge of the equation of state
of asymmetric nuclear matter.",1205.2585v2
2012-05-17,Effect of mechanical stresses on coercive force and saturation remanence of ensemble of dual-phase interacting nanoparticles,"In the dual-phase model of interacting nanoparticles stretching leads to a
decrease in both coercive force $H_c$ and saturation remanence $I_{rs}$, and
compression - to their growth. Magnetostatic interaction between particles also
decreases both $H_c$ and $I_{rs}$. Theoretical analysis was carried out in the
framework of the dual-phase system of interacting particles on the example of
nanoparticles $\gamma$-$Fe_2O_3$, epitaxially coated with cobalt.",1205.3870v1
2012-05-25,Saturation effects on T-cell activation in a model of a multi-stage pathogen,"In previous work, we studied host response to a pathogen which uses a cycle
of immunologically distinct stages to establish and maintain infection. We
showed that for generic parameter values, the system has a unique biologically
meaningful stable fixed point. That paper used a simplified model of T-cell
activation, making proliferation depend linearly on antigen-T-cell encounters.
Here we generalize the way in which T-cell proliferation depends on the sizes
of the antigenic populations. In particular, we allow this response to become
saturated at high levels of antigen. As a result, we show that this family of
generalized models shares the same steady-state behavior properties with the
simpler model contemplated in our previous work.",1205.5735v1
2012-06-11,"Parton Cascades, Small x, and Saturation in High Energy Collisions","These lecture notes are a combination of two lectures and a contribution to
the celebration of Andrzej Bia{\l}as' birthday at the LI Cracow School of
Theoretical Physics in June 2011. I here discuss the dynamics of particle
production in high energy reactions. It includes parton cascades and
hadronization in e+e--ann., small x evolution including the Double Leading Log
approximation and the BFKL equation, saturation at high densities and the BK
equation, and finally the Lund Dipole Cascade model for high energy collisions,
which is implemented in the DIPSY MC.",1206.2168v1
2012-06-29,New Examples of Kochen-Specker Type Configurations on Three Qubits,"A new example of a saturated Kochen-Specker (KS) type configuration of 64
rays in 8-dimensional space (the Hilbert space of a triple of qubits) is
constructed. It is proven that this configuration has a tropical dimension 6
and that it contains a critical subconfiguration of 36 rays. A natural
multicolored generalisation of the Kochen-Specker theory is given based on a
concept of an entropy of a saturated configuration of rays.",1206.6999v3
2012-07-06,A saturation property of structures obtained by forcing with a compact family of random variables,"A method how to construct Boolean-valued models of some fragments of
arithmetic was developed in Krajicek (2011), with the intended applications in
bounded arithmetic and proof complexity. Such a model is formed by a family of
random variables defined on a pseudo-finite sample space. We show that under a
fairly natural condition on the family (called compactness in K.(2011)) the
resulting structure has a property that is naturally interpreted as saturation
for existential types. We also give an example showing that this cannot be
extended to universal types.",1207.1548v2
2012-07-13,Asymptotics and scalings for large product-form networks via the Central Limit Theorem,"The asymptotic behaviour of a closed BCMP network, with $n$ queues and $m_n$
clients, is analyzed when $n$ and $m_n$ become simultaneously large. Our method
relies on Berry-Esseen type approximations coming in the Central Limit Theorem.
We construct critical sequences $m^0_n$, which are necessary and sufficient to
distinguish between saturated and non-saturated regimes for the network.
Several applications of these results are presented. It is shown that some
queues can act as bottlenecks, limiting thus the global efficiency of the
system.",1207.3237v1
2012-08-08,Strong containment of saturated formations of soluble Lie algebras,"It is shown that, if H,K are saturated formations of soluble Lie algebras
over a field of non-zero characteristic and H strongly contains K
non-trivially, then H coincides with the formation generated by the L/N(L) for
L in H, and that H is not locally defined.",1208.1585v4
2012-08-30,Ground state of nonlinear Schrodinger systems with saturable nonlinearity,"We prove the existence of ground state in a multidimensional nonlinear
Schrodinger model of paraxial beam propagation in isotropic local media with
saturable nonlinearity. Such ground states exist in the form of bright
counterpropagating solitons. From the proof, a general threshold condition on
the beam coupling constant for the existence of such fundamental solitons
follows.",1208.6259v1
2012-09-25,The Saturation of Several Universal Inequalities in Information-Processing,"In this paper, we characterize the saturation of four universal inequalities
in quantum information theory, including a variant version of strong
subadditivity inequality for von Neumann entropy, the coherent information
inequality, the Holevo quantity and average entropy inequalities. These results
shed new light on quantum information inequalities.",1209.5545v2
2012-10-15,Evidence for BFKL and saturation dynamics from di-hadron spectra at the LHC,"We demonstrate that rapidity separated di-hadron spectra in high multiplicity
proton-proton collisions at the LHC can be quantitatively described by a
combination of BFKL and saturation dynamics. Based on these results, we predict
the systematics of di-hadron spectra in proton-nucleus collisions at the LHC.",1210.3890v3
2012-10-19,Imprinting Quantum Fluctuations on Hydrodynamic Initial Conditions,"Starting from the two-point covariance function derived in [1], we have
developed a toy model to investigate the effect of gluonic fluctuations on the
transverse energy profile predicted by MC-KLN Color-Glass Condensate initial
conditions. We find that the effect of these fluctuations on the eccentricity
harmonics varies strongly with the correlation length and consequently the
value of the fixed saturation momentum Qs used in [1]. Using approximate values
for the minimum and maximum saturation momenta probed at RHIC in Au-Au
collisions, we estimate the increase in the eccentricity coefficients resulting
from gluonic fluctuations is as large as 10 to 20 percent in central
collisions.",1210.5508v1
2012-10-22,Sudakov Resummation in Small-x Saturation Formalism,"Through an explicit calculation of massive scalar particle (e.g., Higgs
boson) production in high energy pA collisions up to one-loop order, we
demonstrate that the Sudakov-type logarithms in hard processes in small-x
saturation formalism can be systematically separated from the typical small-x
logarithms. The generic feature of the Sudakov logarithms and all order
resummation is derived. We further comment on the phenomenological implications
and extension to other hard processes in the small-x calculations.",1210.5792v1
2012-12-02,"Linearly polarized, Q-switched Er-doped fiber laser based on reduced graphene oxide saturable absorber","We demonstrate generation of linearly polarized pulses from a passively
Q-switched Erbium-doped fiber laser. The cavity was designed using only
polarization maintaining (PM) fibers and components, resulting in linearly
polarized output beam with degree of polarization (DOP) at the level of 97.6%.
Reduced graphene oxide (rGO) was used as a saturable absorber for Q-switched
operation. The laser was capable of delivering 1.85us pulses with 125nJ pulse
energy at 115kHz repetition rate.",1212.0201v1
2013-01-04,Gluon saturation at higher orders and improvement of kinematics,"Standard perturbative calculations lead to pathologically large NLO
corrections to low-$x_{Bj}$ evolution equations like BFKL and BK. Using a more
refined treatment of kinematics in mixed-space, relevant when gluon saturation
sets on, one obtains an improved version of the BK equation, resumming to all
orders the most severe of those large higher order corrections.",1301.0773v1
2013-02-11,On the consistency of the spindown behavior of young and old pulsars,"We study the spindown of pulsars due to gravitational wave emission and show
that r-modes in neutron stars provide a quantitative explanation for the
observed low rotation frequencies of young pulsars if the r-mode saturation
amplitude is sufficiently large. In contrast for such large saturation
amplitudes old hadronic millisecond pulsars would spin down much faster than
observed. We discuss resolutions of this apparent discrepancy that could make
this mechanism consistent with the observational data.",1302.2649v1
2013-02-19,An Algorithm for Computing the Limit Points of the Quasi-component of a Regular Chain,"For a regular chain $R$, we propose an algorithm which computes the
(non-trivial) limit points of the quasi-component of $R$, that is, the set
$\bar{W(R)} \setminus W(R)$. Our procedure relies on Puiseux series expansions
and does not require to compute a system of generators of the saturated ideal
of $R$. We focus on the case where this saturated ideal has dimension one and
we discuss extensions of this work in higher dimensions. We provide
experimental results illustrating the benefits of our algorithms.",1302.4688v1
2013-02-19,A Homological Approach to Factorization,"Mott noted a one-to-one correspondence between saturated multiplicatively
closed subsets of a domain D and directed convex subgroups of the group of
divisibility D. With this, we construct a functor between inclusions into
saturated localizations of D and projections onto partially ordered quotient
groups of G(D). We use this functor to construct many cochain complexes of
o-homomorphisms of po-groups. These complexes naturally lead to some
fundamental structure theorems and some natural homology theory that provide
insight into the factorization behavior of D.",1302.4759v2
2013-02-21,On the toric ideal of a matroid,"Describing minimal generating set of a toric ideal is a well-studied and
difficult problem. In 1980 White conjectured that the toric ideal associated to
a matroid is equal to the ideal generated by quadratic binomials corresponding
to symmetric exchanges. We prove White's conjecture up to saturation, that is
that the saturations of both ideals are equal. In the language of algebraic
geometry this means that both ideals define the same projective scheme.
Additionally we prove the full conjecture for strongly base orderable matroids.",1302.5236v3
2013-03-11,Random packing of spheres in Menger sponge,"Random packing of spheres inside fractal collectors of dimension 2 < d < 3 is
studied numerically using Random Sequential Adsorption (RSA) algorithm. The
paper focuses mainly on the measurement of random packing saturation limit.
Additionally, scaling properties of density autocorrelations in the obtained
packing are analyzed. The RSA kinetics coefficients are also measured. Obtained
results allow to test phenomenological relation between random packing
saturation density and collector dimension. Additionally, performed simulations
together with previously obtained results confirm that, in general, the known
dimensional relations are obeyed by systems having non-integer dimension, at
least for d < 3.",1303.2528v2
2013-03-26,Random generation of optimal saturated designs,"Efficient algorithms for searching for optimal saturated designs are widely
available. They maximize a given efficiency measure (such as D-optimality) and
provide an optimum design. Nevertheless, they do not guarantee a \emph{global}
optimal design. Indeed, they start from an initial random design and find a
local optimal design. If the initial design is changed the optimum found will,
in general, be different. A natural question arises. Should we stop at the
design found or should we run the algorithm again in search of a better design?
This paper uses very recent methods and software for discovery probability to
support the decision to continue or stop the sampling. A software tool written
in SAS has been developed.",1303.6529v2
2013-05-03,Harmonics suppression effect of the quasi-periodic undulator in SASE free-electron-laser,"In this paper, the harmonics suppression effect of QPUs in SASE FEL is
investigated. The numerical results show that the harmonics power is reduced by
using QPUs, but the fundamental radiation power also has a pronounced decrease
as the saturation length gets very long. The cases of employing QPUs as parts
of undulators are studied. The calculations show that if the fraction of QPUs
and their offgap are appropriate in an undulator system, the harmonics
radiation could be suppressed remarkably, meanwhile the fundamental saturation
length does not increase too much.",1305.0694v1
2013-05-17,A characterization of saturated fusion systems over abelian 2-groups,"Given a saturated fusion system $\mathcal{F}$ over a $2$-group $S$, we prove
that $S$ is abelian provided any element of $S$ is $\mathcal{F}$-conjugate to
an element of $Z(S)$. This generalizes a Theorem of Camina--Herzog, leading to
a significant simplification of its proof. More importantly, it follows that
any $2$-block $B$ of a finite group has abelian defect groups if all
$B$-subsections are major. Furthermore, every $2$-block with a symmetric stable
center has abelian defect groups.",1305.4139v2
2013-05-20,Antiferromagnetic Ising model saturation field entropies: ladders and kagome lattice,"Saturation field entropies of antiferromagnetic Ising models on quasi
one-dimensional lattices (ladders) and the kagome lattice are calculated. The
former is evaluated exactly by constructing the corresponding transfer
matrices, while the latter calculation uses Binder's algorithm for efficiently
and exactly computing the partition function of over 1300 spins to give, in
Boltzmann's units, S = 0.393589(6). We comment on the relation of the kagome
lattice to the experimental situation in the spin-ice compound dysprosium
titanium oxide.",1305.4606v2
2013-06-30,Electric Field Effect Thermoelectric Transport in Individual Silicon and Germanium/Silicon Nanowire,"We have simultaneously measured conductance and thermoelectric power (TEP) of
individual silicon and germanium/silicon core/shell nanowires in the field
effect transistor device configuration. As the applied gate voltage changes,
the TEP shows distinctly different behaviors while the electrical conductance
exhibits the turn-off, subthreshold, and saturation regimes respectively. At
room temperature, peak TEP value of $\sim 300 \mu$V/K is observed in the
subthreshold regime of the Si devices. The temperature dependence of the
saturated TEP values are used to estimate the carrier doping of Si nanowires.",1307.0249v1
2013-07-02,Saturations of powers of certain determinantal ideals,"Let $R$ be a Noetherian local ring and $m$ a positive integer. Let $I$ be the
ideal of $R$ generated by the maximal minors of an $m \times (m + 1)$ matrix
$M$ with entries in $R$. Assuming that the grade of the ideal generated by the
$k$-minors of $M$ is at least $m - k + 2$ for $1 \leq \forall k \leq m$, we
will study the associated primes of $I^n$ for $\forall n > 0$. Moreover, we
compute the saturation of $I^n$ for $1 \leq \forall n \leq m$ in the case where
$R$ is a Cohen-Macaulay ring and the entries of $M$ are powers of elements that
form an sop for $R$.",1307.0593v1
2013-07-18,"Tectonic ""short circuit"" of sub-horizontal fluid-saturated bodies as a possible mechanism of the earthquake","An alternative earthquake mechanism is proposed. The traditional stress
mechanism of fracture formation assigned a support role. As a proximate cause
of the earthquake the destruction of the roofs of sub-horizontal
fluid-saturated bodies (SHFB) is considered. This collapse may occur due to
redistribution of fluid pressure within the system of SHFB connected by cracks
(tectonic or other nature). It can cause both shifts of rock blocks
contributing to seismic shocks and various effects characteristic of foreshocks
and aftershocks.",1307.4915v1
2013-10-09,Saturation of Concurrent Collapsible Pushdown Systems,"Multi-stack pushdown systems are a well-studied model of concurrent
computation using threads with first-order procedure calls. While, in general,
reachability is undecidable, there are numerous restrictions on stack behaviour
that lead to decidability. To model higher-order procedures calls, a
generalisation of pushdown stacks called collapsible pushdown stacks are
required. Reachability problems for multi-stack collapsible pushdown systems
have been little studied. Here, we study ordered, phase-bounded and
scope-bounded multi-stack collapsible pushdown systems using saturation
techniques, showing decidability of control state reachability and giving a
regular representation of all configurations that can reach a given control
state.",1310.2631v1
2013-10-17,Countable Degree-1 Saturation of Certain C*-Algebras Which Are Coronas of Banach Algebras,"We study commutants modulo some normed ideal of n-tuples of operators which
satisfy a certain approximate unit condition relative to the ideal. We obtain
results about the quotient of these Banach algebras by their ideal of compact
operators being C*-algebras which have the countable degree-1 saturation
property in the model-theory sense of I. Farah and B. Hart. We also obtain
results about quasicentral approximate units, multipliers and duality.",1310.4862v1
2013-10-28,Phase noise of oscillators with unsaturated amplifiers,"We study the role of amplifier saturation in eliminating feedback noise in
self-sustained oscillators. We extend previous works that use a saturated
amplifier to quench fluctuations in the feedback magnitude, while
simultaneously tuning the oscillator to an operational point at which the
resonator nonlinearity cancels fluctuations in the feedback phase. We consider
a generalized model which features an amplitude-dependent amplifier gain
function. This allows us to determine the total oscillator phase noise in
realistic configurations due to noise in both quadratures of the feedback, and
to show that it is not necessary to drive the resonator to large oscillation
amplitudes in order to eliminate noise in the phase of the feedback.",1310.7524v1
2013-12-09,Sub-Doppler resonances in the back-scattered light from random porous media infused with Rb vapor,"We report on the observation of sub-Doppler resonances on the back-scattered
light from a random porous glass medium with rubidium vapor filling its
interstices. The sub-Doppler spectral lines are the consequence of saturated
absorption where the incident laser beam saturates the atomic medium and the
back-scattered light probes it. Some specificities of the observed spectra
reflect the transient atomic evolution under confinement inside the pores.
Simplicity, robustness and potential miniaturization are appealing features of
this system as a spectroscopic reference.",1312.2599v1
2014-01-04,$D$-optimal saturated designs: a simulation study,"In this work we focus on saturated $D$-optimal designs. Using recent results,
we identify $D$-optimal designs with the solutions of an optimization problem
with linear constraints. We introduce new objective functions based on the
geometric structure of the design and we compare them with the classical
$D$-efficiency criterion. We perform a simulation study. In all the test cases
we observe that designs with high values of $D$-efficiency have also high
values of the new objective functions.",1401.0844v1
2014-01-21,Next-to-leading order improved perturbative QCD + saturation + hydrodynamics model for A+A collisions,"We calculate initial conditions for the hydrodynamical evolution in
ultrarelativistic heavy-ion collisions at the LHC and RHIC in an improved
next-to-leading order perturbative QCD + saturation framework. Using viscous
relativistic hydrodynamics, we show that we obtain a good simultaneous
description of the centrality dependence of charged particle multiplicities,
transverse momentum spectra and elliptic flow at the LHC and at RHIC. In
particular, we discuss how the temperature dependence of the shear viscosity is
constrained by these data.",1401.5319v1
2014-01-26,Rigidity of continuous quotients,"We study countable saturation of the metric reduced products and introduce
continuous fields of metric models indexed by locally compact, separable,
completely metrizable spaces. Saturation of the reduced product depends both on
the underlying index space and the model. By using the Gelfand--Naimark duality
we conclude that the assertion that the \vCech--Stone remainder of the
half-line has only trivial automorphisms is independent from ZFC. The
consistency of this statement follows from Proper Forcing Axiom and this is the
first known example of a connected space with this property.",1401.6689v2
2014-02-07,Analysis of a mosquito-borne epidemic model with vector stages and saturating forces of infection,"We study a mosquito-borne epidemic model where the vector population is
distinct in aquatic and adult stages and a saturating effect of disease
transmission is assumed to ocurr when the number of infectious (humans and
mosquitoes) becomes large enough. Several techniques, including center manifold
analysis and sensitivity analysis, have been used to reveal relevant features
of the model dynamics. We determine the existence of stability-instability
thresholds and the individual role played in such thresholds by the model
parameters.",1402.1719v1
2014-02-08,Periodic Behaviors in Constrained Multi-agent Systems,"In this paper, we provide two discrete-time multi-agent models which generate
periodic behaviors. The first one is a multi-agent system of identical double
integrators with input saturation constraints, while the other one is a
multi-agent system of identical neutrally stable system with input saturation
constraints. In each case, we show that if the feedback gain parameters of the
local controller satisfy a certain condition, the multi-agent system exhibits a
periodic solution.",1402.1862v1
2014-04-01,Saturated absorption at nanowatt power levels using metastable xenon in a high-finesse optical cavity,"Strong saturated absorption at nanowatt power levels has been demonstrated
using metastable xenon in a high-finesse optical cavity. The use of metastable
xenon allows a high quality factor of Q=2*10^8 to be achieved at relatively
high atomic densities without any contamination or damage to the optical
surfaces, which is often a problem when using high-density rubidium or other
alkali atoms. This technique provides a relatively straightforward way to
produce nonlinearities at the single-photon level with possible applications in
quantum communications and computing.",1404.0376v2
2014-04-22,Hosing Instability Suppression in Self-Modulated Plasma Wakefields,"We show that the hosing instability can be suppressed after the saturation of
the self-modulation instability of a long particle bunch if the plasma density
perturbation is linear. We derive scalings for maximum bunch tilts and seeds
for the self-modulation instability to ensure stable propagation beyond
saturation of self-modulation. Numerical solutions of the reduced hosing
equations and three-dimensional particle-in-cell simulations confirm our
analytical findings. Our results may also apply when a train of particle
bunches or laser pulses excites a linear wake.",1404.5387v1
2014-05-13,Influence of the ESR saturation on the power sensitivity of cryogenic sapphire resonators,"Here, we study the paramagnetic ions behavior in presence of a strong
microwave electromagnetic field sustained inside a cryogenic sapphire
whispering gallery mode resonator. The high frequency measurement resolution
that can be now achieved by comparing two CSOs permit for the first time to
observe clearly the non-linearity of the resonator power sensitivity. These
observations that in turn allow us to optimize the CSO operation, are well
explained by the Electron Spin Resonance (ESR) saturation of the paramagnetic
impurities contained in the sapphire crystal.",1405.3081v1
2014-05-27,Cavity controlled spectral singularity,"We study theoretically a PT-symmetric saturable balanced gain-loss system in
a ring cavity configuration. The saturable gain and loss are modeled by
two-level medium with or without population inversion. We show that the
specifics of the spectral singularity can be fully controlled by the cavity and
the atomic detuning parameters. The theory is based on the mean-field
approximation as in standard theory of optical bistability. Further, in the
linear regime we demonstrate the regularization of the singularity in detuned
systems, while larger input power levels are shown to be adequate to limit the
infinite growth in absence of detuning",1405.6812v1
2014-06-04,Non linear evolution: revisiting the solution in the saturation region,"In this paper we revisit the problem of the solution to Balitsky-Kovchegov
equation deeply in the saturation domain. We find that solution has the form of
Levin-Tuchin solution but it depends on variable $\bar{z} = \ln(r^2 Q^2_s) +
\mbox{Const}$ and the value of $\mbox{Const}$ is calculated in this paper. We
propose the solution for full BFKL kernel at large $z$ in the entire kinematic
region that satisfies the McLerram-Venugopalan initial condition",1406.1212v1
2014-06-12,The primitive equations of the atmosphere in presence of vapor saturation,"A modification of the classical primitive equations of the atmosphere is
considered in order to take into account important phase transition phenomena
due to air saturation and condensation. We provide a mathematical formulation
of the problem that appears to be new in this setting, by making use of
differential inclusions and variational inequalities, and which allows to
develop a rather complete theory for the solutions to what turns out to be a
nonlinearly coupled system of non-smooth partial differential equations.
Specifically we prove global existence of quasi-strong and strong solutions,
along with uniqueness results and maximum principles of physical interest.",1406.3165v1
2014-04-30,From minijet saturation to global observables in A + A collisions at the LHC and RHIC,"We review the recent results from the computation of saturated
next-to-leading order perturbative QCD minijet intial conditions combined with
viscous hydrodynamical evolution of ultrarelativistic heavy-ion collisions at
the LHC and RHIC. Comparison with experimental data is shown.",1406.4760v1
2014-07-10,Coherent backscattering of intense light by cold atoms with degenerate energy levels: Diagrammatic treatment,"We present a generalization of the diagrammatic pump-probe approach to
coherent backscattering (CBS) of intense laser light for atoms with degenerate
energy levels. We employ this approach for a characterization of the double
scattering signal from optically pumped atoms with the transition
$J_g\rightarrow J_e=J_g+1$ in the helicity preserving polarization channel. We
show that, in the saturation regime, the internal degeneracy becomes manifest
for atoms with $J_g\geq 1$, leading to a faster decrease of the CBS enhancement
factor with increasing saturation parameter than in the non-degenerate case.",1407.2841v1
2014-08-08,Saturation of Generalized Partially Hyperbolic Attractors,"We prove the saturation of a generalized partially hyperbolic attractor of a
$C^2$ map. As a consequence, we show that any generalized partially hyperbolic
horseshoe-like attractor of a $C^1$-generic diffeomorphism has zero volume. In
contrast, by modification of Poincar\'e cross section of the geometric model,
we build a $C^1$-diffeomorphism with a partially hyperbolic horseshoe-like
attractor of positive volume.",1408.1835v4
2014-08-30,Quantum friction,"We investigate the van der Waals friction between graphene and an amorphous
SiO$_2$ substrate. We find that due to this friction the electric current is
saturated at a high electric field, in agreement with experiment. The
saturation current depends weakly on the temperature, which we attribute to the
quantum friction between the graphene carriers and the substrate optical
phonons. We calculate also the frictional drag between two graphene sheets
caused by van der Waals friction, and find that this drag can induce a voltage
high enough to be easily measured experimentally.",1409.0145v1
2014-09-25,Momentum-resolved study of the saturation intensity in multiple ionization,"We present a momentum-resolved study of strong field multiple ionization of
ionic targets. Using a deconvolution method we are able to reconstruct the
electron momenta from the ion momentum distributions after multiple ionization
up to four sequential ionization steps. This technique allows an accurate
determination of the saturation intensity as well as of the electron release
times during the laser pulse. The measured results are discussed in comparison
to typically used models of over-the-barrier ionization and tunnel ionization.",1409.7251v2
2014-10-27,Energy and particle currents in a driven integrable system,"We study the ratio of the energy and particle currents ($j^E/j^N$) in an
integrable one dimensional system of interacting fermions. Both currents are
driven by a finite (nonzero) dc electric field. In doped insulators, where the
local conserved quantities saturate the so called Mazur bound on the charge
stiffness, $j^E/j^N$ agrees with the linear--response theory, even though such
agreement may be violated for each current alone. However, in the metallic
regime with a non-saturated Mazur bound, the ratio $j^E/j^N$ in a driven system
is shown to be much larger than predicted by the linear--response theory.",1410.7262v1
2014-11-28,Saturation and associated primes of powers of edge ideals,"For the edge ideal I of an arbitrary simple graph G we describe the monomials
of the saturation of a power of I in terms of (vertex) weighted graphs
associated with the monomials. This description allows us to characterize the
embedded associated primes of a power of I as covers of G which contain certain
types of subgraphs of G. As an application, we completely classify the
associated primes of the second and the third power of I in terms of G.",1411.7740v1
2014-12-02,Large $\mathbf{b}$ behaviour in the CGC/saturation approach: BFKL equation with pion loops,"In this paper we proposed a solution to the longstanding problem of the
CGC/saturation approach: the power-like fall of the scattering amplitudes at
large $b$. This decrease leads to the violation of the Froissart theorem and
makes the approach theoretically inconsistent. We showed in the paper that sum
of the pion loops results in the exponential fall of the scattering amplitude
at large impact parameters and in the restoration of the Froissart theorem.",1412.0893v1
2014-12-06,Twist expansion of differential cross-sections of forward Drell-Yan process,"Forward Drell-Yan process at the LHC is a sensitive tool for investigating
higher twist effects in QCD. The expansion of all Drell-Yan structure functions
is performed assuming GBW saturation model and the saturation scale plays the
role of the hadronic scale of OPE. We show that the Lam-Tung relation is broken
at twist 4. The results open the way for a forthcoming analysis of multiple
scattering and higher twist effects.",1412.2289v1
2015-01-21,Multi-plasmon absorption in graphene,"We show that graphene possesses a strong nonlinear optical response in the
form of multi-plasmon absorption, with exciting implications in classical and
quantum nonlinear optics. Specifically, we predict that graphene nano-ribbons
can be used as saturable absorbers with low saturation intensity in the
far-infrared and terahertz spectrum. Moreover, we predict that two-plasmon
absorption and extreme localization of plasmon fields in graphene nano-disks
can lead to a plasmon blockade effect, in which a single quantized plasmon
strongly suppresses the possibility of exciting a second plasmon.",1501.05258v1
2015-01-22,Permanent versus determinant: not via saturations,"Let Det_n denote the closure of the GL_{n^2}(C)-orbit of the determinant
polynomial det_n with respect to linear substitution. The highest weights
(partitions) of irreducible GL_{n^2}(C)-representations occurring in the
coordinate ring of Det_n form a finitely generated monoid S(Det_n). We prove
that the saturation of S(Det_n) contains all partitions lambda with length at
most n and size divisible by n. This implies that representation theoretic
obstructions for the permanent versus determinant problem must be holes of the
monoid S(Det_n).",1501.05528v2
2015-01-25,Stability and bifurcation analysis of a SIR model with saturated incidence rate and saturated treatment,"We study the dynamics of a SIR epidemic model with nonlinear incidence rate,
vertical transmission vaccination for the newborns and the capacity of
treatment, that takes into account the limitedness of the medical resources and
the efficiency of the supply of available medical resources. Under some
conditions we prove the existence of backward bifurcation, the stability and
the direction of Hopf bifurcation. We also explore how the mechanism of
backward bifurcation affects the control of the infectious disease. Numerical
simulations are presented to illustrate the theoretical findings.",1501.06179v1
2015-02-10,Quantum bounds on heat transport through nanojunctions,"We derive rigorous quantum mechanical bounds for the heat current through a
nanojunction connecting two thermal baths at different temperatures. Based on
exact sum rules, these bounds compliment the well-known quantum of thermal
conductance $\kappa_Q \equiv \pi k^2_B T/6\hbar$, which provides a bound for
low-temperature heat transport in all systems, but is saturated only for
noninteracting transport. In contrast, our bounds are saturated at high
temperatures---but still in the quantum regime---, even when interactions are
very strong. We evaluate these bounds for harmonic and strongly anharmonic
junction models and compare with numerical approaches.",1502.03095v2
2015-04-05,Measuring Method of a Surface Property inside the Pore: Application of Kelvin's equation,"Surface analyses inside the nanopore, micropore, and a very narrow pipe are
important topics for development of the chemical engineering. Here, we propose
a measuring method which evaluates the surface coverage of the chemically
modified pore surface and the corrosion rate of the inner surface of the narrow
pipe, etc. The method uses Kelvin's equation that expresses saturated vapor
pressure of a liquid in the pore (pipe). The surface coverage and the corrosion
rate are calculated by measuring saturated vapor pressure of the liquid in the
pore and the pipe, respectively. In this letter, we explain the concept of the
method briefly.",1504.01114v1
2015-05-11,Hartman-Fletcher effect for array of complex barriers,"We calculate the time taken by a wave packet to tunnel through a series of
complex barrier potentials using stationary phase method to show its saturation
(Hartman-Fletcher effect) with number of barriers in various situations. We
numerically study the effect of the coupling between the elastic and inelastic
channels, width of the individual barrier, separation between the consecutive
barriers on the saturation of tunneling time. Nature of HF effect has further
been investigated for more realistic barriers with random inelasticity and also
for emissive inelastic channels.",1505.03163v1
2015-05-18,On sets of graded attribute implications with witnessed non-redundancy,"We study properties of particular non-redundant sets of if-then rules
describing dependencies between graded attributes. We introduce notions of
saturation and witnessed non-redundancy of sets of graded attribute
implications are show that bases of graded attribute implications given by
systems of pseudo-intents correspond to non-redundant sets of graded attribute
implications with saturated consequents where the non-redundancy is witnessed
by antecedents of the contained graded attribute implications. We introduce an
algorithm which transforms any complete set of graded attribute implications
parameterized by globalization into a base given by pseudo-intents.
Experimental evaluation is provided to compare the method of obtaining bases
for general parameterizations by hedges with earlier graph-based approaches.",1505.04677v1
2015-06-19,Complexity of a Disjoint Matching Problem on Bipartite Graphs,"We consider the following question: given an $(X,Y)$-bigraph $G$ and a set $S
\subset X$, does $G$ contain two disjoint matchings $M_1$ and $M_2$ such that
$M_1$ saturates $X$ and $M_2$ saturates $S$? When $|S|\geq |X|-1$, this
question is solvable by finding an appropriate factor of the graph. In
contrast, we show that when $S$ is allowed to be an arbitrary subset of $X$,
the problem is NP-hard.",1506.06157v1
2015-06-22,Reassessing nuclear matter incompressibility and its density dependence,"Experimental giant monopole resonance energies are now known to constrain
nuclear incompressibility of symmetric nuclear matter $K$ and its density slope
$M$ at a particular value of sub-saturation density, the crossing density
$\rho_c$. Consistent with these constraints, we propose a reasonable way to
construct a plausible equation of state of symmetric nuclear matter in a broad
density region around the saturation density $\rho_0$. Help of two additional
empirical inputs, the value of $\rho_0$ and that of the energy per nucleon
$e(\rho_0)$ are needed. The value of $K(\rho_0)$ comes out to be $211.9\pm
24.5$ MeV.",1506.06461v1
2015-07-16,On the physical DGLAP evolution of structure functions and its dependence on the renormalization scale,"Physical anomalous dimensions are a formulation of the DGLAP evolution of
Deep Inelastic structure functions which is independent of factorization scheme
and -scale. In this proceedings we provide an outlook on possible applications,
in particular in the search of saturation effects. As an original contribution
we present a short study of the renormalization scale dependence of physical
evolved structure functions for large initial scale $Q_0^2=30$GeV$^2$",1507.04427v1
2015-07-24,The behavior of the heavy-quarks structure functions at small-$x$,"The behavior of the charm and bottom structure functions
($F_{k}^{i}(x,Q^{2})$, i=c,b; k=2,L) at small-$x$ is considered with respect to
the hard-Pomeron and saturation models. Having checked that this behavior
predicate the heavy flavor reduced cross sections concerning the unshadowed and
shadowed corrections. We will show that the effective exponents for the
unshadowed and saturation corrections are independent of $x$ and $Q^{2}$, and
also the effective coefficients are dependent to $\ln{Q^{2}}$ compared to
Donnachie-Landshoff (DL) and color dipole (CD) models.",1507.06770v1
2015-07-29,Geometrical Scaling in Inelastic Inclusive Particle Production at the LHC,"Analyzing recent ALICE data on inelastic pp scattering at the LHC energies we
show that charged particle distributions exhibit geometrical scaling (GS). We
show also that the inelastic cross-section is scaling as well and that in this
case the quality of GS is better than for multiplicities. Moreover, exponent
$\lambda$ characterizing the saturation scale is for the cross-section scaling
compatible with the one found in deep inelastic ep scattering at HERA. Next, by
parametrizing charged particles distributions by the Tsallis-like formula, we
find a somewhat unexpected solution that still exhibits GS, but differs from
the ""standard"" one where the Tsallis temperature is proportional to the
saturation scale.",1507.08186v1
2015-08-12,Components of V(ρ)\otimes V(ρ),"Kostant asked the following question:
  Let $\mathfrak{g}$ be a simple Lie algebra over the complex numbers. Let
$\lambda$ be a dominant integral weight. Then, $V(\lambda)$ is a component of $
V(\rho)\otimes V(\rho)$ if and only if $\lambda \leq 2\rho$ under the usual
Bruhat-Chevalley order on the set of weights.
  We give an affirmative answer to this question up to a saturation factor. In
particular, the question is answered affirmatively for the special linear Lie
algebras due to the Saturation Theorem of Knutson-Tao.",1508.03071v1
2015-08-26,Voltage quench dynamics of a Kondo system,"We examine the dynamics of a correlated quantum dot in the mixed valence
regime. We perform numerically exact calculations of the current after a
quantum quench from equilibrium by rapidly applying a bias voltage in a wide
range of initial temperatures. The current exhibits short equilibration times
and saturates upon the decrease of temperature at all times, indicating Kondo
behavior both in the transient regime and in steady state. The time-dependent
current saturation temperature matches the Kondo temperature at small times or
small voltages; a substantially increased value is observed outside of linear
response. These signatures are directly observable by experiments in the
time-domain.",1508.06633v1
2015-09-23,Maharam-Types and Lyapunov's Theorem for Vector Measures on Locally Convex Spaces without Control Measures,"We formulate the saturation property for vector measures in lcHs as a
nonseparability condition on the derived Boolean $\sigma$-algebras by drawing
on the topological structure of vector measure algebras. We exploit a
Pettis-like notion of vector integration in lcHs, the
Bourbaki--Kluv\'anek--Lewis integral, to derive an exact version of the
Lyapunov convexity theorem in lcHs without the BDS property. We apply our
Lyapunov convexity theorem to the bang-bang principle in Lyapunov control
systems in lcHs to provide a further characterization of the saturation
property.",1509.06965v1
2015-11-11,Probing proton fluctuations with asymmetric rapidity correlations,"Intrinsic fluctuations of the proton saturation momentum generate asymmetric
rapidity distributions on an event-by-event basis. We argue that the asymmetric
component, $\left<a_1^2\right>$, of the orthogonal polynomial decomposition of
the two-particle rapidity correlation function is a sensitive probe to this
distribution of fluctuations. We present a simple model connecting the
experimentally measured $\left<a_1^2\right>$ to the variance, $\sigma$, of the
distribution of the logarithm of the proton saturation scale. We find that
$\sigma\approx 0. 5-1$ describes the asymmetric component of the rapidity
correlations recently measured by the ATLAS collaboration.",1511.03620v2
2015-11-26,A Discussion on the Transmission Conditions for Saturated Fluid Flow Through Porous Media With Fractal Microstructure,"The present work is aimed to find suitable exchange conditions for saturated
fluid flow in a porous medium, when a fractal microstructure is embedded in the
porous matrix. Two different deterministic models are introduced and rigorously
analyzed. Also, numerical experiments for each of them are presented to verify
the theoretically predicted behavior of the phenomenon and some probabilistic
versions are explored numerically, to gain further insight on the phenomenon.",1511.08511v4
2016-01-27,Deep Saturated Free Electron Laser Oscillators and Frozen Spikes,"We analyze the behavior of Free Electron Laser (FEL) oscillators operating in
the deep saturated regime and point out the formation of sub-peaks of the
optical pulse. They are very stable configurations, having a width
corresponding to a coherence length. We speculate on the physical mechanisms
underlying their growth and attempt an identification with FEL mode locked
structures associated with Super Modes. Their impact on the intra-cavity
nonlinear harmonic generation is also discussed along with the possibility of
exploiting them as cavity out-coupler.",1601.07372v1
2016-03-14,Evidence of strong proton shape fluctuations from incoherent diffraction,"We show within the saturation framework that measurements of exclusive vector
meson production at high energy provide evidence for strong geometric
fluctuations of the proton. In comparison, the effect of saturation scale and
color charge fluctuations is weak. This knowledge will allow detailed future
measurements of the incoherent cross section to tightly constrain the
fluctuating geometry of the proton as a function of the parton momentum
fraction $x$.",1603.04349v2
2016-03-15,"Microcavity with saturable nonlinearity under simultaneous resonant and nonresonant pumping: multistability, Hopf bifurcations and chaotic behaviour","We studied optical response of microcavity non-equilibrium exciton-polariton
Bose-Einstein condensate with saturable nonlinearity under simultaneous
resonant and non-resonant pumping. We demonstrated the emergence of
multistabile behavior due to the satutration of the excitonic absorbtion.
Stable periodic Rabi- type oscillations of the excitonic and photonic
condensate components in the regime of the stationary pump and their transition
to the chaotic dynamics through the cascade of Hopf bifurcations by tuning of
the electrical pump are revealed.",1603.04612v1
2016-04-14,A numerical study of two-phase flow models with dynamic capillary pressure and hysteresis,"Saturation overshoot and pressure overshoot are studied by incorporating
dynamic capillary pressure, capillary pressure hysteresis and hysteretic
dynamic coefficient with a traditional fractional flow equation in one
dimension. Using the method of lines, the discretizations are constructed by
applying Castillo-Grone's mimetic operators in the space direction and explicit
trapezoidal integrator in the time direction. Convergence tests and
conservation property of the schemes are presented. Computed profiles capture
both the saturation overshoot and pressure overshoot phenomena. Comparisons
between numerical results and experiments illustrate the effectiveness and
different features of the models.",1604.04109v3
2016-04-24,Integrable nonlinear parity-time symmetric optical oscillator,"The nonlinear dynamics of a balanced parity-time symmetric optical microring
arrangement are analytically investigated. By considering gain and loss
saturation effects, the pertinent conservation laws are explicitly obtained in
the Stokes domain-thus establishing integrability. Our analysis indicates the
existence of two regimes of oscillatory dynamics and frequency locking, both of
which are analogous to those expected in linear parity-time symmetric systems.
Unlike other saturable parity time symmetric systems considered before, the
model studied in this work first operates in the symmetric regime and then
enters the broken parity-time phase.",1604.07072v1
2016-05-20,Initial stage of cavitation in liquids and its observation by Rayleigh scattering,"A theory is developed for the initial stage of cavitation in the framework of
Zel'dovich-Fisher theory of nucleation in the field of negative pressure, while
taking into account the surface tension dependence on the nanopore radius. A
saturation mechanism is proposed that limits the exponential dependence of the
nucleation rate on the energy required to create nanopores. An estimate of the
saturated density of nanopores at the nucleation stage is obtained. It is shown
that Rayleigh scattering can detect nanopores arising at the initial stage of
cavitation development.",1605.06469v1
2016-05-28,Saturation and bistability of defect-mode intersubband polaritons,"In this article we report about linear and nonlinear optical properties of
intersubband cavity polariton samples, where the resonant photonic mode is a
defect state in a metallo-dielectric photonic crystal slab. By tuning a single
geometric parameter of the resonator, the cavity Q-factor can reach values as
large as 85, with a consequent large cooperativity for the light-matter
interaction. We show that a device featuring large cooperativity leads to sharp
saturation, or even bistability, of the polariton states. This nonlinear
dynamics occurs at the crossover between the weak and the strong coupling
regimes, where the weak critical coupling concept plays a fundamental role.",1605.08893v1
2016-06-28,"Velocity shear, turbulent saturation, and steep plasma gradients in the scrape-off layer of inner-wall limited tokamaks","The narrow power decay-length ($\lambda_q$), recently found in the scrape-off
layer (SOL) of inner-wall limited (IWL) discharges in tokamaks, is studied
using 3D, flux-driven, global two-fluid turbulence simulations. The formation
of the steep plasma profiles measured is found to arise due to radially sheared
$\vec{E}\times\vec{B}$ poloidal flows. A complex interaction between sheared
flows and outflowing plasma currents regulates the turbulent saturation,
determining the transport levels. We quantify the effects of sheared flows,
obtaining theoretical estimates in agreement with our non-linear simulations.
Analytical calculations suggest that the IWL $\lambda_q$ is roughly equal to
the turbulent correlation length.",1606.08564v1
2016-06-28,Single Spin Asymmetry in Forward $pA$ Collisions,"We compute the transverse single spin asymmetry in light hadron production
$p^\uparrow p\to hX$ and $p^\uparrow A\to hX$ including the gluon saturation
effect in the unpolarized nucleon/nucleus. In the forward (large-$x_F$) region,
the dominant contribution comes from the so-called derivative term associated
with the soft gluonic pole. This leads to the cancellation of nuclear effects
in $A_N$ which can be tested at RHIC. We also show that the soft fermionic pole
disappears in the saturation environment.",1606.08640v2
2016-07-06,Measurement of forward direct photon production in p-A at the LHC with ALICE - A probe for nuclear PDFs and saturation,"Probes for the small-x parton densities and predicted effects of gluon
saturation are discussed. At very low x and intermediate Q, only results on
hadronic observables at the LHC are available, which do not provide unambiguous
information. It is shown that the measurement of direct photons at forward
rapidity at the LHC is particularly promising to provide a unique signal. We
further discuss the possibilities to perform such measurements with a detector
upgrade in the ALICE experiment and present the R&D activities ongoing.",1607.01673v1
2016-08-12,Boundary control of cascaded ODE-Heat equations under actuator saturation,"In this paper, we consider boundary stabilization for a cascade of ODE-heat
system with state delay under actuator saturation. To stabilize the system, we
design a state feedback controller via the backstepping method and find a bound
on the domain of attraction. The latter bound is based on Lyapunov method,
whereas the exponential stability of the delayed cascaded systems is proved by
using Halanay's inequality. Numerical examples illustrate the efficiency of the
method.",1608.03729v2
2016-08-30,Fusion systems over a Sylow $p$-subgroup of $\mathrm{G}_2(p)$,"For $S$ a Sylow $p$-subgroup of the group $\mathrm{G}_2(p)$ for $p$ odd, up
to isomorphism of fusion systems, we determine all saturated fusion systems
$\mathcal{F}$ on $S$ with $O_p(\mathcal{F})=1$. For $p \ne 7$, all such fusion
systems are realized by finite groups whereas for $p=7$ there are $29$
saturated fusion systems of which $27$ are exotic.",1608.08399v2
2016-09-19,"Wigner, Husimi and GTMD distributions in the Color Glass Condensate","We study the phase space distributions of gluons inside a nucleon/nucleus in
the small-$x$ regime including the gluon saturation effect. This can be done by
using the relation between the gluon Wigner distribution and the dipole
S-matrix at small-$x$, the latter satisfies the Balitsky-Kovchegov (BK)
equation. By efficiently solving the BK equation with impact parameter
dependence, we compute the Wigner, Husimi and generalized TMD (GTMD)
distributions in the saturation regime. We also investigate the elliptic
angular dependence of these distributions which has been recently shown to be
measurable in DIS experiments.",1609.05773v1
2016-10-16,Non-Hermitian engineering of synthetic saturable absorbers,"We introduce a new type of synthetic saturable absorbers based on quantum
inspired photonic arrays whose linear light transport characteristics can be
derived via bosonic algebra. We demonstrate that the interplay between optical
Kerr nonlinearity, interference effects and non-Hermiticity through radiation
loss leads to a nonlinear optical filtering response with two distinct regimes
of small and large optical transmissions. More interestingly, we show that the
boundary between these two regimes can be very sharp. The threshold optical
intensity that marks this abrupt ""phase transition"" and its steepness can be
engineered by varying the number of the guiding elements. The practical
feasibility of these structures as well as their potential applications in
laser systems and optical signal processing are also discussed.",1610.04896v1
2016-10-20,Spatio-temporal extreme events in a laser with a saturable absorber,"We study extreme events occurring in the transverse $(x,y)$ section of the
field emitted by a broad-area semiconductor laser with a saturable absorber.
The spatio-temporal events on which we perform the statistical analysis are
identified as maxima of the field intensity in the 3D space $(x,y,t)$. We
identify regions in the parameter space where extreme events are more likely to
occur and we study the connection of those extreme events with the cavity
solitons that are known to exist in the same system, both stationary and
self-pulsing.",1610.06452v1
2016-11-30,Mean Flow Evolution of Saturated Forced Shear Flows in Polytropic Atmospheres,"In stellar interiors shear flows play an important role in many physical
processes. So far helioseismology provides only large-scale measurements, and
so the small-scale dynamics remains insufficiently understood. To draw a
connection between observations and three-dimensional DNS of shear driven
turbulence, we investigate horizontally averaged profiles of the numerically
obtained mean state. We focus here on just one of the possible methods that can
maintain a shear flow, namely the average relaxation method. We show that
although some systems saturate by restoring linear marginal stability this is
not a general trend. Finally, we discuss the reason that the results are more
complex than expected.",1611.10131v1
2016-12-23,Paving the Way Towards Precision Physics in Saturation Studies Through Exclusive Diffractive Light Neutral Vector Meson Production,"We perform the first next-to-leading order computation of the $\gamma^{(*)}
\to V$ ($\rho, \phi, \omega$) impact factor in the QCD shockwave approach and
in the most general kinematics. This paves the way to the very first
quantitative study of high-energy nucleon and nucleus saturation beyond the
leading order, in various processes to be measured in $ep$, $eA$, $pp$ and $pA$
collisions at existing and future colliders.",1612.08026v1
2017-01-19,Apparent non-conservation of momentum of light due to strongly coupled nonlinear dynamics in a multimode optical fiber,"The intimate interaction between phase-matched parametric amplification and
strong nonlinear mode coupling in a multimode optical fiber results in a
saturable spatial mode conversion that appears to violate the conservation of
momentum. We investigate, by theory and experiment, this new regime of strong
nonlinear interaction in multimode optical fibers and show that the appearance
of the non-conservation of linear momentum is merely a clever sleight of hand
by nature. This novel saturable mode conversion can potentially be used in a
variety of applications including the generation of exotic quantum states of
light.",1701.05606v3
2017-01-20,Effect of nuclear saturation parameters on possible maximum mass of neutron stars,"In order to systematically examine the possible maximum mass of neutron
stars, which is one of the important properties characterizing the physics in
high-density region, I construct neutron star models by adopting
phenomenological equations of state with various values of nuclear saturation
parameters for low-density region, which are connected to the equation of state
for high-density region characterized by the possible maximum sound velocity in
medium. I derive an empirical formula for the possible maximum mass of neutron
star. If massive neutron stars are observed, it could be possible to get a
constraint on the possible maximum sound velocity for high-density region.",1701.05646v1
2017-02-03,Stability and Instability Conditions for Slotted Aloha with Exponential Backoff,"This paper provides stability and instability conditions for slotted Aloha
under the exponential backoff (EB) model with geometric law $i\mapsto
b^{-i-i_0}$, when transmission buffers are in saturation, i.e., always full. In
particular, we prove that for any number of users and for $b>1$ the system is:
(i) ergodic for $i_0 >1$, (ii) null recurrent for $0<i_0\le 1$, and (iii)
transient for $i_0=0$. Furthermore, when referring to a system with queues and
Poisson arrivals, the system is shown to be stable whenever EB in saturation is
stable with throughput $\lambda_0$ and the system input rate is upper-bounded
as $\lambda<\lambda_0$.",1702.00991v1
2017-02-13,Heteroclinic traveling fronts for a generalized Fisher-Burgers equation with saturating diffusion,"We study the existence of monotone heteroclinic traveling waves for a general
Fisher-Burgers equation with nonlinear and possibly density-dependent
diffusion. Such a model arises, for instance, in physical phenomena where a
saturation effect appears for large values of the gradient. We give an estimate
for the critical speed (namely, the first speed for which a monotone
heteroclinic traveling wave exists) for some different shapes of the reaction
term, and we analyze its dependence on a small real parameter when this brakes
the diffusion, complementing our study with some numerical simulations.",1702.03782v1
2017-03-01,Extreme points and saturated polynomials,"We consider the problem of characterizing the extreme points of the set of
analytic functions f on the bidisk with positive real part and f(0)=1. If one
restricts to those f whose Cayley transform is a rational inner function, one
gets a more tractable problem. We construct families of such f that are extreme
points and conjecture that these are all such extreme points. These extreme
points are constructed from polynomials dubbed saturated, which roughly
speaking means they have no zeros in the bidisk and as many zeros as possible
on the boundary without having infinitely many zeros.",1703.00094v1
2017-03-01,Nonlinear absorption of tetrathiafulvalene radical cation (TTF+) based charge transfer (CT) aggregates in PMMA,"Nolinear Absorption of CT TFF+ aggregates in PMMA matrix was studied with
resonant excitation around 800 nm in the femtoseconds regime with the Z-Scan
technique with 100 Hz pulse repetition rate. The saturated absorption profiles
were fitted with a prepared formula based on steady state rate equations for a
homogeneous ensemble of two levels systems, thin samples and quasi
monochromatic field without the usual assumption of low saturation regime. The
lifetime of the CT state, with the use of this model was estimated in hundred
of fs, of the same order of magnitude of the exciting pulse.",1703.00388v1
2017-04-11,Testing a Saturation-Based Theorem Prover: Experiences and Challenges (Extended Version),"This paper attempts to address the question of how best to assure the
correctness of saturation-based automated theorem provers using our experience
developing the theorem prover Vampire. We describe the techniques we currently
employ to ensure that Vampire is correct and use this to motivate future
challenges that need to be addressed to make this process more straightforward
and to achieve better correctness guarantees.",1704.03391v1
2017-05-12,Obtaining the Current-Flux Relations of the Saturated PMSM by Signal Injection,"This paper proposes a method based on signal injection to obtain the
saturated current-flux relations of a PMSM from locked-rotor experiments. With
respect to the classical method based on time integration, it has the main
advantage of being completely independent of the stator resistance; moreover,
it is less sensitive to voltage biases due to the power inverter, as the
injected signal may be fairly large.",1705.04605v1
2017-05-31,Macroscopic random Paschen-Back effect in ultracold atomic gases,"We consider spin- and density-related properties of single-particle states in
a one-dimensional system with random spin-orbit coupling. We show that the
presence of an additional Zeeman field $\Delta$ induces both nonlinear spin
polarization and delocalization of states localized at $\Delta=0$,
corresponding to a random macroscopic analogue of the Paschen-Back effect.
While the conventional Paschen-Back effect corresponds to a saturated
$\Delta-$dependence of the spin polarization, here the gradual suppression of
the spin-orbit coupling effects by the Zeeman field is responsible both for the
spin saturation and delocalization of the particles.",1705.11157v1
2017-06-06,Scaling and Saturation in Infinite-Dimensional Control Problems with Applications to Stochastic Partial Differential Equations,"We establish the dual notions of scaling and saturation from geometric
control theory in an infinite-dimensional setting. This generalization is
applied to the low-mode control problem in a number of concrete nonlinear
partial differential equations. We also develop applications concerning
associated classes of stochastic partial differential equations (SPDEs). In
particular, we study the support properties of probability laws corresponding
to these SPDEs as well as provide applications concerning the ergodic and
mixing properties of invariant measures for these stochastic systems.",1706.01997v2
2017-06-20,Saturation of Strong Electron-Electron Umklapp Scattering at High Temperature,"We consider clean metals, at finite temperature, in which the inelastic rate,
$\hbar/ \tau_{ee}$, can become of the order of, or larger, than the band
splitting energy. We show that in suchsystems, contrary to the common
knowledge, the umklapp scattering rate becomes independent of both $\tau_{ee}$
and the temperature $T,$ in three dimensional systems. We discuss the relation
of this phenomenon to the saturation of resistivity at high temperature.",1706.06256v2
2017-07-12,A constrained model for MEMS with varying dielectric properties,"A semilinear parabolic equation with constraint modeling the dynamics of a
microelectromechanical system (MEMS) is studied. In contrast to the commonly
used MEMS model, the well-known pull-in phenomenon occurring above a critical
potential threshold is not accompanied by a breakdown of the model, but is
recovered by the saturation of the constraint for pulled-in states. It is shown
that a maximal stationary solution exists and that saturation only occurs for
large potential values. In addition, the existence, uniqueness, and large time
behavior of solutions to the evolution equation are studied.",1707.03590v1
2017-08-09,Electron-electron scattering and conductivity of long multimode channels,"The electron-electron scattering increases the resistance of ballistic
many-mode channels whose width is smaller than their length. We show that this
increase saturates in the limit of infinitely long channels. Because the
mechanisms of angular relaxation of electrons in three and two dimensions are
different, the saturation value of the correction to the resistance is
temperature-independent in the case of three-dimensional channels and is
proportional to the temperature for two-dimensional ones. The spatial behavior
of electron distribution in the latter case is described by an unusual
characteristic length.",1708.02770v3
2017-08-03,NaCl crystal from salt solution with far below saturated concentration under ambient condition,"Under ambient conditions, we directly observed NaCl crystals experimentally
in the rGO membranes soaked in the salt solution with concentration below and
far below the saturated concentration. Moreover, in most probability, the NaCl
crystals show stoichiometries behavior. We attribute this unexpected
crystallization to the cation-{\pi} interactions between the ions and the
aromatic rings of the rGO.",1708.02994v1
2017-08-15,Vicinity effect of massive bodies on YBa2Cu3O6+d being saturated with air components,"We study the influence of the close-lying massive bodies on the YBCO material
while it is being saturated with air components. It has been found the effect
that can be interpreted as attraction/repulsion of the bodies to/from the
samples of hydrated YBCO. This force interaction has been confirmed by a
""direct"" dynamometric method for the Earth as a maximum massive body to be used
in our experiments.",1708.07402v3
2017-09-13,NLO exclusive diffractive processes with saturation,"We present two NLO exclusive impact factors computed in the QCD shock wave
approach. These are the very first steps towards precision studies of a wide
range of high energy exclusive processes with saturation effects in $ep$, $eA$,
$pp$ and $pA$ collisions.",1709.04422v1
2017-10-27,The saturation bifurcation in coupled oscillators,"We examine examples of weakly nonlinear systems whose steady states undergo a
bifurcation with increasing forcing, such that a forced subsystem abruptly
ceases to absorb additional energy, instead diverting it into an initially
quiescent, unforced subsystem. We derive and numerically verify analytical
predictions for the existence and behavior of such saturated states for a class
of oscillator pairs. We also examine related phenomena, including
zero-frequency response to periodic forcing, Hopf bifurcations to
quasiperiodicity, and bifurcations to periodic behavior with multiple
frequencies.",1710.10317v3
2017-11-16,Vector Representation of Preferences on $σ$-Algebras and Fair Division in Saturated Measure Spaces,"The purpose of this paper is twofold. First, we axiomatize preference
relations on a $\sigma$-algebra of a saturated measure space represented by a
vector measure and furnish a utility representation in terms of a nonadditive
measure satisfying the appropriate requirement of continuity and convexity.
Second, we investigate the fair division problems in which each individual has
nonadditive preferences on a $\sigma$-algebra invoking our utility
representation result. We show the existence of individually rational Pareto
optimal partitions, Walrasian equilibria, core partitions, and Pareto optimal
envy-free partitions.",1711.05973v2
2017-11-19,Dynamic cavity effect in Topological Insulator Bi2Te3 based Passive Q-switched Solid State Laser,"Dynamic cavity effect of a Topological Insulator Bi2Te3 based Passive
Q-switched (QS) solid state laser was investigated. With a saturation intensity
as low as a few kW, Bi2Te3 processed by hydrothermal exfoliation serves a
sensitive saturable absorber to initiate Q-switching. Without material damage,
a transition from QS state to CW state was observed when the pumping strength
increases which was explained by the modulation instability spectrum of laser
rate equation.",1711.06994v1
2017-11-21,Presentations of Cluster Modular Groups and Generation by Cluster Dehn Twists,"We give a method to compute presentations of saturated cluster modular
groups. Using this, we obtain finite presentations of the saturated cluster
modular groups of finite mutation type $X_6$ and $X_7$. We verify that the
cluster modular groups of finite mutation type $\widetilde{E}_6$,
$\widetilde{E}_7$, $\widetilde{E}_8$, $G_2^{(*,*)}$, $X_6$ and $X_7$ are
virtually generated by cluster Dehn twists.",1711.07785v5
2017-12-05,"Multiparton interactions, small-x processes and diffraction","The connection between multiparton interaction, diffractive processes and
saturation effects is discussed. The relation of the rise of the gluon density
at small longitudinal momentum fractions x with the occurrence of saturation,
diffraction and multiparton interaction is being studied both experimentally
and theoretically. We illustrate key ideas underlying recent progress, and
stress the role of different theoretical approaches to small-x QCD evolution in
investigations of multiparton interactions.",1712.01726v2
2017-12-07,Systematics of strong nuclear amplification of gluon saturation from exclusive vector meson production in high energy electron-nucleus collisions,"We show that gluon saturation gives rise to a strong modification of the
scaling in both the nuclear mass number $A$ and the virtuality $Q^2$ of the
vector meson production cross-section in exclusive deep-inelastic scattering
off nuclei. We present qualitative analytic expressions for how the scaling
exponents are modified as well as quantitative predictions that can be tested
at an Electron-Ion Collider.",1712.02508v2
2017-12-14,"Global properties of an age-structured virus model with saturated antibody immune response, multi-target cells and general incidence rate","Some viruses, such as human immunodeficiency virus, can infect several types
of cell populations. The age of infection can also affect the dynamics of
infected cells and production of viral particles. In this work, we study a
virus model with infection-age and different types of target cells which takes
into account the saturation effect in antibody immune response and a general
non-linear infection rate. We construct suitable Lyapunov functionals to show
that the global dynamics of the model is completely determined by two critical
values: the basic reproduction number of virus and the reproductive number of
antibody response.",1712.05064v1
2018-03-15,Hypergraph Saturation Irregularities,"Let $\mathcal{F}$ be a family of $r$-graphs. An $r$-graph $G$ is called
$\mathcal{F}$-saturated if it does not contain any members of $\mathcal{F}$ but
adding any edge creates a copy of some $r$-graph in $\mathcal{F}$. The
saturation number $\operatorname{sat}(\mathcal{F},n)$ is the minimum number of
edges in an $\mathcal{F}$-saturated graph on $n$ vertices. We prove that there
exists a finite family $\mathcal{F}$ such that
$\operatorname{sat}(\mathcal{F},n) / n^{r-1}$ does not tend to a limit. This
settles a question of Pikhurko.",1803.05799v1
2018-04-24,On $p$-robust saturation on quadrangulations,"For the Poisson problem in two dimensions, posed on a domain partitioned into
axis-aligned rectangles with up to one hanging node per edge, we envision an
efficient error reduction step in an instance-optimal $hp$-adaptive finite
element method. Central to this is the problem: Which increase in local
polynomial degree ensures $p$-robust contraction of the error in energy norm?
We reduce this problem to a small number of saturation problems on the
reference square, and provide strong numerical evidence for their solution.",1804.09065v1
2018-05-02,"Universal correlations in the nuclear symmetry energy, slope parameter, and curvature","From general Fermi liquid theory arguments, we derive correlations among the
symmetry energy (J), its slope parameter (L), and curvature (K_sym) at nuclear
matter saturation density. We argue that certain properties of these
correlations do not depend on details of the nuclear forces used in the
calculation. We derive as well a global parametrization of the density
dependence of the symmetry energy that we show is more reliable, especially at
low densities, than the usual Taylor series expansion around saturation
density. We then benchmark these predictions against explicit results from
chiral effective field theory.",1805.01000v1
2018-05-29,How it cramps the flow: three regimes for the saturation of parallel ion-beam instabilities,"Motivated by recent advances in laboratory experiments on parallel ion-beam
instabilities, we present a theoretical framework for and simulations of their
evolution towards shock formation and Fermi acceleration. After reviewing the
theory of beam instabilities with a focus on the so-called nonresonant or Bell
instability, which we show to be due to the gyromotion of background ions, we
contrast the saturation of three parameter regimes: (I) the left-handed
""nonresonant"" regime, (II) the right-handed beam-gyroresonant regime, (III) the
balanced, mixed-turbulence regime.",1805.11220v1
2018-06-08,The Saturated Subpaths Decomposition in Z 2 : a short note on generalized Tangential Cover,"In this short note, we generalized the Tangential Cover used in Digital
Geometry in order to use very general geometric predicates. We present the
required notions of saturated $\alpha$-paths of a digital curve as well as
conservative predicates which indeed cover nearly all geometric digital
primitives published so far. The goal of this note is to prove that under a
very general situation, the size of the Tangential Cover is linear with the
number of points of the input curve. The computation complexity of the
Tangential Cover depends on the complexity of incremental recognition of
geometric predicates. Moreover, in the discussion, we show that our approach
does not rely on connectivity of points as it might be though first.",1806.03053v1
2018-06-25,Finding models through graph saturation,"We give a procedure that can be used to automatically satisfy invariants of a
certain shape. These invariants may be written with the operations
intersection, composition and converse over binary relations, and equality over
these operations. We call these invariants \tr{}s that we interpret over
graphs. For questions stated through sets of these sentences, this paper gives
a semi-decision procedure we call graph saturation. It decides entailment over
these \tr{}s, inspired on graph rewriting. We prove correctness of the
procedure. Moreover, we show the corresponding decision problem to be
undecidable. This confirms a conjecture previously stated by the author.",1806.09392v1
2018-07-09,Multiplicity of the saturated special fiber ring of height two perfect ideals,"Let $R$ be a polynomial ring and $I \subset R$ be a perfect ideal of height
two minimally generated by forms of the same degree. We provide a formula for
the multiplicity of the saturated special fiber ring of $I$. Interestingly,
this formula is equal to an elementary symmetric polynomial in terms of the
degrees of the syzygies of $I$. Applying ideas introduced in arXiv:1805.05180,
we obtain the value of the j-multiplicity of $I$ and an effective method for
determining the degree and birationality of rational maps defined by
homogeneous generators of $I$.",1807.03189v2
2018-08-07,Full-wave analysis of reverse saturable absorption in time-domain,"An advanced full-wave time-domain numerical model for reverse saturable
absorption (RSA) is presented and verified against established methods. Rate
equations, describing atomic relaxations and excitation dynamics, are coupled
to Maxwell equations by using a Lorentzian oscillator. These oscillator models
the kinetics-dependent light-matter interaction in the form of averaged
polarizations. The coupled equations are discretized in space and time using a
finite-difference time-domain method which provides a versatile platform to
design complex structures and integrate diverse material models. We believe
that our models are crucial tools enabling for the realization and optimization
of optical limiting and all-optical switching systems.",1808.02436v1
2018-12-10,Collective dynamics of evanescently coupled excitable lasers with saturable absorber,"We present a numerical study of the collective dynamics in a population of
coupled excitable lasers with saturable absorber. At variance with previous
studies where real-valued (lossy) coupling was considered, we focus here on the
purely imaginary coupling (evanescent wave coupling). We show that evanescently
coupled excitable lasers synchronize in a more efficient way compared to the
lossy coupled ones. Furthermore we show that out-of-diagonal disorder-induced
localization of excitability takes place for imaginary coupling too, but it can
be frustrated by nonvanishing linewidth enhancement factor.",1812.03691v1
2018-12-19,Saturated control without velocity measurements for planar robots with flexible joints,"In this work, we propose a passivity-based controller that addresses the
problem of set point regulation for planar robots with two links and flexible
joints. Moreover, the controller is saturated and does not require velocity
measurements. Additionally, we present experiments that corroborate the
theoretical results of this note.",1812.08257v2
2019-03-04,Broadening and saturation effects in dijet azimuthal correlations in p-p and p-Pb collisions at $\mathbf{\sqrt{s_{NN}}} = $ 5.02 TeV,"We demonstrate that the recent forward-forward dijet correlation data
measured by the ATLAS collaboration for proton-proton and proton-lead
collisions are consistent with the broadening effects due to both the gluon
saturation and the resummation of large logarithms of the hard scale (the
so-called Sudakov logarithms). We find that both effects are necessary to
describe the experimental results.",1903.01361v3
2019-04-01,Multi-outcome homodyne detection in a coherent-state light interferometer,"The Cram\'{e}r-Rao bound plays a central role in both classical and quantum
parameter estimation, but finding the observable and the resulting inversion
estimator that saturates this bound remains an open issue for general
multi-outcome measurements. Here we consider multi-outcome homodyne detection
in a coherent-light Mach-Zehnder interferometer and construct a family of
inversion estimators that almost saturate the Cram\'{e}r-Rao bound over the
whole range of phase interval. This provides a clue on constructing optimal
inversion estimators for phase estimation and other parameter estimation in any
multi-outcome measurement.",1904.00557v1
2019-04-16,Equilibria in a large production economy with an infinite dimensional commodity space and price dependent preferences,"We prove the existence of a competitive equilibrium in a production economy
with infinitely many commodities and a measure space of agents whose
preferences are price dependent. We employ a saturated measure space for the
set of agents and apply recent results for an infinite dimensional separable
Banach space such as Lyapunov's convexity theorem and an exact Fatou's lemma to
obtain the result.",1904.07444v2
2019-04-16,Loss and Saturation in Superconducting Travelling-Wave Parametric Amplifiers,"We have developed a coupled-mode analysis framework for superconducting
travelling-wave parametric amplifiers using the full Telegrapher's equations to
incorporate loss-related behaviour. Our model provides an explanation of
previous experimental observations regarding loss in amplifiers, advantages of
concatenating amplifiers to achieve high gains, and signal gain saturation.
This work can be used to guide the design of amplifiers in terms of the choice
of material systems, transmission line geometry, operating conditions, and pump
strength.",1904.07673v1
2019-04-20,Converse estimates for the simultaneous approximation by Bernstein polynomials with integer coefficients,"We prove a weak converse estimate for the simultaneous approximation by
several forms of the Bernstein polynomials with integer coefficients. It is
stated in terms of moduli of smoothness. In particular, it yields a big
$O$-characterization of the rate of that approximation. We also show that the
approximation process generated by these Bernstein polynomials with integer
coefficients is saturated. We identify its saturation rate and the trivial
class.",1904.09417v2
2019-06-03,Nonlinear Absorption and Photocurrent in Weyl Semimetals,"Theory of light absorption and circular photocurrent in Weyl semimetals is
developed for arbitrary large light intensities with account for both elastic
and inelastic relaxation processes of Weyl fermions. The direct optical
transition rate is shown to saturate at large intensity, and the saturation
behaviour depends on the light polarization and on the ratio of the elastic and
inelastic relaxation times. The linear-circular dichroism in absorption is
shown to exceed 10~\% at intermediate light wave amplitudes and fast energy
relaxation. At large intensity $I$, the light absorption coefficient drops as
$1/\sqrt{I}$, and the circular photogalvanic current increases as $\sqrt{I}$.",1906.00686v1
2019-06-04,Controllable pulse patterns in fiber lasers,"An all-optical pulse power editing (PPE) technique is reported. Using the PPE
technique, pulses with different peak powers are output and directed to the
positive or reverse saturable absorption (SA) range of the saturable absorber.
Further, under the combined action of the PPE technique and SA, four pulse
patterns including dissipative soliton (DS), DS molecules, soliton compounds
composed of DS and noise-like pulse (NLP), and pure NLP are controllably
generated in fiber lasers. The results are conducive for developing advanced DS
lasers and can further clarify the onset of pulse dynamic patterns.",1906.01555v2
2019-06-21,Stationary quantum BGK model for bosons and fermions in a bounded interval,"In this paper, we consider the existence problem for a stationary
relaxational models of the quantum Boltzmann equation. More precisely, we
establish the existence of mild solution to the fermionic or bosonic quantum
BGK model in a slab with inflow boundary data. Unlike the classical case, it is
necessary to verify that the quantum local equilibrium state is well-defined,
and the transition from the non-condensed state to the condensated state
(Bosons), or from the non-saturated state to the saturated state (Fermions)
does not arise in our solution space.",1906.08961v1
2019-07-15,The saturation assumption yields optimal convergence of two-level adaptive BEM,"We consider the convergence of adaptive BEM for weakly-singular and
hypersingular integral equations associated with the Laplacian and the
Helmholtz operator in 2D and 3D. The local mesh-refinement is driven by some
two-level error estimator. We show that the adaptive algorithm drives the
underlying error estimates to zero. Moreover, we prove that the saturation
assumption already implies linear convergence of the error with optimal
algebraic rates.",1907.06612v1
2019-07-26,The Continuous Spontaneous Localization Layering Effect from a Lattice Perspective,"For a solid lattice, we rederive the Continuous Spontaneous Localization
(CSL) noise total energy gain of a test mass starting from a Lindblad
formulation, and from a similar starting point rederive the geometry factor
governing center of mass energy gain. We then suggest that the geometry factor
can be used as a way to distinguish between low temperature cantilever motion
saturation arising from CSL noise, and saturation arising from thermal leakage.",1907.11598v4
2019-08-09,The general Nature of Saturated Designs,"We contemplate an experimental situation in a $2^k$-factorial experiment with
acute resource crunch so that we need to conduct just a saturated design [SD] -
with the understanding that precision of the estimates cannot be estimated from
the data. It is known beforehand which effect(s)/interaction(s) are likely to
be negligible. We examine the flexibility to the extent that an experimenter
can make a choice of an SD in order to retain information on all the remaining
[non-negligible] effects/interactions.",1908.03317v2
2019-08-30,Vanishing diffusion limits for planar fronts in bistable models with saturation,"We deal with heteroclinic planar fronts for parameter-dependent
reaction-diffusion equations with bistable reaction and saturating diffusive
term like $$ u_t=\epsilon \, \textrm{div}\, \left(\frac{\nabla u}{\sqrt{1+\vert
\nabla u \vert^2}}\right) + f(u), \quad u=u(x, t), \; x \in \textbf{R}^n, \, t
\in \textbf{R}, $$ analyzing in particular their behavior for $\epsilon \to 0$.
First, we construct monotone and non-monotone planar traveling waves, using a
change of variables allowing to analyze a two-point problem for a suitable
first-order reduction; then, we investigate their asymptotic behavior for
$\epsilon \to 0$, showing in particular that the convergence of the critical
fronts to a suitable step function may occur passing through discontinuous
solutions.",1908.11651v1
2019-09-14,Fusion systems of blocks of finite groups over arbitrary fields,"To any block idempotent $b$ of a group algebra $kG$ of a finite group $G$
over a field $k$ of characteristic $p>0$, Puig associated a fusion system and
proved that it is saturated if the $k$-algebra $kC_G(P)e$ is split, where
$(P,e)$ is a maximal $kGb$-Brauer pair. We investigate in the non-split case
how far the fusion system is from being saturated by describing it in an
explicit way as being generated by the fusion system of a related block
idempotent over a larger field together with a single automorphism of the
defect group.",1909.06666v1
2019-09-15,Destroying Saturation while Preserving Presaturation at an Inaccessible; an Iterated Forcing Argument,"We prove that a large class of presaturated ideals at inaccessible cardinals
can be de-saturated while preserving their presaturation, answering both a
question of Foreman and of Cox and Eskew. We do so by iterating a generalized
version of Baumgartner and Taylor's forcing to add a club with finite
conditions along an inaccessible cardinal, and invoking Foreman's Duality
Theorem.",1909.06704v4
2019-10-29,Saturation and forward jets in proton-lead collisions at the LHC,"We investigate the forward-jet energy spectrum within the Color Glass
Condensate framework at 5 TeV center-of-mass energy. In particular, we focus on
the kinematic range covered by the CMS-CASTOR calorimeter. We show that our
saturation-model calculations are compatible with the CASTOR measurements and
that to optimally reproduce the data, effects of multi-parton interactions need
to be included. We predict a significant nuclear suppression - reaching down to
50% at the lowest considered jet energies $E_{\rm jet} \sim 500 \, {\rm GeV}$.",1910.13116v1
2019-11-29,Bistability in a SIRS model with general nonmonotone and saturated incidence rate,"In this paper, we consider a SIRS model with general nonmonotone and
saturated incidence rate and perform stability and bifurcation analysis. We
show that the system has saddle-node bifurcation and displays bistable
behavior. We obtain the critical thresholds that characterize the dynamical
behaviors of the model. We find with surprise that the system always admits a
disease free equilibrium E0 which is always asymptotically stable. Numerical
simulations are carried out to verify our results.",1911.13002v1
2019-12-13,Lamb-dips and Lamb-peaks in the saturation spectrum of HD,"The saturation spectrum of the R(1) transition in the (2-0) band in HD is
found to exhibit a composite line shape, involving a Lamb-dip and a Lamb-peak.
We propose an explanation for such behavior based on the effects of cross-over
resonances in the hyperfine substructure, which is made quantitative in a
density-matrix calculation. This resolves an outstanding discrepancy on the
rovibrational R(1) transition frequency, which is now determined at 217 105 181
901 (50) kHz and in agreement with current theoretical calculations.",1912.06406v1
2019-12-13,An efficient numerical scheme for fully coupled flow and reactive transport in variably saturated porous media including dynamic capillary effects,"In this paper, we study a model for the transport of an external component,
e.g., a surfactant, in variably saturated porous media. We discretize the model
in time and space by combining a backward Euler method with the linear Galerkin
finite elements. The Newton method and the L-Scheme are employed for the
linearization and the performance of these schemes is studied numerically. A
special focus is set on the effects of dynamic capillarity on the transport
equation.",1912.06731v2
2020-01-24,Convergence of a finite element method for degenerate two-phase flow in porous media,"A finite element method with mass-lumping and flux upwinding, is formulated
for solving the immiscible two-phase flow problem in porous media. The method
approximates directly the wetting phase pressure and saturation, which are the
primary unknowns. The discrete saturation satisfies a maximum principle.
Theoretical convergence is proved via a compactness argument. The proof is
convoluted because of the degeneracy of the phase mobilities and the
unboundedness of the capillary pressure.",2001.08859v1
2020-01-20,Variational inequalities for ferroelectric constitutive modeling,"This paper is concerned with modeling the polarization process in
ferroelectric media. We develop a thermodynamically consistent model, based on
phenomenological descriptions of free energy as well as switching and
saturation conditions in form of inequalities. Thermodynamically consistent
models naturally lead to variational formulations. We propose to use the
concept of variational inequalities. We aim at combining the different
phenomenological conditions into one variational inequality. In our formulation
we use one Lagrange multiplier for each condition (the onset of domain
switching and saturation), each satisfying Karush-Kuhn-Tucker conditions. An
update for reversible and remanent quantities is then computed within one, in
general nonlinear, iteration.",2001.11475v2
2020-02-13,Dynamics Landscape for Acoustic Superradiance,"We analyze the behaviour of acoustic vortex beams interacting with rotating,
fluid-saturated porous materials. Regions of the parameter space that exhibit
distinct dynamical features are identified, with a focus on features that are
relevant to the characterization of rotational superradiance. We discuss the
similarities and differences between two recent proposals to observe acoustic
superradiance with rotating, air-saturated sound absorbers. Finally,
theoretical predictions for macroscopic acoustic scattering, obtained by
averaging over interactions between the fluid and the porous material at the
microscopic level, are compared with predictions of the first-Born
approximation.",2002.05605v2
2020-03-21,Exposing Hidden Alternative Conformations of Small Flexible Molecules in 2D NMR Spectroscopy Using 1H-15N HMBC,"Two-dimensional 1H-15N HMBC NMR spectra of a well-known
anticonvulsant-carbamazepine-dissolved in chloroform, recorded on an NMR
spectrometer and obtained from quantum-chemical calculations prove the
existence of hidden conformers in saturated solutions. A weaker influence of
ring currents was revealed for the hidden conformation of carbamazepine
dissolved in saturated solution, which provides a simple approach for
discovering hidden conformations. Hidden conformers were found in three
different solvents: dimethyl sulfoxide, chloroform, and dichloromethane.",2003.09608v2
2020-06-13,Saturating the Data Processing Inequality for $α-z$ Renyi Relative Entropy,"It has been shown that the $\alpha-z$ R{\'e}nyi relative entropy satisfies
the Data Processing Inequality (DPI) for a certain range of $\alpha$'s and
$z$'s. Moreover, the range is completely characterized by Zhang in `20. We
prove necessary and algebraically sufficient conditions to saturate the DPI for
the $\alpha-z$ R{\'e}nyi relative entropy whenever $1<\alpha\leq 2$ and
$\frac{\alpha}{2}\leq z\leq\alpha$. Moreover, these conditions coincide
whenever $\alpha=z$.",2006.07726v2
2020-06-19,Lipschitz fractions of a complex analytic algebra and Zariski saturation,"This text is the English translation, due to Naoufal Bouchareb, of an
unpublished manuscript of 1969 (the French version is available on HAL as
hal-00384928) inspired by Zariski's theory of saturation. Its publication is
justified by the fact that it appears now as a precursor of the recently
developed study of the Lipschitz geometry (for the outer metric) of germs of
complex analytic spaces. This version contains some new footnotes and an
additional bibliography.",2006.10982v1
2020-06-23,Achieving Performance and Safety in Large Scale Systems with Saturation using a Nonlinear System Level Synthesis Approach,"We present a novel class of nonlinear controllers that interpolates among
differently behaving linear controllers as a case study for recently proposed
Linear and Nonlinear System Level Synthesis framework. The structure of the
nonlinear controller allows for simultaneously satisfying performance and
safety objectives defined for small- and large-disturbance regimes. The
proposed controller is distributed, handles delays, sparse actuation, and
localizes disturbances. We show our nonlinear controller always outperforms its
linear counterpart for constrained LQR problems. We further demonstrate the
anti-windup property of an augmented control strategy based on the proposed
controller for saturated systems via simulation.",2006.12766v1
2020-06-23,Analysis of Methanol Maser Flares in G107.298+5.63 andS255-NIRS3,"A 3D maser model has been used to perform an inverse problem on the light
curves from three high-amplitude maser flares, selected on the basis of
contemporaneous infra-red observations. Plots derived from the model recover
the size of the maser cloud, and two parameters linked to saturation, from
three observational properties of the light curve. Recovered sizes are
consistent with independent interferometric measurements. Maser objects
transition between weak and moderate saturation during a flare.",2006.13124v1
2020-08-03,Nonlinearity continuation method for steady-state groundwater flow modeling in variably saturated conditions,"Application of nonlinearity continuation method to numerical solution of
steady-state groundwater flow in variably saturated conditions is presented. In
order to solve the system of nonlinear equations obtained by finite volume
discretization of steady-state Richards equation, a series of problems with
increasing nonlinearity are solved using the Newton method. This approach is
compared to pseudo-transient method on several test cases, including real site
problems and involving parallel computations.",2008.00730v1
2020-08-13,On the topological entropy of saturated sets for amenable group actions,"Let $(X,\rho,G)$ be a $G-$action topological system, where $G$ is a countable
infinite discrete amenable group and $X$ a compact metric space. We prove a
variational principle for topological entropy of saturated sets for systems
which have specification and uniform separation properties. As an application,
we compute the topological entropy of level sets and irregular sets.",2008.05843v3
2020-11-11,Saturating stable matchings,"I relate bipartite graph matchings to stable matchings. I prove a necessary
and sufficient condition for the existence of a saturating stable matching,
where every agent on one side is matched, for all possible preferences. I
extend my analysis to perfect stable matchings, where every agent on both sides
is matched.",2011.06046v2
2020-11-25,The Poisson saturation of coregular submanifolds,"This paper is devoted to coregular submanifolds in Poisson geometry. We show
that their local Poisson saturation is an embedded Poisson submanifold, and we
give a normal form for this Poisson submanifold around the coregular
submanifold. This result recovers the normal form around Poisson transversals,
and it yields Poisson versions of some normal form/rigidity results around
constant rank submanifolds in symplectic geometry. As an application, we prove
a uniqueness result concerning coisotropic embeddings of Dirac manifolds in
Poisson manifolds. We also show how our results generalize to the setting of
coregular submanifolds in Dirac geometry.",2011.12650v2
2020-12-04,Reviewing the role of the extinction coefficient in radar remote sensing,"This report revisits the role of the extinction coefficient in radar
backscattering-based models for forest monitoring. A review of a number of
works dealing with this issue has revealed a diversity of extinction values
being unclear its dependence on the sensor frequency and the forest type. In
addition, a backscattering model directly derived from the RVoG formulation is
employed to analyse the saturation of backscattering level as a function of
vegetation height and the presence of a decreasing trend of backscatter beyond
the saturation point as suggested in previous works in the literature.
According to this analysis it seems reasonable to think that further research
specially focused on dedicated experimental measurements of the extinction
coefficient should be carried out.",2012.02609v1
2021-01-13,Nonlinear saturation of thermal instabilities,"Low-frequency simulations of a one-layer model with lateral buoyancy
variations (i.e., thermodynamically active) have revealed circulatory motions
resembling quite closely submesoscale observations in the surface ocean rather
than indefinitely growing in the absence of a high-wavenumber instability
cutoff. In this note it is shown that the existence of a convex
pseudoenergy--momentum integral of motion for the inviscid, unforced dynamics
provides a mechanism for the nonlinear saturation of such thermal instabilities
in the zonally symmetric case. The result is an application of
\citet{Arnold-66} and \citet{Shepherd-88a} methods.",2101.05375v2
2020-11-26,Positive Solutions of Competition Model with Saturation,"In this paper, the positive solutions of a diffusive competition model with
saturation are mainly discussed. Under certain conditions, the stability and
multiplicities of coexistence states are analyzed. And by using the topological
degree theory in cones, it is proved that the problem has at least two positive
solutions under certain conditions. Finally, investigating the bifurcation of
coexistence states emanating from the semi-trivial solutions, some instability
and multiplicity results of coexistence state are expressed.",2101.06231v1
2021-02-13,Parameter Dependence and Bell nonlocality,"Bell's theorem asserts that no model that satisfies all of the plausible
physical assumptions of outcome independence (OI), measurement independence
(MI) and Parameter Independence (PI) can reproduce quantum mechanics. Here I
find the optimum model that saturates CHSH inequality for the case that outcome
independence and measurement independence hold but parameter dependence is
allowed. I find the bound as a function of a measure of parameter dependence
and show that the model proposed by [New Journal of Physics,12(8):083051] is
optimal for one-way parameter dependence. The symbolic optimizations to find
the saturating models are performed using the open source software Analytical
Optimizer v1.0.",2102.06920v2
2021-02-15,Metatheory.jl: Fast and Elegant Algebraic Computation in Julia with Extensible Equality Saturation,"We introduce Metatheory.jl: a lightweight and performant general purpose
symbolics and metaprogramming framework meant to simplify the act of writing
complex Julia metaprograms and to significantly enhance Julia with a native
term rewriting system, based on state-of-the-art equality saturation
techniques, and a dynamic first class Abstract Syntax Tree (AST) pattern
matching system that is dynamically composable in an algebraic fashion, taking
full advantage of the language's powerful reflection capabilities. Our
contribution allows to perform general purpose symbolic mathematics,
manipulation, optimization, synthesis or analysis of syntactically valid Julia
expressions with a clean and concise programming interface, both during
compilation or execution of programs.",2102.07888v1
2021-03-05,Nuclear binding energy in holographic QCD,"Saturation of the nuclear binding energy is one of the most important
properties of atomic nuclei. We derive the saturation in holographic QCD, by
building a shell-model-like mean-field nuclear potential from the nuclear
density profile obtained in a holographic multi-baryon effective theory. The
numerically estimated binding energy is close to the experimental value.",2103.03563v3
2021-03-20,Influence of nonlinear- and saturable-absorption on laser lift-off threshold of oxide/metal structure,"In this work, a new model of effective lift-off threshold of oxide/metal
target is presented. The influence of nonlinear processes in the oxide layer on
its removal from the metallic samples using picosecond laser was investigated.
Nonlinear and saturable absorption in the layer was incorporated into modeling
for prediction of effective laser lift-off threshold fluence change with
varying peak intensities in z-scan type experiment for the first time. The new
model coincides well with the experimental results.",2103.11140v2
2021-06-09,"On a convexity property of tensor products of irreducible, rational representations of $SL(n)$","The aim of this note is to point out a convexity property with respect to the
root lattice for the support of the highest weights that occur in a tensor
product of irreducible rational representations of $SL(n)$ over the complex
numbers. The observation is a consequence of the convexity properties of the
saturation cone and the validity of the saturation conjecture for $SL(n)$.",2106.05028v2
2021-06-17,"Equivalence of cubical and simplicial approaches to $(\infty,n)$-categories","We prove that the marked triangulation functor from the category of marked
cubical sets equipped with a model structure for ($n$-trivial, saturated)
comical sets to the category of marked simplicial set equipped with a model
structure for ($n$-trivial, saturated) complicial sets is a Quillen
equivalence. Our proof is based on the theory of cones, previously developed by
the first two authors together with Lindsey and Sattler.",2106.09428v3
2021-06-17,Relating entropies of quantum channels,"In this work, we study two different approaches to defining the entropy of a
quantum channel. One of these is based on the von Neumann entropy of the
corresponding Choi-Jamio{\l}kowski state. The second one is based on the
relative entropy of the output of the extended channel relative to the output
of the extended completely depolarizing channel. This entropy then needs to be
optimized over all possible input states. Our results first show that the
former entropy provides an upper bound on the latter. Next, we show that for
unital qubit channels, this bound is saturated. Finally, we conjecture and
provide numerical intuitions that the bound can also be saturated for random
channels as their dimension tends to infinity.",2106.09629v1
2021-07-07,Newell-Littlewood numbers III: eigencones and GIT-semigroups,"The Newell-Littlewood numbers are tensor product multiplicities of Weyl
modules for the classical groups in the stable range. Littlewood-Richardson
coefficients form a special case. Klyachko connected eigenvalues of sums of
Hermitian matrices to the saturated LR-cone and established defining linear
inequalities. We prove analogues for the saturated NL-cone: an eigenvalue
interpretation; a minimal list of defining linear inequalities; a description
by Extended Horn inequalities, as conjectured in part II of this series; and a
factorization of NL-numbers, on the boundary.",2107.03152v2
2021-08-25,Fell bundles over a countable discrete group and strong Morita equivalence for inclusions of $C^*$-algebras,"We consider two saturated Fell bundles over a countable discrete group, whose
unit fibers are $\sigma$-unital $C^*$-algebras. Then by taking the reduced
cross-sectional $C^*$-algebras, we get two inclusions of $C^*$-algebras. We
suppose that they are strongly Morita equivalent as inclusions of
$C^*$-algebras. Also, we suppose that one of the inclusions of $C^*$-algebras
is irreducible, that is, the relative commutant of one of the unit fiber
algebras, which is a $\sigma$-unital $C^*$-algebra, in the multiplier
$C^*$-algebra of the reduced cross-sectional $C^*$-algebra is trivial. We show
that the two saturated Fell bundles are then equivalent up to some automorphism
of the group.",2108.11013v1
2021-09-21,Double Schubert polynomials do have saturated Newton polytopes,"We prove that double Schubert polynomials have the Saturated Newton Polytope
property. This settles a conjecture by Monical, Tokcan and Yong. Our ideas are
motivated by the theory of multidegrees. We introduce a notion of
standardization of ideals that enables us to study non-standard multigradings.
This allows us to show that the support of the multidegree polynomial of each
Cohen-Macaulay prime ideal, and in particular, that of each Schubert
determinantal ideal is a discrete polymatroid.",2109.10299v3
2021-09-22,Kernels of Localities,"We state a sufficient condition for a fusion system to be saturated. This is
then used to investigate localities with kernels, i.e. localities which are (in
a particular way) extensions of groups by localities. As an application of
these results, we define and study certain products in fusion systems and
localities, thus giving a new method to construct saturated subsystems of
fusion systems.",2109.10962v2
2021-11-02,Saturated feedback stabilizability to trajectories for the Schlögl parabolic equation,"It is shown that there exist a finite number of indicator functions, which
allow us to track an arbitrary given trajectory of the Schl\""ogl model, by
means of an explicit saturated feedback control input whose magnitude is
bounded by a constant independent of the given targeted trajectory. Simulations
are presented showing the stabilizing performance of the explicit feedback
constrained control. Further, such performance is compared to that of a
receding horizon constrained control minimizing the classical energy cost
functional.",2111.01329v1
2021-11-11,Phase Transitions in the Classical Simulability of Open Quantum Systems,"We study the evolution of an open quantum system using a Langevin unravelling
of the density matrix evolution over matrix product states. As the strength of
coupling to and temperature of the environment is increased, we find a
transition where the entanglement of the individual trajectories saturates,
permitting a classical simulation of the system for all times. This is the
Hamiltonian open system counterpart of the saturation in entanglement found in
random circuits with projective or weak measurements. If a system is open,
there is a limit to the advantage in simulating its behaviour on a quantum
computer, even when that evolution harbours important quantum effects.",2111.06408v1
2021-12-23,Deterministic generation of a perfect soliton crystal with a saturable absorber,"We numerically investigate the deterministic generation of a perfect soliton
crystal (PSC) in an optical microresonator functionalized with a saturable
absorber (SA). The SA allows the direct formation of a PSC from an initial,
periodic Turing roll. It prevents passage through a chaotic state, which
induces a stochastic nature as regards the number of generated dissipative Kerr
solitons. We show that PSCs form deterministically, and the number is
controlled by adjusting the input power and SA parameter. Our work provides a
simple approach for obtaining a stable PSC that offers an ultra-high repetition
rate and a high comb output power.",2112.12336v1
2022-01-02,Energy evolution of the overlap functions: increasing ratio of $σ_{el}(s)/σ_{tot}(s)$ and black ring emergence,"We analyse the two possible options of the energy dependency of the elastic
and inelastic overlap functions. These correspond to saturation of the black
disk limit (BEL effect) and to the unitarity saturation (REL effect) at
$s\to\infty$. Relation of the REL effect to increase of the ratio
$\sigma_{el}(s)/\sigma_{tot}(s)$ and emergence of black ring picture at the LHC
is underlined.",2201.00315v3
2022-02-09,Saturation and vanishing ideals,"We consider an homogeneous ideal $I$ in the polynomial ring $S=K[x_1,\dots,$
$x_m]$ over a finite field $K=\mathbb{F}_q$ and the finite set of projective
rational points $\mathbb{X}$ that it defines in the projective space
$\mathbb{P}^{m-1}$. We concern ourselves with the problem of computing the
vanishing ideal $I(\mathbb{X})$. This is usually done by adding the equations
of the projective space $I(\mathbb{P}^{m-1})$ to $I$ and computing the radical.
We give an alternative and more efficient way using the saturation with respect
to the homogeneous maximal ideal.",2202.04683v2
2022-02-15,Accelerating Non-Negative and Bounded-Variable Linear Regression Algorithms with Safe Screening,"Non-negative and bounded-variable linear regression problems arise in a
variety of applications in machine learning and signal processing. In this
paper, we propose a technique to accelerate existing solvers for these problems
by identifying saturated coordinates in the course of iterations. This is akin
to safe screening techniques previously proposed for sparsity-regularized
regression problems. The proposed strategy is provably safe as it provides
theoretical guarantees that the identified coordinates are indeed saturated in
the optimal solution. Experimental results on synthetic and real data show
compelling accelerations for both non-negative and bounded-variable problems.",2202.07258v2
2022-05-10,Color dipole cross section in the DGLAP improved saturation model,"We show that the geometric scaling of the dipole cross section can be
explained using standard DGLAP perturbative evolution. The DGLAP improved
saturation model due to the Laplace transforms method is considered at LO and
NNLO approximations from the experimental data by relying on a
Froissart-bounded parametrization of $F_{2}(x,Q^{2})$. These results are
comparable with Golec-Biernat-W$\ddot{\mathrm{u}}$sthoff (GBW) model in a wide
kinematic region $rQ_{s}$ which takes into account charm mass. The successful
description of ${\sigma}_{\mathrm{dip}}(x,r)/\sigma_{0}$ and
${\sigma}_{\mathrm{dip}}(rQ_{s})/\sigma_{0}$ are presented.",2205.04889v1
2022-06-29,Saturating systems and the rank covering radius,"We introduce the concept of a rank saturating system and outline its
correspondence to a rank-metric code with a given covering radius. We consider
the problem of finding the value of $s_{q^m/q}(k,\rho)$, which is the minimum
$\mathbb{F}_q$-dimension of a $q$-system in $\mathbb{F}_{q^m}^k$ which is rank
$\rho$-saturating. This is equivalent to the covering problem in the rank
metric. We obtain upper and lower bounds on $s_{q^m/q}(k,\rho)$ and evaluate it
for certain values of $k$ and $\rho$. We give constructions of rank
$\rho$-saturating systems suggested from geometry.",2206.14740v2
2022-07-07,Small-x Evolution of the Gluon Generalized Parton Distribution Eg of the Nucleon,"We study the small-$x$ evolution equation for the gluon generalized parton
distribution (GPD) $E_g$ of the nucleon. It is shown that $E_g$ at vanishing
skewness exhibits the Regge behavior identical to the BFKL Pomeron, despite its
association with nucleon helicity-flip processes. We also consider the effect
of gluon saturation and demonstrate that $E_g$ gets saturated in the same way
as its helicity-nonflip counterpart $H_g$. Our result has a direct impact on
the modeling of $E_g$ as well as the small-$x$ contribution to nucleon spin sum
rules.",2207.03378v2
2022-07-19,Coupling between conduction and near-field radiative heat transfer in tip-plane geometry,"We analyze the coupling between conduction and radiative heat transfer in
near-field regime between two coaxial cylinders separated by a vacuum gap. By
solving the heat transport equation in the steady-state regime between metals
or polar materials we highlight a flux saturation mechanism for the radiative
transfer even without non-local effect. In the case of polar materials this
saturation occurs in the separation distances range of 1 to 10 nm which can be
experimentally explored.",2207.09567v1
2022-06-02,On the Optimization of Equivalent Concurrent Computations,"In this submission, we explore the use of equality saturation to optimize
concurrent computations. A concurrent environment gives rise to new
optimization opportunities, like extracting a common concurrent subcomputation.
To our knowledge, no existing equality saturation framework allows such an
optimization. The challenge with concurrent environments is that they require
non-local reasoning since parallel computations are inherently unrelated and
disjoint. This submission presents a new approach to optimizing equivalent
concurrent computations: extending e-graphs to capture equal concurrent
computations in order to replace them with a single computation.",2208.06295v1
2022-09-08,Large-rapidity ridge correlations from Color Glass Condensate,"Within the Color Glass Condensate (CGC) effective field theory, considering
the violation of boost invariance of the rapidity distribution, we correct the
normalization scheme of the longitudinal rapidity ridge correlations. After
this correction, the large-rapidity ridge correlation rebounds after bottoming,
consistent with the observed data from the CMS detector. It is also found that
the correlation rebound appears around the sum of the saturation momentum of
the projectile and target, and moves to larger rapidities at higher collision
energies. These features directly result from the saturation and the quantum
evolution of gluons within the framework of the CGC.",2209.03772v1
2022-10-06,Unintegrated gluon distributions from the color dipole cross section in the BGK saturation model,"We evaluate the unintegrated gluon distribution of the proton starting from a
parametrization of the color dipole cross section including DGLAP evolution and
saturation effects. To this end, we perform the Fourier-Bessel transform of
$\sigma(x,r)/\alpha(r)$. At large transverse momentum of gluons we match the
so-obtained distribution to the logarithmic derivative of the collinear gluon
distribution. We check our approach by calculating the proton structure
function $F_L(x,Q^2)$ finding good agreement with HERA data.",2210.02877v1
2022-10-17,Saturated orbit closures in the Hodge bundle,"We give a new proof of the classification of ${\rm GL}^+(2,\mathbb{R})$-orbit
closures that are saturated for the absolute period foliation of the Hodge
bundle. As a consequence, we obtain a short proof of the classification of
closures of leaves of the absolute period foliation of the Hodge bundle. Our
approach is based on a method for classifying ${\rm GL}^+(2,\mathbb{R})$-orbit
closures using deformations of flat pairs of pants.",2210.08795v2
2022-10-26,Scale-free linear protocol design for global regulated state synchronization of discrete-time double-integrator multi-agent systems subject to actuator saturation,"This paper studies global regulated state synchronization of discrete-time
double-integrator multi-agent systems subject to actuator saturation by
utilizing localized information exchange. We propose a scale-free linear
protocol that achieves global regulated state synchronization for any network
with arbitrary number of agents and arbitrarily directed communication graph
that has a path between each agent and exosystem which generates the reference
trajectory.",2210.14453v1
2022-12-09,A theoretical study of the air-sea drag-saturation in very strong winds,"The goal of this note is to provide a theoretical explanation for the
saturation of the drag coefficient in strong wind conditions. The hydrodynamic
model under consideration takes into account the important effects of airborne
droplets of water in a thin layer above the water surface that effectively
behave as a different fluid between the water and the air. Above this layer the
model is coupled with a log-wind profile for the strong winds blowing above the
sea. The main underlying mechanism governing the behavior of the drag
coefficient is the Kelvin Helmholtz instability for capillary waves on the
water surface and the continuity of shear stress along the intermediate
interface.",2212.04792v1
2023-01-30,Strong Reverse Saturation and Fast-Light in Ruby,"We observe a strong reverse saturation of absorption in ruby at a wavelength
of 473 nm. With an intensity-modulated laser, we observe that the peaks of the
pulses appear more than a hundred microseconds earlier than the reference
signal. A theoretical model based on coherent population oscillation would
suggest a fast-light effect with an extremely large and negative group index of
$-(1.7\pm0.1)\times 10^6$. We propose that this pulse advancement can also be
described by time-dependent absorption of ruby. Our study helps to understand
the nature of the fast- and slow-light effects in transition-metal-doped
crystals such as ruby and alexandrite.",2301.13300v1
2023-03-08,Robust data-driven control design for linear systems subject to input saturations,"This paper deals with the problem of providing a data-driven solution to the
local stabilization of linear systems subject to input saturation. After
presenting a model-based solution to this well-studied problem, a systematic
method to transform model-driven into data-driven LMI conditions is presented.
This technical solution is demonstrated to be equivalent to the recent advanced
results on LMI formulations based on S-procedure or Peterson Lemmas. However,
the advantage of the proposed method relies on its simplicity and its potential
to be applicable to a wide class of problems of stabilization of (non)linear
discrete-time systems. The method is then illustrated on an academic example.",2303.04455v1
2023-03-23,Equational Theorem Proving for Clauses over Strings,"Although reasoning about equations over strings has been extensively studied
for several decades, little research has been done for equational reasoning on
general clauses over strings. This paper introduces a new superposition
calculus with strings and present an equational theorem proving framework for
clauses over strings. It provides a saturation procedure for clauses over
strings and show that the proposed superposition calculus with contraction
rules is refutationally complete. This paper also presents a new decision
procedure for word problems over strings w.r.t. a set of conditional equations
R over strings if R can be finitely saturated under the proposed inference
system.",2303.13257v1
2023-04-24,Existential Calculi of Relations with Transitive Closure: Complexity and Edge Saturations,"We study the decidability and complexity of equational theories of the
existential calculus of relations with transitive closure (ECoR*) and its
fragments, where ECoR* is the positive calculus of relations with transitive
closure extended with complements of term variables and constants. We give
characterizations of these equational theories by using edge saturations and we
show that the equational theory is 1) coNP-complete for ECoR* without
transitive closure; 2) in coNEXP for ECoR* without intersection and
PSPACE-complete for two smaller fragments; 3) $\Pi_{1}^{0}$-complete for ECoR*.
The second result gives PSPACE-upper bounds for some extensions of Kleene
algebra, including Kleene algebra with top w.r.t. binary relations.",2304.12079v1
2023-04-27,Ideals and continuity for quantaloid-enriched categories,"We study ideals in, and continuity of, quantaloid-enriched categories
(Q-categories for short) as a 'many-valued and many-typed' generalization of
domain theory. Abstractly, for any (saturated) class Phi of presheaves, we
define and study the Phi-continuity of Q-categories. Concretely, we compute
three examples of such saturated classes of presheaves - the class of flat
ideals, the class of irreducible ideals and the class of conical ideals - which
are proper generalizations of ideals in domain theory.",2304.14128v1
2023-07-09,Parton shower algorithm with saturation effect,"We extend the previously developed small $x$ parton shower algorithm to
include the kinematic constraint effect and $k_t$ resummation effect. This work
enables the Monte Carlo generator to simultaneously resum large $k_t$ and small
$x$ logarithms in the saturation regime for the first time. It is an important
step towards simulating processes involving multiple well separated hard
scales, such as di-jet production in eA collisions at EIC.",2307.04185v1
2023-08-21,Strangeness production in neutron star matter,"Based on a dynamical model on particle production, the production and
fraction of exotic components in neutron star matter are analyzed. It is found
that there exists a small fraction of strangeness in twice saturation density
matter. For five times saturation density matter, the fraction of strange
baryons can be as high as 25-50\%, depending on the equation of state used. The
neutron-proton asymmetry of dense matter does not significantly impact the
strangeness fraction in neutron star matter. This research provides new
insights into the strange components in neutron stars.",2308.10628v2
2023-08-29,Enhancements on a saturated control for stabilizing a quadcopter: adaptive and robustness analysis in the flat output space,"This paper extends our previous study on an explicit saturated control for a
quadcopter, which ensures both constraint satisfaction and stability thanks to
the linear representation of the system in the flat output space. The novelty
here resides in the adaptivity of the controller's gain to enhance the system's
performance without exciting its parasitic dynamics and avoid lavishing the
input actuation with excessively high gain parameters. Moreover, we provide a
thorough robustness analysis of the proposed controller when additive
disturbances are affecting the system behavior. Finally, simulation and
experimental tests validate the proposed controller.",2308.15177v2
2023-10-31,Harmonics of Lepton-Jet Correlations in inclusive and diffractive scatterings,"Based on our previous work, we study the harmonic coefficient of both
inclusive and diffractive azimuthal angle dependent lepton-jet correlations in
Hadron-Electron Ring Accelerator and the future electron-ion collider.
Numerical calculations for inclusive and diffractive harmonics and the ratio of
harmonics in $e+\text{Au}$~and $e+p$ indicate their strong discriminating power
for non-saturation model and saturation model. Additionally, we demonstrate
that the t-dependent diffractive harmonics can serve as novel observables for
nuclear density profile.",2310.20662v2
2023-10-31,Generating site saturation mutagenesis libraries and transferring them to broad host range plasmids using type IIS restriction enzymes,"Protein engineering is an established method for tailoring enzymatic
reactivity. A commonly used method is directed evolution, where the mutagenesis
and natural selection process is mimicked and accelerated in the laboratory.
Here, we describe a reliable method for generating saturation mutagenesis
libraries by golden gate cloning in a broad host range plasmid containing the
pBBR1 replicon. The applicability is demonstrated by generating a mutant
library of the iron nitrogenase gene cluster (anfHDGK) of Rhodobacter
capsulatus, which is subsequently screened for the improved formation of
molecular hydrogen.",2311.00138v1
2023-11-01,Diffractive single and di-hadron production at the NLO in a saturation framework,"Motivated by the need to increase the precision of theoretical predictions to
test saturation physics at both the LHC and the EIC, we compute the
cross-sections for the diffractive single and di-hadron production at the NLO
in the shockwave formalism.",2311.00383v1
2023-11-08,Sharper analysis of the random graph $d$-process via a balls-in-bins model,"A graph $d$-process starts with an empty graph on $n$ vertices, and adds one
edge at each time step, chosen uniformly at random from those pairs which are
not yet edges and whose both vertices have current degree less than $d$. If, in
the final graph, at most one vertex has degree $d-1$ and all other have degree
$d$, we call the process saturated. We present a new approach to analysing this
process based on random allocation of balls in bins. This allows us to get
improved results on the degree distribution throughout the process and,
consequently, to determine the asymptotic probability of non-saturation of the
process.",2311.04743v1
2023-11-13,Cylindric Schur functions,"We generalize several classical results about Schur functions to the family
of cylindric Schur functions. First, we give a combinatorial proof of a
Murnaghan--Nakayama formula for expanding cylindric Schur functions in the
power-sum basis. We also explore some cases where this formula is
cancellation-free.
  The second result is polynomiality of Kostka coefficients associated with
stretched row-flagged skew Schur functions. This implies polynomiality of
stretched cylindric Kostka coefficients. This generalizes a result by E.
Rassart from 2004.
  Finally, we also show the saturation property for the row-flagged skew Kostka
coefficients which also implies the saturation property for cylindric Schur
functions.",2311.07382v1
2023-11-15,Killing Spinors for Finite Temperature Euclidean Solutions at the BPS Bound,"In a recent paper [arXiv:2308.00038], Anupam, Chowdhury, and Sen conjectured
that the finite temperature Euclidean five-dimensional Cvetic-Youm solution
saturating the BPS bound is supersymmetric. In this paper, we explicitly
construct Killing spinors for this solution in five-dimensional minimal
supergravity. We also expand on the previous discussions of Killing spinors for
the finite temperature Euclidean Kerr-Newman solution saturating the BPS bound.
For both these cases, we show that the total charge gets divided into two
harmonic sources on three-dimensional flat base space.",2311.09427v2
2023-11-23,Saturated theorem along cubes for a measure and applications,"We show that for a minimal system $(X,T)$, the set of saturated points along
cubes with respect to its maximal $\infty$-step pro-nilfactor $X_\infty$ has a
full measure. As an application, it is shown that if a minimal system $(X,T)$
has no non-trivial $(k+1)$-tuples with arbitrarily long finite IP-independence
sets, then it has only at most $k$ ergodic measures and is an almost $k'$ to
one extension of $X_\infty$ for some $k'\leqslant k$. Particularly, for $k=1$
we prove that $(X,T)$ is uniquely ergodic (even regular with respect to
$X_\infty$), which answers a conjecture stated in [3].",2311.14198v1
2023-12-31,Contractibility of the orbit space of a saturated fusion system after Steinberg,"Recently, Steinberg used discrete Morse theory to give a new proof of a
theorem of Symonds that the orbit space of the poset of nontrivial
$p$-subgroups of a finite group is contractible. We extend Steinberg's argument
in two ways, covering more general versions of the theorem that were already
known. In particular, following a strategy of Libman, we give a discrete Morse
theoretic argument for the contractibility of the orbit space of a saturated
fusion system.",2401.00531v2
2024-01-18,Harmonic Generation in a Terawatt X-Ray Free-Electron Laser,"Terawatt x-ray free-electron lasers (XFELs) require high current densities
with strong transverse focusing. The implications on harmonic generation are
discussed using the MINERVA simulation code which self-consistently includes
harmonic generation. We consider helical and planar undulators where the
fundamental is at 1.5 Angstrom and study the associated harmonic generation.
While tapered undulators are needed to reach TW powers at the fundamental, the
taper does not enhance the harmonics because the taper must start before
saturation of the fundamental, with the harmonics saturating earlier.
Nevertheless, the harmonics reach substantial powers and enable enhanced
applications.",2401.09971v1
2024-01-28,Fusion invariant characters of p-groups,"We consider complex characters of a p-group P, which are invariant under a
fusion system F on P. Extending a theorem of B\'arcenas--Cantarero to
non-saturated fusion systems, we show that the number of indecomposable
F-invariant characters of P is greater or equal than the number of F-conjugacy
classes of P. We further prove that these two quantities coincide whenever F is
realized by a p-solvable group. On the other hand, we observe that this is
false for constrained fusion systems in general. Finally, we construct a
saturated fusion system with an indecomposable F-invariant character, which is
not a summand of the regular character of P. This disproves a recent conjecture
of Cantarero--Combariza.",2401.15706v2
2024-01-31,SAT-Based Subsumption Resolution,"Subsumption resolution is an expensive but highly effective simplifying
inference for first-order saturation theorem provers. We present a new
SAT-based reasoning technique for subsumption resolution, without requiring
radical changes to the underlying saturation algorithm. We implemented our work
in the theorem prover Vampire, and show that it is noticeably faster than the
state of the art.",2401.17832v1
2024-02-02,Degenerate diffusion in porous media with hysteresis-dependent permeability,"Hysteresis in the pressure-saturation relation in unsaturated porous media,
which is due to surface tension on the liquid-gas interface, exhibits strong
degeneracy in the resulting mass balance equation. Solutions to such degenerate
equations have been recently constructed by the method of convexification. We
show here that the convexification argument works even if the permeability
coefficient depends on the hysteretic saturation. The problem of uniqueness
remains open in this case.",2402.01278v1
2024-02-15,Exploiting spacetime symmetry in dissipative nonlinear multimode amplifiers for output control,"Time-reversal symmetry enables shaping input waves to control output waves in
many linear and nonlinear systems; however energy dissipation violates such
symmetry. We consider a saturated multimode fiber amplifier in which light
generates heat flow and suffers nonlinear thermo-optical scattering, breaking
time-reversal symmetry. We identify a spacetime symmetry which maps the target
output back to an input field. This mapping employs phase conjugation, gain and
absorption substitution but not time reversal, and holds in steady-state and
for slowly varying inputs. Our results open the possibility of output control
of a saturated multimode fiber amplifier.",2402.10345v1
2024-02-22,"Saturating linear sets in PG$(2,q^4)$","Bonini, Borello and Byrne started the study of saturating linear sets in
Desarguesian projective spaces, in connection with the covering problem in the
rank metric. In this paper we study \emph{$1$-saturating} linear sets in
PG$(2,q^4)$, that is $\mathbb{F}_q$-linear sets in PG$(2,q^4)$ with the
property that their secant lines cover the entire plane. By making use of a
characterization of generalized Gabidulin codes, we prove that the rank of such
a linear set is at least $5$. This answers to a recent question posed by
Bartoli, Borello and Marino.",2402.14387v1
2017-11-11,280 GHz Focal Plane Unit Design and Characterization for the SPIDER-2 Suborbital Polarimeter,"We describe the construction and characterization of the 280 GHz bolometric
focal plane units (FPUs) to be deployed on the second flight of the
balloon-borne SPIDER instrument. These FPUs are vital to SPIDER's primary
science goal of detecting or placing an upper limit on the amplitude of the
primordial gravitational wave signature in the cosmic microwave background
(CMB) by constraining the B-mode contamination in the CMB from Galactic dust
emission. Each 280 GHz focal plane contains a 16 x 16 grid of corrugated
silicon feedhorns coupled to an array of aluminum-manganese transition-edge
sensor (TES) bolometers fabricated on 150 mm diameter substrates. In total, the
three 280 GHz FPUs contain 1,530 polarization sensitive bolometers (765 spatial
pixels) optimized for the low loading environment in flight and read out by
time-division SQUID multiplexing. In this paper we describe the mechanical,
thermal, and magnetic shielding architecture of the focal planes and present
cryogenic measurements which characterize yield and the uniformity of several
bolometer parameters. The assembled FPUs have high yields, with one array as
high as 95% including defects from wiring and readout. We demonstrate high
uniformity in device parameters, finding the median saturation power for each
TES array to be ~3 pW at 300 mK with a less than 6% variation across each array
at one standard deviation. These focal planes will be deployed alongside the 95
and 150 GHz telescopes in the SPIDER-2 instrument, slated to fly from McMurdo
Station in Antarctica in December 2018.",1711.04169v2
2016-09-27,The magnetic properties of the hollow cylindrical ideal remanence magnet,"We consider the magnetic properties of the hollow cylindrical ideal remanence
magnet. This magnet is the cylindrical permanent magnet that generates a
uniform field in the cylinder bore, using the least amount of magnetic energy
to do so. The remanence distribution of this magnet is derived and the
generated field is compared to that of a Halbach cylinder of equal dimensions.
The ideal remanence magnet is shown in most cases to generate a significantly
lower field than the equivalent Halbach cylinder, although the field is
generated with higher efficiency. The most efficient Halbach cylinder is shown
to generate a field exactly twice as large as the equivalent ideal remanence
magnet.",1609.08548v1
2022-07-19,Magnetic Field of a Permanent Magnet,"For magnetic field calculations, cylindrical permanent magnets are often
approximated as ideal, azimuthally symmetric solenoids. Despite the frequent
usage of this approximation, research papers demonstrating the validity and
limitations of this approach are scarcely available. In this paper, the
experimentally derived magnetic field of a cylindrical permanent magnet is
compared with the analytically calculated magnetic field of an ideal solenoid.
An experimental setup for measuring the magnetic field distribution is
demonstrated and employed for gathering the data. The proposed setup allows to
measure the distributions of the axial and radial components of the magnetic
field surrounding the magnet. The experimental data is in a very good agreement
with the theoretical predictions, confirming the validity of using the model of
an ideal solenoid for predicting a magnetic field distribution of a permanent
magnet.",2207.09911v1
2022-09-09,Magnetization dynamics and reversal of two-dimensional magnets,"Micromagnetics simulation based on the classical Landau-Lifshitz-Gilbert
(LLG) equation has long been a powerful method for modeling magnetization
dynamics and reversal of three-dimensional (3D) magnets. For two-dimensional
(2D) magnets, the magnetization reversal always accompanies the collapse of the
magnetization even at low temperatures due to intrinsic strong spin
fluctuation. We propose a micromagnetic theory that explicitly takes into
account the rapid demagnetization and remagnetization dynamics of 2D magnets
during magnetization reversal. We apply the theory to a single-domain magnet to
illustrate fundamental differences in magnetization trajectories and reversal
times for 2D and 3D magnets.",2209.04483v1
2003-07-30,Apparent Sizes and Spectral Line Profiles for Spherical and Disk Masers: Solutions to the Full Equations,"Calculations are performed for the spectral line profiles and images of
astrophysical maser radiation that emerges from isolated spheres and thin disks
viewed edge-on. In contrast to previous investigations where various
approximations are made, the full equations are solved here for the
frequency-dependent radiative transport that includes the thermal motion of the
molecules. The spectral line profiles for spheres and disks are found to
rebroaden to the full thermal Doppler breadth with increasing saturation in
essentially the same way as is well known to occur for a linear maser. The
variation with frequency in the apparent angular sizes of masing spheres and
thin disks is found to be negligible at frequencies within the spectral line
where the flux is significant. Calculations also are performed for spherical
and disk masers that are not isolated, but for which the seed radiation for the
masers is incident from one side as would occur when a strong continuum source
is on the far side of the masers. Again, the spectral line profiles are found
to rebroaden to the full thermal breadths with increasing saturation and there
are no significant variations in the apparent angular sizes with frequency.
However, the full rebroadening does occur at somewhat higher saturation and the
variation of the apparent angular sizes as a function of the degree of
saturation is quite different from that of the isolated masers. Spheres and
disks have served as idealized geometries with which to examine possible
deviations from the linear approximation for astrophysical masers.",0307541v1
2006-02-04,Comprehensive Analysis of RXTE Data from Cyg X-1: Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations,"We present timing and spectral analysis of ~ 2.2 Ms of RXTE archival data
from Cyg X-1. Using a generic Comptonization model we reveal that the spectrum
of Cyg X-1 consists of three components: a thermal seed photon spectrum, a
Comptonized part of the seed photon spectrum and the iron line. We find a
strong correlation between the 0.1-20 Hz frequencies of quasiperiodic
oscillations (QPOs) and the spectral index. Presence of two spectral phases
(states) are clearly seen in the data when the spectral indices saturate at low
and high values of QPO frequencies. This saturation effect was discovered
earlier in a number of black hole candidate (BHC) sources and now we strongly
confirm this phenomenon in Cyg X-1. In the soft state this index-QPO frequency
correlation shows a saturation of the photon index Gamma ~ 2.1 at high values
of the low frequency \nu_{L}. The saturation level of Gamma~ 2.1 is the lowest
value found yet in BHCs. The bolometric luminosity does not show clear
correlation with the index. We also show that Fe K_{\alpha} emission line
strength (equivalent width, EW) correlates with the QPO frequency. The EW
increases from 200 eV in the low/hard state to 1.5 keV in the high/soft state.
The observational correlations revealed compel us to propose a scenario for the
spectral transition and iron line formation which occur in BHC sources. We also
present the spectral state (power-law index) evolution for eight years of Cyg
X-1 observations by RXTE.",0602091v1
2007-02-15,Amplitude Saturation in Beta Cephei Models,"Although the driving mechanism acting in beta Cephei pulsators is well known
(e.g. Dziembowski & Pamyatnykh 1993), problems concerning identification of
amplitude limitation mechanism and non-uniform filling of the theoretical
instability strip, remain to be solved. In the present analysis, these problems
are addressed by non-linear modelling of radial pulsations of these stars. In
this approach radial modes are treated as representative for all acoustic
oscillations.
  Several models of different masses and metallicities were converged to limit
cycles through Stellingwerf (1974) relaxation technique. Resulting peak-to-peak
amplitudes are of order of DeltaV=0.3 mag. Such amplitudes are significantly
larger than those observed in beta Cephei pulsators. Assuming that all acoustic
modes are similar, we show that collective saturation of the driving mechanism
by several acoustic modes can easily lower predicted saturation amplitudes to
the observed level. Our calculations predict significant decrease of saturation
amplitudes as we go to high mass/high luminosity models. However, this effect
is not strong enough to explain scarcity of high mass beta Cephei variables.
  We also discuss robust double-mode behaviour, encountered in our radiative
models. On a single evolutionary track we identify two double-mode domains with
two different mechanisms resposible for double-mode behaviour. The non-resonant
double-mode domain separates first overtone and fundamental mode pulsation
domains. The resonant double-mode domain appears in the middle of the first
overtone pulsation domain. Its origin can be traced to the
2omega_1=omega_0+omega_2 parametric resonance, which destabilizes the first
overtone limit cycle.",0702406v1
2003-08-09,Photo-physical and nonlinear-optical properties of a new polymer: hydroxylated pyridyl para-phenylene,"Photo-physical and nonlinear-optical properties of a new amphiphilic
conjugated polymer: hydroxylated pyridyl para-phenylene (Py-PhPPP) both in
CH2Cl2 solution and in thin films have been investigated. By using Z-scan
technique with nanosecond laser pulses of wavelengths ranging from 430 to 600
nm, the large nonlinear absorption and refraction have been determined in terms
of the effective third-order, nonlinear-optical susceptibilities. These Z-scans
reveal that the nonlinear absorption alters from reverse saturable absorption
to saturable absorption at wavelength of ~ 540 nm. Similarly, alteration from
self-defocusing to self-focusing manifests itself at the same wavelength. The
optical limiting performance of Py-PhPPP in solution is superior to toluene
solution of [60]fullerene (C60) at 532 nm. Both UV-visible absorption spectra
and photoluminescence (PL) spectra show concentration dependence. The PL
spectra also depend on excitation wavelengths. These evidences suggest that the
aggregate formation should play an important role in the nonlinear-optical
properties of the new polymer. We attribute the reverse saturable absorption in
the region of blue and green wavelengths mainly to intra-chain, triplet-triplet
absorption while the absorption bleaching at longer wavelengths is due to
saturation in the absorption band induced by the aggregates.",0308183v1
2005-01-19,Saturation of Electrostatic Potential: Exactly Solvable 2D Coulomb Models,"We test the concepts of renormalized charge and potential saturation,
introduced within the framework of highly asymmetric Coulomb mixtures, on
exactly solvable Coulomb models. The object of study is the average
electrostatic potential induced by a unique ""guest"" charge immersed in a
classical electrolyte, the whole system being in thermal equilibrium at some
inverse temperature $\beta$. The guest charge is considered to be either an
infinite hard wall carrying a uniform surface charge or a charged colloidal
particle. The systems are treated as two-dimensional; the electrolyte is
modelled by a symmetric two-component plasma of point-like $\pm e$ charges with
logarithmic Coulomb interactions. Two cases are solved exactly: the
Debye-H\""uckel limit $\beta e^2\to 0$ and the Thirring free-fermion point
$\beta e^2 = 2$. The results at the free-fermion point can be summarized as
follows: (i) The induced electrostatic potential exhibits the asymptotic
behavior, at large distances from the guest charge, whose form is different
from that obtained in the Debye-H\""uckel (linear Poisson-Boltzmann) theory.
This means that the concept of renormalized charge, developed within the
nonlinear Poisson-Boltzmann theory to describe the screening effect of the
electrolyte cloud, fails at the free-fermion point. (ii) In the limit of an
infinite bare charge, the induced electrostatic potential saturates at a finite
value in every point of the electrolyte region. This fact confirms the
previously proposed hypothesis of potential saturation.",0501442v1
2000-11-28,A geometrical estimation of saturation of partonic densities,"We propose a new criterium for saturation of the density of partons both in
nucleons and nuclei. It is applicable to any multiple scattering model which
would be used to compute the number of strings exchanged in $ep$ and $eA$
collisions. The criterium is based on percolation of strings, and the onset of
percolation is estimated from expectations coming from the study of heavy ion
collisions at high energies. We interpret this onset as an indication of
saturation of the density of partons in the wave function of the hadron. In
order to produce quantitative results, a particular model fitted to describe
present HERA data and generalized to the nuclear case is used. Nevertheless,
with the number of scatterings controlled by the relation between inclusive and
diffractive processes, conclusions are weakly model-dependent as long as
different models are tuned to describe the experimental data. This constitutes
a new approach, based on the eikonal description of soft hadronic collisions,
and different from others which employ either perturbative QCD ideas or
semiclassical methods. It offers an alternative picture for saturation in the
small $Q^2$ region.",0011352v3
2002-02-03,"S-Matrix Unitarity, Impact Parameter Profiles, Gluon Saturation and High-Energy Scattering","A model combining perturbative and non-perturbative QCD is developed to
compute high-energy reactions of hadrons and photons and to investigate
saturation effects that manifest the S-matrix unitarity. Following a functional
integral approach, the S-matrix factorizes into light-cone wave functions and
the universal amplitude for the scattering of two color-dipoles which are
represented by Wegner-Wilson loops. In the framework of the non-perturbative
stochastic vacuum model of QCD supplemented by perturbative gluon exchange, the
loop-loop correlation is calculated and related to lattice QCD investigations.
With a universal energy dependence motivated by the two-pomeron (soft + hard)
picture that respects the unitarity condition in impact parameter space, a
unified description of pp, pip, Kp, gamma* p, and gamma gamma reactions is
achieved in good agreement with experimental data for cross sections, slope
parameters, and structure functions. Impact parameter profiles for pp and
longitudinal gamma* p reactions and the gluon distribution of the proton
xG(x,Q^2,b) are calculated and found to saturate in accordance with S-matrix
unitarity. The c.m. energies and Bjorken x at which saturation sets in are
determined.",0202012v2
2002-06-07,The Colour Glass Condensate,"I briefly review the physical picture of the saturated gluons at small-x as a
Colour Glass Condensate, and the effective theory which forms the basis of this
picture.",0206073v1
2002-06-24,Froissart Bound from Gluon Saturation,"We demonstrate that the dipole-hadron cross-section computed from the
non-linear evolution equation for the Colour Glass Condensate saturates the
Froissart bound in the case of a fixed coupling and for a small dipole (Q^2 >>
Lambda_{QCD}^2). That is, the cross-section increases as the logarithm squared
of the energy, with a proportionality coefficient involving the pion mass and
the BFKL intercept (alpha_s N_c/pi)4 ln 2. The pion mass enters via the
non-perturbative initial conditions at low energy. The BFKL equation emerges as
a limit of the non-linear evolution equation valid in the tail of the hadron
wavefunction. We provide a physical picture for the transverse expansion of the
hadron with increasing energy, and emphasize the importance of the colour
correlations among the saturated gluons in suppressing non-unitary
contributions due to long-range Coulomb tails. We present the first calculation
of the saturation scale including the impact parameter dependence. We show that
the cross-section at high energy exhibits geometric scaling with a different
scaling variable as compared to the intermediate energy regime.",0206241v2
2004-08-19,Numerical analysis of the Balitsky-Kovchegov equation with running coupling: dependence of the saturation scale on nuclear size and rapidity,"We study the effects of including a running coupling constant in high-density
QCD evolution. For fixed coupling constant, QCD evolution preserves the initial
dependence of the saturation momentum $Q_s$ on the nuclear size $A$ and results
in an exponential dependence on rapidity $Y$, $Q^2_s(Y) = Q^2_s(Y_0) \exp{[
\bar\alpha_s d (Y-Y_0) ]}$. For the running coupling case, we re-derive
analytical estimates for the $A$- and $Y$-dependences of the saturation scale
and test them numerically. The $A$-dependence of $Q_s$ vanishes $\propto 1/
\sqrt{Y}$ for large $A$ and $Y$. The $Y$-dependence is reduced to $Q_s^2(Y)
\propto \exp{(\Delta^\prime\sqrt{Y+X})}$ where we find numerically
$\Delta^\prime\simeq 3.2$. We study the behaviour of the gluon distribution at
large transverse momentum, characterizing it by an anomalous dimension
$1-\gamma$ which we define in a fixed region of small dipole sizes. In contrast
to previous analytical work, we find a marked difference between the fixed
coupling ($\gamma \simeq 0.65$) and running coupling ($\gamma \sim 0.85$)
results. Our numerical findings show that both a scaling function depending
only on the variable $r Q_s$ and the perturbative double-leading-logarithmic
expression, provide equally good descriptions of the numerical solutions for
very small $r$-values below the so-called scaling window.",0408216v2
2005-06-16,Saturation 2005 (mini-review),"This talk was given at DIS'05 (Madison, April 27-May 2, 2005). It is a brief
review of ups and downs of high density QCD during the past year.",0506161v1
2006-06-23,A zero-dimensional model for high-energy scattering in QCD,"We investigate a zero-dimensional toy model originally introduced by Mueller
and Salam which mimics high-energy scattering in QCD in the presence of both
gluon saturation and gluon number fluctuations, and hence of Pomeron loops.
Unlike other toy models of the reaction-diffusion type, the model studied in
this paper is consistent with boost invariance and, related to that, it
exhibits a mechanism for particle saturation close to that of the JIMWLK
equation in QCD, namely the saturation of the emission rate due to high-density
effects. Within this model, we establish the dominant high-energy behaviour of
the S-matrix element <S^n> for the scattering between a target obtained by
evolving one particle and a projectile made with exactly n particles.
Remarkably, we find that all such matrix elements approach the black disk limit
S=0 at high rapidity Y, with the same exponential law: <S^n> ~ exp(-Y) for all
values of n. This is so because the S-matrix is dominated by rare target
configurations which involve only few particles. We also find that the bulk
distribution for a saturated system is of the Poisson type.",0606253v3
2006-07-04,"DIS at low x, saturation scale, gluon structure function and vector-meson production","Deep inelastic scattering at low x can be described by essentially only two
fitted parameters. The interpretation of J/Psi photoproduction in terms of the
gluon structure function is elaborated upon.",0607031v1
2007-01-25,Compatibility of phenomenological dipole cross sections with the Balitsky-Kovchegov equation,"Phenomenological models of the dipole cross section that enters in the
description of for instance deep inelastic scattering at very high energies
have had considerable success in describing the available small-x data in both
the saturation region and the so-called extended geometric scaling (EGS)
region. We investigate to what extent such models are compatible with the
numerical solutions of the Balitsky-Kovchegov (BK) equation which is expected
to describe the nonlinear evolution in x of the dipole cross section in these
momentum regions. We find that in the EGS region the BK equation yields results
that are qualitatively different from those of phenomenological studies. In
particular, geometric scaling around the saturation scale is only obtained at
asymptotic rapidities. We find that in this limit, the anomalous dimension
\gamma(r,x) of phenomenological models approaches a limiting function that is
universal for a large range of initial conditions. At the saturation scale,
this function equals approximately 0.44, in contrast to the value 0.628
commonly used in the models. We further investigate the dependence of these
results on the starting distribution, the small-r limit of the anomalous
dimension for fixed rapidities and the x-dependence of the saturation scale.",0701219v2
1995-04-24,Some comments on $N=2$ supersymmetric Yang-Mills,"We comment on some aspects of the semiclassical BPS saturated states close to
the curve $Im a_{D}/a =0$",9504120v1
1998-01-12,Probing Matrix Black Holes,"Black holes in matrix theory may consist of interacting clusters (correlated
domains) which saturate the uncertainty principle. We show that this assumption
qualitatively accounts for the thermodynamic properties of both charged and
neutral black holes, and reproduces the asymptotic geometry seen by probes.",9801070v1
2000-12-30,BPS Vortices in Brane-Antibrane Effective Theory,"We investigate an action which resembles the effective action of
brane-antibrane system derived from boundary string field theory. We find that
the action has smooth vortex solutions which saturate the Bogomol'nyi bound.",0101002v1
2002-08-29,Minimalisation of uncertainty relations in noncommutative quantum mechanics,"The explicit constrtuction of states saturating uncertainty relations
following from basic commutation rules of NCQM is given both in Fock space and
coordinate representation",0208213v1
1995-11-24,Highly saturated packings and reduced coverings,"We introduce and study certain notions which might serve as substitutes for
maximum density packings and minimum density coverings. A body is a compact
connected set which is the closure of its interior. A packing $\cal P$ with
congruent replicas of a body $K$ is $n$-saturated if no $n-1$ members of it can
be replaced with $n$ replicas of $K$, and it is completely saturated if it is
$n$-saturated for each $n\ge 1$. Similarly, a covering $\cal C$ with congruent
replicas of a body $K$ is $n$-reduced if no $n$ members of it can be replaced
by $n-1$ replicas of $K$ without uncovering a portion of the space, and it is
completely reduced if it is $n$-reduced for each $n\ge 1$. We prove that every
body $K$ in $d$-dimensional Euclidean or hyperbolic space admits both an
$n$-saturated packing and an $n$-reduced covering with replicas of $K$. Under
some assumptions on $K\subset \mathbb{E}^d$ (somewhat weaker than convexity),
we prove the existence of completely saturated packings and completely reduced
coverings, but in general, the problem of existence of completely saturated
packings and completely reduced coverings remains unsolved. Also, we
investigate some problems related to the the densities of $n$-saturated
packings and $n$-reduced coverings. Among other things, we prove that there
exists an upper bound for the density of a $d+2$-reduced covering of
$\mathbb{E}^d$ with congruent balls, and we produce some density bounds for the
$n$-saturated packings and $n$-reduced coverings of the plane with congruent
circles.",9511225v1
1998-04-15,Main gap for locally saturated elementary submodels of a homogeneous structure,"We prove a main gap theorem for e-saturated submodels of a homogeneous
structure. We also study the number of e-saturated models, which are not
elementarily embeddable to each other",9804157v1
1998-07-15,More on Weak Diamond,"We deal with the combinatorial principle Weak Diamond, showing that we always
either a local version is not saturated or we can increase the number of
colours. Then we point out a model theoretic consequence of Weak Diamond.",9807180v2
2001-07-29,Weak Diamond,"Under some cardinal arithmetic assumptions, we prove that every stationary
subset of lambda of a right cofinality has the weak diamond. This is a strong
negation of uniformization. We then deal with a weaker version of the weak
diamond- colouring restrictions. We then deal with semi- saturated (normal)
filters.",0107207v1
2005-07-18,Asymptotically saturated toric algebras,"We show the finite generation of certain invariant graded algebras defined on
toric weak log Fano fibrations. These are the toric version of FGA algebras,
recently introduced by Shokurov in connections to the existence of flips.",0507350v1
2006-08-07,Ind- and Pro- definable sets,"We describe the ind- and pro- categories of the category of definable sets,
in some first order theory, in terms of points in a sufficiently saturated
model.",0608163v1
2006-12-11,Subsheaves of a hermitian torsion free coherent sheaf on an arithmetic variety,"In this paper, we consider a finiteness problem of saturated subsheaves of a
hermitian locally free sheaf on an arithmetic variety. As an application, we
could prove the unique existence of an arithmetic Harder-Narasimham filtration.",0612268v1
2007-03-16,Reflexive abelian groups and measurable cardinals and saturated MAD families,"Answering a problem of Eklof and Mekler, we show that there is a reflexive
group of cardinality >= first measurable.",0703493v3
2007-02-14,The propagation of the light beam at the interface between uniform media and periodic media,"We considered the wave propagation between two medias. For description of
physical model choose nonlinear Schredinger equation with saturation parameter.
The solutions of respectively equation are found and analyzed.",0702030v1
2005-05-03,"Parton energy loss, saturation, and recombination at BRAHMS","Particle production as observed with the BRAHMS experiment at RHIC is
presented. Preliminary baryon/meson ratios and nuclear modification factors at
different rapidities will be discussed.",0505004v2
2004-11-19,Generalization of Child-Langmuir Law for Non-Zero Injection Velocities in a Planar Diode,"The Child-Langmuir law relates the voltage applied across a planar diode to
the saturation value J_CL of current density that can be transmitted through it
in case the injection velocity of electrons into the diode is zero. The
Child-Langmuir current density J_CL is, at the same time, (i) the maximum
current density that can be transmitted through a planar diode, (ii) the
current density below which the flow is steady and unidirectional in the long
time limit and (iii) the average transmitted current density for {\em any}
value of injected current density above J_CL. Existing generalizations of
Child-Langmuir law to non-zero velocities of injection are based on the
characteristics (i) and (ii) of J_CL. This paper generalizes the law to
non-zero velocities of injection based on the characteristic (iii) by deriving
an analytical expression for the saturation value of current density. The
analytical expression for the saturation current density is found to be well
supported by numerical computations. A reason behind preferring the saturation
property of the Child-Langmuir current density as the basis for its
generalization is the importance of that property in numerical simulations of
high current diode devices.",0411175v1
2007-05-16,Vortical and Wave Modes in 3D Rotating Stratified Flows: Random Large Scale Forcing,"Utilizing an eigenfunction decomposition, we study the growth and spectra of
energy in the vortical and wave modes of a 3D rotating stratified fluid as a
function of $\epsilon = f/N$. Working in regimes characterized by moderate
Burger numbers, i.e. $Bu = 1/\epsilon^2 < 1$ or $Bu \ge 1$, our results
indicate profound change in the character of vortical and wave mode
interactions with respect to $Bu = 1$. As with the reference state of
$\epsilon=1$, for $\epsilon < 1$ the wave mode energy saturates quite quickly
and the ensuing forward cascade continues to act as an efficient means of
dissipating ageostrophic energy. Further, these saturated spectra steepen as
$\epsilon$ decreases: we see a shift from $k^{-1}$ to $k^{-5/3}$ scaling for
$k_f < k < k_d$ (where $k_f$ and $k_d$ are the forcing and dissipation scales,
respectively). On the other hand, when $\epsilon > 1$ the wave mode energy
never saturates and comes to dominate the total energy in the system. In fact,
in a sense the wave modes behave in an asymmetric manner about $\epsilon = 1$.
With regard to the vortical modes, for $\epsilon \le 1$, the signatures of 3D
quasigeostrophy are clearly evident. Specifically, we see a $k^{-3}$ scaling
for $k_f < k < k_d$ and, in accord with an inverse transfer of energy, the
vortical mode energy never saturates but rather increases for all $k < k_f$. In
contrast, for $\epsilon > 1$ and increasing, the vortical modes contain a
progressively smaller fraction of the total energy indicating that the 3D
quasigeostrophic subsystem plays an energetically smaller role in the overall
dynamics.",0705.2452v2
2007-07-06,Internal sets and internal functions in Colombeau theory,"Inspired by nonstandard analysis, we define and study internal subsets and
internal functions in algebras of Colombeau generalized functions. We prove a
saturation principle for internal sets and provide applications to Colombeau
algebras.",0707.0994v1
2007-07-09,Antikaons and hyperons in nuclear matter with saturation,"We evaluate the antikaon and hyperon spectral functions in a self-consistent
and covariant many-body approach. The computation is based on coupled-channel
dynamics derived from the chiral SU(3) Lagrangian. A novel subtraction scheme
is developed that avoids kinematical singularities and medium-induced power
divergencies all together. Scalar and vector mean fields are used to model
nuclear binding and saturation. The effect of the latter is striking for the
antikaon spectral function that becomes significantly more narrow at small
momenta. Attractive mass shifts of about 30 and 40 MeV are predicted for the
Lambda(1405) and Sigma(1385) resonances. Once scalar and vector mean fields for
the nucleon are switched on the Lambda(1520) resonances dissolves almost
completely in nuclear matter. All together only moderate attraction is
predicted for the nuclear antikaon systems at saturation density. However, at
larger densities we predict a sizable population of soft antikaon modes that
arise from the coupling of the antikaon to a highly collective Lambda(1115)
nucleon-hole state. This may lead to the formation of exotic nuclear systems
with strangeness and antikaon condensation in compact stars at moderate
densities.",0707.1283v2
2007-07-12,Donor binding energy and thermally activated persistent photoconductivity in high mobility (001) AlAs quantum wells,"A doping series of AlAs (001) quantum wells with Si delta-modulation doping
on both sides reveals different dark and post-illumination saturation
densities, as well as temperature dependent photoconductivity. The lower dark
two-dimensional electron density saturation is explained assuming deep binding
energy of Delta_DK = 65.2 meV for Si-donors in the dark. Persistent
photoconductivity (PPC) is observed upon illumination, with higher saturation
density indicating shallow post-illumination donor binding energy. The
photoconductivity is thermally activated, with 4 K illumination requiring
post-illumination annealing to T = 30 K to saturate the PPC. Dark and
post-illumination doping efficiencies are reported.",0707.1796v4
2007-09-05,Evaporation and condensation of spherical interstellar clouds. Self-consistent models with saturated heat conduction and cooling,"Shortened version: The fate of IS clouds embedded in a hot tenuous medium
depends on whether the clouds suffer from evaporation or whether material
condensates onto them. Analytical solutions for the rate of evaporative mass
loss from an isolated spherical cloud embedded in a hot tenuous gas are deduced
by Cowie & McKee (1977). In order to test the validity of the analytical
results for more realistic IS conditions the full hydrodynamical equations must
be treated. Therefore, 2D numerical simulations of the evolution of IS clouds
%are performed with different internal density structures and surrounded by a
hot plasma reservoir. Self-gravity, interstellar heating and cooling effects
and heat conduction by electrons are added. Classical thermal conductivity of a
fully ionized hydrogen plasma and saturated heat flux are considered. Using
pure hydrodynamics and classical heat flux we can reproduce the analytical
results. Heat flux saturation reduces the evaporation rate by one order of
magnitude below the analytical value. The evolution changes totally for more
realistic conditions when interstellar heating and cooling effects stabilize
the self-gravity. Evaporation then turns into condensation, because the
additional energy by heat conduction can be transported away from the interface
and radiated off efficiently from the cloud's inner parts. I.e. that the
saturated heat flux consideration is inevitable for IS clouds embedded in hot
tenuous gas. Various consequences are discussed in the paper.",0709.0623v1
2007-10-15,Non-LTE dust nucleation in sub-saturated vapors,"We use the kinetic theory of nucleation to explore the properties of dust
nucleation in sub-saturated vapors. Due to radiation losses, the sub-critical
clusters have a smaller temperature compared to their vapor. This alters the
dynamical balance between attachment and detachment of monomers, allowing for
stable nucleation of grains in vapors that are sub-saturated for their
temperature. We find this effect particularly important at low densities and in
the absence of a strong background radiation field. We find new conditions for
stable nucleation in the n-T phase diagram. The nucleation in the non-LTE
regions is likely to be at much slower rate than in the super-saturated vapors.
We evaluate the nucleation rate, warning the reader that it does depend on
poorly substantiated properties of the macro-molecules assumed in the
computation. On the other hand, the conditions for nucleation depend only on
the properties of the large stable grains and are more robust. We finally point
out that this mechanism may be relevant in the early universe as an initial
dust pollution mechanism, since once the interstellar medium is polluted with
dust, mantle growth is likely to be dominant over non-LTE nucleation in the
diffuse medium.",0710.2903v2
2008-01-30,The zero-energy Landau levels in graphene as BPS-saturated states,"This paper has been withdrawn by the author, due to the crucial mistake of
the discussion in Sec IV.",0801.4785v2
2008-02-25,Delay Analysis for Wireless Local Area Networks with Multipacket Reception under Finite Load,"To date, most analysis of WLANs has been focused on their operation under
saturation condition. This work is an attempt to understand the fundamental
performance of WLANs under unsaturated condition. In particular, we are
interested in the delay performance when collisions of packets are resolved by
an exponential backoff mechanism. Using a multiple-vacation queueing model, we
derive an explicit expression for packet delay distribution, from which
necessary conditions for finite mean delay and delay jitter are established. It
is found that under some circumstances, mean delay and delay jitter may
approach infinity even when the traffic load is way below the saturation
throughput. Saturation throughput is therefore not a sound measure of WLAN
capacity when the underlying applications are delay sensitive. To bridge the
gap, we define safe-bounded-mean-delay (SBMD) throughput and
safe-bounded-delay-jitter (SBDJ) throughput that reflect the actual network
capacity users can enjoy when they require bounded mean delay and delay jitter,
respectively. The analytical model in this paper is general enough to cover
both single-packet reception (SPR) and multi-packet reception (MPR) WLANs, as
well as carrier-sensing and non-carrier-sensing networks. We show that the SBMD
and SBDJ throughputs scale super-linearly with the MPR capability of a network.
Together with our earlier work that proves super-linear throughput scaling
under saturation condition, our results here complete the demonstration of MPR
as a powerful capacity-enhancement technique for both delay-sensitive and
delay-tolerant applications.",0802.3569v1
2008-09-16,A Rational Approach to the Resonance Region,"Resonance Saturation in QCD can be understood in the large-Nc limit from the
mathematical theory of Pade Approximants to meromorphic functions.",0809.2704v1
2008-09-24,Simplified PMT Model,"A simplified model is proposed based on the characteristics of the
photomultiplier tube (PMT). The Model is compared to the available data, and it
successes to reproduce the saturation profile of the PMT. The model also adds
clarification about how the PMT works.",0809.4210v1
2008-12-11,Diffractive physics in ALICE,"The ALICE experiment at the LHC is presented and a diffractive double gap
trigger is described. Signatures of Pomeron and Odderon are discussed together
with photoproduction of heavy quarks as a possible signature of gluon
saturation.",0812.2176v1
2009-01-08,Computing Inhomogeneous Groebner Bases,"In this paper we describe how an idea centered on the concept of
self-saturation allows several improvements in the computation of Groebner
bases via Buchberger's Algorithm.",0901.1105v1
2009-03-04,Aggregation According to Classical Kinetics--From Nucleation to Coarsening,"We solve the standard Lifshitz-Slyozov (LS) model with conservation of total
particles in the limit of small super-saturation. The new element is an
effective initial condition that follows from the initial exhaustion of
nucleation as described in a previous paper [Farjoun and Neu, Phys. Rev. E 78].
The effective initial condition is characterized by a narrow distribution of
cluster-sizes, all much larger than critical. In the subsequent solution, one
of the LS similarity solutions emerges as the long-time limit, as expected. But
our solution tells more. In particular, there is a ""growth"" era prior to what
is usually called ""coarsening"". During ""growth"" the clusters (all of nearly the
same size much larger than critical) eventually exhaust the super-saturation
(the exhaustion of nucleation in the previous era results from only a small
decrease in super-saturation). This allows the critical size to catch up to the
clusters, and the traditional ""coarsening"" begins: Subcritical clusters
dissolve and fuel the growth of the remaining super-critical clusters. Our
analysis tracks the evolution of cluster sizes during growth and coarsening by
complimentary use of asymptotic and numerical methods. We establish
characteristic times and cluster sizes associated with growth and coarsening
from physical parameters and the initial super-saturation. The emerging
distribution is discontinuous at the largest cluster size, and our model
selects the discontinuous LS similarity solution as the long time limit. There
are strong indications that the smooth similarity solution proposed in the
original LS paper emerges on a, yet longer, late-coarsening time-scale.",0903.0861v1
2009-03-13,Resonance saturation of the chiral couplings at NLO in 1/Nc,"The precision obtainable in phenomenological applications of Chiral
Perturbation Theory is currently limited by our lack of knowledge on the
low-energy constants (LECs). The assumption that the most important
contributions to the LECs come from the dynamics of the low-lying resonances,
often referred to as the resonance saturation hypothesis, has stimulated the
use of large-Nc resonance lagrangians in order to obtain explicit values for
the LECs. We study the validity of the resonance saturation assumption at the
next-to-leading order in the 1/Nc expansion within the framework of Resonance
Chiral Theory (RChT). We find that, by imposing QCD short-distance constraints,
the chiral couplings can be written in terms of the resonance masses and
couplings and do not depend explicitly on the coefficients of the chiral
operators in the Goldstone boson sector of RChT. As we argue, this is the
counterpart formulation of the resonance saturation statement in the context of
the resonance lagrangian. Going beyond leading order in the 1/Nc counting allow
us to keep full control of the renormalization scale dependence of the LEC
estimates.",0903.2440v2
2009-04-28,"Comment on ""An optimized potential for carbon dioxide""","A molecular model for carbon dioxide is assessed regarding vapor-liquid
equilibrium properties. Large deviations, being above 15 %, are found for vapor
pressure and saturated vapor density in the entire temperature range.",0904.4391v1
2009-07-08,On the theory of astronomical maser. I. Statistics of maser radiation,"In this paper we re-analyse the amplification process of broadband continuum
radiation by astronomical masers in one-dimensional case. The basic equations
appropriate for the scalar maser and the random nature of the maser radiation
field are derived from basic physical principles. Comparision with the standard
radiation transfer equation allows us to examine the underlying assumptions
involved in the current theory of astronomical masers. Simulations are carried
out to follow the amplification of different realisations of the broadband
background radiation by the maser. The observable quantities such as intensity,
spectral line profile are obtained by averaging over an ensemble of the
emerging radiation corresponding to the amplified background radiation field.
Our simulations show that the fluctuations of the radiation field inside the
astronomical maser deviates significantly from Gaussian statistics even when
the maser is only partially saturated. Coupling between different frequency
modes and the population pulsing are shown to have increasing importance in the
transport of maser radiation as the maser approaches saturation. Our results
suggest that the standard formulation of radiation transfer provides a
satisfactory description of the intensity and the line narrowing effect in the
unsaturated and partially saturated masers within the framework of
one-dimensional model. Howerver, the application of the same formulation to the
strong saturation regime should be considered with caution.",0907.1326v1
2009-09-22,Experimental study on the cyclic resistance of a natural loess from Northern France,"In order to analyze the instability phenomenon observed along the Northern
High Speed Line of R\'eseau Ferr\'e de France (RFF), soil blocks were taken at
a site near the railway, at four different depths (1.2, 2.2, 3.5 and 4.9 m).
Cyclic triaxial tests were carried out on saturated and unsaturated soil
specimens. The results from tests on initially saturated specimens showed that
the soil taken at 2.2 m depth has the lowest resistance to cyclic loading, in
relation to its highest porosity and lowest clay fraction. This soil was then
studied at unsaturated state with various initial water contents. Unsaturated
soil specimens were first subjected to cyclic loadings to decrease their
volume. These cyclic loadings was stopped when the volume decrease was
approximately equal to the initial pore air volume, or when the pores filled by
air were eliminated and the soil was considered to become saturated.
Afterwards, the back-pressure tubing was saturated with de-aired water and
cycles were applied under undrained condition. Significant effect of initial
water content was evidenced: the lower the initial water content, the higher
the cyclic resistance. This can be explained by the densification of the soil
during the initial cyclic loadings.",0909.3932v1
2009-10-20,The saturation of SASI by parasitic instabilities,"The Standing Accretion Shock Instability (SASI) is commonly believed to be
responsible for large amplitude dipolar oscillations of the stalled shock
during core collapse, potentially leading to an asymmetric supernovae
explosion. The degree of asymmetry depends on the amplitude of SASI, which
nonlinear saturation mechanism has never been elucidated. We investigate the
role of parasitic instabilities as a possible cause of nonlinear SASI
saturation. As the shock oscillations create both vorticity and entropy
gradients, we show that both Kelvin-Helmholtz and Rayleigh-Taylor types of
instabilities are able to grow on a SASI mode if its amplitude is large enough.
We obtain simple estimates of their growth rates, taking into account the
effects of advection and entropy stratification. In the context of the
advective-acoustic cycle, we use numerical simulations to demonstrate how the
acoustic feedback can be decreased if a parasitic instability distorts the
advected structure. The amplitude of the shock deformation is estimated
analytically in this scenario. When applied to the set up of Fernandez &
Thompson (2009a), this saturation mechanism is able to explain the dramatic
decrease of the SASI power when both the nuclear dissociation energy and the
cooling rate are varied. Our results open new perspectives for anticipating the
effect, on the SASI amplitude, of the physical ingredients involved in the
modeling of the collapsing star.",0910.3953v2
2009-11-15,Onset of Instability in Restricted Geometry 4He Film Flow,"An early study of saturated 4He film flow instability is revisited in view of
recent theoretical work by Hiromitsu Takeuchi et al. (arXiv:0909.2144v1
[cond-mat.quant-gas] Sept. 2009). I show additional data that suggests a
qualitative agreement with this theory and discuss the experimental details.",0911.2820v1
2009-11-17,Incompressibility of asymmetric nuclear matter,"The incompressibility $K_sat(\delta)$ of isospin asymmetric nuclear matter at
its saturation density. Our results show that in the expansion of
$K_sat(\delta)$ in powers of isospin asymmetry $\delta$, i.e., $K_sat(\delta
)$=K_{0}+K_{sat,2}\delta^{2}+K_{sat,4}\delta^{4}+O(\delta^{6})$, the magnitude
of the 4th-order K_{sat,4} parameter is generally small. The 2nd-order
K_{sat,2} parameter thus essentially characterizes the isospin dependence of
the incompressibility of asymmetric nuclear matter at saturation density.
Furthermore, the K_{sat,2} can be expressed as
K_{sat,2}=K_{sym}-6L-J_{0}/{K_{0}L in terms of the slope parameter $L$ and the
curvature parameter $K_{\mathrm{sym}}$ of the symmetry energy and the
third-order derivative parameter $J_0$ of the energy of symmetric nuclear
matter at saturation density, and we find the higher order $J_0$ contribution
to K_{sat,2} generally cannot be neglected. Also, we have found a linear
correlation between K_{sym} and $L$ as well as between $J_{0}/K_{0}$ and
$K_{0}$. Using these correlations together with the empirical constraints on
$K_{0}$ and $L$, the nuclear symmetry energy $E_sym(\rho_{0})$ at normal
nuclear density, and the nucleon effective mass, we have obtained an estimated
value of K_{sat,2}=-370 +- 120 MeV for the 2nd-order parameter in the isospin
asymmetry expansion of the incompressibility of asymmetric nuclear matter at
its saturation density.",0911.3330v1
2009-12-09,Mixed scenario of the charged helium surface reconstruction,"Discussed in the paper is the mixed scenario of charged liquid surface
reconstruction when the surface 2D charge density is close to the saturation.
The basic building block of arising honeycomb structure is shown to be a
modified multielectron dimple.",0912.1691v1
2010-05-11,Unitarity: confinement and collective effects in hadron interactions,"We discuss how saturation of unitarity would change phase structure of
hadronic matter at very high temperatures emphasizing the role of the vacuum
state with spontaneously broken chiral symmetry.",1005.1731v1
2010-09-09,Saturated torque formula for planetary migration in viscous disks with thermal diffusion: recipe for protoplanet population synthesis,"We provide torque formulae for low mass planets undergoing type I migration
in gaseous disks. These torque formulae put special emphasis on the horseshoe
drag, which is prone to saturation: the asymptotic value reached by the
horseshoe drag depends on a balance between coorbital dynamics (which tends to
cancel out or saturate the torque) and diffusive processes (which tend to
restore the unperturbed disk profiles, thereby desaturating the torque). We
entertain here the question of this asymptotic value, and we derive torque
formulae which give the total torque as a function of the disk's viscosity and
thermal diffusivity. The horseshoe drag features two components: one which
scales with the vortensity gradient, and one which scales with the entropy
gradient, and which constitutes the most promising candidate for halting inward
type I migration. Our analysis, which is complemented by numerical simulations,
recovers characteristics already noted by numericists, namely that the viscous
timescale across the horseshoe region must be shorter than the libration time
in order to avoid saturation, and that, provided this condition is satisfied,
the entropy related part of the horseshoe drag remains large if the thermal
timescale is shorter than the libration time. Side results include a study of
the Lindblad torque as a function of thermal diffusivity, and a contribution to
the corotation torque arising from vortensity viscously created at the contact
discontinuities that appear at the horseshoe separatrices. For the convenience
of the reader mostly interested in the torque formulae, section 8 is
self-contained.",1009.1913v2
2010-10-21,State Dependent Attempt Rate Modeling of Single Cell IEEE~802.11 WLANs with Homogeneous Nodes and Poisson Packet Arrivals,"Analytical models for IEEE 802.11-based WLANs are invariably based on
approximations, such as the well-known \textit{decoupling approximation}
proposed by Bianchi for modeling single cell WLANs consisting of saturated
nodes. In this paper, we provide a new approach to model the situation when the
nodes are not saturated. We study a State Dependent Attempt Rate (SDAR)
approximation to model $M$ queues (one queue per node) served by the CSMA/CA
protocol as standardized in the IEEE 802.11 DCF MAC protocol. The approximation
is that, when $n$ of the $M$ queues are non-empty, the transmission attempt
probability of the $n$ non-empty nodes is given by the long-term transmission
attempt probability of $n$ ""saturated"" nodes as provided by Bianchi's model.
The SDAR approximation reduces a single cell WLAN with non-saturated nodes to a
""coupled queue system"". When packets arrive to the $M$ queues according to
independent Poisson processes, we provide a Markov model for the coupled queue
system with SDAR service. \textit{The main contribution of this paper is to
provide an analysis of the coupled queue process by studying a lower
dimensional process, and by introducing a certain conditional independence
approximation}. We show that the SDAR model of contention provides an accurate
model for the DCF MAC protocol in single cells, and report the simulation
speed-ups thus obtained by our \textit{model-based simulation}.",1010.4475v1
2010-12-02,Equality Saturation: A New Approach to Optimization,"Optimizations in a traditional compiler are applied sequentially, with each
optimization destructively modifying the program to produce a transformed
program that is then passed to the next optimization. We present a new approach
for structuring the optimization phase of a compiler. In our approach,
optimizations take the form of equality analyses that add equality information
to a common intermediate representation. The optimizer works by repeatedly
applying these analyses to infer equivalences between program fragments, thus
saturating the intermediate representation with equalities. Once saturated, the
intermediate representation encodes multiple optimized versions of the input
program. At this point, a profitability heuristic picks the final optimized
program from the various programs represented in the saturated representation.
Our proposed way of structuring optimizers has a variety of benefits over
previous approaches: our approach obviates the need to worry about optimization
ordering, enables the use of a global optimization heuristic that selects among
fully optimized programs, and can be used to perform translation validation,
even on compilers other than our own. We present our approach, formalize it,
and describe our choice of intermediate representation. We also present
experimental results showing that our approach is practical in terms of time
and space overhead, is effective at discovering intricate optimization
opportunities, and is effective at performing translation validation for a
realistic optimizer.",1012.1802v3
2011-03-15,Can a Bose gas be saturated?,"Bose-Einstein condensation is unique among phase transitions between
different states of matter in the sense that it occurs even in the absence of
interactions between particles. In Einstein's textbook picture of an ideal gas,
purely statistical arguments set an upper bound on the number of particles
occupying the excited states of the system, and condensation is driven by this
saturation of the quantum vapour. Dilute ultracold atomic gases are celebrated
as a realisation of Bose-Einstein condensation in close to its purely
statistical form. Here we scrutinise this point of view using an ultracold gas
of potassium (39K) atoms, in which the strength of interactions can be tuned
via a Feshbach scattering resonance. We first show that under typical
experi-mental conditions a partially condensed atomic gas strongly deviates
from the textbook concept of a saturated vapour. We then use measurements at a
range of interaction strengths and temperatures to extrapolate to the
non-interacting limit, and prove that in this limit the behaviour of a Bose gas
is consistent with the saturation picture. Finally, we provide evidence for the
universality of our observations through additional measurements with a
different atomic species, 87Rb. Our results suggest a new way of characterising
condensation phenomena in different physical systems.",1103.2896v1
2011-03-30,Homology decompositions and groups inducing fusion systems,"We relate the construction of groups which realize saturated fusion systems
and signaliser functors with homology decompositions of p-local finite groups.
We prove that the cohomology ring of Robinson's construction is in some precise
sense very close to the cohomology ring of the fusion system it realizes.",1103.5856v1
2011-03-30,On Two Models of the Light Pulse Delay in a Saturable Absorber,"A comparative analysis of two approaches to description of the light
modulation pulse delay in a saturable absorber is presented. According to the
simplest model, the delay of the optical pulse is a result of distortion of its
shape due to absorption self-modulation in the nonlinear medium. The second
model of the effect, proposed at the beginning of our century, connects the
pulse delay with the so-called ""slow light"" resulting from the group velocity
reduction under conditions of the coherent population oscillations. It is shown
that all the known experimental data on the light pulse delay in saturable
absorbers can be comprehensively described in the framework of the simplest
model of saturable absorber and do not require invoking the effect of coherent
population oscillations with spectral hole-burning and anomalous modifications
of the light group velocity. It is concluded that the effect of group velocity
reduction under conditions of coherent population oscillations has not received
so far any experimental confirmation, and the assertions about real observation
of the ""slow light"" based on this mechanism are groundless.",1103.5868v1
2011-12-06,Analogues of Goldschmidt's thesis for fusion systems,"We extend the results of David Goldschmidt's thesis concerning fusion in
finite groups to saturated fusion systems and to all primes.",1112.1389v1
2011-12-13,The color dipole picture of low-x DIS,"Deep inelastic electron scattering (DIS) from nucleons at low values of the
Bjorken variable $x \cong Q^2/W^2 \lsim ~ 0.1$ proceeds via fluctuations of the
photon into quark-antiquark dipole states that subsequently interact with the
gluon field in the nucleon. Dependent on the interaction energy, $W$, the
color-gauge-invariant dipole interaction with the gluon field in the nucleon,
for any fixed dipole size, contains the limits of i) color transparency and ii)
saturation, where ""saturation"" stands for the approach to a hadronlike
dipole-proton interaction cross section. All essential features of the
experimental results on low-x DIS, as a consequence of the
color-gauge-invariant dipole interaction follow model independently i.e.
without specific ansatz for the dipole cross section. The model-independent
results in particular include the low-x scaling behavior of the photoabsorption
cross section, $\sigma_{\gamma^*p} (W^2,Q^2) = \sigma_{\gamma^*p} (\eta
(W^2,Q^2))$, with definite functional dependence on the low-x scaling variable
$\eta (W^2,Q^2) \cong Q^2/\Lambda^2_{sat} (W^2)$ in the limits of $\eta
(W^2,Q^2) \gg 1$ and $\eta (W^2,Q^2) \ll 1$, respectively. Consistency with the
pQCD-improved parton model implies the definite value of $C_2 \cong 0.29$ for
the exponent in the ""saturation scale"", $\Lambda^2_{sat} (W^2) \approx
(W^2)^{C_2}$. The longitudinal-to-transverse ratio of the photoabsorption cross
section at large $Q^2$ has the definite value of $R = 1/2 \rho$ with $\rho =
4/3$. For $W^2 \to \infty$ at any fixed $Q^2$, the photoabsorption cross
section converges towards a $Q^2$-independent saturation limit that coincides
with the cross section for $Q^2 = 0$ photoproduction.",1112.2885v1
2012-02-13,The Maximal Runaway Temperature of Earth-like Planets,"We generalize the problem of the semi-gray model to cases in which a
non-negligible fraction of the stellar radiation falls on the long-wavelength
range, and/or that the planetary long-wavelength emission penetrates into the
transparent short wavelength domain of the absorption.
  Second, applying the most general assumptions and independently of any
particular properties of an absorber, we show that the greenhouse effect
saturates and any Earth-like planet has a maximal temperature which depends on
the type of and distance to its main-sequence star, its albedo and the primary
atmospheric components which determine the cutoff frequency below which the
atmosphere is optically thick. For example, a hypothetical convection-less
planet similar to Venus, that is optically thin in the visible, could have at
most a surface temperature of 1200-1300K irrespective of the nature of the
greenhouse gas.
  We show that two primary mechanisms are responsible for the saturation of the
runaway greenhouse effect, depending on the value of the wavelength above which
the atmosphere becomes optically thick. Unless this wavelength is small and
resides in the optical region, saturation is achieved by radiating the thermal
flux of the planet through the short wavelength tail of the thermal
distribution. This has the observational implication, the radiation from such a
planet should be skewed towards the NIR. Otherwise, saturation takes place by
radiating through windows in the FIR.",1202.2644v1
2012-03-22,A 1-D modelling of streaming potential dependence on water content during drainage experiment in sand,"The understanding of electrokinetics for unsaturated conditions is crucial
for numerous of geophysical data interpretation. Nevertheless, the behaviour of
the streaming potential coefficient C as a function of the water saturation Sw
is still discussed. We propose here to model both the Richards' equation for
hydrodynamics and the Poisson's equation for electrical potential for
unsaturated conditions using 1-D finite element method. The equations are first
presented and the numerical scheme is then detailed for the Poisson's equation.
Then, computed streaming potentials (SPs) are compared to recently published SP
measurements carried out during drainage experiment in a sand column. We show
that the apparent measurement of DV / DP for the dipoles can provide the SP
coefficient in these conditions. Two tests have been performed using existing
models for the SP coefficient and a third one using a new relation. The results
show that existing models of unsaturated SP coefficients C(Sw) provide poor
results in terms of SP magnitude and behaviour. We demonstrate that the
unsaturated SP coefficient can be until one order of magnitude larger than
Csat, its value at saturation. We finally prove that the SP coefficient follows
a non-monotonous behaviour with respect to water saturation. Key words:
Electrical properties; Electromagnetic theory; Hydrogeophysics; Hydrology;
Permeability and porosity; electrokinetic; streaming potential; self-potential;
water content; water saturation; unsaturated condition; finite element modeling",1203.4921v1
2012-08-13,Model-theoretic properties of ultrafilters built by independent families of functions,"Our results in this paper increase the model-theoretic precision of a widely
used method for building ultrafilters, and so advance the general problem of
constructing ultrafilters whose ultrapowers have a precise degree of
saturation. We begin by showing that any flexible regular ultrafilter makes the
product of an unbounded sequence of finite cardinals large, {thus} saturating
any stable theory. We then prove directly that a ""bottleneck"" in the inductive
construction of a regular ultrafilter on $\lambda$ (i.e. a point after which
all antichains of $P(\lambda)/D$ have cardinality less than $\lambda$)
essentially prevents any subsequent ultrafilter from being flexible, {thus}
from saturating any non-low theory. The paper's three main constructions are as
follows. First, we construct a regular filter $D$ on $\lambda$ so that any
ultrafilter extending $D$ fails to $\lambda^+$-saturate ultrapowers of the
random graph, {thus} of any unstable theory. The proof constructs the omitted
random graph type directly. Second, assuming existence of a measurable cardinal
$\kappa$, we construct a regular ultrafilter on $\lambda > \kappa$ which is
$\lambda$-flexible but not $\kappa^{++}$-good, improving our previous answer to
a question raised in Dow 1975. Third, assuming a weakly compact cardinal
$\kappa$, we construct an ultrafilter to show that $\lcf(\aleph_0)$ may be
small while all symmetric cuts of cofinality $\kappa$ are realized. Thus
certain families of pre-cuts may be realized while still failing to saturate
any unstable theory.",1208.2579v1
2012-08-30,Delineating the saturation boundary: linear vs non-linear QCD evolution from HERA data to LHC phenomenology,"The forthcoming p+Pb run at the LHC will provide crucial in formation on the
initial state effects of heavy ion collisions and on the gluon saturation
phenomena. In turn, most of the saturation inspired phenomenology in heavy ion
collisions borrows substantial empiric information from the analysis of e+p
data, where abundant high quality data on the small-x kinematic region is
available. Indeed, the very precise combined HERA data provides a testing
ground in which the relevance of novel QCD regimes, other than the successful
linear DGLAP evolution, in small-x inclusive DIS data can be ascertained. We
present a study of the dependence of the AAMQS fits, based on the running
coupling BK non-linear evolution equations (rcBK), on the fitted dataset. This
allows for the identification of the kinematical region where rcBK accurately
describes the data, and thus for the determination of its applicability
boundary. It also set important constraints to the saturation models used to
model the early stages of heavy ion collisions. Finally we compare the rcBK
results with NNLO DGLAP fits, obtained with the NNPDF methodology with
analogous kinematical cuts. Further, we explore the impact on LHC phenomenology
of applying stringent kinematical cuts to the low-x HERA data in a DGLAP fit.",1208.6246v1
2012-10-23,Gravitational wave emission and spindown of young pulsars,"The rotation frequencies of young pulsars are systematically below their
theoretical Kepler limit. R-modes have been suggested as a possible explanation
for this observation. With the help of semi-analytic expressions that make it
possible to assess the uncertainties of the r-mode scenario due to the impact
of uncertainties in underlying microphysics, we perform a quantitative analysis
of the spin-down and the emitted gravitational waves of young pulsars. We find
that the frequency to which r-modes spin down a young neutron star is
surprisingly insensitive both to the microscopic details and the saturation
amplitude. Comparing our result to astrophysical data, we show that for a range
of sufficiently large saturation amplitudes r-modes provide a viable spindown
scenario and that all observed young pulsars are very likely already outside
the r-mode instability region. Therefore the most promising sources for
gravitational wave detection are unobserved neutron stars associated with
recent supernovae, and we find that advanced LIGO should be able to see several
of them. We find the remarkable result that the gravitational wave strain
amplitude is completely independent of both the r-mode saturation amplitude and
the microphysics, and depends on the saturation mechanism only within some tens
of per cent. However, the gravitational wave frequency depends on the amplitude
and we provide the required expected timing parameter ranges to look for
promising sources in future searches.",1210.6091v2
2013-05-25,Gluon splitting in a shockwave,"The study of azimuthal correlations in particle production at forward
rapidities in proton-nucleus collisions provides direct information about high
gluon density effects, like gluon saturation, in the nuclear wavefunction. In
the kinematical conditions for proton-lead collisions at the LHC, the forward
di-hadron production is dominated by partonic processes in which a gluon from
the proton splits into a pair of gluons, while undergoing multiple scattering
off the dense gluon system in the nucleus. We compute the corresponding
cross-section using the Colour Glass Condensate effective theory, which enables
us to include the effects of multiple scattering and gluon saturation in the
leading logarithmic approximation at high energy. This opens the way towards
systematic studies of angular correlations in two-gluon production, similar to
previous studies for quark-gluon production in the literature. We consider in
more detail two special kinematical limits: the ""back-to-back correlation
limit"", where the transverse momenta of the produced gluons are much larger
than the nuclear saturation momentum, and the ""double parton scattering limit"",
where the two gluons are produced by a nearly collinear splitting occurring
prior to the collision. We argue that saturation effects remain important even
for relatively high transverse momenta (i.e. for nearly back-to-back
configurations), leading to geometric scaling in the azimuthal distribution.",1305.5926v1
2013-05-29,Resolution-aware network coded storage,"In this paper, we show that coding can be used in storage area networks
(SANs) to improve various quality of service metrics under normal SAN operating
conditions, without requiring additional storage space. For our analysis, we
develop a model which captures modern characteristics such as constrained I/O
access bandwidth limitations. Using this model, we consider two important
cases: single-resolution (SR) and multi-resolution (MR) systems. For SR
systems, we use blocking probability as the quality of service metric and
propose the network coded storage (NCS) scheme as a way to reduce blocking
probability. The NCS scheme codes across file chunks in time, exploiting file
striping and file duplication. Under our assumptions, we illustrate cases where
SR NCS provides an order of magnitude savings in blocking probability. For MR
systems, we introduce saturation probability as a quality of service metric to
manage multiple user types, and we propose the uncoded resolution- aware
storage (URS) and coded resolution-aware storage (CRS) schemes as ways to
reduce saturation probability. In MR URS, we align our MR layout strategy with
traffic requirements. In MR CRS, we code videos across MR layers. Under our
assumptions, we illustrate that URS can in some cases provide an order of
magnitude gain in saturation probability over classic non-resolution aware
systems. Further, we illustrate that CRS provides additional saturation
probability savings over URS.",1305.6864v1
2013-06-19,CSMA/ECA in Non-Saturation,"During the past month we have been trying to understand both the behavior of
CSMA/ECA and how our simulator works. In this report I try to asses some of
those doubts and provide a groundwork for discussion of past and new ideas for
further develop the MAC protocol.",1306.4542v1
2013-09-02,Infrared Saturation and Phases of Gauge Theories with BRST Symmetry,"We investigate the infrared limit of the quantum equation of motion of the
gauge boson propagator in various gauges and models with a BRST symmetry. We
find that the saturation of this equation at low momenta distinguishes between
the Coulomb, Higgs and confining phase of the gauge theory. The Coulomb phase
is characterized by a massless gauge boson. Physical states contribute to the
saturation of the transverse equation of motion of the gauge boson at low
momenta in the Higgs phase, while the saturation is entirely due to unphysical
degrees of freedom in the confining phase. This corollary to the Kugo-Ojima
confinement criterion in linear covariant gauges also is sufficient for
confinement in general covariant gauges with BRST- and anti-BRST symmetry,
maximal Abelian gauges with an equivariant BRST symmetry, non-covariant Coulomb
gauge and in the Gribov-Zwanziger theory.",1309.0497v3
2013-09-29,Threshold Saturation for Spatially-Coupled LDPC and LDGM Codes on BMS Channels,"Spatially-coupled low-density parity-check (LDPC) codes, which were first
introduced as LDPC convolutional codes, have been shown to exhibit excellent
performance under low-complexity belief-propagation decoding. This phenomenon
is now termed threshold saturation via spatial coupling. Spatially-coupled
codes have been successfully applied in numerous areas. In particular, it was
proven that spatially-coupled regular LDPC codes universally achieve capacity
over the class of binary memoryless symmetric (BMS) channels under
belief-propagation decoding.
  Recently, potential functions have been used to simplify threshold saturation
proofs for scalar and vector recursions. In this paper, potential functions are
used to prove threshold saturation for irregular LDPC and low-density
generator-matrix (LDGM) codes on BMS channels, extending the simplified proof
technique to BMS channels. The corresponding potential functions are closely
related to the average Bethe free entropy of the ensembles in the large-system
limit. These functions also appear in statistical physics when the replica
method is used to analyze optimal decoding.",1309.7543v2
2013-09-30,A Simple Proof of Maxwell Saturation for Coupled Scalar Recursions,"Low-density parity-check (LDPC) convolutional codes (or spatially-coupled
codes) were recently shown to approach capacity on the binary erasure channel
(BEC) and binary-input memoryless symmetric channels. The mechanism behind this
spectacular performance is now called threshold saturation via spatial
coupling. This new phenomenon is characterized by the belief-propagation
threshold of the spatially-coupled ensemble increasing to an intrinsic noise
threshold defined by the uncoupled system. In this paper, we present a simple
proof of threshold saturation that applies to a wide class of coupled scalar
recursions. Our approach is based on constructing potential functions for both
the coupled and uncoupled recursions. Our results actually show that the fixed
point of the coupled recursion is essentially determined by the minimum of the
uncoupled potential function and we refer to this phenomenon as Maxwell
saturation. A variety of examples are considered including the
density-evolution equations for: irregular LDPC codes on the BEC, irregular
low-density generator matrix codes on the BEC, a class of generalized LDPC
codes with BCH component codes, the joint iterative decoding of LDPC codes on
intersymbol-interference channels with erasure noise, and the compressed
sensing of random vectors with i.i.d. components.",1309.7910v3
2014-04-05,Induced cooperative motions in a medium driven at the nanoscale: Searching for an optimum excitation period,"Recent results have shown the appearance of induced cooperative motions
called dynamic heterogeneity during the isomerization of diluted azobenzene
molecules in a host glass-former. In this paper we raise the issue of the
coupling between these ""artificial"" heterogeneities and the isomerization
period. How do these induced heterogeneities differ in the saturation regime
and in the linear response regime ? Is there a maximum of the heterogeneous
motion versus isomerization rate and why ? Are the heterogeneity evolution with
the isomerization rate connected with the diffusion or relaxation time
evolution ? We use out of equilibrium molecular dynamics simulations to answer
these questions. We find that the heterogeneity increases in the linear
response regime for large isomerization periods and small perturbations. In
contrast the heterogeneity decreases in the saturation regime, i.e. when the
isomerization half-period ($\tau_{p}/2$) is smaller than the relaxation time of
the material ($\tau_{\alpha}$). This result makes possible a test of the effect
of cooperative motions on the dynamics using the chromophores as Maxwell demons
that destroy or stimulate the cooperative motions. Because the heterogeneities
increase in the linear regime and then decrease in the saturation regime, we
find a maximum for $\tau_{p}/2 \approx \tau_{\alpha}$. The induced excitations
concentration follows a power law evolution versus the isomerization rate and
then saturates. As a consequence the $\alpha$ relaxation time is related to the
excitation concentration with a power law, a result in qualitative agreement
with recent findings in constrained models. This result supports a common
origin for the heterogeneities with constrained models and a similar relation
to the excitation concentration.",1404.1452v1
2014-05-19,Charge-induced phase separation in lipid membranes,"The phase separation in lipid bilayers that include negatively charged lipids
is examined experimentally. We observed phase-separated structures and
determined the membrane miscibility temperatures in several binary and ternary
lipid mixtures of unsaturated neutral lipid, dioleoylphosphatidylcholine
(DOPC), saturated neutral lipid, dipalmitoylphosphatidylcholine (DPPC),
unsaturated charged lipid, dioleoylphosphatidylglycerol
(DOPG$^{\scriptsize{(-)}}$), saturated charged lipid,
dipalmitoylphosphatidylglycerol (DPPG$^{\scriptsize{(-)}}$), and cholesterol.
In binary mixtures of saturated and unsaturated charged lipids, the combination
of the charged head with the saturation of hydrocarbon tail is a dominant
factor for the stability of membrane phase separation.
DPPG$^{\scriptsize{(-)}}$ enhances phase separation, while
DOPG$^{\scriptsize{(-)}}$ suppresses it. Furthermore, the addition of
DPPG$^{\scriptsize{(-)}}$ to a binary mixture of DPPC/cholesterol induces phase
separation between DPPG$^{\scriptsize{(-)}}$-rich and cholesterol-rich phases.
This indicates that cholesterol localization depends strongly on the electric
charge on the hydrophilic head group rather than on the ordering of the
hydrocarbon tails. Finally, when DPPG$^{\scriptsize{(-)}}$ was added to a
neutral ternary system of DOPC/DPPC/Cholesterol (a conventional model of
membrane rafts), a three-phase coexistence was produced. We conclude by
discussing some qualitative features of the phase behaviour in charged
membranes using a free energy approach.",1405.4650v3
2014-06-09,On saturation games,"A graph $G = (V,E)$ is said to be saturated with respect to a monotone
increasing graph property ${\mathcal P}$, if $G \notin {\mathcal P}$ but $G
\cup \{e\} \in {\mathcal P}$ for every $e \in \binom{V}{2} \setminus E$. The
saturation game $(n, {\mathcal P})$ is played as follows. Two players, called
Mini and Max, progressively build a graph $G \subseteq K_n$, which does not
satisfy ${\mathcal P}$. Starting with the empty graph on $n$ vertices, the two
players take turns adding edges $e \in \binom{V(K_n)}{2} \setminus E(G)$, for
which $G \cup \{e\} \notin {\mathcal P}$, until no such edge exists (i.e. until
$G$ becomes ${\mathcal P}$-saturated), at which point the game is over. Max's
goal is to maximize the length of the game, whereas Mini aims to minimize it.
The score of the game, denoted by $s(n, {\mathcal P})$, is the number of edges
in $G$ at the end of the game, assuming both players follow their optimal
strategies. We prove lower and upper bounds on the score of games in which the
property the players need to avoid is being $k$-connected, having chromatic
number at least $k$, and admitting a matching of a given size. In doing so we
demonstrate that the score of certain games can be as large as the Tur\'an
number or as low as the saturation number of the respective graph property. We
also demonstrate that the score might strongly depend on the identity of the
first player to move.",1406.2111v3
2014-08-23,Saturation in the Hypercube and Bootstrap Percolation,"Let $Q_d$ denote the hypercube of dimension $d$. Given $d\geq m$, a spanning
subgraph $G$ of $Q_d$ is said to be $(Q_d,Q_m)$-saturated if it does not
contain $Q_m$ as a subgraph but adding any edge of $E(Q_d)\setminus E(G)$
creates a copy of $Q_m$ in $G$. Answering a question of Johnson and Pinto, we
show that for every fixed $m\geq2$ the minimum number of edges in a
$(Q_d,Q_m)$-saturated graph is $\Theta(2^d)$.
  We also study weak saturation, which is a form of bootstrap percolation. A
spanning subgraph of $Q_d$ is said to be weakly $(Q_d,Q_m)$-saturated if the
edges of $E(Q_d)\setminus E(G)$ can be added to $G$ one at a time so that each
added edge creates a new copy of $Q_m$. Answering another question of Johnson
and Pinto, we determine the minimum number of edges in a weakly
$(Q_d,Q_m)$-saturated graph for all $d\geq m\geq1$. More generally, we
determine the minimum number of edges in a subgraph of the $d$-dimensional grid
$P_k^d$ which is weakly saturated with respect to `axis aligned' copies of a
smaller grid $P_r^m$. We also study weak saturation of cycles in the grid.",1408.5488v2
2014-08-29,The saturation of Frobenius powers of ideals,"This paper proves some special cases in which localization of tight closure
holds. In particular it studies the condition LC relating to bounding the Loewy
lengths of local cohomology of Frobenius iterates of quotient rings.",1408.7100v1
2014-11-08,Differential capacitance of the electric double layer: The interplay between ion finite size and dielectric decrement,"We study the electric double layer by combining the effects of ion finite
size and dielectric decrement. At high surface potential, both mechanisms can
cause saturation of the counter-ion concentration near a charged surface. The
modified Grahame equation and differential capacitance are derived analytically
for a general expression of a permittivity epsilon(n) that depends on the local
ion concentration, n, and under the assumption that the co-ions are fully
depleted from the surface. The concentration at counter-ion saturation is found
for any epsilon(n), and a criterion predicting which of the two mechanisms
(steric vs. dielectric decrement) is the dominant one is obtained. At low
salinity, the differential capacitance as function of surface potential has two
peaks (so-called camel-shape). Each of these two peaks is connected to a
saturation of counter-ion concentration caused either by dielectric decrement
or by their finite size. Because these effects depend mainly on the counter-ion
concentration at the surface proximity, for opposite surface-potential polarity
either the cations or anions play the role of counter-ions, resulting in an
asymmetric camel-shape. At high salinity, we obtain and analyze the crossover
in the differential capacitance from a double-peak shape to a uni-modal one.
Finally, several nonlinear models of the permittivity decrement are considered,
and we predict that the concentration at dielectrophoretic saturation shifts to
higher concentration than those obtained by the linear decrement model.",1411.2092v2
2015-02-04,Effects of liquid pore water on acoustic wave propagation in snow as a Biot-type porous material,"A method to estimate phase velocity and attenuation of acoustic waves in the
presence of liquid water in a snowpack is presented. The method is based on
Biot's theory of wave propagation in porous materials. Empirical relations and
a priori information is used to characterize snow as a porous material as a
function of porosity. Plane wave theory and an equivalent pore fluid are used
to solve Biot's differential equations and to asses the impact of the air and
water in the pore space. The liquid water in the pore space of a snow pack
reduces the velocity of the first compressional wave by roughly 300 m/s for
every 0.1 increase in liquid water saturation. Also the attenuation of the
compressional waves is increased with increasing liquid water content. Two end
member models for compaction are evaluated to asses the importance of an
independent density measurement for an estimate of liquid pore water saturation
in snow with acoustic waves. The two end members correspond to no compaction at
all and to a melting sphere packing where the grains remain in contact. The
change of velocity for the first compressional wave was found to strongly
depend on the compaction model, while the velocity of the second compressional
wave mainly depends on liquid water saturation. Also the attenuation for both
compressional waves depends mainly on the liquid water saturation and only
little on the compaction model. Finally, a simple field experiment illustrates
the potential use of the method to estimate the liquid water content of snow
with acoustic sensors.",1502.01332v1
2015-06-30,Symmetry energy systematics and its high density behavior,"We explore the systematics of the density dependence of nuclear matter
symmetry energy in the ambit of microscopic calculations with various energy
density functionals, and find that the symmetry energy from subsaturation
density to supra-saturation density can be well determined by three
characteristic parameters of the symmetry energy at saturation density $\rho_0
$, i.e., the magnitude $E_{\text{sym}}({\rho_0 })$, the density slope $L$ and
the density curvature $K_{\text{sym}}$. This finding opens a new window to
constrain the supra-saturation density behavior of the symmetry energy from its
(sub-)saturation density behavior. In particular, we obtain $L=46.7 \pm 12.8$
MeV and $K_{\text{sym}}=-166.9 \pm 168.3$ MeV as well as $E_{\text{sym}}({2\rho
_{0}}) \approx 40.2 \pm 12.8$ MeV and $L({2\rho _{0}}) \approx 8.9 \pm 108.7$
MeV based on the present knowledge of $E_{\text{sym}}({\rho_{0}}) = 32.5 \pm
0.5$ MeV, $E_{\text{sym}}({\rho_c}) = 26.65 \pm 0.2$ MeV and $L({\rho_c}) =
46.0 \pm 4.5$ MeV at $\rho_{\rm{c}}= 0.11$ fm$^{-3}$ extracted from nuclear
mass and the neutron skin thickness of Sn isotopes. Our results indicate that
the symmetry energy cannot be stiffer than a linear density dependence.In
addition, we also discuss the quark matter symmetry energy since the deconfined
quarks could be the right degree of freedom in dense matter at high baryon
densities.",1506.09057v1
2015-08-23,Realizing fusion systems inside finite groups,"We show that every (not necessarily saturated) fusion system can be realized
as a full subcategory of the fusion system of a finite group. This result
extends our previous work \cite{Park2010} and complements the related result
\cite{LearyStancu2007} by Leary and Stancu.",1508.05667v1
2015-12-28,Si Nanowire - Array Source Gated Transistors,"Solution processed field-effect transistors based on single crystalline
silicon nanowires (Si NWs) with metal Schottky contacts are demonstrated. The
semiconducting layer was deposited from a nanowire ink formulation at room
temperature. The devices with 230nm thick SiO2 gate insulating layers show
excellent output current-voltage characteristics with early saturation voltages
under 2 volts, constant saturation current and exceptionally low dependence of
saturation voltage with the gate field. Operational principles of these devices
are markedly different from traditional ohmic-contact field-effect transistors
(FETs), and are explained using the source-gated transistor (SGT) concept in
which the semiconductor under the reverse biased Schottky source barrier is
depleted leading to low voltage pinch-off and saturation of drain current.
Device parameters including activation energy are extracted at different
temperatures and gate voltages to estimate the Schottky barrier height for
different electrode materials to establish transistor performance - barrier
height relationships. Numerical simulations are performed using 2D thin-film
approximation of the device structures at various Schottky barrier heights.
Without any adjustable parameters and only assuming low p-doping of the
transistor channel, the modelled data show exceptionally good correlation with
the measured data. From both experimental and simulation results, it is
concluded that source-barrier controlled nanowire transistors have excellent
potential advantages compared with a standard FET including mitigation of
short-channel effects, insensitivity in device operating currents to device
channel length variation, higher on/off ratios, higher gain, lower power
consumption and higher operational speed for solution processable and printable
nanowire electronics.",1512.08501v1
2016-03-01,Noisy Activation Functions,"Common nonlinear activation functions used in neural networks can cause
training difficulties due to the saturation behavior of the activation
function, which may hide dependencies that are not visible to vanilla-SGD
(using first order gradients only). Gating mechanisms that use softly
saturating activation functions to emulate the discrete switching of digital
logic circuits are good examples of this. We propose to exploit the injection
of appropriate noise so that the gradients may flow easily, even if the
noiseless application of the activation function would yield zero gradient.
Large noise will dominate the noise-free gradient and allow stochastic gradient
descent toexplore more. By adding noise only to the problematic parts of the
activation function, we allow the optimization procedure to explore the
boundary between the degenerate (saturating) and the well-behaved parts of the
activation function. We also establish connections to simulated annealing, when
the amount of noise is annealed down, making it easier to optimize hard
objective functions. We find experimentally that replacing such saturating
activation functions by noisy variants helps training in many contexts,
yielding state-of-the-art or competitive results on different datasets and
task, especially when training seems to be the most difficult, e.g., when
curriculum learning is necessary to obtain good results.",1603.00391v3
2016-03-16,Cellular approximations of fusion systems,"In this paper we study the cellularization of classifying spaces of saturated
fusion systems with respect to classifying spaces of finite $p$-groups. We give
explicit criteria to decide when a classifying space is cellular and we give
explicit computations for a family of exotic examples.",1603.05050v1
2016-07-03,The effects of the U$_\textrm{Y}$(1) Chern-Simons term and its baryonic contribution on matter asymmetries and hypermagnetic fields,"In this paper, we study the significance of the U$_\textrm{Y}$(1)
Chern-Simons term in general, and its baryonic contribution in particular, for
the evolution of the matter asymmetries and the hypermagnetic field in the
temperature range $100$GeV$\leq T \leq 10$TeV. We show that an initial helical
hypermagnetic field, denoted by $B_Y^{(0)}$, can grow matter asymmetries from
zero initial value. However, the growth which is initially quadratic with
respect to $B_Y^{(0)}$, saturates for values larger than a critical value. The
inclusion of the baryonic contribution reduces this critical value, leading to
smaller final matter asymmetries. Meanwhile, $B_Y(T_{EW})$ becomes slightly
larger than $B_Y^{(0)}$. In the absence of the U$_\textrm{Y}$(1) Chern-Simons
term, the final values of matter asymmetries grow without saturation.
Conversely, we show that an initial matter asymmetry can grow an initial seed
of hypermagnetic field, provided the Chern-Simons term is taken into account.
The growth process saturates when the matter asymmetry drops abruptly. When the
baryonic contribution is included, the saturation occurs at an earlier time,
and $B_Y (T_{EW})$ becomes larger. We also show the results can be within the
acceptable range of present day data, provided the inverse cascade process is
also taken into account.",1607.00650v3
2016-07-19,Time Reversal with Post-Equalization for OFDM without CP in Massive MIMO,"This paper studies the possibility of eliminating the redundant cyclic prefix
(CP) of orthogonal frequency division multiplexing (OFDM) in massive
multiple-input multiple-output systems. The absence of CP increases the
bandwidth efficiency in expense of intersymbol interference (ISI) and
intercarrier interference (ICI). It is known that in massive MIMO, different
types of interference fade away as the number of base station (BS) antennas
tends to infinity. In this paper, we investigate if the channel distortions in
the absence of CP are averaged out in the large antenna regime. To this end, we
analytically study the performance of the conventional maximum ratio combining
(MRC) and realize that there always remains some residual interference leading
to saturation of signal to interference (SIR). This saturation of SIR is
quantified through mathematical equations. Moreover, to resolve the saturation
problem, we propose a technique based on time-reversal MRC with zero forcing
multiuser detection (TR-ZF). Thus, the SIR of our proposed TR-ZF does not
saturate and is a linear function of the number of BS antennas. We also show
that TR-ZF only needs one OFDM demodulator per user irrespective of the number
of BS antennas; reducing the BS signal processing complexity significantly.
Finally, we corroborate our claims as well as analytical results through
simulations.",1607.05653v1
2016-09-16,On asymptotic dynamics for $L^2$ critical generalized KdV equations with a saturated perturbation,"In this paper, we consider the $L^2$ critical gKdV equation with a saturated
perturbation: $\partial_t u+(u_{xx}+u^5-\gamma u|u|^{q-1})_x=0$, where $q>5$
and $0<\gamma\ll1$. For any initial data $u_0\in H^1$, the corresponding
solution is always global and bounded in $H^1$. This equation has a family of
solitons, and our goal is to classify the dynamics near soliton. Together with
a suitable decay assumption, there are only three possibilities: (i) the
solution converges asymptotically to a solitary wave, whose $H^1$ norm is of
size $\gamma^{-2/(q-1)}$, as $\gamma\rightarrow0$; (ii) the solution is always
in a small neighborhood of the modulated family of solitary waves, but blows
down at $+\infty$; (iii) the solution leaves any small neighborhood of the
modulated family of the solitary waves. This extends the classification of the
rigidity dynamics near the ground state for the unperturbed $L^2$ critical gKdV
(corresponding to $\gamma=0$) by Martel, Merle and Rapha\""el. However, the
blow-down behavior (ii) is completely new, and the dynamics of the saturated
equation cannot be viewed as a perturbation of the $L^2$ critical dynamics of
the unperturbed equation. This is the first example of classification of the
dynamics near ground state for a saturated equation in this context. The cases
of $L^2$ critical NLS and $L^2$ supercritical gKdV, where similar
classification results are expected, are completely open.",1609.05146v3
2016-12-02,"Development of a hybrid learning system based on SVM, ANFIS and domain knowledge: DKFIS","This paper presents the development of a hybrid learning system based on
Support Vector Machines (SVM), Adaptive Neuro-Fuzzy Inference System (ANFIS)
and domain knowledge to solve prediction problem. The proposed two-stage Domain
Knowledge based Fuzzy Information System (DKFIS) improves the prediction
accuracy attained by ANFIS alone. The proposed framework has been implemented
on a noisy and incomplete dataset acquired from a hydrocarbon field located at
western part of India. Here, oil saturation has been predicted from four
different well logs i.e. gamma ray, resistivity, density, and clay volume. In
the first stage, depending on zero or near zero and non-zero oil saturation
levels the input vector is classified into two classes (Class 0 and Class 1)
using SVM. The classification results have been further fine-tuned applying
expert knowledge based on the relationship among predictor variables i.e. well
logs and target variable - oil saturation. Second, an ANFIS is designed to
predict non-zero (Class 1) oil saturation values from predictor logs. The
predicted output has been further refined based on expert knowledge. It is
apparent from the experimental results that the expert intervention with
qualitative judgment at each stage has rendered the prediction into the
feasible and realistic ranges. The performance analysis of the prediction in
terms of four performance metrics such as correlation coefficient (CC), root
mean square error (RMSE), and absolute error mean (AEM), scatter index (SI) has
established DKFIS as a useful tool for reservoir characterization.",1612.00585v1
2017-02-24,A Higher Structure Identity Principle,"We prove a Structure Identity Principle for theories defined on types of
$h$-level 3 by defining a general notion of saturation for a large class of
structures definable in the Univalent Foundations.",1702.07776v1
2017-09-14,A new look at interpretability and saturation,"We investigate the interpretability ordering $\trianglelefteq^*$ using
generalized Ehrenfeucht-Mostowski models. This gives a new approach to proving
inequalities and investigating the structure of types.",1709.04899v2
2018-01-03,A Novel Feature Descriptor for Image Retrieval by Combining Modified Color Histogram and Diagonally Symmetric Co-occurrence Texture Pattern,"In this paper, we have proposed a novel feature descriptors combining color
and texture information collectively. In our proposed color descriptor
component, the inter-channel relationship between Hue (H) and Saturation (S)
channels in the HSV color space has been explored which was not done earlier.
We have quantized the H channel into a number of bins and performed the voting
with saturation values and vice versa by following a principle similar to that
of the HOG descriptor, where orientation of the gradient is quantized into a
certain number of bins and voting is done with gradient magnitude. This helps
us to study the nature of variation of saturation with variation in Hue and
nature of variation of Hue with the variation in saturation. The texture
component of our descriptor considers the co-occurrence relationship between
the pixels symmetric about both the diagonals of a 3x3 window. Our work is
inspired from the work done by Dubey et al.[1]. These two components, viz.
color and texture information individually perform better than existing texture
and color descriptors. Moreover, when concatenated the proposed descriptors
provide significant improvement over existing descriptors for content base
color image retrieval. The proposed descriptor has been tested for image
retrieval on five databases, including texture image databases - MIT VisTex
database and Salzburg texture database and natural scene databases Corel 1K,
Corel 5K and Corel 10K. The precision and recall values experimented on these
databases are compared with some state-of-art local patterns. The proposed
method provided satisfactory results from the experiments.",1801.00879v1
2018-04-03,Fusion systems on p-groups of sectional rank 3,"We study saturated fusion systems on $p$-groups having sectional rank $3$ for
all odd primes $p$. For $p\geq 5$, we obtain a complete classification of the
ones that do not have any non-trivial normal $p$-subgroups.",1804.00883v2
2018-06-22,Saturation Effect on Photoionization-driven Broad Absorption Line Variability,"We study the saturation effect on broad absorption line (BAL) variability
through a variation phenomenon, which shows significant variation in Si IV BAL
but no, or only small, change in C IV BAL (hereafter Phenomenon I). First, we
explore a typical case showing Phenomenon I, quasar SDSS J153715.74+582933.9
(hereafter J1537+5829). We identify four narrow absorption line (NAL) systems
within its Si IV BAL and two additional NAL systems within its C IV BAL, and
confirm their coordinated weakening. Combining with the obvious strengthening
of the ionizing continuum, we attribute the BAL variability in J1537+5829 to
the ionization changes caused by the continuum variations. Secondly, a
statistical study based on multiobserved quasars from SDSS-I/II/III is
presented. We confirm that (1) the moderate anticorrelation between the
fractional variations of Si IV BALs and the continuum in 74 quasars that show
Phenomenon I and (2) the sample showing BAL variations tends to have larger
ionizing continuum variations. These results reveal the ubiquitous effect of
the continuum variability on Phenomenon I and BAL variation. We attribute the
relative lack of variation of C IV BALs in Phenomenon I to the saturation
effects. Nonetheless, these absorbers are not very optically thick in Si IV and
the ionization changes in response to continuum variations could be the main
driver of their variations. Finally, we find that the saturation effect on BAL
variability can well explain many phenomena of BAL variations that have been
reported before.",1806.08673v2
2018-07-02,Deep convolutional encoder-decoder networks for uncertainty quantification of dynamic multiphase flow in heterogeneous media,"Surrogate strategies are used widely for uncertainty quantification of
groundwater models in order to improve computational efficiency. However, their
application to dynamic multiphase flow problems is hindered by the curse of
dimensionality, the saturation discontinuity due to capillarity effects, and
the time-dependence of the multi-output responses. In this paper, we propose a
deep convolutional encoder-decoder neural network methodology to tackle these
issues. The surrogate modeling task is transformed to an image-to-image
regression strategy. This approach extracts high-level coarse features from the
high-dimensional input permeability images using an encoder, and then refines
the coarse features to provide the output pressure/saturation images through a
decoder. A training strategy combining a regression loss and a segmentation
loss is proposed in order to better approximate the discontinuous saturation
field. To characterize the high-dimensional time-dependent outputs of the
dynamic system, time is treated as an additional input to the network that is
trained using pairs of input realizations and of the corresponding system
outputs at a limited number of time instances. The proposed method is evaluated
using a geological carbon storage process-based multiphase flow model with a
2500-dimensional stochastic permeability field. With a relatively small number
of training data, the surrogate model is capable of accurately characterizing
the spatio-temporal evolution of the pressure and discontinuous CO2 saturation
fields and can be used efficiently to compute the statistics of the system
responses.",1807.00882v1
2018-08-03,Assessing saturation physics explanations of collectivity in small collision systems with the IP-Jazma model,"Experimental measurements in collisions of small systems from p+p to
p/d/3He+A at RHIC and the LHC reveal particle emission patterns that are
strikingly similar to those observed in A+A collisions. One explanation of
these patterns is the formation of small droplets of quark-gluon plasma
followed by hydrodynamic evolution. A geometry engineering program was proposed
[1] to investigate these emission patterns, and the experimental data from that
program in p+Au, d+Au, 3He+Au collisions for elliptic and triangular anisotropy
coefficients v2 and v3 follow the pattern predicted by hydrodynamic
calculations [2]. One alternative approach, referred to as initial-state
correlations, suggests that for small systems the patterns observed in the
final-state hadrons are encoded at the earliest moments of the collision, and
therefore require no final-state parton scattering or hydrodynamic evolution
[3,4]. Recently, new calculations using only initial-state correlations, in the
dilute-dense approximation of gluon saturation physics, reported striking
agreement with the v2 patterns observed in p/d/3He+Au data at RHIC [5]. The
reported results are counterintuitive and thus we aim here to reproduce some of
the basic features of these calculations. In this first investigation, we
provide a description of our model, IP-Jazma, and investigate its implications
for saturation scales, multiplicity distributions and eccentricities, reserving
for later work the analysis of momentum spectra and azimuthal anisotropies. We
find that our implementation of the saturation physics model reproduces the
results of the earlier calculation of the multiplicity distribution in d+Au
collisions at RHIC. However, our investigations, together with existing data,
call into question some of the essential elements reported in Ref. [5].",1808.01276v1
2018-09-06,Fusion systems on maximal class $3$-groups of rank two revisited,"We complete the determination of saturated fusion systems on maximal class
3-groups of rank two.",1809.01957v3
2018-11-18,The role of the thermal $f_0(500)$ in chiral symmetry restoration,"We show that the $\sigma/f_0(500)$ state with finite-temperature $T$
corrections to its spectral properties included, plays an essential role for
the description of the scalar susceptibility $\chi_S$, signaling chiral
symmetry restoration. First, we use the $O(4)$ Linear Sigma Model as a testbed
to derive the connection between $\chi_S$ and the $\sigma$ propagator and to
check the validity and reliability of the approach where $\chi_S$ is saturated
by the $\sigma/f_0(500)$ inverse self-energy, which we calculate at finite $T$
to one loop. A more accurate phenomenological description is achieved by
considering the saturation approach as given by the thermal $f_0(500)$ state
generated in Unitarized Chiral Perturbation Theory. Such approach allows to
describe fairly well recent lattice data within the uncertainty range given by
the UChPT parameters. Finally, we compare the UChPT saturated description with
one based on the Hadron Resonance Gas, for which the hadron mass dependences
are extracted from recent theoretical analysis. Several fits to lattice data
are performed, which confirm the validity of the thermal $f_0(500)$ saturated
approach and hence the importance of that thermal state for chiral symmetry
restoration.",1811.07304v2
2018-12-30,Van der Waals equation of state and PVT properties of real fluid,"It is shown that: in the case when two parameters of the Van der Waals
equation of state are defined from the critical temperature and pressure the
exact parametrical solution of the equations of the liquid-vapor phase
equilibrium of the Van der Waals fluid quantitatively describes the
experimental dependencies of the saturated pressure of argon on the temperature
and reduced vapor density, and it gives the quantitative description of the
temperature dependencies of the reduced densities near critical point. When the
parameters are defined from the critical pressure and density the parametric
solution describes quantitatively the experimental dependencies of the
saturated pressure of argon on the density and reduced temperature, it can
describe qualitatively the dependencies of the vapor and liquid densities on
the reduced temperature, and it gives the quantitative description of the
dependencies of the densities on the reduced temperature near critical point.
If the parameters are defined from the critical temperature and density then
the exact solution describes quantitatively the experimental dependencies of
the reduced saturated pressure of argon on the density and temperature, it
describes qualitatively the temperature dependencies of the vapor and liquid
densities of argon, and it gives the quantitative description of the
temperature dependencies of the vapor and liquid densities near critical point.
It is also shown that the Van der Waals equation of state describes
quantitatively the reference experimental PVT- data for the gas and
supercritical fluid states for the under-critical densities of argon, the
dependencies of the saturation pressure on the temperature and vapor density,
and the dependence of the vapor density of argon on temperature if the
parameters are defined from the critical pressure and temperature.",1812.11572v1
2019-05-01,Ultrafast two-dimensional field spectroscopy of terahertz intersubband saturable absorbers,"Intersubband (ISB) transitions in semiconductor multi-quantum well (MQW)
structures are promising candidates for the development of saturable absorbers
at terahertz (THz) frequencies. Here, we exploit amplitude and phase-resolved
two-dimensional (2D) THz spectroscopy on the sub-cycle time scale to observe
directly the saturation dynamics and coherent control of ISB transitions in a
metal-insulator MQW structure. Clear signatures of incoherent pump-probe and
coherent four-wave mixing signals are recorded as a function of the peak
electric field of the single-cycle THz pulses. All nonlinear signals reach a
pronounced maximum for a THz electric field amplitude of 11 kV/cm and decrease
for higher fields. We demonstrate that this behavior is a fingerprint of
THz-driven carrier-wave Rabi flopping. A numerical solution of the
Maxwell-Bloch equations reproduces our experimental findings quantitatively and
traces the trajectory of the Bloch vector. This microscopic model allows us to
design tailored MQW structures with optimized dynamical properties for
saturable absorbers that could be used in future compact semiconductor-based
single-cycle THz sources.",1905.00205v1
2019-05-13,Self-Diffusion of Glycerol in $γ$-Alumina Nanopores: Understanding the Effect of Pore Saturation on the Dynamics of Confined Polyalcohols,"Molecular Dynamics simulations of glycerol confined in $\gamma$-Al$_2$O$_3$
slit nanopores are used to explain controversial and inconsistent observations
reported in the literature regarding the dynamics of viscous fluids in confined
geometries. Analysing the effects of the degree of confinement and pore
saturation in this system, we found that the presence of the solid/liquid
interface and the liquid/gas interface in partially saturated pores are the
main contributors for the disruption of the hydrogen bond network of glycerol.
Despite the reduction of hydrogen bonds between glycerol molecules caused by
the presence of the solid, glycerol molecules near the solid surface can
establish hydrogen bonds with the hydroxyl groups of $\gamma$-Al$_2$O$_3$ that
significantly slow-down the dynamics of the confined fluid compared to the bulk
liquid. On the other hand, the disruption of the hydrogen bond network caused
by the liquid/gas interface in unsaturated pores reduces significantly the
number of hydrogen bonds between glycerol molecules and results in a faster
dynamics than in the bulk liquid. Therefore, we suggest that the discrepancies
reported in the literature are a consequence of measurements carried out under
different pore saturation conditions.",1905.05159v1
2019-05-19,Surface Water Formation on the Natural Surface under Super-saturation: from Local Water Balance to Air Pollutant Deposition,"Heterogeneous nucleation and subsequent growth of surface water occur on the
natural substrate when the water vapor concentration reached the point of
super-saturation. This study focuses on the parameterization of
super-saturation on the canopy-air interface by field observations monitoring
surface water formation (SWF) such as dew and frost in the evergreen shrub at
an urban cite during autumn and winter in 2015-2017. Here we show that both the
interfacial and vertical temperature differences ranged from 1 to 3 K and were
necessary but not sufficient for super-saturated condensation on the natural
surface. Excessive supplies of moisture must exist, continuously contribute to
the growth of the condensed water embryos, originate from both the local and
the external sources such as evapotranspiration and atmospheric advection
driven by the reduced air pressure, cause SWF not only on the ground soil but
also on the vegetation canopy at 1-2 m height. The super-saturation ratio is
mainly determined by the coefficient of thermophoresis deposition, which
approaches to 1. SWF on the natural surface is not only an indicator but also a
weak cleaner of air pollution. The downward thermophoresis deposition of fine
particle and droplets favors SWF and the scavenging of air pollutants. The
removal efficiency of the deposition flux during SWF event for [SO42-+NO3-] is
estimated by ~0.3 mmol (per [Ca2+] meq)/m2(per leaf area).",1905.07701v1
2019-06-05,Equation of state effects in the core collapse of a $20$-$M_\odot$ star,"Uncertainties in our knowledge of the properties of dense matter near and
above nuclear saturation density are among the main sources of variations in
multi-messenger signatures predicted for core-collapse supernovae (CCSNe) and
the properties of neutron stars (NSs). We construct 97 new finite-temperature
equations of state (EOSs) of dense matter that obey current experimental,
observational, and theoretical constraints and discuss how systematic
variations in the EOS parameters affect the properties of cold nonrotating NSs
and the core collapse of a $20\,M_\odot$ progenitor star. The core collapse of
the $20\,M_\odot$ progenitor star is simulated in spherical symmetry using the
general-relativistic radiation-hydrodynamics code GR1D where neutrino
interactions are computed for each EOS using the NuLib library. We conclude
that the effective mass of nucleons at densities above nuclear saturation
density is the largest source of uncertainty in the CCSN neutrino signal and
dynamics even though it plays a subdominant role in most properties of cold NS
matter. Meanwhile, changes in other observables affect the properties of cold
NSs, while having little effect in CCSNe. To strengthen our conclusions, we
perform six octant three-dimensional CCSN simulations varying the effective
mass of nucleons at nuclear saturation density. We conclude that neutrino
heating and, thus, the likelihood of explosion is significantly increased for
EOSs where the effective mass of nucleons at nuclear saturation density is
large.",1906.02009v1
2019-06-28,"Singular Perturbation Theory for a Finite-Dimensional, Discrete-Time Chi Nonlinear System","This paper develops the singular perturbation theory for a particular
discrete-time nonlinear system which models the saturating inductor buck
converter using cycle-by-cycle digital control.",1907.00060v1
2019-08-07,Saturated Free Algebras and Almost Indiscernible Theories,"We extend the concept of ""almost indiscernible theory"" introduced by Pillay
and Sklinos in [Bull. Symb. Log., 2015] (which was itself a modernization and
expansion of Baldwin and Shelah [Algebra Universalis, 1983]), to uncountable
languages and uncountable parameter sequences. Roughly speaking a theory $T$ is
almost indiscernible if some saturated model is in the algebraic closure of an
indiscernible set of sequences. We show that such a theory $T$ is
nonmultidimensional, superstable, and stable in all cardinals $\ge |T |$ . We
prove a structure theorem for sufficiently large $a$-models $M$: Theorem 2.10
which states that over a suitable base, $M$ is in the algebraic closure of an
independent set of realizations of weight one types (in possibly infinitely
many variables). We also explore further the saturated free algebras of Baldwin
and Shelah in both the countable and uncountable context. We study in
particular theories and varieties of $R$-modules, characterizing those rings
$R$ for which the free $R$-module on $|R|^+$ generators is saturated (Theorem
3.15), and pointing out a counterexample to a conjecture from Pillay-Sklinos
(Example 3.16).",1908.02712v5
2019-10-09,Modeling wavefields in saturated elastic porous media based on thermodynamically compatible system theory for multiphase mixtures,"A two-phase model and its application to wavefields numerical simulation are
discussed in the context of modeling of compressible fluid flows in elastic
porous media. The derivation of the model is based on a theory of
thermodynamically compatible systems and on a model of nonlinear
elastoplasticity combined with a two-phase compressible fluid flow model. The
governing equations of the model include phase mass conservation laws, a total
momentum conservation law, an equation for the relative velocities of the
phases, an equation for mixture distortion, and a balance equation for
porosity. They form a hyperbolic system of conservation equations that satisfy
the fundamental laws of thermodynamics. Two types of phase interaction are
introduced in the model: phase pressure relaxation to a common value and
interfacial friction. Inelastic deformations also can be accounted for by
source terms in the equation for distortion. The thus formulated model can be
used for studying general compressible fluid flows in a deformable
elastoplastic porous medium, and for modeling wave propagation in a saturated
porous medium. Governing equations for small-amplitude wave propagation in a
uniform porous medium saturated with a single fluid are derived. They form a
first-order hyperbolic PDE system written in terms of stress and velocities
and, like in Biot's model, predict three types of waves existing in real
fluid-saturated porous media: fast and slow longitudinal waves and shear waves.
For the numerical solution of these equations, an efficient numerical method
based on a staggered-grid finite difference scheme is used. The results of
solving some numerical test problems are presented and discussed",1910.04207v2
2019-10-18,Vapor drainage in the protolunar disk as the cause for the depletion in volatile elements of the Moon,"Lunar rocks are severely depleted in moderately volatile elements such as Rb,
K, and Zn relative to Earth. Identifying the cause of this depletion is
important for understanding how the Earth-Moon system evolved in the aftermath
of the Moon-forming giant impact. We measured the Rb isotopic compositions of
lunar and terrestrial rocks to understand why moderately volatile elements are
depleted in the Moon. Combining our new measurements with previous data reveals
that the Moon has an 87Rb/85Rb ratio higher than Earth by +0.16 permil. This
isotopic composition is consistent with evaporation of Rb into a vapor medium
that was ~99 percent saturated. Evaporation under this saturation can also
explain the previously documented isotopic fractionations of K, Ga, Cu and Zn
of lunar rocks relative to Earth. We show that a possible setting for achieving
the same saturation upon evaporation of elements with such diverse volatilities
is through viscous drainage of a partially vaporized protolunar disk onto
Earth. In the framework of an alpha-disk model, the alpha-viscosity needed to
explain the ~99% saturation calculated here is 0.001 to 0.01, which is
consistent with a vapor disk where viscosity is controlled by magnetorotational
instability.",1910.08530v1
2019-11-18,Pore network modeling of the effects of viscosity ratio and pressure gradient on steady-state incompressible two-phase flow in porous media,"We perform more than 6000 steady-state simulations with a dynamic pore
network model, corresponding to a large span in viscosity ratios and capillary
numbers. From these simulations, dimensionless quantities such as relative
permeabilities, residual saturations, mobility ratios and fractional flows are
computed. Relative permeabilities and residual saturations show many of the
same qualitative features observed in other experimental and modeling studies.
However, while other studies find that relative permeabilities converge to
straight lines at high capillary numbers we find that this is not the case when
viscosity ratios are different from 1. Our conclusion is that departure from
straight lines occurs when fluids mix rather than form decoupled flow channels.
Another consequence of the mixing is that computed fractional flow curves,
plotted against saturation, lie closer to the diagonal than they would
otherwise do. At lower capillary numbers, fractional flow curves have a
classical S-shape. Ratios of average mobility to their high-capillary number
limit values are also considered. These vary, roughly, between 0 and 1,
although values larger than 1 are also observed. For a given saturation and
viscosity ratio, the mobilities are not always monotonically increasing with
the pressure gradient. While increasing the pressure gradient mobilizes more
fluid and activates more flow paths, when the mobilized fluid is more viscous,
a reduction in average mobility may occur.",1911.07490v1
2019-12-09,Topological entropy of the set of generic points for $(α-β)$-shifts,"We prove that all ($\alpha$-$\beta$)-shifts with $0\le \alpha<1$ and
$\beta>2$ are saturated, that is, for any invariant measure, the topological
entropy of the set of generic points coincides with the metric entropy.",1912.03813v1
2020-02-16,Lofty Models of Peano Arithmetic,"If M is a nonstandard model of Peano Arithmetic, then M is lofty iff M has a
simple elementary extension that is recursively saturated. This had previously
been known for countable M.",2002.06639v2
2020-04-12,Heavy-hadron molecules from light-meson-exchange saturation,"In the effective field theory framework the interaction between two heavy
hadrons can be decomposed into a long- and a short-range piece. The long-range
piece corresponds to the one-pion-exchange potential and is relatively
well-known. The short-range piece is given by a series of contact-range
interactions with unknown couplings, which substitute the less well-known
short-range dynamics. While the general structure of the short-range potential
between heavy hadrons is heavily constrained from heavy-quark symmetry, the
couplings are still free parameters. Here we argue that the relative strength
and the sign of these couplings can be estimated from the hypothesis that they
are saturated by the exchange of light mesons, in particular the vector mesons
$\rho$ and $\omega$, i.e. from resonance saturation. However, we propose a
novel saturation procedure that effectively removes form-factor artifacts. From
this we can determine in which spin and isospin configurations the low-energy
constants are most attractive for specific two-heavy-hadron systems. In general
the molecular states with lower isospins and higher spins will be more
attractive and thus more probable candidates to form heavy-hadron molecules.
This pattern is compatible with the interpretation of the $X(3872)$ and
$P_c(4312/4440/4457)$ as molecular states, but it is not applicable to states
with maximum isospin like the $Z_c(3900/4020)$.",2004.05658v2
2020-04-14,Synchrotron-based pore-network modeling of two-phase flow in Nubian Sandstone and implications for capillary trapping of carbon dioxide,"Depleted oil fields in the Gulf of Suez (Egypt) can serve as geothermal
reservoirs for power generation using a CO2-Plume Geothermal (CPG) system,
while geologically sequestering CO2. This entails the injection of a
substantial amount of CO2 into the highly permeable brine-saturated Nubian
Sandstone. Numerical models of two-phase flow processes are indispensable for
predicting the CO2-plume migration at a representative geological scale. Such
models require reliable constitutive relationships, including relative
permeability and capillary pressure curves. In this study, quasi-static
pore-network modelling has been used to simulate the equilibrium positions of
fluid-fluid interfaces, and thus determine the capillary pressure and relative
permeability curves. Three-dimensional images with a voxel size of 0.65 micro
m3 of a Nubian Sandstone rock sample have been obtained using Synchrotron
Radiation X-ray Tomographic Microscopy. From the images, topological properties
of pores/throats were constructed. Using a pore-network model, we performed a
sequential primary drainage-main imbibition cycle of quasi-static invasion in
order to quantify (1) the CO2 and brine relative permeability curves, (2) the
effect of initial wetting-phase saturation (i.e. the saturation at the point of
reversal from drainage to imbibition) on the residual-trapping potential, and
(3) study the relative permeability-saturation hysteresis. The results improve
our understanding of the potential magnitude of capillary trapping in Nubian
Sandstone, essential for future field-scale simulations. Further, an initial
basin-scale assessment of CO2 storage capacity, which incorporates capillary
trapping, yields a range of 14-49 GtCO2 in Nubian Sandstone, Gulf of Suez
Basin.",2004.06792v1
2020-07-03,Properties of nuclear matter in relativistic Brueckner-Hartree-Fock model with high-precision charge-dependent potentials,"Properties of nuclear matter are investigated in the framework of
relativistic Brueckner-Hartree-Fock model with the latest high-precision
charge-dependent Bonn (pvCD-Bonn) potentials, where the coupling between pion
and nucleon is adopted as pseudovector form. These realistic pvCD-Bonn
potentials are renormalized to effective nucleon-nucleon ($NN$) interactions,
$G$ matrices. They are obtained by solving the Blankenbecler-Sugar (BbS)
equation in nuclear medium. Then, the saturation properties of symmetric
nuclear matter are calculated with pvCD-Bonn A, B, C potentials. The energies
per nucleon are around $-10.72$ MeV to $-16.83$ MeV at saturation densities,
$0.139$ fm$^{-3}$ to $0.192$ fm$^{-3}$ with these three potentials,
respectively. It clearly demonstrates that the pseudovector coupling between
pion and nucleon can generate reasonable saturation properties comparing with
pseudoscalar coupling. Furthermore, these saturation properties have strong
correlations with the tensor components of $NN$ potentials, i.e., the $D$-state
probabilities of deuteron, $P_D$ to form a relativistic Coester band. In
addition, the charge symmetry breaking (CSB) and charge independence breaking
(CIB) effects are also discussed in nuclear matter from the partial wave
contributions with these high-precision charge-dependent potentials. In
general, the magnitudes of CSB from the differences between $nn$ and $pp$
potentials are about $0.05$ MeV, while those of CIB are around $0.35$ MeV from
the differences between $np$ and $pp$ potentials. Finally, the equations of
state of asymmetric nuclear matter are also calculated with different asymmetry
parameters. It is found that the effective neutron mass is larger than the
proton one in neutron-rich matter.",2007.01726v1
2020-08-10,Inclusive prompt photon-jet correlations as a probe of gluon saturation in electron-nucleus scattering at small $x$,"We compute the differential cross-section for inclusive prompt photon$+$quark
production in deeply inelastic scattering of electrons off nuclei at small $x$
($e+A$ DIS) in the framework of the Color Glass Condensate effective field
theory. The result is expressed as a convolution of the leading order (in the
strong coupling $\alpha_{\mathrm{s}}$) impact factor for the process and
universal dipole matrix elements, in the limit of hard photon transverse
momentum relative to the nuclear saturation scale $Q_{s,A}(x)$. We perform a
numerical study of this process for the kinematics of the Electron-Ion Collider
(EIC), exploring in particular the azimuthal angle correlations between the
final state photon and quark. We observe a systematic suppression and
broadening pattern of the back-to-back peak in the relative azimuthal angle
distribution, as the saturation scale is increased by replacing proton targets
with gold nuclei. Our results suggest that photon+jet final states in inclusive
$e+A$ DIS at high energies are in general a promising channel for exploring
gluon saturation that is complementary to inclusive and diffractive dijet
production. They also provide a sensitive empirical test of the universality of
dipole matrix elements when compared to identical measurements in
proton-nucleus collisions. However because photon+jet correlations at small $x$
in EIC kinematics require jet reconstruction at small $k_\perp$, it will be
important to study their feasibility relative to photon-hadron correlations.",2008.04372v1
2020-08-24,Phase separation of saturated micellar network and its potential applications for nanoemulsification,"Phase separation of saturated micellar network, as a result of cross-linking
of branched micelles is established in mixed solutions of the anionic
surfactant sodium laurylethersulfate (SLES) and the zwitterionic cocamidopropyl
betaine (CAPB) in the presence of divalent counterions: Ca2+, Zn2+ and Mg2+.
The saturated network appears in the form of droplets, which are heavier than
water and sediment at the bottom of the vessel. In the case of Mg2+, the
sedimented drops coalesce and form a separate multiconnected micellar phase - a
supergiant surfactant micelle. For this phase, the rheological flow curves show
Newtonian and shear-thinning regions. The appearance/disappearance of the
Newtonian region marks the onset of formation of saturated network. The
addition of small organic molecules (fragrances) to the multiconnected micellar
phase leads to an almost spontaneous formation of oil-in-water nanoemulsion.
The nanoemulsification capacity of the multiconnected micellar phase decreases
with the rise of the volume of the oil molecule. A possible role of the network
junctions in the nanoemulsification process can be anticipated. The properties
of the multiconnected micellar phases could find applications in extraction and
separation processes, in drug/active delivery, and for nanoemulsification at
minimal energy input.",2008.10494v1
2020-10-16,"Supercards, Sunshines and Caterpillar Graphs","The vertex-deleted subgraph G-v, obtained from the graph G by deleting the
vertex v and all edges incident to v, is called a card of G. The deck of G is
the multiset of its unlabelled cards. The number of common cards b(G,H) of G
and H is the cardinality of the multiset intersection of the decks of G and H.
A supercard G+ of G and H is a graph whose deck contains at least one card
isomorphic to G and at least one card isomorphic to H. We show how maximum sets
of common cards of G and H correspond to certain sets of permutations of the
vertices of a supercard, which we call maximum saturating sets. We apply the
theory of supercards and maximum saturating sets to the case when G is a
sunshine graph and H is a caterpillar graph. We show that, for large enough n,
there exists some maximum saturating set that contains at least b(G,H)-2
automorphisms of G+, and that this subset is always isomorphic to either a
cyclic or dihedral group. We prove that b(G,H)<=2(n+1)/5 for large enough n,
and that there exists a unique family of pairs of graphs that attain this
bound. We further show that, in this case, the corresponding maximum saturating
set is isomorphic to the dihedral group.",2010.08266v1
2020-10-19,Effects of Parameter Norm Growth During Transformer Training: Inductive Bias from Gradient Descent,"The capacity of neural networks like the widely adopted transformer is known
to be very high. Evidence is emerging that they learn successfully due to
inductive bias in the training routine, typically a variant of gradient descent
(GD). To better understand this bias, we study the tendency for transformer
parameters to grow in magnitude ($\ell_2$ norm) during training, and its
implications for the emergent representations within self attention layers.
Empirically, we document norm growth in the training of transformer language
models, including T5 during its pretraining. As the parameters grow in
magnitude, we prove that the network approximates a discretized network with
saturated activation functions. Such ""saturated"" networks are known to have a
reduced capacity compared to the full network family that can be described in
terms of formal languages and automata. Our results suggest saturation is a new
characterization of an inductive bias implicit in GD of particular interest for
NLP. We leverage the emergent discrete structure in a saturated transformer to
analyze the role of different attention heads, finding that some focus locally
on a small number of positions, while other heads compute global averages,
allowing counting. We believe understanding the interplay between these two
capabilities may shed further light on the structure of computation within
large transformers.",2010.09697v5
2020-11-25,Global random walk solvers for fully coupled flow and transport in saturated/unsaturated porous media (extended version),"In this article, we present new random walk methods to solve flow and
transport problems in unsaturated/saturated porous media, including coupled
flow and transport processes in soils, heterogeneous systems modeled through
random hydraulic conductivity and recharge fields, processes at the field and
regional scales. The numerical schemes are based on global random walk
algorithms (GRW) which approximate the solution by moving large numbers of
computational particles on regular lattices according to specific random walk
rules. To cope with the nonlinearity and the degeneracy of the Richards
equation and of the coupled system, we implemented the GRW algorithms by
employing linearization techniques similar to the $L$-scheme developed in
finite element/volume approaches. The resulting GRW $L$-schemes converge with
the number of iterations and provide numerical solutions that are first-order
accurate in time and second-order in space. A remarkable property of the flow
and transport GRW solutions is that they are practically free of numerical
diffusion. The GRW solutions are validated by comparisons with mixed finite
element and finite volume solutions in one- and two-dimensional benchmark
problems. They include Richards' equation fully coupled with the
advection-diffusion-reaction equation and capture the transition from
unsaturated to saturated flow regimes. For completeness, we also consider
decoupled flow and transport model problems for saturated aquifers.",2011.12889v4
2020-12-09,Electromagnetic Eigenvalue Problems and Nonhermitian Effects in Linear and Saturable Scattering,"In this thesis we address a series of new problems in non-hermitian optical
scattering with increasing degrees of complexity.
  We develop the theory of reflectionless scattering modes, introducing a novel
and broad class of impedance-matched eigenproblems: for a given structure, find
the incident wavefronts and frequencies which are not partially reflected, but
are instead transmitted through the scatterer, or dissipated within it. We
analyze the relevant symmetry properties, and find that they support
exceptional points (EPs) which can be directly probed with steady-state
excitation.
  We study degenerate coherent perfect absorption (CPA EP), which is a specific
example of the new kind of EP mentioned above. We show that the CPA EP is
chiral in a ring resonator, and use this to design a resonator which
predominantly absorbs or reflects light, depending on the direction of
incidence.
  We extend CPA from cavities with a linear dielectric response to include the
saturating nonlinearity and dispersion of a two-level absorbing medium. We show
that the SALT algorithm in the single-mode regime can also be used to find the
saturable CPA modes through a simple mapping. We also clarify the bad-cavity
limit of dispersive but linear CPA, identifying new modes that are hybrids of
the cavity and atomic degrees of freedom.
  We present and solve the general problem of scattering from an arbitrary
cavity with a saturable two-level amplifying or absorbing medium, generalizing
the known phenomenology of bistability that has mainly been studied in
structures with little or no spatial complexity. We carefully analyze the
validity of approximations used for isolated resonances, and find that the
previously used inverse single-pole approximation requires some modification
for the case of scattering.",2012.05035v1
2021-01-07,Particle-in-cell Simulation of the Neutrino Fast Flavor Instability,"Neutrinos drive core-collapse supernovae, launch outflows from neutron star
merger accretion disks, and set the ratio of protons to neutrons in ejecta from
both systems that generate heavy elements in the universe. Neutrinos of
different flavors interact with matter differently, and much recent work has
suggested that fast flavor instabilities are likely ubiquitous in both systems,
but the final flavor content after the instability saturates has not been well
understood. In this work we present particle-in-cell calculations which follow
the evolution of all flavors of neutrinos and antineutrinos through saturation
and kinematic decoherence. We conduct one-dimensional three-flavor simulations
of neutrino quantum kinetics to demonstrate the outcome of this instability in
a few example cases. We demonstrate the growth of both axially symmetric and
asymmetric modes whose wavelength and growth rate match predictions from linear
stability analysis. Finally, we vary the number density, flux magnitude, and
flux direction of the neutrinos and antineutrinos and demonstrate that these
factors modify both the growth rate and post-saturation neutrino flavor
abundances. Weak electron lepton number (ELN) crossings in these simulations
produce both slow growth of the instability and little difference between the
flavor abundances in the initial and final states. In all of these calculations
the same number of neutrinos and antineutrinos change flavor, making the least
abundant between them the limiting factor for post-saturation flavor change.
Many more simulations and multi-dimensional simulations are needed to fully
probe the parameter space of the initial conditions.",2101.02745v2
2021-01-08,Simulating volume-controlled invasion of a non-wetting fluid in volumetric images using basic image processing tools,"A new algorithm is presented for simulating volume-controlled invasion of a
non-wetting phase into voxel images. This method is complementary to the
traditional morphological image opening method which mimics pressure-based
invasion. A key advantage of the volume-based approach is that all saturations
between 0 and 1 can obtained rather than the irregularly and widely spaced
saturation steps obtained by pressure-based methods. Because of the incremental
increases in saturation, it becomes possible to correctly predict defending
phase trapping, which is not the case when pressure-based steps are applied.
The algorithm is validated against morphological image opening and obtains near
perfect agreement at equal saturations as expected from theory. It is also
demonstrated that a volume-controlled capillary pressure curve can be obtained
that displays the characteristic jumps in capillary pressure, and moreover, the
envelop of peak pressures yields the pressure-based capillary pressure obtained
by morphological opening, so in fact the results of the proposed algorithm are
a superset of the morphological approach. Finally, results are compared to
multiphase lattice Boltzmann and qualitatively similar results were achieved in
substantially less time. The lattice Boltzmann method is more flexible in terms
of variable contact angle and inclusion of viscous effects, but for
quasi-static volume-based injection of a non-wetting fluid, the proposed method
is viable alternative.",2101.03240v1
2021-02-02,First Saturation Correction in High Energy Proton-Nucleus Collisions: I. Time evolution of classical Yang-Mills fields beyond leading order,"In high energy proton-nucleus collisions, the single- and double-inclusive
soft gluon productions at the leading order have been calculated and
phenomenologically studied in various approaches for many years. These studies
do not take into account the saturation and multiple rescatterings in the field
of the proton. The first saturation correction to these leading order results
(the terms that are enhanced by the combination $\alpha_s^2 \mu^2$, where
$\mu^2$ is the proton's color charge squared per unit transverse area) has not
been completely derived despite recent attempts using a diagrammatic approach.
This paper is the first in a series of papers towards analytically completing
the first saturation correction to physical observables in high energy
proton-nucleus collisions. Our approach is to analytically solve the classical
Yang-Mills equations in the dilute-dense regime using the Color Glass
Condensate effective theory and compute physical observables constructed from
classical gluon fields. In the current paper, the Yang-Mills equations are
solved perturbatively in the field of the dilute object (the proton).
Next-to-leading order and next-to-next-to-leading order analytic solutions are
explicitly constructed. A systematic way to obtain all higher order analytic
solutions is outlined",2102.01594v1
2021-03-02,An analytic BRDF for materials with spherical Lambertian scatterers,"We present a new analytic BRDF for porous materials comprised of spherical
Lambertian scatterers. The BRDF has a single parameter: the albedo of the
Lambertian particles. The resulting appearance exhibits strong back scattering
and saturation effects that height-field-based models such as Oren-Nayar cannot
reproduce.",2103.01618v1
2021-04-08,Active Power Control of Waked Wind Farms: Compensation of Turbine Saturation and Thrust Force Balance,"Active power control regulates the total power generated by wind farms with
the power consumed on the electricity grid. Due to wake effects, the available
power is reduced and turbulence is increased at downstream wind turbines. Such
effects lead to a design challenge for wind farm control, where the delicate
balance between supply and demand should be maintained, while considering the
load balancing in the wind turbine structures. We propose a control
architecture based on simple feedback controllers that adjusts the demanded
power set points of individual wind turbines to compensate for turbine
saturations and to balance thrust forces. For compensation purposes, the
dynamics of power tracking in the wind turbines is approximated as a pure
time-delay process, and the thrust force balance design is based on an
identified linear model of the turbines. In this paper, we show that the
proposed control architecture allows the generated power to track its reference
even when turbines saturate, while the thrust forces are balanced. In addition,
the result shows that the proposed power dispatch strategy, which considers
thrust force balance, also avoids turbine saturation, being thus beneficial for
energy production. The effectiveness of the proposed feedback controller is
demonstrated using high-fidelity computational fluid dynamics simulations of a
small wind farm.",2104.03894v1
2021-04-24,On loop spaces with marking,"An analogous construction of simplicial homotopy group for Kan complex can be
applied to saturated complicial sets to give monoids. In this paper, we
investigate how the construction of loop spaces of Kan complexes lifts to the
complicial setting and relates to such monoids.",2104.11860v1
2021-04-27,Mitigation of Saturated Cut-sets During Multiple Outages to Enhance Power System Security,"Ensuring reliable operation of large power systems subjected to multiple
outages is a challenging task because of the combinatorial nature of the
problem. Traditional approaches for security assessment are often limited by
their scope and/or speed, resulting in missing of critical contingencies that
could lead to cascading failures. This paper proposes a two-component
methodology to enhance power system security. The first component combines an
efficient algorithm to detect cut-set saturation (called the feasibility test
(FT) algorithm) with real-time contingency analysis (RTCA) to create an
integrated corrective action (iCA), whose goal is to secure the system against
cut-set saturation as well as critical branch overloads. The second component
only employs the results of the FT to create a relaxed corrective action (rCA)
to secure the system against post-contingency cut-set saturation. The first
component is more comprehensive, but the latter is computationally more
efficient. The effectiveness of the two components is evaluated based upon the
number of cascade triggering contingencies alleviated, and the computation
time. The results obtained by analyzing different case-studies on the IEEE
118-bus and 2000-bus synthetic Texas systems indicate that the proposed
two-component methodology successfully enhances the scope and speed of power
system security assessment during multiple outages.",2104.13445v2
2021-05-09,Probabilistic forecast of multiphase transport under viscous and buoyancy forces in heterogeneous porous media,"In this study, we develop a probabilistic approach to map the parametric
uncertainty to the output state uncertainty in first-order hyperbolic
conservation laws. We analyze this problem for nonlinear immiscible two-phase
transport in heterogeneous porous media in the presence of a stochastic
velocity field. The uncertainty in the velocity field can arise from the
incomplete description of either porosity field, injection flux, or both. The
uncertainty in the total-velocity field leads to the spatiotemporal uncertainty
in the saturation field. Given information about the spatial/temporal
statistics of the correlated heterogeneity, we leverage method of distributions
to derive deterministic equations that govern the evolution of single-point CDF
of saturation. Unlike Buckley Leverett equation, the equation for the raw CDF
function is linear in space and time. Hereby, we give routes to circumventing
the computational cost of Monte Carlo scheme while obtaining the full
statistical description of saturation. We conduct a set of numerical
experiments and compare statistics of saturation computed with the method of
distributions, against those obtained using the statistical moment equations
approach and kernel density estimation post-processing of high-resolution Monte
Carlo simulations. This comparison demonstrates that the CDF equations remain
accurate over a wide range of statistical properties, i.e. standard deviation
and correlation length of the underlying random fields, while the corresponding
low-order statistical moment equations significantly deviate from Monte Carlo
results, unless for very small values of standard deviation and correlation
length.",2105.03988v1
2021-05-16,On the theory of Biot-patchy-squirt mechanism for wave propagation in partially saturated double-porosity medium,"Reservoir rocks are usually composed of a coherent heterogeneous porous
matrix saturated by multiple fluids. At long wavelength limit, the composite
material of solid skeleton is usually regarded as homogeneous media. However,
at grain scale or high loading rate, non-uniform fluid flow at internal
interface of heterogeneity plays essential role in wave dispersion and
attenuation. Formulating wave propagation in partially saturated and fractured
rocks is challenging and of great interests in geoscience. Here we raise a
Biot-patchy-squirt (BIPS) model to characterize wave dispersion/attenuation in
fractured poroelastic media saturated by two immiscible fluids. BIPS model
incorporates the mechanism of local fluid-interface flow (LFIF) and squirt flow
into global fluid flow simultaneously. Theoretical analysis show that wave
attenuations caused by viscous dissipation, squirt flow and patchy interface
vibration are distinct from each other. BIPS is intrinsically consistent with
Biot theory, squirt and LFIF model and reduces to such mechanism in limiting
conditions. More interestingly, numerical results show that coupling between
LFIF and squirt flow is of evident importance to P-wave dispersion and
attenuation. Comparisons with experimental data indicate that BIPS model is
computationally reliable and in reasonably good agreement with experimental
data. This study advance our understanding of the fundamental physics of wave
propagation in natural reservoir rocks and push forward the potential
applications of the triple dispersion/attenuation mechanism to wave velocity
estimation in deep earth.",2105.07429v2
2021-06-12,Stiffening of matter in quark-hadron continuity,"We discuss stiffening of matter in quark-hadron continuity. We introduce a
model that relates quark wave functions in a baryon and the occupation
probability of states for baryons and quarks in dense matter. In a dilute
regime, the confined quarks contribute to the energy density through the masses
of baryons, but do not directly contribute to the pressure; hence, the
equations of state are very soft. This dilute regime continues until the low
momentum states for quarks get saturated; this may happen even before baryons
fully overlap, possibly at density slightly above the nuclear saturation
density. After the saturation the pressure grows rapidly while changes in
energy density are modest, producing a peak in the speed of sound. If we use
baryonic descriptions for quark distributions near the Fermi surface, we reach
a description similar to the quarkyonic matter model of McLerran and Reddy.
With a simple adjustment of quark interactions to get the nucleon mass, our
model becomes consistent with the constraints from 1.4-solar mass neutron
stars, but the high density part is too soft to account for two-solar mass
neutron stars. We delineate the relation between the saturation effects and
short range interactions of quarks, suggesting interactions that leave low
density equations of state unchanged but stiffen the high density part.",2106.06687v3
2021-06-21,The importance of kinematic twists and genuine saturation effects in dijet production at the Electron-Ion Collider,"We compute the differential yield for quark anti-quark dijet production in
high-energy electron-proton and electron-nucleus collisions at small $x$ as a
function of the relative momentum $\boldsymbol{P}_\perp$ and momentum imbalance
$\boldsymbol{k}_\perp$ of the dijet system for different photon virtualities
$Q^2$, and study the elliptic and quadrangular anisotropies in the relative
angle between $\boldsymbol{P}_\perp$ and $\boldsymbol{k}_\perp$. We review and
extend the analysis in [1], which compared the results of the Color Glass
Condensate (CGC) with those obtained using the transverse momentum dependent
(TMD) framework. In particular, we include in our comparison the improved TMD
(ITMD) framework, which resums kinematic power corrections of the ratio
$k_\perp$ over the hard scale $Q_\perp$. By comparing ITMD and CGC results we
are able to isolate genuine higher saturation contributions in the ratio
$Q_s/Q_\perp$ which are resummed only in the CGC. These saturation
contributions are in addition to those in the Weizs\""ackerWilliams gluon TMD
that appear in powers of $Q_s/k_\perp$. We provide numerical estimates of these
contributions for inclusive dijet production at the future Electron-Ion
Collider, and identify kinematic windows where they can become relevant in the
measurement of dijet and dihadron azimuthal correlations. We argue that such
measurements will allow the detailed experimental study of both kinematic power
corrections and genuine gluon saturation effects.",2106.11301v3
2021-07-29,Maximize the Foot Clearance for a Hopping Robotic Leg Considering Motor Saturation,"A hopping leg, no matter in legged animals or humans, usually behaves like a
spring during the periodic hopping. Hopping like a spring is efficient and
without the requirement of complicated control algorithms. Position and force
control are two main methods to realize such a spring-like behaviour. The
position control usually consumes the torque resources to ensure the position
accuracy and compensate the tracking errors. In comparison, the force control
strategy is able to maintain a high elasticity. Currently, the position and
force control both leads to the discount of motor saturation ratio as well as
the bandwidth of the control system, and thus attenuates the performance of the
actuator. To augment the performance, this letter proposes a motor saturation
strategy based on the force control to maximize the output torque of the
actuator and realize the continuous hopping motion with natural dynamics. The
proposed strategy is able to maximize the saturation ratio of motor and thus
maximize the foot clearance of the single leg. The dynamics of the two-mass
model is utilized to increase the force bandwidth and the performance of the
actuator. A single leg with two degrees of freedom is designed as the
experiment platform. The actuator consists of a powerful electric motor, a
harmonic gear and encoder. The effectiveness of this method is verified through
simulations and experiments using a robotic leg actuated by powerful high
reduction ratio actuators.",2107.13717v2
2021-08-04,Forced Imbibition in Stratified Porous Media: Fluid Dynamics and Breakthrough Saturation,"Imbibition, the displacement of a nonwetting fluid by a wetting fluid, plays
a central role in diverse energy, environmental, and industrial processes.
While this process is typically studied in homogeneous porous media with
uniform permeabilities, in many cases, the media have multiple parallel strata
of different permeabilities. How such stratification impacts the fluid dynamics
of imbibition, as well as the fluid saturation after the wetting fluid breaks
through to the end of a given medium, is poorly understood. We address this gap
in knowledge by developing an analytical model of imbibition in a porous medium
with two parallel strata, combined with a pore network model that explicitly
describes fluid crossflow between the strata. By numerically solving these
models, we examine the fluid dynamics and fluid saturation left after
breakthrough. We find that the breakthrough saturation of nonwetting fluid is
minimized when the imposed capillary number Ca is tuned to a value Ca$^*$ that
depends on both the structure of the medium and the viscosity ratio between the
two fluids. Our results thus provide quantitative guidelines for predicting and
controlling flow in stratified porous media, with implications for water
remediation, oil/gas recovery, and applications requiring moisture management
in diverse materials.",2108.02051v1
2021-08-11,The Bridge Lemmas between Equivalent Fell Bundles and its Applications,"In this paper, we prove that the induced representation theories of two
equivalent Fell bundles are essentially identical; and we apply our results to
carry the induced representation theory and imprimitivity theorems of saturated
Fell bundles to arbitrary Fell bundles.",2108.05003v1
2021-08-26,Fusion Systems on a Sylow $p$-subgroup of $\mathrm{G}_2(p^n)$ or $\mathrm{PSU}_4(p^n)$,"For any prime $p$ and $S$ a $p$-group isomorphic to a Sylow $p$-subgroup of
$\mathrm{G}_2(p^n)$ or $\mathrm{PSU}_4(p^n)$ with $n\in\mathbb{N}$, we
determine all saturated fusion systems supported on $S$ up to isomorphism.",2108.11691v1
2021-08-27,Multiple moist climate equilibrium states on arid rocky M-dwarf planets: A last-saturation tracer analysis,"Terrestrial-type exoplanets orbiting nearby red dwarf stars (M dwarfs) are
the first potentially habitable exoplanets suitable for atmospheric
characterization in the near future. Understanding the stability of water in
cold-trap regions on such planets is critical because it directly impacts
transmission spectroscopy observations, the global energy budget, and long-term
surface water evolution. Here we diagnose the humidity distribution in
idealized general circulation model (GCM) simulations of terrestrial-type
exoplanets. We use the `tracer of last saturation' technique to study the
saturation statistics of air parcels. We find that on synchronously rotating
planets, the water vapor abundance in the nightside upper troposphere depends
weakly on planetary rotation, while more water vapor builds up in the nightside
lower troposphere on fast-rotating planets. We then discuss how last-saturation
statistics can elucidate the multiple moist climate equilibrium states on
synchronously and asynchronously rotating arid planets. We show that the
multiple moist climate states arise from the cold-trapping competition between
the substellar upper atmosphere and cold surface regions. We find that fast
synchronously rotating planets tend to trap surface water on the nightside as a
result of their weak atmospheric and strong surface cold traps compared to the
slow rotating case. These results elucidate the nature of the water cycle on
arid rocky exoplanets and will aid interpretation of atmospheric observations
in the future.",2108.12458v1
2021-08-30,Accurate electron beam phase-space theory for ionisation injection schemes driven by laser pulses,"After the introduction of the ionization-injection scheme in Laser Wake Field
Acceleration and of related high-quality electron beam generation methods as
two-color or the Resonant Multi Pulse Ionization injection, the theory of
thermal emittance by C. Schroeder et al, has been used to predict the beam
normalised emittance obtainable with those schemes. In this manuscript we
recast and extend such a theory, including both higher order terms in the
polinomial laser field expansion and non polinomial corrections due to the
onset of saturation effects in a single cycle. Also, a very accurate model for
predicting the cycle-averaged $3D$ momentum distribution of the extracted
electrons, including saturation and multi-process events, is proposed and
tested. We show that our theory is very accurate for the selected processes of
Kr$^{8^+\rightarrow10^+}$ and Ar$^{8^+\rightarrow10^+}$, resulting in a a
maximum error below $1\%$ even in deep saturation regime. This highly accurate
prediction of the beam phase-space can be implemented e.g., in laser-envelope
Particle in Cell (PIC) or hybrid PIC-fluid codes, to correctly mimic the
cycle-averaged momentum distribution without the need of resolving the
intra-cycle dynamics. Finally, we introduce further spatial averaging with
Gaussian longitudinal and transverse laser profiles, obtaining expressions for
the whole-beam emittance that fits with Monte Carlo simulations in a saturated
regime, too.",2108.13044v2
2021-10-25,A Nearly Optimal Chattering Reduction Method of Sliding Mode Control With an Application to a Two-wheeled Mobile Robot,"The problem we focus on in this paper is to find a nearly optimal sliding
mode controller of continuous-time nonlinear multiple-input multiple-output
(MIMO) systems that can both reduce chattering and minimize the cost function,
which is a measure of the performance index of dynamics systems. First, the
deficiency of chattering in traditional SMC and the quasi-SMC method are
analyzed in this paper. In quasi-SMC, the signum function of the traditional
SMC is replaced with a continuous saturation function. Then, a chattering
reduction algorithm based on integral reinforcement learning (IRL) is proposed.
Under an initial sliding mode controller, the proposed method can learn the
nearly optimal saturation function using policy iteration. To satisfy the
requirement of the learned saturation function, we treat the problem of
training the saturation function as the constraint of an optimization problem.
The online neural network implementation of the proposed algorithm is presented
based on symmetric radius basis functions and a regularized batch least-squares
(BLS) algorithm to train the control law in this paper. Finally, two examples
are simulated to verify the effectiveness of the proposed method. The second
example is an application to a real-world dynamics model -- a two-wheeled
variable structure robot.",2110.12706v1
2021-12-20,Space-time upscaling of reactive transport in porous media,"Reactive transport in saturated/unsaturated porous media is numerically
upscaled to the space-time scale of a hypothetical measurement through
coarse-grained space-time (CGST) averages. The reactive transport is modeled at
the fine-grained Darcy scale by the actual number of molecules involved in
reactions which undergo advective and diffusive movements described by global
random walk (GRW) simulations. The CGST averages verify identities similar to a
local balance equation which allow us to derive expressions for the flow
velocity and the intrinsic diffusion coefficient in terms of averaged
microscopic quantities. The latter are further used to verify the CGST-GRW
numerical approach. The upscaling approach is applied to biodegradation
processes in saturated aquifers and variably saturated soils and the CGST
averages are compared to classical volume averages. One finds that if the
process is characterized by slow variations in time, as in homogeneous reaction
systems, the differences between the two averages are negligible. Instead, the
differences are significant and can be extremely large in simulations of
time-dependent biodegradation processes in both soils and saturated aquifers.",2112.10692v5
2021-12-27,Sharply doubly transitive groups with saturation conditions,"A number of conditions were found under which a sharply doubly transitive
permutation group has an abelian normal divider.",2112.13526v2
2021-12-30,Abstract key polynomials and distinguished pairs,"In this paper, for a henselian valued field $(K,v)$ of arbitrary rank and an
extension $w$ of $v$ to $K(X),$ we use abstract key polynomials for $w$ to
obtain distinguished pairs and saturated distinguished chains.",2112.15123v1
2022-02-18,Detecting few-body quantum chaos: out-of-time ordered correlators at saturation,"We study numerically and analytically the time dependence and saturation of
out-of-time ordered correlators (OTOC) in chaotic few-body quantum-mechanical
systems: quantum Henon-Heiles system (weakly chaotic), BMN matrix quantum
mechanics (strongly chaotic) and Gaussian random matrix ensembles. The growth
pattern of quantum-mechanical OTOC is complex and nonuniversal, with no clear
exponential regime at relevant timescales in any of the examples studied (which
is not in contradiction to the exponential growth found in the literature for
many-body systems, i.e. fields). On the other hand, the plateau (saturated)
value of OTOC reached at long times decreases with temperature in a simple and
universal way: $\exp(\mathrm{const.}/T^2)$ for strong chaos (including random
matrices) and $\exp(\mathrm{const.}/T)$ for weak chaos. For small matrices and
sufficiently complex operators, there is also another, high-temperature regime
where the saturated OTOC grows with temperature. Therefore, the plateau OTOC
value is a meaningful indicator of few-body quantum chaos. We also discuss some
general consequences of our findings for the AdS/CFT duality.",2202.09443v3
2022-03-28,Embedding short-range correlations in relativistic density functionals through quasi-deuterons,"The formation of clusters at sub-saturation densities constitutes an
essential feature for a reliable modelization of the nuclear matter equation of
state (EoS). Phenomenological models that make use of energy density
functionals (EDFs) offer a convenient approach to account for the presence of
these bound states of nucleons when introduced as additional degrees of
freedom. However, in these models clusters dissolve, by construction, when the
nuclear saturation density is approached from below, revealing inconsistencies
with recent findings that evidence the existence of short-range correlations
(SRCs) even at larger densities.
  In this work, within the EDF framework, a novel approach is proposed to embed
SRCs within a relativistic mean-field model with density dependent couplings.
This is realized through the introduction of suitable in-medium modifications
of the cluster binding energy shifts, which are responsible for describing the
cluster dissolution. As a first exploratory step, the example of a
quasi-deuteron within the generalized relativistic density functional approach
is investigated.
  For the first time, suitable parameterizations of the cluster mass shift at
zero temperature are derived for all baryon densities. They are constrained by
experimental results for the effective deuteron fraction in nuclear matter near
saturation and by microscopic many-body calculations in the low-density limit.
The strength of the deuteron-meson couplings is assessed to be of crucial
importance. The findings of the present study represent a first step to improve
the description of nuclear matter and its EoS at supra-saturation densities in
EDFs by considering correlations in an effective way. Novel effects on some
thermodynamic quantities, such as the matter incompressibility, the symmetry
energy and its slope, are finally discerned and discussed.",2203.14635v1
2022-04-24,A generalization of Alperin fusion theorem and its applications,"Let $\mathcal F$ be a saturated fusion system on a finite $p$-group $S$, and
let $P$ be a strongly $\mathcal F$-closed subgroup of $S$. We define the
concept ``$\mathcal F$-essential subgroups with respect to $P$"" which are some
proper subgroups of $P$ satisfying some technical conditions, and show that an
$\mathcal F$-isomorphism between subgroups of $P$ can be factorised by some
automorphisms of $P$ and $\mathcal F$-essential subgroups with respect to $P$.
When $P$ is taken to be equal $S$, Alperin-Goldschmidt fusion theorem can be
obtained as a special case. We also show that $P\unlhd \mathcal F$ if and only
if there is no $\mathcal F$-essential subgroup with respect to $P$. The
following definition is made: a $p$-group $P$ is strongly resistant in
saturated fusion systems if $P\unlhd \mathcal F$ whenever there is an over
$p$-group $S$ and a saturated fusion system $\mathcal F$ on $S$ such that $P$
is strongly $\mathcal F$-closed. It is shown that several classes of $p$-groups
are strongly resistant, which appears as our third main theorem. We also give a
new necessary and sufficient criteria for a strongly $\mathcal F$-closed
subgroup to be normal in $\mathcal F$. These results are obtained as a
consequences of developing a theory of quasi and semi-saturated fusion systems,
which seems to be interesting for its own right.",2204.11303v2
2022-06-07,On-Surface Synthesis of a Pure and Long-Range-Ordered Titanium(IV)-Porphyrin Contact Layer on Titanium Dioxide,"We show the possibility of tailoring the molecular arrangement, as well as
the chemical and structural modifications, of porphyrins at the monolayer
saturation coverage on TiO2(110) by Synchrotron photoemission, electron
diffraction, STM topography and DFT calculations. Free-base
tetra-phenyl-porphyrins (2H-TPP) adsorb on the oxygen rows, where they can
spontaneously capture two additional hydrogen atoms at their iminic nitrogens
(4H-TPP). Both 2H-TPP and 4H-TPP molecules aggregate into a commensurate phase
at the saturation coverage of one monolayer. Upon sample heating, a
self-metalation reaction sets in at 100C, yielding full metalation of the
saturated monolayer at ~200C. The Ti atoms are extracted from the substrate
and, by simultaneous dehydrogenation of the pyrrolic nitrogen atoms,
incorporated into the porphyrin macrocycle, where they remain coordinated to
two oxygen atoms underneath. Neither the adsorption geometry (on-bridge, atop
the oxygen rows) nor the molecular arrangement change across the
self-metalation transition up to 300C. On one side, the robustness of this
saturation phase makes it a promising system for its implementation into
applications for photocatalysis and photovoltaic devices. On the other side,
the possible manifestation of metal exchange with the very reactive Ti atoms
must be taken into account when designing porphyrin-sensitized solar cells
since the critical temperature for the onset of self-metalation is very close
to the normal operating temperature of photovoltaic devices.",2206.03175v2
2022-07-23,Saturating the one-axis twisting quantum Cramér-Rao bound with a total spin readout,"We show that the lowest quantum Cram\'{e}r-Rao bound achievable in
interferometry with a one-axis twisted spin coherent state is saturated by the
asymptotic method of moments error of a protocol that uses one call to the
one-axis twisting, one call to time-reversed one-axis twisting, and a final
total spin measurement (i.e., a twist-untwist protocol). The result is derived
by first showing that the metrological phase diagram for one-axis twisting is
asymptotically characterized by a single quantum Fisher information value
$N(N+1)/2$ for all times, then constructing a twist-untwist protocol having a
method of moments error that saturates this value. The case of finite-range
one-axis twisting is similarly analyzed, and a simple functional form for the
metrological phase diagram is found in both the short-range and long-range
interaction regimes. Numerical evidence suggests that the finite-range
analogues of twist-untwist protocols can exhibit a method of moments error that
asymptotically saturates the lowest quantum Cram\'{e}r-Rao bound achievable in
interferometry with finite-range one-axis twisted spin coherent states for all
interaction times.",2207.11462v3
2022-09-28,Spiral instabilities: Mode saturation and decay,"This paper continues a series reporting different aspects of the behaviour of
disc galaxy simulations that support spiral instabilities. The focus in this
paper is to demonstrate how linear spiral instabilities saturate and decay, and
how the properties of the disc affect the limiting amplitude of the spirals.
Once again, we employ idealized models that each possess a single instability
that we follow until it has run its course. Remarkably, we find a tight
correlation between the growth rate of the mode and its limiting amplitude,
albeit from only six simulations. We show that non-linear orbit deflections
near corotation cause the mode to saturate, and that the more time available in
a slowly-growing mode creates the critical deflections at lower amplitude. We
also find that scattering at the inner Lindblad resonance is insignificant
until after the mode has saturated. Our objective in this series of papers,
which we believe we have now achieved, has been to develop a convincing and
well-documented account of the physical behaviour of the spiral patterns that
have been observed in simulations by others, and by ourselves, for many
decades. Understanding the simulations is an important step towards the greater
objective, which is to find observational evidence from galaxies that could
confront the identified mechanism.",2209.14256v2
2022-10-01,Spontaneous symmetry breaking and ghost states supported by the fractional nonlinear Schrödinger equation with focusing saturable nonlinearity and PT-symmetric potential,"We report a novel spontaneous symmetry breaking phenomenon and ghost states
existed in the framework of the fractional nonlinear Schr\""odinger (FNLS)
equation with focusing saturable nonlinearity and PT-symmetric potential. The
continuous asymmetric soliton branch bifurcates from the fundamental symmetric
one as the power exceeds some critical value. Intriguingly, the symmetry of
fundamental solitons is broken into two branches of asymmetry solitons (alias
ghost states) with complex conjugate propagation constants, which is solely in
fractional media. Besides, the dipole (antisymmetry) and tripole solitons are
also studied numerically. Moreover, we analyze the influences of fractional
L\'evy index and saturable nonlinear parameters on the symmetry breaking of
solitons in detail. And the stability of fundamental soliton, asymmetric,
dipole and tripole solitons are explored via the linear stability analysis and
direct propagations. Moreover, we explore the elastic/semi-elastic collision
phenomena between symmetric and asymmetric solitons. Meanwhile, we find the
stable excitations from the fractional diffraction with saturation nonlinearity
to integer-order diffraction with Kerr nonlinearity via the adiabatic
excitations of parameters. These results will provide some theoretical basis
for the study of spontaneous symmetry breaking phenomena and related physical
experiments in the fractional media with PT-symmetric potentials.",2210.00277v1
2022-10-18,Effective Constitutive Relations for Simulating CO2 Capillary Trapping in Heterogeneous Reservoirs with Fluvial Sedimentary Architecture,"Carbon dioxide (CO2) storage reservoirs commonly exhibit sedimentary
architecture that reflects fluvial deposition. The heterogeneity in
petrophysical properties arising from this architecture influences the dynamics
of injected CO2. We previously used a geocellular modeling approach to
represent this heterogeneity, including heterogeneity in constitutive
saturation relationships. The dynamics of CO2 plumes in fluvial reservoirs was
investigated during and after injection. It was shown that small-scale
(centimeter to meter) features play a critical role in capillary trapping
processes and have a primary effect on physical- and dissolution-trapping of
CO2, and on the ultimate distribution of CO2 in the reservoir. Heterogeneity in
saturation functions at that small scale enhances capillary trapping (snap
off), creates capillary pinning, and increases the surface area of the plume.
The understanding of these small-scale trapping processes from previous work is
here used to develop effective saturation relationships that represent, at a
larger scale, the integral effect of these processes. While it is generally not
computationally feasible to represent the small-scale heterogeneity directly in
a typical reservoir simulation, the effective saturation relationships for
capillary pressure and relative permeability presented here, along with an
effective intrinsic permeability, allow better representation of the total
physical trapping at the scale of larger model grid cells, as typically used in
reservoir simulations, and thus the approach diminishes limits on cell size and
decreases simulation time in reservoir simulations.",2210.10124v1
2022-10-19,Control Design under Actuator Saturation and Multi-Rate Sampling,"The problem of designing a stabilizing feedback controller in the presence of
saturating actuators and multi-rate (asynchronous) aperiodic state measurements
is studied. Specifically, we consider a scenario in which measurements of the
plant states are collected at the controller end in a sporadic and asynchronous
fashion. A hybrid controller is used to perform a fusion of measurements
sampled at different times. In between sampling events, the controller behaves
as a copy of the plant and provides a feedback control signal based on the
reconstruction of the plant state. The presence of saturation at the plant
input limits the value of the components of this signal to a bounded range.
When a new measurement is available, the controller state undergoes an
instantaneous jump. The resulting system is augmented with a set of timers
triggering the arrival of new measurements and analyzed in a hybrid systems
framework. Relying on Lyapunov tools for hybrid systems and techniques for
control design under saturation, we propose sufficient conditions in the form
of matrix inequalities to ensure regional exponential stability of a closed-set
containing the origin of the plant, i.e., exponential stability with a
guaranteed region of attraction. Specifically, explicit estimates of the basin
of attraction are provided in the form of ellipsoidal sets. Leveraging those
conditions, a design procedure based on semidefinite programming is proposed to
design a stabilizing controller with maximized size of the basin attraction.
The effectiveness of the proposed methodology is shown in an example.",2210.10868v1
2022-10-21,Neutron star mass formula with nuclear saturation parameters for asymmetric nuclear matter,"Low-mass neutron stars are directly associated with the nuclear saturation
parameters because their central density is definitely low. We have already
found a suitable combination of nuclear saturation parameters for expressing
the neutron star mass and gravitational redshift, i.e., $\eta\equiv
(K_0L^2)^{1/3}$ with the incompressibility for symmetric nuclear matter, $K_0$,
and the density-dependent nuclear symmetry energy, $L$. In this study, we newly
find another suitable combination given by $\eta_\tau\equiv (-K_\tau
L^5)^{1/6}$ with the isospin dependence of incompressibility for asymmetric
nuclear matter, $K_\tau$, and derive the empirical relations for the neutron
star mass and gravitational redshift as a function of $\eta_\tau$ and the
normalized central number density. With these empirical relations, one can
evaluate the mass and gravitational redshift of the neutron star, whose central
number density is less than threefold the saturation density, within $\sim
10\%$ accuracy, and the radius within a few \% accuracies. In addition, we
discuss the neutron star mass and radius constraints from the terrestrial
experiments, using the empirical relations, together with those from the
astronomical observations. Furthermore, we find a tight correlation between
$\eta_\tau$ and $\eta$. With this correlation, we derive the constraint on
$K_\tau$ as $-348\le K_\tau\le -237$ MeV, assuming that $L=60\pm 20$ and
$K_0=240\pm 20$ MeV.",2210.11651v1
2022-11-11,Continuum kinetic investigation of the impact of bias potentials in the current saturation regime on sheath formation,"In this work, we examine sheath formation in the presence of bias potentials
in the current saturation regime for pulsed power fusion experiments. It is
important to understand how the particle and heat fluxes at the wall may impact
the wall material and affect electrode degradation. Simulations are performed
using the 1X-1V Boltzmann-Poisson system for a proton-electron plasma in the
presence of bias potentials ranging from 0 to 10 kV. The results indicate that
the sheath near the high potential wall remains generally the same as that of a
classical sheath without the presence of a bias potential. However, the sheath
near the low potential wall becomes more prominent with a larger potential
drop, a significant decrease of electron density, and larger sheath lengths.
The spatially constant current density increases to a saturation value with
increasing bias potential. The current is dominated by the ions at the low
potential wall and by the electrons at the high potential wall. The heat flux
increases to a saturation value at the high potential wall and tends to zero at
the low potential wall with increasing bias potential. The results trend with
theory with differences attributed to the simplified assumptions in the theory
and the kinetic effects considered in the simulations. Due to the significant
computational cost of a well resolved 1X-2V simulation, only one such
simulation is performed for the 5 kV case showing higher current.",2211.06488v3
2022-12-06,"A symmetric chain decomposition of $L(5,n)$","We give a constructive proof that Young's lattice $L(5, n)$ has a partition
into saturated symmetric chains.",2212.02700v4
2022-12-20,The Effects of Connectivity and Automation on Saturation Headway and Capacity at Signalized Intersections,"This paper analyzes the potential effects of connected and automated vehicles
on saturation headway and capacity at signalized intersections. A signalized
intersection is created in Vissim as a testbed, where four vehicle types are
modeled and tested: (I) human-driven vehicles (HVs), (II) connected vehicles
(CVs), (III) automated vehicles (AVs), and (IV) connected automated vehicles
(CAVs). Various scenarios are defined based on different market penetration
rates of these four vehicle types. AVs are assumed to move more cautiously
compared to human drivers. CVs and CAVs are supposed to receive information
about the future state of traffic lights and adjust their speeds to avoid
stopping at the intersection. As a result, their movements are expected to be
smoother with a lower number of stops. The effects of these vehicle types in
mixed traffic are investigated in terms of saturation headway, capacity, travel
time, delay, and queue length in different lane groups of an intersection. A
Python script code developed by Vissim is used to provide the communication
between the signal controller and CVs and CAVs to adjust their speeds
accordingly. The results show that increasing CV and CAV market penetration
rate reduces saturation headway and consequently increases capacity at
signalized intersections. On the other hand, increasing the AV market
penetration rate deteriorates traffic operations. Results also indicate that
the highest increase (80%) and decrease (20%) in lane group capacity are
observed, respectively, in a traffic stream of 100% CAVs and 100% AVs.",2212.09986v1
2022-12-22,Low intensity saturation of an ISB transition by a mid-IR quantum cascade laser,"We demonstrate that absorption saturation of a mid-infrared intersubband
transition can be engineered to occur at moderate light intensities of the
order of 10-20 kW$.$cm$^{-2}$ and at room temperature. The structure consists
of an array of metal-semiconductor-metal patches hosting a judiciously designed
253 nm thick GaAs/AlGaAs semiconductor heterostructure. At low incident
intensity the structure operates in the strong light-matter coupling regime and
exhibits two absorption peaks at wavelengths close to 8.9 $\mu$m. Saturation
appears as a transition to the weak coupling regime - and therefore to a
single-peaked absorption - when increasing the incident intensity. Comparison
with a coupled mode theory model explains the data and permits to infer the
relevant system parameters. When the pump laser is tuned at the cavity
frequency, the reflectivity decreases with increasing incident intensity. When
instead the laser is tuned at the polariton frequencies, the reflectivity
non-linearly increases with increasing incident intensity. At those wavelengths
the system therefore mimics the behavior of a saturable absorption mirror
(SESAM) in the mid-IR range, a technology that is currently missing.",2212.11641v3
2023-01-02,Examination of saturation coverage of short polymers using random sequential adsorption algorithm,"We filled a void with a regular or asymmetric pattern without overlap using a
time-dependent packing method termed random sequential adsorption (RSA). In the
infinite-time limit, the density of coverage frequently hits a limit. This
study focused on the saturation packing of squares and their dimers, trimers,
tetramers, pentamers, and hexamers, all of which were orientated in two
randomly chosen orientations (vertical and horizontal). Our results concurred
with those of previous extrapolation-based research1. We used the ""separating
axis theorem"" to detect if freshly added polygons and previously put ones
overlapped. When RSA insertion became disproportionately sluggish, we concluded
that saturation had been attained. We also discovered that the system's
capacity to fill the area decreased as squares were stretched into dimers and
trimmers. The microstructure of the resultant saturation was also thoroughly
investigated, including block function and the structural arrangement of dimers
and trimers. Based on results of ref2, it is predicted that layer adsorbed onto
a substrate will not hinder diffusion. Moreover, it was found that the adsorbed
rectangles' aspect ratio had an impact on the coverage percentage at the
jamming limit, with aspect ratios of 2 (like dimers here) producing the highest
jamming coverage. As a result, the current results are a more in-depth
expansion of the report in reference3.",2301.00766v1
2023-01-17,Dielectric Saturation in Water from a Long Range Machine Learning Model,"Machine learning-based neural network potentials have the ability to provide
ab initio-level predictions while reaching large length and time scales often
limited to empirical force fields. Traditionally, neural network potentials
rely on a local description of atomic environments to achieve this scalability.
These local descriptions result in short range models that neglect long range
interactions necessary for processes like dielectric screening in polar
liquids. Several approaches to including long range electrostatic interactions
within neural network models have appeared recently, and here we investigate
the transferability of one such model, the self consistent neural network
(SCFNN), which focuses on learning the physics associated with long range
response. By learning the essential physics, one can expect that such a neural
network model should exhibit at least partial transferability. We illustrate
this transferability by modeling dielectric saturation in a SCFNN model of
water. We show that the SCFNN model can predict non-linear response at high
electric fields, including saturation of the dielectric constant, without
training the model on these high field strengths and the resulting liquid
configurations. We then use these simulations to examine the nuclear and
electronic structure changes underlying dielectric saturation. Our results
suggest that neural network models can exhibit transferability beyond the
linear response regime and make genuine predictions when the relevant physics
is properly learned.",2301.07188v1
2023-03-18,Constitutive theory of saturated porous media considering porosity-dependent skeleton strain and chemical activity,"In order to reveal the coupling effect among the chemical activity and the
hydraulic seepage as well as the mechanical properties, a constitutive
theoretical framework considering the chemical activity for saturated porous
media is derived from the mixture theory incorporated with the chemical
thermodynamics. First, to highlight the important role of porosity in the
hydro-mechanical-chemical multi-field coupling mechanism, the solid strain is
divided into the porosity-dependent skeleton strain, the matrix strain and the
mass-exchange strain. The stress and strain state variables are determined from
the energy-conjugated form of the energy balance equation for establishing
constitutive equations. Second, under infinitesimal case, general elastic
constitutive equations including the relationship between mass fraction and its
chemical potential are expressed by the free energy potential. Plastic model
and the constitutive equation of thermodynamic flux and force are derived from
the dissipative potential. Finally, under the guide of this theoretical
framework, the complete swelling constitutive models in the confined
compression are established for bentonite. The corresponding governing
equations are formulated for multi-field two-phase saturated porous media.
Compared with the experimental data, the proposed model can well reflect the
chemical and mechanic coupling characteristics of representative elementary
volume in the different NaCl concentrations of solution for saturated
bentonite.",2303.10374v1
2023-03-28,Globally Intelligent Adaptive Finite-/Fixed- Time Tracking Control for Strict-Feedback Nonlinear Systems via Composite Learning Approaches,"This article focuses on the globally composite adaptive law-based intelligent
finite-/fixed- time (FnT/FxT) tracking control issue for a family of uncertain
strict-feedback nonlinear systems. First, intelligent approximators with new
composite updating laws are developed to model uncertain nonlinear terms, which
encompass prediction errors to enhance intelligent approximators' learning
behaviors and fewer online learning parameters to diminish computational
burden. Then, a novel smooth switching function coupled with robust controllers
is designed to pull system states back when the transients are out of the
approximators' active domain. After that, a modified FnT/FxT backstepping
technique is constructed to render output to follow the reference trajectory,
and an adaptive law is employed to alleviate the impact of external
disturbances. Moreover, input nonlinearities are considered in the design of
control laws. In view of the known actuator magnitude and rate saturations, a
novel adaptive fast FxT auxiliary variable system is established to effectively
diminish saturation time, and further alleviate the impact of the auxiliary
signal on the tracking error. Furthermore, when the input is subject to unknown
magnitude saturation, rate saturation and dead-zone simultaneously, a smooth
function is introduced to approximate the non-smooth input nonlinearities,
where the unknown parameters are modeled via the presented global intelligent
approximators. It is theoretically confirmed that the proposed control
strategies ensure globally FnT/FxT boundedness of all the closed-loop
variables. Finally, the validity of theoretical results is testified via a
simulation case.",2303.15942v4
2023-08-10,Deep Richardson-Lucy Deconvolution for Low-Light Image Deblurring,"Images taken under the low-light condition often contain blur and saturated
pixels at the same time. Deblurring images with saturated pixels is quite
challenging. Because of the limited dynamic range, the saturated pixels are
usually clipped in the imaging process and thus cannot be modeled by the linear
blur model. Previous methods use manually designed smooth functions to
approximate the clipping procedure. Their deblurring processes often require
empirically defined parameters, which may not be the optimal choices for
different images. In this paper, we develop a data-driven approach to model the
saturated pixels by a learned latent map. Based on the new model, the non-blind
deblurring task can be formulated into a maximum a posterior (MAP) problem,
which can be effectively solved by iteratively computing the latent map and the
latent image. Specifically, the latent map is computed by learning from a map
estimation network (MEN), and the latent image estimation process is
implemented by a Richardson-Lucy (RL)-based updating scheme. To estimate
high-quality deblurred images without amplified artifacts, we develop a prior
estimation network (PEN) to obtain prior information, which is further
integrated into the RL scheme. Experimental results demonstrate that the
proposed method performs favorably against state-of-the-art algorithms both
quantitatively and qualitatively on synthetic and real-world images.",2308.05543v1
2023-08-18,Polarization-dependent Intensity Ratios in Double Resonance Spectroscopy,"Double Resonance is a powerful method spectroscopic method that provides an
unambiguous assignment of the rigorous quantum numbers of one state of a
transition. However, there is often ambiguity as to the branch ($\Delta J$) of
the transition. The dependence of the intensity of the double resonance signal
on the relative polarization of pump and probe radiation can be used to resolve
this ambiguity and has been used for this in the past. However, the published
theoretical predictions for this ratio are based upon a weak (i.e.
non-saturating) field approximation. In this paper, we present theoretical
predictions for these intensity ratios for cases where the pump field is
strongly saturating, in the two limits of transitions dominated by homogeneous
and inhomogeneous broadening. While saturation, as can be expected, reduces the
magnitude of the polarization effect (driving the intensity ratio closer to
unity), polarization anisotropy remains even with a strongly saturating probe
field in most cases. For the case of an inhomogeneously broadened line, as when
Doppler broadening linewidth dominates over even the power broadened
homogeneous line width, a large fraction of the low pump power anisotropy
remains. Results are presented for both the case of linear and circular pump
and probe field polarizations. The present predictions are compared with
experimental measurements on CH$_4$ ground state $\rightarrow \nu_3 \rightarrow
3\nu_3$ transitions recently reported by de Oliveira et al and found to be in
better agreement than the weak field predictions.",2308.09828v1
2023-09-01,The Power of Patents: Leveraging Text Mining and Social Network Analysis to Forecast IoT Trends,"Technology has become an indispensable competitive tool as science and
technology have progressed throughout history. Organizations can compete on an
equal footing by implementing technology appropriately. Technology trends or
technology lifecycles begin during the initiation phase. Finally, it reaches
saturation after entering the maturity phase. As technology reaches saturation,
it will be removed or replaced by another. This makes investing in technologies
during this phase unjustifiable. Technology forecasting is a critical tool for
research and development to determine the future direction of technology. Based
on registered patents, this study examined the trends of IOT technologies. A
total of 3697 patents related to the Internet of Things from the last six years
of patenting have been gathered using lens.org for this purpose. The main
people and companies were identified through the creation of the IOT patent
registration cooperation network, and the main groups active in patent
registration were identified by the community detection technique. The patents
were then divided into six technology categories: Safety and Security,
Information Services, Public Safety and Environment Monitoring, Collaborative
Aware Systems, Smart Homes/Buildings, and Smart Grid. And their technical
maturity was identified and examined using the Sigma Plot program. Based on the
findings, information services technologies are in the saturation stage, while
both smart homes/buildings, and smart grid technologies are in the saturation
stage. Three technologies, Safety and Security, Public Safety and Environment
Monitoring, and Collaborative Aware Systems are in the maturity stage.",2309.00707v1
2023-10-05,History Matching for Geological Carbon Storage using Data-Space Inversion with Spatio-Temporal Data Parameterization,"History matching based on monitoring data will enable uncertainty reduction,
and thus improved aquifer management, in industrial-scale carbon storage
operations. In traditional model-based data assimilation, geomodel parameters
are modified to force agreement between flow simulation results and
observations. In data-space inversion (DSI), history-matched quantities of
interest, e.g., posterior pressure and saturation fields conditioned to
observations, are inferred directly, without constructing posterior geomodels.
This is accomplished efficiently using a set of O(1000) prior simulation
results, data parameterization, and posterior sampling within a Bayesian
setting. In this study, we develop and implement (in DSI) a deep-learning-based
parameterization to represent spatio-temporal pressure and CO2 saturation
fields at a set of time steps. The new parameterization uses an adversarial
autoencoder (AAE) for dimension reduction and a convolutional long short-term
memory (convLSTM) network to represent the spatial distribution and temporal
evolution of the pressure and saturation fields. This parameterization is used
with an ensemble smoother with multiple data assimilation (ESMDA) in the DSI
framework to enable posterior predictions. A realistic 3D system characterized
by prior geological realizations drawn from a range of geological scenarios is
considered. A local grid refinement procedure is introduced to estimate the
error covariance term that appears in the history matching formulation.
Extensive history matching results are presented for various quantities, for
multiple synthetic true models. Substantial uncertainty reduction in posterior
pressure and saturation fields is achieved in all cases. The framework is
applied to efficiently provide posterior predictions for a range of error
covariance specifications. Such an assessment would be expensive using a
model-based approach.",2310.03228v1
2023-10-11,Saturation-Aware Angular Velocity Estimation: Extending the Robustness of SLAM to Aggressive Motions,"We propose a novel angular velocity estimation method to increase the
robustness of Simultaneous Localization And Mapping (SLAM) algorithms against
gyroscope saturations induced by aggressive motions. Field robotics expose
robots to various hazards, including steep terrains, landslides, and
staircases, where substantial accelerations and angular velocities can occur if
the robot loses stability and tumbles. These extreme motions can saturate
sensor measurements, especially gyroscopes, which are the first sensors to
become inoperative. While the structural integrity of the robot is at risk, the
resilience of the SLAM framework is oftentimes given little consideration.
Consequently, even if the robot is physically capable of continuing the
mission, its operation will be compromised due to a corrupted representation of
the world. Regarding this problem, we propose a way to estimate the angular
velocity using accelerometers during extreme rotations caused by tumbling. We
show that our method reduces the median localization error by 71.5 % in
translation and 65.5 % in rotation and reduces the number of SLAM failures by
73.3 % on the collected data. We also propose the Tumbling-Induced Gyroscope
Saturation (TIGS) dataset, which consists of outdoor experiments recording the
motion of a lidar subject to angular velocities four times higher than other
available datasets. The dataset is available online at
https://github.com/norlab-ulaval/Norlab_wiki/wiki/TIGS-Dataset.",2310.07844v1
2023-11-08,CGC/saturation approach: Impact-parameter dependent model in next-to-leading order and combined HERA data,"In this paper we confront the next-to-leading order (NLO) CGC/saturation
approach of Ref. [1] with the experimental combined HERA data and obtain its
parameters. The model includes two features that are in accordance with our
theoretical knowledge of deep inelastic scattering. These consist of: $i$) the
use of analytical solution for the non-linear Balitsky-Kovchegov (BK) evolution
equation and $ii$) the exponential behavior of the saturation momentum on the
impact parameter $b$-dependence, characterized by $Q_s$ $\propto\exp( -m b )$
which reproduce the correct behaviour of the scattering amplitude at large $b$
in accord with Froissart theorem. The model results are then compared to data
at small-x for the structure function of the proton $F_{2}$, the longitudinal
structure function $F_{L}$, the charm structure function $F_2^{c\bar{c}}$, the
exclusive vector meson ($J/\psi,\phi,\rho$) production and Deeply Virtual
Compton Scattering (DVCS). We obtain a good agreement for the processes in a
wide kinematic range of $Q^2$ at small $x$. Our results provide a strong guide
for finding an approach, based on Color Glass Condensate/saturation effective
theory for high energy QCD, to make reliable predictions from first principles
as well as for forthcoming experiments like the Electron-Ion Collider and the
LHeC.",2311.06406v1
2024-01-24,Echeloned saturation and forcing axioms,"Addressing a question of Paul Larson we prove the following statement. If
Chang's conjecture fails, Martin's axiom holds and the continuum is greater
than $\aleph_2$, there are no weakly Laver ideals over $\aleph_1$. We also
prove that under Baumgartner's axiom there are no Laver ideals over $\aleph_2$.",2401.13364v1
2024-02-29,The Influence of Color Stimuli on Adolescents' Emotion Playing Mobile Games,"Video games elicit emotions which can be influenced by color stimuli as shown
by previous studies. However, little research has been conducted on whether
this applies to mobile games played by adolescents. Therefore, we examined the
influence of color stimuli hue and saturation on mobile game play. Adolescents
(n=21) played a mobile platformer game with varying hue and saturation per
level for about 25 minutes. We gathered data on emotional states after each
level using the Self-Assessment Manikin questionnaire, recorded time spent in
each level, and collected participant self-reports on their video game
experience. We performed statistical tests, such as ANOVA, which depict no
significant influence of hue and/or saturation on the emotional state of our
players. We conclude that it is possible that color alone is not an effective
measure for eliciting emotion in mobile games, and further research is needed
to consider measures such as time spent in the game and screen size, as these
are unique to mobile games. There was a noticeable variance in emotional
response between male and female players, with a significant interaction of hue
and saturation among male players for valence ratings. This may be an
indication that color preference influences perceived pleasantness.",2402.19064v1
2024-02-29,"Simple, High Saturation Power, Quantum-limited, RF SQUID Array-based Josephson Parametric Amplifiers","High-fidelity quantum non-demolition qubit measurement is critical to error
correction and rapid qubit feedback in large-scale quantum computing.
High-fidelity readout requires passing a short and strong pulse through the
qubit's readout resonator, which is then processed by a sufficiently high
bandwidth, high saturation power, and quantum-limited amplifier. We have
developed a design pipeline that combines time-domain simulation of the
un-truncated device Hamiltonian, fabrication constraints, and maximization of
saturation power. We have realized an amplifier based on a modified NIST
tri-layer Nb fabrication suite which utilizes an array of 25 radio frequency
Superconducting QUantum Interference Devices (rf SQUIDs) embedded within a
low-Q resonator powered by a high-power voltage pump delivered via a diplexer
on the signal port. We show that, despite the intensity of the pump, the device
is quantum-efficient and capable of high-fidelity measurement limited by state
transitions in the transmon. We present experimental data demonstrating up to
-91.2 dBm input saturation power with 20 dB gain, up to 28 MHz instantaneous
bandwidth, and phase-preserving qubit measurements with 62% quantum efficiency.",2402.19435v1
2003-05-24,Correlation between the Mean Matter Density and the Width of the Saturated Lyman Alpha Absorption,"We report a scaling of the mean matter density with the width of the
saturated Lyman alpha absorptions. This property is established using the
``pseudo-hydro'' technique (Croft et al. 1998). It provides a constraint for
the inversion of the Lyman alpha forest, which encounters difficulty in the
saturated region. With a Gaussian density profile and the scaling relation, a
simple inversion of the simulated Lyman alpha forests shows that the
one-dimensional mass power spectrum is well recovered on scales above 2 Mpc/h,
or roughly k < 0.03 s/km, at z=3. The recovery underestimates the power on
small scales, but improvement is possible with a more sophisticated algorithm.",0305481v2
1999-09-29,Universality and saturation of intermittency in passive scalar turbulence,"The statistical properties of a scalar field advected by the non-intermittent
Navier-Stokes flow arising from a two-dimensional inverse energy cascade are
investigated. The universality properties of the scalar field are directly
probed by comparing the results obtained with two different types of injection
mechanisms. Scaling properties are shown to be universal, even though
anisotropies injected at large scales persist down to the smallest scales and
local isotropy is not fully restored. Scalar statistics is strongly
intermittent and scaling exponents saturate to a constant for sufficiently high
orders. This is observed also for the advection by a velocity field rapidly
changing in time, pointing to the genericity of the phenomenon. The persistence
of anisotropies and the saturation are both statistical signatures of the
ramp-and-cliff structures observed in the scalar field.",9909038v1
1996-11-25,The three species monomer-monomer model: A mean-field analysis and Monte Carlo study,"We study the phase diagram and critical behavior of a one dimensional three
species monomer-monomer surface reaction model. Static Monte Carlo simulations
show a phase diagram consisting of a reactive steady state bordered by three
equivalent unreactive phases where the surface is saturated with one monomer
species. The transitions from the reactive to saturated phases are all
continuous, while the transitions between poisoned phases are first-order, with
bicritical points where the reactive phase meets two poisoned phases. A
mean-field cluster analysis predicts all of the qualitative features of the
phase diagram only when correlations up to triplets of adjacent sites are
included. Dynamic Monte Carlo simulations show that the transition from the
reactive to a saturated phase show critical behavior in the directed
percolation universality class, while the bicritical point shows critical
behavior in the even branching annihilating random walk class. The crossover
from bicritical to critical behavior is also studied.",9611197v1
1997-12-26,Critical behavior of a one-dimensional monomer-dimer reaction model with lateral interactions,"A monomer-dimer reaction lattice model with lateral repulsion among the same
species is studied using a mean-field analysis and Monte Carlo simulations. For
weak repulsions, the model exhibits a first-order irreversible phase transition
between two absorbing states saturated by each different species. Increasing
the repulsion, a reactive stationary state appears in addition to the saturated
states. The irreversible phase transitions from the reactive phase to any of
the saturated states are continuous and belong to the directed percolation
universality class. However, a different critical behavior is found at the
point where the directed percolation phase boundaries meet. The values of the
critical exponents calculated at the bicritical point are in good agreement
with the exponents corresponding to the parity-conserving universality class.
Since the adsorption-reaction processes does not lead to a non-trivial local
parity-conserving dynamics, this result confirms that the twofold symmetry
between absorbing states plays a relevant role in determining the universality
class. The value of the exponent $\delta_2$, which characterizes the
fluctuations of an interface at the bicritical point, supports the
Bassler-Brown's conjecture which states that this is a new exponent in the
parity-conserving universality class.",9712301v2
1999-04-20,Low-Temperature Saturation of the Dephasing Time and Effects of Microwave Radiation on Open Quantum Dots,"The dephasing time of electrons in open semiconductor quantum dots, measured
using ballistic weak localization, is found to saturate below ~ 100 mK, roughly
twice the electron base temperature, independent of dot size. Microwave
radiation deliberately coupled to the dots affects quantum interference
indistinguishably from elevated temperature, suggesting that direct dephasing
due to radiation is not the cause of the observed saturation. Coulomb blockade
measurements show that the applied microwaves create sufficient source drain
voltages to account for dephasing due to Joule heating.",9904274v1
2001-01-24,A Continuum Saltation Model for Sand Dunes,"We derive a phenomenological continuum saltation model for aeolian sand
transport that can serve as an efficient tool for geomorphological
applications. The coupled differential equations for the average density and
velocity of sand in the saltation layer reproduce both known equilibrium
relations for the sand flux and the time evolution of the sand flux as
predicted by microscopic saltation models. The three phenomenological
parameters of the model are a reference height for the grain-air interaction,
an effective restitution coefficient for the grain-bed interaction, and a
multiplication factor characterizing the chain reaction caused by the impacts
leading to a typical time or length scale of the saturation transients. We
determine the values of these parameters by comparing our model with wind
tunnel measurements. Our main interest are out of equilibrium situations where
saturation transients are important, for instance at phase boundaries
(ground/sand) or under unsteady wind conditions. We point out that saturation
transients are indispensable for a proper description of sand flux over
structured terrain, by applying the model to the windward side of an isolated
dune, thereby resolving recently reported discrepancies between field
measurements and theoretical predictions.",0101377v2
2001-09-25,Three dimensional hysdrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic flow through porous media,"We report the results of a study of multiphase flow in porous media. A
Darcy's law for steady multiphase flow was investigated for both binary and
ternary amphiphilic flow. Linear flux-forcing relationships satisfying Onsager
reciprocity were shown to be a good approximation of the simulation data. The
dependence of the relative permeability coefficients on water saturation was
investigated and showed good qualitative agreement with experimental data.
Non-steady state invasion flows were investigated, with particular interest in
the asymptotic residual oil saturation. The addition of surfactant to the
invasive fluid was shown to significantly reduce the residual oil saturation.",0109474v1
2003-11-11,Solution of a statistical mechanics model for pulse formation in lasers,"We present a rigorous statistical-mechanics theory of nonlinear many mode
laser systems. An important example is the passively mode-locked laser that
promotes pulse operation when a saturable absorber is placed in the cavity. It
was shown by Gordon and Fischer [1] that pulse formation is a first-order phase
transition of spontaneous ordering of modes in an effective ""thermodynamic""
system, in which intracavity noise level is the effective temperature. In this
paper we present a rigorous solution of a model of passive mode locking. We
show that the thermodynamics depends on a single parameter, and calculate
exactly the mode-locking point. We find the phase diagram and calculate
statistical quantities, including the dependence of the intracavity power on
the gain saturation function, and finite size corrections near the transition
point. We show that the thermodynamics is independent of the gain saturation
mechanism and that it is correctly reproduced by a mean field calculation. The
outcome is a new solvable statistical mechanics system with an unstable
self-interaction accompanied by a natural global power constraint, and an exact
description of an important many mode laser system.",0311241v1
2004-01-05,Electron-Electron Interactions in Isolated and Realistic Quantum Dots: A Density Functional Theory Study,"We use Kohn-Sham spin-density-functional theory to study the statistics of
ground-state spin and the spacing between conductance peaks in the Coulomb
blockade regime for both 2D isolated and realistic quantum dots. We make a
systematic investigation of the effects of electron-electron interaction
strength and electron number on both the peak spacing and spin distributions. A
direct comparison between the distributions from isolated and realistic dots
shows that, despite the difference in the boundary conditions and confining
potential, the statistical properties are qualitatively the same. Strong
even/odd pairing in the peak spacing distribution is observed only in the weak
e-e interaction regime and vanishes for moderate interactions. The probability
of high spin ground states increases for stronger e-e interaction and seems to
saturate around $r_s \sim 4$. The saturated value is larger than previous
theoretical predictions. Both spin and conductance peak spacing distributions
show substantial variation as the electron number increases, not saturating
until $N \sim 150$. To interpret our numerical results, we analyze the spin
distribution in the even $N$ case using a simple two-level model.",0401043v1
2004-01-12,Electron Dephasing in Mesoscopic Metal Wires,"The low-temperature behavior of the electron phase coherence time,
$\tau_{\phi}$, in mesoscopic metal wires has been a subject of controversy
recently. Whereas theory predicts that $\tau_{\phi}(T)$ in narrow wires should
increase as $T^{-2/3}$ as the temperature $T$ is lowered, many samples exhibit
a saturation of $\tau_{\phi}$ below about 1 K. We review here the experiments
we have performed recently to address this issue. In particular we emphasize
that in sufficiently pure Ag and Au samples we observe no saturation of
$\tau_{\phi}$ down to our base temperature of 40 mK. In addition, the measured
magnitude of $\tau_{\phi}$ is in excellent quantitative agreement with the
prediction of the perturbative theory of Altshuler, Aronov and Khmelnitskii. We
discuss possible explanations why saturation of $\tau_{\phi}$ is observed in
many other samples measured in our laboratory and elsewhere, and answer the
criticisms raised recently by Mohanty and Webb regarding our work.",0401182v1
2004-02-03,Behavior of susceptible-infected-susceptible epidemics on heterogeneous networks with saturation,"We investigate saturation effects in susceptible-infected-susceptible (SIS)
models of the spread of epidemics in heterogeneous populations. The structure
of interactions in the population is represented by networks with connectivity
distribution $P(k)$,including scale-free(SF) networks with power law
distributions $P(k)\sim k^{-\gamma}$. Considering cases where the transmission
of infection between nodes depends on their connectivity, we introduce a
saturation function $C(k)$ which reduces the infection transmission rate
$\lambda$ across an edge going from a node with high connectivity $k$. A mean
field approximation with the neglect of degree-degree correlation then leads to
a finite threshold $\lambda_{c}>0$ for SF networks with $2<\gamma \leq 3$. We
also find, in this approximation, the fraction of infected individuals among
those with degree $k$ for $\lambda$ close to $\lambda_{c}$. We investigate via
computer simulation the contact process on a heterogeneous regular lattice and
compare the results with those obtained from mean field theory with and without
neglect of degree-degree correlations.",0402065v2
2004-02-09,Lateral phase separation in mixtures of lipids and cholesterol systems,"In an effort to understand ``rafts'' in biological membranes, we propose
phenomenological models for saturated and unsaturated lipid mixtures, and
lipid-cholesterol mixtures. We consider simple couplings between the local
composition and internal membrane structure, and their influence on transitions
between liquid and ``gel'' membrane phases. Assuming that the gel transition
temperature of the saturated lipid is shifted by the presence of the
unsaturated lipid, and that cholesterol acts as an external field on the chain
melting transition, a variety of phase diagrams are obtained. The phase
diagrams for binary mixtures of saturated/unsaturated lipids and
lipid/cholesterol are in semi-quantitative agreement with the experiments. Our
results also apply to regions in the ternary phase diagram of
lipid/lipid/cholesterol systems.",0402252v1
2004-04-12,Universality of the Mott-Ioffe-Regel limit in metals,"The absence of resistivity saturation in many strongly correlated metals,
including the high-temperature superconductors, is critically examined from the
viewpoint of optical conductivity measurements. Coherent quasiparticle
conductivity, in the form of a Drude peak centred at zero frequency, is found
to disappear as the mean free path (at $\omega$ = 0) becomes comparable to the
interatomic spacing. This basic loss of coherence at the so-called
Mott-Ioffe-Regel (MIR) limit suggests that the universality of the MIR
criterion is preserved even in the presence of strong electron correlations. We
argue that the shedding of spectral weight at low frequencies, induced by
strong correlation effects, is the primary origin of the extended positive
slope of the resistivity to high temperatures observed in all so-called ""bad
metals"". Moreover, in common with those metals which exhibit resistivity
saturation at high temperatures, the scattering rate itself, as extracted from
optical spectra, saturates at a value consistent with the MIR limit. We
consider possible implications that this ceiling in the scattering rate may
have for our understanding of transport within a wide variety of bad metals and
suggest a better method for analysing their optical response.",0404263v1
2005-06-29,Aeolian sans ripples: experimental study of saturated states,"We report an experimental investigation of aeolian sand ripples, performed
both in a wind tunnel and on stoss slopes of dunes. Starting from a flat bed,
we can identify three regimes: appearance of an initial wavelength, coarsening
of the pattern and finally saturation of the ripples. We show that both initial
and final wavelengths, as well as the propagative speed of the ripples, are
linear functions of the wind velocity. Investigating the evolution of an
initially corrugated bed, we exhibit non-linear stable solutions for a finite
range of wavelengths, which demonstrates the existence of a saturation in
amplitude. These results contradict most of the models.",0506758v2
2005-11-24,Experiments on Corn Pressure in Silo Cells -- Translation and Comment of Janssen's Paper from 1895,"The German engineer H.A. Janssen gave one of the first accounts of the often
peculiar behavior of granular material in a paper published in German in 1895.
  From simple experiments with corn he inferred the saturation of pressure with
height in a granular system. Subsequently, Janssen derived the equivalent of
the barometric formula for granular material from the main assumption that the
walls carry part of the weight. The following is a translation of this article.
The wording is chosen as close as possible to the original. While drawings are
copied from the original, figures displaying data are redone for better
readability. The translation is complemented by some bibliographical notes and
an assessment of earlier work, wherein Hagen predicted the saturation of
pressure with depth in 1852, and Huber-Burnand demonstrated that saturation
qualitatively as early as in 1829. We conclude with a brief discussion of more
recent developments resting on Janssen's work.",0511618v1
2006-06-13,"Interface relaxation in electrophoretic deposition of polymer chains: Effects of segmental dynamics, molecular weight, and field","Using different segmental dynamics and relaxation, characteristics of the
interface growth is examined in an electrophoretic deposition of polymer chains
on a three (2+1) dimensional discrete lattice with a Monte Carlo simulation.
Incorporation of faster modes such as crankshaft and reptation movements along
with the relatively slow kink-jump dynamics seems crucial in relaxing the
interface width. As the continuously released polymer chains are driven (via
segmental movements) and deposited, the interface width $W$ grows with the
number of time steps $t$, $W \propto t^{\beta},$ ($\beta \sim 0.4$--$0.8)$,
which is followed by its saturation to a steady-state value $W_s$. Stopping the
release of additional chains after saturation while continuing the segmental
movements relaxes the saturated width to an equilibrium value ($W_s \to W_r$).
Scaling of the relaxed interface width $W_r$ with the driving field $E$, $W_r
\propto E^{-1/2}$ remains similar to that of the steady-state $W_s$ width. In
contrast to monotonic increase of the steady-state width $W_s$, the relaxed
interface width $W_r$ is found to decay (possibly as a stretched exponential)
with the molecular weight.",0606342v1
2006-11-21,Peculiarities of the stacks with finite number of intrinsic Josephson junctions,"We study the breakpoint region on the outermost branch of current-voltage
characteristics of the stacks with different number of intrinsic Josephson
junctions. We show that at periodic boundary conditions the breakpoint region
is absent for stacks with even number of junctions. For stacks with odd number
of junctions and for stacks with nonperiodic boundary conditions the breakpoint
current is increased with number of junctions and saturated at the value
corresponding to the periodic boundary conditions. The region of saturation and
the saturated value depend on the coupling between junctions. We explain the
results by the parametric resonance at the breakpoint and excitation of the
longitudinal plasma wave by the Josephson oscillations. A way for the
diagnostics of the junctions in the stack is proposed.",0611555v2
2007-03-06,Saturation of Spin-Polarized Current in Nanometer Scale Aluminum Grains,"We describe measurements of spin-polarized tunnelling via discrete energy
levels of single Aluminum grains. In high resistance samples ($\sim G\Omega$),
the spin-polarized tunnelling current rapidly saturates as a function of the
bias voltage. This indicates that spin-polarized current is carried only via
the ground state and the few lowest in energy excited states of the grain. At
the saturation voltage, the spin-relaxation rate $T_1^{-1}$ of the highest
excited states is comparable to the electron tunnelling rate: $T_1^{-1}\approx
1.5\cdot 10^6 s^{-1}$ and $10^7s^{-1}$ in two samples. The ratio of $T_1^{-1}$
to the electron-phonon relaxation rate is in agreement with the Elliot-Yafet
scaling, an evidence that spin-relaxation in Al grains is governed by the
spin-orbit interaction.",0703139v2
2004-11-15,Nonlinear evolution of r-modes: the role of differential rotation,"Recent work has shown that differential rotation, producing large scale
drifts of fluid elements along stellar latitudes, is an unavoidable feature of
r-modes in the nonlinear theory. We investigate the role of this differential
rotation in the evolution of the l=2 r-mode instability of a newly born, hot,
rapidly rotating neutron star. It is shown that the amplitude of the r-mode
saturates a few hundred seconds after the mode instability sets in. The
saturation amplitude depends on the amount of differential rotation at the time
the instability becomes active and can take values much smaller than unity. It
is also shown that, independently of the saturation amplitude of the mode, the
star spins down to rotation rates that are comparable to the inferred initial
rotation rates of the fastest pulsars associated with supernova remnants.
Finally, it is shown that, when the drift of fluid elements at the time the
instability sets in is significant, most of the initial angular momentum of the
star is transferred to the r-mode and, consequently, almost none is carried
away by gravitational radiation.",0411072v1
1997-04-21,Unitarity Corrections and High Field Strengths in High Energy Hard Collisions,"Unitarity corrections to the BFKL description of high energy hard scattering
are viewed in large $N_c$ QCD in light-cone quantization. In a center of mass
frame unitarity corrections to high energy hard scattering are manifestly
perturbatively calculable and unrelated to questions of parton saturation. In a
frame where one of the hadrons is initially at rest unitarity corrections are
related to parton saturation effects and involve potential strengths $A_\mu
\sim 1/g.$ In such a frame we describe the high energy scattering in terms of
the expectation value of a Wilson loop. The large potentials $A_\mu \sim 1/g$
are shown to be pure gauge terms allowing perturbation theory to again describe
unitarity corrections and parton saturation effects. Genuine nonperturbative
effects only come in at energies well beyond those energies where unitarity
constraints first become important.",9704369v1
1998-07-17,Saturating the Bound on the Scale of Fermion Mass Generation,"Recently, Jaeger and Willenbrock have shown that the Appelquist and Chanowitz
bound on the scale of top-quark mass generation can formally be saturated in a
particular limit of a two-Higgs doublet model. In this note I present an
alternate derivation of their result. I perform a coupled channel analysis for
f fbar to V_L V_L and V_L V_L to V_L V_L scattering and derive the conditions
on the parameters required for f fbar to V_L V_L scattering to be relevant to
unitarity. I also show that it is not possible to saturate the bound on fermion
mass generation in the two-Higgs model while maintaining tree-level unitarity
in Higgs scattering at high energies.",9807406v2
2000-06-21,The Effective Pressure of a Saturated Gluon Plasma,"The evolution of the gluon plasma produced with saturation initial conditions
is calculated via transport theory for nuclear collisions with 0.1 <sqrt(s) <10
A TeV. The effective longitudinal pressure is found to remain significantly
below the lattice QCD pressure with these initial conditions until the plasma
cools to near the confinement scale. The absolute value of the transverse
energy per unit of rapidity and its dependence on beam energy is shown to
provide a sensitive test of gluon saturation models since the fractional
transverse energy loss due to final state interactions is predicted to be much
smaller and exhibit a weaker energy dependence than nondissipative
hydrodynamics applied throughout the evolution.",0006257v2
2001-04-11,Parton densities and saturation scale from non-linear evolution in DIS on nuclei,"We present the numerical solution of the non-linear evolution equation for
DIS on nuclei for $x = 10^{-2} \div 10^{-7}$. We demonstrate that the solution
to the non-linear evolution equation is quite different from the Glauber -
Mueller formula which was used as the initial condition for the equation.
  We illustrate the energy profit for performing DIS experiments on nuclei.
  However, it turns out that the gain is quite modest: $x_{Au} \simeq 5 x_{\rm
proton} $ for the same parton density.
  We find that the saturation scale $Q^2_s \propto A^{{1/3}}$. For gold the
saturation scale $Q_{s,Au} \simeq 1.5 GeV$ at $x= 10^{-3}$. Such a large value
leads to considerable contribution of the high density QCD phase to RHIC data
and reveals itself in essential damping for both $xG_A$ and $F_{2A}$.",0104108v1
2002-03-22,Elliptic Flow from Minijet Production in Heavy Ion Collisions,"We calculate the contribution to the elliptic flow observable v2 from
two-particle correlations in minijet production in ultrarelativistic heavy ion
collisions. We use a minijet production cross section derived in a model
inspired by saturation approach to high energy scattering. Resulting
differential elliptic flow v2(pT) is an increasing function of pT for
transverse momenta below the saturation scale Qs. At higher transverse momenta
(pT > Qs) differential flow stops growing and becomes approximately constant,
reproducing the elliptic flow saturation data reported by STAR. The centrality
dependence of the minijet contribution to v2 is also in good agreement with the
data.",0203213v4
2002-07-03,Diffractive Hard Dijets and Nuclear Parton Distributions,"Diffraction plays an exceptional role in DIS off heavy nuclei. First,
diffraction into hard dijets is an unique probe of the unintegrated glue in the
target. Second, because diffraction makes 50 per cent of total DIS off a heavy
target, understanding diffraction in a saturation regime is crucial for a
definition of saturated nuclear parton densities. After brief comments on the
Nikolaev-Zakharov (NZ) pomeron-splitting mechanism for diffractive hard dijet
production, I review an extension of the Nikolaev-Schafer-Schwiete (NSS)
analysis of diffractive dijet production off nuclei to the definition of
nuclear partons in the saturation regime. I emphasize the importance of
intranuclear final state interactions for the parton momentum distributions.",0207045v3
2002-07-17,Saturation of Nuclear Partons: the Fermi Statistics or Nuclear Opacity?,"We derive the two-plateau momentum distribution of final state (FS) quarks
produced in deep inelastic scattering (DIS) off nuclei in the saturation
regime. The diffractive plateau which dominates for small transverse momentum p
measures precisely the momentum distribution of quarks in the beam photon, the
role of the nucleus is simply to provide an opacity. The plateau for truly
inelastic DIS exhibits a substantial nuclear broadening of the FS momentum
distribution. We discuss the relationship between the FS quark densities and
the properly defined initial state (IS) nuclear quark densities.The
Weizs\""acker-Williams glue of a nucleus exhibits a substantial nuclear
dilution, still soft IS nuclear sea saturates because of the anti-collinear
splitting of gluons into sea quarks.",0207210v2
2002-07-28,No Froissart Bound from Gluon Saturation,"In the previous work hep-ph/0112140, hep-ph/0204277, we showed that while the
nonlinear QCD evolution equation of Balitsky and Kovchegov (BK) leads to
saturation of the scattering amplitude locally in impact parameter space, it
does not unitarize the total cross section. This result was recently challenged
by Ferreiro, Iancu, Itakura and McLerran (FIIM) who claim that the
dipole-hadron cross section computed from the BK equation saturates the
Froissart bound. In this comment, we point to a fundamental error in the
argument of FIIM which invalidates their conclusion. We show that if the total
cross section violates unitarity for a coloured scattering probe, it does so
also for a colourless scattering probe.",0207335v2
2002-09-25,High Density QCD and Saturation of Nuclear Partons,"We review the recent finding of the two-plateau momentum distribution of sea
quarks in deep inelastic scattering off nuclei in the saturation regime. The
diffractive plateau which dominates for small $\bp$ measures precisely the
momentum distribution of quarks in the beam photon, the r\^ole of the nucleus
is simply to provide an opacity. The plateau for truly inelastic DIS exhibits a
substantial nuclear broadening of the momentum distribution. Despite this
nuclear broadening, the observed final state and initial state sea quark
densities do coincide exactly. We emphasize how the saturated sea is generated
from the nuclear-diluted Weizs\""acker-Williams because of the anti-collinear
splitting of gluons into sea quarks.",0209298v1
2002-10-24,Parton saturation and N_part scaling of semi--hard processes in QCD,"We argue that the suppression of high p_t hadrons discovered recently in
heavy ion collisions at RHIC may be a consequence of saturation in the Color
Glass Condensate. We qualitatively and semi-quantitatively describe the data,
in particular, the dependence upon the number of nucleon participants. We show
that if parton saturation sets in at sufficiently small energy, then in
nucleus-nucleus collisions at RHIC and LHC energies the cross sections of
semi-hard processes should scale approximately with the number of participants,
N_{part}. Our results provide a possible explanation of both the absence of
apparent jet quenching at SPS energies and its presence at RHIC. Under the same
assumption we predict that in semi--central and central pA (dA) collisions at
collider energies the dependence of semi--hard processes on the number of
participating nucleons of the nucleus will change to \sim (N_{part}^A)^{1/2}.
The forthcoming data on dA collisions will provide a crucial test of this
description.",0210332v2
2002-12-12,"High Density QCD, Saturation and Diffractive DIS","We review a consistent description of the fusion and saturation of partons in
the Lorentz-contracted ultrarelativistic nuclei in terms of a nuclear
attenuation of color dipole states of the photon and collective
Weizs\""acker-Williams (WW) gluon structure function of a nucleus. Diffractive
DIS provides a basis for the definition of the WW nuclear glue. The point that
all observables for DIS off nuclei are uniquely calculable in terms of the
nuclear WW glue amounts to a new form of factorization in the saturation
regime.",0212176v1
2002-12-18,Polarized Hyperons from pA Scattering in the Gluon Saturation Regime,"We study the production of transversely polarized Lambda hyperons in
high-energy collisions of protons with large nuclei. The large gluon density of
the target at saturation provides an intrinsic semi-hard scale which should
naturally allow for a weak-coupling QCD description of the process in terms of
a convolution of the quark distribution of the proton with the elementary
quark-nucleus scattering cross section (resummed to all twists) and a
fragmentation function. In this case of transversely polarized Lambda
production we employ a so-called polarizing fragmentation function, which is an
odd function of the transverse momentum of the Lambda relative to the
fragmenting quark. Due to this k_t-odd nature, the resulting Lambda
polarization is essentially proportional to the derivative of the quark-nucleus
cross section with respect to transverse momentum, which peaks near the
saturation momentum scale. Such processes might therefore provide generic
signatures for high parton density effects and for the approach to the
``black-body'' (unitarity) limit of hadronic scattering.",0212260v2
2002-12-19,The Dipole Picture and Saturation in Soft Processes,"We attempt to describe soft hadron interactions in the framework of
saturation models, one based upon the Balitsky-Kovchegov non-linear equation
and another one due to Golec-Biernat and W\""{u}sthoff. For $pp$, $Kp$, and $\pi
p$ scattering the relevant hadronic wave functions are formulated, and total,
elastic cross-sections, and the forward elastic slope are calculated and
compared to experimental data. The saturation mechanism leads to reasonable
reproduction of the data for the quantities analyzed, except for the forward
elastic slope, where the predicted increase with energy is too moderate.",0212284v2
2003-01-15,Nuclear A-dependence near the Saturation Boundary,"The A-dependence of the saturation momentum and the scaling behavior of the
scattering of a small dipole on a nuclear target are studied in the
McLerran-Venugopalan model, in fixed coupling BFKL dynamics and in running
coupling BFKL dynamics. In each case, we find scaling not too far from the
saturation boundary, although for fixed coupling evolution the scaling function
for large A is not the same as for an elementary dipole. We find that $Q_s^2$
is proportional to $A^{1/3}$ in the McLerran-Venugopalan model and in fixed
coupling evolution, however, we find an almost total lack of A-dependence in
$Q_s^2$ in the case of running coupling evolution.",0301109v1
2003-04-16,QCD Saturation and Photoproduction on Proton and Nuclei Targets,"We calculate inclusive photoproduction cross-sections for both proton and
nuclei targets, using a saturation model derived from an approximate solution
to the Balitsky-Kovchegov nonlinear evolution equation. This paper extends our
hypothesis, that one can successfully use the dipole picture and saturation
models to describe soft processes, instead of the soft Pomeron Regge
parametrization. Our fit is compatible with our previous fit to DIS data, and
utilizes the same phenomenological parameters as in our paper devoted to soft
hadronic interactions. Using the Glauber formalism, and no additional
parameters, we calculate the cross-sections for photoproduction on various
nuclei, and compare our results with the relevant data.",0304166v2
2003-04-30,How far is normal nuclear matter from the chiral symmetry restoration?,"Properties of cold nuclear matter are studied within a generalized
Nambu-Jona-Lasinio model formulated on the level of constituent nucleons. The
model parameters are chosen to reproduce simultaneously the observed nucleon
and pion masses in vacuum as well as saturation properties of nuclear matter.
The strongest constraints on these parameters are given by the empirical values
of the nucleon effective mass and compression modulus at nuclear saturation
density. A preferable value of the cut-off momentum, determining density of
active quasinucleon states in the Dirac sea, is estimated to about 400 MeV/c.
With the most reasonable choice of model parameters we have found a first order
phase transition of the liquid-gas type at subsaturation densities and the
gradual restoration of chiral symmetry at about 3 times the saturation density.
Fluctuations of the scalar condensate around its mean-field value are estimated
and shown to be large in the vicinity of chiral transition.",0304296v1
2003-05-23,Saturation and parton level Cronin effect: enhancement vs suppression of gluon production in p-A and A-A collisions,"We note that the phenomenon of perturbative saturation leads to transverse
momentum broadening in the spectrum of partons produced in hadronic collisions.
This broadening has a simple interpretation as parton level Cronin effect for
systems in which saturation is generated by the ""tree level"" Glauber-Mueller
mechanism. For systems where the broadening results form the nonlinear QCD
evolution to high energy, the presence or absence of Cronin effect depends
crucially on the quantitative behavior of the gluon distribution functions at
transverse momenta kt outside the so called scaling window. We discuss the
relation of this phenomenon to the recent analysis by Kharzeev-Levin-McLerran
of the momentum and centrality dependence of particle production in
nucleus-nucleus collisions at RHIC.",0305265v2
2003-06-27,On solutions of the Balitsky-Kovchegov equation with impact parameter,"We numerically analyze the Balitsky-Kovchegov equation with the full
dependence on impact parameter b. We show that due to a particular b-dependence
of the initial condition the amplitude decreases for large dipole sizes r. Thus
the region of saturation has a finite extension in the dipole size r, and its
width increases with rapidity. We also calculate the b-dependent saturation
scale and discuss limitations on geometric scaling. We demonstrate the instant
emergence of the power-like tail in impact parameter, which is due to the long
range contributions. Thus the resulting cross section violates the Froissart
bound despite the presence of a nonlinear term responsible for saturation.",0306279v2
2003-07-07,Geometric Scaling in Inclusive Charm Production,"We show that the cross section for inclusive charm production exhibits
geometric scaling in a large range of photon virtualities. In the HERA
kinematic domain the saturation momentum $Q_{sat}^2(x)$ stays below the hard
scale $\mu_c^2=4m_c^2$, implying charm production probing mostly the color
transparency regime and unitarization effects being almost negligible. We
derive our results considering two saturation models which are able to describe
the DESY ep collider HERA data for the proton structure function at small
values of the Bjorken variable $x$. A striking feature is the scaling on
$\tau=Q_2^2/Q_{sat}^2(x)$ above saturation limit, corroborating recent
theoretical studies.",0307090v2
2003-10-31,Traveling wave fronts and the transition to saturation,"We propose a general method to study the solutions to nonlinear QCD evolution
equations, based on a deep analogy with the physics of traveling waves. In
particular, we show that the transition to the saturation regime of high energy
QCD is identical to the formation of the front of a traveling wave. Within this
physical picture, we provide the expressions for the saturation scale and the
gluon density profile as a function of the total rapidity and the transverse
momentum. The application to the Balitsky-Kovchegov equation for both fixed and
running coupling constants confirms the effectiveness of this method.",0310357v2
2003-12-12,Impact of saturation on s-channel helicity nonconservation for diffractive vector mesons,"As Glauber has shown in 1959, the spin-flip phenomena caused by the
conventional spin-orbit interaction do vanish in the scattering off heavy,
strongly absorbing nuclei. On the other hand, the origin of the s-channel
helicity nonconservation (SCHNC) in diffractive DIS is of the origin different
from simple spin-orbit interaction, and here we demonstrate that SCHNC in
vector meson production survives strong absorption effects in nuclear targets.
The intranuclear absorption often discussed in terms of the saturation effects
introduces a new large scale $Q_A^2$ into the calculation of diffractive vector
meson production amplitudes. Based on the color dipole approach, we show how
the impact of the saturation scale $Q_A^2$ changes from the coherent to
incoherent/quasifree diffractive vector mesons.",0312170v1
2004-08-06,Dilepton low $p_T$ suppression as an evidence of the Color Glass Condensate,"The dilepton production is investigated in proton-nucleus collisions in the
forward region using the Color Glass Condensate approach. The transverse
momentum distribution ($p_T$), more precisely the low $p_T$ region, where the
saturation effects are expected to increase, is analyzed. The ratio between
proton-nucleus and proton-proton differential cross section for RHIC and LHC
energies is evaluated, showing the effects of saturation at small $p_T$, and
presenting a Cronin type peak at moderate $p_T$. These features indicate the
dilepton as a most suitable probe to study the properties of the saturated
regime and the Cronin effect.",0408097v2
2004-09-22,Saturation: Colour Glass Condensate and colour sources,"In the recent years we have seen a lot of activity around systems and
experiments, like DIS at HERA or the heavy-ion experiments at RHIC, involving a
large number of partons due to the high enery and/or the high number of
participants of those experiments. The main problem in this regime is that of
the high parton densities. In fact, in most of the models of multiparticle
production, two contributions to the multiplicity are considered: one
proportional to the number of participant nucleons, $N_{part}$, and a second
one proportional to the number of collisions, $N_{part}^{4/3}$. In order to get
the right multiplicities at RHIC it is necessary to lower the second
contribution. A possible mechanism for this is the saturation. Here, I am going
to review the saturation of parton densities in the initial state, in two
different frameworks: the Colour Glass Condensate %(CGC) and the string
clustering.",0409264v1
2004-11-15,Saturation momentum at fixed and running QCD coupling,"A relationship, linking the saturation momentum in the case of fixed and
running QCD coupling, respectively, is derived from the Balitsky-Kovchegov
equation. It relies on the linear instability of the evolution equation in the
dilute regime. The leading orders of the saturation momenta are mapped onto
each other exactly. For subleading terms a qualitative correspondence is
achieved with a relative error going to zero for large rapidities. The
relationship can also be derived for the Balitsky-Kovchegov equation with a
cutoff accounting for low-density effects and is satisfied by the corresponding
isoline functions. Further implications arise for the existence of
travelling-wave solutions in the two situations.",0411192v2
2005-06-13,Particle Correlations in Saturated QCD Matter,"We study quantitatively angular correlations in the two-particle spectrum
produced by an energetic probe scattering off a dense hadronic target with
sizeable saturation momentum. To this end, two parton inclusive cross sections
for arbitrary projectiles with small color charge density are derived in the
eikonal formalism. Our results are the following: For large momenta of the
observed particles, the perturbative limit with characteristic back-to-back
correlation is recovered. As the trigger momenta get closer to the saturation
scale Q_s, the angular distribution broadens. When the momenta are
significantly smaller than Q_s, the azimuthal distribution is broad but still
peaked back-to-back. However, in a narrow momentum range (0.5 - 1.5) Q_s, we
observe that the azimuthal correlation splits into a double peak with maxima
displaced away from 180 degree. We argue that it is the soft multiple
scattering physics that is responsible for the appearance of this shift in the
angle of maximal correlation. We also point out that when the physical size of
the projectile is particularly small, the double peak structure persists in a
significantly wider range of final state momenta.",0506126v1
2005-10-07,"Color strings, Pomerons and Color Glass Condensate","In the recent experiments like DIS at HERA or the heavy-ion experiments at
RHIC, and also in expected LHC at CERN, the number of involved partons is very
large, due to the high energy and/or the high number of participants of those
experiments. These high parton densities should in principal lead to an
extremely huge multiparticle production, but experimentally we have seen that
this is not the case. So there should be a mechanism that reduces the number of
created particle. Here, I review the problem of parton saturation and its
implications through three in principal different approaches, but somewhat
related: saturation in a geometrical approach, QCD saturation through the Color
Glass Condensate and perturbative Pomeron approach with initial conditions.",0510102v1
2005-11-18,Saturation in diffractive deep inelastic eA scattering,"In this paper we investigate the saturation physics in diffractive deep
inelastic electron-ion scattering. We estimate the energy and nuclear
dependence of the ratio $\sigma^{diff}/\sigma^{tot}$ and predict the $x_{\pom}$
and $\beta$ behavior of the nuclear diffractive structure function
$F_{2,A}^{D(3)}(Q^2, \beta, x_{IP})$. Moreover, we analyze the ratio
$R^{diff}_{A1,A2}(Q^2, \beta, x_{IP}) = F_{2,A1} ^{D(3)}/F_{2,A2} ^{D(3)}$,
which probes the nuclear dependence of the structure of the Pomeron. We show
that saturation physics predicts that approximately 37 % of the events observed
at eRHIC should be diffractive.",0511224v2
2006-05-17,Saturation in High-energy QCD,"In these proceedings, I shall review the basic concepts of perturbative QCD
in its high-energy limit, emphasising the approach to the unitarity limit,
usually referred to as {\em saturation}. I shall explain the basic framework
showing the need for saturation, first, from a simple picture of the
high-energy behaviour, then, giving a short derivation of the equation driving
this evolution. In the second part, I shall exhibit an analogy with statistical
physics and show how this allows to derive {\em geometric scaling} in QCD with
saturation. I shall finally consider the effects of gluon-number fluctuations
on this picture.",0605192v1
2006-06-21,On the probability distribution of the stochastic saturation scale in QCD,"It was recently noticed that high-energy scattering processes in QCD have a
stochastic nature. An event-by-event scattering amplitude is characterised by a
saturation scale which is a random variable. The statistical ensemble of
saturation scales formed with all the events is distributed according to a
probability law whose cumulants have been recently computed. In this work, we
obtain the probability distribution from the cumulants. We prove that it can be
considered as Gaussian over a large domain that we specify and our results are
confirmed by numerical simulations.",0606233v2
2006-07-11,Saturation Physics in Ultra High Energy Cosmic Rays: Heavy Quark Production,"In this work we estimate the heavy quark production in the interaction of
ultra high energy cosmic rays in the atmosphere, considering that the primary
cosmic ray is a proton or a photon. At these energies the saturation momentum
Q_{sat}^2 stays above the hard scale \mu_c^2=4m_c^2, implying charm production
probing the saturation regime. In particular, we show that the ep HERA data
presents a scaling on \tau_c = (Q^2+\mu_c^2)/Q_{sat}^2. We derive our results
considering the dipole picture and the Color Glass Condensate formalism, which
one shows to be able to describe the heavy quark production in photon-proton
and proton-proton collisions. Nuclear effects are considered in computation of
cross sections for scattering on air nuclei. Implications on the flux of prompt
leptons at the earth are analyzed and a large suppression is predicted.",0607125v2
2006-10-31,QCD at high energy: saturation and fluctuation effects,"In these proceedings, I shall review the basic concepts of perturbative QCD
in its high-energy limit. I shall concentrate on the approach to the unitarity
limit, usually referred to as saturation, as well as on the gluon-number
fluctuations the importance of which has recently been discovered. I shall
explain the basic framework showing the need for those phenomena, first, from a
simple picture of the high-energy behaviour, then, giving a short derivation of
the equation driving this evolution. In the second part, I shall exhibit an
analogy with statistical physics and show how this allows to derive geometric
scaling in QCD with saturation. I shall finally consider the effects of
gluon-number fluctuations on this picture and draw the physical consequences,
i.e. a new scaling law, arising from those results.",0610436v1
2007-01-31,Liouville field theory for gluon saturation in QCD at high energy,"We argue that quantum Liouville field theory supplemented with a suitable
source term is the effective theory which describes the short-range
correlations of the gluon saturation momentum in the two-dimensional
impact-parameter space, at sufficiently high energy and for a large number of
colors. This is motivated by recent developments concerning the stochastic
aspects of the high-energy evolution in QCD, together with the manifest scale
invariance of the respective evolution equations and general considerations on
the uncertainty principle. The source term explicitly breaks down the conformal
symmetry of the (pure) Liouville action, thus introducing a physical mass scale
in the problem which is identified with the average saturation momentum. We
construct this source term for the case of a homogeneous distribution and show
that this leads to an interesting theory: the relevant correlation functions
are ultraviolet finite (and not just renormalizable) when computed in
perturbation theory, due to mutual cancellations of the tadpole divergences.
Possible generalizations to inhomogeneous source terms are briefly discussed.",0701276v1
2007-02-08,Geometric Scaling and QCD Dynamics in DIS,"DIS data from HERA show a striking regularity as \sigma^{\gamma^* p} is a
function of the ratio \tau=Q^2/Q_s^2(x) only. The scaling function shows a
break at \tau ~ 1, which has been taken as an indication for saturation.
However, besides saturation also the transition between dominance of
k_t-ordered (DGLAP) and k_t-non-ordered (BFKL) evolution contributes to a break
around this value of \tau, as well as the suppression for small Q^2 due to
finite quark masses and confinement. In this paper we use a dipole cascade
model based on Mueller's dipole model, which also includes energy conservation
and pomeron mergins, to investigate the contributions of these different
effects to the scaling behaviour. As a result we predict that the scaling
function for \tau < 1 will be modified when data for Q^2 > 1 GeV^2 become
available. We also investigate the scaling properties of the charm contribution
and the impact parameter dependence of the saturation scale.",0702087v3
2007-02-13,Universality of QCD traveling-waves with running coupling,"The Balitsky-Kovchegov QCD equation for rapidity evolution describing
saturation effects at high energy admits universal asymptotic traveling-wave
solutions when the nonlinear damping becomes effective. The asymptotic
solutions fall in universality classes depending only on some specific
properties of the solution of the associated linear equation. We derive these
solutions for the recent QCD formulations of the Balitsky-Kovchegov equation
with running coupling constant obtained from quark-loop calculation. While the
associated linear solutions depend in different ways with observables and
higher-order effects, we show that the asymptotic traveling-wave solutions all
belong to the same universality class whose solutions are given. Hence the
influence of saturation stabilizes the QCD evolution with respect to higher
order effects and leads to universal features at high enough rapidity, such as
the form of the traveling waves, the intercept of the saturation scale and
geometric scaling in square-root of the rapidity.",0702131v2
2007-02-16,Exclusive vector meson production at HERA from QCD with saturation,"Following recent predictions that the geometric scaling properties of deep
inelastic scattering data in inclusive gamma*-p collisions are expected also in
exclusive diffractive processes, we investigate the diffractive production of
vector mesons. Using analytic results in the framework of the BK equation at
non-zero momentum transfer, we extend to the non-forward amplitude a
QCD-inspired forward saturation model including charm, following the
theoretical predictions for the momentum transfer dependence of the saturation
scale. We obtain a good fit to the available HERA data and make predictions for
deeply virtual Compton scattering measurements.",0702171v2
1995-12-22,Massless BPS-Saturated States on the Two-Torus Moduli Sub-Space of Heterotic String,"Within a four-dimensional, toroidally compactified heterotic string, we
identify (quantized) charge vectors of electrically charged BPS-saturated
states (along with the tower of SL(2,Z) related dyonic states), which preserve
1/2 of N=4 supersymmetry and become massless along the hyper-surfaces of
enhanced gauge symmetry of the two-torus moduli sub-space. In addition, we
identify charge vectors of the dyonic BPS-saturated states (along with the
tower of SL(2,Z) related states), which preserve 1/4 of N=4 supersymmetry, and
become massless at two points with the maximal gauge symmetry enhancement.",9512188v3
1997-02-28,BPS-Saturated Bound States of Tilted P-Branes in Type II String Theory,"We found BPS-saturated solutions of M-theory and Type II string theory which
correspond to (non-marginally) bound states of p-branes intersecting at angles
different from pi/2. These solutions are obtained by starting with a BPS
marginally bound (orthogonally) intersecting configurations of two p-branes
(e.g, two four-branes of Type II string theory), performing a boost
transformation at an angle with respect to the world-volume of the
configuration, performing T-duality transformation along the boost-direction,
S-duality transformation, and T- transformations along the direction
perpendicular to the boost transformation. The resulting configuration is
non-marginally bound BPS-saturated solution whose static metric possesses the
off-diagonal term which cannot be removed by a coordinate transformation, and
thus signifies an angle (different from pi/2) between the resulting
intersecting p-branes. Additional new p-branes are bound to this configuration,
in order to ensure the stability of such a static, tilted configuration.",9702205v3
1997-06-19,BPS-Saturated Walls in Supersymmetric Theories,"Domain-wall solutions in four-dimensional supersymmetric field theories with
distinct discrete vacuum states lead to the spontaneous breaking of
supersymmetry, either completely or partially. We consider in detail the case
when the domain walls are the BPS-saturated states, and 1/2 of supersymmetry is
preserved. Several useful criteria that relate the preservation of 1/2 of
supersymmetry on the domain walls to the central extension appearing in the N=1
superalgebras are established. We explain how the central extension can appear
in N=1 supersymmetry and explicitly obtain the central charge in various
models: the generalized Wess-Zumino models, and supersymmetric Yang-Mills
theories with or without matter. The BPS-saturated domain walls satisfy the
first-order differential equations which we call the creek equations, since
they formally coincide with the (complexified) equations of motion of an analog
high-viscosity fluid on a profile which is given by the superpotential of the
original problem. Some possible applications are considered.",9706141v3
1997-07-30,Four-dimensional BPS-spectra via M-theory,"We consider the realization of four-dimensional theories with N = 2
supersymmetry as M-theory configurations including a five-brane. Our emphasis
is on the spectrum of massive states, that are realized as two-branes ending on
the five-brane. We start with a determination of the supersymmetries that are
left unbroken by the background metric and five-brane. We then show how the
central charge of the N = 2 algebra arises from the central charge associated
with the M-theory two-brane. This determines the condition for a two-brane
configuration to be BPS-saturated in the four-dimensional sense. By imposing
certain conditions on the moduli, we can give concrete examples of such
two-branes. This leads us to conjecture that vectormultiplet and hypermultiplet
BPS-saturated states correspond to two-branes with the topology of a cylinder
and a disc respectively. We also discuss the phenomenon of marginal stability
of BPS-saturated states.",9707251v2
2000-06-11,BPS Saturated Domain Walls along a Compact Dimension,"Generalized Wess-Zumino models which admit topologically non-trivial BPS
saturated configurations along one compact, spatial dimension are investigated
in various dimensions of space-time. We show that, in a representative model
and for sufficiently large circumference, there are BPS configurations along
the compact dimension containing an arbitrary number of equidistant,
well-separated domain walls. We analyze the spectrum of the bosonic and
fermionic light and massless modes that are localized on these walls. The
masses of the light modes are exponentially suppressed by the ratio of the
distance between the walls and their width. States that are initially localized
on one wall oscillate in time between all the walls. In (2+1) dimensions the
``chirality'' of localized, massless fermions is determined. In the
(1+1)-dimensional case we show how the mass of certain classically BPS
saturated solitons is lifted above the BPS bound by instanton tunneling.",0006077v3
2003-07-29,Nonvanishing quantum corrections to the mass and central charge of the N=2 vortex and BPS saturation,"The one-loop quantum corrections to the mass and central charge of the N=2
vortex in 2+1 dimensions are determined using supersymmetry-preserving
dimensional regularization by dimensional reduction of the corresponding N=1
model with Fayet-Iliopoulos term in 3+1 dimensions. Both the mass and the
central charge turn out to have nonvanishing one-loop corrections which however
are equal and thus saturate the Bogomolnyi bound. We explain BPS saturation by
standard multiplet shortening arguments, correcting a previous claim in the
literature postulating the presence of a second degenerate short multiplet at
the quantum level.",0307282v3
1996-09-15,"Characterizing aleph_epsilon-saturated models of superstable ndop theories by L_{infty, aleph_epsilon}-theory","After the main gap theorem was proved (see [Sh:c]), in discussion, Harrington
expressed a desire for a finer structure - of finitary character (when we have
a structure theorem at all). I point out that the logic L_{infty,aleph_0}(d.q.)
(d.q. stands for dimension quantifier) does not suffice: e.g., for T=Th(lambda
x 2^\omega,E_n)_{n<omega} where (alpha,eta)E_n(beta,nu) =: eta|n=nu|n and for a
subset S of 2^omega we define
  M_S = M | {(alpha,eta): [eta in S -> alpha<omega_1] and [eta in 2^\omega
backslash S -> alpha<omega]}.
  Hence, it seems to me we should try L_{infty,aleph_epsilon}(d.q.)
(essentially, in C we can quantify over sets which are included in the
algebraic closure of finite sets), and Harrington accepts this interpretation.
Here the conjecture is proved for aleph_epsilon-saturated models. I.e., the
main theorem is M equiv_{L_{infty,aleph_epsilon}(d.q.)} N iff M cong N for
aleph_epsilon--saturated models of a superstable countable (first order) theory
T without dop.",9609215v1
2001-01-04,Simple Homogeneous Models,"Geometrical stability theory is a powerful set of model-theoretic tools that
can lead to structural results on models of a simple first-order theory.
Typical results offer a characterization of the groups definable in a model of
the theory. The work is carried out in a universal domain of the theory (a
saturated model) in which the Stone space topology on ultrafilters of definable
relations is compact. Here we operate in the more general setting of
homogeneous models, which typically have noncompact Stone topologies. In this
paper strongly lambda-homogeneous models (M,R) in which the elements of R
induce a symmetric and transitive notion of independence with bounded character
are studied. This notion of independence, defined using a combinatorial
condition called ``dividing'', agrees with forking independence when (M,R) is
saturated. The concept central to the development of geometrical stability
theory for saturated structures, namely the canonical base, is also shown to
exist in this setting.",0101036v2
2001-10-23,On the existence of completely saturated packings and completely reduced covering,"A packing by a body $K$ is collection of congruent copies of $K$ (in either
Euclidean or hyperbolic space) so that no two copies intersect nontrivially in
their interiors. A covering by $K$ is a collection of congruent copies of $K$
such that for every point $p$ in the space there is copy in the collection
containing $p$. A completely saturated packing is one in which it is not
possible to replace a finite number of bodies of the packing with a larger
number and still remain a packing. A completely reduced covering is one in
which it is not possible to replace a finite number of bodies of the covering
with a smaller number and still remain a covering. It was conjectured by G.
Fejes Toth, G. Kuperberg, and W. Kuperberg that completely saturated packings
and commpletely reduced coverings exist for every body $K$ in either
$n$-dimensional Euclidean or $n$-dimensional hyperbolic space. We prove this
conjecture.",0110260v1
2003-11-11,A definable nonstandard model of the reals,"We prove in ZFC the existence of a definable, countably saturated elementary
extension of the reals.
  It seems that it has been taken for granted that there is no distinguished,
definable nonstandard model of the reals. (This means a countably saturated
elementary extension of the reals.) Of course if V=L then there is such an
extension (just take the first one in the sense of the canonical well-ordering
of L), but we mean the existence provably in ZFC. There were good reasons for
this: without Choice we cannot prove the existence of any elementary extension
of the reals containing an infinitely large integer. Still there is one.
  Theorem (ZFC). There exists a definable, countably saturated extension R* of
the reals R, elementary in the sense of the language containing a symbol for
every finitary relation on R.",0311165v1
2005-03-14,Moduli of objects in dg-categories,"To any dg-category $T$ (over some base ring $k$), we define a $D^{-}$-stack
$\mathcal{M}_{T}$ in the sense of \cite{hagII}, classifying certain
$T^{op}$-dg-modules. When $T$ is saturated, $\mathcal{M}_{T}$ classifies
compact objects in the triangulated category $[T]$ associated to $T$. The main
result of this work states that under certain finiteness conditions on $T$
(e.g. if it is saturated) the $D^{-}$-stack $\mathcal{M}_{T}$ is locally
geometric (i.e. union of open and geometric sub-stacks). As a consequence we
prove the algebraicity of the group of auto-equivalences of a saturated
dg-category. We also obtain the existence of reasonable moduli for perfect
complexes on a smooth and proper scheme, as well as complexes of
representations of a finite quiver.",0503269v5
2006-07-24,Computing holes in semi-groups and its applications to transportation problems,"An integer feasibility problem is a fundamental problem in many areas, such
as operations research, number theory, and statistics. To study a family of
systems with no nonnegative integer solution, we focus on a commutative
semigroup generated by a finite set of vectors in $\Z^d$ and its saturation. In
this paper we present an algorithm to compute an explicit description for the
set of holes which is the difference of a semi-group $Q$ generated by the
vectors and its saturation. We apply our procedure to compute an infinite
family of holes for the semi-group of the $3\times 4\times 6$ transportation
problem. Furthermore, we give an upper bound for the entries of the holes when
the set of holes is finite. Finally, we present an algorithm to find all
$Q$-minimal saturation points of $Q$.",0607599v3
2000-09-04,Stable autosolitons in dispersive media with saturable gain and absorption,"We introduce the simplest one-dimensional model of a dispersive optical
medium with saturable dissipative nonlinearity and filtering (dispersive loss)
which gives rise to stable solitary pulses (autosolitons). In the particular
case when the dispersive loss is absent, the same model may also be interpreted
as describing a stationary field in a planar optical waveguide with uniformly
distributed saturable gain and absorption. In a certain region of the model's
parameter space, two coexisting solitary-pulse solutions are found numerically,
one of which may be stable. Solving the corresponding linearized eigenvalue
problem, we identify stability borders for the solitary pulses in their
parametric plane. Beyond one of the borders, the symmetric pulse is destroyed
by asymmetric perturbations, and at the other border it undergoes a Hopf
bifurcation, which may turn it into a breather.",0009011v1
2004-02-17,Saturation of Turbulent Drag Reduction in Dilute Polymer Solutions,"Drag reduction by polymers in turbulent wall-bounded flows exhibits universal
and non-universal aspects. The universal maximal mean velocity profile was
explained in a recent theory. The saturation of this profile and the crossover
back to the Newtonian plug are non-universal, depending on Reynolds number Re,
concentration of polymer $c_p$ and the degree of polymerization $N_p$. We
explain the mechanism of saturation stemming from the finiteness of
extensibility of the polymers, predict its dependence on $c_p$ and $N$ in the
limit of small $c_p$ and large Re, and present the excellent comparison of our
predictions to experiments on drag reduction by DNA.",0402027v1
2004-11-19,Saturation of azimuthal anisotropy in Au + Au collisions at sqrt(s_NN) = 62 - 200 GeV,"New measurements are presented for charged hadron azimuthal correlations at
mid-rapidity in Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV. They are
compared to earlier measurements obtained at sqrt(s_NN) = 130 GeV and in Pb+Pb
collisions at sqrt(s_NN) = 17.2 GeV. Sizeable anisotropies are observed with
centrality and transverse momentum (p_T) dependence characteristic of elliptic
flow (v_2). For a broad range of centralities, the observed magnitudes and
trends of the differential anisotropy, v_2(p_T), change very little over the
collision energy range sqrt(s_NN) = 62-200 GeV, indicating saturation of the
excitation function for v_2 at these energies. Such a saturation may be
indicative of the dominance of a very soft equation of state for sqrt(s_NN) =
62-200 GeV.",0411040v1
1992-12-09,Relativistic Nuclear Matter with Self-Consistent Correlation Energy,"We study relativistic nuclear matter in the $\sigma - \omega$ model including
the ring-sum correlation energy. The model parameters are adjusted
self-consistently to give the canonical saturation density and binding energy
per nucleon with the ring energy included. Two models are considered,
mean-field-theory where we neglect vacuum effects, and the relativistic Hartree
approximation where such effects are included but in an approximate way. In
both cases we find self-consistent solutions and present equations of state. In
the mean-field case the ring energy completely dominates the attractive part of
the energy density and the elegant saturation mechanism of the standard
approach is lost, namely relativistic quenching of the scalar attraction. In
the relativistic Hartree approach the vacuum effects are included in an
approximate manner using vertex form factors with a cutoff of 1 - 2 GeV, the
range expected from QCD. Due to the cutoff, the ring energy for this case is
significantlysmaller, and we obtain self-consistent solutions which preserve
the basic saturation mechanism of the standard relativistic approach.",9212003v1
1993-01-20,Relativistic Ring-Diagram Nuclear Matter Calculations,"A relativistic extension of the particle-particle hole-hole ring-diagram
many-body formalism is developed by using the Dirac equation for
single-particle motion in the medium. Applying this new formalism, calculations
are performed for nuclear matter. The results show that the saturation density
is improved and the equation of state becomes softer as compared to
corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A
potential, nuclear matter is predicted to saturate at an energy per nucleon of
--15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm$^{-1}$, in
excellent agreement with empirical information. The compression modulus is 152
MeV at the saturation point.",9301012v1
1995-06-30,Saturation properties and incompressibility of nuclear matter: A consistent determination from nuclear masses,"Starting with a two-body effective nucleon-nucleon interaction, it is shown
that the infinite nuclear matter model of atomic nuclei is more appropriate
than the conventional Bethe-Weizsacker like mass formulae to extract saturation
properties of nuclear matter from nuclear masses. In particular, the saturation
density thus obtained agrees with that of electron scattering data and the
Hartree-Fock calculations. For the first time using nuclear mass formula, the
radius constant $r_0$=1.138 fm and binding energy per nucleon $a_v$ = -16.11
MeV, corresponding to the infinite nuclear matter, are consistently obtained
from the same source. An important offshoot of this study is the determination
of nuclear matter incompressibility $K_{\infty}$ to be 288$\pm$ 28 MeV using
the same source of nuclear masses as input.",9506032v1
1995-11-07,New QCD Sum Rules for Nucleons in Nuclear Matter,"Two new QCD sum rules for nucleons in nuclear matter are obtained from a
mixed correlator of spin-1/2 and spin-3/2 interpolating fields. These new sum
rules, which are insensitive to the poorly known four-quark condensates,
provide additional information on the nucleon scalar self-energy. These new sum
rules are analyzed along with previous spin-1/2 interpolator-based sum rules
which are also insensitive to the poorly known four-quark condensates. The
analysis indicates consistency with the expectations of relativistic nuclear
phenomenology at nuclear matter saturation density. However, a weaker density
dependence near saturation is suggested. Using previous estimates of in-medium
condensate uncertainties, we find $M^* = 0.64^{+0.13}_{-0.09}$ GeV and
$\Sigma_v = 0.29^{+0.06}_{-0.10}$ GeV at nuclear matter saturation density.",9511007v3
1998-08-26,Saturation Properties of Nuclear Matter with a Nonlocal Confining Solitons,"We examine saturation properties of a quark-based picture of nuclear matter.
Soliton matter consisting of nonlocal confining solitons is used to model
nuclear matter. Each composite nucleon is described by a non-topological
soliton as given by the Global Color Model. We apply techniques and concepts
from the discription of crystal lattices. In particular, the Wigner-Seitz
approximation is used to calculate the properties of the soliton lattice at the
mean-field level. We focus on infinite nuclear matter at around standard
nuclear matter density with the simplest one-parameter assumption for the gluon
propagator. the saturation density and incompressibility are calculated as
functions of the single parameter of the model",9808067v1
2000-07-13,Saturation of low-energy antiproton annihilation on nuclei,"Recent measurements of very low-energy ($p_{L}<100$ MeV/c) $\bar p$
annihilation on light nuclei reveal apparent suppression of annihilation upon
increasing the atomic charge $Z$ and mass number $A$. Using $\bar p$-nucleus
optical potentials $V_{{\rm opt}}$, fitted to $\bar p$-atom energy-shifts and
-widths, we resolve this suppression as due to the strong effective repulsion
produced by the very absorptive $V_{{\rm opt}}$. The low-energy $\bar
p$-nucleus wavefunction is kept substantially outside the nuclear surface and
the resulting reaction cross section saturates as function of the strength of
Im $V_{{\rm opt}}$. This feature, for $E >0$, parallels the recent prediction,
for $E < 0$, that the level widths of $\bar p$ atoms saturate and, hence, that
$\bar p$ deeply bound atomic states are relatively narrow. Antiproton
annihilation cross sections are calculated at $p_{L}=57$ MeV/c across the
periodic table, and their dependence on $Z$ and $A$ is classified and discussed
with respect to the Coulomb focussing effect at very low energies.",0007029v2
2000-08-08,Energy and Centrality Dependence of Rapidity Densities at RHIC,"The energy and centrality dependence of the charged multiplicity per
participant nucleon is shown to be able to differentiate between final-state
saturation and fixed scale pQCD models of initial entropy production in
high-energy heavy-ion collisions. The energy dependence is shown to test the
nuclear enhancement of the mini-jet component of the initial conditions, while
the centrality dependence provides a key test of whether gluon saturation is
reached at RHIC energies. HIJING model predicts that the rapidity density per
participant increases with centrality, while the saturation model prediction is
essentially independent of centrality.",0008014v2
2001-05-22,Chiral Dynamics and Nuclear Matter,"We calculate the equation of state of isospin-symmetric nuclear matter in the
three-loop approximation of chiral perturbation theory. The contributions to
the energy per particle $\bar E(k_f)$ from one- and two-pion exchange diagrams
are ordered in powers of the Fermi momentum $k_f$ (modulo functions of $k_f
/m_\pi$). It is demonstrated that, already at order ${\cal O}(k_f^4)$, two-pion
exchange produces realistic nuclear binding. The underlying saturation
mechanism is surprisingly simple (in the chiral limit), namely the combination
of an attractive $k_f^3$-term and a repulsive $k_f^4$-term. The empirical
saturation point and the nuclear compressibility $K\simeq 250 $MeV are well
reproduced at order ${\cal O}(k_f^5)$ with a momentum cut-off of $\Lambda
\simeq 0.65$ GeV which parametrizes short-range dynamics. No further
short-distance terms are required in our calculation of nuclear matter. In the
same framework we calculate the density-dependent asymmetry energy and find
$A_0\simeq 34 $MeV at the saturation point, in good agreement with the
empirical value. The pure neutron matter equation of state is also in fair
qualitative agreement with sophisticated many-body calculations and a
resummation result of effective field theory, but only for low neutron
densities $\rho_n <0.25 $fm$^{-3}$.",0105057v1
2001-08-13,Relevance of high-momentum nucleons for nuclear phenomena,"A brief review is given concerning the status of the theoretical work on
nucleon spectral functions. A recent concern about the validity of the concept
of spectroscopic factors as deduced from (e,e'p) reactions at higher Q^2, is
discussed in some detail. The consequences of the observed spectral strength
are then considered in the context of nuclear saturation. It is argued that
short-range correlations are mainly responsible for the actual value of the
observed charge density in 208Pb and by extension for the empirical value of
the saturation density of nuclear matter. This observation combined with the
general understanding of the spectroscopic strength suggests that a renewed
study of nuclear matter, emphasizing the self-consistent determination of the
spectral strength due to short-range and tensor correlations, may shed light on
the perennial nuclear saturation problem. First results using such a scheme are
presented.",0108028v1
2001-08-13,Saturation properties of nuclear matter and correlated nucleons,"A brief overview is given of the properties of spectral functions in finite
nuclei as obtained from (e,e'p) experiments. Based on recent experimental data
from this reaction it is argued that the empirical value of the saturation
density of nuclear matter is dominated by short-range correlations. This
observation and the observed fragmentation and depletion of the single-particle
strength in nuclei provide the motivation for attempting a self-consistent
description of the nucleon spectral functions with full inclusion of
short-range and tensor correlations in nuclear matter. Results for these
``second generation'' spectral functions will be discussed with emphasis on the
consequences for the saturation properties of nuclear matter. Arguments are
presented to clarify the obscuring role of pionic long-range correlations in
this long-standing problem.",0108029v1
2004-08-19,Phase Separation of Saturated and Mono-unsaturated Lipids as determined from a Microscopic Model,"A molecular model is proposed of a bilayer consisting of fully saturated DPPC
and mono unsaturated DOPC. The model not only encompasses the constant density
within the hydrophobic core of the bilayer, but also the tendency of chain
segments to align. It is solved within self-consistent field theory. A model
bilayer of DPPC undergoes a main chain transition to a gel phase, while a
bilayer of DOPC does not do so above zero degrees centigrade because of the
double bond which disrupts order. We examine structural and thermodynamic
properties of these membranes and find our results in reasonable accord with
experiment. In particular, order-parameter profiles are in good agreement with
NMR experiments. A phase diagram is obtained for mixtures of these lipids in a
membrane at zero tension. The system undergoes phase separation below the
main-chain transition temperature of the saturated lipid. Extensions to the
ternary DPPC, DOPC, and cholesterol system are outlined.",0408085v2
2005-01-14,Stable one-dimensional periodic waves in Kerr-type saturable and quadratic nonlinear media,"We review the latest progress and properties of the families of bright and
dark one-dimensional periodic waves propagating in saturable Kerr-type and
quadratic nonlinear media. We show how saturation of the nonlinear response
results in appearance of stability (instability) bands in focusing (defocusing)
medium, which is in sharp contrast with the properties of periodic waves in
Kerr media. One of the key results discovered is the stabilization of
multicolor periodic waves in quadratic media. In particular, dark-type waves
are shown to be metastable, while bright-type waves are completely stable in a
broad range of energy flows and material parameters. This yields the first
known example of completely stable periodic wave patterns propagating in
conservative uniform media supporting bright solitons. Such results open the
way to the experimental observation of the corresponding self-sustained
periodic wave patterns.",0501075v1
2006-05-31,Acoustic wave propagation in a macroscopically inhomogeneous porous medium saturated by a fluid,"The equations of motion in a macroscopically inhomogeneous porous medium
saturated by a fluid are derived. As a first verification of the validity of
these equations, a two-layer rigid frame porous system considered as one single
porous layer with a sudden change in physical properties is studied. A simple
wave equation is derived and solved for this system. The reflection and
transmission coefficients are calculated numerically using a wave
splitting-Green's function approach (WS-GF). The reflected and transmitted wave
time histories are also simulated. Experimental results obtained for materials
saturated by air are compared to the results given by this approach and to
those of the classical transfer matrix method (TMM).",0605259v3
2007-04-10,A Rational Approach to Resonance Saturation in large-Nc QCD,"We point out that resonance saturation in QCD can be understood in the
large-Nc limit from the mathematical theory of Pade Approximants to meromorphic
functions. These approximants are rational functions which encompass any
saturation with a finite number of resonances as a particular example,
explaining several results which have appeared in the literature. We review the
main properties of Pade Approximants with the help of a toy model for the
<VV-AA> two-point correlator, paying particular attention to the relationship
among the Chiral Expansion, the Operator Product Expansion and the resonance
spectrum. In passing, we also comment on an old proposal made by Migdal in 1977
which has recently attracted much attention in the context of AdS/QCD models.
Finally, we apply the simplest Pade Approximant to the <VV-AA> correlator in
the real case of QCD. The general conclusion is that a rational approximant may
reliably describe a Green's function in the Euclidean, but the same is not true
in the Minkowski regime due to the appearance of unphysical poles and/or
residues.",0704.1247v1
2007-09-20,Calculation of DOS-Dependent Channel Potentials in FETs in the Saturation Condition,"We calculated functions for the potential, Vch, in the channel of a field
effect transistor with various densities of the localized states (DOS) by using
a device simulator. In the saturation condition, Vch is found to fit
satisfactorily to the analytical function, Vch(y)=Vg(1-(1-y/L) k), where Vg is
the gate bias, y is the position along the channel, and L is the channel
length. The power k, which depends on the DOS, ranges from 0 to 0.5 even with
an extensive variation of DOS. As a result, the total induced charge density in
the saturation condition can be expressed a way similar to the linear condition
by introducing a correction factor, alpha, ranging between 0.65 and 1.0.",0709.3298v1
2007-10-11,Deep inelastic scattering at strong coupling from gauge/string duality : the saturation line,"For gauge theories which admit a dual string description, we analyze deep
inelastic scattering at strong 't Hooft coupling and high energy, in the
vicinity of the unitarity limit. We discuss the onset of unitarity corrections
and determine the saturation line which separates weak scattering from strong
scattering in the parameter space of rapidity and photon virtuality. We
discover that the approach towards unitarity proceeds through two different
mechanisms, depending upon the photon virtuality Q^2 : single Pomeron exchange
at relatively low Q^2 and, respectively, multiple graviton exchanges at higher
Q^2. This implies that the total cross-section at high energy and large Q^2 is
dominated by diffractive processes. This is furthermore suggestive of a
partonic description where all the partons have transverse momenta below the
saturation momentum and occupation numbers of order one.",0710.2148v2
2007-10-27,On The Linear Behaviour of the Throughput of IEEE 802.11 DCF in Non-Saturated Conditions,"We propose a linear model of the throughput of the IEEE 802.11 Distributed
Coordination Function (DCF) protocol at the data link layer in non-saturated
traffic conditions. We show that the throughput is a linear function of the
packet arrival rate (PAR) $\lambda$ with a slope depending on both the number
of contending stations and the average payload length. We also derive the
interval of validity of the proposed model by showing the presence of a
critical $\lambda$, above which the station begins operating in saturated
traffic conditions.
  The analysis is based on the multi-dimensional Markovian state transition
model proposed by Liaw \textit{et al.} with the aim of describing the behaviour
of the MAC layer in unsaturated traffic conditions. Simulation results closely
match the theoretical derivations, confirming the effectiveness of the proposed
linear model.",0710.5238v1
2007-11-22,The Dynamical Dipole Radiation in Dissipative Collisions with Exotic Beams,"Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium
nuclear interaction in regions away from saturation. In this work we present a
selection of reaction observables in dissipative collisions particularly
sensitive to the isovector part of the interaction, i.e. to the symmetry term
of the nuclear Equation of State (EoS). At low energies the behavior of the
symmetry energy around saturation influences dissipation and fragment
production mechanisms. We will first discuss the recently observed Dynamical
Dipole Radiation, due to a collective neutron-proton oscillation during the
charge equilibration in fusion and deep-inelastic collisions. We will review in
detail all the main properties, yield, spectrum, damping and angular
distributions, revealing important isospin effects. Reactions induced by
unstable 132Sn beams appear to be very promising tools to test the
sub-saturation Isovector EoS. Predictions are also presented for deep-inelastic
and fragmentation collisions induced by neutron rich projectiles. The
importance of studying violent collisions with radioactive beams at low and
Fermi energies is finally stressed.",0711.3535v1
2008-02-06,Modelling and Analysis of the Distributed Coordination Function of IEEE 802.11 with Multirate Capability,"The aim of this paper is twofold. On one hand, it presents a
multi-dimensional Markovian state transition model characterizing the behavior
at the Medium Access Control (MAC) layer by including transmission states that
account for packet transmission failures due to errors caused by propagation
through the channel, along with a state characterizing the system when there
are no packets to be transmitted in the queue of a station (to model
non-saturated traffic conditions). On the other hand, it provides a throughput
analysis of the IEEE 802.11 protocol at the data link layer in both saturated
and non-saturated traffic conditions taking into account the impact of both
transmission channel and multirate transmission in Rayleigh fading environment.
Simulation results closely match the theoretical derivations confirming the
effectiveness of the proposed model.",0802.0766v1
2008-03-04,On the High Energy Behaviour of The Total Cross Section in the QCD Dipole Model,"In this paper we perform a numerical study of the tranverse expansion of
hadronic scattering amplitudes in the dipole picture of high energy QCD. We go
beyond the mean field approximation by including fluctuations and also wave
function saturation effects, and the evolution with both a fixed and a running
coupling is investigated. We also study the nonperturbative aspects, and as has
been predicted earlier, our results indicate that the Froissart-Martin bound is
saturated once confinement effects are included in the evolution. Thus the
total cross section increases proportional to the square of the logarithm of
the cms energy. Furthermore it is seen that we obtain a reasonable value for
the proportionality coefficient. The impact of saturation and non-leading
effects on this coefficient is also studied.",0803.0446v3
2008-04-02,Direct numerical simulations of the kappa-mechanism II. The nonlinear saturation and Hertzsprung's progression,"Context: We study the kappa-mechanism that excites radial oscillations in
Cepheid variables.
  Aims: We address the mode couplings that manages the nonlinear saturation of
the instability in direct numerical simulations (DNS).
  Methods: We project the DNS fields onto an acoustic subspace built from the
regular and adjoint eigenvectors that are solutions to the linear-oscillations
equations.
  Results: We determine the time evolution of both the amplitude and kinetic
energy of each mode that propagates in the DNS. More than 98% of the total
kinetic energy is contained in two modes that correspond to the
linearly-unstable fundamental mode and the linearly-stable second overtone.
Because the eigenperiods ratio is close to 1/2, we discover that the nonlinear
saturation is due to a 2:1 resonance between these two modes. An interesting
application of this result concerns the reproduction of Hertzsprung's
progression observed in Bump Cepheids.",0804.0345v2
2008-06-09,Intensity-Dependent Enhancement of Saturable Absorption in PbS-Au4 Nanohybrid Composites: Evidence for Resonant Energy Transfer by Auger Recombination,"Intensity-dependent enhancement of saturable absorption in a film of PbS-Au4
nanohybrid composites has been observed by femtosecond time-resolved transient
absorption measurement at 780 nm. The nonlinear absorption coefficient of
saturable absorption in PbS-Au4 nanohybrid composites is found to be dependent
on excitation irradiance and it is determined to be -2.9 cm/GW at 78 GW/cm2, an
enhancement of nearly fourfold in comparison with that of pure PbS quantum dots
(QDs). The enhancement is attributed to excitation of surface plasmon by
resonant energy transfer between PbS QDs and Au nanoparticles through Auger
recombination.",0806.1374v1
2008-08-15,Wilson lines - color charge densities correlators and the production of eta' in the CGC for pp and pA collisions,"We compute the inclusive differential cross section production of the
pseudo-scalar meson eta' in high-energy proton-proton (pp) and proton-nucleus
(pA) collisions. We use an effective coupling between gluons and eta' meson to
derive a reduction formula that relates the eta' production to a field-strength
tensor correlator. For pA collisions we take into account saturation effects on
the nucleus side by using the Color Glass Condensate formalism to evaluate this
correlator. We derive new results for Wilson line - color charges correlators
in the McLerran-Venugopalan model needed in the computation of eta' production.
The unintegrated parton distribution functions are used to characterize the
gluon distribution inside protons. We show that in pp collisions, the cross
section depends on the parametrization of unintegrated parton distribution
functions and thus, it can be used to put constraints on these distributions.
We also demonstrate that in pA collisions, the cross section is sensitive to
saturation effects so it can be utilized to estimate the value of the
saturation scale.",0808.2154v1
2008-08-21,Gluon saturation effects on J/Psi production in heavy ion collisions,"We consider a novel mechanism for J/Psi production in nuclear collisions
arising due to the high density of gluons. We calculate the resulting J/Psi
production cross section as a function of rapidity and centrality. We evaluate
the nuclear modification factor and show that the rapidity distribution of the
produced J/Psi's is significantly more narrow in AA collisions due to the gluon
saturation effects. Our results indicate that gluon saturation in the colliding
nuclei is a significant source of J/Psi suppression that can be disentangled
from the quark-gluon plasma effects.",0808.2954v2
2008-08-22,Saturated subfields and invariants of finite groups,"Every subfield $\kk(\phi)$ of the field of rational functions
$\kk(x_1,...,x_n)$ is contained in a unique maximal subfield of the form
$\kk(\psi)$. The element $\psi$ is called generative for the element $\phi$. A
subfield of $\kk(x_1,...,x_n)$ is called saturated if it contains a generative
element of each its element. We study the saturation property for subfields of
invariants $\kk(x_1,...,x_n)^G$, where $G$ is a finite group of automorphisms
of the field $\kk(x_1,...,x_n)$.",0808.3132v3
2008-08-28,Stress dependent thermal pressurization of a fluid-saturated rock,"Temperature increase in saturated porous materials under undrained conditions
leads to thermal pressurization of the pore fluid due to the discrepancy
between the thermal expansion coefficients of the pore fluid and of the solid
matrix. This increase in the pore fluid pressure induces a reduction of the
effective mean stress and can lead to shear failure or hydraulic fracturing.
The equations governing the phenomenon of thermal pressurization are presented
and this phenomenon is studied experimentally for a saturated granular rock in
an undrained heating test under constant isotropic stress. Careful analysis of
the effect of mechanical and thermal deformation of the drainage and pressure
measurement system is performed and a correction of the measured pore pressure
is introduced. The test results are modelled using a non-linear
thermo-poro-elastic constitutive model of the granular rock with emphasis on
the stress-dependent character of the rock compressibility. The effects of
stress and temperature on thermal pressurization observed in the tests are
correctly reproduced by the model.",0808.3886v2
2008-09-04,Superposition for Fixed Domains,"Superposition is an established decision procedure for a variety of
first-order logic theories represented by sets of clauses. A satisfiable
theory, saturated by superposition, implicitly defines a minimal term-generated
model for the theory. Proving universal properties with respect to a saturated
theory directly leads to a modification of the minimal model's term-generated
domain, as new Skolem functions are introduced. For many applications, this is
not desired.
  Therefore, we propose the first superposition calculus that can explicitly
represent existentially quantified variables and can thus compute with respect
to a given domain. This calculus is sound and refutationally complete in the
limit for a first-order fixed domain semantics. For saturated Horn theories and
classes of positive formulas, we can even employ the calculus to prove
properties of the minimal model itself, going beyond the scope of known
superposition-based approaches.",0809.0922v3
2008-09-06,Lifetime of the A(v'=0) state and Franck-Condon factor of the A-X(0-0) transition of CaF measured by the saturation of laser-induced fluorescence,"We describe a method for determining the radiative decay properties of a
molecule by studying the saturation of laser-induced fluorescence and the
associated power broadening of spectral lines. The fluorescence saturates
because the molecules decay to states that are not resonant with the laser. The
amplitudes and widths of two hyperfine components of a spectral line are
measured over a range of laser intensities and the results compared to a model
of the laser-molecule interaction. Using this method we measure the lifetime of
the A(v'=0) state of CaF to be tau=19.2 \pm 0.7 ns, and the Franck-Condon
factor for the transition to the X(v=0) state to be Z=0.987 (+0.013 || -0.019).
In addition, our analysis provides a measure of the hyperfine interval in the
lowest-lying state of A(v'=0), Delta_e=4.8 \pm 1.1 MHz.",0809.1150v2
2008-10-17,Reduced Kronecker coefficients and counter-examples to Mulmuley's strong saturation conjecture SH,"We provide counter-examples to Mulmuley's strong saturation conjecture
(strong SH) for the Kronecker coefficients. This conjecture was proposed in the
setting of Geometric Complexity Theory to show that deciding whether or not a
Kronecker coefficient is zero can be done in polynomial time. We also provide a
short proof of the #P-hardness of computing the Kronecker coefficients. Both
results rely on the connections between the Kronecker coefficients and another
family of structural constants in the representation theory of the symmetric
groups: Murnaghan's reduced Kronecker coefficients.
  An appendix by Mulmuley introduces a relaxed form of the saturation
hypothesis SH, still strong enough for the aims of Geometric Complexity Theory.",0810.3163v3
2008-10-17,Fluidization of granular media wetted by liquid $^4$He,"We explore experimentally the fluidization of vertically agitated PMMA
spheres wetted by liquid $^4$He. By controlling the temperature around the
$\lambda$ point we change the properties of the wetting liquid from a normal
fluid (helium I) to a superfluid (helium II). For wetting by helium I, the
critical acceleration for fluidization ($\Gamma_c$) shows a steep increase
close to the saturation of the vapor pressure in the sample cell. For helium II
wetting, $\Gamma_c$ starts to increase at about 75% saturation, indicating that
capillary bridges are enhanced by the superflow of unsaturated helium film.
Above saturation, $\Gamma_c$ enters a plateau regime where the capillary force
between particles is independent of the bridge volume. The plateau value is
found to vary with temperature and shows a peak at 2.1 K, which we attribute to
the influence of the specific heat of liquid helium.",0810.3191v3
2008-12-08,Coherent and incoherent diffractive hadron production in pA collisions and gluon saturation,"We study coherent and incoherent diffractive hadron production in high energy
quarkonium--heavy nucleus collisions as a probe of the gluon saturation regime
of QCD. Taking this process as a model for pA collisions, we argue that the
coherent diffractive gluon production, in which the target nucleus states
intact, exhibits a remarkable sensitivity to the energy, rapidity and atomic
number dependence. The incoherent diffractive gluon production is less
sensitive to the details of the low-x dynamics but can serve as a probe of
fluctuations in the color glass condensate. As a quantitative measure of the
nuclear effects on diffractive hadron production we introduce a new observable
-- the diffractive nuclear modification factor. We discuss possible signatures
of gluon saturation in diffractive gluon production at RHIC, LHC and EIC.",0812.1519v2
2008-12-24,Incompressibility of neutron-rich matter,"The saturation properties of neutron-rich matter are investigated in a
relativistic mean-field formalism using two accurately calibrated models: NL3
and FSUGold. The saturation properties - density, binding energy per nucleon,
and incompressibility coefficient - are calculated as a function of the
neutron-proton asymmetry alpha=(N-Z)/A to all orders in alpha. Good agreement
(at the 10% level or better) is found between these numerical calculations and
analytic expansions that are given in terms of a handful of bulk parameters
determined at saturation density. Using insights developed from the analytic
approach and a general expression for the incompressibility coefficient of
infinite neutron-rich matter, i.e., K0(alpha)=K0+Ktau*alpha^{2}+..., we
construct a Hybrid model with values for K0 and Ktau as suggested by recent
experimental findings. Whereas the Hybrid model provides a better description
of the measured distribution of isoscalar monopole strength in the Sn-isotopes
relative to both NL3 and FSUGold, it significantly underestimates the
distribution of strength in 208Pb. Thus, we conclude that the incompressibility
coefficient of neutron-rich matter remains an important open problem.",0812.4499v2
2009-02-04,On the Saturation of the Magnetorotational Instability via Parasitic Modes,"We investigate the stability of incompressible, exact, non-ideal
magnetorotational (MRI) modes against parasitic instabilities. Both
Kelvin-Helmholtz and tearing-mode parasitic instabilities may occur in the
dissipative regimes accessible to current numerical simulations. We suppose
that a primary MRI mode saturates at an amplitude such that its fastest
parasite has a growth rate comparable to its own. The predicted alpha parameter
then depends critically on whether the fastest primary and parasitic modes fit
within the computational domain and whether non-axisymmetric parasitic modes
are allowed. Hence even simulations that resolve viscous and resistive scales
may not saturate properly unless the numerical domain is large enough to allow
the free evolution of both MRI and parasitic modes. To minimally satisfy these
requirements in simulations with vertical background fields, the vertical
extent of the domain should accommodate the fastest growing MRI mode while the
radial and azimuthal extents must be twice as large. The fastest parasites have
horizontal wavelengths roughly twice as long as the vertical wavelength of the
primary.",0902.0794v2
2009-02-12,Modified Holographic Dark Energy,"In this work, motivated by the energy bound suggested by Cohen {\it et al.},
we propose the modified holographic dark energy (MHDE) model. Choosing the IR
cut-off $L=R_{\rm CC}$ and considering the parameterizations $n^2=2-\lambda a$,
$n^2=2-3\lambda a^2/(1+3a^2)$ and $n^2=2-\lambda a^2/(\beta+a^2)$, we derive
all the physical quantities of the non-saturated MHDE model analytically. We
find that the non-saturated MHDE models with the parameterizations
$n^2=2-\lambda a$ and $n^2=2-3\lambda a^2/(1+3a^2)$ are single-parameter models
in practice. Also, we consider the cosmological constraints on the
non-saturated MHDE, and find that it is well consistent with the observational
data.",0902.2030v4
2009-02-23,Efficiency of Energy Conversion in Thermoelectric Nanojunctions,"Using first-principles approaches, this study investigated the efficiency of
energy conversion in nanojunctions, described by the thermoelectric figure of
merit $ZT$. We obtained the qualitative and quantitative descriptions for the
dependence of $ZT$ on temperatures and lengths. A characteristic temperature:
$T_{0}= \sqrt{\beta/\gamma(l)}$ was observed. When $T\ll T_{0}$, $ZT\propto
T^{2}$. When $T\gg T_{0}$, $ZT$ tends to a saturation value. The dependence of
$ZT$ on the wire length for the metallic atomic chains is opposite to that for
the insulating molecules: for aluminum atomic (conducting) wires, the
saturation value of $ZT$ increases as the length increases; while for
alkanethiol (insulating) chains, the saturation value of $ZT$ decreases as the
length increases. $ZT$ can also be enhanced by choosing low-elasticity bridging
materials or creating poor thermal contacts in nanojunctions. The results of
this study may be of interest to research attempting to increase the efficiency
of energy conversion in nano thermoelectric devices.",0902.3876v3
2009-03-02,A dynamic nonlinear model for saturation in industrial growth,"A general nonlinear logistic equation has been proposed to model long-time
saturation in industrial growth. An integral solution of this equation has been
derived for any arbitrary degree of nonlinearity. A time scale for the onset of
nonlinear saturation in industrial growth can be estimated from an
equipartition condition between nonlinearity and purely exponential growth.
Precise predictions can be made about the limiting values of the annual revenue
and the human resource content that an industrial organisation may attain.
These variables have also been modelled to set up an autonomous first-order
dynamical system, whose equilibrium condition forms a stable node (an attractor
state) in a related phase portrait. The theoretical model has received close
support from all relevant data pertaining to the well-known global company,
IBM.",0903.0282v1
2009-04-22,Comprehensive study of the vapour-liquid equilibria of the pure two-centre Lennard-Jones plus pointdipole fluid,"Results of a systematic investigation of the vapour-liquid equilibria of 38
individual two-centre Lennard-Jones plus axial pointdipole model fluids (2CLJD)
are reported over a range of reduced dipolar momentum 0 $\le \mu^{*2} \le$ 20
and of reduced elongation 0 $\le$ L* $\le$ 1.0. Temperatures investigated are
from about 55 % to about 95 % of the critical temperature of each fluid. The
NpT+Test Particle Method is used for the generation of vapour pressures,
saturated densities, and saturated enthalpies. For the lowest temperatures,
these data are calculated with highly accurate chemical potentials obtained
from the gradual insertion method. Critical temperatures $T*_c$ and densities
$\rho*_c$ are obtained from Guggenheim's equations. Empirical correlations for
critical data $T*_c$ and $\rho*_c$ as well as for saturated densities $\rho'*$,
$\rho''*$, and vapour pressures $p*_\sigma$ are developed as global functions
of the model parameters. They describe the simulation data generally within
their statistical uncertainties. Critical pressures and acentric factors of the
2CLJD fluid can be calculated from these correlations. The present results are
a sound basis for adjustments of the model parameters $\mu^{*2}$, $L*$,
$\sigma$, and $\epsilon$ to experimental VLE data of real fluids.",0904.3413v1
2009-04-23,Comprehensive study of the vapour-liquid equilibria of the pure two-centre Lennard-Jones plus pointquadrupole fluid,"Results of a systematic investigation of the vapour-liquid equilibria (VLE)
of 30 individual two-centre Lennard-Jones plus pointquadrupole model fluids
(2CLJQ) are reported over a range of reduced quadrupolar momentum $0 \le Q^{*2}
\le 4$ and of reduced elongation $0 \le L^* \le 0.8$. Temperatures investigated
are from about 55 % to about 95 % of the critical temperature of each fluid.
Uniformly the $NpT$+Test Particle Method based on molecular dynamics
simulations is used for the generation of vapour pressures, saturated
densities, and saturated enthalpies. Critical temperatures $T^*_{\rm c}$ and
densities $\rho^*_{\rm c}$ are obtained from Guggenheim's equations. Empirical
correlations for critical data $T^*_{\rm c}$ and $\rho^*_{\rm c}$ as well as
for saturated densities $\rho'^*$, $\rho''^*$, and vapour pressures
$p^*_{\sigma}$ are developed as global functions of the model parameters. In
most cases they describe the simulation data within their statistical
uncertainties. Critical pressures and acentric factors of the 2CLJQ fluid can
be calculated from present correlations. The present simulations are a sound
basis for adjustments of the model parameters $Q^{*2}$, $L^*$, $\sigma$, and
$\epsilon$ to experimental VLE data of real fluids.",0904.3679v1
2009-06-26,Existence of a measurable saturated compensation function between subshifts and its applications,"We show the existence of a bounded Borel measurable saturated compensation
function for a factor map between subshifts. As an application, we find the
Hausdorff dimension and measures of full Hausdorff dimension for a compact
invariant set of an expanding nonconformal map on the torus given by an
integer-valued diagonal matrix. These problems were studied in [19] for a
compact invariant set whose symbolic representation is a shift of finite type
under the condition of the existence of a saturated compensation function. We
extend the results by presenting a formula for the Hausdorff dimension for a
compact invariant set whose symbolic representation is a subshift without the
condition and characterizing the invariant ergodic measures of full dimension
as the ergodic equilibrium states of a constant multiple of a measurable
compensation function. For a compact invariant set whose symbolic
representation is a topologically mixing shift of finite type, we study
uniqueness and the properties for the unique invariant ergodic measure of full
dimension by using a measurable compensation function. Our positive results
narrow the possibility of where an example having more than one measure of full
dimension can be found.",0906.4989v1
2009-07-14,e+A physics at a future Electron-Ion Collider,"A future Electron-Ion Colllider (EIC) is the ideal laboratory for studying
the gluon distributions in both nucleons and nuclei for $\sqrt{s}$ = 63 - 158
(40 - 110) GeV/A for e+p (e+A) collisions. Whilst gluon distributions have been
studied extensively in nucleons at HERA, there is very little information on
them for $x <$ 0.1 in nuclei. The rapid increase in the gluon momentum
distribution at low-$x$ in nucleons found at HERA, if not tamed, leads to the
violation of the Froissart Unitarity Bound at small-$x$. This can be achieved
in non-linear QCD by allowing for the recombination of low-$x$ gluons until
saturation of gluon densities occurs. Understanding saturation is an important
goal not just for QCD in general, but also in understanding the initial
conditions of heavy-ion collisions in particular. In this paper, I describe the
physics that will be explored by e+A collisions, where saturation is more
easily explored in this mode at an EIC than in e+p collisions due to the large
nuclear densities achieved.",0907.2431v1
2009-07-30,Isobaric incompressibility of the isospin asymmetric nuclear matter,"The isospin dependence of the saturation properties of asymmetric nuclear
matter, particularly the incompressibility $K_\infty (X) = K_\infty + K_\tau
X^2 + O(X^4)$ at saturation density is systematically studied using density
dependent M3Y interaction. The $K_\tau$ characterizes the isospin dependence of
the incompressibility at saturation density $\rho_0$. The approximate
expression $K_{asy} \approx K_{sym}-6L$ is often used for $K_\tau$ where $L$
and $K_{sym}$ represent, respectively, the slope and curvature parameters of
the symmetry energy at $\rho_0$. It can be expressed accurately as
$K_\tau=K_{sym}-6L-\frac{Q_0}{K_\infty}L$ where $Q_0$ is the third-order
derivative parameter of symmetric nuclear matter at $\rho_0$. The results of
this addendum to Phys. Rev. C 80, 011305(R) (2009) indicate that the $Q_0$
contribution to $K_\tau$ is not insignificant.",0907.5350v2
2009-09-03,Fractal flow patterns in hydrophobic microfluidic pore networks: experimental modeling of two-phase flow in porous electrodes,"Experimental two-phase invasion percolation flow patterns were observed in
hydrophobic micro-porous networks designed to model fuel cell specific porous
media. In order to mimic the operational conditions encountered in the porous
electrodes of polymer electrolyte membrane fuel cells (PEMFCs), micro-porous
networks were fabricated with corresponding microchannel size distributions.
The inlet channels were invaded homogeneously with flow rates corresponding to
fuel cell current densities of 1.0 to 0.1 A/cm2 (Ca 10e-7-10e-8). A variety of
fractal breakthrough patterns were observed and analyzed to quantify flooding
density and geometrical diversity in terms of the total saturation, St, local
saturations, s, and fractal dimension, D. It was found that St increases
monotonically during the invasion process until the breakthrough point is
reached, and s profiles indicate the dynamic distribution of the liquid phase
during the process. Fractal analysis confirmed that the experiments fall within
the flow regime of invasion percolation with trapping. In this work, we propose
to correlate the fractal dimension, D, to the total saturation and use this map
as a parameter for modeling liquid water transport in the GDL.",0909.0758v1
2009-11-11,Saturation of Stationary Inversion States in a Three-Level Traveling-Wave Quantum Amplifier with Bistable Resonator Pumping,"The inversion states of a saturated traveling-wave three-level quantum
paramagnetic amplifier have been investigated under conditions of bistable
resonator pumping. The equations of motion for the vectorial order parameter
have been obtained using adiabatic elimination of fast variables. The exact
solutions for stationary inversion states have been found from these equations.
For high-quality pump resonators, the isolated and the semi-isolated branches
of the inversion ratio have been revealed in stationary solutions. The
existence of the semi-isolated branches means a possibility of collapse of the
inversion state under influence of a saturating signal. Revival of inversion is
possible in this case only by the hard excitation of the pump system. This
nonlinear phenomenon is of a qualitatively another nature than one described by
us in arXiv:0901.0449v1 [nlin.AO], and may be observed at moderate Q-factor of
pump resonator.",0911.2124v1
2010-01-18,The low temperature thermal expansion of single-walled carbon nanotube bundles saturated with nitrogen,"The effect of a N2 impurity on the radial thermal expansion coefficient (ar)
of single-walled carbon nanotube bundles has been investigated in the
temperature interval 2.2 - 43 K by the dilatometric method. Saturation of
nanotube bundles with N2 caused a sharp increase in the positive magnitudes of
ar in the whole range of temperatures used and a very high and wide maximum in
the thermal expansion coefficient (ar)(T) at T about 28 K. The low temperature
desorption of the impurity from the N2-saturated powder of bundles of
single-walled carbon nanotubes with open and closed ends has been investigated.",1001.2992v1
2010-01-28,Gluon saturation effects at forward rapidities at LHC in pp collisions,"We investigate hadrons and direct photon production in pp collisions at the
LHC energy within the color-dipole approach. We show that greatest sensitivity
to gluon saturation effects is reached at very forward rapidities in pp
collisions at LHC (\sqrt{s}=14 TeV). The discrepancies among various saturation
models (fitted to HERA data) results can be about a factor of 2-3 at forward
rapidities. We found that the ratio of direct-photon to pion production can be
about 20-10 at forward rapidities \eta=7-8. Therefore, direct photon production
at forward rapidities should provide a rather clean probe as the background
from radiative hadronic decays is significantly suppressed.",1001.5266v1
2010-01-29,Reactions of C$_2$({\it a}$^3Pi_u$) with selected saturated alkanes: A temperature dependence study,"We present a temperature dependence study on the gas phase reactions of the
C$_2$({\it a}$^3Pi_u$) radical with a selected series of saturated alkanes
(C$_2$H$_6$, C$_3$H$_8$, n-C$_4$H$_10$, i-C$_4$H$_10$, and n-C$_6$H$_14$) by
means of pulsed laser photolysis/laser-induced fluorescence technique. The
bimolecular rate constants for these reactions were obtained between 298 and
673 K. A pronounced negative temperature effect was observed for n-C$_4$H$_10$,
i-C$_4$H$_10$, and n-C$_6$H$_14$ and interpreted in terms of steric hindrance
of the more reactive secondary or tertiary C-H bonds by less reactive CH$_3$
groups. Detailed analysis of our experimental results reveals quantitatively
the temperature dependence of reactivities for the primary, secondary, and
tertiary C-H bonds in these saturated alkanes and further lends support to a
mechanism of hydrogen abstraction.",1001.5342v3
2010-01-31,Saturation of the Anomalous Hall Effect in Critically Disordered Ultra-thin CNi3 Films,"We demonstrate that a distinct high-disorder anomalous Hall effect phase
emerges at the correlated insulator threshold of ultra-thin, amorphous,
ferromagnetic CNi3 films. In the weak localization regime, where the sheet
conductance G >> e^2/h, the anomalous Hall resistance of the films increases
with increasing disorder and the Hall conductance scales as Gxy ~ G^1.6.
However, at sufficiently high disorder the system begins to enter the 2D
correlated insulator regime, at which point the Hall resistance Rxy abruptly
saturates and the scaling exponent becomes 2. Tunneling measurements show that
the saturation behavior is commensurate with the emergence of the 2D Coulomb
gap, suggesting that e-e interactions mediate the high-disorder phase.",1002.0099v1
2010-03-23,From low-bias mobility to high-bias current saturation: fundamental trade-offs in graphene based transistors,"We describe the fundamental trade-offs in engineering the mobility, current
saturation and ON- OFF ratios in graphene transistors. Surprisingly, the
trade-offs arise solely from an asymptotic constraint on the high energy
bandstructure and independent of scattering processes. This places graphite
derivatives (bulk monolayer graphene, uniaxially strained graphene nanoribbons,
carbon nanotubes and bilayer graphene) on the same 3-parameter
mobility-bandgap-scattering length ({\mu} - Egap -{\lambda}) plot, proximal to
other semiconductors. In addition to this low-bias trade-off, the high bias
current bears signatures of the underlying saturation mechanism, arising
through phonon scattering or {\Gamma}-point suppressed density of states
opening bandgap.",1003.4551v3
2010-03-28,On subgroups of saturated or totally bounded paratopological groups,"A paratopological group $G$ is saturated if the inverse $U^{-1}$ of each
non-empty set $U\subset G$ has non-empty interior. It is shown that a
[first-countable] paratopological group $H$ is a closed subgroup of a saturated
(totally bounded) [abelian] paratopological group if and only if $H$ admits a
continuous bijective homomorphism onto a (totally bounded) [abelian]
topological group $G$ [such that for each neighborhood $U\subset H$ of the unit
$e$ there is a closed subset $F\subset G$ with $e\in h^{-1}(F)\subset U$]. As
an application we construct a paratopological group whose character exceeds its
$\pi$-weight as well as the character of its group reflexion. Also we present
several examples of (para)topological groups which are subgroups of totally
bounded paratopological groups but fail to be subgroups of regular totally
bounded paratopological groups.",1003.5355v1
2010-04-07,Spatial fairness in linear wireless multi-access networks,"Multi-access networks may exhibit severe unfairness in throughput. Recent
studies show that this unfairness is due to local differences in the
neighborhood structure: Nodes with less neighbors receive better access. We
study the unfairness in saturated linear networks, and adapt the multi-access
CSMA protocol to remove the unfairness completely, by choosing the activation
rates of nodes appropriately as a function of the number of neighbors. We then
investigate the consequences of this choice of activation rates on the
network-average saturated throughput, and we show that these rates perform well
in a non-saturated setting.",1004.1042v1
2010-05-12,Parametrization of the Relativistic ($σ-ω$) Model for Nuclear Matter,"We have investigated the zero-temperature equation of state (EoS) for
infinite nuclear matter within the $(\sigma-\omega)$ model at all densities
$n_{\mathrm{B}}$ and different proton-neutron asymmetry $\eta\equiv(N-Z)/A$. We
have presented an analytical expression for the compression modulus and found
that nuclear matter ceases to saturate at $\eta$ slightly larger than $0.8$.
Afterward, we have developed an analytical method to determine the strong
coupling constants from the EoS for isospin symmetric nuclear matter, which
allow us to reproduce all the saturation properties with high accuracy. For
various values of the nucleon effective mass and the compression modulus, we
have found that the quartic self-coupling constant $G_4$ is negative, or
positive and very large. Furthermore, we have demonstrated that it is possible
(a) to investigate the EoS in terms of $n_{\mathrm{B}}$ and $\eta$; and (b) to
reproduce all the known saturation properties without $G_4$. We have thus
concluded that the latter is not necessary in the $(\sigma-\omega)$ model.",1005.2030v4
2010-05-18,Numerical Simulations of Gravity-Driven Fingering in Unsaturated Porous Media Using a Non-Equilibrium Model,"This is a computational study of gravity-driven fingering instabilities in
unsaturated porous media. The governing equations and corresponding numerical
scheme are based on the work of Nieber et al. [Ch. 23 in Soil Water Repellency,
eds. C. J. Ritsema and L. W. Dekker, Elsevier, 2003] in which non-monotonic
saturation profiles are obtained by supplementing the Richards equation with a
non-equilibrium capillary pressure-saturation relationship, as well as
including hysteretic effects. The first part of the study takes an extensive
look at the sensitivity of the finger solutions to certain key parameters in
the model such as capillary shape parameter, initial saturation, and capillary
relaxation coefficient. The second part is a comparison to published
experimental results that demonstrates the ability of the model to capture
realistic fingering behaviour.",1005.3297v1
2010-07-07,"Improved current saturation and shifted switching threshold voltage in In2O3 nanowire based, fully transparent NMOS inverters via femtosecond laser annealing","Transistors based on various types of non-silicon nanowires have shown great
potential for a variety of applications, especially for those require
transparency and low-temperature substrates. However, critical requirements for
circuit functionality such as saturated source-drain current, and matched
threshold voltages of individual nanowire transistors in a way that is
compatible with low temperature substrates, have not been achieved. Here we
show that femtosecond laser pulses can anneal individual transistors based on
In2O3 nanowires, improve the saturation of the source-drain current, and
permanently shift the threshold voltage to the positive direction. We applied
this technique and successfully shifted the switching threshold voltages of
NMOS based inverters and improved their noise margin, in both depletion and
enhancement modes. Our demonstration provides a method to trim the parameters
of individual nanowire transistors, and suggests potential for large-scale
integration of nanowire-based circuit blocks and systems.",1007.1168v1
2010-08-03,Universal behavior of the gluon saturation scale at high energy including full NLL BFKL effects,"The universal traveling wave solution to the Balitsky-Kovchegov equation with
running coupling (and other equations in the same universality class) is
extended to subleading orders at large rapidity and small dipole size $r$. The
large rapidity expansion of the logarithm of the saturation scale $Q_s(Y)$ is
derived from that traveling wave solution. In addition to the two already known
leading terms in $Y^{1/2}$ and $Y^{1/6}$, which are determined only by the LL
BFKL kernel, the three following terms in $Y^0$, $Y^{-1/6}$ and $Y^{-1/3}$ are
obtained. They are universal and sensitive to NLL BFKL effects. Initial
condition dependence and NNLL BFKL effects would both start to appear only at
the next order, which is in $Y^{-1/2}$. In the light of these results, the
impact of the precise implementation of the running coupling in gluon
saturation is discussed, \emph{i.e.} parent dipole size prescription \emph{vs.}
Balitsky's prescription, and also the effect of the full NLL corrections, not
yet implemented in numerical simulations.",1008.0498v1
2010-08-04,Channel saturation and conductance quantization in single-atom gold constrictions,"Notwithstanding the discreteness of metallic constrictions, it is shown that
the finite elasticity of stable, single-atom gold constrictions allows for a
continuous and reversible change in conductance, thereby enabling observation
of channel saturation and conductance quantization. The observed channel
saturation and signature for conductance quantization is achieved by
superposition of atomic/subatomic-scale oscillations on a
retracting/approaching gold tip against a gold substrate of a scanning probe.
Results also show that conductance histograms are neither suitable for
evaluating the stability of atomic configurations through peak positions or
peak height nor appropriate for assessing conductance quantization. A large
number of atomic configurations with similar conductance values give rise to
peaks in the conductance histogram. The positions of the peaks and counts at
each peak can be varied by changing the conditions under which the histograms
are made. Histogram counts below 1Go cannot necessarily be assumed to arise
from single-atom constrictions.",1008.0886v1
2010-09-13,On saturated fusion systems and Brauer indecomposability of Scott modules,"Let $p$ be a prime number, $G$ a finite group, $P$ a $p$-subgroup of $G$ and
$k$ an algebraically closed field of characteristic $p$. We study the
relationship between the category $\Ff_P(G)$ and the behavior of
$p$-permutation $kG$-modules with vertex $P$ under the Brauer construction. We
give a sufficient condition for $\Ff_P(G)$ to be a saturated fusion system. We
prove that for Scott modules with abelian vertex, our condition is also
necessary. In order to obtain our results, we prove a criterion for the
categories arising from the data of $(b, G)$-Brauer pairs in the sense of
Alperin-Brou\'e and Brou\'e-Puig to be saturated fusion systems on the
underlying $p$-group.",1009.2391v1
2010-09-21,Asymptotic growth of saturated powers and epsilon multiplicity,"Asymptotic properties of saturated powers of modules over a local domain R
are studied. Under mild conditions, it is shown that the limit as k goes to
infinity of the quotient of the saturation of the k-th power of a module E by
the k-th power of E, when divided by k^{d+e-1}, exists. Here d is the dimension
of R and e is the rank of E. We deduce that under these assumptions, the
epsilon multiplicity of E, defined by Ulrich and Validashti as a limsup,
actually exists as a limit.",1009.4111v4
2010-11-16,Hadron production at the LHC: Any indication of new phenomena,"We confront soft Pomeron and gluon saturation models with the first LHC data
on inclusive hadron production. We claim that while the first type of models
are not able to describe some part of the LHC data, the Colour-Glass-Condensate
(gluon saturation) approach gives an adequate description of the data. Here, we
compare our published predictions with the recently available 7 TeV data. We
firmly believe that if further experimental measurements confirm that the gluon
saturation works, it will be a major discovery.",1011.3591v1
2010-11-30,Temperature induced pore fluid pressurization in geomaterials,"The theoretical basis of the thermal response of the fluid-saturated porous
materials in undrained condition is presented. It has been demonstrated that
the thermal pressurization phenomenon is controlled by the discrepancy between
the thermal expansion of the pore fluid and of the solid phase, the
stress-dependency of the compressibility and the non-elastic volume changes of
the porous material. For evaluation of the undrained thermo-poro-elastic
properties of saturated porous materials in conventional triaxial cells, it is
important to take into account the effect of the dead volume of the drainage
system. A simple correction method is presented to correct the measured pore
pressure change and also the measured volumetric strain during an undrained
heating test. It is shown that the porosity of the tested material, its drained
compressibility and the ratio of the volume of the drainage system to the one
of the tested sample, are the key parameters which influence the most the error
induced on the measurements by the drainage system. An example of the
experimental evaluation of undrained thermoelastic parameters is presented for
an undrained heating test performed on a fluid-saturated granular rock.",1011.6501v1
2010-12-21,Analytical Modeling of Saturation Throughput in Power Save Mode of an IEEE 802.11 Infrastructure WLAN,"We consider a single station (STA) in the Power Save Mode (PSM) of an IEEE
802.11 infrastructure WLAN. This STA is assumed to be carrying uplink and
downlink traffic via the access point (AP). We assume that the transmission
queues of the AP and the STA are saturated, i.e., the AP and the STA always
have at least one packet to send. For this scenario, it is observed that uplink
and downlink throughputs achieved are different. The reason behind the
difference is the long term attempt rates of the STA and the AP due to the PSM
protocol. In this paper we first obtain the the long term attempt rates of the
STA and the AP and using these, we obtain the saturation throughputs of the AP
and the STA. We provide a validation of analytical results using the NS-2
simulator.",1012.4815v1
2011-02-11,Gluon saturation and energy dependence of hadron multiplicity in pp and AA collisions at the LHC,"The recent results in \sqrt{s}=2.76 TeV Pb+Pb collisions at the Large Hadron
Collider (LHC) reported by the ALICE collaboration shows that the power-law
energy-dependence of charged hadron multiplicity in Pb+Pb collisions is
significantly different from p+p collisions. We show that this different
energy-dependence can be explained by inclusion of a strong angular-ordering in
the gluon-decay cascade within the Color-Glass-Condensate (or gluon saturation)
approach. This effect is more important in nucleus-nucleus collisions where the
saturation scale is larger than 1 GeV. Our prescription gives a good
description of the LHC data both in p+p and Pb+Pb collisions.",1102.2385v2
2011-02-25,"Particle Production at High Energy and Large Transverse Momentum - ""The Hybrid Formalism"" Revisited","We revisit the ""`hybrid formalism""' for particle production used recently to
study saturation effects in single hadron multiplicities at forward rapidities
at RHIC and LHC. We point out that at leading twist there is an extra
contribution to the formulae used so far, which corresponds to particle
production via inelastic scattering of the projectile partons on the target
fields. This contribution is expected to be small due to kinematics at very
forward rapidities/very high transverse momenta, but should be significant at
high momenta and very high energies. This contribution is expected to be most
affected by saturation effects and is therefore an interesting object of study
in the context of possible onset of saturation at high energies.",1102.5327v1
2011-02-28,Characterizing and Quantifying Frustration in Quantum Many-Body Systems,"We present a general scheme for the study of frustration in quantum systems.
We introduce a universal measure of frustration for arbitrary quantum systems
and we relate it to a class of entanglement monotones via an exact inequality.
If all the (pure) ground states of a given Hamiltonian saturate the inequality,
then the system is said to be inequality saturating. We introduce sufficient
conditions for a quantum spin system to be inequality saturating and confirm
them with extensive numerical tests. These conditions provide a generalization
to the quantum domain of the Toulouse criteria for classical frustration-free
systems. The models satisfying these conditions can be reasonably identified as
geometrically unfrustrated and subject to frustration of purely quantum origin.
Our results therefore establish a unified framework for studying the
intertwining of geometric and quantum contributions to frustration.",1103.0022v2
2011-03-03,Number fluctuations of sparse quasiparticles in a superconductor,"We have directly measured quasiparticle number fluctuations in a thin film
superconducting Al resonator in thermal equilibrium. The spectrum of these
fluctuations provides a measure of both the density and the lifetime of the
quasiparticles. We observe that the quasiparticle density decreases
exponentially with decreasing temperature, as theoretically predicted, but
saturates below 160 mK to 25-55 per cubic micron. We show that this saturation
is consistent with the measured saturation in the quasiparticle lifetime, which
also explains similar observations in qubit decoherence times.",1103.0758v2
2011-04-06,Nonlinear effects for island coarsening and stabilization during strained film heteroepitaxy,"Nonlinear evolution of three-dimensional strained islands or quantum dots in
heteroepitaxial thin films is studied via a continuum elasticity model and the
development of a nonlinear dynamic equation governing the film morphological
profile. All three regimes of island array evolution are identified and
examined, including a film instability regime at early stage, a nonlinear
coarsening regime at intermediate times, and the crossover to a saturated
asymptotic state, with detailed behavior depending on film-substrate misfit
strains but not qualitatively on finite system sizes. The phenomenon of island
stabilization and saturation, which corresponds to the formation of steady but
non-ordered arrays of strained quantum dots, occurs at later time for smaller
misfit strain. It is found to be controlled by the strength of film-substrate
wetting interaction which would constrain the valley-to-peak mass transport and
hence the growth of island height, and also determined by the effect of elastic
interaction between surface islands and the high-order strain energy of
individual islands at late evolution stage. The results are compared to
previous experimental and theoretical studies on quantum dots coarsening and
saturation.",1104.1121v2
2011-06-30,Violation of the geometric scaling behaviour of the amplitude for running QCD coupling in the saturation region,"In this paper we show that the intuitive guess that the geometric scaling
behaviour should be violated in the case of the running QCD coupling, turns out
to be correct. The scattering amplitude of the dipole with the size $r$ depends
on new dimensional scale: $\Lambda_{QCD}$, even at large values $Y = \ln(1/x)$
and $l\,=\, \ln\Lb \as\Lb r^2\Rb/\as\Lb 1/Q^2_s\Rb\Rb$. However, in this region
we found a new scaling behaviour: the amplitude is a function of $\zeta =
Y\,l$. We state that only in the vicinity of the saturation scale $Q_s$
($\as(Q^2_s)\,\ln \Lb r^2 Q^2_s\Rb\,\leq \, 1$), the amplitude shows the
geometric scaling behaviour. Based on these finding the geometric scaling
behavior that has been seen experimentally, stems from either we have not
probed the proton at HERA and the LHC deeply inside the saturation region or
that there exists the mechanism of freezing of the QCD coupling constant at
$r^2 \approx 1/Q^2_s$.",1106.6257v1
2011-09-08,Back-to-Back Correlations of Di-hadrons in dAu Collisions at RHIC,"We perform a complete theoretical analysis of the azimuthal angular
correlation of two-hadron productions in the forward $dAu$ collisions at RHIC
in the saturation formalism, and obtain a very good agreement with the
experimental data. It is demonstrated that the suppression and broadening of
the away side peak provide a unique signal for the onset of the saturation
mechanism at small-$x$ in a large nucleus. We emphasize that future experiments
of di-hadron correlations in $pA$ collisions at both RHIC and LHC, and in $eA$
collisions at the planned electron-ion collider, shall provide us with a
thorough study and understanding of the strong interaction dynamics in the
saturation regime.",1109.1817v3
2011-09-13,Plane Cremona maps: saturation and regularity of the base ideal,"One studies plane Cremona maps by focusing on the ideal theoretic and
homological properties of its homogeneous base ideal (""indeterminacy locus"").
The {\em leitmotiv} driving a good deal of the work is the relation between the
base ideal and its saturation. As a preliminary one deals with the homological
features of arbitrary codimension 2 homogeneous ideals in a polynomial ring in
three variables over a field which are generated by three forms of the same
degree. The results become sharp when the saturation is not generated in low
degrees, a condition to be given a precise meaning. An implicit goal,
illustrated in low degrees, is a homological classification of plane Cremona
maps according to the respective homaloidal types. An additional piece of this
work relates the base ideal of a rational map to a few additional homogeneous
""companion"" ideals, such as the integral closure, the $\boldsymbol\mu$-fat
ideal and a seemingly novel ideal defined in terms of valuations.",1109.2815v4
2011-09-15,Bounded domain problem for the modified Buckley-Leverett equation,"The focus of the present study is the modified Buckley-Leverett (MBL)
equation describing two-phase flow in porous media. The MBL equation differs
from the classical Buckley-Leverett (BL) equation by including a balanced
diffusive-dispersive combination. The dispersive term is a third order mixed
derivatives term, which models the dynamic effects in the pressure difference
between the two phases. The classical BL equation gives a monotone water
saturation profile for any Riemann problem; on the contrast, when the
dispersive parameter is large enough, the MBL equation delivers non-monotone
water saturation profile for certain Riemann problems as suggested by the
experimental observations. In this paper, we first show that the solution of
the finite interval [0,L] boundary value problem converges to that of the
half-line [0,+\infty) boundary value problem for the MBL equation as L->
+\infty. This result provides a justification for the use of the finite
interval boundary value problem in numerical studies for the half line problem.
Furthermore, we extend the classical central schemes for the hyperbolic
conservation laws to solve the MBL equation which is of pseudo-parabolic type.
Numerical results confirm the existence of non-monotone water saturation
profiles consisting of constant states separated by shocks.",1109.3481v1
2011-09-16,Analysis of the temperature influence on Langmuir probe measurements on the basis of gyrofluid simulations,"The influence of the temperature and its fluctuations on the ion saturation
current and the floating potential, which are typical quantities measured by
Langmuir probes in the turbulent edge region of fusion plasmas, is analysed by
global nonlinear gyrofluid simulations for two exemplary parameter regimes. The
numerical simulation facilitates a direct access to densities, temperatures and
the plasma potential at different radial positions around the separatrix. This
allows a comparison between raw data and the calculated ion saturation current
and floating potential within the simulation. Calculations of the
fluctuation-induced radial particle flux and its statistical properties reveal
significant differences to the actual values at all radial positions of the
simulation domain, if the floating potential and the temperature averaged
density inferred from the ion saturation current is used.",1109.3600v1
2011-09-21,Traffic flow in a Manhattan-like urban system,"In this paper, a cellular automaton model of vehicular traffic in
Manhattan-like urban system is proposed. In this model, the origin-destination
trips and traffic lights have been considered. The system exhibits three
different states, i.e., moving state, saturation state and global deadlock
state. With a grid coarsening method, vehicle distribution in the moving state
and the saturation state has been studied. Interesting structures (e.g.,
windmill-like one, T-shirt-like one, Y-like one) have been revealed. A
metastability of the system is observed in the transition from saturation state
to global deadlock state. The effect of advanced traveller information system
(ATIS), the traffic light period, and the traffic light switch strategy have
also been investigated.",1109.4628v1
2011-11-16,Necessary and sufficient condition for saturating the upper bound of quantum discord,"We revisit the upper bound of quantum discord given by the von Neumann
entropy of the measured subsystem. Using the Koashi-Winter relation, we obtain
a trade-off between the amount of classical correlation and quantum discord in
the tripartite pure states. The difference between the quantum discord and its
upper bound is interpreted as a measure on the classical correlative capacity.
Further, we give the explicit characterization of the quantum states saturating
the upper bound of quantum discord, through the equality condition for the
Araki-Lieb inequality. We also demonstrate that the saturating of the upper
bound of quantum discord precludes any further correlation between the measured
subsystem and the environment.",1111.3837v4
2011-11-22,Sensitivity of neutron to proton ratio toward the high density behavior of symmetry energy in heavy-ion collisions,"The symmetry energy at sub and supra-saturation densities has a great
importance in understanding the exact nature of asymmetric nuclear matter as
well as neutron star, but, it is poor known, especially at supra-saturation
densities. We will demonstrate here that the neutron to proton ratios from
different kind of fragments is able to determine the supra-saturation behavior
of symmetry energy or not. For this purpose, a series of Sn isotopes are
simulated at different incident energies using the Isospin Quantum Molecular
Dynamics (IQMD) model with either a soft or a stiff symmetry energy for the
present study. It is found that the single neutron to proton ratio from free
nucleons as well as LCP's is sensitive towards the symmetry energy, incident
energy as well as isospin asymmetry of the system. However, with the double
neutron to proton ratio, it is true only for the free nucleons. It is possible
to study the high density behavior of symmetry energy by using the neutron to
proton ratio from free nucleons.",1111.5073v2
2011-12-12,QCD saturation at the LHC: comparisons of models to p+p and A+A data and predictions for p+Pb collisions,"In a previous paper (arXiv:1011.1895), we showed that saturation models,
constrained by e+p HERA data on inclusive and diffractive cross-sections, are
in good agreement with p+p data at LHC in the soft sector. Particularly
impressive was the agreement of saturation models with the multiplicity
distribution as a function of $n_{\rm ch.}$. In this paper, we extend these
studies further and consider the agreement of these models with data on bulk
distributions in A+A collisions. We compare our results to data on central and
forward particle production in d+Au collisions at RHIC and make predictions for
inclusive distributions in p+Pb collisions at the LHC.",1112.2445v2
2011-12-23,Threshold Saturation in Spatially Coupled Constraint Satisfaction Problems,"We consider chains of random constraint satisfaction models that are
spatially coupled across a finite window along the chain direction. We
investigate their phase diagram at zero temperature using the survey
propagation formalism and the interpolation method. We prove that the SAT-UNSAT
phase transition threshold of an infinite chain is identical to the one of the
individual standard model, and is therefore not affected by spatial coupling.
We compute the survey propagation complexity using population dynamics as well
as large degree approximations, and determine the survey propagation threshold.
We find that a clustering phase survives coupling. However, as one increases
the range of the coupling window, the survey propagation threshold increases
and saturates towards the phase transition threshold. We also briefly discuss
other aspects of the problem. Namely, the condensation threshold is not
affected by coupling, but the dynamic threshold displays saturation towards the
condensation one. All these features may provide a new avenue for obtaining
better provable algorithmic lower bounds on phase transition thresholds of the
individual standard model.",1112.6320v2
2012-02-13,Error Floor Approximation for LDPC Codes in the AWGN Channel,"This paper addresses the prediction of error floors of low-density
parity-check (LDPC) codes with variable nodes of constant degree in the
additive white Gaussian noise (AWGN) channel. Specifically, we focus on the
performance of the sum-product algorithm (SPA) decoder formulated in the
log-likelihood ratio (LLR) domain. We hypothesize that several published error
floor levels are due to the manner in which decoder implementations handled the
LLRs at high SNRs. We employ an LLR-domain SPA decoder that does not saturate
near-certain messages and find the error rates of our decoder to be lower by at
least several orders of magnitude. We study the behavior of trapping sets (or
near-codewords) that are the dominant cause of the reported error floors.
  We develop a refined linear model, based on the work of Sun and others, that
accurately predicts error floors caused by elementary tapping sets for
saturating decoders. Performance results of several codes at several levels of
decoder saturation are presented.",1202.2826v2
2012-04-03,Generic features of the phase transition in cold and dense quark matter,"We investigate the phase transition in cold and dense quark matter in an
intuitive way that shares common features of the effective model approaches. We
first express the quasi-particle contribution to the thermodynamic potential
with the dynamical mass M and then discuss how we can understand the possible
first-order phase transition with and without the vector interaction from the
saturation curve on the plane of the energy per particle and the density. We
next extend our analysis including inhomogeneity and discuss the relation
between the order of the phase transition and the saturation curve. We
emphasize that the saturation curve is useful to infer qualitative nature of
the phase transition even without knowing the explicit solution of the ground
state.",1204.0594v4
2012-04-10,Saturating the unitarity bound in AdS/CFT_(AdS),"We investigate the holographic description of CFTs defined on the cylinder
and on AdS, which include an operator saturating the unitarity bound. The
standard Klein-Gordon field with the corresponding mass and boundary conditions
on global AdS_(d+1) and on an AdS_(d+1) geometry with AdS_d conformal boundary
contains ghosts. We identify a limit in which the singleton field theory is
obtained from the bulk theory with standard renormalized inner product, showing
that a unitary bulk theory corresponding to an operator which saturates the
unitarity bound can be formulated and that this yields a free field on the
boundary. The normalizability issues found for the standard Klein-Gordon field
on the geometry with AdS_d conformal boundary are avoided for the singleton
theory, which offers interesting prospects for multi-layered AdS/CFT.",1204.2054v1
2012-05-21,Quantum information transfer and models for black hole mechanics,"General features of information transfer between quantum subsystems, via
unitary evolution, are investigated, with applications to the problem of
information transfer from a black hole to its surroundings. A particularly
direct form of quantum information transfer is ""subspace transfer,"" which can
be characterized by saturation of a subadditivity inequality. We also describe
more general unitary quantum information transfer, and categorize different
models for black hole evolution. Evolution that only creates paired excitations
inside/outside the black hole is shown not to extract information, but
information-transferring models exist both in the ""saturating"" and
""non-saturating"" category. The former more closely capture thermodynamic
behavior; the latter generically have enhanced energy flux, beyond that of
Hawking.",1205.4732v3
2012-05-22,Gluon saturation in dijet production in p-Pb collisions at Large Hadron Collider,"We study saturation effects in the production of dijets in p-p and p-Pb
collisions using the framework of high energy factorization. We focus on
central-forward jet configurations, which allow for probing gluon density at
low longitudinal momentum fraction. We find significant suppression of the
central-forward jet decorrelations in p-Pb compared to p-p, which we attribute
to saturation of gluon density in nuclei.",1205.5035v3
2012-08-28,Saturating the random graph with an independent family of small range,"Motivated by Keisler's order, a far-reaching program of understanding basic
model-theoretic structure through the lens of regular ultrapowers, we prove
that for a class of regular filters $D$ on $I$, $|I| = \lambda > \aleph_0$, the
fact that $P(I)/\de$ has little freedom (as measured by the fact that any
maximal antichain is of size $<\lambda$, or even countable) does not prevent
extending $D$ to an ultrafilter $D_1$ on $I$ which saturates ultrapowers of the
random graph. ""Saturates"" means that $M^I/\de_1$ is $\lambda^+$-saturated
whenever M is a model of the theory of the random graph. This was known to be
true for stable theories, and false for non-simple and non-low theories. This
result and the techniques introduced in the proof have catalyzed the authors'
subsequent work on Keisler's order for simple unstable theories. The
introduction, which includes a part written for model theorists and a part
written for set theorists, discusses our current program and related results.",1208.5585v1
2012-09-09,Density dependence of nuclear symmetry energy constrained by mean-field calculations,"We establish a correlation for the symmetry energy at saturation density
$S_{0}$, slope parameter $L$ and curvature parameter $K_{\text{sym}}$ based on
widely different mean field interactions. With the help of this correlation and
available empirical and theoretical information, the density dependent behavior
around the saturation density is determined. We compare the results obtained
with the present approach with those by other analyses. With this obtained
density dependent behavior of the symmetry energy, the neutron skin thickness
of $^{208}$Pb and some properties of neutron stars are investigated. In
addition, it is found that the expression $S(\rho)=S_{0}(\rho
/\rho_{0})^{\gamma}$ or $S(\rho)=12.5(\rho /\rho_{0}) ^{2/3}+C_{p}(\rho
/\rho_{0}) ^{\gamma}$ does not reproduce the density dependence of the symmetry
energy as predicted by the mean-field approach around nuclear saturation
density.",1209.1777v1
2012-09-18,KNO scaling from a nearly Gaussian action for small-x gluons,"Transverse momentum integrated multiplicities in the central region of pp
collisions at LHC energies satisfy Koba-Nielsen-Olesen scaling. We attempt to
relate this finding to multiplicity distributions of soft gluons. KNO scaling
emerges if the effective theory describing color charge fluctuations at a scale
on the order of the saturation momentum is approximately Gaussian. From an
evolution equation for quantum corrections which includes both saturation as
well as fluctuations we find that evolution with the QCD \beta-function
satisfies KNO scaling while fixed-coupling evolution does not. Thus, non-linear
saturation effects and running-coupling evolution are both required in order to
reproduce geometric scaling of the DIS cross section and KNO scaling of virtual
dipoles in a hadron wave function.",1209.4105v1
2012-10-08,CGC predictions for p+A collisions at the LHC and signature of QCD saturation,"We present various predictions for the upcoming p+Pb collisions at \sqrt{S}=5
TeV within the color glass condensate (CGC) formalism, including single
inclusive charged hadron production, single inclusive prompt photon production,
direct photon production, charged hadron multiplicity distribution and
photon-hadron azimuthal correlations. Using the running-coupling
Balitsky-Kovchegov evolution equation for calculating various observables, we
show that the main source of uncertainties is due to less constrained initial
nuclear saturation scale. This gives rise to rather large theoretical
uncertainties for nuclear modification factor R_{pA} at the LHC. Nevertheless,
we propose a simple scheme in which one can still test the main dynamics of the
CGC/saturation in p+A collisions at the LHC.",1210.2385v2
2012-10-30,Measuring Quantum Correlations using Lossy Photon-Number-Resolving Detectors with Saturation,"The variance of difference of photocounts (VDPs) is an established measure of
quantum correlations for quantum states of light. It enables us to discriminate
between the classical correlation of a two-mode coherent state and the quantum
correlation of a twin-beam state. We study the effect of loss and saturation of
the photon-number-resolving detector on the measurement of the VDPs. An
analytic function is derived for this variance, both for the coherent and the
twin-beam states. It is found that the VDPs is no longer a reliable
entanglement measure in the nonlinear regime of the detector response but it
remains useful in some range of values of average photon numbers of the
incident light. We also quantify the linear regime of the detector with
saturation which will be useful for calibration of the detector quantum
efficiency.",1210.8022v3
2012-11-08,"On multidimensional generalized Cramér-Rao inequalities, uncertainty relations and characterizations of generalized $q$-Gaussian distributions","In the present work, we show how the generalized Cram\'er-Rao inequality for
the estimation of a parameter, presented in a recent paper, can be extended to
the mutidimensional case with general norms on $\mathbb{R}^{n}$, and to a wider
context. As a particular case, we obtain a new multidimensional Cram\'er-Rao
inequality which is saturated by generalized $q$-Gaussian distributions. We
also give another related Cram\'er-Rao inequality, for a general norm, which is
saturated as well by these distributions. Finally, we derive uncertainty
relations from these Cram\'er-Rao inequalities. These uncertainty relations
involve moments computed with respect to escort distributions, and we show that
some of these relations are saturated by generalized $q$-Gaussian
distributions. These results introduce extended versions of Fisher information,
new Cram\'er-Rao inequalities, and new characterizations of generalized
$q$-Gaussian distributions which are important in several areas of physics and
mathematics.",1211.2008v2
2012-11-30,Game saturation of intersecting families,"We consider the following combinatorial game: two players, Fast and Slow,
claim $k$-element subsets of $[n]=\{1,2,...,n\}$ alternately, one at each turn,
such that both players are allowed to pick sets that intersect all previously
claimed subsets. The game ends when there does not exist any unclaimed
$k$-subset that meets all already claimed sets. The score of the game is the
number of sets claimed by the two players, the aim of Fast is to keep the score
as low as possible, while the aim of Slow is to postpone the game's end as long
as possible. The game saturation number is the score of the game when both
players play according to an optimal strategy. To be precise we have to
distinguish two cases depending on which player takes the first move. Let
$gsat_F(\mathbb{I}_{n,k})$ and $gsat_S(\mathbb{I}_{n,k})$ denote the score of
the saturation game when both players play according to an optimal strategy and
the game starts with Fast's or Slow's move, respectively. We prove that
$\Omega_k(n^{k/3-5}) \le gsat_F(\mathbb{I}_{n,k}),gsat_S(\mathbb{I}_{n,k}) \le
O_k(n^{k-\sqrt{k}/2})$ holds.",1211.7258v2
2012-12-05,"Probing Nuclear Symmetry Energy and its Imprints on Properties of Nuclei, Nuclear Reactions, Neutron Stars and Gravitational Waves","Significant progress has been made in recent years in constraining nuclear
symmetry energy at and below the saturation density of nuclear matter using
data from both terrestrial nuclear experiments and astrophysical observations.
However, many interesting questions remain to be studied especially at
supra-saturation densities. In this lecture note, after a brief summary of the
currently available constraints on nuclear symmetry energy near the saturation
density we first discuss the relationship between the symmetry energy and the
isopin and momentum dependence of the single-nucleon potential in
isospin-asymmetric nuclear medium. We then discuss several open issues
regarding effects of the tensor force induced neutron-proton short-range
correlation (SRC) on nuclear symmetry energy. Finally, as an example of the
impacts of nuclear symmetry energy on properties of neutron stars and
gravitational waves, we illustrate effects of the high-density symmetry energy
on the tidal polarizability of neutron stars in coalescing binaries.",1212.1178v1
2012-12-10,Simulations of Overstable Inertial-acoustic Modes in Black-Hole Accretion Discs,"We present two-dimensional inviscid hydrodynamic simulations of overstable
inertial-acoustic oscillation modes (p-modes) in black-hole accretion discs.
These global spiral waves are trapped in the inner-most region of the disc, and
are driven overstable by wave absorption at the corotation resonance ($r_c$)
when the gradient of the background disc vortensity (vorticity divided by
surface density) at $r_c$ is positive and the disc inner boundary is
sufficiently reflective. Previous linear calculations have shown that the
growth rates of these modes can be as high as 10% of the rotation frequency at
the disc inner edge. We confirm these linear growth rates and the primary disc
oscillation frequencies in our simulations when the mode amplitude undergoes
exponential growth. We show that the mode growth saturates when the radial
velocity perturbation becomes comparable to the disc sound speed. During the
saturation stage, the primary disc oscillation frequency differs only slightly
(by less than a few percent) from the linear mode frequency. Sharp features in
the fluid velocity profiles at this stage suggest that the saturation results
from nonlinear wave steepening and mode-mode interactions.",1212.2215v1
2012-12-14,1.5 GHz Pulse Generation From a Monolithic Waveguide Laser With a Graphene-Film Saturable Output Coupler,"We fabricate a saturable absorber mirror by coating a graphene film on an
output coupler mirror. This is then used to obtain Q-switched mode-locking from
a diode pumped linear cavity waveguide laser inscribed in Ytterbium-doped
Bismuthate Glass, with high slope and optical conversion efficiencies. The
laser produces mode-locked pulses at 1039nm, with 1.5GHz repetition rate at an
average 202mW output power. This performance is due to the combination of the
graphene saturable absorber with the high quality laser glass.",1212.3401v1
2012-12-20,Saturation in central-forward jet production in p-Pb collisions at LHC,"We show that saturation can manifest itself in central-forward dijet
production in p-A collisions. In spite of large transverse momenta of the jets,
the almost back-to-back dijet configurations are able to probe gluon density at
low x and low kt. We perform our study in the framework of high energy
factorization with the unintegrated gluon density given by a nonlinear QCD
evolution equation. We show that the formalism can successfully account for
features measured in e-p and p-p data and it predicts significant suppression
of the central-forward jet decorrelations in p-Pb compared to p-p, which we
attribute to saturation of gluon density in the nucleus.",1212.5078v1
2012-12-21,Role of Joule Heating on Current Saturation and Transient Behavior of Graphene Transistors,"We use simulations to examine current saturation in sub-micron graphene
transistors on SiO2/Si. We find self-heating is partly responsible for current
saturation (lower output conductance), but degrades current densities >1 mA/um
by up to 15%. Heating effects are reduced if the supporting insulator is
thinned, or in shorter channel devices by partial heat sinking at the contacts.
The transient behavior of such devices has thermal time constants of ~30-300
ns, dominated by the thickness of the supporting insulator and that of device
capping layers (a behavior also expected in ultrathin body SOI transistors).
The results shed important physical insight into the high-field and transient
behavior of graphene transistors.",1212.5629v1
2012-12-24,A puzzle of the pion-photon transition form factor - resolved?,"By means of QCD sum rules in local-duality limit, we analyze the behaviour of
the form factors for the transitions of a real and a virtual photon to some
pseudoscalar meson as functions of the involved momentum transfer. Except for
the findings of BaBar for the neutral-pion form factor, the experimental data
for all these transition form factors are compatible with saturation for large
momentum transfer predicted by pQCD factorization. For light pseudoscalar
mesons, saturation is observed already at relatively small momentum transfer,
whereas for the eta-c meson it sets in only at larger momentum transfer. A
recent measurement of the neutral-pion transition form factor by Belle seems to
resolve this disturbing puzzle as its outcome is compatible with both
saturation for relatively small momentum transfer and the behaviour of the eta
and eta' transition form factors at large momentum transfer.",1212.5898v1
2013-01-04,How strong are the Rossby vortices?,"The Rossby wave instability, associated with density bumps in differentially
rotating discs, may arise in several different astrophysical contexts, such as
galactic or protoplanetary discs. While the linear phase of the instability has
been well studied, the nonlinear evolution and especially the saturation phase
remain poorly understood. In this paper, we test the non-linear saturation
mechanism analogous to that derived for wave-particle interaction in plasma
physics. To this end we perform global numerical simulations of the evolution
of the instability in a two-dimensional disc. We confirm the physical mechanism
for the instability saturation and show that the maximum amplitude of vorticity
can be estimated as twice the linear growth rate of the instability. We provide
an empirical fitting formula for this growth rate for various parameters of the
density bump. We also investigate the effects of the azimuthal mode number of
the instability and the energy leakage in the spiral density waves. Finally, we
show that our results can be extrapolated to 3D discs.",1301.0689v1
2013-01-21,On the Saturation of the Nonlinear Refractive Index in Atomic Gases,"Motivated by the ongoing controversy on the origin of the nonlinear index
saturation and subsequent intensity clamping in femtosecond filaments, we study
the atomic nonlinear polarization induced by a high-intensity and ultrashort
laser pulse in hydrogen by numerically solving the time dependent Schr\""odinger
equation. Special emphasis is given to the efficient modeling of the nonlinear
polarization at central laser frequency corresponding to 800 nm wavelength.
Here, the recently proposed model of the Higher-Order Kerr Effect (HOKE) and
two versions of the Standard model for femtosecond filamentation, including
either a multi-photon or tunnel ionization rate, are compared. We find that
around the clamping intensity the instantaneous HOKE model does not reproduce
the temporal structure of the nonlinear response obtained from the quantum
mechanical results. In contrast, the non-instantaneous charge contributions
included in the Standard models ensure a reasonable quantitative agreement.
Therefore, the physical origin for the observed saturation of the overall
electron response is confirmed to mainly result from contributions of free or
nearly free electrons.",1301.4789v1
2013-02-14,Nonlinear multimodal interference and saturable absorption using a short graded-index multimode optical fiber,"A detailed investigation of the nonlinear multimodal interference in a short
graded-index multimode optical fiber is presented. The analysis is performed
for a specific device geometry, where the light is coupled in and out of the
multimode fiber via single-mode fibers. The same device geometry was recently
used to obtain ultra-low-loss coupling between two single-mode optical fibers
with very different mode-field diameters. Our results indicate the potential
application of this simple geometry for nonlinear devices, such as in nonlinear
switching, optical signal processing, or as saturable absorbers in mode-locked
fiber lasers. Saturable absorption in this all-fiber configuration is discussed
and it is shown that it provides attractive properties that can potentially be
used in high pulse energy mode-locked fiber lasers.",1302.3493v2
2013-03-26,Novel carbon materials: new tunneling systems,"This review covers recent achievements in the studies of quantum properties
of the novel carbon materials (fullerite C60 and bundles of single-walled
nanotubes (SWNT)) saturated with such light-mass species as helium isotopes,
the homonuclear molecular hydrogens, and neon. It is shown that even some heavy
dopants demon-strate kinetic phenomena, in which coherent effects play an
essential role. Two theoretical concepts are surveyed which have been suggested
for the explanation of the anomalous phenomena in saturation kinetics and
linear thermal expansion of doped C60. Most unusual effects have been also
observed in the low-temperature radial ex-pansion of bundles of single-walled
carbon nanotubes saturated with the helium isotopes. First, it was shown that
low-temperature radial expansion of pure SWNT is negative, i.e., a nanotube
shrinks with warming. Second, sa-turation of SWNT bundles with the helium
isotopes entails a huge increase of the negative expansion effect, when the
dopant is He. So far, no detailed physical picture has been put forward. It is
worth mentioning that the dynamics of a single helium atom on an isolated
nanotube corresponds to that of a tight-bound quasiparticle with a band width
of about 10 K.",1303.6581v1
2013-04-19,Quantum Popov robust stability analysis of an optical cavity containing a saturated Kerr medium,"This paper applies results on the robust stability of nonlinear quantum
systems to a system consisting an optical cavity containing a saturated Kerr
medium. The system is characterized by a Hamiltonian operator which contains a
non-quadratic term involving a quartic function of the annihilation and
creation operators. A saturated version of the Kerr nonlinearity leads to a
sector bounded nonlinearity which enables a quantum small gain theorem to be
applied to this system in order to analyze its stability. Also, a non-quadratic
version of a quantum Popov stability criterion is presented and applied to
analyze the stability of this system.",1304.5384v1
2013-06-18,Transfer and characteristic idempotents for saturated fusion systems,"We construct a well-behaved transfer map from the p-local Burnside ring of
the underlying p-group S to the p-local Burnside ring of a saturated fusion
system F. Using this transfer map, we give new results on the characteristic
idempotent of F -- the unique idempotent in the p-local double Burnside ring of
S satisfying properties of Linckelmann and Webb. We describe this idempotent
explicitly both in terms of fixed points and as a linear combination of
transitive bisets. Additionally, using fixed points we determine the map for
Burnside rings given by multiplication with the characteristic idempotent, and
show that this is the transfer map previously constructed. Applying these
results, we show that for every saturated fusion system the ring generated by
all (not necessarily idempotent) characteristic elements in the p-local double
Burnside ring is isomorphic as rings to the p-local ""single"" Burnside ring of
the fusion system, and we disprove a conjecture by Park-Ragnarsson-Stancu on
the composition product of fusion systems.",1306.4162v4
2013-06-18,Heavy quark production and gluon saturation in double parton scattering at LHC,"The production of $c\bar{c}c\bar{c}$, $b\bar{b}b\bar{b}$ and
$c\bar{c}b\bar{b}$ pairs considering double parton scattering at LHC energies
is investigated. We estimate the contribution of saturation effects to the
different final states and predict the energy dependence of the cross sections.
Moreover, we estimate the ratio between the double and single parton scattering
cross sections for the full rapidity range of the LHC and for the rapidity
range of the LHCb experiment. For the full rapidity range we confirm a previous
prediction, namely that for charm production the double parton scattering
contribution becomes comparable with the single parton scattering one at LHC
energies. We also demonstrate that this result remains valid when one
introduces saturation effects in the calculations. Finally we show that the
production of $c\bar{c}b\bar{b}$ contributes significantly to bottom
production. For the LHCb kinematical range the ratio is strongly reduced.",1306.4169v1
2013-06-27,Quasi-pinning and entanglement in the lithium isoelectronic series,"The Pauli exclusion principle gives an upper bound of 1 on the natural
occupation numbers. Recently there has been an intriguing amount of theoretical
evidence that there is a plethora of additional generalized Pauli restrictions
or (in)equalities, of kinematic nature, satisfied by these numbers. Here for
the first time a numerical analysis of the nature of such constraints is
effected in real atoms. The inequalities are nearly saturated, or quasi-pinned.
For rank-six and rank-seven approximations for lithium, the deviation from
saturation is smaller than the lowest occupancy number. For a rank-eight
approximation we find well-defined families of saturation conditions.",1306.6528v2
2013-07-09,"Far-from-equilibrium Sheared Colloidal Liquids: Disentangling Relaxation, Advection, and Shear-induced Diffusion","Using high-speed confocal microscopy, we measure the particle positions in a
colloidal suspension under large amplitude oscillatory shear. Using the
particle positions we quantify the in situ anisotropy of the pair-correlation
function -- a measure of the Brownian stress. From these data, we find two
distinct types of responses as the system crosses over from equilibrium to
far-from-equilibrium states. The first is a nonlinear amplitude saturation that
arises from shear-induced advection, while the second is a linear frequency
saturation due to competition between suspension relaxation and shear rate. In
spite of their different underlying mechanisms, we show that all the data can
be scaled onto a master curve that spans the equilibrium and
far-from-equilibrium regimes, linking small amplitude oscillatory to continuous
shear. This observation illustrates a colloidal analog of the Cox-Merz rule and
its microscopic underpinning. Brownian Dynamics simulations show that
interparticle interactions are sufficient for generating both experimentally
observed saturations.",1307.2500v2
2013-07-18,1.06 μm Q-switched ytterbium-doped fiber laser using few-layer topological insulator Bi2Se3 as a saturable absorber,"Passive Q-switching of an ytterbium-doped fiber (YDF) laser with few-layer
topological insulator (TI) is, to the best of our knowledge, experimentally
demonstrated for the first time. The few-layer TI: Bi2Se3 (2-4 layer thickness)
is fabricated by the liquid-phase exfoliation method, and has a low saturable
optical intensity of 53 MW/cm2 measured by the Z-scan technique. The optical
deposition technique is used to induce the few-layer TI in the solution onto a
fiber ferrule for successfully constructing the fiber-integrated TI-based
saturable absorber (SA). By inserting this SA into the YDF laser cavity, stable
Q-switching operation at 1.06 {\mu}m is achieved. The Q-switched pulses have
the shortest pulse duration of 1.95 {\mu}s, the maximum pulse energy of 17.9 nJ
and a tunable pulse-repetition-rate from 8.3 to 29.1 kHz. Our results indicate
that the TI as a SA is also available at 1 {\mu}m waveband, revealing its
potential as another wavelength-independent SA (like graphene).",1307.4979v1
2013-07-20,A Particle-Water Based Model for Water Retention Hysteresis,"A particle-water discrete element based approach to describe water movement
in partially saturated granular media is presented and tested. Water potential
is governed by both capillary bridges, dominant at low saturations, and the
pressure of entrapped air, dominant at high saturations. The approach captures
the hysteresis of water retention during wetting and drainage by introducing
the local evolution of liquid-solid contact angles at the level of pores and
grains. Extensive comparisons against experimental data are presented. While
these are made without the involvement of any fitting parameters, the method
demonstrates relative high success by achieving a correlation coefficient of at
least 82%, and mostly above 90%. For the tested materials with relatively
mono-disperse grain size, the hysteresis of water retention during cycles of
wetting and drainage has been shown to arise from the dynamics of solid-liquid
contact angles as a function of local liquid volume changes.",1307.5372v2
2013-08-13,Sudakov Double Logarithms Resummation in Hard Processes in Small-x Saturation Formalism,"In this manuscript, we present a complete study of the Sudakov double
logarithms resummation for various hard processes in eA and pA collisions in
the small-x saturation formalism. We first employ a couple of slightly
different formalisms to perform the one-loop analysis of the Higgs boson
production process in pA collisions, and demonstrate that Sudakov-type
logarithms arise as the leading correction and that they can be systematically
resummed in addition to the usual small-x resummation. We further study the
Sudakov double logarithms for other processes such as heavy quark pair
production and back-to-back dijet production in eA and pA collisions through
detailed calculation of the corresponding one-loop diagrams. As the most
important contribution from the one-loop correction, the Sudakov factor should
play an important role in the phenomenological study of saturation physics in
the pA programs at RHIC and the LHC.",1308.2993v1
2013-09-04,Saturated simple and $k$-simple topological graphs,"A simple topological graph $G$ is a graph drawn in the plane so that any pair
of edges have at most one point in common, which is either an endpoint or a
proper crossing. $G$ is called saturated if no further edge can be added
without violating this condition. We construct saturated simple topological
graphs with $n$ vertices and $O(n)$ edges. For every $k>1$, we give similar
constructions for $k$-simple topological graphs, that is, for graphs drawn in
the plane so that any two edges have at most $k$ points in common. We show that
in any $k$-simple topological graph, any two independent vertices can be
connected by a curve that crosses each of the original edges at most $2k$
times. Another construction shows that the bound $2k$ cannot be improved.
Several other related problems are also considered.",1309.1046v2
2013-10-30,Superfast non-linear diffusion: Capillary transport in particulate porous media,"The migration of liquids in porous media, such as sand, has been commonly
considered at high saturation levels with liquid pathways at pore dimensions.
In this letter we reveal a low saturation regime observed in our experiments
with droplets of extremely low volatility liquids deposited on sand. In this
regime the liquid is mostly found within the grain surface roughness and in the
capillary bridges formed at the contacts between the grains. The bridges act as
variable-volume reservoirs and the flow is driven by the capillary pressure
arising at the wetting front according to the roughness length scales. We
propose that this migration (spreading) is the result of interplay between the
bridge volume adjustment to this pressure distribution and viscous losses of a
creeping flow within the roughness. The net macroscopic result is a special
case of non-linear diffusion described by a superfast diffusion equation (SFDE)
for saturation with distinctive mathematical character. We obtain solutions to
a moving boundary problem defined by SFDE that robustly convey a time power law
of spreading as seen in our experiments.",1310.8262v1
2013-11-04,Flux saturation length of sediment transport,"Sediment transport along the surface drives geophysical phenomena as diverse
as wind erosion and dune formation. The main length-scale controlling the
dynamics of sediment erosion and deposition is the saturation length
$L_\mathrm{s}$, which characterizes the flux response to a change in transport
conditions. Here we derive, for the first time, an expression predicting
$L_\mathrm{s}$ as a function of the average sediment velocity under different
physical environments. Our expression accounts for both the characteristics of
sediment entrainment and the saturation of particle and fluid velocities, and
has only two physical parameters which can be estimated directly from
independent experiments. We show that our expression is consistent with
measurements of $L_\mathrm{s}$ in both aeolian and subaqueous transport regimes
over at least five orders of magnitude in the ratio of fluid and particle
density, including on Mars.",1311.0661v1
2013-12-17,"Measurements on Melting Pressure, Metastable Solid Phases, and Molar Volume of Univariant Saturated Helium Mixture","A concentration-saturated helium mixture at the melting pressure consists of
two liquid phases and one or two solid phases. The equilibrium system is
univariant, whose properties depend uniquely on temperature. Four coexisting
phases can exist on singular points, which are called quadruple points. As a
univariant system, the melting pressure could be used as a thermometric
standard. It would provide some advantages compared to the current reference,
namely pure $^3$He, especially at the lowest temperatures below 1 mK. We have
extended the melting pressure measurements of the concentration-saturated
helium mixture from 10 mK to 460 mK. The density of the dilute liquid phase was
also recorded. The effect of the equilibrium crystal structure changing from
hcp to bcc was clearly seen at T=294 mK at the melting pressure P=2.638 MPa. We
observed the existence of metastable solid phases around this point. No
evidence was found for the presence of another, disputed, quadruple point at
around 400 mK. The experimental results agree well with our previous
calculations at low temperatures, but deviate above 200 mK.",1312.4763v2
2014-01-04,Optical Solitons in a Trinal-channel Inverted Nonlinear Photonic Crystal,"Inverted nonlinear photonic crystals are the crystals featuring competition
between linear and nonlinear lattices, with minima of the linear potential
coinciding with maxima of the nonlinear pseudopotential, and vice versa.
Traditional inverted nonlinear photonic crystals only have two channels, and
can be attained experimentally by means of Rhodamine B (RhB, a dye featuring
saturable absorption) doped into the SU-8 polymer. In this paper, a new type of
inverted nonlinear photonic crystal is constructed by juxtaposing three kinds
of channels into a period. These three channels are a purely linear channel, a
saturable self-focusing nonlinear channel, and a saturable self-defocusing
nonlinear channel. This optical device is assumed to be fabricated by means of
SU-8 polymer material periodically doped with two types of active dyes. The
nonlinear propagation of a light field inside this device (passing along the
channel) can be described by a nonlinear Schrodinger equation. Stable
multi-peak fundamental and dipole solitons are found in the first gap of the
system. These solitons sufficiently exhibit some interesting digital
properties, which may have potential in optical communications.",1401.0786v1
2014-02-09,Possibility of a superfluid in high multiplicity p-p and p-Pb collisions,"We consider the case where the saturated and unequilibriated initial stage of
a high multiplicity p-p and p-Pb collision, may, due to high occupation number,
display superfluid properties. The special case of an unequilibrated plasma of
SU(2) gluons formed in the collision of two nuclei with deeply saturated gluon
wave functions is considered. Color gauge symmetry is broken by the presence of
a net non-vanishing, space-time dependent color expectation value. A two
component scenario is envisioned, containing momentum states that are densely
occupied below the saturation scale and a dilute normal fluid of excitations
within this state. The spectrum of these excitations is shown to have an energy
gap and thus it is hard to excite quanta out of the condensed state.
Consequences for the stress energy tensor are outlined, in particular the
possibility of a near invisid flow is discussed.",1402.1912v3
2014-02-14,Enhanced quantum coherence in graphene caused by Pd cluster deposition,"We report on the unexpected increase in the dephasing lengths of a graphene
sheet caused by the deposition of Pd nanoclusters, as demonstrated by weak
localization measurements. The dephasing lengths reached saturated values at
low temperatures. Theoretical calculations indicate the p-type charge transfer
from the Pd clusters, which contributes more carriers. The saturated values of
dephasing lengths often depend on both the carrier concentration and mean free
path. Although some impurities are increased as revealed by decreased
mobilities, the intense charge transfer leads to the improved saturated values
and subsequent improved dephasing lengths.",1402.3386v2
2014-02-20,Lasing of ambient air with microjoule pulse energy pumped by a multi terawatt IR femtosecond laser,"We report on the lasing action of atmospheric air pumped by an 800 nm
femtosecond laser pulse with peak power up to 4 TW. Lasing emission at 428 nm
increases rapidly over a small range of pump laser power, followed by
saturation above ~ 1.5 TW. The maximum lasing pulse energy is measured to be
2.6 uJ corresponding to an emission power in the MW range, while a maximum
conversion efficiency of is measured at moderate pump pulse energy. The optical
gain inside the filament plasma is estimated to be excess of 0.7/cm. The lasing
emission shows a doughnut profile, reflecting the spatial distribution of the
pump-generated white-light continuum that acts as a seed for the lasing. We
attribute the pronounced saturation to the defocusing of the seed in the plasma
amplifying region and to the saturation of the seed intensity.",1402.5019v1
2014-02-20,Saturation effects in forward-forward dijet production in p+Pb collisions,"We study saturation effects in the production of forward dijets in
proton-lead collisions at the Large Hadron Collider, using the framework of
High Energy Factorization. Such configurations, with both jets produced in the
forward direction, probe the gluon density of the lead nucleus at small
longitudinal momentum fraction, and also limit the phase space for emissions of
additional jets. We find significant suppression of the forward dijet azimuthal
correlations in proton-lead versus proton-proton collisions, which we attribute
to stronger saturation of the gluon density in the nucleus than in the proton.
In order to minimize model dependence of our predictions, we use two different
extensions of the Balitsky-Kovchegov equation for evolution of the gluon
density with sub-leading corrections.",1402.5065v2
2014-02-24,Spiraling elliptic breathers in saturable nonlinear media with linear anisotropy,"We have introduced a class of spiraling elliptic breathers in saturable
nonlinear media with linear anisotropy. Two kinds of evolution behaviors of the
breathers, rotating and pendulum-like librating, are both predicted by the
variational approach, and confirmed by the numerical simulation.The spiraling
elliptic breathers can rotate even though they have no initial orbital angular
momentum (OAM). Due to the linear anisotropy of the media, the OAM is no longer
conserved. Therefore, the angular velocity is found to be not a constant but a
periodic function of the propagation distance. When the linear anisotropy is
large enough, the spiraling elliptic breathers can librate like the pendulum.
The spiraling elliptic breathers exist in the media with not only the saturable
nonlinearity but also the nonlocal nonlinearity, as a matter of fact, they are
universal in the nonlinear media with the linear anisotropy.",1402.5736v1
2014-02-26,Femtosecond pulse generation from a Topological Insulator mode-locked fiber laser,"We reported on the generation of femtosecond pulse in an anomalous-dispersion
fiber ring laser by using a polyvinyl alcohol (PVA)-based Topological Insulator
(TI), Bi2Se3 saturable absorber (SA). The PVA-TI composite has a low saturable
optical intensity of 12 MW/cm2 and a modulation depth of ~3.9%. By
incorporating the fabricated PVA-TISA into a fiber laser, mode-locking
operation could be achieved at a low pump threshold of 25 mW. After an
optimization of the cavity parameters, optical pulse with ~660 fs centered at
1557.5 nm wavelength had been generated. The experimental results demonstrate
that the PVA could be an excellent host material for fabricating
high-performance TISA, and also indicate that the filmy PVA-TISA is indeed a
good candidate for ultrafast saturable absorption device.",1402.6529v1
2014-02-28,Charge Symmetry Breaking and Parity Violating Electron-Proton Scattering,"Charge symmetry breaking contributions to the proton's neutral weak form
factors must be understood in order for future measurements of parity violating
electron-proton scattering to be definitively interpreted as evidence of proton
strangeness. We calculate these charge symmetry breaking form factor
contributions using chiral perturbation theory with resonance saturation
estimates for unknown low-energy constants. The uncertainty of the
leading-order resonance saturation estimates is reduced by incorporating
nuclear physics constraints. Higher-order contributions are investigated
through phenomenological vertex form factors. We predict that charge symmetry
breaking form factor contributions are an order of magnitude larger than
expected from naive dimensional analysis but are still an order of magnitude
smaller than current experimental bounds on proton strangeness. This is
consistent with previous calculations using chiral perturbation theory with
resonance saturation.",1402.7169v3
2014-03-05,Geometrical Scaling of Direct-Photon Production in Hadron Collisions from RHIC to the LHC,"We consider pp, dAu and AuAu production of photons at RHIC energies, and PbPb
collisions at LHC energy. We show that the inclusive spectrum of photons in the
transverse momentum range of 1 GeV < pT <= 4 GeV satisfies geometric scaling.
Geometric scaling is a property of hadronic interactions predicted by theories
of gluon saturation, and expresses rates in terms of dimensionless ratios of
the transverse momentum to saturation momentum. We show excellent agreement
with geometric scaling with the only input being the previously measured
dependence of the saturation momentum upon Bjorken x and centrality.",1403.1174v2
2014-04-15,"Tensor invariants, Saturation problems, and Dynkin automorphisms","Let G be a connected almost simple algebraic group with a Dynkin automorphism
{\sigma}. Let G_{\sigma} be the connected almost simple algebraic group
associated to G and {\sigma}. We prove that the dimension of the tensor
invariant space of G_{\sigma} is equal to the trace of {\sigma} on the
corresponding tensor invariant space of G. We prove that if G has the
saturation property then so does G{\sigma}. As a consequence, we show that the
spin group Spin(2n + 1) is of saturation property with factor 2, which
strengthens the results of Belkale-Kumar and Sam in the case of type B_n.",1404.4098v2
2014-04-21,Phase conversion dissipation in multicomponent compact stars,"We propose a mechanism for the damping of density oscillations in
multicomponent compact stars. The mechanism is the periodic conversion between
different phases, i.e., the movement of the interface between them, induced by
pressure oscillations in the star. The damping grows nonlinearly with the
amplitude of the oscillation. We study in detail the case of r-modes in a
hybrid star with a sharp interface, and we find that this mechanism is powerful
enough to saturate the r-mode at very low saturation amplitude, of order
$10^{-10}$, and is therefore likely to be the dominant r-mode saturation
mechanism in hybrid stars with a sharp interface.",1404.5279v4
2014-05-16,General model of phospholipid bilayers in fluid phase within the single chain mean field theory,"Coarse-grained model for saturated (DCPC, DLPC, DMPC, DPPC, DSPC) and
unsaturated (POPC, DOPC) phospholipids is introduced within the Single Chain
Mean Field theory. A single set of parameters adjusted for DMPC bilayers gives
an adequate description of equilibrium and mechanical properties of a range of
saturated lipid molecules that differ only in length of their hydrophobic tails
and unsaturated (POPC, DOPC) phospholipids which have double bonds in the
tails. A double bond is modeled with a fixed angle of 120 degrees, while the
rest of the parameters are kept the same as saturated lipids. The thickness of
the bilayer and its hydrophobic core, the compressibility and the equilibrium
area per lipid correspond to experimentally measured values for each lipid,
changing linearly with the length of the tail. The model for unsaturated
phospholipids also fetches main thermodynamical properties of the bilayers.
This model is used for an accurate estimation of the free energies of the
compressed or stretched bilayers in stacks or multilayers and gives reasonable
estimates for free energies. The proposed model may further be used for studies
of mixtures of lipids, small molecule inclusions, interactions of bilayers with
embedded proteins.",1405.4106v1
2014-05-29,Dispersion-induced dynamics of coupled modes in a semiconductor laser with saturable absorption,"We present an experimental and theoretical study of modal nonlinear dynamics
in a specially designed dual-mode semiconductor Fabry-Perot laser with a
saturable absorber. At zero bias applied to the absorber section, we have found
that with increasing device current, single mode self-pulsations evolve into a
complex dynamical state where the total intensity experiences regular bursts of
pulsations on a constant background. Spectrally resolved measurements reveal
that in this state the individual modes of the device can follow highly
symmetric but oppositely directed spiralling orbits. Using a generalization of
the rate equation description of a semiconductor laser with saturable
absorption to the multimode case, we show that these orbits appear as a
consequence of the interplay between the material dispersion in the gain and
absorber sections of the laser. Our results provide insights into the factors
that determine the stability of multimode states in these systems, and they can
inform the development of semiconductor mode-locked lasers with tailored
spectra.",1405.7641v1
2014-06-06,Saturated Subgraphs of the Hypercube,"We say $G$ is \emph{$(Q_n,Q_m)$-saturated} if it is a maximal $Q_m$-free
subgraph of the $n$-dimensional hypercube $Q_n$. A graph, $G$, is said to be
$(Q_n,Q_m)$-semi-saturated if it is a subgraph of $Q_n$ and adding any edge
forms a new copy of $Q_m$. The minimum number of edges a $(Q_n,Q_m)$-saturated
graph (resp. $(Q_n,Q_m)$-semi-saturated graph) can have is denoted by
$sat(Q_n,Q_m)$ (resp. $s\text{-}sat(Q_n,Q_m)$). We prove that $
\lim_{n\to\infty}\frac{sat(Q_n,Q_m)}{e(Q_n)}=0$, for fixed $m$, disproving a
conjecture of Santolupo that, when $m=2$, this limit is $\frac{1}{4}$. Further,
we show by a different method that $sat(Q_n, Q_2)=O(2^n)$, and that
$s\text{-}sat(Q_n, Q_m)=O(2^n)$, for fixed $m$. We also prove the lower bound
$s-sat(Q_n,Q_2)\geq \frac{m+1}{2}\cdot 2^n$, thus determining $sat(Q_n,Q_2)$ to
within a constant factor, and discuss some further questions.",1406.1766v2
2014-06-24,High-field charge transport on the surface of Bi$_2$Se$_3$,"We present a theoretical study on the high-field charge transport on the
surface of Bi$_2$Se$_3$ and reproduce all the main features of the recent
experimental results, i.e., the incomplete current saturation and the finite
residual conductance in the high applied field regime [Costache {\it et al.},
Phys. Rev. Lett. {\bf 112}, 086601 (2014)]. Due to the hot-electron effect, the
conductance decreases and the current shows the tendency of the saturation with
the increase of the applied electric field. Moreover, the electric field can
excite carriers within the surface bands through interband precession and leads
to a higher conductance. As a joint effect of the hot-electron transport and
the carrier excitation, the conductance approaches a finite residual value in
the high-field regime and the current saturation becomes incomplete. We thus
demonstrate that, contrary to the conjecture in the literature, the observed
transport phenomena can be understood qualitatively in the framework of surface
transport alone. Furthermore, if a constant bulk conductance which is
insensitive to the field is introduced, one can obtain a good quantitative
agreement between the theoretical results and the experimental data.",1406.6223v1
2014-06-28,Azimuthal angle correlations in hadron-nucleus scattering: enhanced diagrams,"In this paper we calculate the contribution to rapidity and angular
correlations of the first Pomeron loop diagram in the dense partonic
environment. This diagram is expected to give the largest contribution to the
density variation mechanism of the angular correlations. We show that this
diagrams leads to sizable contributions to the rapidity correlation functions
of the order of $\sigma_{in} /\Lb \pi R^2\Rb$ where $\sigma_{in}$ is the
inelastic cross section and $R$ is the size of the typical dipole inside the
proton saturation scale. Therefore, the correlations do not depend on the
saturation scale. We demonstrated that density variation mechanism does not
lead to suppression of the angular dependance of the double inclusive cross
section generating the coefficient in front of $\cos^2 \varphi$ in $A^{1/3}$
larger in the case of hadron-nucleus collision than in hadron-hadron
interaction. The angular correlations are suppressed in comparison with the
rapidity ones but only due to large multiplicity of the produced gluons. We
consider this paper as the first attempt of quantitative description of the
density variation mechanism in CGC/saturation approach.",1406.7358v1
2014-08-25,Saturation numbers in tripartite graphs,"Given graphs $H$ and $F$, a subgraph $G\subseteq H$ is an $F$-saturated
subgraph of $H$ if $F\nsubseteq G$, but $F\subseteq G+e$ for all $e\in
E(H)\setminus E(G)$. The saturation number of $F$ in $H$, denoted
$\text{sat}(H,F)$, is the minimum number of edges in an $F$-saturated subgraph
of $H$. In this paper we study saturation numbers of tripartite graphs in
tripartite graphs. For $\ell\ge 1$ and $n_1$, $n_2$, and $n_3$ sufficiently
large, we determine $\text{sat}(K_{n_1,n_2,n_3},K_{\ell,\ell,\ell})$ and
$\text{sat}(K_{n_1,n_2,n_3},K_{\ell,\ell,\ell-1})$ exactly and
$\text{sat}(K_{n_1,n_2,n_3},K_{\ell,\ell,\ell-2})$ within an additive constant.
We also include general constructions of $K_{\ell,m,p}$-saturated subgraphs of
$K_{n_1,n_2,n_3}$ with few edges for $\ell\ge m\ge p>0$.",1408.5927v1
2014-09-16,Photoluminescence Saturation and Exciton Decay Dynamics in Transition Metal Dichalcogenide Monolayers,"We report a photoluminescence (PL) and transient reflection spectroscopy
study of exciton dynamics in monolayer transition transition-metal
dichalcogenides (TMDs). PL saturation in monolayer MoSe2 occurs an excitation
intensity more than two orders of magnitude lower than in monolayer MoS2.
Transient reflection shows that the nonlinear exciton-exciton annihilation is
the dominant exciton decay process in monolayer MoSe2 in contrast to the
previously reported linear exciton decay in monolayer MoS2. In addition, the
exciton lifetime in MoSe2, > 125 ps, is more than an order of magnitude longer
than the several-ps exciton lifetime in MoS2. We find that the dramatically
different exciton decay mechanism and PL saturation behavior of MoSe2 and MoS2
monolayers can be explained by the difference in their exciton lifetime.",1409.4546v2
2014-10-03,Analytical Evaluation of Saturation Throughput of a Cognitive 802.11-based WLAN Overlaid on a WiMAX-TDD Network,"This paper analyzes the saturation throughput of a cognitive single hop WLAN
overlaid on a primary IEEE 802.16e TDD WiMAX network. After the contention
among the secondary nodes, the winner node transmits its data packet in the
empty slots of downlink subframes of WiMAX. Regarding the OFDMA structure as
well as time-scheduled resources in WiMAX, the time duration of opportunities
for the secondary network does not follow simple exponential on-off pattern. To
model the dynamic behavior of opportunities for secondary nodes as well as
contentions to exploit the opportunities, we propose an analytical model
comprised of a discrete-time Markov chain and two inter-related open
multi-class queueing networks. The effects of random number of empty slots at
different frames as the result of random amount of download data, random packet
transmission time at WLAN due to random opportunities in different frames, the
dependency of the number of empty slots at consecutive WiMAX frames, and the
details of 802.11 MAC protocol are included in our analytical approach. We
compare the effect of two resource allocations, i.e., horizontal and vertical
striping on the saturation throughput of the cognitive WLAN. Simulation results
confirm the accuracy of our analytical approach in different conditions.",1410.0826v1
2014-11-21,WS2 as a saturable absorber for ultrafast photonic applications of mode-locked and Q-switched lasers,"Two-dimensional (2D) nanomaterials, especially the transition metal sulfide
semiconductors, have drawn great interests due to their potential applications
in viable photonic and optoelectronic devices, such as saturable absorbers
(SAs) and optical switches, etc. In this work, tungsten disulfide (WS2) based
SA for ultrafast photonic applications was demonstrated. WS2 nanosheets were
prepared using liquid-phase exfoliation method and embedded in polyvinyl
alcohol (PVA) thin film for the practical usage. Saturable absorption was
observed in the WS2-PVA SA at the telecommunication waveband near 1550 nm. By
incorporating WS2-PVA SA into a fiber laser cavity, both stable mode locking
operation and Q-switching operation were achieved. In the mode locking
operation, the laser obtained femtosecond output pulse width and high spectral
purity in the radio frequency spectrum. In the Q-switching operation, the laser
had tunable repetition rate and output pulse energy of a few tens of nano
joule. Our findings suggest that few-layer WS2 nanosheets embedded in PVA thin
film are promising nonlinear optical materials for ultrafast photonic
applications as a mode locker or Q-switcher.",1411.5777v1
2014-11-27,Saturated locally optimal designs under differentiable optimality criteria,"We develop general theory for finding locally optimal designs in a class of
single-covariate models under any differentiable optimality criterion. Yang and
Stufken [Ann. Statist. 40 (2012) 1665-1681] and Dette and Schorning [Ann.
Statist. 41 (2013) 1260-1267] gave complete class results for optimal designs
under such models. Based on their results, saturated optimal designs exist;
however, how to find such designs has not been addressed. We develop tools to
find saturated optimal designs, and also prove their uniqueness under mild
conditions.",1411.7601v1
2014-12-10,Heat transfer coefficient saturation in superconducting Nb tunnel junctions contacted to a NbTiN circuit and an Au energy relaxation layer,"In this paper we present the experimental realization of a Nb tunnel junction
connected to a high-gap superconducting NbTiN embedding circuit. We investigate
relaxation of nonequilibrium quasiparticles in a small volume Au layer between
the Nb tunnel junction and the NbTiN circuit. We find a saturation in the
effective heat-transfer coefficient consistent with a simple theoretical model.
This saturation is determined by the thickness of the Au layer. Our findings
are important for the design of the ideal Au energy relaxation layer for
practical SIS heterodyne mixers and we suggest two geometries, one, using a
circular Au layer and, two, using a half-circular Au layer. Our work is
concluded with an outlook of our future experiments.",1412.3388v1
2014-12-15,Saturable Lorentz model for fully explicit three-dimensional modeling of nonlinear optics,"Inclusion of the instantaneous Kerr nonlinearity in the FDTD framework leads
to implicit equations that have to be solved iteratively. In principle,
explicit integration can be achieved with the use of anharmonic oscillator
equations, but it tends to be unstable and inappropriate for studying
strong-field phenomena like laser filamentation. In this paper, we show that
nonlinear susceptibility can be provided instead by a harmonic oscillator
driven by a nonlinear force, chosen in a way to reproduce the polarization
obtained from the solution of the quantum mechanical two level equations. The
resulting saturable, nonlinearly-driven, harmonic oscillator model reproduces
quantitatively the quantum mechanical solutions of harmonic generation in the
under-resonant limit, up to the 9th harmonic. Finally, we demonstrate that
fully explicit leapfrog integration of the saturable harmonic oscillator is
stable, even for the intense laser fields that characterize laser filamentation
and high harmonic generation.",1412.4748v3
2015-01-27,Rapidity dependence of saturation in inclusive HERA data with the rcBK equation,"The contribution of the different terms of the running-coupling
Balistky-Kovchegov (rcBK) equation to the description of inclusive HERA data is
discussed. Within this framework an alternative definition of the saturation
scale is presented. The definition is based on the ratio of the term
corresponding to the recombination of two dipoles to the term corresponding to
a dipole splitting. A similar ratio is used to study the contribution of the
recombination term to the evolution of inclusive HERA data with rapidity. It is
found that, although the data are well described, the behaviour of the
different terms of the rcBK equation for HERA kinematics is not what it is
naively expected from saturation arguments.",1501.06687v3
2015-01-30,Inverse diffraction for the Atmospheric Imaging Assembly in the Solar Dynamics Observatory,"The Atmospheric Imaging Assembly in the Solar Dynamics Observatory provides
full Sun images every 1 seconds in each of 7 Extreme Ultraviolet passbands.
However, for a significant amount of these images, saturation affects their
most intense core, preventing scientists from a full exploitation of their
physical meaning. In this paper we describe a mathematical and automatic
procedure for the recovery of information in the primary saturation region
based on a correlation/inversion analysis of the diffraction pattern associated
to the telescope observations. Further, we suggest an interpolation-based
method for determining the image background that allows the recovery of
information also in the region of secondary saturation (blooming).",1501.07805v1
2015-01-30,A Study of the Matter of SPH Application to Saturated Soil Problems,"We present an application of SPH to saturated soilproblems. Herein, the
standard SPH formulation was improved to model saturated soil. It is shown that
the proposed formulation could yield several advantages such as: it takes into
account the pore-water pressure in an accurate manner, it automatically
satisfies the dynamics boundary conditions between submerged soil and water,
and it reduced the computational cost. Discussions on the use of the standard
and the new SPH formulations are also given through some numerical tests.
Furthermore, some techniques to obtained correct SPH solution are also proposed
and discussed. To the end, this paper suggests that the proposed SPH
formulation should be considered as the basic formulation for further
developments of SPH for soil-water couple problems",1502.00495v1
2015-02-13,Superstability in Tame Abstract Elementary Classes,"In this paper we address a problem posed by Shelah in 1999 to find a suitable
notion for superstability for abstract elementary classes in which limit models
of cardinality $\mu$ are saturated.
  Theorem 1. Suppose that $\mathcal{K}$ is a $\chi$-tame abstract elementary
class with no maximal models satisfying the joint embedding property and the
amalgamation property. Suppose $\mu$ is a cardinal with
$\mu\geq\beth_{(2^{LS(\mathcal{K})+\chi})^+}$. Let $M$ be a model of
cardinality $\mu$. If $\mathcal{K}$ is both $\chi$-stable and $\mu$-stable and
satisfies the $\mu$-superstability assumptions, then any two $\mu$-limit models
over $M$ are isomorphic over $M$.
  Moreover, we identify sufficient conditions for superlimit models of
cardinality $\mu$ to exist, for model homogeneous models to be superlimit, and
for a union of saturated models to be saturated.",1502.04144v2
2015-02-18,CGC/saturation approach for soft interactions at high energy: a two channel model,"In this paper we continue the development of a model for strong interactions
at high energy, based on two ingredients: CGC/saturation approach and the BFKL
Pomeron. In our approach, the unknown mechanism of confinement of quarks and
gluons, is characterized by several numerical parameters, which are extracted
from the experimental data. We demonstrate that the two channel model,
successfully describes the experimental data, including both the value of the
elastic slope and the energy behavior of the single diffraction cross section.
We show that the disagreement with experimental data of our previous single
channel eikonal model [6] stems from the simplified approach used for the
hadron structure, and is not related to our principal theoretical input, based
on the CGC/saturation approach.",1502.05202v1
2015-03-17,V-type electromagnetically induced transparency and saturation effect at the gas-solid interface,"We theoretically study electromagnetically induced transparency (EIT) in
reflection spectra of V-type system at the gas-solid interface. In addition to
a narrow dip arising from the EIT effect, we find the other particular
saturation effect induced by pump field, which does not exist in $\Lambda$ or
$\Xi$ -type system reflection spectra. The saturation effect only induces an
intensity decrement in the reflection spectra, and there is no influence on the
narrow dip arising from the EIT effect. We detailedly calculate and analyze the
dependence of V-type system reflection spectra on probe field intensity, pump
field intensity, coherent decay rate, and the initial population after the
collision between atoms and the interface.",1503.04950v2
2015-04-23,Simulation Study of Schottky Contact Based Single Si Wire Solar Cell,"We simulate single silicon nanowire (SiNW) solar cells with dissimilar work
function metal contacts. Both short circuit current (ISC) and open circuit
voltage (VOC) have been investigated. Effects of nanowire dimension, minority
carrier lifetime, and contact metal work function difference are understood
through simulations. Both ISC and VOC increase with nanowire length but
saturate due to minority carrier recombination. The saturation length is found
to be five times the diffusion length. The larger the contact work function
difference, the more improved the solar cell characteristics. Large work
function differences may also avoid need for any doping in axial p-i-n nanowire
solar cells. Saturation in ISC as well as degradation in current density with
length can be minimized by spreading the contacts along the length of the
nanowire.",1504.06281v1
2015-05-02,Saturated Sodium Chloride Solution under an External Static Electric Field: a Molecular Dynamics Study,"The behavior of saturated aqueous sodium chloride solutions under a constant
external electric field (E) was studied by molecular dynamics (MD) simulation.
Our dynamic MD simulations have indicated that the irreversible nucleation
process towards crystallization is accelerated by a moderate E, but retarded or
even prohibited under a stronger E, which can be understood by the competition
between self-diffusion and drift motion. The former increases with E resulting
in the acceleration of the nucleation process, and the latter tears oppositely
charged ions more apart under a stronger E leading to the deceleration of
nucleation. Moreover, our steady-state MD simulations have indicated that a
first-order phase transition happens in saturated solutions only when the
applied E is below a certain threshold Ec, and the ratio of crystallized ions
does not change with the electric field. The magnitude of Ec increases with
concentration, because larger clusters are easy to form in a more concentrated
solution and require a stronger E to dissociate them.",1505.00347v1
2015-05-11,Event-by-event fluctuations in perturbative QCD + saturation + hydro model: pinning down QCD matter shear viscosity in ultrarelativistic heavy-ion collisions,"We introduce an event-by-event perturbative-QCD + saturation + hydro (""EKRT"")
framework for ultrarelativistic heavy-ion collisions, where we compute the
produced fluctuating QCD-matter energy densities from next-to-leading order
perturbative QCD using a saturation conjecture to control soft particle
production, and describe the space-time evolution of the QCD matter with
dissipative fluid dynamics, event by event. We perform a simultaneous
comparison of the centrality dependence of hadronic multiplicities, transverse
momentum spectra, and flow coefficients of the azimuth-angle asymmetries,
against the LHC and RHIC measurements. We compare also the computed
event-by-event probability distributions of relative fluctuations of elliptic
flow, and event-plane angle correlations, with the experimental data from Pb+Pb
collisions at the LHC. We show how such a systematic multi-energy and
multi-observable analysis tests the initial state calculation and the
applicability region of hydrodynamics, and in particular how it constrains the
temperature dependence of the shear viscosity-to-entropy ratio of QCD matter in
its different phases in a remarkably consistent manner.",1505.02677v1
2015-06-23,"Nonlinear Processes in Multi-Quantum-Well Plasmonic Metasurfaces:Electromagnetic Response, Saturation Effects, Limits and Potentials","Nonlinear metasurfaces based on coupling a locally enhanced plasmonic
response to intersubband transitions of n-doped multi-quantum-wells (MQWs) have
recently provided second-order susceptibilities orders of magnitude larger than
any other nonlinear flat structure measured so far. Here, we present a
comprehensive theory to characterize the electromagnetic response of nonlinear
processes occurring in ultrathin MQW-based plasmonic metasurfaces, providing a
homogeneous model that takes phase-matching at the unit-cell level and the
influence of saturation and losses into account. In addition, the limits
imposed by saturation of the MQW transitions on the nonlinear response of these
metasurfaces are analytically derived, revealing useful guidelines to design
devices with enhanced performance. Our approach is first validated using
experimental data and then applied to theoretically investigate novel designs
able to achieve significant second-harmonic generation efficiency in the
infrared frequency band.",1506.07095v2
2015-07-06,3D super-resolved in vitro multiphoton microscopy by saturation of excitation,"We demonstrate a significant resolution enhancement beyond the conventional
limit in multiphoton microscopy (MPM) using saturated excitation of
fluorescence. Our technique achieves super-resolved imaging by temporally
modulating the excitation laser-intensity and demodulating the higher harmonics
from the saturated fluorescence signal. The improvement of the lateral and
axial resolutions is measured on a sample of fluorescent microspheres. While
the third harmonic already provides an enhanced resolution, we show that a
further improvement can be obtained with an appropriate linear combination of
the demodulated harmonics. Finally, we present in vitro imaging of fluorescent
microspheres incorporated in HeLa cells to show that this technique performs
well in biological samples.",1507.01408v3
2015-07-28,Gluon saturation and Feynman scaling in leading neutron production,"In this paper we extend the color dipole formalism to the study of leading
neutron production in $e + p \rightarrow e + n + X$ collisions at high energies
and estimate the related observables, which were measured at HERA and may be
analysed in future electron-proton ($ep$) colliders. In particular, we
calculate the Feynman $x_F$ distribution of leading neutrons, which is
expressed in terms of the pion flux and the photon-pion total cross section. In
the color dipole formalism, the photon-pion cross section is described in terms
of the dipole-pion scattering amplitude, which contains information about the
QCD dynamics at high energies and gluon saturation effects. We consider
different models for the scattering amplitude, which have been used to describe
the inclusive and diffractive $ep$ HERA data. Moreover, the model dependence of
our predictions with the description of the pion flux is analysed in detail. We
show that the recently released H1 leading neutron spectra can be reproduced
using the color dipole formalism and that these spectra could help us to
observe more clearly gluon saturation effects in future $ep$ colliders.",1507.07758v1
2015-08-07,Surfactant-aided exfoliation of molydenum disulphide for ultrafast pulse generation through edge-state saturable absorption,"We use liquid phase exfoliation to produce dispersions of molybdenum
disulphide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical
structures of the bile salt surfactants play a crucial role in the exfoliation
and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched
in single and few (<6) layer flakes with large edge to surface area ratio. We
use the dispersions to fabricate free-standing polymer composite wide-band
saturable absorbers to develop mode-locked and Q- switched fibre lasers,
tunable from 1535-1565 and 1030-1070 nm, respectively. We attribute this
sub-bandgap optical absorption and its nonlinear saturation behaviour to
edge-mediated states introduced within the material band-gap of the exfoliated
MoS2 nanoflakes.",1508.01631v2
2015-08-10,Threshold Saturation for Spatially Coupled Turbo-like Codes over the Binary Erasure Channel,"In this paper we prove threshold saturation for spatially coupled turbo codes
(SC-TCs) and braided convolutional codes (BCCs) over the binary erasure
channel. We introduce a compact graph representation for the ensembles of SC-TC
and BCC codes which simplifies their description and the analysis of the
message passing decoding. We demonstrate that by few assumptions in the
ensembles of these codes, it is possible to rewrite their vector recursions in
a form which places these ensembles under the category of scalar admissible
systems. This allows us to define potential functions and prove threshold
saturation using the proof technique introduced by Yedla et al..",1508.02196v1
2015-09-04,Saturation of the f-mode instability in neutron stars: I. Theoretical framework,"The basic formulation describing quadratic mode coupling in rotating
Newtonian stars is presented, focusing on polar modes. Due to the
Chandrasekhar-Friedman-Schutz mechanism, the f-mode (fundamental oscillation)
is driven unstable by the emission of gravitational waves. If the star falls
inside the so-called instability window, the mode's amplitude grows
exponentially, until it is halted by nonlinear effects. Quadratic perturbations
form three-mode networks inside the star, which evolve as coupled oscillators,
exchanging energy. Coupling of the unstable f-mode to other (stable) modes can
lead to a parametric resonance and the subsequent saturation of its amplitude,
thus suppressing the instability. The saturation point determines the amplitude
of the gravitational-wave signal obtained from an individual source, as well as
the evolutionary path of the latter inside the instability window.",1509.01453v2
2015-09-11,Breakdown of compensation and persistence of non-saturating magnetoresistance in WTe2 thin flakes,"We present a detailed study of magnetoresistance \r{ho}xx(H), Hall effect
\r{ho}xy(H), and electrolyte gating effect in thin (<100 nm) exfoliated
crystals of WTe2. We observe quantum oscillations in H of both \r{ho}xx(H) and
\r{ho}xy(H), and identify four oscillation frequencies consistent with previous
reports in thick crystals. \r{ho}xy(H) is linear in H at low H consistent with
near-perfect electron-hole compensation, however becomes nonlinear and changes
sign with increasing H, implying a breakdown of compensation. A field-dependent
ratio of carrier concentrations p/n can consistently explain \r{ho}xx(H) and
\r{ho}xy(H) within a two-fluid model. We also employ an electrolytic gate to
highly electron-dope WTe2 with Li. The non-saturating \r{ho}xx(H) persists to H
= 14 T with magnetoresistance ratio exceeding 2 x 104 %, even with significant
deviation from perfect electron-hole compensation (p/n = 0.84), where the
two-fluid model predicts a saturating \r{ho}xx(H). Our results suggest
electron-hole compensation is not the mechanism for extremely large
magnetoresistance in WTe2, other alternative explanations need to be
considered.",1509.03623v1
2015-10-07,An IMPES scheme for a two-phase flow in heterogeneous porous media using a structured grid,"We develop a numerical scheme for a two-phase immiscible flow in
heterogeneous porous media using a structured grid finite element method, which
have been successfully used for the computation of various physical
applications involving elliptic equations \cite{li2003new, li2004immersed,
chang2011discontinuous, chou2010optimal, kwak2010analysis}. The proposed method
is based on the implicit pressure-explicit saturation procedure. To solve the
pressure equation, we use an IFEM based on the Rannacher-Turek
\cite{rannacher1992simple} nonconforming space, which is a modification of the
work in \cite{kwak2010analysis} where `broken' $P_1$ nonconforming element of
Crouzeix-Raviart \cite{crouzeix1973conforming} was developed.
  For the Darcy velocity, we apply the mixed finite volume method studied in
\cite{chou2003mixed, kwak2010analysis} on the basis of immersed finite element
method (IFEM). In this way, the Darcy velocity of the flow can be computed
cheaply (locally) after we solve the pressure equation. The computed Darcy
velocity is used to solve the saturation equation explicitly. Thus the whole
procedure can be implemented in an efficient way using a structured grid which
is independent of the underlying heterogeneous porous media. Numerical results
show that our method exhibits optimal order convergence rates for the pressure
and velocity variables, and suboptimal rate for saturation.",1510.01839v1
2015-10-21,Exploring Complex-Langevin Methods for Finite-Density QCD,"QCD at non-zero chemical potential ($\mu$) for quark number has a complex
fermion determinant and thus standard simulation methods for lattice QCD cannot
be applied. We therefore simulate this theory using the Complex-Langevin
algorithm with Gauge Cooling in addition to adaptive methods, to prevent
runaway behaviour. Simulations are performed at zero temperature on a $12^4$
lattice with 2 quarks which are light enough that $m_N/3$ is significantly
larger than $m_\pi/2$. Preliminary results are qualitatively as expected. The
quark-number density is close to zero for $\mu < m_N/3$, beyond which it
increases, eventually reaching its saturation value of $3$ for $\mu$
sufficiently large. The chiral condensate decreases as $\mu$ is increased
approaching zero at saturation, while the plaquette increases towards its
quenched value. We have yet to observe the transition to nuclear matter at $\mu
\approx m_N/3$, presumably because the runs for $\mu$ between $m_N/3$ and
saturation have yet to equilibrate.",1510.06367v1
2015-11-18,Robust self-trapping of vortex beams in a saturable optical medium,"We report the first observation of robust self-trapping of vortex beams
propagating in a uniform condensed medium featuring local saturable
self-focusing nonlinearity. Optical vortices with topological charge m=1, that
remain self-trapped over ~ 5 Rayleigh lengths, are excited in carbon disulfide
using a helical light beam at 532 nm and intensities from 8 to 10 GW/cm^2. At
larger intensities, the vortex beams lose their stability, spontaneously
breaking into two fragments. Numerical simulations based on the nonlinear
Schr\""odinger equation including the three-photon absorption and nonpolynomial
saturation of the refractive nonlinearity demonstrate close agreement with the
experimental findings.",1511.06009v2
2015-12-05,Avalanche effect and gain saturation in high harmonic generation,"Optical amplifiers in all ranges of the electromagnetic spectrum exhibit two
essential characteristics: i) the input signal during the propagation in the
medium is multiplied by the avalanche effect of the stimulated emission to
produce exponential growth and ii) the amplification saturates at increasing
input signal. We demonstrate that the strong-field theory in the frame of high
harmonic generation fully supports the appearance of both the avalanche and
saturation effects in the amplification of extreme ultraviolet attosecond pulse
trains. We confirm that the amplification takes place only if the seed pulses
are perfectly synchronized with the driving strong field in the amplifier. We
performed an experimental study and subsequent model calculation on He gas
driven by intense 30-fs-long laser pulses, which was seeded with an attosecond
pulse train at 110 eV generated in a separated Ne gas jet. The comparison of
the performed calculations with the measurements clearly demonstrates that the
pumped He gas medium acted as an amplifier of the extreme ultraviolet pulse
train.",1512.01664v1
2015-12-06,Rates Achievable on a Fiber-Optical Split-Step Fourier Channel,"A lower bound on the capacity of the split-step Fourier channel is derived.
The channel under study is a concatenation of smaller segments, within which
three operations are performed on the signal, namely, nonlinearity, linearity,
and noise addition. Simulation results indicate that for a fixed number of
segments, our lower bound saturates in the high-power regime and that the
larger the number of segments is, the higher is the saturation point. We also
obtain an alternative lower bound, which is less tight but has a simple
closed-form expression. This bound allows us to conclude that the saturation
point grows unbounded with the number of segments. Specifically, it grows as
$c+(1/2)\log(K)$, where $K$ is the number of segments and $c$ is a constant.
The connection between our channel model and the nonlinear Schr\""odinger
equation is discussed.",1512.01843v4
2015-12-11,Saturation of number variance in embedded random matrix ensembles,"We study fluctuation properties of embedded random matrix ensembles of
non-interacting particles. For ensemble of two non-interacting particle
systems, we find that unlike the spectra of classical random matrices,
correlation functions are non-stationary. In the locally stationary region of
spectra, we study the number variance and the spacing distributions. The
spacing distributions follow the Poisson statistics which is a key behavior of
uncorrelated spectra. The number variance varies linearly as in the Poisson
case for short correlation lengths but a kind of regularization occurs for
large correlation lengths, and the number variance approaches saturation
values. These results are known in the study of integrable systems but are
being demonstrated for the first time in random matrix theory. We conjecture
that the interacting particle cases, which exhibit the characteristics of
classical random matrices for short correlation lengths, will also show
saturation effects for large correlation lengths.",1512.03593v1
2015-12-16,Pinning down QCD-matter shear viscosity in A+A collisions via EbyE fluctuations using pQCD + saturation + hydrodynamics,"We compute the initial energy densities produced in ultrarelativistic
heavy-ion collisions from NLO perturbative QCD using a saturation conjecture to
control soft particle production, and describe the subsequent space-time
evolution of the system with hydrodynamics, event by event. The resulting
centrality dependence of the low-$p_T$ observables from this pQCD + saturation
+ hydro (""EKRT"") framework are then compared simultaneously to the LHC and RHIC
measurements. With such an analysis we can test the initial state calculation,
and constrain the temperature dependence of the shear viscosity-to-entropy
ratio $\eta/s$ of QCD matter. Using these constraints from the current RHIC and
LHC measurements we then predict the charged hadron multiplicities and flow
coefficients for the 5.023 TeV Pb+Pb collisions.",1512.05132v1
2016-01-02,Holographic thermalization from non relativistic branes,"In this paper, based on the fundamental principles of Gauge/gravity duality
and considering a \textit{global quench}, we probe the physics of
thermalization for a special class of strongly coupled non relativistic QFTs by
computing the entanglement entropy of the plasma. The isometry group of such
QFTs is comprised of the generators of the Schr\""odinger algebra which could be
precisely realized as an isometry group of the killing generators of an
asymptotically Schr\""odinger $ Dp $ brane space time. In our analysis, we note
that during the pre local stages of the thermal equilibrium the entanglement
entropy has a faster growth in time compared to its relativistic cousin.
However, it shows a linear growth during the post local stages of thermal
equilibrium where the so called tsunami velocity associated with the linear
growth of the entanglement entropy saturates to that of its value corresponding
to the relativistic scenario. Finally, we explore the saturation region and it
turns out that one must constraint certain parameters of the theory in a
specific way in order to have a discontinuous transitions at the point of
saturation.",1601.00136v2
2016-01-21,Saturation of ion irradiation effects in Cr2AlC,"Cr2AlC materials were irradiated with 7 MeV Xe26+ ions and 500 keV He2+ ions
at room temperature. A structural transition with an increased c lattice
parameter and a decreased a lattice parameter occurs after irradiation to doses
above 1 dpa. Nevertheless, the modified structure is stable up to the dose of
5.2 dpa without obvious lattice disorder. The three samples irradiated to doses
above 1 dpa have comparable lattice parameters and hardness values, suggesting
a saturation of irradiation effects in Cr2AlC. The structural transition and
irradiation effects saturation are ascribed to irradiation-induced antisite
defects (CrAl and AlCr) and C interstitials, which is supported by the
calculations of the formation energies of various defects in Cr2AlC. The
irradiation-induced antisite defects and C interstitials may be critical to
understand the excellent resistance to irradiation-induced amorphization of MAX
phases.",1601.05514v1
2016-02-24,Optical switching and bistability in a four-level atomic systems,"We explore the coherent control of nonlinear absorption of intense laser
fields in four-level atomic systems. For instance, in a four-level ladder
system, a coupling field creates electromagnetically induced transparency (EIT)
with Aulter-Townes doublet for the probe field while the control field is
absent. A large absorption peak appears at resonance as the control field is
switched on. We show how such a large absorption leads to optical switching.
Further, this large absorption gets diminished and a transparency window
appears due to the saturation effects as the strength of the probe field is
increased. We further demonstrate that the threshold of the optical bistability
can be modified by suitable choices of the coupling and the control fields. In
a four-level Y-type configuration, the effect of the control field on saturable
absorption (SA) and reverse saturable absorption (RSA) is highlighted in the
context of nonlinear absorption of the probe field. We achieve RSA and SA in a
simple atomic system just by applying a control field.",1602.07596v3
2016-03-22,Locally Conservative Continuous Galerkin FEM for Pressure Equation in Two-Phase Flow Model in Subsurfaces,"A typical two-phase model for subsurface flow couples the Darcy equation for
pressure and a transport equation for saturation in a nonlinear manner. In this
paper, we study a combined method consisting of continuous Galerkin finite
element methods (CGFEMs) followed by a post-processing technique for Darcy
equation and finite volume method (FVM) with upwind schemes for the saturation
transport equation, in which the coupled nonlinear problem is solved in the
framework of operator decomposition. The postprocessing technique is applied to
CGFEM solutions to obtain locally conservative fluxes which ensures accuracy
and robustness of the FVM solver for the saturation transport equation. We
applied both upwind scheme and upwind scheme with slope limiter for FVM on
triangular meshes in order to eliminate the non-physical oscillations. Various
numerical examples are presented to demonstrate the performance of the overall
methodology.",1603.06998v1
2016-04-06,Constraining the supersaturation density equation of state from core-collapse supernova simulations - Excluded volume extension of the baryons,"In this article the role of the supersaturation density equation of state
(EOS) is explored in simulations of failed core-collapse supernova explosions.
Therefore the nuclear EOS is extended via a one-parameter excluded volume
description for baryons, taking into account their finite and increasing volume
with increasing density in excess of saturation density. Parameters are
selected such that the resulting supernova EOS represent extreme cases, with
high pressure variations at supersaturation density which feature extreme stiff
and soft EOS variants of the reference case, i.e. without excluded volume
corrections. Unlike in the interior of neutron stars with central densities in
excess of several times saturation density, central densities of core-collapse
supernovae reach only slightly above saturation density. Hence, the impact of
the supersaturation density EOS on the supernova dynamics as well as the
neutrino signal is found to be negligible. It is mainly determined from the
low- and intermediate-density domain, which is left unmodified within this
generalized excluded volume approach.",1604.01629v1
2016-04-07,Stability of Fluid Queuing Systems with Parallel Servers and Stochastic Capacities,"This note introduces a piecewise-deterministic queueing (PDQ) model to study
the stability of traffic queues in parallel-link transportation systems facing
stochastic capacity fluctuations. The saturation rate (capacity) of the PDQ
model switches between a finite set of modes according to a Markov chain, and
link inflows are controlled by a state-feedback policy. A PDQ system is stable
only if a lower bound on the time-average link inflows does not exceed the
corresponding time-average saturation rate. Furthermore, a PDQ system is stable
if the following two conditions hold: the nominal mode's saturation rate is
high enough that all queues vanish in this mode, and a bilinear matrix
inequality (BMI) involving an underestimate of the discharge rates of the PDQ
in individual modes is feasible. The stability conditions can be strengthened
for two-mode PDQs. These results can be used for design of routing policies
that guarantee stability of traffic queues under stochastic capacity
fluctuations.",1604.02008v6
2016-04-09,Relaxation and Purification for Nonconvex Variational Problems in Dual Banach Spaces: The Minimization Principle in Saturated Measure Spaces,"We formulate bang-bang, purification, and minimization principles in dual
Banach spaces with Gelfand integrals and provide a complete characterization of
the saturation property of finite measure spaces. We also present a new
application of the relaxation technique to large economies with
infinite-dimensional commodity spaces, where the space of agents is modeled as
a finite measure space. We propose a ""relaxation"" of large economies, which is
regarded as a reasonable convexification of original economies. Under the
saturation hypothesis, the relaxation and purification techniques enable us to
prove the existence of Pareto optimal allocations without convexity
assumptions.",1604.02514v3
2016-06-19,On the Inheritance of Orbifold Substructures,"In a previous article, we defined a very flexible notion of suborbifold and
characterized those suborbifolds which can arise as the images of orbifold
embeddings. In particular, suborbifolds are images of orbifold embeddings
precisely when they are saturated and split. This article addresses the problem
of orbifold structure inheritance for three orbifolds
$\mathcal{Q}\subset\mathcal{P}\subset\mathcal{O}$. We identify an appealing but
ultimately inadequate notion of an inherited canonical orbifold substructure.
In particular, we give a concrete example where the orbifold structure of
$\mathcal{Q}$ is canonically inherited from $\mathcal{P}$, and the orbifold
structure of $\mathcal{P}$ is canonically inherited from $\mathcal{O}$, but the
orbifold structure of $\mathcal{Q}$ is not canonically inherited from
$\mathcal{O}$. On the other hand, it is easy to see that when $\mathcal{Q}$ is
embedded in $\mathcal{P}$, and $\mathcal{P}$ is embedded in $\mathcal{O}$, all
of the canonical inherited orbifold substructures will agree. We also
investigate the property of saturation in this context, and give an example of
a suborbifold with the canonical orbifold substructure that is not saturated.",1606.05902v1
2016-07-03,CGC/saturation approach for high energy soft interactions: `soft' Pomeron structure and $v_{n}$ in hadron and nucleus collisions from Bose-Einstein correlation,"In the framework of our model of soft interactions at high energy based on
CGC/saturation approach,we show that Bose-Einstein correlations of identical
gluons lead to large values of $v_n$. We demonstrate how three dimensional
scales of high energy interactions: hadron radius, typical size of the wave
function in diffractive production of small masses (size of the constituent
quark), and the saturation momentum, influence the values of BE correlations,
and in particular, the values of $v_n$. Our calculation shows that the
structure of the `dressed' Pomeron leads to values of $v_n$ which are close to
experimental values for proton-proton scattering, 20\% smaller than the
observed values for proton-lead collisions, and close to lead-lead collisions
for 0-10\% centrality. Bearing this result in mind, we conclude that it is
premature to consider, that the appearance of long range rapidity azimuthal
correlations are due only to the hydrodynamical behaviour of the quark-gluon
plasma.",1607.00594v3
2016-07-22,Collisionality scaling of the electron heat flux in ETG turbulence,"In electrostatic simulations of MAST plasma at electron-gyroradius scales,
using the local flux-tube gyrokinetic code GS2 with adiabatic ions, we find
that the long-time saturated electron heat flux (the level most relevant to
energy transport) decreases as the electron collisionality decreases. At early
simulation times, the heat flux ""quasi-saturates"" without any strong dependence
on collisionality, and with the turbulence dominated by streamer-like radially
elongated structures. However, the zonal fluctuation component continues to
grow slowly until much later times, eventually leading to a new saturated state
dominated by zonal modes and with the heat flux proportional to the collision
rate, in approximate agreement with the experimentally observed collisionality
scaling of the energy confinement in MAST. We outline an explanation of this
effect based on a model of ETG turbulence dominated by zonal-nonzonal
interactions and on an analytically derived scaling of the zonal-mode damping
rate with the electron-ion collisionality. Improved energy confinement with
decreasing collisionality is favourable towards the performance of future,
hotter devices.",1607.06752v2
2016-07-28,Cavity polaritons with Rydberg blockade and long-range interactions,"We study interactions between polaritons, arising when photons strongly
couple to collective excitations in an array of two-level atoms trapped in an
optical lattice inside a cavity. We consider two types of interactions between
atoms: Dipolar forces and atomic saturability, which ranges from hard-core
repulsion to Rydberg blockade. We show that, in spite of the underlying
repulsion in the subsystem of atomic excitations, saturability induces a
broadband bunching of photons for two-polariton scattering states. We interpret
this bunching as a result of interference, and trace it back to the mismatch of
the quantization volumes for atomic excitations and photons. We examine also
bound bipolaritonic states: These include states created by dipolar forces, as
well as a gap bipolariton, which forms solely due to saturability effects in
the atomic transition. Both types of bound states exhibit strong bunching in
the photonic component. We discuss the dependence of bunching on experimentally
relevant parameters.",1607.08323v1
2016-08-22,The virial theorem and ground state energy estimate of nonlinear Schrödinger equations in $\mathbb{R}^2$ with square root and saturable nonlinearities in nonlinear optics,"The virial theorem is a nice property for the linear Schrodinger equation in
atomic and molecular physics as it gives an elegant ratio between the kinetic
and potential energies and is useful in assessing the quality of numerically
computed eigenvalues. If the governing equation is a nonlinear Schrodinger
equation with power-law nonlinearity, then a similar ratio can be obtained but
there seems no way of getting any eigenvalue estimate. It is surprising as far
as we are concerned that when the nonlinearity is either square-root or
saturable nonlinearity (not a power-law), one can develop a virial theorem and
eigenvalue estimate of nonlinear Schrodinger (NLS) equations in R2 with
square-root and saturable nonlinearity, respectively. Furthermore, we show here
that the eigenvalue estimate can be used to obtain the 2nd order term (which is
of order $ln\Gamma$) of the lower bound of the ground state energy as the
coefficient $\Gamma$ of the nonlinear term tends to infinity.",1608.06102v1
2016-09-20,Impact of the tidal p-g instability on the gravitational wave signal from coalescing binary neutron stars,"Recent studies suggest that coalescing neutron stars are subject to a fluid
instability involving the nonlinear coupling of the tide to $p$-modes and
$g$-modes. Its influence on the inspiral dynamics and thus the gravitational
wave signal is, however, uncertain because we do not know precisely how the
instability saturates. Here we construct a simple, physically motivated model
of the saturation that allows us to explore the instability's impact as a
function of the model parameters. We find that for plausible assumptions about
the saturation, current gravitational wave detectors might miss $> 70\%$ of
events if only point particle waveforms are used. Parameters such as the chirp
mass, component masses, and luminosity distance might also be significantly
biased. On the other hand, we find that relatively simple modifications to the
point particle waveform can alleviate these problems and enhance the science
that emerges from the detection of binary neutron stars.",1609.06362v2
2016-10-03,Emergent eddy saturation from an energy constrained eddy parameterisation,"The large-scale features of the global ocean circulation and the sensitivity
of these features with respect to forcing changes are critically dependent upon
the influence of the mesoscale eddy field. One such feature, observed in
numerical simulations whereby the mesoscale eddy field is at least partially
resolved, is the phenomenon of eddy saturation, where the time-mean circumpolar
transport of the Antarctic Circumpolar Current displays relative insensitivity
to wind forcing changes. Coarse-resolution models employing the
Gent--McWilliams parameterisation with a constant Gent--McWilliams coefficient
seem unable to reproduce this phenomenon. In this article, an idealised model
for a wind-forced, zonally symmetric flow in a channel is used to investigate
the sensitivity of the circumpolar transport to changes in wind forcing under
different eddy closures. It is shown that, when coupled to a simple
parameterised eddy energy budget, the Gent--McWilliams coefficient of the form
described in Marshall et al. (2012) [A framework for parameterizing eddy
potential vorticity fluxes, J. Phys. Oceanogr., vol. 42, 539--557], which
includes a linear eddy energy dependence, produces eddy saturation as an
emergent property.",1610.00621v1
2016-10-19,Coupling of Damped and Growing Modes in Unstable Shear Flow,"Analysis of the saturation of the Kelvin-Helmholtz (KH) instability is
undertaken to determine the extent to which the conjugate linearly stable mode
plays a role. For a piecewise-continuous mean flow profile with constant shear
in a fixed layer, it is shown that the stable mode is nonlinearly excited,
providing an injection-scale sink of the fluctuation energy similar to what has
been found for gyroradius-scale drift-wave turbulence. Quantitative evaluation
of the contribution of the stable mode to the energy balance at the onset of
saturation shows that nonlinear energy transfer to the stable mode is as
significant as energy transfer to small scales in balancing energy injected
into the spectrum by the instability. The effect of the stable mode on momentum
transport is quantified by expressing the Reynolds stress in terms of stable
and unstable mode amplitudes at saturation, from which it is found that the
stable mode can produce a sizable reduction in the momentum flux.",1610.06142v4
2016-11-12,Saturating The Bekenstein-Hawking Entropy Bound With Initial Data Sets For Gravitational Collapse,"It is possible to find initial states for gravitational collapse whose
entropy approximately saturates the Bekenstein-Hawking entropy of the final
black hole. The prototypical example of such a state is that envisaged by Zurek
and Thorne, and also by Susskind: for a black hole of mass $\sim M$ , a number
$\sim M^2$ of quanta with energies of order $1/M$ are accreted on a timescale
of order $\sim M^3$, an approximate time-reverse of Hawking evaporation. There
is lore that all initial states which saturate the Bekenstein-Hawking entropy
must involve a formation timescale of this order, $M^3$ , and not the much
shorter dynamical timescale $M$ . Counterexamples to this lore have been found
by Sorkin, Wald and Zhang, and also by Hsu and Reeb, in the form of
semiclassical initial data sets. However the spacetimes that correspond to
these counterexamples possess white holes in the past, as well as black holes
in the future, which casts doubt on their physical relevance. We modify the
counterexamples to eliminate the white holes, yielding formation timescales of
order $M^2$ , and argue that the lore is unfounded.",1611.04044v3
2016-11-15,Phase Jump Method for Efficiency Enhancement in Free-Electron Lasers,"The efficiency of a free-electron laser can be enhanced by sustaining the
growth of the radiation power beyond the initial saturation. One notable method
is undulator tapering, which involves the variation of the gap height and/or
the period along the undulator. Another method is the introduction of phase
jumps, using phase-shifting chicanes in the drift sections separating the
undulator segments. In this article, we develop a physics model of this phase
jump method, and verify it with numerical simulations. The model elucidates the
energy extraction process in the longitudinal phase space. The main ingredient
is the microbunch deceleration cycle, which enables the microbunched electron
beam to decelerate and radiate coherently beyond the initial saturation. The
ponderomotive bucket is stationary, and energy can even be extracted from
electrons outside the bucket. The model addresses the selection criteria for
the phase jump values, and the requirement on the undulator segment length. It
also describes the mechanism of the final saturation. In addition, we discuss
the similarities and differences between the phase jump method and undulator
tapering, by comparing our phase jump model to the classic
Kroll-Morton-Rosenbluth model.",1611.04925v1
2016-12-02,Collective Phenomena in $pp$ and $ep$ Scattering,"Bjorken scaling violation in deep inelastic electron-proton scattering (DIS)
is related to the rise of hadronic cross sections by using the additive quark
model. Of special interest is the connection between saturation in the low-$x$
behavior of the DIS structure functions (SF) and possible slow-down of the $pp$
cross section rise due to saturation effects. We also identify saturation
effects in the DIS SF with phase transition that can be described by the Van
der Waals equation of state.",1612.00797v2
2016-12-15,Reducing Nondeterministic Tree Automata by Adding Transitions,"We introduce saturation of nondeterministic tree automata, a technique that
consists of adding new transitions to an automaton while preserving its
language. We implemented our algorithm on minotaut - a module of the tree
automata library libvata that reduces the size of automata by merging states
and removing superfluous transitions - and we show how saturation can make
subsequent merge and transition-removal operations more effective. Thus we
obtain a Ptime algorithm that reduces the size of tree automata even more than
before. Additionally, we explore how minotaut alone can play an important role
when performing hard operations like complementation, allowing to both obtain
smaller complement automata and lower computation times. We then show how
saturation can extend this contribution even further. We tested our algorithms
on a large collection of automata from applications of libvata in shape
analysis, and on different classes of randomly generated automata.",1612.04981v1
2016-12-21,Operator entanglement entropy of the time evolution operator in chaotic systems,"We study the growth of the operator entanglement entropy (EE) of the time
evolution operator in chaotic, many-body localized and Floquet systems. In the
random field Heisenberg model we find a universal power law growth of the
operator EE at weak disorder, a logarithmic growth at strong disorder, and
extensive saturation values in both cases. In a Floquet spin model, the
saturation value after an initial linear growth is identical to the value of a
random unitary operator (the Page value). We understand these properties by
mapping the operator EE to a global quench problem evolved with a similar
parent-Hamiltonian in an enlarged Hilbert space with the same chaotic, MBL and
Floquet properties as the original Hamiltonian. The scaling and saturation
properties reflect the spreading of the state EE of the corresponding time
evolution. We conclude that the EE of the evolution operator should
characterize the propagation of information in these systems.",1612.07327v2
2017-01-16,Investigating the impact of the gluon saturation effects on the momentum transfer distributions for the exclusive vector meson photoproduction in hadronic collisions,"The exclusive vector meson production cross section is one of the most
promising observables to probe the high energy regime of the QCD dynamics. In
particular, the squared momentum transfer ($t$) distributions are an important
source of information about the spatial distribution of the gluons in the
hadron and about fluctuations of the color fields. In this paper we complement
previous studies on exclusive vector meson photoproduction in hadronic
collisions presenting a comprehensive analysis of the $t$ - spectrum measured
in exclusive $\rho$, $\phi$ and $J/\Psi$ photoproduction in $pp$ and $PbPb$
collisions at the LHC. We compute the differential cross sections taking into
account gluon saturation effects and compare the predictions with those
obtained in the linear regime of the QCD dynamics. Our results show that gluon
saturation suppresses the magnitude of the cross sections and shifts the
position of the dips towards smaller values of $t$.",1701.04340v1
2017-01-18,Hysteretic behavior of electrical conductivity in packings of particles,"We address the problem of predicting saturation-dependent electrical
conductivity {\sigma} in packings of spheres during drainage and imbibition.
The effective-medium approximation (EMA) and the universal power law of
percolation for {\sigma} are used, respectively, at higher and low water
saturations to predict the conductivity, with the crossover between the two
occurring at some intermediate saturation Swx. The main input to the theory is
a single parameter that we estimate using the capillary pressure data. The
predictions are compared with experimental, as well as numerical data for three
distinct types of packings. The results for drainage in all the packings
indicate that the universal power law of percolation is valid over the entire
range of Sw. For imbibition, however, the universal power law crosses over to
the EMA at Swx = 0.5. We also find that the effect of the pore-size
distribution on the {\sigma}-Sw relation is minimal during both drainage and
imbibition.",1701.05076v1
2017-01-23,Saturated absorption competition microscopy,"We introduce the concept of saturated absorption competition (SAC) microscopy
as a means of providing sub-diffraction spatial resolution in fluorescence
imaging. Unlike the post-competition process between stimulated and spontaneous
emission that is used in stimulated emission depletion (STED) microscopy, SAC
microscopy breaks the diffraction limit by emphasizing a pre-competition
process that occurs in the fluorescence absorption stage in a manner that
shares similarities with ground-state depletion (GSD) microscopy. Moreover,
unlike both STED and GSD microscopy, SAC microscopy offers a reduction in
complexity and cost by utilizing only a single continuous-wave laser diode and
an illumination intensity that is ~ 20x smaller than that used in STED. Our
approach can be physically implemented in a confocal microscope by dividing the
input laser source into a time-modulated primary excitation beam and a
doughnut-shaped saturation beam, and subsequently employing a homodyne
detection scheme to select the modulated fluorescence signal. Herein, we
provide both a physico-chemical model of SAC and experimentally demonstrate by
way of a proof-of-concept experiment a transverse spatial resolution of
~lambda/6.",1701.06358v1
2017-03-13,Josephson parametric converter saturation and higher order effects,"Microwave parametric amplifiers based on Josephson junctions have become a
key component of many quantum information experiments. One key limitation which
has not been well predicted by theory is the gain saturation behavior which
determines its ability to process large amplitude signals. The typical
explanation for this behavior in phase-preserving amplifiers based on
three-wave mixing is pump depletion, in which the consumption of pump photons
to produce amplification results in a reduction in gain. However, in this work
we present experimental data and theoretical calculations showing that the
fourth-order Kerr nonlinearities inherent in the Josephson junctions are the
dominant factor in the Josephson Parametric Converter (JPC). The Kerr-based
theory has the unusual property of causing saturation to both lower and higher
gains, depending on bias conditions. This work presents a new methodology for
optimizing device performance in the presence of Kerr nonlinearities while
retaining device tunability, and points to the necessity of controlling
higher-order Hamiltonian terms to make further improvements in parametric
devices.",1703.04425v2
2017-03-14,A Quasi-Linear Time Algorithm Deciding Whether Weak Büchi Automata Reading Vectors of Reals Recognize Saturated Languages,"This work considers weak deterministic B\""uchi automata reading encodings of
non-negative $d$-vectors of reals in a fixed base. A saturated language is a
language which contains all encoding of elements belonging to a set of
$d$-vectors of reals. A Real Vector Automaton is an automaton which recognizes
a saturated language. It is explained how to decide in quasi-linear time
whether a minimal weak deterministic B\""uchi automaton is a Real Vector
Automaton. The problem is solved both for the two standard encodings of vectors
of numbers: the sequential encoding and the parallel encoding. This algorithm
runs in linear time for minimal weak B\""uchi automata accepting set of reals.
Finally, the same problem is also solved for parallel encoding of automata
reading vectors of relative reals.",1703.04834v1
2017-03-24,Definably compact groups definable in real closed fields. I,"We study definably compact definably connected groups definable in a
sufficiently saturated real closed field $R$. We introduce the notion of
group-generic point for $\bigvee$-definable groups and show the existence of
group-generic points for definably compact groups definable in a sufficiently
saturated o-minimal expansion of a real closed field. We use this notion along
with some properties of generic sets to prove that for every definably compact
definably connected group $G$ definable in $R$ there are a connected
$R$-algebraic group $H$, a definable injective map $\phi$ from a generic
definable neighborhood of the identity of $G$ into the group $H\left(R\right)$
of $R$-points of $H$ such that $\phi$ acts as a group homomorphism inside its
domain. This result is used in [2] to prove that the o-minimal universal
covering group of an abelian connected definably compact group definable in a
sufficiently saturated real closed field $R$ is, up to locally definable
isomorphisms, an open connected locally definable subgroup of the o-minimal
universal covering group of the $R$-points of some $R$-algebraic group.",1703.08606v2
2017-05-19,Topological dynamics and excitations in lasers and condensates with saturable gain or loss,"We classify symmetry-protected and symmetry-breaking dynamical solutions for
nonlinear saturable bosonic systems that display a non-hermitian
charge-conjugation symmetry, as realized in a series of recent groundbreaking
experiments with lasers and exciton polaritons. In particular, we show that
these systems support stable symmetry-protected modes that mirror the concept
of zero-modes in topological quantum systems, as well as symmetry-protected
power-oscillations with no counterpart in the linear case. In analogy to
topological phases in linear systems, the number and nature of
symmetry-protected solutions can change. The spectral degeneracies signalling
phase transitions in linear counterparts extend to bifurcations in the
nonlinear context. As bifurcations relate to qualitative changes in the linear
stability against changes of the initial conditions, the symmetry-protected
solutions and phase transitions can also be characterized by topological
excitations, which set them apart from symmetry-breaking solutions. The
stipulated symmetry appears naturally when one introduces nonlinear gain or
loss into spectrally symmetric bosonic systems, as we illustrate for
one-dimensional topological laser arrays with saturable gain and
two-dimensional flat-band polariton condensates with density-dependent loss.",1705.06895v2
2017-06-22,Intertial wave turbulence driven by elliptical instability,"The combination of elliptical deformation of streamlines and vorticity can
lead to the destabilisation of any rotating flow via the elliptical
instability. Such a mechanism has been invoked as a possible source of
turbulence in planetary cores subject to tidal deformations. The saturation of
the elliptical instability has been shown to generate turbulence composed of
non-linearly interacting waves and strong columnar vortices with varying
respective amplitudes, depending on the control parameters and geometry. In
this paper, we present a suite of numerical simulations to investigate the
saturation and the transition from vortex-dominated to wave-dominated regimes.
This is achieved by simulating the growth and saturation of the elliptical
instability in an idealised triply periodic domain, adding a frictional damping
to the geostrophic component only, to mimic its interaction with boundaries. We
reproduce several experimental observations within one idealised local model
and complement them by reaching more extreme flow parameters. In particular, a
wave-dominated regime that exhibits many signatures of inertial wave turbulence
is characterised for the first time. This regime is expected in planetary
interiors.",1706.07378v1
2017-07-21,Solitary waves in nonlocal NLS with dispersion averaged saturated nonlinearities,"A nonlinear Schr\""odinger equation (NLS) with dispersion averaged
nonlinearity of saturated type is considered. Such a nonlocal NLS is of
integro-differential type and it arises naturally in modeling fiber-optics
communication systems with periodically varying dispersion profile (dispersion
management). The associated constrained variational principle is shown to
posses a ground state solution by constructing a convergent minimizing sequence
through the application of a method similar to the classical concentration
compactness principle of Lions. One of the obstacles in applying this
variational approach is that a saturated nonlocal nonlinearity does not satisfy
uniformly the so-called strict sub-additivity condition. This is overcome by
applying a special version of Ekeland's variational principle.",1707.06944v1
2017-08-31,Online Feedback Control for Input-Saturated Robotic Systems on Lie Groups,"In this paper, we propose an approach to designing online feedback
controllers for input-saturated robotic systems evolving on Lie groups by
extending the recently developed Sequential Action Control (SAC). In contrast
to existing feedback controllers, our approach poses the nonconvex constrained
nonlinear optimization problem as the tracking of a desired negative mode
insertion gradient on the configuration space of a Lie group. This results in a
closed-form feedback control law even with input saturation and thus is well
suited for online application. In extending SAC to Lie groups, the associated
mode insertion gradient is derived and the switching time optimization on Lie
groups is studied. We demonstrate the efficacy and scalability of our approach
in the 2D kinematic car on SE(2) and the 3D quadrotor on SE(3). We also
implement iLQG on a quadrator model and compare to SAC, demonstrating that SAC
is both faster to compute and has a larger basin of attraction.",1709.00376v1
2017-09-04,Consensus of second order multi-agents with actuator saturation and asynchronous time-delays,"This article presents the consensus of a saturated second order multi-agent
system with non-switching dynamics that can be represented by a directed graph.
The system is affected by data processing (input delay) and communication
time-delays that are assumed to be asynchronous. The agents have saturation
nonlinearities, each of them is approximated into separate linear and nonlinear
elements. Nonlinear elements are represented by describing functions.
Describing functions and stability of linear elements are used to estimate the
existence of limit cycles in the system with multiple control laws. Stability
analysis of the linear element is performed using Lyapunov-Krasovskii functions
and frequency domain analysis. A comparison of pros and cons of both the
analyses with respect to time-delay ranges, applicability and computation
complexity is presented. Simulation and corresponding hardware implementation
results are demonstrated to support theoretical results.",1709.00951v3
2017-09-04,A Discrete Packing Model of Granular Material Confined in A Vertical Column,"The transmission rules of interparticle forces between granular particles
were analyzed, and a discrete packing model was proposed to calculate the
static pressure at the bottom of granular material confined in a vertical
column. The mechanical analysis and numerical simulation results indicate that
the silo effect is caused by the frictional contacts between border particles
and inner walls, the static pressure at the bottom depends on the external load
initially, and then tends to a saturation pressure (Pn) in an exponential form.
The saturation pressure (Pn) is positive linear related to the container radius
(R) with the same granular matter and stacking manner. The saturation pressure
(Pn) is directly proportional to the particle size (ra), and the increasing or
decreasing characteristic depends on the frictional property of inner walls,
the friction and stacking angle of grains. At last, the predictions of the
aforementioned model are compared with the experimental results from the
literature, and good agreement is achieved.",1709.01001v2
2017-09-18,Saturation of energetic-particle-driven geodesic acoustic modes due to wave-particle nonlinearity,"The nonlinear dynamics of energetic-particle (EP) driven geodesic acoustic
modes (EGAM) is investigated here. A numerical analysis with the global
gyrokinetic particle-in-cell code ORB5 is performed, and the results are
interpreted with the analytical theory, in close comparison with the theory of
the beam-plasma instability. Only axisymmetric modes are considered, with a
nonlinear dynamics determined by wave-particle interaction. Quadratic scalings
of the saturated electric field with respect to the linear growth rate are
found for the case of interest. The EP bounce frequency is calculated as a
function of the EGAM frequency, and shown not to depend on the value of the
bulk temperature. Near the saturation, we observe a transition from adiabatic
to non-adiabatic dynamics, i.e., the frequency chirping rate becomes comparable
to the resonant EP bounce frequency. The numerical analysis is performed here
with electrostatic simulations with circular flux surfaces, and kinetic effects
of the electrons are neglected.",1709.05998v1
2017-10-01,"Cumulant Expansion in Gluon Saturation, and Five and Six-Gluon Azimuthal Correlations","Correlations between the momenta of the final state hadrons measured in
proton or nucleus collisions contain information that sheds light on the
initial conditions and evolutionary dynamics of the collision system. These
correlation measurements have revealed the long-range rapidity correlations in
p-p and p-Pb systems, and they have also made it possible to extract the
elliptic flow coefficient from hadron correlation measurements. In this work,
we calculate five- and six-gluon correlation functions in the framework of
saturation physics by using superdiagrams. We also derive the cumulant
expansion of the gluon correlators that is valid in the gluon saturation limit.
We show that the cumulant expansion of the gluon correlators that is used for
counting the number of diagrams to be calculated does not follow the standard
cumulant expansion. We also explain how these findings can be used in obtaining
experimentally relevant observables such as flow coefficients calculated from
correlations as well as ratios of the correlation functions of different
orders.",1710.00425v2
2017-11-02,Isospin Dependence of the EMC effect and Short range Correlations,"Recent studies have shown that the per-nucleon number of Short-Range
Correlated (SRC) pairs in nuclei and the strength of the EMC effect are
linearly correlated, increasing from light nuclei up to iron and then
saturating. This paper shows that the per-proton number of SRC pairs and the
strength of the EMC effect are linearly correlated and increase from light to
heavy asymmetric neutron-rich nuclei without saturation. These quantities,
calculated per neutron, are also linearly related, but saturate (have constant
value) remarkably early, starting with 12C. We propose that the observed
phenomenological relationships indicate an isospin dependence of the EMC effect
which is associated with the dominance of SRCs by neutron-proton pairs from 3He
to heavy asymmetric neutron-rich nuclei.",1711.00960v2
2017-11-07,Variations of petrophysical properties and spectral induced polarization in response to drainage and imbibition: a study on a correlated random tube network,"We implement a procedure to simulate the drainage and imbibition in random,
two-dimensional, square networks. We compute the resistivity index, the
relative permeability, and the characteristic lengths of a correlated network
at various saturation states, under the assumption that the surface
conductivity can be neglected. These parameters exhibit a hysteretic behaviour.
Then, we calculate the Spectral Induced Polarization (SIP) response of the
medium, under the assumption that the electrical impedance of each tube follows
a local Warburg conductivity model, with identical DC conductivity and
chargeability for all the tubes. We evidence that the shape of the SIP spectra
depends on the saturation state. The analysis of the evolution of the
macroscopic Cole-Cole parameters of the spectra in function of the saturation
also behaves hysteretically, except for the Cole-Cole exponent. We also observe
a power-law relationship between the macroscopic DC conductivity and time
constant and the relative permeability. We also show that the frequency peak of
the phase spectra is directly related to the characteristic length and to the
relative permeability, underlining the potential interest of SIP measurements
for the estimation of the permeability of unsaturated media.",1711.02740v1
2017-11-17,A simple hysteretic constitutive model for unsaturated flow,"In this paper we present a constitutive model to describe unsaturated flow
that considers the hysteresis phenomena. This constitutive model provides
simple mathematical expressions for both saturation and hydraulic conductivity
curves, and a relationship between permeability and porosity. The model is
based on the assumption that the porous media can be represented by a bundle of
capillary tubes with throats or ""ink-bottles"" and a fractal pore size
distribution. Under these hypotheses, hysteretic curves are obtained for
saturation and relative hydraulic conductivity in terms of pressure head.
However, a non-hysteretic relationship is obtained when relative hydraulic
conductivity is expressed as a function of saturation. The proposed
relationship between permeability and porosity is similar to the well-known
Kozeny-Carman equation but depends on the fractal dimension. The performance of
the constitutive model is tested against different sets of experimental data
and previous models. In all of the cases the proposed expressions fit fairly
well the experimental data and predicts values of permeability and hydraulic
conductivity better than others models.",1711.06726v1
2017-11-24,Role of the pair potential for the saturation of generalized Pauli constraints,"The dependence of the (quasi-)saturation of the generalized Pauli constraints
on the pair potential is studied for ground states of few-fermion systems. For
this, we consider spinless fermions in one dimension which are harmonically
confined and interact by pair potentials of the form $|x_i-x_j|^s$ with $-1
\leq s\leq 5$. We use the Density Matrix Renormalization Group approach and
large orbital basis to achieve the convergence on more than ten digits of both
the variational energy and the natural occupation numbers. Our results confirm
that the conflict between energy minimization and fermionic exchange symmetry
results in a universal and non-trivial quasi-saturation of the generalized
Pauli constraints (\emph{quasipinning}), implying tremendous structural
simplifications of the fermionic ground state for all $s$. Those numerically
exact results are complemented by an analytical study based on a
self-consistent perturbation theory which we develop for this purpose. The
respective results for the weak coupling regime eventually elucidate the
singular behaviour found for the specific values $s=2,4,\ldots$, resulting in
an extremely strong quasipinning.",1711.09099v2
2017-12-27,A refinement of the Robertson-Schrödinger uncertainty principle and a Hirschman-Shannon inequality for Wigner distributions,"We propose a refinement of the Robertson-Schrodinger uncertainty principle
(RSUP) using Wigner distributions. This new principle is stronger than the
RSUP. In particular, and unlike the RSUP, which can be saturated by many phase
space functions, the refined RSUP can be saturated by pure Gaussian Wigner
functions only. Moreover, the new principle is technically as simple as the
standard RSUP. In addition, it makes a direct connection with modern harmonic
analysis, since it involves the Wigner transform and its symplectic Fourier
transform, which is the radar ambiguity function. As a by-product of the
refined RSUP, we derive inequalities involving the entropy and the covariance
matrix of Wigner distributions. These inequalities refine the Shanon and the
Hirschman inequalities for the Wigner distribution of a mixed quantum state
$\rho$. We prove sharp estimates which critically depend on the purity of
$\rho$ and which are saturated in the Gaussian case.",1712.09475v1
2018-01-16,Relating unsaturated electrical and hydraulic conductivity of cement-based materials,"Unsaturated hydraulic ($K$) and electrical ($\sigma_b$) conductivity are
often considered durability indicators of cement-based materials. However, $K$
is difficult to measure experimentally. This is due to the large pressure
requirements at low degrees of saturation resulting from the fine pore-size
distribution of cement-based materials. As a result, the commonly-used
analytical models, requiring calibration of $K$ from experimental data, are
often inaccurate at low degrees of saturation. On the other hand, measuring
$\sigma_b$ is rather straight forward. Descriptions of the relationship between
$\sigma_b$ and $K$ may therefore be particularly valuable when $K$ is required.
In this work, we use experimental data from previous works to determine the
feasibility of models employing a van Genuchten-Mualem based framework to
predict $K$ and $\sigma_b$ -- expressions for diffusivity $D$ are also
provided. We then develop analytical expressions relating $K$ and $\sigma_b$
using these models. It is then shown that $K = K(\sigma_b)$ and $\sigma_b =
\sigma_b(K)$ may be determined when either parameter is fully described.
Lastly, we propose a simplified model and discuss the roles of pore-size
distribution, saturation, pore connectivity and tortuosity in characterizing
the relationship between $K$ and $\sigma_b$.",1801.05248v2
2018-01-17,All-fiber all-normal-dispersion femtosecond laser with nonlinear multimodal interference based saturable absorber,"In this letter, we demonstrate the first all-fiber all-normal dispersion
ytterbium-doped oscillator with nonlinear multimodal interference based
saturable absorber capable to generate ultrashort dissipative soliton pulses.
Additional to functioning as a saturable absorber, the use of multimode fiber
segments between single mode fibers also ensures the bandpass filtering via
multimode interference reimaging necessary to obtain dissipative soliton
mode-locking. The oscillator generates dissipative soliton pulses at 1030 nm
with 5.8 mW average power, 5 ps duration and 44.25 MHz repetition rate. Pulses
are dechirped to 276 fs via an external grating compressor. All-fiber cavity
design ensures high stability and $\sim$70 dB sideband suppression is measured
in RF spectrum. Numerical simulations are performed to investigate cavity
dynamics and obtained results well-matched with experimental observations. The
proposed cavity presents an alternative approach to achieve all-fiber
dissipative soliton mode-locking with a simple and low-cost design.",1801.05824v1
2018-01-23,A Wideband Self-Consistent Disk-Averaged Spectrum of Jupiter Near 30 GHz and Its Implications for NH$_{3}$ Saturation in the Upper Troposphere,"We present a new set of measurements obtained with the Combined Array for
Research in Millimeter-wave Astronomy (CARMA) of Jupiter's microwave thermal
emission near the 1.3 cm ammonia (NH$_{3}$) absorption band. We use these
observations to investigate the ammonia mole fraction in the upper troposphere,
near $0.3 < P < 2$ bar, based on radiative transfer modeling. We find that the
ammonia mole fraction must be $\sim2.4\times 10^{-4}$ below the NH$_{3}$ ice
cloud, i.e., at $0.8 < P < 8$ bar, in agreement with results by de Pater et al.
(2001, 2016a). We find the NH$_{3}$ cloud-forming region between $0.3 < P <
0.8$ bar to be globally sub-saturated by 55% on average, in accordance with the
result in Gibson et al. (2005). Although our data are not very sensitive to the
region above the cloud layer, we are able to set an upper limit of $2.4\times
10^{-7}$ on the mole fraction here, a factor of $\sim$10 above the saturated
vapor curve.",1801.07812v1
2018-02-02,Black phosphorus Q-switched and mode-locked Er:ZBLAN fiber lasers at 3.5 um,"With the proposal of dual-wavelength pumping (DWP) scheme, DWP Er:ZBLAN fiber
lasers at 3.5 um have become a fascinating area of research. However, limited
by the absence of suitable saturable absorber, passively Q-switched and
mode-locked fiber lasers have not been realized in this spectral region. Based
on the layer-dependent bandgap and excellent photoelectric characteristics of
black phosphorus (BP), BP is a promising candidate for saturable absorber near
3.5 um. Here, we fabricated a 3.5-um saturable absorber mirror (SAM) by
transferring liquid-phase exfoliated BP flakes onto a gold-coated mirror. With
the as-prepared BP SAM, we realized stable Q-switching and continuous-wave
mode-locking operations in the DWP Er:ZBLAN fiber lasers at 3.5 um. To the best
of our knowledge, it is the first time to achieve passively Q-switched and
mode-locked pulses in 3.5 um spectral region. The research results will not
only promote the development of 3.5-um pulsed fiber lasers but also open the
photonic application of two-dimensional materials in this spectral region",1802.00710v1
2018-02-07,Energy is Entanglement,"We compute the local second variation of the von Neumann entropy of a region
in theories with a gravity dual. For null variations our formula says that the
diagonal part of the Quantum Null Energy Condition is saturated in every state,
thus providing an equivalence between energy and entropy. We prove that the
formula holds at leading order in 1/N, and further argue that it will not be
affected at higher orders. We conjecture that the QNEC is saturated in all
interacting theories. We also discuss the special case of free theories, and
the implications of our formula for the Averaged Null Energy Condition, Quantum
Focusing Conjecture, and gravitational equations of motion. We show that the
leading-order gravitational equations of motion, Einstein's equations, are
equivalent to leading-order saturation of the QFC for Planck-width
deformations.",1802.02584v1
2018-02-22,When gluons go odd: how classical gluon fields generate odd azimuthal harmonics for the two-gluon correlation function in high-energy collisions,"We show that, in the saturation/Color Glass Condensate framework, odd
azimuthal harmonics of the two-gluon correlation function with a long-range
separation in rapidity are generated by the higher-order saturation corrections
in the interactions with the projectile and the target. At the very least, the
odd harmonics require three scatterings in the projectile and three scatterings
in the target. We derive the leading-order expression for the two-gluon
production cross section which generates odd harmonics: the expression includes
all-order interactions with the target and three interactions with the
projectile. We evaluate the obtained expression both analytically and
numerically, confirming that the odd-harmonics contribution to the two-gluon
production in the saturation framework is non-zero.",1802.08166v1
2018-03-12,Supersymmetrising the GSY Soliton,"We supersymmetrise the Hopfion studied in a previous work. This soliton
represents a closed semilocal vortex string in $U(1)$ gauge theory. It carries
nonzero Hopf number due to the additional winding of a phase modulus as one
moves along the closed string. We study this solution in $\mathcal{N}= 2$
supersymmetric QED with two flavours. As a preliminary exercise we compactify
one space dimension and consider a straight vortex with periodic boundary
conditions. It turns out to be 1/2-BPS saturated. An additional winding along
the string can be introduced and it does not spoil the BPS nature of the
object. Next, we consider a ring-like vortex in a non-compact space and show
that the circumference of the ring $L$ can be stabilised once the previously
mentioned winding along the string is introduced. Of course the ring-like
vortex is not BPS but its energy becomes close to the BPS bound if $L$ is
large, which can be guaranteed in the case that we have a large value of the
angular momentum $J$. Thus we arrive at the concept of asymptotically
BPS-saturated solitons. BPS saturation is achieved in the limit $J\rightarrow
\infty$.",1803.04549v2
2018-03-24,Saturated Fully Leafed Tree-Like Polyforms and Polycubes,"We present recursive formulas giving the maximal number of leaves in
tree-like polyforms living in two-dimensional regular lattices and in tree-like
polycubes in the three-dimensional cubic lattice.
  We call these tree-like polyforms and polycubes \emph{fully leafed}.
  The proof relies on a combinatorial algorithm that enumerates rooted directed
trees that we call abundant.
  In the last part, we concentrate on the particular case of polyforms and
polycubes, that we call \emph{saturated}, which is the family of fully leafed
structures that maximize the ratio
  $\mbox{(number of leaves)}/\mbox{ (number of cells)}$.
  In the polyomino case, we present a bijection between the set of saturated
tree-like polyominoes of size $4k+1$ and the set of tree-like polyominoes of
size $k$.
  We exhibit a similar bijection between the set of saturated tree-like
polycubes of size $41k+28$ and a family of polycubes, called $4$-trees, of size
$3k+2$.",1803.09181v1
2018-04-01,Nonlinear Spectroscopic Study of Porphyrin Under cw and Femto-second Laser Pulse Excitation,"Single Beam Transmittance (SBT) was used as nonlinear spectroscopic tool to
investigate the absorption cross-sections and lifetimes of Tetra Phenyl
porphyrin (H2TPP) and its OH- group derivative (H2TPP(OH)4) doped in boric acid
glass (BAG). We have used 671 nm wavelength as exciting wavelength for both CW
(incident intensity up to 1010 W/cm2) and femto-second laser pulse (up to
fluence of 102 mJ/cm2). Under cw laser excitation, H2TPP doped BAG demonstrates
Double Saturable Absorber (DSA) behavior whereas H2TPP(OH)4 doped BAG act as
Revere Saturable Absorber (RSA). Rate equation model espouses to extract the
spectroscopic parameters from the experimental data. Excited state life times
and absorption cross-sections were obtained as parameters for theoretical fit
on SBT data. Porphyrin molecules act as four level systems under cw laser
excitation, whereas in the presence of femto-second laser excitation they act
as a two level system. We have derived the equations for transmitted energy
through the material in the presence of femto-second laser illumination. Both
systems viz., H2TPP and H2TPP(OH)4 doped BAG behaves as saturable absorbers
when excited by femto-second laser pulses.",1804.00288v1
2018-04-15,In depth analysis of the combined HERA data in the dipole models with and without saturation,"We present an updated impact parameter dependent saturation model (IPsat)
determined trough a fit to the combined HERA I and I+II reduced cross section
data. The same HERA data are used to fit the linearized (IPnonsat) version of
the applied dipole amplitude, which makes it possible to estimate the magnitude
of the saturation effects in various experiments. We find that both
parametrizations provide comparable descriptions of the considered data when an
effective confinement scale dynamics is incorporated with quark masses.
Moreover, it is possible to consistently determine the light and charm quark
masses. The role of potentially non-perturbatively large dipoles is examined in
detail, with the result that, especially in case of the structure function
$F_2$, their contribution is numerically significant. Potential to discriminate
between the two models in future $e+p$ and $e+A$ experiments is also
illustrated.",1804.05311v2
2018-04-17,Multivariate Gaussian Process Regression for Multiscale Data Assimilation and Uncertainty Reduction,"We present a multivariate Gaussian process regression approach for parameter
field reconstruction based on the field's measurements collected at two
different scales, the coarse and fine scales. The proposed approach treats the
parameter field defined at fine and coarse scales as a bivariate Gaussian
process with a parameterized multiscale covariance model. We employ a full
bivariate Mat\'{e}rn kernel as multiscale covariance model, with shape and
smoothness hyperparameters that account for the coarsening relation between
fine and coarse fields. In contrast to similar multiscale kriging approaches
that assume a known coarsening relation between scales, the hyperparameters of
the multiscale covariance model are estimated directly from data via
pseudo-likelihood maximization.
  We illustrate the proposed approach with a predictive simulation application
for saturated flow in porous media. Multiscale Gaussian process regression is
employed to estimate two-dimensional log-saturated hydraulic conductivity
distributions from synthetic multiscale measurements. The resulting stochastic
model for coarse saturated conductivity is employed to quantify and reduce
uncertainty in pressure predictions.",1804.06490v1
2018-04-19,Estimation of Tissue Oxygen Saturation from RGB Images based on Pixel-level Image Translation,"Intra-operative measurement of tissue oxygen saturation (StO2) has been
widely explored by pulse oximetry or hyperspectral imaging (HSI) to assess the
function and viability of tissue. In this paper we propose a pixel- level
image-to-image translation approach based on conditional Generative Adversarial
Networks (cGAN) to estimate tissue oxygen saturation (StO2) directly from RGB
images. The real-time performance and non-reliance on additional hardware,
enable a seamless integration of the proposed method into surgical and
diagnostic workflows with standard endoscope systems. For validation, RGB
images and StO2 ground truth were simulated and estimated from HSI images
collected by a liquid crystal tuneable filter (LCTF) endoscope for three tissue
types (porcine bowel, lamb uterus and rabbit uterus). The result show that the
proposed method can achieve visually identical images with comparable accuracy.",1804.07116v1
2018-04-24,The Sprague-Grundy Functions of Saturations of Misere Nim,"We consider mis\`{e}re Nim as a normal-play game obtained from Nim by
removing the terminal position. While explicit formulas are known for the
Sprague-Grundy functions of Nim and Welter's game, no explicit formula is known
for that of mis\`{e}re Nim. All three of these games can be considered as
position restrictions of Nim. What are the differences between them? We point
out that Nim and Welter's game are saturated, but mis\`{e}re Nim is not.
Moreover, we present explicit formulas for the Sprague-Grundy functions of
saturations of mis\`{e}re Nim, which are obtained from mis\`{e}re Nim by
adjoining some moves.",1804.08809v4
2018-05-03,Solvation effects and contact angle saturation in electrowetting,"Electrowetting of nanodrops is studied for aqueous electrolyte mixtures. We
report a new method for controlling the degree of deformation and minimum
attainable contact angle by varying the difference of solvation strengths
between the two solvents, which determines the ratio of ion concentrations.
This implies that the commonly observed saturation of the contact angle with
the applied electric field can be suppressed by increasing the solvation energy
difference, a finding of practical significance for micro and nanofluidics.
Saturation is traced to be caused by the transfer of ions from the drop to the
surrounding medium. Furthermore, we derive an expression, based on the
electrokinetic equations, for the dependency of the drop's contact angle on the
ion concentration and the strength of the solvation potential in the absence of
external electric fields.",1805.01351v2
2018-05-27,Efficiently Modeling the Noise Performance of Short-Pulse Lasers with a Computational Implementation of Dynamical Methods,"Lowering the noise level of short pulse lasers has been a long-standing
effort for decades. Modeling the noise performance plays a crucial role in
isolating the noise sources and reducing them. Modeling to date has either used
analytical or semi-analytical implementation of dynamical methods or Monte
Carlo simulations. The former approach is too simplified to accurately assess
the noise performance in real laser systems, while the latter approach is too
computationally slow to optimize the performance as parameters vary over a wide
range. Here, we describe a computational implementation of dynamical methods
that allows us to determine the noise performance of a passively modelocked
laser within minutes on a desktop computer and is faster than Monte Carlo
methods by a factor on the order of 1000. We apply this method to characterize
a laser that is locked using a fast saturable absorber---for example, a
fiber-based nonlinear polarization rotation---and a laser that is locked using
a slow saturable absorber---for example, a semiconductor saturable absorbing
mirror.",1806.04601v1
2018-06-27,"Towards the Quantum Geometry of Saturated Quantum Uncertainty Relations: The Case of the (Q,P) Heisenberg Observables","This contribution to the present Workshop Proceedings outlines a general
programme for identifying geometric structures--out of which to possibly
recover quantum dynamics as well--associated to the manifold in Hilbert space
of the quantum states that saturate the Schr\""odinger-Robertson uncertainty
relation associated to a specific set of quantum observables which characterise
a given quantum system and its dynamics. The first step in such an exploration
is addressed herein in the case of the observables Q and P of the Heisenberg
algebra for a single degree of freedom system. The corresponding saturating
states are the well known general squeezed states, whose properties are
reviewed and discussed in detail together with some original results, in
preparation of a study deferred to a separated analysis of their quantum
geometry and of the corresponding path integral representation over such
states.",1806.10491v1
2018-07-03,Mode-locked fiber laser with offset splicing between two multimode fibers as a saturable absorber,"A novel mode-locked fiber laser based on offset splicing technology between
two kinds of graded index multimode fibers is proposed and experimentally
demonstrated. The offset splice spot structure acts as a saturable absorber via
nonlinear multimodal interference mechanism. The absorption modulation depth of
the device is 2.8%, with a saturation intensity of 2.5 MW/cm2. The fiber laser
operates at a stable mode-locked state when the pump power reaches 114 mW. The
laser oscillates at 1039 nm with a pulsewidth of 17.6 ps, a repetition rate of
32.619 MHz, and a high signal noise ratio of 65 dB. The fiber laser is superior
in terms of low cost, high damage threshold, and easy fabrication, thus
providing many potential applications in ultrafast photonics and industrial
processing.",1807.01037v1
2018-07-04,Steep cliffs and saturated exponents in three dimensional scalar turbulence,"The intermittency of a passive scalar advected by three-dimensional
Navier-Stokes turbulence at a Taylor-scale Reynolds number of $650$ is studied
using direct numerical simulations on a $4096^3$ grid; the Schmidt number is
unity. By measuring scalar increment moments of high orders, while ensuring
statistical convergence, we provide unambiguous evidence that the scaling
exponents saturate to $1.2$ for moment order beyond about $12$, indicating that
scalar intermittency is dominated by the most singular shock-like cliffs in the
scalar field. We show that the fractal dimension of the spatial support of
steep cliffs is about $1.8$, whose sum with the saturation exponent value of
$1.2$ adds up to the space dimension of $3$, thus demonstrating a deep
connection between the geometry and statistics in turbulent scalar mixing. The
anomaly for the fourth and sixth order moments is comparable to that in the
Kraichnan model for the roughness exponent of $2/3$.",1807.01651v1
2018-07-08,Attractivity of Saturated Equilibria for Lotka-Volterra Systems with Infinite Delays and Feedback Controls,"In this paper, we apply a Lyapunov functional approach to Lotka-Volterra
systems with infinite delays and feedback controls and establish that the
feedback controls have no influence on the attractivity properties of a
saturated equilibrium. This improves previous results by the authors and
others, where, while feedback controls were used mostly to change the position
of a unique saturated equilibrium, additional conditions involving the controls
had to be assumed in order to preserve its global attractivity. The situation
of partial extinction is further analysed, for which the original system is
reduced to a lower dimensional one which maintains its global dynamics
features.",1807.02825v1
2018-07-16,Qualitative Analysis and Optimal Control Strategy of an SIR Model with Saturated Incidence and Treatment,"This paper deals with an SIR model with saturated incidence rate affected by
inhibitory effect and saturated treatment function. Two control functions have
been used, one for vaccinating the susceptible population and other for the
treatment control of infected population. We have analysed the existence and
stability of equilibrium points and investigated the transcritical and backward
bifurcation. The stability analysis of non-hyperbolic equilibrium point has
been performed by using Centre manifold theory. The Pontryagin's maximum
principle has been used to characterize the optimal control whose numerical
results show the positive impact of two controls mentioned above for
controlling the disease. Efficiency analysis is also done to determine the best
control strategy among vaccination and treatment.",1807.05954v1
2018-07-17,Signature of gluon saturation in forward di-hadron correlations at the Large Hadron Collider,"We argue that gluon saturation effects may be visible in Large Hadron
Collider (LHC) data. We look at the centrality dependence of the away-side peak
of two-particle correlations measured in p-Pb collisions, using both ALICE data
at midrapidity, and LHCb data at forward rapidity. Once the collective
flow-like signal measured at the near-side peak is removed from the correlation
function, the centrality dependence of the away-side peak turns out to be much
stronger in the forward region than at midrapidity. We argue that this is a
very specific prediction of the saturation framework, and we compare LHCb data
to a state-of-the-art calculation within the Color Glass Condensate theory.",1807.06388v1
2018-09-11,Analytical model for the intensity dependence of 1500 nm to 980 nm upconversion in Er$^{3+}$: a new tool for material characterization,"We propose a simplified rate-equation model for the 1500 nm to 980 nm
upconversion in Er$^{3+}$. The simplifications, based on typical experimental
conditions as well as on conclusions based on previously published more
advanced models, enable an analytical solution of the rate equations, which
reproduces known properties of upconversion. We have compared the model
predictions with intensity-dependent measurements on four samples with
different optical properties, such as upconversion-luminescence yield and the
characteristic lifetime of the $^4I_{13/2}$ state. The saturation of the
upconversion is in all cases well-described by the model over several orders of
magnitude in excitation intensities. Finally, the model provides a new measure
for the quality of upconverter systems based on Er$^{3+}$ -- the saturation
intensity. This parameter provides valuable information on upconversion
parameters such as the rates of energy-transfer upconversion and
cross-relaxation. In the present investigation, we used the saturation
intensity to conclude that the differences in upconversion performance of the
investigated samples are mainly due to differences in the non-radiative
relaxation rates.",1809.03908v1
2018-09-13,Complexity Growth Following Multiple Shocks,"In this paper by making use of the ""Complexity=Action"" proposal, we study the
complexity growth after shock waves in holographic field theories. We consider
both double black hole-Vaidya and AdS-Vaidya with multiple shocks geometries.
We find that the Lloyd's bound is respected during the thermalization process
in each of these geometries and at the late time, the complexity growth
saturates to the value which is proportional to the energy of the final state.
We conclude that the saturation value of complexity growth rate is independent
of the initial temperature and in the case of thermal initial state, the rate
of complexity is always less than the value for the vacuum initial state such
that considering multiple shocks it gets more smaller. Our results indicate
that by increasing the temperature of the initial state, the corresponding rate
of complexity growth starts far from final saturation rate value.",1809.05044v3
2018-09-13,Yb-doped all fiber picosecond laser based on grade-index multimode fiber with microcavity,"We demonstrate an all-fiber mode-locked laser at all-normal dispersion with a
saturable absorber, which is based on a section of grade-index multimode fiber
with inner microcavity embedded in the splice points. The absorption modulation
depth of this nonlinear saturable absorber is 2.2% in the suitable bent state.
The fiber laser operates at central wavelength of 1035nm with average power of
~1.26mW, pulse-duration of 17.05 ps, repetition rate of 37.098MHz. This kind of
saturable absorber has superiorities of low cost, high stability and high
damage threshold, which may facilitate applications in optical sensing,
material processing and light detection.",1809.07174v2
2018-09-22,Understanding the saturation power of Josephson Parametric Amplifiers made from SQUIDs arrays,"We report on the implementation and detailed modelling of a Josephson
Parametric Amplifier (JPA) made from an array of eighty Superconducting QUantum
Interference Devices (SQUIDs), forming a non-linear quarter-wave resonator.
This device was fabricated using a very simple single step fabrication process.
It shows a large bandwidth (45 MHz), an operating frequency tunable between 5.9
GHz and 6.8 GHz and a large input saturation power (-117 dBm) when biased to
obtain 20 dB of gain. Despite the length of the SQUID array being comparable to
the wavelength, we present a model based on an effective non-linear LC series
resonator that quantitatively describes these figures of merit without fitting
parameters. Our work illustrates the advantage of using array-based JPA since a
single-SQUID device showing the same bandwidth and resonant frequency would
display a saturation power 15 dB lower.",1809.08476v2
2018-09-12,Fast Signal Recovery from Saturated Measurements by Linear Loss and Nonconvex Penalties,"Sign information is the key to overcoming the inevitable saturation error in
compressive sensing systems, which causes information loss and results in bias.
For sparse signal recovery from saturation, we propose to use a linear loss to
improve the effectiveness from existing methods that utilize hard
constraints/hinge loss for sign consistency. Due to the use of linear loss, an
analytical solution in the update progress is obtained, and some nonconvex
penalties are applicable, e.g., the minimax concave penalty, the $\ell_0$ norm,
and the sorted $\ell_1$ norm. Theoretical analysis reveals that the estimation
error can still be bounded. Generally, with linear loss and nonconvex
penalties, the recovery performance is significantly improved, and the
computational time is largely saved, which is verified by the numerical
experiments.",1809.09219v1
2018-10-13,$C_{2k}$-saturated graphs with no short odd cycles,"The saturation number of a graph $F$, written $\textup{sat}(n,F)$, is the
minimum number of edges in an $n$-vertex $F$-saturated graph. One of the
earliest results on saturation numbers is due to Erd\H{o}s, Hajnal, and Moon
who determined $\textup{sat}(n,K_r)$ for all $r \geq 3$. Since then, saturation
numbers of various graphs and hypergraphs have been studied. Motivated by Alon
and Shikhelman's generalized Tur\'an function, Kritschgau et.\ al.\ defined
$\textup{sat}(n,H,F)$ to be the minimum number of copies of $H$ in an
$n$-vertex $F$-saturated graph. They proved, among other things, that
$\textup{sat}(n,C_3,C_{2k}) = 0$ for all $k \geq 3$ and $n \geq 2k +2$. We
extend this result to all odd cycles by proving that for any odd integer $r
\geq 5$, $\textup{sat}(n, C_r,C_{2k}) = 0$ for all $2k \geq r+5$ and $n \geq
2kr$.",1810.05772v1
2018-10-17,Cross-diffusion and traveling waves in porous-media flux-saturated Keller-Segel models,"This paper deals with the analysis of qualitative properties involved in the
dynamics of Keller-Segel type systems in which the diffusion mechanisms of the
cells are driven by porous-media flux-saturated phenomena. We study the
regularization inside the support of a solution with jump discontinuity at the
boundary of the support. We analyze the behavior of the size of the support and
blow--up of the solution, and the possible convergence in finite time towards a
Dirac mass in terms of the three constants of the system: the mass, the
flux--saturated characteristic speed, and the chemoattractant sensitivity
constant. These constants of motion also characterize the dynamics of regular
and singular traveling waves.",1810.07606v1
2018-10-17,Non-local competition slows down front acceleration during dispersal evolution,"We investigate the super-linear spreading in a reaction-diffusion model
analogous to the Fisher-KPP equation, but in which the population is
heterogeneous with respect to the dispersal ability of individuals, and the
saturation factor is non-local with respect to one variable. We prove that the
rate of acceleration is slower than the rate of acceleration predicted by the
linear problem, that is, without saturation. This hindering phenomenon is the
consequence of a subtle interplay between the non-local saturation and the
non-trivial dynamics of some particular curves that carry the mass at the
front. A careful analysis of these trajectories allows us to identify the value
of the rate of acceleration. The article is complemented with numerical
simulations that illustrate some behavior of the model that is beyond our
analysis.",1810.07634v2
2018-10-18,Recovery of Saturated $γ$ Signal Waveforms by Artificial Neural Networks,"Particle may sometimes have energy outside the range of radiation detection
hardware so that the signal is saturated and useful information is lost. We
have therefore investigated the possibility of using an Artificial Neural
Network (ANN) to restore the saturated waveforms of $\gamma$ signals. Several
ANNs were tested, namely the Back Propagation (BP), Simple Recurrent (Elman),
Radical Basis Function (RBF) and Generalized Radial Basis Function (GRBF)
neural networks (NNs) and compared with the fitting method based on the Marrone
model. The GBRFNN was found to perform best.",1810.08200v1
2018-10-30,Two-Photon Absorption and Saturable Absorption of Mid-IR in Graphene,"We report on the response of graphene to high intensity mid-IR radiation and
show that graphene exhibits saturable absorption and significant two-photon
absorption in the spectral region from 1.55 $\mu$m to 3.50 $\mu$m (0.35 eV to
0.80 eV). We find that the effective modulation depth of multilayer graphene is
limited by two-photon absorption which will affect its performance as a laser
mode-locking element. The measured saturation intensities of femtosecond pulses
were found to depend on the third power of photon energy when we combined our
results with others reported in literature, while those of longer pulses were
found to have a square root dependence.",1810.12981v1
2018-12-02,Nearly-Regular Hypergraphs and Saturation of Berge Stars,"Given a graph $G$, we say a $k$-uniform hypergraph $H$ on the same vertex set
contains a Berge-$G$ if there exists an injection $\phi:E(G)\to E(H)$ such that
$e\subseteq\phi(e)$ for each edge $e\in E(G)$. A hypergraph $H$ is
Berge-$G$-saturated if $H$ does not contain a Berge-$G$, but adding any edge to
$H$ creates a Berge-$G$. The saturation number for Berge-$G$, denoted
$\mathrm{sat}_k(n,\text{Berge-}G)$ is the least number of edges in a
$k$-uniform hypergraph that is Berge-$G$-saturated. We determine exactly the
value of the saturation numbers for Berge stars. As a tool for our main result,
we also prove the existence of nearly-regular $k$-uniform hypergraphs, or
$k$-uniform hypergraphs in which every vertex has degree $r$ or $r-1$ for some
$r\in \mathbb{Z}$, and less than $k$ vertices have degree $r-1$.",1812.00472v1
2018-12-11,Capillary transport in low saturated sands: superfast non-linear diffusion model versus direct experimental observations,"We have established in a pilot study, that the spreading of liquids in sandy
porous materials at low levels of saturation, typically less than ten percent
of the available void space, has very distinctive features in comparison to
that at higher saturation levels. In particular, it has been shown, on
theoretical grounds, that the spreading is controlled by a special type of
diffusional process, that its physics can be captured by an equation of the
super-fast diffusion class, and that these findings were supported by
first-of-a-kind experiments. In this paper, we take these findings to the next
level including deeper examination and exposition of the theory, an expanded
set of experiments to address scaling properties, and systematic evaluations of
the predictive performance against these experimental data, keeping in mind
also potential practical applications.",1812.04710v1
2018-12-17,Quantification of nonlinear absorption in ternary As-Sb-Se chalcogenide glasses,"In this article, we studied intensity dependent third order nonlinear optical
response in ternary As40Sb7Se53 and As40Sb10Se50 chalcogenide glasses by
employing nanosecond Z-scan technique. At low intensity, we observed saturable
absorption in As40Sb7Se53 which makes a remarkable transition to reverse
saturable absorption at higher intensities. On the other hand, when the Sb
concentration increased in As40Sb10Se50, saturable absorption disappears and
the sample exhibits only two-photon absorption. Experimental results further
indicate that the strong two-photon absorption in our samples can be exploited
to fabricate high performance solid state optical limiting devices for next
generation all-optical network.",1812.06674v1
2019-01-01,Infrared Laser Locking to Rubidium Saturated Absorption Spectrum via a Photonic Chip Frequency Doubler,"Photonic integrated resonators stand out as reliable frequency converters due
to their compactness and stability, with second-harmonic generation (SHG)
efficiencies of up to 17000%/W reported recently in aluminum nitride
microrings. In this work, a sufficiently strong second-harmonic (SH) signal up
to microwatts was generated by a photonic integrated frequency doubler using a
milliwatt infrared (IR) laser source. Furthermore, increased SHG bandwidth
covering $^{85}$Rb and $^{87}$Rb D$_2$ transition lines as well as saturated
absorption spectroscopy (SAS) were demonstrated by tuning the pump power and
chip temperature. Here, we present, to the best of our knowledge, the first
successful locking of an IR laser to Rb saturated absorption lines via a
photonic chip frequency doubler.",1901.00922v1
2019-01-27,Distributed Nash Equilibrium Seeking for Games in Systems with Bounded Control Inputs,"Noticing that physical limitations are ubiquitous in practical engineering
systems, this paper considers Nash equilibrium seeking for games in systems
where the control inputs are bounded. More specifically, first-order
integrator-type systems with bounded control inputs are firstly considered and
two saturated control strategies are designed to seek for the Nash equilibrium
of the game. Then, we further consider the Nash equilibrium seeking problem for
games in second-order integrator-type systems. As this problem has rarely been
investigated, we firstly propose a centralized seeking strategy without
considering the boundedness of the control inputs, followed by a distributed
counterpart. By further adapting a saturation function into the Nash
equilibrium seeking strategy, a new seeking strategy is then designed for the
considered second-order systems with bounded controls. In the proposed
distributed strategies, consensus protocols are included for information
sharing and the saturation functions are utilized to construct bounded control
inputs. The convergence results are established through conducting Lyapunov
stability analysis. Lastly, by considering the connectivity control of mobile
sensor networks, the proposed methods are numerically verified.",1901.09333v2
2019-01-29,Preferential Root Tropism Induced by Structural Inhomogeneities in 2D Wet Granular Media,"We investigate certain aspects of the physical mechanisms of root growth in a
granular medium and how these roots adapt to changes in water distribution
induced by the presence of structural inhomogeneities in the form of solid
intrusions. Physical intrusions such as a square rod added into the 2D granular
medium modify water distribution by maintaining robust capillary action,
pumping water from the more saturated areas at the bottom of the cell towards
the less saturated areas near the top of the cell while the rest of the medium
is slowly devoid of water via evaporation. This water redistribution induces
`preferential tropism' of roots, guiding the roots and permitting them to grow
deeper into more saturated regions in the soil. This further allows more
efficient access to available water in the deeper sections of the medium
thereby resulting to increased plant lifetime",1901.10402v1
2019-02-21,Thermal radiation and inclusive production in the CGC/saturation approach at high energies,"In this paper, we discuss the inclusive production of hadrons in the
framework of CGC/saturation approach. We argue, that the gluon jet inclusive
production stems from the vicinity of the saturation momentum, even for small
values of the transverse momenta $p_T$. Since in this region, theoretically, we
know the scattering amplitude, we claim that we can provide reliable estimates
for this process. We demonstrate, that in a widely accepted model for
confinement, to describe the experimental data, we require a thermal radiation
term. In this model the parton (quark or gluon) with the transverse momenta of
the order of $Q_s$ decays into hadrons with the given fragmentation functions.
However, we show that other approaches for the confinement could describe the
data, without a need for the thermal emission",1902.07923v2
2019-02-24,Optimality Conditions for Nonconvex Variational Problems with Integral Constraints in Banach Spaces,"This paper exemplifies that saturation is an indispensable structure on
measure spaces to obtain the existence and characterization of solutions to
nonconvex variational problems with integral constraints in Banach spaces and
their dual spaces. We provide a characterization of optimality via the maximum
principle for the Hamiltonian and an existence result without the purification
of relaxed controls, in which the Lyapunov convexity theorem in infinite
dimensions under the saturation hypothesis on the underlying measure space
plays a crucial role. We also demonstrate that the existence of solutions for
certain class of primitives is necessary and sufficient for the measure space
to be saturated.",1902.09533v3
2019-03-14,Symmetry energy at supra-saturation densities via the Gravitational Waves from GW170817,"Motivated by the historical detection of gravitational waves from GW170817,
the neutron star and the neutron drop, i.e., a certain number of neutrons
confined in an external field, are systematically investigated by ab initio
calculations as well as the nonrelativistic and relativistic state-of-art
density functional theories. Strong correlations are found among the neutron
star tidal deformability, the neutron star radius, the root-mean-square radii
of neutron drops, and the symmetry energies of nuclear matter at
supra-saturation densities. From these correlations and the upper limit on the
tidal deformability extracted from GW170817, the neutron star radii, the
neutron drop radii, and the symmetry energy at twice saturation density are
respectively constrained as $R_{1.4M_{\odot}}\leqslant 12.94$ km, $R_{\rm nd}
\leqslant 2.36$ fm, and $E_{\mathrm{sym}}(2\rho_0) \leqslant 53.2$ MeV.",1903.05938v1
2019-04-08,Desaturating EUV observations of solar flaring storms,"Image saturation has been an issue for several instruments in solar
astronomy, mainly at EUV wavelengths. However, with the launch of the
Atmospheric Imaging Assembly (AIA) as part of the payload of the Solar Dynamic
Observatory (SDO) image saturation has become a big data issue, involving
around 10^$ frames of the impressive dataset this beautiful telescope has been
providing every year since February 2010. This paper introduces a novel
desaturation method, which is able to recover the signal in the saturated
region of any AIA image by exploiting no other information but the one
contained in the image itself. This peculiar methodological property, jointly
with the unprecedented statistical reliability of the desaturated images, could
make this algorithm the perfect tool for the realization of a reconstruction
pipeline for AIA data, able to work properly even in the case of long-lasting,
very energetic flaring events.",1904.04211v1
2019-04-17,Low temperature saturation of phase coherence length in topological insulators,"Implementing topological insulators as elementary units in quantum
technologies requires a comprehensive understanding of the dephasing mechanisms
governing the surface carriers in these materials, which impose a practical
limit to the applicability of these materials in such technologies requiring
phase coherent transport. To investigate this, we have performed
magneto-resistance (MR) and conductance fluctuations\ (CF) measurements in both
exfoliated and molecular beam epitaxy grown samples. The phase breaking length
($l_{\phi}$) obtained from MR shows a saturation below sample dependent
characteristic temperatures, consistent with that obtained from CF
measurements. We have systematically eliminated several factors that may lead
to such behavior of $l_{\phi}$ in the context of TIs, such as finite size
effect, thermalization, spin-orbit coupling length, spin-flip scattering, and
surface-bulk coupling. Our work indicates the need to identify an alternative
source of dephasing that dominates at low $T$ in topological insulators,
causing saturation in the phase breaking length and time.",1904.08517v1
2019-04-23,Maser Flare Simulations from Oblate and Prolate Clouds,"We investigated, through numerical models, the flaring variability that may
arise from the rotation of maser clouds of approximately spheroidal geometry,
ranging from strongly oblate to strongly prolate examples. Inversion solutions
were obtained for each of these examples over a range of saturation levels from
unsaturated to highly saturated. Formal solutions were computed for rotating
clouds with many randomly chosen rotation axes, and corresponding averaged
maser light curves plotted with statistical information. The dependence of
results on the level of saturation and on the degree of deformation from the
spherical case were investigated in terms of a variability index and duty
cycle. It may be possible to distinguish observationally between flares from
oblate and prolate objects. Maser flares from rotation are limited to long
timescales (at least a few years) and modest values of the variability index
($\lesssim 100$), and can be aperiodic or quasi-periodic. Rotation is therefore
not a good model for H$_2$O variability on timescales of weeks to months, or of
truly periodic flares.",1904.10347v1
2019-05-01,Anomalous diffusion in an electrolyte saturated paper matrix,"Diffusion of colored dye on water saturated paper substrates has been
traditionally exploited with great skill by renowned water color artists. The
same physics finds more recent practical applications in paper based diagnostic
devices deploying chemicals that react with a bodily fluid yielding
colorimetric signals for disease detection. During spontaneous imbibition
through the tortuous pathways of a porous electrolyte saturated paper matrix, a
dye molecule undergoes diffusion in a complex network of pores. The advancing
front forms a strongly correlated interface that propagates diffusively but
with an enhanced effective diffusivity. We measure this effective diffusivity
and show that it is several orders of magnitude greater than the free solution
diffusivity and has a significant dependence on the solution pH and salt
concentration in the background electrolyte. We attribute this to electrically
mediated interfacial interactions between the ionic species in the liquid dye
and spontaneous surface charges developed at porous interfaces, and introduce a
simple theory to explain this phenomenon.",1905.03347v1
2019-06-10,k-Means Aperture Optimization Applied to Kepler K2 Time Series Photometry of Titan,"Motivated by the Kepler K2 time series of Titan, we present an aperture
optimization technique for extracting photometry of saturated moving targets
with high temporally- and spatially-varying backgrounds. Our approach uses
$k$-means clustering to identify interleaved families of images with similar
Point-Spread Function and saturation properties, optimizes apertures for each
family independently, then merges the time series through a normalization
procedure. By applying $k$-means aperture optimization to the K2 Titan data, we
achieve $\leq$0.33% photometric scatter in spite of background levels varying
from 15% to 60% of the target's flux. We find no compelling evidence for
signals attributable to atmospheric variation on the timescales sampled by
these observations. We explore other potential applications of the $k$-means
aperture optimization technique, including testing its performance on a
saturated K2 eclipsing binary star. We conclude with a discussion of the
potential for future continuous high-precision photometry campaigns for
revealing the dynamical properties of Titan's atmosphere.",1906.04220v1
2019-06-26,Level inversion in kaonic nuclei and the high-density nuclear equation of state,"It is very difficult for any nuclear model to pin down the saturation
property and high-density equation of state (EOS) simultaneously because of
high nonlinearity of the nuclear many-body problem. In this work, we propose,
for the first time, to use the special property of light kaonic nuclei to
characterize the relation between saturation property and high-density EOS.
With a series of relativistic mean-field models, this special property is found
to be the level inversion between orbitals $2S_{1/2}$ and $1D_{5/2}$ in light
kaonic nuclei. This level inversion can serve as a theoretical laboratory to
group the incompressibility at saturation density and the EOS at supra-normal
densities simultaneously.",1906.10868v1
2019-07-18,The closure-complement-frontier problem in saturated polytopological spaces,"Let $X$ be a space equipped with $n$ topologies $\tau_1,...,\tau_n$ which are
pairwise comparable and saturated, and for each $1\leq i\leq n$ let $k_i$ and
$f_i$ be the associated topological closure and frontier operators,
respectively. Inspired by the closure-complement theorem of Kuratowski, we
prove that the monoid of set operators $\mathcal{KF}_n$ generated by
$\{k_i,f_i:1\leq i\leq n\}\cup\{c\}$ (where $c$ denotes the set complement
operator) has cardinality no more than $2p(n)$ where
$p(n)=\frac{5}{24}n^4+\frac{37}{12}n^3+\frac{79}{24}n^2+\frac{101}{12}n+2$. The
bound is sharp in the following sense: for each $n$ there exists a saturated
polytopological space $(X,\tau_1,...,\tau_n)$ and a subset $A\subseteq X$ such
that repeated application of the operators $k_i, f_i, c$ to $A$ will yield
exactly $2p(n)$ distinct sets. In particular, following the tradition for
Kuratowski-type problems, we exhibit an explicit initial set in $\mathbb{R}$,
equipped with the usual and Sorgenfrey topologies, which yields $2p(2)=120$
distinct sets under the action of the monoid $\mathcal{KF}_2$.",1907.08203v3
2019-08-05,Free surface lump wave dynamics of a saturated superfluid Helium film with nontrivial boundary condition at the substrate surface,"In this article, the free surface wave dynamics of a saturated superfluid
Helium film is considered under the condition that there exists a very weak
downward localized superfluid flow into the substrate. For saturated film, the
effect of surface tension plays a decisive role in the surface wave evolution
dynamics of the system. The free surface evolution is shown to be governed by
forced Kadomtsev Petviashvili-I equation, with the forcing function depending
on downward superfluid velocity at the substrate surface. Exact as well as
perturbative free surface lump wave solutions of the (2+1) dimensional
nonlinear evolution equation are obtained and the effect of the leakage
velocity function on the lump wave solutions are shown.",1908.01512v2
2019-08-13,Superfast amplification and superfast nonlinear saturation of perturbations as the mechanism of turbulence,"Ruelle predicted that the maximal amplification of perturbations in
homogeneous isotropic turbulence is exponential $e^{\sigma \sqrt{Re} t}$ (where
$\sigma \sqrt{Re}$ is the maximal Liapunov exponent). In our earlier works, we
predicted that the maximal amplification of perturbations in fully developed
turbulence is faster than exponential $e^{\sigma \sqrt{Re} \sqrt{t} +\sigma_1
t}$. That is, we predicted superfast initial amplification of perturbations.
Built upon our earlier numerical verification of our prediction, here we
conduct a large numerical verification with resolution up to $2048^3$ and
Reynolds number up to $6210$. Our direct numerical simulation here confirms our
analytical prediction. Our numerical simulation also demonstrates that such
superfast amplification of perturbations leads to superfast nonlinear
saturation. We conclude that such superfast amplification and superfast
nonlinear saturation of ever existing perturbations serve as the mechanism for
the generation, development and persistence of fully developed turbulence.",1908.04838v1
2019-08-13,TCAD model for TeraFET detectors operating in a large dynamic range,"We present technology computer-aided design (TCAD) models for AlGaAs/InGaAs
and AlGaN/GaN and silicon TeraFETs, plasmonic field effect transistors (FETs),
for terahertz (THz) detection validated over a wide dynamic range. The modeling
results are in good agreement with the experimental data for the AlGaAs/InGaAs
heterostructure FETs (HFETs) and, to the low end of the dynamic range, with the
analytical theory of the TeraFET detectors. The models incorporate the response
saturation effect at high intensities of the THz radiation observed in
experiments and reveal the physics of the response saturation associated with
different mechanisms for different material systems. These mechanisms include
the gate leakage, the velocity saturation and the avalanche effect.",1908.04845v1
2019-08-17,"Enhanced stability, bistability, and exceptional points in saturable active photonic couplers","A generic photonic coupler with active and lossy parts, gain saturation and
asymmetric characteristics is examined. Saturable activity is shown to be able
to enhance the overall stability of the steady states, prevent evolution to
undesirable unbounded modes and allow for bistable operation in specific
regions of parametric space. Both stability and bistability are studied in the
phase space of the system, where the basins of attraction of each state are
identified, providing an accurate description of the dependence of the electric
fields on the initial conditions. Continuous families of exceptional points are
detected via suitable regulation of the coupling and asymmetry features of the
configuration. In this way, a complete description of the nonlinear dynamics
landscape is provided, which should be crucial for multiple application-driven
designs incorporating such a ubiquitous optical component.",1908.06304v1
2019-10-10,Stochastic DC Optimal Power Flow With Reserve Saturation,"We propose an optimization framework for stochastic optimal power flow with
uncertain loads and renewable generator capacity. Our model follows previous
work in assuming that generator outputs respond to load imbalances according to
an affine control policy, but introduces a model of saturation of generator
reserves by assuming that when a generator's target level hits its limit, it
abandons the affine policy and produces at that limit. This is a particularly
interesting feature in models where wind power plants, which have uncertain
upper generation limits, are scheduled to provide reserves to balance load
fluctuations. The resulting model is a nonsmooth nonconvex two-stage stochastic
program, and we use a stochastic approximation method to find stationary
solutions to a smooth approximation. Computational results on 6-bus and 118-bus
test instances demonstrates that by considering the effects of saturation, our
model can yield solutions with lower expected generation costs (at the same
target line violation probability level) than those obtained from a model that
enforces the affine policy to stay within generator limits with high
probability.",1910.04667v1
2019-10-21,Contextual Prediction Difference Analysis for Explaining Individual Image Classifications,"Much effort has been devoted to understanding the decisions of deep neural
networks in recent years. A number of model-aware saliency methods were
proposed to explain individual classification decisions by creating saliency
maps. However, they are not applicable when the parameters and the gradients of
the underlying models are unavailable. Recently, model-agnostic methods have
also received attention. As one of them, \textit{Prediction Difference
Analysis} (PDA), a probabilistic sound methodology, was proposed. In this work,
we first show that PDA can suffer from saturated classifiers. The saturation
phenomenon of classifiers exists widely in current neural network-based
classifiers. To explain the decisions of saturated classifiers better, we
further propose Contextual PDA, which runs hundreds of times faster than PDA.
The experiments show the superiority of our method by explaining image
classifications of the state-of-the-art deep convolutional neural networks.",1910.09086v2
2019-10-22,Improving the Gating Mechanism of Recurrent Neural Networks,"Gating mechanisms are widely used in neural network models, where they allow
gradients to backpropagate more easily through depth or time. However, their
saturation property introduces problems of its own. For example, in recurrent
models these gates need to have outputs near 1 to propagate information over
long time-delays, which requires them to operate in their saturation regime and
hinders gradient-based learning of the gate mechanism. We address this problem
by deriving two synergistic modifications to the standard gating mechanism that
are easy to implement, introduce no additional hyperparameters, and improve
learnability of the gates when they are close to saturation. We show how these
changes are related to and improve on alternative recently proposed gating
mechanisms such as chrono initialization and Ordered Neurons. Empirically, our
simple gating mechanisms robustly improve the performance of recurrent models
on a range of applications, including synthetic memorization tasks, sequential
image classification, language modeling, and reinforcement learning,
particularly when long-term dependencies are involved.",1910.09890v2
2019-11-06,From Parton Saturation to Proton Spin: the Impact of BFKL Equation and Reggeon Evolution,"Lev Lipatov was a giant in the field of strong interactions and a dominant
force in high-energy QCD for many decades. His work deeply influenced both how
we think about QCD and how we perform calculations in the theory. Below we
describe the work in two related research directions: the physics of parton
saturation and proton spin at small $x$. Both developments would have been
impossible without Lipatov's groundbreaking work. Saturation physics would not
have happened without the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation. The
recent progress in our theoretical understanding of the proton spin
contribution coming from small-$x$ partons started with the seminal paper by
Kirschner and Lipatov resumming double logarithms of energy in the Reggeon
evolution.",1911.02651v1
2019-12-19,Nuclear and neutron-star matter from local chiral interactions,"We report a quantum Monte Carlo calculation of the equation of state of
symmetric nuclear matter using local interactions derived from chiral effective
field theory up to next-to-next-to-leading order fit to few-body observables
only. The empirical saturation density and energy are well reproduced within
statistical and systematic uncertainties. We have also derived the symmetry
energy as a function of the density, finding good agreement with available
experimentally derived constraints at saturation and twice saturation density.
We find that the corresponding pressure is also in excellent agreement with
recent constraints extracted from gravitational waves of the neutron-star
merger GW170817 by the LIGO-Virgo detection.",1912.09411v2
2019-12-23,Empirical constraints on the high-density equation of state from multi-messenger observables,"We search for possible correlations between neutron star observables and
thermodynamic quantities that characterize high density nuclear matter. We
generate a set of model-independent equations of state describing stellar
matter from a Taylor expansion around saturation density. Each equation of
state which is a functional of the nuclear matter parameters is
thermodynamically consistent, causal and compatible with astrophysical
observations. We find that the neutron star tidal deformability and radius are
strongly correlated with the pressure, the energy density and the sound
velocity at different densities. Similar correlations are also exhibited by a
large set of mean-field models based on non-relativistic and relativistic
nuclear energy density functionals. These model independent correlations can be
employed to constrain the equation of state at different densities above
saturation from measurements of NS properties with multi-messenger
observations. In particular, precise constraints on the radius of PSR
J0030+0451 thanks to NICER observations would allow to better infer the
properties of matter around two times the nuclear saturation density.",1912.11131v1
2019-12-31,A new physics-preserving IMPES scheme for incompressible and immiscible two-phase flow in heterogeneous porous media,"In this work we consider a new efficient IMplicit Pressure Explicit
Saturation (IMPES) scheme for the simulation of incompressible and immiscible
two-phase flow in heterogeneous porous media with capillary pressure. Compared
with the conventional IMPES schemes, the new IMPES scheme is inherently
physics-preserving, namely, the new algorithm is locally mass conservative for
both phases and it also enjoys another appealing feature that the total
velocity is continuous in the normal direction. Moreover, the new scheme is
unbiased with regard to the two phases and the saturations of both phases are
bounds-preserving if the time step size is smaller than a certain value. The
key ideas in the new scheme include that the Darcy flows for both phases are
rewritten in the formulation based on the total velocity and an auxiliary
velocity referring to as the capillary potential gradient, and the total
discretized conservation equation is obtained by the summation of the
discretized conservation equation for each phase. The upwind strategy is
applied to update the saturations explicitly, and the upwind mixed finite
element methods are used to solve the pressure-velocity systems which can be
decoupled. We also present some interesting examples to demonstrate the
efficiency and robustness of the new algorithm.",1912.13340v1
2020-01-16,"Slow-to-Start Traffic Model: Condensation, Saturation and Scaling Limits","We consider a one-dimensional traffic model with a slow-to-start rule. The
initial position of the cars in $\mathbb R$ is a Poisson process of parameter
$\lambda$. Cars have speed 0 or 1 and travel in the same direction. At time
zero the speed of all cars is 0; each car waits an exponential time to switch
speed from $0$ to $1$ and stops when it collides with a stopped car. When the
car is no longer blocked, it waits a new exponential time to assume speed one,
and so on. We study the emergence of condensation for the saturated regime
$\lambda>1$ and the critical regime $\lambda=1$, showing that in both regimes
all cars collide infinitely often and each car has asymptotic mean velocity
$1/\lambda$. In the saturated regime the moving cars form a point process whose
intensity tends to 1. The remaining cars condensate in a set of points whose
intensity tends to zero as $1/\sqrt t$. We study the scaling limit of the
traffic jam evolution in terms of a collection of coalescing Brownian motions.",2001.05796v1
2020-02-11,Maser Flares Driven by Variations in Pumping and Background Radiation,"We simulate maser flares by varying either the pump rate or the background
level of radiation in a 3D model of a maser cloud. We investigate the effect of
different cloud shapes, saturation levels and viewpoints. Results are
considered for clouds with both uniform and internally variable unsaturated
inversion. Pumping and background variations are represented by several
different driving functions, some of which are light curves drawn from
observations. We summarise the pumping variability results in terms of three
observable parameters, the maximum flux density achieved, a variability index
and duty cycle. We demonstrate typical ranges of the flux density that may
result from viewing an aspherical object from random viewpoints. The best
object for a flare is a prolate cloud, viewed close to its long axis and driven
from unsaturated conditions to at least modest saturation. Results for
variation of the background level are qualitatively different from the variable
pumping results in that they tend to produce short intervals of low flux
density under conditions of moderate saturation and sufficient variability to
be consistent with strong flaring. Variable background models typically have a
significantly higher duty cycle than those with variable pumping.",2002.04490v1
2020-02-11,Soft diffraction within the QCD color dipole picture,"In this work we consider the QCD parton saturation models to describe soft
interactions at the high energy limit. The total and elastic cross sections as
well as the elastic slope parameter are obtained for proton-proton and
pion-proton collisions and compared to recent experimental results. The
analyses are done within the color dipole formalism taking into account
saturation models which have been tested against DIS data. The main point is
that the match between soft and hard interaction occurs in the saturation
region which can be described by high density QCD approaches. Discussion is
performed on the main theoretical uncertainties associated with calculations.",2002.04586v2
2020-03-03,Saturation for the Butterfly Poset,"Given a finite poset $\mathcal P$, we call a family $\mathcal F$ of subsets
of $[n]$ $\mathcal P$-saturated if $\mathcal F$ does not contain an induced
copy of $\mathcal P$, but adding any other set to $\mathcal F$ creates an
induced copy of $\mathcal P$. The induced saturated number of $\mathcal P$,
denoted by $\text{sat}^*(n,\mathcal P)$, is the size of the smallest $\mathcal
P$-saturated family with ground set $[n]$. In this paper we are mainly
interested in the four-point poset called the butterfly. Ferrara, Kay, Kramer,
Martin, Reiniger, Smith and Sullivan showed that the saturation number for the
butterfly lies between $\log_2{n}$ and $n^2$. We give a linear lower bound of
$n+1$. We also prove some other results about the butterfly and the poset
$\mathcal N$.",2003.01621v1
2020-04-08,"The COVID-19 pandemic: growth patterns, power law scaling, and saturation","More and more countries show a significant slowdown in the number of new
COVID-19 infections due to effective governmentally instituted lockdown and
social distancing measures. We have analyzed the growth behavior of the top 25
most affected countries by means of a local slope analysis and found three
distinct patterns that individual countries follow depending on the strictness
of the lockdown protocols: exponential rise and fall, power law, or logistic.
For countries showing power law growth we have determined the scaling
exponents. For countries that showed a strong slowdown in the rate of
infections we have extrapolated the expected saturation of the number of
infections and the expected final date. Two different extrapolation methods
(logistic and parabolic) were used. Both methods agree on the order of
magnitude of saturation and end dates. Global infections rates are analyzed
with the same methods. The relevance and accuracy of these extrapolations is
discussed.",2004.03859v1
2020-04-16,Self-acceleration and energy channeling in the saturation of the ion-sound instability in a bounded plasma,"A novel regime of the saturation of the Pierce-type ion-sound instability in
bounded ion-beam-plasma system is revealed in 1D PIC simulations. It is found
that the saturation of the instability is mediated by the oscillating virtual
anode potential structure. The periodically oscillating potential barrier
separates the incoming beam ions into two groups. One component forms a
supersonic beam which is accelerated to an energy exceeding the energy of the
initial cold ion beam. The other component is organized as a self-consistent
phase space structure of trapped ions with a wide energy spread - the ion hole.
The effective temperature (energy spread) of the ions trapped in the hole is
lower than the initial beam energy. In the final stage the ion hole expands
over the whole system length.",2004.07513v1
2020-05-05,Exploring the relationship between nuclear matter and finite nuclei with chiral two- and three-nucleon forces,"We address the connection between the saturating behavior of infinite nuclear
matter and the description of finite nuclei based on state-of-the-art chiral
two- and three-nucleon forces. We observe that chiral two- and three-nucleon
interactions (at N2LO and at N3LO) which have been found to predict realistic
binding energies and radii for a wide range of finite nuclei (from p-shell
nuclei up to nickel isotopes) are unable to saturate infinite nuclear matter.
On the other hand, it has been shown that, when the fits of the cD and cE
couplings of the chiral three-nucleon interactions include the constraint of
nuclear matter saturation in addition to, as is typically the case, the triton
binding energy, medium-mass nuclei are underbound and their radii are
sytematically too large. We discuss this apparent inconsistency and perform
test calculations for various scenarios to shed light on the issue.",2005.01958v2
2020-05-14,The diffractive saturable loss mechanism in Kerr-lens mode-locked lasers: direct observation and simulation,"Passive mode-locking critically relies on a saturable loss mechanism to form
ultrashort pulses. However, in Kerr-lens mode-locking (KLM), no actual
absorption takes place, but rather losses appear due to diffraction, and actual
light must escape the cavity. The Kerr-lens effect works to generate through
diffraction an effective instantaneous saturable absorber that delicately
depends on the interplay between the spatial and temporal profiles of the
pulse. Despite the importance of KLM as a technique for generating ultrafast
pulses and the fundamental role of the diffraction losses in its operation,
these losses were never directly observed. Here, we measure the light that
leaks out due to diffraction losses in a hard-aperture Kerr-lens mode-locked
Ti:Sapphire laser, and compare the measured results with a numerical theory
that explicitly calculates the spatio-temporal behavior of the pulse.",2005.06937v3
2020-06-11,Wave-particle interactions in a long traveling wave tube with upgraded helix,"We investigate the interaction of electromagnetic waves and electron beams in
a 4 meters long traveling wave tube (TWT). The device is specially designed to
simulate beam-plasma experiments without appreciable noise. This TWT presents
an upgraded slow wave structure (SWS) that results in more precise measurements
and makes new experiments possible. We introduce a theoretical model describing
wave propagation through the SWS and validated by the experimental dispersion
relation, impedance, phase and group velocities. We analyze nonlinear effects
arising from the beam-wave interaction, such as the modulation of the electron
beam and the wave growth and saturation process. When the beam current is low,
the wave growth coefficient and saturation amplitude follow the linear theory
predictions. However, for high values of current, nonlinear space charge
effects become important and these parameters deviate from the linear
predictions, tending to a constant value. After saturation, we also observe
trapping of the beam electrons, which alters the wave amplitude along the TWT.",2006.06710v2
2020-06-21,An Entropy-based Proof of Threshold Saturation for Nonbinary SC-LDPC Ensembles on the BEC,"In this paper we are concerned with the asymptotic analysis of nonbinary
spatially-coupled low-density parity-check (SC-LDPC) ensembles defined over
GL$\left(2^{m}\right)$ (the general linear group of degree $m$ over
GF$\left(2\right)$). Our purpose is to prove threshold saturation when the
transmission takes place on the binary erasure channel (BEC). To this end, we
establish the duality rule for entropy for nonbinary variable-node (VN) and
check-node (CN) convolutional operators to accommodate the nonbinary density
evolution (DE) analysis. Based on this, we construct the explicit forms of the
potential functions for uncoupled and coupled DE recursions. In addition, we
show that these functions exhibit similar monotonicity properties as those for
binary LDPC and SC-LDPC ensembles over general binary memoryless symmetric
(BMS) channels. This leads to the threshold saturation theorem and its converse
for nonbinary SC-LDPC ensembles on the BEC, following the proof technique
developed by S. Kumar et al.",2006.11740v1
2020-06-22,Capillary transport in paper porous materials at low saturation levels,"The problem of capillary transport in fibrous porous materials at low levels
of liquid saturation has been addressed. It has been demonstrated, that the
process of liquid spreading in this type of porous materials at low saturation
can be described macroscopically by a similar super-fast, non-linear diffusion
model as that, which had been previously identified in experiments and
simulations in particulate porous media. The macroscopic diffusion model has
been underpinned by simulations using a microscopic network model. The
theoretical results have been qualitatively compared with available
experimental observations using persistent liquids.",2006.12419v1
2020-06-28,Resonant forward-scattered field in the high-saturation regime: Elastic and inelastic contributions,"We measure the resonant forward scattering of light by a highly saturated
atomic medium through the flashes emitted immediately after an abrupt
extinction of the probe beam. The experiment is done in a dilute regime where
the phenomena are well captured using the independent scattering approximation.
Comparing our measurements to a model based on Maxwell-Bloch equations, our
experimental results are consistent with contributions from only the elastic
component, whereas the attenuation of the coherent transmission power is linked
to the elastic and inelastic scatterings. In the large saturation regime and at
the vicinity of the atomic resonance, we derive an asymptotic expression
relating the elastic scattering power to the forward-scattered power.",2006.15540v2
2020-07-14,Insights into nuclear saturation density from parity violating electron scattering,"The saturation density of nuclear matter $\rho_0$ is a fundamental nuclear
physics property that is difficult to predict from fundamental principles. The
saturation density is closely related to the interior density of a heavy
nucleus, such as $^{208}$Pb. We use parity violating electron scattering to
determine the average interior weak charge and baryon densities in $^{208}$Pb.
This requires not only measuring the weak radius $R_{\rm wk}$ but also
determining the surface thickness of the weak charge density $a$. We obtain
$\rho_0=0.150\pm0.010$ fm$^{-3}$, where the 7\% error has contributions form
the PREX error on the weak radius, an assumed 10\% uncertainty in the surface
thickness $a$, and from the extrapolation to infinite nuclear matter. These
errors can be improved with the upcoming PREX II results and with a new parity
violating electron scattering experiment, at a somewhat higher momentum
transfer, to determine $a$.",2007.07117v2
2020-07-15,A Graph Theoretic Approach to Power System Vulnerability Identification,"During major power system disturbances, when multiple component outages occur
in rapid succession, it becomes crucial to quickly identify the transmission
interconnections that have limited power transfer capability. Understanding the
impact of an outage on these critical interconnections (called saturated
cut-sets) is important for enhancing situational awareness and taking correct
actions. This paper proposes a new graph theoretic approach for analyzing
whether a contingency will create a saturated cut-set in a meshed power
network. A novel feature of the proposed algorithm is that it lowers the
solution time significantly making the approach viable for real-time
operations. It also indicates the minimum amount by which the power transfer
through the critical interconnections should be reduced so that
post-contingency saturation does not occur. Robustness of the proposed
algorithm for enhanced situational awareness is demonstrated using the IEEE-118
bus system as well as a 17,000+ bus model of the Western Interconnection (WI).
Comparisons made with different approaches for power system vulnerability
assessment prove the utility of the proposed scheme for aiding power system
operations during extreme exigencies.",2007.07859v1
2020-07-24,All-fiber mode-locked ytterbium-doped fiber laser with a saturable absorber based on nonlinear Kerr beam cleanup effect,"We theoretically and experimentally demonstrate a novel mode-locked
ytterbium-doped fiber laser with a saturable absorber based on nonlinear Kerr
beam cleanup effect. The saturable absorber was formed by a 2-m graded-index
multimode fiber and a single-mode fiber segment served as a diaphragm. With an
all-normal-dispersion-fiber configuration, the laser generated dissipative
soliton pulses with pulse duration of 26.38 ps and pulse energy more than 0.25
nJ; output pulses could be compressed externally to 615.7 fs. Moreover, the
self-starting mode-locking operation of this laser exhibited a high stability
with a measured signal-to-noise ratio of 73.4 dB in the RF spectrum.",2007.12334v2
2020-07-27,Is there slow particle transport in the MBL phase?,"We analyze the saturation value of the bipartite entanglement and number
entropy starting from a random product state deep in the MBL phase. By studying
the probability distributions of these entropies we find that the growth of the
saturation value of the entanglement entropy stems from a significant
reshuffling of the weight in the probability distributions from the bulk to the
exponential tails. In contrast, the probability distributions of the saturation
value of the number entropy are converged with system size, and exhibit a sharp
cut-off for values of the number entropy which correspond to one particle
fluctuating across the boundary between the two halves of the system. Our
results therefore rule out slow particle transport deep in the MBL phase and
confirm that the slow entanglement entropy production stems uniquely from
configurational entanglement.",2007.13767v1
2020-08-07,Robust photon transmission in nonlinear parity-time-symmetric cavities,"We explore the photon transfer in the nonlinear parity-time-symmetry system
of two coupled cavities, which contains nonlinear gain and loss dependent on
the intracavity photons. Analytical solution to the steady state gives a
saturated gain, which satisfy the parity-time symmetry automatically. The
eigen-frequency self-adapts the nonlinear saturated gain to reach the maximum
efficiency in the steady state. We find that the saturated gain in the weak
coupling regime does not match the loss in the steady state, exhibiting an
appearance of a spontaneous symmetry-breaking. The photon transmission
efficiency in the parity-time-symmetric regime is robust against the variation
of the coupling strength, which improves the results of the conventional
methods by tuning the frequency or the coupling strength to maintain optimal
efficiency. Our scheme provides an experimental platform for realizing the
robust photon transfer in cavities with nonlinear parity-time symmetry.",2008.02949v1
2020-08-13,Resistivity saturation in Kondo insulators,"Resistivities of heavy-fermion insulators typically saturate below a
characteristic temperature $T^*$. For some, metallic surface states,
potentially from a non-trivial bulk topology, are a likely source of residual
conduction. Here, we establish an alternative mechanism: At low temperature, in
addition to the charge gap, the scattering rate turns into a relevant energy
scale, invalidating the semiclassical Boltzmann picture. Finite lifetimes of
intrinsic carriers limit conduction, impose the existence of a crossover $T^*$,
and control - now on par with the gap - the quantum regime emerging below it.
We showcase the mechanism with realistic many-body simulations and elucidate
how the saturation regime of the Kondo insulator Ce$_3$Bi$_4$Pt$_3$, for which
residual conduction is a bulk property, evolves under external pressure and
varying disorder. Using a phenomenological formula we derived for the quantum
regime, we also unriddle the ill-understood bulk conductivity of SmB$_6$ -
demonstrating that our mechanism is widely applicable to correlated narrow-gap
semiconductors.",2008.05846v1
2020-08-21,Vacuum-Induced Saturation in Plasmonic Nanoparticles,"Vacuum fluctuations are a fundamental feature of quantized fields. It is
usually assumed that observations connected to vacuum fluctuations require a
system well isolated from other influences. In this work, we demonstrate that
effects of the quantum vacuum can already occur in simple colloidal
nano-assemblies prepared by wet chemistry. We claim that the electromagnetic
field fluctuations at the zero-point level saturate the absorption of dye
molecules self-assembled at the surface of plasmonic nano-resonators. For this
effect to occur, reaching the strong coupling regime between the plasmons and
excitons is not required. This intriguing effect of vacuum-induced saturation
(VISA) is discussed within a simple quantum optics picture and demonstrated by
comparing the optical spectra of hybrid gold-core dye-shell nanorods to
electromagnetic simulations.",2008.09395v1
2020-09-04,First-principles study of ultrafast and nonlinear optical properties of graphite thin films,"We theoretically investigate ultrafast and nonlinear optical properties of
graphite thin films based on first-principles time-dependent density functional
theory. We first calculate electron dynamics in a unit cell of graphite under a
strong pulsed electric field and explore the transient optical properties of
graphite. It is shown that the optical response of graphite shows a sudden
change from conducting to insulating phase at a certain intensity range of the
applied electric field. It also appears as a saturable absorption, the
saturation in the energy transfer from the electric field to electrons. We next
investigate a light propagation in graphite thin films by solving coupled
dynamics of the electrons and the electromagnetic fields simultaneously. It is
observed that the saturable absorption manifests in the propagation with small
attenuation in the spatial region where the electric field amplitude is about
$4 \sim 7 \times 10^{-2}$ V/Angstrom.",2009.01979v2
2020-09-25,Fundamental limitations to no-jerk gearshifts of multi-speed transmission architectures in electric vehicles,"Multi-speed transmissions can enhance the performance and reduce the overall
cost of an electric vehicle, but they also introduce a challenge: avoiding
gearshift jerk, which may sometimes prove to be impossible in the presence of
motor and clutch saturation. In this article, we introduce three theorems that
explicitly define the fundamental limitations to no-jerk gearshifts resulting
from motor or actuator saturation. We compare gearshifts that consist of
transferring transmission torque from one friction clutch to another, to the
case in which one of the clutches is a one-way clutch. We show that systems
with a one-way clutch are more prone to motor saturation, causing gearshift
jerk to be more often inevitable. We also study the influence of planetary
gearsets on the gearshift dynamical trajectories, and expose the impact on the
no-jerk limitations. This work offers tools to compare transmission
architectures during the conceptual design phase of a new electric vehicle.",2009.12410v2
2020-09-28,Pulse-duration dependence of saturable and reverse saturable absorption in ZnCo2O4 microflowers,"We employed open-aperture Z-scan technique to unveil the third-order optical
nonlinearity in ZnCo2O4 (ZCO) microflowers. Our results indicate that
intersystem crossing (ISC) lifetime can be used as simple tool to demonstrate
remarkably contrasting optical nonlinearity in ZCO. Ultrafast transient
absorption measurements reveal that ISC from singlet to triplet state takes
place in 5 ps. For femtosecond laser pulses, when the pulse duration is shorter
than ISC lifetime, saturable absorption (SA) takes place for all intensities.
On the contrary, when the pulse duration is longer than ISC for nanosecond
excitation, we observe transition from SA to reverse SA (RSA) at higher
intensities via excited-state absorption. We envisage that benefiting from SA
and RSA, ZCO emerges as potential candidate for mode locking and optical
limiting devices.",2009.13226v2
2020-10-15,Experimental vulnerability analysis of QKD based on attack ratings,"Inspired by the methodology used for classical cryptographic hardware, we
consider the use of attack ratings in the context of QKD security evaluation.
To illustrate the relevance of this approach, we conduct an experimental
vulnerability assessment of CV-QKD against saturation attacks, for two
different attack strategies. The first strategy relies on inducing detector
saturation by performing a large coherent displacement. This strategy is
experimentally challenging and therefore translates into a high attack rating.
We also propose and experimentally demonstrate a second attack strategy that
simply consists in saturating the detector with an external laser. The low
rating we obtain indicates that this attack constitutes a primary threat for
practical CV-QKD systems. These results highlight the benefits of combining
theoretical security considerations with vulnerability analysis based on attack
ratings, in order to guide the design and engineering of practical QKD systems
towards the highest possible security standards.",2010.07815v2
2020-10-15,Non-saturating GAN training as divergence minimization,"Non-saturating generative adversarial network (GAN) training is widely used
and has continued to obtain groundbreaking results. However so far this
approach has lacked strong theoretical justification, in contrast to
alternatives such as f-GANs and Wasserstein GANs which are motivated in terms
of approximate divergence minimization. In this paper we show that
non-saturating GAN training does in fact approximately minimize a particular
f-divergence. We develop general theoretical tools to compare and classify
f-divergences and use these to show that the new f-divergence is qualitatively
similar to reverse KL. These results help to explain the high sample quality
but poor diversity often observed empirically when using this scheme.",2010.08029v1
2020-10-21,On the Saturation Phenomenon of Stochastic Gradient Descent for Linear Inverse Problems,"Stochastic gradient descent (SGD) is a promising method for solving
large-scale inverse problems, due to its excellent scalability with respect to
data size. The current mathematical theory in the lens of regularization theory
predicts that SGD with a polynomially decaying stepsize schedule may suffer
from an undesirable saturation phenomenon, i.e., the convergence rate does not
further improve with the solution regularity index when it is beyond a certain
range. In this work, we present a refined convergence rate analysis of SGD, and
prove that saturation actually does not occur if the initial stepsize of the
schedule is sufficiently small. Several numerical experiments are provided to
complement the analysis.",2010.10916v2
2020-10-21,"Painting with Hue, Saturation, and Brightness Control by Nanoscale 3D Printing","Varying only the in-plane or out-of-plane dimensions of nanostructures
produces a wide range of colourful elements in metasurfaces and thin films.
However, achieving shades of grey and control of colour saturation remains
challenging. Here, we introduce a hybrid approach to colour generation based on
the tuning of nanostructure geometry in all three dimensions. Through
two-photon polymerization lithography, we systematically investigated colour
generation from the simple single nanopillar geometry made of
low-refractive-index material; realizing grayscale and full colour palettes
with control of hue, saturation, brightness through tuning of height, diameter,
and periodicity of nanopillars. Arbitrary colourful and grayscale images were
painted by mapping desired prints to precisely controllable parameters during
3D printing. We extend our understanding of the scattering properties of the
low-refractive-index nanopillar to demonstrate grayscale inversion and colour
desaturation, with steganography at the level of single nanopillars.",2010.11035v2
2020-12-18,Moments and saturation properties of eigenstates,"Eigenvalues are defined for any element of an algebra of observables and do
not require a representation in terms of wave functions or density matrices. A
systematic algebraic derivation based on moments is presented here for the
harmonic oscillator, together with a perturbative treatment of anharmonic
systems. In this process, a collection of inequalities is uncovered which
amount to uncertainty relations for higher-order moments saturated by the
harmonic-oscillator excited states. Similar saturation properties hold for
anharmonic systems order by order in perturbation theory. The new method, based
on recurrence relations for moments of a state combined with positivity
conditions, is therefore able to show new physical features.",2012.10321v1
2020-12-21,Hybrid Beamforming for Millimeter Wave Full-Duplex under Limited Receive Dynamic Range,"Full-duplex millimeter wave (mmWave) communication has shown increasing
promise for self-interference cancellation via hybrid precoding and combining.
This paper proposes a novel mmWave multiple-input multiple-output (MIMO) design
for configuring the analog and digital beamformers of a full-duplex
transceiver. Our design is the first to holistically consider the key practical
constraints of analog beamforming codebooks, a minimal number of radio
frequency (RF) chains, limited channel knowledge, beam alignment, and a limited
receive dynamic range. To prevent self-interference from saturating the
receiver of a full-duplex device having limited dynamic range, our design
addresses saturation on a per-antenna and per-RF chain basis. Numerical results
evaluate our design in a variety of settings and validate the need to prevent
receiver-side saturation. These results and the corresponding insights serve as
useful design references for practical full-duplex mmWave transceivers.",2012.11647v1
2021-01-06,Modelling wave dispersion in fluid saturating periodic scaffolds,"Acoustic waves in a slightly compressible fluid saturating porous periodic
structure are studied using two complementary approaches: 1) the periodic
homogenization (PH) method provides effective model equations for a general
dynamic problem imposed in a bounded medium, 2) harmonic acoustic waves are
studied in an infinite medium using the Floquet-Bloch (FB) wave decomposition.
  In contrast with usual simplifications, the advection phenomenon of the
Navier-Stokes equations is accounted for. For this, an acoustic approximation
is applied to linearize the advection term. The homogenization results are
based the periodic unfolding method combined with the asymptotic expansion
technique providing a straight upscaling procedure which leads to the
macroscopic model defined in terms of the effective model parameters. These are
computed using the characteristic responses of the porous microstructure.
  Using the FB theory, we derive dispersion equations for the scaffolds
saturated by the inviscid, or the viscous, barotropic fluids, whereby the
advection due to a permanent flow in the porous structures is respected. A
computational study is performed for the numerical models obtained using the
finite element discretization. For the FB methods-based dispersion analysis,
quadratic eigenvalue problems must be solved. The numerical examples show
influences of the microstructure size and of the advection generating an
anisotropy of the acoustic waves dispersion.",2101.01969v1
2021-01-25,Asymmetric Si-slot Coupler with Nonreciprocal Response Based on Graphene Saturable Absorption,"We present the study of a proof-of-concept integrated device that can be used
as a nonlinear broadband isolator. The device is based on the asymmetric
loading of a highly-confining silicon-slot photonic coupler with graphene
layers, whose ultrafast and low-threshold saturable absorption can be exploited
for nonreciprocal transmission between the cross-ports of the coupler. The
structure is essentially a non-Hermitian system, whose exceptional points are
briefly discussed. The nonlinear device is modeled with a coupled Schrodinger
equation system whose validity is checked by full-vector finite element-based
beam-propagation method simulations in CW. The numerically computed performance
reveals a nonreciprocal intensity range (NRIR) in the vicinity of 100 mW peak
power with a bandwidth spanning tens of nanometers, from CW down to ps-long
pulses. Finally, the combination of saturable absorption and self-phase
modulation (Kerr effect) in graphene is studied, indicating the existence of
two NRIR with opposite directionality.",2101.10210v2
2021-01-27,Maximizing performance of quantum cascade laser-pumped molecular lasers,"Quantum cascade laser (QCL)-pumped molecular lasers (QPMLs) have recently
been introduced as a new source of powerful (>1 mW), tunable (>1 THz),
narrow-band (<10 kHz), continuous-wave terahertz radiation. The performance of
these lasers depends critically on molecular collision physics, pump
saturation, and on the design of the laser cavity. Using a validated
three-level model that captures the essential collision and saturation
behaviors of the QPML gas nitrous oxide (N2O),we explore how threshold pump
power and output terahertz power depend on pump power, gas pressure, as well as
on the diameter, length, and output-coupler transmissivity of a cylindrical
cavity.The analysis indicates that maximum power occurs as pump saturation is
minimized in a manner that depends much more sensitively on pressure than on
cell diameter, length, or transmissivity. A near-optimal compact laser cavity
can produce more than 10 mW of power tunable over frequencies above 1 THz when
pumped by a multi-watt QCL.",2101.11158v2
2021-02-14,Modeling Electrical Resistance Drift with Ultrafast Saturation of OTS Selectors,"Crossbar array architecture is an essential design element for densely
connected Non-Volatile Memory(NVM) applications. To overcome intrinsic sneak
current problem of crossbar arrays, each memory unit is serially attached to a
selector unit with highly nonlinear current-voltage (I-V) characteristics.
Recently, Ovonic Threshold Switching (OTS) materials are preferred as selectors
due to their fabrication compatibility with PRAM, MRAM or ReRAM technologies;
however, OTS selectors suffer from the temporal drift of its threshold voltage.
First, based on Poole-Frenkel conduction, we present time and temperature
dependent model that predicts temporally evolving I-V characteristics,including
threshold voltage of OTS selectors. Second, we report an ultrafast saturation
($\sim 10^3$ seconds) of the drift and extend the model to predict the time of
drift saturation. Our model shows excellent agreement with OTS devices
fabricated with 8 nm technology node at 25{\deg}C and 85{\deg}C ambient
temperatures. The proposed model plays a significant role in understanding OTS
device internals and the development of reliable threshold voltage jump table.",2102.07264v1
2021-02-16,Realizability and tameness of fusion systems,"A saturated fusion system over a finite $p$-group $S$ is a category whose
objects are the subgroups of $S$ and whose morphisms are injective
homomorphisms between the subgroups satisfying certain axioms. A fusion system
over $S$ is realized by a finite group $G$ if $S$ is a Sylow $p$-subgroup of
$G$ and morphisms in the category are those induced by conjugation in $G$. One
recurrent question in this subject is to find criteria as to whether a given
saturated fusion system is realizable or not.
  One main result in this paper is that a saturated fusion system is realizable
if all of its components (in the sense of Aschbacher) are realizable. Another
result is that all realizable fusion systems are tame: a finer condition on
realizable fusion systems that involves describing automorphisms of a fusion
system in terms of those of some group that realizes it. Stated in this way,
these results depend on the classification of finite simple groups, but we also
give more precise formulations whose proof is independent of the
classification.",2102.08278v4
2021-03-15,On saturation of Berge hypergraphs,"A hypergraph $H=(V(H), E(H))$ is a Berge copy of a graph $F$, if $V(F)\subset
V(H)$ and there is a bijection $f:E(F)\rightarrow E(H)$ such that for any $e\in
E(F)$ we have $e\subset f(e)$. A hypergraph is Berge-$F$-free if it does not
contain any Berge copies of $F$. We address the saturation problem concerning
Berge-$F$-free hypergraphs, i.e., what is the minimum number $sat_r(n,F)$ of
hyperedges in an $r$-uniform Berge-$F$-free hypergraph $H$ with the property
that adding any new hyperedge to $H$ creates a Berge copy of $F$. We prove that
$sat_r(n,F)$ grows linearly in $n$ if $F$ is either complete multipartite or it
possesses the following property: if $d_1\le d_2\le \dots \le d_{|V(F)|}$ is
the degree sequence of $F$, then $F$ contains two adjacent vertices $u,v$ with
$d_F(u)=d_1$, $d_F(v)=d_2$. In particular, the Berge-saturation number of
regular graphs grows linearly in $n$.",2103.08437v1
2021-03-28,Fixed points theorems for unsaturated and saturated classes of contractive mappings in Banach spaces,"Based on the technique of enriching contractive type mappings, a technique
that has been used successfully in some recent papers, we introduce the concept
of {\it saturated} class of contractive mappings. We show that, from this
perspective, the contractive type mappings in the metric fixed point theory can
be separated into two distinct classes, unsaturated and saturated, and that,
for any unsaturated class of mappings, the technique of enriching contractive
type mappings provides genuine new fixed point results. We illustrate the
concept by surveying some significant fixed point results obtained recently for
five remarkable unsaturated classes of contractive mappings. In the second part
of the paper, we also identify some classes of saturated classes of contractive
mappings, whose main feature is that they cannot be enlarged by means of the
technique of enriching the contractive mappings.",2103.15148v1
2021-04-05,First Saturation Correction in High Energy Proton-Nucleus Collisions: II. Single Inclusive Semi-Hard Gluon Production,"Exploiting recently obtained analytic solutions of classical Yang-Mills
equations for higher order perturbations in the field of the dilute object
(proton), we derive the complete first saturation correction to the single
inclusive semi-hard gluon production in high energy proton-nucleus collisions
by applying the Lehmann-Symanzik-Zimmermann reduction formula. We thus finalize
the program started by Balitsky (see Ref.~\cite{Balitsky:2004rr}) and
independently by Chirilli, Kovchegov and Wertepny (see
Ref.~\cite{Chirilli:2015tea}) albeit using a very different approach to carry
out our calculations. We extracted the functional dependence of gluon spectrum
on the color charge densities of the colliding objects; thus our results can be
used to evaluate complete first saturation correction to the double/multiple
inclusive gluon productions.",2104.01879v1
2021-04-08,Landau Damping in the Transverse Modulational Dynamics of Co-Propagating Light and Matter Beams,"The optomechanical coupling and transverse stability of a co-propagating
monochromatic electromagnetic wave and mono-energetic beam of two-level atoms
is investigated in the collisionless regime. The coupled dynamics are studied
through a Landau stability analysis of the coupled gas- kinetic and paraxial
wave equations, including the effect of the electronic nonlinearity. The
resulting dispersion relation captures the interaction of kinetic and
saturation effects and shows that for blue detuning the combined nonlinear
interaction is unstable below a critical wavenumber which reduces to the result
of Bespalov and Talanov in the limit of a negligible kinetic nonlinearity. For
red detuning we find that under a saturation parameter threshold exists whereby
the system stabilizes unconditionally. With negligible saturation, an
optomechanical form of Landau damping stabilizes all wavenumbers above a
critical wavenumber determined by the combined strength of the kinetic and
refractive optomechanical feedback. The damping is mediated primarily by atoms
traveling along the primary diagonals of the Talbot carpet.",2104.04100v1
2021-04-24,Optimizing Regular Expressions via Rewrite-Guided Synthesis,"Regular expressions are pervasive in modern systems. Many real-world regular
expressions are inefficient, sometimes to the extent that they are vulnerable
to complexity-based attacks, and while much research has focused on detecting
inefficient regular expressions or accelerating regular expression matching at
the hardware level, we investigate automatically transforming regular
expressions to remove inefficiencies. We reduce this problem to general
expression optimization, an important task necessary in a variety of domains
even beyond compilers, e.g., digital logic design, etc. Syntax-guided synthesis
(SyGuS) with a cost function can be used for this purpose, but ordered
enumeration through a large space of candidate expressions can be prohibitively
expensive. Equality saturation is an alternative approach which allows
efficient construction and maintenance of expression equivalence classes
generated by rewrite rules, but the procedure may not reach saturation, meaning
global minimality cannot be confirmed. We present a new approach called
rewrite-guided synthesis (ReGiS), in which a unique interplay between SyGuS and
equality saturation-based rewriting helps to overcome these problems, resulting
in an efficient, scalable framework for expression optimization.",2104.12039v3
2021-05-19,Topological Insulators: An in-depth Review of their Use in Modelocked Fiber Lasers,"Topological Insulators (TIs) exhibit exciting optical properties, which opens
up a new pathway to generate ultrashort pulses from fiber lasers. Layered TIs
display distinct saturable absorption property due to excited state absorption,
as compared to their bulk structures. Moreover, the electronic structures of
the films of TIs depend on the thickness of the films due to the quantum
confinement of the electrons. By virtue of this, the nanoparticles of TIs play
a key role in all-fiber modelocked laser. By tweaking the crystal structures of
TIs, it is possible to generate ultrashort pulses across the visible,
near-infrared and mid-infrared wavelengths. Starting from the crystal
structures and density of states calculations, how different topological
insulators can be fabricated and integrated as an efficient passive saturable
absorber in all-fiber modelocked lasers with the capability of producing
fundamental to high-harmonic pulse generation are described clearly in this
review report. Moreover, this report reviews the current state-of-art of
TI-based saturable absorbers and their applications in different regimes of
modelocked fiber lasers.",2105.09195v1
2021-05-26,Moment-based superresolution: Formalism and applications,"Sensitivity limits are usually determined using the Cram\'er-Rao bound.
Recently this approach has been used to obtain the ultimate resolution limit
for the estimation of the separation between two incoherent point sources.
However, methods that saturate these resolution limits, usually require the
full measurement statistics, which can be challenging to access. In this work,
we introduce a simple superresolution protocol to estimate the separation
between two thermal sources which relies only on the average value of a single
accessible observable. We show how optimal observables for this technique may
be constructed for arbitrary thermal sources, and we study their sensitivities
when one has access to spatially resolved intensity measurements (direct
imaging) and photon counting after spatial mode demultiplexing. For
demultiplexing, our method is optimal, i.e. it saturates the quantum
Cram\'er-Rao bound. We also investigate the impact of noise on the optimal
observables, their measurement sensitivity and on the scaling with the number
of detected photons of the smallest resolvable separation. For low signals in
the image plane, we demonstrate that our method saturates the Cram\'er-Rao
bound even in the presence of noise.",2105.12396v2
2021-05-25,Improved Constraints for the XUV Luminosity Evolution of Trappist-1,"We re-examine the XUV luminosity evolution of TRAPPIST-1 utilizing new
observational constraints (XUV and bolometric luminosity) from multi-epoch
X-ray/UV photometry. Following the formalism presented in Fleming et al.
(2020), we infer that TRAPPIST-1 maintained a saturated XUV luminosity,
relative to the bolometric luminosity, of $\log_{10}$(L$_{\rm XUV}$/L$_{\rm
bol}$) $= -3.03_{-0.23}^{+0.25}$ at early times for a period of $t_{sat} =
3.14_{-1.46}^{+2.22}$ Gyr. After the saturation phase, we find L$_{\rm XUV}$
decayed over time by an exponential rate of $\beta_{\rm XUV} =
-1.17_{-0.28}^{+0.27}$. Compared to our inferred age of the system, ${\rm age}
= 7.96_{-1.87}^{+1.78}$ Gyr, our result for $t_{sat}$ suggests that there is
only a $\sim4\%$~chance that TRAPPIST-1 still remains in the saturated phase
today, which is significantly lower than the previous estimate of 40\%. Despite
this reduction in $t_{sat}$, our results remain consistent in the conclusion
that the TRAPPIST-1 planets likely received an extreme amount XUV energy -- an
estimated integrated XUV energy of $\sim10^{30}-10^{32}$ erg over the star's
lifetime.",2105.12562v1
2021-07-02,Nonlinear intensity dependence of terahertz edge photocurrents in graphene,"We report on the observation of terahertz radiation induced edge
photogalvanic currents in graphene, which are nonlinear in intensity. The
increase of the radiation intensities up to MW/cm$^2$ results in a complex
nonlinear intensity dependence of the photocurrent. The nonlinearity is
controlled by the back gate voltage, temperature and radiation frequency. A
microscopic theory of the nonlinear edge photocurrent is developed. Comparison
of the experimental data and theory demonstrates that the nonlinearity of the
photocurrent is caused by the interplay of two mechanisms, i.e. by direct
inter-band optical transitions and Drude-like absorption. Both photocurrents
saturate at high intensities, but have different intensity dependencies and
saturation intensities. The total photocurrent shows a complex sign-alternating
intensity dependence. The functional behaviour of the saturation intensities
and amplitudes of both kinds of photogalvanic currents depending on gate
voltages, temperature, radiation frequency and polarization is in a good
agreement with the developed theory.",2107.01016v1
2021-07-15,Optical solitons in saturable cubic-quintic nonlinear media with nonlinear dispersion,"We study an intense-short pulse propagation in a saturable cubic-quintic
nonlinear media in the presence of nonlinear dispersion within the framework of
an extended variational approach. We derive an effective equation for the pulse
width and demonstrate how the saturation due to nonlinearity is achieved in
presence of nonlinear dispersion. We find that the nonlinear dispersion can
change the pulse width and induce motion in the system. The direction of
induced motion depends on the sign of nonlinear dispersion. The pulse is
energetically stable at an equilibrium width. A disturbance can, however,
induce oscillation in pulse width, the frequency of which is always smaller due
to nonlinear dispersion. We check dynamical stability by a direct numerical
simulation.",2107.07536v1
2021-07-19,Saturation of Thermal Complexity of Purification,"We purify the thermal density matrix of a free harmonic oscillator as a
two-mode squeezed state, characterized by a squeezing parameter and squeezing
angle. While the squeezing parameter is fixed by the temperature and frequency
of the oscillator, the squeezing angle is otherwise undetermined, so that the
complexity of purification is obtained by minimizing the complexity of the
squeezed state over the squeezing angle. The resulting complexity of the
thermal state is minimized at non-zero values of the squeezing angle and
saturates to an order one number at high temperatures, indicating that there is
no additional operator cost required to build thermal states beyond a certain
temperature. We also review applications in which thermal density matrices
arise for quantum fields on curved spacetimes, including Hawking radiation and
a simple model of decoherence of cosmological density perturbations in the
early Universe. The complexity of purification for these mixed states also
saturates as a function of the effective temperature, which may have
interesting consequences for the quantum information stored in these systems.",2107.08969v1
2021-07-26,Gluon saturation in proton and its contribution to single inclusive soft gluon production in high energy proton-nucleus collisions,"The leading order single inclusive soft gluon production in high energy
proton-nucleus (pA) collisions has been studied by various approaches for more
than two decades. The first correction due to the gluon saturation in proton
was analytically attempted recently through a diagrammatic approach in which
only partial results were obtained. An important feature of the first
saturation correction is that it includes both initial state and final state
interactions. In this paper, we present the complete result derived from the
Color Glass Condensate framework. Our approach is to analytically solve the
classical Yang-Mills equations in the dilute-dense regime and then use the
Lehmann-Symanzik-Zimmermann (LSZ) reduction formula to obtain gluon production
from classical gluon fields.",2107.12338v1
2021-07-28,Widom factors for generalized Jacobi measures,"We study optimal lower and upper bounds for Widom factors $W_{\infty,n}(K,w)$
associated with Chebyshev polynomials for the weights $w(x)=\sqrt{1+x}$ and
$w(x)=\sqrt{1-x}$ on compact subsets of $[-1,1]$. We show which sets saturate
these bounds. We consider Widom factors $W_{2,n}(\mu)$ for $L_2(\mu)$ extremal
polynomials for measures of the form $d\mu(x)=(1-x)^\alpha (1+x)^\beta
d\mu_K(x)$ where $\alpha+\beta\geq 1$, $\alpha,\beta\in\mathbb{N}\cup \{0\}$
and $\mu_K$ is the equilibrium measure of a compact regular set $K$ in $[-1,1]$
with $\pm 1\in K$. We show that for such measures the improved lower bound
$[W_{2,n}(\mu)]^2\geq 2S(\mu)$ holds. For the special cases
$d\mu(x)=(1-x^2)d\mu_K(x)$, $d\mu(x)=(1-x)d\mu_K(x)$, $d\mu(x)=(1+x)d\mu_K(x)$
we determine which sets saturate this lower bound and discuss how saturated
lower bounds for $[W_{2,n}(\mu)]^2$ and $W_{\infty,n}(K,w)$ are related.",2107.13245v1
2021-08-23,Rewrite Rule Inference Using Equality Saturation,"Many compilers, synthesizers, and theorem provers rely on rewrite rules to
simplify expressions or prove equivalences. Developing rewrite rules can be
difficult: rules may be subtly incorrect, profitable rules are easy to miss,
and rulesets must be rechecked or extended whenever semantics are tweaked.
Large rulesets can also be challenging to apply: redundant rules slow down
rule-based search and frustrate debugging. This paper explores how equality
saturation, a promising technique that uses e-graphs to apply rewrite rules,
can also be used to infer rewrite rules. E-graphs can compactly represent the
exponentially large sets of enumerated terms and potential rewrite rules. We
show that equality saturation efficiently shrinks both sets, leading to faster
synthesis of smaller, more general rulesets.
  We prototyped these strategies in a tool dubbed ruler. Compared to a similar
tool built on CVC4, ruler synthesizes 5.8X smaller rulesets 25X faster without
compromising on proving power. In an end-to-end case study, we show
ruler-synthesized rules which perform as well as those crafted by domain
experts, and addressed a longstanding issue in a popular open source tool.",2108.10436v1
2021-08-24,Approximate Petz recovery from the geometry of density operators,"We derive a new bound on the effectiveness of the Petz map as a universal
recovery channel in approximate quantum error correction using the second
sandwiched R\'{e}nyi relative entropy $\tilde{D}_{2}$. For large Hilbert
spaces, our bound implies that the Petz map performs quantum error correction
with order-$\epsilon$ accuracy whenever the data processing inequality for
$\tilde{D}_{2}$ is saturated up to terms of order $\epsilon^2$ times the
inverse Hilbert space dimension. Conceptually, our result is obtained by
extending arXiv:2011.03473, in which we studied exact saturation of the data
processing inequality using differential geometry, to the case of approximate
saturation. Important roles are played by (i) the fact that the exponential of
the second sandwiched R\'{e}nyi relative entropy is quadratic in its first
argument, and (ii) the observation that the second sandwiched R\'{e}nyi
relative entropy satisfies the data processing inequality even when its first
argument is a non-positive Hermitian operator.",2108.10893v4
2021-09-17,Extremal Chaos,"In maximally chaotic quantum systems, a class of out-of-time-order
correlators (OTOCs) saturate the Maldacena-Shenker-Stanford (MSS) bound on
chaos. Recently, it has been shown that the same OTOCs must also obey an
infinite set of (subleading) constraints in any thermal quantum system with a
large number of degrees of freedom. In this paper, we find a unique analytic
extension of the maximally chaotic OTOC that saturates all the subleading chaos
bounds which allow saturation. This extremally chaotic OTOC has the feature
that information of the initial perturbation is recovered at very late times.
Furthermore, we argue that the extremally chaotic OTOC provides a
K\""{a}llen-Lehmann-type representation for all OTOCs. This representation
enables the identification of all analytic completions of maximal chaos as
small deformations of extremal chaos in a precise way.",2109.08693v2
2021-10-04,HDR-cGAN: Single LDR to HDR Image Translation using Conditional GAN,"The prime goal of digital imaging techniques is to reproduce the realistic
appearance of a scene. Low Dynamic Range (LDR) cameras are incapable of
representing the wide dynamic range of the real-world scene. The captured
images turn out to be either too dark (underexposed) or too bright
(overexposed). Specifically, saturation in overexposed regions makes the task
of reconstructing a High Dynamic Range (HDR) image from single LDR image
challenging. In this paper, we propose a deep learning based approach to
recover details in the saturated areas while reconstructing the HDR image. We
formulate this problem as an image-to-image (I2I) translation task. To this
end, we present a novel conditional GAN (cGAN) based framework trained in an
end-to-end fashion over the HDR-REAL and HDR-SYNTH datasets. Our framework uses
an overexposed mask obtained from a pre-trained segmentation model to
facilitate the hallucination task of adding details in the saturated regions.
We demonstrate the effectiveness of the proposed method by performing an
extensive quantitative and qualitative comparison with several state-of-the-art
single-image HDR reconstruction techniques.",2110.01660v2
2021-10-05,Exploring the Limits of Large Scale Pre-training,"Recent developments in large-scale machine learning suggest that by scaling
up data, model size and training time properly, one might observe that
improvements in pre-training would transfer favorably to most downstream tasks.
In this work, we systematically study this phenomena and establish that, as we
increase the upstream accuracy, the performance of downstream tasks saturates.
In particular, we investigate more than 4800 experiments on Vision
Transformers, MLP-Mixers and ResNets with number of parameters ranging from ten
million to ten billion, trained on the largest scale of available image data
(JFT, ImageNet21K) and evaluated on more than 20 downstream image recognition
tasks. We propose a model for downstream performance that reflects the
saturation phenomena and captures the nonlinear relationship in performance of
upstream and downstream tasks. Delving deeper to understand the reasons that
give rise to these phenomena, we show that the saturation behavior we observe
is closely related to the way that representations evolve through the layers of
the models. We showcase an even more extreme scenario where performance on
upstream and downstream are at odds with each other. That is, to have a better
downstream performance, we need to hurt upstream accuracy.",2110.02095v1
2021-10-13,Statistical-mechanical analysis of adaptive filter with clipping saturation-type nonlinearity,"In most practical adaptive signal processing systems, e.g., active noise
control, active vibration control, and acoustic echo cancellation, substantial
nonlinearities that cannot be neglected exist. In this paper, we analyze the
behaviors of an adaptive system in which the output of the adaptive filter has
the clipping saturation-type nonlinearity by a statistical-mechanical method.
We discuss the dynamical and steady-state behaviors of the adaptive system by
asymptotic analysis, steady-state analysis, and numerical calculation. As a
result, it has become clear that the saturation value has the critical point at
which the system's mean-square stability and instability switch. The obtained
theory well explains the strange behaviors around the critical point observed
in the computer simulation. Finally, the exact value of the critical point is
also derived.",2110.06517v5
2021-10-15,Z3RO Precoder Canceling Nonlinear Power Amplifier Distortion in Large Array Systems,"Large array-based transmission uses the combination of a massive number of
antenna elements and clever precoder designs to achieve array gain and
spatially multiplex different users. These precoders require linear front-ends,
and more specifically linear power amplifiers (PAs). However, this reduces
energy efficiency since PAs are most efficient close to saturation, where they
generate most nonlinear distortion. Moreover, the use of conventional
precoders, such as \gls{mrt}, induces a coherent combining of distortion at the
user location, degrading the signal quality. In this work, a linear precoder is
proposed that allows working close to saturation while canceling the coherent
combining of the third order nonlinear \gls{pa} distortion at the user
location. In contrast to other solutions, the zero third-order distortion
(Z3RO) precoder does not require prior knowledge of the signal statistics and
the PA model. The design consists of saturating a single or a few antennas on
purpose together with an opposite phase shift to compensate for the distortion
of all other antennas. The resulting array gain penalty becomes negligible as
the number of base station antennas grows large.",2110.07891v1
2021-12-08,Accessing subnuclear fluctuations and saturation with multiplicity dependent $J/ψ$ production in p+p and p+Pb collisions,"We study the production of $J/\psi$ vector mesons as a function of charged
hadron multiplicity in p+p and p+Pb collisions at LHC energies. We employ the
color glass condensate framework, using running coupling Balitsky-Kovchegov
evolved dipole amplitudes, to compute gluon and $c\bar{c}$-pair production. We
use fragmentation functions to obtain charged hadrons, and explore two
different hadronization schemes for the $J/\psi$: non-relativistic quantum
chromodynamics and the improved color evaporation model. In our framework,
event-by-event multiplicity fluctuations of both hadrons and $J/\psi$ are
driven by geometric and saturation scale normalization fluctuations. Studying
the correlation between $J/\psi$ and hadron multiplicity, we show that the
characteristic difference between forward and backward rapidity in p+Pb
collisions is a result of different degrees of saturation probed at different
rapidities. We demonstrate that experimental data on heavy-flavor production as
a function of event activity provide stringent constraints on the fluctuating
proton structure.",2112.04611v1
2021-12-17,Binomial expansion for saturated and symbolic powers of sums of ideals,"There are two different notions for symbolic powers of ideals existing in the
literature, one defined in terms of associated primes, the other in terms of
minimal primes. Elaborating on an idea known to Eisenbud, Herzog, Hibi, and
Trung, we interpret both notions of symbolic powers as suitable saturations of
the ordinary powers. We prove a binomial expansion formula for saturated powers
of sums of ideals. This gives a uniform treatment to an array of existing and
new results on both notions of symbolic powers of such sums: binomial expansion
formulas, computations of depth and regularity, and criteria for the equality
of ordinary and symbolic powers.",2112.09338v1
2021-12-27,Mathematics of Parking: Varying Parking Rate,"In the classical parking problem, unit intervals (""car lengths"") are placed
uniformly at random without overlapping. The process terminates at saturation,
i.e. until no more unit intervals can be stowed. In this paper, we present a
generalization of this problem in which the unit intervals are placed with an
exponential distribution with rate parameter $\lambda$. We show that the
mathematical expectation of the number of intervals present at saturation
satisfies a certain integral equation. Using Laplace transforms and Tauberian
theorems, we investigate the asymptotic behavior of this function and describe
a way to compute the corresponding limits for large $\lambda$. Then, we derive
another integral equation for the derivative of this function and use it to
compute the above limits for small $\lambda$ with the help of some asymptotic
results for integral equations. We also show that the corresponding limits
converge to the uniform case as $\lambda$ vanishes, yielding the well-known
Renyi constant. Finally, we reveal the asymptotic behavior of the variance of
the intervals at saturation.",2112.13695v1
2022-01-05,Uncertainty in solar wind forcing explains polar cap potential saturation,"Extreme space weather events occur during intervals of strong solar wind
electric fields. Curiously during these intervals, their impact on measures of
the Earth's response, like the polar cap index, is not as high as expected.
Theorists have put forward a host of explanations for this saturation effect,
but there is no consensus. Here we show that the saturation is merely a
perception created by uncertainty in the solar wind measurements, especially in
the measurement times. Correcting for the uncertainty reveals that extreme
space weather events elicit a ~300% larger impact than previously thought.
Furthermore, they point to a surprisingly general result relevant to any
correlation study: uncertainty in the measurement time can cause a system's
linear response to be perceived as non-linear.",2201.02137v1
2022-01-22,The saturation of the VSI in protoplanetary disks via parametric instability,"The vertical shear instability (VSI) is a robust and potentially important
phenomenon in irradiated protoplanetary disks (PPDs), yet the mechanism by
which it saturates remains poorly understood. Global simulations suggest that
the non-linear evolution of the VSI is dominated by radially propagating
inertial wavetrains (called `body modes'), but these are known to be
susceptible to a parametric instability. In this paper, we propose that the
global VSI saturates via this secondary instability, which initiates a
redistribution of energy from the large scales to smaller-scale inertial waves,
and finally into a turbulent cascade. We present an analytic theory of the
instability in a simple idealised model that captures the main physical and
mathematical details of the problem. In addition, we conduct numerical
simulations with the SNOOPY code to consolidate the theory. Once the parametric
instability prevails, the VSI is likely far more disordered and incoherent than
current global simulations suggest. We also argue that it is challenging to
capture parametric instability in global simulations unless the radial
resolution is very fine, possibly $\sim 300$ grid cells per scale height in
radius.",2201.09038v1
2022-01-28,Machine learning-based method of calorimeter saturation correction for helium flux analysis with DAMPE experiment,"DAMPE is a space-borne experiment for the measurement of the cosmic-ray
fluxes at energies up to around 100 TeV per nucleon. At energies above several
tens of TeV, the electronics of DAMPE calorimeter would saturate, leaving
certain bars with no energy recorded. In the present work we discuss the
application of machine learning techniques for the treatment of DAMPE data, to
compensate the calorimeter energy lost by saturation.",2201.12185v3
2022-02-23,Unravelling Saturable Absorption of Thulium-doped Fibres for New Level of Integrated Femtosecond Pulse Generation,"The ultrashort pulse laser operation is crucially defined by engaging
explicit modulators. Conventionally, they are laborious to incorporate into an
all-fibre design or involve the design of sophisticated cavities. We exploit
Thulium-doped fibre as the gain and simple, highly integrated saturable
absorber with a modulation depth of 23% and a high thermal damage threshold.
Hence, pulses as short as 350fs carrying 1nJ energy at a repetition rate of
45MHz have been demonstrated. The laser average output power showed long-term
stability with ~1%. The utilised concept of all-fibre saturable absorber
provides technological grounds for a down-scaled, highly integrated laser
architecture.",2202.11370v1
2022-03-10,Out-of-time-order correlators of nonlocal block-spin and random observables in integrable and nonintegrable spin chains,"Out-of-time-order correlators (OTOC) in the Ising Floquet system, that can be
both integrable and nonintegrable is studied. Instead of localized spin
observables, we study contiguous symmetric blocks of spins or random operators
localized on these blocks as observables. We find only power-law growth of OTOC
in both integrable and nonintegrable regimes. In the non-integrable regime,
beyond the scrambling time, there is an exponential saturation of the OTOC to
values consistent with random matrix theory. This motivates the use of
""pre-scrambled"" random block operators as observables. A pure exponential
saturation of OTOC in both integrable and nonintegrable system is observed,
without a scrambling phase. Averaging over random observables from the Gaussian
unitary ensemble, the OTOC is found to be exactly same as the operator
entanglement entropy, whose exponential saturation has been observed in
previous studies of such spin-chains.",2203.05494v1
2022-03-19,Soft Pomeron in the Colour Glass Condensate approach,"In this paper we suggest a new approach to the structure of the soft Pomeron:
based on the $t$-channel unitarity, we expressed the exchange of the soft
Pomeron through the interaction of the dipole of small size of the order of
$1/Q_s(Y)$ ($Q_s(Y)$ is the saturation momentum) with the hadrons. Therefore,
it is shown that the typical distances in soft processes are small $r \sim
1/Q_s\Lb \h Y \Rb $, where $Y \,=\,ln s$. The saturation momentum, which
determines the energy dependence of the scattering amplitude is proportional to
$ Q^2_s\Lb \h Y \Rb \propto\,\exp\Lb\h \lambda\,Y\Rb$, with $\lambda
\approx\,0.2$, and this behaviour is in perfect agreement with phenomenological
Donnachie-Landshoff Pomeron. We demonstrate that the saturation models could
describe the experimental data for $\sigma_{tot},\sigma_{el},\sigma_{diff} $
and $B_{el}$. Hence our approach is a good first approximation to start
discussion of the soft processes in CGC approach on the solid theoretical
basis.",2203.10296v1
2022-03-25,Quantum thermometry in diffraction-limited systems,"We investigate the ultimate quantum limit of resolving the temperatures of
two thermal sources affected by the diffraction. More quantum Fisher
information can be obtained with the priori information than that without the
priori information. We carefully consider two strategies: the simultaneous
estimation and the individual estimation. The simultaneous estimation of two
temperatures is proved to satisfy the saturation condition of quantum
Cram\'{e}r bound and performs better than the individual estimation in the case
of small degree of diffraction given the same resources. However, in the case
of high degree of diffraction, the individual estimation performs better. In
particular, at the maximum diffraction, the simultaneous estimation can not get
any information, which is supported by a practical measurement, while the
individual estimation can still get the information. In addition, we find that
for the individual estimation, a practical and feasible estimation strategy by
using the full Hermite-Gauss basis can saturate the quantum Cram\'{e}r bound
without being affected by the attenuation factor at the maximum diffraction.
using the full Hermite-Gauss basis can saturate the quantum Cram\'er bound
without being affected by the attenuation factor at the maximum diffraction.",2203.13466v1
2022-03-30,Saturated total-population dependent branching process and viral markets,"Interesting posts are continually forwarded by the users of the online social
network (OSN). Such propagation leads to re-forwarding of the post to some of
the previous recipients, which increases as the post reaches a large number of
users. Consequently, the effective forwards (after deleting the re-forwards)
reduce, eventually leading to the saturation of the total number of copies. We
model this process as a new variant of the branching process, the `saturated
total-population-dependent branching process', and analyse it using the
stochastic approximation technique. Notably, we obtain deterministic
trajectories which approximate the total and unread copies of the post
`asymptotically and almost surely' over any finite time window; this trajectory
depends only on four parameters related to the network characteristics.
Further, we provide expressions for the peak unread copies, maximum outreach
and the life span of the post. We observe known exponential growth but with
time-varying rates. We also validate our theory through detailed simulations on
the SNAP Twitter dataset.",2203.16239v2
2022-04-07,The saturation problem for refined Littlewood-Richardson coefficients,"Given partitions $\lambda,\mu,\nu$ with at most $n$ nonzero parts and a
permutation $w \in S_n$, the refined Littlewood-Richardson coefficient
$c_{\lambda \mu}^\nu(w)$ is the multiplicity of the irreducible $GL_n
\mathbb(C)$ module $V(\nu)$ in the so-called Kostant-Kumar submodule
$K(\lambda, w, \mu)$ of the tensor product $V(\lambda) \otimes V(\mu)$. We
derive a hive model for these coefficients and prove that the saturation
property holds if $w$ is $312$-avoiding, $231$-avoiding or a commuting product
of such elements. This generalizes the classical Knutson-Tao saturation
theorem.",2204.03399v1
2022-04-18,Securing Signal-free Intersections against Strategic Jamming Attacks: A Macroscopic Approach,"We consider the security-by-design of a signal-free intersection for
connected and autonomous vehicles in the face of strategic jamming attacks. We
use a fluid model to characterize macroscopic traffic flow through the
intersection, where the saturation rate is derived from a vehicle coordination
algorithm. We model jamming attacks as sudden increase in communication latency
induced on vehicle-to-infrastructure connectivity; such latency triggers the
safety mode for vehicle coordination and thus reduces the intersection
saturation rate. A strategic attacker selects the attacking rate, while a
system operator selects key design parameters, either the saturation rate or
the recovery rate. Both players' actions induce technological costs and jointly
determine the mean travel delay. By analyzing the equilibrium of the security
game, we study the preferable level of investment in the intersection's nominal
discharging capability or recovery capability.",2204.08187v2
2022-05-10,Machine learning and atomic layer deposition: predicting saturation times from reactor growth profiles using artificial neural networks,"In this work we explore the application of deep neural networks to the
optimization of atomic layer deposition processes based on thickness values
obtained at different points of an ALD reactor. We introduce a dataset designed
to train neural networks to predict saturation times based on the dose time and
thickness values measured at different points of the reactor for a single
experimental condition. We then explore different artificial neural network
configurations, including depth (number of hidden layers) and size (number of
neurons in each layers) to better understand the size and complexity that
neural networks should have to achieve high predictive accuracy. The results
obtained show that trained neural networks can accurately predict saturation
times without requiring any prior information on the surface kinetics. This
provides a viable approach to minimize the number of experiments required to
optimize new ALD processes in a known reactor. However, the datasets and
training procedure depend on the reactor geometry.",2205.08378v1
2022-05-27,Rotational level spacings in HD from vibrational saturation spectroscopy,"The R(1), R(3) and P(3) ro-vibrational transitions in the (2-0) overtone band
of the HD molecule are measured in Doppler-free saturation using the technique
of NICE-OHMS spectroscopy. For the P(3) line, hitherto not observed in
saturation, we report a frequency of $203\,821\,936\,805\,(60)$ kHz. The
dispersive line shapes observed in the three spectra show strong correlations,
allowing for extraction of accurate information on rotational level spacings.
This leads to level spacings of $\Delta_{(J=3)-(J=1)}= 13\,283\,245\,098\,(30)$
kHz in the $v=0$ ground state, and $\Delta_{(J=4)-(J=2)}=
16\,882\,368\,179\,(20)$ kHz in the $v=2$ excited vibration in HD. These
results show that experimental values for the rotational spacings are
consistently larger than those obtained with advanced ab initio theoretical
calculations at 1.5$\sigma$, where the uncertainty is determined by theory. The
same holds for the vibrational transitions where systematic deviations of
1.7-1.9$\sigma$ are consistently found for the five lines accurately measured
in the (2-0) band.",2205.13877v1
2022-06-21,New possibilities in identification of binary choice models with fixed effects,"We study the identification of binary choice models with fixed effects. We
provide a condition called sign saturation and show that this condition is
sufficient for the identification of the model. In particular, we can guarantee
identification even with bounded regressors. We also show that without this
condition, the model is not identified unless the error distribution belongs to
a small class. The same sign saturation condition is also essential for
identifying the sign of treatment effects. A test is provided to check the sign
saturation condition and can be implemented using existing algorithms for the
maximum score estimator.",2206.10475v4
2022-07-05,On the two-point function of the Potts model in the saturation regime,"We consider the Random-Cluster model on $\mathbb{Z}^d$ with interactions of
infinite range of the form $J_x = \psi(x)\mathsf{e}^{-\rho(x)}$ with $\rho$ a
norm on $\mathbb{Z}^d$ and $\psi$ a subexponential correction. We first provide
an optimal criterion ensuring the existence of a nontrivial saturation regime
(that is, the existence of $\beta_{\rm sat}(s)>0$ such that the inverse
correlation length in the direction $s$ is constant on $[0,\beta_{\rm
sat}(s))$), thus removing a regularity assumption used in a previous work of
ours. Then, under suitable assumptions, we derive sharp asymptotics (which are
not of Ornstein-Zernike form) for the two-point function in the whole
saturation regime $(0,\beta_{\rm sat}(s))$. We also obtain a number of
additional results for this class of models, including sharpness of the phase
transition, mixing above the critical temperature and the strict monotonicity
of the inverse correlation length in $\beta$ in the regime $(\beta_{\rm
sat}(s), \beta_{\rm c})$.",2207.02193v2
2022-07-15,Exact antichain saturation numbers via a generalisation of a result of Lehman-Ron,"For given positive integers $k$ and $n$, a family $\mathcal{F}$ of subsets of
$\{1,\dots,n\}$ is $k$-antichain saturated if it does not contain an antichain
of size $k$, but adding any set to $\mathcal{F}$ creates an antichain of size
$k$. We use sat$^*(n, k)$ to denote the smallest size of such a family. For all
$k$ and sufficiently large $n$, we determine the exact value of sat$^*(n, k)$.
Our result implies that sat$^*(n, k)=n(k-1)-\Theta(k\log k)$, which confirms
several conjectures on antichain saturation. Previously, exact values for
sat$^*(n,k)$ were only known for $k$ up to $6$.
  We also prove a generalisation of a result of Lehman-Ron which may be of
independent interest. We show that given $m$ disjoint chains in the Boolean
lattice, we can create $m$ disjoint skipless chains that cover the same
elements (where we call a chain skipless if any two consecutive elements differ
in size by exactly one).",2207.07391v2
2022-07-15,Krylov complexity from integrability to chaos,"We apply a notion of quantum complexity, called ""Krylov complexity"", to study
the evolution of systems from integrability to chaos. For this purpose we
investigate the integrable XXZ spin chain, enriched with an integrability
breaking deformation that allows one to interpolate between integrable and
chaotic behavior. K-complexity can act as a probe of the integrable or chaotic
nature of the underlying system via its late-time saturation value that is
suppressed in the integrable phase and increases as the system is driven to the
chaotic phase. We furthermore ascribe the (under-)saturation of the late-time
bound to the amount of disorder present in the Lanczos sequence, by mapping the
complexity evolution to an auxiliary off-diagonal Anderson hopping model. We
compare the late-time saturation of K-complexity in the chaotic phase with that
of random matrix ensembles and find that the chaotic system indeed approaches
the RMT behavior in the appropriate symmetry class. We investigate the
dependence of the results on the two key ingredients of K-complexity: the
dynamics of the Hamiltonian and the character of the operator whose time
dependence is followed.",2207.07701v2
2022-07-25,Fluctuation of Chern Numbers in a Parametric Random Matrix Model,"Band-touching Weyl points in Weyl semimetals give rise to many novel
characteristics, one of which the presence of surface Fermi-arc states that is
topologically protected. The number of such states can be computed by the Chern
numbers at different momentum slices, which fluctuates with changing momentum
and depends on the distribution of Weyl points in the Brillouin zone. For
realistic systems, it may be difficult to locate the momenta at which these
Weyl points and Fermi-arc states appear. Therefore, we extend the analysis of a
parametric random matrix model proposed by Walker and Wilkinson to find the
statistics of their distributions. Our numerical data shows that Weyl points
with opposite polarities are short range correlated, and the Chern number
fluctuation only grows linearly for a limited momentum difference before it
saturates. We also find that the saturation value scales with the total number
of bands. We then compute the short-range correlation length from perturbation
theory, and derive the dependence of the Chern number fluctuation on the
momentum difference, showing that the saturation results from the short-range
correlation.",2207.12562v1
2022-07-28,Saturation of Rogue Wave Amplification over Steep Shoals,"The shoaling of surface gravity waves has been acknowledged as a mechanism of
rogue wave formation. This problem is generally reduced to water waves passing
over a step, but non-equilibrium physics allows finite slopes to be considered.
Using non-homogeneous spectral analysis of a spatially varying energy density
ratio we describe the dependence of the amplification as a function of the
slope steepness. Increasing the slope increases the amplification of rogue wave
probability, until this amplification saturates at steep slopes. In contrast,
the increase of the down slope of a subsequent de-shoal zone leads to a
monotonic decrease in the rogue wave probability, thus featuring a strong
asymmetry between shoaling and de-shoaling zones. Due to the saturation of the
rogue wave amplification at steep slopes, our model is applicable beyond its
range of validity up to a step, thus elucidating why previous models based on a
step could describe the physics of steep finite slopes. We also explain why the
rogue wave probability increases over a shoal while it is lower in shallower
water.",2207.13869v3
2022-08-26,Saturation of multidimensional 0-1 matrices,"A 0-1 matrix $M$ is saturating for a 0-1 matrix $P$ if $M$ does not contain a
submatrix that can be turned into $P$ by flipping any number of its $1$-entries
to $0$-entries, and changing any $0$-entry to $1$-entry of $M$ introduces a
copy of $P$. Matrix $M$ is semisaturating for $P$ if changing any $0$-entry to
$1$-entry of $M$ introduces a new copy of $P$, regardless of whether $M$
originally contains $P$ or not. The functions $ex(n;P)$ and $sat(n;P)$ are the
maximum and minimum possible number of $1$-entries a $n\times n$ 0-1 matrix
saturating for $P$ can have, respectively. Function $ssat(n;P)$ is the minimum
possible number of $1$-entries a $n\times n$ 0-1 matrix semisaturating for $P$
can have.
  Function $ex(n;P)$ has been studied for decades, while investigation on
$sat(n;P)$ and $ssat(n;P)$ was initiated recently. In this paper, we make
nontrivial generalization of results regarding these functions to
multidimensional 0-1 matrices. In particular, we find the exact values of
$ex(n;P,d)$ and $sat(n;P,d)$ when $P$ is a $d$-dimensional identity matrix.
Then we give the necessary and sufficient condition for a multidimensional 0-1
matrix to have bounded semisaturation function.",2208.12682v1
2022-08-28,Classical information entropy of parton distribution functions and an application in finding gluon saturation,"Entropy or information is a fundamental quantity contained in a system in
statistical mechanics and information theory. In this paper, a definition of
classical information entropy of parton distribution functions is suggested.
The extensive and supper-additive properties of the defined entropy are
discussed. The concavity is also deduced for the defined entropy. As an
example, the classical information entropy of the gluon distribution of the
proton is presented. There are some particular features of the evolution of the
information entropy in the saturating domain, which can be used in finding the
signals of gluon saturation.",2208.13151v4
2022-09-05,Competition between phonon mediated superconductivity and carriers localization in field-effect doped molybdenum dichalcogenides,"Superconductivity occurs in electrochemically doped molybdenum
dichalcogenides samples thicker than four layers. While the critical
temperature (Tc) strongly depends on the field effect geometry (single or
double gate) and on the sample (MoS2 or MoSe2), Tc always saturates at high
doping. The pairing mechanism and the complicate dependence of Tc on doping,
samples and field-effect geometry are currently not understood. Previous
theoretical works assumed homogeneous doping of a single layer and attributed
the Tc saturation to a charge density wave instability, however the calculated
values of the electron-phonon coupling in the harmonic approximation were one
order of magnitude larger than the experimental estimates based on transport
data. Here, by performing fully relativistic first principles calculations
accounting for the sample thickness, the field-effect geometry and
anharmonicity, we rule out the occurrence of charge density waves in the
experimental doping range and demonstrate a suppression of one order of
magnitude in the electron-phonon coupling, now in excellent agreement with
transport data. By solving the anisotropic Migdal-Eliashberg equations, we
explain the behaviour of Tc in different systems and geometries. From an
analysis of mobility data, we propose that the Tc saturation is due to carriers
localization and disorder.",2209.01973v1
2022-09-06,On the saturation of late-time growth of complexity in supersymmetric JT gravity,"In this work we use the modified replica trick, proposed in arXiv:2205.01150,
to compute the late time behaviour of complexity for JT gravity with ${\cal N}
= 1$ and ${\cal N} = 2$ supersymmetries. For the ${\cal N} = 1$ theory, we
compute the late time behaviour of complexity defined by the ``quenched
geodesic length"" and obtain the expected saturation of complexity at time $t
\sim e^{S_0}$, to a constant value with time-independent variance. For the
${\cal N} = 2$ theory, we explicitly compute complexity at the disk level which
yields the late-time linear growth of complexity. However, we comment on the
expectation of the late-time saturation by speculating the trumpet partition
function and the non-perturbative corrections to the spectral correlation,
relevant for the late-time behaviour of complexity. Furthermore, we compute the
matter correlation functions for both the theories.",2209.02441v2
2022-09-07,Small Proofs from Congruence Closure,"Satisfiability Modulo Theory (SMT) solvers and equality saturation engines
must generate proof certificates from e-graph-based congruence closure
procedures to enable verification and conflict clause generation. Smaller proof
certificates speed up these activities. Though the problem of generating proofs
of minimal size is known to be NP-complete, existing proof minimization
algorithms for congruence closure generate unnecessarily large proofs and
introduce asymptotic overhead over the core congruence closure procedure. In
this paper, we introduce an O(n^5) time algorithm which generates optimal
proofs under a new relaxed ""proof tree size"" metric that directly bounds proof
size. We then relax this approach further to a practical O(n \log(n)) greedy
algorithm which generates small proofs with no asymptotic overhead. We
implemented our techniques in the egg equality saturation toolkit, yielding the
first certifying equality saturation engine. We show that our greedy approach
in egg quickly generates substantially smaller proofs than the state-of-the-art
Z3 SMT solver on a corpus of 3760 benchmarks.",2209.03398v1
2022-09-09,The fractional saturable impurity,"We examine analytically and numerically the effect of fractionality on a
saturable bulk and surface impurity embedded in a 1D lattice. We use a
fractional Laplacian introduced previously by us, and by the use of lattice
Green functions we are able to obtain the bound state energies and amplitude
profiles, as a function of the fractional exponent $s$ and saturable impurity
strength $\chi$ for both, surface and bulk impurity. The transmission is
obtained in closed form as a function of $s$ and $\chi$, showing strong
deviations from the standard case, at small fractional exponent values. The
selftrapping of an initially-localized excitation is qualitatively similar for
the bulk and surface mode, but in all cases complete confinement is obtained at
$s\rightarrow 0$, as shown theoretically and observed numerically.",2209.04074v1
2022-10-04,A Fuzzy Logic-based Cascade Control without Actuator Saturation for the Unmanned Underwater Vehicle Trajectory Tracking,"An intelligent control strategy is proposed to eliminate the actuator
saturation problem that exists in the trajectory tracking process of unmanned
underwater vehicles (UUV). The control strategy consists of two parts: for the
kinematic modeling part, a fuzzy logic-refined backstepping control is
developed to achieve control velocities within acceptable ranges and errors of
small fluctuations; on the basis of the velocities deducted by the improved
kinematic control, the sliding mode control (SMC) is introduced in the dynamic
modeling to obtain corresponding torques and forces that should be applied to
the vehicle body. With the control velocities computed by the kinematic model
and applied forces derived by the dynamic model, the robustness and accuracy of
the UUV trajectory without actuator saturation can be achieved.",2210.01706v1
2022-10-10,Decreasing ultrafast X-ray pulse durations with saturable absorption and resonant transitions,"Saturable absorption is a nonlinear effect where a material's ability to
absorb light is frustrated due to a high influx of photons and the creation of
electron vacancies. Experimentally induced saturable absorption in copper
revealed a reduction in the temporal duration of transmitted X-ray laser
pulses, but a complete understanding of this process is still missing. In this
computational work, we employ non-local thermodynamic equilibrium plasma
simulations to study the interaction of femtosecond X-rays and copper.
Following the onset of frustrated absorption, we find that a $K\text{--}M$
resonant transition occurring at highly charged states turns copper opaque
again. The changes in absorption generate a transient transparent window
responsible for the shortened transmission signal. We also propose using
fluorescence induced by the incident beam as an alternative source to achieve
shorter X-ray pulses. Intense femtosecond X-ray pulses are valuable to probe
the structure and dynamics of biological samples or to reach extreme states of
matter. Shortened pulses could be relevant for emerging imaging techniques.",2210.04938v1
2022-10-11,Components of $V(ρ) \otimes V(ρ)$ and dominant weight polyhedra for affine Kac-Moody Lie algebras,"Kostant asked the following question: Let $\mathfrak{g}$ be a simple Lie
algebra over the complex numbers. Let $\lambda$ be a dominant integral weight.
Then, $V(\lambda)$ is a component of $V(\rho)\otimes V(\rho)$ if and only if
$\lambda \leq 2 \rho$ under the usual Bruhat-Chevalley order on the set of
weights. In an earlier work with R. Chirivi and A. Maffei the second author
gave an affirmative answer to this question up to a saturation factor. The aim
of the current work is to extend this result to untwisted affine Kac-Moody Lie
algebra $\mathfrak{g}$ associated to any simple Lie algebra
$\mathring{\mathfrak{g}}$ (up to a saturation factor). In fact, we prove the
result for affine $sl_n$ without any saturation factor. Our proof requires some
additional techniques including the Goddard-Kent-Olive construction and study
of the characteristic cone of non-compact polyhedra.",2210.05473v2
2022-10-19,Saturation level of turbulence in collapsing gas clouds,"We investigate the physical mechanism that decides the saturation level of
turbulence in collapsing gas clouds. We perform a suite of high-resolution
numerical simulations following the collapse of turbulent gas clouds with
various effective polytropic exponents $\gamma_{\rm eff}$, initial Mach numbers
$\mathcal{M}_0$, and initial turbulent seeds. Equating the energy injection
rate by gravitational contraction and the dissipation rate of turbulence, we
obtain an analytic expression of the saturation level of turbulence, and
compare it with the numerical results. Consequently, the numerical results are
well described by the analytic model, given that the turbulent driving scale in
collapsing gas clouds is one-third of Jeans length of collapsing core. These
results indicate that the strength of turbulence at the first core formation in
the early universe/present-day star-formation process can be estimated solely
by $\gamma_{\rm eff}$.",2210.10299v1
2022-10-20,Spectral analysis of multidimensional current-driven plasma instabilities and turbulence in hollow cathode plumes,"Large-amplitude current-driven instabilities in hollow cathode plumes can
generate energetic ions responsible for cathode sputtering and spacecraft
degradation. A 2D2V (two dimensions each in configuration [D] and velocity [V]
spaces) grid-based Vlasov--Poisson (direct kinetic) solver is used to study
their growth and saturation, which comprises four stages: linear growth,
quasilinear resonance, nonlinear fill-in, and saturated turbulence. The linear
modal growth rate, nonlinear saturation process, and ion velocity and energy
distribution features in the turbulent regime are analyzed. Backstreaming ions
are generated for large electron drifts, several ion acoustic periods after the
potential field becomes turbulent. Interscale phase-space transfer and locality
are analyzed for the Vlasov equation. The multidimensional study sheds light on
the interactions between longitudinal and transverse plasma instabilities, as
well as the inception of plasma turbulence.",2210.11056v2
2022-10-28,Freedom near Lightcone and ANEC Saturation,"Averaged Null Energy Conditions (ANECs) hold in unitary quantum field
theories. In conformal field theories, ANECs in states created by the
application of the stress tensor to the vacuum lead to three constraints on the
stress-tensor three-point couplings, depending on the choice of polarization.
The same constraints follow from considering two-point functions of the stress
tensor in a thermal state and focusing on the contribution of the stress tensor
in the operator product expansion (OPE). One can observe this in holographic
Gauss-Bonnet gravity, where ANEC saturation coincides with the appearance of
superluminal signal propagation in thermal states. We show that, when this
happens, the corresponding generalizations of ANECs for higher-spin
multi-stress tensor operators with minimal twist are saturated as well and all
contributions from such operators to the thermal two-point functions vanish in
the lightcone limit. This leads to a special near-lightcone behavior of the
thermal stress-tensor correlators -- they take the vacuum form, independent of
temperature.",2210.16274v3
2022-11-15,Molecular $P_ψ$ pentaquarks from light-meson exchange saturation,"Theoretical predictions for the spectrum of heavy meson-baryon bound states
are a fundamental tool for disentangling the nature of the different pentaquark
states that have been observed in experimental facilities. Here we explore this
spectrum in a phenomenological model that describes the heavy meson-baryon
interaction in terms of a contact-range interaction, where the coupling
strength is saturated by the exchange of light scalar and vector mesons, i.e.
$\sigma$, $\rho$ and $\omega$ exchanges. Saturation determines the couplings
modulo an unknown proportionality constant that can be calibrated from a
molecular candidate. If we use the $P_{\psi}^N(4312)$ as input, we predict a
series of molecular pentaquarks including the $P_{\psi}^N(4440)$ and
$P_{\psi}^N(4457)$, the recent $P_{\psi s}^{\Lambda}(4338)$ and the $P_{\psi
s}^{\Lambda}(4459)$.",2211.08211v1
2022-11-20,Safe Control Under Input Limits with Neural Control Barrier Functions,"We propose new methods to synthesize control barrier function (CBF)-based
safe controllers that avoid input saturation, which can cause safety
violations. In particular, our method is created for high-dimensional, general
nonlinear systems, for which such tools are scarce. We leverage techniques from
machine learning, like neural networks and deep learning, to simplify this
challenging problem in nonlinear control design. The method consists of a
learner-critic architecture, in which the critic gives counterexamples of input
saturation and the learner optimizes a neural CBF to eliminate those
counterexamples. We provide empirical results on a 10D state, 4D input
quadcopter-pendulum system. Our learned CBF avoids input saturation and
maintains safety over nearly 100% of trials.",2211.11056v1
2022-11-28,Inverse saturable absorption mechanism and design optimization of mode-locked fiber lasers with a nonlinear amplifying loop mirror,"From the point of view of the differential phase delay experienced by the two
counterpropagating optical fields, the self-starting of the mode-locked fiber
laser with a nonlinear amplifying loop mirror (NALM) is theoretically studied.
Although it is generally believed that NALM shows a saturable absorption effect
on both continuous wave (CW) light and pulses, we find a counter-intuitive fact
that cross-phase modulation (XPM) leads to opposite signs of differential
nonlinear phase shifts (NPSs) in these two cases, resulting in inverse
saturable absorption (ISA) during pulse formation process. The ISA is not
helpful for the self-starting of laser mode-locking and can be alleviated by
introducing a non-reciprocal phase shifter into the fiber loop. In addition, we
analyze the influences of gain-fiber position, splitting ratio, and optical
attenuator in the fiber loop, on the differential NPS and self-starting
process. These results are helpful for optimizing the design of NALM and
lowering the self-starting threshold of the high-repetition-rate mode-locked
fiber laser.",2211.15150v1
2022-12-04,Enhanced intrinsic voltage gain in artificially stacked bilayer CVD graphene field effect transistors,"We report on electronic transport in dual-gate, artificially stacked bilayer
graphene field effect transistors (BiGFETs) fabricated from large-area chemical
vapor deposited (CVD) graphene. The devices show enhanced tendency to current
saturation, which leads to reduced minimum output conductance values. This
results in improved intrinsic voltage gain of the devices when compared to
monolayer graphene FETs. We employ a physics based compact model originally
developed for Bernal stacked bilayer graphene FETs (BSBGFETs) to explore the
observed phenomenon. The improvement in current saturation may be attributed to
increased charge carrier density in the channel and thus reduced saturation
velocity due to carrier-carrier scattering.",2212.01877v1
2022-12-12,Physics-preserving IMPES based multiscale methods for immiscible two-phase flow in highly heterogeneous porous media,"In this paper, we propose a physics-preserving multiscale method to solve an
immiscible two-phase flow problem, which is modeled as a coupling system
consisting of Darcy's law and mass conservation equations. We use a new
Physics-preserving IMplicit Pressure Explicit Saturation (P-IMPES) scheme in
order to maintain the local conservation of mass for both phases. Besides, this
scheme is unbiased and if the time step is smaller than a certain value, the
saturation of both phases are bounds-preserving. When updating velocity,
MGMsFEM serves as an efficient solver by computing the unknowns on a coarse
grid. We follow the operation splitting techinque to deal with the two-phase
flow. In particular, we use an upwind strategy to iterate the saturation
explicitly and the MGMsFEM is utilized to compute velocity with a decoupled
system on a coarse mesh. To show the efficiency and robustness of the proposed
method, we design a set of interesting experiments. A rigorous analysis is also
included to serve as a theoretical base of the method, which is well verified
by the numerical results. Both simulations and analysis indicate that the
method attains a good balance between accuracy and computation cost.",2212.05942v1
2022-12-17,A Thermodynamic Treatment\\ of Partially Saturated Soils \\ Revealing the Structure of Effective Stress,"A rigorous thermodynamic treatment of partially saturated soils is developed
using a minimal number of assumptions. The derivation is carried out in a way
that does not require to explicitly track the complex shapes of interfaces
between the solid, fluid and gas domains. Instead, suction is the property
being recovered explicitly through the minimisation of energy around an ideal
`suctionless limit', while considering the different compressibilities of the
three domains. In interpreting experimental data the derivation ensures the
thermodynamic equilibrium between the chemical potentials of the soil and
measurement cells, while carefully distinguishing intrinsic from measured
pressures and suctions. A most general expression for the effective stress of
partially saturated soils is then derived that is strictly linked to the
soil-water retention curve (SWRC). The structure of the effective stress
broadly depends on the three thermodynamic densities characterising the solid,
fluid and gas domains. Special cases of SWRC are explored, which reveals
conditions for which the structure of the effective stress may agree with
previously proposed empirical relationships.",2212.08868v1
2022-12-22,"Scaling, saturation, and upper bounds in the failure of topologically interlocked structures","Topological Interlocking Structures (TIS) have been increasingly studied in
the past two decades. However, some fundamental questions concerning the
effects of Young's modulus and the friction coefficient on the structural
mechanics of the most common type of TIS application - centrally loaded slabs -
are not yet clear. Here, we present a first-of-its-kind parametric study based
on the Level-Set-Discrete-element-Method that aims to clarify how these two
parameters affect multiple aspects of the behavior and failure of
centrally-loaded TIS slabs. This includes the evolution of the structural
response up to and including failure, the foremost structural response
parameters, and the residual carrying capacity. We find that the structural
response parameters in TIS slabs scale linearly with Young's modulus, that they
saturate with the friction coefficient, and that the saturated response
provides an upper-bound on the capacity of centrally loaded TIS slabs reported
in the literature. This, together with additional findings, insights, and
observations, comprise a novel contribution to our understanding of the
interlocked structural form.",2212.11554v1
2022-12-28,Examination of saturation coverage of polygons using random sequential adsorption algorithm,"The goal of random sequential adsorption (RSA), a time-dependent packing
method, is to create a regular or asymmetric covering of an empty space that
can fit in the allocated space without overlapping. The density of coverage
tends to reach a limit in the infinite-time limit. We attempt to estimate
saturated packing of oriented 2-D polygons, including squares(4-sides), regular
pentagons (5-sides), regular hexagons (6-sides), regular heptagons (7-sides),
regular octagons (8-sides), regular nonagons (9-sides), regular decagons
(10-sides), and regular dodecagons (12-sides), in this study. We obtained
results that are consistent with previous, extrapolation-based studies1. We
utilised the ""separating axis theorem"" to determine if there is overlap between
arriving polygons and those that have previously been placed. Saturation as a
lower limit is considered to have been reached when RSA addition becomes
excessively slow, according to us.",2212.13849v2
2023-01-04,Saturation of fishbone instability by self-generated zonal flows in tokamak plasmas,"Gyrokinetic simulations of the fishbone instability in DIII-D tokamak plasmas
find that self-generated zonal flows can dominate the nonlinear saturation by
preventing coherent structures from persisting or drifting in the energetic
particle phase space when the mode frequency down-chirps. Results from the
simulation with zonal flows agree quantitatively, for the first time, with
experimental measurements of the fishbone saturation amplitude and energetic
particle transport. Moreover, the fishbone-induced zonal flows are likely
responsible for the formation of an internal transport barrier that was
observed after fishbone bursts in this DIII-D experiment. Finally, gyrokinetic
simulations of a related ITER baseline scenario show that the fishbone induces
insignificant energetic particle redistribution and may enable high performance
scenarios in ITER burning plasma experiments.",2301.01792v4
2023-01-30,High-Density behavior of symmetry energy and speed of sound in the dense matter within an effective chiral model,"With an effective chiral model, we investigate how the mesonic cross
couplings $\sigma-\rho$ and $\omega-\rho$ affect the density content of the
symmetry energy and its higher-order slope parameters. Earlier mentioned
cross-couplings are crucial to controlling the density content of symmetry
energy. For this purpose, we did a case study for different values of the
symmetry energy $J_1$, defined at density 0.1 fm$^{-3}$ in the range (23.4 -
25.2) for a fixed value of the slope of the symmetry energy $L_0 = 60$ MeV at
saturation density and investigate its effect on the higher-order coefficients
and their influence on the underlying equation of state. We found that the
model with $J_1= 24.6$ MeV is more favorable with the pure neutron matter (PNM)
constraints obtained from $\chi$EFT calculations. In addition, we show that all
of our models predict a monotonically increasing speed of sound up to four
times the saturation density. The speed of sound decreases/saturates above that
point and approaches the conformal limit approximately $\sqrt{1/3}~c$ at the
center of the maximum mass star.",2301.12690v1
2023-02-13,Complexity growth for one-dimensional free-fermionic lattice models,"Complexity plays a very important part in quantum computing and simulation
where it acts as a measure of the minimal number of gates that are required to
implement a unitary circuit. We study the lower bound of the complexity
[Eisert, Phys. Rev. Lett. 127, 020501 (2021)] for the unitary dynamics of the
one-dimensional lattice models of non-interacting fermions. We find
analytically using quasiparticle formalism, the bound grows linearly in time
and followed by a saturation for short-ranged tight-binding Hamiltonians. We
show numerical evidence that for an initial Neel state the bound is maximum for
tight-binding Hamiltonians as well as for the long-range hopping models.
However, the increase of the bound is sub-linear in time for the later, in
contrast to the linear growth observed for short-range models. The upper bound
of the complexity in non-interacting fermionic lattice models is calculated,
which grows linearly in time even beyond the saturation time of the lower
bound, and finally, it also saturates.",2302.06305v3
2023-03-10,Indirect Adaptive Optimal Control in the Presence of Input Saturation,"In this paper, we propose a combined Magnitude Saturated Adaptive Control
(MSAC)-Model Predictive Control (MPC) approach to linear quadratic tracking
optimal control problems with parametric uncertainties and input saturation.
The proposed MSAC-MPC approach first focuses on a stable solution and parameter
estimation, and switches to MPC when parameter learning is accomplished. We
show that the MSAC, based on a high-order tuner, leads to parameter convergence
to true values while providing stability guarantees. We also show that after
switching to MPC, the optimality gap is well-defined and proportional to the
parameter estimation error. We demonstrate the effectiveness of the proposed
MSAC-MPC algorithm through a numerical example based on a linear second-order,
two input, unstable system.",2303.06221v1
2023-03-12,Scale-aware Two-stage High Dynamic Range Imaging,"Deep high dynamic range (HDR) imaging as an image translation issue has
achieved great performance without explicit optical flow alignment. However,
challenges remain over content association ambiguities especially caused by
saturation and large-scale movements. To address the ghosting issue and enhance
the details in saturated regions, we propose a scale-aware two-stage high
dynamic range imaging framework (STHDR) to generate high-quality ghost-free HDR
image. The scale-aware technique and two-stage fusion strategy can
progressively and effectively improve the HDR composition performance.
Specifically, our framework consists of feature alignment and two-stage fusion.
In feature alignment, we propose a spatial correct module (SCM) to better
exploit useful information among non-aligned features to avoid ghosting and
saturation. In the first stage of feature fusion, we obtain a preliminary
fusion result with little ghosting. In the second stage, we conflate the
results of the first stage with aligned features to further reduce residual
artifacts and thus improve the overall quality. Extensive experimental results
on the typical test dataset validate the effectiveness of the proposed STHDR in
terms of speed and quality.",2303.06575v1
2023-03-17,Comment on arXiv:2210.01114: Optical Saturation Produces Spurious Evidence for Photoinduced Superconductivity in K$_3$C$_{60}$,"In the manuscript arXiv:2210.01114, Dodge and co-authors discuss the
influence of pump-probe profile deformations on the reconstructed
non-equilibrium optical conductivity of K$_3$C$_{60}$. They state that when
pump-induced saturation of the probe response is taken into account, the
reconstructed optical properties are not superconducting-like, as was claimed
in a number of experimental reports by our group. We show here that the
conclusion reached by Dodge et al. is unjustified. In fact, independent of the
specific model, including the problematic saturation profile proposed by the
authors, the reconstructed optical properties are those of a finite temperature
superconductor. The true fingerprint of superconductivity, which is the
$1/\omega$ divergence of the imaginary conductivity, $\sigma_{2}(\omega)$, is
retained and is virtually independent of the chosen model. The only
model-dependent feature is the degree of gapping in $\sigma_{1}(\omega)$. In
all cases the extracted optical properties reflect the presence of residual
quasiparticles, which at finite temperatures are inevitably present alongside
the superfluid.",2303.10169v1
2023-03-25,Inverted loss engineering in functional material covered waveguides,"Optical waveguides, covered with thin films, which transmittance can be
controlled by external action, are widely used in various applications from
optical modulators to saturable absorbers. It is natural to suggest that the
waveguide losses will be proportional to the covering material absorption. We
demonstrate that under certain conditions this simple assumption fails.
Instead, we observe the reduction of the film material absorption can lead to
an increase in the waveguide propagation losses. For this, we use a side
polished fiber covered with a single-walled carbon nanotube thin film whose
absorption is attenuated either due to saturable absorption or electrochemical
gating. For the films thicker than 50 nm, we observe saturable absorption to
turn into light induced absorption with nonmonotonic dependence on the incident
power. With a numerical simulation and analytical approach, we identify that
this nontrivial behavior comes from mode reshaping and predict required
parameters for its observation.",2303.14512v1
2023-03-30,Stability analysis of an SIR model with saturated infection rate and saturated treatment rate,"Treatment rate has always been one of the most important factors affecting
the spread of infectious diseases. In this paper, we study a treatment function
SIR model with treatment rate related to the maximum treatment capacity, whose
infection rate is also saturated nonlinear. By calculating and analyzing based
on planar dynamic system, the existence and stability of disease-free
equilibrium point of the model are found. And it is also found that the
situation is more complex for the endemic equilibrium point of the model. Under
the conditions of meeting different parameters, the number of endemic
equilibrium points may be zero, one or two, and the behavior of the endemic
equilibrium point may be a saddle point, a stable or unstable anti-saddle point
or center, or even a degenerate case.",2303.17298v1
2023-03-31,A flatness-based saturated controller design for a quadcopter with experimental validation,"Using the properties of differential flatness, a controllable system, such as
a quadcoper model, may be transformed into a linear equivalent system via a
coordinate change and an input mapping. This is a straightforward advantage for
the quadcopter's controller design and its real-time implementation. However,
one significant hindrance is that, while the dynamics become linear in the new
coordinates (the flat output space), the input constraints become convoluted.
This paper addresses an explicit pre-stabilization based control scheme which
handles the input constraints for the quadcopter in the flat output space with
a saturation component. The system's stability is shown to hold by
Lyapunov-stability arguments. Moreover, the practical viability of the proposed
method is validated both in simulation and experiments over a nano-drone
platform. Hence, the flatness-based saturated controller not only ensures
stability and constraints satisfaction, but also requires very low
computational effort, allowing for embedded implementations.",2303.18021v1
2023-03-31,Pathologies in satisfaction classes,"We study subsets of countable recursively saturated models of $\mathsf{PA}$
which can be defined using pathologies in satisfaction classes. More precisely,
we characterize those subsets $X$ such that there is a satisfaction class $S$
where $S$ behaves correctly on an idempotent disjunction of length $c$ if and
only if $c \in X$. We generalize this result to characterize several types of
pathologies including double negations, blocks of extraneous quantifiers, and
binary disjunctions and conjunctions. We find a surprising relationship between
the cuts which can be defined in this way and arithmetic saturation: namely, a
countable nonstandard model is arithmetically saturated if and only if every
cut can be the ""idempotent disjunctively correct cut"" in some satisfaction
class. We describe the relationship between types of pathologies and the
closure properties of the cuts defined by these pathologies.",2303.18069v1
2023-05-28,Josephson parametric amplifier with Chebyshev gain profile and high saturation,"We demonstrate a Josephson parametric amplifier design with a band-pass
impedance matching network based on a third-order Chebyshev prototype. We
measured eight amplifiers operating at 4.6 GHz that exhibit gains of 20 dB with
less than 1 dB gain ripple and up to 500 MHz bandwidth. The amplifiers further
achieve high output saturation powers around -73 dBm based on the use of
rf-SQUID arrays as their nonlinear element. We characterize the system readout
efficiency and its signal-to-noise ratio near saturation using a Sycamore
processor, finding the data consistent with near quantum limited noise
performance of the amplifiers. In addition, we measure the amplifiers'
intermodulation distortion in two-tone experiments as a function of input power
and inter-tone detuning, and observe excess distortion at small detuning with a
pronounced dip as a function of signal power, which we interpret in terms of
power-dependent dielectric losses.",2305.17816v1
2023-06-21,Analysis of a Crank-Nicolson finite difference scheme for (2+1)D perturbed nonlinear Schrödinger equations with saturable nonlinearity,"We analyze a Crank-Nicolson finite difference discretization for the
perturbed (2+1)D nonlinear Schr\""odinger equation with saturable nonlinearity
and a perturbation of cubic loss. We show the boundedness, the existence and
uniqueness of a numerical solution. We establish the error bound to prove the
convergence of the numerical solution. Moreover, we find that the convergence
rate is at the second order in both time step and spatial mesh size under a
mild assumption. The numerical scheme is validated by the extensive simulations
of the (2+1)D saturable nonlinear Schr\""odinger model with cubic loss. The
simulations for travelling solitons are implemented by using an accelerated
imaginary-time evolution scheme and the Crank-Nicolson finite difference
method.",2306.12287v1
2023-06-22,ACC Saturator: Automatic Kernel Optimization for Directive-Based GPU Code,"Automatic code optimization is a complex process that typically involves the
application of multiple discrete algorithms that modify the program structure
irreversibly. However, the design of these algorithms is often monolithic, and
they require repetitive implementation to perform similar analyses due to the
lack of cooperation. To address this issue, modern optimization techniques,
such as equality saturation, allow for exhaustive term rewriting at various
levels of inputs, thereby simplifying compiler design.
  In this paper, we propose equality saturation to optimize sequential codes
utilized in directive-based programming for GPUs. Our approach simultaneously
realizes less computation, less memory access, and high memory throughput. Our
fully-automated framework constructs single-assignment forms from inputs to be
entirely rewritten while keeping dependencies and extracts optimal cases.
Through practical benchmarks, we demonstrate a significant performance
improvement on several compilers. Furthermore, we highlight the advantages of
computational reordering and emphasize the significance of memory-access order
for modern GPUs.",2306.13002v2
2023-06-30,Upscaling and Effective Behavior for Two-Phase Porous-Medium Flow using a Diffuse Interface Model,"We investigate two-phase flow in porous media and derive a two-scale model,
which incorporates pore-scale phase distribution and surface tension into the
effective behavior at the larger Darcy scale. The free-boundary problem at the
pore scale is modeled using a diffuse interface approach in the form of a
coupled Allen-Cahn Navier-Stokes system with an additional momentum flux due to
surface tension forces. Using periodic homogenization and formal asymptotic
expansions, a two-scale model with cell problems for phase evolution and
velocity contributions is derived. We investigate the computed effective
parameters and their relation to the saturation for different fluid
distributions, in comparison to commonly used relative permeability saturation
curves. The two-scale model yields non-monotone relations for relative
permeability and saturation. The strong dependence on local fluid distribution
and effects captured by the cell problems highlights the importance of
incorporating pore-scale information into the macro-scale equations.",2306.17644v1
2023-07-18,Partially Saturated Granular Flow in a Rotating Drum: The Role of Cohesion,"Partially saturated granular flows are common in various natural and
industrial processes, such as landslides, mineral handling, and food
processing. We conduct experiments and apply the Discrete Element Method (DEM)
to study granular flows in rotating drums under partially saturated conditions.
We focus on varying the strength of cohesion (surface tension) and rotation
rate within the modes of rolling flow and cascading flow. With an increase in
surface tension, a rolling mode can possess a steeper slope and correspondingly
needs a higher rotation rate to transition to a cascading. The depth of the
flowing region increases with increasing cohesion, while the sensitivity is
reduced for cases of high cohesion. We propose a dimensionless number CE that
captures the combined effects of rotation, gravity and cohesion on the dynamic
angle of repose and flow depth. In addition, we extract statistical information
on the formation of clusters within the flow. We find a power law relation
between the cluster size distribution and its probability, which indicates that
stronger cohesion can promote the formation of larger clusters, and we discuss
how cohesion impact on flows manifested by cluster formation.",2307.09682v1
2023-07-19,On the equivalence between squeezing and entanglement potential for two-mode Gaussian states,"The maximum amount of entanglement achievable under passive transformations
by continuous-variable states is called the entanglement potential. Recent work
has demonstrated that the entanglement potential is upper-bounded by a simple
function of the squeezing of formation, and that certain classes of two-mode
Gaussian states can indeed saturate this bound, though saturability in the
general case remains an open problem. In this study, we introduce a larger
class of states that we prove saturates the bound, and we conjecture that all
two-mode Gaussian states can be passively transformed into this class, meaning
that for all two-mode Gaussian states, entanglement potential is equivalent to
squeezing of formation. We provide an explicit algorithm for the passive
transformations and perform extensive numerical testing of our claim, which
seeks to unite the resource theories of two characteristic quantum properties
of continuous-variable systems.",2307.10386v1
2023-07-20,Hybrid FEM and peridynamic simulation of hydraulic fracture propagation in saturated porous media,"This paper presents a hybrid modeling approach for simulating hydraulic
fracture propagation in saturated porous media: ordinary state-based
peridynamics is used to describe the behavior of the solid phase, including the
deformation and crack propagation, while FEM is used to describe the fluid flow
and to evaluate the pore pressure. Classical Biot poroelasticity theory is
adopted. The proposed approach is first verified by comparing its results with
the exact solutions of two examples. Subsequently, a series of pressure- and
fluid-driven crack propagation examples are solved and presented. The
phenomenon of fluid pressure oscillation is observed in the fluid-driven crack
propagation examples, which is consistent with previous experimental and
numerical evidences. All the presented examples demonstrate the capability of
the proposed approach in solving problems of hydraulic fracture propagation in
saturated porous media.",2307.10929v1
2023-07-20,Numerical simulation of forerunning fracture in saturated porous solids with hybrid FEM/Peridynamic model,"In this paper, a novel hybrid FEM and Peridynamic modeling approach proposed
in Ni et al. (2020) is used to predict the dynamic solution of hydro-mechanical
coupled problems. A modified staggered solution algorithm is adopted to solve
the coupled system. A one-dimensional dynamic consolidation problem is solved
first to validate the hybrid modeling approach, and both -convergence and
-convergence studies are carried out to determine appropriate discretization
parameters for the hybrid model. Thereafter, dynamic fracturing in a
rectangular dry/fully saturated structure with a central initial crack is
simulated both under mechanical loading and fluid-driven conditions. In the
mechanical loading fracture case, fixed surface pressure is applied on the
upper and lower surfaces of the initial crack near the central position to
force its opening. In the fluid-driven fracture case, the fluid injection is
operated at the centre of the initial crack with a fixed rate. Under the action
of the applied external force and fluid injection, forerunning fracture
behavior is observed both in the dry and saturated conditions.",2307.11121v1
2023-07-31,Confidence Interval and Uncertainty Propagation Analysis of SAFT-type Equations of State,"Thermodynamic models and, in particular, SAFT-type equations are vital in
characterizing complex systems. This paper presents a framework for sampling
parameter distributions in PC-SAFT and SAFT-VR Mie equations of state to
understand parameter confidence intervals and correlations. We identify
conserved quantities contributing to significant correlations. Comparing the
equations of state, we find that additional parameters introduced in the
SAFT-VR Mie equation increase relative uncertainties (1\%-2\% to 3\%-4\%) and
introduce more correlations. When incorporating association through additional
parameters, relative uncertainties increase, but correlations slightly
decrease. We investigate how uncertainties propagate to derived properties and
observe small uncertainties for that data with which the parameters were
regressed, especially for saturated-liquid volumes. However, extrapolating to
saturated-vapour volumes yields larger uncertainties due to the larger
isothermal compressibility. Near the critical point, uncertainties in saturated
volumes diverge due to increased sensitivity of the isothermal compressibility
to parameter uncertainties. This effect significantly impacts bulk properties,
particularly isobaric heat capacity, where uncertainties near the critical
point become extremely large, even when these uncertainties are small. We
emphasize that even small uncertainties near the critical point lead to
divergences in predicted properties.",2308.00171v1
2023-08-29,Not all that is $β_0$ is $β$-function: the DGLAP resummation and the running coupling in NLO JIMWLK,"We reanalyze the origin of the large transverse logarithms associated with
the QCD one loop beta-function coefficient in the NLO JIMWLK Hamiltonian. We
show that some of these terms are not associated with the running of the QCD
coupling constant but rather with the DGLAP evolution. The DGLAP-like
resummation of these logarithms is mandatory within the JIMWLK Hamiltonian, as
long as the color correlation length in the projectile is larger than that in
the target. This regime in fact covers the whole range of rapidities at which
JIMWLK evolution is supposed to be applicable. We derive the RG equation that
resums these logarithms to all orders in alpha_s in the JIMWLK Hamiltonian.
This is a nonlinear equation for the eikonal scattering matrix S(x). We solve
this equation and perform the DGLAP resummation in two simple cases: the dilute
limit, where both the projectile and the target are far from saturation, and
the saturated regime, where the target correlation length also determines its
saturation momentum.",2308.15545v1
2023-09-01,A Semi-classical Spacetime Region with Maximum Entropy,"We consider a 4D spherically-symmetric static finite spacetime region as a
collection of quanta in the semi-classical Einstein equation and study the
entropy including the self-gravity. For sufficiently excited states, we
estimate the entropy in a WKB-like method considering local consistency with
thermodynamics and find its upper bound. The saturation condition uniquely
determines the entropy-maximized spacetime as a radially uniform dense
configuration with near-Planckian curvatures and a surface just outside the
Schwarzschild radius. The interior metric is a non-perturbative solution in
$\hbar$, leading to the species bound. The maximum entropy then saturates the
Bousso bound and coincides with the Bekenstein-Hawking formula. Thus, the
Bousso bound in this class of spacetime is verified by constructing the
saturating configuration that has no horizon and stores information inside.",2309.00602v3
2023-09-05,Bound-preserving discontinuous Galerkin methods for compressible two-phase flows in porous media,"This paper presents a numerical study of immiscible, compressible two-phase
flows in porous media, that takes into account heterogeneity, gravity,
anisotropy, and injection/production wells. We formulate a fully implicit
stable discontinuous Galerkin solver for this system that is accurate, that
respects the maximum principle for the approximation of saturation, and that is
locally mass conservative. To completely eliminate the overshoot and undershoot
phenomena, we construct a flux limiter that produces bound-preserving
elementwise average of the saturation. The addition of a slope limiter allows
to recover a pointwise bound-preserving discrete saturation. Numerical results
show that both maximum principle and monotonicity of the solution are
satisfied. The proposed flux limiter does not impact the local mass error and
the number of nonlinear solver iterations.",2309.01908v1
2023-09-07,Chasing Consistency in Text-to-3D Generation from a Single Image,"Text-to-3D generation from a single-view image is a popular but challenging
task in 3D vision. Although numerous methods have been proposed, existing works
still suffer from the inconsistency issues, including 1) semantic
inconsistency, 2) geometric inconsistency, and 3) saturation inconsistency,
resulting in distorted, overfitted, and over-saturated generations. In light of
the above issues, we present Consist3D, a three-stage framework Chasing for
semantic-, geometric-, and saturation-Consistent Text-to-3D generation from a
single image, in which the first two stages aim to learn parameterized
consistency tokens, and the last stage is for optimization. Specifically, the
semantic encoding stage learns a token independent of views and estimations,
promoting semantic consistency and robustness. Meanwhile, the geometric
encoding stage learns another token with comprehensive geometry and
reconstruction constraints under novel-view estimations, reducing overfitting
and encouraging geometric consistency. Finally, the optimization stage benefits
from the semantic and geometric tokens, allowing a low classifier-free guidance
scale and therefore preventing oversaturation. Experimental results demonstrate
that Consist3D produces more consistent, faithful, and photo-realistic 3D
assets compared to previous state-of-the-art methods. Furthermore, Consist3D
also allows background and object editing through text prompts.",2309.03599v1
2023-09-12,Exceptional point proximity-driven mode-locking in coupled microresonators,"We show theoretically and numerically that mode-locking is feasible with a
coupled-cavity system with gain and loss, notably, without any natural
saturable absorber. We highlight that in the vicinity of the exceptional point,
system $Q$ exhibits substantial modulation even with minor refractive index
changes and a minimal Kerr effect contribution. Leveraging this unique
behaviour, we propose an unprecedented approach wherein the lossy auxiliary
cavity functions as an efficient artificial saturable absorber, thus
facilitating mode-locking. This approach is not only novel, but also presents
considerable advantages over conventional systems where both gain and saturable
absorption are contained within a single microcavity. These benefits include
reduced operational power and ease of post-adjustment, achievable through the
manipulation of the coupling strength between the two microcavities.",2309.05912v1
2023-09-20,Insights into neutron star equation of state by machine learning,"Due to its powerful capability and high efficiency in big data analysis,
machine learning has been applied in various fields. We construct a neural
network platform to constrain the behaviors of the equation of state of nuclear
matter with respect to the properties of nuclear matter at saturation density
and the properties of neutron stars. It is found that the neural network is
able to give reasonable predictions of parameter space and provide new hints
into the constraints of hadron interactions. As a specific example, we take the
relativistic mean field approximation in a widely accepted Walecka-type model
to illustrate the feasibility and efficiency of the platform. The results show
that the neural network can indeed estimate the parameters of the model at a
certain precision such that both the properties of nuclear matter around
saturation density and global properties of neutron stars can be saturated. The
optimization of the present modularly designed neural network and extension to
other effective models are straightforward.",2309.11227v1
2023-09-30,Optimal Local Measurements in Many-body Quantum Metrology,"Quantum measurements are key to quantum metrology. Constrained by
experimental capabilities, collective measurements on a large number of copies
of metrological probes can pose significant challenges. Therefore, the locality
in quantum measurements must be considered. In this work, we propose a method
dubbed as the ""iterative matrix partition"" approach to elucidate the underlying
structures of optimal local measurements, with and without classical
communications, that saturate the quantum Cram\'er-Rao Bound (qCRB).
Furthermore, we find that while exact saturation is possible for all two-qubit
pure states, it is generically restrictive for multi-qubit pure states.
However, we demonstrate that the qCRB can be universally saturated in an
approximate manner through adaptive coherent controls, as long as the initial
state is separable and the Hamiltonian allows for interaction. Our results
bridge the gap between theoretical proposals and experiments in many-body
metrology and can find immediate applications in noisy intermediate-scale
quantum devices.",2310.00285v1
2023-09-30,Optimal Control of Grid-Interfacing Inverters With Current Magnitude Limits,"Grid-interfacing inverters act as the interface between renewable resources
and the electric grid, and have the potential to offer fast and programmable
controls compared to synchronous generators. With this flexibility there has
been significant research efforts into determining the best way to control
these inverters. Inverters are limited in their maximum current output in order
to protect semiconductor devices, presenting a nonlinear constraint that needs
to be accounted for in their control algorithms. Existing approaches either
simply saturate a controller that is designed for unconstrained systems, or
assume small perturbations and linearize a saturated system. These approaches
can lead to stability issues or limiting the control actions to be too
conservative.
  In this paper, we directly focus on a nonlinear system that explicitly
accounts for the saturation of the current magnitude. We use a Lyapunov
stability approach to determine a stability condition for the system,
guaranteeing that a class of controllers would be stabilizing if they satisfy a
simple SDP condition. With this condition we fit a linear-feedback controller
by sampling the output (offline) model predictive control problems. This
learned controller has improved performances with existing designs.",2310.00473v2
2023-10-07,A Polynomial Upper Bound for Poset Saturation,"Given a finite poset $\mathcal P$, we say that a family $\mathcal F$ of
subsets of $[n]$ is $\mathcal P$-saturated if $\mathcal F$ does not contain an
induced copy of $\mathcal P$, but adding any other set to $\mathcal F$ creates
an induced copy of $\mathcal P$. The induced saturation number of $\mathcal P$,
denoted by $\text{sat}^*(n,\mathcal P)$, is the size of the smallest $\mathcal
P$-saturated family with ground set $[n]$. In this paper we prove that the
saturation number for any given poset grows at worst polynomially. More
precisely, we show that $\text{sat}^*(n, \mathcal P)=O(n^c)$, where
$c\leq|\mathcal{P}|^2/4+1$ is a constant depending on $\mathcal P$ only. We
obtain this result by bounding the VC-dimension of our family.",2310.04634v1
2023-10-20,Transfer systems for rank two elementary Abelian groups: characteristic functions and matchstick games,"We prove that Hill's characteristic function $\chi$ for transfer systems on a
lattice $P$ surjects onto interior operators for $P$. Moreover, the fibers of
$\chi$ have unique maxima which are exactly the saturated transfer systems. In
order to apply this theorem in examples relevant to equivariant homotopy
theory, we develop the theory of saturated transfer systems on modular
lattices, ultimately producing a ``matchstick game'' that puts saturated
transfer systems in bijection with certain structured subsets of covering
relations. After an interlude developing a recursion for transfer systems on
certain combinations of bounded posets, we apply these results to determine the
full lattice of transfer systems for rank two elementary Abelian groups.",2310.13835v1
2023-10-22,Characterizing the heterogeneity of membrane liquid-ordered domains,"We use a lattice model of a ternary mixture containing saturated and
unsaturated lipids with cholesterol (Chol), to study the structural properties
characterizing the coexistence between the liquid-disordered and liquid-ordered
phases. Depending on the affinity of the saturated and unsaturated lipids, the
system may exhibit macroscopic (thermodynamic) liquid-liquid phase separation,
or be divided into small-size liquid-ordered domains surrounded by a
liquid-disordered matrix. In both cases, it is found that the nano-scale
structure of the liquid-ordered regions is heterogeneous, and that they are
partitioned into Chol-rich sub-domains and Chol-free, gel-like, nano-clusters.
This emerges as a characteristic feature of the liquid-ordered state, which
helps distinguishing between liquid-ordered domains in a two-phase mixture, and
similar-looking domains in a one-phase mixture that are rich in saturated
lipids and Chol, but are merely thermal density fluctuations. The
nano-structure heterogeneity of the liquid-ordered phase can be detected by
suitable experimental spectroscopic methods, and is observed also in atomistic
computer simulations.",2310.14316v1
2023-11-03,Forward dijet production at the LHC within an impact parameter dependent TMD approach,"We investigate possible signatures of gluon saturation using forward $p+A \to
j+j+X$ di-jet production processes at the Large Hadron Collider. In the forward
rapidity region, this is a highly asymmetric process where partons with large
longitudinal momentum fraction \(x\) in the dilute projectile are used as a
probe to resolve the small \(x\) partonic content of the dense target. Such
dilute-dense processes can be described in the factorization framework of
Improved Transverse Momentum Distributions (ITMDs). We present a new model for
ITMDs where we explicitly introduce the impact parameter (\(b\)) dependence in
the ITMDs, to properly account for the nuclear enhancement of gluon saturation
effects, and discuss the phenomenological consequences for $p-Pb$, $p-Xe$ and
$p-O$ collisions at the LHC. While the case of $p-p$ and $e-p$ collisions is
used to fix the model parameters, we find that, on average, the nuclear
enhancement of the saturation scale is noticeably weaker than expected from
naive scaling with a simple dependence on the atomic number. Since our model
explicitly accounts for event-by-event fluctuations of the nuclear geometry, it
can also be applied to study forward central correlations in $p-A$ collisions.",2311.01965v2
2023-11-28,Transverse Energy-Energy Correlators in the Color-Glass Condensate at the Electron-Ion Collider,"We investigate the transverse energy-energy correlators (TEEC) in the
small-$x$ regime at the upcoming Electron-Ion Collider (EIC). Focusing on the
back-to-back production of electron-hadron pairs in both $ep$ and $eA$
collisions, we establish a factorization theorem given in terms of the hard
function, quark distributions, soft functions, and TEEC jet functions, where
the gluon saturation effect is incorporated. Numerical results for TEEC in both
$ep$ and $eA$ collisions are presented, together with the nuclear modification
factor $R_A$. Our analysis reveals that TEEC observables in deep inelastic
scattering provide a valuable approach for probing gluon saturation phenomena.
Our findings underscore the significance of measuring TEEC at the EIC,
emphasizing its efficacy in advancing our understanding of gluon saturation and
nuclear modifications in high-energy collisions.",2311.17142v1
2023-12-06,Low-momentum relativistic nucleon-nucleon potentials I: Nuclear matter,"A series of relativistic one-boson-exchange potentials for two-nucleon
system, denoted as OBEP$\Lambda$, is constructed with a momentum cutoff
$\Lambda$ ranging from $\infty$ to 2 fm$^{-1}$. These potentials are developed
by simultaneous fitting to nucleon-nucleon ($NN$) scattering phase shifts,
low-energy scattering length, effective range, and the binding energy of the
deuteron. The momentum-space matrix elements of the low-momentum OBEP$\Lambda$
($\Lambda\leqslant 3$ fm$^{-1}$) demonstrate consistency with the universal
behaviors observed in other realistic $NN$ potentials evolved by
renormalization group methods. These OBEP$\Lambda$s are applied to calculate
the equation of state of symmetric nuclear matter (SNM) within either the
nonrelativistic (NR) Brueckner-Hartree-Fock (BHF) or relativistic
Brueckner-Hartree-Fock (RBHF) frameworks. The results show that the saturation
properties of SNM are reproduced qualitatively from the RBHF calculation, but
not from the NR-BHF calculation. This study highlights the relativistic
mechanism in explaining the saturation properties of nuclear matter. The
remaining discrepancy in reproducing empirical saturation properties in the
RBHF calculation using the OBEP$\Lambda$s signals the necessity of including
three-nucleon correlations or genuine three-nucleon forces.",2312.03403v1
2023-12-07,Direct data-driven control of input saturated systems: a LMI-based approach,"In this paper, we revisit three intricate control challenges in the context
of input-saturated systems, adopting a direct data-driven perspective.
Diverging from the traditional two-stage process involving system
identification and model-based control, our approach dispenses with the need
for an explicit model description. By harnessing a combination of data-based
closed-loop representation, Lyapunov theory, instrumental variables, and a
generalized sector condition, we formulate data-driven linear matrix
inequalities (LMIs). These LMIs are employed to maximize the basin of
attraction, minimize the closed-loop reachable set with bounded disturbances,
and propose a new data-driven $\ell_2$-gain minimization. Through
demonstrations on benchmark examples, we shed light on the merits and
limitations of transitioning from indirect to direct design strategies for
input-saturated plants, emphasizing notable advantages in handling nonlinear
dynamics.",2312.04272v2
2023-12-12,Purcell enhanced emission and saturable absorption of cavity-coupled CsPbBr$_3$ quantum dots,"Halide perovskite semiconductors have emerged as promising materials for the
development of solution-processed, scalable, high performance optoelectronic
devices such as light-emitting diodes (LEDs) as well as coherent single photon
emitters. Their integration to nanophotonic cavities for radiative enhancement
and strong nonlinearity is underexplored. In this work, we demonstrate
cavity-enhanced emission and saturable absorption using colloidal CsPbBr$_3$
perovskite quantum dots coupled to a high-Q cavity mode of a circular Bragg
grating structure designed to facilitate integration of solution-processed
materials . We achieve an order of magnitude increase in brightness and 8-fold
increase in the spontaneous emission rate for the cavity-coupled emitters. This
result indicates the possibility of achieving transform-limited photon
coherence for the halide perovskites at cryogenic temperatures. We also observe
saturable absorption of the emitters through intensity-dependent cavity quality
factor. These results pave the way towards achieving improved photon
indistinguishability and strong optical nonlinearities for cavity coupled
perovskite systems.",2312.07800v1
2023-12-24,On corrugation mode radial wavelengths of the vertical shear instability,"The vertical shear instability (VSI) is a promising mechanism to drive
turbulence in protoplanetary disks. Numerical simulations in the literature
demonstrate that the VSI non-linear saturation is predominated by the linear
corrugation modes. These modes possess vertical wavelengths crucially longer
than radial wavelengths. This paper aims to investigate the natural radial
wavelength of corrugation modes upon VSI saturation, by a series of numerical
simulations conducted in Athena++ at different grid resolutions, disk aspect
ratios, and viscosity parameterized by $\nu$. We find a sign of convergence
emerges at 64 cells per gas scale height for fiducial simulations, below which
a continuous reduction of wavelengths with grid resolution is observed.
Synthetic ALMA molecular line observations of $^{12}\rm CO(2-1)$ are performed
to inspect the observability of the corrugation modes feature, which is
significantly diminished with more than 32 cells per scale height. Flared and
viscous disks, exhibiting longer saturation wavelengths, may mitigate the
observational difficulty.",2312.15414v2
2023-12-26,Sliding Mode Control for 3-D Uncalibrated and Constrained Vision-based Shape Servoing within Input Saturation,"This paper designs a servo control system based on sliding mode control for
the shape control of elastic objects. In order to solve the effect of
non-smooth and asymmetric control saturation, a Gaussian-based continuous
differentiable asymmetric saturation function is used for this goal. The
proposed detection approach runs in a highly real-time manner. Meanwhile, this
paper uses sliding mode control to prove that the estimation stability of the
deformation Jacobian matrix and the system stability of the controller are
combined, which verifies the control stability of the closed-loop system
including estimation. Besides, an integral sliding mode function is designed to
avoid the need for second-order derivatives of variables, which enhances the
robustness of the system in actual situations. Finally, the Lyapunov theory is
used to prove the consistent final boundedness of all variables of the system.",2312.16048v1
2024-01-21,Weak rainbow saturation numbers of graphs,"For a fixed graph $H$, we say that an edge-colored graph $G$ is \emph{weakly
$H$-rainbow saturated} if there exists an ordering $e_1, e_2, \ldots, e_m$ of
$E\left(\overline{G}\right)$ such that, for any list $c_1, c_2, \ldots, c_m$ of
pairwise distinct colors from $\mathbb{N}$, the non-edges $e_i$ in color $c_i$
can be added to $G$, one at a time, so that every added edge creates a new
rainbow copy of $H$. The \emph{weak rainbow saturation number} of $H$, denoted
by $rwsat(n,H)$, is the minimum number of edges in a weakly $H$-rainbow
saturated graph on $n$ vertices. In this paper, we show that for any non-empty
graph $H$, the limit $\lim_{n\to \infty} \frac{rwsat(n, H)}{n}$ exists. This
answers a question of Behague, Johnston, Letzter, Morrison and Ogden [{\it SIAM
J. Discrete Math.} (2023)]. We also provide lower and upper bounds on this
limit, and in particular, we show that this limit is nonzero if and only if $H$
contains no pendant edges.",2401.11525v1
2024-01-30,Coherent $γ^*$-nucleus scattering and coherent nuclear states,"In the context of a McLerran-Venugopalan (MV) model for a large nucleus,
coherent scattering of a virtual photon on that nucleus is evaluated in the
$A_-=0$ gauge, the gauge appropriate for the target nucleus. The evaluation of
the scattering in $A_-=0$ gauge is very intricate compared to the usual $A_+=0$
gauge evaluation natural for the scattering process, but has the advantage of
directly giving the scattering in terms of a partonic description of the
nucleus. In the limit where a tagged forward jet puts the dipole-nucleus
scattering in the saturation regime the coherent reactions are equal to the
inelastic reactions. In terms of the nuclear wave function the coherent
reactions come from color singlet and zero total transverse momentum
quark-antiquark pairs in the wave function and in the saturation regime the
nuclear wave function is a coherent state for these pairs. In the saturation
region half of all quarks (or antiquarks) come from zero momentum and color
charge pairs.",2401.17087v1
2024-02-21,Linearity of the co-moving velocity,"The co-moving velocity is a new variable in the description of immiscible
two-phase flow in porous media. It is the saturation-weighted average over the
derivatives of the seepage velocities of the two immiscible fluids with respect
to saturation. Based on analysis of relative permeability data and
computational modeling, it has been proposed that the co-moving velocity is
linear when plotted against the derivative of the average seepage velocity with
respect to the saturation, the flow derivative. I show here that it is enough
to demand that the co-moving velocity is characterized by an additive parameter
in addition to the flow derivative to be linear. This has profound consequences
for relative permeability theory as it leads to a differential equation
relating the two relative permeabilities describing the flow. I present this
equation together with two solutions.",2402.13826v2
2024-02-23,Logarithmic A$_{\rm inf}$-cohomology,"We extend the construction of A$_{\rm inf}$-cohomology by
Bhatt-Morrow-Scholze to the context of log $p$-adic formal schemes over a log
perfectoid base. In particular, using coordinates, we prove comparison theorems
between log A$_{\rm inf}$-cohomology with other $p$-adic cohomology theories,
including log de Rham, log (q-)crystalline, log prismatic, and Kummer \'etale
cohomology, as well as the derived A$_{\rm inf}$-cohomology of certain infinite
root stacks. Along the way, we define and give a combinatorial characterization
of a new class of maps between saturated log schemes, called pseudo-saturated
maps, which is of independent interest. They are related to (and slightly
weaker than) the notion of quasi-saturated maps and maps of Cartier type
studied by Tsuji.",2402.15154v1
2024-02-23,Safety-Conscious Pushing on Diverse Oriented Surfaces with Underactuated Aerial Vehicles,"Pushing tasks performed by aerial manipulators can be used for contact-based
industrial inspections. Underactuated aerial vehicles are widely employed in
aerial manipulation due to their widespread availability and relatively low
cost. Industrial infrastructures often consist of diverse oriented work
surfaces. When interacting with such surfaces, the coupled gravity compensation
and interaction force generation of underactuated aerial vehicles can present
the potential challenge of near-saturation operations. The blind utilization of
these platforms for such tasks can lead to instability and accidents, creating
unsafe operating conditions and potentially damaging the platform. In order to
ensure safe pushing on these surfaces while managing platform saturation, this
work establishes a safety assessment process. This process involves the
prediction of the saturation level of each actuator during pushing across
variable surface orientations. Furthermore, the assessment results are used to
plan and execute physical experiments, ensuring safe operations and preventing
platform damage.",2402.15243v1
2024-02-29,Getting Saturated with Induction,"Induction in saturation-based first-order theorem proving is a new exciting
direction in the automation of inductive reasoning. In this paper we survey our
work on integrating induction directly into the saturation-based proof search
framework of first-order theorem proving. We describe our induction inference
rules proving properties with inductively defined datatypes and integers. We
also present additional reasoning heuristics for strengthening inductive
reasoning, as well as for using induction hypotheses and recursive function
definitions for guiding induction. We present exhaustive experimental results
demonstrating the practical impact of our approach as implemented within
Vampire.
  This is an extended version of a Principles of Systems Design 2022 paper with
the same title and the same authors.",2402.18954v1
2024-02-29,Program Synthesis in Saturation,"We present an automated reasoning framework for synthesizing recursion-free
programs using saturation-based theorem proving. Given a functional
specification encoded as a first-order logical formula, we use a first-order
theorem prover to both establish validity of this formula and discover program
fragments satisfying the specification. As a result, when deriving a proof of
program correctness, we also synthesize a program that is correct with respect
to the given specification. We describe properties of the calculus that a
saturation-based prover capable of synthesis should employ, and extend the
superposition calculus in a corresponding way. We implemented our work in the
first-order prover Vampire, extending the successful applicability of
first-order proving to program synthesis.
  This is an extended version of an Automated Deduction -- CADE 29 paper with
the same title and the same authors.",2402.18962v1
2024-03-14,Compactness of quantics tensor train representations of local imaginary-time propagators,"Space-time dependence of imaginary-time propagators, vital for \textit{ab
initio} and many-body calculations based on quantum field theories, has been
revealed to be compressible using Quantum Tensor Trains (QTTs) [Phys. Rev. X
{\bf 13}, 021015 (2023)]. However, the impact of system parameters, like
temperature, on data size remains underexplored. This paper provides a
comprehensive numerical analysis of the compactness of local imaginary-time
propagators in QTT for one-time/-frequency objects and two-time/-frequency
objects, considering truncation in terms of the Frobenius and maximum norms. We
employ random pole models to study worst-case scenarios. The numerical analysis
reveals several key findings. For one-time/-frequency objects and
two-time/-frequency objects, the bond dimensions saturate at low temperatures,
especially for truncation in terms of the Frobenius norm. We provide
counting-number arguments for the saturation of bond dimensions for the
one-time/-frequency objects, while the origin of this saturation for
two-time/-frequency objects remains to be clarified. This paper's findings
highlight the critical need for further research on the selection of truncation
methods, tolerance levels, and the choice between imaginary-time and
imaginary-frequency representations in practical applications.",2403.09161v1
2024-03-22,Proper Rainbow Saturation Numbers for Cycles,"We say that an edge-coloring of a graph $G$ is proper if every pair of
incident edges receive distinct colors, and is rainbow if no two edges of $G$
receive the same color. Furthermore, given a fixed graph $F$, we say that $G$
is rainbow $F$-saturated if $G$ admits a proper edge-coloring which does not
contain any rainbow subgraph isomorphic to $F$, but the addition of any edge to
$G$ makes such an edge-coloring impossible. The maximum number of edges in a
rainbow $F$-saturated graph is the rainbow Tur\'an number, whose study was
initiated in 2007 by Keevash, Mubayi, Sudakov, and Verstra\""ete. Recently,
Bushaw, Johnston, and Rombach introduced study of a corresponding saturation
problem, asking for the minimum number of edges in a rainbow $F$-saturated
graph. We term this minimum the proper rainbow saturation number of $F$,
denoted $\mathrm{sat}^*(n,F)$. We asymptotically determine
$\mathrm{sat}^*(n,C_4)$, answering a question of Bushaw, Johnston, and Rombach.
We also exhibit constructions which establish upper bounds for
$\mathrm{sat}^*(n,C_5)$ and $\mathrm{sat}^*(n,C_6)$.",2403.15602v1
2009-08-10,Tunnel magnetoresistance of magnetic junctions with cubic symmetry of the layers,"A tunnel magnetic junction is considered with magnetic hard and magnetic soft
layers of cubic symmetry. The magnetic switching is analyzed of the layers by a
magnetic field perpendicular to the initial magnetizations. In such a
situation, an additional peak of the TMR ratio appears at the magnetic field
value lower substantially than the anisotropy energy of the soft layer.",0908.1278v1
2014-09-03,Photo-induced Magnetic Force Between Nanostructures,"Photo-induced magnetic force between nanostructures, at optical frequencies,
is investigated theoretically. Till now optical magnetic effects are not used
in scanning probe microscopy because of the vanishing natural magnetism with
increasing frequency. On the other hand, artificial magnetism in engineered
nanostructures led to the development of measurable optical magnetism. Here,
two examples of nanoprobes that are able to generate strong magnetic dipolar
fields at optical frequency are investigated: first an ideal magnetically
polarizable nanosphere and then a circular cluster of silver nanospheres that
has a loop-like collective plasmonic resonance equivalent to a magnetic dipole.
Magnetic forces are evaluated based on nanostructure polarizabilities, i.e.
induced magnetic dipoles, and magnetic-near field evaluations. As an initial
assessment on the possibility of a magnetic nanoprobe to detect magnetic
forces, we consider two identical magnetically polarizable nanoprobes and
observe magnetic forces in the order of piconewtons thereby bringing it within
detection limits of conventional atomic force microscopes at ambient pressure
and temperature. The detection of magnetic force is a promising method in
studying optical magnetic transitions that can be the basis of innovative
spectroscopy applications.",1409.1188v2
2021-03-10,Searching for Magnetic Monopoles with the Earth's Magnetic Field,"Magnetic monopoles have long been predicted in theory and could exist as a
stable object in our universe. As they move around in galaxies, magnetic
monopoles could be captured by astrophysical objects like stars and planets.
Here, we provide a novel method to search for magnetic monopoles by detecting
the monopole moment of the Earth's magnetic field. Using over six years of
public geomagnetic field data obtained by the Swarm satellites, we apply
Gauss's law to measure the total magnetic flux, which is proportional to the
total magnetic charge inside the Earth. To account for the secular variation of
satellite altitudes, we define an altitude-rescaled magnetic flux to reduce the
dominant magnetic dipole contribution. The measured magnetic flux is consistent
with the existing magnetic field model that does not contain a monopole moment
term. We therefore set an upper limit on the magnetic field strength at Earth's
surface from magnetic monopoles to be $|B_{\rm m}| < 0.13$ nT at 95% confidence
level, which is less than $2\times 10^{-6}$ of Earth's magnetic field strength.
This constrains the abundance of magnetically-charged objects, including
magnetic black holes with large magnetic charges.",2103.06286v1
2007-05-31,Geometry-induced frustration of magnetization in a planar soft-hard magnetic system,"We computationally study the frustrated magnetic configurations of a thin
soft magnetic layer with the boundary condition fixed by underlying hard
magnets. Driven by geometrical constraints and external magnetic field,
transitions between frustrated energy minima result in magnetic hysteretic
behavior. The presence of soft-magnet introduces strong undulations in the
energy landscape in a length scale set by the magnetic property of the soft
magnet. We propose a possible use of the phenomena to locally control the
movement of magnetic nanoparticles.",0705.4490v1
2014-05-19,Scaling laws of free magnetic energy stored in a solar emerging flux region,"This Letter reports scaling laws of free magnetic energy stored in a solar
emerging flux region which is a key to understanding the energetics of solar
active phenomena such as solar flares and coronal mass ejections. By performing
3-dimensional magnetohydrodynamic simulations that reproduce several emerging
flux regions of different magnetic configurations, we derive power law
relationships among emerged magnetic flux, free magnetic energy and relative
magnetic helicity in these emerging flux regions. Since magnetic flux is an
observable quantity, the scaling law between magnetic flux and free magnetic
energy may give a way to estimate invisible free magnetic energy responsible
for solar active phenomena.",1405.4587v1
2020-09-24,Magnetic winding: what is it and what is it good for?,"Magnetic winding is a fundamental topological quantity that underpins
magnetic helicity and measures the entanglement of magnetic field lines. Like
magnetic helicity, magnetic winding is also an invariant of ideal
magnetohydrodynamics. In this article we give a detailed description of what
magnetic winding describes, how to calculate it and how to interpret it in
relation to helicity. We show how magnetic winding provides a clear topological
description of magnetic fields (open or closed) and we give examples to show
how magnetic winding and helicity can behave differently, thus revealing
different and imporant information about the underlying magnetic field.",2009.11708v1
2022-10-31,HTS Dipole Magnet with a Mechanical Energy Transfer in the Magnetic Field,"There were designed and successfully tested at Fermilab several high
temperature superconducting (HTS) model magnets for particle accelerators. Some
of them worked in a persistent current mode continuously generating magnetic
field in the iron dominated magnet gap. In the paper was investigated a novel
HT dipole magnet concept with a mechanical energy transfer in the magnetic
field. To pump the energy in the superconducting HTS dipole magnet used a
detachable magnetizer. The HTS dipole magnet was build and successfully tested
at a liquid nitrogen temperature. Discussed the magnet design, test results,
the proposed approach limits, and efficiency.",2211.00105v1
2023-08-03,Magnetic interactions in IV-VI diluted magnetic semiconductors,"Diluted magnetic semiconductors (DMS) are interesting because of the
interplay between the electronic and magnetic subsystems. We describe selected
magnetic properties of IV-VI diluted magnetic semiconductors, looking at the
similarities and differences between magnetic properties of II-VI, IV-VI, and
III-V DMS. We focus on the influence of the crystalline and electronic
structure of the material on its magnetic properties, especially on the
exchange interactions among magnetic ions. We describe methods of determination
of the exchange parameters by using different experimental techniques, such as
measurements of magnetic susceptibility, magnetization, and specific heat. We
follow the development in the material technology from bulk crystals to thin
films and nanostructures.",2308.01780v1
2009-05-27,Higher-order effects on the incompressibility of isospin asymmetric nuclear matter,"Analytical expressions for the saturation density as well as the binding
energy and incompressibility at the saturation density of asymmetric nuclear
matter are given exactly up to 4th-order in the isospin asymmetry delta =(rho_n
- rho_p)/rho using 11 characteristic parameters defined at the normal nuclear
density rho_0. Using an isospin- and momentum-dependent modified Gogny (MDI)
interaction and the SHF approach with 63 popular Skyrme interactions, we have
systematically studied the isospin dependence of the saturation properties of
asymmetric nuclear matter, particularly the incompressibility $K_{sat}(\delta
)=K_{0}+K_{sat,2}\delta ^{2}+K_{sat,4}\delta ^{4}+O(\delta ^{6})$ at the
saturation density. Our results show that the magnitude of the high-order
$K_{sat,4}$ parameter is generally small compared to that of the $K_{\sat,2}$
parameter. The latter essentially characterizes the isospin dependence of the
incompressibility at the saturation density and can be expressed as
$K_{sat,2}=K_{sym}-6L-\frac{J_{0}}{K_{0}}L$, Furthermore, we have constructed a
phenomenological modified Skyrme-like (MSL) model which can reasonably describe
the general properties of symmetric nuclear matter and the symmetry energy
predicted by both the MDI model and the SHF approach. The results indicate that
the high-order $J_{0}$ contribution to $K_{sat,2}$ generally cannot be
neglected. In addition, it is found that there exists a nicely linear
correlation between $K_{sym}$ and $L$ as well as between $J_{0}/K_{0}$ and
$K_{0}$. These correlations together with the empirical constraints on $K_{0}$,
$L$, $E_{sym}(\rho_{0})$ and the nucleon effective mass lead to an estimate of
$K_{sat,2}=-370\pm 120$ MeV.",0905.4323v2
2013-07-02,Impact-parameter dependent Color Glass Condensate dipole model and new combined HERA data,"The Impact-Parameter dependent Color Glass Condensate (b-CGC) dipole model is
based on the Balitsky-Kovchegov non-linear evolution equation and improves the
Iancu-Itakura-Munier dipole model by incorporating the impact-parameter
dependence of the saturation scale. Here we confront the model to the recently
released high precision combined HERA data and obtain its parameters. The b-CGC
results are then compared to data at small-x for the structure function, the
longitudinal structure function, the charm structure function, exclusive vector
meson (J/\psi, \phi, \rho) production and Deeply Virtual Compton Scattering
(DVCS). We also compare our results with the Impact-Parameter dependent
Saturation model (IP-Sat). We show that most features of inclusive DIS and
exclusive diffractive data, including the Q^2, W, |t| and x dependence are
correctly reproduced in both models. Nevertheless, the b-CGC and the IP-Sat
models give different predictions beyond the current HERA kinematics, namely
for the structure functions at very low x and high virtualities Q^2, and for
the exclusive diffractive vector meson and DVCS production at high t. This can
be traced back to the different power-law behavior of the saturation scale in
x, and to a different impact-parameter b dependence of the saturation scale in
these models. Nevertheless, both models give approximately similar saturation
scale Q_S<1 GeV for the proton in HERA kinematics, and also both models lead to
the same conclusion that the typical impact-parameter probed in the total
\gamma^{*}p cross-section is about b\approx 2\div 3 GeV^{-1}. Our results
provide a benchmark for further investigation of QCD at small-x in heavy ion
collisions at RHIC and the LHC and also at future experiments such as an
Electron-Ion Collider and the LHeC.",1307.0825v3
2013-10-25,High Energy Collisions of Dense Hadrons in Quantum Chromodynamics : LHC Phenomenology and Universality of Parton Distributions,"As the value of the longitudinal momentum carried by partons in a
ultra-relativistic hadron becomes small, one observes a growth of their
density. When the parton density becomes close to a value of order
$1/\alpha_s$, it does not grow any longer, it saturates. These high density
effects seem to be well described by the Color Glass Condensate effective field
theory. On the experimental side, the LHC provides the best tool ever for
reaching the saturated phase of hadronic matter. For this reason saturation
physics is a very active branch of QCD during these past and coming years since
saturation theories and experimental data can be compared. I first deal with
the phenomenology of the proton-lead collisions performed in winter 2013 at the
LHC and whose data are about to be available. I compute the di-gluon production
cross-section which provides the simplest observable for finding quantitative
evidences of saturation in the kinematic range of the LHC. I also discuss the
limit of the strongly correlated final state at large transverse momenta and by
the way, generalize parton distribution to dense regime. The second main topic
is the quantum evolution of the quark and gluon spectra in nucleus-nucleus
collisions having in mind the proof of its universal character. This result is
already known for gluons and here I detail the calculation carefully. For
quarks universality has not been proved yet but I derive an intermediate
leading order to next-to leading order recursion relation which is a crucial
step for extracting the quantum evolution. Finally I briefly present an
independent work in group theory. I detail a method I used for computing traces
involving an arbitrary number of group generators, a situation often
encountered in QCD calculations.",1310.6935v4
2015-05-14,Sharp bounds on the radius of relativistic charged spheres: Guilfoyle's stars saturate the Buchdahl-Andréasson bound,"Buchdahl, by imposing a few physical assumptions on the matter, i.e., its
density is a nonincreasing function of the radius and the fluid is a perfect
fluid, and on the configuration, such as the exterior is the Schwarzschild
solution, found that the radius $r_0$ to mass $m$ ratio of a star would obey
the Buchdahl bound $r_0/m\geq9/4$. He noted that the bound was saturated by the
Schwarzschild interior solution, the solution with $\rho_{\rm m}(r)= {\rm
constant}$, where $\rho_{\rm m}(r)$ is the energy density of the matter at $r$,
when the central central pressure blows to infinity. Generalizations of this
bound have been studied. One generalization was given by Andr\'easson by
including electrically charged matter and imposing that $p+2p_T \leq\rho_{\rm
m}$, where $p$ is the radial pressure and $p_T$ the tangential pressure. His
bound is given by $r_0/m\geq9/\left(1+\sqrt{1+3\,q^2/r_0^2}\right)^{2}$, the
Buchdahl-Andr\'easson bound, with $q$ being the star's total electric charge.
Following Andr\'easson's proof, the configuration that saturates the Buchdahl
bound is an uncharged shell, rather than the Schwarzschild interior solution.
By extension, the configurations that saturate the Buchdahl-Andr\'easson bound
are charged shells. One expects then, in turn, that there should exist an
electrically charged equivalent to the interior Schwarzschild limit. We find
here that this equivalent is provided by the equation $\rho_{\rm m}(r) +
{Q^2(r)}/ {\left(8\pi\,r^4\right)}= {\rm constant}$, where $Q(r)$ is the
electric charge at $r$. This equation was put forward by Cooperstock and de la
Cruz, and Florides, and realized in Guilfoyle's stars. When the central
pressure goes to infinity Guilfoyle's stars are configurations that saturate
the Buchdahl-Andr\'easson bound. It remains to find a proof in Buchdahl's
manner such that these configurations are the limiting configurations of the
bound.",1505.03863v1
2015-06-14,CO$_2$ dissolution in a background hydrological flow,"We investigate the long time steady-state dissolution of CO$_{2}$ in a deep
saline aqquifer in the presence of a background hydrological flow. In
steady-state, the distribution of CO$_2$ in the groundwater upstream of the
aquifer involves a balance between three competing effects: (i) the
buoyancy-driven flow of CO$_2$ saturated water; (ii) the diffusion of CO$_2$
from saturated to under-saturated water; and (iii) the advection associated
with the oncoming background flow. This leads to three limiting regimes. In the
limit of very slow diffusion, a nearly static intrusion of dense fluid may
extend a finite distance upstream, balanced by the pressure gradient associated
with the oncoming background flow. In the limit of fast diffusion relative to
the flow, a gradient zone may become established in which the along aquifer
diffusive flux balances the advection associated with the background flow.
However, if the buoyancy-driven flow speed exceeds the background hydrological
flow speed, then a third, intermediate regime may become established. In this
regime, a convective recirculation develops upstream of the anticline involving
the vertical diffusion of CO$_2$ from an upstream propagating flow of dense
CO$_2$ saturated water into the downstream propagating flow of CO$_2$
unsaturated water. For each limiting case, we find analytical solutions for the
distribution of CO$_2$ upstream of the anticline, and test our analysis with
full numerical simulations. A key result is that, although there may be very
different controls on the distribution and extent of CO$_2$ bearing water
upstream of the anticline, in each case the dissolution rate is given by the
product of the background volume flux and the difference in concentration
between the CO$_2$ saturated water and the original aquifer water upstream.",1506.04433v2
2016-02-02,Conductance saturation in a series of highly transmitting molecular junctions,"Understanding the properties of electronic transport across metal-molecule
interfaces is of central importance for controlling a large variety of
molecular-based devices such as organic light emitting diodes, nanoscale
organic spin-valves and single-molecule switches. One of the primary
experimental methods to reveal the mechanisms behind electronic transport
through metal-molecule interfaces is the study of conductance as a function of
molecule length in molecular junctions. Previous studies focused on transport
governed either by tunneling or hopping, both at low conductance. However, the
upper limit of conductance across molecular junctions has not been explored,
despite the great potential for efficient information transfer, charge
injection and recombination processes. Here, we study the conductance
properties of highly transmitting metal-molecule-metal interfaces, using a
series of single-molecule junctions based on oligoacenes with increasing
length. We find that the conductance saturates at an upper limit where it is
independent of molecule length. Furthermore, we show that this upper limit can
be controlled by the character of the orbital hybridization at the
metal-molecule interface. Using two prototype systems, in which the molecules
are contacted by either Ag or Pt electrodes, we reveal two different origins
for the saturation of conductance. In the case of Ag-based molecular junctions,
the conductance saturation is ascribed to a competition between energy level
alignment and level broadening, while in the case of Pt-based junctions, the
saturation is attributed to a band-like transport. The results are explained by
an intuitive model, backed by ab-initio transport calculations. Our findings
shed light on the mechanisms that constrain the conductance at the high
transmission limit, providing guiding principles for the design of highly
conductive metal-molecule interfaces.",1602.00956v1
2016-10-19,Do fast stellar centroiding methods saturate the Cramér-Rao lower bound?,"One of the most demanding tasks in astronomical image processing---in terms
of precision---is the centroiding of stars. Upcoming large surveys are going to
take images of billions of point sources, including many faint stars, with
short exposure times. Real-time estimation of the centroids of stars is crucial
for real-time PSF estimation, and maximal precision is required for
measurements of proper motion.
  The fundamental Cram\'{e}r-Rao lower bound sets a limit on the
root-mean-squared-error achievable by optimal estimators. In this work, we aim
to compare the performance of various centroiding methods, in terms of
saturating the bound, when they are applied to relatively low signal-to-noise
ratio unsaturated stars assuming zero-mean constant Gaussian noise. In order to
make this comparison, we present the ratio of the root-mean-squared-errors of
these estimators to their corresponding Cram\'{e}r-Rao bound as a function of
the signal-to-noise ratio and the full-width at half-maximum of faint stars.
  We discuss two general circumstances in centroiding of faint stars: (i) when
we have a good estimate of the PSF, (ii) when we do not know the PSF. In the
case that we know the PSF, we show that a fast polynomial centroiding after
smoothing the image by the PSF can be as efficient as the maximum-likelihood
estimator at saturating the bound. In the case that we do not know the PSF, we
demonstrate that although polynomial centroiding is not as optimal as PSF
profile fitting, it comes very close to saturating the Cram\'{e}r-Rao lower
bound in a wide range of conditions. We also show that the moment-based method
of center-of-light never comes close to saturating the bound, and thus it does
not deliver reliable estimates of centroids.",1610.05873v1
2019-02-13,Nonlinear saturation and oscillations of collisionless zonal flows,"In homogeneous drift-wave (DW) turbulence, zonal flows (ZFs) can be generated
via a modulational instability (MI) that either saturates monotonically or
leads to oscillations of the ZF energy at the nonlinear stage. This dynamics is
often attributed as the predator--prey oscillations induced by ZF collisional
damping; however, similar dynamics is also observed in collisionless ZFs, in
which case a different mechanism must be involved. Here, we propose a
semi-analytic theory that explains the transition between the oscillations and
saturation of collisionless ZFs within the quasilinear Hasegawa--Mima model. By
analyzing phase-space trajectories of DW quanta (driftons) within the
geometrical-optics (GO) approximation, we argue that the parameter that
controls this transition is $N\sim\gamma_{{\rm MI}}/\omega_{{\rm DW}}$, where
$\gamma_{{\rm MI}}$ is the MI growth rate and $\omega_{{\rm DW}}$ is the linear
DW frequency. We argue that at $N\ll1$, ZFs oscillate due to the presence of
so-called passing drifton trajectories, and we derive an approximate formula
for the ZF amplitude as a function of time in this regime. We also show that at
$N\gtrsim1$, the passing trajectories vanish and ZFs saturate monotonically,
which can be attributed to phase mixing of higher-order sidebands. A
modification of $N$ that accounts for effects beyond the GO limit is also
proposed. These analytic results are tested against both quasilinear and
fully-nonlinear simulations. They also explain the earlier numerical results by
Connaughton $\textit{et al}$. [J. Fluid Mech. $\textbf{654}$, 207 (2010)] and
Gallagher $\textit{et al}$. [Phys. Plasmas $\textbf{19}$, 122115 (2012)] and
offer a revised perspective on what the control parameter is that determines
the transition from the oscillations to saturation of collisionless ZFs.",1902.04970v1
2020-03-12,Multichannel asymmetric transmission through a dimer defect with saturable inter-site nonlinearity,"We consider the asymmetric transmission properties of a Discrete Nonlinear
Schr{\""o}dinger type dimer with a saturable nonlinear intersite coupling
between the dimer sites, in addition to a cubic onsite nonlinearity and
asymmetric linear onsite potentials. In contrast to previously studied cases
with pure onsite nonlinearities, the transmission coefficient for stationary
transmission is shown to be a multivalued function of the transmitted
intensity, in regimes of low saturability and small or moderate transmitted
intensity. The corresponding backward transfer map is analyzed analytically and
numerically, and shown to have either one or three distinct solutions for
saturable coupling, and zero or two solutions for the purely cubic nonlinear
coupling. As saturation strength is increased, the multi-solution regimes
disappear through bifurcations and the single-valued regime of the onsite model
is recovered. The existence of multiple solution branches yields novel
mechanisms for asymmetric left/right stationary transmission: in addition to
shifts of the positions of transmission peaks, peaks for transmission in one
direction may correspond to nonexistence of stationary solutions propagating in
the opposite direction, at the corresponding branch and transmitted intensity.
Moreover, one of these transmission channels behaves as a nearly perfect mirror
for incoming signals. The linear stability of the stationary solutions is
analyzed, and instabilities are typically observed, and illustrated by direct
numerical simulations, in regimes with large transmission coefficient.
Intersite nonlinearities are found to prevent the formation of a localized
dimer mode in the instability-induced dynamics. Finally, the partial reflection
and transmission of a Gaussian excitation is studied, and the asymmetric
transmission properties are compared to previously studied onsite models.",2003.05963v2
2020-04-16,Direct Astrophysical Tests of Chiral Effective Field Theory at Supranuclear Densities,"Recent observations of neutron stars with gravitational waves and X-ray
timing provide unprecedented access to the equation of state (EoS) of cold
dense matter at densities difficult to realize in terrestrial experiments. At
the same time, predictions for the EoS with reliable uncertainty estimates from
chiral effective field theory ($\chi$EFT) bound our theoretical ignorance. In
this work, we analyze astrophysical data using a nonparametric representation
of the neutron-star EoS conditioned on $\chi$EFT to directly constrain the
underlying physical properties of the compact objects. We discuss how the data
alone constrain the EoS at high densities when we condition on $\chi$EFT at low
densities. We also demonstrate how to exploit astrophysical data to directly
test the predictions of $\chi$EFT for the EoS up to twice nuclear saturation
density, and estimate the density at which these predictions might break down.
We find that the existence of massive pulsars, gravitational waves from
GW170817, and NICER observations of PSR J0030+0451 favor $\chi$EFT predictions
for the EoS up to nuclear saturation density over a more agnostic analysis by
as much as a factor of 7 for the quantum Monte Carlo (QMC) calculations used in
this work. While $\chi$EFT predictions using QMC are fully consistent with
gravitational-wave data up to twice nuclear saturation density, NICER
observations suggest that the EoS stiffens relative to these predictions at
nuclear saturation density. Additionally, we marginalize over the uncertainty
in the density at which $\chi$EFT begins to break down, constraining the radius
of a $1.4\,M_\odot$ neutron star to $R_{1.4}=11.40^{+1.38}_{-1.04}$
($12.54^{+0.71}_{-0.63}$) km and the pressure at twice nuclear saturation
density to $p(2n_\mathrm{sat})=14.2^{+18.1}_{-8.4}$ ($28.7^{+15.3}_{-15.0}$)
MeV/fm$^3$ with massive pulsar and gravitational-wave (and NICER) data.",2004.07744v3
2021-03-09,Saturating Receiver and Receptor Competition in Synaptic DMC: Deterministic and Statistical Signal Models,"Synaptic communication is based on a biological Molecular Communication (MC)
system which may serve as a blueprint for the design of synthetic MC systems.
However, the physical modeling of synaptic MC is complicated by the possible
saturation of the molecular receiver caused by the competition of
neurotransmitters (NTs) for postsynaptic receptors. Receiver saturation renders
the system behavior nonlinear in the number of released NTs and is commonly
neglected in existing analytical models. Furthermore, due to the ligands'
competition for receptors (and vice versa), the individual binding events at
the molecular receiver are in general statistically dependent and the binomial
model for the statistics of the received signal does not apply. In this work,
we propose a novel deterministic model for receptor saturation in terms of a
state-space description based on an eigenfunction expansion of Fick's diffusion
equation. The presented solution is numerically stable and computationally
efficient. Employing the proposed deterministic model, we show that saturation
at the molecular receiver reduces the peak-value of the expected received
signal and accelerates the clearance of NTs as compared to the case when
receptor occupancy is neglected. We further derive a statistical model for the
received signal in terms of the hypergeometric distribution which accounts for
the competition of NTs for receptors and the competition of receptors for NTs.
The proposed statistical model reveals how the signal statistics are shaped by
the number of released NTs, the number of receptors, and the binding kinetics
of the receptors, respectively, in the presence of competition. We show that
the impact of these parameters on the signal variance depends on the relative
numbers of NTs and receptors. The accuracy of the proposed deterministic and
statistical models is verified by particle-based computer simulations.",2103.05341v2
2021-04-09,Parton rescattering and gluon saturation in dijet production at EIC,"Large angle gluon radiations induced by multiple parton scatterings
contribute to dijet production in deeply inelastic scattering off a large
nucleus at the Electron-Ion Collider. Within the generalized high-twist
approach to multiple parton scattering, such contributions at the leading order
in perturbative QCD and large Bjorken momentum fraction $x_B$ can be expressed
as a convolution of the multiple parton scattering amplitudes and the
transverse momentum dependent (TMD) two-parton correlation matrix elements. We
study this medium-induced dijet spectrum and its azimuthal angle correlation
under the approximation of small longitudinal momentum transfer in the
secondary scattering and the factorization of two-parton correlation matrix
elements as a product of quark and gluon TMD parton distribution function
(PDF). Using a simple model for gluon saturation based on the parametrized
gluon TMD PDF, we can calculate the $x_B$ and $Q^2$ dependence of the
saturation scale and parton transport coefficient $\hat q$. Contributions to
dijet cross section from double scattering are power-suppressed and only become
sizable for mini-jets at small transverse momentum. We find that the total
dijet correlation for these mini-jets, which also includes the contribution
from single scattering, is sensitive to the transverse momentum broadening in
the quark TMD PDF at large $x$ and saturation in the gluon TMD PDF at small $x$
inside the nucleus. The correlation from double scattering is also found to
increase with the dijet rapidity gap and have a quadratic nuclear-size
dependence because of the Landau-Pomeranchuk-Migdal (LPM) interference in gluon
emission induced by multiple scattering. Experimental measurements of such
unique features in the dijet correlation can shed light on the LPM interference
in strong interaction and gluon saturation in large nuclei.",2104.04520v4
2021-09-15,Continuous-wave stability and multi-pulse structures in a universal Complex Ginzburg-Landau model for passively mode-locked lasers with saturable absorber,"The dynamics and stability of continuous-wave and multi-pulse structures are
studied theoretically, for a generalized model of passively mode-locked fiber
laser with an arbitrary nonlinearity. The model is characterized by a complex
Ginzburg-Landau equation with saturable nonlinearity of a general form
($I^m/(1+\Gamma I)^n$), where $I$ is the field intensity, $m$ and $n$ are two
positive real numbers and $\Gamma$ is the optical field saturation power. The
analysis of fixed-point solutions of the governing equations, reveals an
interesting loci of singular points in the amplitude-frequency plane consisting
of zero, one or two fixed points depending upon the values of $m$ and $n$. The
stability of continuous waves is analyzed within the framework of the
modulational-instability theory, results demonstrate a bifurcation in the
continuous-wave amplitude growth rate and propagation constant characteristic
of multi-periodic wave structures. In the full nonlinear regime these
multi-periodic wave structures turn out to be multi-pulse trains, unveiled via
numerical simulations of the model nonlinear equation the rich variety of which
is highlighted by considering different combinations of values for the pair
($m$,$n$). Results are consistent with previous analyses of the dynamics of
multi-pulse structures in several contexts of passively mode-locked lasers with
saturable absorber, as well as with predictions about the existence of
multi-pulse structures and bound-state solitons in optical fibers with strong
optical nonlinearity such as cubic-quintic and saturable nonlinearities.",2109.07179v1
2021-12-09,Network mechanisms of working memory: the role of neuronal nonlinearities,"The oculomotor delayed-response (ODR) task is a common experimental paradigm
of working memory (WM) study, in which a monkey must fixate its gaze on the
center of a screen and, following a brief cue that flashes on the screen, keep
fixating for several more seconds before shifting its gaze to the location
where the cue flashed. Consequently, in the delay period between the cue and
the response the monkey must maintain a memory of cue location.
Electrophysiological recordings from the prefrontal area of the cortex (PFC)
revealed neurons that display selective persistent activity: their firing rate
change induced by the cue persists through delay period, but only in response
to a confined range of cue locations. This suggests that the representation of
the cue is maintained in the network by a change in network activity profile.
In this work, we study a network of rate-model neurons that is capable of
preserving information about a past input, owing to structured connectivity and
nonlinearities in the neuronal transfer function (TFs). Particularly, we focus
on the acceleration of the TF close to firing threshold and the concavity
around TF saturation. Any memory mechanism which exploits TF saturation means
that some neurons must fire close to their saturation rates; with our model,
however, we show that a certain relation between the excitatory and inhibitory
neurons' TFs can cause an effective saturation in the network without forcing
the neurons into the saturating parts of their TFs. In addition, this mechanism
enables the erasure of memory at the end of the delay by a global excitatory
signal. Finally, we demonstrate the mechanism in a model network of spiking
neurons which describes with more detail the oscillatory dynamics in the state
transition due to the interaction of membrane and synaptic time constants which
is neglected in the rate model.",2112.05091v1
2022-11-18,Numerical simulation of two-phase flow in gas diffusion layer and gas channel of proton exchange membrane fuel cells,"Liquid water within the cathode Gas Diffusion Layer (GDL) and Gas Channel
(GC) of Proton Exchange Membrane Fuel Cells (PEMFCs) is strongly coupled to gas
transport properties, thereby affecting the electrochemical conversion rates.
In this study, the GDL and GC regions are utilized as the simulation domain,
which differs from previous studies that only focused on any one of them. A
volume-of-fluid method is adopted to numerically investigate the two-phase flow
(gas and liquid) behavior, e.g., water transport pattern evolution, water
coverage ratio as well as local and total water saturation. To obtain GDL
geometries, an in-house geometry-based method is developed for GDL
reconstruction. Furthermore, to study the effect of GDL carbon fiber diameter,
the same procedure is used to reconstruct three GDL structures by varying the
carbon fiber diameter but keeping the porosity and geometric dimensions
constant. The wall wettability is introduced with static contact angles at
carbon fiber surfaces and channel walls. The results show that the GDL fiber
microstructure has a significant impact on the two-phase flow patterns in the
cathode field. Different stages of two-phase flow pattern evolution in both
cathode domains are observed. Due to the difference in wettability, the water
coverage of the GDL/GC interface is smaller than that of the channel side and
top walls. It is also found that the water saturation inside the GDLs
stabilizes after the water breakthrough, while local water saturation at the
interface keeps irregular oscillations. Last but not the least, a water
saturation balance requirement between the GDL and GC is observed. In terms of
varying fiber diameter, a larger fiber diameter would result in less water
saturation in the GDL but more water in the GC, in addition to faster water
movement throughout the total domain.",2211.10084v1
2022-12-15,Microscopic theory of nonlinear phase space filling in polaritonic lattices,"We develop a full microscopic theory for a nonlinear phase space filling
(NPSF) in strongly coupled two-dimensional polaritonic lattices. Ubiquitous in
polaritonic experiments, the theoretical description of NPSF, remains limited
to perturbative treatment and homogeneous samples. In this study, we go beyond
the existing theoretical description and discover the broad scope of regimes
where NPSF crucially modifies the optical response. Studying the quantum
effects of non-bosonicity, cooperative light-matter coupling, and Coulomb
blockade, we reveal several regimes for observing the nonlinear Rabi splitting
quench due to the phase space filling. Unlike prior studies, we derive
nonlinear Rabi frequency scaling all the way to the saturation limit and show
that the presence of a lattice potential leads to qualitatively distinct
nonlinearity. We concentrate on three regimes of NPSF: 1) planar; 2) fractured;
and 3) ultralocalized. In planar saturation, the Rabi frequency decreases
exponentially as a function of exciton density. For the fractured case, where
excitons form a lattice with sites exceeding the exciton size, we discover fast
NPSF at low occupation in the lattice. This is followed by slower NPSF as the
medium becomes fully saturated. This behavior is particularly pronounced in the
presence of Coulomb (or Rydberg) blockade, where regions of fast and slow NPSF
depend on the strength of repulsion. For the ultralocalized NPSF, we observe
the square-root saturation typical to the collection of two-level systems. Our
findings can help describing recent observations of strong nonlinearity in
heterobilayers of transition metal dichalcogenides where Moir{\'e} lattices
emerge naturally [Nature \textbf{591}, 61 (2021)]. The theory also opens the
prospects for engineering strongly nonlinear responses of polaritonic lattices
with patterned samples, driving polaritonics into the quantum regime.",2212.07968v2
2023-03-19,Noninvasive in vivo photoacoustic measurement of internal jugular venous oxygenation in humans,"In many clinical conditions, such as head trauma, stroke, and low cardiac
output states, the brain is at risk for hypoxic-ischemic injury. The metabolic
rate and oxygen consumption of the brain are reflected in internal jugular
venous oxygen saturation (sijvO2). The current gold standard for monitoring
brain oxygenation is invasive; it requires jugular vein catheterization under
fluoroscopic guidance and therefore is rarely used. Photoacoustic (PA)
measurement, on the other hand, can estimate the oxygen consumption of the
brain non-invasively in real time. Such a convenient method can potentially aid
earlier detection and prevention of impending hypoxic brain injury. A
dual-wavelength photoacoustic tomography (PAT) and ultrasound imaging (US)
system was used to image the internal jugular vein (IJV) and estimate the
sijvO2 in seven healthy volunteers. The system captured simultaneous
co-registered PAT and US images at a rate of five frames per second. For each
volunteer, the internal jugular vein was identified under ultrasound guidance,
then, additional PA images from two optical wavelengths were collected and used
to estimate the oxygen saturation of the internal jugular vein. For each
volunteer, the oxygen saturation was calculated from transverse and
longitudinal views of the internal jugular vein. The average sijvO2 was 72 +/-
7 %. The preliminary results are encouraging and agree with those reported in
the literature. Photoacoustic images were successfully used to calculate the
blood hemoglobin oxygen saturation in the internal jugular vein. These results
raise confidence that this emerging technology can be used clinically for
accurate, noninvasive estimation of sijvO2. In addition, the fast
co-registration with US images makes the technique suitable for studying the
temporal variations of oxygen saturation in response to physiologic challenges
in clinical settings.",2303.10775v1
2024-02-06,Saturation of fishbone instability through zonal flows driven by energetic particle transport in tokamak plasmas,"Gyrokinetic and kinetic-MHD simulations are performed for the fishbone
instability in the DIII-D discharge #178631, chosen for validation of
first-principles simulations to predict the energetic particle (EP) transport
in an ITER prefusion baseline scenario. Fishbone modes are found to generate
zonal flows, which dominate the fishbone saturation. The underlying mechanisms
of the two-way fishbone-zonal flows nonlinear interplay are discussed in
details. Numerical and analytical analyses identify the fishbone-induced EP
redistribution as the dominant generation mechanism for zonal flows. The zonal
flows modify the nonlinear dynamics of phase space zonal structures, which
reduces the amount of EPs able to resonate with the mode, leading to an early
fishbone saturation. Simulation results including zonal flows agree
quantitatively with DIII-D experimental measurements of the fishbone saturation
amplitude and EP transport, supporting this novel saturation mechanism by
self-generated zonal flows. Moreover, the wave-particle mode-locking mechanism
is shown to determine quantitatively the fishbone frequency down-chirping, as
evident in GTC simulation results in agreement with predictions from analytical
theory. Finally, the fishbone-induced zonal flows are possibly responsible for
the formation of an ion-ITB in the DIII-D discharge. Based on the low EP
transport and the large zonal flow shearing rates associated with the fishbone
instability in gyrokinetic simulations of the ITER scenario, it is conjectured
that high performance scenarios could be designed in ITER burning plasmas
through fishbone-induced ITBs.",2402.03797v1
2006-05-18,Small-scale magnetic buoyancy and magnetic pumping effects in a turbulent convection,"We determine the nonlinear drift velocities of the mean magnetic field and
nonlinear turbulent magnetic diffusion in a turbulent convection. We show that
the nonlinear drift velocities are caused by the three kinds of the
inhomogeneities, i.e., inhomogeneous turbulence; the nonuniform fluid density
and the nonuniform turbulent heat flux. The inhomogeneous turbulence results in
the well-known turbulent diamagnetic and paramagnetic velocities. The nonlinear
drift velocities of the mean magnetic field cause the small-scale magnetic
buoyancy and magnetic pumping effects in the turbulent convection. These
phenomena are different from the large-scale magnetic buoyancy and magnetic
pumping effects which are due to the effect of the mean magnetic field on the
large-scale density stratified fluid flow. The small-scale magnetic buoyancy
and magnetic pumping can be stronger than these large-scale effects when the
mean magnetic field is smaller than the equipartition field. We discuss the
small-scale magnetic buoyancy and magnetic pumping effects in the context of
the solar and stellar turbulent convection. We demonstrate also that the
nonlinear turbulent magnetic diffusion in the turbulent convection is
anisotropic even for a weak mean magnetic field. In particular, it is enhanced
in the radial direction. The magnetic fluctuations due to the small-scale
dynamo increase the turbulent magnetic diffusion of the toroidal component of
the mean magnetic field, while they do not affect the turbulent magnetic
diffusion of the poloidal field.",0605444v1
2019-09-09,Photospheric magnetic structure of coronal holes,"In this study, we investigate in detail the photospheric magnetic structure
of 98 coronal holes using line-of-sight magnetograms of SDO/HMI, and for a
subset of 42 coronal holes using HINODE/SOT G-band filtergrams. We divided the
magnetic field maps into magnetic elements and quiet coronal hole regions by
applying a threshold at $\pm 25$ G. We find that the number of magnetic bright
points in magnetic elements is well correlated with the area of the magnetic
elements (cc=$0.83\pm 0.01$). Further, the magnetic flux of the individual
magnetic elements inside coronal holes is related to their area by a power law
with an exponent of $1.261\pm 0.004$ (cc=$0.984\pm 0.001$). Relating the
magnetic elements to the overall structure of coronal holes, we find that on
average ($69\pm 8$) % of the overall unbalanced magnetic flux of the coronal
holes arises from long-lived magnetic elements with lifetimes > 40 hours. About
($22\pm 4$) % of the unbalanced magnetic flux arises from a very weak
background magnetic field in the quiet coronal hole regions with a mean
magnetic field density of about 0.2 to 1.2 G. This background magnetic field is
correlated to the flux of the magnetic elements with lifetimes of > 40 h
(cc=$0.88\pm 0.02$). The remaining flux arises from magnetic elements with
lifetimes < 40 hours. By relating the properties of the magnetic elements to
the overall properties of the coronal holes, we find that the unbalanced
magnetic flux of the coronal holes is completely determined by the total area
that the long-lived magnetic elements cover (cc=$0.994\pm 0.001$).",1909.03806v1
2006-08-14,Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy,"The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too.",0608307v3
2007-06-13,Nonlinear turbulent magnetic diffusion and effective drift velocity of large-scale magnetic field in a two-dimensional magnetohydrodynamic turbulence,"We study a nonlinear quenching of turbulent magnetic diffusion and effective
drift velocity of large-scale magnetic field in a developed two-dimensional MHD
turbulence at large magnetic Reynolds numbers. We show that transport of the
mean-square magnetic potential strongly changes quenching of turbulent magnetic
diffusion. In particularly, the catastrophic quenching of turbulent magnetic
diffusion does not occur for the large-scale magnetic fields $B \gg B_{\rm eq}
/ \sqrt{\rm Rm}$ when a divergence of the flux of the mean-square magnetic
potential is not zero, where $B_{\rm eq}$ is the equipartition mean magnetic
field determined by the turbulent kinetic energy and Rm is the magnetic
Reynolds number. In this case the quenching of turbulent magnetic diffusion is
independent of magnetic Reynolds number. The situation is similar to
three-dimensional MHD turbulence at large magnetic Reynolds numbers whereby the
catastrophic quenching of the alpha effect does not occur when a divergence of
the flux of the small-scale magnetic helicity is not zero.",0706.1846v1
2007-10-26,Magnetic fluctuations and formation of large-scale inhomogeneous magnetic structures in a turbulent convection,"Magnetic fluctuations generated by a tangling of the mean magnetic field by
velocity fluctuations are studied in a developed turbulent convection with
large magnetic Reynolds numbers. We show that the energy of magnetic
fluctuations depends on magnetic Reynolds number only when the mean magnetic
field is smaller than $B_{eq} / 4 Rm^{1/4}$, where $B_{eq}$ is the
equipartition mean magnetic field determined by the turbulent kinetic energy
and Rm is magnetic Reynolds number. Generation of magnetic fluctuations in a
turbulent convection with a nonzero mean magnetic field results in a decrease
of the total turbulent pressure and may cause formation of the large-scale
inhomogeneous magnetic structures even in an originally uniform mean magnetic
field. This effect is caused by a negative contribution of the turbulent
convection to the effective mean Lorentz force. The inhomogeneous large-scale
magnetic fields are formed due to the excitation of the large-scale
instability. The energy for this instability is supplied by the small-scale
turbulent convection. The discussed effects might be useful for understanding
the origin of the solar nonuniform magnetic fields, e.g., sunspots.",0710.5052v1
2013-11-18,"Fabrication, properties, and applications of flexible magnetic films","Flexible magnetic devices, i.e., magnetic devices fabricated on flexible
substrates, are very attractive in application of detecting magnetic field in
arbitrary surface, non-contact actuators, and microwave devices due to the
stretchable, biocompatible, light-weight, portable, and low cost properties.
Flexible magnetic films are essential for the realization of various
functionalities of flexible magnetic devices. To give a comprehensive
understanding for flexible magnetic films and related devices, we have reviewed
recent advances in the studies of flexible magnetic films including fabrication
methods, magnetic and transport properties of flexible magnetic films, and
their applications in magnetic sensors, actuators, and microwave devices. Three
typical methods were introduced to prepare the flexible magnetic films.
Stretching or bending the flexible magnetic films offers a good way to apply
mechanical strain on magnetic films, so that magnetic anisotropy, exchanged
bias, coercivity, and magnetoresistance can be effectively manipulated.
Finally, a series of examples were shown to demonstrate the great potential of
flexible magnetic films for future applications.",1311.4318v1
2021-10-31,Shape Programmable Magnetic Pixel Soft Robot,"Magnetic response soft robot realizes programmable shape regulation with the
help of magnetic field and produces various actions. The shape control of
magnetic soft robot is based on the magnetic anisotropy caused by the orderly
distribution of magnetic particles in the elastic matrix. In the previous
technologies, magnetic programming is coupled with the manufacturing process,
and the orientation of magnetic particles cannot be modified, which brings
restrictions to the design and use of magnetic soft robot. This paper presents
a magnetic pixel robot with shape programmable function. By encapsulating
NdFeB/gallium composites into silicone shell, a thermo-magnetic response
functional film with lattice structure are fabricated. Basing on
thermal-assisted magnetization technique, we realized the discrete
magnetization region distribution on the film. Therefore, we proposed a
magnetic coding technique to realize the mathematical response action design of
software robot. Using these methods, we prepared several magnetic soft robots
based on origami structure. The experiments show that the behavior mode of
robot can be flexibly and repeatedly regulated by magnetic encoding technique.
This work provides a basis for the programmed shape regulation and motion
design of soft robot.",2111.00422v2
2022-02-07,Magnetism of QCD matter and pion mass from tensor-type spin polarization and anomalous magnetic moment of quarks,"We investigate the magnetism of QCD matter and pion mass under magnetic field
considering the contribution from the tensor-type spin polarization and the
anomalous magnetic moment (AMM) of quarks. It is found that the tensor-type
spin polarization (TSP) induces the magnetic catalysis of chiral condensate and
diamagnetism (negative magnetic susceptibility) of quark matter at low
temperature, both neutral and charged pion masses increase quickly with
magnetic field in the case of TSP. The anomalous magnetic moment (AMM) of
quarks induces magnetic inhibition and a magnetic dependent AMM causes inverse
magnetic catalysis at finite temperature, and the neutral pion mass decreases
with magnetic field while the charged pion mass shows nonmonotonic behavior
with the magnetic field, which is qualitatively in agreement with lattice
result. However, the magnetic susceptibility is positive at low temperature
with AMM. In the current framework, our results show the irreconcilable
contradiction between the diamagnetism and inverse magnetic catalysis.",2202.03226v1
2022-10-06,Current-induced perpendicular effective magnetic field in magnetic heterostructures,"Generation of perpendicular effective magnetic field or perpendicular spins
({\sigma}z) is central for the development of energy-efficient, scalable, and
external-magnetic-field-free spintronic memory and computing technologies.
Here, we report the first identification and the profound impacts of a
significant effective perpendicular magnetic field that can arise from
asymmetric current spreading within magnetic microstrips and Hall bars. This
effective perpendicular magnetic field can exhibit all the three
characteristics that have been widely assumed in the literature to ""signify""
the presence of a flow of {\sigma}z, i.e., external-magnetic-field-free current
switching of uniform perpendicular magnetization, a sin2{\phi}-dependent
contribution in spin-torque ferromagnetic resonance signal of in-plane
magnetization ({\phi} is the angle of the external magnetic field with respect
to the current, and a {\phi}-independent but field-dependent contribution in
the second harmonic Hall voltage of in-plane magnetization. This finding
suggests that it is critical to include current spreading effects in the
analyses of various spin polarizations and spin-orbit torques in magnetic
heterostructure. Technologically, our results provide perpendicular effective
magnetic field induced by asymmetric current spreading as a novel, universally
accessible mechanism for efficient, scalable, and external-magnetic-field-free
magnetization switching in memory and computing technologies.",2210.02916v1
2010-03-09,MAGNETIC ANOMALY IN SUPERCONDUCTING FeSe,"Synthesis, electrical and magnetic characterization of superconducting
FeSe0.85 compound is reported. An anomaly in the magnetization against
temperature around 90K is observed. Magnetic characterization of a commercial
compound with nominal FeSe stoichiometry is also presented. The overall
magnetic behaviors as well as the magnetic anomaly in both compounds are
discussed in terms of magnetic impurities and secondary phases. Keyword: A.
Superconductors",1003.1966v1
2011-05-19,Ultra-fast spin avalanches in crystals of molecular magnets in terms of magnetic detonation,"Recent experiments (Decelle et al., Phys. Rev. Lett. 102, 027203 (2009))
discovered an ultra-fast regime of spin avalanches in crystals of magnetic
magnets, which was three orders of magnitude faster than the traditionally
studied magnetic deflagration. The new regime has been hypothetically
identified as magnetic detonation. Here we demonstrate the possibility of
magnetic detonation in the crystals, as a front consisting of a leading shock
and a zone of Zeeman energy release. We study the dependence of the magnetic
detonation parameters on the applied magnetic field. We find that the magnetic
detonation speed only slightly exceeds the sound speed in agreement with the
experimental observations.",1105.3962v1
2013-07-18,Interaction effect detected by compared of the irreversible and remanent initial magnetization curves in Ni-Cu-Zn ferrites,"A new technique for estimation of magnetic interaction effects of initial
magnetization curves has been proposed. It deals with remanence, and initial
irreversible magnetization, curves. The method is applied for single-phase
polycrystalline Ni0.85-xCu0.15ZnxFe2O4, (x = 0, 0.2, 0.4 and 0.6), which were
synthesized by a standard ceramic technology. A study of the initial reversible
and irreversible magnetization processes in ferrite materials was carried out.
The field dependence of the irreversible, and reversible, magnetizations was
determined by magnetic losses of minor hysteresis loops obtained from different
points of an initial magnetization curve. The influence of Zn-substitutions in
Ni-Cu ferrites over irreversible magnetization processes and interactions in
magnetic systems has been analyzed.",1307.4881v1
2013-10-15,Plasticity-Induced Magnetization in Amorphous Magnetic Solids,"Amorphous magnetic solids, like metallic glasses, exhibit a novel effect: the
growth of magnetic order as a function of mechanical strain under athermal
conditions in the presence of a magnetic field. The magnetic moment increases
in steps whenever there is a plastic event. Thus plasticity induces the
magnetic ordering, acting as the effective noise driving the system towards
equilibrium. We present results of atomistic simulations of this effect in a
model of a magnetic amorphous solid subjected to pure shear and a magnetic
field. To elucidate the dependence on external strain and magnetic field we
offer a mean-field theory that provides an adequate qualitative understanding
of the observed phenomenon.",1310.3979v1
2017-09-11,Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2,"The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour
and we report here a neutron diffraction investigation into the magnetic
ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the
anti-Sr2MnO2Sb2-type structure and orders antiferromagnetically below TN = 105
K. We consider both its long-range magnetic structure and its magnetic
microstructure, and the onset of magnetic order. It adopts the multi-k vector
""2k"" magnetic structure (k = (0.5 0 0.5) and k = (0 0.5 0.5) and has
similarities with related iron oxychalcogenides, illustrating the robust nature
of the ""2k"" magnetic structure.",1709.03323v1
2022-12-07,Quark condensate and magnetic moment in a strong magnetic field,"This paper studies the quark condensate, magnetic moment, magnetic
polarization, and magnetic susceptibility in a strong external magnetic field
by employing the Dyson-Schwinger equations (DSE). The results show that these
physical quantities as functions of the magnetic field. We note that the
quark's spin polarizations are approximately proportional to the magnetic field
magnitude. For comparison, we investigate the magnetic moments and
susceptibility of the nucleon in the constituent quark model framework and
demonstrate that both these quantities increase as the magnetic field rises.",2212.03508v2
2023-12-26,Magnetic vortex control with current-induced axial magnetization in centrosymmetric Weyl materials,"We consider magnetic Weyl metals as a platform to achieve current control of
magnetization textures with transport currents, utilizing their underlying band
geometry. We show that the transport current in a Weyl semimetal produces an
axial magnetization due to orbital magnetic moments of the Weyl electrons. The
associated axial magnetization can generate a torque acting on the localized
magnetic moments. For the case of a magnetic vortex in a nanodisk of Weyl
materials, this current-induced torque can be used to reverse its circulation
and polarity. We discuss the axial magnetization torques in Weyl metals on
general symmetry grounds, and compare their strength to current-induced torques
in more conventional materials.",2312.16122v1
2004-09-08,Magnetic and electronic phase transformations in (Sm0.65Sr0.35)MnO3 induced by temperature and magnetic field,"Temperature (4.2-260 K) and magnetic field (0-50 kOe) dependencies of the dc
electrical resistance, dc magnetization, and ac magnetic susceptibility of
(Sm0.65Sr0.35)MnO3 prepared from high purity components have been studied.",0409213v1
2008-02-20,Anomalous Magnetic Properties of Sr2YRuO6,"Anomalous magnetic properties of the double perovskite ruthenates compound
Sr2YRuO6 are reported here. Magnetization measurements as a function of
temperature in low magnetic fields show clear evidence for two components of
magnetic order (TM1 ~ 32K and TM2 ~ 27K) aligned opposite to each other with
respect to the magnetic field direction even though only Ru5+moments can order
magnetically in this compound. The second component of the magnetic order at
TM2 ~ 27K results only in a magnetization reversal, and not in the negative
magnetization when the magnetization is measured in the field cooled (FC) mode.
Isothermal magnetization (M-H) measurements show hysteresis with maximum
coercivity (Hc) and remnant magnetization (Mr) at T ~ 27 K, corroborating the
presence of the two oppositely aligned magnetic moments, each with a
ferromagnetic component. The two components of magnetic ordering are further
confirmed by the double peak structure in the heat capacity measurements. These
anomalous properties have significance to some of the earlier results obtained
for the Cu-substituted superconducting Sr2YRu1-xCuxO6 compounds.",0802.2953v2
2014-09-05,"Analysis of the magnetic field, force, and torque for two-dimensional Halbach cylinders","The Halbach cylinder is a construction of permanent magnets used in
applications such as nuclear magnetic resonance apparatus, accelerator magnets
and magnetic cooling devices. In this paper the analytical expression for the
magnetic vector potential, magnetic flux density and magnetic field for a two
dimensional Halbach cylinder are derived. The remanent flux density of a
Halbach magnet is characterized by the integer $p$. For a number of
applications the force and torque between two concentric Halbach cylinders are
important. These quantities are calculated and the force is shown to be zero
except for the case where $p$ for the inner magnet is one minus $p$ for the
outer magnet. Also the force is shown never to be balancing. The torque is
shown to be zero unless the inner magnet $p$ is equal to minus the outer magnet
$p$. Thus there can never be a force and a torque in the same system.",1409.1712v1
2018-12-18,(Self-)Magnetized Bose-Einstein Condensate stars,"We study magnetic field effects on the Equations of State (EoS) and the
structure of Bose-Einstein Condensate (BEC) stars, i.e. a compact object
composed by a gas of interacting spin one bosons formed up by the pairing of
two neutrons. To include the magnetic field in the thermodynamic description,
we suppose that particle-magnetic field and particle-particle interactions are
independent. We consider two configurations for the magnetic field: one where
it constant and externally fixed, and another where it is produced by the
bosons by self-magnetization. Since the magnetic field produces the splitting
of pressures in the directions along and perpendicular to the magnetic axis,
stable configurations of self-magnetized and magnetized BEC stars are studied
using the recently found $\gamma$-structure equations that describe axially
symmetric objects. The magnetized BEC stars are, in general spheroidal, less
massive and smaller than the non-magnetic ones, being these effects more
relevant at low densities. For the self-magnetized BEC stars their inner
profiles of magnetic field can be computed as a function of the equatorial
radii. The values obtained for the core and surface magnetic fields are in
agreement with those typical of compact objects.",1812.07657v1
2019-12-03,Internally-Balanced Magnetic Mechanisms Using Magnetic Spring for Producing Large Amplified Clamping Force,"To detach a permanent magnet with a controlled force much smaller than its
original attractive force, the Internally-Balanced Magnetic Unit (IB Magnet)
was invented and has been applied to magnetic devices such as wall-climbing
robots, ceil-dangling drones, and modular swarm robots. In contrast to its
drastic reduction rate on the control force, the IB Magnet has two major
problems on its nonlinear spring which cancels out the internal force on the
magnet: complicated design procedure and trade-off relationship between
balancing precision and mechanism volume. This paper proposes a principle of a
new balancing method for the IB Magnet which uses a like-pole pair of magnets
as a magnetic spring, whose repulsive force ideally equals the attractive force
of an unlike-pole pair exactly. To verify the proposed principle, the authors
realized a prototype model of the IB Magnet using magnetic spring and verified
through experiments its reduction rate is comparable to those of conventional
IB Magnets. Moreover, the authors discussed and realized a robotic clamp as an
application example containing proposed IB Magnets as its internal mechanism.",1912.01292v1
2020-09-14,Voltage-driven Magnetization Switching via Dirac Magnetic Anisotropy and Spin--orbit Torque in Topological-insulator-based Magnetic Heterostructures,"Electric-field control of magnetization dynamics is fundamentally and
technologically important for future spintronic devices. Here, based on
electric-field control of both magnetic anisotropy and spin--orbit torque, two
distinct methods are presented for switching the magnetization in topological
insulator (TI)/magnetic-TI hybrid systems. The magnetic anisotropy energy in
magnetic TIs is formulated analytically as a function of the Fermi energy, and
it is confirmed that the out-of-plane magnetization is always favored for the
partially occupied surface band. Also proposed is a transistor-like device with
the functionality of a nonvolatile magnetic memory that uses voltage-driven
writing and the (quantum) anomalous Hall effect for readout. For the
magnetization reversal, by using parameters of Cr-doped
Bi_{1-x}Sb_{x})_{2}Te_{3}, the estimated source-drain current density and gate
voltage are of the orders of $10^4$--$10^5$~A/cm$^2$ and 0.1~V, respectively,
below 20~K and the writing requires no external magnetic field. Also discussed
is the possibility of magnetization switching by the proposed method in
TI/ferromagnetic-insulator bilayers with the magnetic proximity effect.",2009.06187v1
2021-07-10,Photoinduced Magnetic Force Microscopy: Enabling Direct and Exclusive Detection of Optical Magnetism,"Modern optical nano-elements pursue ever-smaller sizes and individualized
functionalities. Those elements that can efficiently manipulate the magnetic
field of light boast promising future applications with a great challenge: the
magnetic near field is irretrievable from conventional optical far-field
characterization. Here we propose photoinduced magnetic force microscopy to
directly and exclusively sense the magnetic field of light at the nanoscale.
The proposed instrument exploits a magnetic nanoprobe with exclusive magnetic
excitation under structured light illumination. The magnetic nanoprobe detects
the photoinduced magnetic force, which is defined as the dipolar Lorentz force
exerted on the photoinduced magnetic dipole in the nanoprobe. Since the
resulting magnetic force is proportional to the incident magnetic field, the
measured force reveals the magnetic near-field distribution at the nanoscale.
The proposed instrument represents a fundamental step towards comprehensive
electric and magnetic near-field detection and/or manipulation in single
nano-element optical devices.",2107.04739v1
2022-08-31,Second-order phase transition of silicon from a band insulator to metal induced by strong magnetic fields,"We present the second-order phase transition from a band insulator to metal
that is induced by a strong magnetic field. The magnetic-field dependences of
the magnetization and energy band gap of a crystalline silicon immersed in a
magnetic field are investigated by means of the nonperturbative
magnetic-field-containing relativistic tight-binding approximation method
[Phys. Rev. B 97, 195135 (2018)]. It is shown that the energy band gap
disappears at the critical magnetic field of 2.22x$10^4$ (T). At the critical
magnetic field, the magnetic-field dependence of the magnetization exhibits a
kink behavior, which means that this phenomenon is the second-order phase
transition from a band insulator to metal. It is found that in strong magnetic
fields above the critical magnetic field, namely in the metallic phase, the
oscillation of the magnetization appears. It is shown that this magnetic
oscillation comes from the energy bands in the magnetic Brillouin zone that
change from the occupied states to unoccupied states or vice vasa.",2208.14690v1
2023-07-18,Yu-Shiba-Rusinov tips: imaging spins at the atomic scale with full magnetic sensitivity,"Measurements of magnetic properties at the atomic scale require probes
capable of combining high spatial resolution with spin sensitivity.
Spin-polarized scanning tunneling microscopy (SP-STM) fulfills these conditions
by using atomically sharp magnetic tips. The imaging of spin structures results
from the tunneling magneto-conductance that depends on the imbalance in the
local density of spin-up and spin-down electrons. Spin-sensitive tips are
generally formed from bulk materials or by coating non-magnetic tips with a
thin magnetic layer. However, ferromagnetic materials generate stray magnetic
fields which can influence the magnetic structure of the probed system, while
the magnetization of antiferromagnetic materials is difficult to set tip by
externally applied magnetic fields. Here, we use functionalized
Yu-Shiba-Rusinov (YSR) tips prepared by attaching magnetic adatoms at the apex
of a superconducting cluster to image magnetic interactions at the atomic
scale. We demonstrate that YSR tips are capable of sensing different
magnetization directions, conferring them full magnetic sensitivity. We
additionally show that the finite size of the tip superconducting cluster makes
it robust against relatively strong magnetic fields, making YSR tips capable of
visualizing magnetic field driven transitions of the spin texture.",2307.09534v1
2024-03-20,Molecular Dynamics Simulations of Microscopic Structural Transition and Macroscopic Mechanical Properties of Magnetic Gels,"Magnetic gels with embedded micro/nano-sized magnetic particles in
crosslinked polymer networks can be actuated by external magnetic fields, with
changes in their internal microscopic structures and macroscopic mechanical
properties. We investigate the responses of such magnetic gels to an external
magnetic field, by means of coarse-grained molecular dynamics simulations. We
find that the dynamics of magnetic particles are determined by the interplay of
between magnetic dipole-dipole interactions, polymer elasticity and thermal
fluctuations. The corresponding microscopic structures formed by the magnetic
particles such as elongated chains can be controlled by the external magnetic
field. Furthermore, the magnetic gels can exhibit reinforced macroscopic
mechanical properties, where the elastic modulus increases algebraically with
the magnetic moments of the particles in the form of
$\propto(m-m_{\mathrm{c}})^{2}$ when magnetic chains are formed. This
simulation work can not only serve as a tool for studying the microscopic and
the macroscopic responses of the magnetic gels, but also facilitate future
fabrications and practical controls of magnetic composites with desired
physical properties.",2403.13481v1
2017-02-07,Characteristics of Low-Latitude Coronal Holes near the Maximum of Solar cycle 24,"We investigate the statistics of 288 low-latitude coronal holes extracted
from SDO/AIA-193 filtergrams over the time range 2011/01/01 to 2013/12/31. We
analyse the distribution of characteristic coronal hole properties, such as the
areas, mean AIA-193 intensities, and mean magnetic field densities, the local
distribution of the SDO/AIA-193 intensity and the magnetic field within the
coronal holes, and the distribution of magnetic flux tubes in coronal holes. We
find that the mean magnetic field density of all coronal holes under study is
3.0 +- 1.6 G, and the percentage of unbalanced magnetic flux is 49 +- 16 %. The
mean magnetic field density, the mean unsigned magnetic field density, and the
percentage of unbalanced magnetic flux of coronal holes depend strongly
pairwise on each other, with correlation coefficients cc > 0.92. Furthermore,
we find that the unbalanced magnetic flux of the coronal holes is predominantly
concentrated in magnetic flux tubes: 38 % (81 %) of the unbalanced magnetic
flux of coronal holes arises from only 1 % (10 %) of the coronal hole area,
clustered in magnetic flux tubes with field strengths > 50 G (10 G). The
average magnetic field density and the unbalanced magnetic flux derived from
the magnetic flux tubes correlate with the mean magnetic field density and the
unbalanced magnetic flux of the overall coronal hole (cc > 0.93). These
findings give evidence that the overall magnetic characteristics of coronal
holes are governed by the characteristics of the magnetic flux tubes.",1702.02050v1
2019-12-09,Field Dependence of Magnetic Disorder in Nanoparticles,"The performance characteristics of magnetic nanoparticles towards
application, e.g. in medicine, imaging, or as sensors, is directly determined
by their magnetization relaxation and total magnetic moment. In the commonly
assumed picture, nanoparticles have a constant overall magnetic moment
originating from the magnetization of the single-domain particle core
surrounded by a surface region hosting spin disorder. In contrast, this work
demonstrates the significant increase of the magnetic moment of ferrite
nanoparticles with applied magnetic field. At low magnetic field, the
homogeneously magnetized particle core initially coincides in size with the
structurally coherent grain of 12.8(2) nm diameter, indicating a strong
coupling between magnetic and structural disorder. Applied magnetic fields
gradually polarize the uncorrelated, disordered surface spins, resulting in a
magnetic volume more than 20\% larger than the structurally coherent core. The
intraparticle magnetic disorder energy increases sharply towards the
defect-rich surface as established by the field-dependence of the magnetization
distribution. In consequence, these findings illustrate how the nanoparticle
magnetization overcomes structural surface disorder. This new concept of
intraparticle magnetization is deployable to other magnetic nanoparticle
systems, where the in-depth knowledge of spin disorder and associated magnetic
anisotropies will be decisive for a rational nanomaterials design.",1912.04081v2
2021-04-23,Interesting magnetic response of the nuclear fuel material UO2,"Magnetic response of uranium dioxide (UO2) has been investigated through
temperature and magnetic field dependent dc magnetization measurements. UO2 is
a paramagnet at room temperature. The magnetic susceptibility, however,
deviates from Curie-Weiss (CW) like paramagnetic behavior below T = 280 K.
Further down the temperature UO2 undergoes phase transition to an
antiferromagnetic state below TN = 30.6 K. The zero field cooled (ZFC) and
field cooled (FC) magnetizations exhibit some distinct thermomagnetic
irreversibility below TN. The temperature dependence of the FC magnetization is
more like a ferromagnet, whereas ZFC magnetization exhibits distinct structures
not usually observed in the antiferromagnets. In low applied magnetic field
this thermomagnetic irreversibility in magnetization exists in a subtle way
even in the paramagnetic regime above TN up to a fairly high temperature, but
vanishes in high applied magnetic fields. Deviation from CW law and
irreversibility between ZFC and FC magnetization indicate that the paramagnetic
state above TN is not a trivial one. Magnetic response below TN changes
significantly with the increase in the applied magnetic field. Thermomagnetic
irreversibility in magnetization initially increases with the increase in the
strength of applied magnetic field, but then gets reduced in the high applied
fields. A subtle signature of a magnetic field induced phase transition is also
observed in the isothermal magnetic field vartaion of magnetization. All these
experimetal results highlight the non-trivial nature of the antiferromagnetic
state in UO2",2104.11412v1
1998-01-12,Persistent Currents and Magnetization in two-dimensional Magnetic Quantum Systems,"Persistent currents and magnetization are considered for a two-dimensional
electron (or gas of electrons) coupled to various magnetic fields.
Thermodynamic formulae for the magnetization and the persistent current are
established and the ``classical'' relationship between current and
magnetization is shown to hold for systems invariant both by translation and
rotation. Applications are given, including the point vortex superposed to an
homogeneous magnetic field, the quantum Hall geometry (an electric field and an
homogeneous magnetic field) and the random magnetic impurity problem (a random
distribution of point vortices).",9801106v1
1999-03-20,Magnetism Controlled Vortex Matter,"We discuss a new class of phenomena based on strong interaction between
magnetic superstructures and vortices in superconductors in combined
heterogeneous structures. An inhomogeneous magnetization can pin vortices or
create them spontaneously changing drastically properties of the
superconductor. On the other hand, the interaction between magnetic moments
mediated by vortices can result in specific types of magnetic ordering. The
same interaction can create coupled magnetic-superconducting defects. We
discuss possible experimental observation of magnetism controlled vortex matter
in superconducting films with magnetic nanoscale dots or stripes and layered
systems with alternating superconducting and magnetic layers.",9903312v1
1999-04-07,Perpendicular transport and magnetization processes in magnetic multilayers with strongly and weakly coupled magnetic layers,"Within the framework of a two-band tight-binding model, we have performed
calculations of giant magnetoresistance, exchange coupling and thermoelectric
power (TEP) for a system consisting of three magnetic layers separated by two
non-magnetic spacers with the first two magnetic layers strongly
antiferromagnetically exchange-coupled. We have shown how does the GMR relate
with the corresponding regions of magnetic structure phase diagrams and
computed some relevant hysteresis loops, too. The GMR may take negative values
for specific layers thicknesses, and the TEP reveals quite pronounced
oscillations around a negative bias.",9904086v1
2003-07-16,Magnetic moment of an electron gas on the surface of constant negative curvature,"The magnetic moment of an electron gas on the surface of constant negative
curvature is investigated. It is shown that the surface curvature leads to the
appearance of the region of the monotonic dependence $M(B)$ at low magnetic
fields. At high magnetic fields, the dependence of the magnetic moment on a
magnetic field is the oscillating one. The effect of the surface curvature is
to increase the region of the monotonic dependence of the magnetic moment and
to break the periodicity of oscillations of the magnetic moment as a function
of an inverse magnetic field.",0307401v1
2004-12-27,Magnetization suppression of Type-II Superconductors by external alternating magnetic field,"The effect of suppression of static magnetization of an anisotropic hard
superconductor by alternating magnetic field is analyzed theoretically. The
magnetic moment suppression dynamics is described with respect to the
magnetization loop of the superconductor. It is found that in some cases the
magnetic moment varies nonmonotonically with the growth in amplitude
$\mathrm{h}$ of the alternating field. Effect of transition, induced by
$\mathrm{\mathbf{h}}(t)$, of superconductor form paramagnetic into the
diamagnetic state is considered. The amplitude of alternating magnetic field
$\mathrm{h}_{c}(\delta,\vartheta)$ for which the complete suppression of the
magnetization occurs is calculated as the function of anisotropy parameter
$\delta$ and it orientation angle $\vartheta$ with respect to the
crystallographic axes of the sample.",0412695v1
2010-06-21,Dynamics of magnetic charges in artificial spin ice,"Artificial spin ice has been recently implemented in two-dimensional arrays
of mesoscopic magnetic wires. We propose a theoretical model of magnetization
dynamics in artificial spin ice under the action of an applied magnetic field.
Magnetization reversal is mediated by domain walls carrying two units of
magnetic charge. They are emitted by lattice junctions when the the local field
exceeds a critical value $H_c$ required to pull apart magnetic charges of
opposite sign. Positive feedback from Coulomb interactions between magnetic
charges induces avalanches in magnetization reversal.",1006.4075v2
2010-11-08,Neutrino magnetic moment in a magnetized plasma,"The contribution of a magnetized plasma to the neutrino magnetic moment is
calculated. It is shown that only part of the additional neutrino energy in
magnetized plasma connecting with its spin and magnetic field strength defines
the neutrino magnetic moment. It is found that the presence of magnetized
plasma does not lead to the considerable increase of the neutrino magnetic
moment in contrast to the results presented in literature previously.",1011.1779v1
2011-03-08,Permanent magnets including undulators and wigglers,"After a few historic remarks on magnetic materials we introduce the basic
definitions related to permanent magnets. The magnetic properties of the most
common materials are reviewed and the production processes are described.
Measurement techniques for the characterization of macroscopic and microscopic
properties of permanent magnets are presented. Field simulation techniques for
permanent magnet devices are discussed. Today, permanent magnets are used in
many fields. This article concentrates on the applications of permanent magnets
in accelerators starting from dipoles and quadrupoles on to wigglers and
undulators.",1103.1573v1
2013-02-20,Non-magnetic doping induced magnetism in Li doped SnO2 nanoparticles,"We address the possibility of non-magnetic doping induced magnetism, in Li
doped SnO2 nano-particles. The compounds have been prepared by solid state
route at equilibrium and were found to be crystallized in single rutile phase.
The magnetization measurements have shown that Li-doping induces magnetism in
SnO2 for a particular range of Li concentration. However, for other Li
concentrations, including pure SnO2, the samples exhibit diamagnetism. To
investigate the possible origin of the induced magnetism, we have studied the
variation of the magnetization as a function of the average nano-particle
radius. Possible scenarios for the appearance of magnetism in these compounds
are discussed.",1302.4869v1
2013-12-04,Titan Magnetic Tail: Does its Configuration correspond to the Induced Magnetosphere?,"Magnetic field structure observed in numerous Cassini flybys in the region of
Titan interaction with the corotating flow of Kronian magnetosheric plasma
contradicts the classical picture of the ideal induced magnetosphere produced
by the magnetic field line draping about the obstacle. Clear draping is
observed only upstream the Titan, but not in the Titan magnetic wake. We
consider the magnetic field tension downstream the Titan magnetic tail and show
that the magnetic field direction is not consistent with the induced
magnetosphere produced by magnetic field lines draping. We arrive at the
conclusion that the mechanisms alternative to the induced magnetosphere
formation should be considered for the Titan magnetic surrounding.",1401.3729v1
2015-06-05,On the magnetization process of ferromagnetic materials,"The present article concludes that a ferromagnetic sample could be considered
like a paramagnetic system where the role of magnetic moments plays magnetic
domains. Based on this conclusion and taking into account presence of an
anisotropic field the formula which describes magnetization dependence on the
external magnetic field is derived. Expressions for a remanent magnetization
and a coercive force are presented. The new parameter to characterize a
magnetic stiffness of a material is introduced. A physical expression for a
dynamic magnetic susceptibility as a function of material's characteristics,
external magnetic field, and a temperature is given.",1506.01805v3
2015-05-19,Electromagnetic acceleration of permanent magnets,"We consider the acceleration of the permanent magnets, consisting of
neodymium iron boron by means of the running magnetic field gradient. It is
shown that the specific magnetic moment per nucleon in neodymium iron boron is
determined by the remained magnetization of the substance. The maximum
accessable gradient of the magnetic field accelerating the permanent magnets is
determined by the coercive force thirty kilogauss. For the neodymium iron boron
magnets this gradient is equal to twenty kilogauss divided by one centimeter.
The finite velocity of the magnets six kilometers per second, the length of
acceleration is six hundred thirty-seven meters.",1508.04078v1
2016-04-03,Soliton collisions in soft magnetic nanotube with uniaxial anisotropy,"The structure of stable magnetic solitons of various orders in soft magnetic
nanotube with uniaxial magnetic anisotropy has been studied using numerical
simulation. Solitons of even order are immobile in axially applied magnetic
field. Odd solitons show decreased mobility with respect to that of head-to
head domain wall. Solitons of various orders can participate in nanotube
magnetization reversal process. Various coalescence and decomposition processes
in soliton assembly are considered. It is shown that the general magnetization
state of magnetic nanotube consists of chains of magnetic solitons of various
orders.",1604.00614v1
2017-01-15,Magnetic Catalysis in Antiferromagnetic Films,"We study the low-temperature behavior of antiferromagnets in two spatial
dimensions that are subjected to a magnetic field oriented perpendicular to the
staggered magnetization order parameter. The evaluation of the partition
function is carried to two-loop order within the systematic effective
Lagrangian technique. Low-temperature series that are valid in weak magnetic
and staggered fields are derived for the pressure, staggered magnetization, and
magnetization. Remarkably, at $T$=0, the staggered magnetization is enhanced by
the magnetic field, implying that the phenomenon of magnetic catalysis also
emerges in antiferromagnetic films.",1701.04085v1
2023-05-26,"Practical Concepts for Design, Construction and Application of Halbach Magnets in Magnetic Resonance","This review is a compilation of relevant concepts in designing Halbach
multipoles for magnetic resonance applications. The main focus is on providing
practical guidelines to plan, design and build such magnets. Therefore,
analytical equations are presented for estimating the magnetic field from ideal
to realistic systems. Various strategies of homogenizing magnetic fields are
discussed together with concepts of opening such magnets without force, or
combining them for variable fields. Temperature compensation and other
practical aspects are also reviewed. For magnetic resonance two polarities (di-
and quadrupole) are of main interest, but higher polarities are also included.",2305.17227v2
2023-08-24,Non-reciprocal coherent all-optical switching between magnetic multi-states,"We present experimental and computational findings of the laser-induced
non-reciprocal motion of magnetization during ultrafast photo-magnetic
switching in garnets. We found distinct coherent magnetization precession
trajectories and switching times between four magnetization states, depending
on both directions of the light linear polarization and initial magnetic state.
As a fingerprint of the topological symmetry, the choice of the switching
trajectory is governed by an interplay of the photo-magnetic torque and
magnetic anisotropy. Our results open a plethora of possibilities for designing
energy-efficient magnetization switching routes at arbitrary energy landscapes.",2308.12771v1
2023-08-28,Revisiting the Wu-Yang approach to magnetic charge,"The Wu-Yang fiber bundle approach to magnetic charge has an overlooked
feature -- a disk-like sheet current density and associated magnetic field at
the equator where the Northern hemisphere and Southern hemisphere Dirac string
vector potentials connect. This disk magnetic field plays a role similar to the
Dirac string in the Dirac approach to magnetic charge. Placing an electric
charge near the disk magnetic field gives rise to a non-zero field momentum.
This implies that the Wu-Yang construction is not a true magnetic charge -- it
is a Coulomb magnetic field plus a disk magnetic field and planar current
density.",2308.14706v1
2024-01-19,Modelling and dynamics of pendulum systems subjected to a nonstationary magnetic field,"The prepared doctoral dissertation focuses on studying dynamics of systems
composed of magnetic pendulums subjected to a non-stationary magnetic field. A
magnetic pendulum is a physical pendulum with a magnet attached to its end and
is placed in an external magnetic field. The non-stationary external magnetic
field is generated by an electric coil placed under the pendulum and powered by
a time-varying current signal. The presented research mainly concerns the
oscillations in one potential well of a single magnetic pendulum, as well as
the control of the energy flow between two torsionally coupled magnetic
pendulums.",2401.10594v1
1999-09-27,Topological Constraints on the Relaxation of Complex Magnetic Fields,"Newly emerging magnetic flux can show a complicated linked or interwoven
topology of the magnetic field. The complexity of this linkage or knottedness
of magnetic flux is related to the free energy stored in the magnetic field.
Magnetic reconnection provides a process to release this energy on the time
scale of the dynamics. At the same time it approximately conserves the total
magnetic helicity. Therefore the conservation of total magnetic helicity is a
crucial constraint for the relaxation of complex magnetic fields. However, the
total magnetic helicity is only the first, most elementary, quantity of an
infinite series of topological invariants of the magnetic field. All these
invariants are strictly conserved in ideal magnetohydrodynamics. As an example
a preliminary set of these invariants is derived. The relevance of these higher
order invariants for the final state of relaxation under magnetic reconnection
and their implications for the release of magnetic energy are discussed.",9909443v1
2007-10-22,Observation of magnetization reversal and negative magnetization in a double perovskite compound Sr2YbRuO6,"Detailed magnetic properties of the compound Sr2YbRuO6 are presented here.
The compound belongs to the family of double perovskites forming a monoclinic
structure. Magnetization meas-urements reveal clear evidence for two components
of magnetic ordering aligned opposite to each other, leading to a magnetization
reversal, compensation temperature (T* = 34 K) and neg-ative magnetization at
low temperatures and low magnetic fields. Heat capacity measurements
corroborate the presence of two components in the magnetic ordering and a
noticeable third anomaly at low temperatures (~15 K) which cannot be attributed
the Schottky effect. The calcu-lated magnetic entropy is substantially lower
than that expected for the ground states of the or-dered moments of Ru5+ and
Yb3+, indicating the presence of large crystal field effects and/ or
in-complete magnetic ordering and/or magnetic frustrations well above the
magnetic ordering. An attempt is made to explain the magnetization reversal
within the frameworks of available models.",0710.4043v3
2008-05-21,Energetic Analysis of Magnetic Transitions in Ultra-small Nanoscopic Magnetic Rings,"In this article, we report on experimental and theoretical investigations of
magnetic transitions in cobalt rings of size (diameter, width and thickness)
comparable to the exchange length of cobalt. Magnetization measurements were
performed for two sets of magnetic ring arrays: ultra-small magnetic rings
(outer diameter 13 nm, inner diameter 5nm and thickness 5 nm) and small
thin-walled magnetic rings (outer diameter 150 nm, width 5 nm and thickness 5
nm). This is the first report on the fabrication and magnetic properties of
such small rings. Our calculations suggest that if the magnetic ring's sizes
are comparable to, or smaller than, the exchange length of the magnetic
material, then only two magnetic states are important - the pure single domain
state and the flux closure vortex state. The onion-shape magnetic state does
not arise. Theoretical calculations are based on an energetic analysis of pure
and slightly distorted single domain and flux closure vortex magnetic states.
Based on the analytical calculations, a phase diagram is also derived for
ultra-small ring structures exhibiting the region for vortex magnetic state
formations as a function of material parameter.",0805.3191v2
2010-01-29,Orbital magnetization of the electron gas on a two-dimensional kagome lattice under a perpendicular magnetic field,"The orbital magnetization of the electron gas on a two-dimensional kagome
lattice under a perpendicular magnetic field is theoretically investigated. The
interplay between the lattice geometry and magnetic field induce nontrivial
$k$-space Chern invariant in the magnetic Brillouin zone, which turns to result
in profound effects on the magnetization properties. We show that the
Berry-phase term in the magnetization gives a paramagnetic contribution, while
the conventional term brought about by the magnetic response of the magnetic
Bloch bands produces a diamagnetic contribution. As a result, the superposition
of these two components gives rise to a delicate oscillatory structure in the
magnetization curve when varying the electron filling factor. The relationship
between this oscillatory behavior and the Hofstadter energy spectrum is
revealed by selectively discussing the magnetization and its two components at
the commensurate fluxes of $f$=1/4, 1/3, and 1/6, respectively. In particular,
we reveal as a typical example the fractal structure in the magnetic
oscillations by tuning the commensurate flux around $f$=1/4. The
finite-temperature effect on the magnetization is also discussed.",1001.5330v1
2014-10-08,An optimized magnet for magnetic refrigeration,"A magnet designed for use in a magnetic refrigeration device is presented.
The magnet is designed by applying two general schemes for improving a magnet
design to a concentric Halbach cylinder magnet design and dimensioning and
segmenting this design in an optimum way followed by the construction of the
actual magnet. The final design generates a peak value of 1.24 T, an average
flux density of 0.9 T in a volume of 2 L using only 7.3 L of magnet, and has an
average low flux density of 0.08 T also in a 2 L volume. The working point of
all the permanent magnet blocks in the design is very close to the maximum
energy density. The final design is characterized in terms of a performance
parameter, and it is shown that it is one of the best performing magnet designs
published for magnetic refrigeration.",1410.1987v1
2016-12-28,"Magnetic structure of Cu2MnBO5 ludwigite: thermodynamic, magnetic properties and neutron diffraction study","We report on the thermodynamic, magnetic properties and the magnetic
structure of ludwigite-type Cu2MnBO5. The specific heat, the low-field
magnetization and the paramagnetic susceptibility were studied on a single
crystal and combined with powder neutron diffraction data. The temperature
dependence of the specific heat and the neutron diffraction pattern reveal a
single magnetic phase transition at T=92 K, which corresponds to the magnetic
ordering into a ferromagnetic phase. The cation distribution and the values and
directions of magnetic moments of ions in different crystallographic sites are
established. The magnetic moments of Cu2+ and Mn3+ ions occupying different
magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their
directions do not coincide with the directions of the principal
crystallographic axes.The small value of the magnetic moment of copper ions
occupying site 2a is indicative of partial disordering of the magnetic moments
on this site. The magnetization measurements show a strong temperature
hysteresis of magnetization, which evidences for field-dependent transitions
below the phase transition temperature.",1612.08805v1
2017-12-18,Magnetic and universal magnetocaloric behavior of rare-earth substituted DyFe0.5Cr0.5O3,"We report the effect of partial substitution of Dy-site by rare-earths (R=Gd,
Er and La)on the magnetic and magnetocaloric behavior of a mixed metal oxide
DyFe0.5Cr0.5O3.Structural studies reveal that substitution of Dy by R has a
minimal influence on the crystal structure. Magnetic and heat capacity studies
show that the magnetic transition around 121 K observed for DyFe0.5Cr0.5O3
remains unchanged with rare-earth substitution, whereas the lower magnetic
transition temperature is suppressed/enhanced by magnetic/non-magnetic
substitution. In all these compounds, the second order nature of magnetic
transition is confirmed by Arrott plots. As compared to DyFe0.5Cr0.5O3, the
values of magnetic entropy change and relative cooling power are increased with
magnetic rare-earth substitution while it decreases with non-magnetic
rare-earth substitution. In all these compounds, magnetic entropy change
follows the power law dependence of magnetic field and the value of the
exponent n indicate the presence of ferromagnetic correlation in an
antiferromagnetic state. A phenomenological universal master curve is also
constructed for all the compounds by normalizing the entropy change with
rescaled temperature using a single reference temperature. This master curve
also reiterates the second order nature of the magnetic phase transition in
such mixed metal oxides.",1712.06396v1
2018-02-08,Nonspecific biological effects of weak magnetic fields depend on molecular rotations,"The radical pair mechanism is a leading hypothesis in animal magnetic
navigation. This mechanism associates the magnetic sense with the visual
system, the radical pairs in cryptochromes of the eye retina being specialized
magnetic receptors that modulate rhodopsin-mediated photoreception. There are
also nonspecific magnetic effects in biology, which occur mostly by chance and
originate from the interaction of weak magnetic fields with the magnetic
moments dispersed all over the organism at the microscopic level. The radical
pair mechanism cannot explain this type of response for many reasons. We have
previously shown that the above interaction has a finite probability of
resulting in an observable. Here, we develop our physical model of nonspecific
magnetic effects for the case of magnetic moments located in rotating
molecules. We generalize the results of recent experiments on gene expression
in plants in a constant magnetic field, and show that the precession of the
magnetic moments that reside on rotating molecules can be slowed relative to
the immediate biophysical structures. In quantum mechanical language, the
crossing of the quantum levels of magnetic moments conjointly with molecular
rotations explain nonspecific magnetic effects and leads to magnetic
field-dependences that are in good agreement with the experiment.",1802.02903v1
2019-05-22,"Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5","YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits
magnetic ordering and dielectric anomaly above 200 K. Partial substitution of
Fe with other magnetic and non-magnetic ion affects the magnetic and the
structural properties of the system. We report detailed investigation of
structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M=Co, Ni
and Ga). We observed that the partial replacement of Ni and Co in place of Fe,
results in magnetic dilution and broadening of the magnetic transition and
shifting towards lower temperature. The replacement of Fe with non-magnetic Ga
also results in shifting of the magnetic transition to the lower temperature
side. The observed dielectric relaxation behavior in these compounds is due to
the charge carrier hoping. This study highlights the impacts of magnetic and
non-magnetic doping at the magnetic site on magnetic and dielectric properties
in layered perovskite compound YBaCuFeO5.",1905.08982v2
2019-11-08,Magnetic glassy state at low spin state of Co3+ in EuBaCo2O5+δ (δ = 0.47) cobaltite,"The magnetic glassy state is a fascinating phenomenon, which results from the
kinetic arrest of the first order magnetic phase transition. Interesting
properties, such as metastable magnetization and nonequilibrium magnetic
phases, are naturally developed in the magnetic glassy state. Here, we report
magnetic glass property in the low spin state of Co3+ in EuBaCo2O5+{\delta}
({\delta} = 0.47) cobaltite at low temperature (T < 60 K). The measurements of
magnetization under the cooling and heating in unequal fields, magnetization
relaxation and thermal cycling of magnetization show the kinetic arrest of low
magnetization state below 60 K. The kinetically arrested low temperature
magnetic phase is further supported through the study of isothermal magnetic
entropy, which shows the significant entropy change. The present results will
open a new window to search the microscopic relation between the spin state
transitions and the kinetic arrest induced magnetic glassy phenomena in complex
materials.",1911.03258v1
2020-07-17,Unraveling nanoscale magnetic ordering in Fe3O4 nanoparticle assemblies via x-rays,": Understanding the correlations between magnetic nanoparticles is important
for nanotechnologies, such as high-density magnetic recording and biomedical
applications, where functionalized magnetic particles are used as contrast
agents and for drug delivery. The ability to control the magnetic state of
individual particles depends on the good knowledge of magnetic correlations
between particles when assembled. Inaccessible via standard magnetometry
techniques, nanoscale magnetic ordering in self-assemblies of Fe3O4
nanoparticles is here unveiled via x-ray resonant magnetic scattering (XRMS).
Measured throughout the magnetization process, the XRMS signal reveals
size-dependent inter-particle magnetic correlations. Smaller (5 nm) particles
show little magnetic correlation, even when tightly close-packed, yielding to
mostly magnetic disorder in the absence of external field, which is
characteristic of superparamagnetic behavior. In contrast, larger (11 nm)
particles tend to be strongly correlated, yielding a mix of magnetic orders
including ferromagnetic and anti-ferromagnetic orders. These strong magnetic
correlations are present even when the particles are sparsely distributed.",2007.09226v1
2021-12-02,Magnetic correction to the Anomalous Magnetic Moment of Electron,"We investigate the leading order correction of anomalous magnetic moment
(AMM) to the electron in weak magnetic field and find that the magnetic
correction is negative and magnetic field dependent, indicating a magnetic
catalysis effect for the electron gas. In the laboratory to measure the $g-2$,
the magnitude of the magnetic field $B$ is several $\mathrm{T}$,
correspondingly the magnetic correction to the AMM of electron/muon is around
$10^{-34}$/$10^{-42}$, therefore the magnetic correction can be safely
neglected in current measurement. However, when the magnitude of the magnetic
field strength is comparable with the electron mass, the magnetic correction of
electron's AMM will become considerable. This general magnetic correction to
charged fermion's AMM can be extended to study QCD matter under strong magnetic
field.",2112.01051v1
2022-08-07,Mixels: Fabricating Interfaces using Programmable Magnetic Pixels,"In this paper, we present Mixels, programmable magnetic pixels that can be
rapidly fabricated using an electromagnetic printhead mounted on an
off-the-shelve 3-axis CNC machine. The ability to program magnetic material
pixel-wise with varying magnetic force enables Mixels to create new tangible,
tactile, and haptic interfaces. To facilitate the creation of interactive
objects with Mixels, we provide a user interface that lets users specify the
high-level magnetic behavior and that then computes the underlying magnetic
pixel assignments and fabrication instructions to program the magnetic surface.
Our custom hardware add-on based on an electromagnetic printhead and hall
effect sensor clips onto a standard 3-axis CNC machine and can both write and
read magnetic pixel values from magnetic material. Our evaluation shows that
our system can reliably program and read magnetic pixels of various strengths,
that we can predict the behavior of two interacting magnetic surfaces before
programming them, that our electromagnet is strong enough to create pixels that
utilize the maximum magnetic strength of the material being programmed, and
that this material remains magnetized when removed from the magnetic plotter.",2208.03804v1
1998-10-20,HST Observations of the Broad Absorption Line Quasar PG 0946+301,"We analyze HST and ground based spectra of the brightest BALQSO in the UV:
PG~0946+301. A detailed study of the absorption troughs as a function of
velocity is presented, facilitated by the use of a new algorithm to solve for
the optical depth as a function of velocity for multiplet lines. We find
convincing evidence for saturation in parts of the troughs. This supports our
previous assertion that saturation is common in BALs and therefore cast doubts
on claims for very high metallicity in BAL flows. Due to the importance of BAL
saturation we also discuss its evidence in other objects. In PG~0946+301 large
differences in ionization as a function of velocity are detected and our
findings supports the hypothesis that the line of sight intersects a number of
flow components that combine to give the appearance of the whole trough. Based
on the optical depth profiles, we develop a geometrical-kinematical model for
the flow. We have positively identified 16 ions of 8 elements (H~I, C~III,
C~IV, N~III, N~IV, N~V, O~III, O~IV, O~V, O~VI, Ne~V, Ne~VIII, P~V, Si~IV, S~V,
S~VI) and have a probable identifications of Mg~X and S~IV. Unlike earlier
analysis of IUE data, we find no evidence for BALs arising from excited ionic
states in the HST spectrum of PG~0946+301.",9810309v1
2003-02-17,Time evolution of X-ray coronal activity in PMS stars; a possible relation with the evolution of accretion disks,"We investigate the evolution of X-ray stellar activity from the age of the
youngest known star forming regions (SFR), < 1Myr, to about 100 Myr, i.e. the
zero age main sequence (ZAMS) for a ~ 1M_sun star. We consider five SFR of
varying age (Rho Ophiuchi, the Orion Nebula Cluster, NGC 2264, Chamaeleon I,
and Eta Chamaeleontis) and two young clusters (the Pleiades and NGC 2516).
Optical and X-ray data for these regions are retrieved both from archival
observations and recent literature, and reanalyzed here in a consistent manner
so to minimize systematic differences in the results. We study trends of L_X
and L_X/L_bol as a function of stellar mass and association age. For low mass
stars (M < 1M_sun) we observe an increase in L_X/L_bol in the first 3-4 Myr and
a subsequent leveling off at the saturation level (L_X/L_bol ~ -3). Slowly
evolving very low mass stars then retain saturated levels down to the oldest
ages here considered, while for higher mass stars activity begins to decline at
some age after ~10^7 years. We find our data consistent with the following
tentative picture: low mass PMS stars with no circumstellar accretion disk have
saturated activity, consistently with the activity-Rossby number relation
derived for MS stars. Accretion and/or the presence of disks somehow lowers the
observed activity levels; disk dissipation and/or the decrease of mass
accretion rate in the first few Myrs of PMS evolution is therefore responsible
for the observed increase of L_X/L_bol with time.",0302329v1
2004-06-10,A more informative picture of the HST Ultra Deep Field,"The Hubble Space Telescope has obtained some of its well-deserved impact by
producing stunning three-color (RGB) pictures from three-band imaging data.
Here we produce a new RGB representation of the $I$, $V$, and $B$ bandpass
images of the HST Ultra Deep Field (HUDF). Our representation is based on
principles set forth elsewhere (Lupton et al 2004, PASP, 116, 133--137). The
principal difference between our RGB representation of the data and the more
traditional representation provided by the Space Telescope Science Institute is
that the (necessarily) nonlinear transformation between data values and RGB
values is done in a color-preserving (i.e., hue- and saturation-preserving)
way. For example, if one of the image pixel values saturates the dynamic range
of the RGB representation, all three of the R, G, and B values in the
representation are truncated such that the hue and saturation of the pixel is
the same as it would have been if the pixel had had lower flux but the same
astronomical color. This, in effect, makes the bright parts of the
representation an informative color map, not ""whited out"" as they are in
traditional representations. For the HUDF, this difference is seen best in the
centers of bright galaxies, which show significant detail not visible in the
more traditional representation.",0406274v2
2004-07-19,On the saturation of corotation resonances: a numerical study,"[Abridged] The torque exerted by an external potential on a two-dimensional
gaseous disk at non-co-orbital corotation resonances is studied by means of
numerical simulations. The degree of saturation of these resonances is
important in determining whether an eccentric giant planet embedded in a
protoplanetary disk experiences an eccentricity excitation or damping. We
perform calculations restricted to one or two resonances to investigate the
properties of two neighboring corotation resonances, as well as the properties
of a corotation resonance that overlaps a Lindblad resonance. We find that
these properties hardly differ from the case of an isolated corotation
resonance. In particular, although the torque of two neighboring corotation
resonances may differ from the sum of the torques of the corresponding
resonances considered as isolated, it never exceeds the sum of the fully
unsaturated isolated corotation resonances, and it saturates in a fashion
similar to an isolated resonance. Similarly, the presence of an underlying
Lindblad resonance hardly affects the corotation torque, even if that resonance
implies a torque strong enough to significantly redistribute the azimuthally
averaged surface density profile, in which case the corotation torque scales
with the resulting vortensity gradient. This set of numerical experiments thus
essentially validates previous analytic studies. As a side result, we show that
corotation libration islands misrepresented by a mesh of too low resolution can
lead to a strongly overestimated corotation torque. This may be an explanation
why the eccentricity of embedded Jupiter-sized planets was never observed to
undergo an excitation in the numerical simulations performed so far.",0407403v1
2004-07-22,The nature of premaximum halts of classical nova outbursts: V723 Cassiopeiae and V463 Scuti,"We present a new interpretation of long premaximum halts of nova outbursts.
For V723 Cas (Nova Cas 1995) and V463 Sct (Nova Sct 2000), we have reproduced
light curves, excluding the brightness maxima, starting from the long
premaximum halt through the late decay phase of the outbursts using a
steady-state optically thick wind model. When the hydrogen-rich envelope of the
white dwarf (WD) is massive enough, the star expands to \sim 100 R_\sun or over
and its surface temperature decreases to below 7000 K. At this supergiant
mimicry stage, the changes in both the photospheric radius and the temperature
are small against the large increase in the envelope mass. These changes cause
a saturation in visual magnitude that lasts a long time before it begins to
decline. This saturation is known as the premaximum halt of a classical nova
outburst. The visual magnitude during the saturation is close to the bolometric
magnitude, which is an upper limit for a given WD mass. Since the WD masses are
estimated to be 0.59 M_\sun for V723 Cas and 1.1 M_\sun for V463 Sct by fitting
the decline rate of nova light curves, we can determine the absolute magnitude
of premaximum halts. It is a refined Eddington luminosity. Thus, the premaximum
halt of a nova works as a standard candle.",0407471v2
2006-04-11,Accurate Astrometry and Photometry of Saturated and Coronagraphic Point Spread Functions,"Accurate astrometry and photometry of saturated and coronagraphic point
spread functions (PSFs) are fundamental to both ground- and space-based high
contrast imaging projects. For ground-based adaptive optics imaging,
differential atmospheric refraction and flexure introduce a small drift of the
PSF with time, and seeing and sky transmission variations modify the PSF flux
distribution. For space-based imaging, vibrations, thermal fluctuations and
pointing jitters can modify the PSF core position and flux. These effects need
to be corrected to properly combine the images and obtain optimal
signal-to-noise ratios, accurate relative astrometry and photometry of detected
objects as well as precise detection limits. Usually, one can easily correct
for these effects by using the PSF core, but this is impossible when high
dynamic range observing techniques are used, like coronagrahy with a
non-transmissive occulting mask, or if the stellar PSF core is saturated. We
present a new technique that can solve these issues by using off-axis satellite
PSFs produced by a periodic amplitude or phase mask conjugated to a pupil
plane. It will be shown that these satellite PSFs track precisely the PSF
position, its Strehl ratio and its intensity and can thus be used to register
and to flux normalize the PSF. A laboratory experiment is also presented to
validate the theory. This approach can be easily implemented in existing
adaptive optics instruments and should be considered for future extreme
adaptive optics coronagraph instruments and in high-contrast imaging space
observatories.",0604256v1
2001-06-27,Angle of repose and segregation in cohesive granular matter,"We study the effect of fluids on the angle of repose and the segregation of
granular matter poured into a silo. The experiments are conducted in two
regimes where: (i) the volume fraction of the fluid is small and it forms
liquid bridges between particles, and (ii) the particles are completely
immersed in the fluid. The data is obtained by imaging the pile formed inside a
quasi-two dimensional silo through the transparent glass side walls. In the
first series of experiments, the angle of repose is observed to increase
sharply with the volume fraction of the fluid and then saturates at a value
that depends on the size of the particles. We systematically study the effect
of viscosity by using water-glycerol mixtures to vary it over at least three
orders of magnitude while keeping the surface tension almost constant. Besides
surface tension, the viscosity of the fluid is observed to have an effect on
the angle of repose and the extent of segregation. In case of bidisperse
particles, segregation is observed to decrease and finally saturate depending
on the size ratio of the particles and the viscosity of the fluid. The sharp
initial change and the subsequent saturation in the extent of segregation and
angle of repose occurs over similar volume fraction of the fluid. In the second
series of experiments, particles are poured into a container filled with a
fluid. Although the angle of repose is observed to be unchanged, segregation is
observed to decrease with an increase in the viscosity of the fluid.",0106572v1
2004-06-10,"Cluster growth in far-from-equilibrium particle models with diffusion, detachment, reattachment and deposition","Monolayer cluster growth in far-from-equilibrium systems is investigated by
applying simulation and analytic techniques to minimal hard core particle
(exclusion) models. The first model (I), for post-deposition coarsening
dynamics, contains mechanisms of diffusion, attachment, and slow activated
detachment (at rate epsilon<<1) of particles on a line. Simulation shows three
successive regimes of cluster growth: fast attachment of isolated particles;
detachment allowing further (epsilon t)^(1/3) coarsening of average cluster
size; and t^(-1/2) approach to a saturation size going like epsilon^(-1/2).
Model II generalizes the first one in having an additional mechanism of
particle deposition into cluster gaps, suppressed for the smallest gaps. This
model exhibits early rapid filling, leading to slowing deposition due to the
increasing scarcity of deposition sites, and then continued power law (epsilon
t)^(1/2) cluster size coarsening through the redistribution allowed by slow
detachment. The basic (epsilon t)^(1/3) domain growth laws and epsilon^(-1/2)
saturation in model I are explained by a simple scaling picture. A second,
fuller approach is presented which employs a mapping of cluster configurations
to a column picture and an approximate factorization of the cluster
configuration probability within the resulting master equation. This allows
quantitative results for the saturation of model I in excellent agreement with
the simulation results. For model II, it provides a one-variable scaling
function solution for the coarsening probability distribution, and in
particular quantitative agreement with the cluster length scaling and its
amplitude.",0406252v1
2006-11-06,Some aspects of electrical conduction in granular systems of various dimensions,"We report on measurements of the electrical conductivity in both a 2D
triangular lattice of metallic beads and in a chain of beads. The
voltage/current characteristics are qualitatively similar in both experiments.
At low applied current, the voltage is found to increase logarithmically in a
good agreement with a model of widely distributed resistances in series. At
high enough current, the voltage saturates due to the local welding of
microcontacts between beads. The frequency dependence of the saturation voltage
gives an estimate of the size of these welded microcontacts. The DC value of
the saturation voltage (~ 0.4 V per contact) gives an indirect measure of the
number of welded contact carrying the current within the 2D lattice. Also, a
new measurement technique provides a map of the current paths within the 2D
lattice of beads. For an isotropic compression of the 2D granular medium, the
current paths are localized in few discrete linear paths. This
quasi-onedimensional nature of the electrical conductivity thus explains the
similarity between the characteristics in the 1D and 2D systems.",0611135v2
2007-03-16,Dimension and Relative Frequencies,"We show how to calculate the finite-state dimension (equivalently, the
finite-state compressibility) of a saturated sets $X$ consisting of {\em all}
infinite sequences $S$ over a finite alphabet $\Sigma_m$ satisfying some given
condition $P$ on the asymptotic frequencies with which various symbols from
$\Sigma_m$ appear in $S$. When the condition $P$ completely specifies an
empirical probability distribution $\pi$ over $\Sigma_m$, i.e., a limiting
frequency of occurrence for {\em every} symbol in $\Sigma_m$, it has been known
since 1949 that the Hausdorff dimension of $X$ is precisely $\CH(\pi)$, the
Shannon entropy of $\pi$, and the finite-state dimension was proven to have
this same value in 2001.
  The saturated sets were studied by Volkmann and Cajar decades ago. It got
attention again only with the recent developments in multifractal analysis by
Barreira, Saussol, Schmeling, and separately Olsen. However, the powerful
methods they used -- ergodic theory and multifractal analysis -- do not yield a
value for the finite-state (or even computable) dimension in an obvious manner.
  We give a pointwise characterization of finite-state dimensions of saturated
sets. Simultaneously, we also show that their finite-state dimension and strong
dimension coincide with their Hausdorff and packing dimension respectively,
though the techniques we use are completely elementary. Our results
automatically extend to less restrictive effective settings (e.g.,
constructive, computable, and polynomial-time dimensions).",0703085v1
2000-06-21,Cosmology with Curvature-Saturated Gravitational Lagrangian R/\sqrt{1 + l^4 R^2},"We argue that the Lagrangian for gravity should remain bounded at large
curvature, and interpolate between the weak-field tested Einstein-Hilbert
Lagrangian L_EH = R /16 pi G and a pure cosmological constant for large R with
the curvature-saturated ansatz L_cs=L_EH/ \sqrt{1+l^4 R^2}, where l is a length
parameter expected to be a few orders of magnitude above the Planck length. The
curvature-dependent effective gravitational constant defined by dL/dR = 1/16 pi
G_eff is G_eff = G \sqrt{1+l^4 R^2}^{3}, and tends to infinity for large $R$,
in contrast to most other approaches where G_eff-> 0. The theory possesses
neither ghosts nor tachyons. In a curvature-saturated cosmology, the
coordinates with ds^2 = a^2 [da^2/B(a) - dx^2 - dy^2- dz^2] are most convenient
since the curvature scalar becomes a linear function of $B(a)$. Solutions with
a big-bang singularity have a much milder behavior of the curvature than in
Einstein's theory. In synchronized time, the metric is given by ds^2 = dt^2 -
t^{6/5(dx^2 + dy^2+ dz^2). On the technical side we show that two different
conformal transformations make L_cs asymptotically equivalent to the
Gurovich-ansatz L= | R |^{4/3} on the one hand, and to Einstein's theory with a
minimally coupled scalar field with self-interaction on the other.",0006074v2
1996-09-18,Avoidance of Collapse by Circular Current-Carrying Cosmic String Loops,"Earlier attempts to calculate the nonlinear dynamical evolution of Witten
type superconducting vacuum vortex defects relied on the use of approximate
conducting string models that were too simple to take proper account of the
effect of current saturation. This effect is however allowed for adequately in
a newly developed class of rather more complicated, though still conveniently
analytic, conducting string models. These more realistic models have recently
been employed by Larsen and Axenides for investigating the collapse of circular
string loops in the case for which angular momentum is absent. The present work
extends this investigation to the generic case of circular string loops for
which angular momentum is present, so that there will be a centrifugal
potential barrier. This barrier will prevent collapse unless the initial
conditions are such that the relevant current saturation limit is attained, in
which case the string description of the vortex defect will break down, so that
its subsequent fate is hard to foresee. On the other hand if saturation is
avoided one would expect that the loop will eventually radiate away its excess
energy and settle down into a vorton type equilibrium state.",9609401v1
2002-11-22,QCD Saturation and $γ^*-γ^*$ Scattering,"Two photon collisions at high energy have an important theoretical advantage:
the simplicity of the initial state, which gives us a unique opportunity to
calculate these processes for large virtualities of both photons in
perturbative QCD approach. In this paper we study QCD saturation in two photon
collisions in the framework of the Glauber-Mueller approach. The
Glauber-Mueller formula is derived emphasizing the impact parameter dependence
($b_t$) of the dipole-dipole amplitude. It is shown that non-perturbative QCD
contributions are needed to describe large $b_t $-behaviour, and the way how to
deal with them is suggested. Our approach can be viewed as the model for the
saturation in which the entire impact parameter dependence is determined by the
initial conditions. The unitarity bound for the total cross section, its energy
dependence as well aspredictions for future experiments are discussed.It is
argued that the total cross section increases faster than any power of $
\log(1/x)$ in a wide range of energy or $x$, namely $\sigma(\gamma^*-\gamma^*)
  \propto (1/Q^2) exp(a \sqrt{\ln(1/x)}) \leq 1/m^2_{\pi}$ where $exp(a
\sqrt{\ln(1/x)})$ reflects the $x$ dependence of the gluon density $xG \propto
exp(2 a \sqrt{\ln(1/x)})$ and $m_{\pi}$ is the pion mass.",0211348v2
2005-05-06,Saturation Physics and Deuteron--Gold Collisions at RHIC,"We present a review of parton saturation/Color Glass Condensate physics in
the context of deuteron-gold ($d+Au$) collisions at RHIC. Color Glass
Condensate physics is a universal description of all high energy hadronic and
nuclear interactions. It comprises classical (McLerran-Venugopalan model and
Glauber-Mueller rescatterings) and quantum evolution (JIMWLK and BK equations)
effects both in small-$x$ hadronic and nuclear wave functions and in the high
energy scattering processes. Proton-nucleus (or $d+A$) collisions present a
unique opportunity to study Color Glass Condensate predictions, since many
relevant observables in proton-nucleus collisions are reasonably
well-understood theoretically in the Color Glass Condensate approach. In this
article we review the basics of saturation/Color Glass Condensate physics and
reproduce derivations of many important observables in proton
(deuteron)--nucleus collisions. We compare the predictions of Color Glass
physics to the data generated by $d+Au$ experiments at RHIC and observe an
agreement between the data and the theory, indicating that Color Glass
Condensate has probably been discovered at RHIC. We point out further
experimental measurements which need to be carried out to test the discovery.",0505052v2
1997-07-18,No saturation of the quantum Bogomolnyi bound by two-dimensional supersymmetric solitons,"We reanalyse the question whether the quantum Bogomolnyi bound is saturated
in the two-dimensional supersymmetric kink and sine-Gordon models. Our starting
point is the usual expression for the one-loop correction to the mass of a
soliton in terms of sums over zero-point energies. To regulate these sums, most
authors put the system in a box with suitable boundary conditions, and impose
an ultraviolet cut-off. We distinguish between an energy cut-off and a mode
number cut-off, and show that they lead to different results. We claim that
only the mode cut-off yields correct results, and only if one considers exactly
the same number of bosonic and fermionic modes in the total sum over
bound-state and zero-point energies. To substantiate this claim, we show that
in the sine-Gordon model only the mode cut-off yields a result for the quantum
soliton mass that is consistent with the exact result for the spectrum as
obtained by Dashen et al. from quantising the so-called breather solution. In
the supersymmetric case, our conclusion is that contrary to previous claims the
quantum Bogomolnyi bound is not saturated in any of the two-dimensional models
considered.",9707163v1
1998-10-28,Non-Extreme Black Holes of Five Dimensional N=2 AdS Supergravity,"We derive and analyse the full set of equations of motion for non-extreme
static black holes (including examples with the spatial curvatures k=-1 and
k=0) in D=5 N=2 gauged supergravity by employing the techniques of ""very
special geometry"". These solutions turn out to differ from those in the
ungauged supergravity only in the non-extremality function, which has an
additional term (proportional to the gauge coupling g), responsible for the
appearance of naked singularities in the BPS-saturated limit. We derive an
explicit solution for the STU model of gauged supergravity which is
incidentally also a solution of D=5 N=4 and N=8 gauged supergravity. This
solution is specified by three charges, the asymptotic negative cosmological
constant (minimum of the potential) and a non-extremality parameter. While its
BPS-saturated limit has a naked singularity, we find a lower bound on the
non-extremality parameter (or equivalently on the ADM mass) for which the
non-extreme solutions are regular. When this bound is saturated the extreme
(non-supersymmetric) solution has zero Hawking temperature and finite entropy.
Analogous qualitative features are expected to emerge for black hole solutions
in D=4 gauged supergravity as well.",9810227v2
2006-01-20,The Viscosity Bound Conjecture and Hydrodynamics of M2-Brane Theory at Finite Chemical Potential,"Kovtun, Son and Starinets have conjectured that the viscosity to entropy
density ratio $\eta/s$ is always bounded from below by a universal multiple of
$\hbar$ i.e., $\hbar/(4\pi k_{B})$ for all forms of matter. Mysteriously, the
proposed viscosity bound appears to be saturated in all computations done
whenever a supergravity dual is available. We consider the near horizon limit
of a stack of M2-branes in the grand canonical ensemble at finite R-charge
densities, corresponding to non-zero angular momentum in the bulk. The
corresponding four-dimensional R-charged black hole in Anti-de Sitter space
provides a holographic dual in which various transport coefficients can be
calculated. We find that the shear viscosity increases as soon as a background
R-charge density is turned on. We numerically compute the few first corrections
to the shear viscosity to entropy density ratio $\eta/s$ and surprisingly
discover that up to fourth order all corrections originating from a non-zero
chemical potential vanish, leaving the bound saturated. This is a sharp signal
in favor of the saturation of the viscosity bound for event horizons even in
the presence of some finite background field strength. We discuss implications
of this observation for the conjectured bound.",0601159v3
2005-08-30,Hybrid Shrinkage Estimators Using Penalty Bases For The Ordinal One-Way Layout,"This paper constructs improved estimators of the means in the Gaussian
saturated one-way layout with an ordinal factor. The least squares estimator
for the mean vector in this saturated model is usually inadmissible. The hybrid
shrinkage estimators of this paper exploit the possibility of slow variation in
the dependence of the means on the ordered factor levels but do not assume it
and respond well to faster variation if present. To motivate the development,
candidate penalized least squares (PLS) estimators for the mean vector of a
one-way layout are represented as shrinkage estimators relative to the penalty
basis for the regression space. This canonical representation suggests further
classes of candidate estimators for the unknown means: monotone shrinkage (MS)
estimators or soft-thresholding (ST) estimators or, most generally, hybrid
shrinkage (HS) estimators that combine the preceding two strategies. Adaptation
selects the estimator within a candidate class that minimizes estimated risk.
Under the Gaussian saturated one-way layout model, such adaptive estimators
minimize risk asymptotically over the class of candidate estimators as the
number of factor levels tends to infinity. Thereby, adaptive HS estimators
asymptotically dominate adaptive MS and adaptive ST estimators as well as the
least squares estimator. Local annihilators of polynomials, among them
difference operators, generate penalty bases suitable for a range of numerical
examples.",0508599v1
2006-09-11,Thresholds for breather solutions on the Discrete Nonlinear Schrödinger Equation with saturable and power nonlinearity,"We consider the question of existence of periodic solutions (called breather
solutions or discrete solitons) for the Discrete Nonlinear Schr\""odinger
Equation with saturable and power nonlinearity. Theoretical and numerical
results are proved concerning the existence and nonexistence of periodic
solutions by a variational approach and a fixed point argument. In the
variational approach we are restricted to DNLS lattices with Dirichlet boundary
conditions. It is proved that there exists parameters (frequency or
nonlinearity parameters) for which the corresponding minimizers satisfy
explicit upper and lower bounds on the power. The numerical studies performed
indicate that these bounds behave as thresholds for the existence of periodic
solutions. The fixed point method considers the case of infinite lattices.
Through this method, the existence of a threshold is proved in the case of
saturable nonlinearity and an explicit theoretical estimate which is
independent on the dimension is given. The numerical studies, testing the
efficiency of the bounds derived by both methods, demonstrate that these
thresholds are quite sharp estimates of a threshold value on the power needed
for the the existence of a breather solution. This it justified by the
consideration of limiting cases with respect to the size of the nonlinearity
parameters and nonlinearity exponents.",0609023v2
2005-06-16,Effective mass and decay of $Θ^+$ in nuclear matter in quark-meson coupling model,"The in-medium mass of a $\thetaplus$, $\mtheta^*$, in cold symmetric nuclear
matter is calculated by using the quark-meson coupling model. The $\Theta^+$ is
treated as an MIT bag with the quark content $uudd\bar s$. Bag parameters for a
free $\thetaplus$ are fixed to reproduce the observed mass of the $\thetaplus$.
In doing so, we use three different values of the $s$-quark mass since the mass
of the $s$-quark is not well known. As usual, the strengths of the $u$ and $d$
quark couplings to $\sigma$- and $\omega$-meson fields are determined to fit
the nuclear saturation properties. However, the coupling constant $g_\sigma^s$
between the $s$-quark and the $\sigma$-meson cannot be fixed from the
saturation properties, and thus we treat $g_\sigma^s$ as a free parameter and
investigate how $\mtheta^*$ depends on $g_\sigma^s$. %$\mtheta^*$ is calculated
up to 2.5 times the nuclear saturation density, %and we find that We find that
$\mtheta^*$ depends significantly on the value of $g_\sigma^s$ but not on the
mass of the $s$-quark. Chemical potentials of the $\Theta^+$ and the $K+N$
system are calculated to discuss the decay of a $\Theta^+$ in nuclear matter.
We calculate the effective mass of a kaon in nuclear matter in two ways; using
the optical potential of $K^-$ in matter and using quark model. By comparing
the effective masses calculated from these two methods, we find the magnitude
of the real part of the optical potential that is consistent with the usual
quark model is about 100 MeV.",0506052v1
2005-07-06,Relativistic Transport Approach to Collective Nuclear Dynamics,"The isoscalar giant monopole resonance (ISGMR) and isovector giant dipole
resonance (IVGDR) in finite nuclei are studied in the framework of a
relativistic transport approach. The kinetic equations are derived within an
effective nucleon-meson field theory in the Relativistic Mean Field (RMF)
scheme, even extended to density dependent vertices. Small amplitude
oscillations are analysed using the Relativistic Vlasov (RV) approach, i.e.
neglecting nucleon collision terms. The time evolution of the isoscalar
monopole moment and isovector dipole moment and the corresponding Fourier power
spectra are discussed. In the case of ^{208}Pb we study in detail the
dependence of the monopole response on the effective mass and symmetry energy
at saturation given by the used covariant effective interaction. We show that a
reduced m^* and a larger a_4 can compensate the effect on the ISGMR energy
centroid of a much larger compressibility modulus K_{nm}. This result is
important in order to overcome the conflicting determination of the nuclear
compressibility between non-relativistic and relativistic effective
interactions. For the symmetry energy dynamical effects, we carefully analyze
the influence of the inclusion of an effective isovector scalar channel,
  \delta-meson field, with constant and density dependent couplings. We show
the relevance of the $slope$ (or pressure) of the symmetry energy at saturation
on the ISGMR and IVGDR modes for neutron-rich systems. Density dependent
vertices are not much affecting our conclusions. Following as a guidance some
extended dispersion relations in nuclear matter, we see two main reasons for
that, the smoothness of the density dependences around saturation and the
presence of compensation effects coming from rearrangement terms.",0507014v1
2006-01-31,Equation of state for isospin asymmetric nuclear matter using Lane potential,"A mean field calculation for obtaining the equation of state (EOS) for
symmetric nuclear matter from a density dependent M3Y interaction supplemented
by a zero-range potential is described. The energy per nucleon is minimized to
obtain the ground state of symmetric nuclear matter. The saturation energy per
nucleon used for nuclear matter calculations is determined from the
co-efficient of the volume term of Bethe-Weizs\""acker mass formula which is
evaluated by fitting the recent experimental and estimated atomic mass excesses
from Audi-Wapstra-Thibault atomic mass table by minimizing the mean square
deviation. The constants of density dependence of the effective interaction are
obtained by reproducing the saturation energy per nucleon and the saturation
density of spin and isospin symmetric cold infinite nuclear matter. The EOS of
symmetric nuclear matter, thus obtained, provide reasonably good estimate of
nuclear incompressibility. Once the consants of density dependence are
determined, EOS for asymmetric nuclear matter is calculated by adding to the
isoscalar part, the isovector component of the M3Y interaction that do not
contribute to the EOS of symmetric nuclear matter. These EOS are then used to
calculate the pressure, the energy density and the velocity of sound in
symmetric as well as isospin asymmetric nuclear matter.",0601098v2
2001-07-31,Properties of Elastic Waves in a non-Newtonian (Maxwell) Fluid-Saturated Porous Medium,"The present study investigates novelties brought about into the classic
Biot's theory of propagation of elastic waves in a fluid-saturated porous solid
by inclusion of non-Newtonian effects that are important, for example, for
hydrocarbons. Based on our previous results (Tsiklauri and Beresnev: 2001,
Phys. Rev. E, 63, 046304), we have investigated the propagation of rotational
and dilatational elastic waves, through calculating their phase velocities and
attenuation coefficients as a function of frequency. We found that the
replacement of an ordinary Newtonian fluid by a Maxwell fluid in the
fluid-saturated porous solid results in: (a) an overall increase of the phase
velocities of both the rotational and dilatational waves. With the increase of
frequency these quantities tend to a fixed, higher, as compared to the
Newtonian limiting case, level which is not changing with the decrease of the
Deborah number $\alpha$. (b) the overall decrease of the attenuation
coefficients of both the rotational and dilatational waves. With the increase
of frequency these quantities tend to a progressively lower, as compared to the
Newtonian limiting case, levels as $\alpha$ decreases. (c) Appearance of
oscillations in all physical quantities in the deeply non-Newtonian regime.",0107078v2
2001-03-23,Entropy production and wave packet dynamics in the Fock space of closed chaotic many-body systems,"Highly excited many-particle states in quantum systems such as nuclei, atoms,
quantum dots, spin systems, quantum computers etc., can be considered as
``chaotic'' superpositions of mean-field basis states (Slater determinants,
products of spin or qubit states). This is due to a very high level density of
many-body states that are easily mixed by a residual interaction between
particles (quasi-particles). For such systems, we have derived simple
analytical expressions for the time dependence of energy width of wave packets,
as well as for the entropy, number of principal basis components and inverse
participation ratio, and tested them in numerical experiments. It is shown that
the energy width $\Delta (t)$ increases linearly and very quickly saturates.
The entropy of a system increases quadratically, $S(t) \sim t^2$ at small
times, and after, can grow linearly, $S(t) \sim t$, before the saturation.
Correspondingly, the number of principal components determined by the entropy,
$N_{pc} \sim exp{(S(t))}$, or by the inverse participation ratio, increases
exponentially fast before the saturation. These results are explained in terms
of a cascade model which describes the flow of excitation in the Fock space of
basis components. Finally, a striking phenomenon of damped oscillations in the
Fock space at the transition to an equilibrium is discussed.",0103129v1
2007-05-09,Energy dependence of jet transport parameter and parton saturation in quark-gluon plasma,"We study the evolution and saturation of the gluon distribution function in
the quark-gluon plasma as probed by a propagating parton and its effect on the
computation of jet quenching or transport parameter $\hat{q}$. For thermal
partons, the saturation scale $Q^2_s$ is found to be proportional to the Debye
screening mass $\mu_D^2$. For hard probes, evolution at small $x=Q^2_s/6ET$
leads to jet energy dependence of $\hat{q}$. We study this dependence for both
a conformal gauge theory in weak and strong coupling limit and for (pure gluon)
QCD. The energy dependence can be used to extract the shear viscosity $\eta$ of
the medium since $\eta$ can be related to the transport parameter for thermal
partons in a transport description. We also derive upper bounds on the
transport parameter for both energetic and thermal partons. The later leads to
a lower bound on shear viscosity-to-entropy density ratio which is consistent
with the conjectured lower bound $\eta/s\geq 1/4\pi$. We also discuss the
implications on the study of jet quenching at the BNL Relativistic Heavy Ion
Collider and the CERN Large Hadron Collider and the bulk properties of the
dense matter.",0705.1352v4
2007-10-27,Saturation Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects,"In this paper, we provide a saturation throughput analysis of the IEEE 802.11
protocol at the data link layer by including the impact of both transmission
channel and capture effects in Rayleigh fading environment. Impacts of both
non-ideal channel and capture effects, specially in an environment of high
interference, become important in terms of the actual observed throughput. As
far as the 4-way handshaking mechanism is concerned, we extend the
multi-dimensional Markovian state transition model characterizing the behavior
at the MAC layer by including transmission states that account for packet
transmission failures due to errors caused by propagation through the channel.
This way, any channel model characterizing the physical transmission medium can
be accommodated, including AWGN and fading channels. We also extend the Markov
model in order to consider the behavior of the contention window when employing
the basic 2-way handshaking mechanism.
  Under the usual assumptions regarding the traffic generated per node and
independence of packet collisions, we solve for the stationary probabilities of
the Markov chain and develop expressions for the saturation throughput as a
function of the number of terminals, packet sizes, raw channel error rates,
capture probability, and other key system parameters. The theoretical
derivations are then compared to simulation results confirming the
effectiveness of the proposed models.",0710.5236v1
2008-01-08,Studying Turbulence from Doppler-broadened Absorption Lines: Statistics of Logarithms of Intensity,"We continue our work on developing techniques for studying turbulence with
spectroscopic data. We show that Doppler-broadened absorption spectral lines,
in particularly, saturated absorption lines, can be used within the framework
of the earlier-introduced technique termed the Velocity Coordinate spectrum
(VCS). The VCS relates the statistics of fluctuations along the velocity
coordinate to the statistics of turbulence, thus it does not require spatial
coverage by sampling directions in the plane of the sky. We consider lines with
different degree of absorption and show that for lines of optical depth less
than one, our earlier treatment of the VCS developed for spectral emission
lines is applicable, if the optical depth is used instead of intensity. This
amounts to correlating the logarithms of absorbed intensities. For larger
optical depths and saturated absorption lines, we show, that the amount of
information that one can use is, inevitably, limited by noise. In practical
terms, this means that only wings of the line are available for the analysis.
In terms of the VCS formalism, this results in introducing an additional
window, which size decreases with the increase of the optical depth. As a
result, strongly saturated absorption lines carry the information only about
the small scale turbulence. Nevertheless, the contrast of the fluctuations
corresponding to the small scale turbulence increases with the increase of the
optical depth, which provides advantages for studying turbulence combining
lines with different optical depths. Combining different absorption lines one
can tomography turbulence in the interstellar gas in all its complexity.",0801.1151v1
2008-07-10,Nonequilibrium carriers in an intrinsic graphene under interband photoexcitation,"We study nonequilibrium carriers (electrons and holes) in an intrinsic
graphene at low temperatures under far- and mid-infrared (IR) radiation in a
wide range of its intensities. The energy distributions of carriers are
calculated using a quasiclassic kinetic equation which accounts for the energy
relaxation due to acoustic phonons and the radiative generation-recombination
processes associated with thermal radiation and the carrier photoexcitation by
incident radiation. It is found that the nonequilibrium distributions are
determined by an interplay between weak energy relaxation on acoustic phonons
and generation-recombination processes as well as by the effect of pumping
saturation. Due to the effect of saturation, the carrier distribution functions
can exhibit plateaus around the pumping region at elevated intensities. As
shown, at sufficiently strong mid-IR pumping, the population inversion can
occur below the pumping energy. The graphene dc conductivity as a function of
the pumping intensity exhibits a pronounced nonlinearity with a sub-linear
region at fairly low intensities and a saturation at a strong pumping. However,
an increase in the pumping intensity in very wide range leads only to a modest
increase in the carrier concentration and, particularly, the dc conductivity.
The graphene conductivity at mid-IR irradiation exhibit strong sensitivity to
mechanisms of carrier momentum relaxation.",0807.1590v1
2008-12-23,"A probable vacuum state containing a large number of hydrogen atom of excited state or ground state K, Rb or Cs atom","The linear Stark effect shows that the first excited state of hydrogen atom
has large permanent electric dipole moment (EDM), d(H)=3eao (ao is Bohr
radius). Using special capacitors our experiments discovered that the ground
state K, Rb or Cs atom is polar atom with a large EDM of the order of eao as
hydrogen atom of excited state. Their capacitance(C) at different voltage (V)
was measured. The C-V curve shows that the saturation polarization of K, Rb or
Cs vapor has be observed when the field E more than ten to the fifth power V/m.
When the saturation polarization appeared, nearly all K, Rb or Cs atoms(more
than 98 percent) turned toward the direction of the field, and C is
approximately equal to Co (Co is vacuum capacitance) or their dielectric
constant is nearly the same as vacuum! K, Rb or Cs vapor just exist in the
lowest energy state, so we see the vacuum state containing a large number of
atoms! Due to the saturation polarization of hydrogen vapor of excited state is
easily appears, we conjecture that a vacuum state containing a large number of
hydrogen atom of excited state may exist at early Universe when the absolute
temperature T is approximately equal to ten to the fifth power K.",0812.4424v1
2009-05-04,A completeness result for a realisability semantics for an intersection type system,"In this paper we consider a type system with a universal type $\omega$ where
any term (whether open or closed, $\beta$-normalising or not) has type
$\omega$. We provide this type system with a realisability semantics where an
atomic type is interpreted as the set of $\lambda$-terms saturated by a certain
relation. The variation of the saturation relation gives a number of
interpretations to each type. We show the soundness and completeness of our
semantics and that for different notions of saturation (based on weak head
reduction and normal $\beta$-reduction) we obtain the same interpretation for
types. Since the presence of $\omega$ prevents typability and realisability
from coinciding and creates extra difficulties in characterizing the
interpretation of a type, we define a class ${\mathbb U}^+$ of the so-called
positive types (where $\omega$ can only occur at specific positions). We show
that if a term inhabits a positive type, then this term is $\beta$-normalisable
and reduces to a closed term. In other words, positive types can be used to
represent abstract data types. The completeness theorem for ${\mathbb U}^+$
becomes interesting indeed since it establishes a perfect equivalence between
typable terms and terms that inhabit a type. In other words, typability and
realisability coincide on ${\mathbb U}^+$. We give a number of examples to
explain the intuition behind the definition of ${\mathbb U}^+$ and to show that
this class cannot be extended while keeping its desired properties.",0905.0354v1
2009-05-04,Dark Energy from Large-Scale Structure Lensing Information,"Wide area Large-Scale Structure (LSS) surveys are planning to map a
substantial fraction of the visible universe to quantify dark energy through
Baryon Acoustic Oscillations (BAO). At increasing redshift, for example that
probed by proposed 21-cm intensity mapping surveys, gravitational lensing
potentially limits the fidelity (Hui et al., 2007) because it distorts the
apparent matter distribution. In this paper we show that these distortions can
be reconstructed, and actually used to map the distribution of intervening dark
matter. The lensing information for sources at z=1-3 allows accurate
reconstruction of the gravitational potential on large scales, l <~ 100, which
is well matched for Integrated Sachs-Wolfe (ISW) effect measurements of dark
energy and its sound speed, and a strong constraint for modified gravity models
of dark energy.
  We built an optimal quadratic lensing estimator for non-Gaussian sources,
which is necessary for LSS. The phenomenon of ""information saturation"" (Rimes &
Hamilton, 2005) saturates reconstruction at mildly non-linear scales, where the
linear source power spectrum Delta^2 ~ 0.2-0.5. We find that steeper power
spectra, saturate more quickly. We compute the effective number densities of
independent lensing sources for LSS lensing, and find that they increase
rapidly with redshifts. For LSS/21-cm sources at z ~ 2-4, the lensing
reconstruction is limited by cosmic variance at l<~ 100.",0905.0499v1
2009-11-11,Interference Mitigation Through Limited Receiver Cooperation,"Interference is a major issue limiting the performance in wireless networks.
Cooperation among receivers can help mitigate interference by forming
distributed MIMO systems. The rate at which receivers cooperate, however, is
limited in most scenarios. How much interference can one bit of receiver
cooperation mitigate? In this paper, we study the two-user Gaussian
interference channel with conferencing decoders to answer this question in a
simple setting. We identify two regions regarding the gain from receiver
cooperation: linear and saturation regions. In the linear region receiver
cooperation is efficient and provides a degrees-of-freedom gain, which is
either one cooperation bit buys one more bit or two cooperation bits buy one
more bit until saturation. In the saturation region receiver cooperation is
inefficient and provides a power gain, which is at most a constant regardless
of the rate at which receivers cooperate. The conclusion is drawn from the
characterization of capacity region to within two bits. The proposed strategy
consists of two parts: (1) the transmission scheme, where superposition
encoding with a simple power split is employed, and (2) the cooperative
protocol, where one receiver quantize-bin-and-forwards its received signal, and
the other after receiving the side information decode-bin-and-forwards its
received signal.",0911.2053v1
2009-12-26,Complexity Analysis of Unsaturated Flow in Heterogeneous Media Using a Complex Network Approach,"In this study, we investigate the complexity of two-phase flow (air/water) in
a heterogeneous soil sample by using complex network theory, where the supposed
porous media is non-deformable media, under the time-dependent gas pressure.
Based on the different similarity measurements (i.e., correlation, Euclidean
metrics) over the emerged patterns from the evolution of saturation of
non-wetting phase of a multi-heterogeneous soil sample, the emerged complex
networks are recognized. Understanding of the properties of complex networks
(such degree distribution, mean path length, clustering coefficient) can be
supposed as a way to analysis of variation of saturation profiles structures
(as the solution of finite element method on the coupled PDEs) where complexity
is coming from the changeable connection and links between assumed nodes. Also,
the path of evolution of the supposed system will be illustrated on the state
space of networks either in correlation and Euclidean measurements. The results
of analysis showed in a closed system the designed complex networks approach to
small world network where the mean path length and clustering coefficient are
low and high, respectively. As another result, the evolution of macro -states
of system (such mean velocity of air or pressure) can be scaled with
characteristics of structure complexity of saturation. In other part, we tried
to find a phase transition criterion based on the variation of non-wetting
phase velocity profiles over a network which had been constructed over
correlation distance.",0912.4991v2
2010-01-03,Nuclear limits on properties of pulsars and gravitational waves,"Pulsars are among the most mysterious astrophysical objects in the Universe
and are believed to be rotating neutron stars formed in supernova explosions.
They are unique testing grounds of dense matter theories and gravitational
physics and also provide links among nuclear physics, particle physics and
General Relativity. Neutron stars may exhibit some of the most extreme and
exotic characteristics that could not be found elsewhere in the Universe. Their
properties are largely determined by the equation of state (EOS) of
neutron-rich matter, which is the chief ingredient in calculating neutron star
structure and properties of related phenomena, such as gravitational wave
emission from deformed pulsars. Presently, the EOS of neutron-rich matter is
still very uncertain mainly due to the poorly known density dependence of the
nuclear symmetry energy especially at supra-saturation densities. Nevertheless,
significant progress has been made recently in constraining the density
dependence of the nuclear symmetry energy mostly at sub-saturation densities
using terrestrial nuclear reactions. While there are still some uncertainties
especially at supra-saturation densities, these constraints could provide
useful information on the limits of the global properties of pulsars and the
gravitational waves to be expected from them. Here we review our recent work on
constraining properties of pulsars and gravitational radiation with data from
terrestrial nuclear laboratories.",1001.0353v1
2010-04-08,Phase transition in saturated porous media: pore-fluid segregation in consolidation,"Consider the consolidation process typical of soils, this phenomenon is
expected not to exhibit a unique state of equilibrium, depending on the
\textit{external loading} and the constitutive parameters. Beyond the standard
solution, also pore-fluid segregation, which is typically associated with
fluidization of the granular material, can arise. Pore-fluid segregation has
been recognized as a phenomenon typical of the short time behavior of a
saturated porous slab or a saturated porous sphere, during consolidation. In
both circumstances Biot's three dimensional model provides time increasing
values of the water pressure (and fluid mass density) at the center of the slab
(or of the sphere), at early times, if the Lam\'{e} constant $\mu$ of the
skeleton is different from zero. This localized pore-fluid segregation is known
in the literature as Mandel--Cryer effect. In this paper a non linear
poromechanical model is formulated. The model is able to describe the
occurrence of two states of equilibrium and the switching from one to the other
by considering a kind of \textit{phase transition}. Extending classical Biot's
theory a more than quadratic strain energy potential is postulated, depending
on the strain of the porous material and the variation of the fluid mass
density (measured with respect to the skeleton reference volume). When the
consolidating pressure is strong enough the existence of two distinct minima is
proven.",1004.1310v1
2010-10-13,Revisiting the thermodynamics of hardening plasticity for unsaturated soils,"A thermodynamically consistent extension of the constitutive equations of
saturated soils to unsaturated conditions is often worked out through the use a
unique 'effective' interstitial pressure, accounting equivalently for the
pressures of the saturating fluids acting separately on the internal solid
walls of the pore network. The natural candidate for this effective
interstitial pressure is the space averaged interstitial pressure. In contrast
experimental observations have revealed that, at least, a pair of stress state
variables was needed for a suitable framework to describe
stress-strain-strength behaviour of unsaturated soils. The thermodynamics
analysis presented here shows that the most general approach to the behaviour
of unsaturated soils actually requires three stress state variables: the
suction, which is required to describe the invasion of the soil by the liquid
water phase through the retention curve; two effective stresses, which are
required to describe the soil deformation at water saturation held constant.
However a simple assumption related to the plastic flow rule leads to the final
need of only a Bishop-like effective stress to formulate the stress-strain
constitutive equation describing the soil deformation, while the retention
properties still involve the suction and possibly the deformation. Commonly
accepted models for unsaturated soils, that is the Barcelona Basic Model and
any approach based on the use of an effective averaged interstitial pressure,
appear as special extreme cases of the thermodynamic formulation proposed here.",1010.2598v1
2010-10-13,Is the degree of saturation a good candidate for Bishop's X parameter?,"In unsaturated soil mechanics, the quest for an effective stress playing the
same role as Terzaghi's effective stress does for saturated soils has
introduced a long standing debate, dating back to the 1960s. Several
contributions have been proposed since the early work of Bishop. It is well
recognized to date that a single constitutive stress is not sufficient by
itself to catch the main features of the behaviour of unsaturated soils and it
is often combined with matric suction. In this paper, focus is given to a
largely used formulation for such a constitutive stress, based on the use of an
averaged pore pressure. In particular, this paper discusses on thermodynamics
bases the validity of the choice of the factor X weighting the fluid pressures
contribution to the constitutive stress. This factor is usually assumed to be
equal to the degree of saturation of water. In this work it is shown that the
choice of this natural candidate implies restrictive assumptions on the plastic
flow rule. As shown from experimental data obtained from a literature review,
this choice may not be pertinent for certain classes of materials, particularly
high plasticity clays.",1010.2608v1
2010-12-29,Barrier Lowering and Backscattering Extraction in Short-Channel MOSFETs,"In this work we propose a fully experimental method to extract the barrier
lowering in short-channel saturated MOSFETs using the Lundstrom backscattering
transport model in a one sub-band approximation and carrier degeneracy. The
knowledge of the barrier lowering at the operative bias point in the inversion
regime is of fundamental importance in device scaling. At the same time we
obtain also an estimate of the backscattering ratio and of the saturation
inversion charge. Respect to previously reported works on extraction of
transport parameters based on the Lundstrom model, our extraction method is
fully consistent with it, whereas other methods make a number of approximations
in the calculation of the saturation inversion charge which are inconsistent
with the model. The proposed experimental extraction method has been validated
and applied to results from device simulation and measurements on short-channel
poly-Si/SiON gate nMOSFETs with gate length down to 70 nm. Moreover we propose
an extension of the backscattering model to the case of 2D geometries (e.g.
bulk MOSFETs). We found that, in this case, the backscattering is governed by
the carrier transport in a few nanometers close to the silicon/oxide interface
and that the value of the backscattering ratio obtained with a 1D approach can
be significantly different from the real 2D value.",1012.5978v1
2011-05-04,Homogeneity tests for Michaelis-Menten curves with application to fluorescence resonance energy transfer data,"Resonance energy transfer methods are in wide use for evaluating
protein-protein interactions and protein conformational changes in living
cells. Fluorescence resonance energy transfer (FRET) measures energy transfer
as a function of the acceptor:donor ratio, generating FRET saturation curves.
Modeling these curves by Michaelis-Menten kinetics allows characterization by
two parameters, which serve to evaluate apparent affinity between two proteins
and to compare this affinity in different experimental conditions. To reduce
the effect of sampling variability, several statistical samples of the
saturation curve are generated in the same biological conditions. Here we study
three procedures to determine whether statistical samples in a collection are
homogeneous, in the sense that they are extracted from the same regression
model. From the hypothesis testing viewpoint, we considered an F test and a
procedure based on bootstrap resampling. The third method analyzed the problem
from the model selection viewpoint, and used the Akaike information criterion
(AIC). Although we only considered the Michaelis-Menten model, all statistical
procedures would be applicable to any other nonlinear regression model. We
compared the performance of the homogeneity testing methods in a Monte Carlo
study and through analysis in living cells of FRET saturation curves for
dimeric complexes of CXCR4, a seven-transmembrane receptor of the G
protein-coupled receptor family. We show that the F test, the bootstrap
procedure and the model selection method lead in general to similar
conclusions, although AIC gave the best results when sample sizes were small,
whereas the F test and the bootstrap method were more appropriate for large
samples. In practice, all three methods are easy to use simultaneously and show
consistency, facilitating conclusions on sample homogeneity.",1105.0780v1
2011-05-12,Approximation by Semigroups of Spherical Operators,"This paper discusses the approximation by %semigroups of operators of class
($\mathscr{C}_0$) on the sphere and focuses on a class of so called
exponential-type multiplier operators. It is proved that such operators form a
strongly continuous semigroup of contraction operators of class
($\mathscr{C}_0$), from which the equivalence between approximation for these
operators and $K$-functionals introduced by the operators is given. As
examples, the constructed $r$-th Boolean of generalized spherical Abel-Poisson
operator and $r$-th Boolean of generalized spherical Weierstrass operator
denoted by $\oplus^r V_t^{\gamma}$ and $\oplus^r W_t^{\kappa}$ separately ($r$
is any positive integer, $0<\gamma,\kappa\leq1$ and $t>0$) satisfy that
  $\|\oplus^r V_t^{\gamma}f - f\|_{\mathcal{X}}\approx
\omega^{r\gamma}(f,t^{1/\gamma})_{\mathcal{X}}$ and $\|\oplus^r W_t^{\kappa}f -
f\|_{\mathcal{X}}\approx \omega^{2r\gamma}(f,t^{1/(2\kappa)})_{\mathcal{X}}$,
for all $f\in \mathcal{X}$, where $\mathcal{X}$ is a Banach space of continuous
functions or $\mathcal{L}^p$-integrable functions ($1\leq p<\infty$) and
$\|\cdot\|_{\mathcal{X}}$ is the norm on $\mathcal{X}$ and
$\omega^s(f,t)_{\mathcal{X}}$ is the moduli of smoothness of degree $s>0$ for
$f\in \mathcal{X}$. The saturation order and saturation class of the regular
exponential-type multiplier operators with positive kernels are also obtained.
Moreover, it is proved that $\oplus^r V_t^{\gamma}$ and $\oplus^r W_t^{\kappa}$
have the same saturation class if $\gamma=2\kappa$.",1105.2393v1
2011-05-19,On Spectrum of kappa-Resplendent Models,"We prove that some natural ""outside"" property is equivalent (for a first
order class) to being stable.
  For a model, being resplendent is a strengthening of being kappa-saturated.
Restricting ourselves to the case kappa > |T| for transparency, a model M is
kappa-resplendent means: when we expand M by <kappa individual constants (c_i:i
< alpha), if (M, c_i)_ {i<alpha} has an elementary extension expandable to be a
model of T' where Th((M,c_i)_{i<alpha}) subseteq T', |T'| < kappa then already
(M,c_i)_{i<\alpha} can be expanded to a model of T'.
  Trivially any saturated model of cardinality lambda is lambda-resplendent. We
ask: how may kappa-resplendent models of a (first order complete) theory T of
cardinality lambda are there? Naturally we restrict ourselves to cardinals
lambda=lambda^ kappa + 2^ {|T|}. Then we get a complete and satisfying answer:
this depends just on T being stable or unstable. In this case proving that for
stable T we get few, is not hard; in fact every resplendent model of T is
saturated hence determined by its cardinality up to isomorphism. The inverse is
more problematic because naturally we have to use Skolem functions with any
alpha<kappa places. Normally we use relevant partition theorems (Ramsey theorem
or Erd\H{o}s-Rado theorem), but in our case the relevant partitions theorems
fails so we have to be careful.",1105.3774v2
2011-07-16,Spatially-Coupled Codes and Threshold Saturation on Intersymbol-Interference Channels,"Recently, it has been observed that terminated low-density-parity-check
(LDPC) convolutional codes (or spatially-coupled codes) appear to approach
capacity universally across the class of binary memoryless channels. This is
facilitated by the ""threshold saturation"" effect whereby the belief-propagation
(BP) threshold of the spatially-coupled ensemble is boosted to the maximum
a-posteriori (MAP) threshold of the underlying constituent ensemble.
  In this paper, we consider the universality of spatially-coupled codes over
intersymbol-interference (ISI) channels under joint iterative decoding. More
specifically, we empirically show that threshold saturation also occurs for the
considered problem. This can be observed by first identifying the EXIT curve
for erasure noise and the GEXIT curve for general noise that naturally obey the
general area theorem. From these curves, the corresponding MAP and the BP
thresholds are then numerically obtained. With the fact that regular LDPC codes
can achieve the symmetric information rate (SIR) under MAP decoding,
spatially-coupled codes with joint iterative decoding can universally approach
the SIR of ISI channels. For the dicode erasure channel, Kudekar and Kasai
recently reported very similar results based on EXIT-like curves.",1107.3253v2
2011-12-20,Finding D-optimal designs by randomised decomposition and switching,"The Hadamard maximal determinant (maxdet) problem is to find the maximum
determinant D(n) of a square {+1, -1} matrix of given order n. Such a matrix
with maximum determinant is called a saturated D-optimal design. We consider
some cases where n > 2 is not divisible by 4, so the Hadamard bound is not
attainable, but bounds due to Barba or Ehlich and Wojtas may be attainable. If
R is a matrix with maximal (or conjectured maximal) determinant, then G = RR^T
is the corresponding Gram matrix. For the cases that we consider, maximal or
conjectured maximal Gram matrices are known. We show how to generate many
Hadamard equivalence classes of solutions from a given Gram matrix G, using a
randomised decomposition algorithm and row/column switching. In particular, we
consider orders 26, 27 and 33, and obtain new saturated D-optimal designs (for
order 26) and new conjectured saturated D-optimal designs (for orders 27 and
33).",1112.4671v5
2012-02-26,Dependent dreams: recounting types,"We investigate the class of models of a general dependent theory. We continue
math.LO/0702292 in particular investigating so called ""decomposition of types"";
thesis is that what holds for stable theory and for Th(Q,<) hold for dependent
theories. Another way to say this is: we have to look at small enough
neighborhood and use reasonably definable types to analyze a type. We note the
results understable without reading. First, a parallel to the ""stability
spectrum"", the ""recounting of types"", that is assume lambda = lambda^{< lambda}
is large enough, M a saturated model of T of cardinality lambda, let bold
S_{aut}(M) be the number of complete types over M up to being conjugate, i.e.
we identify p,q when some automorphism of M maps p to q . Whereas for
independent T the number is 2^lambda, for dependent T the number is <= lambda
moreover it is <= | alpha |^{|T|} when lambda = aleph_alpha. Second, for stable
theories ""lots of indiscernibility exists"" a ""too good indiscernible existence
theorem"" saying, e.g. that if the type tp (d_beta ; {d_beta : beta < alpha}) is
increasing for alpha < kappa = cf(kappa) and kappa > 2^{|T|} then <d_alpha :
alpha in S> is indiscernible for some stationary S subseteq kappa. Third, for
stable T,a model is kappa-saturated iff it is aleph_epsilon-saturated and every
infinite indiscernible set (of elements) of cardinality < kappa can be
increased. We prove here an analog. Fourth, for p in S(M), the number of
ultrafilters on the outside definable subsets of M extending p has an absolute
bound 2^{|T|} . Restricting ourselves to one phi(x, y), the number is finite,
with an absolute found (well depending on T and phi).",1202.5795v1
2012-04-25,A Simple Proof of Threshold Saturation for Coupled Scalar Recursions,"Low-density parity-check (LDPC) convolutional codes (or spatially-coupled
codes) have been shown to approach capacity on the binary erasure channel (BEC)
and binary-input memoryless symmetric channels. The mechanism behind this
spectacular performance is the threshold saturation phenomenon, which is
characterized by the belief-propagation threshold of the spatially-coupled
ensemble increasing to an intrinsic noise threshold defined by the uncoupled
system.
  In this paper, we present a simple proof of threshold saturation that applies
to a broad class of coupled scalar recursions. The conditions of the theorem
are verified for the density-evolution (DE) equations of irregular LDPC codes
on the BEC, a class of generalized LDPC codes, and the joint iterative decoding
of LDPC codes on intersymbol-interference channels with erasure noise. Our
approach is based on potential functions and was motivated mainly by the ideas
of Takeuchi et al. The resulting proof is surprisingly simple when compared to
previous methods.",1204.5703v3
2012-07-02,Moist turbulent Rayleigh-Benard convection with Neumann and Dirichlet boundary conditions,"Turbulent Rayleigh-Benard convection with phase changes in an extended layer
between two parallel impermeable planes is studied by means of
three-dimensional direct numerical simulations for Rayleigh numbers between
10^4 and 1.5\times 10^7 and for Prandtl number Pr=0.7. Two different sets of
boundary conditions of temperature and total water content are compared:
imposed constant amplitudes which translate into Dirichlet boundary conditions
for the scalar field fluctuations about the quiescent diffusive equilibrium and
constant imposed flux boundary conditions that result in Neumann boundary
conditions. Moist turbulent convection is in the conditionally unstable regime
throughout this study for which unsaturated air parcels are stably and
saturated air parcels unstably stratified. A direct comparison of both sets of
boundary conditions with the same parameters requires to start the turbulence
simulations out of differently saturated equilibrium states. Similar to dry
Rayleigh-Benard convection the differences in the turbulent velocity
fluctuations, the cloud cover and the convective buoyancy flux decrease across
the layer with increasing Rayleigh number. At the highest Rayleigh numbers the
system is found in a two-layer regime, a dry cloudless and stably stratified
layer with low turbulence level below a fully saturated and cloudy turbulent
one which equals classical Rayleigh-Benard convection layer. Both are separated
by a strong inversion that gets increasingly narrower for growing Rayleigh
number.",1207.0420v1
2012-09-27,Derivation of soil-specific streaming potential electrical parameters from hydrodynamic characteristics of partially saturated soils,"Water movement in unsaturated soils gives rise to measurable electrical
potential differences that are related to the flow direction and volumetric
fluxes, as well as to the soil properties themselves. Laboratory and field data
suggest that these so-called streaming potentials may be several orders of
magnitudes larger than theoretical predictions that only consider the influence
of the relative permeability and electrical conductivity on the self potential
(SP) data. Recent work has partly improved predictions by considering how the
volumetric excess charge in the pore space scales with the inverse of water
saturation. We present a new theoretical approach that uses the flux-averaged
excess charge, not the volumetric excess charge, to predict streaming
potentials. We present relationships for how this effective excess charge
varies with water saturation for typical soil properties using either the water
retention or the relative permeability function. We find large differences
between soil types and the predictions based on the relative permeability
function display the best agreement with field data. The new relationships
better explain laboratory data than previous work and allow us to predict the
recorded magnitudes of the streaming potentials following a rainfall event in
sandy loam, whereas previous models predict three orders of magnitude too small
values. We suggest that the strong signals in unsaturated media can be used to
gain information about fluxes (including very small ones related to film flow),
but also to constrain the relative permeability function, the water retention
curve, and the relative electrical conductivity function.",1209.6335v1
2013-01-25,A Proof of Threshold Saturation for Spatially-Coupled LDPC Codes on BMS Channels,"Low-density parity-check (LDPC) convolutional codes have been shown to
exhibit excellent performance under low-complexity belief-propagation decoding
[1], [2]. This phenomenon is now termed threshold saturation via spatial
coupling. The underlying principle behind this appears to be very general and
spatially-coupled (SC) codes have been successfully applied in numerous areas.
Recently, SC regular LDPC codes have been proven to achieve capacity
universally, over the class of binary memoryless symmetric (BMS) channels,
under belief-propagation decoding [3], [4].
  In [5], [6], potential functions are used to prove that the BP threshold of
SC irregular LDPC ensembles saturates, for the binary erasure channel, to the
conjectured MAP threshold (known as the Maxwell threshold) of the underlying
irregular ensembles. In this paper, that proof technique is generalized to BMS
channels, thereby extending some results of [4] to irregular LDPC ensembles. We
also believe that this approach can be expanded to cover a wide class of
graphical models whose message-passing rules are associated with a Bethe free
energy.",1301.6111v2
2013-02-07,"Saturation effects in exclusive rhoT, rhoL meson electroproduction","We use recent results for the gamma*L -> rhoL and gamma*T -> rhoT impact
factors, computed in the impact parameter representation within the collinear
factorization scheme, to get predictions for the polarized cross-sections
sigmaT and sigmaL of the diffractive leptoproduction of the rho meson at high
energy. In this approach the helicity amplitude is a convolution of the
scattering amplitude of a color dipole with a target, together with the virtual
gamma wave function and with the first moments of the rho meson wave function
(in the transverse momentum space), given by the distribution amplitudes up to
twist 3 for the gamma*T -> rhoT impact factor and up to twist 2 for the gamma*L
-> rhoL impact factor. Combining these results with recent dipole models fitted
to DIS data, which include saturation effects, we show that the predictions are
in good agreement with HERA data for photon virtuality (Q**2) larger than
typically 5 GeV**2, without free parameters and with a weak dependence on the
choice of the factorization scale, i.e. the shape of the DAs, for both
longitudinally and transversely polarized rho meson. For lower values of Q**2,
the inclusion of saturation effects is not enough to provide a good description
of HERA data. We believe that it is a signal of a need for higher twist
contributions in the rho meson DAs. We also analyze the radial distributions of
dipoles between the initial gamma* and the final rho meson states.",1302.1766v1
2013-09-29,Resolving the Puzzle of the Pion-Photon Transition Form Factor,"We investigate the form factors for pseudoscalar-meson-photon transitions by
means of dispersive QCD sum rules and demonstrate that most of the measurements
done so far (in particular, those by BaBar for $\eta,$ $\eta',$ and $\eta_c$
and those by Belle for $\pi^0$) are, on the one hand, compatible with each
other and with the saturation required by factorization theorems obtained from
perturbative QCD and, on the other hand, give a hint that saturation is
effective already at relatively low momentum transfers $Q^2;$ this hypothesis
is supported by experimental data for the charged-pion elastic form factor
available in the range $Q^2\approx2-4\;\{GeV}^2.$ The only exception are the
BaBar results for the $\pi^0\gamma$ transition form factor, which do not fit
into such picture. We point out that results expected from SHMS at JLab on the
pion elastic form factor in the region $Q^2\approx5-8\;\{GeV}^2$ will provide
the ultimate test of saturation and factorization and strongly impact our
general view of the form factors up to infinitely large $Q^2.$",1309.7605v2
2013-10-10,Instability of Evaporation Fronts in the Interstellar Medium,"The neutral component of the interstellar medium is segregated into the cold
neutral medium (CNM) and warm neutral medium (WNM) as a result of thermal
instability. It was found that a plane-parallel CNM-WNM evaporation interface,
across which the CNM undergoes thermal expansion, is linearly unstable to
corrugational disturbances, in complete analogy with the Darrieus-Landau
instability (DLI) of terrestrial flames. We perform a full linear stability
analysis as well as nonlinear hydrodynamic simulations of the DLI of such
evaporation fronts in the presence of thermal conduction. We find that the DLI
is suppressed at short length scales by conduction. The length and time scales
of the fastest growing mode are inversely proportional to the evaporation flow
speed of the CNM and its square, respectively. In the nonlinear stage, the DLI
saturates to a steady state where the front deforms to a finger-like shape
protruding toward the WNM, without generating turbulence. The evaporation rate
at nonlinear saturation is larger than the initial plane-parallel value by a
factor of 2.4 when the equilibrium thermal pressure is 1800 k_B cm^-3 K. The
degrees of front deformation and evaporation-rate enhancement at nonlinear
saturation are determined primarily by the density ratio between the CNM and
WNM. We demonstrate that the Field length in the thermally unstable medium
should be resolved by at least four grid points to obtain reliable numerical
outcomes involving thermal instability.",1310.2940v2
2013-10-16,Effect of saccades in tongue electrotactile stimulation for vision substitution applications,"The visual substitution paradigm aims to facilitate the life of blind people.
Generally one uses electro-stimulating devices where electrodes are arranged
into arrays to stimulate the skin or the tongue mucosa to send signals of
visual type to the subjects. When an electro-stimulation signal is applied
continuously (e.g. when static visual scenes are displayed for a long period of
time), the receptors of the affected region can get saturated and the patient
may lose the displayed information. We propose here some mechanisms that
ameliorate the quality of perception of the electro-stimulation information.
The electrical signal is encoded as 2D scenes projected onto the tongue via a
Tongue Display Unit, i.e. an electro-tactile stimulator formed by a 12x12
matrix of electrodes. We propose to apply stochastic saccades on this signal.
Our assumption is that this eye-inspired mechanism should make the visual
substitution more efficient (by improving the perception) because of the
reduction of the tactile receptors saturation. The influence of saccades was
evaluated by a series of experiments. Results revealed a benefit on the
persistence of perception due to saccades. This work helps to prevent the
saturation of receptors on the tongue. Therefore increasing the quality of
vision by the way of the electro-stimulation. It allows new enhancement
features to retinal prosthesis devices which suffer from the same phenomenon.",1310.4480v1
2013-10-22,Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy,"Knowledge of the electron sampling depth and related saturation effects is
important for quantitative analysis of X-ray absorption spectroscopy data, yet
for oxides with the perovskite structure no quantitative values are so far
available. Here we study absorption saturation in films of two of the
most-studied perovskites, LCMO and YBCO, at the L2,3 edge of Mn and Cu,
respectively. By measuring the electron-yield intensity as a function of photon
incidence angle and film thickness, the sampling depth d, photon attenuation
length, lambda, and the ratio lambda/d have been independently determined
between 50 and 300 K. The extracted sampling depth dLCMO=3 nm for LCMO at high
temperatures in its polaronic insulator state (150-300K) is not much larger
than values reported for pure transition metals (d Co or Ni=2-2.5nm) at room
temperature, but it is smaller than dYBCO=3.9 nm for metallic YBCO that is in
turn smaller than the value reported for Fe3O4 (d=4.5 nm) The measured dLCMO
increases to 4.5 nm when LCMO is in the metallic state at low temperatures.
These results indicate that a universal rule of thumb for the sampling depth in
oxides cannot be assumed, and that it can be measurably influenced by
electronic phase transitions that derive from strong correlations.",1310.5998v1
2013-11-08,Threshold Saturation for Nonbinary SC-LDPC Codes on the Binary Erasure Channel,"We analyze the asymptotic performance of nonbinary spatially-coupled
low-density parity-check (SC-LDPC) code ensembles defined over the general
linear group on the binary erasure channel. In particular, we prove threshold
saturation of belief propagation decoding to the so called potential threshold,
using the proof technique based on potential functions introduced by Yedla
\textit{et al.}, assuming that the potential function exists. We rewrite the
density evolution of nonbinary SC-LDPC codes in an equivalent vector recursion
form which is suited for the use of the potential function. We then discuss the
existence of the potential function for the general case of vector recursions
defined by multivariate polynomials, and give a method to construct it. We
define a potential function in a slightly more general form than one by Yedla
\textit{et al.}, in order to make the technique based on potential functions
applicable to the case of nonbinary LDPC codes. We show that the potential
function exists if a solution to a carefully designed system of linear
equations exists. Furthermore, we show numerically the existence of a solution
to the system of linear equations for a large number of nonbinary LDPC code
ensembles, which allows us to define their potential function and thus prove
threshold saturation.",1311.2003v4
2013-11-18,A Numerical Study of Methods for Moist Atmospheric Flows: Compressible Equations,"We investigate two common numerical techniques for integrating reversible
moist processes in atmospheric flows in the context of solving the fully
compressible Euler equations. The first is a one-step, coupled technique based
on using appropriate invariant variables such that terms resulting from phase
change are eliminated in the governing equations. In the second approach, which
is a two-step scheme, separate transport equations for liquid water and vapor
water are used, and no conversion between water vapor and liquid water is
allowed in the first step, while in the second step a saturation adjustment
procedure is performed that correctly allocates the water into its two phases
based on the Clausius-Clapeyron formula. The numerical techniques we describe
are first validated by comparing to a well-established benchmark problem.
Particular attention is then paid to the effect of changing the time scale at
which the moist variables are adjusted to the saturation requirements in two
different variations of the two-step scheme. This study is motivated by the
fact that when acoustic modes are integrated separately in time (neglecting
phase change related phenomena), or when sound-proof equations are integrated,
the time scale for imposing saturation adjustment is typically much larger than
the numerical one related to the acoustics.",1311.4265v4
2013-12-30,Deviations from Matthiessen rule and resistivity saturation effects in Gd and Fe,"According to earlier first-principles calculations, the spin-disorder
contribution to the resistivity of rare-earth metals in the paramagnetic state
is strongly underestimated if Matthiessen's rule is assumed to hold. To
understand this discrepancy, the resistivity of paramagnetic Fe and Gd is
evaluated by taking into account both spin and phonon disorder. Calculations
are performed using the supercell approach within the linear muffin-tin orbital
method. Phonon disorder is modeled by introducing random displacements of the
atomic nuclei, and the results are compared with the case of fictitious
Anderson disorder. In both cases the resistivity shows a nonlinear dependence
on the square of the disorder potential, which is interpreted as a resistivity
saturation effect. This effect is much stronger in Gd than in Fe. The
non-linearity makes the phonon and spin-disorder contributions to the
resistivity non-additive, and the standard procedure of extracting the
spin-disorder resistivity by extrapolation from high temperatures becomes
ambiguous. An ""apparent"" spin-disorder resistivity obtained through such
extrapolation is in much better agreement with experiment compared to the
results obtained by considering only spin disorder. By analyzing the spectral
function of the paramagnetic Gd in the presence of Anderson disorder, the
resistivity saturation is explained by the collapse of a large area of the
Fermi surface due to the disorder-induced mixing between the electronic and
hole sheets.",1312.7802v1
2014-03-27,Stability of metal-rich very massive stars,"We revisit the stability of very massive nonrotating main-sequence stars at
solar metallicity, with the goal of understanding whether radial pulsations set
a physical upper limit to stellar mass. Models of up to 938 solar masses are
constructed with the Mesa code, and their linear stability in the fundamental
mode, assumed to be the most dangerous, is analysed with a fully nonadiabatic
method. Models above 100 MSun have extended tenuous atmospheres (""shelves"")
that affect the stability of the fundamental. Even when positive, this growth
rate is small, in agreement with previous results. We argue that small growth
rates lead to saturation at small amplitudes that are not dangerous to the
star. A mechanism for saturation is demonstrated involving nonlinear parametric
coupling to short-wavelength g modes and the damping of the latter by radiative
diffusion. The shelves are subject to much more rapidly growing strange modes.
This also agrees with previous results but is extended here to higher masses.
The strange modes probably saturate via shocks rather than mode coupling but
have very small amplitudes in the core, where almost all of the stellar mass
resides. Although our stellar models are hydrostatic, the structure of their
outer parts suggests that optically thick winds, driven by some combination of
radiation pressure, transsonic convection, and strange modes, are more likely
than pulsation in the fundamental mode to limit the main-sequence lifetime.",1403.7241v2
2014-04-11,Interference Allocation Scheduler for Green Multimedia Delivery,"One of the key challenges in wireless networking is how to allocate the
available radio resources in order to maximise key service delivery parameters
such as the aggregate throughput and the multimedia quality of experience
(QoE). We propose a novel and effective scheduling policy that allocates
resource blocks, such that interference power is shifted towards
capacity-saturated users, while improving the throughput of unsaturated users.
The highlight of the research is that the proposed scheme can dramatically
improve the performance of cells that have a high discrepancy in its
signal-to-noise-ratio (SNR) distribution, which is typical in urban areas. The
results show that a \emph{free-lunch} solution is possible, whereby for a
negligible performance degradation in the saturated users, a large improvement
in the non-saturated users can be obtained. However, on average, the number of
free-lunch user pairings are low. By relaxing the degradation constraints, the
\emph{non-free-lunch} solution can yield a greater multi-user throughput gain.
Motivated by surge in mobile multimedia traffic, we further demonstrate that
the proposed scheduling may have a profound impact on both energy efficiency
and QoE of multimedia service delivery.",1404.3111v1
2014-07-22,b-CGC versus IP-Sat and high precision combined HERA data,"The Impact-Parameter dependent Color Glass Condensate (b-CGC) and Saturation
(IP-Sat) dipole models incorporate key features of small-x physics properties
and match smoothly to the perturbative QCD regime at large $Q^2$ for a given
$x$. Although both models include saturation effects and depend on
impact-parameter, the former is based on the non-linear BK equation, while the
latter is based on DGLAP evolution. After confronting the models to the
recently released high precision combined HERA data, we show that in both
models, the typical impact-parameter probed in the total $\gamma^{*}p$
cross-section is about $b\approx 2\div 3\,\text{GeV}^{-1}$ and the proton
saturation scale is $Q_S<1$ GeV in HERA kinematics. We show that most features
of inclusive DIS and exclusive diffractive data at HERA are correctly
reproduced in both models. Nevertheless, the b-CGC and the IP-Sat models give
significantly different predictions beyond the current HERA kinematics for the
structure functions at very low x and high virtualities $Q^2$, and for the
exclusive diffractive vector meson and DVCS production at high $t$.",1407.5956v2
2014-09-12,Extended linear regime of cavity-QED enhanced optical circular birefringence induced by a charged quantum dot,"Giant optical Faraday rotation (GFR) and giant optical circular birefringence
(GCB) induced by a single quantum-dot spin in an optical microcavity can be
regarded as linear effects in the weak-excitation approximation if the input
field lies in the low-power limit [Hu et al, Phys.Rev. B {\bf 78}, 085307(2008)
and ibid {\bf 80}, 205326(2009)]. In this work, we investigate the transition
from the weak-excitation approximation moving into the saturation regime
comparing a semiclassical approximation with the numerical results from a
quantum optics toolbox [S.M. Tan, J. Opt. B {\bf 1}, 424 (1999)]. We find that
the GFR and GCB around the cavity resonance in the strong coupling regime are
input-field independent at intermediate powers and can be well described by the
semiclassical approximation. Those associated with the dressed state resonances
in the strong coupling regime or merging with the cavity resonance in the
Purcell regime are sensitive to input field at intermediate powers, and cannot
be well described by the semiclassical approximation due to the quantum dot
saturation. As the GFR and GCB around the cavity resonance are relatively
immune to the saturation effects, the rapid read out of single electron spins
can be carried out with coherent state and other statistically fluctuating
light fields. This also shows that high speed quantum entangling gates, robust
against input power variations, can be built exploiting these linear effects.",1409.3787v2
2014-09-15,Tighter quantum uncertainty relations follow from a general probabilistic bound,"Uncertainty relations (URs) like the Heisenberg-Robertson or the time-energy
UR are often considered to be hallmarks of quantum theory. Here, a simple
derivation of these URs is presented based on a single classical inequality
from estimation theory, a Cram\'er-Rao-like bound. The Heisenberg-Robertson UR
is then obtained by using the Born rule and the Schr\""odinger equation. This
allows a clear separtion of the probabilistic nature of quantum mechanics from
the Hilbert space structure and the dynamical law. It also simplifies the
interpretation of the bound. In addition, the Heisenberg-Robertson UR is
tightened for mixed states by replacing one variance by the so-called quantum
Fisher information. Thermal states of Hamiltonians with evenly-gapped energy
levels are shown to saturate the tighter bound for natural choices of the
operators. This example is further extended to Gaussian states of a harmonic
oscillator. For many-qubit systems, we illustrate the interplay between
entanglement and the structure of the operators that saturate the UR with
spin-squeezed states and Dicke states.",1409.4440v3
2014-09-22,Triple- and Quadruple-Gluon Azimuthal Correlations from Glasma and Higher-Dimensional Ridges,"We calculate the triple- and quadruple-gluon inclusive distributions with
arbitrary rapidity and azimuthal angle dependences in the gluon saturation
regime by using glasma diagrams. Also, we predict higher-dimensional ridges in
triple- and quadruple-hadron correlations for p-p and p-Pb collisions at LHC,
which have yet to be measured. In p-p and p-Pb collisions at the top LHC
energies, gluon saturation is expected to occur since smaller Bjorken-$x$
values are being probed. Glasma diagrams, which are enhanced at small-$x$,
include the gluon saturation effects, and they are used for calculating the
long-range rapidity correlations (""ridges"") and $v_n$ moments of the azimuthal
distribution of detected hadrons. The glasma description reproduces the
systematics of the data on both p-p and p-Pb ridges. As an alternative,
relativistic hydrodynamics has also been applied to these small systems quite
successfully. With the triple- and quadruple-gluon azimuthal correlations, this
work aims to set the stage by going beyond the double-gluon azimuthal
correlations in order to settle unambiguously the origin of ""collectivity"" in
p-p and p-Pb collisions. We derive the triple- and quadruple-gluon azimuthal
correlation functions in terms of unintegrated gluon distributions at arbitrary
rapidities and azimuthal angles of the produced gluons. Then, unintegrated
gluon distributions from the running coupling Balitsky-Kovchegov evolution
equation are used to calculate the triple- and quadruple-gluon correlations for
various parameters of gluon momenta, initial scale for small-$x$ evolution and
beam energy.",1409.6347v2
2014-10-07,"Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing","Large-scale molecular simulations are performed to investigate tensile
failure of polymer interfaces as a function of welding time $t$. Changes in the
tensile stress, mode of failure and interfacial fracture energy $G_I$ are
correlated to changes in the interfacial entanglements as determined from
Primitive Path Analysis. Bulk polymers fail through craze formation, followed
by craze breakdown through chain scission. At small $t$ welded interfaces are
not strong enough to support craze formation and fail at small strains through
chain pullout at the interface. Once chains have formed an average of about one
entanglement across the interface, a stable craze is formed throughout the
sample. The failure stress of the craze rises with welding time and the mode of
craze breakdown changes from chain pullout to chain scission as the interface
approaches bulk strength. The interfacial fracture energy $G_I$ is calculated
by coupling the simulation results to a continuum fracture mechanics model. As
in experiment, $G_I$ increases as $t^{1/2}$ before saturating at the average
bulk fracture energy $G_b$. As in previous simulations of shear strength,
saturation coincides with the recovery of the bulk entanglement density. Before
saturation, $G_I$ is proportional to the areal density of interfacial
entanglements. Immiscibiltiy limits interdiffusion and thus suppresses
entanglements at the interface. Even small degrees of immisciblity reduce
interfacial entanglements enough that failure occurs by chain pullout and $G_I
\ll G_b$.",1410.1917v1
2014-11-13,Stretched String with Self-Interaction at High Resolution: Spatial Sizes and Saturation,"We model the (holographic) QCD Pomeron as a long and stretched (fixed impact
parameter) transverse quantum string in flat $D_\perp=3$ dimensions. After
discretizing the string in $N$ string bits, we analyze its length, mass and
spatial distribution for large $N$ or low-x ($x=1/N$), and away from its
Hagedorn point. The string bit distribution shows sizable asymmetries in the
transverse plane that may translate to azimuthal asymmetries in primordial
particle production in the Pomeron kinematics, and the flow moments in minimum
bias $pp$ and $pA$ events. At moderately low-x and relatively small string
self-interactions $g_s\approx \alpha_s$ (the gauge coupling), a pre-saturation
phase is identified whereby the string transverse area undergoes a sharp
transition from a large diffusive growth to a small fixed size area set by few
string lengths $l_s$. For lower values of $x$ the transverse string bit density
is shown to increase as $1/x$ before saturating at the Bekenstein bound of one
bit per Planck area with the Planck length $l_P/l_s\approx \alpha_s^{2/3}$. We
argue that the effects of the AdS$_5$ curvature on the interacting string maybe
estimated using an effective transverse dimension between the interacting
string bits. The result is a smoother transition with a transverse string bit
density increasing as $1/x^{0.31}$.",1411.3653v2
2015-02-10,Ultrafast dynamic conductivity and scattering rate saturation of photoexcited charge carriers in silicon investigated with a midinfrared continuum probe,"We employ ultra-broadband terahertz-midinfrared probe pulses to characterize
the optical response of photoinduced charge-carrier plasmas in high-resistivity
silicon in a reflection geometry, over a wide range of excitation densities
(10^{15}-10^{19} cm^{-3}) at room temperature. In contrast to conventional
terahertz spectroscopy studies, this enables one to directly cover the
frequency range encompassing the resultant plasma frequencies. The intensity
reflection spectra of the thermalized plasma, measured using sum-frequency
(up-conversion) detection of the probe pulses, can be modeled well by a
standard Drude model with a density-dependent momentum scattering time of
approx. 200 fs at low densities, reaching approx. 20 fs for densities of
approx. 10^{19} cm^{-3}, where the increase of the scattering rate saturates.
This behavior can be reproduced well with theoretical results based on the
generalized Drude approach for the electron-hole scattering rate, where the
saturation occurs due to phase-space restrictions as the plasma becomes
degenerate. We also study the initial sub-picosecond temporal development of
the Drude response, and discuss the observed rise in the scattering time in
terms of initial charge-carrier relaxation, as well as the optical response of
the photoexcited sample as predicted by finite-difference time-domain
simulations.",1502.02829v1
2015-06-04,Subcentric linking systems,"Linking systems are crucial for studying the homotopy theory of fusion
systems, but are also of interest from an algebraic point of view. We propose a
definition of a linking system associated to a saturated fusion system which is
more general than the one currently in the literature and thus allows a more
flexible choice of objects of linking systems. More precisely, we define
subcentric subgroups of fusion systems in a way that every quasicentric
subgroup of a saturated fusion system is subcentric. Whereas the objects of
linking systems in the current definition are always quasicentric, the objects
of our linking systems only need to be subcentric. We prove that, associated to
each saturated fusion system $\mathcal{F}$, there is a unique linking system
whose objects are the subcentric subgroups of $\mathcal{F}$. Furthermore, the
nerve of such a subcentric linking system is homotopy equivalent to the nerve
of the centric linking system associated to $\mathcal{F}$. We believe that the
existence of subcentric linking systems opens a new way for a classification of
fusion systems of characteristic $p$-type. The various results we prove about
subcentric subgroups give furthermore some evidence that the concept is of
interest for studying extensions of linking systems and fusion systems.",1506.01458v3
2015-07-13,Compactification tuning for nonlinear localized modes in sawtooth lattices,"We discuss the properties of nonlinear localized modes in sawtooth lattices,
in the framework of a discrete nonlinear Schr\""odinger model with general
on-site nonlinearity. Analytic conditions for existence of exact compact
three-site solutions are obtained, and explicitly illustrated for the cases of
power-law (cubic) and saturable nonlinearities. These nonlinear compact modes
appear as continuations of linear compact modes belonging to a flat dispersion
band. While for the linear system a compact mode exists only for one specific
ratio of the two different coupling constants, nonlinearity may lead to
compactification of otherwise non-compact localized modes for a range of
coupling ratios, at some specific power. For saturable lattices, the
compactification power can be tuned by also varying the nonlinear parameter.
Introducing different on-site energies and anisotropic couplings yield further
possibilities for compactness tuning. The properties of strongly localized
modes are investigated numerically for cubic and saturable nonlinearities, and
in particular their stability over large parameter regimes is shown. Since the
linear flat band is isolated, its compact modes may be continued into compact
nonlinear modes both for focusing and defocusing nonlinearities. Results are
discussed in relation to recent realizations of sawtooth photonic lattices.",1507.03433v2
2015-08-18,Scheme to increase the output average spectral flux of the European XFEL at $14.4$ keV,"Techniques like inelastic X-ray scattering (IXS) and nuclear resonance
scattering (NRS) are currently limited by the photon flux available at X-ray
sources. At $14.4$ keV, third generation synchrotron radiation sources produce
a maximum of $10^{10}$ photons per second in a meV bandwidth. In this work we
discuss about the possibility of increasing this flux a thousand-fold by
exploiting high repetition rate self-seeded pulses at the European XFEL. Here
we report on a feasibility study for an optimized configuration of the SASE2
beamline at the European XFEL which combines self-seeding and undulator
tapering techniques in order to increase the average spectral flux at $14.4$
keV. In particular, we propose to perform monochromatization at $7.2$ keV with
the help of self-seeding, and amplify the seed in the first part of output
undulator. The amplification process can be stopped at a position well before
saturation, where the electron beam gets considerable bunching at the 2nd
harmonic of the coherent radiation. A second part of the output undulator
follows, tuned to the 2nd harmonic frequency, i.e. at $14.4$ keV and is used to
obtain saturation at this energy. One can further prolong the exchange of
energy between the photon and the electron beam by tapering the last part of
the output undulator. We performed start-to-end simulations and demonstrate
that self-seeding, combined with undulator tapering, allows one to achieve more
than a hundred-fold increase in average spectral flux compared with the nominal
SASE regime at saturation, resulting in a maximum flux of order $10^{13}$
photons per second in a meV bandwidth.",1508.04339v1
2015-09-08,Relativistic Mean-Field Models with Scaled Hadron Masses and Couplings: Hyperons and Maximum Neutron Star Mass,"An equation of state of cold nuclear matter with an arbitrary isotopic
composition is studied within a relativistic mean-field approach with hadron
masses and coupling constants depending self-consistently on the scalar
mean-field. All hadron masses decrease universally with the scalar field
growth, whereas meson-nucleon coupling constants can vary differently. More
specifically we focus on two modifications of the KVOR model studied
previously. One extension of the model (KVORcut) demonstrates that the equation
of state stiffens if the increase of the scalar-field magnitude with the
density is bounded from above at some value for baryon densities above the
saturation nuclear density. This can be realized if the nucleon vector-meson
coupling constant changes rapidly as a function of the scalar field slightly
above the desired value. The other version of the model (MKVOR) utilizes a
smaller value of the nucleon effective mass at the nuclear saturation density
and a saturation of the scalar field in the isospin asymmetric matter induced
by a strong variation of the nucleon isovector-meson coupling constant as
function of the scalar field. A possibility of hyperonization of the matter in
neutron star interiors is incorporated. Our equations of state fulfill majority
of known empirical constraints including the pressure-density constraint from
heavy-ion collisions, direct Urca constraint, gravitational-baryon mass
constraint for the pulsar J0737-3039B, and the constraint on the maximum mass
of the neutron stars.",1509.02538v2
2015-09-09,Pinning down QCD-matter shear viscosity in ultrarelativistic heavy-ion collisions via EbyE fluctuations using pQCD + saturation + hydrodynamics,"We introduce an event-by-event pQCD + saturation + hydro (""EKRT"") framework
for high-energy heavy-ion collisions, where we compute the produced fluctuating
QCD-matter energy densities from next-to-leading order (NLO) perturbative QCD
(pQCD) using saturation to control soft particle production, and describe the
space-time evolution of the QCD matter with viscous hydrodynamics, event by
event (EbyE). We compare the computed centrality dependence of hadronic
multiplicities, p_T spectra and flow coefficients v_n against LHC and RHIC
data. We compare also the computed EbyE probability distributions of relative
fluctuations of v_n, as well as correlations of 2 and 3 event-plane angles,
with LHC data. Our systematic multi-energy and -observable analysis not only
tests the initial state calculation and applicability of hydrodynamics, but
also makes it possible to constrain the temperature dependence of the shear
viscosity-to-entropy ratio, eta/s(T), of QCD matter in its different phases.
Remarkably, we can describe all these different flow observables and
correlations consistently with eta/s(T) that is independent of the collision
energy.",1509.02767v1
2015-11-23,Diffractive Dijet Production in Deep Inelastic Scattering and Photon-Hadron Collisions in the Color Glass Condensate,"We study exclusive dijet production in coherent diffractive processes in deep
inelastic scattering and real (and virtual) photon-hadron ($\gamma^{(*)}$-h)
collisions in the Color Glass Condensate formalism at leading order. We show
that the diffractive dijet cross section is sensitive to the color-dipole
orientation in the transverse plane, and is a good probe of possible
correlations between the $q\bar{q}$-dipole transverse separation vector $\r$
and the dipole impact parameter $\b$. We also investigate the diffractive dijet
azimuthal angle correlations and $t$-distributions in $\gamma^{(*)}$-h
collisions and show that they are sensitive to gluon saturation effects in the
small-$x$ region. In particular, we show that the $t$-distribution of
diffractive dijet photo-production off a proton target exhibits a dip-type
structure in the saturation region. This effect is similar to diffractive
vector meson production. Besides, at variance with the inclusive case, the
effect of saturation leads to stronger azimuthal correlations between the jets.",1511.07452v2
2015-12-03,Atom-Field Entanglement in Cavity QED: Nonlinearity and Saturation,"We investigate the degree of entanglement between an atom and a driven cavity
mode, in the presence of dissipation. Previous work has shown that in the limit
of weak driving fields, the steady state entanglement is proportional to the
square of the driving intensity. This quadratic dependence is due to the
generation of entanglement by the creation of pairs of photons/excitations. In
this work we investigate the entanglement between an atom and a cavity in the
presence of multiple photons. Nonlinearity of the atomic response is needed to
generate entanglement, but as that nonlinearity saturates the entanglement
vanishes. We posit that this is due to spontaneous emission, which puts the
atom in the ground state and the atom-field state into a direct product state.
An intermediate value of the driving field, near the field that saturates the
atomic response, optimizes the atom-field entanglement. In a parameter regime
for which multiphoton resonances occur, we find that entanglement recurs at
those resonances. \cite{Shamailov-10} In this regime, we find that the
entanglement decreases with increaing photon number. We also investigate, in
the bimodal regime of Alsing et. al.\cite{Alsing-91-DressedState}
\cite{Alsing-92-DSS}\cite{Carm-15-X}, the entanglement as a function of atom
and/or cavity detuning. Here we find that there is evidence of a phase
transition in the entanglement, which occurs at $2\epsilon/g \geq 1$.",1512.00936v2
2016-01-13,Low-threshold RNGH instabilities in quantum cascade lasers,"A theoretical study on low-threshold multimode instabilities in quantum
cascade lasers (QCLs) and laser diodes (LDs) is presented. Previously, low
threshold Risken-Nummedal-Graham-Haken (RNGH) instabilities were reported in
several experimental studies of QCLs. They were attributed so far to the
combined effect of the induced grating of carrier population and of a built-in
saturable absorption feature that may be present in the monolithic
single-section cavity of these Fabry-P\'erot lasers. Here we show that
low-threshold RNGH instabilities in QCLs occur due to a carrier coherence
grating induced in the gain medium and not due to intracavity saturable
absorption. We find that QCLs with a few mm long cavity exhibit intermittent
RNGH self-pulsations while regular self-pulsations are possible in short-cavity
QCLs, with the cavity length of 100 um or smaller. We examine a transient
behavior to RNGH self-pulsations in short-cavity QCLs and find features that
resemble cooperative superradiance. Our findings open a practical way of
achieving ultra-short pulse production regimes in the mid-infrared spectral
range. Applying same approach to semiconductor laser diodes (LDs) we explain
the absence of RNGH self-pulsation in LDs based on a quantum well gain media,
while practically established method for reaching the ultrafast coherent
emission regimes in LDs is to incorporate a separately contacted saturable
absorber section in the LD cavity.",1601.03212v2
2016-02-12,A few-emitter solid-state multi-exciton laser,"We report a combined experimental and theoretical study of non-conventional
lasing from higher multi-exciton states of a few quantum dot-photonic crystal
nanocavity. We show that the photon output is fed from saturable quantum
emitters rather than a non-saturable background despite being rather
insensitive to the spectral position of the mode. Although the exciton
transitions of each quantum dot are detuned by up to $160$ cavity linewidths,
we observe that strong excitation populates a multitude of closely spaced
multi-exciton states, which partly overlap spectrally with the mode. The
limited number of emitters is confirmed by a complete saturation of the mode
intensity at strong pumping, providing sufficient gain to reach stimulated
emission, whilst being accompanied by a distinct lasing threshold. Detailed
second-order photon-correlation measurements unambiguously identify the
transition to lasing for strong pumping and, most remarkably, reveal
super-thermal photon bunching with $g^{(2)}(0)>2$ below lasing threshold. Based
on our microscopic theory, a pump-rate dependent $\beta$-factor $\beta(P)$ is
needed to describe the nanolaser and account for the interplay of multi-exciton
transitions in the few-emitter gain medium. Moreover, we theoretically predict
that the super-thermal bunching is related to dipole-anticorrelated
multi-exciton recombination channels via sub- and super-radiant coupling below
and above lasing threshold, respectively. Our results provide new insights into
the microscopic light-matter-coupling of spatially separated emitters coupled
to a common cavity mode and, thus, provides a complete understanding of
stimulated emission in nanolasers with discrete emitters.",1602.03998v2
2016-04-25,Spatially Coupled Turbo-Like Codes,"In this paper, we introduce the concept of spatially coupled turbo-like codes
(SC-TCs) as the spatial coupling of a number of turbo-like code ensembles. In
particular, we consider the spatial coupling of Berrou et al. parallel
concatenated codes (PCCs) and Benedetto et al. serially concatenated codes
(SCCs). Furthermore, we propose two extensions of braided convolutional codes
(BCCs), a class of turbo-like codes which have an inherent spatially coupled
structure, to higher coupling memories, and show that these yield improved
belief propagation (BP) thresholds as compared to the original BCC ensemble. We
derive the exact density evolution (DE) equations for SC-TCs and analyze their
asymptotic behavior on the binary erasure channel. We also consider the
construction of families of rate-compatible SC-TC ensembles. Our numerical
results show that threshold saturation of the belief propagation (BP) decoding
threshold to the maximum a-posteriori threshold of the underlying uncoupled
ensembles occurs for large enough coupling memory. The improvement of the BP
threshold is especially significant for SCCs and BCCs, whose uncoupled
ensembles suffer from a poor BP threshold. For a wide range of code rates,
SC-TCs show close-to-capacity performance as the coupling memory increases. We
further give a proof of threshold saturation for SC-TC ensembles with identical
component encoders. In particular, we show that the DE of SC-TC ensembles with
identical component encoders can be properly rewritten as a scalar recursion.
This allows us to define potential functions and prove threshold saturation
using the proof technique recently introduced by Yedla et al..",1604.07315v2
2016-06-29,Colorability Saturation Games,"We consider the following two-player game: Maxi and Mini start with the empty
graph on $n$ vertices and take turns, always adding one additional edge to the
graph such that the chromatic number is at most $k$, where $k \in \mathbb{N}$
is a given parameter. The game is over when the graph is saturated and no
further edge can be inserted. Maxi wants to maximize the length of the game
while Mini wants to minimize it. The score $s(n,\chi_{>k})$ denotes the number
of edges in the final graph, given that both players followed an optimal
strategy.
  This colorability game belongs to the family of \emph{saturation games} that
are known to provide beautiful and challenging problems despite being defined
via simple combinatorial rules. The analysis of colorability saturation games
has been initiated recently by Hefetz, Krivelevich, Naor, and Stojakovi\'c
(2016). In this paper, we improve their results by providing almost matching
lower and upper bounds on the score of the game that hold for arbitrary choices
of $k$ and $n>k$. In addition, we study the specific game with $k=4$ in more
details and prove that its score is $n^2/3+O(n)$.",1606.09099v6
2016-07-01,Forward production of Drell-Yan dileptons at high energies and low dilepton invariant masses in a $k_t$-factorization approach: Do we see onset of saturation?,"We discuss Drell-Yan production of dileptons at high energies in forward
rapidity region in a hybrid high-energy approach. This approach uses
unintegrated gluon distributions in one proton and collinear quark/antiquark
distributions in the second proton. Corresponding momentum-space formula for
the differential cross sections in high-energy approximation has been derived.
The relation to the commonly used dipole approach is discussed. We conclude and
illustrate that some results of the dipole approaches are too approximate, as
far as kinemtics is considered, and in fact cannot be used for real
experiments. We find that the dipole formula is valid only in very
forward/backward rapidity regions ($|y| >$ 5). Some differential cross sections
for low-mass dilepton production are shown and compared to the LHCb and ATLAS
experimental data. In distinction to dipole approaches, we include four
Drell-Yan structure functions (the impact of interference structure functions
is rather small for typical experimental cuts). We find that both side
contributions ($g q/\bar q$ and $q/\bar q g$) have to be included even for the
LHCb rapidity coverage which is in contradiction with what is usually done in
the dipole approach. We present results for different unintegrated gluon
distributions from the literature (some of them include saturation effects). We
see no clear hints of saturation even at small $M_{ll}$.",1607.00238v1
2016-10-12,Symmetry energy and density,"The nuclear equation-of-state is a topic of highest current interest in
nuclear structure and reactions as well as in astrophysics. In particular, the
equation-of-state of asymmetric matter and the symmetry energy representing the
difference between the energy densities of neutron matter and of symmetric
nuclear matter are not sufficiently well constrained at present. The density
dependence of the symmetry energy is conventionally expressed in the form of
the slope parameter L describing the derivative with respect to density of the
symmetry energy at saturation. Results deduced from nuclear structure and
heavy-ion reaction data are distributed around a mean value L=60 MeV.
  Recent studies have more thoroughly investigated the density range that a
particular observable is predominantly sensitive to. Two thirds of the
saturation density is a value typical for the information contained in
nuclear-structure data. Higher values exceeding saturation have been shown to
be probed with meson production and collective flows at incident energies in
the range of up to about 1 GeV/nucleon.
  From the measurement of the elliptic-flow ratio of neutrons with respect to
light charged particles in recent experiments at the GSI laboratory, a new more
stringent constraint for the symmetry energy at suprasaturation density has
been deduced. It confirms, with a considerably smaller uncertainty, the
moderately soft to linear density dependence of the symmetry energy previously
deduced from the FOPI-LAND data. Future opportunities offered by FAIR will be
discussed.",1610.03650v1
2016-10-20,Strong correlations of neutron star radii with the slopes of nuclear matter incompressibility and symmetry energy at saturation,"We examine the correlations of neutron star radii with the nuclear matter
incompressibility, symmetry energy, and their slopes, which are the key
parameters of the equation of state (EoS) of asymmetric nuclear matter. The
neutron star radii and the EoS parameters are evaluated using a representative
set of 24 Skyrme-type effective forces and 18 relativistic mean field models,
and two microscopic calculations, all describing 2$M_\odot$ neutron stars.
Unified EoSs for the inner-crust-core region have been built for all the
phenomenological models, both relativistic and non-relativistic. Our
investigation shows the existence of a strong correlation of the neutron star
radii with the linear combination of the slopes of the nuclear matter
incompressibility and the symmetry energy coefficients at the saturation
density. Such correlations are found to be almost independent of the neutron
star mass in the range $0.6\text{-}1.8M_{\odot}$. This correlation can be
linked to the empirical relation existing between the star radius and the
pressure at a nucleonic density between one and two times saturation density,
and the dependence of the pressure on the nuclear matter incompressibility, its
slope and the symmetry energy slope. The slopes of the nuclear matter
incompressibility and the symmetry energy coefficients as estimated from the
finite nuclei data yield the radius of a $1.4M_{\odot}$ neutron star in the
range $11.09\text{-}12.86$ km.",1610.06344v1
2016-10-22,Massive Corrections to Entanglement in Minimal E8 Toda Field Theory,"In this letter we study the exponentially decaying corrections to saturation
of the second R\'enyi entropy of one interval of length L in minimal E8 Toda
field theory. It has been known for some time that the entanglement entropy of
a massive quantum field theory in 1+1 dimensions saturates to a constant value
for m1 L <<1 where m1 is the mass of the lightest particle in the spectrum.
Subsequently, results by Cardy, Castro-Alvaredo and Doyon have shown that there
are exponentially decaying corrections to this behaviour which are
characterised by Bessel functions with arguments proportional to m1 L. For the
von Neumann entropy the leading correction to saturation takes the precise
universal form -K0(2m1 L)/8 whereas for the R\'enyi entropies leading
corrections which are proportional to K0(m1 L) are expected. Recent numerical
work by P\'almai for the second R\'enyi entropy of minimal E8 Toda has found
next-to-leading order corrections decaying as exp(-2m1 L) rather than the
expected exp(-m1 L). In this paper we investigate the origin of this result and
show that it is incorrect. An exact form factor computation of correlators of
branch point twist fields reveals that the leading corrections are proportional
to K0(m1 L) as expected.",1610.07040v2
2016-11-05,Improved measurement of the hyperfine structure of the laser cooling level $4f^{12}(^3 H_6)5d_{5/2}6s^2$ $(J=9/2)$ in $^{169}$Tm,"We report on the improved measurement of the hyperfine structure of
$4f^{12}(^3 H_6)5d_{5/2}6s^2$ $(J=9/2)$ excited state in Tm-169 which is
involved in the second-stage laser cooling of Tm. To measure the absolute value
of the hyperfine splitting interval we used Doppler-free frequency modulation
saturated absorption spectroscopy of Tm atoms in a vapor cell. The sign of the
hyperfine constant was determined independently by spectroscopy of laser cooled
Tm atoms. The hyperfine constant of the level equals $A_J=-422.112(32)$ MHz
that corresponds to the energy difference between two hyperfine sublevels of
$-2110.56(16)$~MHz. In relation to the saturated absorption measurement we
quantitatively treat contributions of various mechanisms into the line
broadening and shift. We consider power broadening in the case when Zeeman
sublevels of atomic levels are taken into account. We also discuss the line
broadening due to frequency modulation and relative intensities of transitions
in saturated-absorption experiments.",1611.01679v1
2016-12-13,Expectation values of twist fields and universal entanglement saturation of the free massive boson,"The evaluation of vacuum expectation values (VEVs) in massive integrable
quantum field theory (QFT) is a nontrivial renormalization-group ""connection
problem"" -- relating large and short distance asymptotics -- and is in general
unsolved. This is particularly relevant in the context of entanglement entropy,
where VEVs of branch-point twist fields give universal saturation predictions.
We propose a new method to compute VEVs of twist fields associated to
continuous symmetries in QFT. The method is based on a differential equation in
the continuous symmetry parameter, and gives VEVs as infinite form-factor
series which truncate at two-particle level in free QFT. We verify the method
by studying U(1) twist fields in free models, which are simply related to the
branch-point twist fields. We provide the first exact formulae for the VEVs of
such fields in the massive uncompactified free boson model, checking against an
independent calculation based on angular quantization. We show that logarithmic
terms, overlooked in the original work of Callan and Wilczek [Phys. Lett. B333
(1994)], appear both in the massless and in the massive situations. This
implies that, in agreement with numerical form-factor observations by Bianchini
and Castro-Alvaredo [Nucl. Phys. B913 (2016)], the standard power-law
short-distance behavior is corrected by a logarithmic factor. We discuss how
this gives universal formulae for the saturation of entanglement entropy of a
single interval in near-critical harmonic chains, including log log
corrections.",1612.04238v2
2017-01-09,On the tensor semigroup of affine kac-moody lie algebras,"In this paper, we are interested in the decomposition of the tensor product
of two representations of a symmetrizable Kac-Moody Lie algebra $\mathfrak g$.
Let $P\_+$ be the set of dominant integral weights. For $\lambda\in P\_+$ ,
$L(\lambda)$ denotes the irreducible, integrable, highest weight representation
of g with highest weight $\lambda$. Let $P\_{+,\mathbb Q}$ be the rational
convex cone generated by $P\_+$. Consider the tensor cone $\Gamma(\mathfrak g)
:= \{(\lambda\_1 ,\lambda\_2, \mu) $\in$ P\_{+,\mathbb Q}^3\,| \exists N
\textgreater{} 1 L(N\mu) \subset L(N \lambda\_1)\otimes L(N \lambda\_2)\}$. If
$\mathfrak g$ is finite dimensional, $\Gamma(\mathfrak g)$ is a polyhedral
convex cone described in 2006 by Belkale-Kumar by an explicit finite list of
inequalities. In general, $\Gamma(\mathfrak g)$ is nor polyhedral, nor closed.
In this article we describe the closure of $\Gamma(\mathfrak g)$ by an explicit
countable family of linear inequalities, when $\mathfrak g$ is untwisted
affine. This solves a Brown-Kumar's conjecture in this case. We also obtain
explicit saturation factors for the semigroup of triples $(\lambda\_1,
\lambda\_2 , \mu) $\in$ P\_+^3$ such that $L(\mu) $\subset$ L(\lambda\_1)
\otimes L(\lambda\_2)$. Note that even the existence of such saturation factors
is not obvious since the semigroup is not finitely generated. For example, in
type $A , we prove that any integer $d\geq 2$ is a saturation factor,
generalizing the case ${\tilde A}\_1$ shown by Brown-Kumar.",1701.02176v2
2017-01-31,Attainability of the quantum information bound in pure state models,"The attainability of the quantum Cram\'er-Rao bound [QCR], the ultimate limit
in the precision of the estimation of a physical parameter, requires the
saturation of the quantum information bound [QIB]. This occurs when the Fisher
information associated to a given measurement on the quantum state of a system
which encodes the information about the parameter coincides with the quantum
Fisher information associated to that quantum state. Braunstein and Caves [PRL
{\bf 72}, 3439 (1994)] have shown that the QIB can always be achieved via a
projective measurement in the eigenvectors basis of an observable called
symmetric logarithmic derivative. However, such projective measurement depends,
in general, on the value of the parameter to be estimated. Requiring,
therefore, the previous knowledge of the quantity one is trying to estimate.
For this reason, it is important to investigate under which situation it is
possible to saturate the QCR without previous information about the parameter
to be estimated. Here, we show the complete solution to the problem of which
are all the initial pure states and the projective measurements that allow the
global saturation of the QIB, without the knowledge of the true value of the
parameter, when the information about the parameter is encoded in the system by
a unitary process.",1701.09144v1
2017-02-24,A step function density profile model for the convective stability of CO2 geological sequestration,"The convective stability associated with carbon sequestration is usually
investigated by adopting an unsteady diffusive basic profile. The method of
normal modes is not applicable due to the time dependence of the nonlinear base
profile. Therefore, the instability is quantified either in terms of critical
times at which the boundary layer instability sets in or in terms of long time
evolution of initial disturbances. This paper adopts an unstably stratified
basic profile having a step function density with top heavy carbon saturated
layer (boundary layer) overlying a lighter carbon free layer (ambient brine).
The resulting configuration resembles that of the Rayleigh-Taylor problem with
buoyancy diffusion at the interface separating the two layers. The
discontinuous reference state satisfies the governing system of equations and
boundary conditions and pertains to an unstably stratified motionless state.
Our model accounts for anisotropy in both diffusion and permeability and
chemical reaction between the carbon dioxide rich brine and host mineralogy. We
proceed by supposing that the carbon dioxide that has accumulated below the top
cap rock forms a layer of carbon saturated brine of some thickness that
overlies a carbon-free brine layer. The resulting stratification remains stable
until the thickness of the carbon saturated layer is sufficient to induce the
fluid to overturn. With this formulation for the reference state, the stability
calculations will be in terms of critical boundary layer thickness instead of
critical times, although the two formulations are homologous. This approach is
tractable by the classical normal mode analysis. Even though it yields only
conservative threshold instability conditions, it offers the advantage for an
analytically tractable linear and weakly nonlinear studies.",1702.07623v1
2017-04-10,Slow light in saturable absorbers : Progress in the resolution of a controversy,"There are two opposing models in the analysis of the slow transmission of
light pulses through saturable absorbers. The canonical incoherent bleaching
model simply explains the slow transmission by combined effects of saturation
and of non-instantaneous response of the medium resulting in absorption of the
front part of the incident pulse larger than that of its rear. The second
model, referred to as the coherent-population-oscillations (CPO) model,
considers light beams whose intensity is slightly pulse modulated and
attributes the time delay of the transmitted pulse to a reduction of the group
velocity. We point out some inconsistencies in the CPO model and show that the
two models lie in reality on the same hypotheses, the equations derived in the
duly rectified CPO model being local expressions of the integral equations
obtained in the incoherent bleaching model. For large modulation index, the CPO
model, based on linearized equations, breaks down. The incoherent bleaching
model then predicts that the transmitted light should vanish when the intensity
of the incident light is strictly zero. This point is confirmed by the
experiments that we have performed on ruby with square-wave incident pulses and
we show that the whole shape of the observed pulses agrees with that derived
analytically by means of the incoherent bleaching model. We also determine in
this model the corresponding evolution of the fluorescence light, which seems
to have been evidenced in other experiments.",1704.02820v2
2017-05-08,Empirical model of the Gibbs free energy for saline solutions of arbitrary concentration: Application for H2O-NaCl solutions at 423.15K-573.15K and pressures from saturation up to 5kbar,"An empirical model of the concentration dependence of the excess Gibbs free
energy Gex for saline solutions is proposed. Our simple analytical form of Gex
allows obtaining equations of state of saline solutions equally precise in the
whole range of the salt concentrations, from dilute solutions up to the limit
of solubility. Our equation for Gex includes one term responsible for
concentration dependence of Gex at low salt concentrations and two terms of
Margules type dependent on powers of mole fractions of the components. These
terms contain four parameters dependent on temperature and pressure. As an
example of application of the proposed model we took the system H2O-NaCl. For
fixed T and P, our four-parameter form of Gex allows precisely reproduce
experimental data for NaCl water solutions, including both regions of low and
high concentrations. An introduction of temperature dependence of the
parameters allowed us to build a precise analytic fit of experimental data on
osmotic coefficients of NaCl solutions for saturation pressures of NaCl at
temperatures 423.15K-573.15K. On the basis of PVTx data by Driesner (2007) the
model was extended towards pressures up to 5kbar. Our form of Gex allows
obtaining the molar volumes, activities of components and other thermodynamic
properties of NaCl-H2O solutions in the range of temperatures 423.15K-573.15K
and pressures from saturation up to 5kbar in the whole range of concentrations
possible for H2O-NaCl solutions (from zero up to approximately 10 molal at
573.15K).",1705.02901v2
2017-06-11,A numerical method for efficient 3D inversions using Richards equation,"Fluid flow in the vadose zone is governed by Richards equation; it is
parameterized by hydraulic conductivity, which is a nonlinear function of
pressure head. Investigations in the vadose zone typically require
characterizing distributed hydraulic properties. Saturation or pressure head
data may include direct measurements made from boreholes. Increasingly, proxy
measurements from hydrogeophysics are being used to supply more spatially and
temporally dense data sets. Inferring hydraulic parameters from such datasets
requires the ability to efficiently solve and deterministically optimize the
nonlinear time domain Richards equation. This is particularly important as the
number of parameters to be estimated in a vadose zone inversion continues to
grow. In this paper, we describe an efficient technique to invert for
distributed hydraulic properties in 1D, 2D, and 3D. Our algorithm does not
store the Jacobian, but rather computes the product with a vector, which allows
the size of the inversion problem to become much larger than methods such as
finite difference or automatic differentiation; which are constrained by
computation and memory, respectively. We show our algorithm in practice for a
3D inversion of saturated hydraulic conductivity using saturation data through
time. The code to run our examples is open source and the algorithm presented
allows this inversion process to run on modest computational resources.",1706.03381v1
2017-06-21,Nuclear modification of forward $D$ production in pPb collisions at the LHC,"We study nuclear modification factors for single $D$ meson and semileptonic
decay lepton $l$ ($=e,\mu$) production in minimum bias proton-nucleus (p$A$)
collisions at the LHC in the color-glass-condensate (CGC) framework at leading
order in strong coupling. In our numerical computations, transverse momentum
($k_\perp$) dependent multi-point Wilson line correlators are employed for
describing target nucleus for p$A$ and proton for pp. The projectile proton is
treated with unintegrated gluon distribution function, which is also
$k_\perp$-dependent. The rapidity evolutions of these functions in the small
Bjorken $x$ region are taken into account by solving running coupling
Balitsky-Kovchegov (BK) equation at leading logarithmic accuracy. For
simplicity, we employ Kartvelishvili's type fragmentation function and a simple
model for lepton energy distribution from seileptonic decay, respectively, to
compute differential cross sections for $D$ and $l$ production. The gluon
saturation scale inside the heavy nucleus is enhanced and dependent on $x$,
which we take into account by replacing the initial saturation scale in the BK
equation with a larger value for the heavy nucleus. We show that the saturation
effect leads to perceptible nuclear suppression of $D$ production at forward
rapidity. Our numerical results predict similar nuclear suppressions in p$A$
collisions for forward $l$ production at lower transverse momentum
$p_\perp<2\;{\rm GeV}$. Numerical tables on the nuclear modifications of $D$
and $l$ are listed in this note.",1706.06728v2
2017-07-18,Saturation properties of helium drops from a Leading Order description,"Saturation properties are directly linked to the short-range scale of the
two-body interaction of the particles. The case of helium is particular, from
one hand the two-body potential has a strong repulsion at short distances. On
the other hand, the extremely weak binding of the helium dimer locates this
system very close to the unitary limit allowing for a description based on an
effective theory. At leading order of this theory a two- and a three-body term
appear, each one characterized by a low energy constant. In a potential model
this description corresponds to a soft potential model with a two-body term
purely attractive plus a three-body term purely repulsive constructed to
describe the dimer and trimer binding energies. Here we analyse the capability
of this model to describe the saturation properties making a direct link
between the low energy scale and the short-range correlations. We will show
that the energy per particle, $E_N/N$, can be obtained with reasonable accuracy
at leading order extending the validity of this approximation, characterizing
universal behavior in few-boson systems close to the unitary limit, to the
many-body system.",1707.05628v2
2017-08-30,Effects of Arrival Type and Degree of Saturation on Queue Length Estimation at Signalized Intersections,"Purpose of this study is evaluation of the relationship between different
arrival types and degree of saturation (X) with overestimations of HCM 2010
procedure for estimating the back of queue within a study area. Further
analysis is performed to establish the relationship between queue length and
delay and also between each of them individually and X in cases with
overestimation. The analyses are based on the 50th percentile queue lengths for
data collected at four signalized intersections along a corridor in 4 time
periods (off peak period and AM, Noon and PM peak periods). Based on the
statistical test results, arrival type did not play a role in overestimations.
However, there is a significant relationship between the overestimations on
minor and major street and different ranges of X. On minor streets, about 59%
of the overestimations are at X values less than half; while near 23% of the
overestimations are at oversaturation condition with X values greater than 1.
The relationship between amount of overestimations and degree of saturation
should be established based on the numerical amount of overestimations versus X
values rather than the relative amounts; since the statistical comparison
between the relative amount of overestimations and X values, resulted in a
wrong idea of the real world condition. There was a significant correlation
between field queue and delay data of the cases with overestimated queue length
in all cases on major and minor streets. Also, field queue is correlated to X,
in all cases on minor and major streets.",1708.09439v1
2017-09-05,Constraints on Flavored 2d CFT Partition Functions,"We study the implications of modular invariance on 2d CFT partition functions
with abelian or non-abelian currents when chemical potentials for the charges
are turned on, i.e. when the partition functions are ""flavored"". We begin with
a new proof of the transformation law for the modular transformation of such
partition functions. Then we proceed to apply modular bootstrap techniques to
constrain the spectrum of charged states in the theory. We improve previous
upper bounds on the state with the greatest ""mass-to-charge"" ratio in such
theories, as well as upper bounds on the weight of the lightest charged state
and the charge of the weakest charged state in the theory. We apply the
extremal functional method to theories that saturate such bounds, and in
several cases we find the resulting prediction for the occupation numbers are
precisely integers. Because such theories sometimes do not saturate a bound on
the full space of states but do saturate a bound in the neutral sector of
states, we find that adding flavor allows the extremal functional method to
solve for some partition functions that would not be accessible to it
otherwise.",1709.01533v3
2018-02-28,Photonic glass for high contrast structural color,"Non-iridescent structural colors based on disordered arrangement of
monodisperse spherical particles, also called photonic glass, show low color
saturation due to gradual transition in reflectivity. No significant
improvement is usually expected from particles optimization, as the Mie
resonances are broad for small dielectric particles with moderate refractive
index. Moreover, the short range order of a photonic glass alone is also
insufficient to cause sharp spectral features. We show here, that the
combination of a well-chosen particle geometry with the short range order of a
photonic glass has strong synergetic effects. We demonstrate how core-shell
particles can be used to obtain a sharp transition in the reflection spectrum
of photonic glass which is essential to achieve a strong color saturation. The
Fourier transform required for a highly saturated color can be achieved by
shifting the first zero position of the motif Fourier transform to smaller wave
numbers in respect to the peak of the lattice Fourier transform. We show that
this can be obtained by choosing a non-monotonous refractive index distribution
from the center of the particle through the shell and into the background
material. The first-order theoretical predictions are confirmed by numerical
simulations.",1802.10536v1
2018-03-05,Numerical Simulation of Oscillating Multiphase Heat Transfer in Parallel plates using Pseudopotential Multiple-Relaxation-Time Lattice Boltzmann Method,"Multiphase flows frequently occur in many important engineering and
scientific applications, but modeling of such flows is a rather challenging
task due to complex interfacial dynamics between different phases, let alone if
the flow is oscillating in the porous media. Using humid air as the working
fluid in the thermoacoustic refrigerator is one of the research focus to
improve the thermoacoustic performance, but the corresponding effect is the
condensation of humid air in the thermal stack. Due to the small sized spacing
of thermal stack and the need to explore the detailed condensation process in
oscillating flow, a mesoscale numerical approach need to be developed. Over the
decades, several types of Lattice Boltzmann (LB) models for multiphase flows
have been developed under different physical pictures, for example the
color-gradient model, the Shan-Chen model, the nonideal pressure tensor model
and the HSD model. In the current study, a pseudopotential
Multiple-Relaxation-Time (MRT) LBM simulation was utilized to simulate the
incompressible oscillating flow and condensation in parallel plates. In the
initial stage of condensation, the oscillating flow benefits to accumulate the
saturated vapor at the exit regions, and the velocity vector of saturated vapor
clearly showed the flow over the droplets. It was also concluded that if the
condensate can be removed out from the parallel plates, the oscillating flow
and condensation will continuously feed the cold surface to form more water
droplets. The effect of wettability to the condensation was discussed, and it
turned out that by increasing the wettability, the saturated water vapor was
easier to condense on the cold walls, and the distance between each pair of
droplets was also strongly affected by the wettability.",1803.01756v1
2018-04-06,Performance Comparison of Constant Envelope and Zero-forcing Precoders in Multiuser Massive MIMO,"In this article, the adoption and performance of a constant envelope (CE)
type spatial precoder is addressed in large-scale multiuser MIMO based cellular
network. We first formulate an efficient computing solution to obtain the
antenna samples of such CE precoder. We then evaluate the achievable CE
precoder based multiuser downlink (DL) system performance and compare it with
the corresponding performance of more ordinary zero-forcing (ZF) spatial
precoder. We specifically also analyze how realistic highly nonlinear power
amplifiers (PAs) affect the achievable DL performance, as the individual PA
units in large-array or massive MIMO systems are expected to be small, cheap
and operating close to saturation for increased energy-efficiency purposes. It
is shown that the largely reduced peak-to-average power ratio (PAPR) of the PA
input signals in the CE precoder based system allows for pushing the PA units
harsher towards saturation, while allowing to reach higher
signal-to-interference-plus-noise ratio (SINRs) at the intended receivers
compared to the classical ZF precoder based system. The obtained results
indicate that the CE precoder can outperform the ZF precoder by up to 5-6 dBs,
in terms of the achievable SINRs, when the PA units are pushed towards their
saturating region. Such large gains are a substantial benefit when seeking to
improve the spectral and energy-efficiencies of the mobile cellular networks.",1804.02224v1
2018-04-09,Non-linear hydrodynamic instability and turbulence in eccentric astrophysical discs with vertical structure,"Non-linear evolution of the parametric instability of inertial waves inherent
to eccentric discs is studied by way of a new local numerical model. Mode
coupling of tidal deformation with the disc eccentricity is known to produce
exponentially growing eccentricities at certain mean-motion resonances.
However, the details of an efficient saturation mechanism balancing this growth
still are not fully understood. This paper develops a local numerical model for
an eccentric quasi-axisymmetric shearing box which generalises the often-used
cartesian shearing box model. The numerical method is an overall second order
well-balanced finite volume method which maintains the stratified and
oscillatory steady-state solution by construction. This implementation is
employed to study the non-linear outcome of the parametric instability in
eccentric discs with vertical structure. Stratification is found to constrain
the perturbation energy near the mid-plane and localise the effective region of
inertial wave breaking that sources turbulence. A saturated marginally sonic
turbulent state results from the non-linear breaking of inertial waves and is
subsequently unstable to large-scale axisymmetric zonal flow structures. This
resulting limit-cycle behaviour reduces access to the eccentric energy source
and prevents substantial transport of angular momentum radially through the
disc. Still, the saturation of this parametric instability of inertial waves is
shown to damp eccentricity on a time-scale of a thousand orbital periods. It
may thus be a promising mechanism for intermittently regaining balance with the
exponential growth of eccentricity from the eccentric Lindblad resonances and
may also help explain the occurrence of ""bursty"" dynamics such as the superhump
phenomenon.",1804.03249v1
2018-04-19,A Non-standard Model for Microbial Enhanced Oil Recovery Including the Oil-water Interfacial Area,"In this work we present a non-standard model for microbial enhanced oil
recovery including the oil-water interfacial area. Including the interfacial
area in the model, we eliminate the hysteresis in the capillary pressure
relationship. One of the characteristics that a surfactant should have, it is
biological production at the oil-water interface. Therefore, we consider the
production rate of surfactants not only as a function of the nutrient
concentration, but also the interfacial area. To solve the model equations, we
use an efficient and robust linearization scheme that considers a linear
approximation of the capillary pressure gradient. A comprehensive, 1D
implementation based on two-point flux approximation of the model is achieved.
We consider different parameterizations for the interfacial tension and
residual oil saturation reduction. Illustrative numerical simulations are
presented, where we study the spatial distribution and evolution in time of the
average pressure, water saturation, interfacial area, capillary pressure,
residual oil saturation and bacterial, nutrient and surfactant concentrations.
Inclusion of the interfacial area in the model leads to different predictions
of oil recovery. The model can also be used to design new experiments
contributing to a better understanding and optimization of MEOR.",1804.07085v1
2018-05-16,Many-Body Quantum Interference and the Saturation of Out-of-Time-Order Correlators,"Out-of-time-order correlators (OTOCs) have been proposed as sensitive probes
for chaos in interacting quantum systems. They exhibit a characteristic
classical exponential growth, but saturate beyond the so-called scrambling or
Ehrenfest time $\tau_{\rm E}$ in the quantum correlated regime. Here we present
a path-integral approach for the entire time evolution of OTOCs for bosonic
$N$-particle systems. We first show how the growth of OTOCs up to $\tau_{\rm E}
= (1/\lambda) \log N$ is related to the Lyapunov exponent $\lambda$ of the
corresponding chaotic mean-field dynamics in the semiclassical large-$N$ limit.
Beyond $\tau_{\rm E}$, where simple mean-field approaches break down, we
identify the underlying quantum mechanism responsible for the saturation. To
this end we express OTOCs by coherent sums over contributions from different
mean-field solutions and compute the dominant many-body interference term
amongst them. Our method further applies to the complementary semiclassical
limit $\hbar \rightarrow 0$ for fixed $N$, including quantum-chaotic single-
and few-particle systems.",1805.06377v2
2018-07-16,CGC/saturation approach: secondary Reggeons and $ρ={\rm Re/Im}$ dependence on energy,"In this letter we demonstrate that a model which is based on the
CGC/saturation approach, is able to describe soft interaction collisions for
the wide range of $W=\sqrt{s} = 30 \,GeV \div\, 13 \,TeV$ including the new
TOTEM data at 13 TeV. We have incorporated the secondary Reggeons in our
approach which enables us to describe the complete set of the soft data,
including the energy behaviour of $\rho $ the ratio of the real to imaginary
parts of the elastic scattering amplitude. We argue that it is premature to
claim that an odderon contribution is necessary, but estimate its possible
strength as $1 mb$ to the real part of the amplitude at W = 13 \,TeV. We show
that the odderon contribution depends on the value of energy leading to ${\rm
Re A\Lb s, t=0\Rb} $= 8 mb at W=21.2 \,GeV. Bearing this in mind we do not
believe that $\rho$ at high energies is the appropriate observable for
detecting the odderon contribution. The successful description of the soft data
in the wide range of energy strengthens our claim that the CGC/saturation
approach is the only viable candidate for an effective theory for high energy
QCD.",1807.06459v2
2018-07-28,Exclusive diffractive vector meson production: A comparison between the dipole model and the leading twist shadowing approach,"With the imminent construction of an electron-ion collider in the USA, both
saturation physics and nuclear shadowing physics will be important for the same
processes for the first time. In particular for exclusive production of vector
mesons, such as the J/$\psi$. In this paper we investigate the underlying
assumptions commonly made when phenomenologically investigating this process
from a shadowing and saturation perspective respectively. We use the bSat model
which is commonly used to describe saturation physics, and a calculation by
M.G. Ryskin which is commonly used when describing nuclear shadowing at leading
twist. It is expected that the bSat model is equivalent to Ryskin's result in
the hard scattering and non-relativistic limits. By explicitly taking these
limits we show that the bSat model does indeed become equivalent to Ryskin's
result. However, two more approximations are needed for this result. Firstly,
the factorisation and renormalisation scales in the bSat model has to be
independent of the dipole radius, and secondly, we need to omit a term in the
overlap between the vector meson and virtual photon wave functions. We show
that for the typical dipole radius of the J/$\psi$, the different
approximations off-set each other and the bSat model agrees very well with
Ryskin's calculation in hard-scattering and non-relativistic limits.",1807.10888v4
2018-08-24,Magnetoresistance from Fermi Surface Topology,"Extremely large non-saturating magnetoresistance has recently been reported
for a large number of both topologically trivial and non-trivial materials.
Different mechanisms have been proposed to explain the observed
magnetotransport properties, yet without arriving to definitive conclusions or
portraying a global picture. In this work, we investigate the transverse
magnetoresistance of materials by combining the Fermi surfaces calculated from
first principles with the Boltzmann transport theory approach relying on the
semiclassical model and the relaxation time approximation. We first consider a
series of simple model Fermi surfaces to provide a didactic introduction into
the charge-carrier compensation and open-orbit mechanisms leading to
non-saturating magnetoresistance. We then address in detail magnetotransport in
three representative materials: (i) copper, a prototypical nearly free-electron
metal characterized by the open Fermi surface that results in an intricate
angular magnetoresistance, (ii) bismuth, a topologically trivial semimetal in
which very large magnetoresistance is known to result from charge-carrier
compensation, and (iii) tungsten diphosphide WP2, a recently discovered type-II
Weyl semimetal that holds the record of magnetoresistance in compounds. In all
three cases our calculations show excellent agreement with both the field
dependence of magnetoresistance and its anisotropy measured at low
temperatures. Furthermore, the calculations allow for a full interpretation of
the observed features in terms of the Fermi surface topology. These results
will help addressing a number of outstanding questions, such as the role of the
topological phase in the pronounced large non-saturating magnetoresistance
observed in topological materials.",1808.08178v1
2018-08-27,Hydro-micromechanical modeling of wave propagation in saturated granular media,"Biot's theory predicts the wave velocities of a saturated poroelastic
granular medium from the elastic properties, density and geometry of its dry
solid matrix and the pore fluid, neglecting the interaction between constituent
particles and local flow. However, when the frequencies become high and the
wavelengths comparable with particle size, the details of the microstructure
start to play an important role. Here, a novel hydro-micromechanical numerical
model is proposed by coupling the lattice Boltzmann method (LBM) with the
discrete element method (DEM. The model allows to investigate the details of
the particle-fluid interaction during propagation of elastic waves While the
DEM is tracking the translational and rotational motion of each solid particle,
the LBM can resolve the pore-scale hydrodynamics. Solid and fluid phases are
two-way coupled through momentum exchange. The coupling scheme is benchmarked
with the terminal velocity of a single sphere settling in a fluid. To mimic a
pressure wave entering a saturated granular medium, an oscillating pressure
boundary condition on the fluid is implemented and benchmarked with
one-dimensional wave equations. Using a face centered cubic structure, the
effects of input waveforms and frequencies on the dispersion relations are
investigated. Finally, the wave velocities at various effective confining
pressures predicted by the numerical model are compared with with Biot's
analytical solution, and a very good agreement is found. In addition to the
pressure and shear waves, slow compressional waves are observed in the
simulations, as predicted by Biot's theory.",1808.08921v1
2018-09-27,RPC performance vs FE electoronics and detector parameters,"The first Resistive Plate Chambers detectors were developed for cosmic ray
experiments, where low rate capability, good time resolution and low cost per
unit of area were needed. These same features, except for the low rate
capability, were required in the muon spectrometers of the collider experiments
like LHC. For this purpose newRPCdetectors with increased rate capability were
developed. The rate capability improvement has been achieved thanks to the
transition from streamer to saturated avalanche regime, in which the average
charge produced in the gas dicharge is smaller. The price to pay for this
working mode switch is the transfer of the amplification from the detector to
the FE electorinics. The High luminosity LHC and the future colliders will
require even greater rate capability in the muon spectrometer compared to the
current one. For this reason, further improving of the rate capability is
required. The transition from the saturated avalanche to a low saturated
avalanche regime moves in this direction and needs a new front end electronics
with better signal to noise ratio, because the average induced charge on the
electrode is even smaller. The front end electronics design is crucial for the
RPC performances. In this paper we discuss the performances of the RPC detector
changing the front end design and the detector parameters.",1809.10497v1
2018-10-08,"Quantum chaos, thermalization and entanglement generation in real-time simulations of the BFSS matrix model","We study numerically the onset of chaos and thermalization in the
Banks-Fischler-Shenker-Susskind (BFSS) matrix model with and without fermions,
considering Lyapunov exponents, entanglement generation, and quasinormal
ringing. We approximate the real-time dynamics in terms of the most general
Gaussian density matrices with parameters which obey self-consistent equations
of motion, thus extending the applicability of real-time simulations beyond the
classical limit. Initial values of these Gaussian density matrices are
optimized to be as close as possible to the thermal equilibrium state of the
system. Thus attempting to bridge between the low-energy regime with a
calculable holographic description and the classical regime at high energies,
we find that quantum corrections to classical dynamics tend to decrease the
Lyapunov exponents, which is essential for consistency with the
Maldacena-Shenker-Stanford (MSS) bound at low temperatures. The entanglement
entropy is found to exhibit an expected ""scrambling"" behavior - rapid initial
growth followed by saturation. At least at high temperatures the entanglement
saturation time appears to be governed by classical Lyapunov exponents. Decay
of quasinormal modes is found to be characterized by the shortest time scale of
all. We also find that while the bosonic matrix model becomes non-chaotic in
the low-temperature regime, for the full BFSS model with fermions the leading
Lyapunov exponent, entanglement saturation time, and decay rate of quasinormal
modes all remain finite and non-zero down to the lowest temperatures.",1810.03378v1
2018-10-14,Gas transport in partially-saturated sand packs,"Understanding gas transport in porous media and its mechanism has broad
applications in various research areas, such as carbon sequestration in deep
saline aquifers and gas explorations in reservoir rocks. Gas transport is
mainly controlled by pore space geometrical and morphological characteristics.
In this study, we apply a physically-based model developed using concepts from
percolation theory (PT) and the effective-medium approximation (EMA) to better
understand diffusion and permeability of gas in packings of angular and rounded
sand grains as well as glass beads. Two average sizes of grain i.e., 0.3 and
0.5 mm were used to pack sands in a column of 6 cm height and 4.9 cm diameter
so that the total porosity of all packs was near 0.4. Water content, gas-filled
porosity (also known as gas content), gas diffusion, and gas permeability were
measured at different capillary pressures. The X-ray computed tomography method
and the 3DMA-Rock software package were applied to determine the average pore
coordination number z. Results showed that both saturation-dependent diffusion
and permeability of gas showed almost linear behavior at higher gas-filled
porosities, while deviated substantially from linear scaling at lower gas
saturations. Comparing the theory with the diffusion and permeability
experiments showed that the determined value of z ranged between 2.8 and 5.3,
not greatly different from X-ray computed tomography results. The obtained
results clearly indicate that the effect of the pore-throat size distribution
on gas diffusion and permeability was minimal in these sand and glass bead
packs.",1810.05965v1
2018-12-27,Can Image Enhancement be Beneficial to Find Smoke Images in Laparoscopic Surgery?,"Laparoscopic surgery has a limited field of view. Laser ablation in a
laproscopic surgery causes smoke, which inevitably influences the surgeon's
visibility. Therefore, it is of vital importance to remove the smoke, such that
a clear visualization is possible. In order to employ a desmoking technique,
one needs to know beforehand if the image contains smoke or not, to this date,
there exists no accurate method that could classify the smoke/non-smoke images
completely. In this work, we propose a new enhancement method which enhances
the informative details in the RGB images for discrimination of smoke/non-smoke
images. Our proposed method utilizes weighted least squares optimization
framework~(WLS). For feature extraction, we use statistical features based on
bivariate histogram distribution of gradient magnitude~(GM) and Laplacian of
Gaussian~(LoG). We then train a SVM classifier with binary smoke/non-smoke
classification task. We demonstrate the effectiveness of our method on Cholec80
dataset. Experiments using our proposed enhancement method show promising
results with improvements of 4\% in accuracy and 4\% in F1-Score over the
baseline performance of RGB images. In addition, our approach improves over the
saturation histogram based classification methodologies Saturation
Analysis~(SAN) and Saturation Peak Analysis~(SPA) by 1/5\% and 1/6\% in
accuracy/F1-Score metrics.",1812.10784v1
2019-02-23,Effects of multiple scattering on angle-independent structural color in disordered colloidal materials,"Disordered packings of colloidal spheres show angle-independent structural
color when the particles are on the scale of the wavelength of visible light.
Previous work has shown that the positions of the peaks in the reflectance
spectra can be predicted accurately from a single-scattering model that
accounts for the effective refractive index of the material. This agreement
shows that the main color peak arises from short-range correlations between
particles. However, the single-scattering model does not quantitatively
reproduce the observed color: the main peak in the reflectance spectrum is much
broader and the reflectance at low wavelengths is much larger than predicted by
the model. We use a combination of experiment and theory to understand these
features. We find that one significant contribution to the breadth of the main
peak is light that is scattered, totally internally reflected from the boundary
of the sample, and then scattered again. The high reflectance at low
wavelengths also results from multiple scattering but can be traced to the
increase in the scattering cross-section of individual particles with
decreasing wavelength. Both of these effects tend to reduce the saturation of
the structural color, which limits the use of these materials in applications.
We show that while the single-scattering model cannot reproduce the observed
saturations, it can be used to design materials in which multiple scattering is
suppressed and the color saturated, even in the absence of absorbing
components.",1902.08733v2
2019-02-24,Adaptive Estimators Show Information Compression in Deep Neural Networks,"To improve how neural networks function it is crucial to understand their
learning process. The information bottleneck theory of deep learning proposes
that neural networks achieve good generalization by compressing their
representations to disregard information that is not relevant to the task.
However, empirical evidence for this theory is conflicting, as compression was
only observed when networks used saturating activation functions. In contrast,
networks with non-saturating activation functions achieved comparable levels of
task performance but did not show compression. In this paper we developed more
robust mutual information estimation techniques, that adapt to hidden activity
of neural networks and produce more sensitive measurements of activations from
all functions, especially unbounded functions. Using these adaptive estimation
techniques, we explored compression in networks with a range of different
activation functions. With two improved methods of estimation, firstly, we show
that saturation of the activation function is not required for compression, and
the amount of compression varies between different activation functions. We
also find that there is a large amount of variation in compression between
different network initializations. Secondary, we see that L2 regularization
leads to significantly increased compression, while preventing overfitting.
Finally, we show that only compression of the last layer is positively
correlated with generalization.",1902.09037v2
2019-03-14,Constraining compact star properties with nuclear saturation parameters,"A set of hadronic equations of state (EoSs) derived from relativistic density
functional theory and constrained by terrestrial experiments, astrophysical
observations, in particular by the GW170817 event, and chiral effective field
theory ($\chi$EFT) of neutron matter is used to explore the sensitivity of the
EoS parameterization on the few nuclear matter characteristics defined at the
saturation density. We find that the gross properties of compact stars are most
sensitive to the isoscalar skewness coefficient $Q_{\text{sat}}$ and the
isovector slope coefficient $L_{\text{sym}}$ around saturation density, since
the higher order coefficients, such as $K_{\text{sym}}$, are fixed by our
model. More specifically, (i) among these $Q_{\text{sat}}$ is the dominant
parameter controlling both the maximum mass and the radii of compact stars
while $L_{\rm sym}$ is constrained somewhat by $\chi$EFT of neutron matter;
(ii) massive enough ($M\sim 2.0~M_{\odot})$ compact stars featuring both
hyperons and $\Delta$ resonances can be obtained if the value of
$Q_{\text{sat}}$ is large enough; (iii) the emergence of $\Delta$'s reduces the
radius of a canonical mass ($M\sim 1.4~M_{\odot})$ compact star thus easing the
tension between the predictions of the relativistic density functionals and the
inferences from the X-ray observation of nearby isolated neutron stars.",1903.06057v2
2019-04-15,Time evolution of entanglement entropy of moving mirrors influenced by strongly coupled quantum critical fields,"The evolution of the Von Neumann entanglement entropy of a $n$-dimensional
mirror influenced by the strongly coupled $d$-dimensional quantum critical
fields with a dynamic exponent $z$ is studied by the holographic approach. The
dual description is a $n+1$-dimensional probe brane moving in the
$d+1$-dimensional asymptotic Lifshitz geometry ended at $r=r_b$, which plays a
role as the UV energy cutoff. Using the holographic influence functional
method, we find that in the linear response region, by introducing a harmonic
trap for the mirror, which serves as a IR energy cutoff, the Von Neumann
entropy at late times will saturate by a power-law in time for generic values
of $z$ and $n$. The saturated value and the relaxation rate depend on the
parameter $\alpha\equiv 1+(n+2)/z$, which is restricted to $1<\alpha <3$ but
$\alpha \ne 2$. We find that the saturated values of the entropy are
qualitatively different for the theories with $1<\alpha<2$ and $2<\alpha<3$.
Additionally, the power law relaxation follows the rate $\propto
t^{-2\alpha-1}$. This probe brane approach provides an alternative way to study
the time evolution of the entanglement entropy in the linear response region
that shows the similar power-law relaxation behavior as in the studies of
entanglement entropies based on Ryu-Takayanagi conjecture. We also compare our
results with quantum Brownian motion in a bath of relativistic free fields.",1904.06831v2
2019-04-29,Probing chiral interactions up to next-to-next-to-next-to-leading order in medium-mass nuclei,"We study ground-state energies and charge radii of closed-shell medium-mass
nuclei based on novel chiral nucleon-nucleon (NN) and three-nucleon (3N)
interactions, with a focus on exploring the connections between finite nuclei
and nuclear matter. To this end, we perform in-medium similarity
renormalization group (IM-SRG) calculations based on chiral interactions at
next-to-leading order (NLO), N$^2$LO, and N$^3$LO, where the 3N interactions at
N$^2$LO and N$^3$LO are fit to the empirical saturation point of nuclear matter
and to the triton binding energy. Our results for energies and radii at N$^2$LO
and N$^3$LO overlap within uncertainties, and the cutoff variation of the
interactions is within the EFT uncertainty band. We find underbound
ground-state energies, as expected from the comparison to the empirical
saturation point. The radii are systematically too large, but the agreement
with experiment is better. We further explore variations of the 3N couplings to
test their sensitivity in nuclei. While nuclear matter at saturation density is
quite sensitive to the 3N couplings, we find a considerably weaker dependence
in medium-mass nuclei. In addition, we explore a consistent momentum-space SRG
evolution of these NN and 3N interactions, exhibiting improved many-body
convergence. For the SRG-evolved interactions, the sensitivity to the 3N
couplings is found to be stronger in medium-mass nuclei.",1904.12611v2
2019-05-15,Nb$_x$Ti$_{1-x}$N low timing jitter single-photon detectors with unity internal efficiency at 1550 nm and 2.5 K,"The requirements in quantum optics experiments for high single photon
detection efficiency, low timing jitter, low dark count rate and short dead
time have been fulfilled with the development of superconducting nanowire
single photon detectors. Although they offer a detection efficiency above 90%,
achieving a high time resolution in devices made of amorphous materials is a
challenge, particularly at temperatures above 0.8 K. Devices made from niobium
nitride and niobium titanium nitride allow to reach the best timing jitter, but
in turn have stronger requirements in terms of film quality to achieve a high
efficiency. Here we take advantage of the flexibility of reactive co-sputter
deposition to tailor the composition of NbxTi1-xN superconducting films, and
show that a Nb fraction of x = 0.62 allows for the fabrication of detectors
from films as thick as 9 nm and covering an active area of 20 {\mu}m, with a
wide detection saturation plateau at telecom wavelengths and in particular at
1550 nm. This is a signature of an internal detection efficiency saturation,
achieved while maintaining the high time resolution associated with NbTiN and
operation at 2.5K. With our optimized recipe, we reliably fabricated detectors
with high critical current densities reaching a saturation plateau at 1550 nm
with 80% system detection efficiency, and with a FWHM timing jitter as low as
19.47 ps.",1905.06091v1
2019-05-21,Time resolution and dynamic range of field effect transistor based terahertz detectors,"We studied time resolution and response power dependence of three terahertz
detectors based on significantly different types of field effect transistors.
We analyzed the photoresponse of custom-made Si junctionless FETs, Si MOSFETs
and GaAs-based high electron mobility transistors detectors. Applying
monochromatic radiation of high power, pulsed, line-tunable molecular THz
laser, which operated at frequencies in the range from 0.6-3.3 THz, we
demonstrated that all these detectors have at least nanosecond response time.
We showed that detectors yield a linear response in a wide range of radiation
power. At high powers the response saturates varying with radiation power P as
$U = R_0 P/(1+P/P_s)$, where $R_0$ is the low power responsivity, $P_s$ is the
saturation power. We demonstrated that the linear part response decreases with
radiation frequency increase as $R_0 \propto f^{-3}$, whereas the power at
which signal saturates increases as $P_s \propto f^3$. We discussed the
observed dependences in the framework of the Dyakonov-Shur mechanism and
detector-antenna impedance matching. Our study showed that FET transistors can
be used as ultrafast room temperature detectors of THz radiation and that their
dynamic range extends over many orders of magnitude of power of incoming THz
radiation. Therefore, when embedded with current driven read out electronics
they are very well adopted for operation with high power pulsed sources.",1905.08602v1
2019-05-22,Short echo time relaxation-enhanced MR spectroscopy reveals broad downfield resonances,"Purpose: Most MR spectroscopy (MRS) pulse sequences rely on broadband
excitation with water saturation and typically focus on upfield signals. By
contrast, the downfield spectrum, which contains many potentially useful
resonances, is typically not targeted because conventional water-suppressed
techniques indirectly saturate the labile protons through exchange.
Relaxation-enhanced MRS (RE-MRS) uses frequency-selective excitation while
actively avoiding bulk water perturbation, thereby enabling high-quality
downfield spectroscopy. However, RE-MRS typically requires very long (typically
>40 ms) echo times (TEs) due to its localization module, which inevitably
decreases sensitivity and filters shorter T2 components. Here, we overcome this
limitation by combining RE-MRS and image selected in vivo spectroscopy (ISIS)
localization, abbreviated iRE-MRS, which in turn allows very short TEs (5 ms
using our hardware).
  Methods: Experiments were performed in vitro for validation as well as and in
in vivo rat brains at 9.4T.
  Results: The new iRE-MRS methodology was validated in phantoms where good
performance was noted. When the downfield spectrum was investigated at short
TEs in in vivo rat brains, iRE-MRS provided very high sensitivity; the ensuing
downfield spectra encompassed numerous broad peaks, as well as a broad
baseline. All downfield spectral peaks were highly attenuated by increasing TEs
as well as by applying water saturation, although to different extent. The
signal ratios also varied between TEs, suggesting that exchange rates are
different among the downfield signals.
  Conclusions: Short-TE iRE 1H downfield MRS opens new directions in the
investigation of in vivo downfield metabolites and their role on healthy and
disease processes.",1905.09158v1
2019-06-17,Wrist02 -- Reliable Peripheral Oxygen Saturation Readings from Wrist-Worn Pulse Oximeters,"Peripheral blood oxygen saturation Sp02 is a vital measure in healthcare.
Modern off-the-shelf wrist-worn devices, such as the Apple Watch, FitBit, and
Samsung Gear, have an onboard sensor called a pulse oximeter. While pulse
oximeters are capable of measuring both Sp02 and heart rate, current wrist-worn
devices use them only to determine heart rate, as Sp02 measurements collected
from the wrist are believed to be inaccurate. Enabling oxygen saturation
monitoring on wearable devices would make these devices tremendously more
useful for health monitoring and open up new avenues of research. To the best
of our knowledge, we present the first study of the reliability of Sp02 sensing
from the wrist. Using a custom-built wrist-worn pulse oximeter, we find that
existing algorithms designed for fingertip sensing are a poor match for this
setting, and can lead to over 90% of readings being inaccurate and unusable. We
further show that sensor placement and skin tone have a substantial effect on
the measurement error, and must be considered when designing wrist-worn Sp02
sensors and measurement algorithms. Based on our findings, we propose
\codename, an alternative approach for reliable Sp02 sensing. By selectively
pruning data, \codename achieves an order of magnitude reduction in error
compared to existing algorithms, while still providing sufficiently frequent
readings for continuous health monitoring.",1906.07545v1
2019-09-24,"Saturations of Subalgebras, SAGBI Bases, and U-invariants","Given a polynomial ring $P$ over a field $K$, an element $g \in P$, and a
$K$-subalgebra $S$ of $P$, we deal with the problem of saturating $S$ with
respect to $g$, i.e. computing $Sat_g(S) = S[g, g^{-1}]\cap P$. In the general
case we describe a procedure/algorithm to compute a set of generators for
$Sat_g(S)$ which terminates if and only if it is finitely generated.
  Then we consider the more interesting case when $S$ is graded. In particular,
if $S$ is graded by a positive matrix $W$ and $g$ is an indeterminate, we show
that if we choose a term ordering $\sigma$ of $g$-DegRev type compatible with
$W$, then the two operations of computing a $\sigma$-SAGBI basis of $S$ and
saturating $S$ with respect to $g$ commute.
  This fact opens the doors to nice algorithms for the computation of
$Sat_g(S)$. In particular, under special assumptions on the grading one can use
the truncation of a $\sigma$-SAGBI basis and get the desired result.
  Notably, this technique can be applied to the problem of directly computing
some $U$-invariants, classically called semi-invariants, even in the case that
$K$ is not the field of complex numbers.",1909.10901v3
2019-11-11,Extracting many-body correlators of saturated gluons with precision from inclusive photon+dijet final states in deeply inelastic scattering,"We highlight the principal results of a computation in the Color Glass
Condensate effective field theory (CGC EFT) of the next-to-leading order (NLO)
impact factor for inclusive photon+dijet production at Bjorken $x_{\rm Bj} \ll
1$ in deeply inelastic electron-nucleus (e+A DIS) collisions. When combined
with extant results for next-to-leading log $x_{\rm Bj}$ JIMWLK renormalization
group (RG) evolution of gauge invariant two-point (""dipole"") and four-point
(""quadrupole"") correlators of light-like Wilson lines, the inclusive
photon+dijet e+A DIS cross-section can be determined to $\sim 10$\% accuracy.
Our computation simultaneously provides the ingredients to compute fully
inclusive DIS, inclusive photon, inclusive dijet and inclusive photon+jet
channels to the same accuracy. This makes feasible quantitative extraction of
many-body correlators of saturated gluons and precise determination of the
saturation scale $Q_{S,A}(x_{\rm Bj})$ at a future Electron-Ion Collider. An
interesting feature of our NLO result is the structure of the violation of the
soft gluon theorem in the Regge limit. Another is the appearance in gluon
emission of time-like non-global logs which also satisfy JIMWLK RG evolution.",1911.04519v2
2020-02-09,"Growth, saturation and collapse of laser-driven plasma density gratings","The plasma density grating induced by intersecting intense laser pulses can
be utilized as an optical compressors, polarizers, waveplates and photonic
crystals for the manipulation of ultra-high-power laser pulses. However, the
formation and evolution of the plasma density grating are still not fully
understood as linear models are adopted to describe them usually. In this
paper, two nonlinear theoretical models are presented to study the formation
process of the plasma density grating. In the first model, a nonlinear
analytical solution based on the fluid equations is presented while in the
second model a particle-mesh method is adopted to investigate the kinetic
effects. It is found that both models can describe the plasma density grating
formation at different stages, well beyond the linear growth stage. More
importantly, the second model can reproduce the phenomenon of ""ion
wave-breaking"" of plasma density grating, which eventually induces the
saturation of plasma density grating. Using the second model, the saturation
time of the plasma density grating is obtained as a function of laser intensity
and plasma density, which can be applied to estimate the lifetime of the plasma
density grating in experiments. The results from these two nonlinear models are
verified using particle-in-cell simulations.",2002.03340v3
2020-02-27,Scaling exponents saturate in three-dimensional isotropic turbulence,"From a database of direct numerical simulations of homogeneous and isotropic
turbulence, generated in periodic boxes of various sizes, we extract the
spherically symmetric part of moments of velocity increments and first verify
the following (somewhat contested) results: the $4/5$-ths law holds in an
intermediate range of scales and that the second order exponent over the same
range of scales is {\it{anomalous}}, departing from the self-similar value of
$2/3$ and approaching a constant of $0.72$ at high Reynolds numbers. We compare
with some typical theories the dependence of longitudinal exponents as well as
their derivatives with respect to the moment order $n$, and estimate the most
probable value of the H\""older exponent. We demonstrate that the transverse
scaling exponents saturate for large $n$, and trace this trend to the presence
of large localized jumps in the signal. The saturation value of about $2$ at
the highest Reynolds number suggests, when interpreted in the spirit of
fractals, the presence of vortex sheets rather than more complex singularities.
In general, the scaling concept in hydrodynamic turbulence appears to be more
complex than even the multifractal description.",2002.11900v2
2020-03-27,Fakernet -- small and fast FPGA-based TCP and UDP communication,"A common theme of data acquisition systems is the transport of data from
digitising front-end modules to stable storage and online analysis. A good
choice today is to base this on the ubiquitous, commercially and cheaply
available Ethernet technology. A firmware building block to turn already the
FPGA of front-end electronics into a TCP data source and UDP control interface
using a data-flow architecture is presented. The overall performance targets
are to be able to saturate a 1 Gbps network link with outbound data, while
using few FPGA resources. The goal is to replace the use of custom data buses
and protocols with ordinary Ethernet equipment. These objectives are achieved
by being just-enough conforming, such that no special drivers are needed in the
PC equipment interfacing with the here presented Fakernet system. An important
design choice is to handle all packet-data internally as 16-bit words, thus
reducing the clock-speed requirements. An advantageous circumstance is that
even at 1 Gbps speeds, for local network segments, the round-trip times are
usually well below 500 microseconds. Thus, less than 50 kiB of unacknowledged
data needs to be in-flight, allowing to saturate a network link without TCP
window scaling. The Fakernet system has so far been shown to saturate a 100
Mbps link at 11.7 MB/s of TCP output data, and able to do 32-bit control
register accesses at over 450 kword/s.",2003.12527v1
2020-03-27,Lensing Mechanism Meets Small-$x$ Physics: Single Transverse Spin Asymmetry in $p^{\uparrow}+p$ and $p^{\uparrow}+A$ Collisions,"We calculate the single transverse spin asymmetry (STSA) in polarized
proton-proton ($p^{\uparrow}+p$) and polarized proton-nucleus
($p^{\uparrow}+A$) collisions ($A_N$) generated by a partonic lensing
mechanism. The polarized proton is considered in the quark-diquark model while
its interaction with the unpolarized target is calculated using the
small-$x$/saturation approach, which includes multiple rescatterings and
small-$x$ evolution. The phase required for the asymmetry is caused by a
final-state gluon exchange between the quark and diquark, as is standard in the
lensing mechanism of Brodsky, Hwang and Schmidt. Our calculation combines the
lensing mechanism with small-$x$ physics in the saturation framework. The
expression we obtain for the asymmetry $A_N$ of the produced quarks has the
following properties: (i) The asymmetry is generated by the dominant elastic
scattering contribution and $1/N_c^2$ suppressed inelastic contribution (with
$N_c$ the number of quark colors); (ii) The asymmetry grows or oscillates with
the produced quark's transverse momentum $p_T$ until the momentum reaches the
saturation scale $Q_s$, and then only falls off as $1/p_T$ for larger momenta;
(iii) The asymmetry decreases with increasing atomic number $A$ of the target
for $p_T$ below or near $Q_s$, but is independent of $A$ for $p_T$
significantly above $Q_s$. We discuss how these properties may be qualitatively
consistent with the data on $A_N$ published by the PHENIX collaboration and
with the preliminary data on $A_N$ reported by the STAR collaboration.",2003.12650v2
2020-04-30,Non-local Entanglement and Fast Scrambling in De-Sitter Holography,"We study holographic entanglement and information scrambling in de-Sitter
(dS) space in the context of the DS/dS correspondence. We find that our
previously identified non-local entanglement structure of dS vacua can be
extended out of the time-reflection symmetric slice. We extend the geometry to
a two-sided configuration and calculate the zero-time mutual information
between two intervals on different sides when there is a localized shock wave
in the bulk. Interestingly, we find that the information scrambling time
saturates the fast scrambler bound proposed by Sekino and Susskind and that the
shock wave renders a wormhole to be traversable. Furthermore, we calculate a
two-sided out-of-time-ordered correlator (OTOC) in the late time regime and we
see that, before scrambling, it exponentially grows with an exponent whose
value saturates the maximal bound of chaos proposed by Maldacena, Shenker and
Stanford. At the end, we provide an explanation why the exponential growing of
the late-time OTOC with the maximal bound of chaos saturated and the
traversability of the wormhole are simple results of the non-local entanglement
structure and point out that this is a realization of the ER=EPR proposal.",2005.00021v4
2020-05-29,Core swelling in spherical nuclei: An indication of the saturation of nuclear density,"Background: Nuclear radius is one of the most important and basic properties
of atomic nuclei and its evolution is closely related to the saturation of the
nuclear density in the internal region but the systematics of the nuclear radii
for the neutron-rich unstable nuclei is not well known.
  Purpose: Motivated by the recent interaction cross section measurement which
indicates the 48Ca core swelling in the neutron-rich Ca isotopes, we explore
the mechanism of the enhancement of the neutron and proton radii for spherical
nuclei.
  Methods: Microscopic Hartree-Fock calculations with three sets of Skyrme-type
effective interactions are performed for the neutron-rich Ca, Ni and Sn
isotopes. The total reaction cross sections for the Ca isotopes are evaluated
with the Glauber model to compare them with the recent cross section data.
  Results: We obtain good agreement with the measured cross sections and charge
radii. The neutron and proton radii of the various ""core"" configurations are
extracted from the full Hartree-Fock calculation and discuss the core swelling
mechanism.
  Conclusions: The core swelling phenomena occur depending on the properties of
the occupying valence single-neutron states to minimize the energy loss that
comes from the saturation of the densities in the internal region, which
appears to be prominent in light nuclei such as Ca isotopes.",2005.14352v1
2020-06-23,Invariants ideals in Leavitt Path algebras,"It is known that the ideals of a Leavitt path algebra $L_K(E)$ generated by
$\Pl(E)$, by $\Pc(E)$ or by $\Pec(E)$ are invariant under isomorphism. Though
the ideal generated by $\Pb(E)$ is not invariant we find its \lq\lq
natural\rq\rq\ replacement (which is indeed invariant): the one generated by
the vertices of $\Pbp$ (vertices with pure infinite bifurcations). We also give
some procedures to construct invariant ideals from previous known invariant
ideals. One of these procedures involves topology, so we introduce the $\tops$
topology and relate it to annihilators in the algebraic counterpart of the
work. To be more explicit: if $H$ is a hereditary saturated subset of vertices
providing an invariant ideal, its exterior $\ext(H)$ in the $\tops$ topology of
$E^0$ generates a new invariant ideal. The other constructor of invariant
ideals is more categorical in nature. Some hereditary sets can be seen as
functors from graphs to sets (for instance $\Pl$, etc). Thus a second method
emerges from the possibility of applying the induced functor to the quotient
graph. The easiest example is the known socle chain $\soc^{(1)}(\
)\subset\soc^{(2)}(\ )\subset\cdots$ all of which are proved to be invariant.
We generalize this idea to any hereditary and saturated invariant functor.
Finally we investigate a kind of composition of hereditary and saturated
functors which is associative.",2006.12876v1
2020-07-27,EUV irradiation of exoplanet atmospheres occurs on Gyr timescales,"Exoplanet atmospheres are known to be vulnerable to mass loss through
irradiation by stellar X-ray and extreme-ultraviolet emission. We investigate
how this high-energy irradiation varies with time by combining an empirical
relation describing stellar X-ray emission with a second relation describing
the ratio of Solar X-ray to extreme-ultraviolet emission. In contrast to
assumptions commonly made when modelling atmospheric escape, we find that the
decline in stellar extreme-ultraviolet emission is much slower than in X-rays,
and that the total extreme-ultraviolet irradiation of planetary atmospheres is
dominated by emission after the saturated phase of high energy emission (which
lasts around 100 Myr after the formation of the star). The extreme-ultraviolet
spectrum also becomes much softer during this slow decline. Furthermore, we
find that the total combined X-ray and extreme-ultraviolet emission of stars
also occurs mostly after this saturated phase. Our results suggest that models
of atmospheric escape that focus on the saturated phase of high-energy emission
are over-simplified, and when considering the evolution of planetary
atmospheres it is necessary to follow EUV-driven escape on Gyr timescales. This
may make it more difficult to use stellar age to separate the effects of
photoevaporation and core-powered mass-loss when considering the origin the
planet radius valley.",2007.13731v2
2020-08-22,Gravitational wave asteroseismology for low-mass neutron stars,"The fundamental ($f$-) mode gravitational waves from cold low-mass neutron
stars are systematically studied with various equations of state (EOSs)
characterized by the nuclear saturation parameters, especially focusing on the
phenomena of the avoided crossing with the first pressure ($p_1$-) mode. We
find that the $f$-mode frequency and the average density for the neutron star
at the avoided crossing can be expressed as a function of the parameter,
$\eta$, which is the specific combination of the nuclear saturation parameters.
Owing to these relations, we can derive the empirical formula expressing the
$f$-mode frequency for a low-mass neutron star, whose central density is larger
than that for the neutron star at the avoided crossing, as a function of $\eta$
and the square root of the stellar average density, $x$. On the other hand, we
also derive the empirical formula expressing the $f$-mode frequency for a
neutron star, whose central density is less than that for the neutron star at
the avoided crossing, as a function of $x$ independently of the adopted EOS.
Furthermore, adopting the empirical formula of $x$ as a function of $\eta$ and
$u_c$, which is the ratio of the stellar central density to the saturation
density, we can also rewrite our empirical formula for the $f$-mode frequency
to a function of $\eta$ and $u_c$. So, by observing the $f$-mode gravitational
wave from a low-mass neutron star, whose mass or gravitational redshift is
known, one could evaluate the values of $\eta$ and $u_c$, which enables us to
severely constrain the EOS for neutron star matter.",2008.09839v1
2020-09-24,Large magnetoresistance in the iron-free pnictide superconductor LaRu$_2$P$_2$,"The magnetoresistance of iron pnictide superconductors is often dominated by
electron-electron correlations and deviates from the H$^2$ or saturating
behaviors expected for uncorrelated metals. Contrary to similar Fe-based
pnictide systems, the superconductor LaRu$_2$P$_2$ (T$_c$ = 4 K) shows no
enhancement of electron-electron correlations. Here we report a non-saturating
magnetoresistance deviating from the H$^2$ or saturating behaviors in
LaRu$_2$P$_2$. We have grown and characterized high quality single crystals of
LaRu$_2$P$_2$ and measured a magnetoresistance following H$^{1.3}$ up to 22 T.
We discuss our result by comparing the bandstructure of LaRu$_2$P$_2$ with Fe
based pnictide superconductors. The different orbital structures of Fe and Ru
leads to a 3D Fermi surface with negligible bandwidth renormalization in
LaRu$_2$P$_2$, that contains a large open sheet over the whole Brillouin zone.
We show that the large magnetoresistance in LaRu$_2$P$_2$ is unrelated to the
one obtained in materials with strong electron-electron correlations and that
it is compatible instead with conduction due to open orbits on the rather
complex Fermi surface structure of LaRu$_2$P$_2$.",2009.11585v1
2020-11-03,Growth of respiratory droplets in cold and humid air,"The ambient conditions surrounding liquid droplets determine their growth or
shrinkage. However, the precise fate of a liquid droplet expelled from a
respiratory puff as dictated by its surroundings and the puff itself has not
yet been fully quantified. From the view of airborne disease transmission, such
as SARS-CoV-2, knowledge of such dependencies are critical. Here we employ
direct numerical simulations (DNS) of a turbulent respiratory vapour puff and
account for the mass and temperature exchange with respiratory droplets and
aerosols. In particular, we investigate how droplets respond to different
ambient temperatures and relative humidity (RH) by tracking their Lagrangian
statistics. We reveal and quantify that in cold and humid environments, as
there the respiratory puff is supersaturated, expelled droplets can first
experience significant growth, and only later followed by shrinkage, in
contrast to the monotonic shrinkage of droplets as expected from the classical
view by William F. Wells (1934). Indeed, cold and humid environments diminish
the ability of air to hold water vapour, thus causing the respiratory vapour
puff to super-saturate. Consequently, the super-saturated vapour field drives
the growth of droplets that are caught and transported within the humid puff.
To analytically predict the likelihood for droplet growth, we propose a model
for the axial RH based on the assumption of a quasi-stationary jet. Our model
correctly predicts super-saturated RH conditions and is in good quantitative
agreement with our DNS. Our results culminate in a temperature-RH map that can
be employed as an indicator for droplet growth or shrinkage.",2011.01515v1
2020-11-17,Collapse and cavitation during drying of water-saturated PDMS sponges with closed porosity,"In this paper, we study the drying of water-saturated porous
polydimethylsiloxane (PDMS) elastomers with closed porosity in which the
evaporation of water is possible only via the diffusion across the PDMS.
Starting from water/PDMS emulsions, we fabricate soft macroporous samples with
different pore diameter distributions and average diameters ranging from 10 to
300 $\mu$m. In these materials, the drying may lead either to a collapsed state
with low porosity or to the cavitation and reopening of a fraction of the
pores. Using optical microscopy and porosity measurements, we showed the
importance of the pore diameters and interactions on the result of drying. At
pore diameters lower than 30 $\mu$m, the majority of pores remain collapsed. We
attribute the permanence of the collapse of most small pores to a low
probability of cavitation and to the adhesion of the pore walls. Pores with
diameters larger than 100 $\mu$m tend to reopen after the water they contain
cavitates. The behavior of pores with diameters ranging from 30 to 100 $\mu$m
depends on the porosity and drying temperature. We also visualize collective
cavitation upon drying of sponges initially saturated with a sodium chloride
solution. In this case, the cavitation in the largest pores leads to reopening
of small pores in a neighboring zone of the sample. To our knowledge, our
results present the first experimental proof of the pore-size-dependent and
cooperative nature of the response of soft sponges with closed porosity to
drying.",2011.08570v1
2021-01-08,Dynamics of droplets under electrowetting effect with voltages exceeding the contact angle saturation threshold,"Electrowetting-on-dielectric (EWOD) is a powerful tool in many
droplet-manipulation applications with a notorious weakness caused by
contact-angle saturation (CAS), a phenomenon limiting the equilibrium contact
angle of an EWOD-actuated droplet at high applied voltage. In this paper, we
study the spreading behaviours of droplets on EWOD substrates with the range of
applied voltage exceeding the saturation limit. We experimentally find that at
the initial stage of spreading, the driving force at the contact line still
follows the Young-Lippmann law even if the applied voltage is higher than the
CAS voltage. We then theoretically establish the relation between the initial
contact-line velocity and the applied voltage using the force balance at the
contact line. We also find that the amplitude of capillary waves on the droplet
surface generated by the contact-line's initial motion increases with the
applied voltage. We provide a working framework utilising EWOD with voltages
beyond CAS by characterising the capillary waves formed on the droplet surface
and their self-similar behaviours. We finally propose a theoretical model of
the wave profiles taking into account the viscous effects and verify this model
experimentally. Our results provide avenues to utilise the EWOD effect with
voltages beyond CAS threshold and have strong bearing on emerging applications
such as digital microfluidic and ink-jet printing.",2101.02821v3
2021-01-13,Analytic quasi-steady evolution of a marginally unstable wave in the presence of drag and scattering,"The 1D bump-on-tail problem is studied in order to determine the influence of
drag on quasi-steady solutions near marginal stability ($1-\gamma_d/\gamma_L\ll
1$) when effective collisions are much larger than the instability growth rate
($\nu \gg \gamma$). In this common tokamak regime, it is rigorously shown that
the paradigmatic Berk-Breizman cubic equation for the nonlinear mode evolution
reduces to a much simpler differential equation, dubbed the time-local cubic
equation, which can be solved directly. It is found that in addition to
increasing the saturation amplitude, drag introduces a shift in the apparent
oscillation frequency by modulating the saturated wave envelope. Excellent
agreement is found between the analytic solution for the mode evolution and
both the numerically integrated Berk-Breizman cubic equation and fully
nonlinear 1D Vlasov simulations. Experimentally isolating the contribution of
drag to the saturated mode amplitude for verification purposes is explored but
complicated by the reality that the amount of drag can not be varied
independently of other key parameters in realistic scenarios. While the effect
of drag is modest when the ratio of drag to scattering $\alpha/\nu$ is very
small, it can become substantial when $\alpha/\nu \gtrsim 0.5$, suggesting that
drag should be accounted for in quantitative models of fast-ion-driven
instabilities in fusion plasmas.",2101.04875v1
2021-02-09,Chain ordering of phospholipids in membranes containing cholesterol: What matters?,"Cholesterol (CHOL) drives lipid segregation and is thus a key player for the
formation of lipid rafts and followingly for the ability of a cell to, e.g.,
enable selective agglomeration of proteins. The lipid segregation is driven by
cholesterol's affinity for saturated lipids, which stands directly in relation
to the ability of cholesterol to order the individual phospholipid (PL) acyl
chains. In this work, Molecular Dynamics simulations of DPPC
(Dipalmitoylphosphatidylcholine, saturated lipid) and DLiPC
(Dilineoylphosphatidylcholine, unsaturated lipid) mixtures with cholesterol are
used to elucidate the underlying mechanisms of the cholesterol ordering effect.
To this end, all enthalpic contributions, experienced by the PL molecules, are
recorded as a function of the PL's acyl chain order. This involves, the PL-PL,
the PL-cholesterol interaction, the interaction of the PLs with water, and the
interleaflet interaction. This systematic analysis allows one to unravel
differences of saturated and unsaturated lipids in terms of the different
interaction factors. It turns out that cholesterol's impact on chain ordering
stems not only from direct interactions with the PLs but is also indirectly
present in the other energy contributions. Furthermore, the analysis sheds
light on the relevance of the entropic contributions, related to the degrees of
freedom of the acyl chain.",2102.04996v3
2021-04-05,Auxiliary Function Approach for Determining Symmetry Energy at Supra-saturation Densities,"Nuclear symmetry energy $E_{\rm{sym}}(\rho)$ at density $\rho$ is normally
expanded or simply parameterized as a function of $\chi=(\rho-\rho_0)/3\rho_0$
in the form of $E_{\rm{sym}}(\rho)\approx
S+L\chi+2^{-1}K_{\rm{sym}}\chi^2+6^{-1}J_{\rm{sym}}\chi^3+\cdots$ using its
magnitude $S$, slope $L $, curvature $K_{\rm{sym}}$ and skewness $J_{\rm{sym}}$
at the saturation density $\rho_0$ of nuclear matter. Much progress has been
made in recent years in constraining especially the $S$ and $L$ parameters
using various terrestrial experiments and astrophysical observations. However,
such kind of expansions/parameterizations do not converge at supra-saturation
densities where $\chi$ is not small enough, hindering an accurate determination
of high-density $E_{\rm{sym}}(\rho)$ even if its characteristic parameters at
$\rho_0$ are all well determined by experiments/observations. By expanding the
$E_{\rm{sym}}(\rho)$ in terms of a properly chosen auxiliary function
$\Pi_{\rm{sym}}(\chi,\Theta_{\rm{sym}})$ with a parameter $\Theta_{\rm{sym}}$
fixed accurately by an experimental $E_{\rm{sym}}(\rho_{\rm{r}})$ value at a
reference density $\rho_{\rm{r}}$, we show that the shortcomings of the
$\chi$-expansion can be completely removed or significantly reduced in
determining the high-density behavior of $E_{\rm{sym}}(\rho)$. In particular,
using two significantly different auxiliary functions, we show that the new
approach effectively incorporates higher $\chi$-order contributions and
converges to the same $E_{\rm{sym}}(\rho)$ much faster than the conventional
$\chi$-expansion at densities $\lesssim3\rho_0$. Several quantitative
demonstrations using Monte Carlo simulations are given.",2104.02185v2
2021-04-06,Bounded Inputs Total Energy Shaping for Mechanical Systems,"Designing control systems with bounded input is a practical consideration
since realizable physical systems are limited by the saturation of actuators.
The actuators' saturation degrades the performance of the control system, and
in extreme cases, the stability of the closed-loop system may be lost. However,
actuator saturation is typically neglected in the design of control systems,
with compensation being made in the form of over-designing the actuator or by
post-analyzing the resulting system to ensure acceptable performance. The
bounded input control of fully actuated systems has been investigated in
multiple studies, but it is not generalized for under actuated mechanical
systems. This article proposes a systematic framework for finding the upper
bound of control effort in underactuated systems, based on interconnection and
the damping assignment passivity based control (IDA-PBC) approach. The proposed
method also offers design variables for the control law to be tuned,
considering the actuator's limit. The major difficulty in finding the control
input upper bounds is the velocity dependent kinetic energy related terms.
Thus, the upper bound of velocity is computed using a suitable Lyapunov
candidate as a function of closed-loop system parameters. The validity and
application of the proposed method are investigated in detail through two
benchmark systems.",2104.02337v1
2021-04-07,Rotation-Activity Relation of Ca II and Mg I Infrared Emission Lines of Young Stars,"To reveal the detail of the internal structure, the relationship between
chromospheric activity and the Rossby number, N_R (= rotational period P /
convective turnover time tau_c), has been extensively examined for
main-sequence stars. The goal of our work is to apply the same methods to
pre-main-sequence (PMS) stars and identify the appropriate model of tau_c for
them. Yamashita et al. (2020) investigated the relationship between N_R and
strengths of the Ca II infrared triplet (IRT; lambda 8498, 8542, 8662 A)
emission lines of 60 PMS stars. Their equivalent widths are converted into the
emission line to stellar bolometric luminosity ratio (R'). The 54 PMS stars
have N_R < 10^{-1.0} and show R' \sim 10^{-4.2} as large as the maximum R' of
the zero-age main-sequence (ZAMS) stars. However, because all R' was saturated
against N_R, it was not possible to estimate the appropriate tau_c model for
the PMS stars. We noticed that Mg I emission lines at 8808 A is an optically
thin chromospheric line, appropriate for determination of the adequate tau_c
for PMS stars. Using the archive data of the Anglo-Australian Telescope
(AAT)/the University College London Echelle Spectrograph (UCLES), we
investigated the Mg I line of 52 ZAMS stars. After subtracting photospheric
absorption component, the Mg I line is detected as an emission line in 45 ZAMS
stars, whose R' is between 10^{-5.9} and 10^{-4.1}. The Mg I line is not
saturated yet in ""the saturated regime for the Ca II emission lines"", i.e.
10^{-1.6} < N_R < 10^{-0.8}. Therefore, the adequate tau_c for PMS stars can be
determined by measuring of their R' values.",2104.02910v1
2021-05-04,Deep-learning-based coupled flow-geomechanics surrogate model for CO$_2$ sequestration,"A deep-learning-based surrogate model capable of predicting flow and
geomechanical responses in CO2 storage operations is presented and applied. The
3D recurrent R-U-Net model combines deep convolutional and recurrent neural
networks to capture the spatial distribution and temporal evolution of
saturation, pressure and surface displacement fields. The method is trained
using high-fidelity simulation results for 2000 storage-aquifer realizations
characterized by multi-Gaussian porosity and log-permeability fields. These
numerical solutions are expensive because the domain that must be considered
for the coupled problem includes not only the storage aquifer but also a
surrounding region, overburden and bedrock. The surrogate model is trained to
predict the 3D CO2 saturation and pressure fields in the storage aquifer, and
2D displacement maps at the Earth's surface. Detailed comparisons between
surrogate model and full-order simulation results for new (test-case)
storage-aquifer realizations are presented. The saturation, pressure and
surface displacement fields provided by the surrogate model display a high
degree of accuracy, both for individual test-case realizations and for ensemble
statistics. Finally, the the recurrent R-U-Net surrogate model is applied with
a rejection sampling procedure for data assimilation. Although the observations
consist of only a small number of surface displacement measurements,
significant uncertainty reduction in pressure buildup at the top of the storage
aquifer (caprock) is achieved.",2105.01334v1
2021-06-01,Symmetry potentials and in-medium nucleon-nucleon cross sections within the Nambu-Jona-Lasinio model in relativistic impulse approximation,"In the relativistic impulse approximation (RIA), we study symmetry potentials
and in-medium nucleon-nucleon (NN) cross sections with the Nambu-Jona-Lasinio
(NJL) model that features chiral symmetry. The chiral symmetry that plays a
fundamental role in the nonperturbative physics in the strong interaction is
anticipated to add restrictive effects on the symmetry potentials and in-medium
NN cross sections. For comparison, we also perform the study with the usual
relativistic mean-field (RMF) model. The numerical results with the NJL and RMF
models are similar at saturation density and below, since a priori fit was made
to saturation properties. With the increase of nuclear density, the chiral
symmetry starts to be restored partially in the NJL model, resulting in the
explicit fall of the scalar density. In a large energy span, the symmetry
potential acquires a significant rise for the partial restoration of the chiral
symmetry, compared to the one with the RMF model. It is found that the
in-medium NN cross sections in the RIA with the NJL and RMF models both
increase with the density in the energy region interested in this study,
whereas those with the NJL model increase sharply as long as a clear chiral
symmetry restoration takes place. The different tendency of observables in
density can be transmitted to the different energy dependence in the RIA. The
NJL model is shown to have characteristic energy-dependent symmetry potentials
and NN cross sections beyond saturation point, apart from the RMF models.",2106.00429v1
2021-06-07,Learning to Guide a Saturation-Based Theorem Prover,"Traditional automated theorem provers have relied on manually tuned
heuristics to guide how they perform proof search. Recently, however, there has
been a surge of interest in the design of learning mechanisms that can be
integrated into theorem provers to improve their performance automatically. In
this work, we introduce TRAIL, a deep learning-based approach to theorem
proving that characterizes core elements of saturation-based theorem proving
within a neural framework. TRAIL leverages (a) an effective graph neural
network for representing logical formulas, (b) a novel neural representation of
the state of a saturation-based theorem prover in terms of processed clauses
and available actions, and (c) a novel representation of the inference
selection process as an attention-based action policy. We show through a
systematic analysis that these components allow TRAIL to significantly
outperform previous reinforcement learning-based theorem provers on two
standard benchmark datasets (up to 36% more theorems proved). In addition, to
the best of our knowledge, TRAIL is the first reinforcement learning-based
approach to exceed the performance of a state-of-the-art traditional theorem
prover on a standard theorem proving benchmark (solving up to 17% more
problems).",2106.03906v1
2021-06-28,"A Low Power Threshold, Ultrathin Optical Limiter Based on a Nonlinear Zone Plate","Ultrathin optical limiters are needed to protect light sensitive components
in miniaturized optical systems. However, it has proven challenging to achieve
a sufficiently low optical limiting threshold. In this work, we theoretically
show that an ultrathin optical limiter with low threshold intensity can be
realized using a nonlinear zone plate. The zone plate is embedded with
nonlinear saturable absorbing materials that allow the device to focus low
intensity light, while high intensity light is transmitted as a plane wave
without a focal spot. Based on this proposed mechanism, we use the
finite-difference time-domain method to computationally design a zone plate
embedded with InAs quantum dots as the saturable absorbing material. The device
has a thickness of just 0.5 $\mu m$ and exhibits good optical limiting behavior
with a threshold intensity as low as 0.45 kW/$cm^2$, which is several orders of
magnitude lower than current ultrathin flat-optics-based optical limiters. This
design can be optimized for different operating wavelengths and threshold
intensities by using different saturable absorbing materials. Additionally, the
diameter and focal length of the nonlinear zone plate can be easily adjusted to
fit different systems and applications. Due to its flexible design, low power
threshold, and ultrathin thickness, this optical limiting concept may be
promising for application in miniaturized optical systems.",2106.15025v1
2021-07-13,Eddy saturation in a reduced two-level model of the atmosphere,"Eddy saturation describes the nonlinear mechanism in geophysical flows
whereby, when average conditions are considered, direct forcing of the zonal
flow increases the eddy kinetic energy, while the energy associated with the
zonal flow does not increase. Here we present a minimal baroclinic model that
exhibits complete eddy saturation. Starting from Phillips' classical
quasi-geostrophic two-level model on the beta channel of the mid-latitudes, we
derive a reduced order model comprising of six ordinary differential equations
including parameterised eddies. This model features two physically realisable
steady state solutions, one a purely zonal flow and one where, additionally,
finite eddy motions are present. As the baroclinic forcing in the form of
diabatic heating is increased, the zonal solution loses stability and the eddy
solution becomes attracting. After this bifurcation, the zonal components of
the solution are independent of the baroclinic forcing, and the excess of heat
in the low latitudes is efficiently transported northwards by finite eddies, in
the spirit of baroclinic adjustment.",2107.05864v1
2021-08-18,Mining for Gluon Saturation at Colliders,"Quantum chromodynamics (QCD) is the theory of strong interactions of quarks
and gluons collectively called partons, the basic constituents of all nuclear
matter. Its non-abelian character manifests in nature in the form of two
remarkable properties: color confinement and asymptotic freedom. At high
energies, perturbation theory can result in the growth and dominance of very
gluon densities at small-x. If left uncontrolled, this growth can result in
gluons eternally growing violating a number of mathematical bounds. The
resolution to this problem lies by balancing gluon emissions by recombinating
gluons at high energies : phenomena of gluon saturation. High energy nuclear
and particle physics experiments have spent the past decades quantifying the
structure of protons and nuclei in terms of their fundamental constituents
confirming predicted extraordinary behavior of matter at extreme density and
pressure conditions. In the process they have also measured seemingly
unexpected phenomena. We will give a state of the art review of the underlying
theoretical and experimental tools and measurements pertinent to gluon
saturation physics. We will argue for the need of high energy
electron-proton/ion colliders such as the proposed EIC (USA) and LHeC (Europe)
to consolidate our knowledge of QCD in the small x kinematic domains.",2108.08254v1
2021-10-12,Streaming Instability with Multiple Dust Species: II. Turbulence and Dust-Gas Dynamics at Nonlinear Saturation,"The streaming instability is a fundamental process that can drive dust-gas
dynamics and ultimately planetesimal formation in protoplanetary discs. As a
linear instability, it has been shown that its growth with a distribution of
dust sizes can be classified into two distinct regimes, fast- and slow-growth,
depending on the dust-size distribution and the total dust-to-gas density ratio
$\epsilon$. Using numerical simulations of an unstratified disc, we bring three
cases in different regimes into nonlinear saturation. We find that the
saturation states of the two fast-growth cases are similar to its
single-species counterparts. The one with maximum dimensionless stopping time
$\tau_\mathrm{s,max}=0.1$ and $\epsilon=2$ drives turbulent vertical dust-gas
vortices, while the other with $\tau_\mathrm{s,max}=2$ and $\epsilon=0.2$ leads
to radial traffic jams and filamentary structures of dust particles. The dust
density distribution for the former is flat in low densities, while the one for
the latter has a low-end cutoff. By contrast, the one slow-growth case results
in a virtually quiescent state. Moreover, we find that in the fast-growth
regime, significant dust segregation by size occurs, with large particles
moving towards dense regions while small particles remain in the diffuse
regions, and the mean radial drift of each dust species is appreciably altered
from the (initial) drag-force equilibrium. The former effect may skew the
spectral index derived from multi-wavelength observations and change the
initial size distribution of a pebble cloud for planetesimal formation. The
latter along with turbulent diffusion may influence the radial transport and
mixing of solid materials in young protoplanetary discs.",2110.06248v1
2021-10-20,Selective crystal growth of indium selenide compounds from saturated solutions grown in a selenium vapor,"Indium selenide compounds are promising materials for energy conversion,
spintronic applications, and chemical sensing. However, it is difficult to grow
stoichiometric indium selenide crystals due to the high equilibrium selenium
vapor pressure and the complicated phase equilibrium system of indium selenide
compounds. In this paper, we apply a novel and convenient crystal growth
method, in which the saturated solution is grown by the application of a
selenium vapor. In this method, selenium vapor at a pressure higher than the
saturated vapor pressure is applied to molten indium, such that the selenium
continuously dissolves into the indium solution until the solubility at the
growth temperature is reached; then a slow cooling process results in
crystallization. The selenium dose is matched to its solubility so that indium
selenide compounds can be selectively grown just by controlling the temperature
without the need to consider the chemical ratio in the solution. The pressure
of the vapor is controlled during the whole growth process so that any
deviation from a stoichiometric composition in the crystal can be controlled.
Both InSe and In2Se3 were successfully grown using this method, and we have
investigated the growth mechanism and found the growth window for each
compound. This study presents a novel and convenient approach to fabricating
transitional metal chalcogenides without deficiencies in the chalcogen element.",2110.10345v1
2021-10-21,The Acoustic Resonant Drag Instability with a Spectrum of Grain Sizes,"We study the linear growth and nonlinear saturation of the ""acoustic Resonant
Drag Instability"" (RDI) when the dust grains, which drive the instability, have
a wide, continuous spectrum of different sizes. This physics is generally
applicable to dusty winds driven by radiation pressure, such as occurs around
red-giant stars, star-forming regions, or active galactic nuclei. Depending on
the physical size of the grains compared to the wavelength of the radiation
field that drives the wind, two qualitatively different regimes emerge. In the
case of grains that are larger than the radiation's wavelength -- termed the
constant-drift regime -- the grain's equilibrium drift velocity through the gas
is approximately independent of grain size, leading to strong correlations
between differently sized grains that persist well into the saturated nonlinear
turbulence. For grains that are smaller than the radiation's wavelength --
termed the non-constant-drift regime -- the linear instability grows more
slowly than the single-grain-size RDI and only the larger grains exhibit
RDI-like behavior in the saturated state. A detailed study of grain clumping
and grain-grain collisions shows that outflows in the constant-drift regime may
be effective sites for grain growth through collisions, with large collision
rates but low collision velocities.",2110.11422v2
2021-11-12,Elastic Properties of Confined Fluids from Molecular Modeling to Ultrasonic Experiments on Porous Solids,"Fluids confined in nanopores are ubiquitous in nature and technology. In
recent years, the interest in confined fluids has grown, driven by research on
unconventional hydrocarbon resources -- shale gas and shale oil, much of which
are confined in nanopores. When fluids are confined in nanopores, many of their
properties differ from those of the same fluid in the bulk. These properties
include density, freezing point, transport coefficients, thermal expansion
coefficient, and elastic properties. The elastic moduli of a fluid confined in
the pores contribute to the overall elasticity of the fluid-saturated porous
medium and determine the speed at which elastic waves traverse through the
medium. Wave propagation in fluid-saturated porous media is pivotal for
geophysics, as elastic waves are used for characterization of formations and
rock samples. In this paper, we present a comprehensive review of experimental
works on wave propagation in fluid-saturated nanoporous media, as well as
theoretical works focused on calculation of compressibility of fluids in
confinement. We discuss models that bridge the gap between experiments and
theory, revealing a number of open questions that are both fundamental and
applied in nature. While some results were demonstrated both experimentally and
theoretically (e.g. the pressure dependence of compressibility of fluids),
others were theoretically predicted, but not verified in experiments (e.g.
linear scaling of modulus with the pore size). Therefore, there is a demand for
the combined experimental-modeling studies on porous samples with various
characteristic pore sizes. The extension of molecular simulation studies from
simple model fluids to the more complex molecular fluids is another open area
of practical interest.",2111.06914v1
2021-11-19,Accurate Photometry of Saturated Stars Using the Point-Spread-Function Wing Technique with Spitzer,"We report Spitzer 3.6 and 4.5 $\mu$m photometry of 11 bright stars relative
to Sirius, exploiting the unique optical stability of the Spitzer Space
Telescope point spread function (PSF). Spitzer's extremely stable beryllium
optics in its isothermal environment enables precise comparisons in the wings
of the PSF from heavily saturated stars. These bright stars stand as the
primary sample to improve stellar models, and to transfer the absolute flux
calibration of bright standard stars to a sample of fainter standards useful
for missions like JWST and for large groundbased telescopes. We demonstrate
that better than 1% relative photometry can be achieved using the PSF wing
technique in the radial range of 20--100\arcsec\ for stars that are fainter
than Sirius by 8 mag (from outside the saturated core to a large radius where a
high signal-to-noise profile can still be obtained). We test our results by (1)
comparing the [3.6]$-$[4.5] color with that expected between the WISE W1 and W2
bands, (2) comparing with stars where there is accurate $K_{\text{S}}$
photometry, and (3) also comparing with relative fluxes obtained with the DIRBE
instrument on COBE. These tests confirm that relative photometry is achieved to
better than 1%.",2111.10054v1
2021-12-02,Fertilization of liquid-saturated porous medium with multicomponent gases due to surface temperature oscillation,"We study non-isothermal diffusive transport of a weakly-soluble two-component
substance in a liquid-saturated porous medium being in contact with the
reservoir of this substance. Particular attention is given to the example case
of infiltration of nitrogen and oxygen from the atmosphere under the annual
temperature oscillation. The surface temperature of the porous medium
half-space oscillates in time, which results in a decaying solubility wave
propagating deep into the porous medium. In such a system, the zones of
saturated solution and nondissolved phase coexist with the zones of
undersaturated solution; these zones migrate with time. Moreover, the
solubility of a multicomponent substance depends on its composition, which
results in a much more intricate mathematical model of solubility as compared
to the single-component case. We describe the phenomenon of formation of a
near-surface bubbly horizon due to the temperature oscillation. An analytical
theory of the phenomenon is developed. For multicomponent solutions we report
the formation of diffusion boundary layer, which is not possible for
single-component solutions. We construct an analytical theory for this boundary
layer; in particular, we derive effective boundary conditions for the problem
of the diffusive transport beyond this layer.",2112.01290v1
2022-01-17,Single-pion contribution to the Gerasimov--Drell--Hearn sum rule and related integrals,"Phenomenological amplitudes obtained in partial-wave analyses (PWA) of
single-pion photoproduction are used to evaluate the contribution of this
process to the Gerasimov-Drell-Hearn (GDH), Baldin and
Gell-Mann-Goldberger-Thirring (GGT) sum rules, by integrating up to 2 GeV in
photon energy. Our study confirms that the single-pion contribution to all
these sum rules converges even before the highest considered photon energy, but
the levels of saturation are very different in the three cases. Single-pion
production almost saturates the GDH sum rule for the proton, while a large
fraction is missing in the neutron case. The Baldin integrals for the proton
and the neutron are both saturated to about four fifths of the predicted total
strength. For the GGT sum rule, the wide variability in predictions precludes
any definitive statement.",2201.06495v4
2022-02-16,Physical factors governing the shape of the Miram curve knee in thermionic emission,"In a current density versus temperature (J-T) (Miram) curve in thermionic
electron emission, experimental measurements demonstrate there is a smooth
transition between the exponential region and the saturated emission regions,
which is sometimes referred to as the ""roll-off"" or ""Miram curve knee"". The
shape of the Miram curve knee is an important figure of merit for thermionic
vacuum cathodes. Specifically, cathodes with a sharp Miram curve knee at low
temperature with a flat saturated emission current are typically preferred. Our
previous work on modeling nonuniform thermionic emission revealed that the
space charge effect and patch field effect are key pieces of physics which
impact the shape of the Miram curve knee. This work provides a more complete
understanding of the physical factors connecting these physical effects and
their relative impact on the shape of the knee, including the smoothness, the
temperature, and the flatness of the saturated emission current density. For
our analyses, we use a periodic, equal-width striped (""zebra crossing"") work
function distribution as a model system and illustrate how the space charge and
patch field effects restrict the emission current density near the Miram curve
knee. The results indicate there are three main physical parameters which
significantly impact the shape of the Miram curve. Such physical knowledge
directly connects the patch size, work function values, anode-cathode voltage,
and anode-cathode gap distance to the shape of the Miram curve, providing new
understanding and a guide to the design of thermionic cathodes used as electron
sources in vacuum electronic devices (VEDs).",2202.08247v1
2022-03-10,Understanding Electrolyte Filling of Lithium-Ion Battery Electrodes on the Pore Scale Using the Lattice Boltzmann Method,"Electrolyte filling is a time-critical step during battery manufacturing that
also affects the battery performance. The underlying physical phenomena during
filling mainly occur on the pore scale and are hard to study experimentally. In
this paper, a computational approach, i.e.\ the lattice Boltzmann method, is
used to study the filling process and corresponding pore-scale phenomena in 3D
lithium-ion battery cathodes. The electrolyte flow through the nanoporous
binder is simulated using a homogenization approach. Besides the process time,
the influence of structural and physico-chemical properties is investigated.
Those are the particle size, the binder distribution, and the volume fraction
and wetting behavior of active material and binder. Optimized filling
conditions are discussed by capillary pressure-saturation relationships. It is
shown how the aforementioned influencing factors affect the electrolyte
saturation. Moreover, the amount of the entrapped residual gas phase and the
corresponding size distribution of the gas agglomerates are analyzed in detail.
Both factors are shown to have a strong impact on mechanisms that can adversely
affect the battery performance. The results obtained here indicate how the
filling process, the final electrolyte saturation, and potentially also the
battery performance can be optimized by adapting process parameters and the
electrode and electrolyte design.",2203.05218v1
2022-05-19,Saturation and recurrence of quantum complexity in random local quantum dynamics,"Quantum complexity is a measure of the minimal number of elementary
operations required to approximately prepare a given state or unitary channel.
Recently, this concept has found applications beyond quantum computing -- in
studying the dynamics of quantum many-body systems and the long-time properties
of AdS black holes. In this context Brown and Susskind \cite{BrownSusskind17}
conjectured that the complexity of a chaotic quantum system grows linearly in
time up to times exponential in the system size, saturating at a maximal value,
and remaining maximally complex until undergoing recurrences at
doubly-exponential times. In this work we prove the saturation and recurrence
of complexity in two models of chaotic time evolutions based on (i) random
local quantum circuits and (ii) stochastic local Hamiltonian evolution. Our
results advance an understanding of the long-time behaviour of chaotic quantum
systems and could shed light on the physics of black hole interiors. From a
technical perspective our results are based on establishing new quantitative
connections between the Haar measure and high-degree approximate designs, as
well as the fact that random quantum circuits of sufficiently high depth
converge to approximate designs.",2205.09734v2
2022-06-24,A critical analysis of the assumptions underlying the formulation of maximum potential intensity for tropical cyclones,"Emanuel's concept of maximum potential intensity (E-PI) estimates the maximum
velocity of tropical cyclones from environmental parameters assuming thermal
wind (gradient-wind and hydrostatic balances) and slantwise neutrality in the
free troposphere. E-PI's key equation relates proportionally the radial
gradients of saturated moist entropy and angular momentum. Here the E-PI
derivation is reconsidered to show that the thermal wind and slantwise
neutrality imply zero radial gradients of saturation entropy and angular
momentum at an altitude where, for a given radius, the tangential wind has a
maximum. It is further shown that, while E-PI's key equation requires that, at
the point of maximum tangential wind, the air temperature must increase towards
the storm center, the thermal wind equation dictates the opposite. From the
analysis of the equations of motion at the altitude of maximum tangential wind
in the free troposphere, it is concluded that here the air flow must be
supergradient. This implies that the supergradiency factor (a measure of the
gradient-wind imbalance) must change in the free troposphere as the air flow
tends to restore the balance. It is shown that such a change modifies the
derivative of saturation entropy over angular momentum, which cannot therefore
remain constant in the free troposphere as E-PI requires. The implications of
these findings for the internal coherence of E-PI, including its boundary layer
closure, are discussed.",2206.12382v3
2022-07-06,Adaptive Identification with Guaranteed Performance Under Saturated-Observation and Non-Persistent Excitation,"This paper investigates the adaptive identification and prediction problems
for stochastic dynamical systems with saturated observations, which arise from
various fields in engineering and social systems, but up to now still lack
comprehensive theoretical studies including performance guarantees needed in
practical applications. With this impetus, the paper has made the following
main contributions: (i) To introduce a two-step Quasi-Newton (TSQN) algorithm
to improve the performance of the identification, which is applicable to a
typical class of nonlinear stochastic systems with outputs observed under
possibly varying saturation. (ii) To establish the global convergence of both
the parameter estimators and adaptive predictors and to prove the asymptotic
normality, under the weakest possible non-persistent excitation (PE) condition,
which can be applied to stochastic feedback systems with general non-stationary
and correlated system signals or data. (iii) To establish useful probabilistic
estimation error bounds for any given finite length of data, using either
martingale inequalities or Monte Carlo experiments. A numerical example is also
provided to illustrate the performance of the proposed identification
algorithm.",2207.02422v5
2022-07-21,Impact of pedestal density gradient and collisionality on ELM dynamics,"BOUT++ turbulence simulations are conducted to capture the underlying physics
of the small ELM characteristics achieved by increasing separatrix density via
controlling strike points from vertical to horizontal divertor plates for three
EAST discharges. BOUT ++ linear simulations show that the most unstable modes
change from high-n ideal ballooning modes to the intermediate-n
peeling-ballooning modes and eventually to peeling-ballooning stable plasmas in
the pedestal. Nonlinear simulations show that the fluctuation is saturated at a
high level for the lowest separatrix density. The elm size decreases with
increasing the separatrix density, until the fraction of this energy lost
during the ELM crash becomes less than 1% of the pedestal stored energy,
leading to small ELMs. Simulations indicate that small ELMs can be triggered
either by the marginally peeling-ballooning instability near the peak pressure
gradient position inside pedestal or by a local instability in the pedestal
foot with a larger separatrix density gradient. The pedestal collisionality
scan for type-I ELMs with steep pedestal density gradient shows that both
linear growth rate and elm size decrease with collisionality increasing. While
the pedestal collisionality and pedestal density width scan with a weak
pedestal density gradient indicate small ELMs can either be triggered by high-n
ballooning mode or by low-n peeling mode in low collisionality region 0.04~0.1.
The simulations indicate the weaker the linear unstable modes near marginal
stability with small linear growth rate, the lower nonlinearly saturated
fluctuation intensity and the smaller turbulence spreading from the linear
unstable zone to stable zone in the nonlinear saturation phase, leading to
small ELMs.",2207.10594v2
2022-08-17,"Characteristic, dynamic, and near saturation regions of Out-of-time-order correlation in Floquet Ising models","We study characteristic, dynamic, and saturation regimes of the
out-of-time-order correlation (OTOC) in the constant field Floquet system with
and without longitudinal field. In the calculation of OTOC, we take local spins
in longitudinal and transverse directions as observables which are local and
non-local in terms of Jordan-Wigner fermions, respectively. We use the exact
analytical solution of OTOC for the integrable model (without longitudinal
field term) with transverse direction spins as observables and numerical
solutions for other integrable and nonintegrable cases. OTOCs generated in both
cases depart from unity at a kick equal to the separation between the
observables when the local spins in the transverse direction and one additional
kick is required when the local spins in the longitudinal direction. The number
of kicks required to depart from unity depends on the separation between the
observables and is independent of the Floquet period and system size. In the
dynamic region, OTOCs show power-law growth in both models, the integrable
(without longitudinal field) as well as the nonintegrable (with longitudinal
field). The exponent of the power-law increases with increasing separation
between the observables. Near the saturation region, OTOCs grow linearly with a
very small rate.",2208.08283v1
2022-10-18,$λ$-MIMO: Massive MIMO via Modulo Sampling,"Massive multiple-input multiple-output (M-MIMO) architecture is the workhorse
of modern communication systems. Currently, two fundamental bottlenecks,
namely, power consumption and receiver saturation, limit the full potential
achievement of this technology. These bottlenecks are intricately linked with
the analog-to-digital converter (ADC) used in each radio frequency (RF) chain.
The power consumption in MIMO systems grows exponentially with the ADC's bit
budget while ADC saturation causes permanent loss of information. This
motivates the need for a solution that can simultaneously tackle the
above-mentioned bottlenecks while offering advantages over existing
alternatives such as low-resolution ADCs. Taking a radically different approach
to this problem, we propose $\lambda$-MIMO architecture which uses modulo ADCs
($M_\lambda$-ADC) instead of a conventional ADC. Our work is inspired by the
Unlimited Sampling Framework. $M_\lambda$-ADC in the RF chain folds high
dynamic range signals into low dynamic range modulo samples, thus alleviating
the ADC saturation problem. At the same time, digitization of modulo signal
results in high resolution quantization. In the novel $\lambda$-MIMO context,
we discuss baseband signal reconstruction, detection and uplink achievable
sum-rate performance. The key takeaways of our work include, (a) leveraging
higher signal-to-quantization noise ratio (SQNR), (b) detection and average
uplink sum-rate performances comparable to a conventional, infinite-resolution
ADC when using a $1$-$2$ bit $M_\lambda$-ADC. This enables higher order
modulation schemes e.g. $1024$ QAM that seemed previously impossible, (c)
superior trade-off between energy efficiency and bit budget, thus resulting in
higher power efficiency. Numerical simulations and modulo ADC based hardware
experiments corroborate our theory and reinforce the clear benefits of
$\lambda$-MIMO approach.",2210.10193v1
2022-11-09,Deterministic Random Walk Model in NetLogo and the Identification of Asymmetric Saturation Time in Random Graph,"Interactive programming environments are powerful tools for promoting
innovative network thinking, teaching science of complexity, and exploring
emergent phenomena. This paper reports on our recent development of the
deterministic random walk model in NetLogo, a leading platform for
computational thinking, eco-system thinking, and multi-agent cross-platform
programming environment. The deterministic random walk is foundational to
modeling dynamical processes on complex networks. Inspired by the temporal
visualizations offered in NetLogo, we investigated the relationship between
network topology and diffusion saturation time for the deterministic random
walk model. Our analysis uncovers that in Erd\H{o}s-R\'{e}nyi graphs, the
saturation time exhibits an asymmetric pattern with a considerable probability
of occurrence. This behavior occurs when the hubs, defined as nodes with
relatively higher number of connections, emerge in Erd\H{o}s-R\'{e}nyi graphs.
Yet, our analysis yields that the hubs in Barab\'{a}si-Albert model stabilize
the the convergence time of the deterministic random walk model. These findings
strongly suggest that depending on the dynamical process running on complex
networks, complementing characteristics other than the degree need to be taken
into account for considering a node as a hub. We have made our development
open-source, available to the public at no cost at
https://github.com/bravandi/NetLogo-Dynamical-Processes.",2211.05189v2
2022-11-11,Parallelization of Garfield++ and neBEM to simulate space charge effects in RPCs,"Numerical simulation of avalanches, saturated avalanches, and streamers can
help us understand the detector physics of Resistive Plate Chambers (RPC). 3D
Monte Carlo simulation of an avalanche inside an RPC, the transition from
avalanche to saturated avalanche to streamer may help the search for the
optimum voltage and alternate gas mixtures. This task is dauntingly
resource-hungry, especially when space charge effects become important, which
often coincides with important regimes of operation of these devices. By
modifying the electric field inside the RPC dynamically, the space charge plays
a crucial role in determining the response of the detector. In this work, a
numerical model has been proposed to calculate the dynamic space-charge field
inside an RPC and the same has been implemented in the Garfield++ framework. By
modeling space charge as the large number of line charges and using the
multithreading technique OpenMP to calculate electric field, drift line,
electron gain, and space charge field, it has been possible to maintain time
consumption within reasonable limits. For this purpose, a new class,
pAvalancheMC has been introduced in Garfield++. The calculations have been
successfully verified with those from existing solvers and an example is
provided to show the performance of pAvalancheMC. Moreover, the details of the
transition of an avalanche into a saturated avalanche have been discussed. The
induced charge distribution is calculated for a timing RPC and results are
verified with the experiment.",2211.06361v3
2022-11-28,The effect of saturated thermal conduction on clouds in a hot plasma,"We numerically investigate the internal evolution of multiphase clouds, which
are at rest with respect to an ambient, highly ionized medium (HIM)
representing the hot component of the circumgalactic medium (CGM).
Time-dependent saturated thermal conduction and its implications like
condensation rates and mixing efficiency are assessed in multiphase clouds. Our
simulations are carried out by using the adaptive mesh refinement code Flash.
We perform a grid of models of which we present here those characteristic for
the presented study. The model clouds are initially in both hydrostatic and
thermal equilibrium and are in pressure balance with the HIM. Thus, they have
steep gradients in both temperature and density at the interface to HIM leading
to non-negligible thermal conduction. Several physical processes are considered
numerically or semi-analytically: thermal conduction, radiative cooling and
external heating of gas, self-gravity, mass diffusion, and dissociation of
molecules and ionization of atoms. It turns out that saturated thermal
conduction triggers a continuous condensation irrespective of cloud mass.
Dynamical interactions with ambient HIM all relate to the radial density
gradient in the clouds: (1) mass flux due to condensation is the higher the
more homogeneous the clouds are; (2) mixing of condensed gas with cloud gas is
easier in low-mass clouds, because of their shallower radial density gradient;
thus (3) accreted gas is distributed more efficiently. A distinct and
sub-structured transition zone forms at the interface between cloud and HIM,
which starts at smaller radii and is much narrower as deduced from analytical
theory.",2211.15284v1
2023-01-17,"Parametric instability in warped astrophysical discs: growth, saturation and feedback","Attempts to understand the dynamics of warped astrophysical discs have
garnered significant attention, largely motivated by the growing catalogue of
observed distorted systems. Previous studies have shown that the evolution of
the warp is crucially regulated by the internal flow fields established by the
undulating geometry. These are typically modelled as laminar horizontal,
shearing flows which oscillate back and forth at approximately the orbital
frequency. However this shearing motion is known to be susceptible to a
hydrodynamic, parametric instability of inertial waves which might modify the
warped dynamics. Whilst the linear growth phase is well understood, the
subsequent nonlinear saturation combined with the self-consistent feedback onto
the warp has not been studied. In this work, we implement a novel numerical
setup using the recent ring model framework of Fairbairn and Ogilvie, within
the Lagrangian code GIZMO. We formally identify several locally growing modes
in the simulation, as predicted by a three-mode coupling analysis of the
instability, and find decent agreement with the theoretical growth rates. We
understand the saturation mechanism as a wave breaking process which suppresses
the growth of shorter wavelength parametric couplings first, whilst allowing
the longest mode to dominate the final quasi-steady, wavelike turbulence. The
Reynolds stresses, transporting energy from the warp to the small scales, can
be effectively modelled using a time-dependent, anisotropic viscous alpha model
which closely captures the amplitude and phase evolution of the warp.
Consequently, this model might help inform future global studies which are
commonplace but typically don't resolve the parametric instability.",2301.07176v1
2023-01-29,Revealing a deep connection between factorization and saturation: New insight into modeling high-energy proton-proton and nucleus-nucleus scattering in the EPOS4 framework,"It is known that multiple partonic scatterings in high-energy proton-proton
($pp$) collisions must happen in parallel. However, a rigorous parallel
scattering formalism, taking energy sharing properly into account, fails to
reproduce factorization, which on the other hand is the basis of almost all
$pp$ event generators. In addition, binary scaling in nuclear scatterings is
badly violated. These problems are usually ``solved'' by simply not considering
strictly parallel scatterings, which is not a solution. I will report on new
ideas (leading to EPOS4), which allow recovering perfectly factorization, and
also binary scaling in $AA$ collisions, in a rigorous unbiased parallel
scattering formalism. In this new approach, dynamical saturation scales play a
crucial role, and this seems to be the missing piece needed to reconcile
parallel scattering with factorization. From a practical point of view, one can
compute within the EPOS4 framework parton distribution functions (EPOS PDFs)
and use them to compute inclusive $pp$ cross sections. So, for the first time,
one may compute inclusive jet production (for heavy or light flavors) at very
high transverse momentum ($p_{t}$) and at the same time in the same formalism
study flow effects at low $p_{t}$ in high-multiplicity $pp$ events, making
EPOS4 a full-scale ``general purpose event generator''. I discuss applications,
essentially multiplicity dependencies (of particle ratios, mean $p_{t}$, charm
production) which are very strongly affected by the saturation issues discussed
in this paper.",2301.12517v2
2023-03-08,MCTS-GEB: Monte Carlo Tree Search is a Good E-graph Builder,"Rewrite systems [6, 10, 12] have been widely employing equality saturation
[9], which is an optimisation methodology that uses a saturated e-graph to
represent all possible sequences of rewrite simultaneously, and then extracts
the optimal one. As such, optimal results can be achieved by avoiding the
phase-ordering problem. However, we observe that when the e-graph is not
saturated, it cannot represent all possible rewrite opportunities and therefore
the phase-ordering problem is re-introduced during the construction phase of
the e-graph. To address this problem, we propose MCTS-GEB, a domain-general
rewrite system that applies reinforcement learning (RL) to e-graph
construction. At its core, MCTS-GEB uses a Monte Carlo Tree Search (MCTS) [3]
to efficiently plan for the optimal e-graph construction, and therefore it can
effectively eliminate the phase-ordering problem at the construction phase and
achieve better performance within a reasonable time. Evaluation in two
different domains shows MCTS-GEB can outperform the state-of-the-art rewrite
systems by up to 49x, while the optimisation can generally take less than an
hour, indicating MCTS-GEB is a promising building block for the future
generation of rewrite systems.",2303.04651v3
2023-03-17,"Optical IRSs: Power Scaling Law, Optimal Deployment, and Comparison with Relays","The line-of-sight (LOS) requirement of free-space optical (FSO) systems can
be relaxed by employing optical relays or optical intelligent reflecting
surfaces (IRSs). In this paper, we show that the power reflected from FSO IRSs
and collected at the receiver (Rx) lens may scale quadratically or linearly
with the IRS size or may saturate at a constant value. We analyze the power
scaling law for optical IRSs and unveil its dependence on the wavelength,
transmitter (Tx)-to-IRS and IRS-to-Rx distances, beam waist, and Rx lens size.
We also consider the impact of linear, quadratic, and focusing phase shift
profiles across the IRS on the power collected at the Rx lens for different IRS
sizes. Our results reveal that surprisingly the powers received for the
different phase shift profiles are identical, unless the IRS operates in the
saturation regime. Moreover, IRSs employing the focusing (linear) phase shift
profile require the largest (smallest) size to reach the saturation regime. We
also compare optical IRSs in different power scaling regimes with optical
relays in terms of the outage probability, diversity and coding gains, and
optimal placement. Our results show that, at the expense of a higher hardware
complexity, relay-assisted FSO links yield a better outage performance at high
signal-to-noise-ratios (SNRs), but optical IRSs can achieve a higher
performance at low SNRs. Moreover, while it is optimal to place relays
equidistant from Tx and Rx, the optimal location of optical IRSs depends on the
phase shift profile and the power scaling regime they operate in.",2303.10124v1
2023-04-04,On A Saturated Poromechanical Framework and Its Relation to Abaqus Soil Mechanics and Biot Poroelasticity Frameworks,"We introduce a conservational and constitutive framework for a closed and
isothermal two-phase material system consisting of a deformable porous solid
matrix and a fully saturating, single-phase, and compressible pore fluid
without inter-phase mass exchange. We re-derive a generalized fluid mass
balance law using fundamental transport rules. We also summarize from the
literature a fundamental force balance law for the fluid-solid mixture that
does not require any effective stress law a priori. We show that the two
conservation laws are coupled naturally to second-order without any
constitutive prerequisites. This differs from Biot poroelasticity, which first
postulates first-order fluid-solid coupling as two linearized constitutive
relationships and then enforces them into simple Eulerian form of conservation
laws. Next, we examine a limiting-case unsaturated soil mechanics framework
implemented in Abaqus, by assuming isothermal conditions, full saturation, and
no adsorption, and then relate it to our framework. We prove that (1) the two
mass balance laws are always equivalent regardless of fluid constitutive
behaviors, and (2) the two force balance laws are equivalent in their specific
forms with a linearly elastic solid skeleton. Finally, taking advantage of a
fundamental pore constitutive law, we show how our framework, and by extension
the limiting-case Abaqus framework, naturally gives rise to the distinction
between drained and undrained settings, and reduces to Biot poroelasticity
under simplifying conditions. Notably, our framework indicates the presence of
an additional solid-to-fluid coupling term when the solid particle velocity is
non-orthogonal to the Darcy velocity.",2304.02148v1
2023-05-02,Frequency-modulated combs via on-chip field enhancement,"Frequency-modulated (FM) combs feature flat intensity spectra with a linear
frequency chirp, useful for metrology and sensing applications. Generating FM
combs in semiconductor lasers generally requires a fast saturable gain, usually
limited by the intrinsic gain medium properties. Here, we show how a spatial
modulation of the laser gain medium can enhance the gain saturation dynamics
and nonlinearities to generate self-starting FM combs. We demonstrate this with
tapered planarized THz quantum cascade lasers (QCLs). While simple ridge THz
QCLs typically generate combs which are a mixture of amplitude and frequency
modulation, the on-chip field enhancement resulting from extreme spatial
confinement leads to an ultrafast saturable gain regime, generating a pure FM
comb with a flatter intensity spectrum, a clear linear frequency chirp and very
intense beatnotes up to -30 dBm. The observed linear frequency chirp is
reproduced using a spatially inhomogeneous mean-field theory model which
confirms the crucial role of field enhancement. In addition, the modified
spatial temperature distribution within the waveguide results in an improved
hightemperature comb operation, up to a heat sink temperature of 115 K, with
comb bandwidths of 600 GHz at 90 K. The spatial inhomogeneity also leads to
dynamic switching between various harmonic states in the same device.",2305.01483v2
2023-05-25,"Rotating spokes, potential hump and modulated ionization in radio frequency magnetron discharges","In this work, the rotating spoke mode in the radio frequency (RF) magnetron
discharge, which features the potential hump and the RF-modulated ionization,
is observed and analyzed by means of the two dimensional axial-azimuthal (z-y)
particle-in-cell/Monte Carlo collision method. The kinetic model combined with
the linear analysis of the perturbation reveals that the cathode sheath (axial)
electric field $E_z$ triggers the gradient drift instability (GDI), deforming
the local potential until the instability condition is not fulfilled and the
fluctuation growth stops in which moment the instability becomes saturated. The
potential deformation consequently leads to the formation of the potential
hump, surrounding which the azimuthal electric field $E_y$ is present. The
saturation level of $E_y$ is found to be synchronized with and proportional to
the time-changing voltage applied at the cathode, resulting in the
RF-modulation of the electron heating in the $E_y$ due to $\nabla B$ drift. In
the instability saturated stage, it is shown that the rotation velocity and
direction of the spoke present in the simulations agree well with the
experimental observation. In the instability linear stage, the instability mode
wavelength and the growth rate are also found to be in good agreement with the
prediction of the GDI linear fluid theory.",2305.15941v1
2023-06-20,Spectral and Krylov Complexity in Billiard Systems,"In this work, we investigate spectral complexity and Krylov complexity in
quantum billiard systems at finite temperature. We study both circle and
stadium billiards as paradigmatic examples of integrable and non-integrable
quantum-mechanical systems, respectively. We show that the saturation value and
time scale of spectral complexity may be used to probe the non-integrability of
the system since we find that when computed for the circle billiard, it
saturates at a later time scale compared to the stadium billiards. This
observation is verified for different temperatures. Furthermore, we study the
Krylov complexity of the position operator and its associated Lanczos
coefficients at finite temperature using the Wightman inner product. We find
that the growth rate of the Lanczos coefficients saturates the conjectured
universal bound at low temperatures. Additionally, we also find that even a
subset of the Lanczos coefficients can potentially serve as an indicator of
integrability, as they demonstrate erratic behavior specifically in the circle
billiard case, in contrast to the stadium billiard. Finally, we also study
Krylov entropy and verify its early-time logarithmic relation with Krylov
complexity in both types of billiard systems.",2306.11632v1
2023-08-10,Globally optimal interferometry with lossy twin Fock probes,"Parity or $J_{z}^{2}$ readouts of a Mach-Zehnder (MZ) interferometer probed
with a twin Fock input state allow to saturate the optimal sensitivity
attainable among all product states with a fixed total number of particles, but
only when the interferometer phase $\theta$ is near zero. When more general
Dicke state probes are used, the parity readout saturates the QFI at
$\theta=0$, whereas better-than-standard quantum limit performance of the
$J_{z}^{2}$ readout is restricted to an $o(\sqrt{N})$ occupation imbalance. We
show that a method of moments readout of two quadratic spin observables
$J_{z}^{2}$ and $J_{+}^{2}+J_{-}^{2}$ is globally optimal for Dicke state
probes, i.e., the error saturates the QFI for all $\theta$. In the lossy
setting, we derive the time-inhomogeneous Markov process describing the effect
of particle loss on twin Fock states, showing that method of moments readout of
four at-most-quadratic spin observables is sufficient for globally optimal
estimation of $\theta$ when two or more particles are lost. The analysis
culminates in a numerical calculation of the QFI matrix for distributed MZ
interferometry on the four mode state $\vert {N\over 4},{N\over 4},{N\over
4},{N\over 4}\rangle$ and its lossy counterparts, showing that an advantage for
estimation of any linear function of the local MZ phases $\theta_{1}$,
$\theta_{2}$ (compared to independent probing of the MZ phases by two copies of
$\vert{N\over 4},{N\over 4}\rangle$) appears when more than one particle is
lost.",2308.05871v1
2023-08-20,A Method to Measure Photometries of Moderately-Saturated UVOT Sources,"For bright transients such as Gamma-Ray Bursts (GRBs), the
Ultra-Violet/Optical Telescope (UVOT) operates under event mode at early
phases, which records incident positions and arrival time for each photon. The
event file is able to be screened into many exposures to study the early light
curve of GRBs with a high time resolution, including in particular the rapid
brightening of the UV/Optical emission. Such a goal, however, is hampered for
some extremely bright GRBs by the saturation in UVOT event images. For
moderately saturated UVOT sources, in this work we develop the method proposed
in Jin et al. (2023) to recover their photometries. The basic idea is to assume
a stable point spread function (PSF) of UVOT images, for which the counts in
the core region (i.e., an aperture of a radius of 5 arcsec) and the wing region
(i.e., an annulus ranging from 15 arcsec to 25 arcsec) should be a constant and
the intrinsic flux can be reliably inferred with data in the ring. We
demonstrate that in a given band, a tight correlation does hold among the
background-removed count rates in the core and the wing. With the new method,
the bright limit of measuring range for UVOT V and B bands increases ~ 1.7 mag,
while only ~ 0.7 mag for U band due to the lack of bright calibration sources.
Systematic uncertainties are ~ 0.2 mag for V, B and U bands.",2308.10171v1
2023-08-24,The key to the enhanced performance of slab-like topologically interlocked structures with non-planar blocks,"Topologically interlocked structures are assemblies of interlocking blocks
that hold together solely through contact. Such structures have been shown to
exhibit high strength, energy dissipation, and crack arrest properties. Recent
studies on topologically interlocked structures have shown that both the peak
strength and work-to-failure saturate with increasing friction coefficient.
However, this saturated structural response is only achievable with
nonphysically high values of the friction coefficient. For beam-like
topologically interlocked structures, non-planar blocks provide an alternate
approach to reach similar structural response with friction properties of
commonly used materials. It remains unknown whether non-planar blocks have
similar effects for slab-like assemblies, and what the achievable structural
properties are. Here, we consider slab-like topologically interlocked
structures and show, using numerical simulations, that non-planar blocks with
wave-like surfaces allow for saturated response capacity of the structure with
a realistic friction coefficient. We further demonstrate that non-planar
morphologies cause a non-linear scaling of the work-to-failure with peak
strength and result in significant improvements of the work-to-failure and
ultimate deflection - values that cannot be attained with planar-faced blocks.
Finally, we show that the key morphology parameter responsible for the enhanced
performance of non-planar blocks with wave-like surfaces is the local angle of
inclination at the hinging points of the loaded block. These findings shed new
light on topologically interlocked structures with non-planar blocks, allowing
for a better understanding of their strengths and energy absorption.",2308.12683v2
2023-09-02,Electric-field induced droplet vertical vibration and horizontal motion: Experiments and simulations,"In this work, Electrowetting on Dielectric (EWOD) and electrostatic induction
(ESI) are employed to manipulate droplet on the PDMS-ITO substrate. Firstly, we
report large vertical vibrations of the droplet, induced by EWOD, within a
voltage range of 40 to 260 V. The droplet's transition from a vibrating state
to a static equilibrium state are investigated in detail. It is indicated that
the contact angle changes synchronously with voltage during the vibration. The
electric signal in the circuit is measured to analyze the vibration state that
varies with time. By studying the influence of driving voltage on the contact
angle and the amplitude in the vibration, it is shown that the saturation
voltage of both contact angle and amplitude is about 120 V. The intrinsic
connection between contact angle saturation and amplitude saturation is
clarified by studying the surface energy of the droplet. A theoretical model is
constructed to numerically simulate the vibration morphology and amplitude of
the droplet. Secondly, we realize the horizontal motion of droplets by ESI at
the voltage less than 1000 V. The charge and electric force on the droplet are
numerically calculated. The frictional resistance coefficients of the droplet
are determined by the deceleration of the droplet. Under consideration of
frictional resistance of the substrate and viscous resistance of the liquid,
the motion of the droplet is calculated at 400 V and 1000 V, respectively. This
work introduces a new method for manipulating various forms of droplet motion
using the single apparatus.",2309.00910v1
2023-09-22,AnglE-optimized Text Embeddings,"High-quality text embedding is pivotal in improving semantic textual
similarity (STS) tasks, which are crucial components in Large Language Model
(LLM) applications. However, a common challenge existing text embedding models
face is the problem of vanishing gradients, primarily due to their reliance on
the cosine function in the optimization objective, which has saturation zones.
To address this issue, this paper proposes a novel angle-optimized text
embedding model called AnglE. The core idea of AnglE is to introduce angle
optimization in a complex space. This novel approach effectively mitigates the
adverse effects of the saturation zone in the cosine function, which can impede
gradient and hinder optimization processes. To set up a comprehensive STS
evaluation, we experimented on existing short-text STS datasets and a newly
collected long-text STS dataset from GitHub Issues. Furthermore, we examine
domain-specific STS scenarios with limited labeled data and explore how AnglE
works with LLM-annotated data. Extensive experiments were conducted on various
tasks including short-text STS, long-text STS, and domain-specific STS tasks.
The results show that AnglE outperforms the state-of-the-art (SOTA) STS models
that ignore the cosine saturation zone. These findings demonstrate the ability
of AnglE to generate high-quality text embeddings and the usefulness of angle
optimization in STS.",2309.12871v6
2023-10-13,"Parallel scattering, saturation, and generalized Abramovskii-Gribov-Kancheli (AGK) theorem in the EPOS4 framework, with applications for heavy-ion collisions at $\sqrt{s_{NN}}$ of 5.02 TeV and 200 GeV","Ultrarelativistic heavy-ion collisions will first realize many
nucleon-nucleon scatterings, happening instantaneously and therefore
necessarily in parallel, due to the short collision time. An appropriate
quantum mechanical tool to treat that problem is S-matrix theory, and it has
been known for a long time how to derive a simple geometric probabilistic
picture, still widely used, and here the Abramovskii-Gribov-Kancheli (AGK)
theorem plays a crucial role. All this is done in a scenario where energy
conservation is not taken care of, but this is needed, in particular for Monte
Carlo simulations. When introducing energy-momentum sharing properly, the AGK
theorem does not apply anymore, nor do simple geometric concepts such as binary
scaling. I will discuss this (very serious) problem, and how it can be solved,
in the EPOS4 framework. When connecting the multiple Pomeron approach (for
parallel scatterings) and perturbative QCD, one is actually forced to implement
in a very particular way saturation scales, in order to get an approach free of
contradictions. One recovers a generalized AGK theorem (gAGK), valid at large
$p_{t}$ (larger than the relevant saturation scales). I discuss how gAGK is
related to factorization (in proton-proton scatterings) and binary scaling (in
heavy-ion collisions). I will show some applications, using this new approach
as an initial condition for hydrodynamical evolutions, for heavy-ion collisions
at $\sqrt{s_{NN}}$ of 5.02 TeV and 200 GeV, to get some idea about the energy
dependence.",2310.09380v2
2023-10-24,Adapted Thermodynamical Model for the Prediction of Adsorption in Nanoporous Materials,"In this paper, we introduce a novel, adapted approach for computing gas
adsorption properties in porous materials. We analyze the Dubinin-Polanyi's
adsorption model and investigate various frameworks to estimate its required
essential components. Those are linked to physicochemical properties of the
adsorbates, such as the vapor saturation pressure and density in the adsorbed
state. To conduct this analysis, we obtain adsorption isotherms for several
metal-organic frameworks, encompassing a range of pore sizes, shapes, and
chemical compositions. We then apply and evaluate multiple combinations of
models for saturation pressure and density.
  After the evaluation of the method, we propose a working thermodynamic model
for computing adsorption isotherms, which entails using the critical isochore
as an approximation of the saturation pressure above the critical point and
applying Hauer's method with a universal thermal expansion coefficient for
density in the adsorbed state. This framework is applicable not only to
simulated isotherms but also to experimental data from the literature for
various molecules and structures, demonstrating robust predictive capabilities
and high transferability. Our method showcases superior performance in terms of
accuracy, generalizability, and simplicity compared to existing methods
currently in use. For the first time, a method starting from a single
adsorption curve and based on physically interpretable parameters can predict
adsorption properties across a wide range of operating conditions.",2310.15885v1
2023-11-01,Sparsity independent Lyapunov exponent in the Sachdev-Ye-Kitaev model,"The saturation of a recently proposed universal bound on the Lyapunov
exponent has been conjectured to signal the existence of a gravity dual. This
saturation occurs in the low temperature limit of the dense Sachdev-Ye-Kitaev
(SYK) model, $N$ Majorana fermions with $q$-body ($q>2$) infinite-range
interactions. We calculate certain Out of Time Order Correlators (OTOC) for
$N\le 64$ fermions for a highly sparse SYK model and find no significant
dependence of the Lyapunov exponent on sparsity up to near the percolation
limit where the Hamiltonian breaks up into blocks. This suggests that in the
sparse case, the Lyapunov exponent also saturates the low-temperature bound. A
key ingredient to reaching $N = 64$ is the development of a novel quantum spin
model simulation library that implements highly-optimized matrix-free Krylov
subspace methods on Graphical Processing Units (GPUs). This leads to a
significantly lower simulation time as well as vastly reduced memory usage over
previous approaches, while using modest computational resources. Strong
sparsity-driven statistical fluctuations require both the use of a vastly
larger number of disorder realizations with respect to the dense limit and a
careful finite size scaling analysis. Our results potentially broadens the
landscape of theories that may have a gravity analogue.",2311.00639v1
2023-11-12,"Advanced Feedback Linearization Control for Tiltrotor UAVs: Gait Plan, Controller Design, and Stability Analysis","Three challenges, however, can hinder the application of Feedback
Linearization: over-intensive control signals, singular decoupling matrix, and
saturation. Activating any of these three issues can challenge the stability
proof. To solve these three challenges, first, this research proposed the drone
gait plan. The gait plan was initially used to figure out the control problems
in quadruped (four-legged) robots; applying this approach, accompanied by
Feedback Linearization, the quality of the control signals was enhanced. Then,
we proposed the concept of unacceptable attitude curves, which are not allowed
for the tiltrotor to travel to. The Two Color Map Theorem was subsequently
established to enlarge the supported attitude for the tiltrotor. These theories
were employed in the tiltrotor tracking problem with different references.
Notable improvements in the control signals were witnessed in the tiltrotor
simulator. Finally, we explored the control theory, the stability proof of the
novel mobile robot (tilt vehicle) stabilized by Feedback Linearization with
saturation. Instead of adopting the tiltrotor model, which is over-complicated,
we designed a conceptual mobile robot (tilt-car) to analyze the stability
proof. The stability proof (stable in the sense of Lyapunov) was found for a
mobile robot (tilt vehicle) controlled by Feedback Linearization with
saturation for the first time. The success tracking result with the promising
control signals in the tiltrotor simulator demonstrates the advances of our
control method. Also, the Lyapunov candidate and the tracking result in the
mobile robot (tilt-car) simulator confirm our deductions of the stability
proof. These results reveal that these three challenges in Feedback
Linearization are solved, to some extents.",2311.06725v1
2023-11-12,A Nonlinear Negative Imaginary Systems Framework with Actuator Saturation for Control of Electrical Power Systems,"In the transition to net zero, it has been suggested that a massive expansion
of the electric power grid will be required to support emerging renewable
energy zones. In this paper, we propose the use of battery-based feedback
control and nonlinear negative imaginary systems theory to reduce the need for
such an expansion by enabling the more complete utilization of existing grid
infrastructure. By constructing a novel Lur'e-Postnikov-like Lyapunov function,
a stability result is developed for the feedback interconnection of a nonlinear
negative imaginary system and a nonlinear negative imaginary controller.
Additionally, a new class of nonlinear negative imaginary controllers is
proposed to deal with actuator saturation. We show that in this control
framework, the controller eventually leaves the saturation boundary, and the
feedback system is locally stable in the sense of Lyapunov. This provides
theoretical support for the application of battery-based control in electrical
power systems. Validation through simulation results for
single-machine-infinite-bus power systems supports our results. Our approach
has the potential to enable a transmission line to operate at its maximum power
capacity, as stability robustness is ensured by the use of a feedback
controller.",2311.06820v1
2024-01-19,From Market Saturation to Social Reinforcement: Understanding the Impact of Non-Linearity in Information Diffusion Models,"Diffusion of information in networks is at the core of many problems in AI.
Common examples include the spread of ideas and rumors as well as marketing
campaigns. Typically, information diffuses at a non-linear rate, for example,
if markets become saturated or if users of social networks reinforce each
other's opinions. Despite these characteristics, this area has seen little
research, compared to the vast amount of results for linear models, which
exhibit less complex dynamics. Especially, when considering the possibility of
re-infection, no fully rigorous guarantees exist so far.
  We address this shortcoming by studying a very general non-linear diffusion
model that captures saturation as well as reinforcement. More precisely, we
consider a variant of the SIS model in which vertices get infected at a rate
that scales polynomially in the number of their infected neighbors, weighted by
an infection coefficient $\lambda$. We give the first fully rigorous results
for thresholds of $\lambda$ at which the expected survival time becomes
super-polynomial. For cliques we show that when the infection rate scales
sub-linearly, the threshold only shifts by a poly-logarithmic factor, compared
to the standard SIS model. In contrast, super-linear scaling changes the
process considerably and shifts the threshold by a polynomial term. For stars,
sub-linear and super-linear scaling behave similar and both shift the threshold
by a polynomial factor. Our bounds are almost tight, as they are only apart by
at most a poly-logarithmic factor from the lower thresholds, at which the
expected survival time is logarithmic.",2401.10818v1
2024-01-28,WetSpongeCake: a Surface Appearance Model Considering Porosity and Saturation,"Wet powdered materials, such as wet ground or moist walls, are common in the
real world. Despite their particle size being larger than the wavelength, they
remain invisible from a macro view. Reproducing these appearances accurately is
crucial for various applications. Existing methods use different approaches,
such as Monte Carlo path tracing on implicit shapes, which is accurate but
computationally expensive. Another approach involves modeling powdered
materials with a medium using the radiative transfer equation, but these
methods are computationally intensive and lack intuitive parameters. Some works
represent porosity with cylinder-shaped holes on surfaces, but they have
limitations. In this paper, we propose a practical BSDF model called
WetSpongeCake for wet powdered materials. This model includes controllable
physical parameters to faithfully reproduce real-world appearances while
remaining computationally efficient. We reformulate Monte Carlo light transport
on implicit shapes into a medium, utilizing an equivalent phase function for
light transport within ellipsoid-shaped particles and a modified RTE for
porosity and saturation effects. Our novel WetSpongeCake BSDF integrates this
medium into the SpongeCake framework, allowing representation of various wet
powdered material appearances, including both reflection and transmission. We
showcase our model with examples, such as wet paper, sand saturated with
different liquids, and sculptures made of multiple particles.",2401.15628v2
2024-02-05,The footprint of nuclear saturation properties on the neutron star $f$ mode oscillation frequencies: a machine learning approach,"We investigate the intricate relationships between the non-radial \(f\) mode
oscillation frequencies of neutron stars (NS)s and the corresponding nuclear
matter equation of state (EOS) using a machine learning (ML) approach within
the ambit of the relativistic mean field (RMF) framework for nuclear matter.
With two distinct parameterizations of the Walecka model, namely, (1) with
non-linear self interactions of the scalar field (NL) and, (2) a density
dependent Bayesian model (DDB), we perform a thorough examination of the \(f\)
mode frequency in relation to various nuclear saturation properties. The
correlations between the \(f\) mode frequencies and nuclear saturation
properties reveal, through various analytical and ML methods, the complex
nature of NSs and their potential as the cosmic laboratory for studying extreme
states of matter. A principal component analysis (PCA) has been performed using
mixed datasets from DDB and NL models to discriminate the relative importance
of the different components of the EOS on the $f$ mode frequencies.
Additionally, a {\it Random forest feature importance} analysis also elucidates
the distinct roles of these properties in determining the \(f\) mode frequency
across a spectrum of NS masses. Our findings are further supported by symbolic
regression searches, yielding high-accuracy relations with strong Pearson
coefficients and minimal errors. These relations suggest new methodologies for
probing NS core characteristics, such as energy density, pressure, and speed of
sound from observations of non-radial \(f\) mode oscillations of NSs.",2402.03054v1
2024-03-08,Beam-driven Electron Cyclotron Harmonic and Whistler-mode Waves as Seen in Particle-In-Cell Simulations,"Recent study has demonstrated that electron cyclotron harmonic (ECH) waves
can be excited by a low energy electron beam. Such waves propagate at
moderately oblique wave normal angles ~70. The potential role of beam-driven
ECH waves in affecting electron dynamics in Earth's plasma sheet is not known.
Using two-dimensional Darwin particle-in-cell simulations with initial electron
distributions that represent typical plasma conditions in the plasma sheet, we
explore the excitation and saturation of such beam-driven ECH waves. Both ECH
and whistler-mode waves are excited in the simulation and propagate at oblique
wave normal angles. Compared with the whistler-mode waves, ECH waves grow much
faster and have more intense saturation amplitudes. Cold, stationary electrons
are first accelerated by ECH waves through cyclotron resonance and then
accelerated in the parallel direction by both the ECH and whistler-mode waves
through Landau resonance. Beam electrons, on the other hand, are decelerated in
the parallel direction and scattered to larger pitch angles. The relaxation of
the electron beam and the continuous heating of the cold electrons contribute
to the saturation of ECH waves and suppress the excitation of whistler-mode
waves. When the ratio of plasma to electron cyclotron frequency wpe/wce
increases, the ECH wave amplitude increases while the whistler-mode wave
amplitude decreases. Our work reveals the importance of ECH and whistler-mode
waves in reshaping sub-thermal electron distributions and improves our
understanding on the potential effects of wave-particle interactions in
trapping ionospheric electron outflows and forming anisotropic (field-aligned)
electron distributions in the plasma.",2403.05675v1
2024-03-13,Suppression of diffraction in deep-inelastic scattering on nuclei and dynamical mechanism of leading twist nuclear shadowing,"Using the leading twist approach (LTA) to nuclear shadowing, we calculate the
ratios of diffractive and usual parton distributions for a heavy nucleus (Pb)
and the proton, $R_{A/p}=(f_{i/A}^{D(3)}/f_{i/A})/(f_{i/p}^{D(3)}/f_{i/p})$,
for coherent and summed (coherent plus quasi-elastic) nuclear deep-inelastic
scattering. We find that $R_{A/p} \approx 0.5-1$ for quarks and $R_{A/p}
\approx 0.5-1.3$ for gluons in a broad range of $x$, which reaffirms the
difference from the nuclear enhancement of $R_{A/p}$ predicted in the gluon
saturation framework. We demonstrate that the magnitude of $R_{A/p}$ is
controlled by the cross section of the interaction of hadronic fluctuations of
the virtual photon with target nucleons, which explains an enhancement of
$R_{A/p}$ in the color dipole model and its suppression in LTA. We argue that
the black disk limit of LTA corresponds to $R_{A/p}=1$ and $R^{\rm
coh}_{A/p}=0.86$ for the summed and coherent scattering, respectively. Relying
on an intuitive definition of the saturation scale, we show that the ratio of
the saturation scales of a heavy nucleus and proton $Q_{sA}^2(b)/Q_{sp}^2(b)
\approx 1$ at small impact parameters $b$ due to the strong leading twist
nuclear shadowing and diluteness of the nuclear density.",2403.08342v1
2006-02-02,Evolution of Rotating Molecular Cloud Core with Oblique Magnetic Field,"We studied the collapse of rotating molecular cloud cores with inclined
magnetic fields, based on three-dimensional numerical simulations.The numerical
simulations start from a rotating Bonnor-Ebert isothermal cloud in a uniform
magnetic field. The magnetic field is initially taken to be inclined from the
rotation axis. As the cloud collapses, the magnetic field and rotation axis
change their directions. When the rotation is slow and the magnetic field is
relatively strong, the direction of the rotation axis changes to align with the
magnetic field, as shown earlier by Matsumoto & Tomisaka. When the magnetic
field is weak and the rotation is relatively fast, the magnetic field inclines
to become perpendicular to the rotation axis. In other words, the evolution of
the magnetic field and rotation axis depends on the relative strength of the
rotation and magnetic field. Magnetic braking acts to align the rotation axis
and magnetic field, while the rotation causes the magnetic field to incline
through dynamo action. The latter effect dominates the former when the ratio of
the angular velocity to the magnetic field is larger than a critical value
\Omega_0/ B_0 > 0.39 G^1/2 c_s^-1, where B_0, \Omega_0, G, and c_s^-1 denote
the initial magnetic field, initial angular velocity, gravitational constant,
and sound speed, respectively. When the rotation is relatively strong, the
collapsing cloud forms a disk perpendicular to the rotation axis and the
magnetic field becomes nearly parallel to the disk surface in the high density
region. A spiral structure appears due to the rotation and the wound-up
magnetic field in the disk.",0602034v1
2017-02-06,The formation of magnetic depletions and flux annihilation due to reconnection in the heliosheath,"The misalignment of the solar rotation axis and the magnetic axis of the Sun
produces a periodic reversal of the Parker spiral magnetic field and the
sectored solar wind. The compression of the sectors is expected to lead to
reconnection in the heliosheath (HS). We present particle-in-cell simulations
of the sectored HS that reflect the plasma environment along the Voyager 1 and
2 trajectories, specifically including unequal positive and negative azimuthal
magnetic flux as seen in the Voyager data \citep{Burlaga03}. Reconnection
proceeds on individual current sheets until islands on adjacent current layers
merge. At late time bands of the dominant flux survive, separated by bands of
deep magnetic field depletion. The ambient plasma pressure supports the strong
magnetic pressure variation so that pressure is anti-correlated with magnetic
field strength. There is little variation in the magnetic field direction
across the boundaries of the magnetic depressions. At irregular intervals
within the magnetic depressions are long-lived pairs of magnetic islands where
the magnetic field direction reverses so that spacecraft data would reveal
sharp magnetic field depressions with only occasional crossings with jumps in
magnetic field direction. This is typical of the magnetic field data from the
Voyager spacecraft \citep{Burlaga11,Burlaga16}. Voyager 2 data reveals that
fluctuations in the density and magnetic field strength are anti-correlated in
the sector zone as expected from reconnection but not in unipolar regions. The
consequence of the annihilation of subdominant flux is a sharp reduction in the
""number of sectors"" and a loss in magnetic flux as documented from the Voyager
1 magnetic field and flow data \citep{Richardson13}.",1702.01697v1
2020-07-23,Signal Enhancement for Magnetic Navigation Challenge Problem,"Harnessing the magnetic field of the Earth for navigation has shown promise
as a viable alternative to other navigation systems. A magnetic navigation
system collects its own magnetic field data using a magnetometer and uses
magnetic anomaly maps to determine the current location. The greatest challenge
with magnetic navigation arises when the magnetic field measurements from the
magnetometer encompass the magnetic field from not just the Earth, but also
from the vehicle on which it is mounted. It is difficult to separate the Earth
magnetic anomaly field, which is crucial for navigation, from the total
magnetic field reading from the sensor. The purpose of this challenge problem
is to decouple the Earth and aircraft magnetic signals in order to derive a
clean signal from which to perform magnetic navigation. Baseline testing on the
dataset has shown that the Earth magnetic field can be extracted from the total
magnetic field using machine learning (ML). The challenge is to remove the
aircraft magnetic field from the total magnetic field using a trained model.
This challenge offers an opportunity to construct an effective model for
removing the aircraft magnetic field from the dataset by using a scientific
machine learning (SciML) approach comprised of an ML algorithm integrated with
the physics of magnetic navigation.",2007.12158v2
2023-04-13,High-performance descriptor for magnetic materials: Accurate discrimination of magnetic structure,"The magnetic structure is crucial in determining the physical properties
inherent in magnetic compounds. We present an adequate descriptor for magnetic
structure with proper magnetic symmetry and high discrimination performance,
which does not depend on artificial choices for coordinate origin, axis, and
magnetic unit cell in crystal. We extend the formalism called ``smooth overlap
of atomic positions'' (SOAP), providing a numerical representation of atomic
configurations to that of magnetic moment configurations. We introduce the
descriptor in terms of the vector spherical harmonics to describe a magnetic
moment configuration and partial spectra from the expansion coefficients. We
discuss that the lowest-order partial spectrum is insufficient to discriminate
the magnetic structures with different magnetic anisotropy, and a higher-order
partial spectrum is required in general to differentiate detailed magnetic
structures on the same atomic configuration. We then introduce the fourth-order
partial spectrum and evaluate the discrimination performance for different
magnetic structures, mainly focusing on the difference in magnetic symmetry.
The modified partial spectra that are defined not to reflect the difference of
magnetic anisotropy are also useful in evaluating magnetic structures obtained
from the first-principles calculations performed without spin-orbit coupling.
We apply the present method to the symmetry-classified magnetic structures for
the crystals of Mn$_3$Ir and Mn$_3$Sn, which are known to exhibit anomalous
transport under the antiferromagnetic order, and examine the discrimination
performance of the descriptor for different magnetic structures on the same
crystal.",2304.06282v2
2023-08-25,Coexistence of non-trivial van der Waals magnetic orders enable field-free spin-orbit torque switching at room temperature,"The discovery of van der Waals (vdW) materials exhibiting non-trivial and
tunable magnetic interactions at room temperature can give rise to exotic
magnetic states, which are not readily attainable with conventional materials.
Such vdW magnets can provide a unique platform for studying new magnetic
phenomena and realising magnetization dynamics for energy-efficient and
non-volatile spintronic memory and logic technologies. Recent developments in
vdW magnets have revealed their potential to enable spin-orbit torque (SOT)
induced magnetization dynamics. However, the deterministic and field-free SOT
switching of vdW magnets at room temperature has been lacking, prohibiting
their potential applications. Here, we demonstrate magnetic field-free and
deterministic SOT switching of a vdW magnet (Co0.5Fe0.5)5GeTe2 (CFGT) at room
temperature, capitalizing on its non-trivial intrinsic magnetic ordering. We
discover a coexistence of ferromagnetic and antiferromagnetic orders in CFGT at
room temperature, inducing an intrinsic exchange bias and canted perpendicular
magnetism. The resulting canted perpendicular magnetization of CFGT introduces
symmetry breaking, facilitating successful magnetic field-free magnetization
switching in the CFGT/Pt heterostructure devices. Furthermore, the SOT-induced
magnetization dynamics and their efficiency are evaluated using 2nd harmonic
Hall measurements. This advancement opens new avenues for investigating tunable
magnetic phenomena in vdW material heterostructures and realizing field-free
SOT-based spintronic technologies.",2308.13408v1
2001-06-05,On Nonlinear Alfvén Waves Generated by Cosmic Ray Streaming Instability,"Nonlinear damping of parallel propagating Alfv\'en waves in high-$\beta$
plasma is considered. Trapping of thermal ions and Coulomb collisions are taken
into account. Saturated damping rate is calculated. Applications are made for
cosmic ray propagation in the Galaxy.",0106078v1
2005-01-05,The Impact of Gravitational Redshift on Systemic Water Maser Emission in NGC 4258,"NGC 4258 is well known for its 22 GHz water maser features that appear to
reside in a thin Keplerian disk orbiting at R_0=0.13 pc. The influence of
gravitational redshift on the level of maser saturation and the line strength
and width of systemic water maser emission is studied. The effective
gravitational velocity shift along the gain path through the disk amounts to
about twice the thermal velocity width of H2O molecules at 500 K for a masing
ring of thickness 0.2R_0. This GR induced frequency shift has a sign opposite
to the shift caused by the projected velocity difference vector of Keplerian
motion on the blue side of the systemic maser emission and has the same sign on
the red systemic side. Consequently, the negative optical depth that a line
photon sees as it traverses the masing disk along a path of minimal Keplerian
velocity gradient is larger on the blue side. Note that one is not concerned
here with an overall shift in the maser spectrum caused by the fact that the
masing ring as a whole is located in the black hole's potential well, i.e., it
is the change in the gravitational potential along the gain path that matters.
It is found, for a Schwarzschild metric, that saturation is enhanced
(suppressed) for systemic blue-shifted (red-shifted) maser features by
gravitational redshift of line photons. Approaching peak flux systemic features
are, on average, brighter, due to saturation, and wider (~2 km/s), due to
rebroadening, than their receding counterparts (~1 km/s). The effects are
consistent with observations that span several years, i.e., over periods longer
than needed for disk material to move through the systemic emission region.
Further confirmation of this effect can follow by combining all available
systemic 22 GHz data over the past two decades (abridged).",0501069v2
2005-05-18,The Large-Scale Electrochemistry and Possible Consequences of Deep Impact Mission to Tempel 1,"Some consequences of hypervelocity impact onto the comet Tempel 1 nucleus are
considered under assumption that SP comets are fragments of massive icy
envelopes of Ganymede-like bodies saturated by products of ice electrolysis
that underwent global explosions.",0505377v3
1996-09-20,Variationnal study of ferromagnetism in the t1-t2 Hubbard chain,"A one-dimensional Hubbard model with nearest and (negative) next-nearest
neighbour hopping is studied variationally. This allows to exclude saturated
ferromagnetism for $U < U_c$. The variational boundary $U_c (n)$ has a minimum
at a ``critical density'' $n_c$ and diverges for $n \rightarrow 1$.",9609198v1
1999-02-17,Trapping and Mobilization of Residual Fluid During Capillary Desaturation in Porous Media,"We discuss the problem of trapping and mobilization of nonwetting fluids
during immiscible two phase displacement processes in porous media. Capillary
desaturation curves give residual saturations as a function of capillary
number. Interpreting capillary numbers as the ratio of viscous to capillary
forces the breakpoint in experimental curves contradicts the theoretically
predicted force balance. We show that replotting the data against a novel
macroscopic capillary number resolves the problem for discontinuous mode
displacement.",9902236v1
1999-09-09,Mesoscopic fluctuations of the Coulomb drag,"We consider mesoscopic fluctuations of the Coulomb drag coefficient $\rho_D$
in the system of two separated two-dimensional electron gases. It is shown that
at low temperatures sample to sample fluctuations of $\rho_D$ exceed its
ensemble average. It means that in such a regime the sign of $\rho_D$ is random
and the temperature dependence almost saturates $\rho_D \sim 1/\sqrt{T}$.",9909133v1
2000-02-13,Phase-coherence time saturation in mesoscopic systems: wave function collapse,"A finite phase-coherence time $\tau_{\phi}^{meas}$ emerges from iterative
measurement onto a quantum system. For a rapid sequence, the phase-coherence
time is found explicitly. For the stationary charge conduction problem, it is
bounded. At all order, in the time-interval of measurements, we propose a
general expression for $\tau_{\phi}^{meas}$.",0002188v1
2002-04-02,Fast crack propagation by surface diffusion,"We present a continuum theory which describes the fast growth of a crack by
surface diffusion. This mechanism overcomes the usual cusp singularity by a
self-consistent selection of the crack tip radius. It predicts the saturation
of the steady state crack velocity appreciably below the Rayleigh speed and tip
blunting. Furthermore, it includes the possibility of a tip splitting
instability for high applied tensions.",0204056v1
2002-10-10,Dephasing from interactions and spin disorder,"We calculate the dephasing rate of the electrons in the presence of
interactions and elastic spin disorder scattering. In the frame of a
self-consistent diagrammatic treatment, we obtain saturation of the dephasing
rate in the limit of zero temperature for spin-orbit disorder in 2 dimensions.
This result is in agreement with relevant experiments.",0210223v1
2003-04-12,An extension of Tasaki's flat-band Hubbard model,"We present a new class of flat-band Hubbard models which have saturated
ferromagnetic ground states at two distinct electron numbers for different
values of parameters. The models are extensions of Tasaki's flat-band models.",0304295v4
2005-11-20,Tension-Induced Morphological Transition in Mixed Lipid Bilayers,"Recently, Rozovsky et al. reported on the morphology and dynamics of
superstructures in three-component lipid bilayers containing saturated and
unsaturated lipids as well as cholesterol [J. Am. Chem. Soc. 127, 36 (2005)].
We comment that the observed sequence of the stripe to hexagonal morphological
transition in mixed bilayers can be attributed to an enhanced membrane surface
tension that is induced by the vesicle adhesion on the solid surface.",0511492v1
1997-06-17,Partial Representations and Amenable Fell Bundles over Free Groups,"We show that a Fell bundle B = {B_t}_{t \in F}, over an arbitrary free group
F, is amenable, whenever it is orthogonal (in the sense that B_x^* B_y = 0, if
x and y are distinct generators of F) and semi-saturated (in the sense that
B_{ts} coincides with the closed linear span of B_t B_s, when the
multiplication ``ts'' involves no cancelation).",9706001v1
2004-06-09,A toy model for the coincidence problem,"The measured values of the matter energy density and the vacuum energy
density are obtained using an adiabatic black hole percolating model at the
critical point. The percolation of black holes is related with an expanding
isotropic universe filled with the most entropic fluid saturating the
holographic bound.",0406035v2
1993-10-25,Hadron Production Ratios as Probes of Confinement and Freeze-Out,"Particle production in central S-A collisions at 200 GeV/A energy is analysed
within a thermal model. Present data imply that the strange particles freeze
out at a higher temperature than the non-strange particles and that the
strangeness saturation is incomplete.",9310345v1
1999-05-13,Drell-Hearn-Gerasimov Sum Rule for the Nucleon in the Large-N_c Limit,"We show that the Drell-Hearn-Gerasimov sum rule for the nucleon is entirely
saturated by the \Delta resonance in the limit of a large number of colors, N_c
\to \infty. Corrections are at relative order 1/N_c^2.",9905334v1
2000-10-24,Low x Physics,"This is a talk, given at Diffraction'2000, Sept. 2 - 7, Centraro, Italy. In
this talk, we present the arguments, that a new QCD regime - gluon saturation,
has been reached at HERA.",0010272v1
2000-11-01,Introduction to Diffractive Photoprocesses,"The objectives of my talk are to provide a very brief introduction to
diffractive photoprocesses in general and the colour dipole model in
particular; and to comment on possible gluon saturation effects at HERA and
beyond.",0011007v1
2001-05-31,Effective field theory for the small-x evolution,"The small-x behavior of structure functions in the saturation region is
determined by the non-linear generalization of the BFKL equation. I suggest the
effective field theory for the small-x evolution which solves formally this
equation. The result is the 2+1 functional integral for the structure functions
at small x.",0105334v1
2001-11-29,Particle Production in High-energy Heavy-ion Collisions,"Particle production mechanisms in high-energy heavy-ion collisions are
reviewed in connection with recent experimental data from RHIC. Implications on
mini-jet production, parton saturation and jet quenching are discussed.",0111404v1
2001-11-30,pQCD at the Kinematical Boundary of its Applicability,"I examines the applicability and possible need for a re-formulation of pQCD,
as we know it, in the DIS limit of small $Q^2$ and $x$. Gluon saturation,
implied by s-channel unitarity, and its possible experimental signatures are
critically assessed.",0111453v1
2002-02-25,High Energy QCD and the Large Nc Limit,"We review recent progress in understanding QCD at high energies and the role
played in it by the large Nc limit. We discuss unitarization of total hadronic
cross sections and saturation of structure functions at high energies.",0202238v1
2002-06-10,"Chiral Lagrangian from gauge invariant,nonlocal, dynamical quark model","Parameters of Gasser Leutwyler chiral Lagrangian are proved saturated by
dynamical quark self energy Sigma(k^2) in a gauge invariant, nonlocal,
dynamical quark model.",0206090v2
2002-08-29,Taming the BFKL Intercept via Gluon Saturation,"We show that the inclusion of parton density effects in the perturbative
small-x evolution reduces the strength of the powerlike growth of total
hadronic cross sections.",0208265v1
2002-09-10,Dynamics of Particle Production in Relativistic Nuclear Collisions,"Saturation models for particle production in relativistic nuclear collisions
are discussed. In particular, I show that the predictions from the high density
QCD for the qualitative shape of $dN/dy$ are very sensitive to the form of the
unintegrated gluon distribution.",0209102v1
2002-12-11,Selected Topics in Rapidity Gap Physics,"This talk will review selected topics in rapidity gap physics. In particular
I will discuss diffractive jet production and the possibility of searching for
the higgs boson using diffraction at the LHC; the dipole picture of diffraction
and saturation; and those processes where a large momentum is transferred
across the rapidity gap, for which there has been recent progress both
experimentally and theoretically.",0212154v1
2003-09-11,QCD Saturation and Soft Processes,"We show that an approximate solution to the amended non-linear
Balitsky-Kovchegov evolution equation which was formulated for hard QCD
processes, can be extended to provide a good description of photoproduction and
soft hadronic (non perturbative) reactions.",0309125v1
2003-12-03,Beyond BFKL,"The Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution equation is known to be
``unstable'' with respect to fluctuations in gluon virtuality, transverse
momentum and energy requiring to go beyond the leading order BFKL. Still, these
instabilities point to fruitful improvements of our deep understanding of QCD.
Recent applications to next-leading order and to saturation problems are
outlined.",0312043v1
2004-04-22,Predicting F2D3 from the colour glass condensate model,"We confront the colour glass condensate motivated dipole model
parameterization of Iancu, Itakura and Munier with the available HERA data on
the diffractive structure function F2D3 and with existing dipole model
parameterizations. Reasonably good agreement is found with only two adjustable
parameters. We caution against interpreting the success of the model as
compelling evidence for low-x perturbative saturation dynamics.",0404192v1
2004-08-03,Diffractive photon dissociation in the saturation regime,"Using the Good and Walker picture, we derive a simple formula for diffractive
dissociation that can apply to recent data collected at HERA in the low Q2
regime.",0408038v1
2004-08-03,"Color Glass Condensate at the LHC: hadron multiplicities in $pp$, $pA$ and $AA$ collisions","We make quantitative predictions for the rapidity and centrality dependencies
of hadron multiplicities in $AA$, $pA$ and $pp$ collisions at the LHC energies
basing on the ideas of parton saturation in the Color Glass Condensate.",0408050v1
2004-08-31,Small x QCD,"A review of some theoretical aspects of small x QCD physics is given, with a
particular emphasis to the relation between the BFKL and the colour dipole
approaches. The nonlinear evolution equations one may construct, as a better
approximation beyond the linear analysis, are discussed together with their
relation to a possible saturation regime.",0408352v1
2005-05-27,Parametric form of QCD travelling waves,"We derive parametric travelling-wave solutions of non-linear QCD equations.
They describe the evolution towards saturation in the geometric scaling region.
The method, based on an expansion in the inverse of the wave velocity, leads to
a solvable hierarchy of differential equations. A universal parametric form of
travelling waves emerges from the first two orders of the expansion.",0505237v1
2005-07-13,"Saturation, traveling waves and fluctuations","In this talk I discuss the high energy asymptotics of QCD scattering, and its
similarity to a reaction-diffusion process. I also discuss detailed numerical
studies of the mean field approximation to this picture, i.e., the
Balitsky-Kovchegov equation.",0507153v1
2005-11-14,Limiting energy dependence of spin parameters in small-angle elastic pp-scattering,"We consider limiting behavior with energy of spin parameters at small values
of t close to zero which corresponds to the saturation of the Froissart-Martin
bound for the total cross sections.",0511163v3
2006-08-18,Nuclear matter in the chiral quark soliton model with vector mesons,"We study the nuclear matter solution in the chiral quark soliton model
coupled to $\rho$ and $\omega$ vector mesons based on the Wigner-Seitz
approximation. It is shown that the vector mesons stabilize the soliton at
high-density region. As a result, the saturation property and incompressibility
are significantly improved.",0608197v1
2006-09-25,High energy pA collisions in the Color Glass Condensate approach,"We present a brief review of phenomenological applications of the gluon
saturation approach to the proton-nucleus collisions at high energies.",0609258v2
2006-11-21,Diffraction 2006: Theoretical Summary,"This paper presents a summary of the theoretical presentations to the
international workshop ""Diffraction 2006"". The range of topics covered during
the workshop was quite broad and this summary is therefore somewhat selective
covering recent developments in BFKL physics, exclusive processes, saturation
dynamics, DIS and structure functions and coherence in QCD.",0611275v1
1995-05-03,A Stringy Test of the Fate of the Conifold,"By studying string loop corrections to superpotential of type II strings
compactified on Calabi-Yau threefolds we find a quantum stringy test and a
confirmation of a recent proposal of Strominger on the fate of the conifold
singularity. We also propose a connection between the spectrum of Bogomolnyi
saturated solitons and one-loop string partition function of $N=2$ topological
strings.",9505023v1
1996-03-06,Gravitating BPS Dyons witout a Dilaton,"We describe curved-space BPS dyon solutions, the ADM mass of which saturates
the gravitational version of the Bogomol'nyi bound. This generalizes
self-gravitating BPS monopole solutions of Gibbons et al. when there is no
dilaton.",9603027v1
1996-12-11,Introduction to Supersymmetry,"These lectures give a self-contained introduction to supersymmetry from a
modern perspective. Emphasis is placed on material essential to understanding
duality. Topics include: central charges and BPS-saturated states,
supersymmetric nonlinear sigma models, N=2 Yang-Mills theory, holomorphy and
the N=2 Yang-Mills beta function, supersymmetry in 2, 6, 10, and 11 spacetime
dimensions.",9612114v1
1997-12-08,BPS Saturated Amplitudes and Non-perturbative String Theory,"The study of the special F^4 and R^4 in the effective action for the
Spin(32)/Z_2 and type II strings sheds some light on D-brane calculus and on
instanton contribution counting. The D-instanton case is discussed separately.",9712079v3
1999-09-29,On The Size of The Graviton,"We propose an approximate wavefunction of the bound state of $N$ $D0$-branes.
Its spread grows as $N^{1\over 3}$ per particle, i.e. it saturates the
Polchinski's bound.",9909213v3
1999-11-08,The Contribution of Instanton-Antiinstanton Fluctuations to the Ground State Energy in Supersymmetric Quantum Mechanical Models,"I show that the method of finding if the ground state energy is nonzero or
not by saturating the functional integral directly with
instanton-anti-instanton type fluctuations is not reliable either for the
double or for the triple well potential models in supersymmetric quantum
mechanics.",9911050v1
2002-08-22,On uncertainty relations in noncommutative quantum mechanics,"We discuss the uncertainty relations in quantum mechanics on noncommutative
plane. In particular, we show that, for a given state at most one out of three
basic nontrivial uncertainty relations can be saturated. We consider also in
some detail the case of angular momentum eigenstates.",0208162v2
2003-11-19,Universality of the shear viscosity in supergravity,"Kovtun, Son and Starinets proposed a bound on the shear viscosity of any
fluid in terms of its entropy density. We argue that this bound is always
saturated for gauge theories at large 't Hooft coupling, which admit
holographically dual supergravity description.",0311175v1
1994-09-02,Projective Stationary Sets and Strong Reflection Principle,"We study projective stationary sets. The Projective Stationary Reflection
principle is the statement that every projective stationary set contains an
increasing continuous $\in$--chain of length $\omega_1$. We show that if
Martin's Maximum holds, then the Projective Stationary Reflection Principle
holds. Also it is equivalent to the Strong Reflection Principle. We show that
the saturation of the nonstationary ideal on $\omega_1$ is equivalent to a
certain kind of reflection.",9409202v1
1996-01-15,"Saturated filters at successors of singulars, weak reflection and yet another weak club principle","Suppose that lambda is the successor of a singular cardinal mu whose
cofinality is an uncountable cardinal kappa. We give a sufficient condition
that the club filter of lambda concentrating on the points of cofinality kappa
is not lambda^+-saturated. The condition is phrased in terms of a notion that
we call weak reflection. We discuss various properties of weak reflection",9601219v1
1998-08-29,Polycyclic-by-finite group algebras are catenary,"We show that group algebras kG of polycyclic-by-finite groups G, where k is a
field, are catenary: Given prime ideals P and P' of kG, with P contained in P',
all saturated chains of primes between P and P' have the same length.",9808123v1
2000-10-23,Recent Progress in Algebraic Combinatorics,"A survey of recent progress in three areas of algebraic combinatorics: (1)
the Saturation Conjecture for Littlewood-Richardson coefficients, (2) the n!
and (n+1)^{n-1} conjectures, and (3) longest increasing subsequences of
permutations.",0010218v2
2003-03-02,Quantum Generalization of the Horn Conjecture,"We prove a theorem which implies a quantum (multiplicative) analogue of the
Horn conjecture, and also of the saturation conjecture. We obtain
transversality statements for quantum schubert calculus in any characteristic
and also determine the smallest power of q in an arbitrary (small quantum)
product of Schubert varieties in a Grassmannian.",0303013v4
2003-05-08,Regularity and Saturation in Biprojective Spaces,"The paper is being withdrawn since the results are incorporated in paper
arxiv.org/abs/math.AG/0306195.",0305125v4
2005-08-29,"Base point free theorems--saturation, b-divisors, and canonical bundle formula--","We reformulate base point free theorems. Our formulation is flexible and has
some important applications. One of the main purposes of this paper is to prove
a generalization of the base point free theorem in Fukuda's paper: On
numerically effective log canonical divisors.",0508554v3
2006-01-10,About one singularity of the property of disturbed differential systems equivalence to linear differential equations,"In this paper we consider the families of morphisms of vector fibre bundles
(\cite{Mill1}) defined by the linear systems of differential equations. We
proving that the specified families of morphisms is not saturated
(\cite{Mill2}).",0601212v1
2006-01-11,About one characteristic of set of linear differential systems with non-negative coefficients,"The families of morphisms of vector fibre bundle (\cite{Mill1}) defined by
the linear systems of differential equations with non-negative coefficients is
considered. Authors proved that the specified families of morphisms is not
saturated (\cite{Mill2}).",0601241v1
2006-01-11,About one characteristic of set of linear Hamiltonian systems,"The families of morphisms of vector fibre bundle (\cite{Mill1}) defined by
the linear Hamiltonian systems of differential equations is considered. Authors
proved that the specified families of morphisms is not saturated
(\cite{Mill2}).",0601244v1
2006-01-19,"About one singularity of the property of disturbed differential systems, that equivalents to linear differential equations","This paper is devoted to the study of the family of morphisms of vector
bundle, defined by the systems equivalence to linear differential equations. It
is proved, that the specified families of the morphisms of vector bundle is not
saturated.",0601461v1
2007-02-15,Model theory and Kaehler geometry,"We survey and explain some recent work at the intersection of model theory
and bimeromorphic geometry (classification of compact complex manifolds).
Included here are the essential saturation of the many sorted structure
$\mathcal{C}$ of compact Kaehler manifolds, the conjectural role of
hyperkaehler manifolds in the description of strongly minimal sets in
$\mathcal{C}$ and Campana's work on the isotriviality of hyperkaehler families
and its connection with the nonmultidimensionality conjecture.",0702468v1
2003-03-04,Quadratic solitons as nonlocal solitons,"We show that quadratic solitons are equivalent to solitons of a nonlocal Kerr
medium. This provides new physical insight into the properties of quadratic
solitons, often believed to be equivalent to solitons of an effective saturable
Kerr medium. The nonlocal analogy also allows for novel analytical solutions
and the prediction of novel bound states of quadratic solitons.",0303003v1
1998-06-05,Alternative Linear Chiral Models for Nuclear Matter,"The equation of state of a family of alternative linear chiral models in the
mean field approximation is discussed. We investigate the analogy between some
of these models with current models in the literature, and we show that it is
possible to reproduce very well the saturation properties of nuclear matter.",9806020v1
1999-09-15,Saturation of the width of the strength function,"The strength function of a single state $|d>$ is studied using the deformed
Gaussian orthogonal ensemble. In particular we study the dependence of the
spreading width of $|d>$ on the degree of mixing.",9909033v1
2000-01-31,Nuclear Saturation with QCD sum rules,"The scalar and vectorial self energies obtained through QCD sum rules are
introduced in the Quantum Hadrodynamics (QHD) equations. This QHD and QCD
mixing show us that the effect of the density on the coupling constants is very
small.",0001065v2
2002-04-12,Nuclear matter with off-shell propagation,"Symmetric nuclear matter is studied within the conserving, self-consistent
T-matrix approximation. This approach involves off-shell propagation of
nucleons in the ladder diagrams. The binding energy receives contributions from
the background part of the spectral function, away form the quasiparticle peak.
The Fermi energy at the saturation point fulfills the Hugenholz-Van Hove
relation. In comparison to the Brueckner-Hartree-Fock approach, the binding
energy is reduced and the equation of state is harder",0204034v1
2003-01-07,Introduction: GDH and related topics,"The formulation of the Gerasimov-Drell-Hearn sum rule is revisited, showing
its connection with other sum rules occurring in electron scattering and
discussing the problem of its saturation, both from the theoretical and
experimental point of v iew. The generalisation to other nuclear targets is
also reported.",0301014v1
2007-03-22,Rapidity dependence of the photon to pion production ratio in high energy collisions,"We investigate rapidity dependence of the ratio of photon and pion production
cross sections in high energy proton (deuteron) - nucleus collisions at RHIC
and LHC. This ratio, and its rapidity dependence can be a sensitive probe of
high density QCD (Color Glass Condensate) dynamics and shed further light on
the role of saturation physics at RHIC and LHC.",0703069v1
2001-09-04,Biot's theory of propagation of elastic waves in a fluid-saturated porous solid revisited: introduction of non-zero boundary slip velocity,"This paper has been withdrawn by the author due to the physically
inconsistent assumption of constant slip velocity, instead, see a new improved
model - physics/0201045.",0109007v2
2005-11-01,Ultraslow light in inhomogeneously broadened media,"We calculate the characteristics of ultraslow light in an inhomogeneously
broadened medium. We present analytical and numerical results for the group
delay as a function of power of the propagating pulse. We apply these results
to explain the recently reported saturation behavior [Baldit {\it et al.}, \prl
{\bf 95}, 143601 (2005)] of ultraslow light in rare earth ion doped crystal.",0511002v1
2006-04-07,Enhanced production of coherent pulsed radiation at 125 nm: the route towards a tabletop VUV laser,"A novel approach is used to enhance by nearly two orders of magnitude the
conversion efficiency of a 125 nm-coherent source, based on four-wave mixing in
room-temperature mercury vapor. Saturation issues are observed and discussed.",0604054v1
2006-04-10,Superluminal pulse reflection from a weakly absorbing dielectric slab,"Group delay for a reflected light pulse from a weakly absorbing dielectric
slab is theoretically investigated, and large negative group delay is found for
weak absorption near a resonance of the slab ($Re(kd)=m\pi$). The group delays
for both the reflected and transmitted pulses will be saturated with the
increase of the absorption.",0604074v1
2006-04-20,Optimal dense coding with arbitrary pure entangled states,"We examine dense coding with an arbitrary pure entangled state sharing
between the sender and the receiver. Upper bounds on the average success
probability in approximate dense coding and on the probability of conclusive
results in unambiguous dense coding are derived. We also construct the optimal
protocol which saturates the upper bound in each case.",0604149v2
2007-05-15,Forward hadron production in high energy pA collisions: from RHIC to LHC,"We present a calculation of Pi, D and B mesons production at RHIC and LHC
energies based upon the KKT model of gluon saturation. We discuss dependence of
the nuclear modification factor on rapidity and transverse momentum.",0705.2193v2
2007-05-16,Near-Extreme Black Holes and the Universal Relaxation Bound,"A fundamental bound on the relaxation time \tau of a perturbed
thermodynamical system has recently been derived, \tau \geq \hbar/\pi T, where
$T$ is the system's temperature. We demonstrate analytically that black holes
saturate this bound in the extremal limit and for large values of the azimuthal
number m of the perturbation field.",0705.2306v1
2007-06-13,Recent developments in small-x physics,"Recent theoretical progress in understanding high-energy scattering beyond
the mean field approximation is reviewed. The role of Lorentz invariance and
pomeron loops in the evolution, the relation between high-energy QCD and
statistical physics and results for the saturation momentum and the scattering
amplitude are discussed.",0706.1866v1
2007-06-21,Stochastic Lorentz forces on a point charge moving near the conducting plate,"The influence of quantized electromagnetic fields on a nonrelativistic
charged particle moving near a conducting plate is studied. We give a
field-theoretic derivation of the nonlinear, non-Markovian Langevin equation of
the particle by the method of Feynman-Vernon influence functional. This
stochastic approach incorporates not only the stochastic noise manifested from
electromagnetic vacuum fluctuations, but also dissipation backreaction on a
charge in the form of the retarded Lorentz forces. Since the imposition of the
boundary is expected to anisotropically modify the effects of the fields on the
evolution of the particle, we consider the motion of a charge undergoing
small-amplitude oscillations in the direction either parallel or normal to the
plane boundary. Under the dipole approximation for nonrelativistic motion,
velocity fluctuations of the charge are found to grow linearly with time in the
early stage of the evolution at the rather different rate, revealing strong
anisotropic behavior. They are then asymptotically saturated as a result of the
fluctuation-dissipation relation, and the same saturated value is found for the
motion in both directions. The observational consequences are discussed. plane
boundary. Velocity fluctuations of the charge are found to grow linearly with
time in the early stage of the evolution at the rate given by the relaxation
constant, which turns out to be smaller in the parallel case than in the
perpendicular one in a similar configuration. Then, they are asymptotically
saturated as a result of the fluctuation-dissipation relation. For the
electron, the same saturated value is obtained for motion in both directions,
and is mainly determined by its oscillatory motion. Possible observational
consequences are discussed.",0706.3075v3
2007-06-28,Shear Viscosity to Entropy within a Parton Cascade,"The shear viscosity is calculated by means of the perturbative kinetic
partonic cascade BAMPS with CGC initial conditons for various saturation
momentum scale Q_s. eta/s ~ 0.15 stays approximately constant when going from
RHIC to LHC.",0706.4212v1
2007-06-29,Investigating the extended geometric scaling region at LHC with polarized and unpolarized final states,"We present predictions for charged hadron production and Lambda polarization
in p-p and p-Pb collisions at the LHC using the saturation inspired DHJ model
for the dipole cross section in the extended geometric scaling region.",0706.4430v1
2007-07-12,Maltsiniotis's first conjecture for K_1,"We show that K_1 of an exact category agrees with K_1 of the associated
triangulated derivator. More generally we show that K_1 of a Waldhausen
category with cylinders and a saturated class of weak equivalences coincides
with K_1 of the associated right pointed derivator.",0707.1892v2
2007-08-26,Orbit semigroups and the representation type of quivers,"We show that a finite, connected quiver Q without oriented cycles is a Dynkin
or Euclidean quiver if and only if all orbit semigroups of representations of Q
are saturated.",0708.3413v2
2007-09-02,Saturation effects in elastic scattering at the LHC,"The problems linked to the extraction of the basic parameters of the hadron
elastic scattering amplitude at the LHC are explored. The impact of the Black
Disk Limit (BDL)$-$ which constitutes a new regime of the scattering processes
  - on the determination of these values is examined.",0709.0100v1
2007-11-15,Cohomology of groups in o-minimal structures: acyclicity of the infinitesimal subgroup,"By recent work on some conjectures of Pillay, each definably compact group in
a saturated o-minimal structure is an expansion of a compact Lie group by a
torsion free normal divisible subgroup, called its infinitesimal subgroup. We
show that the infinitesimal subgroup is cohomologically acyclic. This implies
that the functorial correspondence between definably compact groups and Lie
groups preserves the cohomology.",0711.2502v1
2007-11-22,Spectral saturation: inverting the spectral Turan theorem,"We prove that if the spectral radius of a graph G of order n is larger than
the spectral radius of the r-partite Turan graph of the same order, then G
contains various supergraphs of the complete graph of order r+1. In particular
G contains a complete r-partite graph of size log n with one edge added to the
first part. These results complete a project of Erdos from 1963. We also give
corresponding stability results.",0711.3488v1
2008-02-21,Palindromic Saturation,"We consider two {seemingly} different definitions of infinite words which
contain {the} utmost number of palindromes. We show that these two definitions
coincide. {The keynote of the proof is a meticulous inspection of properties of
complete return words and the application of some basic graph theory.} In fact,
we provide another proof of the result announced in \cite{Zamboni}.",0802.2995v2
2008-05-22,Bedforms in a turbulent stream.Part 2: Formation of ripples by primary linear instability and of dunes by non-linear pattern coarsening,"It is widely accepted that both ripples and dunes form in rivers by primary
linear instability, the wavelength of the former scaling on the grain size,
that of the latter being controled by the water depth. We revisit here this
problem, using the computation of the turbulent flow over a wavy bottom
performed in Part 1. The details of the different mechanisms controlling
sediment transport are encoded into three quantities: the saturated flux, the
saturation length and the threshold shear stress. Theses quantities are
modelled in the case of erosion and momentum limited bed loads. This framework
allows to give a clear picture of the instability in terms of dynamical
mechanisms. The relation between the wavelength at which ripples form and the
flux saturation length is quantitatively derived. Inverting the problem,
experimental data is used to determine the saturation length as a function of
grain size and shear velocity. Finally, using the systematic expansion of the
flow field with respect to the corrugation amplitude, we discuss the non-linear
selection of ripple aspect ratio. Investingating the effect of a free surface
on the linear instability, we show that the excitation of standing waves at the
surface has a stabilising effect, independently of the details of the flow and
sediment transport models. Consequently, the shape of the dispersion relation
is such that dunes can not result from a primary linear instability. We present
the results of field experiments performed in the natural sandy Leyre river,
which evidence the formation of ripples by a linear instability and the
formation of dunes by a non-linear pattern coarsening limited by the free
surface. We show that mega-dunes form when the sand bed presents
heterogeneities such as a wide distribution of grain sizes.",0805.3417v2
2008-05-30,"The ""footprints'' of irreversibility","We reformulate the result for the entropy production given in Phys. Rev.
Lett. 98, 080602 (2007) in terms of the relative entropy of microscopic
trajectories. By a combination with the Crook's theorem, we identify the path
variables that are sufficient to fully identify irreversibility. We show that
work saturates the relative entropy, and derive the entropy production for
stochastic descriptions.",0805.4703v1
2008-06-17,"Open Letter to the OSA Topical Meeting ""Slow and Fast Light""","The question is raised about whether the pulse delay in a saturable absorber
has anything to do with the ""slow light"" and group velocity reduction. We also
wonder why the 40-years-old trivial interpretation of the effect remains so far
ignored.",0806.2732v1
2008-07-27,Formation of aeolian ripples and sand sorting,"We present a continuous model capable of demonstrating some salient features
of aeolian sand ripples: the realistic asymmetric ripple shape, coarsening of
ripple field at the nonlinear stage of ripple growth, saturation of ripple
growth for homogeneous sand, typical size segregation of sand and formation of
armoring layers of coarse particles on ripple crests and windward slopes if
sand is inhomogeneous.",0807.4284v2
2008-10-19,Reflective Scattering and Unitarity,"Interpretation of unitarity saturation as reflective scattering is discussed.
Analogies with optics and Berry phase alongside with the experimental
consequences of the proposed interpretation at the LHC energies are considered.",0810.3391v1
2008-10-21,Tunnelling for Large N,"In this brief note, by applying the stochastic approach to multiple fields,
we estimate the probability of tunneling between vacua in a landscape with
$\cal N$ fields. We find that the probability can be enhanced by large $\cal
N$. When $\cal N$ saturates the dS entropy of some vacuum, the corresponding
vacuum will be extremely unstable and be expected to rapidly decay. We discuss
the implications of this result.",0810.3654v1
2008-11-26,Features of elastic scattering at small t at the LHC,"The problems linked with the extraction of the basic parameters of the hadron
elastic scattering amplitude at the LHC are explored. It is shown that one
should take into account the saturation regime which will lead to new effects
at the LHC.",0811.4369v1
2009-01-26,Have we seen anything beyond (N)NLO DGLAP at HERA?,"The evidence from HERA for parton saturation, and other low-$x$ effects
beyond the conventional DGLAP formalism, is recalled and critically reviewed in
the light of new data and analyses presented at the conference.",0901.4001v1
2009-02-02,From nuclear matter to Neutron Stars,"Neutron stars are the most dense objects in the observable Universe and
conventionally one uses nuclear theory to obtain the equation of state (EOS) of
dense hadronic matter and the global properties of these stars. In this work,
we review various aspects of nuclear matter within an effective Chiral model
and interlink fundamental quantities both from nuclear saturation as well as
vacuum properties and correlate it with the star properties.",0902.0262v1
2009-03-05,The Dynamics of EEG Entropy,"EEG time series are analyzed using the diffusion entropy method. The
resulting EEG entropy manifests short-time scaling, asymptotic saturation and
an attenuated alpha-rhythm modulation. These properties are faithfully modeled
by a phenomenological Langevin equation interpreted within a neural network
context.",0903.1078v1
2009-04-29,"Comment on ""An optimized potential for carbon dioxide"" [J. Chem. Phys. 122, 214507 (2005)]","A molecular model for carbon dioxide is assessed regarding vapor-liquid
quilibrium properties.Large deviations, being above 15 %, are found for vapor
pressure and saturated vapor density in the entire temperature range.",0904.4622v1
2009-05-07,Bernstein polynomials and spectral numbers for linear free divisors,"We discuss Bernstein polynomials of reductive linear free divisors. We define
suitable Brieskorn lattices for these non-isolated singularities, and show the
analogue of Malgrange's result relating the roots of the Bernstein polynomial
to the residue eigenvalues on the saturation of these Brieskorn lattices.",0905.0971v4
2009-05-07,Exclusive vector meson production in electron-ion collisions,"We calculate the nuclear cross section for coherent and incoherent vector
meson production within the QCD color dipole picture, including saturation
effects. Theoretical estimates for scattering on both light and heavy nuclei
are given over a wide range of energy.",0905.1143v1
2009-09-29,Dynamical Phase Trajectories in Baryon and Isospin Density Spaces,"We review recent results obtained for charge asymmetric systems at Fermi and
intermediate energies, ranging from 30 MeV/u to 1 GeV/u. Observables sensitive
to the isospin dependent part of nuclear interaction are discussed, providing
information on the symmetry energy behavior from sub- to supra-saturation
densities.",0909.5312v1
2009-10-21,Discovery of photon index saturation in the black hole binary GRS 1915+105,"We present a study of the correlations between spectral, timing properties
and mass accretion rate observed in X-rays from the Galactic Black Hole (BH)
binary GRS 1915+105 during the transition between hard and soft states. We
analyze all transition episodes from this source observed with RXTE,
coordinated with Ryle Radio Telescope (RT) observations. We show that
broad-band energy spectra of GRS 1915+105 during all these spectral states can
be adequately presented by two Bulk Motion Comptonization (BMC) components: a
hard component (BMC1, photon index Gamma_1=1.7-3.0) with turnover at high
energies and soft thermal component (BMC2, Gamma_2=2.7-4.2) with characteristic
color temperature <1 keV, and the redskewed iron line (LAOR) component. We also
present observable correlations between the index and the normalization of the
disk ""seed"" component. The use of ""seed"" disk normalization, which is
presumably proportional to mass accretion rate in the disk, is crucial to
establish the index saturation effect during the transition to the soft state.
We discovered the photon index saturation of the soft and hard spectral
components at values of 4.2 and 3 respectively. We present a physical model
which explains the index-seed photon normalization correlations. We argue that
the index saturation effect of the hard component (BMC1) is due to the soft
photon Comptonization in the converging inflow close to BH and that of soft
component is due to matter accumulation in the transition layer when mass
accretion rate increases. In addition to our spectral model components we also
find a strong feature of ""blackbody-like"" bump which color temperature is about
4.5 keV in eight observations of the intermediate and soft states. We discuss a
possible origin of this ""blackbody-like"" emission.",0910.4099v1
2009-11-07,Low-x QCD at the LHC with the ALICE detector,"We give a brief review of the physics of gluon saturation and non-linear QCD
evolution at small values of the Bjorken-$x$ variable. We discuss the ALICE
capability for low-$x$ studies at the LHC. In particular, we concentrate on the
heavy quark production in the CGC framework and its observation with the ALICE
Muon Spectrometer.",0911.1458v1
2009-12-10,Envelope Soliton Oscillator for UWB,"An electronic oscillator is shown to support an envelope soliton pulse. The
oscillator comprises a loop, formed by a nonlinear transmission line, an
amplifier, a bandpass filter and a saturable absorber. The soliton is suitable
for ultra-wideband radio-frequency communication; its existence and stability
are demonstrated with simulations.",0912.1906v1
2009-12-30,A class of compact subsets for non-sober topological spaces,"We define a class of subsets of a topological space that coincides with the
class of compact saturated subsets when the space is sober, and with enough
good properties when the space is not sober. This class is introduced
especially in view of applications to capacity theory.",0912.5469v3
2010-01-12,Threshold Saturation via Spatial Coupling: Why Convolutional LDPC Ensembles Perform so well over the BEC,"Convolutional LDPC ensembles, introduced by Felstrom and Zigangirov, have
excellent thresholds and these thresholds are rapidly increasing as a function
of the average degree. Several variations on the basic theme have been proposed
to date, all of which share the good performance characteristics of
convolutional LDPC ensembles. We describe the fundamental mechanism which
explains why ""convolutional-like"" or ""spatially coupled"" codes perform so well.
In essence, the spatial coupling of the individual code structure has the
effect of increasing the belief-propagation (BP) threshold of the new ensemble
to its maximum possible value, namely the maximum-a-posteriori (MAP) threshold
of the underlying ensemble. For this reason we call this phenomenon ""threshold
saturation."" This gives an entirely new way of approaching capacity. One
significant advantage of such a construction is that one can create
capacity-approaching ensembles with an error correcting radius which is
increasing in the blocklength. Our proof makes use of the area theorem of the
BP-EXIT curve and the connection between the MAP and BP threshold recently
pointed out by Measson, Montanari, Richardson, and Urbanke. Although we prove
the connection between the MAP and the BP threshold only for a very specific
ensemble and only for the binary erasure channel, empirically a threshold
saturation phenomenon occurs for a wide class of ensembles and channels. More
generally, we conjecture that for a large range of graphical systems a similar
saturation of the ""dynamical"" threshold occurs once individual components are
coupled sufficiently strongly. This might give rise to improved algorithms as
well as to new techniques for analysis.",1001.1826v2
2010-02-22,Almost sure asymptotics for the random binary search tree,"We consider a (random permutation model) binary search tree with n nodes and
give asymptotics on the loglog scale for the height H_n and saturation level
h_n of the tree as n\to\infty, both almost surely and in probability. We then
consider the number F_n of particles at level H_n at time n, and show that F_n
is unbounded almost surely.",1002.3896v1
2010-08-02,TeV Scale Cross-Sections and the Pomeranchuck Singularity,"We have investigated the detailed structure of $l$-plane singularities of
scattering amplitude saturating the Froissart bound. A self-consistent analysis
of these singularities provides us secondary terms in the Froissart bound.
These secondary terms lead to ghosts in the $l$-plane, which can only be
removed by introducing an odderon singularity. Phenomenological implications of
this analysis are also discussed.",1008.0218v1
2010-08-02,Studies of scaling properties in deep inelastic scattering,"We study the scaling properties in deep inelastic scattering using the most
recent combined structure function data $F_2$ from the H1 and ZEUS
collaborations. We also perform a direct fit to the $F_2$ data inspired by the
scaling properties. Our analysis favours the QCD saturation mechanism from the
Balitski Kovchegiv equation wuth running coupling.",1008.0261v1
2010-08-31,Unitarity and the color confinement,"We discuss how confinement property of QCD results in the rational
unitarization scheme and how unitarity saturation leads to appearance of a
hadron liquid phase at very high temperatures.",1008.5247v1
2010-09-22,A Simple Proof of Thue's Theorem on Circle Packing,"A simple proof of Thue theorem on Circle Packing is given. The proof is only
based on density analysis of Delaunay triangulation for the set of points that
are centers of circles in a saturated circle configuration.",1009.4322v1
2010-10-31,"Graphene Q-switched, tunable fiber laser","We demonstrate a wideband-tunable Q-switched fiber laser exploiting a
graphene saturable absorber. We get ~2us pulses, tunable between 1522 and
1555nm with up to~40nJ energy. This is a simple and low-cost light source for
metrology, environmental sensing and biomedical diagnostics.",1011.0115v1
2010-11-11,"UHE neutrinos: higher twists, scales, saturation","It is shown that in the ultra-high energy neutrino interactions the higher
twist corrections brought about by the non-conservation of the top-bottom
current dramatically change the longitudinal structure function, $F_L$. To the
Double Leading Log Approximation simple and numerically accurate formulas for
$F_L$ and $\sigma^{\nu N}$ are derived.",1011.2611v1
2010-12-02,A direct proof of the five element basis theorem,"We present a direct proof of the consistency of the existence of a five
element basis for the uncountable linear orders. Our argument is based on the
approach of notion of saturation of Aronszajn trees considered by Koenig,
Larson, Moore and Velickovic and simplifies the original proof of Moore.",1012.0596v2
2010-12-15,A Duality of Quantale-Enriched Categories,"We describe a duality for quantale-enriched categories that extends the
Lawson duality for continuous dcpos: for any saturated class J of modules that
commute with certain weighted limits, and under an appropriate choice of
morphisms, the category of J-cocomplete and J-continuous quantale-enriched
categories is self-dual.",1012.3351v1
2010-12-21,Rapidity and centrality dependence of azimuthal correlations in high energy d+Au collisions,"We discuss azimuthal correlations in $dAu$ collisions at different rapidities
and centralities and argue that experimentally observed depletion of the
back-to-back peak can be quantitatively explained by gluon saturation in the
Color Glass Condensate of the Gold nucleus.",1012.4709v1
2011-02-20,Conformal symmetry and the Balitsky-Kovchegov equation,"Solutions to the Balitsky-Kovchegov equation are considered which respect an
SO(3) subgroup of the conformal group. The symmetry dictates a specific
dependence of the saturation scale on the impact parameter. Applications to
deep inelastic scattering are considered.",1102.4040v2
2011-03-07,Does parton saturation at high density explain hadron multiplicities at LHC?,"An addendum to our previous papers in Phys. Lett. B539 (2002) 46 and Phys.
Lett. B502 (2001) 51, contributed to the CERN meeting ""First data from the LHC
heavy ion run"", March 4, 2011",1103.1259v1
2011-03-24,On a question of L.A. Shemetkov concerning the intersection of $\cal F$-maximal subgroups of finite groups,"We investigate the influence of the intersection of the $\cal F$-maximal
subgroups on the structure of a finite group. In particular, answering a
question of L.A Shemetkov we give conditions under which a hereditary saturated
formation $\cal F$ has a property that for any finite group $G$, the ${\cal
F}$-hypercentre of $G$ coincides with the intersection of all $\cal F$-maximal
subgroups of $G$.",1103.4729v1
2011-03-31,Local definitions of formations of finite groups,"A problem of constructing of local definitions for formations of finite
groups is discussed in the article. The author analyzes relations between local
definitions of various types. A new proof of existence of an
$\omega$-composition satellite of an $\omega$-solubly saturated formation is
obtained. It is proved that if a non-empty formation of finite groups is
$\mathfrak X$-local by F\""{o}rster, then it has an $\mathfrak X$-composition
satellite.",1103.6259v1
2011-04-21,Symmetric chain decomposition of necklace posets,"A finite ranked poset is called a symmetric chain order if it can be written
as a disjoint union of rank-symmetric, saturated chains. If $P$ is any
symmetric chain order, we prove that $P^n/\mathbb{Z}_n$ is also a symmetric
chain order, where $\mathbb{Z}_n$ acts on $P^n$ by cyclic permutation of the
factors.",1104.4147v3
2011-04-21,A Resolution of the Paradox of Enrichment,"The paradox of enrichment was observed by M. Rosenzweig in a class of
predator-prey models. Two of the parameters in the models are crucial for the
paradox. These two parameters are the prey's carrying capacity and prey's
half-saturation for predation. Intuitively, increasing the carrying capacity
due to enrichment of the prey's environment should lead to a more stable
predator-prey system. Analytically, it turns out that increasing the carrying
capacity always leads to an unstable predator-prey system that is susceptible
to extinction from environmental random perturbations. This is the so-called
paradox of enrichment. Our resolution here rests upon a closer investigation on
a dimensionless number $H$ formed from the carrying capacity and the prey's
half-saturation. By recasting the models into dimensionless forms, the models
are in fact governed by a few dimensionless numbers including $H$. The effects
of the two parameters: carrying capacity and half-saturation are incorporated
into the number $H$. In fact, increasing the carrying capacity is equivalent
(i.e. has the same effect on $H$) to decreasing the half-saturation which
implies more aggressive predation. Since there is no paradox between more
aggressive predation and instability of the predator-prey system, the paradox
of enrichment is resolved.
  We also further explore spatially dependent models for which the phase space
is infinite dimensional. The spatially independent limit cycle which is
generated by a Hopf bifurcation from an unstable steady state, is linearly
stable in the infinite dimensional phase space. Numerical simulations indicate
that the basin of attraction of the limit cycle is riddled. This shows that
spatial perturbations can sometimes (neither always nor never) remove the
paradox of enrichment near the limit cycle!",1104.4355v2
2011-04-29,Ytterbium- and chromium-doped fibre laser: from chaotic self-pulsing to passive Q-switching,"A spontaneously chaotic, self-pulsing ytterbium-doped fibre laser is
partially stabilized into the passively Q-switched mode of operation using a
chromium-doped saturable absorber fibre. This original all-fibre laser produces
sustained and stable trains of smooth pulses at high repetition rate.",1104.5657v1
2011-06-14,Monte Carlo study of carrier-light coupling in terahertz quantum cascade lasers,"We present a method for self-consistently including the optical cavity field
into Monte Carlo-based carrier transport simulations. This approach allows for
an analysis of the actual lasing operation in quantum cascade lasers,
considering effects such as gain saturation and longitudinal mode competition.
Simulation results for a terahertz quantum cascade laser are found to be
consistent with experiment.",1106.2739v1
2011-06-17,"Connected components of definable groups, and o-minimality II","We study the connected components G^00, G^000 and their quotients for a group
G definable in a saturated o-minimal expansion of a real closed field. We show
that G^00/G^000 is naturally the quotient of a connected compact commutative
Lie group by a dense finitely generated subgroup. We also highlight the role of
universal covers of semisimple Lie groups.",1106.3442v1
2011-07-06,Forward and Mueller-Navelet Jets,"We discuss the production of forward jets in high energy processes where one
probes a dense hadronic wavefunction. In particular, and as a signature of
parton saturation, we discuss the possibility of a strong momentum
decorrelation in Mueller-Navelet jets which leads to a geometric scaling
behavior.",1107.1269v1
2011-07-29,Neutrinoless Double Beta Decay and Heavy Sterile Neutrinos,"The experimental rate of neutrinoless double beta decay can be saturated by
the exchange of virtual sterile neutrinos, that mix with the ordinary neutrinos
and are heavier than 200 MeV. Interestingly, this hypothesis is subject only to
marginal experimental constraints, because of the new nuclear matrix elements.
This possibility is analyzed in the context of the Type I seesaw model,
performing also exploratory investigations of the implications for heavy
neutrino mass spectra, rare decays of mesons as well as neutrino-decay search,
LHC, and lepton flavor violation. The heavy sterile neutrinos can saturate the
rate only when their masses are below some 10 TeV, but in this case, the
suppression of the light-neutrino masses has to be more than the ratio of the
electroweak scale and the heavy-neutrino scale; i.e., more suppressed than the
naive seesaw expectation. We classify the cases when this condition holds true
in the minimal version of the seesaw model, showing its compatibility (1) with
neutrinoless double beta rate being dominated by heavy neutrinos and (2) with
any light neutrino mass spectra. The absence of excessive fine-tunings and the
radiative stability of light neutrino mass matrices, together with a saturating
sterile neutrino contribution, imply an upper bound on the heavy neutrino
masses of about 10 GeV. We extend our analysis to the Extended seesaw scenario,
where the light and the heavy sterile neutrino contributions are completely
decoupled, allowing the sterile neutrinos to saturate the present experimental
bound on neutrinoless double beta decay. In the models analyzed, the rate of
this process is not strictly connected with the values of the light neutrino
masses, and a fast transition rate is compatible with neutrinos lighter than
100 meV.",1108.0004v2
2011-10-10,Chief factors covered by projectors of soluble Leibniz algebras,"Let F be a saturated formation of soluble Leibniz algebras. Let K be an
F-projector and A/B a chief factor of the soluble Leibniz algebra L. It is
well-known that if A/B is F-central, then K covers A/B. I prove the converse:
if K covers A/B, then A/B is F-central.",1110.1932v1
2011-10-18,A survey of the parameter space of the compressible liquid drop model as applied to the neutron star inner crust,"We present a systematic survey the range of predictions of the neutron star
inner crust composition, crust-core transition densities and pressures, and
density range of the nuclear `pasta' phases at the bottom of the crust provided
by the compressible liquid drop model in the light of current experimental and
theoretical constraints on model parameters. Using a Skyrme-like model for
nuclear matter, we construct baseline sequences of crust models by consistently
varying the density dependence of the bulk symmetry energy at nuclear
saturation density, $L$, under two conditions: (i) that the magnitude of the
symmetry energy at saturation density $J$ is held constant, and (ii) $J$
correlates with $L$ under the constraint that the pure neutron matter (PNM) EoS
satisfies the results of ab-initio calculations at low densities. Such baseline
crust models facilitate consistent exploration of the $L$ dependence of crustal
properties. The remaining surface energy and symmetric nuclear matter
parameters are systematically varied around the baseline, and different
functional forms of the PNM EoS at sub-saturation densities implemented, to
estimate theoretical `error bars' for the baseline predictions. Inner crust
composition and transition densities are shown to be most sensitive to the
surface energy at very low proton fractions and to the behavior of the
sub-saturation PNM EoS. Recent calculations of the energies of neutron drops
suggest that the low-proton-fraction surface energy might be higher than
predicted in Skyrme-like models, which our study suggests may result in a
greatly reduced volume of pasta in the crust than conventionally predicted.",1110.4043v2
2011-11-29,"Numerical simulation of turbulent sediment transport, from bed load to saltation","Sediment transport is studied as a function of the grain to fluid density
ratio using two phase numerical sim- ulations based on a discrete element
method (DEM) for particles coupled to a continuum Reynolds averaged description
of hydrodynamics. At a density ratio close to unity (typically under water),
vertical velocities are so small that sediment transport occurs in a thin layer
at the surface of the static bed, and is called bed load. Steady, or
'saturated' transport is reached when the fluid borne shear stress at the
interface between the mobile grains and the static grains is reduced to its
threshold value. The number of grains transported per unit surface is therefore
limited by the flux of horizontal momentum towards the surface. However, the
fluid velocity in the transport layer remains almost undisturbed so that the
mean grain velocity scales with the shear velocity u\ast. At large density
ratio (typically in air), the vertical velocities are large enough to make the
transport layer wide and dilute. Sediment transport is then called saltation.
In this case, particles are able to eject others when they collide with the
granular bed, a process called splash. The number of grains transported per
unit surface is selected by the balance between erosion and deposition and
saturation is reached when one grain is statistically replaced by exactly one
grain after a collision, which has the consequence that the mean grain velocity
remains independent of u\ast. The influence of the density ratio is
systematically studied to reveal the transition between these two transport
regimes. Based on the mechanisms identified in the steady case, we discuss the
transient of saturation of sediment transport and in particular the saturation
time and length. Finally, we investigate the exchange of particles between the
mobile and static phases and we determine the exchange time of particles.",1111.6898v2
2011-12-13,Strongly inessential elements of a perfect height 2 ideal,"In this paper we expand on some results exposed in a previous one, in which
we introduced the concept of inessential and strongly inessential generators in
a standard basis of a saturated homogeneous ideal. The appearance of strongly
inessential elements seemed to be a non generic situation; in this paper we
analyze their presence in a perfect height 2 ideal with the greatest number of
generators, according to Dubreil's inequality.",1112.2875v1
2011-12-19,Forward physics hard processes and saturation: theory and phenomenology review,"Selected aspects of the theory and phenomenology of production of forward
jets at the LHC and RHIC are overviewed. In the theory part we discuss basics
of frameworks originating from the BFKL dynamics while in the phenomenology
part we present results for forward-central jet correlations at the LHC and
forward di-jet production at RHIC.",1112.4361v1
2012-01-16,"Comment on ""Rotary Photon Drag Enhanced by a Slow-Light Medium [1]""","The observations reported by Franke-Arnold et al (SCIENCE Reports, 1 July
2011 p. 65) do not provide evidence of slow light enhanced rotary photon drag
as claimed, but arise from well-known saturable absorption phenomena consistent
with the use of a spectrally broad light source, as described in their
theoretical analysis (supporting online material)",1201.3226v1
2012-02-11,On Patchworks and Hierarchies,"Motivated by questions in biological classification, we discuss some
elementary combinatorial and computational properties of certain set systems
that generalize hierarchies, namely, 'patchworks', 'weak patchworks', 'ample
patchworks' and 'saturated patchworks' and also outline how these concepts
relate to an apparently new 'duality theory' for cluster systems that is based
on the fundamental concept of 'compatibility' of clusters.",1202.2460v1
2012-04-26,Sub-Wavelength Nonlinear Accelerating Beams,"We show that optical nonlinearities allow sub-wavelength beams to propagate
in circular trajectories without being attenuated in spite of their partially
evanescent spectrum. Such beams are exact solutions to Maxwell's equations with
Kerr or saturable nonlinearity.",1204.5866v1
2012-05-02,A remark on the definability of the Fitting subgroup and the soluble radical,"Let $G$ be an arbitrary group. We show that if the Fitting subgroup of $G$ is
nilpotent then it is definable. We show also that the class of groups whose
Fitting subgroup is nilpotent of class at most $n$ is elementary. We give an
example of a group (arbitrary saturated) whose Fitting subgroup is definable
but not nilpotent. Similar results for the soluble radical are given.",1205.0573v1
2012-05-21,Tricritical quantum point and inflationary cosmology,"The holographic protection due to inflationary cosmology is a conse- quence
of a quantum tricritical point. In this scenario a closed spacetime solution
transitions into an inflationary de Sitter spacetime. Saturation of the
holographic entropy bound is prevented by the phase change in the topology of
the early universe.",1205.4710v1
2012-06-06,Nonlinear extension of the CCFM equation,"In order to study such effects like parton saturation in final states at the
LHC one of the approaches is to combine physics of the BK and the CCFM
evolution equations. We report on recently obtained resummed form of the BK
equation and nonlinear extension of the CCFM equation.",1206.1223v1
2012-06-13,Fusion systems on bicyclic 2-groups,"We classify all (saturated) fusion systems on bicyclic 2-groups. Here, a
bicyclic group is a product of two cyclic subgroups. This extends previous work
on fusion systems on metacyclic 2-groups (see [Craven-Glesser, 2012] and
[Sambale, 2012]). As an application we prove Olsson's Conjecture for all blocks
with bicyclic defect groups.",1206.2962v3
2012-09-14,The Color Glass Condensate and some applications,"We give an elementary discussion of parton saturation and its description by
the effective theory of the Color Glass Condensate. We report on progress in
calculating multi-gluon correlators. The latter are necessary for many
phenomenological applications, upon some of which we briefly touch.",1209.3183v1
2012-09-14,Passively Q-switched Ytterbium and Chromium all-fibre laser,"A chromium-doped saturable absorber fibre stabilizes an otherwise
spontaneously chaotic ytterbium- doped fibre laser. This original passively
Q-switched all-fibre laser produces sustained and stable trains of smooth
pulses at high repetition rate.",1209.3222v1
2012-10-11,The bar instability revisited,"The river bar instability is revisited, using a hydrodynamical model based on
Reynolds averaged Navier-Stokes equations. The results are contrasted with the
standard analysis based on shallow water Saint-Venant equations. We first show
that the stability of both transverse modes (ripples) and of small wavelength
inclined modes (bars) predicted by the Saint-Venant approach are artefacts of
this hydrodynamical approximation. When using a more reliable hydrodynamical
model, the dispersion relation does not present any maximum of the growth rate
when the sediment transport is assumed to be locally saturated. The analysis
therefore reveals the fundamental importance of the relaxation of sediment
transport towards equilibrium as it it is responsible for the stabilisation of
small wavelength modes. This dynamical mechanism is characterised by the
saturation number, defined as the ratio of the saturation length to the water
depth Lsat/H. This dimensionless number controls the transition from ripples
(transverse patterns) at small Lsat/H to bars (inclined patterns) at large
Lsat/H. At a given value of the saturation number, the instability presents a
threshold and a convective-absolute transition, both controlled by the channel
aspect ratio {\beta}. We have investigated the characteristics of the most
unstable mode as a function of the main parameters, Lsat/H, {\beta} and of a
subdominant parameter controlling the relative influence of drag and gravity on
sediment transport. As previously found, the transition from alternate bars to
multiple bars is mostly controlled by the river aspect ratio {\beta}. By
contrast, in the alternate bar regime (large Lsat/H), the selected wavelength
does not depend much on {\beta} and approximately scales as H^(2/3)L^(1/3)/C,
where C is the Ch\'ezy number.",1210.3223v1
2012-11-16,Some aspects of final states and QCD evolution equations,"In order to study such effects like parton saturation in final states at the
LHC one of the approaches is to combine physics of the BK and the CCFM
evolution equations. We report on recently obtained resummed form of the BK
equation and nonlinear extension of the CCFM equation - the KGBJS equation.",1211.3777v1
2012-11-28,Trees of Fusion Systems,"We define a `tree of fusion systems' and give a sufficient condition for its
completion to be saturated. We apply this result to enlarge an arbitrary fusion
system by extending the automorphism groups of certain of its subgroups.",1211.6700v3
2013-01-28,On some automatic continuity theorems,"We give characterizations of unital uniform topological algebras and
saturated locally multiplicatively convex algebras by means of multiplicative
linear functionals. Some automatic continuity theorems in advertibly complete
uniform topological algebras are extended to a larger class of algebras.
Consequences and applications are given.",1301.6549v1
2013-02-08,Short probabilistic proof of the Brascamp-Lieb and Barthe theorems,"We give a short proof of the Brascamp-Lieb theorem, which asserts that a
certain general form of Young's convolution inequality is saturated by Gaussian
functions. The argument is inspired by Borell's stochastic proof of the
Pr\'ekopa-Leindler inequality and applies also to the reversed Brascamp-Lieb
inequality, due to Barthe.",1302.2066v1
2013-03-21,Droplet condensation and isoperimetric towers,"We consider a variational problem in a planar convex domain, motivated by
statistical mechanics of crystal growth in a saturated solution. The minimizers
are constructed explicitly and are completely characterized.",1303.5202v1
2013-04-02,"The BPS spectrum of the 4d N=2 SCFT's H_1, H_2, D_4, E_6, E_7, E_8","Extending results of arXiv:1112.3984, we show that all rank 1 N=2 SCFT's in
the sequence H_1, H_2, D_4 E_6, E_7, E_8 have canonical finite BPS chambers
containing precisely 2 h(F)=12(Delta-1) hypermultiplets. The BPS spectrum of
the canonical BPS chambers saturates the conformal central charge c, and
satisfies some intriguing numerology.",1304.0614v1
2013-05-13,An interatomic potential for saturated hydrocarbons based on the modified embedded-atom method,"In this work, we developed an interatomic potential for saturated
hydrocarbons using the modified embedded-atom method (MEAM), a reactive
semi-empirical many-body potential based on density functional theory and pair
potentials. We parameterized the potential by fitting to a large experimental
and first-principles (FP) database consisting of 1) bond distances, bond
angles, and atomization energies at 0 K of a homologous series of alkanes and
their select isomers from methane to n-octane, 2) the potential energy curves
of H$_2$, CH, and C$_2$ diatomics, 3) the potential energy curves of hydrogen,
methane, ethane, and propane dimers, i.e., (H$_2$)$_2$, (CH$_4$)$_2$,
(C$_2$H$_6$)$_2$, and (C$_3$H$_8$)$_2$, respectively, and 5)
pressure-volume-temperature (PVT) data of a dense high-pressure methane system
with the density of 0.5534 g/cc. We compared the atomization energies and
geometries of a range of linear alkanes, cycloalkanes, and free radicals
calculated from the MEAM potential to those calculated by other commonly used
reactive potentials for hydrocarbons, i.e., second-generation reactive
empirical bond order (REBO) and reactive force field (ReaxFF). MEAM reproduced
the experimental and/or FP data with accuracy comparable to or better than REBO
or ReaxFF. The experimental PVT data for a relatively large series of methane,
ethane, propane, and butane systems with different densities were predicted
reasonably well by MEAM. Although the MEAM formalism has been applied to atomic
systems with predominantly metallic bonding in the past, the current work
demonstrates the promising extension of the MEAM potential to covalently bonded
molecular systems, specifically saturated hydrocarbons and saturated
hydrocarbon-based polymers.",1305.2759v7
2013-06-15,Thresholds of Spatially Coupled Systems via Lyapunov's Method,"The threshold, or saturation phenomenon of spatially coupled systems is
revisited in the light of Lyapunov's theory of dynamical systems. It is shown
that an application of Lyapunov's direct method can be used to quantitatively
describe the threshold phenomenon, prove convergence, and compute threshold
values. This provides a general proof methodology for the various systems
recently studied. Examples of spatially coupled systems are given and their
thresholds are computed.",1306.3610v1
2013-06-19,Nonlinear Control of Absorption in Graphene-based 1D Photonic Crystal,"Perfect, narrow-band absorption is achieved in an asymmetric 1D photonic
crystal with a monolayer graphene defect. Thanks to the large third order
nonlinearity of graphene and field localization in the defect layer we
demonstrate the possibility to achieve controllable, saturable absorption for
the pump frequency.",1306.4607v1
2013-07-25,Neutron Star Matter,"In this presentation I discuss two aspects of the neutron-matter equation of
state. One relates to the symmetry energy of nuclear matter and empirical
constraints on its slope parameter at saturation density. The second deals with
spatially inhomogeneous chiral phases of deconfined quark matter in the inner
core of a neutron star.",1307.6714v1
2013-10-31,Absolute Algebra III - The saturated spectrum,"Let B1 denote the set {0,1} with the usual operations except that $1+1=1$, in
other words, the smallest characteristic 1 semifield . We compare two possible
analogues of the notion of prime ideal for B1--algebras. We then consider the
relations between these notions and Deitmar's theory of F1--schemes.",1310.8399v1
2013-11-15,A theorem of Mislin for cohomology of fusion systems and applications to block algebras of finite groups,"We give an algebraic proof for a theorem of Mislin in the case of cohomology
of saturated fusion systems defined on p-groups when p is odd. Some
applications of this theorem to block algebras of finite groups are also given.",1311.3944v2
2013-11-28,Potential of a longitudinally focusing insertion for a storage ring X-ray FEL,"In present work we investigate the potential of a longitudinally focusing
device to compress bunches passing an undulator for a synchrotron storage ring.
If integrated into a storage ring similar to PETRAIII such device could
potentially produce continuous $\sim$1ps pulses of photons in the $nm$ range
with peak pulse powers of tens of GW. Even without operating in FEL saturation
mode the longitudinal focusing can provide means to increase the brightness and
shorten the photon pulse length.",1311.7428v1
2013-12-20,"Thermalization, Isotropization and Elliptic Flow from Nonequilibrium Initial Conditions with a Saturation Scale","In this article we report on our results about the computation of the
elliptic flow of the quark-gluon-plasma produced in relativistic heavy ion
collisions, simulating the expansion of the fireball by solving the
relativistic Boltzmann equation for the parton distribution function tuned at a
fixed shear viscosity to entropy density ratio $\eta/s$. Our main goal is to
put emphasis on the role of a saturation scale in the initial gluon spectrum,
which makes the initial distribution far from a thermalized one. We find that
the presence of the saturation scale reduces the efficiency in building-up the
elliptic flow, even if the thermalization process is quite fast $\tau_{therm}
\approx 0.8 \,\rm fm/c$ and the pressure isotropization even faster
$\tau_{isotr} \approx 0.3 \,\rm fm/c$. The impact of the non-equilibrium
implied by the saturation scale manifests for non-central collisions and can
modify the estimate of the viscosity respect to the assumption of full
thermalization in $p_T$-space. We find that the estimate of $\eta/s$ is
modified from $\eta/s \approx 2/4\pi$ to $\eta/s \approx 1/4\pi$ at RHIC and
from $\eta/s \approx 3/4\pi$ to $\eta/s \approx 2/4\pi$ at LHC. We complete our
investigation by a study of the thermalization and isotropization times of the
fireball for different initial conditions and values of $\eta/s$ showing how
the latter affects both isotropization and thermalization. Lastly, we have seen
that the range of values explored by the phase-space distribution function $f$
is such that at $p_T<0.5\, \rm GeV$ the inner part of the fireball stays with
occupation number significantly larger than unity despite the fast longitudinal
expansion, which might suggest the possibility of the formation of a transient
Bose-Einstein Condensate.",1312.6060v2
2014-01-10,On a general definition of the squared Brunt-Väisälä Frequency associated with the specific moist entropy potential temperature,"The squared Brunt-V\""{a}is\""{a}l\""{a} Frequency (BVF) is computed in terms of
the moist entropy potential temperature recently defined in Marquet (2011).
Both homogeneously saturated and non-saturated versions of $N^2$ (the squared
BVF) are derived. The method employed for computing these special homogeneous
cases relies on the expression of density written as a function of pressure,
total water content and specific moist entropy only. The associated
conservative variable diagrams are discussed and compared with existing ones.
Despite being obtained without any simplification, the formulations for $N^2$
remain nicely compact and are clearly linked with the squared BVF expressed in
terms of the adiabatic non-saturated and saturated lapse rates. As in previous
similar expressions, the extreme homogeneous solutions for $N^2$ are of course
different, but they are not analytically discontinuous. This allows us to
define a simple bridging expression for a single general shape of $N^2$,
depending only on the basic mean atmospheric quantities and on a transition
parameter, to be defined (or parameterized) in connection with the type of
application sought. This integrated result remains a linear combination (with
complex but purely local weights) of two terms only, namely the environmental
gradient of the moist entropy potential temperature and the environmental
gradient of the total water content. Simplified versions of the various
equations are also proposed for the case in which the moist entropy potential
temperature is approximated by a function of both so-called moist-conservative
variables of Betts (1973).",1401.2379v2
2014-01-19,Almost Prime Coordinates for Anisotropic and Thin Pythagorean Orbits,"We make an observation which doubles the exponent of distribution in certain
Affine Sieve problems, such as those considered by Liu-Sarnak, Kontorovich, and
Kontorovich-Oh. As a consequence, we decrease the known bounds on the
saturation numbers in these problems.",1401.4701v1
2014-01-30,Fitting N$^{3}$LO pseudopotentials through central plus tensor Landau parameters,"Landau parameters determined from phenomenological finite-range interactions
are used to get an estimation of N$^3$LO pseudopotentials parameters. The
parameter sets obtained in this way are shown to lead to consistent results
concerning saturation properties. The uniqueness of this procedure is
discussed, and an estimate of the error induced by the truncation at N$^3$LO is
given.",1401.7914v1
2014-03-13,A Sensitive Identification of Warm Debris Disks in the Solar Neighborhood Through Precise Calibration of Saturated WISE Photometry,"We present a sensitive search for WISE W3 (12um) and W4 (22um) excesses from
warm optically thin dust around Hipparcos main sequence stars within 75pc from
the Sun. We use contemporaneously measured photometry from WISE, remove sources
of contamination, and derive and apply corrections to saturated fluxes to
attain optimal sensitivity to >10um excesses. We use data from the WISE All-Sky
Survey Catalog rather than the AllWISE release, because we find that its
saturated photometry is better behaved, allowing us to detect small excesses
even around saturated stars in WISE. Our new discoveries increase by 45% the
number of stars with warm dusty excesses and expand the number of known debris
disks (with excess at any wavelength) within 75pc by 29%. We identify 220
Hipparcos debris disk-host stars, 108 of which are new detections at any
wavelength. We present the first measurement of a 12um and/or 22um excess for
10 stars with previously known cold (50-100 K) disks. We also find five new
stars with small but significant W3 excesses, adding to the small population of
known exozodi, and we detect evidence for a W2 excess around HIP96562 (F2V),
indicative of tenuous hot (780 K) dust. As a result of our WISE study, the
number of debris disks with known 10-30um excesses within 75pc (379) has now
surpassed the number of disks with known >30um excesses (289, with 171 in
common), even if the latter have been found to have a higher occurrence rate in
unbiased samples.",1403.3435v1
2014-03-18,Landscape disruption effects in a meta-epidemic model with steady state demographics and migrations saturation,"We continue the investigations of an ecosystem where a epidemic-affected
population can move between two connected patches, by considering what happens
to the system when the migration paths are interrupted in one direction, or
when the infected are not able to exert the effort for migrating into the other
patch.",1403.4470v1
2014-04-24,The number of orthogonal conjugations,"After a short introduction to anti-linearity, bounds for the number of
orthogonal (skew) conjugations are proved. They are saturated if the dimension
of the Hilbert space is a power of two. For the other dimensions this is an
open problem.",1404.6052v1
2014-05-12,Geometrical scaling and its breaking in high energy collisions,"We report on recent analyses of different pieces of data, which exhibit
Geometrical Scaling (GS) and its breaking. GS is a consequence of the existence
of an intermediate energy scale, called saturation momentum, and allows to
relate data at different energies, of different systems and also at different
multiplicities and/or centralities.",1405.2671v1
2014-05-19,Black hole mass determination in the X-ray binary 4U 1630--47: Scaling of spectral and variability characteristics,"We present the results of a comprehensive investigation on the evolution of
spectral and timing properties of the Galactic black hole candidate 4U 1630--47
during its spectral transitions. In particular, we show how a scaling of the
correlation of the photon index of the Comptonized spectral component Gamma
with low frequency of quasi-periodic oscillations (QPO), nu_L and mass
accretion rate, $\dot M$ can be applied to the black hole mass and the
inclination angle estimates. We analyze the transition episodes observed with
the {\it Rossi} X-ray Timing Explorer (RXTE) and BeppoSAX satellites. We find
that the broadband X-ray energy spectra of 4U~1630--47 during all spectral
states can be modeled by a combination of a thermal component, a Comptonized
component and a red-skewed iron line component. We also establish that Gamma
monotonically increases during transition from the low-hard state to the
high-soft state and then saturates for high mass accretion rates. The index
saturation levels vary for different transition episodes. Correlations of Gamma
versus nu_L also shows saturation at Gamma ~ 3. Gamma-Mdot and Gamma-nu_L
correlations with their index saturation revealed in 4U~1630--47 are similar to
those established in a number of other BHCs and can be considered as an
observational evidence for the presence of a black hole in these sources. The
scaling technique, which relies on XTE J1550--564, GRO 1655-40 and H 1743-322
as reference sources, allows us to evaluate a black hole mass in 4U~1630--47
yielding M_{BH}~10+/- 0.1 solar masses, and to constrain the inclination angle
of i< 70 degrees.",1405.4711v1
2014-06-02,Nuclear matter with JISP16 NN interaction,"Saturation properties of the JISP16 NN interaction are studied in symmetric
nuclear matter calculations, with special attention paid to the convergence
properties with respect to the number of partial waves. We also present results
of pure neutron matter calculations with the JISP16 interaction.",1406.0529v1
2014-06-23,Non-linear evolution equation for gluon density at large values of coupling constant,"The recently proposed nonlinear evolution equation \cite{Kutak:2013hda} for
unintegrated gluon densities valid for large values of the QCD coupling
constant $\bar{\alpha} _s$ is presented. In particular we outline its
derivation, numerical solution and obtained saturation scale.",1406.5897v1
2014-06-26,Strongly stable ideals and Hilbert polynomials,"The \texttt{StronglyStableIdeals} package for \textit{Macaulay2} provides a
method to compute all saturated strongly stable ideals in a given polynomial
ring with a fixed Hilbert polynomial. A description of the main method and
auxiliary tools is given.",1406.6924v2
2014-07-11,"Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength","Self-healing of polymer films often takes place as the molecules diffuse
across a damaged region, above their melting temperature. Using molecular
dynamics simulations we probe the healing of polymer films and compare the
results with those for thermal welding of homopolymer slabs. The two processes
differ in their interfacial structure since damage leads to increased
polydispersity and more short chains. A polymer sample was cut into two
separate films that were then held together in the melt state. The recovery of
the damaged film was followed as time elapsed and polymer molecules diffused
across the interface. The mass uptake and formation of entanglements, as
obtained from primitive path analysis, are extracted and correlated with the
interfacial strength obtained from shear simulations. We find that the
interdiffusion is significantly faster in the damaged film compared to welding
because of the presence of short chains. Though interfacial entanglements
increase more rapidly for the damaged films, a large fraction of them are near
chain ends. As a result, the interfacial strength of the healing film increases
more slowly than for welding. For both healing and welding, the interfacial
strength saturates as the bulk entanglement density is recovered across the
interface. However, the saturation strength of the damaged film is below the
bulk strength for the polymer sample. At saturation, cut chains remain near the
healing interface. They are less entangled and thus mechanically weaken the
interface. When the interfacial strength saturates, the number of interfacial
entanglements scales with the corresponding bulk entanglement density. Chain
stiffness increases the density of entanglements, which increases the
interfacial strength. Our results show that a few entanglements across the
interface are sufficient to resist interfacial chain pullout and enhance the
mechanical strength.",1407.3198v1
2014-07-21,Conditions for a Schunck class to be a formation,"A Schunck class H is determined by the class X of primitives contained in H.
We give necessary and sufficient conditions on X for H to be a saturated
formation.",1407.5692v2
2014-08-02,On the saturation number for cubic surfaces,"We investigate the density of rational points on the Fermat cubic surface and
the Cayley cubic surface whose coordinates have few prime factors. The key
tools used are the weighted sieve, the circle method and universal torsors.",1408.0402v2
2014-08-15,A presentation theorem for continuous logic and Metric Abstract Elementary Classes,"We give a presentation theorem for continuous first-order logic and Metric
Abstract Elementary classes in terms of $L_{\omega_1, \omega}$ and Abstract
Elementary Classes, respectively. This presentation is accomplished by
analyzing dense subsets that are closed under functions. We extend this
correspondence to types and saturation.",1408.3624v3
2014-10-03,Filtrations of Totally Reflexive Modules,"In this paper, we will introduce a subcategory of totally reflexive modules
that have a saturated filtration by other totally reflexive modules. We will
prove these are precisely the totally reflexive modules with an
upper-triangular presentation matrix. We conclude with an investigation of the
ranks of $\operatorname{Ext}^1$ of two such modules over a specific ring.",1410.0732v1
2014-10-08,Moduli of parabolic sheaves on a polarized logarithmic scheme,"We generalize the construction of moduli spaces of parabolic sheaves given by
Maruyama and Yokogawa in [MY92] to the case of a projective fine saturated log
scheme with a fixed global chart. Furthermore we construct moduli spaces of
parabolic sheaves without fixing the weights.",1410.2212v2
2014-10-09,The generic pair conjecture for dependent finite diagrams,"This paper generalizes Shelah's generic pair conjecture (now theorem) for the
measurable cardinal case from first order theories to finite diagrams. We use
homogeneous models in the place of saturated models.",1410.2516v4
2014-11-18,Strong monogamy of quantum entanglement for multi-qubit W-class states,"We provide a strong evidence for strong monogamy inequality of multi-qubit
entanglement recently proposed in [B. Regula {\em et al.}, Phys. Rev. Lett.
{\bf 113}, 110501 (2014)]. We consider a large class of multi-qubit generalized
W-class states, and analytically show that the strong monogamy inequality of
multi-qubit entanglement is saturated by this class of states.",1411.4721v1
2014-12-01,The subgroup homology decomposition for fusion systems is sharp,"We extend Dwyer's sharp subgroup homology decomposition of the classifying
space of a finite group to arbitrary saturated fusion systems and arbitrary
Mackey functors.",1412.0378v2
2014-12-24,Why are there three generations of fermions in the standard model?,"We show that by decomposing the gauge fields in fermion degrees of freedom
and by saturating the remaining degrees of freedom as dynamical fields in the
Lagrangian one might explain the proliferation of fermion states in the
standard model Lagrangian. Thus the mere presence of the gauge symmetry $U(1)_Y
\times SU(2)_L \times SU(3)_c$ is essential.",1412.7658v1
2015-01-09,"Monitoring of saline tracer movement with vertically distributed self-potential measurements at the HOBE agricultural test site, Voulund, Denmark","The self-potential (SP) method is sensitive to water fluxes in saturated and
partially saturated porous media, such as those associated with rainwater
infiltration and groundwater recharge. We present a field-based study at the
Voulund agricultural test site, Denmark, that is, to the best of our knowledge,
the first to focus on the vertical self-potential distribution prior to and
during a saline tracer test. A coupled hydrogeophysical modeling framework is
used to simulate the SP response to precipitation and saline tracer
infiltration. A layered hydrological model is first obtained by inverting
dielectric and matric potential data. The resulting model that compares
favorably with electrical resistance tomography models is subsequently used to
predict the SP response. The electrokinetic contribution (caused by water
fluxes in a charged porous soil) is modeled by an effective excess charge
approach that considers both water saturation and pore water salinity. Our
results suggest that the effective excess charge evolution prior to the tracer
injection is better described by a recent flux-averaged model based on soil
water retention functions than by a previously proposed volume-averaging model.
This is the first time that raw vertically distributed SP measurements have
been explained by a physically based model. The electrokinetic contribution
cannot alone reproduce the SP data during the tracer test and an
electro-diffusive contribution (caused by concentration gradients) is needed.
The predicted amplitude of this contribution is too small to perfectly explain
the data, but the shape is in accordance with the field data. This discrepancy
is attributed to imperfect descriptions of electro-diffusive phenomena in
partially saturated soils, unaccounted soil heterogeneity, and discrepancies
between the measured and predicted electrical conductivities in the tracer
infiltration area.",1501.02277v1
2015-03-08,Structure Constants for Immaculate Functions,"The immaculate functions, $\mathfrak{S}_{\alpha}$, were introduced as a
Schur-like basis for $\operatorname{\mathsf{Nsym}}$. We investigate facts about
their structure constants. These are analogues of Littlewood-Richardson
coefficents. We will give a new proof of the left Pieri rule for the
$\mathfrak{S}_{\alpha}$, a translation invariance property for the structure
coefficients of the $\mathfrak{S}_{\alpha}$, and a counterexample to an
$\mathfrak{S}_{\alpha}$-analogue of the saturation conjecture.",1503.02285v2
2015-04-01,On Stability of the Linearized Spacecraft Attitude Control System,"This note is concerned with the stability and stabilization of the linearized
spacecraft attitude control system. Necessary and sufficient conditions are
respectively provided to guarantee that the considered systems are polynomially
stable and stable in the Lyapunov sense. These two classes of conditions
guarantee that the linearized spacecraft attitude control system can be
respectively stabilized semi-globally and globally by saturated linear state
feedback.",1504.00114v1
2015-05-12,Microfiber-based few-layer black phosphorus saturable absorber for ultra-fast fiber laser,"Few-layer black phosphorus (BP), as the most alluring graphene analogue owing
to its similar structure as graphene and thickness dependent direct band-gap,
has now triggered a new wave of research on two-dimensional (2D) materials
based photonics and optoelectronics. However, a major obstacle of practical
applications for few-layer BPs comes from their instabilities of laser-induced
optical damage. Herein, we demonstrate that, few-layer BPs, fabricated through
the liquid exfoliation approach, can be developed as a new and practical
saturable absorber (SA) by depositing few-layer BPs with microfiber. The
saturable absorption property of few-layer BPs had been verified through an
open-aperture z-scan measurement at the telecommunication band and the
microfiber-based BP device had been found to show a saturable average power of
~4.5 mW and a modulation depth of 10.9%, which is further confirmed through a
balanced twin detection measurement. By further integrating this optical SA
device into an erbium-doped fiber laser, it was found that it can deliver the
mode-locked pulse with duration down to 940 fs with central wavelength tunable
from 1532 nm to 1570 nm. The prevention of BP from oxidation through the
'lateral interaction scheme' owing to this microfiber-based few-layer BP SA
device might partially mitigate the optical damage problem of BP. Our results
not only demonstrate that black phosphorus might be another promising SA
material for ultrafast photonics, but also provide a practical solution to
solve the optical damage problem of black phosphorus by assembling with
waveguide structures such as microfiber.",1505.03035v2
2015-09-22,Surface ages of mid-size Saturnian satellites,"The observations of the surfaces of the mid sized Saturnian satellites made
by Cassini Huygens mission have shown a variety of features that allows study
of the processes that took place and are taking place on those worlds. Research
of the Saturnian satellite surfaces has clear implications for Saturn history
and surroundings. In a recent paper, the production of craters on the mid sized
Saturnian satellites by Centaur objects was calculated considering the current
Solar System. We have compared our results with crater counts from Cassini
images and we have noted that the number of observed small craters is less than
our calculated number. In this paper we estimate the age of the surface for
each observed terrain on each mid sized satellite of Saturn. We have noticed
that since there are less observed small craters than calculated (except on
Iapetus), this results in younger ages. This could be the result of efficient
endogenous or exogenous process(es) for erasing small craters and or crater
saturation at those sizes. The size limit from which the observed number of
smaller craters is less than the calculated is different for each satellite,
possibly indicating processes that are unique to each, but other potential
common explanations would be crater saturation and or deposition of E ring
particles. These processes are also suggested by the findings that the smaller
craters are being preferentially removed, and the erasure process is gradual.
On Enceladus, only mid and high latitude plains have remnants of old terrains;
the other regions could be young; the regions near the South Polar Terrain
could be as young as 50 Myr old. On the contrary for Iapetus, all the surface
is old and it notably registers a primordial source of craters. As the crater
size is decreased, it would be perceived to approach saturation until D less
than 2 km craters, where saturation is complete.",1509.06773v1
2015-10-02,Analog Optical Computing Primitives in Silicon Photonics,"Optical computing accelerators may help alleviate bandwidth and power
consumption bottlenecks in electronics. We show an approach to implementing
logarithmic-type analog co-processors in silicon photonics and use it to
perform the exponentiation operation. The function is realized by exploiting
nonlinear-absorption-enhanced Raman amplification saturation in a silicon
waveguide.",1510.00489v1
2015-10-09,Arithmetic graphs of finite groups,"In this paper we introduced an arithmetic graph function which associates
with every group G the directed graph whose vertices corresponds to the
divisors of |G|. With the help of such functions we introduced arithmetic
graphs of classes of groups, in particular of hereditary saturated formations.
We formulated the problem of the recognition of classes of groups by arithmetic
graph functions and investigated this problem for some arithmetic graph
functions.",1510.02568v1
2015-10-21,On cuts in ultraproducts of linear orders I,"For an ultrafilter $D$ on a cardinal $\kappa,$ we wonder for which pair
$(\theta_1, \theta_2)$ of regular cardinals, we have: for any
$(\theta_1+\theta_2)^+-$saturated dense linear order $J, J^{\kappa}/ D$ has a
cut of cofinality $(\theta_1, \theta_2).$ We deal mainly with the case
$\theta_1, \theta_2 > 2^\kappa.$",1510.06278v3
2015-10-26,Problems related to the concentration of eigenfunctions,"We survey recent results related to the concentration of eigenfunctions. We
also prove some new results concerning ball-concentration, as well as showing
that eigenfunctions saturating lower bounds for $L^1$-norms must also, in a
measure theoretical sense, have extreme concentration near a geodesic.",1510.07723v1
2015-11-07,Propagation of Acoustical Wave in Finite Cylindrical Solid Bar surrounded by Semi-Infinite Porous Media saturated with Fluid,"We established the propagation equation of acoustical wave in media with the
solid/porous media cylindrical boundary and obtained the analytic solution. We
suggested the boundary condition on solid-porous media cylindrical boundary.
Based on that, we introduced the dispersion equation, and constructed the
algorithm to perform numerical calculation and analysis of dispersion equation.",1511.03134v1
2016-04-21,On the Ramsey Numbers of Trees with Small Diameter,"We estimate the Ramsey number r(T) = r(T,T) for various trees T, obtaining a
precise value for r(T) for a large number of trees of diameter 3. Furthermore
we prove that all trees of diameter 3 are Ramsey unsaturated as defined by
Balister, Lehel, and Schelp in their article ""Ramsey unsaturated and saturated
graphs.""",1604.06513v1
2016-07-04,Branching Random Walks on Binary Strings for Evolutionary Processes,"In this article, we study branching random walks on graphs modeling
division-mutation processes inspired by adaptive immunity. We apply the theory
of expander graphs on mutation rules in evolutionary processes and obtain
estimates for the cover times of the branching random walks. This analysis
reveals an unexpected saturation phenomenon : increasing the mutation rate
above a certain threshold does not enhance the speed of state-space
exploration.",1607.00927v1
2016-08-15,Narumi-Katayama Index of Total Transformation Graphs,"The Narumi-Katayama index of a graph was introduced in 1984 for representing
the carbon skeleton of a saturated hydrocarbons and is defined as the product
of degrees of all the vertices of the graph. In this paper, we examine the
Narumi-Katayama index of different total transformation graphs.",1608.04319v1
2016-08-16,Saturation effects in low-x DIS structure functions and related hadronic total cross sections,"High-energy nucleon total cross sections are related to low-x DIS structure
functions by using the additive quark model.",1608.04646v1
2016-09-21,An Indecomposable and unconditionally saturated Banach space,"We construct an indecomposable reflexive Banach space $X_{ius}$ such that
every infinite dimensional closed subspace contains an unconditional basic
sequence. We also show that every operator $T\in \mathcal{B}(X_{ius})$ is of
the form $\lambda I+S$ with $S$ a strictly singular operator.",1609.06509v1
2016-11-01,Two-dimensional extremely short optical pulses in silicene with random electric fields,"We investigate an influence of the random external electric field on the 2D
extremely short optical pulses propagation in the silicene. The random electric
field is perpendicular to the silicene plane. An effective equation has the
form of a wave equation with saturating nonlinearity. We analyze the
dependences of the electromagnetic field intensity on the parameters of a
problem.",1611.01106v1
2016-11-14,Control of Fusion by Abelian Subgroups of the Hyperfocal Subgroup,"We prove that an isomorphism between saturated fusion systems over the same
finite p-group is detected on the elementary abelian subgroups of the
hyperfocal subgroup if p is odd, and on the abelian subgroups of the hyperfocal
subgroup of exponent at most 4 if p = 2. For odd p, this has implications for
mod p group cohomology.",1611.04403v1
2016-11-14,On the quasi-$\mathfrak{F}$-hypercenter of a finite group,"In this paper some properties of the $\mathfrak{F}^*$-hypercenter of a finite
group are studied where $\mathfrak{F}^*$ is the class of all finite
quasi-$\mathfrak{F}$-groups for a hereditary saturated formation $\mathfrak{F}$
of finite groups. In particular, it is shown that the quasinilpotent
hypercenter of a finite group coincides with the intersection of all maximal
quasinilpotent subgroups.",1611.04507v1
2016-11-28,The Nonlinear Theory of FEL,"The nonlinear theory of relyativistic strophotron is developed. Classical
equations of motion are averaged over fast oscillations. The slow motion phase
and saturation parameter are found different from usual undulator oscillation
parameters. In the strong field approximation the analytical expression of gain
is found on higher harmonics of main resonance frequency.",1611.09249v2
2017-06-01,"Quantales and their modules: projective objects, ideals, and congruences","In this paper we characterize the projective modules over an arbitrary
quantale, and then we apply such a characterization in order to define the K_0
group of a quantale. Then we study congruences of quantales and quantale
modules by means of their ideals and of saturated elements w.r.t. a binary
relation.",1706.00135v1
2017-07-13,The study on quantum material WTe2,"WTe2 and its sister alloys have attracted tremendous attentions recent years
due to the large non-saturating magnetoresistance and topological non-trivial
properties. Herein, we briefly review the electrical property studies on this
new quantum material.",1707.04132v1
2017-09-06,Chaos in Saw Map,"We consider dynamics of a scalar piecewise linear ""saw map"" with infinitely
many linear segments. In particular, such maps are generated as a Poincar\'e
map of simple two-dimensional discrete time piecewise linear systems involving
a saturation function. Alternatively, these systems can be viewed as a feedback
loop with the so-called stop hysteresis operator. We analyze chaotic sets and
attractors of the ""saw map"" depending on its parameters.",1709.01962v1
2017-09-11,Dual virtual element method in presence of an inclusion,"We consider a Darcy problem for saturated porous media written in dual
formulation in presence of a fully immersed inclusion. The lowest order virtual
element method is employ to derive the discrete approximation. In the present
work we study the effect of cells with cuts on the numerical solution, able to
geometrically handle in a more natural way the inclusion tips. The numerical
results show the validity of the proposed approach.",1709.03519v1
2017-09-25,Star Saturation Number of Random Graphs,"For a given graph $F$, the $F$-saturation number of a graph $G$ is the
minimum number of edges in an edge-maximal $F$-free subgraph of $G$. Recently,
the $F$-saturation number of the Erd\H{o}s$\text{\bf--}$R\'enyi random graph
$\mathbbmsl{G}(n, p)$ has been determined asymptotically for any complete graph
$F$. In this paper, we give an asymptotic formula for the $F$-saturation number
of $\mathbbmsl{G}(n, p)$ when $F$ is a star graph.",1709.08433v1
2017-10-09,The small index property for homogeneous models in AECs,"We prove a version of a small index property theorem for strong amalgamation
classes. Our result builds on an earlier theorem by Lascar and Shelah (in their
case, for saturated models of uncountable first-order theories). We then study
versions of the small index property for various non-elementary classes. In
particular, we obtain the small index property for quasiminimal pregeometry
structures.",1710.02920v1
2017-10-19,Fusion systems containing pearls,"An $\mathcal{F}$-essential subgroup is called a pearl if it is either
elementary abelian of order $p^2$ or non-abelian of order $p^3$. In this paper
we start the investigation of fusion systems containing pearls: we determine a
bound for the order of $p$-groups containing pearls and we classify the
saturated fusion systems on $p$-groups containing pearls and having sectional
rank at most $4$.",1710.07088v2
2017-11-12,Double plasma resonance instability as a source of solar zebra emission,"The double plasma resonance (DPR) instability plays a basic role in the
generation of solar radio zebras. In the plasma, consisting of the loss-cone
type distribution of hot electrons and much denser and colder background
plasma, this instability generates the upper-hybrid waves, which are then
transformed into the electromagnetic waves and observed as radio zebras. In the
present paper we numerically study the double plasma resonance instability from
the point of view of the zebra interpretation. We use a 3-dimensional
electromagnetic particle-in-cell (3-D PIC) relativistic model. First using the
multi-mode model, we study details of the double plasma resonance instability.
We show how the distribution function of hot electrons changes during this
instability. Then we show that there is a very good agreement between results
obtained by the multi-mode and specific-mode models, which is caused by a
dominance of the wave with the maximal growth rate. Therefore, for computations
in a broad range of model parameters, we use the specific-mode model. We
compute the maximal growth rates of the double plasma resonance instability.
The results are compared with the analytical ones. We find a very good
agreement between numerical and analytical growth rates. We also compute
saturation energies of the upper-hybrid waves in a very broad range of
parameters. We find that the saturation energies of the upper-hybrid waves show
maxima and minima at almost the same values of
$\omega_\mathrm{UH}/\omega_\mathrm{ce}$ as the growth rates. Furthermore, we
find that the saturation energy of the upper-hybrid waves is proportional to
the density of hot electrons. The maximum saturated energy can be up to one
percent of the kinetic energy of hot electrons. All these findings can be used
in the interpretation of solar radio zebras.",1711.04281v1
2017-11-23,Hidden attractors in aircraft control systems with saturated inputs,"In the paper, the control problem with limitations on the magnitude and rate
of the control action in aircraft control systems, is studied. Existence of
hidden oscillations in the case of actuator position and rate limitations is
demonstrated by the examples of piloted aircraft pilot involved oscillations
(PIO) phenomenon and the airfoil flutter suppression system.",1711.10302v1
2017-12-08,$\mathcal{N}=2$ SCFT with minimal flavor central charge,"We list 4d interacting $\mathcal{N}=2$ SCFT with minimal flavor central
charge from the theory space constructed using 6d $(2,0)$ theory. For $ADE$ and
$C_N$ flavor groups, our theory saturates the bound found using bootstrap
method, but other cases have higher values. We find interesting rank one SCFTs
with $B_3, G_2, F_4, C_4\times U(1), C_1\times U(1)$ flavor symmetry. Many
physical properties of these theories are also studied.",1712.03244v1
2018-01-10,Recovery of Binary Sparse Signals with Biased Measurement Matrices,"This work treats the recovery of sparse, binary signals through
box-constrained basis pursuit using biased measurement matrices. Using a
probabilistic model, we provide conditions under which the recovery of both
sparse and saturated binary signals is very likely. In fact, we also show that
under the same condition, the solution of the boxed-constrained basis pursuit
program can be found using boxed-constrained least-squares.",1801.03381v1
2018-01-16,Centralizers of normal subsystems revisited,"In this paper we revisit two concepts which were originally introduced by
Aschbacher and are crucial in the theory of saturated fusion systems: Firstly,
we give a new approach to defining the centralizer of a normal subsystem.
Secondly, we revisit the construction of the product of two normal subsystems
which centralize each other.",1801.05256v2
2018-04-10,Counterexamples for Cohen-Macaulayness of Lattice Ideals,"Let $\mathscr{L}\subset \mathbb{Z}^n$ be a lattice, $I$ its corresponding
lattice ideal, and $J$ the toric ideal arising from the saturation of
$\mathscr{L}$. We produce infinitely many examples, in every codimension, of
pairs $I,J$ where one of these ideals is Cohen--Macaulay but the other is not.",1804.03647v1
2018-04-19,On Bogomolny equations in the Skyrme model,"Using the concept of strong necessary conditions (CSNC), we derive a complete
decomposition of the minimal Skyrme model into a sum of three coupled BPS
submodels with the same topological bound. The bounds are saturated if
corresponding Bogomolny equations, different for each submodel, are obeyed.",1804.09020v1
2018-06-11,Discontinuous Galerkin method for coupling hydrostatic free surface flows to saturated subsurface systems,"We formulate a coupled surface/subsurface flow model that relies on
hydrostatic equations with free surface in the free flow domain and on the
Darcy model in the subsurface part. The model is discretized using the local
discontinuous Galerkin method, and a statement of discrete energy stability is
proved for the fully non-linear coupled system.",1806.03909v1
2018-08-09,On Toric Orbits in the Affine Sieve,"We give a detailed analysis of a heuristic model for the failure of
""saturation"" in instances of the Affine Sieve having toral Zariski closure.
Based on this model, we formulate precise conjectures on several classical
problems of arithmetic interest, and test these against empirical data.",1808.03235v1
2018-09-06,GANs beyond divergence minimization,"Generative adversarial networks (GANs) can be interpreted as an adversarial
game between two players, a discriminator D and a generator G, in which D
learns to classify real from fake data and G learns to generate realistic data
by ""fooling"" D into thinking that fake data is actually real data. Currently, a
dominating view is that G actually learns by minimizing a divergence given that
the general objective function is a divergence when D is optimal. However, this
view has been challenged due to inconsistencies between theory and practice. In
this paper, we discuss of the properties associated with most loss functions
for G (e.g., saturating/non-saturating f-GAN, LSGAN, WGAN, etc.). We show that
these loss functions are not divergences and do not have the same equilibrium
as expected of divergences. This suggests that G does not need to minimize the
same objective function as D maximize, nor maximize the objective of D after
swapping real data with fake data (non-saturating GAN) but can instead use a
wide range of possible loss functions to learn to generate realistic data. We
define GANs through two separate and independent D maximization and G
minimization steps. We generalize the generator step to four new classes of
loss functions, most of which are actual divergences (while traditional G loss
functions are not). We test a wide variety of loss functions from these four
classes on a synthetic dataset and on CIFAR-10. We observe that most loss
functions converge well and provide comparable data generation quality to
non-saturating GAN, LSGAN, and WGAN-GP generator loss functions, whether we use
divergences or non-divergences. These results suggest that GANs do not conform
well to the divergence minimization theory and form a much broader range of
models than previously assumed.",1809.02145v1
2018-10-19,A Survey on The Ideal Structure of Leavitt Path Algebras,"There is an extensive recent literature on the graded, non-graded, prime,
primitive, maximal ideals of Leavitt path algebras. In this introductory level
survey, we will be giving an overview of different types of ideals and the
correspondence between the lattice of ideals and the lattice of hereditary and
saturated subsets of the graph over which the Leavitt path algebra is
constructed.",1810.08602v1
2018-10-22,Keisler's order via Boolean ultrapowers,"In this paper, we provide a new characterization of Keisler's order in terms
of saturation of Boolean ultrapowers. To do so, we apply and expand the
framework of 'separation of variables' recently developed by Malliaris and
Shelah. We also show that good ultrafilters on Boolean algebras are precisely
the ones which capture the maximum class in Keisler's order, answering a
question posed by Benda in 1974.",1810.09428v2
2019-01-04,Local saturation and square everywhere,"We show that it is consistent relative to a huge cardinal that for all
infinite cardinals $\kappa$, $\square_\kappa$ holds and there is a stationary
$S \subseteq \kappa^+$ such that $\mathrm{NS}_{\kappa^+} \restriction S$ is
$\kappa^{++}$-saturated.",1901.02821v4
2019-02-13,HADES RV Programme with HARPS-N at TNG. X. The non-saturated regime of the stellar activity-rotation relationship for M-Dwarfs,"Aims. We aim to extend the relationship between X-ray luminosity (Lx) and
rotation period (Prot) found for main-sequence FGK stars and test whether it
also holds for early-M dwarfs, especially in the non-saturated regime (Lx
{\alpha} P_{rot}^{-2}) which corresponds to slow rotators. Methods. We use the
luminosity coronal activity indicator (Lx) of a sample of 78 early-M dwarfs
with masses in the range from 0.3 to 0.75 Msun from the HArps-N red Dwarf
Exoplanet Survey (HADES) radial velocity (RV) programme collected from ROSAT
and XMM-Newton. The determination of the rotation periods (P_{rot}) was done by
analysing time-series of high-resolution spectroscopy of the Ca ii H & K and
H{\alpha} activity indicators. Our sample principally covers the slow rotation
regime with rotation periods from 15 to 60 days. Results. Our work extends to
the low mass regime the observed trend for more massive stars showing a
continuous shift of the Lx/Lbol vs. Prot power-law towards longer rotation
period values and includes the determination, in a more accurate way, of the
value of the rotation period at which the saturation occurs (P_{sat}) for M
dwarf stars. Conclusions. We conclude that the relations between coronal
activity and stellar rotation for FGK stars also hold for early-M dwarfs in the
non-saturated regime, indicating that the rotation period is sufficient to
determine the ratio Lx/Lbol.",1902.04868v1
2019-02-26,Dynamics of fracturing saturated porous media and self-organization of rupture,"Analytical solutions and a vast majority of numerical ones for fracture
propagation in saturated porous media yield smooth behavior while experiments,
field observations and a few numerical solutions reveal stepwise crack
advancement and pressure oscillations. To explain this fact, we invoke
self-organization of rupture observed in fracturing solids, both dry and fully
saturated, when two requirements are satisfied: i) the external drive has a
much slower timescale than fracture propagation; and ii) the increment of the
external load (drive) is applied only when the internal rearrangement of
fracture is over. These requirements are needed to obtain clean Self Organised
Criticality (SOC) in quasi-static situations. They imply that there should be
no restriction on the fracture velocity i.e. algorithmically the fracture
advancement rule should always be independent of the crack velocity. Generally,
this is not the case when smooth answers are obtained which are often
unphysical. Under the above conditions hints of Self Organized Criticality are
evident in heterogeneous porous media in quasi-static conditions using a
lattice model, showing stepwise advancement of the fracture and pressure
oscillations. We extend this model to incorporate inertia forces and show that
this behavior still holds. By incorporating the above requirements in numerical
fracture advancement algorithms for cohesive fracture in saturated porous
continua we also reproduce stepwise advancements and pressure oscillations both
in quasi-static and dynamic situations. Since dynamic tests of dry specimens
show that the fracture advancement velocity is not constant we replicate such
an effect with a model of a debonding beam on elastic foundation. This is the
first step before introducing the interaction with a fluid.",1902.10082v1
2019-03-13,Cryogenic Subthreshold Swing Saturation in FD-SOI MOSFETs described with Band Broadening,"In the standard MOSFET description of the drain current $I_{D}$ as a function
of applied gate voltage $V_{GS}$, the subthreshold swing $SS(T)\equiv
dV_{GS}/d\log I_{D}$ has a fundamental lower limit as a function of temperature
$T$ given by $SS(T) = \ln10~k_BT/e$. However, recent low-temperature studies of
different advanced CMOS technologies have reported $SS$(4K or lower) values
that are at least an order of magnitude larger. Here, we present and analyze
the saturation of $SS(T)$ in 28nm fully-depleted silicon-on-insulator (FD-SOI)
devices for both n- and p-type MOSFETs of different gate oxide thicknesses and
gate lengths down to 4K. Until now, the increase of interface-trap density
close to the band edge as temperature decreases has been put forward to
understand the saturation. Here, an original explanation of the phenomenon is
presented by considering a disorder-induced tail in the density of states at
the conduction (valence) band edge for the calculation of the MOS channel
transport by applying Fermi-Dirac statistics. This results in a subthreshold
$I_{D}\sim e^{eV_{GS}/k_BT_0}$ for $T_0=35$K with saturation value $SS(T<T_0) =
\ln 10~k_BT_0/e$. The proposed model adequately describes the experimental data
of $SS(T)$ from 300 down to 4K using $k_BT_0 \simeq 3$meV for the width of the
exponential tail and can also accurately describe $SS(I_{D})$ within the whole
subthreshold region. Our analysis allows a direct determination of the
technology-dependent band-tail extension forming a crucial element in future
compact modeling and design of cryogenic circuits.",1903.05409v1
2019-04-17,Controlling group and phase velocities in bidirectional mode-locked fiber lasers,"A bidirectional mode-locked fiber laser producing two correlated frequency
combs of the same repetition rate is demonstrated. The intensity dependence of
pulse and phase velocities are measured simultaneously. As expected, the phase
delay is determined by the linear and nonlinear indices of refraction. The
nonlinear Kerr effect contribution to the pulse velocity is dwarfed by a
contribution from saturable gain dynamics.",1904.08132v1
2019-06-14,Signed Radon measure-valued solutions of flux saturated scalar conservation laws,"We prove existence and uniqueness for a class of signed Radon measure-valued
entropy solutions of the Cauchy problem for a first order scalar hyperbolic
conservation law in one space dimension. The initial data of the problem is a
finite superposition of Dirac masses, whereas the flux is Lipschitz continuous
and bounded. The solution class is determined by an additional condition which
is needed to prove uniqueness.",1906.06230v1
2019-07-20,ITMD factorization and broadening effects in production of forward di-jets,"I report on the recent result of comparison of forward-forward dijet
correlations in azimuthal angle as measured by the ATLAS collaboration in the
proton-proton and proton-lead collisions to calculations within ITMD
factorization framework [1]. The comparison shows that the broadening effect
due to interplay of both the gluon saturation and the Sudakov resummation is
necessary to describe the data.",1907.08794v1
2019-11-22,A stochastic approach to enhanced diffusion,"We provide examples of initial data which saturate the enhanced diffusion
rates proved for general shear flows which are H\""{o}lder regular or Lipschitz
continuous with critical points, and for regular circular flows, establishing
the sharpness of those results. Our proof makes use of a probabilistic
interpretation of the dissipation of solutions to the advection diffusion
equation.",1911.09995v1
2019-12-03,The Penrose inequality for perturbations of the Schwarzschild initial data,"We show that in the conformally flat case the Penrose inequality is satisfied
for the Schwarzschild initial data with a small addition of the axially
symmetric traceless exterior curvature. In this class the inequality is
saturated only for data related to special sections of the Schwarzschild
spacetime.",1912.01301v1
2019-12-16,R-group and Whittaker space of some genuine representations,"For a unitary unramified genuine principal series representation of a
covering group, we study the associated R-group. We prove a formula relating
the R-group to the dimension of the Whittaker space for the irreducible
constituents of such a principal series representation. Moreover, for saturated
covers of a semisimple simply-connected group, we also propose a simpler
conjectural formula for such dimensions. This latter conjectural formula is
verified in several cases, including covers of the symplectic groups.",1912.07408v1
2019-12-28,Exclusive diffractive processes including saturation effects at next-to-leading order,"In the framework of the QCD shock-wave approach, we review our results on the
description of diffractive production of various final states (jets, meson) at
next-to-leading order. This is applied to exclusive diffractive dijet
electroproduction at HERA.",1912.12434v1
2020-03-07,A Study of Selectively Digital Etching Silicon-Germanium with Nitric and Hydrofluoric Acids,"A digital etching method was proposed to achieve excellent control of etching
depth. The digital etching characteristics of p+ Si and Si0.7Ge0.3 using the
combinations of HNO3 oxidation and BOE oxide removal processes were studied.
Experiments showed that oxidation saturates with time due to low activation
energy. A physical model was presented to describe the wet oxidation process
with nitric acid. The model was calibrated with experimental data and the
oxidation saturation time, final oxide thickness, and selectivity between
Si0.7Ge0.3 and p+ Si were obtained. The digital etch of laminated Si0.7Ge0.3/p+
Si was also investigated. The depth of the tunnels formed by etching SiGe
layers between two Si layers was found in proportion to digital etching cycles.
And oxidation would also saturate and the saturated relative etched amount per
cycle (REPC) was 0.5 nm (4 monolayers). A corrected selectivity calculation
formula was presented. The oxidation model was also calibrated with
Si0.7Ge0.3/p+ Si stacks, and selectivity from model was the same with the
corrected formula. The model can also be used to analyze process variations and
repeatability. And it could act as a guidance for experiment design.
Selectivity and repeatability should make a trade-off.",2003.03529v1
2020-03-10,Fusion systems on a Sylow $p$-subgroup of $SU_4(p)$,"We determine, for $p$ odd, all saturated fusion systems on a Sylow
$p$-subgroup $S$ of the unitary group $SU_4(p)$ and we prove that they are all
realizable by finite groups. In particular, we prove that $S$ does not support
any exotic fusion systems.",2003.04842v2
2020-04-27,Metasurfaces help lasers to mode-lock,"Metasurface saturable absorbers may result in versatile mode-locking that
allows one to obtain stable ultrashort laser pulses with high repetition rates
and peak powers, along with broadband operation, within fiber to solid-state
laser cavities.",2004.12596v1
2020-06-07,In-Ear Measurement of Blood Oxygen Saturation: An Ambulatory Tool Needed To Detect The Delayed Life-Threatening Hypoxaemia in COVID-19,"Non-invasive ambulatory estimation of blood oxygen saturation has emerged as
an important clinical requirement to detect hypoxemia in the delayed
post-infective phase of COVID-19, where dangerous hypoxia may occur in the
absence of subjective breathlessness. This immediate clinical driver, combined
with the general quest for more personalised health data, means that pulse
oximetry measurement of capillary oxygen saturation (SpO2) will likely expand
into both the clinical and consumer market of wearable health technology in the
near future. In this study, we set out to establish the feasibility of SpO2
measurement from the ear canal as a convenient site for long term monitoring,
and perform a comprehensive comparison with the right index finger - the
conventional clinical measurement site. During resting SpO2 estimation, we
found a root mean square difference of 1.47% between the two measurement sites,
with a mean difference of 0.23% higher SpO2 in the right ear canal. Through the
simultaneous recording of pulse oximetry from both the right ear canal and
index finger during breath holds, we observe a substantial improvement in
response time between the ear and finger that has a mean of 12.4 seconds and a
range of 4.2 - 24.2 seconds across all subjects. Factors which influence this
response time, termed SpO2 delay, such as the sex of a subject are also
explored. Furthermore, we examine the potential downsides of ear canal blood
oxygen saturation measurement, namely the lower photoplethysmogram amplitude,
and suggest ways to mitigate this disadvantage. These results are presented in
conjunction with previously discovered benefits such as robustness to
temperature, making the case for measurement of SpO2 from the ear canal being
both convenient and superior to conventional finger measurement sites for
continuous non-intrusive long term monitoring in both clinical and
everyday-life settings.",2006.04231v1
2020-10-26,The logarithmic Bogomolov-Tian-Todorov theorem,"We prove that the log smooth deformations of a proper log smooth saturated
log Calabi-Yau space are unobstructed.",2010.13656v3
2020-11-06,Upper bounds for Betti numbers from constraints on the Hilbert function,"We describe an algorithm for finding sharp upper bounds for the total Betti
numbers of a saturated ideal given certain constraints on its Hilbert function.
This algorithm is implemented in the Macaulay2 package, MaxBettiNumbers, along
with variations that produce ideals with maximal total Betti numbers.",2011.03401v1
2021-03-25,Random walker derivation of Archie's law,"The empirical Archie's law, relating the measured electrical resistivity of
an electrolyte-saturated rock to its connected porosity, is derived by
consideration of the fractal character of the pore space. The derivation thus
imposes some conditions on the implementation and meaning of Archie's law.",2103.14099v1
2021-05-05,Hennessy-Milner Properties via Topological Compactness,"We give Hennessy-Milner classes for intuitionistic, dual-intuitionistic and
bi-intuitionistic logic interpreted in intuitionistic Kripke models, and
generalise these results to modal (dual- and bi-)intuitionistic logics. Our
main technical tools are image-compact and pre-image-compact relations that
provide a semantical description of modal saturation properties.",2105.01855v1
2021-05-28,Poisson catenarity in Poisson nilpotent algebras,"We prove that for the iterated Poisson polynomial rings known as Poisson
nilpotent algebras (or Poisson-CGL extensions), the Poisson prime spectrum is
catenary, i.e., all saturated chains of inclusions of Poisson prime ideals
between any two given Poisson prime ideals have the same length.",2105.13737v1
2021-06-13,Uniform in time $L^\infty$-estimates for an attraction-repulsion chemotaxis system with double saturation,"In this paper we focus on an attraction-repulsion chemotaxis model with
consumed signals, formulated in bounded and smooth domains $\Omega$ of $\R^n$,
with $n\geq 2$. We derive sufficient conditions on its data yielding global and
bounded classical solutions to the related zero-flux Cauchy problem.",2106.07038v2
2021-07-20,Normalizers of sets of components in fusion systems,"We describe some new ways to construct saturated fusion subsystems,
including, as a special case, the normalizer of a set of components of the
ambient fusion system. This was motivated in part by Aschbacher's construction
of the normalizer of one component, and in part by joint work with three other
authors where we had to construct the normalizer of all of the components.",2107.09494v2
2021-09-01,Small Strong Blocking Sets by Concatenation,"Strong blocking sets and their counterparts, minimal codes, attracted lots of
attention in the last years. Combining the concatenating construction of codes
with a geometric insight into the minimality condition, we explicitly provide
infinite families of small strong blocking sets, whose size is linear in the
dimension of the ambient projective spaces. As a byproduct, small saturating
sets are obtained.",2109.00584v2
2021-09-28,Normalizers and centralizers of subnormal subsystems of fusion systems,"Every saturated fusion system corresponds to a group-like structure called a
regular locality. In this paper we study (suitably defined) normalizers and
centralizers of partial subnormal subgroups of regular localities. This leads
to a reasonable notion of normalizers and centralizers of subnormal subsystems
of fusion systems.",2109.14038v2
2022-02-11,Saturable time-varying mirror based on an ENZ material,"We report a switchable time-varying mirror, composed of an ITO-Au stack,
which can be efficiently modulated in time with over a ten-fold increase in
reflectivity, with a change of 0.6. Upon interacting with the time-varying
mirror, the frequency content of a reflected pulse is extended to 31 THz. This
originates from the shortening of the response time of the mirror beyond
saturation, as confirmed by a time-varying model and by further four-wave
mixing experiments. A temporal response unbounded by the pump bandwidth opens
new avenues for spectral manipulation from time-varying systems with impact for
communication networks, optical switching and computing.
  We report a switchable time-varying mirror, composed of an ITO-Au bilayer,
displaying a ten-fold modulation of reflectivity ($\Delta R \approx 0.6$),
which saturates for a driving pump intensity $I_{\mathrm{pump}}\approx
100$~GW/cm$^2$. Upon interacting with the saturated time-varying mirror, the
frequency content of a reflected pulse is extended up to 31 THz, well beyond
the pump spectral content (2.8 THz). We interpret the spectral broadening as a
progressive shortening of the mirror rise time from 110 fs to sub 30 fs with
increasing pump power, which is confirmed by four-wave mixing experiments and
partially captured by a linear time-varying model of the mirror. A temporal
response unbounded by the pump bandwidth opens new avenues for spectral
manipulation from time-varying systems with impact for communication networks,
optical switching and computing.",2202.05937v4
2022-02-23,Miscellaneous problems about packing and covering,"In this paper we discuss various special problems on packing and covering.
Among others we survey the problems and results concerning finite arrangements,
Minkowskian, saturated, compact, and totally separable packings. We discuss
shortest path problems and questions about stability of packings.",2202.11366v1
2022-04-13,On chains associated with abstract key polynomials,"In this paper, for a henselian valued field $(K, v)$ of arbitrary rank and an
extension $w$ of $v$ to $K(X),$ we use abstract key polynomials for $w$ to give
a connection between complete sets, saturated distinguished chains and Okutsu
frames. Further, for a valued field $(K, v),$ we also obtain a close connection
between complete set of ABKPs for $w$ and Maclane-Vaqui\'e chains of $w.$",2204.06428v1
2022-08-11,A nonlinear attraction-repulsion Keller-Segel model with double sublinear absorptions: criteria toward boundedness,"This paper generalizes and extends to the case of nonlinear effects and
logistic perturbations some results recently developed in the literature where,
for the linear counterpart and in absence of logistics, criteria toward
boundedness for an attraction-repulsion Keller-Segel system with double
saturation are derived.",2208.05678v1
2022-12-07,Compactness in Team Semantics,"We provide two proofs of the compactness theorem for extensions of
first-order logic based on team semantics. First, we build upon L\""uck's
ultraproduct construction for team semantics and prove a suitable version of
{\L}o\'s' Theorem. Second, we show that by working with suitably saturated
models, we can generalize the proof of Kontinen and Yang to sets of formulas
with arbitrarily many variables.",2212.03677v1
2022-12-12,Tight concentration of star saturation number in random graphs,"For given graphs $F$ and $G$, the minimum number of edges in an
inclusion-maximal $F$-free subgraph of $G$ is called the $F$-saturation number
and denoted $\mathrm{sat}(G, F)$. For the star $F=K_{1,r}$, the asymptotics of
$\mathrm{sat}(G(n,p),F)$ is known. We prove a sharper result: whp
$\mathrm{sat}(G(n,p), K_{1,r})$ is concentrated in a set of 2 consecutive
points.",2212.06101v1
2022-12-16,On maximal rational poylhedral fans,"In this paper we study the geometry and combinatorics of the possible
rational polyhedral fans with a given set of rays.
  The main questions we consider are when such fans are projective, complete,
or simplicial. To answer these questions we use techniques of invariant theory
to characterize the quotients of maximal saturated open sets in torus
representations.",2212.08240v1
2023-01-19,Spanning the full range of neutron star properties within a microscopic description,"The high-density behavior of nuclear matter is analyzed within a relativistic
mean-field description with non-linear meson interactions. To assess the model
parameters and their output, a Bayesian inference technique is used. The
Bayesian setup is limited only by a few nuclear saturation properties, the
neutron star maximum mass larger than 2 M$_\odot$, and the low-density pure
neutron matter equation of state (EOS) produced by an accurate N$^3$LO
calculation in chiral effective field theory. Depending on the strength of the
non-linear scalar vector field contribution, we have found three distinct
classes of EOSs, each one correlated to different star properties
distributions. If the non-linear vector field contribution is absent, the
gravitational maximum mass and the sound velocity at high densities are the
greatest. However, it also gives the smallest speed of sound at densities below
three times saturation density. On the other hand, models with the strongest
non-linear vector field contribution predict the largest radii and tidal
deformabilities for 1.4 M$_\odot$ stars, together with the smallest mass for
the onset of the nucleonic direct Urca processes and the smallest central
baryonic densities for the maximum mass configuration. These models have the
largest speed of sound below three times saturation density, but the smallest
at high densities, in particular, above four times saturation density the speed
of sound decreases approaching approximately $\sqrt{0.4}c$ at the center of the
maximum mass star. On the contrary, a weak non-linear vector contribution gives
a monotonically increasing speed of sound. A 2.75 M$_\odot$ NS maximum mass was
obtained in the tail of the posterior with a weak non-linear vector field
interaction. We found that pQCD favors models with a large non-linear vector
field contribution or hyperons.",2301.08169v4
2023-01-19,A note on five dimensional kissing arrangements,"The kissing number $\tau(d)$ is the maximum number of pairwise
non-overlapping unit spheres each touching a central unit sphere in the
$d$-dimensional Euclidean space. In this note we report on how we discovered a
new, previously unknown arrangement of $40$ unit spheres in dimension $5$. Our
arrangement saturates the best known lower bound on $\tau(5)$, and refutes a
`belief' of Cohn--Jiao--Kumar--Torquato.",2301.08272v1
2023-01-22,On the size of maximum cut in planar graphs,"We show that the size of maximum cut in a planar graph with $m$ edges is at
least $2m/3$. We also show that maximal planar graphs saturate this bound.",2301.09170v2
2023-01-24,Margolus-Levitin quantum speed limit for an arbitrary fidelity,"The Mandelstam-Tamm and Margolus-Levitin quantum speed limits are two
well-known evolution time estimates for isolated quantum systems. These bounds
are usually formulated for fully distinguishable initial and final states, but
both have tight extensions to systems that evolve between states with an
arbitrary fidelity. However, the foundations of these extensions differ in some
essential respects. The extended Mandelstam-Tamm quantum speed limit has been
proven analytically and has a clear geometric interpretation. Furthermore,
which systems saturate the limit is known. The derivation of the extended
Margolus-Levitin quantum speed limit, on the other hand, is based on numerical
estimates. Moreover, the limit lacks a geometric interpretation, and no
complete characterization of the systems reaching it exists. In this paper, we
derive the extended Margolus-Levitin quantum speed limit analytically and
describe the systems that saturate the limit in detail. We also provide the
limit with a symplectic-geometric interpretation, which indicates that it is of
a different character than most existing quantum speed limits. At the end of
the paper, we analyze the maximum of the extended Mandelstam-Tamm and
Margolus-Levitin quantum speed limits and derive a dual version of the extended
Margolus-Levitin quantum speed limit. The maximum limit is tight regardless of
the fidelity of the initial and final states. However, the conditions under
which the maximum limit is saturated differ depending on whether or not the
initial state and the final state are fully distinguishable. The dual limit is
also tight and follows from a time reversal argument. We describe the systems
that saturate the dual quantum speed limit.",2301.10063v3
2023-02-09,The QCD shockwave approach at NLO: towards precision physics in gluonic saturation,"We review the recent developments of the QCD shockwave approach at
Next-to-Leading Order. The general method of this effective action is sketched,
and illustrated by the case of diffractive processes.",2302.04526v1
2023-04-02,The variety of polar simplices II,"We discuss the space $VPS(Q,H)$ of ideals with Hilbert function $H=(1,n,n,
\ldots )$ that are apolar to a full rank quadric $Q$. We prove that its
components of saturated ideals are closely related to the locus of Gorenstein
algebras and to the Slip component in border apolarity. We also point out an
important error in~\cite{RS} and provide the necessary corrections.",2304.00533v1
2023-04-26,A model of surface roughness effect on triboelectric charging of particles,"Tribocharging increases due to deformation and penetration of surface
asperities, enlarging the real contact area. These experimental results
translate into a theoretical description of particle charging that resolves the
surface topology. Based on these findings, we propose a model that predicts the
dependence of the particles' saturation charge on the impact velocity and
surface roughness.",2304.13441v1
2023-06-04,Global Transonic Solution of Hot Accretion Flow with Thermal Conduction,"We examine the effect of thermal conduction on the low-angular momentum hot
accretion flow (HAF) around non-rotating black holes accreting mass at very low
rate. While doing so, we adopt the conductive heat flux in the saturated form,
and solve the set of dynamical equations corresponding to a steady,
axisymmetric, viscous, advective accretion flow using numerical methods. We
study the dynamical and thermodynamical properties of accreting matter in terms
of the input parameters, namely energy ($\varepsilon_0$), angular momentum
($\ell_0$), viscosity parameter ($\alpha$), and saturation constant ($\Phi_{\rm
s}$) regulating the effect of thermal conduction. We find that $\Phi_{\rm s}$
plays a pivotal role in deciding the transonic properties of the global
accretion solutions. In general, when $\Phi_{\rm s}$ is increased, the critical
point ($r_{\rm c}$) is receded away from the black hole, and flow variables are
altered particularly in the outer part of the disc. To quantify the physically
acceptable range of $\Phi_{\rm s}$, we compare the global transonic solutions
with the self-similar solutions, and observe that the maximum saturation
constant ($\Phi^{\rm max}_{\rm s}$) estimated from the global solutions exceeds
the saturated thermal conduction limit ($\Phi_{\rm sc}$) derived from the
self-similar formalism. Moreover, we calculate the correlation between $\alpha$
and $\Phi^{\rm max}_{\rm s}$ and find ample disagreement between global
solutions and self-similar solutions. Further, using the global flow variables,
we compute the Bernoulli parameter ($Be$) which remains positive all throughout
the disc, although flow becomes loosely unbound for higher $\Phi_{\rm s}$.
Finally, we indicate the relevance of this work in the astrophysical context in
explaining the possibility of massloss/outflows from the unbound disc.",2306.02453v1
2023-06-20,Extremal bounds for pattern avoidance in multidimensional 0-1 matrices,"A 0-1 matrix $M$ contains another 0-1 matrix $P$ if some submatrix of $M$ can
be turned into $P$ by changing any number of $1$-entries to $0$-entries. $M$ is
$\mathcal{P}$-saturated where $\mathcal{P}$ is a family of 0-1 matrices if $M$
avoids every element of $\mathcal{P}$ and changing any $0$-entry of $M$ to a
$1$-entry introduces a copy of some element of $\mathcal{P}$. The extremal
function ex$(n,\mathcal{P})$ and saturation function sat$(n,\mathcal{P})$ are
the maximum and minimum possible weight of an $n\times n$
$\mathcal{P}$-saturated 0-1 matrix, respectively, and the semisaturation
function ssat$(n,P)$ is the minimum possible weight of an $n\times n$
$\mathcal{P}$-semisaturated 0-1 matrix $M$, i.e., changing any $0$-entry in $M$
to a $1$-entry introduces a new copy of some element of $\mathcal{P}$.
  We study these functions of multidimensional 0-1 matrices. We give upper
bounds on parameters of minimally non-$O(n^{d-1})$ $d$-dimensional 0-1
matrices, generalized from minimally nonlinear 0-1 matrices in two dimensions,
and we show the existence of infinitely many minimally non-$O(n^{d-1})$
$d$-dimensional 0-1 matrices with all dimensions of length greater than $1$.
For any positive integers $k,d$ and integer $r\in[0,d-1]$, we construct a
family of $d$-dimensional 0-1 matrices with both extremal function and
saturation function exactly $kn^r$ for sufficiently large $n$. We show that no
family of $d$-dimensional 0-1 matrices has saturation function strictly between
$O(1)$ and $\Theta(n)$ and we construct a family of $d$-dimensional 0-1
matrices with bounded saturation function and extremal function
$\Omega(n^{d-\epsilon})$ for any $\epsilon>0$. Up to a constant multiplicative
factor, we fully settle the problem of characterizing the semisaturation
function of families of $d$-dimensional 0-1 matrices, which we prove to always
be $\Theta(n^r)$ for some integer $r\in[0,d-1]$.",2306.11934v1
2023-09-27,The greatest GOES soft X-ray flares: Saturation and recalibration over two Hale cycles,"The solar soft X-ray observations from the GOES satellites provide one of the
best quantitative records of solar activity, with nearly continuous flare
records since 1975. We present a uniform analysis of the entire time series for
1975 to 2022 at NOAA class C1 level or above, to characterize the occurrence
distribution function (ODF) of the flares observed in the 1-8 A spectral band.
The analysis includes estimations of the peak fluxes of the 12 flares that
saturated the 1-8 A time series. Our new estimates include NOAA's recently
established correction factor (1.43) to adjust the GOES-1 through GOES-15 data
covering 1975-2016. For each of the 12 saturated events we have made new
estimates of peak fluxes based on fits to the rise and fall of the flare time
profile, and have validated our extrapolation schemes by comparing with
artificially truncated but unsaturated X10-class events. SOL2003-11-04 now has
a peak flux of 4.32e-3 W/m^2. This corresponds to X43 on the new scale, or X30
on the old scale. We provide a list in the Appendix for peak fluxes of all 38
events above 10^-3 W/m^2, the GOES X10 level, including the 12 saturated
events. The full list now gives us a first complete sample from which we obtain
an occurrence distribution function (ODF) for peak energy flux , often
represented as a power law dF/dE ~ E^-alpha, for which we find alpha = 1.973 +-
0.014 in the range M1 to X3. The power-law description fails at the high end,
requiring a downward break in the ODF above the X10 level. We give a tapered
powerlaw description of the resulting CCDF (complementary cumulative
distribution function) and extrapolate it into the domain of ""superflares,""
i.e. flares with bolometric energies > 10^33 erg. Extrapolation of this fit
provides estimates of 100-yr and 1000-yr GOES peak fluxes that agree reasonably
well with other such estimates using different data sets and methodology.",2310.11457v1
2023-10-22,On the saturation number for singular cubic surfaces,"We investigate the distribution of rational points on singular cubic
surfaces, whose coordinates have few prime factors. The key tools used are
universal torsors, the circle method and results on linear equations in primes.",2310.14327v1
2023-11-17,The Newton polytope of the Kronecker product,"We study the Kronecker product of two Schur functions $s_\lambda\ast s_\mu$,
defined as the image of the characteristic map of the product of two $S_n$
irreducible characters. We prove special cases of a conjecture of
Monical--Tokcan--Yong that its monomial expansion has a saturated Newton
polytope. Our proofs employ the Horn inequalities for positivity of
Littlewood-Richardson coefficients and imply necessary conditions for the
positivity of Kronecker coefficients.",2311.10276v1
2023-12-10,Intermode coupling in a fiber loop laser at low temperatures,"We experimentally study an unequally-spaced optical comb (USOC), which is
generated by a unidirectional fiber loop laser operated at low temperatures.
The underlying mechanism responsible for USOC formation is explored using both
close and open loop measurements. The role played by dispersion is investigated
using radio frequency spectrum measurements. By integrating a saturable
absorber into the loop, a lasing state is revealed, in which mode locking
coexists with the USOC.",2312.05838v1
2024-01-06,Local positive logic,"We develop the basic model theory of local positive logic, a new logic that
mixes positive logic (where negation is not allowed) and local logic (where
models omit types of infinite distant pairs). We study several basic model
theoretic notions such as compactness, positive closedness (existential
closedness), completeness (irreducibility), type spaces and retractors
(saturated models).",2401.03260v1
2024-01-08,Global entropy solutions to a degenerate parabolic-parabolic chemotaxis system for flux-limited dispersal,"Existence of global finite-time bounded entropy solutions to a
parabolic-parabolic system proposed in [15] is established in bounded domains
under no-flux boundary conditions for nonnegative bounded initial data. This
modification of the classical Keller-Segel model features degenerate diffusion
and chemotaxis that are both subject to flux-saturation. The approach is based
on Schauder's fixed point theorem and calculus of functions of bounded
variation.",2401.03887v1
2024-02-12,A saturation theorem for submonoids of nilpotent groups and the Identity Problem,"If $M$ is a submonoid of a finitely generated nilpotent group $G$, and $MG'$
is a finite index subgroup of $G$, then $M$ itself is a finite index subgroup
of $G$. If $MG'=G$, then $M=G$. This generalizes a well-known theorem for
subgroups of finitely generated nilpotent groups. As a result, we give an
algorithm for the Identity Problem in nilpotent groups.",2402.07337v1
2024-02-18,Criteria for nilpotency of fusion systems,"Let $p$ be an odd prime and let $\mathcal{F}$ be a fusion system over a
finite $p$-group $P$. A fusion system $\mathcal{F}$ is said to be nilpotent if
$\mathcal{F}=\mathcal{F}_{P}(P)$. In this paper we provide new criteria for
saturated fusion systems $\mathcal{F}$ to be nilpotent, which can be viewed as
extension of the $p$-nilpotency theorem of Glauberman and Thompson for fusion
systems attributed to Kessar and Linckelmann.",2402.11629v1
2002-11-03,Magnetically induced signatures in a thin film superconductor,"We study the interaction between a one dimensional magnetic nanostructure and
a thin film superconductor. It is shown that different magnetic distributions
produce characteristic magnetic field signatures. Moreover, the magnetic
structure can induce a weak link in the superconducting film, or be positioned
directly above a predefined nonsuperconducting weak link. We estimate the
magnetic flux associated with such a structure, and discuss a general
expression for the energy calculated within the London model.",0211043v1
2004-09-25,Nano-mechanical magnetization reversal,"The dynamics of the ferromagnetic order parameter in thin magnetic films is
strongly affected by the magnetomechanical coupling at certain resonance
frequencies. By solving the equation of motion of the coupled mechanical and
magnetic degrees of freedom we show that the magnetic-field induced
magnetization switching can be strongly accelerated by the lattice and
illustrate the possibility of magnetization reversal by mechanical actuation.",0409681v1
2005-10-26,Ferroelectricity in spiral magnets,"It was recently observed that materials showing most striking multiferroic
phenomena are frustrated spin-density-wave magnets. We present a simple
phenomenological theory, which describes the orientation of the induced
electric polarization for various incommensurate magnetic states, its
dependence on temperature and magnetic field, and anomalies of dielectric
susceptibility at magnetic transitions. We show that electric polarization can
be induced at domain walls and that magnetic vortices carry electric charge.",0510692v1
2007-07-13,Magnetic Flux Effects in Statistical Magnetism of Electron Gas,"The effects of magnetic flux in statistical magnetisms, including Pauli
paramagnetism, Landau diamagnetism, and De Hass-van Alphen oscillation, are
discussed. It is shown that the diamagnetism could be much increased by the
fractional magnetic flux, and the amplitude of the magnetic oscillation of De
Hass-van Alphen can be amplified by the quantum effect of the flux.",0707.1920v1
2008-05-18,Effect of spin diffusion on spin torque in magnetic nanopillars,"We present systematic magnetoelectronic measurements of magnetic nanopillars
with different structures of polarizing magnetic layers. The magnetic reversal
at small magnetic field, the onset of magnetic dynamics at larger field, and
the magnetoresistance exhibit a significant dependence on the type of the
polarizing layer. We performed detailed quantitative modeling showing that the
differences can be explained by the effects of spin-dependent electron
diffusion.",0805.2706v1
2012-06-05,Negative magnetic relaxation in superconductors,"It was observed that the trapped magnetic moment of HTS tablets or annuli
increases in time (negative relaxation) if they are not completely magnetized
by a pulsed magnetic field. It is shown, in the framework of the Bean
critical-state model, that the radial temperature gradient appearing in tablets
or annuli during a pulsed field magnetization can explain the negative magnetic
relaxation in the superconductor.",1206.0861v1
2016-08-19,Vesicles in magnetic fields,"Liposome vesicles tend to align with an applied magnetic field. This is due
to the directional magnetic susceptibility difference of the lipids which form
the membrane of these vesicles. In this work a model of liposome vesicles
exposed to magnetic field is presented. Starting from the base energy of a
lipid membrane in a magnetic field, the force applied to the surrounding fluids
is derived. This force is then used to investigate the dynamics of vesicle in
the presence of magnetic fields.",1608.05587v1
2012-11-20,Magnetic Cluster Excitations,"Magnetic clusters, i.e., assemblies of a finite number (between two or three
and several hundred) of interacting spin centers which are magnetically
decoupled from their environment, can be found in many materials ranging from
inorganic compounds, magnetic molecules, artificial metal structures formed on
surfaces to metalloproteins. The magnetic excitation spectra in them are
determined by the nature of the spin centers, the nature of the magnetic
interactions, and the particular arrangement of the mutual interaction paths
between the spin centers. Small clusters of up to four magnetic ions are ideal
model systems to examine the fundamental magnetic interactions which are
usually dominated by Heisenberg exchange, but often complemented by anisotropic
and/or higher-order interactions. In large magnetic clusters which may
potentially deal with a dozen or more spin centers, the possibility of novel
many-body quantum states and quantum phenomena are in focus. In this review the
necessary theoretical concepts and experimental techniques to study the
magnetic cluster excitations and the resulting characteristic magnetic
properties are introduced, followed by examples of small clusters demonstrating
the enormous amount of detailed physical information which can be retrieved.
The current understanding of the excitations and their physical interpretation
in the molecular nanomagnets which represent large magnetic clusters is then
presented, with an own section devoted to the subclass of the single-molecule
magnets which are distinguished by displaying quantum tunneling of the
magnetization. Finally, some quantum many-body states are summarized which
evolve in magnetic insulators characterized by built-in or field-induced
magnetic clusters. The review concludes addressing future perspectives in the
field of magnetic cluster excitations.",1211.4688v1
2014-01-08,Generating buoyant magnetic flux ropes in solar-like convective dynamos,"Our Sun exhibits strong convective dynamo action which results in magnetic
flux bundles emerging through the stellar surface as magnetic spots.
Global-scale dynamo action is believed to generate large-scale magnetic
structures in the deep solar interior through the interplay of convection,
rotation, and shear. Portions of these large-scale magnetic structures are then
believed to rise through the convective layer, forming magnetic loops which
then pierce the photosphere as sunspot pairs. Previous global simulations of 3D
MHD convection in rotating spherical shells have demonstrated mechanisms
whereby large-scale magnetic wreaths can be generated in the bulk of the
convection zone. Our recent simulations have achieved sufficiently high levels
of turbulence to permit portions of these wreaths to become magnetically
buoyant and rise through the simulated convective layer through a combination
of magnetic buoyancy and advection by convective giant cells. These buoyant
magnetic loops are created in the bulk of the convective layer as strong
Lorentz force feedback in the cores of the magnetic wreaths dampen small-scale
convective motions, permitting the amplification of local magnetic energies to
over 100 times the local kinetic energy. While the magnetic wreaths are largely
generated the shearing of axisymmetric poloidal magnetic fields by axisymmetric
rotational shear (the $\Omega$-effect), the loops are amplified to their peak
field strengths before beginning to rise by non-axisymmetric processes. This
further extends and enhances a new paradigm for the generation of emergent
magnetic flux bundles, which we term turbulence-enabled magnetic buoyancy.",1401.1826v1
2014-05-05,The magnetic shielding for the neutron decay spectrometer aSPECT,"Many experiments in nuclear and neutron physics are confronted with the
problem that they use a superconducting magnetic spectrometer which potentially
affects other experiments by their stray magnetic field. The retardation
spectrometer aSPECT consists, inter alia, of a superconducting magnet system
that produces a strong longitudinal magnetic field of up to 6.2T. In order not
to disturb other experiments in the vicinity of aSPECT, we had to develop a
magnetic field return yoke for the magnet system. While the return yoke must
reduce the stray magnetic field, the internal magnetic field and its
homogeneity should not be affected. As in many cases, the magnetic shielding
for aSPECT must manage with limited space. In addition, we must ensure that the
additional magnetic forces on the magnet coils are not destructive. In order to
determine the most suitable geometry for the magnetic shielding for aSPECT, we
simulated a variety of possible geometries and combinations of shielding
materials of non-linear permeability. The results of our simulations were
checked through magnetic field measurements both with Hall and nuclear magnetic
resonance probes. The experimental data are in good agreement with the
simulated values: The mean deviation from the simulated exterior magnetic field
is (-1.7+/-4.8)%. However, in the two critical regions, the internal magnetic
field deviates by 0.2% respectively <1E-4 from the simulated values.",1405.0957v1
2014-07-15,Magnetic nanoparticle traveling in external magnetic field,"A set of equations describing the motion of a free magnetic nanoparticle in
an external magnetic field in a vacuum, or in a medium with negligibly small
friction forces is postulated. The conservation of the total particle momentum,
i.e. the sum of the mechanical and the total spin momentum of the nanoparticle
is taken into account explicitly. It is shown that for the motion of a
nanoparticle in uniform magnetic field there are three different modes of
precession of the unit magnetization vector and the director that is parallel
the particle easy anisotropy axis. These modes differ significantly in the
precession frequency. For the high-frequency mode the director points
approximately along the external magnetic field, whereas the frequency and the
characteristic relaxation time of the precession of the unit magnetization
vector are close to the corresponding values for conventional ferromagnetic
resonance. On the other hand, for the low-frequency modes the unit
magnetization vector and the director are nearly parallel and rotate in unison
around the external magnetic field. The characteristic relaxation time for the
low-frequency modes is remarkably long. This means that in a rare assembly of
magnetic nanoparticles there is a possibility of additional resonant absorption
of the energy of alternating magnetic field at a frequency that is much smaller
compared to conventional ferromagnetic resonance frequency. The scattering of a
beam of magnetic nanoparticles in a vacuum in a non-uniform external magnetic
field is also considered taking into account the precession of the unit
magnetization vector and director.",1407.3964v1
2018-12-30,Magnetic properties of an antiferromagnetic spin-1/2 XYZ model in the presence of different magnetic fields: finite-size effects of inhomogeneity property,"Magnetic and thermodynamic properties of the anisotropic XYZ spin-1/2 finite
chain under both homogeneous and inhomogeneous magnetic fields are
theoretically studied at low temperature. Using exact diagonalization method
(ED), we study the magnetization, magnetic susceptibility and specific heat of
the model characterized in terms of the finite correlation length in the
presence of three different magnetic fields including longitudinal, transverse
and transverse staggered magnetic fields. The magnetization, susceptibility and
the specific heat of the model are investigated under two conditions
separately: I) when the model is putted in the presence of homogeneous magnetic
fields; II) when finite inhomogeneities are considered for all applied magnetic
fields in the Hamiltonian. We show that for the finite-size XYZ chains at low
temperature, the evident magnetization plateaus gradually convert to their
counterpart quasi-plateaus when the transverse magnetic field increases.
Moreover, the influence of the transverse and staggered transverse magnetic
fields, and their corresponding inhomogeneities on the magnetization process,
magnetic susceptibility, and specific heat are reported in detail. Our exact
results illustrate that by altering the inhomogeneity parameters, magnetization
plateaus gradually convert to their counterpart quasi-plateaus. The specific
heat manifests Schottky-type maximum, double-peak and triple-peak, as well as,
transformation between them by varying considered inhomogeneity parameters in
the Hamiltonian.",1812.11468v2
2019-04-18,Insight into the magnetic behavior of Sr$_2$IrO$_4$:A spontaneous magnetization study,"Sr$_2$IrO$_4$ is a weak ferromagnet where the spin arrangement is canted
anti-ferromagnetic (AF). Moreover, the spin-structure coupling plays and
important role in magnetic behavior of Sr$_2$IrO$_4$. In this concern the
magnetization under zero applied field i.e. spontaneous magnetization would be
interesting to study and would give insight into the novel magnetic behavior of
Sr$_2$IrO$_4$. Sophisticated techniques like neutron diffraction, $\mu$
\textit{SR} etc has been used to understand the magnetic behavior of
Sr$_2$IrO$_4$ under zero applied field. To understand the magnetic behavior we
have performed detail field and temperature dependent magnetization study, the
measured field and temperature dependent magnetic data is analyzed rigorously.
We have attempted the understand the temperature dependance of spontaneous
magnetization, remanent magnetization and coercive force. We observe that the
spontaneous magnetization extracted from Arrott plot shows that the
Sr$_2$IrO$_4$ is not an ideal ferromagnet. The temperature dependent coercive
field is found to follows Guant's model of strong domain wall pinning. Our
investigation explicit the temperature dependence of various magnetic
properties shows the magnetic transitions from paramagnetic to ferromagnetic
phase with $T_c$ around 225 K and a low temperature evolution of magnetic
magnetic moment around $T_M$ $\sim$90 K.",1904.08792v1
2020-01-08,Non-equilibrium spin dynamics in the temperature and magnetic field dependence of magnetization curves of ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ and its composite with BaTiO$_3$,"A comparative study of the non-equilibrium magnetic phenomena (magnetic
blocking, memory, exchange bias and aging effect) has been presented for
ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ (CFO) and its composite with
non-magnetic BaTiO$_3$ (BTO). Synchrotron X-Ray diffraction patterns have
confirmed coexistence of CFO and BTO structures in composite, but magnetic spin
dynamics have been remarkably modified. The blocking phenomenon of
ferrimagnetic domains below the room temperature has been studied by different
modes of (zero field cooled and field cooled) magnetic measurements in
collaboration with magnetic fields ON and OFF modes and time dependent
magnetization. The applications of unconventional protocols during time
dependent magnetization measurement at different stages of the temperature and
field dependence of the magnetization curves have been useful to reveal the
non-equilibrium dynamics of magnetic spin order. The applying of off-field
relaxation experiments has made possible to tune the magnetic state and
coercivity of the systems. The role of interfacial coupling between magnetic
and non-magnetic particles has been understood on different magnetic phenomena
(meta-stable magnetic state, exchange bias and memory effect) by comparing the
experimental results of Co$_{1.75}$Fe$_{1.25}$O$_4$ spinel oxide and its
composite with BaTiO$_3$ particles.",2001.02602v2
2021-09-24,Fluidic Endogenous Magnetism and Magnetic Monopole Clues from Liquid Metal Droplet Machine,"Magnetism and magnetic monopole are classical issues in basic physics.
Conventional magnets are generally composed of rigid materials with shapes and
structures unchangeable which may face challenges sometimes to answer the above
questions. Here, from an alternative other than rigid magnet, we disclosed an
unconventional way to generate endogenous magnetism and then construct magnetic
monopole through tuning liquid metal machine. Through theoretical
interpretation and conceptual experiments, we illustrated that when gallium
base liquid metal in solution rotates under actuation of an external electric
field, it forms an endogenous magnetic field inside which well explains the
phenomenon that two such discrete metal droplets could easily fuse together,
indicating their reciprocal attraction via N and S poles. Further, we conceived
that the self-driving liquid metal motor was also an endogenous magnet owning
the electromagnetic homology. When liquid metal in solution swallowed aluminum
inside, it formed a spin motor and dynamically variable charge distribution
which produced an endogenous magnetic field. This finding explains the
phenomena that there often happened reflection collision and attraction fusion
between running liquid metal motors which were just caused by the dynamic
adjustment of their N and S polarities. Finally, we conceived that such
endogenous magnet could lead to magnetic monopole and four technical routes
were suggested as: 1. Matching the interior flow field of liquid metal
machines; 2. Superposition between external electric effect and magnetic field;
3. Composite construction between magnetic particles and liquid metal motor; 4.
Chemical ways such as via galvanic cell reaction. Overall, the fluidic
endogenous magnet and the promising magnetic monopole it enabled may lead to
unconventional magnetoelectric devices and applications in the near future.",2111.02867v1
2022-05-13,Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films,"Epitaxially strained SrRuO3 films have been a model system for understanding
the magnetic anisotropy in metallic oxides. In this paper, we investigate the
anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties
using high-quality epitaxially strained (compressive and tensile) SrRuO3 films
grown by machine-learning-assisted molecular beam epitaxy. The element-specific
magnetic properties and the hybridization between the Ru 4d and O 2p orbitals
were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption
spectroscopy and X-ray magnetic circular dichroism measurements. The
magnetization curves for the Ru 4d and O 2p magnetic moments are identical,
irrespective of the strain type, indicating the strong magnetic coupling
between the Ru and O ions. The electronic structure and the orbital magnetic
moment relative to the spin magnetic moment are isotropic despite the
perpendicular and in-plane magnetic anisotropy in the compressive-strained and
tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a
negligibly small contribution to the magnetic anisotropy. This result
contradicts Bruno model, where magnetic anisotropy arises from the difference
in the orbital magnetic moment between the perpendicular and in-plane
directions. Contributions of strain-induced electric quadrupole moments to the
magnetic anisotropy are discussed, too.",2205.06563v1
2023-09-21,Integrable Magnetic Fluid Hyperthermia Systems for 3D Magnetic Particle Imaging,"Background: Combining magnetic particle imaging (MPI) and magnetic fluid
hyperthermia (MFH) offers the ability to perform localized hyperthermia and
magnetic particle imaging-assisted ther-mometry of hyperthermia treatment. This
allows precise regional selective heating inside the body without invasive
interventions. In current MPI-MFH platforms, separate systems are used, which
require object transfer from one system to another. Here, we present the
design, development and evaluation process for integrable MFH platforms, which
extends a commercial MPI scanner with the functionality of MFH. Methods: The
biggest issue of integrating magnetic fluid hyperthermia platforms into a
magnetic par-ticle imaging system is the magnetic coupling of the devices,
which induces high voltage in the imaging system, and is harming its
components. In this paper we use a self-compensation approach derived from
heuristic algorithms to protect the magnetic particle imaging scanner. The
integrable platforms are evaluated regarding electrical and magnetic
characteristics, cooling capability, field strength, the magnetic coupling to a
replica of the magnetic particle imaging system's main solenoid and particle
heating. Results: The MFH platforms generate suitable magnetic fields for
magnetic heating of particles and are compatible with a commercial magnetic
particle imaging scanner. In combination with the imaging system, selective
heating with a gradient field and steerable heating positioning using the MPI
focus fields are possible. Conclusion: The proposed MFH platforms serve as a
therapeutic tool to unlock MFH functionality of a commercial magnetic particle
imaging scanner, enabling its use in future preclinical trials of MPI-guided,
spatially selective magnetic hyperthermia therapy.",2309.12186v1
2002-05-15,Magnetic Fluctuations with a Zero Mean Field in a Random Fluid Flow with a Finite Correlation Time and a Small Magnetic Diffusion,"Magnetic fluctuations with a zero mean field in a random flow with a finite
correlation time and a small yet finite magnetic diffusion are studied.
Equation for the second-order correlation function of a magnetic field is
derived. This equation comprises spatial derivatives of high orders due to a
non-local nature of magnetic field transport in a random velocity field with a
finite correlation time. For a random Gaussian velocity field with a small
correlation time the equation for the second-order correlation function of the
magnetic field is a third-order partial differential equation. For this
velocity field and a small magnetic diffusion with large magnetic Prandtl
numbers the growth rate of the second moment of magnetic field is estimated.
The finite correlation time of a turbulent velocity field causes an increase of
the growth rate of magnetic fluctuations. It is demonstrated that the results
obtained for the cases of a small yet finite magnetic diffusion and a zero
magnetic diffusion are different. Astrophysical applications of the obtained
results are discussed.",0205233v1
2005-06-30,Magnetic versus nonmagnetic doping effects on the magnetic ordering in the Haldane chain compound PbNi2V2O8,"A study of an impurity driven phase-transition into a magnetically ordered
state in the spin-liquid Haldane chain compound PbNi2V2O8 is presented. Both,
macroscopic magnetization as well as 51V nuclear magnetic resonance (NMR)
measurements reveal that the spin nature of dopants has a crucial role in
determining the stability of the induced long-range magnetic order. In the case
of nonmagnetic (Mg2+) doping on Ni2+ spin sites (S=1) a metamagnetic transition
is observed in relatively low magnetic fields. On the other hand, the magnetic
order in magnetically (Co2+) doped compounds survives at much higher magnetic
fields and temperatures, which is attributed to a significant anisotropic
impurity-host magnetic interaction. The NMR measurements confirm the predicted
staggered nature of impurity-liberated spin degrees of freedom, which are
responsible for the magnetic ordering. In addition, differences in the
broadening of the NMR spectra and the increase of nuclear spin-lattice
relaxation in doped samples, indicate a diverse nature of electron spin
correlations in magnetically and nonmagnetically doped samples, which begin
developing at rather high temperatures with respect to the antiferromagnetic
phase transition.",0506808v1
2006-09-15,Superconducting pipes and levitating magnets,"Motivated by a beautiful demonstration of the Faraday's and Lenz's law in
which a small neodymium magnet falls slowly through a conducting
non-ferromagnetic tube, we consider the dynamics of a magnet falling through a
superconducting pipe. Unlike the case of normal conducting pipes, in which the
magnet quickly reaches the terminal velocity, inside a superconducting tube the
magnet falls freely. On the other hand, to enter the pipe the magnet must
overcome a large electromagnetic energy barrier. For sufficiently strong
magnets, the barrier is so large that the magnet will not be able to penetrate
it and will be suspended over the front edge. We calculate the work that must
done to force the magnet to enter a superconducting tube. The calculations show
that superconducting pipes are very efficient at screening magnetic fields. For
example, the magnetic field of a dipole at the center of a short pipe of radius
$a$ and length $L \approx a$ decays, in the axial direction, with a
characteristic length $\xi \approx 0.26 a$. The efficient screening of the
magnetic field might be useful for shielding highly sensitive superconducting
quantum interference devices, SQUIDs. Finally, the motion of the magnet through
a superconducting pipe is compared and contrasted to the flow of ions through a
trans-membrane channel.",0609141v1
2007-02-18,Planar Atom Trap and Magnetic Resonance 'Lens' Designs,"We present various planar magnetic designs that create points above the plane
where the magnitude of the static magnetic field is a local minimum. Structures
with these properties are of interest in the disciplines of neutral atom
confinement, magnetic levitation, and magnetic resonance imaging. Each planar
permanent magnet design is accompanied by the equivalent planar single
non-crossing conductor design. Presented designs fall into three categories
producing: a) zero value magnetic field magnitude point minima, b) non-zero
magnetic field magnitude point minima requiring external bias magnetic field,
and c) self-biased non-zero magnetic field magnitude point minima. We also
introduce the Principle of Amperean Current Doubling in planar perpendicularly
magnetized thin films that can be used to improve the performance of each
permanent magnet design we present. Single conductor current-carrying designs
are suitable for single layer lithographic fabrication, as we experimentally
demonstrate. Finally, we present the case that nanometer scale recording of
perpendicular anisotropy thin magnetic films using presently available data
storage technology can provide the ultimate miniaturization of the presented
designs.",0702154v1
2008-05-26,Magnetic field induced incommensurate resonance in cuprate superconductors,"The influence of a uniform external magnetic field on the dynamical spin
response of cuprate superconductors in the superconducting state is studied
based on the kinetic energy driven superconducting mechanism. It is shown that
the magnetic scattering around low and intermediate energies is dramatically
changed with a modest external magnetic field. With increasing the external
magnetic field, although the incommensurate magnetic scattering from both low
and high energies is rather robust, the commensurate magnetic resonance
scattering peak is broadened. The part of the spin excitation dispersion seems
to be an hourglass-like dispersion, which breaks down at the heavily low energy
regime. The theory also predicts that the commensurate resonance scattering at
zero external magnetic field is induced into the incommensurate resonance
scattering by applying an external magnetic field large enough.",0805.3922v2
2010-10-22,Dissipation in dynamos at low and high magnetic Prandtl numbers,"Using simulations of helically driven turbulence, it is shown that the ratio
of kinetic to magnetic energy dissipation scales with the magnetic Prandtl
number in power law fashion with an exponent of approximately 0.6. Over six
orders of magnitude in the magnetic Prandtl number the magnetic field is found
to be sustained by large-scale dynamo action of alpha-squared type. This work
extends a similar finding for small magnetic Prandtl numbers to the regime of
large magnetic Prandtl numbers. At large magnetic Prandtl numbers, most of the
energy is dissipated viscously, lowering thus the amount of magnetic energy
dissipation, which means that simulations can be performed at magnetic Reynolds
numbers that are large compared to the usual limits imposed by a given
resolution. This is analogous to an earlier finding that at small magnetic
Prandtl numbers, most of the energy is dissipated resistively, lowering the
amount of kinetic energy dissipation, so simulations can then be performed at
much larger fluid Reynolds numbers than otherwise. The decrease in magnetic
energy dissipation at large magnetic Prandtl numbers is discussed in the
context of underluminous accretion found in some quasars.",1010.4805v2
2011-07-08,Antimagnets: Controlling magnetic fields with superconductor-metamaterial hybrids,"Magnetism is very important in science and technology, from magnetic
recording to energy generation to trapping cold atoms. Physicists have managed
to master magnetism - to create and manipulate magnetic fields- almost at will.
Surprisingly, there is at least one property which until now has been elusive:
how to 'switch off' the magnetic interaction of a magnetic material with
existing magnetic fields without modifying them. Here we introduce the
antimagnet, a design to conceal the magnetic response of a given volume from
its exterior, without altering the external magnetic fields, somehow analogous
to the recent theoretical proposals for cloaking electromagnetic waves with
metamaterials. However, different from these devices requiring extreme material
properties, our device is feasible and needs only two kinds of available
materials: superconductors and isotropic magnetic materials. Antimagnets may
have applications in magnetic-based medical techniques such as MRI or in
reducing the magnetic signature of vessels or planes.",1107.1647v1
2012-06-29,Enhancement of critical current density in superconducting/magnetic multi-layers with slow magnetic relaxation dynamics and large magnetic susceptibility,"We propose to use superconductor-magnet multi-layer structure to achieve high
critical current density by invoking polaronic mechanism of pinning. The
magnetic layers should have large magnetic susceptibility to enhance the
coupling between vortices and magnetization in magnetic layers. The relaxation
of the magnetization should be slow. When the velocity of vortices is low, they
are dressed by nonuniform magnetization and move as polarons. In this case, the
viscosity of vortices proportional to the magnetic relaxation time is enhanced
significantly. As velocity increases, the polarons dissociate and the viscosity
drops to the usual Bardeen-Stephen one, resulting in a jump in the I-V curve.
Experimentally the jump shows up as a depinning transition and the
corresponding current at the jump is the depinning current. For Nb and proper
magnet multi-layer structure, we estimate the critical current density $J_c\sim
10^{9}\ \rm{A/m^2}$ at magnetic field $B\approx 1$ T.",1206.6929v2
2013-03-07,Complex Magnetic Phase Diagram of a Geometrically Frustrated Sm Lattice: SmPd2Al3 case,"Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry
and neutron diffraction. SmPd2Al3 represents a distinctive example of the Sm
magnetism exhibiting complex magnetic behavior at low temperatures with four
consecutive magnetic phase transitions at 3.4, 3.9, 4.3 and 12.5 K. The rich
magnetic phase diagram of this compound reflects the specific features of the
Sm3+ ion, namely the energy nearness of the ground-state multiplet J = 5/2 and
the first excited multiplet J = 7/2 in conjunction with strong crystal field
influence. Consequently, a significantly reduced Sm magnetic moment in
comparison with the theoretical Sm3+ free-ion value is observed. Despite the
strong neutron absorption by natural samarium and the small Sm magnetic moment
(~ 0.2 {\mu}B) we have successfully determined the magnetic k-vector (1/3, 1/3,
0) of the phase existing in the temperature interval 12.5 - 4.3 K. This
observation classifies the SmPd2Al3 compound as a magnetically frustrated
system. The complex magnetic behavior of this material is further illustrated
by kinetic effects of the magnetization inducing rather complicated magnetic
structure with various metastable states.",1303.1607v1
2013-05-20,Magnetization of neutron star matter,"The magnetization of neutron star matter in magnetic fields is studied by
employing the FSUGold interaction. It is found that the magnetic
susceptibilities of the charged particles (proton, electron and muon) can be
larger than that of neutron. The effects of the anomalous magnetic moments
(AMM) of each component on the magnetic susceptibility are examined in detail.
It is found that the proton and electron AMM affect their respective magnetic
susceptibility evidently in strong magnetic fields. In addition, they are the
protons instead of the electrons that contribute most significantly to the
magnetization of the neutron star matter in a relative weak magnetic field, and
the induced magnetic field due to the magnetization can be appear to be very
large. Finally, the effect of the density-dependent symmetry energy on the
magnetization is discussed.",1305.4533v1
2014-03-11,Piezo-Voltage Manipulation of the Magnetization and Magnetic Reversal in Thin Fe Film,"We carefully investigated the in-plane magnetic reversal and corresponding
magnetic domain structures in Fe/GaAs/piezo-transducer heterostructure using
longitudinal magneto-optical Kerr microscopy. The coexistence of the <100>
cubic magnetic anisotropy and uniaxial magnetic anisotropy was observed in our
Fe thin film grown on GaAs. The induced deformation along [110] orientation can
effectively manipulate the magnetic reversal with magnetic field applied along
magnetic uniaxial hard [110] axes. The control of two-jump magnetization
switching to one-jump magnetization switching during the magnetic reversal was
achieved by piezo-voltages with magnetic field applied in [100] direction. The
additional uniaxial anisotropy induced by piezo-voltages at -75 /75V are
-1.400/1400 J/m3 .",1403.2469v1
2014-09-29,Review and comparison of magnet designs for magnetic refrigeration,"One of the key issues in magnetic refrigeration is generating the magnetic
field that the magnetocaloric material must be subjected to. The magnet
constitutes a major part of the expense of a complete magnetic refrigeration
system and a large effort should therefore be invested in improving the magnet
design. A detailed analysis of the efficiency of different published permanent
magnet designs used in magnetic refrigeration applications is presented in this
paper. Each design is analyzed based on the generated magnetic flux density,
the volume of the region where this flux is generated and the amount of magnet
material used. This is done by characterizing each design by a figure of merit
magnet design efficiency parameter, $\Lambda_\mathrm{cool}$. The designs are
then compared and the best design found. Finally recommendations for designing
the ideal magnet design are presented based on the analysis of the reviewed
designs.",1409.8046v1
2015-04-22,Magnetized stars with differential rotation and a differential toroidal field,"We have succeeded in obtaining magnetized equilibrium states with
differential rotation and differential toroidal magnetic fields. If an internal
toroidal field of a proto-neutron star is wound up from the initial poloidal
magnetic field by differential rotation, the distribution of the toroidal
magnetic field is determined by the profile of this differential rotation.
However, the distributions of the toroidal fields in all previous magnetized
equilibrium studies do not represent the magnetic winding by the differential
rotation of the star. In this paper, we investigate a formulation of a
differential toroidal magnetic field that represents the magnetic field wound
up by differential rotation. We have developed two functional forms of
differential toroidal fields which correspond to a v-constant and a j-constant
field in analogy to differential rotations. As the degree of the differential
becomes very high, the toroidal magnetic field becomes highly localized and
concentrated near the rotational axis. Such a differential toroidal magnetic
field would suppress the low-T/|W| instability more efficiently even if the
total magnetic field energy is much smaller than that of a non-differential
toroidal magnetic field.",1504.05961v2
2016-04-01,Photoinduced Magnetic Nanoprobe Excited by Azimuthally Polarized Vector Beam,"The concept of magnetic nanoprobes (or magnetic nanoantennas) providing a
magnetic near-field enhancement and vanishing electric field is presented and
investigated, together with their excitation. It is established that a
particular type of cylindrical vector beams called azimuthally electric
polarized vector beams yield strong longitudinal magnetic field on the beam
axis where the electric field is ideally null. These beams with an electric
polarization vortex and cylindrical symmetry are important in generating high
magnetic to electric field contrast, i.e., large local field admittance, and in
allowing selective excitation of magnetic transitions in matter located on the
beam axis. We demonstrate that azimuthally polarized vector beam excitation of
a photoinduced magnetic nanoprobe made of a magnetically polarizable nano
cluster leads to enhanced magnetic near field with resolution beyond
diffraction limit. We introduce two figures of merit as magnetic field
enhancement and local field admittance normalized to that of a plane wave that
are useful to classify magnetic nanoprobes and their excitation. The
performance of magnetic nanoprobe and azimuthal polarized beams is quantified
in comparison to other illumination options and with several defect scenarios.",1604.00379v1
2016-09-23,Chirality-driven orbital magnetic moments as a new probe for topological magnetic structures,"When electrons are driven through unconventional magnetic structures, such as
skyrmions, they experience emergent electromagnetic fields that originate
several Hall effects. Independently, ground state emergent magnetic fields can
also lead to orbital magnetism, even without the spin-orbit interaction. The
close parallel between the geometric theories of the Hall effects and of the
orbital magnetization raises the question: does a skyrmion display topological
orbital magnetism? Here we first address the smallest systems with nonvanishing
emergent magnetic field, trimers, characterizing the orbital magnetic
properties from first-principles. Armed with this understanding, we study the
orbital magnetism of skyrmions, and demonstrate that the contribution driven by
the emergent magnetic field is topological. This means that the topological
contribution to the orbital moment does not change under continous deformations
of the magnetic structure. Furthermore, we use it to propose a new experimental
protocol for the identification of topological magnetic structures, by soft
x-ray spectroscopy.",1609.07529v1
2017-02-24,Angle-dependence and optimal design for magnetic bubblecade with maximum speed,"Unidirectional magnetic domain-wall motion is a key concept underlying
next-generation application devices. Such motion has been recently demonstrated
by applying an alternating magnetic field, resulting in the coherent
unidirectional motion of magnetic bubbles. Here we report the optimal
configuration of applied magnetic field for the magnetic bubblecade, the
coherent unidirectional motion of magnetic bubbles, driven by a tilted
alternating magnetic field. The tilted alternating magnetic field induces
asymmetric expansion and shrinkage of the magnetic bubbles under the influence
of the Dzyaloshinskii-Moriya interaction, resulting in continuous shift of the
bubbles in time. By realizing the magnetic bubblecade in PtCoPt films, we find
that the bubblecade speed is sensitive to the tilt angle with a maximum at an
angle, which can be explained well by a simple analytical form within the
context of the domain-wall creep theory. A simplified analytic formula for the
angle for maximum speed is then given as a function of the amplitude of the
alternating magnetic field. The present observation provides a practical design
rule for memory and logic devices based on the magnetic bubblecade.",1702.07439v1
2018-09-13,On the role of magnetic fields in star formation,"Magnetic fields are observed in star forming regions. However simulations of
the late stages of star formation that do not include magnetic fields provide a
good fit to the properties of young stars including the initial mass function
(IMF) and the multiplicity. We argue here that the simulations that do include
magnetic fields are unable to capture the correct physics, in particular the
high value of the magnetic Prandtl number, and the low value of the magnetic
diffusivity. The artificially high (numerical and uncontrolled) magnetic
diffusivity leads to a large magnetic flux pervading the star forming region.
We argue further that in reality the dynamics of high magnetic Prandtl number
turbulence may lead to local regions of magnetic energy dissipation through
reconnection, meaning that the regions of molecular clouds which are forming
stars might be essentially free of magnetic fields. Thus the simulations that
ignore magnetic fields on the scales on which the properties of stellar masses,
stellar multiplicities and planet-forming discs are determined, may be closer
to reality than those which include magnetic fields, but can only do so in an
unrealistic parameter regime.",1809.04921v1
2019-03-28,Micromagnetics of rare-earth efficient permanent magnets,"The development of permanent magnets containing less or no rare-earth
elements is linked to profound knowledge of the coercivity mechanism.
Prerequisites for a promising permanent magnet material are a high spontaneous
magnetization and a sufficiently high magnetic anisotropy. In addition to the
intrinsic magnetic properties the microstructure of the magnet plays a
significant role in establishing coercivity. The influence of the
microstructure on coercivity, remanence, and energy density product can be
understood by {using} micromagnetic simulations. With advances in computer
hardware and numerical methods, hysteresis curves of magnets can be computed
quickly so that the simulations can readily provide guidance for the
development of permanent magnets. The potential of rare-earth reduced and free
permanent magnets is investigated using micromagnetic simulations. The results
show excellent hard magnetic properties can be achieved in grain boundary
engineered NdFeB, rare-earth magnets with a ThMn12 structure, Co-based
nano-wires, and L10-FeNi provided that the magnet's microstructure is
optimized.",1903.11922v1
2020-04-24,Observation of magnetic domains in uniaxial magnets via small-angle electron diffraction and Foucault imaging,"Observation of magnetic domains is important in understanding the magnetic
properties of magnetic materials and devices. In this study, we report that the
magnetic domains of M-type hexaferrites with uniaxial anisotropy can be
visualized via small-angle electron diffraction and Foucault imaging. The
position of the diffraction pattern spots has the same period as that of
magnetic domains in a Sc-substituted hexaferrite
(BaFe$_{12-x-\delta}$Sc$_x$Mg$_\delta$O$_{19}$). Conversely, the spots were
observed four times longer than the period of magnetic domains in hexaferrite
without substitution (BaFe$_{12}$O$_{19}$), demonstrating the long-range order
of the Bloch walls. When the specimen was tilted, the magnetic deflection
effect, as well as the periodic spots of magnetic domains, occurred. Thus, we
were able to visualize the magnetic domains with different magnetization
directions and domain orientations by selecting deflection spots. The results
indicate that the technique utilized in this study is useful in observing the
magnetic materials with uniaxial anisotropy.",2004.11589v1
2021-01-12,Modeling of Thermal Magnetic Fluctuations in Nanoparticle Enhanced Magnetic Resonance Detection,"We present a systematic numerical modeling investigation of magnetization
dynamics and thermal magnetic moment fluctuations of single magnetic domain
nanoparticles in a configuration applicable to enhancing inductive magnetic
resonance detection signal to noise ratio (SNR). Previous proposals for
oriented anisotropic single magnetic domain nanoparticle amplification of
magnetic flux in MRI coil focused only on the coil pick-up voltage signal
enhancement. Here we extend the analysis to the numerical evaluation of the SNR
by modeling the inherent thermal magnetic noise introduced into the detection
coil by the insertion of such anisotropic nanoparticle-filled coil core. We
utilize the Landau-Lifshitz-Gilbert equation under the Stoner-Wohlfarth single
magnetic domain (macrospin) assumption to simulate the magnetization dynamics
in such nanoparticles due to AC drive field as well as thermal noise. These
simulations are used to evaluate the nanoparticle configurations and shape
effects on enhancing SNR. Finally, we explore the effect of narrow band
filtering of the broadband magnetic moment thermal fluctuation noise on the
SNR. Our results provide the impetus for relatively simple modifications to
existing MRI systems for achieving enhanced detection SNR in scanners with
modest polarizing magnetic fields.",2101.04649v1
2021-04-27,Mechanism of parametric pumping of magnetization precession in a nanomagnet. Parametric mechanism of current-induced magnetization reversal,"A mechanism of current-induced magnetization reversal based on the parametric
resonance is described. The source of the magnetization reversal is a
current-induced magnetic field, which is applied perpendicularly to the easy
axis of magnetic anisotropy of a ferromagnetic nanomagnet. The current-induced
magnetic field was measured in a FeCoB nanomagnet to be 60 Gauss at a current
density of 65 mA/um2. Two mechanisms of the magnetization reversal are
described and calculated. The first mechanism is the reversal by a RF
electrical current, which modulated at a frequency close to the precession
frequency of the nanomagnet. The second mechanism is the reversal by a DC
electrical current, in which the magneto-resistance and the current dependency
of the induced magnetic field create a positive feedback loop, which amplifies
a random tiny thermal fluctuation into a large magnetization precession leading
to the magnetization reversal. The combination of the proposed mechanism with
conventional magnetization-reversal mechanisms such as the Spin Torque and the
Spin-Orbit Torque can improve the performance of a Magnetic Random Access
Memory.",2104.13008v1
2021-05-02,Magnetic textures in a hexaferrite thin film and their response to magnetic fields revealed by phase microscopy,"We investigated magnetic textures in a Sc-doped hexaferrite film by means of
phase microscopy (PM) with a hole-free phase plate in a transmission electron
microscope. In a zero magnetic field, the stripe-shaped magnetic domains
coexist with magnetic bubbles. The magnetization in both magnetic domains was
oriented perpendicular to the film and the domain walls have an in-plane
magnetization. In the remnant state at 9.2 mT, several magnetic bubbles were
formed with the formation of stripe-shaped magnetic domains, and the
out-of-plane component in the stripe-shaped domains gradually appeared as the
film thickness increased. As the film thickness increases further, the magnetic
bubbles with clockwise or counter-clockwise spin helicities formed a triangular
lattice. These results in the remnant state suggest that the domain wall energy
in the magnetic bubble domains is lower in the thicker region.",2105.00396v1
2022-04-20,Control of magnetic susceptibility of probiotic strain Lactobacillus Rhamnosus GG,"The paper investigates the increase in the natural magnetically controlled
properties of probiotic microorganisms Lactobacillus rhamnosus GG (LGG) and
their ability to form magnetic sensitive inclusions (MsI). The magnetic
susceptibility of LGG was increased by modifying the nutrient medium
composition and by cultivating the probiotic culture in a constant magnetic
field. Therefore, this study can be useful for their further use as
magnetically controlled vectors, since it is being extensively researched for
the use in targeted drug delivery in cancer treatment, for the prevention of
chemotherapy complications, etc. The results of this study indicate that
growing microorganisms with natural magnetically-guided properties in a
modified medium with iron chelate and in an external magnetic field leads to an
increase in the magnetic susceptibility of LGG by 1,8 and 2,6 times,
respectively, compared with the control. The best magnetic susceptibility was
recorded for LGG suspensions, which were grown in a constant magnetic field and
cultured in modified medium with iron chelate. The LGG suspension, grown both
in a constant magnetic field and on a modified medium with iron chelate, had
the highest magnetic susceptibility and was 4.8 times larger than the control.",2204.09338v1
2022-09-22,Stacking and Layer dependence of magnetic properties in Ti\textsubscript{2}C and Fe\textsubscript{2}C,"Magnetic MXenes are turning out to be an important family of materials for
exploring 2D magnetism. However, investigations into the inter-dependence of
layer thickness, stacking patterns and magnetism in these materials, from a
microscopic point of view, is still lacking. In this work, we have used Density
Functional Theory (DFT) based calculations to understand the effects of layer
thickness and stacking on the magnetic properties in two magnetic MXenes,
Ti$_{2}$C and Fe$_{2}$C in their monolayer and bilayer forms. The ground state
magnetic structures, magnetic moments, magnetic exchange interactions, magnetic
transition temperatures and magnetic anisotropy energies are calculated and
analysed using their electronic structures and standardised models. We find
that in both systems increase in layer thickness (monolayer to bilayer) affects
the ground state magnetic configuration which is driven by the changes in the
magnetic exchange interactions. While the effects of stacking pattern is rather
weak in Ti$_{2}$C, they are substantial, both qualitatively and quantitatively
in Fe$_{2}$C. The computed results are analysed from their electronic
structures. The results suggest that fascinating physical effects can be
obtained in Fe$_{2}$C by tuning the layer thickness and stacking patterns,
making it more suitable for device applications.",2209.10765v1
2023-01-04,Magnetic light amplification by stimulated emission of radiation in subwavelength systems of a dielectric cavity and magnetic quantum emitters,"We propose a magnetic laser in a subwavelength system consisting of a
high-refractive-index dielectric cavity and an active medium formed by magnetic
quantum emitters. Stimulated emissions of magnetic quantum emitters induced by
their coherent interactions with quantized magnetic fields of a cavity are
theoretically considered. The condition to archive such a magnetic laser is
obtained. Numerical results show that magnetic lasers are feasible in some
realistic systems, for example, a silicon disk of high-quality whispering
gallery modes with embedded emitters. Furthermore, the competitions between the
electric interaction and magnetic one in terms of their Purcell factors are
also considered in some magnetic laser achievable systems. In a
wavelength-scale silicon block of a high-order magnetic mode, the ratio of
magnetic Purcell factor to the electric one can reach more than ~10^3 large.
Our results open up ways to enhanced magnetic light-matter interactions.",2301.01418v2
2023-04-23,Magnetism and Fermiology of Kagome Magnet YMn6Sn4Ge2,"Kagome lattice magnets are an interesting class of materials as they can host
topological properties in their magnetic and electronic structures. YMn6Sn6 is
one such compound in which a series of competing magnetic phases is stabilized
by an applied magnetic field, and both an enigmatic topological Hall effect and
a Dirac crossing close to the Fermi energy have been realized. This material
also shows a magnetization-induced Lifshitz transition and evidence of a unique
charge spin coupling in one of the magnetic phases, namely the fan-like phase.
Tuning the magnetism, and thus the interplay with the electronic states, opens
new avenues for precise control of these novel properties. Here, we demonstrate
the extreme sensitivity of the magnetic phases in YMn6Sn4Ge2 through the
investigation of structural, magnetic, and transport properties. The high
sensitivity to small doping provides great potential for engineering the
magnetic phases and associated electronic properties in this family of
rare-earth kagome magnets.",2304.11502v1
2023-06-02,Accelerating the electronic-structure calculation of magnetic systems by equivariant neural networks,"Complex spin-spin interactions in magnets can often lead to magnetic
superlattices with complex local magnetic arrangements, and many of the
magnetic superlattices have been found to possess non-trivial topological
electronic properties. Due to the huge size and complex magnetic moment
arrangement of the magnetic superlattices, it is a great challenge to perform a
direct DFT calculation on them. In this work, an equivariant deep learning
framework is designed to accelerate the electronic calculation of magnetic
systems by exploiting both the equivariant constraints of the magnetic
Hamiltonian matrix and the physical rules of spin-spin interactions. This
framework can bypass the costly self-consistent iterations and build a direct
mapping from a magnetic configuration to the ab initio Hamiltonian matrix.
After training on the magnets with random magnetic configurations, our model
achieved high accuracy on the test structures outside the training set, such as
spin spiral and non-collinear antiferromagnetic configurations. The trained
model is also used to predict the energy bands of a skyrmion configuration of
NiBrI containing thousands of atoms, showing the high efficiency of our model
on large magnetic superlattices.",2306.01558v1
2023-08-10,Change ratios of magnetic helicity and magnetic free energy during major solar flares,"Magnetic helicity is an important concept in solar physics, with a number of
theoretical statements pointing out the important role of magnetic helicity in
solar flares and coronal mass ejections (CMEs). Here we construct a sample of
47 solar flares, which contains 18 no-CME-associated confined flares and 29
CME-associated eruptive flares. We calculate the change ratios of magnetic
helicity and magnetic free energy before and after these 47 flares. Our
calculations show that the change ratios of magnetic helicity and magnetic free
energy show distinct different distributions in confined flares and eruptive
flares. The median value of the change ratios of magnetic helicity in confined
flares is $-0.8$%, while this number is $-14.5$% for eruptive flares. For the
magnetic free energy, the median value of the change ratios is $-4.3$% for
confined flares, whereas this number is $-14.6$% for eruptive flares. This
statistical result, using observational data, is well consistent with the
theoretical understandings that magnetic helicity is approximately conserved in
the magnetic reconnection, as shown by confined flares, and the CMEs take away
magnetic helicity from the corona, as shown by eruptive flares.",2308.05366v1
2002-04-09,Local Circumstellar Magnetic Fields Around Evolved Stars,"I argue that the presence of magnetic fields around evolved stars, e.g.,
asymptotic giant branch stars, and in PNe, does not necessarily imply that the
magnetic field plays a global dynamical role in shaping the circumstellar
envelope. Instead, I favor magnetic fields with small coherence lengths, which
result from stellar magnetic spots or from jets blown by an accreting
companion. Although the magnetic field does not play a global role in shaping
the circumstellar envelope, it may enhance local motion (turbulent) via
magnetic tension and reconnection. The locally strong magnetic tension may
enforce coherence flow which may favor the masing process.",0204157v1
1998-02-25,Magnetization Controlled Superconductivity in a Film with Magnetic Dots,"We consider a superconducting film with Magnetic Dots Array (MDA) placed on
it. Magnetic moments of these dots are supposed to be normal to the film and
strong enough to create vortices in the superconducting film. Magnetic
interaction between dots is negligible. Below the superconducting transition
temperature of the film in zero magnetic field the MDA with randomly magnetized
dots produces resistive state of the film. Paradoxically, in a finite magnetic
field the film with MDA is superconductive.",9802276v1
1999-05-21,Magnetic Field Induced Ordering in Quasi-One-Dimensional Quantum Magnets,"Three-dimensional magnetic ordering transitions are studied theoretically in
strongly anisotropic quantum magnets. An external magnetic field can drive
quasi-one-dimensional subsystems with a spin gap into a gapless regime, thus
inducing long-range three-dimensional magnetic ordering due to weak residual
magnetic coupling between the subsystems. Compounds with higher spin degrees of
freedom, such as N-leg spin-1/2 ladders, are shown to have cascades of ordering
transitions. At high magnetic fields, zero-point fluctuations within the
quasi-1D subsystems are suppressed, causing quantum corrections to the ordering
temperature to be reduced.",9905331v1
2000-04-05,Spin 1/2 Magnetic Impurity in a 2D Magnetic System Close to Quantum Critical Point,"We consider a magnetic impurity in a spin liquid state of a magnetic system
which is close to the quantum phase transition to the magnetically ordered
state. There is similarity between this problem and the Kondo problem. We
derive the impurity Green's function, consider renormalizations of the magnetic
moments of the impurity, calculate critical indexes for the magnetic
susceptibilities and finally consider specific heat and magnetic interaction of
two impurities.",0004057v1
2000-04-14,Magnetic Field Effects on Neutron Diffraction in the Antiferromagnetic Phase of $UPt_3$,"We discuss possible magnetic structures in UPt$_3$ based on our analysis of
elastic neutron-scattering experiments in high magnetic fields at temperatures
$T<T_N$. The existing experimental data can be explained by a single-{\bf q}
antiferromagnetic structure with three independent domains. For modest in-plane
spin-orbit interactions, the Zeeman coupling between the antiferromagnetic
order parameter and the magnetic field induces a rotation of the magnetic
moments, but not an adjustment of the propagation vector of the magnetic order.
A triple-{\bf q} magnetic structure is also consistent with neutron
experiments, but in general leads to a non-uniform magnetization in the
crystal. New experiments could decide between these structures.",0004253v1
2003-07-08,Asymmetric Lineshape due to Inhomogeneous Broadening of the Crystal-Field Transitions in Mn12ac Single Crystals,"The lineshape of crystal-field transitions in single crystals of Mn12ac
molecular magnets is determined by the magnetic history. The absorption lines
are symmetric and Gaussian for the non-magnetized state obtained by zero-field
cooling (zfc). In the magnetized state which is reached when the sample is
cooled in a magnetic field (fc), however, they are asymmetric even in the
absence of an external magnetic field. These observations are quantitatively
explained by inhomogeneous symmetrical (Gaussian) broadening of the
crystal-field transitions combined with a contribution of off-diagonal
components of the magnetic susceptibility to the effective magnetic
permeability.",0307164v1
2005-01-17,Frustration effects in magnetic molecules,"By means of exact diagonalization we study the ground-state and the
low-temperature physics of the Heisenberg antiferromagnet on the cuboctahedron
and the icosidodecahedron. Both are frustrated magnetic polytopes and
correspond to the arrangement of magnetic atoms in the magnetic molecules
Cu12La8 and Mo72Fe30. The interplay of strong quantum fluctuations and
frustration influences the ground state spin correlations drastically and leads
to an interesting magnetization process at low temperatures. Furthermore the
frustration yields low-lying non-magnetic excitations resulting in an extra
low-temperature peak in the specific heat.",0501376v1
2005-09-28,About low field memory and negative magnetization in semiconductors and polymers,"Ginzburg-Landau bulk magnetization of itinerant electrons can provide a
negative effective field in the Weiss model by coupling to localized magnetic
moments. The coupling enforces remnant magnetization, which can be negative or
positive depending on the sample magnetic history. Stable magnetic
susceptibility of coupled nonequilibrium subsystems with magnetization reversal
is always positive. Gauss-scale fields could be expected for switching between
negative and positive remnant moments in semiconductors with coupling at
ambient temperatures. Negative magnetization in ultra-high conducting polymers
is also discussed within the developed framework.",0509712v1
2005-10-10,Magnetic dipole-vortex interaction in a bilayer superconductor/soft-magnet heterostructure,"We study the penetration of the nonuniform magnetic field, created by a
magnetic dipole with out-of-plane magnetization, into a film heterostructure
composed of a type-II superconductor layer and a soft-magnet layer. In the
framework of the London approach, the energy of the magnetic dipole-vortex
interaction is derived and the critical value of the dipole moment for the
first appearance of a vortex in the superconducting constituent is found for
two cases of the layer ordering, namely when the dipole is located near the
superconducting or, respectively, the magnetic constituent.",0510251v1
2005-10-18,Local field of magnetic islands: role of their shape,"I analyze in details distribution of local magnetic field induced by micro-
and nano-magnets. I consider three kinds of elongated magnetic islands:
ellipse-, diamond- and rectangular shaped islands which were magnetized
uniformly along long axis. This report concentrates on the role of their shape
upon distribution of the field. Calculations show that unlike
rectangular-shaped magnet, ellipse-shaped and diamond-shaped ones produce much
more localized field in proximity of its magnetic poles. Additionally in the
case of ellipse-shaped islands the magnitude of induced field is large. This
two facts favor arrays of ellipse-shaped magnetic islands to build
zero-dimensional spin traps in a hybrid based on Ferromagnet/Semiconductor
structure.",0510486v1
2005-11-23,Nonequilibrium Magnetization of a Two-Dimensional Electron Gas in a Static Magnetic Field,"Using a sensitive DC torque magnetometer we measure the orbital magnetization
by sweeping the density at fixed magnetic fields on GaAs-AlGaAs
heterostructures. At low temperatures strong nonequilibrium magnetization
signals dominate the data. In literature the observation of nonequilibrium
signals are often associated with eddy currents generated by sweeping the
magnetic field. The elimination of a changing magnetic field then poses a
question regarding the origin of these signals. Our data suggests another
source of nonequilibrium magnetization potentially due to the change of area
occupied by compressible and incompressible states as one sweeps the Fermi
energy from one Landau level to the next.",0511569v1
2006-04-01,Magnetization reversal through synchronization with a microwave,"Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a
circularly-polarized microwave can reverse the magnetization of a Stoner
particle through synchronization. In comparison with magnetization reversal
induced by a static magnetic field, it can be shown that when a proper
microwave frequency is used the minimal switching field is much smaller than
that of precessional magnetization reversal. A microwave needs only to overcome
the energy dissipation of a Stoner particle in order to reverse magnetization
unlike the conventional method with a static magnetic field where the switching
field must be of the order of magnetic anisotropy.",0604013v1
2006-05-01,Possible magnetic-field-induced voltage and thermopower in diluted magnetic semiconductors,"In diluted magnetic semiconductors, the carrier concentration and the
magnetization of local moments are strongly coupled, since the magnetic
interaction is mediated by the carriers. It is predicted that this coupling
leads to an electric polarization due to an applied magnetic-field gradient and
to the appearance of a magnetic-field-dependent voltage. An expression for this
voltage is derived within Landau theory and its magnitude is estimated for
(Ga,Mn)As. Furthermore, a large contribution to the thermopower based on the
same mechanism is predicted. The role of fluctuations is also discussed. These
predictions hold both if the magnetization is uniform and if it shows
stripe-like modulations, which are possible at lower temperatures.",0605043v1
2006-05-22,Kondo-transport spectroscopy of single molecule magnets,"We demonstrate that in a single molecule magnet (SMM) strongly coupled to
electrodes the Kondo effect involves all magnetic excitations. This Kondo
effect is induced by the quantum tunneling of the magnetic moment (QTM).
Importantly, the Kondo temperature $T_K$ can be much larger than the magnetic
splittings. We find a strong modulation of the Kondo effect as function of the
transverse anisotropy parameter or a longitudinal magnetic field. For both
integer and half-integer spin this can be used for an accurate transport
spectroscopy of the magnetic states in low magnetic fields on the order of the
easy-axis anisotropy parameter. We set up a relationship between the Kondo
effects for successive integer and half-integer spins.",0605514v1
2006-07-19,Magnetic-Field Induced Gap in One-Dimensional Antiferromagnet KCuGaF$_6$,"Magnetic susceptibility and specific heat measurements in magnetic fields
were performed on an $S=1/2$ one-dimensional antiferromagnet KCuGaF$_6$.
Exchange interaction was evaluated as $J/k_{\rm B}\simeq 100$ K. However, no
magnetic ordering was observed down to 0.46 K. It was found that an applied
magnetic field induces a staggered magnetic susceptibility obeying the Curie
law and an excitation gap, both of which should be attributed to the
antisymmetric interaction of the Dzyaloshinsky-Moriya type and/or the staggered
$g$-tensor. With increasing magnetic field $H$, the gap increases almost in
proportion to $H^{2/3}$.",0607469v1
1998-11-18,Magnetic field profiling for selected-states magnetic-resonance spectroscopy (SSMRS) and Stern-Gerlach spectroscopy (MGRS) in condensed matter,"A method was presented of profiling the magnetic field, with a zero vector of
magnetic flux density $B_{r}$ and strong gradient G, enabling conditions for
the Stern-Gerlach spectroscopy to be accomplished in condensed matter (the
method has been called magnetic field gradient spectroscopy - MGRS), as well
the previously proposed magnetic resonance spectroscopy for selected energy
states (SSMRS). Magnetic field distribution in a model electromagnet were shown
when condition $B_{r}= 0$ for resultant magnetic field was satisfied within the
sample",9811034v1
2007-08-22,Neutron channelling in a magnetic tube trap,Neutron channelling in a magnetic tube trap is discussed,0708.3042v1
2007-11-13,Magnetic nanowires as permanent magnet materials,"We present the fabrication of metallic magnetic nanowires using a low
temperature chemical process. We show that pressed powders and magnetically
oriented samples exhibit a very high coercivity (6.5 kOe at 140 K and 4.8 kOe
at 300 K). We discuss the magnetic properties of these metamaterials and show
that they have the suitable properties to realize ""high temperature magnets""
competitive with AlNiCo or SmCo permanent magnets. They could also be used as
recording media for high density magnetic recording.",0711.1978v1
2008-06-28,Effect of magnetization and magnetic field variation on stationary axisymmetric equilibrium,"The inclusion of plasma magnetization in the equations of stationary
equilibrium is derived, and its effect on the determination of axisymmetric
equilibrium calculated. A factor of 2 on the pressure gradient arises in the
equilibrium equation from the force felt by the dipole moment density. The
algebraic and differential equation formulations are compared both with and
without consideration of magnetization, revealing the effects of both
magnetization and magnetic field variation on the equilibrium, which become
more pronounced for high pressures in a weak external field. The equivalence of
the magnetized equilibrium equation with the standard equilibrium equation in
the limit of vanishing magnetization is demonstrated.",0806.4696v2
2008-10-07,Multiple magnetic barriers in graphene,"We study the behavior of charge carriers in graphene in inhomogeneous
perpendicular magnetic fields. We consider two types of one-dimensional
magnetic profiles, uniform in one direction: a sequence of N magnetic barriers,
and a sequence of alternating magnetic barriers and wells. In both cases, we
compute the transmission coefficient of the magnetic structure by means of the
transfer matrix formalism, and the associated conductance. In the first case
the structure becomes increasingly transparent upon increasing N at fixed total
magnetic flux. In the second case we find strong wave-vector filtering and
resonant effects. We also calculate the band structure of a periodic magnetic
superlattice, and find a wave-vector-dependent gap around zero-energy.",0810.1236v1
2008-12-10,Magnetic monopole and the nature of the static magnetic field,"We investigate the factuality of the hypothetical magnetic monopole and the
nature of the static magnetic field. It is shown from many aspects that the
concept of the massive magnetic monopoles clearly is physically untrue. We
argue that the static magnetic field of a bar magnet, in fact, is the static
electric field of the periodically quasi-one-dimensional electric-dipole
superlattice, which can be well established in some transition metals with the
localized d-electron. This research may shed light on the perfect unification
of magnetic and electrical phenomena.",0812.2048v1
2011-07-14,Magnetic instability induced by tunnel current in single Co nanoparticles,"Measurements of magnetic hysteresis loops in single Co nanoparticles at
dilution refrigerator temperatures are presented. The nanoparticles are in
electric contact with bulk Al leads via tunnel junctions. The tunnel current
versus magnetic field displays a magnetic hysteresis loop. The magnetic
switching field is reduced by current, and the magnetization of the
nanoparticle can be switched by applying a voltage pulse, demonstrating that
the magnetic stability of the nanoparticle is diminished by electron transport.
Additional transitions and random switches of magnetization can be driven by
large currents.",1107.2850v3
2011-08-09,"Magnetic phases of a highly frustrated magnet, ZnCr2O4, up to an ultra-high magnetic field of 600 T","The Faraday rotation and magneto-optical absorption spectral measurements
were conducted to reveal the full-magnetization process and map out a magnetic
phase diagram of a typical geometrical frustrated magnet, ZnCr2O4, by using the
electromagnetic flux compression method in ultra-magnetic fields up to 600 T. A
fully polarized ferromagnetic phase is observed in which the absorption spectra
associated with an exciton-magnon-phonon transition disappears. Furthermore,
prior to the fully polarized ferromagnetic phase above 410 T, we found a novel
magnetic phase above 350 T followed by a canted 3:1 phase.",1108.1932v1
2012-01-04,Origin of training effect of exchange bias in Co/CoO due to irreversible thermoremanent magnetization of the magnetically diluted antiferromagnet,"The irreversible thermoremanent magnetization of a sole, magnetically diluted
epitaxial antiferromagnetic Co$_{1-y}$O(100) layer is determined by the mean of
its thermoremanent magnetizations at positive and negative remanence. During
hysteresis-loop field cycling, thermoremanent magnetization exhibits successive
reductions, consistent with the training effect (TE) of the exchange bias
measured for the corresponding Co$_{1-y}$O(100)/Co bilayer. The TE of exchange
bias is shown to have its microscopic origin in the TE of the irreversible
thermoremanent magnetization of the magnetically diluted AFM.",1201.0831v1
2012-03-21,Percolation and orientational ordering in systems of magnetic nanorods,"Based on Monte Carlo (MC) computer simulations we study the structure
formation of a system of magnetic nanorods. Our model particles consist of
fused spheres with permanent magnetic dipole moments, as inspired by recent
experiments. The resulting system behaves significantly different from a system
of hard (non-magnetic) rods or magnetic rods with a single longitudinal dipole.
In particular, we observe for the magnetic nanorods a significant decrease of
the percolation threshold (as compared to non-magnetic rods) at low densities,
and a stabilization of the high-density nematic phase. Moreover, the
percolation threshold is tunable by an external magnetic field.",1203.4707v1
2012-07-10,Micromagnetic simulation of magnetic small-angle neutron scattering from two-phase nanocomposites,"The recent development of a micromagnetic simulation methodology - suitable
for multiphase magnetic nanocomposites - permits the computation of the
magnetic microstructure and of the associated magnetic small-angle neutron
scattering (SANS) cross section of these materials. In this review article we
summarize results on the micromagnetic simulation of magnetic SANS from
two-phase nanocomposites. The decisive advantage of this approach resides in
the possibility to srutinize the individual magnetization Fourier contributions
to the total magnetic SANS cross section, rather than their sum, which is
generally obtained from experiment. The procedure furnishes unique and
fundamental information regarding magnetic neutron scattering from nanomagnets.",1207.2331v1
2013-04-10,A proposed new route to d0 magnetism in semiconductors,"Here we propose to induce magnetism in semiconductor utilizing the unique
properties of the interstitial defect to act as the magnetic impurity within
the alpha-PbO crystal structure. The Pbi interstitial generates the p-localized
state with two on-site electrons to obey the Hund's rule for their ordering. It
is demonstrated that instead of Pb interstitial other non-magnetic impurities
of s^2p^{x} outer shell configuration can be applied to induce d0 magnetism
with possibility to tune the local magnetic moments mu_B by varying a number of
electrons 1< x< 3. The magnetic coupling between such defects is found to be
driven by the long-range order interactions that in combination with high
defect solubility promises the magnetic percolation to remain above the room
temperature.",1304.2945v1
2013-11-21,A new Approach for Magnetic Curves in 3D Riemannian Manifolds,"A magnetic field is defined by the property that its divergence is zero in a
three dimensional oriented Riemannian manifold. Each magnetic field generates a
magnetic flow whose trajectories are curves called as magnetic curves. In this
paper, we give a new variational approach to studies the magnetic flow
asociated with the Killing magnetic field in a three dimensional oriented
Riemann manifold, And then, we investigate the trajectories of the magnetic
fields called as N-magnetic and B-magnetic curves.",1311.5348v3
2014-03-13,Monte Carlo simulated dynamical magnetization of single-chain magnets,"Here, a dynamical Monte-Carlo (DMC) method is used to study
temperature-dependent dynamical magnetization of famous Mn2Ni system as typical
example of single-chain magnets with strong magnetic anisotropy. Simulated
magnetization curves are in good agreement with experimental results under
typical temperatures and sweeping rates, and simulated coercive fields as
functions of temperature are also consistent with experimental curves. Further
analysis indicates that the magnetization reversal is determined by both
thermal-activated effects and quantum spin tunnelings. These can help explore
basic properties and applications of such important magnetic systems.",1403.3188v2
2014-09-25,Atomistic simulation of sub-nanosecond non-equilibrium field cooling processes for magnetic data storage applications,"Thermally assisted magnetic writing is an important technology utilizing
temperature dependent magnetic properties to enable orientation of a magnetic
data storage medium. Using an atomistic spin model we study non-equilibrium
field cooled magnetization processes on sub-nanosecond timescales required for
device applications. We encapsulate the essential physics of the process in a
TRM-T curve and show that for fast timescales heating to the Curie temperature
is necessary where the magnetic relaxation time is shortest. Furthermore we
demonstrate the requirement for large magnetic fields to achieve a high
thermoremanent magnetization necessary for fast recording or data rates.",1409.7377v1
2015-05-13,Optical detection of magnetic orders in HgCr$_2$O$_4$ frustrated spin magnet under pulsed high magnetic fields,"A magneto-optical survey was conducted for HgCr$_2$O$_4$ powder samples under
pulsed high magnetic fields of up to 55 T. Intensity changes in magnetic fields
observed for the exciton-magnon-phonon optical transition spectra coincide well
with those of magnetization, lattice distortion from X-ray diffraction, and
electron-magnetic resonances. The last-ordered phase was detected prior to the
fully polarized magnetic phase, similarly to the other chromium spinel oxide,
ZnCr$_2$O$_4$ and CdCr$_2$O$_4$.",1505.03216v1
2015-07-22,Magnetic Response Functions in Landau Levels,"We propose a new quantization rule which generates Landau levels consistent
with the zero-field magnetic response functions from the semiclassical theory.
It reproduces the Onsager's rule in the leading order, and re-formulates
corrections from the Berry phase and magnetic moment effect in terms of one
single magnetic response: the zero-field magnetization. It can yield higher
order corrections by including successively magnetic susceptibility and higher
order magnetic response functions. In application, it can be easily applied to
obtain Landau levels in lattice models. Moreover, it provides an experimental
method of measuring different magnetic response functions directly from the
measurement of Landau level fan diagram or Hofstadter spectrum.",1507.06342v2
2016-02-29,Gyrotropic skyrmion modes in ultrathin magnetic circular dots,"We calculate low-frequency gyrotropic spin excitation modes of the skyrmion
ground state ultrathin cylindrical magnetic dots. The skyrmion is assumed to be
stabilized at room temperature and zero external magnetic field due to an
interplay of the isotropic and Dzyaloshinskii-Moriya exchange interactions,
perpendicular magnetic anisotropy and magnetostatic interaction. We consider
Bloch- and Neel-type magnetic skyrmions and assume that the dot magnetization
does not depend on the thickness coordinate. The skyrmion gyrotropic
frequencies are calculated in GHz range as a function of the skyrmion
equilibrium radius, dot radius and the dot magnetic parameters. Recent
experiments on magnetic skyrmion gyrotropic dynamics in nanodots are discussed.",1603.00072v1
2016-04-05,Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2,"We performed magnetic susceptibility and neutron powder diffraction
experiments on the ternary compound Pr5Ru3Al2. It belongs to the
noncentrosymmetric and nonmirrorsymmetric cubic I213 space group. The
previously reported ferromagnetic transition at 24 K was not detected in our
improved quality samples. Instead, magnetic ordering was observed in the DC
magnetic susceptibility at 3.8 K. Neutron powder diffraction further indicates
that an incommensurate magnetic structure is established below 3.8 K, with the
magnetic modulation vector (0.066, 0.066, 0.066) (r.l.u.). Using the magnetic
representation analysis, we propose the block helical structure as a candidate
for the incommensurate magnetic structure.",1604.01149v1
2016-06-08,Magnetic energy of sc ferromagnetic films with three layers as described by third order perturbed Heisenberg Hamiltonian,"The solution of third order perturbed Heisenberg Hamiltonian of simple cubic
ferromagnetic ultra-thin films with three layers were found. All the magnetic
energy parameters such as spin exchange interaction, magnetic dipole
interaction, second order magnetic anisotropy, fourth order magnetic
anisotropy, applied magnetic field, demagnetization factor and stress induced
anisotropy were included in the third order perturbed Heisenberg Hamiltonian.
3-D plots of stress induced anisotropy, out of plane magnetic field,
demagnetization factor and spin exchange interaction are presented in this
manuscript. Magnetic easy and hard directions were determined using these 3-D
plots. MATLAB program was employed to solve the equation with seven parameters.",1606.02439v1
2016-07-19,MHD flow and heat transfer due to the axisymmetric stretching of a sheet with induced magnetic field,"The full MHD equations, governing the flow due to the axisymmetric stretching
of a sheet in the presence of a transverse magnetic field, can be cast in a
self similar form. This allows evaluation of the induced magnetic field and its
effect on the flow and heat transfer. The problem involves three parameters-
the magnetic Prandtl number, the magnetic interaction number, and the Prandtl
number. Numerical solutions are obtained for the velocity field, the magnetic
field, and the temperature, at different values of the magnetic Prandtl number
and the magnetic interaction number. The contributions of the viscous
dissipation, Joule heating, and streamwise diffusion to the heat flux toward
the sheet are assessed.",1607.05722v1
2017-02-27,Magnetization reversal by superconducting current in $\varphi_0$ Josephson junctions,"We study magnetization reversal in a $\varphi_0$ Josephson junction with
direct coupling between magnetic moment and Josephson current. Our simulations
of magnetic moment dynamics show that by applying an electric current pulse, we
can realize the full magnetization reversal. We propose different protocols of
full magnetization reversal based on the variation of the Josephson junction
and pulse parameters, particularly, electric current pulse amplitude, damping
of magnetization and spin-orbit interaction. We discuss experiments which can
probe the magnetization reversal in $\varphi_0$-junctions.",1702.08394v4
2017-05-16,An approach to 1000 T using the Electro-Magnetic Flux Compression,"An ultra-high magnetic field was generated by the electro-magnetic flux
compression technique under a reduced seed magnetic field condition and
achieved maximum magnetic field intensity was investigated. An ordinal pickup
coil measurement fails due to the dielectric breakdown at around 500 T. On the
other hand, by utilizing the magneto-optical Faraday rotation method with a
small probe, the measureable maximum magnetic field increased significantly. It
was found that reduced seed field increases the maximum magnetic field, but
with a reduced size of the final bore. A highest magnetic field over 763 T and
possibly up to 985 T approaching 1000 T was detected.",1705.05520v1
2018-01-09,Magneto-electric effect in doped magnetic ferroelectrics,"We propose a model of magneto-electric effect in doped magnetic
ferroelectrics. This magneto-electric effect does not involve the spin-orbit
coupling and is based purely on the Coulomb interaction. We calculate magnetic
phase diagram of doped magnetic ferroelectrics. We show that magneto-electric
coupling is pronounced only for ferroelectrics with low dielectric constant. We
find that magneto-electric coupling leads to modification of magnetization
temperature dependence in the vicinity of ferroelectric phase transition. A
peak of magnetization appears. We find that magnetization of doped magnetic
ferroelectrics strongly depends on applied electric field.",1801.03114v1
2018-03-03,Long Range Magnetic order stabilized by acceptors,"Tuning magnetic order in magnetic semiconductors is a long sought goal. A
proper concentration of acceptors can dramatically suppress local magnetic
order in favor of the long one. Using Mn and an acceptor codoped LiZnAs as an
example, we demonstrate, by first-principles calculation, the emergence of a
long-range magnetic order. This intriguing phenomenon can be understood from an
interplay between an acceptor-free magnetism and a band coupling magnetism. Our
observation thus lays the ground for a precise control of the magnetic order in
future spintronic devices.",1803.01179v1
2018-05-24,Searching the weakest link: Demagnetizing fields and magnetization reversal in permanent magnets,"Magnetization reversal in permanent magnets occurs by the nucleation and
expansion of reversed domains. Micromagnetic theory offers the possibility to
localize the spots within the complex structure of the magnet where
magnetization reversal starts. We compute maps of the local nucleation field in
a Nd2Fe14B permanent magnet using a model order reduction approach. Considering
thermal fluctuations in numerical micromagnetics we can also quantify the
reduction of the coercive field due to thermal activation. However, the major
reduction of the coercive field is caused by the soft magnetic grain boundary
phases and misorientation if there is no surface damage.",1805.09798v1
2019-06-04,Deterministic magnetization switching by voltage-control of magnetic anisotropy and Dzyaloshinskii-Moriya interaction under in-plane magnetic field,"Based on the micromagnetic simulations the magnetization switching in a
triangle magnetic element by voltage-control of magnetic anisotropy and
Dzyaloshinskii-Moriya interaction under in-plane magnetic field is proposed.
The proposed switching scheme is not the toggle switching but the deterministic
switching where the magnetic state is determined by the polarity of the applied
voltage pulse. The mechanism and conditions for the switching are clarified.
The results provide a fast and low-power writing method for magnetoresistive
random access memories.",1906.01254v1
2019-06-14,Friedel oscillations in 2D electron gas from spin-orbit interaction in a parallel magnetic field,"Effects associated with the interference of electron waves around a magnetic
point defect in two-dimensional electron gas with combined Rashba-Dresselhaus
spin-orbit interaction in the presence of a parallel magnetic field are
theoretically investigated. The effect of a magnetic field on the anisotropic
spatial distribution of the local density of states and the local density of
magnetization is analyzed. The existence of oscillations of the density of
magnetization with scattering by a non-magnetic defect and the contribution of
magnetic scattering (accompanied by spin-flip) in the local density of electron
states are predicted.",1906.06043v1
2019-06-21,Magnetic lattices for ultracold atoms,"This article reviews the development in our laboratory of magnetic lattices
comprising periodic arrays of magnetic microtraps created by patterned magnetic
films to trap periodic arrays of ultracold atoms. Recent achievements include
the realisation of multiple Bose-Einstein condensates in a 10 micron-period
one-dimensional magnetic lattice; the fabrication of sub-micron-period square
and triangular magnetic lattice structures suitable for quantum tunnelling
experiments; the trapping of ultracold atoms in a sub-micron-period triangular
magnetic lattice; and a proposal to use long-range interacting Rydberg atoms to
achieve spin-spin interactions between sites in a large-spacing magnetic
lattice.",1906.08918v1
2020-08-26,A Magnetic Velocity Verlet Method,"We discuss an extension of the velocity Verlet method that accurately
approximates the kinetic-energy-conserving charged particle motion that comes
from magnetic forcing. For a uniform magnetic field, the method is shown to
conserve both particle kinetic energy and magnetic dipole moment better than
midpoint Runge-Kutta. We then use the magnetic velocity Verlet method to
generate trapped particle trajectories, both in a cylindrical magnetic mirror
machine setup, and for dipolar fields like the earth's magnetic field. Finally,
the method is used to compute an example of (single) mirror motion in the
presence of a magnetic monopole field, where the trajectory can be described in
closed form.",2008.11810v1
2021-02-26,Distinctive magnetic properties of CrI3 and CrBr3 monolayers caused by spin-orbit coupling,"After the discovery of magnetism in monolayer CrI3, the magnetic properties
of different 2D materials from the chromium-trihalide family are intuitively
assumed to be similar, yielding magnetic anisotropy from the spin-orbit
coupling on halide ligands. Here we reveal significant differences between the
CrI3 and CrBr3 magnetic monolayers in their magnetic anisotropy, resulting
Curie temperature, hysteresis in external magnetic field, and evolution of
magnetism with strain, all predominantly attributed to distinctly different
interplay of atomic contributions to spin-orbit coupling in two materials.",2102.13325v1
2021-06-01,Impact of magnetic domains on magnetic flux concentrators,"The impact of magnetic domains in magnetic flux concentrators is studied
using the simulation software MuMax3. First, the simulation parameters are
validated using experimental results from magnetic force microscopy; second the
simulation output is benchmarked with the one obtained using Comsol
Multiphysics. Finally, the impact of magnetic domain is assessed, showing how
micromagnetic effects can become relevant, if not dominant, when scaling the
gap between the MFC and the sensor.",2106.00370v2
2021-10-16,A stretched exponential-based approach for the magnetic properties of spin glasses,"The spin glasses show intriguing characteristic features that are not well
understood yet, as for instance its aging, rejuvenation and memory effects.
Here a model based on a stretched exponential decay of its magnetization is
proposed, which can describe the main magnetic features of spin glasses
observed in experiments as the time-decay of thermoremament magnetization, the
relaxation of zero field cooled magnetization, the ac and dc magnetization as a
function of temperature and others. In principle, the here proposed model could
be adapted to describe other glassy systems.",2110.08625v2
2021-12-06,Magnetism of two-dimensional magnets in the presence of random fields,"In low-dimensional magnets, thermal agitation and spatial disorders generate
strong spin fluctuations that suppress the long-range magnetic ordering. We
develop an analytical equation for the equilibrium magnetization of
two-dimensional magnets at finite temperatures in the presence of the random
magnetic field. We find that the random field induces a first-order phase
transition in addition to the reduced Curie temperature. The first-order phase
transition persists even in the presence of the moderate external magnetic
field.",2112.03343v1
2022-04-11,Deformation of a magnetic liquid drop and unsteady flow inside and outside it in a non-stationary magnetic field,"Small steady-state deformational oscillations of a drop of a viscous magnetic
liquid in a non-stationary uniform magnetic field are theoretically
investigated for low Reynolds numbers. The drop is suspended in another viscous
magnetic liquid immiscible with the former. The non-stationary magnetic field
causes flow inside and outside the drop. The inertia is taken into account by
regarding the flow as essentially unsteady. The variation of the magnetic field
is so slow that the approximation of quasi-stationary magnetic field may be
used.",2204.05387v2
2022-10-06,MagNet: machine learning enhanced three-dimensional magnetic reconstruction,"Three-dimensional (3D) magnetic reconstruction is vital to the study of novel
magnetic materials for 3D spintronics. Vector field electron tomography (VFET)
is a major in house tool to achieve that. However, conventional VFET
reconstruction exhibits significant artefacts due to the unavoidable presence
of missing wedges. In this article, we propose a deep-learning enhanced VFET
method to address this issue. A magnetic textures library is built by
micromagnetic simulations. MagNet, an U-shaped convolutional neural network, is
trained and tested with dataset generated from the library. We demonstrate that
MagNet outperforms conventional VFET under missing wedge. Quality of
reconstructed magnetic induction fields is significantly improved.",2210.03066v1
2022-10-30,Controlling magnetic anisotropy in amplitude expansion of phase field crystal model,"The amplitude expansion for a magnetic phase-field-crystal (magnetic APFC)
model enables a convenient coarse-grained description of crystalline structures
under the influence of magnetic fields. Considering higher-order magnetic
coupling terms, we demonstrate the possibility of tuning the magnetic
anisotropy in these models. This allows for reproducing the easy and hard
direction of magnetization. Such a result can be achieved without increasing
the computational cost, enabling simulations of the manipulation of dislocation
networks and microstructures in ferromagnetic materials. As a demonstration, we
report on the simulation of the shrinkage of a spherical grain with the
magnetic anisotropy of Fe.",2210.16855v1
2023-12-13,Enhanced Magnetic Field Amplification by Ion-Beam Weibel Instability in Weakly Magnetized Astrophysical Shocks,"We examine the evolution of ion-beam Weibel instability at strong
collisionless shocks in weakly magnetized media. We find that a finite
background magnetic field substantially affects both linear and nonlinear
phases of the instability, depending on whether the background electrons behave
magnetized or not. Particle-in-cell simulations for magnetized electrons
identify a dynamo-like mechanism of magnetic field amplification, which
eventually leads to spontaneous magnetic reconnection. We conclude that this
scenario is applicable to typical young supernova remnant shocks.",2312.07933v1
2019-11-14,Real time observation of a stationary magneton,"The magnetic dipole field geometry of subatomic elementary particles like the
electron differs from the classical macroscopic field imprint of a bar magnet.
It resembles more like an eight figure or else joint double quantum-dots
instead of the classical, spherical more uniform field of a bar magnet. This
actual subatomic quantum magnetic field of an electron at rest, is called
Quantum Magnet or else a Magneton. Normally, a macroscale bar magnet should
behave like a relative giant Quantum Magnet with identical magnetic dipole
field imprint since all of its individual magnetons collectively inside the
material, dipole moments are uniformly aligned forming the total net field of
the magnet. However due to Quantum Decoherence (QDE) phenomenon at the
macroscale and macroscopic magnetic field imaging sensors limitations which
cannot pickup these rapid quantum magnetization fluctuations, this field is
masked and not visible at the macroscale. By using the relative inexpensive
submicron resolution Ferrolens quantum magnetic optical sensor and method, we
can actually make this net magneton field visible on macroscale magnets. We
call this net total field herein, Quantum Field of Magnet (QFM) differentiating
it therefore from the field of the single subatomic magneton thus quantum
magnet. Additionally, the unique potential of the Ferrolens device to display
also the magnetic flux lines of this macroscopically projected giant Magenton
gives us the unique opportunity to study the individual magnetic flux lines
geometrical pattern that of a single subatomic magneton. We describe this
particular magnetic flux of the magneton observed, quantum magnetic flux.
Therefore a novel observation has been made that the QFM of the Magnet-Magneton
consists of a dipole vortex shaped magnetic flux geometrical pattern
responsible for creating the classical macroscopic N-S field of the magnet.",1911.05735v1
2002-05-12,The Role of Magnetic Helicity Transport in Nonlinear Galactic Dynamos,"We consider the magnetic helicity balance for the galactic dynamo in the
framework of the local dynamo problem, as well as in the no-z model (which
includes explicitly the radial distribution of the magnetic fields). When
calculating the magnetic helicity balance we take into account the
redistribution of the small-scale and large-scale magnetic fields between the
magnetic helicities, as well as magnetic helicity transport and diffusion due
to small-scale turbulence. We demonstrate that the magnetic helicity flux
through the galactic disc boundaries leads to a steady-state magnetic field
with magnetic energy comparable to the equipartition energy of the turbulent
motions of the interstellar medium. If such flux is ignored, the steady-state
magnetic field is found to be much smaller than the equipartition field. The
total magnetic helicity flux through the boundaries consists of both an
advective flux and a diffusive flux. The exact ratio of these contributions
seems not to be crucial for determining the strength of the steady-state
magnetic field and its structure. However at least some diffusive contribution
is needed to smooth the magnetic helicity profile near to the disc boundaries.
The roles of various transport coefficients for magnetic helicity are
investigated, and the values which lead to magnetic field configurations
comparable with those observed are determined.",0205165v1
2004-01-22,The magnetic field of pulsars and the gravito-magnetic theory,"Many authors have considered a gravitational origin of the magnetic field of
celestial bodies. Especially, the so-called Wilson-Blackett formula has been
investigated, both theoretically and observationally. It appeared possible to
deduce this formula from general relativity, e. g., by application of a special
interpretation of gravito-magnetic theory. More consequences of the latter
theory for pulsars will be considered in this work. As an example, the standard
quadrupolar charge density for pulsars can be deduced from the gravito-magnetic
theory. Moreover, a new magnetic dipole moment from electromagnetic origin is
found, generated in the basic magnetic field from gravito-magnetic origin. In
general, for thirteen accreting, slowly rotating, binary pulsars the agreement
between the observed magnetic field and the gravito-magnetic prediction is
better than between the observed value and the value from the standard magnetic
dipole radiation model. At present, an analogous comparison for five isolated
pulsars appears to be difficult. For a sample of 100 pulsars the averaged
(gravito-)magnetic field, extracted from the magnetic dipole spin-down model,
is in fair agreement with the gravito-magnetic prediction. Unfortunately, the
(gravito-)magnetic field has not yet directly been measured. Finally, it is
found that the first and second order braking indices only depend on the
magnetic field from electromagnetic origin.",0401468v1
2001-08-29,The Finite Energy Constant Magnetization of the Two - Dimensional Ising Model,"We suggest the new definition of the magnetization. For the two - dimensional
Ising model with the free boundary conditions we calculate any derivative of
this magnetization for zero magnetic field.",0108489v1
2002-07-08,The Magnetization by the Finite Energy Constant Magnetic Field in the Two - Dimentional Ising Model,"We suggest the new definition of the magnetization. For the two - dimensional
Ising model with the free boundary conditions we calculate this magnetization.",0207200v1
2009-11-12,Coherent states in the presence of a variable magnetic field,"We introduce magnetic coherent states for a particle in a variable magnetic
field. They provide a pure state quantization of the phase space R^{2N} endowed
with a magnetic symplectic form.",0911.2451v1
2010-06-07,Solitary Magnetic Bubbles,"Stability and attractor property of free-floating axisymmetric magnetic
bubbles in high-conductivity plasmas is (tentatively, numerically)
demonstrated. The existence of compact non-singular axisymmetric magnetic
equilibria is proved. Being attractors, the solitary magnetic bubbles should
exist in nature.",1006.1368v1
2011-06-18,Magnetic curves corresponding to Killing magnetic fields in $E^3$,"We explicitly determine all magnetic curves corresponding to the Killing
magnetic fields on the 3-dimensional Euclidean space.",1106.3673v1
2012-01-13,Development for Hardware for Programming of Spatial Magnetic Field Distributions in Nuclear Magnetic Resonance and Magnetic Resonance Imaging,"The proposal of a project aimed on a design of hardware for programming 3D
Magnetic Field shapes over sample volume in NMR and MRI is described.",1201.2764v1
2012-09-27,Growth of a localized seed magnetic field in a turbulent medium,"Turbulence dynamo deals with amplification of a seed magnetic field in a
turbulent medium and has been studied mostly for uniform or spatially
homogeneous seed magnetic fields. However, some astrophysical processes (e.g.
jets from active galaxies, galactic winds, or ram-pressure stripping in galaxy
clusters) can provide localized seed magnetic fields. In this paper, we
numerically study amplification of localized seed magnetic fields in a
turbulent medium. Throughout the paper, we assume that driving scale of
turbulence is comparable to the size of the system. Our findings are as
follows. First, turbulence can amplify a localized seed magnetic field very
efficiently. The growth rate of magnetic energy density is as high as that for
a uniform seed magnetic field. This result implies that a magnetic field
ejected from an astrophysical object can be a viable source of magnetic field
in a cluster. Second, the localized seed magnetic field disperses and fills the
whole system very fast. If turbulence in a system (e.g. a galaxy cluster or a
filament) is driven at large scales, we expect that it takes a few large-eddy
turnover times for magnetic field to fill the whole system. Third, growth and
turbulence diffusion of a localized seed magnetic field are also fast in high
magnetic Prandtl number turbulence. Fourth, even in decaying turbulence, a
localized seed magnetic field can ultimately fill the whole system. Although
the dispersal rate of magnetic field is not fast in purely decaying turbulence,
it can be enhanced by an additional forcing.",1209.6130v1
2013-01-28,Two-dimensional Ising model in a finite magnetic field for the square lattice of infinite sites-Partition function and Magnetization,"The partition function and magnetization equations are derived for the
two-dimensional nearest neighbour Ising models in a magnetic field.",1302.1084v1
2014-07-08,Competing magnetic phases and field-induced dynamics in DyRuAsO,"Analysis of neutron diffraction, dc magnetization, ac magnetic
susceptibility, heat capacity, and electrical resistivity for DyRuAsO in an
applied magnetic field are presented at temperatures near and below those at
which the structural distortion (T_S = 25 K) and subsequent magnetic ordering
(T_N = 10.5 K) take place. Powder neutron diffraction is used to determine the
antiferromagnetic order of Dy moments of magnitude 7.6(1) mu_B in the absence
of a magnetic field, and demonstrate the reorientation of the moments into a
ferromagnetic configuration upon application of a magnetic field. Dy magnetism
is identified as the driving force for the structural distortion. The magnetic
structure of analogous TbRuAsO is also reported. Competition between the two
magnetically ordered states in DyRuAsO is found to produce unusual physical
properties in applied magnetic fields at low temperature. An additional phase
transition near T* = 3 K is observed in heat capacity and other properties in
fields greater than about 3 T. Magnetic fields of this magnitude also induce
spin-glass-like behavior including thermal and magnetic hysteresis, divergence
of zero-field-cooled and field-cooled magnetization, frequency dependent
anomalies in ac magnetic susceptibility, and slow relaxation of the
magnetization. This is remarkable since DyRuAsO is a stoichiometric material
with no disorder detected by neutron diffraction, and suggests analogies with
spin-ice compounds and related materials with strong geometric frustration.",1407.2184v1
2016-08-16,Magnetic Dirichlet Laplacian with radially symmetric magnetic field,"The aim of the paper is to derive spectral estimates on the eigenvalue
moments of the magnetic Dirichlet Laplacian defined on the two-dimensional disk
with a radially symmetric magnetic field.",1608.04555v1
2017-03-30,Relative magnetic helicity as a diagnostic of solar eruptivity,"The discovery of clear criteria that can deterministically describe the
eruptive state of a solar active region would lead to major improvements on
space weather predictions. Using series of numerical simulations of the
emergence of a magnetic flux rope in a magnetized coronal, leading either to
eruptions or to stable configurations, we test several global scalar quantities
for the ability to discriminate between the eruptive and the non-eruptive
simulations. From the magnetic field generated by the three-dimensional
magnetohydrodynamical simulations, we compute and analyse the evolution of the
magnetic flux, of the magnetic energy and its decomposition into potential and
free energies, and of the relative magnetic helicity and its decomposition.
Unlike the magnetic flux and magnetic energies, magnetic helicities are able to
markedly distinguish the eruptive from the non-eruptive simulations. We find
that the ratio of the magnetic helicity of the current-carrying magnetic field
to the total relative helicity presents the highest values for the eruptive
simulations, in the pre-eruptive phase only. We observe that the eruptive
simulations do not possess the highest value of total magnetic helicity. In the
framework of our numerical study, the magnetic energies and the total relative
helicity do not correspond to good eruptivity proxies. Our study highlights
that the ratio of magnetic helicities diagnoses very clearly the eruptive
potential of our parametric simulations. Our study shows that
magnetic-helicity-based quantities may be very efficient for the prediction of
solar eruptions.",1703.10562v1
2017-05-17,Magnetic Transport in Spin Antiferromagnets for Spintronics Applications,"Had magnetic monopoles been ubiquitous as electrons are, we would probably
have had a different form of matter, and power plants based on currents of
these magnetic charges would have been a familiar scene of modern technology.
Magnetic dipoles do exist, however, and in principle one could wonder if we can
use them to generate magnetic currents. In the present work, we address the
issue of generating magnetic currents and magnetic thermal currents in
electrically-insulating low-dimensional Heisenberg antiferromagnets by invoking
the (broken) electricity-magnetism duality symmetry. The ground state of these
materials is a spin-liquid state that can be described well via~the
Jordan--Wigner fermions, which permit an easy definition of the magnetic
particle and thermal currents. The magnetic and magnetic thermal conductivities
are calculated in the present work using the bond--mean field theory. The
spin-liquid states in these antiferromagnets are either gapless or gapped
liquids of spinless fermions whose flow defines a current just as the one
defined for electrons in a Fermi liquid. The driving force for the magnetic
current is a magnetic field with a gradient along the magnetic conductor. We
predict the generation of a magneto-motive force and realization of magnetic
circuits using low-dimensional Heisenberg antiferromagnets. The present work is
also about claiming that what the experiments in spintronics attempt to do is
trying to treat the magnetic degrees of freedoms on the same footing as the
electronic ones.",1705.06318v2
2017-12-26,Evolution of Relative Magnetic Helicity: New Boundary Conditions for the Vector Potential,"We recently proposed a method to calculate the relative magnetic helicity in
a finite volume for a given magnetic field which however required the flux to
be balanced separately on all the sides of the considered volume. In order to
allow finite magnetic fluxes through the boundaries, a Coulomb gauge is
constructed that allows for global magnetic flux balance. We tested and
verified our method in a theoretical fore-free magnetic field model. We apply
the new method to the former calculation data and found a difference of less
than 1.2\%. We also applied our method to the magnetic field above active
region NOAA 11429 obtained by a new photospheric-data-driven MHD model code
GOEMHD3. We analyzed the magnetic helicity evolution in the solar corona using
our new method. It was found that the normalized magnetic helicityis equal to
-0.038 when fast magnetic reconnection is triggered. This value is comparable
to the previous value (-0.029) in the MHD simulations when magnetic
reconnection happened and the observed normalized magnetic helicity (-0.036)
from the eruption of newly emerging active regions. We found that only 8\% of
the accumulated magnetic helicity is dissipated after it is injected through
the bottom boundary. This is in accordance with the Woltjer conjecture. Only
2\% of magnetic helicity injected from the bottom boundary escapes through the
corona. This is consistent with the observation of magnetic clouds, which could
take away magnetic helicity into the interplanetary space, in the case
considered here, several halo CMEs and two X-class solar flares origin from
this active region.",1712.09219v1
2018-11-30,Double bit in-plane magnetic skyrmions on a track,"A magnetic skyrmion isusually refers to a twisted spin texture surrounded by
uniformly aligned out-of-plane spinsin the background of a uniformly magnetized
state. The invariance of the magnetic skyrmion conserves its topological charge
under any continuous transformations of the spin textures, leads to which
represents the robustness of a magnetic skyrmion their texture against external
perturbations, making it ideal to use skyrmions as . Such a behaviour is
required for an ideal information carriers. To date, most magnetic skyrmion
studies have been performedfocused on in perpendicularly magnetized systems,
where the skyrmion topological number is determined by the relative orientation
between the core and /outer perpendicular magnetization directions of the
skyrmion is either up/down or down/up. Here we show that there also exists a
new type of magnetic skyrmion with surrounding spins to be uniformly aligned to
the in-plane direction. By continuous transformation and relaxation of the spin
textures of out-of-plane skyrmions, we showed that an in-plane skyrmion, where
the background magnetization is in the in-plane direction, is also possible.
Different from the conventional perpendicular magnetic skyrmionsContrary to the
skyrmions in a perpendicularly magnetized state, the in-plane magnetic
skyrmions with opposite signs of topological charges can inherentlycharges can
inherently coexist in the in-plane magnetization system coexist. Moreover, the
iIn-plane skyrmions of opposite charge can move together by an electric current
and exhibit with an opposite spin Hall effect. These findings showdemonstrate
the inherent possibility of a double-bit transfer in a single magnetic wire
that is not possible in a perpendicularly magnetized system.",1811.12552v1
2019-10-13,A systematically study of thermal width of heavy quarkonia in a finite temperature magnetized background from holography,"By simulating the finite temperatures magnetized background in the RHIC and
LHC energies, we systematically study the characteristics of thermal widths and
potentials of heavy quarkonia. It is found that the magnetic field has less
influence on the real potential, but has a significant influence on the
imaginary potential, especially in the low deconfined temperature. Extracted
from the effect of thermal worldsheet fluctuations about the classical
configuration, the thermal width of $\Upsilon(1s)$ in the finite temperature
magnetized background is investigated. It is found that at the low deconfined
temperature the magnetic field can generate a significant thermal fluctuation
of the thermal width of $\Upsilon(1s)$, but with the increase of temperature,
the effect of magnetic field on the thermal width becomes less important, which
means the effect of high temperature completely exceeds that of magnetic field
and magnetic field become less important at high temperature. The thermal width
decreases with the increasing rapidity at the finite temperature magnetized
background. It is also observed that the effect of the magnetic field on the
thermal width when dipole moving parallel to the magnetic field direction are
larger than that moving perpendicular to the magnetic field direction, which
implies that the magnetic field tends to enhance thermal fluctuation when
dipole moving parallel to the direction of magnetic field. The thermal width of
$\Upsilon(1S)$ hardly changes with the increasing temperature when dipole
moving perpendicular to the magnetic field. But when dipole moving parallel to
the magnetic field, the thermal width at low temperature is obviously larger
than that at high temperature.",1910.05668v1
2021-09-03,"Investigating the Magnetic Field outside small Accelerator Magnet Analogs via Experiment, Simulation, and Theory","Particle accelerators use powerful and complex magnetic fields to turn,
shape, and eventually collide beams of near-light-speed particles, yet the
fundamental magnetic principles behind the accelerator magnets can be
understood by undergraduate students. In this paper we use small-scale
accelerator magnet analogs in a multi-faceted, low-cost exploration of the
magnetic field exterior to accelerator magnets. These fields are best
understood using the multipole expansion of the field. If we assume that the
magnetic field is created by ideal magnetic dipoles, we can derive a
theoretical model that shows that each accelerator magnet configuration is
dominated by a single multipole moment and obeys $B \propto 1/r^{l+2}$, where
$l$ is the multipole order (with $l = 1, 2, 3, 4$ for the dipole, quadrupole,
octopole, and hexadecapole moments, respectively). Using commercially available
NdFeB magnets and the magnetic field sensor inside a smartphone, we
experimentally verify the power-law dependence of the accelerator magnet
configurations. Finally, we use the open-source Python library Magpylib to
simulate the magnetic field of the permanent magnet configurations, showing
good agreement between theory, experiment, and simulation.",2109.03057v4
2021-12-02,Heisenberg representation of nonthermal ultrafast laser excitation of magnetic precessions,"We derive the Heisenberg representation of the ultrafast inverse Faraday
effect that provides the time evolution of magnetic vectors of a magnetic
system during its interaction with a laser pulse. We obtain a time-dependent
effective magnetic operator acting in the Hilbert space of the total angular
momentum that describes a process of nonthermal excitation of magnetic
precessions in an electronic system by a circularly polarized laser pulse. The
magnetic operator separates the effect of the laser pulse on the magnetic
system from other magnetic interactions. The effective magnetic operator
provides the equations of motion of magnetic vectors during the excitation by
the laser. We show that magnetization dynamics calculated with these equations
is equivalent to magnetization dynamics calculated with the time-dependent
Schr\""odinger equation, which takes into account the interaction of an
electronic system with the electric field of light. We model and compare
laser-induced precessions of magnetic sublattices of an easy-plane and an
easy-axis antiferromagnetic systems. Using these models, we show how the
ultrafast inverse Faraday effect induces a net magnetic moment in
antiferromagnets and demonstrate that a crystal field environment and the
exchange interaction play essential roles for laser-induced magnetization
dynamics even during the action of a pump pulse. Using our approach, we show
that light-induced precessions can start even during the action of the pump
pulse with a duration several tens times shorter than the period of induced
precessions and affect the position of magnetic vectors after the action of the
pump pulse.",2112.01350v1
2022-07-20,Hot magnetic halo of NGC628 (M74),"In several spiral galaxies that are observed face-on, large-scale ordered
magnetic fields (the so-called magnetic arms) were found. One of the
explanations was the action of the magnetic reconnection, which leads to a
higher ordering of the magnetic fields. Because it simultaneously converts the
energy of the magnetic fields into thermal energy of the surroundings, magnetic
reconnection has been considered as a heating mechanism of the interstellar
medium for many years. Until recently, no clear observational evidence for this
phenomenon was found. We search for possible signatures of gas heating by
magnetic reconnection effects in the radio and X-ray data for the face-on
spiral galaxy NGC628 (M74), which presents pronounced magnetic arms and
evidence for vertical magnetic fields. The strengths and energy densities of
the magnetic field in the spiral and magnetic arms were derived, as were the
temperatures and thermal energy densities of the hot gas, for the disk and halo
emission. In the regions of magnetic arms, higher order and lower energy
density of the magnetic field is found than in the stellar spiral arms. The
global temperature of the hot gas is roughly constant throughout the disk. The
comparison of the findings with those obtained for the starburst galaxy M83
suggests that magnetic reconnection heating may be present in the halo of
NGC628. The joint analysis of the properties of the magnetic fields and the hot
gas in NGC628 also provided clues for possible tidal interaction with the
companion galaxy.",2207.09917v1
2022-09-07,Atypical magnetic behavior in the incommensurate $[CH_3NH_3][Ni(HCOO)_3]$ hybrid perovskite,"A plethora of temperature induced phase transitions have been observed in
$[CH_3NH_3][M(HCOO)_3]$ compounds, where M is Co(II) or Ni(II). Among them, the
nickel compound exhibits a combination of magnetic and nuclear
incommensurabil-ity below N\'eel temperature. Despite the fact that the
zero-field behavior has been previously addressed, here we study in depth the
macroscopic magnetic behavior of this compound to unveil the origin of the
atypical magnetic response found in it and in its parent family of formate
perovskites. In particular, they show a puzzling magnetization reversal in the
curves measured starting from low temperatures, after cooling under zero field.
The first atypical phenomena is the im-possibility of reaching zero
magnetization, even by nullifying the applied external field and even
compensating it for the influence earth's magnetic field. Relatively large
magnetic fields are needed to switch the magnetization from negative to
positive values or vice versa, which is compatible with a soft-ferromagnetic
system. The atypical path found in its first magnetization curve and hysteresis
loop at low temperatures is the most noticeable feature. The magnetization
curve switches from more than 1200 Oe from the first magnetization loop to the
subsequent magnetization loops. A feature that cannot be explained using a
model based on unbalanced pair of domains. As a result, we decipher this
behavior in light of the incommensurate structure of this material. We propose,
in particular, that the applied magnetic field induces a mag-netic phase
transition from a magnetically incommensurate structure to a magnetically
commensurate structure.",2209.03093v1
2022-12-02,A promising formation channel for symbiotic X-ray binaries: cases of IGR J17329-2731 and 4U 1700+24,"Recent observations demonstrate that the symbiotic X-ray binary (SyXB) IGR
J17329-2731 contains a highly magnetized neutron star (NS) which accretes
matter through the wind from its giant star companion, and suggest that 4U
1700+24 may also have a highly magnetized NS. Accretion-induced collapse (AIC)
from oxygen-neon-magnesium white dwarf (ONeMg WD) + red giant (RG) star
binaries is one promising channel to form these SyXBs, while other long
standing formation channels have difficulties to produce these SyXBs. By
considering non-magnetic and magnetic ONeMg WDs, I investigate the evolution of
ONeMg WD + RG binaries with the MESA stellar evolution code for producing SyXBs
with non-magnetic or magnetized NSs. In the pre-AIC evolution with magnetic
confinement, the mass accumulation efficiency of the accreting WD is increased
at low mass transfer rate compared to the non-magnetic case. The newborn NSs
formed via AIC of highly magnetized WDs could inherit the large magnetic field
through conservation of magnetic flux, and the systems could have a long age
compatible with that of the red giant companions. These young and highly
magnetized NSs could accrete matters from the stellar wind of the giant
companions to that shine as those observed SyXBs, and could preserve their high
magnetic field during this time. The MESA calculation results show that the
initial parameter (initial RG mass and orbital period) space for the AIC with
magnetic confinement to form SyXBs with highly magnetized NSs shifts to be
lower and narrower compared to that of the no magnetic confinement case.",2212.00997v2
2023-07-28,Reversible magnetic domain reorientation induced by magnetic field pulses with fixed direction,"Nanoscale magnetic domains with controllable configurations could be used for
classical and quantum applications, where the switching of magnetization
configurations is an essential operation for information processing. Here, we
report that the magnetic domain reorientation in a notched ferromagnetic
nanotrack can be realized and effectively controlled by applying uniform
magnetic field pulses in a fixed in-plane direction perpendicular to the
nanotrack. Our micromagnetic simulation results show that the configurations of
magnetic domains in the notched nanotrack can be switched between a
head-to-head state and a tail-to-tail state in a reversible manner driven by
magnetic field pulses, while it is unnecessary to reverse the direction of the
magnetic field. Such a unique magnetic domain reorientation dynamics is found
to depend on magnetic parameters and nanotrack geometries. The reorientation
dynamics of magnetic domains also depends on the strength and length of the
applied magnetic field pulse. In addition, we point out that the notches at the
center of the nanotrack play an important role for the stabilization of the
head-to-head and tail-to-tail states during the magnetic domain reorientation.
We also qualitatively explain the field-induced reorientation phenomenon with a
simplified two-dimensional macrospin model. Our results may make it possible to
build spintronic devices driven by a fixed magnetic field. Our findings may
also motivate future studies to investigate the classical and quantum
applications based on nanoscale magnetic domains.",2307.15263v1
2023-09-14,Disentangling the Entangled Linkages of Relative Magnetic Helicity,"Magnetic helicity, $H$, measures magnetic linkages in a volume. The early
theoretical development of helicity focused on magnetically closed systems in
$\mathcal{V}$ bounded by $\mathcal{S}$. For magnetically closed systems,
$\mathcal{V}\in\mathbb{R}^3=\mathcal{V}+\mathcal{V}^*$, no magnetic flux
threads the boundary, $\hat{\boldsymbol{n}}\cdot\boldsymbol{B}|_\mathcal{S}=0$.
Berger and Field (1984) and Finn and Antonsen (1985) extended the definition of
helicity to relative helicity, $\mathcal{H}$, for magnetically open systems
where magnetic flux may thread the boundary. Berger (1999,2003) expressed this
relative helicity as two gauge invariant terms that describe the self helicity
of magnetic field that closes inside $\mathcal{V}$ and the mutual helicity
between the magnetic field that threads the boundary $\mathcal{S}$ and the
magnetic field that closes inside $\mathcal{V}$. The total magnetic field that
permeates $\mathcal{V}$ entangles magnetic fields that are produced by current
sources $\boldsymbol{J}$ in $\mathcal{V}$ with magnetic fields that are
produced by current sources $\boldsymbol{J}^*$ in $\mathcal{V}^*$. Building on
this fact, we extend Berger's expressions for relative magnetic helicity to
eight gauge invariant quantities that simultaneously characterize both of these
self and mutual helicities and attribute their origins to currents
$\boldsymbol{J}$ in $\mathcal{V}$ and/or $\boldsymbol{J}^*$ in $\mathcal{V}^*$,
thereby disentangling the domain of origin for these entangled linkages. We
arrange these eight terms into novel expressions for internal and external
helicity (self) and internal-external helicity (mutual) based on their domain
of origin. The implications of these linkages for interpreting magnetic energy
is discussed and new boundary observables are proposed for tracking the
evolution of the field that threads the boundary.",2309.07776v1
1996-12-23,A Fresh Look at Axions and SN 1987A,"We re-examine the very stringent limits on the axion mass based on the
strength and duration of the neutrino signal from SN 1987A, in the light of new
measurements of the axial-vector coupling strength of nucleons, possible
suppression of axion emission due to many-body effects, and additional emission
processes involving pions. The suppression of axion emission due to nucleon
spin fluctuations induced by many-body effects degrades previous limits by a
factor of about 2. Emission processes involving thermal pions can strengthen
the limits by a factor of 3-4 within a perturbative treatment that neglects
saturation of nucleon spin fluctuations. Inclusion of saturation effects,
however, tends to make the limits less dependent on pion abundances. The
resulting axion mass limit also depends on the precise couplings of the axion
and ranges from 0.5x10**(-3) eV to 6x10**(-3) eV.",9612222v1
1997-11-10,Confronting Synchrotron Shock and Inverse Comptonization Models with GRB Spectral Evolution,"The time-resolved spectra of gamma-ray bursts (GRBs) remain in conflict with
many proposed models for these events. After proving that most of the bursts in
our sample show evidence for spectral ""shape-shifting"", we discuss what
restrictions that BATSE time-resolved burst spectra place on current models. We
find that the synchrotron shock model does not allow for the steep low-energy
spectral slope observed in many bursts, including GRB 970111. We also determine
that saturated Comptonization with only Thomson thinning fails to explain the
observed rise and fall of the low-energy spectral slope seen in GRB 970111 and
other bursts. This implies that saturated Comptonization models must include
some mechanism which can cause the Thomson depth to increase intially in
pulses.",9711100v1
1998-10-02,Gravity-modes in ZZ Ceti Stars. II. Effects of Turbulent Dissipation,"We investigate dynamical interactions between turbulent convection and g-mode
pulsations in ZZ Ceti variables (DAVs). Since our understanding of turbulence
is rudimentary, we are compelled to settle for order of magnitude results. A
key feature of these interactions is that convective response times are much
shorter than pulsation periods. Thus the dynamical interactions enforce near
uniform horizontal velocity inside the convection zone. They also give rise to
a narrow shear layer in the region of convective overshoot at the top of the
radiative interior. Turbulent damping inside the convection zone is negligible
for all modes, but that in the region of convective overshoot may be
significant for a few long period modes near the red edge of the instability
strip. These conclusions are in accord with those reached earlier by Brickhill.
Our major new result concerns nonlinear damping arising from the
Kelvin-Helmholtz instability of the aforementioned shear layer. Amplitudes of
overstable modes saturate where dissipation due to this instability balances
excitation by convective driving. This mechanism of amplitude saturation is
most effective for long period modes, and it may play an important role in
defining the red edge of the instability strip.",9810038v1
1999-03-29,GRB990123: The Case for Saturated Comptonization,"The recent simultaneous detection of optical, X-ray and gamma-ray photons
from GRB990123 during the burst provides the first broadband multi-wavelength
characterization of the burst spectrum and evolution. Here we show that a
direct correlation exists between the time-varying gamma-ray spectral shape and
the prompt optical emission. This combined with the unique signatures of the
time-resolved spectra of GRB990123 convincingly supports earlier predictions of
the saturated Comptonization model. Contrary to other suggestions, we find that
the entire continuum from optical to gamma-rays can be generated from a single
source of leptons (electrons and pairs). The optical flux only appears to lag
the gamma-ray flux due to the high initial Thomson depth of the plasma. Once
the plasma has completely thinned out, the late time afterglow behavior of our
model is the same as in standard models based on the Blandford-McKee (1976)
solution.",9903438v1
1999-05-03,Neutron star properties in the quark-meson coupling model,"The effects of internal quark structure of baryons on the composition and
structure of neutron star matter with hyperons are investigated in the
quark-meson coupling (QMC) model. The QMC model is based on mean-field
description of nonoverlapping spherical bags bound by self-consistent exchange
of scalar and vector mesons. The predictions of this model are compared with
quantum hadrodynamic (QHD) model calibrated to reproduce identical nuclear
matter saturation properties. By employing a density dependent bag constant
through direct coupling to the scalar field, the QMC model is found to exhibit
identical properties as QHD near saturation density. Furthermore, this modified
QMC model provides well-behaved and continuous solutions at high densities
relevant to the core of neutron stars. Two additional strange mesons are
introduced which couple only to the strange quark in the QMC model and to the
hyperons in the QHD model. The constitution and structure of stars with
hyperons in the QMC and QHD models reveal interesting differences. This
suggests the importance of quark structure effects in the baryons at high
densities.",9905010v1
1999-05-06,How Saturated are Absorption Lines in the Broad Absorption Line Quasar PG 1411+442 ?,"Recently, convincing evidence was found for extremely large X-ray absorption
by column densities $> 10^{23} cm^{-2}$ in broad absorption line quasars. One
consequence of this is that any soft X-ray emission from these QSOs would be
the scattered light or leaked light from partially covering absorbing material.
A detection of the unabsorbed soft X-ray and absorbed hard X-ray compo nent
will allow to determine the total column density as well as the effective
covering factor of the absorbing material, which can be hardly obtained from
the UV absorption lines. Brinkmann et al. (1999) showed that both the
unabsorbed and absorbed components are detected in the nearby very bright broad
absorption line quasar PG 1411+442. In this letter, we make a further analysis
of the broad band X-ray spectrum and the UV spectrum from HST, and demonstrate
that broad absorption lines are completely saturated at the bottom of
absorption troughs.",9905054v1
1999-05-14,Observations of Small Scale ISM Structure in Dense Atomic Gas,"We present high resolution (R~170,000) Kitt Peak National Observatory Co'ude
Feed telescope observations of the interstellar KI 7698 angstrom line towards 5
multiple star systems with saturated NaI components. We compare the KI
absorption line profiles in each of the two (or three) lines of sight in these
systems, and find significant differences between the sight-lines in 3 out of
the 5 cases. We infer that the small scale structure traced by previous NaI
observations is also present in at least some of the components with saturated
NaI absorption lines, and thus the small scale structures traced by the neutral
species are occurring at some level in clouds of all column densities. We
discuss the implications of that conclusion and a potential explanation by
density inhomogeneities.",9905189v1
1999-05-18,Strong Field Gravity and X-Ray Observations of 4U1820-30,"The behavior of quasi-periodic oscillations (QPOs) at frequencies near 1 kHz
in the x-ray emission from the neutron star x-ray binary 4U1820-30 has been
interpreted as evidence for the existence of the marginally stable orbit, a key
prediction of strong-field general relativity. The signature of the marginally
stable orbit is a saturation in QPO frequency, assumed to track inner disk
radius, versus mass accretion rate. Previous studies of 4U1820-30 have used
x-ray count rate as an indicator of mass accretion rate. However, x-ray count
rate is known to not correlate robustly with mass accretion rate or QPO
frequency in other sources. Here, we examine the QPO frequency dependence on
two other indicators of mass accretion rate: energy flux and x-ray spectral
shape. Using either of these indicators, we find that the QPO frequency
saturates at high mass accretion rates. We interpret this as strong evidence
for the existence of the marginally stable orbit.",9905236v1
2000-04-14,The saturation of disk heating in the solar neighborhood and evidence for a merger 9 Gyrs ago,"We re-examine the age-velocity dispersion relation in the solar neighborhood
using improved stellar age estimates that are based on Hipparcos parallaxes and
recent stellar evolution calculations. The resulting relation shows that the
Milky Way stellar disk was relatively quiescent, suffering little heating or
dispersion increase between 3 and 9 Gyrs. However, at an age of 9 Gyrs there is
an abrupt increase in the stellar velocity dispersions. To explain the abrupt
increase (by almost a factor of 2) in dispersions we propose that the Milky Way
suffered a minor merger 9 Gyrs ago that created the thick disk. The quiescent
phase is consistent with inefficient heating caused by scattering from tightly
wound transient spiral structure. It is possible that many galaxy disks have
radial velocity dispersions at the point where heating from spiral structure
becomes inefficient. Surface brightness profiles and dispersion measurements
can be used to predict spiral arm winding numbers at this saturation point. A
comparison between the observed and predicted winding numbers could test this
hypothesis and also search for evidence of merger induced disk heating in
nearby galaxies.",0004210v3
2000-06-09,"R-modes in Neutron Stars with Crusts: Turbulent Saturation, Spin-down, and Crust Melting","Rossby waves (r-modes) have been suggested as a means to regulate the spin
periods of young or accreting neutron stars, and also to produce observable
gravitational wave radiation. R-modes involve primarily transverse,
incompressive motions of the star's fluid core. However, neutron stars gain
crusts early in their lives: therefore, r-modes also imply shear in the fluid
beneath the crust. We examine the criterion for this shear layer to become
turbulent, and derive the rate of dissipation in the turbulent regime. Unlike
dissipation from a viscous boundary layer, turbulent energy loss is nonlinear
in mode energy and can therefore cause the mode to saturate at amplitudes
typically much less than unity. This energy loss also reappears as heat below
the crust. We study the possibility of crust melting as well as its
implications for the spin evolution of low-mass X-ray binaries. Lastly, we
identify some universal features of the spin evolution that may have
observational consequences.",0006123v1
2002-01-28,Rotation and Activity in Mid-M to L Dwarfs,"We analyze rotation velocities and chromospheric (H-alpha) activity, derived
from multi-year, high-resolution spectra, in 56 mid-M to L dwarfs. Rotational
velocities are found to increase from mid-M to L. This is consistent with a
lengthening of spin-down timescale with later type, though in the L types the
trend may also be a function of stellar age. From M5 to M8.5, a saturation-type
rotation-activity relation is seen, similar to that in earlier types. However,
the saturation velocity in our case is much higher, at about 12 km/s. A sharp
drop in activity is observed at about M9, with later types showing little or no
H-alpha emission, in spite of rapid rotation. This may be due to the very high
resistivities in the predominantly neutral atmospheres of these cool objects.",0201455v1
2002-01-31,Elemental Abundances in Stellar Coronae with XMM-Newton,"The XMM-Newton Reflection Grating Spectrometer Team has obtained observations
ofa large number of coronal sources of various activity levels, ages, and
spectraltypes. In particular, X-ray bright RS CVn binary systems display
saturated coronal emission with spectral lines characteristic of hot (10-30 MK)
plasma. Furthermore, we have obtained XMM-Newton data from young solar analogs
both within and outside the X-ray saturation regime. We have simultaneously
analyzed the EPIC MOS and RGS data from these objects and have obtained coronal
abundances of various elements (e.g., C, N, O, Ne, Mg, Si, Fe). We show that
there is evidence for a transition from an Inverse First Ionization Potential
(FIP) effect in most active stars to a ``normal'' solar-like FIP effect in less
active stars. We discuss this result with regard to photospheric abundances.",0201530v1
2002-08-20,Saturation of the corotation resonance in a gaseous disk,"We determine the torque exerted in a steady state by an external potential on
a three-dimensional gaseous disk at a non-coorbital corotation resonance. Our
model accounts for the feedback of the torque on the surface density and
vorticity in the corotation region, and assumes that the disk has a barotropic
equation of state and a nonzero effective viscosity. The ratio of the torque to
the value given by the formula of Goldreich & Tremaine depends essentially on a
single dimensionless parameter, which quantifies the extent to which the
resonance is saturated. We discuss the implications for the eccentricity
evolution of young planets.",0208363v2
2003-04-11,Mechanisms of the Vertical Secular Heating of a Stellar Disk,"We investigate the nonlinear growth stages of bending instability in stellar
disks with exponential radial density profiles.We found that the unstable modes
are global (the wavelengths are larger than the disk scale lengths) and that
the instability saturation level is much higher than that following from a
linear criterion. The instability saturation time scales are of the order of
one billion years or more. For this reason, the bending instability can play an
important role in the secular heating of a stellar disk in the $z$ direction.
In an extensive series of numerical $N$-body simulations with a high spatial
resolution, we were able to scan in detail the space of key parameters (the
initial disk thickness $z_0$, the Toomre parameter $Q$, and the ratio of dark
halo mass to disk mass $M_{\rm h} / M_{\rm d}$). We revealed three distinct
mechanisms of disk heating in the $z$ direction: bending instability of the
entire disk, bending instability of the bar, and heating on vertical
inhomogeneities in the distribution of stellar matter.",0304215v1
2004-07-27,Stability of hydrodynamical relativistic planar jets. I. Linear evolution and saturation of Kelvin-Helmholtz modes,"The effects of relativistic dynamics and thermodynamics in the development of
Kelvin-Helmholtz instabilities in planar, relativistic jets along the early
phases (namely linear and saturation phases) of evolution has been studied by a
combination of linear stability analysis and high-resolution numerical
simulations for the most unstable first reflection modes in the temporal
approach. Three different values of the jet Lorentz factor (5, 10 and 20) and a
few different values of specific internal energy of the jet matter (from 0.08
to $60.0 c^2$) have been considered. Figures illustrating the evolution of the
perturbations are also shown.",0407548v1
2005-07-08,Hot Accretion With Saturated Conduction,"Observations of the hot gas surrounding Sgr A* and a few other nearby
galactic nuclei imply electron and proton mean free paths comparable to the gas
capture radius: hot accretion likely proceeds under weakly-collisional
conditions in these systems. As a result, thermal conduction, rather than
convection, may be important on all scales and affect the global flow
properties. The self-similar ADAF solution of Narayan & Yi (1994) is
generalized to include a saturated form of thermal conduction, as is
appropriate for the weakly-collisional regime of interest. Conduction provides
extra heating and yet it reduces the free-free radiative efficiency of the
accretion flow (by potentially large factors). These idealized solutions
suggest that thermal conduction may be an important physical ingredient to
understand hot accretion onto dim accreting black holes. Conduction could also
play a role in reducing the rate at which black holes capture ambient gas and
in providing an evaporation mechanism for an underlying cold thin disk.",0507189v1
2005-12-22,Air Shower Properties with the Gluon Saturation Model BBL,"The hadronic interaction model BBL implements the ideas of gluon saturation
due to large densities. When approaching the black body limit at high energies,
leading partons acquire large transverse momenta which breaks up their
coherence. This leads to a suppression of forward scattering, and is therefore
important for air showers. We discuss some general aspects of this new approach
and their influence on air shower properties as seen by fluorescence and
surface detectors: The position of the shower maximum is reduced due to
stronger absorption in the atmosphere. The lateral distribution functions
become flatter for the same reason. Muons are produced abundantly due to high
multiplicities in the mid-rapidity region. The response of water Cherenkov
detectors and comparisons to other interaction models are shown.",0512564v1
2006-10-18,A Local Model for Angular Momentum Transport in Accretion Disks Driven by the Magnetorotational Instability,"We develop a local model for the exponential growth and saturation of the
Reynolds and Maxwell stresses in turbulent flows driven by the
magnetorotational instability. We first derive equations that describe the
effects of the instability on the growth and pumping of the stresses. We
highlight the relevance of a new type of correlations that couples the
dynamical evolution of the Reynolds and Maxwell stresses and plays a key role
in developing and sustaining the magnetorotational turbulence. We then
supplement these equations with a phenomenological description of the triple
correlations that lead to a saturated turbulent state. We show that the
steady-state limit of the model describes successfully the correlations among
stresses found in numerical simulations of shearing boxes.",0610565v1
2006-11-09,Nonsaturated Holographic Dark Energy,"It has been well established by today that the concept of holographic dark
energy (HDE) does entail a serious candidate for the dark energy of the
universe. Here we deal with models where the holographic bound for dark energy
is not saturated for a large portion of the history of the universe. This is
particularly compelling when the IR cutoff is set by the Hubble scale, since
otherwise a transition from a decelerated to an accelerated era cannot be
obtained for a spatially flat universe. We demonstrate by three generic but
disparate dynamical models, two of them containing a variable Newton constant,
that transition between the two eras is always obtained for the IR cutoff in
the form of the Hubble scale and the nonsaturated HDE. We also give arguments
of why such a choice for the dark energy is more consistent and favored over
the widely accepted saturated form.",0611299v2
1993-06-15,Locally Frozen Defects in Random Sequential Adsorption with Diffusional Relaxation,"Random sequential adsorption with diffusional relaxation, of two by two
square objects on the two-dimensional square lattice is studied by Monte Carlo
computer simulation. Asymptotically for large lattice sizes, diffusional
relaxation allows the deposition process to reach full coverage. The coverage
approaches the full occupation value, 1, as a power-law with convergence
exponent near 1/2. For a periodic lattice of finite (even) size $L$, the final
state is a frozen random rectangular grid of domain walls connecting
single-site defects. The domain sizes saturate at L**0.8. Prior to saturation,
i.e., asymptotically for infinite lattice, the domain growth is power-law with
growth exponent near, or possibly somewhat smaller than, 1/2.",9306034v1
1996-10-08,Characterization of the Noise in Secondary Ion Mass Spectrometry Depth Profiles,"The noise in the depth profiles of secondary ion mass spectrometry (SIMS) is
studied using different samples under various experimental conditions. Despite
the noise contributions from various parts of the dynamic SIMS process, its
overall character agrees very well with the Poissonian rather than the Gaussian
distribution in all circumstances. The Poissonian relation between the measured
mean-square error (MSE) and mean can be used to describe our data in the range
of four orders. The departure from this relation at high counts is analyzed and
found to be due to the saturation of the channeltron used. Once saturated, the
detector was found to exhibit hysteresis between rising and falling input flux
and output counts.",9610061v1
1997-07-28,Lattice dependence of saturated ferromagnetism in the Hubbard model,"We investigate the instability of the saturated ferromagnetic ground state
(Nagaoka state) in the Hubbard model on various lattices in dimensions d=2 and
d=3. A variational resolvent approach is developed for the Nagaoka instability
both for U = infinity and for U < infinity which can easily be evaluated in the
thermodynamic limit on all common lattices. Our results significantly improve
former variational bounds for a possible Nagaoka regime in the ground state
phase diagram of the Hubbard model. We show that a pronounced particle-hole
asymmetry in the density of states and a diverging density of states at the
lower band edge are the most important features in order to stabilize Nagaoka
ferromagnetism, particularly in the low density limit.",9707286v2
1998-04-28,Macroscopic Equations of Motion for Two Phase Flow in Porous Media,"The established macroscopic equations of motion for two phase immiscible
displacement in porous media are known to be physically incomplete because they
do not contain the surface tension and surface areas governing capillary
phenomena. Therefore a more general system of macroscopic equations is derived
here which incorporates the spatiotemporal variation of interfacial energies.
These equations are based on the theory of mixtures in macroscopic continuum
mechanics. They include wetting phenomena through surface tensions instead of
the traditional use of capillary pressure functions. Relative permeabilities
can be identified in this approach which exhibit a complex dependence on the
state variables. A capillary pressure function can be identified in equilibrium
which shows the qualitative saturation dependence known from experiment. In
addition the new equations allow to describe the spatiotemporal changes of
residual saturations during immiscible displacement.",9804299v1
1998-10-28,Evidence for saturation of channel transmission from conductance fluctuations in atomic-size point contacts,"The conductance of atomic size contacts has a small, random, voltage
dependent component analogous to conductance fluctuations observed in diffusive
wires (UCF). A new effect is observed in gold contacts, consisting of a marked
suppression of these fluctuations when the conductance of the contact is close
to integer multiples of the conductance quantum. Using a model based on the
Landauer-Buettiker formalism we interpret this effect as evidence that the
conductance tends to be built up from fully transmitted (i.e., saturated)
channels plus a single, which is partially transmitted.",9810384v2
1999-11-05,Hierarchical model for the scale-dependent velocity of seismic waves,"Elastic waves of short wavelength propagating through the upper layer of the
Earth appear to move faster at large separations of source and receiver than at
short separations. This scale dependent velocity is a manifestation of Fermat's
principle of least time in a medium with random velocity fluctuations. Existing
perturbation theories predict a linear increase of the velocity shift with
increasing separation, and cannot describe the saturation of the velocity shift
at large separations that is seen in computer simulations. Here we show that
this long-standing problem in seismology can be solved using a model developed
originally in the context of polymer physics. We find that the saturation
velocity scales with the four-third power of the root-mean-square amplitude of
the velocity fluctuations, in good agreement with the computer simulations.",9911075v1
1999-12-08,Comparison of energy and phase relaxation in metallic wires,"We have measured the phase coherence time, $\tau_{\phi},$ in long, narrow
wires of Au, Ag, and Cu, over the temperature range 40 mK-6 K. In the Cu and Au
wires, $\tau_{\phi}$ saturates at low temperature. In the Ag wire,
$\tau_{\phi}$ continues to increase down to the lowest temperatures measured;
moreover, its temperature dependence below about 1 K is consistent with
theoretical predictions of Altshuler, Aronov and Khmelnitskii published in
1982. These results cast doubt on recent assertions that saturation of
$\tau_{\phi}$ at low temperature is a universal phenomenon in metal wires. We
compare these results with those of recent experiments on energy relaxation in
similar metallic wires. The results of the two experiments are strongly
correlated, suggesting that a single (unknown) mechanism is the cause of the
enhanced phase and energy relaxation observed in some samples.",9912137v1
2000-01-29,Tractable non-local correlation density functionals for flat surfaces and slabs,"A systematic approach for the construction of a density functional for van
der Waals interactions that also accounts for saturation effects is described,
i.e. one that is applicable at short distances. A very efficient method to
calculate the resulting expressions in the case of flat surfaces, a method
leading to an order reduction in computational complexity, is presented.
Results for the interaction of two parallel jellium slabs are shown to agree
with those of a recent RPA calculation (J.F. Dobson and J. Wang, Phys. Rev.
Lett. 82, 2123 1999). The method is easy to use; its input consists of the
electron density of the system, and we show that it can be successfully
approximated by the electron densities of the interacting fragments. Results
for the surface correlation energy of jellium compare very well with those of
other studies. The correlation-interaction energy between two parallel jellia
is calculated for all separations d, and substantial saturation effects are
predicted.",0001429v1
2000-02-15,Charge-Reversal Instability in Mixed Bilayer Vesicles,"Bilayer vesicles form readily from mixtures of charged and neutral
surfactants. When such a mixed vesicle binds an oppositely-charged object, its
membrane partially demixes: the adhesion zone recruits more charged surfactants
from the rest of the membrane. Given an unlimited supply of adhering objects
one might expect the vesicle to remain attractive until it was completely
covered. Contrary to this expectation, we show that a vesicle can instead
exhibit {\it adhesion saturation,} partitioning spontaneously into an
attractive zone with definite area fraction, and a repulsive zone. The latter
zone rejects additional incoming objects because counterions on the interior of
the vesicle migrate there, effectively reversing the membrane's charge. The
effect is strongest at high surface charge densities, low ionic strength, and
with thin, impermeable membranes. Adhesion saturation in such a situation has
recently been observed experimentally [H. Aranda-Espinoza {\it et al.}, {\sl
Science} {\bf285} 394--397 (1999)].",0002230v1
2001-05-26,Discrete saturation thickness and anomalous potential height of native ultrathin aluminum oxide tunnel barriers,"We have investigated planar metal - insulator - metal tunnel junctions with
aluminum oxide as dielectricum. These oxide barriers were grown on an aluminum
electrode in pure oxygen at room temperature till saturation. We observed
discrete barrier widths separated by \Delta s \approx 0.38 nm, corresponding to
the addition of one layer of oxygen atoms. The minimum thickness of s_0 \approx
0.54 nm is due to a double layer of oxygen. We found a strong and systematic
dependence of the barrier height \Phi_0 on the thickness s like \Phi_0 \approx
2.5 eV / s^2(nm), which nearly coincides with the kinetic electron energy E =
h^2/2ms^2 for which the deBroglie wavelength matches the width of the barrier.",0105511v1
2002-03-19,Persistent Non-ergodic Fluctuations in Mesoscopic Insulators,"We give a detailed and rigorous picture of the mesoscopic conductance
fluctuations in the deep insulating regime (DIR) within the Nguyen, Spivak and
Shklovskii model including spin-orbit coupling (SO). Without SO, we find that
fluctuations of the log-conductance are persistent above a saturation field $%
B_s$, where one has that the log-conductance is approximately a stationary
random process. In contrast, in the SO case the saturation field $B_s$ is
negligible and the stationarity is well realized. We find non-vanishing
disorder fluctuations of the field average of the log-conductance as a
quantitative measure of the lack of ergodicity in the mean square sense. As a
consequence the commonly used criterion to test the ergodicity based on the
equivalence of the variance in disorder and the variance in the field is not
fulfilled. Using the replica approach, we derive the weak localization analogs
of the `cooperon and diffuson.",0203380v1
2002-05-09,Many-body and correlation effects on parametric polariton amplificazion in semiconductor microcavities,"Very efficient amplification of light-matter waves (polaritons), that are a
superposition of cavity photons and excitons [1] has recently been
reported[2-11]. The optical gain curve versus the pump power shows a threshold
and then saturates to a maximum value[7,11]. Very recently it has been shown
that this limit-value of gain can be greatly enhanced by increasing the
exciton-photon coupling rate, allowing to approach room temperature
operation11. This anomalous enhancement is in contrast with results from
present theories[12,13] describing the process. Here we clarify the mechanisms
determining gain saturation and explain the observed giant amplification. We
show that this enhancement origins from the non-instantaneous nature of
exciton-exciton collisions in semiconductors[14] due to many-body correlations.
We find that the exciton-photon coupling is able to alter the exciton dynamics
during collisions and hence to modify the coupling mechanism at the basis of
amplification. These results give precise indications to favour room
temperature operation for the realization of all-optical microscopic switches
and amplifiers and demonstrate that exciton-exciton collisions in
semiconductors can be controlled and engineered.",0205199v1
2002-05-21,Is weak temperature dependence of electron dephasing possible?,"The first-principle theory of electron dephasing by disorder-induced two
state fluctuators is developed. There exist two mechanisms of dephasing. First,
dephasing occurs due to direct transitions between the defect levels caused by
inelastic electron-defect scattering. The second mechanism is due to violation
of the time reversal symmetry caused by time-dependent fluctuations of the
scattering potential. These fluctuations originate from an interaction between
the dynamic defects and conduction electrons forming a thermal bath. The first
contribution to the dephasing rate saturates as temperature decreases. The
second contribution does not saturate, although its temperature dependence is
rather weak, $\propto T^{1/3}$. The quantitative estimates based on the
experimental data show that these mechanisms considered can explain the weak
temperature dependence of the dephasing rate in some temperature interval.
However, below some temperature dependent on the model of dynamic defects the
dephasing rate tends rapidly to zero. The relation to earlier studies of the
dephasing caused by the dynamical defects is discussed.",0205438v1
2002-07-02,Relaxation to steady states and dynamical exponents in deposition models,"Considering some deposition models with limited mobility, we show that the
typical decay of the interface width to its saturation value is exponential,
which defines the crossover or saturation time \tau. We present a method to
calculate a characteristic time \tau_0 proportional to \tau and estimate the
dynamical exponent z. In one dimensional substrates of lengths L <~ 2048, the
method is applied to the Family model, the restricted solid-on-solid (RSOS)
model and the ballistic deposition. Effective exponents z_L converge to
asymptotic values consistent with the corresponding continuum theories. For the
two-dimensional Family model, the expected dynamic scaling hypothesis suggests
a particular definition of \tau_0 that leads to z=2, improving previous
calculations based on data collapse methods. For the two-dimensional RSOS
model, we obtain z ~ 1.6 and \alpha < 0.4, in agreement with recent large scale
simulations.",0207088v1
2002-08-02,Instability of quasi-liquid on the edges and vertices of snow crystals,"In this paper, we show theoretically that there exists quasi-liquid on the
edges and vertices of snow crystals between -4C and -22C, while the basal and
prism faces have no quasi-liquid layers. Investigating the macroscopic theory
of quasi-liquid and applying to the edges and vertices of the crystal, we find
that the quasi-liquid becomes unstable above the critical supersaturation
point, which is above the water saturation point. The thickness of this
unstable quasi-liquid layer continues growing indefinitely. We interpret this
behavior as corresponding to continuous production and overflow onto
neighboring faces in a real system. We hypothesize that the unstable growth of
snow crystals originates from the edges and vertices, and it is due to the
overflow of quasi-liquid from the edges and vertices onto the neighboring
faces, which are rough and lack quasi-liquid. Our hypothesis accounts for the
qualitative behavior of the relations between the morphological instability and
the water saturation in the snow phase diagram.",0208036v1
2002-12-20,Capillary forces in the acoustics of patchy-saturated porous media,"A linearized theory of the acoustics of porous elastic formations, such as
rocks, saturated with two different viscous fluids is generalized to take into
account a pressure discontinuity across the fluid boundaries. The latter can
arise due to the surface tension of the membrane separating the fluids. We show
that the frequency-dependent bulk modulus $\tilde{K}(\omega)$ for wave lengths
longer than the characteristic structural dimensions of the fluid patches has a
similar analytic behavior as in the case of a vanishing membrane stiffness and
depends on the same parameters of the fluid-distribution topology. The effect
of the capillary stiffness can be accounted by renormalizing the coefficients
of the leading terms in the low-frequency asymptotic of $\tilde{K}(\omega)$.",0212534v2
2003-03-31,The droplet evaporation/condensation transition in a finite volume,"A fluid in the NVT ensemble at T less than the critical temperature T_c and
rho = N/V somewhat in excess of rho_coex (density of the saturated gas in the
gas-liquid transition) is considered. For V->infinity, a macroscopic liquid
droplet coexists with surrounding saturated gas according to the lever rule.
For finite V, droplets can only exist if they exceed a minimum size. A
(rounded) first order transition of the system occurs when the droplet
evaporates into the supersaturated gas.Simulation evidence for this transition
is given for a Lennard-Jones model and interpreted by a phenomenological
theory. At the transition, the chemical potential difference mu_t-mu_coex
scales like L^(-d/(d+1)) for a cubic volume V=L^d in d dimensions, as
L->infinity.",0303642v1
2003-06-04,The Absence Of Saturation Of The Level Number Variance In A Rectangular Box,"The variance of the number of levels in an energy interval around a level
with large quantum numbers (semiclassical quantization) is studied for a
particle in a rectangular box. Sampling involves changing the ratio of the
rectangle's sides while keeping the area constant. For sufficiently narrow
intervals, one finds the usual linear growth with the width of the interval.
For wider intervals, the variance undergoes large, non-decaying oscillations
around what is expected to be the saturation value. These oscillations can be
explained as a superposition of just a few harmonics that correspond to the
shortest periodic orbits in the rectangle. The analytical and numerical results
are in excellent agreement.",0306110v1
2003-07-01,Efficient nonlinear room-temperature spin injection from ferromagnets into semiconductors through a modified Schottky barrier,"We suggest a consistent microscopic theory of spin injection from a
ferromagnet (FM) into a semiconductor (S). It describes tunneling and emission
of electrons through modified FM-S Schottky barrier with an ultrathin heavily
doped interfacial S layer . We calculate nonlinear spin-selective properties of
such a reverse-biased FM-S junction, its nonlinear I-V characteristic, current
saturation, and spin accumulation in S. We show that the spin polarization of
current, spin density, and penetration length increase with the total current
until saturation. We find conditions for most efficient spin injection, which
are opposite to the results of previous works, since the present theory
suggests using a lightly doped resistive semiconductor. It is shown that the
maximal spin polarizations of current and electrons (spin accumulation) can
approach 100% at room temperatures and low current density in a nondegenerate
high-resistance semiconductor.",0307030v4
2003-09-03,Intrusion and extrusion of water in hydrophobic mesopores,"We present experimental and theoretical results on intrusion-extrusion cycles
of water in hydrophobic mesoporous materials, characterized by independent
cylindrical pores. The intrusion, which takes place above the bulk saturation
pressure, can be well described using a macroscopic capillary model. Once the
material is saturated with water, extrusion takes place upon reduction of the
externally applied pressure; Our results for the extrusion pressure can only be
understood by assuming that the limiting extrusion mechanism is the nucleation
of a vapour bubble inside the pores. A comparison of calculated and
experimental nucleation pressures shows that a proper inclusion of line tension
effects is necessary to account for the observed values of nucleation barriers.
Negative line tensions of order $10^{-11} \mathrm{J.m}^{-1}$ are found for our
system, in reasonable agreement with other experimental estimates of this
quantity.",0309077v1
2003-10-31,Statistical theory of high-gain free-electron laser saturation,"We propose a new approach, based on statistical mechanics, to predict the
saturated state of a single-pass, high-gain free-electron laser (FEL). In
analogy with the violent relaxation process in self-gravitating systems and in
the Euler equation of 2D turbulence, the initial relaxation of the laser can be
described by the statistical mechanics of an associated Vlasov equation. The
Laser field intensity and the electron bunching parameter reach
quasi-stationary values that are well fitted by a Vlasov stationary state if
the number of electrons $N$ is sufficiently large. Finite $N$ effects
(granularity) finally drive the system to Boltzmann-Gibbs statistical
equilibrium, but this occurs on times that are unphysical (i.e. excessively
long undulators). All theoretical predictions are successfully tested in finite
$N$ numerical experiments. Our results may provide important hints to the
optimization of the length of the FEL undulator.",0310754v2
2004-08-19,Charge dynamics of Ca_{2-x}Na_{x}CuO_{2}Cl_{2} as a correlated electron system with the ideal tetragonal lattice,"We report the reflectivity and the resistivity measurement of
Ca_{2-x}Na_{x}CuO_{2}Cl_{2} (CNCOC), which has a single-CuO2-plane lattice with
no orthorhombic distortion. The doping dependence of the in-plane optical
conductivity spectra for CNCOC is qualitatively the same to those of other
cuprates, but a slight difference between CNCOC and LSCO, i.e., the absence of
the 1.5 eV peak in CNCOC, can be attributed to the smaller charge-stripe
instability in CNCOC. The temperature dependence of the optical onductivity
spectra of CNCOC has been analyzed both by the two-component model
(Drude+Lorentzian) and by the one-component model (extended-Drude analysis).
The latter analysis gives a universal trend of the scattering rate Gamma(omega)
with doping. It was also found that Gamma(omega) shows a saturation behavior at
high frequencies, whose origin is the same as that of resistivity saturation at
high temperatures.",0408423v1
2004-08-26,High-pressure phase relations of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ single crystals,"We have investigated the pressure dependence of the superconducting
transition temperature $T_{c}$ up to 18 GPa of
Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ single crystals ranging from the
highly underdoped through the nearly optimally doped to the highly overdoped
level. For all three samples studied, $T_{c}$ is found to increase initially
and then saturate at a critical pressure $P_{c}$ but decrease modestly with
further compression. Oxygen doping tends to reduce the increase in $T_{c}$ and
$P_{c}$. A new high-pressure phase diagram between the saturated $T_{c}$ and
$P_{c}$ is then obtained. Theoretical interpretation is given by using the
competition between the hole carrier density and pairing interaction strength
based on the high-pressure transport data of the resistivity and Hall
coefficient in this system.",0408587v2
2004-10-24,In situ observation of the generation and annealing kinetics of E' centers induced in amorphous SiO2 by 4.7eV laser irradiation,"The kinetics of E' centers induced in silica by 4.7eV laser irradiation was
investigated observing in situ their optical absorption band at 5.8 eV. After
exposure the defects decay due to reaction with diffusing molecular hydrogen of
radiolytic origin. Hydrogen-related annealing is active also during exposure
and competes with the photo-induced generation of the centers until a
saturation is reached. The concentrations of E' and H2 at saturation are
proportional, so indicating that the UV-induced generation processes of the two
species are correlated. These results are consistent with a model in which E'
and hydrogen are generated from a common precursor Si-H.",0410608v2
2005-01-21,Two-dimensional metal-insulator transition and in-plane magnetoresistance in a high mobility strained Si quantum well,"The apparent metal-insulator transition is observed in a high quality
two-dimensional electron system (2DES) in the strained Si quantum well of a
Si/Si_{1-x}Ge_x heterostructure with mobility \mu=1.9 x 10^5 cm^2/Vs at density
n=1.45 x 10^{11} cm^{-2}. The critical density, at which the thermal
coefficient of low T resistivity changes sign, is ~ 0.32 x 10^{11} cm^{-2}, so
far the lowest observed in the Si 2D systems. In-plane magnetoresistance study
was carried out in the higher density range where the 2DES shows the
metallic-like behavior. It is observed that the in-plane magnetoresistance
first increases as ~ B_{ip}^2 and then saturates to a finite value \rho(B_c)
for B_{ip} > B_c. The full spin-polarization field B_c decreases monotonically
with n but appears to saturate to a finite value as n approaches zero.
Furthermore, \rho(B_c)/\rho(0) ~ 1.8 for all the densities ranging from 0.35 x
10^{11} to 1.45 x 10^{11} cm^{-2} and, when plotted versus B_{ip}/B_c,
collapses onto a single curve.",0501532v2
2005-01-25,Pattern scaling in the axial segregation of granular materials in a rotating tube,"Granular mixtures frequently segregate by grain size along the axis of
partially-filled, horizontal, rotating tubes. When segregation approaches
saturation at the surface, a well-defined pattern of bands with wavelength
$\lambda$ emerges. The long-term dynamics of the pattern involves a much slower
coarsening process. We characterized the initial saturated wavelength $\lambda$
as a function of the diameter of the tube $D$ for a filling fraction of 30 %,
for $1.9 {\rm cm} \leq D \leq 11.5 {\rm cm}$. We also studied the initial
growth-rate of the bands as $D$ varies. We find that $\lambda/D$ is not
constant, but rather increases rapidly for small $D$. The growth-rate of bands
decreases with smaller $D$ and segregation is suppressed completely for
sufficiently small $D$. These relatively simple features are not captured by
any of the existing models of axial segregation.",0501606v1
2005-02-13,Transport properties in correlated systems: An analytical model,"Several studies have so far investigated transport properties of strongly
correlated systems. Interesting features of these materials are the lack of
resistivity saturation well beyond the Mott-Ioffe-Regel limit and the scaling
of the resistivity with the hole density in underdoped cuprates. Due to the
strongly correlated nature of these materials, mainly numerical techniques have
been employed. A key role in this regards is thought to be played by the
continuous transfer of spectral weight from coherent to incoherent states. In
this paper we employ a simple analytical expression for the electronic Green's
function to evaluate both quasi-particle and transport properties in correlated
systems. Our analytical approach permits to enlighten the specific role of the
spectral transfer due to the correlation on different features. In particular
we investigate the dependence of both quasi-particle and transport scattering
rate on the correlation degree and the criterion for resistivity saturation.
systems.",0502297v3
2005-03-07,Zero temperature dynamics of Ising model on a densely connected small world network,"The zero temperature quenching dynamics of the ferromagnetic Ising model on a
densely connected small world network is studied where long range bonds are
added randomly with a finite probability $p$. We find that in contrast to the
sparsely connected networks and random graph, there is no freezing and an
initial random configuration of the spins reaches the equilibrium configuration
within a very few Monte Carlo time steps in the thermodynamic limit for any $p
\ne 0$. The residual energy and the number of spins flipped at any time shows
an exponential relaxation to equilibrium. The persistence probability is also
studied and it shows a saturation within a few time steps, the saturation value
being 0.5 in the thermodynamic limit. These results are explained in the light
of the topological properties of the network which is highly clustered and has
a novel small world behaviour.",0503138v2
2005-04-25,Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation,"Time-resolved magneto-optical Kerr spectroscopy of ferromagnetic InMnAs
reveals two distinct {\em demagnetization} processes -- fast ($<1$ ps) and slow
($\sim$100 ps). Both components diminish with increasing temperature and are
absent above the Curie temperature. The fast component rapidly grows with pump
power and saturates at high fluences ($>10$ mJ/cm$^2$); the saturation value
indicates a {\em complete quenching} of ferromagnetism on a sub-picosecond time
scale. We attribute this fast dynamics to spin heating through $p$-$d$ exchange
interaction between photo-carriers and Mn ions while the $\sim$100 ps component
is interpreted as spin-lattice relaxation.",0504611v2
2005-05-02,The Memory Effect in Electron Glasses,"We present a theory for the memory effect in electron glasses. In fast gate
voltage sweeps it is manifested as a dip in the conductivity around the
equilibration gate voltage. We show that this feature, also known as anomalous
field effect, arises from the long-time persistence of correlations in the
electronic configuration. We argue that the gate voltage at which the memory
dip saturates is related to an instability caused by the injection of a
critical number of excess carriers. This saturation threshold naturally
increases with temperature. On the other hand, we argue that the gate voltage
beyond which memory is erased, is temperature independent. Using standard
percolation arguments, we calculate the anomalous field effect as a function of
gate voltage, temperature, carrier density and disorder. Our results are
consistent with experiments, and in particular, they reproduce the observed
scaling of the width of the memory dip with various parameters.",0505021v3
2005-05-13,Localized activity profiles and storage capacity of rate-based autoassociative networks,"We study analytically the effect of metrically structured connectivity on the
behavior of autoassociative networks. We focus on three simple rate-based model
neurons: threshold-linear, binary or smoothly saturating units. For a
connectivity which is short range enough the threshold-linear network shows
localized retrieval states. The saturating and binary models also exhibit
spatially modulated retrieval states if the highest activity level that they
can achieve is above the maximum activity of the units in the stored patterns.
In the zero quenched noise limit, we derive an analytical formula for the
critical value of the connectivity width below which one observes spatially
non-uniform retrieval states. Localization reduces storage capacity, but only
by a factor of 2~3. The approach that we present here is generic in the sense
that there are no specific assumptions on the single unit input-output function
nor on the exact connectivity structure.",0505349v1
2005-10-24,Mobility in semiconducting carbon nanotubes at finite carrier density,"Carbon nanotube field-effect transistors operate over a wide range of
electron or hole density, controlled by the gate voltage. Here we calculate the
mobility in semiconducting nanotubes as a function of carrier density and
electric field, for different tube diameters and temperature. The low-field
mobility is a non-monotonic function of carrier density, and varies by as much
as a factor of 4 at room temperature. At low density, with increasing field the
drift velocity reaches a maximum and then exhibits negative differential
mobility, due to the non-parabolicity of the bandstructure. At a critical
density $\rho_c\sim$ 0.35-0.5 electrons/nm, the drift velocity saturates at
around one third of the Fermi velocity. Above $\rho_c$, the velocity increases
with field strength with no apparent saturation.",0510638v1
2006-01-17,Statistical mechanics and Vlasov equation allow for a simplified hamiltonian description of single pass free electron laser saturated dynamics,"A reduced Hamiltonian formulation to reproduce the saturated regime of a
single pass free electron laser, around perfect tuning, is here discussed.
Asymptotically, $N\_m$ particles are found to organize in a dense cluster, that
evolves as an individual massive unit. The remaining particles fill the
surrounding uniform sea, spanning a finite portion of phase space,
approximately delimited by the average momenta $\omega\_+$ and $\omega\_-$.
These quantities enter the model as external parameters, which can be
self-consistently determined within the proposed theoretical framework. To this
aim, we make use of a statistical mechanics treatment of the Vlasov equation,
that governs the initial amplification process. Simulations of the reduced
dynamics are shown to successfully capture the oscillating regime observed
within the original $N$-body picture.",0601362v1
2006-03-17,Low velocity quantum reflection of Bose-Einstein condensates,"We studied quantum reflection of Bose-Einstein condensates at normal
incidence on a square array of silicon pillars. For incident velocities of
2.5-26 mm/s observations agreed with theoretical predictions that the
Casimir-Polder potential of a reduced density surface would reflect slow atoms
with much higher probability. At low velocities (0.5-2.5 mm/s), we observed
that the reflection probability saturated around 60% rather than increasing
towards unity. We present a simple model which explains this reduced
reflectivity as resulting from the combined effects of the Casimir-Polder plus
mean field potential and predicts the observed saturation. Furthermore, at low
incident velocities, the reflected condensates show collective excitations.",0603463v1
2006-03-20,Dynamic fluctuations of elastic lines in random environments,"We study the fluctuations of the two-time dependent global roughness of
finite size elastic lines in a quenched random environment. We propose a
scaling form for the roughness distribution function that accounts for the
two-time, temperature, and size dependence. At high temperature and in the
final stationary regime before saturation the fluctuations are as the ones of
the Edwards-Wilkinson interface evolving from typical initial conditions. We
analyze the variation of the scaling function within the aging regime and with
the distance from saturation. We speculate on the relevance of our results to
describe the fluctuations of other non-equilibrium systems such as models at
criticality.",0603503v2
2006-04-12,Low-frequency Noise in Josephson Junctions for Superconducting Qubits,"We have studied low-frequency resistance fluctuations in shadow-evaporated
Al/AlOx/Al tunnel junctions. Between 300 K and 5 K the spectral density follows
a 1/f-law. Below 5 K, individual defects distort the 1/f-shape of the spectrum.
The spectral density decreases linearly with temperature between 150 K and 1 K
and saturates below 0.8 K. At 4.2 K, the spectral density is about two orders
of magnitude lower than expected from a recent survey [D. J. Van Harlingen et
al., Phys. Rev. B 70, 064510 (2004)]. Due to the saturation below 0.8 K the
estimated qubit dephasing times at 100 mK are only about two times longer than
calculated by Van Harlingen et al.",0604306v2
2006-07-24,Saturated Hydrocarbons on Silicon: Quantifying Desorption with Scanning Tunneling Microscopy and Quantum Theory,"Electron stimulated desorption of cyclopentene from the Si(100)-2x1 surface
is studied experimentally with cryogenic UHV STM and theoretically with
transport, electronic structure, and dynamical calculations. Unexpectedly for a
saturated hydrocarbon on silicon, desorption is observed at bias magnitudes as
low as 2.5 V, albeit the desorption yields are a factor of 500 to 1000 lower
than previously reported for unsaturated molecules on silicon. The low
threshold voltage for desorption can be attributed to hybridization of the
molecule with the silicon surface, which results in low-lying ionic resonances
within 2-3 eV of the Fermi level. These resonances are long-lived, spatially
localized and displaced in equilibrium with respect to the neutral state,
resulting, upon excitation, in symmetric (positive ion) or asymmetric (negative
ion) motion of the silicon dimer atoms. This study highlights the importance of
nuclear dynamics in silicon-based molecular electronics and suggests new
guidelines for the control of such dynamics.",0607621v2
2006-10-05,Carrier transport in 2D graphene layers,"Carrier transport in gated 2D graphene monolayers is theoretically considered
in the presence of scattering by random charged impurity centers with density
$n_i$. Excellent quantitative agreement is obtained (for carrier density $n >
10^{12} \rm{cm}^{-2}$) with existing experimental data (Ref.
\onlinecite{kn:novoselov2004, kn:novoselov2005, kn:zhang2005, kn:kim2006,
kn:fuhrer2006}). The conductivity scales linearly with $n/n_i$ in the theory,
and shows extremely weak temperature dependence. The experimentally observed
asymmetry between electron and hole conductivities is explained by the
asymmetry in the charged impurity configuration in the presence of the gate
voltage, while the high-density saturation of conductivity for the highest
mobility samples is explained as a crossover between the long-range and the
point scattering dominated regimes. We argue that the experimentally observed
saturation of conductivity at low density arises from the charged impurity
induced inhomogeneity in the graphene carrier density which becomes severe for
$n \lesssim n_i \sim 10^{12} \rm{cm}^{-2}$.",0610157v2
2006-10-27,Optical response of high-$T_c$ cuprates: possible role of scattering rate saturation and in-plane anisotropy,"We present a generalized Drude analysis of the in-plane optical conductivity
$\sigma_{ab}$($T$,$\omega$) in cuprates taking into account the effects of
in-plane anisotropy. A simple ansatz for the scattering rate
$\Gamma$($T$,$\omega$), that includes anisotropy, a quadratic frequency
dependence and saturation at the Mott-Ioffe-Regel limit, is able to reproduce
recent normal state data on an optimally doped cuprate over a wide frequency
range. We highlight the potential importance of including anisotropy in the
full expression for $\sigma_{ab}$($T$,$\omega$) and challenge previous
determinations of $\Gamma$($\omega$) in which anisotropy was neglected and
$\Gamma$($\omega$) was indicated to be strictly linear in frequency over a wide
frequency range. Possible implications of our findings for understanding
thermodynamic properties and self-energy effects in high-$T_c$ cuprates will
also be discussed.",0610763v1
2006-11-28,Intraband versus interband scattering rate effects in neutron irradiated MgB2,"One of the most important predictions of the two-gap theory of
superconductivity concerns the role of interband scattering (IBS) by
impurities. IBS is expected to decrease the critical temperature, Tc, of MgB2
to a saturation value of about 20 K, where the two gaps merge to a single one.
These predictions have been partially contradicted by experiments. In fact, Tc
does not saturate in irradiated samples, but decreases linearly with residual
resistivity and the merging of the gaps has been observed at a much lower Tc
(11 K). In this paper we argue that, while at low level of disorder IBS is the
leading mechanism that suppresses superconductivity, at higher disorder the
experimental results can only be understood if the smearing of the density of
states due to intraband electron lifetime effects is considered.",0611700v1
2007-01-21,Dynamical control of electron spin coherence in a quantum dot,"We investigate the performance of dynamical decoupling methods at suppressing
electron spin decoherence from a low-temperature nuclear spin reservoir in a
quantum dot. The controlled dynamics is studied through exact numerical
simulation, with emphasis on realistic pulse delays and long-time limit. Our
results show that optimal performance for this system is attained by a periodic
protocol exploiting concatenated design, with control rates substantially
slower than expected from the upper spectral cutoff of the bath. For a known
initial electron spin state, coherence can saturate at long times, signaling
the creation of a stable ``spin-locked'' decoherence-free subspace. Analytical
insight on saturation is obtained for a simple echo protocol, in good agreement
with numerical results.",0701507v1
2007-02-19,Wang-Landau Algorithm: a Theoretical Analysis of the Saturation of the Error,"In this work we present a theoretical analysis of the convergence of the
Wang-Landau algorithm [Phys. Rev. Lett. 86, 2050 (2001)] which was introduced
years ago to calculate the density of states in statistical models. We study
the dynamical behavior of the error in the calculation of the density of
states.We conclude that the source of the saturation of the error is due to the
decreasing variations of the refinement parameter. To overcome this limitation,
we present an analytical treatment in which the refinement parameter is scaled
down as a power law instead of exponentially. An extension of the analysis to
the N-fold way variation of the method is also discussed.",0702414v3
2006-06-14,Rigid upper bounds for the angular momentum and centre of mass of non-singular asymptotically anti-de Sitter space-times,"We prove upper bounds on angular momentum and centre of mass in terms of the
Hamiltonian mass and cosmological constant for non-singular asymptotically
anti-de Sitter initial data sets satisfying the dominant energy condition. We
work in all space-dimensions larger than or equal to three, and allow a large
class of asymptotic backgrounds, with spherical and non-spherical conformal
infinities; in the latter case, a spin-structure compatibility condition is
imposed. We give a large class of non-trivial examples saturating the
inequality. We analyse exhaustively the borderline case in space-time dimension
four: for spherical cross-sections of Scri, equality together with completeness
occurs only in anti-de Sitter space-time. On the other hand, in the toroidal
case, regular non-trivial initial data sets saturating the bound exist.",0606064v2
1992-12-22,Upper Bounds on the Lightest Higgs Boson Mass in General Supersymmetric Standard Models,"In a general supersymmetric standard model there is an upper bound $m_h$ on
the tree level mass of the $CP=+1$ lightest Higgs boson which depends on the
electroweak scale, $\tan \beta$ and the gauge and Yukawa couplings of the
theory. When radiative corrections are included, the allowed region in the
$(m_h,m_t)$ plane depends on the scale $\Lambda$, below which the theory
remains perturbative, and the supersymmetry breaking scale $\Lambda_s$, that we
fix to $1\ TeV$. In the minimal model with $\Lambda=10^{16}\ GeV$: $m_h<130\
GeV$ and $m_t<185\ GeV$. In non-minimal models with an arbitrary number of
gauge singlets and $\Lambda=10^{16}\ GeV$: $m_h<145\ GeV$ and $m_t<185\ GeV$.
We also consider supersymmetric standard models with arbitrary Higgs sectors.
For models whose couplings saturate the scale $\Lambda=10^{16}\ GeV$ we find
$m_h<155\ GeV$ and $m_t<190\ GeV$. As one pushes the saturation scale $\Lambda$
down to $\Lambda_s$, the bounds on $m_h$ and $m_t$ increase. For instance, in
models with $\Lambda=10\ TeV$, the upper bounds for $m_h$ and $m_t$ go to $415\
GeV$ and $385\ GeV$, respectively.",9212305v1
1993-11-29,Unitarity Constraints for Transverse Gauge Bosons at LEP and Supercolliders,"Using asymptotic helicity amplitudes for Vector-Vector, Vector-Higgs and
Higgs-Higgs scattering, we establish the unitarity constraints on the $SU(2)_c$
conserving and $W_\mu$ depending interactions, which at sufficiently high
energies may create strong forces among the transverse vector boson and Higgs
states. We then derive upper bounds for the couplings of these interactions,
which depend on the high energy scale where unitarity is saturated. If \eg\,
unitarity is saturated at 1TeV, then $\lambda_W \lsim 0.12$ is obtained. The
implied relations between the present and future LEP results, and the possible
observations of strong effects at supercolliders, are also discussed",9311370v1
1995-02-07,$γγ\to π^0 π^0$ and $η\to π^0 γγ$ at low energy within the Extended Nambu Jona-Lasinio Model,"Within the Extended Nambu Jona-Lasinio model, we calculate the $O(p^6)$
counterterms entering the low-energy expansion of the $\gamma \gamma \to \pi^0
\pi^0$ and the $\eta \to \pi^0 \gamma \gamma$ amplitudes in Chiral Perturbation
Theory. For $\gamma \gamma \to \pi^0 \pi^0$ our results are compatible with
both the experimental data and the two-loop calculation using meson resonance
saturation. For the $\eta$ decay we find $\Gamma(\eta\to\pi^0
\gamma\gamma)=0.58\pm 0.3$ eV which is in agreement with experiment within one
standard deviation. We also give predictions for the neutral pion
polarizabilities and compare them with the results obtained from resonance
saturation.",9502243v1
1995-03-07,$η\to π^{0} γγ$ and $γγ\to π^{0} π^{0}$ in $O(p^{6})$ chiral perturbation theory,"$\eta \rightarrow \pi^{0} \gamma \gamma$ and $\ggpipi$ are considered in
$O(p^{6})$ chiral perturbation theory. In addition to the usual $\rho,\omega$
contributions, there are two $O(p^{6})$ operators (${\cal L}_{6,m}$) arising
from explicit chiral symmetry breaking. Since only one of the two operators
contributes to $\etapigg$, the coefficient of this operator ($\equiv d_3$) can
be determined in two ways : (i) from the measured decay rate of $\eta
\rightarrow \pi^{0} \gamma \gamma$, and (ii) by assuming the resonance
saturations of the low energy coefficients in the $O(p^{6})$ chiral lagrangian.
We find that two methods lead to vastly different values of $d_3$, which would
indicate that either the measured decay rate for $\eta \rightarrow \pi^{0}
\gamma \gamma$ is too large by a factor of $2 \sim 3$, or the resonance
saturation assumptions do not work for $d_3$.",9503253v1
1995-07-04,Baby Skyrmion Strings,"We provide analytical and numerical evidence of the existence of classically
stable, string-like configurations in a 2+1 dimensional analog of the Skyrme
model. The model contains a conserved topological charge usually called the
baryon number. Our strings are non-topological solitons which have a constant
baryon number per unit length. The energy per length containing one baryon is,
however, less than the energy of an isolated baryon (radially symmetric ``baby
Skyrmion"") in a region of the parameter space, which suggests a degree of
stability for our configurations. In a limiting case, our configuration
saturates a Bogomolnyi-type bound and is degenerate in energy per baryon with
the baby Skyrmion. In another limiting case, the energies are still degenerate
but do not saturate the corresponding Bogomolnyi-type bound. Nonetheless, we
expect the string to be stable here. Both limiting cases are solvable
analytically.",9507223v1
1997-09-18,Four-quark Operators Relevant to B Meson Lifetimes from QCD Sum Rules,"At the order of 1/m_b^3, the B meson lifetimes are controlled by the hadronic
matrix elements of some four-quark operators. The nonfactorizable magnitudes of
these four-quark operator matrix elements are analyzed by QCD sum rules in the
framework of heavy quark effective theory. The vacuum saturation for
color-singlet four-quark operators is justified at hadronic scale, and the
nonfactorizable effect is at a few percent level. However for color-octet
four-quark operators, the vacuum saturation is violated sizably that the
nonfactorizable effect cannot be neglected for the B meson lifetimes. The
implication to the extraction of some of the parameters from B decays is
discussed. The B meson lifetime ratio is predicted as
\tau(B^-)/\tau(B^0)=1.09\pm 0.02. However, the experimental result of the
lifetime ratio \tau(\Lambda_b)/\tau(B^0) still cannot be explained.",9709386v2
1997-10-29,On Chemical Equilibrium in Nuclear Collisions,"The data on average hadron multiplicities in central A+A collisions measured
at CERN SPS are analysed with the ideal hadron gas model. It is shown that the
full chemical equilibrium version of the model fails to describe the
experimental results. The agreement of the data with the off-equilibrium
version allowing for partial strangeness saturation is significantly better.
The freeze-out temperature of about 180 MeV seems to be independent of the
system size (from S+S to Pb+Pb) and in agreement with that extracted in e+e-,
pp and p{\bar p} collisions. The strangeness suppression is discussed at both
hadron and valence quark level. It is found that the hadronic strangeness
saturation factor gamma_S increases from about 0.45 for pp interactions to
about 0.7 for central A+A collisions with no significant change from S+S to
Pb+Pb collisions. The quark strangeness suppression factor lambda_S is found to
be about 0.2 for elementary collisions and about 0.4 for heavy ion collisions
independently of collision energy and type of colliding system",9710529v1
1998-11-19,Self-consistent treatment of the quark condensate and hadrons in nuclear matter,"We calculate the contribution of pions to the $\bar qq$-expectation value
$\kappa(\rho)= <M|\bar qq|M>$ in symmetric nuclear matter. We employ exact pion
propagator renormalized by nucleon-hole and isobar-hole excitations.
Conventional straightforward calculation leads to the ""pion condensation"" at
unrealistically small values of densities, causing even earlier restoration of
chiral symmetry. This requires a self-consistent approach, consisting in using
the models, which include direct dependence of in-medium mass values on
$\kappa(\rho)$, e.g. the Nambu-Jona-Lasinio-model. We show, that in the
self-consistent approach the $\rho$-dependence of the condensate is described
by a smooth curve. The ""pion condensate "" point is removed to much higher
values of density. The chiral restoration does not take place at least while
$\rho<2.8\rho_0$ with $\rho_0$ being the saturation value. Validity of our
approach is limited by possible accumulation of heavier baryons (delta isobars)
in the ground state of nuclear matter. For the value of effective nucleon mass
at the saturation density we found $m^*(\rho_0)=0.6m$, consistent with nowadays
results of other authors.",9811391v1
1999-05-03,Unitarization of the BFKL Pomeron on a Nucleus,"We analyze the evolution equation describing all multiple hard pomeron
exchanges in a hadronic or nuclear structure functions that was proposed
earlier. We construct a perturbation series providing us with an exact solution
to the equation outside of the saturation region. The series demonstrates how
at moderately high energies the corrections to the single BFKL pomeron exchange
contribution which are due to the multiple pomeron exchanges start unitarizing
total deep inelastic scattering cross section. We show that as energy increases
the scattering cross section of the quark-antiquark pair of a fixed transverse
separation on a hadron or nucleus given by the solution of our equation inside
of the saturation region unitarizes and becomes independent of energy. The
corresponding F_2 structure function also unitarizes and becomes linearly
proportional to ln s. We also discuss possible applications of the developed
technique to diffraction.",9905214v3
1999-05-20,Finite energy chiral sum rules in QCD,"A set of well known chiral sum rules, expected to be valid in QCD, is
confronted with experimental data on the vector and axial-vector hadronic
spectral functions, obtained from tau-lepton decay by the ALEPH collaboration.
The Das-Mathur-Okubo sum rule, the first and second Weinberg sum rules, and the
electromagnetic pion mass difference sum rule are not well saturated by the
data. Instead, a modified set of sum rules having additional weight factors
that vanish at the end of the integration range on the real axis, is found to
be precociously saturated by the data to a remarkable extent.",9905411v1
1999-09-21,Scaling of transverse energies and multiplicities with atomic number and energy in ultrarelativistic nuclear collisions,"We compute how the initial energy density and produced gluon, quark and
antiquark numbers scale with atomic number and beam energy in ultrarelativistic
heavy ion collisions. The computation is based on the argument that the effect
of all momentum scales can be estimated by performing the computation at one
transverse momentum scale, the saturation momentum. The initial numbers are
converted to final ones by assuming kinetic thermalisation and adiabatic
expansion. The main emphasis of the study is at LHC and RHIC energies but it is
observed that even at SPS energies this approach leads to results which are not
unreasonable: what is usually described as a completely soft nonperturbative
process can also be described in terms of gluons and quarks. The key element is
the use of the saturation scale.",9909456v1
1999-10-05,Combined analysis of the unitarity triangle and CP violation in the Standard Model,"We perform a combined analysis of the unitarity triangle and of the CP
violating parameter epsilon'/epsilon using the most recent determination of the
relevant experimental data and, whenever possible, hadronic matrix elements
from lattice QCD. We discuss the role of the main non-perturbative parameters
and make a comparison with other recent analyses. We use lattice results for
the matrix element of Q_8 obtained without reference to the strange quark mass.
Since a reliable lattice determination of the matrix element of Q_6 is still
missing, the theoretical predictions for epsilon'/epsilon suffer from large
uncertainties. By evaluating this matrix element with the vacuum-saturation
approximation, we typically find as central value epsilon'/epsilon = (4 - 7) x
10^(-4). We conclude that the experimental data suggest large deviation of the
value of the matrix element of Q_6 from the vacuum-saturation approximation,
possibly due to penguin contractions.",9910236v1
2000-01-25,"A Pomeron Approach to Hadron-Nucleus and Nucleus-Nucleus ""Soft"" Interactions at High Energy","We formulate a generalization of the Glauber formalism for hadron-nucleus and
nucleus-nucleus collisions based on the Pomeron approach to high energy
interactions. Our treatment is based on two physical assumptions (i.e. two
small parameters) : (i) that only sufficiently small distances contribute to
the Pomeron structure; and (ii) the triple Pomeron vertex $G_{3P}/g_{P-N}
  \ll 1$ (where $g_{P-N}$ is the Pomeron-nucleon vertex) is small. A systematic
method is developed for calculating the total, elastic and diffractive
dissociation cross sections as well as the survival probability of large
rapidity gap processes and inclusive observables, both for hadron - nucleus and
nucleus-nucleus collisions. Our approach suggests saturation of the density of
the produced hadrons in nucleus-nucleus collisions, the value of the saturation
density turns out to be large and depends on the number of nucleons in the
lightest nucleus.",0001260v1
2000-03-06,An estimate of higher twist at small x and low Q^2 based upon a saturation model,"We investigate the influence of higher twist corrections to deep inelastic
structure functions in the low-$Q^2$ and small-$x$ HERA region. We review the
general features of the lowest-order QCD diagrams which contribute to twist-4
at small-$x$, in particular the sign structure of longitudinal and transverse
structure functions which offers the possibility of strong cancellations in
$F_2$. For a numerical analysis we perform a twist analysis of the saturation
model which has been very successful both in describing the structure function
and the DIS diffractive cross section at HERA. As the main conclusion, twist 4
corrections are not small in $F_L$ or $F_T$ but in $F_2=F_L + F_T$ they almost
cancel. This indicates the limitation on the use of the DGLAP formalism at
small $x$ and $Q^2$. We point out that $F_L$ analysis needs a large twist-4
correction. We also indicate the region of validity of the twist expansion.",0003042v4
2000-04-05,Unitarity at small Bjorken x,"This paper presents a solution to the nonlinear small x ``projectile side''
evolution equations as derived by Balitskii in 1996. The solution is based on
functional Fokker-Planck methods. The fixed point at small x is explicitly
calculated and all correlation functions in this limit are determined. They
show clear saturation and unitarization properties. Scaling laws that hold
during the saturation phase and throughout the whole course of the evolution
are established. The corresponding Langevin equations are given as a basis for
numerical simulations opening the field for future studies of dynamical issues
of the evolution not analytically accessible. The methods used may be extended
to the ``target side'' equations of Jalilian-Marian, Kovner, Leonidov and
Weigert.",0004044v3
2000-04-11,"Different Hagedorn temperatures for mesons and baryons from experimental mass spectra, compound hadrons, and combinatorial saturation","We analyze the light-flavor particle mass spectra and show that in the region
up to ~1.8GeV the Hagedorn temperature for baryons is about 30% smaller than
for mesons, reflecting the fact that the number of baryon states grows more
rapidly with the mass. We also show that the spectra are well reproduced in a
model where hadrons are compound objects of quanta, whose available number
increases with mass. The rapid growth of number of hadronic states is a
combinatorial effect. We also point out that an upper limit on the excitation
energy of these quanta results in a maximum number of hadron states that can be
formed. According to this combinatorial saturation, no more light-flavor hadron
resonances exist above a certain mass.",0004104v2
2000-08-28,From colored glass condensate to gluon plasma: equilibration in high energy heavy ion collisions,"The initial distribution of gluons at the very early times after a high
energy heavy ion collision is described by the bulk scale $Q_s$ of gluon
saturation in the nuclear wavefunction. The subsequent evolution of the system
towards kinetic equilibrium is described by a non-linear Landau equation for
the single particle distributions \cite{Mueller1,Mueller2}. In this paper, we
solve this equation numerically for the idealized initial conditions proposed
by Mueller, and study the evolution of the system to equilibrium. We discuss
the sensitivity of our results on the dynamical screening of collinear
divergences. In a particular model of dynamical screening, the convergence to
the hydrodynamic limit is seen to be rapid relative to hydrodynamic time
scales. The equilibration time, the initial temperature, and the chemical
potential are shown to have a strong functional dependence on the initial gluon
saturation scale $Q_s$.",0008294v1
2000-11-20,Nonlinear Gluon Evolution in the Color Glass Condensate: I,"We consider a nonlinear evolution equation recently proposed to describe the
small-$x$ hadronic physics in the regime of very high gluon density. This is a
functional Fokker-Planck equation in terms of a classical random color source,
which represents the color charge density of the partons with large $x$. In the
saturation regime of interest, the coefficients of this equation must be known
to all orders in the source strength. In this first paper of a series of two,
we carefully derive the evolution equation, via a matching between classical
and quantum correlations, and set up the framework for the exact background
source calculation of its coefficients. We address and clarify many of the
subtleties and ambiguities which have plagued past attempts at an explicit
construction of this equation. We also introduce the physical interpretation of
the saturation regime at small $x$ as a Color Glass Condensate. In the second
paper we shall evaluate the expressions derived here, and compare them to known
results in various limits.",0011241v1
2001-01-11,Enhanced Minijet Production in $A-A$ Collisions from Gluons with Large Transverse Momenta,"We find supersaturation for the intrinsic gluon distribution of nuclei, i.e.
the low $x$ unintegrated nuclear gluon distribution peaks at intermediate
transverse momenta $k_t=Q_s$ and vanishes at zero $k_t$. Taking into account
the intrinsic transverse momenta of the gluons and the saturation scale $p_s$
of the produced gluons, we calculate the minijet cross section arising from
gluon gluon scattering for RHIC energies. For central collisions at
$\sqrt{s}=200GeV$ the saturation scale $p_s \approx 1.4$ GeV is larger due to
intrinsic $k_t$ effects and increases with energy. Our theoretical results on
charged particle multiplicity agree very well with the recent experimental data
from RHIC.",0101115v2
2001-02-08,Diffractive parton distributions from the saturation model,"We review diffractive deep inelastic scattering (DIS) in the light of the
collinear factorization theorem. This theorem allows to define diffractive
parton distributions in the leading twist approach. Due to its selective final
states, diffractive DIS offers interesting insight into the form of the
diffractive parton distributions which we explore with the help of the
saturation model. We find Regge-like factorization with the correct energy
dependence measured at HERA. A remarkable feature of diffractive DIS is the
dominance of the twist-4 contribution for small diffractive masses. We quantify
this effect and make a comparison with the data.",0102093v4
2001-04-02,"Multiplicities and Transverse Energies in Central AA Collisions at RHIC and LHC from pQCD, Saturation and Hydrodynamics","We compute the particle multiplicities and transverse energies at central and
nearly central AA collisions at RHIC and LHC. The initial state is computed
from perturbative QCD supplemented by the conjecture of saturation of produced
partons. The expansion stage is described in terms of hydrodynamics assuming
longitudinal boost invariance and azimuthal symmetry. Transverse flow effects,
a realistic list of hadrons and resonance decays are included. Comparison with
the data of the multiplicities at $\sqrt s=56$ AGeV and 130 AGeV from RHIC is
done and predictions for the full RHIC energy and LHC energy are made for the
multiplicities and transverse energies. The reduction from the initially
released minijet transverse energy to the $E_T$ in the final state is less than
in the one-dimensional case but still dramatic: a factor of 2.7 at RHIC, and
3.6 at the LHC.",0104010v2
2001-04-03,Parton densities and dipole cross-sections at small x in large nuclei,"Unintegrated gluon densities in nuclei, dipole-nucleus cross-sections and
quark densities are numerically investigated in the high-colour limit, with the
scattering on a heavy nucleus exactly described by the sum of fan diagrams of
BFKL pomerons. The initial condition for the evolution in rapidity is quickly
forgotten, and the gluon density presents a ""supersaturation"" pattern, as
previous studies indicated. Both dipole-nucleus cross-sections and quark
densities present the expected saturation features. Identifying the position in
transverse momentum $l$ of the maximum of the gluon distribution with the
saturation momentum $Q_s(y,b)$, at large rapidities all distributions depend
only on one variable $[l/Q_s(y,b)]$ or $[rQ_s(y,b)]$.",0104038v2
2001-05-25,How Protons Shatter Colored Glass,"We consider the implications of the Color Glass Condensate for the central
region of p+A collisions. We compute the k_t distribution of radiated gluons
and their rapidity distribution dN/dy analytically, both in the perturbative
regime and in the region between the two saturation momenta. We find an
analytic expression for the number of produced gluons which is valid when the
saturation momentum of the proton is much less than that of the nucleus. We
discuss the scaling of the produced multiplicity with A. We show that the slope
of the rapidity density dN/dy provides an experimental measure for the
renormalization-group evolution of the color charge density of the Color Glass
Condensate (CGC). We also argue that these results are easily generalized to
collisions of nuclei of different A at central rapidity, or with the same A but
at a rapidity far from the central region.",0105268v2
2001-11-16,Determination of vector meson properties by matching resonance saturation to a constituent quark model,"The properties of mesonic resonances can be calculated in terms of the
low-energy coefficients of chiral perturbation theory (chiPT) by extending
unitarized chiPT to higher energies. On the other hand these low-energy
coefficients can be calculated in two different models, namely (i) by assuming
resonance saturation and (ii) within a constituent quark model. By matching the
expressions of the two models combined with the results of unitarized chiPT and
the Weinberg sum rules the properties of vector and axial-vector mesons can be
calculated in the combined large-N_c and chiral limit.",0111204v2
2002-03-26,Constraints on possible phase transitions above the nuclear saturation density,"We compare different models for hadronic and quark phases of cold baryon-rich
matter in an attempt to find a deconfinement phase transition between them. For
the hadronic phase we consider Walecka-type mean-field models which describe
well the nuclear saturation properties. We also use the variational chain model
which takes into account correlation effects. For the quark phase we consider
the MIT bag model, the Nambu-Jona-Lasinio and the massive quasiparticle models.
By comparing pressure as a function of baryon chemical potential we find that
crossings of hadronic and quark branches are possible only in some exceptional
cases while for most realistic parameter sets these branches do not cross at
all. Moreover, the chiral phase transition, often discussed within the
framework of QCD motivated models, lies in the region where the quark phases
are unstable with respect to the hadronic phase. We discuss possible physical
consequences of these findings.",0203241v1
2002-06-03,A simple model for nuclear structure functions at small $x$ in the dipole picture,"A simple model for nuclear structure functions in the region of small x and
small and moderate $Q^2$, is presented. It is a parameter-free extension, in
the Glauber-Gribov approach to nuclear collisions, of a saturation model for
the nucleon. A reasonable agreement with experimental data on ratios of nuclear
structure functions is obtained. Nuclear effects in the
longitudinal-to-transverse cross section ratios are found to be small.
Predictions of the model for values of $x$ smaller than those available to
present experiments are given. The unintegrated gluon distribution and the
behaviour of the saturation scale which result from this model are shown and
discussed.",0206017v2
2002-07-03,Instantons and Saturation in the Colour Dipole Picture,"We pursue the intriguing possibility that larger-size instantons build up
diffractive scattering, with the marked instanton-size scale $<\rho> \approx
0.5$ fm being reflected in the conspicuous ``geometrization'' of soft QCD. As
an explicit illustration, the known instanton contribution to DIS is
transformed into the intuitive colour dipole picture. With the help of lattice
results, the $q \bar{q}$-dipole size r is carefully increased towards hadronic
dimensions. Unlike pQCD, one now observes a competition between two crucial
length scales: the dipole size r and the size $\rho$ of the background
instanton that is sharply localized around $<\rho> \approx 0.5$ fm. For r
exceeding $<\rho>$, the dipole cross section indeed saturates towards a
geometrical limit, proportional to the area $\pi <\rho>^2$, subtended by the
instanton.",0207052v2
2002-07-03,Saturation and Wilson Line Distributions,"We introduce a Wilson line distribution function bar{W}_tau(v) to study gluon
saturation at small Feynman x_F, or large tau=ln(1/x_F). This new distribution
can be obtained from the distribution W_tau(alpha) of the Color Glass
Condensate model and the JIMWLK renormalization group equation. bar{W}_tau(v)
is physically more relevant, and mathematically simpler to deal with because of
unitarity of the Wilson line v. A JIMWLK equation is derived for bar{W}_tau(v);
its properties are studied. These properties are used to complete Mueller's
derivation of the JIMWLK equation, though for bar{W}_tau(v) and not
W_tau(alpha). They are used to derive a generalized Balitsky-Kovchegov equation
for higher multipole amplitudes. They are also used to compute the unintegrated
gluon distribution at x_F=0, yielding a completely flat spectrum in transverse
momentum squared k^2, with a known height. This is similar but not identical to
the mean field result at small k^2.",0207058v2
2002-07-31,Diffractive dissociation from non-linear evolution in DIS on nuclei,"The process of single diffractive dissociation off nuclei is considered on a
basis of solutions to the nonlinear evolution equation. The relevant saturation
scales $Q_{s A}^D(x,x_0)$ are determined and their dependences on Bjorken $x$,
atomic number $A$, and minimal rapidity gap $Y_0\equiv \ln 1/x_0$ are
investigated. The solutions are shown to posses the geometrical scaling in a
broad kinematic region for $x$ well below $x_0$. A detailed theoretical
discussion of saturation scale and scaling is presented.
  The ratio $\sigma^{diff}/\sigma^{tot}$ is computed for several nuclei. We
predict that at $x\simeq 10^{-4}$ this ratio is of the order 25% which is much
larger to the one of proton. This result indicates a possibility to observe a
very strong nuclear shadowing.",0207374v2
2003-03-12,Investigating the Drell-Yan transverse momentum distribution in the color dipole approach,"We study the influence of unitarity corrections on the Drell-Yan transverse
momentum distribution within the color dipole approach. These unitarity
corrections are implemented through the multiple scattering Glauber-Mueller
approach, which is contrasted with a phenomenological saturation model. The
process is analyzed for the center of mass energies of the Relativistic Heavy
Ion Collider (RHIC, $\sqrt{s}=500$ GeV) and of the Large Hadron Collider (LHC,
$\sqrt{s}=14$ TeV). In addition, the results are extrapolated down to current
energies of proton-proton collisions, where non-asymptotic corrections to the
dipole approach are needed. It is also shown that in the absence of saturation,
the dipole approach can be related to the QCD Compton process.",0303100v2
2003-03-25,Screening effects in the ultrahigh energy neutrino interactions,"We study possible saturation effects in the total cross-section describing
interaction of ultrahigh energy neutrinos with nucleons. This analysis is
performed within the two approaches, i.e. within the Golec-Biernat W\""usthoff
saturation model and within the scheme unifying the DGLAP and BFKL dynamics
incorporating non-linear screening effects which follow from the
Balitzki-Kovchegov equation. The structure functions in both approaches are
constrained by HERA data. It is found that screening effects affect
extrapolation of the neutrino-nucleon total cross-sections to ultrahigh
neutrino energies $E_{\nu}$ and reduce their magnitude by a factor equal to
about 2 at $E_{\nu} \sim 10^{12}GeV$. This reduction becomes amplified by
nuclear shadowing in the case of the neutrino-nucleus cross-sections and
approximate estimate of this effect is performed.",0303209v4
2003-05-14,QCD Saturation in the Semi-classical Approach,"In this paper the semi-classical approach to the solution of non-linear
evolution equation is developed. We found the solution in the entire kinematic
region to the non-linear evolution equation that governs the dynamics in the
high parton density QCD. The large impact parameter ($b_t$) behavior of the
solution is discussed as well as the way how to include the non-perturbative
QCD corrections in this region of $b_t$. The geometrical scaling behavior and
other properties of the solution in the saturation (Color Glass Condensate)
kinematic domain are analyzed. We obtain the asymptotic behavior for the
physical observables and found the unitarity bounds for them.",0305150v2
2003-06-13,Additional $J/Ψ$ Suppression from High Density Effects,"At high energies the saturation effects associated to the high parton density
should modify the behavior of the observables in proton-nucleus and
nucleus-nucleus scattering. In this paper we investigate the saturation effects
in the nuclear $J/\Psi$ production and estimate the modifications in the energy
dependence of the cross section as well as in the length of the nuclear medium.
In particular, we calculate the ratio of $J/\Psi$ to Drell-Yan cross sections
and show that it is strongly modified if the high density effects are included.
Moreover, our results are compared with the data from the NA50 Collaboration
and predictions for the RHIC and LHC kinematic regions are presented. We
predict an additional $J/\Psi$ suppression associated to the high density
effects.",0306129v2
2003-09-25,Perturbative Odderon in the Dipole Model,"We show that, in the framework of Mueller's dipole model, the perturbative
QCD odderon is described by the dipole model equivalent of the BFKL equation
with a $C$-odd initial condition. The eigenfunctions and eigenvalues of the
odderon solution are the same as for the dipole BFKL equation and are given by
the functions $E^{n,\nu}$ and $\chi (n,\nu)$ correspondingly, where the $C$-odd
initial condition allows only for odd values of $n$. The leading high-energy
odderon intercept is given by $\alpha_{odd} - 1 = \frac{2 \as N_c}{\pi} \chi
(n=1 ,\nu=0) = 0$ in agreement with the solution found by Bartels, Lipatov and
Vacca. We proceed by writing down an evolution equation for the odderon
including the effects of parton saturation. We argue that saturation makes the
odderon solution a decreasing function of energy.",0309281v2
2003-09-25,Finite energy chiral sum rules in QCD,"The saturation of QCD chiral sum rules of the Weinberg-type is analyzed using
ALEPH and OPAL experimental data on the difference between vector and
axial-vector correlators (V-A). The sum rules exhibit poor saturation up to
current energies below the tau-lepton mass. A remarkable improvement is
achieved by introducing integral kernels that vanish at the upper limit of
integration. The method is used to determine the value of the finite remainder
of the (V-A) correlator, and its first derivative, at zero momentum:
$\bar{\Pi}(0) = - 4 \bar{L}_{10} = 0.0257 \pm 0.0003 ,$ and
$\bar{\Pi}^{\prime}(0) = 0.065 \pm 0.007 {GeV}^{-2}$. The dimension $d=6$ and
$d=8$ vacuum condensates in the Operator Product Expansion are also determined:
  $<{\cal {O}}_{6}> = -(0.004 \pm 0.001) {GeV}^6,$ and $<{\cal {O}}_{8}> =
-(0.001 \pm 0.006) {GeV}^8.$",0309285v2
2003-10-31,Open charm production in heavy ion collisions and the Color Glass Condensate,"We consider the production of open charm in heavy ion collisions in the
framework of the Color Glass Condensate. In the central rapidity region at
RHIC, for the charm quark yield we expect N(coll) (number of collisions)
scaling in the absence of final-state effects. At higher energies, or forward
rapidities at RHIC, the saturation scale exceeds the charm quark mass; we find
that this results in the approximate N(part) (number of participants) scaling
of charm production in AA collisions and N(part)^A scaling in p(d)A collisions,
similarly to the production of high pT gluons discussed earlier. We also show
that the saturation phenomenon makes spectra harder as compared to the naive
parton model approach. We then discuss the energy loss of charm quarks in hot
and cold media and argue that the hardness of the spectrum implies very slow
dependence of the quenching factor on pT.",0310358v1
2003-12-26,"Elliptic flow orientation, saturation and low $p_t$ behavior","We consider general model with factorization between macroscopic flow and
matter decay distribution. We show universality of $p_t^2$ behavior of elliptic
flow at small $p_t$ for identified final particles in the symmetric nucleus
collision. At high $p_t$ we compare non-relativistic and relativistic models
for boosted decay distribution. In the relativistic models with distribution
having power-like tail we show existence of elliptic flow saturation. This
means that the elliptic flow value $v_2$ tend to constant at high $p_t$. We
discuss the importance of determination of elliptic flow orientation which can
help us to compare different models. For example, we introduce potential
expansion model which can reproduce azimuthal asymmetry but based on the
assumption that there are only cold strong forces and no thermalization. This
model show opposite sign of elliptic flow orientation in comparison with
thermal model. We also show that at small $p_t$ sign of elliptic flow can
change due to sign of second derivative of decay distribution. This fact tell
us that we must more carefully link elliptic flow sign and properties of the
model.",0312352v1
2004-01-06,Towards a New Global QCD Analysis: Solution to the Non-Linear Equation at Arbitrary Impact Parameter,"A numerical solution is presented for the non-linear evolution equation that
governs the dynamics of high parton density QCD. It is shown that thesolution
falls off as $e^{-b/R}$ at large values of the impact parameter $b$. The
power-like tail of the amplitude appears in impact parameter distributions only
after the inclusion of dipoles of size larger than the target, a configuration
for which the non-linear equation is not valid. The value, energy and impact
parameterof the saturation scale $Q_s(y=\ln(1/x),b)$) are calculated both for
fixed and running QCD coupling cases. It is shown that the solution exhibits
geometrical scaling behaviour. The radius of interaction increases as the
rapidity in accordance with the Froissart theorem. The solution we obtain
differs from previous attempts, where an anzatz for $b$ behaviour was made. The
solutions for running and fixed $\as$ differ. For running $\as$ we obtain a
larger radius of interaction (approximately twice as large), a steeper rapidity
dependence, and a larger value of the saturation scale.",0401021v2
2004-05-13,Density saturation and the decrease of the normalised width of the multiplicity distribution in high energy pp collisions,"It is experimentally observed that the width of the KNO multiplicity
distribution --or the negative binomial parameter 1/k-- for pp collisions, in
the energy region 10 to 1800 GeV, is an increasing function of the energy. We
argue that in models with parton or string saturation such trend will necessary
change: at some energy the distribution will start to become narrower. In the
framework of percolating strings, we have estimated the change to occur at an
energy of the order of 5--10 TeV.",0405116v2
2004-05-18,Evidence for the saturation of the Froissart bound,"It is well known that fits to high energy data cannot discriminate between
asymptotic ln(s) and ln^2(s) behavior of total cross section. We show that this
is no longer the case when we impose the condition that the amplitudes also
describe, on average, low energy data dominated by resonances. We demonstrate
this by fitting real analytic amplitudes to high energy measurements of the
gamma p total cross section, for sqrt(s) > 4 GeV. We subsequently require that
the asymptotic fit smoothly join the sqrt(s) = 2.01 GeV cross section described
by Dameshek and Gilman as a sum of Breit-Wigner resonances. The results
strongly favor the high energy ln^2(s) fit of the form sigma_{gamma p} = c_0 +
c_1 ln(nu/m) + c_2 ln^2(nu/m) + beta_{P'}/sqrt(nu/m), basically excluding a
ln(s) fit of the form sigma_{\gamma p} = c_0 + c_1 ln(nu/m) +
beta_P'/sqrt(\nu/m), where nu is the laboratory photon energy. This evidence
for saturation of the Froissart bound for gamma p interactions is confirmed by
applying the same analysis to pi p data using vector meson dominance.",0405174v1
2004-06-11,The spread of the gluon k_t-distribution and the determination of the saturation scale at hadron colliders in resummed NLL BFKL,"The transverse momentum distribution of soft hadrons and jets that accompany
central hard-scattering production at hadron colliders is of great importance,
since it has a direct bearing on the ability to separate new physics signals
from Standard Model backgrounds. We compare the predictions for the gluonic
k_t-distribution using two different approaches: resummed NLL BFKL and DGLAP
evolution. We find that as long as the initial and final virtualities (k_t)
along the emission chain are not too close to each other, the NLL resummed BFKL
results do not differ significantly from those obtained using standard DGLAP
evolution. The saturation momentum Q_s(x), calculated within the resummed BFKL
approach, grows with 1/x even slower than in the leading-order DGLAP case.",0406135v2
2004-06-14,Saturation In Deep Inelastic Scattering,"The solution to the BFKL equation grows like a power of center of mass
energy, s, violating unitarity conditions at high energies. The growth of the
cross section can be tamed by taking into account multiple pomeron exchanges.
This is known as saturation and it is expressed in the Balitsky-Kovchegov
equation. Conservation of energy should also slow down the growth of the cross
section, and our aim in this work is to study the effects of enforcing energy
conservation in DIS-events. Using the dipole picture, onium-onium collisions
can be viewed, in the large N_c and the leading logarithmic limits, as the
scattering of a collection of color dipoles. We construct a Monte Carlo
program, based on Mueller's model and using energy conservation, to study
onium-onium and onium-nucleus collisions. Dipole fusion processes will be
important at high gluon densities and should also slow down the growth of the
cross section. We propose an expression for the fusion factor and use it in our
Monte Carlo to study its effects.",0406150v1
2004-08-09,Unintegrated gluon distribution from modified BK equation,"We investigate the recently proposed nonlinear equation for the unintegrated
gluon distribution function which includes the subleading effects at small $x$.
We obtained numerically the solution to this equation in $(x,k)$ space, and
also the integrated gluon density. The subleading effects affect strongly the
normalization and the $x$ and $k$ dependence of the gluon distribution. We show
that the saturation scale $Q_s(x)$, which is obtained from this model, is
consistent with the one used in the saturation model by Golec-Biernat and
W\""usthoff. We also estimate the nonlinear effects by looking at the relative
normalization of the solutions to the linear and nonlinear equations. It turns
out that the differences are quite large even in the nominally dilute regime,
that is when $Q^2 \gg Q_s^2$. Finally, we calculate the dipole-nucleon cross
section.",0408117v3
2004-08-20,Cronin effect and high-p_T suppression from the Color Glass Condensate,"I give a pedagogical survey of the nuclear collective effects associated with
gluon saturation and their impact on particle production in high-energy proton
(or deuteron)-nucleus collisions at RHIC. At central rapidity, the theory
predicts a Cronin peak due to independent multiple scattering off the valence
quarks in the nucleus. At forward rapidities, the peak flattens out and
disappears very fast, because of the correlations induced through quantum
evolution in the nuclear gluon distribution at small x. Also, the ratio R_{pA}
between the particle yield in proton-nucleus and proton-proton collisions is
rapidly suppressed when increasing the rapidity, because of saturation effects
which slow down the evolution of the nucleus compared to that of the proton.
This behaviour could be responsible for a similar trend observed in the
deuteron-nucleus collisions at RHIC.",0408228v1
2004-08-30,Higher Order Effects in Non Linear Evolution from a Veto in Rapidities,"Higher order corrections to the Balitsky-Kovchegov equation have been
estimated by introducing a rapidity veto which forbids subsequent emissions to
be very close in rapidity and is known to mimic higher order corrections to the
linear BFKL equation. The rapidity veto constraint has been first introduced
using analytical arguments obtaining a power growth with energy, Q_s (Y) ~
exp(lambda Y), of the saturation scale of lambda ~ 0.45. Then a numerical
analysis for the non-linear Balitsky-Kovchegov equation has been carried out
for phenomenological rapidities: when a veto of about two units of rapidity is
introduced for a fixed value of the coupling constant of alpha_s = 0.2 the
saturation scale lambda decreases from ~ 0.6 to ~ 0.3, and when running
coupling effects are taken into account it decreases from ~ 0.4 to ~ 0.3.",0408333v1
2004-11-18,A modified Balitsky-Kovchegov equation,"We propose a modified version of the Balitsky-Kovchegov (B-K) evolution
equation, which includes the main NLO corrections. We use the result that the
main NLO corrections to the BFKL kernel are the LO DGLAP corrections.
  We present a numerical solution of the modified nonlinear equation, and
compare with the solution of the unmodified B-K equation. We show that the
saturation momentum has a sharp increase in the LHC energy range. Our numerical
solution indicates that the influence of the pre-asymptotic corrections,
related to the full anomolous dimensions of the DGLAP equation, are rather
large. These corrections moderate the energy behaviour of the amplitude, as
well as the value of the saturation scale. All our calculations are made with a
fixed value of $\alpha_{s}$.",0411242v2
2004-11-30,A Langevin equation for high energy evolution with pomeron loops,"We show that the Balitsky-JIMWLK equations proposed to describe non-linear
evolution in QCD at high energy fail to include the effects of fluctuations in
the gluon number, and thus to correctly describe both the low density regime
and the approach towards saturation. On the other hand, these fluctuations are
correctly encoded (in the limit where the number of colors is large) in
Mueller's color dipole picture, which however neglects saturation. By combining
the dipole picture at low density with the JIMWLK evolution at high density, we
construct a generalization of the Balitsky hierarchy which includes the
particle number fluctuations, and thus the pomeron loops. After an additional
coarse-graining in impact parameter space, this hierarchy is shown to reduce to
a Langevin equation in the universality class of the stochastic
Fisher-Kolmogorov-Petrovsky-Piscounov (sFKPP) equation. This equation implies
that the non-linear effects in the evolution become important already in the
high momentum regime where the average density is small, which signals the
breakdown of the BFKL approximation.",0411405v1
2004-12-22,Saturation effects in pp scattering in the impact-parameter representation,"The impact of unitarity is considered in different approaches to saturation
in impact-parameter space. The energy and momentum-transfer dependence of the
total and differential cross sections and of the ratio of the real to imaginary
parts of the scattering amplitude are obtained in a model that includes soft
and hard pomeron contributions, coupled to hadrons via the electromagnetic form
factor. It is shown that the hard pomeron may significantly contribute to soft
physics at the LHC. A similar conclusion can also be reached in the framework
of non-linear approaches to unitarisation of the BFKL pomeron.",0412338v1
2005-02-18,Nuclear size and rapidity dependence of the saturation scale from QCD evolution and experimental data,"The solutions of the Balitsky-Kovchegov evolution equations are studied
numerically and compared with known analytical estimations. The rapidity and
nuclear size dependences of the saturation scale are obtained for the cases of
fixed and running coupling constant. These same dependences are studied in
experimental data, on lepton-nucleus, deuteron-nucleus and nucleus-nucleus
collisions, through geometric scaling and compared with the theoretical
calculations.",0502167v1
2005-03-07,Fluctuating pulled fronts & Pomerons,"I give a physical discussion of the influence of particle number fluctuations
on the high energy evolution in QCD. I emphasize the event-by-event description
and the correspondence with the problem of `fluctuating pulled fronts' in
statistical physics. I show that the correlations generated by fluctuations
reduce the phase-space for BFKL evolution up to saturation. Because of that,
the evolution `slows down', and the rate for the energy increase of the
saturation momentum is considerably decreased. Also, the stochastic aspects
inherent in fluctuations lead to the breakdown of geometric scaling and of the
BFKL approximation. Finally, I explain the diagrammatic interpretation of the
particle number fluctuations as initiators of the Pomeron loops.",0503062v1
2005-03-29,Investigating the role of average color dipole size in BFKL Pomeron phenomenology,"Based on the QCD dipole picture of the BFKL Pomeron, we investigate the role
played by the saturation scale, Q_{sat}, in obtaining physical values for the
affective strong coupling in phenomenological fits to small-x HERA data. The
dependence on this scale appears since the collection of color dipoles
characterizing the proton target have average size 1/Q_{sat}, which is energy
dependent. Physically, this means most of the color dipoles are above but
sufficiently close to the border between a saturated and the dilute system. The
analysis is first performed in the leading-logs BFKL approach in the
saddle-point approximation and it could shed light in further investigations
using resummed NLO BFKL kernels",0503282v2
2005-07-13,Instanton-Induced Processes - An Overview,"A first part of this review is devoted to a summary of our extensive studies
of the discovery potential for instanton(I)-induced, deep-inelastic processes
at HERA. Included are some key issues about I-perturbation theory, an
exploitation of crucial lattice constraints and a status report about the
recent I-search results by the HERA collaborations H1 and ZEUS in relation to
our predictions. Next follows a brief outline of an ongoing project concerning
a broad exploration of the discovery potential for hard instanton processes at
the LHC. I then turn to an overview of our work on high-energy processes,
involving larger-sized instantons. I shall mainly focus on the phenomenon of
saturation at small Bjorken-x from an instanton perspective. In such a
framework, the saturation scale is associated with the conspicuous average
instanton size (~0.5 fm), as known from lattice simulations. Another central
and intriguing result is the identification of the ""Colour Glass Condensate""
with the QCD sphaleron state.",0507160v1
2005-09-23,Nonlinear evolution of pomeron and odderon in momentum space,"The small x evolution of the QCD pomeron and the QCD odderon is investigated
in the mean field limit of the Color Glass Condensate. The resulting system of
coupled nonlinear evolution equations is transformed to the momentum space and
analyzed at a very small momentum transfer. The main properties of the C-even
and C-odd dipole densities in momentum space are obtained analytically. The
critical scaling dimension is found for the odderon and the universal
asymptotic behavior of the solutions is determined for small and large gluon
momenta. We find that the same saturation scale characterizes both the pomeron
and the odderon and both densities depend on the momentum only through the
geometric scaling variable. The absorptive effects are found to cause a strong
suppression of the odderon exchange amplitude for momenta below saturation
scale and only a moderate suppression for larger momenta.",0509270v1
2005-11-08,The Energy Dependence of the Saturation Scale,"At low $x \cong Q^2/W^2 << 1$, in deep inelastic scattering, the photon
fluctuates into a $q \bar q$ vector state that interacts via two gluons with
the proton. The energy dependence is determined by the saturation scale, in our
approach given by $\Lambda^2_{sat} (W^2) \sim (W^2)^{C_2}$. Imposing DGLAP
evolution, we find $C_2^{theory} = 0.27$ in agreement with the
model-independent analysis of the HERA data. Different values of the exponent
$C_2$ are correlated with different ratios of the longitudinal to transverse
structure function. This stresses the need for experiments to separate
longitudinal and transverse contributions in deep inelastic scattering.",0511091v2
2005-12-08,The Decoherence Time in High Energy Heavy Ion Collisions,"We calculate the decoherence time of the ground state wave function of a
nucleus in a high energy heavy ion collision. We define this time as the decay
time of the ratio Tr D^2 / (Tr D)^2 of traces of the density matrix D. We find
that this time is smaller or equal to 1/Q_s, where the saturation scale Q_s is
defined within the color glass condensate model of parton saturation. Our
result supports the notion that the extremely rapid entropy production deduced
for the early stage of heavy ion collisions at collider energies is to a large
extent caused by the decoherence of the initial-state wave functions.",0512100v2
2006-02-10,Spin-glass model of QCD near saturation,"We establish a connection between the cascading of gluon momenta modeled with
the diffusive approximation of the Balitsky-Fadin-Kuraev-Lipatov kernel and the
thermodynamics of directed polymers on a tree with disorder. Using known
results on the low-temperature spin-glass phase of this statistical-mechanic
problem we describe the dynamical phase space of gluon transverse momenta near
saturation including its fluctuation pattern. It exhibits a nontrivial
clustering structure, analoguous to ``hot spots'', whose distributions are
derived and possess universal features in common with other spin-glass systems.",0602095v3
2006-04-26,Color Glass Condensates in dense quark matter and quantum Hall states of gluons,"We apply the effective theory of color glass condensate to the analysis of
gluon states in dense quark matter, in which the saturation region of gluons is
also present. We find that in the region two point function of gluons shows
algebraic long range order. The order is completely the same as the one gluons
show in the dense quark matter, which form quantum Hall states. The order leads
to the vanishing of massless gluon pole. We also find that the saturation
region of gluons extends from small $x$ to even large $x\lesssim 1$ in much
dense quark matter. We point out a universality that the color glass condensate
is a property of hadrons at high energy and of quark matter at high baryon
density.",0604222v1
2006-05-15,Forward gluon production in hadron-hadron scattering with Pomeron loops,"We discuss new physical phenomena expected in particle production in
hadron-hadron collisions at high energy, as a consequence of Pomeron loop
effects in the evolution equations for the Color Glass Condensate. We focus on
gluon production in asymmetric, `dilute-dense', collisions : a dilute
projectile scatters off a dense hadronic target, whose gluon distribution is
highly evolved. This situation is representative for particle production in
proton-proton collisions at forward rapidities (say, at LHC) and admits a
dipole factorization similar to that of deep inelastic scattering (DIS). We
show that at sufficiently large forward rapidities, where the Pomeron loop
effects become important in the evolution of the target wavefunction, gluon
production is dominated by `black spots' (saturated gluon configurations) up to
very large values of the transverse momentum, well above the average saturation
momentum in the target. In this regime, the produced gluon spectrum exhibits
diffusive scaling, so like DIS at sufficiently high energy.",0605174v1
2006-06-20,Hadronic forward scattering: Predictions for the Large Hadron Collider and cosmic rays,"The status of hadron-hadron interactions is reviewed, with emphasis on the
forward and near-forward scattering regions. From analyticity, Finite Energy
Sum Rules are introduced from which new analyticity constraints are derived
that exploit the many very accurate low energy experimental cross sections,
i.e., they constrain the values of the asymptotic cross sections and their
derivatives at low energies just above the resonance regions, allowing us new
insights into duality. A new robust fitting technique is introduced in order to
`clean up' large data samples that are contaminated by outliers. Using our
analyticity constraints, new methods of fitting high energy hadronic data are
introduced which result in much more precise estimates of the fit parameters,
allowing accurate extrapolations to much higher energies. It's shown that the
$\gamma p$, $\pi^\pm p$ and nucleon-nucleon cross sections {\em all} go
asymptotically as $\ln^2s$, saturating the Froissart bound, while conclusively
ruling out $\ln s$ and $s^{\alpha}$ ($\alpha\sim 0.08$) behavior. Implications
of this saturation for predictions of $\sigma_{pp}$ and $\rho_{pp}$ at the LHC
and for cosmic rays p-air cross sections are given.",0606215v2
2006-06-27,Exclusive diffractive processes at HERA within the dipole picture,"We present a simultaneous analysis, within an impact parameter dependent
saturated dipole model, of exclusive diffractive vector meson (J/psi, phi and
rho) production, deeply virtual Compton scattering and the total gamma* p cross
section data measured at HERA. Various cross sections measured as a function of
the kinematic variables Q^2, W and t are well described, with little
sensitivity to the details of the vector meson wave functions. We determine the
properties of the gluon density in the proton in both longitudinal and
transverse dimensions, including the impact parameter dependent saturation
scale. The overall success of the description indicates universality of the
emerging gluon distribution and proton shape.",0606272v2
2006-11-08,One-dimensional model for QCD at high energy,"We propose a stochastic particle model in (1+1)-dimensions, with one
dimension corresponding to rapidity and the other one to the transverse size of
a dipole in QCD, which mimics high-energy evolution and scattering in QCD in
the presence of both saturation and particle-number fluctuations, and hence of
Pomeron loops. The model evolves via non-linear particle splitting, with a
non-local splitting rate which is constrained by boost-invariance and multiple
scattering. The splitting rate saturates at high density, so like the gluon
emission rate in the JIMWLK evolution. In the mean field approximation obtained
by ignoring fluctuations, the model exhibits the hallmarks of the BK equation,
namely a BFKL-like evolution at low density, the formation of a traveling wave,
and geometric scaling. In the full evolution including fluctuations, the
geometric scaling is washed out at high energy and replaced by diffusive
scaling. It is likely that the model belongs to the universality class of the
reaction-diffusion process. The analysis of the model sheds new light on the
Pomeron loops equations in QCD and their possible improvements.",0611105v1
1993-12-14,Instantons in Schwinger Model,"The known calculations of the fermion condensate $<\bar{\psi}\psi>$ and the
correlator $<\bar{\psi}\psi(x) ~\bar{\psi}\psi(0)>$ have been interpreted in
terms of {\em localized} instanton solutions minimizing the {\em effective}
action. Their size is of order of massive photon Compton wavelength $\mu^{-1}$.
At high temperature, these instantons become quasistatic and present the
2-dimensional analog of the `walls' found recently in 4-dimensional gauge
theories. In spite of the static nature of these solutions, they should not be
interpreted as `thermal solitons' living in Minkowski space: the mass of these
would-be solitons does not display itself in the physical correlators. At small
but nonzero fermion mass, the high-T partition function of $QED_2$ is saturated
by the rarefied gas of instantons and antiinstantons with density $\propto
m~\exp\{-S^{inst.}\}~=~m~\exp\{-\pi T/\mu\}$ to be confronted with the dense
strongly correlated instanton-antiinstanton liquid saturating the partition
function at $T=0$.",9312110v1
1995-09-20,Rotating Black Holes which Saturate a Bogomol'nyi Bound,"We construct and study the electrically charged, rotating black hole solution
in heterotic string theory compactified on a $(10-D)$ dimensional torus. This
black hole is characterized by its mass, angular momentum, and a $(36-2D)$
dimensional electric charge vector. One of the novel features of this solution
is that for $D >5$, its extremal limit saturates the Bogomol'nyi bound. This is
in contrast with the $D=4$ case where the rotating black hole solution develops
a naked singularity before the Bogomol'nyi bound is reached. The extremal black
holes can be superposed, and by taking a periodic array in $D>5$, one obtains
effectively four dimensional solutions without naked singularities.",9509108v1
1995-12-28,T-Duality of p-Branes,"We investigate possible existence of duality symmetries which exchange the
Kaluza-Klein modes with the wrapping modes of a BPS saturated $p$-brane on a
torus. Assuming the validity of the conjectured $U$-duality symmetries of type
II and heterotic string theories and $M$-theory, we show that for a BPS
saturated $p$-brane there is an SL(2,Z) symmetry that mixes the Kaluza-Klein
modes on a $(p+1)$ dimensional torus $T^{(p+1)}$ with the wrapping modes of the
$p$-brane on $T^{(p+1)}$. The field that transforms as a modular parameter
under this SL(2,Z) transformation has as its real part the component of the
$(p+1)$-form gauge field on $T^{(p+1)}$, and as its imaginary part the volume
of $T^{(p+1)}$, measured in the metric that couples naturally to the $p$-brane.",9512203v2
1996-05-08,Near-BPS-Saturated Rotating Electrically Charged Black Holes as String States,"We construct generating solutions for general D-dimensional ($4 \le D \le 9$)
rotating, electrically charged, black holes in the effective action of
toroidally compactified heterotic (or Type IIA) string. The generating solution
is parameterized by the ADM mass, two electric charges and $[{D-1}\over 2]$
angular momenta (as well as the asymptotic values of one toroidal modulus and
the dilaton field). For $D \ge 6$, those are generating solutions for {\it
general} black holes in toroidally compactified heterotic (or type IIA) string.
Since in the BPS-limit (extreme limit) these solutions have singular horizons
or naked singularities, we address the near extreme solutions with all the
angular momenta small enough. In this limit, the thermodynamic entropy can be
cast in a suggestive form, which has a qualitative interpretation as
microscopic entropy of (near)-BPS-saturated charged string states of toroidally
compactified heterotic string, whose target-space angular momenta are
identified as $[{{D-1}\over 2}]$ U(1) left-moving world-sheet currents.",9605051v1
1997-10-15,Domain Walls Zoo in Supersymmetric QCD,"Solving numerically the equations of motion for the effective lagrangian
describing supersymmetric QCD with the SU(2) gauge group, we find a menagerie
of complex domain wall solutions connecting different chirally asymmetric
vacua. Some of these solutions are BPS saturated walls; they exist when the
mass of the matter fields does not exceed some critical value m < m* <
4.67059... There are also sphaleron branches (saddle points of the ebergy
functional). In the range m* < m < m** \approx 4.83, one of these branches
becomes a local minimum (which is not a BPS saturated one). At m > m*, the
complex walls disappear altogether and only the walls connecting a chirally
asymmetric vacuum with the chirally symmetric one survive.",9710123v1
1997-11-11,BPS-spectra in four dimensions from M-theory,"I review my work together with Piljin Yi on the spectrum of BPS-saturated
states in N = 2 supersymmetric Yang-Mills theories. In an M-theory description,
such states are realized as certain two-brane configurations. We first show how
the central charge of the N = 2 algebra arises from the two-form central charge
of the eleven-dimensional supersymmetry algebra, and derive the condition for a
two-brane configuration to be BPS-saturated. We then discuss how the topology
of the two-brane determines the type of BPS-multiplet. Finally, we discuss the
phenomenon of marginal stability and show how it is related to the mutual
non-locality of states.",9711076v1
1998-04-25,Multi-Pronged Strings and BPS Saturated Solutions in SU(N) Supersymmetric Yang-Mills Theory,"Extending our previous work on SU(3), we construct spherically symmetric BPS
saturated regular configurations of N=4 SU(N) supersymmetric Yang-Mills theory
preserving 1/4 supersymmetry, and investigate their features. We also give
exact solutions in the case some of the free parameters of the general
solutions take certain values. These field theory BPS states correspond to the
string theory BPS states of multi-pronged strings connecting N different
D3-branes by regarding the N=4 supersymmetric Yang-Mills theory as an effective
field theory on parallel D3-branes. We compare our solutions with multi-pronged
strings in string picture.",9804164v2
1999-01-12,Classical Corrections in String Cosmology,"An important element in a model of non-singular string cosmology is a phase
in which classical corrections saturate the growth of curvature in a
deSitter-like phase with a linearly growing dilaton (an `algebraic fixed
point'). As the form of the classical corrections is not well known, here we
look for evidence, based on a suggested symmetry of the action, scale factor
duality and on conformal field theory considerations, that they can produce
this saturation. It has previously been observed that imposing scale factor
duality on the $O(\alpha')$ corrections is not compatible with fixed point
behavior. Here we present arguments that these problems persist to all orders
in $\alpha'$. We also present evidence for the form of a solution to the
equations of motion using conformal perturbation theory, examine its
implications for the form of the effective action and find novel fixed point
structure.",9901044v1
1999-07-05,Supersymmetric Baryonic Branes,"We derive an energy bound for a `baryonic' D5-brane probe in the $adS_5\times
S^5$ background near the horizon of $N$ D3-branes. Configurations saturating
the bound are shown to be 1/4 supersymmetric $S^5$-wrapped D5-branes, with a
total Born-Infeld charge $N$. Previous results are recovered as a special case.
We derive a similar energy bound for a `baryonic' M5-brane probe in the
background of $N$ M5-branes. Configurations saturating the bound are again 1/4
supersymmetric and, in the $adS_7\times S^4$ near-horizon limit, provide a
worldvolume realization of the `baryon string' vertex of the
(2,0)-supersymmetric six-dimensional conformal field theory on coincident
M5-branes. For the full M5-background we find a worldvolume realization of the
Hanany-Witten effect in M-theory.",9907022v3
1999-12-17,Calculating the tension of domain wall junctions and vortices in generalized Wess-Zumino models,"We study BPS saturated objects with axial geometry (wall junctions, vortices)
in generalized Wess-Zumino models. It is observed that the tension of such
objects is negative in general (although ``exceptional'' models are possible).
We show how an ambiguity in the definition of central charges does not affect
physical quantities, and we comment on the stability of the junctions and
vortices. We illustrate these issues in two classes of models with Z_N
symmetry. On the basis of analytical large N calculations and numerical
calculations at finite N, we argue that the domain wall junctions in these
models are indeed BPS saturated, and we calculate the junction tensions
explicitly.",9912162v1
2002-07-08,The anomaly in the central charge of the supersymmetric kink from dimensional regularization and reduction,"We show that the anomalous contribution to the central charge of the
1+1-dimensional N=1 supersymmetric kink that is required for BPS saturation at
the quantum level can be linked to an analogous term in the extra momentum
operator of a 2+1-dimensional kink domain wall with spontaneous parity
violation and chiral domain wall fermions. In the quantization of the domain
wall, BPS saturation is preserved by nonvanishing quantum corrections to the
momentum density in the extra space dimension. Dimensional reduction from 2+1
to 1+1 dimensions preserves the unbroken N=1/2 supersymmetry and turns these
parity-violating contributions into the anomaly of the central charge of the
supersymmetric kink. On the other hand, standard dimensional regularization by
dimensional reduction from 1 to (1-epsilon) spatial dimensions, which also
preserves supersymmetry, obtains the anomaly from an evanescent counterterm.",0207051v2
2002-10-29,Holography in a Radiation-dominated Universe with a Positive Cosmological Constant,"We discuss the holographic principle in a radiation-dominated, closed
Friedmann-Robertson-Walker (FRW) universe with a positive cosmological
constant. By introducing a cosmological D-bound on the entropy of matter in the
universe, we can write the Friedmann equation governing the evolution of the
universe in the form of the Cardy formula. When the cosmological D-bound is
saturated, the Friedmann equation coincides with the Cardy-Verlinde formula
describing the entropy of radiation in the universe. As a concrete model, we
consider a brane universe in the background of Schwarzschild-de Sitter black
holes. It is found that the cosmological D-bound is saturated when the brane
crosses the black hole horizon of the background. At that moment, the Friedmann
equation coincides with the Cardy-Verlinde formula describing the entropy of
radiation matter on the brane.",0210272v3
2004-03-13,A Note on Curvature Fluctuation of Noncommutative Inflation,"An elegant approach, which incorporates the effect of the stringy spacetime
uncertainty relation, to calculate power spectra of fluctuations during
inflation has been suggested by Brandenberger and Ho. In this approach, one of
important features is the appearance of an upper bound on the comoving momentum
$k$, at which the stringy spacetime uncertainty relation is saturated. As a
result, the time-dependent upper bound leads us to choose naturally a set of
initial vacua for each mode, in which the stringy uncertainty relation is
saturated. In this note, with that set of vacua we calculate power spectrum of
curvature fluctuation for a power law inflation, up to the leading order of a
parameter describing the spacetime noncommutativity. It turns out that this
choice of initial vacuum has a significant effect on the power spectrum of
fluctuations.",0403134v2
2004-04-28,"New developments in the quantization of supersymmetric solitons (kinks, vortices and monopoles)","We discuss the one-loop quantum corrections to the mass M and central charge
Z of supersymmetric solitons: the kink, the vortex and the monopole. Contrary
to previous expectations and published results, in each of these cases there
are nonvanishing quantum corrections to the mass. For the N=1 kink and the N=2
monopole a new anomaly in Z rescues BPS saturation (M=Z); for the N=2 vortex,
BPS saturation is rescued for two reasons: (i) the quantum fluctuations of the
Higgs field acquire a nontrivial phase due to the winding of the classical
solution, and (ii) a fermionic zero mode used in the literature is shown not to
be normalizable.",0404223v1
1998-07-28,The honeycomb model of GL(n) tensor products I: proof of the saturation conjecture,"We introduce the honeycomb model of BZ polytopes, which calculate
Littlewood-Richardson coefficients, the tensor product rule for GL(n). Our main
result is the existence of a particularly well-behaved honeycomb with given
boundary conditions (choice of triple of representations to be tensored
together). This honeycomb is necessarily integral, which proves the ""saturation
conjecture"", extending results of Klyachko to give a complete answer to which
L-R coefficients are positive. This in turn has as a consequence Horn's
conjecture from 1962 characterizing the spectrum of the sum of two Hermitian
matrices.",9807160v4
2000-10-01,Bass Numbers of Semigroup-Graded Local Cohomology,"Given a module M over a ring R which has a grading by a semigroup Q, we
present a spectral sequence that computes the local cohomology of M at any
Q-graded ideal I in terms of Ext modules. This method is used to obtain
finiteness results for the local cohomology of graded modules over semigroup
rings; in particular we prove that for a semigroup Q whose saturation is
simplicial, the Bass numbers of such local cohomology modules are finite.
Conversely, if the saturation of Q is not simplicial, one can find a graded
ideal I and a graded R-module M whose local cohomology at I in some degree has
an infinite-dimensional socle. We introduce and exploit the combinatorially
defined essential set of a semigroup.",0010003v2
2002-10-17,The generalized triangle inequalities in symmetric spaces and buildings with applications to algebra,"In this paper we apply our results on the geometry of polygons in Cartan
subspaces, symmetric spaces and buildings to four problems in algebraic group
theory. Two of these problems are generalizations of the problems of finding
the constraints on the eigenvalues (resp. singular values) of a sum (resp.
product) when the eigenvalues (singular values) of each summand (factor) are
fixed. The other two problems are related to the computation of the structure
constants of the Hecke and representation rings associated with a split
reductive algebraic group over Q and its complex Langlands' dual. We give a new
proof of the ``Saturation Conjecture'' for GL(m) as a consequence of our
solution of the corresponding ``saturation problem'' for the Hecke structure
constants for all split reductive algebraic groups over Q.",0210256v5
2005-01-19,Hyperbolicity of holomorphic foliations with parabolic leaves,"In this paper, we study a notion of hyperbolicity for hyperbolicity
foliations with 1-dimensional parabolic leaves, namely the non-existence of
holomorphic cylinders along the foliation - holomorphic maps from $\D^{n-1}
\times \C$ to the manifold sending each $\{*\} \times \C$ to a leaf. We
construct a tensor, that is a leaf-wise holomorphic section of a bundle above
the foliated manifold, which vanishes on an open saturated set if and only if
there exists such a cylinder through each point of this open set. Thanks to
this study, we prove that open sets saturated by compact leaves are union of
holomorphic cylinders along the foliation. We also give some more specific
results and examples in the case of a compact manifold, and of foliations with
one compact leaf or without any compact leaves.",0501292v1
2005-01-28,Equidimensionality of convolution morphisms and applications to saturation problems,"We study the fibers of Mirkovic-Vilonen convolution morphisms. We prove their
equidimensionality when all the coweights in question are minuscule, and some
related statements. We give applications to saturation problems for structure
constants of Hecke and representation rings. An erratum has been added to
correct insufficiencies in the proofs of Lemma 9.4 and Corollary 9.5 as they
appeared in the published version.",0501504v5
2005-02-04,Classifying spectra of saturated fusion systems,"The assignment of classifying spectra to saturated fusion systems was
suggested by Linckelmann and Webb and has been carried out by Broto, Levi and
Oliver. A more rigid (but equivalent) construction of the classifying spectra
is given in this paper. It is shown that the assignment is functorial for
fusion-preserving homomorphisms in a way which extends the assignment of stable
p-completed classifying spaces to finite groups, and admits a transfer theory
analogous to that for finite groups. Furthermore the group of homotopy classes
of maps between classifying spectra is described, and in particular it is shown
that a fusion system can be reconstructed from its classifying spectrum
regarded as an object under the stable classifying space of the underlying
p-group.",0502092v5
2005-05-12,Saturated chains in composition posets,"We study three different poset structures on the set of all compositions. In
the first case, the covering relation consists of inserting a part of size one
to the left or to the right, or increasing the size of some part by one. The
resulting poset was studied by the author in ""A poset classifying
non-commutative term orders"", and then in ""Standard paths in another
composition poset"" where some results about generating functions for standard
paths in this poset was established.
  The latter article was inspired by the work of Bergeron, Bousquet-M{\'e}lou
and Dulucq on ""Standard paths in the composition poset"", where they studied a
poset where there are additional cover relations which allows the insertion of
a part of size one anywhere in the composition. Finally, following a suggestion
by Richard Stanley we study yet a third which is an extension of the previous
two posets. This poset is related to quasi-symmetric functions.
  For these posets, we study generating functions for saturated chains of fixed
width k. We also construct ``labeled'' non-commutative generating functions and
their associated languages.",0505262v2
2006-02-21,An approach to non-standard analysis,"This note has two principal aims: to portray an essence of Non-Standard
Analysis as a particular structure (which we call lim-rim), noting its
interplay with the notion of ultrapower, and to present a construction of
Non-Standard Analysis, viewed as a matter of mathematics, where the set *A of
non-standard elements of a set A - ""the adjunction of all possible limits"" is a
""good"" kind of lim-rim which plays a role analogous to the algebraic closure of
a field - ""the adjunction of all roots of polynomials"". In the same spirit as
with algebraic closures, one has uniqueness up to isomorphism, and also
universality and homogeneity, provided one has enough Generalized Continuum
Hypothesis. The cardinality of *A will be just something like 2^(2^|A|), and
one has a high degree of saturation.",0602469v4
2006-07-19,Saturation and Irredundancy for Spin(8),"We explicitly calculate the triangle inequalities for the group PSO(8).
Therefore we explicitly solve the eigenvalues of sum problem for this group
(equivalently describing the side-lengths of geodesic triangles in the
corresponding symmetric space for the Weyl chamber-valued metric). We then
apply some computer programs to verify two basic questions/conjectures. First,
we verify that the above system of inequalities is irredundant. Then, we verify
the ``saturation conjecture'' for the decomposition of tensor products of
finite-dimensional irreducible representations of Spin(8). Namely, we show that
for any triple of dominant weights a, b, c such that a+b+c is in the root
lattice, and any positive integer N, the tensor product of the irreducible
representations V(a) and V(b) contains V(c) if and only if the tensor product
of V(Na) and V(Nb) contains V(Nc).",0607454v1
2007-02-10,Dependent theories and the generic pair conjecture,"We try to understand complete types over a somewhat saturated model of a
complete first order theory which is dependent (previously called NIP), by
""decomposition theorems for such types"". Our thesis is that the picture of
dependent theory is the combination of the one for stable theories and the one
for the theory of dense linear order or trees (and first we should try to
understand the quite saturated case). As a measure of our progress, we give
several applications considering some test questions; in particular we try to
prove the generic pair conjecture and do it for measurable cardinals.",0702292v6
2007-03-21,A note on strong negative partition relations,"We analyze a natural function definable from a scale at a singular cardinal,
and using this function we are able to obtain quite strong negative
square-brackets partition relations at successors of singular cardinals. The
proof of our main result makes use of club-guessing, and as a corollary we
obtain a fairly easy proof of a difficult result of Shelah connecting weak
saturation of a certain club-guessing ideal with strong failures of
square-brackets partition relations. We then investigate the strength of weak
saturation of such ideals and obtain some results on stationary reflection.",0703647v2
2000-12-22,"Elimination of Chaos in Multimode, Intracavity-doubled Lasers in the Presence of Spatial Hole-burning","In this paper possibilities of a stabilization of large amplitude
fluctuations in an intracavity-doubled solid-state laser are studied. The
modification of the cross-saturation coefficient by the effect of spatial
hole-burning is taken into account. The stabilization of the laser radiation by
an increase of the number of modes, as proposed by James et al. (1990) and
Magni et al. (1993), is analyzed. It is found that when the cross-saturation
coefficient is modulated by the spatial hole-burning the stabilization is not
always possible. We propose a new way of obtaining a stable steady-state
configuration based on an increase of the strength of nonlinearity, which leads
to a strong cancellation of modes, so that during the evolution all of the
modes, but a single one, are canceled. Such a steady-state solution is found to
be stable with respect to small perturbations.",0012051v1
2001-03-13,One- and two-dimensional solitons in saturable media,"Very narrow spatial bright solitons in (1+1)D and (2+1)D versions of
cubic-quintic and full saturable models are studied, starting from the full
system of the Maxwell's equations, rather than from the paraxial (NLS)
approximation. For the solitons with both TE and TM polarizations, it is shown
that there always exists a finite minimum width, and they cease to exist at a
critical value of the propagation constant, at which their width diverges. Full
similarity of the results obtained for both nonlinearities suggests that the
same general conclusions apply to narrow solitons in any non-Kerr model.",0103014v1
2002-07-22,Frequency Dependence of Quantum Localization in a Periodically Driven System,"We study the quantum localization phenomena for a random matrix model
belonging to the Gaussian orthogonal ensemble (GOE). An oscillating external
field is applied on the system. After the transient time evolution, energy is
saturated to various values depending on the frequencies. We investigate the
frequency dependence of the saturated energy. This dependence cannot be
explained by a naive picture of successive independent Landau-Zener transitions
at avoided level crossing points. The effect of quantum interference is
essential. We define the number of Floquet states which have large overlap with
the initial state, and calculate its frequency dependence. The number of
Floquet states shows approximately linear dependence on the frequency, when the
frequency is small. Comparing the localization length in Floquet states and
that in energy states from the viewpoint of the Anderson localization, we
conclude that the Landau-Zener picture works for the local transition processes
between levels.",0207038v1
2002-12-13,Stable vortex and dipole vector solitons in a saturable nonlinear medium,"We study both analytically and numerically the existence, uniqueness, and
stability of vortex and dipole vector solitons in a saturable nonlinear medium
in (2+1) dimensions. We construct perturbation series expansions for the vortex
and dipole vector solitons near the bifurcation point where the vortex and
dipole components are small. We show that both solutions uniquely bifurcate
from the same bifurcation point. We also prove that both vortex and dipole
vector solitons are linearly stable in the neighborhood of the bifurcation
point. Far from the bifurcation point, the family of vortex solitons becomes
linearly unstable via oscillatory instabilities, while the family of dipole
solitons remains stable in the entire domain of existence. In addition, we show
that an unstable vortex soliton breaks up either into a rotating dipole soliton
or into two rotating fundamental solitons.",0212034v1
2004-01-12,Waveguiding properties of optical vortex solitons,"We study the properties of linear and nonlinear waveguides induced by optical
vortex solitons in both self-defocusing and self-focusing nonlinear media, for
the case of a saturable nonlinear response. We demonstrate that the
vortex-induced waveguides can guide both fundamental and first-order guided
modes which together with the vortex may form, for larger amplitudes of the
guide modes, different types of composite vortex-mode vector solitons. In the
case of the self-focusing saturable medium, we demonstrate that a
large-amplitude guided mode can stabilize the ring-like vortex structure which
usually decays due to azimuthal modulational instability.",0401013v1
2005-11-01,Discrete soliton mobility in two-dimensional waveguide arrays with saturable nonlinearity,"We address the issue of mobility of localized modes in two-dimensional
nonlinear Schr\""odinger lattices with saturable nonlinearity. This describes
e.g. discrete spatial solitons in a tight-binding approximation of
two-dimensional optical waveguide arrays made from photorefractive crystals. We
discuss numerically obtained exact stationary solutions and their stability,
focussing on three different solution families with peaks at one, two, and four
neighboring sites, respectively. When varying the power, there is a repeated
exchange of stability between these three solutions, with symmetry-broken
families of connecting intermediate stationary solutions appearing at the
bifurcation points. When the nonlinearity parameter is not too large, we
observe good mobility, and a well defined Peierls-Nabarro barrier measuring the
minimum energy necessary for rendering a stable stationary solution mobile.",0511003v2
2006-10-24,Moving solitons in the discrete nonlinear Schrödinger equation,"Using the method of asymptotics beyond all orders, we evaluate the amplitude
of radiation from a moving small-amplitude soliton in the discrete nonlinear
Schr\""odinger equation. When the nonlinearity is of the cubic type, this
amplitude is shown to be nonzero for all velocities and therefore
small-amplitude solitons moving without emitting radiation do not exist. In the
case of a saturable nonlinearity, on the other hand, the radiation is found to
be completely suppressed when the soliton moves at one of certain isolated
`sliding velocities'. We show that a discrete soliton moving at a general speed
will experience radiative deceleration until it either stops and remains pinned
to the lattice, or--in the saturable case--locks, metastably, onto one of the
sliding velocities. When the soliton's amplitude is small, however, this
deceleration is extremely slow; hence, despite losing energy to radiation, the
discrete soliton may spend an exponentially long time travelling with virtually
unchanged amplitude and speed.",0610059v4
1998-12-11,Flow angle from intermediate mass fragment measurements,"Directed sideward flow of light charged particles and intermediate mass
fragments was measured in different symmetric reactions at bombarding energies
from 90 to 800 AMeV. The flow parameter is found to increase with the charge of
the detected fragment up to Z = 3-4 and then turns into saturation for heavier
fragments. Guided by simple simulations of an anisotropic expanding thermal
source, we show that the value at saturation can provide a good estimate of the
flow angle, $\Theta_{flow}$, in the participant region. It is found that
$\Theta_{flow}$ depends strongly on the impact parameter. The excitation
function of $\Theta_{flow}$ reveals striking deviations from the ideal
hydrodynamical scaling. The data exhibit a steep rise of $\Theta_{\flow}$ to a
maximum at around 250-400 AMeV, followed by a moderate decrease as the
bombarding energy increases further.",9812005v1
2002-02-08,Modeling of the saturation current of a fission chamber taking into account the distorsion of electric field due to space charge effects,"Fission chambers were first made fifty years ago for neutron detection. At
the moment, the French Atomic Energy Commission \textsf{(CEA-Cadarache)} is
developing a sub-miniature fission chamber technology with a diameter of 1.5 mm
working in the current mode (Bign). To be able to measure intense fluxes, it is
necessary to adjust the chamber geometry and the gas pressure before testing it
under real neutron flux. In the present paper, we describe a theoretical method
to foresee the current-voltage characteristics (sensitivity and saturation
plateau) of a fission chamber whose geometrical features are given, taking into
account the neutron flux to be measured (spectrum and intensity). The proposed
theoretical model describes electric field distortion resulting from charge
collection effect. A computer code has been developed on this model basis. Its
application to 3 kinds of fission chambers indicates excellent agreement
between theoretical model and measured characteristics.",0202004v1
2003-05-13,Particle dependence of elliptic flow in Au+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV,"The elliptic flow parameter ($v_2$) for $K_S^0$ and $\Lambda+\bar{\Lambda}$
has been measured at mid-rapidity in Au + Au collisions at
$\sqrt{s_{_{NN}}}=200$ GeV by the STAR collaboration. The $v_2$ values for both
$K_S^{0}$ and $\Lambda+\bar{\Lambda}$ saturate at moderate $p_T$, deviating
from the hydrodynamic behavior observed in the lower $p_T$ region. The
saturated $v_2$ values and the $p_T$ scales where the deviation begins are
particle dependent. The particle-type dependence of $v_2$ shows features
expected from the hadronization of a partonic ellipsoid by coalescence of
co-moving quarks. These results will be discussed in relation to the nuclear
modification factor ($R_{CP}$) which has also been measured for $K_S^0$ and
$\Lambda+\bar{\Lambda}$ by the STAR collaboration.",0305008v3
2004-05-19,BRAHMS results in the context of saturation and quantum evolution,"We report BRAHMS results from RHIC d+Au and p+p collisions at
Sqrt(s_NN)=200GeV. A remarkable change in the nuclear modification factor RdAu
is seen as the pseudorapidity of the detected charged hadrons changes from zero
at mid-rapidity to 3.2 at the most forward angle studied during the 2003 run.
For pseudorapidity eta>1 the suppression of the Rcp factor is more pronounced
in the sample of central events in contrast to the behavior at mid-rapidity
where the central events show higher enhancement compared to the semi-central
sample. These results are consistent with a saturated Au wave function strongly
affected by quantum evolution at higher values of rapidity.",0405018v1
2004-08-16,Pseudorapidity Asymmetry and Centrality Dependence of Charged Hadron Spectra in d+Au Collisions at $\sqrt{s_{NN}}=200$ GeV,"The pseudorapidity asymmetry and centrality dependence of charged hadron
spectra in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV are presented. The
charged particle density at mid-rapidity, its pseudorapidity asymmetry and
centrality dependence are reasonably reproduced by a Multi-Phase Transport
model, by HIJING, and by the latest calculations in a saturation model. Ratios
of transverse momentum spectra between backward and forward pseudorapidity are
above unity for \pT below 5 GeV/$c$. The ratio of central to peripheral spectra
in d+Au collisions shows enhancement at 2 $<$ \pT $<$ 6 GeV/$c$, with a larger
effect at backward rapidity than forward rapidity. Our measurements are in
qualitative agreement with gluon saturation and in contrast to calculations
based on incoherent multiple partonic scatterings.",0408016v2
2006-01-05,High pT Suppression in CuCu Collsions at 200 GeV/NN at RHIC,"Collisions between hadronic systems at relativistic energies provide a window
on the small-x gluon distributions of fast moving nuclei. It has been predicted
that gluon saturation effects will manifest themselves as a suppression in the
transverse momentum (pT) distribution at a scale which is connected with the
rapidity of the measured particles. Saturation effects are most evident at
large (pseudo)-rapidity, i.e., at small angles relative to the beam direction.
The dependence of the nuclear modification factor on the number of participants
provides a constraint on the mechanism underlying the high-pT suppression. Here
we present results for the nuclear modification factor Rcp at forward rapidity
as a function of system mass comparing results from CuCu, AuAu and dAu
collsions at 200 GeV/NN.",0601011v1
1996-10-08,Nuclear Density-Dependent Effective Coupling Constants in the Mean-Field Theory,"It is shown that the equation of state of nuclear matter can be determined
within the mean-field theory of $\sigma \omega$ model provided only that the
nucleon effective mass curve is given. We use a family of the possible nucleon
effective mass curves that reproduce the empirical saturation point in the
calculation of the nuclear binding energy curves in order to obtain
density-dependent effective coupling constants. The resulting density-dependent
coupling constants may be used to study a possible equation of state of nuclear
system at high density or neutron matter. Within the constraints used in this
paper to $M^*$ of nuclear matter at saturation point and zero density, neutron
matter of large incompressibility is strongly bound at high density while soft
neutron matter is weakly bound at low density. The study also exhibits the
importance of surface vibration modes in the study of nuclear equation of
state.",9610010v1
1996-12-10,Saturation properties and liquid-gas phase transition of nucleus,"Saturation properties and liquid-gas phase transition of nucleus are analysed
in the framework of Hatree-Fock theory. We modify Hill-Wheller formula with a
finite-size-effect parameter by fitting the zero-temperature properties of
nucleus. Employing Gogny effective interaction and phenomenological expression
of Coulomb energy, we give the critical temperature of liquid-gas phase
transition of nucleus being about 12 MeV, which agrees with the result
extracted from heavy-ion collision experiments. It is pointed out that a
phenomenological formula of surface energy of hot nucleus is not avaliable in
the region where nucleon density is far away from the normal density.",9612022v1
1997-06-16,Strangeness and Pion Production as Signals of QCD Phase Transition,"A systematic analysis of data on strangeness and pion production in
nucleon-nucleon and central nucleus-nucleus collisions is presented. It is
shown that at all collision energies the pion/baryon and strangeness/pion
ratios indicate saturation with the size of the colliding nuclei. The energy
dependence of the saturation level suggests that the transition to the Quark
Gluon Plasma occurs between 15 AGeV/c (BNL AGS) and 160 AGeV/c (CERN SPS)
collision energies. The experimental results interpreted in the framework of a
statistical approach show that the effective number of degrees of freedom
increases in the course of the phase transition and that the plasma created at
CERN SPS energies may have a temperature of about 280 MeV (energy density 10
GeV/fm-3). The presence of the phase transition can lead to the non-monotonic
collision energy dependence of the strangeness/pion ratio. After an initial
increase the ratio should drop to the characteristic value for the QGP. Above
the transition region the ratio is expected to be collision energy independent.
Experimental studies of central Pb+Pb collisions in the energy range 20--160
AGeV/c are urgently needed in order to localize the threshold energy, and study
the properties of the QCD phase transition.",9706036v1
1997-11-14,The role of tensor force in nuclear matter saturation,"Using a relativistic Dirac-Brueckner analysis the pion contribution to the
ground state energy of nuclear matter is studied. Evidence is presented that
the role of the tensor force in the saturation mechanism is substantially
reduced compared to its dominant role in a usual non-relativistic treatment.
The reduction of the pion contribution in nuclear matter is due to many-body
effects present in a relativistic treatment. In particular, we show that the
damping of OPEP is actually due to the decrease of $M^*/M$ with increasing
density.",9711029v1
1997-12-10,$Q^2$--Dependence of the Gerasimov-Drell-Hearn Sum Rule,"We test the Gerasimov-Drell-Hearn (GDH) sum rule numerically by calculating
the total photon absorption cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ on
the nucleon via photon excitation of baryon resonances in the constituent quark
model. A total of seventeen, low-lying, non-strange baryon resonances are
included in this calculation. The transverse and longitudinal interference
cross section, $\sigma_{1/2}^{TL}$, is found to play an important role in the
study of the $Q^2$ variation of the sum rule. The results show that the GDH sum
rule is saturated by these resonances at a confidence level of 94%. In
particular, the $P_{33}(1232)$ excitation largely saturates the sum rule at
$Q^2 = 0$, and dominates at small $Q^2$. The GDH integral has a strong
$Q^2$-dependence below $Q^2= 1.0 {GeV}^2$ and changes its sign around $Q^2= 0.3
{GeV}^2$. It becomes weakly $Q^2$-dependent for $Q^2 > 1.0 {GeV}^2$ because of
the quick decline of the resonance contributions. We point out that the $Q^2$
variation of the GDH sum rule is very important for understanding the nucleon
spin structure in the non-perturbative QCD region.",9712036v1
2000-11-07,Nuclear matter properties in the relativistic mean field model with sigma-omega coupling,"The possibility of extending the linear sigma-omega model by introducing a
sigma-omega coupling phenomenologically is explored. It is shown that, in
contrast to the usual Walecka model, not only the effective nucleon mass M* but
also the effective sigma meson mass m*_sigma and the effective omega meson mass
m*_omega are nucleon density dependent. When the model parameters are fitted to
the nuclear saturation point (the nuclear radius constant r_0=1.14fm and volume
energy a_1=16.0MeV) as well as to the effective nucleon mass M*=0.85M, the
model yields m*_sigma=1.09m_sigma and m*_omega=0.90m_omega at the saturation
point, and the nuclear incompressibility K_0=501MeV. The lowest value of K_0
given by this model by adjusting the model parameters is around 227MeV.",0011025v1
2001-04-24,Saturation of Elliptic Flow and the Transport Opacity of the Gluon Plasma at RHIC,"Differential elliptic flow and particle spectra are calculated taking into
account the finite transport opacity of the gluon plasma produced in Au+Au at
Ecm ~ 130 A GeV at RHIC. Covariant numerical solutions of the ultrarelativistic
Boltzmann equation are obtained using the MPC parton cascade technique. For
typical pQCD (~3 mb) elastic cross sections, extreme initial gluon densities,
dN/deta ~ 15000, are required to reproduce the elliptic flow saturation pattern
reported by STAR. However, we show that the solutions depend mainly on the
transport opacity, $\chi=\int dz \sigma_t\rho_g$, and thus the data can also be
reproduced with dN/deta ~ 1000, but with extreme elastic parton cross sections,
\~45 mb. We demonstrate that the spectra and elliptic flow are dominated by
numerical artifacts unless parton subdivisions ~100-1000 are applied to retain
Lorentz covariance for RHIC initial conditions.",0104073v3
2002-05-30,Energy dependence of string fragmentation function and $φ$ meson production,"The $\phi$ meson productions in $Au+Au$ and/or $Pb+Pb$ collisions at AGS,
SPS, RHIC, and LHC energies have been studied systematically with a hadron and
string cascade model LUCIAE. After considering the energy dependence of the
model parameter $\alpha$ in string fragmentation function and adjusting it to
the experimental data of charged multiplicity to a certain extent, the model
predictions for $\phi$ meson yield, rapidity, and/or transverse mass
distributions are compatible with the experimental data at AGS, SPS and RHIC
energies. A calculation for $Pb+Pb$ collisions at LHC energy is given as well.
The obtained fractional variable in string fragmentation function shows a
saturation in energy dependence. It is discussed that the saturation of
fractional variable in string fragmentation function might be a qualitative
representation of the energy dependence of nuclear transparency.",0205078v1
2002-10-04,The structure of nuclear systems derived from low momentum nucleon-nucleon potentials,"Various nuclear structure observables are evaluated employing low-momentum
nucleon-nucleon (NN) potentials $V_{\rm low-k}$ derived from the CD-Bonn and
Nijmegen NN interactions $V_{NN}$. By construction, the high momentum modes of
the original $V_{NN}$ are integrated out in $V_{\rm low-k}$, with the
requirement that the deuteron binding energy and low energy phase shifts of
$V_{NN}$ are exactly reproduced. Using this interaction, we evaluate the bulk
properties (binding energy and saturation density) of nuclear matter and finite
nuclei, in particular their dependence on the cut-off parameter. We also study
the pairing gap and the residual interaction in nuclear matter in terms of the
Landau parametrization. At low and medium densities, the HF and BHF binding
energies for nuclear matter calculated with the $V_{\rm low-k}$'s derived from
the CD-Bonn and Nijmegen potentials are nearly identical. The pairing gaps and
Landau parameters derived from $V_{\rm low-k}$ are remarkably close to those
given by the full-space $V_{NN}$. The $V_{\rm low-k}$ interactions, however,
fail to reproduce the saturation property of nuclear matter at higher densities
if the cut-off for the high momentum modes is assumed density independent.",0210010v1
2003-04-28,An interpretation of saturation phenomena as Glauber-Gribov multiple parton scatterings,"We compare two formalism that describe minijet production in pA and AA
collisions: pQCD supplemented by Glauber-Gribov multiple semihard parton
scatterings (pQCD+Glauber), and the Colour Glass Condensate (CGC). We argue
that in a suitable limit they are equivalent to each other, the PQCD+Glauber
model being more accurate from a numerical point of view. Finally, we analyze
RHIC data on Au-Au integrated charged multiplicities in the pQCD+Glauber
framework, and conclude that at least at central rapidity there is no sign of
gluon saturation.",0304083v1
2003-05-18,Meson and baryon elliptic flow at high pT from parton coalescence,"The large and saturating differential elliptic flow v2(pT) observed in Au+Au
reactions at RHIC so far could only be explained assuming an order of magnitude
denser initial parton system than estimated from perturbative QCD.
Hadronization via parton coalescence can resolve this ``opacity puzzle''
because it enhances hadron elliptic flow at large pT relative to that of
partons at the same transverse momentum. An experimentally testable consequence
of the coalescence scenario is that v2(pT) saturates at about 50% higher values
for baryons than for mesons. In addition, if strange quarks have weaker flow
than light quarks, hadron v2 at high pT decreases with relative strangeness
content.",0305049v1
2003-08-27,Nuclear incompressibility using the density dependent M3Y effective interaction,"A density dependent M3Y effective nucleon-nucleon (NN) interaction which was
based on the G-matrix elements of the Reid-Elliott NN potential has been used
to determine the incompressibity of infinite nuclear matter. The nuclear
interaction potential obtained by folding in the density distribution functions
of two interacting nuclei with this density dependent M3Y effective interaction
had been shown earlier to provide excellent descriptions for medium and high
energy $\alpha$ and heavy ion elastic scatterings as well as $\alpha$ and heavy
cluster radioactivities. The density dependent parameters have been chosen to
reproduce the saturation energy per nucleon and the saturation density of spin
and isospin symmetric cold infinite nuclear matter. The result of such
calculations for nuclear incompressibility using the density dependent M3Y
effective interaction based on the G-matrix elements of Reid-Elliott NN
potential predicts a value of about 300 MeV for nuclear incompressibility.",0308075v1
2004-04-29,Kaon and antikaon properties in cold nuclear medium,"We present results of a self-consistent calculation for the kaon and antikaon
spectral functions in cold nuclear matter, using as input the kaon-nucleon and
antikaon-nucleon scattering amplitudes of the vacuum. We investigate the effect
of in-medium pion dressing on the antikaon-nucleon scattering amplitudes and
antikaon spectral function. We find the influence of pion dressing to be minor
on the antikaon spectral function and limited on the hyperon resonances causing
only a small additional broadening. An exception is the \Sigma(1690). At
nuclear saturation density an attractive mass shift of about 20 MeV and width
of about 130 MeV is obtained. The kaon shows a repulsive mass increase of 36
MeV and a small width of the quasiparticle peak at saturation density.",0404088v2
2005-09-25,A statistical model analysis of yields and fluctuations in 200 GeV Au-Au collisions,"We show that the simultaneous measurement of yields and fluctuations is
capable of falsifying and constraining the statistical hadronization model. We
show how such a measurement can test for chemical non-equilibrium, and
distinguish between a high temperature chemically equilibrated freeze-out from
a supercooled freeze-out with an over-saturated phase space. We perform a fit,
and show that both yields and fluctuations measured at RHIC 200 GeV can be
accounted for within the second scenario, with both the light and strange quark
phase space saturated significantly above detailed balance. We point to the
simultaneous fit of the $K/\pi$ fluctuation and the $K^*/K^-$ ratio as evidence
that the effect of hadronic re-interactions after freeze-out is small.",0509067v1
2006-03-31,High density behaviour of nuclear symmetry energy,"Role of the isospin asymmetry in nuclei and neutron stars, with an emphasis
on the density dependence of the nuclear symmetry energy, is discussed. The
symmetry energy is obtained using the isoscalar as well as isovector components
of the density dependent M3Y effective interaction. The constants of density
dependence of the effective interaction are obtained by reproducing the
saturation energy per nucleon and the saturation density of spin and isospin
symmetric cold infinite nuclear matter. Implications for the density dependence
of the symmetry energy in case of a neutron star are discussed, and also
possible constraints on the density dependence obtained from finite nuclei are
compared.",0603073v2
2006-04-17,Gluon Saturation Effects in Relativistic U+U Collisions,"We examine entropy production in relativistic U+U collisions on the basis of
a Color Glass Condensate (CGC) type picture as implemented in the
Kharzeev-Levin-Nardi model (KLN). In this framework, we find that the peak
entropy density produced in tip-on-tip U+U collisions is about 30% greater than
that seen in central Au+Au collisions. Although the resulting difference in the
produced charged particle multiplicity between tip-on-tip and side-on-side
collisions is smaller than that predicted by previous Glauber model estimates,
it is still large enough to allow for experimental discrimination between
average orientations of the uranium nuclei. We also point out that in the
saturation/CGC approach the collision geometry plays a more important role than
previously believed, and that the observed centrality dependence of the
produced particle multiplicity per participant in Au+Au collisions can be
qualitatively reproduced even without running coupling effects.",0604038v1
2006-11-13,QCD susceptibilities and nuclear matter saturation in a chiral theory: inclusion of pion loops,"We derive the equation of state of symmetric nuclear matter in a relativistic
theory with $\sigma$ and $\omega$ exchange. We take a chiral version of this
model which insures all the chiral constraints. Going beyond the mean field
approach we introduce the effects of the pion loops. For the parameters of the
model, in order to fix those linked to pion exchange, we exploit the most
recent information on the short-range part of the spin-isospin interaction. For
those linked to the scalar meson exchange we make use of an analysis of lattice
results on the nucleon mass evolution with the quark mass. With these inputs we
are able reach a correct description of the saturation properties. From the
equation of state of symmetric nuclear matter we alsoderive the density
dependence of the quark condensate and of the QCD susceptibilities.",0611042v1
2007-03-09,From QCD to nuclear matter saturation,"We discuss a relativistic chiral theory of nuclear matter with $\sigma$ and
$\omega$ exchange using a formulation of the $\sigma$ model in which all the
chiral constraints are automatically fulfilled. We establish a relation between
the nuclear response to the scalar field and the QCD one which includes the
nucleonic parts. It allows a comparison between nuclear and QCD information.
Going beyond the mean field approach we introduce the effects of the pion loops
supplemented by the short-range interaction. The corresponding Landau-Migdal
parameters are taken from spin-isospin physics results. The parameters linked
to the scalar meson exchange are extracted from lattice QCD results. These
inputs lead to a reasonable description of the saturation properties,
illustrating the link between QCD and nuclear physics. We also derive from the
corresponding equation of state the density dependence of the quark condensate
and of the QCD susceptibilities.",0703022v1
2007-03-23,Phase transitions in isolated strongly interacting systems,"Thermodynamical properties of the nuclear matter at sub-saturation densities
were investigated using a simple van der Waals-like equation of state with an
additional term representing the symmetry energy. First-order
isospin-asymmetric liquid-gas phase transition appears restricted to isolated
isospin-asymmetric systems while the symmetric systems will undergo
fragmentation decay resembling the second-order phase transition. The density
dependence of the symmetry energy scaling with the Fermi energy satisfactorily
describes the symmetry energy at sub-saturation nuclear densities. The
deconfinement-confinement phase transition from the quark-gluon plasma to the
confined quark matter appears in the isolated systems continuous in energy
density while discontinuous in quark density. A transitional state of the
confined quark matter has a negative pressure and after hadronization an
explosion scenario can take place which can offer explanation for the HBT
puzzle as a signature of the phase transition.",0703077v2
1997-08-21,Amplitude equations for coupled electrostatic waves in the limit of weak instability,"We consider the simplest instabilities involving multiple unstable
electrostatic plasma waves corresponding to four-dimensional systems of mode
amplitude equations. In each case the coupled amplitude equations are derived
up to third order terms. The nonlinear coefficients are singular in the limit
in which the linear growth rates vanish together. These singularities are
analyzed using techniques developed in previous studies of a single unstable
wave. In addition to the singularities familiar from the one mode problem,
there are new singularities in coefficients coupling the modes. The new
singularities are most severe when the two waves have the same linear phase
velocity and satisfy the spatial resonance condition $k_2=2k_1$. As a result
the short wave mode saturates at a dramatically smaller amplitude than that
predicted for the weak growth rate regime on the basis of single mode theory.
In contrast the long wave mode retains the single mode scaling. If these
resonance conditions are not satisfied both modes retain their single mode
scaling and saturate at comparable amplitudes.",9708004v1
1998-04-28,The Dynamics of Granular Segregation Patterns in a Long Drum Mixer,"We have studied the early time evolution of granular segregation patterns in
a horizontal rotating cylinder partially filled with a sand/salt mixture. The
growth of concentration fluctuations starting from premixed initial conditions
was analyzed using Fourier techniques. In one mixture, we observed generally
merging dynamics in the segregated bands up to the onset of saturation. At the
threshold of saturation, we found a spectrum of wavelengths with a broad peak.
The peak position was nearly independent of the tube rotation rate. The overall
growth rate of Fourier modes had a maximum at a particular value of the angular
rotation frequency. In a slightly different mixture, we observed transient
traveling waves when the larger grains were in the majority. We measured the
wave speed as a function of several parameters using presegregated initial
conditions to launch waves of various wavelengths.",9804004v2
2000-12-31,Spectral Characteristics of Ultrashort Pulses in Kerr-lens Mode-Locked Lasers,"A number of factors that influence spectral position of the femtosecond pulse
in a Kerr-lens modelocked Cr:LiSGaF laser have been identified: high-order
dispersion, gain saturation, reabsorption from the ground state, and stimulated
Raman scattering. Using the one-dimensional numerical model for the simulation
of the laser cavity, the relative contributions of different factors have been
compared. The Raman effect provides the largest self-frequency shift from the
gain peak (up to 60 nm), followed by the gain saturation (25 nm), while the
high-order dispersion contribution is insignificant (5 nm). Comparison with the
experimental data confirm that the stimulated Raman scattering is a main cause
of the ultrashort pulse self-frequency shift observed in Cr:LiSGaF and Cr:LiSAF
lasers",0101004v2
2002-07-31,Drift Wave versus Interchange Turbulence in Tokamak Geometry: Linear versus Nonlinear Mode Structure,"The competition between drift wave and interchange physics in general
E-cross-B drift turbulence is studied with computations in three dimensional
tokamak flux tube geometry. For a given set of background scales, the parameter
space can be covered by the plasma beta and drift wave collisionality. At large
enough plasma beta the turbulence breaks out into ideal ballooning modes and
saturates only by depleting the free energy in the background pressure
gradient. At high collisionality it finds a more gradual transition to
resistive ballooning. At moderate beta and collisionality it retains drift wave
character, qualitatively identical to simple two dimensional slab models. The
underlying cause is the nonlinear vorticity advection through which the self
sustained drift wave turbulence supersedes the linear instabilities, scattering
them apart before they can grow, imposing its own physical character on the
dynamics. This vorticity advection catalyses the gradient drive, while
saturation occurs solely through turbulent mixing of pressure disturbances.
This situation persists in the whole of tokamak edge parameter space. Both
simplified isothermal models and complete warm ion models are treated.",0207126v1
2003-12-11,Influence of squirt flow on fundamental guided waves propagation in borehole embedded in saturated porous media,"In this paper, the reservoir is modeled by homogeneous two-phase media based
on BISQ model. We focus on the effects of the squirt flow on the fundamental
guided waves propagation in borehole embedded in saturated porous media excited
by monopole, dipole and quadrupole point sources. The full waveforms acoustic
logging in a fluid-filled borehole are simulated. The curves of velocity
dispersion, attenuation coefficients and excitation of the fundamental guided
waves have shown that velocity dispersions are almost independent of the
characteristic squirt flow length, attenuations of guided waves are enhanced
due to the squirt flow, and excitations of guided waves are decreased due to
the squirt flow. It is possible to estimate the characteristic squirt flow
length by attenuation coefficients of the guided waves from acoustical logging
data.",0312069v2
2004-01-15,Nonlinear Variation of Light-Pressure-Induced Multilevel Atomic Line Shifts with Vapor Pressure in Helium Spectroscopy,"This paper has been temporarily withdrawn. Highly nonlinear dependences of
4He 2^3S - 2^3P lines on pressure were observed in vapor cell saturation
spectroscopy. Line shifts agree with those expected from light-pressure-induced
perturbation of atomic velocity distribution. In the lin-perp-lin pump and
probe polarization configuration, multilevel atomic structure must be taken
into account. For a two-level atom, the shift magnitude is determined by the
collisional time constant, but when the system has dark states there is an
additional time constant due to optical pumping. The collisional and optical
time constants compete, and become equal at a certain pressure p_0. Saturation
signal vanishes at p_0 whereas signal due to light pressure remains. This leads
to a dependence of line centers on pressure that exhibits apparently singular
behavior at p_0. The 2S - 2P(J=1) line shift reaches the natural half width.
Vapor cells may be more suitable for investigation of this effect than atomic
beams since the shifts vanish at sufficiently high pressures. Two ways of
controlling the shifts for the helium 2P fine structure measurement are
discussed.",0401075v2
2004-08-03,Absence of saturation for finite injected currents in axially symmetric cavity diode,"The Child-Langmuir law is investigated numerically using a fully
electromagnetic particle-in-cell code for a closed axially symmetric diode. It
is found that the average current transmitted to the anode increases with the
injected current even after the formation of virtual cathode in both the
non-relativistic and relativistic cases. The increase is found to be a power
law. In other words, the time averaged fraction $f$ of electrons reaching the
anode varies with the input current as, $f\sim J_{\rm IN}^{-\beta}$ where
$\beta < 1$. In contrast, for an infinite parallel plate diode, $f \sim J_{\rm
IN}^{-1}$. The possibility of asymptotic saturation is also discussed.",0408014v1
2004-09-16,Criteria for the experimental observation of multi-dimensional optical solitons in saturable media,"Criteria for experimental observation of multi-dimensional optical solitons
in media with saturable refractive nonlinearities are developed. The criteria
are applied to actual material parameters (characterizing the cubic
self-focusing and quintic self-defocusing nonlinearities, two-photon loss, and
optical-damage threshold) for various glasses. This way, we identify operation
windows for soliton formation in these glasses. It is found that two-photon
absorption sets stringent limits on the windows. We conclude that, while a
well-defined window of parameters exists for two-dimensional solitons (spatial
or spatiotemporal), for their three-dimensional spatiotemporal counterparts
such a window \emph{does not} exist, due to the nonlinear loss in glasses.",0409081v1
2004-10-01,Saturation of Cs2 Photoassociation in an Optical Dipole Trap,"We present studies of strong coupling in single-photon photoassociation of
cesium dimers using an optical dipole trap. A thermodynamic model of the trap
depletion dynamics is employed to extract absolute rate coefficents. From the
dependence of the rate coefficient on the photoassociation laser intensity, we
observe saturation of the photoassociation scattering probability at the
unitarity limit in quantitative agreement with the theoretical model by Bohn
and Julienne [Phys. Rev. A, 60, 414 (1999)]. Also the corresponding power
broadening of the resonance width is measured. We could not observe an
intensity dependent light shift in contrast to findings for lithium and
rubidium, which is attributed to the absence of a p or d-wave shape resonance
in cesium.",0410006v1
2005-09-20,Properties of the odd harmonics of the radiation from SASE FEL with a planar undulator,"Recent theoretical and experimental studies have shown that Self-Amplified
Spontaneous Emission Free Electron Laser (SASE FEL) with a planar undulator
holds a potential for generation of relatively strong coherent radiation at the
third harmonic of the fundamental frequency. Here we present detailed study of
the nonlinear harmonic generation in the SASE FEL obtained with time-dependent
FEL simulation code. Using similarity techniques we present universal
dependencies for temporal, spectral, and statistical properties of the odd
harmonics of the radiation from SASE FEL. In particular, we derived universal
formulae for radiation power of the odd harmonics at saturation. It was also
found that coherence time at saturation falls inversely proportional to
harmonic number, and relative spectrum bandwidth remains constant with harmonic
number.",0509164v1
2005-09-22,"Saturable Absorber, Coherent Population Oscillations, and ""Slow Light""","The paper presents a critical analysis of publications devoted to one of the
methods for production of the so-called ""slow light"" (the light with an
anomalously low group velocity) due to extremely high local steepness of the
dispersion curve of the medium. The method in point employs for this purpose
the effect of coherent population oscillations accompanied by burning of a
narrow spectral hole in the homogeneously broadened absorption spectrum.
Physical model of the effect proposed in the studies under consideration is
based on analysis of response of a nonlinear medium to a low-frequency
intensity modulation of the incident light beam. We show that all the
observations described in these papers can be easily interpreted in the
framework of the simplest model of saturable absorber and have nothing to do
with the effects of hole burning and group velocity reduction.",0509181v1
2005-09-28,A High Temperature Calcium Vapor Cell for Spectroscopy on the 4s^2 1S0 to 4s4p 3P1 Intercombination Line,"We have demonstrated a high temperature vapor cell for absorption
spectroscopy on the Ca intercombination line. The cell uses a dual chamber
design to achieve the high temperatures necessary for an optically dense vapor
while avoiding the necessity of high temperature vacuum valves and
glass-to-metal seals. We have observed over 50 percent absorption in a single
pass through the cell. Although pressure broadening in the cell prevented us
from performing saturated-absorption spectroscopy, the broadening resulted in
higher signal-to-noise ratios by allowing us to probe the atoms with
intensities much greater than the 0.2 uW/cm^2 saturation intensity of the
unbroadened transition.",0509239v1
1997-01-09,Systematic and statistical errors in homodyne measurements of the density matrix,"We study both systematic and statistical errors in radiation density matrix
measurements. First we estimate the minimum number of scanning phases needed to
reduce systematic errors below a fixed threshold. Then, we calculate the
statistical errors, intrinsic in the procedure that gives the density matrix.
We present a detailed study of such errors versus the detectors quantum
efficiency $\eta$ and the matrix indexes in the number representation, for
different radiation states. For unit quantum efficiency, and for both coherent
and squeezed states, the statistical errors of the diagonal matrix elements
saturate for large n. On the contrary, off-diagonal errors increase with the
distance from the diagonal. For non unit quantum efficiency the statistical
errors along the diagonal do not saturate, and increase dramatically versus
both $1-\eta$ and the matrix indexes.",9701010v1
2003-04-14,Ground state entanglement in quantum spin chains,"A microscopic calculation of ground state entanglement for the XY and
Heisenberg models shows the emergence of universal scaling behavior at quantum
phase transitions. Entanglement is thus controlled by conformal symmetry. Away
from the critical point, entanglement gets saturated by a mass scale. Results
borrowed from conformal field theory imply irreversibility of entanglement loss
along renormalization group trajectories. Entanglement does not saturate in
higher dimensions which appears to limit the success of the density matrix
renormalization group technique. A possible connection between majorization and
renormalization group irreversibility emerges from our numerical analysis.",0304098v4
2004-08-30,Quantum correlations in bound-soliton pairs and trains in fiber lasers,"Quantum correlations in pairs and arrays (trains) of bound solitons modeled
by the complex Ginzburg-Landau equation (CGLE) are calculated numerically, on
the basis of linearized equations for quantum fluctuations. We find strong
correlations between the bound solitons, even though the system is dissipative.
Some degree of the correlation between the photon-number fluctuations of stable
bound soliton pairs and trains is attained and saturates after passing a
certain distance. The saturation of the photon-number correlations is explained
by the action of non- conservative terms in the CGLE. Photon-number-correlated
bound soliton trains offer novel possibilities to produce multipartite
entangled sources for quantum communication and computation.",0408175v1
2005-11-09,Phase time for a tunneling particle,"We study the nature of tunneling phase time for various quantum mechanical
structures such as networks and rings having potential barriers in their arms.
We find the generic presence of Hartman effect, with superluminal velocities as
a consequence, in these systems. In quantum networks it is possible to control
the `super arrival' time in one of the arms by changing the parameters on
another arm which is spatially separated from it. This is yet another quantum
nonlocal effect. Negative time delays (time advancement) and `ultra Hartman
effect' with negative saturation times have been observed in some parameter
regimes. In presence and absence of Aharonov-Bohm (AB) flux quantum rings show
Hartman effect. We obtain the analytical expression for the saturated phase
time. In the opaque barrier regime this is independent of even the AB flux
thereby generalizing the Hartman effect. We also briefly discuss the concept of
""space collapse or space destroyer"" by introducing a free space in between two
barriers covering the ring. Further we show in presence of absorption the
reflection phase time exhibits Hartman effect in contrast to the transmission
phase time.",0511089v1
2007-01-05,Quantum jumps of saturation level rigidity and anomalous oscillations of level number variance in the semiclassical spectrum of a modified Kepler problem,"We discover quantum Hall like jumps in the saturation spectral rigidity in
the semiclassical spectrum of a modified Kepler problem as a function of the
interval center. These jumps correspond to integer decreases of the radial
winding numbers in classical periodic motion. We also discover and explain
single harmonic dominated oscillations of the level number variance with the
width of the energy interval. The level number variance becomes effectively
zero for the interval widths defined by the frequency of the shortest periodic
orbit. This signifies that there are virtually no variations from sample to
sample in the number of levels on such intervals.",0701023v1
2007-03-20,Atom-wall dispersive forces from master equation formalism,"Using the general expressions for level shifts obtained from the master
equation for a small system interacting with a large one considered as a
reservoir, we calculate the dispersive potentials between an atom and a wall in
the dipole approximation. We analyze in detail the particular case of a
two-level atom in the presence of a perfectly conducting wall. We study the van
der Waals as well as the resonant interactions. All distance regimes as well as
the high and low temperature regimes are considered. We show that the
Casimir-Polder interaction can not be considered as a direct result of the
vacuum fluctuations only. Concerning the interaction between the atom and the
wall at high temperature, which show that a saturation of the potential for all
distances occurs. This saturated potential coincides exactly with that obtained
in the London-van der Waals limit.",0703186v1
2007-04-02,Causal dissipative hydrodynamics for QGP fluid in 2+1 dimensions,"In 2nd order causal dissipative theory, space-time evolution of QGP fluid is
studied in 2+1 dimensions. Relaxation equations for shear stress tensors are
solved simultaneously with the energy-momentum conservation equations.
Comparison of evolution of ideal and viscous QGP fluid, initialized under the
same conditions, e.g. same equilibration time, energy density and velocity
profile, indicate that in a viscous dynamics, energy density or temperature of
the fluid evolve slowly, than in an ideal fluid. Cooling gets slower as
viscosity increases. Transverse expansion also increases in a viscous dynamics.
For the first time we have also studied elliptic flow of 'quarks' in causal
viscous dynamics. It is shown that elliptic flow of quarks saturates due to
non-equilibrium correction to equilibrium distribution function, and can not be
mimicked by an ideal hydrodynamics.",0704.0134v2
2007-04-18,Multiple quantum wells for passive ultra short laser pulse generation,"Solid state lasers are demanding independent control in the gain media and
cavity loss to achieve ultra short laser pulses using passive mode-locking.
Recently, laser mode-locking is achieved with a MBE structure with multiple
quantum wells, designed to achieve two functions; Bragg mirror and changes in
absorption to control the cavity dynamics. The use of an AlGaAs/AlAs Bragg
mirror with a 15 nm GaAs saturable absorber used in a Cr:LiSAF tuneable laser
proved to be effective to produce femtosecond pulses. The use of saturable
absorbers thus far is a trial and error procedure that is changing due to the
correlation with more predictive procedures.",0704.2437v1
2007-04-19,Average $p_t$ as a probe of high energy QCD dynamics,"Average transverse momentum of hadrons produced in high energy collisions is
proposed as a diagnostic probe of high density (saturation) physics. We show
that by introducing and varying a transverse momentum cutoff in the definition
of the average transverse momentum, one can eliminate the uncertainty in the
overall magnitude of the leading order hadron production cross section in high
energy collisions, and semi-quantitatively map the different dynamical regions
predicted by the saturation physics. We discuss the applications of this method
to pion production at RHIC and LHC and make quantitative predictions for the
average transverse momentum of produced pions in the kinematics appropriate for
the RHIC and LHC experiments.",0704.2628v1
2007-05-10,Manifestations of fine features of the density of states in the transport properties of KOs2O6,"We performed high-pressure transport measurements on high-quality single
crystals of KOs2O6, a beta-pyrochlore superconductor. While the resistivity at
high temperatures might approach saturation, there is no sign of saturation at
low temperatures, down to the superconducting phase. The anomalous resistivity
is accompanied by a nonmetallic behavior in the thermoelectric power (TEP) up
to temperatures of at least 700 K, which also exhibits a broad hump with a
maximum at 60 K. The pressure influences mostly the low-energy electronic
excitations. A simple band model based on enhanced density of states in a
narrow window around the Fermi energy (EF) explains the main features of this
unconventional behavior in the transport coefficients and its evolution under
pressure.",0705.1401v1
2007-05-22,Study of sediment transport in the saltation regime,"We present a study of sediment transport in the creeping and saltation
regime. In our model, a bed of particles is simulated with the conventional
event-driven method. The particles are considered as hard disks in a 2d domain,
with periodic boundary conditions in horizontal direction. The flow of the
fluid over this bed of particles is modeled by imposing a force on each
particle that depends on the velocity of the fluid and its height above the
bed. We considered two velocity profiles for the fluid, parabolic and
logarithmic. The first one models laminar flow and the second corresponds to
turbulent flow. For each case we investigated the behavior of the saturated
flux. We found that for the logarithmic profile, the saturated flux shows a
quadratic increase with the strength of the flow, and for parabolic profile, a
cubic increase. The velocity distribution functions are used to interpret the
results.",0705.3143v1
2007-06-01,Effect of Electron Interaction on Statistics of Conductance Oscillations in Open Quantum Dots: Does the Dephasing Time Saturate?,"We perform self-consistent quantum transport calculations in open quantum
dots taking into account the effect of electron interaction. We demonstrative
that in the regime of the ultralow temperatures $2\pi k_BT\lesssim\Delta$
($\Delta $ being the mean level spacing), the electron interaction strongly
affects the conductance oscillations and their statistics leading to a drastic
deviation from the corresponding predictions for noninteracting electrons. In
particular, it causes smearing of conductance oscillations, which is similar to
the effect of temperature or inelastic scattering. For $2\pi k_BT\gtrsim\Delta$
the influence of electron interaction on the conductance becomes strongly
diminished. Our calculations (that are free from phenomenological parameters of
the theory) are in good quantitative agreement with the observed ultralow
temperature statistics (Huibers \textit{et al.}, Phys. Rev. Lett. \textbf{81},
1917 (1998)). Our findings question a conventional interpretation of the
ultralow temperature saturation of the coherence time in open dots which is
based on the noninteracting theories where the electron interaction is
neglected and the agrement with the experiment is achieved by introducing
additional phenomenological channels of dephasing.",0706.0125v1
2007-06-04,High-Dispersion Optical Spectra of Nearby Stars Younger Than The Sun,"We present high-dispersion (R~16,000) optical (3900-8700 A) spectra of 390
stars obtained with the Palomar 60 inch telescope. The majority of stars
observed are part of the Spitzer Legacy Science Program ""The Formation and
Evolution of Planetary Systems."" Through detailed analysis we determine stellar
properties for this sample, including radial and rotational velocities, Li I
6708 and Ha equivalent widths, the chromospheric activity index R'_HK, and
temperature- and gravity-sensitive line ratios. Several spectroscopic binaries
are also identified. From our tabulations, we illustrate basic age- and
rotation-related correlations among measured indices. One novel result is that
Ca II chromospheric emission appears to saturate at vsini values above ~30
km/s, similar to the well established saturation of X-rays that originate in
the spatially separate coronal regions.",0706.0542v1
2007-06-07,Simulation of symmetric nuclei and the role of Pauli potential in binding energies and radii,"It is shown that the use of a density dependent effective Pauli potential
together with a nucleon-nucleon interaction potential plays a crucial role to
reproduce not only the binding energies but also the matter root mean square
radii of medium mass range spin-isospin saturated nuclei. This study is
performed with a semiclassical Monte Carlo many-body simulation within the
context of a simplified nucleon-nucleon interaction to focus on the effect of
the genuine correlations due to the fermionic nature of nucleons. The procedure
obtained is rather robust and it does not depend on the detailed features of
the nucleon-nucleon interaction. For nuclei below saturation the density
dependence may be represented in terms either of the nucleon number, $A$, or
the associated Fermi momenta. When testing the simulation procedure for
idealized ""infinite"" symmetric nuclear matter within the corresponding range of
densities, it turns out that finite size effects affect the Pauli potential
strength parametrization in systems up to about 120 particles while remaining
approximately stable for larger systems.",0706.0958v2
2007-06-28,Free flux flow magneto-resistance of single crystal BSCCO,"Measurement of the free flux flow resistance in monocrystalline highly
anisotropic BSCCO reveals a low field magneto-resistive effect nearly 100 times
that expected from a naive application of the Bardeen-Stephen rule R/Rn =
B/Bc2. Furthermore in the vortex solid phase it saturates to a constant value
at about Hc2/100 as if the vortices were moving 100 times faster than expected.
An attempt to account for this behavior by a combination of sheared planar
vortex flow obeying the BS rule and the quasi-particle c axis conductivity
between the Josephson coupled superconducting planes is only partially
successful. In particular it is unable to account for the saturation feature
which occurs in both optimally and underdoped samples in the low temperature
vortex solid phase.",0706.4261v1
2007-07-16,Constraining interacting dark energy models with flux destabilization,"A destabilization in the transfer energy flux from the vacuum to radiation,
for two vacuum decay laws relevant to the dark energy problem, is analyzed
using the Landau-Lifshitz fluctuation hydrodynamic theory. Assuming thermal (or
near thermal) equilibrium between the vacuum and radiation, at the earliest
epoch of the Universe expansion, we show that the law due to
renormalization-group running of the cosmological constant term, with
parameters chosen not to spoil the primordial nucleosynthesis scenario, does
soon drive the flux to fluctuate beyond its statistical average value thereby
distorting the cosmic background radiation spectrum beyond observational
limits. While the law coming from the saturated holographic dark energy does
not lead the flux to wildly fluctuate, a more realistic non--saturated form
shows again such anomalous behavior.",0707.2299v2
2007-07-30,Heating and Turbulence Driving by Galaxy Motions in Galaxy Clusters,"Using three-dimensional hydrodynamic simulations, we investigate heating and
turbulence driving in an intracluster medium (ICM) by orbital motions of
galaxies in a galaxy cluster. We consider Ng member galaxies on isothermal and
isotropic orbits through an ICM typical of rich clusters. An introduction of
the galaxies immediately produces gravitational wakes, providing perturbations
that can potentially grow via resonant interaction with the background gas.
When Ng^{1/2}Mg_11 < 100, where Mg_11 is each galaxy mass in units of 10^{11}
Msun, the perturbations are in the linear regime and the resonant excitation of
gravity waves is efficient to generate kinetic energy in the ICM, resulting in
the velocity dispersion sigma_v ~ 2.2 Ng^{1/2}Mg_11 km/s. When Ng^{1/2}Mg_11 >
100, on the other hand, nonlinear fluctuations of the background ICM destroy
galaxy wakes and thus render resonant excitation weak or absent. In this case,
the kinetic energy saturates at the level corresponding to sigma_v ~ 220 km/s.
The angle-averaged velocity power spectra of turbulence driven in our models
have slopes in the range of -3.7 to -4.3. With the nonlinear saturation of
resonant excitation, none of the cooling models considered are able to halt
cooling catastrophe, suggesting that the galaxy motions alone are unlikely to
solve the cooling flow problem.",0707.4330v1
2007-08-30,Aggregate Dynamics in an Evolutionary Network Model,"We analyze a model of interacting agents (e.g. prebiotic chemical species)
which are represended by nodes of a network, whereas their interactions are
mapped onto directed links between these nodes. On a fast time scale, each
agent follows an eigendynamics based on catalytic support from other nodes,
whereas on a much slower time scale the network evolves through selection and
mutation of its nodes-agent. In the first part of the paper, we explain the
dynamics of the model by means of characteristic snapshots of the network
evolution and confirm earlier findings on crashes an recoveries in the network
structure. In the second part, we focus on the aggregate behavior of the
network dynamics. We show that the disruptions in the network structure are
smoothed out, so that the average evolution can be described by a growth regime
followed by a saturation regime, without an initial random regime. For the
saturation regime, we obtain a logarithmic scaling between the average
connectivity per node $\mean{l}_{s}$ and a parameter $m$, describing the
average incoming connectivity, which is independent of the system size $N$.",0708.4212v1
2007-09-10,On the Dipole Swing and the Search for Frame Independence in the Dipole Model,"Small-x evolution in QCD is conveniently described by Mueller's dipole model
which, however, does not include saturation effects in a way consistent with
boost invariance. In this paper we first show that the recently studied zero
and one dimensional toy models exhibiting saturation and explicit boost
invariance can be interpreted in terms positive definite k-> k+1 dipole
vertices. Such k-> k+1 vertices can in the full model be generated by combining
the usual dipole splitting with k-1 simultaneous dipole swings. We show that,
for a system consisting of N dipoles, one needs to combine the dipole splitting
with at most N-1 simultaneous swings in order to generate all colour
correlations induced by the multiple dipole interactions.",0709.1371v2
2007-09-12,"""Slow Light"" and ""Slow Current""","It is shown that the effect of hole-burning under conditions of coherent
population oscillations as well as the light pulse delay in a saturable
absorber (a modification of the ""slow light"" effect) can be interpreted, in a
comprehensive way, in terms of {\it intensity spectrum} of the light and {\it
intensity-related susceptibility} of the non-linear medium. The physical
content of these effects is illustrated by a simple electric circuit with a
non-linear resistor which realizes a full analog of the saturable absorber. In
this case the effect of hole-burning in the absorption spectrum of the medium
is converted in to the effect of hole-burning in the frequency dependence of
resistance of the non-linear resistor and the effect of ""slow light"" -- in to
the effect of ""slow current"".",0709.1764v1
2007-09-26,High-resolution saturation spectroscopy of singly-ionized iron with a pulsed uv laser,"We describe the design and realization of a scheme for uv laser spectroscopy
of singly-ionized iron (Fe II) with very high resolution. A buffer-gas cooled
laser ablation source is used to provide a plasma close to room temperature
with a high density of Fe II. We combine this with a scheme for pulsed-laser
saturation spectroscopy to yield sub-Doppler resolution. In a demonstration
experiment, we have examined an Fe II transition near 260 nm, attaining a
linewidth of about 250 MHz. The method is well-suited to measuring transition
frequencies and hyperfine structure. It could also be used to measure small
isotope shifts in isotope-enriched samples.",0709.4032v1
2007-09-28,Dynamics of the triple contact line on a non-isothermal heater at partial wetting,"The dynamics of the triple gas-liquid-solid contact line is analysed for the
case where the gas is the saturated vapour corresponding to the liquid, like in
the vapour bubble in boiling. It is shown that even small superheating (with
respect to the saturation temperature) causes evaporation of the adsorption
liquid film and the true triple contact is established. It is shown that the
hydrodynamic contact line singularity cannot be relaxed with the Navier slip
condition under such circumstances. Augmented with the second derivative slip
condition is proposed to be applied. For the partial wetting conditions, a
non-stationary contact line problem where the contact line motion is caused by
evaporation or condensation is treated in the lubrication approximation in the
vicinity of the contact line. High heat fluxes in this region require the
transient heat conduction inside the heater to be accounted for. Two 2D
problems, those of drop retraction with no phase change and of drop evaporation
are solved and analysed as illustrations of the proposed approach.",0709.4631v3
2007-10-09,"Controlling suction by vapour equilibrium technique at different temperatures, application to the determination of the water retention properties of MX80 clay","Problems related to unsaturated soils are frequently encountered in
geotechnical or environmental engineering works. In most cases, for the purpose
of simplicity, the problems are studied by considering the suction effects on
volume change or shear strength under isothermal conditions. Under isothermal
condition, very often, a temperature independent water retention curve is
considered in the analysis, which is obviously a simplification. When the
temperature changes are too significant to be neglected, it is necessary to
account for the thermal effects. In this paper, a method for controlling
suction using the vapour equilibrium technique at different temperatures is
presented. First, calibration of various saturated saline solutions was carried
out from temperature of 20 degrees C to 60 degrees C. A mirror psychrometer was
used for the measurement of relative humidity generated by saturated saline
solutions at different temperatures. The results obtained are in good agreement
with the data from the literature. This information was then used to determine
the water retention properties of MX80 clay, which showed that the retention
curve is shifting down with increasing of temperature.",0710.1850v1
2007-10-15,Large nonlinear absorption and refraction coefficients of carbon nanotubes estimated from femtosecond Z-scan measurements,"Nonlinear transmission of 80 and 140 femtosecond pulsed light with $0.79 \mu
m$ wavelength through single walled carbon nanotubes suspended in water
containing sodium dodecyl sulphate is studied. Pulse-width independent
saturation absorption and negative cubic nonlinearity are observed,
respectively, in open and closed aperture Z-scan experiments. The theoretical
expressions derived to analyze the z-dependent transmission in the saturable
limit require two photon absorption coefficient $\beta_0\sim$ $1.4 cm/MW$ and a
nonlinear index $\gamma \sim -5.5 \times10^{-11} cm^2/W$ to fit the data.",0710.2721v2
2007-10-15,Current saturation and Coulomb interactions in organic single-crystal transistors,"Electronic transport through rubrene single-crystal field effect transistors
(FETs) is investigated experimentally in the high carrier density regime (n ~
0.1 carrier/molecule). In this regime, we find that the current does not
increase linearly with the density of charge carriers, and tends to saturate.
At the same time, the activation energy for transport unexpectedly increases
with increasing n. We perform a theoretical analysis in terms of a well-defined
microscopic model for interacting Frohlich polarons, that quantitatively
accounts for our experimental observations. This work is particularly
significant for our understanding of electronic transport through organic FETs.",0710.2845v2
2007-10-29,Deep inelastic scattering off a N=4 SYM plasma at strong coupling,"By using the AdS/CFT correspondence we study the deep inelastic scattering of
an R-current off a N=4 supersymmetric Yang-Mills (SYM) plasma at finite
temperature and strong coupling. Within the supergravity approximation valid
when the number of colors is large, we compute the structure functions by
solving Maxwell equations in the space-time geometry of the AdS_5 black
three-brane. We find a rather sharp transition between a low energy regime
where the scattering is weak and quasi-elastic, and a high-energy regime where
the current is completely absorbed. The critical energy for this transition
determines the plasma saturation momentum in terms of its temperature T and the
Bjorken x variable: Q_s=T/x. These results suggest a partonic picture for the
plasma where all the partons have transverse momenta below the saturation
momentum and occupation numbers of order one.",0710.5297v2
2007-11-19,Wilson line correlator in the MV model: relating the glasma to deep inelastic scattering,"In the color glass condensate framework the saturation scale measured in deep
inelastic scattering of high energy hadrons and nuclei can be determined from
the correlator of Wilson lines in the hadron wavefunction. These same Wilson
lines give the initial condition of the classical field computation of the
initial gluon multiplicity and energy density in a heavy ion collision. In this
paper the Wilson line correlator in both adjoint and fundamental
representations is computed using exactly the same numerical procedure that has
been used to calculate gluon production in a heavy ion collision. In particular
the discretization of the longitudinal coordinate has a large numerical effect
on the relation between the color charge density parameter g^2 mu and the
saturation scale Qs. Our result for this relation is Qs = 0.6 g^2 mu, which
results in the classical Yang-Mills value for the ""gluon liberation
coefficient"" c = 1.1.",0711.3039v3
2007-12-17,Impact parameter dependent colour glass condensate dipole model,"We show that the colour glass condensate dipole model of Iancu, Itakura and
Munier, improved to include the impact parameter dependence, gives a good fit
to the total gamma* p cross section measured at HERA if the anomalous dimension
at the saturation scale, gamma_s, is treated as a free parameter. We find that
the optimum value of gamma_s = 0.46 is close to the value determined from
numerical solution of the Balitsky-Kovchegov equation. The impact parameter
dependent saturation scale is generally less than 0.5 GeV^2 in the HERA
kinematic regime for the most relevant impact parameters b ~ 2-3 GeV^{-1}. We
compare predictions of the model to data on the longitudinal and heavy flavour
structure functions, exclusive diffractive vector meson production and deeply
virtual Compton scattering at HERA. The model is found to be deficient for
observables sensitive to moderately small dipole sizes, where an alternative
model with explicit DGLAP evolution performs better. The energy dependence of
exclusive diffractive processes is shown to provide an important discriminator
between different dipole model cross sections.",0712.2670v2
2007-12-21,A nuclear matter description based on quark structure of the nucleon and pion exchange,"We investigate the possibility to describe nuclear matter in an approach
constrained by the prominent features of quantum chromodynamics. We mapped the
in-medium nucleon self-energies of a point coupling relativistic mean-field
model on self-energies obtained in effective theories of QCD. More precisely,
the contributions to the nucleon self-energy have been separated into the short
range part, driven principally by the quark structure of the nucleon described
in a quark-diquark picture, and the long range part, dictated by pion dynamics
and determined using in-medium chiral perturbation theory. A saturation point,
although unrealistic, is obtained without any free parameter. A realistic
description of nuclear matter saturation properties has been obtained with the
inclusion of a small phenomenological correction term to the short range part
of the self-energy.",0712.3661v3
2007-12-21,Front motion and localized states in an asymmetric bistable activator-inhibitor system with saturation,"We study the spatiotemporal properties of coherent states (peaks, holes, and
fronts) in a bistable activator-inhibitor system that exhibits biochemical
saturated autocatalysis, and in which fronts do not preserve spatial parity
symmetry. Using the Gierer-Meinhardt prototype model, we find the conditions in
which two distinct pinning regions are formed. The first pinning type is known
in the context of variational systems while the second is structurally
different due to the presence of a heteroclinic bifurcation between two uniform
states. The bifurcation also separates the parameter regions of
counterpropagating fronts, leading in turn to the growth or contraction of
activator domains. These phenomena expand the range of pattern formation theory
and its biomedical applications: activator domain retraction suggests potential
therapeutic strategies for patterned pathologies, such as cardiovascular
calcification.",0712.3790v2
2008-01-01,Unitarity Constraints on Semi-hard Jet Production in Impact Parameter Space,"The perturbative QCD formula for minijet production consitutes an important
ingredient in models describing the total cross section and multiparticle
production in hadron-hadron scattering at high energies. Using arguments based
on s-channel unitarity we set bounds on the minimum value of p_T for which the
leading twist minijet formula can be used. For large impact parameters where
correlations between partons appear to be small we find that the minimum value
of p_T should be greater than 2.5 GeV for LHC energies and greater than 3.5 GeV
for cosmic ray energies of about 50 TeV. We also argue that for collisions with
values of impact parameters typical for heavy particle production the values of
minimum p_T are likely to be considerably larger. We also analyze and quantify
the potential role of saturation effects in the gluon density. We find that
although saturation effects alone are not sufficient to restore unitarity, they
are likely to play an important role at LHC energies.",0801.0303v1
2008-01-03,Albite feldspar dissolution kinetics as a function of the Gibbs free energy at high pCO_2,"We are currently measuring the dissolution kinetics of albite feldspar at 100
deg C in the presence of high levels of dissolved CO_2 (pCO_2 = 9 MPa) as a
function of the saturation state of the feldspar (Gibbs free energy of
reaction, \Delta G). The experiments are conducted using a flow through
reactor, thereby allowing the dissolution reactions to occur at a fixed pH and
at constant, but variable saturation states. Preliminary results indicate that
at far-from-equilibrium conditions, the dissolution kinetics of albite are
defined by a rate plateau, with R \approx 5.0 x 10^{-10} mol m^{-2} s^{-1} at
-70 < \Delta G < -40 kJ mol^{-1}. At \Delta G > -40 kJ mol^{-1}, the rates
decrease sharply, revealing a strong inverse relation between the dissolution
rate and free energy. Based on the experiments carried out to date, the
dissolution rate-free energy data correspond to a highly non-linear and
sigmoidal relation, in accord with recent studies.",0801.0548v1
2008-01-04,Classical Dynamics of the Time-Dependent Elliptical Billiard,"In this work we study the nonlinear dynamics of the static and the driven
ellipse. In the static case, we find numerically an asymptotical algebraic
decay for the escape of an ensemble of non-interacting particles through a
small hole due to the integrable structure of the phase space of the system.
Furthermore, for a certain hole position a saturation value in the decay that
can be tuned arbitrarily by varying the eccentricity of the ellipse is observed
and explained. When applying harmonic boundary oscillations this saturation
value caused by librator type orbits is gradually destroyed via two fundamental
processes which are discussed in detail. As a result, an amplitude dependent
emission rate is obtained in the long time behavior of the decay, suggesting
that the driven elliptical billiard can be used as a controllable source of
particles.",0801.0686v1
2008-01-22,Multi-$\bar{K}$ nuclei and kaon condensation,"We extend previous relativistic mean-field (RMF) calculations of multi-$\bar
K$ nuclei, using vector boson fields with SU(3) PPV coupling constants and
scalar boson fields constrained phenomenologically. For a given core nucleus,
the resulting $\bar K$ separation energy $B_{\bar K}$, as well as the
associated nuclear and $\bar K$-meson densities, saturate with the number
$\kappa$ of $\bar K$ mesons for $\kappa > \kappa_{\rm sat} \sim 10$. Saturation
appears robust against a wide range of variations, including the RMF nuclear
model used and the type of boson fields mediating the strong interactions.
Because $B_{\bar K}$ generally does not exceed 200 MeV, it is argued that
multi-$\bar K$ nuclei do not compete with multihyperonic nuclei in providing
the ground state of strange hadronic configurations and that kaon condensation
is unlikely to occur in strong-interaction self-bound strange hadronic matter.
Last, we explore possibly self-bound strange systems made of neutrons and
${\bar K}^0$ mesons, or protons and $K^-$ mesons, and study their properties.",0801.3335v2
2008-02-12,Nonlinear Saturation of g-modes in Proto-Neutron Stars: Quieting the Acoustic Engine,"According to Burrows et al.'s acoustic mechanism for core-collapse supernova
explosions, the primary, l=1, g-mode in the core of the proto-neutron star is
excited to an energy of ~ 10^{50} ergs and damps by the emission of sound
waves. Here we calculate the damping of the primary mode by the parametric
instability, i.e., by nonlinear, 3-mode coupling between the low-order primary
mode and pairs of high-order g-modes. We show that the primary mode is strongly
coupled to highly resonant, neutrino damped pairs with n>10; such short
wavelength interactions cannot be resolved in the simulations. We find that the
parametric instability saturates the primary mode energy at ~10^{48} ergs, well
below the energy needed to drive an explosion. We therefore conclude that
acoustic power is unlikely to be energetically significant in core-collapse
supernova explosions.",0802.1522v3
2008-02-13,Effects of spatial dispersion in near-field radiative heat transfer between two parallel metallic surfaces,"We study the heat transfer between two parallel metallic semi-infinite media
with a gap in the nanometer-scale range. We show that the near-field radiative
heat flux saturates at distances smaller than the metal skin depth when using a
local dielectric constant and investigate the origin of this effect. The effect
of non-local corrections is analysed using the Lindhard-Mermin and
Boltzmann-Mermin models. We find that local and non-local models yield the same
heat fluxes for gaps larger than 2 nm. Finally, we explain the saturation
observed in a recent experiment as a manifestation of the skin depth and show
that heat is mainly dissipated by eddy currents in metallic bodies.",0802.1899v1
2008-02-20,Gluon multiplicity in coherent diffraction of onium on a heavy nucleus,"We derive the cross section for the diffractive gluon production in high
energy onium-nucleus collisions that includes the low-x evolution effects in
the rapidity interval between the onium and the produced gluon and in the
rapidity interval between the gluon and the target nucleus. We analyze our
result in two limiting cases: when the onium size is much smaller than the
saturation scale and when its size is much larger than the saturation scale. In
the later case the gluon multiplicity is very small in the quasi-classical case
and increases when the low-x evolution effects in onium become significant. We
discuss the implications of our result for the RHIC, LHC and EIC phenomenology.",0802.2954v2
2008-02-25,Data Traffic Dynamics and Saturation on a Single Link,"The dynamics of User Datagram Protocol (UDP) traffic over Ethernet between
two computers are analyzed using nonlinear dynamics which shows that there are
two clear regimes in the data flow: free flow and saturated. The two most
important variables affecting this are the packet size and packet flow rate.
However, this transition is due to a transcritical bifurcation rather than
phase transition in models such as in vehicle traffic or theorized large-scale
computer network congestion. It is hoped this model will help lay the
groundwork for further research on the dynamics of networks, especially
computer networks.",0802.3554v3
2008-03-27,Optimal factorial designs for cDNA microarray experiments,"We consider cDNA microarray experiments when the cell populations have a
factorial structure, and investigate the problem of their optimal designing
under a baseline parametrization where the objects of interest differ from
those under the more common orthogonal parametrization. First, analytical
results are given for the $2\times 2$ factorial. Since practical applications
often involve a more complex factorial structure, we next explore general
factorials and obtain a collection of optimal designs in the saturated, that
is, most economic, case. This, in turn, is seen to yield an approach for
finding optimal or efficient designs in the practically more important nearly
saturated cases. Thereafter, the findings are extended to the more intricate
situation where the underlying model incorporates dye-coloring effects, and the
role of dye-swapping is critically examined.",0803.3911v1
2008-03-31,Stabilization of dipole solitons in nonlocal nonlinear media,"We address the stabilization of dipole solitons in nonlocal nonlinear
materials by two different approaches. First, we study the properties of such
solitons in thermal nonlinear media, where the refractive index landscapes
induced by laser beams strongly depend on the boundary conditions and on the
sample geometry. We show how the sample geometry impacts the stability of
higher-order solitons in thermal nonlinear media and reveal that dipole
solitons can be made dynami-cally stable in rectangular geometries in contrast
to their counterparts in thermal samples with square cross-section. Second, we
discuss the impact of the saturation of the nonlocal nonlinear response on the
properties of multipole solitons. We find that the saturable response also
stabi-lizes dipole solitons even in symmetric geometries, provided that the
input power exceeds a criti-cal value.",0803.4398v1
2008-04-01,Novel Sets of Coupling Expansion Parameters for low-energy pQCD,"In quantum theory, physical amplitudes are usually presented in the form of
Feynman perturbation series in powers of coupling constant $\al .$ However, it
is known that these amplitudes are not regular functions at $\alpha=0 .$
  For QCD, we propose new sets of expansion parameters ${\bf w}_k(\as)$ that
reflect singularity at $\as=0 $ and should be used instead of powers $\as^k.$
Their explicit form is motivated by the so called Analytic Perturbation Theory.
These parameters reveal saturation in a strong coupling case at the level
$\as^{eff}(\as\gg1)={\bf w}_1(\as\gg 1) \sim 0.5 .$ They can be used for
quanitative analysis of divers low-energy amplitudes.
  We argue that this new picture with non-power sets of perturbation expansion
parameters, as well as the saturation feature, is of a rather general nature.",0804.0083v1
2008-04-01,Soliton structures in a molecular chain model with saturation,"In the present work, we study, by means of a one-dimensional lattice model,
the collective excitations corresponding to intra molecular ones of a chain
like proteins. It is shown that such excitations are described by the Nonlinear
Schrodinger equation with saturation. The solutions obtained here are the bell
solitons, bubbles, kinks and crowdons. Since they belong to different sectors
on the parametric space, the bubble condensation could give place to some
important changes of face in this kind of nonlinear system. Additionally, it is
shown that the limiting velocity of the solitons is the velocity of sound waves
corresponding to longitudinal vibrations of molecules.",0804.0222v2
2008-04-01,Decoherence of Bell states by local interactions with a dynamic spin environment,"We study the evolution of a system of two qubits, each of which interacts
locally with a spin chain with nontrivial internal Hamiltonian. We present an
exact solution to this problem and analyze the dependence of decoherence on the
distance between the interaction sites. In the strong coupling regime we find
that decoherence increases with increasing distance. In the weak coupling
regime the dependence of decoherence with distance is not generic (i.e., it
varies according to the initial state). Decoherence becomes independent of
distance when the latter is over a saturation length $l$. Numerical results for
the Ising chain suggest that the saturation scale is related to the correlation
length $\xi$. For strong coupling we display evidence of the existence of
non--Markovian effects (such as environment--induced interactions between the
qubits). As a consequence the system can undergo a quasiperiodic sequence of
``sudden deaths and revivals'' of entanglement, with a time scale related to
the distance between qubits.",0804.0241v2
2008-05-31,The Emerging QCD Frontier: The Electron Ion Collider,"The self-interactions of gluons determine all the unique features of QCD and
lead to a dominant abundance of gluons inside matter already at moderate $x$.
Despite their dominant role, the properties of gluons remain largely
unexplored. Tantalizing hints of saturated gluon densities have been found in
$e$+p collisions at HERA, and in d+Au and Au+Au collisions at RHIC. Saturation
physics will have a profound influence on heavy-ion collisions at the LHC. But
unveiling the collective behavior of dense assemblies of gluons under
conditions where their self-interactions dominate will require an Electron-Ion
Collider (EIC): a new facility with capabilities well beyond those In this
paper I outline the compelling physics case for $e$+A collisions at an EIC and
discuss briefly the status of machine design concepts. of any existing
accelerator.",0806.0048v1
2008-06-04,Particle Multiplicities in Nuclear Collisions at the LHC from Saturation Physics,"The inclusion of running coupling effects in the BK-JIMWLK evolution
equations considerably reduces the energy dependence of the saturation scale
with respect to previous estimates based on fits to HERA data. We discuss how
such slowdown affects the expectations for particle multiplicities in Pb-Pb
collisions at LHC energies. Our prediction is based on the use of
k_t-factorization and on the use of unintegrated gluon distributions taken from
the numerical solutions of the BK equation with running coupling. We obtain a
central value dN/d\eta(sqrt{s}=5.5 TeV)(\eta=0)~1390.",0806.0672v1
2008-06-04,Relativistic mean-field theory applied to the study of neutron star properties,"Nuclear physics can be applied in various ways to the study of neutron stars.
This thesis reports on one such application, where the relativistic mean-field
approximation has been employed to calculate the equations of state of matter
in the neutron star interior. In particular the equations of state of nuclear
and neutron star matter of the NL3, PK1 and FSUGold parameter sets were
derived. A survey of available literature on neutron stars is presented and we
use the derived equations of state to reproduce the properties of saturated
nuclear matter as well as the mass-radius relationship of a static, spherical
symmetric neutron star. Results are compared to published values of the
properties of saturated nuclear matter and to available observational data of
the mass-radius relationship of neutron stars.",0806.0747v2
2008-06-30,On Internal Consistency of Holographic Dark Energy Models,"Holographic dark energy (HDE) models, underlain by an effective quantum field
theory (QFT) with a manifest UV/IR connection, have become a convincing
candidate for the dark energy in the universe. On the other hand, the maximum
number of quantum states a conventional QFT in the box of size $L$ is capable
to describe, refer to those boxes which are on the brink of experiencing a
sudden collapse to a black hole. Another restriction on the underlying QFT is
that the UV cutoff, which cannot be chosen independently of the IR cutoff and
therefore becomes a function of time in a cosmological setting, should stay the
largest energy scale even in the standard cosmological epochs preceding a dark
energy dominated one. We show that, irrespective of whether one deals with the
saturated form of HDE or takes a certain degree of non-saturation in the past,
the above restrictions cannot be met in a radiation-dominated universe, an
epoch in the history of the universe which is expected to be perfectly
describable within conventional QFT.",0806.4825v2
2008-07-01,Deconfinement phase transition in hybrid neutron stars from the Brueckner theory with three-body forces and a quark model with chiral mass scaling,"We study the properties of strange quark matter in equilibrium with normal
nuclear matter. Instead of using the conventional bag model in quark sector, we
achieve the confinement by a density-dependent quark mass derived from
in-medium chiral condensates. In nuclear matter, we adopt the equation of state
from the Brueckner-Bethe-Goldstone approach with three-body forces. It is found
that the mixed phase can occur, for a reasonable confinement parameter, near
the normal nuclear saturation density, and goes over into pure quark matter at
about 5 times the saturation. The onset of mixed and quark phases is compatible
with the observed class of low-mass neutron stars, but it hinders the
occurrence of kaon condensation.",0807.0200v1
2008-07-02,A note on the connection between the universal relaxation bound and the covariant entropy bound,"A recently proposed universal lower-bound to the characteristic relaxation
times of perturbed thermodynamic systems, derived from quantum information
theory and (classical) thermodynamics and known to be saturated for (certain)
black holes, is investigated in the light of the gravity/thermodynamics
connection. A statistical-mechanical property, unrelated to gravity, essential
for the validity of the generalized covariant entropy bound, namely the
existence of a lower-limiting value l* for the size of thermodynamic systems,
is found to provide a way to understand the universal relaxation bound, thus
regardless of the kind of foundations (i.e. whether conventional or
information-based) of the statistical-mechanical description. As a by-product
an example of a conventional system (i.e. not a black hole) seemingly
saturating the universal relaxation bound is provided.",0807.0300v2
2008-07-09,Ultrafast switching time and third order nonlinear coefficients of microwave treated single walled carbon nanotube suspensions,"Microwave treated water soluble and amide functionalized single walled carbon
nanotubes have been investigated using femtosecond degenerate pump-probe and
nonlinear transmission experiments. The time resolved differential transmission
using 75 femtosecond pulse with the central wavelength of 790 nm shows a
bi-exponential ultrafast photo-bleaching with time constants of of 160 fs (130
fs) and 920 fs (300 fs) for water soluble (amide functionalized) nanotubes.
Open and closed aperture z-scans show saturation absorption and positive
(negative) nonlinear refraction for water soluble (amide functionalized)
nanotubes. Two photon absorption coefficient,beata ~250 cm/GW (650 cm/GW) and
nonlinear index, gamma ~ 15 cm^2/pW (-30 cm^2/pW) are obtained from the
theoretical fit in the saturation limit to the data for two types of nanotubes.",0807.1441v1
2008-07-21,Characterisation of a silicon photomultiplier device for applications in liquid argon based neutrino physics and dark matter searches,"The performance of a silicon photomultiplier has been assessed at low
temperature in order to evaluate its suitability as a scintillation readout
device in liquid argon particle physics detectors. The gain, measured as 2.1E6
for a constant over-voltage of 4V was measured between 25degC and -196degC and
found to be invariant with temperature, the corresponding single photoelectron
dark count rate reducing from 1MHz to 40Hz respectively. Following multiple
thermal cycles no deterioration in the device performance was observed. The
photon detection efficiency (PDE) was assessed as a function of photon
wavelength and temperature. For an over-voltage of 4V, the PDE, found again to
be invariant with temperature, was measured as 25% for 460nm photons and 11%
for 680nm photons. Device saturation due to high photon flux rate, observed
both at room temperature and -196degC, was again found to be independent of
temperature. Although the output signal remained proportional to the input
signal so long as the saturation limit was not exceeded, the photoelectron
pulse resolution and decay time increased slightly at -196degC.",0807.3220v2
2008-07-24,Ideals with an assigned initial ideal,"The stratum St(J,<) (the homogeneous stratum Sth(J,<) respectively) of a
monomial ideal J in a polynomial ring R is the family of all (homogeneous)
ideals of R whose initial ideal with respect to the term order < is J. St(J,<)
and Sth(J,<) have a natural structure of affine schemes. Moreover they are
homogeneous w.r.t. a non-standard grading called level. This property allows us
to draw consequences that are interesting from both a theoretical and a
computational point of view. For instance a smooth stratum is always isomorphic
to an affine space (Corollary 3.6). As applications, in Sec. 5 we prove that
strata and homogeneous strata w.r.t. any term ordering < of every saturated
Lex-segment ideal J are smooth. For Sth(J,Lex) we also give a formula for the
dimension. In the same way in Sec. 6 we consider any ideal R in k[x0,..., xn]
generated by a saturated RevLex-segment ideal in k[x,y,z]. We also prove that
Sth(R,RevLex) is smooth and give a formula for its dimension.",0807.3877v4
2008-08-02,Hot accretion with outflow and thermal conduction,"We present self-similar solutions for advection -dominated accretion flows
with thermal conduction in the presence of outflows. Possible effects of
outflows on the accretion flow are parametrized and a saturated form of thermal
conduction, as is appropriate for the weakly-collisional regime of interest, is
included in our model. While the cooling effect of outflows is noticeable,
thermal conduction provides an extra heating source. In comparison to accretion
flows without winds, we show that the disc rotates faster and becomes cooler
because of the angular momentum and energy flux which are taking away by the
winds. But thermal conduction opposes the effects of winds and not only
decreases the rotational velocity, but increases the temperature. However,
reduction of the surface density and the enhanced accretion velocity are
amplified by both of the winds and the thermal conduction. We find that for
stronger outflows, a higher level of saturated thermal conduction is needed to
significantly modify the physical profiles of the accretion flow.",0808.0245v1
2008-08-07,Gluon density and $F_{2}$ functions from BK equation with local impact parameter dependence in DIS on nuclei,"The DIS process on nuclei is considered in the framework of LO BK equation
with local impact parameter dependence. Solving BK equation parameters for
initial conditions of GBW type found in \cite{Serg1} were used. Integrated
gluon density function and $F_2$ nucleus structure function for different
nuclei are calculated. Obtained results are compared with the different
parameterizations of integrated gluon density function from
\cite{Flor,Eskola1,Eskola2,Tywon}. The anomalous dimensions and saturation
scales for different nuclei are calculated at different energies. Fitting
obtained results, expressions for the form of saturation scale are obtained for
the proton and different nuclei as functions of impact parameter and energy.",0808.1040v3
2008-08-08,Spontaneous recoil effects of optical pumping on trapped atoms,"The recoil effects of spontaneous photon emissions during optical pumping of
a trapped three-level atom are exactly calculated. Without resort to the
Lamb-Dicke approximation, and considering arbitrary detuning and saturation of
the pump laser, the density of recoil shifts in phase space is derived. It is
shown that this density is not of Gaussian shape, and that it becomes isotropic
in phase space only for a branching ratio corresponding to fluorescence
scattering but unfavorable for optical pumping. The dependence of its
anisotropy on the laser saturation is discussed in the resonant case, and the
mapping of moments of the atom's center-of-mass motion due to the pumping is
presented. Moreover, it is shown how optimum parameters for protecting the
center-of-mass quantum state from pump-induced disturbance depend on the
specific property to be protected.",0808.1272v1
2008-08-21,In medium T-matrix for nuclear matter with three-body forces - binding energy and single particle properties,"We present spectral calculations of nuclear matter properties including
three-body forces. Within the in-medium T-matrix approach, implemented with the
CD-Bonn and Nijmegen potentials plus the three-nucleon Urbana interaction, we
compute the energy per particle in symmetric and neutron matter. The three-body
forces are included via an effective density dependent two-body force in the
in-medium T-matrix equations. After fine tuning the parameters of the
three-body force to reproduce the phenomenological saturation point in
symmetric nuclear matter, we calculate the incompressibility and the energy per
particle in neutron matter. We find a soft equation of state in symmetric
nuclear matter but a relatively large value of the symmetry energy. We study
the the influence of the three-body forces on the single-particle properties.
For symmetric matter the spectral function is broadened at all momenta and all
densities, while an opposite effect is found for the case of neutrons only.
Noticeable modification of the spectral functions are realized only for
densities above the saturation density. The modifications of the self-energy
and the effective mass are not very large and appear to be strongly suppressed
above the Fermi momentum.",0808.2929v1
2008-09-08,Effect of Disorder on the Quantum Coherence in Mesoscopic Wires,"We present phase coherence time measurements in quasi-one-dimensional
mesoscopic wires made from high mobility two-dimensional electron gas. By
implanting gallium ions into a GaAs/AlGaAs heterojunction we are able to vary
the diffusion coefficient over 2 orders of magnitude. We show that in the
diffusive limit, the decoherence time follows a power law as a function of
diffusion coefficient as expected by theory. When the disorder is low enough so
that the samples are semi-ballistic, we observe a new and unexpected regime in
which the phase coherence time is independent of disorder. In addition, for all
samples the temperature dependence of the phase coherence time follows a power
law down to the lowest temperatures without any sign of saturation and strongly
suggests that the frequently observed low temperature saturation is not
intrinsic.",0809.1381v3
2008-09-10,Entanglement of Solitons in the Frenkel-Kontorova Model,"We investigate entanglement of solitons in the continuum-limit of the
nonlinear Frenkel-Kontorova chain. We find that the entanglement of solitons
manifests particle-like behavior as they are characterized by localization of
entanglement. The von-Neumann entropy of solitons mixes critical with
noncritical behaviors. Inside the core of the soliton the logarithmic increase
of the entropy is faster than the universal increase of a critical field,
whereas outside the core the entropy decreases and saturates the constant value
of the corresponding massive noncritical field. In addition, two solitons
manifest long-range entanglement that decreases with the separation of the
solitons more slowly than the universal decrease of the critical field.
Interestingly, in the noncritical regime of the Frenkel-Kontorova model,
entanglement can even increase with the separation of the solitons. We show
that most of the entanglement of the so-called internal modes of the solitons
is saturated by local degrees of freedom inside the core, and therefore we
suggest using the internal modes as carriers of quantum information.",0809.1857v1
2008-09-17,J/Psi production in heavy ion collisions and gluon saturation,"We calculate the inclusive J/Psi production in heavy ion collisions including
the effects of gluon saturation in the wave functions of the colliding nuclei.
We argue that the dominant production mechanism in proton--nucleus and
nucleus--nucleus collisions for heavy nuclei is different from the one in
hadron-hadron interactions. We find that the rapidity distribution of primary
J/Psi production is more peaked around midrapidity than the analogous
distribution in elementary pp collisions. We discuss the consequences of this
fact on the experimentally observed J/Psi suppression in Au-Au collisions at
RHIC energies.",0809.2933v2
2008-09-26,Covariant and self consistent vertex corrections for pions and isobars in nuclear matter,"We evaluate the pion and isobar propagators in cold nuclear matter self
consistently applying a covariant form of the isobar-hole model. Migdal's
vertex correction effects are considered systematically in the absence of
phenomenological soft form factors. Saturated nuclear matter is modeled by
scalar and vector mean fields for the nucleon. It is shown that the short-range
dressing of the pi N Delta vertex has a significant effect on the pion and
isobar properties. Using realistic parameters sets we predict a downward shift
of about 50 MeV for the Delta resonance at nuclear saturation density. The
pionic soft modes are much less pronounced than in previous studies.",0809.4604v1
2008-09-29,DNS of the kappa-mechanism,"We present a purely-radiative hydrodynamic model of the kappa-mechanism that
sustains radial oscillations in Cepheid variables. We determine the physical
conditions favourable for the kappa-mechanism to occur by the means of a
configurable hollow in the radiative conductivity profile. By starting from
these most favourable conditions, we complete nonlinear direct numerical
simulations (DNS) and compare them with the results given by a linear-stability
analysis of radial modes. We find that well-defined instability strips are
generated by changing the location and shape of the conductivity hollow. For a
given position in the layer, the hollow amplitude and width stand out as the
key parameters governing the appearance of unstable modes driven by the
kappa-mechanism. The DNS confirm both the growth rates and structures of the
linearly-unstable modes. The nonlinear saturation that arises is produced by
intricate couplings between the excited fundamental mode and higher damped
overtones. These couplings are measured by projecting the DNS fields onto an
acoustic subspace built from regular and adjoint eigenvectors and a 2:1
resonance is found to be responsible for the saturation of the kappa-mechanism
instability.",0809.4949v1
2008-10-10,The effect of undrained heating on a fluid-saturated hardened cement paste,"The effect of undrained heating on volume change and induced pore pressure
increase is an important point to properly understand the behaviour and
evaluate the integrity of an oil well cement sheath submitted to rapid
temperature changes. This thermal pressurization of the pore fluid is due to
the discrepancy between the thermal expansion coefficients of the pore fluid
and of the solid matrix. The equations governing the undrained
thermo-hydro-mechanical response of a porous material are presented and the
effect of undrained heating is studied experimentally for a saturated hardened
cement paste. The measured value of the thermal pressurization coefficient is
equal to 0.6MPa/&deg;C. The drained and undrained thermal expansion
coefficients of the hardened cement paste are also measured in the heating
tests. The anomalous thermal behaviour of cement pore fluid is back analysed
from the results of the undrained heating test.",0810.1810v2
2008-10-16,Oscillator topologies on a paratopological group and related number invariants,"We introduce and study oscillator topologies on paratopological groups and
define certain related number invariants. As an application we prove that a
Hausdorff paratopological group $G$ admits a weaker Hausdorff group topology
provided $G$ is 3-oscillating. A paratopological group $G$ is 3-oscillating
(resp. 2-oscillating) provided for any neighborhood $U$ of the unity $e$ of $G$
there is a neighborhood $V\subset G$ of $e$ such that $V^{-1}VV^{-1}\subset
UU^{-1}U$ (resp. $V^{-1}V\subset UU^{-1}$). The class of 2-oscillating
paratopological groups includes all collapsing, all nilpotent paratopological
groups, all paratopological groups satisfying a positive law, all
paratopological SIN-group and all saturated paratopological groups (the latter
means that for any nonempty open set $U\subset G$ the set $U^{-1}$ has nonempty
interior). We prove that each totally bounded paratopological group $G$ is
countably cellular; moreover, every cardinal of uncountable cofinality is a
precaliber of $G$. Also we give an example of a saturated paratopological group
which is not isomorphic to its mirror paratopological group as well as an
example of a 2-oscillating paratopological group whose mirror paratopological
group is not 2-oscillating.",0810.3028v2
2008-10-17,Recent developments in the techniques of controlling and measuring suction in unsaturated soils,"The difficulty of measuring and controlling suction in unsaturated soils is
one of the reasons why the development of the mechanics of unsaturated soils
has not been as advanced as that of saturated soils. However, significant
developments have been carried out in the last decade in this regard. In this
paper, a re-view of some developments carried out in the techniques of
controlling suction by using the axis translation, the osmotic method and the
vapour control technique is presented. The paper also deals with some recent
de-velopments in the direct measurement of suction by using high capacity
tensiometers and in the measurement of high suction by using high range
psychrometers. The recent progresses made in these techniques have been
significant and will certainly help further experimental investigation of the
hydromechanical behaviour of un-saturated soils.",0810.3221v1
2008-10-23,Quantum Limits and Robustness of Nonlinear Intracavity Absorption Spectroscopy,"We investigate the limits of intracavity absorption spectroscopy with
nonlinear media. Using a common theoretical framework, we compare the detection
of a trace gas within an undriven cavity with gain near and above threshold, a
driven cavity with gain kept just below threshold, and a cavity driven close to
the saturation point of a saturable absorber. These phase-transition-based
metrology methods are typically quantum-limited by spontaneous emission, and we
compare them to the empty cavity shotnoise-limited case. Although the
fundamental limits achievable with nonlinear media do not surpass the empty
cavity limits, we show that nonlinear methods are more robust against certain
technical noise models. This recognition may have applications in spectrometer
design for devices operating in non-ideal field environments.",0810.4209v1
2008-10-31,Adsorption properties and third sound propagation in superfluid $^4$He films on carbon nanotubes,"We consider the adsorption properties of superfluid $^4$He films on carbon
nanotubes. One major factor in the adsorption is the surface tension force
arising from the very small diameter of the nanotubes. Calculations show that
surface tension keeps the film thickness on the tubes very thin even when the
helium vapor is increased to the saturated pressure. The weakened Van der Waals
force due to the cylindrical geometry also contributes to this. Both of these
effects act to lower the predicted velocity of third sound propagation along
the tubes. It does not appear that superfluidity will be possible on
single-walled nanotubes of diameter about one nm, since the film thickness is
less than 3 atomic layers even at saturation. Superfluidity is possible on
larger-diameter nanotube bundles and multi-walled nanotubes, however. We have
observed third sound signals on nanotube bundles of average diameter 5 nm which
are sprayed onto a Plexiglass surface, forming a network of tubes.",0810.5627v1
2008-11-11,Baryon Stopping as a new Probe of Geometric Scaling,"We suggest to use net-baryon rapidity distributions in central relativistic
heavy-ion collisions at SPS, RHIC and LHC energies in order to probe saturation
physics. Within the color glass condensate framework based on small-coupling
QCD, net-baryon rapidity distributions are shown to exhibit geometric scaling.
In a comparison with RHIC data in Au + Au collisions at sqrt(s_NN) = 62.4 GeV
and 200 GeV the gradual approach to the gluon saturation regime is
investigated. Predictions for net-baryon rapidity spectra and the mean rapidity
loss in central Pb + Pb collisions at LHC energies of sqrt (s_NN) = 5.5 TeV are
made.",0811.1721v3
2008-11-25,Production and evolution path of dileptons at HADES energies,"Dilepton production in intermediate energy nucleus-nucleus collisions as well
as in elementary proton-proton reactions is analysed within the UrQMD transport
model. For C+C collisions at 1 AGeV and 2 AGeV the resulting invariant mass
spectra are compared to recent HADES data. We find that the experimental
spectrum for C+C at 2 AGeV is slightly overestimated by the theoretical
calculations in the region around the vector meson peak, but fairly described
in the low mass region, where the data is satisfactorily saturated by the
Dalitz decay of the $\eta$ meson and the $\Delta$ resonance. At 1 AGeV an
underestimation of the experimental data is found, pointing that at lower
energies the low mass region is not fully saturated by standardly parametrized
$\Delta$ Dalitz decays alone. Furthermore, predictions for dilepton spectra for
$pp$ reactions at 1.25 GeV, 2.2 GeV and 3.5 GeV and Ar+KCl reactions at 1.75
AGeV are presented. The study is complemented by a detailed investigation of
the role of absorption of the parent particles on the corresponding dilepton
yields in the regime which has so far been probed by HADES.",0811.4073v2
2008-12-02,Saturation effects in experiments on the thermal Casimir effect,"We address three different problematic Casimir experiments in this work. The
first is the classical Casimir force measured between two metal half spaces;
here in the form of the Casimir pressure measurement between a gold sphere and
a gold plate as performed by Decca et al. [Phys. Rev. D 75, 077101 (2007)];
theory predicts a large negative thermal correction, absent in the high
precision experiment. The second experiment is the measurement of the Casimir
force between a metal plate and a laser irradiated semiconductor membrane as
performed by Chen et al. [Phys. Rev. B 76, 035338 (2007)]; the change in force
with laser intensity is larger than predicted by theory. The third experiment
is the measurement of the Casimir force between an atom and a wall in the form
of the measurement by Obrecht et al. [Phys. Rev. Lett. 98 063201 (2007)] of the
change in oscillation frequency of a Rb Bose-Einstein condensate trapped to a
fused silica wall; the change is smaller than predicted by theory. We show that
saturation effects can explain the discrepancies between theory and experiment
observed in all these cases.",0812.0509v1
2008-12-05,Embedding solenoids in foliations,"In this paper we find smooth embeddings of solenoids in smooth foliations. We
show that if a smooth foliation F of a manifold M contains a compact leaf L
with H^1(L;R)= 0 and if the foliation is a product foliation in some saturated
open neighbourhood U of L, then there exists a foliation F' on M which is
C^1-close to F, and F' has an uncountable set of solenoidal minimal sets
contained in U that are pair wise non-homeomorphic. If H^1(L;R) is not 0, then
it is known that any sufficiently small perturbation of F contains a saturated
product neighbourhood. Thus, our result can be thought of as an instability
result complementing the stability results of Reeb, Thurston and Langevin and
Rosenberg.",0812.1085v2
2008-12-18,Bulk-mediated surface diffusion on a cylinder: propagators and crossovers,"We consider the effective surface motion of a particle that freely diffuses
in the bulk and intermittently binds to that surface. From an exact approach we
derive various regimes of the effective surface motion characterized by
physical rates for binding/unbinding and the bulk diffusivity. We obtain a
transient regime of superdiffusion and, in particular, a saturation regime
characteristic for the cylindrical geometry. This saturation, however, in a
finite system is not terminal but eventually turns over to normal surface
diffusion. The first passage behavior of particles to the cylinder surface is
derived. Consequences for actual systems are discussed.",0812.3627v1
2008-12-19,Coronal activity from the ASAS eclipsing binaries,"We combine the catalogue of eclipsing binaries from the All Sky Automated
Survey (ASAS) with the ROSAT All Sky Survey (RASS). The combination results in
836 eclipsing binaries that display coronal activity and is the largest sample
of active binary stars assembled to date. By using the (V-I) colors of the ASAS
eclipsing binary catalogue, we are able to determine the distances and thus
bolometric luminosities for the majority of eclipsing binaries that display
significant stellar activity. A typical value for the ratio of soft X-ray to
bolometric luminosity is L_X/L_bol ~ a few x 10^-4, similar to the ratio of
soft X-ray to bolometric flux F_X/F_bol in the most active regions of the Sun.
Unlike rapidly rotating isolated late-type dwarfs -- stars with significant
outer convection zones -- a tight correlation between Rossby number and
activity of eclipsing binaries is absent. We find evidence for the saturation
effect and marginal evidence for the so-called ""super-saturation"" phenomena.
Our work shows that wide-field stellar variability searches can produce a high
yield of binary stars with strong coronal activity.
  The combined ASAS and RASS catalogue, as well as the results of this work are
available for download in a form of a file.",0812.3909v1
2009-01-16,On the Capacity of the Discrete-Time Channel with Uniform Output Quantization,"This paper provides new insight into the classical problem of determining
both the capacity of the discrete-time channel with uniform output quantization
and the capacity achieving input distribution. It builds on earlier work by
Gallager and Witsenhausen to provide a detailed analysis of two particular
quantization schemes. The first is saturation quantization where overflows are
mapped to the nearest quantization bin, and the second is wrapping quantization
where overflows are mapped to the nearest quantization bin after reduction by
some modulus. Both the capacity of wrapping quantization and the capacity
achieving input distribution are determined. When the additive noise is
gaussian and relatively small, the capacity of saturation quantization is shown
to be bounded below by that of wrapping quantization. In the limit of
arbitrarily many uniform quantization levels, it is shown that the difference
between the upper and lower bounds on capacity given by Ihara is only 0.26
bits.",0901.2545v1
2009-02-04,Prime and almost prime integral points on principal homogeneous spaces,"We develop the affine sieve in the context of orbits of congruence subgroups
of semi-simple groups acting linearly on affine space. In particular we give
effective bounds for the saturation numbers for points on such orbits at which
the value of a given polynomial has few prime factors. In many cases these
bounds are of the same quality as what is known in the classical case of a
polynomial in one variable and the orbit is the integers. When the orbit is the
set of integral matrices of a fixed determinant we obtain a sharp result for
the saturation number, and thus establish the Zariski density of matrices all
of whose entries are prime numbers. Among the key tools used are explicit
approximations to the generalized Ramanujan conjectures for such groups and
sharp and uniform counting of points on such orbits when ordered by various
norms.",0902.0692v1
2009-02-11,Quantum corrections to solitons and BPS saturation,"We review our work of the past decade on one-loop quantum corrections to the
mass M and central charge Z of solitons in supersymmetric field theories: the
kink, the vortex, and the monopoles (focussing on the kink and the monopoles
here). In each case a new feature was needed to obtain BPS saturation: a new
anomaly-like contribution to Z for the kink and the N=2 monopole, the effect of
classical winding of the quantum vortex contributing to Z, surface terms
contributing to M of the N=4 monopole and to Z of the N=2 and N=4 monopoles,
and composite operator renormalization for the currents of the ""finite"" N=4
model. We use dimensional regularization, modified to preserve susy and be
applicable to solitons, and suitable renormalization conditions. In the mode
expansion of bosonic and fermionic quantum fields, zero modes appear then as
massless nonzero modes.",0902.1904v1
2009-04-20,Relaxation in the 3D ordered CoTAC spin chain by quantum nucleation of 0D domain walls,"We have shown that resonant quantum tunnelling of the magnetisation (QTM),
until now observed only in 0D cluster systems (SMMs), occurs in the molecular
Ising spin chain, CoTAC ([(CH_3)_3NH]CoCl_3 - 2H_2O) which orders as a canted
3D-antiferromagnet at T_C=4.15 K. This effect was observed around a resonant
like field value of 1025 Oe. We present here measurements of the relaxation of
the magnetisation as a function of time, from the zero field cooled (ZFC)
antiferromagnet state and from the saturated ferromagnet state. We show that,
at the resonant field, the relaxation from the saturated state occurs in a
complicated process, whereas, surprisingly, in the case of the ZFC state, the
relaxation is exponential.",0904.2984v1
2009-04-22,Experimental Autoignition of C4-C6 Saturated and Unsaturated Methyl and Ethyl Esters,"Autoignition delay times, ?, of methyl crotonate, methyl acrylate, ethyl
butanoate, ethyl crotonate, and ethyl acrylate were studied in shock tube
experiments. A series of mixtures diluted with argon, of varying fuel/oxygen
equivalence ratios (?=0.25, 0.4, 1.0, and 2.0), were measured behind reflected
shock waves over the temperature range of 1280-1930 K, pressure range of 7-9.65
atm, during which the logarithm of ? varies linearly as a function of the
inverse temperature for all equivalence ratios. The ignition delay time
decreases as temperature rises. The dependence of ? on temperature, and
reactant concentrations is given in an empirical correlation. The results
provide a database for the validation of small saturated and unsaturated esters
kinetic mechanisms at elevated temperatures and pressure combustion.",0904.3539v1
2009-04-29,Vapor-liquid equilibria simulation and an equation of state contribution for dipole-quadrupole interactions,"A systematic investigation on vapor-liquid equilibria (VLE) of dipolar and
quadrupolar fluids is carried out by molecular simulation to develop a new
Helmholtz energy contribution for equations of state (EOS). Twelve two-center
Lennard-Jones plus point dipole and point quadrupole model fluids (2CLJDQ) are
studied for different reduced dipolar moments mu^{*2}=6,12, reduced quadrupolar
moments Q^{*2}=2,4 and reduced elongations L^*=0, 0.505,1. Temperatures cover a
wide range from about 55% to about 95% of the critical temperature of each
fluid. The NpT + test particle method is used for the calculation of vapor
pressure, saturated densities and saturated enthalpies.Critical data and the
acentric factor are obtained from fits to the simulation data.On the basis of
this data, an EOS contribution for the dipole-quadrupole cross-interactions of
non-spherical molecules is developed. The expression is based on a third-order
perturbation theory and the model constants are adjusted to the present 2CLJDQ
simulation results. When applied to mixtures, the model is found to be in
excellent agreement to results from simulation and experiment. The new EOS
contribution is also compatible with segment-based EOS, like the various forms
of the Statistical Associating Fluid Theory (SAFT) EOS.",0904.4637v1
2009-05-04,The Non-Linear Fisher Information content of cosmic shear surveys,"We quantify the Fisher information content of the cosmic shear survey
two-point function as a function of noise and resolution. The two point
information of dark matter saturates at the trans-linear scale. We investigate
the impact of non-linear non-Gaussianity on the information content for
lensing, which probes the same dark matter. To do so we heavily utilize N-body
simulations in order to probe accurately the non-linear regime. While we find
that even in a perfect survey, there is no clear saturation scale, we observe
that non-linear growth induced non-Gaussianity could lead to a factor of ~4
reduction for the common Dark Energy figure of merit. This effect is however
mitigated by realistic levels of shot noise and we find that for future
surveys, the effect is closer to a factor of 1.5. To do so, we develop a new
scheme to compute the relevant covariant matrix. It leads us to claim an
unbiased estimator with an order of magnitude improvement in accuracy with only
twice more simulations than previously used. Finally, we evaluate the error on
the errors using bootstrap methods.",0905.0501v1
2009-05-05,Relativistic calculation of the pion loop correlation energy in nuclear matter in a theory including confinement,"We present a relativistic calculation of the saturation properties of nuclear
matter which contains the correlation energy. Pion loops are incorporated on
top of a relativistic Hartree-Fock (RHF) approach based on a chiral theory. It
includes the effect of nucleon structure through its response to the background
chiral invariant scalar field. All the parameters which enter the RHF
calculation are fixed or strongly constrained by hadron phenomenology or
lattice data. The new input for the correlation energy is the Landau-Migdal
parameter g? governing the short-range part of the spin-isospin interaction. We
find that the inclusion of the correlation energy improves the description of
the saturation properties of nuclear matter.",0905.0605v1
2009-05-06,Scaling in Plateau-to-Plateau Transition: A Direct Connection of Quantum Hall Systems with Anderson Localization Model,"The quantum Hall plateau transition was studied at temperatures down to 1 mK
in a random alloy disordered high mobility two-dimensional electron gas. A
perfect power-law scaling with \kappa=0.42 was observed from 1.2K down to 12mK.
This perfect scaling terminates sharply at a saturation temperature of
T_s~10mK. The saturation is identified as a finite-size effect when the quantum
phase coherence length (L_{\phi} ~ T^{-p/2}) reaches the sample size (W) of
millimeter scale. From a size dependent study, T_s \propto W^{-1} was observed
and p=2 was obtained. The exponent of the localization length, determined
directly from the measured \kappa and p, is \nu=2.38, and the dynamic critical
exponent z = 1.",0905.0885v1
2009-05-11,Spatial and temporal features of dense contaminant transport: experimental investigation and numerical modeling,"We investigate the spatial and temporal features of dense contaminant plumes
dynamics in porous materials. Our analysis is supported by novel experimental
results concerning pollutant concentration profiles inside a vertical column
setup. We describe the experimental methods and elucidate the salient outcomes
of the measurements, with focus on miscible fluids in homogeneous saturated
media. By resorting to a finite elements approach, we numerically solve the
equations that rule the pollutants migration and compare the simulation results
with the experimental data. Finally, we qualitatively explore the interfacial
dynamics behavior between the dense contaminant plume and the lighter resident
fluid that saturates the column.",0905.1575v1
2009-05-18,Long-term evolution and gravitational wave radiation of neutron stars with differential rotation induced by r-modes,"In a second-order r-mode theory, S'a & Tom'e found that the r-mode
oscillation in neutron stars (NSs) could induce stellar differential rotation,
which leads to a saturation state of the oscillation spontaneously. Based on a
consideration of the coupling of the r-modes and the stellar spin and thermal
evolutions, we carefully investigate the influences of the r-mode-induced
differential rotation on the long-term evolutions of isolated NSs and NSs in
low-mass X-ray binaries, where the viscous damping of the r-modes and its
resultant effects are taken into account. The numerical results show that, for
both kinds of NSs, the differential rotation can prolong the duration of the
r-mode saturation state significantly. As a result, the stars can keep nearly
constant temperature and angular velocity over a thousand years. Moreover, due
to the long-term steady rotation of the stars, persistent quasi-monochromatic
gravitational wave radiation could be expected, which increases the
detectibility of gravitational waves from both nascent and accreting old NSs.",0905.2804v1
2009-05-26,Resonance saturation at next-to-leading order,"A proper estimation of the chiral low-energy constants of Chiral Perturbation
Theory is a very important task. To this end resonance chiral Lagrangians have
been used fruitfully. We have studied the determination of chiral couplings at
next-to-leading (NLO) order in the 1/N(C) expansion, keeping full control of
the renormalization scale dependence. We find that, by imposing short-distance
constraints coming from QCD, resonance saturation at NLO in 1/N(C) is
satisfied. In other words, the chiral couplings can be written in terms of the
resonance masses and couplings and do not depend explicitly on the coefficients
of the chiral operators in the Goldstone boson sector of Resonance Chiral
Theory.",0905.4299v1
2009-06-01,A class of stable perturbations for a minimal mass soliton in three dimensional saturated nonlinear Schrödinger equations,"In this result, we develop the techniques of \cite{KS1} and \cite{BW} in
order to determine a class of stable perturbations for a minimal mass soliton
solution of a saturated, focusing nonlinear Schr\""odinger equation {c} i u_t +
\Delta u + \beta (|u|^2) u = 0 u(0,x) = u_0 (x), in $\reals^3$. By projecting
into a subspace of the continuous spectrum of $\mathcal{H}$ as in \cite{S1},
\cite{KS1}, we are able to use a contraction mapping similar to that from
\cite{BW} in order to show that there exist solutions of the form e^{i
\lambda_{\min} t} (R_{min} + e^{i \mathcal{H} t} \phi + w(x,t)), where $e^{i
\mathcal{H} t} \phi + w(x,t)$ disperses as $t \to \infty$. Hence, we have long
time persistance of a soliton of minimal mass despite the fact that these
solutions are shown to be nonlinearly unstable in \cite{CP1}.",0906.0375v2
2009-06-08,CMB Constraints on WIMP Annihilation: Energy Absorption During the Recombination Epoch,"We compute in detail the rate at which energy injected by dark matter
annihilation heats and ionizes the photon-baryon plasma at z ~ 1000, and
provide accurate fitting functions over the relevant redshift range for a broad
array of annihilation channels and DM masses. The resulting perturbations to
the ionization history can be constrained by measurements of the CMB
temperature and polarization angular power spectra. We show that models which
fit recently measured excesses in 10-1000 GeV electron and positron cosmic rays
are already close to the 95% confidence limits from WMAP. The recently launched
Planck satellite will be capable of ruling out a wide range of DM explanations
for these excesses. In models of dark matter with Sommerfeld-enhanced
annihilation, where sigma v rises with decreasing WIMP velocity until some
saturation point, the WMAP5 constraints imply that the enhancement must be
close to saturation in the neighborhood of the Earth.",0906.1197v2
2009-06-08,Semi-inclusive Deep Inelastic Scattering at small x,"We study the semi-inclusive hadron production in deep inelastic scattering at
small $x$. A transverse momentum dependent factorization is found consistent
with the results calculated in the small-$x$ approaches, such as the
color-dipole framework and the color glass condensate, in the appropriate
kinematic region at the lowest order. The transverse momentum dependent quark
distribution can be studied in this process as a probe for the small-$x$
saturation physics. Especially, the ratio of quark distributions as a function
of transverse momentum at different $x$ demonstrates strong dependence on the
saturation scale. The $Q^2$ dependence of the same ratio is also studied by
applying the Collins-Soper-Sterman resummation method.",0906.1454v2
2009-06-09,Discrete Family of Dissipative Soliton Pairs in Mode-Locked Fiber Lasers,"We numerically investigate the formation of soliton pairs (bound states) in
mode-locked fiber ring lasers. In the distributed model (complex cubic-quintic
Ginzburg-Landau equation) we observe a discrete family of soliton pairs with
equidistantly increasing peak separation. This family was identified by two
alternative numerical schemes and the bound state instability was disclosed by
a linear stability analysis. Moreover, similar families of unstable bound state
solutions have been found in a more realistic lumped laser model with an
idealized saturable absorber (instantaneous response). We show that a
stabilization of these bound states can be achieved when the finite relaxation
time of the saturable absorber is taken into account. The domain of stability
can be controlled by varying this relaxation time.",0906.1589v1
2009-06-11,On the background estimation by time slides in a network of gravitational wave detectors,"Time shifting the outputs of Gravitational Wave detectors operating in
coincidence is a convenient way to estimate the background in a search for
short duration signals. However this procedure is limited as increasing
indefinitely the number of time shifts does not provide better estimates. We
show that the false alarm rate estimation error saturates with the number of
time shifts. In particular, for detectors with very different trigger rates
this error saturates at a large value. Explicit computations are done for 2
detectors, and for 3 detectors where the detection statistic relies on the
logical ``OR'' of the coincidences of the 3 couples in the network.",0906.2120v2
2009-06-25,Sound speed in water-saturated glass beads as a function of frequency and porosity,"Sound propagation in water-saturated granular sediments is known to depend on
the sediment porosity, but few data in the literature address both the
frequency and porosity dependency. To begin to address this deficiency, a
fluidized bed technique was used to control the porosity of an artificial
sediment composed of glass spheres of 265 {\mu}m diameter. Time-of-flight
measurements and the Fourier phase technique were utilized to determine the
sound speed for frequencies from 300 to 800 kHz and porosities from 0.37 to
0.43. A Biot-based model qualitatively describes the porosity dependence.",0906.4798v2
2009-06-27,Multiphase modeling and qualitative analysis of the growth of tumor cords,"In this paper a macroscopic model of tumor cord growth is developed, relying
on the mathematical theory of deformable porous media. Tumor is modeled as a
saturated mixture of proliferating cells, extracellular fluid and extracellular
matrix, that occupies a spatial region close to a blood vessel whence cells get
the nutrient needed for their vital functions. Growth of tumor cells takes
place within a healthy host tissue, which is in turn modeled as a saturated
mixture of non-proliferating cells. Interactions between these two regions are
accounted for as an essential mechanism for the growth of the tumor mass. By
weakening the role of the extracellular matrix, which is regarded as a rigid
non-remodeling scaffold, a system of two partial differential equations is
derived, describing the evolution of the cell volume ratio coupled to the
dynamics of the nutrient, whose higher and lower concentration levels determine
proliferation or death of tumor cells, respectively. Numerical simulations of a
reference two-dimensional problem are shown and commented, and a qualitative
mathematical analysis of some of its key issues is proposed.",0906.5077v1
2009-06-29,Multi-$\bar{K}$ hypernuclei,"Relativistic mean field calculations of multi-$\bar{K}$ hypernuclei are
performed by adding $K^-$ mesons to particle-stable configurations of nucleons,
$\Lambda$ and $\Xi$ hyperons. For a given hypernuclear core, the calculated
$\bar{K}$ separation energy $B_{\bar{K}}$ saturates with the number of
$\bar{K}$ mesons for more than roughly 10 mesons, with $B_{\bar{K}}$ bounded
from above by 200 MeV. The associated baryonic densities saturate at values 2-3
times nuclear-matter density within a small region where the $\bar{K}$-meson
densities peak, similarly to what was found for multi-$\bar{K}$ nuclei. The
calculations demonstrate that particle-stable multistrange $\{N,\Lambda,\Xi \}$
configurations are stable against strong-interaction conversions $\Lambda \to N
\bar{K}$ and $\Xi \to N \bar{K} \bar{K}$, confirming and strengthening the
conclusion that kaon condensation is unlikely to occur in strong-interaction
self-bound strange hadronic matter.",0906.5344v2
2009-07-03,Dissipation effects in the ratchetlike Fermi acceleration,"Ac driven asymmetric pulses can be used to control the Fermi acceleration
between three different motions, ${\bf A:}$ the {\it accelerated} mode; ${\bf
D:}$ the {\it decelerated} mode and ${\bf H:}$ the {\it hyperaccelerated} mode.
In this work we show that dissipation strongly affects the particles velocity,
reducing the possibility for an accurate control of the dynamics. The
saturation time, where the mean velocity starts to be constant due to
dissipation, decays with a power law $\sim\gamma^{-\beta}$, where $\gamma$ is
the dissipation parameter and $\beta$ is close to 1. The value of the saturated
mean velocity also decays with a power law with exponent $\beta\sim0.6$ for the
case ${\bf H}$, and $\beta\sim0.3$ for the case ${\bf A}$. In the case ${\bf
D}$ this velocity is almost constant for small dissipations.",0907.0628v1
2009-07-20,Testing Non-linear Evolution with Running Coupling Corrections in $ep$ and $pp$ collisions,"The perturbative QCD predicts that the growth of the gluon density at
small-$x$ (high energies) should saturate, forming a Color Glass Condensate
(CGC), which is described in mean field approximation by the Balitsky-Kovchegov
(BK) equation. Recently, the next-to-leading order corrections for the BK
equation were derived and a global fit of the inclusive $ep$ HERA data was
performed, resulting in a parameterization for the forward scattering
amplitude. In this paper we compare this parameterization with the predictions
of other phenomenological models and investigate the saturation physics in
diffractive deep inelastic electron-proton scattering and in the forward hadron
production in $pp$ collisions. Our results demonstrate that the running
coupling BK solution is able to describe these observables.",0907.3416v2
2009-07-21,"Wavet, a Custom Device Able to Measure Viscoelastic Properties of Wood Under Water-Saturated Conditions Up to 140 deg C (WAVET : Environmental Vibration Analyser for Wood)","This work presents an innovative experimental device conceived to
characterize the time-dependent behavior of hygroscopic materials, as wood, at
controlled moisture content and temperature. This device, the WAVET, permits
the determination of the viscoelastic properties of samples, using harmonic
tests at frequencies varying from 5.10-3 Hz to 10 Hz. Conceived to work up to 5
bar, it allows tests in dry or water-saturated conditions to be performed over
the temperature range 0\degree C to 140\degree C. In spite of these severe
working conditions, the careful device design, together with a rigorous data
analysis, allows a rigorous determination of the storage and loss modulus and
the loss factor. The results collected for several species of wood emphasize
the ability of the WAVET to underline the influence of numerous parameters,
namely specie, material direction, anatomical and macromolecular structure, on
the rheological properties and notably on the softening temperature. The WAVET
also establishes a efficient tool to follow the modifications of the
constitutive amorphous polymers of materials submitted to hydrothermal
treatments, in relation to the evolution of their viscoelastic properties.",0907.3676v1
2009-07-27,Understanding saturation and AA collisions with an eA collider,"The initial conditions in high energy nucleus-nucleus collisions are
determined by the small momentum fraction part of the nuclear wavefunction.
This is the regime of gluon saturation and the most direct way to
experimentally study it would be deep inelastic scattering at a high energy
electron ion collider (EIC). This talk discusses some of the connections
between physics at the EIC and the initial stage of relativistic heavy ion
collisions. We argue that measurements at an EIC will provide detailed
high-precision information about the parameters for the initial conditions,
transverse geometry and longitudinal correlations that will be crucial in
understanding the initial stage of a heavy ion collision.",0907.4588v2
2009-09-16,Influence of wettability on liquid water transport in gas diffusion layer of proton exchange membrane fuel cells (PEMFC),"Water management is a key factor that limits PEFC's performance. We show how
insights into this problem can be gained from pore-scale simulations of water
invasion in a model fibrous medium. We explore the influence of contact angle
on the water invasion pattern and water saturation at breakthrough and show
that a dramatic change in the invasion pattern, from fractal to compact, occurs
as the system changes from hydrophobic to hydrophilic. Then, we explore the
case of a system of mixed wettability, i.e. containing both hydrophilic and
hydrophobic pores. The saturation at breakthrough is studied as a function of
the fraction of hydrophilic pores. The results are discussed in relation with
the water management problem, the optimal design of a GDL and the fuel cell
performance degradation mechanisms. We outline how the study could be extended
to 3D systems, notably from binarised images of GDLs obtained by X ray
microtomography.",0909.2947v1
2009-09-18,Analyse en dépendances à l'aide des grammaires d'interaction,"This article proposes a method to extract dependency structures from
phrase-structure level parsing with Interaction Grammars. Interaction Grammars
are a formalism which expresses interactions among words using a polarity
system. Syntactical composition is led by the saturation of polarities.
Interactions take place between constituents, but as grammars are lexicalized,
these interactions can be translated at the level of words. Dependency
relations are extracted from the parsing process: every dependency is the
consequence of a polarity saturation. The dependency relations we obtain can be
seen as a refinement of the usual dependency tree. Generally speaking, this
work sheds new light on links between phrase structure and dependency parsing.",0909.3444v1
2009-09-30,Large energy soliton erbium-doped fiber laser with a graphene-polymer composite mode locker,"Due to its unique electronic property and the Pauli Blocking Principle,
atomic layer graphene possesses wavelength-independent ultrafast saturable
absorption, which can be exploited for the ultrafast photonics application.
Through chemical functionalization, a graphene-polymer nanocomposite membrane
was fabricated and firstly used to mode lock a fiber laser. Stable mode locked
solitons with 3 nJ pulse energy, 700 fs pulse width at the 1590 nm wavelength
have been directly generated from the laser. We show that graphene-polymer
nanocomposites could be an attractive saturable absorber for high power fiber
laser mode locking.",0909.5540v1
2009-10-16,A continuous time random walk model of transport in variably saturated heterogeneous porous media,"We propose a unified physical framework for transport in variably saturated
porous media. This approach allows fluid flow and solute migration to be
treated as ensemble averages of fluid and solute particles, respectively. We
consider the cases of homogeneous and heterogeneous porous materials. Within a
fractal mobile-immobile (MIM) continuous time random walk framework, the
heterogeneity will be characterized by algebraically decaying particle
retention-times. We derive the corresponding (nonlinear) continuum limit
partial differential equations and we compare their solutions to Monte Carlo
simulation results. The proposed methodology is fairly general and can be used
to track fluid and solutes particles trajectories, for a variety of initial and
boundary conditions.",0910.3044v1
2009-10-27,Low density symmetry energy effects in the neutron star crust properties,"The form of the nuclear symmetry energy $E_s$ around saturation point density
leads to a different crust-core transition point in the neutron star and affect
the crust properties. We show that the knowledge about $E_s$ close to the
saturation point is not sufficient, because the very low density behaviour is
relevant. We also claim that crust properties are strongly influenced by the
very high density behavior of $E_s$, so in order to conclude about the form of
low density part of the symmetry energy one must isolate properly the high
density part.",0910.5066v3
2009-10-27,Casimir experiments showing saturation effects,"We address several different Casimir experiments where theory and experiment
disagree. First out is the classical Casimir force measurement between two
metal half spaces; here both in the form of the torsion pendulum experiment by
Lamoreaux and in the form of the Casimir pressure measurement between a gold
sphere and a gold plate as performed by Decca et al.; theory predicts a large
negative thermal correction, absent in the high precision experiments. The
third experiment is the measurement of the Casimir force between a metal plate
and a laser irradiated semiconductor membrane as performed by Chen et al.; the
change in force with laser intensity is larger than predicted by theory. The
fourth experiment is the measurement of the Casimir force between an atom and a
wall in the form of the measurement by Obrecht et al. of the change in
oscillation frequency of a 87 Rb Bose-Einstein condensate trapped to a fused
silica wall; the change is smaller than predicted by theory. We show that
saturation effects can explain the discrepancies between theory and experiment
observed in all these cases.",0910.5137v1
2009-10-31,Saturated fusion systems as idempotents in the double Burnside ring,"We give a new, unexpected characterization of saturated fusion systems on a
p-group S in terms of idempotents in the p-local double Burnside ring of S that
satisfy a Frobenius reciprocity relation, and reformulate fusion-theoretic
phenomena in the language of idempotents. Interpreting our results in stable
homotopy, we answer a long-standing question on stable splittings of
classifying spaces of finite groups, and generalize the Adams--Wilkerson
criterion for recognizing rings of invariants in the cohomology of an
elementary abelian p-group. This work is partly motivated by a conjecture of
Haynes Miller which proposes retractive transfer triples as a purely
homotopy-theoretic model for p-local finite groups. We take an important step
toward proving this conjecture by showing that a retractive transfer triple
gives rise to a p-local finite group when two technical assumptions are made,
thus reducing the conjecture to proving those two assumptions.",0911.0085v3
2009-11-07,Femtosecond carrier dynamics and saturable absorption in graphene suspensions,"Nonlinear optical properties and carrier relaxation dynamics in graphene,
suspended in three different solvents, are investigated using femtosecond (80
fs pulses) Z-scan and degenerate pumpprobe spectroscopy at 790 nm. The results
demonstrate saturable absorption property of graphene with a nonlinear
absorption coefficient, $beta$, of ~2 to 9x10^-8 cm/W. Two distinct time scales
associated with the relaxation of photoexcited carriers, a fast one in the
range of 130-330 fs (related to carrier-carrier scattering) followed by a
slower one in 3.5-4.9 ps range (associated with carrier-phonon scattering) are
observed.",0911.1415v2
2009-11-10,"Twist expansion of the nucleon structure functions, F2 and FL, in the DGLAP improved saturation model","Higher twist effects in the deeply inelastic scattering are studied. We start
with a short review of the theoretical results on higher twists in QCD. Within
the saturation model we perform a twist analysis of the nucleon structure
functions FT and FL at small value of the Bjorken variable x. The parameters of
the model are fitted to the HERA F2 data, and we derive a prediction for the
longitudinal structure function FL. We conclude that for FL the higher twist
corrections are sizable whereas for F2 = FT + FL there is a nearly complete
cancellation of twist-4 corrections in FT and FL. We discuss a few consequences
for future LHC measurements.",0911.1935v1
2009-11-19,Strongly coupled Skyrme-Faddeev-Niemi hopfions,"The strongly coupled limit of the Skyrme-Faddeev-Niemi model (i.e., without
quadratic kinetic term) with a potential is considered on the spacetime S^3 x
R. For one-vacuum potentials two types of exact Hopf solitons are obtained.
Depending on the value of the Hopf index, we find compact or non-compact
hopfions. The compact hopfions saturate a Bogomolny bound and lead to a
fractional energy-charge formula E \sim |Q|^{1/2}, whereas the non-compact
solitons do not saturate the bound and give E \sim |Q|. In the case of
potentials with two vacua compact shell-like hopfions are derived. Some remarks
on the influence of the potential on topological solutions in the full
Skyrme-Faddeev-Niemi model or in (3+1) Minkowski space are also made.",0911.3673v3
2009-11-25,Nonlinear pair production in scattering of photons on ultra-short laser pulses at high energy,"We consider scattering of a photon on a short intense laser pulse at high
energy. We argue that for ultra-short laser pulses the interaction is coherent
over the entire length of the pulse. At low pulse intensity $I$ the total cross
section for electron-positron pair production is proportional to $I$. However,
at pulse intensities higher than the characteristic value $I_s$, the total
cross section saturates -- it becomes proportional to the logarithm of
intensity. This nonlinear effect is due to multi-photon interactions. We derive
the total cross section for pair production at high energies by resuming the
multi-photon amplitudes to all orders in intensity. We calculate the saturation
intensity $I_s$ and show that it is significantly lower than the Schwinger's
critical value. We discuss possible experimental tests.",0911.4964v2
2009-12-15,Zero-range processes with saturated condensation: the steady state and dynamics,"We study a class of zero-range processes in which the real-space condensation
phenomenon does not occur and is replaced by a saturated condensation: that is,
an extensive number of finite-size ""condensates"" in the steady state. We
determine the conditions under which this occurs, and investigate the dynamics
of relaxation to the steady state. We identify two stages: a rapid initial
growth of condensates followed by a slow process of activated evaporation and
condensation. We analyze these nonequilibrium dynamics with a combination of
meanfield approximations, first-passage time calculations and a
fluctuation-dissipation type approach.",0912.3009v2
2009-12-21,Statistical and coherence properties of radiation from X-ray free electron lasers,"We describe statistical and coherence properties of the radiation from x-ray
free electron lasers (XFEL). It is shown that the X-ray FEL radiation before
saturation is described with gaussian statistics. Particularly important is the
case of the optimized X-ray FEL, studied in detail. Applying similarity
techniques to the results of numerical simulations allowed us to find universal
scaling relations for the main characteristics of an X-ray FEL operating in the
saturation regime: efficiency, coherence time and degree of transverse
coherence. We find that with an appropriate normalization of these quantities,
they are functions of only the ratio of the geometrical emittance of the
electron beam to the radiation wavelength. Statistical and coherence properties
of the higher harmonics of the radiation are highlighted as well.",0912.4161v1
2010-01-07,AdS black disk model for small-x DIS,"Using the approximate conformal invariance of QCD at high energies we
consider a simple AdS black disk model to describe saturation in DIS. Deep
inside saturation the structure functions have the same power law scaling, F_T
~ F_L ~ 1/x^w, where w is related to the expansion rate of the black disk with
energy. Furthermore, the ratio F_L /F_T is given by the universal value
(1+w)/(3+w), independently of the target. For virtual photon-photon scattering
at high energies we obtain explicit expressions and ratios for the total cross
sections of transverse and longitudinal photons in terms of the single
parameter w.",1001.1157v2
2010-01-12,Bulk sensitive x-ray absorption spectroscopy free of self-absorption effects,"We demonstrate a new method of x-ray absorption spectroscopy (XAS) that is
bulk sensitive, like traditional fluorescence yield measurements, but is not
affected by self-absorption or saturation effects. This measure of XAS is
achieved by scanning the incident photon energy through an absorption edge and
using an energy sensitive photon detector to measure the partial fluorescence
yield (PFY). The x-ray emission from any element or core-hole excitation that
is not resonant with the absorption edge under investigation is selected from
the PFY. It is found that the inverse of this PFY spectrum, which we term
inverse partial fluorescence yield (IPFY), is linearly proportional to the
x-ray absorption cross-section without any corrections due to saturation or
self-absorption effects. We demonstrate this technique on the Cu L and Nd M
absorption edges of the high-Tc cuprate LNSCO by measuring the O K PFY and
comparing the total electron yield, total fluorescence yield and IPFY spectra.",1001.1925v2
2010-02-01,On saturation of betatron acceleration of dust particles behind shock fronts,"Possible saturation of betatron acceleration of dust particles behind strong
shock fronts from supernovae is considered. It is argued that the efficiency of
the nonthermal dust destruction should be substantially lower than the value
estimated from a traditional description of betatron acceleration of dust
grains behind radiative shock waves. The inhibition of the nonthermal
destruction can be connected with the mirror instability developed in the dust
component behind strong shocks with the velocity 3 times exceeding the Alfv\'en
speed. The instability develops on characteristic time scales much shorter the
age of a supernova remnant, thus its influence on the efficiency of dust
destruction can be substantial: in the range of shock velocities 100 km
s$^{-1}<v_s<300$ km s$^{-1}$ the destruction efficiency can be an order of
magnitude lower that normally estimated.",1002.0223v1
2010-02-15,On Barbs and Labels in Reactive Systems,"Reactive systems (RSs) represent a meta-framework aimed at deriving
behavioral congruences for those computational formalisms whose operational
semantics is provided by reduction rules. RSs proved a flexible specification
device, yet so far most of the efforts dealing with their behavioural semantics
focused on idem pushouts (IPOs) and saturated (also known as dynamic)
bisimulations. In this paper we introduce a novel, intermediate behavioural
equivalence: L-bisimilarity, which is able to recast both its IPO and saturated
counterparts. The equivalence is parametric with respect to a set L of RSs
labels, and it is shown that under mild conditions on L it is indeed a
congruence. Furthermore, L-bisimilarity can also recast the notion of barbed
semantics for RSs, proposed by the same authors in a previous paper. In order
to provide a suitable test-bed, we instantiate our proposal by addressing the
semantics of (asynchronous) CCS and of the calculus of mobile ambients.",1002.2869v1
2010-03-02,Dynamical correlation functions of the mesoscopic pairing model,"We study the dynamical correlation functions of the Richardson pairing model
(also known as the reduced or discrete-state BCS model) in the canonical
ensemble. We use the Algebraic Bethe Ansatz formalism, which gives exact
expressions for the form factors of the most important observables. By summing
these form factors over a relevant set of states, we obtain very precise
estimates of the correlation functions, as confirmed by global sum-rules
(saturation above 99% in all cases considered). Unlike the case of many other
Bethe Ansatz solvable theories, simple two-particle states are sufficient to
achieve such saturations, even in the thermodynamic limit. We provide explicit
results at half-filling, and discuss their finite-size scaling behavior.",1003.0582v1
2010-03-17,"Comment on ""Measurement of x-ray absorption spectra of overdoped high-temperature cuprate superconductors: Inapplicability of the single-band Hubbard model""","In a recent Letter, Peets, et al. measured the x-ray intensity at the oxygen
K-edge in overdoped La$_{2-x}$Sr$_x$CuO$_{4\pm\delta}$ (LSCO) and
Tl$_2$Ba$_2$CuO$_{6+\delta}$. They claimed that, unlike the underdoped samples
of LSCO and YBa$_2$Cu$_3$O$_x$ in which the integrated intensity increases at
least linearly with doping, it saturates abruptly for a hole count exceeding
$x\approx 0.23$. They interpreted the saturation as a breakdown of the 1-band
Hubbard model in the cuprates. However, we show that their results are in
quantitative agreement with the 1-band Hubbard model.",1003.3412v2
2010-03-23,Dynamic Nuclear Polarization in Double Quantum Dots,"We theoretically investigate the controlled dynamic polarization of lattice
nuclear spins in GaAs double quantum dots containing two electrons. Three
regimes of long-term dynamics are identified, including the build up of a large
difference in the Overhauser fields across the dots, the saturation of the
nuclear polarization process associated with formation of so-called ""dark
states,"" and the elimination of the difference field. We show that in the case
of unequal dots, build up of difference fields generally accompanies the
nuclear polarization process, whereas for nearly identical dots, build up of
difference fields competes with polarization saturation in dark states. The
elimination of the difference field does not, in general, correspond to a
stable steady state of the polarization process.",1003.4508v2
2010-04-19,Saturation field of frustrated chain cuprates: broad regions of predominant interchain coupling,"An efficient and precise thermodynamic method to extract the interchain
coupling (IC) of spatially anisotropic 2D or 3D spin-1/2 systems from their
empirical saturation field H_s (T=0) is proposed. Using density-matrix
renormalization group, hard-core boson, and spin-wave theory we study how H_s
is affected by an antiferromagnetic (AFM) IC between frustrated chains
described in the J_1-J_2-spin model with ferromagnetic 1st and AFM 2nd neighbor
in-chain exchange. A complex 3D-phase diagram has been found. For Li2CuO2 and
Y2Ca2Cu5O10, we show that H_s is solely determined by the IC and predict H_s
approx 61 T for the latter.Using H_s approx 55 T from our high-field pulsed
measurements one reads out a weak IC for Li2CuO2 close to that from neutron
scattering.",1004.3300v3
2010-04-30,"Fluctuations, Saturation, and Diffractive Excitation in High Energy Collisions","Diffractive excitation is usually described by the Good--Walker formalism for
low masses, and by the triple-Regge formalism for high masses. In the
Good--Walker formalism the cross section is determined by the fluctuations in
the interaction. In this paper we show that by taking the fluctuations in the
BFKL ladder into account, it is possible to describe both low and high mass
excitation by the Good--Walker mechanism. In high energy $pp$ collisions the
fluctuations are strongly suppressed by saturation, which implies that pomeron
exchange does not factorise between DIS and $pp$ collisions. The Dipole Cascade
Model reproduces the expected triple-Regge form for the bare pomeron, and the
triple-pomeron coupling is estimated.",1004.5502v2
2010-05-04,Gluon saturation and inclusive hadron production at LHC,"In high density QCD the hadron production stems from decay of mini-jets that
have the transverse momenta of the order of the saturation scale. It is shown
in this paper that this idea is able to describe in a unique fashion both the
inclusive hadron production for \sqrt{s} \geq 546 GeV including the first data
from LHC and the deep inelastic scattering at HERA. Recently reported data from
ALICE, CMS and ATLAS including inclusive charged-hadron transverse-momentum and
multiplicity distribution in pp collisions are well described in our approach.
We provide predictions for the upcoming LHC measurements.",1005.0631v2
2010-05-06,Saturation spectra of low lying states of Nitrogen: reconciling experiment with theory,"The hyperfine constants of the levels 2p2(3P)3s 4P_J, 2p2(3P)3p 4Po_J and
2p2(3P)3p 4Do_J, deduced by Jennerich et al. [Eur. Phys. J. D 40 (2006) 81]
from the observed hyperfine structures of the transitions 2p2(3P)3s 4P_J -
2p2(3P)3p 4Po_J' and 2p2(3P)3s 4P_J - 2p2(3P)3p 4Do_J' recorded by saturation
spectroscopy in the near-infrared, strongly disagree with the ab initio values
of J\""onsson et al. [J. Phys. B: At. Mol. Opt. Phys. 43 (2010) 115006]. We
propose a new interpretation of the recorded weak spectral lines. If the latter
are indeed reinterpreted as crossover signals, a new set of experimental
hyperfine constants is deduced, in very good agreement with the ab initio
predictions.",1005.0953v2
2010-05-08,Mechanism for current saturation and energy dissipation in graphene transistors,"From a combination of careful and detailed theoretical and experimental
studies, we demonstrate that the Boltzmann theory including all scattering
mechanisms gives an excellent account, with no adjustable parameters, of high
electric field transport in single as well as double-oxide graphene
transistors. We further show unambiguously that scattering from the substrate
and superstrate surface optical (SO) phonons governs the high field transport
and heat dissipation over a wide range of experimentally relevant parameters.
Models that neglect SO phonons altogether or treat them in a simple
phenomenological manner are inadequate. We outline possible strategies for
achieving higher current and complete saturation in graphene devices.",1005.1351v1
2010-05-20,Large amplitude behavior of the bulk viscosity of dense matter,"We study the bulk viscosity of dense matter, taking into account non-linear
effects which arise in the large amplitude ""supra-thermal"" region where the
deviation $\mu_\Delta$ of the chemical potentials from chemical equilibrium
fulfills $\mu_\Delta>T$. This regime is relevant to unstable modes such as
r-modes, which grow in amplitude until saturated by non-linear effects. We
study the damping due to direct and modified Urca processes in hadronic matter,
and due to nonleptonic weak interactions in strange quark matter. We give
general results valid for an arbitrary equation of state of dense matter and
find that the viscosity can be strongly enhanced by supra-thermal effects. Our
study confirms previous results on quark matter and shows that the non-linear
enhancement is even stronger in the case of hadronic matter. Our results can be
applied to calculations of the r-mode-induced spin-down of fast-rotating
neutron stars, where the spin-down time will depend on the saturation amplitude
of the r-mode",1005.3769v1
2010-06-02,Single Phase Slip Limited Switching Current in 1-Dimensional Superconducting Al Nanowires,"An Aluminum nanowire switches from superconducting to normal as the current
is increased in an upsweep. The switching current (I_s) averaged over upsweeps
approximately follows the depairing critical current (I_c) but falls below it.
Fluctuations in I_s exhibit three distinct regions of behaviors and are
non-monotonic in temperature: saturation well below the critical temperature
T_c, an increase as T^{2/3} at intermediate temperatures, and a rapid decrease
close to T_c. Heat dissipation analysis indicates that a single phase slip is
able to trigger switching at low and intermediate temperatures, whereby the
T^{2/3} dependence arises from the thermal activation of a phase slip, while
saturation at low temperatures provides striking evidence that the phase slips
by macroscopic quantum tunneling.",1006.0420v2
2010-06-02,Environmentally Activated Tunneling Events in a Hybrid Single-Electron Box,"We have measured individual tunneling events and Coulomb step shapes in
single-electron boxes with opaque superconductor-normal metal tunnel junctions.
We observe anomalous broadening of the Coulomb step with decreasing temperature
in a manner that is consistent with activation of first-order tunneling events
by an external dissipative electromagnetic environment. We demonstrate that the
rates for energetically unfavourable tunneling events saturate to finite values
at low temperatures, and that the saturation level can be suppressed by more
than an order of magnitude by a capacitive shunt near the device. The findings
are important in assessing the performance limits of any single-electronic
device. In particular, master equation based simulations show that the
electromagnetic environment realized in the capacitively shunted devices allows
for a metrologically accurate charge pump based on hybrid tunnnel junctions.",1006.0479v3
2010-06-22,"Saturation and Scaling of Multiplicity, Mean p_T and p_T Distributions from 200 GeV < sqrt{s} < 7 TeV","The multiplicity, average transverse momentum, and charged particle
transverse momentum distributions have recently been measured in LHC
experiments. The multiplicity and average transverse momentum grow with beam
energy. Such growth is expected in the theory of the Color Glass Condensate, a
theory that incorporates the physics of saturation into the evolution of the
gluon distribution. We show that the energy dependence of the $p\overline{p}$
data and the LHC data for $pp$ scattering at \sqrt{s} > 200 GeV may be simply
described using a minimal amount of model input. Such a description uses
parameters consistent with the Color Glass Condensate descriptions of HERA and
RHIC experimental data.",1006.4293v2
2010-07-26,Measurements of charge carrier mobilities and drift velocity saturation in bulk silicon of <111> and <100> crystal orientation at high electric fields,"The mobility of electrons and holes in silicon depends on many parameters.
Two of them are the electric field and the temperature. It has been observed
previously that the mobility in the transition region between ohmic transport
and saturation velocities is a function of the orientation of the crystal
lattice.
  This paper presents a new set of parameters for the mobility as function of
temperature and electric field for <111> and <100> crystal orientation. These
parameters are derived from time of flight measurements of drifting charge
carriers in planar p^+nn^+ diodes in the temperature range between -30{\deg}C
and 50{\deg}C and electric fields of 2x10^3 V/cm to 2x10^4 V/cm.",1007.4432v2
2010-08-06,High field transport in graphene,"In this work, high field carrier transport in two dimensional (2D) graphene
is investigated. Analytical models are applied to estimate the saturation
currents in graphene, based on the high scattering rate of optical phonon
emission. Non-equilibrium (hot) phonon effect was studied by Monte Carlo (MC)
simulations. MC simulation confirms that hot phonon effects play a dominant
role in current saturation in graphene. Current degradation due to elastic
scattering events is much smaller compared to the hot phonon effect. Transient
phenomenon as such as velocity overshoot was also studied using MC simulation.
The simulation results shows promising potential for graphene to be used in
high speed electronic devices by shrinking the channel length below 100nm if
electrostatic control can be exercised in the absence of a band gap.",1008.1161v2
2010-08-11,Uncovering the Dominant Scatterer in Graphene Sheets on SiO2,"We have measured the impact of atomic hydrogen adsorption on the electronic
transport properties of graphene sheets as a function of hydrogen coverage and
initial, pre-hydrogenation field-effect mobility. Our results are compatible
with hydrogen adsorbates inducing intervalley mixing by exerting a short-range
scattering potential. The saturation coverages for different devices are found
to be proportional to their initial mobility, indicating that the number of
native scatterers is proportional to the saturation coverage of hydrogen. By
extrapolating this proportionality, we show that the field-effect mobility can
reach $1.5 \times 10^4$ cm$^2$/V sec in the absence of the hydrogen-adsorbing
sites. This affinity to hydrogen is the signature of the most dominant type of
native scatterers in graphene-based field-effect transistors on SiO$_2$.",1008.2007v1
2010-08-18,Evolution of Holographic Entanglement Entropy after Thermal and Electromagnetic Quenches,"We study the evolution and scaling of the entanglement entropy after two
types of quenches for a 2+1 field theory, using holographic techniques. We
study a thermal quench, dual to the addition of a shell of uncharged matter to
four dimensional Anti-de Sitter (AdS_4) spacetime, and study the subsequent
formation of a Schwarzschild black hole. We also study an electromagnetic
quench, dual to the addition of a shell of charged sources to AdS_4, following
the subsequent formation of an extremal dyonic black hole. In these backgrounds
we consider the entanglement entropy of two types of geometries, the infinite
strip and the round disc, and find distinct behavior for each. Some of our
findings naturally supply results analogous to observations made in the
literature for lower dimensions, but we also uncover several new phenomena,
such as (in some cases) a discontinuity in the time derivative of the
entanglement entropy as it nears saturation, and for the electromagnetic
quench, a logarithmic growth in the entanglement entropy with time for both the
disc and strip, before settling to saturation.",1008.3027v2
2010-08-23,Saturated fusion systems with parabolic families,"Let G be group; a finite p-subgroup S of G is a Sylow p-subgroup if every
finite p-subgroup of G is conjugate to a subgroup of S. In this paper, we
examine the relations between the fusion system over S which is given by
conjugation in G and a certain chamber system C, on which G acts chamber
transitively with chamber stabilizer N_G(S). Next, we introduce the notion of a
fusion system with a parabolic family and we show that a chamber system can be
associated to such a fusion system. We determine some conditions the chamber
system has to fulfill in order to assure the saturation of the underlying
fusion system. We give an application to fusion systems with parabolic families
of classical type.",1008.3815v2
2010-08-24,Two Particle Correlations at Forward Rapidity in STAR,"During the 2008 run RHIC provided high luminosity in both p+p and d+Au
collisions at $\sqrt{s_{NN}}= 200$ GeV. Electromagnetic calorimeter acceptance
in STAR was enhanced by the new Forward Meson Spectrometer (FMS), and is now
almost contiguous from $-1<\eta<4$ over the full azimuth. This large acceptance
provides sensitivity to the gluon density in the nucleus down to $x\approx
10^{-3}$, as expected for $2\rightarrow 2$ parton scattering. Measurements of
the azimuthal correlation between a forward $\pi^{0}$ and an associated
particle at large rapidity are sensitive to the low-x gluon density. Data
exhibit the qualitative features expected from gluon saturation. A comparison
to calculations using the Color Glass Condensate (CGC) model is presented.",1008.3989v1
2010-08-30,Initial Conditions and Global Event Properties from Color Glass Condensate,"Perturbative unitarization from non-linear effects is thought to deplete the
gluon density for transverse momenta below the saturation scale. Such effects
also modify the distribution of gluons produced in heavy-ion collisions in
transverse impact parameter space. I discuss some of the consequences for the
initial conditions for hydrodynamic models of heavy-ion collisions and for hard
``tomographic'' probes. Also, I stress the importance of realistic modelling of
the fluctuations of the valence sources for the small-x fields in the impact
parameter plane. Such models can now be combined with solutions of
running-coupling Balitsky-Kovchegov evolution to obtain controlled predictions
for initial conditions at the LHC.",1008.5162v1
2010-09-07,First-principles calculations of graphene nanoribbons in gaseous environments: Structural and electronic properties,"The stability of graphene nanoribbons in the presence of typical atmospheric
molecules is systematically investigated by means of density functional theory.
We calculate the edge formation free energy of five different edge
configurations passivated by H, H$_2$, O, O$_2$, N$_2$, CO, CO$_2$, and H$_2$O,
respectively. In addition to the well known hydrogen passivated armchair and
zig-zag edges, we find the zig-zag edge saturated by oxygen atoms to be
particularly stable under atmospheric conditions. Saturation by oxygen leads to
the formation of metallic states strictly localized on the oxygen atoms.
Finally, the vibrational spectrum of the hydrogen and oxygen passivated ribbons
are calculated and compared.",1009.1242v2
2010-09-15,"Symmetric quivers, invariant theory, and saturation theorems for the classical groups","Let G denote either a special orthogonal group or a symplectic group defined
over the complex numbers. We prove the following saturation result for G: given
dominant weights \lambda^1, ..., \lambda^r such that the tensor product
V_{N\lambda^1} \otimes ... \otimes V_{N\lambda^r} contains nonzero G-invariants
for some N \ge 1, we show that the tensor product V_{2\lambda^1} \otimes ...
\otimes V_{2\lambda^r} also contains nonzero G-invariants. This extends results
of Kapovich-Millson and Belkale-Kumar and complements similar results for the
general linear group due to Knutson-Tao and Derksen-Weyman. Our techniques
involve the invariant theory of quivers equipped with an involution and the
generic representation theory of certain quivers with relations.",1009.3040v2
2010-10-22,Surface Polar Phonon Dominated Electron Transport in Graphene,"The effects of surface polar phonons on electronic transport properties of
monolayer graphene are studied by using a Monte Carlo simulation. Specifically,
the low-field electron mobility and saturation velocity are examined for
different substrates (SiC, SiO2, and HfO2) in comparison to the intrinsic case.
While the results show that the low-field mobility can be substantially reduced
by the introduction of surface polar phonon scattering, corresponding
degradation of the saturation velocity is not observed for all three substrates
at room temperature. It is also found that surface polar phonons can influence
graphene electrical resistivity even at low temperature, leading potentially to
inaccurate estimation of the acoustic phonon deformation potential constant.",1010.4772v1
2010-11-03,Transitions to three-dimensional flows in a cylinder driven by oscillations of the sidewall,"The transition from two-dimensional to three-dimensional flows in a finite
circular cylinder driven by an axially oscillating sidewall is explored in
detail. The complete symmetry group of this flow, including a spatio-temporal
symmetry related to the oscillating sidewall, is $Z_2\times O(2)$. Previous
studies in flows with the same symmetries, such as symmetric bluff-body wakes
and periodically forced rectangular cavities, were unable to obtain the
theoretically predicted bifurcation to modulated traveling waves. In the
simpler cylindrical geometry, where the azimuthal direction is physically
periodic, we have found these predicted modulated traveling waves as stable
fully saturated nonlinear solutions for the first time. A careful analysis of
the base states and their linear stability identifies different parameter
regimes where three-dimensional states that are either synchronous with the
forcing or quasiperiodic, corresponding to different symmetry-breaking
processes. These results are in good agreement with theoretical predictions and
previous results in similar flows. These different regimes are separated by
three codimension-two bifurcation points that are yet to be fully analyzed
theoretically. Finally, the saturated nonlinear states and their properties in
different parameter regimes are analyzed.",1011.1029v1
2010-11-15,"Saturation and Scaling of Multiplicity, Mean p_T and p_T Distributions from 200 GeV < sqrt{s} < 7 TeV - Addendum","In the previous paper we have argued that the LHC data on multiplicity,
average transverse momentum, and charged particle transverse momentum
distributions are well described with minimal modeling in terms of a saturation
scale Q_sat(s). As a consequence, the p_T spectra should exhibit geometric
scaling. In this short note we show that recently released CMS data at
sqrt{s}=0.9, 2.36 and 7 TeV fall on a universal curve when plotted in terms of
suitably defined scaling variable \tau.",1011.3403v3
2010-11-16,Forcibly driven coherent soft phonons in GeTe with intense THz-rate pump fields,"We propose an experimental technique to generate large amplitude coherent
phonons with irradiation of THz-rate pump pulses and to study the dynamics of
phase transition in GeTe ferroelectrics. When a single pump pulse irradiates
the sample at various pump power densities, the frequency of the soft phonon
decreases sub-linearly and saturates at higher pump powers. By contrast, when
THz-rate pump pulse sequence irradiates the sample at matched time intervals to
forcibly drive the oscillation, a large red-shift of the phonon frequency is
observed without saturation effects. After excitation with a four pump pulse
sequence, the coherent soft phonon becomes strongly damped leading to a near
critical damping condition. This condition indicates that the lattice is driven
to a precursor state of the phase transition.",1011.3624v2
2010-11-18,Scalar field in nuclear matter: the roles of spontaneous chiral symmetry breaking and nucleon structure,"Chiral theories with spontaneous symmetry breaking such as the
Nambu-Jona-Lasinio (NJL) model lead to the existence of a scalar mode. We
present in a detailed manner how the corresponding low momentum effective
lagrangian involving the scalar field can be constructed starting from the NJL
model. We discuss the relevance of the scalar mode for the problem of the
nuclear binding and saturation. We show that it depends on the nucleon mass
origin with two extreme cases. If this origin is entirely due to confinement
the coupling of this mode to the nucleons vanishes, making it irrelevant for
the nuclear binding problem. If instead it is entirely due to spontaneous
symmetry breaking it couples to the nucleons but nuclear matter collapses. It
is only in the case of a mixed origin with spontaneous breaking that nuclear
matter can be stable and reach saturation. We describe models of nucleon
structure where this balance is achieved. We also show how chiral constraints
and confinement modify the QCD sum rules for the mass evolution in nuclear
matter.",1011.4280v1
2010-11-21,Asymptotic analysis of stresses near a crack tip in a two dimensional colloidal packing saturated with liquid,"The consolidation of colloidal particles in drying colloidal dispersions is
influenced by various factors such as particle size and shape, and
inter-particle potential. The capillary pressure induced by the menisci, formed
between the top layer of particles in the packed bed, compresses the bed of
particles while the constraints enforced by the boundaries result in tensile
stresses in the packing. Presence of flaws or defects in the bed determines its
ultimate strength under such circumstances. In this study, we determine the
asymptotic stress distribution around a flaw in a two dimensional colloidal
packing saturated with liquid and compare the results with those obtained from
the full numerical solution of the problem. Using the Griffith's criterion for
equilibrium cracks, we relate the critical capillary pressure at equilibrium to
the crack size and the mechanical properties of the packed bed. The analysis
also gives the maximum allowable flaw size for obtaining a crack free packing.",1011.4626v2
2010-11-23,Detection of saturated absorption spectroscopy at high sensitivity with displaced crossovers,"We present an experimental approach to detect the saturated absorption
spectroscopy different from conventional scheme. Using this approach,
crossovers are removed to avoid their overlap with other peaks in the spectrum
and sensitivity of detection could be enhanced, so the spectrum could reflect
energy structure of atoms more explicitly. On the other hand, without harmful
influence from crossovers, locking range of the error signal is significantly
increased and symmetry of the dispersion line shape is perfectly reserved, so
reliability of frequency stabilization could be improved.",1011.5145v3
2010-11-29,Topographic phase boundary shifts and saturation for anisotropic ion straggle during sputter etching,"Surfaces sputtered by ion beam bombardment have been known to exhibit
patterns whose behavior is modeled with stochastic partial differential
equations. A widely accepted model is the Cuerno-Barabasi model which is robust
in its predictions of sputtered surface morphologies. An understanding of the
factors responsible for such surface topographies can be achieved by using
scaling arguments on the stochastic model. For such explanations, knowledge of
the coefficients is crucial. The more so since these vary with different
materials, the sputtering process itself generates non-equilibrium surfaces
within some finite timescale, and the implication of recent results of surface
topographies unexplained by the continuum theory. We calculate and study these
coefficients as functions of the sputtering parameters for yet unreported cases
of anisotropic ion energy distribution within the sputtered material.
Consequently, we present phase diagrams for the significant case of anisotropic
ion straggle. We observe shifts in the phase boundaries when the collision
cascade geometry rotates, and we also found saturation behavior in the
diagrams; in which case the boundaries become independent of the penetration
depths. Our results indicate a possible origin of yet unexplained nanodot
topographies arising from oblique incidence ion etching of amorphized surfaces.",1011.6234v1
2010-12-19,Breakdown of kT-factorization and J/Psi production in dA collisions,"In spite of the sweeping coherence effects in high energy hadron and nuclei
collisions, $k_T$-factorization can be recovered for the inclusive gluon
production in $pA$ collisions at the leading logarithmic order. In open charm
production at RHIC $k_T$-factorization holds numerically with about 10-20%
accuracy. This allows to extrapolate the cold nuclear matter effect observed in
light and charm meson production in $dA$ collisions to that in $AA$ ones.
Unlike the open charm, the breakdown of factorization in $J/\psi$ production is
severe. Indeed, already at the lowest order in gluon density the main
contribution to the inclusive cross section is proportional to the square of
gluon density in the nucleus. As a consequence, one cannot infer the cold
nuclear matter effect on $J/\psi$ production in $AA$ collisions from that in
$dA$. We present the calculation of $J/\psi$ multiplicity in the framework of
the CGC (color glass condensate)/saturation and show that it agrees with the
experimental data.",1012.4212v1
2010-12-23,Near-field radiative heat transfer and van der Waals friction between closely spaced graphene and amorphous SiO$_2$,"We study the radiative heat transfer and the van der Waals friction between
graphene and an amorphous SiO$_2$ substrate. We study the surface
phonon-polaritons contribution to the low-field mobility as a function of
temperature and of carrier density. We find that the electric current saturate
at a high electric field, in agreement with experiment. The saturation current
depends weakly on the temperature, which we attribute to the ""quantum"" friction
between the graphene carriers and the substrate optical phonons. We calculate
the frictional drag between two graphene sheets caused by van der Waals
friction, and find that this drag can induce a high enough voltage which can be
easily measured experimentally. We find that for nonsuspended graphene the
near-field radiative heat transfer, and the heat transfer due to direct
phononic coupling, are of the same order of magnitude at low electric field.
The phononic contribution to the heat transfer dominates at high field. For
large separation between graphene and the substrate the heat transfer is
dominated by the near-field radiative heat transfer.",1012.5212v1
2011-01-11,Diffractive hadron production in DIS off heavy nuclei and gluon saturation,"We calculate the cross section for diffractive hadron production in deep
inelastic scattering off heavy nuclei in the framework of gluon
saturation/color glass condensate. We analyze the kinematic region of the
future Electron-Ion Collider. We argue that coherent and incoherent diffractive
channels are very sensitive to the structure of the nuclear matter at low $x$.
This expresses itself in a characteristic dependence of the cross sections on
rapidity and transverse momentum of the produced hadron and on the nuclear
weight. We also discuss dependence on the scattering angle and argue that both
coherent and incoherent cross sections may be within experimental reach at EIC.",1101.2179v2
2011-01-19,Constraints on the density dependence of the symmetry energy from heavy ion collisions,"Constraints on the Equation of State for symmetric matter (equal neutron and
proton numbers) have been extracted from energetic collisions of heavy ions
over a range of energies. Collisions of neutron-deficient and neutron-rich
heavy ions now provide initial constraints on the EoS of neutron-rich matter at
sub-saturation densities from isospin diffusions and neutron proton ratios.
This article reviews the experimental constraints on the density dependence of
Symmetry Energy at sub-saturation density.",1101.3648v1
2011-01-21,Improvement of the crossed undulator design for effective circular polarization control in X-ray FELs,"The production of X-ray radiation with a high degree of circular polarization
constitutes an important goal at XFEL facilities. A simple scheme to obtain
circular polarization control with crossed undulators has been proposed so far.
In its simplest configuration the crossed undulators consist of pair of short
planar undulators in crossed position separated by an electromagnetic phase
shifter. An advantage of this configuration is a fast helicity switching. A
drawback is that a high degree of circular polarization (over 90%) can only be
achieved for lengths of the insertion devices significantly shorter than the
gain length, i.e. at output power significantly lower than the saturation power
level. The obvious and technically possible extension considered in this paper,
is to use a setup with two or more crossed undulators separated by phase
shifters. This cascade crossed undulator scheme is distinguished, in
performance, by a fast helicity switching, a high degree of circular
polarization (over 95%) and a high output power level, comparable with the
saturation power level in the baseline undulator at fundamental wavelength. We
present feasibility study and exemplifications for the LCLS baseline in the
soft X-ray regime.",1101.4085v1
2011-02-01,A congestion model for cell migration,"This paper deals with a class of macroscopic models for cell migration in a
saturated medium for two-species mixtures. Those species tend to achieve some
motion according to a desired velocity, and congestion forces them to adapt
their velocity. This adaptation is modelled by a correction velocity which is
chosen minimal in a least-square sense. We are especially interested in two
situations: a single active species moves in a passive matrix (cell migration)
with a given desired velocity, and a closed-loop Keller-Segel type model, where
the desired velocity is the gradient of a self-emitted chemoattractant. We
propose a theoretical framework for the open-loop model (desired velocities are
defined as gradients of given functions) based on a formulation in the form of
a gradient flow in the Wasserstein space. We propose a numerical strategy to
discretize the model, and illustrate its behaviour in the case of a prescribed
velocity, and for the saturated Keller-Segel model.",1102.0147v1
2011-02-02,Threshold Saturation on Channels with Memory via Spatial Coupling,"We consider spatially coupled code ensembles. A particular instance are
convolutional LDPC ensembles. It was recently shown that, for transmission over
the memoryless binary erasure channel, this coupling increases the belief
propagation threshold of the ensemble to the maximum a-posteriori threshold of
the underlying component ensemble. This paved the way for a new class of
capacity achieving low-density parity check codes. It was also shown
empirically that the same threshold saturation occurs when we consider
transmission over general binary input memoryless channels.
  In this work, we report on empirical evidence which suggests that the same
phenomenon also occurs when transmission takes place over a class of channels
with memory. This is confirmed both by simulations as well as by computing EXIT
curves.",1102.0406v1
2011-02-04,Two-particle azimuthal correlations at forward rapidity in STAR,"During the 2008 run the Relativistic Heavy Ion Collider (RHIC) at the
Brookhaven Nation Laboratiory (BNL), NY, provided high luminosity in both p+p
and d+Au collisions at $\sqrt{s_{NN}}=200\mathrm{\,GeV}$. Electromagnetic
calorimeter acceptance in STAR was enhanced by the new Forward Meson
Spectrometer (FMS), and is now almost contiguous from $-1<\eta\4$ over the full
azimuth. This allows measurements of the azimuthal correlation between a
forward neutral pion and a second particle in a very large rapidity range.
Di-hadron azimuthal correlations provide sensitivity to the low longitudinal
momentum fraction ($x$) component of the gluon density in the nuclear target.
Initial state nonlinear effects are in fact expected to appear in d+Au
collisions when the dense part of the nucleus is probed. The analysis in this
thesis shows that such correlations and their dependence on rapidity,
transverse momentum and collision centrality are qualitative consistent with
the existence of gluon saturation effects in the relativistic nucleus.
Theoretical expectations for azimuthal correlations between a dilute system
(deuteron) and a saturated target (Gold nucleus) have been explored.",1102.0931v1
2011-02-15,Saturation of front propagation in a reaction-diffusion process describing plasma damage in porous low-k materials,"We propose a three-component reaction-diffusion system yielding an asymptotic
logarithmic time-dependence for a moving interface. This is naturally related
to a Stefan-problem for which both one-sided Dirichlet-type and von
Neumann-type boundary conditions are considered. We integrate the dependence of
the interface motion on diffusion and reaction parameters and we observe a
change from transport behavior and interface motion \sim t^1/2 to logarithmic
behavior \sim ln t as a function of time. We apply our theoretical findings to
the propagation of carbon depletion in porous dielectrics exposed to a low
temperature plasma. This diffusion saturation is reached after about 1 minute
in typical experimental situations of plasma damage in microelectronic
fabrication. We predict the general dependencies on porosity and reaction
rates.",1102.3084v2
2011-02-16,Parallel Complexity of Random Boolean Circuits,"Random instances of feedforward Boolean circuits are studied both
analytically and numerically. Evaluating these circuits is known to be a
P-complete problem and thus, in the worst case, believed to be impossible to
perform, even given a massively parallel computer, in time much less than the
depth of the circuit. Nonetheless, it is found that for some ensembles of
random circuits, saturation to a fixed truth value occurs rapidly so that
evaluation of the circuit can be accomplished in much less parallel time than
the depth of the circuit. For other ensembles saturation does not occur and
circuit evaluation is apparently hard. In particular, for some random circuits
composed of connectives with five or more inputs, the number of true outputs at
each level is a chaotic sequence. Finally, while the average case complexity
depends on the choice of ensemble, it is shown that for all ensembles it is
possible to simultaneously construct a typical circuit together with its
solution in polylogarithmic parallel time.",1102.3310v2
2011-02-16,Quantum phenomena in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with 3He. A giant isotope effect,"The radial thermal expansion {\alpha}r of bundles of single-walled carbon
nanotubes saturated with 3He up to the molar concentration 9.4% has been
investigated in the temperature interval 2.1-9.5 K by high-sensitivity
capacitance dilatometry. In the interval 2.1-7 K a negative {\alpha}r was
observed, with a magnitude which exceeded the largest negative {\alpha}r values
of pure and 4He-saturated nanotubes by three and two orders of magnitude,
respectively. The contributions of the two He isotope impurities to the
negative thermal expansion of the nanotube bundles are most likely connected
with the spatial redistribution of 4He and 3He atoms by tunneling at the
surface and inside nanotube bundles. The isotope effect turned out to be huge,
probably owing to the higher tunneling probability of 3He atoms.",1102.3334v1
2011-02-26,The thermodynamic approach to multifractal analysis,"Most results in multifractal analysis are obtained using either a
thermodynamic approach based on existence and uniqueness of equilibrium states
or a saturation approach based on some version of the specification property. A
general framework incorporating the most important multifractal spectra was
introduced by Barreira and Saussol, who used the thermodynamic approach to
establish the multifractal formalism in the uniformly hyperbolic setting,
unifying many existing results. We extend this framework to apply to a broad
class of non-uniformly hyperbolic systems, including examples with phase
transitions. In the process, we compare this thermodynamic approach with the
saturation approach and give a survey of many of the multifractal results in
the literature.",1102.5427v2
2011-03-15,Liquid-Droplet as a model for the rotation curve problem,"The dynamics of large scale gravitational structures like galaxies, local
groups and clusters is studied based on the so-called {\it Liquid-Droplet}
model describing the saturation property of the nuclear force. Using the
assumption that the gravitational force is also saturated over large scale
structures, it is argued that the Newtonian gravitational potential may be
replaced by an effective {\it Machian} gravitational potential. Application of
this new potential at these large scale structures may give the rotation curves
in good agreement with observations. Then, the virial theorem for this kind of
gravitational interaction is developed and also the Tully-Fisher relation is
obtained. A physical explanation is given for the so-called {\it constant}
acceleration in the MOND as the {\it effective} gravitational strength of these
structures. Finally, a brief argument is given for comparison with dark matter
models.",1103.3057v3
2011-03-18,Weak turbulence theory of the non-linear evolution of the ion ring distribution,"The nonlinear evolution of an ion ring instability in a low-beta
magnetospheric plasma is considered. The evolution of the two-dimensional ring
distribution is essentially quasilinear. Ignoring nonlinear processes the
time-scale for the quasilinear evolution is the same as for the linear
instability 1/t_ql gamma_l. However, when nonlinear processes become important,
a new time scale becomes relevant to the wave saturation mechanism. Induced
nonlinear scattering of the lower-hybrid waves by plasma electrons is the
dominant nonlinearity relevant for plasmas in the inner magnetosphere and
typically occurs on the timescale 1/t_ql w(M/m)W/nT, where W is the wave energy
density, nT is the thermal energy density of the background plasma, and M/m is
the ion to electron mass ratio, which has the consequence that the wave
amplitude saturates at a low level, and the timescale for quasilinear
relaxation is extended by orders of magnitude.",1103.3715v1
2011-03-23,Imprints of Nuclear Symmetry Energy on Properties of Neutron Stars,"Significant progress has been made in recent years in constraining the
density dependence of nuclear symmetry energy using terrestrial nuclear
laboratory data. Around and below the nuclear matter saturation density, the
experimental constraints start to merge in a relatively narrow region. At
supra-saturation densities, there are, however, still large uncertainties.
After summarizing the latest experimental constraints on the density dependence
of nuclear symmetry energy, we highlight a few recent studies examining
imprints of nuclear symmetry energy on the binding energy, energy release
during hadron-quark phase transitions as well as the $w$-mode frequency and
damping time of gravitational wave emission of neutron stars.",1103.4652v1
2011-03-29,Accumulation of beneficial mutations in one dimension,"When beneficial mutations are relatively common, competition between multiple
unfixed mutations can reduce the rate of fixation in well-mixed asexual
populations. We introduce a one dimensional model with a steady accumulation of
beneficial mutations. We find a transition between periodic selection and
multiple-mutation regimes. In the multiple-mutation regime, the increase of
fitness along the lattice bears a striking similarity to surface growth
phenomena, with power law growth and saturation of the interface width. We also
find significant differences compared to the well-mixed model. In our lattice
model, the transition between regimes happens at a much lower mutation rate due
to slower fixation times in one dimension. Also the rate of fixation is reduced
with increasing mutation rate due to the more intense competition, and it
saturates with large population size.",1103.5685v2
2011-04-01,Finite Pressure Corrections to Nucleon Structure Function Inside a Nuclear Medium,"Our model calculations performed in the frame of the Relativistic Mean Field
(RMF) approach show how important are the modifications of nucleon Structure
Function (SF) in Nuclear Matter (NM) above the saturation point. They
originated from the conservation of a parton longitudinal momenta - essential
in the explanation of the EMC effect at the saturation point of NM. For higher
density the finite pressure corrections emerge from the Hugenholtz -van Hove
(HH) theorem valid for NM and asks to modify the nucleon SF. The density
evolution of the nuclear SF seems to be stronger for higher densities. Here we
show that the course of Equation o State (EoS) in our modified Walecka model is
very close to that obtained from extensive DBHF calculations with a Bonn A
potential. The nuclear compressibility decreases. Our model - a nonlinear
extension of nuclear RMF, has no additional parameters.",1104.0093v4
2011-04-06,Quantum entanglement in SU(3) lattice Yang-Mills theory at zero and finite temperatures,"We examine the entanglement properties of the Yang-Mills theory by
calculating $\alpha$ entanglement entropy with $\alpha=2$ using a SU(3)
quenched lattice gauge simulation both in the confinement and the deconfinement
phases. In the confinement phase, the derivative of the $\alpha$ entropy with
respect to the size $l$ of the subregion, whose entanglement properties are
interested in, scales as $1/l^3$, and a clear discontinuity cannot be found
within our statistical errors. The $\alpha$ entropy in the deconfinement phase
saturates at large $l$. The saturation value is comparable with the thermal
entropy of the pure Yang-Mills theory, indicating that the $\alpha$ entropy
obeys the volume law at large $l$ in the deconfinement phase.",1104.1011v1
2011-05-03,The advection-condensation model and water vapour PDFs,"The statistically steady humidity distribution resulting from an interaction
of advection, modeled as an uncorrelated random walk of moist parcels on an
isentropic surface, and a vapour sink, modeled as immediate condensation
whenever the specific humidity exceeds a specified saturation humidity, is
explored with theory and simulation. A source supplies moisture at the
deep-tropical southern boundary of the domain, and the saturation humidity is
specified as a monotonically decreasing function of distance from the boundary.
The boundary source balances the interior condensation sink, so that a
stationary spatially inhomogeneous humidity distribution emerges. An exact
solution of the Fokker-Planck equation delivers a simple expression for the
resulting probability density function (PDF) of the water vapour field and also
of the relative humidity. This solution agrees completely with a numerical
simulation of the process, and the humidity PDF exhibits several features of
interest, such as bimodality close to the source and unimodality further from
the source. The PDFs of specific and relative humidity are broad and
non-Gaussian. The domain averaged relative humidity PDF is bimodal with
distinct moist and dry peaks, a feature which we show agrees with middleworld
isentropic PDFs derived from the ERA interim dataset.",1105.0470v1
2011-05-17,The Ridge from the BFKL evolution and beyond,"We show that the long-range rapidity correlations between the produced
charged-hadron pairs from two BFKL parton showers generate considerable
azimuthal angle correlations. These correlations have no 1/N_c suppression. The
effect of gluon saturation on these correlations are discussed and we show that
it is important. We show that a pronounced ridge-like structure emerges by
going from the BFKL to the saturation region. We show that the ridge structure
at high-energy proton-proton and nucleus-nucleus collisions has the same origin
and its main feature can be understood due to initial-state effects. Although
the effects of final-state interactions in the latter case can be
non-negligible.",1105.3275v2
2011-05-17,Jaynes Cummings treatment of superconducting resonators with dielectric loss due to two-level systems,"We perform a quantum mechanical analysis of superconducting resonators
subject to dielectric loss arising from charged two-level systems. We present
numerical and analytical descriptions of the dynamics of energy decay from the
resonator within the Jaynes-Cummings model. Our analysis allows us to
distinguish the strong and weak coupling regimes of the model and to describe
within each regime cases where the two-level system is unsaturated or
saturated. We find that the quantum theory agrees with the classical model for
weak coupling. However, for strong coupling the quantum theory predicts lower
loss than the classical theory in the unsaturated regime. Also, in contrast to
the classical theory, the photon number at which saturation occurs in the
strong coupling quantum theory is independent of the coupling between the
resonator and the two-level system.",1105.3446v1
2011-05-26,Calibration and performance of the photon-counting detectors for the Ultraviolet Imaging Telescopes (UVIT) of the Astrosat observatory,"We describe calibration data, and discuss performance of the photon-counting
flight detectors for the Ultraviolet Imaging Telescopes on the Astrosat
observatory. The paper describes dark current, flat field and light-spot images
for FUV, NUV, and Visible band detectors at more than one wavelength setting
for each. We also report on nominal gain and low-gain operations, full- and
sub-window read rates, and non-photon-counting modes of operation, all expected
to be used in flight. We derive corrections to the event centroids from the
CMOS readout arrays, for different centroid algorithms. We derive spatial
resolution values for each detector and plots of point-source signal saturation
for different flux levels. We also discuss ways to correct for saturation in
extended object images.",1105.5361v1
2011-05-31,Universality for the Noisy Slepian-Wolf Problem Via Spatial Coupling,"We consider a noisy Slepian-Wolf problem where two correlated sources are
separately encoded and transmitted over two independent binary memoryless
symmetric channels. Each channel capacity is assumed to be characterized by a
single parameter which is not known at the transmitter. The receiver has
knowledge of both the source correlation and the channel parameters. We call a
system universal if it retains near-capacity performance without channel
knowledge at the transmitter. Kudekar et al. recently showed that terminated
low-density parity-check (LDPC) convolutional codes (a.k.a. spatially-coupled
LDPC ensembles) can have belief-propagation thresholds that approach their
maximum a-posteriori thresholds. This was proven for binary erasure channels
and shown empirically for binary memoryless symmetric channels. They also
conjectured that the principle of spatial coupling is very general and the
phenomenon of threshold saturation applies to a very broad class of graphical
models. In this work, we derive an area theorem for the joint decoder and
empirically show that threshold saturation occurs for this problem. As a
result, we demonstrate near-universal performance for this problem using the
proposed spatially-coupled coding system. A similar result is also discussed
briefly for the 2-user multiple-access channel.",1105.6374v1
2011-08-01,BPS Saturated String Amplitudes: K3 Elliptic Genus and Igusa Cusp Form,"We study BPS saturated one-loop amplitudes in type II string theory
compactified on K3 x T^2. The classes of amplitudes we consider are only
sensitive to the very basic topological data of the internal K3 manifold. As a
consequence, the integrands of the former are related to the elliptic genus of
K3, which can be decomposed into representations of the internal N=4
superconformal algebra. Depending on the precise choice of external states
these amplitudes capture either only the contribution of the short multiplets
or the full series including intermediate multiplets. In the latter case we can
define a generating functional for the whole class, which we show is given by
the weight ten Igusa cusp form chi_{10} of Sp(4,Z). We speculate on possible
algebraic implications of our result on the BPS states of the N=4 type II
compactification.",1108.0323v2
2011-08-02,Composition and stability of hybrid stars with hyperons and quark color-superconductivity,"The recent measurement of a $1.97\pm 0.04$ solar-mass pulsar places a
stringent lower bound on the maximum mass of compact stars and therefore
challenges the existence of any agents that soften the equation of state of
ultra-dense matter. We investigate whether hyperons and/or quark matter can be
accommodated in massive compact stars by constructing an equation of state
based on a combination of phenomenological relativistic hyper-nuclear density
functional and an effective model of quantum chromodynamics (the
Nambu-Jona-Lasinio model). Stable configurations are obtained with $M \ge 1.97
M_{\sun}$ featuring hyper-nuclear and quark matter in color superconducting
state if the equation of state of nuclear matter is stiff above the saturation
density, the transition to quark matter takes place at a few times the nuclear
saturation density, and the repulsive vector interactions in quark matter are
substantial.",1108.0559v2
2011-08-08,On the small-x evolution of the color quadrupole and the Weizsäcker-Williams gluon distribution,"Color quadrupoles have been found to be important in the proper description
of observables sensitive to the small-x regime in nuclei as well as in the
operator definition of the Weizs\""acker-Williams gluon distribution. In this
paper, we derive the small-x evolution equation of the quadrupole and the
Weizs\""acker-Williams gluon distribution without taking large N_c limit and
study the properties of the equation in both dilute and saturation regime. We
find that the quadrupole evolution follows the BFKL evolution in the dilute
regime and then saturates in the dense region due to nonlinear terms. This
leads us to conclude that the Weizs\""acker-Williams gluon distribution should
obey the same geometrical behavior as the dipole gluon distribution as found in
the inclusive DIS measurement.",1108.1752v2
2011-08-16,Heralded Single-Photon Emission from the Mollow Triplet Sidebands of a Quantum Dot,"Emission from a resonantly excited quantum emitter is a fascinating research
topic within quantum optics and a useful source for different types of quantum
light fields. The resonance spectrum consists of a single spectral line below
saturation of a quantum emitter which develops into a triplet at powers above
saturation of the emitter. The spectral properties of the triplet strongly
depends on pump power and detuning of the excitation laser. The three closely
spaced photon channels from the resonance fluorescence have different photon
statistical signatures. We present a detailed photon-statistics analysis of the
resonance fluorescence emission triplet from a solid state-based artificial
atom, i.e. a semiconductor quantum dot. The photon correlation measurements
demonstrate both 'single' and 'heralded' photon emission from the Mollow
triplet sidebands. The ultra-bright and narrowband emission (5.9 MHz into the
first lens) can be conveniently frequency-tuned by laser detuning over 15 times
its linewidth ({\Delta \nu} \approx 1.0 GHz). These unique properties make the
Mollow triplet sideband emission a valuable light source for, e.g.quantum light
spectroscopy and quantum information applications.",1108.3225v1
2011-08-29,Rayleigh-Benard convection with phase changes in a Galerkin model,"The transition to turbulence in Rayleigh-Benard convection with phase changes
and the resulting convective patterns are studied in a three-dimensional
Galerkin model. Our study is focused to the conditionally unstable regime of
moist convection in which the stratification is stable for unsaturated air
parcels and unstable for saturated parcels. We perform a comprehensive
statistical analysis of the transition to convection that samples the
dependence of attractors (or fixed points) in the phase space of the model on
the dimensionless parameters. Conditionally unstable convection can be
initiated either from a fully unsaturated linearly stable equilibrium or a
fully saturated linearly unstable equilibrium. Highly localized moist
convection can be found in steady state, in oscillating recharge-discharge
regime or turbulent in dependence on the aspect ratio and the degree of stable
stratification of the unsaturated air. Our phase space analysis predicts
parameter ranges for which self-sustained convective regimes in the case of
subcritical conditional instability can be observed. The observed regime
transitions for moist convection bear some similarities to transitions to
turbulence in simple shear flows.",1108.5611v1
2011-08-31,Blending margins: The modal logic K has nullary unification type,"We investigate properties of the formula $p \to \Box p$ in the basic modal
logic K. We show that K satisfies an infinitary weaker variant of the rule of
margins $\phi \to \Box\phi / \phi, \neg\phi$, and as a consequence, we obtain
various negative results about admissibility and unification in K. We describe
a complete set of unifiers (i.e., substitutions making the formula provable) of
$p \to \Box p$, and use it to establish that K has the worst possible
unification type: nullary. In well-behaved transitive modal logics,
admissibility and unification can be analyzed in terms of projective formulas,
introduced by Ghilardi; in particular, projective formulas coincide for these
logics with formulas that are admissibly saturated (i.e., derive all their
multiple-conclusion admissible consequences) or exact (i.e., axiomatize a
theory of a substitution). In contrast, we show that in K, the formula $p \to
\Box p$ is admissibly saturated, but neither projective nor exact. All our
results for K also apply to the basic description logic ALC.",1108.6240v2
2011-09-02,On Angular Correlations and High Energy Evolution,"We address the question to what extent JIMWLK evolution is capable of taking
into account angular correlations in a high energy hadronic wave function. Our
conclusion is that angular (and indeed other) correlations in the wave function
cannot be reliably calculated without taking into account Pomeron loops in the
evolution. As an example we study numerically the energy evolution of angular
correlations between dipole scattering amplitudes in the framework of the large
$N_c$ approximation to JIMWLK evolution (the ""`projectile dipole model""').
Target correlations are introduced via averaging over (isotropic) ensemble of
anisotropic initial conditions. We find that correlations disappear very
quickly with rapidity even inside the saturation radius. This is in accordance
with our physical picture of JIMWLK evolution. The actual correlations inside
the saturation radius in the target QCD wave function, on the other hand should
remain sizable at any rapidity.",1109.0347v1
2011-09-03,Small-${\it x}$ and Forward Measurements at STAR,"Measurements of azimuthal differences between forward di-pions are sensitive
to the low-${\it x}$ gluon content of the proton and provide the best
opportunity to probe for gluon saturation in nuclei. Previously reported
analyses have shown that the gluon saturation regime may have been reached at
STAR by looking at forward di-pions in d+Au collisions. Further insight into
the uncorrelated pedestal below the near-side and away-side peaks in azimuthal
correlations may be provided by differentiating between d+Au and p+Au
collisions, by tagging on intact neutrons in the deuteron beam in d+Au
collisions. Comparisons to recent theories indicate that multi-parton
interactions play a more significant role in d+Au collisions than p+Au
collisions and offer a unique opportunity to study correlations between leading
partons inside nucleons. The general features found for the peaks in forward
di-pion azimuthal correlations in d+Au collisions are also present in p+Au
collisions.",1109.0649v1
2011-09-06,Electron Transport Properties of Bilayer Graphene,"Electron transport in bilayer graphene is studied by using a first principles
analysis and theMonte Carlo simulation under conditions relevant to potential
applications. While the intrinsic properties are found to be much less
desirable in bilayer than in monolayer graphene, with significantly reduced
mobilities and saturation velocities, the calculation also reveals the dominant
influence of extrinsic factors such as the substrate and impurities.
Accordingly, the difference between two graphene forms are more muted in
realistic settings although the velocity-field characteristics remain
substantially lower in the bilayer. When bilayer graphene is subject to an
interlayer bias, the resulting changes in the energy dispersion lead to
stronger electron scattering at the bottom of the conduction band. The mobility
decreases significantly with the size of the generated bandgap, whereas the
saturation velocity remains largely unaffected.",1109.1035v1
2011-09-06,Gluon saturation effects on the color singlet J/Psi production in high energy dA and AA collisions,"We derive the formulae for the cross section of J/Psi production in high
energy pA and AA collisions taking into account the gluon saturation/color
glass condensate effects. We then perform the numerical calculations of the
corresponding nuclear modification factors and find a good agreement between
our calculations and the experimental data on J/Psi production in dA
collisions. We also observe that cold nuclear modification effects alone cannot
describe the data on J/Psi production in AA collisions. Additional final state
suppression (at RHIC) and enhancement (at LHC) mechanisms are required to
explain the experimental observations.",1109.1250v1
2011-09-16,Neon Insights from Old Solar X-rays: a Plasma Temperature Dependence of the Coronal Neon Content,"An analysis using modern atomic data of fluxes culled from the literature for
O VIII and Ne IX lines observed in solar active regions by the P78 and Solar
Maximum Mission satellites confirms that the coronal Ne/O abundance ratio
varies by a factor of two or more, and finds an increase in Ne/O with
increasing active region plasma temperature. The latter is reminiscent of
evidence for increasing Ne/O with stellar activity in low-activity coronae that
reaches a ""neon saturation"" in moderately active stars at approximately twice
the historically accepted solar value of about 0.15 by number. We argue that
neon saturation represents the underlying stellar photospheric compositions,
and that low activity coronae, including that of the Sun, are generally
depleted in neon. The implication would be that the solar Ne/O abundance ratio
should be revised upward by a factor of about two to n(Ne)/n(O)~0.3. Diverse
observations of neon in the local cosmos provide some support for such a
revision. Neon would still be of some relevance for reconciling helioseismology
with solar models computed using recently advocated chemical mixtures with
lower metal content.",1109.3661v1
2011-09-20,Molecular explanation for why talc surfaces can be both hydrophilic and hydrophobic,"While individual water molecules adsorb strongly on a talc surface
(hydrophilic behavior), a droplet of water beads up on the same surface
(hydrophobic behavior). To rationalize this dichotomy, we investigate the
influence of the microscopic structure of the surface and the strength of
adhesive (surface-water) interactions on surface hydrophobicity. We show that
at low relative humidity, the competition between adhesion and the favorable
entropy of being in the vapor phase determines the surface coverage. However,
at saturation, it is the competition between adhesion and cohesion (water-water
interactions) that determines surface hydrophobicity. The adhesive interactions
in talc are strong enough to overcome the unfavorable entropy, and water
adsorbs strongly on talc surfaces. However, they are too weak to overcome the
cohesive interactions, and water thus beads up on talc surfaces. Surprisingly,
even (talc-like) surfaces that are highly adhesive, do not fully wet at
saturation. Instead, a water droplet forms on top of a strongly adsorbed
monolayer of water. Our results imply that the interior of hydrophobic zeolites
suspended in water may contain adsorbed water molecules at pressures much
smaller than the intrusion pressure.",1109.4284v1
2011-09-30,Quasi-compactons in inverted nonlinear photonic crystals,"We study large-amplitude one-dimensional solitary waves in photonic crystals
featuring competition between linear and nonlinear lattices, with minima of the
linear potential coinciding with maxima of the nonlinear pseudopotential, and
vice versa (inverted nonlinear photonic crystals, INPhCs), in the case of the
saturable self-focusing nonlinearity. Such crystals were recently fabricated
using a mixture of SU-8 and Rhodamine-B optical materials. By means of
numerical methods and analytical approximations, we find that large-amplitude
solitons are broad sharply localized stable pulses (quasi-compactons, QCs).
With the increase of the totalpower, P, the QC's centroid performs multiple
switchings between minima and maxima of the linear potential. Unlike cubic
INPhCs, the large-amplitude solitons are mobile in the medium with the
saturable nonlinearity. The threshold value of the kick necessary to set the
soliton in motion is found as a function of P. Collisions between moving QCs
are considered too.",1110.0049v1
2011-10-03,Universal Codes for the Gaussian MAC via Spatial Coupling,"We consider transmission of two independent and separately encoded sources
over a two-user binary-input Gaussian multiple-access channel. The channel
gains are assumed to be unknown at the transmitter and the goal is to design an
encoder-decoder pair that achieves reliable communication for all channel gains
where this is theoretically possible. We call such a system \emph{universal}
with respect to the channel gains.
  Kudekar et al. recently showed that terminated low-density parity-check
convolutional codes (a.k.a. spatially-coupled low-density parity-check
ensembles) have belief-propagation thresholds that approach their maximum
a-posteriori thresholds. This was proven for binary erasure channels and shown
empirically for binary memoryless symmetric channels. It was conjectured that
the principle of spatial coupling is very general and the phenomenon of
threshold saturation applies to a very broad class of graphical models. In this
work, we derive an area theorem for the joint decoder and empirically show that
threshold saturation occurs for this problem. As a result, we demonstrate
near-universal performance for this problem using the proposed
spatially-coupled coding system.",1110.0252v1
2011-10-14,Optimization of the baseline and the parent muon energy for a low energy neutrino factory,"We discuss the optimal setup for a low energy neutrino factory in order to
achieve a 5\sigma-discovery of a nonzero mixing angle \theta_{13}, a nonzero CP
phase \delta_{CP}, and the mass hierarchy. We explore parent muon energies in
the range 5--16 GeV, and baselines in the range 500--5000 km. We present the
results in terms of the reach in sin^2\theta_{13}, emphasizing the dependence
of the optimal baseline on the true value of \delta_{CP}. We show that the
sensitivity of a given setup typically increases with parent muon energy,
reaching saturation for higher energies. The saturation energy is larger for
longer baselines; we present an estimate of this dependence. In the light of
the recent indications of a large \theta_{13}, we also determine how these
preferences would change if indeed a large \theta_{13} is confirmed. In such a
case, the baselines ~2500 km (~1500 km) may be expected to lead to hierarchy
determination (\delta_{CP} discovery) with the minimum exposure.",1110.3289v2
2011-10-19,Evaluating the robustness of top coatings comprising plasma-deposited fluorocarbons in electrowetting systems,"Thin dielectric stacks comprising a main insulating layer and a hydrophobic
top coating are commonly used in low voltage electrowetting systems. However,
in most cases, thin dielectrics fail to endure persistent electrowetting
testing at high voltages, namely beyond the saturation onset, as electrolysis
indicates dielectric failure. Careful sample inspection via optical microscopy
revealed possible local delamination of the top coating under high electric
fields. Thus, improvement of the adhesion strength of the hydrophobic top
coating to the main dielectric is attempted through a plasma-deposited
fluorocarbon interlayer. Interestingly enough the proposed dielectric stack
exhibited a) resistance to dielectric breakdown, b) higher contact angle
modulation range, and c) electrowetting cycle reversibility. Appearance of
electrolysis in the saturation regime is inhibited, suggesting the use of this
hydrophobic dielectric stack for the design of more efficient electrowetting
systems. The possible causes of the improved performance are investigated by
nanoscratch characterization.",1110.4238v1
2011-10-25,Allen-Cahn and Cahn-Hilliard-like equations for dissipative dynamics of saturated porous media,"We consider a saturated porous medium in the regime of solid-fluid
segregation under an applied pressure on the solid constituent. We prove that,
depending on the dissipation mechanism, the dynamics is described either by a
Cahn-Hilliard or by an Allen-Cahn-like equation. More precisely, when the
dissipation is modeled via the Darcy law we find that, for small deformation of
the solid and small variations of the fluid density, the evolution equation is
very similar to the Cahn-Hilliard equation. On the other hand, when only the
Stokes dissipation term is considered, we find that the evolution is governed
by an Allen-Cahn-like equation. We use this theory to describe the formation of
interfaces inside porous media. We consider a recently developed model proposed
to study the solid-liquid segregation in consolidation and we are able to fully
describe the formation of an interface between the fluid-rich and the
fluid-poor phase.",1110.5457v2
2011-10-29,Comparative investigation of third and fifth harmonic generation in atomic and molecular gases driven by mid-infrared ultrafast laser pulses,"We report on the comparative experimental investigation on third and fifth
harmonic generation (THG and FHG) in atomic and molecular gases driven by
mid-infrared ultrafast laser pulses at a wavelength of ~1500 nm. We observe
that the conversion efficiencies of both the THG and FHG processes saturate at
similar peak intensities close to ~1.5\times1014 W/cm2 for argon, nitrogen, and
air, whose ionization potentials are close to each other. Near the saturation
intensity, the ratio of yields of the FHG and THG reaches ~10-1 for all the
gases. Our results show that high-order Kerr effects do exist, whereas they are
insufficient to balance the Kerr self-focusing without the assistance of plasma
generation.",1110.6505v1
2011-10-30,Gluon-decay cascade in AA collisions at the LHC and saturation,"We extract the energy-dependence of the gluon-jet decay cascade from e^+e^-
annihilation data and show that this energy-dependence has power-low behavior
for the average transverse momentum of jet bigger than 1 GeV. We show that the
observed different power-law energy-dependence of hadron multiplicity in AA
compared to pp collisions at the LHC is due to the enhanced gluon-decay effect
before hadronization. This effect is more important for AA collisions where the
saturation scale is larger than 1 GeV. Here we confront our published
predictions in arXiv:1102.2385 for the rapidity distribution of the charged
hadron production with the recently released data from the CMS collaboration in
AA collisions and show that our predictions is in perfect agreement with the
data.",1110.6642v1
2011-11-09,Charged particle multiplicities in pA interactions at the LHC from the Color Glass Condensate,"The forthcoming LHC measurement of hadron multiplicity in proton-nucleus
collisions is a crucial test of the k_t factorization and gluon saturation
based models. Here, we provide quantitative predictions for the pseudorapidity
distribution of charged particles produced in minimum bias proton-nucleus
collisions at the LHC based on the idea of gluon saturation in the color-glass
condensate framework. Our formulation gives good descriptions of the LHC and
RHIC data for the charged-hadron multiplicities in both proton-proton and
nucleus-nucleus collisions, and also the deep inelastic scattering at HERA at
small Bjorken-x.",1111.2312v2
2011-11-12,An effective-charge model for the trapping of impurities of fluids in channels with nanostructured walls,"We present model equations for the trapping and accumulation of particles in
a short cylindrical channel with nanostructured inner walls when a fluid passes
through, carrying a moderate load of impurities. The basic ingredient of the
model is the introduction of a phenomenological ""effective-charge density"" of
the walls, related to the electrical charges exposed in the nanotexture, and
which is gradually reduced as the flow runs through the channel and the trapped
impurities cover the internal walls. By solving the proposed equations, three
regimes are predicted for the channel: a linear or clean-filter regime, a
logarithmic or half-saturation regime, and the saturation limit. It is proposed
that experimentally testing these regimes may help to understand the enhanced
trapping capability observed in many diverse nanotextured channel structures.",1111.2920v3
2011-11-13,Gluon saturation in $pA$ collisions at the LHC: KLN model predictions for hadron multiplicities,"The upcoming p+Pb run at the LHC will probe the nuclear gluon distribution at
very small Bjorken x (from $x \sim 10^{-4}$ at mid-rapidity down to $x \sim
10^{-6}$ in the proton fragmentation region) and will allow to test approaches
based on parton saturation. Here, we present the predictions of the KLN model
for hadron multiplicities and multiplicity distributions in p+Pb collisions at
a center-of-mass energy of 4.4 TeV. We also compare the model to the existing
pp, dA and AA data from RHIC and LHC.",1111.3031v2
2011-11-14,Information storage capacity of discrete spin systems,"Understanding the limits imposed on information storage capacity of physical
systems is a problem of fundamental and practical importance which bridges
physics and information science. There is a well-known upper bound on the
amount of information that can be stored reliably in a given volume of discrete
spin systems which are supported by gapped local Hamiltonians. However, all the
previously known systems were far below this theoretical bound, and it remained
open whether there exists a gapped spin system that saturates this bound. Here,
we present a construction of spin systems which saturate this theoretical limit
asymptotically by borrowing an idea from fractal properties arising in the
Sierpinski triangle. Our construction provides not only the best classical
error-correcting code which is physically realizable as the energy ground space
of gapped frustration-free Hamiltonians, but also a new research avenue for
correlated spin phases with fractal spin configurations.",1111.3275v3
2011-11-29,"Two solar-mass compact stars: structure, composition, and cooling","I discuss the structure and composition of massive (two solar-mass) neutron
stars containing hypernuclear and deconfined quark matter in color
superconducting states. Stable configurations featuring such matter are
obtained if the equation of state of hadronic matter is stiff above the
saturation density, the transition to quark matter takes place at a few times
the nuclear saturation density, and the repulsive vector interactions in quark
matter are substantial. I also discuss our recent progress in understanding the
cooling of massive compact stars with color superconducting quark cores.",1111.6929v3
2011-12-02,Geometric scaling in ultrahigh energy neutrinos and nonlinear perturbative QCD,"The ultrahigh energy neutrino cross section is a crucial ingredient in the
calculation of the event rate in high energy neutrino telescopes. Currently
there are several approaches which predict different behaviors for its
magnitude for ultrahigh energies. In this contribution is presented a summary
of current predictions based on the non-linear QCD evolution equations, the
so-called perturbative saturation physics. In particular, predictions are shown
based on the parton saturation approaches and the consequences of geometric
scaling property at high energies are discussed. The scaling property allows an
analytical computation of the neutrino scattering on nucleon/nucleus at high
energies, providing a theoretical parameterization.",1112.0555v1
2011-12-05,One-loop Factorization for Inclusive Hadron Production in $pA$ Collisions in the Saturation Formalism,"We demonstrate the QCD factorization for inclusive hadron production in $pA$
collisions in the saturation formalism at one-loop order, with explicit
calculation of both real and virtual gluon radiation diagrams. The collinear
divergences associated with the incoming parton distribution of the nucleon and
the outgoing fragmentation function of the final state hadron, as well as the
rapidity divergence with small-$x$ dipole gluon distribution of the nucleus are
factorized into the splittings of the associated parton distribution and
fragmentation functions and the energy evolution of the dipole gluon
distribution function. The hard coefficient function is evaluated at one-loop
order, and contains no divergence.",1112.1061v1
2011-12-16,Small-Signal Capacitance and Current Parameter Modeling in Large-Scale High-Frequency Graphene Field-Effect Transistors,"The analytical model of the small-signal current and capacitance
characteristics of RF graphene FET is presented. The model is based on explicit
distributions of chemical potential in graphene channels (including ambipolar
conductivity at high source-drain bias) obtained in the framework of
drift-diffusion current continuity equation solution. Small-signal
transconductance and output conductance characteristics are modeled taking into
account the two modes of drain current saturation including drift velocity
saturation or electrostatic pinch-off. Analytical closed expression for the
complex current gain and the cutoff frequency of high-frequency GFETs are
obtained. The model allows describe an impact of parasitic resistances,
capacitances, interface traps on extrinsic current gain and cut-off frequency.",1112.3856v1
2011-12-17,A note on $\aleph_α$-saturated o-minimal expansions of real closed fields,"We give necessary and sufficient conditions for a polynomially bounded
o-minimal expansion of a real closed field (in a language of arbitrary
cardinality) to be $\aleph_{\alpha}$-saturated. The conditions are in terms of
the value group, residue field, and pseudo- Cauchy sequences of the natural
valuation on the real closed field. This is achieved by an analysis of types,
leading to the trichotomy. Our characterization provides a construction method
for saturated models, using fields of generalized power series.",1112.4078v3
2011-12-18,Uncommon Suffix Tries,"Common assumptions on the source producing the words inserted in a suffix
trie with $n$ leaves lead to a $\log n$ height and saturation level. We provide
an example of a suffix trie whose height increases faster than a power of $n$
and another one whose saturation level is negligible with respect to $\log n$.
Both are built from VLMC (Variable Length Markov Chain) probabilistic sources;
they are easily extended to families of sources having the same properties. The
first example corresponds to a ""logarithmic infinite comb"" and enjoys a non
uniform polynomial mixing. The second one corresponds to a ""factorial infinite
comb"" for which mixing is uniform and exponential.",1112.4131v2
2012-01-27,Calibration System with Optical Fibers for Calorimeters at Future Linear Collider Experiments,"We report on several versions of the calibration and monitoring system
dedicated to scintillator tile calorimeters built within the CALICE
collaboration and intended for future linear collider experiments. Whereas the
first, a 1 m3 analogue hadron calorimeter prototype, was already built and
tested in beam, second-technological prototype-is currently being developed.
Both prototypes are based on scintillating tiles that are individually read out
by new photodetectors, silicon photomultipliers (SiPMs). Since the SiPM
response shows a strong dependence on the temperature and bias voltage and the
SiPM saturates due to the limited number of pixels, it needs to be monitored.
The monitoring system has to have sufficient flexibility to perform several
different tasks. The self-calibration property of the SiPMs can be used for the
gain monitoring using a low intensity of the LED light. A routine monitoring of
all SiPMs during test beam operations is achieved with a fixed-intensity light
pulse. The full SiPM response function is cross-checked by varying the light
intensity from zero to the saturation level. We concentrate especially on the
last aspect - the high dynamic range.",1201.5762v1
2012-02-03,Dark lattice solitons in one-dimensional waveguide arrays with defocusing saturable nonlinearities and alternating couplings,"In the present work, we examine ""binary"" waveguide arrays, where the coupling
between adjacent sites alternates between two distinct values $C_1$ and $C_2$
and a saturable nonlinearity is present on each site. Motivated by experimental
investigations of this type of system in fabricated LiNbO$_3$ arrays, we
proceed to analyze the nonlinear wave excitations arising in the
self-defocusing nonlinear regime, examining, in particular, dark solitons and
bubbles. We find that such solutions may, in fact, possess a reasonably wide,
experimentally relevant parametric interval of stability, while they may also
feature both prototypical types of instabilities, namely exponential and
oscillatory ones, for the same configuration. The spectral properties of the
linearization around the solutions and the presence of two bands and associated
mini-gaps are discussed and the nontrivial differences from the standard cubic
discrete nonlinear Schr{\""o}dinger model are highlighted.",1202.0830v3
2012-02-29,Fluctuating Glasma initial conditions and flow in heavy ion collisions,"We compute initial conditions in heavy-ion collisions within the Color Glass
Condensate (CGC) framework by combining the impact parameter dependent
saturation model (IP-Sat) with the classical Yang-Mills description of initial
Glasma fields. In addition to fluctuations of nucleon positions, this IP-Glasma
description includes quantum fluctuations of color charges on the length-scale
determined by the inverse nuclear saturation scale Q_s. The model naturally
produces initial energy fluctuations that are described by a negative binomial
distribution. The ratio of triangularity to eccentricity is close to that in a
model tuned to reproduce experimental flow data. We compare transverse momentum
spectra and v_(2,3,4)(p_T) of pions from different models of initial conditions
using relativistic viscous hydrodynamic evolution.",1202.6646v2
2012-03-02,One-Loop BPS amplitudes as BPS-state sums,"Recently, we introduced a new procedure for computing a class of one-loop
BPS-saturated amplitudes in String Theory, which expresses them as a sum of
one-loop contributions of all perturbative BPS states in a manifestly T-duality
invariant fashion. In this paper, we extend this procedure to all BPS-saturated
amplitudes of the form \int_F \Gamma_{d+k,d} {\Phi}, with {\Phi} being a weak
(almost) holomorphic modular form of weight -k/2. We use the fact that any such
{\Phi} can be expressed as a linear combination of certain absolutely
convergent Poincar\'e series, against which the fundamental domain F can be
unfolded. The resulting BPS-state sum neatly exhibits the singularities of the
amplitude at points of gauge symmetry enhancement, in a chamber-independent
fashion. We illustrate our method with concrete examples of interest in
heterotic string compactifications.",1203.0566v4
2012-03-04,Properties of inclusive hadron production in Deep Inelastic Scattering on heavy nuclei at low x,"In this paper we present a comprehensive study of inclusive hadron production
in DIS at low $x$. Properties of the hadron spectrum are different in different
kinematic regions formed by three relevant momentum scales: photon virtuality
$Q^2$, hadron transverse momentum $k_T$ and the saturation momentum $Q_s(x)$.
We investigate each kinematic region and derive the corresponding asymptotic
formulas for the cross section at the leading logarithmic order. We also
analyze the next-leading-order (NLO) corrections to the BFKL kernel that are
responsible for the momentum conservation. In particular, we establish the
asymptotic behavior of the forward elastic dipole--nucleus scattering amplitude
at high energies deeply in the saturation regime and a modification of the
pomeron intercept. We study the nuclear effect on the inclusive cross section
using the nuclear modification factor and its logarithmic derivative. We argue
that the later is proportional to the difference between the anomalous
dimension of the gluon distribution in nucleus and in proton and thus is a
direct measure of the coherence effects. To augment our arguments and present
quantitative results we performed numerical calculations in the kinematic
region that may be accessible by the future DIS experiments.",1203.0775v1
2012-03-27,High multiplicity pp events and J/ψ production at LHC,"We discuss the dependence of J/\psi\ production on the charged particle
multiplicity in proton-proton collisions at LHC energies. We show that, in the
framework of parton saturation or string interaction models, the hard J/\psi\
production exhibits a significant growth with the multiplicity, which is
stronger than linear in the high density domain. This departure from linearity,
that should affect any hard observable, applies for high multiplicity
proton-proton collisions in the central rapidity region and is a consequence of
the parton saturation or the strong interaction among colour ropes that take
place at LHC energies. Our assumption, the existence of coherence effects
present in proton-proton collisions at high energy, can also be checked by
studying the particular shape of the probability distribution associated to the
J/\psi\ production.",1203.5936v1
2012-03-28,Mendler-style Iso-(Co)inductive predicates: a strongly normalizing approach,"We present an extension of the second-order logic AF2 with iso-style
inductive and coinductive definitions specifically designed to extract programs
from proofs a la Krivine-Parigot by means of primitive (co)recursion
principles. Our logic includes primitive constructors of least and greatest
fixed points of predicate transformers, but contrary to the common approach, we
do not restrict ourselves to positive operators to ensure monotonicity, instead
we use the Mendler-style, motivated here by the concept of monotonization of an
arbitrary operator on a complete lattice. We prove an adequacy theorem with
respect to a realizability semantics based on saturated sets and
saturated-valued functions and as a consequence we obtain the strong
normalization property for the proof-term reduction, an important feature which
is absent in previous related work.",1203.6158v1
2012-03-31,Breakdown of chiral symmetry during saturation of the Tayler instability,"We study spontaneous breakdown of chiral symmetry during the nonlinear
evolution of the Tayler instability. We start with an initial steady state of
zero helicity. Within linearized perturbation calculations, helical
perturbations of this initial state have the same growth rate for either sign
of helicity. Direct numerical simulations (DNS) of the fully nonlinear
equations, however, show that an infinitesimal excess of one sign of helicity
in the initial perturbation gives rise to a saturated helical state. We further
show that this symmetry breaking can be described by weakly nonlinear
finite--amplitude equations with undetermined coefficients which can be deduced
solely from symmetry consideration. By fitting solutions of the amplitude
equations to data from DNS we further determine the coefficients of the
amplitude equations.",1204.0081v2
2012-03-31,A viscoplasticity model with an enhanced control of the yield surface distortion,"A new model of metal viscoplasticity, which takes combined isotropic,
kinematic, and distortional hardening into account, is presented. The basic
modeling assumptions are illustrated using a new two-dimensional rheological
analogy. This demonstrative rheological model is used as a guideline for the
construction of constitutive relations. The nonlinear kinematic hardening is
captured using the well-known Armstrong-Frederick approach. The distortion of
the yield surface is described with the help of a so-called distortional
backstress. A distinctive feature of the model is that any smooth convex
saturated form of the yield surface which is symmetric with respect to the
loading direction can be captured. In particular, an arbitrary sharpening of
the saturated yield locus in the loading direction combined with a flattening
on the opposite side can be covered. Moreover, the yield locus evolves smoothly
and its convexity is guaranteed at each hardening stage. A strict proof of the
thermodynamic consistency is provided. Finally, the predictive capabilities of
the material model are verified using the experimental data for a very high
work hardening annealed aluminum alloy 1100 Al.",1204.0086v1
2012-04-05,Prompt photon production and photon-hadron correlations at RHIC and the LHC from the Color Glass Condensate,"We investigate inclusive prompt photon and semi-inclusive prompt
photon-hadron production in high energy proton-nucleus collisions using the
Color Glass Condensate (CGC) formalism which incorporates non-linear dynamics
of gluon saturation at small x via Balitsky-Kovchegov equation with running
coupling. For inclusive prompt photon production, we rewrite the cross-section
in terms of direct and fragmentation contributions and show that the direct
photon (and isolated prompt photon) production is more sensitive to gluon
saturation effects. We then analyze azimuthal correlations in photon-hadron
production in high energy proton-nucleus collisions and obtain a strong
suppression of the away-side peak in photon-hadron correlations at forward
rapidities, similar to the observed mono-jet production in deuteron-gold
collisions at forward rapidity at RHIC. We make predictions for the nuclear
modification factor R_{p(d)A} and photon-hadron azimuthal correlations in
proton(deuteron)-nucleus collisions at RHIC and the LHC at various rapidities.",1204.1319v2
2012-04-17,Locality for quantum systems on graphs depends on the number field,"Adapting a definition of Aaronson and Ambainis [Theory Comput. 1 (2005),
47--79], we call a quantum dynamics on a digraph ""saturated Z-local"" if the
nonzero transition amplitudes specifying the unitary evolution are in exact
correspondence with the directed edges (including loops) of the digraph. This
idea appears recurrently in a variety of contexts including angular momentum,
quantum chaos, and combinatorial matrix theory. Complete characterization of
the digraph properties that allow such a process to exist is a long-standing
open question that can also be formulated in terms of minimum rank problems. We
prove that saturated Z-local dynamics involving complex amplitudes occur on a
proper superset of the digraphs that allow restriction to the real numbers or,
even further, the rationals. Consequently, among these fields, complex numbers
guarantee the largest possible choice of topologies supporting a discrete
quantum evolution. A similar construction separates complex numbers from the
skew field of quaternions. The result proposes a concrete ground for
distinguishing between complex and quaternionic quantum mechanics.",1204.3681v2
2012-05-03,What ecological factors shape species-area curves in neutral models?,"Understanding factors that shape biodiversity and species coexistence across
scales is of utmost importance in ecology, both theoretically and for
conservation policies. Species-area relationships (SARs), measuring how the
number of observed species increases upon enlarging the sampled area,
constitute a convenient tool for quantifying the spatial structure of
biodiversity. While general features of species-area curves are quite universal
across ecosystems, some quantitative aspects can change significantly. Several
attempts have been made to link these variations to ecological forces. Within
the framework of spatially explicit neutral models, here we scrutinize the
effect of varying the local population size (i.e. the number of individuals per
site) and the level of habitat saturation (allowing for empty sites). We
conclude that species-area curves become shallower when the local population
size increases, while habitat saturation, unless strongly violated, plays a
marginal role. Our findings provide a plausible explanation of why SARs for
microorganisms are flatter than those for larger organisms.",1205.0665v1
2012-05-14,Holographic Pomeron: Saturation and DIS,"We briefly review the approach to dipole-dipole scattering in holographic QCD
developed in ARXIV:1202.0831. The Pomeron is modeled by exchanging closed
strings between the dipoles and yields Regge behavior for the elastic
amplitude. We calculate curvature corrections to this amplitude in both a
conformal and confining background, identifying the holographic direction with
the virtuality of the dipoles. The it wee-dipole density is related to the
string tachyon diffusion in both virtuality and the transverse directions. We
give an explicit derivation of the dipole saturation momentum both in the
conformal and confining metric. Our holographic result for the dipole-dipole
cross section and the it wee-dipole density in the conformal limit are shown to
be identical in form to the BFKL pomeron result when the non-critical string
transverse dimension is $D_\perp=3$. The total dipole-dipole cross section is
compared to DIS data from HERA.",1205.3223v3
2012-05-17,Heavy Sterile Neutrinos and Neutrinoless Double Beta Decay,"Sterile neutrinos of mass up to a few tens of TeV can saturate the present
experimental bound of neutrinoless double beta decay process. Due to the
updated nuclear matrix elements, the bound on mass and mixing angle is now
improved by one order of magnitude. We have performed a detailed analysis of
neutrinoless double beta decay for the minimal Type I seesaw scenario. We have
shown that in spite of the naive expectation that the light neutrinos give the
dominant contribution, sterile neutrinos can saturate the present experimental
bound of neutrinoless double beta decay process. However, in order to be
consistent with radiative stability of light neutrino masses, the mass scale of
sterile neutrinos should be less than 10 GeV.",1205.3867v1
2012-05-23,The Unique Pure Gaussian State Determined by the Partial Saturation of the Uncertainty Relations of a Mixed Gaussian State,"Let {\rho} the density matrix of a mixed Gaussian state. Assuming that one of
the Robertson--Schr\""odinger uncertainty inequalities is saturated by {\rho},
e.g.
({\Delta}^{{\rho}}X_1)^2({\Delta}^{{\rho}}P_1)^2={\Delta}^{{\rho}}(X_1,P_1)^2+(1/4)\hbar^2,
we show that there exists a unique pure Gaussian state whose Wigner
distribution is dominated by that of {\rho} and having the same variances and
covariance {\Delta}^{{\rho}}X_1,{\Delta}^{{\rho}}P_1, and
{\Delta}^{{\rho}}(X_1,P_1) as {\rho}. This property can be viewed as an
analytic version of Gromov's non-squeezing theorem in the linear case, which
implies that the intersection of a symplectic ball by a single plane of
conjugate coordinates determines the radius of this ball.",1205.5222v1
2012-06-11,Analytic approach to the motion of cosmological phase transition fronts,"We consider the motion of planar phase-transition fronts in first-order phase
transitions of the Universe. We find the steady state wall velocity as a
function of a friction coefficient and thermodynamical parameters, taking into
account the different hydrodynamic modes of propagation. We obtain analytical
approximations for the velocity by using the thin wall approximation and the
bag equation of state. We compare our results to those of numerical
calculations and discuss the range of validity of the approximations. We
analyze the structure of the stationary solutions. Multiple solutions may exist
for a given set of parameters, even after discarding non-physical ones. We
discuss which of these will be realized in the phase transition as the
stationary wall velocity. Finally, we discuss on the saturation of the friction
at ultra-relativistic velocities and the existence of runaway solutions.",1206.2339v2
2012-06-30,Hypernclear in the improved quark mass density- dependent model,"The improved quark mass density- dependent model, which has been successfully
used to describe the properties of both finite nuclei and bulk nuclear matter,
is extended to include the strange quark. The parameters of the model are
determined by the saturation properties of bulk matter. Then the given
parameter set is employed to investigate both the properties of strange
hadronic matter and those of $\Lambda$ hypernuclei. Bulk strange hadronic
matter consisting of nucleons, $\Lambda$- hyperons and $\Xi$- hyperons is
studied under mean-field approximation. Among others, density dependence of the
effective baryon mass, saturation properties and stability of the physical
system are discussed. For single-$\Lambda$ hypernuclei, single particle
energies of $\Lambda$ hyperon is evaluated. In particular, it is found that the
present model produces a small spin-orbit interaction, which is in agreement
with the experimental observations. The above results show that the present
model can consistently describe the properties of strange hadronic matter, as
well as those of single $\Lambda$ hypernuclei within an uniform
parameterization.",1207.0070v1
2012-07-03,Robust Dequantized Compressive Sensing,"We consider the reconstruction problem in compressed sensing in which the
observations are recorded in a finite number of bits. They may thus contain
quantization errors (from being rounded to the nearest representable value) and
saturation errors (from being outside the range of representable values). Our
formulation has an objective of weighted $\ell_2$-$\ell_1$ type, along with
constraints that account explicitly for quantization and saturation errors, and
is solved with an augmented Lagrangian method. We prove a consistency result
for the recovered solution, stronger than those that have appeared to date in
the literature, showing in particular that asymptotic consistency can be
obtained without oversampling. We present extensive computational comparisons
with formulations proposed previously, and variants thereof.",1207.0577v2
2012-07-31,Particle Production in pA Collisions and QCD Saturation,"The forthcoming LHC measurements in proton-nucleus (pA) collisions at forward
rapidities can discriminate between the color glass condensate (CGC) and
alternative approaches including standard collinear factorization one. We
report some of our recent predictions based on gluon saturation/CGC formalism
for pA collisions at the LHC including the charged hadron multiplicity
distribution, the nuclear modification factor for single inclusive hadron and
prompt photon production, and the azimuthal angle correlation of the
semi-inclusive hadron-photon production.",1208.0026v2
2012-09-12,Channel Length Scaling of MoS2 MOSFETs,"In this article, we investigate electrical transport properties in ultrathin
body (UTB) MoS2 two-dimensional (2D) crystals with channel lengths ranging from
2 {\mu}m down to 50 nm. We compare the short channel behavior of sets of
MOSFETs with various channel thickness, and reveal the superior immunity to
short channel effects of MoS2 transistors. We observe no obvious short channel
effects on the device with 100 nm channel length (Lch) fabricated on a 5 nm
thick MoS2 2D crystal even when using 300 nm thick SiO2 as gate dielectric, and
has a current on/off ratio up to ~109. We also observe the on-current
saturation at short channel devices with continuous scaling due to the carrier
velocity saturation. Also, we reveal the performance limit of short channel
MoS2 transistors is dominated by the large contact resistance from the Schottky
barrier between Ni and MoS2 interface, where a fully transparent contact is
needed to achieve a high-performance short channel device.",1209.2525v1
2012-09-19,Single Dirac-cone on the Cs-covered topological insulator surface Sb2Te3(0001),"Using angle-resolved photoelectron spectroscopy we investigate the surface
electronic structure of the three-dimensional topological insulator (TI)
Sb2Te3(0001). Our data show the presence of a topological surface state in the
bulk energy gap with the Dirac-point located above the Fermi level. The
adsorption of Cs-atoms on Sb2Te3(0001) gives rise to a downward energy shift of
the electronic valence band states which saturates at a value of ~200 meV. For
the saturation coverage the Dirac-point of the linearly dispersive surface
state resides in close proximity to the Fermi level. The electronic structure
of the Cs/Sb2Te3 interface therefore considerably deviates from previously
studied metal-TI interfaces based on the isostructural compound Bi2Se3 which
points to the importance of atomic composition in these hetero systems.",1209.4263v1
2012-09-23,A gauged baby Skyrme model and a novel BPS bound,"The baby Skyrme model is a well-known nonlinear field theory supporting
topological solitons in two space dimensions. Its action functional consists of
a potential term, a kinetic term quadratic in derivatives (the ""nonlinear sigma
model term"") and the Skyrme term quartic in first derivatives. The limiting
case of vanishing sigma model term (the so-called BPS baby Skyrme model) is
known to support exact soliton solutions saturating a BPS bound which exists
for this model. Further, the BPS model has infinitely many symmetries and
conservation laws. Recently it was found that the gauged version of the BPS
baby Skyrme model with gauge group U(1) and the usual Maxwell term, too, has a
BPS bound and BPS solutions saturating this bound. This BPS bound is determined
by a superpotential which has to obey a superpotential equation, in close
analogy to the situation in supergravity. Further, the BPS bound and the
corresponding BPS solitons only may exist for potentials such that the
superpotential equation has a global solution. We also briefly describe some
properties of soliton solutions.",1209.5103v1
2012-10-18,Eigenvalues of Hermitian matrices and equivariant cohomology of Grassmannians,"The saturation theorem of [Knutson-Tao '99] concerns the nonvanishing of
Littlewood-Richardson coefficients. In combination with work of [Klyachko '98],
it implies [Horn '62]'s conjecture about eigenvalues of sums of Hermitian
matrices. This eigenvalue problem has a generalization [Friedland '00] to
majorized sums of Hermitian matrices.
  We further illustrate the common features between these two eigenvalue
problems and their connection to Schubert calculus of Grassmannians. Our main
result gives a Schubert calculus interpretation of Friedland's problem, via
equivariant cohomology of Grassmannians. In particular, we prove a saturation
theorem for this setting. Our arguments employ the aformentioned work together
with [Thomas-Yong '12].",1210.5003v2
2012-11-04,Flame Acceleration in Channels with Obstacles in the Deflagration-to-Detonation Transition,"It was demonstrated recently in Bychkov et al., Phys. Rev. Lett. 101 (2008)
164501, that the physical mechanism of flame acceleration in channels with
obstacles is qualitatively different from the classical Shelkin mechanism. The
new mechanism is much stronger, and is independent of the Reynolds number. The
present study provides details of the theory and numerical modeling of the
flame acceleration. It is shown theoretically and computationally that flame
acceleration progresses noticeably faster in the axisymmetric cylindrical
geometry as compared to the planar one, and that the acceleration rate reduces
with increasing initial Mach number and thereby the gas compressibility.
Furthermore, the velocity of the accelerating flame saturates to a constant
value that is supersonic with respect to the wall. The saturation state can be
correlated to the Chapman-Jouguet deflagration as well as the fast flames
observed in experiments. The possibility of transition from deflagration to
detonation in the obstructed channels is demonstrated.",1211.0655v1
2012-11-12,Theory of self-organized traffic at light signal,"Based on numerical simulations of a three-phase traffic flow model, a
probabilistic theory of traffic at the light signal is developed. We have found
that very complex spatiotemporal self-organized phenomena determine features of
city traffic. We have revealed that the breakdown of {\it green wave} in a city
is initiated by the emergence of a moving synchronized flow pattern (MSP)
within the green wave. It turns out that a sequence of
F$\rightarrow$S$\rightarrow$J transitions (F -- free flow, S -- synchronized
flow, J -- moving queue) lead to traffic breakdown at the light signal. Both
spontaneous and induced breakdowns of the green wave have been found. From a
study of a variety of scenarios for arrival traffic, we have found that there
are the infinite number of capacities of traffic at the light signal, which are
in a capacity range between a minimum capacity and maximum capacity; each of
the capacities gives a flow rate at which under-saturated traffic is in a
metastable state with respect to the transition to over-saturated traffic. The
maximum capacity depends crucially on a time-dependence of the flow rate: The
larger the number of vehicles that arrive the light signal during the green
phase, the larger the maximum capacity.",1211.2535v1
2012-11-13,Quarkonium at non-zero isospin density,"We calculate the energies of quarkonium bound states in the presence of a
medium of nonzero isospin density using lattice QCD. The medium, created using
a canonical (fixed isospin charge) approach, induces a reduction of the
quarkonium energies. As the isospin density increases, the energy shifts first
increase and then saturate. The saturation occurs at an isospin density close
to that where previously a qualitative change in the behaviour of the energy
density of the medium has been observed, which was conjectured to correspond to
a transition from a pion gas to a Bose-Einstein condensed phase. The reduction
of the quarkonium energies becomes more pronounced as the heavy-quark mass is
decreased, similar to the behaviour seen in two-colour QCD at non-zero quark
chemical potential. In the process of our analysis, the $\eta_b$-$\pi$ and
$\Upsilon$-$\pi$ scattering phase shifts are determined at low momentum. An
interpolation of the scattering lengths to the physical pion mass gives
$a_{\eta_b,\pi} = 0.0025(8)(6)$ fm and $a_{\Upsilon,\pi} = 0.0030(9)(7)$ fm.",1211.3156v3
2012-11-29,Polymer Welding: Strength Through Entanglements,"Large-scale simulations of thermal welding of polymers are performed to
investigate the rise of mechanical strength at the polymer-polymer interface
with the welding time. The welding process is in the core of integrating
polymeric elements into devices as well as in thermal induced healing of
polymers; processes that require development of interfacial strength equal to
that of the bulk. Our simulations show that the interfacial strength saturates
at the bulk shear strength much before polymers diffuse by their radius of
gyration. Along with the strength increase, the dominant failure mode changes
from chain pullout at the interface to chain scission as in the bulk. Formation
of sufficient entanglements across the interface, which we track using a
Primitive Path Analysis is required to arrest catastrophic chain pullout at the
interface. The bulk response is not fully recovered until the density of
entanglements at the interface reaches the bulk value. Moreover, the increase
of interfacial strength before saturation is proportional to the number of
interfacial entanglements between chains from opposite sides.",1211.6796v1
2012-12-03,Recent progress on the determination of the symmetry Energy,"We summarize the current status on constraining the density dependence of the
symmetry energy from terrestrial laboratory measurements and astrophysical
observations. While the value $E_{sym}({\rho_{0}})$ and density slope $L$ of
the symmetry energy at saturation density $\rho_{0}$ can vary largely depending
on the data or methods, all the existing constraints are essentially consistent
with $E_{sym}({\rho_{0}}) = 31 \pm 2$ MeV and $L = 50 \pm 20$ MeV. The
determination of the supra-saturation density behavior of the symmetry energy
remains a big challenge.",1212.0284v1
2012-12-11,Spatial correlations of Rydberg excitations in optically driven atomic ensembles,"We study the emergence of many-body correlations in the stationary state of
continuously-driven, strongly-interacting dissipative system. Specifically, we
examine resonant optical excitations of Rydberg states of atoms interacting via
long-range dipole-dipole and van der Waals potentials employing exact numerical
solutions of the density matrix equations and Monte-Carlo simulations.
Collection of atoms within a blockade distance form a ""superatom"" that can
accommodate at most one Rydberg excitation. The superatom excitation
probability saturates to 1/2 for coherently driven atoms, but is significantly
higher for incoherent driving, approaching unity as the number of atoms
increases. In the steady state of uniformly-driven, extended one-dimensional
system, the saturation of superatoms leads to quasi-crystallization of Rydberg
excitations whose correlations exhibit damped spatial oscillations. The
behavior of the system under the van der Waals interaction potential can be
approximated by an analytically soluble model based on a ""hard-rod"" interatomic
potential.",1212.2423v1
2012-12-12,Lifshitz field theories with SDiff symmetries,"We consider Lifshitz field theories with a dynamical critical exponent z
equal to the dimension of space d and with a large group of base space
symmetries, concretely space coordinate transformations with unit determinant
(""Special Diffeomorphisms""). The field configurations of the theories
considered may have the topology of skyrmions, vortices or monopoles, although
we focus our detailed investigations on skyrmions. The resulting Lifshitz field
theories have a BPS bound and exact soliton solutions saturating the bound, as
well as time-dependent topological Q-ball solutions. Finally, we investigate
the U(1) gauged versions of the Lifshitz field theories coupled to a
Chern-Simons gauge field, where the BPS bound and soliton solutions saturating
the bound continue to exist.",1212.2741v2
2012-12-21,Inclusive hadron and photon production at LHC in dipole momentum space,"Using a momentum space model for the dipole scattering amplitude we present
an analysis of the saturation effects at LHC energies, describing the data on
proton-proton and proton-lead collisions. The model is based on the asymptotic
solutions of the Balitsky-Kovchegov equation, being ideal in the saturation
domain where the target wave function has a high occupation number. We also
make predictions for the nuclear modification ratios on charged hadron and
prompt photon production in the forward region, where the high parton density
effects are important.",1212.5549v2
2012-12-24,Interplay between the symmetry energy and the strangeness content of neutron stars,"The effect of the density dependence of the nucleonic equation of state and
the hyperon meson couplings on the star properties, including strangeness
content, mass and radius, are studied within a relativistic mean field
formalism. It is shown that there is still lacking information on the nucleonic
equation of state at supra-saturation densities and on the hyperon interactions
in nuclear matter that will allow a clear answer to the question whether the
mass of the pulsar J1614-2230 could rule out exotic degrees of freedom from the
interior of compact stars. We show that some star properties are affected in a
similar way by the density dependence of the symmetry energy and the hyperon
content of the star. To disentangle these two effects it is essential to have a
good knowledge of the equation of state at supra-saturation densities. A linear
correlation between the radius and the strangeness content of a star with a
fixed mass is obtained.",1212.5911v3
2013-01-03,Strangeness-driven phase transition in (proto)- neutron star matter,"The phase diagram of a system constituted of neutrons, protons,
$\Lambda$-hyperons and electrons is evaluated in the mean-field approximation
in the complete three-dimensional space given by the baryon, lepton and strange
charge. It is shown that the phase diagram at sub-saturation densities is
strongly affected by the electromagnetic interaction, while it is almost
independent of the electric charge at supra-saturation density. As a
consequence, stellar matter under the condition of strangeness equilibrium is
expected to experience a first as well as a second-order strangeness-driven
phase transition at high density, while the liquid-gas phase transition is
expected to be quenched. An RPA calculation indicates that the presence of this
critical point might have sizable implications for the neutrino propagation in
core-collapse supernovae.",1301.0390v2
2013-01-08,High Frequency Geodesic Acoustic Modes in Electron Scale Turbulence,"In this work the finite $\beta$-effects of an electron branch of the geodesic
acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is
presented. The work is based on a fluid description of the ETG mode retaining
non-adiabatic ions and the dispersion relation for el-GAMs driven non-linearly
by ETG modes is derived. The ETG growth rate from the fluid model is compared
to the results found from gyrokinetic simulations with good agreement. A new
saturation mechanism for ETG turbulence through the interaction with el-GAMs is
found, resulting in a significantly enhanced ETG turbulence saturation level
compared to the mixing length estimate. It is shown that the el-GAM may be
stabilized by an increase in finite $\beta$ as well as by increasing
non-adiabaticity. The decreased GAM growth rates is due to the inclusion of the
Maxwell stress.",1301.1435v2
2013-01-31,The Third Proof of Lovász's Cathedral Theorem,"A graph $G$ with a perfect matching is called saturated if $G+e$ has more
perfect matchings than $G$ for any edge $e$ that is not in $G$. Lov\'asz gave a
characterization of the saturated graphs called the cathedral theorem, with
some applications to the enumeration problem of perfect matchings, and later
Szigeti gave another proof. In this paper, we give a new proof with our
preceding works which revealed canonical structures of general graphs with
perfect matchings. Here, the cathedral theorem is derived in quite a natural
way, providing more refined or generalized properties. Moreover, the new proof
shows that it can be proved without using the Gallai-Edmonds structure theorem.",1301.7597v3
2013-02-01,BFKL Pomeron calculus: solution to equations for nucleus-nucleus scattering in the saturation domain,"In this paper we solve the equation for nucleus-nucleus scattering in the
BFKL Pomeron calculus, suggested by Braun. We find these solutions analytically
at high energies as well as numerically in the entire region of energies inside
the saturation region. The semi-classical approximation is used to select out
the infinite set of the parasite solutions. The nucleus-nucleus cross sections
at high energy are estimated and compared with the Glauber-Gribov approach. It
turns out that the exact formula gives the estimates that are very close to the
ones based on Glauber-Gribov formula which is important for the practical
applications",1302.0128v1
2013-02-01,Three-body force effect on off-shell mass operator and spectral functions in nuclear matter,"Within the framework of the Brueckner theory, the off-shell behaviors of the
mass operator $M(k,\omega)=V(k,\omega)+iW(k,\omega)$, i.e., its dependence upon
the momentum $k$ and upon the nucleon frequency $\omega$, are investigated by
including nuclear three-body force (TBF). The first two terms of the hole-line
expansion of the mass operator are taken into account. The TBF effects on their
off-shell properties are discussed. A comparison is made between the on-shell
and off-shell values of $M_{1}$. The nucleon spectral function and nucleon
momentum distribution are also calculated, and the calculation shows that they
are hardly affected by the TBF effect at the saturation density. At a high
density two times greater than the saturation density, inclusion of the TBF may
lead to a visible effect on the spectral function and may enhance the depletion
of the hole states.",1302.0202v2
2013-02-05,Scaling of Non-Saturating MR and quantum oscillations in pristine and ion-implanted HOPG,"A wide variety of resistive and field dependent behaviors have been
previously observed in both doped and non-doped Highly Oriented Pyrolytic
Graphite (HOPG). We find HOPG samples to vary significantly in their
temperature dependent resistances, even between portions taken from the same
sample, yet they exhibit consistent non-saturating magnetoresistance (MR). The
scaling behavior of the MR is shown to be characteristic of a model based on
the Hall effect in granular materials. In addition to the large, field-linear
MR, all samples exhibit Shubnikov-de Haas (SdH) oscillations. Additional
samples were doped via ion-implantation by boron and phosphorous, but show no
signs of superconductivity nor any systematic change in their magnetoresistive
behavior. Analysis of the SdH data gives a 2D carrier density in agreement with
previous results, and a large mean-free path relative to crystallite size, even
in samples with thin ion-implanted surface layers.",1302.1229v1
2013-02-06,Nonequilbrium work by charge control in a Josephson junction,"We consider a single Josephson junction in the presence of time varying gate
charge, and examine the nonequilibrium work done by the charge control in the
framework of fluctuation theorems. We obtain the probability distribution
functions of the works performed by forward protocol and by its time reversed
protocol, which from the Crooks relation gives the estimation of the free
energy changes \Delta F =0. The reliability of \Delta F estimated from the
Jarzynksi equality is crucially dependent on protocol parameters, while
Bennett's acceptance ratio method confirms consistently \Delta F=0. The error
of the Jarzynski estimator either grows or becomes saturated as the duration of
the work protocol increases, which depends on the protocol rapidity determining
the existence of the oscillatory motion of the phase difference across the
junction. The average of the work also shows similar behaviors and its
saturation value is given by the relative weight of the oscillatory trajectory
with respect to running trajectories with constant acceleration. We discuss
non-negativity of the work average and its relation to heat and entropy
production associated with the circuit control.",1302.1273v1
2013-02-13,A Carbon Nanotube Immunosensor for Salmonella,"Antibody-functionalized carbon nanotube devices have been suggested for use
as bacterial detectors for monitoring of food purity in transit from the farm
to the kitchen. Here we report progress towards that goal by demonstrating
specific detection of Salmonella in complex nutrient broth solutions using
nanotube transistors functionalized with covalently-bound anti-Salmonella
antibodies. The small size of the active device region makes them compatible
with integration in large-scale arrays. We find that the on-state current of
the transistor is sensitive specifically to the Salmonella concentration and
saturates at low concentration (<1000 cfu/ml). In contrast, the carrier
mobility is affected comparably by Salmonella and other bacteria types, with no
sign of saturation even at much larger concentrations (10^8 cfu/ml).",1302.2959v1
2013-02-15,Nonlinear effects and the behavior of total hadronic and photonic cross sections,"In this work we use an eikonalized minijet model where the effects of the
first nonlinear corrections to the DGLAP equations are taken into account. The
contributions coming from gluon recombination effects are included in the
DGLAP+GLRMQ approach for the free proton in the context of saturation models.
The parameters of the model are fixed to fit total $pp$ and $\bar p p$ cross
sections, including the very recent data from LHC, HiRes and P. Auger
Collaborations. Glauber and multiple scattering approximations are then used to
describe the inclusive inelastic proton-Air cross section. Photoproduction
cross sections, without change of parameters fixed before, are also obtained
from the model using Vector Meson Dominance and the Additive Quark Model. We
show and discuss our main results as well as the implications of saturation
effects in the behavior of total hadronic and photonic cross sections at very
high energies.",1302.3765v3
2013-02-16,Effect of Temperature Wave on Diffusive Transport of Weakly-Soluble Substances in Liquid-Saturated Porous Media,"We study the effect of surface temperature oscillations on diffusive
transport of solutes of weaklysoluble substances through liquid-saturated
porous media. Temperature wave induced by these oscillations and decaying deep
in the porous massif creates the solubility wave along with the corresponding
solute diffusion flux wave. When the non-dissolved fraction is immobilized in
pores---for gases the bubbles can be immobilized by the surface tension force,
for solids (e.g., limestone, gas-hydrates) the immobilization of non-dissolved
phase is obvious---the only remaining mechanisms of mass transport are related
to solute flux through liquid in pores. We evaluate analytically the generated
time-average mass flux for the case of medium everywhere littered with
non-dissolved phase and reveal the significant effect of the temperature wave
on the substance release from the massif and non-dissolved mass redistribution
within the massif. Analytical theory is validated with numerical calculations.",1302.3966v3
2013-02-18,Quantitative Study of Different Forms of Geometrical Scaling in Deep Inelastic Scattering at HERA,"We use recently proposed method of ratios to assess the quality of
geometrical scaling in deep inelastic scattering for different forms of the
saturation scale. We consider original form of geometrical scaling (motivated
by the Balitski-Kovchegov (BK) equation with fixed coupling) studied in more
detail in our previous paper, and four new hypotheses: phenomenologically
motivated case with $Q^2$ dependent exponent $\lambda$ that governs small $x$
dependence of the saturation scale, two versions of scaling (running coupling 1
and 2) that follow from the BK equation with running coupling, and diffusive
scaling suggested by the QCD evolution equation beyond mean field
approximation. It turns out that more sophisticated scenarios: running coupling
scaling and diffusive scaling are disfavored by the combined HERA data on
$e^+p$ deep inelastic structure function $F_2$.",1302.4227v1
2013-02-21,High-Field Electrical and Thermal Transport in Suspended Graphene,"We study the intrinsic transport properties of suspended graphene devices at
high fields (>1 V/um) and high temperatures (>1000 K). Across 15 samples, we
find peak (average) saturation velocity of 3.6x10^7 cm/s (1.7x10^7 cm/s), and
peak (average) thermal conductivity of 530 W/m/K (310 W/m/K), at 1000 K. The
saturation velocity is 2-4 times and the thermal conductivity 10-17 times
greater than in silicon at such elevated temperatures. However, the thermal
conductivity shows a steeper decrease at high temperature than in graphite,
consistent with stronger effects of second-order three-phonon scattering. Our
analysis of sample-to-sample variation suggests the behavior of ""cleaner""
devices most closely approaches the intrinsic high-field properties of
graphene. This study reveals key features of charge and heat flow in graphene
up to device breakdown at ~2230 K in vacuum, highlighting remaining unknowns
under extreme operating conditions.",1302.5440v2
2013-02-28,Multiple light scattering on the F = 1 - F' = 0 transition in a cold and high density 87Rb vapor,"We report an experimental study of near resonance light scattering on the $F
= 1 \rightarrow F' = 0$ component of the $D_2$ line in atomic $^{87}Rb$.
Experiments are performed on spatially bi-Gaussian ultracold gas samples having
peak densities ranging from about $5 \cdot 10^{12} - 5 \cdot 10^{13}$
atoms/cm$^{3}$ and for a range of resonance saturation parameters and detunings
from atomic resonance. Time resolution of the scattered light intensity reveals
dynamics of multiple light scattering, optical pumping, and saturation effects.
The experimental results in steady-state are compared qualitatively with
theoretical models of the light scattering process. The steady-state line shape
of the excitation spectrum is in good qualitative agreement with these models.",1303.0037v1
2013-03-01,Performance of Spatially-Coupled LDPC Codes and Threshold Saturation over BICM Channels,"We study the performance of binary spatially-coupled low-density parity-check
codes (SC-LDPC) when used with bit-interleaved coded-modulation (BICM) schemes.
This paper considers the cases when transmission takes place over additive
white Gaussian noise (AWGN)channels and Rayleigh fast-fading channels. The
technique of upper bounding the maximum-a-posteriori (MAP) decoding performance
of LDPC codes using an area theorem is extended for BICM schemes. The upper
bound is computed for both the optimal MAP demapper and the suboptimal
max-log-MAP (MLM) demapper. It is observed that this bound approaches the noise
threshold of BICM channels for regular LDPC codes with large degrees. The rest
of the paper extends these techniques to SC-LDPC codes and the phenomenon of
threshold saturation is demonstrated numerically. Based on numerical evidence,
we conjecture that the belief-propagation (BP) decoding threshold of SC-LDPC
codes approaches the MAP decoding threshold of the underlying LDPC ensemble on
BICM channels. Numerical results also show that SC-LDPC codes approach the BICM
capacity over different channels and modulation schemes.",1303.0296v1
2013-03-11,Interplay between localization and absorption in disordered waveguides,"This work presents results of ab-initio simulations of continuous wave
transport in disordered absorbing waveguides. Wave interference effects cause
deviations from diffusive picture of wave transport and make the diffusion
coefficient position- and absorption-dependent. As a consequence, the true
limit of a zero diffusion coefficient is never reached in an absorbing random
medium of infinite size, instead, the diffusion coefficient saturates at some
finite constant value. Transition to this absorption-limited diffusion exhibits
a universality which can be captured within the framework of the
self-consistent theory (SCT) of localization. The results of this work (i)
justify use of SCT in analyses of experiments in localized regime, provided
that absorption is not weak; (ii) open the possibility of diffusive description
of wave transport in the saturation regime even when localization effects are
strong.",1303.2717v1
2013-03-14,Quantum Flutter: Signatures and Robustness,"We investigate the motion of an impurity particle injected with finite
velocity into an interacting one-dimensional quantum gas. Using large-scale
numerical simulations based on matrix product states, we observe and
quantitatively analyze long-lived oscillations of the impurity momentum around
a non-zero saturation value, called quantum flutter. We show that the quantum
flutter frequency is equal to the energy difference between two branches of
collective excitations of the model. We propose an explanation of the finite
saturation momentum of the impurity based on the properties of the edge of the
excitation spectrum. Our results indicate that quantum flutter exists away from
integrability, and provide parameter regions in which it could be observed in
experiments with ultracold atoms using currently available technology.",1303.3583v3
2013-03-15,Polariton condensation with saturable molecules dressed by vibrational modes,"Polaritons, mixed light-matter quasiparticles, undergo a transition to a
condensed, macroscopically coherent state at low temperatures or high
densities. Recent experiments show that coupling light to organic molecules
inside a microcavity allows condensation at room temperature. The molecules act
as saturable absorbers with transitions dressed by molecular vibrational modes.
Motivated by this we calculate the phase diagram and spectrum of a modified
Tavis-Cummings model, describing vibrationally dressed two-level systems,
coupled to a cavity mode. Coupling to vibrational modes can induce re-entrance,
i.e. a normal-condensed-normal sequence with decreasing temperature and can
drive the transition first order.",1303.3720v3
2013-03-17,"Collisionless shock formation, spontaneous electromagnetic fluctuations and streaming instabilities","Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent
numerical simulations and experiments have shown how they can arise from the
encounter of two collisionless plasma shells. When the shells interpenetrate,
the overlapping region turns unstable, triggering the shock formation. As a
first step towards a microscopic understanding of the process, we analyze here
in detail the initial instability phase. On the one hand, 2D relativistic PIC
simulations are performed where two symmetric initially cold pair plasmas
collide. On the other hand, the instabilities at work are analyzed, as well as
the field at saturation and the seed field which gets amplified. For mildly
relativistic motions and onward, Weibel modes govern the linear phase. We
derive an expression for the duration of the linear phase in good agreement
with the simulations. This saturation time constitutes indeed a lower-bound for
the shock formation time.",1303.4095v2
2013-03-27,Transient Charge and Energy Balance in Graphene Induced by Ultrafast Photoexcitation,"Ultrafast optical pump-probe spectroscopy measurement on monolayer graphene
observes significant optical nonlinearities. We show that strongly photoexcited
graphene monolayers with 35 fs pulses quasi-instantaneously build up a
broadband, inverted Dirac fermion population. Optical gain emerges and directly
manifests itself via a negative conductivity at the near-infrared region for
the first 200fs, where stimulated emission completely compensates absorption
loss in the graphene layer. To quantitatively investigate this transient,
extremely dense photoexcited Dirac-fermion state, we construct a
two-chemical-potential model, in addition to a time-dependent transient carrier
temperature above lattice temperature, to describe the population inverted
electronic state metastable on the time scale of tens of femtoseconds generated
by a strong exciting pulse. The calculated transient optical conductivity
reveals a complete bleaching of absorption, which sets the saturation density
during the pulse propagation. Particularly, the model calculation reproduces
the negative optical conductivity at lower frequencies in the states close to
saturation, corroborating the observed femtosecond stimulated emission and
optical gain in the wide near-infrared window.",1303.6902v2
2013-03-27,Local Superfluidity at the Nanoscale,"We have performed quantum Monte Carlo simulations measuring the finite size
and temperature superfluid response of helium-4 to the linear and rotational
motion of the walls of a nanopore. Within the two-fluid model, the portion of
the normal liquid dragged along with the boundaries is dependent on the type of
motion and the resulting anisotropic superfluid density saturates far below
unity at T=0.5 K. The origin of the saturation is uncovered by computing the
spatial distribution of superfluidity, with only the core of the nanopore
exhibiting any evidence of phase coherence. The superfluid core displays
scaling behavior consistent with Luttinger liquid theory, thereby providing an
experimental test for the emergence of a one dimensional quantum liquid.",1303.6954v2
2013-04-09,Over saturation behavior of SiPMs at high photon exposure,"Several types of Silicon Photomultipliers were exposed to short pulsed laser
light (~ 30 ps FWHM) with its intensity varying from single photon to well
above the number of microcells of the device. We observed a significant
deviation of the output of SiPMs from the expected behavior although such
response curve is considered to be rather trivial. We also noticed that the
output exceeds the maximum expected pulse height, which should be defined as
the total number of pixels times the single photon pulse height. At the highest
light intensity (~ 500 times the number of pixels) that we tested, the signal
output reached up to twice the maximum theoretical pulse height, and still did
not fully saturate.",1304.2493v3
2013-04-17,The search for Nanobubbles by using specular and off-specular Neutron Reflectometry,"We apply specular and off-specular neutron reflection at the hydrophobic
silicon/water interface to check for evidence of nanoscopic air bubbles whose
presence is claimed after an ad hoc procedure of solvent exchange. Nanobubbles
and/or a depletion layer at the hydrophobic/water interface have long been
discussed and generated a plethora of controversial scientific results. By
combining neutron reflectometry (NR), off-specular reflectometry (OSS) and
grazing incidence small angle neutron scattering (GISANS), we studied the
interface between hydrophobized silicon and heavy water before and after
saturation with nitrogen gas. Our specular reflectometry results can be
interpreted by assuming a sub-molecular sized depletion layer and the
off-specular measurements show no change with nitrogen super saturated water.
This picture is consistent with the assumption that, following the solvent
exchange, no additional nanobubbles are introduced at significant
concentrations (if present at all). Furthermore, we discuss the results, in
terms of the maximum surface coverage of nanobubbles that could be present on
the hydrophobic surface compatibly with the sensitivity limit of these
techniques.",1304.4809v2
2013-04-28,"Hidden Fermi Liquid, Scattering Rate Saturation and Nernst Effect: a DMFT Perspective","We investigate the transport properties of a correlated metal within
dynamical mean field theory. Canonical Fermi liquid behavior emerges only below
a very low temperature scale $T_{FL}$. Surprisingly the quasiparticle
scattering rate follows a quadratic temperature dependence up to much higher
temperatures and crosses over to saturated behavior around a temperature scale
$T_{sat}$. We identify these quasiparticles as constituents of the hidden Fermi
liquid. The non-Fermi liquid transport above $T_{FL}$, in particular the
linear-in-$T$ resistivity, is shown to be a result of a strongly temperature
dependent band dispersion. We derive simple expressions for resistivity, Hall
angle, thermoelectric power and Nernst coefficient in terms of a temperature
dependent renormalized band structure and the quasiparticle scattering rate. We
discuss possible tests of the DMFT picture of transport using ac measurements.",1304.7486v1
2013-05-30,Maximum Palinstrophy Growth in 2D Incompressible Flows,"In this study we investigate vortex structures which lead to the maximum
possible growth of palinstrophy in two-dimensional incompressible flows on a
periodic domain. The issue of palinstrophy growth is related to a broader
research program focusing on extreme amplification of vorticity-related
quantities which may signal singularity formation in different flow models.
Such extreme vortex flows are found systematically via numerical solution of
suitable variational optimization problems. We identify several families of
maximizing solutions parameterized by their palinstrophy, palinstrophy and
energy and palinstrophy and enstrophy. Evidence is shown that some of these
families saturate estimates for the instantaneous rate of growth of
palinstrophy obtained using rigorous methods of mathematical analysis, thereby
demonstrating that this analysis is in fact sharp. In the limit of small
palinstrophies the optimal vortex structures are found analytically, whereas
for large palinstrophies they exhibit a self-similar multipolar structure. It
is also shown that the time evolution obtained using the instantaneously
optimal states with fixed energy and palinstrophy as the initial data saturates
the upper bound for the maximum growth of palinstrophy in finite time. Possible
implications of this finding for the questions concerning extreme behavior of
flows are discussed.",1305.7259v2
2013-05-31,Drop-port study of microresonator frequency combs: power transfer and time-domain characterization,"We use a drop-port geometry to study power transfer in silicon nitride
on-chip microresonator frequency comb generators. In sharp contrast with the
traditional transmission geometry, we observe smooth output spectra with
comparable powers in the pump and adjacent comb lines. An observation of
saturation in the drop-port output power is explained semi-empirically by
introducing pump saturation into a coupling of modes model. Autocorrelation
measurements are performed on the drop-port output, without the need to filter
out or suppress the strong pump line as is necessary in thru-port experiments.
Passively mode-locked pulses are observed with a normal dispersion microcavity.",1305.7420v2
2013-06-10,"Transverse Momentum of Protons, Pions and Kaons in High Multiplicity pp and pA Collisions: Evidence for the Color Glass Condensate?","The CMS experiment at the Large Hadron Collider has recently presented data
on the average transverse momentum of protons, kaons and pions as a function of
particle multiplicity. We relate the particle multiplicity to saturation
momentum using recently published computations of the interaction radius
determined from the theory of the Color Glass Condensate. We show that the pp
and the pA experimental data scale in terms of these saturation momenta.
Computing transverse momentum spectra for identified particles using
Boltzmann-type distributions and relating different associated multiplicities
using geometric scaling, these simple distributions reproduce the observed
dependence of the mean transverse momentum on particle multiplicities seen in
both pp and pA interactions for pions to good accuracy, and to fair agreement
for protons and kaons.",1306.2350v1
2013-06-20,Dynamical entanglement entropy with angular momentum and U(1) charge,"We consider time-dependent entanglement entropy (EE) for a 1+1 dimensional
CFT in the presence of angular momentum and U(1) charge. The EE saturates,
irrespective of the initial state, to the grand canonical entropy after a time
large compared with the length of the entangling interval. We reproduce the CFT
results from an AdS dual consisting of a spinning BTZ black hole and a flat
U(1) connection. The apparent discrepancy that the holographic EE does not a
priori depend on the U(1) charge while the CFT EE does, is resolved by the
charge-dependent shift between the bulk and boundary stress tensors. We show
that for small entangling intervals, the entanglement entropy obeys the first
law of thermodynamics, as conjectured recently. The saturation of the EE in the
field theory is shown to follow from a version of quantum ergodicity; the
derivation indicates that it should hold for conformal as well as massive
theories in any number of dimensions.",1306.4974v2
2013-06-30,IP-Sat: Impact-Parameter dependent Saturation model; revised,"In this talk, we present a global analysis of available small-x data on
inclusive DIS and exclusive diffractive processes, including the latest data
from the combined HERA analysis on reduced cross sections within the
Impact-Parameter dependent Saturation (IP-Sat) Model. The impact-parameter
dependence of dipole amplitude is crucial in order to have a unified
description of both inclusive and exclusive diffractive processes. With the
parameters of model fixed via a fit to the high-precision reduced
cross-section, we compare model predictions to data for the structure
functions, the longitudinal structure function, the charm structure function,
exclusive vector mesons production and Deeply Virtual Compton Scattering
(DVCS). Excellent agreement is obtained for the processes considered at small x
in a wide range of Q^2.",1307.0165v1
2013-07-03,A new mechanism for saturating unstable r-modes in neutron stars,"We consider a new mechanism for damping the oscillations of a mature neutron
star. The new dissipation channel arises if superfluid vortices are forced to
cut through superconducting fluxtubes. This mechanism is interesting because
the oscillation modes need to exceed a critical amplitude in order for it to
operate. Once it acts the effect is very strong (and nonlinear) leading to
efficient damping. The upshot of this is that modes are unlikely to ever evolve
far beyond the critical amplitude. We consider the effect of this new
dissipation channel on the r-modes, that may be driven unstable by the emission
of gravitational waves. Our estimates show that the fluxtube cutting leads to a
saturation threshold for the instability that can be smaller than that of other
proposed mechanisms. This suggests that the idea may be of direct astrophysical
relevance.",1307.0985v1
2013-07-10,Electric dipole response of 208Pb from proton inelastic scattering: constraints on neutron skin thickness and symmetry energy,"The electric dipole (E1) response of 208Pb has been precisely determined by
measuring Coulomb excitation induced by proton scattering at very forward
angles. The electric dipole polarizability, defined as inverse energy-weighted
sum rule of the E1 strength, has been extracted as 20.1+-0.6 fm^3. The data can
be used to constrain the neutron skin thickness of 208Pb to
0.168(+-0.009)_expt(+-0.013)_theo(+-0.021)_est fm, where the subscript ""expt""
refers to the experimental uncertainty, ""theor"" to the theoretical confidence
band and ""est"" to the uncertainty associated with the estimation of the
symmetry energy at the saturation density. In addition, a constraint band has
been extracted in the plane of the symmetry energy (J) and its slope parameter
(L) at the saturation density.",1307.2706v2
2013-07-26,Global Attractivity and Extinction for Lotka-Volterra systems with infinite delay and feedback controls,"The paper deals with a multiple species Lotka-Volterra model with infinite
distributed delays and feedback controls, for which we assume a weak form of
diagonal dominance of the instantaneous negative intra-specific terms over the
infinite delay effect in both the population variables and controls. General
sufficient conditions for the existence and attractivity of a saturated
equilibrium are established. When the saturated equilibrium is on the boundary
of $\R^n_+$, sharper criteria for the extinction of all or part of the
populations are given. While the literature usually treats the case of
competitive systems only, here no restrictions on the signs of the intra- and
inter-specific delayed terms are imposed. Moreover, our technique does not
require the construction of Lyapunov functionals.",1307.7039v1
2013-08-02,Three jet production and gluon saturation effects in p-p and p-Pb collisions within high-energy factorization,"We analyze three jet production in the central-forward and forward rapidity
regions in proton-proton and proton-lead collisions at LHC energies. Our
calculation relies on high-energy factorization with a single off-shell gluon
obeying small x evolution equation which includes saturation. The calculations
are made using two independent Monte Carlo codes implementing tree-level gauge
invariant off-shell matrix elements. We calculate differential cross sections
for azimuthal decorrelations and unbalanced jet transverse momenta and discuss
them in the context of differences in the evolution of the unintegrated gluon
densities.",1308.0452v3
2013-08-06,Heavy quark pair production in high energy pA collisions: Open heavy flavors,"We study open heavy flavor meson production in proton-nucleus (pA) collisions
at RHIC and LHC energies within the Color Glass Condensate framework. We use
the unintegrated gluon distribution at small Bjorken's x in the proton obtained
by solving the Balitsky-Kovchegov equation with running coupling correction and
constrained by global fitting of HERA data. We change the initial saturation
scale of the gluon distribution for the heavy nucleus. The gluon distribution
with McLerran-Venugopalan model initial condition is also used for comparison.
We present transverse momentum spectra of single D and B productions in pA
collisions, and the so-called nuclear modification factor. The azimuthal angle
correlation of open heavy flavor meson pair is also computed to study the
modification due to the gluon saturation in the heavy nucleus at the LHC.",1308.1258v1
2013-09-03,The plasma oscillations in a two-dimensional electron-hole liquid under influence Rashba spin-orbit coupling,"The plasma oscillations of the two-dimensional electron-hole system in the
presence of a Rashba spin-orbit coupling are studied. Only the intra-Landau
level excitations are taken into account when the electrons and holes are
situated on their lowest Landau levels, the filling factor $v^{2}$ being less
than 1. The ground state of the two-dimensional electron-hole system is
supposed to be the electron-hole liquid. The dispersion relations for the
optical and acoustical plasmon modes were obtained. The acoustical plasmon
branch has a linear dispersion law in the range of small wave vectors and
monotonically increases with saturation at higher values of wave vectors. The
optical plasmon branch has a quadratic dependence in the range of long
wavelength and a monotonic increasing with saturation as in the case of
acoustical branch.",1309.0716v1
2013-09-05,Quantum Joule-Thomson Effect in a Saturated Homogeneous Bose Gas,"We study the thermodynamics of Bose-Einstein condensation in a weakly
interacting quasi-homogeneous atomic gas, prepared in an optical-box trap. We
characterise the critical point for condensation and observe saturation of the
thermal component in a partially condensed cloud, in agreement with Einstein's
textbook picture of a purely statistical phase transition. Finally, we observe
the quantum Joule-Thomson effect, namely isoenthalpic cooling of an
(essentially) ideal gas. In our experiments this cooling occurs spontaneously,
due to energy-independent collisions with the background gas in the vacuum
chamber. We extract a Joule-Thomson coefficient $\mu_{\rm JT} > 10^9$ K/bar,
about ten orders of magnitude larger than observed in classical gases.",1309.1441v3
2013-09-10,Spectral Sum Rules and Magneto-Roton as Emergent Graviton in Fractional Quantum Hall Effect,"We consider gapped fractional quantum Hall states on the lowest Landau level
when the Coulomb energy is much smaller than the cyclotron energy. We introduce
two spectral densities, \rho_T(\omega) and \bar \rho_T(\omega), which are
proportional to the probabilities of absorption of circularly polarized
gravitons by the quantum Hall system. We prove three sum rules relating these
spectral densities with the shift S, the q^4 coefficient of the static
structure factor S_4, and the high-frequency shear modulus of the ground state
\mu_\infty, which is precisely defined. We confirm an inequality, first
suggested by Haldane, that S_4 is bounded from below by |S-1|/8. The Laughlin
wavefunction saturates this bound, which we argue to imply that systems with
ground state wavefunctions close to Laughlin's absorb gravitons of
predominantly one circular polarization. We consider a nonlinear model where
the sum rules are saturated by a single magneto-roton mode. In this model, the
magneto-roton arises from the mixing between oscillations of an internal metric
and the hydrodynamic motion. Implications for experiments are briefly
discussed.",1309.2638v1
2013-09-13,Non-linear evolution of unintegrated gluon density at large values of coupling constant,"We propose an evolution equation for unintegrated gluon densities that is
valid for large values of the QCD coupling constant $\bar{\alpha} _s$. Our
approach is based on the linear resummation model introduced by Sta\'{s}to. We
generalize the model including a non-linear term in the diffusive regime. The
validity of the diffusive evolution at strong coupling is supported by the
AdS/CFT consideration, as well as perturbative arguments. We solve the
evolution equation numerically and extract the saturation scale, which we
compare with the weak coupling counterpart.",1309.3450v3
2013-09-23,Saturation of black hole lasers in Bose-Einstein condensates,"To obtain the end-point evolution of the so-called black hole laser
instability, we study the set of stationary solutions of the Gross-Pitaevskii
equation for piecewise constant potentials which admit a homogeneous solution
with a supersonic flow in the central region between two discontinuities. When
the distance between them is larger than a critical value, we recover that the
homogeneous solution is unstable, and we identify the lowest energy state. We
show that it can be viewed as determining the saturated value of the first
(node-less) complex frequency mode which drives the instability. We also
classify the set of stationary solutions and establish their relation both with
the set of complex frequency modes and with known soliton solutions. Finally,
we adopt a procedure \`a la Pitaevski-Baym-Pethick to construct the effective
functional which governs the transition from the homogeneous to non-homogeneous
solutions.",1309.5869v2
2013-09-27,Planck's uncertainty principle and the saturation of Lorentz boosts by Planckian black holes,"A basic inconsistency arises when the Theory of Special Relativity meets with
quantum phenomena at the Planck scale. Specifically, the Planck length is
Lorentz invariant and should not be affected by a Lorentz boost. We argue that
Planckian relativity must necessarily involve the effect of black hole
formation. Recent proposals for resolving the noted inconsistency seem
unsatisfactory in that they ignore the crucial role of gravity in the
saturation of Lorentz boosts. Furthermore, an invariant length at he Planck
scale amounts to a universal quantum of resolution in the fabric of spacetime.
We argue, therefore, that the universal Planck length requires an extension of
the Uncertainty Principle as well. Thus, the noted inconsistency lies at the
core of Quantum Gravity. In this essay we reflect on a possible resolution of
these outstanding problems.",1309.7186v1
2013-10-08,"Ultrafast and widely tuneable vertical-external-cavity surface-emitting laser, mode-locked by a graphene-integrated distributed Bragg reflector","We report a versatile and cost-effective way of controlling the unsaturated
loss, modulation depth and saturation fluence of graphene-based saturable
absorbers (GSAs), by changing the thickness of a spacer between SLG and a
high-reflection mirror. This allows us to modulate the electric field intensity
enhancement at the GSA from 0 up to 400%, due to the interference of incident
and reflected light at the mirror. The unsaturated loss of the
SLG-mirror-assembly can be reduced to$\sim$0. We use this to mode-lock a VECSEL
from 935 to 981nm. This approach can be applied to integrate SLG into various
optical components, such as output coupler mirrors, dispersive mirrors,
dielectric coatings on gain materials. Conversely, it can also be used to
increase absorption (up to 10%) in various graphene based photonics and
optoelectronics devices, such as photodetectors.",1310.2132v1
2013-10-11,Fluid dynamics with saturated minijet initial conditions in ultrarelativistic heavy-ion collisions,"Using next-to-leading order perturbative QCD and a conjecture of saturation
to suppress the production of low-energy partons, we calculate the initial
energy densities and formation times for the dissipative fluid dynamical
evolution of the quark-gluon plasma produced in ultrarelativistic heavy-ion
collisions. We identify the framework uncertainties and demonstrate the
predictive power of the approach by a good global agreement with the measured
centrality dependence of charged particle multiplicities, transverse momentum
spectra and elliptic flow simultaneously for the Pb+Pb collisions at the LHC
and Au+Au at RHIC. In particular, the shear viscosity in the different phases
of QCD matter is constrained in this new framework simultaneously by all these
data.",1310.3105v1
2013-10-17,Numerical Modeling of Nanoparticles Transport with Two-Phase Flow in Porous Media Using Iterative Implicit Method,"In this paper, we introduce a mathematical model to describe the
nanoparticles transport carried by a two-phase flow in a porous medium
including gravity, capillary forces and Brownian diffusion. Nonlinear iterative
IMPES scheme is used to solve the flow equation, and saturation and pressure
are calculated at the current iteration step and then the transport equation is
soved implicitly. Therefore, once the nanoparticles concentration is computed,
the two equations of volume of the nanoparticles available on the pore surfaces
and the volume of the nanoparticles entrapped in pore throats are solved
implicitly. The porosity and the permeability variations are updated at each
time step after each iteration loop. Two numerical examples, namely, regular
heterogeneous permeability and random permeability are considered. We monitor
the changing of the fluid and solid properties due to adding the nanoparticles.
Variation of water saturation, water pressure, nanoparticles concentration and
porosity are presented graphically.",1310.4769v1
2013-10-18,Sivers Function in the Quasi-Classical Approximation,"We calculate the Sivers function in semi-inclusive deep inelastic scattering
(SIDIS) and in the Drell-Yan process (DY) by employing the quasi-classical
Glauber-Mueller/ McLerran-Venugopalan approximation. Modeling the hadron as a
large ""nucleus"" with non-zero orbital angular momentum (OAM), we find that its
Sivers function receives two dominant contributions: one contribution is due to
the OAM, while another one is due to the local Sivers function density in the
nucleus. While the latter mechanism, being due to the ""lensing"" interactions,
dominates at large transverse momentum of the produced hadron in SIDIS or of
the di-lepton pair in DY, the former (OAM) mechanism is leading in saturation
power counting and dominates when the above transverse momenta become of the
order of the saturation scale. We show that the OAM channel allows for a
particularly simple and intuitive interpretation of the celebrated sign flip
between the Sivers functions in SIDIS and DY.",1310.5028v2
2013-10-21,A family of steady two-phase generalized Forchheimer flows and their linear stability analysis,"We model multi-dimensional two-phase flows of incompressible fluids in porous
media using generalized Forchheimer equations and the capillary pressure.
Firstly, we find a family of steady state solutions whose saturation and
pressure are radially symmetric and velocities are rotation-invariant. Their
properties are investigated based on relations between the capillary pressure,
each phase's relative permeability and Forchheimer polynomial. Secondly, we
analyze the linear stability of those steady states.
  The linearized system is derived and reduced to a parabolic equation for the
saturation. This equation has a special structure depending on the steady
states which we exploit to prove two new forms of the lemma of growth of
Landis-type in both bounded and unbounded domains. Using these lemmas,
qualitative properties of the solution of the linearized equation are studied
in details. In bounded domains, we show that the solution decays exponentially
in time. In unbounded domains, in addition to their stability, the solution
decays to zero as the spatial variables tend to infinity. The Bernstein",1310.5723v1
2013-10-22,Experimental effects on dynamics and thermodynamics in nuclear reactions on the symmetry energy as seen by the CHIMERA 4$π$ detector,"Heavy ion collisions have been widely used in the last decade to constraint
the parameterizations of the symmetry energy term of nuclear equation of state
(EOS) for asymmetric nuclear matter as a function of baryonic density. In the
Fermi energy domain one is faced with variations of the density within a narrow
range of values around the saturation density $\rho_0$=0.16 fm$^{-3}$ down
towards sub-saturation densities. The experimental observables which are
sensitive to the symmetry energy are constructed starting from the detected
light particles, clusters and heavy fragments that, in heavy ion collisions,
are generally produced by different emission mechanisms at different stages and
time scales of the reaction. In this review the effects of dynamics and
thermodynamics on the symmetry energy in nuclear reactions are discussed and
characterized using an overview of the data taken so far with the CHIMERA
multi-detector array.",1310.5836v1
2013-10-28,Obtaining localization properties efficiently using the Kubo-Greenwood formalism,"We establish, through numerical calculations and comparisons with a recursive
Green's function based implementation of the Landauer-B\""uttiker formalism, an
efficient method for studying Anderson localization in quasi-one-dimensional
and two-dimensional systems using the Kubo-Greenwood formalism. Although the
recursive Green's function method can be used to obtain the localization length
of a mesoscopic conductor, it is numerically very expensive for systems that
contain a large number of atoms transverse to the transport direction. On the
other hand, linear-scaling has been achieved with the Kubo-Greenwood method,
enabling the study of effectively two-dimensional systems. While the
propagating length of the charge carriers will eventually saturate to a finite
value in the localized regime, the conductances given by the Kubo-Greenwood
method and the recursive Green's function method agree before the saturation.
The converged value of the propagating length is found to be directly
proportional to the localization length obtained from the exponential decay of
the conductance.",1310.7518v2
2013-11-05,Exciton-exciton annihilation in MoSe2 monolayers,"We investigate the excitonic dynamics in MoSe2 monolayer and bulk samples by
femtosecond transient absorption microscopy. Excitons are resonantly injected
by a 750-nm and 100-fs laser pulse, and are detected by a probe pulse tuned in
the range of 790 - 820 nm. We observe a strong density-dependent initial decay
of the exciton population in monolayers, which can be well described by the
exciton-exciton annihilation. Such a feature is not observed in the bulk under
comparable conditions. We also observe the saturated absorption induced by
exciton phase-space filling in both monolayers and the bulk, which indicates
their potential applications as saturable absorbers.",1311.1079v1
2013-11-06,"Steering, incompatibility, and Bell inequality violations in a class of probabilistic theories","We show that connections between a degree of incompatibility of pairs of
observables and the strength of violations of Bell's inequality found in recent
investigations can be extended to a general class of probabilistic physical
models. It turns out that the property of universal uniform steering is
sufficient for the saturation of a generalised Tsirelson bound, corresponding
to maximal violations of Bell's inequality. It is also found that a limited
form of steering is still available and sufficient for such saturation in some
state spaces where universal uniform steering is not given. The techniques
developed here are applied to the class of regular polygon state spaces, giving
a strengthening of known results. However, we also find indications that the
link between incompatibility and Bell violation may be more complex than
originally envisaged.",1311.1462v2
2013-11-06,Charm production in double parton scattering at the LHC,"We calculate $c\bar{c}c\bar{c}$ and $b\bar{b}b\bar{b}$ production cross
section in Double Parton Scattering (DPS) processes at the energies of LHC. In
our calculation we include saturation effects in the gluon distribution. For
charm production, our results confirm the prediction of a previous work in
which saturation effects were neglected, namely that at the energies of LHC
charm production in DPS processes becomes comparable with charm production in
SPS. We also estimate the production of $c\bar{c}b\bar{b}$ in DPS. Our results
indicate that at $\sqrt{s}=14$ TeV half of the total amount of bottom produced
in proton-proton collisions comes from this process.",1311.2473v1
2013-11-14,Nuclear Entalpies,"In a compressed Nuclear Matter (NM) an increasing pressure between the
nucleons starts to increase the ratio of a nucleon Fermi to average single
particle energy and in accordance with the Hugenholtz-van Hove theorem the
longitudinal Momentum Sum Rule (MSR) is broken in a Relativistic Mean Field
(RMF) approach. We propose to benefit from the concept of enthalpy in order to
show how to fulfill the MSR above a saturation density with pressure
corrections. As a result a nucleon mass can decrease with density, making the
Equation of State (EoS) softer. The course of the EoS in our modified RMF model
is close to a semi-empirical estimate and to results obtained from extensive
DBHF calculations with a Bonn A potential, which produce the EoS stiff enough
to describe neutron star properties (mass-radius constraint), especially the
most massive known neutron star. The presented model has proper saturation
properties, including good values of a compressibility and a spin-orbit term.",1311.3591v2
2013-11-25,Photoassociation of ultracold LiRb* molecules: observation of high efficiency and unitarity-limited rate saturation,"We report the production of ultracold heteronuclear 7Li85Rb molecules in
excited electronic states by photoassociation (PA) of ultracold 7Li and 85Rb
atoms. PA is performed in a dual-species 7Li-85Rb magneto-optical trap (MOT)
and the PA resonances are detected using trap loss spectroscopy. We identify
several strong PA resonances below the Li (2s 2S1/2) + Rb (5p 2P3/2) asymptote
and experimentally determine the long range C6 dispersion coefficients. We find
a molecule formation rate (P_LiRb) of 3.5x10^7 s^-1 and a PA rate coefficient
(K_PA) of 1.3x10^-10 cm^3/s, the highest among heteronuclear bi-alkali
molecules. At large PA laser intensity, we observe the saturation of the PA
rate coefficient (K_PA) close to the theoretical value at the unitarity limit.",1311.6297v2
2013-11-26,Coherent chirped pulse laser network in Mickelson phase conjugating configuration,"The mechanisms of nonlinear phase-locking of a large fiber amplifier array
are analyzed. It is shown that Michelson phase conjugating configuration with
double passage through array of fiber amplifiers have the definite advantages
compared to one-way fiber array coupled in a Mach-Zehnder configuration.
Regardless to amount of synchronized fiber amplifiers Michelson
phase-conjugating interferometer is expected to do a perfect compensation of
the phase-piston errors and collimation of backwardly amplified fiber beams on
entrance/output beamsplitter. In both configurations the nonlinear
transformation of the stretched pulse envelope due to gain saturation is
capable to randomize the position of chirp inside envelope thus it may reduce
the visibility of interference pattern at output beamsplitter. A certain
advantages are inherent to the $sech$-form temporal envelope because of
exponential precursor and self-similar propagation in gain medium. The Gaussian
envelope is significantly compressed in a deep gain saturation regime and
frequency chirp position inside pulse envelope is more deformed.",1311.6703v4
2013-11-27,Analyzing the Dual Space of the Saturated Ideal of a Regular Set and the Local Multiplicities of its Zeros,"In this paper, we are concerned with the problem of counting the
multiplicities of a zero-dimensional regular set's zeros. We generalize the
squarefree decomposition of univariate polynomials to the so-called pseudo
squarefree decomposition of multivariate polynomials, and then propose an
algorithm for decomposing a regular set into a finite number of simple sets.
From the output of this algorithm, the multiplicities of zeros could be
directly read out, and the real solution isolation with multiplicity can also
be easily produced. As a main theoretical result of this paper, we analyze the
structure of dual space of the saturated ideal generated by a simple set as
well as a regular set. Experiments with a preliminary implementation show the
efficiency of our method.",1311.6897v2
2013-12-14,Analysis of a class of degenerate parabolic equations with saturation mechanisms,"We analyze a family of degenerate parabolic equations with linear growth
Lagrangian having the form $u_t=\div (\varphi(u)\psi(\nabla u/u))$. Here
$|\psi|\le 1$ and saturates at infinity. We present a simple and natural set of
assumptions on the functions $\psi,\varphi$, under which: 1) these equations
fall in the framework provided by \cite{ACMEllipticFLDE, ACMMRelat} and hence
they are well posed, 2) we can ensure finite propagation speed for these
models, 3) a Rankine--Hugoniot analysis on traveling fronts is also performed.
On the particular case of $\varphi(u)=u$ we get more detailed information on
the spreading rate of compactly supported solutions and some interesting
connections with optimal mass transportation theory.",1312.4034v5
2013-12-22,A General Criterion for Liquefaction in Granular Layers with Heterogeneous Pore Pressure,"Fluid-saturated granular and porous layers can undergo liquefaction and lose
their shear resistance when subjected to shear forcing. In geosystems, such a
process can lead to severe natural hazards of soil liquefaction, accelerating
slope failure, and large earthquakes. Terzaghi's principle of effective stress
predicts that liquefaction occurs when the pore pressure within the layer
becomes equal to the applied normal stress on the layer. However, under dynamic
loading and when the internal permeability is relatively small the pore
pressure is spatially heterogeneous and it is not clear what measurement of
pore pressure should be used in Terzaghi's principle. Here, we show
theoretically and demonstrate using numerical simulations a general criterion
for liquefaction that applies also for the cases in which the pore pressure is
spatially heterogeneous. The general criterion demands that the average pore
pressure along a continuous surface within the fluid-saturated granular or
porous layer is equal to the applied normal stress.",1312.6422v1
2014-01-09,The equation of state and symmetry energy of low density nuclear matter,"The symmetry energy of nuclear matter is a fundamental ingredient in the
investigation of exotic nuclei, heavy-ion collisions and astrophysical
phenomena. A recently developed quantum statistical (QS) approach that takes
the formation of clusters into account predicts low density symmetry energies
far above the usually quoted mean field limits. A consistent description of the
symmetry energy has been developed that joins the correct low-density limit
with values calculated from quasi-particle approaches valid near the saturation
density. The results are confronted with experimental values for free symmetry
energies and internal symmetry energies, determined at sub-saturation densities
and temperatures below 10 MeV using data from heavy-ion collisions. There is
very good agreement between the experimental symmetry energy values and those
calculated in the QS approach",1401.2074v1
2014-01-10,GaAs Quantum Dot Thermometry Using Direct Transport and Charge Sensing,"We present measurements of the electron temperature using gate defined
quantum dots formed in a GaAs 2D electron gas in both direct transport and
charge sensing mode. Decent agreement with the refrigerator temperature was
observed over a broad range of temperatures down to 10 mK. Upon cooling nuclear
demagnetization stages integrated into the sample wires below 1 mK, the device
electron temperature saturates, remaining close to 10 mK. The extreme
sensitivity of the thermometer to its environment as well as electronic noise
complicates temperature measurements but could potentially provide further
insight into the device characteristics. We discuss thermal coupling
mechanisms, address possible reasons for the temperature saturation and
delineate the prospects of further reducing the device electron temperature.",1401.2330v1
2014-01-20,All Superparticles are BPS,"The generic action for an N-extended superparticle in D-dimensional Minkowski
spacetime is shown to have ""hidden"" supersymmetries (related by ""dualities"" to
the manifest supersymmetries) such that the full supersymmetry algebra is
BPS-saturated; the exceptions (which include, trivially, the massless case) are
those for which the manifest supersymmetry algebra is already BPS-saturated.
Moreover, it is shown that any ""non-BPS"" superparticle action is a gauge-fixed
version of the ""BPS"" superparticle action for which all supersymmetries are
manifest. An example is the N=1 massive D=10 superparticle, which actually has
N=2 supersymmetry and is equivalent to the action for a D0-brane of IIA
superstring theory.",1401.5116v2
2014-01-23,Nonlinear Photoluminescence Properties of Trions in Hole-doped Single-walled Carbon Nanotubes,"We studied the excitation density dependence of photoluminescence (PL)
spectra of excitons and trions (charged excitons) in hole-doped single-walled
carbon nanotubes. We found that the PL intensity of trions exhibited a strong
nonlinear saturation behavior as the excitation density increased, whereas that
of excitons exhibited a weak sublinear behavior. The strong PL saturation of
trions is attributed to depletion of doped holes that are captured by excitons
in the formation processes. Moreover, the effective radiative lifetime of a
trion was evaluated to be approximately 20 ns.",1401.5873v1
2014-01-27,On Efficiency and Validity of Previous Homeplug MAC Performance Analysis,"The Medium Access Control protocol of Power Line Communication networks
(defined in Homeplug and IEEE 1901 standards) has received relatively modest
attention from the research community. As a consequence, there is only one
analytic model that complies with the standardised MAC procedures and considers
unsaturated conditions. We identify two important limitations of the existing
analytic model: high computational expense and predicted results just prior to
the predicted saturation point do not correspond to long-term network
performance. In this work, we present a simplification of the previously
defined analytic model of Homeplug MAC able to substantially reduce its
complexity and demonstrate that the previous performance results just before
predicted saturation correspond to a transitory phase. We determine that the
causes of previous misprediction are common analytical assumptions and the
potential occurrence of a transitory phase, that we show to be of extremely
long duration under certain circumstances. We also provide techniques, both
analytical and experimental, to correctly predict long-term behaviour and
analyse the effect of specific Homeplug/IEEE 1901 features on the magnitude of
misprediction errors.",1401.6803v2
2014-01-27,Elliptic Flow and Shear Viscosity of the Shattered Color Glass Condensate,"In this talk, we report on our results about the computation of the elliptic
flow of the quark-gluon-plasma produced in relativistic heavy ion collisions,
simulating the expansion of the fireball by solving the relativistic Boltzmann
equation for the parton distribution function tuned at a fixed shear viscosity
to entropy density ratio $\eta/s$. We emphasize the role of saturation in the
initial gluon spectrum modelling the shattering of the color glass condensate,
causing the initial distribution to be out of equilibrium. We find that the
saturation reduces the efficiency in building-up the elliptic flow, even if the
thermalization process is quite fast $\tau_{therm} \approx 0.8 \,\rm fm/c$. and
the pressure isotropization even faster $\tau_{isotr} \approx 0.3 \,\rm fm/c$.
The impact of the initial non-equilibrium manifests for non-central collisions
and can modify the estimate of the viscosity respect to the assumption of full
thermalization in $p_T$-space.",1401.6903v1
2014-01-28,A Two-Level Variant of Additive Schwarz Preconditioning for Use in Reservoir Simulation,"The computation time for reservoir simulation is dominated by the linear
solver. The sets of linear equations which arise in reservoir simulation have
two distinctive features: the problems are usually highly anisotropic, with a
dominant vertical flow direction, and the commonly used fully implicit method
requires a simultaneous solution for pressure and saturation or molar
concentration variables. These variables behave quite differently, with the
pressure feeling long-range effects while the saturations vary locally. In this
paper we review preconditioned iterative methods used for solving the linear
system equations in reservoir simulation and their parallelisation. We then
propose a variant of the classical additive Schwarz preconditioner designed to
achieve better results on a large number of processors and discuss some
directions for future research.",1401.7227v3
2014-02-07,"Qualitative behavior for flux-saturated mechanisms: Traveling waves, waiting time and smoothing effects","This paper is devoted to the analysis of qualitative properties of
flux-saturated type operators in dimension one. Specifically, we study
regularity properties and smoothing effects, discontinuous interfaces, the
existence of traveling wave profiles, sub- and super-solutions and waiting time
features. The aim of the paper is to better understand these kind of phenomena
throughout two prototypic operators: The relativistic heat equation and the
porous media flux-limited equation. As an important consequence of our results
we deduce that solutions to the one-dimensional relativistic heat equation
become smooth inside their support on the long time run.",1402.1679v2
2014-02-18,Constraints on the skewness coefficient of symmetric nuclear matter within the nonlinear relativistic mean field model,"Within the nonlinear relativistic mean field (NL-RMF) model, we show that
both the pressure of symmetric nuclear matter at supra-saturation densities and
the maximum mass of neutron stars are sensitive to the skewness coefficient
$J_0$ of symmetric nuclear matter. Using experimental constraints on the
pressure of symmetric nuclear matter at supra-saturation densities from flow
data in heavy ion collisions and the astrophysical observation of a large mass
neutron star PSR J0348+0432, with the former favoring a smaller $J_0$ while the
latter a larger $J_0$, we extract a constraint of $-494 \mathrm{MeV}\leq
J_0\leq -10 \mathrm{MeV}$ based on the NL-RMF model. This constraint is
compared with the results obtained in other analyses.",1402.4242v2
2014-03-08,"Interactions of Airy beams, nonlinear accelerating beams, and induced solitons in Kerr and saturable nonlinear media","We investigate numerically interactions between two in-phase or out-of-phase
Airy beams and nonlinear accelerating beams in Kerr and saturable nonlinear
media in one transverse dimension. We discuss different cases in which the
beams with different intensities are launched into the medium, but accelerate
in opposite directions. Since both the Airy beams and nonlinear accelerating
beams possess infinite oscillating tails, we discuss interactions between
truncated beams, with finite energies. During interactions we see solitons and
soliton pairs generated that are not accelerating. In general, the higher the
intensities of interacting beams, the easier to form solitons; when the
intensities are small enough, no solitons are generated. Upon adjusting the
interval between the launched beams, their interaction exhibits different
properties. If the interval is large relative to the width of the first lobes,
the generated soliton pairs just propagate individually and do not interact
much. However, if the interval is comparable to the widths of the maximum
lobes, the pairs strongly interact and display varied behavior.",1403.1952v1
2014-03-25,Coexistence of fast photodarkening and slow photobleaching in Ge19As21Se60 thin films,"We experimentally demonstrate the coexistence of two opposite photo-effects,
viz. fast photodarkening (PD) and slow photobleaching (PB) in Ge19As21Se60 thin
films, when illuminated with a laser of wavelength 671nm, PD appears to begin
instantaneously upon light illumination and saturates in tens of seconds. By
comparison, PB is a slower process that starts only after PD has saturated.
Although we could observe the coexistence of PD/PB even at moderate, one order
of magnitude lower intensity of 0.2 W/cm2, the kinetics of transformation is
significantly slowed down. However, both PD and PB follow stretched exponetial
dependence on time. Modeling of overall change as a linear sum of two
contributions suggests that the changes in As and Ge parts of glass network
respond to light indepndent of each other.",1403.6359v1
2014-03-25,Multipacting saturation in parallel plate and micro-pulse electron gun,"A novel parallel plate model is proposed that divided the electron cloud into
three parts at saturation, and it is studied in detail using both an analytical
approach and PIC (Particle In Cell) code simulations. As one part of the
electron cloud, ribbons modes are suggested by tracking the trajectory of
individual particle, and the aim of this mode form is to simplify the progress
of multipacting effect in the parallel plate so as to be eliminated by
optimizing RF parameters. The micro-pulse electron gun (MPG) has demonstrated
the potential to address the need for high peak and average current electron
beams, hence studying the multipacting in MPG is essential. On the basis of
multipacting studying in the parallel plate, it is clear that increasing the
cavity voltage is of interest in yielding high quality beams in the gun.",1403.6360v2
2014-03-31,Penetration depth scaling for impact into wet granular packings,"We present experimental measurements of penetration depths for the impact of
spheres into wetted granular media. We observe that the penetration depth in
the liquid saturated case scales with projectile density, size, and drop height
in a fashion consistent with the scaling observed in the dry case, but that
penetration depths into saturated packings tend to be smaller. This result
suggests that, for the range of impact energies observed, the stopping force is
set by static contact forces between grains within the bed, and that the
presence of liquid serves, primarily, to enhance these contact forces. The
enhancement to the stopping force has a complicated dependence on liquid
fraction, accompanied by a change in the drop-height dependence, that must be
the consequence of accompanying changes in the conformation of the liquid phase
in the interstices.",1403.8124v4
2014-04-01,The Search for Gluon Saturation in pA Collisions,"In this talk, I reviewed the recent theoretical progress towards the
exploration of the gluon saturation phenomenon in $pA$ collisions at both RHIC
and the LHC. Two important pillars of this exploration are the single inclusive
forward hadron productions and forward dihadron correlations, which have both
been computed up to one-loop order within the small-$x$ factorization
formalism. Furthermore, detailed numerical study for the single inclusive
hadron production at next-to-leading order provides us good description of the
low transverse momentum data measured in $dAu$ collisions at RHIC with
significantly reduced uncertainty. In addition, the one-loop calculation for
dihadron productions in $pA$ collisions shows that there is a new type of large
logarithm, which is known as the Sudakov factor, arising in the back-to-back
correlation limit.",1404.0179v1
2014-04-08,Fingerprints of Inelastic Transport at the Surface of the Topological Insulator Bi2Se3: Role of Electron-Phonon Coupling,"We report on electric-field and temperature dependent transport measurements
in exfoliated thin crystals of Bi$_{2}$Se$_{3}$ topological insulator. At low
temperatures ($< 50$ K) and when the chemical potential lies inside the bulk
gap, the crystal resistivity is strongly temperature dependent, reflecting
inelastic scattering due to the thermal activation of optical phonons. A linear
increase of the current with voltage is obtained up to a threshold value at
which current saturation takes place. We show that the activated behavior, the
voltage threshold and the saturation current can all be quantitatively
explained by considering a single optical phonon mode with energy $\hbar \Omega
\approx 8$ meV. This phonon mode strongly interacts with the surface states of
the material and represents the dominant source of scattering at the surface at
high electric fields.",1404.2198v1
2014-04-10,Existence of optimal ultrafilters and the fundamental complexity of simple theories,"In the first edition of Classification Theory, the second author
characterized the stable theories in terms of saturation of ultrapowers. Prior
to this theorem, stability had already been defined in terms of counting types,
and the unstable formula theorem was known. A contribution of the ultrapower
characterization was that it involved sorting out the global theory, and
introducing nonforking, seminal for the development of stability theory. Prior
to the present paper, there had been no such characterization of an unstable
class. In the present paper, we first establish the existence of so-called
optimal ultrafilters on Boolean algebras, which are to simple theories as
Keisler's good ultrafilters are to all theories. Then, assuming a supercompact
cardinal, we characterize the simple theories in terms of saturation of
ultrapowers. To do so, we lay the groundwork for analyzing the global structure
of simple theories, in ZFC, via complexity of certain amalgamation patterns.
This brings into focus a fundamental complexity in simple unstable theories
having no real analogue in stability.",1404.2919v2
2014-04-18,Predictions for the Spatial Distribution of Gluons in the Initial Nuclear State,"We make predictions for the t-differential cross section of exclusive vector
meson production (EVMP) in electron-ion collisions, with the aim of comparing
DGLAP evolution to CGC models. In the current picture for the high-energy
nucleus, nonlinear effects need to be understood in terms of low-$x$ gluon
radiation and recombination as well as how this leads to saturation. EVMP
grants experimental access to the edge region of the highly-boosted nuclear
wavefunction, where the saturation scale for CGC calculations becomes
inaccessible to pQCD. On the other hand, DGLAP evolution requires careful
consideration of unitarity effects. The existing $J/{\psi}$ photoproduction
data in ep collisions provides a baseline for these theoretical calculations.
Under different small-$x$ frameworks we obtain a measurable distinction in both
the shape and normalization of the differential cross section predictions.
These considerations are relevant for heavy ion collisions because the initial
state may be further constrained, thus aiding in quantitative study of the
quark-gluon plasma.",1404.4743v1
2014-05-20,Periodic and Hyperbolic Soliton Solutions of a Number of Nonlocal PT-Symmetric Nonlinear Equations,"For a number of nonlocal nonlinear equations such as nonlocal, nonlinear
Schr\""odinger equation (NLSE), nonlocal Ablowitz-Ladik (AL), nonlocal,
saturable discrete NLSE (DNLSE), coupled nonlocal NLSE, coupled nonlocal AL and
coupled nonlocal, saturable DNLSE, we obtain periodic solutions in terms of
Jacobi elliptic functions as well as the corresponding hyperbolic soliton
solutions. Remarkably, in all the six cases, we find that unlike the
corresponding local cases, all the nonlocal models simultaneously admit both
the bright and the dark soliton solutions. Further, in all the six cases, not
only $\dn(x,m)$ and $\cn(x,m)$ but even their linear superposition is shown to
be an exact solution. Finally, we show that the coupled nonlocal NLSE not only
admits solutions in terms of Lam\'e polynomials of order 1, but it also admits
solutions in terms of Lam\'e polynomials of order 2, even though they are not
the solutions of the uncoupled nonlocal problem. We also remark on the possible
integrability in certain cases.",1405.5267v1
2014-05-26,A numerical study of two-phase miscible flow through porous media with a Lagrangian model,"The multiphase flow mechanism in miscible displacement through porous media
is an important topic in various applications, such as petroleum engineering,
low Reynolds number suspension flows, dusty gas dynamics, and fluidized beds.
To simulate such flows, volume averaging spatial operators are considered to
incorporate pressure drag and skin friction experienced by a porous medium. In
this work, a streamline-based Lagrangian methodology is extended for an
efficient numerical approach to handle dispersion and diffusion of solvent
saturation during a miscible flow. Overall pressure drag on the diffusion and
dispersion of solvent saturation is investigated. Numerical results show
excellent agreement with the results obtained from asymptotic analysis. The
present numerical simulations indicate that the nonlinear effects due to skin
friction and pressure drag cannot be accurately captured by Darcy's method if
the contribution of the skin friction dominates over that of the pressure drag.
Moreover, mass conservation law is investigated, which is an important feature
for enhanced oil recovery, and the results help to guide a good agreement with
theory. This investigation examines how the flow regime may be optimized for
enhanced oil recovery methods.",1405.6449v2
2014-06-10,Azimuthal quadrupole correlation from gluon interference in 200 GeV and 7 TeV p+p collisions,"The Balitskii-Fadin-Kuraev-Lipatov (BFKL) multi-Pomeron model of Levin and
Rezaeian, with extension to the gluon saturation region, is applied to
long-range pseudorapidity correlations on relative azimuth for low momentum
final-state hadrons produced in $\sqrt{s}$ = 200~GeV and 7~TeV p+p collisions.
The multi-Pomeron exchange probabilities in the model were estimated by fitting
the minimum-bias p+p multiplicity frequency distributions. The multi-Pomeron
model prediction for the amplitude of the minimum-bias average quadrupole
correlation, proportional to $\cos 2(\phi_1 - \phi_2)$, is consistent with the
200~GeV data when theoretically expected gluon saturation momentum scales are
used. Correlation predictions for the high multiplicity 7~TeV p+p collision
data are also consistent with the long-range pseudorapidity correlations at
small relative azimuth observed in the data. The results presented here show
that the present application of a multiple parton-shower, gluon interference
mechanism for generating the long-range pseudorapidity, azimuthal quadrupole
correlation is not excluded by the data.",1406.2736v2
2014-06-26,Nonlinear Optimal Filter Technique For Analyzing Energy Depositions In TES Sensors Driven Into Saturation,"We present a detailed thermal and electrical model of superconducting
transition edge sensors (TESs) connected to quasiparticle (qp) traps, such as
the W TESs connected to Al qp traps used for CDMS (Cryogenic Dark Matter
Search) Ge and Si detectors. We show that this improved model, together with a
straightforward time-domain optimal filter, can be used to analyze pulses well
into the nonlinear saturation region and reconstruct absorbed energies with
optimal energy resolution.",1406.7030v1
2014-07-01,Passive Mode-Locking and Tilted Waves in Broad-Area Vertical-Cavity Surface-Emitting Lasers,"We show experimentally and theoretically that an electrically biased
$200\,\mu$m multi-transverse mode Vertical-Cavity Surface-Emitting Laser can be
passively mode-locked using optical feedback from a distant Resonant Saturable
Absorber Mirror. This is achieved when one cavity is placed at the Fourier
plane of the other. Such non conventional optical feedback leads to the
formation of two tilted plane waves traveling in the external cavity with
opposite transverse components and alternating in time at every round-trip.
Each of these plane waves gives birth to a train of mode-locked pulses
separated by twice the external cavity round-trip, while the two trains are
time shifted by a round-trip. A large portion of the transverse section of the
device contributes to mode-locked emission leading to pulses of approximately 1
W peak power and 10 ps width. We discuss how inhomogeneities in the transverse
section of the saturable absorber select the emitted tilted waves, thus leading
to tunable emission over 4 nm.",1407.0296v1
2014-07-22,Proving Threshold Saturation for Nonbinary SC-LDPC Codes on the Binary Erasure Channel,"We analyze nonbinary spatially-coupled low-density parity-check (SC-LDPC)
codes built on the general linear group for transmission over the binary
erasure channel. We prove threshold saturation of the belief propagation
decoding to the potential threshold, by generalizing the proof technique based
on potential functions recently introduced by Yedla et al.. The existence of
the potential function is also discussed for a vector sparse system in the
general case, and some existence conditions are developed. We finally give
density evolution and simulation results for several nonbinary SC-LDPC code
ensembles.",1407.5783v1
2014-07-24,Saturated Graphs of Prescribed Minimum Degree,"A graph $G$ is $H$-saturated if it contains no copy of $H$ as a subgraph but
the addition of any new edge to $G$ creates a copy of $H$. In this paper we are
interested in the function sat$_{t}(n,p)$, defined to be the minimum number of
edges that a $K_{p}$-saturated graph on $n$ vertices can have if it has minimum
degree at least $t$. We prove that sat$_{t}(n,p) = tn - O(1)$, where the limit
is taken as $n$ tends to infinity. This confirms a conjecture of Bollob\'as
when $p = 3$. We also present constructions for graphs that give new upper
bounds for sat$_{t}(n,p)$ and discuss an analogous problem for saturated
hypergraphs.",1407.6664v2
2014-07-29,$^3$H/$^3$He ratio as a probe of the nuclear symmetry energy at sub-saturation densities,"Within the newly updated version of the Ultra-relativistic quantum molecular
dynamics (UrQMD) model in which the Skyrme potential energy-density functional
is introduced, the yield ratio between $^3$H and $^3$He clusters emitted from
central $^{40}$Ca+$^{40}$Ca, $^{96}$Zr+$^{96}$Zr, $^{96}$Ru+$^{96}$Ru, and
$^{197}$Au+$^{197}$Au collisions in the beam energy range from 0.12 to 1
GeV$/$nucleon is studied. The recent FOPI data for the $^3$H$/$$^3$He ratio are
compared with UrQMD calculations using 13 Skyrme interactions (all exhibiting
similar values of iso-scalar incompressibility but very different density
dependences of the symmetry energy). It is found that the $^3$H$/$$^3$He ratio
is sensitive to the nuclear symmetry energy at sub-saturation densities. Model
calculations with moderately soft to linear symmetry energies are in agreement
with the experimental FOPI data. This result is in line with both, the recent
constraints on the low-density symmetry energy available in the literature and
our previous results for the high-density symmetry energy obtained with the
elliptic flow of free nucleons and hydrogen isotopes as a sensitive probe.",1407.7625v1
2014-07-30,Constraining the density slope of nuclear symmetry energy at subsaturation densities using electric dipole polarizability in $^{208}$Pb,"Nuclear structure observables usually most effectively probe the properties
of nuclear matter at subsaturation densities rather than at saturation density.
We demonstrate that the electric dipole polarizibility $\alpha _ {\text{D}}$ in
$^{208}$Pb is sensitive to both the magnitude $E_{\text{sym}}(\rho_{\text{c}})$
and density slope $L(\rho_{\text{c}})$ of the symmetry energy at a
subsaturation cross density $\rho_{\text{c}} = 0.11$ fm$^{-3}$. Using the
experimental data of $\alpha _ {\text{D}}$ in $^{208}$Pb from RCNP and the
recent accurate constraint of $E_{\text{sym}}(\rho_{\text{c}})$ from the
binding energy difference of heavy isotope pairs, we extract a value of
$L(\rho_{\text{c}}) = 47.3 \pm 7.8$ MeV. The implication of the present
constraint of $L(\rho_{\text{c}})$ to the symmetry energy at saturation
density, the neutron skin thickness of $^{208}$Pb and the core-crust transition
density in neutron stars is discussed.",1407.8054v2
2014-07-31,Passive mode-locking under higher order effects,"The response of a passive mode-locking mechanism, where gain and spectral
filtering are saturated with the energy and loss saturated with the power, is
examined under the presence of higher order effects. These include third order
dispersion, self-steepening and Raman gain. The locking mechanism is maintained
even with these terms; mode-locking occurs for both the anomalous and normal
regimes. In the anomalous regime, these perturbations are found to affect the
speed but not the structure of the (locked) pulses. In fact, these pulses
behave like solitons of a classical nonlinear Schrodinger equation and as such
a soliton perturbation theory is used to verify the numerical observations. In
the normal regime, the effect of the perturbations is small, in line with
recent experimental observations. The results in the normal regime are verified
mathematically using a WKB type asymptotic theory. Finally, bi-solitons are
found to behave as dark solitons on top of a stable background and are
significantly affected by these perturbations.",1408.0041v1
2014-08-28,Channeling Effect in Polycrystalline Deuterium-Saturated CVD Diamond Target Bombarded by Deuterium Ion Beam,"At the ion accelerator HELIS at the LPI, the neutron yield is investigated in
DD reactions within a polycrystalline deuterium-saturated CVD diamond, during
an irradiation of its surface by a deuterium ion beam with the energy less than
30 keV. The measurements of the neutron flux in the beam direction are
performed in dependence on the target angle, \b{eta}, with respect to the beam
axis. These measurements are performed using a multichannel detector based on
He3 counters. A significant anisotropy in neutron yield is observed, it was
higher by a factor of 3 at \b{eta}=0 compared to that at \b{eta} = +-45{\deg}.
The possible reasons for the anisotropy, including ion channeling, are
discussed.",1408.7109v2
2014-09-11,Coherent inelastic backscattering of laser light from three isotropic atoms,"We study the impact of double and triple scattering contributions on coherent
backscattering of laser light from saturated isotropic atoms, in the helicity
preserving polarization channel. Using the recently proposed diagrammatic
pump-probe approach, we analytically derive single-atom spectral responses to a
classical polychromatic driving field, combine them self-consistently to double
and triple scattering processes, and numerically deduce the corresponding
elastic and inelastic spectra, as well as the total backscattered intensities.
We find that account of the triple scattering contribution leads to a faster
decay of phase-coherence with increasing saturation of the atomic transition as
compared to double scattering alone, and to a better agreement with the
experiment on strontium atoms.",1409.3597v2
2014-09-12,The Direct and Converse Inequalities for Jackson-Type Operators on Spherical Cap,"Approximation on the spherical cap is different from that on the sphere which
requires us to construct new operators. This paper discusses the approximation
on the spherical cap. That is, so called Jackson-type operator
$\{J_{k,s}^m\}_{k=1}^{\infty}$ is constructed to approximate the function
defined on the spherical cap $D(x_0,\gamma)$. We thus establish the direct and
inverse inequalities and obtain saturation theorems for
$\{J_{k,s}^m\}_{k=1}^{\infty}$ on the cap $D(x_0,\gamma)$. Using methods of
$K$-functional and multiplier, we obtain the inequality \begin{eqnarray*}
C_1\:\| J_{k,s}^m(f)-f\|_{D,p}\leq \omega^2\left(f,\:k^{-1}\right)_{D,p} \leq
C_2 \max_{v\geq k}\| J_{v,s}^m(f) - f\|_{D,p} \end{eqnarray*} and that the
saturation order of these operators is $O(k^{-2})$, where
$\omega^2\left(f,\:t\right)_{D,p}$ is the modulus of smoothness of degree 2,
the constants $C_1$ and $C_2$ are independent of $k$ and $f$.",1409.3807v1
2014-09-19,Quasi-Stable ideals and Borel-fixed ideals with a given Hilbert Polynomial,"The present paper investigates properties of quasi-stable ideals and of
Borel-fixed ideals in a polynomial ring $k[x_0,\dots,x_n]$, in order to design
two algorithms: the first one takes as input $n$ and an admissible Hilbert
polynomial $P(z)$, and outputs the complete list of saturated quasi-stable
ideals in the chosen polynomial ring with the given Hilbert polynomial. The
second algorithm has an extra input, the characteristic of the field $k$, and
outputs the complete list of saturated Borel-fixed ideals in $k[x_0,\dots,x_n]$
with Hilbert polynomial $P(z)$. The key tool for the proof of both algorithms
is the combinatorial structure of a quasi-stable ideal, in particular we use a
special set of generators for the considered ideals, the Pommaret basis.",1409.5569v2
2014-09-25,Nuclear Matter from Effective Quark-Quark Interaction,"We study neutron matter and symmetric nuclear matter with the quark-meson
model for the two-nucleon interaction. The Bethe-Bruckner-Goldstone many-body
theory is used to describe the correlations up to the three hole-line
approximation with no extra parameters. At variance with other non-relativistic
realistic interactions, the three hole-line contribution turns out to be
non-negligible and to have a substantial saturation effect. The saturation
point of nuclear matter, the compressibility, the symmetry energy and its slope
are within the phenomenological constraints. Since the interaction also
reproduces fairly well the properties of the three nucleon system, these
results indicate that the explicit introduction of the quark degrees of freedom
within the considered constituent quark model is expected to reduce the role of
three-body forces.",1409.7206v2
2014-09-30,Error-correction of linear codes via colon ideals,"We show that errors in data transmitted through linear codes can be thought
of as codewords of minimum weight of new linear codes. To determine errors we
can then use methods specific to finding such special codewords. One of these
methods consists of finding the primary decomposition of the saturation of a
certain homogeneous ideal. When good words (i.e. vectors with a unique nearest
neighbor) are error-corrected, the saturated ideal is just the prime ideal of a
point (so the primary decomposition is superfluously determined); we show that
this ideal can be computed by coloning the original homogeneous ideal with a
power of a certain variable. We then determine the smallest such power for any
linear code.",1409.8387v2
2014-10-07,Thermal properties of asymmetric nuclear matter with an improved isospin- and momentum-dependent interaction,"Thermal properties of asymmetric nuclear matter, including the temperature
dependence of the symmetry energy, single-particle properties, and differential
isospin fractionation, are investigated with different neutron-proton effective
mass splittings using an improved isospin- and momentum-dependent interaction.
In this improved interaction, the momentum-dependence of the isoscalar
single-particle potential at saturation density is well fitted to that
extracted from optical model analyses of proton-nucleus scattering data up to
nucleon kinetic energy of 1 GeV, and the isovector properties, i.e., the slope
of the nuclear symmetry energy, the momentum-dependence of the symmetry
potential, and the symmetry energy at saturation density can be flexibly
adjusted via three parameters $x$, $y$, and $z$, respectively. Our results
indicate that the nucleon phase-space distribution in equilibrium, the
temperature dependence of the symmetry energy, and the differential isospin
fractionation can be significantly affected by the isospin splitting of nucleon
effective mass.",1410.1604v2
2014-10-08,Inverse semigroup actions on groupoids,"We define inverse semigroup actions on topological groupoids by partial
equivalences. From such actions, we construct saturated Fell bundles over
inverse semigroups and non-Hausdorff \'etale groupoids. We interpret these as
actions on C*-algebras by Hilbert bimodules and describe the section algebras
of these Fell bundles.
  Our constructions give saturated Fell bundles over non-Hausdorff \'etale
groupoids that model actions on locally Hausdorff spaces. We show that these
Fell bundles are usually not Morita equivalent to an action by automorphisms.
That is, the Packer-Raeburn Stabilisation Trick does not generalise to
non-Hausdorff groupoids.",1410.2051v5
2014-10-08,"Resonance dynamics in the coherent $η$ meson production in the $(p,p^\prime)$ reaction on the spin-isospin saturated nucleus","For the forward going proton and $\eta$ meson, the coherent $\eta$ meson
production in the $(p,p^\prime)$ reaction on the spin-isospin saturated nucleus
occurs only due to the $\eta$ meson exchange interaction between the beam
proton and nucleus. In this process, the nucleon in the nucleus can be excited
to resonances $N^*$ and the $\eta$ meson in the final state can arise due to
$N^* \to N\eta$. We investigate the dynamics of resonances, including nucleon
Born terms, and their interferences in the coherently added cross section of
this reaction. We discuss the importance of $N(1520)$ resonance and show the
sensitivity of the cross section to the hadron nucleus interaction.",1410.2062v1
2014-10-20,Why mean $p_{\rm T}$ is interesting,"We discuss energy dependence of mean $p_{\rm T}$ correlation with $N_{\rm
ch}$ basing on general features of high energy collisions such as saturation
and geometrical scaling. We use Color Glass Condensate calculation of an
effective interaction radius that scales as a third root of multiplicity, and
then saturates. With this model input we construct scaling variable for $<
p_{\rm T} > (N_{\rm ch})$ at different energies both for pp and pPb collisions,
and show that recent ALICE data indeed does exhibit this scaling property. We
discuss energy dependence of the interaction radius and argue that since the
radius cannot grow too large, a universal behavior of $< p_{\rm T} >$ for large
multiplicities is expected.",1410.5220v2
2014-10-28,Dark counts initiated by macroscopic quantum tunneling in NbN superconducting photon detectors,"We perform measurements of the switching current distributions of three w =
120 nm wide, 4 nm thick NbN superconducting strips which are used for
single-photon detectors. These strips are much wider than the diameter the
vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We
discover evidence of macroscopic quantum tunneling by observing the saturation
of the standard deviation of the switching distributions at temperatures around
2 K. We analyze our results using the Kurkijarvi-Garg model and find that the
escape temperature also saturates at low temperatures, confirming that at
sufficiently low temperatures, macroscopic quantum tunneling is possible in
quasi-2D strips and can contribute to dark counts observed in single photon
detectors.",1410.7689v2
2014-11-03,Equation of state of nuclear matter from empirical constraints,"From empirically determined values of some of the characteristic constants
associated with homogeneous nuclear matter at saturation and sub-saturation
densities, within the framework of a Skyrme-inspired energy density functional,
we construct an equation of state (EoS) of nuclear matter.This EoS is then used
to predict values of density slope parameters of symmetry energy $L(\rho)$,
isoscalar incompressibility $K(\rho)$ and a few related quantities. The close
consonance of our predicted values with the currently available ones for the
density dependence of symmetry energy and incompressibility gleaned from
diverse approaches offers the possibility that our method may help in settling
their values in tighter bounds. Extrapolation of our EoS at supranormal
densities shows that it is in good harmony with the one extracted from
experimental data.",1411.0404v1
2014-11-11,Cooperative quasi-Cherenkov radiation,"We study the features of cooperative parametric (quasi-Cherenkov) radiation
arising when initially unmodulated electron (positron) bunches pass through a
crystal (natural or artificial) under the conditions of dynamical diffraction
of electromagnetic waves in the presence of shot noise. A detailed numerical
analysis is given for cooperative THz radiation in artificial crystals. The
radiation intensity above 200~MW$/$cm$^2$ is obtained in simulations.
  In two- and three-wave diffraction cases, the peak intensity of cooperative
radiation emitted at small and large angles to particle velocity is
investigated as a function of the particle number in an electron bunch. The
peak radiation intensity appeared to increase monotonically until saturation is
achieved. At saturation, the shot noise causes strong fluctuations in the
intensity of cooperative parametric radiation.
  It is shown that the duration of radiation pulses can be much longer than the
particle flight time through the crystal. This enables a thorough experimental
investigation of the time structure of cooperative parametric radiation
generated by electron bunches available with modern accelerators.
  The complicated time structure of cooperative parametric (quasi-Cherenkov)
radiation can be observed in artificial (electromagnetic, photonic) crystals in
all spectral ranges (X-ray, optical, terahertz, and microwave).",1411.2960v1
2014-11-19,Quantum enhanced precision in a collective measurement,"We explore the role of $\textit{collective measurements}$ on precision in
estimation of a single parameter. Collective measurements are represented by
observables which commute with all permutations of the probe particles. We show
that with this constraint, quantum bits(qubits) outperform classical
bits(non-superposable bits) in optimizing precision. Specifically, we prove
that while precision in a collective measurement is loosely bounded by
$O\left(\frac{1}{N}\right)$ for $N$ classical bits, using qubits it is tightly
bounded by $O\left(\frac{1}{N^2}\right)$. This bound is consistent with quantum
metrology protocols with the collective measurement requiring an entangled
probe state to saturate. Finally, we construct a canonical measurement protocol
that saturates this bound.",1411.5090v3
2014-11-26,"Higher dimensional Frobenius problem: Maximal saturated cone, growth function and rigidity","We consider $m$ integral vectors $X_1,...,X_m \in \mathbb{Z}^s$ located in a
half-space of $\mathbb{R}^s$ ($m\ge s\geq 1$) and study the structure of the
additive semi-group $X_1 \mathbb{N} +... + X_m \mathbb{N}$. We introduce and
study maximal saturated cone and directional growth function which describe
some aspects of the structure of the semi-group. When the vectors $X_1, ...,
X_m$ are located in a fixed hyperplane, we obtain an explicit formula for the
directional growth function and we show that this function completely
characterizes the defining data $(X_1, ..., X_m)$ of the semi-group. The last
result will be applied to the study of Lipschitz equivalence of Cantor sets
(see [H. Rao and Y. Zhang, Higher dimensional Frobenius problem and Lipschitz
equivalence of Cantor sets, Preprint 2014]).",1411.7118v1
2014-12-10,Wave-particle interactions with parallel whistler waves: nonlinear and time-dependent effects revealed by Particle-in-Cell simulations,"We present a self-consistent Particle-in-Cell simulation of the resonant
interactions between anisotropic energetic electrons and a population of
whistler waves, with parameters relevant to the Earths radiation belt. By
tracking PIC particles, and comparing with test-particle simulations we
emphasize the importance of including nonlinear effects and time evolution in
the modeling of wave-particle interactions, which are excluded in the resonant
limit of quasi- linear theory routinely used in radiation belt studies. In
particular we show that pitch angle diffusion is enhanced during the linear
growth phase, and it rapidly saturates well before a single bounce period. This
calls into question the widely used bounce average performed in most radiation
belt diffusion calculations. Furthermore we discuss how the saturation is
related to the fact that the domain in which the,particles pitch angle diffuse
is bounded, and to the well-known problem of $90^\circ$ diffusion barrier
diffusion barrier.",1412.3229v2
2014-12-16,Asymmetric Wave Propagation Through Saturable Nonlinear Oligomers,"In the present paper we consider nonlinear dimers and trimers (more
generally, oligomers) embedded within a linear Schr{\""o}dinger lattice where
the nonlinear sites are of saturable type. We examine the stationary states of
such chains in the form of plane waves, and analytically compute their
reflection and transmission coefficients through the nonlinear oligomer, as
well as the corresponding rectification factors which clearly illustrate the
asymmetry between left and right propagation in such systems. We examine not
only the existence but also the dynamical stability of the plane wave states.
Lastly, we generalize our numerical considerations to the more physically
relevant case of Gaussian initial wavepackets and confirm that the asymmetry in
the transmission properties also persists in the case of such wavepackets.",1412.4856v1
2014-12-19,Iterated fractional Tikhonov regularization,"Fractional Tikhonov regularization methods have been recently proposed to
reduce the oversmoothing property of the Tikhonov regularization in standard
form, in order to preserve the details of the approximated solution. Their
regularization and convergence properties have been previously investigated
showing that they are of optimal order. This paper provides saturation and
converse results on their convergence rates. Using the same iterative
refinement strategy of iterated Tikhonov regularization, new iterated
fractional Tikhonov regularization methods are introduced. We show that these
iterated methods are of optimal order and overcome the previous saturation
results. Furthermore, nonstationary iterated fractional Tikhonov regularization
methods are investigated, establishing their convergence rate under general
conditions on the iteration parameters. Numerical results confirm the
effectiveness of the proposed regularization iterations.",1412.6540v1
2015-02-02,Growing Probability of Additional Offspring with a Beneficial Reversal Allele in the Decoupled Continuous-time Mutation-selection Model,"The growing probabilities of additional offspring with the beneficial
reversal allele for various population sizes, $N$, sequence lengths, $L$,
selective advantages, $s$, fitness parameters, $k$, and measuring parameters,
$C$, were calculated in an asymmetric sharply-peaked landscape using the
decoupled continuous-time mutation-selection model. The growing probability in
the stochastic region was inversely proportional to the measuring parameter
when $C<1/Ns^*$, bent when $C\approx 1/Ns^*$ and became saturated when
$C>1/Ns^*$, where $s^*$ is the effective selective advantage. The saturated
growing probability in the stochastic region was approximately the effective
selective advantage when $C\gg 1/Ns^*$ and $s^*\ll 1$. The present study
suggests that the growing probability in the stochastic region in an asymmetric
sharply-peaked landscape in the decoupled continuous-time mutation-selection
model can be described using the theoretical formula for the growing
probability in the Moran two-allele model. The selective advantage ratio, which
represents the ratio of the effective selective advantage to the selective
advantage, does not depend on the population size, selective advantage,
measuring parameter, and fitness parameter; instead the selective advantage
ratio decreases with increasing the sequence length.",1502.00415v1
2015-02-08,LineSwitch: Efficiently Managing Switch Flow in Software-Defined Networking while Effectively Tackling DoS Attacks,"Software Defined Networking (SDN) is a new networking architecture which aims
to provide better decoupling between network control (control plane) and data
forwarding functionalities (data plane). This separation introduces several
benefits, such as a directly programmable and (virtually) centralized network
control. However, researchers showed that the required communication channel
between the control and data plane of SDN creates a potential bottleneck in the
system, introducing new vulnerabilities. Indeed, this behavior could be
exploited to mount powerful attacks, such as the control plane saturation
attack, that can severely hinder the performance of the whole network.
  In this paper we present LineSwitch, an efficient and effective solution
against control plane saturation attack. LineSwitch combines SYN proxy
techniques and probabilistic blacklisting of network traffic. We implemented
LineSwitch as an extension of OpenFlow, the current reference implementation of
SDN, and evaluate our solution considering different traffic scenarios (with
and without attack). The results of our preliminary experiments confirm that,
compared to the state-of-the-art, LineSwitch reduces the time overhead up to
30%, while ensuring the same level of protection.",1502.02234v1
2015-02-11,Hydrogenation at low temperatures does not always lead to saturation: the case of HNCO,"Context. It is generally agreed that hydrogenation reactions dominate
chemistry on grain surfaces in cold, dense molecular cores, saturating the
molecules present in ice mantles. Aims. We present a study of the low
temperature reactivity of solid phase isocyanic acid (HNCO) with hydrogen
atoms, with the aim of elucidating its reaction network. Methods. Fourier
transform infrared spectroscopy and mass spectrometry were employed to follow
the evolution of pure HNCO ice during bombardment with H atoms. Both multilayer
and monolayer regimes were investigated. Results. The hydrogenation of HNCO
does not produce detectable amounts of formamide (NH2CHO) as the major product.
Experiments using deuterium reveal that deuteration of solid HNCO occurs
rapidly, probably via cyclic reaction paths regenerating HNCO. Chemical
desorption during these reaction cycles leads to loss of HNCO from the surface.
Conclusions. It is unlikely that significant quantities of NH2CHO form from
HNCO. In dense regions, however, deuteration of HNCO will occur. HNCO and DNCO
will be introduced into the gas phase, even at low temperatures, as a result of
chemical desorption.",1502.03282v1
2015-02-16,Coherence properties of the radiation from FLASH,"FLASH is the first free electron laser user facility operating in the vacuum
ultraviolet and soft x-ray wavelength range. Many user experiments require
knowledge of the spatial and temporal coherence properties of the radiation. In
this paper we present an analysis of the coherence properties of the radiation
for the fundamental and for the higher odd frequency harmonics. We show that
temporal and spatial coherence reach maximum close to the FEL saturation but
may degrade significantly in the post-saturation regime. We also find that the
pointing stability of short FEL pulses is limited due to the fact that
non-azimuthal FEL eigenmodes are not sufficiently suppressed. We discuss
possible ways for improving the degree of transverse coherence and the pointing
stability.",1502.04486v1
2015-03-02,A Novel Image Steganographic Approach for Hiding Text in Color Images using HSI Color Model,"Image Steganography is the process of embedding text in images such that its
existence cannot be detected by Human Visual System (HVS) and is known only to
sender and receiver. This paper presents a novel approach for image
steganography using Hue-Saturation-Intensity (HSI) color space based on Least
Significant Bit (LSB). The proposed method transforms the image from RGB color
space to Hue-Saturation-Intensity (HSI) color space and then embeds secret data
inside the Intensity Plane (I-Plane) and transforms it back to RGB color model
after embedding. The said technique is evaluated by both subjective and
Objective Analysis. Experimentally it is found that the proposed method have
larger Peak Signal-to Noise Ratio (PSNR) values, good imperceptibility and
multiple security levels which shows its superiority as compared to several
existing methods",1503.00388v1
2015-03-02,Absorption Coefficients of the Methane-Nitrogen Binary Ice System: Implications for Pluto,"The methane-nitrogen phase diagram of Prokhvatilov and Yantsevich (1983)
indicates that at temperatures relevant to the surfaces of icy dwarf planets
like Pluto, two phases contribute to the methane absorptions: nitrogen
saturated with methane $\bf{\bar{N_{2}}}$:CH$_{4}$ and methane saturated with
nitrogen $\bf{\bar{CH_{4}}}$:N$_{2}$. No optical constants are available so far
for the latter component limiting construction of a proper model, in compliance
with thermodynamic equilibrium considerations. New optical constants for solid
solutions of methane diluted in nitrogen (N$_{2}$:CH$_{4}$) and nitrogen
diluted in methane (CH$_{4}$:N$_{2}$) are presented at temperatures between 40
and 90 K, in the wavelength range 1.1-2.7 $\mu$m at different mixing ratios.
These optical constants are derived from transmission measurements of crystals
grown from the liquid phase in closed cells. A systematic study of the changes
of methane and nitrogen solid mixtures spectral behavior with mixing ratio and
temperature is presented.",1503.00703v1
2015-03-05,Do We Need More Training Data?,"Datasets for training object recognition systems are steadily increasing in
size. This paper investigates the question of whether existing detectors will
continue to improve as data grows, or saturate in performance due to limited
model complexity and the Bayes risk associated with the feature spaces in which
they operate. We focus on the popular paradigm of discriminatively trained
templates defined on oriented gradient features. We investigate the performance
of mixtures of templates as the number of mixture components and the amount of
training data grows. Surprisingly, even with proper treatment of regularization
and ""outliers"", the performance of classic mixture models appears to saturate
quickly ($\sim$10 templates and $\sim$100 positive training examples per
template). This is not a limitation of the feature space as compositional
mixtures that share template parameters via parts and that can synthesize new
templates not encountered during training yield significantly better
performance. Based on our analysis, we conjecture that the greatest gains in
detection performance will continue to derive from improved representations and
learning algorithms that can make efficient use of large datasets.",1503.01508v1
2015-03-08,Direct Observationof DegenerateTwo-Photon Absorption and Its Saturation in WS2 and MoS2 Monolayer and Few-Layer Films,"The optical nonlinearity of WS2, MoS2 monolayer and few-layer films was
investigated using the Z-scan technique with femtosecond pulses from the
visible to the near infrared. The dependence of nonlinear absorption of the WS2
and MoS2 films on layer number and excitation wavelength was studied
systematically. WS2 with 1~3 layers exhibits a giant two-photon absorption
(TPA) coefficient. Saturation of TPA for WS2 with 1~3 layers and MoS2 with
25~27 layers was observed. The giant nonlinearity of WS2 and MoS2 is attributed
to two dimensional confinement, a giant exciton effect and the band edge
resonance of TPA.",1503.02258v2
2015-03-31,Minimal energy solutions and infinitely many bifurcating branches for a class of saturated nonlinear Schrödinger systems,"We prove a conjecture which was recently formulated by Maia, Montefusco,
Pellacci saying that minimal energy solutions of the saturated nonlinear
Schr\""odinger system \begin{align*}
  - \Delta u + \lambda_1 u &= \frac{\alpha u(\alpha u^2+\beta v^2)}{1+s(\alpha
u^2+\beta v^2)}
  \qquad\text{in }\mathbb{R}^n, \newline
  - \Delta v + \lambda_2 v &= \frac{\beta v(\alpha u^2+\beta v^2)}{1+s(\alpha
u^2+\beta v^2)}\qquad\text{in
  }\mathbb{R}^n \end{align*} are necessarily semitrivial whenever
$\alpha,\beta,\lambda_1,\lambda_2>0$ and
$0<s<\max\{\frac{\alpha}{\lambda_1},\frac{\beta}{\lambda_2}\}$ except for the
symmetric case $\lambda_1=\lambda_2,\alpha=\beta$. Moreover it is shown that
for most parameter samples $\alpha,\beta,\lambda_1,\lambda_2$ there are
infinitely many branches containing seminodal solutions which bifurcate from a
semitrivial solution curve parametrized by $s$.",1503.08974v1
2015-04-06,More on Heisenberg's model for high energy nucleon-nucleon scattering,"We revisit Heisenberg's model for nucleon-nucleon scattering which admits a
saturation of the Froissart bound. We examine its uniqueness, and find that up
to certain natural generalizations, it is the only action that saturates the
bound. We find that we can extract also sub-leading behaviour for $\sigma_{\rm
tot}(s)$ from it, though that requires a knowledge of the wavefunction solution
that is hard to obtain, and a black-disk model allows the calculation of
$\sigma_{elastic}(s)$ as well.
  The wavefunction solution is analyzed perturbatively, and its source is
interpreted. Generalizations to several mesons, addition of vector mesons, and
curved space regimes are also found. We discuss the relations between
Heisenberg's model and holographic models that are dual to QCD-like theories.",1504.01328v1
2015-04-18,Black phosphorus a new saturable absorber material for ultrashort pulse generation,"Low-dimensional materials, due to their versatile properties are very
interesting for numerous electronics and optoelectronics applications. Recently
rediscovered black phosphorus, with a graphite-like structure can be exfoliated
up to the single atomic layer. In contrary to graphene it possesses a direct
band gap controllable by the number of stacked atomic layers. For those
reasons, it is now intensively investigated. Here we demonstrate, that black
phosphorus can serve as a broadband saturable absorber and can be used for
ultrashort optical pulse generation. The mechanically exfoliated ~300 nm thick
layers of black phosphorus were transferred onto the fiber core and under
pulsed excitation at 1560 nm wavelength its transmission increases by 4.4%. It
was used to generate 272 fs-short pulses at 1550 nm and 739 fs at 1910 nm. The
obtained results shows that black phosphorus can be effectively used for
ultrashort pulse generation and proves its great potential to future
applications.",1504.04731v1
2015-04-23,Modeling of dual-metal Schottky contacts based silicon micro and nano wire solar cells,"We study solar cell properties of single silicon wires connected at their
ends to two dissimilar metals of different work functions. Effects of wire
dimensions, the work functions of the metals, and minority carrier lifetimes on
short circuit current as well as open circuit voltage are studied. The most
efficient photovoltaic behavior is found to occur when one metal makes a
Schottky contact with the wire, and the other makes an Ohmic contact. As wire
length increases, both short circuit current and open circuit voltage increase
before saturation occurs. Depending on the work function difference between the
metals and the wire dimensions, the saturation length increases by
approximately an order of magnitude with a two order magnitude increase in
minority carrier length. However current per surface area exposed to light is
found to decrease rapidly with increase in length. The use of a multi-contact
interdigitated design for long wires is investigated to increase the
photovoltaic response of the devices.",1504.06279v1
2015-04-27,Full-duplex MAC Protocol Design and Analysis,"The idea of in-band full-duplex (FD) communications revives in recent years
owing to the significant progress in the self-interference cancellation and
hardware design techniques, offering the potential to double spectral
efficiency. The adaptations in upper layers are highly demanded in the design
of FD communication systems. In this letter, we propose a novel medium access
control (MAC) using FD techniques that allows transmitters to monitor the
channel usage while transmitting, and backoff as soon as collision happens.
Analytical saturation throughput of the FD-MAC protocol is derived with the
consideration of imperfect sensing brought by residual self- interference (RSI)
in the PHY layer. Both analytical and simulation results indicate that the
normalized saturation throughput of the proposed FD-MAC can significantly
outperforms conventional CSMA/CA under various network conditions.",1504.06957v1
2015-05-09,Stability analysis of the Biot/squirt models for wave propagation in saturated porous media,"This work is concerned with the Biot/squirt (BISQ) models for wave
propagation in saturated porous media. We show that the models allow
exponentially exploding solutions, as time goes to infinity, when the
characteristic squirt-flow coefficient is negative or has a non-zero imaginary
part. We also show that the squirt-flow coefficient does have non-zero
imaginary parts for some experimental parameters. Because the models are
linear, the existence of such exploding solutions indicates instability of the
BISQ models. This result calls on a reconsideration of the widely used BISQ
theory. Furthermore, we demonstrate that the 3D isotropic BISQ model is stable
when the squirt-flow coefficient is positive. In particular, the original Biot
model is unconditionally stable where the squirt-flow coefficient is 1.",1505.02283v1
2015-05-12,Single-cell measurement of red blood cell oxygen affinity,"Oxygen is transported throughout the body by hemoglobin in red blood cells.
While the oxygen affinity of blood is well understood and is routinely assessed
in patients by pulse oximetry, variability at the single-cell level has not
been previously measured. In contrast, single-cell measurements of red blood
cell volume and hemoglobin concentration are taken millions of times per day by
clinical hematology analyzers and are important factors in determining the
health of the hematologic system. To better understand the variability and
determinants of oxygen affinity on a cellular level, we have developed a system
that quantifies the oxygen saturation, cell volume and hemoglobin concentration
for individual red blood cells in high-throughput. We find that the variability
in single-cell saturation peaks at an oxygen partial pressure of 2.5%, which
corresponds to the maximum slope of the oxygen-hemoglobin dissociation curve.
In addition, single-cell oxygen affinity is positively correlated with
hemoglobin concentration, but independent of osmolarity, which suggests
variation in the hemoglobin to 2-3 DPG ratio on a cellular level. By
quantifying the functional behavior of a cellular population, our system adds a
new dimension to blood cell analysis and other measurements of single-cell
variability.",1505.04119v1
2015-05-21,The lattice gluon propagator in renormalizable $ξ$ gauges,"We study the SU(3) gluon propagator in renormalizable $R_\xi$ gauges
implemented on a symmetric lattice with a total volume of (3.25 fm)$^4$ for
values of the guage fixing parameter up to $\xi=0.5$. As expected, the
longitudinal gluon dressing function stays constant at its tree-level value
$\xi$. Similar to the Landau gauge, the transverse $R_\xi$ gauge gluon
propagator saturates at a non-vanishing value in the deep infrared for all
values of $\xi$ studied. We compare with very recent continuum studies and
perform a simple analysis of the found saturation with a dynamically generated
effective gluon mass.",1505.05897v1
2015-05-23,Mid-infrared ultra-short mode-locked fiber laser utilizing topological insulator Bi2Te3 nano-sheets as the saturable absorber,"The newly-emergent two-dimensional topological insulators (TIs) have shown
their unique electronic and optical properties, such as good thermal
management, high nonlinear refraction index and ultrafast relaxation time.
Their narrow energy band gaps predict their optical absorption ability further
into the mid-infrared region and their possibility to be very broadband light
modulators ranging from the visible to the mid-infrared region. In this paper,
a mid-infrared mode-locked fluoride fiber laser with TI Bi2Te3 nano-sheets as
the saturable absorber is presented. Continuous wave lasing, Q-switched and
continuous-wave mode-locking (CW-ML) operations of the laser are observed
sequentially by increasing the pump power. The observed CW-ML pulse train has a
pulse repetition rate of 10.4 MHz, a pulse width of ~6 ps, and a center
wavelength of 2830 nm. The maximum achievable pulse energy is 8.6 nJ with
average power up to 90 mW. This work forcefully demonstrates the promising
applications of two-dimensional TIs for ultra-short laser operation and
nonlinear optics in the mid-infrared region.",1505.06322v1
2015-05-30,Layered posets and Kunen's universal collapse,"We develop the theory of layered posets, and use the notion of layering to
prove a new iteration theorem (Theorem 6): if $\kappa$ is weakly compact then
any universal Kunen iteration of $\kappa$-cc posets (each possibly of size
$\kappa$) is $\kappa$-cc, as long as direct limits are used sufficiently often.
This iteration theorem simplifies and generalizes the various chain condition
arguments for universal Kunen iterations in the literature on saturated ideals,
especially in situations where finite support iterations are not possible. We
also provide two applications: (1) For any $n \ge 1$, a wide variety of
$<\omega_{n-1}$-closed, $\omega_{n+1}$-cc posets of size $\omega_{n+1}$ can
consistently be absorbed (as regular suborders) by quotients of saturated
ideals on $\omega_n$ (see Theorem 7 and Corollary 8); and (2) For any $n \in
\omega$, the Tree Property at $\omega_{n+3}$ is consistent with the Chang's
Conjecture $(\omega_{n+3}, \omega_{n+1}) \twoheadrightarrow (\omega_{n+1},
\omega_n)$ (Theorem 9).",1506.00158v5
2015-06-08,Partite Saturation Problems,"We look at several saturation problems in complete balanced blow-ups of
graphs. We let $H[n]$ denote the blow-up of $H$ onto parts of size $n$ and
refer to a copy of $H$ in $H[n]$ as 'partite' if it has one vertex in each part
of $H[n]$. We then ask how few edges a subgraph $G$ of $H[n]$ can have such
that $G$ has no partite copy of $H$ but such that the addition of any new edge
from $H[n]$ creates a partite $H$. When $H$ is a triangle this value was
determined by Ferrara, Jacobson, Pfender, and Wenger. Our main result is to
calculate this value for $H=K_4$ when $n$ is large. We also give exact results
for paths and stars and show that for $2$-connected graphs the answer is linear
in $n$ whilst for graphs which are not $2$-connected the answer is quadratic in
$n$. We also investigate a similar problem where $G$ is permitted to contain
partite copies of $H$ but we require that the addition of any new edge from
$H[n]$ creates an extra partite copy of $H$. This problem turns out to be much
simpler and we attain exact answers for all cliques and trees.",1506.02445v1
2015-06-15,The Nuclear Symmetry Energy in Heavy Ion Collisions,"In this contribution I discuss the nuclear symmetry energy in the regime of
hadronic degrees of freedom. The density dependence of the symmetry energy is
important from very low densities in supernova explosions, to the structure of
neutron-rich nuclei around saturation density, and to several times saturation
density in neutron stars. Heavy ion collisions are the only means to study this
density dependence in the laboratory. Numerical simulations of transport
theories are used to extract the equation-of-state, and thus also the symmetry
energy. I discuss some examples, which relate particularly to the high density
symmetry energy, which is of particular interest today. I review the status and
point out some open problems in the determination of the symmetry energy in
heavy ion collisions.",1506.04687v1
2015-06-18,Homaloidal nets and ideals of fat points I,"One considers plane Cremona maps with proper base points and the {\em base
ideal} generated by the linear system of forms defining the map. The object of
this work is the interweave between the algebraic properties of the base ideal
and those of the ideal of these points fattened by the virtual multiplicities
arising from the linear system. One reveals conditions which naturally regulate
this association, with particular emphasis on the homological side. While most
classical numerical inequalities concern the three highest virtual
multiplicities, here one emphasizes also the role of one single highest
multiplicity. In this vein one describes classes of Cremona maps for large and
small value of the highest virtual multiplicity. One also deals with the
delicate property as to when the base ideal is non-saturated and the structure
of its saturation.",1506.05836v3
2015-06-22,Neutron star structure in an in-medium modified chiral soliton model,"We study the internal structure of a static and spherically symmetric neutron
star in the framework of an in-medium modified chiral soliton model. The
Equations of State describing an infinite and asymmetric nuclear matter are
obtained introducing the density dependent functions into the low energy free
space Lagrangian of the model starting from the phenomenology of pionic atoms.
The parametrizations of density dependent functions are related to the
properties of isospin asymmetric nuclear systems at saturation density of
symmetric nuclear matter $\rho_0\simeq 0.16$~fm$^{-3}$. Our results,
corresponding to the compressibility of symmetric nuclear matter in the range
$250\,\mbox{MeV}\le K_0\le 270\,\mbox{MeV}$ and the slop parameter value of
symmetry energy in the range $30\,\mbox{MeV}\le L_S\le 50\,\mbox{MeV}$, are
consistent with the results from other approaches and with the experimental
indications. Using the modified Equations of State, near the saturation density
of symmetric nuclear matter $\rho_0$, the extrapolations to the high density
and highly isospin asymmetric regions have been performed. The calculations
showed that the properties of $\sim 1.4M_\odot$ and $\sim 2M_\odot$ neutron
stars can be well reproduced in the framework of present approach.",1506.06481v1
2015-06-25,Experimental study of ultracold neutron production in pressurized superfluid helium,"We have investigated experimentally the pressure dependence of the production
of ultracold neutrons (UCN) in superfluid helium in the range from saturated
vapor pressure to 20bar. A neutron velocity selector allowed the separation of
underlying single-phonon and multiphonon pro- cesses by varying the incident
cold neutron (CN) wavelength in the range from 3.5 to 10{\AA}. The predicted
pressure dependence of UCN production derived from inelastic neutron scattering
data was confirmed for the single-phonon excitation. For multiphonon based UCN
production we found no significant dependence on pressure whereas calculations
from inelastic neutron scattering data predict an increase of 43(6)% at 20bar
relative to saturated vapor pressure. From our data we conclude that applying
pressure to superfluid helium does not increase the overall UCN production rate
at a typical CN guide.",1506.07785v2
2015-06-26,Shapes for maximal coverage for two-dimensional random sequential adsorption,"The random sequential adsorption of various particle shapes is studied in
order to determine the influence of particle anisotropy on the saturated random
packing. For all tested particles there is an optimal level of anisotropy which
maximizes the saturated packing fraction. It is found that a concave shape
derived from a dimer of disks gives a packing fraction of 0.5833, which is
comparable to the maximum packing fraction of ellipsoids and spherocylinders
and higher than any other studied shape. Discussion why this shape is so
beneficial for random sequential adsorption is given.",1506.08164v2
2015-06-26,Laser stabilization using saturated absorption in a cavity QED system,"We consider the phase stability of a local oscillator (or laser) locked to a
cavity QED system comprised of atoms with an ultra-narrow optical transition.
The atoms are cooled to millikelvin temperatures and then released into the
optical cavity. Although the atomic motion introduces Doppler broadening, the
standing wave nature of the cavity causes saturated absorption features to
appear, which are much narrower than the Doppler width. These features can be
used to achieve an extremely high degree of phase stabilization, competitive
with the current state-of-the-art. Furthermore, the inhomogeneity introduced by
finite atomic velocities can cause optical bistability to disappear, resulting
in no regions of dynamic instability and thus enabling a new regime accessible
to experiments where optimum stabilization may be achieved.",1506.08210v1
2015-07-21,Analysis of an offloading scheme for data centers in the framework of fog computing,"In the context of fog computing, we consider a simple case when data centers
are installed at the edge of the network and assume that if a request arrives
at an overloaded data center, then it is forwarded to a neighboring data center
with some probability. Data centers are assumed to have a large number of
servers and that traffic at some of them is causing saturation. In this case
the other data centers may help to cope with this saturation regime by
accepting some of the rejected requests. Our aim is to qualitatively estimate
the gain achieved via cooperation between neighboring data centers. After
proving some convergence results, related to the scaling limits of loss
systems, for the process describing the number of free servers at both data
centers, we show that the performance of the system can be expressed in terms
of the invariant distribution of a random walk in the quarter plane. By using
and developing existing results in the technical literature, explicit formulas
for the blocking rates of such a system are derived.",1507.05746v2
2015-07-21,Fluctuations and the rapidity dependence of charged particles spectra in fixed centrality bins in p$A$ collisions,"We argue that large fluctuations in the saturation momentum are necessary to
explain the ATLAS and ALICE data on pA collisions measured at the LHC. Using a
form for the distribution of fluctuations motivated by theoretical studies of
the non-linear evolution equations for the Color Glass Condensate, we find a
remarkably good agreement between theory and the measured distributions. If the
saturation momentum fluctuates, we argue that the cross section for a proton
probe should also fluctuate, consistent with previous observations. Finally we
discuss these results and their possible consistency with what is known about
multiplicity fluctuations in such collisions, and attempts to describe the
ridge effect from properties of the initial state.",1507.05976v2
2015-07-27,Nuclear matter equation of state from a quark-model nucleon-nucleon interaction,"Starting from a realistic constituent quark model for the nucleon-nucleon
interaction, we derive the equation of state (EOS) of nuclear matter within the
Bethe-Brueckner-Goldstone approach up to three-hole-line level, without need to
introduce three-nucleon forces. To estimate the uncertainty of the calculations
both the gap and the continuous choices for the single-particle potential are
considered and compared. The resultant EOS is compatible with the
phenomenological analysis on the saturation point, the incompressibility, the
symmetry energy at low density and its slope at saturation, together with the
high-density pressure extracted from flow data on heavy ion collisions.
Although the symmetry energy is appreciably larger in the gap choice in the
high-density region, the maximum neutron star masses derived from the
continuous-choice EOS and the gap-choice EOS are similar and close to two solar
masses, which is again compatible with recent observational data. Comparison
with other microscopic EOS is presented and discussed.",1507.07288v2
2015-08-17,Universal scaling of the logarithmic negativity in massive quantum field theory,"We consider the logarithmic negativity, a measure of bipartite entanglement,
in a general unitary 1+1-dimensional massive quantum field theory, not
necessarily integrable. We compute the negativity between a finite region of
length $r$ and an adjacent semi-infinite region, and that between two
semi-infinite regions separated by a distance $r$. We show that the former
saturates to a finite value, and that the latter tends to zero, as
$r\rightarrow\infty$. We show that in both cases, the leading corrections are
exponential decays in $r$ (described by modified Bessel functions) that are
solely controlled by the mass spectrum of the model, independently of its
scattering matrix. This implies that, like the entanglement entropy, the
logarithmic negativity displays a very high level of universality, allowing one
to extract information about the mass spectrum. Further, a study of sub-leading
terms shows that, unlike the entanglement entropy, a large-$r$ analysis of the
negativity allows for the detection of bound states.",1508.04026v2
2015-08-18,CGC/saturation approach for soft interactions at high energy: long range rapidity correlations,"In this paper we continue our program to build a model for high energy soft
interactions, that is based on the CGC/saturation approach.The main result of
this paper is that we have discovered a mechanism that leads to large long
range rapidity correlations, and results in large values of the correlation
function $R\Lb y_1,y_2\Rb \,\geq \,1$, which is independent of $y_1$ and $
y_2$. Such behaviour of the correlation function, provides strong support for
the idea, that at high energies the system of partons that is produced, is not
only dense, but also has strong attractive forces acting between the partons.",1508.04236v1
2015-08-20,Exploring sd-shell nuclei from two- and three-nucleon interactions with realistic saturation properties,"We study ground- and excited-state properties of all sd-shell nuclei with
neutron and proton numbers 8 <= N,Z <= 20, based on a set of low-resolution
two- and three-nucleon interactions that predict realistic saturation
properties of nuclear matter. We focus on estimating the theoretical
uncertainties due to variation of the resolution scale, the low-energy
couplings, as well as from the many-body method. The experimental two-neutron
and two-proton separation energies are reasonably well reproduced, with an
uncertainty range of about 5 MeV. The first excited 2+ energies also show
overall agreement, with a more narrow uncertainty range of about 500 keV. In
most cases, this range is dominated by the uncertainties in the Hamiltonian.",1508.05040v1
2015-08-27,Density-Dependent Electron Transport and Precise Modeling of GaN HEMTs,"We report on the direct measurement of two-dimensional sheet charge density
dependence of electron transport in AlGaN/GaN high electron mobility
transistors. Pulsed IV measurements established increasing electron velocities
with decreasing sheet charge densities, resulting in saturation velocity of 1.9
x 10^7 cm/s at a low sheet charge density of 7.8 x 10^11 cm-2. A new optical
phonon emission-based electron velocity model for GaN is also presented. It
accommodates stimulated LO phonon emission which clamps the electron velocity
with strong electron-phonon interaction and long LO phonon lifetime in GaN. A
comparison with the measured density-dependent saturation velocity shows that
it captures the dependence rather well. Finally, the experimental result is
applied in TCAD-based device simulator to predict DC and small signal
characteristics of a reported GaN HEMT. Good agreement between the simulated
and reported experimental results validated the measurement presented in this
report and established accurate modeling of GaN HEMTs.",1508.07050v1
2015-09-10,Tunneling diodes under environmental effects,"We examine the robustness of single-molecule tunneling diodes to
thermal-environmental effects. The diode comprises three fragments: two
different conjugated chemical groups at the boundaries, and a saturated moiety
in between, breaking conjugation. In this setup, molecular electronic levels
localized on the conjugated groups independently shift with applied bias. While
in the forward polarity a resonance condition is met, enhancing conductance, in
the reversed direction molecular electronic states shift away from each other,
resulting in small tunneling currents. In the absence of interactions with a
thermal environment (consisting e.g. internal vibrations, solvent),
rectification ratios reach three orders of magnitude. We introduce decoherence
and inelastic-dissipative effects phenomenologically, by using the ""voltage
probe"" approach. We find that when $\gamma_d \lesssim v$, with $\gamma_d$ the
interaction energy of electrons with the environment and $v$ the tunneling
energy across the saturated link, the diode is still highly effective, though
rectification ratios are cut down by a factor of 2-4 compared to the coherent
limit. To further enhance rectification ratios in molecular diodes we suggest a
refined design involving four orbitals, with a pair of closely spaced states at
each conjugated moiety.",1509.03006v1
2015-09-13,High-Mobility Holes in Dual-Gated WSe$_2$ Field-Effect Transistors,"We demonstrate dual-gated $p$-type field-effect transistors (FETs) based on
few-layer tungsten diselenide (WSe$_2$) using high work-function platinum
source/drain contacts, and a hexagonal boron nitride top-gate dielectric. A
device topology with contacts underneath the WSe$_2$ results in $p$-FETs with
$I_{ON}$/$I_{OFF}$ ratios exceeding 10$^7$, and contacts that remain Ohmic down
to cryogenic temperatures. The output characteristics show current saturation
and gate tunable negative differential resistance. The devices show intrinsic
hole mobilities around 140 cm$^2$/Vs at room temperature, and approaching 4,000
cm$^2$/Vs at 2 K. Temperature-dependent transport measurements show a
metal-insulator transition, with an insulating phase at low densities, and a
metallic phase at high densities. The mobility shows a strong temperature
dependence consistent with phonon scattering, and saturates at low
temperatures, possibly limited by Coulomb scattering, or defects.",1509.03896v1
2015-09-22,Black phosphorus mode-locked Er-doped ZBLAN fiber laser at 2.8 um wavelength,"Mid-infrared saturable absorber mirror is successfully fabricated by
transferring the mechanically exfoliated black phosphorus onto the gold-coated
mirror. With the as-prepared black phosphorus saturable absorber mirror, a
continuous-wave passively mode-locked Er:ZBLAN fiber laser is demonstrated at
the wavelength of 2.8 um, which delivers a maximum average output power of 613
mW, a repetition rate of 24 MHz and a pulse duration of 42 ps. To the best of
our knowledge, it is the first time to demonstrate black phosphorus mode-locked
laser at 2.8 um wavelength. Our results demonstrate the feasibility of black
phosphorus flake as a new two-dimensional material for application in
mid-infrared ultrafast photonics.",1509.06479v1
2015-09-22,Gauge fixing and the gluon propagator in renormalizable xi gauges,"Covariant $R_\xi$ gauge fixing is notoriously difficult for large lattice
volumes, large $\xi$ and small $N_c$. We thoroughly test different convergence
techniques, which allows the gauge fixing of lattice configurations with a
total volume of (3.25 fm)$^4$, up to $\xi=0.5$. We are able to study the gluon
propagator in the infrared region and its dependence on the gauge fixing
parameter $\xi$. As expected, the longitudinal gluon dressing functions stay
constant at their tree-level value $\xi$. Similar to the Landau gauge, the
transverse $R_\xi$ gauge gluon propagators saturate at a non-vanishing value in
the deep infrared for all values of $\xi$ studied. We compare with very recent
continuum studies and perform a simple analysis of the found saturation with a
dynamically generated effective gluon mass.",1509.06737v1
2015-09-23,Building prime models in fully good abstract elementary classes,"We show how to build primes models in classes of saturated models of abstract
elementary classes (AECs) having a well-behaved independence relation:
  $\mathbf{Theorem.}$
  Let $K$ be an almost fully good AEC that is categorical in $\text{LS} (K)$
and has the $\text{LS} (K)$-existence property for domination triples. For any
$\lambda > \text{LS} (K)$, the class of Galois saturated models of $K$ of size
$\lambda$ has prime models over every set of the form $M \cup \{a\}$.
  This generalizes an argument of Shelah, who proved the result when $\lambda$
is a successor cardinal.",1509.07024v6
2015-10-05,Sensitive Identification of Nearby Debris Disks via Precise Calibration of WISE Data,"Using data from the WISE All-Sky Survey, we have found >100 new infrared
excess sources around main-sequence Hipparcos stars within 75pc. Our empirical
calibration of WISE photospheric colors and removal of non-trivial
false-positive sources are responsible for the high confidence (>99.5%) of
detections, while our corrections to saturated W1 (3.4um) and W2 (4.6um)
photometry have for the first time allowed us to search for new infrared excess
sources around bright field stars in WISE. The careful calibration and
filtering of the WISE data have allowed us to probe excess fluxes down to
roughly 8% of the photospheric emission at 22um around saturated stars in WISE.
We expect that the increased sensitivity of our survey will not only aid in
understanding the evolution of debris disks, but will also benefit future
studies using WISE.",1510.01327v1
2015-10-12,Formulations of moist thermodynamics for atmospheric modelling,"Internal energy, enthalpy and entropy are the key quantities to study
thermodynamic properties of the moist atmosphere, because they correspond to
the First (internal energy and enthalpy) and Second (entropy) Laws of
thermodynamics. The aim of this chapter is to search for analytical formulas
for the specific values of enthalpy and entropy and for the moist-air mixture
composing the atmosphere.
  The Third Law of thermodynamics leads to the definition of absolute reference
values for thermal enthalpies and entropies of all atmospheric species. It is
shown in this Chapter 22 that it is possible to define and compute a general
moist-air entropy potential temperature, which is really an equivalent of the
moist-air specific entropy in all circumstances (saturated, or not saturated).
Similarly, it is shown that it is possible to define and compute the moist-air
specific enthalpy, which is different from the thermal part of what is called
Moist-Static-Energy in atmospheric studies.",1510.03239v1
2015-10-21,On the convective overstability in protoplanetary discs,"This paper explores the driving of low-level hydrodynamical activity in
protoplanetary-disc dead zones. A small adverse radial entropy gradient,
ordinarily stabilised by rotation, excites oscillatory convection (`convective
overstability') when thermal diffusion, or cooling, is neither too strong nor
too weak. I revisit the linear theory of the instability, discuss its
prevalence in protoplanetary discs, and show that unstable modes are exact
nonlinear solutions in the local Boussinesq limit. Overstable modes cannot grow
indefinitely, however, as they are subject to a secondary parametric
instability that limits their amplitudes to relatively low levels. If parasites
set the saturation level of the ensuing turbulence then the convective
overstability is probably too weak to drive significant angular momentum
transport or to generate vortices. But I also discuss an alternative, and far
more vigorous, saturation route that generates radial `layers' or `zonal flows'
(witnessed also in semiconvection). Numerical simulations are required to
determine which outcome is favoured in realistic discs, and consequently how
important the instability is for disc dynamics.",1510.06247v1
2015-10-25,CGC/saturation approach for soft interactions at high energy: survival probability of the central exclusive production,"We estimate the value of the survival probability for central exclusive
production, in a model, which is based on the CGC/saturation approach. Hard and
soft processes are described in the same framework. At LHC energies, we obtain
a small value for the survival probability. The source of the small value, is
the impact parameter dependence of the hard amplitude. Our model has
successfully described a large body of soft data: elastic, inelastic and
diffractive cross sections,inclusive production and rapidity correlations, as
well as the $t$-dependence of deep inelastic diffractive production of vector
mesons",1510.07249v2
2015-10-30,Saturation in random graphs,"A graph $H$ is $K_s$-saturated if it is a maximal $K_s$-free graph, i.e., $H$
contains no clique on $s$ vertices, but the addition of any missing edge
creates one. The minimum number of edges in a $K_s$-saturated graph was
determined over 50 years ago by Zykov and independently by Erd\H{o}s, Hajnal
and Moon. In this paper, we study the random analog of this problem: minimizing
the number of edges in a maximal $K_s$-free subgraph of the Erd\H{o}s-R\'enyi
random graph $G(n,p)$. We give asymptotically tight estimates on this minimum,
and also provide exact bounds for the related notion of weak saturation in
random graphs. Our results reveal some surprising behavior of these parameters.",1510.09187v2
2015-10-30,"Kato-Nakayama spaces, infinite root stacks, and the profinite homotopy type of log schemes","For a log scheme locally of finite type over $\mathbb{C}$, a natural
candidate for its profinite homotopy type is the profinite completion of its
Kato-Nakayama space. Alternatively, one may consider the profinite homotopy
type of the underlying topological stack of its infinite root stack. Finally,
for a log scheme not necessarily over $\mathbb{C}$, another natural candidate
is the profinite \'etale homotopy type of its infinite root stack. We prove
that, for a fine saturated log scheme locally of finite type over $\mathbb{C}$,
these three notions agree. In particular, we construct a comparison map from
the Kato-Nakayama space to the underlying topological stack of the infinite
root stack, and prove that it induces an equivalence on profinite completions.
In light of these results, we define the profinite homotopy type of a general
fine saturated log scheme as the profinite \'etale homotopy type of its
infinite root stack.",1511.00037v2
2015-11-02,"Identify influential spreaders in complex networks, the role of neighborhood","Identifying the most influential spreaders is an important issue in
controlling the spreading processes in complex networks. Centrality measures
are used to rank node influence in a spreading dynamics. Here we propose a node
influence measure based on the centrality of a node and its neighbors'
centrality, which we call the neighborhood centrality. By simulating the
spreading processes in six real-world networks, we find that the neighborhood
centrality greatly outperforms the basic centrality of a node such as the
degree and coreness in ranking node influence and identifying the most
influential spreaders. Interestingly, we discover a saturation effect in
considering the neighborhood of a node, which is not the case of the larger the
better. Specifically speaking, considering the 2-step neighborhood of nodes is
a good choice that balances the cost and performance. If further step of
neighborhood is taken into consideration, there is no obvious improvement and
even decrease in the ranking performance. The saturation effect may be
informative for studies that make use of the local structure of a node to
determine its importance in the network.",1511.00441v1
2015-11-07,Thermodynamic law from the entanglement entropy bound,"From black hole thermodynamics, the Bekenstein bound has been proposed as a
universal thermal entropy bound. It has been further generalized to an
entanglement entropy bound which is valid even in a quantum system. In a
quantumly entangled system, the non-negativity of the relative entropy leads to
the entanglement entropy bound. When the entanglement entropy bound is
saturated, a quantum system satisfies the thermodynamics-like law with an
appropriately defined entanglement temperature. We show that the saturation of
the entanglement entropy bound accounts for a universal feature of the
entanglement temperature proportional to the inverse of the system size. In
addition, we show that the deformed modular Hamiltonian under a global quench
also satisfies the generalized entanglement entropy boundary after introducing
a new quantity called the entanglement chemical potential.",1511.02288v2
2015-11-11,Cluster expansions and chiral symmetry at large density in 2-color QCD,"$SU(N_c)$ lattice gauge theories with $N_f$ flavors of massless staggered
fermions are considered at high quark chemical potential $\mu$ and any
temperature $T$. In the strong coupling regime (sufficiently small $\beta$)
they have been shown to possess a chiral phase of intact global $U(N_f)\times
U(N_f)$ symmetry. The proof is by cluster expansions which converge in the
infinite volume limit. Extension to weaker coupling does not appear feasible in
the presence of complex fermion determinant. For theories with real
determinant, however, such as 2-color QCD with fundamental fermions, or any
$N_c$ with even $N_f$ and adjoint fermions, such large $\mu$ cluster expansions
can be used to show chiral behavior of fermionic lattice observables at any
gauge coupling. Unfortunately, this absence of color
superfluidity/superconductivity at high $\mu$ appears to be a lattice artifact
due to lattice saturation, a serious problem plaguing the standard finite
density formalism on the lattice. Some possible ways of circumventing
saturation are discussed.",1511.03733v1
2015-11-16,Asymptotics of surface-plasmon redshift saturation at sub-nanometric separations,"Many promising nanophotonics endeavours hinge upon the unique plasmonic
properties of nanometallic structures with narrow non-metallic gaps, which
support super-concentrated bonding modes that singularly redshift with
decreasing separations. In this letter, we present a descriptive physical
picture, complemented by elementary asymptotic formulae, of a nonlocal
mechanism for plasmon-redshift saturation at subnanometric gap widths. Thus, by
considering the electron-charge and field distributions in the close vicinity
of the metal-vacuum interface, we show that nonlocality is asymptotically
manifested as an effective potential discontinuity. For bonding modes in the
near-contact limit, the latter discontinuity is shown to be effectively
equivalent to a widening of the gap. As a consequence, the resonance-frequency
near-contact asymptotics are a renormalisation of the corresponding local ones.
Specifically, the renormalisation furnishes an asymptotic plasmon-frequency
lower bound that scales with the $1/4$-power of the Fermi wavelength. We
demonstrate these remarkable features in the prototypical cases of nanowire and
nanosphere dimers, showing agreement between our elementary expressions and
previously reported numerical computations.",1511.04895v1
2015-11-24,Leptons from heavy-quark semileptonic decay in pA collisions within the CGC framework,"We study single lepton production from semileptonic decays of heavy flavor
hadrons ($D,B\rightarrow~l$) in pp and p$A$ collisions at RHIC and the LHC
within the saturation/Color-Glass-Condensate (CGC) framework. Using the gluon
distribution function obtained with the dipole amplitude, whose energy
dependence is described by the Balitsky-Kovchegov equation with running
coupling effect, we compute the transverse-momentum ($p_\perp$) spectra of the
lepton yields at mid and forward rapidities. We find that a large fraction of
leptons at low $p_\perp$ stems from the saturation regime of the incoming
gluons in the target, especially in p$A$ collisions at the LHC. The resultant
$p_\perp$ spectra is slightly harder than the data, but the nuclear
modification factor seems consistent with the data within some uncertainty. We
also update the nuclear modification factors for J/$\psi$ and $D$ meson at the
LHC energy.",1511.07698v4
2015-11-24,Signal Processing and Electronic Noise in LZ,"The electronics of the LUX-ZEPLIN (LZ) experiment, the 10-tonne dark matter
detector to be installed at the Sanford Underground Research Facility (SURF),
consists of low-noise dual-gain amplifiers and a 100-MHz, 14-bit data
acquisition system for the TPC PMTs. Pre-prototypes of the analog amplifiers
and the 32-channel digitizers were tested extensively with simulated pulses
that are similar to the prompt scintillation light and the electroluminescence
signals expected in LZ. These studies are used to characterize the noise and to
measure the linearity of the system. By increasing the amplitude of the test
signals, the effect of saturating the amplifier and the digitizers was studied.
The RMS ADC noise of the digitizer channels was measured to be 1.19 $\pm$ 0.01
ADCC. When a high-energy channel of the amplifier is connected to the
digitizer, the measured noise remained virtually unchanged, while the noise
added by a low-energy channel was estimated to be 0.38 $\pm$ 0.02 ADCC (46
$\pm$ 2$\mu$V). A test facility is under construction to study saturation,
mitigate noise and measure the performance of the LZ electronics and data
acquisition chain.",1511.07752v1
2015-11-29,Probing electronic lifetimes and phonon anharmonicities in high-quality chemical vapor deposited graphene by magneto-Raman spectroscopy,"We present a magneto-Raman study on high-quality single-layer graphene grown
by chemical vapor deposition (CVD) that is fully encapsulated in hexagonal
boron nitride by a dry transfer technique. By analyzing the Raman D, G, and 2D
peaks, we find that the structural quality of the samples is comparable to
state-of-the-art exfoliated graphene flakes. From B field dependent Raman
measurements, we extract the broadening and associated lifetime of the G peak
due to anharmonic effects. Furthermore, we determine the decay width and
lifetime of Landau level (LL) transitions from magneto-phonon resonances as a
function of laser power. At low laser power, we find a minimal decay width of
140 1/cm highlighting the high electronic quality of the CVD-grown graphene. At
higher laser power, we observe an increase of the LL decay width leading to a
saturation with the corresponding lifetime saturating at a minimal value of 18
fs.",1511.08984v1
2015-12-13,Čerenkov free-electron laser in side-wall configuration,"In this paper, we have proposed a \v{C}erenkov free-electron laser (CFEL)
with metallic side walls, which are used to confine an electromagnetic surface
mode supported by a thin dielectric slab placed on top of a conducting surface.
This leads to an enhancement in coupling between the optical mode and the
co-propagating electron beam, and consequently, performance of the CFEL is
improved. We set up coupled Maxwell-Lorentz equations for the system, in
analogy with an undulator based conventional FEL, and obtain formulas for the
small-signal gain and growth rate. It is shown that small signal gain and
growth rate in this configuration are larger compared to the configuration
without the side walls. In the nonlinear regime, we solve the coupled
Maxwell-Lorentz equations numerically and study the saturation behaviour of the
system. It is found that the \v{C}erenkov FEL with side walls saturates
quickly, and produces powerful coherent terahertz radiation.",1512.04022v2
2015-12-28,A convergent mass conservative numerical scheme based on mixed finite elements for two-phase flow in porous media,"In this work we present a mass conservative numerical scheme for two-phase
flow in porous media. The model for flow consists on two fully coupled,
non-linear equations: a degenerate parabolic equation and an elliptic equation.
The proposed numerical scheme is based on backward Euler for the temporal
discretization and mixed finite element method (MFEM) for the discretization in
space. Continuous, semi-discrete (continuous in space) and fully discrete
variational formulations are set up and the existence and uniqueness of
solutions is discussed. Error estimates are presented to prove the convergence
of the scheme. The non-linear systems within each time step are solved by a
robust linearization method. This iterative method does not involve any
regularization step. The convergence of the linearization scheme is rigorously
proved under the assumption of a Lipschitz continuous saturation. The case of a
H\""older continuous saturation is also discussed, a rigorous convergence proof
being given for Richards' equation. Numerical results are presented to sustain
the theoretical findings.",1512.08387v2
2015-12-29,Extended anti-de Sitter Hypergravity in $2+1$ Dimensions and Hypersymmetry Bounds,"In a recent paper (JHEP {\bf 1508} (2015) 021), we have investigated
hypersymmetry bounds in the context of simple anti-de Sitter hypergravity in
$2+1$ dimensions. We showed that these bounds involved non linearly the
spin-$2$ and spin-$4$ charges, and were saturated by a class of extremal black
holes, which are $\frac14$-hypersymmetric. We continue the analysis here by
considering $(M,N)$-extended anti-de Sitter hypergravity models, based on the
superalgebra $osp(M \vert 4) \oplus osp(N \vert 4)$. The asymptotic symmetry
superalgebra is then the direct sum of two-copies of a $W$-superalgebra that
contains $so(M)$ (or $so(N)$) Kac-Moody currents of conformal weight $1$,
fermionic generators of conformal weight $5/2$ and bosonic generators of
conformal weight $4$ in addition to the Virasoro generators. The nonlinear
hypersymmetry bounds on the conserved charges are derived and shown to be
saturated by a class of extreme hypersymmetric black holes which we explicitly
construct.",1512.08603v1
2015-12-29,Characterization of the GEM foil materials,"Systematic studies on the GEM foil material are performed to measure the
moisture diffusion rate and saturation level. These studies are important
because the presence of this compound inside the detector's foil can possibly
change its mechanical and electrical properties and, in such a way, the
detector performance can be affected. To understand this phenomenon, a model is
developed with COMSOL Multhiphysics v. 4.3, which described the adsorption and
diffusion within the geometry of GEM foil, the concentration profiles and the
time required to saturate the foil. The COMSOL model is verified by
experimental observations on a GEM foil sample. This note will describe the
model and its experimental verification results.",1512.08621v1
2016-01-11,Terahertz Saturable Absorption in Superconducting Metamaterials,"We present a superconducting metamaterial saturable absorber at terahertz
frequencies. The absorber consists of an array of split ring resonators (SRRs)
etched from a 100nm YBaCu3O7 (YBCO) film. A polyimide spacer layer and gold
ground plane are deposited above the SRRs, creating a reflecting perfect
absorber. Increasing either the temperature or incident electric field (E)
decreases the superconducting condensate density and corresponding kinetic
inductance of the SRRs. This alters the impedance matching in the metamaterial,
reducing the peak absorption. At low electric fields, the absorption was
optimized near 80% at T=10K and decreased to 20% at T=70K. For E=40kV/cm and
T=10K, the peak absorption was 70% decreasing to 40% at 200kV/cm, corresponding
to a modulation of 43%.",1601.02496v2
2016-01-17,Metallic ferromagnetism supported by a single band in a multi-band Hubbard model,"We construct a multi-band Hubbard model on the lattice obtained by
""decorating"" a closely packed $d$-dimensional lattice $\mathcal{M}$ (such as
the triangular lattice) where $d\ge2$. We take the limits in which the Coulomb
interaction and the band gap become infinitely large. Then there remains only a
single band with finite energy, on which electrons are supported. Let the
electron number be $N_\mathrm{e}=|\mathcal{M}|-N_\mathrm{h}$, where
$|\mathcal{M}|$ corresponds to the electron number which makes the lowest
(finite energy) band half-filled, and $N_\mathrm{h}$ is the number of ""holes"".
It is expected that the model exhibits metallic ferromagnetism if
$N_\mathrm{h}/|\mathcal{M}|$ is nonvanishing but sufficiently small. We prove
that the ground states exhibit saturated ferromagnetism if
$N_\mathrm{h}\le(\text{const.})|\mathcal{M}|^{2/(d+2)}$, and exhibit (not
necessarily saturated) ferromagnetism if
$N_\mathrm{h}\le(\mathrm{const.})|\mathcal{M}|^{(d+1)/(d+2)}$. This may be
regarded as a rigorous example of metallic ferromagnetism provided that the
system size $|\mathcal{M}|$ is not too large.",1601.04265v2
2016-01-21,Interference and dynamics of light from a distance-controlled atom pair in an optical cavity,"Interference is central to quantum physics and occurs when indistinguishable
paths exist, like in a double-slit experiment. Replacing the two slits with two
single atoms introduces optical non-linearities for which nontrivial
interference phenomena are predicted. Their observation, however, has been
hampered by difficulties in preparing the required atomic distribution,
controlling the optical phases and detecting the faint light. Here we overcome
all of these experimental challenges by combining an optical lattice for atom
localisation, an imaging system with single-site resolution, and an optical
resonator for light steering. We observe resonator-induced saturation of
resonance fluorescence for constructive interference of the scattered light and
nonzero emission with huge photon bunching for destructive interference. The
latter is explained by atomic saturation and photon pair generation. Our
experimental setting is scalable and allows one to realize the Tavis-Cummings
model for any number of atoms and photons, explore fundamental aspects of
light-matter interaction, and implement new quantum information processing
protocols.",1601.05757v1
2016-01-25,On the fractional cell kill law governing the lysis of solid tumors,"We present in silico simulations and mathematical analyses supporting several
hypotheses that explain the saturation expressed in the fractional cell kill
law that governs the lysis of tumor cells by cytotoxic CD8 + T cells (CTLs). In
order to give insight into the significance of the parameters appearing in such
law, a hybrid cellular automaton model describing the spatio-temporal evolution
of tumor growth and its interaction with the cell-mediated immune response is
used. When the CTLs eradicate efficiently the tumor cells, the model predicts a
correlation between the morphology of the tumors and the rate at which they are
lysed. As the effectiveness of the effector cells is decreased, the saturation
gradually disappears. This limit is thoroughly discussed and a new fractional
cell kill is proposed.",1601.07144v3
2016-02-04,Noisy Metrology: A saturable lower bound on quantum Fisher information,"In order to provide a guaranteed precision and a more accurate judgement
about the true value of the Cram\'{e}r-Rao bound and its scaling behavior, an
upper bound (equivalently a lower bound on the quantum Fisher information) for
precision of estimation is introduced. Unlike the bounds previously introduced
in the literature, the upper bound is saturable and yields a practical
instruction to estimate the parameter through preparing the optimal initial
state and optimal measurement. The bound is based on the underling dynamics and
its calculation is straightforward and requires only the matrix representation
of the quantum maps responsible for encoding the parameter. This allows us to
apply the bound to open quantum systems whose dynamics are described by either
semigroup or non-semigroup maps. Reliability and efficiency of the method to
predict the ultimate precision limit are demonstrated by {three} main examples.",1602.01691v5
2016-02-04,Twist expansion of forward Drell-Yan process,"We present a twist expansion of differential cross-sections of the forward
Drell-Yan process at the high energies. The expansion of all invariant
form-factors is performed assuming GBW saturation model and the saturation
scale plays the role of the hadronic scale of OPE. Some expilicit predictions
for LHC experiments are given. It is shown also how the Lam-Tung relation is
broken at twist 4 what provides a sensitive probe for searching of higher
twists.",1602.01762v2
2016-02-18,Spread of entanglement for small subsystems in holographic CFTs,"We develop an analytic perturbative expansion to study the propagation of
entanglement entropy for small subsystems after a global quench, in the context
of the AdS/CFT correspondence. Opposite to the large interval limit, in this
case the evolution of the system takes place at timescales that are shorter in
comparison to the local equilibration scale and thus, different physical
mechanisms govern the dynamics and subsequent thermalization. In particular, we
show that the heuristic picture in terms of a ""entanglement tsunami"" does not
apply in this regime. We find two crucial differences. First, that the
instantaneous rate of growth of the entanglement is not constrained by
causality, but rather its time average. And second, that the approach to
saturation is always continuous, regardless the shape of the entangling
surface. Our analytic expansion also enables us to verify some previous
numerical results, namely, that the saturation time is non-monotonic with
respect to the chemical potential. All of our results are pertinent to CFTs
with a classical gravity dual formulation.",1602.05934v2
2016-02-29,Proof of Control of a UAV and a UGV Cooperating to Manipulate an Object,"This paper focuses on the control of a system composed of an Unmanned Aerial
Vehicle (UAV) and an Unmanned Ground Vehicle (UGV) which cooperate to
manipulate an object. The two units are subject to actuator saturations and
cooperate to move the object to a desired pose, characterized by its position
and inclination. The paper proposes a control strategy where the ground vehicle
is tasked to deploy the object to a certain position, whereas the aerial
vehicle adjusts its inclination. The ground vehicle is governed by a saturated
proportional-derivative control law. The aerial vehicle is regulated by means
of a cascade control specifically designed for this problem that is able to
exploit the mechanical interconnection. The stability of the overall system is
proved through Input-to-State Stability and Small Gain theorem arguments. To
solve the problem of constraints satisfaction, a nonlinear Reference Governor
scheme is implemented. Numerical simulations are provided to demonstrate the
effectiveness of the proposed method.",1602.08987v2
2016-03-06,Proof of Threshold Saturation for Spatially Coupled Sparse Superposition Codes,"Recently, a new class of codes, called sparse superposition or sparse
regression codes, has been proposed for communication over the AWGN channel. It
has been proven that they achieve capacity using power allocation and various
forms of iterative decoding. Empirical evidence has also strongly suggested
that the codes achieve capacity when spatial coupling and approximate message
passing decoding are used, without need of power allocation. In this note we
prove that state evolution (which tracks message passing) indeed saturates the
potential threshold of the underlying code ensemble, which approaches in a
proper limit the optimal threshold. Our proof uses ideas developed in the
theory of low-density parity-check codes and compressive sensing.",1603.01817v1
2016-03-07,Graph Theoretic Investigations on Inefficiencies in Network Models,"We consider network models where information items flow %are sent from a
source to a sink node. We start with a model where routing is constrained by
energy available on nodes in finite supply (like in Smartdust) and efficiency
is related to energy consumption. We characterize graph topologies ensuring
that every saturating flow under every energy-to-node assignment is maximum and
provide a polynomial-time algorithm for checking this property. We then
consider the standard flow networks with capacity on edges, where again
efficiency is related to maximality of saturating flows, and a traffic model
for selfish routing, where efficiency is related to latency at a Wardrop
equilibrium. Finally, we show that all these forms of inefficiency yield
different classes of graphs (apart from the acyclic case, where the last two
forms generate the same class). Interestingly, in all cases inefficient graphs
can be made efficient by removing edges; this resembles a well-known
phenomenon, called Braess's paradox.",1603.01983v2
2016-03-14,Saturation of repeated quantum measurements,"We study sequential measurement scenarios where the system is repeatedly
subjected to the same measurement process. We first provide examples of such
repeated measurements where further repetitions of the measurement do not
increase our knowledge on the system after some finite number of measurement
steps. We also prove, however, that repeating the L\""uders measurement of an
unsharp two-outcome observable never saturates in this sense, and we
characterize the observable measured in the limit of infinitely many
repetitions. Our result implies that a repeated measurement can be used to
correct the inherent noise of an unsharp observable.",1603.04271v2
2016-03-15,Threshold Saturation of Spatially Coupled Sparse Superposition Codes for All Memoryless Channels,"We recently proved threshold saturation for spatially coupled sparse
superposition codes on the additive white Gaussian noise channel. Here we
generalize our analysis to a much broader setting. We show for any memoryless
channel that spatial coupling allows generalized approximate message-passing
(GAMP) decoding to reach the potential (or Bayes optimal) threshold of the code
ensemble. Moreover in the large input alphabet size limit: i) the GAMP
algorithmic threshold of the underlying (or uncoupled) code ensemble is simply
expressed as a Fisher information; ii) the potential threshold tends to
Shannon's capacity. Although we focus on coding for sake of coherence with our
previous results, the framework and methods are very general and hold for a
wide class of generalized estimation problems with random linear mixing.",1603.04591v1
2016-03-19,Efficiency enhancement of a harmonic lasing free-electron laser,"The harmonic lasing free-electron laser amplifier, in which two wigglers is
employed in order for the fundamental resonance of the second wiggler to
coincide with the third harmonic of the first wiggler to generate ultraviolet
radiation, is studied. A set of coupled nonlinear first-order differential
equations describing the nonlinear evolution of the system, for a long electron
bunch, is solved numerically by CYRUS code. Solutions for the non-averaged and
averaged equations are compared. Remarkable agreement is found between the
averaged and non-averaged simulation for the evolution of the third harmonic.
Thermal effects in the form of longitudinal velocity spread are also
investigated. For efficiency enhancement, the second wiggler field is set to
decrease linearly and nonlinearly at the point where the radiation of the third
harmonic saturates. The optimum starting point and the slope of the tapering of
the amplitude of the wiggler are found by a successive run of the code. It is
found that tapering can increase the saturated power of the third harmonic
considerably. In order to reduce the length of the wiggler, the prebunched
electron beam is considered.",1603.06031v1
2016-03-21,Model-Independent Inference of Neutron Star Radii from Moment of Inertia Measurements,"A precise moment of inertia measurement for PSR J0737-3039A in the double
pulsar system is expected within the next five years. We present here a new
method of mapping the anticipated measurement of the moment of inertia directly
into the neutron star structure. We determine the maximum and minimum values
possible for the moment of inertia of a neutron star of a given radius based on
physical stability arguments, assuming knowledge of the equation of state only
at densities below the nuclear saturation density. If the equation of state is
trusted up to the nuclear saturation density, we find that a measurement of the
moment of inertia will place absolute bounds on the radius of PSR J0737-3039A
to within $\pm$1 km. The resulting combination of moment of inertia, mass, and
radius measurements for a single source will allow for new, stringent
constraints on the dense-matter equation of state.",1603.06594v2
2016-04-13,Quasi-geostrophic dynamics in the presence of moisture gradients,"The derivation of a quasi-geostrophic (QG) system from the rotating shallow
water equations on a midlatitude beta-plane coupled with moisture is presented.
Condensation is prescribed to occur whenever the moisture at a point exceeds a
prescribed saturation value. It is seen that a slow condensation time scale is
required to obtain a consistent set of equations at leading order. Further,
since the advecting wind fields are geostrophic, changes in moisture (and
hence, precipitation) occur only via non-divergent mechanisms. Following
observations, a saturation profile with gradients in the zonal and meridional
directions is prescribed. A purely meridional gradient has the effect of
slowing down the dry Rossby waves, through a reduction in the ""equivalent
gradient"" of the background potential vorticity. A large scale unstable moist
mode results on the inclusion of a zonal gradient by itself, or in conjunction
with a meridional moisture gradient. For gradients that are are representative
of the atmosphere, the most unstable moist mode propagates zonally in the
direction of increasing moisture, matures over an intraseasonal timescale and
has small phase speed.",1604.03656v1
2016-04-17,A numerical study of two-phase flow with dynamic capillary pressure using an adaptive moving mesh method,"Motivated by observations of saturation overshoot, this paper investigates
numerical modeling of two-phase flow incorporating dynamic capillary pressure.
The effects of the dynamic capillary coefficient, the infiltrating flux rate
and the initial and boundary values are systematically studied using a
travelling wave ansatz and efficient numerical methods. The travelling wave
solutions may exhibit monotonic, non-monotonic or plateau-shaped behaviour.
Special attention is paid to the non-monotonic profiles. The travelling wave
results are confirmed by numerically solving the partial differential equation
using an accurate adaptive moving mesh solver. Comparisons between the computed
solutions using the Brooks-Corey model and the laboratory measurements of
saturation overshoot verify the effectiveness of our approach.",1604.04863v1
2016-04-23,Micro-mechanical Failure Analysis of Wet Granular Matter,"We employ a novel fluid-particle model to study the shearing behavior of
granular soils under different saturation levels, ranging from the dry material
via the capillary bridge regime to higher saturation levels with percolating
clusters. The full complexity of possible liquid morphologies is taken into
account, implying the formation of isolated arbitrary-sized liquid clusters
with individual Laplace pressures that evolve by liquid exchange via films on
the grain surface. Liquid clusters can grow in size, shrink, merge and split,
depending on local conditions, changes of accessible liquid and the pore space
morphology determined by the granular phase. This phase is represented by a
discrete particle model based on Contact Dynamics, where capillary forces
exerted from a liquid phase add to the motion of spherical particles. We study
the macroscopic response of the system due to an external compression force at
various liquid contents with the help of triaxial shear tests. Additionally,
the change in liquid cluster distributions during the compression due to the
deformation of the pore space is evaluated close to the critical load.",1604.06881v1
2016-04-26,Saturation and solvability in abstract elementary classes with amalgamation,"$\mathbf{Theorem.}$
  Let $K$ be an abstract elementary class (AEC) with amalgamation and no
maximal models. Let $\lambda > \text{LS} (K)$. If $K$ is categorical in
$\lambda$, then the model of cardinality $\lambda$ is Galois-saturated.
  This answers a question asked independently by Baldwin and Shelah. We deduce
several corollaries: $K$ has a unique limit model in each cardinal below
$\lambda$, (when $\lambda$ is big-enough) $K$ is weakly tame below $\lambda$,
and the thresholds of several existing categoricity transfers can be improved.
  We also prove a downward transfer of solvability (a version of superstability
introduced by Shelah):
  $\mathbf{Corollary.}$
  Let $K$ be an AEC with amalgamation and no maximal models. Let $\lambda > \mu
> \text{LS} (K)$. If $K$ is solvable in $\lambda$, then $K$ is solvable in
$\mu$.",1604.07743v3
2016-05-10,Creation and counting of defects in a temperature quenched Bose-Einstein Condensate,"We study the spontaneous formation of defects in the order parameter of a
trapped ultracold bosonic gas while crossing the critical temperature for
Bose-Einstein Condensation (BEC) at different rates. The system has the shape
of an elongated ellipsoid, whose transverse width can be varied to explore
dimensionality effects. For slow enough temperature quenches we find a
power-law scaling of the average defect number with the quench rate, as
predicted by the Kibble-Zurek mechanism. A breakdown of such a scaling is found
for fast quenches, leading to a saturation of the average defect number. We
suggest an explanation for this saturation in terms of the mutual interactions
among defects.",1605.02982v1
2016-05-12,Effects of symmetry energy in $^{132}\rm {Sn}+^{124}\rm {Sn}$ reaction at 300 MeV/nucleon,"Based on the recently updated Isospin-dependent Boltzmann-Uehling-Uhlenbeck
(IBUU) transport model, we studied the effects of symmetry energy on the
neutron to proton n/p ratio and the $\pi^{-}/\pi^{+}$ ratio in central
$^{132}\rm {Sn}+^{124}\rm {Sn}$ reaction at 300 MeV/nucleon. It is found that
the n/p ratio and the $\pi^{-}/\pi^{+}$ ratio in central $^{132}\rm
{Sn}+^{124}\rm {Sn}$ reaction at 300 MeV/nucleon mainly probe the symmetry
energy in the density region 1-1.5 times saturation density. However, the
$\pi^{-}/\pi^{+}$ ratio may be able to probe the density-dependent symmetry
energy above 1.5 times saturation density by making some kinematic restrictions
such as the azimuthal angle and kinetic energy cuts of emitting pions.",1605.03701v2
2016-05-13,Bayesian $D$-optimal designs for error-in-variables models,"Bayesian optimality criteria provide a robust design strategy to parameter
misspecification. We develop an approximate design theory for Bayesian
$D$-optimality for non-linear regression models with covariates subject to
measurement errors. Both maximum likelihood and least squares estimation are
studied and explicit characterisations of the Bayesian $D$-optimal saturated
designs for the Michaelis-Menten, Emax and exponential regression models are
provided. Several data examples are considered for the case of no preference
for specific parameter values, where Bayesian $D$-optimal saturated designs are
calculated using the uniform prior and compared to several other designs,
including the corresponding locally $D$-optimal designs, which are often used
in practice.",1605.04055v1
2016-05-14,Highly anisotropic electronic transport properties of monolayer and bilayer phosphorene from first principles,"The intrinsic carrier transport dynamics in phosphorene is theoretically
examined. Utilizing a density functional theory treatment, the low-field
mobility and the saturation velocity are characterized for both electrons and
holes in the monolayer and bilayer structures. The analysis clearly elucidates
the crystal orientation dependence manifested through the anisotropic band
structure and the carrier-phonon scattering rates. In the monolayer, the hole
mobility in the armchair direction is estimated to be approximately five times
larger than in the zigzag direction at room temperature (460 cm$^2$/Vs vs. 90
cm$^2$/Vs). The bilayer transport, on the other hand, exhibits a more modest
anisotropy with substantially higher mobilities (1610 cm$^2$/Vs and 760
cm$^2$/Vs, respectively). The calculations on the conduction-band electrons
indicate a comparable dependence while the characteristic values are generally
smaller by about a factor of two. The variation in the saturation velocity is
found to be less pronounced. With the anticipated superior performance and the
diminished anisotropy, few-layer phosphorene offers a promising opportunity
particularly in p-type applications.",1605.04377v1
2016-05-25,Extremal bootstrapping: go with the flow,"The extremal functional method determines approximate solutions to the
constraints of crossing symmetry, which saturate bounds on the space of unitary
CFTs. We show that such solutions are characterized by extremality conditions,
which may be used to flow continuously along the boundaries of parameter space.
Along the flow there is generically no further need for optimization, which
dramatically reduces computational requirements, bringing calculations from the
realm of computing clusters to laptops. Conceptually, extremality sheds light
on possible ways to bootstrap without positivity, extending the method to
non-unitary theories, and implies that theories saturating bounds, and
especially those sitting at kinks, have unusually sparse spectra. We discuss
several applications, including the first high-precision bootstrap of a
non-unitary CFT.",1605.08087v1
2016-05-30,Doppler-free spectroscopy on Cs D$_1$ line with a dual-frequency laser,"We report on Doppler-free laser spectroscopy in a Cs vapor cell using a
dual-frequency laser system tuned on the Cs D$_1$ line. Using
counter-propagating beams with crossed linear polarizations, an original
sign-reversal of the usual saturated absorption dip and large increase in
Doppler-free atomic absorption is observed. This phenomenon is explained by
coherent population trapping (CPT) effects. The impact of laser intensity and
light polarization on absorption profiles is reported in both single-frequency
and dual-frequency regimes. In the latter, frequency stabilization of two diode
lasers was performed, yielding a beat-note fractional frequency stability at
the level of $3 \times 10^{-12}$ at 1 s averaging time. These performances are
about an order of magnitude better than those obtained using a conventional
single-frequency saturated absorption scheme.",1605.09245v1
2016-04-28,A Mathematical Model of the Rainwater Flows in a Green Roof,"A model is presented for the gravity-driven flow of rainwater descending
through the soil layer of a green roof, treated as a porous medium on a flat
permeable surface representing an efficient drainage layer. A fully saturated
zone is shown to occur. It is typically a thin layer, relative to the total
soil thickness, and lies at the bottom of the soil layer. This provides a
bottom boundary condition for the partially saturated upper zone. It is shown
that after the onset of rainfall, well-defined fronts of water can descend
through the soil layer. Also the rainwater flow is relatively quick compared
with the moisture uptake by the roots of the plants in the roof. In separate
models the exchanges of water are described between the (smaller-scale) porous
granules of soil, the roots and the rainwater in the inter-granule pores.",1605.09727v1
2016-05-31,Rigid ideals,"An ideal $I$ on a cardinal $\kappa$ is called \emph{rigid} if all
automorphisms of $P(\kappa)/I$ are trivial. An ideal is called
\emph{$\mu$-minimal} if whenever $G\subseteq P(\kappa)/I$ is generic and $X\in
P(\mu)^{V[G]}\setminus V$, it follows that $V[X]=V[G]$. We prove that the
existence of a rigid saturated $\mu$-minimal ideal on $\mu^+$, where $\mu$ is a
regular cardinal, is consistent relative to the existence of large cardinals.
The existence of such an ideal implies that GCH fails. However, we show that
the existence of a rigid saturated ideal on $\mu^+$, where $\mu$ is an
\emph{uncountable} regular cardinal, is consistent with GCH relative to the
existence of an almost-huge cardinal. Addressing the case $\mu=\omega$, we show
that the existence of a rigid \emph{presaturated} ideal on $\omega_1$ is
consistent with CH relative to the existence of an almost-huge cardinal. The
existence of a \emph{precipitous} rigid ideal on $\mu^+$ where $\mu$ is an
uncountable regular cardinal is equiconsistent with the existence of a
measurable cardinal.",1606.00040v2
2016-06-02,Matrix Product Density Operators: Renormalization Fixed Points and Boundary Theories,"We consider the tensors generating matrix product states and density
operators in a spin chain. For pure states, we revise the renormalization
procedure introduced by F. Verstraete et al. in 2005 and characterize the
tensors corresponding to the fixed points. We relate them to the states
possessing zero correlation length, saturation of the area law, as well as to
those which generate ground states of local and commuting Hamiltonians. For
mixed states, we introduce the concept of renormalization fixed points and
characterize the corresponding tensors. We also relate them to concepts like
finite correlation length, saturation of the area law, as well as to those
which generate Gibbs states of local and commuting Hamiltonians. One of the
main result of this work is that the resulting fixed points can be associated
to the boundary theories of two-dimensional topological states, through the
bulk-boundary correspondence introduced by Cirac et al. in 2011.",1606.00608v3
2016-06-14,Normal-metal quasiparticle traps for superconducting qubits,"The presence of quasiparticles in superconducting qubits emerges as an
intrinsic constraint on their coherence. While it is difficult to prevent the
generation of quasiparticles, keeping them away from active elements of the
qubit provides a viable way of improving the device performance. Here we
develop theoretically and validate experimentally a model for the effect of a
single small trap on the dynamics of the excess quasiparticles injected in a
transmon-type qubit. The model allows one to evaluate the time it takes to
evacuate the injected quasiparticles from the transmon as a function of trap
parameters. With the increase of the trap size, this time decreases
monotonically, saturating at the level determined by the quasiparticles
diffusion constant and the qubit geometry. We determine the characteristic trap
size needed for the relaxation time to approach that saturation value.",1606.04591v1
2016-06-29,New correlations between viscosity and surface tension for saturated normal fluids,"New correlations between viscosity and surface tension are proposed and
checked for saturated normal fluids. The proposed correlations contain three or
four adjustable coefficients for every fluid. They were obtained by fitting 200
data points, ranging from the triple point to a point very near to the critical
one. Forty substances were considered, including simple fluids (such as rare
gases), simple hydrocarbons, refrigerants, and some other substances such as
carbon dioxide and water. Two correlation models with three adjustable
coefficients were checked, and the results showed that the one based on the
modified Pelofsky expression gives the better overall results. A new
4-coefficient correlation is then proposed which clearly improves the results,
giving the lowest overall deviations for 32 out of the 40 substances considered
and absolute average deviations below 10% for all of them.",1606.09105v1
2016-06-29,Improved Correlation for Viscosity from Surface Tension Data for Saturated Normal Fluids,"Several correlations between viscosity and surface tension for saturated
normal fluids have been proposed in the literature. Usually, they include three
or four adjustable coefficients for every fluid and give generally good
results. In this paper we propose a new and improved four-coefficient
correlation which was obtained by fitting data ranging from the triple point to
a point very near to the critical one. Fifty four substances were considered,
including simple fluids (such as rare gases), simple hydrocarbons,
refrigerants, and some other substances such as carbon dioxide, water or
ethanol. The new correlation clearly improves the results obtained with those
previously available since it gives absolute average deviations below1% for 40
substances and below 2.1% for 10 substances more.",1606.09108v1
2016-06-30,Does Your DNS Recursion Really Time Out as Intended? A Timeout Vulnerability of DNS Recursive Servers,"Parallelization is featured by DNS recursive servers to do time-consuming
recursions on behalf on clients. As common DNS configurations, recursive
servers should allow a reasonable timeout for each recursion which may take as
long as several seconds. However, it is proposed in this paper that recursion
parallelization may be exploited by attackers to compromise the recursion
timeout mechanism for the purpose of DoS or DDoS attacks. Attackers can have
recursive servers drop early existing recursions in service by saturating
recursion parallelization. The key of the proposed attack model is to reliably
prolong service times for any attacking queries. As means of prolong service
times, serval techniques are proposed to effectively avoiding cache hit and
prolonging overall latency of external DNS lookups respectively. The impacts of
saturated recursion parallelization on timeout are analytically provided. The
testing on BIND servers demonstrates that with carefully crafted queries, an
attacker can use a low or moderate level of query load to successfully
overwhelm a target recursive server from serving the legitimate clients.",1607.00269v2
2016-07-08,Mass ordering of spectra from fragmentation of saturated gluon states in high multiplicity proton-proton collisions,"The mass ordering of mean transverse momentum $\left<p_T\right>$ and of the
Fourier harmonic coefficient $v_2 (p_T)$ of azimuthally anisotropic particle
distributions in high energy hadron collisions is often interpreted as evidence
for the hydrodynamic flow of the matter produced. We investigate an alternative
initial state interpretation of this pattern in high multiplicity proton-proton
collisions at the LHC. The QCD Yang-Mills equations describing the dynamics of
saturated gluons are solved numerically with initial conditions obtained from
the Color Glass Condensate based IP-Glasma model. The gluons are subsequently
fragmented into various hadron species employing the well established Lund
string fragmentation algorithm of the PYTHIA event generator. We find that this
ab initio initial state approach reproduces characteristic features of bulk
spectra, in particular the particle mass dependence of $\left<p_T\right>$ and
$v_2 (p_T)$.",1607.02496v2
2016-07-11,Forward di-jet production in p+Pb collisions in the small-x improved TMD factorization framework,"We study the production of forward di-jets in proton-lead and proton-proton
collisions at the Large Hadron Collider. Such configurations, with both jets
produced in the forward direction, impose a dilute-dense asymmetry which allows
to probe the gluon density of the lead or proton target at small longitudinal
momentum fractions. Even though the jet momenta are always much bigger than the
saturation scale of the target, $Q_s$, the transverse momentum imbalance of the
di-jet system may be either also much larger than $Q_s$, or of the order $Q_s$,
implying that the small-$x$ QCD dynamics involved is either linear or
non-linear, respectively. The small-$x$ improved TMD factorization framework
deals with both situation in the same formalism. In the latter case, which
corresponds to nearly back-to-back jets, we find that saturation effects induce
a significant suppression of the forward di-jet azimuthal correlations in
proton-lead versus proton-proton collisions.",1607.03121v1
2016-07-13,Comparison of Models of Fast Saturable Absorption in Passively Modelocked Lasers,"Fast saturable absorbers (FSAs) play a critical role in stabilizing many
passively modelocked lasers. The most commonly used averaged model to study
these lasers is the Haus modelocking equation (HME) that includes a third-order
nonlinear FSA. However, it predicts a narrow region of stability that is
inconsistent with experiments. To better replicate the laser physics, averaged
laser models that include FSAs with higher-than-third-order nonlinearities have
been introduced. Here, we compare three common FSA models to each other and to
the HME using the recently-developed boundary tracking algorithms. The three
FSA models are the cubic-quintic model, the sinusoidal model, and the algebraic
model. We find that all three models predict the existence of a stable
high-energy solution that is not present in the HME and have a much larger
stable operating region. We also find that all three models predict
qualitatively similar stability diagrams. We conclude that averaged laser
models that include FSAs with higher-than-third-order nonlinearity should be
used when studying the stability of passively modelocked lasers.",1607.03713v1
2016-07-20,Nonlocal topological valley transport at large valley Hall angles,"Berry curvature hot spots in two-dimensional materials with broken inversion
symmetry are responsible for the existence of transverse valley currents, which
give rise to giant nonlocal dc voltages. Recent experiments in high-quality
gapped graphene have highlighted a saturation of the nonlocal resistance as a
function of the longitudinal charge resistivity $\rho_{{\rm c}, xx}$, when the
system is driven deep into the insulating phase. The origin of this saturation
is, to date, unclear. In this work we show that this behavior is fully
compatible with bulk topological transport in the regime of large valley Hall
angles (VHAs). We demonstrate that, for a fixed value of the valley diffusion
length, the dependence of the nonlocal resistance on $\rho_{{\rm c}, xx}$
weakens for increasing VHAs, transitioning from the standard $\rho^3_{{\rm c},
xx}$ power-law to a result that is independent of $\rho_{{\rm c}, xx}$.",1607.05902v1
2016-07-20,Characterization of qubit chains by Feynman probes,"We address the characterization of qubit chains and assess the performances
of local measurements compared to those provided by Feynman probes, i.e.
nonlocal measurements realized by coupling a single qubit regis- ter to the
chain. We show that local measurements are suitable to estimate small values of
the coupling and that a Bayesian strategy may be successfully exploited to
achieve optimal precision. For larger values of the coupling Bayesian local
strategies do not lead to a consistent estimate. In this regime, Feynman probes
may be exploited to build a consistent Bayesian estimator that saturates the
Cram\'er-Rao bound, thus providing an effective characterization of the chain.
Finally, we show that ultimate bounds to precision, i.e. saturation of the
quantum Cram\'er-Rao bound, may be achieved by a two-step scheme employing
Feynman probes followed by local measurements.",1607.06124v2
2016-07-28,Entanglement Entropy of Local Operators in Quantum Lifshitz Theory,"We study the growth of entanglement entropy(EE) of local operator excitation
in the quantum Lifshitz model which has dynamic exponent z = 2. Specifically,
we act a local vertex operator on the groundstate at a distance $l$ to the
entanglement cut and calculate the EE as a function of time for the state's
subsequent time evolution. We find that the excess EE compared with the
groundstate is a monotonically increasing function which is vanishingly small
before the onset at $t \sim l^2$ and eventually saturates to a constant
proportional to the scaling dimension of the vertex operator. The
quasi-particle picture can interpret the final saturation as the exhaustion of
the quasi-particle pairs, while the diffusive nature of the time scale $t \sim
l^2$ replaces the common causality constraint in CFT calculation. To further
understand this property, we compute the excess EE of a small disk probe far
from the excitation point and find chromatography pattern in EE generated by
quasi-particles of different propagation speeds.",1607.08631v1
2016-07-30,Environmental Instability and Degradation of Single- and Few-Layer WTe2 Nanosheets in Ambient Conditions,"Since the discovery of large, non-saturating magnetoresistance in bulk WTe2
which allows microexfoliation, single- and few-layer WTe2 crystals have
attracted increasing interests. However, as it mentioned in existing studies,
WTe2 flakes appear to degrade in ambient conditions. Here we report
experimental observations of saturating degradation in few-layer WTe2 through
Raman spectroscopy characterization and careful monitoring of the degradation
of single-, bi- and tri-layer (1L, 2L & 3L) WTe2 over long time. Raman peak
intensity decreases during WTe2 degradation and 1L flakes degrade faster than
2L and 3L flakes. The relatively faster degradation in 1L WTe2 could be
attributed to low energy barrier of oxygen reaction with WTe2. We further
investigate the degradation mechanisms of WTe2 using XPS and AES and find that
oxidation of Te and W atoms is the main reason of WTe2 degradation. In
addition, we observe oxidation occurs only in the depth of 0.5nm near the
surface, and the oxidized WTe2 surface could help prevent inner layers from
further degradation.",1608.00097v2
2016-08-11,Modulation of sensory information processing by a neuroglobin in C. elegans,"Sensory receptor neurons match their dynamic range to ecologically relevant
stimulus intensities. How this tuning is achieved is poorly understood in most
receptors. We show that in the C. elegans URX O2 sensing neurons two putative
molecular O2 sensors, a neuroglobin and O2-binding soluble guanylate cyclases,
work antagonistically to sculpt a slowly sigmoidal O2 response curve tuned to
approach saturation when O2 reaches 21%. glb-5 imposes this sigmoidal function
by inhibiting O2-evoked Ca2+ responses in URX when O2 levels fall. Without
GLB-5, the URX response curve approaches saturation at 15% O2. Behaviorally,
GLB-5 signaling broadens the O2 preference of C. elegans while maintaining
strong avoidance of 21% O2. Our computational aerotaxis model suggests that the
relationship between GLB-5-modulated URX responses and reversal behavior is
sufficient to broaden O2-preference. Thus, a neuroglobin can shift neural
information coding leading to a change in perception and altered behavior.",1608.03477v2
2016-08-26,Energy dependence of dissociative $\mathrm{J/}ψ$ photoproduction as a signature of gluon saturation at the LHC,"We have developed a model in which the quantum fluctuations of the proton
structure are characterised by hot spots, whose number grows with decreasing
Bjorken-$x$. Our model reproduces the $F_2(x,Q^2)$ data from HERA at the
relevant scale, as well as the exclusive and dissociative $\mathrm{J/}\psi$
photoproduction data from H1 and ALICE. Our model predicts that for
$W_{\gamma\mathrm{p}} \approx 500$ GeV, the dissociative $\mathrm{J/}\psi$
cross section reaches a maximum and then decreases steeply with energy, which
is in qualitatively good agreement to a recent observation that the
dissociative $\mathrm{J/}\psi$ background in the exclusive $\mathrm{J/}\psi$
sample measured in photoproduction by ALICE decreases as energy increases. Our
prediction provides a clear signature for gluon saturation at LHC energies.",1608.07559v2
2016-08-27,Logic programming: laxness and saturation,"A propositional logic program $P$ may be identified with a $P_fP_f$-coalgebra
on the set of atomic propositions in the program. The corresponding
$C(P_fP_f)$-coalgebra, where $C(P_fP_f)$ is the cofree comonad on $P_fP_f$,
describes derivations by resolution. That correspondence has been developed to
model first-order programs in two ways, with lax semantics and saturated
semantics, based on locally ordered categories and right Kan extensions
respectively. We unify the two approaches, exhibiting them as complementary
rather than competing, reflecting the theorem-proving and proof-search aspects
of logic programming. While maintaining that unity, we further refine lax
semantics to give finitary models of logic programs with existential variables,
and to develop a precise semantic relationship between variables in logic
programming and worlds in local state.",1608.07708v2
2016-09-01,Rigidity of Free Boundary Surfaces in Compact 3-Manifolds with Strictly Convex Boundary,"In this paper we obtain an analogue of Toponogov theorem in dimension 3 for
compact manifolds $M^3$ with nonnegative Ricci curvature and strictly convex
boundary $\partial M$. Here we obtain a sharp upper bound for the length
$L(\partial\Sigma)$ of the boundary $\partial\Sigma$ of a free boundary minimal
surface $\Sigma^2$ in $M^3$ in terms of the genus of $\Sigma$ and the number of
connected components of $\partial\Sigma$, assuming $\Sigma$ has index one.
After, under a natural hypothesis on the geometry of $M$ along $\partial M$, we
prove that if $L(\partial\Sigma)$ saturates the respective upper bound, then
$M^3$ is isometric to the Euclidean 3-ball and $\Sigma^2$ is isometric to the
Euclidean disk. In particular, we get a sharp upper bound for the area of
$\Sigma$, when $M^3$ is a strictly convex body in $\mathbb R^3$, which is
saturated only on the Euclidean 3-balls (by the Euclidean disks). We also
consider similar results for stationary stable surfaces.",1609.00366v2
2016-09-07,Role of acoustic phonons in frequency dependent thermal conductivity of graphene,"We study the effect of the electron-phonon interaction on the finite
frequency dependent electronic thermal conductivity of two dimensional
graphene. We calculate it for various acoustic phonons present in graphene and
characterized by different dispersion relations using the memory function
approach. It is found that the thermal conductivity $\kappa(T)$ in the zero
frequency limit follows different power law for the longitudinal/transverse and
the flexural acoustic phonons. For the longitudinal/transverse phonons,
$\kappa(T) \sim T^{-1}$ at the low temperature and saturates at the high
temperature. These signatures are qualitatively agree with the results
predicted by the Boltzmann equation. Similarly, for the flexural phonons, we
find that $\kappa(T)$ shows $T^{1/2}$ law at the low temperature and then
saturates at the high temperature. In the finite frequency regime, we observe
that the real part of the thermal conductivity, $\text{Re}[\kappa(\omega,T)]$
follows $\omega^{-2}$ behavior at the low frequency and becomes frequency
independent at the high frequency.",1609.01941v1
2016-09-13,Nonlinear amplitude dynamics in flagellar beating,"The physical basis of flagellar and ciliary beating is a major problem in
biology which is still far from completely understood. The fundamental
cytoskeleton structure of cilia and flagella is the axoneme, a cylindrical
array of microtubule doublets connected by passive crosslinkers and dynein
motor proteins. The complex interplay of these elements leads to the generation
of self-organized bending waves. Although many mathematical models have been
proposed to understand this process, few attempts have been made to assess the
role of dyneins on the nonlinear nature of the axoneme. Here, we investigate
the nonlinear dynamics of flagella by considering an axonemal sliding control
mechanism for dynein activity. This approach unveils the nonlinear selection of
the oscillation amplitudes, which are typically either missed or prescribed in
mathematical models. The explicit set of nonlinear equations are derived and
solved numerically. Our analysis reveals the spatiotemporal dynamics of dynein
populations and flagellum shape for different regimes of motor activity, medium
viscosity and flagellum elasticity. Unstable modes saturate via the coupling of
dynein kinetics and flagellum shape without the need of invoking a nonlinear
axonemal response. Hence, our work reveals a novel mechanism for the saturation
of unstable modes in axonemal beating.",1609.03837v2
2016-09-16,CMOS-Memristor Dendrite Threshold Circuits,"Non-linear neuron models overcomes the limitations of linear binary models of
neurons that have the inability to compute linearly non-separable functions
such as XOR. While several biologically plausible models based on dendrite
thresholds are reported in the previous studies, the hardware implementation of
such non-linear neuron models remain as an open problem. In this paper, we
propose a circuit design for implementing logical dendrite non-linearity
response of dendrite spike and saturation types. The proposed dendrite cells
are used to build XOR circuit and intensity detection circuit that consists of
different combinations of dendrite cells with saturating and spiking responses.
The dendrite cells are designed using a set of memristors, Zener diodes, and
CMOS NOT gates. The circuits are designed, analyzed and verified on circuit
boards.",1609.04921v1
2016-09-25,Pro-aperiodic monoids via saturated models,"We apply Stone duality and model theory to study the structure theory of free
pro-aperiodic monoids. Stone duality implies that elements of the free
pro-aperiodic monoid may be viewed as elementary equivalence classes of
pseudofinite words. Model theory provides us with saturated words in each such
class, i.e., words in which all possible factorizations are realized. We give
several applications of this new approach, including a solution to the word
problem for $\omega$-terms that avoids using McCammond's normal forms, as well
as new proofs and extensions of other structural results concerning free
pro-aperiodic monoids.",1609.07736v2
2016-09-29,Broadband frequency conversion via adiabatically tapered $χ^{(2)}$ waveguide in photonic integrated circuits,"We propose to use the integrated aluminum nitride waveguide with engineered
width variation to achieve optical frequency conversion based on $\chi^{(2)}$
nonlinear effect on a photonic chip. We show that in an adiabatically tapered
waveguide, the frequency conversion has a much broader bandwidth and the
efficiency within the bandwidth is almost constant, which is favorable for
short pulses. We demonstrate both analytically and numerically an ""area law""
for the frequency conversion, i.e. the product of bandwidth and efficiency is
conserved as long as peak conversion efficiency does not saturate. The
adiabatic structure shows higher saturation thresholds in pump power or
interaction length, outperforming the conventional uniform waveguide design.
With our approach, high-efficiency and wavefront-keeping conversion for short
pulses is possible on a photonic chip, which will surely find applications for
scalable on-chip information processing.",1609.09221v1
2016-10-02,Alkali doping of graphene: the crucial role of high temperature annealing,"The doping efficiency of lithium deposited at cryogenic temperatures on
epitaxial and CVD monolayer graphene has been investigated under ultra-high
vacuum conditions. Change of charge carrier density was monitored by gate
voltage shift of the Dirac point and by Hall measurements, in low and high
doping regimes. It was found that pre-annealing the graphene greatly enhanced
the maximum levels of doping that could be achieved: doping saturated at
$\Delta n = 2\times 10^{13}$ e$^-$/cm$^2$ without annealing, independent of
sample type or previous processing; after a 900 K anneal, the saturated doping
rose one order of magnitude to $\Delta n = 2\times 10^{14}$ e$^-$/cm$^2$.",1610.00301v1
2016-10-06,Correlations between critical parameters and bulk properties of nuclear matter,"The present work starts by providing a clear identification of correlations
between critical parameters ($T_c$, $P_c$, $\rho_c$) and bulk quantities at
zero temperature of relativistic mean-field models (RMF) presenting third and
fourth order self-interactions in the scalar field $\sigma$. Motivated by the
nonrelativistic version of this RMF model, we show that effective nucleon mass
($M^*$) and incompressibility ($K_o$), at the saturation density, are
correlated with $T_c$, $P_c$, and $\rho_c$, as well as, binding energy and
saturation density itself. We verify agreement of results with previous
theoretical ones regarding different hadronic models. Concerning recent
experimental data of the symmetric nuclear matter critical parameters, our
study allows a prediction of $T_c$, $P_c$ and $\rho_c$ compatible with such
values, by combining them, through the correlations found, with previous
constraints related to $M^*$ and $K_o$. An improved RMF parametrization, that
better agrees with experimental values for $T_c$, is also indicated.",1610.01974v1
2016-10-14,Modelling large-deforming fluid-saturated porous media using an Eulerian incremental formulation,"The paper deals with modelling fluid saturated porous media subject to large
deformation. An Eulerian incremental formulation is derived using the problem
imposed in the spatial configuration in terms of the equilibrium equation and
the mass conservation. Perturbation of the hyperelastic porous medium is
described by the Biot model which involves poroelastic coefficients and the
permeability governing the Darcy flow. Using the material derivative with
respect to a convection velocity field we obtain the rate formulation which
allows for linearization of the residuum function. For a given time
discretization with backward finite difference approximation of the time
derivatives, two incremental problems are obtained which constitute the
predictor and corrector steps of the implicit time-integration scheme.
Conforming mixed finite element approximation in space is used. Validation of
the numerical model implemented in the SfePy code is reported for an isotropic
medium with a hyperelastic solid phase. The proposed linearization scheme is
motivated by the two-scale homogenization which will provide the local material
poroelastic coefficients involved in the incremental formulation.",1610.05103v2
2016-10-17,Drell-Yan production at forward rapidities: a hybrid factorization approach,"We discuss the Drell-Yan production of dileptons at high energies in the
forward rapidity region of proton-proton collisions in a hybrid high-energy
approach. This approach uses unintegrated gluon distributions in one proton and
collinear quark/antiquark distributions in the second proton.
  We compute various distributions for the case of low-mass dilepton production
and compare to the LHCb and ATLAS experimental data on dilepton mass
distributions. In distinction to dipole approaches, we include four Drell-Yan
structure functions as well as cuts at the level of lepton kinematics. The
impact of the interference structure functions is rather small for typical
experimental cuts. We find that both side contributions ($g q/\bar q$ and
$q/\bar q g$) have to be included even for the LHCb rapidity coverage which is
in contradiction with what is usually done in the dipole approach. We present
results for different unintegrated gluon distributions from the literature.
Some of them include saturation effects, but we see no clear hints of
saturation even at small $M_{ll}$.",1610.05123v1
2016-10-21,Scale-Dependent Pedotransfer Functions Reliability for Estimating Saturated Hydraulic Conductivity,"Saturated hydraulic conductivity Ksat is a fundamental characteristic in
modeling flow and contaminant transport in soils and sediments. Therefore, many
models have been developed to estimate Ksat from easily measureable parameters,
such as textural properties, bulk density, etc. However, Ksat is not only
affected by textural and structural characteristics, but also by scale e.g.,
internal diameter and height. Using the UNSODA database and the contrast
pattern aided regression (CPXR) method, we recently developed scale-dependent
pedotransfer functions to estimate Ksat from textural data, bulk density, and
sample dimensions. The main objectives of this study were evaluating the
proposed pedotransfer functions using a larger database, and comparing them
with seven other models. For this purpose, we selected more than nineteen
thousands soil samples from all around the United States. Results showed that
the scale-dependent pedotransfer functions estimated Ksat more accurately than
seven other models frequently used in the literature.",1610.06958v1
2016-10-28,Anharmonic particles: suppressing van der Waals forces by an external field,"We study the classical thermal component of Casimir, or van der Waals, forces
between point particles with highly anharmonic dipole Hamiltonians when they
are subjected to an external electric field. Using a model for which the
individual dipole moments saturate in a strong field (a model that mimics the
charges in a neutral, perfectly conducting sphere), we find that the resulting
Casimir force depends strongly on the strength of the field, as demonstrated by
analytical results. For a certain angle between external field and center to
center axis, the fluctuation force can be tuned and suppressed to arbitrarily
small values. We compare the forces between these anharmonic particles to those
between harmonic ones, and also provide a simple formula for asymptotically
large external fields, which we expect to be generally valid for the case of
saturating dipole moments.",1610.09192v1
2016-10-31,Homogeneous Atomic Fermi Gases,"We report on the creation of homogeneous Fermi gases of ultracold atoms in a
uniform potential. In the momentum distribution of a spin-polarized gas, we
observe the emergence of the Fermi surface and the saturated occupation of one
particle per momentum state. This directly confirms Pauli blocking in momentum
space. For the spin-balanced unitary Fermi gas, we observe spatially uniform
pair condensates. For thermodynamic measurements, we introduce a hybrid
potential that is harmonic in one dimension and uniform in the other two. The
spatially resolved compressibility reveals the superfluid transition in a
spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong
attraction in the polaronic regime of a partially polarized Fermi gas.",1610.10100v1
2016-11-01,Phenomenology of hard diffraction at high energies,"We present some of the topics covered in two lectures under the same title
that were given at the ""Summer School on High Energy Physics at the LHC: New
trends in HEP"" in Natal, Brazil. In this contribution we give a brief review on
the application of perturbative QCD to the hard diffractive processes. Some
examples of phenomenology for the diffractive production of $W/Z$, heavy
$Q\bar{Q}$ and quarkonium in hadron-hadron reactions are presented. It is also
discussed the exclusive diffractive processes in $ep$ interactions. They are in
general driven by the gluon content of proton which is strongly subject to
parton saturation effects in the very high energy limit. These saturation
effects are well described within the color dipole formalism. We present some
examples of corresponding phenomenology as the elastic vector meson production
and the DVCS relying on the color dipole approach.",1611.00378v2
2016-12-09,Analyzing the Synergy between Broadcast Polling and Piggybacking in WiMAX Networks,"In this work we present a model for analyzing the combined use of broadcast
polling and piggybacking in Worldwide Interoperability for Microwave Access
(WiMAX) networks. For an accurate analysis of piggybacking, the model focuses
on the realistic case of limited up-link bandwidth and non-trivial queueing
capability at the subscriber stations. We first model the activity of a
subscriber station using a Markov chain and its queue as an M/G/1 system with
vacations in order to facilitate the analysis of the piggyback mechanism. We
then derive a set of fixed point equations that describe not only the
contention process at the network level but also bandwidth allocation to
contending and piggybacked requests. Our model uses a minimal set of
assumptions and is generic in the sense that it is customizable through a set
of parameters. It can also reproduce the system performance in both saturated
and non-saturated conditions. After validating our analysis through extensive
simulations, we shed light on the aspects of the synergy between broadcast
polling and piggybacking and unveil the pros and cons of using the latter.",1612.03042v1
2016-12-23,Note on the saturation of the norm inequalities between diamond and nuclear norm,"The diamond norm plays an important role in quantum information and operator
theory. Recently, it has also been proposed as a regularizer for low-rank
matrix recovery. The norm constants that bound the diamond norm in terms of the
nuclear norm (also known as trace norm) are explicitly known. This note
provides a simple characterization of all operators saturating the upper and
the lower bound.",1612.07931v3
2016-12-29,Effects of non-physiological blood pressure artefacts on measures of cerebral autoregulation,"Cerebral autoregulation refers to regulation mechanisms that aim to maintain
cerebral blood flow approximately constant. It is often assessed by
autoregulation index (ARI), which uses arterial blood pressure and cerebral
blood flow velocity time series to produce a ten-scale index of autoregulation
performance (0 denoting the absence of and 9 the strongest autoregulation).
Unfortunately, data are rarely free from various artefacts. Here, we consider
four of the most common non-physiological blood pressure artefacts (saturation,
square wave, reduced pulse pressure and impulse) and study their effects on ARI
for a range of different artefact sizes. We show that a sufficiently large
saturation and square wave always result in ARI reaching the maximum value of
9. The pulse pressure reduction and impulse artefact lead to a more diverse
behaviour. Finally, we characterised the critical size of artefacts, defined as
the minimum artefact size that, on average, leads to a 10\% deviation of ARI",1612.09486v1
2017-01-04,Parton saturation scaling function for exclusive production of vector mesons and Deeply Virtual Compton Scattering,"We provide a universal expression of cross sections for the exclusive vector
meson production and Deeply Virtual Compton Scattering (DVCS) in photon-proton
and photon-nucleus interactions based on the geometric scaling phenomenon. The
theoretical parameterization based on the scaling property depends only on the
single variable $\tau_A = Q^2/Q_{\mathrm{sat}}^2$, where the saturation scale,
$Q_{\mathrm{sat}}$, drives the energy dependence and the corresponding nuclear
effects. This phenomenological result describes all available data from
DESY-HERA for $\rho,\,\phi,\,J/\psi$ production and DVCS measurements. A
discussion on the size of nuclear shadowing corrections on photon-nucleus
interaction is also done.",1701.01141v3
2017-01-25,NS saturated and $Δ_1$-definable,"We show that under the assumption of the existence of the canonical inner
model with one Woodin cardinal $M_1$, there is a model of $\ZFC$ in which $\NS$
is $\aleph_2$-saturated and $\Delta_1$-definable with $\omega_1$ as a parameter
which answers a question of Sy-David Friedman and Liuzhen Wu. We also show that
starting from an arbitrary universe with a Woodin cardinal, there is a model
with $\NS$ saturated and $\Delta_1$-definable with a ladder system $\vec{C}$
and a full Suslin tree $T$ as parameters. Both results rely on a new coding
technique whose presentation is the main goal of this article.",1701.07230v5
2017-01-30,Probing Nuclear PDF and Gluon Saturation At The LHC with Forward Direct Photons,"In relativistic nuclear collisions some of the important aspects to be
addressed are the effects of the nuclear PDF and the gluon saturation. In the
LHC the best way to address these questions is by means of pA collisions and in
particular through the measurement of direct photon production in the forward
direction. In order to achieve this measurement a new forward calorimeter
(FoCal) is proposed as an upgrade to the ALICE experiment. The proposed
detector will cover the range 3.5 < $\eta$ < 5, probing the gluon distributions
at x$\sim$10$^{-5}$ and Q$\sim p_{\rm T}$ > 4 GeV. We will discuss performance
studies and demonstrate that extremely high-granularity calorimetry is required
for such measurement. We will also present a few results from R\&D for this
project.",1701.08677v1
2017-01-31,NIMROD Modeling of Quiescent H-mode: Reconstruction Considerations and Saturation Mechanism,"The extended-MHD NIMROD code [C.R. Sovinec and J.R. King, J. Comput. Phys.
229, 5803 (2010)] models broadband-MHD activity from a reconstruction of a
quiescent H-mode shot on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614
(2002)]. Computations with the reconstructed toroidal and poloidal ion flows
exhibit low-n perturbations (n=1-5) that grow and saturate into a
turbulent-like MHD state. The workflow used to project the reconstructed state
onto the NIMROD basis functions re-solves the Grad-Shafranov equation and
extrapolates profiles to include scrape-off-layer currents. Evaluation of the
transport from the turbulent-like MHD state leads to a relaxation of the
density and temperature profiles.",1702.00050v1
2017-02-07,Calibrating High Intensity Absorption Imaging of Ultracold Atoms,"Absorption imaging of ultracold atoms is the foundation for quantitative
extraction of information from experiments with ultracold atoms. Due to the
limited exposure time available in these systems, the signal-to-noise ratio is
largest for high intensity absorption imaging where the intensity of the
imaging light is on the order of the saturation intensity. In this case, the
absolute value of the intensity of the imaging light enters as an additional
parameter making it more sensitive to systematic errors. Here, we present a
novel and robust technique to determine the imaging intensity in units of the
effective saturation intensity to better than 5%. We do this by measuring the
momentum transferred to the atoms by the imaging light while varying its
intensity. We further utilize the method to quantify the purity of the
polarization of the imaging light and to determine the correct imaging
detuning.",1702.01943v2
2017-02-09,Equilibrium configurations of large nanostructures using the embedded saturated-fragments stochastic density functional theory,"An \emph{ab initio} Langevin dynamics approach is developed based on
stochastic density functional theory (sDFT) within a new \emph{embedded
saturated } \emph{fragment }formalism, applicable to covalently bonded systems.
The forces on the nuclei generated by sDFT contain a random component natural
to Langevin dynamics and its standard deviation is used to estimate the
friction term on each atom by satisfying the fluctuation\textendash dissipation
relation. The overall approach scales linearly with system size even if the
density matrix is not local and is thus applicable to ordered as well as
disordered extended systems. We implement the approach for a series of silicon
nanocrystals (NCs) of varying size with a diameter of up to $3$nm corresponding
to $N_{e}=3000$ electrons and generate a set of configurations that are
distributed canonically at a fixed temperature, ranging from cryogenic to room
temperature. We also analyze the structure properties of the NCs and discuss
the reconstruction of the surface geometry.",1702.02714v2
2017-01-30,Characterization of gas diffusion electrodes for metal-air batteries,"Gas diffusion electrodes are commonly used in high energy density metal-air
batteries for the supply of oxygen. Hydrophobic binder materials ensure the
coexistence of gas and liquid phase in the pore network. The phase distribution
has a strong influence on transport processes and electrochemical reactions. In
this article we present 2D and 3D Rothman-Keller type multiphase
Lattice-Boltzmann models which take into account the heterogeneous wetting
behavior of gas diffusion electrodes. The simulations are performed on FIB-SEM
3D reconstructions of an Ag model electrode for predefined saturation of the
pore space with the liquid phase. The resulting pressure-saturation
characteristics and transport correlations are important input parameters for
modeling approaches on the continuum scale and allow for an efficient
development of improved gas diffusion electrodes.",1702.04670v1
2017-02-16,A comparative study of fluid-particle coupling methods for fully resolved lattice Boltzmann simulations,"The direct numerical simulation of particulate systems offers a unique
approach to study the dynamics of fluid-solid suspensions by fully resolving
the submerged particles and without introducing empirical models. For the
lattice Boltzmann method, different variants exist to incorporate the
fluid-particle interaction into the simulation. This paper provides a detailed
and systematic comparison of two different methods, namely the momentum
exchange method and the partially saturated cells method by Noble and
Torczynski. Three subvariants of each method are used in the benchmark scenario
of a single heavy sphere settling in ambient fluid to study their
characteristics and accuracy for particle Reynolds numbers from 185 up to 365.
The sphere must be resolved with at least 24 computational cells per diameter
to achieve velocity errors below 5%. The momentum exchange method is found to
be more accurate in predicting the streamwise velocity component whereas the
partially saturated cells method is more accurate in the spanwise components.
The study reveals that the resolution should be chosen with respect to the
coupling dynamics, and not only based on the flow properties, to avoid large
errors in the fluid-particle interaction.",1702.04910v1
2017-03-02,Rigidity of volume-minimizing hypersurfaces in Riemannian 5-manifolds,"In this paper we generalize the main result of [4] for manifolds that are not
necessarily Einstein. In fact, we obtain an upper bound for the volume of a
locally volume-minimizing closed hypersurface $\Sigma$ of a Riemannian
5-manifold $M$ with scalar curvature bounded from below by a positive constant
in terms of the total traceless Ricci curvature of $\Sigma$. Furthermore, if
$\Sigma$ saturates the respective upper bound and $M$ has nonnegative Ricci
curvature, then $\Sigma$ is isometric to $\mathbb{S}^4$ up to scaling and $M$
splits in a neighborhood of $\Sigma$. Also, we obtain a rigidity result for the
Riemannian cover of $M$ when $\Sigma$ minimizes the volume in its homotopy
class and saturates the upper bound.",1703.00930v2
2017-03-13,C-SHORe: Higher-Order Verification via Collapsible Pushdown System Saturation,"Higher-order recursion schemes (HORS) have received much attention as a
useful abstraction of higher-order functional programs with a number of new
verification techniques employing HORS model-checking as their centrepiece. We
give an account of the C-SHORe tool, which contributed to the ongoing quest for
a truly scalable model-checker for HORS by offering a different, automata
theoretic perspective. C-SHORe implements the first practical model-checking
algorithm that acts on a generalisation of pushdown automata equi-expressive
with HORS called collapsible pushdown systems (CPDS). At its core is a
backwards saturation algorithm for CPDS. Additionally, it is able to use
information gathered from an approximate forward reachability analysis to guide
its backward search. Moreover, it uses an algorithm that prunes the CPDS prior
to model-checking and a method for extracting counter-examples in negative
instances. We provide an up-to-date comparison of C-SHORe with the
state-of-the-art verification tools for HORS. The tool and additional material
are available from http://cshore.cs.rhul.ac.uk.",1703.04429v2
2017-03-16,"Optical Thickness, Spin Temperature, and Correction Factor for Density of the Galactic HI Gas","A method to determine the spin temperature of the local (Vlsr=0 km/s) HI gas
using saturated brightness temperature of the 21-cm line in the radial-velocity
degenerate regions (VDR) is presented. The spin temperatures is determined to
be Ts= 146.2 +/- 16.1 K by measuring saturated brightness in the VDR toward the
Galactic Center, 146.8 +/- 10.7 K by chi^2 fitting of expected brightness
distribution to observation around the VDR, and 144.4 +/- 6.8 K toward the
local arm. Assuming Ts=146 K, a correction factor Gamma for the HI density,
defined by the ratio of the true HI density for finite optical thickness to
that calculated by assuming optically thin HI, was obtained to be Gamma~1.2
(optical depth tau~0.3) in the local HI gas, ~1.8 (~1.3) toward the arm and
anti-center, and as high as ~3.6 (~2.7) in the Galactic Center direction. It is
suggested that the HI density and mass in the local arm could be ~2 times, and
that in the inner Galaxy ~3.6 times, greater than the currently estimated
values.",1703.05565v1
2017-03-21,Reconstructing the topology of the elementary self-embedding monoids of countable saturated structures,"Every transformation monoid comes equipped with a canonical topology-the
topology of pointwise convergence. For some structures, the topology of the
endomorphism monoid can be reconstructed from its underlying abstract monoid.
This phenomenon is called automatic homeomorphicity.
  In this paper we show that whenever the automorphism group of a countable
saturated structure has automatic homeomorphicity and a trivial center, then
the monoid of elementary self-embeddings has automatic homeomorphicity, too.
  As a second result we strengthen a result by Lascar by showing that whenever
$\mathbf{A}$ is a countable $\aleph_0$-categorical $G$-finite structure whose
automorphism group has a trivial center and if $\mathbf{B}$ is any other
countable structure, then every isomorphism between the monoids of elementary
self-embeddings is a homeomorphism.",1703.07429v1
2017-04-02,J/$ψ$ production as a function of charged-particle pseudorapidity density in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV,"We report measurements of the inclusive J/$\psi$ yield and average transverse
momentum as a function of charged-particle pseudorapidity density ${\rm
d}N_{\rm ch}/{\rm d}\eta$ in p-Pb collisions at $\sqrt{s_{\rm NN}}= 5.02$ TeV
with ALICE at the LHC. The observables are normalised to their corresponding
averages in non-single diffractive events. An increase of the normalised
J/$\psi$ yield with normalised ${\rm d}N_{\rm ch}/{\rm d}\eta$, measured at
mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward
rapidity, a saturation of the relative yield is observed for high
charged-particle multiplicities. The normalised average transverse momentum at
forward and backward rapidities increases with multiplicity at low
multiplicities and saturates beyond moderate multiplicities. In addition, the
forward-to-backward nuclear modification factor ratio is also reported, showing
an increasing suppression of J/$\psi$ production at forward rapidity with
respect to backward rapidity for increasing charged-particle multiplicity.",1704.00274v2
2017-04-10,A Representation of Weyl-Heisenberg Lie Algebra in the Quaternionic Setting,"Using a left multiplication defined on a right quaternionic Hilbert space,
linear self-adjoint momentum operators on a right quaternionic Hilbert space
are defined in complete analogy with their complex counterpart. With the aid of
the so-obtained position and momentum operators, we study the Heisenberg
uncertainty principle on the whole set of quaternions and on a quaternionic
slice, namely on a copy of the complex plane inside the quaternions. For the
quaternionic harmonic oscillator, the uncertainty relation is shown to saturate
on a neighborhood of the origin in the case we consider the whole set of
quaternions, while it is saturated on the whole slice in the case we take the
slice-wise approach. In analogy with the complex Weyl-Heisenberg Lie algebra,
Lie algebraic structures are developed for the quaternionic case. Finally, we
introduce a quaternionic displacement operator which is square integrable,
irreducible and unitary, and we study its properties.",1704.02946v2
2017-04-13,Poincaré series of Lie lattices and representation zeta functions of arithmetic groups,"We compute explicit formulae for Dirichlet generating functions enumerating
finite-dimensional irreducible complex representations of potent and saturable
principal congruence subgroups of $\mathrm{SL}_4^m(\mathfrak{o})$
($m\in\mathbb{N}$) for $\mathfrak{o}$ a compact DVR of characteristic $0$ and
odd residue field characteristic. In doing so we develop a novel method for
computing Poincar\'e series associated with commutator matrices of
$\mathfrak{o}$-Lie lattices with finite abelianization and whose rank-loci
enjoy an additional smoothness property. We give explicit formulae for the
abscissa of convergence of the representation zeta functions of potent and
saturable FAb $p$-adic analytic groups whose associated Lie lattices satisfy
the hypotheses of the aforementioned method. As a by-product of our
computations we find that not all $4\times 4$ traceless matrices over a finite
quotient of $\mathfrak{o}$ admit shadow-preserving lifts, thus disproving that
smooth loci of constant centralizer dimension in $\mathfrak{sl}_4(\mathbb{C})$
ensure presence of shadow-preserving lifts for almost all primes as suggested
in a previous paper by Avni, Klopsch, Onn and Voll.",1704.04165v3
2017-04-16,Superradiant Instability and Backreaction of Massive Vector Fields around Kerr Black Holes,"We study the growth and saturation of the superradiant instability of a
complex, massive vector (Proca) field as it extracts energy and angular
momentum from a spinning black hole, using numerical solutions of the full
Einstein-Proca equations. We concentrate on a rapidly spinning black hole
($a=0.99$) and the dominant $m=1$ azimuthal mode of the Proca field, with real
and imaginary components of the field chosen to yield an axisymmetric
stress-energy tensor and, hence, spacetime. We find that in excess of $9\%$ of
the black hole's mass can be transferred into the field. In all cases studied,
the superradiant instability smoothly saturates when the black hole's horizon
frequency decreases to match the frequency of the Proca cloud that
spontaneously forms around the black hole.",1704.04791v2
2017-04-21,Imprint of Nucleon Radius on the Slowly Rotating Neutron Star Properties,"We have studied the effect of free space nucleon radius on the nuclear matter
and slowly rotating neutron star properties within a relativistic mean field
model with the inclusion of omega-rho mixing nonlinear term. We use the same
density dependent radius as in our previous work. However, in the present work
we utilize the parameter sets with more proper symmetric nuclear matter (SNM)
predictions for a number of different nucleon radii. To this end, the isoscalar
parameters in each parameter set and the cutoff parameter $\beta$ are adjusted
by fitting the corresponding SNM properties at sub-saturation density to the
prediction of IUFSU parameter set. We have obtained that the assumption of
composite nucleons with free space radius $r \le 0.83$ fm is still compatible
with the currently acceptable nuclear matter (NM) properties beyond the
saturation density. We have also found that the effect of free space nucleon
radius could be imprinted in the radius, moment of inertia, and crust
properties of the slowly rotating neutron star.",1704.06545v1
2017-04-21,Trapping in bottlenecks: interplay between microscopic dynamics and large scale effects,"We investigate the appearance of trapping states in pedestrian flows through
bottlenecks as a result of the interplay between the geometry of the system and
the microscopic stochastic dynamics. We model the flow trough a bottleneck via
a Zero Range Process on a one dimensional periodic lattice. Particle are
removed from the lattice sites with rates proportional to the local occupation
numbers. The bottleneck is modelled by a particular site of the lattice where
the updating rate saturates to a constant value as soon as the local occupation
number exceeds a fixed threshold. We show that, for any finite value of such
threshold, the stationary particle current saturates to the limiting bottleneck
rate when the total particle density in the system exceeds the bottleneck rate
itself.",1704.06592v1
2017-04-25,"Universality of Confluent, Self-Loop Deterministic Partially Ordered NFAs is Hard","An automaton is partially ordered if the only cycles in its transition
diagram are self-loops. The expressivity of partially ordered NFAs (poNFAs) can
be characterized by the Straubing-Th\'erien hierarchy. Level 3/2 is recognized
by poNFAs, level 1 by confluent, self-loop deterministic poNFAs as well as by
confluent poDFAs, and level 1/2 by saturated poNFAs. We study the universality
problem for confluent, self-loop deterministic poNFAs. It asks whether an
automaton accepts all words over its alphabet. Universality for both NFAs and
poNFAs is a PSpace-complete problem. For confluent, self-loop deterministic
poNFAs, the complexity drops to coNP-complete if the alphabet is fixed but is
open if the alphabet may grow. We solve this problem by showing that it is
PSpace-complete if the alphabet may grow polynomially. Consequently, our result
provides a lower-bound complexity for some other problems, including inclusion,
equivalence, and $k$-piecewise testability. Since universality for saturated
poNFAs is easy, confluent, self-loop deterministic poNFAs are the simplest and
natural kind of NFAs characterizing a well-known class of languages, for which
deciding universality is as difficult as for general NFAs.",1704.07860v1
2017-04-28,Delayed feedback control of self-mobile cavity solitons in a wide-aperture laser with a saturable absorber,"We investigate the spatiotemporal dynamics of cavity solitons in a broad area
vertical-cavity surface-emitting laser with saturable absorption subjected to
time-delayed optical feedback. Using a combination of analytical, numerical and
path continuation methods we analyze the bifurcation structure of stationary
and moving cavity solitons and identify two different types of traveling
localized solutions, corresponding to slow and fast motion. We show that the
delay impacts both stationary and moving solutions either causing drifting and
wiggling dynamics of initially stationary cavity solitons or leading to
stabilization of intrinsically moving solutions. Finally, we demonstrate that
the fast cavity solitons can be associated with a lateral mode-locking regime
in a broad-area laser with a single longitudinal mode.",1704.08869v1
2017-05-05,Bifurcation structure of cavity soliton dynamics in a VCSEL with saturable absorber and time-delayed feedback,"We consider a wide-aperture surface-emitting laser with a saturable absorber
section subjected to time-delayed feedback. We adopt the mean-field approach
assuming a single longitudinal mode operation of the solitary VCSEL. We
investigate cavity soliton dynamics under the effect of time- delayed feedback
in a self-imaging configuration where diffraction in the external cavity is
negligible. Using bifurcation analysis, direct numerical simulations and
numerical path continuation methods, we identify the possible bifurcations and
map them in a plane of feedback parameters. We show that for both the
homogeneous and localized stationary lasing solutions in one spatial dimension
the time-delayed feedback induces complex spatiotemporal dynamics, in
particular a period doubling route to chaos, quasiperiodic oscillations and
multistability of the stationary solutions.",1705.02250v1
2017-05-09,Mechanisms of near-surface structural evolution in nanocrystalline materials during sliding contact,"The wear-driven structural evolution of nanocrystalline Cu was simulated with
molecular dynamics under constant normal loads, followed by a quantitative
analysis. While the microstructure far away from the sliding contact remains
unchanged, grain growth accompanied by partial dislocations and twin formation
was observed near the contact surface, with more rapid coarsening promoted by
higher applied normal loads. The structural evolution continues with increasing
number of sliding cycles and eventually saturates to a stable distinct layer of
coarsened grains, separated from the finer matrix by a steep gradient in grain
size. The coarsening process is balanced by the rate of material removal when
the normal load is high enough. The observed structural evolution leads to an
increase in hardness and decrease in friction coefficient, which also saturate
after a number of sliding cycles. This work provides important mechanistic
understanding of nanocrystalline wear, while also introducing a methodology for
atomistic simulations of cyclic wear damage under constant applied normal
loads.",1705.03132v2
2017-05-10,Optimal measurements for simultaneous quantum estimation of multiple phases,"A quantum theory of multiphase estimation is crucial for quantum-enhanced
sensing and imaging and may link quantum metrology to more complex quantum
computation and communication protocols. In this letter we tackle one of the
key difficulties of multiphase estimation: obtaining a measurement which
saturates the fundamental sensitivity bounds. We derive necessary and
sufficient conditions for projective measurements acting on pure states to
saturate the maximal theoretical bound on precision given by the quantum Fisher
information matrix. We apply our theory to the specific example of
interferometric phase estimation using photon number measurements, a convenient
choice in the laboratory. Our results thus introduce concepts and methods
relevant to the future theoretical and experimental development of
multiparameter estimation.",1705.03687v1
2017-05-17,"Parallel-in-Space-and-Time Simulation of the Three-Dimensional, Unsteady Navier-Stokes Equations for Incompressible Flow","In this paper we combine the Parareal parallel-in-time method together with
spatial parallelization and investigate this space-time parallel scheme by
means of solving the three-dimensional incompressible Navier-Stokes equations.
Parallelization of time stepping provides a new direction of parallelization
and allows to employ additional cores to further speed up simulations after
spatial parallelization has saturated. We report on numerical experiments
performed on a Cray XE6, simulating a driven cavity flow with and without
obstacles. Distributed memory parallelization is used in both space and time,
featuring up to 2,048 cores in total. It is confirmed that the
space-time-parallel method can provide speedup beyond the saturation of the
spatial parallelization.",1705.06149v1
2017-05-18,Generation of forerunner electron beam during interaction of ion beam pulse with plasma,"The long-time evolution of the two-stream instability of a cold ion beam
pulse propagating though the background plasma is investigated using a
large-scale one-dimensional electrostatic kinetic simulation. The three stages
of the instability are identified and investigated in detail. After the initial
linear growth and saturation by the electron trapping, a portion of the
initially trapped electrons becomes detrapped and moves ahead of the ion beam
pulse forming a {forerunner} electron beam, which causes a secondary two-stream
instability that preheats the upstream plasma electrons. Consequently, the
self-consistent nonlinear-driven turbulent state is set up at the head of the
ion beam pulse with the saturated plasma wave sustained by the influx of the
cold electrons from the upstream of the beam that lasts until the final stage
when the beam ions become trapped by the plasma wave. The beam ion trapping
leads to the nonlinear heating of the beam ions that eventually extinguishes
the instability.",1705.06806v1
2017-05-22,Accretion Dynamics on Wet Granular Materials,"Wet granular aggregates are common precursors of construction materials,
food, and health care products. The physical mechanisms involved in the mixing
of dry grains with a wet substrate are not well understood and difficult to
control. Here, we study experimentally the accretion of dry grains on a wet
granular substrate by measuring the growth dynamics of the wet aggregate. We
show that this aggregate is fully saturated and its cohesion is ensured by the
capillary depression at the air-liquid interface. The growth dynamics is
controlled by the liquid fraction at the surface of the aggregate and exhibits
two regimes. In the viscous regime, the growth dynamics is limited by the
capillary-driven flow of liquid through the granular packing to the surface of
the aggregate. In the capture regime, the capture probability depends on the
availability of the liquid at the saturated interface, which is controlled by
the hydrostatic depression in the material. We propose a model that
rationalizes our observations and captures both dynamics based on the evolution
of the capture probability with the hydrostatic depression.",1705.07783v1
2017-05-23,On Controllable Abundance Of Saturated-input Linear Discrete Systems,"Several theorems on the volume computing of the polyhedron spanned by a
n-dimensional vector set with the finite-interval parameters are presented and
proved firstly, and then are used in the analysis of the controllable regions
of the linear discrete time-invariant systems with saturated inputs. A new
concept and continuous measure on the control ability, control efficiency of
the input variables, and the diversity of the control laws, named as the
controllable abundance, is proposed based on the volume computing of the
regions and is applied to the actuator placing and configuring problems, the
optimizing problems of dynamics and kinematics of the controlled plants, etc..
The numerical experiments show the effectiveness of the new concept and methods
for investigating and optimizing the control ability and efficiency.",1705.08064v2
2017-05-30,Can hail and rain nucleate cloud droplets?,"We present results from moist convection in a mixture of pressurized sulfur
hexa-flouride (liquid and vapor) and helium (gas) to model the wet and dry
components of the earth's atmosphere. To allow for homogeneous nucleation, we
operate the experiment close to critical conditions. We report on the
nucleation of microdroplets in the wake of large cold liquid drops falling
through the supersaturated atmosphere and show that the homogeneous nucleation
is caused by isobaric cooling of the saturated sulfur hexaflouride vapor. Our
results carry over to atmospheric clouds: falling hail and cold rain drops may
enhance the heterogeneous nucleation of microdroplets in their wake under
supersaturated atmospheric conditions. We also observed that under appropriate
conditions settling microdroplets form a rather stable horizontal cloud layer,
which separates regions of super and sub critical saturation.",1705.10501v1
2017-06-02,Dynamics and instabilities of Lasing Light Bullets in Passively Mode-Locked Semiconductor Lasers,"Recently, the existence of robust three-dimensional light bullets (LBs) was
predicted theoretically in the output of a laser coupled to a distant saturable
absorber. In this manuscript, we analyze the stability and the range of
existence of these dissipative localized structures and provide guidelines and
realistic parameter sets for their experimental observation. In order to reduce
the complexity of the analysis, we first approximate the three-dimensional
problem by a reduced equation governing the dynamics of the transverse profile.
This effective theory provides an intuitive picture of the LB formation
mechanism. Moreover, it allows us to perform a detailed multi-parameter
bifurcation study and to identify the different mechanisms of instability. It
is found that the LBs experience dominantly either homogeneous oscillation or
symmetry breaking transversal waves radiation. In addition, our analysis
reveals several non-intuitive scaling behaviors as functions of the linewidth
enhancement factors and the saturation parameters. Our results are confirmed by
direct numerical simulations of the full system.",1706.00630v1
2017-06-03,Reduced work function of graphene by metal adatoms,"In this paper, the work function of graphene doped by different metal adatoms
and at different concentrations is investigated. Density functional theory is
used to maximize the reduction of the work function. In general, the work
function drops significantly before reaching saturation. For example in the
case of Cs doping, the work function saturates at 2.05 eV with a modest 8 %
doping. The adsorption of different concentrations on metal adatoms on graphene
is also studied. Our calculations show that the adatoms prefer to relax at
hollow sites. The transfer of electron from metallic dopants to the graphene
for all the studied systems shifts the Fermi energy levels above the
Dirac-point and the doped graphenes become metallic. The value of Fermi energy
shifts depends on the type of metallic dopants and its concentrations. A detail
analysis of the electronic structure in terms of band structure and density of
states, absorption energy, and charge transfer for each adatom-graphene system
is presented.",1706.00913v1
2017-06-16,Fusion systems and localities -- a dictionary,"Linking systems were introduced to provide algebraic models for $p$-completed
classifying spaces of fusion systems. Every linking system over a saturated
fusion system $\mathcal{F}$ corresponds to a group-like structure called a
locality. Given such a locality $\mathcal{L}$, we prove that there is a
one-to-one correspondence between the partial normal subgroups of $\mathcal{L}$
and the normal subsystems of the fusion system $\mathcal{F}$. This is then used
to obtain a kind of dictionary, which makes it possible to translate between
various concepts in localities and corresponding concepts in fusion systems. As
a byproduct, we obtain new proofs of many known theorems about fusion systems
and also some new results. For example, we show in this paper that, in any
saturated fusion system, there is a sensible notion of a product of normal
subsystems.",1706.05343v4
2017-06-22,Magneto-resistance oscillations induced by high-intensity terahertz radiation,"We report on observation of pronounced terahertz radiation-induced
magneto-resistivity oscillations in AlGaAs/GaAs two-dimensional electron
systems, the THz analog of the microwave induced resistivity oscillations
(MIRO). Applying high power radiation of a pulsed molecular laser we
demonstrate that MIRO, so far observed at low power only, are not destroyed
even at very high intensities. Experiments with radiation intensity ranging
over five orders of magnitude from $0.1$ W/cm$^2$ to $10^4$ W/cm$^2$ reveal
high-power saturation of the MIRO amplitude, which is well described by an
empirical fit function $I/(1 + I/I_s)^\beta$ with $\beta \sim 1$. The
saturation intensity Is is of the order of tens of W/cm$^2$ and increases by
six times by increasing the radiation frequency from $0.6$ to $1.1$ THz. The
results are discussed in terms of microscopic mechanisms of MIRO and compared
to nonlinear effects observed earlier at significantly lower excitation
frequencies.",1706.07239v1
2017-06-22,A method for rapid determination of oil and water content in geological formations,"A novel method utilizing Fast Neutron Resonance Transmission Radiography is
proposed for rapid, non-destructive and quantitative determination of the
weight fractions of oil and water in cores taken from subterranean or
underwater geological formations. Its ability to distinguish water from oil
stems from the unambiguously-specific energy-dependence of the neutron
cross-sections for the principal elemental constituents. Furthermore, the fluid
weight fractions permit determining core porosity and oil and water
saturations. In this article we show results of experimental determination of
oil and water weight fractions in 10 cm thick samples of Berea Sandstone and
Indiana Limestone formations, followed by calculation of their porosity and
fluid saturations. The technique may ultimately permit rapid, accurate and
non-destructive evaluation of relevant petro-physical properties in thick
intact cores. It is suitable for all types of formations including tight
shales, clays and oil sands.",1706.07689v1
2017-07-02,Rate-Splitting for Max-Min Fair Multigroup Multicast Beamforming in Overloaded Systems,"In this paper, we consider the problem of achieving max-min fairness amongst
multiple co-channel multicast groups through transmit beamforming. We
explicitly focus on overloaded scenarios in which the number of transmitting
antennas is insufficient to neutralize all inter-group interference. Such
scenarios are becoming increasingly relevant in the light of growing
low-latency content delivery demands, and also commonly appear in multibeam
satellite systems. We derive performance limits of classical beamforming
strategies using DoF analysis unveiling their limitations; for example, rates
saturate in overloaded scenarios due to inter-group interference. To tackle
interference, we propose a strategy based on degraded beamforming and
successive interference cancellation. While the degraded strategy resolves the
rate-saturation issue, this comes at a price of sacrificing all spatial
multiplexing gains. This motivates the development of a unifying strategy that
combines the benefits of the two previous strategies. We propose a beamforming
strategy based on rate-splitting (RS) which divides the messages intended to
each group into a degraded part and a designated part, and transmits a
superposition of both degraded and designated beamformed streams. The
superiority of the proposed strategy is demonstrated through DoF analysis.
Finally, we solve the RS beamforming design problem and demonstrate significant
performance gains through simulations.",1707.00304v1
2017-07-05,Robust Multi-Image HDR Reconstruction for the Modulo Camera,"Photographing scenes with high dynamic range (HDR) poses great challenges to
consumer cameras with their limited sensor bit depth. To address this, Zhao et
al. recently proposed a novel sensor concept - the modulo camera - which
captures the least significant bits of the recorded scene instead of going into
saturation. Similar to conventional pipelines, HDR images can be reconstructed
from multiple exposures, but significantly fewer images are needed than with a
typical saturating sensor. While the concept is appealing, we show that the
original reconstruction approach assumes noise-free measurements and quickly
breaks down otherwise. To address this, we propose a novel reconstruction
algorithm that is robust to image noise and produces significantly fewer
artifacts. We theoretically analyze correctness as well as limitations, and
show that our approach significantly outperforms the baseline on real data.",1707.01317v1
2017-07-10,Probing Saturation Physics in the Real Compton Scattering at Ultraperipheral $pPb$ Collisions,"The Real Compton Scattering in ultraperipheral $pPb$ collisions at RHIC and
LHC energies is investigated and predictions for the squared transverse
momentum ($t$) and rapidity ($Y$) distributions are presented. The scattering
amplitude is assumed to be given by the sum of the Reggeon and Pomeron
contributions and the Pomeron one is described by the Color Dipole formalism
taking into account the non - linear (saturation) effects in the QCD dynamics.
We demonstrate that the behaviour of the cross sections at large -- $t$ and/or
$Y$ is dominated by the Pomeron contribution and is strongly affected by the
non -- linear effects present in the QCD dynamics. These results indicate that
a future experimental analysis of this process can be useful to probe the QCD
dynamics at high energies.",1707.02806v2
2017-07-13,Non-integrability and Chaos with Unquenched Flavor,"We study (non-)integrability and the presence of chaos in gravity dual
backgrounds of strongly coupled gauge theories with unquenched flavor,
specifically of the four-dimensional N=2 super Yang-Mills theory and the
three-dimensional ABJM theory. By examining string motion on the geometries
corresponding to backreacted D3/D7 and D2/D6 systems, we show that integrable
theories with quenched flavor become non-integrable when the virtual quark
loops are taken into account. For the string solutions in the backreacted D3/D7
system, we compute the leading Lyapunov exponent which turns out to saturate to
a positive value as the number of flavors increases. The exponent depends very
weakly on the number of flavors when they approach the number of colors. This
suggests that once a particular flavor number in the theory is reached, a
further increase does not lead to more severe chaotic phenomena, implying
certain saturation effects on chaos.",1707.04033v2
2017-07-25,Non-Saturated Throughput Analysis of Coexistence of Wi-Fi and Cellular With Listen-Before-Talk in Unlicensed Spectrum,"This paper analyzes the coexistence performance of Wi-Fi and cellular
networks conditioned on non-saturated traffic in the unlicensed spectrum. Under
the condition, the time-domain behavior of a cellular small-cell base station
(SCBS) with a listen-before-talk (LBT) procedure is modeled as a Markov chain,
and it is combined with a Markov chain which describes the time-domain behavior
of a Wi-Fi access point. Using the proposed model, this study finds the optimal
contention window size of cellular SCBSs in which total throughput of both
networks is maximized while satisfying the required throughput of each network,
under the given traffic densities of both networks. This will serve as a
guideline for cellular operators with respect to performing LBT at cellular
SCBSs according to the changes of traffic volumes of both networks over time.",1707.07843v1
2017-07-26,Ground-state properties of unitary bosons: from clusters to matter,"The properties of cold Bose gases at unitarity have been extensively
investigated in the last few years both theoretically and experimentally. In
this paper we use a family of interactions tuned to two-body unitarity and very
weak three-body binding to demonstrate the universal properties of both
clusters and matter. We determine the universal properties of finite clusters
up to 60 particles and, for the first time, explicitly demonstrate the
saturation of energy and density with particle number and compare with bulk
properties. At saturation in the bulk we determine the energy, density, two-
and three-body contacts and the condensate fraction. We find that uniform
matter is more bound than three-body clusters by nearly two orders of
magnitude, the two-body contact is very large in absolute terms, and yet the
condensate fraction is also very large, greater than 90%. Equilibrium
properties of these systems may be experimentally accessible through rapid
quenching of weakly-interacting boson superfluids.",1707.08546v2
2017-07-27,Nominal vs. actual supersaturation of solutions,"Following the formalism of the Classical Nucleation Theory beyond the dilute
solution approximation, this paper considers a difference between the actual
solute supersaturation (given by the present-to-saturated solute activity
ratio) and the nominal supersaturation (given by the present-to-saturated
solute concentration ratio) due to formation of subcritical transient solute
clusters, called heterophase fluctuations. Based on their distribution
function, we introduce an algebraic equation of supersaturation that couples
the nominal supersaturation of a binary metastable solution with its actual
supersaturation and a function of the specific interface energy and
temperature. The applicability of this approach is validated by comparison to
simulation data [E. Clouet et al., Phys. Rev. B \textbf{69}, 064109 (2004)] on
nucleation of Al$_{3}$Zr and Al$_{3}$Sc in model binary Al alloys.",1707.08777v3
2017-07-27,Delta isobars and nuclear saturation,"We construct a nuclear interaction in chiral effective field theory with
explicit inclusion of the $\Delta$-isobar $\Delta(1232)$ degree of freedom at
all orders up to next-to-next-to-leading order (NNLO). We use pion-nucleon
($\pi N$) low-energy constants (LECs) from a Roy-Steiner analysis of $\pi N$
scattering data, optimize the LECs in the contact potentials up to NNLO to
reproduce low-energy nucleon-nucleon scattering phase shifts, and constrain the
three-nucleon interaction at NNLO to reproduce the binding energy and
point-proton radius of $^{4}$He. For heavier nuclei we use the coupled-cluster
method to compute binding energies, radii, and neutron skins. We find that
radii and binding energies are much improved for interactions with explicit
inclusion of $\Delta(1232)$, while $\Delta$-less interactions produce nuclei
that are not bound with respect to breakup into $\alpha$ particles. The
saturation of nuclear matter is significantly improved, and its symmetry energy
is consistent with empirical estimates.",1707.09028v2
2017-08-06,Power-law citation distributions are not scale-free,"We analyze time evolution of statistical distributions of citations to
scientific papers published in one year. While these distributions can be
fitted by a power-law dependence we find that they are nonstationary and the
exponent of the power law fit decreases with time and does not come to
saturation. We attribute the nonstationarity of citation distributions to
different longevity of the low-cited and highly-cited papers. By measuring
citation trajectories of papers we found that citation careers of the low-cited
papers come to saturation after 10-15 years while those of the highly-cited
papers continue to increase indefinitely: the papers that exceed some citation
threshold become runaways. Thus, we show that although citation distribution
can look as a power-law, it is not scale-free and there is a hidden dynamic
scale associated with the onset of runaways. We compare our measurements to our
recently developed model of citation dynamics based on
copying/redirection/triadic closure and find explanations to our empirical
observations.",1708.01859v1
2017-08-08,"Degree of dimerization, effective polarizability of molecules and heat capacity of the saturated water vapor","The work is devoted to the investigation of properties of water vapor. The
main attention is focused on the physical nature of its effective
polarizability and heat capacity at constant volume. We show that the specific
temperature dependencies of these characteristics are mainly caused by thermal
vibration excitations of water dimers. In connection with this we determine
normal coordinates for the dimer vibrations. We investigate fluctuations of the
dipole moments of dimers in details and consider their contributions to the
dielectric permittivity of the water vapor. We also took into account the
contribution of the interparticle interactions on the heat capacity. Analyzing
the behavior of the effective polarizability and heat capacity we defined the
temperature dependence of the dimer concentration on the coexistence
vapor-liquid curve. The noticeable dimerization in the saturated water vapor
takes place only for temperatures T/Tc > 0.8 (Tc is the critical temperature).
It is important to note that the successful reproduction of the effective
polarizability and heat capacity can serve good test for the correct
description of the dimer concentration in different approaches.",1708.02483v1
2017-08-10,A linear domain decomposition method for partially saturated flow in porous media,"The Richards equation is a nonlinear parabolic equation that is commonly used
for modelling saturated/unsaturated flow in porous media. We assume that the
medium occupies a bounded Lipschitz domain partitioned into two disjoint
subdomains separated by a fixed interface $\Gamma$. This leads to two problems
defined on the subdomains which are coupled through conditions expressing flux
and pressure continuity at $\Gamma$. After an Euler implicit discretisation of
the resulting nonlinear subproblems a linear iterative ($L$-type) domain
decomposition scheme is proposed. The convergence of the scheme is proved
rigorously. In the last part we present numerical results that are in line with
the theoretical finding, in particular the unconditional convergence of the
scheme. We further compare the scheme to other approaches not making use of a
domain decomposition. Namely, we compare to a Newton and a Picard scheme. We
show that the proposed scheme is more stable than the Newton scheme while
remaining comparable in computational time, even if no parallelisation is being
adopted. Finally we present a parametric study that can be used to optimize the
proposed scheme.",1708.03224v1
2017-06-26,Conservation laws and constitutive equations for an electro-active polymer,"Ionic electro-active polymer (Nafion for example) can be used as sensor or
actuator. To this end, a thin film of the water-saturated material is
sandwiched between two electrodes. Water saturation causes a quasi-complete
dissociation of the polymer and the release of small cations. The application
of an electric field across the thickness results in the bending of the strip.
Conversely, a voltage can be detected between the two electrodes when the strip
is bent. This phenomenon involves multiphysics couplings of
electro-mechanical-chemical type. The system is modeled by a deformable porous
medium in which flows an ionic solution and we use a continuous medium
approach. Maxwell's equations and conservation laws of mass, linear momentum
and energy are first written at the microscopic scale for each phase and
interfaces, then for the complete material using an average technique.
Thermodynamics of linear irreversible processes provides the constitutive
equations : a Kelvin-Voigt stress-strain relation,generalized Fourier's and
Darcy's laws and a Nernst-Planck equation.",1708.05056v1
2017-08-24,Nuclear symmetry energy with mesonic cross-couplings in the effective chiral model,"The effective chiral model is extended by introducing the contributions from
the cross-couplings between isovector and isoscalar mesons. These
cross-couplings are found to be instrumental in improving the density content
of the nuclear symmetry energy. The nuclear symmetry energy as well as its
slope and curvature parameters at the saturation density are in harmony with
those deduced from a diverse set of experimental data. The equation of state
for pure neutron matter at sub-saturation densities is also in accordance with
the ones obtained from different microscopic models. The maximum mass of
neutron star is consistent with the measurement and the radius at the canonical
mass of the neutron star is within the empirical bounds.",1708.07291v1
2017-08-30,Fast scrambling in holographic Einstein-Podolsky-Rosen pair,"We demonstrate that a holographic model of the Einstein-Podolsky-Rosen pair
exhibits fast scrambling. Strongly entangled quark and antiquark in
$\mathcal{N}=4$ super Yang-Mills theory are considered. Their gravity dual is a
fundamental string whose endpoints are uniformly accelerated in opposite
direction. We slightly increase the acceleration of the endpoint and show that
it quickly destroys the correlation between the quark and antiquark. The proper
time scale of the destruction is $\tau_\ast\sim \beta \ln S$ where $\beta$ is
the inverse Unruh temperature and $S$ is the entropy of the accelerating quark.
We also evaluate the Lyapunov exponent from correlation function as
$\lambda_L=2\pi/\beta$, which saturates the Lyapunov bound. Our results suggest
that the fast scrambling or saturation of the Lyapunov bound do not directly
imply the existence of an Einstein dual. When we slightly decrease the
acceleration, the quark and antiquark are causally connected and an ""one-way
traversable wormhole"" is created on the worldsheet. It causes the divergence of
the correlation function between the quark and antiquark.",1708.09493v2
2017-09-04,Entropy production and isotropization in Yang-Mills theory with use of quantum distribution function,"We investigate thermalization process in relativistic heavy ion collisions in
terms of the Husimi-Wehrl (HW) entropy defined with the Husimi function, a
quantum distribution function in a phase space. We calculate the semiclassical
time evolution of the HW entropy in Yang-Mills field theory with the
phenomenological initial field configuration known as the McLerran-Venugopalan
model in a non-expanding geometry, which has instabilty triggered by initial
field fluctuations. HW-entropy production implies the thermalization of the
system and it reflects the underlying dynamics such as chaoticity and
instability. By comparing the production rate with the Kolmogorov-Sina\""i rate,
we find that the HW entropy production rate is significantly larger than that
expected from chaoticity. We also show that the HW entropy is finally saturated
when the system reaches a quasi-stationary state. The saturation time of the HW
entropy is comparable with that of pressure isotropization, which is around $1$
fm/c in the present calculation in the non-expanding geometry.",1709.00979v1
2017-09-04,Chaotic strings in AdS/CFT,"Holographic theories with classical gravity duals are maximally chaotic;
i.e., they saturate the universal bound on the rate of growth of chaos. It is
interesting to ask whether this property is true only for leading large $N$
correlators or if it can show up elsewhere. In this Letter we consider the
simplest setup to tackle this question: a Brownian particle coupled to a
thermal ensemble. We find that the four-point out-of-time-order correlator that
diagnoses chaos initially grows at an exponential rate that saturates the chaos
bound, i.e., with a Lyapunov exponent $\lambda_L=2\pi/\beta$. However, the
scrambling time is parametrically smaller than for plasma excitations,
$t_*\sim\beta \log \sqrt{\lambda}$ instead of $t_*\sim\beta \log N^2$. Our
result shows that, at least in certain cases, maximal chaos can be attained in
the probe sector without the explicit need of gravitational degrees of freedom.",1709.01052v3
2017-09-04,"On ill-posedness concepts, stable solvability and saturation","We consider different concepts of well-posedness and ill-posedness and their
relations for solving nonlinear and linear operator equations in Hilbert
spaces. First, the concepts of Hadamard and Nashed are recalled which are
appropriate for linear operator equations. For nonlinear operator equations,
stable respective unstable solvability is considered, and the properties of
local well-posedness and ill-posedness are investigated. Those two concepts
consider stability in image space and solution space, respectively, and both
seem to be appropriate concepts for nonlinear operators which are not onto
and/or not, locally or globally, injective. Several example situations for
nonlinear problems are considered, including the prominent autoconvolution
problems and other quadratic equations in Hilbert spaces.
  It turns out that for linear operator equations, well-posedness and
ill-posedness are global properties valid for all possible solutions,
respectively. The special role of the nullspace is pointed out in this case.
  Finally, non-injectivity also causes differences in the saturation behavior
of Tikhonov and Lavrentiev regularization of linear ill-posed equations. This
is examined at the end of this study.",1709.01109v1
2017-09-13,Mirror-assisted coherent backscattering from the Mollow sidebands,"In front of a mirror, the radiation of weakly driven large disordered clouds
presents an interference fringe in the backward direction, on top of an
incoherent background. Although strongly driven atoms usually present little
coherent scattering, we here show that the mirror-assisted version can produce
high contrast fringes, for arbitrarily high saturation parameters. The contrast
of the fringes oscillates with the Rabi frequency of the atomic transition and
the distance between the mirror and the atoms, due to the coherent interference
between the carrier and the Mollow sidebands of the saturated resonant
fluorescence spectrum emitted by the atoms. The setup thus represents a
powerful platform to study the spectral properties of ensembles of correlated
scatterers.",1709.04529v1
2017-09-20,The Saturated and Supercritical Stirling Cycle Thermodynamic Heat Engine Cycle,"On the assumption that experimentally validated tabulated thermodynamic
properties of saturated fluids published by the National Institute of Standards
and Technology are accurate, a theoretical thermodynamic cycle can be
demonstrated that produces a net-negative entropy generation to the universe.
The experimental data on the internal energy can also be used to obtain a
simple, empirical equation for the change in internal energy of a real fluid
undergoing isothermal expansion and compression. This demonstration provides
experimental evidence to the theory that temperature-dependent intermolecular
attractive forces can be an entropic force that can enhance the thermodynamic
efficiency of a real-fluid macroscopic heat engine to exceed that of the Carnot
efficiency.",1709.06852v4
2017-09-24,Regge phenomenology of photoproduction of $π^-Δ^{++}$ and scaling with saturation of trajectory,"In this work we investigate the reaction $\gamma p\to\pi^-\Delta^{++}$ in the
Reggeized model for $\pi(138)+\rho(775)+a_2(1320)$ exchanges in the
$t$-channel. For a convergence of the reaction cross section at high energies
the minimal forms of proton and $\Delta^{++}$ exchanges are introduced in the
direct and crossed channels for gauge invariance of $\pi$ Regge-pole exchange.
The role of spin-2 tensor meson $a_2$ is found to be crucial to agree with
existing data at high energies. Electromagnetic multipoles of $\Delta^{++}$
baryon are analyzed in the $\Delta$ resonance region. Based on the constituents
counting rule the scaled differential cross section at $E_\gamma=4$ GeV is
reproduced with the Regge trajectory saturated at large momentum transfer $-t$.",1709.08175v2
2017-09-25,Theoretical analysis of electrostatic energy harvester configured as Bennet's doubler based on Q-V cycles,"This paper presents theoretical analysis of a MEMS electrostatic energy
harvester configured as the Bennet's doubler. Steady-state operation of the
doubler circuit can be approximated by a right-angled trapezoid Q-V cycle. A
similarity between voltage doubler and resistive-based charge-pump circuit is
highlighted. By taking electromechanical coupling into account, the analytical
solution of the saturation voltage is the first time derived, providing a
greater comprehension of the system performance and multi-parameter effects.
The theoretical approach is verified by results of circuit simulation for two
cases of mathematically idealized diode and of Schottky diode. Development of
the doubler/multiplier circuits that can further increase the saturation
voltage is investigated.",1709.08754v1
2017-10-13,Fermi-momentum dependence of relativistic effective mass below saturation from superscaling of quasielastic electron scattering,"The relativistic effective mass $M^*$, and Fermi momentum, $k_F$, are
important ingredients in the determination of the nuclear equation of state,
but they have rarely been extracted from experimental data below saturation
density where translationally invariant nuclear matter becomes unstable against
clusterization into the existing atomic nuclei. Using a novel kind of
superscaling analysis of the quasielastic cross section electron scattering
data involving a suitable selection criterion and $^{12}$C as a reference
nucleus, the global scaling properties of the resulting set of data for 21
nuclei ranging from $^2$H to $^{238}$U are then analyzed. We find that a subset
of a third of the about $20000$ data approximately scales to an universal
superscaling function with a more constrained uncertainty band than just the
reference $^{12}$C case and provides $M^*$ as a function of $k_F$.",1710.04988v1
2017-10-14,Gassmann Theory Applies to Nanoporous Media,"Recent progress in extraction of unconventional hydrocarbon resources has
ignited the interest in the studies of nanoporous media. Since many
thermodynamic and mechanical properties of nanoscale solids and fluids differ
from the analogous bulk materials, it is not obvious whether wave propagation
in nanoporous media can be described using the same framework as in macroporous
media. Here we test the validity of Gassmann equation using two published sets
of ultrasonic measurements for a model nanoporous medium, Vycor glass,
saturated with two different fluids, argon and n-hexane. Predictions of the
Gassmann theory depend on the bulk and shear moduli of the dry samples, which
are known from ultrasonic measurements, and the bulk moduli of the solid and
fluid constituents. The solid bulk modulus can be estimated from
adsorption-induced deformation or from elastic effective medium theory. The
fluid modulus can be calculated according to the Tait-Murnaghan equation at the
solvation pressure in the pore. Substitution of these parameters into the
Gassmann equation provides predictions consistent with measured data. Our
findings set up a theoretical framework for investigation of fluid-saturated
nanoporous media using ultrasonic elastic wave propagation.",1710.05216v2
2017-10-20,Extremal problems on saturation for the family of $k$-edge-connected graphs,"Let $\mathcal{F}$ be a family of graphs. A graph $G$ is
$\mathcal{F}$-saturated if $G$ contains no member of $\mathcal{F}$ as a
subgraph but $G+e$ contains some member of $\mathcal{F}$ whenever $e\in
E(\overline{G})$. The saturation number and extremal number of $\mathcal{F}$,
denoted $sat(n,\mathcal{F})$ and $ex(n,\mathcal{F})$ respectively, are the
minimum and maximum numbers of edges among $n$-vertex $\mathcal{F}$-saturated
graphs. For $k\in\mathbb{N}$, let $\mathcal{F}_k$ and $\mathcal{F}'_k$ be the
families of $k$-connected and $k$-edge-connected graphs, respectively. Wenger
proved $sat(n,\mathcal{F}_k)=(k-1)n-{k\choose2}$, we prove
$sat(n,\mathcal{F}'_k)=(k-1)(n-1)-\lfloor{\frac {n}{k+1}}\rfloor{k-1 \choose
2}$. We also prove $ex(n,\mathcal{F}'_k)=(k-1)n-{k\choose2}$ and characterize
when equality holds. Finally, we give a lower bound on the spectral radius for
$\mathcal{F}_k$-saturated and $\mathcal{F}'_k$-saturated graphs.",1710.07432v2
2017-10-23,Chiral interactions up to next-to-next-to-next-to-leading order and nuclear saturation,"We present an efficient Monte Carlo framework for perturbative calculations
of infinite nuclear matter based on chiral two-, three-, and four-nucleon
interactions. The method enables the incorporation of all many-body
contributions in a straightforward and transparent way, and makes it possible
to extract systematic uncertainty estimates by performing order-by-order
calculations in the chiral expansion as well as the many-body expansion. The
versatility of this new framework is demonstrated by applying it to chiral
low-momentum interactions, exhibiting a very good many-body convergence up to
fourth order. Following these benchmarks, we explore new chiral interactions up
to next-to-next-to-next-to-leading order (N$^3$LO). Remarkably, simultaneous
fits to the triton and to saturation properties can be achieved, while all
three-nucleon low-energy couplings remain natural. The theoretical
uncertainties of nuclear matter are significantly reduced when going from
next-to-next-to-leading order to N$^3$LO.",1710.08220v3
2017-10-26,Saturation of the Quantum Null Energy Condition in Far-From-Equilibrium Systems,"The Quantum Null Energy Condition (QNEC) is a new local energy condition that
a general Quantum Field Theory (QFT) is believed to satisfy, relating the
classical null energy condition (NEC) to the second functional derivative of
the entanglement entropy in the corresponding null direction. We present the
first series of explicit computations of QNEC in a strongly coupled QFT, using
holography. We consider the vacuum, thermal equilibrium, a homogeneous
far-from-equilibrium quench as well as a colliding system that violates NEC.
For vacuum and the thermal phase QNEC is always weaker than NEC. While for the
homogeneous quench QNEC is satisfied with a finite gap, we find the interesting
result that the colliding system can saturate QNEC, depending on the null
direction.",1710.09837v1
2017-11-06,On classes of finite groups with simple non-abelian chief factors,"Let $\mathfrak{J}$ be a class of non-abelian simple groups and $\mathfrak{X}$
be a class of groups. A chief factor $H/K$ of a group $G$ is called
$\mathfrak{X}$-central in $G$ provided $(H/K)\rtimes
G/C_G(H/K)\in\mathfrak{X}$. We say that $G$ is a
$\mathfrak{J}cs$-$\mathfrak{X}$-\emph{group} if every chief
$\mathfrak{X}$-factor of $G$ is $\mathfrak{X}$-central and other chief factors
of $G$ are simple $\mathfrak{J}$-groups. We use $\mathfrak{X}_{\mathfrak{J}cs}$
to denote the class of all $\mathfrak{J}cs$-$\mathfrak{X}$-groups. A subgroup
$U$ of a group $G$ is called $\mathfrak{X}$-\emph{maximal} in $G$ provided that
$(a)$ $U\in\mathfrak{X}$, and $(b)$ if $U\leq V \leq G$ and $V\in\mathfrak{X}$,
then $U = V$. In this paper we described the structure of
$\mathfrak{J}cs$-$\mathfrak{H}$-groups for a solubly saturated formation
$\mathfrak{H}$ and all hereditary saturated formations $\mathfrak{F}$
containing all nilpotent groups such that the
$\mathfrak{F}_{\mathfrak{J}cs}$-hypercenter of $G$ coincides with the
intersection of all $\mathfrak{F}_{\mathfrak{J}cs}$-maximal subgroups of $G$
for every group $G$.",1711.01686v1
2017-11-07,Dominant Kinetic Pathways of Graphene Growth in Chemical Vapor Deposition: The Role of Hydrogen,"The most popular way to produce graphene nowadays is chemical vapor
deposition, where, surprisingly, H$_2$ gas is routinely supplied even though it
is a byproduct itself. In this study, by identifying dominant growing pathways
via multiscale simulations, we unambiguously reveal the central role hydrogen
played in graphene growth. Hydrogen can saturate the edges of a growing
graphene island to some extent, depending on the H$_2$ pressure. Although
graphene etching by hydrogen has been observed in experiment, hydrogen
saturation actually stabilizes graphene edges by reducing the detachment rates
of carbon-contained species. Such a new picture well explains some puzzling
experimental observations and is also instrumental in growth protocol
optimization for two-dimensional atomic crystal van der Waals epitaxy.",1711.02244v1
2017-12-11,Strangeness Production in low energy Heavy Ion Collisions via Hagedorn Resonances,"A novel, unorthodox picture of the dynamics of heavy ion collisions is
developed using the concept of Hagedorn states. A prescription of the bootstrap
of Hagedorn states respecting the conserved quantum numbers baryon number B,
strangeness S, isospin I is implememted into the GiBUU transport model. Using a
strangeness saturation suppression factor suitable for
nucleon-nucleon-collisions, recent experimental data for the strangeness
production by the HADES collaboration in Au+Au and Ar+KCl is reasonable well
described. The experimental observed exponential slopes of the energy
distributions are nicely reproduced. Thus, a dynamical model using Hagedorn
resonance states, supplemented by a strangeness saturation suppression factor,
is able to explain essential features (multiplicities, exponential slope) of
experimental data for strangeness production in nucleus-nucleus collisions
close to threshold.",1712.04018v2
2017-12-13,Tensor Fermi liquid parameters in nuclear matter from chiral effective field theory,"We compute from chiral two- and three-body forces the complete quasiparticle
interaction in symmetric nuclear matter up to twice nuclear matter saturation
density. Second-order perturbative contributions that account for
Pauli-blocking and medium polarization are included, allowing for an
exploration of the full set of central and noncentral operator structures
permitted by symmetries and the long-wavelength limit. At the Hartree-Fock
level, the next-to-next-to-leading order three-nucleon force contributes to all
noncentral interactions, and their strengths grow approximately linearly with
the nucleon density up that of saturated nuclear matter. Three-body forces are
shown to enhance the already strong proton-neutron effective tensor
interaction, while the corresponding like-particle tensor force remains small.
We also find a large isovector cross-vector interaction but small
center-of-mass tensor interactions in the isoscalar and isovector channels. The
convergence of the expansion of the noncentral quasiparticle interaction in
Landau parameters and Legendre polynomials is studied in detail.",1712.05013v1
2017-12-15,Predictions on three-particle azimuthal correlations in proton-proton collisions,"The ridge signal, which is long-ranged in rapidity, in the di-hadron
correlations in high-multiplicity p-p and p-A collisions opened up a whole new
research area in high-energy QCD. Although the ridge had been observed in A-A
collisions and interpreted as a result of the radial flow of quark-gluon
plasma, it had not appeared until recently in the data of small collision
systems such as p-p and p-A, nor had it been predicted theoretically or seen in
the event generators. There are two competing approaches that attempt to
explain the systematics of the di-hadron ridge signal; hydrodynamics and gluon
saturation physics (color glass condensate/glasma). In this work, we present
predictions for the transverse momentum and rapidity dependence of the
three-particle correlation function within the gluon saturation physics.
Tri-hadron correlations can be measured, and the data can possibly rule out one
of the two alternative approaches.",1712.05571v1
2017-12-20,Influence of the nuclear matter equation of state on the r-mode instability using the finite-range simple effective interaction,"The characteristic physical properties of rotating neutron stars under the
r-mode oscillation are evaluated using the finite-range simple effective
interaction. Emphasis is given on examining the influence of the stiffness of
both the symmetric and asymmetric parts of the nuclear equation of state on
these properties. The amplitude of the r-mode at saturation is calculated using
the data of particular neutron stars from the considerations of ""spin
equilibrium"" and ""thermal equilibrium"". The upper limit of the r-mode
saturation amplitude is found to lie in the range 10^{-8}-10^{-6}, in agreement
with the predictions of earlier work.",1712.07273v1
2017-12-31,Estimation of Gaussian quantum states,"We derive several expressions for the quantum Fisher information matrix
(QFIM) for the multi-parameter estimation of multi-mode Gaussian quantum
states, the corresponding symmetric logarithmic derivatives, and conditions for
saturability of the quantum Cram\'{e}r-Rao bound. This bound determines the
ultimate precision with which parameters encoded into quantum states can be
estimated. We include expressions for mixed states, for the case when the
Williamson decomposition of the covariance matrix is known, expressions in
terms of infinite series, and expressions for pure states. We also discuss
problematic behavior when some modes are pure, and present a method that allows
the use of expressions that are defined only for mixed states, to compute QFIM
for states with any number of pure modes.",1801.00299v4
2018-01-06,Massive neutron star with strangeness in a relativistic mean-field model with a high-density cut-off,"The properties of strangeness neutron star are studied within relativistic
mean-field (RMF) model via including a logarithmic interaction as a function of
scalar meson field. This logarithmic interaction, named as the $\sigma$-cut
potential, can largely reduce the attractive contributions of scalar meson
field at high density without any influence on nuclear structure around normal
saturation density. In this work, the TM1 parameter set is chosen as the RMF
interaction, while the strengths of logarithmic interaction are constrained by
the properties of finite nuclei so that we can obtain a reasonable effective
nucleon-nucleon interaction. The hyperons, $\Lambda,~\Sigma$, and $\Xi$ are
also considered in neutron stars within this framework, whose coupling
constants with mesons are determined by the latest hyperon-nucleon and
$\Lambda$-$\Lambda$ potentials extracted from the experimental data of
hypernuclei. The maximum mass of neutron star can be larger than two solar mass
with these hyperons. Furthermore, the nucleon mass at high density will be
saturated due to this additional $\sigma$-cut potential, which is consistent
with the conclusions from the microscopic calculations such as,
Brueckner-Hartree-Fock theory and quark mean-field model.",1801.01984v1
2018-01-09,Fake Colorized Image Detection,"Image forensics aims to detect the manipulation of digital images. Currently,
splicing detection, copy-move detection and image retouching detection are
drawing much attentions from researchers. However, image editing techniques
develop with time goes by. One emerging image editing technique is
colorization, which can colorize grayscale images with realistic colors.
Unfortunately, this technique may also be intentionally applied to certain
images to confound object recognition algorithms. To the best of our knowledge,
no forensic technique has yet been invented to identify whether an image is
colorized. We observed that, compared to natural images, colorized images,
which are generated by three state-of-the-art methods, possess statistical
differences for the hue and saturation channels. Besides, we also observe
statistical inconsistencies in the dark and bright channels, because the
colorization process will inevitably affect the dark and bright channel values.
Based on our observations, i.e., potential traces in the hue, saturation, dark
and bright channels, we propose two simple yet effective detection methods for
fake colorized images: Histogram based Fake Colorized Image Detection
(FCID-HIST) and Feature Encoding based Fake Colorized Image Detection
(FCID-FE). Experimental results demonstrate that both proposed methods exhibit
a decent performance against multiple state-of-the-art colorization approaches.",1801.02768v2
2018-01-20,Boundary-based Image Forgery Detection by Fast Shallow CNN,"Image forgery detection is the task of detecting and localizing forged parts
in tampered images. Previous works mostly focus on high resolution images using
traces of resampling features, demosaicing features or sharpness of edges.
However, a good detection method should also be applicable to low resolution
images because compressed or resized images are common these days. To this end,
we propose a Shallow Convolutional Neural Network(SCNN), capable of
distinguishing the boundaries of forged regions from original edges in low
resolution images. SCNN is designed to utilize the information of chroma and
saturation. Based on SCNN, two approaches that are named Sliding Windows
Detection (SWD) and Fast SCNN, respectively, are developed to detect and
localize image forgery region. In this paper, we substantiate that Fast SCNN
can detect drastic change of chroma and saturation. In image forgery detection
experiments Our model is evaluated on the CASIA 2.0 dataset. The results show
that Fast SCNN performs well on low resolution images and achieves significant
improvements over the state-of-the-art.",1801.06732v2
2018-01-23,Transport Dynamics of Parton Interactions in pp Collisions at LHC Energies,"We investigate the transport dynamics of partons in proton-proton collisions
at the Large Hadron Collider using a Boltzmann transport approach, the parton
cascade model. The calculations include semi-hard pQCD interaction of partons
populating the nucleons and provide a space-time description of the collision
in terms of cascading partons undergoing scatterings and fragmentations. Parton
production and number of collisions rise rapidly with increase in center of
mass energy of the collision. For a given center of mass energy, the number of
parton interactions is seen to rise stronger than linear with decreasing impact
parameter before saturating for very central collisions. The strangeness
enhance factor $\gamma_s$ for the semi-hard processes is found to rise rapidly
and saturate towards the highest collision energies. Overall, our study
indicates a significant amount of partonic interactions in proton-proton
collisions, which supports the observation of fluid-like behavior for high
multiplicity proton-proton collisions observed in the experiments.",1801.07482v1
2018-02-19,Complexity Growth with Lifshitz Scaling and Hyperscaling Violation,"Using complexity=action proposal we study the growth rate of holographic
complexity for Lifshitz and hyperscaling violating geometries. We will consider
both one and two sided black branes in an Einstein-Maxwell-Dilaton
gravitational theory. We find that in either case Lloyd's bound is violated and
the rate of growth of complexity saturates to a value which is greater than
twice the mass of the corresponding black brane. This value reduces to the mass
of the black brane in the isotropic case. We show that in two sided black brane
the saturation happens from above while for one sided black brane it happens
from below.",1802.06740v4
2018-02-22,Shear strength of wet granular materials: macroscopic cohesion and effective stress,"Rheometric measurements on assemblies of wet polystyrene bead assemblies, in
steady uniform quasistatic shear flow, for varying liquid content within the
small saturation (pendular) range of isolated liquid bridges, are supplemented
with a systematic study by discrete numerical simulations. Numerical results
and experimental ones agree quantitatively is the intergranular friction
coefficient is set to 0.09, suitable for the dry material. Shear resistance and
solid fraction are recorded as functions of the reduced pressure p, comparing
normal stress to capillary bridge tensile strength. The Mohr-Coulomb relation
with p-independent cohesion c applies for p above 2. The assumption that
contact force contributions to stress act as effective stresses predicts shear
strength quite well throughout the numerically investigated range of
parameters.. A generalized Mohr-Coulomb cohesion c is defined, which relates to
the dry material internal friction, coordination numbers and capillary force
network anisotropy. The Rumpf formula approximation, ignoring capillary shear
stress is correct for the larger saturation range within the pendular regime,
but fails to describe its decrease for small liquid contents.",1802.08172v1
2018-02-22,Exponentially fast dynamics of chaotic many-body systems,"We demonstrate analytically and numerically that in isolated quantum systems
of many interacting particles, the number of many-body states participating in
the evolution after a quench increases exponentially in time, provided the
eigenstates are delocalized in the energy shell. The rate of the exponential
growth is defined by the width $\Gamma$ of the local density of states (LDOS)
and is associated with the Kolmogorov-Sinai entropy for systems with a well
defined classical limit. In a finite system, the exponential growth eventually
saturates due to the finite volume of the energy shell. We estimate the time
scale for the saturation and show that it is much larger than $\hbar/\Gamma$.
Numerical data obtained for a two-body random interaction model of bosons and
for a dynamical model of interacting spin-1/2 particles show excellent
agreement with the analytical predictions.",1802.08265v2
2018-02-26,An Energy Balance Based Method for Parameter Identification of a Free-Flying Robot Grasping An Unknown Object,"The estimation of inertial parameters of a robotic system is crucial for
better trajectory tracking performance, specially when model-based controllers
are used for carrying out precise tasks. In this paper, we consider the
scenario of grasping an object of unknown properties by a free-flyer space
robot with limited actuation. The problem is to find the inertial parameters of
the complete system after grasping has been performed. Excitation is provided
in inertial space, and the excitation trajectories are found by optimization.
Truncated Fourier series are used to represent the reference as well as tracked
trajectory. An approach based on the energy balance between the actuation work
and the rate of change of kinetic energy is introduced to calculate the number
of harmonics in the Fourier series used to represent the executed trajectory,
while trying to find a balance between accounting for saturation effects and
keeping out noise. The effect of input saturation on parameter estimation is
also studied. Simulation results using the Space CoBot free-flyer robot are
presented to show the feasibility of the approach.",1802.09338v2
2018-02-27,"Hot and Dense Homogeneous Nucleonic Matter Constrained by Observations, Experiment, and Theory","We construct a new class of phenomenological equations of state for
homogeneous matter for use in simulations of hot and dense matter in local
thermodynamic equilibrium. We construct a functional form which respects
experimental, observational and theoretical constraints on the nature of matter
in various density and temperature regimes. Our equation of state matches (i)
the virial coefficients expected from nucleon-nucleon scattering phase shifts,
(ii) experimental measurements of nuclear masses and charge radii, (iii)
observations of neutron star radii, (iv) theory results on the equation of
state of neutron matter near the saturation density, and (v) theory results on
the evolution of the EOS at finite temperatures near the saturation density.
Our analytical model allows one to compute the variation in the thermodynamic
quantities based on the uncertainties in the nature of the nucleon-nucleon
interaction. Finally, we perform a correction to ensure the equation of state
is causal at all densities, temperatures, and electron fractions.",1802.09710v1
2018-03-06,Impact of the electron to ion mass ratio on unstable systems in particle-in-cell simulations,"The evolution of the Buneman and two-stream instabilities driven by a cold
dilute mildly relativistic electron beam is studied as a function of the
ion\'\s charge-to-mass ratio. The growth rates of both instabilities are
comparable for the selected parameters if the charge-to-mass ratio of protons
is used and the Buneman instability outgrows the two-stream instability for a
larger ratio. Particle-in-cell (PIC) simulations show that both instabilities
grow independently during their linear growth phase. The much lower saturation
amplitude of the Buneman instability implies that it saturates first even if
the linear growth rates of both instabilities are equal. The electron phase
space holes it drives coalesce. Their spatial size increases in time and they
start interacting with the two-stream mode, which triggers the onset of
electrostatic turbulence. A reduced charge-to-mass ratio results in stronger
turbulence and ion heating and in an increased energy loss of the relativistic
electron beam compared to that in a simulation with the correct ratio.",1803.02190v2
2018-03-07,Saturation and negative temperature coefficient of electrical resistivity in liquid iron-sulfur alloys at high densities from first principles calculations,"We report results on electronic transport properties of liquid Fe-S alloys at
conditions of planetary cores, computed by first-principle techniques in the
Kubo-Greenwood formalism. We describe a combined effect of resistivity
saturation due to temperature, compression, and chemistry by comparing the
electron mean free path from the Drude response of optical conductivity to the
mean interatomic distance. At high compression and high sulfur concentration
the Ioffe-Regel condition is satisfied, and the temperature coefficient of
resistivity changes sign from positive to negative. We show that this happens
due to a decrease of the $d$-density of states at the Fermi level in response
to thermal broadening.",1803.02649v1
2018-03-08,Learning Effective Binary Visual Representations with Deep Networks,"Although traditionally binary visual representations are mainly designed to
reduce computational and storage costs in the image retrieval research, this
paper argues that binary visual representations can be applied to large scale
recognition and detection problems in addition to hashing in retrieval.
Furthermore, the binary nature may make it generalize better than its
real-valued counterparts. Existing binary hashing methods are either two-stage
or hinging on loss term regularization or saturated functions, hence converge
slowly and only emit soft binary values. This paper proposes Approximately
Binary Clamping (ABC), which is non-saturating, end-to-end trainable, with fast
convergence and can output true binary visual representations. ABC achieves
comparable accuracy in ImageNet classification as its real-valued counterpart,
and even generalizes better in object detection. On benchmark image retrieval
datasets, ABC also outperforms existing hashing methods.",1803.03004v1
2018-03-11,Bulk Matter and the Boundary Quantum Null Energy Condition,"We investigate the quantum null energy condition (QNEC) in holographic CFTs,
focusing on half-spaces and particular classes of states. We present direct,
and in certain cases nonperturbative, calculations for both the diagonal and
off- diagonal variational derivatives of entanglement entropy. In d > 2, we
find that the QNEC is saturated. We compute relations between the off-diagonal
variation of entanglement, boundary relative entropy, and the bulk stress
tensor. Strong subadditivity then leads to energy conditions in the bulk. In d
= 2, we find that the QNEC is in general not saturated when the Ryu-Takayanagi
surface intersects bulk matter. Moreover, when bulk matter is present the QNEC
can imply new bulk energy conditions. For a simple class of states, we derive
an example that is stronger than the bulk averaged null energy condition and
reduces to it in certain limits.",1803.03997v1
2018-03-22,Geometrical scaling description for the exclusive production of vector mesons and deeply virtual Compton scattering,"In this work, we investigate the exclusive production of particles in
scattering processes in the so-called saturation region. Within this scheme the
phenomenon of geometric scaling takes place: cross sections are functions only
of a dimensionless combination of the relevant kinematic variables, which
happens both in inclusive and diffractive cases, as in the production of vector
mesons. In particular, the scaling variable is given in general by $\tau =
Q^2/Q_s^2$, where $Q^2$ is the photon virtuality and $Q_s$ represents the
saturation scale, which drives the energy dependence and the corresponding
nuclear effects. Based on the scaling property, we are able to derive a
universal expression for the cross sections for the exclusive vector meson
production and deeply virtual Compton scattering (DVCS) in both photon-proton
and photon-nucleus interactions. This phenomenological result describes all
available data from DESY-HERA for $\rho$, $\phi$ and $J/\psi$ production and
DVCS measurements. A discussion is also carried out on the size of nuclear
shadowing corrections on photon-nucleus interaction.",1803.08442v2
2018-03-25,Connectivity-Preserving Consensus of Multi-Agent Systems with Bounded Actuation,"This paper investigates the impact of bounded actuation on the
connectivity-preserving consensus of two classes of multi-agent systems, with
kinematic agents and with Euler- Lagrange agents. The investigation establishes
that: (1) there exists a class of gradient-based controls which drive kinematic
multi-agent systems to connectivity-preserving consensus even if they saturate;
(2) actuator saturation restricts the initial states from which Euler-Lagrange
multi-agent systems can be synchronized while preserving their local
connectivity; (3) Euler-Lagrange multi-agent systems with unbounded actuation
can achieve connectivity-preserving consensus without velocity measurements or
exact system dynamics; and (4) a proposed indirect coupling control strategy
drives Euler-Lagrange multi-agent systems with limited actuation and starting
from rest to connectivitypreserving consensus without requiring velocity
measurements and including in the presence of uncertain dynamics and
timevarying delays.",1803.09309v1
2018-03-31,Evolution of complexity following a quantum quench in free field theory,"Using a recent proposal of circuit complexity in quantum field theories
introduced by Jefferson and Myers, we compute the time evolution of the
complexity following a smooth mass quench characterized by a time scale $\delta
t$ in a free scalar field theory. We show that the dynamics has two distinct
phases, namely an early regime of approximately linear evolution followed by a
saturation phase characterized by oscillations around a mean value. The
behavior is similar to previous conjectures for the complexity growth in
chaotic and holographic systems, although here we have found that the
complexity may grow or decrease depending on whether the quench increases or
decreases the mass, and also that the time scale for saturation of the
complexity is of order $\delta t$ (not parametrically larger).",1804.00107v3
2018-04-02,Joint Tx Power Allocation and Rx Power Splitting for SWIPT System with Multiple Nonlinear Energy Harvesting Circuits,"We study the joint transmit (Tx) power allocation and receive (Rx) power
splitting for simultaneous wireless information and power transfer (SWIPT).
Considering the practical scenario of nonlinear energy harvesting (EH), we
adopt the realistic nonlinear EH model for analysis. To address the critical
nonlinearity issue due to the saturation, we propose to use multiple EH
circuits in parallel. An important problem is to maximize the achievable rate
by jointly optimizing Tx power allocation and Rx power splitting, which is a
nonconvex problem. In this paper, we first derive the optimal solution for any
number of EH circuits. Then we study how the number of EH circuits required to
avoid the saturation should be determined. From the obtained results, we draw
useful and interesting insights into the SWIPT system with nonlinear EH.
Numerical results demonstrate that employing multiple EH circuits substantially
enhances the SWIPT performance with nonlinear EH.",1804.00387v1
2018-03-16,Semantic Adversarial Examples,"Deep neural networks are known to be vulnerable to adversarial examples,
i.e., images that are maliciously perturbed to fool the model. Generating
adversarial examples has been mostly limited to finding small perturbations
that maximize the model prediction error. Such images, however, contain
artificial perturbations that make them somewhat distinguishable from natural
images. This property is used by several defense methods to counter adversarial
examples by applying denoising filters or training the model to be robust to
small perturbations.
  In this paper, we introduce a new class of adversarial examples, namely
""Semantic Adversarial Examples,"" as images that are arbitrarily perturbed to
fool the model, but in such a way that the modified image semantically
represents the same object as the original image. We formulate the problem of
generating such images as a constrained optimization problem and develop an
adversarial transformation based on the shape bias property of human cognitive
system. In our method, we generate adversarial images by first converting the
RGB image into the HSV (Hue, Saturation and Value) color space and then
randomly shifting the Hue and Saturation components, while keeping the Value
component the same. Our experimental results on CIFAR10 dataset show that the
accuracy of VGG16 network on adversarial color-shifted images is 5.7%.",1804.00499v1
2018-04-03,Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta$_2$NiSe$_5$,"Femtosecond time-resolved mid-infrared reflectivity is used to investigate
the electron and phonon dynamics occurring at the direct band gap of the
excitonic insulator Ta$_2$NiSe$_5$ below the critical temperature of its
structural phase transition. We find that the phonon dynamics show a strong
coupling to the excitation of free carriers at the \Gamma\ point of the
Brillouin zone. The optical response saturates at a critical excitation fluence
$F_C = 0.30~\pm~0.08$~mJ/cm$^2$ due to optical absorption saturation. This
limits the optical excitation density in Ta$_2$NiSe$_5$ so that the system
cannot be pumped sufficiently strongly to undergo the structural change to the
high-temperature phase. We thereby demonstrate that Ta$_2$NiSe$_5$ exhibits a
blocking mechanism when pumped in the near-infrared regime, preventing a
nonthermal structural phase transition.",1804.00882v1
2018-04-09,Exclusive vector meson production with leading neutrons in a saturation model for the dipole amplitude in mixed space,"We investigate $\rho$ vector meson production in $ep$ collisions at HERA with
leading neutrons in the dipole formalism. The interaction of the dipole and the
pion is described in a mixed-space approach, in which the dipole-pion
scattering amplitude is given by the Marquet-Peschanski-Soyez saturation model,
which is based on the travelling wave solutions of the nonlinear
Balitsky-Kovchegov equation. We estimate the magnitude of the absorption
effects and compare our results with a previous analysis of the same process in
full coordinate space. In contrast with this approach, the present study leads
to absorption $K$ factors in the range of those predicted by previous
theoretical studies on semi-inclusive processes.",1804.03266v3
2018-04-12,Controlling breath figure patterns on PDMS by concentration variation of ethanol-methanol binary vapors,"In this paper, the self-assembly of condensed droplets on smooth and
constrained surfaces under saturated vapor atmosphere of ethanol and methanol
binary system is reported. Hexagonally ordered array of pores are obtained on
smooth surfaces with saturated vapors of binary liquids without the assistance
of any additives. The results show that the addition of small amount of ethanol
to methanol plays a role very similar to that of surface active agents in
inducing the formation of regular droplet array. The effect of constraints on
self-assembled droplet pattern such as movement of contact line and depinning
of contact line is also investigated. It is observed that the pore size, pore
shape, pore depth and ring diameter are influenced by the atmosphere of binary
vapors in addition to the commonly held attribution to the surface tension of
the solvent. Contact angle studies of the patterned substrates showed
hydrophobicity with very high adhesiveness to water and Wenzel's state of
wetting.",1804.04392v1
2018-04-18,Duality between unprovability and provability in forward proof-search for Intuitionistic Propositional Logic,"The inverse method is a saturation based theorem proving technique; it relies
on a forward proof-search strategy and can be applied to cut-free calculi
enjoying the subformula property. Here we apply this method to derive the
unprovability of a goal formula G in Intuitionistic Propositional Logic. To
this aim we design a forward calculus FRJ(G) for Intuitionistic unprovability
which is prone to constructively ascertain the unprovability of a formula G by
providing a concise countermodel for it; in particular we prove that the
generated countermodels have minimal height. Moreover, we clarify the role of
the saturated database obtained as result of a failed proof-search in FRJ(G) by
showing how to extract from such a database a derivation witnessing the
Intuitionistic validity of the goal.",1804.06689v1
2018-05-01,Nonlinear Saturation of Kinetic Ballooning Modes by Zonal fields in Toroidal Plasmas,"Kinetic ballooning modes (KBM) are widely believed to play a critical role in
disruptive dynamics as well as turbulent transport in tokamaks. While the
nonlinear evolution of ballooning modes has been proposed as a mechanism for
detonation in tokamak plasmas, the role of kinetic effects in such nonlinear
dynamics remains largely unexplored. In this work global gyrokinetic simulation
results of KBM nonlinear behavior are presented. Instead of the finite-time
singularity predicted by ideal MHD theory, the kinetic instability is shown to
develop into an intermediate nonlinear regime of exponential growth, followed
by a nonlinear saturation regulated by spontaneously generated zonal fields. In
the intermediate nonlinear regime, rapid growth of localized current sheet is
observed.",1805.00402v1
2018-05-04,Homodyne-detector-blinding attack in continuous-variable quantum key distribution,"We propose an efficient strategy to attack a continuous-variable quantum key
distribution (CV-QKD) system, that we call homodyne detector blinding. This
attack strategy takes advantage of a generic vulnerability of homodyne
receivers: a bright light pulse sent on the signal port can lead to a
saturation of the detector electronics. While detector saturation has already
been proposed to attack CV-QKD, the attack we study in this paper has the
additional advantage of not requiring an eavesdropper to be phase locked with
the homodyne receiver. We show that under certain conditions, an attacker can
use a simple laser, incoherent with the homodyne receiver, to generate bright
pulses and bias the excess noise to arbitrary small values, fully comprising
CV-QKD security. These results highlight the feasibility and the impact of the
detector blinding attack. We finally discuss how to design countermeasures in
order to protect against this attack.",1805.01620v2
2018-05-12,Quark mean-field model for nuclear matter with or without bag,"We propose the new quark mean-field bag (QMFB) model by incorporating the bag
confinement mechanism in the original quark mean-field model. Nuclear matter
and neutron star properties are studied with the QMFB model. For the study of
the bag effect, we newly fit 12 parameter sets by reproducing the empirical
saturation properties of nuclear matter. Quark confinement is found to be
mainly demonstrated by the bag after it is included in the model, instead of
the confining potential. For nuclear matter, the bag decreases the binding
energy and increases the symmetry energy. For neutron star, the bag affects
significantly the radius $R$ of a $1.4M_\odot$ star, with the maximum mass only
slightly modified. The bag also has a large suppression effect on the
well-accepted $R$ vs $L$ dependence, with $L$ the symmetry energy slope at the
saturation density.",1805.04678v2
2018-05-15,Forward di-hadron back-to-back correlations in $\boldsymbol{pA}$ collisions from rcBK evolution,"We study the disappearance of the away-side peak of the di-hadron correlation
function in p+A vs p+p collisions at forward rapidities, when the scaterring
process presents a manifest dilute-dense asymmetry. We improve the
state-of-the-art description of this phenomenon in the framework of the Color
Glass Condensate (CGC), for hadrons produced nearly back-to-back. In that case,
the gluon content of the saturated nuclear target can be described with
transverse-momentum-dependent gluon distributions, whose small-$x$ evolution we
calculate numerically by solving the Balitsky-Kovchegov equation with running
coupling corrections. We first show that our formalism provides a good
description of the disappearance of the away-side azimuthal correlations in
d+Au collisions observed at BNL Relativistic Heavy Ion Collider (RHIC)
energies. Then, we predict the away-side peak of upcoming p+Au data at
$~\sqrt[]{s}=200$ GeV to be suppressed by about a factor 2 with respect to p+p
collisions, and we propose to study the rapidity dependence of that suppression
as a complementary strong evidence of gluon saturation in experimental data.",1805.05711v1
2018-05-15,A high dynamic range optical detector for measuring single photons and bright light,"Detecting light is fundamental to all optical experiments and applications.
At the single photon level, the quantised nature of light requires specialised
detectors, which typically saturate for more than one photon, rendering the
measurement of bright light impossible. Saturation can be partially overcome by
multiplexing single-photon-sensitive detectors, enabling measurement up to tens
of photons. However, current approaches are still far from bridging the gap to
bright light levels. Here, we report on a massively-multiplexed single-photon
detector, which exhibits a dynamic range of 123 dB, from optical energies as
low as $\mathbf{10^{-7}}$ photons per pulse to $\mathbf{\sim2.5\times10^{5}}$
photons per pulse. This allows us to calibrate a single photon detector
directly to a power meter. The use of a single-photon sensitive detector
further allows us to characterise the nonclassical features of a variety of
quantum states. This device will find application where high dynamic range and
single-photon sensitivity are required.",1805.05881v2
2018-05-15,Expanding cosmological civilizations on the back of an envelope,"We present a simplified description of expansionistic life in the standard
relativistic cosmology. The resulting model is exactly integrable, yielding a
simple set of predictive formulas. This allows one to quickly propose new
scenarios for the life appearance rate and the dominant expansion speed and
evaluate the observable consequences. These include the expected number and
angular size of visible expanding domains, the total eclipsed fraction of the
sky, and the life-saturated fraction of the universe. We also propose a simple
anthropic bound on observable quantities, as a function of the dominant
expansion velocity alone. The goal is to create a simple and intuition-building
tool for use in the context of cosmology, extragalactic SETI, and futures
studies. We discuss the general predictions of this framework, including
conditions giving rise to an ""extragalactic Fermi paradox,"" in which zero
civilizations are visible beyond the Milky Way. This can occur even if a
substantial fraction of the universe is already saturated with ambitious life.",1805.06329v1
2018-05-17,Saturated configuration interaction calculations for five-valent Ta and Db,"Accurate atomic structure calculations of complicated atoms with 4 or more
valence electrons begin to push the memory and time limits of supercomputers.
This paper presents a robust method of decreasing the size of \textit{ab
initio} configuration interaction and many-body perturbation theory
calculations without undermining the accuracy of the resulting atomic spectra.
Our method makes it possible to saturate the CI matrix in atoms with many
valence electrons. We test our method on the five-valence-electron atom
tantalum and verify the convergence of the calculated energies. We then apply
the method to calculate spectra and isotope shifts of tantalum's superheavy
analogue dubnium. Isotope-shift calculations can be used to predict the spectra
of superheavy isotopes which may be produced in astrophysical phenomena.",1805.06615v1
2018-05-24,An Accurate Data Cleaning Procedure for Electron Cyclotron Emission Imaging on EAST Tokamak Based on Methodology of Machine Learning,"A new data cleaning procedure for electron cyclotron emission imaging (ECEI)
of EAST tokamak is constructed. Machine learning techniques, including SVM and
Decision tree, are applied to identifying saturated, zero, and weak signals of
ECEI raw data, which not only reduces the effort of researchers for data
analysis, but also improves the accuracy of data preprocessing. To enhance the
reliability of the procedure, proper training sets are sampled based on massive
raw data from the experiments of ECEI on EAST tokamak. Window size of temporal
signal, kernel function, and other model parameters are obtained after model
training. Consequently, the recognition rates of saturated, zero, and weak
signals in raw data are 99.4%, 99.86%, and 99.9%, respectively, which proves
the accuracy of this procedure.",1805.09540v1
2018-05-28,The Nuclear Symmetry Energy at Sub-saturation Densities,"The density dependence of the nuclear symmetry energy governs important
aspects of very neutron rich systems such as heavy nuclei and their collisions,
neutron stars and their mergers. Many analyses of experimental data have
generated constraints on the symmetry energy and its first derivative at
saturation density, rho_0 ~ 2.7xE14 g/cm3.
  We show that each analysis does not accurately constrain the symmetry energy
at rho_0, but rather at a lower density, rho_s, that is most sensitively probed
by that analysis. Using published constraints on the symmetry energy and its
first derivative at rho_0, we constrain the symmetry energy within a density
range of 0.25rho_0 to 0.75rho_0 that is relevant to the inner crusts of neutron
stars and to the neutrino-sphere of core-collapse supernovae. With appropriate
data, the symmetry energy can be similarly constrained over a wider density
range.",1805.10757v1
2018-05-29,Entangling power of time-evolution operators in integrable and nonintegrable many-body systems,"The entangling power and operator entanglement entropy are state independent
measures of entanglement. Their growth and saturation is examined in the
time-evolution operator of quantum many-body systems that can range from the
integrable to the fully chaotic. An analytically solvable integrable model of
the kicked transverse field Ising chain is shown to have ballistic growth of
operator von Neumann entanglement entropy and exponentially fast saturation of
the linear entropy with time. Surprisingly a fully chaotic model with
longitudinal fields turned on shares the same growth phase, and is consistent
with a random matrix model that is also exactly solvable for the linear entropy
entanglements. However an examination of the entangling power shows that its
largest value is significantly less than the nearly maximal value attained by
the nonintegrable one. The importance of long-range spectral correlations, and
not just the nearest neighbor spacing, is pointed out in determing the growth
of entanglement in nonintegrable systems. Finally an interesting case that
displays some features peculiar to both integrable and nonintegrable systems is
briefly discussed.",1805.11632v1
2018-06-11,Mechanism of slow equilibration of isolated quantum systems,"We discuss the approach toward equilibrium of an isolated quantum system. For
a wide class of systems we argue that the time-averaged expectation value of a
local operator in any initial state is bounded by the so-called deviation
function, which characterizes maximal deviation from the equilibrium for all
states with a given value of energy fluctuations. We provide numerical evidence
that the bound is approximately saturated by the initial configurations with
spatial inhomogeneities at macroscopic level. In this way the deviation
function establishes an explicit connection between the macroscopically
observed timescales associated with transport and properties of microscopic
matrix elements. The form of the deviation function indicates that among the
slowest states which saturate the bound there are also those with arbitrarily
long equilibration times.",1806.04187v1
2018-06-15,On the exact minimization of saturated loss functions for robust regression and subspace estimation,"This paper deals with robust regression and subspace estimation and more
precisely with the problem of minimizing a saturated loss function. In
particular, we focus on computational complexity issues and show that an exact
algorithm with polynomial time-complexity with respect to the number of data
can be devised for robust regression and subspace estimation. This result is
obtained by adopting a classification point of view and relating the problems
to the search for a linear model that can approximate the maximal number of
points with a given error. Approximate variants of the algorithms based on
ramdom sampling are also discussed and experiments show that it offers an
accuracy gain over the traditional RANSAC for a similar algorithmic simplicity.",1806.05833v2
2018-06-14,Coherent and incoherent production of vector mesons in ultraperipheral collisions of Xenon-ions within the QCD parton saturation approach,"In this paper we analyse the exclusive vector meson photoproduction in the
recent run using Xenon-ions at energy of 5.44 TeV performed by the Large Hadron
Collider. We focus on the ultraperipheral collisions and provide theoretical
predictions for coherent and incoherent cross sections within the color dipole
approach and gluon saturation framework. The rapidity distribution is
investigated in both cases and comparison to other approaches available at
literature is done. We show that the expected yields are enough to perform
reliable cross section measurements for light mesons as $\rho^0$ and $\phi$.",1806.06701v1
2018-06-18,Confronting impact parameter dependent JIMWLK evolution with HERA data,"The small-$x$ evolution of protons is determined from numerical solutions of
the JIMWLK equations, starting from an initial condition at moderate $x$ for a
finite size proton. The resulting dipole amplitude is used to calculate the
total reduced cross section $\sigma_r$ and charm reduced cross section
$\sigma_{rc}$, as well as diffractive vector meson production. We compare
results to experimental data from HERA and discuss fundamental problems arising
from the regime sensitive to non-perturbative physics. We emphasize that
information on the gluonic content of the proton, gluon spatial distributions
and correlations over wide ranges in $x$, which can in principle be constrained
by our study, are essential ingredients for describing the initial state in
proton-proton and proton-ion collisions. Future electron nucleus collisions at
an electron-ion collider will provide important additional insight for heavier
nuclei. We further demonstrate that it is not possible to probe gluon
saturation in electron-proton collision at HERA energies and that
electron-heavy ion collisions will be essential to access the saturation
regime.",1806.06783v1
2018-06-20,Three-dimensional particle-in-cell modeling of parametric instabilities near the quarter-critical density in plasmas,"The nonlinear regime of laser-plasma interaction including both
two-plasmon--decay (TPD) and stimulated Raman scattering (SRS) instabilities
has been studied in three-dimensional (3-D) particle-in-cell simulations with
parameters relevant to the inertial confinement fusion (ICF) experiments. SRS
and TPD develop in the same region in plasmas, and the generation of fast
electrons can be described accurately with only the full model including both
SRS and TPD. The growth of instabilities in the linear stage is found to be in
good agreement with analytical theories. In the saturation stage the enhanced
low-frequency density perturbations driven by the daughter waves of the SRS
sidescattering can saturate the TPD and consequently inhibit the fast-electron
generation. The fast-electron flux in 3-D modeling is up to an order of
magnitude smaller than previously reported in 2-D TPD simulations, bringing it
close to the results of ICF experiments.",1806.07510v2
2018-07-04,Quantum correlations in two-level atomic system over Herring-Flicker coupling,"We study the thermal quantum correlations in tripartite atomic system under
the existence of Herring-Flicker (HF) coupling among the atoms. We explore two
topologically distinct configurations of three coupled two-level atoms, viz.,
loop and line, differing in their coupling pattern. Further, the systems having
asymmetric arrangement of atoms are quantum mechanically correlated more
strongly than systems having symmetric arrangements. The variable nature of HF
coupling leads to the increase of both concurrence and discord from zero to a
saturation value from where they decrease to zero as a function of inter-atomic
distance. Further separation leads to both the quantities attaining another
saturation value. This controlled correlations play an important role in the
design of quantum data buses that can transfer quantum states to establish
quantum communication. The systems coupled via HF coupling will be efficient
for this task as they are maximally entangled in parametrically controlled
manner. Thus, these systems will be propitious for various quantum protocols
such as secure communication, quantum cryptography, quantum key distribution
etc.",1807.01805v4
2018-07-06,Latest predictions from the EbyE NLO EKRT model,"We present the latest results from the NLO pQCD + saturation + viscous
hydrodynamics (EbyE NLO EKRT) model. The parameters in the EKRT saturation
model are fixed by the charged hadron multiplicity in the 0-5 \% 2.76 TeV Pb+Pb
collisions. The $\sqrt{s}$, $A$ and centrality dependence of the initial
particle production follows then from the QCD dynamics of the model. This
allows us to predict the $\sqrt{s}$ and $A$ dependence of the particle
production. We show that our results are in an excellent agreement with the
low-$p_T$ data from 2.76 TeV and 5.02 TeV Pb+Pb collisions at the LHC as well
as with the data from the 200 GeV Au+Au collisions at RHIC. In particular, we
study the centrality dependences of hadronic multiplicities, flow coefficients,
and various flow correlations. Furthermore, the nuclear mass number dependence
of the initial particle production and hydrodynamic evolution can be tested in
the 5.44 TeV Xe+Xe collisions at the LHC. To this end, we show our predictions
for charged particle multiplicities, and in particular, show how the
deformations of the Xe nuclei reflect into the flow coefficients.",1807.02378v1
2018-07-08,CGC/saturation approach: re-visiting the problem of odd harmonics in angular correlations,"In this paper we demonstrate that the selection of events with different
multiplicities of produced particles, leads to the violation of the azimuthal
angular symmetry, $\phi \to \pi - \phi$. We find for LHC and lower energies,
that this violation can be so large for the events with multiplicities $n \geq
2 \bar{n}$, where $\bar{n}$ is the mean multiplicity, that it leads to almostno
suppression of $v_n$, with odd $n$. However, this can only occur if the typical
size of the dipole in DIS with a nuclear target is small, or $Q^2 \,>\,Q^2_s\Lb
A, Y_{\rm min},b\Rb$, where $Q_s$ is the saturation momentum of the nucleus at
$Y = Y_{\rm min}$. In the case of large sizes of dipoles, when $Q^2
\,<\,Q^2_s\Lb A, Y_{\rm min},b\Rb$, we show that $v_n =0$ for odd $n$.
Hadron-nucleus scattering is discussed.",1807.02783v1
2018-07-10,Anode current saturation of ALD-coated Planacon MCP-PMTs,"We have measured and compared the characteristics of ALD-coated Planacon
MCP-PMTs (XP85112/A1-Q-L) with their non-ALD counterparts (XP85012/A1-Q). While
the later show excellent performance, the ALD-coated sensors have surprisingly
low current saturation levels (~two orders of magnitude lower than expected)
and extremely high gain recovery time (more than 7 orders of magnitude higher
than expected). We suspect that these problems might be caused by the
unexpected side-effects of the ALD process. To make a definite conclusion, more
samples need to be tested, preferably from different production runs. If our
observation were confirmed, it would mean a serious technological setback for
ALD-coated MCP-PMTs.",1807.03804v2
2018-07-13,Effects of $^4$He film on quartz tuning forks in $^3$He at ultra-low temperatures,"In pure superfluid $^3$He-B at ultra-low temperatures, quartz tuning fork
oscillator response is expected to saturate when the dissipation caused by the
superfluid medium becomes substantially smaller than the internal dissipation
of the oscillator. However, even with small amount of $^4$He covering the
surfaces, we have observed saturation already at significantly higher
temperatures than anticipated, where we have other indicators to prove that the
$^3$He liquid is still cooling. We found that this anomalous behavior has a
rather strong pressure dependence, and it practically disappears above the
crystallization pressure of $^4$He. We also observed a maximum in the fork
resonance frequency at temperatures where the transition in quasiparticle flow
from the hydrodynamic to the ballistic regime is expected. We suggest that such
anomalous features derive from the superfluid $^4$He film on the oscillator
surface.",1807.05084v2
2018-07-17,Nuclear and neutron matter equations of state from high-quality potentials up to fifth order of the chiral expansion,"We present predictions for the equation of state of symmetric nuclear and
pure neutron matter based on recent high-quality nucleon-nucleon potentials
from leading order to fifth order in the chiral expansion. We include as well
the next-to-next-to-leading order (N2LO) chiral three-nucleon force whose
low-energy constants cD and cE are fitted to the binding energies of 3H and 3He
as well as the \b{eta}-decay lifetime of 3H. The ground state energy per
particle is computed in the particle- particle ladder approximation up to a few
times saturation density. Due to the soft character of the interactions,
uncertainties due to the convergence in many-body perturbation theory are
small. We find that nuclear matter saturation is reproduced quantitatively at
N3LO and N4LO, and therefore we encourage the application of these interactions
in finite nuclei, where the description of ground- state energies and charge
radii of medium-mass nuclei may be improved.",1807.06640v1
2018-07-18,Linearity of Saturation for Berge Hypergraphs,"For a graph $F$, we say a hypergraph $H$ is Berge-$F$ if it can be obtained
from $F$ be replacing each edge of $F$ with a hyperedge containing it. We say a
hypergraph is Berge-$F$-saturated if it does not contain a Berge-$F$, but
adding any hyperedge creates a copy of Berge-$F$. The $k$-uniform saturation
number of Berge-$F$, $\mathrm{sat}_k(n,\text{Berge-}F)$ is the fewest number of
edges in a Berge-$F$-saturated $k$-uniform hypergraph on $n$ vertices. We show
that $\mathrm{sat}_k(n,\text{Berge-}F) = O(n)$ for all graphs $F$ and
uniformities $3\leq k\leq 5$, partially answering a conjecture of English,
Gordon, Graber, Methuku, and Sullivan. We also extend this conjecture to Berge
copies of hypergraphs.",1807.06947v1
2018-07-26,A Transition of Saturable and Reverse Saturable Absorption between Monolayer and Bilayer/Multilayer of TMDCs,"The nonlinear absorption of two-dimensional molybdenum disulfide was analyzed
using the Z-scan technique. Sample size corresponding to a number of layer
determines the band gap in the materials which play the key role for
nonlinearity. Exciton dipole transition from ground state to excited state for
monolayer and bilayer/multilayer is determined by the excitation source, ESA
and GSA values. If the band gap is wider than the excitation source, two-photon
excitation process is dominant which requires the larger ESA than GSA. For
narrower bandgap, one-photon excitation is favorable because of the larger GSA
than ESA. In addition, defects, the temperature may alter the band gap.
Therefore, the transition from RSA to SA and vice versa is determined by the
number of layers in materials, temperature, and defects for a given excitation
energy.",1807.09945v2
2018-08-09,Optical bistability and nonlinear dynamics by saturation of cold Yb atoms in a cavity,"We observed optical bistability as well as oscillations in the upper bistable
branch when cold ytterbium atoms are dispersively coupled to a high finesse
optical cavity. Comparable previous observations were explained by atomic
density oscillations in case of a Bose-Einstein-Condensate or optical pumping
in case of a cold cloud of cesium. Both explanations do not apply in our case
of thermal atoms with only a single ground state. We propose a simple two-level
model including saturation to describe our experimental results. This paper
introduces the experimental setup, derives the mentioned model and compares it
to our experimental data. Good quantitative agreement supports our model.",1808.03132v1
2018-08-17,PT-symmetric potentials with imaginary asymptotic saturation,"We point out that PT-symmetric potentials $V_{PT}(x)$ having imaginary
asymptotic saturation: $V_{PT}(x=\pm \infty) =\pm i V_1, V_1 \in \Re$ are
devoid of scattering states and spectral singularity. We show the existence of
real (positive and negative) discrete spectrum both with and without complex
conjugate pair(s) of eigenvalues (CCPEs). If the states are arranged in the
ascending order or real part of discrete eigenvalues, the initial states have
few nodes but latter ones oscillate fast. Both real and imaginary parts of
$\psi(x)$ vanish asymptotically, $|\psi(x)|$ for the CCPEs are asymmetric and
for real energies these are symmetric about origin. For CCPEs $E_{\pm}$ the
eigenstates $\psi_{\pm}$ follow an interesting property that $|\psi_+(x)|= N
|\psi_-(-x)|, N \in \Re^+$. We remark that, the fast oscillating real discrete
energy states discussed are likely to be confused with: reflectionless states,
one dimensional version of von Neumann states of Hermitian and spectral
singularity state of complex PT-symmetric potentials.",1808.05828v2
2018-08-18,"Surface permeability, capillary transport and the Laplace-Beltrami problem","We have established previously, in a lead-in study, that the spreading of
liquids in particulate porous media at low saturation levels,
characteristically less than 10% of the void space, has very distinctive
features in comparison to that at higher saturation levels. In particular, we
have found that the dispersion process can be accurately described by a special
class of partial differential equations, the super-fast non-linear diffusion
equation. The results of mathematical modelling have demonstrated very good
agreement with experimental observations. However, any enhancement of the
accuracy and predictive power of the model, keeping in mind practical
applications, requires the knowledge of the effective surface permeability of
the constituent particles, which defines the global, macroscopic permeability
of the particulate media. In the paper, we demonstrate how this quantity can be
determined through the solution of the Laplace-Beltrami Dirichlet problem, we
study this using the well-developed surface finite element method.",1808.06077v1
2018-08-20,Influence of fluids on $V_\mathrm{P}/V_\mathrm{S}$ ratio: Increase or decrease?,"The evolution of $V_\mathrm{P}/V_\mathrm{S}$ with increasing fluid-saturated
porosity is computed for isotropic rocks containing spheroidal pores.
$V_\mathrm{P}/V_\mathrm{S}$ is shown to either decrease or increase with
increasing porosity, depending on the aspect ratio $\alpha$ of the pores, fluid
to solid bulk modulus ratio $\zeta$, and initial Poisson's ratio $\nu_0$ of the
solid. A critical initial Poisson's ratio $\nu_\mathrm{0,crit}$ is computed,
separating cases where $V_\mathrm{P}/V_\mathrm{S}$ increases (if
$\nu_0<\nu_\mathrm{0,crit}$) or \emph{decreases} (if
$\nu_0>\nu_\mathrm{0,crit}$) with increasing porosity. For thin cracks and
highly compressible fluids, $\nu_\mathrm{0,crit}$ is approximated by
$0.157\,\zeta/\alpha$, whereas for spherical pores $\nu_\mathrm{0,crit}$ is
given by $0.2 + 0.8\zeta$. If $\nu_0$ is close to $\nu_\mathrm{0,crit}$, the
evolution of $V_\mathrm{P}/V_\mathrm{S}$ with increasing fluid-saturated
porosity is near neutral and depends on subtle changes in pore shape and fluid
properties. This regime is found to be relevant to partially dehydrated
serpentinites in subduction zone conditions (porosity of aspect ratio near 0.1
and $\zeta$ in the range 0.01--0.1), and makes detection of these rocks and
possibly elevated fluid pressures difficult from $V_\mathrm{P}/V_\mathrm{S}$
only.",1808.06387v2
2018-08-22,PT-symmetry breaking in multilayers with resonant loss and gain locks light propagation direction,"Using the Maxwell-Bloch equations for resonantly absorbing and amplifying
media, we study the temporal dynamics of light propagation through the
PT-symmetric structures with alternating loss and gain layers. This approach
allows us to precisely describe the response of the structure near the
exceptional points of PT-symmetry breaking phase transition and, in particular,
take into account the nonlinear effect of loss and gain saturation in the
PT-symmetry broken state. We reveal that in this latter state the multilayer
system possesses a lasing-like behavior releasing the pumped energy in the form
of powerful pulses. We predict locking of pulse direction due to the
PT-symmetry breaking, as well as saturation-induced irreversibility of phase
transition and nonreciprocal transmission.",1808.07477v1
2018-08-18,A lattice Boltzmann model for two-phase flow in porous media,"In this paper, a lattice Boltzmann (LB) model with double distribution
functions is proposed for two-phase flow in porous media where one distribution
function is used for pressure governed by the Poisson equation, and the other
is applied for saturation evolution described by the convection-diffusion
equation with a source term. We first performed a Chapman-Enskog analysis, and
show that the macroscopic nonlinear equations for pressure and saturation can
be recovered correctly from present LB model. Then in the framework of LB
method, we develop a local scheme for pressure gradient or equivalently
velocity, which may be more efficient than the nonlocal second-order
finite-difference schemes. We also perform some numerical simulations, and the
results show that the developed LB model and local scheme for velocity are
accurate and also have a second-order convergence rate in space. Finally,
compared to the available pore-scale LB models for two-phase flow in porous
media, the present LB model has more potential in the study of the large-scale
problems.",1808.07554v1
2018-08-23,Microscopic theory of capillary pressure hysteresis based on pore-space accessivity and radius-resolved saturation,"Continuum models of porous media use macroscopic parameters and state
variables to capture essential features of pore-scale physics. We propose a
macroscopic property ""accessivity"" ($\alpha$) to characterize the network
connectivity of different sized pores in a porous medium, and macroscopic state
descriptors ""radius-resolved saturations"" ($\psi_w(F),\psi_n(F)$) to
characterize the distribution of fluid phases within. Small accessivity
($\alpha\to0$) implies serial connections between different sized pores, while
large accessivity ($\alpha\to1$) corresponds to more parallel arrangements, as
the classical capillary bundle model implicitly assumes. Based on these
concepts, we develop a statistical theory for quasistatic immiscible
drainage-imbibition in arbitrary cycles, and arrive at simple algebraic
formulae for updating $\psi_n(F)$ that naturally capture capillary pressure
hysteresis, with $\alpha$ controlling the amount of hysteresis. These concepts
may be used to interpret hysteretic data, upscale pore-scale observations, and
formulate new constitutive laws by providing a simple conceptual framework for
quantifying connectivity effects, and may have broader utility in continuum
modeling of transport, reactions, and phase transformations in porous media.",1808.09804v2
2018-09-10,Density decay and growth of correlations in the Game of Life,"We study the Game of Life as a statistical system on an $L\times L$ square
lattice with periodic boundary conditions. Starting from a random initial
configuration of density $\rho_{\rm in}=0.3$ we investigate the relaxation of
the density as well as the growth with time of spatial correlations. The
asymptotic density relaxation is exponential with a characteristic time
$\tau_L$ whose system size dependence follows a power law $\tau_L\propto L^z$
with $z=1.66\pm 0.05$ before saturating at large system sizes to a constant
$\tau_\infty$. The correlation growth is characterized by a time dependent
correlation length $\xi_t$ that follows a power law $\xi_t\propto
t^{1/z^\prime}$ with $z^\prime$ close to $z$ before saturating at large times
to a constant $\xi_\infty$. We discuss the difficulty of determining the
correlation length $\xi_\infty$ in the final ""quiescent"" state of the system.
The decay time $t_{\rm q}$ towards the quiescent state is a random variable, we
present simulational evidence as well as a heuristic argument indicating that
for large $L$ its distribution peaks at a value $t_{\rm q}^*(L) \simeq
2\tau_\infty\log L$.",1809.03266v2
2018-09-18,A Simple Approximation for a Hard Routing Problem,"We consider a routing problem which plays an important role in several
applications, primarily in communication network planning and VLSI layout
design. The original underlying graph algorithmic task is called Disjoint Paths
problem. In most applications, one can encounter its capacitated
generalization, which is known as the Unsplitting Flow problem. These
algorithmic tasks are very hard in general, but various efficient
(polynomial-time) approximate solutions are known. Nevertheless, the
approximations tend to be rather complicated, often rendering them impractical
in large, complex networks. Our goal is to present a solution that provides a
simple, efficient algorithm for the unsplittable flow problem in large directed
graphs. The simplicity is achieved by sacrificing a small part of the solution
space. This also represents a novel paradigm of approximation: rather than
giving up finding an exact solution, we restrict the solution space to its most
important subset and exclude those that are marginal in some sense. Then we
find the exact optimum efficiently within the subset. Specifically, the
sacrificed parts (i.e., the marginal instances) only contain scenarios where
some edges are very close to saturation. Therefore, the excluded part is not
significant, since the excluded almost saturated solutions are typically
undesired in practical applications, anyway.",1809.06562v1
2018-09-28,Standing lattice solitons in the discrete NLS equation with saturation,"We consider standing lattice solitons for discrete nonlinear Schrodinger
equation with saturation (NLSS), where so-called transparent points were
recently discovered. These transparent points are the values of the governing
parameter (e.g., the lattice spacing) for which the Peierls-Nabarro barrier
vanishes. In order to explain the existence of transparent points, we study a
solitary wave solution in the continuous NLSS and analyse the singularities of
its analytic continuation in the complex plane. The existence of a quadruplet
of logarithmic singularities nearest to the real axis is proven and applied to
two settings: (i) the fourth-order differential equation arising as the
next-order continuum approximation of the discrete NLSS and (ii) the
advance-delay version of the discrete NLSS.",1809.10828v1
2018-10-01,Few $T$ copies in $H$-saturated graphs,"A graph is $F$-saturated if it is $F$-free but the addition of any edge
creates a copy of $F$. In this paper we study the quantity $\mathrm{sat}(n, H,
F)$ which denotes the minimum number of copies of $H$ that an $F$-saturated
graph on $n$ vertices may contain. This parameter is a natural saturation
analogue of Alon and Shikhelman's generalized Tur\'an problem, and letting $H =
K_2$ recovers the well-studied saturation function. We provide a first
investigation into this general function focusing on the cases where the host
graph is either $K_s$ or $C_k$-saturated. Some representative interesting
behavior is:
  (a) For any natural number $m$, there are graphs $H$ and $F$ such that
$\mathrm{sat}(n, H, F) = \Theta(n^m)$.
  (b) For many pairs $k$ and $l$, we show $\mathrm{sat}(n, C_l, C_k) = 0$. In
particular, we prove that there exists a triangle-free $C_k$-saturated graph on
$n$ vertices for any $k > 4$ and large enough $n$.
  (c) $\mathrm{sat}(n, K_3, K_4) = n-2$, $\mathrm{sat}(n, C_4, K_4) \sim
\frac{n^2}{2}$, and $\mathrm{sat}(n, C_6, K_5) \sim n^3$.
  We discuss several intriguing problems which remain unsolved.",1810.00939v2
2018-10-01,Exact stationary solutions of the Kolmogorov-Feller equation in a bounded domain,"We present the first detailed analysis of the statistical properties of jump
processes bounded by a saturation function and driven by Poisson white noise,
being a random sequence of delta pulses. The Kolmogorov-Feller equation for the
probability density function (PDF) of such processes is derived and its
stationary solutions are found analytically in the case of the symmetric
uniform distribution of pulse sizes. Surprisingly, these solutions can exhibit
very complex behavior arising from both the boundedness of pulses and
processes. We show that all features of the stationary PDF (number of branches,
their form, extreme values probability, etc.) are completely determined by the
ratio of the saturation function width to the half-width of the pulse-size
distribution. We verify all theoretical results by direct numerical
simulations.",1810.00992v2
2018-10-13,Confinement and crowding control the morphology and dynamics of a model bacterial chromosome,"Motivated by recent experiments probing shape, size and dynamics of bacterial
chromosomes in growing cells, we consider a polymer model consisting of a
circular backbone to which side-loops are attached, confined to a cylindrical
cell. Such a model chromosome spontaneously adopts a helical shape, which is
further compacted by molecular crowders to occupy a nucleoid-like subvolume of
the cell. With increasing cell length, the longitudinal size of the chromosome
increases in a non-linear fashion to finally saturate, its morphology gradually
opening up while displaying a changing number of helical turns. For shorter
cells, the chromosome extension varies non-monotonically with cell size, which
we show is associated with a radial to longitudinal spatial reordering of the
crowders. Confinement and crowders constrain chain dynamics leading to
anomalous diffusion. While the scaling exponent for the mean squared
displacement of center of mass grows and saturates with cell length, that of
individual loci displays broad distribution with a sharp maximum.",1810.05869v1
2018-09-04,Determination of water permeability for cementitious materials with minimized batch effect,"Values of water permeability for cementitious materials reported in the
literature show a large scatter. This is partially attributed to the fact that
materials used in different studies are different. To eliminate the effects of
cements, specimen preparation, curing conditions and other batch effects, this
study employs a long cylindrical cement paste to prepare all specimens for a
variety of permeability determination methods, such as beam bending,
sorptivity, Katz Thompson and Kozeny Carman equations. Permeabilities
determined by these methods are then used in a moisture transport model.
Compared with the measured mass loss curves, we found that permeability
determined by the beam bending method provides much closer results to the
measured ones than other methods. The difference results from that the
saturated specimen is used in the beam bending method while specimens in other
methods are dried (or rewetted). As already shown in the literature, the
microstructure of the dried or rewetted specimens is altered and different to
the original microstructure of the water saturated specimens.",1810.06463v1
2018-10-17,A (Bounded) Bestiary of Feynman Integral Calabi-Yau Geometries,"We define the rigidity of a Feynman integral to be the smallest dimension
over which it is non-polylogarithmic. We argue that massless Feynman integrals
in four dimensions have a rigidity bounded by 2(L-1) at L loops, and we show
that this bound may be saturated for integrals that we call marginal: those
with (L+1)D/2 propagators in (even) D dimensions. We show that marginal Feynman
integrals in D dimensions generically involve Calabi-Yau geometries, and we
give examples of finite four-dimensional Feynman integrals in massless $\phi^4$
theory that saturate our predicted bound in rigidity at all loop orders.",1810.07689v2
2018-10-31,Enhanced Quasi-Maximum Likelihood Decoding of Short LDPC Codes based on Saturation,"In this paper, we propose an enhanced quasi-maximum likelihood (EQML) decoder
for LDPC codes with short block lengths. After the failure of the conventional
belief propagation (BP) decoding, the proposed EQML decoder selects unreliable
variable nodes (VNs) and saturates their associated channel output values to
generate a list of decoder input sequences. Each decoder input sequence in the
list is then decoded by the conventional BP decoder to obtain the most likely
codeword. To improve the accuracy of selecting unreliable VNs, we propose an
edge-wise selection method based on the sign fluctuation of VNs' extrinsic
messages. A partial pruning stopping (PPS) rule is also presented to reduce the
decoding latency. Simulation results show that the proposed EQML decoder
outperforms the conventional BP decoder and the augmented BP decoder for short
LDPC codes. It even approaches the performance of ML decoding within 0.3 dB in
terms of frame error rate. In addition, the proposed PPS rule achieves a lower
decoding latency compared to the list decoding stopping rule.",1810.13111v2
2018-11-12,Fully Implicit Multidimensional Hybrid Upwind Scheme for Coupled Flow and Transport,"Robust and accurate fully implicit finite-volume schemes applied to
Darcy-scale multiphase flow and transport in porous media are highly desirable.
Recently, a smooth approximation of the saturation-dependent flux coefficients
based on Implicit Hybrid Upwinding (IHU) has been proposed to improve the
nonlinear convergence in fully implicit simulations with buoyancy. Here, we
design a truly multidimensional extension of this approach that retains the
simplicity and robustness of IHU while reducing the sensitivity of the results
to the orientation of the computational (Cartesian) grid. This is achieved with
the introduction of an adaptive, local coupling between the fluxes that takes
the flow pattern into account. We analyze the mathematical properties of the
proposed methodology to show that the scheme is monotone in the presence of
competing viscous and buoyancy forces and yields saturations remaining between
physical bounds. Finally, we demonstrate the efficiency and accuracy of the
scheme on challenging two-dimensional two-phase examples with buoyancy, with an
emphasis on the reduction of the grid orientation effect.",1811.04830v3
2018-11-22,Revised theoretical limit of subthreshold swing in field-effect transistors,"This letter reports a temperature-dependent limit for the subthreshold swing
in MOSFETs that deviates from the Boltzmann limit at deep-cryogenic
temperatures. Below a critical temperature, the derived limit saturates to a
value that is independent of temperature and proportional to the extent of a
band tail. Since the saturation is universally observed in different types of
MOSFETs (regardless of dimension or semiconductor material), the band tail is
attributed to the finite periodicity of the lattice in a semiconductor volume,
and to a lesser extent to additional lattice perturbations such as defects or
disorder.",1811.09146v3
2018-11-30,Signature of quantum chaos in operator entanglement in 2d CFTs,"We study operator entanglement measures of the unitary evolution operators of
(1+1)-dimensional conformal field theories (CFTs), aiming to uncover their
scrambling and chaotic behaviors. In particular, we compute the bi-partite and
tri-partite mutual information for various configurations of input and output
subsystems, and as a function of time. We contrast three different CFTs: the
free fermion theory, compactified free boson theory at various radii, and CFTs
with holographic dual. We find that the bi-partite mutual information exhibits
distinct behaviors for these different CFTs, reflecting the different
information scrambling capabilities of these unitary operators; while a
quasi-particle picture can describe well the case the free fermion and free
boson CFTs, it completely fails for the case of holographic CFTs. Similarly,
the tri-partite mutual information also distinguishes the unitary evolution
operators of different CFTs. In particular, its late-time behaviors, when the
output subsystems are semi-infinite, are quite distinct for these theories. We
speculate that for holographic theories the late-time saturation value of the
tri-partite mutual information takes the largest possible negative value and
saturates the lower bound among quantum field theories.",1812.00013v1
2018-12-10,The $φ^4$ model with the BPS preserving defect,"The $\phi^4$ model is coupled to an impurity in a way that preserves one-half
of the BPS property. This means that the antikink-impurity bound state is still
a BPS solution, i.e., a zero-pressure solution saturating the topological
energy bound. The kink-impurity bound state, on the other hand, does not
saturate the bound, in general. We found that, although the impurity breaks
translational invariance, it is, in some sense, restored in the BPS sector
where the energy of the antikink-impurity solution does not depend on their
mutual distance. This is reflected in the existence of a generalised
translational symmetry and a zero mode. We also investigate scattering
processes. In particular, we compare the antikink-impurity interaction close to
the BPS regime, which presents a rather smooth, elastic like nature, with other
scattering processes. However, even in this case, after exciting a sufficiently
large linear mode on the incoming antikink, we can depart from the close-to-BPS
regime. This results, for example, in a backward scattering.",1812.04007v2
2018-12-12,Upper bound of density for packing of congruent hyperballs in hyperbolic $3-$space,"In \cite{Sz17-2} we proved that to each saturated congruent hyperball packing
exists a decomposition of $3$-dimensional hyperbolic space $\mathbb{H}^3$ into
truncated tetrahedra. Therefore, in order to get a density upper bound for
hyperball packings, it is sufficient to determine the density upper bound of
hyperball packings in truncated simplices. In this paper we prove, using the
above results and the results of papers \cite{M94} and \cite{Sz14}, that the
density upper bound of the saturated congruent hyperball (hypersphere) packings
related to the corresponding truncated tetrahedron cells is realized in a
regular truncated tetrahedra with density $\approx 0.86338$. Furthermore, we
prove that the density of locally optimal congruent hyperball arrangement in
regular truncated tetrahedron is not a monotonically increasing function of the
height (radius) of corresponding optimal hyperball, contrary to the ball
(sphere) and horoball (horosphere) packings.",1812.06785v1
2018-12-31,Microscopic 3D measurement of shiny surfaces based on a multi-frequency phase-shifting scheme,"Microscopic fringe projection profilometry is a powerful 3D measurement
technique with a theoretical measurement accuracy better than one micron
provided that the measured targets can be imaged with good fringe visibility.
However, practically, the 3D shape of the measured surface can hardly be fully
reconstructed due to the defocus of the dense fringes and complex surface
reflexivity characteristics, which lead to low fringe quality and intensity
saturation. To address this problem, we propose to calculate phases of these
highlighted areas from a subset of the fringe sequence which is not subjected
to the intensity saturation. By using the proposed multi-frequency
phase-shifting scheme, the integrity of the 3D surface reconstruction can be
significantly improved. The ultimate phase maps obtained from unsaturated
intensities are used to achieve high-accuracy 3D recovering of shiny surfaces
based on a phase stereo matching method. Experimental results on different
metal surfaces show that our approach is able to retrieve the complete
morphology of shiny surfaces with high accuracy and fidelity.",1901.00381v1
2019-01-08,Constraint to chiral invariant masses of nucleons from GW170817 in an extended parity doublet model,"We construct nuclear matter based on an extended parity doublet model
including four light nucleons $N(939)$, $N(1440)$, $N(1535)$, and $N(1650)$. We
exclude some values of the chiral invariant masses by requiring the saturation
properties of normal nuclear matter; saturation density, binding energy,
incompressibility, and symmetry energy. We find further constraint to the
chiral invariant masses from the tidal deformability determined by the
observation of the gravitational waves from neutron star merger GW170817. Our
result shows that the chiral invariant masses are larger than about $600\,$MeV.
We also give some predictions on the symmetry energy and the slope parameters
in the high density region, which will be measured in future experiments.",1901.02167v2
2019-01-08,The semi-algebraic geometry of saturated optimal designs for the Bradley-Terry model,"Optimal design theory for nonlinear regression studies local optimality on a
given design space. We identify designs for the Bradley--Terry paired
comparison model with small undirected graphs and prove that every saturated
D-optimal design is represented by a path. We discuss the case of four
alternatives in detail and derive explicit polynomial inequality descriptions
for optimality regions in parameter space. Using these regions, for each point
in parameter space we can prescribe a D-optimal design.",1901.02375v3
2019-01-09,Recovering saturated images for high dynamic Kernel-Phase analysis Application to the determination of dynamical masses for the system Gl 494AB,"Kernel-phase observables extracted from mid- to high-Strehl images are
proving to be a powerful tool to probe within a few angular resolution elements
of point sources. The attainable contrast is however limited by the dynamic
range of the imaging sensors. The Fourier interpretation of images with pixels
exposed beyond the saturation has so far been avoided. We show that in cases
where the image is dominated by the light of a point source, we can use an
interpolation to reconstruct the otherwise lost pixels with an accuracy
sufficient to enable the extraction of kernel-phases from the patched image. We
demonstrate the usability of our method by applying it to archive images of the
Gl 494AB system, taken with the Hubble Space Telescope in 1997. Using this new
data point along with other resolved observations and radial velocity
measurements, we produce improved constraints on the orbital parameters of the
system, and consequently the masses of its components.",1901.02824v2
2018-12-30,Performance modelling of access control mechanisms for local and vehicular wireless networks,"Carrier sense multiple access collision avoidance (CSMA/CA) is the basic
scheme upon which access to the shared medium is regulated in many wireless
networks. With CSMA/CA a station willing to start a transmission has first to
find the channel free for a given duration otherwise it will go into
\emph{backoff}, i.e. refraining for transmitting for a randomly chosen delay.
Performance analysis of a wireless network employing CSMA/CA regulation is not
an easy task: except for simple network configuration analytical solution of
key performance indicators (KPI) cannot be obtained hence one has to resort to
formal modelling tools. In this paper we present a performance modelling study
targeting different kind of CSMA/CA based wireless networks, namely: the IEEE
802.11 Wireless Local Area Networks (WLANs) and the 802.11p Vehicular Ad Hoc
Networks (VANETs), which extends 802.11 with priorities over packets. The
modelling framework we introduce allows for considering: i) an arbitrarily
large number of stations, ii) different traffic conditions
(saturated/non-saturated), iii) different hypothesis concerning the shared
channel (ideal/non-ideal). We apply statistical model checking to assess KPIs
of different network configurations.",1901.04285v1
2019-01-19,Towards a better understanding of the symmetry energy within neutron stars,"The LIGO-Virgo collaboration ground-breaking detection of the binary
neutron-star merger event, GW170817, has expanded efforts to understand the
Equation of State (EoS) of nuclear matter. These measurements provide new
constraints on the overall pressure, but do not, by itself, elucidate its
microscopic origins, including the pressure arising from the symmetry energy,
that governs much of the internal structure of a neutron star. To correlate
microscopic constraints from nuclear measurements to the GW170817 constraints,
we calculate neutron star properties with more than 200 Skyrme energy density
functionals that describe properties of nuclei. Calculated neutron-star radii
(R) and the tidal deformabilities which show a strong correlation with pressure
at twice saturation density. By combining the neutron star EoS extracted from
the GW170817 event and the EoS of symmetric matter from nucleus-nucleus
collision experiments, we extract the density dependence of the symmetry
pressure from 1.2 to 4.5 times saturation density. While the uncertainties in
the symmetry pressure are large, they can be reduced with new experimental and
astrophysical results.",1901.07673v1
2019-01-23,Quantum coherence across bosonic superconductor-anomalous metal-insulator transitions,"After decades of explorations, suffering from low critical temperature and
subtle nature, whether a metallic ground state exists in a two-dimensional
system beyond Anderson localization is still a mystery. Supremely, phase
coherence could be the key that unlocks its intriguing nature. This work
reveals how quantum phase coherence evolves across bosonic
superconductor-metal-insulator transitions via magneto-conductance quantum
oscillations in high-Tc superconducting films. A robust intervening anomalous
metallic state characterized by both resistance and oscillation amplitude
saturations in the low temperature regime is detected. By contrast, with
decreasing temperature the oscillation amplitude monotonically grows on the
superconducting side, but decreases at low temperatures on the insulating side.
It suggests that the saturation of phase coherence plays a prominent role in
the formation of this anomalous metallic state.",1901.07706v1
2019-01-25,Evanescent Field Functional Cu3-xP Nanoparticles as Effective Saturable Absorbers with high Repeatability for Femtosecond Soliton Pulse generation,"Recently, a new emerging field about heavily-doped colloidal plasmonic
nanocrystals (NCs) has attracted great attention due to their lower and
expediently adjustable free carrier densities, lower and tunable LSPR band in
the spectral range from NIR to MIR and higher optical nonlinearity. These new
kinds of plasmonic materials will show huge potential and opportunities for
nonlinear optical applications, such as ultrafast switching, nonlinear sensing
and pulse laser generation. In this work, we demonstrate that high-quality
mode-locking and Q-switching pulses at 1560 nm can both be generated by using
controllable concentration of Cu3-xP NCs solution and fabricating evanescently
interacted saturable absorbers. Furthermore, the plasmonic NCs material has
good reproduction for fabricating SA devices and promising potential for
large-scale industrial production. Our results may attract great attention for
further investigations of heavily-doped plasmonic NCs as next generation, cheap
and solution-processed element for fascinating applications in optoelectronic
devices.",1901.08714v1
2019-01-28,Calculated threshold of supratransmission phenomena in waveguide arrays with saturable nonlinearity,"In this work, we consider a semi-infinite discrete nonlinear Schr\""odinger
equation with saturable nonlinearity driven at one edge by a driving force. The
equation models the dynamics of coupled photorefractive waveguide arrays. It
has been reported that when the frequency of the driving force is in the
forbidden band, energy can be transmitted along the lattices provided that the
driving amplitude is above a critical value. This nonlinear tunneling is called
supratransmission. Here, we explain the source of supratransmission using
geometric illustrations. Approximations to the critical amplitude for
supratransmission are presented as well.",1901.09518v1
2019-01-30,On the Theoretical Limits of Beam Steering in mmWave Massive MIMO Channels,"Analog Beamsteering (ABS) has emerged as a low complexity, power efficient
solution for MillimeterWave (mmWave) massive Multiple Input Multiple Output
(MIMO) systems. Moreover, driven by the low spatial correlation between the
User Terminals (UTs) with high number of transmit antennas (massive MIMO) at
the Base Station (BS), ABS can be used to support Multi User (MU) MIMO
scenarios instead of digital or Hybrid Beamforming (HBF). However, we show in
this paper, that even with high number of transmit antennas, the HBF can
achieve better Spectral Efficiency (SE) compared to the MU ABS even in pure
Line of Sight (LoS) channels. Moreover, we prove that the MU ABS saturates to a
constant SE at high transmit Signal to Noise Ratio (SNR) and we theoretically
derive an approximation to that saturation bound in this paper. On the other
hand, we highlight that the HBF's SE scales with the transmit SNR even in high
SNR regime. Finally, given the same power consumption and hardware complexity
as the MU ABS case, we show that HBF asymptotically achieves the optimal SE
(ideal non interference scenario) when increasing the number of transmit
antennas.",1901.11404v1
2019-01-16,Impact of Non-Linear High-Power Amplifiers on Cooperative Relaying Systems,"In this paper, we investigate the impact of the high-power amplifier
non-linear distortion on multiple relay systems by introducing the soft
envelope limiter, traveling wave tube amplifier, and solid-state power
amplifier to the relays. The system employs amplify-and-forward either fixed or
variable gain relaying and uses the opportunistic relay selection with outdated
channel state information to select the best relay. The results show that the
performance loss is small at low rates; however, it is significant for high
rates. In particular, the outage probability and the bit error rate are
saturated by an irreducible floor at high rates. The same analysis is pursued
for the capacity and shows that it is saturated by a detrimental ceiling as the
average signal-to-noise ratio becomes higher. This result contrasts the case of
the ideal hardware where the capacity grows indefinitely. Moreover, the results
show that the capacity ceiling is proportional to the impairment's parameter
and for some special cases the impaired systems practically operate in
acceptable conditions. Closed-forms and high SNR asymptotes of the outage
probability, the bit error rate, and the capacity are derived. Finally,
analytical expressions are validated by the Monte Carlo simulation.",1902.03176v1
2019-02-14,A note on rainbow saturation number of paths,"For a fixed graph $F$ and an integer $t$, the \dfn{rainbow saturation number}
of $F$, denoted by $sat_t(n,\mathfrak{R}(F))$, is defined as the minimum number
of edges in a $t$-edge-colored graph on $n$ vertices which does not contain a
\dfn{rainbow copy} of $F$, i.e., a copy of $F$ all of whose edges receive a
different color, but the addition of any missing edge in any color from $[t]$
creates such a rainbow copy. Barrus, Ferrara, Vardenbussche and Wenger prove
that $sat_t(n,\mathfrak{R}(P_\ell))\ge n-1$ for $\ell\ge 4$ and
$sat_t(n,\mathfrak{R}(P_\ell))\le \lceil \frac{n}{\ell-1} \rceil \cdot
\binom{\ell-1}{2}$ for $t\ge \binom{\ell-1}{2}$, where $P_\ell$ is a path with
$\ell$ edges. In this short note, we improve the upper bounds and show that
$sat_t(n,\mathfrak{R}(P_\ell))\le \lceil \frac{n}{\ell} \rceil \cdot
\left({{\ell-2}\choose {2}}+4\right)$ for $\ell\ge 5$ and $t\ge 2\ell-5$.",1902.05222v3
2019-02-15,Measuring algorithmic complexity in chaotic lasers,"Thanks to the simplicity and robustness of its calculation methods,
algorithmic (or Kolmogorov) complexity appears as a useful tool to reveal
chaotic dynamics when experimental time series are too short and noisy to apply
Takens' reconstruction theorem. We measure the complexity in chaotic regimes,
with and without extreme events (sometimes called optical rogue waves), of
three different all-solid-state lasers: Kerr lens mode locking femtosecond Ti:
Sapphire (""fast"" saturable absorber), Nd:YVO4 + Cr:YAG (""slow"" saturable
absorber) and Nd:YVO4 with modulated losses. We discuss how complexity
characterizes the dynamics in an understandable way in all cases, and how it
provides a correction factor to the horizon of predictability given by Lyapunov
exponents. This approach may be especially convenient to implement schemes of
chaos control in real time.",1902.05790v2
2019-02-19,Thermal Emission from Semi-classical Dynamical Systems,"Recently the bound on the Lyapunov exponent $\lambda_L \le 2\pi T/ \hbar$ in
thermal quantum systems was conjectured by Maldacena, Shenker, and Stanford. If
we naively apply this bound to a system with a fixed Lyapunov exponent
$\lambda_L$, it might predict the existence of the lower bound on temperature
$T \ge \hbar \lambda_L/ 2\pi $. Particularly, it might mean that chaotic
systems cannot be zero temperature quantum mechanically. Even classical
dynamical systems, which are deterministic, might exhibit thermal behaviors
once we turn on quantum corrections. We elaborate this possibility by
investigating semi-classical particle motions near the hyperbolic fixed point
and show that indeed quantum corrections may induce energy emission which obeys
a Boltzmann distribution. We also argue that this emission is related to
acoustic Hawking radiation in quantum fluid. Besides, we discuss when the bound
is saturated and show that a particle motion in an inverse harmonic potential
and $c=1$ matrix model may saturate the bound although they are integrable.",1902.06940v2
2019-02-19,A Bound on Thermal Relativistic Correlators at Large Spacelike Momenta,"We consider thermal Wightman correlators in a relativistic quantum field
theory in the limit where the spatial momenta of the insertions become large
while their frequencies stay fixed. We show that, in this limit, the size of
these correlators is bounded by $e^{-\beta R}$, where $R$ is the radius of the
smallest sphere that contains the polygon formed by the momenta. We show that
perturbative quantum field theories can saturate this bound through suitably
high-order loop diagrams. We also consider holographic theories in
$d$-spacetime dimensions, where we show that the leading two-point function of
generalized free-fields saturates the bound in $d = 2$ and is below the bound
for $d > 2$. We briefly discuss interactions in holographic theories and
conclude with a discussion of several open problems.",1902.07203v1
2019-02-25,Universal Hall coefficient correction in strongly coupled Cr-SiO$_2$ nanogranular metals,"The microstructure and electrical transport of Cr$_x$(SiO$_2$)$_{1-x}$
nanogranular films with Cr volume faction $x$$\simeq$0.67 and 0.72 are
systematically investigated. The transmission electron microscopy images and
elemental mappings indicate that the films are quite inhomogeneous: some Cr
granules directly connect to others while some Cr granules with size $\sim$1 to
$\sim$3\,nm disperse in the SiO$_2$ dielectric matrix. For each film, the Hall
coefficient $R_H$ varies linearly with the natural logarithm of temperature,
i.e., $\Delta R_H$$\propto$$\ln T$, above $\sim$60\,K, saturates at
$\sim$60\,K, and retains the saturating value below $\sim$60\,K. The
temperature dependence of Hall coefficient can be explained by the recent
theory in granular metals and originates from \emph{virtual diffusion} of
electrons through the metallic granules. For the conductivity $\sigma$, a
robust $\Delta \sigma$$\propto$$\sqrt{T}$ law is observed from $\sim$50 down to
2\,K. The behavior of the conductivity stems from the ``Altshuler-Aronov""
correction, whose influence on the Hall coefficient is not present in the
films.",1902.09264v1
2019-03-02,A complete Heyting algebra whose Scott space is non-sober,"We prove that (1) for any complete lattice $L$, the set $\mathcal{D}(L)$ of
all nonempty saturated compact subsets of the Scott space of $L$ is a complete
Heyting algebra (with the reverse inclusion order); and (2) if the Scott space
of a complete lattice $L$ is non-sober, then the Scott space of
$\mathcal{D}(L)$ is non-sober. Using these results and the Isbell's example of
a non-sober complete lattice, we deduce that there is a complete Heyting
algebra whose Scott space is non-sober, thus give a positive answer to a
problem posed by Jung. We will also prove that a $T_0$ space is well-filtered
iff its upper space (the set $\mathcal{D}(X)$ of all nonempty saturated compact
subsets of $X$ equipped with the upper Vietoris topology) is well-filtered,
which answers another open problem.",1903.00615v1
2019-03-04,Mixed-Triggered Reliable Control for Singular Networked Cascade Control Systems with Randomly Occurring Cyber Attack,"In this paper, the issue of mixed-triggered reliable dissipative control is
investigated for singular networked cascade control systems (NCCSs) with
actuator saturation and randomly occurring cyber attacks. In order to utilize
the limited communication resources effectively, a more general mixed-triggered
scheme is established which includes both schemes namely time-triggered and
event-triggered in a single framework. In particular, two main factors are
incorporated to the proposed singular NCCS model namely, actuator saturation
and randomly occurring cyber attack, which is an important role to damage the
overall network security. By employing Lyapunov-Krasovskii stability theory, a
new set of sufficient conditions in terms of linear matrix inequalities (LMIs)
is derived to guarantee the singular NCCSs to be admissible and strictly
(Q,S,R)-dissipative. Subsequently, a power plant boiler-turbine system based on
a numerical example is provided to demonstrate the effectiveness of the
proposed control scheme.",1903.01024v1
2019-03-07,ENIGMA-NG: Efficient Neural and Gradient-Boosted Inference Guidance for E,"We describe an efficient implementation of clause guidance in
saturation-based automated theorem provers extending the ENIGMA approach.
Unlike in the first ENIGMA implementation where fast linear classifier is
trained and used together with manually engineered features, we have started to
experiment with more sophisticated state-of-the-art machine learning methods
such as gradient boosted trees and recursive neural networks. In particular the
latter approach poses challenges in terms of efficiency of clause evaluation,
however, we show that deep integration of the neural evaluation with the ATP
data-structures can largely amortize this cost and lead to competitive
real-time results. Both methods are evaluated on a large dataset of theorem
proving problems and compared with the previous approaches. The resulting
methods improve on the manually designed clause guidance, providing the first
practically convincing application of gradient-boosted and neural clause
guidance in saturation-style automated theorem provers.",1903.03182v1
2019-03-11,Observer-Based Drag-Tracking Guidance for Entry Vehicles Considering Input Saturation Constraint,"This paper studies the drag-tracking guidance design problem of uncertain
entry vehicles. With employing a Nussbaum type function to deal with input
saturation constraint, an output feedback guidance law (bank angle magnitude)
with a high-gain observer is constructed that makes the drag-tracking error
converge near zero in the presence of uncertainties. It is also worthy to claim
that, in contrast to the existing results whose envelope of uncertainty merely
depends on the drag error, the considered uncertainty is allowed to be not
bigger than a function of drag error and integral term of drag error, which
inevitably occurs in practice. The Monte Carlo simulation is done to illustrate
the advantage of the developed method.",1903.04931v1
2019-03-19,Quasilinear Approach of the Whistler Heat-Flux Instability in the Solar Wind,"The hot beaming (or strahl) electrons responsible for the main electron
heat-flux in the solar wind are believed to be self-regulated by the
electromagnetic beaming instabilities, also known as the heat-flux
instabilities. Here we report the first quasi-linear theoretical approach of
the whistler unstable branch able to characterize the long-term saturation of
the instability as well as the relaxation of the electron velocity
distributions. The instability saturation is not solely determined by the drift
velocities, which undergo only a minor relaxation, but mainly from a concurrent
interaction of electrons with whistlers that induces (opposite) temperature
anisotropies of the core and beam populations and reduces the effective
anisotropy. These results might be able to (i) explain the low intensity of the
whistler heat-flux fluctuations in the solar wind (although other explanations
remain possible and need further investigation), and (ii) confirm a reduced
effectiveness of these fluctuations in the relaxation and isotropization of the
electron strahl and in the regulation of the electron heat-flux.",1903.08005v1
2019-04-01,Modulational stability of nonlinear saturated gravity waves,"Stationary gravity waves, such as mountain lee waves, are effectively
described by Grimshaw's dissipative modulation equations even in high altitudes
where they become nonlinear due to their large amplitudes. In this theoretical
study, a wave-Reynolds number is introduced to characterize general solutions
to these modulation equations. This non-dimensional number relates the vertical
linear group velocity with wavenumber, pressure scale height and kinematic
molecular/eddy viscosity. It is demonstrated by analytic and numerical methods
that Lindzen-type waves in the saturation region, i.e. where the wave-Reynolds
number is of order unity, destabilize by transient perturbations. It is
proposed that this mechanism may be a generator for secondary waves due to
direct wave-mean-flow interaction. By assumption the primary waves are exactly
such that altitudinal amplitude growth and viscous damping are balanced and by
that the amplitude is maximized. Implications of these results on the relation
between mean-flow acceleration and wave breaking heights are discussed.",1904.00666v1
2019-04-08,QCD evolution based evidence for the onset of gluon saturation in exclusive photo-production of vector mesons,"We investigate photo-production of vector mesons J/Psi and Upsilon measured
both at HERA and LHC, using 2 particular fits of inclusive unintegrated gluon
distributions, based on non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta
gluon; KS) and next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution
(Hentschinski-Sabio Vera-Salas gluon; HSS). We find that linear next-to-leading
order evolution can only describe production at highest energies, if
perturbative corrections are increased to unnaturally large values; rendering
this corrections to a perturbative size, the growth with energy is too strong
and the description fails. At the same time, the KS gluon, which we explore
both with and without non-linear corrections, requires the latter to achieve an
accurate description of the energy dependence of data. We interpret this
observation as a clear signal for the presence of high gluon densities in the
proton, characteristic for the onset of gluon saturation.",1904.04394v2
2019-04-21,Oxidized silicon sulfide: stability and electronic properties of a novel two-dimensional material,"Isolated oxygen impurities and fully oxidized structures of four stable
two-dimensional (2D) SiS structures are investigated by {\em ab initio} density
functional calculations. Binding energies of oxygen impurities for all the four
2D SiS structures are found larger than those for phosphorene, due to the lower
electronegativity of Si atoms. The most stable configurations of isolated
oxygen impurities for different 2D SiS structures are decided and the
corresponding 2D structures with saturated oxidation (SiSO) are predicted.
Among all the four fully oxidized structures, $\alpha$-SiSO is demonstrated to
be stable by phonon spectra calculations and molecular dynamics (MD)
simulations. Electronic structure calculations indicate that $\alpha$-SiSO
monolayer is semiconducting with a direct band gap of ${\approx}2.28$~eV, which
can be effectively tuned by in-layer strain. The value of band gap and
thermodynamic stability are found depending sensitively on the saturation level
of oxygen.",1904.09614v1
2019-04-25,JPEG XT Image Compression with Hue Compensation for Two-Layer HDR Coding,"We propose a novel JPEG XT image compression with hue compensation for
two-layer HDR coding. LDR images produced from JPEG XT bitstreams have some
distortion in hue due to tone mapping operations. In order to suppress the
color distortion, we apply a novel hue compensation method based on the
maximally saturated colors. Moreover, the bitstreams generated by using the
proposed method are fully compatible with the JPEG XT standard. In an
experiment, the proposed method is demonstrated not only to produce images with
small hue degradation but also to maintain well-mapped luminance, in terms of
three kinds of criterion: TMQI, hue value in CIEDE2000, and the maximally
saturated color on the constant-hue plane.",1904.11315v1
2019-05-06,Insights on Skyrme parameters from GW170817,"The binary neutron-star merger event, GW170817, has cast a new light on
nuclear physics research. Using a neutron-star model that includes a crust
equation of state (EoS), we calculate the properties of a 1.4 solar-mass
neutron star. The model incorporates more than 200 Skyrme energy density
functionals, which describe nuclear matter properties, in the outer liquid core
region of the neutron star. We find a power-law relation between the
neutron-star tidal deformability, $\Lambda$, and the neutron-star radius, R.
Without an explicit crust EoS, the model predicts smaller R and the difference
becomes significant for stars with large radii. To connect the neutron star
properties with nuclear matter properties, we confront the predicted values for
$\Lambda$, against the Taylor expansion coefficients of the Skyrme
interactions. There is no pronounced correlation between Skyrme parameters in
symmetric nuclear matter and neutron star properties. However, we find the
strongest correlation between $\Lambda$ and $K_{sym}$, the curvature of the
density dependence of the symmetry energy at saturation density. At twice the
saturation density, our calculations show a strong correlation between
$\Lambda$ and total pressure providing guidance to laboratory nucleus-nucleus
collision experiments.",1905.02601v1
2019-05-15,Maximal Quantum Fisher Information for Mixed States,"We study quantum metrology for unitary dynamics. Analytic solutions are given
for both the optimal unitary state preparation starting from an arbitrary mixed
state and the corresponding optimal measurement precision. This represents a
rigorous generalization of known results for optimal initial states and upper
bounds on measurement precision which can only be saturated if pure states are
available. In particular, we provide a generalization to mixed states of an
upper bound on measurement precision for time-dependent Hamiltonians that can
be saturated with optimal Hamiltonian control. These results make precise and
reveal the full potential of mixed states for quantum metrology.",1905.06101v2
2019-05-17,Pattern formation induced by intraspecific interactions in a predator-prey system,"Differential diffusion is a source of instability in population dynamics
systems when species diffuse with different rates. Predator-prey systems show
this instability only under certain specific conditions, usually requiring
Holling-type functionals involved. Here we study the effects of intraspecific
cooperation and competition on diffusion-driven instability in a predator-prey
system with a different structure. We conduct the analysis on a generalized
population dynamics that bounds intraspecific and interspecific interactions
with Verhulst-type saturation terms instead of Holling-type functionals. We
find that instability occurs due to the intraspecific saturation or
intraspecific interactions, both cooperative and competitive. We present
numerical simulations and show spatial patterns due to diffusion.",1905.07256v1
2019-05-23,ENIGMAWatch: ProofWatch Meets ENIGMA,"In this work we describe a new learning-based proof guidance -- ENIGMAWatch
-- for saturation-style first-order theorem provers. ENIGMAWatch combines two
guiding approaches for the given-clause selection implemented for the E ATP
system: ProofWatch and ENIGMA. ProofWatch is motivated by the watchlist (hints)
method and based on symbolic matching of multiple related proofs, while ENIGMA
is based on statistical machine learning. The two methods are combined by using
the evolving information about symbolic proof matching as an additional
information that characterizes the saturation-style proof search for the
statistical learning methods. The new system is experimentally evaluated on a
large set of problems from the Mizar Library. We show that the added
proof-matching information is considered important by the statistical machine
learners, and that it leads to improvements in E's Performance over ProofWatch
and ENIGMA.",1905.09565v2
2019-05-25,Subregion complexity in holographic thermalization with dS boundary,"We study the time evolution of holographic subregion complexity (HSC) in
Vaidya spacetime with dS boundary. The subregion on the boundary is chosen to
be a sphere within the cosmological horizon. It is found that the behaviour of
HSC is similar to that in cases with flat boundary. The whole evolution can be
divided into four stages: First, it grows almost linearly, then the growth
slows down; After reaching a maximum it drops down quickly and gets to
saturation finally. The linear growth rate in the first stage is found to
depend almost only on the the mass parameter. As the subregion size approaches
the cosmological horizon, this stage is expected to last forever with the
subsequent three stages washed out. The saturation time $\tilde{t}_{sat}$
depends almost only on the subregion size $\tilde{R}$ as $\tilde{t}_{sat} =
\tanh^{-1} (\tilde{R})$ which is linear in $\tilde{R}$ when $\tilde{R}$ is
small but logarithmically divergent as $\tilde{R}$ approaches the cosmological
horizon.",1905.10605v3
2019-05-26,Avoiding Scalability Collapse by Restricting Concurrency,"Saturated locks often degrade the performance of a multithreaded application,
leading to a so-called scalability collapse problem. This problem arises when a
growing number of threads circulating through a saturated lock causes the
overall application performance to fade or even drop abruptly. This problem is
particularly (but not solely) acute on oversubscribed systems (systems with
more threads than available hardware cores). In this paper, we introduce GCR
(generic concurrency restriction), a mechanism that aims to avoid the
scalability collapse. GCR, designed as a generic, lock-agnostic wrapper,
intercepts lock acquisition calls, and decides when threads would be allowed to
proceed with the acquisition of the underlying lock. Furthermore, we present
GCR-NUMA, a non-uniform memory access (NUMA)-aware extension of GCR, that
strives to ensure that threads allowed to acquire the lock are those that run
on the same socket. The extensive evaluation that includes more than two dozen
locks, three machines and three benchmarks shows that GCR brings substantial
speedup (in many cases, up to three orders of magnitude) in case of contention
and growing thread counts, while introducing nearly negligible slowdown when
the underlying lock is not contended. GCR-NUMA brings even larger performance
gains starting at even lighter lock contention.",1905.10818v2
2019-05-27,Skew key polynomials and a generalized Littlewood-Richardson rule,"Young's lattice is a partial order on integer partitions whose saturated
chains correspond to standard Young tableaux, one type of combinatorial object
that generates the Schur basis for symmetric functions. Generalizing Young's
lattice, we introduce a new partial order on weak compositions that we call the
key poset. Saturated chains in this poset correspond to standard key tableaux,
the combinatorial objects that generate the key polynomials, a nonsymmetric
polynomial generalization of the Schur basis. Generalizing skew Schur
functions, we define skew key polynomials in terms of this new poset. Using
weak dual equivalence, we give a nonnegative weak composition
Littlewood-Richardson rule for the key expansion of skew key polynomials,
generalizing the flagged Littlewood-Richardson rule of Reiner and Shimozono.",1905.11526v3
2019-06-12,Outcoupling from a Bose-Einstein condensate in the strong-field limit,"Atoms can be extracted from a trapped Bose-Einstein condensate (BEC) by
driving spin-flips to untrapped states. The coherence properties of the BEC are
transfered to the released atoms, creating a coherent beam of matter refered to
as an atom laser. In this work, the extraction of atoms from a BEC is
investigated numerically by solving a coupled set of Gross-Pitaevskii equations
in up to three dimensions. The result is compared to experimental data and a
semiclassical rate model. In the weak-coupling regime, quantitative agreement
is reached between theory and experiment and a semiclassical rate model. In the
strong-coupling regime, the atom laser enters a trapped state that manifests
itself in a saturation of the rate of out-coupled atoms observed in new
experimental data. The semiclassical rate model fails, but the numerical
descriptions yield qualitative agreement with experimental data at the onset of
saturation.",1906.05196v1
2019-06-15,Constraints on nonlocality in networks from no-signaling and independence,"Generalising the concept of Bell nonlocality to networks leads to novel forms
of correlations, the characterization of which is however challenging. Here we
investigate constraints on correlations in networks under the two natural
assumptions of no-signaling and independence of the sources. We consider the
``triangle network'', and derive strong constraints on correlations even though
the parties receive no input, i.e. each party performs a fixed measurement. We
show that some of these constraints are tight, by constructing explicit local
models (i.e. where sources distribute classical variables) that can saturate
them. However, we also observe that other constraints can apparently not be
saturated by local models, which opens the possibility of having nonlocal (but
non-signaling) correlations in the triangle network.",1906.06495v2
2019-06-17,Doppler-free saturation of the cascade fluorescence that follows excitation of the $5s \to 6p $ transition in atomic rubidium,"We present an experimental scheme that produces Doppler-free spectra of the
$5s \to 6p $ second resonance transition in atomic rubidium. The experiment
uses the saturation of the cascade fluorescence that occurs when thermal
rubidium atoms interact with two counterpropagating $420 $ nm laser beams of
comparable intensity. Part of the excited atomic population goes through the
$5p_{3/2}$ level which then decays by emission of $780$ nm photons. Narrow dips
appear in this otherwise broad $780$ nm fluorescence, which allows resolution
of the $6p_{3/2}$ hyperfine structure. A rate equation model is used to
interpret the spectra. It is also shown that these narrow peaks can be used to
lock the frequency of the $420 $ nm laser. Using a second beam modulated in
frequency produces three sets of spectra with known frequency spacings that can
be used to perform an all-optical measurement of the hyperfine splittings of
the $6p_{3/2} $ manifold in rubidium.",1906.07114v1
2019-06-16,Fronts in two-phase porous flow problems: effects of hysteresis and dynamic capillarity,"In this work, we study the behaviour of saturation fronts for two phase flow
through a long homogeneous porous column. In particular, the model includes
hysteresis and dynamic effects in the capillary pressure and hysteresis in the
permeabilities. The analysis uses travelling wave approximation. Entropy
solutions are derived for Riemann problems that are arising in this context.
These solutions belong to a much broader class compared to the standard Oleinik
solutions, where hysteresis and dynamic effects are neglected. The relevant
cases are examined and the corresponding solutions are categorized. They
include non-monotone profiles, multiple shocks and self-developing stable
saturation plateaus. Numerical results are presented that illustrate the
mathematical analysis. Finally, we compare experimental results with our
theoretical findings.",1906.08134v2
2019-06-19,Entropy Variations and Light Ray Operators from Replica Defects,"We study the defect operator product expansion (OPE) of displacement
operators in free and interacting conformal field theories using replica
methods. We show that as $n$ approaches $1$ a contact term can emerge when the
OPE contains defect operators of twist $d-2$. For interacting theories and
general states we give evidence that the only possibility is from the defect
operator that becomes the stress tensor in the $n\to 1$ limit. This implies
that the quantum null energy condition (QNEC) is always saturated for CFTs with
a twist gap. As a check, we show independently that in a large class of near
vacuum states, the second variation of the entanglement entropy is given by a
simple correlation function of averaged null energy operators as studied by
Hofman and Maldacena. This suggests that sub-leading terms in the the defect
OPE are controlled by a defect version of the spin-3 non-local light ray
operator and we speculate about the possible origin of such a defect operator.
For free theories this contribution condenses to a contact term that leads to
violations of QNEC saturation.",1906.08274v1
2019-06-24,Burst behavior due to quasimode excited by stimulated Brillouin scattering in high-intensity laser-plasma interaction,"The strong-coupling mode, called quasimode, will be excited by stimulated
Brillouin scattering (SBS) in high-intensity laser-plasma interaction. And SBS
of quasimode will compete with SBS of fast mode (or slow mode) in multi-ion
species plasmas, thus leading to a low-frequency burst behavior of SBS
reflectivity. The competition of quasimode and ion-acoustic wave (IAW) is an
important saturation mechanism of SBS in high-intensity laser-plasma
interaction. These results give a clear explanation to the low-frequency
periodic burst behavior of SBS and should be considered as a saturation
mechanism of SBS in high-intensity laser-plasma interaction.",1906.11616v1
2019-07-06,The saturation number of powers of graded ideals,"Let $S=K[x_1,\ldots,x_n]$ be the polynomial ring in $n$ variables over a
field $K$ with maximal ideal $\frak{m}=(x_1,...,x_n)$, and let $I$ be a graded
ideal of $S$. In this paper, we define the saturation number $\sat(I)$ of $I$
to be the smallest non-negative integer $k$ such that $I:\mm^{k+1}= I:\mm^k$.
We show that $f(k)$ is linearly bounded, and that $f(k)$ is a quasi-linear
function for $k\gg 0$, if $I$ is a monomial ideal. Furthermore, we show that
$\sat(I^k)=k$ if $I$ is a principal Borel ideal and prove that $\sat(I_{d,n}^k)
=\max\{l\:\; (kd-l)/(k-l) \leq n\},$ where $I_{d,n}$ is the squarefree Veronese
ideal generated in degree $d$. \end{abstract}",1907.03154v3
2019-07-08,Matter-Geometry entanglement in quantum cosmology,"We present a study of the evolution of entanglement entropy of matter and
geometry in quantum cosmology. For a variety of Gaussian initial states and
their linear combinations, and with evolution defined with respect to a
relational time, we show numerically that (i) entanglement entropy increases
rapidly at very early times, and subsequently saturates to a constant non-zero
value, and (ii) that the saturation value of this entropy is a linear function
of the energy associated to the quantum state: $S_{\text{ent}}^\psi = \gamma
\langle \hat{H} \rangle_\psi$. These results suggest a remnant of quantum
entanglement in the macroscopic Universe from the era of the Big Bang,
independent of the initial state parameters, and a ""First Law"" associated with
matter-gravity entanglement entropy in quantum gravity.",1907.03776v3
2019-07-10,Nonlinear evolution of the whistler heat flux instability,"We use the one-dimensional TRISTAN-MP particle-in-cell code to model the
nonlinear evolution of the whistler heat flux instability that was proposed by
Gary et al. (1999, 2000) to regulate the electron heat flux in the solar wind
and astrophysical plasmas. The simulations are initialized with electron
velocity distribution functions typical for the solar wind. We perform a set of
simulations at various initial values of the electron heat flux and
$\beta_{e}$. The simulations show that parallel whistler waves produced by the
whistler heat flux instability saturate at amplitudes consistent with the
spacecraft measurements. The simulations also reproduce the correlations of the
saturated whistler wave amplitude with the electron heat flux and $\beta_{e}$
revealed in the spacecraft measurements. The major result is that parallel
whistler waves produced by the whistler heat flux instability do not
significantly suppress the electron heat flux. The presented simulations
indicate that coherent parallel whistler waves observed in the solar wind are
unlikely to regulate the heat flux of solar wind electrons.",1907.04878v1
2019-07-01,Direct Measurement of the Elastohydrodynamic Lift Force at the Nanoscale,"We present the first direct measurement of the elastohydrodynamic lift force
acting on a sphere moving within a viscous liquid, near and along a soft
substrate under nanometric confinement. Using atomic force microscopy, the lift
force is probed as a function of the gap size, for various driving velocities,
viscosities, and stiffnesses. The force increases as the gap is reduced and
shows a saturation at small gap. The results are in excellent agreement with
scaling arguments and a quantitative model developed from the soft lubrication
theory, in linear elasticity, and for small compliances. For larger
compliances, or equivalently for smaller confinement length scales, an
empirical scaling law for the observed saturation of the lift force is given
and discussed.",1907.05849v2
2019-07-17,Unitarity Entropy Bound: Solitons and Instantons,"We show that non-perturbative entities such as solitons and instantons
saturate bounds on entropy when the theory saturates unitarity. Simultaneously,
the entropy becomes equal to the area of the soliton/instanton. This is
strikingly similar to black hole entropy despite absence of gravity. We explain
why this similarity is not an accident. We present a formulation that allows to
apply the entropy bound to instantons. The new formulation also eliminates
apparent violations of the Bekenstein entropy bound by some
otherwise-consistent unitary systems. We observe that in QCD, an isolated
instanton of fixed size and position violates the entropy bound for strong 't
Hooft coupling. At critical 't Hooft coupling the instanton entropy is equal to
its area.",1907.07332v1
2019-07-23,Stability of Big Surface Bubbles: Impact of Evaporation and Bubbles Size,"Surface bubbles have attracted much interest in the past decades. In this
article, we propose to explore the lifetime and thinning dynamics of
centimetric surface bubbles. We study the impact of the bubbles size as well as
that of the atmospheric humidity through a careful control and systematic
variation of the relative humidity in the measuring chamber. We first adress
the question of the drainage under saturated water vapor conditions and show
that a model including both capillary and gravity driven drainage provides the
best prediction for this process. Additionally, unprecedented statistics on the
bubbles lifetimes confirm experimentally that this parameter is set by
evaporation to leading order. We make use of a model based on the overall
thinning dynamics of the thin film and assume a rupture thickness of the order
10-100 nm to obtain a good representation of these data. For experiments
conducted far from saturation, the convective evaporation of the bath is shown
to dominate the overall mass loss in the cap film due to evaporation.",1907.09734v2
2019-07-24,Inherent Limit to Coherent Phonon Generation under Non-Resonant Light Field Driving,"Coherent manipulation of quasi-particles is a crucial method to realize
ultrafast switching of the relating macroscopic order. In this letter, we
studied coherent phonon generation under strong light field which allows to
induce non-perturbative nonlinear optical phenomena in solids. The efficiency
of coherent phonon generation starts to saturate and deviate from the
pronounced linear power dependence when the light intensity goes into the
non-perturbative regime. We propose a novel theoretical model based on Floquet
picture and show that the saturation is due to a limitation of the driving
force inherent in non-resonant driving of the electronic system in the
non-perturbative regime.",1907.10335v1
2019-07-25,Capturing the shear and secondary compression wave: High frame rate ultrasound imaging in saturated foams,"We experimentally observe the shear and secondary compression wave inside
soft porous water-saturated melamine foams by high frame rate ultrasound
imaging. Both wave speeds are supported by the weak frame of the foam. The
first and second compression waves show opposite polarity, as predicted by Biot
theory. Our experiments have direct implications for medical imaging: Melamine
foams exhibit a similar microstructure as lung tissue. In the future, combined
shear wave and slow compression wave imaging might provide new means of
distinguishing malignant and healthy pulmonary tissue.",1907.11276v2
2019-07-27,Adaptive Flight Control in the Presence of Limits on Magnitude and Rate,"Input constraints as well as parametric uncertainties must be accounted for
in the design of safe control systems. This paper presents an adaptive
controller for multiple-input-multiple-output (MIMO) plants with input
magnitude and rate saturation in the presence of parametric uncertainties. A
filter is introduced in the control path to accommodate the presence of rate
limits. An output feedback adaptive controller is designed to stabilize the
closed loop system even in the presence of this filter. The overall control
architecture includes adaptive laws that are modified to account for the
magnitude and rate limits. Analytical guarantees of bounded solutions and
satisfactory tracking are provided. Three flight control simulations with
nonlinear models of the aircraft dynamics are provided to demonstrate the
efficacy of the proposed adaptive controller for open loop stable and unstable
systems in the presence of uncertainties in the dynamics as well as input
magnitude and rate saturation.",1907.11913v1
2019-07-31,Critical slowing down in the bistable regime of circuit quantum electrodynamics,"We investigate the dynamics of the bistable regime of the generalized
Jaynes-Cummings Hamiltonian (GJC), realised by a circuit quantum
electrodynamics (cQED) system consisting of a transmon qubit coupled to a
microwave cavity. In this regime we observe critical slowing down in the
approach to the steady state. By measuring the response of the cavity to a step
function drive pulse we characterize this slowing down as a function of driving
frequency and power. We find that the critical slowing down saturates as the
driving power is increased. We compare these results with the predictions of
analytical and numerical calculations both with and without the Duffing
approximation. We find that the Duffing approximation incorrectly predicts that
the critical slowing down timescale increases exponentially with the drive,
whereas the GJC model accurately predicts the saturation seen in our data,
suggesting a different process of quantum activation.",1907.13592v1
2019-08-02,Realization of Ohmic-contact and velocity saturation in organic field-effect transistors by crystallized monolayer,"The contact resistance limits the down-scaling and operating range of OFETs.
With the monolayer (1L) organic crystals and non-destructive
metal/semiconductor interfaces, intrinsic mobility of 12.5 cm2V-1s-1 and Ohmic
contact resistance of 40 ohm-cm were achieved. The on/off ratio maintained at
10^3 even at a small VDS of -0.1 mV. High current density of 4.2 uA/um was
achieved with the 1L-crystal as the active layer. At such high current density,
the velocity saturation and channel self-heating effects are observed in OFETs
for the first time. In addition to the low contact resistance and
high-resolution lithography, we suggest the thermal management of the high
mobility OFETs will be the next major challenge to achieve high-speed densely
integrated flexible electronics.",1908.01032v1
2019-08-15,Probabilistic Saturations and Alt's Problem,"Alt's problem, formulated in 1923, is to count the number of four-bar
linkages whose coupler curve interpolates nine general points in the plane.
This problem can be phrased as counting the number of solutions to a system of
polynomial equations which was first solved numerically using homotopy
continuation by Wampler, Morgan, and Sommese in 1992. Since there is still not
a proof that all solutions were obtained, we consider upper bounds for Alt's
problem by counting the number of solutions outside of the base locus to a
system arising as the general linear combination of polynomials. In particular,
we derive effective symbolic and numeric methods for studying such systems
using probabilistic saturations that can be employed using both finite fields
and floating-point computations. We give bounds on the size of finite field
required to achieve a desired level of certainty. These methods can also be
applied to many other problems where similar systems arise such as computing
the volumes of Newton-Okounkov bodies and computing intersection theoretic
invariants including Euler characteristics, Chern classes, and Segre classes.",1908.06020v1
2019-08-18,State Synchronization for Homogeneous Networks of Non-introspective Agents in Presence of Input Saturation -A Scale-free Protocol Design,"This paper studies global and semi-global regulated state synchronization of
homogeneous networks of non-introspective agents in presence of input
saturation based on additional information exchange where the reference
trajectory is given by a so-called exosystem which is assumed to be globally
reachable. Our protocol design methodology does not need any knowledge of the
directed network topology and the spectrum of the associated Laplacian matrix.
Moreover, the proposed protocol is scalable and achieves synchronization for
any arbitrary number of agents.",1908.06535v1
2019-08-19,A hue-preserving tone mapping scheme based on constant-hue plane without gamut problem,"We propose a novel hue-preserving tone mapping scheme. Various tone mapping
operations have been studied so far, but there are very few works on color
distortion caused in image tone mapping. First, LDR images produced from HDR
ones by using conventional tone mapping operators (TMOs) are pointed out to
have some distortion in hue values due to clipping and rounding quantization
processing. Next,we propose a novel method which allows LDR images to have the
same maximally saturated color values as those of HDR ones. Generated LDR
images by the proposed method have smaller hue degradation than LDR ones
generated by conventional TMOs. Moreover, the proposed method is applicable to
any TMOs. In an experiment, the proposed method is demonstrated not only to
produce images with small hue degradation but also to maintain well-mapped
luminance, in terms of three objective metrics: TMQI, hue value in CIEDE2000,
and the maximally saturated color on the constant-hue plane in the RGB color
space.",1908.06557v1
2019-08-26,Robustness of interferometric complementarity under Decoherence,"Interferometric complementarity is known to be one of the most nonclassical
manifestations of the quantum formalism. It is commonly known as wave-particle
duality and has been studied presently from the perspective of quantum
information theory where wave and particle nature of a quantum system, called
quanton, are characterised by coherence and path distinguishability
respectively. We here consider the effect of noisy detectors on the
complementarity relation. We report that by suitably choosing the initial
quanton and the detector states along with the proper interactions between the
quanton and the detectors, one can reduce the in uence of noisy environment on
complementarity, thereby pushing it towards saturation. To demonstrate this,
three kinds of noise on detectors and their roles on the saturation of the
complementarity relation are extensively studied. We also observe that for
fixed values of parameters involved in the process, asymmetric quanton state
posses low value of coherence while it can have a higher amount of
distinguishability, and hence it has the potential to enhance the duality
relation.",1908.09697v2
2019-08-28,A physically based model for the electrical conductivity of water-saturated porous media,"Electrical conductivity is one of the most commonly used geophysical method
for reservoir and environmental studies. Its main interest lies in its
sensitivity to key properties of storage and transport in porous media. Its
quantitative use therefore depends on the efficiency of the petrophysical
relationship to link them. In this work, we develop a new physically based
model for estimating electrical conductivity of saturated porous media. The
model is derived assuming that the porous media is represented by a bundle of
tortuous capillary tubes with a fractal pore-size distribution. The model is
expressed in terms of the porosity, electrical conductivity of the pore liquid
and the microstructural parameters of porous media. It takes into account the
interface properties between minerals and pore water by introducing a surface
conductivity. Expressions for the formation factor and hydraulic tortuosity are
also obtained from the model derivation. The model is then successfully
compared with published data and performs better than previous models. The
proposed approach also permits to relate the electrical conductivity to other
transport properties such as the hydraulic conductivity.",1908.10601v1
2019-08-31,Effective modelling of adsorption monolayers built of complex molecules,"Random sequential adsorption algorithm is a popular tool for modelling
structure of monolayers built in irreversible adsorption experiments. However,
this algorithm becomes very inefficient when the density of molecules in a
layer rises. This problem has already been solved for a very limited range of
basic shapes. This study presents a solution that can be used for any molecule
occupying the surface that can be modelled by any number of different disks.
Additionally, the presented algorithm stops when there is no possibility to add
another shape to the monolayer. This allows to study properties of fully
saturated, two-dimensional random packings built of complex shapes. For
instance, the presented algorithm has been used to determine the mean saturated
packing fractions of monolayers built of dimers and fibrinogen.",1909.00289v2
2019-09-02,Remarkable nuances of crystallization: From ordinary crystal nucleation to rival mechanisms of crystallite coalescence,"Crystal growth and crystal coalescence processes in supercooled systems
strongly depend on the concentration of crystallization centers. We perform
atomistic dynamics simulations of the crystallization process in the ultrathin
metallic film at different supercooling levels corresponding to supercooled
liquid and amorphous solid states. Scaled relations are applied to identify the
characteristic regimes in the time-dependent crystalline nuclei concentration:
steady-state nucleation regime, saturation regime and coalescence regime. We
show that the crystal growth at the saturation regime appears due to mixing
nucleation and coalescence processes. We find that the crystallite coalescence
realizes mainly through the mechanism of restructurization/absorption of
crystal nuclei, whereas the mechanism of oriented attachment is manifested only
at low levels of supercooling.",1909.00771v1
2019-09-09,Convergence of least squares estimators in the adaptive Wynn algorithm for a class of nonlinear regression models,"The paper continues the authors' work on the adaptive Wynn algorithm in a
nonlinear regression model. In the present paper it is shown that if the mean
response function satisfies a condition of `saturated identifiability', which
was introduced by Pronzato \cite{Pronzato}, then the adaptive least squares
estimators are strongly consistent. The condition states that the regression
parameter is identifiable under any saturated design, i.e., the values of the
mean response function at any $p$ distinct design points determine the
parameter point uniquely where, typically, $p$ is the dimension of the
regression parameter vector. Further essential assumptions are compactness of
the experimental region and of the parameter space together with some natural
continuity assumptions. If the true parameter point is an interior point of the
parameter space then under some smoothness assumptions and asymptotic
homoscedasticity of random errors the asymptotic normality of adaptive least
squares estimators is obtained.",1909.03763v1
2019-09-11,Momentum-space entanglement after a quench in one-dimensional disordered fermionic systems,"We numerically investigate the momentum-space entanglement entropy and
entanglement spectrum of the random-dimer model and its generalizations, which
circumvent Anderson localization, after a quench in the Hamiltonian parameters.
The type of dynamics that occurs depends on whether or not the Fermi level of
the initial state is near the energy of the delocalized states present in these
models. If the Fermi level of the initial state is near the energy of the
delocalized states, we observe an interesting slow logarithmic-like growth of
the momentum-space entanglement entropy followed by an eventual saturation.
Otherwise, the momentum-space entanglement entropy is found to rapidly
saturate. We also find that the momentum-space entanglement spectrum reveals
the presence of delocalized states in these models for long times after the
quench and the many-body entanglement gap decays logarithmically in time when
the Fermi level is near the energy of the delocalized states.",1909.05140v1
2019-09-18,Probing parton saturation with forward $Z^0$-boson production at small transverse momentum in p+p and p+A collisions,"We calculate and compare the differential cross sections for forward
$Z^0$-boson production at small transverse momentum, in proton-proton and
proton-nucleus collisions, using both the collinear and dilute-dense
factorization frameworks. In both cases, we implement a Sudakov resummation of
the large logarithms generated by soft-gluon emissions, which is essential in
order to describe the transverse momentum distribution of forward $Z^0$ bosons
measured at the Tevatron and the LHC. We further compute the nuclear
modification factor in the dilute-dense framework, hoping to single out signals
of saturation effects at small values of $x$. Our predictions are compared with
those obtained in the collinear factorization framework, using two different
nuclear parton distribution functions.",1909.08572v2
2019-09-19,Extremal rays of the embedded subgroup saturation cone,"We examine the extremal rays of the cone of dominant weights $(\mu,
\widehat\mu)$ for groups $G\subseteq \widehat G$ for which there exists $N
\gg0$ such that $$ \left(V(N\mu)\otimes V(N\widehat \mu)\right)^G\ne (0). $$ We
exhibit formulas for a class of rays (""type I"") on any regular face of the
cone. These rays are identified thanks to a generalization of Fulton's
conjecture, which we prove along the way. We verify that the remaining rays
(""type II"") on the face are the images of extremal rays for a smaller cone
under a certain map, whose formula is given. A procedure is given for finding
the rays of the cone not on any regular face. This is a generalization of the
work of Belkale and Kiers on extremal rays for the saturated tensor cone; the
specialization is given by $\widehat G = G\times G$ with the diagonal embedding
of $G$. We include several examples to illustrate the formulas.",1909.09262v4
2019-09-22,Model Reference Adaptive Control Allocation for Constrained Systems with Guaranteed Closed Loop Stability,"This paper proposes an adaptive control allocation approach for uncertain
over-actuated systems with actuator saturation. The proposed method does not
require uncertainty estimation or a persistent excitation assumption. Using the
element-wise non-symmetric projection algorithm, the adaptive parameters are
restricted to satisfy certain optimality conditions leading to overall closed
loop system stability. Furthermore, a sliding mode controller with a
time-varying sliding surface, working in tandem with the adaptive control
allocation, is proposed to guarantee the outer loop stability and reference
tracking in the presence of control allocation errors and disturbances.
Simulation results are provided, where the Aerodata Model in Research
Environment is used as an over-actuated system with actuator saturation, to
demonstrate the effectiveness of the proposed method.",1909.10036v1
2019-09-26,Synthesizing Structured CAD Models with Equality Saturation and Inverse Transformations,"Recent program synthesis techniques help users customize CAD models(e.g., for
3D printing) by decompiling low-level triangle meshes to Constructive Solid
Geometry (CSG) expressions. Without loops or functions, editing CSG can require
many coordinated changes, and existing mesh decompilers use heuristics that can
obfuscate high-level structure.
  This paper proposes a second decompilation stage to robustly ""shrink""
unstructured CSG expressions into more editable programs with map and fold
operators. We present Szalinski, a tool that uses Equality Saturation with
semantics-preserving CAD rewrites to efficiently search for smaller equivalent
programs. Szalinski relies on inverse transformations, a novel way for solvers
to speculatively add equivalences to an E-graph. We qualitatively evaluate
Szalinski in case studies, show how it composes with an existing mesh
decompiler, and demonstrate that Szalinski can shrink large models in seconds.",1909.12252v3
2019-09-30,Multiplicity of the saturated special fiber ring of height three Gorenstein ideals,"Let $R$ be a polynomial ring over a field and $I \subset R$ be a Gorenstein
ideal of height three that is minimally generated by homogeneous polynomials of
the same degree. We compute the multiplicity of the saturated special fiber
ring of $I$. The obtained formula depends only on the number of variables of
$R$, the minimal number of generators of $I$, and the degree of the syzygies of
$I$. Applying results from arXiv:1805.05180, we get a formula for the
$j$-multiplicity of $I$ and an effective method to study a rational map
determined by a minimal set of generators of $I$.",1909.13633v2
2019-10-17,Entropic Bounds For Unitary Testers and Mutually Unbiased Unitary Bases,"We define the entropic bounds, i.e minimal uncertainty for pairs of unitary
testers in distinguishing between unitary transformations not unlike the well
known entropic bounds for observables. We show that in the case of specific
sets of testers which pairwise saturate the trivial zero bound, the testers are
all equivalent in the sense their statistics are the same. On the other hand,
when maximal bounds are saturated by such sets of testers, the unitary
operators would form unitary bases which are mutually unbiased. This resembles
very much the role of mutually unbiased bases in maximizing the entropic bounds
for observables. We show how such a bound can be useful in certain quantum
cryptographic protocols.",1910.07665v3
2019-10-21,Heavy quarkonium in saturated environment of high-multiplicity pp collisions,"High-multiplicity pp collisions exhibit features, traditionally associated
with nuclear effects. Coherence motivates to treat high-multiplicity pp, pA and
AA collisions on an equal footing. We rely on the phenomenological
parametrization for mean multiplicities of light hadrons and J/psi, assuming
their linear dependence on N_{coll} in pA collisions. The results of this
approach underestimate the recently measured production rate of J/psi at very
high hadronic multiplicities. The linear dependence of J/psi multiplicity on
N_{coll} is subject to predicted nonlinear corrections, related to mutual
boosting of the saturation scales in colliding dense parton clouds. A
parameter-free calculation of the non-linear corrections allows to explain data
for pT-integrated yield of J/psi at high hadronic multiplicities. Calculations
are in a good accord with data binned in several pT-intervals as well. As was
predicted, Upsilon and J/psi are equally suppressed at forward rapidities in pA
collisions. Consequently, their fractional multiplicities at forward rapidities
in pp collisions are equal as well, and their magnitude agrees with data.",1910.09682v2
2019-10-25,Large impact parameter behaviour in the CGC/saturation approach: a new non-linear equation,"In this paper we propose a solution to the long standing problem in the
CGC/saturation approach: the power-like fall off of the scattering amplitudes
at large $b$. We propose a new non-linear equation, which takes into account
random walks both in transverse momenta of the produced gluons and in their
impact parameters. We demonstrate, that this equation is in accord with
previous attempts to include the diffusion in impact parameters in the BFKL
evolution equation. We show in the paper, that the solution to a new equation
results in the exponential decrease of the scattering amplitude at large impact
parameter, and in the restoration of the Froissart theorem.",1910.11662v2
2019-10-28,Simple encoding of higher derivative gauge and gravity counterterms,"Invoking increasingly higher dimension operators to encode novel UV physics
in effective gauge and gravity theories traditionally means working with
increasingly more finicky and difficult expressions. We demonstrate that local
higher derivative supersymmetric-compatible operators at four-points can be
absorbed into simpler higher-derivative corrections to scalar theories, which
generate the predictions of Yang-Mills and Gravity operators by suitable
replacements of color-weights with color-dual kinematic weights as per
Bern-Carrasco-Johansson double-copy. We exploit that Jacobi-satisfying
representations can be composed out of other Jacobi-satisfying representations,
and show that at four-points only a small number of building blocks are
required to generate the predictions of higher-derivative operators. We find
that this construction saturates the higher-derivative operators contributing
to the four-point supersymmetric open and closed-string tree amplitudes,
presenting a novel representation of the four-point supersymmetric open string
making this structure manifest, as well as identifying the only four additional
gauge-invariant building blocks required to saturate the four-point bosonic
open string.",1910.12850v2
2019-10-31,A Nonisothermal Thermodynamical Model Of Liquid-vapor Interaction With Metastability,"The paper concerns the construction of a compressible liquid-vapor relaxation
model which is able to capture the metastable states of the non isothermal van
der Waals model as well as saturation states. Starting from the Gibbs
formalism, we propose a dynamical system which complies with the second law of
thermodynamics. Numerical simulations illustrate the expected behaviour of
metastable states: an initial metastable condition submitted to a certain
perturbation may stay in the metastable state or reaches a saturation state.
The dynamical system is then coupled to the dynamics of the compressible fluid
using an Euler set of equations supplemented by convection equations on the
fractions of volume, mass and energy of one of the phases.",1910.14525v1
2019-11-16,A spatio-temporal multi-scale model for Geyer saturation point process: application to forest fire occurrences,"Because most natural phenomena exhibit dependence at multiple scales like
locations of earthquakes or forest fire occurrences, spatio-temporal
single-scale point process models are unrealistic in many applications. This
motivates us to construct generalizations of classical Gibbs models. In this
paper, we extend the Geyer saturation point process model to the
spatio-temporal multi-scale framework. The simulation process is carried out
through a birth-death Metropolis-Hastings algorithm. In a simulation study, we
compare two common methods for statistical inference in Gibbs models: the
pseudo-likelihood and logistic likelihood approaches that we tailor to this
model. Finally, we illustrate this new model on forest fire occurrences
modeling in Southern France.",1911.06999v2
2019-11-18,Safe squeezing for antisparse coding,"Spreading the information over all coefficients of a representation is a
desirable property in many applications such as digital communication or
machine learning. This so-called antisparse representation can be obtained by
solving a convex program involving an $\ell_\infty$-norm penalty combined with
a quadratic discrepancy. In this paper, we propose a new methodology, dubbed
safe squeezing, to accelerate the computation of antisparse representation. We
describe a test that allows to detect saturated entries in the solution of the
optimization problem. The contribution of these entries is compacted into a
single vector, thus operating a form of dimensionality reduction. We propose
two algorithms to solve the resulting lower dimensional problem. Numerical
experiments show the effectiveness of the proposed method to detect the
saturated components of the solution and illustrates the induced computational
gains in the resolution of the antisparse problem.",1911.07508v2
2019-11-30,Spatiotemporal mode-locking in lasers with large modal dispersion,"Dissipative nonlinear wave dynamics have been investigated extensively in
mode-locked lasers with single transverse-mode, whereas there are few studies
related to three-dimensional nonlinear dynamics within lasers. Recently,
spatiotemporal mode-locking (STML) was proposed in lasers with small modal
(i.e., transverse-mode) dispersion, which has been considered to be critical
for achieving STML in those cavities because the small dispersion can be easily
balanced. Here, we demonstrate that STML can also be achieved in multimode
lasers with much larger modal dispersion, where we find that the intracavity
saturable absorber plays an important role for counteracting the large modal
dispersion. Furthermore, we observe a new STML phenomenon of passive nonlinear
auto-selection of single-mode mode-locking, resulting from the interaction
between spatiotemporal saturable absorption and spatial gain competition. Our
work significantly broadens the design possibilities for useful STML lasers
thus making them much more accessible for applications, and extends the
explorable parameter space of the novel dissipative spatiotemporal nonlinear
dynamics that can be achieved in these lasers.",1912.00161v2
2019-12-03,Optimal management of impaired self-avoiding random walks for minimizing spatial coverage,"Self-avoidance is a common mechanism to improve the efficiency of a random
walker for covering a spatial domain. However, how this efficiency decreases
when self-avoidance is impaired or limited by other processes has remained
largely unexplored. Here we use simulations to study the case when the
self-avoiding signal left by a walker both (i) saturates after successive
revisits to a site, and (ii) evaporates, or dissappears, after some
characteristic time. We surprisingly reveal that the mean cover time becomes
minimum for intermediate values of the evaporation time, leading to the
existence of a nontrivial optimum management of the self-avoiding signal. We
argue that this is a consequence of complex blocking effects caused by the
interplay with the signal saturation and, remarkably, we show that the optimum
becomes more and more significant as the domain size increases.",1912.04402v1
2019-12-10,Feedback control of surface roughness in a one-dimensional KPZ growth process,"Control of generically scale-invariant systems, i.e., targeting specific
cooperative features in non-linear stochastic interacting systems with many
degrees of freedom subject to strong fluctuations and correlations that are
characterized by power laws, remains an important open problem. We study the
control of surface roughness during a growth process described by the
Kardar--Parisi--Zhang (KPZ) equation in $(1+1)$ dimensions. We achieve the
saturation of the mean surface roughness to a prescribed value using non-linear
feedback control. Numerical integration is performed by means of the
pseudospectral method, and the results are used to investigate the coupling
effects of controlled (linear) and uncontrolled (non-linear) KPZ dynamics
during the control process. While the intermediate time kinetics is governed by
KPZ scaling, at later times a linear regime prevails, namely the relaxation
towards the desired surface roughness. The temporal crossover region between
these two distinct regimes displays intriguing scaling behavior that is
characterized by non-trivial exponents and involves the number of controlled
Fourier modes. Due to the control, the height probability distribution becomes
negatively skewed, which affects the value of the saturation width.",1912.04789v1
2019-12-10,Equilibria and Systemic Risk in Saturated Networks,"We undertake a fundamental study of network equilibria modeled as solutions
of fixed point equations for monotone linear functions with saturation
nonlinearities. The considered model extends one originally proposed to study
systemic risk in networks of financial institutions interconnected by mutual
obligations and is one of the simplest continuous models accounting for shock
propagation phenomena and cascading failure effects. It also characterizes Nash
equilibria of constrained quadratic network games with strategic
complementarities. We first derive explicit expressions for network equilibria
and prove necessary and sufficient conditions for their uniqueness encompassing
and generalizing results available in the literature. Then, we study jump
discontinuities of the network equilibria when the exogenous flows cross
certain regions of measure 0 representable as graphs of continuous functions.
Finally, we discuss some implications of our results in the two main motivating
applications. In financial networks, this bifurcation phenomenon is responsible
for how small shocks in the assets of a few nodes can trigger major aggregate
losses to the system and cause the default of several agents. In constrained
quadratic network games, it induces a blow-up behavior of the sensitivity of
Nash equilibria with respect to the individual benefits.",1912.04815v2
2019-12-11,Multi-gluon correlations and evidence of saturation from dijet measurements at an Electron Ion Collider,"We study inclusive and diffractive dijet production in electron-proton and
electron-nucleus collisions within the Color Glass Condensate effective field
theory. We compute dijet cross sections differentially in both mean dijet
transverse momentum $\mathbf{P}$ and recoil momentum $\mathbf{\Delta}$, as well
as the anisotropy in the relative angle between $\mathbf{P}$ and
$\mathbf{\Delta}$. We use the nonlinear Gaussian approximation to compute
multiparticle correlators for general small $x$ kinematics, employing running
coupling Balitsky-Kovchegov evolution to determine the dipole amplitude at
small $x$. Our results cover a much larger kinematic range than accessible in
previous computations performed in the correlation limit approximation, where
it is assumed that $|\mathbf{P}| \gg |\mathbf{\Delta}|$. We validate this
approximation in its range of applicability and quantify its failure for
$|\mathbf{P}| \lesssim |\mathbf{\Delta}|$. We also predict significant
target-dependent deviations from the correlation limit approximation for
$|\mathbf{P}| > |\mathbf{\Delta}|$ and $|\mathbf{P}| \lesssim Q_s$, which
offers a straightforward test of gluon saturation and access to multi-gluon
distributions at a future electron ion collider.",1912.05586v1
2019-12-26,Exclusion Inside or at the Border of Conformal Bootstrap Continent,"How large can anomalous dimensions be in conformal field theories? What can
we do to attain larger values? One attempt to obtain large anomalous dimensions
efficiently is to use the Pauli exclusion principle. Certain operators
constructed out of constituent fermions cannot form bound states without
introducing non-trivial excitations. To assess the efficiency of this
mechanism, we compare them with the numerical conformal bootstrap bound as well
as with other interacting field theory examples. In two dimensions, it turns
out to be the most efficient: it saturates the bound and is located at the
(second) kink. In higher dimensions, it more or less saturates the bound but it
may be slightly inside.",1912.11748v2
2020-01-03,Fell bundles over quasi-lattice ordered groups and $\mathrm{C}^*$-algebras of compactly aligned product systems,"We define notions of semi-saturatedness and orthogonality for a Fell bundle
over a quasi-lattice ordered group. We show that a compactly aligned product
system of Hilbert bimodules can be naturally extended to a semi-saturated and
orthogonal Fell bundle whenever it is simplifiable. Conversely, a
semi-saturated and orthogonal Fell bundle is completely determined by the
positive fibres and its cross sectional $\mathrm{C}^*$-algebra is isomorphic to
a relative Cuntz--Pimsner algebra of a simplifiable product system of Hilbert
bimodules. We show that this correspondence is part of an equivalence between
bicategories and use this to generalise several results of Meyer and the author
in the context of single correspondences. We apply functoriality for relative
Cuntz--Pimsner algebras to study Morita equivalence between
$\mathrm{C}^*$-algebras attached to compactly aligned product systems over
Morita equivalent $\mathrm{C}^*$-algebras.",2001.00998v3
2020-01-06,Stochastic Rounding: Algorithms and Hardware Accelerator,"Algorithms and a hardware accelerator for performing stochastic rounding (SR)
are presented. The main goal is to augment the ARM M4F based multi-core
processor SpiNNaker2 with a more flexible rounding functionality than is
available in the ARM processor itself. The motivation of adding such an
accelerator in hardware is based on our previous results showing improvements
in numerical accuracy of ODE solvers in fixed-point arithmetic with SR,
compared to standard round to nearest or bit truncation rounding modes.
Furthermore, performing SR purely in software can be expensive, due to
requirement of a pseudorandom number generator (PRNG), multiple masking and
shifting instructions, and an addition operation. Also, saturation of the
rounded values is included, since rounding is usually followed by saturation,
which is especially important in fixed-point arithmetic due to a narrow dynamic
range of representable values. The main intended use of the accelerator is to
round fixed-point multiplier outputs, which are returned unrounded by the ARM
processor in a wider fixed-point format than the arguments.",2001.01501v4
2020-01-15,Ultrafast strong-field absorption in gapped graphene,"We study theoretically the strong-field absorption of an ultrafast optical
pulse by a gapped graphene monolayer. At low field amplitudes, the absorbance
in the pristine graphene is equal to the universal value of $2.3$ percent.
Although the ultrafast optical absorption for low field amplitudes is
independent of the polarization, linear or circular, of the applied optical
pulse, for high field amplitudes, the absorption strongly depends on the pulse
polarization. For a linearly polarized pulse, the optical absorbance is
saturated at the value of $\approx 1.4$ percent for the pulse's amplitude of
$\geq 0.4~\mathrm{V/\AA}$, but no such saturation is observed for a circularly
polarized pulse. For the gapped graphene, the absorption of a linearly
polarized pulse has a weak dependence on the bandgap, while for a circularly
polarized pulse, the absorption is very sensitive to the bandgap. %Opening a
bandgap in graphene by placing in on, for example, SiC substrate strongly
modify the ultrafast absorption at small field amplitudes.",2001.05410v1
2020-02-03,Chiral symmetry restoration and the thermal $f_0(500)$ state,"We analize the role played by the thermal $f_0(500)$ state or $\sigma$ in
chiral symmetry restoration. The temperature corrections to the spectral
properties of that state are included in order to provide a better description
of the scalar susceptibility $\chi_S$ around the transition region. We use the
Linear Sigma Model to establish the relation between $\chi_S$ and the $\sigma$
propagator, which is used as a benchmark to test the approach where $\chi_S$ is
saturated by the $f_0(500)$ inverse self-energy. Within such saturation
approach, a peak for $\chi_S$ around the chiral transition is obtained when
considering the $f_0(500)$ generated as a $\pi\pi$ scattering pole within
Unitarized Chiral Perturbation Theory at finite temperature. That approach
yields results complying with lattice data when the uncertainties of the
low-energy constants are taken into account. Those uncertainties and the
unitarization method are used to check the robustness of this approximation.
Finally, we will discuss some recent results within the chiral lagrangian
framework related to the topological susceptibility and its connection with
chiral and $U_A(1)$ restoration.",2002.00796v1
2020-02-06,Constraints and correlations of nuclear matter parameters from a density-dependent van der Waals model,"A recently proposed density-dependent van der Waals model, with only $4$ free
parameters adjusted to fix binding energy, saturation density, symmetry energy,
and incompressibility, is analyzed under symmetric and asymmetric nuclear
matter constraints. In a previous paper, it was shown that this model is fully
consistent with the constraints related to the binary neutron star merger event
named GW170817 and reported by the LIGO and Virgo collaboration. Here, we show
that it also describes satisfactorily the low and high-density regions of
symmetric nuclear matter, with all the main constraints satisfied. We also
found a linear correlation between the incompressibility and the skewness
parameter, both at the saturation density and show how it relates to the
crossing point presented in the incompressibility as a function of the density.
In the asymmetric matter regime, other linear correlations are found, namely,
the one between the symmetry energy ($J$) and its slope ($L_0$), and other one
establishing the symmetry energy curvature as a function of the combination
given by $3J-L_0$.",2002.02437v1
2020-02-14,Limits of Transmit and Receive Array Gain in Massive MIMO,"In this paper, we consider the transmit and receive antenna array gain of
massive MIMO systems. In particular, we look at their dependence on the number
of antennas in the array, and the antenna spacing for uniform linear and
uniform circular arrays. It is known that the transmit array gain saturates at
a certain antenna spacing, but the receive array gain had not been considered.
With our physically consistent analysis based on the Multiport Communication
Theory, we show that the receive array gain does not saturate, but that there
is a peak at a certain antenna spacing when there is no decoupling network at
the receiver. As implementing a decoupling network for massive MIMO would be
almost impossible, this is a reasonable assumption. Furthermore, we analyze how
the array gain changes depending on the antenna spacing and the size of the
antenna array and derive design recommendations.",2002.06107v2
2020-02-24,Beyond Camera Motion Blur Removing: How to Handle Outliers in Deblurring,"Camera motion deblurring is an important low-level vision task for achieving
better imaging quality. When a scene has outliers such as saturated pixels, the
captured blurred image becomes more difficult to restore. In this paper, we
propose a novel method to handle camera motion blur with outliers. We first
propose an edge-aware scale-recurrent network (EASRN) to conduct deblurring.
EASRN has a separate deblurring module that removes blur at multiple scales and
an upsampling module that fuses different input scales. Then a salient edge
detection network is proposed to supervise the training process and constraint
the edges restoration. By simulating camera motion and adding various light
sources, we can generate blurred images with saturation cutoff. Using the
proposed data generation method, our network can learn to deal with outliers
effectively. We evaluate our method on public test datasets including the GoPro
dataset, Kohler's dataset and Lai's dataset. Both objective evaluation indexes
and subjective visualization show that our method results in better deblurring
quality than other state-of-the-art approaches.",2002.10201v3
2020-02-24,Revised Estimates of Ocean Surface Drag in Strong Winds,"Air-sea drag governs the momentum transfer between the atmosphere and the
ocean, and remains largely unknown in hurricane winds. We revisit the momentum
budget and eddy-covariance methods to estimate the surface drag coefficient in
the laboratory. Our drag estimates agree with field measurements in
low-to-moderate winds, and previous laboratory measurements in hurricane-force
winds. The drag coefficient saturates at $2.6 \times 10^{-3}$ and $U_{10}
\approx 25\ m\ s^{-1}$, in agreement with previous laboratory results by
Takagaki et al. (2012). During our analysis, we discovered an error in the
original source code used by Donelan et al. (2004). We present the corrected
data and describe the correction procedure. Although the correction to the data
does not change the key finding of drag saturation in strong winds, its
magnitude and wind speed threshold are significantly changed. Our findings
emphasize the need for an updated and unified drag parameterization based on
field and laboratory data.",2002.10590v2
2020-02-26,Bandwidth-Optimized Parallel Algorithms for Sparse Matrix-Matrix Multiplication using Propagation Blocking,"Sparse matrix-matrix multiplication (SpGEMM) is a widely used kernel in
various graph, scientific computing and machine learning algorithms. It is well
known that SpGEMM is a memory-bound operation, and its peak performance is
expected to be bound by the memory bandwidth. Yet, existing algorithms fail to
saturate the memory bandwidth, resulting in suboptimal performance under the
Roofline model. In this paper we characterize existing SpGEMM algorithms based
on their memory access patterns and develop practical lower and upper bounds
for SpGEMM performance. We then develop an SpGEMM algorithm based on outer
product matrix multiplication. The newly developed algorithm called PB-SpGEMM
saturates memory bandwidth by using the propagation blocking technique and by
performing in-cache sorting and merging. For many practical matrices, PB-SpGEMM
runs 20%-50% faster than the state-of-the-art heap and hash SpGEMM algorithms
on modern multicore processors. Most importantly, PB-SpGEMM attains performance
predicted by the Roofline model, and its performance remains stable with
respect to matrix size and sparsity.",2002.11302v1
2020-03-01,Anti-Windup Approximations of Oblique Projected Dynamics for Feedback-based Optimization,"In this paper we study how high-gain anti-windup schemes can be used to
implement projected dynamical systems in control loops that are subject to
saturation on a (possibly unknown) set of admissible inputs. This insight is
especially useful for the design of autonomous optimization schemes that
realize a closed-loop behavior which approximates a particular optimization
algorithm (e.g., projected gradient or Newton descent) while requiring only
limited model information. In our analysis we show that a saturated integral
controller, augmented with an anti-windup scheme, gives rise to a perturbed
projected dynamical system. This insight allows us to show uniform convergence
and robust practical stability as the anti-windup gain goes to infinity.
Moreover, for a special case encountered in autonomous optimization we show
robust convergence, i.e., convergence to an optimal steady-state for finite
gains. Apart from being particularly suited for online optimization of
large-scale systems, such as power grids, these results are potentially useful
for other control and optimization applications as they shed a new light on
both anti-windup control and projected gradient systems.",2003.00478v1
2020-03-01,Data analysis on Coronavirus spreading by macroscopic growth laws,"To evaluate the effectiveness of the containment on the epidemic spreading of
the new Coronavirus disease 2019, we carry on an analysis of the time evolution
of the infection in a selected number of different Countries, by considering
well-known macroscopic growth laws, the Gompertz law, and the logistic law. We
also propose here a generalization of Gompertz law. Our data analysis permits
an evaluation of the maximum number of infected individuals. The daily data
must be compared with the obtained fits, to verify if the spreading is under
control. From our analysis it appears that the spreading reached saturation in
China, due to the strong containment policy of the national government. In
Singapore a large growth rate, recently observed, suggests the start of a new
strong spreading. For South Korea and Italy, instead, the next data on new
infections will be crucial to understand if the saturation will be reached for
lower or higher numbers of infected individuals.",2003.00507v3
2020-03-07,Efficient Nonnegative Tensor Factorization via Saturating Coordinate Descent,"With the advancements in computing technology and web-based applications,
data is increasingly generated in multi-dimensional form. This data is usually
sparse due to the presence of a large number of users and fewer user
interactions. To deal with this, the Nonnegative Tensor Factorization (NTF)
based methods have been widely used. However existing factorization algorithms
are not suitable to process in all three conditions of size, density, and rank
of the tensor. Consequently, their applicability becomes limited. In this
paper, we propose a novel fast and efficient NTF algorithm using the element
selection approach. We calculate the element importance using Lipschitz
continuity and propose a saturation point based element selection method that
chooses a set of elements column-wise for updating to solve the optimization
problem. Empirical analysis reveals that the proposed algorithm is scalable in
terms of tensor size, density, and rank in comparison to the relevant
state-of-the-art algorithms.",2003.03572v1
2020-03-09,How ice grows from premelting films and water droplets,"Close to the triple point, the surface of ice is covered by a thin liquid
layer (so-called quasi-liquid layer) which crucially impacts growth and melting
rates. Experimental probes cannot observe the growth processes below this
layer, and classical models of growth by vapor deposition do not account for
the formation of premelting films. Here, we develop a mesoscopic model of
liquid-film mediated ice growth, and identify the various resulting growth
regimes. At low saturation, freezing proceeds by terrace spreading, but the
motion of the buried solid is conveyed through the liquid to the outer
liquid-vapor interface. At higher saturations water droplets condense, a large
crater forms below, and freezing proceeds undetectably beneath the droplet. Our
approach is a general framework that naturally models freezing close to three
phase coexistence and provides a first principle theory of ice growth and
melting which may prove useful in the geosciences.",2003.04252v2
2020-03-10,On the limit of a two-phase flow problem in thin porous media domains of Brinkman-type,"We study the process of two-phase flow in thin porous media domains of
Brinkman-type. This is generally described by a model of coupled, mixed-type
differential equations of fluids' saturation and pressure. To reduce the model
complexity, different approaches that utilize the thin geometry of the domain
have been suggested.
  We focus on a reduced model that is formulated as a single nonlocal evolution
equation of saturation. It is derived by applying standard asymptotic analysis
to the dimensionless coupled model, however, a rigid mathematical derivation is
still lacking. In this paper, we prove that the reduced model is the analytical
limit of the coupled two-phase flow model as the geometrical parameter of
domain's width--length ratio tends to zero. Precisely, we prove the convergence
of weak solutions for the coupled model to a weak solution for the reduced
model as the geometrical parameter approaches zero.",2003.04812v1
2020-03-18,"Modeling Streaming Potential in Porous and Fractured Media, Description and Benefits of the Effective Excess Charge Density Approach","Self-potential signals can be generated by different sources and can be
decomposed in various contributions. Streming potential is the contribution due
to the water flux in the subsurface and is of particular interest in
hydrogeophysics and reservoir characterization. Being able to estimate water
fluxes in porous and fractured media using streaming potential data relies on
our understanding of the electrokinetic coupling at the mineral-solution
interface and our capacity to understand, model, and upscale this phenomenon.
Two main approaches have been proposed to predict streaming potential
generation in geological media. One of these approaches is based on determining
the excess charge which is effectively dragged in the medium by water flow. In
this chapter, we describe how to model the streaming potential by considering
this effective excess charge density, how it can be defined, calculated and
upscaled. We provide a short overview of the theoretical basis of this approach
and we describe different applications to both water saturated and partially
saturated soils and fractured media.",2003.08241v1
2020-03-21,"Central exclusive $χ_{c,b}$ production at high energy colliders and gluon saturation approach","The central exclusive production of $\chi_{c}$ and $\chi_{b}$ at the LHC,
RHIC and Tevatron energies is analyzed, using the recent unintegrated parton
distribution (UGDs) functions available in the package TMDlib. Comparison with
data is performed, which tests the underlying assumptions basing the
theoretical approach and it can constrain the unintegrated gluon distribution
function at the small-$x$ region. Predictions for LHC energies using recent
UGDs based in CCFM formalism are provided. It is explored the underlying
uncertainties on this production as the choice for the unintegrated gluon
distribution and factorization scale is done. Moreover, based on the parton
saturation model for the gluon distribution, analytical expressions for the
rapidity distributions are proposed. The prompt production of $J/\psi+\gamma$
and $\Upsilon+\gamma$ is computed for the first time for LHC energies within
the very same formalism used for $\chi$ production.",2003.09552v2
2020-03-26,Evaluation of radon adsorption efficiency values in xenon with activated carbon fibers,"The radioactive noble gas radon-222 ($\mathrm{^{222}Rn}$, or Rn) produced in
the uranium series is a crucial background source in many underground
experiments. We have estimated the adsorption property of Rn with Activated
Carbon Fibers (ACFs) in air (Air), argon (Ar), and xenon (Xe) gas. In this
study, we evaluated six ACFs, named A-7, A-10, A-15, A-20, A-25, and S-25,
provided from UNITIKA Ltd. We measured intrinsic radioactivity of these ACF
samples, and found A-20's radioactivity of the uranium series is
$<5.5$~$\mathrm{mBq/kg}$ with $90\%$ confidence level. In Air and Ar gas, we
found ACF A-15 has the adsorption efficiency of $1/10000$ reduction at maximum
before saturation of Rn adsorption, and more than $97\%$ adsorption efficiency
after the saturation. In Xe gas, we found ACF A-20 has the best Rn adsorption
ability among tested ACFs. We also found S-25, A-25, and A-15 have similar Rn
adsorption performance.",2003.11705v2
2020-03-27,Characterization of the dissolution of water microdroplets in oil,"Water in oil emulsions have a wide range of applications from chemical
technology to microfluidics, where the stability of water droplets is of
paramount importance. Here using an accessible and easily reproducible
experimental setup we describe and characterize the dissolution of water in
oil, which renders nanoliter-sized droplets unstable, resulting in their
shrinkage and disappearance in a time scale of hours. This process has
applicability in creating miniature reactors for crystallization. We test
multiple oils and their combinations with surfactants exhibiting widely
different rates of dissolution. We derived simple analytical equations to
determine the product of the diffusion coefficient and the relative saturation
density of water in oil from the measured dissolution data. By measuring the
moisture content of mineral and silicone oils with Karl Fischer titration
before and after saturating them with water, we calculated the diffusion
coefficient of water in these two oils",2003.12494v3
2020-03-31,Investigating the diffractive gluon jet production in lepton-ion collisions,"We study the diffractive jet production in electron-ion collisions in the
kinematical region where the mass $M_X$ of the diffractive final state is
larger than $Q^2$. Based on parton saturation framework predictions are done
for the kinematics of future or possible $eA$ machines as the EIC, LHeC,
HE-LHeC and FCC-eA. We analyze the differential cross section as a function of
jet (gluon) transverse momentum and from the experimental point of view this
observable could be used to extract the saturation scale as a function of
$x_{I\!\!P}$.",2003.13882v2
2020-03-31,COVID-19 epidemic outcome predictions based on logistic fitting and estimation of its reliability,"Since the first outbreak of the COVID-19 epidemic at the end of 2019, data
has been made available on the number of infections, deaths and recoveries for
all countries of the World, and that data can be used for statistical analysis.
The primary interest of this paper is how well the logistic equation can
predict the outcome of COVID-19 epidemic in any regions of the World assuming
that the methodology of the testing process, namely the data collection method
and social behavior is not changing over the course of time. Besides the social
relevance, this study has two scientific purposes: we investigate if a simple
saturation model can describe the trend of the COVID-19 epidemic and if so, we
would like to determine, from which point during the epidemic the fitting
parameters provide reliable predictions. We also give estimations for the
outcome of this epidemic in several countries based on the logistic model and
the data available on 27 March, 2020. Based on the saturated cases in China, we
have managed to find some criteria to judge the reliability of the predictions.",2003.14160v1
2020-03-27,Saturation of the Infrared Absorption by Carbon Dioxide in the Atmosphere,"Based on new radiative transfer numerical evaluations, we reconsider an
argument presented by Schack in 1972 that says that saturation of the
absorption of infrared radiation by carbon dioxide in the atmosphere sets in as
soon as the relative concentration of carbon dioxide exceeds a lower limit of
approximately 300 ppm. We provide a concise brief and explicit representation
of the greenhouse effect of the earth's atmosphere. We find an equilibrium
climate sensitivity (temperature increase $\Delta T$ due to doubling of
atmospheric $CO_2$ concentration) of $\Delta T \simeq 0.5 ^0C$. We elaborate on
the consistency of these results on $\Delta T$ with results observationally
obtained by satellite-based measurements of short-time radiation-flux versus
surface-temperature changes.",2004.00708v2
2020-04-02,Weak saturation numbers of complete bipartite graphs in the clique,"The notion of weak saturation was introduced by Bollob\'as in 1968. Let $F$
and $H$ be graphs. A spanning subgraph $G \subseteq F$ is weakly
$(F,H)$-saturated if it contains no copy of $H$ but there exists an ordering
$e_1,\ldots,e_t$ of $E(F)\setminus E(G)$ such that for each $i \in [t]$, the
graph $G \cup \{e_1,\ldots,e_i\}$ contains a copy $H'$ of $H$ such that $e_i
\in H'$. Define $wsat(F,H)$ to be the minimum number of edges in a weakly
$(F,H)$-saturated graph. In this paper, we prove for all $t \ge 2$ and $n \ge
3t-3$, that $wsat(K_n,K_{t,t}) = (t-1)(n + 1 - t/2)$, and we determine the
value of $wsat(K_n,K_{t-1,t})$ as well. For fixed $2 \le s < t$, we also obtain
bounds on $wsat(K_n,K_{s,t})$ that are asymptotically tight.",2004.01289v2
2020-04-08,Nuclear shadowing in deep inelastic scattering on nuclei at very small x,"Nuclear shadowing corrections to the structure functions of deep inelastic
scattering on intermediate-mass nuclei are calculated at very small values of
Bjorken x and small values of Q^2 (Q^2<5 Gev^2). The two-component approach
developed in previous works of authors for a description of the nucleon
structure functions of deep inelastic scattering is used. It is shown that the
hard component of the nucleon structure functions that arises, in terms of the
colour dipole model, from qq-pairs with a high transverse momentum, is almost
not shadowed. It is shown that a change of the slope of the shadowing curve
with a decrease of x depends, at small values of x, on the relative
contribution of the hard component to the nucleon structure function (this
contribution is a function of x and Q^2) and on a size of gluon saturation
effects. It is shown that an accounting for saturation effects becomes
essential for predictions of shadowing at x<10^-4, depending on a value of Q^2.
Results of numerical calculations of nuclear shadowing for several nuclei are
compared with available data of the E665 and the NMC collaborations.",2004.03843v1
2020-04-15,Crossed products of dual operator spaces and a characterization of groups with the approximation property,"Let $ G $ be a locally compact group. We study the categories of $
L^{\infty}(G) $-comodules and $ L(G) $-comodules in the setting of dual
operator spaces and the associated crossed products. It is proved that every $
L^{\infty}(G) $-comodule is non-degenerate and saturated, whereas every $ L(G)
$-comodule is non-degenerate if and only if every $ L(G) $-comodule is
saturated if and only if $ G $ has the approximation property in the sense of
Haagerup and Kraus [14]. This allows us to extend known results from the
duality theory of crossed products of von Neumann algebras (such as
Takesaki-duality and the Digernes-Takesaki theorem) to the recent theory of
crossed products of dual operator spaces. As applications, we obtain a
characterization of groups with the approximation property in terms of the
related crossed products improving a recent result of Crann and Neufang [9] and
we generalize a theorem of Anoussis, Katavolos and Todorov [2] providing a less
technical proof of it. Furthermore, this approach provides an answer to a
question raised by the authors in [2].",2004.07169v1
2020-04-20,S3Library: Automatically Eliminating C/C++ Buffer Overflow using Compatible Safer Libraries,"Annex K of C11, bounds-checking interfaces, recently introduced a set of
alternative functions to mitigate buffer overflows, primarily those caused by
string/memory functions. However, poor compatibility limits their adoption.
Failure oblivious computing can eliminate the possibility that an attacker can
exploit memory errors to corrupt the address space and significantly increase
the availability of systems.
  In this paper, we present S3Library (Saturation-Memory-Access Safer String
Library), which is compatible with the standard C library in terms of function
signature. Our technique automatically replaces unsafe deprecated memory/string
functions with safer versions that perform bounds checking and eliminate buffer
overflows via boundless memory. S3Library employs MinFat, a very compact
pointer representation following the Less is More principle, to encode metadata
into unused upper bits within pointers. In addition, S3Library utilizes
Saturation Memory Access to eliminate illegal memory accesses into boundless
padding area. Even if an out-of-bounds access is made, the fault program will
not be interrupted. We implement our scheme within the LLVM framework on X86-64
and evaluate our approach on correctness, security, runtime performance and
availability.",2004.09062v1
2020-04-25,Scale-free Linear Observer-based Protocol Design for Global Regulated State Synchronization of Homogeneous Multi-agent Systems with Non-introspective Agents Subject to Input Saturation,"This paper studies global regulated state synchronization of homogeneous
networks of non-introspective agents in presence of input saturation. We
identify three classes of agent models which are neutrally stable,
double-integrator, and mixed of double-integrator, single-integrator and
neutrally stable dynamics. A \textit{scale-free linear observer-based} protocol
design methodology is developed based on localized information exchange among
neighbors where the reference trajectory is given by a so-called exosystem
which is assumed to be globally reachable. Our protocols do not need any
knowledge about the communication network topology and the spectrum of
associated Laplacian matrix. Moreover, the proposed protocol is scalable and is
designed based on only knowledge of agent models and achieves synchronization
for any communication graph with arbitrary number of agents.",2004.13479v1
2020-04-28,Nuclear Symmetry Energy and Neutron Skin Thickness of $^{208}Pb $ using a finite range effective interaction,"We use a finite range simple effective interaction to construct nuclear
equations of state for the study of the density dependence of the nuclear
symmetry energy. The EoSs provide good descriptions of the nuclear symmetry
energy at a subsaturation density $\rho_c=0.11$ fm$^{-3}$ and at a density
around two times the saturation density $\rho_0$. We obtain a correlation
between the neutron skin thickness in $^{208}$Pb and the density slope
parameter at the subsaturation density. A linear relation is obtained between
the neutron skin thickness and the parameter
$\beta^{\prime}=\frac{L(\rho_c)}{3E_s(\rho_0)}$, where $E_s(\rho_0)$ and
$L(\rho_c)$ are respectively the nuclear symmetry energy at saturation density
and the density slope parameter at the subsaturation density.",2004.14205v2
2020-05-03,BAlN alloy for enhanced two-dimensional electron gas characteristics of GaN-based high electron mobility transistor,"The emerging wide bandgap BAlN alloys have potentials for improved
III-nitride power devices including high electron mobility transistor (HEMT).
Yet few relevant studies have been carried. In this work, we have investigated
the use of the B0.14Al0.86N alloy as part or entirety of the interlayer between
the GaN buffer and the AlGaN barrier in the conventional GaN-based high
electron mobility transistor (HEMT). The numerical results show considerable
improvement of the two-dimensional electron gas (2DEG) concentration with small
2DEG leakage into the ternary layer by replacing the conventional AlN
interlayer by either the B0.14Al0.86N interlayer or the B0.14Al0.86N/AlN hybrid
interlayer. Consequently, the transfer characteristics can be improved. The
saturation current can be enhanced as well. For instance, the saturation
currents for HEMTs with the 0.5 nm B0.14Al0.86N/0.5 nm AlN hybrid interlayer
and the 1 nm B0.14Al0.86N interlayer are 5.8% and 2.2% higher than that for the
AlN interlayer when VGS-Vth= +3 V.",2005.01161v1
2020-05-05,Rayleigh-Bénard instability of an Ellis fluid saturating a porous medium,"Unlike the power-law model, the Ellis model describes the apparent viscosity
of a shear-thinning fluid with no singularity in the limit of a vanishingly
small shear stress. In particular, this model matches the Newtonian behaviour
when the shear stresses are very small. The emergence of the Rayleigh-B\'enard
instability is studied when a horizontal pressure gradient, yielding a basic
throughflow, is prescribed in a horizontal porous layer. The threshold
conditions for the linear instability of this system are obtained both
analytically and numerically. In the case of a negligible flow rate, the onset
of the instability occurs for the same parametric conditions reported in the
literature for a Newtonian fluid saturating a porous medium. On the other hand,
when high flow rates are considered, a negligibly small temperature difference
imposed across the horizontal boundaries is sufficient to trigger the
convective instability.",2005.02021v1
2020-05-15,Investigating the inclusive transverse spectra in high-energy $pp$ collisions in the context of geometric scaling framework,"The presence of geometric scaling within the $p_T$ spectra of produced
hadrons at high energy $pp$ collisions using small-$x$ $k_T$-factorization is
investigated. It is proposed a phenomenological parameterization for the
unintegrated gluon distribution in the scaling range which reproduces the
features of the differential cross section both in the saturated and dilute
perturbative QCD regimes. As the saturation scale acts as an effective
regulator of the infrared region (IR), the extension of the model to quantities
usually associated to soft physics is studied. The approach is applied to
compute the average $p_T$ and the rapidity distribution of produced gluons at
high energies.",2005.07760v2
2020-05-21,The Rise of Cosmological Complexity: Saturation of Growth and Chaos,"We compute the circuit complexity of scalar curvature perturbations on FLRW
cosmological backgrounds with fixed equation of state $w$ using the language of
squeezed vacuum states. Backgrounds that are accelerating and expanding, or
decelerating and contracting, exhibit features consistent with chaotic
behavior, including linearly growing complexity. Remarkably, we uncover a bound
on the growth of complexity for both expanding and contracting backgrounds
$\lambda \leq \sqrt{2} \ |H|$, similar to other bounds proposed independently
in the literature. The bound is saturated for expanding backgrounds with an
equation of state more negative than $w = -5/3$, and for contracting
backgrounds with an equation of state larger than $w = 1$. For expanding
backgrounds that preserve the null energy condition, de Sitter space has the
largest rate of growth of complexity (identified as the Lyapunov exponent), and
we find a scrambling time that is similar to other estimates up to order one
factors.",2005.10854v1
2020-06-04,Diffusion and operator entanglement spreading,"Understanding the spreading of the operator space entanglement entropy
($OSEE$) is key in order to explore out-of-equilibrium quantum many-body
systems. Here we argue that for integrable models the dynamics of the $OSEE$ is
related to the diffusion of the underlying quasiparticles. We derive the
logarithmic bound $1/2\ln(t)$ for the $OSEE$ of some simple, i.e., low-rank,
diagonal local operators. We numerically check that the bound is saturated in
the rule $54$ chain, which is representative of interacting integrable systems.
Remarkably, the same bound is saturated in the spin-1/2 Heisenberg $XXZ$ chain.
Away from the isotropic point and from the free-fermion point, the $OSEE$ grows
as $1/2\ln(t)$, irrespective of the chain anisotropy, suggesting universality.
Finally, we discuss the effect of integrability breaking. We show that strong
finite-time effects are present, which prevent from probing the asymptotic
behavior of the $OSEE$.",2006.02788v2
2020-06-11,Pore Scale Study of Gas Bubble Nucleation and Migration in Porous Media,"The behavior of gas bubbles in porous media includes bubble nucleation and
growth, migration, coalescence, and trapping. These processes are significantly
affected by the pore-scale characteristics and heterogeneity of the sediment.
In this study, experiments are performed using a microfluidic chip in which
different gas bubble behavior mechanisms are observed. Based on the microscale
experiments, eight major gas bubble behavior mechanisms are identified. In
addition, a mesoscale experiment is designed and performed to study the impacts
of soil layering and heterogeneity on the formation and distribution of
biogenic gas generation via denitrification. The results show that the
pore-scale characteristics of soil significantly affect the distribution and
migration pattern of biogenic gas bubbles. As a result, the water saturation
may vary locally between fully saturated (in fine sand), to about 80% in zones
where the gas is allowed to migrate freely (coarse sand), to even close to 0%
in the zone where the gas gets trapped under layers with higher air entry
value.",2006.06851v1
2020-06-15,Analytic insights on the information content of new observables,"Uncertainty quantification has emerged as a rapidly growing field in nuclear
science. Theoretical predictions of physical observables often involve
extrapolations to regions that are poorly constrained by laboratory experiments
and astrophysical observations. Without properly quantified theoretical errors,
such model predictions are of limited value. Also, one often deals with
theoretical constructs that involve fundamental quantities that are not
accessible to experiment or observation. Particularly relevant in this context
is the pressure of pure neutron matter. In this contribution we develop an
analytic framework to answer the question of ""How can new data reduce
uncertainties of current theoretical models?"" [P.-G. Reinhard and W.
Nazarewicz, Phys. Rev. C81, 051303(R) (2010)]. Simple and insightful
expressions are obtained to quantify the impact of one or two new observables
on theoretical uncertainties in two critical quantities: the slope of the
symmetry energy at saturation density and the pressure of pure neutron matter
at twice nuclear matter saturation density.",2006.08405v1
2020-06-18,Stability of Internal States in Recurrent Neural Networks Trained on Regular Languages,"We provide an empirical study of the stability of recurrent neural networks
trained to recognize regular languages. When a small amount of noise is
introduced into the activation function, the neurons in the recurrent layer
tend to saturate in order to compensate the variability. In this saturated
regime, analysis of the network activation shows a set of clusters that
resemble discrete states in a finite state machine. We show that transitions
between these states in response to input symbols are deterministic and stable.
The networks display a stable behavior for arbitrarily long strings, and when
random perturbations are applied to any of the states, they are able to recover
and their evolution converges to the original clusters. This observation
reinforces the interpretation of the networks as finite automata, with neurons
or groups of neurons coding specific and meaningful input patterns.",2006.10828v1
2020-06-25,Thermal radiation and inclusive production in the running coupling $k_T$ -- factorization approach,"The characteristics of the thermal radiation are investigated using a two -
component model, with the hard component being described by the Color Glass
Condensate formalism. The inclusive transverse momentum spectra of charged
hadrons produced in proton - proton and proton - nucleus collisions at LHC
energies and large - $p_T$ are estimated using the running coupling $k_T$ -
factorization formula and the solution of the Balitsky - Kovchegov equation.
Our results indicate that the thermal term is necessary to describe the
experimental data and that the effective thermal temperature has an energy
dependence similar to the saturation scale. We demonstrate that the enhancement
of the thermal temperature in $pPb$ collisions is consistent with that
predicted by the saturation scale.",2006.14335v1
2020-06-25,Quantumized Microwave Detection Based on $Λ$-Type Three-level Superconducting System: HMM Modeling and Performance Prediction,"We adopt artificial $\Lambda$-type three-level system with superconducting
devices for microwave signal detection, where the signal intensity reaches the
level of discrete photons instead of continuous waveform. Based on the state
transition principles of the three-level system, we propose a statistical model
for microwave signal detection. Moreover, we investigate the achievable
transmission rate and signal detection based on the statistical model. It is
predicted that the proposed detection can achieve significantly higher
sensitivity compared with the currently deployed 4G/5G communication system. We
further characterize the received signal considering the saturation phonomenon,
which reveals negligible performance degradation caused by saturation under
weak received power regime.",2006.14497v3
2020-06-28,Recursive Analytic Solution of Nonlinear Optimal Regulators,"The paper develops an optimal regulator for a general class of multi-input
affine nonlinear systems minimizing a nonlinear cost functional with infinite
horizon. The cost functional is general enough to enforce saturation limits on
the control input if desired. An efficient algorithm utilizing tensor algebra
is employed to compute the tensor coefficients of the Taylor series expansion
of the value function (i.e., optimal cost-to-go). The tensor coefficients are
found by solving a set of nonlinear matrix equations recursively generalizing
the well-known linear quadratic solution. The resulting solution generates the
optimal controller as a nonlinear function of the state vector up to a
prescribed truncation order. Moreover, a complete convergence of the computed
solution together with an estimation of its applicability domain are provided
to further guide the user. The algorithm's computational complexity is shown to
grow only polynomially with respect to the series order. Finally, several
nonlinear examples including some with input saturation are presented to
demonstrate the efficacy of the algorithm to generate high order Taylor series
solution of the optimal controller.",2006.15685v1
2020-06-29,Bright high-purity quantum emitters in aluminium nitride integrated photonics,"Solid-state quantum emitters (QEs) are fundamental in photonic-based quantum
information processing. There is strong interest to develop high-quality QEs in
III-nitride semiconductors because of their sophisticated manufacturing driven
by large and growing applications in optoelectronics, high voltage power
transistors, and microwave amplifiers. Here, we report the generation and
direct integration of QEs in an aluminium nitride-based photonic integrated
circuit platform. For individual waveguide-integrated QEs, we measure an
off-chip count rate exceeding $6 \times 10^{4}$ counts per second (cps)
(saturation rate > $8.6 \times 10^{4}$ cps). In an unpatterned thin-film
sample, we measure antibunching with $g^{(2)}(0) \sim 0.05$ and photon count
rates exceeding $8 \times 10^{5}$ cps (saturation rate > $1 \times 10^{6}$
cps). Although spin and detailed optical linewidth measurements are left for
future work, these results already show the potential for high-quality QEs
monolithically integrated in a wide range of III-nitride device technologies
that would enable new quantum device opportunities and industrial scalability.",2006.16276v1
2020-07-09,Formation of dispersive shock waves in a saturable nonlinear medium,"We use the Gurevich-Pitaevskii approach based on the Whitham averaging method
for studying the formation of dispersive shock waves in an intense light pulse
propagating through a saturable nonlinear medium. Although the Whitham
modulation equations cannot be diagonalized in this case, the main
characteristics of the dispersive shock can be derived by means of an analysis
of the properties of these equations at the boundaries of the shock. Our
approach generalizes a previous analysis of step-like initial intensity
distributions to a more realistic type of initial light pulse and makes it
possible to determine, in a setting of experimental interest, the value of
measurable quantities such as the wave-breaking time or the position and light
intensity of the shock edges.",2007.05087v1
2020-07-12,Verifying the upper bound on the speed of scrambling with the analogue Hawking radiation of trapped ions,"A general bound on the Lyapunov exponent of a quantum system is given by
$\lambda_L\leq2\pi\,T/\hbar$, where $T$ is the system temperature, as
established by Maldacena, Shenker, and Stanford (MSS). This upper bound is
saturated when the system under consideration is the exact holographic dual of
a black hole. It has also been shown that an inverted harmonic oscillator (IHO)
may exhibit the behavior of thermal energy emission, in close analogy to the
Hawking radiation emitted by black holes. We demonstrate that the Lyapunov
exponent of the IHO indeed saturates the MSS bound, with an effective
temperature equal to the analogue black hole radiation temperature, and propose
using a trapped ion as a physical implementation of the IHO. We derive the
corresponding out-of-time-ordered correlation function (OTOC) diagnosing
quantum chaos, and theoretically show, for an experimentally realizable setup,
that the effective temperature of the trapped-ion-IHO matches the upper MSS
bound for the speed of scrambling.",2007.05949v1
2020-07-13,Non-linear equation in the re-summed next-to-leading order of perturbative QCD: the leading twist approximation,"In this paper, we use the re-summation procedure, suggested in
Refs.\cite{DIMST,SALAM,SALAM1,SALAM2}, to fix the BFKL kernel in the NLO.
However, we suggest a different way to introduce th non-linear corrections in
the saturation region, which is based on the leading twist non-linear equation.
In the kinematic region:$\tau\,\equiv\,r^2 Q^2_s(Y)\,\leq\,1$ , where $r$
denotes the size of the dipole, $Y$ its rapidity and $Q_s$ the saturation
scale, we found that the re-summation contributes mostly to the leading twist
of the BFKL equation. Assuming that the scattering amplitude is small, we
suggest using the linear evolution equation in this region. For $\tau \,>\,1$
we are dealing with the re-summation of $\Lb \bas \,\ln \tau\Rb^n$ and other
corrections in NLO approximation for the leading twist.We find the BFKL kernel
in this kinematic region and write the non-linear equation, which we solve
analytically. We believe the new equation could be a basis for a consistent
phenomenology based on the CGC approach.",2007.06214v2
2020-07-18,Modeling lasers and saturable absorbers via multilevel atomic media in the Meep FDTD software: Theory and implementation,"This technical note describes the physical model, numerical implementation,
and validation of multilevel atomic media for lasers and saturable absorbers in
Meep: a free/open-source finite-difference time-domain (FDTD) software package
for electromagnetics simulation. Simulating multilevel media in the time domain
involves coupling rate equations for the populations of electronic energy
levels with Maxwell's equations via a generalization of the Maxwell--Bloch
equations. We describe the underlying equations and their implementation using
a second-order discretization scheme, and also demonstrate their equivalence to
a quantum density-matrix model. The Meep implementation is validated using a
separate FDTD density-matrix model as well as a frequency-domain solver based
on steady-state ab-initio laser theory (SALT).",2007.09329v3
2020-07-19,"QHSL: a quantum hue, saturation, and lightness color model","Quantum image processing employs quantum computing to capture, manipulate,
and recover images in various formats. This requires representations of encoded
images using the quantum mechanical composition of any potential computing
hardware. In this study, a quantum hue, saturation, and lightness (QHSL) color
model is proposed to organize and conceptualize color-assignment attributes
using the properties of quantum mechanics (i.e., entanglement and parallelism).
The proposed color model is used to define representations of a two-dimensional
QHSL image and investigate its data storage, chromatic transformation, and
pseudocolor applications. The QHSL representation is introduced for the
production of quantum images using triple perceptually relevant components. The
efficient use of QHSL images is further explored for applications in the fields
of computer vision and image analysis.",2007.09659v1
2020-07-30,Maximally self-interacting dark matter: models and predictions,"We study self-interacting dark matter (SIDM) scenarios, where the $s$-wave
self-scattering cross section almost saturates the Unitarity bound. Such
self-scattering cross sections are singly parameterized by the dark matter
mass, and are featured by strong velocity dependence in a wide range of
velocities. They may be indicated by observations of dark matter halos in a
wide range of masses, from Milky Way's dwarf spheroidal galaxies to galaxy
clusters. We pin down the model parameters that saturates the Unitarity bound
in well-motivated SIDM models: the gauged $L_{\mu} - L_{\tau}$ model and
composite asymmetric dark matter model. We discuss implications and predictions
of such model parameters for cosmology like the $H_{0}$ tension and dark-matter
direct-detection experiments, and particle phenomenology like the beam-dump
experiments.",2007.15522v2
2020-08-04,Towards mitigation of apparent tension between nuclear physics and astrophysical observations by improved modeling of neutron star matter,"Observations of neutron stars (NSs) by the LIGO-Virgo and NICER
collaborations have provided reasonably precise measurements of their various
macroscopic properties. In this paper, we employ a Bayesian framework to
combine them and place improved joint constraints on the properties of NS
equation of state (EoS). We use a hybrid EoS formulation that employs a
parabolic expansion-based nuclear empirical parameterization around the nuclear
saturation density augmented by a generic 3-segment piecewise polytrope model
at higher densities. Within the $90 \%$ credible level this parameterization
predicts $R_{1.4} = 12.57_{-0.92}^{+0.73}$ km and $\Lambda_{1.4} =
550_{-225}^{+223}$ for the radius and dimensionless tidal deformability,
respectively, of a $1.4 M_{\odot}$ NS. Finally, we show how the construction of
the full NS EoS based solely on the nuclear empirical parameters at saturation
density leads to certain tension with the astrophysical data, and how the
hybrid approach provides a resolution to it.",2008.01582v2
2020-08-07,Fast Identification of Saturated Cut-sets using Graph Search Techniques,"When multiple outages occur in rapid succession, it is important to know
quickly if the power transfer capability of different interconnections (or
cut-sets) of the power network are limited. The algorithm developed in this
paper identifies such limited cut-sets very fast, thereby enhancing the
real-time situational awareness of power system operators. The significance of
the proposed approach is described using the IEEE 39-bus test system, while its
computational benefits are demonstrated using relatively large test-cases
containing thousands of buses. The results indicate that the proposed network
analysis can estimate the impact of an outage on any cut-set of the system and
screen out the cut-set that gets saturated by the largest margin, very quickly.",2008.02951v1
2020-08-05,Modeling of relative permeabilities including dynamic wettability transition zones,"Wettability is a pore-scale property that impacts the relative movement and
distribution of fluids in a porous medium. There are reservoir fluids that
provoke the surface within pores to undergo a wettability change. This
wettability change, in turn, alters the dynamics of relative permeabilities at
the Darcy scale. Thus, modeling the impact of wettability change in relative
permeabilities is essential to understand fluids interaction in porous media.
In this study, we include time-dependent wettability change into the relative
permeability--saturation relation by modifying the existing relative
permeability function. To do so, we assume the wettability change is
represented by the sorption-based model that is exposure time and chemistry
dependent. This pore-scale model is then coupled with a triangular
bundle-of-tubes model to simulate exposure time-dependent relative
permeabilities data. The simulated data is used to characterize and quantify
the wettability dynamics in the relative permeability--saturation curves. This
study further shows the importance of accurate prediction of the relative
permeability in a dynamically altering porous medium.",2008.06572v1
2020-08-17,Saturation of the inverse cascade in surface gravity wave turbulence,"We report on the observation of surface gravity wave turbulence at scales
larger than the forcing ones in a large basin. In addition to the downscale
transfer usually reported in gravity wave turbulence, an upscale transfer is
observed, interpreted as the inverse cascade of weak turbulence theory. A
steady state is achieved when the inverse cascade reaches a scale in between
the forcing wavelength and the basin size, but far from the latter. This
inverse cascade saturation, which depends on the wave steepness, is probably
due to the emergence of nonlinear dissipative structures such as sharp-crested
waves.",2008.08467v1
2020-08-21,Enhanced Tensor Polarization in Solid-State Targets,"We report measurements of enhanced tensor polarization on solid-state
targets. The results here represent an increase in tensor polarization over
that previously achieved in high energy and nuclear scattering experiments that
focused on the measurement of tensor polarized observables. Enhancement
techniques are used which require RF produced close to the Larmor frequency of
the target spins and use selective semi-saturation resulting from two sources
of irradiation, microwave for the DNP process and the additional RF used to
manipulate the population of the energy levels in the target material. The spin
dynamics of the solid target are used to align the spins enhancing the ensemble
average to improve the figure of merit of the scattering experiment. Target
rotation at an optimized rate can lead to additional enhancement by applying
selective semi-saturation in polycrystalline materials that possess a Pake
doublet in their NMR signal.",2008.09515v1
2020-08-26,"Quantum walks with quantum chaotic coins: Of the Loschmidt echo, classical limit and thermalization","Coined discrete-time quantum walks are studied using simple deterministic
dynamical systems as coins whose classical limit can range from being
integrable to chaotic. It is shown that a Loschmidt echo like fidelity plays a
central role and when the coin is chaotic this is approximately the
characteristic function of a classical random walker. Thus the classical
binomial distribution arises as a limit of the quantum walk and the walker
exhibits diffusive growth before eventually becoming ballistic. The coin-walker
entanglement growth is shown to be logarithmic in time as in the case of
many-body localization and coupled kicked rotors, and saturates to a value that
depends on the relative coin and walker space dimensions. In a coin dominated
scenario, the chaos can thermalize the quantum walk to typical random states
such that the entanglement saturates at the Haar averaged Page value, unlike in
a walker dominated case when atypical states seem to be produced.",2008.11318v4
2020-08-31,A fractal model for the electrical conductivity of water-saturated porous media during mineral precipitation-dissolution processes,"Precipitation and dissolution are prime processes in carbonate rocks and
being able to monitor them is of major importance for aquifer and reservoir
exploitation or environmental studies. Electrical conductivity is a physical
property sensitive both to transport phenomena of porous media and to
dissolution and precipitation processes. However, its quantitative use depends
on the effectiveness of the petrophysical relationship to relate the electrical
conductivity to hydrological properties of interest. In this work, we develop a
new physically-based model to estimate the electrical conductivity by upscaling
a microstructural description of water-saturated fractal porous media. This
model is successfully compared to published data from both unconsolidated and
consolidated samples, or during precipitation and dissolution numerical
experiments. For the latter, we show that the permeability can be linked to the
predicted electrical conductivity.",2008.13673v1
2020-09-02,Resonance overlap and non-linear features of the beam-plasma system,"The beam-plasma instability can be addressed as a reduced model in several
contexts of plasma physics, from space to fusion plasma. In this paper, we
review and refine some non-linear features of this model. Specifically, by
analyzing the dependence of the non-linear velocity spread as a function of the
linear growth rate, we discuss the effective size of the resonance in view of
its role in the spectral overlap at saturation. The relevance of this
characterization relies on the necessity of a quantitative determination of the
overlap degree to discriminate among different transport regimes of the self
consistent dynamics. The analysis is enriched with a study of the phase-space
dynamics by means of the Lagrangian Coherent Structure technique, in order to
define the transport barriers of the system describing the relevant features of
the overlap process. Finally, we discuss relevant features related to the mode
saturation levels.",2009.01629v1
2020-09-07,Handling actuator magnitude and rate saturation in uncertain over-actuated systems: A modified projection algorithm approach,"This paper proposes a projection algorithm which can be employed to bound
actuator signals, in terms of both magnitude and rate, for uncertain systems
with redundant actuators. The investigated closed loop control system is
assumed to contain an adaptive control allocator to distribute the total
control input among actuators. Although conventional control allocation methods
can handle actuator rate and magnitude constraints, they cannot consider
actuator uncertainty. On the other hand, adaptive allocators manage uncertainty
and actuator magnitude limits. The proposed projection algorithm enables
adaptive control allocators to handle both magnitude and rate saturation
constraints. A mathematically rigorous analysis is provided to show that with
the help of the proposed projection algorithm, the performance of the adaptive
control allocator can be guaranteed, in terms of error bounds. Simulation
results are presented, where the Aero-Data Model In Research Environment
(ADMIRE) is used as an over-actuated system, to demonstrate the effectiveness
of the proposed method.",2009.03024v1
2020-09-09,Guessing Numbers and Extremal Graph Theory,"For a given number of colors, $s$, the guessing number of a graph is the
(base $s$) logarithm of the cardinality of the largest family of colorings of
the vertex set of the graph such that the color of each vertex can be
determined from the colors of the vertices in its neighborhood. This quantity
is related to problems in network coding, circuit complexity and graph entropy.
We study the guessing number of graphs as a graph property in the context of
classic extremal questions, and its relationship to the forbidden subgraph
property. We find the extremal number with respect to the property of having
guessing number $\leq a$, for fixed $a$. Furthermore, we find an upper bound on
the saturation number for this property, and a method to construct further
saturated graphs that lie between these two extremes. We show that, for a fixed
number of colors, bounding the guessing number is equivalent to forbidding a
finite set of subgraphs.",2009.04529v1
2020-09-10,Subradiance with saturated atoms: population enhancement of the long-lived states,"Dipole-dipole interactions are at the origin of long-lived collective atomic
states, often called subradiant, which are explored for their potential use in
novel photonic devices or in quantum protocols. Here, we study subradiance
beyond linear optics and experimentally demonstrate a two hundred-fold increase
in the population of these modes, as the saturation parameter of the driving
field is increased. We attribute this enhancement to a mechanism similar to
optical pumping through the well-coupled superradiant states. The lifetimes are
unaffected by the pump strength, as the system is ultimately driven toward the
single-excitation sector.",2009.05172v2
2020-09-17,A generalisation of Schenkman's theorem,"Let $G$ be a finite group and let $\mathfrak{F}$ be a hereditary saturated
formation. We denote by $\mathbf{Z}_{\mathfrak{F}}(G)$ the product of all
normal subgroups $N$ of $G$ such that every chief factor $H/K$ of $G$ below $N$
is $\mathfrak{F}$-central in $G$, that is, \[ (H/K) \rtimes
(G/\mathbf{C}_{G}(H/K)) \in \mathfrak{F}. \]A subgroup $A \leq G$ is said to be
$\mathfrak{F}$-subnormal in the sense of Kegel, or $K$-$\mathfrak{F}$-subnormal
in $G$, if there is a subgroup chain \[ A = A_0 \leq A_1 \leq \ldots \leq A_n =
G \] such that either $A_{i-1} \trianglelefteq A_{i}$ or $A_i / (A_{i-1})_{A_i}
\in \mathfrak{F}$ for all $i = 1, \ldots , n$. In this paper, we prove the
following generalisation of Schenkman's Theorem on the centraliser of the
nilpotent residual of a subnormal subgroup: Let $\mathfrak{F}$ be a hereditary
saturated formation and let $S$ be a $K$-$\mathfrak{F}$-subnormal subgroup of
$G$. If $\mathbf{Z}_{\mathfrak{F}}(E) = 1$ for every subgroup $E$ of $G$ such
that $S \leq E$ then $\mathbf{C}_{G}(D) \leq D$, where $D = S^{\mathfrak{F}}$
is the $\mathfrak{F}$-residual of $S$.",2009.08145v1
2020-09-28,An Analytical Solution of the Balitsky-Kovchegov Equation with the Homogeneous Balance Method,"Nonlinear QCD evolution equations are essential tools in understanding the
saturation of partons at small Bjorken $x_{\rm B}$, as they are supposed to
restore an upper bound of unitarity for the cross section of high energy
scattering. In this paper, we present an analytical solution of
Balitsky-Kovchegov (BK) equation using the homogeneous balance method. The
obtained analytical solution is similar to the solution of a traveling wave. By
matching the gluon distribution in the dilute region which is determined from
the global analysis of experimental data (CT14 analysis), we get a definitive
solution of the dipole-proton forward scattering amplitude in the momentum
space. Based on the acquired scattering amplitude and the behavior of geometric
scaling, we present also a new estimated saturation scale $Q_s^2(x)$.",2009.13325v2
2020-10-16,Aging-Induced Dynamics for Statically Indeterminate System,"Statically indeterminate systems are experimentally demonstrated to be in
fact dynamical at the microscopic scale. Take the classic ladder-wall problem,
for instance. Depending on the Young's modulus of the wall, it may take up to
twenty minutes before its weight saturates. This finding is shown to be shared
by other statically indeterminate systems, such as a granule silo and a beam
with three support points. We believe that the aging effect is responsible for
this surprising phenomenon because it can be correlated with the evolution of
microscopic contact area with the wall and floor. Finally, a heuristic and
simple method is introduced that can uniquely determine and analytically solve
the saturated weight without invoking detailed material properties.",2010.08289v2
2020-10-20,Study of the structural defects on carbon nanotubes in metal matrix composites processed by severe plastic deformation,"Carbon nanotubes (CNT) have been recently proposed as stabilizers against
grain growth that can happen even at low temperature inputs in nano-crystalline
and ultrafine-grained materials obtained by severe plastic deformation. In this
study, we analyzed the evolution of the structural defects on the nanotubes in
CNT-reinforced nickel matrix composites with different reinforcement weight
fractions. The composites were processed by high pressure torsion, and we used
Raman spectroscopy as the main characterization technique. The results indicate
that for CNT subjected to highly energetic processing, it is not sufficient to
analyze only the ID/IG ratio (as proposed in the available literature), but it
is also necessary to evaluate the shifting of the G band, which traces the
amorphization trajectory undergone by the CNT. Furthermore, we observed that
the deformation suffered by the CNT is related to the accumulated strain and
varies with the partial CNT fractions of these composites. This is related to
their capacity to withstand the plastic strain that occurs during deformation.
In addition, the defective state reaches a saturation before achieving the
saturation in the microstructural refinement. These results will help to
efficiently optimize the processing of this type of engineering composites.",2010.10085v1
2020-10-20,Analysis of the phase-locking dynamics of a III-V-on-silicon frequency comb laser,"We present the detailed characterization of the phase dynamics of a telecom
hybrid III-V-on-silicon passively mode-locked laser with a ring cavity. We
explore the various regimes of operation as a function of gain current and
saturable absorber bias voltage. We use a stepped-heterodyne measurement to
quantify the spectral chirp and reconstruct the pulse envelop. With this
technique we are able to identify regimes of near-transform-limited operation
and we assess the degradation of mode-locking in the comb phase relationship
when saturable absorber bias voltage is changed. Finally, we present a
preliminary study of the phase-locking in hybrid mode-locked operation and
demonstrate transform-limited pulses.",2010.10362v1
2020-10-22,Trajectory Tracking for Robotic Arms with Input Saturation and Only Position Measurements,"In this work, we propose a passivity-based control approach that addresses
the trajectory tracking problem for a class of mechanical systems that
comprises a broad range of robotic arms. The resulting controllers can be
naturally saturated and do not require velocity measurements. Moreover, the
proposed methodology does not require the implementation of observers, and the
structure of the closed-loop system permits the identification of a Lyapunov
function, which eases the convergence analysis. To corroborate the
effectiveness of the methodology, we perform experiments with the Philips
Experimental Robot Arm.",2010.11712v1
2020-10-23,Investigating Saturation Effects in Integrated Gradients,"Integrated Gradients has become a popular method for post-hoc model
interpretability. De-spite its popularity, the composition and relative impact
of different regions of the integral path are not well understood. We explore
these effects and find that gradients in saturated regions of this path, where
model output changes minimally, contribute disproportionately to the computed
attribution. We propose a variant of IntegratedGradients which primarily
captures gradients in unsaturated regions and evaluate this method on ImageNet
classification networks. We find that this attribution technique shows higher
model faithfulness and lower sensitivity to noise com-pared with standard
Integrated Gradients. A note-book illustrating our computations and results is
available at https://github.com/vivekmig/captum-1/tree/ExpandedIG.",2010.12697v1
2020-11-04,Universality in asymptotic bounds and its saturation in $2$D CFT,"We study asymptotics of three point coefficients (light-light-heavy) and two
point correlators in heavy states in unitary, compact $2$D CFTs. We prove an
upper and lower bound on such quantities using numerically assisted Tauberian
techniques. We obtain an optimal upper bound on the spectrum of operators
appearing with fixed spin from the OPE of two identical scalars. While all the
CFTs obey this bound, rational CFTs come close to saturating it. This mimics
the scenario of bounds on asymptotic density of states and thereby pronounces
an universal feature in asymptotics of 2D CFTs. Next, we clarify the role of
smearing in interpreting the asymptotic results pertaining to considerations of
eigenstate thermalization in 2D CFTs. In the context of light-light-heavy three
point coefficients, we find that the order one number in the bound is sensitive
to how close the light operators are from the $\frac{c}{32}$ threshold. In
context of two point correlator in heavy state, we find the presence of an
enigmatic regime which separates the $AdS_3$ thermal physics and the BTZ black
hole physics. Furthermore, we present some new numerical results on the
behavior of spherical conformal block.",2011.02482v1
2020-11-06,Estimating the nuclear saturation parameter via low-mass neutron star asteroseismology,"We examine the fundamental ($f$-) and the 1st pressure ($p_1$-) mode
frequencies in gravitational waves from cold neutron stars constructed with
various unified realistic equations of state. With the calculated frequencies,
we derive the empirical formulae for the $f$- and $p_1$-mode frequencies, $f_f$
and $f_{p_1}$, as a function of the square root of the stellar average density
and the parameter ($\eta$), which is a combination of the nuclear saturation
parameters. With our empirical formulae, we show that by simultaneously
observing the $f$- and $p_1$-mode gravitational waves, when $1.5\lesssim
f_{p_1}/f_f\lesssim 2.5$ (which corresponds to neutron star models with the
mass of $\lesssim 0.9M_\odot$), one could estimate the value of $\eta$ within
$\sim 10\%$ accuracy, which makes a strong constraint on the EOS for neutron
star matter. In addition, we find that the maximum $f$-mode frequency is
strongly associated with the minimum radius of neutron star. That is, if one
would observe a larger frequency of the $f$-mode, one might constrain the upper
limit of the minimum neutron star radius.",2011.03167v1
2020-11-10,SWCNT@BNNT with 1D van der Waals Heterostructure with a High Optical Damage Threshold for Laser Mode-locking,"Single-walled carbon nanotube encapsulated in boron nitrite nanotube
(SWCNT@BNNT) is a novel nanomaterial with a one-dimensional van der Waals
(1D-vdW) heterostructure. In this paper, we demonstrated that the SWCNT@BNNT
has an enhanced optical power tolerance compared to that of the pristine SWCNT
while exhibiting an optical saturable absorption properties. Under optical
power intensity of 13kW/cm2, the lifetime of the SWCNT@BNNT is found to be
2,270 times longer than SWCNT for 1% degradation in absorbance. A short-cavity
mode-locked laser with a high repetition rate of 1 GHz has been realized using
the SWCNT@BNNT as the saturable absorber. We have shown that the technique of
fabricating nanomaterial with a 1D-vdW heterostructure can modify and enhance
the optical properties of the encapsulated nanomaterials.",2011.04647v1
2020-11-12,Configurational Entropy of Optical Bright Similariton in Tapered Graded-Index Waveguide,"Configurational entropy (CE) consists of a family of entropic measures of
information used to describe the shape complexity of spatially-localized
functions with respect to a set of parameters. We obtain the Differential
Configurational Entropy (DCE) for similariton waves traveling in tapered
graded-index optical waveguides modeled by a generalized nonlinear
Schr\""odinger equation. It is found that for similariton's widths lying within
a certain range, DCE attains minimum saturation values as the nonlinear wave
evolves along the effective propagation variable $\zeta(t)$. In particular,
saturation is achieved earlier for lower values of the width, which we show
correspond to global minima of the DCE. Such low entropic values lead to
minimum dispersion of momentum modes as the similariton waves propagate along
tapered graded-index waveguides, and should be of importance in guiding their
design.",2011.06926v1
2020-11-16,Note on entropy dynamics in the Brownian SYK model,"We study the time evolution of R\'enyi entropy in a system of two coupled
Brownian SYK clusters evolving from an initial product state. The R\'enyi
entropy of one cluster grows linearly and then saturates to the coarse grained
entropy. This Page curve is obtained by two different methods, a path integral
saddle point analysis and an operator dynamics analysis. Using the Brownian
character of the dynamics, we derive a master equation which controls the
operator dynamics and gives the Page curve for purity. Insight into the physics
of this complicated master equation is provided by a complementary path
integral method: replica diagonal and non-diagonal saddles are responsible for
the linear growth and saturation of R\'enyi entropy, respectively.",2011.08158v2
2020-11-18,Leading neutron production at the EIC and LHeC: estimating the impact of the absorptive corrections,"Leading neutron (LN) production in $ep$ collisions at high energies is
investigated using the color dipole formalism and taking into account
saturation effects. We update the treatment of absorptive effects and estimate
the impact of these effects on LN spectra in the kinematical range that will be
probed by the Electron Ion Collider (EIC) and by the Large Hadron electron
Collider (LHeC). We demonstrate that Feynman scaling, associated to saturation,
is not violated by the inclusion of absorptive effects. Moreover, our results
indicate that the LN spectrum is strongly suppressed at small photon
virtualities. These results suggest that absorptive effects cannot be
disregarded in future measurements of the $\gamma \pi$ cross section to be
extracted from data on leading neutron production.",2011.09515v1
2020-12-02,Adaptive prescribed-time disturbance observer using nonsingular terminal sliding mode control: Extended Kalman filter and particle swarm optimization,"In this paper, adaptive prescribed finite time stabilization of uncertain
single-input and single-output nonlinear systems is considered in the presence
of unknown states, unknown parameters, external load disturbance, and
non-symmetric input saturation. A prescribed finite time disturbance observer
is designed to approximate the unmeasured external disturbance. Also, a
nonsingular prescribed finite time terminal sliding mode control is proposed
for the closed-loop control of the system with the non-symmetric input
saturation. Extended Kalman filter algorithm is employed for the real-time
estimations of the states and unknown parameters of the system. Moreover,
particle swarm optimization algorithm is used to obtain the design parameters
of the proposed disturbance observer and controller. To show the performance of
designed control scheme, the proposed approach is employed to guarantee
prescribed finite time stabilization of nonlinear vibration of a nonlocal
strain gradient nanobeam. Finally, numerical simulations are performed to
illustrate the effectiveness and performance of the developed adaptive control
scheme for the vibration control of nanobeam in comparison to the conventional
sliding mode control.",2012.01026v1
2020-12-02,Homogenization of large deforming fluid-saturated porous structures,"The two-scale computational homogenization method is proposed for modelling
of locally periodic fluid-saturated media subjected a to large deformation
induced by quasistatic loading. The periodic heterogeneities are relevant to
the mesoscopic scale at which a double porous medium constituted by
hyperelastic skeleton and an incompressible viscous fluid is featured by large
contrasts in the permeability. Within the Eulerian framework related to the
current deformed configuration, the two-scale homogenization approach is
applied to a linearized model discretized in time, being associated with an
incremental formulation. For this, the equilibrium equation and the mass
conservation expressed in the spatial configuration are differentiated using
the material derivative with respect to a convection velocity field. The
homogenization procedure of the linearized equations provides effective
(homogenized) material properties are computed to constitute the incremental
macroscopic problem. The coupled algorithm for the multiscale problem is
implemented using the finite element method. Illustrative 2D numerical
simulations of a poroelastic medium are presented including a simple validation
test.",2012.03730v1
2020-12-10,Global linear and nonlinear gyrokinetic modelling of Alfvén eigenmodes in ITER,"Linear and nonlinear modelling of Alfv\'enic instabilities, most notably
toroidal Alfv\'en eigenmodes (TAEs), obtained by using the global nonlinear
electromagnetic gyrokinetic model of the code ORB5 are presented for the 15 MA
scenario of the ITER tokamak. Linear simulations show that elliptic Alfv\'en
eigenmodes and odd-parity TAEs are only weakly damped but not excited by alpha
particles, whose drive favours even-parity TAEs. Low mode number TAEs are found
to be global, requiring global treatment. Nonlinearly, even with double the
nominal EP density, single mode simulations lead to saturation with negligible
EP transport however multi-mode simulations predict that with double the
nominal EP density, enhanced saturation and significant EP redistribution will
occur.",2012.05651v1
2020-12-12,Heterochromatic nonlinear optical responses in upconversion nanoparticles for point spread function engineering,"Point spread function (PSF) engineering of the emitter can code higher
spatial frequency information of an image to break diffraction limit but suffer
from the complexed optical systems. Here we present a robust strategy to
simultaneously achieve diverse PSFs from upconversion nanoparticles under a
single doughnut-shape scanning beam. By saturating the four-photon state, the
high-frequency information can be extracted through the doughnut emission PSF.
In contrast, the complementary lower frequency information can be carried out
by the Gaussian-like emission PSF, as a result of over-saturated at the
two-photon state. With the Fourier domain heterochromatic fusion, we verify the
capability of the synthesised PSF to cover both low and high-frequency
information, yielding the overall enhanced image quality. We show a spatial
resolution of 40 nm, 1/24th of the excitation wavelength. This work suggests a
new scope for developing nonlinear multi-colour emitting probes to improve
image quality and noise control in nanoscopy.",2012.06704v2
2020-12-14,Saturation of Newton polytopes of type A and D cluster variables,"We study Newton polytopes for cluster variables in cluster algebras
$\mathcal{A}(\Sigma)$ of types A and D. A famous property of cluster algebras
is the Laurent phenomenon: each cluster variable can be written as a Laurent
polynomial in the cluster variables of the initial seed $\Sigma$. The cluster
variable Newton polytopes are the Newton polytopes of these Laurent
polynomials. We show that if $\Sigma$ has principal coefficients or boundary
frozen variables, then all cluster variable Newton polytopes are saturated. We
also characterize when these Newton polytopes are \emph{empty}; that is, when
they have no non-vertex lattice points.",2012.07500v2
2020-12-17,"Topological structures on saturated sets, optimal orbits and equilibrium states","Pfister and Sullivan proved that if a topological dynamical system $(X,T)$
satisfies almost product property and uniform separation property, then for
each nonempty compact %convex subset $K$ of invariant measures, the entropy of
saturated set $G_{K}$ satisfies \begin{equation}\label{Bowen's topological
entropy}
  h_{top}^{B}(T,G_{K})=\inf\{h(T,\mu):\mu\in K\}, \end{equation} where
$h_{top}^{B}(T,G_{K})$ is Bowen's topological entropy of $T$ on $G_{K}$, and
$h(T,\mu)$ is the Kolmogorov-Sinai entropy of $\mu$. In this paper, we
investigate topological complexity of $G_{K}$ by replacing Bowen's topological
entropy with upper capacity entropy and packing entropy and obtain the
following formulas: \begin{equation*}
  h_{top}^{UC}(T,G_{K})=h_{top}(T,X)\ \mathrm{and}\
h_{top}^{P}(T,G_{K})=\sup\{h(T,\mu):\mu\in K\}, \end{equation*} where
$h_{top}^{UC}(T,G_{K})$ is the upper capacity entropy of $T$ on $G_{K}$ and
$h_{top}^{P}(T,G_{K})$ is the packing entropy of $T$ on $G_{K}.$ In the proof
of these two formulas, uniform separation property is unnecessary.",2012.09482v2
2020-12-18,Resonant Shattering Flares as Multimessenger Probes of the Nuclear Symmetry Energy,"The behaviour of the nuclear symmetry energy near saturation density is
important for our understanding of dense nuclear matter. This density
dependence can be parameterised by the nuclear symmetry energy and its
derivatives evaluated at nuclear saturation density. In this work we show that
the core-crust interface mode of a neutron star is sensitive to these
parameters, through the (density-weighted) shear-speed within the crust, which
is in turn dependent on the symmetry energy profile of dense matter. We
calculate the frequency at which the neutron star quadrupole ($\ell = 2$)
crust-core interface mode must be driven by the tidal field of its binary
partner to trigger a Resonant Shattering Flare (RSF). We demonstrate that
coincident multimessenger timing of an RSF and gravitational wave chirp from a
neutron star merger would enable us to place constraints on the symmetry energy
parameters that are competitive with those from current nuclear experiments.",2012.10322v2
2020-12-28,Entanglement Monotones from Complementarity Relations,"Bohr's complementarity and Schr\""odinger's entanglement are two prominent
physical characters of quantum systems. In this letter, we formally connect
them. It is known that complementarity relations for wave-particle duality are
saturated only for pure, single-quanton, quantum states. For mixed states, the
wave-particle quantifiers never saturate a complementarity relation and can
even reach zero for a maximally mixed state. To fully characterize a quanton,
it is not enough to consider its wave-particle aspect; we have also to regard
its quantum correlations with other systems. Here we prove that for any
complete complementarity relation involving predictability and visibility
measures that satisfy the criteria established in the literature, these
corresponding quantum correlations are entanglement monotones.",2012.14471v4
2020-12-30,Correcting thermal-emission-induced detector saturation in infrared reflection or transmission spectroscopy,"We found that temperature-dependent infrared spectroscopy measurements (i.e.,
reflectance or transmittance) using a Fourier-transform spectrometer can have
substantial errors, especially for elevated sample temperatures and collection
using an objective lens (e.g., using an infrared microscope). These errors
arise as a result of partial detector saturation due to thermal emission from
the measured sample reaching the detector, resulting in nonphysical apparent
reduction of reflectance or transmittance with increasing sample temperature.
Here, we demonstrate that these temperature-dependent errors can be corrected
by implementing several levels of optical attenuation that enable ""convergence
testing"" of the measured reflectance or transmittance as the thermal-emission
signal is reduced, or by applying correction factors that can be inferred by
looking at the spectral regions where the sample is not expected to have a
substantial temperature dependence.",2012.14987v2
2021-01-01,Period-doubling bifurcation in spatiotemporal mode-locked lasers,"Period-doubling bifurcation is a universal dynamic of nonlinear systems,
which has been extensively investigated in laser systems with a single
transverse mode. This study presents an experimental observation and
theoretical investigation of the period-doubling bifurcation in spatiotemporal
mode-locked (STML) multimode fiber lasers. In the period-doubling state, it is
observed that the pulse train modulation varies with the transverse-mode, and
the output beam profile fluctuates rapidly and periodically. The numerical
simulations conducted in this study are in good agreement with the experimental
observations. Furthermore, a simple iterative model is proposed by considering
the mode-dependent saturable absorption effect, and the experimental results
can be qualitatively interpreted by this model. Based on these results,
spatiotemporal saturable absorption is believed to be the key factor for the
unique spatiotemporal characteristic of period-doubling bifurcation in
multimode lasers. This study contributes to the understanding of the complex
spatiotemporal dynamics in STML multimode lasers and to the discovery of novel
dynamics in high-dimensional nonlinear systems.",2101.00149v1
2021-01-05,Equality Saturation for Tensor Graph Superoptimization,"One of the major optimizations employed in deep learning frameworks is graph
rewriting. Production frameworks rely on heuristics to decide if rewrite rules
should be applied and in which order. Prior research has shown that one can
discover more optimal tensor computation graphs if we search for a better
sequence of substitutions instead of relying on heuristics. However, we observe
that existing approaches for tensor graph superoptimization both in production
and research frameworks apply substitutions in a sequential manner. Such
sequential search methods are sensitive to the order in which the substitutions
are applied and often only explore a small fragment of the exponential space of
equivalent graphs. This paper presents a novel technique for tensor graph
superoptimization that employs equality saturation to apply all possible
substitutions at once. We show that our approach can find optimized graphs with
up to 16% speedup over state-of-the-art, while spending on average 48x less
time optimizing.",2101.01332v2
2021-01-07,"Regression-based causal inference with factorial experiments: estimands, model specifications, and design-based properties","Factorial designs are widely used due to their ability to accommodate
multiple factors simultaneously. The factor-based regression with main effects
and some interactions is the dominant strategy for downstream data analysis,
delivering point estimators and standard errors via one single regression.
Justification of these convenient estimators from the design-based perspective
requires quantifying their sampling properties under the assignment mechanism
conditioning on the potential outcomes. To this end, we derive the sampling
properties of the factor-based regression estimators from both saturated and
unsaturated models, and demonstrate the appropriateness of the robust standard
errors for the Wald-type inference. We then quantify the bias-variance
trade-off between the saturated and unsaturated models from the design-based
perspective, and establish a novel design-based Gauss--Markov theorem that
ensures the latter's gain in efficiency when the nuisance effects omitted
indeed do not exist. As a byproduct of the process, we unify the definitions of
factorial effects in various literatures and propose a location-shift strategy
for their direct estimation from factor-based regressions. Our theory and
simulation suggest using factor-based inference for general factorial effects,
preferably with parsimonious specifications in accordance with the prior
knowledge of zero nuisance effects.",2101.02400v2
2021-01-10,Tuning Dzyaloshinskii-Moriya Interaction in Ferrimagnetic GdCo: A First Principles Approach,"We present a systematic analysis of our ability to tune chiral
Dzyaloshinskii-Moriya Interactions (DMI) in compensated ferrimagnetic
Pt/GdCo/Pt1-xWx trilayers by cap layer composition. Using first principles
calculations, we show that the DMI increases rapidly for only ~ 10% W and
saturates thereafter, in agreement with experiments. The calculated DMI shows a
spread in values around the experimental mean, depending on the atomic
configuration of the cap layer interface. The saturation is attributed to the
vanishing of spin orbit coupling energy at the cap layer and the simultaneous
constancy at the bottom interface. Additionally, we predict the DMI in
Pt/GdCo/X (X=Ta, W, Ir) and find that W in the cap layer favors a higher DMI
than Ta and Ir that can be attributed to the difference in d-band alignment
around the Fermi level. Our results open up exciting combinatorial
possibilities for controlling the DMI in ferrimagnets towards nucleating and
manipulating ultrasmall high-speed skyrmions.",2101.03449v1
2021-01-11,"Generalized saturation problems for cliques, paths, and stars","A graph $G$ is $F$-saturated if it does not contain any copy of $F$, but the
addition of any missing edge in $G$ creates at least one copy of $F$. Inspired
by work of Alon and Shikhelman regarding a similar question for $F$-free
graphs, Kritschgau, Methuku, Tait, and Timmons introduced the parameter of
$\text{sat}_H(n,F)$ to denote the minimum number of copies of some subgraph $H$
in an $F$-saturated graph on $n$ vertices. In this paper, we address this
generalized saturation problem with special focus on $\text{sat}_{K_r}(n,S_t)$
and $\text{sat}_{S_r}(n,S_t)$ This relates to recent work by Chakraborti and
Loh regarding $\text{sat}_{K_r}(n,K_t)$ and by Ergemlidze, Methuku, Tait, and
Timmons regarding $\text{sat}_{S_r}(n,K_t)$. We also provide some results
regarding paths and arbitrary trees.",2101.04213v4
2021-01-12,Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone,"In subduction zones, seismic slip at shallow crustal depths can lead to the
generation of tsunamis. Large slip displacements during tsunamogenic
earthquakes are attributed to the low coseismic shear strength of the
fluid-saturated and non-lithified clay-rich fault rocks. However, because of
experimental challenges in confining these materials, the physical processes
responsible of the coseismic reduction in fault shear strength are poorly
understood. Using a novel experimental setup, we measured pore fluid pressure
during simulated seismic slip in clay-rich materials sampled from the deep
oceanic drilling of the P\=apaku thrust (Hikurangi subduction zone, New
Zealand). Here we show that at seismic velocity, shear-induced dilatancy is
followed by pressurisation of fluids. The thermal and mechanical pressurisation
of fluids, enhanced by the low permeability of the fault, reduces the energy
required to propagate earthquake rupture. We suggest that fluid-saturated
clay-rich sediments, occurring at shallow depth in subduction zones, can
promote earthquake rupture propagation and slip because of their low
permeability and tendency to pressurise when sheared at seismic slip
velocities.",2101.04336v2
2021-01-13,Saturating PI control of stable nonlinear systems using singular perturbations,"This paper presents an anti-windup PI controller, using a saturating
integrator, for a single-input single-output stable nonlinear plant, whose
steady-state input-output map is increasing. We prove that, under reasonable
assumptions, there exists an upper bound on the controller gain such that for
any constant reference input, the corresponding equilibrium point of the
closed-loop system is exponentially stable, with a ""large"" region of
attraction. When the state of the closed-loop system converges to this
equilibrium point, then the tracking error tends to zero. The closed-loop
stability analysis employs Lyapunov methods in the framework of singular
perturbations theory. Finally, we show that if the plant satisfies the
asymptotic gain property, then the closed-loop system is globally
asymptotically stable for any sufficiently small controller gain. The
effectiveness of the proposed PI controller is proved by showing how it
performs as part of the control algorithm of a synchronverter (a special type
of DC to AC power converter).",2101.05122v2
2021-01-23,Nonlinear plane waves in saturated porous media with incompressible constituents,"We consider the propagation of nonlinear plane waves in porous media within
the framework of the Biot-Coussy biphasic mixture theory. The tortuosity effect
is included in the model, and both constituents are assumed incompressible
(Yeoh-type elastic skeleton, and saturating fluid). In this case, the linear
dispersive waves governed by Biot's theory are either of compression or
shear-wave type, and nonlinear waves can be classified in a similar way. In the
special case of a neo-Hookean skeleton, we derive the explicit expressions for
the characteristic wave speeds, leading to the hyperbolicity condition. The
sound speeds for a Yeoh skeleton are estimated using a perturbation approach.
Then we arrive at the evolution equation for the amplitude of acceleration
waves. In general, it is governed by a Bernoulli equation. With the present
constitutive assumptions, we find that longitudinal jump amplitudes follow a
nonlinear evolution, while transverse jump amplitudes evolve in an almost
linearly degenerate fashion.",2101.09507v3
2021-01-27,Observation of photon recoil effects in single-beam absorption spectroscopy with an ultracold strontium gas,"We report on observing photon recoil effects in the absorption of a single
monochromatic light at 689~nm through an ultracold $^{88}$Sr gas, where the
recoil frequency is comparable to natural linewidth of the narrow-line
transition $5\mathrm{s^2}\, ^1\textrm{S}_0 - 5\mathrm{s}5\mathrm{p}\,
^3\textrm{P}_1$ in strontium. In the regime of high-saturation, the absorption
profile becomes asymmetric due to the photon-recoil shift, which is of the same
order as the natural linewidth. The lineshape is described by an extension of
the optical Bloch equations including the momentum transfers to atoms during
emission and absorption of photons. Our work reveals the photon recoil effects
in a simplest single-beam absorption setting, which is of significant relevance
to other applications such as saturation spectroscopy, Ramsey interferometry,
and absorption imaging.",2101.11176v2
2021-02-01,Temporal Cavity Solitons in a Laser-based Microcomb: A Path to a Self-Starting Pulsed Laser without Saturable Absorption,"We theoretically present a design of self-starting operation of microcombs
based on laser-cavity solitons in a system composed of a micro-resonator nested
in and coupled to an amplifying laser cavity. We demonstrate that it is
possible to engineer the modulational-instability gain of the system's zero
state to allow the start-up with a well-defined number of robust solitons. The
approach can be implemented by using the system parameters, such as the cavity
length mismatch and the gain shape, to control the number and repetition rate
of the generated solitons. Because the setting does not require saturation of
the gain, the results offer an alternative to standard techniques that provide
laser mode-locking.",2102.01164v1
2021-02-08,Curse of Dimensionality for TSK Fuzzy Neural Networks: Explanation and Solutions,"Takagi-Sugeno-Kang (TSK) fuzzy system with Gaussian membership functions
(MFs) is one of the most widely used fuzzy systems in machine learning.
However, it usually has difficulty handling high-dimensional datasets. This
paper explores why TSK fuzzy systems with Gaussian MFs may fail on
high-dimensional inputs. After transforming defuzzification to an equivalent
form of softmax function, we find that the poor performance is due to the
saturation of softmax. We show that two defuzzification operations, LogTSK and
HTSK, the latter of which is first proposed in this paper, can avoid the
saturation. Experimental results on datasets with various dimensionalities
validated our analysis and demonstrated the effectiveness of LogTSK and HTSK.",2102.04271v1
2021-02-15,Breaking Reciprocity in a non-Hermitian Photonic Coupler with Saturable Absorption,"We study the breaking of reciprocity in non-Hermitian coupled photonic
waveguides by the simultaneous action of the nonlinear effect of saturable
absorption, and the presence of exceptional points. The nonlinear response of
such a system is studied in depth, giving physical insight into the operational
principles and fundamental limitations, while producing analytical and
semi-analytical results for the transmission and nonreciprocal intensity range.
We numerically validate the theoretical results and assess important
performance metrics for the nonreciprocal operation of such a device. This
novel class of passive non-resonant devices can offer on-chip broadband
nonreciprocal operation, making them potentially very important for high-speed
applications.",2102.07483v1
2021-02-20,High resolution imaging with anomalous saturated excitation,"The nonlinear fluorescence emission has been widely applied for the high
spatial resolution optical imaging. Here, we studied the fluorescence anomalous
saturating effect of the nitrogen vacancy defect in diamond. The fluorescence
reduction was observed with high power laser excitation. It increased the
nonlinearity of the fluorescence emission, and changed the spatial frequency
distribution of the fluorescence image. We used a differential excitation
protocol to extract the high spatial frequency information. By modulating the
excitation laser's power, the spatial resolution of imaging was improved
approximate 1.6 times in comparison with the confocal microscopy. Due to the
simplicity of the experimental setup and data processing, we expect this method
can be used for improving the spatial resolution of sensing and biological
labeling with the defects in solids.",2102.10363v1
2021-02-25,Supercontinuum Generation by Saturated Second-Order Nonlinear Interactions,"We propose a new approach to supercontinuum generation and
carrier-envelope-offset detection based on saturated second-order nonlinear
interactions in dispersion-engineered nanowaveguides. The technique developed
here broadens the interacting harmonics by forming stable bifurcations of the
pulse envelopes due to an interplay between phase-mismatch and pump depletion.
We first present an intuitive heuristic model for spectral broadening by
second-harmonic generation of femtosecond pulses, and show that this model
agrees well with experiments. Then, having established strong agreement between
theory and experiment, we develop scaling laws that determine the energy
required to generate an octave of bandwidth as a function of input pulse
duration, device length, and input pulse chirp. These scaling laws suggest that
future realization based on this approach could enable supercontinuum
generation with orders of magnitude less energy than current state-of-the-art
devices.",2102.12856v5
2021-02-25,Integration questions in separably good characteristics,"Let G be a reductive group over an algebraically closed field k of separably
good characteristic p>0 for G. Under these assumptions a Springer isomorphism
from the reduced nilpotent scheme of the Lie algebra of G to the reduced
unipotent scheme of G always exists. This allows to integrate any p-nilpotent
element of Lie(G) into a unipotent element of G. One should wonder whether such
a punctual integration can lead to a systematic integration of p-nil
subalgebras of Lie(G). We provide counterexamples of the existence of such an
integration in general as well as criteria to integrate some p-nil subalgebras
of Lie(G) (that are maximal in a certain sense). This requires to generalise
the notion of infinitesimal saturation first introduced by P. Deligne and to
extend one of his theorem on infinitesimally saturated subgroups of G to the
previously mentioned framework.",2102.13077v6
2021-02-26,A wavelength-tunable mode-locked Yb-doped fiber laser based on nonlinear Kerr beam clean-up effect,"We demonstrate a novel approach to achieve wavelength-tunable ultrashort
pulses from an all-fiber mode-locked laser with a saturable absorber based on
nonlinear Kerr beam clean-up effect. This saturable absorber was formed by a
single-mode fiber spliced to a graded-index multimode fiber, and its tunable
band-pass filter effect is studied by a numerical model. By adjusting the
bending condition of graded-index multimode fiber, the laser could produce
dissipative soliton pulses with their central wavelength tunable from1040 nm to
1063 nm. The pulse width of output laser could be compressed externally to 791
fs, and the signal to noise ratio of its radio frequency spectrum was measured
to be 75.5 dB. This work provides a new idea for the design of
wavelength-tunable mode-locked laser which can be used as an attractive light
source in communication system.",2102.13428v3
2021-03-02,Shortening X-ray Pulse Duration via Saturable Absorption,"To shorten the duration of x-ray pulses, we present a nonlinear optical
technique using atoms with core-hole vacancies (core-hole atoms) generated by
inner-shell photoionization. The weak Coulomb screening in the core-hole atoms
results in decreased absorption at photon energies immediately above the
absorption edge. By employing this phenomenon, referred to as saturable
absorption, we successfully reduce the duration of x-ray free-electron laser
pulses (photon energy: 9.000 keV, duration: 6-7 fs, fluence:
2.0-3.5$\times$10$^5$ J/cm$^2$) by $\sim$35%. This finding that core-hole atoms
are applicable to nonlinear x-ray optics is an essential stepping stone for
extending nonlinear technologies commonplace at optical wavelengths to the hard
x-ray region.",2103.01510v2
2021-03-03,Critical Parameters for Scalable Distributed Learning with Large Batches and Asynchronous Updates,"It has been experimentally observed that the efficiency of distributed
training with stochastic gradient (SGD) depends decisively on the batch size
and -- in asynchronous implementations -- on the gradient staleness.
Especially, it has been observed that the speedup saturates beyond a certain
batch size and/or when the delays grow too large. We identify a data-dependent
parameter that explains the speedup saturation in both these settings. Our
comprehensive theoretical analysis, for strongly convex, convex and non-convex
settings, unifies and generalized prior work directions that often focused on
only one of these two aspects. In particular, our approach allows us to derive
improved speedup results under frequently considered sparsity assumptions. Our
insights give rise to theoretically based guidelines on how the learning rates
can be adjusted in practice. We show that our results are tight and illustrate
key findings in numerical experiments.",2103.02351v1
2021-03-04,A vertex scheme for two-phase flow in heterogeneous media,"This paper presents the numerical solution of immiscible two-phase flows in
porous media, obtained by a first-order finite element method equipped with
mass-lumping and flux up-winding. The unknowns are the physical phase pressure
and phase saturation. Our numerical experiments confirm that the method
converges optimally for manufactured solutions. For both structured and
unstructured meshes, we observe the high-accuracy wetting saturation profile
that ensures minimal numerical diffusion at the front. Performing several
examples of quarter-five spot problems in two and three dimensions, we show
that the method can easily handle heterogeneities in the permeability field.
Two distinct features that make the method appealing to reservoir simulators
are: (i) maximum principle is satisfied, and (ii) mass balance is locally
conserved.",2103.03285v2
2021-03-07,"Assignments of the $X(4140)$, $X(4500)$, $X(4630)$ and $X(4685)$ based on the QCD sum rules","In this article, we take into account our previous calculations based on the
QCD sum rules, and tentatively assign the $X(4630)$ as the
$D_s^*\bar{D}_{s1}-D_{s1}\bar{D}_s^*$ tetraquark molecular state or
$[cs]_P[\bar{c}\bar{s}]_A+[cs]_A[\bar{c}\bar{s}]_P$ tetraquark state with the
$J^{PC}=1^{-+}$, and assign the $X(3915)$ and $X(4500)$ as the 1S and 2S
$[cs]_A[\bar{c}\bar{s}]_A$ tetraquark states respectively with the
$J^{PC}=0^{++}$. Then we extend our previous works to investigate the LHCb's
new tetraquark candidate $X(4685)$ as the first radial excited state of the
$X(4140)$ with the QCD sum rules, and obtain the mass
$M_{X}=4.70\pm0.12\,\rm{GeV}$, which is in very good agreement with the
experimental value $4684 \pm 7 {}^{+13}_{-16}\,\rm{MeV}$. Furthermore, we
investigate the two-meson scattering state contributions in details, and
observe that the two-meson scattering states alone cannot saturate the QCD sum
rules, the contributions of the tetraquark states play an un-substitutable
role, we can saturate the QCD sum rules with or without the two-meson
scattering states.",2103.04236v3
2021-03-09,Impact of intrinsic charm amount in the nucleon and saturation effects on the prompt atmospheric $ν_μ$ flux for IceCube,"The predictions for the atmospheric neutrino flux at high energies strongly
depend on the contribution of prompt neutrinos, which are determined by the
production of charmed meson in the atmosphere at very forward rapidities. In
this paper we estimate the related cross sections taking into account the
presence of an intrinsic charm (IC) component in the proton wave function and
the QCD dynamics modified by the onset of saturation effects. The impact on the
predictions for the prompt neutrino flux is investigated assuming different
values for the probability to find the IC in the nucleon. Comparison with the
IceCube data is performed and conclusions are drawn.",2103.05503v2
2021-03-10,Effects of confinement on the dynamics and correlation scales in active fluids,"We study the influence of solid boundaries on dynamics and structure of
active fluids as the height of the container, $z$, changes. Along the varying
dimension, the geometry systematically increases, therefore, the confinement
($z$) transits from ""strong confinement"", to ""intermediate confinement"" and to
""weak confinement"" (close to ""unconfined""). In horizontal dimensions ($x,y$),
the system remains ""unconfined"". Through tracking the tracers dispersed in the
active fluids in three dimensions we observed that activity level,
characterized by velocity fluctuations of flow tracers, increases as system
size increases. Concomitantly, the velocity-velocity temporal correlation
changes from weak correlation to strong positive correlation, indicating
""memory"" in active flows. We estimate the characteristic size of the flow
structure by integrating the velocity-velocity spatial correlation function.
The integral increases as confinement becomes weaker and saturates at
approximately 400 microns as the system becomes ""unconfined"". This saturation
indicates an intrinsic length scale which, along with the small-scale isotropy,
demonstrates the multi-scale nature of this kinesin-driven bundled microtubule
system.",2103.06334v1
2021-03-11,Quasi-static perforation of the ceramic foam core sandwich panels impregnated with Newtonian and non-Newtonian fluids,"In this research, Mechanical response and energy absorption of ceramic foam
sandwich panels filled with Newtonian and non-Newtonian fluid subjected to
quasi-static indentation loads were investigated experimentally. In addition,
the effects of number of face-sheet layers (face-sheet thickness) and boundary
conditions on the mechanical response and energy absorption of sandwich panels
were discussed. Sandwich panels consisted of two glass/epoxy face-sheets with
different thicknesses (4 and 8 layers) and an open cell ceramic foam core. This
foam saturated with Newtonian (Glycerol) and non-Newtonian (mixture of Ethylene
glycol and Aerosil) fluids. Sandwich panels were tested in two different kinds
of supporting conditions, simply-supported and fully fixed (clamped). Results
showed that damage area in neat composite and STF filled sandwich panels are
much higher than the glycerol filled foam core sandwich panels. Also, STF
saturated sandwich panels absorbed higher energy compared with two other type
of sandwich panels during quasi-static punch shear test.",2103.06952v1
2021-03-16,Prediction of three-phase relative permeabilities of Berea sandstone using lattice Boltzmann method,"Three-phase flows through a pore network of Berea sandstone are studied
numerically under critical interfacial tension condition. Results show that the
relative permeability of each fluid increases as its own saturation increases.
The specific interfacial length between wetting and non-wetting fluids
monotonously decreases with increasing the saturation of intermediate-wetting
fluid, while the other two specific interfacial lengths exhibit a
non-monotonous variation. As the wetting (non-wetting) fluid becomes less
wetting (non-wetting), the relative permeability of wetting fluid monotonously
increases, while the other two relative permeabilities show a non-monotonous
trend. Due to the presence of spreading layer, the specific interfacial length
between wetting and non-wetting fluids always stabilizes at a low level. As the
viscosity ratio of wetting (non-wetting) to intermediate-wetting fluids
increases, the relative permeability of wetting (non-wetting) fluid increases.
With the viscosity ratio deviating from unity, the phase interfaces become
increasingly unstable, leading to an increased specific interfacial length.",2103.08787v1
2021-03-17,Nonlinear coupling of reversed shear Alfven eigenmode and toroidal Alfven eigenmode during current ramp,"Two novel nonlinear mode coupling processes for reversed shear Alfven
eigenmode (RSAE) nonlinear saturation are proposed and investigated. In the
first process, RSAE nonlinearly couples to a co-propagating toroidal Alfven
eigenmode (TAE) with the same toroidal and poloidal mode numbers, and generates
a geodesic acoustic mode (GAM). In the second process, RSAE couples to a
counter-propagating TAE and generates an ion acoustic wave quasi-mode (IAW).
The condition for the two processes to occur is favored during current ramp.
Both processes contribute to effectively saturate the Alfvenic instabilities,
as well as nonlinearly transfer of energy from energetic fusion alpha particles
to fuel ions in burning plasmas.",2103.09446v1
2021-03-24,Nuclear matter in relativistic Brueckner-Hartree-Fock theory with Bonn potential in the full Dirac space,"Starting from the Bonn potential, relativistic Brueckner-Hartree-Fock (RBHF)
equations are solved for nuclear matter in the full Dirac space, which provides
a unique way to determine the single-particle potentials and avoids the
approximations applied in the RBHF calculations in the Dirac space with
positive-energy states (PESs) only. The uncertainties of the RBHF calculations
in the Dirac space with PESs only are investigated, and the importance of the
RBHF calculations in the full Dirac space is demonstrated. In the RBHF
calculations in the full Dirac space, the empirical saturation properties of
symmetric nuclear matter are reproduced, and the obtained equation of state
agrees with the results based on the relativistic Green's function approach up
to the saturation density.",2103.12960v1
2021-03-24,Ripple-Type Control for Enhancing Resilience of Networked Physical Systems,"Distributed control agents have been advocated as an effective means for
improving the resiliency of our physical infrastructures under unexpected
events. Purely local control has been shown to be insufficient, centralized
optimal resource allocation approaches can be slow. In this context, we put
forth a hybrid low-communication saturation-driven protocol for the
coordination of control agents that are distributed over a physical system and
are allowed to communicate with peers over a ""hotline"" communication network.
According to this protocol, agents act on local readings unless their control
resources have been depleted, in which case they send a beacon for assistance
to peer agents. Our ripple-type scheme triggers communication locally only for
the agents with saturated resources and it is proved to converge. Moreover,
under a monotonicity assumption on the underlying physical law coupling control
outputs to inputs, the devised control is proved to converge to a configuration
satisfying safe operational constraints. The assumption is shown to hold for
voltage control in electric power systems and pressure control in water
distribution networks. Numerical tests corroborate the efficacy of the novel
scheme.",2103.13505v1
2021-04-08,"Comment on ""Unconventional enhancement of ferromagnetic interactions in Cd-doped GdFe2Zn20 single crystals studied by ESR and 57Fe Mossbauer spectroscopies""","In the recent publication, Phys. Rev. B 102, 144420 (2020), Cabrera-Baez et
al. present a study of the effects of Cd-substitution for Zn in the
ferromagnetic compound GdFe2Zn20. As part of this paper, they claim that for
GdFe2Zn18.6Cd1.4 the effective moment of Gd is reduced by 25% and the saturated
moment of Gd is reduced by over 40%. We regrew representative members of the
GdFe2Zn(20-x)Cdx series and did not find any such reductions. In addition, we
measured several crystals from the growth batch that was used by Cabrera-Baez
et al. and did not see such reductions. Although there is a modest increase in
TC with Cd substitution, there is no significant change in the Gd effective
moment or the saturated moment associated with the low temperature
ferromagnetic state.",2104.03770v1
2021-04-12,A-FMI: Learning Attributions from Deep Networks via Feature Map Importance,"Gradient-based attribution methods can aid in the understanding of
convolutional neural networks (CNNs). However, the redundancy of attribution
features and the gradient saturation problem, which weaken the ability to
identify significant features and cause an explanation focus shift, are
challenges that attribution methods still face. In this work, we propose: 1) an
essential characteristic, Strong Relevance, when selecting attribution
features; 2) a new concept, feature map importance (FMI), to refine the
contribution of each feature map, which is faithful to the CNN model; and 3) a
novel attribution method via FMI, termed A-FMI, to address the gradient
saturation problem, which couples the target image with a reference image, and
assigns the FMI to the difference-from-reference at the granularity of feature
map. Through visual inspections and qualitative evaluations on the ImageNet
dataset, we show the compelling advantages of A-FMI on its faithfulness,
insensitivity to the choice of reference, class discriminability, and superior
explanation performance compared with popular attribution methods across
varying CNN architectures.",2104.05527v1
2021-04-15,Evolution of Anti-de Sitter black holes in Einstein-Maxwell-dilaton theory,"We study the nonlinear evolution of the spherical symmetric black holes under
a small neutral scalar field perturbation in Einstein-Maxwell-dilaton theory
with coupling function $f(\phi)=e^{-b\phi}$ in asymptotic anti-de Sitter
spacetime. The non-minimal coupling between scalar and Maxwell fields allows
the transmission of the energy from the Maxwell field to the scalar field, but
also behaves as a repulsive force for the scalar. The scalar field oscillates
with damping amplitude and converges to a final value by a power law. The
irreducible mass of the black hole increases abruptly at initial times and then
saturates to the final value exponentially. The saturating rate is twice the
decaying rate of the dominant mode of the scalar. The effects of the black hole
charge, the cosmological constant and the coupling parameter on the evolution
are studied in detail. When the initial configuration is a naked singularity
spacetime with a large charge to mass ratio, a horizon will form soon and hide
the singularity.",2104.07281v1
2021-04-15,Cross-beam energy transfer saturation by ion trapping-induced detuning,"The performance of direct-drive inertial confinement fusion implosions relies
critically on the coupling of laser energy to the target plasma. Cross-beam
energy transfer (CBET), the resonant exchange of energy between intersecting
laser beams mediated by ponderomotively driven ion-acoustic waves (IAW),
inhibits this coupling by scattering light into unwanted directions. The
variety of beam intersection angles and varying plasma conditions in an
implosion results in IAWs with a range of phase velocities. Here we show that
CBET saturates through a resonance detuning that depends on the IAW phase
velocity and that results from trapping-induced modifications to the ion
distribution functions. For smaller phase velocities, the modifications to the
distribution functions can rapidly thermalize in the presence of mid-Z ions,
leading to a blueshift in the resonant frequency. For larger phase velocities,
the modifications can persist, leading to a redshift in the resonant frequency.
Ultimately, these results may reveal pathways towards CBET mitigation and
inform reduced models for radiation hydrodynamics codes to improve their
predictive capability.",2104.07725v1
2021-04-14,Analysis of Screening Effects on Terahertz Photoconductive Devices using a Fully-Coupled Multiphysics Approach,"The terahertz current generated by a photoconductive device (PCD) saturates
as the power of the input optical pump is increased. This behavior is induced
by various screening effects that stem from the interactions between
electromagnetic (EM) fields and semiconductor carriers. In this work, these
screening effects are numerically analyzed for the first time using a
fully-coupled multiphysics approach. Unlike the previously developed simulation
frameworks, this approach rigorously models the nonlinear coupling between the
EM fields and the carriers and therefore is capable of accounting for the
screening effects. It is demonstrated that the results obtained using this
multiphysics approach and actual experiments are in excellent agreement. The
optical- and radiation-field screening effects are identified in the simulation
results and the optical-field screening is found to play a more dominant role
in the saturation of the PCD output under high optical pump power levels.",2105.00820v1
2021-05-04,Advanced Phase-Change Materials for Enhanced Meta-Displays,"Structural colors generated due to light scattering from static
all-dielectric metasurfaces have successfully enabled high-resolution,
high-saturation and wide-gamut color printing applications. Despite recent
advances, most demonstrations of these structure-dependent colors lack
post-fabrication tunability that hinders their applicability for front-end
dynamic display technologies. Phase-change materials (PCMs), with significant
contrast of their optical properties between their amorphous and crystalline
states, have demonstrated promising potentials in reconfigurable nanophotonics.
Herein, we leverage a tunable all-dielectric reflective metasurface made of a
newly emerged class of low-loss optical PCMs with superb characteristics, i.e.,
antimony trisulphide (Sb$_2$S$_3$), antimony triselenide (Sb$_2$Se$_3$), and
binary germanium-doped selenide (GeSe$_3$), to realize switchable,
high-saturation, high-efficiency and high-resolution structural colors. Having
polarization sensitive building blocks, the presented metasurface can generate
two different colors when illuminated by two orthogonally polarized incident
beams. Such degrees of freedom (i.e., structural state and polarization) enable
a single reconfigurable metasurface with fixed geometrical parameters to
generate four distinct wide-gamut colors suitable for a wide range of
applications, including tunable full-color printing and displays, information
encryption, and anti-counterfeiting.",2105.01313v1
2021-05-11,Implicit and semi-implicit second-order time stepping methods for the Richards equation,"This study concerns numerical methods for efficiently solving the Richards
equation where different weak formulations and computational techniques are
analyzed. The spatial discretizations are based on standard or mixed finite
element methods. Different implicit and semi-implicit temporal discretization
techniques of second-order accuracy are studied. To obtain a linear system for
the semi-implicit schemes, we propose second-order techniques using
extrapolation formulas and/or semi-implicit Taylor approximations for the
temporal discretization of nonlinear terms. A numerical convergence study and a
series of numerical tests are performed to analyze efficiency and robustness of
the different schemes. The developed scheme, based on the proposed temporal
extrapolation techniques and the mixed formulation involving the saturation and
pressure head and using the standard linear Lagrange element, performs better
than other schemes based on the saturation and the flux and using the
Raviart-Thomas elements. The proposed semi-implicit scheme is a good
alternative when implicit schemes meet convergence issues.",2105.05224v1
2021-05-20,Optimal Frobenius light cone in spin chains with power-law interactions,"In many-body quantum systems with spatially local interactions, quantum
information propagates with a finite velocity, reminiscent of the ``light cone""
of relativity. In systems with long-range interactions which decay with
distance $r$ as $1/r^\alpha$, however, there are multiple light cones which
control different information theoretic tasks. We show an optimal (up to
logarithms) ``Frobenius light cone"" obeying $t\sim r^{\min(\alpha-1,1)}$ for
$\alpha>1$ in one-dimensional power-law interacting systems with finite local
dimension: this controls, among other physical properties, the butterfly
velocity characterizing many-body chaos and operator growth. We construct an
explicit random Hamiltonian protocol that saturates the bound and settles the
optimal Frobenius light cone in one dimension. We partially extend our
constraints on the Frobenius light cone to a several operator $p$-norms, and
show that Lieb-Robinson bounds can be saturated in at most an exponentially
small $e^{-\Omega(r)}$ fraction of the many-body Hilbert space.",2105.09960v2
2021-05-25,Algorithms to generate saturated random sequential adsorption packings built of rounded polygons,"We present the algorithm for generating strictly saturated random sequential
adsorption packings built of rounded polygons. It can be used to study various
properties of such packings built of a wide variety of different shapes and in
modelling monolayers obtained during the irreversible adsorption processes of
complex molecules. Here, we apply the algorithm to study the densities of
packings built of rounded regular polygons. Contrary to packings built of
regular polygons, where packing fraction grows with an increasing number of
polygon sides, the packing fraction reaches its maximum for packings built of
rounded regular triangles. With a growing number of polygon sides and
increasing rounding radius, the packing fractions tend to the limit given by a
packing built of disks. However, they are still slightly denser, even for the
rounded 25-gon, which is the highest-sided regular polygon studied here.",2105.11867v1
2021-05-30,Mackey's obstruction map for discrete graded algebras,"G.W. Mackey's celebrated obstruction theory for projective representations of
locally compact groups was remarkably generalized by J. M. G. Fell and R. S.
Doran to the wide area of saturated Banach *-algebraic bundles.
  Analogous obstruction is suggested here for discrete group graded algebras
which are not necessarily saturated, i.e. strongly graded in the discrete
context. The obstruction is a map assigning a certain second cohomology class
to every equivariance class of absolutely simple graded modules.
  The set of equivariance classes of such modules is equipped with an
appropriate multiplication, namely a graded product, such that the obstruction
map is a homomorphism of abelian monoids. Graded products, essentially arising
as pull-backs of bundles, admit many nice properties, including a way to twist
graded algebras and their graded modules.
  The obstruction class turns out to determine the fine part that appears in
the Bahturin-Zaicev-Sehgal decomposition, i.e. the graded Artin-Wedderburn
theorem for graded simple algebras which are graded Artinian, in case where the
base algebras (i.e. the unit fiber algebras) are finite-dimensional over
algebraically closed fields.",2105.14585v2
2021-06-01,Comparing Test Sets with Item Response Theory,"Recent years have seen numerous NLP datasets introduced to evaluate the
performance of fine-tuned models on natural language understanding tasks.
Recent results from large pretrained models, though, show that many of these
datasets are largely saturated and unlikely to be able to detect further
progress. What kind of datasets are still effective at discriminating among
strong models, and what kind of datasets should we expect to be able to detect
future improvements? To measure this uniformly across datasets, we draw on Item
Response Theory and evaluate 29 datasets using predictions from 18 pretrained
Transformer models on individual test examples. We find that Quoref, HellaSwag,
and MC-TACO are best suited for distinguishing among state-of-the-art models,
while SNLI, MNLI, and CommitmentBank seem to be saturated for current strong
models. We also observe span selection task format, which is used for QA
datasets like QAMR or SQuAD2.0, is effective in differentiating between strong
and weak models.",2106.00840v1
2021-06-14,Nonclassical states of light in a nonlinear Michelson interferometer,"Nonlinear quantum metrology schemes can lead to faster than Heisenberg
limited scalings for the measurement uncertainty. We study a Michelson
interferometer embedded in a Kerr medium [Luis and Rivas, Phys. Rev. A 92,
022104 (2015)] that leads to non-linear, intensity dependent phase shifts
corresponding to relative changes in the lengths of its two arms. The quantum
Cramer-Rao bound on the minimum achievable measurement uncertainties is worked
out and the requirements, in practice, to saturate the bound are investigated.
The choice of input state of light into the interferometer and the read out
strategy at the output end are discussed. The ideal, non-classical states of
light that must be used to saturate the bound are found to be highly
susceptible to photon loss noise. We identify optimal states at each noise
level that are both resilient to noise and capable of giving the enhanced
sensitivities and discuss practical implementations of the interferometry
scheme using such states.",2106.07420v2
2021-06-17,Exploring the Properties and Evolution of Neural Network Eigenspaces during Training,"In this work we explore the information processing inside neural networks
using logistic regression probes \cite{probes} and the saturation metric
\cite{featurespace_saturation}. We show that problem difficulty and neural
network capacity affect the predictive performance in an antagonistic manner,
opening the possibility of detecting over- and under-parameterization of neural
networks for a given task. We further show that the observed effects are
independent from previously reported pathological patterns like the ``tail
pattern'' described in \cite{featurespace_saturation}. Finally we are able to
show that saturation patterns converge early during training, allowing for a
quicker cycle time during analysis",2106.09526v3
2021-06-18,Decoding the Density Dependence of the Nuclear Symmetry Energy,"The large imbalance in the neutron and proton densities in very neutron rich
systems increases the nuclear symmetry energy so that it governs many aspects
of neutron stars and their mergers. Extracting the density dependence of the
symmetry energy therefore constitutes an important scientific objective. Many
analyses have been limited to extracting values for the symmetry energy, $S_0$,
and its ``derivative'', $L$, at saturation density $\rho_0 \approx 2.6 \times
10^{14}~\mathrm{g/cm^3}$ $\approx 0.16~\mathrm{nucleons/fm^{3}}$, resulting in
constraints that appear contradictory. We show that most experimental
observables actually probe the symmetry energy at densities far from $\rho_0$,
making the extracted values of $S_0$ or $L$ imprecise. By focusing on the
densities these observables actually probe, we obtain a detailed picture of the
density dependence of the symmetry energy from $0.25\rho_0$ to $1.5\rho_0$.
From this experimentally derived density functional, we extract
$L_{01}=53.1\pm6.1 MeV$ at $\rho \approx 0.10~\mathrm{fm^{-3}}$, a neutron skin
thickness for $^{208}Pb$ of $R_{np} =$ $0.23\pm0.04$ fm, a symmetry pressure at
saturation density of $P_0=3.2\pm1.2 MeV/fm^3$ and suggests a radius for a 1.4
solar mass neutron star of $13.1\pm0.6$ km.",2106.10119v1
2021-06-23,"Thermodynamics of Wetting, Prewetting and Surface Phase Transitions with Surface Binding","In living cells, protein-rich condensates can wet the cell membrane and
surfaces of membrane-bound organelles. Interestingly, many phase-separating
proteins also bind to membranes leading to a molecular layer of bound
molecules. Here we investigate how binding to membranes affects wetting,
prewetting and surface phase transitions. We derive a thermodynamic theory for
a three-dimensional bulk in the presence of a two-dimensional, flat membrane.
At phase coexistence, we find that membrane binding facilitates complete
wetting and thus lowers the wetting angle. Moreover, below the saturation
concentration, binding facilitates the formation of a thick layer at the
membrane and thereby shifts the prewetting phase transition far below the
saturation concentration. The distinction between bound and unbound molecules
near the surface leads to a large variety of surface states {and complex
surface phase diagrams with a rich topology of phase transitions. Our work
suggests that surface phase transitions combined with molecular binding
represent a versatile mechanism to control the formation of protein-rich
domains at intra-cellular surfaces.",2106.12565v3
2021-06-26,Probing gluon number density with electron-dijet correlations at EIC,"We propose a novel way of studying the gluon number density (the so-called
Weizs\""acker-Williams gluon distribution) using the planned Electron Ion
Collider. Namely, with the help of the azimuthal correlations between the total
transverse momentum of the dijet system and the scattered electron, we examine
an interplay between the effect of the soft gluon emissions (the Sudakov form
factor) and the gluon saturation effects. The kinematic cuts are chosen such
that the dijet system is produced in the forward direction in the laboratory
frame, which provides an upper bound on the probed longitudinal fractions of
the hadron momentum carried by scattered gluons. Further cuts enable us to use
the factorization formalism that directly involves the unpolarized
Weizs\""acker-Williams gluon distribution. We find this observable to be very
sensitive to the soft gluon emission and moderately sensitive to the gluon
saturation.",2106.13964v2
2021-06-27,Can a liquid drop on a substrate be in equilibrium with saturated vapor?,"It is well-known that liquid and saturated vapor, separated by a flat
interface in an unbounded space, are in equilibrium. One would similarly expect
a liquid drop, sitting on a flat substrate, to be in equilibrium with the vapor
surrounding it. Yet, it is not: as shown in this work, the drop evaporates.
Mathematically, this conclusion is deduced using the diffuse-interface model,
but it can also be reformulated in terms of the maximum-entropy principle,
suggesting model independence. Physically, evaporation of drops is due to the
so-called Kelvin effect, which gives rise to a liquid-to-vapor mass flux in all
cases where the boundary of the liquid phase is convex.",2106.14221v2
2021-06-27,Capillary condensation of saturated vapor in a corner formed by two intersecting walls,"The dynamics of saturated vapor between two intersecting walls is examined.
It is shown that, if the angle $\phi$ between the walls is sufficiently small,
the vapor becomes unstable, and spontaneous condensation occurs in the corner,
similar to the so-called capillary condensation of vapor into a porous medium.
As a result, an ever-growing liquid meniscus develops near the corner. The
diffuse-interface model and the lubrication approximation are used to
demonstrate that the meniscus grows if and only if $\phi+2\theta<\pi$, where
$\theta$ is the contact angle corresponding to the fluid/solid combination
under consideration. This criterion has a simple physical explanation: if it
holds, the meniscus surface is concave -- hence, the Kelvin effect causes
condensation. Once the thickness of the condensate exceeds by an order of
magnitude the characteristic interfacial thickness, the volume of the meniscus
starts to grow linearly with time. If the near-vertex region of the corner is
smoothed, the instability can be triggered off only by finite-size
perturbations, such that include enough liquid to cover the smoothed aria by a
microscopically-thin liquid film.",2106.14224v4
2021-07-01,Some products in fusion systems and localities,"The theory of saturated fusion systems resembles in many parts the theory of
finite groups. However, some concepts from finite group theory are difficult to
translate to fusion systems. For example, products of normal subsystems with
other subsystems are only defined in special cases. In this paper the theory of
localities is used to prove the following result: Suppose $\mathcal{F}$ is a
saturated fusion system over a $p$-group $S$. If $\mathcal{E}$ is a normal
subsystem of $\mathcal{F}$ over $T\leq S$, and $\mathcal{D}$ is a subnormal
subsystem of $N_{\mathcal{F}}(T)$ over $R\leq S$, then there is a subnormal
subsystem $\mathcal{E}\mathcal{D}$ of $\mathcal{F}$ over $TR$, which plays the
role of a product of $\mathcal{E}$ and $\mathcal{D}$ in $\mathcal{F}$. If
$\mathcal{D}$ is normal in $N_{\mathcal{F}}(T)$, then $\mathcal{E}\mathcal{D}$
is normal in $\mathcal{F}$. It is shown along the way that the subsystem
$\mathcal{E}\mathcal{D}$ is closely related to a naturally arising product in
certain localities attached to $\mathcal{F}$.",2107.00301v2
2021-07-16,Using saturated count models for user-friendly synthesis of categorical data,"Over the past three decades, synthetic data methods for statistical
disclosure control have continually evolved, but mainly within the domain of
survey data sets. There are certain characteristics of administrative
databases, such as their size, which present challenges from a synthesis
perspective and require special attention. This paper, through the fitting of
saturated count models, presents a synthesis method that is suitable for
administrative databases that is tuned by two parameters. The method allows
large categorical data sets to be synthesized quickly and allows risk and
utility metrics to be satisfied a priori, that is, prior to synthetic data
generation. The paper explores how the flexibility afforded by two-parameter
count models (the negative binomial and Poisson-inverse Gaussian) can be
utilised to protect respondents' - especially uniques' - privacy in synthetic
data. Finally, an empirical example is carried out through the synthesis of a
database which can be viewed as a good substitute to the English School Census.",2107.08062v2
2021-07-18,Probing gluon density fluctuations at large momentum transfer $|t|$ at HERA,"The information on the gluonic structure and its fluctuations is captured by
the differential $|t|$ spectrum in diffractive events. The incoherent
cross-section is sensitive to the fluctuations in the target wavefunction in
such events. We investigate the incoherent $ep$ cross-section in $J/\psi$
photoproduction using the impact-parameter dependent dipole model. The spatial
gluonic structure is modelled as hotspots of gluon density having substructure
where this substructure is modelled as hotspots within hotspots. We find that
three levels of the substructure provide a good description of all the data,
available up to $|t|=30~$GeV$^2$. We investigate these fluctuations in both the
saturated and non-saturated dipole models and compare our predictions with the
HERA Data.",2107.08395v2
2021-07-20,Logarithmic expansion of many-body wave packets in random potentials,"Anderson localization confines the wave function of a quantum particle in a
one-dimensional random potential to a volume of the order of the localization
length $\xi$. Nonlinear add-ons to the wave dynamics mimic many-body
interactions on a mean field level, and result in escape from the Anderson cage
and in unlimited subdiffusion of the interacting cloud. We address quantum
corrections to that subdiffusion by (i) using the ultrafast unitary Floquet
dynamics of discrete-time quantum walks, (ii) an interaction strength ramping
to speed up the subdiffusion, and (iii) an action discretization of the
nonlinear terms. We observe the saturation of the cloud expansion of $N$
particles to a volume $\sim N\xi$. We predict and observe a universal
intermediate logarithmic expansion regime which connects the mean-field
diffusion with the final saturation regime and is entirely controlled by
particle number $N$. The temporal window of that regime grows exponentially
with the localization length $\xi$.",2107.09385v2
2021-07-21,Bootstrapping 2d $φ^4$ Theory with Hamiltonian Truncation Data,"We combine the methods of Hamiltonian Truncation and the recently proposed
generalisation of the S-matrix bootstrap that includes local operators to
determine the two-particle scattering amplitude and the two-particle form
factor of the stress tensor at $s>0$ in the 2d $\phi^4$ theory. We use the form
factor of the stress tensor at $s\le 0$ and its spectral density computed using
Lightcone Conformal Truncation (LCT), and inject them into the generalized
S-matrix bootstrap set-up. The obtained results for the scattering amplitude
and the form factor are fully reliable only in the elastic regime. We
independently construct the ""pure"" S-matrix bootstrap bounds (bootstrap without
including matrix elements of local operators), and find that the sinh-Gordon
model and its analytic continuation the ""staircase model"" saturate these
bounds. Surprisingly, the $\phi^4$ two-particle scattering amplitude also very
nearly saturates these bounds, and moreover is extremely close to that of the
sinh-Gordon/staircase model.",2107.10286v1
2021-07-22,Bounds on Quantum Information Storage and Retrieval,"We present certain universal bounds on the capacity of quantum information
storage and on the time scale of its retrieval for a generic quantum field
theoretic system. The capacity, quantified by the microstate entropy, is
bounded from above by the surface area of the object measured in units of a
Goldstone decay constant. The Goldstone bosons are universally present due to
the spontaneous breaking of Poincare and internal symmetries by the
information-storing object. Applied to a black hole, the bound reproduces the
Bekenstein-Hawking entropy. However, the relation goes beyond gravity. The
minimal time-scale required for retrieving the quantum information from a
system is equal to its volume measured in units of the same Goldstone scale.
For a black hole this reproduces the Page time as well as the quantum
break-time. The same expression for the information retrieval time is shared by
non-gravitational saturated states in gauge theories, including QCD. The
saturated objects exhibit some universal signatures such as the emission of
ultra-soft radiation. Similar bounds apply to non-relativistic many-body
systems.",2107.10616v1
2021-08-09,A study of non-linear Langevin dynamics under non-Gaussian noise with quartic cumulant,"We consider a non-linear Langevin equation in presence of non-Gaussian noise
originating from non-linear bath. We claim, the parameters in the Langevin
equation are not physical. The physical parameters are obtained from a
path-integral description of the system, where the Langevin parameters are
related to the physical parameters by renormalisation flow equations. Then we
compute both numerically and analytically the velocity two point function and
show that it saturates to the bath temperature even in presence of
non-linearity. We also find the velocity four point function numerically and
show that it saturates to the analytically evaluated thermal velocity four
point function when the non-linear FDR [1] is satisfied. When the non-linear
FDR, which is a manifestation of time reversibility of thermal bath, is
violated then the system does not seem to thermalise. Rather, its velocity four
point function settles to a steady state.",2108.04284v3
2021-08-19,"Logarithmic, noise-induced dynamics in the Anderson insulator","We study the dynamical behavior of the Anderson insulator in the presence of
a local noise. We show that the noise induces logarithmically slow energy and
entanglement growth, until the system reaches an infinite-temperature state,
where both quantities saturate to extensive values. The saturation value of the
entanglement entropy approaches the average entanglement entropy over all
possible product states. At infinite temperature, we find that a density
excitation spreads logarithmically with time, without any signs of asymptotic
diffusive behavior. In addition, we provide a theoretical picture which
qualitatively reproduces the phenomenology of particle transport.",2108.08861v2
2021-08-20,2D optical rogue waves affected by transverse carrier diffusion in broad-area semiconductor lasers with a saturable absorber,"Statistics and dynamics of 2D rogue waves in a broad-area semiconductor laser
with an intracavity saturable absorber are numerically investigated under the
effect of transverse carrier diffusion. We show that lateral diffusion of
carriers alters the statistics of rogue waves by enhancing their formation in
smaller ratios of carrier lifetimes in the active and passive materials while
suppressing them when the ratio is larger. Temporal dynamics of the emitted
rogue waves is also studied and shown that finite nonzero transverse carrier
diffusion coefficient gives them a longer duration. To further approach the
realistic experimental situation, we also investigated statistics and dynamics
of rogue waves by simulating a circular disk-shape pump which replaces the flat
pump profile typically used in numerical simulations of broad-area lasers. We
show that finite pump shape reduces the number emitted rogue waves per unit
area for large carrier lifetime ratios and increases that for smaller values of
the ratio in both below and above laser threshold. Temporal width of the
emitted rogue waves is also shown to reduce as a consequence of removing the
nonphysical effects of infinite flat pump on carrier dynamics.",2108.09254v1
2021-08-26,In vivo functional and structural retina imaging using multimodal photoacoustic remote sensing microscopy and optical coherence tomography,"We have developed a multimodal photoacoustic remote sensing (PARS) microscope
combined with swept source optical coherence tomography for in vivo,
non-contact retinal imaging. Building on the proven strength of multiwavelength
PARS imaging, the system is applied for estimating retinal oxygen saturation in
the rat retina. The capability of the technology is demonstrated by imaging
both microanatomy and the microvasculature of the retina in vivo. To our
knowledge this is the first time a non-contact photoacoustic imaging technique
is employed for in vivo oxygen saturation measurement in the retina.",2108.12279v1
2021-08-28,Evaporation-driven density instabilities in saturated porous media,"Soil salinization is a major cause of soil degradation and hampers plant
growth. For soils saturated with saline water, the evaporation of water induces
accumulation of salt near the top of the soil. The remaining liquid gets an
increasingly larger density due to the accumulation of salt, giving a
gravitationally unstable situation, where instabilities in the form of fingers
can form. These fingers can hence lead to a net downwards transport of salt. We
here investigate the appearance of these fingers through a linear stability
analysis and through numerical simulations. The linear stability analysis gives
criteria for onset of instabilities for a large range of parameters.
Simulations using a set of parameters give information also about the
development of the fingers after onset. With this knowledge we can predict
whether and when the instabilities occur, and their effect on the salt
concentration development near the top boundary.",2108.12690v1
2021-08-30,Predicting the Effect of European Air Traffic on Cirrus Cloud Cover,"The purpose of this study is to provide more insight into the role of
anthropogenic cirrus formation through air traffic, by investigating the
high-density European airspace over a period spanning several recent years
including the start of the COVID-19 pandemic (2015-2020). Several data
resources are combined, exploiting the strengths of each product within an
all-encompassing framework on a high spatio-temporal resolution. Data from
METEOSAT SEVIRI have been combined and validated with CALIPSO's CALIOP data to
deduce temporal cirrus cloud cover variability over a rectangular region bound
by (10 degrees W - 35 degrees N) and (40 degrees E - 60 degrees N). Cirrus
clouds are correlated with air traffic. Meteorology was incorporated into the
analysis as it is of major influence on the formation and lifetime of cirrus.
Both a logistic regression model and a Random Forest model were built to assess
cirrus cloud cover variability imposed by meteorology. The impact of aviation
on cirrus cover in 1) super-saturated an 2) sub-saturated air have been
evaluated separately. A description of all the datasets involved, including the
main research methodology and main results, are presented.",2108.13364v1
2021-09-08,Subleading Bounds on Chaos,"Chaos, in quantum systems, can be diagnosed by certain out-of-time-order
correlators (OTOCs) that obey the chaos bound of Maldacena, Shenker, and
Stanford (MSS). We begin by deriving a dispersion relation for this class of
OTOCs, implying that they must satisfy many more constraints beyond the MSS
bound. Motivated by this observation, we perform a systematic analysis
obtaining an infinite set of constraints on the OTOC. This infinite set
includes the MSS bound as the leading constraint. In addition, it also contains
subleading bounds that are highly constraining, especially when the MSS bound
is saturated by the leading term. These new bounds, among other things, imply
that the MSS bound cannot be exactly saturated over any duration of time,
however short. Furthermore, we derive a sharp bound on the Lyapunov exponent
$\lambda_2 \le \frac{6\pi}{\beta}$ of the subleading correction to maximal
chaos.",2109.03826v2
2021-09-16,Stabilization of physical systems via saturated controllers with only partial state measurements,"This paper provides a constructive passivity-based control approach to solve
the set-point regulation problem for input-affine continuous nonlinear systems
while considering saturation in the inputs. As customarily in passivity-based
control, the methodology consists of two steps: energy shaping and damping
injection. In terms of applicability, the proposed controllers have two
advantages concerning other passivity-based control techniques: (i) the energy
shaping is carried out without solving partial differential equations, and (ii)
the damping injection is performed without measuring the passive output. The
proposed methodology is suitable to control a broad range of physical systems,
e.g., mechanical, electrical, and electro-mechanical systems. We illustrate the
applicability of the technique by designing controllers for systems in
different physical domains, where we validate the analytical results via
simulations and experiments.",2109.08111v2
2021-09-17,Relaxation of saturated random sequential adsorption packings of discorectangles aligned on a line,"Relaxation of the packing of elongated particles (discorectangles) aligned on
a line was studied numerically. The aspect ratio (length-to-width ratio) for
the discorectangles was varied within the range $\varepsilon \in [1;50]$. The
initial jamming (saturated) state was produced using the basic variant of the
random sequential adsorption (RSA) model with random positions and orientations
of particles. The relaxation was performed by allowing rotational and
translational diffusion motions of the particles wile their centers remained
located on the line. The effects of the aspect ratio $\varepsilon$ on the
kinetics of relaxation, the orientation order parameter and the distribution
function of the distances between nearest-neighbor discorectangles were
analyzed. The transport properties of the resulting 1D systems were also
analyzed by using the diffusion of a tracer particle (random walker) between
the nearest-neighbor discorectangles. In the relaxed states the anomalous
diffusion was observed having a hopping exponent $d_w>2$ dependent upon
$\varepsilon$.",2109.08453v2
2021-09-26,Multirate iterative scheme with multiphysics finite element method for a fluid-saturated poroelasticity,"In this paper, we propose a multirate iterative scheme with multiphysics
finite element method for a fluid-saturated poroelasticity model. Firstly, we
reformulate the original model into a fluid coupled problem to apply the
multiphysics finite element method for the discretization of the space
variables, and we design a multirate iterative scheme on the time scale which
solve a generalized Stokes problem in the coarse time size and solve the
diffusion problem in the finer time size according to the characteristics of
the poroelasticity problem. Secondly, we prove that the multirate iterative
scheme is stable and the numerical solution satisfies some energy conservation
laws, which are important to ensure the uniqueness of solution to the decoupled
computing problem. Also, we analyze the error estimates to prove that the
proposed numerical method doesn't reduce the precision of numerical solution
and greatly reduces the computational cost. Finally, we give the numerical
tests to verify the theoretical results and draw a conclusion to summary the
main results in this paper.",2109.12726v1
2021-09-27,Towards Bootstrapping RG flows: Sine-Gordon in AdS,"The boundary correlation functions for a Quantum Field Theory (QFT) in an
Anti-de Sitter (AdS) background can stay conformally covariant even if the bulk
theory undergoes a renormalization group (RG) flow. Studying such correlation
functions with the numerical conformal bootstrap leads to non-perturbative
constraints that must hold along the entire flow. In this paper we carry out
this analysis for the sine-Gordon RG flows in AdS$_2$, which start with a free
(compact) scalar in the UV and end with well-known massive integrable theories
that saturate many S-matrix bootstrap bounds. We numerically analyze the
correlation functions of both breathers and kinks and provide a detailed
comparison with perturbation theory near the UV fixed point. Our bounds are
often saturated to one or two orders in perturbation theory, as well as in the
flat-space limit, but not necessarily in between.",2109.13261v1
2021-09-28,The Impact of Sub-Resolution Porosity on Numerical Simulations of Multiphase Flow,"Sub-resolution porosity (SRP) is an ubiquitous, yet often ignored, feature in
Digital Rock Physics. It embodies the trade-off between image resolution and
field-of-view, and it is a direct result of choosing an imaging resolution that
is larger than the smallest pores in a heterogeneous rock sample. In this
study, we investigate the impacts of SRP on multiphase flow in porous rocks. To
do so, we use our newly developed Multiphase Micro-Continuum model to perform
first-of-a-kind direct numerical simulations of two-phase flow in porous
samples containing SRP. We show that SRP properties (porosity, permeability,
wettability) can impact predicted absolute permeabilities, fluid breakthrough
times, residual saturations, and relative permeabilities by factors of up to 2,
1.5, 3, and 20, respectively. In particular, our results reveal that SRP can
function as a persistent connector preventing the formation of isolated wetting
fluid domains during drainage, thus dramatically increasing relative
permeabilities to both fluids at low saturations. Overall, our study confirms
previous evidence that the influence of SRP cannot be disregarded without
incurring significant errors in numerical predictions or experimental analyses
of multiphase flow in heterogeneous porous media.",2109.13903v1
2021-10-03,Minimal Diamond-Saturated Families,"For a given fixed poset $\mathcal P$ we say that a family of subsets of $[n]$
is $\mathcal P$-saturated if it does not contain an induced copy of $\mathcal
P$, but whenever we add to it a new set, an induced copy of $\mathcal P$ is
formed. The size of the smallest such family is denoted by $\text{sat}^*(n,
\mathcal P)$. For the diamond poset $\mathcal D_2$ (the two-dimensional Boolean
lattice), Martin, Smith and Walker proved that $\sqrt n\leq\text{sat}^*(n,
\mathcal D_2)\leq n+1$. In this paper we prove that $\text{sat}^*(n, \mathcal
D_2)\geq (2\sqrt2-o(1))\sqrt n$. We also explore the properties that a
diamond-saturated family of size $c\sqrt n$, for a constant $c$, would have to
have.",2110.01118v4
2021-10-06,Regularized inverse Brascamp--Lieb inequalities,"Given any (forward) Brascamp--Lieb inequality on euclidean space, a famous
theorem of Lieb guarantees that gaussian near-maximizers always exist.
Recently, Barthe and Wolff used mass transportation techniques to establish a
counterpart to Lieb's theorem for all non-degenerate cases of the inverse
Brascamp--Lieb inequality. Here we build on work of Chen--Dafnis--Paouris and
employ heat-flow techniques to understand the inverse Brascamp--Lieb inequality
for certain regularized input functions, in particular extending the
Barthe--Wolff theorem to such a setting. Inspiration arose from work of
Bennett, Carbery, Christ and Tao for the forward inequality, as well as Wolff's
surprising observation that the gaussian saturation property for the inverse
Brascamp--Lieb inequality implies the gaussian saturation property for both the
forward Brascamp--Lieb inequality and Barthe's reverse Brascamp--Lieb
inequality.",2110.02841v1
2021-10-14,Synchronization and Balancing around Simple Closed Polar Curves with Bounded Trajectories and Control Saturation,"The problem of synchronization and balancing around simple closed polar
curves is addressed for unicycle-type multi-agent systems. Leveraging the
concept of barrier Lyapunov function in conjunction with bounded Lyapunov-like
curve-phase potential functions, we propose distributed feedback control laws
and show that the agents asymptotically stabilize to the desired closed curve,
their trajectories remain bounded within a compact set, and their turn-rates
adhere to the saturation limits. We also characterize the explicit nature of
the boundary of this trajectory-constraining set based on the magnitude of the
safe distance of the exterior boundary from the desired curve. We further
establish a connection between the perimeters and areas of the
trajectory-constraining set with that of the desired curve. We obtain bounds on
different quantities of interest in the post-design analysis and provide
simulation results to illustrate the theoretical findings.",2110.07248v1
2021-10-15,Bound-Preserving Finite-Volume Schemes for Systems of Continuity Equations with Saturation,"We propose finite-volume schemes for general continuity equations which
preserve positivity and global bounds that arise from saturation effects in the
mobility function. In the case of gradient flows, the schemes dissipate the
free energy at the fully discrete level. Moreover, these schemes are
generalised to coupled systems of non-linear continuity equations, such as
multispecies models in mathematical physics or biology, preserving the bounds
and the dissipation of the energy whenever applicable. These results are
illustrated through extensive numerical simulations which explore known
behaviours in biology and showcase new phenomena not yet described by the
literature.",2110.08186v3
2021-10-19,Scission configuration in the self-consistent calculations with neck constraint,"The calculations of the potential energy surface are essential in the
theoretical description of the fission process. In the constrained
self-consistent approach, the smooth evolution of nuclear shape is described
from the ground state until a very elongated one with a narrow neck. In all
microscopic calculations, the rupture of the neck at scission is associated
with a substantial change of nuclear matter density distribution and rapid
energy decrease. In this paper, we show that there is no discontinuity of the
potential energy surface at scission when multi-constrained calculations are
applied with the neck constraint. An early rupture of the neck at lower
quadrupole and octupole moments is discussed as competitive with the
conventional fission path. We discuss the neck properties in the scission
configuration. We find that the neck radius in the asymmetric fission mode
cannot decrease below 2 fm, and the nuclear matter density cannot decrease
below the saturation density. In the compact fission mode, nuclear density may
go down to half of the saturation density before the rupture of the neck.",2110.10028v1
2021-10-19,Chaotic synchronization in optical frequency combs,"Using a discrete mode approach we investigate the intermodal dynamics in a
frequency comb with nonlinear coupling due to four-wave mixing. In the presence
of sufficient saturable absorption, phase space collapses into a single state,
and all modes tightly lock with identical phase. In case of a purely reactive
nonlinearity, a less constrained locking mechanism emerges, which keeps phase
differences of neighboring modes loosely bounded and leads to the formation of
quasi-periodic breathers. Analysis of the underlying nonlinear correlations
identifies a chaotic synchronization process as the origin of this previously
unreported locking mechanism. Despite their rather large Lyapunov exponent and
correlation dimension, the highly chaotic dynamics may be easily overlooked by
common diagnostic approaches for laser mode-locking. This finding may finally
explain numerous unexplained reports on laser self mode-locking in the absence
of an effective saturable absorber mechanism and the formation of
self-frequency modulated combs in semiconductor lasers.",2110.10045v1
2021-10-24,Quantitative absorption imaging of optically dense effective two-level systems,"Absorption imaging is a commonly adopted method to acquire, with high
temporal resolution, spatial information on a partially transparent object. It
relies on the interference between a probe beam and the coherent response of
the object. In the low saturation regime, it is well described by a Beer
Lambert attenuation. In this paper we theoretically derive the absorption of a
$\sigma$ polarized laser probe by an ensemble of two-level systems in any
saturation regime. We experimentally demonstrate that the absorption cross
section in dense $^{87}$Rb cold atom ensembles is reduced, with respect to the
single particle response, by a factor proportional to the optical density b of
the medium. To explain this reduction, we developed a model that incorporates,
in the single particle response, the incoherent electromagnetic background
emitted by the surrounding ensemble. We show that it qualitatively reproduces
the experimental results. Our calibration factor that has a universal
dependence on optical density $b$ for $\sigma$ polarized light : $\alpha$ =
1.17(9) + 0.255(2)b allows to obtain quantitative and absolute, in situ, images
of dense quantum systems.",2110.12505v1
2021-11-02,Supersensitivity of Kerr phase estimation with two-mode squeezed vacuum states,"We analytically investigate the sensitivity of Kerr nonlinear phase
estimation in a Mach-Zehnder interferometer with two-mode squeezed vacuum
states. We find that such a metrological scheme could access a sensitivity
scaling over the Boixo \emph{et al.}'s generalized sensitivity limit [S. Boixo
\emph{et al}., Phys. Rev. Lett. \textbf{98}, 090401 (2007)], which is saturable
with celebrated NOON states. We also show that parity detection is a
quasioptimal measurement which can nearly saturate the quantum Cram\'er-Rao
bound in the aforementioned situation. Moreover, we further clarify the
supersensitive performance observed in the above scheme is due to the
restriction of Boixo \emph{et al}.'s generalized sensitivity limit (BGSL) to
probe states with fixed photon numbers. To conquer this problem, we generalize
the BGSL into the case with probe states of a fluctuating number of photons, to
which our scheme belongs.",2111.01375v2
2021-11-04,A Hofmann-Mislove theorem for approach spaces,"The Hofmann-Mislove theorem says that the ordered set of open filters of the
open-set lattice of a sober topological space is isomorphic to the ordered set
of compact saturated sets (ordered by reverse inclusion) of that space. This
paper concerns a metric analogy of this result. To this end, the notion of
compact functions of approach spaces is introduced. Such functions are an
analog of compact subsets in the enriched context. It is shown that for a sober
approach space $X$, the metric space of proper open $[0,\infty]$-filters of the
metric space of upper regular functions of $X$ is isomorphic to the opposite of
the metric space of inhabited and saturated compact functions of $X$,
establishing a Hofmann-Mislove theorem for approach spaces.",2111.02665v2
2021-11-05,Black-Hole-Like Saturons in Gross-Neveu,"It has been argued recently that objects of maximal microstate entropy
permitted by unitarity, the so-called saturons, have properties similar to
black holes. We demonstrate the existence of such objects in Gross-Neveu model.
From the large-$N$ scaling of $S$-matrix, we deduce the connection between the
entropy of the bound-state and the unitarity of scattering. We observe that
upon saturation of unitarity, the bound state exhibits a remarkable
correspondence with a black hole. The scaling of its entropy is identical to
Bekenstein-Hawking entropy. The saturon decays via Hawking's thermal rate of
temperature given by the inverse size. The information retrieval time from the
Gross-Neveu saturon is isomorphic to Page's time. Our observations indicate
that black hole properties are exhibited by saturated states in simple
calculable models.",2111.03620v1
2021-11-28,NoFADE: Analyzing Diminishing Returns on CO2 Investment,"Climate change continues to be a pressing issue that currently affects
society at-large. It is important that we as a society, including the Computer
Vision (CV) community take steps to limit our impact on the environment. In
this paper, we (a) analyze the effect of diminishing returns on CV methods, and
(b) propose a \textit{``NoFADE''}: a novel entropy-based metric to quantify
model--dataset--complexity relationships. We show that some CV tasks are
reaching saturation, while others are almost fully saturated. In this light,
NoFADE allows the CV community to compare models and datasets on a similar
basis, establishing an agnostic platform.",2111.14059v1
2021-11-29,Non-standard entanglement structure of local unitary self-dual models as a saturated situation of repeatability in general probabilistic theories,"We study the entanglement structure, i.e., the structure of quantum composite
system from operational aspects. The structure is not uniquely determined in
General Probabilistic Theories (GPTs) even if we impose reasonable postulate
about local systems. In this paper, we investigate the possibility that the
standard entanglement structure can be determined uniquely by repeatability of
measurement processing and its saturated situation called self-duality.
Surprisingly, self-duality cannot determine the standard entanglement structure
even if we additionally impose local unitary symmetry assumption. In this
paper, we show the existence of infinite structures of quantum composite system
such that it is self-dual with local unitary symmetry. Besides, we also show
the existence of a structure of quantum composite system such that
non-orthogonal states in the structure are perfectly distinguishable. In
addition, as a byproduct, we derive an sufficient condition to achieve the
detection of the entanglement property with a finite number of parameterized
minimizations.",2111.15019v3
2021-12-07,Complexity for Open Quantum System,"We study the complexity for an open quantum system. Our system is a harmonic
oscillator coupled to a one-dimensional massless scalar field, which acts as
the bath. Specifically, we consider the reduced density matrix by tracing out
the bath degrees of freedom for both regular and inverted oscillator and
computed the complexity of purification (COP) and complexity by using the
operator-state mapping. We found that when the oscillator is regular the COP
saturates quickly for both underdamped and overdamped oscillators.
Interestingly, when the oscillator is underdamped, we discover a kink like
behaviour for the saturation value of COP with varying damping coefficient. For
the inverted oscillator, we found a linear growth of COP with time for all
values of bath-system interaction. However, when the interaction is increased
the slope of the linear growth decreases, implying that the unstable nature of
the system can be regulated by the bath.",2112.03955v1
2021-12-15,Nonlinear intensity dependence of photogalvanics and photoconductance induced by terahertz laser radiation in twisted bilayer graphene close to magic angle,"We report on the observation of the nonlinear intensity dependence of the
bulk photogalvanic current and photoconductivity in the twisted graphene with
small twist angles close to the second magical angle. We show that terahertz
radiation results in the photoresponses, which is caused by indirect optical
transitions (free carrier absorption), direct interband transitions and optical
transitions between Moir\'e subbands. The relative contribution of these
absorption channels depends on the Fermi level position with respect to the
multiple Moir\'e subbands of the twisted graphene. The interplay of these
absorption channels results in oscillations of the photoresponses with
variation of the gate voltage. We show that the photoresponse saturates at high
intensities. For different absorption channels it has different intensity
dependencies and saturation intensities. The latter depends non-monotonically
on the Fermi level position, which is controlled by the gate voltage.",2112.07971v1
2021-12-15,Laser-lithographically written micron-wide superconducting nanowire single-photon detectors,"We demonstrate the fabrication of micron-wide tungsten silicide
superconducting nanowire single-photon detectors on a silicon substrate using
laser lithography. We show saturated internal detection efficiencies with wire
widths from 0.59$\mu$m to 1.43$\mu$m under illumination at 1550nm. We
demonstrate both straight wires, as well as meandered structures. Single-photon
sensitivity is shown in devices up to 4mm in length. Laser-lithographically
written devices allow for fast and easy structuring of large areas while
maintaining a saturated internal efficiency for wire width around 1$\mu$m.",2112.07976v1
2021-12-21,Generalized Few-Shot Semantic Segmentation: All You Need is Fine-Tuning,"Generalized few-shot semantic segmentation was introduced to move beyond only
evaluating few-shot segmentation models on novel classes to include testing
their ability to remember base classes. While the current state-of-the-art
approach is based on meta-learning, it performs poorly and saturates in
learning after observing only a few shots. We propose the first fine-tuning
solution, and demonstrate that it addresses the saturation problem while
achieving state-of-the-art results on two datasets, PASCAL-5i and COCO-20i. We
also show that it outperforms existing methods, whether fine-tuning multiple
final layers or only the final layer. Finally, we present a triplet loss
regularization that shows how to redistribute the balance of performance
between novel and base categories so that there is a smaller gap between them.",2112.10982v3
2021-12-23,A formula for symbolic powers,"Let $S$ be a Cohen-Macaulay ring which is local or standard graded over a
field, and let $I$ be an unmixed ideal that is also generically a complete
intersection. Our goal in this paper is multi-fold. First, we give a
multiplicity-based characterization of when an unmixed subideal $J \subseteq
I^{(m)}$ equals the $m$-th symbolic power $I^{(m)}$ of $I$. Second, we provide
a saturation-type formula to compute $I^{(m)}$ and employ it to deduce a
theoretical criterion for when $I^{(m)}=I^m$. Third, we establish an explicit
linear bound on the exponent that makes the saturation formula effective, and
use it to obtain lower bounds for the initial degree of $I^{(m)}$. Along the
way, we prove a conjecture (in fact, a generalized version of it) due to
Eisenbud and Mazur about ${\rm ann}_S(I^{(m)}/I^m)$, and we propose a
conjecture connecting the symbolic defect of an ideal to Jacobian ideals.",2112.12588v2
2022-01-01,On structure theorems and non-saturated examples,"For any minimal system $(X,T)$ and $d\geq 1$ there is an associated minimal
system $(N_{d}(X), \mathcal{G}_{d}(T))$, where $\mathcal{G}_{d}(T)$ is the
group generated by $T\times\cdots\times T$ and $T\times T^2\times\cdots\times
T^{d}$ and $N_{d}(X)$ is the orbit closure of the diagonal under
$\mathcal{G}_{d}(T)$. It is known that the maximal $d$-step pro-nilfactor of
$N_d(X)$ is $N_d(X_d)$, where $X_d$ is the maximal $d$-step pro-nilfactor of
$X$.
  In this paper, we further study the structure of $N_d(X)$. We show that the
maximal distal factor of $N_d(X)$ is $N_d(X_{dis})$ with $X_{dis}$ being the
maximal distal factor of $X$, and prove that as minimal systems $(N_{d}(X),
\mathcal{G}_{d}(T))$ has the same structure theorem as $(X,T)$. In addition, a
non-saturated metric example $(X,T)$ is constructed, which is not $T\times
T^2$-saturated and is a Toeplitz minimal system.",2201.00152v1
2022-01-24,Novel Nussbaum-Type Function based Safe Adaptive Distributed Consensus Control with Arbitrary Unknown Control Direction,"Existing Nussbaum function based methods on the consensus of multi-agent
systems require (partial) identical unknown control directions of all agents
and cause dangerous dramatic control shocks. This paper develops a novel
saturated Nussbaum function to relax such limitations and proposes a Nussbaum
function based control scheme for the consensus problem of multi-agent systems
with arbitrary non-identical unknown control directions and safe control
progress. First, a novel type of the Nussbaum function with different
frequencies is proposed in the form of saturated time-elongation functions,
which provides a more smooth and safer transient performance of the control
progress. Furthermore, the novel Nussbaum function is employed to design
distributed adaptive control algorithms for linearly parameterized multi-agent
systems to achieve average consensus cooperatively without dramatic control
shocks. Then, under the undirected connected communication topology, all the
signals of the closed-loop systems are proved to be bounded and asymptotically
convergent. Finally, two comparative numerical simulation examples are carried
out to verify the effectiveness and the superiority of the proposed approach
with smaller control shock amplitudes than traditional Nussbaum methods.",2201.09453v1
2022-02-05,Saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride molecules,"We report an experimental investigation on the Doppler-free saturated
absorption spectroscopy of buffer-gas-cooled Barium monofluoride (BaF)
molecules in a 4~K cryogenic cell. The obtained spectra with a resolution of
19~MHz, much smaller than previously observed in absorption spectroscopy,
clearly resolve the hyperfine transitions. Moreover, we use these
high-resolution spectra to fit the hyperfine splittings of excited $A(v=0)$
state and find the hyperfine splitting of the laser-cooling-relevant
$A^2\Pi_{1/2}(v=0, J=1/2, +)$ state is about 18 MHz, much higher than the
previous theoretically predicted value. This provides important missing
information for laser cooling of BaF molecules.",2202.02463v2
2022-02-08,Using Genetic Programming to Predict and Optimize Protein Function,"Protein engineers conventionally use tools such as Directed Evolution to find
new proteins with better functionalities and traits. More recently,
computational techniques and especially machine learning approaches have been
recruited to assist Directed Evolution, showing promising results. In this
paper, we propose POET, a computational Genetic Programming tool based on
evolutionary computation methods to enhance screening and mutagenesis in
Directed Evolution and help protein engineers to find proteins that have better
functionality. As a proof-of-concept we use peptides that generate MRI contrast
detected by the Chemical Exchange Saturation Transfer contrast mechanism. The
evolutionary methods used in POET are described, and the performance of POET in
different epochs of our experiments with Chemical Exchange Saturation Transfer
contrast are studied. Our results indicate that a computational modelling tool
like POET can help to find peptides with 400% better functionality than used
before.",2202.04039v2
2022-02-11,Weight polytopes and saturation of Demazure characters,"For $G$ a reductive group and $T\subset B$ a maximal torus and Borel
subgroup, Demazure modules are certain $B$-submodules, indexed by elements of
the Weyl group, of the finite irreducible representations of $G$. In order to
describe the $T$-weight spaces that appear in a Demazure module, we study the
convex hull of these weights - the Demazure polytope. We characterize these
polytopes both by vertices and by inequalities, and we use these results to
prove that Demazure characters are saturated, in the case that $G$ is simple of
classical Lie type. Specializing to $G=GL_n$, we recover results of Fink,
M\'esz\'aros, and St. Dizier, and separately Fan and Guo, on key polynomials,
originally conjectured by Monical, Tokcan, and Yong.",2202.05405v3
2022-02-12,Scaling properties of exclusive vector meson production cross section from gluon saturation,"It is already known from phenomenological studies that in exclusive
deep-inelastic scattering off nuclei there appears to be a scaling behavior of
vector meson production cross section in both nuclear mass number, $A$, and
photon virtuality, $Q^{2}$, which is strongly modified due to gluon saturation
effects. In this work we continue those studies in a realistic setup based upon
using the Monte Carlo event generator Sar{\em t}re. We make quantitative
predictions for the kinematics of the Electron-Ion Collider, focusing on this
$A$ and $Q^{2}$ scaling picture, along with establishing a small region of
squared momentum transfer, $t$, where there are signs of this scaling that may
potentially be observed at the EIC. Our results are represented as pseudo-data
of vector meson production diffractive cross section and/or their ratios, which
are obtained by parsing data collected by the event generator through smearing
functions, emulating the proposed detector resolutions for the future EIC.",2202.05981v2
2022-02-18,Self-Kerr effect across the yellow $\mathrm{Cu_2O}$ Rydberg series,"We investigate the nonlinear refraction induced by Rydberg excitons in
$\mathrm{Cu_2O}$. Using a high-precision interferometry imaging technique that
spatially resolves the nonlinear phase shift, we observe significant shifts at
extremely low laser intensity near each exciton resonance. From this, we derive
the nonlinear index $\mathrm{n_2}$, present the $\mathrm{n_2}$ spectrum for
$n\geq 5$ and report large $\mathrm{n_2}$ values of order $10^{-3}$ mm$^2$/mW.
Moreover, we observe a rapid saturation of the Kerr nonlinearity and find that
the saturation intensity $\mathrm{I_{sat}}$ decreases as $n^{-7}$. We explain
this with the Rydberg blockade mechanism, whereby giant Rydberg interactions
limit the exciton density, resulting in a maximum phase shift of 0.5 rad in our
setup.",2202.09239v1
2022-02-27,New efficient algorithms for computing Gröbner bases of saturation ideals (F4SAT) and colon ideals (Sparse-FGLM-colon),"This paper is concerned with linear algebra based methods for solving exactly
polynomial systems through so-called Gr\""obner bases, which allow one to
compute modulo the polynomial ideal generated by the input equations. This is a
topical issue in non-linear algebra and more broadly in computational
mathematics because of its numerous applications in engineering and computing
sciences. Such applications often require geometric computing features such as
representing the closure of the set difference of two solution sets to given
polynomial systems. Algebraically, this boils down to computing Gr\""obner bases
of colon and/or saturation polynomial ideals. In this paper, we describe and
analyze new Gr\""obner bases algorithms for this task and present
implementations which are more efficient by several orders of magnitude than
the state-of-the-art software.",2202.13387v2
2022-03-03,Quantum Entanglement in the Sachdev-Ye-Kitaev Model and its Generalizations,"Entanglement is one of the most important concepts in quantum physics. We
review recent progress in understanding the quantum entanglement in many-body
systems using large-$N$ solvable models: the Sachdev-Ye-Kitaev (SYK) model and
its generalizations. We present the study of entanglement entropy in the
original SYK Model using three different approaches: the exact diagonalization,
the eigenstate thermalization hypothesis, and the path-integral representation.
For coupled SYK models, the entanglement entropy shows linear growth and
saturation at the thermal value. The saturation is related to replica wormholes
in gravity. Finally, we consider the steady-state entanglement entropy of
quantum many-body systems under repeated measurements. The traditional symmetry
breaking in the enlarged replica space leads to the measurement-induced
entanglement phase transition.",2203.01513v1
2022-03-16,Categoricity transfer for short AECs with amalgamation over sets,"Let ${\bf K}$ be an $\mathrm{LS}({\bf K})$-short abstract elementary class
and assume more than the existence of a monster model (amalgamation over sets
and arbitrarily large models). Suppose ${\bf K}$ is categorical in some
$\mu>\mathrm{LS}({\bf K})$, then it is categorical in all $\mu'\geq\mu$. Our
result removes the successor requirement of $\mu$ made by Grossberg-VanDieren,
at the cost of using shortness instead of tameness; and of using amalgamation
over sets instead of over models. It also removes the primes requirement by
Vasey which assumes tameness and amalgamation over models. As a corollary, we
obtain an alternative proof of the upward categoricity transfer for first-order
theories by Morley and Shelah. In our construction, we simplify Vasey's results
to build a weakly successful frame. This allows us to use Shelah-Vasey's
argument to obtain primes for sufficiently saturated models. If we replace the
categoricity assumption by $\mathrm{LS}({\bf K})$-superstability, ${\bf K}$ is
already excellent for sufficiently saturated models. This sheds light on the
investigation of the main gap theorem for uncountable first-order theories
within ZFC.",2203.08956v1
2022-04-05,Scalable global state synchronization of discrete-time double integrator multi-agent systems with input saturation via linear protocol (Completed Version),"This paper studies scalable global state synchronization of discrete-time
double integrator multi-agent systems in presence of input saturation based on
localized information exchange. A scale-free collaborative linear dynamic
protocols design methodology is developed for discrete-time multi-agent systems
with both full and partial-state couplings. And the protocol design methodology
does not need any knowledge of the directed network topology and the spectrum
of the associated Laplacian matrix. Meanwhile, the protocols are parametric
based on a parameter set in which the designed protocols can guarantee the
global synchronization result. Furthermore, the proposed protocol is scalable
and achieves synchronization for any arbitrary number of agents.",2204.02129v2
2022-04-10,Nonlinear Optical Limiting with Hybrid Nanostructures of NiCo2O4 and Multiwall Carbon Nanotubes,"Nonlinear optical (NLO) response in terms of reverse saturable absorption
(RSA) has been exploited extensively for optical limiting. Here, we
experimentally demonstrate that flower-like hybrid nanostructures of NiCo2O4
and Multiwall Carbon Nanotubes (NCO@MWCNT) exhibit a strong non-linearity in
their absorption, specifically an excited state absorption (ESA) induced RSA,
when exposed to nanosecond laser pulses. We obtain strong nonlinear absorption
coefficient (\b{eta}) and nonlinear refractive index (n2) in hybrid NCO@MWCNT,
the values that are 2-times and 2-orders of magnitude higher, respectively
compared to NCO or MWCNT alone. This offers straightforward application in
optical limiting with optical limiting (FOL) and optical onset (FON) threshold
ca. 2-10 times lower than benchmark NLO materials, e.g., graphene, family of
2-D transition metal dichalcogenides (TMDC) materials and recently established
NCO. Notably, for femtosecond pumping, NLO response of NCO@MWCNT is dominated
by saturable absorption (SA) with a week contribution from two photon
absorption (TPA), arising respectively from MWCNT and NCO. A remarkable sign
reversal along with a larger amplitude is obtained for n2 thanks to the charge
transfer from MWCNT to NCO.",2204.04751v1
2022-04-15,Nuclear matter calculations with the phenomenological three-nucleon interaction,"Employing the concept of three-body radial distribution function and using
the two-body correlation functions, calculated based on the lowest order
constrained variational method, we investigated the effect of the three-body
force (TBF) on the nuclear matter properties, for Argonne and Urbana
$\it{v_{14}}$ potentials. As such, the results for nuclear matter density,
incompressibility, energy per nucleon, and symmetry energy are presented at the
saturation point. The inclusion of a phenomenological TBF resulted in closer
values of the saturation density, incompressibility, and symmetry energy to the
empirical ones for the symmetric nuclear matter. This is especially the case
for the Urbana $\it{v_{14}}$ potential. In addition, an empirically-verified
parabolic approximation of the interaction energy was utilized to perform an
approximate study of the nuclear matter with neutron excess. Hence, at
densities higher than about 0.3~fm$^{-3}$ and for proton-to-neutron density
ratios close to the symmetric nuclear matter, the inclusion of TBF resulted in
an extra attraction for the Argonne as compared to the Urbana $\it{v_{14}}$
potential.",2204.07468v1
2022-04-27,Theoretical Study of the Enhancement of Light Saturation Phenomena of Krypton at Critical Ionization Photon Energies,"By calculating the correlation between the total photoionization
cross-section of the ground state of the Kr atom and photon energy, three
particular photon energies close to the near inner orbital energy of 1.75 keV,
1.90 keV, and 14.30 keV are determined in this work. The dynamical simulation
under 17.50 keV photon energy in the experimental conditions is achieved by
implementing the Monte Carlo method and optimizing the photon flux modeling
parameters. As a result, our calculated data are more consistent with the
experimental phenomena. The light saturation phenomenon of Kr at 1.75 keV, 1.90
keV, 14.30 keV, and 17.50 keV energies is further calculated and researched
using the optimized photon flux model theory. We statistically compare the main
ionization paths under those four specific photon energies and calculate the
population changes of various hollow atoms. The results demonstrate that the
ratio of hollow atoms produced at the critical ionization photon energy is
high. Furthermore, the change of position is smooth, showing the significant
difference between the generation mode of ions with low photon energy and those
with high photon energy, which has important reference significance for
studying hollow atoms with medium and high charge states.",2204.12955v2
2022-04-28,A geometric perspective: experimental evaluation of the quantum Cramer-Rao bound,"The power of quantum sensing rests on its ultimate precision limit,
quantified by the quantum Cram\'er-Rao bound (QCRB), which can surpass
classical bounds. In multi-parameter estimation, the QCRB is not always
saturated as the quantum nature of associated observables may lead to their
incompatibility. Here we explore the precision limits of multi-parameter
estimation through the lens of quantum geometry, enabling us to experimentally
evaluate the QCRB via quantum geometry measurements. Focusing on two- and
three-parameter estimation, we elucidate how fundamental quantum uncertainty
principles prevent the saturation of the bound. By linking a metric of
""quantumness"" to the system geometric properties, we investigate and
experimentally extract the attainable QCRB for three-parameter estimations.",2204.13777v1
2022-05-05,Distinctive ionic transport of freshly excised human epileptogenic brain tissue,"Epileptogenic lesions have higher concentrations of sodium than does normal
brain tissue. Such lesions are palpably recognized by a surgeon and then
excised in order to eliminate epileptic seizures with their associated abnormal
electrical behavior. Here we study the frequency-dependent electrical
conductivities of lesion-laden tissues excised from the brains of epilepsy
patients. The low-frequency (< 1000 Hz) conductivity of biological tissue
primarily probes extracellular solvated sodium-cations traveling parallel to
membranes within regions bounded by blockages. This conductivity rises
monotonically toward saturation as the frequency surpasses the rate with which
diffusing solvated sodium cations encounter blockages. We find that saturation
occurs at dramatically higher frequencies in excised brain tissue containing
epileptogenic lesions than it does in normal brain tissue. By contrast, such an
effect is not reported for tumors embedded in other excised biological tissue.
All told, epileptogenic lesions generate frequency-dependent conductivities
that differ qualitatively from those of both normal brain tissues and tumors.",2205.02888v1
2022-05-08,The saturated pairwise interaction Gibbs point process as a joint species distribution model,"In an effort to effectively model observed patterns in the spatial
configuration of individuals of multiple species in nature, we introduce the
saturated pairwise interaction Gibbs point process.
  Its main strength lies in its ability to model both attraction and repulsion
within and between species, over different scales.
  As such, it is particularly well-suited to the study of associations in
complex ecosystems.
  Based on the existing literature, we provide an easy to implement fitting
procedure as well as a technique to make inference for the model parameters.
  We also prove that under certain hypotheses the point process is locally
stable, which allows us to use the well-known `coupling from the past'
algorithm to draw samples from the model.
  Different numerical experiments show the robustness of the model.
  We study three different ecological datasets, demonstrating in each one that
our model helps disentangle competing ecological effects on species'
distribution.",2205.03967v2
2022-05-15,Saturation for Small Antichains,"For a given positive integer $k$ we say that a family of subsets of $[n]$ is
$k$-antichain saturated if it does not contain $k$ pairwise incomparable sets,
but whenever we add to it a new set, we do find $k$ such sets. The size of the
smallest such family is denoted by $\text{sat}^*(n, \mathcal A_{k})$. Ferrara,
Kay, Kramer, Martin, Reiniger, Smith and Sullivan conjectured that
$\text{sat}^*(n, \mathcal A_{k})=(k-1)n(1+o(1))$, and proved this for $k\leq
4$. In this paper we prove this conjecture for $k=5$ and $k=6$. Moreover, we
give the exact value for $\text{sat}^*(n, \mathcal A_5)$ and $\text{sat}^*(n,
\mathcal A_6)$. We also give some open problems inspired by our analysis.",2205.07392v2
2022-05-16,Peridynamic modeling for impact failure of wet concrete considering the influence of saturation,"In this paper, a modified intermediately homogenized peridynamic (IH-PD)
model for analyzing impact failure of wet concrete has been presented under the
configuration of ordinary state-based peridynamic theory. The meso-structural
properties of concrete are linked to the macroscopic mechanical behavior in the
IH-PD model, where the heterogeneity of concrete is taken into account, and the
calculation cost does not increase. Simultaneously, the porosity of concrete is
considered, which is implemented by deleting the bond between two material
points, as well as the influence of porosity on the mechanical properties of
concrete. Moreover, the effective bulk and shear modulus of cement mortar in
wet concrete (saturated and unsaturated concrete) are calculated respectively.
The dynamic model for wet concrete is described from three aspects: strength,
dynamic increase factor, and equation of state. Validation of the proposed
model is established through analyzing some benchmark tests and comparing with
the corresponding experiment and other available numerical results.",2205.07555v2
2022-05-17,Design of saturated boundary control for hyperbolic systems with in-domain disturbances,"Boundary feedback control design is studied for 1D hyperbolic systems with an
in-domain disturbance and a boundary feedback controller under the effect of
actuator saturation. Nonlinear semigroup theory is used to prove well-posedness
of mild solution pairs to the closed-loop system. Sufficient conditions in the
form of dissipation functional inequalities are derived to establish global
stability for the closed-loop system and $\mathcal{L}^2$-stability in presence
of in-domain disturbances. The control design problem is then recast as an
optimization problem over linear matrix inequality constraints. Numerical
results are shown to validate the effectiveness of the proposed control design.",2205.08194v1
2022-05-18,Degenerations and order of graphs realized by finite abelian groups,"Let G_1 and G_2 be two groups. If a group homomorphism \varphi : G_1
\longrightarrow G_2 maps a \in G_1 into b \in G_2 such that \varphi(a) = b,
then we say a degenerates to b and if every element of G_1 degenerates to
elements in G_2, then we say G_1 degenerates to G_2. In this paper, we study
degeneration in graphs and show that degeneration in groups is a particular
case of degeneration in graphs. We exhibit some interesting properties of
degeneration in graphs. We use this concept to present a pictorial
representation of graphs realized by finite abelian groups. We discus some
partial orders on the set T_p_1 \dots T_p_n of all graphs realized by finite
abelian p_r-groups, where each p_r, 1 \leq r \leq n, is a prime number. We show
that each finite abelian p_r-group of rank n can be identified with saturated
chains of Young diagrams in the poset T_p_1 \dots T_p_n. We present a
combinatorial formula which represents the degree of a projective
representation of a symmetric group. This formula determines the number of
different saturated chains in T_p_1 \cdots T_p_n and the number of finite
abelian groups of different orders.",2205.08795v2
2022-05-22,Moon and background removal algorithm for all-sky imager,"All-sky imagers (ASIs) are used to record auroral activities from the ground
but are often contaminated by the moon. Here, we studied the THEMIS ASIs data
and developed an algorithm to eliminate the moon which can be generalized to
other types of ASIs. With our algorithm, the ASI pixels within the moon's
surface are typically saturated and thus removed by the algorithm. The ASI
pixels within the moon's glow are close to but not saturated and thus can be
calibrated by the algorithm to recover auroral structures within the glow. For
pixels far away from the moon or when there is no moon, the algorithm preserves
typical auroral forms, from the transient features of auroral streamers and
pulsating aurora to more stable features of pre-onset arcs. Note that the
algorithm does not treat clouds, which is a known limitation.",2205.10882v1
2022-06-08,Time-dependent and quasi-steady features of fast neutrino-flavor conversion,"Despite the theoretical indication that fast neutrino-flavor conversion (FFC)
ubiquitously occurs in core-collapse supernova and binary neutron star merger,
the lack of global simulations has been the greatest obstacle to study their
astrophysical consequences. In this {\it Letter}, we present large-scale ($50
{\rm km}$) simulations of FFC in spherical symmetry by using a novel approach.
We effectively rescale the oscillation scale of FFC by reducing the number of
injected neutrinos in the simulation box, and then extrapolate back to the case
of the target density of neutrinos with a convergence study. We find that FFC
in all models achieves quasi-steady state in the non-linear regime, and its
saturation property of FFC is universal. We also find that temporal- and
spatial variations of FFC are smeared out at large radii due to phase
cancellation through neutrino self-interactions. Finally, we provide a new
diagnostic quantity, ELN-XLN angular crossing, to assess the non-linear
saturation of FFC.",2206.04097v3
2022-06-06,Finite element method modeling of expansion of irradiated rocks: focusing on the minerals,"Finite element method (FEM) modeling of the volumetric expansion phenomenon
associated with the accumulation of irradiation was performed on rocks in a
concrete for nuclear power plant. The FEM mesh of sandstone, tuff, and granite
was created based on microscopic images, and the volumetric expansion due to
irradiation was calculated. The saturated value of the volume expansion due to
irradiation accumulation was calculated, and it was shown that the saturated
value of the volume expansion was well explained by the experimental value. In
addition, the FEM analysis indicates that irradiation-induced degradation of
rock propagates through a localized concentration of stress followed by
fracture with cracks spreading throughout the rock.",2206.07140v1
2022-06-18,"Absolute frequencies of H13C14N hydrogen cyanide transitions in 1,5 μm region with saturated spectroscopy and sub-kHz scanning laser","The wide span and high density of lines in its rovibrational spectrum render
hydrogen cyanide a useful spectroscopic media for referencing absolute
frequencies of lasers in optical communication and dimensional metrology. We
determined, for the first time to the best of our knowledge, the molecular
transitions' center frequencies of the H13C14N isotope in the range from 1526
nm to 1566 nm with 1,3e-10 fractional uncertainty. We investigated the
molecular transitions with a highly coherent and widely tunable scanning laser
that was precisely referenced to a Hydrogen maser through an optical frequency
comb. We demonstrated an approach to stabilize the operational conditions
needed to maintain the constantly low pressure of the hydrogen cyanide to carry
out the saturated spectroscopy with the third-harmonic synchronous
demodulation. We demonstrated approximately a fourtyfold improvement in the
line centers' resolution compared to the previous result.",2206.09232v2
2022-06-25,Effects of MAC Parameters on the Performance of IEEE 802.11 DCF in NS-3,"This paper presents the design procedure of the NS-3 script for WLAN that is
organized according to the hierarchical manner of TCP/IP model. We configure
all layers by using NS-3 model objects and set and modify the values used by
objects to investigate the effects of MAC parameters (access mechanism, CWmin,
CWmax and retry limit) on the performance metrics viz. packet delivery ratio,
packet lost ratio, aggregated throughput, and average delay. The simulation
results show that RTS/CTS access mechanism outperforms basic access mechanism
in saturated state, whereas the MAC parameters have no significant impact on
network performance in non-saturated state. A higher value of CWmin improves
the aggregated throughput in expense of average delay. The tradeoff
relationships among the performance metrics are also observed in results for
the optimal values of MAC parameters. Our design procedure represents a good
guideline for new NS-3 users to design and modify script and results greatly
benefit the network design and management.",2206.12615v1
2022-06-26,Topological bulk solitons in a nonlinear photonic Chern insulator,"Nonlinearities in lattices with topological band structures can induce
topological interfaces in the bulk of structures and give rise to bulk solitons
in the topological bandgaps. Here we study a photonic Chern insulator with
saturable nonlinearity and show the existence of topological bulk solitons. The
fundamental bulk solitons exhibit as semi-vortex solitons, where only one
pseudospin component has a nonzero vorticity. The bulk solitons have equal
angular momentum at different valleys. This phenomenon is a direct outcome of
the topology of the linear host lattice and the angular momentum can be changed
by switching the sign of the nonlinearity. The bulk solitons bifurcate from the
linear bulk band edge and terminate when their powers saturate. We find that
these bulk solitons are stable within the whole spectrum range. Moreover, these
bulk solitons are robust against lattice disorders both from on-site energies
and hopping amplitudes. Our work extends the study of Chern insulators into the
nonlinear regime and highlights the interplay between topology and
nonlinearity.",2206.12865v2
2022-06-30,Flow correlations from a hydrodynamics model with dynamical freeze-out and initial conditions based on perturbative QCD and saturation,"We extend the applicability of the hydrodynamics, perturbative QCD and
saturation -based EKRT (Eskola-Kajantie-Ruuskanen-Tuominen) framework for
ultrarelativistic heavy-ion collisions to peripheral collisions by introducing
dynamical freeze-out conditions. As a new ingredient compared to the previous
EKRT computations we also introduce a non-zero bulk viscosity. We compute
various hadronic observables and flow correlations, including normalized
symmetric cumulants, mixed harmonic cumulants and flow-transverse momentum
correlations, and compare them against measurements from the BNL Relativistic
Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). We
demonstrate that the inclusion of the dynamical freeze-out and bulk viscosity
allows a better description of the measured flow coefficients in peripheral
collisions and enables the use of an extended centrality range when
constraining the properties of QCD matter in the future.",2206.15207v3
2022-07-04,Segmentation Guided Deep HDR Deghosting,"We present a motion segmentation guided convolutional neural network (CNN)
approach for high dynamic range (HDR) image deghosting. First, we segment the
moving regions in the input sequence using a CNN. Then, we merge static and
moving regions separately with different fusion networks and combine fused
features to generate the final ghost-free HDR image. Our motion segmentation
guided HDR fusion approach offers significant advantages over existing HDR
deghosting methods. First, by segmenting the input sequence into static and
moving regions, our proposed approach learns effective fusion rules for various
challenging saturation and motion types. Second, we introduce a novel memory
network that accumulates the necessary features required to generate plausible
details in the saturated regions. The proposed method outperforms nine existing
state-of-the-art methods on two publicly available datasets and generates
visually pleasing ghost-free HDR results. We also present a large-scale motion
segmentation dataset of 3683 varying exposure images to benefit the research
community.",2207.01229v1
2022-07-04,Ground state bistability of cold atoms in a cavity,"We experimentally demonstrate an optical bistability between two hyperfine
atomic ground states, using a single mode of an optical resonator in the
collective strong coupling regime. Whereas in the familiar case, the bistable
region is created through atomic saturation, we report an effect between states
of high quantum purity, which is essential for future information storage. The
nonlinearity of the transitions arise from cavity-assisted pumping between
ground states of cold, trapped atoms and the stability depends on the intensity
of two driving lasers. We interpret the phenomenon in terms of the recent
paradigm of first-order, driven-dissipative phase transitions, where the
transmitted and driving fields are understood as the order and control
parameters, respectively. The saturation-induced bistability is recovered for
infinite drive in one of the controls. The order of the transition is confirmed
experimentally by hysteresis in the order parameter when either of the two
control parameters is swept repeatedly across the bistability region and the
underlying phase diagram is predicted in line with semiclassical mean-field
theory.",2207.01724v1
2022-07-06,Evidence of boron pairs in highly boron laser doped silicon,"Secondary Ions Mass Spectroscopy and Hall effect measurements were performed
on boron doped silicon with concentration between 0.02 at.% and 12 at.%.
Ultra-high boron doping was made by saturating the chemisorption sites of a Si
wafer with BCl3, followed by nanosecond laser anneal (Gas Immersion Laser
Doping). The boron concentration varies thus nearly linearly with the number of
process repetitions. However, it is not the case for the hole concentration
which tends to saturate at high boron concentration. The difference between
boron and hole concentration increases as the square of boron concentration,
pointing towards the formation of boron pairs as the dominant contribution to
the increase of inactive boron.",2207.02520v1
2022-07-07,Highlight Specular Reflection Separation based on Tensor Low-rank and Sparse Decomposition Using Polarimetric Cues,"This paper is concerned with specular reflection removal based on tensor
low-rank decomposition framework with the help of polarization information. Our
method is motivated by the observation that the specular highlight of an image
is sparsely distributed while the remaining diffuse reflection can be well
approximated by a linear combination of several distinct colors using a
low-rank and sparse decomposition framework. Unlike current solutions, our
tensor low-rank decomposition keeps the spatial structure of specular and
diffuse information which enables us to recover the diffuse image under strong
specular reflection or in saturated regions. We further define and impose a new
polarization regularization term as constraint on color channels. This
regularization boosts the performance of the method to recover an accurate
diffuse image by handling the color distortion, a common problem of
chromaticity-based methods, especially in case of strong specular reflection.
Through comprehensive experiments on both synthetic and real polarization
images, we demonstrate that our method is able to significantly improve the
accuracy of highlight specular removal, and outperform the competitive methods
to recover the diffuse image, especially in regions of strong specular
reflection or in saturated areas.",2207.03543v1
2022-07-08,Cubical models of higher categories without connections,"We prove that each of the model structures for ($n$-trivial, saturated)
comical sets on the category of marked cubical sets having only faces and
degeneracies (without connections) is Quillen equivalent to the corresponding
model structure for ($n$-trivial, saturated) complicial sets on the category of
marked simplicial sets, as well as to the corresponding comical model
structures on cubical sets with connections. As a consequence, we show that the
cubical Joyal model structure on cubical sets without connections is equivalent
to its analogues on cubical sets with connections and to the Joyal model
structure on simplicial sets. We also show that any comical set without
connections may be equipped with connections via lifting, and that this can be
done compatibly on the domain and codomain of any fibration or cofibration of
comical sets.",2207.03636v2
2022-07-22,Planar Laser Induced Fluorescence Mapping of a Carbon Laser Produced Plasma,"We present measurements of ion velocity distribution profiles obtained by
laser induced fluorescence (LIF) on an explosive laser produced plasma (LPP).
The spatio-temporal evolution of the resulting carbon ion velocity distribution
was mapped by scanning through the Doppler-shifted absorption wavelengths using
a tunable, diode-pumped laser. The acquisition of this data was facilitated by
the high repetition rate capability of the ablation laser (1 Hz) which allowed
the accumulation of thousand of laser shots in short experimental times. By
varying the intensity of the LIF beam, we were able to explore the effects of
fluorescence power against laser irradiance in the context of evaluating the
saturation versus the non-saturation regime. The small beam size of the LIF
beam led to high spatial resolution of the measurement compared to other ion
velocity distribution measurement techniques, while the fast-gated operation
mode of the camera detector enabled the measurement of the relevant electron
transitions.",2207.10843v1
2022-07-31,Symmetry Regularization and Saturating Nonlinearity for Robust Quantization,"Robust quantization improves the tolerance of networks for various
implementations, allowing reliable output in different bit-widths or fragmented
low-precision arithmetic. In this work, we perform extensive analyses to
identify the sources of quantization error and present three insights to
robustify a network against quantization: reduction of error propagation, range
clamping for error minimization, and inherited robustness against quantization.
Based on these insights, we propose two novel methods called symmetry
regularization (SymReg) and saturating nonlinearity (SatNL). Applying the
proposed methods during training can enhance the robustness of arbitrary neural
networks against quantization on existing post-training quantization (PTQ) and
quantization-aware training (QAT) algorithms and enables us to obtain a single
weight flexible enough to maintain the output quality under various conditions.
We conduct extensive studies on CIFAR and ImageNet datasets and validate the
effectiveness of the proposed methods.",2208.00338v1
2022-08-12,Direct Route to Thermodynamic Uncertainty Relations and Their Saturation,"Thermodynamic uncertainty relations (TURs) bound the dissipation in
non-equilibrium systems from below by fluctuations of an observed current.
Contrasting the elaborate techniques employed in existing proofs, we here prove
TURs directly from the Langevin equation. This establishes the TUR as an
inherent property of overdamped stochastic equations of motion. In addition, we
extend the transient TUR to currents and densities with explicit
time-dependence. By including current-density correlations we, moreover, derive
a new sharpened TUR for transient dynamics. Our arguably simplest and most
direct proof, together with the new generalizations, allows us to
systematically determine conditions under which the different TURs saturate and
thus allows for a more accurate thermodynamic inference. Finally we outline the
direct proof also for Markov jump dynamics.",2208.06402v4
2022-08-17,Direct calculation of the planar NaCl-aqueous solution interfacial free energy at the solubility limit,"Salty water is the most abundant electrolyte aqueous mixture on Earth,
however, very little is known about the NaCl-saturated solution interfacial
free energy. Here, we provide the first direct estimation of this magnitude for
several NaCl crystallographic planes by means of the Mold Integration
technique, a highly efficient computational method to evaluate interfacial free
energies with anisotropic crystal resolution. Making use of the JC-SPC/E model,
one of the most benchmarked force fields for NaCl/water solutions, we measure
the interfacial free energy of four different planes, (100), (110), (111), and
(11-2) with the saturated solution at normal conditions. We find high
anisotropy between the different crystal orientations with values ranging from
100 to 150 mJ/m2 and the average value of the distinct planes being 137(20)
mJ/m2. This value for the coexistence interfacial free energy is in reasonable
agreement with previous extrapolations from nucleation studies. Our work
represents a milestone in the computational calculation of interfacial free
energies between ionic crystals and aqueous solutions.",2208.08322v3
2022-08-18,Ultra-Efficient DC-gated all-optical graphene switch,"The ultrafast response and broadband absorption of all-optical graphene
switches are highly desirable features for on-chip photonic switching. However,
because graphene is an atomically thin material, its absorption of guided
optical modes is relatively low, resulting in high saturation thresholds and
switching energies for these devices. To boost the absorption of graphene, we
present a practical design of an electrically-biased all-optical graphene
switch that is integrated into silicon slot waveguides, which strongly confine
the optical mode in the slotted region and enhance its interaction with
graphene. Moreover, the design incorporates a silicon slab layer and a hafnia
dielectric layer to electrically tune the saturation threshold and the
switching energy of the device by applying DC voltages of <0.5 V. Using this
device, a high extinction ratio (ER) of 10.3dB, a low insertion loss (IL) of
<0.7dB, and an ultra-efficient switching energy of 79fJ/bit at 0.23V bias are
attainable for a 40um long switch. The reported performance metrics for this
device are highly promising and are expected to serve the needs of
next-generation photonic computing systems.",2208.08610v1
2022-08-29,Dynamic RF Beam Codebook Reduction for Cost-Efficient mmWave Full-Duplex Systems,"The recent attempts to realize full-duplex (FD) communications in millimeter
wave (mmWave) systems have garnered a significant amount of interest for its
potential. In this paper, we present a cost-efficient design of mmWave FD
systems, where the system dynamically reduces the RF beam codebook in a
computationally efficient manner, so that it is comprised of the RF beams that
will prevent the Rx receive chain from saturating due to the self-interference
(SI). The analog beamformer will suppress the SI to the level that the residual
SI can be completely removed with digital SI cancellation, allowing the digital
beamformer to concentrate on the desired channel, free of the SI. To reduce the
computation required for the proposed method, we propose two sufficient
conditions that prevent the Rx side saturations, which are practically tight.
Through performance valuations conducted in realistically modeled mmWave FD
scenarios, we demonstrate that the proposed design achieves comparable
performance with the ideal FD and other benchmarks with significantly lower
costs.",2208.13547v1
2022-08-30,Geometric scaling in leading neutron events at HERA,"This analysis provides new fits of the GBW model and the impact
parameter-dependent saturation model (bSat or IP-Sat) to the leading neutron
structure function HERA data in one pion exchange approximation. Both
parametrizations of the dipole cross section provide good descriptions of the
considered data. It is shown here for the first time that the experimental
leading neutron production HERA data exhibits geometric scaling, which in this
context means that the total $\gamma^* \pi^*$ cross section is a function of
only one dimensionless variable $\tau = Q^2/Q_s^2(x)$. The geometric scaling
region extends over a broad range of $Q^2$ and can be attributed to the
presence of a saturation boundary which manifests at $Q^2\geq Q^2_s$. The
scaling behaviour in leading neutron events is profoundly similar to what has
been observed for the inclusive DIS events.",2208.14200v1
2022-09-03,Understanding the Quality Factor of Mass-Loaded Tensioned Resonators,"Mechanical resonators featuring large tensile stress have enabled a range of
experiments in quantum optomechanics and novel sensing. Many sensing
applications require functionalizing tensioned resonators by appending
additional mass to them. However, this may dramatically change the resonator
mode quality factor, and hence its sensitivity. In this work, we investigate
the effect of the crossover from no mass load to a large mass load on the mode
shape and quality factor of a tensioned resonator. We show through an
analytical model and finite element analysis that as the load mass increases,
surprisingly, the resonator mode shape becomes independent of the exact load
mass, and therefore, its quality factor saturates. We validate this saturation
effect experimentally by measuring the quality factor of a silicon nitride
trampoline resonator while varying the load mass in a controlled manner.",2209.01488v1
2022-09-06,Massive neutron stars with small radii in relativistic mean-field models optimized to nuclear ground states,"We present an equation of state (EoS) for neutron stars using the
relativistic mean-field model with isoscalar- and isovector-meson mixing.
Taking into account the results of the neutron skin thickness, $R_{\rm skin}$,
of $^{208}$Pb reported by the PREX collaboration, the dimensionless tidal
deformability of a canonical neutron star observed from GW170817, and a $2.6$
$M_{\odot}$ compact star implied by the secondary component of GW190814, a new
effective interaction is constructed so as to reproduce the saturation
condition of nuclear matter and the ground-state properties of finite,
closed-shell nuclei. We find that the neutron star EoS exhibits the rapid
stiffening around twice the nuclear saturation density, which is caused by the
soft nuclear symmetry energy, $E_{\rm sym}$. It is also noticeable that the
thick $R_{\rm skin}$ from the PREX-2 experiment can be achieved with the small
slope parameter of $E_{\rm sym}$ stemming from the isoscalar-meson mixing.
Thus, we speculate that the secondary component of GW190814 is the heaviest
neutron star ever discovered.",2209.02861v1
2022-09-15,Optimal control for maximally creating and maintaining a superposition state of a two-level system under the influence of Markovian decoherence,"Reducing decoherence is an essential step toward realizing general-purpose
quantum computers beyond the present noisy intermediate-scale quantum (NISQ)
computers. To this end, dynamical decoupling (DD) approaches in which external
fields are applied to qubits are often adopted. We numerically study DD using a
two-level model system (qubit) under the influence of Markovian decoherence by
using quantum optimal control theory with slightly modified settings, in which
the physical objective is to maximally create and maintain a specified
superposition state in a specified control period. An optimal pulse is
numerically designed while systematically varying the values of dephasing,
population decay, pulse fluence, and control period as well as using two kinds
of objective functionals. Although the decrease in purity due to the
decoherence gives rise to the upper limit of the target expectation value,
i.e., the saturated value, the optimally shaped pulse effectively deals with
the decoherence by gradually creating the target superposition state to realize
the saturated value as much as possible.",2209.07062v2
2022-09-19,Transverse momentum broadening from NLL BFKL to all orders in pQCD,"We study, to all orders in perturbative QCD, the universal behavior of the
saturation momentum $Q_s(L)$ controlling the transverse momentum distribution
of a fast parton propagating through a dense QCD medium with large size $L$.
Due to the double logarithmic nature of the quantum evolution of the saturation
momentum, its large $L$ asymptotics is obtained by slightly departing from the
double logarithmic limit of either next-to-leading log (NLL) BFKL or leading
order DGLAP evolution equations. At fixed coupling, or in conformal
$\mathcal{N}=4$ SYM theory, we derive the large $L$ expansion of $Q_s(L)$ up to
order $\alpha_s^{3/2}$. In QCD with massless quarks, where conformal symmetry
is broken by the running of the strong coupling constant, the one-loop QCD
$\beta$-function fully accounts for the universal terms in the $Q_s(L)$
expansion. Therefore, the universal coefficients of this series are known
exactly to all orders in $\alpha_s$.",2209.08900v1
2022-09-30,Quantum Discord and Logarithmic Negativity in the Generalized n-qubit Werner State,"Quantum Discord (QD) is a measure of the total quantum non-local correlations
of a quantum system. The formalism of quantum discord has been applied to
various two-qubit mixed states and it has been reported that there is a
non-zero quantum discord even when the states are unentangled. To this end, we
have calculated the Quantum Discord for higher than two qubit mixed state, that
is, the generalized n-qubit Werner state with a bipartite split. We found that
the QD saturates to a straight line with unit slope in the thermodynamic limit.
Qualitative studies of entanglement between the two subsystems using
logarithmic negativity revealed that the entanglement content between them
increases non-uniformly with the number of qubits leading to its saturation. We
have proved the above claims both analytically and numerically.",2210.00096v1
2022-10-03,Data Budgeting for Machine Learning,"Data is the fuel powering AI and creates tremendous value for many domains.
However, collecting datasets for AI is a time-consuming, expensive, and
complicated endeavor. For practitioners, data investment remains to be a leap
of faith in practice. In this work, we study the data budgeting problem and
formulate it as two sub-problems: predicting (1) what is the saturating
performance if given enough data, and (2) how many data points are needed to
reach near the saturating performance. Different from traditional
dataset-independent methods like PowerLaw, we proposed a learning method to
solve data budgeting problems. To support and systematically evaluate the
learning-based method for data budgeting, we curate a large collection of 383
tabular ML datasets, along with their data vs performance curves. Our empirical
evaluation shows that it is possible to perform data budgeting given a small
pilot study dataset with as few as $50$ data points.",2210.00987v1
2022-10-05,Spectral broadening from turbulence in multiscale lower hybrid current drive simulations,"The scattering of lower hybrid (LH) waves due to scrape-off layer (SOL)
filaments is investigated. It is revealed that scattering can account for the
LH spectral gap without any ad hoc modification to the wave-spectrum. This is
shown using a multiscale simulation approach which allows, for the first time,
the inclusion of full-wave scattering physics in ray-tracing/Fokker-Planck
calculations. In this approach, full-wave scattering probabilities are
calculated for a wave interacting with a statistical ensemble of filaments.
These probabilities are coupled to ray-tracing equations using radiative
transfer (RT) theory. This allows the modeling of scattering along the entire
ray-trajectory, which can be important in the multi-pass regime. Simulations
are conducted for lower hybrid current drive (LHCD) in Alcator C-Mod, resulting
in excellent agreement with experimental current and hard X-ray (HXR) profiles.
A region in filament parameter space is identified in which the impact of
scattering on LHCD is saturated. Such a state coincides with experimental LHCD
measurements, suggesting saturation indeed occurs in C-Mod, and therefore the
exact statistical properties of the filaments are not important.",2210.02344v2
2022-10-05,Structure of saturated RSA ellipse packings,"Motivated by the recent observation of liquid glass in suspensions of
ellipsoidal colloids, we examine the structure of (asymptotically) saturated
RSA ellipse packings. We determine the packing fractions $\phi_{\rm s}(\alpha)$
to high precision, finding an empirical analytic formula that predicts
$\phi_{\rm s}(\alpha)$ to within less than $0.1\%$ for all $\alpha \leq 10$.
Then we explore how these packings' positional-orientational order varies with
$\alpha$. We find a transition from tip/side- to side/side-contact-dominated
structure at $\alpha = \alpha_{\rm TS} \simeq 2.4$. At this aspect ratio, the
peak value $g_{\rm max}$ of packings' positional-orientational paircorrelation
functions is minimal, and systems can be considered maximally locally
disordered. For smaller (larger) $\alpha$, $g_{\rm max}$ increases
exponentially with deceasing (increasing) $\alpha$. Local nematic order and
structures comparable to the precursor domains observed in experiments
gradually emerge as $\alpha$ increases beyond $3$. For $\alpha \gtrsim 5$,
single-layer lamellae become more prominent, and long-wavelength density
fluctuations increase with $\alpha$ as packings gradually approach the rod-like
limit.",2210.02388v2
2022-10-10,Intermodulation Distortion in a Josephson Traveling Wave Parametric Amplifier,"Josephson traveling wave parametric amplifiers enable the amplification of
weak microwave signals close to the quantum limit with large bandwidth, which
has a broad range of applications in superconducting quantum computing and in
the operation of single-photon detectors. While the large bandwidth allows for
their use in frequency-multiplexed detection architectures, an increased number
of readout tones per amplifier puts more stringent requirements on the dynamic
range to avoid saturation. Here, we characterize the undesired mixing processes
between the different frequency-multiplexed tones applied to a Josephson
traveling wave parametric amplifier, a phenomenon also known as intermodulation
distortion. The effect becomes particularly significant when the amplifier is
operated close to its saturation power. Furthermore, we demonstrate that
intermodulation distortion can lead to significant crosstalk and reduction of
fidelity for multiplexed readout of superconducting qubits. We suggest using
large detunings between the pump and signal frequencies to mitigate crosstalk.
Our work provides insights into the limitations of current Josephson traveling
wave parametric amplifiers and highlights the importance of performing further
research on these devices.",2210.04799v1
2022-10-13,Self-Supervised Learning of Linear Precoders under Non-Linear PA Distortion for Energy-Efficient Massive MIMO Systems,"Massive multiple input multiple output (MIMO) systems are typically designed
under the assumption of linear power amplifiers (PAs). However, PAs are
typically most energy-efficient when operating close to their saturation point,
where they cause non-linear distortion. Moreover, when using conventional
precoders, this distortion coherently combines at the user locations, limiting
performance. As such, when designing an energy-efficient massive MIMO system,
this distortion has to be managed. In this work, we propose the use of a neural
network (NN) to learn the mapping between the channel matrix and the precoding
matrix, which maximizes the sum rate in the presence of this non-linear
distortion. This is done for a third-order polynomial PA model for both the
single and multi-user case. By learning this mapping a significant increase in
energy efficiency is achieved as compared to conventional precoders and even as
compared to perfect digital pre-distortion (DPD), in the saturation regime.",2210.07037v1
2022-10-17,Scattering-induced splitting of solitons in the discrete NLS equation with saturable nonlinearity,"We study systematically the scattering of solitons on localized impurities in
the discrete nonlinear Schr\""odinger (DNLS) equation with a saturable
nonlinearity. We show that, apart from the generic scenario of the outcome of
the scattering process, namely the emergence of a reflected and a transmitted
soliton, other effects can occur. In particular, it is found that, in the case
of an attractive impurity, a soliton trapped at the impurity can coexist with
the reflected and transmitted ones. This effect, which resembles the behaviour
of a quantum particle interacting with a narrow impurity, has not previously
reported for discrete setting. Parameter regimes are explored for determining
soliton splitting on the impurity with special attention to equal soliton
splitting.",2210.09450v1
2022-10-24,A Theory of Stable Market Segmentations,"We consider a monopolistic seller in a market that may be segmented. The
surplus of each consumer in a segment depends on the price that the seller
optimally charges, which depends on the set of consumers in the segment. We
study which segmentations may result from the interaction among consumers and
the seller. Instead of studying the interaction as a non-cooperative game, we
take a reduced-form approach and introduce a notion of stability that any
resulting segmentation must satisfy. A stable segmentation is one that, for any
alternative segmentation, contains a segment of consumers that prefers the
original segmentation to the alternative one. Our main result characterizes
stable segmentations as efficient and saturated. A segmentation is saturated if
no consumers can be shifted from a segment with a high price to a segment with
a low price without the seller optimally increasing the low price. We use this
characterization to constructively show that stable segmentations always exist.
Even though stable segmentations are efficient, they need not maximize average
consumer surplus, and segmentations that maximize average consumer surplus need
not be stable. Finally, we relate our notion of stability to solution concepts
from cooperative game theory and show that stable segmentations satisfy many of
them.",2210.13194v1
2022-11-09,The Mathematical Theory Of Diffusion In Solids: Time Dependent First Kind Boundary Conditions,"A new solution to the mono-dimensional diffusion equation for time-variable
first kind boundary condition is presented where the time-variable function at
the surface is derived proposing a surface saturation model. This solution may
be helpful in the treatment of diffusion processes where the overall time of
diffusion is comparable with the time taken by the surface of the solid body to
saturate achieving a dynamical equilibrium between the diffusing elements
supplied by the external source and the ones transferred internally through the
diffusion kinetic mechanisms. Worked examples for constant diffusion
coefficient are presented and discussed.",2211.05065v5
2022-11-10,NLO computation of diffractive di-hadron production in a saturation framework,"The cross-sections of diffractive double hadron photo- or electroproduction
with large $p_T$, on a nucleon or a nucleus, are calculated to NLO accuracy. A
hybrid formalism mixing collinear factorization and high energy small-$x$
factorization, more precisely the shockwave formalism for the latter, is used
to derive the results. The cancellation of divergences is explicitly shown, and
the finite parts of the NLO differential cross-sections are found. We work in
arbitrary kinematics such that both photoproduction and leptoproduction are
considered. The results are therefore usable, to detect saturation effects, at
both the future EIC or already at LHC, using Ultra Peripheral Collisions.",2211.05774v2
2022-11-15,On the sound velocity bound in neutron stars,"It has been suggested in the literature that the sound velocity of the
nuclear matter $v_s$ violates the so-called sound velocity bound $v_s \le
c/\sqrt{3}$ at high density, where $c$ is the speed of light. In this paper, we
revisit this issue and confront the current measurements of mass, radius, and
tidal deformability of neutron stars with $10^5$ different equations of state
which are parametrized at low density and saturates the sound velocity bound
beyond twice the saturation density where the equation of state has not been
constrained yet, by which we can conservatively obtain the maximum mass of the
neutron stars compatible both with the observed properties of neutron stars and
the sound velocity bound. We find that majority of the models are eliminated by
the incompatibility with the observations and, especially, the recently
detected massive pulsar ($2.35\pm 0.17 M_\odot$) is hardly realized by our
simulations. Our study strongly supports the violation of the sound velocity
bound.",2211.07874v1
2022-11-16,Absolute frequency measurement of the $6s^2~^1S_0 \to 6s6p~^3P_1$ $F=3/2\to F'=5/2$ $^{\text{201}}$Hg transition with background-free saturation spectroscopy,"We report the development of a method for eliminating background-induced
systematic shifts affecting precise measurements of saturation absorption
signals. With this technique, we measured the absolute frequency of the
$6s^2~^1\text{S}_0 \to 6s6p~^3\text{P}_1$ transition in $^{201a}\text{Hg}$
($F=3/2\to F'=5/2$) to be $1181541111051(83)$~kHz. The measurement was
referenced with an optical frequency comb synchronized to the frequency of the
local representation of the UTC. This specific atomic line is situated on the
steep slope of the Doppler background at room temperature, which results in
frequency systematic shift. We determined the dependence of this shift on the
properties of both the spectral line and the background of the measured signal.",2211.09197v1
2022-11-17,Measurement uncertainty relation for three observables,"In this work we establish rigorously a measurement uncertainty relation (MUR)
for three unbiased qubit observables, which was previously shown to hold true
under some presumptions. The triplet MUR states that the uncertainty, which is
quantified by the total statistic distance between the target observables and
the jointly implemented observables, is lower bounded by an incompatibility
measure that reflects the joint measurement conditions. We derive a necessary
and sufficient condition for the triplet MUR to be saturated and the
corresponding optimal measurement. To facilitate experimental tests of MURs we
propose a straightforward implementation of the optimal joint measurements. The
exact values of incompatibility measure are analytically calculated for some
symmetric triplets when the corresponding triplet MURs are not saturated. We
anticipate that our work may enrich the understanding of quantum
incompatibility in terms of MURs and inspire further applications in quantum
information science. This work presents a complete theory relevant to a
parallel work [Y.-L. Mao, et al., Testing Heisenberg's measurement uncertainty
relation of three observables, arXiv:2211.09389] on experimental tests.",2211.09816v3
2022-11-19,Robust mode-locking in a hybrid ultrafast laser based on nonlinear multimodal interference,"We experimentally demonstrate the realization of a
half-polarization-maintaining (half-PM) fiber laser, in which mode-locking is
provided by a reflective multimode-interference saturable absorber (SA). In the
specially designed SA, linearly polarized light is coupled into a 15-cm-long
graded-index multimode fiber (GIMF) through the PM fiber, and then reflected
back to the PM structure through a mirror pigtailed with a single-mode fiber
(SMF). The modulation depth and saturation peak power are measured to be 1.5%
and 0.6 W, respectively. The proposed SA device is incorporated into a novel
half-PM erbium-doped fiber oscillator, which generates soliton pulses with 409
fs temporal duration at a 33.3 MHz repetition rate. The proposed fiber laser is
compared with a conventional non-PM fiber laser mode-locked by nonlinear
polarization evolution (NPE) in terms of optical properties such as spectral
bandwidth, pulse duration, and stability performance. Short- and long-time
stability tests and superior noise performance corroborate robust mode-locking
in this setup.",2211.10600v1
2022-11-20,"The weak saturation number of $\boldsymbol{K_{2, t}}$","For two graphs $G$ and $F$, we say that $G$ is weakly $F$-saturated if $G$
contains no copy of $F$ as a subgraph and one could join all the nonadjacent
pairs of vertices of $G$ in some order so that a new copy of $F$ is created at
each step. The weak saturation number $\mathrm{wsat}(n, F)$ is the minimum
number of edges of a weakly $F$-saturated graph on $n$ vertices. In this paper,
we examine $\mathrm{wsat}(n, K_{s, t})$, where $K_{s, t}$ is the complete
bipartite graph with parts of sizes $s$ and $ t $.
  We determine $\mathrm{wsat}(n, K_{2, t})$, correcting a previous report in
the literature. It is also shown that $\mathrm{wsat}(s+t,
K_{s,t})=\binom{s+t-1}{2}$ if $\gcd(s, t)=1$ and $\mathrm{wsat}(s+t,
K_{s,t})=\binom{s+t-1}{2}+1$, otherwise.",2211.10939v3
2022-11-23,MPMICE: A hybrid MPM-CFD model for simulating coupled problems in porous media. Application to earthquake-induced submarine landslides,"In this paper, we describe a soil-fluid-structure interaction model that
combines soil mechanics (saturated sediments), fluid mechanics (seawater or
air), and solid mechanics (structures). The formulation combines the Material
Point Method, which models large deformation of the porous media and the
structure, with the Implicit Continuous-fluid Eulerian, which models complex
fluid flows. We validate the model and simulate the whole process of
earthquake-induced submarine landslides. We show that this model captures
complex interactions between saturated sediment, seawater, and structure, so we
can use the model to estimate the impact of potential submarine landslides on
offshore structures.",2211.12761v1
2022-11-25,Free volume theory explains the unusual behavior of viscosity in a non-confluent tissue during morphogenesis,"A recent experiment on zebrafish blastoderm morphogenesis showed that the
viscosity ({\eta}) of a non-confluent embryonic tissue grows sharply until a
critical cell packing fraction ({\phi}S). The increase in {\eta} up to {\phi}S
is similar to the behavior observed in several glass-forming materials, which
suggests that the cell dynamics is sluggish or glass-like. Surprisingly, {\eta}
is a constant above {\phi}S. To determine the mechanism of this unusual
dependence of {\eta} on {\phi}, we performed extensive simulations using an
agent-based model of a dense non-confluent two-dimensional tissue. We show that
polydispersity in the cell size, and the propensity of the cells to deform,
results in the saturation of the available free area per cell beyond a critical
packing fraction. Saturation in the free space not only explains the viscosity
plateau above {\phi}S but also provides a relationship between equilibrium
geometrical packing to the dramatic increase in the relaxation dynamics.",2211.14242v2
2022-11-30,Computationally Efficient Reinforcement Learning: Targeted Exploration leveraging Simple Rules,"Model-free Reinforcement Learning (RL) generally suffers from poor sample
complexity, mostly due to the need to exhaustively explore the state-action
space to find well-performing policies. On the other hand, we postulate that
expert knowledge of the system often allows us to design simple rules we expect
good policies to follow at all times. In this work, we hence propose a simple
yet effective modification of continuous actor-critic frameworks to incorporate
such rules and avoid regions of the state-action space that are known to be
suboptimal, thereby significantly accelerating the convergence of RL agents.
Concretely, we saturate the actions chosen by the agent if they do not comply
with our intuition and, critically, modify the gradient update step of the
policy to ensure the learning process is not affected by the saturation step.
On a room temperature control case study, it allows agents to converge to
well-performing policies up to 6-7x faster than classical agents without
computational overhead and while retaining good final performance.",2211.16691v3
2022-10-15,Convolutional Long Short-Term Memory (convLSTM) for Spatio-Temporal Forecastings of Saturations and Pressure in the SACROC Field,"A machine learning architecture composed of convolutional long short-term
memory (convLSTM) is developed to predict spatio-temporal parameters in the
SACROC oil field, Texas, USA. The spatial parameters are recorded at the end of
each month for 30 years (360 months), approximately 83% (300 months) of which
is used for training and the rest 17% (60 months) is kept for testing. The
samples for the convLSTM models are prepared by choosing ten consecutive frames
as input and ten consecutive frames shifted forward by one frame as output.
Individual models are trained for oil, gas, and water saturations, and pressure
using the Nesterov accelerated adaptive moment estimation (Nadam) optimization
algorithm. A workflow is provided to comprehend the entire process of data
extraction, preprocessing, sample preparation, training, testing of machine
learning models, and error analysis. Overall, the convLSTM for spatio-temporal
prediction shows promising results in predicting spatio-temporal parameters in
porous media.",2212.00796v1
2022-12-04,Global stabilizability to trajectories for the Schlögl equation in a Sobolev norm,"The stabilizability to trajectories of the Schl\""ogl model is investigated in
the norm of the natural state space for strong solutions, which is strictly
contained in the standard pivot space of square integrable functions. As
actuators a finite number of indicator functions are used and the control input
is subject to a bound constraint. A stabilizing saturated explicit feedback
control is proposed, where the set of actuators and the input bound are
independent of the targeted trajectory. Further, the existence of open-loop
optimal stabilizing constrained controls and related first-order optimality
conditions are investigated. These conditions are then used to compute
stabilizing receding horizon based controls. Results of numerical simulations
are presented comparing their stabilizing performance with that of saturated
explicit feedback controls.",2212.01888v1
2022-12-14,Parameterizations of Immiscible Two-Phase Flow in Porous Media,"A fundamental variable characterizing immiscible two-phase flow in porous
media is the wetting saturation, which is the ratio between the pore volume
filled with wetting fluid and the total pore volume. More generally, this
variable comes from a specific choice of coordinates on some underlying space,
the domain of variables that can be used to express the volumetric flow rate.
The underlying mathematical structure allows for the introduction of other
variables containing the same information, but which are more convenient from a
theoretical point of view. We introduce along these lines polar coordinates on
this underlying space, where the angle plays a role similar to the wetting
saturation. We derive relations between these new variables based on the Euler
homogeneity theorem. We formulate these relations in a coordinate-free fashion
using differential forms. Lastly, we discuss and interpret the co-moving
velocity in terms of this coordinate-free representation.",2212.07285v1
2022-12-16,Indiscernibles and satisfaction classes in arithmetic,"We investigate the theory PAI (Peano Arithmetic with Indiscernibles). Models
of PAI are of the form (M, I), where M is a model of PA, I is an unbounded set
of order indiscernibles over M, and (M, I) satisfies the extended induction
scheme for formulae mentioning I. Our main results are Theorems A and B below.
  Theorem A. Let M be a nonstandard model of PA of any cardinality. M has an
expansion to a model of PAI iff M has an inductive partial satisfaction class.
  Theorem A yields the following corollary, which provides a new
characterization of countable recursively saturated models of PA:
  Corollary. A countable model M of PA is recursively saturated iff M has an
expansion to a model of PAI.
  Theorem B. There is a sentence s in the language obtained by adding a unary
predicate I(x) to the language of arithmetic such that given any nonstandard
model M of PA of any cardinality, M has an expansion to a model of PAI + s iff
M has a inductive full satisfaction class.",2212.08411v1
2022-12-18,Scaling of out-of-time ordered correlators in a non-Hermitian kicked rotor model,"We investigate the dynamics of the out-of-time-ordered correlators (OTOCs)
via a non-Hermitian extension of the quantum kicked rotor model, where the
kicking potential satisfies $\mathcal{PT}$-symmetry. The spontaneous
$\cal{PT}$-symmetry breaking emerges when the strength of the imaginary part of
the kicking potential exceeds a threshold value. We find, both analytically and
numerically, that in the broken phase of $\cal{PT}$ symmetry, the OTOCs rapidly
saturate with time evolution. Interestingly, the late-time saturation value
scales as a pow-law in the system size. The mechanism of such scaling law
results from the interplay between the effects of nonlocal operator in OTOCs
and the time reversal induced by non-Hermitian driven potential.",2212.09194v1
2022-12-23,Control of Positive Systems with an Unknown State-Dependent Power Law Input Delay and Input Saturation,"This paper is motivated by a class of positive systems with an input that is
subject to an unknown state-dependent power law delay as well as saturation.
For example, biological networks have non-negative protein concentration
states. Mass action kinetics in these systems result in power law behavior,
while complex interactions cause signal propagation delays. Incomplete network
characterization makes delay state-dependence unknown. Manipulating network
activity via modulated protein concentrations to attain desired performance is
restricted by upper-bounds on concentration actuator authority. Here, an
innovative control law exploits system dynamics to compensate for control
domain restrictions. A Lyapunov stability analysis establishes that the
reference tracking error of the closed-loop system is uniformly ultimately
bounded. Numerical simulations on a human coagulation model show controller
efficacy and better performance compared to the relevant literature. This
example application steps toward personalized, closed-loop treatments for
trauma coagulopathy, which currently has 30% mortality with open-loop clinical
approaches.",2212.12095v1
2023-01-03,The dipole cross section by the unintegrated gluon distribution at small $x$,"We apply a previously developed scheme to consistently include the improved
saturation model for the unintegrated gluon distribution (UGD) in order to
evaluate, in the framework of $k_{t}$ factorization, at small $x$ at the
next-to-leading order (NLO) in $\alpha_{s}$. We start the unintegrated gluon
distribution with a parametrization of the deep inelastic structure function
for electromagnetic scattering with protons, and then extract the color dipole
cross section, which preserves its behavior success in a wide range of
$k_{t}^{2}$ in comparisons with the UGD models (M. Hentschinski, A. Sabio Vera
and C. Salas (HSS), I.P.Ivanov and N.N.Nikolaev (IN) and G. Watt, A.D. Martin
and M.G. Ryskin (WMR)) . These results show that the geometric scaling holds
for the improved saturation model in a wide kinematic region $rQ_{s}$, and are
comparable with the Golec-Biernat-W$\ddot{\mathrm{u}}$sthoff (GBW) model. The
unintegrated gluon distribution at low and high momentum transfer in a wide
range of $x$ is considered.",2301.01083v4
2023-01-04,Nucleon Energy Correlators for the Color Glass Condensate,"We demonstrate the recently proposed nucleon energy-energy correlator
(nucleon EEC) $f_{\rm EEC}(x,\theta)$ can unveil the gluon saturation in the
small-$x$ regime in $eA$ collisions. The novelty of this probe is that it is
fully inclusive just like the deep-inelastic scattering (DIS), with no
requirements of jets or hadrons, but still provides an evident portal to the
small-$x$ dynamics through the shape of the $\theta$-distribution. We find that
the saturation prediction is significantly different from the expectation of
the collinear factorization.",2301.01788v2
2023-01-04,A GOA-Based Fault-Tolerant Trajectory Tracking Control for an Underwater Vehicle of Multi-Thruster System without Actuator Saturation,"This paper proposes an intelligent fault-tolerant control (FTC) strategy to
tackle the trajectory tracking problem of an underwater vehicle (UV) under
thruster damage (power loss) cases and meanwhile resolve the actuator
saturation brought by the vehicle's physical constraints. In the proposed
control strategy, the trajectory tracking component is formed by a refined
backstepping algorithm that controls the velocity variation and a sliding mode
control deducts the torque/force outputs; the fault-tolerant component is
established based on a Grasshopper Optimization Algorithm (GOA), which provides
fast convergence speed as well as satisfactory accuracy of deducting optimized
reallocation of the thruster forces to compensate for the power loss in
different fault cases. Simulations with or without environmental perturbations
under different fault cases and comparisons to other traditional FTCs are
presented, thus verifying the effectiveness and robustness of the proposed
GOA-based fault-tolerant trajectory tracking design.",2301.01827v1
2023-01-08,Saturation Numbers for Berge Cliques,"Let $F$ be a graph and $\mathcal{H}$ be a hypergraph, both embedded on the
same vertex set. We say $\mathcal{H}$ is a Berge-$F$ if there exists a
bijection $\phi:E(F)\to E(\mathcal{H})$ such that $e\subseteq \phi(e)$ for all
$e\in E(F)$. We say $\mathcal{H}$ is Berge-$F$-saturated if $\mathcal{H}$ does
not contain any Berge-$F$, but adding any missing edge to $\mathcal{H}$ creates
a copy of a Berge-$F$.
  The saturation number $\mathrm{sat}_k(n,\text{Berge-}F)$ is the least number
of edges in a Berge-$F$-saturated $k$-uniform hypergraph on $n$ vertices.
  We show
  \[
  \mathrm{sat}_k(n,\text{Berge-}K_\ell)\sim \frac{\ell-2}{k-1}n,
  \]
  for all $k,\ell\geq 3$. Furthermore, we provide some sufficient conditions to
imply that $\mathrm{sat}_k(n,\text{Berge-}F)=O(n)$ for general graphs $F$.",2301.02973v2
2023-01-30,Exploring Inelasticity in the S-Matrix Bootstrap,"The modern S-Matrix Bootstrap provides non-perturbative bounds on low-energy
aspects of scattering amplitudes, leveraging the constraints of unitarity,
analyticity and crossing. Typically, the solutions saturating such bounds also
saturate the unitarity constraint as much as possible, meaning that they are
almost exclusively elastic. This is expected to be unphysical in $d>2$ because
of Aks' theorem. We explore this issue by adding inelasticity as an additional
input, both using a primal approach in general dimensions which extends the
usual ansatz, and establishing a dual formulation in the 2d case. We then
measure the effects on the low-energy observables where we observe stronger
bounds than in the standard setup.",2301.13219v3
2023-02-02,Studies of the equation-of-state of nuclear matter by heavy-ion collisions at intermediate energy in the multi-messenger era,"The study of the equation-of-state (EoS) describing the properties of nuclear
matter away from the normal conditions is a relevant and intriguing topic of
modern nuclear physics. The last decades have witnessed a substantial
experimental progress in derivation of the symmetric matter term of the EoS and
of the so-called symmetry energy for the asymmetric matter, especially at
densities below the saturation point. But it is only in recent years that the
opening of the multi-messenger astronomy era, triggered by detection of
gravitational waves due to the neutron star mergers, has renewed and enlarged
the interest in high-density EoS, being the main ingredient for determining the
structure and properties of neutron stars. In this paper we review our
knowledge obtained from heavy-ion collisions up to the 1 GeV/nucleon regime, on
the EoS above nuclear saturation density. Special emphasis is given on the
still few results on symmetry energy at high densities and their
interconnections with multi-messenger astronomy findings.",2302.01453v1
2023-02-18,Distributed Optimization for Reactive Power Sharing and Stability of Inverter-Based Resources Under Voltage Limits,"Reactive power sharing and containment of voltages within limits for
inverter-based resources (IBRs) are two important, yet coupled objectives in ac
networks. In this article, we propose a distributed control technique to
simultaneously achieve these objectives. Our controller consists of two
components: a purely local nonlinear integral controller which adjusts the IBR
voltage setpoint, and a distributed primal-dual optimizer that coordinates
reactive power sharing between the IBRs. The controller prioritizes the voltage
containment objective over reactive power sharing at all points in time;
excluding the IBRs with saturated voltages, it provides reactive power sharing
among all the IBRs. Considering the voltage saturation and the coupling between
voltage and angle dynamics, a formal closed-loop stability analysis based on
singular perturbation theory is provided, yielding practical tuning guidance
for the overall control system. To validate the effectiveness of the proposed
controller for different case studies, we apply it to a low-voltage microgrid
and a microgrid adapted from the CIGRE medium-voltage network benchmark, both
simulated in the MATLAB/Simulink environment.",2302.09241v2
2023-02-19,A robust multiplicity result in a generalized diffusive predator-prey model,"This paper analyzes the generalized spatially heterogeneous diffusive
predator-prey model introduced by the authors in \cite{LGMH20}, whose
interaction terms depend on a saturation coefficient $m(x)\gneq0$. As the
amplitude of the saturation term, measured by $\|m\|_\infty$, blows up to
infinity, the existence of, at least, two coexistence states, is established in
the region of the parameters where the semitrivial positive solution is
linearly stable, regardless the sizes and the shapes of the remaining function
coefficients in the setting of the model. In some further special cases, an
$S$-shaped component of coexistence states can be constructed, which causes the
existence of, at least, three coexistence states, though this multiplicity
occurs within the parameter regions where the semitrivial positive solution is
linearly unstable. Therefore, these multiplicity results inherit a rather
different nature.",2302.09684v1
2023-02-27,Distributed Fixed-Time Consensus Control for Multiple AUV Systems with Input Saturations,"This study proposes a new distributed control method based on an adaptive
fuzzy control for multiple collaborative autonomous underwater vehicles (AUVs)
to track a desired formation shape within a fixed time. First, a formation
control protocol based on a fixed-time backstepping sliding mode control is
designed, in which the consensus cooperative tracking errors for each AUV will
be formulated. Then, to compensate for the saturated control torques, an
adaptive auxiliary variable is introduced. Finally, a fixed-time adaptive fuzzy
logic control (FLC) is derived to approximate the unknown dynamics, in which
the adaptive laws of the FLC is derived such that the adaptive signals and
errors can be convergent within a fixed time. The fixed time convergence is
desired in practice because it provides an exciting property that the global
convergence of the whole system is independent with the initial states of the
AUVs. The computer simulation results for a consensus formation control of four
AUVs show that the proposed formation control can provide high tracking
performance with lower and smoother control efforts",2302.14162v1
2023-02-28,Confined-state physics and signs of fermionization of moiré excitons in WSe$_2$/MoSe$_2$ heterobilayers,"We revisit and extend the standard bosonic interpretation of interlayer
excitons in the moir\'e potential of twisted heterostructures of
transition-metal dichalcogenides. In our experiments, we probe a high quality
MoSe$_2$/WSe$_2$ van der Waals bilayer heterostructure via density-dependent
photoluminescence spectroscopy and reveal strongly developed, unconventional
spectral shifts of the emergent moir\'e exciton resonances. The observation of
saturating blueshifts of successive exciton resonances allow us to explain
their physics in terms of a model utilizing fermionic saturable absorbers. This
approach is strongly inspired by established quantum-dot models, which
underlines the close analogy of interlayer excitons trapped in pockets of the
moir\'e potential, and quantum emitters with discrete eigenstates.",2302.14489v2
2023-03-14,The improved saturation model in nuclei,"We consider the nuclear shadowing in deep-inelastic scattering corresponding
to kinematic regions accessible by future experiments at electron-ion
colliders. The gluon distribution at low $x$ is obtained using an improved
dipole model on the impact parameter for nuclei. The nuclear shadowing at small
$x$ is defined within the color dipole formalism with respect to the mass
number $A$. Its behavior is predicted for light nuclei in a wide range of the
impact parameter $b$ and the transverse dipole size $r$. The nuclear saturation
at large-$r$ is observable. The behavior of the nuclear ratio
$\sigma^{A}_{\mathrm{dip}}/\sigma_{0}$ is similar to the
Golec-Biernat-W$\ddot{\mathrm{u}}$sthoff (GBW) model in a wide range of $r$ and
$A$ at small $x$. The results are compared with nCETQ15 parametrization group.",2303.07654v3
2023-03-15,A Momentum Two-gradient Direction Algorithm with Variable Step Size Applied to Solve Practical Output Constraint Issue for Active Noise Control,"Active noise control (ANC) has been widely utilized to reduce unwanted
environmental noise. The primary objective of ANC is to generate an anti-noise
with the same amplitude but the opposite phase of the primary noise using the
secondary source. However, the effectiveness of the ANC application is impacted
by the speaker's output saturation. This paper proposes a two-gradient
direction ANC algorithm with a momentum factor to solve the saturation with
faster convergence. In order to make it implemented in real-time, a
computation-effective variable step size approach is applied to further reduce
the steady-state error brought on by the changing gradient directions. The time
constant and step size bound for the momentum two-gradient direction algorithm
is analyzed. Simulation results show that the proposed algorithm performs
effectively in the time-unvaried and time-varied environment.",2303.08397v1
2023-03-26,Constraining nuclear symmetry energy with the charge radii of mirror-pair nuclei,"The nuclear charge radius plays a vital role in determining the equation of
state of isospin asymmetric nuclear matter.
  Based on the correlation between the differences in charge radii of
mirror-partner nuclei and the slope parameter ($L$) of symmetry energy at the
nuclear saturation density, an analysis of the calibrated slope parameter $L$
was performed in finite nuclei. In this study, relativistic and
non-relativistic energy density functionals were employed to constrain the
nuclear symmetry energy through the available databases of the mirror-pair
nuclei $^{36}$Ca-$^{36}$S, $^{38}$Ca-$^{38}$Ar, and $^{54}$Ni-$^{54}$Fe. The
deduced nuclear symmetry energy was located in the range 29.89-31.85 MeV, and
$L$ of the symmetry energy essentially covered the range 22.50-51.55 MeV at the
saturation density. Moreover, the extracted $L_s$ at the sensitivity density
$\rho_{s}=0.10~\mathrm{fm}^{-3}$ was located in the interval range 30.52-39.76
MeV.",2303.14667v2
2023-03-27,$α$ + core structure described with an additional interaction in the nuclear matter saturation region,"In a phenomenological approach, the $\alpha$ + core structure is investigated
in the $^{20}$Ne, $^{44}$Ti, $^{94}$Mo, $^{104}$Te, and $^{212}$Po nuclei
through the local potential model using a double-folding nuclear potential with
effective nucleon-nucleon interaction of M3Y + $c_{\mathrm{sat}}\delta(s)$
type, where the term $c_{\mathrm{sat}}\delta(s)$ acts only between the
saturation regions of $\alpha$-cluster and core. Properties such as energy
levels, $\alpha$-widths, $B(E2)$ transition rates, and half-lives are
calculated, and good level of agreement with experimental data is obtained in
general. It is shown the inclusion of the term $c_{\mathrm{sat}}\delta(s)$ is
determinant for a better description of the experimental energy levels compared
to the ground state bands produced with the simple M3Y interaction. The
properties calculated for $^{104}$Te reinforce the superallowed $\alpha$-decay
feature for this nucleus, as indicated in previous studies.",2303.14927v1
2023-03-31,Lamb dip of a Quadrupole Transition in H$_2$,"The saturated absorption spectrum of the hyperfine-less S(0) quadrupole line
in the (2-0) band of H$_2$ is measured at $\lambda=1189$ nm, using the
NICE-OHMS technique under cryogenic conditions (72~K). It is for the first time
that a Lamb dip of a molecular quadrupole transition is recorded. At low
(150-200 W) saturation powers a single narrow Lamb dip is observed, ruling out
an underlying recoil doublet of 140 kHz. Studies of Doppler-detuned resonances
show that the red-shifted recoil component can be made visible for low
pressures and powers, and prove that the narrow Lamb dip must be interpreted as
the blue recoil component. A transition frequency of 252\,016\,361\,164\,(8)
kHz is extracted, which is off by -2.6 (1.6) MHz from molecular quantum
electrodynamical calculations therewith providing a challenge to theory.",2303.17818v1
2023-04-03,Constraints on the in-medium nuclear interaction from chiral symmetry and Lattice-QCD,"In this paper we discuss the combined effects on nuclear matter properties of
the quark confinement mechanism in nucleon and of the chiral effective
potential resulting from the spontaneous breaking of the chiral symmetry in
nuclear matter. Based on the Nambu-Jona-Lasinio predictions, it is shown that
the chiral potential acquires a specific scalar field cubic dependence, which
contributes to the three-body interaction. We also discuss the constraints
induced by Lattice-QCD on the model parameters governing the saturation
properties. We introduce the term ""QCD-connected parameters"" for these
quantities. We demonstrate that chiral symmetry and Lattice-QCD provide
coherent constraints on the in-medium nuclear interaction, suggesting a
fundamental origin of the saturation mechanism.",2304.01036v1
2023-04-10,Better Together: Unifying Datalog and Equality Saturation,"We present egglog, a fixpoint reasoning system that unifies Datalog and
equality saturation (EqSat). Like Datalog, it supports efficient incremental
execution, cooperating analyses, and lattice-based reasoning. Like EqSat, it
supports term rewriting, efficient congruence closure, and extraction of
optimized terms.
  We identify two recent applications--a unification-based pointer analysis in
Datalog and an EqSat-based floating-point term rewriter--that have been
hampered by features missing from Datalog but found in EqSat or vice-versa. We
evaluate egglog by reimplementing those projects in egglog. The resulting
systems in egglog are faster, simpler, and fix bugs found in the original
systems.",2304.04332v4
2023-04-10,Criticality versus uniformity in deep neural networks,"Deep feedforward networks initialized along the edge of chaos exhibit
exponentially superior training ability as quantified by maximum trainable
depth. In this work, we explore the effect of saturation of the tanh activation
function along the edge of chaos. In particular, we determine the line of
uniformity in phase space along which the post-activation distribution has
maximum entropy. This line intersects the edge of chaos, and indicates the
regime beyond which saturation of the activation function begins to impede
training efficiency. Our results suggest that initialization along the edge of
chaos is a necessary but not sufficient condition for optimal trainability.",2304.04784v1
2023-04-21,The Effect of Particle Size and Concentration on Low-Frequency Terahertz Scattering in Granular Compacts,"Fundamental knowledge of scattering in granular compacts is essential to
ensure accuracy of spectroscopic measurements and determine material
characteristics such as size and shape of scattering objects. Terahertz
time-domain spectroscopy (THz-TDS) was employed to investigate the effect of
particle size and concentration on scattering in specially fabricated compacts
consisting of borosilicate microspheres in a polytetrafluoroethylene (PTFE)
matrix. As expected, increasing particle size leads to an increase in overall
scattering contribution. At low concentrations, the scattering contribution
increases linearly with concentration. Scattering increases linearly at low
concentrations, saturates at higher concentrations with a maximum level
depending on particle size, and that the onset of saturation is independent of
particle size. The effective refractive index becomes sublinear at high
particle concentrations and exceeds the linear model at maximum density, which
can cause errors in calculations based on it, such as porosity. The observed
phenomena are attributed to the change in the fraction of photons propagating
ballistically versus being scattered. At low concentrations, photons travel
predominately ballistically through the PTFE matrix. At high concentrations,
the photons again propagate ballistically through adjacent glass microspheres.
In the intermediate regime, photons are predominately scattered.",2304.10974v1
2023-04-24,TextMesh: Generation of Realistic 3D Meshes From Text Prompts,"The ability to generate highly realistic 2D images from mere text prompts has
recently made huge progress in terms of speed and quality, thanks to the advent
of image diffusion models. Naturally, the question arises if this can be also
achieved in the generation of 3D content from such text prompts. To this end, a
new line of methods recently emerged trying to harness diffusion models,
trained on 2D images, for supervision of 3D model generation using view
dependent prompts. While achieving impressive results, these methods, however,
have two major drawbacks. First, rather than commonly used 3D meshes, they
instead generate neural radiance fields (NeRFs), making them impractical for
most real applications. Second, these approaches tend to produce over-saturated
models, giving the output a cartoonish looking effect. Therefore, in this work
we propose a novel method for generation of highly realistic-looking 3D meshes.
To this end, we extend NeRF to employ an SDF backbone, leading to improved 3D
mesh extraction. In addition, we propose a novel way to finetune the mesh
texture, removing the effect of high saturation and improving the details of
the output 3D mesh.",2304.12439v1
2023-04-28,Molecular charmed baryons and pentaquarks from light-meson exchange saturation,"The spectrum of the $c qq$ baryons contains a few states whose nature is not
clearly a three-quark composite and which might have a sizable baryon-meson
component. Examples include the $\Sigma_c(2800)$ or the $\Lambda_c(2940)$. Here
we explore the spectrum of two-body systems composed of a light, octet baryon
and a charmed meson (or antimeson) within a simple contact-range theory in
which the couplings are saturated by light-meson exchanges. This results in the
prediction of a series of composite anticharmed pentaquarks ($\bar{c} q qqq $)
and singly-charmed baryons ($c \bar{q} qqq $). Among the later we find
$J=\tfrac{1}{2}$ $\Xi D$ and $J=\tfrac{3}{2}$ $\Xi D^*$ bound states with
masses matching those of the recently observed $\Omega_c(3185)$ and
$\Omega_c(3327)$ baryons.",2304.14855v1
2023-05-02,F2: Designing a Key-Value Store for Large Skewed Workloads,"Today's key-value stores are either disk-optimized, focusing on large data
and saturating device IOPS, or memory-optimized, focusing on high throughput
with linear thread scaling assuming plenty of main memory. However, many
practical workloads demand high performance for read and write working sets
that are much larger than main memory, over a total data size that is even
larger. They require judicious use of memory and disk, and today's systems do
not handle such workloads well. We present F2, a new key-value store design
based on compartmentalization -- it consists of five key components that work
together in well-defined ways to achieve high throughput -- saturating disk and
memory bandwidths -- while incurring low disk read and write amplification. A
key design characteristic of F2 is that it separates the management of hot and
cold data, across the read and write domains, and adapts the use of memory to
optimize each case. Through a sequence of new latch-free system constructs, F2
solves the key challenge of maintaining high throughput with linear thread
scalability in such a compartmentalized design. Detailed experiments on
benchmark data validate our design's superiority, in terms of throughput, over
state-of-the-art key-value stores, when the available memory resources are
scarce.",2305.01516v1
2023-05-08,Tweaking Spectral Topology and Exceptional Points by Nonlinearity in Non-Hermitian Polariton Systems,"Exceptional points (EPs) with their intriguing spectral topology have
attracted considerable attention in a broad range of physical systems, with
potential sensing applications driving much of the present research in this
field. Here we theoretically demonstrate the realization of EPs in a system
with significant nonlinearity, a non-equilibrium exciton-polariton condensate.
With the possibility to control loss and gain and nonlinearity by optical
means, this system allows for a comprehensive analysis of the interplay of
nonlinearities (Kerr-type and saturable gain) and non-Hermiticity. Not only do
we find that EPs can be intentionally shifted in parameter space by the
saturable gain, we also observe intriguing rotations and intersections of
Riemann surfaces, and find nonlinearity-enhanced sensing capabilities. Our
results are quite general in nature and illustrate the potential of tailoring
spectral topology and related phenomena in non-Hermitian systems by
nonlinearity.",2305.04855v1
2023-05-12,Saturated Non-Monotonic Activation Functions,"Activation functions are essential to deep learning networks. Popular and
versatile activation functions are mostly monotonic functions, some
non-monotonic activation functions are being explored and show promising
performance. But by introducing non-monotonicity, they also alter the positive
input, which is proved to be unnecessary by the success of ReLU and its
variants. In this paper, we double down on the non-monotonic activation
functions' development and propose the Saturated Gaussian Error Linear Units by
combining the characteristics of ReLU and non-monotonic activation functions.
We present three new activation functions built with our proposed method:
SGELU, SSiLU, and SMish, which are composed of the negative portion of GELU,
SiLU, and Mish, respectively, and ReLU's positive portion. The results of image
classification experiments on CIFAR-100 indicate that our proposed activation
functions are highly effective and outperform state-of-the-art baselines across
multiple deep learning architectures.",2305.07537v2
2023-05-17,Evolution of Coupled Weakly-Driven Waves in a Dissipative Plasma,"The nonlinear collisional dynamics of coupled driven plasma waves in the
presence of background dissipation is studied analytically within kinetic
theory. Sufficiently near marginal stability, phase space correlations are
poorly preserved and time delays become unimportant. The system is then shown
to be governed by two first-order coupled autonomous differential equations of
cubic order for the wave amplitudes and two complementary first-order equations
for the evolution of their phases. That system of equations can be decoupled
and further simplified to a single second-order differential equation of
Li\'enard's type for each amplitude. Numerical solutions for this equation are
obtained in the general case while analytic solutions are obtained for special
cases in terms of parameters related to the spacing of the resonances of the
two waves in frequency space, e.g., wave lengths and oscillation frequencies.
These parameters are further analyzed to find classes of quasi-steady
saturation and pulsating scenarios. To classify equilibrium points, local
stability analysis is applied, and bifurcation conditions are determined. When
the two waves saturate at similar amplitude levels, their combined signal is
shown to invariably exhibit amplitude beating and phase jumps of nearly $\pi$.
The obtained analytical results can be used to benchmark simulations and to
interpret eigenmode amplitude measurements in fusion experiments.",2305.10322v1
2023-05-23,The covariety of saturated numerical semigroups with fixed Frobenius number,"In this work we will show that if $F$ is a positive integer, then
${\mathrm{Sat}}(F)=\{S\mid S \mbox{ is a saturated numerical semigroup with
Frobenius number } F\}$ is a covariety. As a consequence, we present two
algorithms: one that computes ${\mathrm{Sat}}(F),$ and the other which computes
all the elements of ${\mathrm{Sat}}(F)$ with a fixed genus.
  If $X\subseteq S\backslash \Delta(F)$ for some $S\in {\mathrm{Sat}}(F),$ then
we will see that there is the least element of ${\mathrm{Sat}}(F)$ containing a
$X$. This element will denote by ${\mathrm{Sat}}(F)[X].$
  If $S\in{\mathrm{Sat}}(F),$ then we define the ${\mathrm{Sat}}(F)$-rank of
$S$ as the minimum of $\{\mbox{cardinality}(X)\mid S={\mathrm{Sat}}(F)[X]\}.$
In this paper, also we present an algorithm to compute all the element of
${\mathrm{Sat}}(F)$ with a given
  ${\mathrm{Sat}}(F)$-rank.",2305.13881v1
2023-05-24,A discrete-time Pontryagin maximum principle under rate constraints,"Limited bandwidth and limited saturation in actuators are practical concerns
in control systems. Mathematically, these limitations manifest as constraints
being imposed on the control actions, their rates of change, and more
generally, the global behavior of their paths. While the problem of actuator
saturation has been studied extensively, little attention has been devoted to
the problem of actuators having limited bandwidth. While attempts have been
made in the direction of incorporating frequency constraints on state-action
trajectories before, rate constraints on the control at the design stage have
not been studied extensively in the discrete-time regime. This article
contributes toward filling this lacuna. In particular, we establish a new
discrete-time Pontryagin maximum principle with rate constraints being imposed
on the control trajectories, and derive first-order necessary conditions for
optimality. A brief discussion on the existence of optimal control is included,
and numerical examples are provided to illustrate the results.",2305.14940v1
2023-05-24,Breaking the Curse of Quality Saturation with User-Centric Ranking,"A key puzzle in search, ads, and recommendation is that the ranking model can
only utilize a small portion of the vastly available user interaction data. As
a result, increasing data volume, model size, or computation FLOPs will quickly
suffer from diminishing returns. We examined this problem and found that one of
the root causes may lie in the so-called ``item-centric'' formulation, which
has an unbounded vocabulary and thus uncontrolled model complexity. To mitigate
quality saturation, we introduce an alternative formulation named
``user-centric ranking'', which is based on a transposed view of the dyadic
user-item interaction data. We show that this formulation has a promising
scaling property, enabling us to train better-converged models on substantially
larger data sets.",2305.15333v1
2023-05-31,Composite Triggered Intermittent Control for Constrained Spacecraft Attitude Tracking,"This paper focuses on the spacecraft attitude control problem with
intermittent actuator activation, taking into account the attitude rotation
rate limitation and input saturation issue simultaneously. To address this
problem, we first propose a composite event-trigger mechanism, which composed
of two state-dependent trigger that governing the activation and deactivation
of actuators. Subsequently, by introducing the cascaded decomposition of
Backstepping control philosophy, the designed trigger mechanism is then applied
to the decomposed dynamical subsystem, providing a layered intermittent
stabilization strategy.
  Further, the basic intermittent attitude controller is extended to a
""constrained version"" by introducing a strictly bounded virtual control law and
an input saturation compensation auxiliary system.
  By analyzing the local boundedness of the system on each inter-event time
interval, a uniformly, strictly decreasing upper boundary of the lumped system
is further characterized, thereby completing the proof of the system's
uniformly ultimately boundedness (UUB). Finally, numerical simulation results
are illustrated to demonstrate the effectiveness of the proposed scheme.",2305.19644v1
2023-06-07,Surface Saturation Current Densities of Perovskite Thin Films from Suns-Photoluminescence Quantum Yield Measurements,"We present a simple, yet powerful analysis of Suns-photoluminescence quantum
yield measurements that can be used to determine the surface saturation current
densities of thin film semiconductors. We apply the method to state-of-the-art
polycrystalline perovskite thin films of varying absorber thickness. We show
that the non-radiative bimolecular recombination in these samples originates
from the surfaces. To the best of our knowledge, this is the first study to
demonstrate and quantify non-linear (bimolecular) surface recombination in
perovskite thin films.",2306.04194v1
2023-06-07,Forward $γ$+jet production in proton-proton and proton-lead collisions at LHC within the FoCal calorimeter acceptance,"Using the small-$x$ Improved Transverse Momentum Dependent factorization
(ITMD), which, for a general two-to-two massless scattering can be proved
within the Color Glass Condensate (CGC) theory for transverse momenta of
particles greater than the saturation scale, we provide predictions for
isolated forward photon and jet production in proton-proton and proton-nucleus
collisions within the planned ALICE FoCal detector acceptance. We study
azimuthal correlations, $p_T$ spectra, as well as normalized ratios of
proton-proton cross sections for different energies. The only TMD distribution
needed for that process is the ""dipole"" TMD gluon distribution, which in our
computations is based on HERA data and undergoes momentum space BK evolution
equation with DGLAP corrections and Sudakov resummation. We conclude, that the
process provides an excellent probe of the dipole TMD gluon distribution in
saturation regime.",2306.04706v2
2023-06-19,Frame potential of Brownian SYK model of Majorana and Dirac fermions,"We consider the Brownian SYK, i.e. a system of $N$ Majorana (Dirac) fermions
with a white-noise $q$-body interaction term. We focus on the dynamics of the
Frame potentials, a measure of the scrambling and chaos, given by the moments
of the overlap between two independent realisations of the model. By means of a
Keldysh path-integral formalism, we compute its early and late-time value. We
show that, for $q>2$, the late time path integral saddle point correctly
reproduces the saturation to the value of the Haar frame potential. On the
contrary, for $q=2$, the model is quadratic and consistently we observe
saturation to the Haar value in the restricted space of Gaussian states
(Gaussian Haar). The latter is characterised by larger system size corrections
that we correctly capture by counting the Goldstone modes of the Keldysh saddle
point. Finally, in the case of Dirac fermions, we highlight and resolve the
role of the global $U(1)$ symmetry.",2306.11160v3
2023-06-21,Multiplicity distribution and entropy of produced gluons in deep inelastic scattering at high energies,"In this paper we found the multiplicity distribution of the produced gluons
in deep inelastic scattering at large $z=\ln\LbQ^2_s/Q^2\Rb\,\,\gg\,\,1$ where
$ Q_s $ is the saturation momentum and $Q^2$ is the photon virtuality. It turns
out that this distribution at large $n > \bar{n}$ almost reproduces the KNO
scaling behaviour with the average number of gluons $ \bar{n} \propto \exp\Lb
z^2/2 \kappa\Rb$, where $\kappa = 4.88 $ in the leading order of perturbative
QCD. TheKNO function $\Psi\Lb \frac{n}{\bar{n}}\Rb = \exp\Lb -\,n/\bar{n}\Rb$.
For $n < \bar{n}$ we found that $\sigma_n \propto\Big( z - \sqrt{2
\,\kappa\,\ln (n-1)}\Big)/(n-1)$. Such small $n$ determine the value of entropy
of produced gluons $S_E = 0.3\, z^2/(2\,\kappa)$ at large $z$. The factor $0.3$
stems from the non-perturbative corrections that provide the correct behaviour
of the saturation momentum at large $b$.",2306.12055v1
2023-06-21,Softening the UV without New Particles,"We explore an odd class of QFTs where a hierarchy problem is resolved with
new dynamics as opposed to new particles. The essential element of our
construction is a $U(1)$ pseudo-NG boson with symmetry breaking interactions
all characterized by a large number $N$ of units of the fundamental charge. In
the resulting effective theory, quantum corrections, like those to the
effective potential and mass, which are normally power divergent and saturated
at the UV cut-off, are instead saturated at a much lower scale. This critical
scale, which does not involve any new particle, corresponds to the onset of
unsuppressed multiparticle production in scattering processes. Remarkably this
all happens within the tractable domain of weak coupling. Terms involving
arbitrarily high powers of the Goldstone field must however be taken into
account. In particular, a truncation to the renormalizable part of the
effective Lagrangian would completely miss the physics.",2306.12489v2
2023-06-26,Hot hole transport and noise phenomena in silicon at cryogenic temperatures from first principles,"The transport properties of hot holes in silicon at cryogenic temperatures
exhibit several anomalous features, including the emergence of two distinct
saturated drift velocity regimes and a non-monotonic trend of the current noise
versus electric field at microwave frequencies. Despite prior investigations,
these features lack generally accepted explanations. Here, we examine the
microscopic origin of these phenomena by extending a recently developed
ab-initio theory of high-field transport and noise in semiconductors. We find
that the drift velocity anomaly may be attributed to scattering dominated by
acoustic phonon emission, leading to an additional regime of drift velocity
saturation at temperatures $\sim 40$ K for which the acoustic phonon occupation
is negligible; while the non-monotonic trend in the current noise arises due to
the decrease in momentum relaxation time with electric field. The former
conclusion is consistent with the findings of prior work, but the latter
distinctly differs from previous explanations. This work highlights the use of
high-field transport and noise phenomena as sensitive probes of microscopic
charge transport phenomena in semiconductors.",2306.14986v1
2023-06-30,Analytical prediction of the temperature and the lifetime of an evaporating spherical droplet,"In this paper, we propose to predict analytically the temperature of an
evaporating spherical droplet. To do so, we first review, from data in the
literature, the effect of temperature on the physical parameters involved in
cooling-induced evaporation, namely the saturating vapor pressure, the
diffusion coefficient of vapor in air, the liquid density, the enthalpy of
vaporization and the thermal conductivity of air. These data support a series
of approximations that allows us to derive an implicit equation for the liquid
temperature. We propose a quadratic approximation of the variation of the
saturating vapor concentration with temperature to obtain an explicit
prediction of the drop temperature. As a result, an analytical prediction of
the droplet lifetime including the cooling effect is proposed.",2306.17534v1
2023-07-10,Graph Convolutional Networks for Simulating Multi-phase Flow and Transport in Porous Media,"Numerical simulation of multi-phase fluid dynamics in porous media is
critical for many subsurface applications. Data-driven surrogate modeling
provides computationally inexpensive alternatives to high-fidelity numerical
simulators. While the commonly used convolutional neural networks (CNNs) are
powerful in approximating partial differential equation solutions, it remains
challenging for CNNs to handle irregular and unstructured simulation meshes.
However, subsurface simulation models often involve unstructured meshes with
complex mesh geometries, which limits the application of CNNs. To address this
challenge, here we construct surrogate models based on Graph Convolutional
Networks (GCNs) to approximate the spatial-temporal solutions of multi-phase
flow and transport processes. We propose a new GCN architecture suited to the
hyperbolic character of the coupled PDE system, to better capture the
saturation dynamics. Results of 2D heterogeneous test cases show that our
surrogates predict the evolutions of the pressure and saturation states with
high accuracy, and the predicted rollouts remain stable for multiple timesteps.
Moreover, the GCN-based models generalize well to irregular domain geometries
and unstructured meshes that are unseen in the training dataset.",2307.04449v1
2023-07-11,Signatures of Ultralight Bosons in Compact Binary Inspiral and Outspiral,"Ultralight bosons are well-motivated particles from various physical and
cosmological theories, and can be spontaneously produced during the
superradiant process, forming a dense hydrogen-like cloud around the spinning
black hole. After the growth saturates, the cloud slowly depletes its mass
through gravitational-wave emission. In this work we study the orbit dynamics
of a binary system containing such a gravitational atom saturated in various
spin-0,1,2 superradiant states, taking into account both the effects of
dynamical friction and the cloud mass depletion. We estimate the significance
of mass depletion, finding that although dynamical friction could dominate the
inspiral phase, it typically does not affect the outspiral phase driven by the
mass depletion. Focusing on the large orbit radius, we investigate the
condition to observe the outspiral, and the detectability of the cloud via
pulsar-timing signal in the case of black hole-pulsar binary.",2307.05181v2
2023-02-02,Reducing cartel recruitment is the only way to lower violence in Mexico,"Every year, Mexican cartels lose many members due to conflict with other
cartels and arrests. Yet, despite their losses, cartels have managed to
increase violence for years. We address this puzzle by leveraging data on the
number of homicides, missing persons and arrests in Mexico for the past ten
years, along with information on the interactions among cartels aiming to
estimate the size of cartels' population. We model recruitment, incapacitation
by the state, conflict and saturation as the reasons why cartels vary in size.
Results show that by 2022 cartels have between 160,000 and 185,000 units,
becoming one of the top employers in the country. Recruiting at least 350
people per week is essential to avoid their collapse due to the aggregate
effect of incapacitation, conflict and saturation. Furthermore, we test the
effects of two policy scenarios aimed at decreasing cartel violence. We show
that given the state of violence, increasing current levels of incapacitation
leads to a rise in homicides and cartel members. Conversely, reducing
recruitment provides substantial benefits in terms of violence reduction and
decreasing cartel population, calling for structural investments in a proactive
strategy that targets individuals at risk rather than a traditional reactive
approach centred around incapacitation.",2307.06302v1
2023-07-16,Seis2Rock: A Data-Driven Approach to Direct Petrophysical Inversion of Pre-Stack Seismic Data,"The inversion of petrophysical parameters from seismic data represents a
fundamental step in the process of characterizing the subsurface. We propose a
novel, data-driven approach named Seis2Rock that utilizes optimal basis
functions learned from well log information to directly link band-limited
petrophysical reflectivities to pre-stack seismic data. Seis2Rock is composed
of two stages: training and inference. During training, a set of optimal basis
functions are identified by performing singular value decomposition on one or
more synthetic AVO gathers created from measured or rock-physics synthesized
elastic well-logs. In inference, seismic pre-stack data are first projected
into a set of band-limited petrophysical properties using the previously
computed basis functions; this is followed by regularized post-stack seismic
inversion of the individual properties. In this work, we apply the Seis2Rock
methodology to a synthetic dataset based on the Smeaheia reservoir model and
the open Volve field dataset. Numerical results reveal the ability of the
proposed method in recovering accurate porosity, shale content, and water
saturation models. Finally, the proposed methodology is applied in the context
of reservoir monitoring to invert time-lapse, pre-stack seismic data for water
saturation changes.",2307.07969v2
2023-07-20,Practical Active Noise Control: Restriction of Maximum Output Power,"This paper presents some recent algorithms developed by the authors for
real-time adaptive active noise (AANC) control systems. These algorithms
address some of the common challenges faced by AANC systems, such as speaker
saturation, system divergence, and disturbance rejection. Speaker saturation
can introduce nonlinearity into the adaptive system and degrade the noise
reduction performance. System divergence can occur when the secondary speaker
units are over-amplified or when there is a disturbance other than the noise to
be controlled. Disturbance rejection is important to prevent the adaptive
system from adapting to unwanted signals. The paper provides guidelines for
implementing and operating real-time AANC systems based on these algorithms.",2307.10913v1
2023-08-01,Black Holes as Neutrino Factories,"Ultralight bosons near rotating black holes can grow significantly via
superradiant energy extraction, potentially reaching field values close to the
Planck scale, thereby turning black holes into effective transducers for these
fields. The interaction between a boson field and fermions can initiate a
parametric production of fermions, potentially halting the exponential growth
and leading to a saturated state of the boson cloud. This dynamic offers a
framework for establishing limits on boson-neutrino interactions, which have
traditionally been restricted by neutrino self-interaction considerations. At
the saturation phase, boson clouds have the capacity to propel neutrinos to
TeV-scale energies, generating fluxes that surpass atmospheric neutrino fluxes
from nearby black holes. This mechanism extends to dark sector fermions,
leading to the generation of boosted dark matter. These fluxes open novel
avenues for observation through high-energy neutrino detectors like IceCube, as
well as through dark matter direct detection, by directing observational
efforts towards targeted black holes.",2308.00741v2
2023-08-08,Exceptional Point Degeneracy as Desirable Operation Point of Oscillator Array with Discrete Nonlinear Gain and Radiating Elements,"An oscillator array prefers to operate at an exceptional point of degeneracy
(EPD) occurring in a waveguide periodically loaded with discrete nonlinear gain
and radiating elements. The system maintains a steady-state degenerate mode of
oscillation at a frequency of 3 GHz, even when the small-signal nonlinear gain
values are nonuniform along the array. Contrarily to the original expectation
of zero phase shift associated to the designed EPD using small-signal gain,
after reaching saturation, the time domain signal in consecutive unit cells
displays a $\pi$ phase shift. Hence, we demonstrate that the saturated system
oscillates at a distinct EPD, associated to a $\pi$ phase shift between
consecutive cells, than the one at which the system was originally designed
using small-signal gain. This new EPD at which the nonlinear system is landing
is associated to higher power efficiency. Finally, we demonstrate that the
oscillation frequency is independent of the length of the array, contrarily to
what happens ordinary oscillating systems based on one-dimensional cavity
resonances. These findings may have a high impact on high-power radiating
arrays with distributed active elements.",2308.04562v1
2023-08-17,Improving Modular Bootstrap Bounds with Integrality,"We implement methods that efficiently impose integrality -- i.e., the
condition that the coefficients of characters in the partition function must be
integers -- into numerical modular bootstrap. We demonstrate the method with a
number of examples where it can be used to strengthen modular bootstrap
results. First, we show that, with a mild extra assumption, imposing
integrality improves the bound on the maximal allowed gap in dimensions of
operators in theories with a $U(1)^c$ symmetry at $c=3$, and reduces it to the
value saturated by the $SU(4)_1$ WZW model point of $c=3$ Narain lattices
moduli space. Second, we show that our method can be used to eliminate all but
a discrete set of points saturating the bound from previous Virasoro modular
bootstrap results. Finally, when central charge is close to $1$, we can
slightly improve the upper bound on the scaling dimension gap.",2308.08725v1
2023-08-24,Quantized distributed Nash equilibrium seeking under DoS attacks: A quantized consensus based approach,"This paper studies distributed Nash equilibrium (NE) seeking under
Denial-of-Service (DoS) attacks and quantization. The players can only exchange
information with their own direct neighbors. The transmitted information is
subject to quantization and packet losses induced by malicious DoS attacks. We
propose a quantized distributed NE seeking strategy based on the approach of
dynamic quantized consensus. To solve the quantizer saturation problem caused
by DoS attacks, the quantization mechanism is equipped to have zooming-in and
holding capabilities, in which the holding capability is consistent with the
results in quantized consensus under DoS. A sufficient condition on the number
of quantizer levels is provided, under which the quantizers are free from
saturation under DoS attacks. The proposed distributed quantized NE seeking
strategy is shown to have the so-called maximum resilience to DoS attacks.
Namely, if the bound characterizing the maximum resilience is violated, an
attacker can deny all the transmissions and hence distributed NE seeking is
impossible.",2308.12617v1
2023-08-31,The nuclear liquid-gas transition in QCD,"We estimate the nuclear saturation density and the binding energy in a
nuclear liquid from precision data on the coupling of the four-quark scattering
vertex in the vector channel, computed within functional QCD. We show that this
coupling is directly related to the density-density potential and the latter is
used for the estimates. In a first qualitative computation we find a saturation
density of 0.2 fm${}^{-3}$ and an upper bound for the binding energy of 21.5
MeV, in agreement with the empirical values of 0.16 fm${}^{-3}$ and 16 MeV,
respectively. We also use the scattering vertex for constructing an emergent
low-energy effective theory for the liquid gas transition from QCD correlation
function, whose coupling parameters can be determined within QCD. As a first
consistency check of this construction we estimate the in-medium reduction of
the nucleon pole mass.",2308.16594v1
2023-08-31,Neutron Star vs Quark Star in the Multimessenger Era,"Neutron stars (NSs) which could contain exotic degrees of freedom in the core
and the self-bound quark stars (QSs) made purely of absolutely stable
deconfined quark matter are still two main candidates for the compact objects
observed in pulsars and gravitational wave (GW) events in binary star mergers.
We perform a Bayesian model-agnostic inference of the properties of NSs and QSs
by combining multi-messenger data of GW170817, GW190425, PSR J0030+0451, PSR
J0740+6620, PSR J1614-2230, PSR J0348+0432 as well as ab initio calculations
from perturbative quantum chromodynamics and chiral effective field theory. We
find the NS scenario is strongly favored against the QS scenario with a Bayes
factor of NS over QS $\mathcal{B}^\text{NS}_\text{QS} = 11.5$. In addition, the
peak of the squared sound velocity $c_s^2 \sim 0.5c^2$ around $3.5$ times
nuclear saturation density $n_0$ observed in the NS case disappears in the QS
case which suggests that the $c_s^2$ first increases and then saturates at
$c_s^2 \sim 0.5c^2$ above $\sim 4n_0$. The sound velocity and trace anomaly are
found to approach the conformal limit in the core of heavy NSs with mass $M
\gtrsim 2M_{\odot}$, but not in the core of QSs.",2308.16783v1
2023-09-05,Enumeration of saturated and unsaturated substituted N-heterocycles,"Mathematical and computational approaches in chemistry and biochemistry fill
a gap in respect to the analysis of the physicochemical features of compounds
and their functionality and provide an overview of known as well as yet
unknown, but hypothetically possible structures. Nitrogen containing
heterocycles such as aziridine, azetidine and pyrrolidine bear a high potential
in pharmacology, biotechnology and synthetic biology. Here, we present a
mathematical enumeration procedure for all possible azaheterocycles with at
least one substituent depending on the number of atoms in the ring, in the
sense of saturated and unsaturated congeners. One subgroup belonging to that
substance class is constituted by ring-shaped amino acids with a secondary
amino group such as proline. A recursion formula is derived, which results in a
modified Lucas number series. Moreover, an explicit formula for determining the
number of such substances based on the Golden Ratio is given and a second one,
based on binomial coefficients, is newly derived. This enumeration is a helpful
tool for construction or complementation of virtual compound databases and for
computer-assisted chemical synthesis route planning.",2309.02343v1
2023-09-06,Dynamic scaling relation in quantum many-body systems,"In delocalized systems, particle number fluctuations, also known as quantum
surface roughness, and the mean-square displacement exhibit a temporal
power-law growth followed by a saturation to a system-size-dependent value. We
use simple scaling arguments to show that these quantities satisfy the
Family-Vicsek scaling law and derive a dynamic scaling relation between the
dynamical exponents, assuming that the saturation times of both quantities
scale similarly with the system size. This relation clarifies the mechanism
behind quantum surface roughness growth and suggests that diffusive quantum
many-body systems belong to the Edwards-Wilkinson universality class. Moreover,
it provides a convenient way to assess quantum transport in cold-atom
experiments. We numerically verify our results by studying two non-interacting
models and one interacting model having regimes with distinct dynamical
exponents.",2309.03273v1
2023-09-13,On Kostant's conjecture for components of $V(ρ)\otimes V(ρ)$,"For a complex simple Lie algebra $\mathfrak{g}$ or rank $r$, let $\rho$ be
the half sum of positive roots and $P(2\rho)\subset \mathbb{R}^r$ be the convex
hull of all dominant weights $\lambda$ of the form $\lambda=2\rho-\sum_{i=1}^r
a_i\alpha_i$ with $a_i\in \mathbb{Z}_{\geq 0}$ for $1\leq i\leq r$.
  We show that if $\lambda$ is a vertex of $P(2\rho)$, then $V(\lambda)$
appears in $V(\rho) \otimes V(\rho)$ with multiplicity one, proving partially
(for the vertices of $P(2\rho)$) a conjecture of Kostant describing components
of $V(\rho)\otimes V(\rho)$. This result allows us to give an alternative proof
for a weaker form of the conjecture (up to saturation factor) for any
$\mathfrak{g}$. Further, using works of Knutson-Tau on the saturation property
of $\mathfrak{sl_{r+1}}$, our results give an alternative proof of Kostant's
conjecture in the particular case $\mathfrak{g}=\mathfrak{sl_{r+1}}$.",2309.06890v2
2023-09-16,gym-saturation: Gymnasium environments for saturation provers (System description),"This work describes a new version of a previously published Python package -
gym-saturation: a collection of OpenAI Gym environments for guiding
saturation-style provers based on the given clause algorithm with reinforcement
learning. We contribute usage examples with two different provers: Vampire and
iProver. We also have decoupled the proof state representation from
reinforcement learning per se and provided examples of using a known ast2vec
Python code embedding model as a first-order logic representation. In addition,
we demonstrate how environment wrappers can transform a prover into a problem
similar to a multi-armed bandit. We applied two reinforcement learning
algorithms (Thompson sampling and Proximal policy optimisation) implemented in
Ray RLlib to show the ease of experimentation with the new release of our
package.",2309.09022v1
2023-10-02,"High-energy picosecond pulses with a single spatial mode from a passively mode-locked, broad-area semiconductor laser","We present a mode-locked semiconductor laser oscillator that emits few
picosecond pulses (5-8ps at 379MHz repetition) with record peak power (112W)
and pulse energy (0.5nJ) directly out of the oscillator (with no amplifier). To
achieve this high power performance we employ a high-current broad-area,
spatially multi-mode diode amplifier (0.3x5mm), placed in an external cavity
that enforces oscillation in a single spatial mode. Consequently, the
brightness of the beam is near-ideal ($M^2 = 1.3$). Mode locking is achieved by
dividing the large diode chip (edge emitter) into two sections with independent
electrical control: one large section for gain and another small section for a
saturable absorber. Precise tuning of the reverse voltage on the absorber
section allows to tune the saturation level and recovery time of the absorber,
which provides a convenient control knob to optimize the mode-locking
performance for various cavity conditions.",2310.01229v1
2023-10-04,On extra dimensions and the cosmological constant problem,"We consider a massive scalar field with a coordinate-dependent mass in
higher-dimensional spacetime. The field satisfies Dirichlet boundary conditions
on a brane representing the four-dimensional world. Despite being massive, the
theory is scale-invariant. We quantize the theory calculating the zero-point
energy. We find the lower bound for the uncertainty product in the uncertainty
principle. We show that the zero-point energy density could be small if large
extra dimensions exist. Identifying the zero-point energy as a source of dark
energy, we extract the four-dimensional cosmological constant from
higher-dimensional theory, considering quantum fluctuations close to the brane
surface. We examine numerically ten- and eleven-dimensional spaces. The
resulting zero-point energy is parameterized by the number of extra dimensions
and the additional dimensionless {\it saturation parameter}, expressing the
deviation from perfect saturation of the uncertainty principle. Letting the
parameter to be small and of order of the fine-structure constant, we reproduce
the experimental value of the cosmological constant in four dimensions.",2310.02837v2
2023-10-10,Silent White Light,"We investigate the intra-waveguide statistics manipulation of broadband light
by combining semiconductor quantum dot physics with quantum optics. By cooling
a quantum dot superluminescent diode to liquid nitrogen temperature of $77K$,
Blazek et al. [Phys. Rev. A 84, 63840 (2011)] have demonstrated a
temperature-dependent reduction of the second-order intensity correlation
coefficient from two for thermal amplified spontaneous emission light to
$g^{(2)}(T=190 K)\approx 1.33$. Here, we model the broadband photon statistics
assuming amplified spontaneous emission radiation in a pumped, saturable
quantum dot gain medium. We demonstrate that, by an intensity increase due to
the quantum dot occupation dynamics via the temperature-tuned quasi Fermi
levels, together with the saturation nonlinearity, a statistics manipulation
from thermal Bose-Einstein statistics towards Poissonian statistics can be
realized, thus producing ""silent white light"". Such intensity-noise reduced
broadband radiation is relevant for many applications like optical coherence
tomography, optical communication or optical tweezers.",2310.06834v1
2023-10-14,Safe Region Multi-Agent Formation Control With Velocity Tracking,"This paper provides a solution to the problem of safe region formation
control with reference velocity tracking for a second-order multi-agent system
without velocity measurements. Safe region formation control is a control
problem where the agents are expected to attain the desired formation while
reaching the target region and simultaneously ensuring collision and obstacle
avoidance. To tackle this control problem, we break it down into two distinct
objectives: safety and region formation control, to provide a completely
distributed algorithm. Region formation control is modeled as a high-level
abstract objective, whereas safety and actuator saturation are modeled as a
low-level objective designed independently, without any knowledge of the
former, and being minimally invasive. Our approach incorporates connectivity
preservation, actuator saturation, safety considerations, and lack of velocity
measurement from other agents with second-order system dynamics which are
important constraints in practical applications. Both internal safety for
collision avoidance among agents and external safety for avoiding unsafe
regions are ensured using exponential control barrier functions. We provide
theoretical results for asymptotic convergence and numerical simulation to show
the approach's effectiveness.",2310.09681v1
2023-10-16,Performance Enhancement via XPM Suppression in a Linear all-PM NPE Mode-locked Fiber Oscillator,"We demonstrate strong performance enhancement of an all
polarization-maintaining fiber oscillator mode-locked using NPE in a linear
self-stabilized fiber interferometer via suppression of cross-phase modulation
(XPM). Numerical simulations reveal that XPM significantly affects the
saturable absorber dynamics resulting in distortions of mode-locked
steady-states. In the experiment, we construct an oscillator with XPM
suppression, employing an intra-cavity YVO4 crystal, and compare its
characteristics with a reference oscillator in standard configuration. It is
shown, that XPM suppression not only lowers the mode-locking threshold by more
than 40%, but further results in improved spectral pulse quality at the output
ports and reduced nonlinear loss of the artificial saturable absorber.",2310.10164v1
2023-10-17,Diffractive single hadron production in a saturation framework at the NLO,"We calculate the cross-sections of diffractive single hadron photo- or
electroproduction with large $p_T$, on a nucleon or a nucleus in the shockwave
formalism. We use the hybrid formalism mixing collinear factorization with high
energy small-$x$ factorization with the impact factors computed at
next-to-leading order accuracy. We prove the cancellation of divergence and we
determine the finite parts of the differential cross-sections. We work in
general kinematics such that both photoproduction and leptoproduction are
considered. The results can be used to detect saturation effects, at both the
future EIC or already at LHC, using Ultra-Peripheral Collisions.",2310.11066v2
2023-10-19,High Dynamic Range mmWave Massive MU-MIMO with Householder Reflections,"All-digital massive multiuser (MU) multiple-input multiple-output (MIMO) at
millimeter-wave (mmWave) frequencies is a promising technology for
next-generation wireless systems. Low-resolution analog-to-digital converters
(ADCs) can be utilized to reduce the power consumption of all-digital
basestation (BS) designs. However, simultaneously transmitting user equipments
(UEs) with vastly different BS-side receive powers either drown weak UEs in
quantization noise or saturate the ADCs. To address this issue, we propose high
dynamic range (HDR) MIMO, a new paradigm that enables simultaneous reception of
strong and weak UEs with low-resolution ADCs. HDR MIMO combines an adaptive
analog spatial transform with digital equalization: The spatial transform
focuses strong UEs on a subset of ADCs in order to mitigate quantization and
saturation artifacts; digital equalization is then used for data detection. We
demonstrate the efficacy of HDR MIMO in a massive MU-MIMO mmWave scenario that
uses Householder reflections as spatial transform.",2310.12835v3
2023-10-19,Eureka-Moments in Transformers: Multi-Step Tasks Reveal Softmax Induced Optimization Problems,"In this work, we study rapid, step-wise improvements of the loss in
transformers when being confronted with multi-step decision tasks. We found
that transformers struggle to learn the intermediate tasks, whereas CNNs have
no such issue on the tasks we studied. When transformers learn the intermediate
task, they do this rapidly and unexpectedly after both training and validation
loss saturated for hundreds of epochs. We call these rapid improvements
Eureka-moments, since the transformer appears to suddenly learn a previously
incomprehensible task. Similar leaps in performance have become known as
Grokking. In contrast to Grokking, for Eureka-moments, both the validation and
the training loss saturate before rapidly improving. We trace the problem back
to the Softmax function in the self-attention block of transformers and show
ways to alleviate the problem. These fixes improve training speed. The improved
models reach 95% of the baseline model in just 20% of training steps while
having a much higher likelihood to learn the intermediate task, lead to higher
final accuracy and are more robust to hyper-parameters.",2310.12956v1
2023-10-20,Terahertz Saturable Absorption from Relativistic High-Temperature Thermodynamics in Black Phosphorus,"Thanks to its tunable infrared band-gap and to its anisotropic conduction
properties, black phosphorus represents a very unique 2D material, whose
potential in the engineering of new devices still needs to be fully explored.
We investigate here the nonlinear terahertz (THz) electrodynamics of black
phosphorus along the more conducting armchair direction. Similarly to the case
of other 2D systems like graphene and topological insulators, the THz saturable
absorption properties of black phosphorus can be understood within a
thermodynamic model by assuming a fast thermalization of the electron bath.
While black phosphorus does not display the presence of massless fermions at
ambient pressure and temperature, our analysis shows that its anomalous THz
nonlinear properties can be accounted for by a relativistic massive Dirac
dispersion, provided the Fermi temperature is low enough. An optimal tuning of
the Fermi level therefore represents a strategy to engineer strong THz
nonlinear response in other massive Dirac materials as in transition metal
dichalchogenides or high-temperature superconductors.",2310.13587v1
2023-10-27,Nonadiabatic nonlinear non-Hermitian quantized pumping,"We analyze a quantized pumping in a nonlinear non-Hermitian photonic system
with nonadiabatic driving. The photonic system is made of a waveguide array,
where the distances between adjacent waveguides are modulated. It is described
by the Su-Schrieffer-Heeger model together with a saturated nonlinear gain term
and a linear loss term. A topological interface state between the topological
and trivial phases is stabilized by the combination of a saturated nonlinear
gain term and a linear loss term. We study the pumping of the topological
interface state. We define the transfer-speed ratio $\omega /\Omega $ by the
ratio of the pumping speed $% \omega $ of the center of mass of the wave packet
to the driving speed $ \Omega $ of the topological interface. It is quantized
as $\omega /\Omega =1$ in the adiabatic limit. It remains to be quantized for
slow driving even in the nonadiabatic regime, which is a nonadiabatic quantized
pump. On the other hand, there is almost no pump for fast driving. We find a
transition in pumping as a function of the driving speed.",2310.17987v1
2023-10-27,Entanglement entropy of proton and its relation to thermodynamics entropy,"I discuss the thermodynamics-based derivation of the formula for the
entanglement entropy of a system of gluons. The derivation is based on
\cite{Kutak:2011rb}, where saturation and the Unruh effect were used to obtain
and discuss the entropy of gluons. The formula agrees, in the high-energy
limit, up to a numerical factor, with more recent results by
\cite{Kharzeev:2017qzs}, where arguments based on the density matrix and
bipartition of the proton were used to obtain the formula. Furthermore, I
present arguments based on the properties of evolution equations as to why the
saturation-based approach, as well as the double leading logarithmic limit of
BFKL, agree in the functional form of the expression for entanglement entropy.",2310.18510v2
2023-10-30,"Scalar field, nucleon structure and relativistic chiral theory for nuclear matter","The work that Peter Schuck and I carried out during the nineties in
collaboration with the Lyon and Darmstadt theory groups is summarized. I
retrace how our theoretical developments combined with experimental results
concerning the in-medium modification of the pion-pion interaction allowed a
clarification of the chiral status of the sigma meson introduced in
relativistic theories of nuclear matter. This enabled us to build a
relativistic chiral theory, now called the chiral confining model of nuclear
matter, which includes the effect of the nucleon substructure, namely the
response of the nucleon to the nuclear scalar field generating an efficient and
natural contribution to the saturation mechanism. Using parameters from a
QCD-connected version of the chiral confining model, I describe the relative
roles of the chiral scalar field and two-pion (or two-rho) exchange for the
in-medium $NN$ attractive interaction and the associated sources of three-body
interactions needed for the saturation mechanism.",2310.19532v1
2023-11-20,Nonlinear Optical Trapping of Gold Nanoparticles,"This paper presents the most complete framework to date for understanding the
nonlinear optical trapping of highly absorbing nanoparticles within the dipole
regime. Highly absorbing and plasmonic particles garner considerable interest
due to their enhanced optical interactions, yet traditional linear theory fails
to predict their trapping behavior, particularly in the longitudinal direction.
We introduce a more comprehensive theory that incorporates four-wave mixing and
two-photon absorption, addressing significant gaps in the current literature.
Our research shows TPA to be crucial for longitudinal trapping stability.
Furthermore, our findings propose a novel phenomenon of multiple split traps in
both saturable absorption and reverse saturable absorption regimes. Our
framework extends beyond existing models by including factors such as
self-induced back-action and scattering forces, aligning theoretical
predictions with experimental observations, and laying a robust foundation for
future nonlinear optical trapping and manipulation research.",2311.12135v1
2023-11-27,Effects of hyperon potentials and symmetry energy in quark deconfinement,"In this letter we discuss how the results of recent nuclear experiments that
correspond to measurements at low densities can affect the equation of state at
large densities and temperatures, changing the particle composition and
ultimately influencing deconfinement to quark matter. In particular, saturation
values of the hyperon potentials affect the hyperon content, while the symmetry
energy at saturation directly regulates how the stiffness of the equation of
state changes with isospin. We make use of a chiral model that describes
nucleons, hyperons, and quarks to show how astrophysical conditions, such as
the ones in neutron stars, present the ideal ground to study the effects of
these two quantities in dense matter. In this case, for small charge fraction/
large isospin asymmetry, the couplings that reproduce different symmetry energy
slopes can significantly modify deconfinement, with quantitative changes in the
critical chemical potential depending on the deconfining potential. On the
other hand, different values of the parameter that controls the hyperon
potentials (kept within a range close to experimental data) do not affect
deconfinement significantly.",2311.15968v3
2023-12-06,Implications of Gamma Ray Burst GRB221009A for Extra Dimensions,"Anomalous high energy photons, known as GRB221009A, with 18 TeV and 251 TeV
were observed by LHAASO and Carpet-2 recently. Such observation of high energy
gamma-ray bursts from distant source causes a mystery since high energy photons
suffer severe attenuation before reaching the earth. One possibility is the
existence of axion-like particles (ALP), and high energy photons at the source
can convert to these ALPs which travel intergalactically. In this paper, we
study the effects of extra dimensions on the conversion probability between
photon and ALPs. The conversion probability saturates and may reach almost
$100\%$ for high energy photons. We show that the size of extra dimension
affects the energy at which saturation occurs. The observations of high-energy
photons may support the possibility of smaller extra dimension.",2312.03314v1
2023-12-07,Energy dependent nuclear suppression from gluon saturation in exclusive vector meson production,"We calculate the exclusive $\mathrm{J}/\psi$ photoproduction cross section at
high energies from the Color Glass Condensate approach. The results are
compared to the center-of-mass energy dependent $\gamma+A\to\mathrm{J}/\psi+A$
cross sections extracted from measurements in ultra peripheral heavy ion
collisions at RHIC and LHC. We predict strong saturation-driven nuclear
suppression at high energies, while LHC data prefers even stronger suppression.
We explore the effect of nucleon shape fluctuations on the nuclear suppression
in the coherent and incoherent cross sections, and show that the most recent
measurement of the $|t|$-differential incoherent $\mathrm{J}/\psi$ cross
section prefers large event-by-event fluctuations of the nucleon substructure
in heavy nuclei, comparable to that found for a free proton.",2312.04194v1
2023-12-11,Cryogenic RPWELL: a novel charge-readout element for dual-phase argon TPCs,"The first operation of a cryogenic Resistive Plate WELL (RPWELL) detector in
the saturated vapor of liquid argon is reported. The RPWELL detector was
composed of a Thick Gas Electron Multiplier (THGEM) electrode coupled to a
metallic anode via Fe$_2$O$_3$/YSZ ceramics (Fe$_2$O$_3$ in weight equal to
75$\%$), with tunable bulk resistivity in the range 10$^{9}$ - 10$^{12}$
$\Omega\cdot$cm. The detector was operated at liquid argon temperature in
saturated argon vapor (90~K, 1.2~bar) and characterized in terms of its
effective charge gain and stability against discharges. Maximum stable gain of
G$\approx$17 was obtained, without discharges. In addition, preliminary results
from novel 3D-printed thermoplastic plates doped with carbon nanotubes are
presented.",2312.06809v1
2023-12-13,Mapping the influence of impurities with varying interaction strength on nucleation in the 2D Ising model,"We study nucleation of magnetisation reversal in the two dimensional Ising
model at non-zero external field and in the presence of randomly placed static
and dynamic impurities. Impurity-spin interaction strengths are varied fixing
other interaction strengths. We observe a decrease in the nucleation rate when
the total interaction strength with impurities is decreased in the case of
static impurities. The nucleation rate saturates with respect to interaction
strength when the impurity density is low. However the nucleation rate does not
saturate for high impurity density. Similar behaviour is observed with dynamic
impurities both at low and high densities. We explore a broad range of both
spin-symmetric and spin-antisymmetric interaction strengths and map the regime
for which the impurities act as a surfactant, decreasing the surface energy of
the nucleating phase. We also characterise different nucleation regimes
observed at different values of interaction strength. These include regimes
where impurities are included or excluded from the nucleus, and a region in
which we observe cross nucleation of impurity clusters at the nucleus boundary.",2312.08342v1
2023-12-14,Anisotropic swelling due to hydration in fibrous biomaterials,"Naturally occurring protein fibres often undergo anisotropic swelling when
hydrated. Within a tendon, a hydrated collagen fibril's radius expands by 40\%
but its length only increases by 5\%. The same effect, with similar magnitude,
is observed for keratin microfibrils within hair. Nevertheless, current
explanations for swelling anisotropy are based on molecular details that are
unique to each material. Here, we describe a coarse-grained liquid-crystalline
elastomer model for biomaterial hydration that allows for anisotropic swelling.
We show that our model is consistent with previously observed behavior for both
hair fibers and collagen fibrils. Despite a non-linear relationship between
water saturation and relative humidity, we find that the squared deformation in
the axial and radial directions is approximately linear with water saturation.
We further find that anisotropic swelling is linear with respect to volume and
shape changes. Hair and collagen exhibit remarkably similar behavior under
hydration. We suggest that our model may also be useful for other biomaterials
that exhibit anisotropic swelling.",2312.08771v1
2023-12-18,Krylov complexity for non-local spin chains,"Building upon recent research in spin systems with non-local interactions,
this study investigates operator growth using the Krylov complexity in
different non-local versions of the Ising model. We find that the non-locality
results in a faster scrambling of the operator to all sites. While the
saturation value of Krylov complexity of local integrable and local chaotic
theories differ by a significant margin, this difference is much suppressed
when non-local terms are introduced in both regimes. This results from the
faster scrambling of information in the presence of non-locality. In addition,
we investigate the behavior of level statistics and spectral form factor as
probes of quantum chaos to study the integrability breaking due to non-local
interactions. Our numerics indicate that in the non-local case, late time
saturation of Krylov complexity distinguishes between different underlying
theories, while the early time complexity growth distinguishes different
degrees of non-locality.",2312.11677v2
2023-12-19,Solvable entanglement dynamics in quantum circuits with generalized dual unitarity,"We study the non-equilibrium dynamics of kicked Ising models in $1+1$
dimensions which have interactions alternating between odd and even bonds in
time. These models give rise to time-evolution equivalent to quantum circuits
having both the global property of tri-unitarity (three 'arrows of time') and
also the local property of second-level dual-unitarity, which constrains the
behavior of pairs of local gates underlying the circuit under a space-time
rotation. We identify a broad class of initial product states wherein the
effect of the environment on a small subsystem can be exactly represented by
influence matrices with simple Markovian structures, resulting in the
subsystem's full dynamics being efficiently computable. We further find
additional conditions under which the dynamics of entanglement can be solved
for all times, yielding rich phenomenology ranging from linear growth at half
the maximal speed allowed by locality, followed by saturation to maximum
entropy (i.e., thermalization to infinite temperature); to entanglement growth
with saturation to extensive but sub-maximal entropy. Our findings extend our
knowledge of interacting quantum systems whose thermalizing dynamics can be
efficiently and analytically computed, going beyond the well-known examples of
integrable models, Clifford circuits, and dual-unitary circuits.",2312.12239v1
2023-12-19,The entanglement membrane in exactly solvable lattice models,"Entanglement membrane theory is an effective coarse-grained description of
entanglement dynamics and operator growth in chaotic quantum many-body systems.
The fundamental quantity characterizing the membrane is the entanglement line
tension. However, determining the entanglement line tension for microscopic
models is in general exponentially difficult. We compute the entanglement line
tension in a recently introduced class of exactly solvable yet chaotic unitary
circuits, so-called generalized dual-unitary circuits, obtaining a non-trivial
form that gives rise to a hierarchy of velocity scales with $v_E<v_B$. We find
that these circuits saturate certain bounds on entanglement growth that are
also saturated in holographic models. Furthermore, we relate the entanglement
line tension to temporal entanglement and correlation functions. We also find
new methods of constructing generalized dual-unitary gates beyond qubits that
display behavior unique to local dimension $\geq3$. Our results shed light on
entanglement membrane theory in microscopic Floquet lattice models and enable
us to perform non-trivial checks on the validity of its predictions by
comparison to exact and numerical calculations.",2312.12509v1
2023-12-19,"An integrated EOS, pore-crush, strength and damage model framework for near-field ground-shock","An integrated Equation of State (EOS) and strength/pore-crush/damage model
framework is provided for modeling near to source (near-field) ground-shock
response, where large deformations and pressures necessitate coupling EOS with
pressure-dependent plastic yield and damage. Nonlinear pressure-dependence of
strength up to high-pressures is combined with a Modified Cam-Clay-like
cap-plasticity model in a way to allow degradation of strength from pore-crush
damage, what we call the ""Yp-Cap"" model. Nonlinear hardening under compaction
allows modeling the crush-out of pores in combination with a fully saturated
EOS, i.e., for modeling partially saturated ground-shock response, where
air-filled voids crush. Attention is given to algorithmic clarity and
efficiency of the provided model, and the model is employed in example
numerical simulations, including finite element simulations of underground
explosions to exemplify its robustness and utility.",2312.12577v2
2023-12-29,Latent Idiom Recognition for a Minimalist Functional Array Language using Equality Saturation,"Accelerating programs is typically done by recognizing code idioms matching
high-performance libraries or hardware interfaces. However, recognizing such
idioms automatically is challenging. The idiom recognition machinery is
difficult to write and requires expert knowledge. In addition, slight
variations in the input program might hide the idiom and defeat the recognizer.
  This paper advocates for the use of a minimalist functional array language
supporting a small, but expressive, set of operators. The minimalist design
leads to a tiny sets of rewrite rules, which encode the language semantics.
Crucially, the same minimalist language is also used to encode idioms. This
removes the need for hand-crafted analysis passes, or for having to learn a
complex domain-specific language to define the idioms.
  Coupled with equality saturation, this approach is able to match the core
functions from the BLAS and PyTorch libraries on a set of computational
kernels. Compared to reference C kernel implementations, the approach produces
a geometric mean speedup of 1.46x for C programs using BLAS, when generating
such programs from the high-level minimalist language.",2312.17682v1
2023-12-31,Improvement on the Linearity Response of PandaX-4T with new Photomultiplier Tubes Bases,"With the expanding reach of physics, xenon-based detectors such as PandaX-4T
in the China Jinping Underground Laboratory aim to cover an energy range from
sub-keV to multi-MeV. A linear response of the photomultiplier tubes (PMTs) is
required for both scintillation and electroluminescence signals. Through a
dedicated bench test, we investigated the cause of the non-linear response in
the Hamamatsu R11410-23 PMTs used in PandaX-4T. The saturation and suppression
of the PMT waveform observed during the commissioning of PandaX-4T were caused
by the high-voltage divider base. The bench test data validated the
de-saturation algorithm used in the PandaX-4T data analysis. We also confirmed
the improvement in linearity of a new PMT base design, which will be used to
upgrade the PMT readout system in PandaX-4T.",2401.00373v1
2024-01-26,Newton polytopes of dual $k$-Schur polynomials,"Rado's theorem about permutahedra and dominance order on partitions reveals
that each Schur polynomial is M-convex, or equivalently, it has a saturated
Newton polytope and this polytope is a generalized permutahedron as well. In
this paper we show that the support of each dual $k$-Schur polynomial indexed
by a $k$-bounded partition coincides with that of the Schur polynomial indexed
by the same partition, and hence the two polynomials share the same saturated
Newton polytope. The main result is based on our recursive algorithm to
generate a semistandard $k$-tableau for a given shape and $k$-weight. As
consequences, we obtain the M-convexity of dual $k$-Schur polynomials, affine
Stanley symmetric polynomials and cylindric skew Schur polynomials.",2401.14632v1
2024-01-28,New exact analytical solution of the nonlinear Gribov-Levin-Ryskin-Mueller-Qiu equation,"The GLR-MQ equation is a nonlinear evolution equation that takes into account
the shadowing effect, which tames the growth of the gluon at small-$x$. In this
study, we analytically solve for the first time the nonlinear GLR-MQ equation
using the homogeneous balance method. The definite solution of the GLR-MQ
equation is obtained by fitting the MSTW2008LO gluon distribution data. We find
that the geometric scaling is an intrinsic property of our analytical solution
and the gluon distribution functions from our solution are able to reproduce
the MSTW2008LO data. These results indicate that our analytical solution from
the homogeneous balance method is valid to describe the gluon behavior at
small-$x$. Moreover, the saturation scale $Q_s$ has been extracted from our
analytical solution, we find that the energy-dependent saturation scale obeys
the exponential law $Q_s^2\,\propto\,Q_0^2 e^{\lambda Y}$.",2401.15651v1
2024-01-28,Improvements of readout signal integrity in mid-infrared superconducting nanowire single photon detectors,"Superconducting nanowire single-photon detectors (SNSPDs) with high timing
resolution and low background counts in the mid infrared (MIR) have the
potential to open up numerous opportunities in fields such as exoplanet
searches, direct dark matter detection, physical chemistry, and remote sensing.
One challenge in pushing SNSPD sensitivity to the MIR is a decrease in the
signal-to-noise ratio (SNR) of the readout signal as the critical currents
become increasingly smaller. We overcome this trade-off with a new device
architecture that employs impedance matching tapers and superconducting
nanowire avalanche photodetectors to demonstrate increased SNR while
maintaining saturated internal detection efficiency at 7.4 {\mu}m and getting
close to saturation at 10.6 {\mu}m. This work provides a novel platform for
pushing SNSPD sensitivity to longer wavelengths while improving the scalability
of the readout electronics.",2401.15764v1
2024-01-29,A theory-independent bound saturated by quantum mechanics,"Tsirelson's original inequality for the precession protocol, first introduced
for the harmonic oscillator but applicable to all uniformly-precessing systems,
serves as a monopartite test of quantumness. Given that the system is
undergoing a uniform precession, the signs of the positions of a classical
oscillator must satisfy that inequality, which is violated by certain quantum
states. We consider this inequality for measurements with finitely many
outcomes in a theory-independent manner. We derive a general bound which
depends only on the minimum positive and negative values of the spectrum of the
observable. Given any such two values, we construct a quantum observable that
saturates this bound. A notable example is the angular momentum of a spin-$3/2$
particle. We also relate our findings to the recently-introduced notion of
constrained conditional probabilities.",2401.16147v1
2023-12-25,New characterizations for supersolvability of fusion system and $p$-nilpotency of finite groups,"Let $p$ be a prime, $S$ be a $p$-group and $\mathcal{F}$ be a saturated
fusion system over $S$. Then $\mathcal{F}$ is said to be supersolvable, if
there exists a series of $S$, namely $1 = S_0 \leq S_1 \leq \cdots \leq S_n =
S$, such that $S_{i+1}/S_i$ is cyclic, $i=0,1,\cdots, n-1$, $S_i$ is strongly
$\mathcal{F}$-closed, $i=0,1,\cdots,n$. In this paper, we investigate the
characterizations for supersolvability of $\mathcal{F}_S (G)$ under the
assumption that certain subgroups of $G$ satisfy different kinds of generalized
normalities in section \ref{1003}. Moreover, we obtain the more advanced and
remarkable result of characterizations for generalized saturated fusion system
$\mathcal{F}$ in section \ref{Section 4}. Finally, we apply the results in
section \ref{1003} and \ref{Section 4} and give characterizations for
$p$-nilpotency of finite groups under the assumption that some subgroups of $G$
satisfy different kinds of generalized normalities.",2402.01073v3
2024-02-02,Confinement in the Transverse Field Ising model on the Heavy Hex lattice,"We study the emergence of confinement in the transverse field Ising model on
a decorated hexagonal lattice. Using an infinite tensor network state optimised
with belief propagation we show how a quench from a broken symmetry state leads
to striking nonthermal behaviour underpinned by persistent oscillations and
saturation of the entanglement entropy. We explain this phenomenon by
constructing a minimal model based on the confinement of elementary
excitations, which take the form of various flavors of hadronic quasiparticles
due to the unique structure of the lattice. Our model is in excellent agreement
with our numerical results. For quenches to larger values of the transverse
field and/or from non-symmetry broken states, our numerical results displays
the expected signatures of thermalisation: a linear growth of entanglement
entropy in time, propagation of correlations and the saturation of observables
to their thermal averages. These results provide a physical explanation for the
unexpected simulability of a recent large scale quantum computation.",2402.01558v2
2024-02-02,Efficiency of neural quantum states in light of the quantum geometric tensor,"Neural quantum state (NQS) ans\""atze have shown promise in variational Monte
Carlo algorithms by their theoretical capability of representing any quantum
state. However, the reason behind the practical improvement in their
performance with an increase in the number of parameters is not fully
understood. In this work, we systematically study the efficiency of restricted
Boltzmann Machines (RBMs) to represent the ground states in different phases of
the spin-1 bilinear-biquadratic model, as the hidden layer density $\alpha$
increases. We train our ansatz by minimizing two different loss functions: 1)
energy, and 2) infidelity of the NQS ansatz w.r.t. that of the exact ground
state. We observe that the accuracy of our ansatz saturates with $\alpha$ in
both cases. We demonstrate that this can be explained by looking at the
spectrum of the quantum geometric tensor (QGT). We find that the rank of the
QGT saturates beyond a certain $\alpha$, and we emphasize that it corresponds
to the \textit{dimension of the relevant manifold} for an optimized NQS. This
provides a useful diagnostics for the practical representation power of an NQS
ansatz.",2402.01565v2
2024-02-05,Nonlocal growth of quantum conditional mutual information under decoherence,"Local measurements cannot create entanglement, but they can convert
short-range entanglement to long-range entanglement, as in quantum
teleportation. This phenomenon of measurement-induced entanglement (MIE) has
been widely discussed in recent work on measurement-induced entanglement phase
transitions and related phenomena. Here, we situate MIE in a broader context of
the growth of long-range conditional mutual information (CMI) under
decoherence. We upper-bound the rate at which decoherence can generate
long-range CMI, and derive a characterization of states that saturate this
bound. We point out that the structure of states saturating the CMI upper bound
can be very different under different decoherent dynamics and provide explicit
examples. We additionally explore the dynamics of CMI in random quantum
circuits subject to random local decoherence, as a function of circuit depth.
We argue that the universality class of the finite-depth teleportation
transition, as well as its lower critical dimension, are different for erasures
than for measurements.",2402.03439v1
2024-03-12,Predicting the Slowing of Stellar Differential Rotation by Instability-Driven Turbulence,"Differentially rotating stars and planets transport angular momentum
internally due to turbulence at rates that have long been a challenge to
predict reliably. We develop a self-consistent saturation theory, using a
statistical closure approximation, for hydrodynamic turbulence driven by the
axisymmetric Goldreich--Schubert--Fricke (GSF) instability at the stellar
equator with radial differential rotation. This instability arises when fast
thermal diffusion eliminates the stabilizing effects of buoyancy forces in a
system where a stabilizing entropy gradient dominates over the destabilizing
angular momentum gradient. Our turbulence closure invokes a dominant three-wave
coupling between pairs of linearly unstable eigenmodes and a near-zero
frequency, viscously damped eigenmode that features latitudinal jets. We derive
turbulent transport rates of momentum and heat, and provide them in analytic
forms. Such formulae, free of tunable model parameters, are tested against
direct numerical simulations; the comparison shows good agreement. They improve
upon prior quasi-linear or ``parasitic saturation"" models containing a free
parameter. Given model correspondences, we also extend this theory to heat and
compositional transport for axisymmetric thermohaline instability-driven
turbulence in certain regimes.",2403.07395v1
2024-03-12,Maxwell's Demon at Work: Efficient Pruning by Leveraging Saturation of Neurons,"When training deep neural networks, the phenomenon of $\textit{dying
neurons}$ $\unicode{x2013}$units that become inactive or saturated, output zero
during training$\unicode{x2013}$ has traditionally been viewed as undesirable,
linked with optimization challenges, and contributing to plasticity loss in
continual learning scenarios. In this paper, we reassess this phenomenon,
focusing on sparsity and pruning. By systematically exploring the impact of
various hyperparameter configurations on dying neurons, we unveil their
potential to facilitate simple yet effective structured pruning algorithms. We
introduce $\textit{Demon Pruning}$ (DemP), a method that controls the
proliferation of dead neurons, dynamically leading to network sparsity.
Achieved through a combination of noise injection on active units and a
one-cycled schedule regularization strategy, DemP stands out for its simplicity
and broad applicability. Experiments on CIFAR10 and ImageNet datasets
demonstrate that DemP surpasses existing structured pruning techniques,
showcasing superior accuracy-sparsity tradeoffs and training speedups. These
findings suggest a novel perspective on dying neurons as a valuable resource
for efficient model compression and optimization.",2403.07688v1
2024-03-22,A Surface Hydrothermal Source of Nitriles and Isonitriles,"Giant impacts can generate transient hydrogen-rich atmospheres, reducing
atmospheric carbon. The reduced carbon will form hazes that rain out onto the
surface and can become incorporated into the crust. Once heated, a large
fraction of the carbon would be converted into graphite. The result is that
local regions of the Hadean crust were plausibly saturated with graphite. We
explore the consequences of such a crust for a prebiotic surface hydrothermal
vent scenario. We model a surface vent fed by nitrogen-rich volcanic gas from
high-temperature magmas passing through graphite-saturated crust. We consider
this occurring at pressures of 1-1000 bar and temperatures of 1500-1700 degC.
The equilibrium with graphite purifies the left-over gas, resulting in
substantial quantities of nitriles (0.1% HCN and 1 ppm HC3N) and isonitriles
(0.01% HNC) relevant for prebiotic chemistry. We use these results to predict
gas-phase concentrations of methyl isonitrile of ~ 1 ppm. Methyl isocyanide can
participate in the non-enzymatic activation and ligation of the monomeric
building blocks of life, and surface, or shallow, hydrothermal environments
provide its only known equilibrium geochemical source.",2403.15135v2
2024-03-31,There and Back Again: A Netlist's Tale with Much Egraphin',"EDA toolchains are notoriously unpredictable, incomplete, and error-prone;
the generally-accepted remedy has been to re-imagine EDA tasks as compilation
problems. However, any compiler framework we apply must be prepared to handle
the wide range of EDA tasks, including not only compilation tasks like
technology mapping and optimization (the ""there""} in our title), but also
decompilation tasks like loop rerolling (the ""back again""). In this paper, we
advocate for equality saturation -- a term rewriting framework -- as the
framework of choice when building hardware toolchains. Through a series of case
studies, we show how the needs of EDA tasks line up conspicuously well with the
features equality saturation provides.",2404.00786v1
2024-04-01,Universal Bound on Effective Central Charge and Its Saturation,"The effective central charge (denoted by $c_{\text{eff}}$) is a measure of
entanglement through a conformal interface, while the transmission coefficient
(encoded in the coefficient $c_{LR}$ of the two-point function of the
energy-momentum tensor across the interface) is a measure of energy
transmission through the interface. It has been pointed out that these two are
generally different. In this article, we propose the inequalities, $0 \leq
c_{LR} \leq c_{\text{eff}} \leq \min (c_L,c_R)$. They have the simple but
important implication that the amount of energy transmission can never exceed
the amount of information transmission. We verify them using the AdS/CFT
correspondence and in examples beyond holography. We also show that these
inequalities are sharp by constructing a class of interfaces that saturate
them.",2404.01515v1
2024-04-04,Nuclear Matter Equation of State in the Brueckner-Hartree-Fock Approach and Standard Skyrme Energy-Density Functionals,"The equation of state of asymmetric nuclear matter as well as the neutron and
proton effective masses and their partial-wave and spin-isospin decomposition
are analyzed within the Brueckner--Hartree--Fock approach. Theoretical
uncertainties for all these quantities are estimated by using several
phase-shift-equivalent nucleon-nucleon forces together with two types of
three-nucleon forces, phenomenological and microscopic. It is shown that the
choice of the three-nucleon force plays an important role above saturation
density, leading to different density dependencies of the energy per particle.
These results are compared to the standard form of the Skyrme energy-density
functional and we find that it is not possible to reproduce the BHF predictions
in the $(S,T)$ channels in symmetric and neutron matter above saturation
density, already at the level of the two-body interaction, and even more
including the three-body interaction.",2404.03583v1
2003-05-06,How Spectral Shapes of Magnetic Energy and Magnetic Helicity Influence their Respective Decay Time Scales,"It is shown that in magnetohydrodynamics, the shapes of the magnetic energy
and magnetic helicity spectra can influence whether the magnetic helicity
resistive dissipation time scale is longer, equal to, or shorter than that of
magnetic energy. The calculations highlight that magnetic helicity need not
always dissipate significantly more slowly than magnetic energy. While this may
be implicitly understood in detailed studies of magnetic helicity in plasma
devices, it is not sufficiently emphasized in elementary discussions comparing
magnetic helicity vs. magnetic energy evolution. Measuring magnetic energy and
helicity decay times may provide a posteriori insight into the initial spectra.",0305069v2
2000-04-26,Magnetic relaxation and magnetization field dependence measurements in La0.5Ca0.5MnO3,"We reported a systematic change in the average magnetic relaxation rate,
after the application and removal of a 5 T magnetic field, in a polycrystalline
sample of La0.5Ca0.5MnO3. Magnetic relaxation measurements and magnetization
versus field curves were taken from 10 K to 160 K. The long time behavior of
the relaxation curves was approximately logarithmic in all cases. Keywords:
Charge Ordering, Relaxation, Magnetic measurements",0004460v2
2004-08-30,Optical Studies of Zero-Field Magnetization of CdMnTe Quantum Dots: Influence of Average Size and Composition of Quantum Dots,"We show that through the resonant optical excitation of spin-polarized
excitons into CdMnTe magnetic quantum dots, we can induce a macroscopic
magnetization of the Mn impurities. We observe very broad (4 meV linewidth)
emission lines of single dots, which are consistent with the formation of
strongly confined exciton magnetic polarons. Therefore we attribute the
optically induced magnetization of the magnetic dots results to the formation
of spin-polarized exciton magnetic polarons. We find that the photo-induced
magnetization of magnetic polarons is weaker for larger dots which emit at
lower energies within the QD distribution. We also show that the photo-induced
magnetization is stronger for quantum dots with lower Mn concentration, which
we ascribe to weaker Mn-Mn interaction between the nearest neighbors within the
dots. Due to particular stability of the exciton magnetic polarons in QDs,
where the localization of the electrons and holes is comparable to the magnetic
exchange interaction, this optically induced spin alignment persists to
temperatures as high as 160 K.",0408658v1
2005-04-23,New Method to Calculate the Sign and Relative Strength of Magnetic Interactions in Low-Dimensional Systems on the Basis of Structural Data,"The connection of strength of magnetic interactions and type ordering the
magnetic moments with crystal chemical characteristics in low-dimensional
magnets is investigated. The new method to calculate the sign and relative
strength of magnetic interactions in low-dimensional systems on the basis of
the structural data is proposed. This method allows to estimate magnetic
interactions not only inside low-dimensional fragments but also between them,
and also to predict the possibility of the occurrence of magnetic phase
transitions and anomalies of the magnetic interactions. Moreover, it can be
used for search of low-dimensional magnets among the compounds whose crystal
structures are known. The possibilities of the method are illustrated in an
example of research of magnetic interactions in familiar low-dimensional
magnets SrCu2(BO3)2, CaCuGe2O6, CaV4O9, Cu2Te2O5Cl2, Cu2Te2O5Br2, BaCu2Si2O7,
BaCu2Ge2O7, BaCuSi2O6, LiCu2O2, and NaCu2O2.",0504599v3
2006-02-14,Semiclassical pseudodifferential calculus and the reconstruction of a magnetic field,"We give a procedure for reconstructing a magnetic field and electric
potential from boundary measurements related to the magnetic Schroedinger
operator in three and higher dimensions.",0602290v1
1999-01-29,Gravimetric Measurement of Magnetic Field Gradient Spatial Distribution,"Magnetic interaction between a weighing sample and an external magnetic field
allows to measure characteristics of magnetic field (a sample with known
magnetic characteristics), as well as the magnetic properties of a sample (a
known magnetic field). Measurement of materials magnetic permeability is a well
known application of this method. In this paper we restrict ourselves to the
measurement of magnetic field spatial distribution, which was achieved by
scanning of samples from known materials along the vertical axis. Field
measurements by Hall detector were done to calibrate obtained data. Such
measurements are of great interest in some branches of physics, in particular,
in accelerator physics, where the quality of magnetic system parts eventually
determine the quality of accelerated bunches. Development of a simple and cheep
device for measurement of magnetic field spatial distribution is an urgent
problem. The developed system for gravimetric measurement of magnetic field
gradients partially solves this problem.",9901058v1
1999-05-06,A Brief Note on Jupiter's Magnetism,"A recent model which gives the contribution of the earth's solid core to geo
magnetism is seen to explain Jupiter's magnetism also.",9905014v1
2008-01-30,How to use magnetic field information for coronal loop identification?,"The structure of the solar corona is dominated by the magnetic field because
the magnetic pressure is about four orders of magnitude higher than the plasma
pressure. Due to the high conductivity the emitting coronal plasma (visible
e.g. in SOHO/EIT) outlines the magnetic field lines. The gradient of the
emitting plasma structures is significantly lower parallel to the magnetic
field lines than in the perpendicular direction. Consequently information
regarding the coronal magnetic field can be used for the interpretation of
coronal plasma structures. We extrapolate the coronal magnetic field from
photospheric magnetic field measurements into the corona. The extrapolation
method depends on assumptions regarding coronal currents, e.g. potential fields
(current free) or force-free fields (current parallel to magnetic field). As a
next step we project the reconstructed 3D magnetic field lines on an EIT-image
and compare with the emitting plasma structures. Coronal loops are identified
as closed magnetic field lines with a high emissivity in EIT and a small
gradient of the emissivity along the magnetic field.",0801.4573v1
2011-02-23,Possibility of conversion of neutron star to quark star in presence of high magnetic field,"Recent results and data suggests that high magnetic field in neutron stars
(NS) strongly affects the characteristic (radius, mass) of the star. They are
even separated as a class known as magnetars, for whom the surface magnetic
field are greater than $10^{14}$ G. In this work we discuss the effect of such
high magnetic field on the phase transition of NS to quark star (QS). We study
the effect of magnetic field on the transition from NS to QS including the
magnetic field effect in equation of state (EoS). The inclusion of the magnetic
field increases the range of baryon number density, for which the flow
velocities of the matter in the respective phase are finite. The magnetic field
helps in initiation of the conversion process. The velocity of the conversion
front however decreases due to the presence of magnetic field, as the presence
of magnetic field reduces the effective pressure (P). The magnetic field of the
star gets decreased by the conversion process, and the resultant QS has lower
magnetic field than that of the initial NS.",1102.4660v2
2011-03-06,"The Influence of Magnetic Anisotropy on the Kondo Effect and Spin-Polarized Transport through Magnetic Molecules, Adatoms and Quantum Dots","Transport properties in the Kondo regime of a nanosystem displaying uniaxial
magnetic anisotropy (such as a magnetic molecule, magnetic adatom or quantum
dot coupled to a localized magnetic moment) are analyzed theoretically. In
particular, the influence of spin-polarized transport through a local orbital
of the system and exchange coupling of conduction electrons to the system's
magnetic core on the Kondo effect is discussed. The numerical renormalization
group method is applied to calculate the spectral functions and linear
conductance in the case of the parallel and antiparallel configurations of the
electrodes' magnetic moments. It is shown that both the magnetic anisotropy as
well as the exchange coupling between electrons tunneling through the
conducting orbital and magnetic core play an important role in formation of the
Kondo resonance, leading generally to its suppression. Specific transport
properties of such a system appear also as a nontrivial behavior of tunnel
magnetoresistance. It is also shown that the Kondo effect can be restored by an
external magnetic field in both the parallel and antiparallel magnetic
configurations.",1103.1128v2
2011-03-18,Study of the interplay between magnetic shear and resonances using Hamiltonian models for the magnetic field lines,"The issue of magnetic confinement in magnetic fusion devices is addressed
within a purely magnetic approach. Using some Hamiltonian models for the
magnetic field lines, the dual impact of low magnetic shear is shown in a
unified way. Away from resonances, it induces a drastic enhancement of magnetic
confinement that favors robust internal transport barriers (ITBs) and
stochastic transport reduction. When low-shear occurs for values of the winding
of the magnetic field lines close to low-order rationals, the amplitude
thresholds of the resonant modes that break internal transport barriers by
allowing a radial stochastic transport of the magnetic field lines may be quite
low. The approach can be applied to assess the robustness versus magnetic
perturbations of general (almost) integrable magnetic steady states, including
non-axisymmetric ones such as the important single helicity steady states. This
analysis puts a constraint on the tolerable mode amplitudes compatible with
ITBs and may be proposed as a possible explanation of diverse experimental and
numerical signatures of their collapses.",1103.3595v1
2012-04-26,Axisymmetric and stationary structures of magnetized barotropic stars with extremely strong magnetic fields deep inside,"We have succeeded in obtaining magnetized star models that have extremely
strong magnetic fields in the interior of the star. In our formulation,
arbitrary functions of the magnetic flux function appear in the expression for
the current density. By appropriately choosing the functional form for one of
the arbitrary functions that corresponds to the distribution of the toroidal
current density, we have obtained configurations with magnetic field
distributions that are highly localized within the central part and near the
magnetic axis region. The absolute values of the central magnetic fields are
stronger than those of the surface region by two orders of magnitude. By
applying our results to magnetars, the internal magnetic poloidal fields could
be 10^17 G, although the surface magnetic fields are about 10^15 G in the case
of magnetars. For white dwarfs, the internal magnetic poloidal fields could be
10^12 G, when the surface magnetic fields are 10^9-10^10 G .",1204.5830v2
2014-08-05,Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films,"We investigate the magnetization dynamics through the magnetoimpedance effect
in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance
response is dependent on the thickness of the non-magnetic Cu spacer material,
a fact associated to the kind of the magnetic interaction between the
ferromagnetic layers. Thus, we present an experimental study on asymmetric
magnetoimpedance in ferromagnetic films with biphase magnetic behavior and
explore the possibility of tuning the linear region of the magnetoimpedance
curves around zero magnetic field by varying the thickness of the non-magnetic
spacer material, and probe current frequency. We discuss the experimental
magnetoimpedance results in terms of the different mechanisms governing the
magnetization dynamics at distinct frequency ranges, quasi-static magnetic
properties, thickness of the non-magnetic spacer material, and the kind of the
magnetic interaction between the ferromagnetic layers. The results place
ferromagnetic films with biphase magnetic behavior exhibiting asymmetric
magnetoimpedance effect as a very attractive candidate for application as probe
element in the development of auto-biased linear magnetic field sensors.",1408.0992v1
2014-10-10,Comparison of adjustable permanent magnetic field sources,"A permanent magnet assembly in which the flux density can be altered by a
mechanical operation is often significantly smaller than comparable
electromagnets and also requires no electrical power to operate. In this paper
five permanent magnet designs in which the magnetic flux density can be altered
are analyzed using numerical simulations, and compared based on the generated
magnetic flux density in a sample volume and the amount of magnet material
used. The designs are the concentric Halbach cylinder, the two half Halbach
cylinders, the two linear Halbach arrays and the four and six rod mangle. The
concentric Halbach cylinder design is found to be the best performing design,
i.e. the design that provides the most magnetic flux density using the least
amount of magnet material. A concentric Halbach cylinder has been constructed
and the magnetic flux density, the homogeneity and the direction of the
magnetic field are measured and compared with numerical simulation and a good
agreement is found.",1410.2681v1
2014-11-25,Computing with spins and magnets,"The possible use of spin and magnets in place of charge and capacitors to
store and process information is well known. Magnetic tunnel junctions are
being widely investigated and developed for magnetic random access memories.
These are two terminal devices that change their resistance based on switchable
magnetization of magnetic materials. They utilize the interaction between
electron spin and magnets to read information from the magnets and write onto
them. Such advances in memory devices could also translate into a new class of
logic devices that offer the advantage of nonvolatile and reconfigurable
information processing over transistors. Logic devices having a transistor-like
gain and directionality could be used to build integrated circuits without the
need for transistor-based amplifiers and clocks at every stage. We review
device characteristics and basic logic gates that compute with spins and
magnets from the mesoscopic to the atomic scale, as well as materials,
integration, and fabrication challenges and methods.",1411.6960v1
2015-02-27,RC-circuit-like dynamic characteristic of the magnetic domain wall in ferromagnetic nanowires,"We have investigated dynamic behaviors of the magnetic domain wall under
perpendicular magnetic field pulses in ferromagnetic nanowires using
micromagnetic simulations. It has been found that the perpendicular magnetic
field pulse can trigger the magnetic domain wall motion, where all the field
torques are kept to be on the plane of nanowire strip. The magnetic domain wall
speed faster than several hundreds meters per second is predicted without the
Walker breakdown for the perpendicular magnetic driving field stronger than
$200~\mathrm{mT}$. Interestingly, the dynamic behavior of the moving magnetic
domain wall driven by perpendicular magnetic field pulses is explained by
charging- and discharging-like behaviors of an electrical RC-circuit model,
where the charging and the discharging of ""magnetic charges"" on the nanowire
planes are considered. The concept of the RC-model-like dynamic characteristic
of the magnetic domain wall might be promising for spintronic functional device
applications based on the magnetic domain wall motion.",1502.07807v1
2015-03-30,Effects of non-radial magnetic field on measuring magnetic helicity transport across solar photosphere,"It is generally believed that the evolution of magnetic helicity has a close
relationship with solar activity. Before the launch of SDO, earlier studies
have mostly used MDI/SOHO line of sight magnetograms and assumed that magnetic
fields are radial when calculating magnetic helicity injection rate from
photospheric magnetograms. However, this assumption is not necessarily true.
Here we use the vector magnetograms and line of sight magnetograms, both taken
by HMI/SDO, to estimate the effects of non-radial magnetic field on measuring
magnetic helicity injection rate. We find that: 1) The effect of non-radial
magnetic field on estimating tangential velocity is relatively small; 2) On
estimating magnetic helicity injection rate, the effect of non-radial magnetic
field is strong when active regions are observed near the limb and is
relatively small when active regions are close to disk center; 3) The effect of
non-radial magnetic field becomes minor if the amount of accumulated magnetic
helicity is the only concern.",1503.08563v1
2015-08-18,A self-consistent study of magnetic field effects on hybrid stars,"In this work we study the effects of strong magnetic fields on hybrid stars
by using a full general-relativity approach, solving the coupled
Maxwell-Einstein equation in a self-consistent way. The magnetic field is
assumed to be axi-symmetric and poloidal. We take into consideration the
anisotropy of the energy-momentum tensor due to the magnetic field, magnetic
field effects on equation of state, the interaction between matter and the
magnetic field (magnetization), and the anomalous magnetic moment of the
hadrons. The equation of state used is an extended hadronic and quark SU(3)
non-linear realization of the sigma model that describes magnetized hybrid
stars containing nucleons, hyperons and quarks. According to our results, the
effects of the magnetization and the magnetic field on the EoS do not play an
important role on global properties of these stars. On the other hand, the
magnetic field causes the central density in these objects to be reduced,
inducing major changes in the populated degrees of freedom and, potentially,
converting a hybrid star into a hadronic star.",1508.04431v1
2015-09-05,Magnetic and magnetocaloric properties of quasi-one-dimensional Ising spin chain CoV$_{2}$O$_{6}$,"We have investigated the magnetic and magnetocaloric properties of
antiferromagnetic Ising spin chain CoV$_{2}$O$_{6}$ by magnetization and heat
capacity measurements. Both monoclinic $\alpha$-CoV$_{2}$O$_{6}$ and triclinic
$\gamma$-CoV$_{2}$O$_{6}$ exhibit field-induced metamagnetic transition from
antiferromagnetic to ferromagnetic state via an intermediate ferrimagnetic
state with 1/3 magnetization plateau. Due to this field-induced metamagnetic
transition, these systems show large conventional as well as inverse
magnetocaloric effects. In $\alpha$-CoV$_{2}$O$_{6}$, we observe field-induced
complex magnetic phases and multiple magnetization plateaux at low temperature
when the field is applied along $c$ axis. Several critical temperatures and
fields have been identified from the temperature and field dependence of
magnetization, magnetic entropy change and heat capacity to construct the
$H$-$T$ phase diagram. As compared to $\alpha$-CoV$_{2}$O$_{6}$,
$\gamma$-CoV$_{2}$O$_{6}$ displays a relatively simple magnetic phase diagram.
Due to the large magnetic entropy change and adiabatic temperature change at
low or moderate applied magnetic field, $\gamma$-CoV$_{2}$O$_{6}$ may be
considered as a magnetic refrigerant in the low-temperature region.",1509.01690v2
2015-11-16,Observation of Magnetic Superviscosity in Metglas 2605SA1,"A quasi time constant for magnetic domain relaxation of Metglas 20605SA1 has
been measured to be 2.6 hours. The effective relative magnetic permeability has
been measured to be 57,000 after relaxation.",1511.05127v1
2017-01-12,Interplay of iron and rare-earth magnetic order in rare-earth iron pnictide superconductors under magnetic field,"The magnetic properties of iron pnictide superconductors with magnetic
rare-earth ions under strong magnetic field are investigated based on the
cluster self-consistent field method. Starting from an effective Heisenberg
model, we present the evolution of magnetic structures on magnetic field in
RFeAsO (R=Ce, Pr, Nd, Sm, Gd and Tb) and RFe2As2 (R=Eu) compounds. It is found
that spin-flop transition occurs in both rare-earth and iron layers under
magnetic field, in good agreement with the experimental results. The interplay
between rare-earth and iron spins plays a key role in the magnetic-field-driven
magnetic phase transition, which suggests that the rare-earth layers can
modulate the magnetic behaviors of iron layers. In addition, the factors that
affect the critical magnetic field for spin-flop transition are also discussed.",1701.03258v1
2017-01-19,Linear Stability Analysis of a Levitated Nanomagnet in a Static Magnetic Field: Quantum Spin Stabilized Magnetic Levitation,"We theoretically study the levitation of a single magnetic domain nanosphere
in an external static magnetic field. We show that apart from the stability
provided by the mechanical rotation of the nanomagnet (as in the classical
Levitron), the quantum spin origin of its magnetization provides two additional
mechanisms to stably levitate the system. Despite of the Earnshaw theorem, such
stable phases are present even in the absence of mechanical rotation. For large
magnetic fields, the Larmor precession of the quantum magnetic moment
stabilizes the system in full analogy with magnetic trapping of a neutral atom.
For low magnetic fields, the magnetic anisotropy stabilizes the system via the
Einstein-de Haas effect. These results are obtained with a linear stability
analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy
in a Ioffe-Pritchard magnetic field.",1701.05410v3
2017-02-28,Chemical Responsive Single Crystal Organic Magnet,"Materials that change their magnetic properties in response to the external
stimuli have long been of interest for their potential applicability in
magnetic storage device, spintronics and smart magnetic materials. Organic
materials are suitable candidates for such materials due to their chemical
diversity, flexibility and designablity. However, most methods used for
changing magnetism are inefficient or destructive to the magnetic material.
Hence there is a need for innovation in this field. Here we report
high-performance magnetic control of a gas-responsive single-molecule magnet
(SMM). The results exhibit that the magnetic properties of the SMM can be
significantly changed according to the gas environment it is in and some of the
magnetic states can be reversibly transformed or coexistent in the SMM through
artificial control. More importantly, the monocrystalline structure of the SMM
remains unchanged during the transformation process except for slight change of
the lattice constant. Thus, this work opens up new insights into the
stimuli-responsive magnetic materials which have great prospects for
application in artificial design magnetic network and also highlight their
potential as smart materials.",1703.00006v2
2017-09-13,Contactless and absolute linear displacement detection based upon 3D printed magnets combined with passive radio-frequency identification,"Within this work a passive and wireless magnetic sensor, to monitor linear
displacements is proposed. We exploit recent advances in 3D printing and
fabricate a polymer bonded magnet with a spatially linear magnetic field
component corresponding to the length of the magnet. Regulating the magnetic
compound fraction during printing allows specific shaping of the magnetic field
distribution. A giant magnetoresistance magnetic field sensor is combined with
a radio-frequency identification tag in order to passively monitor the exerted
magnetic field of the printed magnet. Due to the tailored magnetic field, a
displacement of the magnet with respect to the sensor can be detected within
the sub-mm regime. The sensor design provides good flexibility by controlling
the 3D printing process according to application needs. Absolute displacement
detection using low cost components and providing passive operation, long term
stability and longevity renders the proposed sensor system ideal for structural
health monitoring applications.",1709.04220v1
2018-02-14,Axisymmetric magnetic modes of neutron stars having mixed poloidal and toroidal magnetic fields,"We calculate axisymmetric magnetic modes of a neutron star possessing a mixed
poloidal and toroidal magnetic field, where the toroidal field is assumed to be
proportional to a dimensionless parameter $\zeta_0$. Here, we assume an
isentropic structure for the neutron star and consider no effects of rotation.
Ignoring the equilibrium deformation due to the magnetic field, we employ a
polytrope of the index $n=1$ as the background model for our modal analyses.
For the mixed poloidal and toroidal magnetic field with $\zeta_0\not=0$,
axisymmetric spheroidal and toroidal modes are coupled. We compute axisymmetric
spheroidal and toroidal magnetic modes as a function of the parameter $\zeta_0$
from $0$ to $\sim 1$ for the surface field strengths $B_S=10^{14}$G and
$10^{15}$G. We find that the frequency $\omega$ of the magnetic modes decreases
with increasing $\zeta_0$. We also find that the frequency of the spheroidal
magnetic modes is almost exactly proportional to $B_S$ for $\zeta_0\lesssim 1$
but that this proportionality holds only when $\zeta_0\ll 1$ for the toroidal
magnetic modes. The wave patterns of the spheroidal magnetic modes and toroidal
magnetic modes are not strongly affected by the coupling so long as
$\zeta_0\lesssim 1$. We find no unstable modes having $\omega^2<0$.",1802.04957v1
2018-05-07,Single-shot multi-level all-optical magnetization switching mediated by spin-polarized hot electron transport,"All-optical ultrafast magnetization switching in magnetic material thin film
without the assistance of an applied external magnetic field is being explored
for future ultrafast and energy-efficient magnetic storage and memories. It has
been shown that femto-second light pulses induce magnetization reversal in a
large variety of magnetic materials. However, so far, only GdFeCo-based
ferrimagnetic thin films exhibit magnetization switching via a single optical
pulse. Here we demonstrate the single-pulse switching of Co/Pt multilayers
within a magnetic spin-valve structure ([Co/Pt] / Cu / GdFeCo) and further show
that the four possible magnetic configurations of the spin valve can be
accessed using a sequence of single femto-second light pulses. Our experimental
study reveals that the magnetization final state of the ferromagnetic [Co/Pt]
layer is determined by spin-polarized hot electrons generated by the light
pulse interactions with the GdFeCo layer. This work provides a new approach to
deterministically switch ferromagnetic layers and a pathway to engineering
materials for opto-magnetic multi-bit recording.",1805.02432v1
2018-09-19,Effect of external magnetic field on nucleon mass in hot and dense medium : Inverse Magnetic Catalysis in Walecka Model,"Vacuum to nuclear matter phase transition has been studied in presence of
constant external background magnetic field with the mean field approximation
in Walecka model. The anomalous nucleon magnetic moment has been taken into
account using the modified ""weak"" field expansion of the fermion propagator
having non-trivial correction terms for charged as well as for neutral
particles. The effect of nucleon magnetic moment is found to favour the
magnetic catalysis effect at zero temperature and zero baryon density. However,
extending the study to finite temperatures, it is observed that the anomalous
nuclear magnetic moment plays a crucial role in characterizing the qualitative
behaviour of vacuum to nuclear matter phase transition even in case of the weak
external magnetic fields . The critical temperature corresponding to the vacuum
to nuclear medium phase transition is observed to decrease with the external
magnetic field which can be identified as the inverse magnetic catalysis in
Walecka model whereas the opposite behaviour is obtained in case of vanishing
magnetic moment indicating magnetic catalysis.",1809.07028v1
2018-12-13,Measuring Earth's Magnetic Field Using a Smartphone Magnetometer,"I use the magnetometers of a smartphone to measure the magnitude of the
earth's magnetic field. A method for eliminating bias due to internal magnetic
fields in the phone is proposed.",1901.00857v1
2019-10-17,Magnetic textures and dynamics in magnetic Weyl semimetals,"Recent theoretical and experimental attemps have been successful in finding
magnetic Weyl semimetal phases, which show both nodal-point structure in the
electronic bands and magnetic orders. Beyond uniform ferromagnetic or
antiferromagnetic orders, nonuniform magnetic textures, such as domain walls
and skyrmions, may even more enrich the properties of the Weyl electrons in
such materials. This article gives a topical review on interplay between Weyl
electrons and magnetic textures in those magnetic Weyl semimetals. The basics
of magnetic textures in non-topological magnetic metals are reviewed first, and
then the effect of magnetic textures in Weyl semimetals is discussed, regarding
the recent theoretical and experimental progress therein. The idea of the
fictitious ""axial gauge fields"" is pointed out, which effectively describes the
effect of magnetic textures on the Weyl electrons and can well account for the
properties of the electrons localized around magnetic domain walls.",1910.07774v1
2019-12-03,Magnetic Force Microscopy Revealing Molecule Impact on Magnetic Tunnel Junction Based Molecular Devices at Room Temperature,"Commercially successful magnetic tunnel junction can harness the unmatched
capabilities of molecular device elements by solving decade-old fabrication
issues. Utilization of magnetic tunnel junction as a testbed for molecules also
enables unprecedented magnetic studies of molecular spintronics devices. This
paper utilizes magnetic force microscopy (MFM) to vividly show that
organometallic molecules when bridged between two ferromagnetic electrodes
along the magnetic tunnel junction edges, transformed the magnetic electrodes
itself. Molecules impacted several hundred-micron areas of ferromagnetic
electrodes at room temperature. Complementary, magnetic resonance and
magnetometer studies supported the dramatic MFM results. Molecule induced
changes in the magnetic electrodes impacted the transport of the magnetic
tunnel junction and stabilized as much as six orders smaller current at room
temperature. Magnetic tunnel junction based molecular devices can be a gateway
to a vast range of commercially viable futuristic logic and memory devices that
are controlled by the molecular quantum states near room temperature.",1912.01316v1
2019-12-12,Potential analysis of holographic Schwinger effect in the magnetized background,"We study the holographic Schwinger effect with magnetic field at RHIC and LHC
energies by using the AdS/CFT correspondence. We consider both weak and strong
magnetic field cases with $B\ll T^2$ and $B\gg T^2$ solutions respectively.
Firstly, we calculate separating length of the particle pairs at finite
magnetic field. It is found that for both weak and strong magnetic field
solutions the maximum value of separating length decreases with the increase of
magnetic field , which can be inferred that the virtual electron-positron pairs
become real particles more easily. We also find that the magnetic field reduces
the potential barrier and the critical field for the weak magnetic field
solution, thus favors the Schwinger effect. With strong magnetic field
solution, the magnetic field enhances the Schwinger effect when the pairs are
in perpendicular to the magnetic field although the magnetic field increases
the critical electric field.",1912.05806v2
2019-12-24,The origin and effect of hemispheric helicity imbalance in solar dynamo,"In this paper we study the effects of hemispheric imbalance of magnetic
helicity density on breaking the equatorial reflection symmetry of the dynamo
generated large-scale magnetic field. Our study employs the axisymmetric dynamo
model which takes into account the nonlinear effect of magnetic helicity
conservation. We find that the evolution of the net magnetic helicity density,
in other words, the magnetic helicity imbalance, on the surface follows the
evolution of the parity of the large-scale magnetic field. Random fluctuations
of the $\alpha$-effect and the helicity fluxes can inverse the causal
relationship, i.e., the magnetic helicity imbalance or the imbalance of
magnetic helicity fluxes can drive the magnetic parity breaking. We also found
that evolution of the net magnetic helicity of the small-scale fields follows
the evolution of the net magnetic helicity of the large-scale fields with some
time lag. We interpret this as an effect of the difference of the magnetic
helicity fluxes out of the Sun from the large and small scales.",1912.11285v2
2020-03-09,Magnetic Noise Enabled Biocompass,"The discovery of magnetic protein provides a new understanding of a
biocompass at the molecular level. However, the mechanism by which magnetic
protein enables a biocompass is still under debate, mainly because of the
absence of permanent magnetism in the magnetic protein at room temperature.
Here, based on a widely accepted radical pair model of a biocompass, we propose
a microscopic mechanism that allows the biocompass to operate without a finite
magnetization of the magnetic protein in a biological environment. With the
structure of the magnetic protein, we show that the magnetic fluctuation,
rather than the permanent magnetism, of the magnetic protein can enable
geomagnetic field sensing. An analysis of the quantum dynamics of our
microscopic model reveals the necessary conditions for optimal sensitivity. Our
work clarifies the mechanism by which magnetic protein enables a biocompass.",2003.13816v2
2020-04-25,Pulse-assisted magnetization switching in magnetic nanowires at picosecond and nanosecond timescales with low energy,"Detailed understanding of spin dynamics in magnetic nanomaterials is
necessary for developing ultrafast, low-energy and high-density spintronic
logic and memory. Here, we develop micromagnetic models and analytical
solutions to elucidate the effect of increasing damping and uniaxial anisotropy
on magnetic field pulse-assisted switching time, energy and field requirements
of nanowires with perpendicular magnetic anisotropy and yttrium iron
garnet-like spin transport properties. A nanowire is initially magnetized using
an external magnetic field pulse (write) and self-relaxation. Next, magnetic
moments exhibit deterministic switching upon receiving 2.5 ns-long external
magnetic pulses in both vertical polarities. Favorable damping
({\alpha}~0.1-0.5) and anisotropy energies (10^4-10^5 J m^-3) allow for as low
as picosecond magnetization switching times. Magnetization reversal with fields
below coercivity was observed using spin precession instabilities. A
competition or a nanomagnetic trilemma arises among the switching rate, energy
cost and external field required. Developing magnetic nanowires with optimized
damping and effective anisotropy could reduce the switching energy barrier down
to 3163kBT at room temperature. Thus, pulse-assisted picosecond and low energy
switching in nanomagnets could enable ultrafast nanomagnetic logic and cellular
automata.",2004.12243v1
2020-05-02,Optically driven ultrafast magnetic order transitions in two-dimensional ferrimagnets,"Laser-induced switching and manipulation of the spins in magnetic materials
are of great interest to revolutionize future magnetic storage technology and
spintronics with fastest speed and least power dissipative. Inspired by the
recent discovery of intrinsic two-dimensional (2D) magnets, which provide
unique platform to explore the new phenomenon for light-control magnetism in
the 2D limit, we propose to realize light can efficiently tune magnetic
properties of 2D ferrimagnets in early time. Here, using the 2D ferrimagnetic
MXenes as prototype systems, our real-time density functional theory (TDDFT)
simulation show that laser pulses can directly induce ultrafast spin-selective
charge transfer between two magnetic sublattices on a few femtoseconds, and
further generate dramatic changes in the magnetic structure of these MXenes,
including a magnetic order transition from ferrimagnetic (FiM) to transient
ferromagnetic (FM). The microscopic mechanism underpinning this ultrafast
switching of magnetic order in MXenes is governed by optically induced
inter-site spin transfer (OISTR) effect, which theoretically enables the
ultrafast direct optical manipulation of the magnetic state in MXenes-based
materials. Our results open new opportunities to optically manipulate the spin
in 2D magnets.",2005.00871v1
2020-06-03,Structural and magnetic properties of small symmetrical and asymmetrical sized fullerene dimers,"Magnetism in carbon nanostructures is of high scientific interest, which
could lead to novel magnetic materials. The magnetic properties of symmetrical
and asymmetrical sized small fullerene dimers have been investigated using spin
polarized density functional theory. The interaction energies depict that small
fullerene cages form stable dimer structures and symmetrical sized fullerene
dimers are found more stable than asymmetrical sized dimers. The dimerization
of fullerene cages in different modes leads to change in their magnetic
properties. The non-magnetic fullerene cages become magnetic after formation of
dimer (C20-C20, C24-C24, C32-C32, C40-C40, C20-C24, C40-C44 and
C44-C50),whereas the magnetism of magnetic fullerenes is enhanced or lowered
after dimerization (C28-C28 C36-C36, C24-C28, C28-C32, C32-C36 and C36-C40).
The individual cages of dimer structures show ferromagnetic interactions
amongst them and resultant magnetic moment strongly depends on the type of
inter-connecting bonds. The magnetism may also be explained based on distortion
of carbon cages and change in the density of states (DOS) in dimer
configuration. The calculations presented show strong possibility of
experimental synthesis of small fullerene based magnetic dimers.",2006.02233v1
2020-09-03,Coincidence inelastic neutron scattering for detection of two-spin magnetic correlations,"Inelastic neutron scattering (INS) is one powerful technique to study the
low-energy single-spin dynamics of magnetic materials. A variety of quantum
magnets show novel magnetic correlations such as quantum spin liquids. These
novel magnetic correlations are beyond the direct detection of INS. In this
paper we propose a coincidence technique, coincidence inelastic neutron
scattering (cINS), which can detect the two-spin magnetic correlations of the
magnetic materials. In cINS there are two neutron sources and two neutron
detectors with an additional coincidence detector. Two neutrons from the two
neutron sources are incident on the target magnetic material, and they are
scattered by the electron spins of the magnetic material. The two scattered
neutrons are detected by the two neutron detectors in coincidence with the
coincidence probability described by a two-spin Bethe-Salpeter wave function.
Since the two-spin Bethe-Salpeter wave function defines the momentum-resolved
dynamical wave function with two spins excited, cINS can explicitly detect the
two-spin magnetic correlations of the magnetic material. Thus, it can be
introduced to study the various spin valence bond states of the quantum
magnets.",2009.01680v2
2020-10-19,Magnetic texture based magnonics,"The spontaneous magnetic orders arising in ferro-, ferri- and
antiferromagnets stem from various magnetic interactions. Depending on the
interplay and competition among the Heisenberg exchange interaction,
Dzyaloshinskii-Moriya exchange interaction, magnetic dipolar interaction and
crystal anisotropies, a great variety of magnetic textures may be stabilized,
such as magnetic domain walls, vortices, Skyrmions and spiral helical
structures. While each of these spin textures responds to external forces in a
specific manner with characteristic resonance frequencies, they also interact
with magnons, the fundamental collective excitation of the magnetic order,
which can propagate in magnetic materials free of charge transport and
therefore with low energy dissipation. Recent theories and experiments found
that the interplay between spin waves and magnetic textures is particularly
interesting and rich in physics. In this review, we introduce and discuss the
theoretical framework of magnons living on a magnetic texture background, as
well as recent experimental progress in the manipulation of magnons via
magnetic textures. The flexibility and reconfigurability of magnetic textures
are discussed regarding the potential for applications in information
processing schemes based on magnons.",2010.09180v1
2020-12-09,Optimization of a NdFeB permanent magnet configuration for in-vivo drug delivery experiments,"We propose a new concept of magnetic focusing for targeting and accumulation
of functionalized superparamagnetic nanoparticles in living organs through
composite configurations of different permanent magnets. The proposed setups
fulfill two fundamental requirements for in vivo experiments: 1) reduced size
of the magnets to best focusing on small areas representing the targeted organs
of mice and rats and 2) maximization of the magnetic driving force acting on
the magnetic nanoparticles dispersed in blood. To this aim, several
configurations of permanent magnets organized with different degrees of
symmetry have been tested. The product B*grad(B) proportional to the magnetic
force has been experimentally measured, over a wide area (20x20 mm^2), at a
distance corresponding to the hypothetical distance of the mouse organ from the
magnets. A non-symmetric configuration of mixed shape permanent magnets
resulted in particularly promising to achieve the best performances for further
in vivo experiments.",2012.05059v1
2021-01-15,Magnetized Rutherford scattering angle for electron-ion collision in plasma,"Rutherford scattering formula plays an important role in plasma classical
transport. It is urgent to need a magnetized Rutherford scattering formula
since the magnetic field increases significantly in different fusion areas
(e.g. tokamak magnetic field, self-generated magnetic field, and compressed
magnetic field). The electron-ion Coulomb collisions perpendicular to the
external magnetic field are studied in this paper. The scattering angle is
defined according to the electron trajectory and asymptotic line (without
magnetic field). A magnetized Rutherford scattering formula is obtained
analytically under the weak magnetic field approximation. It is found that the
scattering angle decreases as external magnetic field increases. It is easy to
find the scattering angle decreasing significantly as incident distance, and
incident velocity increasing. It is shown that the theoretical results agree
well with numerical calculation by checking the dependence of scattering angle
on external magnetic field.",2101.05943v1
2021-04-02,Highly Complex Magnetic Structures Resulting From Hierarchical Phase Separation in AlCo(Cr)FeNi High Entropy Alloys,"Magnetic high entropy alloys (HEAs) are a new category of high-performance
magnetic materials, with multi-component concentrated compositions and complex
multi-phase structures. Although there have been numerous reports of their
interesting magnetic properties, there is very limited understanding about the
interplay between their hierarchical multi-phase structures and their local
magnetic structures. By employing high spatial resolution correlative magnetic,
structural and chemical studies, we reveal the influence of a hierarchically
decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of
magnetic vortex states within individual A2 (disordered BCC) precipitates,
which are distributed in an ordered B2 matrix that is weakly ferromagnetic.
Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains
of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are
also observed. These results provide important insight into the origin of
coercivity in this HEA, which can be attributed to a complex magnetization
process that includes the successive reversal of magnetic vortices.",2104.00943v1
2021-06-28,Stability of a Magnetically Levitated Nanomagnet in Vacuum: Effects of Gas and Magnetization Damping,"In the absence of dissipation a non-rotating magnetic nanoparticle can be
stably levitated in a static magnetic field as a consequence of the spin origin
of its magnetization. Here we study the effects of dissipation on the stability
of the system, considering the interaction with the background gas and the
intrinsic Gilbert damping of magnetization dynamics. At large applied magnetic
fields we identify magnetization switching induced by Gilbert damping as the
key limiting factor for stable levitation. At low applied magnetic fields and
for small particle dimensions magnetization switching is prevented due to the
strong coupling of rotation and magnetization dynamics, and the stability is
mainly limited by the gas-induced dissipation. In the latter case, high vacuum
should be sufficient to extend stable levitation over experimentally relevant
timescales. Our results demonstrate the possibility to experimentally observe
the phenomenon of quantum spin stabilized magnetic levitation.",2106.14858v3
2021-12-21,Tunable room temperature magnetic skyrmions in centrosymmetric kagome magnet Mn$_4$Ga$_2$Sn,"The successful realization of skyrmion-based spintronic devices depends on
the easy manipulation of underlying magnetic interactions in the
skyrmion-hosting materials. Although the mechanism of skyrmion formation in
non-centrosymmetric magnets is comprehensively established, the stabilization
process of different skyrmion-like magnetic textures in centrosymmetric magnets
needs further investigation. Here, we utilize Lorentz transmission electron
microscopy study to report the finding of a tunable skyrmion lattice up to room
temperature in a centrosymmetric kagome ferromagnet Mn$_4$Ga$_2$Sn. We
demonstrate that a controlled switching between the topological skyrmions and
non-topological type-II magnetic bubbles can be realized at the optimal
magnetic anisotropy. We find that the topological skyrmions are the
energetically most stable magnetic objects in the centrosymmetric hexagonal
magnets, whereas application of in-plane magnetic field stabilizes type-II
magnetic bubbles as an excited state. The present study is a significant step
towards understanding of the skyrmion stabilization mechanism in
centrosymmetric materials for their future applications.",2112.11259v2
2022-02-25,Magnetic-Field-Dependent Thermodynamic Properties of Square and Quadrupolar Artificial Spin Ice,"Applied magnetic fields are an important tuning parameter for artificial spin
ice (ASI) systems, as they can drive phase transitions between different
magnetic ground states, or tune through regimes with high populations of
emergent magnetic excitations (e.g., monopole-like quasiparticles). Here, using
simulations supported by experiments, we investigate the thermodynamic
properties and magnetic phases of square and quadrupolar ASI as a function of
applied in-plane magnetic fields. Monte Carlo simulations are used to generate
field-dependent maps of the magnetization, the magnetic specific heat, the
thermodynamic magnetization fluctuations, and the magnetic order parameters,
all under equilibrium conditions. These maps reveal the diversity of magnetic
orderings and the phase transitions that occur in different regions of the
phase diagrams of these ASIs, and are experimentally supported by
magneto-optical measurements of the equilibrium ""magnetization noise"" in
thermally-active ASIs.",2202.12486v1
2022-03-23,R&D works for Superconducting Magnet for Future Accelerator Applications in Japan,"KEK cryogenics science center is developing superconducting magnet technology
for future accelerator science. Three major technological categories are
focused; 1) high precision 3D magnetic field technology based on the g-2/EDM
magnet developments, 2) rad-hard superconducting magnet technology based on the
COMET magnet developments, and 3) high magnetic field superconducting magnet
technology for future colliders based on the LHC MQXA and HL-LHC D1 magnet
developments. Extensive studies including Nb3Sn conductor and magnet
developments for high field magnets and HTS for rad-hard superconducting
magnets are ongoing with various collaboration programs such as the US-Japan
research collaboration.",2203.12118v1
2022-04-26,Slow spin dynamics and quantum tunneling of magnetization in the dipolar antiferromagnet DyScO$_3$,"We present a comprehensive study of static and dynamic magnetic properties in
the Ising-like dipolar antiferromagnet (AFM) DyScO$_3$\ by means of DC and AC
magnetization measurements supported by classical Monte-Carlo calculations. Our
AC-susceptibility data show that the magnetic dynamics exhibit a clear
crossover from an Arrhenius-like regime to quantum tunneling of magnetization
(QTM) at $T^* = 10$ K. Below $T_{\mathrm{N}} = 3.2$ K DyScO$_3$ orders in an
antiferromagnetic $GxAy$-type magnetic structure and the magnetization dynamics
slow down to the minute timescale. The low-temperature magnetization curves
exhibit complex hysteretic behavior, which depends strongly on the magnetic
field sweep rate. We demonstrate that the low-field anomalies on the
magnetization curve are related to the metamagnetic transition, while the
hysteresis at higher fields is induced by a strong magnetocaloric effect. Our
theoretical calculations, which take into account dipolar interaction between
Dy$^{3+}$ moments, reproduce essential features of the magnetic behavior of
DyScO$_3$. We demonstrate that DyScO$_3$ represents a rare example of inorganic
compound, which exhibits QTM at a single-ion level and magnetic order due to
classical dipolar interaction.",2204.12398v1
2022-05-08,Two-dimensional characterization of three-dimensional magnetic bubbles in Fe$_3$Sn$_2$ nanostructures,"We report differential phase contrast scanning transmission electron
microscopy (TEM) of nanoscale magnetic objects in Kagome ferromagnet
Fe$_3$Sn$_2$ nanostructures. This technique can directly detect the deflection
angle of a focused electron beam, thus allowing clear identification of the
real magnetic structures of two magnetic objects including three-ring and
complex arch-shaped vortices in Fe$_3$Sn$_2$ by Lorentz transmission electron
microscopy imaging. Numerical calculations based on real material-specific
parameters well reproduced the experimental results, showing that the magnetic
objects can be attributed to integral magnetizations of two types of complex
three-dimensional (3D) magnetic skyrmion bubbles with depth-modulated spin
twisting. Magnetic configurations obtained using the high-resolution TEM are
generally considered as two-dimensional (2D) magnetic objects previously. Our
results imply the importance of the integral magnetizations of underestimated
3D magnetic structures in 2D TEM magnetic characterizations.",2205.03751v2
2022-05-09,"Controlling magnetic exchange and anisotropy by non-magnetic ligand substitution in layered MPX3 (M = Ni, Mn; X = S, Se)","Recent discoveries in two-dimensional (2D) magnetism have intensified the
investigation of van der Waals (vdW) magnetic materials and further improved
our ability to tune their magnetic properties. Tunable magnetism has been
widely studied in antiferromagnetic metal thiophosphates MPX3. Substitution of
metal ions M has been adopted as an important technique to engineer the
magnetism in MPX3. In this work, we have studied the previously unexplored
chalcogen X substitutions in MPX3 (M = Mn/Ni; X = S/Se). We synthesized the
single crystals of MnPS3-xSex (0 < x < 3) and NiPS3-xSex (0 < x < 1.3) and
investigated the systematic evolution of the magnetism with varying x. Our
study reveals the effective tuning of magnetic interactions and anisotropies in
both MnPS3 and NiPS3 upon Se substitution. Such efficient engineering of the
magnetism provides a suitable platform to understand the low-dimensional
magnetism and develop future magnetic devices.",2205.04585v1
2022-05-28,Finite element simulation for validation of multi-dipole line cusp magnetic field configuration for MPD,"A Multi-dipole line cusp configured Plasma Device (MPD) having six
electromagnets with embedded Vacoflux-50 as a core material has been operated
with a capability to experimentally control the field-free region, the radial
profile of magnetic field, and pole magnetic field by changing magnet current.
For the validation of multi-dipole line cusp magnetic field (MMF) configuration
in a 3-D geometry, a finite element simulation has been performed using COMSOL
software. This paper presents 3-D magnetic field simulation results of
multi-pole line cusp magnetic field configuration performed over the 1.2m
length and 40cm diameter chamber in the vacuum condition. The simulation
results show good agreement with the experimentally measured magnetic field
profile. The performed magnetic field simulation results clearly capture that
this configuration has full control over a null region (nearly field-free
region) as well is capable to change the magnetic field values and radial
variation of the magnetic field. Moreover, the magnetic field profiles over the
end cross-section of the device have been discussed.",2205.14381v1
2022-05-20,A Sacrificial Magnet Concept for Field Dependent Surface Science Studies,"We demonstrate a straightforward approach to integrating a magnetic field
into a low-temperature scanning tunneling microscope (STM) by adhering an NdFeB
permanent magnet to a magnetizable sample plate. To render our magnet concept
compatible with high-temperature sample cleaning procedures, we make the
irreversible demagnetization of the magnet a central part of our preparation
cycle. After sacrificing the magnet by heating it above its Curie temperature,
we use a transfer tool to attach a new magnet in-situ prior to transferring the
sample into the STM. We characterize the magnetic field created by the magnet
using the Abrikosov vortex lattice of superconducting NbSe2. Excellent
agreement between the distance dependent magnetic fields from experiments and
simulations allows us to predict the magnitude and orientation of magnetic flux
at any location with respect to the magnet and the sample plate. Our concept is
an accessible solution for field-dependent surface science studies that require
fields in the range of up to 400 mT and otherwise detrimental heating
procedures.",2206.02529v1
2022-07-14,Formation of Quiescent Prominence Magnetic Field by Supergranulations,"To understand the formation of quiescent solar prominences, the origin of
their magnetic field structures, i.e., magnetic flux ropes (MFRs), must be
revealed. We use three-dimensional magnetofriction simulations in a spherical
subdomain to investigate the role of typical supergranular motions in the
long-term formation of a prominence magnetic field. Time-dependant horizontal
supergranular motions with and without the effect of Coriolis force are
simulated on the solar surface via Voronoi tessellation. The vortical motions
by the Coriolis effect at boundaries of supergranules inject magnetic helicity
into the corona. The helicity is transferred and accumulated along the polarity
inversion line (PIL) as strongly sheared magnetic field via helicity
condensation. The diverging motions of supergranules converge opposite magnetic
polarities at the PIL and drive the magnetic reconnection between footpoints of
the sheared magnetic arcades to form an MFR. The magnetic network,
negative-helicity MFR in the northern hemisphere, and fragmented-to-continuous
formation process of magnetic dip regions are in agreement with observations.
Although diverging supergranulations, differential rotation, and meridional
flows are included, the simulation without the Coriolis effect can not produce
an MFR or sheared arcades to host a prominence. Therefore Coriolis force is a
key factor for helicity injection and the formation of magnetic structures of
quiescent solar prominences.",2207.06598v1
2022-11-28,Algorithms for magnetic symmetry operation search and identification of magnetic space group from magnetic crystal structure,"A crystal symmetry search is crucial for computational crystallography and
materials science. Although algorithms and implementations for the crystal
symmetry search have been developed, their extension to magnetic space groups
(MSGs) remains limited. In this paper, algorithms for determining magnetic
symmetry operations of magnetic crystal structures, identifying magnetic
space-group types of given MSGs, searching for transformations to a BNS
setting, and symmetrizing the magnetic crystal structures using the MSGs are
presented. The determination of magnetic symmetry operations is numerically
stable and is implemented with minimal modifications from the existing crystal
symmetry search. Magnetic space-group types and transformations to the BNS
setting are identified by a two-step approach combining space-group type
identification and the use of affine normalizers. Point coordinates and
magnetic moments of the magnetic crystal structures are symmetrized by
projection operators for the MSGs. An implementation is distributed with a
permissive free software license in spglib v2.0.2:
https://github.com/spglib/spglib.",2211.15008v2
2023-02-22,Controllable CVD-Growth of 2D Cr5Te8 Nanosheets with Thickness-Dependent Magnetic Domains,"As a typical 2D magnetic material with self-intercalated structure, Cr5Te8
exhibits many fascinating magnetic properties. Although the ferromagnetism of
2D Cr5Te8 has been reported, the study of its magnetic domain is still blank.
Herein, we successfully fabricated 2D Cr5Te8 nanosheets with controlled
thickness and lateral size by chemical vapor deposition (CVD). Then magnetic
property measurement system suggested Cr5Te8 nanosheets possessing intense
out-of-plane ferromagnetism with the Curie temperature of 179 K. Most
importantly, we found magnetic bubbles and thickness-dependent maze-like
magnetic domains by cryogenic magnetic force microscopy (MFM) for the first
time. The domain width of the maze-like magnetic domains increases rapidly with
decreasing sample thickness, while domain contrast decreases. This indicates
dipolar interaction is the dominant role over exchange interaction and magnetic
anisotropy. Our work not only paves a way for the controllable growth of 2D
magnetic materials, but also suggests new directions for controlling magnetic
phases and systematically adjusting domain properties.",2302.11422v2
2023-03-11,Magnetic field imaging by cosmic-ray muons (Magic-$μ$) -- First feasibility simulation for strong magnetic fields,"We have proposed a novel application for cosmic-ray muography, called
Magic-$\mu$, which is short for Magnetic field Imaging by Cosmic-ray Muons. The
general goal of Magic-$\mu$ is to detect the presence of a magnetic field or
magnetic flux density whose three-dimensional distribution is unknown.
Depending on the application, Magic-$\mu$ can have three detection modes. The
first is ""magnetic field imaging,"" which is detecting the presence of a
magnetic field in specific voxels within a region of space. The other two
modes, transmission and deflection, aim not only to detect the presence but
also to measure the flux density of the magnetic field. We have performed a
feasibility study using the PHITS Monte Carlo simulation code, for strong and
weak magnetic fields. In this paper, we first give an overview of the concept
and basic principles of magnetic field muography. Then, the results of the
feasibility study on magnetic field imaging for a strong magnetic field (more
than 500 mT) are presented.",2303.06290v3
2023-05-30,Magnetic field regression using artificial neural networks for cold atom experiments,"Accurately measuring magnetic fields is essential for magnetic-field
sensitive experiments in fields like atomic, molecular, and optical physics,
condensed matter experiments, and other areas. However, since many experiments
are conducted in an isolated vacuum environment that is inaccessible to
experimentalists, it can be challenging to accurately determine the magnetic
field. Here, we propose an efficient method for detecting magnetic fields with
the assistance of an artificial neural network (NN). Instead of measuring the
magnetic field directly at the desired location, we detect magnetic fields at
several surrounding positions, and a trained NN can accurately predict the
magnetic field at the target location. After training, we achieve a relative
error of magnetic field magnitude (magnitude of error over the magnitude of
magnetic field) below 0.3$\%$, and we successfully apply this method to our
erbium quantum gas apparatus. This approach significantly simplifies the
process of determining magnetic fields in isolated vacuum environments and can
be applied to various research fields across a wide range of magnetic field
magnitudes.",2305.18822v1
2023-07-06,Plasmon-enhanced optical control of magnetism at the nanoscale via the inverse Faraday effect,"The relationship between magnetization and light has been the subject of
intensive research for the past century, focusing on the impact of magnetic
moments on light polarization. Conversely, the manipulation of magnetism
through polarized light is being investigated to achieve all-optical control of
magnetism in spintronics. While remarkable discoveries such as single pulse
all-optical switching of the magnetization in thin films and sub-micrometer
structures have been reported, the demonstration of local optical control of
magnetism at the nanoscale has remained elusive. Here, we show that exciting
gold nanodiscs with circularly polarized femtosecond laser pulses leads to the
generation of sizeable local magnetic fields that enable ultrafast local
control of the magnetization of an adjacent magnetic film. In addition, we find
that the highest magnetic fields are generated when exciting the sample at a
wavelength larger than that of the actual plasmonic resonance of the gold
nanodiscs, so avoiding undesired heating effects due to absorption. Our study
paves the way for light-driven control in nanoscale spintronic devices and
provides important insights into the generation of magnetic fields in plasmonic
nanostructures.",2307.03326v1
2023-07-14,Parker Bounds on Monopoles with Arbitrary Charge from Galactic and Primordial Magnetic Fields,"We present a comprehensive study of Parker-type bounds on magnetic monopoles
with arbitrary magnetic charge, including minicharged monopoles and magnetic
black holes. We derive the bounds based on the survival of galactic magnetic
fields, seed magnetic fields, as well as primordial magnetic fields. We find
that monopoles with different magnetic charges are best constrained by
different astrophysical systems: while monopoles with a Dirac charge are
tightly constrained by seed galactic magnetic fields, minicharged monopoles are
strongly constrained by primordial magnetic fields, and magnetic black holes by
the density of dark matter. We also assess the viability of the various types
of monopoles as dark matter, by studying whether they can cluster with galaxies
hosting magnetic fields.",2307.07553v2
2023-10-10,Skyrmions and magnetic bubbles in spin-orbit coupled metallic magnets,"Motivated by the observation of Skyrmion-like magnetic textures in 2D
itinerant ferromagnets Fe$_n$GeTe$_2$ ($n \geq3$), we develop a microscopic
model combining itinerant magnetism and spin-orbit coupling on a triangular
lattice. The ground state of the model in the absence of magnetic field
consists of filamentary magnetic domain walls revealing a striking similarity
with our magnetic force microscopy experiments on Fe$_3$GeTe$_2$. In the
presence of magnetic field, these filaments were found to break into large size
magnetic bubbles in our experiments. We identify uniaxial magnetic anisotropy
as an important parameter in the model that interpolates between magnetic
Skyrmions and ferromagnetic bubbles. Consequently, our work uncovers new
topological magnetic textures that merge properties of Skyrmions and
ferromagnetic bubbles.",2310.06521v1
2023-11-10,Exchange stiffness proportional to power of magnetization in permalloy co-doped with Mo and Cu,"The exchange stiffness of magnetic materials is one of the essential
parameters governing magnetic texture and its dynamics in magnetic devices. The
effect of single-element doping on exchange stiffness has been investigated for
several doping elements for permalloy (NiFe alloy), a soft magnetic material
whose soft magnetic properties can be controlled by doping. However, the impact
of more practical multi-element doping on the exchange stiffness of permalloy
is unknown. This study investigates the typical magnetic properties, including
exchange stiffness, of permalloy systematically co-doped with Mo and Cu using
broadband ferromagnetic resonance spectroscopy. We find that the exchange
stiffness, which decreases with increasing doping levels, is proportional to a
power of magnetization, which also decreases with increasing doping levels. The
magnetization, $M_{\rm s}$, dependence of the exchange stiffness constant, $A$,
of all the investigated samples, irrespective of the doping levels of each
element, lies on a single curve expressed as $A\propto M_{\rm s}^n$ with
exponent $n$ close to 2. This empirical power-law relationship provides a
guideline for predicting unknown exchange stiffness in non-magnetic
element-doped permalloy systems.",2311.05852v2
2024-02-18,Deep learning methods for Hamiltonian parameter estimation and magnetic domain image generation in twisted van der Waals magnets,"The application of twist engineering in van der Waals magnets has opened new
frontiers in the field of two-dimensional magnetism, yielding distinctive
magnetic domain structures. Despite the introduction of numerous theoretical
methods, limitations persist in terms of accuracy or efficiency due to the
complex nature of the magnetic Hamiltonians pertinent to these systems. In this
study, we introduce a deep-learning approach to tackle these challenges.
Utilizing customized, fully connected networks, we develop two
deep-neural-network kernels that facilitate efficient and reliable analysis of
twisted van der Waals magnets. Our regression model is adept at estimating the
magnetic Hamiltonian parameters of twisted bilayer CrI3 from its magnetic
domain images generated through atomistic spin simulations. The generative
model excels in producing precise magnetic domain images from the provided
magnetic parameters. The trained networks for these models undergo thorough
validation, including statistical error analysis and assessment of robustness
against noisy injections. These advancements not only extend the applicability
of deep-learning methods to twisted van der Waals magnets but also streamline
future investigations into these captivating yet poorly understood systems.",2402.11434v1
2001-08-29,Jet Collimation by Small-Scale Magnetic Fields,"A popular model for jet collimation is associated with the presence of a
large-scale and predominantly toroidal magnetic field originating from the
central engine (a star, a black hole, or an accretion disk). Besides the
problem of how such a large-scale magnetic field is generated, in this model
the jet suffers from the fatal long-wave mode kink magnetohydrodynamic
instability. In this paper we explore an alternative model: jet collimation by
small-scale magnetic fields. These magnetic fields are assumed to be local,
chaotic, tangled, but are dominated by toroidal components. Just as in the case
of a large-scale toroidal magnetic field, we show that the ``hoop stress'' of
the tangled toroidal magnetic fields exerts an inward force which confines and
collimates the jet. The magnetic ``hoop stress'' is balanced either by the gas
pressure of the jet, or by the centrifugal force if the jet is spinning. Since
the length-scale of the magnetic field is small (< the cross-sectional radius
of the jet << the length of the jet), in this model the jet does not suffer
from the long-wave mode kink instability. Many other problems associated with
the large-scale magnetic field are also eliminated or alleviated for
small-scale magnetic fields. Though it remains an open question how to generate
and maintain the required small-scale magnetic fields in a jet, the scenario of
jet collimation by small-scale magnetic fields is favored by the current study
on disk dynamo which indicates that small-scale magnetic fields are much easier
to generate than large-scale magnetic fields.",0108469v1
2003-10-20,Cyclic evolution and reversal of the solar magnetic field. I. The large-scale magnetic fields,"On the base of the solar magnetic field measurements obtained in Stanford in
1976--2003 the properties of the cyclic evolution of the large-scale magnetic
field are investigated. Some regularities are found in longitudinal and
latitudinal evolution of the magnetic field in cycles 21, 22 and 23. The cyclic
development of the large-scale magnetic field can be divided into two main
phases. The phase I, which includes a period approximately from two years
before and until three years after the maximum of the solar cycle, is studied
in detail. It is found that before the reversal of the large-scale magnetic
field the neutral line of the magnetic field in antipodal longitudinal
intervals shifts from the equator to opposite directions in cycles 21 and 22,
but not in cycle 23. During the sign reversal of the large-scale magnetic field
in cycles 21 and 22 in the antipodal longitudinal intervals the magnetic field
of opposite polarity is observed in all latitudes, thereby forming an
equatorial dipole. After the magnetic field reversal a longitudinal oscillation
of the magnetic neutral line with regard to the equator takes place, which has
a period about 2 years and damps to the minimum of the 11-year cycle. The
intervening longitudinal intervals of the large-scale magnetic field correspond
to positions of the active longitudes of sunspot activity, thus indicating a
close connection of the large-scale and the local magnetic fields. In evolution
of the large-scale magnetic field a periodicity with period $1.23\pm0.16$ year
is revealed, which is close to the period found by helioseismological methods
in variations of the solar rotation near the tachocline.",0310539v1
2009-03-16,Relationship between photospheric currents and coronal magnetic helicity for force-free bipolar fields,"The origin and evolution of the magnetic helicity in the solar corona are not
well understood. For instance, the magnetic helicity of an active region is
often about $10^{42}$ Mx$^2$ ($10^{26}$ Wb$^{2}$), but the observed processes
whereby it is thought to be injected into the corona do not yet provide an
accurate estimate of the resulting magnetic helicity budget or time evolution.
The variation in magnetic helicity is important for understanding the physics
of flares, coronal mass ejections, and their associated magnetic clouds. To
shed light on this topic, we investigate here the changes in magnetic helicity
due to electric currents in the corona for a single twisted flux tube that may
model characteristic coronal structures such as active region filaments,
sigmoids, or coronal loops. For a bipolar photospheric magnetic field and
several distributions of current, we extrapolated the coronal field as a
nonlinear force-free field. We then computed the relative magnetic helicity, as
well as the self and mutual helicities. Starting from a magnetic configuration
with a moderate amount of current, the amount of magnetic helicity can increase
by 2 orders of magnitude when the maximum current strength is increased by a
factor of 2. The high sensitivity of magnetic helicity to the current density
can partially explain discrepancies between measured values on the photosphere,
in the corona, and in magnetic clouds. Our conclusion is that the magnetic
helicity strongly depends on both the strength of the current density and also
on its distribution. Only improved measurements of current density at the
photospheric level will advance our knowledge of the magnetic helicity content
in the solar atmosphere.",0903.2697v1
2011-03-29,Relationship between vertical and horizontal magnetic fields in the quiet Sun,"Vertical magnetic fields have been known to exist in the internetwork region
for decades, while the properties of horizontal magnetic fields have recently
been extensively investigated with \textit{Hinode}. Vertical and horizontal
magnetic fields in the internetwork region are considered to be separate
entities and have thus far not been investigated in a unified way. We discover
clear positional association between the vertical and horizontal magnetic
fields in the internetwork region with \textit{Hinode}. Essentially all of the
horizontal magnetic patches are associated with the vertical magnetic patches.
Alternatively, half of the vertical magnetic patches accommodate the horizontal
magnetic patches. These horizontal patches are located around the borders of
the vertical patches. The intrinsic magnetic field strength as obtained with
the Stokes $V$ line ratio inside the horizontal patches is weak, and is in
sub-equipartition field regime ($B<700$ G), while the field strength outside
the horizontal patches ranges from weak to strong (kG) fields. Vertical
magnetic patches are known to be concentrated on mesogranular and supergranular
boundaries, while the horizontal magnetic patches are found only on the
mesogranular boundaries. These observations provide us with new information on
the origin of the vertical and horizontal internetwork magnetic fields, in a
unified way. We conjecture that internetwork magnetic fields are provided by
emergence of small-scale flux tubes with bipolar footpoints, and the vertical
magnetic fields of the footpoints are intensified to kG fields due to
convective collapse. Resultant strong vertical fields are advected by the
supergranular flow, and eventually form the network fields.",1103.5556v1
2011-11-15,Spin waves in nanosized magnetic films,"We have studied spin excitations in nanosized magnetic films in the
Heisenberg model with magnetic dipole and exchange interactions by the spin
operator diagram technique. Dispersion relations of spin waves in thin magnetic
films (in two-dimensional magnetic monolayers and in two-layer magnetic films)
and the spin-wave resonance spectrum in N-layer structures are found. For thick
magnetic films generalized Landau-Lifshitz equations are derived from first
principles. Landau-Lifshitz equations have the integral (pseudodifferential)
form, but not differential one. Spin excitations are determined by simultaneous
solution of the Landau-Lifshitz equations and the equation for the
magnetostatic potential. For normal magnetized ferromagnetic films the spin
wave damping has been calculated in the one-loop approximation for a diagram
expansion of the Green functions at low temperature. In thick magnetic films
the magnetic dipole interaction makes a major contribution to the relaxation of
long-wavelength spin waves. Thin films have a region of low relaxation of
long-wavelength spin waves. In thin magnetic films four-spin-wave processes
take place and the exchange interaction makes a major contribution to the
damping. It is found that the damping of spin waves propagating in magnetic
monolayer is proportional to the quadratic dependence on the temperature and is
very low for spin waves with small wavevectors. Spin-wave devices on the base
of nanosized magnetic films are proposed -- tunable narrow-band spin-wave
filters with high quality at the microwave frequency range and field-effect
transistor (FET) structures contained nanosized magnetic films under the gate
electrode. Spin-wave resonances in nanosized magnetic films can be used to
construct FET structures operating in Gigahertz and Terahertz frequency bands.",1111.3532v1
2011-11-30,Relation of Astrophysical Turbulence and Magnetic Reconnection,"Astrophysical fluids are generically turbulent and this must be taken into
account for most transport processes. We discuss how the preexisting turbulence
modifies magnetic reconnection and how magnetic reconnection affects the MHD
turbulent cascade. We show the intrinsic interdependence and interrelation of
magnetic turbulence and magnetic reconnection, in particular, that strong
magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence
entails fast reconnection. We follow the approach in Eyink, Lazarian & Vishniac
2011 to show that the expressions of fast magnetic reconnection in Lazarian &
Vishniac 1999 can be recovered if Richardson diffusion of turbulent flows is
used instead of ordinary Ohmic diffusion. This does not revive, however, the
concept of magnetic turbulent diffusion which assumes that magnetic fields can
be mixed up in a passive way down to a very small dissipation scales. On the
contrary, we are dealing the reconnection of dynamically important magnetic
field bundles which strongly resist bending and have well defined mean
direction weakly perturbed by turbulence. We argue that in the presence of
turbulence the very concept of flux-freezing requires modification. The
diffusion that arises from magnetic turbulence can be called reconnection
diffusion as it based on reconnection of magnetic field lines. The reconnection
diffusion has important implications for the continuous transport processes in
magnetized plasmas and for star formation. In addition, fast magnetic
reconnection in turbulent media induces the First order Fermi acceleration of
energetic particles, can explain solar flares and gamma ray bursts. However,
the most dramatic consequence of these developments is the fact that the
standard flux freezing concept must be radically modified in the presence of
turbulence.",1112.0022v1
2012-10-13,Full-disk nonlinear force-free field extrapolation of SDO/HMI and SOLIS/VSM magnetograms,"Extrapolation codes in Cartesian geometry for modelling the magnetic field in
the corona do not take the curvature of the Sun's surface into account and can
only be applied to relatively small areas, e.g., a single active region. We
compare the analysis of the photospheric magnetic field and subsequent
force-free modeling based on full-disk vector maps from Helioseismic and
Magnetic Imager (HMI) on board solar dynamics observatory (SDO) and Vector
Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of
the Sun (SOLIS). We use Helioseismic and Magnetic Imager and Vector
Spectromagnetograph photospheric magnetic field measurements to model the
force-free coronal field above multiple solar active regions, assuming magnetic
forces to dominate. We solve the nonlinear force-free field equations by
minimizing a functional in spherical coordinates over a full disk excluding the
poles. After searching for the optimum modeling parameters for the particular
data sets, we compare the resulting nonlinear force-free model fields. We
compare quantities like the total magnetic energy content and free magnetic
energy, the longitudinal distribution of the magnetic pressure and surface
electric current density using our spherical geometry extrapolation code. The
magnetic field lines obtained from nonlinear force-free extrapolation based on
Helioseismic and Magnetic Imager and Vector Spectromagnetograph data have good
agreement. However, the nonlinear force-free extrapolation based on
Helioseismic and Magnetic Imager data have more contents of total magnetic
energy, free magnetic energy, the longitudinal distribution of the magnetic
pressure and surface electric current density compared to the one from Vector
Spectromagnetograph data.",1210.3668v1
2012-12-04,Evolution of Primordial Magnetic Fields from Phase Transitions,"We consider the evolution of primordial magnetic fields generated during
cosmological, electroweak or QCD, phase transitions. We assume that the
magnetic field generation can be described as an injection of magnetic energy
to cosmological plasma at a given scale determined by the moment of magnetic
field generation. A high Reynolds number ensures strong coupling between
magnetic field and fluid motions. The subsequent evolution of the magnetic
field is governed by decaying hydromagnetic turbulence. Both our numerical
simulations and a phenomenological description allow us to recover ""universal""
laws for the decay of magnetic energy and the growth of magnetic correlation
length in the turbulent (low viscosity) regime. In particular, we show that
during the radiation dominated epoch, energy and correlation length of
non-helical magnetic fields scale as conformal time to the powers -1/2 and
+1/2, respectively. For helical magnetic fields, energy and correlation length
scale as conformal time to the powers -1/3 and +2/3, respectively. The
universal decay law of the magnetic field implies that the strength of magnetic
field generated during the QCD phase transition could reach $\sim 10^{-9}$\,G
with the present day correlation length $\sim 50$ kpc. The fields generated at
the electroweak phase transition could be as strong as $\sim 10^{-10}$ G with
correlation lengths reaching $\sim 0.3$\,kpc. These values of the magnetic
fields are consistent with the lower bounds of the extragalactic magnetic
fields.",1212.0596v2
2014-06-21,Quark stars under strong magnetic fields,"Within the confined isospin- and density-dependent mass model, we study the
properties of strange quark matter (SQM) and quark stars (QSs) under strong
magnetic fields. The equation of state of SQM under a constant magnetic field
is obtained self-consistently and the pressure perpendicular to the magnetic
field is shown to be larger than that parallel to the magnetic field, implying
that the properties of magnetized QSs generally depend on both the strength and
the orientation of the magnetic fields distributed inside the stars. Using a
density-dependent magnetic field profile which is introduced to mimic the
magnetic field strength distribution in a star, we study the properties of
static spherical QSs by assuming two extreme cases for the magnetic field
orientation in the stars, i.e., the radial orientation in which the local
magnetic fields are along the radial direction and the transverse orientation
in which the local magnetic fields are randomly oriented but perpendicular to
the radial direction. Our results indicate that including the magnetic fields
with radial (transverse) orientation can significantly decrease (increase) the
maximum mass of QSs, demonstrating the importance of the magnetic field
orientation inside the magnetized compact stars.",1406.5610v2
2014-12-10,Joint inverse cascade of magnetic energy and magnetic helicity in MHD turbulence,"We show that oppositely directed fluxes of energy and magnetic helicity
coexist in the inertial range in fully developed magnetohydrodynamic (MHD)
turbulence with small-scale sources of magnetic helicity. Using a helical shell
model of MHD turbulence, we study the high Reynolds number magnetohydrodynamic
turbulence for helicity injection at a scale that is much smaller than the
scale of energy injection. In a short range of scales larger than the forcing
scale of magnetic helicity, a bottleneck-like effect appears, which results in
a local reduction of the spectral slope. The slope changes in a domain with a
high level of relative magnetic helicity, which determines that part of the
magnetic energy related to the helical modes at a given scale. If the relative
helicity approaches unity, the spectral slope tends to $-3/2$. We show that
this energy pileup is caused by an inverse cascade of magnetic energy
associated with the magnetic helicity. This negative energy flux is the
contribution of the pure magnetic-to-magnetic energy transfer, which vanishes
in the non-helical limit. In the context of astrophysical dynamos, our results
indicate that a large-scale dynamo can be affected by the magnetic helicity
generated at small scales. The kinetic helicity, in particular, is not involved
in the process at all. An interesting finding is that an inverse cascade of
magnetic energy can be provided by a small-scale source of magnetic helicity
fluctuations without a mean injection of magnetic helicity.",1412.3225v1
2015-04-29,The formation of regular interarm magnetic fields in spiral galaxies,"Observations of regular magnetic fields in several nearby galaxies reveal
magnetic arms situated between the material arms. The nature of these magnetic
arms is a topic of active debate. Previously we found a hint that taking into
account the effects of injections of small-scale magnetic fields generated,
e.g., by turbulent dynamo action, into the large-scale galactic dynamo can
result in magnetic arm formation. We now investigate the joint roles of an
arm/interarm turbulent diffusivity contrast and injections of small-scale
magnetic field on the formation of large-scale magnetic field (""magnetic arms"")
in the interarm region. We use the relatively simple ""no-$z$"" model for the
galactic dynamo. This involves projection on to the galactic equatorial plane
of the azimuthal and radial magnetic field components; the field component
orthogonal to the galactic plane is estimated from the solenoidality condition.
We find that addition of diffusivity gradients to the effect of magnetic field
injections makes the magnetic arms much more pronounced. In particular, the
regular magnetic field component becomes larger in the interarm space compared
to that within the material arms.The joint action of the turbulent diffusivity
contrast and small-scale magnetic field injections (with the possible
participation of other effects previously suggested) appears to be a plausible
explanation for the phenomenon of magnetic arms.",1504.07824v3
2016-06-08,Simulation and experiments of Stacks of High Temperature Superconducting Coated Conductors Magnetized by Pulsed Field Magnetization with Multi-Pulse Technique,"High temperature superconducting (HTS) bulks or stacks of coated conductors
(CCs) can be magnetized to become trapped field magnets (TFMs). The magnetic
fields of such TFMs can break the limitation of conventional magnets (<2 T), so
they show potential for improving the performance of many electrical
applications that use permanent magnets like rotating machines. Towards
practical or commercial use of TFMs, effective in situ magnetization is one of
the key issues. The pulsed field magnetization (PFM) is among the most
promising magnetization methods in virtue of its compactness, mobility and low
cost. However, due to the heat generation during the magnetization, the trapped
field and flux acquired by PFM usually cannot achieve the full potential of a
sample (acquired by the field cooling or zero field cooling method). The
multi-pulse technique was found to effectively improve the trapped field by PFM
in practice. In this work, a systematic study on the PFM with successive pulses
is presented. A 2D electromagnetic-thermal coupled model with comprehensive
temperature dependent parameters is used to simulate a stack of CCs magnetized
by successive magnetic pulses. An overall picture is built to show how the
trapped field and flux evolve with different pulse sequences and the evolution
patterns are analyzed. Based on the discussion, an operable magnetization
strategy of PFM with successive pulses is suggested to provide more trapped
field and flux. Finally, experimental results of a stack of CCs magnetized by
typical pulse sequences are presented for demonstration.",1606.07732v1
2017-08-25,Statistics of magnetic field measurements and evolution of magnetic field of OBA stars,"We review the measurements of magnetic fields of OBA stars. Based on these
data we confirm that magnetic fields are distributed according to a lognormal
law with a mean log(B)=-0.5 (B in kG) with a standard deviation sigma=0.5. The
shape of the magnetic field distribution is similar to that for neutron stars.
This finding is in favor of the hypothesis that the magnetic field of a neutron
star is determined mainly by the magnetic field of its predecessor, the massive
OB star. Further, we model the evolution of an ensemble of magnetic massive
stars in the Galaxy. We use our own population synthesis code to obtain the
distribution of stellar radii, ages, masses, temperatures, effective magnetic
fields and magnetic fluxes from the pre-main sequence (PMS) via zero age main
sequence (ZAMS) up to the terminal age main sequence (TAMS) stages. A
comparison of the obtained in our model magnetic field distribution (MFD) with
that obtained from the recent measurements of the stellar magnetic field allows
us to conclude that the evolution of magnetic fields of massive stars is slow
if not absent. The shape of the real MFD shows no indications of the magnetic
desert proposed previously. Based on this finding we argue that the observed
fraction of magnetic stars is determined by physical conditions at the PMS
stage of stellar evolution.",1708.07816v2
2017-08-22,A pico-Tesla magnetic sensor with PZT bimorph and permanent magnet proof mass,"Ferromagnetic-ferroelectric composites have attracted interests in recent
years for use as magnetic field sensors. The sensing is based on
magneto-electric (ME) coupling between the electric and magnetic subsystems and
is mediated by mechanical strain. Such sensors for AC magnetic fields require a
bias magnetic field to achieve pT-sensitivity. Here we discuss measurements and
theory for a novel passive, AC magnetic sensor that does not require a bias
magnetic field and is based on a PZT bimorph with a permanent magnet proof
mass. Mechanical strain on the PZT bimorph in this case is produced by
interaction between the applied AC magnetic field and remnant magnetization of
the permanent magnet, resulting in an induced voltage across PZT. Our studies
have been performed on sensors with a bimorph of oppositely poled PZT platelets
and a NdFeB permanent magnet proof mass. Magnetic floor noise N on the order of
100 pT per sqrHz and 10 nT per sqrHz are measured at 1 Hz and 10 Hz,
respectively. When the AC magnetic field is applied at the bending resonance of
40 Hz for the bimorph, the measured N 700 pT per sqrHz. We also discuss a
theory for the magneto-electro-mechanical coupling at low frequency and bending
resonance in the sensor and theoretical estimates of ME voltage coefficients
are in very good agreement with the data.",1709.01794v1
2017-12-13,Studying the transfer of magnetic helicity in solar active regions with the connectivity-based helicity flux density method,"In the solar corona, magnetic helicity slowly and continuously accumulates in
response to plasma flows tangential to the photosphere and magnetic flux
emergence through it. Analyzing this transfer of magnetic helicity is key for
identifying its role in the dynamics of active regions (ARs). The
connectivity-based helicity flux density method was recently developed for
studying the 2D and 3D transfer of magnetic helicity in ARs. The method takes
into account the 3D nature of magnetic helicity by explicitly using knowledge
of the magnetic field connectivity, which allows it to faithfully track the
photospheric flux of magnetic helicity. Because the magnetic field is not
measured in the solar corona, modeled 3D solutions obtained from force-free
magnetic field extrapolations must be used to derive the magnetic connectivity.
Different extrapolation methods can lead to markedly different 3D magnetic
field connectivities, thus questioning the reliability of the
connectivity-based approach in observational applications. We address these
concerns by applying this method to the isolated and internally complex AR
11158 with different magnetic field extrapolation models. We show that the
connectivity-based calculations are robust to different extrapolation methods,
in particular with regards to identifying regions of opposite magnetic helicity
flux. We conclude that the connectivity-based approach can be reliably used in
observational analyses and is a promising tool for studying the transfer of
magnetic helicity in ARs and relate it to their flaring activity.",1712.04691v1
2018-05-09,The Effects of Magnetic Field Strength on Properties of Wind Generated from Hot Accretion Flow,"Observations indicate that wind can be generated in hot accretion flow. By
performing numerical simulations, Yuan et al. studied the detailed properties
of wind generated from weakly magnetized accretion flow. However, properties of
wind generated from strongly magnetized hot accretion flow have not been
studied. In this paper, we study the properties of wind generated from both
weakly and strongly magnetized accretion flow. We focus on how the magnetic
field strength affects the wind properties. We solve time-steady
two-dimensional magnetohydrodynamic (MHD) equations of black hole accretion in
the presence of large-scale magnetic field. We assume self-similarity in radial
direction. The magnetic field is assumed to be evenly symmetric with the
equatorial plane. We find that wind exists in both weakly and strongly
magnetized accretion flow. When magnetic field is weak (magnetic pressure is
more than 2 orders of magnitude smaller than gas pressure), wind is driven by
gas pressure gradient and centrifugal forces. When magnetic field is strong
(magnetic pressure is slightly smaller than gas pressure), wind is driven by
gas pressure gradient and magnetic pressure gradient forces. The power of wind
in strongly magnetized case is just slightly larger than that in weakly
magnetized case. The power of wind lies in a range $ P_W \sim 10^{-4}-10^{-3}
\dot M_{\rm in} c^2 $, with $ \dot M_{\rm in} $ and $ c $ being mass inflow
rate and speed of light, respectively. The possible role of wind in active
galactic nuclei feedback is briefly discussed.",1805.03378v1
2018-08-08,Magnetic Gradiometer for Detection of Zero- and Ultralow-Field Nuclear Magnetic Resonance,"Magnetic sensors are important for detecting nuclear magnetization signals in
nuclear magnetic resonance (NMR). As a complementary analysis tool to
conventional high-field NMR, zero- and ultralow-field (ZULF) NMR detects
nuclear magnetization signals in the sub-microtesla regime. Current ZULF NMR
systems are always equipped with high-quality magnetic shieldings to ensure
that ambient magnetic field noise does not dwarf the magnetization signal. An
alternative approach is to separate the magnetization signal from the noise
based on their differing spatial profiles, as can be achieved using a magnetic
gradiometer. Here, we present a gradiometric ZULF NMR spectrometer with a
magnetic gradient noise of 17 fT_{rms}{cm}^{-1}{Hz}^{-1/2} in the frequency
range of 100-400 Hz, based on a single vapor cell (0.7x0.7x1.0{cm}^3). With
applied white magnetic-field noise, we show that the gradiometric spectrometer
achieves 13-fold enhancement in the signal-to-noise ratio (SNR) compared to the
single-channel configuration. By reducing the influence of common-mode magnetic
noise, this work enables the use of compact and low-cost magnetic shields.
Gradiometric detection may also prove to be beneficial for eliminating
systematic errors in ZULF-NMR experiments searching for exotic spin-dependent
interactions and molecular parity violation.",1808.02743v1
2019-01-30,Comparative Study of the Surface Potential of Magnetic and Non-magnetic Spherical Objects in a Magnetized RF Discharge Plasma,"We report measurements of the time-averaged surface floating potential of
magnetic and non-magnetic spherical probes (or large dust particles) immersed
in a magnetized capacitively coupled discharge. In this study, the size of the
spherical probes is taken greater than the Debye length. The surface potential
of a spherical probe first increases, i.e. becomes more negative at low
magnetic field (B $<$ 0.05 T), attains a maximum value and decreases with
further increase of the magnetic field strength (B $>$ 0.05 T). The rate of
change of the surface potential in the presence of a B-field mainly depends on
the background plasma and types of material of the objects. The results show
that the surface potential of the magnetic sphere is higher (more negative)
compared to the non-magnetic spherical probe. Hence, the smaller magnetic
sphere collects more negative charges on its surface than a bigger non-magnetic
sphere in a magnetized plasma. The different sized spherical probes have nearly
the same surface potential above a threshold magnetic field (B $>$ 0.03 T),
implicating a smaller role of size dependence on the surface potential of
spherical objects. The variation of the surface potential of the spherical
probes is understood on the basis of a modification of the collection currents
to their surface due to charge confinement and cross-field diffusion in the
presence of an external magnetic field.",1901.10955v4
2019-02-27,Relative magnetic field line helicity,"Context. Magnetic helicity is an important quantity in studies of magnetized
plasmas as it provides a measure of the geometrical complexity of the magnetic
field in a given volume. A more detailed description of the spatial
distribution of magnetic helicity is given by the field line helicity that
expresses the amount of helicity associated to individual field lines, rather
than in the full analysed volume. Aims. Magnetic helicity is not a
gauge-invariant quantity in general, unless it is computed with respect to a
reference field, yielding the so called relative magnetic helicity. The field
line helicity corresponding to the relative magnetic helicity has only been
examined under specific conditions so far. This work aims to define the field
line helicity corresponding to relative magnetic helicity in the most general
way. In addition to its general form, we provide the expression for the
relative magnetic field line helicity in a few commonly used gauges, and
reproduce known results as a limit of our general formulation. Methods. By
starting from the definition of relative magnetic helicity, we derive the
corresponding field line helicity, and we note the assumptions it is based on.
Results. We check that the developed quantity reproduces relative magnetic
helicity by using three different numerical simulations. For these cases we
also show the morphology of field line helicity in the volume, and on the
photospheric plane. As an application to solar situations, we compare the
morphology of field line helicity on the photosphere with that of the
connectivity-based helicity flux density in two reconstructions of an active
region's magnetic field. We discuss how the derived relative magnetic field
line helicity has a wide range of applications, notably in solar physics and
magnetic reconnection studies.",1902.10410v1
2019-09-05,"The Magnetic Early B-type Stars III: A main sequence magnetic, rotational, and magnetospheric biography","Magnetic confinement of stellar winds leads to the formation of
magnetospheres, which can be sculpted into Centrifugal Magnetospheres (CMs) by
rotational support of the corotating plasma. The conditions required for the
CMs of magnetic early B-type stars to yield detectable emission in H$\alpha$ --
the principal diagnostic of these structures -- are poorly constrained. A key
reason is that no detailed study of the magnetic and rotational evolution of
this population has yet been performed. Using newly determined rotational
periods, modern magnetic measurements, and atmospheric parameters determined
via spectroscopic modelling, we have derived fundamental parameters, dipolar
oblique rotator models, and magnetospheric parameters for 56 early B-type
stars. Comparison to magnetic A- and O-type stars shows that the range of
surface magnetic field strength is essentially constant with stellar mass, but
that the unsigned surface magnetic flux increases with mass. Both the surface
magnetic dipole strength and the total magnetic flux decrease with stellar age,
with the rate of flux decay apparently increasing with stellar mass. We find
tentative evidence that multipolar magnetic fields may decay more rapidly than
dipoles. Rotational periods increase with stellar age, as expected for a
magnetic braking scenario. Without exception, all stars with H$\alpha$ emission
originating in a CM are 1) rapid rotators, 2) strongly magnetic, and 3) young,
with the latter property consistent with the observation that magnetic fields
and rotation both decrease over time.",1909.02530v1
2020-04-24,Observation of magnetic domain and bubble structures in magnetoelectric Sr$_3$Co$_2$Fe$_{24}$O$_{41}$,"The magnetic domain and bubble structures in the Z-type hexaferrite
Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ were investigated using Lorentz microscopy. This
hexaferrite exhibits a room-temperature magnetoelectric effect that is
attributed to its transverse conical spin structure (TC phase). Upon heating,
the TC phase transforms into a ferrimagnetic phase with magnetic moments in the
hexagonal $ab$ plane between 410 and 480 K (FM2 phase) and into another
ferrimagnetic phase with moments parallel to the $c$ axis between 490 and 680 K
(FM1 phase). Accordingly, in this study, the magnetic domain structures in
Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ were observed to change dramatically with
temperature. In the TC phase, irregular fine magnetic domains were observed
after cooling the specimen from the FM2 to TC phase. In the FM1 phase, striped
magnetic domain walls with pairs of bright and dark contrast were formed
parallel to the $c$ axis. Upon applying an external magnetic field, the striped
magnetic domain walls transformed into magnetic bubbles. The topology of the
magnetic bubbles was dependent on the angle between the external magnetic field
($H$) direction and the easy $c$ axis. Namely, magnetic bubbles with the
topological number $N$ = 1 (type I) were created for $H//c$, whereas magnetic
bubbles with $N$ = 0 (type II) were created when the magnetic field was tilted
from the c axis by 5{\deg}. We attribute the high magnetocrystalline anisotropy
of Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ to the emergence of magnetic bubbles in the
FM1 phase.",2004.11591v1
2020-06-12,Odd-even layer-number effect and layer-dependent magnetic phase diagrams in MnBi2Te4,"The intrinsic magnetic layered topological insulator MnBi2Te4 with nontrivial
topological properties and magnetic order has become a promising system for
exploring exotic quantum phenomena such as quantum anomalous Hall effect.
However, the layer-dependent magnetism of MnBi2Te4, which is fundamental and
crucial for further exploration of quantum phenomena in this system, remains
elusive. Here, we use polar reflective magnetic circular dichroism
spectroscopy, combined with theoretical calculations, to obtain an in-depth
understanding of the layer-dependent magnetic properties in MnBi2Te4. The
magnetic behavior of MnBi2Te4 exhibits evident odd-even layer-number effect,
i.e. the oscillations of the coercivity of the hysteresis loop (at {\mu}0Hc)
and the spin-flop transition (at {\mu}0H1), concerning the Zeeman energy and
magnetic anisotropy energy. In the even-number septuple layers, an anomalous
magnetic hysteresis loop is observed, which is attributed to the
thickness-independent surface-related magnetization. Through the linear-chain
model, we can clarify the odd-even effect of the spin-flop field and determine
the evolution of magnetic states under the external magnetic field. The
mean-field method also allows us to trace the experimentally observed magnetic
phase diagrams to the magnetic fields, layer numbers and especially,
temperature. Overall, by harnessing the unusual layer-dependent magnetic
properties, our work paves the way for further study of quantum properties of
MnBi2Te4.",2006.07216v1
2021-05-31,Theoretical development in the viscosity of ferrofluid,"The viscosity of ferrofluid has an important role in liquid sealing of the
hard disk drives, biomedical applications as drug delivery, hyperthermia, and
magnetic resonance imaging. In the absence of a magnetic field, the viscosity
of ferrofluid depends on the volume concentration of magnetic nanoparticles
including surfactant layers. However, under the influence of a stationary
magnetic field, the viscosity of ferrofluid depends on the angle between the
applied magnetic field and vorticity in the flow. If this angle is 90o, then
there is a maximum increase in the viscosity. If the magnetic field and the
vorticity in the flow are parallel to each other, then there is no change in
the viscosity since the applied magnetic field does not change the speed of the
rotation of magnetic nanoparticles in the fluid. The viscosity of ferrofluid in
the presence of an alternating magnetic field demonstrates interesting
behavior. When field frequency matches with the relaxation time, known as
resonance condition, then there is no impact of an alternating magnetic field
in the viscosity of ferrofluid. If the frequency of an alternating magnetic
field is less than resonance frequency, then an alternating magnetic field
increases the viscosity of ferrofluid. Using higher frequency than resonance
condition reduces the viscosity of ferrofluid and researchers reported this
incident as the negative viscosity effect. If the frequency of an alternating
magnetic field tends to infinite, then ferrofluid ceases to feel a magnetic
field. In this case, there is no impact of an alternating magnetic field on the
viscosity of ferrofluid.",2105.14721v1
2021-08-19,Quantized edge magnetizations and their symmetry protection in one-dimensional quantum spin systems,"The bulk electric polarization works as a nonlocal order parameter that
characterizes topological quantum matters. Motivated by a recent paper [H.
Watanabe \textit{et al.}, Phys. Rev. B {\bf 103}, 134430 (2021)], we discuss
magnetic analogs of the bulk polarization in one-dimensional quantum spin
systems, that is, quantized magnetizations on the edges of one-dimensional
quantum spin systems.The edge magnetization shares the topological origin with
the fractional edge state of the topological odd-spin Haldane phases. Despite
this topological origin, the edge magnetization can also appear in
topologically trivial quantum phases. We develop straightforward field
theoretical arguments that explain the characteristic properties of the edge
magnetization. The field theory shows that a U(1) spin-rotation symmetry and a
site-centered or bond-centered inversion symmetry protect the quantization of
the edge magnetization. We proceed to discussions that quantum phases on
nonzero magnetization plateaus can also have the quantized edge magnetization
that deviates from the magnetization density in bulk. We demonstrate that the
quantized edge magnetization distinguishes two quantum phases on a
magnetization plateau separated by a quantum critical point. The edge
magnetization exhibits an abrupt stepwise change from zero to $1/2$ at the
quantum critical point because the quantum phase transition occurs in the
presence of the symmetries protecting the quantization of the edge
magnetization. We also show that the quantized edge magnetization can result
from the spontaneous ferrimagnetic order.",2108.08458v2
2021-08-27,Effects of anisotropy on strongly magnetized neutron and strange quark stars in general relativity,"We investigate the properties of anisotropic, spherically symmetric compact
stars, especially neutron stars and strange quark stars, made of strongly
magnetized matter. The neutron stars are described by SLy equation of state,
the strange quark stars by an equation of state based on the MIT Bag model. The
stellar models are based on an a priori assumed density dependence of the
magnetic field and thus anisotropy. Our study shows that not only the presence
of a strong magnetic field and anisotropy, but also the orientation of the
magnetic field itself, have an important influence on the physical properties
of stars. Two possible magnetic field orientations are considered, a radial
orientation, where the local magnetic fields point in the radial direction, and
a transverse orientation, where the local magnetic fields are perpendicular to
the radial direction. Interestingly, we find that for a transverse orientation
of the magnetic field, the stars become more massive with increasing anisotropy
and magnetic field strength and increase in size, since the repulsive,
effective anisotropic force increases in this case. In the case of a radially
orientated magnetic field, however, the masses and radii of the stars decrease
with increasing magnetic field strength, because of the decreasing effective
anisotropic force. Importantly, we also show that in order to achieve
hydrostatic equilibrium configurations of magnetized matter, it is essential to
account for both the local anisotropy effects as well as the anisotropy effects
caused by a strong magnetic field. Otherwise, hydrostatic equilibrium is not
achieved for magnetized stellar models.",2108.12436v1
2021-11-03,Anisotropic magnetocaloric effect of CrI$_{3}$: A theoretical study,"CrI$_{3}$ is considered to be a promising candidate for spintronic devices
and data storage. We derived the Heisenberg Hamiltonian for CrI$_{3}$ from
density functional calculations using the Liechtenstein formula. Moreover, the
Monte--Carlo simulations with the Sucksmith--Thompson method were performed to
analyze the effect of magnetic anisotropy energy on the thermodynamic
properties. Our method successfully reproduced the negative sign of isothermal
magnetic entropy changes when a magnetic field was applied along the hard
plane. We found that the temperature dependence of the magnetocrystalline
anisotropy energy is not negligible at temperatures slightly above the Curie
temperature. We clarified that the origin of this phenomenon is attributed to
anisotropic magnetic susceptibility and magnetization anisotropy. The
difference between the entropy change of the easy axis and the hard plane is
proportional to the temperature dependence of the magnetic anisotropy energy,
implying that the anisotropic entropy term is the main source of the
temperature dependence of the free energy difference when magnetizing in a
specific direction other than the easy axis. We also investigated the magnetic
susceptibility that can be used for the characterization of the negative sign
of the entropy change in the case of a hard plane. The competition of
magnetocrystalline anisotropy energy and external magnetic field at low
temperature and low magnetic field region causes a high magnetic susceptibility
as the fluctuation of magnetization. Meanwhile, the anisotropy energy is
suppressed at a sufficient magnetic field applied along the hard axis, the
magnetization is fully rotated to the direction of the external magnetic field.",2111.02063v1
2023-01-22,FCC structured ferromagnetic ultra-thin films with two spin layers described by fourth order perturbed Heisenberg Hamiltonian,"Fourth order perturbation was applied to study a small variation of the
azimuthal angle of spin of fcc structured ferromagnetic thin films with two
spin layers. The variation of magnetic energy and the orientation of magnetic
easy axis with the fourth order magnetic anisotropy constant in two spin layers
was investigated. When the second order magnetic anisotropy constant at the top
spin layer is higher than that of bottom spin layer, the total magnetic energy
is slightly higher. Some spikes appeared in the 2D plot of of magnetic energy
versus azimuthal angle of spin. According to the 3D plots, the peak value of
the magnetic energy gradually decreases with the increase of the stress induced
anisotropy constant, and thereafter the peak value of the magnetic energy
gradually increases with the increase of the stress induced anisotropy
constant. The angle between magnetic easy and hard directions was not 90
degrees. The magnetic easy and hard directions of the film with a higher second
order magnetic anisotropy constant of top layer are different from the magnetic
easy and hard directions of the film with a lower second order magnetic
anisotropy constant of top layer. When the second order magnetic anisotropy
constant of the bottom layer is increased, the total magnetic energy does not
change.",2301.09137v1
2005-01-25,Magnetic Fields in Diffuse H I and Molecular Clouds,"This book chapter reviews the current state of observations of magnetic
fields in diffuse H I and in dense molecular clouds. It covers techniques for
measuring magnetic fields, the analysis of the observations, and the role of
magnetic fields in the physics of interstellar clouds and in the star formation
process.",0501550v1
1998-10-25,Orbital Magnetism in Disordered Mesoscopic Metals,"The theory of orbital magnetism in disordered metals is reviewed, and
extended to include a broad range of temperatures and fields. Sample-to-sample
fluctuations in the orbital magnetic susceptibility are studied. In a given
sample these fluctuations manifest themselves in aperiodic sample-specific
oscillations of susceptibility and magnetization, when the strength of the
magnetic field is changed.",9810330v1
2000-09-07,"Intermediate spin, Schrödinger cat states and nano-magnets","Quantum tunneling of nano-magnets finds a natural description in terms of
intermediate spin. Periodic magnetic effects correspond to a change of flux by
the flux quantum $\Phi_{0}$. Schr\""odinger cat states with different
superpositions of the applied magnetic field occur. The molecular magnet
Fe$_{8}$ is discussed and oscillations are predicted for Mn$_{12}$.",0009100v1
2002-01-14,Polaron percolation in diluted magnetic semiconductors,"We theoretically study the development of spontaneous magnetization in
diluted magnetic semiconductors as arising from a percolation of bound magnetic
polarons. Within the framework of a generalized percolation theory we derive
analytic expressions for the Curie temperature and the magnetization, obtaining
excellent quantitative agreement with Monte Carlo simulation results and good
qualitative agreement with experimental results.",0201229v1
2003-07-11,Magnetic and transport percolation in diluted magnetic semiconductors,"The ferromagnetic transition in a diluted magnetic semiconductor with
localized charge carriers is inevitably a percolation transition. In this work
we theoretically study the correlation between this magnetic percolation and
transport properties of the sample, including the possibility of a simultaneous
transport percolation. We find nontrivial signatures of the percolating
magnetic clusters in the transport properties of the system, including
interesting non-monotonic temperature dependence of the system resistivity.",0307294v1
2003-09-05,Reduction of Magnetic Noise in Magnetic Resonance Force Microscopy,"We study the opportunity to reduce a magnetic noise produced by a uniform
cantilever with a ferromagnetic particle in magnetic resonance force microscopy
(MRFM) applications. We demonstrate theoretically a significant reduction of
magnetic noise and the corresponding increase of the MRFM relaxation time using
a nonuniform cantilever.",0309158v1
2003-09-24,Non conservation of the magnetization current across magnetic hetero-structures,"We show that when the magnetizations on opposite sides of a junction are not
collinear, the magnetization current is not conserved as the junction is
crossed. Thus the usual treatment of this problem needs to be modified. We
argue that this is due to an implicit assumption of an external torque that is
required to clamp the magnetization in place. The physical consequence of this
is explored.",0309555v1
2005-11-21,Magnetization reversal in the anisotropy-dominated regime using time-dependent magnetic fields,"We study magnetization reversal using various r.f. magnetic pulses. We show
numerically that switching is possible with simple sinusoidal pulses; however
the optimum approach is to use a frequency-swept (chirped) r.f. magnetic pulse,
the shape of which can be derived analytically. Switching times of the order of
nanoseconds can be achieved with relatively small r.f. fields, independent of
the anisotropy's strength.",0511497v1
2004-01-08,Coordinate noncommutativity in strong non-uniform magnetic fields,"Noncommuting spatial coordinates are studied in the context of a charged
particle moving in a strong non-uniform magnetic field. We derive a relation
involving the commutators of the coordinates, which generalizes the one
realized in a strong constant magnetic field. As an application, we discuss the
noncommutativity in the magnetic field present in a magnetic mirror.",0401048v2
2007-11-07,Magnetic properties of bi-phase micro- and nanotubes,"The magnetic configurations of bi-phase micro- and nanotubes consisting of a
ferromagnetic internal tube, an intermediate non-magnetic spacer, and an
external magnetic shell are investigated as a function of their geometry. Based
on a continuum approach we obtained analytical expressions for the energy which
lead us to obtain phase diagrams giving the relative stability of
characteristic internal magnetic configurations of the bi-phase tubes.",0711.1101v1
2008-06-16,"The fraction of Bose-Einstein condensed triplons in TlCuCl3 from magnetization M(T,H)-data","In this study we calculate the fraction of condensed magnetic quasiparticles
of TlCuCl3 from magnetization M(T,H)-data. It is independent of the direction
of the magnetic field and slightly decreases with increasing magnetic field.",0806.2519v1
2009-03-03,Remarks on eigenvalue estimates and semigroup domination,"We present an overview over recent results concerning semi-classical spectral
estimates for magnetic Schroedinger operators. We discuss how the constants in
magnetic and non-magnetic eigenvalue bounds are related and we prove, in an
abstract setting, that any non-magnetic Lieb-Thirring-type inequality implies a
magnetic Lieb-Thirring-type inequality with possibly a larger constant.",0903.0561v1
2009-10-21,A Generalized Approach to Determination of Magnetic Shielding Factor for Physics Package of Rb Atomic Clock,"In this paper we report generalized approach to calculate magnetic shielding
factor (MSF) of multi-layer mu metal concentric cylindrical shields for
arbitrary length to radius ratios and different values of magnetic
permeability. We report in this paper the generalized results on the magnetic
shielding factor of multi-layered magnetic shields used in Rb atomic clocks",0910.4031v1
2009-12-01,"Control of magnetic vortex wall chirality, polarity and position by a magnetic field","The seeding of vortex domain walls in V-shaped nanowires by a magnetic field
has been investigated via simulations and Scanning Electron Microscopy with
Polarization Analysis (SEMPA). It is found that the orientation of the magnetic
field can be used to purposely tune the chirality, polarity and position of
single vortex domain walls in soft magnetic nanowires.",0912.0178v1
2010-01-19,Theory of the Anomalous Magnetic Moment of the Electron,"It is shown that it follows from our model of the electron that its magnetic
moment has an anomalous part if the magnetic field energy is taken into
account. That means that the magnetic moment of our model of the electron is
1.0000565 times larger than the measured magnetic moment of the electron.",1001.3371v2
2010-10-18,Induced plasma magnetization due to magnetic monopoles,"When magnetic monopoles are introduced in plasma equations, the propagation
of electromagnetic waves is modified. In this work is shown that this
modification leads to the emergence of a ponderomotive force which induces a
magnetization of the plasma. As a result, a cyclotron frequency is induced in
electrons. This frequency is proportional to the square of the magnetic charge.",1010.3462v1
2011-07-11,Electrical conductivity of quark matter in magnetic field,"Fermion currents in dense quark matter embedded into magnetic field are under
intense discussions motivated by Chiral Magnetic Effect. We argue that
conductivity of quark matter may be independent of the magnetic field direction
and not proportional to the magnetic field strength.",1107.1990v3
2011-10-05,Quadratic helicities and the energy of magnetic fields,"Two non-local asymptotic invariants of magnetic fields for the ideal
magnetohydrodynamics are introduced. The velocity of variation of the
invariants for a non-ideal magnetohydrodynamics with a small magnetic
dissipation is estimated. By means of the invariants the spectra of
electromagnetic fields are investigated. A possible role of higher magnetic
helicities during a relaxation of magnetic fields is discussed.",1110.0997v1
2012-01-04,Magnetic dipole moment of a moving electric dipole,"The current density of a moving electric dipole is expressed as the sum of
polarization and magnetization currents. The magnetic field due to the latter
current is that of a magnetic dipole moment that is consistent with the
relativistic transformations of the polarization and magnetization of
macroscopic electrodynamics.",1201.0938v2
2012-02-12,Entropy Maximization and Instability of Uniformly Magnetized Plasma,"A regime where a uniformly magnetized plasma could be unstable to a spatial
perturbation in the magnetic field is explored. In this regime, a uniformly
magnetized state does not maximize the entropy. The physical implication is
discussed in the context of the current generation, the magnetic reconnection,
and the dynamo effect.",1202.2583v2
2012-03-26,Thermo-magneto coupling in a dipole plasma,"On a dipole plasma, we observe the generation of magnetic moment, as the
movement of the levitating magnet-plasma compound, in response to
electron-cyclotron heating and the increase of $\beta$ (magnetically-confined
thermal energy). We formulate a thermodynamic model with interpreting heating
as injection of microscopic magnetic moment; the corresponding chemical
potential is the ambient magnetic field.",1203.5680v1
2012-10-29,Phase deformed magnetic Berezin transforms on $\mathbb{C}^{n}$: A formula representing phase deformed magnetic Berezin transforms as functions of the magnetic Laplacian on $\mathbb{C}^{n}$,"We introduce a new class of a phase deformed magnetic berezin transforms and
we give two formulae representing these transforms as a functions of the
magnetic laplacian on $\mathbb{C}^{n}.$ As a consequence, we give an inequality
of diamagnetic type.",1210.7734v1
2012-12-20,Magnetic properties of the RbNd(WO4)2 single crystal,"The magnetic investigations as a function of temperature and magnetic field
for the rubidium neodymium double tungstate RbNd(WO4)2 single crystal have been
performed. The magnetization was measured in the temperature range from 4.2 to
100 K and for the magnetic field up to 1.5 T. The crystal field and exchange
parameters were found.",1212.4997v1
2014-06-14,Computer Simulations on Barkhausen effects and Magnetizations in Fe Nano-Structure Systems,"The magnetization processes in Fe nano-systems are investigated using the
numerical simulations based on classical magnetic dipole moment interactions.
The domain energies are calculated from moment-moment interactions over whole
systems using large scale computing resources. The results directly show most
of basic magnetization phenomena. The Barkhausen effects are represented with
jumps and terraces of magnetization steps induced from external field changes
of {\Delta}H.",1406.3688v1
2015-01-28,Experimental Characterization of Magnetic Materials for the Magnetic Shielding of Cryomodules in Particle Accelerators,"The magnetic properties of two important passive magnetic shielding materials
(A4K and Amumetal) for accelerator applications, subjected to various
processing and heat treatment conditions are studied comprehensively over a
wide range of temperatures: from Cryogenic to room temperature. We analyze the
effect of processing on the extent of degradation of the magnetic properties of
both materials and investigate the possibility of restoring these properties by
re-annealing.",1501.07312v1
2015-08-11,Transport between metals and magnetic insulators,"We derive the Onsager response matrix of fluctuation-mediated spin-collinear
transport through a ferromagnetic insulator and normal metal interface driven
by a temperature difference, spin accumulation, or magnetic field. We predict
magnon-squeezing spin currents, magnetic field-induced cooling (magnon Peltier
effect), temperature induced magnetization (thermal magnetic field) as well as
universal spin Seebeck/Peltier coefficients.",1508.02486v2
2019-01-17,Observations of solar small-scale magnetic flux-sheet emergence,"Aims. Moreno-Insertis et al. (2018) recently discovered two types of flux
emergence in their numerical simulations: magnetic loops and magnetic sheet
emergence. Whereas magnetic loop emergence has been documented well in the last
years, by utilising high-resolution full Stokes data from ground-based
telescopes as well as satellites, magnetic sheet emergence is still an
understudied process. We report here on the first clear observational evidence
of a magnetic sheet emergence and characterise its development.
  Methods. Full Stokes spectra from the Hinode spectropolarimeter were inverted
with the SIR code to obtain solar atmospheric parameters such as temperature,
line-of-sight velocities and full magnetic field vector information.
  Results. We analyse a magnetic flux emergence event observed in the quiet-sun
internetwork. After a large scale appearance of linear polarisation, a magnetic
sheet with horizontal magnetic flux density of up to 194 Mx/cm$^{2}$ hovers in
the low photosphere spanning a region of 2 to 3 arcsec. The magnetic field
azimuth obtained through Stokes inversions clearly shows an organised structure
of transversal magnetic flux density emerging. The granule below the magnetic
flux-sheet tears the structure apart leaving the emerged flux to form several
magnetic loops at the edges of the granule.
  Conclusions. A large amount of flux with strong horizontal magnetic fields
surfaces through the interplay of buried magnetic flux and convective motions.
The magnetic flux emerges within 10 minutes and we find a longitudinal magnetic
flux at the foot points of the order of $\sim$$10^{18}$ Mx. This is one to two
orders of magnitude larger than what has been reported for small-scale magnetic
loops. The convective flows feed the newly emerged flux into the pre-existing
magnetic population on a granular scale.",1901.05870v1
2019-02-06,Iron oxide nanoparticles for magnetic hyperthermia,"Assemblies of magnetic nanoparticles show a great potential for application
in biomedicine, in particular, in magnetic hyperthermia. However, to achieve
desired therapeutic effect in magnetic hyperthermia the assembly of
nanoparticles should have a sufficiently high specific absorption rate in
alternating magnetic field of moderate amplitude and frequency.",1902.02220v1
2021-02-26,Magnetic Curves in $C$-manifolds,"In this paper, we study normal magnetic curves in $C$-manifolds. We prove
that magnetic trajectories with respect to the contact magnetic fields are
indeed $\theta_{\alpha }$-slant curves with certain curvature functions. Then,
we give the parametrizations of normal magnetic curves in $\mathbb{R}^{2n+s}$
with its structures as a $C$-manifold.",2102.13623v1
2021-04-14,Non-resonant circles for strong magnetic fields on surfaces,"We study non-resonant circles for strong magnetic fields on a closed,
connected, oriented surface and show how these can be used to prove the
existence of trapping regions and of periodic magnetic geodesics with
prescribed low speed. As a corollary, there exist infinitely many periodic
magnetic geodesics for every low speed in the following cases: i) the surface
is not the two-sphere, ii) the magnetic field vanishes somewhere.",2104.06733v1
2022-01-19,Using the Standard Linear Ramps of the CMS Superconducting Magnet for Measuring the Magnetic Flux Density in the Steel Flux Return Yoke,"The principal difficulty in large magnetic systems having an extensive flux
return yoke is to characterize the magnetic flux distribution in the yoke steel
blocks. Continuous measurements of the magnetic flux density in the return yoke
are not possible and the usual practice uses software modelling of the magnetic
system with special 3D computer programs. The flux return yoke of the Compact
Muon Solenoid (CMS) magnet encloses a 3.8 T superconducting solenoid with a
6-m-diameter by 12.5-m-length free bore and consists of five dodecagonal
three-layered barrel wheels around the coil and four endcap disks at each end.
The yoke steel blocks serve as the absorber plates of the muon detection
system. A TOSCA 3D model of the CMS magnet has been developed to describe the
magnetic field outside of the solenoid volume, which was measured with a
field-mapping machine. To verify the magnetic flux distribution calculated in
the yoke steel blocks, direct measurements of the magnetic flux density with 22
flux loops installed in selected regions of the yoke were performed during the
CMS magnet test in 2006 when four ""fast"" discharges of the CMS coil were
triggered manually to test the magnet protection system. No fast discharge of
the CMS magnet from its operational current of 18.2 kA, which corresponds to a
central magnetic flux density of 3.8 T, has been performed that time. For the
first time, in this paper we present measurements of the magnetic flux density
in the steel blocks of the return yoke based on the several standard linear
discharges of the CMS magnet from the operational magnet current of 18.2 kA. To
provide these measurements, the voltages induced in the flux loops have been
measured with six 16-bit DAQ modules and integrated offline over time. The
results of the measurements during magnet linear ramps performed with a current
rate as low as 1-1.5 A/s are presented and discussed.",2201.07557v1
2022-11-15,Eigenvalue estimates for the magnetic Hodge Laplacian on differential forms,"In this paper we introduce the magnetic Hodge Laplacian, which is a
generalization of the magnetic Laplacian on functions to differential forms. We
consider various spectral results, which are known for the magnetic Laplacian
on functions or for the Hodge Laplacian on differential forms, and discuss
similarities and differences of this new ``magnetic-type'' operator.",2211.08019v1
2024-03-04,Development of a Static Magnetic Diode,"This report experimentally demonstrates the feasibility of applying an
electrical current though a stationary graphene structure to induce magnetic
non-reciprocity or, in other words, to create a static magnetic diode, and
thereby validate the suggestion of Prat-Camps [1] et al. regarding the use of
graphene for such a purpose. The described graphene-based static magnetic diode
is assessed against the rotating copper magnetic diode of Prat-Camps and found
to be comparable.",2403.02193v1
1997-08-03,A Vorticity-Magnetic Field Dynamo Instability,"We generalize the mean field magnetic dynamo to include local evolution of
the mean vorticity in addition to the mean magnetic field. The coupled
equations exhibit a general mean field dynamo instability that enables the
transfer of turbulent energy to the magnetic field and vorticity on larger
scales. The growth of the vorticity and magnetic field both require helical
turbulence which can be supplied by an underlying global rotation. The dynamo
coefficients are derived including the backreaction from the mean magnetic
field to lowest order. We find that a mean vorticity field can actually seed
exponential growth of mean magnetic field from only a small scale seed magnetic
field, without the need for a seed mean magnetic field. The equations decouple
when the fluctuating velocity and magnetic field cross-correlations vanish,
resulting in the separate mean field magnetic and mean field vorticity dynamo
equations.",9708019v1
2002-05-18,Magnetic Helicity Tensor for an Anisotropic Turbulence,"The evolution of the magnetic helicity tensor for a nonzero mean magnetic
field and for large magnetic Reynolds numbers in an anisotropic turbulence is
studied. It is shown that the isotropic and anisotropic parts of the magnetic
helicity tensor have different characteristic times of evolution. The time of
variation of the isotropic part of the magnetic helicity tensor is much larger
than the correlation time of the turbulent velocity field. The anisotropic part
of the magnetic helicity tensor changes for the correlation time of the
turbulent velocity field. The mean turbulent flux of the magnetic helicity is
calculated as well. It is shown that even a small anisotropy of turbulence
strongly modifies the flux of the magnetic helicity. It is demonstrated that
the tensor of the magnetic part of the alpha-effect for weakly inhomogeneous
turbulence is determined only by the isotropic part of the magnetic helicity
tensor. Astrophysical applications of the obtained results are discussed.",0205314v1
2006-09-22,Buoyant magnetic flux ropes in a magnetized stellar envelope: Idealized numerical 2.5-D MHD simulations,"Context: The context of this paper is buoyant toroidal magnetic flux ropes,
which is a part of flux tube dynamo theory and the framework of solar-like
magnetic activity. Aims: The aim is to investigate how twisted magnetic flux
ropes interact with a simple magnetized stellar model envelope--a magnetic
""convection zone""--especially to examine how the twisted magnetic field
component of a flux rope interacts with a poloidal magnetic field in the
convection zone. Method: Both the flux ropes and the atmosphere are modelled as
idealized 2.5-dimensional concepts using high resolution numerical
magneto-hydrodynamic (MHD) simulations. Results: It is illustrated that twisted
toroidal magnetic flux ropes can interact with a poloidal magnetic field in the
atmosphere to cause a change in both the buoyant rise dynamics and the flux
rope's geometrical shape. The details of these changes depend primarily on the
polarity and strength of the atmospheric field relative to the field strength
of the flux rope. It is suggested that the effects could be verified
observationally.",0609630v1
2000-07-03,Interaction of Mesoscopic Magnetic Textures with Superconductors,"We analyze magnetic textures in a thin magnetic film and screening currents
induced by these textures in a superconducting film. The films are supposed to
be parallel and close to each other, but interact only via magnetic fields. We
consider also vortices inside superconducting film and their interaction with
magnetic textures. As examples of magnetic textures we consider magnetic dot
and magnetic vortex. We derive the condition at which spontaneous formation of
a vortex or a coupled vortex-magnetic defect is energetically favorable. It is
proven that the normal component of magnetic field generated by a magnetic dot
changes sign in the presence of the superconducting vortex.",0007016v1
2002-04-29,Electron Magnetic Resonance: The Modified Bloch Equation,"We find a modified Bloch equation for the electronic magnetic moment when the
magnetic moment explicitly contains a diamagnetic contribution (a magnetic
field induced magnetic moment arising from the electronic orbital angular
momentum) in addition to the intrinsic magnetic moment of the electron. The
modified Bloch is coupled to equations of motion for the position and momentum
operators. In the presence of static and time varying magnetic field
components, the magnetic moment oscillates out of phase with the magnetic field
and power is absorbed by virtue of the magnetic field induced magnetic moment,
even in the absence of coupling to the environment. We explicitly work out the
spectrum and absorption for the case of a $p$ state electron.",0204604v1
2002-11-21,Magnetic levitation force between a superconducting bulk magnet and a permanent magnet,"The current density in a disk-shaped superconducting bulk magnet and the
magnetic levitation force exerted on the superconducting bulk magnet by a
cylindrical permanent magnet are calculated from first principles. The effect
of the superconducting parameters of the superconducting bulk is taken into
account by assuming the voltage-current law and the material law. The magnetic
levitation force is dominated by the remnant current density, which is induced
by switching off the applied magnetizing field. High critical current density
and flux creep exponent may increase the magnetic levitation force. Large
volume and high aspect ratio of the superconducting bulk can enhance the
magnetic levitation force further.",0211470v1
2003-06-23,Magnetic-field and current-density distributions in thin-film superconducting rings and disks,"We show how to calculate the magnetic-field and sheet-current distributions
for a thin-film superconducting annular ring (inner radius a, outer radius b,
and thickness d<<a) when either the penetration depth obeys lambda < d/2 or, if
lambda > d/2, the two-dimensional screening length obeys Lambda = 2 lambda^2/d
<< a for the following cases: (a) magnetic flux trapped in the hole in the
absence of an applied magnetic field, (b) zero magnetic flux in the hole when
the ring is subjected to an applied magnetic field, and (c) focusing of
magnetic flux into the hole when a magnetic field is applied but no net current
flows around the ring. We use a similar method to calculate the magnetic-field
and sheet-current distributions and magnetization loops for a thin,
bulk-pinning-free superconducting disk (radius b) containing a dome of magnetic
flux of radius a when flux entry is impeded by a geometrical barrier.",0306585v1
2006-08-08,Anomalous Hall Resistivity of TbBaCo2O5.53 with Non-trivial Magnetic Structure,"To investigate the Hall resistivity rH of systems with non-trivial spin
structures, transport and magnetic properties of the oxygen deficient
perovskite system TbBaCo2O5.53 with non-trivial magnetic structures have been
adopted. As has been already known, the system exhibits, with decreasing
temperature T, a transition to a ferromagnetic (FM) phase with non-collinear
magnetic structure at TC 280 K in zero magnetic field and with further
decreasing T, the spontaneous magnetization begins to decrease at T1~260 K and
becomes zero at TN 245 K, where an antiferromagnetic (AFM) phase with
non-collinear magnetic structure is realized. The metamagnetic behavior is
induced by the relatively small magnetic field H (< 5 T) in the T region
between ~200 K and T1. In this T region, unusual H dependence of rH has been
observed. By analyzing the observed rH and magnetization M, the H dependence of
the anomalous Hall coefficients Rs has been obtained at various fixed
temperatures. Based on the magnetic structure reported previously by our group,
the possible relevance of the non-trivial magnetic structure to the observed
unusual behavior of rH is pointed out.",0608185v1
2006-12-04,Magnetic-dipole induced appearance of vortices in a bilayered superconductor/soft-magnet heterostructure,"The penetration of the magnetic field of an infinitesimal magnetic dipole
into a bilayered type-II superconductor/soft-magnet heterostructure is studied
on the basis of the classical London approach. The critical values of the
dipole moment for the first appearance of a single magnetic vortex and,
respectively, a magnetic vortex-antivortex pair in the superconductor
constituent are obtained, when the magnetic dipole faces the superconductor or
the soft-magnet constituent. This reveals that the soft-magnet constituent
inhibits penetration of vortices into the superconductor constituent, when the
dipole faces the soft-magnet constituent.",0612083v1
2007-04-12,Rich magnetic phase diagram in the Kagome-staircase compound Mn3V2O8,"Mn3V2O8 is a magnetic system in which S = 5/2 Mn2+ is found in the kagome
staircase lattice. Here we report the magnetic phase diagram for temperatures
above 2 K and applied magnetic fields below 9 T, characterized by measurements
of the magnetization and specific heat with field along the three unique
lattice directions. At low applied magnetic fields, the system first orders
magnetically below Tm1 ~ 21 K, and then shows a second magnetic phase
transition at Tm2 ~ 15 K. In addition, a phase transition that is apparent in
specific heat but not seen in magnetization is found for all three applied
field orientations, converging towards Tm2 as H -> 0. The magnetic behavior is
highly anisotropic, with critical fields for magnetic phase boundaries much
higher when the field is applied perpendicular to the Kagome staircase plane
than when applied in-plane. The field-temperature (H - T) phase diagrams are
quite rich, with 7 distinct phases observed.",0704.1581v1
2007-09-07,Frustration-driven successive metamagnetic transitions in TbB4,"Resonant magnetic x-ray diffraction experiments on the Shastry-Sutherland
lattice TbB$_4$ were carried out under strong pulsed magnetic fields up to 30
T. TbB$_4$ exhibits a multi-step magnetization process above 16 T when magnetic
fields are applied along the c-axis. We examined the intensity of the 010
magnetic reflection as a function of magnetic field and found that the
magnetization plateau phases are accompanied by large XY components of magnetic
moments, in contrast to normal fractional magnetization plateau phases. The
magnetization was calculated using a simple spin model deduced from the above
result. Finally we propose that frustration is the key to understanding the
observed multi-step magnetization.",0709.0977v2
2007-10-09,Fermion Production in Strong Magnetic Field and its Astrophysical Implications,"We calculate the effective potential of a strong magnetic field induced by
fermions with anomalous magnetic moments which couple to the electromagnetic
field in the form of the Pauli interaction. For a uniform magnetic field, we
find the explicit form of the effective potential. It is found that the
non-vanishing imaginary part develops for a magnetic field stronger than a
critical field and has a quartic form which is quite different from the
exponential form of the Schwinger process. We also consider a linear magnetic
field configuration as an example of inhomogeneous magnetic fields. We find
that the imaginary part of the effective potential is nonzero even below the
critical field and shows an exponentially decreasing behavior with respect to
the inverse of the magnetic field gradient, which is the non-perturbative
characteristics analogous to the Schwinger process. These results imply the
instability of the strong magnetic field to produce fermion pairs as a purely
magnetic effect. The possible applications to the astrophysical phenomena with
strong magnetic field are also discussed.",0710.1670v1
2008-05-14,Phenomenological theory of magnetization reversal in nanosystems with competing anisotropies,"The interplay between intrinsic and surface/interface-induced magnetic
anisotropies strongly in- fluences magnetization processes in nanomagnetic
systems. We develop a micromagnetic theory to describe the field-driven
reorientation in nanomagnets with cubic and uniaxial anisotropies. Spin
configurations in competing phases and parameters of accompanying multidomain
states are calculated as functions of the applied field and the magnetic
anisotropies. The constructed magnetic phase diagrams allow to classify
different types of the magnetization reversal and to provide detailed analysis
of the switching processes in magnetic nanostructures. The calculated
magnetization profiles of isolated domain walls show that the equilibrium
parameters of such walls are extremely sensitive to applied magnetic field and
values of the competing anisotropies and can vary in a broad range. For
nanolayers with perpendicular anisotropy the geometrical parameters of stripe
domains have been calculated as functions of a bias field. The results are
applied to analyse the magnetization processes as observed in various
nanosystems with competing anisotropies, mainly, in diluted magnetic
semiconductor films (Ga,Mn)As.",0805.1984v2
2010-05-27,High-Field Magnetization of CeRu2Al10,"The magnetization measurements of CexLa1-xRu2Al10 (x = 1, 0.75) under the
high magnetic field were performed in order to obtain the information for the
long-range order (LRO) in CeRu2Al10. We successfully obtained the magnetic
phase diagram of these two compounds for the applied magnetic field along the
a-axis which is the magnetization easy axis, and found that the LRO for x = 1
disappears at ~50 T which is the critical field to the paramagnetic phase. For
x = 0.75, the critical magnetic field decreases to ~37 T by La substitution.
The magnetic phase diagram and magnetization curve are qualitatively consistent
with the recent Hanzawa's mean field calculation results obtained by assuming
the dimer of Ce ions whose crystalline electric field ground state has a large
magnetic anisotropy. These results support the singlet pair formation scenario
recently proposed by Tanida et al.. We also pointed out the possibility of the
appearance of the field-induced magnetic phase between ~40 T and ~50 T for x =
1.",1005.5079v1
2010-10-15,Synthesis and magnetic properties of Mn12-based single molecular magnets with benzene and pentafluorobenzene carboxylate ligands,"We report on the synthesis and magnetic properties of Mn12-based single
molecular magnets (SMMs) with benzene and pentafluorobenzene carboxylate
ligands. The changes in ligand structure are shown to have a decisive effect on
magnetic properties of produced complexes. The compound with benzene
demonstrates unusual magnetic behaviour, namely, temperature dependencies of
magnetization taken under the zero field cooled and field cooled conditions are
split below 10 K and furthermore remnant magnetization and coercive force
remain nonzero in this temperature range. In contrast, compound with
pentafluorobenzene displays the customary signatures of a blocking temperature
at 3K. The effect of ligand substitution was theoretically studied within local
density approximation taking into account on-site Coloumb repulsion.
Calculation results confirm that the electronic structure and the magnetic
exchange interactions between different Mn atoms strongly depend on the type of
ligands.",1010.3057v1
2011-07-14,Magneto-sensitive elastomers in a homogeneous magnetic field: a regular rectangular lattice model,"A theory of mechanical behaviour of the magneto-sensitive elastomers is
developed in the framework of a linear elasticity approach. Using a regular
rectangular lattice model, different spatial distributions of magnetic
particles within a polymer matrix are considered: isotropic, chain-like and
plane-like. It is shown that interaction between the magnetic particles results
in the contraction of an elastomer along the homogeneous magnetic field. With
increasing magnetic field the shear modulus for the shear deformation
perpendicular to the magnetic field increases for all spatial distributions of
magnetic particles. At the same time, with increasing magnetic field the
Young's modulus for tensile deformation along the magnetic field decreases for
both chain-like and isotropic distributions of magnetic particles and increases
for the plane-like distribution of magnetic particles.",1107.2768v1
2011-11-27,A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3,"We present magnetic characterization of a binary rare-earth intermetallic
compound Er5Si3, crystallizing in Mn5Si3-type hexagonal structure, through
magnetization, heat-capacity, electrical resistivity, and magnetoresistance
measurements. Our investigations confirm that the compound exhibits two
magnetic transitions with decreasing temperature, first one at 35 K and the
second one at 15 K. The present results reveal that the second magnetic
transition is a disorder-broadened first-order transition, as shown by thermal
hysteresis in the measured data. Another important finding is that, below 15 K,
there is a magnetic-field-induced transition with a hysteretic effect with the
electrical resistance getting unusually enhanced at this transition and the
magnetorsistance (MR) is found to exhibit intriguing magnetic-field dependence
indicating novel magnetic phase-co-existence phenomenon. It thus appears that
this compound is characterized by interesting magnetic anomalies in the
temperature-magnetic-field phase diagram.",1111.6240v1
2012-02-15,Ferroelectricity induced by interatomic magnetic exchange interaction,"Multiferroics, where two or more ferroic order parameters coexist, is one of
the hottest fields in condensed matter physics and materials science[1-9].
However, the coexistence of magnetism and conventional ferroelectricity is
physically unfavoured[10]. Recently several remedies have been proposed, e.g.,
improper ferroelectricity induced by specific magnetic[6] or charge orders[2].
Guiding by these theories, currently most research is focused on frustrated
magnets, which usually have complicated magnetic structure and low magnetic
ordering temperature, consequently far from the practical application. Simple
collinear magnets, which can have high magnetic transition temperature, have
never been considered seriously as the candidates for multiferroics. Here, we
argue that actually simple interatomic magnetic exchange interaction already
contains a driving force for ferroelectricity, thus providing a new microscopic
mechanism for the coexistence and strong coupling between ferroelectricity and
magnetism. We demonstrate this mechanism by showing that even the simplest
antiferromagnetic (AFM) insulator MnO, can display a magnetically induced
ferroelectricity under a biaxial strain.",1202.3381v2
2012-03-01,Observations of Cool-Star Magnetic Fields,"Cool stars like the Sun harbor convection zones capable of producing
substantial surface magnetic fields leading to stellar magnetic activity. The
influence of stellar parameters like rotation, radius, and age on cool-star
magnetism, and the importance of the shear layer between a radiative core and
the convective envelope for the generation of magnetic fields are keys for our
understanding of low-mass stellar dynamos, the solar dynamo, and also for other
large-scale and planetary dynamos. Our observational picture of cool-star
magnetic fields has improved tremendously over the last years. Sophisticated
methods were developed to search for the subtle effects of magnetism, which are
difficult to detect particularly in cool stars. With an emphasis on the
assumptions and capabilities of modern methods used to measure magnetism in
cool stars, I review the different techniques available for magnetic field
measurements. I collect the analyses on cool-star magnetic fields and try to
compare results from different methods, and I review empirical evidence that
led to our current picture of magnetic fields and their generation in cool
stars and brown dwarfs.",1203.0241v1
2012-06-02,Electric dipoles on magnetic monopoles in spin ice,"The close connection of electricity and magnetism is one of the cornerstones
of modern physics. This connection plays crucial role from the fundamental
point of view and in practical applications, including spintronics and
multiferroic materials. A breakthrough was a recent proposal that in magnetic
materials called spin ice the elementary excitations have a magnetic charge and
behave as magnetic monopoles. I show that, besides magnetic charge, there
should be an electric dipole attached to each magnetic monopole. This opens new
possibilities to study and to control such monopoles by electric field. Thus
the electric--magnetic analogy goes even further than usually assumed: whereas
electrons have electric charge and magnetic dipole (spin), magnetic monopoles
in spin ice, while having magnetic charge, also have electric dipole.",1206.0402v1
2012-06-30,On conservation of the of crystal lattice symmetry in transition at Curie point in exchange magnets,"We show that symmetry of the crystal lattice of exchange magnets (containing
only 3d magneto-active elements) does not change at the Curie point; only the
magnetic symmetry of the crystal is decreasing in the transition point. In the
non-exchange magnets (containing only rare-earth magneto-active elements), on
the contrary, both the magnetic and crystal-chemical symmetry decrease at the
Curie point. There is isotropic magnetic phase in exchange magnets; and their
magnetic symmetry is described by color groups of magnetic symmetry of P-type.
Non-exchange magnets do not have isotropic phase; their symmetry is described
by color groups of magnetic symmetry of Q-type.",1207.0049v1
2012-07-30,Magnetic energy harvesting and concentration at distance by transformation optics,"Magnetic energy is one the main agents powering our society: generating
energy in power plants, keeping information in magnetic memories, moving our
devices with motors. All of these applications require a certain spatial
distribution of magnetic energy, for example concentrating it in a transformer
core or in a magnetic sensor. We introduce in this work a way to collect
magnetic energy and distribute it in space with unprecedented efficiency and
flexibility, allowing very large concentration of magnetic energy in a free
space region, an enhanced magnetic coupling between two magnetic sources, and
the transfer of magnetic energy from a source to a given distant point
separated by empty space. All these features are achieved with a single device,
a magnetic shell designed by transformation optics.",1207.7030v1
2012-11-30,Spontaneous magnetization and magnetic susceptibility of LaVO3,"Five characteristic temperatures of TM = 148 K, TN = 142 K, Tt = 138 K, Tf ~
125 K and Tg ~ 50 K were found by the measurements of the magnetization curves
at various temperature. The spontaneous magnetization appears below TM. It
increases up to M_{S} simeq 2 times 10^{-4} mu_{B} at Tt and then decreases
steeply below Tt, which qualitatively agrees with the temperature dependence of
magnetization obtained under field-cooling (FC) condition. On the other hand,
the slope of the magnetization curve, namely the magnetic susceptibility, drops
below TN, which coincides with the temperature dependence of magnetization
obtained under zero-FC condition, although the magnetization curves were
obtained under FC condition. The temperature dependence of the spontaneous
magnetization shows a minimum at Tf and a drop at Tg although there is no
anomaly in the temperature dependence of FC or ZFC magnetization.",1211.7179v1
2013-02-01,Frequency Adapted Phase Transition of Interacting Nano-Magnetic Ensemble,"Each single domain nano-magnet acts as a magnetic dipole in addition it
oscillates its magnetization about the easy axis and rotates coherently
depending upon temperature and anisotropy. In an ensemble of nano-magnets, the
relaxation time of a nano-magnet tunes with the long range dipolar interaction
which in turn is determined by the particle size, density and the number of
nano-magnets present in the ensemble. Hence, the aggregation of interacting
nano-magnetic dipoles, demonstrates both experimentally and theoretically as a
model system to detect intriguing co-operative physical phenomena. Here we show
a new variant of phase transition from paramagnetic to diamagnetic phase by
changing the frequency of the applied sinusoidal magnetic field for a
nano-magnetic ensemble. This phenomenon unravels a new insight of physics and
it may be significant on the design and development of magnetic devices. The
simulation of the system is well in agreement with the experimental results.",1302.0086v1
2013-03-30,Defect-Induced Magnetism in Solids,"In the last years the number of nominally non-magnetic solids showing
magnetic order induced by some kind of defects has increased continuously. From
the single element material graphite to several covalently bonded non-magnetic
compounds, the influence of defects like vacancies and/or non-magnetic ad-atoms
on triggering magnetic order has attracted the interest of experimentalists and
theoreticians. We review and discuss the main theoretical approach as well as
recently obtained experimental evidence based on different experimental methods
that supports the existence of defect-induced magnetism (DIM) in non-magnetic
as well as in magnetic materials.",1304.0137v1
2013-04-22,Chiral Disorder and Random Matrix Theory with Magnetism,"We revisit the concept of chiral disorder in QCD in the presence of a QED
magnetic field |eH|. Weak magnetism corresponds to |eH| < 1/rho^2 with
rho\approx (1/3) fm the vacuum instanton size, while strong magnetism the
reverse. Asymptotics (ultra-strong magnetism) is in the realm of perturbative
QCD. We analyze weak magnetism using the concept of the quark return
probability in the diffusive regime of chiral disorder. The result is in
agreement with expectations from chiral perturbation theory. We analyze strong
and ultra-strong magnetism in the ergodic regime using random matrix theory
including the effects of finite temperature. The strong magnetism results are
in agreement with the currently reported lattice data in the presence of a
small shift of the Polyakov line. The ultra-strong magnetism results are
consistent with expectations from perturbative QCD. We suggest a chiral random
matrix effective action with matter and magnetism to analyze the QCD phase
diagram near the critical points under the influence of magnetism.",1304.6020v2
2013-10-30,Passive Magnetic Shielding in Gradient Fields,"The effect of passive magnetic shielding on dc magnetic field gradients
imposed by both external and internal sources is studied. It is found that for
concentric cylindrical or spherical shells of high permeability material,
higher order multipoles in the magnetic field are shielded progressively
better, by a factor related to the order of the multipole. In regard to the
design of internal coil systems for the generation of uniform internal fields,
we show how one can take advantage of the coupling of the coils to the
innermost magnetic shield to further optimize the uniformity of the field.
These results demonstrate quantitatively a phenomenon that was previously
well-known qualitatively: that the resultant magnetic field within a passively
magnetically shielded region can be much more uniform than the applied magnetic
field itself. Furthermore we provide formulae relevant to active magnetic
compensation systems which attempt to stabilize the interior fields by sensing
and cancelling the exterior fields close to the outermost magnetic shielding
layer. Overall this work provides a comprehensive framework needed to analyze
and optimize dc magnetic shields, serving as a theoretical and conceptual
design guide as well as a starting point and benchmark for finite-element
analysis.",1310.8242v1
2013-11-12,Magnetic and Dielectric Properties in Multiferroic Cu3Mo2O9 under High Magnetic Fields,"The magnetic and dielectric properties under high magnetic fields are studied
in the single crystal of Cu3Mo2O9. This multiferroic compound has distorted
tetrahedral spin chains. The effects of the quasi-one dimensionality and the
geometrical spin frustration are expected to appear simultaneously. We measure
the magnetoelectric current and the differential magnetization under the pulsed
magnetic field up to 74 T. We also measure the electric polarization versus the
electric field curve/loop under the static field up to 23 T. Dielectric
properties change at the magnetic fields where the magnetization jumps are
observed in the magnetization curve. Moreover, the magnetization plateaus are
found at high magnetic fields.",1311.2706v1
2013-12-04,Quantum s = 1/2 Antiferromagnets on Archimedean Lattices: The Route from Semiclassical Magnetic Order to Nonmagnetic Quantum States,"We investigate ground states of $s$=1/2 Heisenberg antiferromagnets on the
eleven two-dimensional (2D) Archimedian lattices by using the coupled cluster
method. Magnetic interactions and quantum fluctuations play against each other
subtly in 2D quantum magnets and the magnetic ordering is thus sensitive to the
features of lattice topology. Archimedean lattices are those lattices that have
2D arrangements of regular polygons and they often build the underlying
magnetic lattices of insulating quasi-two-dimensional quantum magnetic
materials. Hence they allow a systematic study of the relationship between
lattice topology and magnetic ordering. We find that the Archimedian lattices
fall into three groups: those with semiclassical magnetic ground-state
long-range order, those with a magnetically disordered (cooperative quantum
paramagnetic) ground state, and those with a fragile magnetic order. The most
relevant parameters affecting the magnetic ordering are the coordination number
and the degree of frustration present.",1312.1203v1
2014-01-18,Evolution of the 2D antiferromagnetism with temperature and magnetic field in multiferroic Ba$_2$CoGe$_2$O$_7$,"We report on spherical neutron polarimetry and unpolarized neutron
diffraction in zero magnetic field as well as flipping ratio and static
magnetization measurements in high magnetic fields on the multiferroic square
lattice antiferromagnet Ba$_2$CoGe$_2$O$_7$. We found that in zero magnetic
field the magnetic space group is $Cm'm2'$ with sublattice magnetization
parallel to the [100] axis of this orthorhombic setting. The spin canting has
been found to be smaller than $0.2^\circ$ in the ground state. This assignment
is in agreement with the field-induced changes of the magnetic domain structure
below 40 mT as resolved by spherical neutron polarimetry. The magnitude of the
ordered moment has been precisely determined. Above the magnetic ordering
temperature short-range magnetic fluctuations are observed. Based on the
high-field magnetization data, we refined the parameters of the recently
proposed microscopic spin model describing the multiferroic phase of
Ba$_2$CoGe$_2$O$_7$.",1401.4517v1
2014-01-27,Topological magnetic crystalline insulators and co-representation theory,"Gapless surface states of time reversal invariant topological insulators are
protected by the anti-unitary nature of the time reversal operation. Very
recently, this idea was generalized to magnetic structures, in which time
reversal symmetry is explicitly broken, but there is still an anti-unitary
symmetry operation combining time reversal symmetry and crystalline symmetry.
These topological phases in magnetic structures are dubbed ""topological
magnetic crystalline insulators"". In this work, we present a general theory of
topological magnetic crystalline insulators in different types of magnetic
crystals based on the co-representation theory of magnetic crystalline symmetry
groups. We construct two concrete tight-binding models of topological magnetic
crystalline insulators, the $\hat{C}_4\Theta$ model and the $\hat{\bf
\tau}\Theta$ model, in which topological surface states and topological
invariants are calculated explicitly. Moreover, we check different types of
anti-unitary operators in magnetic systems and find that the systems with
$\hat{C}_4\Theta$, $\hat{C}_6\Theta$ and $\hat{\bf \tau}\Theta$ symmetry are
able to protect gapless surface states. Our work will pave the way to search
for topological magnetic crystalline insulators in realistic magnetic
materials.",1401.6922v1
2014-02-28,The role of magnetic fields in pre-main sequence stars,"Strong, kilo-Gauss, magnetic fields are required to explain a range of
observational properties in young, accreting pre-main sequence (PMS) systems.
We review the techniques used to detect magnetic fields in PMS stars. Key
results from a long running campaign aimed at characterising the large scale
magnetic fields in accreting T Tauri stars are presented. Maps of surface
magnetic flux in these systems can be used to build 3-D models exploring the
role of magnetic fields and the efficiency with which magnetic fields can
channel accretion from circumstellar disks on to young stars. Long-term
variability in T Tauri star magnetic fields strongly point to a dynamo origin
of the magnetic fields. Studies are underway to quantify how changes in
magnetic fields affect their accretion properties. We also present the first
results from a new programme that investigates the evolution of magnetic fields
in intermediate mass (1.5-3 Msun) pre-main sequence stars as they evolve from
being convective T Tauri stars to fully radiative Herbig AeBe stars.",1402.7130v1
2014-05-09,A Statistical Study on Property of Spatial Magnetic Field for Solar Active Region,"Magnetic fields dominate most solar activities, there exist direct relations
between solar flare and the distributions of magnetic field, and also its
corresponding magnetic energy. In this paper, the statistical results about the
relationships between the spatial magnetic field and solar flare are given
basing on vector magnetic field observed by the Solar Magnetic Field Telescope
(SMFT) at Huairou Solar Observing Station (HSOS). The spatial magnetic fields
are obtained by extrapolated photosphere vector magnetic field observed by
SMFT. There are 23 active regions with flare eruption are chosen as data
samples, which were observed from 1997 to 2007. The results are as follows: 1.
Magnetic field lines become lower after flare for 16(69%) active regions; 2.
The free energy are decreased after flare for 17 (74%) active regions. It can
conclude that for most active regions the changes of magnetic field after solar
flare are coincident with the previous observations and studies.",1405.2149v1
2014-08-06,Permanent magnet with MgB2 bulk superconductor,"Superconductors with persistent zero-resistance currents serve as permanent
magnets for high-field applications requiring a strong and stable magnetic
field, such as magnetic resonance imaging (MRI). The recent global helium
shortage has quickened research into high-temperature superconductors (HTSs)
materials that can be used without conventional liquid-helium cooling to 4.2 K.
Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB2)
makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week
with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in
this magnet is uniformly distributed, as for single-crystalline
neodymium-iron-boron. Magnetic hysteresis loop of the MgB2 permanent bulk
magnet was detrmined. Because MgB2 is a simple-binary-line compound that does
not contain rare-earth metals, polycrystalline bulk material can be
industrially fabricated at low cost and with high yield to serve as strong
magnets that are compatible with conventional compact cryocoolers, making MgB2
bulks promising for the next generation of Tesla-class permanent-magnet
applications.",1408.1277v1
2014-08-17,Creation of magnetic spots at the neutron star surface,"According to the partially screened gap scenario, an efficient
electron-positron pair creation, a general precondition of radio-pulsar
activity, relies on the existence of magnetic spots, i.e., local concentrations
of strong and small scale magnetic field structures at the surface of neutron
stars. They have a strong impact on the surface temperature, which is
potentially observable. Here we reinforce the idea that such magnetic spots can
be formed by extracting magnetic energy from the toroidal field that resides in
deep crustal layers, via Hall drift. We study and discuss the magneto-thermal
evolution of qualitatively different neutron star models and initial magnetic
field configurations that lead to the creation of magnetic spots. We find that
magnetic spots can be created on a timescale of $10^4$ years with magnetic
field strengths $\gtrsim 5\times 10^{13}$ G, provided almost the whole magnetic
energy is stored in its toroidal component, and that the conductivity in the
inner crust is not too large. The lifetime of the magnetic spots is at least
$\sim$one million of years, being longer if the initial field permeates both
core and crust.",1408.3833v1
2014-09-28,Surface and interface effects on a magnetic Chern insulator,"Effects of an open surface on a magnetic Chern insulator are investigated in
comparison with those of an interface to a capping magnetic layer. In magnets,
an open surface often perturbs the magnetic order by a reconstruction of the
magnetic moment directions near the surface. On the other hand, in topological
insulators, it leads to the formation of topologically protected surface
states. These two contrasting effects may coexist in magnetic Chern insulators,
which give rise to nontrivial surface reconstruction. For instance, the chiral
edge current is largely enhanced by the edge reconstruction in a
two-dimensional magnetic Chern insulator realized in a quarter-filled Kondo
lattice model on a triangular lattice. We here show that the edge
reconstruction can be described semiquantitatively by a simple junction model
between the bulk topological magnetic state and a ferromagnetic capping layer.
We further clarify how the chiral edge current is affected by the magnetic
structure in the capping layer. Our results indicate that the topological edge
state can be controlled magnetically through the junctions.",1409.7939v1
2014-09-29,Validation of the magnetic energy vs. helicity scaling in solar magnetic structures,"We assess the validity of the free magnetic energy - relative magnetic
helicity diagram for solar magnetic structures. We used two different methods
of calculating the free magnetic energy and the relative magnetic helicity
budgets: a classical, volume-calculation nonlinear force-free (NLFF) method
applied to finite coronal magnetic structures and a surface-calculation NLFF
derivation that relies on a single photospheric or chromospheric vector
magnetogram. Both methods were applied to two different data sets, namely
synthetic active-region cases obtained by three-dimensional
magneto-hydrodynamic (MHD) simulations and observed active-region cases, which
include both eruptive and noneruptive magnetic structures. The derived
energy--helicity diagram shows a consistent monotonic scaling between relative
helicity and free energy with a scaling index 0.84$\pm$0.05 for both data sets
and calculation methods. It also confirms the segregation between noneruptive
and eruptive active regions and the existence of thresholds in both free energy
and relative helicity for active regions to enter eruptive territory. We
consider the previously reported energy-helicity diagram of solar magnetic
structures as adequately validated and envision a significant role of the
uncovered scaling in future studies of solar magnetism.",1409.8117v1
2014-12-29,Electrically Tunable Magnetism in Magnetic Topological Insulators,"The external controllability of the magnetic properties in topological
insulators would be important both for fundamental and practical interests.
Here we predict the electric-field control of ferromagnetism in a thin film of
insulating magnetic topological insulators. The decrease of band inversion by
the application of electric fields results in a reduction of magnetic
susceptibility, and hence in the modification of magnetism. Remarkably, the
electric field could even induce the magnetic quantum phase transition from
ferromagnetism to paramagnetism. We further propose a topological transistor
device in which the dissipationless charge transport of chiral edge states is
controlled by an electric field. In particular, the field-controlled
ferromagnetism in magnetic topological insulator can be used for voltage based
writing of magnetic random access memories in magnetic tunnel junctions. The
simultaneous electrical control of magnetic order and chiral edge transport in
such devices may lead to electronic and spintronic applications for topological
insulators.",1412.8237v5
2014-12-29,Magnetic balltracking: Tracking the photospheric magnetic flux,"Context: One aspect of understanding the dynamics of the quiet Sun is to
quantify the evolution of the flux within small-scale magnetic features. These
features are routinely observed in the quiet photosphere and were given various
names, such as pores, knots, magnetic patches. Aims: This work presents a new
algorithm for tracking the evolution of the broad variety of small-scale
magnetic features in the photosphere, with a precision equal to the
instrumental resolution. Methods: We have developed a new technique to track
the evolution of the individual magnetic features from magnetograms, called
""magnetic balltracking"". It quantifies the flux of the tracked features, and it
can track the footpoints of magnetic field lines inferred from magnetic field
extrapolation. The algorithm can detect and quantify flux emergence, as well as
flux cancellation. Results: The capabilities of magnetic balltracking are
demonstrated with the detection and the tracking of two cases of magnetic flux
emergence that lead to the brightening of X-ray loops. The maximum emerged flux
ranges from 10^{18} Mx to 10^{19} Mx (unsigned flux) when the X-ray loops are
observed.",1412.8294v1
2015-01-27,Magnetic behavior of the metal organic framework solid: [(CH3)2NH2][Co(HCOO)3],"In this study we examine the phase transitions in single crystals of
[(CH3)2NH2]Co(HCOO)3], using magnetization and specific heat measurements as a
function of temperature and magnetic field. Magnetisation measurements indicate
a transition at 15 K that is associated with an antiferromagnetic transition.
The results of the isothermal magnetization versus magnetic field curves
demonstrate the presence of a single-ion magnet phase, coexisting with
antiferromagnetism. A peak in specific heat is seen at 15 K, corresponding to
the magnetic transition. The enthalpy of the transition evaluated from the area
under the specific heat peak decreases with the application of magnetic field
of upto8 T. This is suggestive of long range antiferromagnetic magnetic order,
giving way to single-ion magnetic behavior under external field. In experiments
at high temperatures, corresponding to the well-known structural transition in
this system, the specific heat measurements, shows a peak at ~155K, that is
insensitive to applied magnetic field. The magnetisation in this temperature
range, while it exhibits a paramagnetic behavior, shows a distinct jump that
has been attributed to a spin-state transition of Co2+ associated with the
structural transition.",1501.06651v1
2015-03-27,Magnetized relativistic stellar models in Eddington-inspired Born-Infeld gravity,"We consider the structure of the magnetic fields inside the neutron stars in
Eddington-inspired Born-Infeld (EiBI) gravity. In order to construct the
magnetic fields, we derive the relativistic Grad-Shafranov equation in EiBI,
and numerically determine the magnetic distribution in such a way that the
interior magnetic fields should be connected to the exterior distribution.
Then, we find that the magnetic distribution inside the neutron stars in EiBI
is qualitatively similar to that in general relativity, where the deviation of
magnetic distribution in EiBI from that in general relativity is almost
comparable to uncertainty due to the equation of state (EOS) for the neutron
star matter. However, we also find that the magnetic fields in the crust region
are almost independent of the coupling constant in EiBI, which suggests a
possibility to obtain the information about the crust EOS independently of the
gravitational theory via the observations of the phenomena associated with the
crust region. In any case, since the imprint of EiBI gravity on the magnetic
fields is weak, the magnetic fields could be a poor probe of gravitational
theories, considering many magnetic uncertainties.",1503.07942v2
2015-05-24,Magnetic reversal modes in multisegmented nanowire arrays with long aspect ratio,"A detailed numerical analysis of the magnetization reversal processes in
multisegmented nanowire arrays was developed. The nanowires have a long aspect
ratio and are formed by magnetic and non-magnetic sections alternately arranged
in such a way that the array resembles magnetic layers separated by
non-magnetic layers. Attention has been focused on the influence of
magnetostatic interaction in the magnetic pattern formation of these magnetic
nanostructures. Results from a magnetic correlation function among layers show
that three different reversal modes can be detected depending on the number and
distance between the magnetic segments. As a consequence of the different
reversal modes, a non-monotonic behavior of the annihilation field in function
of the distance between the layers is evidenced. Thus, these results are
important for the production of magnetic devices with multisegmented nanowire
arrays.",1505.06491v2
2015-06-03,Proximity-induced magnetism in transition-metal substituted graphene,"We investigate the interactions between two identical magnetic impurities
substituted into a graphene superlattice. Using a first-principles approach, we
calculate the electronic and magnetic properties for transition-metal
substituted graphene systems with varying spatial separation. These
calculations are compared for three different magnetic impurities, manganese,
chromium, and vanadium. We determine the electronic band structure, density of
states, and Millikan populations (magnetic moment) for each atom, as well as
calculate the exchange parameter between the two magnetic atoms as a function
of spatial separation. We find that the presence of magnetic impurities
establishes a distinct magnetic moment in the graphene lattice, where the
interactions are highly dependent on the spatial and magnetic characteristic
between the magnetic atoms and the carbon atoms, which leads to either
ferromagnetic or antiferromagnetic behavior. Furthermore, through an analysis
of the calculated exchange energies and partial density of states, it is
determined that interactions between the magnetic atoms can be classified as an
RKKY interaction.",1506.01319v1
2015-06-26,Non-axisymmetric magnetic modes of neutron stars with purely poloidal magnetic fields,"We calculate non-axisymmetric oscillations of neutron stars magnetized by
purely poloidal magnetic fields. We use polytropes of index $n=1$ and 1.5 as a
background model, where we ignore the equilibrium deformation due to the
magnetic field. Since separation of variables is not possible for the
oscillation of magnetized stars, we employ finite series expansions for the
perturbations using spherical harmonic functions. Solving the oscillation
equations as the boundary and eigenvalue problem, we find two kinds of discrete
magnetic modes, that is, stable (oscillatory) magnetic modes and unstable
(monotonically growing) magnetic modes. For isentropic models, the frequency or
the growth rate of the magnetic modes is exactly proportional to $B_{\rm S}$,
the strength of the field at the surface. The oscillation frequency and the
growth rate are affected by the buoyant force in the interior, and the stable
stratification tends to stabilize the unstable magnetic modes.",1507.00314v2
2015-09-02,Dynamo model for the inverse transfer of magnetic energy in a nonhelical decaying magnetohydrodynamic turbulence,"The inverse cascade of magnetic energy occurs when helicity or rotational
instability exists in the magnetohydrodynamic (MHD) system. This well known
phenomenon has been considered as a basis for the large scale magnetic field in
universe. However nonhelical magnetic energy in a decaying MHD system also
migrates toward the large scale, which holds vital clues to the origin of large
scale magnetic field in a quiescent astrophysical system. Zeldovich's rope
dynamo model is considered as a basic and symbolistic model of magnetic field
amplification. However, the rope model assuming specific external forces like
buoyancy or Coriolis force is not appropriate for a decaying turbulent system
without any external force. So we suggest a new dynamo model based on magnetic
induction equation excluding a forcing source. This model shows the expansion
and growth of magnetic field (flux) is basically the redistribution of energy
in the system. The transfer of magnetic energy is in fact a successive
induction of magnetic field resulted from the interaction between the fluid
motion and seed magnetic field. We also discuss about an analytic theorem based
on the scaling invariant MHD equation.",1509.00788v3
2015-10-16,Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy,"We have studied the magnetic layer thickness dependence of the orbital
magnetic moment in magnetic heterostructures to identify contributions from
interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlO$_x$ and
Pt/Co/Pt, which possess significant interface contribution to the perpendicular
magnetic anisotropy, are studied as model systems. X-ray magnetic circular
dichroism spectroscopy is used to evaluate the relative orbital moment, i.e.
the ratio of the orbital to spin moments, of the magnetic elements constituting
the heterostructures. We find that the relative orbital moment of Co in
Pt/Co/Pt remains constant against its thickness whereas the moment increases
with decreasing Co layer thickness for Pt/Co/AlO$_x$, suggesting that a
non-zero interface orbital moment exists for the latter system. For
Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray
absorption spectra shows that a particular oxidized Co state in Pt/Co/AlO$_x$,
absent in other heterosturctures, may give rise to the interface orbital moment
in this system. These results show element specific contributions to the
interface orbital magnetic moments in ultrathin magnetic heterostructures.",1510.04756v1
2015-11-23,Magnetic neutron scattering by magnetic vortices in thin submicron-sized soft ferromagnetic cylinders,"Using analytical expressions for the magnetization textures of thin
submicron-sized magnetic cylinders in vortex state, we derive closed-form
algebraic expressions for the ensuing small-angle neutron scattering (SANS)
cross sections. Specifically, for the perpendicular and parallel scattering
geometries, we have computed the magnetic SANS cross sections for the case of
small vortex-center displacements without formation of magnetic charges on the
side faces of the cylinder. The results represent a significant qualitative and
quantitative step forward in SANS-data analysis on isolated magnetic
nanoparticle systems, which are commonly assumed to be homogeneously or
stepwise-homogeneously magnetized. We suggest a way to extract the fine details
of the magnetic vortex structure during the magnetization process from the SANS
measurements in order to help resolving the long standing question of the
magnetic vortex displacement mode.",1511.07282v1
2015-12-04,Numerical calculations of magnetic properties of nanostructures,"Magnetic force microscopy and scanning tunneling microscopy data could be
used to test computer numerical models of magnetism. The elaborated numerical
model of a face-centered lattice Ising spins is based on pixel distribution in
the image of magnetic nanostructures obtained by using scanning microscope.
Monte Carlo simulation of the magnetic structure model allowed defining the
temperature dependence of magnetization; calculating magnetic hysteresis curves
and distribution of magnetization on the surface of submonolayer and monolayer
nanofilms of cobalt, depending on the experimental conditions. Our developed
package of supercomputer parallel software destined for a numerical simulation
of the magnetic-force experiments and allows obtaining the distribution of
magnetization in one-dimensional arrays of nanodots and on their basis. There
has been determined interpretation of magneto-force microscopy images of
magnetic nanodots states. The results of supercomputer simulations and
numerical calculations are in the good compliance with experimental data.",1512.01309v1
2016-01-21,Vortex Dynamics-Mediated Low-Field Magnetization Switching in an Exchange-Coupled System,"A magnetic vortex has attracted significant attention since it is a
topologically stable magnetic structure in a soft magnetic nanodisk. Many
studies have been devoted to understanding the nature of magnetic vortex in
isolated systems. Here we show a new aspect of a magnetic vortex the dynamics
of which strongly affects the magnetic structures of environment. We exploit a
nanodot of an exchange-coupled bilayer with a soft magnetic Ni81Fe19
(permalloy; Py) having a magnetic vortex and a perpendicularly magnetized
L10-FePt exhibiting a large switching field (Hsw). The vortex dynamics with
azimuthal spin waves makes the excess energy accumulate in the Py, which
triggers the reversed-domain nucleation in the L10-FePt at a low magnetic
field. Our results shed light on the non-local mechanism of a reversed-domain
nucleation, and provide with a route for efficient Hsw reduction that is needed
for ultralow-power spintronic devices.",1601.05521v1
2016-03-17,Trends in magnetism of free Rh clusters via relativistic ab-initio calculations,"A fully relativistic ab-initio study on free Rh clusters of 13-135 atoms is
performed to identify general trends concerning their magnetism and to check
whether concepts which proved to be useful in interpreting magnetism of 3d
metals are applicable to magnetism of 4d systems. We found that there is no
systematic relation between local magnetic moments and coordination numbers. On
the other hand, the Stoner model appears well-suited both as a criterion for
the onset of magnetism and as a guide for the dependence of local magnetic
moments on the site-resolved density of states at the Fermi level. Large
orbital magnetic moments antiparallel to spin magnetic moments were found for
some sites. The intra-atomic magnetic dipole Tz term can be quite large at
certain sites but as a whole it is unlikely to affect the interpretation of
x-ray magnetic circular dichroism experiments based on the sum rules.",1603.05394v1
2016-05-09,Magnetic phase diagram of TbMn$_{1-x}$Fe$_x$O$_3$ $(0 \leq x \leq 1)$ substitutional solid solution,"We present the magnetic phase diagram of TbMn1-xFexO3 substitutional solid
solution in the whole concentration range 0 <= x <= 1 as determined from
magnetization and specific heat measurements. We have found that the dominant
magnetic ion in the concentration range 0 <= x < 0.3 is manganese, while iron
ions do not create independent magnetic structure, but strongly affect magnetic
properties of the parent compound by reducing transition to magnetically
ordered state and transition into a cycloidal phase. The magnetism in the
concentration range 0.3 < x <= 1 is driven by the Fe sublattice. The manganese
ions again do not order in long range magnetic ordered state, but stabilize
four different magnetic structures of Fe sublattice above 2 K. The magnetic
ordering of Tb sublattice was observed only on parent compounds TbMnO3 and
TbFeO3 and for doping level below 0.1, or over 0.9.",1605.02503v2
2016-07-28,Effective penetration length and interstitial vortex pinning in superconducting films with regular arrays of defects,"In order to compare magnetic and non-magnetic pinning we have nanostructured
two superconducting films with regular arrays of pinning centers: Cu
(non-magnetic) dots in one case, and Py (magnetic) dots in the other. For low
applied magnetic fields, when all the vortices are pinned in the artificial
inclusions, magnetic dots prove to be better pinning centers, as has been
generally accepted. Unexpectedly, when the magnetic field is increased and
interstitial vortices appear, the results are very different: we show how the
stray field generated by the magnetic dots can produce an effective reduction
of the penetration length. This results in strong consequences in the transport
properties, which, depending on the dot separation, can lead to an enhancement
or worsening of the transport characteristics. Therefore, the election of the
magnetic or non-magnetic character of the pinning sites for an effective
reduction of dissipation will depend on the range of the applied magnetic
field.",1607.08416v1
2016-09-12,Induced magnetism at the interfaces of a Fe/V superlattice investigated by resonant magnetic x-ray scattering,"The induced magnetic moments in the V 3d electronic states of interface
atomic layers in a Fe(6ML)/V(7ML) superlattice was investigated by x-ray
resonant magnetic scattering. The first V atomic layer next to Fe was found to
be strongly antiferromagnetically polarized relatively to Fe and the magnetic
moments of the next few atomic layers in the interior V region decay
exponentially with increasing distance from the interface, while the magnetic
moments of the Fe atomic layers largely remain bulk-like. The induced V moments
decay more rapidly as observed by x-ray magnetic scattering than in standard
x-ray magnetic circular dichroism. The theoretical description of the induced
magnetic atomic layer profile in V was found to strongly rely on the interface
roughness within the superlattice period. These results provide new insight
into interface magnetism by taking advantage of the enhanced depth sensitivity
to the magnetic profile over a certain resonant energy bandwidth in the
vicinity of the Bragg angles.",1609.03486v1
2016-12-20,Magnetic fields in turbulent quark matter and magnetar bursts,"We analyze the magnetic field evolution in dense quark matter with unbroken
chiral symmetry, which can be found inside quark and hybrid stars. The magnetic
field evolves owing to the chiral magnetic effect in the presence of the
electroweak interaction between quarks. In our study, we also take into account
the magnetohydrodynamic turbulence effects in dense quark matter. We derive the
kinetic equations for the spectra of the magnetic helicity density and the
magnetic energy density as well as for the chiral imbalances. On the basis of
the numerical solution of these equations, we find that turbulence effects are
important for the behavior of small scale magnetic fields. It is revealed that,
under certain initial conditions, these magnetic fields behave similarly to the
electromagnetic flashes of some magnetars. We suggest that fluctuations of
magnetic fields, described in frames of our model, which are created in the
central regions of a magnetized compact star, can initiate magnetar bursts.",1612.06540v2
2017-01-16,Dynamics of magnetic nano particles in a viscous fluid driven by rotating magnetic fields,"The rotational dynamics of magnetic nano particles in rotating magnetic
fields in the presence of thermal noise is studied both theoretically and by
performing numerical calculations. Kinetic equations for the dynamics of
particles with uniaxial magnetic anisotropy are studied and the phase lag
between the rotating magnetic moment and the driving field is obtained. It is
shown that for large enough anisotropy energy the magnetic moment is locked to
the anisotropy axis so that the particle behaves like a rotating magnetic
dipole. The corresponding rigid dipole model is analyzed both numerically by
solving the appropriate Fokker-Planck equation and analytically by applying an
effective field method. In the special case of a rotating magnetic field
applied analytic results are obtained in perfect agreement with numerical
results based on the Fokker-Planck equation. The analytic formulas derived are
not restricted to small magnetic fields or low frequencies and are therefore
important for applications. The illustrative numerical calculations presented
are performed for magnetic parameters typical for iron oxide.",1702.04673v1
2017-07-04,Wigner function and kinetic phenomena for chiral plasma in a strong magnetic field,"By using the exact solutions of the Weyl equation in a constant magnetic
field, the equal-time Wigner function for magnetized chiral plasma is derived.
It is found that the dependence of the Wigner function on the component of
momentum along the magnetic field is asymmetric and is correlated with the
fermion chirality. Such a dependence is principal for reproducing the correct
chiral magnetic and chiral separation effects. In the lowest Landau level
approximation, the equation for the equal-time Wigner function in a strong
magnetic field is derived. By making use of this equation, it is found that the
longitudinal collective modes in a strong magnetic field are gapped plasmons
whose gap is determined by the magnetic field. Unlike the ordinary magnetic
field, an axial one allows for the dispersion law of the collective excitations
asymmetric in the wave vector. The thermoelectric phenomena for chiral fermions
in strong magnetic and axial magnetic fields are studied and the corresponding
transport coefficients are calculated.",1707.01105v2
2017-07-14,Insights into the orbital magnetism of noncollinear magnetic systems,"The orbital magnetic moment is usually associated with the relativistic
spin-orbit interaction, but recently it has been shown that noncollinear
magnetic structures can also be its driving force. This is important not only
for magnetic skyrmions, but also for other noncollinear structures, either
bulk-like or at the nanoscale, with consequences regarding their experimental
detection. In this work we present a minimal model that contains the effects of
both the relativistic spin-orbit interaction and of magnetic noncollinearity on
the orbital magnetism. A hierarchy of models is discussed in a step-by-step
fashion, highlighting the role of time-reversal symmetry breaking for
translational and spin and orbital angular motions. Couplings of spin-orbit and
orbit-orbit type are identified as arising from the magnetic noncollinearity.
We recover the atomic contribution to the orbital magnetic moment, and a
nonlocal one due to the presence of circulating bound currents, exploring
different balances between the kinetic energy, the spin exchange interaction,
and the relativistic spin-orbit interaction. The connection to the scalar spin
chirality is examined. The orbital magnetism driven by magnetic noncollinearity
is mostly unexplored, and the presented model contributes to laying its
groundwork.",1707.04518v1
2017-08-11,"Magnetic Charge and Photon Mass: Physical String Singularities, Dirac Condition, and Magnetic Confinement","We find exact, simple solutions to the Proca version of Maxwell's equations
with magnetic sources. Several properties of these solutions differ from the
usual case of magnetic charge with a massless photon: (i) the string
singularities of the usual 3-vector potentials become real singularities in the
magnetic fields; (ii) the different 3-vector potentials become gauge
inequivalent and physically distinct solutions; (iii) the magnetic field
depends on $r$ and $\theta$ and thus is no longer rotationally symmetric; (iv)
a combined system of electric and magnetic charge carries a field angular
momentum even when the electric and magnetic charges are located at the same
place i.e. for dyons); (v) for these dyons one recovers the standard Dirac
condition despite the photon being massive. We discuss the reason for this. We
conclude by proposing that the string singularity in the magnetic field of an
{\it isolated} magnetic charge suggests a confinement mechanism for magnetic
charge, similar to the flux tube confinement of quarks in QCD.",1708.06229v2
2017-09-06,Record High Magnetic Anisotropy in Chemically Engineered Iridium Dimer,"Exploring giant magnetic anisotropy in small magnetic nanostructures is of
both fundamental interest and technological merit for information storage. To
prevent spin flipping at room temperature due to thermal fluctuation, large
magnetic anisotropy energy (MAE) over 50 meV in magnetic nanostructure is
desired for practical applications. We chose one of the smallest magnetic
nanostructures-Ir2 dimer, to investigate its magnetic properties and explore
possible approach to engineer the magnetic anisotropy. Through systematic
first-principles calculations, we found that the Ir2 dimer already possesses
giant MAE of 77 meV. We proposed an effective way to enhance the MAE of the Ir2
dimer to 223~294 meV by simply attaching a halogen atom at one end of the Ir-Ir
bond. The underlying mechanism for the record high MAE is attributed to the
modification of the energy diagram of the Ir2 dimer by the additional
halogen-Ir bonding, which alters the spin-orbit coupling Hamiltonian and hence
the magnetic anisotropy. Our strategy can be generalized to design other
magnetic molecules or clusters with giant magnetic anisotropy.",1709.01878v1
2018-01-08,The contribution of magnetic monopoles to ponderomotive forces in plasmas,"It is well--known that when magnetic monopoles are introduced in plasma
equations the propagation of electromagnetic waves is modified. This occurs
because of Maxwell equations acquire a symmetrical structure due to the
existence of electric and magnetic charge current densities. In this work we
study the nonlinear phenomena of ponderomotive forces associated to the
presence of magnetic monopoles in a plasma. We generalize the Washimi-Karpman
result for the ponderomotive force on electric charges to take into account the
symmetrical form of Maxwell equations in the presence of magnetic charges. It
is shown that the general ponderomotive force on this plasma depends
non--trivially on the magnetic monopoles, through the slowly temporal and
spatial variations of the electromagnetic field amplitudes. The magnetic
charges introduce corrections even if the plasma is unmagnetized. This last
force induces a magnetization of the plasma, and therefore a cyclotron
frequency (proportional to the square of the magnetic charge) is induced for
electrons. Finally, the magnetic monopoles also experience a ponderomotive
force due to the electrons. This force accelerates the magnetic charges along
the direction of propagation of the electromagnetic waves. The possible
consequences for experimental detection are discussed.",1801.02570v2
2018-01-17,Magnetic effect on dynamical tide in rapidly rotating astronomical objects,"By numerically solving the equations of rotating magnetohydrodynamics (MHD),
the magnetic effect on dynamical tide is studied. It is found that magnetic
field has a significant impact not only on the flow structure, i.e. the
internal shear layers in rotating flow can be destroyed in the presence of a
moderate or stronger magnetic field (in the sense that the Alfv\'en velocity is
at least of the order of 0.1 of the surface rotational velocity), but also on
the dispersion relation of waves excited by tidal force such that the range of
tidal resonance is broadened by magnetic field. A major result is that the
total tidal dissipation scales as square of the field strength, which can be
used to estimate the strength of internal magnetic field in the astronomical
object of a binary system. Moreover, with a moderate or stronger field the
ratio of the magnetic dissipation to the viscous dissipation is almost
inversely proportional to magnetic Prandtl number (i.e. the ratio of viscosity
to magnetic diffusivity), and therefore in the astrophysical situation at small
magnetic Prandtl number magnetic dissipation dominates over viscous dissipation
with a moderate or stronger field.",1801.05552v2
2018-02-01,An analytical computation of magnetic field generated from a cylinder ferromagnet,"An analytical formulation to compute a magnetic field generated from an
uniformly magnetized cylinder ferromagnet is developed. Exact solutions of the
magnetic field generated from the magnetization pointing in an arbitrary
direction are derived, which are applicable both inside and outside the
ferromagnet. The validities of the present formulas are confirmed by comparing
them with demagnetization coefficients estimated in earlier works. The results
will be useful for designing practical applications, such as high-density
magnetic recording and microwave generators, where nanostructured ferromagnets
are coupled to each other through the dipole interactions and show cooperative
phenomena such as synchronization. As an example, the magnetic field generated
from a spin torque oscillator for magnetic recording based on microwave
assisted magnetization reversal is studied.",1802.00384v1
2018-02-08,Manipulating Anomalous Hall Antiferromagnets with Magnetic Fields,"The symmetry considerations that imply a non-zero anomalous Hall effect (AHE)
in certain non-collinear antiferromagnets also imply both non-zero orbital
magnetization and a net spin magnetization. We have explicitly evaluated the
orbital magnetizations of several anomalous Hall effect antiferromagnets and
find that they tend to dominate over spin magnetizations, especially so when
spin-orbit interactions are weak. Because of the greater relative importance of
orbital magnetization the coupling between magnetic order and an external
magnetic field is unusual. We explain how magnetic fields can be used to
manipulate magnetic configurations in these systems, pointing in particular to
the important role played by the response of orbital magnetization to the
Zeeman-like spin exchange fields.",1802.03044v2
2018-03-01,On Magnetic Inhibition Theory in Non-resistive Magnetohydrodynamic Fluids,"We investigate why the non-slip boundary condition for the velocity, imposed
in the direction of impressed magnetic fields, can contribute to the magnetic
inhibition effect based on the nonhomogeneous magnetic Rayleigh--Taylor (abbr.
NMRT) problem in non-resistive magnetohydrodynamic (abbr. MHD) fluids.
Exploiting an infinitesimal method in Lagrangian coordinates, the idea of
(equivalent) magnetic tension, and the differential version of magnetic flux
conservation, we give an explanation of physical mechanism for the magnetic
inhibition phenomenon in a non-resistive MHD fluid. Moreover, we find that the
magnetic energy in the non-resistive MHD fluid depends on the displacement of
fluid particles, and thus can be regarded as elastic potential energy.
Motivated by this observation, we further use the well-known minimum potential
energy principle to explain the physical meaning of the stability/instability
criteria in the NMRT problem. As a result of the analysis, we further extend
the results on the NMRT problem to the stratified MHD fluid case. We point out
that our magnetic inhibition theory can be used to explain the inhibition
phenomenon of other instabilities, such as thermal instability, magnetic
buoyancy instability, and so on, by impressed magnetic fields in non-resistive
MHD fluids.",1803.00307v2
2018-04-13,Standing wave approach in the theory of x-ray magnetic reflectivity,"We have developed the extension of the exact x-ray resonant magnetic
reflectivity theory taking into account the small value of the magnetic terms
in the x-ray susceptibility tensor. We have shown that squared standing waves
(forth powder of the total electric field module) determine the output of the
magnetic addition to the total reflectivity from a magnetic multilayer. The
approach gives the easily understandable results especially for the
reflectivity part with the rotated polarization and the obtained relationship
can essentially speed up the calculation of the asymmetry ratio of the magnetic
reflectivity relative the sign of the circular polarization in the incident
radiation. The connection of the magnetic contribution with the standing wave
structure in the magnetic multilayer means that the magnetic reflectivity with
rotated polarization possesses higher sensitivity to the depth profiles of
magnetization and magnetic elements depth distribution than the secondary
radiation registration at the specular reflection condition.",1804.05104v1
2018-04-27,Excitation and coherent control of magnetization dynamics in magnetic tunnel junctions using acoustic pulses,"We experimentally study magnetization dynamics in magnetic tunnel junctions
driven by femtosecond-laser-induced surface acoustic waves. The acoustic pulses
induce a magnetization precession in the free layer of the magnetic tunnel
junction through magnetoelastic coupling. The frequency and amplitude of the
precession shows a pronounced dependence on the applied magnetic field and the
laser excitation position. Comparing the acoustic-wave-induced precession
frequencies with precession induced by charge currents and with micromagnetic
simulations we identify spatially non-uniform magnetization modes localized
close the edge regions as being responsible for the optically induced
magnetization dynamics. The experimental scheme even allows us to coherently
control the magnetization precession using two acoustic pulses. This might
prove important for future applications requiring ultrafast spin manipulation.
Additionally, our results directly pinpoint the importance of acoustic pulses
since they could be relevant when investigating optically-induced temperature
effects in magnetic structures.",1804.10503v1
2018-05-10,Magnetic field mediated conductance oscillation in graphene p-n junctions,"The electronic transport of graphene p-n junctions under perpendicular
magnetic field is investigated in theory. Under low magnetic field, the
transport is determined by the resonant tunneling of Landau levels and
conductance versus magnetic field shows a Shubnikov-de Haas oscillation. At
higher magnetic field, the p-n junction subjected to the quasi-classical regime
and the formation of snake states results in periodical backscattering and
transmission as magnetic field varies. The conductance oscillation pattern is
mediated both by magnetic field and the carrier concentration on bipolar
regions. For medium magnetic field between above two regimes, the combined
contributions of resonant tunneling, snake states oscillation and Aharanov-Bohm
interference induce irregular oscillation of conductance. At very high magnetic
field, the system is subjected to quantum Hall regime. Under disorder, the
quantum tunneling at low magnetic field is slightly affected and the
oscillation of snake states at higher magnetic field is suppressed. In the
quantum Hall regime, the conductance is a constant as predicted by the mixture
rule.",1805.03859v1
2018-05-30,Nonequilibrium Magnetic Oscillation with Cylindrical Vector Beams,"Magnetic oscillation is a generic property of electronic conductors under
magnetic fields and widely appreciated as a useful probe of their electronic
band structure, i.e., the Fermi surface geometry. However, the usage of the
strong static magnetic field makes the measurement insensitive to the magnetic
order of the target material. That is, the magnetic order is anyhow turned into
a forced ferromagnetic one. Here we theoretically propose an experimental
method of measuring the magnetic oscillation in a magnetic-order-resolved way
by using the azimuthal cylindrical vector (CV) beam, an example of topological
lightwaves. The azimuthal CV beam is unique in that when focused tightly, it
develops a pure longitudinal magnetic field. We argue that this characteristic
focusing property and the discrepancy in the relaxation timescale between
conduction electrons and localized magnetic moments allow us to develop the
nonequilibrium analog of the magnetic oscillation measurement. Our optical
method would be also applicable to metals the under ultra-high pressure of
diamond anvil cells.",1805.11831v2
2018-06-15,The turbulent pressure of magnetoconvection for slow and rapid rotation,"Motivated by recent simulations of sunspot formation, we extend the theory of
the pressure difference between magnetized and non-magnetized gas by Dicke to
include rotating turbulence. While the (vertical) background field provides a
positive-definite magnetic pressure difference between the magnetized and the
unmagnetized gas, Reynolds stress and Maxwell stress of turbulence strongly
modify this result. With the quasilinear approximation we demonstrate that the
influence of the turbulence differs between the high-conductivity and the
low-conductivity limits. Sufficiently small magnetic Reynolds numbers lead to
magnetic pressure suppression where indeed the pressure excess can even assume
negative values. Box simulations of magnetoconvection subject to a vertical
magnetic field carried out with the Nirvana code confirm this overall picture.
They also demonstrate how a global rotation {\em reduces} the negative magnetic
pressure effect. For rapid rotation the total magnetic pressure difference
caused by large-scale magnetic fields { and} turbulence even fully disappears
for small field strengths. Magnetic fields of moderate strength thus neither
reduce nor enhance the turbulence pressure of rapidly rotating convection.
Consequences of this phenomenon for the star formation efficiency are shortly
discussed.",1806.05877v1
2018-08-22,Invariants of magnetic Laplacians on periodic graphs,"We consider a magnetic Laplacian with periodic magnetic potentials on
periodic discrete graphs. Its spectrum consists of a finite number of bands,
where degenerate bands are eigenvalues of infinite multiplicity. We obtain a
specific decomposition of the magnetic Laplacian into a direct integral in
terms of minimal forms. A minimal form is a periodic function defined on edges
of the periodic graph with a minimal support on the period. It is crucial that
fiber magnetic Laplacians (matrices) have the minimal number of coefficients
depending on the quasimomentum and the minimal number of coefficients depending
on the magnetic potential. We show that these numbers are invariants for the
magnetic Laplacians on periodic graphs. Using this decomposition, we estimate
the position of each band, the Lebesgue measure of the magnetic Laplacian
spectrum and a variation of the spectrum under a perturbation by a magnetic
field in terms of these invariants and minimal forms. In addition, we consider
an inverse problem: we determine necessary and sufficient conditions for
matrices depending on the quasimomentum on a finite graph to be fiber magnetic
Laplacians. Moreover, similar results for magnetic Schr\""odinger operators with
periodic potentials are obtained.",1808.07762v1
2018-10-25,Magnetic force sensing using a self-assembled nanowire,"We present a scanning magnetic force sensor based on an individual
magnet-tipped GaAs nanowire (NW) grown by molecular beam epitaxy. Its magnetic
tip consists of a final segment of single-crystal MnAs formed by sequential
crystallization of the liquid Ga catalyst droplet. We characterize the
mechanical and magnetic properties of such NWs by measuring their flexural
mechanical response in an applied magnetic field. Comparison with numerical
simulations allows the identification of their equilibrium magnetization
configurations, which in some cases include magnetic vortices. To determine a
NW's performance as a magnetic scanning probe, we measure its response to the
field profile of a lithographically patterned current-carrying wire. The NWs'
tiny tips and their high force sensitivity make them promising for imaging weak
magnetic field patterns on the nanometer-scale, as required for mapping
mesoscopic transport and spin textures or in nanometer-scale magnetic
resonance.",1810.10865v1
2018-12-25,Magnetic Monopoles and Dark Matter,"Schwinger's idea about the magnetic world of the early Universe, in which
magnetic charges (monopoles) and magnetic atoms (g$^{+}$g$^{-}$) could be
formed, is developed. In the present-day Universe magnetic charges with
energies in the GeV range can be formed in the magnetospheres of young pulsars
in super strong magnetic fields. Spectroscopic features of magnetic atoms and
possibilities for their observations are discussed. Relic magnetic atoms can
contribute up to 18% to the dark matter density. The gamma-ray excess at our
Galactic center could arise under two-photon annihilation of magnetic charges
as a cooperative effect from neutron stars. A sharp physical difference of
Schwinger's magnetic world from Dirac's present-day electric world is pointed
out. Artificial magnetic monopoles are also mentioned briefly.",1901.02341v1
2019-01-10,Ultrafast magnetization dynamics in uniaxial ferrimagnets with compensation point. GdFeCo,"We derive an effective Lagrangian in the quasi-antiferromagnetic
approximation that allows to describe the magnetization dynamics for uniaxial
f-d (rare-earth - transition metal) ferrimagnet near the magnetization
compensation point in the presence of external magnetic field. We perform
calculations for the parameters of GdFeCo, a metallic ferrimagnet with
compensation point that is one of the most promising materials in ultrafast
magnetism. Using the developed approach, we find the torque that acts on the
magnetization due to ultrafast demagnetization pulse that can be caused either
by ultrashort laser or electrical current pulse. We show that the torque is
non-zero only in the non-collinear magnetic phase that can be acquired by
applying external magnetic field to the material. The coherent response of
magnetization dynamics amplitude and its timescale exhibits critical behavior
near certain values of the magnetic field corresponding to a spin-flop like
phase transition. Understanding the underlying mechanisms for these effects
opens the way to efficient control of the amplitude and the timescales of the
spin dynamics, which is one of the central problems in the field of ultrafast
magnetism.",1901.03072v2
2019-02-21,Self-induced Magnetic Flux Structure in the Magnetic Superconductor RbEuFe$_4$As$_4$,"We report an unusual enhancement of the magnetic induction in single crystals
of the magnetic superconductor RbEuFe$_4$As$_4$ , highlighting the interplay
between superconducting and magnetic subsystems in this material. Contrary to
the conventional Meissner expulsion of magnetic flux below the superconducting
transition temperature, we observe a substantial boost of the magnetic flux
density upon approaching the magnetic transition temperature, Tm. Direct
imaging of the flux evolution with a magneto-optical technique, shows that the
magnetic subsystem serves as an internal magnetic flux pump, drawing Abrikosov
vortices from the surface, while the superconducting subsystem controls their
conveyance into the bulk of the magnetic superconductor via a peculiar
self-organized critical state.",1902.08125v1
2019-03-11,Spin-glass state and reversed magnetic anisotropy induced by Cr doping in the Kitaev magnet $α$-RuCl$_3$,"Magnetic properties of the substitution series Ru$_{1-x}$Cr$_x$Cl$_3$ were
investigated to determine the evolution from the anisotropic Kitaev magnet
$\alpha$-RuCl$_3$ with $J_{\rm eff} = 1/2$ magnetic Ru$^{3+}$ ions to the
isotropic Heisenberg magnet CrCl$_3$ with $S = 3/2$ magnetic Cr$^{3+}$ ions.
Magnetization measurements on single crystals revealed a reversal of the
magnetic anisotropy under doping, which we argue to arise from the competition
between anisotropic Kitaev and off-diagonal interactions on the Ru-Ru links and
approximately isotropic Cr-Ru and isotropic Cr-Cr interactions. In addition,
combined magnetization, ac susceptibility and specific-heat measurements
clearly show the destabilization of the long-range magnetic order of
$\alpha$-RuCl$_3$ in favor of a spin-glass state of Ru$_{1-x}$Cr$_x$Cl$_3$ for
a low doping of $x\backsimeq0.1$. The corresponding freezing temperature as a
function of Cr content shows a broad maximum around $x\backsimeq0.45$.",1903.04248v3
2019-03-26,Dynamical evolution of magnetic fields in the intracluster medium,"We investigate the evolution of magnetic fields in galaxy clusters starting
from constant primordial fields using highly resolved ($\approx \rm 4 ~kpc$)
cosmological MHD simulations. The magnetic fields in our sample exhibit
amplification via a small-scale dynamo and compression during structure
formation. In particular, we study how the spectral properties of magnetic
fields are affected by mergers, and we relate the measured magnetic energy
spectra to the dynamical evolution of the intracluster medium. The magnetic
energy grows by a factor of $\sim$ 40-50 in a time-span of $\sim 9$ Gyr and
equipartition between kinetic and magnetic energy occurs on a range of scales
($< 160 \rm ~kpc$ at all epochs) depending on the turbulence state of the
system. We also find that, in general, the outer scale of the magnetic field
and the MHD scale are not simply correlated in time. The effect of major
mergers is to shift the peak magnetic spectra to it smaller scales, whereas the
magnetic amplification only starts after $\lesssim$ 1 Gyr. In contrast,
continuous minor mergers promote the steady growth of the magnetic field. We
discuss the implications of these findings in the interpretation of future
radio observations of galaxy clusters.",1903.11052v1
2019-04-22,Strain-Induced Reversible Manipulation of Orbital Magnetic Moments in Ni/Cu Multilayers on Ferroelectric BaTiO3,"Controlling magnetic anisotropy by orbital magnetic moments related to
interfacial strains has considerable potential for the development of future
devices using spins and orbitals. For the fundamental physics, the relationship
between strain and orbital magnetic moment is still unknown, because there are
few tools to probe changes of orbital magnetic moment. In this study, we
developed an electric-field- (E)-induced X-ray magnetic circular dichroism
(EXMCD) technique to apply E to a ferroelectric BaTiO3 substrate. We reversibly
tuned the interfacial lattice constants of Ni/Cu multilayers on BaTiO3 using
this technique. As the domain structures in BaTiO3 are modulated by E, EXMCD
measurements reveal that the changes in the magnetic anisotropy of Ni/Cu films
are induced through the modulation of orbital magnetic moments in Ni with
magneto-elastic contributions. The strained Ni layer that induces the
perpendicular magnetic anisotropy without E is released at E = 8 kV/cm, and
in-plane magnetization also occurs. We observed that EXMCD measurements
clarified the origin of the reversible changes in perpendicular magnetic
anisotropy and established the relationship between macroscopic inverse
magnetostriction effects and microscopic orbital moment anisotropy.",1904.09719v1
2019-04-25,Magnetic-field-induced quantized anomalous Hall effect in intrinsic magnetic topological insulator MnBi$_2$Te$_4$,"In a magnetic topological insulator, nontrivial band topology conspires with
magnetic order to produce exotic states of matter that are best exemplified by
quantum anomalous Hall (QAH) insulators and axion insulators. Up till now, such
magnetic topological insulators are obtained by doping topological insulators
with magnetic atoms. The random magnetic dopants, however, inevitably introduce
disorders that hinder further exploration of quantum effects in the material.
Here, we resolve this dilemma by probing quantum transport in MnBi$_2$Te$_4$
thin flake - a topological insulator with intrinsic magnetic order. In this
layered van der Waals crystal, the ferromagnetic layers couple anti-parallel to
each other, so MnBi$_2$Te$_4$ is an antiferromagnet. A magnetic field, however,
aligns all the layers and induces an interlayer ferromagnetic order; we show
that a quantized anomalous Hall response emerges in atomically thin
MnBi$_2$Te$_4$ under a moderate magnetic field. MnBi$_2$Te$_4$ therefore
becomes the first intrinsic magnetic topological insulator exhibiting quantized
anomalous Hall effect. The result establishes MnBi$_2$Te$_4$ as an ideal arena
for further exploring various topological phenomena.",1904.11468v1
2019-05-22,Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers,"Perpendicularly magnetized CoFeB layers with ultra-thin non-magnetic
insertion layers are very widely used as the electrodes in magnetic tunnel
junctions for spin transfer magnetic random access memory devices. Exchange
interactions play a critical role in determining the thermal stability of
magnetic states in such devices and their spin torque switching efficiency.
Here the exchange constant of free layers incorporated in full magnetic tunnel
junction layer stacks, specifically CoFeB free layers with W insertion layers
is determined by magnetization measurements in a broad temperature range. A
significant finding is that the exchange constant decreases significantly and
abruptly with W insertion layer thickness. The perpendicular magnetic
anisotropy shows the opposite trend; it initially increases with W insertion
layer thickness and shows a broad maximum for approximately one monolayer (0.3
nm) of W. These results highlight the interdependencies of magnetic
characteristics required to optimize the performance of magnetic tunnel
junction devices.",1905.09329v1
2019-07-24,Electron doping induced magnetic glassy state in phase separated YBaCo$_2$O$_{5.5-δ}$,"The structural, magnetic and transport properties of the layered
RBaCo$_2$O$_{5.5}$ cobaltites are sensitive to the oxygen stoichiometry. In
this present study, we report the presence of a low-temperature magnetic glassy
state in electron-doped polycrystalline YBaCo$_2$O$_{5.5}$ cobaltite. The ac
magnetization studies show the absence of conventional spin glass features,
while the various dc magnetization studies demonstrate the presence of
non-equilibrium magnetic glassy state at low temperature. The magnetic glassy
state of this sample results from the kinetic arrest of the first order ferro
(or ferri) to antiferromagnetic transition. The role of electron doping in the
occurrence of magnetic glassy phenomena is discussed in terms of magnetic phase
separation involving the Co3+/Co2+ clusters of the ferrimagnetic phase in the
Co3+/Co3+ antiferromagnetic matrix.",1907.10248v1
2019-08-27,Effect of Magnetisation of Bulk Superconductors on Permanent Magnets for Reversible Braking Applications,"Magnetisation of superconductors are often measured under isothermal and
uniform magnetic fields. Magnetisation measurements in an unrestricted
thermodynamic state and in non uniform magnetic fields naturally emerge from
permanent magnets in comparison with size of superconducting bulk are needed
for practical applications. A stationary Type II superconductor bulk sample is
magnetised (FC and ZFC) at liquid nitrogen temperatures in the presence of a
stationary permanent magnet. Magnetic field produced by magnetised
superconductor and permanent magnet as a function of distance are measured
along a straight line, a supposed path of another moving permanent magnet. A
moving magnet is introduced and moved along the same straight line. Force
acting on moving magnet as a function of distance are measured due to
magnetisation in superconductor and stationary magnet. Both field and force
measurements are quasi static. These experimental results combined with
simulation results show insight in to the transfer of energy stored in
magnetisation to thermal energy and the effect of rate of this energy transfer
in AC response of superconductors which are otherwise not possible with
isothermal studies. A possible application of reversible braking with bulk
superconductors for motors and generators is explored. Future similar
measurements with Type I superconductor would provide more insights in to this
study.",1908.10297v1
2019-09-26,Coherent charge and magnetic ordering in Ho/Y superlattice revealed by element-selective x-ray scattering,"Magnetic rare-earth / non-magnetic metal superlattices are well-known to
display chiral spin helices in the rare-earth layers that propagate coherently
across the non-magnetic layers. However, the underlying mechanism that
preserves the magnetic phase and chirality coherence across the non-magnetic
layers has remained elusive. In this Letter, we use resonant and
element-specific x-ray scattering to evidence directly the formation of two
fundamentally different long-range modulations in a Holmium/Yttrium (Ho/Y)
multilayer: the known Ho chiral spin helix with periodicity 25 {\AA}, and a
newly observed charge density wave with periodicity 16 {\AA} that propagates
through both the Ho and non-magnetic Y layer. With x-ray circular magnetic
dichroism measurements ruling out the existence of a magnetic proximity effect
induced moment in the non-magnetic Y layers, we propose that the charge density
wave is also chiral, thus providing the means for the transmittance of magnetic
chirality coherence between Ho layers.",1909.12372v2
2019-11-05,Analysis of magnetization induced error field in superconducting magnets,"The field error due to magnetization of superconductors in a superconducting
magnet can significantly compromise the field homogeneity which is extremely
important for NMR magnets. This is especially true for high Tc superconducting
magnets. In this paper, the error field induced by the magnetization of
superconducting wires or tapes is analyzed using a magnetic dipole field model.
It uses experimentally measured magnetization of superconducting wires, and
eludes the need of assuming screening current and its distribution as in
previous methods. The field error of a REBCO coil calculated by this model and
by a screening current model shows complete agreement. A few cases of field
error distribution along the coil axis are calculated. The results are in
qualitative agreement with experiments in the literature. This model would be
particularly useful for magnets wound by multifilamentary wires or tapes where
the filament sizes vary and filament bridging may occur hence screening current
distribution is unknown. This model can also be used as a base for numerical
calculations of the field error of a large practical magnet.",1911.02139v1
2019-11-18,Anisotropic magnetic properties of trigonal ErAl$_2$Ge$_2$ single crystal,"We report the anisotropic magnetic properties of the ternary compound
ErAl$_2$Ge$_2$. Single crystals of this compound were grown by high temperature
solution growth technique,using Al:Ge eutectic composition as flux. From the
powder x-ray diffraction we confirmed that ErAl$_2$Ge$_2$ crystallizes in the
trigonal CaAl$_2$Si$_2$-type crystal structure. The anisotropic magnetic
properties of a single crystal were investigated by measuring the magnetic
susceptibility, magnetization, heat capacity and electrical resistivity. A bulk
magnetic ordering occurs around 4 K inferred from the magnetic susceptibility
and the heat capacity. The magnetization measured along the $ab$-plane
increases more rapidly than along the $c$-axis suggesting the basal $ab$-plane
as the easy plane of magnetization. The magnetic susceptibility, magnetization
and the $4f$-derived part of the heat capacity in the paramagnetic regime
analysed based on the point charge model of the crystalline electric field
(CEF) indicate a relatively low CEF energy level splitting.",1911.07589v1
2019-12-03,Nanoscale Tantalum Layer Controlling the Magnetic Coupling between Two Ferromagnetic Electrodes via Insulator of a Magnetic Tunnel Junction,"Ability to tailor the nature of the magnetic coupling between two
ferromagnetic electrodes can enable the realization of new spintronics device
systems. This paper discusses our finding that deposition of an ultrathin
tantalum (Ta) on the NiFe top electrode reversed the nature of
inter-ferromagnetic electrode coupling. We observed that the deposition of ~ 5
nm Ta on the top of a magnetic tunnel junction with Ta( 2 nm)/Co(5 nm)/NiFe (5
nm)/AlOx( 2 nm)/NiFe (10-15 nm) configuration changed the magnetic coupling
between two ferromagnetic electrodes from antiferromagnetic to ferromagnetic.
We investigated Ta effect using multiple magnetic characterizations like
ferromagnetic resonance, magnetometry, and polarized neutron reflectometry.
Ferromagnetic resonance characterization was very sensitive for detecting the
changes in magnetic coupling via the insulating spacer. This simple approach of
adding Ta film to alter the magnetic coupling can impact the other burgeoning
areas like molecular spintronics. We found that preexisting magnetic coupling
between two ferromagnetic electrodes impacted the resultant magnetic properties
of magnetic tunnel junctions based molecular spintronics devices.",1912.01331v1
2019-12-16,3D printing of polymer-bonded anisotropic magnets in an external magnetic field and by a modified production process,"The possibility of producing polymer-bonded magnets with the aid of additive
processes, such as 3D printing, opens up a multitude of new areas of
application. Almost any structures and prototypes can be produced
cost-effectively in small quantities. Extending the 3D printing process allows
the manufacturing of anisotropic magnetic structures by aligning the magnetic
easy axis of ferromagnetic particles inside a paste-like compound material
along an external magnetic field. This is achieved by two different approaches:
First, the magnetic field for aligning the particles is provided by a permanent
magnet. Secondly, the 3D printing process itselfs generates an anisotropic
behavior of the structures. An inexpensive and customizable end-user fused
filament fabrication 3D printer is used to print the magnetic samples. The
magnetical properties of different magnetic anisotropic Sr ferrite and SmFeN
materials are investigated and discussed.",1912.07374v1
2019-12-29,Stabilizing effect of magnetic helicity on magnetic cavities in the intergalactic medium,"We investigate the effect of magnetic helicity on the stability of buoyant
magnetic cavities as found in the intergalactic medium. In these cavities, we
insert helical magnetic fields and test whether or not helicity can increase
their stability to shredding through the Kelvin-Helmholtz instability and, with
that, their lifetime. This is compared to the case of an external vertical
magnetic field which is known to reduce the growth rate of the Kelvin-Helmholtz
instability. By comparing a low-helicity configuration with a high helicity one
with the same magnetic energy we find that an internal helical magnetic field
stabilizes the cavity. This effect increases as we increase the helicity
content. Stabilizing the cavity with an external magnetic field requires
instead a significantly stronger field at higher magnetic energy. We conclude
that the presence of helical magnetic fields is a viable mechanism to explain
the stability of intergalactic cavities on time scales longer than 100 Myr.",1912.12723v3
2020-01-09,Two-dimensional magnetic nanoelectromechanical resonators,"Two-dimensional (2D) layered materials possess outstanding mechanical,
electronic and optical properties, making them ideal materials for
nanoelectromechanical applications. The recent discovery of 2D magnetic
materials has promised a new class of magnetically active nanoelectromechanical
systems (NEMS). Here we demonstrate resonators made of 2D CrI3, whose
mechanical resonances depend on the magnetic state of the material. We quantify
the underlining effects of exchange and anisotropy magnetostriction by
measuring the field dependence of the resonance frequency under a magnetic
field parallel and perpendicular to the easy axis, respectively. Furthermore,
we show efficient strain tuning of magnetism in 2D CrI3 as a result of the
inverse magnetostrictive effect using the NEMS platform. Our results establish
the basis for mechanical detection of magnetism and magnetic phase transitions
in 2D layered magnetic materials. The new magnetic NEMS may also find
applications in magnetic actuation and sensing.",2001.03153v1
2020-01-27,Non-exponential magnetic relaxation in magnetic nanoparticles for hyperthermia,"Magnetic nanoparticle based hyperthermia emerged as a potential tool for
treating malignant tumours. The efficiency of the method relies on the
knowledge of magnetic properties of the samples; in particular, knowledge of
the frequency dependent complex magnetic susceptibility is vital to optimize
the irradiation conditions and to provide feedback for material science
developments. We study the frequency-dependent magnetic susceptibility of an
aqueous ferrite suspension for the first time using non-resonant and resonant
radiofrequency reflectometry. We identify the optimal measurement conditions
using a standard solenoid coil, which is capable of providing the complex
magnetic susceptibility up to 150 MHz. The result matches those obtained from a
radiofrequency resonator for a few discrete frequencies. The agreement between
the two different methods validates our approach. Surprisingly, the dynamic
magnetic susceptibility cannot be explained by an exponential magnetic
relaxation behavior even when we consider a particle size-dependent
distribution of the relaxation parameter.",2001.09774v1
2020-02-25,Noncollinear magnetic structure and magnetoelectric coupling in buckled honeycomb Co$_4$Nb$_2$O$_9$:A single crystal neutron diffraction study,"Through analysis of single crystal neutron diffraction data, we present the
magnetic structures of magnetoelectric Co4Nb2O9 under various magnetic fields.
In zero-field, neutron diffraction experiments below TN=27 K reveal that the
Co2+ moments order primarily along the a* direction without any spin canting
along the c axis, manifested by the magnetic symmetry C2/c'. The moments of
nearest neighbor Co atoms order ferromagnetically with a small cant away from
the next nearest neighbor Co moments along the c axis. In the applied magnetic
field H//a, three magnetic domains were aligned with their major magnetic
moments perpendicular to the magnetic field with no indication of magnetic
phase transitions. The influences of magnetic fields on the magnetic structures
associated with the observed magnetoelectric coupling are discussed.",2002.10599v1
2020-03-18,Thermally induced generation and annihilation of magnetic chiral skyrmion bubbles and achiral bubbles in Mn-Ni-Ga Magnets,"Magnetic chiral skyrmion bubbles and achiral bubbles are two independent
magnetic domain structures, in which the former with equivalent winding number
to skyrmions offers great promise as information carriers for further
spintronic devices. Here, in this work, we experimentally investigate the
generation and annihilation of magnetic chiral skyrmion bubbles and achiral
bubbles in the Mn-Ni-Ga thin plate by using the Lorentz transmission electron
microscopy (L-TEM). The two independent magnetic domain structures can be
directly controlled after the field cooling manipulation by varying the titled
angles of external magnetic fields. By imaging the magnetization reversal with
increasing temperature, we found an extraordinary annihilation mode of magnetic
chiral skyrmion bubbles and a non-linear frequency for the winding number
reversal. Quantitative analysis of such dynamics was performed by using L-TEM
to directly determine the barrier energy for the magnetization reversal of
magnetic chiral skyrmion bubbles.",2003.08035v1
2020-03-22,Magnetization steps in the molecular magnet Ni$_4$Mo$_{12}$ revealed by complex exchange bridges,"We study the behavior of the magnetization and the magnetic susceptibility of
molecular magnets with complex bridging structure. Our computations are based
on a post-Hartree-Fock method accounting for the intricate network of
interatomic bonds and an effective spin-like Hamiltonian that captures the
essential magnetic features of magnetic molecules. The devised method and the
constructed Hamiltonian are further employed to characterize the magnetic
properties of the molecular magnet Ni$_4$Mo$_{12}$. The obtained results
reproduce both quantitatively and qualitatively the main features of the
magnetic spectrum. Furthermore, the computations for the magnetization and the
low-field susceptibility are in very good agreement with their experimental
counterparts. In this respect, they improve upon the results obtained with
conventional Heisenberg models.",2003.12475v1
2020-07-24,Can the dynamics of test particles around charged stringy black holes mimic the spin of Kerr black holes?,"We study the motion of electrically charged particles, magnetic monopoles,
and magnetic dipoles around electrically and magnetically charged stringy black
holes. From the analysis of the radius of the innermost stable circular orbit
(ISCO) of electrically charged particles, we show that the electric charge $Q$
of stringy black holes can mimic well the spin of Kerr black holes; the black
hole magnetic charge $Q_m$ can mimic spins up to $a_* \simeq 0.85$ for magnetic
dipoles; the magnetic charge parameter $g$ of a magnetic monopole can mimic
spins up to $a_* \simeq 0.8$. This is due to the destructive character of the
magnetic field and such a result excludes the existence of an appreciable black
hole magnetic charge in astrophysical black holes from the observation of
rapidly rotating objects with dimensionless spin up to $a_* \simeq 0.99$. We
then consider the magnetar SGR (PSR) J1745-2900 as a magnetic dipole orbiting
the supermassive black hole Sagittarius A* (Sgr A*). We show that Sgr A* may be
interpreted as a stringy black hole with magnetic charge $Q_{\rm m}/M \leq
0.4118$.",2007.12462v1
2020-07-28,Magnetic bubbles in an M-type hexagonal ferrite observed by hollow-cone Foucault imaging and small-angle electron diffraction,"We report hollow-cone imaging and small-angle electron diffraction of
nanoscale magnetic textures such as magnetic-striped domains and magnetic
bubbles of M-type hexagonal ferrite
BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$. The advantage of the hollow-cone
Foucault method is that magnetic domains with various directions of
magnetization can be visualized under an infocus condition. Moreover, the
contrast of magnetic domain walls in magnetic bubbles depends on the
inclination angle of the illumination beam. The combination of small-angle
electron diffraction and hollow-cone Foucault imaging proves that magnetization
at domain walls exhibits in-plane directions in the magnetic-striped domains
and magnetic bubbles.",2007.13994v1
2020-08-04,Magnetism and anomalous transport in the Weyl semimetal PrAlGe: Possible route to axial gauge fields,"In magnetic Weyl semimetals, where magnetism breaks time-reversal symmetry,
large magnetically sensitive anomalous transport responses are anticipated that
could be useful for topological spintronics. The identification of new magnetic
Weyl semimetals is therefore in high demand, particularly since in these
systems Weyl node configurations may be easily modified using magnetic fields.
Here we explore experimentally the magnetic semimetal PrAlGe, and unveil a
direct correspondence between easy-axis Pr ferromagnetism and anomalous Hall
and Nernst effects. With sizes of both the anomalous Hall conductivity and
Nernst effect in good quantitative agreement with first principles
calculations, we identify PrAlGe as a system where magnetic fields can connect
directly to Weyl nodes via the Pr magnetization. Furthermore, we find the
predominantly easy-axis ferromagnetic ground state co-exists with a low density
of nanoscale textured magnetic domain walls. We describe how such nanoscale
magnetic textures could serve as a local platform for tunable axial gauge
fields of Weyl fermions.",2008.01476v1
2020-09-14,Calculation of permanent magnet arrangements for stellarators: A linear least-squares method,"A problem arising in several engineering areas is to design magnets outside a
volume that produce a desired magnetic field inside it. One instance of this
problem is stellarator design, where it has recently been shown that permanent
magnets can provide the required shaping of the magnetic field. Here we
demonstrate a robust and efficient algorithm REGCOIL_PM to calculate the
spatial distribution of these permanent magnets. The procedure involves a small
number of fixed-point iterations, with a linear least-squares problem solved at
each step. The method exploits the Biot-Savart Law's exact linearity in
magnetization density and approximate linearity in magnet size, for magnets far
from the target region. No constraint is placed on the direction of
magnetization, so Halbach solutions are found naturally, and the magnitude of
the magnetization can be made uniformly equal to a target value.",2009.06535v1
2020-09-24,Magnetic Field Induced Phase Transition in Spinel GeNi2O4,"Cubic spinel GeNi2O4 exhibits intriguing magnetic properties with two
successive antiferromagnetic phase transitions (TN1 12.1 and TN2 11.4 K) with
the absence of any structural transition. We have performed detailed heat
capacity and magnetic measurements in different crystallographic orientations.
A new magnetic phase in presence of magnetic field (H > 4 T) along the [111]
direction is revealed, which is not observed when the magnetic field is applied
along the [100] and [110] directions. High field neutron powder diffraction
measurements confirm such a change in magnetic phase, which could be ascribed
to a spin reorientation in the presence of magnetic field. A strong magnetic
anisotropy and competing magnetic interactions play a crucial role on the
complex magnetic behavior in this cubic system.",2009.11960v1
2020-10-06,An ultra-stable 1.5 tesla permanent magnet assembly for qubit experiments at cryogenic temperatures,"Magnetic fields are a standard tool in the toolbox of every physicist, and
are required for the characterization of materials, as well as the polarization
of spins in nuclear magnetic resonance or electron paramagnetic resonance
experiments. Quite often a static magnetic field of sufficiently large, but
fixed magnitude is suitable for these tasks. Here we present a permanent magnet
assembly that can achieve magnetic field strengths of up to 1.5T over an air
gap length of 7mm. The assembly is based on a Halbach array of neodymium
(NdFeB) magnets, with the inclusion of the soft magnetic material Supermendur
to boost the magnetic field strength inside the air gap. We present the design,
simulation and characterization of the permanent magnet assembly, measuring an
outstanding magnetic field stability with a drift rate of |D| < 2.8 ppb/h. Our
measurements demonstrate that this assembly can be used for spin qubit
experiments inside a dilution refrigerator, successfully replacing the more
expensive and bulky superconducting solenoids.",2010.02455v2
2020-10-10,Dynamics of charged and magnetized particles around cylindrical black holes immersed in external magnetic field,"This paper investigates the motion and acceleration of a particle that is
electrically and magnetically charged, which rotates around a cylindrical black
hole in the presence of an external asymptotically uniform magnetic field
parallel to the z axis. Basically, the work considers the circular orbits of
particles rotating around the central object and studies the dependence of the
most internal stable circular orbits (ISCO) on the so-called magnetic coupling
parameters, which are responsible for the interaction between the external
magnetic field and magnetized and charged particles. It is also shown that the
ISCO radius decreases with increasing magnetized parameter. Therefore,
collisions of magnetized particles around a cylindrical black hole immersed in
an external magnetic field were also studied, and it was shown that the
magnetic field can act as a particle accelerator around non-rotating
cylindrical black holes.",2010.04969v1
2020-10-30,Characterization of microscopic ferromagnetic defects in thin films using magnetic microscope based on Nitrogen-Vacancy centres,"In this work we present results acquired by applying magnetic field imaging
technique based on Nitrogen-Vacancy centres in diamond crystal for
characterization of magnetic thin films defects. We used the constructed
wide-field magnetic microscope for measurements of two kinds of magnetic
defects in thin films. One family of defects under study was a result of
non-optimal thin film growth conditions. The magnetic field maps of several
regions of the thin films created under very similar conditions to previously
published research revealed microscopic impurity islands of ferromagnetic
defects, that potentially could disturb the magnetic properties of the surface.
The second part of the measurements was dedicated to defects created post
deposition - mechanical defects introduced in ferromagnetic thin films. In both
cases, the measurements identify the magnetic field amplitude and distribution
of the magnetic defects. In addition, the magnetic field maps were correlated
with the corresponding optical images. As this method has great potential for
quality control of different stages of magnetic thin film manufacturing process
and it can rival other widely used measurement techniques, we also propose
solutions for the optimization of the device in the perspective of high
throughput.",2010.16197v1
2020-11-20,An Investigation of Commercial Iron Oxide Nanoparticles: Advanced Structural and Magnetic Properties Characterization,"Magnetic nanoparticles (MNPs) have been extensively used as tiny heating
sources in magnetic hyperthermia therapy, contrast agents in magnetic resonance
imaging (MRI), tracers in magnetic particle imaging (MPI), carriers for
drug/gene delivery, etc. There have emerged many magnetic
nanoparticle/microbeads suppliers since the last decade, such as Ocean
NanoTech, Nanoprobes, US Research Nanomaterials, Miltenyi Biotec, micromod
Partikeltechnologie GmbH, and nanoComposix, etc. In this paper, we report the
physical and magnetic characterizations on iron oxide nanoparticle products
from Ocean NanoTech. Standard characterization tools such as Vibrating-Sample
Magnetometer (VSM), X-Ray Diffraction (XRD), Dynamic Light Scattering (DLS),
Transmission Electron Microscopy (TEM), and Zeta Potential Analyzer are used to
provide magnetic nanoparticle customers and researchers with an overview of
these iron oxide nanoparticle products. In addition, the dynamic magnetic
responses of these iron oxide nanoparticles in aqueous solutions are
investigated under low and high frequency alternating magnetic fields, giving a
standardized operating procedure for characterizing the MNPs from Ocean
NanoTech, thereby yielding the best of magnetic nanoparticles for different
applications.",2011.10215v1
2021-01-26,Understanding Magnetism in Double Double Perovskites: A Complex Multiple Magnetic Sublattice System,"Understanding magnetism in multiple magnetic sublattice system, driven by the
interplay of varied nature of magnetic exchanges, is on one hand challenging
and on other hand intriguing. Motivated by the recent synthesis of AA'BB'O_6
double double perovskites with multiple magnetic ions both at A- and B-sites,
we investigate the mechanism of magnetic behavior in these interesting class of
compounds. We find that the magnetism in such multiple sublattice compounds is
governed by the interplay and delicate balance between two distinct mechanisms,
a) kinetic energy-driven multiple sublattice double exchange mechanism and b)
the conventional super-exchange mechanism. The derived spin Hamiltonian based
on first-principles calculations is solved by the classical Monte Carlo
technique which reproduces the observed magnetic properties. Finally, the
influence of off-stoichiometry, as in experimental samples, is discussed. Some
of these double double perovskite compounds are found to possess large total
magnetic moment and also are found to be half-metallic, which raises the hope
of future applications of these large magnetic moment half-metallic oxides in
spintronics and memory devices.",2101.10822v1
2021-03-16,Efficient field-free perpendicular magnetization switching by a magnetic spin Hall effect,"Current induced spin-orbit torques driven by the conventional spin Hall
effect are widely used to manipulate the magnetization. This approach, however,
is nondeterministic and inefficient for the switching of magnets with
perpendicular magnetic anisotropy that are demanded by the high-density
magnetic storage and memory devices. Here, we demonstrate that this limitation
can be overcome by exploiting a magnetic spin Hall effect in noncollinear
antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows
generation of the out-of-plane spin current carrying spin polarization induced
by an in-plane charge current. This spin current drives an out-of-plane
anti-damping torque providing deterministic switching of perpendicular
magnetization of an adjacent Ni/Co multilayer. Compared to the conventional
spin-orbit torque devices, the observed switching does not need any external
magnetic field and requires much lower current density. Our results demonstrate
great prospects of exploiting the magnetic spin Hall effect in noncollinear
antiferromagnets for low-power spintronics.",2103.09011v1
2021-05-09,"Degenerate magnetic ground state and metastable state on trihexagonal Co-sublattices in Co3Sn2(S,Se)2 single crystals","A trihexagonal lattice has been predicted to retain a degenerate magnetic
state which enriches physical properties. Especially, Co3Sn2S2, possessing
trihexagonal Co-sublattices, has been observed to own topological quantum
properties. Experimentally, Co3Sn2S2 has been reported to have hidden magnetic
phases due to magnetic anomalies. To clarify the hidden magnetic phase, we
fabricated high-quality single crystals of Co3Sn2S2-xSex (x = 0, 0.26, & 0.86).
The Se-substitution is intended to broaden the distance between Co atoms. For
each Se-composition, magnetizations of single-crystalline Co3Sn2S2-xSex
implicate that the magnetic ground state consists of the out-of-plane
ferromagnetism and the in-plane antiferromagnetism: Being degenerate.
Meanwhile, along out-of-plane, remanent magnetizations of Co3Sn2S2-xSex have a
first-order phase transition, so Co3Sn2S2-xSex owns an excited magnetic state,
denoted as the metastable state. Consequently, we have provided semiclassical
magnetic structures of the degenerate ground state and the metastable state via
both magnetic symmetries and experimental constraints. Moreover, we have
discovered mechanisms raising degeneracy and metastability.",2105.03892v1
2021-07-02,Off-axis gyration induces large-area circular motion of anisotropic microparticles in a dynamic magnetic trap,"Magnetic tweezers are crucial for single-molecule and atomic
characterization, and biomedical isolation of microparticle carriers. The
trapping component of magnetic tweezing can be relying on a magnetic potential
well that can confine the relevant species to a localized region. Here, we
report that magnetic microparticles with tailored anisotropy can transition
from localized off-axis gyration to large-area locomotion in a rotating
magnetic trap. The microparticles, consisting of assemblies of magnetic cores,
are observed to either rotate about its structural geometric center or gyrate
about one of the magnetic cores, the switching of which can be modulated by the
external field. Raising the magnetic field strength above a threshold, the
particles can go beyond the traditional synchronous-rotation and
asynchronous-oscillation modes, and into a scenario of large-area circular
motion. This results in peculiar retrograde locomotion related to the
magnetization maxima of the microparticle. Our finding suggests the important
role of the microparticle's magnetic morphology in the controlled transport of
microparticles and developing smart micro-actuators and micro-robot devices.",2107.00869v1
2021-07-27,Nonreciprocal magnon excitations by the Dzyaloshinskii-Moriya interaction on the basis of bond magnetic toroidal multipoles,"The microscopic conditions for the emergence of nonreciprocal magnon
excitations in noncentrosymmetric magnets are theoretically investigated. We
show that asymmetric magnon excitations appear when a bond magnetic toroidal
dipole becomes active, which is defined as a parallel component between the
Dzyaloshinskii-Moriya vector and the averaged spin moments at the ends of the
bonds. Depending on magnetic structures accompanying the bond magnetic toroidal
dipoles, the higher-rank magnetic toroidal multipoles can also be activated in
a magnetic cluster, which describes various angle dependences of asymmetric
magnon excitations. We demonstrate a variety of asymmetric magnon excitations
for two magnetic systems in the noncentrosymmetric lattice structures; a
one-dimensional breathing chain under a uniform crystalline electric field and
a three-dimensional layered breathing kagome structure. We show that a bottom
shift of magnon bands occurs by the magnetic toroidal dipole and a valley
splitting occurs by the magnetic toroidal octupole under magnetic orderings.",2107.12743v1
2021-07-27,Biermann Battery Magnetic Fields in ICF Capsules: Total Magnetic Flux Generation,"This paper focuses on the process of magnetic flux generation in ICF
implosions. Hot-spots are shown to be dominated by fields generated during
stagnation, when the temperature and density gradients are largest. A scaling
of hot-spot magnetic flux is derived and compared with simulations, revealing
that perturbations with both larger amplitudes and higher mode numbers generate
more magnetic flux. The model allows for greater understanding of which target
designs will be susceptible to MHD effects. For example, the model can be used
to ascertain the time when most magnetic flux is generated. If generation is
weighted more towards early times, then more high-mode magnetic field loops
will be present. A hot-spot with no high-mode perturbations at time of peak
neutron production can still contain significant magnetic flux on those scales.
By assuming that magnetic flux is deposited at the hot-spot edge by Nernst
advection, the model can be used to post-process radiation-hydrodynamics data
to estimate magnetic field strengths and magnetizations.",2107.13036v1
2021-09-23,Tuning magnetic antiskyrmion stability in tetragonal inverse Heusler alloys,"The identification of materials supporting complex, tunable magnetic order at
ambient temperatures is foundational to the development of new magnetic device
architectures. We report the design of Mn2XY tetragonal inverse Heusler alloys
that are capable of hosting magnetic antiskyrmions whose stability is sensitive
to elastic strain. We first construct a universal magnetic Hamiltonian
capturing the short- and long- range magnetic order which can be expected in
these materials. This model reveals critical combinations of magnetic
interactions that are necessary to approach a magnetic phase boundary, where
the magnetic structure is highly susceptible to small perturbations such as
elastic strain. We then computationally search for quaternary Mn2(X1,X2)Y
alloys where these critical interactions may be realized and which are likely
to be synthesizable in the inverse Heusler structure. We identify the
Mn2Pt(1-z)X(z)Ga family of materials with X=Au, Ir, Ni as an ideal system for
accessing all possible magnetic phases, with several critical compositions
where magnetic phase transitions may be actuated mechanically.",2109.11423v1
2021-10-29,Two types of magnetic bubbles in MnNiGa observed via Lorentz microscopy,"Magnetic bubbles are remarkable spin structures that developed in uniaxial
magnets with strong magnetocrystalline anisotropy. Several contradictory
reports have been published concerning the magnetic bubble structure in a
metallic magnet MnNiGa: Biskyrmions or type-II bubbles. Lorentz microscopy in
polycrystalline MnNiGa was used to explain the magnetic bubble structure.
Depending on the connection between the magnetic easy axis and the observation
plane, two types of magnetic bubbles were formed. Magnetic bubbles with
180{\deg} domains were formed if the easy axis was away from the direction
perpendicular to the observation plane. The contrast of biskyrmion is
reproduced by this form of a magnetic bubble. When the easy axis was
approximately perpendicular to the observing plane, type-II bubbles were
observed in the same specimen. The findings will fill a knowledge gap between
prior reports on magnetic bubbles in MnNiGa.",2110.15507v1
2021-12-02,Hamilton-Jacobi Equations of Nonholonomic Magnetic Hamiltonian Systems,"In order to describe the impact of different geometric structures and
constraints for the dynamics of a Hamiltonian system, in this paper, for a
magnetic Hamiltonian system defined by a magnetic symplectic form, we first
drive precisely the geometric constraint conditions of magnetic symplectic form
for the magnetic Hamiltonian vector field.which are called the Type I and Type
II of Hamilton-Jacobi equation. Secondly, for the magnetic Hamiltonian system
with nonholonomic constraint, we first define a distributional magnetic
Hamiltonian system, then derive its two types of Hamilton-Jacobi equation.
Moreover, we generalize the above results to nonholonomic reducible magnetic
Hamiltonian system with symmetry. We define a nonholonomic reduced
distributional magnetic Hamiltonian system, and prove two types of
Hamilton-Jacobi theorem. These research work reveal the deeply internal
relationships of the magnetic symplectic structure, nonholonomic constraint,
the distributional two-form, and the dynamical vector field of the nonholonomic
magnetic Hamiltonian system.",2112.00961v2
2021-12-31,Tunable magnetic field source for magnetic field imaging microscopy,"In this work we present a novel, compact, power efficient magnetic field
source design for magnetic field imaging microscopy. The device is based on a
pair of diametrically magnetized permanent magnet cylinders with
electro-mechanical rotation control and ferrite field concentrators. A Hall
probe and NV centers in diamond are used to demonstrate a proof of concept of a
proposed magnetic field setup and to characterise the homogeneity of the
produced magnetic field on a micrometer scale. Numerical simulation results are
compared with experimental results showing good agreement of the distribution
of the magnetic field in the setup. As a result, a magnetic field source with a
tunable field amplitude in the range from 1 mT to 222 mT is demonstrated,
achieving a magnetic field homogeneity of 2 ppm/$\mu$m or 0.5 $\mu$T/$\mu$m at
222 mT in a 25$\times$25 $\mu$m field of view.",2112.15359v1
2022-01-01,"Nanomagnetism in porous amorphous palladium, a sequel. A possible light-weight magnet","Magnetism is a very relevant subject that permeates our everyday lives.
However, magnetism keeps taking us from surprise to surprise which seems to
indicate that it is a phenomenon not well understood. For example, we found
that bulk amorphous palladium becomes magnetic; so, naturally one should ask,
could defective palladium develop magnetism? In particular, would amorphous
porous palladium become magnetic? Here we show that the answer to that question
is affirmative, this defective topology of Pd is magnetic, with a magnetism
that depends on the amount of sample porosity and on the topology of their
structures. Clearly, if magnetism exists in porous amorphous palladium, this
indicates the possibility of developing light-weight magnets, useful when a
maximized magnetism/weight ratio is demanded, well suited for space and
aeronautical applications.",2201.00086v1
2022-02-19,Controlling degeneracy and magnetization switching in an artificial spin ice system of peanut-shaped nanomagnets,"Using extensive numerical simulations, we probe the magnetization switching
in two-dimensional artificial spin ice (ASI) system consisting of peanut-shaped
nanomagnets. We also investigated the effect of the external magnetic field on
the degeneracy of the magnetic states in such a system. The switching field is
found to be one order smaller in the proposed ASI system with peanut-shaped
nanomagnets as compared to the conventionally used highly-anisotropic
nanoisland such as elliptically shaped nanomagnets. The metastable 2-in/2-out
(Type II) magnetic state is robust at the remanence. We are also able to access
the other possible microstates corresponding to Type II magnetic configurations
by carefully varying the external magnetic field. It implies that one can
control the degeneracy of the magnetic state by the application of a suitable
magnetic field. Interestingly, the magnetic charge neutrality breaks due to the
defects induced by removing nanomagnets. In such a case, the system also
appears to have a 1-out/3-in or 3-out/1-in (Type III) spin state, reminiscent
of a magnetic monopole. We believe that our study is highly desirable in the
context of developing the next-generation spintronics-based devices for future
technologies.",2202.09536v1
2022-05-10,Non-hermitian off-diagonal magnetic response of Dirac fermions,"We perform a comparative study for the magnetization dynamics within linear
response theory of one and two dimensional massive Dirac electrons, after
switching on either a real (hermitian) or an imaginary (non-hermitian) magnetic
field. While hermitian dc magnetic fields polarize the spins in the direction
of the external magnetic field, non-hermitian magnetic fields induce only off
diagonal response. An imaginary dc magnetic field perpendicular to the mass
term induces finite magnetization in the third direction only according to the
right hand rule. This can be understood by analyzing the non-hermitian equation
of motion of the spin, which becomes analogous to a classical particle in
crossed electric and magnetic fields. Therein, the spin expectation value, the
mass term and imaginary magnetic field play the role of the classical momentum,
magnetic and electric field, respectively. The latter two create a drift
velocity perpendicular to them, which gives rise to the off-diagonal component
of the dc spin susceptibility, similarly to how the Hall effect develops in the
classical description.",2205.04795v2
2022-05-13,Interaction of in-plane magnetic skyrmions with 90$^\circ$ magnetic domain walls: micromagnetic simulations,"$90^\circ$ pinned magnetic domain walls can be observed in thin magnetic
layers attached to a ferroelectric substrate. The main stabilization mechanism
of the noncollinear magnetic texture is the strain transfer which is
responsible for imprinting of the ferroelectic domains into the uniaxial
anisotropy of the ferromagnet. Here, we investigate by means of micromagnetic
simulations how the interfacial Dzyaloshinkii-Moriya interaction influences the
$90^\circ$ domain wall structure. It is shown that Dzyaloshinskii-Moriya
interaction induces a large out-of-plane magnetization component, strongly
dependent on the domain wall type. In particular, it is shown that this
out-of-plane magnetization component is crucial for the transport of the
in-plane magnetic skyrmions, also known as bimerons, through the magnetic
domain walls. Based on the results of micromagnetic simulations, a concept of
in-plane magnetic skyrmion valve based on two $90^\circ$ pinned magnetic domain
walls is introduced.",2205.06876v1
2022-05-16,Magneto-Transport Properties of Kagome Magnet TmMn$_6$Sn$_6$,"Kagome magnet usually hosts nontrivial electronic or magnetic states drawing
great interests in condensed matter physics. In this paper, we report a
systematic study on transport properties of kagome magnet TmMn$_6$Sn$_6$. The
prominent topological Hall effect (THE) has been observed in a wide temperature
region spanning over several magnetic phases and exhibits strong temperature
and field dependence. This novel phenomenon due to non-zero spin chirality
indicates possible appearance of nontrival magnetic states accompanying with
strong fluctuations. The planar applied field drives planar Hall effect(PHE)
and anistropic magnetoresisitivity(PAMR) exhibiting sharp disconnections in
angular dependent planar resistivity violating the empirical law. By using an
effective field, we identify a magnetic transition separating the PAMR into two
groups belonging to various magnetic states. We extended the empirical formula
to scale the field and temperature dependent planar magnetoresistivity and
provide the understandings for planar transport behaviors with the crossover
between various magnetic states. Our results shed lights on the novel transport
effects in presence of multiple nontrivial magnetic states for the kagome
lattice with complicated magnetic structures.",2205.07806v2
2022-06-14,Frustration and ordering in Ising chain in an external magnetic field with third-neighbor interactions,"In this paper, the frustration properties of the Ising model on a
one-dimensional monoatomic equidistant lattice in an external magnetic field
are investigated, taking into account the exchange interactions of atomic spins
at the sites of the first, second, and third neighbors. Exact analytical
expressions for the thermodynamic functions of the system are obtained by the
Kramers--Wannier transfer-matrix method. A magnetic phase diagram of the ground
state of such a spin system is constructed and studied thoroughly. The points
and lines of frustrations of the system depending on the values and signs of
exchange interactions and on an external magnetic field are found. The criteria
for the occurrence of magnetic frustrations in the presence of competition
between the energies of exchange interactions and an external magnetic field
are formulated. The peculiar features are investigated and the values of
entropy and magnetization of the ground state of this model are obtained in the
frustration regime and beyond it. Various types of behavior of entropy,
magnetization, and magnetic susceptibility depending on the model parameters
are revealed.",2206.06753v1
2022-10-06,Field and temperature tuning of magnetic diode in permalloy honeycomb lattice,"The observation of magnetic diode behavior with ultra-low forward voltage of
5 mV renders new venue for energetically efficient spintronic device research
in the unconventional system of two-dimensional permalloy honeycomb lattice.
Detailed understanding of temperature and magnetic field tuning of diode
behavior is imperative to any practical application. Here, we report a
comprehensive study in this regard by performing electrical measurements on
magnetic diode sample as functions of temperature and magnetic field. Magnetic
diode is found to persist across the broad temperature range. Magnetic field
application unveils a peculiar reentrant characteristic where diode behavior is
suppressed in remnant field but reappears after warming to room temperature.
Analysis of I-V data suggests a modest energy gap, 0.03-0.1 eV, which is
comparable to magnetic Coulomb's interaction energy between emergent magnetic
charges on honeycomb vertices in the reverse biased state. It affirms the role
of magnetic charge correlation in unidirectional conduction in 2D honeycomb
lattice. The experimental results are expected to pave way for the utilization
of magnetic diode in next generation spintronic device applications.",2210.03184v1
2022-12-05,Magnetic Field Experiments Using a Phone,"To make physics experiments more directly relevant to everyday life and help
students realize how their smart phones or tablets can be used as sensors for
scientific measurements, we designed two introductory physics experiments to
measure vector magnetic fields. These experiments were initially developed for
students working remotely in an online course setting. However, the experiments
can also be used for in-person laboratory activities. The first activity uses
the phone's three-dimensional sensors to determine the vector components and
orientation of the background magnetic field at the students' locations. The
resulting vector magnetic field is compared to the expected Earth's magnetic
field for their location. The second experiment uses the phone sensors to
measure the magnet field produced by the small magnet found in the speaker of
common earbuds, or in-ear headphones. The students then carefully investigate
the dependence of the magnitude of the field on the axial distance between the
speaker magnet and the phone's sensors. Using a ring magnet approximation,
advanced Excel curve-fitting methods are introduced to determine the radius of
the magnet in the earbud and the distance between the magnet's location and the
external surface of the earbud housing.",2212.02258v1
2022-12-16,Strong toroidal magnetic fields sustained by the elastic crust in a neutron star,"We investigate new solutions for magnetized neutron stars with a barotropic
core in magnetohydrodynamic (MHD) equilibrium and a magneto-elastic crust,
which was neglected by previous studies concerning stars in MHD equilibrium.
The Lorentz force of the barotropic star is purely irrotational and the
structures of magnetic fields are constrained. By contrast, a solenoidal
component of the Lorentz force exists in the elastic crust and the structures
of the magnetic fields are less restricted. We find that the minor solenoidal
component in the elastic crust is important for sustaining the strong magnetic
field in the core. Unlike previous studies, the toroidal magnetic field exists
in the entire region of the core, and we obtain equilibrium states with large
toroidal magnetic fields, where the toroidal magnetic energy is larger than the
poloidal magnetic energy. The elastic force of the crust sustains an order of
$10^{15}~\mathrm{G}$ toroidal magnetic field in the core, and the maximum
strength of the toroidal magnetic field is approximately proportional to the
crust thickness.",2212.08309v1
2023-02-27,Energy Partition of Thermal and Nonthermal Particles in Magnetic Reconnection,"Magnetic reconnection has long been known to be the most important mechanism
as quick conversion of magnetic field energy into plasma kinetic energy. In
addition, energy dissipation by reconnection has gained attention not only as a
plasma heating mechanism, but also as a plasma mechanism for accelerating
nonthermal particles. However, the energy partitioning of thermal and
nonthermal plasmas during magnetic reconnection is not understood. Here, we
studied energy partition as a function of plasma sheet temperature and guide
magnetic field. In relativistic reconnection with anti-parallel magnetic field
or weak guide magnetic field, it was found that the nonthermal energy density
can occupy more than $90 \%$ of the total kinetic plasma energy density, but
strengthening the guide magnetic field suppresses the efficiency of the
nonthermal particle acceleration. In nonrelativistic reconnection for
anti-parallel magnetic field, most dissipated magnetic field energy is
converted into thermal plasma heating. For a weak guide magnetic field with a
moderate value, however, the nonthermal particle acceleration efficiency was
enhanced, but strengthening the guide-field beyond the moderate value
suppresses the efficiency.",2302.13517v1
2023-03-10,New Research Trends in Electrically Tunable 2D van der Waals Magnetic Materials,"The recent discovery of two-dimensional (2D) van der Waals (vdW) magnetic
materials has provided new, unprecedented opportunities for both fundamental
science and technological applications. Unlike three-dimensional (3D) magnetic
systems, the electric manipulation of vdW magnetism (e.g., magnetization state,
magnetic anisotropy, magnetic ordering temperature) down to the monolayer limit
at ambient conditions enables high efficiency operation and low energy
consumption, which has the potential to revolutionize the fields of
spintronics, spin-caloritronics, and valleytronics. This article provides an
in-depth analysis of the recent progress, emerging opportunities, and technical
challenges in the electric manipulation of magnetic functionalities of a wide
variety of 2D vdW magnetic systems ranging from metals to semiconductors and
heterostructures. The state-of-the-art understanding of the mechanisms behind
the electric modulation of magnetism in these 2D vdW magnetic systems will
drive future research towards novel applications in spintronics,
spin-caloritronics, valleytronics, and quantum computation.",2303.05748v1
2023-03-20,Six-degree-of-freedom Localization Under Multiple Permanent Magnets Actuation,"Localization of magnetically actuated medical robots is essential for
accurate actuation, closed loop control and delivery of functionality. Despite
extensive progress in the use of magnetic field and inertial measurements for
pose estimation, these have been either under single external permanent magnet
actuation or coil systems. With the advent of new magnetic actuation systems
comprised of multiple external permanent magnets for increased control and
manipulability, new localization techniques are necessary to account for and
leverage the additional magnetic field sources. In this letter, we introduce a
novel magnetic localization technique in the Special Euclidean Group SE(3) for
multiple external permanent magnetic field actuation and control systems. The
method relies on a milli-meter scale three-dimensional accelerometer and a
three-dimensional magnetic field sensor and is able to estimate the full 6
degree-of-freedom pose without any prior pose information. We demonstrated the
localization system with two external permanent magnets and achieved
localization errors of 8.5 ? 2.4 mm in position norm and 3.7 ? 3.6? in
orientation, across a cubic workspace with 20 cm length.",2303.11059v1
2023-04-03,Bloch-type magnetic skyrmions in two-dimensional lattice,"Magnetic skyrmions in two-dimensional lattice are a prominent topic of
condensed matter physics and material science. Current research efforts in this
field are exclusively constrained to Neel-type and antiskyrmion, while
Bloch-type magnetic skyrmions are rarely explored. Here, we report the
discovery of Bloch-type magnetic skyrmions in two-dimensional lattice of
MnInP2Te6, using firstprinciples calculations and Monte-Carlo simulations.
Arising from the joint effect of broken inversion symmetry and strong
spin-orbit coupling, monolayer MnInP2Te6 presents large Dzyaloshinskii-Moriya
interaction. This, along with ferromagnetic exchange interaction and
out-ofplane magnetic anisotropy, gives rise to skyrmion physics in monolayer
MnInP2Te6, without needing magnetic field. Remarkably, different from all
previous works on two-dimensional lattice,the resultant magnetic skyrmions
feature Bloch-type, which is protected by D3 symmetry.Furthermore, the
Bloch-type magnetic bimerons are also identified in monolayer MnTlP2Te6. The
phase diagrams of these Bloch-type topological magnetisms under magnetic field,
temperature and strain are mapped out. Our results greatly enrich the research
on magnetic skyrmions in twodimensional lattice.",2304.00671v1
2023-05-07,Numerical simulation of a rotating magnetic sail for space applications,"The Magnetic Sail is a space propulsion system that utilizes the interaction
between solar wind particles and an artificial dipole magnetic field generated
by a spacecraft's coil to produce thrust without the need for additional plasma
or propellant. To reduce the size of the sail while improving the efficiency of
capturing solar wind, a new type of rotating magnetic sail with an initial
rotation speed is proposed. This study evaluates the thrust characteristics,
attitude, and size design factors of a rotating magnetic sail using a 3-D
single-component particle numerical simulation. The results show that an
increase in rotational speed significantly increases the thrust of the rotating
magnetic sail. The thrust is most significant when the magnetic moment of the
sail is parallel to the direction of particle velocity. The study also found
that the potential for the application of the rotating magnetic sail is
greatest in orbits with high-density and low-speed space plasma environments.
It suggests that a rotating magnetic sail with a magnetic moment (Mm) of
10^3-10^4 Am^2 operating at an altitude of 400 km in Low Earth Orbit (LEO) can
achieve a similar thrust level to that of a rotating magnetic sail operating at
1 AU (astronomical unit) of 10^7-10^8 Am^2.",2305.04212v1
2023-07-18,Field-induced magnetic structures in the chiral polar antiferromagnet Ni$_2$InSbO$_6$,"We have performed $^{115}$In-NMR spectroscopy for Ni$_{2}$InSbO$_6$ with
corundum-related crystal structure to reveal magnetic structures that develop
in high magnetic fields. At low fields Ni$_{2}$InSbO$_6$ shows a helical
magnetic order with a long wavelength because of its chiral and polar crystal
structure. The field-induced magnetic state was not investigated by microscopic
experiment because an extremely high magnetic field is required to modify the
antiferromagnetically coupled helical structure. From the analysis of our
$^{115}$In-NMR spectra obtained at high magnetic fields, we confirm that the
canted antiferromagnetic structure appears in fields applied in the $[110]$
direction and the propagation vector of magnetic helix is rotated toward the
field direction for fields in the $[001]$ direction. We discuss the effect of
magnetic field that modifies the magnetic structure of an antiferromagnetic
chiral magnet.",2307.09082v1
2023-08-22,Magical or magnetic? Less commonly taught facts about real-world permanent magnets and their diverse interactions with objects,"Permanent magnets are fascinating. They generate magnetic field and act as
the key component in compasses, motors, speakers for practical applications.
They are also made into magnetic toys for entertainment and education with
magical magnetic tricks. Some of these tricks fueled the recent upsurge for
magnetic-responsive objects including but not limited to a LK-99 mixture. A
lack of full consideration of the magnetic interactions seems to be the reason
why some tricks like ""half levitation"" is misinterpreted, and the situation is
not really rectified in the following replications and discussions. Here I
would like to go through some less commonly taught facts about real-world
permanent magnets starting from the nonuniformity to their combined effects
with other factors. Based on these facts, I will also break down the situation
of some examples of how permanent magnets diversely interact even with ordinary
objects, as one may have seen from recent sources. I believe this discussion is
useful both in an informative and educational way, helping those who want to
think deeper about magnetic mechanism beyond a simple attract/repel
terminology.",2308.11542v1
2023-09-07,Magnetization reversal in Fe(001) films grown by magnetic field assisted molecular beam epitaxy,"We studied the influence of a magnetic field (MF) on epitaxial growth and
magnetic properties of Fe(001) films deposited on MgO(001). Thanks to modular
sample holders and a specialized manipulator in our multi-chamber ultrahigh
vacuum system, the films could be deposited and annealed in an in-plane MF of
100 mT. In situ scanning tunnelling microscopy showed that MF had a strong
influence on the film morphology, and, in particular, on the structure of
surface steps. The magnetic properties were studied ex situ using magneto-optic
Kerr effect (MOKE) magnetometry and microscopy. We showed that the moderate
in-plane magnetic field applied during growth has the visible impact on the
magnetic properties. The observed angular dependence of the MOKE loops and
domain structures were discussed based on a magnetization reversal model. In
particular we found that magnetization reversal occurs via 90{\deg} domains and
the reversal differs for the no-field and in-field grown samples, in
correlation with the film morphology.",2309.03583v1
2023-09-22,Electric control of optically-induced magnetization dynamics in a van der Waals ferromagnetic semiconductor,"Electric control of magnetization dynamics in two-dimensional (2D) magnetic
materials is an essential step for the development of novel spintronic
nanodevices. Electrostatic gating has been shown to greatly affect the static
magnetic properties of some van der Waals magnets, but the control over their
magnetization dynamics is still largely unexplored. Here we show that the
optically-induced magnetization dynamics in the van der Waals ferromagnet
Cr$_2$Ge$_2$Te$_6$ can be effectively controlled by electrostatic gates, with a
one order of magnitude change in the precession amplitude and over 10% change
in the internal effective field. In contrast to the purely thermally-induced
mechanisms previously reported for 2D magnets, we find that coherent
opto-magnetic phenomena play a major role in the excitation of magnetization
dynamics in Cr$_2$Ge$_2$Te$_6$. Our work sets the first steps towards electric
control over the magnetization dynamics in 2D ferromagnetic semiconductors,
demonstrating their potential for applications in ultrafast opto-magnonic
devices.",2309.12776v1
2023-09-26,Soft X-ray phase nano-microscopy of micrometre-thick magnets,"Imaging of nanoscale magnetic textures within extended material systems is of
critical importance both to fundamental research and technological
applications. Whilst high resolution magnetic imaging of thin nanoscale samples
is well-established with electron and soft X-ray microscopy, the extension to
micrometer-thick systems with hard X-rays currently limits high resolution
imaging to rare-earth magnets. Here we overcome this limitation by establishing
soft X-ray magnetic imaging of micrometer-thick systems using the pre-edge
phase X-ray Magnetic Circular Dichroism signal, thus making possible the study
of a wide range of magnetic materials. By performing dichroic
spectro-ptychography, we demonstrate high spatial resolution imaging of
magnetic samples up to 1.7 {\mu}m thick, an order of magnitude higher than
conventionally possible with absorption-based techniques. This new regime of
magnetic imaging makes possible the study of extended non rare-earth systems
that have until now been inaccessible, from magnetic textures for future
spintronic applications to non-rare-earth permanent magnets.",2309.14969v1
2023-10-03,Permanent Magnets Based on Hard Ferrite Ceramics,"Permanent magnets are integral components in many of the modern technologies
that are critical for the transition to a sustainable society. However, most of
the high-performance (BHmax > 100 kJ/m3) permanent magnets that are currently
employed contain rare earth elements (REE), which have long been classified as
critical materials with a high supply risk and concerns regarding pollution in
their mining. Therefore, suitable REE-lean/free magnets must be developed in
order to ensure the sustainability of clean energy generation and electric
mobility. The REE-free hexagonal ferrites (or hexaferrites) are the most used
permanent magnets across all applications, with an 85 wt.% pie of the permanent
magnet market. They are the dominant lower-grade option (BHmax < 25 kJ/m3) due
to their relatively good hard magnetic properties, high Curie temperature (>700
K), low cost and good chemical stability. In recent years, the hexaferrites
have also emerged as candidates for substituting REE-based permanent magnets in
applications requiring intermediate magnetic performance (25-100 kJ/m3), due to
considerable performance improvements achieved through chemical tuning,
nanostructuring and compaction/sintering optimization. This chapter reviews the
state-of-the-art sintering strategies being investigated with the aim of
manufacturing hexaferrite magnets with optimized magnetic properties,
identifying key challenges and highlighting the natural future steps to be
followed.",2310.02106v1
2023-10-25,Phase Change Induced Magnetic Switching through Metal-insulator Transition in VO2/TbFeCo Films,"The ability to manipulate spins in magnetic materials is essential in
designing spintronics devices. One method for magnetic switching is through
strain. In VO2 on TiO2 thin films, while VO2 remains rutile across the
metal-insulator transition, the in-plane lattice area expands going from low
temperature insulating phase to high temperature conducting phase. In a
VO2/TbFeCo bilayer, the expansion of the VO2 lattice area exerts tension on the
amorphous TbFeCo layer. Through the strain effect, magnetic properties,
including the magnetic anisotropy and magnetization, of TbFeCo can be changed.
In this work, the changes in magnetic properties of TbFeCo on VO2/TiO2(011) are
demonstrated using anomalous Hall effect measurements. Across the
metal-insulator transition, TbFeCo loses perpendicular magnetic anisotropy, and
the magnetization in TbFeCo turns from out-of-plane to in-plane. Using
atomistic simulations, we confirm these tunable magnetic properties originating
from the metal-insulator transition of VO2. This study provides the groundwork
for controlling magnetic properties through a phase transition.",2310.17045v1
2023-12-05,THz-Driven Coherent Magnetization Dynamics in a Labyrinth Domain State,"Terahertz (THz) light pulses can be used for an ultrafast coherent
manipulation of the magnetization. Driving the magnetization at THz frequencies
is currently the fastest way of writing magnetic information in ferromagnets.
Using time-resolved resonant magnetic scattering, we gain new insights to the
THz-driven coherent magnetization dynamics on nanometer length scales. We
observe ultrafast demagnetization and coherent magnetization oscillations that
are governed by a time-dependent damping. This damping is determined by the
interplay of lattice heating and magnetic anisotropy reduction revealing an
upper speed limit for THz-induced magnetization switching. We show that in the
presence of nanometer-sized magnetic domains, the ultrafast magnetization
oscillations are associated with a correlated beating of the domain walls. The
overall domain structure thereby remains largely unaffected which highlights
the applicability of THz-induced switching on the nanoscale.",2312.02654v1
2023-12-18,Doping-control of excitons and magnetism in few-layer CrSBr,"Magnetism in two-dimensional materials reveals phenomena distinct from bulk
magnetic crystals, with sensitivity to charge doping and electric fields in
monolayer and bilayer van der Waals magnet CrI3. Within the class of layered
magnets, semiconducting CrSBr stands out by featuring stability under ambient
conditions, correlating excitons with magnetic order and thus providing strong
magnon-exciton coupling, and exhibiting peculiar magneto-optics of
exciton-polaritons. Here, we demonstrate that both exciton and magnetic
transitions in bilayer and trilayer CrSBr are sensitive to voltage-controlled
field-effect charging, exhibiting bound exciton-charge complexes and
doping-induced metamagnetic transitions. Moreover, we demonstrate how these
unique properties enable optical probes of local magnetic order, visualizing
magnetic domains of competing phases across metamagnetic transitions induced by
magnetic field or electrostatic doping. Our work identifies few-layer CrSBr as
a rich platform for exploring collaborative effects of charge, optical
excitations, and magnetism.",2312.11041v1
2023-12-18,Enhancing thermal stability of optimal magnetization reversal in nanoparticles,"Energy-efficient switching of nanoscale magnets requires the application of a
time-varying magnetic field characterized by microwave frequency. At finite
temperatures, even weak thermal fluctuations create perturbations in the
magnetization that can accumulate in time, break the phase locking between the
magnetization and the applied field, and eventually compromise magnetization
switching. It is demonstrated here that the magnetization reversal is mostly
disturbed by unstable perturbations arising in a certain domain of the
configuration space of a nanomagnet. The instabilities can be suppressed and
the probability of magnetization switching enhanced by applying an additional
stimulus such as a weak longitudinal magnetic field that ensures bounded
dynamics of the perturbations. Application of the stabilizing longitudinal
field to a uniaxial nanomagnet makes it possible to reach a desired probability
of magnetization switching even at elevated temperatures. The principle of
suppressing instabilities provides a general approach to enhancing thermal
stability of magnetization dynamics.",2312.11293v1
2023-12-19,Pseudo-fermion functional renormalization group with magnetic fields,"The pseudo-fermion functional renormalization group is generalized to treat
spin Hamiltonians with finite magnetic fields, enabling its application to
arbitrary spin lattice models with linear and bilinear terms in the spin
operators. We discuss in detail an efficient numerical implementation of this
approach making use of the system's symmetries. Particularly, we demonstrate
that the inclusion of small symmetry breaking magnetic seed fields regularizes
divergences of the susceptibility at magnetic phase transitions. This allows
the investigation of spin models within magnetically ordered phases at $T=0$ in
the physical limit of vanishing renormalization group parameter $\Lambda$. We
explore the capabilities and limitations of this method extension for
Heisenberg models on the square, honeycomb and triangular lattices. While the
zero-field magnetizations of these systems are systematically overestimated,
the types of magnetic orders are correctly captured, even if the local
orientations of the seed field are chosen differently than the spin
orientations of the realized magnetic order. Furthermore, the magnetization
curve of the square lattice Heisenberg antiferromagnet shows good agreement
with error controlled methods. In the future, the inclusion of magnetic fields
in the pseudo-fermion functional renormalization group, which is also possible
in three dimensional spin systems, will enable a variety of additional
interesting applications such as the investigation of magnetization plateaus.",2312.12097v1
2024-01-02,Development of the CMS Magnetic Field Map,"This article focuses on pioneering work on the performance of the
three-dimensional (3D) magnetic field map in the entire volume of the Compact
Muon Solenoid (CMS) detector at the Large Hadron Collider at CERN. In the CMS
heterogeneous magnetic system, the magnetic flux is created by a
superconducting solenoid coil enclosed in a steel flux-return yoke. To describe
the CMS magnetic flux distribution, a system of the primitive 3D volumes
containing the values of the magnetic flux density measured inside the
superconducting coil inner volume and modelled outside the coil across a
special mesh of reference nodes was developed. This system, called the CMS
magnetic field map, follows the geometric features of the yoke and allows the
interpolation of the magnetic flux density between the nodes to obtain the
magnetic field values at any spatial point inside a cylinder of 18 m in
diameter and 48 m in length, where all the CMS sub-detectors are located. The
geometry of the volumes is described inside one 30{\deg} azimuthal sector of
the CMS magnet. To obtain the values of the magnetic flux density components
across the entire azimuth angle of the CMS detector, rotational symmetry is
applied.",2401.01913v1
2024-01-15,Calculating Magnetic Properties of Two-Dimensional Materials for Memory Applications,"Calculating magnetic properties of two-dimensional materials is crucial for
implementing memory devices (like USB drive, RAM, hard disk drive of computers)
having reduced size. Two dimensional materials can be implemented as a thin
film which can reduce the size of memory devices. These materials as well as
devices made with magnetic two-dimensional materials are of current research
interest in industry and academia. From the materials project database, crystal
structure file of 30 two dimensional materials have been downloaded to
calculate their magnetic properties. BURAI Quantum espresso software has been
used to extract magnetic properties of 30 two dimensional (2D) materials. These
30 materials have magnetic Fe, Ni, Co, Mn, and Cr atoms in their molecular
structure. Magnetic materials play a key and vital role in today's modern-day
technology. There are five different types of magnetic materials. The
classification magnetic materials are diamagnetism, paramagnetic,
ferromagnetism, ferrimagnetism, and anti-ferromagnetism. Total energy of
different magnetic configurations has been calculated to find the most stable
magnetic configurations of these materials.",2401.07980v1
2024-01-25,Magnetic fields of protoplanetary disks,"We review the current status of studies on accretion and protoplanetary disks
of young stars with large-scale magnetic fields. Observational data on magnetic
fields of the disks are compiled and analysed. Modern analytical and numerical
MHD models of protoplanetary disks are discussed. The mechanisms of angular
momentum transport via turbulence, magnetic tensions and outflows are outlined.
We consider the influence of Ohmic dissipation, magnetic ambipolar diffusion,
magnetic buoyancy, and the Hall effect on the evolution of the magnetic flux in
disks. Modern MHD models of accretion disks show that the magnetic field can
influence the structure of protoplanetary disks. We argue that the available
observational data on the magnetic fields in protoplanetary disks can be
interpreted within the framework of fossil magnetic field theory. We summarize
the problems of the modern theory of accretion and protoplanetary disks with
magnetic fields and also outline the prospects for further research.",2401.14180v1
2024-02-28,Magnetization fluctuations and magnetic aftereffect probed via the anomalous Hall effect,"Taking advantage of the anomalous Hall effect, we electrically probe
low-frequency magnetization fluctuations at room temperature in a thin
ferromagnetic Pt/Co/AlO$_x$ layer stack with perpendicular magnetic anisotropy.
We observe a strong enhancement of the Hall voltage fluctuations within the
hysteretic region of the magnetization loop. Analyzing both the temporal
evolution of the anomalous Hall voltage and its frequency-dependent noise power
density, we identify two types of magnetic noise: abrupt changes in the
magnetic domain configuration, evident as Barkhausen-like steps in the Hall
voltage time trace, yield a noise power density spectrum scaling with frequency
as $1/f^{\beta}$ with $\beta\approx 1.9$. In contrast, quasi-stationary
magnetization configurations are connected with a magnetic noise power density
with an exponent $\beta\approx 0.9$. The observation of Barkausen steps and
relaxation effects shows that the magnetic system is in a non-stationary state
in the hysteresis region, such that the fluctuation-dissipation theorem cannot
be expected to hold. However, the time-dependent change in the Hall voltage for
constant magnetic field strength resembles the integrated noise power.",2402.18436v1
2024-03-14,Chiral gauge field in fully-spin polarized Weyl semimetal with magnetic domain walls,"Modulation of magnetization in magnetic Weyl semimetals leads to the shift of
Weyl points in momentum space, which effectively serves as the
chirality-dependent gauge field for the Weyl fermions. Here, we theoretically
study such a magnetization-induced chiral gauge field, in a fully
spin-polarized Weyl ferromagnet $\rm{Co}_3\rm{Sn}_2\rm{S}_2$. From a
tight-binding model of $\rm{Co}_3\rm{Sn}_2\rm{S}_2$ on stacked kagome lattice
with magnetism, we calculate the magnetization-dependent evolution of the Weyl
points in momentum space, resulting in the chiral gauge field. In the presence
of the magnetic domain wall structure, we evaluate the chiral magnetic field
arising from the spatial profile of the chiral gauge field. We find that a
magnetic domain wall in $\rm{Co}_3\rm{Sn}_2\rm{S}_2$ gives rise to a giant
chiral magnetic field for the Weyl fermions, which reaches the order of a few
hundred tesla to induce the Landau quantization. Such a giant chiral magnetic
field may also influence the novel transport phenomena, such as the charge
pumping by the domain wall motion, compatible with the spin-motive force.",2403.09535v1
2024-04-01,"Harnessing Interlayer Magnetic Coupling for Efficient, Field-Free Current-Induced Magnetization Switching in a Magnetic Insulator","Owing to the unique features of low Gilbert damping, long spin-diffusion
lengths and zero Ohmic losses, magnetic insulators are promising candidate
materials for next-generation spintronic applications. However, due to the
localized magnetic moments and the complex metal-oxide interface between
magnetic insulators and heavy metals, spin-functional Dzyaloshinskii-Moriya
interactions or spin Hall and Edelstein effects are weak, which diminishes the
performance of these typical building blocks for spintronic devices. Here, we
exploit the exchange coupling between metallic and insulating magnets for
efficient electrical manipulation of heavy metal/magnetic insulator
heterostructures. By inserting a thin Co layer, we enhance the spin-orbit
torque efficiency by more than 20 times, which significantly reduces the
switching current density. Moreover, we demonstrate field-free current-induced
magnetization switching caused by a symmetry-breaking non-collinear magnetic
texture. Our work launches magnetic insulators as an alternative platform for
low-power spintronic devices.",2404.00845v1
2001-11-16,Astrophysical Polarimetric Signature Against TeV Fundamental Planck Scale,"I present the analysis of data of astrophysical polarimetric observations
that gives the signature of the fundamental extra dimension Planck scale
magnitude essentially higher than $~1TeV$. Magnetic conversion of photons into
the fundamental particles (scalars, gravitons) is the probable mechanism that
can produce noticeable amount of polarization of optical radiation of
astrophysical objects, especially, of distant extragalactic sources. The
results of magnetic conversion process of optical light of extragalactic
sources are presented for a number of situations including: (a) intergalactic
magnetic field, (b) galaxy cluster magnetic field, (c) magnetic conversion in
the typical galaxy magnetic field, (d) magnetic conversion of CMB radiation.",0111316v1
2003-02-24,Thermal Conduction in Magnetized Turbulent Gas,"Using numerical methods, we systematically study in the framework of ideal
MHD the effect of magnetic fields on heat transfer within a turbulent gas. We
measure the rates of passive scalar diffusion within magnetized fluids and make
the comparisons a) between MHD and hydro simulations, b) between different MHD
runs with different values of the external magnetic field (up to the energy
equipartition value), c) between thermal conductivities parallel and
perpendicular to magnetic field. We do not find apparent suppression of
diffusion rates by the presence of magnetic fields, which implies that magnetic
fields do not suppress heat diffusion by turbulent motions.",0302503v1
2004-09-07,Spectropolarimetry and Infrared Photometry of Magnetic White Dwarfs: Vacuum Polarization Effect or Magnetic CIA?,"We present brief review of two probable physical mechanisms that can explain
the results of photometric and spectropolarimetric observations of magnetic
white dwarfs: vacuum polarization effect into a strong magnetic field and,
so-called, magnetic collision induced absorption (magnetic CIA). Both
mechanisms provide observed rotation of polarization ellipse and suppression of
spectral energy distributions. The results of spectropolarimetric observations
of magnetic white dwarfs made at Russian BTA-6m and the results of the near
infrared photometric observations with Russian-Italian AZT-24 telescope located
at Campo Imperatore are also presented.",0409152v1
2006-06-28,A Universal Magnetic Helicity Integral,"A magnetic helicity integral is proposed which can be applied to domains
which are not magnetically closed, i.e. have a non-vanishing normal component
of the magnetic field on the boundary. In contrast to the relative helicity
integral, which was previously suggested for magnetically open domains, it does
not rely on a reference field and thus avoids all problems related to the
choice of a particular reference field. Instead it uses a gauge condition on
the vector potential, which corresponds to a particular topologically unique
closure of the magnetic field in the external space. The integral has
additional elegant properties and is easy to compute numerically in practice.
For magnetically closed domains it reduces to the classical helicity integral.",0606694v1
1996-07-30,Non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets,"In this paper we study in a large-S expansion effects of substituting spins
by non-magnetic impurities in two- and three- dimensional Heisenberg
antiferromagnets in a weak magnetic field. In particular, we demonstrate a
novel mechanism where magnetic moments are induced around non-magnetic
impurities when magnetic field is present. As a result, Curie-type behaviour in
magnetic susceptibility can be observed well below the Neel temperature, in
agreement with what is being observed in $La_2Cu_{1-x}Zn_{x}O_4$ and
$Sr(Cu_{1-x}Zn_x)_2O_3$ compounds.",9607213v1
1998-12-31,Magnetic skyrmion lattices in heavy fermion superconductor UPt3,"Topological analysis of nearly SO(3)_{spin} symmetric Ginzburg--Landau
theory, proposed for UPt$_{3}$ by Machida et al, shows that there exists a new
class of solutions carrying two units of magnetic flux: the magnetic skyrmion.
These solutions do not have singular core like Abrikosov vortices and at low
magnetic fields they become lighter for strongly type II superconductors.
Magnetic skyrmions repel each other as $1/r$ at distances much larger then the
magnetic penetration depth $\lambda$, forming a relatively robust triangular
lattice. The magnetic induction near $H_{c1}$ is found to increase as
$(H-H_{c1})^{2}$. This behavior agrees well with experiments.",9812435v2
1999-07-07,Exotic structures on magnetic multilayers,"To characterize the possible magnetic structures created on magnetic
multilayers a model has been formulated and studied. The interlayer
inhomogeneous structures found indicate either (i) a regular periodic, (ii) a
quasiperiodic change in the magnetization or (iii) spatially chaotic glass
states. The magnetic structures created depend mainly on the ratio of the
magnetic anisotropy constant to the exchange constant.
  With the increase of this ratio the periodic structures first transform into
the quasiperiodic and then into the chaotic glass states. The same tendency
arises with the depolarization of the magnetic moments of the first layer
deposited on the substrate.",9907099v1
2000-05-17,Conversion of free magnetic polaron into vortex lattice in diluted magnetic semiconductors in quantizing magnetic fields,"We show that in strong (quantizing) magnetic fields ""ordinary"" free magnetic
polaron in diluted magnetic semiconductors (of type $A^2MeB^6$, where Me=Fe,
Mn) exists in the form of vortex lattice quite similar to that in type II
superconductors (Abricosov vortex lattice). The region of external parameters
(like external magnetic field and temperature), where such lattice exists, is
determined from the condition that lattice dimension is less or equal to
polaron localization radius.",0005285v1
2000-10-20,Properties of a magnetic superconductor with weak magnetization - application to $ErNi_2B_2C$,"Using a Ginsburg-Landau free energy functional, we study the $H-T$ phase
diagram of a weak magnetic superconductor, where the magnetization from the
magnetic component is marginal in supporting a spontaneous vortex phase in
absence of external magnetic field. In particular, the competition between the
spiral state and spontaneous vortex phase is analysed. Our theory is applied to
understand the magnetic properties of $ErNi_2B_2C$.",0010307v1
2000-10-26,Magnetic storage device with improved temporal stability,"The current efforts to fabricate non-volatile magnetic recording media with a
high areal density is deteriorated by the increasing temporal instability of
the stored information. If the stored energy per magnetic particle competes
with the thermal energy, spontaneous magnetic reversal processes may occur.
Deposition of the magnetic particles on top of an antiferromagnetic substrate
will increase its energy barrier due to the exchange coupling between the two
subsystems. For this the magnetic moments of the antiferromagnet in the
vicinity of the magnetic particle have to deviate from their undisturbed
arrangement. This disturbation vanishes within a few lattice constants. In the
framework of a classical spin model we calculate the spin arrangements and the
resulting energy barriers for typical systems.",0010420v1
2000-12-15,Effective Interaction Hamiltonian of Polaron Pairs in Diluted Magnetic Semiconductors,"The magnetic interaction of a pair of bound magnetic polarons (BMP) in
diluted magnetic semiconductors (DMS) is analyzed via a generalized
Hubbard-type Hamiltonian for two carriers in the presence of effective magnetic
fields arising from the magnetic polarization of their respective polarons. For
the case where the magnetic fields at the two sites have equal magnitude but
are allowed to have arbitrary directions, it is shown that the energy of the
two polarons is minimized for a ferromagnetic configuration of the carrier
spins (in contrast to the case of hydrogenic centers in nonmagnetic
semiconductors) if polaron fields are strong enough. A modified Heisenberg-type
Hamiltonian is constructed to describe the low energy states of the resulting
system.",0012279v1
2002-05-15,Magnetism in a lattice of spinor Bose condensates,"We study the ground state magnetic properties of ferromagnetic spinor
Bose-Einstein condensates confined in a deep optical lattices. In the Mott
insulator regime, the ``mini-condensates'' at each lattice site behave as
mesoscopic spin magnets that can interact with neighboring sites through both
the static magnetic dipolar interaction and the light-induced dipolar
interaction. We show that such an array of spin magnets can undergo a
ferromagnetic or anti-ferromagnetic phase transition under the magnetic dipolar
interaction depending on the dimension of the confining optical lattice. The
ground-state spin configurations and related magnetic properties are
investigated in detail.",0205319v1
2003-05-28,Magnetic light,"In this paper we report on the observation of novel and highly unusual
magnetic state of light. It appears that in small holes light quanta behave as
small magnets so that light propagation through such holes may be affected by
magnetic field. When arrays of such holes are made, magnetic light of the
individual holes forms novel and highly unusual two-dimensional magnetic light
material. Magnetic light may soon become a great new tool for quantum
communication and computing.",0305661v1
2003-06-18,Evidence for the coexistence of low-dimensional magnetism and long-range order in Ca3CoRhO6,"We report the results of neutron powder diffraction studies on the spin-chain
compound Ca3CoRhO6 in the temperature range 3 to 293 K. Bragg peaks due to
magnetic ordering start appearing below about 100 K. The most interesting
observation is that there is a diffuse magnetic peak superimposed over the
strongest magnetic Bragg peak. The diffuse magnetic intensity is observed below
as well above 100 K. This finding provides a new insight into the physics of
this compound as though the low-dimensional magnetic interaction coexists with
long range magnetic order - a novel situation among quasi one-dimensional
oxides.",0306481v1
2003-07-10,Tunable Magnetic Relaxation In Magnetic Nanoparticles,"We investigate the magnetization dynamics of a conducting magnetic
nanoparticle weakly coupled to source and drain electrodes, under the
assumption that all relaxation comes from exchange of electrons with the
electrodes. The magnetization dynamics is characterized by a relaxation time
$t_1$, which strongly depends on temperature, bias voltage, and gate voltage.
While a direct measure of a nanoparticle magnetization might be difficult, we
find that $t_1$ can be determined through a time resolved transport
measurement. For a suitable choice of gate voltage and bias voltage, the
magnetization performs a bias-driven Brownian motion regardless of the presence
of anisotropy.",0307256v1
2003-12-11,Current-Driven Switching in Magnetic Multilayer Nanopillars,"We summarize our recent findings on how the current-driven magnetization
switching in nanofabricated magnetic multilayers is affected by an applied
magnetic field, changes of temperature, magnetic coupling between the
ferromagnetic layers, variations in the multilayer structure, and the relative
rotation of the layers' magnetizations. We show how these results can be
interpreted with a model describing current-driven excitations as an effective
current-dependent magnetic temperature.",0312287v1
2003-12-22,Microscopic origin of the adiabatic change of magnetization in molecular magnets,"A microscopic model of the molecular magnet V15 is used to study mechanisms
for the adiabatic change of the magnetization in time-dependent magnetic
fields. Effects of the Dzyaloshinskii-Moriya interaction, the most plausible
source for the energy-level repulsions that lead to adiabatic changes of the
magnetization, are studied in detail. We find that the energy-level repulsions
that result from this interaction exhibit a strong dependence on the direction
of the applied field. We also discuss the role of magnetic anisotropy in the
molecule Mn12 -acetate.",0312581v1
2004-07-01,Propagation of a magnetic domain wall in magnetic wires with asymmetric notches,"The propagation of a magnetic domain wall (DW) in a submicron magnetic wire
consisting of a magnetic/nonmagnetic/magnetic trilayered structure with
asymmetric notches was investigated by utilizing the giant magnetoresistance
effect. The propagation direction of a DW was controlled by a pulsed local
magnetic field, which nucleates the DW at one of the two ends of the wire. It
was found that the depinning field of the DW from the notch depends on the
propagation direction of the DW.",0407006v1
2004-09-03,Manipulating Current-Induced Magnetization Switching,"We summarize our recent findings on how current-driven magnetization
switching and magnetoresistance in nanofabricated magnetic multilayers are
affected by varying the spin-scattering properties of the non-magnetic spacers,
the relative orientations of the magnetic layers, and spin-dependent scattering
properties of the interfaces and the bulk of the magnetic layers. We show how
our data are explained in terms of current-dependent effective magnetic
temperature.",0409085v1
2004-12-14,Entry of magnetic flux into a magnetically shielded type-II superconductor filament,"In the framework of the London approximation the magnetic flux penetration
into a type-II superconductor filament surrounded by a soft-magnet sheath and
exposed to a transverse external magnetic field is studied. The lower
transverse critical field as well as the critical field and the critical
current of the first vortex nucleation at the superconductor/magnet interface
are calculated on the basis of an exact solution for a vortex of arbitrary
plane configuration. The Bean-Livingston barrier against the vortex nucleation
is shown to strongly depend on the magnet sheath parameters.",0412350v1
2004-12-15,"Magnetic behavior of the spin-chain compounds,Ca3CuIrO6 and Ca3CuRhO6","The spin-chain compounds, Ca3CuIrO6 and Ca3CuRhO6, crystallizing in a
K4CdCl6-derived monoclinic structure, are investigated by ac and dc
magnetization, isothermal remnant magnetization as well as heat capacity
measurements. The results reveal the existence of a magnetic ordering in the
vicinity of 15 K for both the compounds, but the transition appears to be of a
complex nature. The existence of a spin-glass component is strongly indicated
by the results. We propose that topological effects play a role on magnetism of
these compounds. The magnetic properties for these two compounds are
interestingly similar as though isoelectronic chemical substitution at the
octahedral coordination site does not significantly interfere in the magnetic
exchange process.",0412386v1
2004-12-17,Hysteresis loops of magnetic thin films with perpendicular anisotropy,"We model the magnetization of quasi two-dimensional systems with easy
perpendicular (z-)axis anisotropy upon change of external magnetic field along
z. The model is derived from the Landau-Lifshitz-Gilbert equation for
magnetization evolution, written in closed form in terms of the z component of
the magnetization only. The model includes--in addition to the external
field--magnetic exchange, dipolar interactions and structural disorder. The
phase diagram in the disorder/interaction strength plane is presented, and the
different qualitative regimes are analyzed. The results compare very well with
observed experimental hysteresis loops and spatial magnetization patterns, as
for instance for the case of Co-Pt multilayers.",0412461v1
2005-01-19,Anisotropic magnetization of RuEu1.5Ce0.5Sr2Cu2O10 (Ru-1222) thin films,"A dc magnetic study is reported on c-axis oriented epitaxial thin films of
EuSr2Eu1.5Ce0.5Cu2O10 (Ru-1222) on (100) SrTiO3 wafers. Magnetic measurements
on 200 and 500 nm thick films were performed with the magnetic field either
parallel or perpendicular to the wafer. We found that the films order
magnetically at 180 K. The easy axis of the magnetization is in the basal plane
and the Ru5+ ions are in their high-spin state, as deduced from the isothermal
magnetization curves at low temperatures. The anisotropy ratio was found to be
7.5. The observed results are compared to data of the Ru-1222 ceramic material.",0501454v1
2005-03-31,Boundary conditions for magnetization in magnetic nano-elements,"We show that the dynamic magnetization at the edges of a thin magnetic
element with finite lateral size can be described by new effective boundary
conditions that take into account inhomogeneous demagnetizing fields near the
element edges. These fields play a dominant role in the effective pinning of
the dynamic magnetization at the boundaries of mesoscopic and nano-sized
magnetic elements. The derived effective boundary conditions generalize
well-known Rado-Weertman boundary conditions and are reduced to them in the
limiting case of a very thin magnetic element.",0503745v1
2005-03-31,Spectroscopy of Magnetic Excitations in Magnetic Superconductors Using Vortex Motion,"In magnetic superconductors a moving vortex lattice is accompanied by an ac
magnetic field which leads to the generation of spin waves. At resonance
conditions the dynamics of vortices in magnetic superconductors changes
drastically, resulting in strong peaks in the dc I-V characteristics at
voltages at which the washboard frequency of vortex lattice matches the spin
wave frequency $\omega_s({\bf g})$, where ${\bf g}$ are the reciprocal vortex
lattice vectors. We show that if washboard frequency lies above the magnetic
gap, peaks in the I-V characteristics in borocarbides and cuprate layered
magnetic superconductors are strong enough to be observed over the background
determined by the quasiparticles.",0504006v1
2005-06-20,Monte Carlo study of half-magnetization plateau and magnetic phase diagram in pyrochlore antiferromagnetic Heisenberg model,"The antiferromagnetic Heisenberg model on a pyrochlore lattice under external
magnetic field is studied by classical Monte Carlo simulation. The model
includes bilinear and biquadratic interactions; the latter effectively
describes the coupling to lattice distortions. The magnetization process shows
a half-magnetization plateau at low temperatures, accompanied with strong
suppression of the magnetic susceptibility. Temperature dependence of the
plateau behavior is clarified. Finite-temperature phase diagram under the
magnetic field is determined. The results are compared with recent experimental
results in chromium spinel oxides.",0506500v2
2005-07-13,Novel Magnetic and Thermodynamic Properties of Thiospinel Compound CuCrZrS$_{4}$,"We have carried out dc magnetic susceptibility, magnetization and specific
heat measurements on thiospinel CuCrZrS$_{4}$. Below $T_{\rm C}^{*} =$ 58 K, dc
magnetic susceptibility and magnetization data show ferromagnetic behavior with
a small spontaneous magnetization 0.27 $\mu_{\rm B}/$f. u..
  In dc magnetic susceptibility, large and weak irreversibilities are observed
below $T_{\rm f} =$ 6 K and in the range $T_{\rm f}< T < T_{\rm C}^{*}$
respectively.
  We found that there is no anomaly as a peak or step in the specific heat at
$T_{\rm C}^{*}$.",0507314v1
2005-08-26,Kinetic arrest of the first order ferromagnetic to antiferromagnetic transition in Ce(Fe$_{0.96}$Ru$_{0.04}$)$_2$ : formation of a magnetic-glass,"We present results of dc magnetization and magnetic relaxation study showing
the kinetic arrest of a first order ferromagnetic to antiferromagnetic
transition in Ce(Fe$_{0.96}$Ru$_{0.04}$)$_2$. This leads to the formation of a
non-ergodic glass-like magnetic state. The onset of the magnetic-glass
transformation is tracked through the slowing down of the magnetization
dynamics. This glassy state is formed with the assistance of an external
magnetic field and this is distinctly different from the well known
'spin-glass' state.",0508625v1
2005-09-26,Charge and Magnetization Inhomogeneities in Diluted Magnetic Semiconductors,"It is predicted that III-V diluted magnetic semiconductors can exhibit
stripe-like modulations of magnetization and carrier concentration. This
inhomogeneity results from the strong dependence of the magnetization on the
carrier concentration. Within Landau theory, a characteristic temperature T*
below the Curie temperature is found so that below T* the equilibrium
magnetization shows modulations, which are strongly anharmonic. Wavelength and
amplitude of the modulation rise for decreasing temperature, starting from zero
at T*. Above T* the equilibrium state is homogeneous, but the coupling between
charge and magnetization leads to the appearance of an electrically charged
layer in domain walls.",0509653v2
2005-11-05,Ratchet Effect in Magnetization Reversal of Stoner Particles,"A new strategy is proposed aimed at substantially reducing the minimal
magnetization switching field for a Stoner particle. Unlike the normal method
of applying a static magnetic field which must be larger than the magnetic
anisotropy, a much weaker field, proportional to the damping constant in the
weak damping regime, can be used to switch the magnetization from one state to
another if the field is along the motion of the magnetization. The concept is
to constantly supply energy to the particle from the time-dependent magnetic
field to allow the particle to climb over the potential barrier between the
initial and the target states.",0511135v1
2006-01-17,Electric field control of magnetization dynamics in ZnMnSe/ZnBeSe diluted-magnetic-semiconductor heterostructures,"We show that the magnetization dynamics in diluted magnetic semiconductors
can be controlled separately from the static magnetization by means of an
electric field. The spin-lattice relaxation (SLR) time of magnetic Mn2+ ions
was tuned by two orders of magnitude by a gate voltage applied to n-type
modulation-doped (Zn,Mn)Se/(Zn,Be)Se quantum wells. The effect is based on
providing an additional channel for SLR by a two-dimensional electron gas
(2DEG). The static magnetization responsible for the giant Zeeman spin
splitting of excitons was not influenced by the 2DEG density.",0601383v1
2006-02-03,X-ray magnetic circular dichroism study of Re 5d magnetism in Sr2CrReO6,"We have measured Re 5d spin and orbital magnetic moments in the ferrimagnetic
double perovskite Sr2CrReO6 by X-ray magnetic circular dichroism at the L_{2,3}
edges. In fair agreement with recent band-structure calculations [Vaitheeswaran
et. al., Ref 1], at the Re site a large 5d spin magnetic moment of -0.68 mu_B
and a considerable orbital moment of +0.25 mu_B have been detected. We found
that the Curie temperature of the double perovskites A2BB'O6 scales with the
spin magnetic moment of the 'non-magnetic' B' ion.",0602071v1
2006-04-24,Observation of a transverse magnetization in the ordered phases of the pyrochlore magnet Gd2Ti2O7,"We have performed a detailed transverse magnetization study of the pyrochlore
antiferromagnet Gd2Ti2O7. A transverse magnetization of about 10^{-3}M_{sat} is
observed in the low-temperature ordered phases. These measurements result in
the refinement of the Gd2Ti2O7 phase diagrams. Observation of a transverse
magnetization indicates loss of the cubic symmetry in some of the magnetic
phases and provides new information for a better understanding of the
complicated magnetic ordering of Gd2Ti2O7.",0604544v1
2006-07-05,Instabilities of switching processes in synthetic antiferromagnets,"It is shown that magnetic states and field-driven reorientation transitions
in synthetic antiferromagnets crucially depend on contributions of higher-order
anisotropies. A phenomenological macrospin model is derived to describe the
magnetic states of two antiferromagnetically coupled magnetic thin film
elements. The calculated phase diagrams show that magnetic states with
out-of-plane magnetization, symmetric escaped spin-flop phases, exist in a
broad range of the applied magnetic field. Due to the formation of such states
and concomitant multidomain patterns, the switching processes in toggle
magnetic random access memory devices (MRAM) can radically deviate from
predictions within oversimplified models.",0607124v1
2006-09-21,High Temperature Superconductivity - Magnetic Mechanisms,"A brief history is offered concerning the relation of magnetism to
superconductivity, and the possibility that magnetic correlations are
responsible for certain types of superconductors. A central focus is on high
temperature cuprate superconductivity and the important question of whether its
d-wave pairing is caused by antiferromagnetic or singlet correlations.
Connected with this question is the much debated relation of the pseudogap
phase to the superconducting phase, and whether lattice degrees of freedom are
relevant or not.",0609559v1
2007-02-07,Vacuum fluctuations and the spin current in mesoscopic structures with collinear magnetic order,"We show that in magnetic nanostructures with a homogeneous magnetic order,
the equilibrium spin current can be nonzero. For example, this is the case of a
wide magnetic ring with the magnetization along the ring axis. The physical
reason of this effect is a variation of the orientation of anisotropy axis
inducing a spin torque acting on the magnetic ions. The mechanism of the spin
current generation is related to the quantum vacuum fluctuations in the
magnetic system.",0702168v2
2007-02-28,Non-collinear coupling between magnetic adatoms in carbon nanotubes,"The long range character of the exchange coupling between localized magnetic
moments indirectly mediated by the conduction electrons of metallic hosts often
plays a significant role in determining the magnetic order of low-dimensional
structures. In addition to this indirect coupling, here we show that the direct
exchange interaction that arises when the moments are not too far apart may
induce a non-collinear magnetic order that cannot be characterized by a
Heisenberg-like interaction between the magnetic moments. We argue that this
effect can be manipulated to control the magnetization alignment of magnetic
dimers adsorbed to the walls of carbon nanotubes.",0703007v1
1995-09-27,Does Magnetic Charge Imply a Massive Photon ?,"In Abelian theories of monopoles the magnetic charge is required to be
enormous. Using the electric-magnetic duality of electromagnetism it is argued
that the existence of such a large, non-perturbative magnetic coupling should
lead to a phase transition where magnetic charge is permanently confined and
the photon becomes massive. The apparent masslessness of the photon could then
be used as an argument against the existence of such a large, non-perturbative
magnetic charge. Finally it is shown that even in the presence of this
dynamical mass generation the Cabbibo-Ferrari formulation of magnetic charge
gives a consistent theory.",9509157v1
1997-04-05,Can Magnetic Charge and Quantum Mechanics Co-exist ?,"It is proven that if more than a single magnetic charge exists it is
impossible to define a proper quantum mechanical angular momentum operator for
an electrically charged particle in the field of the magnetic charges. Assuming
that quantum mechanics is correct we conclude that free magnetic charges (i.e.
magnetic charges with a Coulomb-like magnetic field) can not exist. The only
apparent way to avoid this conclusion is if magnetic charges do exist, they
must be permanently confined in monopole anti-monopole pairs, much in the same
way quarks are thought to be confined.",9704042v2
2006-09-06,Magnetization-induced optical second-harmonic generation and local surface plasmons in magnetic $Co_x Ag_{1-x}$ nanogranular films,"Spectroscopy of magnetization-induced second-harmonic generation (MSHG) is
studied in magnetic Co$_{x}$Ag$_{1-x}$ granular films containing Co
nanoparticles. A strong resonance of the magnetic contrast of the
second-harmonic generation (SHG) intensity is observed in the two-photon energy
range from 3,8 eV to 4,5 eV. The local surface plasmons exited in magnetic Co
nanogranules in this spectral range assist MSHG and are responsible for a
significant enhancement of the SHG magnetic contrast due to the resonances of
local optical fields.",0609010v1
2005-01-26,Destroying the superfluid state of fermionic atoms by the magnetic field in Feshbach resonance experiments,"We show that the superfluid state (SF) of fermionic atoms exist only for the
magnetic fields lesser than the critical magnetic field. This critical magnetic
field is determined by the equality of the Zeeman energy splitting for atoms
with different spin projections to the energy gap of fermionic atoms without a
magnetic field. For magnetic fields usually using in Feshbach resonance
experiments a SF state is lost because these fields are much more than the
critical field. We show that the transition temperature $ T_c $ of the SF state
decreases as the magnetic field increases.",0501137v1
2006-05-03,Effect of Magnetization Inhomogeneity on Magnetic Microtraps for Atoms,"We report on the origin of fragmentation of ultracold atoms observed on a
permanent magnetic film atom chip. A novel technique is used to characterize
small spatial variations of the magnetic field near the film surface using
radio frequency spectroscopy of the trapped atoms. Direct observations indicate
the fragmentation is due to a corrugation of the magnetic potential caused by
long range inhomogeneity in the film magnetization. A model which takes into
account two-dimensional variations of the film magnetization is consistent with
the observations.",0605028v2
2006-08-03,Magnetization of rotating ferrofluids: the effect of polydispersity,"The influence of polydispersity on the magnetization is analyzed in a
nonequilibrium situation where a cylindrical ferrofluid column is enforced to
rotate with constant frequency like a rigid body in a homogeneous magnetic
field that is applied perpendicular to the cylinder axis. Then, the
magnetization and the internal magnetic field are not longer parallel to each
other and their directions differ from that of the applied magnetic field.
Experimental results on the transverse magnetization component perpendicular to
the applied field are compared and analyzed as functions of rotation frequency
and field strength with different polydisperse Debye models that take into
account the polydispersity in different ways and to a varying degree.",0608033v1
2007-07-02,Manipulating the magnetic structure by electric fields in multiferroic ErMn2O5,"Based on measurements of soft x-ray magnetic diffraction under in-situ
applied electric field, wereport on significantly manipulation and exciting of
commensurate magnetic order in multiferroic ErMn2O5. The induced magnetic
scattering intensity arises at the commensurate magnetic Bragg position whereas
the initial magnetic signal almost persists. We demonstrate the possibility to
imprint a magnetic response function in ErMn2O5 by applying electric field.",0707.0180v2
2007-10-02,Magnetic relaxation in the Bianchi-I universe,"Extended Einstein-Maxwell model and its application to the problem of
evolution of magnetized Bianchi-I Universe are considered. The evolution of
medium magnetization is governed by a relaxation type extended constitutive
equation. The series of exact solutions to the extended master equations is
obtained and discussed. The anisotropic expansion of the Bianchi-I Universe is
shown to become non-monotonic (accelerated/decelerated) in both principal
directions (along the magnetic field and orthogonal to it). A specific type of
expansion, the so-called evolution with hidden magnetic field, is shown to
appear when the magnetization effectively screens the magnetic field and the
latter disappears from the equations for gravitational field.",0710.0615v1
2007-10-19,Depressed Surface Magnetization in Thin La0.8MnO3 Films,"A systematic study the magnetization in La0.8.MnO3 films of thickness varying
from ultra-thin to bulk-like has been conducted. The study reveals suppression
of the bulk magnetization for films up to at least 1600 A. In addition, the
surface (top 50 A) of all films exhibits depressed magnetization as observed by
x-ray magnetic circular dichroism (XMCD). The reduced surface magnetization is
attributed to the coexistence of magnetic and nonmagnetic components of the
same chemical composition.",0710.3793v1
2007-11-19,Room Temperature Magnetocaloric Effect in Ni-Mn-In,"We have studied the effect of magnetic field on a non-stoichiometric Heusler
alloy Ni$_{50}$Mn$_{35}$In$_{15}$ that undergoes a martensitic as well as a
magnetic transition near room temperature. Temperature dependent magnetization
measurements demonstrate the influence of magnetic field on the structural
phase transition temperature. From the study of magnetization as a function of
applied field, we show the occurrence of inverse-magnetocaloric effect
associated with this magneto-structural transition. The magnetic entropy change
attains a value as high as 25 J/kg-K (at 5 T field) at room temperature as the
alloy transforms from the austenitic to martensitic phase with a concomitant
magnetic ordering.",0711.2896v1
2008-03-26,The commensurate phase of multiferroic HoMn2O5 studied by X-ray magnetic scattering,"The commensurate phase of multiferroic HoMn2O5 was studied by X-ray magnetic
scattering, both off resonance and in resonant conditions at the Ho-L3 edge.
Below 40 K, magnetic ordering at the Ho sites is induced by the main Mn
magnetic order parameter, and its temperature dependence is well accounted for
by a simple Curie-Weiss susceptibility model. A lattice distortion of
periodicity twice that of the magnetic order is also evidenced. Azimuthal scans
confirm the model of the magnetic structure recently refined from neutron
diffraction data for both Mn and Ho sites, indicating that the two sublattices
interact via magnetic superexchange.",0803.3779v1
2008-09-11,Ferromagnetic ordering in dilute magnetic dielectrics with and without free carriers,"The state of art in the theoretical and experimental studies of transition
metal doped oxides (dilute magnetic dielectrics) is reviewed. The available
data show that the generic non-equilibrium state of oxide films doped with
magnetic impurities may either favor ferromagnetism with high Curie temperature
or result in highly inhomogeneous state without long-range magnetic order. In
both case concomitant defects (vacancies, interstitial ions play crucial part.",0809.2005v1
2008-10-28,"Anomalous magnetization behavior in Ce(Fe,Si)2","We report the effect of Si doping on the magnetization behavior of CeFe2. It
is found that Si stabilizes the dynamic antiferromagnetic state of CeFe2.
Multi-step magnetization behavior, unusual relaxation effect, thermal and
magnetic history dependence, which are signatures of martensitic scenario, are
found to be present in this system. We also show that one can induce the
magnetization steps with the help of appropriate measurement protocol. Detailed
magnetization relaxation studies have been carried out to understand the
dynamics of magnetic phase transition.",0810.5017v1
2008-10-29,Contrasting the magnetic response between magnetic-glass and reentrant spin-glass,"Magnetic-glass is a recently identified phenomenon in various classes of
magnetic systems undergoing a first order magnetic phase transition. We shall
highlight here a few experimentally determined characteristics of
magnetic-glass and the relevant set of experiments, which will enable to
distinguish a magnetic-glass unequivocally from the well known phenomena of
spin-glass and reentrant spin-glass.",0810.5215v2
2009-01-13,Magnetic field observations of low-mass stars,"Direct measurements of magnetic fields in low-mass stars of spectral class M
have become available during the last years. This contribution summarizes the
data available on direct magnetic measurements in M dwarfs from Zeeman analysis
in integrated and polarized light. Strong magnetic fields at kilo-Gauss
strength are found throughout the whole M spectral range, and so far all field
M dwarfs of spectral type M6 and later show strong magnetic fields. Zeeman
Doppler images from polarized light find weaker fields, which may carry
important information on magnetic field generation in partially and fully
convective stars.",0901.1719v1
2009-01-19,Toroidal moments as indicator for magneto-electric coupling: the case of BiFeO_3 versus FeTiO_3,"In this paper we present an analysis of the magnetic toroidal moment and its
relation to the various structural modes in R3c-distorted perovskites with
magnetic cations on either the perovskite A or B site. We evaluate the toroidal
moment in the limit of localized magnetic moments and show that the full
magnetic symmetry can be taken into account by considering small induced
magnetic moments on the oxygen sites. Our results give a transparent picture of
the possible coupling between magnetization, electric polarization, and
toroidal moment, thereby highlighting the different roles played by the various
structural distortions in multiferroic BiFeO_3 and in the recently discussed
isostructural material FeTiO_3, which has been predicted to exhibit electric
field-induced magnetization switching.",0901.2812v1
2009-01-28,"Concurrent Magnetic and Metal-Insulator Transitions in (Eu,Sm)B_6 Single Crystals","The effects of magnetic doping on a EuB_6 single crystal were investigated
based on magnetic and transport measurements. A modest 5% Sm substitution for
Eu changes the magnetic and transport properties dramatically and gives rise to
concurrent antiferromagnetic and metal-insulator transitions (MIT) from
ferromagnetic MIT for EuB6. Magnetic doping simultaneously changes the
itinerant carrier density and the magnetic interactions. We discuss the origin
of the concurrent magnetic MIT in (Eu,Sm)B_6.",0901.4384v1
2009-02-03,Tuning Magnetic Avalanches in Mn12-ac,"Using micron-sized Hall sensor arrays to obtain time-resolved measurements of
the local magnetization, we report a systematic study in the molecular magnet
Mn$_{12}$-acetate of magnetic avalanches controllably triggered in different
fixed external magnetic fields and for different values of the initial
magnetization. The speeds of propagation of the spin-reversal fronts are in
good overall agreement with the theory of magnetic deflagration of Garanin and
Chudnovsky \cite{Garanin}.",0902.0531v2
2009-03-25,Two dimensional frustrated magnets in high magnetic field,"Frustrated magnets in high magnetic field have a long history of offering
beautiful surprises to the patient investigator. Here we present the results of
extensive classical Monte Carlo simulations of a variety of models of two
dimensional magnets in magnetic field, together with complementary spin wave
analysis. Striking results include (i) a massively enhanced magnetocaloric
effect in antiferromagnets bordering on ferromagnetic order, (ii) a route to an
$m=1/3$ magnetization plateau on a square lattice, and (iii) a cascade of phase
transitions in a simple model of AgNiO$_2$.",0903.4370v1
2009-04-07,Unconventional magnetism in small gold organic molecules,"We present a theoretical study of the magnetic properties of
dicyclopentadienyl metallocene and phthalocyanine molecules, that contain the
transition metal atoms M = Fe, Co, Ni, Cu, Zn, Ir, Pt and Au. Our most
important prediction is that gold and copper molecules are magnetic. We find
that the magnetism of these molecules is fairly unconventional: the gold atom
itself is weakly magnetic or even non-magnetic. Its role is rather to induce
magnetism in the surrounding carbon and nitrogen atoms, producing a sort of
spin density wave.",0904.1138v1
2009-05-02,Voltage-assisted Magnetization Switching in Ultrathin Fe80Co20 Alloy Layers,"Growing demands for the voltage-driven spintronic applications with
ultralow-power consumption have led to new interest in exploring the
voltage-induced magnetization switching in ferromagnetic metals. In this study,
we observed a large perpendicular magnetic anisotropy change in Au(001) /
ultrathin Fe80Co20(001) / MgO(001) / Polyimide / ITO junctions, and succeeded
in realizing a clear switching of magnetic easy axis between in-plane and
perpendicular directions. Furthermore, employing a perpendicularly magnetized
film, voltage-induced magnetization switching in the perpendicular direction
under the assistance of magnetic fields was demonstrated. These pioneering
results may open a new window of electric-field controlled spintronics devices.",0905.0185v1
2009-06-26,Relaxation Mechanism for Ordered Magnetic Materials,"We have formulated a relaxation mechanism for ferrites and ferromagnetic
metals whereby the coupling between the magnetic motion and lattice is based
purely on continuum arguments concerning magnetostriction. This theoretical
approach contrasts with previous mechanisms based on microscopic formulations
of spin-phonon interactions employing a discrete lattice. Our model explains
for the first time the scaling of the intrinsic FMR linewidth with frequency,
and 1/M temperature dependence and the anisotropic nature of magnetic
relaxation in ordered magnetic materials, where M is the magnetization. Without
introducing adjustable parameters our model is in reasonable quantitative
agreement with experimental measurements of the intrinsic magnetic resonance
linewidths of important class of ordered magnetic materials, insulator or
metals.",0906.4979v1
2009-07-10,Quantized magnetic confinement in quantum wires,"Ballistic quantum wires are exposed to longitudinal profiles of perpendicular
magnetic fields composed of a spike (magnetic barrier) and a homogeneous part.
An asymmetric magnetoconductance peak as a function of the homogeneous magnetic
field is found, comprising quantized conductance steps in the interval where
the homogeneous magnetic field and the magnetic barrier have identical
polarities, and a characteristic shoulder with several resonances in the
interval of opposite polarities. The observations are interpreted in terms of
inhomogeneous diamagnetic shifts of the quantum wire modes leading to magnetic
confinement.",0907.1802v1
2009-07-28,Chiral Magnetic conductivity,"Gluon field configurations with nonzero topological charge generate
chirality, inducing P- and CP-odd effects. When a magnetic field is applied to
a system with nonzero chirality, an electromagnetic current is generated along
the direction of the magnetic field. The induced current is equal to the Chiral
Magnetic conductivity times the magnetic field. In this article we will compute
the Chiral Magnetic conductivity of a high-temperature plasma for nonzero
frequencies. This allows us to discuss the effects of time-dependent magnetic
fields, such as produced in heavy ion collisions, on chirally asymmetric
systems.",0907.5007v1
2010-05-15,Thermodynamics of strongly frustrated magnet in a field: Ising antiferromagnet on triangular Husimi lattice,"Some strongly frustrated magnets such as the ""spin-ice"" compounds fail to
produce any magnetic order at finite temperatures even in the presence of
magnetic field. Still they have very unusual low-temperature thermodynamic
properties related to the field-induced ground state transitions. Here we show
that general qualitative picture of such peculiar thermodynamics can be
obtained in the antiferromagnetic Ising model on the triangular Husimi lattice.
The analytical results for this model show magnetic plateaus, entropy spikes,
crossing points and peculiarities in magnetic susceptibility and specific heat
behavior reflecting the existence of ground state transitions. These signatures
of strong frustration may help in search of new frustrated magnets and in the
interpretation of experimental data.",1005.2650v1
2010-05-17,Quantization of edge currents along magnetic barriers and magnetic guides,"We investigate the edge conductance of particles submitted to an Iwatsuka
magnetic field, playing the role of a purely magnetic barrier. We also consider
magnetic guides generated by generalized Iwatsuka potentials. In both cases we
prove quantization of the edge conductance. Next, we consider magnetic
perturbations of such magnetic barriers or guides, and prove stability of the
quantized value of the edge conductance. Further, we establish a sum rule for
edge conductances. Regularization within the context of disordered systems is
discussed as well.",1005.2788v1
2010-07-02,Spin-polarizing properties of heterostructures with magnetic nano elements,"The problem of electron resonant and non-resonant scatterings on two
magnetized barriers is studied in the one-dimension. The transfer-matrix is
built up to exactly calculate the coefficient of the electron transmittance
through the system of two magnetic barriers with non-collinear magnetizations.
The polarization of the transmitted electron wave for resonance and
non-resonance transmittances is calculated. The transmittance coefficient and
spin polarization can be drastically enhanced and controlled by the angle
between the barrier magnetizations",1007.0421v1
2010-09-22,Direct Measurement of Effective Magnetic Diffusivity in Turbulent Flow of Liquid Sodium,"The first direct measurements of effective magnetic diffusivity in turbulent
flow of electro-conductive fluids (the so-called beta-effect) under magnetic
Reynolds number Rm >> 1 are reported. The measurements are performed in a
nonstationary turbulent flow of liquid sodium, generated in a closed toroidal
channel. The peak level of the Reynolds number reached Re \approx 3 10^6, which
corresponds to the magnetic Reynolds number Rm \approx 30. The magnetic
diffusivity of the liquid metal was determined by measuring the phase shift
between the induced and the applied magnetic fields. The maximal deviation of
magnetic diffusivity from its basic (laminar) value reaches about 50% .",1009.4333v1
2010-11-03,Critical Magnetic Field Ratio of Anisotropic Magnetic Superconductors,"The upper critical field, the lower critical field and the critical magnetic
field ratio of anisotropic magnetic superconductors are calculated by
Ginzburg-Landau theory analytically. The effect of the Ginzburg-Landau
parameter(\kappa_0), magnetic susceptibility(\chi) and magnetic-to- anisotropic
parameter ratio(\theta) on the critical field ratio are considered. We find
that the value of critical magnetic field ratio with \chi < 0, higher
\kappa_0,and higher \theta case are shown the higher value. And, the
diamagnetic superconductors with highly anisotropic and the ferromagnetic
superconductors are shown the highest and the lowest, respectively.",1011.0783v1
2010-11-18,Possibility of exchange switching ferromagnet - antiferromagnet junctions,"Current flowing is studied in magnetic junctions consisting of a
ferromagnetic metal (FM), antiferromagnetic conductor (AFM) and a nonmagnetic
metal closing the electric circuit. The FM layer with high anisotropy and
pinned spins of the magnetic atoms in the lattice acts as a spin injector
relative to the AFM layer. To obtain resulting magnetization in the AFM layer,
magnetic field is applied, which may be varied to control the magnetization.
The spin-polarized current from the FM layer creates a torque and makes it
possible to switch the magnetization. A possibility is shown to lower the
threshold current density by the orders of magnitude by means of the magnetic
field.",1011.4303v1
2010-12-03,Magnetic Field Structure near the Galactic Plane,"We bring the two color maps for the plane component magnetic field of our
Galaxy in coordinates of (R;l) and (DM;l). It was shown that magnetic field has
reversals of the direction in neighbor spiral arms, in agreement with known
models for the Galactic magnetic field. For the Sagittarius spiral arm region
there is, however, some disagreement with standard magnetic field models. The
major discrepancy is the fact that in the Sagittarius arm region the magnetic
field in Southern hemisphere of the Galaxy, have opposite direction to the
field of the Northern hemisphere. We think that the Sagittarius spiral arm, at
last the magnetic spiral arm in this region is not symmetric to the Galactic
plane, and is located mainly in Northern hemisphere.",1012.0646v1
2011-01-20,Controllable manipulation of superconductivity using magnetic vortices,"The magneto-transport of a superconducting/ferromagnetic hybrid structure
consisting of a superconducting thin film in contact with an array of magnetic
nanodots in the so-called ""magnetic vortex-state"" exhibits interesting
properties. For certain magnetic states, the stray magnetic field from the
vortex array is intense enough to drive the superconducting film into the
normal state. In this fashion, the normal-to-superconducting phase transition
can be controlled by the magnetic history. The strong coupling between
superconducting and magnetic subsystems allows characteristically ferromagnetic
properties, such as hysteresis and remanence, to be dramatically transferred
into the transport properties of the superconductor.",1101.3846v1
2011-03-09,"Specifications, quality control, manufacturing, and testing of accelerator magnets","The performance of the magnets plays an important role in the functioning of
an accelerator. Most of the magnets are designed at the accelerator laboratory
and built by industry. The link between the laboratory and the manufacturer is
the contract containing the Technical Specifications of the magnets. For an
overview of the contents of the Technical Specifications, the specifications
for the magnets of ALBA (bending, quadrupole, and sextupole) are described in
this paper. The basic rules of magnet design are reviewed in Appendix A.",1103.1815v1
2011-06-12,Anomalies in the Multicritical Behavior of Staggered Magnetic and Direct Magnetic Susceptibilities of Iron Group Dihalides,"In this study, the temperature dependencies of magnetic response functions of
the anhydrous dihalides of iron-group elements are examined in the neighborhood
of multi-critical points (tricritical, critical end point, double critical end
point) and first order transition temperatures within molecular field
approximation. Our findings reveal the fact that metamagnetic Ising system
exhibits anomalies in the temperature dependence of the magnetic response
functions for r<0.3. In addition, we extensively investigated how an inter- and
intra-layer exchange interaction ratio can influence magnetic response
properties of these systems. Finally, a comparison is made with related works.",1106.2308v1
2011-07-08,Ferromagnetism in lead graphite-pencils and magnetic composite with CoFe2O4 particles,"This work has been initiated with a curiosity to investigate the elemental
composition and magnetic response of different grades of lead pencils (6B, 2B,
HB, 2H, 5H) that people use in daily life. Interestingly, experimental results
landed with a great achievement of observing soft magnetism in lead pencils,
indicating a wide scope of magnetic tuning for room temperature applications. A
novel magnetic composite has been synthesized by mixing different concentration
of CoFe2O4 (CF) nanoparticles in 5H and 6B pencils for studying the magnetic
tailoring aspects using pencils. Our results showed different possibilities of
controlling disorder induced ferromagnetic parameters and a simple approach of
producing sufficiently high coercive magnetic composite using pencils.",1107.1662v1
2011-11-01,Measurement of magnetic permeability of steel laminations of Booster gradient magnets,"New experiments at Fermilab require higher beam intensities at Booster,
resulting in higher influence of magnet steel on the beam. In order to
carefully take these effects into account it is necessary to know geometric and
material properties of magnets. This work is dedicated to the measurement of
magnetic permeability of steel laminations of Booster gradient magnets as a
complex function of frequency in the frequency range from several megahertz up
to 1 GHz. The magnetic permeability is estimated by analyzing S-parameters of
microstrip lines made up from laminated steel.",1111.0247v3
2011-11-28,Magnetic stars from a FEROS cool Ap star survey,"New magnetic Ap stars with split Zeeman components are presented. These stars
were discovered from observations with the FEROS spectrograph at the ESO 2.2-m
telescope. Fifteen new magnetic stars are analysed here. Several stars with
very strong magnetic fields were found, including HD\,70702 with a 15-kG, and
HD\,168767 with a 16.5-kG magnetic field strength measured using split Zeeman
components of spectral lines and by comparison with synthetic calculations. The
physical parameters of the stars were estimated from photometric and
spectroscopic data. Together with previously published results for stars with
strong magnetic fields, the relationship between magnetic field strength and
rotation period is discussed.",1111.6448v1
2011-12-08,Spintronic devices on the base of magnetic nanostructures,"Two types of spintronic devices on the base of magnetic nanostructures
containing silicon dioxide films with cobalt nanoparticles SiO2(Co) on GaAs
substrate - magnetic sensors and field-effect transistor governed by applied
magnetic field - are studied. Magnetic sensors are based on the injection
magnetoresistance effect. This effect manifests itself in avalanche suppression
by the magnetic field in GaAs near the SiO2(Co)/GaAs interface. Field-effect
transistor contains the SiO2(Co) film under gate. It is found that the magnetic
field action leads to great changes in electron mobility in the channel due to
the interaction between spins of Co nanoparticles and electron spins.",1112.1798v1
2012-01-10,Direct observation of magnetic phase coexistence and magnetization reversal in a Gd$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin film,"We have investigated the ferrimagnetic domain structure in a
Gd$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin film using magnetic force microscopy. We
observe clear signs of phase separation, with magnetic islands embedded in a
non-magnetic matrix. We also directly visualize the reversal of magnetization
of ferrimagnetic domains as a function of temperature and attribute it to a
change in the balance of magnetization of anti-aligned Mn and Gd sublattices.",1201.2144v1
2012-05-14,Effects of the randomly distributed magnetic field on the phase diagrams of the Ising Nanowire I: discrete distributions,"The effect of the random magnetic field distribution on the phase diagrams
and ground state magnetizations of the Ising nanowire is investigated with
effective field theory with correlations. Trimodal distribution chosen as a
random magnetic field distribution. The variation of the phase diagrams with
that distribution parameters obtained and some interesting results found such
as reentrant behavior. Also for the trimodal distribution, ground state
magnetizations for different distribution parameters determined which can be
regarded as separate partially ordered phases of the system.",1205.3219v1
2012-06-06,Magnetic field dependent impact ionization in InSb,"Carrier generation by impact ionization and subsequent recombination under
the influence of magnetic field has been studied for InSb slab. A simple
analytic expression for threshold electric field as a function of magnetic
field is proposed. Impact ionization is suppressed by magnetic field. However,
surface recombination is dependent on the polarity of magnetic field:
strengthened in one direction and suppressed on the opposite direction. The
former contributes quadratic increase to threshold electric field, and the
latter gives additional linear dependence on magnetic field. Based on this
study, electrical switching devices driven by magnetic field can be designed.",1206.1094v1
2012-08-28,Thermodynamic investigations in the precursor region of FeGe,"High-resolution DC magnetization and AC-specific heat data of the cubic
helimagnet FeGe have been measured as function of temperature and magnetic
field. The magnetization data as well as the isothermal susceptibility data
confirm the complexity of the magnetic phase diagram in the vicinity of the
onset of long-rang magnetic order (Tc = 278.5 K) and the existence of a
segmented A-phase region. Moreover, these data revealed independent and clear
indications of phase boundaries and crossovers within the A-phase region.
Together with the anomalies in the specific-heat data around Tc and at small
magnetic fields (H < 600 Oe) a complex magnetic phase diagram of FeGe is
obtained.",1208.5646v1
2012-09-17,Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles,"The magnetic properties of densely packed magnetic nanoparticles (MNP)
assemblies are investigated from Monte Carlo simulations. The case of iron
oxide nanoparticles is considered as a typical example of MNP. The main focus
is put on particle size and size polydispersity influences on the magnetization
curve. The particles are modeled as uniformly magnetized spheres isolated one
from each other by a non magnetic layer representing the organic coating. A
comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder
samples differing by their size is given.",1209.3566v1
2012-11-02,Effect of Spin Torque on Magnetization Switching Speed Having Nonuniform Spin Distribution,"We study the influence of the spin torque, which depends on the space and
time derivative of magnetization, on magnetization reversal time in a
ferromagnetic fine particle. The spin torque operates to dissipate the angular
momentum of the magnetization precession, and the torque increases in a spin
vortex structure. We calculate the magnetization reversal time under a DC
magnetic field using the Landau-Lifshitz-Gilbert equation containing a spin
torque term. We found that the spin torque changes the magnetization switching
speed significantly during the reversal process by maintaining a spin vortex in
an intermediate state.",1211.0360v1
2012-11-06,Spin Wave Scattering in Ferromagnetic Cross,"Spin wave scattering in the right angle ferromagnetic cross was measured.
Shape anisotropy defined magnetization ground states at zero biasing magnetic
fields. Scattering of the spin waves in the center of ferromagnetic cross is
strongly dependent on the amplitude and angle of the biasing magnetic field.
Micromagnetic simulations indicate that low in-plane biasing magnetic fields
rotate the magnetization of the cross center while the arms stay axially
magnetized due to the shape anisotropy. We discuss effect of biasing magnetic
fields on the spin wave scattering and approaches to an effective spin wave
switch based on the fabricated structure.",1211.1259v1
2012-11-23,Non-reciprocal light diffraction by a vortex magnetic particle,"We report a theoretical study of light diffraction by a spherical magnetic
particle with a vortex magnetization distribution. It is shown that the
intensity of the diffracted light involves a non-reciprocal contribution. This
contribution depends on the vorticity of particle magnetization. It appears due
to the excitation of an electric quadrupole, magnetic dipole and the addition
to the electric dipole moment in the particle, that depend on the particle
magnetization vorticity. The estimation of the non-reciprocal contrbution for a
cobalt particle and two linear polarizations of the incident light fits the
data of recent experimental studies in the lattice of triangle magnetic
particles by an order of magnitude.",1211.5459v1
2012-12-05,"Influence of Magnetic Anisotropy on Laser-induced Precession of Magnetization in Ferromagnetic Semiconductor (Ga,Mn)As","The laser-induced precession of magnetization in (Ga,Mn)As samples with
different magnetic anisotropy was studied by the time-resolved magneto-optical
method. We observed that the dependence of the precession amplitude on the
external magnetic field depends strongly on the magnetic anisotropy of
(Ga,Mn)As and we explain this phenomenon in terms of competing cubic and
uniaxial anisotropies. We also show that the corresponding anisotropy fields
can be deduced from the magnetic field dependence of the precession frequency.",1212.0962v1
2013-06-13,Temperature- and Magnetic-Field-Tuning of Magnetic Phases in Multiferroic NdFe3(BO3)4,"We report the low-temperature coexistence in NdFe3(BO3)4 of an incommensurate
magnetic phase with a strained commensurate magnetic phase that is primarily at
the surface of the crystal. Increasing the temperature or magnetic field
decreases the incommensurability and stabilizes the commensurate magnetic phase
above Tic ~14 K or Hic = 0.9 T. A comparison to published studies indicates the
onset of longitudinal magnetostriction and electric polarization at the
magnetic-field-induced transition, which may arise due to a basal plane
spin-flop and canting of the moments along the field direction.",1306.3152v1
2013-07-10,Spintronic Oscillator Based on Magnetic Field Feedback,"We present a circuit design of a spintronic oscillator based on magnetic
tunnel junction. In this design, a dc current is passed through a magnetic
tunnel junction which is connected to a feed-back wire below it. Any
fluctuation in the magnetization direction of the free layer of MTJ, drives a
fluctuating current through the feed-back wire, which exerts a magnetic field
on the free layer. This in turn can amplify the magnetization fluctuations of
the free layer. If the dc current passing through the MTJ is more than a
critical value, continuous precessing states of the magnetization are possible.",1307.2744v1
2013-07-19,X-ray diffraction by magnetic charges (monopoles),"Magnetic charges, or magnetic monopoles, may form in the electronic structure
of magnetic materials where ions are deprived of symmetry with respect to
spatial inversion. Predicted in 2009, the strange magnetic, pseudoscalars have
recently been found different from zero in simulations of electronic structures
of some magnetically ordered, orthorhombic, lithium orthophosphates (LiMPO4).
We prove that magnetic charges in lithium orthophosphates diffract x-rays tuned
in energy to an atomic resonance, and to guide future experiments we calculate
appropriate unit-cell structure factors for monoclinic LiCoPO4 and orthorhombic
LiNiPO4.",1307.5164v1
2013-07-31,External magnetic fields and the chiral phase transition in QED at nonzero chemical potential,"Inspired by recent discussions of inverse magnetic catalysis in the
literature, we examine the effects of a uniform external magnetic field on the
chiral phase transition in quenched ladder QED at nonzero chemical potential.
In particular, we study the behaviour of the effective potential as the
strength of the magnetic field is varied while the chemical potential is held
constant. For a certain range of the magnetic field, the effective potential
develops a local maximum. Inverse magnetic catalysis is observed at this
maximum, whereas the usual magnetic catalysis is observed at the true minimum
of the effective potential.",1307.8222v1
2013-09-24,Magnetic fields in A stars besides Ap stars,"I review ongoing efforts to understand the incidence of magnetism in
intermediate-mass stars that are different from the magnetic Ap stars. This
includes the search for magnetic fields in chemically peculiar stars of the Am
and HgMn types as well as in normal A and late-B stars. I discuss different
techniques for detection of weak stellar magnetic fields and present a critical
evaluation of the recent magnetic detections in non-Ap stars. Special attention
is given to the magnetic status of HgMn stars and to the discovery of weak
polarization signatures in Sirius and Vega.",1309.6313v1
2013-10-22,Magnetic Fields in Low-mass Stars: An Overview of Observational Biases,"Stellar magnetic dynamos are driven by rotation, rapidly rotating stars
produce stronger magnetic fields than slowly rotating stars do. The Zeeman
effect is the most important indicator of magnetic fields, but Zeeman
broadening must be disentangled from other broadening mechanisms, mainly
rotation. The relations between rotation and magnetic field generation, between
Doppler and Zeeman line broadening, and between rotation, stellar radius, and
angular momentum evolution introduce several observational biases that affect
our picture of stellar magnetism. In this overview, a few of these relations
are explicitly shown, and the currently known distribution of field
measurements is presented.",1310.5820v1
2013-11-01,Magnetic Generation due to Mass Difference between Charge Carriers,"The possibility of spontaneous magnetization due to the ""asymmetry in mass""
of charge carriers in a system is investigated. Analysis shows that when the
masses of positive and negative charge carriers are identical, no magnetization
is predicted. However, if the masses of two species are different, spontaneous
magnetic field would appear, either due to the equipartition of magnetic energy
or due to fluctuations together with a feedback mechanism. The conditions for
magnetization to occur are also obtained, in the form of n-T phase diagram. The
theory proposed here, if confirmed by future observations and/or experiments,
would provide a new insight on the origin of magnetic fields in the universe.",1311.0074v1
2014-01-08,Increasing the magnetic sensitivity of liquid crystals by rod-like magnetic nanoparticles,"Magnetic Fr\'eedericksz transition was studied in ferronematics based on the
nematic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene
(6CHBT). 6CHBT was doped with rod-like magnetic particles of different size and
volume concentration. The volume concentrations of magnetic particles in the
prepared ferronematics were $\phi_1$ = 10$^{-4}$ and $\phi_2$ = 10$^{-3}$. The
structural changes were observed by capacitance measurements that demonstrate a
significant influence of the concentration, the shape anisotropy, and/or the
size of the magnetic particles on the magnetic response of these ferronematics.",1401.1695v1
2014-01-16,"Quench protection analysis in accelerator magnets, a review of the tools","As accelerator magnets see the increase of their magnetic field and stored
energy, quench protection becomes a critical part of the magnet design. Due to
the complexity of the quench phenomenon interweaving magnetic, electrical and
thermal analysis, the use of numerical codes is a key component of the process.
In that respect, we propose here a review of several tools commonly used in the
magnet design community.",1401.3934v1
2014-02-25,Magnetic field control of ferroelectric polarization and magnetization of LiCu2O2 compound,"A spin model of LiCu2O2 compound with ground state of ellipsoidal helical
structure has been adopted. Taking into account the interchain coupling and
exchange anisotropy, we focus on the magnetoelectric properties in a rotating
magnetic field and perform the Monte Carlo simulation on a two-dimensional
lattice. A prominent anisotropic response is observed in the magnetization and
polarization curves, qualitatively coinciding with the behaviors that detected
in the experiment. In addition, the influences of the magnetic field with
various magnitudes are also explored and analyzed in detail. As the magnetic
field increases, a much smoother polarization of angle dependence is exhibited,
indicating the strong correlation between the magnetic and ferroelectric
orders.",1402.6648v1
2014-04-19,High-precision description and new properties of a spin-1 particle in a magnetic field,"The exact Foldy-Wouthuysen Hamiltonian is derived for a pointlike spin-1
particle with a normal magnetic moment in a nonuniform magnetic field. For a
uniform magnetic field, it is exactly separated into terms linear and quadratic
in spin. New unexpected properties of a particle with an anomalous magnetic
moment are found. Spin projections of a particle moving in a uniform magnetic
field are not integer and the tensor polarization is asymmetric in the plane
orthogonal to the field. Previously described spin-tensor effects caused by the
tensor magnetic polarizability exist not only for nuclei but also for pointlike
particles.",1404.4953v2
2014-05-16,Magnetoelectric surface acoustic wave resonator with ultrahigh magnetic field sensitivity,"A magnetoelectric surface acoustic wave (MESAW) type device based on
piezoelectric/magnetostrictive heterostructure was proposed to use as weak
magnetic field sensor. Unlike conventional magnetoelectric bulk laminates or
film stacks collecting magnetic field induced electrical charge, the MESAW
detects the shift of the center frequency, which highly depends on the magnetic
field due to the giant delta E effect and the phase velocity dispersion. The
magnetic field sensitivity can reach 10^(-11) Tesla in consideration of 100 Hz
frequency accuracy. Additionally, the unique working mechanism of MESAW allows
a broadband detection of weak magnetic field even with no bias magnetic field.",1405.4076v2
2014-05-22,Magnetic phases of erbium orthochromite,"Erbium orthochromite, ErCrO3, is a distorted-perovskite which has
antiferromagnetic ground state below 10 K while Cr3+ magnetic moments order at
133 K. The temperature dependence of magnetization is studied across different
magnetic phases for ErCrO3 and different magnetization isotherms are analyzed.
In the presence of external magnetic field, polycrystalline ErCrO3 develops
weak ferromagnetism from antiferromagnetic ground state. These magnetic phase
transitions are observed to be of first order which is justified by thermal
hysteresis and Arrott-plots.",1405.5636v1
2014-06-18,Spin-lattice coupling induced weak dynamical magnetism in EuTiO_3 at high temperatures,"EuTiO_3, which is a G-type antiferromagnet below T_N = 5.5 K, has some
fascinating properties at high temperatures, suggesting that macroscopically
hidden dynamically fluctuating weak magnetism exists at high temperatures. This
conjecture is substantiated by magnetic field dependent magnetization
measurements, which exhibit pronounced anomalies below 200 K becoming more
distinctive with increasing magnetic field strength. Additional results from
muon spin rotation (${\mu}$SR) experiments provide evidence for weak
fluctuating bulk magnetism induced by spin-lattice coupling which is strongly
supported in increasing magnetic field.",1406.4915v1
2014-09-17,Terahertz Magnetic Modulator based on Magnetically-Clustered Nanoparticles,"Random orientation of liquid-suspended magnetic nanoparticles (Ferrofluid)
gives rise to zero net magnetic orientation. An external magnetic field tends
to align them into clusters, leading to a strong linear dichroism on a
propagating wave. Using 10 nm-sized Fe3O4, we experimentally realize a
polarization-sensitive magnetic modulator operating at terahertz wavelengths.
We reached a modulation depth of 66% using a field of 35 mT. The proposed
concept offers a solution towards fundamental terahertz magnetic modulators.",1409.4963v1
2015-03-27,Spin superradiance by magnetic nanomolecules and nanoclusters,"Spin dynamics of assemblies of magnetic nanomolecules and nanoclusters can be
made coherent by inserting the sample into a coil of a resonant electric
circuit. Coherence is organized through the arising feedback magnetic field of
the coil. The coupling of a magnetic sample with a resonant circuit induces
fast spin relaxation and coherent spin radiation, that is, superradiance. We
consider spin dynamics described by a realistic Hamiltonian, typical of
magnetic nanomolecules and nanoclusters. The role of magnetic anisotropy is
studied. A special attention is paid to geometric effects related to the mutual
orientation of the magnetic sample and resonator coil.",1503.08036v1
2015-04-05,Magnetic states in multiply-connected flat nano-elements,"Flat magnetic nano-elements are an essential component of current and future
spintronic devices. By shaping an element it is possible to select and
stabilize chosen metastable magnetic states, control its magnetization
dynamics. Here, using a recent significant development in mathematics of
conformal mapping, complex variable based approach to the description of
magnetic states in planar nano-elements is extended to the case when elements
are multiply-connected (that is, contain holes or magnetic anti-dots). We show
that presence of holes implies a certain restriction on the set of magnetic
states of nano-element.",1504.01162v1
2015-04-28,"""Switching"" of Magnetic Anisotropy in a fcc Antiferromagnet with Direction-Dependent Interactions","Direction-dependent anisotropic exchange is a common feature of magnetic
systems with strong spin-orbit coupling. Here we study the effect of such
exchange upon macroscopic magnetic anisotropy for a face-centered-cubic model.
By several theoretical techniques, we show that, both in the paramagnetic and
ordered phases, the magnetic anisotropy is induced by fluctuations. Moreover,
the magnetic anisotropy differs in the paramagnetic and ordered phases: in the
paramagnetic phase the susceptibility is maximum along the $\langle111\rangle$
directions, while the magnetic moments orient along $\langle110\rangle$ or
$\langle100\rangle$ in the ordered phase. We suggest that such ""anisotropy
switching"" can be a common feature of strongly spin-orbit coupled magnets.",1504.07607v1
2015-07-20,On the Unique Reconstruction of Induced Spherical Magnetizations,"Recovering spherical magnetizations $m$ from magnetic field data in the
exterior is a highly non-unique problem. A spherical Hardy-Hodge decomposition
supplies information on what contributions of the magnetization $m$ are
recoverable but it does not supply geophysically suitable constraints on $m$
that would guarantee uniqueness for the entire magnetization. In this paper, we
focus on the case of induced spherical magnetizations and show that uniqueness
is guaranteed if one assumes that the magnetization is compactly supported on
the sphere. The results are based on ideas presented in Baratchart et al.
(2013) for the planar setting.",1507.07570v3
2015-10-27,Evidence for a re-entrant character of magnetism of sigma-phase Fe-Mo alloys: non-linear susceptibilities,"Non-linear ac magnetic susceptibility terms viz. quadratic, chi2, and cubic,
chi3, were measured versus temperature and frequency for a series of the
sigma-phase Fe(100-x)Mo(x) (47<x<53) compounds. Clear evidence was found that
the ground magnetic state of the samples is mixed i.e. constituted by two
phases: a spin glass (SG) and a ferromagnet (FM), hence the magnetism of the
investigated samples can be regarded as re-entrant (RSG). Based on the present
data, previously reported magnetic phase diagram has been upgraded [J.
Przewoznik, S. M. Dubiel,J. Alloy. Comp., 630 (2015) 222].",1510.07811v1
2015-11-12,Influence of intermolecular interactions on magnetic observables,"Very often it is an implied paradigm of molecular magnetism that magnetic
molecules in a crystal interact so weakly that measurements of dc magnetic
observables reflect ensemble properties of single molecules. But the number of
cases where the assumption of virtually non-interacting molecules does not hold
grows steadily. A deviation from the non-interacting case can especially
clearly be seen in clusters with antiferromagnetic couplings, where steps of
the low-temperature magnetization curve are smeared out with increasing
intermolecular interaction. In this investigation we demonstrate with examples
in one-, two, and three space dimensions how intermolecular interactions
influence typical magnetic observables such as magnetization, susceptibility
and specific heat.",1511.03856v1
2015-11-12,Magnetization switching by microwaves initially rotating in opposite direction to precession,"A common understanding of magnetization switching in microwave-assisted
magnetization reversal is that the rotation direction of the microwaves should
be the same with the precession direction of the magnetization. In this letter
however, we show that microwaves initially rotating opposite to the
magnetization precession destabilize the magnetization at an equilibrium and
induces the switching more efficiently, when the microwave frequency depends on
time. This argument is analytically deduced from energy balance equation. We
also establish a model satisfying this condition, and confirm magnetization
switching solely by microwaves by using numerical simulation.",1511.04051v1
2016-01-22,Phenomenological Magnetic Model in Tsai-Type Approximants,"Motivated by recent discovery of canted ferromagnetism in Tsai-type
approximants Au-Si-RE (RE = Tb, Dy, Ho), we propose a phenomenological magnetic
model reproducing their magnetic structure and thermodynamic quantities. In the
model, cubic symmetry ($m\bar{3}$) of the approximately-regular icosahedra
plays a key role in the peculiar magnetic structure determined by a neutron
diffraction experiment. Our magnetic model does not only explain magnetic
behaviors in the quasicrystal approximants, but also provides a good starting
point for the possibility of coexistence between magnetic long-range order and
aperiodicity in quasicrystals.",1601.05905v1
2016-01-23,Nonlinear magnetization dynamics of antiferromagnetic spin resonance induced by intense terahertz magnetic field,"We report on the nonlinear magnetization dynamics of a HoFeO3 crystal induced
by a strong terahertz magnetic field resonantly enhanced with a split ring
resonator and measured with magneto-optical Kerr effect microscopy. The
terahertz magnetic field induces a large change (~40%) in the spontaneous
magnetization. The frequency of the antiferromagnetic resonance decreases in
proportion to the square of the magnetization change. A modified
Landau-Lifshitz-Gilbert equation with a phenomenological nonlinear damping term
quantitatively reproduced the nonlinear dynamics.",1601.06213v1
2016-03-29,Switching local magnetization by electric-field-induced domain wall motion,"Electric field effect on magnetism is an appealing technique for manipulating
the magnetization at a low cost of energy. Here, we show that the local
magnetization of the ultra-thin Co film can be switched by just applying a gate
electric field without an assist of any external magnetic field or current
flow. The local magnetization switching is explained by the nucleation and
annihilation of the magnetic domain through the domain wall motion induced by
the electric field. Our results lead to external field free and ultra-low
energy spintronic applications.",1603.08688v1
2016-06-30,Quantized chiral magnetic current from reconnections of magnetic flux,"We introduce a new mechanism for the chiral magnetic effect that does not
require an initial chirality imbalance. The chiral magnetic current is
generated by reconnections of magnetic flux that change the magnetic helicity
of the system. The resulting current is entirely determined by the change of
magnetic helicity, and it is quantized.",1606.09611v2
2016-07-08,Third Order Perturbed Energy of Cobalt Ferrite Thick Films,"Magnetic properties and easy axis orientation of cobalt ferrite films with
applied magnetic field and number of layers were studied. According to our
theoretical studies explained in this manuscript, the magnetically easy and
hard directions of cobalt ferrite films solely depend on in plane and out of
plane magnetic fields. According to 3-D and 2-D plots, there are many easy and
hard directions at one particular value of in plane or out of plane magnetic
field. The magnetic properties were investigated for cobalt ferrite films with
thickness up to 10,000 unit cells. The total magnetic energy was calculated for
a unit spin of cobalt.",1607.02323v1
2016-10-20,Dual atomic interferometer with a tunable point of minimum magnetic sensitivity,"Atomic interferometers are often affected by magnetic field fluctuations.
Using the clock transition at zero magnetic field minimizes the effect of these
fluctuations. There is another transition in rubidium that minimizes the
magnetic sensitivity at 3.2 G.We combine the previous two transitions to obtain
minimum magnetic sensitivity at a tunable magnetic field between 2.2 and 3.2 G.
The two interferometers evolve independently from each other and we control the
magnetic sensitivity by changing the population in both transitions with a
microwave pulse.",1610.06271v2
2016-12-10,Origin of Strong Magnetic Fields of Magnetars,"Since there is 3P2 neutron superfluid in neutron star interior, it can be
treated as a system of magnetic dipoles. Under the presence of background
magnetic field, the magnetic dipoles tend to align in the same direction. When
the temperature is lower than 10**7K, the strong magnetic fields of the
magnetars may originate from the induced magnetic moment of the 3P2 neutron
Cooper pairs in the anisotropic neutron superfluid. And this gives a convenient
explanation of the strong magnetic field of magnetars.",1612.04656v1
2017-01-01,Electrical Transport of perpendicularly magnetized L10-MnGa and MnAl films,"Ferromagnetic films of L10-ordered MnGa and MnAl that exhibit giant
perpendicular magnetic anisotropy and great controllability in the magnetism
and structural disorders show promise not only in the applications in magnetic
recording, permanent magnets and spintronics, but also in controllable studies
of disorder-relevant electrical transport phenomena. In this article, we review
the intriguing experimental observations of the orbital two-channel Kondo
effect and anomalous Hall effect in L10-ordered MnGa and MnAl thin films with
perpendicular magnetic anisotropy. We also give a perspective with regards to
the future technological and fundamental applications of these perpendicularly
magnetized Mn-based binary alloy films.",1701.00191v1
2017-01-30,On slowly rotating magnetized white dwarfs,"Rotating magnetized white dwarfs are studied within the framework of general
relativity using Hartle's formalism. Matter inside magnetized white dwarfs is
described by an equation of state of particles under the action of a constant
magnetic field which introduces anisotropic pressures. Our study is done for
values of magnetic field below $10^{13}$ G -a threshold of the maximum magnetic
field obtained by the cylindrical metric solution- and typical densities of
WDs. The effects of the rotation and magnetic field combined are discussed, we
compute relevant magnitudes such as the moment of inertia, quadrupole moment
and eccentricity.",1701.08792v1
2017-04-23,Controlling the Kelvin Force: Basic Strategies and Applications to Magnetic Drug Targeting,"Motivated by problems arising in magnetic drug targeting, we propose to
generate an almost constant Kelvin (magnetic) force in a target subdomain,
moving along a prescribed trajectory. This is carried out by solving a
minimization problem with a tracking type cost functional. The magnetic sources
are assumed to be dipoles and the control variables are the magnetic field
intensity, the source location and the magnetic field direction. The resulting
magnetic field is shown to effectively steer the drug concentration, governed
by a drift-diffusion PDE, from an initial to a desired location with limited
spreading.",1704.06872v1
2017-06-05,Generalized magnetic mirrors,"We propose generalized magnetic mirrors that can be achieved by excitations
of sole electric resonances. Conventional approaches to obtain magnetic mirrors
rely heavily on exciting the fundamental magnetic dipoles, whereas here we
reveal that besides magnetic resonances, electric resonances of higher orders
can be also employed to obtain highly efficient magnetic mirrors. Based on the
electromagnetic duality, it is also shown that electric mirrors can be achieved
by exciting magnetic resonances. We provide direct demonstrations of the
generalized mirrors proposed in a simple system of one-dimensional periodic
array of all-dielectric wires, which may shed new light to many advanced fields
of photonics related to resonant multipolar excitations and interferences.",1706.01398v2
2018-01-16,Neutron Anomalous Magnetic Moment in Dense Magnetized Systems,"In this work, we calculate the neutron anomalous magnetic moment supposing
that this value can depend on the density and magnetic field of system. We
employ the lowest order constraint variation (LOCV) method and $AV_{18}$
nuclear potential to calculate the medium dependency of the neutron anomalous
magnetic moment. It is confirmed that the neutron anomalous magnetic moment
increases by increasing the density, while it decreases as the magnetic field
grows. The energy and equation of state for the system have also been
investigated.",1801.05277v1
2018-01-30,Possible relation between pulsar rotation and evolution of magnetic inclination,"The pulsar timing is observed to be different from predicted by a simple
magnetic dipole radiation. We choose eight pulsars whose braking index was
reliably determined. Assuming the smaller values of braking index are dominated
by the secular evolution of the magnetic inclination, we calculate the
increasing rate of the magnetic inclination for each pulsar. We find a possible
relation between the rotation frequency of each pulsar and the inferred
evolution of the magnetic inclination. Due to the model-dependent fit of the
magnetic inclination and other effects, more observational indicators for the
change rate of magnetic inclination are needed to test the relation.",1801.09915v1
2018-02-22,Phase transition of vortex states in two-dimensional superconductors under a oscillating magnetic field from the chiral helimagnet,"We have investigated vortex states in two-dimensional superconductors under a
oscillating magnetic field from a chiral helimagnet. We have solved the
two-dimensional Ginzburg-Landau equations with finite element method. We have
found that when the magnetic field from the chiral helimagnet increases,
vortices appear all at once in all periodic regions. This transition is
different from that under the uniform magnetic field. Under the composite
magnetic field with the oscillating and uniform fields (down-vortices),
vortices antiparallel to the uniform magnetic field disappear. Then, the small
uniform magnetic field easily remove down-vortices.",1802.07937v1
2018-03-19,Dynamics of a Magnetic Needle Magnetometer: Sensitivity to Landau-Lifshitz-Gilbert Damping,"An analysis of a single-domain magnetic needle in the presence of an external
magnetic field ${\bf B}$ is carried out with the aim of achieving a high
precision magnetometer. We determine the uncertainty $\Delta B$ of such a
device due to Gilbert dissipation and the associated internal magnetic field
fluctuations that gives rise to diffusion of the magnetic needle axis direction
${\bf n}$ and the needle orbital angular momentum. The levitation of the
magnetic needle in a magnetic trap and its stability are also analyzed.",1803.10064v2
2018-12-20,Self-Organized Criticality of Domain Walls and Magnetization Curve,"We propose a kind of Ginzburg--Landau equation with quenched randomness.
There is a pinning--depinning transition in the system when the external
magnetic force is changed. The transition is self-organized when the external
magnetic field is slowly changed under the demagnetizing effect. The total
magnetization increases stepwise and the probability distribution of the
increase in the total magnetization approximately obeys a power law. A
hysteresis loop is obtained when the external magnetic field is changed
reciprocally. In our model, the coercivity in the magnetization curve is
expressed as the critical value for the pinning-depinning transition.",1812.08344v1
2019-04-22,Problematic nature of plasmoid theory of magnetic reconnection,"Plasmoid theory uses two-coordinate models to explain fast magnetic
reconnection, which occurs on an Alfv\'enic, not a resistive time scale, in
plasmas that are evolving in the near-ideal limit. The primary application has
been to three-dimensional naturally-occurring plasmas. A magnetic field
representation that applies to all magnetic fields allows features of magnetic
evolution in toroidal and natural plasmas to be compared. This comparison
illustrates why plasmoid models of magnetic field evolution are not robust
solutions to Maxwell's equations. Despite five-hundred papers on plasmoid
models, they provide a problematic description of fast magnetic reconnection.",1904.09836v2
2019-07-02,Stellarators with permanent magnets,"It is shown that the magnetic-field coils of a stellarator can, at least in
principle, be substantially simplified by the use of permanent magnets. Such
magnets cannot create toroidal magnetic flux but they can be used to shape the
plasma and thus to create poloidal flux and rotational transform, thereby
easing the requirements on the magnetic-field coils. As an example, a
quasiaxisymmetric stellarator configuration is constructed with only 8 circular
coils (all identical) and permanent magnets.",1907.01363v2
2019-07-30,Graphical Magnetogranulometry of EMG909,"The magnetization curve of the ferrofluid EMG909 is measured. It can
adequately be described by a superposition of four Langevin terms. The
effective dipole strength of the magnetic particles in this fluid is
subsequently obtained by a graphical rectification of the magnetization curve
based on the inverse Langevin function. The method yields the arithmetic and
the harmonic mean of the magnetic moment distribution function, and a guess for
the geometric mean and the relative standard deviation. It has the advantage
that it does not require a prejudiced guess of the distribution function of the
poly-disperse suspension of magnetic particles.",1907.12779v2
2020-01-17,Generation of focusing ion beams by magnetized electron sheath acceleration,"We present the first 3D particle-in-cell simulations of laser driven
sheath-based ion acceleration in a kilotesla-level applied magnetic field. The
applied magnetic field creates two distinct stages in the acceleration process
associated with the time-evolving magnetization of the hot electron sheath and
results in a focusing, magnetic field-directed ion source of multiple species
with strongly enhanced energy and number. The benefits of adding the magnetic
field are downplayed in 2D simulations, which strongly suggests the feasibility
of observing magnetic field effects under experimentally relevant conditions.",2001.06117v1
2020-02-17,Periodic Magnetic Geodesics on Heisenberg Manifolds,"We study the dynamics of magnetic flows on Heisenberg groups. Let $H$ denote
the three-dimensional simply connected Heisenberg Lie group endowed with a
left-invariant Riemannian metric and an exact, left-invariant magnetic field.
Let $\Gamma$ be a lattice subgroup of $H,$ so that $\Gamma\backslash H$ is a
closed nilmanifold. We first find an explicit description of magnetic geodesics
on $H$, then determine all closed magnetic geodesics and their lengths for
$\Gamma \backslash H$. We then consider two applications of these results: the
density of periodic magnetic geodesics and marked magnetic length spectrum
rigidity.",2002.06982v1
2020-12-23,Magnetic Moment Tensor Potentials for collinear spin-polarized materials reproduce different magnetic states of bcc Fe,"We present the magnetic Moment Tensor Potentials (mMTPs), a class of
machine-learning interatomic potentials, accurately reproducing both
vibrational and magnetic degrees of freedom as provided, e.g., from
first-principles calculations. The accuracy is achieved by a two-step
minimization scheme that coarse-grains the atomic and the spin space. The
performance of the mMTPs is demonstrated for the prototype magnetic system bcc
iron, with applications to phonon calculations for different magnetic states,
and molecular dynamics simulations with fluctuating magnetic moments.",2012.12763v2
2021-07-08,Warm Magnets,"Warm magnets are magnets that function in normal ambient temperature
conditions. These types are mostly using a soft steel yoke for field
amplification and either Copper or Aluminium coils or permanent magnets to
generate the field. Magnets powered with such normal-conducting coils are often
also called classical, iron dominated or resistive magnets. Since decades these
types of magnets are the workhorse for most linear and circular accelerators
and beam transfer lines.",2107.03965v1
2022-01-25,Design and Description of the CMS Magnetic System Model,"This review describes the composition of the Compact Muon Solenoid (CMS)
detector and the methodology for modelling the heterogeneous CMS magnetic
system, starting with the formulation of the magnetostatics problem for
modelling the magnetic flux of the CMS superconducting solenoid enclosed in a
steel flux-return yoke. The review includes a section on the magnetization
curves of various types of steel used in the CMS magnet yoke. The evolution of
the magnetic system model over 20 years is presented in the discussion section
and is well illustrated by the CMS model layouts and the magnetic flux
distribution.",2201.10478v1
2022-03-22,Nanoscale magnetism probed in a matter-wave interferometer,"We explore a wide range of fundamental magnetic phenomena by measuring the
dephasing of matter-wave interference fringes upon application of a variable
magnetic gradient. The versatility of our interferometric Stern-Gerlach
technique enables us to study alkali atoms, organic radicals and fullerenes in
the same device, with magnetic moments ranging from a Bohr magneton to less
than a nuclear magneton. We find evidence for magnetization of a supersonic
beam of organic radicals and, most notably, observe a strong magnetic response
of a thermal C$_{60}$ beam consistent with high-temperature atom-like
deflection of rotational magnetic moments.",2203.11866v1
2022-04-15,Energy Extraction via Magnetic Reconnection in the Ergosphere of a rotating non-Kerr Black Hole,"Magnetic reconnection process in the ergosphere is investigated for a
relativistic plasma around a rotating non-Kerr black hole. For a rotating
non-Kerr black hole immersed in magnetic field generated by an externally
material, anti-parallel magnetic field line could form in the ergosphere due to
the frame dragging. Therefore, magnetic reconnection could occur in the
ergosphere. Such magnetic reconnection may generate negative energy at infinity
by redistributing the angular momentum during the process. The results show
that, with the effect of the deformed parameter, extraction of energy from a
rotating non-Kerr black hole by magnetic reconnection could be enhanced in the
presence of a positive deformed parameter.",2204.07338v1
2022-06-21,Magnetic Forces in Paramagnetic Fluids,"An overview of the effect of a magnetic field gradient on fluids with linear
magnetic susceptibilities is given. It is shown that two commonly encountered
expressions, the magnetic field gradient force and the concentration gradient
force for paramagnetic species in solution are equivalent for incompressible
fluids. The magnetic field gradient and concentration gradient forces are
approximations of the Kelvin force and Korteweg-Helmholtz force densities,
respectively. The criterion for the appearance of magnetically induced
convection is derived. Experimental work in which magnetically induced
convection plays a role is reviewed.",2206.10529v4
2022-09-09,Quantum Stoner-Wohlfarth model of two-dimensional single domain magnets,"The Stoner-Wohlfarth (SW) model is a classical model for magnetic hysteresis
of single-domain particles. For two-dimensional magnets at finite temperature,
the SW model must be extended to include intrinsic strong spin fluctuations. We
predict several fundamentally different hysteresis properties between 2D and 3D
magnets. The magnetization switching diagram known as the Asteroid figure in
the conventional SW model becomes highly temperature dependent and asymmetric
with respect to the transverse and longitudinal magnetic fields. Our results
provide new insights for 2D magnetic materials based spintronics applications.",2209.04479v1
2022-10-16,On the angular anisotropy of the randomly-averaged magnetic neutron scattering cross section of nanoparticles,"We calculate the magnetic SANS cross section of dilute ensembles of uniformly
magnetized and randomly-oriented Stoner-Wohlfarth particles using the
Landau-Lifshitz equation. The focus of our study is on the angular anisotropy
of the magnetic SANS signal as it can be seen on a two-dimensional
position-sensitive detector. Depending on the symmetry of the magnetic
anisotropy of the particles (e.g. uniaxial, cubic), an anisotropic magnetic
SANS pattern may result, even in the demagnetized state or at the coercive
field. The case of inhomogeneously magnetized particles and the effects of a
particle-size distribution and interparticle correlations are discussed.",2210.08406v1
2022-10-23,An experimental analysis from the magnetic interactions in nanowire arrays,"We study the magnetic interactions experimentally in nanostructures of
nanowire arrays. The intensity value obtained from the interactions provides
information about its magnetic behavior. We observed two types of experimental
magnetic behavior, i. e., demagnetized and magnetized. Our approach represents
the first experimental way to analyze the magnetic behavior of a nanostructure
considering its magnetic dependence, which is very important for applications
in sensors, for example.",2210.12783v1
2022-12-29,Magnetically enhanced thin film coarsening by a magnetic XPFC model allowing to decouple magnetic anisotropy and magnetostriction,"External magnetic fields provide a macroscopic control mechanism to influence
the microstructure of polycrystalline materials. We model the influence of
strong magnetic fields on grain growth in thin films with a magnetic extended
phase field crystal (XPFC) model. The magneto-structural effects are
incorporated into the correlation function in reciprocal space. With this
approach magnetic anisotropy, magnetostriction and mobility of grain boundary
can be controlled and a variety of geometrical and topological properties
consistent with experimental results can be determined.",2212.14416v1
2023-02-26,Low-temperature thermal Hall conductivity of Pr2Zr2O7 single crystal,"To probe the peculiar excitations spinons and magnetic monopoles in the
quantum spin ice candidate Pr2Zr2O7, we studied the low-temperature thermal
Hall conductivity (\k{appa}xy) and thermal conductivity (\k{appa}xx) of
Pr2Zr2O7 single crystal with magnetic fields applied along the [111] axis. The
magnetic field dependencies of \k{appa}xx suggest the roles of magnetic
excitations in thermal conductivity, that is, the emergent magnetic monopoles
can transport heat at T > 1.4 K and spinons mainly scatter phonons at lower
temperatures. The finite \k{appa}xy was observed at low fields of several Tesla
and was discussed to be related to the magnetic excitations, including magnetic
monopoles as well as spinons.",2302.13300v1
2023-04-27,Effective Tight-Binding Model of Compensated Ferrimagnetic Weyl Semimetal with Spontaneous Orbital Magnetization,"The effective tight-binding model with compensated ferrimagnetic
inverse-Heusler lattice Ti$_{2}$MnAl, candidate material of magnetic Weyl
semimetal, is proposed. The energy spectrum near the Fermi level, the
configurations of the Weyl points, and the anomalous Hall conductivity are
calculated. We found that the orbital magnetization is finite, while the total
spin magnetization vanishes, at the energy of the Weyl points. The magnetic
moments at each site are correlated with the orbital magnetization, and can be
controlled by the external magnetic field.",2304.14009v1
2023-07-02,Unveiling Stable One-dimensional Magnetic Solitons in Magnetic Bilayers,"We propose a novel model which efficiently describes the magnetization
dynamics in a magnetic bilayer system. By applying a particular gauge
transformation to the Landau-Lifshitz-Gilbert (LLG) equation, we successfully
convert the model into an exactly integrable framework. Thus the obtained
analytical solutions allows us to predict a 1D magnetic soliton pair existed by
tunning the thickness of the spacing layer between the two ferrimagnetic
layers. The decoupling-unlocking-locking transition of soliton motion is
determined at various interaction intensitiy. Our results have implications for
the manipulation of magnetic solitons and the design of magnetic soliton-based
logic devices.",2307.00471v1
2023-07-04,Phonon-induced magnetization dynamics in Co-doped iron garnets,"The developing field of strain-induced magnetization dynamics offers a
promising path toward efficiently controlling spins and phase transitions.
Understanding the underlying mechanisms is crucial in finding the optimal
parameters supporting the phononic switching of magnetization. Here, we present
an experimental and numerical study of time-resolved magnetization dynamics
driven by the resonant excitation of an optical phonon mode in iron garnets.
Upon pumping the latter with an infrared pulse obtained from a free-electron
laser, we observe spatially-varying magnetization precession, with its phase
depending on the direction of an external magnetic field. Our micromagnetic
simulations effectively describe the magnetization precession and switching in
terms of laser-induced changes in the crystal's magneto-elastic energy.",2307.01907v1
2024-02-29,Magnetic catalysis and diamagnetism from pion fluctuations,"In the framework of Nambu--Jona-Lasinio model beyond mean field
approximation, the effects of pion fluctuations on (inverse) magnetic catalysis
and magnetic susceptibility are studied. The negative magnetic susceptibility
at low temperature is observed when contributions from both neutral and charged
pions are taken into account. In weak field approximation, it is observed that
at finite temperature, the magnetic inhibition effect in the chiral limit,
resulting from the difference between the transverse and longitudinal
velocities of neutral pions, converts to weak magnetic catalysis when
considering a non-zero current quark mass. Moreover, the magnetic catalysis is
amplified by the charged pions.",2402.19193v1
2007-03-08,3D Relativistic Magnetohydrodynamic Simulations of Magnetized Spine-Sheath Relativistic Jets,"Numerical simulations of weakly magnetized and strongly magnetized
relativistic jets embedded in a weakly magnetized and strongly magnetized
stationary or weakly relativistic (v = c/2) sheath have been performed. A
magnetic field parallel to the flow is used in these simulations performed by
the new GRMHD numerical code RAISHIN used in its RMHD configuration. In the
numerical simulations the Lorentz factor $\gamma = 2.5$ jet is precessed to
break the initial equilibrium configuration. In the simulations sound speeds
are $\lesssim c/\sqrt 3$ in the weakly magnetized simulations and $\lesssim
0.3c$ in the strongly magnetized simulations. The Alfven wave speed is
$\lesssim 0.07c$ in the weakly magnetized simulations and $\lesssim 0.56c$ in
the strongly magnetized simulations. The results of the numerical simulations
are compared to theoretical predictions from a normal mode analysis of the
linearized relativistic magnetohydrodynamic (RMHD) equations capable of
describing a uniform axially magnetized cylindrical relativistic jet embedded
in a uniform axially magnetized relativistically moving sheath. The theoretical
dispersion relation allows investigation of effects associated with maximum
possible sound speeds, Alfven wave speeds near light speed and relativistic
sheath speeds. The prediction of increased stability of the weakly magnetized
system resulting from c/2 sheath speeds and the stabilization of the strongly
magnetized system resulting from c/2 sheath speeds is verified by the numerical
simulation results.",0703190v1
1999-11-03,Flux pinning by regular arrays of ferromagnetic dots,"The pinning of flux lines by two different types of regular arrays of
submicron magnetic dots is studied in superconducting Pb films; rectangular Co
dots with in-plane magnetization are used as pinning centers to investigate the
influence of the magnetic stray field of the dots on the pinning phenomena,
whereas multilayered Co/Pt dots with out-of-plane magnetization are used to
study the magnetic interaction between the flux lines and the magnetic moment
of the dots. For both types of pinning arrays, matching anomalies are observed
in the magnetization curves versus perpendicular applied field at integer and
rational multiples of the first matching field, which correspond to stable flux
configurations in the artificially created pinning potential. By varying the
magnetic domain structure of the Co dots with in-plane magnetization, a clear
influence of the stray field of the dots on the pinning efficiency is found.
For the Co/Pt dots with out-of-plane magnetization, a pronounced field
asymmetry is observed in the magnetization curves when the dots are magnetized
in a perpendicular field prior to the measurement. This asymmetry can be
attributed to the interaction of the out-of-plane magnetic moment of the Co/Pt
dots with the local field of the flux lines and indicates that flux pinning is
stronger when the magnetic moment of the dot and the field of the flux line
have the same polarity.",9911033v1
2006-12-13,A Model for Predicting Magnetic Targeting of Multifunctional Particles in the Microvasculature,"A mathematical model is presented for predicting magnetic targeting of
multifunctional carrier particles that are designed to deliver therapeutic
agents to malignant tissue in vivo. These particles consist of a nonmagnetic
core material that contains embedded magnetic nanoparticles and therapeutic
agents such as photodynamic sensitizers. For in vivo therapy, the particles are
injected into the vascular system upstream from malignant tissue, and captured
at the tumor using an applied magnetic field. The applied field couples to the
magnetic nanoparticles inside the carrier particle and produces a force that
attracts the particle to the tumor. In noninvasive therapy the applied field is
produced by a permanent magnet positioned outside the body. In this paper a
mathematical model is developed for predicting noninvasive magnetic targeting
of therapeutic carrier particles in the microvasculature. The model takes into
account the dominant magnetic and fluidic forces on the particles and leads to
an analytical expression for predicting their trajectory. An analytical
expression is also derived for predicting the volume fraction of embedded
magnetic nanoparticles required to ensure capture of the carrier particle at
the tumor. The model enables rapid parametric analysis of magnetic targeting as
a function of key variables including the size of the carrier particle, the
properties and volume fraction of the embedded magnetic nanoparticles, the
properties of the magnet, the microvessel, the hematocrit of the blood and its
flow rate.",0612116v1
2007-06-27,Magnetic Energy and Helicity Budgets in the Active-Region Solar Corona. I. Linear Force-Free Approximation,"We self-consistently derive the magnetic energy and relative magnetic
helicity budgets of a three-dimensional linear force-free magnetic structure
rooted in a lower boundary plane. For the potential magnetic energy we derive a
general expression that gives results practically equivalent to those of the
magnetic Virial theorem. All magnetic energy and helicity budgets are
formulated in terms of surface integrals applied to the lower boundary, thus
avoiding computationally intensive three-dimensional magnetic field
extrapolations. We analytically and numerically connect our derivations with
classical expressions for the magnetic energy and helicity, thus presenting a
so-far lacking unified treatment of the energy/helicity budgets in the
constant-alpha approximation. Applying our derivations to photospheric vector
magnetograms of an eruptive and a noneruptive solar active regions, we find
that the most profound quantitative difference between these regions lies in
the estimated free magnetic energy and relative magnetic helicity budgets. If
this result is verified with a large number of active regions, it will advance
our understanding of solar eruptive phenomena. We also find that the
constant-alpha approximation gives rise to large uncertainties in the
calculation of the free magnetic energy and the relative magnetic helicity.
Therefore, care must be exercised when this approximation is applied to
photospheric magnetic field observations. Despite its shortcomings, the
constant-alpha approximation is adopted here because this study will form the
basis of a comprehensive nonlinear force-free description of the energetics and
helicity in the active-region solar corona, which is our ultimate objective.",0706.4122v1
2008-08-06,Cluster Magnetic Fields from Galactic Outflows,"We performed cosmological, magneto-hydrodynamical simulations to follow the
evolution of magnetic fields in galaxy clusters, exploring the possibility that
the origin of the magnetic seed fields are galactic outflows during the
star-burst phase of galactic evolution. To do this we coupled a semi-analytical
model for magnetized galactic winds as suggested by \citet{2006MNRAS.370..319B}
to our cosmological simulation. We find that the strength and structure of
magnetic fields observed in galaxy clusters are well reproduced for a wide
range of model parameters for the magnetized, galactic winds and do only weakly
depend on the exact magnetic structure within the assumed galactic outflows.
Although the evolution of a primordial magnetic seed field shows no significant
differences to that of galaxy clusters fields from previous studies, we find
that the magnetic field pollution in the diffuse medium within filaments is
below the level predicted by scenarios with pure primordial magnetic seed
field. We therefore conclude that magnetized galactic outflows and their
subsequent evolution within the intra-cluster medium can fully account for the
observed magnetic fields in galaxy clusters. Our findings also suggest that
measuring cosmological magnetic fields in low-density environments such as
filaments is much more useful than observing cluster magnetic fields to infer
their possible origin.",0808.0919v2
2008-08-27,Magnetic phase evolution in the spinel compounds Zn$_{1-x}$Co$_x$Cr$_2$O$_4$,"We present the magnetic properties of complete solid solutions of
ZnCr$_2$O$_4$ and CoCr$_2$O$_4$: two well-studied oxide spinels with very
different magnetic ground states. ZnCr$_2$O$_4$, with non-magnetic $d^{10}$
cations occupying the A site and magnetic $d^3$ cations on the B site, is a
highly frustrated antiferromagnet. CoCr$_2$O$_4$, with magnetic $d^7$ cations
(three unpaired electrons) on the A site as well, exhibits both N\'eel
ferrimagnetism as well as commensurate and incommensurate non-collinear
magnetic order. More recently, CoCr$_2$O$_4$ has been studied extensively for
its polar behavior which arises from conical magnetic ordering. Gradually
introducing magnetism on the A site of ZnCr$_2$O$_4$ results in a transition
from frustrated antiferromagnetism to glassy magnetism at low concentrations of
Co, and eventually to ferrimagnetic and conical ground states at higher
concentrations. Real-space Monte-Carlo simulations of the magnetic
susceptibility suggest that the first magnetic ordering transition and features
of the susceptibility across $x$ are captured by near-neighbor self- and
cross-couplings between the magnetic A and B atoms. We present as a part of
this study, a method for displaying the temperature dependence of magnetic
susceptibility in a manner which helps distinguish between compounds possessing
purely antiferromagnetic interactions from compounds where other kinds of
ordering are present.",0808.3789v3
2010-07-28,A Theory about Electric Current and Heating in Plasma,"The traditional generalized Ohm's law in MHD do not explicitly present the
relation of electric currents and electric fields in fully ionized plasma, and
lead to some unexpected concepts, such as ""the magnetic frozen-in plasma"",
magnetic reconnection etc. In the present paper, we solve the balance equation
can give exact solution of the velocities of electrons and ions, and then
derived the electric current in fully ionized plasma. In the case ignoring
boundary condition, there is no electric current in the plane perpendicular to
the magnetic field when external forces are ignored. The electric field in the
plane perpendicular to magnetic field do not contribute to the electric
currents, so do the induced electric field from the motion of the plasma across
magnetic field. The lack of induced electric current will keep magnetic field
in space unaffected. The velocity of the bulk velocity of the plasma
perpendicular to magnetic field is not free, it is decided by electromagnetic
field and the external forces. We conclude that the bulk velocity of the fully
ionized plasma is not coupled with the magnetic field. The motion of the plasma
do not change the magnetic field in space, but the plasma will be confined by
magnetic field.
  Due to the confinement of magnetic field, the plasma kinetic energy will be
transformed into plasma thermal energy by the Lamor motion and collisions
between the same species of particles inside plasma. Because the electric field
perpendicular to magnetic field do not contribute electric current, the
variation of magnetic field will transfer energy directly into the plasma
thermal energy by induced electric field. The heating of plasma could be from
the kinetic energy and the variation of magnetic field.",1007.4959v1
2011-03-05,Physics and measurements of magnetic materials,"Magnetic materials, both hard and soft, are used extensively in several
components of particle accelerators. Magnetically soft iron-nickel alloys are
used as shields for the vacuum chambers of accelerator injection and extraction
septa; Fe-based material is widely employed for cores of accelerator and
experiment magnets; soft spinel ferrites are used in collimators to damp
trapped modes; innovative materials such as amorphous or nanocrystalline core
materials are envisaged in transformers for high-frequency polyphase resonant
convertors for application to the International Linear Collider (ILC). In the
field of fusion, for induction cores of the linac of heavy-ion inertial fusion
energy accelerators, based on induction accelerators requiring some 107 kg of
magnetic materials, nanocrystalline materials would show the best performance
in terms of core losses for magnetization rates as high as 105 T/s to 107 T/s.
After a review of the magnetic properties of materials and the different types
of magnetic behaviour, this paper deals with metallurgical aspects of
magnetism. The influence of the metallurgy and metalworking processes of
materials on their microstructure and magnetic properties is studied for
different categories of soft magnetic materials relevant for accelerator
technology. Their metallurgy is extensively treated. Innovative materials such
as iron powder core materials, amorphous and nanocrystalline materials are also
studied. A section considers the measurement, both destructive and
non-destructive, of magnetic properties. Finally, a section discusses magnetic
lag effects.",1103.1069v1
2011-11-30,Self-Similar Solutions for Viscous and Resistive ADAF,"In this paper, the self-similar solution of resistive advection dominated
accretion flows (ADAF) in the presence of a pure azimuthal magnetic field is
investigated. The mechanism of energy dissipation is assumed to be the
viscosity and the magnetic diffusivity due to turbulence in the accretion flow.
It is assumed that the magnetic diffusivity and the kinematic viscosity are not
constant and vary by position and $\alpha$-prescription is used for them. In
order to solve the integrated equations that govern the behavior of the
accretion flow, a self-similar method is used. The solutions show that the
structure of accretion flow depends on the magnetic field and the magnetic
diffusivity. As, the radial infall velocity and the temperature of the flow
increase, and the rotational velocity decreases. Also, the rotational velocity
for all selected values of magnetic diffusivity and magnetic field is
sub-Keplerian. The solutions show that there is a certain amount of magnetic
field that the rotational velocity of the flow becomes zero. This amount of the
magnetic field depends on the gas properties of the disc, such as adiabatic
index and viscosity, magnetic diffusivity, and advection parameters. The
solutions show the mass accretion rate increases by adding the magnetic
diffusivity and in high magnetic pressure case, the ratio of the mass accretion
rate to the Bondi accretion rate decreases as magnetic field increases. Also,
the study of Lundquist and magnetic Reynolds numbers based on resistivity
indicates that the linear growth of magnetorotational instability (MRI) of the
flow decreases by resistivity. This property is qualitatively consistent with
resistive magnetohydrodynamics (MHD) simulations.",1111.7302v1
2012-03-01,Magnetic properties of carbon nanodisk and nanocone powders,"We have investigated the magnetic properties of carbon powders which consist
of nanodisks, nanocones, and a small fraction of carbon-black particles.
Magnetization measurements were carried out using a superconducting quantum
interference device in magnetic fields $-5<\mu_{0}H<5\:\mathrm{T}$ for
temperatures in the range $2\leq T<350\:\mathrm{K}$. Measurements of the
magnetization $M$ versus temperature $T$ and magnetic field $\mu_{0}H$ for
these carbon samples show diamagnetism and paramagetism with an additional
ferromagnetic contribution. The ferromagnetic magnetization is in agreement
with the calculated magnetization from Fe impurities as determined by the
particle-induced x-ray emission method ($<75\:\mu\mathrm{g/g}$). Magnetization
measurements in weak magnetic fields show thermal hysteresis, and for strong
fields the magnetization $M$ decreases as $M\sim aT^{-\alpha}$ with $\alpha<1$,
which is slower than the Curie law ($\alpha=1$), when the temperature
increases. The magnetization $M$ versus magnetic field $\mu_{0}H$ shows
paramagnetic free-spin $S=\frac{1}{2}$ and $\frac{3}{2}$ behaviors for
temperatures $T=2\:\mathrm{K}$ and $15\leq T\leq50\:\mathrm{K}$, respectively.
A tendency for localization of electrons was found by electron spin resonance
when the temperature $T$ decreases ($2<T<40\:\mathrm{K}$). The magnetic
properties in these carbon cone and disk powder samples are more complex than a
free-spin model predicts, which is apparently valid only for the temperature
$T=2\:\mathrm{K}$.",1203.0284v3
2013-01-21,Increase of magnetic hyperthermia efficiency due to dipolar interactions in low anisotropy magnetic nanoparticles : theoretical and experimental results,"When magnetic nanoparticles (MNPs) are single-domain and magnetically
independent, their magnetic properties and the conditions to optimize their
efficiency in magnetic hyperthermia applications are now well-understood.
However, the influence of magnetic interactions on magnetic hyperthermia
properties is still unclear. Here, we report hyperthermia and high-frequency
hysteresis loop measurements on a model system consisting of MNPs with the same
size but a varying anisotropy, which is an interesting way to tune the relative
strength of magnetic interactions. A clear correlation between the MNP
anisotropy and the squareness of their hysteresis loop in colloidal solution is
observed : the larger the anisotropy, the smaller the squareness. Since low
anisotropy MNPs display a squareness higher than the one of magnetically
independent nanoparticles, magnetic interactions enhance their heating power in
this case. Hysteresis loop calculations of independent and coupled MNPs are
compared to experimental results. It is shown that the observed features are a
natural consequence of the formation of chains and columns of MNPs during
hyperthermia experiments: in these structures, when the MNP magnetocristalline
anisotropy is small enough to be dominated by magnetic interactions, the
hysteresis loop shape tends to be rectangular, which enhance their efficiency.
On the contrary, when MNPs do not form chains and columns, magnetic
interactions reduces the hysteresis loop squareness and the efficiency of MNPs
compared to independent ones. The present work should improve the understanding
and interpretation of magnetic hyperthermia experiments.",1301.5590v1
2013-01-25,Does Magnetic Field-Rotation Misalignment Solve the Magnetic Braking Catastrophe in Protostellar Disk Formation?,"Stars form in dense cores of molecular clouds that are observed to be
significantly magnetized. In the simplest case of a laminar (non-turbulent)
core with the magnetic field aligned with the rotation axis, both analytic
considerations and numerical simulations have shown that the formation of a
large, $10^2\au$-scale, rotationally supported protostellar disk is suppressed
by magnetic braking in the ideal MHD limit for a realistic level of core
magnetization. This theoretical difficulty in forming protostellar disks is
termed ""magnetic braking catastrophe"". A possible resolution to this problem,
proposed by \citeauthor{HennebelleCiardi2009} and \citeauthor{Joos+2012}, is
that misalignment between the magnetic field and rotation axis may weaken the
magnetic braking enough to enable disk formation. We evaluate this possibility
quantitatively through numerical simulations. We confirm the basic result of
\citeauthor{Joos+2012} that the misalignment is indeed conducive to disk
formation. In relatively weakly magnetized cores with dimensionless
mass-to-flux ratio $\gtrsim 5$, it enabled the formation of rotationally
supported disks that would otherwise be suppressed if the magnetic field and
rotation axis are aligned. For more strongly magnetized cores, disk formation
remains suppressed, however, even for the maximum tilt angle of $90\degree$. If
dense cores are as strongly magnetized as indicated by OH Zeeman observations
(with a mean dimensionless mass-to-flux ratio $\sim 2$), it would be difficult
for the misalignment alone to enable disk formation in the majority of them. We
conclude that, while beneficial to disk formation, especially for the
relatively weak field case, the misalignment does not completely solve the
problem of catastrophic magnetic braking in general.",1301.6545v1
2013-03-06,Fast Diffusion of Magnetic Field in Turbulence and Origin of Cosmic Magnetism,"Turbulence is believed to play important roles in the origin of cosmic
magnetism. While it is well known that turbulence can efficiently amplify a
uniform or spatially homogeneous seed magnetic field, it is not clear whether
or not we can draw a similar conclusion for a localized seed magnetic field.
The main uncertainty is the rate of magnetic field diffusion on scales larger
than the outer scale of turbulence. To measure the diffusion rate of magnetic
field on those large scales, we perform a numerical simulation in which the
outer scale of turbulence is much smaller than the size of the system. We
numerically compare diffusion of a localized seed magnetic field and a
localized passive scalar. We find that diffusion of the magnetic field can be
much faster than that of the passive scalar and that turbulence can efficiently
amplify the localized seed magnetic field. Based on the simulation result, we
construct a model for fast diffusion of magnetic field. Our model suggests that
a localized seed magnetic field can fill the whole system in (L_sys/L) times
the large-eddy turnover time and that growth of the magnetic field stops in
max(15, L_sys/L) times the large-eddy turnover time, where L_sys is the size of
the system and $L$ is the driving scale. Our finding implies that, regardless
of the shape of the seed field, fast magnetization is possible in turbulent
systems, such as large-scale structure of the universe or galaxies.",1303.1227v1
2013-04-11,Field induced phase transitions and phase diagrams in BiFeO_3-like multiferroics,"The incommensurate magnetic structures and phase diagrams of multiferroics
has been explored on the basis of accurate micromagnetic analysis taking into
account the spin flexoelecric interaction (Lifshitz invariant). The objects of
the study are BiFeO_3-like single crystals and epitaxial films grown on the
<111> substrates. The main control parameters are the magnetic field, the
magnetic anisotropy, and the epitaxial strain in the case of films. We predict
novel quasi-cycloidal structures induced by external magnetic field or by
epitaxial strain in the BiFeO_3-films. Phase diagrams representing the regions
of homogeneous magnetic states and incommensurate structures stability are
constructed for the two essential geometries of magnetic field (magnetic field
oriented parallel to the principal crystal axis C_3 and perpendicular to this
direction C_3). It is shown that the direction of applied magnetic field
substantially affects a set of magnetic phases, properties of incommensurate
structures, character of phase transitions. Novel conical type of cycloidal
ordering is revealed during the transition from incommensurate cycloidal
structure into homogeneous magnetic state. Elaborated phase diagrams allow
estimate appropriate combination of control parameters (magnetic field,
magnetic anisotropy, exchange stiffness) required to the destruction of
cycloidal ordering corresponding to the transition into homogeneous structure.
The results show that the magnitude of critical magnetic field suppressing
cycloid is lowered in multiferroics films comparing to single crystals, it can
be also lowered by the selection of orientation of magnetic field. Our results
can be useful for strain engineering of new multiferroic functional materials
on demand.",1304.3204v1
2014-10-07,Origin of Magnetic Field in the Intracluster Medium: Primordial or Astrophysical?,"The origin of magnetic fields in clusters of galaxies is still an unsolved
problem, which is largely due to our poor understanding of initial seed
magnetic fields. If the seed magnetic fields have primordial origins, it is
likely that large-scale pervasive magnetic fields were present before the
formation of the large-scale structure. On the other hand, if they were ejected
from astrophysical bodies, they were highly localized in space at the time of
injection. In this paper, using turbulence dynamo models for high magnetic
Prandtl number fluids, we find constraints on the seed magnetic fields. The
hydrodynamic Reynolds number based on the Spitzer viscosity in the intracluster
medium (ICM) is believed to be less than $O(10^2)$, while the magnetic Reynolds
number can be much larger than that. In this case, if the seed magnetic fields
have primordial origins, they should be stronger than $O(10^{-11})$G, which is
very close to the upper limit of $O(10^{-9})$G set by the cosmic microwave
background (CMB) observations. On the other hand, if the seed magnetic fields
were ejected from astrophysical bodies, any seed magnetic fields stronger than
$O(10^{-9})$G can safely magnetize the intracluster medium. Therefore, it is
less likely that primordial magnetic fields are the direct origin of
present-day magnetic fields in the ICM.",1410.1893v1
2015-03-12,Successive magnetic phase transitions in $\bmα$-RuCl$_3$: XY-like frustrated magnet on the honeycomb lattice,"The layered compound $\alpha$-RuCl$_3$ is composed of a honeycomb lattice of
magnetic Ru$^{3+}$ ions with the $4d^5$ electronic state. We have investigated
the magnetic properties of $\alpha$-RuCl$_3$ via magnetization and specific
heat measurements using single crystals. It was observed that $\alpha$-RuCl$_3$
undergoes a structural phase transition at $T_{t}\,{\simeq}\,150$ K accompanied
by fairly large hysteresis. This structural phase transition is expected to be
similar to that observed in closely related CrCl$_3$. The magnetizations and
magnetic susceptibilities are strongly anisotropic, which mainly arise from the
anisotropic $g$-factors, i.e., $g_{ab}\,{\simeq}\,2.5$ and $g_c\,{\simeq}\,0.4$
for magnetic fields parallel and perpendicular to the $ab$ plane, respectively.
These $g$-factors and the obtained entropy indicate that the effective spin of
Ru$^{3+}$ is one-half, which results from the low-spin state. Specific heat
data show that magnetic ordering occurs in four steps at zero magnetic field.
The successive magnetic phase transitions should be ascribed to the competition
among exchange interactions. The magnetic phase diagram for
$H\,{\parallel}\,ab$ is obtained. We discuss the strongly anisotropic
$g$-factors in $\alpha$-RuCl$_3$ and deduce that the exchange interaction is
strongly XY-like. $\alpha$-RuCl$_3$ is magnetically described as a
three-dimensionally coupled XY-like frustrated magnet on a honeycomb lattice.",1503.03591v1
2015-07-01,Coronal heating in multiple magnetic threads,"Context. Heating the solar corona to several million degrees requires the
conversion of magnetic energy into thermal energy. In this paper, we
investigate whether an unstable magnetic thread within a coronal loop can
destabilise a neighbouring magnetic thread. Aims. By running a series of
simulations, we aim to understand under what conditions the destabilisation of
a single magnetic thread can also trigger a release of energy in a nearby
thread. Methods. The 3D magnetohydrodynamics code, Lare3d, is used to simulate
the temporal evolution of coronal magnetic fields during a kink instability and
the subsequent relaxation process. We assume that a coronal magnetic loop
consists of non-potential magnetic threads that are initially in an equilibrium
state. Results. The non-linear kink instability in one magnetic thread forms a
helical current sheet and initiates magnetic reconnection. The current sheet
fragments, and magnetic energy is released throughout that thread. We find
that, under certain conditions, this event can destabilise a nearby thread,
which is a necessary requirement for starting an avalanche of energy release in
magnetic threads. Conclusions. It is possible to initiate an energy release in
a nearby, non-potential magnetic thread, because the energy released from one
unstable magnetic thread can trigger energy release in nearby threads, provided
that the nearby structures are close to marginal stability.",1507.00259v1
2017-02-20,How Anomalous Resistivity Accelerates Magnetic Reconnection,"Whether turbulence induced anomalous resistivity (AR) can facilitate a fast
magnetic reconnection in collisionless plasma is a subject of active debate for
decades. Recent space observations suggest that the reconnection rate can be
higher than the Hall-reconnection rate and turbulent dissipation is required.
In this paper, using particle-in-cell simulations, we present a case study of
how AR produced by Buneman instability accelerates magnetic reconnection. We
first show that the AR/drag produced by Buneman instability in a thin electron
current layer 1) can dissipate magnetic energy stored in the current layer
through dissipation of the kinetic energy of electron beams; 2) The
inhomogeneous drag caused by wave couplings spontaneously breaks the magnetic
field lines and causes impulsive fast non-Hall magnetic reconnection on
electron-scales with a mean rate reaching 0.6 $V_A$. We then show that a
Buneman instability driven by intense electron beams around the x-point in a 3D
magnetic reconnection significantly enhances the dissipation of the magnetic
energy. Electron-scale magnetic reconnections driven by the inhomogeneous drag
around the x-line enhances the reconnection electric field and the in-plane
perpendicular magnetic field. About 40\% of the released magnetic energy is
converted into the electron thermal energy by AR while 50\% is converted into
the kinetic energy of the electron beams through the acceleration by the
reconnection electric field. The enhanced magnetic energy dissipation is
balanced by a net Poynting flux in-flow. About 10\% of the released magnetic
energy is brought out by an enhanced Poynting flux out-flow. These results
suggest that AR with sufficient intensity and electron-scale inhomogeneity can
significantly accelerate magnetic reconnection.",1702.06109v2
2017-06-19,Origin and Structures of Solar Eruptions II: Magnetic Modeling (Invited Review),"The topology and dynamics of the three-dimensional magnetic field in the
solar atmosphere govern various solar eruptive phenomena and activities, such
as flares, coronal mass ejections, and filaments/prominences. We have to
observe and model the vector magnetic field to understand the structures and
physical mechanisms of these solar activities. Vector magnetic fields on the
photosphere are routinely observed via the polarized light, and inferred with
the inversion of Stokes profiles. To analyze these vector magnetic fields, we
need first to remove the 180$^\circ$ ambiguity of the transverse components and
correct the projection effect. Then, the vector magnetic field can be served as
the boundary conditions for a force-free field modeling after a proper
preprocessing. The photospheric velocity field can also be derived from a time
sequence of vector magnetic fields. Three-dimensional magnetic field could be
derived and studied with theoretical force-free field models, numerical
nonlinear force-free field models, magnetohydrostatic models, and
magnetohydrodynamic models. Magnetic energy can be computed with
three-dimensional magnetic field models or a time series of vector magnetic
field. The magnetic topology is analyzed by pinpointing the positions of
magnetic null points, bald patches, and quasi-separatrix layers. As a well
conserved physical quantity, magnetic helicity can be computed with various
methods, such as the finite volume method, discrete flux tube method, and
helicity flux integration method. This quantity serves as a promising parameter
characterizing the activity level of solar active regions.",1706.05769v1
2017-07-20,Micrometer-scale Magnetic Imaging of Geological Samples Using a Quantum Diamond Microscope,"Remanent magnetization in geological samples may record the past intensity
and direction of planetary magnetic fields. Traditionally, this magnetization
is analyzed through measurements of the net magnetic moment of bulk millimeter
to centimeter sized samples. However, geological samples are often
mineralogically and texturally heterogeneous at submillimeter scales, with only
a fraction of the ferromagnetic grains carrying the remanent magnetization of
interest. Therefore, characterizing this magnetization in such cases requires a
technique capable of imaging magnetic fields at fine spatial scales and with
high sensitivity. To address this challenge, we developed a new instrument,
based on nitrogen-vacancy centers in diamond, which enables direct imaging of
magnetic fields due to both remanent and induced magnetization, as well as
optical imaging, of room-temperature geological samples with spatial resolution
approaching the optical diffraction limit. We describe the operating principles
of this device, which we call the quantum diamond microscope (QDM), and report
its optimized image-area-normalized magnetic field sensitivity (20
uT.um/Hz^1/2), spatial resolution (5 um), and field of view (4 mm), as well as
trade-offs between these parameters. We also perform an absolute magnetic field
calibration for the device in different modes of operation, including
three-axis (vector) and single-axis (projective) magnetic field imaging.
Finally, we use the QDM to obtain magnetic images of several terrestrial and
meteoritic rock samples, demonstrating its ability to resolve spatially
distinct populations of ferromagnetic carriers.",1707.06714v1
2017-12-20,Optical Manipulation of Magnetic Vortex Visualized in situ by 4D Electron Microscopy,"Understanding the fundamental dynamics of topological vortex and antivortex
naturally formed in micro/nanoscale ferromagnetic building blocks under
external perturbations is crucial to magnetic vortex based information
processing and spintronic devices. All previous studies have focused on
magnetic vortex-core switching via external magnetic fields, spin-polarized
currents, or spin waves, which have largely prohibited the investigation of
novel spin configurations that could emerge from the ground states in
ferromagnetic disks and their underlying dynamics. Here, we report in situ
visualization of femtosecond laser quenching induced magnetic vortex change in
various symmetric ferromagnetic Permalloy disks by Lorentz phase imaging using
4D electron microscopy. Besides the switching of magnetic vortex chirality and
polarity, we observed with distinct occurrence frequencies a plenitude of
complex magnetic structures that have never been observed by magnetic field or
current assisted switching. These complex magnetic structures consist of a
number of newly created topological magnetic defects (vortex and antivortex)
strictly conserving the topological winding number, demonstrating the direct
impact of topological invariant on the magnetization dynamics in ferromagnetic
disks. Their spin configurations show mirror or rotation symmetry due to the
geometrical confinement of the disks. Combined micromagnetic simulations with
the experimental observations reveal the underlying magnetization dynamics and
formation mechanism of the optical quenching induced complex magnetic
structures. Their distinct occurrence rates are pertinent to their
formation-growth energetics and pinning effects at the disk edge. Based on
these findings, we propose a paradigm of optical-quenching-assisted fast
switching of vortex cores for the control of magnetic vortex based information
recording and spintronic devices.",1712.07280v1
2018-02-05,Magnetized advective accretion flows: formation of magnetic barriers in Magnetically Arrested Discs,"We discuss the importance of large scale strong magnetic field in the removal
of angular momentum outward, as well as the possible origin of different kinds
of magnetic barrier in advective, geometrically thick, sub-Keplerian accretion
flows around black holes. The origin of this large scale strong magnetic field
near the event horizon is due to the advection of the magnetic flux by the
accreting gas from the environment, say, the interstellar medium or a companion
star, because of flux freezing. In this simplest vertically averaged,
1.5-dimensional disc model, we choose the maximum upper limit of the magnetic
field, which the disc around a black hole can sustain. In this so called
magnetically arrested disc (MAD) model, the accreting gas either decelerates or
faces the magnetic barrier near the event horizon by the accumulated magnetic
field depending on the geometry. The magnetic barrier may knock the matter to
infinity. We suggest that these types of flow are the building block to produce
jets and outflows in the accreting system. We also find that in some cases,
when matter is trying to go back to infinity after knocking the barrier, matter
is prevented being escaped by the cumulative action of strong gravity and the
magnetic tension, hence by another barrier. In this way, magnetic field can
lock the matter in between these two barriers and it might be a possible
explanation for the formation of episodic jet.",1802.01594v1
2018-05-03,Influence of magnetic disorders on Quantum Anomalous Hall Effect in Magnetic Topological Insulator Films beyond the two-dimensional limit,"Quantum anomalous Hall effect (QAHE) has been experimentally realized in
magnetic topological insulator (MTI) thin films fabricated on magnetically
doped (Bi,Sb)2Te3. In a MTI thin film with the magnetic easy axis along the
normal direction (z-direction), orientations of magnetic dopants are randomly
distributed around the magnetic easy axis, acting as magnetic disorders. With
the aid of the non-equilibrium Green's function and Landauer-Buttiker
formalism, we numerically study the influence of magnetic disorders on QAHE in
a MTI thin film modeled by a three-dimensional tight-binding Hamiltonian. It is
found that, due to the existence of gapless side surface states, QAHE is
protected even in the presence of magnetic disorders as long as the z-component
of magnetic moment of all magnetic dopants are positive. More importantly, such
magnetic disorders also suppress the dissipation of the chiral edge states and
enhance the quality of QAHE in MTI films. In addition, the effect of magnetic
disorders depends very much on the film thickness, and the optimal influence is
achieved at certain thickness. These findings are new features for QAHE in
three-dimensional systems, not present in two-dimensional systems.",1805.01126v1
2018-05-16,The origin and early evolution of a bipolar magnetic region in the solar photosphere,"Finding the formation mechanisms for bipolar configurations of strong local
magnetic field under control of the relatively weak global magnetic field of
the Sun is a key problem of the physics of solar activity. This study is aimed
at discriminating whether the magnetic field or fluid motion plays a primary,
active role in this process. The very origin and early development stage of
Active Region 12548 are investigated based on SDO/HMI observations of 2016 May
20--25. Full-vector magnetic and velocity fields are analyzed in parallel. The
leading and trailing magnetic polarities are found to grow asymmetrically in
terms of their amplitude, magnetic flux, and the time variation of these
quantities. The leading-polarity magnetic element originates as a compact
feature against the background of a distributed trailing-polarity field, with
an already existing trailing-polarity magnetic element. No signs of strong
horizontal magnetic fields are detected between the two magnetic poles. No
predominant upflow between their future locations precedes the origin of this
bipolar magnetic region (BMR); instead, upflows and downflows are mixed, with
some prevalence of downflows. Any signs of a large-scale horizontal divergent
flow from the area where the BMR develops are missing; in contrast, a normal
supergranulation and mesogranulation pattern is preserved. This scenario of
early BMR evolution is in strong contradiction with the expectations based on
the model of a rising $\Omega$-shaped loop of a flux tube of strong magnetic
field, and an \emph{in situ} mechanism of magnetic-field amplification and
structuring should operate in this case.",1805.06486v2
2018-08-22,Analytic solution of a magnetized tori with magnetic polarization around Kerr black holes,"We present the first family of magnetically polarized equilibrium tori around
a Kerr black hole. The models were obtained in the test fluid approximation by
assuming that the tori is a linear media, making it is possible to characterize
the magnetic polarization of the fluid through the magnetic susceptibility
$\chi_{m}$. The magnetohydrodynamic (MHD) structure of the models was solved by
following the Komissarov approach, but with the aim of including the magnetic
polarization of the fluid, the integrability condition for the magnetic
counterpart was modified. We build two kinds of magnetized tori depending on
whether the magnetic susceptibility is constant in space or not. In the models
with constant $\chi_{m}$, we find that the paramagnetic tori ($\chi_{m}>0$) are
more dense and less magnetized than the diamagnetic ones ($\chi_{m}<0$) in the
region between the inner edge, $r_{in}$, and the center of the disk, $r_{c}$;
however, we find the opposite behavior for $r>r_{c}$. Now, in the models with
non-constant $\chi_{m}$, the tori become more magnetized than the Komissarov
solution in the region where $\partial\chi_{m}/\partial r<0$, and less
magnetized when $\partial\chi_{m}/\partial r>0$. Nevertheless, it is worth
mentioning that in all solutions presented in this paper the magnetic pressure
is greater than the hydrodynamic pressure. These new equilibrium tori can be
useful for studying the accretion of a magnetic media onto a rotating black
hole.",1808.07400v1
2018-11-21,"Exploring interfacial exchange coupling and sublattice effect in heavy metal/ferrimagnetic insulator heterostructures using Hall measurements, x-ray magnetic circular dichroism, and neutron reflectometry","We use temperature-dependent Hall measurements to identify contributions of
spin Hall, magnetic proximity, and sublattice effects to the anomalous Hall
signal in heavy metal/ferrimagnetic insulator heterostructures with
perpendicular magnetic anisotropy. This approach enables detection of both the
magnetic proximity effect onset temperature and the magnetization compensation
temperature and provides essential information regarding the interfacial
exchange coupling. Onset of a magnetic proximity effect yields a local extremum
in the temperature-dependent anomalous Hall signal, which occurs at higher
temperature as magnetic insulator thickness increases. This magnetic proximity
effect onset occurs at much higher temperature in Pt than W. The magnetization
compensation point is identified by a sharp anomalous Hall sign change and
divergent coercive field. We directly probe the magnetic proximity effect using
x-ray magnetic circular dichroism and polarized neutron reflectometry, which
reveal an antiferromagnetic coupling between W and the magnetic insulator.
Finally, we summarize the exchange-coupling configurations and the anomalous
Hall-effect sign of the magnetized heavy metal in various heavy metal/magnetic
insulator heterostructures.",1811.08574v2
2019-01-07,Unconventional magnetization textures and domain-wall pinning in Sm-Co magnets,"The most powerful magnets for high temperature applications are Sm-Co-based
alloys with a microstructure that combines magnetically soft and hard regions.
The microstructure consists of a dense domain-wall-pinning network that endows
the material with remarkable magnetic hardness. A precise understanding of the
coupling between magnetism and microstructure is essential for enhancing the
performance of Sm-Co magnets, but experiments and theory have not yet converged
to a unified model. Here, we combine transmission electron microscopy, atom
probe tomography, and nanometer-resolution off-axis electron holography with
micromagnetic simulations to show that the magnetization processes in Sm-Co
magnets result from an interplay between curling instabilities and pinning
effects at the intersections between magnetically soft and hard regions. We
also find that topologically non-trivial magnetic domains separated by a
complex network of domain walls play a key role in the magnetic state. Our
findings reveal a previously hidden aspect of magnetism and provide insight
into the full potential of high-performance magnetic materials.",1901.01922v3
2019-02-25,"The effects of surface fossil magnetic fields on massive star evolution: I. Magnetic field evolution, mass-loss quenching and magnetic braking","Surface magnetic fields have a strong impact on stellar mass loss and
rotation and, as a consequence, on the evolution of massive stars. In this work
we study the influence of an evolving dipolar surface fossil magnetic field
with an initial field strength of 4 kG on the characteristics of 15 M$_{\odot}$
solar metallicity models using the Geneva stellar evolution code. Non-rotating
and rotating models considering two different scenarios for internal angular
momentum transport are computed, including magnetic field evolution, mass-loss
quenching, and magnetic braking. Magnetic field evolution results in weakening
the initially strong magnetic field, however, in our models an observable
magnetic field is still maintained as the star evolves towards the red
supergiant phase. At the given initial mass of the models, mass-loss quenching
is modest. Magnetic braking greatly enhances chemical element mixing if radial
differential rotation is allowed for, on the other hand, the inclusion of
surface magnetic fields yields a lower surface enrichment in the case of near
solid-body rotation. Models including surface magnetic fields show notably
different trends on the Hunter diagram (plotting nitrogen abundance vs $v \sin
i$) compared to those that do not. The magnetic models agree qualitatively with
the anomalous `Group 2 stars', showing slow surface rotation and high surface
nitrogen enhancement on the main sequence.",1902.09333v1
2019-09-29,Experimental identification of electric dipoles induced by magnetic monopoles in Tb2Ti2O7,"The fundamental principles of electrodynamics allow an electron carrying both
electric monopole (charge) and magnetic dipole (spin) but prohibit its magnetic
counterpart. Recently it was predicted that the magnetic ""monopoles"" carrying
emergent magnetic charges in spin ice systems can induce electric dipoles. The
inspiring prediction offers a novel way to study magnetic monopole excitations
and magnetoelectric coupling. However, no clear example has been identified up
to now. Here, we report the experimental evidence for electric dipoles induced
by magnetic monopoles in spin frustrated Tb2Ti2O7. The magnetic field applied
to pyrochlore Tb2Ti2O7 along [111] direction, brings out a ""3-in-1-out""
magnetic monopole configuration, and then induces a subtle structural phase
transition at Hc~2.3 T. The transition is evidenced by the non-linear phonon
splitting under magnetic fields and the anomalous crystal-field excitations of
Tb3+ ions. The observations consistently point to the displacement of the
oxygen O"" anions along [111] axis which gives rise to the formation of electric
dipoles. The finding demonstrates that the scenario of magnetic monopole having
both magnetic charge and electric dipole is realized in Tb2Ti2O7 and sheds
light into the coupling between electricity and magnetism of magnetic monopoles
in spin frustrated systems.",1909.13199v1
2019-11-14,Suspensions of magnetic nanogels at zero field: equilibrium structural properties,"Magnetic nanogels represent a cutting edge of magnetic soft matter research
due to their numerous potential applications. Here, using Langevin dynamics
simulations, we analyse the influence of magnetic nanogel concentration and
embedded magnetic particle interactions on the self-assembly of magnetic
nanogels at zero field. For this, we calculated radial distribution functions
and structure factors for nanogels and magnetic particles within them. We found
that, in comparison to suspensions of free magnetic nanoparticles, where the
self-assembly is already observed if the interparticle interaction strength
exceeds the thermal fluctuations by approximately a factor of three,
self-assembly of magnetic nanogels only takes place by increasing such ratio
above six. This magnetic nanogel self-assembly is realised by means of
favourable close contacts between magnetic nanoparticles from different
nanogels. It turns out that for high values of interparticle interactions,
corresponding to the formation of internal rings in isolated nanogels, in their
suspensions larger magnetic particle clusters with lower elastic penalty can be
formed by involving different nanogels. Finally, we show that when the
self-assembly of these nanogels takes place, it has a drastic effect on the
structural properties even if the volume fraction of magnetic nanoparticles is
low.",1911.06031v1
2020-02-13,"A new family of disorder-free Rare-Earth-based kagomé lattice magnets: structure and magnetic characterizations of RE3BWO9 (RE=Pr, Nd, Gd-Ho) Boratotungstates","Exploration of rare-earth (RE)-based Kagome lattice magnets with spin-orbital
entangled jeff=1/2 moments will provide new platform for investigating the
exotic magnetic phases. Here, we report a new family of RE3BWO9
(RE=Pr,Nd,Gd-Ho) boratotungstates with magnetic RE3+ ions arranged on Kagome
lattice, and perform its structure and magnetic characterizations. This serial
compounds crystallize in hexagonal coordinated structure with space group P63
(No.173), where magnetic RE3+ ions have distorted Kagom\'e lattice connections
within the ab plane and stacked in a AB-type fashion along c axis. The
interlayer RE-RE separation is comparable with that of intralayer distance,
forming 3-dimensional (3D) exchange coupled magnetic framework of RE3+ ions.
The magnetic susceptibility data of RE3BWO9 (RE=Pr, Nd, Gd-Ho) reveal dominant
antiferromagnetic interactions between magnetic RE3+ ions, but without visible
magnetic ordering down to 2 K. The magnetization analyses for different RE3+
ions show diverse anisotropic behaviors, make RE3BWO9 as an appealing
Kagome-lattice antiferromagnet to explore exotic magnetic phases.",2002.05420v1
2020-05-19,Numerical Analysis of the Screening Current-Induced Magnetic Field in the HTS Insert Dipole Magnet Feather-M2.1-2,"Screening currents are field-induced dynamic phenomena which occur in
superconducting materials, leading to persistent magnetization. Such currents
are of importance in ReBCO tapes, where the large size of the superconducting
filaments gives rise to strong magnetization phenomena. In consequence,
superconducting accelerator magnets based on ReBCO tapes might experience a
relevant degradation of the magnetic field quality in the magnet aperture,
eventually leading to particle beam instabilities. Thus, persistent
magnetization phenomena need to be accurately evaluated. In this paper, the 2D
finite element model of the Feather-M2.1-2 magnet is presented. The model is
used to analyze the influence of the screening current-induced magnetic field
on the field quality in the magnet aperture. The model relies on a coupled
field formulation for eddy current problems in time-domain. The formulation is
introduced and verified against theoretical references. Then, the numerical
model of the Feather-M2.1-2 magnet is detailed, highlighting the key
assumptions and simplifications. The numerical results are discussed and
validated with available magnetic measurements. A satisfactory agreement is
found, showing the capability of the numerical tool in providing accurate
analysis of the dynamic behavior of the Feather-M2.1-2 magnet.",2005.09467v2
2020-07-14,"Inverse energy transfer in decaying, three dimensional, nonhelical magnetic turbulence due to magnetic reconnection","It has been recently shown numerically that there exists an inverse transfer
of magnetic energy in decaying, nonhelical, magnetically dominated,
magnetohydrodynamic turbulence in 3-dimensions (3D). We suggest that magnetic
reconnection is the underlying physical mechanism responsible for this inverse
transfer. In the two-dimensional (2D) case, the inverse transfer is easily
inferred to be due to smaller magnetic islands merging to form larger ones via
reconnection. We find that the scaling behaviour is similar between the 2D and
the 3D cases, i.e., the magnetic energy evolves as $t^{-1}$, and the magnetic
power spectrum follows a slope of $k^{-2}$. We show that on normalizing time by
the magnetic reconnection timescale, the evolution curves of the magnetic field
in systems with different Lundquist numbers collapse onto one another.
Furthermore, transfer function plots show signatures of magnetic reconnection
driving the inverse transfer. We also discuss the conserved quantities in the
system and show that the behaviour of these quantities is similar between the
2D and 3D simulations, thus making the case that the dynamics in 3D could be
approximately explained by what we understand in 2D. Lastly, we also conduct
simulations where the magnetic field is subdominant to the flow. Here, too, we
find an inverse transfer of magnetic energy in 3D. In these simulations, the
magnetic energy evolves as $ t^{-1.4}$ and, interestingly, a dynamo effect is
observed.",2007.07325v1
2020-10-17,Creation and confirmation of Hopfions in magnetic multilayer systems,"Topological solitons have been studied for decades in classical field
theories, and have started recently to impact condensed matter physics. Among
those solitons, magnetic skyrmions are two-dimensional particle-like objects
with a continuous winding of the magnetization, and magnetic Hopfions are
three-dimensional topological solitons that can be formed from a closed loop of
a twisted skyrmion string. Whereas intense research is underway with magnetic
skyrmions towards a fundamental understanding and potential applications in
advanced storage and logic devices, the experimental creation and confirmation
of magnetic Hopfions has been elusive so far. Theoretical models suggest that
Hopfions can be stabilized in frustrated or chiral magnetic systems, and that
target skymions can be transformed into Hopfions by adapting their
perpendicular magnetic anisotropy. Here, we present experimental evidence of
magnetic Hopfions that were created in magnetic Ir/Co/Pt multilayers shaped
into nanoscale disks, which are known to host target skyrmions. The
three-dimensional spin texture, which distinguishes magnetic Hopfions from
target skyrmions was confirmed by combining two advanced element-specific
magnetic X-ray microscopy techniques with about 20-30nm lateral resolution,
using X-ray magnetic circular dichroism effect as magnetic contrast mechanism
in surface-sensitive X-ray photoemission electron microscopy and bulk-sensitive
soft x-ray transmission microscopy. We anticipate that these results will
stimulate further investigations of Hopfions with different topologies and
their potential application in three-dimensional spintronics devices.",2010.08674v1
2020-10-22,Chiral channel network from magnetization textures in 2D MnBi2Te4,"When atomically thin van der Waals (vdW) magnet forms long-period moir\'e
pattern with a magnetic substrate, the sensitive dependence of interlayer
magnetic coupling on the atomic registries can lead to moir\'e defined
magnetization textures in the two-dimensional (2D) magnets. The recent
discovery of 2D magnetic topological insulators such as MnBi2Te4 leads to the
interesting possibility to explore the interplay of such magnetization textures
with the topological surface states, which we explore here with a minimal model
established for 2D MnBi2Te4. The sign flip of the exchange gap across a
magnetization domain wall gives rise to a single in-gap chiral channel on each
surface. In the periodic magnetization textures, such chiral spin channels at
the domain walls couple to form a network and superlattice minibands emerge. We
find that in magnetization textures with closed domain wall geometries, the
formed superlattice miniband is a gapped Dirac cone featuring orbital
magnetization from the current circulation in the close loops of chiral
channels, while in magnetization textures with open domain wall geometries,
gapless mini-Dirac cone is found instead. The miniband Bloch states feature a
spatial texture of spin and local current density, which are clear
manifestation of the spin-momentum locked chiral channels at the domain walls.
The results suggest a new platform to engineer spin and current flows through
the manipulation of magnetization domains for spintronic devices.",2010.11424v1
2020-11-23,Unraveling the origin of magnetic fields in galaxies,"Despite their ubiquity, there are many open questions regarding galactic and
cosmic magnetic fields. Specifically, current observational constraints cannot
rule out if magnetic fields observed in galaxies were generated in the Early
Universe or are of astrophysical nature. Motivated by this we use our magnetic
tracers algorithm to investigate whether the signatures of primordial magnetic
fields persist in galaxies throughout cosmic time. We simulate a Milky Way-like
galaxy in four scenarios: magnetised solely by primordial magnetic fields,
magnetised exclusively by SN-injected magnetic fields, and two combined
primordial + SN magnetisation cases. We find that once primordial magnetic
fields with a comoving strength $B_0 >10^{-12}$ G are considered, they remain
the primary source of galaxy magnetisation. Our magnetic tracers show that,
even combined with galactic sources of magnetisation, when primordial magnetic
fields are strong, they source the large-scale fields in the warm metal-poor
phase of the simulated galaxy. In this case, the circumgalactic and
intergalactic medium can be used to probe $B_0$ without risk of pollution by
magnetic fields originated in the galaxy. Furthermore, whether magnetic fields
are primordial or astrophysically-sourced can be inferred by studying local gas
metallicity. As a result, we predict that future state-of-the-art observational
facilities of magnetic fields in galaxies will have the potential to unravel
astrophysical and primordial magnetic components of our Universe.",2011.11648v2
2021-02-06,Negative Turbulent Magnetic Diffusivity $β$ effect in a Magnetically Forced System,"We have studied the large scale dynamo process forced with helical magnetic
energy. The magnetically driven dynamo is not so well studied as kinetically
forced dynamo. It has been thought to represent the amplification of magnetic
field in the stellar corona, accretion disk, or plasma lab. However, the
interaction between the helical magnetic field and plasma is a more fundamental
phenomenon that can be extended to the early Universe. The scale-invariant
helical magnetic field not only explains the currently observed large scale
astrophysical magnetic fields but also has information on the horizon scale in
the early Universe.
  The interaction between magnetic field and plasma is inherently non-linear,
making its mechanism difficult to understand. But, if the plasma system is
driven with helical field, the process can be linearized with alpha&betaand
large scale magnetic field. Conventionally, alpha effect is thought to transfer
magnetic field to the large scale regime, and betaeffect diffuses magnetic
field. However, these conclusions are based on the incompletely derived
alpha&beta. To get the exact profiles of evolving alpha&\b{eta}, we solved a
coupled semi-analytic equation set and applied the result to simulation data
for the large scale magnetic helicity and magnetic energy.
  Our result shows that the averaged alpha effect decreases before making a
significant contribution to the amplification of large scale B field. Rather,
betaeffect, which keeps negative, de facto plays a key role in the
amplification of large scale B field with Laplacian. And, this negative
diffusivity accounts for the attenuation of plasma kinetic energy",2102.03500v4
2021-05-02,Tunable Néel-Bloch magnetic twists in Fe3GeTe2 with van der Waals structure,"The advent of ferromagnetism in two-dimensional (2D) van der Waals (vdW)
magnets has stimulated high interest in exploring topological magnetic
textures, such as skyrmions for use in future skyrmion-based spintronic
devices. To engineer skyrmions in vdW magnets by transforming Bloch-type
magnetic bubbles into N\'eel-type skyrmions, the heterostructure of heavy
metal/vdW magnetic thin film has been made to induce interfacial
Dzyaloshinskii-Moriya interaction (DMI). However, the unambiguous
identification of the magnetic textures inherent to vdW magnets, e.g., whether
the magnetic twists (skyrmions/domain walls) are N\'eel- or Bloch-type, is
unclear. Here we demonstrate that the N\'eel- or Bloch-type magnetic twists can
be tuned in the vdW magnet Fe3GeTe2 (FGT) with/without interfacial DMI. We use
an in-plane magnetic field to align the modulation wavevector q of the
magnetizations in order to distinguish the N\'eel- or Bloch-type magnetic
twists. We observe that q is perpendicular to the in-plane field in the
heterostructure (Pt/oxidized-FGT/FGT/oxidized-FGT), while q aligns at a rotated
angle with respect to the field direction in the thin plate by thinning bulk
FGT. We find that the aligned domain wall twists hold fan-like modulations,
coinciding qualitatively with our computational results.",2105.00468v1
2021-05-10,Parameterization of magnetic vector potentials and fields for efficient multislice calculations of elastic electron scattering,"The multislice method, which simulates the propagation of the incident
electron wavefunction through a crystal, is a well-established method for
analyzing the multiple scattering effects that an electron beam may undergo.
The inclusion of magnetic effects into this method proves crucial towards
simulating magnetic differential phase contrast images at atomic resolution,
enhanced magnetic interaction of vortex beams with magnetic materials,
calculating magnetic Bragg spots, or searching for magnon signatures, to name a
few examples. Inclusion of magnetism poses novel challenges to the efficiency
of the multislice method for larger systems, especially regarding the
consistent computation of magnetic vector potentials and magnetic fields over
large supercells. We present in this work a tabulation of parameterized
magnetic values for the first three rows of transition metal elements computed
from atomic density functional theory calculations, allowing for the efficient
computation of approximate magnetic vector fields across large crystals using
only structural and magnetic moment size and direction information.
Ferromagnetic bcc Fe and tetragonal FePt are chosen as examples in this work to
showcase the performance of the parameterization versus directly obtaining
magnetic vector fields from the unit cell spin density by density functional
theory calculations, both for the quantities themselves and the resulting
magnetic signal from their respective use in multislice calculations.",2105.04195v1
2022-01-03,Exchange Bias and Interface-related Effects in Two-dimensional van der Waals Magnetic Heterostructures: Open Questions and Perspectives,"The exchange bias (EB) effect is known as a fundamentally and technologically
important magnetic property of a magnetic bilayer film. It is manifested as a
horizontal shift in a magnetic hysteresis loop of a film subject to cooling in
the presence of a magnetic field. The EB effect in van der Waals (vdW)
heterostructures offers a novel approach for tuning the magnetic properties of
the newly discovered single-layer magnets, as well as adds a new impetus to
magnetic vdW heterostructures. Indeed, intriguing EB effects have recently been
reported in a variety of low-dimensional vdW magnetic systems ranging from a
weakly interlayer-coupled vdW magnet (e.g., Fe3GeTe2) to a bilayer composed of
two different magnetic vdW materials (e.g., Fe3GeTe2/CrCl3, Fe3GeTe2/FePS3,
Fe3GeTe2/MnPS3), to bilayers of two different vdW defective magnets (e.g.,
VSe2/MoS2), or to metallic ferromagnet/vdW defective magnet interfaces (e.g.,
Fe/MoS2). Despite their huge potential in spintronic device applications, the
physical origins of the observed EB effects have remained elusive to
researchers. We present here a critical review of the EB effect and associated
phenomena such as magnetic proximity (MP) in various vdW heterostructure
systems and propose approaches to addressing some of the emerging fundamental
questions.",2201.00479v1
2022-02-15,The effect of inter-particle hydrodynamic and magnetic interactions in a magnetorheological fluid,"A magnetorheological fluid, which consists of magnetic particles suspended in
a viscous fluid, flows freely with well-dispersed particles in a the absence of
a magnetic field, but particle aggregation results in flow cessation when a
field is applied. The mechanism of dynamical arrest is examined by analysing
interactions between magnetic particles in a magnetic field subject to a shear
flow. An isolated spherical magnetic particle undergoes a transition between a
rotating state at low magnetic field and a static orientation at high magnetic
field. The effect of interactions for spherical dipolar and polarisable
particles with static orientation is examined for a dilute viscous suspension.
There are magnetic interactions due to the magnetic field disturbance at one
particle caused by the dipole moment of another, hydrodynamic interactions due
to the antisymmetric force moment of a non-rotating particle in a shear flow,
and a modification of the magnetic field due to the particle magnetic moment
density. When there is a concentration variation, the torque balance condition
results in a disturbance to the orientation of the particle magnetic moment.
The net force and the drift velocity due to these disturbances is calculated,
and the collective motion generated is equivalent to an anisotropic diffusion
process. When the magnetic field is in the flow plane, the diffusion
coefficients in the two directions perpendicular to the field direction are
negative, implying that concentration fluctuations are unstable in these
directions. This instability could initiate field-induced dynamical arrest in a
magnetorheological fluid.",2202.07488v1
2022-06-24,Quark anomalous magnetic moment leads to the inverse magnetic catalysis phenomena of chiral restoration and deconfinement phase transitions in $μ_B-T$ plane,"The effect of quark anomalous magnetic moment (AMM) to chiral restoration and
deconfinement phase transitions in baryon chemical potential-temperature
$(\mu_B-T)$ plane under magnetic fields is investigated in frame of a
Pauli-Villars regularized PNJL model. It's found that the quark AMM plays the
role of inverse catalysis to the phase transitions, and large quark AMM will
change the magnetic catalysis phenomena of phase transitions to inverse
magnetic catalysis in the whole $\mu_B-T$ plane. For a fixed magnetic field,
the critical temperature $T_c$ and critical baryon chemical potential $\mu_B^c$
decreases with quark AMM. The stronger the magnetic field is, the inverse
catalysis effect of AMM becomes more important. For a small AMM
$\kappa=\kappa_1$, it shows the magnetic catalysis effect for critical
temperature $T_c$ at vanishing $\mu_B$ with increasing magnetic field, and
(inverse) magnetic catalysis effect for critical baryon chemical potential
$\mu_B^c$ at vanishing $T$ under (weak) strong magnetic field. At finite $T$
and $\mu_B$, there exist some crossings of the phase transition lines with
different magnetic field. For a large AMM $\kappa=\kappa_2$, we obtain the
inverse magnetic catalysis effect in the whole $\mu_B-T$ plane, and no
crossings of phase transition lines happen.",2206.12054v1
2022-07-14,UI$_3$ -- 5f-electron magnetic van der Waals material,"We grew high-quality single crystals of the 5f electron van der Waals
compound UI$_3$ and investigated them by measurements of specific heat and
magnetization as functions of temperature and magnetic field. UI$_3$ behaves as
an antiferromagnet with a first-order magnetic phase transition at the Ne\'el
temperature $T_N$ = 2.65 K. It is characterized by a sharp symmetric
specific-heat peak which is gradually shifted to lower temperatures by
increasing magnetic field applied along either the a- or b-axis. The behavior
in magnetic fields reveals orthorhombic magnetocrystalline anisotropy with the
hard magnetization direction along the c-axis. The 2-K a- and b-axis
magnetization curves exhibit a metamagnetic transition at the critical field
$H_c$ = 3 T and 1.8 T, respectively. In higher fields, when the long-range
antiferromagnetism is suppressed by a metamagnetic transition, signs of
short-range magnetic ordering of antiferromagnetic correlations in the
paramagnetic state show up both in specific heat and magnetization. The
anomalous S-shape field dependence of a-axis magnetization well above $H_c$ can
be understood as the crossover from the correlated paramagnetic regime to the
high-field polarized paramagnet. The magnetic phase diagrams for the magnetic
field applied along the a- and b-axis, respectively, designed using the
mentioned experimental results are presented. We have also found that the
UI$_3$ crystals are easily cleavable which predisposes this material for direct
investigation of 5f electron magnetism in the 2D limit on exfoliated atomically
thin samples.",2207.06880v1
2022-07-27,Effective and asymptotic criticality of structurally disordered magnets,"Changes in magnetic critical behaviour of quenched structurally-disordered
magnets are usually exemplified in experiments and in MC simulations by diluted
systems consisting of magnetic and non-magnetic components. By our study we aim
to show, that similar effects can be observed not only for diluted magnets with
non-magnetic impurities, but may be implemented, e.g., by presence of two (and
more) chemically different magnetic components as well. To this end, we
consider a model of the structurally-disordered quenched magnet where all
lattice sites are occupied by Ising-like spins of different length $L$. In such
random spin length Ising model the length $L$ of each spin is a random variable
governed by the distribution function $p(L)$. We show that this model belongs
to the universality class of the site-diluted Ising model. This proves that
both models are described by the same values of asymptotic critical exponents.
However, their effective critical behaviour differs. As a case study we
consider a quenched mixture of two different magnets, with values of elementary
magnetic moments $L_1=1$ and $L_2=s$, and of concentration $c$ and $1-c$,
correspondingly. We apply field-theoretical renormalization group approach to
analyze the renormalization group flow for different initial conditions,
triggered by $s$ and $c$, and to calculate effective critical exponents further
away from the fixed points of the renormalization group transformation. We show
how the effective exponents are governed by difference in properties of the
magnetic components.",2207.13655v1
2023-04-13,Chirality-Induced Magnetization of Magnetite by an RNA Precursor,"Life is homochiral and homochirality is a fundamental feature of living
systems on Earth. While the exact mechanism that led to homochirality is still
not fully understood, any realistic scenario on the origins of life needs to
address the emergence of homochirality. In order to impose and maintain
chirality in a prebiotic network, an environmental factor functioning as a
chiral agent is demanded. Magnetized surfaces are prebiotically plausible
chiral agents, shown to be effective in enantioseparation of
ribose-aminooxazoline (RAO), a ribonucleic acid (RNA) precursor, due to the
chiral-induced spin selectivity (CISS) effect. As such, mechanisms for breaking
the magnetic symmetry of magnetic minerals are of the utmost importance. Here
we report the avalanche magnetization of magnetite $(Fe_{3}O_{4})$ by the
crystallization of enantiopure RAO. The observed breaking of the magnetic
symmetry is induced by the chiral molecules due to the CISS effect and spreads
out across the magnetic surface like an avalanche, providing a way to uniformly
magnetize a magnetic surface without fully covering it. Considered together
with our previous results on enantioseparation by crystallization on a magnetic
surface, chirality-induced avalanche magnetization paves the way for a
cooperative feedback between chiral molecules and magnetic surfaces. With this
feedback, a weak natural bias in the net magnetization can be amplified and
spin-selective processes can be accommodated on magnetic minerals on a
persistent basis.",2304.09095v1
2023-06-13,Imaging magnetism evolution of magnetite to megabar pressure range with quantum sensors in diamond anvil cell,"High-pressure diamond anvil cells have been widely used to create novel
states of matter. Nevertheless, the lack of universal in-situ magnetic
measurement techniques at megabar pressures makes it difficult to understand
the underlying physics of materials' behavior at extreme conditions, such as
high-temperature superconductivity of hydrides and the formation or destruction
of the local magnetic moments in magnetic systems, etc. Here we break through
the limitations of pressure on quantum sensors and develop the in-situ magnetic
detection technique at megabar pressures with high sensitivity
(~1{\mu}T/Hz^(1\2)) and sub-microscale spatial resolution. By directly imaging
the magnetic field and the evolution of magnetic domains, we observe the
macroscopic magnetic transition of Fe3O4 in the megabar pressure range from
strong ferromagnetism ({\alpha}-Fe3O4) to weak ferromagnetism ({\beta}-Fe3O4)
and finally to non-magnetism ({\gamma}-Fe3O4). The scenarios for magnetic
changes in Fe3O4 characterized here shed light on the direct magnetic
microstructure observation in bulk materials at high pressure and contribute to
understanding the mechanism of magnetic moment suppression related to spin
crossover. The presented method can potentially investigate the spin-orbital
coupling and magnetism-superconductivity competition in magnetic systems.",2306.07840v1
2023-09-19,Field Orientation Dependent Magnetic Phases In Weyl Semimetal Co3Sn2S2,"Magnetism plays a key role in the emergence of topological phenomena in the
Weyl semimetal Co3Sn2S2, which exhibits a ferromagnetic (FM) interactions along
the c-axis of the crystal and an antiferromagnetic (AFM) interactions within
the ab plane. Extensive studies on the temperature dependence of the magnetism
with the magnetic field along the c-axis have uncovered a number of magnetic
phases. Currently, the nature and origins of the reported magnetic phases are
under debate. Here we report on magnetic field orientation effects on the
magnetism in Co3Sn2S2. The shape of the hysteresis loop of the Hall resistance
at a fixed temperature is found to change from rectangular to bow-tie-like as
the magnetic field is tilted from the c-axis towards the ab plane, resembling
that reported for magnetic fields along the c-axis as the temperature
approaches the Curie temperature from below. Unlike their temperature-dependent
counterparts, the newly observed bow-tie-like hysteresis loops show exchange
bias. Our results showcase the contribution of the in-plane AFM interactions to
the magnetism in Co3Sn2S2 and demonstrate a new way to tune its magnetic
phases. They also shed light on the temperature-dependent magnetic phases
occurring in the magnetic field along the c-axis of the crystal.",2309.10221v1
2023-11-16,Meridional Circulations of the Solar Magnetic Fields of Different Strength,"The meridional circulation of the solar magnetic fields in Solar Cycles 21-24
was considered. Data from both ground-based and space observatories were used.
Three types of time-latitude distributions of photospheric magnetic fields and
their meridional circulations were identified depending on the magnetic field
intensity. (i) low-strength magnetic fields. They were distributed evenly
across latitude and weakly depended on the magnetic fields of active regions
and their cycle variation; (ii) medium-strength magnetic fields. For these
fields a wave-like, pole-to-pole, antiphase meridional circulation with a
period of approximately 22 years was revealed. The velocities of meridional
flows were slower at the minima of solar activity, when they were at high
latitudes in the opposite hemispheres, and maximal at the solar maxima, when
the positive- and negative-polarity waves crossed the equator. The meridional
circulation of these fields reflects the solar global magnetic field dynamics
and determines the solar polar field reversal; (iii) high-strength (active
region) magnetic fields. They were distributed symmetrically in the Northern
and Southern hemispheres. Magnetic fields of both leading and following sunspot
polarity migrated from high to low latitudes. The meridional-flow velocities of
high-strength magnetic fields were higher at the rising and maxima phases than
at the minima. Some of the high-latitude active region magnetic fields were
captured by the second type meridional circulation flows and transported along
with them to the appropriate pole. But the magnetic fields of active regions
are not the main ones in the solar polar field reversal. The results indicate
that high-strength magnetic fields were not the main source of weak ones.",2311.09900v1
2024-02-03,Drivers of Magnetic Field Amplification at Oblique Shocks: In-Situ Observations,"Collisionless shocks are ubiquitous structures throughout the universe. Shock
waves in space and astrophysical plasmas convert the energy of a fast-flowing
plasma to other forms of energy, including thermal and magnetic energies.
Plasma turbulence and high-amplitude electric and magnetic fluctuations are
necessary for effective energy conversion and particle acceleration. We survey
and characterize in-situ observations of reflected ions and magnetic field
amplification rates at quasi-perpendicular shocks under a wide range of
upstream conditions. We report magnetic amplification factors as high as 25
times the upstream magnetic field in our current dataset. Reflected ions
interacting with the incoming plasma create magnetic perturbations which cause
magnetic amplification in upstream and downstream regions of
quasi-perpendicular shocks. Our observations show that in general magnetic
amplification increases with the fraction of reflected ions, which itself
increases with Mach number. Both parameters plateau once full reflection is
reached. Magnetic amplification continuously increases with the inverse of the
magnetization parameter of the upstream plasma. We find that the extended foot
region upstream of shocks and nonlinear processes within that region are key
factors for intense magnetic amplification. Our observations at
non-relativistic shocks provide the first experimental evidence that below a
certain magnetization threshold, the magnetic amplification efficiency at
quasi-perpendicular shocks becomes comparable to that at the quasi-parallel
shocks.",2402.02014v1
2024-02-15,Understanding and tuning magnetism in layered Ising-type antiferromagnet FePSe3 for potential 2D magnet,"Recent development in two-dimensional (2D) magnetic materials have motivated
the search for new van der Waals magnetic materials, especially Ising-type
magnets with strong magnetic anisotropy. Fe-based MPX3 (M = transition metal, X
= chalcogen) compounds such as FePS3 and FePSe3 both exhibit an Ising-type
magnetic order, but FePSe3 receives much less attention compared to FePS3. This
work focuses on establishing the strategy to engineer magnetic anisotropy and
exchange interactions in this less-explored compound. Through chalcogen and
metal substitutions, the magnetic anisotropy is found to be immune against S
substitution for Se whereas tunable only with heavy Mn substitution for Fe. In
particular, Mn substitution leads to a continuous rotation of magnetic moments
from the out-of-plane direction towards in-plane. Furthermore, the magnetic
ordering temperature displays non-monotonic doping dependence for both
chalcogen and metal substitutions but due to different mechanisms. These
findings provide deeper insight into the Ising-type magnetism in this important
van der Waals material, shedding light on the study of other Ising-type
magnetic systems as well as discovering novel 2D magnets for potential
applications in spintronics.",2402.10155v1
2024-03-24,Strongly asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction,"Electrical switching of magnetization is central to spintronics. Despite the
enormous efforts on the spin torques and the Dzyaloshinskii-Moriya interaction
(DMI) effects, some fundamental physics for electrical switching of
magnetization is still missing as indicated by a number of remarkable
long-standing puzzles. Here, we report the discovery of the long-range
intralayer DMI effect widely existing in magnetic heterostructure, which is
distinct from the yet-known DMI effects as it describes the chiral coupling of
two orthogonal magnetic domains within the same magnetic layer via the
mediation of an adjacent heavy metal layer. The long-range intralayer DMI
generates a strong perpendicular effective magnetic field (H_DMI^z) on the
perpendicular magnetization. Characteristically, H_DMI^z varies with the
sign/magnitude of the interfacial DMI constant, the applied in-plane magnetic
fields, and the distribution of the perpendicular magnetic anisotropy. The
long-range intralayer DMI results in striking consequences including the
strongly asymmetric current/field switching of perpendicular magnetization,
hysteresis loop shift of perpendicular magnetization in the absence of in-plane
direct current, and sharp, complete switching of perpendicular magnetization
purely by an in-plane magnetic field. Utilizing the long-range intralayer DMI
effect, we demonstrate programable, complete Boolean logic operations (i.e.,
AND, NAND, NOT, OR, and NOR) within a single spin-orbit torque device. These
results will stimulate the investigation of the long-range intralayer DMI
effect and its impacts on a variety of spintronic devices.",2403.16035v1
2012-02-24,Magnetic field amplification in electron phase-space holes and related effects,"Three-dimensional electron phase space holes are shown to be positive charges
on the plasma background which produce a radial electric field and force the
trapped electron component into an azimuthal drift. In this way electron holes
generate magnetic fields in the hole. We solve the cylindrical hole model
exactly for the hole charge, electric potential and magnetic field. In electron
holes, the magnetic field is amplified on the flux tube of the hole;
equivalently, in ion holes the field would be decreased. The flux tube adjacent
to the electron hole is magnetically depleted by the external hole dipole
field. This causes magnetic filamentation. It is also shown that holes are
massive objects, each carrying a finite magnetic moment. Binary magnetic dipole
interaction of these moments will cause alignment of the holes into chains
along the magnetic field or, in the three-dimensional case, produce a magnetic
fabric in the volume of hole formation. Since holes, in addition to being
carriers of charges and magnetic moments, also have finite masses, they behave
like quasi-particles, performing ExB, magnetic field, and diamagnetic drifts.
In an inhomogeneous magnetic field, their magnetic moments experience torque
which causes nutation of the hole around the direction of the magnetic field
presumably giving rise to low frequency magnetic modulations like pulsations. A
gas of many such holes may allow for a kinetic description in which holes
undergo binary dipole interactions. This resembles the polymeric behaviour.
Both magnetic field generation and magnetic structure formation is of interest
in auroral, solar coronal and shock physics, in particular in the problem of
magnetic field filamentation in relativistic foreshocks and cosmic ray
acceleration.",1202.5428v1
1998-06-09,PG 0946+301: the Rosetta Stone of BALQSOs?,"We describe the motivation and features of a multiwavelength spectroscopic
campaign on broad absorption line (BAL) QSO PG~0946+301. The main goal of this
project is to determine the ionization equilibrium and abundances (IEA) in BAL
outflows. Previous studies of IEA in BALQSOs were based on the assumption that
the BALs are not saturated so that the column densities inferred from the
apparent optical depths are realistic. This critical assumption is at odds with
several recent observations and with analysis of existing data which indicate
that the absorption troughs are heavily saturated even when they are not black.
In addition, X-ray observations, which are important for constraining the
ionizing continuum, were not available for those objects that had UV spectral
data. Quantifying the level of saturation in the BALs necessitates UV
spectroscopy with much higher S/N and broader spectral coverage than currently
exist. After taking into account the capabilities of available observatories,
our best hope for a substantial improvement in understanding the IEA in BALQSOs
is to concentrate considerable observational resources on the most promising
object. Our studies of available HST and ground-based spectra show that
PG~0946+301 is by far the best candidate for such a program. This BALQSO is at
least five times brighter, shortward of 1000 A rest frame, than any other
object, and due to its low redshift it has an especially sparse Lya forest. At
the same time PG~0946+301 is a typical BALQSO and therefore its IEA should be
representative. To this effect we are developing a multiwavelength
spectroscopic campaign (UV, FUV, X-ray and optical) on BALQSO PG 0946+301. We
discuss the goals and feasibility of each observational component: HST, FUSE,
ASCA and ground-based.",9806131v1
2003-02-26,Multiwavelength studies of the Seyfert 1 galaxy NGC7469. I - Far UV observations with FUSE,"We obtained far-ultraviolet spectra of the Seyfert 1 galaxy NGC 7469 using
the FUSE on 1999 December 6. Our spectra cover the wavelength range 990-1187 A
with a resolution of 0.05 A. We see broad emission lines of CIII, NIII, OVI,
and HeII as well as intrinsic absorption lines in the OVI 1032,1038 resonance
doublet. The absorption arises in two distinct kinematic components at systemic
velocities of -569 km/s and -1898 km/s. Both components are very highly
ionized- no significant Ly beta absorption is present. The higher blueshift
component is not quite saturated, and it has a total OVI column density of
8e14/cm2. It covers more than 90% of the continuum and broad-line emission. The
lower blue shift component is heavily saturated and covers only 50% of the
continuum and broad-line emission. It too has a column density of 8e14/cm2, but
this is less certain due to the high saturation. We set an upper limit of
<1.5e18/cm2 on the OVI column density of this component. Its line depth is
consistent with coverage of only the continuum, and thus this component may lie
interior to the broad emission-line gas. The component at -569 km/s has a
velocity comparable to the high-ionization X-ray absorption lines seen in the
XMM-Newton grating spectrum of NGC 7469, and photoionization models show that
the observed column densities of OVI and HI are compatible with their formation
in the same gas as that causing the X-ray absorption. The gas at -1898 km/s has
lower ionization and column density, and no significant X-ray absorption is
associated with it.",0302552v1
2005-03-03,How To Distinguish Neutron Star and Black Hole X-ray Binaries? Spectral index and Quasi-Periodic Oscillation Frequency Correlation,"Recent studies have revealed strong correlations between 1-10 Hz frequencies
of quasiperiodic oscillations (QPOs) and the spectral power law index of
several Black Hole (BH) candidate sources when seen in the low/hard state, the
steep power-law (soft) state, and in transition between these states. In the
soft state these index-QPO frequency correlations show a saturation of the
photon index about 2.7 at high values of the low frequency. This saturation
effect was previously identified as a black hole signature. In this paper we
argue that this saturation does not occur, at least for one neutron star (NS)
source 4U 1728-34, for which the index monotonically increases with the low
frequency to the values of 6 and higher. We base this conclusion on our
analysis about 1.5 Msec of RXTE archival data for 4U 1728-34. We reveal the
spectral evolution of the Comptonized blackbody spectra when the source
transitions from the hard to soft states. The hard state spectrum is a typical
thermal Comptonization spectrum of the soft photons which originate in the disk
and the NS outer photospheric layers. The hard state photon index is about 2.
The soft state spectrum consists of two blackbody components which are only
slightly Comptonized. Thus we can claim (as expected from theory) that in NS
sources thermal equilibrium is established for the soft state. To the contrary
in BH sources, the equilibrium is never established due to the presence of the
BH horizon. The emergent BH spectrum, even in the high/soft state, has a power
law component. We also show that the presence of Fe K_alpha emission-line
strengths, QPOs, and the link between them does not depend on radio flux in 4U
1728-34.",0503081v1
2006-10-04,Correction of SOHO CELIAS/SEM EUV Measurements saturated by extreme solar flare events,"The solar irradiance in the Extreme Ultraviolet (EUV) spectral bands has been
observed with a 15 sec cadence by the SOHO Solar EUV Monitor (SEM) since 1995.
During remarkably intense solar flares the SEM EUV measurements are saturated
in the central (zero) order channel (0.1 -- 50.0 nm) by the flare soft X-ray
and EUV flux. The first order EUV channel (26 -- 34 nm) is not saturated by the
flare flux because of its limited bandwidth, but it is sensitive to the arrival
of Solar Energetic Particles (SEP). While both channels detect nearly equal SEP
fluxes, their contributions to the count rate is sensibly negligible in the
zero order channel but must be accounted for and removed from the first channel
count rate. SEP contribution to the measured SEM signals usually follows the
EUV peak for the gradual solar flare events. Correcting the extreme solar flare
SEM EUV measurements may reveal currently unclear relations between the flare
magnitude, dynamics observed in different EUV spectral bands, and the measured
Earth atmosphere response. A simple and effective correction technique based on
analysis of SEM count-rate profiles, GOES X-ray, and GOES proton data has been
developed and used for correcting EUV measurements for the five extreme solar
flare events of July 14, 2000, October 28, November 2, November 4, 2003, and
January 20, 2005. Although none of the 2000 and 2003 flare peaks were
contaminated by the presence of SEPs, the January 20, 2005 SEPs were unusually
prompt and contaminated the peak. The estimated accuracy of the correction is
about 7.5% for large X-class events.",0610123v1
2007-01-31,Entropy of entanglement and correlations induced by a quench: Dynamics of a quantum phase transition in the quantum Ising model,"Quantum Ising model in one dimension is an exactly solvable example of a
quantum phase transition. We investigate its behavior during a quench from a
paramagnetic to ferromagnetic phase caused by a gradual turning off of the
transverse field at a fixed rate characterized by the quench time $\tau_Q$. In
agreement with Kibble-Zurek mechanism, quantum state of the system after the
transition exhibits a characteristic correlation length $\hat\xi$ proportional
to the square root of the quench time $\tau_Q$. The inverse of this correlation
length determines average density of defects after the transition. In this
paper, we show that $\hat\xi$ also controls the entropy of entanglement of a
block of $L$ spins with the rest of the system. For large $L$, this entropy
saturates at $\frac16\log_2\hat\xi$, as might have been expected from the
Kibble-Zurek mechanism. Close to the critical point, the entropy saturates when
the block size $L\approx\hat\xi$, but -- in the subsequent evolution in the
ferromagnetic phase -- a somewhat larger length scale
$l=\sqrt{\tau_Q}\ln\tau_Q$ develops as a result of quantum dephasing, and the
entropy saturates when $L\approx l$. We also study the spin-spin correlation.
We find that close to the critical point ferromagnetic correlations decay
exponentially with the dynamical correlation length $\hat\xi$, but in the
following evolution this correlation function becomes oscillatory at distances
less than this scale. However, both the wavelength and the correlation length
of these oscillations are still determined by $\hat\xi$. We also derive
probability distribution for the number of kinks in a finite spin chain after
the transition.",0701768v2
2005-01-26,Inherently Global Nature of Topological Charge Fluctuations in QCD,"We have recently presented evidence that in configurations dominating the
regularized pure-glue QCD path integral, the topological charge density
constructed from overlap Dirac operator organizes into an ordered space-time
structure. It was pointed out that, among other properties, this structure
exhibits two important features: it is low-dimensional and geometrically
global, i.e. consisting of connected sign-coherent regions with local
dimensions 1<= d < 4, and spreading over arbitrarily large space--time
distances. Here we show that the space-time structure that is responsible for
the origin of topological susceptibility indeed exhibits global behavior. In
particular, we show numerically that topological fluctuations are not saturated
by localized concentrations of most intense topological charge density. To the
contrary, the susceptibility saturates only after the space-time regions with
most intense fields are included, such that geometrically global structure is
already formed. We demonstrate this result both at the fundamental level (full
topological density) and at low energy (effective density). The drastic
mismatch between the point of fluctuation saturation (~ 50% of space-time at
low energy) and that of global structure formation (<4% of space-time at low
energy) indicates that the ordered space-time structure in topological charge
is inherently global and that topological charge fluctuations in QCD cannot be
understood in terms of individual localized pieces. Description in terms of
global brane-like objects should be sought instead.",0501025v3
2003-12-16,Chiral approach to nuclear matter: Role of explicit short-range NN-terms,"We extend a recent chiral approach to nuclear matter by including the most
general (momentum-independent) NN-contact interaction. Iterating this
two-parameter contact-vertex with itself and with one-pion exchange the
emerging energy per particle exhausts all terms possible up-to-and-including
fourth order in the small momentum expansion. The equation of state of pure
neutron matter, $\bar E_n(k_n)$, can be reproduced very well up to quite high
neutron densities of $\rho_n=0.5\fmd$ by adjusting the strength of a repulsive
$nn$-contact interaction. Binding and saturation of isospin-symmetric nuclear
matter is a generic feature of our perturbative calculation. Fixing the maximum
binding energy per particle to $-\bar E(k_{f0})= 15.3 $MeV we find that any
possible equilibrium density $\rho_0$ lies below $\rho_0^{\rm max}=0.191\fmd$.
The additional constraint from the neutron matter equation of state leads
however to a somewhat too low saturation density of $\rho_0 =0.134 \fmd$. We
also investigate the effects of the NN-contact interaction on the complex
single-particle potential $U(p,k_f)+i W(p,k_f)$. We find that the effective
nucleon mass at the Fermi-surface is bounded from below by $M^*(k_{f0}) \geq
1.4 M$. This property keeps the critical temperature of the liquid-gas phase
transition at somewhat too high values $T_c \geq 21 $MeV. The downward bending
of the asymmetry energy $A(k_f)$ above nuclear matter saturation density is a
generic feature of the approximation to fourth order. Altogether, there is
within this complete fourth-order calculation no ""magic"" set of adjustable
short-range parameters with which one could reproduce simultaneously and
accurately all semi-empirical properties of nuclear matter.",0312057v1
2005-04-08,Hadron Production and Phase Changes in Relativistic Heavy Ion Collisions,"We study soft hadron production in relativistic heavy ion collisions in a
wide range of reaction energy, 4.8 GeV <sqrt{s_ NN}<200 GeV, and make
predictions about yields of particles using the statistical hadronization
model. In fits to experimental data, we obtain both statistical parameters as
well as physical properties of the hadron source. We identify the properties of
the fireball at the critical energy threshold, 6.26 GeV < sqrt{s_NN}^cr} <7.61
GeV, delineating for higher energies hadronization of an entropy rich phase. In
terms of the chemical composition, one sees a phase which at low energy is
chemically under-saturated, and which turns into a chemically over-saturated
state persisting up to the maximum accessible energy. Assuming that there is no
change in physical mechanisms in the energy range 15>sqrt{s_NN} \ge 200 GeV, we
use continuity of particle yields and statistical parameters to predict the
hadron production at sqrt{s_NN}=62.4 GeV, and obtain total yields of hadrons at
sqrt{s_NN}=130 GeV. We consider, in depth, the pattern we uncover within the
hadronization condition, and discuss possible mechanisms associated with the
identified rapid change in system properties at sqrt{s_NN ^cr}. We propose that
the chemically over-saturated 2+1 flavor hadron matter system undergoes a 1st
order phase transition.",0504028v5
2007-11-22,Constraining the Symmetry Energy: A Journey in the Isospin Physics from Coulomb Barrier to Deconfinement,"Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium
nuclear interaction in regions away from saturation. In this work we present a
selection of reaction observables in dissipative collisions particularly
sensitive to the isovector part of the interaction, i.e. to the symmetry term
of the nuclear Equation of State (EoS). At low energies the behavior of the
symmetry energy around saturation influences dissipation and fragment
production mechanisms. We will first discuss the recently observed Dynamical
Dipole Radiation, due to a collective neutron-proton oscillation during the
charge equilibration in fusion and deep-inelastic collisions. Important Iso-EOS
effects are stressed. Reactions induced by unstable 132Sn beams appear to be
very promising tools to test the sub-saturation Isovector EoS. New Isospin
sensitive observables are also presented for deep-inelastic, fragmentation
collisions and Isospin equilibration measurements (Imbalance Ratios). The high
density symmetry term can be derived from isospin effects on heavy ion
reactions at relativistic energies (few AGeV range), that can even allow a
``direct'' study of the covariant structure of the isovector interaction in the
hadron medium. Rather sensitive observables are proposed from collective flows
and from pion/kaon production. The possibility of the transition to a mixed
hadron-quark phase, at high baryon and isospin density, is finally suggested.
Some signatures could come from an expected ``neutron trapping'' effect. The
importance of studying violent collisions with radioactive beams from low to
relativistic energies is finally stressed.",0711.3546v1
2008-02-04,Coronal Structure and Abundances in Young Fast Rotators,"AB Dor, Speedy Mic and Rst137B are in their early post-T Tauri evolutionary
phase (<100Myr), at the age of fastest rotation in the life of late-type stars.
They straddle the coronal saturation-supersaturation boundary first defined by
young stars in open clusters. High resolution Chandra X-ray spectra have been
analysed to study their coronal properties as a function of coronal activity
parameters Rossby number, $L_X/L_{bol}$ and a coronal temperature index. Plasma
emission measure distributions as a function of temperature show broad peaks at
T~10e7K. Differences between stars suggest that as supersaturation is reached
the DEM slope below the temperature of peak DEM becomes shallower, while the
DEM drop-off above this temperature becomes more pronounced. A larger sample
comprising our three targets and 22 active stars studied in the recent
literature reveals a general increase of plasma at T>10e7 toward the
saturated-supersaturated boundary but a decline beyond this among
supersaturated stars. All three of the stars studied in detail here show lower
coronal abundances of the low FIP elements Mg, Si and Fe, relative to the high
FIP elements S, O and Ne, as compared to the solar mixture. The coronal Fe
abundances of the stellar sample are inversely correlated with Lx/Lbol,
declining slowly with rising Lx/Lbol, but with a much more sharp decline at
Lx/Lbol>3x10e-4. For dwarfs the Fe abundance is also well-correlated with
Rossby number. The coronal O/Fe ratios for dwarfs show a clear increase with
decreasing Rossby number, apparently reaching saturation at [O/Fe]=0.5 at the
coronal supersaturation boundary. Similar increases in O/Fe with increasing
coronal temperature and $L_X/L_{bol}$ are seen.",0802.0326v1
2008-02-06,CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations,"We use the COMPLETE data to derive new calibrations of the X-factor and the
13CO abundance within Perseus. We divide Perseus into six sub-regions. The
standard X factor, X=N(H2)/W(12CO), is derived both for the whole Perseus
Complex and for each of the six sub-regions with values consistent with
previous estimates. The X factor is heavily affected by the saturation of the
emission above AV~4 mag, and variations are found between regions. We derive
linear fits to relate W(12CO) and AV using only points below 4 mag of
extinction, this yields a better estimation of the AV than the X-factor. We
derive linear relations of W(13CO), N(13CO) and W(C18O) with AV . The
extinction threshold above which 13CO(1-0) and C18O(1-0) are detected is about
1 mag larger than previous estimates. 12CO(1-0) and 13CO(1-0) lines saturate
above 4 and 5 mag, respectively, whereas C18O(1-0) never saturates (up to 10
mag). Approximately 60% of the positions with 12CO emission have sub-thermally
excited lines, and almost all positions have 12CO excitation temperatures below
the dust temperature. Using the Meudon PDR code we find that 12CO and 13CO
emission can be explained by uniform slab models with densities ranging between
about 10^3 and 10^4 cm-3. Local variations in the volume density and
non-thermal motions (linked to different star formation activity) can explain
the observations. Higher densities are needed to reproduce CO data toward
active star forming sites, where the larger internal motions driven by the
young protostars allow more photons from the embedded high density cores to
escape the cloud. In the most quiescent region, the 12CO and 13CO emission
appears to arise from an almost uniform thin layer of molecular material at
densities around 10^4 cm-3.",0802.0708v1
2008-11-21,Characterising the Gravitational Instability in Cooling Accretion Discs,"We perform numerical analyses of the structure induced by gravitational
instabilities in cooling gaseous accretion discs. For low enough cooling rates
a quasi-steady configuration is reached, with the instability saturating at a
finite amplitude in a marginally stable disc. We find that the saturation
amplitude scales with the inverse square root of the cooling parameter beta =
t_cool / t_dyn, which indicates that the heating rate induced by the
instability is proportional to the energy density of the induced density waves.
We find that at saturation the energy dissipated per dynamical time by weak
shocks due is of the order of 20 per cent of the wave energy. From Fourier
analysis of the disc structure we find that while the azimuthal wavenumber is
roughly constant with radius, the mean radial wavenumber increases with radius,
with the dominant mode corresponding to the locally most unstable wavelength.
We demonstrate that the density waves excited in relatively low mass discs are
always close to co-rotation, deviating from it by approximately 10 per cent.
This can be understood in terms of the flow Doppler-shifted phase Mach number
-- the pattern speed self-adjusts so that the flow into spiral arms is always
sonic. This has profound effects on the degree to which transport through
self-gravity can be modelled as a viscous process. Our results thus provide (a)
a detailed description of how the self-regulation mechanism is established for
low cooling rates, (b) a clarification of the conditions required for
describing the transport induced by self-gravity through an effective
viscosity, (c) an estimate of the maximum amplitude of the density perturbation
before fragmentation occurs, and (d) a simple recipe to estimate the density
perturbation in different thermal regimes.",0811.3629v1
2010-06-21,Keck ESI Observations of Metal-Poor Damped Lyman-α Systems,"We present the first results from a survey of SDSS quasars selected for
strong H I damped Lyman-{\alpha} (DLA) absorption with corresponding low
equivalent width absorption from strong low-ion transitions (e.g. C II
{\lambda}1334 and Si II {\lambda}1260). These metal-poor DLA candidates were
selected from the SDSS DR5 quasar spectroscopic database, and comprise a large
new sample for probing low metallicity galaxies. Medium-resolution echellette
spectra from the Keck ESI spectrograph for an initial sample of 35 systems were
obtained to explore the metal-poor tail of the DLA distribution and to
investigate the nucleosynthetic patterns at these metallicities. We have
estimated saturation corrections for the moderately under-resolved spectra, and
systems with very narrow Doppler parameter (b \le 5 km s-1) will likely have
underestimated abundances. For those systems with Doppler parameters b > 5 km
s-1, we have measured low metallicity DLA gas with [X/H] < -2.4 for at least
one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that
several DLA systems have [X/H] < -2.8, including five DLA systems with both low
equivalent widths and low metallicity in transitions of both C II and O I. All
of the measured DLA metallicities, however, exceed or are consistent with a
metallicity of at least 1/1000 of solar, regardless of the effects of
saturation in our spectra. Our results indicate that the metal-poor tail of
galaxies at z \sim 3 drops exponentially at [X/H]< -3. The observed ratio of
[C/O] for values of [O/H] < -2.5 exceeds values seen in moderate metallicity
DLA systems, and also exceeds theoretical nucleosynthesis predictions for
higher mass Population III stars.",1006.4119v1